Investigations of Ionic Liquids Based on Chloroiodates ...

Investigations of Ionic Liquids Based on

Chloroiodates, Bromostannates, and

Chloromanganates: Towards Their

Application in Redox Flow Batteries

Economic Evaluation of Battery Design Concepts and

Development of a Battery Test Software

INAUGURALDISSERTATION

zur Erlangung des Doktorgrades

der Fakultät für Chemie und Pharmazie

der Albert-Ludwigs-Universität Freiburg im Breisgau

vorgelegt von

Dipl.-Chem. Simeon Benedikt Burgenmeister

aus Tübingen

2017

Die vorliegende Arbeit wurde von September 2013 bis Mai 2017 am Institut für Anorganische

und Analytische Chemie der Albert-Ludwigs-Universität Freiburg unter der Anleitung von

Prof. Dr. Ingo Krossing angefertigt.

Dekan der Fakultät für Chemie und Pharmazie Prof. Dr. Manfred Jung

Vorsitzender des Promotionsausschusses: Prof. Dr. Stefan Weber

Referent: Prof. Dr. Ingo Krossing

Korreferent: Prof. Dr. Sebastian Hasenstab-Riedel

Tag der mündlichen Prüfung: 7. Juli 2017

Der Hauptteil des Kapitels “Structure and Properties of Novel Chloroiodate(III) Ionic Liquids” dieser

Arbeit wurde bei der Zeitschrift Chemistry – a European Journal (Wiley-VCH Verlag GmbH & Co. KGaA,

Weinheim) unter folgendem Titel veröffentlicht:

„From Square-planar [ICl4]– to Novel Chloroiodates(III)? A Systematic Experimental and Theoretical

Investigation of their Ionic Liquids“ von Benedikt Burgenmeister, Karsten Sonnenberg, Sebastian Riedel

und Ingo Krossing.

Eine Genehmigung zur Reproduktion des Artikels im Rahmen dieser Dissertationsschrift wurde bei

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim eingeholt. Die Nummerierungen von Tabellen,

Abbildungen, Gleichungen und Referenzen wurden im Sinne eines konsistenten Aufbaus der Arbeit

angepasst. Die Publikation enthält Beiträge von M. Sc. Karsten Sonnenberg (AG Riedel, FU Berlin) und

Ergebnisse aus meiner Diplomarbeit an der Albert-Ludwigs-Universität Freiburg (2013), die im Rahmen

meiner Dissertation weitergeführt und vertieft wurden.

Auf weitere Ergebnisse und Beiträge Dritter, die in dieser Dissertation, enthalten sind wird zu Beginn

jedes Kapitels explizit hingewiesen. Dazu gehören insbesondere die Ergebnisse aus der Bachelorarbeit

von B. Sc. Niklas Gebel und der Masterarbeit von M. Sc. Maximilian Schmucker sowie Ergebnisse aus

den Forschungspraktika von M. Sc. Sarah Jenne und M. Sc. Tobias Fischer.

Das dieser Arbeit zugrundeliegende Vorhaben wurde mit Mitteln des Bundesministeriums für Bildung

und Forschung unter dem Förderkennzeichen 03SF0526A gefördert. Die Verantwortung für den Inhalt

dieser Veröffentlichung liegt beim Autor.

Danksagung

Ich danke Herrn Prof. Dr. Ingo Krossing für die Möglichkeit, diese Arbeit unter seiner Anleitung

anzufertigen. Insbesondere möchte ich mich für den kreativen Spielraum und das mir damit

entgegengebrachte Vertrauen bedanken, ohne die ich viele Teile dieser Arbeit nicht oder nicht mit

Begeisterung hätte durchführen können. Das Wissen und die Erfahrung, auch bei schwierigen Themen

ein offenes Ohr zu finden, hat mir die Ruhe gegeben, um auch anspruchsvolle Aufgaben zu meistern.

Herrn Prof. Dr. Sebastian Hasenstab-Riedel danke ich für die Übernahme des Korreferats und die

immer wieder anregenden wissenschaftlichen Diskussionen.

Herrn Prof. Dr. Koslowski danke ich für die Bereitschaft, die Arbeit des Drittprüfers zu übernehmen.

Heinrich Stülpnagel unterstützte mich mit Verstand, Herz und Zuversicht bei meinen Aufgaben im

Rahmen des Kommunikationsmanagements für das IL-RFB-Projekte und bei der Vorbereitung von

diversen Projektmeetings. Er öffnete mir die Augen für neue Möglichkeiten, gemeinschaftlich Wege

und Ziele zu finden und zu erreichen.

Mit Michael Hog durchlebte ich die Höhen und Tiefen des Projekts von Anfang an und bis zu diesem

Punkt. Gemeinsam haben wir immer einen Weg gefunden.

Carola Sturm führte mit beeindruckender Geduld und großer Zuverlässigkeit die Viskositäts- und die

unzähligen DSC-Messungen durch. Sie ermöglichte meinen Umzug in ihr Labor, was mich in meinem

Arbeitsalltag zunächst einmal räumlich sehr entlastete. Durch wertvolle Gespräche, Unterstützung in

vielerlei Hinsicht und „Celebrations“ hast du es bald zu „unserem“ Büro und zu einem Ort gemacht,

den ich vermissen werde.

Karsten Sonnenberg war ein verlässlicher Draht zur AG Riedel und die wöchentlichen Telefonate waren

nur selten Arbeit. Niklas Gebel leistete durch seine zuverlässige Arbeit und seine Freude im Laboralltag

einen großen Beitrag zu dieser Arbeit. Sarah Jenne und Tobias Fischer führten seine Arbeit in ihren

Forschungspraktika fort.

Maximilian Schmucker bearbeitete mit viel Elan das Thema seiner Masterarbeit und übernahm schnell

und bereitwillig große Verantwortung im BMBF-Projekt, was mich in der Phase des Schreibens sehr

entlastete. Alexei Schmidt führte mit Geduld und Witz einen schwierigen Teil meiner Arbeit fort. Beide

lasen Teile dieser Dissertation Korrektur.

Katharina Pütz und Andreas Ermantraut machten die Betreuung des LAFP zur Freude. Werner Deck

leitete den EFK und das LAFP und trug dazu bei, dass ich lernte, mit großen Ansätzen von

Carbonylverbindungen sicher umzugehen.

Markus Melder und die Mitarbeiter der Mechanikwerkstatt des Instituts waren eine große Hilfe beim

Finden von Lösungen für allerlei große und kleine technische Probleme und fertigten mit viel Geduld

auch den x-ten Tefloneinsatz. Daniel Himmel half bei allerlei quantenchemischen, Valentin Radke bei

elektrochemischen, Anke Hoffman bei informationstechnischen und Harald Scherer bei NMR-

spektroskopischen Fragestellungen. Boumahdi Benkmil und Thilo Ludwig halfen bei der Durchführung

von Einkristall- und Pulverdiffraktometrie und Daniel Kratzert löste nicht nur Strukturen, sondern auch

einige Probleme bei deren Verfeinerung. Fadime Bitgül führte NMR-spektroskopische Messungen

durch, Brigitte Breitling, Vera Brucksch und Stefanie Kuhl bahnten Wege durch den bürokratischen

Dschungel.

Dr. Martin Wiesenmayer vom Projektträger Jülich war ein verlässlicher und hilfreicher

Ansprechpartner im Rahmen des BMBF-Projekts IL-RFB. Kolja Bromberger akzeptierte mit Freude alle

chemischen Unwägbarkeiten des Projekts und half an etlichen Stellen durch Know-How und eine

komplementäre Sichtweise. Prithiv Mohan ließ sich auf das Experiment einer riesigen Schraubzelle ein

und schuf ein überzeugendes Ergebnis. Die Industriepartner Dr. Thomas Schubert, Dr. Boyan Iliev, Dr.

Michael Schuster und Dr. Holger Kühnlein trugen immer wieder wertvolle Blickwinkel auf

wissenschaftliche Fragestellungen des Projektes bei.

Von David Allen, Jon Kabat-Zinn, Jörg Blömeling, Pamela Alean-Kirkpatrick, Matthias Mayer und Hans

Aerts lernte ich im Laufe der Promotion viele bereichernde Fähigkeiten. Meine Chemielehrer Frau

Berthold, Herr Schumacher und Frau Krauch legten den Grundstein für den Weg bis zu diesem Punkt.

Microsoft stellte kommentarlose bzw. sicherheitsbedingt die Unterstützung von EPS-Grafiken im April

2017 ein und leiste damit, wie so oft, einen kleinen, aber entscheidenden Beitrag, um meine Fähigkeit

zur inneren Ruhe zu trainieren.

Die momentanen und früheren Mitgliedern des Arbeitskreises Krossing, Alexander Rupp, Heike Haller,

Franziska Scholz, Philipp Eiden, Mathias Hill, Mario Sander, Olaf Petersen, Tobias Engesser, Miriam

Schwab, Pengcheng Zhang, Meipin Liu, Jennifer Beck, Valentin Dybbert, Ulf Breddemann, Stefan Meier,

Samuel Fehr, Arthur Martens, Philippe Weis, Simon Weigel, Jan Bohnenberger, Lea Eisele, Kim Glootz,

Wiebke Unkrig, Marcel Schorpp und Ian Riddlestone, unterstützten bei großen und kleinen Problemen

des Laboralltags.

Das L&D-Team+, Caro, Andreas, Heike, Alexis, Birte, Timon, Jens, Ricardo, Jojo, Phil, Lisa, die gesamte

Good Company, alle Mitwirkenden der Stadtoper und meine Familie waren ein unverzichtbarer Teil

der letzten Jahre.

Ihnen allen möchte ich an dieser Stelle herzlich danken.

Und was könnte ich schreiben, was könnte ich sagen, um die Unterstützung und Liebe zu

beschreiben, die ich von meiner Sophia jeden Tag geschenkt bekomme?

If love is the answer,

I have found mine.

Abstract

The present work is concerned with the evaluation of the concept of redox flow batteries based on the

use of ionic liquids (IL) as their active materials. One of the two basic working principles of these

batteries is the oxidation of metal (hybrid IL-RFB) or a halometallate (IL-RFB) in the anolyte and the

reduction of polyhalides in the catholyte for the discharge process. The second principle is based on

the oxidation of manganese and the reduction of chloromanganates(III) or (IV) to form

chloromanganates(II) in the discharged state. For both types of batteries, halide anions are the charge

balancing species.

A general method was developed to estimate the specific energy, the energy density, and the cost of

the chemicals per stored energy, to judge the economic potential of batteries in the early stages of

chemical research. The proposed (hybrid) IL-RFBs based on tin, aluminium, and manganese were found

to offer competitive performance when compared to the established all-vanadium chemistry.

To evaluate the possibility of using I2Cl6 based ILs as a positive active material, a systematic

investigation on the existence of chloroiodates apart from the well-known [ICl4]–, namely [I2Cl7]– and

[I3Cl10]–, was undertaken. Concluding from DFT and ab initio quantum-chemical calculations, their

thermodynamic stability is limited by the elimination of dichlorine to form iodine (I) compounds. This

prediction was confirmed on the experimental side by analysing mixtures of 1-hexyl-3-

methylimidazoliumchlorid ([HMIM]Cl), 1-butyl-1-methylpyrrolidinium chloride and tetraethyl-

ammonium chloride (cooperation with the WG Riedel, FU Berlin) with 0.5, 1.0 and 1.5 equivalents of

I2Cl6, using scXRD, ion chromatography, NMR- and Raman spectroscopy. The hitherto unknown [I2Cl7]–

anion is proposed to be the predominating species in mixtures with 1.0 equivalents of I2Cl6.

The concept for a membrane-free Sn/Br2 Hybrid-IL-RFB was investigated by synthesising novel

bromostannate(IV) ILs using the [HMIM]+ cation and studying their phase behaviour via differential

scanning calorimetry. Through calculation of a thermodynamic cycle, the dismutation of

[HMIM][SnBr5] was found to be driven by the large lattice enthalpy of [HMIM]2[SnBr6], for which a

crystal structure was obtained. The competing complexation of bromide anions in mixtures of the

bromostannate ILs with bromine was studied by NMR and Raman spectroscopy. Batteries based on

these ILs showed high discharge current densities, though all charging attempts so far were

unsuccessful.

Though synthetic attempts did not yield the desired positive active material based on

chloromanganate(IV), the open circuit voltage of 3.0 V obtained for a first All-Mn-IL battery is

promising. The battery was set up using a phosphonium based chloromanganate(II) IL and could be

cycled in a limited range for the state of charge.

All battery tests were controlled using a software programmed as part of this thesis. It is designed to

allow for the implementation of pumps, thermostats and thermal sensors of the planned flow setup.

Kurzzusammenfassung

Die vorliegende Arbeit beschäftigt sich mit der Erforschung von Redox-Flow-Batterien auf Basis von

ionischen Flüssigkeiten (ionic liquids, ILs) als Aktivmassen. Eines der zwei grundsätzlichen

Funktionsprinzipien ist die Oxidation eines Metalls (Hybrid-IL-RFB) oder Metallhalogenids (IL-RFB) im

Anolyten und die Reduktion von Polyhalogenverbindungen im Katholyten während des

Entladevorgangs. Das zweite Prinzip beruht auf der Oxidation von elementarem Mangan und der

Reduktion von Chloromanganaten(III) oder (IV) unter Bildung von Chloromanganaten(II) im entladenen

Zustand. Für beide Funktionsprinzipien sind Halogenidionen die ladungsausgleichenden Spezies.

Eine allgemein anwendbare Methode zur Abschätzung von spezifischen Energien, Energiedichten und

Kosten der Chemikalien pro speicherbarer Energie wurde entwickelt. Damit kann das ökonomische

Potential von Batterien im frühen, chemischen Forschungsstadium ermittelt werden. Die

vorgeschlagenen (Hybrid-)IL-RFB auf Basis von Zinn, Aluminium und Mangan erwiesen sich innerhalb

dieser Abschätzung als ökonomisch konkurrenzfähig im Vergleich zur etablierten All-Vanadium-

Chemie.

Die Möglichkeit, ionische Flüssigkeiten auf Basis von I2Cl6 als Aktivmassen zu verwenden, wurde durch

eine systematische Erforschung von bisher unbekannten Chloroiodaten [I2Cl7]– und [I3Cl10]– untersucht.

Quantenchemischen Rechnungen (ab initio und DFT) zeigten, dass die Stabilität dieser Chloroiodate in

Bezug auf die reduktive Eliminierung von elementarem Chlor limitiert ist. Diese Vorhersage

bewahrheitete sich in den experimentellen Arbeiten, bei denen Mischungen von 1-Hexyl-3-

methylimidazoliumchlorid ([HMIM]Cl), 1-Butyl-1-methylpyrrolidiniumchlorid und Tetraethyl-

ammoniumchlorid (in Kooperation mit der AG Riedel, FU Berlin) mit 0.5, 1.0 and 1.5 Äquivalenten I2Cl6

mittels Einkristalldiffraktometrie, Ionenchromatographie, sowie Raman- und NMR-Spektroskopie

untersucht wurden. Das bis dato unbekannte [I2Cl7]– wurde als die vorherrschende anionische Spezies

in Mischungen mit einem Äquivalent I2Cl6 identifiziert.

Das Konzept einer membranfreien Sn/Br2 Hybrid-IL-RFB wurde ausgehend von der Synthese der neuen

Bromostannat(IV)-ILs untersucht. Dazu wurde zunächst deren Phasenverhalten mittels Differenz-

Thermoanalyse studiert. Über die Berechnung eines Kreisprozesses wurde die Dismutierung von

[HMIM][SnBr5] als Resultat der hohen Gitterenergie von [HMIM]2[SnBr6] erklärt, von welchem auch

eine Einkristallstruktur erhalten wurde. Die konkurrierende Komplexierung von Bromidionen in

Mischungen der Bromostannat(IV)-ILs mit Brom wurde mithilfe von Raman- und NMR-Spektroskopie

untersucht. Batterien auf Basis dieser ILs zeigten hohe Entladestromdichten, wobei alle Versuche,

derartige Batterien zu laden, bisher scheiterten.

Obgleich die Versuche zur Synthese von Chloromanganat(IV)-ILs nicht erfolgreich verliefen, zeigte eine

erste All-Mn-IL-Batterie eine hohe Leerlaufspannung von 3.0 V. Die Batterie wurde mit einer

phosphoniumbasierten Chloromanganat(II)-IL aufgebaut und konnte in einem begrenzten Umfang

ihrer Kapazität zykliert werden.

Alle Batteriemessungen wurden mit einer im Rahmen dieser Dissertation programmierten Software

gesteuert. Sie ist darauf ausgelegt, auch die Steuerung von Pumpen, Thermostaten und

Thermosensoren des geplanten Flow-Betriebs zu übernehmen.

Abbreviations and Constants

IL-RFB ionic liquid redox flow battery

(MF)-Hyb-IL-RFB (membrane-free) hybrid ionic liquid redox flow battery

OCV open circuit voltage

SOC state of charge of a battery (in %)

SHE standard hydrogen electrode

UME ultramicroelectrode

RBF round bottom flask

[cat]X salt composed of an organic cation [cat] and a halide X

[Nwxyz]+/[Pwxyz]+ ammonium/phosphonium cations with hydrocarbon substituents of a

chain length indicated by the indices w,x,y and z

[NEt4]+ tetraethyl ammonium

[NBu4]+ tetrabutyl ammonium

[bipyH2]2+ 2,2’-dihydro-2,2’-bipyridinium

[NTf2]– bis((trifluoromethyl)sulfonyl)imide

[OTf]– trifluoromethanesulfonate

[DCA]– dicyanamide

Fc / Fc+ ferrocene / ferrocenium

DCM dichloromethane

iPrOH isopropyl alcohol

o-DFB ortho-difluorbenzol

MeCN acetonitrile

pn 1,2-diaminopropane

scXRD single crystal X-ray diffraction

pXRD powder X-ray diffraction

EDX energy-dispersive X-ray spectroscopy

(F-)IR (far) infrared

NMR nuclear magnetic resonance

DSC differential scanning calorimetry

IC ion chromatography

� amount of substance � mass � molar mass � potential (battery measurement) � electrical resistance � electrical current � Charge � potential (cyclic voltammetry) density conductivity � viscosity

� = 96 485 C mol–1 Farraday constant[1]

[1] P. Atkins, J. de Paula, Atkins’ Physical Chemistry, OUP Oxford, 2006.

1

Table of Content

A Introduction .......................................................................................................................... 5

A.1 Motivation ............................................................................................................................... 5

Why Ionic Liquids?........................................................................................................... 6

Why Redox Flow Batteries? ............................................................................................ 6

A.2 Overview over the Areas of Research Concerned .................................................................. 9

Terms and Definitions used Throughout this Work ........................................................ 9

Redox Flow Batteries ..................................................................................................... 10

Ionic Liquids ................................................................................................................... 14

Redox Flow Batteries Based on Ionic Liquids ................................................................ 17

A.3 Analytical Methods ............................................................................................................... 19

Raman Spectroscopy ..................................................................................................... 19

Electrochemical Characterization of Batteries .............................................................. 21

A.4 Objectives of this Work ......................................................................................................... 27

References ......................................................................................................................................... 29

B IL-RFB: Membrane-Free Concepts and Economic Potential ................................................... 33

B.1 Concepts for a Membrane-Free Flow Battery ....................................................................... 33

General Considerations ................................................................................................. 33

Concepts for a Membrane-Free Hybrid IL Redox Flow Battery System ........................ 35

Discussion ...................................................................................................................... 38

B.2 Tool for the Evaluation of the Economic Potential of IL-RFB Concepts ................................ 41

Scope, General Approach and Systems Studied ........................................................... 42

Equations ....................................................................................................................... 46

Results and Discussion .................................................................................................. 49

Conclusion ..................................................................................................................... 52

References ......................................................................................................................................... 53

2

C Structure and Properties of Novel Chloroiodate(III) Ionic Liquids ........................................... 55

C.1 Introduction ........................................................................................................................... 57

C.2 Results and Discussion ........................................................................................................... 61

Quantum Chemical Calculations I: Structures in the Gas Phase and Thermodynamics 61

Syntheses, Melting Points and Crystal Structures ......................................................... 64

Quantum Chemical Calculations II: Computed Raman Spectra .................................... 71

Identification of the Anions in the Mixtures by Vibrational Spectroscopy ................... 73

C.3 Conclusion and Outlook ........................................................................................................ 77

C.4 Electronic Supporting Information ........................................................................................ 79

Synthesis ........................................................................................................................ 80

Quantum Chemical Calculations.................................................................................... 84

Single-Crystal X-Ray Diffraction ..................................................................................... 88

References ......................................................................................................................................... 92

D Membrane-Free Sn/Br2 Hybrid IL-RFB ................................................................................... 97

D.1 Introduction ........................................................................................................................... 97

Bromostannate Salts and Ionic Liquids.......................................................................... 98

Tin Deposition from Ionic Liquids .................................................................................. 98

Polybromide Ionic Liquids ............................................................................................. 99

Tin and Polybromide Based Batteries.......................................................................... 100

D.2 Results and Discussion ......................................................................................................... 101

Bromostannate(IV)-ILs ................................................................................................. 101

Mixed Bromostannate(IV) and Polybromide ILs.......................................................... 111

Electrochemical Measurements on the System Sn/[HMIM]Br/Br2/SnBr4 ................... 119

D.3 Conclusion and Outlook ...................................................................................................... 137

D.4 Experimental ........................................................................................................................ 139

Theoretical Methods ................................................................................................... 141

Bromostannate Ionic Liquids ....................................................................................... 142

3

Mixtures of [HMIM]Br, Br2, and SnBr4......................................................................... 148

Electrochemistry ......................................................................................................... 151

References ....................................................................................................................................... 155

D.5 Appendix ............................................................................................................................. 158

Crystallographic data for [HMIM]2[SnBr6] ................................................................... 158

E Investigation Towards an All-Mn Hybrid IL-RFB .................................................................. 161

E.1 Introduction ........................................................................................................................ 161

Chloromanganate Salts and Ionic Liquids ................................................................... 161

Manganese Deposition from Ionic Liquids .................................................................. 163

Manganese and Manganese Salts in Batteries ........................................................... 164

E.2 Results and Discussion ........................................................................................................ 165

Chloromanganate(II) Ionic Liquids .............................................................................. 165

Attempted Synthesis of Chloromanganate(IV) ILs ...................................................... 169

All-Mn Hybrid Ionic Liquid Battery Tests ..................................................................... 171

E.3 Conclusion and Outlook ...................................................................................................... 177

E.4 Experimental ....................................................................................................................... 179

Synthesis of Chloromanganat(II) Ionic Liquids ............................................................ 180

Attempted Synthesis of Chloromanganats(IV) ............................................................ 182

Electrochemical Measurements on Solutions of [P666 14]2[MnCl4] in MeCN ................ 187

References ....................................................................................................................................... 189

E.5 Appendix ............................................................................................................................. 191

Crystallographic data for [NEt4]4[MnCl4][MnCl5] ......................................................... 191

Cyclic Voltammetry ..................................................................................................... 192

Powder Diffractogram of K2[MnCl6] ............................................................................ 193

F Development of a Battery Test Setup ................................................................................. 195

F.1 Hardware I: Battery Test Setup for Static Liquid Active Materials ...................................... 195

Test Cell ........................................................................................................................... 195

4

Source Measure Unit, Temperature Control, Environmental Sealing ............................. 197

F.2 Software: bbat ..................................................................................................................... 199

Documentation ................................................................................................................ 201

User Interaction: pcontrol and extras ............................................................................. 203

Inner Workings: script Folder .......................................................................................... 203

F.3 Hardware II: Progress Towards a Flow-Battery Test Setup ................................................. 207

Flow Test Cell ................................................................................................................... 207

Process Engineering ......................................................................................................... 209

References ....................................................................................................................................... 213

F.4 Appendix: bbat Source Code and Documentation .............................................................. 215

documentation ................................................................................................................ 215

testlibrary ........................................................................................................................ 231

pcontrol & extras ............................................................................................................. 238

script ................................................................................................................................ 243

script/lib ........................................................................................................................... 252

script/gnuplot .................................................................................................................. 270

G Conclusion and Outlook ..................................................................................................... 273

Lebenslauf ................................................................................................................................ 277

A.1 Motivation

5

A Introduction

A.1 Motivation

The conviction that the climate change observed throughout the world is caused by human

greenhouse gas emissions has become, despite some exceptions, a politically and scientifically

accepted truth. This recognition was shown most prominently by 195 countries signing the Paris

Agreement, which entered into force on 4 November 2016, and thereby agreed to work towards the

goal of limiting the increase in the global average temperature compared to pre-industrial levels to

well below 2 °C and to pursue efforts to reach only a 1.5 °C increase.[1]

It was predicted that, in order to reach the 1.5 °C goal, carbon dioxide emissions, which are the

dominating cause for global warming, must reach a net zero between the years 2045 to 2060.[2] This

demands a tremendous effort starting as soon as possible, since the window for this change to happen

is closing rapidly.[2]

85 % of the CO2 emitted by Germany in 2013 was caused by the energy sector.[3] This is due to the large

share of 80 % of the total primary energy consumption being provided by fossile fuels, with nuclear

energy and renewable energies having a share of only 8 and 12 %, respectively.[3] The largest share of

the energy related CO2 emission, 45 %, is due to the production of electricity, 19 % are caused by street

traffic, 13 % by households (mostly heating) and the residual 23 % by the industry, the public sector

and a few minor consumers.[3] There are many ways in which the primary energy consumption can and

will have to be lowered, like for example more efficient devices, improved building insulation, or a

general decrease in consumption. It seems likely, at least at the moment that a large share of the street

traffic will be using electric energy in the future. This means that the emission of CO2 can be lowered

by a total of 64 % if the energy used for the production of electricity and the energy consumed by

street traffic will be produced from renewable sources.

One of the troublesome aspects of renewable energy is that the energy is not provided on demand,

but in a fluctuating way. This problem can be met by finding creative ways of shifting the energy

demand, for example by equipping millions of fridges with cold storage devices and charging them only

at times when there is excess energy available[4] or by running washing machines on a remotely

controlled schedule. Another way is to regulate the supply of electricity to the consumer by using

storage systems for the electrical energy. Besides the established pumped hydroelectric energy

storage, two major technologies are investigated at the moment. One is chemical storage, e.g. the

A Introduction

6

production of hydrogen from electricity, the other is electrochemical storage devices, in other words,

secondary batteries, which are the topic of this work.

Why Ionic Liquids?

Ionic liquids (ILs), which are commonly defined as salts with a melting point of 100 °C[5] and often

exhibit melting points below room temperature (RTILs), were first systematically studied and

developed as an electrolyte for battery applications.[6] Since these early times, they have also found

widespread use as a new type of solvent, in synthesis and catalysis, and numerous other applications.[5]

They have, however, not been investigated systematically as an active material for batteries, which

means that the IL itself is used to store the energy, and not merely as a solvent, transporting agent, or,

as in the case of Zn/Br2 batteries, as a complexing agent to reduce the vapour pressure of bromine in

an otherwise aqueous system.

The lifetime of conventional batteries is often limited by changes in the structure of the solid active

materials. In redox flow batteries, this limitation is overcome by dissolving the active materials in a

solvent, though at the cost of a significantly reduced energy density. For cost reasons, the employed

solvent is often water, and so the choice of active materials is limited by its electrochemical potential

window. Since ILs are liquid without the addition of a solvent and typically exhibit a very broad

electrochemical window, their use as active material could potentially combine high energy density

with a long lifetime and additionally allow for the use of active materials, which are not usable in

aqueous solution.

Why Redox Flow Batteries?

From the preliminary results obtained by myself and Dipl.-Chem. Michael Hog during the work on our

diploma theses, it became clear that the achievable energy density would most likely not be able to

compete with existing technologies, like li-ion batteries.[7,8] The alternative use case would be

stationary applications, like the large-scale storage of renewable energies.

For stationary applications, a more complicated redox flow setup is viable, which has the benefit of

allowing to independently scale storage capacity (volume of the tanks) and power output (number of

stacks/specific design). This allows for the batteries to be assembled specifically for each use case.

Compared with the established redox flow systems, the energy densities most likely to be achieved

using ILs were very competitive. Additionally, though there certainly are safety issues associated with

A.1 Motivation

7

storing large amounts of bromine, they are no fire hazard, which is also true for ionic liquids. Both are

certainly not as flammable as Li-ion batteries, which is especially important when thinking of large-

scale applications.

The sum of these considerations led to the decision to investigate the technology of redox flow

batteries based on ionic liquids.

A Introduction

8

A.2 Overview over the Areas of Research Concerned

9


The section of this overview which is concerned with ionic liquids is based on the respective chapter

of the introduction to my diploma thesis.[8]

Terms and Definitions used Throughout this Work

Electrochemical cells designed to be used as a convenient source of electrical energy are commonly

referred to as batteries. If the battery can only be discharged once, it is more precisely called a primary

battery, if it can be discharged and charged multiple times, it is called a secondary battery. Since this

work is only concerned with the development of secondary batteries, they will be referred to simply

as “batteries” and the distinction will only be made explicitly, when it is considered helpful for the

reader.

In electrochemical cells, the anode is the electrode at which the oxidation of a chemically active

substance takes place, and the electrode at which the corresponding reduction proceeds is called the

cathode. The respective half cells are called the anodic and the cathodic half-cell, containing the

anolyte and the catholyte. If this convention were followed for secondary batteries, the names of the

electrodes, half-cells, and electrolytes would be different when referring to the charging or the

discharging process. The convention, which will be followed throughout this work, is to define the

name of the electrode in respect to the processes which occur during discharge. This means that the

negative pole, which is in contact with the negative electrochemically active material, is always called

the anode, and the positive pole, which is in contact with the positive electrochemically active material,

is always called the cathode, independent of the actual local reactions occurring.

A redox flow battery (RFB) is typically defined as a battery in which the active material is dissolved in

a solvent throughout all states of charge. A flow battery, in which a phase change of the active material

is observed during operation, for example the deposition of metal, is commonly referred to as a hybrid

redox flow battery (Hyb-RFB).[9] Since this work is also concerned with membrane-free flow batteries,

these shall at some points be abbreviated as MF-Hyb-IL-RFB.

A Introduction

10

Redox Flow Batteries

Many organic and inorganic redox couples have been studied for use as positive/negative active

materials in redox flow batteries, selected examples being Br2/[S2]2–, Ce4+/Zn, Cr2+/Fe3+ couples.[9] The

most common drawback to these battery systems is cross contamination due to the leaching of the

two active materials through the membrane. However, the vanadium RFB and the Zn/Br2 Hyb-RFB

have reached commercialisation and will be covered in more detail in the following sections.

A.2.2.1 General Considerations in Respect to the Physical Design of Redox Flow Batteries

The typical layout of a redox flow battery is shown in Figure 1. The active materials are dissolved in a

solvent and the residual catholyte and anolyte stored in tanks. For charging and discharging, the liquids

are pumped through a cell stack, where the two half cells are separated by a membrane. The space

between the solid electrode plate and the membrane is often filled with a carbon felt to increase the

electrochemically active surface area.

This concept and design of RFBs can easily be seen as a given fact, since development of the technology

started as early as 1971[9] and nowadays commercial products are readily available. Many chemical

species have been investigated as active materials, of which a selection will be covered in the following

sections. However, the chemical systems investigated in this work are significantly different from these

established, mostly aqueous systems. Therefore, this section aims to look at the building principle of

RFBs in a broader perspective by comparing it with the building principle of typical solid state batteries.

In classical batteries, like the Li-ion or the lead-acid battery, the active material is solid and the two

active masses are typically separated by a macroporous insulator.[10] The ions needed to counteract

the charge imbalance produced by electrons being transferred from the anode to the cathode are

transported by the electrolyte, which fills the gap between the electrodes including the pores of the

separator. Since the active masses in redox flow batteries are dissolved in a liquid phase, their electrical

insulation becomes a more challenging part of the chemical design. No liquid electrolyte is needed,

but a solid and selective ion exchange membrane, which is designed to minimize crossover of the active

masses and to only transfer the charge balancing ions. A cheaper alternative to these costly

membranes are micro porous separators, though with the downside of a non-selective operation.

Key goals in the physical design of batteries are to achieve a high power density and a high energy

density at the lowest price possible. To ensure a small inner resistance and high power density, the

surface of the electrode should be as large as possible and the distance between the electrodes as

small as possible. However, this can be contradictive with the measures needed to achieve a low cost


11

pump

graphite

composite

electrodes

catholyte

membrane or

porous

separator

e e

anolyte

pump

source/sink

carbon felt

Figure 1: Schematic layout of a redox flow battery. Electron flow is depicted for the discharge of the battery. For a hybrid redox flow battery, one of the carbon felts is removed and metal is deposited in one of the half-cells.

and a high energy density, which is ensuring that the weight and volume fraction of the chemically

inactive parts, like the electrode, but also the casing etc., are kept as low as possible.

For lithium Ion batteries, a common building principle is using thin sheets of copper and aluminium as

current collectors with a thin layer of solid active material bound to them.[10] This is viable, since the

energy density of the solids used is comparatively high and the total amount of electrode materials

stays reasonable. Additionally, the conductivity of the organic electrolyte is low if compared to

aqueous electrolytes, which further amplifies the need for a small electrode distance. If trying to use

the same approach with a vanadium based, liquid electrolyte, which has a much lower energy density,

the tiny amounts of energy contained in the thin liquid film would lead to a vast amount of electrode

material and membrane needed to achieve the same storage capacity as the named Li-ion battery.

One solution would be to increase the distance of the electrodes and thereby increase the volume that

can be occupied by the active material relative to the surface area of the electrode. However, this

would come at the cost of a strongly increased inner resistance. The technological solution found for

this problem is a medium distance of the electrodes, filled with a carbon felt that increases the surface

area.[9] The active material, which would be depleted in a short time, is continuously replaced by

pumping the solution through the cell stack. It follows naturally that, despite the chemical challenges

of a battery, the design of a suitable stack is a key requirement for the technological and economical

prospects of a flow battery.

A Introduction

12

An approach on how to adapt these building principles to the specific characteristics of a RFB utilizing

ILs as its active material is the concept of a membrane-free Hyb-IL-RFB. This concept will be covered

briefly in the section regarding IL-RFBs within this chapter and discussed in detail in Section B.1.

A.2.2.2 Vanadium Redox Flow Batteries

The most advanced redox flow battery in terms of its commercialisation is the all-vanadium redox flow

battery (generation 1 vanadium redox flow battery, G1-VRFB). Its energy density is 25 Wh kg–1 in

respect to a 2 M vanadium solution in sulfuric acid[11] and has an OCV of 1.6 V[9]. Life times of more

than 200 000 cycles for practical installations have been reported (Sumitomo Electric Industries,

Japan).[9] The (formalized) redox reactions occurring during discharge are[9]:

ox V2+ ⟶ V3+ + e–

red [VO2]+ + 2 H+ + e– ⟶ [VO]2+ + H2O

V2+ + [VO2]+ + 2 H+ ⟶ V3+ + [VO]2+ + H2O

Since it utilizes the same element as active material in both half-cells, capacity fade due to cross

contamination of the active materials does not lead to a permanent capacity loss. Drawbacks are the

low energy density and an upper operational temperature limit of 40 °C due to the irreversible

precipitation of V2O5.[9] Both can be improved by using a mixed acid electrolyte, which allows for a

2.5 M concentration and operation at up to 50 °C.[12]

A typical pristine electrolyte, before the first operation, is composed of an equimolar solution of

vanadium(III) and vanadium(IV). The active material is then oxidized and reduced to obtain a battery

with a solution of vanadium(III) in the anolyte and vanadium(IV) in the catholyte. At this point, the

average oxidation state of vanadium is still 3.5. However, due to side reactions, like parasitic hydrogen

and oxygen evolution and also due to crossover of the active materials through the membrane during

operation, the average oxidation state can shift. This corresponds to an imbalance in the state of

charge of the two half-cell electrolytes and lowers the available capacity. The original capacity can be

restored by electrochemically oxidizing or reducing one of the electrolytes or, in the case of a higher

average oxidation state, by adding a reducing agent, like carbohydrates, to the vanadium(V) containing

catholyte.[13] The carbohydrates are oxidized to form CO2 and H2O and hence lead to a balanced

electrolyte.

As has been described in the previous section, a typical configuration for a VRFB stack is two solid

electrodes made of a polymer graphite composite, two carbon felts of high surface area and a

membrane as a separator. The power density achieved through different flow layouts of these stacks


13

is a key cost factor for the price of the cell, since in case of a high power density, less of all of these

materials, and especially of the expensive membrane, need to be used.[14] The total cost of the system

also largely depends on whether a high or a low power to capacity ratio is desired.[14] For a

1 MW/4 MWh system, 48 % of the costs are due to the battery chemicals, whereas the next highest

cost fraction is 22 % for the membrane. For a 1 MW/0.25 MWh system, the membrane costs are even

higher, contributing 42 % of the total system costs.

Though many large scale commercial installations have been commissioned, and the number of papers

published on this type of battery did breach 300 in 2014, there is still little research attributed to this

type of battery, when compared to technologies like Li-Ion batteries or fuel cells.[15]

For the generation 2 vanadium redox flow battery (G2-VRFB), the bromide salts of vanadium are used

in a mixed HCl/HBr electrolyte.[16] Improvements include a higher energy density of 25–50 Wh kg–1 and

a wider operational temperature window.[16] Upon oxidation during charging, polyhalide anions

including [ClBr2]– form, which are complexed in an organic layer in similarity to the Zn/Br2 Hyb-RFB.

A.2.2.3 Zn/Br2 Hybrid Redox Flow Battery

The concept of a hybrid Zn/Br2 battery is based on the reactions:

ox Zn ⟶ Zn2+ + e–

red [Br3]– + 2 e– ⟶ 3 Br–

Zn + [Br3]– ⟶ Zn2+ + 3Br–

The tribromide shown in the reaction scheme is only symbolic, since complexing agents are used to

decrease the hazards involved with bromine vapour and form an organic polybromide layer at the

bottom of the catholyte tank.[17] A third pump is used to pump this layer through the stack during

discharge. A myriad of different complexing agents have been reported[10], many of which are variants

of tetraalkylammonium salts. HBr, NaBr and KBr are often added as supporting electrolytes[9,10], and a

porous separator or cation exchange membrane is used in combination with carbon felts in the

bromine containing half-cell.[17]

Advantages of the Zn/Br2 battery are its energy density of 65–80 Wh kg–1[9,18], an OCV of 1.8 V[18], and

the low cost of the chemicals involved. The major drawback of the system is the hard to control zinc

deposition morphology, with dendrites threatening to short circuiting the cell by perforating the

membrane.[9]

A Introduction

14

N

[BMP]+

butyl

NNalkyl

ethyl

butyl

hexyl

octyl

[EMIM]+

[BMIM]+

[HMIM]+

[OMIM]+

alkyl =

PF

F

FF

FF

[PF6]- [BF4]

-

B

F

F

FF

Al

Cl

Cl

ClCl

[AlCl4]-⁻

NSO2CF3

[NTf2]-

F3CO2S

Ionic Liquids

This section is intended to give a brief overview on the history of research on ILs and their general

properties. More information related to the specific ILs relevant to this work will be given in the

introductions to the respective chapters.

As has been stated previously, ILs are commonly defined as salts having a melting point below 100 °C.[5]

Most ILs consist of an organic cation and a polyatomic anion, and the first report[5] about such liquid

salts was published early in the 20th century.[19] In 1978, the U.S. Airforce Academy was looking for

electrolytes for a possible aluminum/chlorine battery and thereby rediscovered a family of ILs that had

first been mentioned in 1948.[5] These ILs were based on alkylpyridinium cations and aluminum halides,

but since the pyridinium cation was prone to chemical and electrochemical reduction, it was soon

replaced by dialkylimidazolium. IL-stability towards water was achieved by replacing haloaluminate

anions with water stable anions in 1992.[20][5] Some of the most commonly employed anions and

cations are shown in Figure 2. Since these times, research was undertaken by a growing number of

scientists, leading to a drastic increase in publications on the topic starting around the year 2000.[5]

Figure 2: Cations and anions often employed in the synthesis of ionic liquids.

A.2.3.1 Synthesis

The most commonly used starting materials, which are the halogen salts of dialkylimidazolium,

dialkylpyrrolidinium, tetraalkylammonium and -phosphonium, are typically synthesized by

quaternization reactions of the free amine or phosphine with a haloalkane. Nowadays, these salts are

readily available from commercial sources and were kindly supplied by IoLiTec for this work, so their

synthesis will not be covered here.


15

The synthetic route for ILs based on these cations follows mostly two routes starting from the

mentioned halide salts.[10] The first route, which is also employed for all ILs studied in this work, is the

addition of Lewis acids, like metal halides or halogens, to the [cat]X halide salt. The exact type of anion

obtained as an adduct of the Lewis acid and the Lewis basic halide depends strongly on the

stochiometric ratio of the two components. For example, the addition of one equivalent of AlCl3 to

1-ethyl-3-methyl-imidazolium chloride ([EMIM]Cl) yields the [AlCl4]– anion, however, for higher

stochiometric ratios of AlCl3, the formation of complicated mixtures of larger anions like [Al2Cl7]– and

even [Al3Cl10]– is observed.[21]

The second synthetic route is based on metathesis reactions for which the [cat]X salt is mixed with a

silver or lithium salt of the desired anion. The resulting silver/lithium halide salt has to be insoluble in

the formed IL and can then be removed by filtration.[5]

A.2.3.2 Physical Properties

The basic physical properties of some common imidazolium based ionic liquids are shown in Table 1.

Melting points are usually measured through differential scanning calorimetry (DSC), but are

sometimes hard to determine due to glass and other more complex phase transitions.[5] In general, the

melting points of ILs increase with the number of charges per ion. Lower melting points are found for

less symmetric ions and often with increasing ion size.[5] Influences by more specific interactions

between cation and anion for certain combinations thereof are also common.[5]

In regard to organic cations, which are usually designed to carry only one positive charge, the

symmetry and the length of alkyl substituents are the most influencing factors for the melting points.

For imidazolium cations, the substitution pattern is important, with the most common modification

being the variation of the length of one alkyl chain substituent, as is also seen in the data shown in

Table 1. For 1-alkyl-3-methyl-imidazolium cation ([RMIM]+), melting points decrease on lengthening

the alkyl chain, but start to increase as decyl substituents are reached. The first decline is due to a

decrease in packing efficiency and the later increase can be attributed to growing van der Waals

forces.[5] Melting points also increase with increased branching of the substituents, since rotational

freedom of the alkyl chain is hindered, which results in lower melting entropies.[5]

ILs often behave as Newtonian fluids[5] and can vary in their viscosity from 10 to 20.000 mPa s and

more. The viscosity is strongly dependent on temperature and on purity, for example, a concentration

of 2 wt% water can lower the viscosity of [BMIM][BF4] by 50 %.[5] For comparison, the viscosities of

pentane, water, and sulfuric acid are 0.224, 0.891, and 27 mPa s respectively.[30] Viscosity increases in

A Introduction

16

most cases with the length of the alkyl substituents and the symmetry of the organic cation. It is not

generally correlated to the size of the anion and rather influenced by anion specific interaction with

the cations.[5]

The properties of Lewis acid based ILs change on variation of the molar ratio of their components. This

is also shown in Table 1 for the ILs resulting from mixtures of [EMIM]Cl and AlCl3 with molar ratios of

1:1 and 1:2.

The upper limit of the liquid range is usually determined by the decomposition temperature, which is

determined through thermogravimetric analysis (TGA) and can be as high as 350 °C.[5]

A.2.3.3 Electrochemical Properties

One of the limiting factors for the use of a specific solvent for electrochemical applications is its

potential window. For ILs, this is usually defined by the potentials for the reduction of the cation and

the oxidation of the anion.[5] These can be measured through cyclic voltammetry and can be

significantly influenced by impurities like water or halides.

The cathodic limit for [RMIM]+ cations is usually set by the reduction of the hydrogen atom in the

2-position.[5] The anodic limit is reduced in basic aluminum chloride ILs that contain free chloride, since

it is more easily oxidized than chloride coordinated to aluminum.[5] In acidic mixtures, the anodic

(reduction) limit of these ILs is further lowered due to the reduction of aggregated anions.[5]

ILs exhibit good conductivity compared to other non-aqueous solvents, but are less conductive than

concentrated solutions of salts in water. Temperature dependence is often linear above room

temperature (Arrhenius behavior) though negative deviations are observed when approaching the

glass transition temperature of the respective IL and conductivities are best explained with the Vogel-

Table 1: Basic physical properties of some common ILs at room temperature if not noted otherwise.

melting point ° C

viscosity mPa s

pot. windowa) V

conductivity mS cm–1

[EMIM]Cl 82[22] – – – [BMIM]Cl 69[23] – – – [HMIM]Cl –75b),[24] 716[24] – 0.30[25] [EMIM][PF6][26] 62 6.3c) – 5.9c) [EMIM][BF4][27] 12 38 4.5c) 13.1 [BMIM][BF4][28] –81b)[24] 233e) – 8.6 [EMIM][NTf2][26] –15 6 4.1f) 4.7 [EMIM][AlCl4] 7[20] 16g)[20] 4.4h)[5,29] 20.9[20] [EMIM][Al2Cl7]h) –96[20] 12f)[20] 2.9i)[5,29] 13.7[20] a) Values depend strongly on residual water content; b) glass transition temperature; c) at 80 °C; d) Pt electrode; e) at 30°; f) glassy carbon electrode; g) at 20°C; h) W electrode; i) equilibrium of different anionic species.


17

Tammann-Fulcher equation in this region.[5] Again, impurities have a strong effect, potentially due to

the resulting decrease or increase in viscosity.[5] Accordingly, the addition of a co-solvent can

significantly increase conductivity and is associated with effects like solvation of the anion, decreased

ion pairing and thus resulting greater mobility of the charge carriers.[5] For high mole fractions of co-

solvent, conductivity decreases caused by the lowering of the concentration of charge carriers.

There is a strong interest in ILs as possible electrolytes for the deposition of metals such as aluminum,

titanium and tungsten.[31] These materials offer excellent corrosion stability but cannot be deposited

from aqueous solution. Even though a lot of metals have already been successfully deposited from ILs,

the mechanism of these reactions is still unclear and more research is needed to develop controlled

and reproducible processes. A literature overview for the deposition of tin and manganese from ILs

will be given in Chapters D and E, respectively.

Redox Flow Batteries Based on Ionic Liquids

In IL-RFBs, anionic complexes of the active materials are created by the addition of an appropriate

[cat]X salt. Typically, and preferably, the resulting salts then have a melting point below RT and do not

need a solvent to be used in a redox flow battery.

There have been some minor investigations towards this or a similar goal, which are covered as a side

topic in recent reviews.[32] Most notably, a patent was filed in 2010 by Noack et. al. in which they

suggest the use of many different redox couples in ionic liquids for the application in a flow battery

and demonstrate a static cell based on a 0.5 M solution of VCl3 in 2-hydroxyethylformiate.[35] Since

then, no report has been published about further work on these systems.

Despite these efforts, no systematic investigation has been performed in which the ionic liquid itself is

the redox couple and is transformed in the process of charging and discharging.

The first active materials envisioned for application in an IL-RFB battery in this project, were aluminium

and bromine. The respective ILs were well studied, aluminium is cheap, was expected to exhibit a high

potential for the three-electron oxidation, and the polybromide ILs were known to exhibit excellent

conductivities. In the battery concept, polybromide anions are reduced at the cathode and the

produced bromide ions are transferred to the anolyte via the ion selective membrane. In the anodic

half-cell, aluminium is oxidized and dissolved in a bromoaluminate IL.

A Introduction

18

Figure 3: Schematic representation of the concept of an Al/Br2 Hyb-IL battery.

The reactions occurring during discharge are:

ox 2 Al0 +2 [AlBr4]– + 6 Br– ⟶ 2 [Al2Br7]– +6 e–

red [Br9]– +6 e– ⟶ [Br3]– +6 Br–

2 Al0 + [Br9]– ⟶ 2 [Al2Br7]– + [Br3]–

During charging, bromide ions are oxidized and aluminium is deposited from an [Al2Br7]– containing IL.

A Lewis acidic mixture was selected, since the required metal deposition is not observed for neutral

and Lewis basic mixtures.[33] The concept is shown for a static configuration in Figure 3 for an Al/Br2 IL

battery. The membrane-free concept is introduced in the section describing the objectives of this work

and in more detail in Section B.1.

A.3 Analytical Methods

19


The major concern of this work was the synthesis of anionic coordination complexes and their

transformation through electrochemical reactions. Many analytical methods including nuclear

magnetic resonance (NMR), (far-) infrared ((F-)IR), and Raman spectroscopy, powder and single crystal

X-ray diffraction (pXRD, scXRD), quantum-chemical calculations (QCC), elemental analysis (EA), ion

chromatography (IC), differential scanning calorimetry (DSC), measurement of viscosity and

conductivity, cyclic voltammetry (CV), and chronoamperometry (CA) were employed for the

investigation. Raman spectroscopy and electrochemical characterization of batteries were most

strongly relied upon and will be covered explicitly in this section.

Raman Spectroscopy

Physicist C.V. Raman first observed an effect, which was later named in honour of its discoverer, that

when matter is irradiated using monochromatic light, the scattered light includes a small amount with

a slightly shifted frequency.[34] This shift is caused by an interaction of the electromagnetic wave with

the irradiated compound and its vibrational states. The interaction relevant for the Raman scattering

is only observed when the compound has vibrational modes in which its polarizability changes.[34] For

such an interaction, the energy of the scattered wave or photon is increased or decreased by the

amount of energy stored in the vibrational mode. If the respective vibration was excited before the

interaction (Stokes scattering), the energy of the scattered photon is increased, and it is lowered if the

vibration was not excited but is excited after the interaction (anti-Stokes scattering).[34] The first

comprehensive publication about Raman spectroscopy, the analytical method based on this effect,

was published by Kohlrausch in 1943 and gained in popularity with the event of high energy lasers.[34]

In combination with IR spectroscopy, most of the vibrations of a molecule can be studied, though not

all frequencies are Raman and IR active. For molecules with an inversion centre, the exclusion rule

applies, which means that only those vibrations symmetrical to the inversion centre are Raman active,

and all others are only IR active.[34]

A.3.1.1 Normal Modes for Selected Coordination Polyhedra

Particles moving in three-dimensional space have three degrees of freedom. When particles, in this

case atoms, are combined to form molecules, the total number of degrees of freedom for the molecule

is three times the number of its atoms N. When reserving three degrees of freedom for the translation

of the complete molecule in space, and three for its rotation split into the components for three axes

A Introduction

20

(two for linear molecules), then the remaining 3N – 6 degrees of freedom for non-linear molecules are

related to its internal movements.[34] The combined internal movements of the atoms of the molecule

can be split into the 3N – 6 independent vibrations, its so called normal modes, which can be visualized

and be assigned to a specific frequency.[34] For symmetrical molecules or coordination complexes,

some of these normal modes can be degenerate, which means they are closely related and exhibit the

same frequency. The lower the symmetry, and the higher the number of atoms in the molecule or

coordination complex, the more non-degenerate normal modes are present, and the more complex

becomes their visualisation. In these cases, quantum-chemical calculations can be of great help to

visualise the vibrational modes and to calculate their expected frequencies.

The normal modes of an octahedral, a tetrahedral, and a trigonal bipyramidal coordination complex

are shown in Figure 4. Additionally, the frequencies of the Raman and IR active modes are listed for a

number of coordination complexes, most of which are of relevance for this work.

Figure 4: Representation of the normal modes for coordination complexes with octahedral, trigonal bipyramidal and tetrahedral geometry and their respective symmetry symbol. Raman and IR activity are shown in a shaded or empty box, respectively, ν6 of the octahedron is inactive in both. The figure was created based on molecular representations and symmetry symbols as given in [36] and [37]. Vibrational frequencies in cm–1 are listed as assigned and reported for [NEt4]2[SnIVBr6][38], Cs2MnIVF6

[39], K2MnIVCl6 (IR[40]

, Raman: own measurement and assignment, see Section E.2.2), [Co(pn)3][MnIIICl6] (pn = 1,2-diaminopropane), [NBu4][SnIVCl5][41], [NEt4][SnIVBr5][41], SnCl4[42], SnBr4

[42], [NEt4][MnIICl4][43].


21

When comparing the frequencies of SnBr4, SnCl4 and [MnCl4]2–, or [MnCl6]3– and [MnCl6]2–, general

trends are observable, namely that the vibrational frequency depends not only on the geometry, but

also on the type of bonding, the mass of the ligand and the central atom, the oxidation states and in

general the electronic structure of the molecule or coordination complex in focus.[36] The vibrational

modes for more complicated cases, like for example [I2Cl7]– or [I3Cl10]– with a C2 and a C1 symmetry,

respectively, will be covered in detail in Section C.2.3.

Electrochemical Characterization of Batteries

A.3.2.1 Open Circuit Voltage, State of Charge and Self-Discharge

One of the key properties of a battery is its open circuit voltage (OCV, UOC), which is the voltage

measured when no external current is allowed to flow. For many battery types, the OCV reaches its

highest value at a state of charge (SOC) of 100 % and decreases for lower SOCs due to changes in the

concentration of the active masses, morphology changes and other effects.[18] It can therefore often

be used as an indicator for the current SOC of the battery, if the exact relationship has been

determined experimentally. This can be done by charging and discharging the battery, while

intermediately measuring the OCV at regular intervals. The self-discharge behaviour of a battery can

then be tested by charging a battery to a certain SOC, stopping the current flow and then observing

the change of the OCV over time.

A.3.2.2 Terminal Voltage, Inner Resistance and Linear Sweep Experiment

Stopping the current flow to observe the present OCV would not be necessary, if the internal resistance

Ri of the battery was neglectable. In this case, the terminal voltage UT, which is the voltage measured

when an external current I is flowing between the two poles of a battery, would be equal to the OCV.

However, the resistance of the electrolyte, the separator, potential losses on transfer of the electrons

to the electrode and other losses lead to a terminal voltage which is lower than the OCV.[18] This

correlation is shown in a simplified version in Figure 5 a).

A comparatively simple measurement to obtain a voltage-current diagram is a linear sweep

experiment, during which the terminal voltage of a battery is changed linearly at a fixed rate, e.g.

0.1 V s–1, and the observed current flow is recorded. An example of such an experiment is shown in

Figure 5 b). In this case, the linear sweep was started at a terminal voltage of 0 V, resulting in a

discharge current of 10 mA, and stopped at a charging voltage of 2 V, with a resulting charging current

of 7 mA. However, it is a common behaviour for batteries that the current obtained at a fixed terminal

A Introduction

22

I

U

UOC

Re I

R i I

R i I

charge

discharge

power output

internal heat lossesUT

−5

0

5

0.0 0.5 1.0 1.5 2.0

cu

rre

nt

/ m

A

potential / V

a) b)

Figure 5: a) Simplified schematic of the relationship between the terminal voltage UT and the current I for an assumed constant inner resistance Ri while charging or discharging. The internal and external potential losses can be calculated by multiplying the internal or the external resistance (Ri, Re) with the current I. The figure was modified based on a scheme in [18]. b) Sweep measurement performed for a terminal voltage of 0 to 2 V at a sweep rate of 0.1 V s–1 on a membrane-free Sn/Br2 IL battery. The measurement is depicted with reversed x and y axes compared to the figures in the rest of the work in order to be visually compatible with figure a).

voltage decreases over time. This is due to a local depletion in the concentration of the charged active

masses,[18] a non-equilibrium state which is reversed through diffusion, or in the case of flow batteries

by forced convection, when the current flow is stopped. A result obtained by a sweep measurement is

therefore always a combination of this time dependent drop in the current and all other effects which

are only related to the current flow.

A.3.2.3 Polarisation Curves and Area Specific Resistance

A polarisation experiment is a more sophisticated measurement procedure compared to the linear

sweep. It allows to specifically obtain information about the effects caused by a changing current flow

and to isolate them from the time dependent changes on current and terminal voltage. The specific

form of this widely applied method was adopted from a procedure suggested by our collaboration

partner Kolja Bromberger from Fraunhofer ISE.

In this experiment, the battery is subjected to predefined and increasing charge and discharge

currents. The measurement is typically performed at an SOC 50 %, but charging polarisations or

discharging polarisations can also be measured at an SOC 0 % and 100 %, respectively. In all cases, the

currents are only applied for a short interval, after which the current flow is interrupted for a resting

phase. This phase has to be set to be long enough to allow the battery to recover into a state close to

the electrochemical equilibrium before the next current step is applied. A respective experiment is

shown in Figure 6. The parameters typically used for the characterization of the static test cells were


23

a 15 second current pulse followed by a resting state of 45 seconds. The currents were set to

experimentally determined values based on an upper limit for the terminal voltage during charging as

defined individually for each tested battery, and a lower limit of 0 V for the terminal voltage during

discharge.

From the obtained values, the area specific resistance (ASR) can be calculated for each current pulse,

the results being characteristic for the battery under testing. If measured and calculated in a

standardised way for multiple batteries, the ASR values become a valuable tool to judge and compare

the performance of different cell designs and/or different chemical systems.

In our case, the ASR values were calculated, as suggested by Kolja Bromberger, based on the difference

of the voltage ΔU between the last measurement point of the OCV UOC and the first measurement

point for the terminal voltage U1 measured at the specified current I1 0.5 seconds later. With the

electrode surface A, the ASR is obtained according to Equation (1).

�� = �� − �� ∙ � = ∆�� ∙ � (1)

The ASR can then be plotted against the current density as schematically shown in Figure 7. Often, a

drop in the ASR is observed when moving from small to intermediate currents. For small currents,

potential losses due to kinetic effects dominate the ASR, but are outweighed in the intermediate region

by the potential drop due to the inner resistance of the cell.[44] In this intermediate region, the ASR is

constant and increases only on moving to even higher currents, where a mass transport limitation is

Figure 6: Polarisation measurement for an Sn/Br2 IL battery. A slow, time dependent decrease/increase for the terminal voltage during discharging/charging can be seen for the current pulses. ΔU is defined as the difference between the first measurement point of the terminal Voltage U1 for a specific current pulse and the last measurement point UOC for the OCV before the current pulse. In conjunction with the current I1 at the first measurement point of the current pulse, the ASR can be calculated.

A Introduction

24

j

ASR

ohmic

kinetic

mass

transport

Figure 7: Schematic representation of the area specific resistance (ASR) plotted against the current density j. With increasing current densities the value of the ASR is dominated by kinetic, ohmic, and mass transport losses.

encountered. Here, the electrical current is limited by the transport of the active mass towards the

electrode, which is achieved either by diffusion in a static cell, or by forced convection in a flow cell.

A.3.2.4 Cycling Tests

A typical experiment for batteries, which are in a more advanced state in their development, are

cycling tests. The battery is charged and discharged at a constant current up to a limiting upper and

lower potential (galvanostatically), or the same process is conducted using a constant charge and

discharge potential until a limiting charge or discharge current is reached (potentiostatic). The

coulombic efficiency, which is calculated as the ratio between the charge transferred during charging

QC and the charge received during discharge QD, is a measure for side reactions and self-discharge

during this process. The energy efficiency depends on the terminal voltage during charging and

discharging. It is therefore dependent on the inner resistance of the battery and the applied currents.

These can be specified in terms of C-rates, where a rate of 1 C corresponds to a complete discharge of

the battery within one hour, a rate of 2 C to a discharge in 30 minutes and so forth. The cycle lifetime

can be measured by observing the rate of the decrease in capacity for increasing cycle counts.

A.3.2.5 Theoretical and Practical Energy Densities and Specific Energies

The calculation of theoretical specific energies and energy densities will be covered in more detail in

Section B.2.2 and will therefore only be discussed briefly here. These values are calculated based on

the mass and the density of the active materials, on the charge transferred during operation, and on

the OCV. The figures obtained are significantly larger than the practical values, which typically also

include all other parts of the battery, like, for example, electrodes, casing, electrolyte and separator.[18]


25

The practical values can also be specified in respect to a defined discharge current using the respective

terminal voltage, in which case they are even lower, though closest to values obtained during real

application.[18] For RFBs, the theoretical values are commonly given based on the mass and density of

the electrolyte and the concentration of the active material in conjunction with the OCV.

A Introduction

26

A.4 Objectives of this Work

27


At the beginning of this work, there were two central objectives for this dissertation, which had

resulted from ideas I developed during the work on the topic of my diploma thesis[8].

The first objective was the exploration, whether a liquid catholyte based on chloroiodates(III) could be

found, which would allow for the use of metal chlorides instead of metal bromides in the anolyte.

Quantum-chemical calculations and unexpected bands in Raman spectra of mixtures of [HMIM]Cl with

more than one equivalent of ICl3 pointed in the direction that the up to this point unknown [I2Cl7]–

anion or even the [I3Cl10]– anion might be accessible. The envisioned redox reactions, shown here in

combination with a Sn(II)/Sn(IV) negative active material, would be:

ox 2 [SnII2Cl5]– + 4 Cl– ⟶ [SnIVCl5]– + SnIVCl4 + 4 e–

red [IIII2Cl7]– + 4 e– ⟶ [II

2Cl3]– + 4 Cl–

2 [SnII2Cl5]– + [IIII

2Cl7]– ⟶ [SnIVCl5]– + SnIVCl4 + [II2Cl3]–

Such an electrolyte was considered beneficial since, in the discharged state, it would still be composed

of complex anions and, not of chloride ions, which would be the case when utilizing a trichloride ionic

liquid. The effect would be a lower melting point, a lower viscosity and a higher conductivity.

Additionally, the electrochemical potential was expected to be slightly higher than that offered by

polybromide ILs.

The second objective was to investigate the feasibility of a membrane-free Hyb-IL-RFB. The idea was

that a thin film of [HMIM]2[SnX6] (X = Br, Cl) could form on contact of a tin electrode with a polyhalide

IL and function as a separator for the operation of a Hyb-IL-RFB. This idea was sparked by the study of

the phase behaviour of chlorostannate(IV) ILs in combination with finding a thin film of solid on a

membrane used in a battery test with a chemistry similar to the one shown in the reaction scheme

above. A schematic of the original concept is shown in Figure 8 and is explained in more detail in

Section B.1.

A Introduction

28

C

2e

Sn

4e

[SnCl 5 ] -

Cl-

Sn4+

l3+ /+

l-

[HMIM]+

Figure 8: Schematic representation of the concept for a membrane-free Sn/ICl3 Hyb-IL battery.

During the work on these topics, I developed the concept of an All-Mn Hyb-IL-RFB, which consequently

became an additional objective. The envisioned redox reactions were:

ox Mn0 + 3 Cl– ⟶ [MnIICl3]– + 2 e–

red [MnIVCl5]– + 2 e– ⟶ [MnIICl3]– + 2 Cl–

Mn0 + Cl– + [MnIVCl5]– ⟶ 2 [MnIICl3]2–

Since the chloromanganates(IV) were known to be highly oxidative compounds and their stability in

ILs was questionable, the chloromanganates(III) were seen as alternative, though at the cost of a

lowered energy density. The system was thought to be beneficial from a conceptual stand point, since

it employs only one element as active material in both half cells and cross contamination is therefore

not as relevant as for flow batteries utilizing two different chemical species. Additionally, manganese

is cheap, available worldwide, and its compounds generally exhibit a low toxicity. Since the concept is

also a hybrid system, a membrane free variant was conceivable, though the first step would be to

explore whether or not the system could work at all.

Two further objectives were coined during the work on the thesis. One was the programming of a

battery testing software that could eventually control the whole flow system including pumps,

thermostats and thermal sensors. Though there is software available to perform general battery

testing, and software like LabVIEW (National Instruments) that allows to control a complete flow setup,

there exists no cheap and open source system that can be modified at will and is transparent in

operation.

When the first results showed that IL-RFBs could be technologically viable, the question arose, if they

were economically competitive. Hence, a tool to estimate the cost structure of the active materials for

IL-RFBs was developed to answer this question and additionally to have a guiding tool for promising

directions of the research on IL-RFBs.


29

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[1] United Nations, “Paris Agreement”, can be found under https://treaties.un.org, 2017.

[2] J. Rogelj, G. Luderer, R. C. Pietzcker, E. Kriegler, M. Schaeffer, V. Krey, K. Riahi, Nat. Clim. Change

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Wärme-System (Themen 2013), Forschungsverbund Erneuerbare Energien, Berlin, 2014.

[5] P. Wasserscheid, T. Welton, Ionic Liquids in Synthesis, Wiley-VCH, Weinheim, 2007.

[6] A. A. Fannin Jr, D. A. Floreani, L. A. King, J. S. Landers, B. J. Piersma, D. J. Stech, R. L. Vaughn, J. S.

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[17] C. Ponce de León, A. Frías-Ferrer, J. González-García, D. A. Szánto, F. C. Walsh, J. Power Sources

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[18] C. H. Hamann, W. Vielstich, Elektrochemie, Wiley-VCH, 2005.

[19] P. Walden, Bull. Acad. Imper. Sci. (St. Petersburg) 1914, 8, 405.

A Introduction

30

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[22] A. Bagno, F. D’Amico, G. Saielli, ChemPhysChem 2007, 8, 873.

[23] U. Domańska, E. Bogel-Łukasik, R. Bogel-Łukasik, Chem. Eur. J. 2003, 9, 3033.

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[26] A. B. McEwen, H. L. Ngo, K. LeCompte, J. L. Goldman, J. Electrochem. Soc. 1999, 146, 1687.

[27] J. Fuller, R. T. Carlin, R. A. Osteryoung, J. Electrochem. Soc. 1997, 144, 3881.

[28] P. a. Z. Suarez, S. Einloft, J. E. L. Dullius, R. F. d. Souza, J. Dupont, J. Chim. Phys. 1998, 95, 1626.

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31

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A Introduction

32

B.1 Concepts for a Membrane-Free Flow Battery

33

B IL-RFB: Membrane-Free Concepts and Economic Potential


Though this work in general and this section in particular mainly concentrates on tin and bromine as

active materials for a membrane-free IL-RFBs, the general principle does apply to similar Hyb-IL-RFBs

based on other elements.

General Considerations

In a classical Redox flow battery, in which both active masses are liquid, a membrane is indispensable

to prevent direct reaction of the oxidizing and the reductive species. As has been stated in the

introduction, the need to use an ion exchange membrane has several drawbacks like

� high price

� increase in inner cell resistance

� possible mechanical failure

� not preventing crossover completely.

These limitations apply in the same manner to IL-RFBs. The crossover of ions is especially problematic

in cells which, unlike the V-RFB, use different elements in both half cells and can lead to an irreversible

capacity fade.[1]

The need for a membrane is less pronounced in hybrid redox flow cells, in which the reaction of the

reducing and the oxidizing species is hindered by the limited surface of the phase boundary. However,

for Hyb-IL-RFBs, additional considerations have to be made.

As has been described in the introduction, the ILs used in IL-RFBs are formed by combining the active

material with a [cat]X salt. On charging a Hyb-IL-RFB, part of the active material is removed from the

anolyte and deposited as solid metal. The remaining [cat]X salt often has a higher melting point

compared to the original IL and also a dramatically decreased electrical conductivity.

This problem is mirrored in the catholyte, where, on discharging, the active material is reduced and

again, the [cat]X salt remains. The composition of the liquid and solid phases for both charged and

discharged state of an Sn/Br2 Hyb-IL-RFB are listed in the top section of Table 2.


34

Table 2: Overview over all chemical species present different SOCs in a Sn/Br2 battery both for a Hyb-IL-RFB and a MF-IL-RFB configuration. For the Hyb-IL-RFB an SOC of 100 % and of 0 % would potentially lead to the formation of solids in the anolyte and the catholyte depending on the cation.

Hyb-IL-RFB

SOC Anode Anolyte Catholyte Cathode

100 % Inert | Sn [cat][Br] [cat][Br9] Inert 50 % Inert | 0.5 Sn [cat][SnBr5] [cat][Br5] Inert 0 % Inert [cat][SnBr4][SnBr5] [cat][Br] Inert

MF-IL-RFB

SOC Anode Electrolyte Cathode

100 % Inert | Sn [cat][Br9] inert 50 % Inert | 0.5 Sn [cat]Br + 0.5 [SnBr4] + 2 Br2

a) Inert 0 % Inert [cat][SnBr4][SnBr5] Inert a) Complex formation within these mixtures will be discussed in Section D.2.2.

The limitations placed on this type of battery can be reduced by charging and discharging only to a

certain level of SOC. This will prevent high ohmic resistance caused by a low conductivity on one side

of the cell or, in some cases prevent the formation of solids, which would be even worse. However,

this does increase the price per kWh significantly.

A different solution to this problem would be the omission of the membrane. In this case, the mixture

of anolyte and catholyte, simply called electrolyte for membrane-free cells, would never be depleted

of active material, since the active material of the charged state is continually replaced by the active

material of the discharged state. The compositions of the electrolyte for an SOC of 0, 50 and 100 % are

shown in the bottom section of Table 2. Not only can the battery be charged and discharged safely for

the whole SOC range, it also employs only half of the amount of [cat]X salt compared to its counterpart

with membrane.

With all its benefits, the challenge for the membrane-free system is to prevent direct reaction between

oxidizing and the reducing agent and also to understand the complex behaviour of the ternary liquid

phase. The next section will cover three concepts to overcome these challenges.


35

Concepts for a Membrane-Free Hybrid IL Redox Flow Battery System

Three concepts for a membrane-free Hyb-IL-RFB will be presented in this section. The working principle

will be described in a separate subchapter for each system and exemplarily for one chemical system

each. They will then be critically discussed together in the last section.

B.1.2.1 One Tank, One Liquid Phase

An enhanced version of the original concept (Figure 8) for the membrane-free IL-RFB is shown in

Figure 9. The electrolyte is a mixture of SnBr4 and Br2 which is saturated with [HMIM]Br, resulting in a

layer of [HMIM]2[SnBr6] floating at the surface of the liquid phase. This saturation ensures that if

bromine reacts with the tin electrode, the local concentration of SnBr4 increases, which leads to the

immediate formation of [HMIM]2[SnBr6] on the electrode, thus protecting it from further attack.

Bromostannates(II) like [SnBr3]– could also be an intermediate oxidation product of this reaction.

However, this is not expected to influence the formation of the protective layer significantly, since the

bromostannate(II) would be oxidized to a bromostannate(IV) right away on contact with further

bromine. Alternatively, on contact with the stronger Lewis acid SnBr4, it would be transformed to SnBr2

and probably precipitate on the electrode. A possible comproportionation reaction between Sn(0) and

Sn(IV) is thermodynamically unfavoured.[2]

The experimental results for the investigation of this behaviour of the ternary liquid phase will be

presented and discussed in Chapter D.

B.1.2.2 Two Tanks, One Electrolyte

Figure 10 shows a schematic drawing of a concept which makes use of the different vapour pressures

of the active materials. The concept is shown here with aluminium as the active material, but could in

a similar fashion be applied to the Sn/Br2 system. The electrolyte in the right tank contains mainly the

metal salt. Upon charging, it is electrolyzed and the formed bromine is continuously removed from the

liquid through the application of a pressure or a thermal gradient towards a second tank on the left.

On discharge, the bromine is added to one side of the half-cell. Since the electrolyte has only a limited

capacity for Al2Br6, it precipitates in the tank for low states of charge


36

SnBr4/Br2

saturated with

[HMIM]BrSn

with protective

layer of

[HMIM]2[SnBr6]

pump

expanded

graphite

2e

4e

[HMIM]2[SnBr6]

2e

[HMIM]Br

saturated with

Al2Br6

Al

pump Al2Br6

exp.

graph.

vacuum /

t em perat ure

Br2

valve

porous

separator

2e 3e

Figure 9: Schematic drawing of a membrane-free Hyb-IL-RFB utilizing a mixed [HMIM]Br/SnBr4/Br2 electrolyte and a protective layer of [HMIM]2[SnBr4] to prevent direct reaction of Sn and Br2. Since the density of [HMIM]2[SnBr6] is lower than the density of the mixed electrolyte, it floats on the surface of the liquid phase.

Figure 10: Membrane-free IL-RFB utilizing differences in the vapour pressures of the active materials. A porous separator might be used to limit the mixing of the bromine enriched side of the cell with the side containing the aluminium electrode.


37

B.1.2.3 One Tank, Two Liquid Phases

The third concept relies on the continuous separation of the active material with a higher vapour

pressure and lower density, leading to the formation of two layers in one tank. Two variants of a

possible flow configuration are shown in Figure 11. In the configuration depicted with dashed lines,

the liquids are passed in parallel to the electrodes. The bromine enriched phase is taken from the top

of the tank, and fed back to the top of the tank, while the phase, which is rich in SnBr4, is cycled in the

lower part of the tank. The other configuration relies on a high conversion rate of bromine while

flowing through a porous electrode without any separator and then hitting the tin electrode

orthogonally to the plane. The direction of the flow has to be reversed for charge and discharge.

Figure 11: Concept of a membrane-free IL-RFB making use of the higher vapour pressure and lower density of one component of the active material. The flow configuration in dashed lines uses a porous separator, the one in filled lines a porous electrode without a separator.


38

Discussion

The first concept presented in Section B.1.2.1 is advantageous compared to the other two concepts in

terms of the necessary process engineering. While it can be operated at elevated temperature, its basic

principle does not rely on it. The vapour pressure can be kept as low as possible and does not have to

be maximized for the system to work efficiently. However, the metal deposition could be more

challenging when performed through a layer of salt. Also, if the conditions in the battery might change

due to a malfunction, so that the protective layer gets damaged or dissolve completely at a high state

of charge, a direct reaction between the metal and the halogen would be unhindered and a significant

amount of energy would be released.

The second and third option do not rely on a protective layer on the tin electrode and are therefore

chemically less complex systems. A safety concern could be the inherent high vapour pressure of

bromine. This is especially the case for the second concept since the bromine is stored in an external

tank without any IL additive that could reduce the vapour pressure. It might be possible, though, to

keep this tank at a lower temperature to help the removal of bromine from the IL phase and to reduce

the vapour pressure. For example, a heat pump could be used to transfer thermal energy from the

bromine tank to the tank containing the electrolyte, but the cost of this thermal pumping has to be

weighed against the benefits of a membrane-free system.

For the third concept, keeping the whole apparatus under a pure bromine atmosphere would help in

increasing the rate of a phase separation and reduce the temperature needed for this process. As long

as the temperature of the electrolyte is kept below its atmospheric boiling point, the resulting reduced

pressure inside the apparatus compared to the environment would also be an effective measure to

prevent any leakage of bromine vapour. Since any battery will produce excess heat on charging and

discharging, the heat energy might in this setup be put to good use for the phase separation process.

In conclusion, from a conceptual point of view, systems one and three seem to be the most promising.

The main challenge for both systems is understanding the ternary phase system, which is in this work

consists of Br2, SnBr4 and [HMIM]Br. For the first system, the formation of a protective layer on a tin

electrode and for the third concept, the formation of two layers in a heated tank with condenser at

the top need to be studied.

So far, the feasibility of these concepts has only been judged from a chemical perspective. Another

part of the equation is the question: can the outlined challenges and the necessary investment in

research be outweighed by the economic prospects of a membrane free system? To get an insight into


39

this matter, a tool for the evaluation of the economic potential of specific battery chemistries at the

concept stage will be presented and applied to both IL-RFBs and membrane-free Hyb-IL-RFBs in the

next section.


40

B.2 Tool for the Evaluation of the Economic Potential of IL-RFB Concepts

41


As soon as our preliminary studies had shown that and how an IL-RFB could work in principle, the

question arose: Do these types of battery have economic potential? Of course, this question is not an

easy one to answer for any technology until its potential does unfold. Especially considering the early

state of the research of the project at that time, any answer, let alone a precise answer, was difficult

to give.

The approach taken in an attempt to answer the question, was partly inspired by the German

translation of an essay titled “The Fermi solution”, which I read several years ago.[3] “Fermi problems”

are named after the famous physicist Enrico Fermi, who challenged his students with questions which

were deliberately chosen to seem very hard to answer at least without further help or information.

One of the questions mentioned in the essay is: How many piano tuners are there in Chicago? Fermi’s

approach on answering such questions was to split the problem into sub problems for which an

estimate can be given either by common sense or by using knowledge already available. In this case,

the number of inhabitants of Chicago was known to be three million, the number of persons in a

household estimated to four and every third household was assumed to own a piano. If a piano is

tuned once every ten years, and a piano tuner can tune four pianos a day, working 250 days per year,

this comes down to an estimate of 25 piano tuners in Chicago. It could be 15 or 60, but probably not

250 or two. Arriving at such a reasonable estimate is possible following many different paths, and

typically the errors in overestimating some parts of the calculation are counterbalanced by

underestimating other parts. Another famous example of this way of thinking is that, by dropping

pieces of paper from above his head as he witnessed the blast wave of the world’s first atomic

explosion, Fermi was able to estimate the released energy to be equivalent to 10 kt of TNT within

moments after the paper had touched the ground. Several weeks later, and after all data had been

meticulously analysed, his estimate was confirmed to be off only by a factor of less than two.

In this spirit, namely that a reasonable estimate is almost always possible and usually better than

simply stating that no precise answer can be given, a tool to evaluate the economic potential of the

different proposed IL-RFB concepts was developed. The goal was to get both a rough estimate whether

or not the concepts could compete with existing technologies and an idea on the direction that would

be most promising for further research. The approach taken is one that does trade a reduced precision

in terms of the resulting numbers for the flexibility to easily compare a large variety of batteries

including a great amount of different stochiometric ratios as well as several different types of battery

chemistries.


42

Based on the results obtained by this tool, some alternative battery chemistries were not pursued

since the results clearly showed that they would not be economical. Only the most favourable systems,

which were also experimentally investigated in the project, will be discussed in the following chapters.

Though more precise numbers can be calculated at the present state of the research and will be

presented in the respective subchapters, the tool will be presented here not only to explain certain

aspects of the direction of the research taken, but also because it can in principal be applied to any

type of battery and could provide a guideline in early stages of research beyond the IL-RFB project.

Scope, General Approach and Systems Studied

B.2.1.1 Scope of the Model

The crucial part for an economic feasibility were considered the energy densities for the different IL-

RFB concepts and the price of the electrolyte per stored energy.

The energy density, or volumetric energy density, is economically relevant because the tanks of an RFB

usually consume the most space of the whole setup, and space in itself and the derived size of the

housing and barrier basin for the battery are a cost factor.

The economically most significant measurement entity for the electrolyte is the price per stored

amount of energy in € kWh–1. Splitting the price to specify contributions from each component was

considered helpful to give an idea on which part of the battery could benefit the most from further

development.

The specific energy, or gravimetric energy density, was considered less relevant for the envisioned

stationary application, but is the basis value for the calculation of prices per stored energy. The cost

for pumps and the cell stack was estimated to be roughly the same as for common V-RFBs.

B.2.1.2 General Approach

Many of the materials to be used in the IL-RFBs were at this stage of the project not commercially

available or had not even been synthesized at all. It was therefore decided to estimate the prices of

the electrolyte by using world market prices for the elements constituting the active materials. For the

[cat]X salts, Dr. Thomas Schubert, CEO and founder of IoLiTec GmbH, kindly provided us with price

estimates for both [HMIM]+ and [N2225]+/[P2225]+ at a 10 t scale. All values are listed in Table 3.


43

Table 3: Specific price �� and experimental (��.) and estimated (��.) values for the density of components

used to calculate densities of ILs and Active Materials ρ!"#!. (right side).

Component ��. g cm–1

��. g cm–1

��

€ kg–1 Ionic Liquids !"#!.

g cm–1 ��. g cm–1

Deviation %

[BMIM]Cl 1.08[4],a) – – [BMIM][AlCl4] 1.39 1.24[5] +12 [HMIM]Cl 1.03[4],a) – 50g) [BMIM][Al2Cl7] 1.51 1.34[5] +13 [HMIM]Br 1.23[6],b) – 50g) SnBr4 4.26 3.34[7] +28 [N2225]Cl – 1.03c) 25g) AlCl3 1.80 2.48[7] –27 [N2225]Br – 1.08d) 25g) AlBr3 3.10 3.2[7] –2 Cl2/Cl– – 1.57[2],e) 4h,i) MnCl2 4.13 2.98[7] +39 Br2/Br– – 3.14[2],f) 4[8],h) Al 2.70[2] – 2[9],h) Mn 7.44[2] – 3[8],h) Sn 7.29[2] – 20[9],h)

a) Value at 25 °C ; b) value at 20 °C; c) value for [HMIM]Cl; d) value for [HMIM]Br; e) density of liquid Cl2 at its boiling point of –34 °C; f) density of liquid Br2 at 20 °C; g) price estimates for 10t scale as stated by Dr. Thomas Schubert, IoLiTec GmbH, used with his kind permission; h) original value in $, converted with an assumed exchange rate of 1.0 to €.

To be able to specify prices in € kWh–1, the specific energy in Wh kg–1 needed to be calculated. It

depends on the active material, the exact stoichiometric ratio of the active material in relation to the

[cat]X salt and on the OCV of the chemical system for this specific stoichiometric ratio.

Since the contributions of two half cells to the Open Circuit Voltage $�� can not be separated, a useful

specific energy can only be calculated for the combination of two half cells, which is to say a specific

battery.

Energy densities in Wh L–1 can be calculated from specific energies using the gravimetric densities of

the electrolytes of the concerned battery. Since the densities values were not known at the time,

estimated densities were calculated from the densities of the constituent elements and the densities

of the used [cat]X salts according to the equations in the next section. No experimental densities for

salts of [N2225]+ could be obtained. Since its molar mass (172.3 g mol–1) is similar to the molar mass of

[HMIM]+ (167.3 g mol–1), the density of the respective [HMIM]+ salts was used.

The density values for elements and [cat]X cations as well as the resulting calculated values for

literature known ILs and pure active materials are listed in Table 3. The deviations when compared to

experimental values are as high as 40 % but were considered tolerable for the intended rough estimate

to be produced by this model. Though the calculation of the IL densities from the known densities of

compounds like SnBr4 rather than from the constituting elements would probably have been more

precise, the approach is more versatile if the densities are calculated from the easily obtainable

element densities.


44

The tool to actually calculate the desired values for the energy density, specific energy and the price

per stored amount of energy, was implemented as an Excel sheet with multiple subpages. By specifying

molar masses, densities and prices in the first sheet for all employed materials and elements, then

using these to define the composition of positive and negative half cells in the second and third sheet

and finally combining these half cells to form the desired batteries in the last sheet, a reliable and very

flexible tool was obtained. The design eliminates the need to enter formulas and material properties

multiple times and instead references all cells back to properties defined in prior sheets, thereby saving

time and reducing errors.

B.2.1.3 Studied Systems and Concepts

The electrolytes for Al/Br2, Sn/Br2, All-Mn IL-RFBs and, to have a reference standard, V-RFBs were

analysed. For the IL based RFBs, hybrid concept with membrane (Hyb-IL-RFB), a hybrid concept with a

limited SOC range as explained in Section B.1.1 (Hyb-IL-RFB lim. SOC) and a membrane-free hybrid

system (MF-Hyb-RFB) were taken into account. For Sn, a system utilizing an Sn(II) IL without the

deposition of metal (IL-RFB) was studied as well.

RFBs based on ICl3 electrolytes have not been considered, since the first results showed that the

interhalide half-cell behaves more complicated than anticipated. A discussion on this matter will be

given in Chapter C.

For the membrane-free variant, only the concept in its original form presented in the introduction was

analysed. Concept 1 presented in Section B.1.2 is a modified version for which a calculation will be

discussed in Chapter D. For concept 2, the energy density, specific energy and specific price approach

the values of the active materials for large systems, since the IL is only used in a small circulating part

of the RFB. All values for concept 3 should be equal to the original concept, since the electrolyte is

identical in both concepts.

The OCVs and exact stoichiometries for the charged and discharged constitution of the electrolyte are

given in Table 4.

The stoichiometries are those deemed viable based on first experiments. On further research, all

systems showed individual characteristics and the need for custom modifications. For the systems

studied in this work, namely the Sn MF-Hyb-IL-RFB and the All-Mn Hyb-IL-RFB, the findings along with

updated calculations will be presented in the separate chapters (Chapter D and E, respectively). The

general trend and the conclusions made from the following calculated values are presented here to


45

Table 4: Overview over OCV values and stoichiometries used for the analysed IL-RFB systems and concepts. All salts set in italic font were later found to be problematic due to various reasons which will be discussed in the respective chapters alongside updated calculations.

SOC 100 % SOC 0 % OCV Composition Composition

Al/Br2 V Anode Anolyte Catholyte Anode Anolyte Catholyte

Hyb-IL-RFB 1.8a)[10

] 8 Al 8[cat][Br] 3[cat][Br9] – 8[cat][AlBr4] 3[cat][Br]

Hyb-IL-RFB lim. SOC 1.1[11] 2 Al 2[cat][AlBr4] [cat][Br9] – 2[cat][Al2Br7] [cat][Br3] MF-Hyb-IL-RFB 1.1b) 8 Al 3[cat][Br9] – [cat][Al2Br7] + 2[cat][Al3Br10]

Sn/Br2

IL-RFB 1.0c) – 3[cat][SnBr3] [cat][Br9] – 3[cat][SnBr5] [cat][Br3] Hyb-IL-RFB 1.15b) 2Sn 2[cat][Br] [cat][Br9] – 2[cat][SnBr5] [cat][Br] Hyb-IL-RFB lim. SOC 1.15b) 3Sn 3[cat][SnBr5] 2[cat][Br9] – 3[cat][SnBr5][SnBr4] 2[cat][Br3] MF-Hyb-IL-RFB 1.15 2Sn [cat][Br9] – [cat][SnBr5][SnBr4]

All-Mn

Hyb-IL-RFB 3.0b) Mn [cat][Cl] [cat][MnCl5] – [cat][MnCl3] [cat][MnCl3]

Hyb-IL-RFB lim. SOC 3.0b) Mn [cat]2[MnCl4] [cat][MnCl5] – 2[cat][MnCl3] [cat][MnCl3]

MF-Hyb-IL-RFB 3.0b) Mn [cat]2[MnCl6] – 2[cat][MnCl3]

All-V

V-RFB 1.4[1] – 2M V2+ 2M [VO2]+ – 2M V3+ 2M [VO]2+ a) Estimate based on battery measurement with anolyte [HMIM]Br : AlBr3 = 3 : 2 and catholyte [HMIM][Br9] using a Al cathode and Ni anode[10]; b) estimated value based on experiments with similar electrolyte; c) value measured by Karsten Sonnenberg, FU Berlin, for an [OMIM][SnBr3] anolyte and an [OMIM][Br9] catholyte using TF6 inert electrodes.

give an insight into the reasoning of the research direction and because the general method and the

resulting trends do still apply.

OCV values were measured in batteries utilizing the stoichiometries listed or estimated based on

similar half-cell combinations as indicated.


46

Equations

B.2.2.1 Single Half-Cell

For any half-cell electrolyte, the weight fraction w� for every component x was calculated from its

molar mass M� and the total molar mass of the half-cell electrolyte M(� in its relevant composition

using Equation (1).

)�,(� = ��(� (2)

As given in Equation (3), it is then multiplied by the density of the component + to yield the density

fraction Ρ�, which is the fraction of weight it contributes per volume to the total density of the

complete half-cell electrolyte ρ(�.

-�,(� = )�,(� ∙ � (3)

The density of the complete electrolyte of one half-cell is the sum over all density fractions from the

first component to the last component . as shown in Equation (4).

(� = -�,(� / -0,(� / … / -2,(� (4)

The Theoretic Specific Charge of this electrolyte is calculated in Equation (5) with the Faraday Constant F and the charge number z which specifies the number of electrons transferred per atom of the active

mass.

5�,(��6 = � ∙ 7�(� (5)

The Theoretic Charge Density of a half-cell 58,(��6 is obtained through Equation (6).

58,(��6 = 5�,(��6 ∙ (� (6)


47

B.2.2.2 Half-Cell Combinations

Since the numbers of charges transferred per atom z" and z9 for two half-cells of a battery may be

different, but a stoichiometric reaction of the two half-cells is desired, a charge factor : has to be

applied according to Equation (7).

: = 7"7; → 7" = : ∙ 7; (7)

The total molar mass of the battery �="� for the stoichiometric combination of both half-cells will be

defined according to Equation (8), �(�," and �(�,; being the molar masses of the half-cells > and ?.

�="� = �(�," / : ∙ �(�,; (8)

The weight fractions of the two half-cells )(�," and )(�,; can be calculated with Equations (9) a and b.

)(�," = �(�,"�="� and )(�,; = : ∙ �(�,;�="� (9)

The weight fractions )�,="� and )2,="� of every component @ in half-cell > and component . in half-

cell ? in respect to the total molar mass of the battery �="�, can be obtained by multiplication with

the weight fraction of its half-cell )(�,A and )(�,;, respectively.

)�,="� = )(�," ∙ )� and )2,="� = )(�,; ∙ )2 (10)

The density fractions of the half-cells B(�," and B(�,;, as well as the total density ="� of the battery

electrolyte can then be calculated according to Equation (3) and (4).

The Theoretic Specific Charge 5�,="��6 and Theoretic Charge Density 58,="��6 of the battery can be

calculated using Equations (11) and (12) .

5�,="��6 = � ∙ 7"�="� = � ∙ : ∙ 7;�="� (11)

58,="��6 = 5�,="��6 ∙ ="� (12)


48

With the open circuit voltage �CD, the theoretic specific energy E��6 and theoretic energy density E8�6are obtained.

E��6 = 5�,="��6 ∙ �� (13)

E8�6 = 58,="��6 ∙ �� (14)

The price per energy �+F for each component @ is obtained using its price per mass �+� in Equation 15.

��G = )�,="� ∙ �� E�,��6 (15)

Finally, the total price of the battery electrolyte �="�G is obtained as the sum of the price for each of its

components.

�="�G = ��G / �0G / … �HG (16)

The stoichiometry of the charged state has been used for the calculation of all charge and energy

densities.


49

0

50

100

150

200

250

Hyb−IL−R

FB

Hyb−IL−R

FB lim

. SOC

MF−H

yb−IL−RFB

IL−RFB

Hyb−IL−R

FB

Hyb−IL−R

FB lim

. SOC

MF−H

yb−IL−RFB

Hyb−IL−R

FB

Hyb−IL−R

FB lim

. SOC

MF−H

yp−IL−RFB

V−R

FB

Specific

Energ

y / W

h k

g −1

Al/Br2 Sn/Br2 All−Mn V−RFB

Results and Discussion

Since the results of this model are only a rough estimate for the concerned properties of an IL-RFB, the

exact numeric results will not be discussed, but rather the general trends and relative values between

the different chemical systems and concepts.

B.2.3.1 Specific Energies

The results for the calculation of the specific energies are presented in Figure 12. The lowest numbers

are found for the Sn(II)/Br2 IL-RFB along with the Hyb-IL-RFBs, when only the limited SOC range is

considered, but are still double the value of V-RFBs. The highest specific energies are found for the

membrane-free systems, and are up to six times the value of the V-RFB. The Al/Br2 Hyb-IL-RFB performs

comparably, as it profits from a higher OCV value, which is achieved only if pure [cat]Br is used as the

anolyte in the charged state.

Figure 12: Specific energies for Al/Br2 , Sn/Br2, All-Mn and all-vanadium RFBs.

B.2.3.2 Energy Densities

Specific energies were converted to energy densities by means of the estimated density of the

concerned electrolyte. These electrolyte densities were later determined experimentally and are

compared to the calculated values in Table 5. The calculated densities of the ILs are overestimated by


50

0

100

200

300

400

500

600

700

800

900

Hyb−IL−R

FB

Hyb−IL−R

FB lim

. SOC

MF−H

yb−IL−RFB

IL−RFB

Hyb−IL−R

FB

Hyb−IL−R

FB lim

. SOC

MF−H

yb−IL−RFB

Hyb−IL−R

FB

Hyb−IL−R

FB lim

. SOC

MF−H

yp−IL−RFB

V−R

FB

En

erg

y D

en

sity /

Wh

L −1

Al/Br2 Sn/Br2 All−Mn V−RFB

a margin of 4 to 49 %. This applies linearly to the energy densities presented in Figure 13 but does not

affect the validity of the observable trends. Even if the density had been overestimated by 100 %, the

energy densities would still be better than those promised by a V-RFB by a factor of 2 to 10. In

comparison with other Hyb-RFBs, for example the Zn/Br2 system with an energy density of 65–

75 Wh kg–1 [1], the values are still promising.

If precise numbers for charge and energy densities and are needed at a later stage of the project,

experimental density should be used for their calculation as soon as they are available.

Figure 13: Energy densities for Al/Br2 , Sn/Br2, All-Mn and All-Vanadium RFBs. Due to overestimations in the densitiy of the concerned ILs, the values are up to 50 % too high for IL-RFBs. For the V-RFB, a density of 1.4 kg L–1 was used.[12]

Table 5: Calculated densities of ILs and Active Materials ρ!"#!. compared to experimental values determined at a later stage in the project.

ILs IAJI. g cm–1

K+L. g cm–1

Deviation %

[HMIM][AlBr4] 2.20 1.62[11] +37 [HMIM][Al2Br7] 2.50 1.94[11] +30 [HMIM]2[SnBr6] 2.66 2.01a) +32 [HMIM][SnBr5][SnBr4]0.5 3.43 2.3b) +49 [HMIM][Br3] 1.98 1.6[11] +24 [HMIM][Br9] 2.61 2.55c) +2 [N2225][Al2Br7] 2.50 1.93[11] +30

a) Crystallographic density, Section D.2.1.1; b) approximate stoichiometry, value for 50 °C; c) crystallographic density[13].


51

B.2.3.3 Prices per Stored Energy

Figure 14 shows the estimated price per stored energy split into the cost of the main components of

an IL-RFB and, in comparison, the figure for the V-RFB. The price for the V-RFB was set to 7.5 € L–1 ,

which leads to a total price of 200 € kWh–1 for an OCV of 1.4 V, a concentration of 2 M of the active

species in both half-cells and a density of 1.4 kg L–1. Real market prices for the electrolyte are hard to

come by, the lowest numbers concluded from personal communications on conferences are

100 $ kWh–1.

For the IL-RFBs the main factor in price is the [cat]X salt. Assuming the use of the [N2225]+ cation, all

prices are below 200 € kWh–1. If it was possible to drop the price of the [cat]X salt significantly, it would

lead to a very competitive price, especially for the All-Mn Hyb-IL-RFB. Tin is the only metal that does

significantly contribute to the price of the total electrolyte of any of the analysed battery. However,

the prices are calculated from elemental metals and could be lower for compounds like SnBr4.

Figure 14: Prices per stored energy for Al/Br2 , Sn/Br2, All-Mn and all-vanadium RFBs. The sum of the light and dark green columns reflect the cost for batteries utilizing the [HMIM]+ cation.


52

Conclusion

The tool1 presented in this study, and which gives access to an estimate for the economic potential of

specific battery chemistries. Since it is designed to be used in the early stages of chemical research,

the scope of the model is limited to estimating the specific energy, the energy density, as well as the

first time investment concerning the battery chemicals but does not include costs of operation, safety

and maintenance. From this limited viewing angle, all presented battery systems seem viable when

considering the V-RFB as an established reference technology.

The membrane-free concept is a chemically challenging system that could yield a highly competitive

battery both for aluminium and tin. The All-Mn Hyb-IL-RFB could have less safety issues than the

batteries utilizing bromine, and, assuming the price of the [cat]X salt can be reduced, could offer a very

competitive price.

First results for the Sn/ICl3, membrane-free Sn/Br2 and the All-Mn Hyb-IL-RFB will be presented in the

next chapters.

1 The Excel file is provided on the DVD accompanying this dissertation and will be made available on the server of the work group.


53

References

[1] M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mjalli, M. Saleem, J. Electrochem.

Soc. 2011, 158, R55-R79.

[2] A. F. Holleman, E. Wiberg, G. Fischer, Lehrbuch der Anorganischen Chemie, Walter de Gruyter,

Berlin, New York, 2007.

[3] P. A. Tipler, Physik. Hans Christian von Baeyer “Essay: Fermis Lösung”, Spektrum Akademischer

Verlag, Heidelberg, 1994.

[4] J. G. Huddleston, A. E. Visser, W. M. Reichert, H. D. Willauer, G. A. Broker, R. D. Rogers, Green

Chem. 2001, 3, 156.

[5] A. A. Fannin Jr, D. A. Floreani, L. A. King, J. S. Landers, B. J. Piersma, D. J. Stech, R. L. Vaughn, J. S.

Wilkes, L. Williams John, J. Phys. Chem. 1984, 88, 2614.

[6] J.-G. Li, Y.-F. Hu, S.-F. Sun, Y.-S. Liu, Z.-C. Liu, J. Chem. Thermodyn. Thermochem. 2010, 42, 904.

[7] D. R. Lide, CRC Handbook of Chemistry and Physics, 84th Edition, Cleveland, Ohio, 2003.

[8] U. S. Geological Survey, Mineral commodity summaries 2013: Geological Survey, US Govt.

Printing Office, Reston, Virginia, 2013.

[9] Commodity Price Data, The World Bank, 2013.

[10] M. Hog, Diploma Thesis, University of Freiburg, Freiburg im Breisgau, 2013.

[11] M. Hog, Dissertation, University of Freiburg, Freiburg im Breisgau, 2017.

[12] GfE Metalle und Materialien GmbH, “Vanadium Electrolyte Solution 1.6 M, data sheet”, can be

found under http://www.gfe.com/en/product-range/vanadium-chemicals/applications/energy-

storage/.

[13] H. Haller, M. Hog, F. Scholz, H. Scherer, I. Krossing, S. Riedel, Z. Naturforsch., B: Chem. Sci. 2013,

68b, 1103.


54

55

C Structure and Properties of Novel Chloroiodate(III) Ionic Liquids

The first clues that mixtures of [cat]Cl salts with more than 0.5 equivalents of I2Cl6 could yield liquid

positive active material for IL batteries were obtained during the work on my diploma thesis.[1] Thus,

at the beginning of the work on this dissertation, a mixture of [BMP]Cl with 1.0 equivalents of I2Cl6 was

prepared and found to be a homogeneous liquid at room temperature. The IL was then used as the

positive active material in a membrane-free Sn/ICl3 IL battery utilising a tin and a TF6 electrode. Though

the cell showed a starting OCV of 1.38 V and could be discharged with a maximum current of 1.4 mA,

the OCV dropped over the course of the following days and the battery could not be recharged. Upon

opening the cell, evidence for the formation of iodine was obtained by analysing the solid products via

Raman spectroscopy. It was therefore decided that for a first investigation of the inherently challenging

concept of a membrane-free battery, the simpler and better understood polybromide ILs would be

more suitable. Nevertheless, ILs based on I2Cl6 were further studied to understand their structure and

properties and to evaluate if these novel compounds could be useful for other IL-RFB concepts.

The following chapter is based on the manuscript “From Square-planar [ICl4]– to Novel

Chloroiodates(III)? A Systematic Experimental and Theoretical Investigation of their Ionic Liquids” by

Benedikt Burgenmeister, Karsten Sonnenberg, Sebastian Riedel and Ingo Krossing, which has been

published as a full paper in Chemistry – A European Journal (© 2017 WILEY-VCH Verlag GmbH & Co.

KGaA, Weinheim, http://dx.doi.org/10.1002/chem.201701555) and is reprinted here with permission

from John Wiley and Sons. The report includes the results for [HMIM][ICl4] which were obtained during

my diploma thesis, as were quantum-chemical calculations on the structure of chloroiodates [IxClx+y+1]–

(x = 1,2,3, y = 0 … 2x) and computed Raman spectra (PBE0/def2-TZVPP). The calculations were further

refined during the work on the dissertation (CCSD(T)/def2-TZVPP for x = 3 and all calculations using

A’QZ basis sets), and additional Raman spectra were computed (RI-MP2/def2-TZVPP). The figures

containing representations of the calculated structures were reworked based on the figures included

in my diploma thesis.

Karsten Sonnenberg (AG Riedel, FU Berlin) conducted all experiments for mixtures based on [NEt4]Cl.

Tobias Fischer synthesised [BMP][ICl4] during the research internship he conducted under my

supervision. Sabine Zylsdorf introduced me to ion chromatography and helped with the first

measurements.

Compared to the original manuscript, the abstract was removed, and the numbering and

nomenclature of subchapters, figures and tables have been modified for a uniform format.


56

C.1 Introduction

57

C.1 Introduction

Polyhalide salts include a large range of mono- or multi-charged anions, their structures varying from

isolated moieties to large networks depending on the employed cation. This long known material class

has been subject of a renewed interest and reviews on recent developments were published.[2,3]

Such polyhalogen monoanions can be described – and often also synthesized – by the addition of one

or several equivalents of a neutral dihalogens X2 to a halide Y–. The formation of these complexes can

be explained by donor-acceptor interactions, for which the term halogen-bonding has been

established.[4] The simplest form are isopolyhalogen anions, in which both the anion and all other

atoms are the same (X = Y). Numerous compounds comprising anions composed of more than one and

even several di-halogen molecules exist.[5] Organic salts of these anions exhibit relatively low melting

points, for example 82 °C in the case of [N(C3H7)4][I5][5] and can be considered to be ionic liquids (ILs)

according to the common definition of an IL being a salt with a melting point below 100 °C. By

employing asymmetric cations typically used in IL-chemistry, melting points can be even further

lowered to yield room temperature ionic liquids (RTILs), like [HMIM][Br9][6] or [P1,10,10,10][Br3][7]

([HMIM]+ = 1-hexyl-3-methylimidazolium, [P1,10,10,10]+ = tridecylmethylphosphonium). In the solid state

structures of [NCH3(C4H9)3]2[Br20] (m.p. 10°C) and [BMP]2[Br20] (m.p. 9 °C, [BMP]+ = 1-butyl-1-

methylpyrrolidinium chloride), two and three dimensional polybromide networks were identified,

respectively.[8]

By combining more than one kind of halogen, for example dihalogens X2 or interhalogens XYn with

halides Z–, a great variety of polyinterhalogen monoanions is accessible. It has to be noted, though,

that if Z– is more electropositive than X or Y, redox reactions can occur upon mixing of the components.

After a rearrangement reaction, the formal oxidation state of –I will reside on the more electronegative

elements X or Y. If restricting the possible combinations by allowing only two elements, still two

general building principles exist. The first is the addition of homoatomic dihalogen molecules to a

different, more electronegative halogen anion, yielding polyinterhalogen monoanions like those in

[N(CH3)4][ClI4] (m.p. 110 °C) or [N(C2H5)4][ClBr6] (m.p. 53 °C). Those were already described by

Chattaway and Hoyle, and are also found in RTILs like [HMIM][ClBr2][9] or [P1,10,10,10][BrI2].[10] The second

possibility is to add neutral interhalogen molecules, in which one of the atoms has an oxidation state

of greater than zero, to a single halogen anion of the more electronegative element. One example of

a compound containing this anion type is [N(C4H9)4][ICl4] (m.p. 137-139 °C),[11] which can be considered

to be an adduct of ICl3 and Cl–. ILs of triatomic anions of the general type [XY2]– have already been

studied as reagents in organic synthesis[12] and as electrolytes for dye sensitized solar cells[10]. However,


58

both for ILs and in general, very few examples are known, in which more than one equivalent of the

molecular interhalogen species is bound, or put alternatively, in which more than one element in the

oxidation state of I or higher is present in the resulting monoanion. Table 6 gives an overview on the

hitherto reported anions [XnYm]– with X being the more electropositive element and the number of n

being > 1. Compared to the classical interhalides, in which the more electropositive atom is in the

central position (e.g. [ICl2]–), anions like [I2Cl3]– exhibit a non-classical structure, with the

electronegative element in the center surrounded by coordinating interhalogens.[3]

Table 6: Known interhalogen monoanions [XnYm]– with more than one atom X in a formal oxidation state of > 0.

Interhal. n = 2 3 4

BrF3 [Br2F7]–[13–15] [Br3F10]–[13,16] – ICl [I2Cl3]–[17,18] – – IBr [I2Br3]–[19] [I3Br4]–[20,21] [I4Br5]–[22]

The structure of the penta- and hepta-interhalogen monoanions with a maximum oxidation state of I

is similar to their homoatomic counterparts, though for example in the case of [I3Br4]–, both a trigonal

planar[21] and a trigonal pyramidal[20] conformation was found. For [I4Br5]–, two crystal structures with

a syn/anti configuration depending on the used solvent were published recently.[22] It is interesting to

note, that Yagi and Popov could isolate some of their organic [I2Cl3]– salts only as red oils, instead of

crystalline materials.[18] Though the amount of solvent in these oils was not determined, it could be an

indication that these anions tend to form low melting salts or even ILs. The anions [Br2F7]– and

[Br3F10]–, in which bromine has an oxidation state of +III, do not have an isostructural homoatomic

counterpart but the structure of [Br2F7]– has instead been compared to the structure of [Au2F7]–.[13,14,16]

A schematic representation of these two anions is given in Figure 15.

Figure 15: Schematic drawing of the [Br2F7]– and [Br3F10]– anions identified by Kraus et al. via scXRD.[16]

Inorganic salts of the tetrachloroiodate anion were published as early as 1839,[23] its molecular

structure was later determined by single crystal X-Ray Diffraction (scXRD),[24,25] and further analysed

C.1 Introduction

59

by UV/VIS,[11] vibrational[26,26,27] and NQR Spectroscopy.[28] The relative instability of tetrachloroiodate

salts in respect to the elimination of elemental dichlorine to yield the [ICl2]– anion, was investigated on

experimental grounds both for the decomposition in solution[11] and in the solid state[29]. Buckles and

Mills noted that the evolution of dichlorine from the tetramethylammonium salts was faster than for

the tetrabutylammonium salts, and that, upon irradiation, the chlorination of the butyl residue

combined with the evolution of HCl took place.[11] Like many others after them[30], they also studied

the reactivity of organic tetrachloroiodate salts towards double bond containing organic substances. If

compared to reactions with elemental dichlorine, they found a similar, but more controlled reaction

under the influence of these salts.

Here, we have investigated salts and ionic liquids obtained through the addition of 0.5 to 1.5

equivalents of I2Cl6 to [HMIM]Cl, [BMP]Cl and [NEt4]Cl (= tetraethylammonium chloride) and

characterized the products through vibrational and NMR-spectroscopy, scXRD and Ion

Chromatography (IC). The thermodynamics of their formation as well as spectroscopic characteristics

were in addition investigated by DFT and ab initio methods up to the CCSD(T)/A’QZ level. Although the

[ICl4]– anion has been known for over 170 years, in this report we present for the first time an

investigation of the existence of the anions [I2Cl7]– and [I3Cl10]–.


60

C.2 Results and Discussion

61


Quantum Chemical Calculations I: Structures in the Gas Phase and Thermodynamics

The absence of any reports of anions like [I2Cl7]– or [I3Cl10]–, in spite of the long history of research on

the related anion [ICl4]–, raises the question about the thermodynamic stability of these anions.

Generally, two modes of decomposition were considered: the decomplexation reaction to yield [ICl4]–

and I2Cl6 and alternatively the elimination of dichlorine to yield compounds comprising iodine in the

oxidation state +I, which is analogous to the reported behaviour[11,29] for the [ICl4]– anion. To shed some

light on these questions, we have performed extensive quantum-chemical calculations for monoanions

containing up to three iodine atoms in either the oxidation state +I or +III. A summary of all optimized

structures is shown in Figure 16, whereas the thermodynamics of their formation is given in Table 8.

C.2.1.1 Structure Optimizations

For a given connectivity of atoms, structure optimizations were performed using a DFT functional

(PBE0 or B3LYP), all further structure optimizations were then started from this structure to yield

energies for both RI-DFT[31,31,32] (BP86, B3LYP-D3BJ, PBE0) and RI-MP2[33–35] methods using def2-

TZVPP[36] basis sets. Several bonding situations can be considered for the series of compounds [I2Cl2+2x]

(x = 0, 1, 2) and even more for [I3Cl4+2x] (x = 0, 1, 2, 3). As a model complex, several possible structures

and modes of connection were calculated for the [I2Cl5]– anion and can be found in the ESI. The most

stable isomer is by a margin of 30 to 70 kJ mol–1 the isomer shown in Figure 16. For the [I3Cl4+2x]–

(x = 0, 1, 2, 3) series, linear and trigonal pyramidal geometries have been considered, the energetic

differences with respect to their trigonal pyramidal isomers are listed in the bottom section of

Table 8. For the linear [I3Cl6]– and [I3Cl8]–, other linear isomers of lower symmetry (different order of

the I(I) and I(III) units) show 1 to 18 kJ mol–1 higher ΔG values in RI-DFT calculations. All bond lengths

given in Figure 16 are taken from RI-MP2 optimized structures, since they show the smallest deviations

from crystallographic determined bond lengths of known compounds, cf. the compilation in Table 7.

Table 7: Comparison of bond lengths and bond angles of calculated structures with crystallographic data. All calculations were made using def2-TZVPP basis sets, the crystallographic value given for [ICl4]– is the mean value listed in Table 4 below.

[ICl2]– [ICl4]– [I2Cl3]– [Cl–ICl]– / pm [Cl–ICl3]– / pm [Cl–IClICl]– / pm [ClI–ClICl]– / pm [ClI–Cl–ICl]– / ° Cryst. data 255M2[37] 249.7 241.7[19] 271.8[19] 101.54[19] RI-DFT/BP86 260.6 255.2 250.3 271.6 117.1 RI-DFT/B3-LYP-D3BJ

260.6 254.4 249.3 273.7 110.5

RI-DFT/PBE0 256.1 250.8 245.4 269.4 114.9 RI-MP2 254.9 249.6 243.6 269.4 107.0


62

Except for this variation in bond lengths, the structures obtained from RI-DFT calculations are similar

to those obtained from RI-MP2 calculations. For the linear isomers of [I3Cl6]– and [I3Cl8]– however,

calculations with both B3LYP-D3BJ and RI-MP2 require an additional tilting of the [ICl4]– groups to break

the vertical mirror plane. In the trigonal pyramidal isomer of [I3Cl10]–, the minimum structure for both

methods is found by further tilting of two of the three [ICl3] groups, thereby breaking the C3 symmetry.

In the structures of [I2Cl7]– and pyramidal [I3Cl10]–, the distances from the iodine atoms to the central

chlorine atom are the longest I–Cl bonds within the respective anion. This seems to be similar to the

Figure 16 Molecular structures and bond lengths based on RI-MP2/def2–TZVPP optimisations given with their respective point group. Arrows to the right and down indicate an addition of ICl, vertical arrows the addition of 0.5 I2Cl6 and arrows to the left, the addition of a dichlorine molecule. For the series [I3Cl4+2x]– (x = 0, 1, 2, 3), both a trigonal pyramidal and an alternative, linear stereoisomer is shown.


63

structures observed for the hitherto known non-classical interhalides.

C.2.1.2 Charge Distribution

In Figure 17, the electrostatic potential, mapped onto a surface of constant electron density of

0.01 e Å–3, is shown for the structures of [ICl4]– (a), [I2Cl7]– (b) and [I3Cl10]– (c) obtained through RI-

MP2/def2-TZVPP calculations. Generally, the negative charge rests mostly upon the chlorine atoms,

while the iodine atoms surface has a higher electrostatic potential. This is true for all three anions,

though the local potential becomes less negative as the charge is distributed across the surface of the

larger anions, even leading to a slightly positive electrostatic potential surrounding the iodine atoms

in [I3Cl10]–.

a) b) c)

Figure 17: Electrostatic potential from lower (blue) to higher (red) for the [ICl4]– (a), [I2Cl7]– (b) and [I3Cl10]– (c) calculated at the RI-MP2/def2-TZVPP level and mapped on a surface of constant electron density of 0.01 e Å–3.

C.2.1.3 Thermodynamic Values

To increase the accuracy for the electronic energy values obtained by the methods employed for

structure optimizations, single point CCSD(T)[38–41] calculations were performed on RI-MP2 optimized

structures and extrapolated to the aug-cc-pV(Q+d)Z[42] (chlorine)/aug-cc-pwCVQZ-PP (iodine)[42] basis

sets (see ESI for details) to yield the quality of an approximate CCSD(T)/A’QZ level. Thermodynamic

values from BP86/def2-TZVPP frequency calculations were added to yield the differences of standard

molar enthalpy ΔrH° and standard Gibbs energy ΔrG° at room temperature and atmospheric pressure

listed in Table 6. In general, the RI-DFT energies show less than 30 kJ mol–1 deviation from the

CCSD(T)/A’QZ values, an exception being the complexation of chloride with ICl (–46 kJ mol–1). For RI-

MP2 and CCSD(T) calculations with def2-TZVPP basis sets, the deviations are generally smaller and

below 20 kJ mol–1. For the molecular ions [I2Cl3+2x]– (x = 0, 1, 2) and [I3Cl4+2x]– (x = 0, 1, 2, 3), deviations

for the complexation energies are below 6 kJ mol–1. The general trend for all employed methods and

basis sets is, that the complexation of 0.5 to 1.0 equivalents of I2Cl6 by the Cl– ion is exothermic by

more than 190 kJ mol–1. Further complexation is less and less exothermic. Reductive elimination of

dichlorine becomes increasingly favourable with growing numbers of iodine and chlorine atoms,

though, as stated above, absolute values vary considerably. At our best extrapolated CCSD(T)/A’QZ


64

level of theory, the reductive elimination of dichlorine gas is exergonic for [I3Cl10]– (–15 kJ mol–1), [I3Cl8]–

(–5 kJ mol–1) and [I2Cl7]– (–2 kJ mol–1), but endergonic by only +1 kJ mol–1 for [I3Cl6]–.

Table 8: Gas-phase reaction enthalpies ΔrH° and Gibbs energies ΔrG° at room temperature and a pressure of one bar calculated for the given reactions. All CCSD(T) calculations where performed as single point calculations based on the RI-MP2/def2-TZVPP optimized structures. The most reliable results at the approximated CCSD(T)/A’QZ level shown in bold were extrapolated from RI–MP2/A’QZ values, details are given in the ESI.

Reaction ΔrG° ΔrH° ΔrH° A’QZ a) def2-TZVPP CCSD(T) CCSD(T) CCSD(T) RI-MP2 PBE0 B3LYP-D3BJ BP86

Cl– + 0.5 I2Cl6 → [ICl4]– –183 –195 –213 –217 –225 –221 –228 [ICl2]– + 0.5 I2Cl6 → [I2Cl5]– –105 –86 –87 –92 –85 –89 –84 [ICl4]– + 0.5 I2Cl6 → [I2Cl7]– –46 –56 –54 –60 –49 –60 –48 [I2Cl3]– + 0.5 I2Cl6 → [I3Cl6]– –24 –59 –56 –64 –54 –65 –54 [I2Cl5]– + 0.5 I2Cl6 → [I3Cl8]– –15 –48 –44 –52 –42 –55 –41 [I2Cl7]– + 0.5 I2Cl6 → [I3Cl10]– –12 –43 –38 –46 –34 –50 –33

Cl– + ICl → [ICl2]– –137 –169 –182 –189 –204 –206 –215 [ICl2]– + ICl → [I2Cl3]– –52 –83 –82 –90 –92 –99 –98 [ICl4]– + ICl → [I2Cl5]– –32 –59 –56 –65 –64 –74 –70 [I2Cl3]– + ICl → [I3Cl4]– –42 –51 –49 –54 –35 –46 –27 [I2Cl5]– + ICl → [I3Cl6]– –25 –40 –35 –41 –19 –36 –10 [I2Cl7]– + ICl → [I3Cl8]– –12 –29 –26 –28 –10 –26 –1

0.5 I2Cl6 → Cl2 + ICl –16 42 22 54 57 76 83 [ICl4]– → Cl2 + [ICl2]– 31 69 53 81 78 92 97 [I2Cl5]– → Cl2 + [I2Cl3]– 11 45 27 56 50 66 69 [I2Cl7]– → Cl2 + [I2Cl5]– –2 39 20 49 42 63 61 [I3Cl6]– → Cl2 + [I3Cl4]– 1 34 16 44 38 56 57 [I3Cl8]– → Cl2 + [I3Cl6]– –5 33 14 43 34 57 52 [I3Cl10]– → Cl2 + [I3Cl8]– –15 28 10 36 34 53 51 [I3Cl4]– (pyr. → lin.) [I3Cl4]– 11 1 2 2 –8 –5 –15 [I3Cl6]– (pyr. → lin.) [I3Cl6]– 4 4 4 2 –1 0 –8 [I3Cl8]– (pyr. → lin.) [I3Cl8]– 3 11 11 12 –9 2 –19 [I3Cl10]– (pyr. → lin.) [I3Cl10]– 1 8 8 4 –1 2 –11

a) Chlorine: aug-cc-pV(Q+d)Z, iodine: aug-cc-pwCVQZ-PP.

The fact that all enthalpy values for the elimination of dichlorine are only slightly endothermic in the

gas phase, suggests that it might be possible to experimentally shift the equilibrium of the reaction to

one side or the other by increasing or decreasing the partial pressure of Cl2 over samples containing

these anions. The experimental results of our quest to stabilize and identify the anions [I2Cl7]– and

[I3Cl10]– are in agreement with this suggestion and are presented in the next chapters.

Syntheses, Melting Points and Crystal Structures

A schematic overview of all performed reactions, utilized salts and desired products is given in

Figure 18. All compounds were prepared by the addition of 0.5 to 1.5 equivalents of I2Cl6 to the

respective cation chloride salt (cation = [HMIM]+, [BMP]+ or [NEt4]+).


65

Figure 18: Schematic overview of the planned reactions, utilized salts and desired products. [NEt4]+ = tetraethylammonium, [HMIM]+ = 1-hexyl-3-methyl-imidazolium, [BMP]+ = 1-butyl-1-methylpyrrolidinium.

C.2.2.1 Refining the Synthetic Procedure

The initially utilized synthetic route was the sublimation of I2Cl6 on top of the cooled cation chloride.

This was intended to further purify the commercial I2Cl6 and also to achieve a slow reaction of the two

components, while allowing the mixture to reach room temperature. However, the Raman spectra of

the obtained mixtures were inconclusive. To identify whether or not during the sublimation and

subsequent warming, chlorine gas was lost from the mixtures, the compound resulting from the

reactions of [BMP]Cl with 1.5 equivalents of I2Cl6 was treated with aqueous solution of Na2[S2O3] and

then analysed by ion chromatography (IC). The results indicated a lower than expected chlorine

content with deviations of 30 % from the expected ratio of I– to Cl–. The final procedure, applied to all

reactions sketched in Figure 18, was therefore modified. The reactions were performed by adding

[cat]Cl directly to the frozen I2Cl6. Next, the vessels were closed under an argon atmosphere. The

mixtures of the two solids were then stirred for several hours to days at room temperature. Raman

spectra of these reactions were recorded directly within the closed reaction vessels to prevent any loss

of dichlorine gas.

C.2.2.2 Spectroscopic Characterization of [cat][ICl4] Salts

With this refined procedure, yellow to orange solids were obtained for the three cations upon reaction

with 0.5 I2Cl6. The dominating anion by comparison to the literature known Raman bands is clearly

[ICl4]–. A small additional band at around 266 to 267 cm–1 for mixtures with [NEt4]Cl, [HMIM]Cl and

[BMP]Cl respectively, is attributed to the minor presence of [ICl2]–, since the frequencies are similar to

those reported (K[ICl2] aq. sol.: 272 cm–1 [27]) and calculated (RI-MP2/def2–TZVPP: 279 cm–1). Figure 19

shows two exemplarily selected Raman spectra of [BMP][ICl4]: one directly after the synthesis, and the

second after several months of storage in a non-greased, and thus not perfectly sealed round bottom


66

Figure 19: Raman spectra of mixtures [BMP]Cl : 0.5 I2Cl6 directly after synthesis and after several month of storage in a non-greased round bottom flask.

flask that was exposed to daylight. The minor band of [ICl2]– grows significantly over time. The NMR

spectra (given in the ESI), show signs of degradation/chlorination at the butyl chain. Similar

observations were made by Buckles and Mills, who described the loss of chlorine / chlorination of the

butyl chain in [NBu4][ICl4] under illumination.[11]

The melting behaviour of [NEt4][ICl4] was already described by Chattaway and Hoyle as a slow

transition, from colour changes at 130 °C to forming a dark orange liquid that evolved bubbles. For

[HMIM][ICl4] and [BMP][ICl4], only the last transition to form orange liquids with simultaneous

evolution of gas was observed at (62 ± 5) °C and (85 ± 5) °C, respectively. With these “melting points”,

both salts could be considered as ionic liquids. Yet, the evolution of gas shows that these compounds

are not stable in the liquid form under atmospheric pressure. Consequently, the real melting points

could deviate from those observed due to melting point depression and the possible formation of

[ICl2]– as the by-product of the gas evolution. Nevertheless, scXRD is in agreement with the assignment.

C.2.2.3 Molecular Structures by scXRD

Crystals from these reactions were analysed and the crystal structures of three [ICl4]– salts were

determined. Bond lengths and angles of the [ICl4]– anions are summarized in Table 4, general

crystallographic information is given in the ESI. The structures of the organic cations are typical and

shall not be discussed. Bond angles Cl-I-Cl are generally close to 90 or 180 °, and bond lengths dICl are

similar to previously reported values as in K[ICl4]∙H2O[25].


67

Table 9: Bond lengths and angles for the [ICl4]– anions in crystals structures of salts with [NEt4]+, [HMIM]+ and [BMP]+ cations. The last three rows show intermolecular properties.

[NEt4][ICl4] [HMIM][ICl4](1) [HMIM][ICl4](2) [BMP][ICl4] K[ICl4]∙H2O[25]

Cl1(4)-I1(2) / pm 250.30(6) 251.25(5) 254.86(6) 249.0(1) 253Cl2(5)-I1(2) / pm 250.00(6) 250.57(4) 249.16(4) 250.1(2) 247Cl3(6)-I1(2) / pm sym. equiv. Cl1 248.05(5) 246.65(6) 248.0(2) 242Cl4(7)-I1(2) / pm sym. equiv. Cl2 sym. equiv. Cl2 sym. equiv. Cl5 246.8(2) 260mean bond length / pm 250.2 250.1 250.0 249.0 250.5Cl-plane l1(2) / pm 0.0000(0) 4.93(4) 2.22(4) 1.46(8) –Cl(u)-I(v)-Cl(w)/° 1-1-1: 180.00(0) 1-1-3: 177.74(2) 4-2-6: 178.98(2) 1-1-3: 178.28(5) 1-1-2: 177.3Cl(x)-I(v)-Cl(y) /° 2-1-2: 180.00(0) 2-1-2: 175.79(2) 5-2-5: 179.17(2) 2-1-4: 179.00(5) 3-1-4: 179.1Cl(u)-I(v)-Cl(x) /° 1-1-2: 90.00(0) 1-1-2: 91.15(1) 4-2-5: 90.28(1) 1-1-2: 90.33(5) 1-1-3: 89.2shortest Cl(x)-Cl(y) / pm 2-2: 334.5(2) 2-2: 357.16(7) 5-5: 326.16(8) 1-3: 332.5(2) 352inter Cl(x)-I(y) / pm 2-1: 456.07(6) 4-1: 369.22(6) – 4-1: 367.4(2) –shortest Cl(x)-N(y)/K 2-1: 464.34 (3) 2-1: 368.1(2) 5-1: 375.8(2) 3-1: 423.4(1) 323angle [ICl4]– planes / ° 56.33(2) 68.34(3) – 86.26 (5) –

C.2.2.4 Packing Motives in the Solid State Structures:

A typical motive for the arrangement of the [ICl4]– anions in the solid state structures is an angled

orientation of [ICl4]– anions, in which a chlorine atom points at the iodine atom of one or two

neighbouring [ICl4]– units. As an example, the structure of [BMP][ICl4] is shown in Figure 20, whereas

graphical representation of the crystal structures of [HMIM][ICl4] and [NEt4][ICl4] can be found in the

ESI.

Figure 20: Crystal structure of [BMP][ICl4] viewed in the 100 (left) and 010 direction (right). The [ICl4]– units form zig zag chains which are isolated from one another by the [BMP]+ cations and show the closest contact in a direction from Cl(1) to Cl(3) (332.5 pm) and from Cl(4) to I(1) (367.4 pm) in the b c plane.


68

In the structure of [HMIM][ICl4], the chlorine atom with the longest bond (Cl4-I2, 254.9 pm) is also the

one closest to the (non-bonding) iodine of a neighbouring [ICl4]– anion (Cl4-I1, 369.2 pm; cf. ΣrvdW(Cl,I)

= 373 pm[43]). This elongation of the iodine chlorine bond is not observed in the structure of [BMP][ICl4],

in which the shortest bond (Cl4-I1, 246.8 pm) is the one closest to the next iodine atom (Cl4-I1,

367.4 pm) and the longest bond is the one just opposite (Cl2-I1, 250.1 pm). The bond lengths are

almost the same for the two symmetry independent chlorine atoms of [NEt4][ICl4] (Cl1-I1, 250.3 pm ;

Cl2-I1, 250.0 pm ). The two symmetry equivalent chlorine atoms on opposite sides of the central iodine

are framed by the iodine atoms of neighbouring [ICl4]– anions at a distance of 456.07 pm, which is

significantly longer than the closest contacts in the [HMIM]+ and [BMP]+ salts. In the electrostatic

potential plot of [ICl4]– shown in Figure 18 a), the highest potential is found at a ring surrounding an

axis through the iodine and perpendicular to the plane defined by the iodine and chlorine atoms. The

lowest potentials are situated on rings perpendicular to the I–Cl bond at the chlorine atoms. This

charge distribution suggests that the angular configuration of the [ICl4]– molecules found in all

presented structures, could minimize coulombic repulsion of neighbouring anions.

C.2.2.5 Hirshfeld Analysis

An exemplarily selected Hirshfeld analysis is shown for [HMIM][ICl4] in Figure 21 a) and b). Contacts

shorter or close to the sum of the van der Waals radii are found from the hydrogen atoms in the

imidazolium rings (H2-Cl4: 274 pm, H3-Cl2: 273 pm H4-Cl6: 290 pm; ΣrvdW(H,Cl) = 284 pm[43]), the

hydrogen atoms on the first carbon atom of the alkyl chain to the chlorine atoms of the [ICl4]– units

(disordered, shortest distance H5AB-Cl3: 275 pm) and in Cl–Cl interactions between neighbouring

[ICl4]– anions (Cl5-Cl5: 326 pm, ΣrvdW(Cl,Cl) = 350 pm[43]). The strong positive influence of hydrogen

bonds from the imidazolium ring to the respective anion on the physical properties of imidazolium

based ionic liquids has been shown before.[44] It could contribute to the observed lowest melting point

of all [ICl4]– salts in this investigation. Compared to these bonds in N,N’-dimethylimidazolium

methylsulfate (average H-O: 209.1 pm, ΣrvdW(H,O): 261 pm[43]), with an average H-O distance 50 pm

shorter than the sum of their van der Waals radii,[45] the interaction seems to be much weaker. This is

in agreement with the more diffuse charge of the chlorine atom compared to the oxygen atom in the

sulfate. Except for the absence of the imidazolium ring and its hydrogen bonds, the Hirshfeld plots for

[BMP][ICl4] and [NEt4][ICl4] show similar results and are included in the ESI.


69

Figure 21: Hirshfeld surface of the two symmetry independent [ICl4]– anions in the crystal structure of [HMIM][ICl4], showing contacts at distances shorter (red) and longer (blue) than the sum of the van der Waals radii. Hydrogen bonding is observed from the hydrogens in the imidazolium ring and the 1-position of the butyl chain to the chlorine atoms of the [ICl4]– units. Neighbouring [ICl4]– units shown on the right side, show contacts closer than the sum of their van der Waals radii as well (Cl5-Cl5: 326 pm, ΣrvdW(Cl,Cl) = 350 pm[43]). The hexyl chain of [HMIM]+ is disordered over two positions.

The shortest – non-bonding – distance of a nitrogen to a chlorine atom is found in [HMIM][ICl4] (N1-

Cl3, 368.1 pm, ΣrvdW(N,Cl) = 330 pm[43]), probably because the sp2 nitrogen atom is more accessible

than the sp3 nitrogen in the investigated quaternary ammonium salts.

C.2.2.6 The Systems [cat][Cl] + 1.0 or 1.5 I2Cl6

By mixing the two components according to the refined procedure at room temperature,

homogeneous red liquids (1 eq) and suspensions of a red liquid and an orange solid (1.5 eq) were

obtained. For the mixture [BMP]Cl : 1.0 I2Cl6, crystals with the same unit cell as [BMP][ICl4] were

obtained upon cooling in a fridge at 4 °C. The [BMP]Cl mixtures with 1.5 equivalents of I2Cl6 formed a

homogeneous liquid after heating to 40 °C. Upon cooling to room temperature, an orange precipitate

reformed that was identified as I2Cl6 via Raman spectroscopy. Despite many attempts, no single

crystals of the targeted anions could be obtained. The distribution of the anionic charge shown in

Figure 17, combined with the lowering of the symmetry of the larger anions compared to [ICl4]–, could

explain their reluctance to form crystalline phases. Compared to the mixtures with 0.5 equivalents of

I2Cl6, further limitations with respect to the stability of both the cationic and the anionic part of the

mixtures were observed for higher stoichiometric ratios of I2Cl6: Thus, the NMR spectrum of the neat

mixture of [HMIM]Cl with 1.0 equivalents of I2Cl6 shows numerous additional signals especially in the

aromatic region, if compared to the expected signals for the unaltered [HMIM]+ cation. According to

preliminary NMR analyses, this is due to a chlorination of the imidazolium ring and indicates that the


70

reactivity of the system is increased by the incorporation of a higher stoichiometric ratio of I2Cl6.

Concluding from this, the [HMIM]+ cation is not suitable for the preparation of anionic species in

mixtures with I2Cl6.

According to visual inspection as well as the line widths of the signals in the 1H-NMR spectrum, the

viscosity of the mixtures of [BMP]Cl and [NEt4]Cl with 1.0 and 1.5 equivalents of I2Cl6 seems to be higher

than the viscosity of the respective mixture with [HMIM]Cl. This could be induced by the imidazolium

cation, which is known to form ILs of lower viscosity compared to their ammonium counterparts, or

due to the products of the reaction of [HMIM]+ with I2Cl6. These products include most likely small

anionic ICl-complexes, which could have a lower viscosity than the compounds based on the larger

anionic I2Cl6-complexes. Since the signals in the 1H-NMR spectra were too broad to judge the stability

of the [BMP]+ and [NEt4]+ cations, it was instead confirmed by recording 13C-NMR spectra. All NMR

spectra are given in the ESI and suggest that the cations are compatible with the chloroiodate anions

at least for a few days, but decompose over months, probably under the influence of light and with

chlorination in the side chains distant from the onium atom.

C.2.2.7 Gas Evolution and I:Cl Ratios with Ion Chromatography

Upon opening the vessels containing the [BMP]+ mixtures resulting from the reaction with 1.0 and 1.5

equivalents of I2Cl6, evolution of a gas was observed. Samples analysed by IC showed deviations from

the expected chloride to iodide ratio, but deviations are much smaller than for the initially employed

procedure. The results are summarized and compared to the analysis of the starting material in

Table 10. Since samples that were kept briefly in the open atmosphere also showed a significant

alteration in their Raman spectra compared to the spectra recorded on the closed vessels, it is likely

that the evaporation of dichlorine took place during the preparation of the IC samples and that the

composition of the mixtures in the closed vessels is closer to the intended stoichiometric ratio. This

experimental observation of a moderate chlorine pressure over these mixtures is in good accordance

with the results from quantum- chemical calculations shown in Table 8. The elimination of dichlorine

from the anions [I2Cl7]– and [I3Cl10]– is exergonic by –2 and –15 kJ mol–1, and thus much more favourable

than for [ICl4]– (+31 kJ mol–1). This trend, that larger anions should have a higher tendency to eliminate

dichlorine, or, in other words, should exhibit a higher equilibrium pressure of dichlorine, can be seen

in the results from Ion Chromatography as well. However, with a sustained chlorine pressure and as

long as secondary reactions with the cations do not occur, the substances should be stable.


71

Table 10: Molar ratios x of iodide to chloride in mixtures of [BMP]Cl and I2Cl6 which were treated with aqueous solutions of Na2[S2O3] and analysed by ion chromatography. The ratio n(ICl) to n(Itotal) gives the maximal fraction of ICl that could be present in the bulk mixture.

I2Cl6 [BMP]Cl + 1 I2Cl6 [BMP]Cl + 1.5 I2Cl6 x = n(Cl)/n(I) Δx x = n(Cl)/n(I) Δx n(ICl)/n(Itotal) x = n(Cl)/n(I) Δx n(ICl)/n(Itotal) theoretical 3:1 / 3.00 – 7:2 / 3.50 – – 10:3 / 3.33 – –

found 1 3.06 1.9 % 3.33 -4.3 % 7.4 % 2.92 -12.7 % 21.1 %found 2 3.02 0.5 % 3.41 -2.0 % 3.5 % 2.99 -10.4 % 17.3 %found 3 3.01 0.4 % 3.42 -1.7 % 3.0 % 2.99 -10.4 % 17.3 %mean 3.03 0.9 % 3.39 -2.7 % 4.6 % 2.97 -11.1 % 18.6 %σ 0.03 0.9 % 0.05 1.4 % 2.5 % 0.05 1.4 % 2.3 %

In conclusion and by contrast to the findings for [HMIM]Cl, the room temperature liquid mixtures of

1.0 and 1.5 equivalents of I2Cl6 with [BMP]Cl and [NEt4]Cl appear to be stable enough to allow for the

investigation of the anionic complexes formed, when synthesized in closed vessels.

Quantum Chemical Calculations II: Computed Raman Spectra

To help in analysing experimental Raman spectra of liquid mixtures of 1.0 and 1.5 equivalents of I2Cl6

with [BMP]Cl and [NEt4]Cl, theoretical Raman spectra were computed and are depicted together with

the relevant Raman active modes for [ICl4]–, [I2Cl7]–, [I3Cl10]– in Figure 22. Frequencies obtained from

both PBE0/def2-TZVPP and RI-MP2/def2-TZVPP calculations are included, since they showed the

smallest deviation from experimental Raman spectra of [BMP][ICl4] (cf. comparison in Table 11).

Table 11 Comparison between bands from computed Raman spectra for the [ICl4]– anion with an experimental spectrum of [BMP][ICl4] (w. n. = wave number, dev. = deviation, rel. int. = relative intensity).

method w. n.

cm–1

dev. %

rel. int. dev. %

w. n.

cm–1

dev. %

rel. int. dev. %

w. n.

cm–1

dev. %

[BMP][ICl4] exp. 133 -- 0.13 -- 256 -- 0.54 -- 283 --

BP86 114 –14 0.34 164 223 –13 0.59 10 255 –10B3LYP/D3BJ 118 –11 0.29 123 231 –10 0.68 26 262 –7PBE0 122 –8 0.3 131 250 –3 0.69 27 277 –2RI-MP2 122 –8 0.17 31 261 2 0.71 31 288 2

To simplify analysis of the vibrational modes, only those with relative intensities greater than 0.05 and

with frequencies above 75 cm–1 are included and assigned in Figure 22.


72

Figure 22: Computed Raman spectra, vibrational modes and frequencies calculated with PBE0/def2-TZVPP and RI-MP2/def2-TZVPP (bold). Only modes with relative intensities greater than 0.05 and frequencies higher than 75 cm–1 are shown, the numbers refer to the lists of all modes supplied in the ESI. Scissoring, rocking and wagging modes have been grouped under the letter “A” and exhibit frequencies between 90 to 140 cm–1. Vibrations involving the bridging chlorine atoms follow with frequencies from 144 to 220 cm–1 and are summarized under letter “B”. Stretching modes are identified in groups by a number “1”, “2” or “3” and a letter “C”, ”D“ or “E”. The numbers “1” and “2” refer to vibrations of chlorine atoms on opposite sides of an iodine atom, with the number “1” referring to the central [ICl4] group in the linear isomer of [I3Cl10]–. The number “3” is reserved for the chlorine atoms on opposite sides of the central chlorine atom. The symmetric and antisymmetric vibrations of atoms “3” show the highest frequencies of all modes of the respective molecule and range from 310 to 354 cm–1. There is little overlap with the frequencies of chlorine atoms grouped with numbers “1” and “2”, though the overlap is stronger in between the groups “1” and “2” (240 to 320 cm–1). Symmetric out of phase stretching, totally symmetric stretching and antisymmetric stretching modes are identified by the letters “C”, “D” and “E”, respectively.


73

Identification of the Anions in the Mixtures by Vibrational Spectroscopy

The Raman spectra of the liquid phase of mixtures of [NEt4]Cl and [BMP]Cl were measured after stirring

for several hours to days. For reactions with more than 0.5 equivalents of I2Cl6, the spectra were

recorded prior to opening the vessels for other analytical measurements, to prevent the evaporation

of dichlorine gas. The spectra are depicted in Figure 23 and the frequencies of the observed bands for

reactions with 1.0 and 1.5 equivalents are listed and assigned in Table 12. Since the [HMIM]+ cation

quickly decomposes under consumption of the anionic species, the Raman bands of the [HMIM]+ salts

are given in the experimental section but will not be discussed in detail. The recorded spectra of [NEt4]+

and [BMP]+ salts were compared either with experimental spectra of clearly identifiable substances or

with computed spectra based on RI-MP2/def2-TZVPP calculations (cf. above and Table 11).

a)

b)

Figure 23: Raman spectra of compounds resulting from the addition of approx. 0.5, 1.0 and 1.5 of I2Cl6 to a) [NEt4]Cl and b) [BMP]Cl. Spectra in grey / with dashed lines are either computed spectra from RI-MP2/def2-TZVPP calculations (labelled “comp.”) or experimental spectra of compounds that could exist in the synthesized mixtures (no extra labelling).

rel. in

ten

sity

[BMP]Cl : 1.5 [I2Cl6]

comp. [I3Cl10]- (pyr.)

I2Cl6

rel. in

ten

sity

[BMP]Cl : 1.5 [I2Cl6]

comp. [I2Cl7]-

I2Cl6

rel. in

ten

sity

[BMP]Cl : 1.0 [I2Cl6]

comp. [I2Cl7]-

I2Cl6[BMP][ICl4]

100200300

rel. in

ten

sity

wave number / cm-1

[BMP][ICl4]

comp. [ICl4]-

comp. [ICl2]-

rel. in

ten

sity

[NEt4]Cl : 1.5 [I2Cl6]

comp. [I3Cl10]- (lin.)

rel. in

ten

sity

[NEt4]Cl : 1.5 [I2Cl6]

comp. [I2Cl7]-

I2Cl6[NEt4][ICl4]

rel. in

ten

sity

[NEt4]Cl : 1.0 [I2Cl6]

comp. [I2Cl7]-

I2Cl6[NEt4][ICl4]

100200300

rel. in

ten

sity

wave number / cm-1

[NEt4][ICl4]

comp. [ICl4]-


74

C.2.4.1 Mixtures Aiming at [I2Cl7]–

The spectrum of [BMP]Cl : 1.0 I2Cl6 is in good agreement with the computed spectrum of [I2Cl7]–. A

clear indication is the presence of the band at 216 cm–1, which is in the expected region for vibrations

of a bridging chlorine atom. A further hint is the appearance of two (107 and 141 cm–1) instead of one

band (133 cm–1) in the region of the scissoring modes. This also follows from the calculated spectra

(122 vs. 103 and 130 cm–1). However, it has to be noted that the observed bands are very broad, which

could conceal the presence of small amounts of [ICl4]–, dissolved I2Cl6 or

[I3Cl10]–. The same holds true for [NEt4]Cl : 1.05 I2Cl6, where the unexpectedly intense band at

276 cm–1 could possibly be explained by the presence of [ICl4]– in this mixture.

C.2.4.2 Mixtures Aiming at [I3Cl10]–

The situation becomes less clear for the stoichiometry [cat]Cl : 1.5 I2Cl6. The bands of the [BMP]+

mixture do not show good agreement with the computed spectrum for

[I3Cl10]– - neither in the pyramidal nor planar form. Compared to the spectrum of [BMP]Cl : 1.0 I2Cl6,

the decrease in relative intensity of the band at 278 cm–1 and the small shift of the highest frequency

band from 333 to 337 cm–1 do not follow the trend of the computed spectra. A better fit is provided

by the combination of the computed bands of [I2Cl7]– and the experimental bands of I2Cl6. A clear

assignment is even more difficult for the mixture [NEt4]Cl : 1.5 I2Cl6. The best fit is provided by a

combination of I2Cl6, calculated [I2Cl7]– and [NEt4][ICl4], but definitive answers about the real

composition of the mixture are hard to give.

Since the clearest Raman spectra were obtained for the [BMP]+ compounds, far infrared spectra were

also recorded for these substances. However, the evaporation of chlorine could not be suppressed in

the ATR measurements, so the bands are given in the experimental section in the ESI, but no

conclusions about the anionic composition can be drawn from them.


75

Table 12: Observed and calculated Raman bands for [NEt4][ICl4] and the mixtures of [NEt4]Cl and [BMP]Cl with 1.0 and 1.5 I2Cl6. Bands in square brackets are attributed to an absorption of the spectrometer. The bands for [BMP][ICl4] are given in Table 11.

I2Cl6 [NH4][ICl4] aq. Sol.[27]

[I2Cl7]– sim. a) [NEt4][ICl4] [NEt4]Cl + 1.0 I2Cl6

b) [NEt4]Cl + 1.5 I2Cl6

b)c) [BMP]Cl + 1.0 I2Cl6

d) [BMP]Cl + 1.5 [I2Cl6]d)

[77 (vw)] [77 (vw)] [79 (w)] 84 (vw)

94, 103 (vw) 103(w) 104 (w) 107 (vs, sh) 110 (vw, sh) 110 (vw, br)

118 (vw) 128 140 (vw)

138(w) 139 (w)

130 (vw) 141 (vw) 143 (vw) 143 (vw)

199 (vw) 204 (vw, sh)

210 (vw) 216 (vw) 216 (vw, br)

220 (vw) 219 (vw, br) 235 (vw) 234 (vw)

261 256 (m) 259 (sh) 284, 284 (m)

276 (vs) 276 (vs) 278 (m) 278 (s)

288 279 (vs) 311 (vw), 314 (w) 301 (s) 302 (m) 314 (w)

315 (m) 313 (vs) 313 (m)

332 (vs) 329 (s) 330 (m) 333 (m) 337 (vs)

344 (vs) 343 (m)

a) RI-MP2/def2-TZVPP; b) recorded at room temperature; c) recorded at the top of the vessel; d) recorded in Schlenk tubes previously frozen in liquid nitrogen.


76

C.3 Conclusion and Outlook

77

C.3 Conclusion and Outlook

We have presented an extensive thermodynamic study on the gas-phase structures and stabilities of

chloroiodate anions incorporating up to three iodine atoms in the oxidation states of either +I or +III.

After careful analysis of experimental and calculated data, the constitution of the experimental

mixtures of [HMIM]Cl, [BMP]Cl and [NEt4]Cl with 0.5, 1.0 and 1.5 equivalents of I2Cl6 was evaluated.

The reaction with 0.5 equivalents I2Cl6 yielded, as expected, the salts [cat][ICl4] that are stable in closed

vessels over a period of days to weeks. The existence of novel and larger chloroiodate anions was

investigated by means of Raman spectroscopy and supported by computed Raman spectra and

thermodynamics. Thus, the formerly unknown [I2Cl7]– anion is the main anionic species in mixtures of

[BMP]Cl and [NEt4]Cl with 1.0 equivalents of I2Cl6. However, the tendency of these materials to lose

dichlorine is marked (both, based on experimental observation and calculated thermodynamics). This

tendency, or the increased chloroiodate-reactivity of these mixes, makes the [HMIM]+ cation

incompatible with this anion, due to facile and fast ring chlorination. Yet, all of these mixtures are

homogeneous liquids at RT even with a symmetrically substituted ammonium cation like [NEt4]+. This

is in contrast to the respective [ICl4]– salts and is possibly due to the reduced symmetry and greater

charge distribution in the anion as suggested by calculated electrostatic potential plots. Though three

new crystal structures for the [ICl4]– salts of [HMIM]+, [NEt4]+ and [BMP]+ were determined,

crystallographic proof for the existence of the [I2Cl7]– anion could not be obtained, despite many

attempts.

Although the combination of [BMP]Cl with 1.5 equivalents of I2Cl6 yields a homogeneous liquid phase

at 40°C, the existence of [I3Cl10]– cannot be clearly deduced from the experimental Raman spectra. This

is coherent with the decreasing gas phase complexation energy for the stepwise addition of ½ I2Cl6 to

a chloride anion as well as the further increased tendency to lose dichlorine, as shown in our quantum-

chemical calculations. Further research is needed to better understand the behaviour and to clarify, if

cations like [NEt]4+ are stable over largely extended periods of time in this harsh environment. After

several months, also the else rather stable [BMP]+ cation showed signs of side chain chlorination in the

investigated mixtures. An interesting objective for further research could be to determine, whether or

not the aggressive nature can be channelled into selective reactivity to yield a valuable tool in

synthesis.


78

C.4 Electronic Supporting Information

79


General: All reactions were performed under argon inert atmosphere using standard Schlenk

techniques and a vacuum of < 3 × 10-2 mbar. MBraun Labmaster sp glove boxes were used with H2O

and O2 contents < 0.1 ppm.

Chemicals: The manufacturer and grade of purity of the commercial chemicals used are listed in

Table 13. For the reactions with [BMP]Cl and [HMIM]Cl, I2Cl6 was stored at –30°C but otherwise and

used as received. (FT-Raman (RT): 77 (vw), 84 (vw), 110 (vw, br), 118 (vw), 143 (vw), 199 (vw), 313 (vs),

344 (vs) cm– 1.) For the reactions with [NEt4]Cl, I2Cl6 was freshly prepared by quantitative reaction of

Cl2 with I2 at −30°C. (FT-Raman (RT): 82 (m), 117 (w), 143 (w), 199 (w), 314 (vs), 344 (vs) cm– 1.)

Table 13: Manufacturer, purity and purification of chemicals used.

manufacturer purity purification

Cl2 Linde 99.8 % – I2 Grüssing GmbH 99.5 % – I2Cl6 Sigma-Aldrich 97 % – [BMP]Cl IoLiTec GmbH 99 % dryinga) [HMIM]Cl IoLiTec GmbH 98 % dryingb) [NEt4]Cl – – dryingc) Certified IC Standard I– Fluka 1000 (± 4) mg L–1 – Certified IC Multielement Standard (F–,Cl–, Br–, NO3

–, PO43–, SO4

2–) Fluka 10 (± 0.02) mg L–1 –

Na2[S2O3] ∙ 5H2O Carl Roth GmbH + Co. KG p.a. – a) Heated to 120 °C under vacuum for 10 h, ground in a mortar (glove box); procedure repeated three times; b) heated to 60 °C under vacuum for 7 h and stored in a glove box; c) heated to 100 °C under vacuum.

Ion Chromatography: A Metrohm 882 Compact ICplus equipped with a Metrosep A Supp5 250/4.0

column was used to record chromatogramms. A solution containing 1 mmol L–1 NaHCO3 and

3 mmol NaCO3 in 10/90 % acetone/ultrapure water was used as eluent. Calibration was performed

using the certified standards listed in Table 13, which were diluted to concentrations of 0.5, 1, 5 and

10 mg L–1.

Samples of approximately 30 to 50 mg of either I2Cl6 or the liquid phase of mixtures of [BMP]Cl with

1.0 or 1.5 equivalents of I2Cl6 were transferred to a volumetric flask and weighed. A solution containing

approximately double the amount of Na2[S2O3] needed for stohiometric reaction in ultrapure water

was added and well shaken until no more dark particles were visible in the white suspension. It was

then filtered through a syringe filter and diluted to yield solutions containing approximately 10 mg L–1

of I–, which were then analysed via Ion Chromatography.


80

Raman Spectra: A Bruker Vertex 70 spectrometer equipped with a RAM II module and a Nd–YAG laser

operating at 1064 nm was used to record the spectra with a resolution of 4 cm–1. Intensities were

assigned letters according to their relative intensities and appearance (very strong (vs) > 0.8, strong (s)

> 0.6, medium (m) > 0.4, weak (w) > 0.2, very weak < 0.2 (vw), shoulder (sh), broad (br)). Where

indicated (N2), samples were cooled with liquid nitrogen previous to recording the spectra.

F-IR Spectra: Spectra were recorded on a Nicolet 760 Magna IR using a diamond ATR unit and

processed using the baseline correction and advanced ATR correction of Omnic 7.2 (Thermo Electron

Corporation).

NMR Spectra: Liquid phases of neat samples of mixtures containing [HMIM]+ or [BMP]+were analysed

in flame sealed 3mm NMR-tubes with and without external lock on toluene. Spectra were recorded on

a Bruker Avance DPX 200 Mhz, a BRUKER Avance III 300 MHz NMR or a BRUKER Avance II+ 400 MHz

and were calibrated according to literature values for the respective N-Me group of the organic cation

in solution ([HMIM]Cl, [BMP]Cl).

Spectra of neat liquid phases containing the [NEt4]+ cation were measured on a JOEL ECS 400

Multicanal in 5mm NMR-tubes with lock on a capilary containing acetone-d6 inside the tube and

alaysed with MestReNova 7.1.2. The spectra were calibrated according to literature values for the CH2-

group of [NEt4][BF4][46].

Signals from solvents providing external lock are ommitted in the listing of the signals and all spectra

are shown in Figure 24.

DSC: Thermal analysis via DSC measurements could not be performed: No crucibles that are

compatible with the aggressive nature of the compounds and at the same time are able to circumvent

the evaporation of gaseous dihalogens are available for our DSC set up (Setaram, DSC 131).

Synthesis

C.4.1.1 Synthesis of [cat][ICl4] salts

[NEt4][ICl4]: I2Cl6 (1.4 g, 3.0 mmol, 0.5 eq.) was added to [NEt4]Cl (1.0 g, 6.0 mmol) and stirred. An

immediate reaction was observed. A yellow solid (100 %) was obtained.

FT-Raman (RT): NO = 67 (s), 140 (vw), 256 (s), 267 (w), 279 (s), 2950-3000 (vw) cm– 1.

FT-Raman (N2): NO = 66 (w), 139 (vw), 257 (s), 270 (m), 280 (s), 2950-3000 (vw) cm– 1.

[HMIM][ICl4]: [HMIM]Cl (1.47 g, 7.27 mmol) and I2Cl6 (1.61 g, 3.46 mmol, 0.48 eq) were heated from


81

−30 to 62 ◦C. A homogenous orange liquid was obtained, which crystalized upon slowly cooling to RT

(3.09 g, 100 %).

1H–NMR (400.16 MHz, neat, 300 K): P = 0.75-0.99 (m, 2.6 H), 0.99-1.08 (m, 0.3 H), 1.19-1.49 (m, 5.0

H), 1.49-1.58 (m, 0.6 H), 1.67-1.90 (b, 0.7 H), 1.90-2.16 (b, 2.0 H), 3.83-4.23 (b, 3.3 H), 4.23-4.69 (b, 2.2

H), 7.50-7.82 (m, 2.0 H), 8.68-9.01 (b, 1.0 H) ppm.

FT-Raman (RT): NO = 77 (m), 133 (w), 267 (vs), 284 (vs), 599 (vw), 623 (vw), 658 (vw), 1023 (vw), 1105

(vw), 1337 (vw), 1387 (vw), 1416 (vw), 1571 (vw), 2728 (vw), 2872 (vw), 2935 (vw), 2955 (vw), 3162

(vw) cm−1.

[BMP][ICl4]: [BMP]Cl (1.75 g, 9.85 mmol) and I2Cl6 (2.34 g, 5.02 mmol, 0.51 eq) were heated from −192

to 85 ◦C. A homogenous orange liquid was obtained, which crystallized upon slowly cooling to RT (4.09

g, 100 %).

FT-Raman (RT): NO = 75 (w), 134 (w), 256 (m), 267 (w), 283 (s), 1440-1460 (vw), 2860-3040 (vw) cm−1.

ATR-IR (RT): NO = 148 (vw), 242 (vs), 264 (vs), 282 (w, sh) cm−1.

A liquid phase, which had developed in a sample that had been stored for several months in a non-

greased round bottom flask, was analysed.

1H–NMR (200.13 MHz, neat, 300 K): P = 0.73-1.16 (m, 3.0 H), 1.16-1.49 (m, 2.1 H), 1.49-1.64 (m, 2.0 H),

1.64-1.99 (b, 2.3 H), 1.99-2.44 (b, 8.0 H), 2.79-3.20 (m, 5.2 H), 3.20-3.39 (b, 2.1 H), 3.39-3.80 (b, 8.1 H),

4.01-4.34 (b, 0.7 H), 5.81-6.04 (b, 0.3 H) ppm.

13C-NMR (50.32 MHz, neat, 300 K): P = 12.3 (s, 1.0 C), 18.2 (s, 1.0 C), 20.4 (s, 3.3 C), 23.9 (s, 0.6 C), 24.0

(s, 0.9 C), 32.2 (s, 0.6 C), 47.2 (s, 1.0 C), 47.4 (s, 0.6 C), 54.2 (s, 0.6 C), 60.3 (s, 0.6 C), 62.6 (s, 0.9 C), 63.0

(s, 2.0 C), 63.2 (s, 0.6 C), 63.4 (s, 0.6 C) ppm.

FT-Raman (RT): NO = 76 (w), 133 (w), 267 (s), 283 (vs), 902 (vw), 1451 (vw), 2872 (vw), 2961 (vw), 2961

(vw), 2961 (vw), 2961 (vw), 3064 (vw)

C.4.1.2 Synthesis of Mixtures [cat]Cl + 1.0 I2Cl6

[HMIM]Cl + 1.0 I2Cl6: [HMIM]Cl (4.40 g, 21.70 mmol) was cooled to –192 °C and I2Cl6 (9.86 g,

21.1 mmol, 0.97 eq) sublimed on top. The mixture was allowed to reach RT and was stirred for 3 days.

A homogeneous red liquid was obtained (14.15 g, 99 %).

1H–NMR (400.16MHz, neat, 300 K): P = 1.41-1.50 (m, 3.0 H), 1.82-2.05 (m, 6.1 H), 2.32-2.58 (m, 2.1 H),

4.07 (s, 1.0 H), 4.22-4.41 (m, 0.82 H), 4.42-4.46 (b, 0.36 H), 4.46-4.51 (b, 0.77 H), 4.51-4.53 (b, 0.37 H),

4.53-4.56 (b, 0.31 H), 4.71-4.83 (b, 1.25 H), 6.59-6.79 (m, 0.74 H), 7.90-7.97 (m, 0.24 H), 7.97-8.02 (m,

0.22 H), 8.91-8.97 (b, 0.34 H), 8.97-9.03 (b, 0.14 H), 9.03-9.15 (m, 0.23 H), 9.15-9.28 (b, 0.25 H) ppm.

FT-Raman (RT): NO = 78 (s), 135 (m), 287 (vs), 325 (vs), 810 (vw), 1412 (vw), 1439 (vw), 2869 (vw), 2911

(vw), 2941 (vw), 3005 (vw) cm−1.


82

[BMP]Cl + 1.0 I2Cl6: [BMP]Cl (1.16 g, 6.50 mmol) and I2Cl6 (3.14 g, 6.73 mmol, 1.04 eq) were combined

at –192 °C and stirred over night at room temperature. A homogenous red liquid was obtained (4.29 g,

100 %).

1H–NMR (300.18 MHz, neat, 300 K): P = 0.48-1.19 (b, 3 H, CH2CH2CH2CH3), 1.20-1.58 (b, 2 H,

CH2CH2CH2CH3), 1.58-1.93 (b, 2 H, CH2CH2CH2CH3), 1.93-2.59 (b, 4 H, NCH2CH2CH2CH2), 2.60-3.11 (b,

3 H, NCH3), 3.12-4.80 (b, 6 H, CH2CH2CH2CH3, NCH2CH2CH2CH2) ppm.

13C-NMR (75.48 MHz, neat, 300 K): P = 11.8 (s, 1 C, CH2CH2CH2CH3), 17.5 (s, 1 C, CH2CH2CH2CH3), 19.7

(s, 2 C, NCH2CH2CH2CH2), 23.3 (s, 1 C, CH2CH2CH2CH3), 47.2 (s, 1 C, NCH3), 62.3 (s, 1 C, CH2CH2CH2CH3),

62.7 (s, 1 C, NCH2CH2CH2CH2) ppm.

FT-Raman (RT): NO = 77 (m), 106 (w, sh), 138 (w), 219 (vw, br), 277 (vs), 310 (m), 332 (vs), 525 (vw), 904

(vw), 1054 (vw), 1120 (vw), 1452 (vw), 1484 (vw), 2873 (vw), 2963 (vw), 2985 (vw), 3027 (vw).

FT-Raman (N2): NO = 77 (vw), 107 (vs, sh), 141 (vw), 216 (vw, br), 278 (m), 314 (w), 333 (m), 521 (vw),

1451 (vw), 2872 (vw), 2892 (vw), 2911 (vw), 2942 (vw), 2965 (vw), 2984 (vw), 3009 (vw),

3026 (vw cm–1.

ATR-IR (RT): NO = 264 (vs), 280 (vs), 306 (m, sh), 329 (w) cm–1.

C.4.1.3 Synthesis of Mixtures [cat][Cl] + 1.5 I2Cl6

[BMP]Cl + 1.5 I2Cl6: [BMP]Cl (0.97 g, 5.48 mmol) and I2Cl6 (3.75 g, 8.03 mmol, 1.47 eq) were combined

at –192 °C and stirred over night at room temperature. After heating to 40 °C, a homogenous red liquid

was obtained (4.71 g, 100 %). Upon leaving the mixture at room temperature and after the raman

spectra had been recorded, a small amount of an orange solid precipitated.

1H–NMR (300.18 MHz, neat, 300 K): P = 0.40-1.23 (b, 3 H, CH2CH2CH2CH3), 1.23-1.60 (b, 2 H,

CH2CH2CH2CH3), 1.61-1.97 (b, 2 H, CH2CH2CH2CH3), 1.97-2.62 (b, 4 H, NCH2CH2CH2CH2), 2.63-3.13 (b,

3 H, NCH3), 3.14-4.80 (b, 6 H, CH2CH2CH2CH3, NCH2CH2CH2CH2) ppm.

13C–NMR (75.48 MHz, neat, 300 K): P = 11.9 (s, 1 C, CH2CH2CH2CH3), 17.5 (s, 1 C, CH2CH2CH2CH3), 19.7

(s, 2 C, NCH2CH2CH2CH2), 23.3 (s, 1 C, CH2CH2CH2CH3), 47.2 (s, 1 C, NCH3), 62.4 (s, 1 C, CH2CH2CH2CH3),

62.7 (s, 2 C, NCH2CH2CH2CH2) ppm.

FT-Raman (RT): NO = 77 (m), 106 (w, sh), 142 (w), 239 (vw), 276 (m), 314 (m, sh), 336 (vs), 528 (vw), 903

(vw), 1452 (vw), 2873 (vw), 2897 (vw), 2941 (vw), 2964 (vw) cm–1.

FT-Raman (N2): NO = 79 (w), 110 (vw, sh), 143 (vw), 204 (vw, sh), 219 (vw, br), 278 (s), 315 (m), 337 (vs),

444 (vw), 508 (vw), 1450 (vw), 2867 (vw), 2890 (vw), 2939 (vw), 2962 (vw), 2982 (vw), 3000 (vw), 3037

(vw) cm–1.

ATR-IR (RT): NO = 228 (w), 266 (vs), 280 (vs), 303 (s), 329 (m), 334 (m) cm–1.


83

[NEt4]Cl + 1.0 [I2Cl6]: I2Cl6 (1.00 g, 2.14 mmol, 1.0 eq.) was added to [NEt4]Cl (0.344 g, 2.08 mmol) and

stirred. An immediate reaction was observed. A red liquid (100 %) was obtained.

FT-Raman (RT) : NO = 103 (w), 138 (w), 216 (vw), 235 (vw), 276 (vs), 301 (s), 329 (s), 1458 (vw), 2941

(vw), 2992 (vw) cm¬1.

FT-Raman (N2): NO = 106 (w), 140 (w), 236 (vw), 278 (vs), 304 (s), 330 (s), 1458 (vw), 2940 (vw), 2992

(vw) cm¬1.

1H-NMR (401 MHz, neat, RT): P = 1.34.31 (b, 3H, CH3), 1.56 (b, 2H, CH2), 7.73 ppm.

13C-NMR (101 MHz, neat, RT): P =6.6 (CH3), 51.3 (CH2) ppm.

[NEt4]Cl + 1.5 [I2Cl6]: I2Cl6 (2.18 g, 4.67 mmol, 1.55 eq.) was added to [NEt4]Cl (0.501 g, 3.02 mmol) and

stirred. An immediate reaction was observed. A red liquid with orange solid (100 %) was obtained.

Raman spectra are given both for the top of the vessel and for the bottom of the vessel.

FT-Raman (bottom, RT): NO = 108 (w), 142 (w), 200 (w), 275 (m), 314 (s), 344 (vs), 1459 (vw), 2942 (vw),

2991 (vw) cm– 1.

FT-Raman (bottom, N2): NO = 114 (w), 143 (w), 201 (w), 235 (vw), 278 (m), 303 (sh), 315 (vs), 330 (m),

346 (vs), 1458 (vw), 2939 (vw), 2992 (vw) cm– 1.

FT-Raman (top, RT): NO = 104 (w), 139 (w), 234 (vw), 259 (sh), 276 (vs), 302 (m), 313 (m), 330 (m), 343

(m), 1459 (vw), 2941 (vw), 2992 (vw) cm– 1.

FT-Raman (top, N2): NO = 113 (w), 143 (w), 201 (w), 238 (vw), 258 (w), 278 (vs), 315 (vs), 329 (m), 346

(s), 1458 (vw), 2940 (vw), 2992 (vw) cm– 1.

1H-NMR (401 MHz, neat, RT): P = 0.20-2.45 (b, CH3), 2.45-4.2 (b, CH2) ppm.

13C-NMR (101 MHz, neat, RT): P = 6.8 (b, CH3), 51.3 (b, CH2) ppm

C.4.1.4 Additional Figures

The measured NMR spectra are shown in Figure 24.


84

Figure 24: 13C- and 1H-NMR spectra of neat liquid phases resulting from mixtures of [NEt4]+, [BMP]+ and [HMIM]Cl with 0.5 to 1.5 equivalents of I2Cl6 respectively. The spectra of [BMP]Cl : 0.5 I2Cl6, which are shown in grey, were recorded of a liquid phase that had developed after several months in a non-greased round bottom flask.

Quantum Chemical Calculations

All quantum-chemical calculations were performed with the Turbomole program package V6.4 [47,48]

and 7.1[48,49]. For structure optimisations, RI-DFT[31,31,32] (BP86, B3LYP-D3BJ, PBE0) and RI-MP2[33–35]

methods were used on def2-TZVPP[36] basis sets, whereas single point calculations based on RI-

MP2/def2-TZVPP structures were computed using the combinations CCSD(T)[38–40]/def2-TZVPP and RI-

MP2/A’QZ (A’QZ = aug-cc-pV(Q+d)Z[42] for chlorine and aug-cc-pwCVQZ-PP[50] for iodine). A weighted

core-valence basis set was chosen for iodine to accurately account for correlation effects[50] from the

4d-shell electrons, as recommended by the Turbomole manual. From these single point calculations,

approximate CCSD(T)/A’QZ electronic energies � were obtained similar to the method described by

Dunning et al.[51] and many others[52] using Equation (17).

��QRSTU/WXYZ [ ��QRSTU/\�]0^TZ_88 (17)

/ �`a^b80/WXYZ– �`a^b80/\�]0^TZ_88

For a given connectivity of atoms, structure optimizations were performed using a DFT functional and

starting with the highest possible symmetry. The symmetry was then reduced stepwise until no

imaginary frequencies were found in the calculated vibrational spectra, which were determined

analytically (aoforce[34]) for RI-DFT and numerically (numforce) for RI-MP2 calculations. Intensities for

theoretical Raman spectra were calculated using the programs egrad[53] and intense of Turbomole and

overlapped with a Lorentz function for spectra graphics. RI-MP2/def2-TZVPP electron densities and


85

charge distribution were calculated using Turbomole and plotted with gOpenMol[54]. Molecular

structure representations were produced using Diamond 3.0a.[55] Thermodynamic functions at room

temperature and a pressure of 1 bar were calculated using the tool freeh (default symmetry, scaling

factor 1) provided with Turbomole based on frequencies obtained from BP86/def2-TZVPP calculations.

It provides thermodynamic values for the molar Internal Energy �, from which the molar Enthalpy d

can be calculated following Equation (18).

d = � / � ∙ e (18)

With the molar Entropy �, the molar Gibbs Enthalpy f is obtained with Equation (19).

f = d / e ∙ � (19)

C.4.2.1 Energies, Entropy and Vibrational Spectra

The electronic energies of all investigated anions as well as their internal energy and entropy at

298.15 K and a pressure of 1 bar are given in Table 13. Frequencies of vibrational modes and intensities

of [I2Cl7]– and [I3Cl10]– in a pyramidal and a linear isomer along with relative intensities for both IR and

Raman are given in Table 15.


86

Table 14: Calculated electronic Energies �, as well as Internal Energy � and Entropy � at 298.15 K and 1 bar pressure for chloroiodate anions. All values are given in kJ mol–1.

� � �

Basis set def2-TZVPP approx. A’QZ A’QZ def2-TZVPP

BP86 B3LYP-D3BJ PBE0 RI-MP2 SP-CCSD(T) approx. SP-CCSD(T) SP-RI-MP2 BP86 BP86

Cl– –1208580.70 –1208307.70 –1208037.90 –1207082.64 –1207146.19 –1207276.35 –1207212.81 3.7 45.7

Cl2 –2416771.40 –2416229.30 –2415695.00 –2413785.80 –2413920.04 –2414101.83 –2413967.58 9.9 66.7

ICl –1990452.00 –1989791.20 –1989548.30 –1987103.14 –1987124.97 –1982732.72 –1982710.89 9.3 73.9

[ICl2]– –3199248.50 –3198305.70 –3197791.60 –3194376.02 –3194454.11 –3190178.81 –3190100.73 16.7 87.8

½ I2Cl6 –4407312.50 –4406102.60 –4405306.20 –4400948.5 –4401072.95 –4396882.43 –4396757.98 27.5 82.5

[ICl4]– –5616119.20 –5614628.60 –5613566.40 –5608245.38 –5608429.20 –5604351.48 –5604167.66 31.2 116.4

[I2Cl3]– –5189801.10 –5188198.40 –5187434.40 –5181571.49 –5181663.12 –5172997.36 –5172905.72 30.9 130.0

[I2Cl7]– –10023481.00 –10020793.00 –10018923.00 –10009254.9 –10009556.90 –10001291.00 –10000989 62.4 147.5

[I3Cl4]– (pyr) –7180310.80 –7178058.80 –7177040.50 –7168741.82 –7168847.29 –7155792.80 –7155687.33 46.4 188.7

[I3Cl6]– (pyr) –9597142.20 –9594347.70 –9592776.40 –9582575.31 –9582786.55 –9569931.86 –9569720.62 62.1 203.2

[I3Cl8]– (pyr) –12013969.00 –12010637.00 –12008509.00 –11996407.40 –11996723.60 –11984070.50 –11983754.40 77.8 231.0

[I3Cl10]– (pyr) –14430795.00 –14426923.00 –14424241.00 –14410232.40 –14410656.90 –14398203.90 –14397779.30 93.5 254.1

[I3Cl4]– (lin) –7180322.90 –7178061.60 –7177046.30 –7168737.77 –7168843.00 –7155789.23 –7155683.99 43.9 159.4

[I3Cl6]– (lin) –9597150.00 –9594347.70 –9592777.60 –9582572.97 –9582782.43 –9569927.60 –9569718.15 62.0 203.0

[I3Cl8]– (lin) –12013988.00 –12010636.00 –12008518.00 –11996395.30 –11996712.90 –11984059.20 –11983741.60 77.8 239.0

[I3Cl10]–(lin) –14430806.00 –14426921.00 –14424241.00 –14410227.90 –14410648.50 –14398195.90 –14397775.30 93.5 260.8

Table 15: Calculated wave numbers (w. n.) and relative intensities calculated for [I2Cl7]– and [I3Cl10]– in a pyramidal and a linear isomer. All calculations were performed using def2-TZVPP basis sets.

[I2Cl7]– [I3Cl10]– (pyr.) [I3Cl10]–(lin.)

PBE0 RI-MP2 PBE0 RI-MP2 PBE0 RI-MP2

w.n. IR Raman w.n. IR Raman w.n. IR Raman w.n. IR Raman w.n. IR Raman w.n. IR Raman

cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity

1 11 0.00 0.38 21 0.00 0.58 8 0.00 0.51 9 0.00 0.75 8 0.00 0.00 12 0.00 0.00 2 15 0.00 1.00 23 0.00 0.16 8 0.00 0.51 13 0.00 0.38 13 0.00 0.00 16 0.00 0.00 3 22 0.00 0.42 36 0.00 0.25 18 0.00 0.31 24 0.00 0.43 16 0.00 0.00 22 0.00 0.00 4 54 0.01 0.12 57 0.01 0.05 20 0.00 0.10 26 0.00 0.14 16 0.00 1.00 22 0.00 0.61


87

[I2Cl7]– [I3Cl10]– (pyr.) [I3Cl10]–(lin.)

PBE0 RI-MP2 PBE0 RI-MP2 PBE0 RI-MP2

w.n. IR Raman w.n. IR Raman w.n. IR Raman w.n. IR Raman w.n. IR Raman w.n. IR Raman

cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity cm–1 rel. intensity 5 60 0.00 0.02 63 0.00 0.02 20 0.00 0.10 28 0.00 0.25 21 0.00 0.28 30 0.00 0.17 6 65 0.00 0.07 73 0.00 0.07 23 0.00 0.04 34 0.00 0.07 25 0.00 0.83 37 0.00 0.29 7 89 0.01 0.01 94 0.01 0.02 44 0.01 0.01 48 0.00 0.01 47 0.01 0.00 52 0.00 0.37 8 96 0.00 0.02 101 0.00 0.05 44 0.01 0.01 51 0.01 0.02 48 0.00 0.49 54 0.00 0.00 9 102 0.00 0.09 103 0.00 0.10 46 0.00 0.05 52 0.01 0.02 53 0.01 0.00 56 0.02 0.00 10 132 0.00 0.02 130 0.00 0.02 57 0.00 0.01 61 0.01 0.10 62 0.00 0.00 69 0.00 0.07 11 132 0.00 0.08 130 0.00 0.07 58 0.00 0.02 63 0.00 0.07 62 0.00 0.08 73 0.00 0.00 12 137 0.01 0.01 140 0.01 0.01 58 0.00 0.02 66 0.00 0.10 90 0.00 0.13 92 0.00 0.17 13 137 0.83 0.01 141 1.00 0.01 98 0.00 0.03 99 0.00 0.11 91 0.00 0.00 95 0.00 0.00 14 194 0.02 0.01 210 0.03 0.09 98 0.00 0.02 100 0.00 0.13 95 0.02 0.00 100 0.01 0.00 15 197 0.04 0.04 220 0.03 0.03 98 0.00 0.02 103 0.00 0.10 104 0.01 0.00 106 0.01 0.00 16 276 0.09 0.28 284 0.08 0.43 126 0.00 0.01 130 0.00 0.02 108 0.00 0.06 109 0.00 0.05 17 276 0.43 0.22 284 0.42 0.40 129 0.01 0.01 132 0.00 0.01 132 0.00 0.07 136 0.00 0.03 18 292 1.00 0.02 310 0.71 0.04 129 0.01 0.01 134 0.00 0.01 133 0.08 0.00 137 0.01 0.00 19 294 0.56 0.01 311 0.91 0.06 141 0.00 0.03 135 0.00 0.04 134 0.04 0.00 138 0.03 0.00 20 310 0.17 0.18 314 0.25 0.26 142 0.00 0.03 139 0.00 0.04 140 0.00 0.06 138 0.00 0.05 21 328 0.00 0.80 332 0.00 1.00 142 0.00 0.03 141 0.00 0.04 140 0.00 0.00 139 0.04 0.00 22 144 0.00 0.01 167 0.02 0.01 168 0.61 0.00 180 0.76 0.00 23 171 0.40 0.08 184 0.45 0.30 170 0.00 0.10 186 0.00 0.16 24 171 0.40 0.08 195 0.67 0.25 236 0.53 0.00 257 0.00 0.38 25 281 0.01 0.10 288 0.01 0.36 242 0.00 0.19 264 0.52 0.00 26 282 0.01 0.09 289 0.01 0.31 282 0.00 0.72 288 0.00 1.00 27 282 0.01 0.09 289 0.03 0.35 282 0.05 0.00 288 0.04 0.00 28 300 1.00 0.10 312 0.41 0.02 290 0.00 0.21 295 0.00 0.27 29 300 0.54 0.09 315 1.00 0.03 299 0.33 0.00 316 0.00 0.03 30 300 0.54 0.09 320 0.79 0.03 301 0.00 0.02 316 0.37 0.00 31 334 0.61 0.24 336 0.66 0.39 304 1.00 0.00 318 1.00 0.00 32 334 0.61 0.24 339 0.72 0.41 339 0.33 0.00 344 0.00 0.31 33 350 0.03 1.00 354 0.08 1.00 340 0.00 0.22 346 0.28 0.00


88

C.4.2.2 Additional Figures for Quantum-Chemical Calculations

Figure 25 shows several conceivable bonding modes for the [I2Cl5]– anion, which have been calculated

to establish the bonding mode for all other calculations.

Figure 25: Three alternative modes of bonding for the [I2Cl5]– anion all of which are 30 to 70 kJ mol–1 less stable than the isomer shown in the top left corner.

Single-Crystal X-Ray Diffraction

Crystallographic data can be obtained free of charge from the Cambridge Crystallographic Data Centre

via https://summary.ccdc.cam.ac.uk/structure-summary-form with the CCDC number 1539087 for

[NEt4][ICl4], 1536438 for [HMIM][ICl4] and 1537006 for [BMP][ICl4], while a summary is given in

Table 16.

Table 16 Crystallographic details of the salts [Cat][ICl4].

[N(Et)4][ICl4] [HMIM][ICl4] [BMP][ICl4]

Empirical formula C8H20NICl4 C10H19N2ICl4 C9H20NICl4 Formula weight 398.95 435.97 410.96 Temperature /K 101.76 100.03 100(2) Wavelength / Å 0.71073 0.71073 0.71073 Crystal system Orthorhombic Monoclinic Monoclinic Space group Pbam P21/m P21/n a /Å 8.6636(3) 8.5617(5) 8.2487(3) b / Å 10.4334(3) 16.4100(10) 8.5561(3) c / Å 8.3445(3) 12.2792(8) 22.0374(8) α / ° 90 90 90 Β / ° 90 104.730(3) 90.916(2) γ / ° 90 90 90 Volume / Å3 754.27(4) 1668.50(18) 1555.13(10) Z 2 4 4 Density (calculated) Mg/m3 1.757 1.736 1.755 2 Θ range for data collection /° 2.441 to 30.580 2.755 to 28.28 1.848 to 27.593 Data points, restraints, parameters 1233, 151, 89 4265, 158 ,212 3603, 844, 325 R (all data), wR (all data) 0.0211, 0.0461 0.0180, 0.0369 0.0407, 0.0749 Largest diff. peak and hole / e∙Å-3 0.475, -0.974 0.635, -0.414 1.655, -1.698


89

Single crystals were coated with perfluoroether oil, mounted on a micromount at room temperature

and measured after shock-cooling the crystals to 100 K. Data was collected using a Bruker SMART

APEX2 CCD area detector and Mo-Kα radiation. SAINT was used for data reduction and scaling and

absorption correction was performed by SADABS-2014/5, -2008/1 and -2014/3 respectively.[56] The

structures were solved by intrinsic phasing using SHELXT[57] and were refined by full matrix least

squares minimization on F2 using all reflections with SHELXL[58] in the ShelXle[59] GUI or Olex2[60].

Idealized positions of all hydrogen atoms were calculated using a riding model and all graphical

representations of the crystal structures were prepared using Ortep-3 for Windows[61].

C.4.3.1 Additional Figures of the Single Crystal Structures

The composing ions of [HMIM][ICl4] and [BMP][ICl4] are given in Figure 26 a) and b), whereas the unit

cells of [HMIM][ICl4] and [NEt4][ICl4] are shown in Figure 27 and Figure 29, respectively. Figure 28

shows Hirshfeld surface plots of [NEt4][ICl4] and [BMP][ICl4].

a) b)

Figure 26: Section of the crystal structures of a) [HMIM][ICl4] and b) [BMP][ICl4]. Figure a) includes two symmetry-independent [ICl4]– anions, which are located in two adjacent unit cells and figure b) shows the disordered [BMP]+ cation.


90

Figure 27: Crystal structure of [HMIM][ICl4] viewed in 100 (left) and 010 directions (right). The [ICl4]– units residing close to the a-b plane show the shortest I-Cl distance towards an [ICl4]– unit sitting across the b-c plane of the next unit cell in c direction. The 21 axis in the 010 direction of the P21/m space group can be clearly seen in the 100 view on the left.

a) b)

Figure 28: Hirshfeld plots for a) [NEt4][ICl4] and b) [BMP][ICl4], both of which are showing contacts shorter than the sum of the van der Waals radii for H-Cl and Cl-Cl interactions..


91

Figure 29: Crystal structure of [Net4][ICl4] viewed from the 001 (top) and 100 directions (bottom), hydrogen atoms have been omitted for clarity. Cations and anions form a layered structure, in which the I(1)-Cl(1) distance between neighbouring anions is 456.1 pm.


92

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[60] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. a. K. Howard, H. Puschmann, J. Appl. Crystallogr.

2009, 42, 339.


95

[61] L. J. Farrugia, J. Appl. Crystallogr. 2012, 45, 849.


96

D.1 Introduction

97

D Membrane-Free Sn/Br2 Hybrid IL-RFB

The Sn/polyhalide IL battery was originally envisioned by Prof. Krossing and kindly handed out as the

topic of my diploma thesis. The membrane-free setup was a further development devised by myself

and based on the results obtained in this period.

The experiments on the bulk mixtures of SnBr4 and [HMIM]Br, the mixtures thereof with Br2, and the

battery tests starting from an SOC of 100 % were carried out by Niklas Gebel during the work on his

bachelor thesis, which he conducted under my direct supervision. Carola Sturm performed the

viscosity measurements and prepared and measured all DSC samples based on the procedure and

directions provided. Thilo Ludwig calculated the powder diffractrogram from the crysrtal structure of

[HMIM]2[SnBr6]. The bulk mixtures of [HMIM]Br with SnBr4 and Br2 were prepared by Sarah Jenne and

Tobias Fischer during their research internships performed under my direction. Sarah Jenne

additionally measured the conductivity for the mixtures [HMIM]Br + 2 Br2 and [HMIM]Br + 2 Br2 + SnBr4

and conducted the charging experiments for the tempered membrane-free batteries.

D.1 Introduction

The general concept of a membrane-free Hyb-IL-RFB has already been outlined in Section B.1. From

the first experiments with the Sn/ICl3 system presented in Chapter C, it became clear that this system

is not ideal as a first step in the research towards a membrane-free battery. For once, the ICl3-based

electrolyte is not particularly stable in respect to the elimination of dichlorine, and additionally, it

comprises two sorts of halogen atoms, iodine and chlorine, and hence adds another complication to

an already challenging concept. For these reasons, it was decided to focus first on a chemically less

complex system, namely the combination of Sn, SnBr4, Br2 and [HMIM]Br. The strategy chosen for the

research towards the envisioned battery was to initially look at the batteries’ components separately,

to understand them in detail, and only then step by step combining them to finally form the

electrochemical system and to study its characteristics. The first step was to synthesize the hitherto

unknown ILs based on SnBr4. The [HMIM]Br cation was chosen, because it had shown to provide a

good balance between low melting points and moderate viscosities in its ILs. Additionally, a candidate

for the oxidative side based on [HMIM]Br, namely [HMIM][Br9], had already been studied in detail and

found to have an excellent electronic conductivity. The second step was to look at the ternary system

formed between [HMIM]Br, SnBr4 and Br2. If at this point no major and unscalable barrier had been

hit, the third step was adding electrodes and to see if the system could function as a battery. As always,

the unmentioned step zero is a study of the literature.


98

Bromostannate Salts and Ionic Liquids

Elemental tin reacts readily at room temperature with Br2 to form SnBr2 and SnBr4.[1] While SnBr2 is

composed of bent molecules with a lone pair in the gas phase, it polymerizes to form chains in the

solid state.[1] Each Sn(II) is then the centre of a pseudo tetrahedron lined out by two bridging and one

terminal bromine atom and a lone pair. Solid SnBr4 has a melting point of 29.1 °C and is, like its lighter

group 14 homologues, composed of molecules. The tendency for group 14 elements in the oxidation

state +II to undergo a disproportionation reaction towards the oxidation states 0 and +IV decreases

with increasing element mass. The process is endothermic for Pb(II), but exothermic for all lighter

homologues, thus, the Sn(II) halides are only kinetically but not thermodynamically stable at room

temperature.[1]

Multiple bromostannates(II) anions are known in the solid state and in solution. For example, [SnBr3]–

anions were studied via Raman spectroscopy in solution[2] and additionally as [Sn2Br5]– in inorganic

melts[3]. Both anions were identified in the solid state in multiple organic and inorganic salts by pXRD,

Mössbauer and Raman spectroscopy.[3,4] Even fourfold negatively charged octahedra are found in

Cs4SnIIBr6.[1]

For bromostannates(IV), both the [SnBr5]– [5]anion and the [SnBr6]2– [5,6] dianion were studied in solution

via Raman Spectroscopy. The [SnBr5]– anion was identified in solid [NEt4][SnBr5] via Raman

Spectroscopy as well.[5] However, only very few examples of such salts have been crystallographically

analysed, and a CCDC search yields only one donor free structure comprising a trigonal bipyramidal

[SnBr5]–.[7] The salt was obtained through heterolytic dissociation of SnBr4 in solution and the cationic

species is a [SnBr3]+ unit coordinated by the three nitrogen atoms of the neutral, three dentate

tris(pyrazol-1-yl)methane ligand. In comparison, more than 20 crystal structures with many different

organic and inorganic cations were found for the [SnBr6]2– anion in the CCDC. Though some

chlorostannate(II) ILs have been synthesized and investigated, [8,9] to the best of my knowledge, there

have been no reports on ILs based on either bromostannates in the oxidation state +II or +IV.

Tin Deposition from Ionic Liquids

In most cases, the study of tin deposition is motivated by its use as a corrosion inhibiting coating for

other metals. In aqueous solutions, it is typically deposited from Sn(II) salts in acidic and from Sn(IV)

salts in basic conditions.[10] However, the aqueous process is associated with problems like the

evolution of hydrogen or the precipitation of hydroxide salts.[10]

D.1 Introduction

99

A number of reports have been published on the successful deposition of tin from solution in ionic

liquids, e.g. [EMIM]Cl/AlCl3[11], [EMIM]Cl/ZnCl2[12] or [BMP][NTf2][13], and deep eutectic solvents based

on choline chloride[14]. In these studies, tin was either brought into the solvent through anodic

dissolution as Sn(II), or added to the liquid as SnCl2. Hussey et al. also attempted a deposition from

SnCl4 dissolved in basic or acidic chloroaluminate ILs, but were unsuccessful. [11]

Endres et al. studied deposition from [BMP][DCA], BMP[OTf] and [EMIM][DCA] and found that the

morphology of the tin deposit depends both on the anion and the cation. Dendrite free deposits were

only obtained for [BMP][OTf]. [10]

Despite the promising fact that tin deposition from ionic liquids has been demonstrated, there have

been no reports on successful deposition from Sn(IV) species or from any bromostannate salts

dissolved in ILs. Additionally, no attempts were made to electrodeposit tin from ILs, which contain tin

as the anion.

Polybromide Ionic Liquids

An overview over the great variety of polyhalogen salts and the long history of research on the derived

class of materials was already given in the introduction to the section concerning the results on novel

interhalogen complexes based on ICl3 Chapter C. This section will therefore only give a brief overview

on polybromides and the properties of their salts and ILs.

In 2010, Chen et al. reported the first systematic study on the Raman spectra of polybromides prepared

by reaction of [NEt4]Br with 1 to 5 equivalents of Br2 vapour.[15] With the help of calculated spectra,

they were able to assign the observed bands to the monoanions [Br3]–, [Br5]–, [Br7]– and [Br9]–.

Subsequently, crystal structures were reported for the larger of these anions [Br5]– to [Br9]–[16] and an

even larger [Br11]–[17] anion was characterized by Riedel et al.

The remarkable conductivity of solutions of [NEt4]Br in a mixed solvent composed of bromine and

nitrobenzene was already investigated by Gileadi et al. in 1980.[18] They ascribed their observations to

a Grotthus type hopping mechanism, which is also used to explain the high proton conductivity of

water.


100

By employing a cation typically used for the preparation of ILs, namely [HMIM]+, in combination with

4 equivalents of bromine, the RTIL [HMIM][Br9] with a very high conductivity of 52 mS cm–1 at room

temperature is obtained.[19] The high conductivities, combined with the high percentage of bromine

contained in these materials, make them ideal candidates for the application in IL-RFBs.

Tin and Polybromide Based Batteries

To the best of my knowledge, elemental tin has not been used in a battery as active material to this

point, though it has been investigated as a potential storage material in lithium ion batteries, since tin

and lithium form alloys of high Li content.[20] Recently, an investigation into the mechanism of the

electrochemical reactions for the Sn(II)/Sn(IV) system in aqueous solution has been published.[21] The

authors state their motive to be the evaluation of this system for an aqueous Sn/Br2 RFB, though no

further research in this direction is presented. Presser et al. report on their first experiments for a

tin/vanadium redox electrolyte, which is hoped to combine the storage capacity of batteries with the

energy density of capacitors.[22] From the presented data, the working principle of the device and the

potential of the envisioned technology are not clearly deducible. The most prominent use of

polybromide salts for batteries is the Zn/Br2 Hyb-RFB, which has already been discussed in the

introduction.

D.2 Results and Discussion

101


Bromostannate(IV)-ILs

D.2.1.1 Synthesis of the Bulk Mixtures, pXRD and scXRD Analysis

Mixtures of the ratio x = SnBr4/[HMIM]Br = 2.0, 1.5, 1.0, and 0.50 were synthesized in the scale of

grams by addition of SnBr4 to [HMIM]Br. The observed points of homogenisation for the mixtures

increase in order of rising content of [HMIM]Br from 48 (± 5) to 52 (± 5) , 85 (± 5) and 185 (± 10) °C

when heated in an oil bath. For all mixtures of x < 2, a phase separation and the precipitation of a solid

is observed below these temperatures. While the product for x = 0.50 formed a homogeneous solid

block at room temperature, the substance for x = 1.0 formed long yellow needles (approximately 10 x

1 mm). Under a microscope equipped with a polarisation filter, they were found to be polycrystalline,

and through isolation of one of the smaller crystals, the crystal structure of [HMIM]2[SnBr6] was

obtained. The individual ions are shown in Figure 30 and the unit cell in Figure 31. Bond angles for the

[SnBr6]2– anion deviate less than 1.6° from the expected 90° and 180° and Sn–Br bond length are

between 258.5 and 261.6 pm, which is similar to previously reported values.[23] The hexyl chain of the

[HMIM]+ cation is disordered over three positions, two of which differ only slightly in their position,

whereas the third is rotated by 180° at the first carbon atom of the chain. More crystallographic data

is included in the Appendix.

Figure 30: Cation and anion as found in the crystal structure of [HMIM]2[SnBr6]. The two symmetry equivalent bromine anions are labeled Br(2) and Br(#2). All other bromine atoms are symmetry independent, though the octahedron is only slightly distorted (see Appendix). The hexyl chain is disordered over three positions, with one disordered moiety overlapping the left chain in the picture omitted for clarity. Hydrogen atoms are not included for the same reason.


102

a) b) b

Figure 31: Section of the crystal structure of [HMIM]2[SnBr6] with two positions of the disordered hexyl chain shown. a) Cations and anions form a layer structure to a certain degree in the a-c plane. b) [SnBr6]2– anions are arranged in rows in b direction which are surrounded by imidazolium rings and disordered hexyl chains.

Since the solid products of stoichiometric ratios 2.0, 1.0 and 0.5 were visually homogeneous at room

temperature, they were analysed by pXRD. The obtained diffractograms are shown in Figure 32 along

with a diffractogram calculated from the crystal structure of [HMIM]2[SnBr6]. The calculation is in good

agreement with the reflexes obtained for both stoichiometric ratios 1.0 and 0.5. Hence it might be,

that the yellow needles found for x = 1.0 are composed of crystalline [HMIM]2[SnBr6] and amorphous

SnBr4. The small shift of the reflexes towards smaller angles is due to the crystal structure being

recorded at 100 K and the powder diffractograms at room temperature. Since neither the

Figure 32: pXRD analysis for the homogeneous solids obtained for x = 2.0, 1.0, 0.5. The calculated diffractogram is based on the crystal structure of [HMIM]2[SnBr6] and is in good agreement with the reflexes obtained for both stoichiometric ratios 1.0 and 0.5 but not with those for the 2.0 ratio.


103

diffractogram of SnBr4 nor the diffractogram of [HMIM]2[SnBr6] are found to fit the observed reflexes

of the compound obtained for a stoichiometric ratio x = 2.0, its composition remains unclear.

D.2.1.2 Raman Spectroscopy

Concluding from the Raman spectra shown in Figure 19 and the assignment of the observed bands as

listed in Table 17, SnBr4 and [SnBr6]2– are the predominant tin bromide species in the solid phase of

the synthesized bulk mixtures at room temperature. When heated to temperatures above their

respective melting points in sealed 3mm NMR tubes, the liquid phase is metastable when cooled back

down to room temperature and the equilibrium is shifted towards [SnBr5]– for all mixtures with a

stoichiometric coefficient of x ≥ 1. The characteristic symmetric stretching frequencies of the tin (IV)

complexes are marked with dotted vertical lines in Figure 19.

In mixtures with a stoichiometric ratio of x > 1, a liquid-liquid phase separation takes place for the

metastable liquids at room temperature and a small amount of a transparent liquid can be observed

alongside a slightly yellow liquid phase. For x = 1.5 the phase separation is reversed and a

homogeneous liquid is obtained when stored at 60 °C. Based on the Raman spectra, the transparent

liquid seems to be mostly composed of SnBr4.


104

Figure 33: Raman spectra for bulk mixtures of [HMIM]Br with 0.5 to 2.0 equivalents of SnBr4. For metastable liquids at room temperature above a stoichiometric ratio of 1.0, a liquid-liquid phase separation is observed and the spectra are given both for the transparent and the slightly yellow liquid.

Table 17: Observed bands in the bulk mixtures of [HMIM]Br with 0.5, 1.0, 1.5 and 2.0 equivalents of SnBr4. The bands are assigned to SnBr4, [SnBr5]– and [SnBr6]2– according to their literature values[5,6,24] listed in Figure 4 of the introduction. Values at around 140 cm–1 and 285 cm–1 cannot be assigned unambiguously.

[HMIM]2

[SnBr6] [HMIM]Br + 1 SnBr4

[HMIM]Br + 1.5 SnBr4

[HMIM]Br

+ 2 SnBr4

solid liquid (yellow)

solid liqid (yellow)

liquid (transp.)

solid liquid (yellow)

liquid (transp.)

88 (w, sh) 87 (vs) 87 (w) 88 (m) 87 (vs) 87 (w) 88 (m)

99 (w) 98 (w) 98 (vw, sh) 100 (w) 102 (w) 102 (w) 102 (w) 140 (vw, sh) 142 (w, sh) 140 (vw, sh) 135 (vw) 148 (w) 148 (w) 149 (vw) 149 (vw) 152 (vw) 152 (vw) 152 (vw) 152 (vw) 184 (vs) 184 (vs) 183 (vw) 184 (m) 183 (vw, sh) 184 (m) 183 (vw, sh) 200 (vw, sh) 198 (vw, sh) 198 (vs) 200 (vw) 198 (vs) 198 (vw) 199 (w) 198 (vs) 198 (vw)

221 (vw) 220 (vw) 220 (vs) 220 (w) 221 (vs) 220 (vs) 220 (m) 221 (vs)

253 (vw) 253 (vw) 251 (vw) 254 (vw)

276 (vw) 280 (vw) 279 (vw) 276 (vw) 281 (vw) 278 (vw)

285 (vw) 287 (vw, sh)

285 (vw) 287 (vw, sh)


105

D.2.1.3 1H- and 119Sn-NMR Spectroscopy

NMR-Spectra where measured of the metastable neat liquids for x < 1 at room temperature and in

CD3CN for [HMIM]2[SnBr6]. As has been pointed out in the section concerning the Raman spectra,

phase separation is observed for the mixtures of x < 1. For this reason, measurements at 80 °C have

also been performed. All spectra are shown in Figure 34.

The 1H-NMR signal of the H(2) atom (label g in Figure 34), has been used as an in situ probe for the

Hydrogen-Bond-Accepting (HBA) ability of the anions in ionic liquids by Spange et al.[25] A shifts towards

lower field indicate an increase in the HBA ability of the anion. This behaviour is also observed in the

spectra of the [HMIM]Br/SnBr4 ionic liquids, where the signal for the H(2) atom is shifted from

approximately 8.6 ppm in the 1.0 mixture to approximately 8.5 ppm for the ratios 1.5 and 2.0, which

contain a lower concentration of [SnBr5]– and more SnBr4. This is in agreement with the concept

proposed by Spange et al. since the [SnBr5]– is expected to have a greater HBA ability than SnBr4 due

to its negative charge. This can also be seen as indication, that the stoichiometric ratio in the yellow

phase of the two stoichiometries 1.5 and 2.0 is identical at room temperature.

Only one 119Sn-NMR signal is obtained for the different bromostannate complexes, which were found

to be present in the bulk mixtures by Raman spectroscopy. This implies, that the exchange of bromide

anions between the neutral and the anionic complexes proceeds faster than the time scale of the NMR

experiment. A similar behaviour was reported for chlorostannate(II) ILs.[9] An approximately linear

correlation is observed, when plotting the stoichiometric ratio [HMIM]Br/SnBr4 against the chemical

shift of the 119Sn-NMR signal. This linear fit can be used to estimate the complexation equilibrium in

ternary mixtures with bromine and will be further discussed in the respective section.

Figure 34: 1H-NMR and 119Sn-NMR spectra for neat, metastable liquid mixtures of [HMIM]Br with 1.0, 1.5 and 2.0 equivalents of SnBr4 and for [HMIM]2[SnBr6] in MeCN. For the neat mixtures, 119Sn-NMR spectra were also recorded at 80 °C.


106

The signal of the mixture of [HMIM]Br with 2.0 equivalents of SnBr4 does not follow the linear

relationship observed for the other mixtures. Most likely since only the ionic, yellow phase is analysed

in the NMR experiment and the residual SnBr4 at the bottom of the tube masks the true composition

of the mixture.

When comparing the 119Sn NMR spectra at room temperature with the ones recorded at 80 °C, the

signals for the mixtures of x = 0.67 and 1.0 move towards lower chemical shifts, whereas the signal for

the mixture of x = 0.5 moves the opposite direction. A possible explanation for this behaviour would

be, that a general temperature dependent shift to lower ppm values is combined with the dissolution

of some of the SnBr4 phase in the ionic phase of the mixtures of x = 1.5 and 2.0 at elevated

temperatures. In this case, only the temperature shift would be seen for the mixture x = 1.0, both

phenomena would cancel each other’s effect for the mixture with a ratio of x =1.5, and the effect of

the dissolution of SnBr4 would outweigh the temperature effect for x = 2.0. However, the shift in the

signals could also be due to a shift in the equilibria between the different tin species and a clear answer

can only be given by performing additional experiments.

D.2.1.4 Viscosity of [HMIM]Br Saturated with SnBr4

A low viscosity is generally desired for the liquids used in RFBs to yield a high electrolyte conductivity

and to reduce pumping losses. The cell stack has to be designed to accommodate the viscosity by

employing an appropriate combination of channel diameters and channel lengths. For a membrane-

free Hyp-IL-RFB, the viscosity of the Sn-rich phase would be the limiting factor in the stack-design, since

all phases containing bromine showed a significantly lower viscosity as determined by visual

inspection.

The dynamic viscosity of a liquid phase composed of [HMIM]Br saturated with SnBr4 was found to be

between 42.9 and 24.9 Pa s for a temperature range of 45 to 60 °C. This is a drastic increase, if

compared to the dynamic viscosity of SnBr4 of 1.56 to 1.24 Pa s in the same temperature range.

Compared to the viscosity of typical electrolytes in the V-RFB of approximately 2 mPa s at room

temperature[26], these are high values. However, the charge density would also be significantly higher,

thus counterweighing the increased viscosity by a decreased pumping volume for a similar power

output when viewed only from a mass transport perspective.


107

D.2.1.5 Phase Behaviour by DSC

To obtain a clearer insight into the phase behaviour of the system SnBr4/[HMIM]Br, a wide range of

compositions was synthesized by mixing SnBr4 and [HMIM]2[SnBr6] in 50 µL aluminium crucibles in a

glove box followed by heating in our DSC apparatus. This approach was taken, since small quantities

of ground [HMIM]2[SnBr6] are much easier to handle and weigh than small quantities of viscous

[HMIM]Br and since it does not react with SnBr4 at room temperature. Additionally, both the reaction

enthalpies (first heating) and the phase behaviour of the equilibrated mixture (fourth heating) can be

studied. A graphical representation of the results is given in Figure 35, whereas the exact numbers for

all transitions observed during the first and the fourth heating are given in Table 26 in the experimental

section. Since two components of different molar mass are present in the crucibles, the enthalpy has

not been given as kJ mol–1 but instead as J g–1.

Pure [HMIM]2[SnBr6], as determined by pXRD and elemental analysis, shows a transition at 165 °C

which consists of a smaller and a larger signal observed during all four cycles. The main transition is

assumed to be the melting of [HMIM]2[SnBr6] with an enthalpy of 59 kJ mol–1. Since the thermal

behaviour of all mixtures with SnBr4 is much more complicated and more relevant to the topic of this

work, [HMIM]2[SnBr6] will not be discussed further in this section.

The first transition for all mixtures, as depicted in Figure 35 a), is endothermic and occurs at a Tpeak of

28 to 30 °C, which is close to the literature melting point of SnBr4 at 29.1 °C.[27] Since the associated

enthalpy per mass of the sample also increases with increasing fraction of SnBr4, the transition is

assigned to the melting of SnBr4 in the crucibles. The next transition is endothermic as well and

observed for all mixtures at an Tonset of 35 to 39 °C. The highest enthalpy values, 56 J g–1 and

59 J g–1, are observed for mole fractions of 0.49 and 0.60 SnBr4, respectively. This corresponds to an

enthalpy of 38 kJ mol–1 for the mixture containing 0.49 SnBr4, when calculated using the molar mass

of [HMIM][SnBr5]. The enthalpy decreases both for mixtures of intermediate SnBr4 content and for

mixtures containing more and less SnBr4. It could be, that this transition is associated with the

formation of a liquid phase, which is saturated in SnBr4, as observed for the bulk mixtures at similar

temperatures for the stoichiometric ratios 1.5 and 2.0 SnBr4/[HMIM]Br. This could explain the

observed maximum of enthalpy at a mole fraction of 0.6 SnBr4, since the relative amount of this phase

compared to the total amount of substance in the crucible would be maximized at this stoichiometric

ratio. This is supported by the fact, that in the fourth cycle no signal at the melting point of SnBr4 is

observed for a mole fraction of 0.6 SnBr4, but is observed for all mixtures containing more SnBr4.

However, the second maximum at a mole fraction of 0.49 SnBr4 does not fit to this explanation and

the measurements should be reproduced to clarify this point.


108

a) b)

Figure 35: DSC analysis for the system SnBr4/[HMIM]Br synthesized by combining SnBr4 and [HMIM]2[SnBr6] in DSC crucibles with subsequent heating. Enthalpy values are given only for the transitions measured in crucibles with crimped lids (see experimental). Since two components of different molar mass are present in the crucibles, the enthalpy has not been given as kJ mol–1 but instead as J g–1. a) Transitions observed for the mixtures during the first heating listed corresponding to the mole fraction X SnBr4. b) Transitions observed in the fourth heating of the mixtures.

An exothermal transition is observed for all mixtures with a mole fraction of < 0.6 SnBr4 at

temperatures above 70 °C. The enthalpy is approximately –50 J g–1 for 0.55 and 0.57 SnBr4, and more

than –400 J g–1 for 0.49, 0.47 0.44 SnBr4 and –200 J g–1 for 0.40 SnBr4. One explanation to consider is,

that the formation of [SnBr5]– anions is inhibited up to this point and proceeds exothermally. When

calculating the molar enthalpy for the signal observed in the composition of 0.49 SnBr4 by using the

molar mass of [HMIM][SnBr5], a value of –307 kJ mol–1 is obtained. This is approximately double the

value of the gas phase formation of [SnBr5]– from SnBr4 and [SnBr6]2– as discussed in the next chapter.

A clear and unambiguous explanation of this behaviour cannot be given at this point.


109

The transitions observed for the equilibrated mixtures are much clearer. The transition at 28 °C for

mixtures of mole fractions > 0.6 SnBr4 is attributed to the melting of SnBr4, whereas the transition at

around 15 °C observed for all mole fractions between 0.57 and 0.75 SnBr4 is most likely the SnBr4 rich

phase observed in the bulk mixtures. The observed decrease in enthalpy for the transition at 15 °C and

the increase in enthalpy for the transition at 28 °C per sample mass with rising content of SnBr4 are

consistent with this interpretation. No transitions are observed for mixtures of mole fractions 0.47.

0.49 and 0.55 SnBr, where a supercooled melt of [HMIM][SnBr5] might be present. All smaller

transitions below 10 °C are of minor relevance to the topic of this work and will not be discussed

further.

D.2.1.6 Thermodynamic Cycle for the Dismutation of [HMIM][SnBr5]

To get an insight into the thermodynamic driving forces behind the formation of [HMIM]2[SnBr6] and

SnBr4 instead of [HMIM][SnBr5] in equimolar mixtures of [HMIM]Br and SnBr4 at room temperature, a

thermodynamic cycle was calculated and is shown in Figure 36. The values for the lattice energies of

[HMIM]2[SnBr6] and [HMIM][SnBr5] were calculated using an approach proposed by Jenkins which is

based on the molecular volume of the studied salt.[28] The molecular volume of [HMIM]2[SnBr6] was

obtained through scXRD and, using the volume of [SnBr6]2– and Br– as listed in the same publication by

Jenkins, approximate volumes of [HMIM]+ and [SnBr5]– were derived.

For the calculation of its lattice energy, [HMIM]2[SnBr6] was treated as a MX2 compound (M = cation,

X = anion), since the formula proposed by Jenkins for M2X was found to be unreliable in previous

calculations performed in our work group. The value obtained in this way is approximately three times

the value of [HMIM][SnBr5], which is the same factor attained in calculations performed with the well

proven formula established by Kapustinskii (304 vs. 879 kJ mol–1 for [HMIM][SnBr5] and

[HMIM]2[SnBr6], respectively). More details for these calculations are given in the experimental

section.

In sum of the performed calculations, the formation of solid [HMIM]2[SnBr6] and SnBr4 is favoured

compared to the formation of solid [HMIM][SnBr5] by more than 100 kJ mol–1 and is energetically

driven by the comparatively large lattice enthalpy of [HMIM]2[SnBr6]. However, the driving force is

reversed when considering the corresponding reaction in the gas phase, where the formation of

[SnBr6]2– and SnBr4 from two [SnBr5]– anions is endothermic by more than 300 kJ mol–1. When splitting

this reaction in the contributions of forming Br– and SnBr4 from [SnBr5]– and the formation of the

dianion [SnBr6]2– from Br– and [SnBr5]–, both are approximately equally endothermic.


110

Figure 36: Thermodynamic cycle for the transformation of solid [HMIM][SnBr5] to solid [HMIM]2[SnBr6] and solid SnBr4 at 298 K. The reaction enthalpy in the gas phase ∆h!�SiUd° was calculated on a RI-MP2/def2-TZVPP

level, the enthalpy of sublimation for SnBr4 ∆�k;d° is derived from experimental values[29] and the lattice enthalpies ∆#"�d° are obtained through a method proposed by Jenkins[28] using the respective molecular volumes of the composing ions. More details are given in the experimental section.

From an experimental point of view, the situation in the liquid phase seems to be somewhere in

between the two extremes of the situations in the gas phase and in the solid state. Since a

homogeneous liquid phase composed of [HMIM][SnBr5] is obtained at approximately 80 °C, the value

for the Gibbs energy should be close to zero for the reaction of liquid SnBr4 and solid [HMIM]2[SnBr6]

to form liquid [HMIM][SnBr5] at this temperature.


111

Mixed Bromostannate(IV) and Polybromide ILs

D.2.2.1 Constitution of the Electrolyte in Membrane-free Sn/Br2 Batteries for Varying SOCs

During the discharge of a Sn/Br2 membrane-free Hyb-IL-RFB, the electrolyte is transformed from a

polybromide to a mixed polybromide bromostannate and finally to a pure bromostannate IL. During

this reaction, the tin electrode dissolves under oxidation and bromine is reduced to bromide at the

cathode.

Polybromide ILs of multiple stoichiometric ratios could be chosen as the starting electrolyte. The exact

polybromide species formed in these ILs would depend on the cation employed and the exact

stoichiometric ratio chosen. For example, in the case of [HMIM]+ a stoichiometric ratio of

Br2 : [HMIM]Br of 1 : 1, would lead to an [HMIM][Br3] IL, whereas a stoichiometric ratio of 4 : 1, would

result in a [HMIM][Br9] IL. These ILs inherently have different properties in respect to viscosity,

conductivity and bromine vapour pressure. However, it is important to note, that the exact

stoichiometric ratio of the oxidant (Br2) and the [cat]X salt (e.g. [HMIM]Br) in the charged state does

also determine the stoichiometric ratio of the oxidized active material (SnBr4) and the halide salt

([HMIM]Br) in the discharged state. This is to say, that depending on the kind of polybromide used as

the starting material, different bromostannate ILs, as described in the previous sections, are formed.

This principle is visualized in the diagram shown in Figure 37. The diagonal lines correspond to changes

in the constitution of the electrolyte for different SOCs of a specific battery with a fixed ratio of the

sum of oxidant and oxidized metal to complexing bromide (and its corresponding cation).

On the x-axis, the stoichiometric ratio SnBr4/Br– is shown. The synthesized bulk mixtures for

stoichiometries 0.5, 1.0, 1.5 and 2.0 are marked with angled crosses. As has been discussed in the

previous sections, the ILs and salts obtained for these stoichiometries were homogeneous liquids only

at temperatures above room temperature. To determine whether or not the addition of bromine

would decrease this temperature of homogenisation, samples of the bulk mixtures were combined in

NMR tubes with varying amounts of bromine to yield ternary mixtures. The mixtures obtained in this

way are depicted along vertical lines above the respective bromostannate salt or IL in Figure 37. It was

found, that even [HMIM]2[SnBr6], with its relatively high melting point of 165 °C, forms a liquid phase

at room temperature on the addition of two equivalents of bromine. The grey area marks the

approximate boundary of the ternary phases, which are homogeneous liquids at room temperature.

Through these experiments, a clearer insight into the phase behaviour of the ternary mixtures was

obtained and it becomes clear, that a membrane-free battery starting from [HMIM]+ 2 eq. Br2 can not


112

Figure 37: Diagram showing the constitution of electrolytes in a Sn/Br2 membrane-free Hyb-IL-RFB for all states of charge and different stoichiometric ratios of active material to complexing Br–. The y-axis corresponds to SOCs of 100 %, the x-axis to SOCs of 0 %. All compositions for intermediate SOCs can be determined by following the dashed lines depicted for five different stoichiometries. The area shaded in grey covers compositions, which are expected to be biphasic at room temperature based on the results for the synthesized mixtures.

be discharged to low SOCs at room temperature due to the formation of solids. However, a battery

starting from [HMIM]Br + 4 eq. Br2 could at least be discharged to a SOC of 25 % at room temperature

and to a SOC of 0 % at 40 °C. However, the good solubility of [HMIM]2[SnBr6] does raise questions

about the stability of the protective layer envisioned to build and protect the tin electrode from

reaction with bromine. The rate of direct reaction, which corresponds to the rate of self-discharge, will

certainly depend on the local concentrations of Br2 and SnBr4 within a flow cell. Due to the complex

nature of this question, it will be treated in the context of the results attained in the battery

measurements.


113

Based on the preliminary results obtained from the reactions in NMR tubes, bulk ternary mixtures were

prepared by combining [HMIM]Br with either one or two equivalents of Br2 and adding 0.4 or 1.0 and

1.0 or 1.5 equivalents of SnBr4, respectively. The synthesized bulk mixtures are marked with angled

crosses in Figure 37. The mixtures of [HMIM]Br + 1.0 Br2 + 1.0 SnBr4 and of [HMIM]Br + 2.0 Br2 +

0.4 SnBr4 had homogenisation points of approximately 40 and 45 °C, respectively. Below these

temperatures, a small amount of solid precipitated. The other two mixtures with higher SnBr4 content

were homogeneous at room temperature.

D.2.2.2 Raman Spectroscopy

To better understand the constitution of the ternary mixtures, Raman spectra of samples of the bulk

mixtures were recorded in the metastable liquid state in flame sealed NMR-tubes. The spectra are

shown in Figure 38, whereas the frequencies of the observed bands are compared with the

characteristic frequencies of the relevant complexes in Table 12. The spectrum of the mixture of

[HMIM]Br with one equivalent of Br2 depicted in Figure 38 a) shows only the literature known bands

of the [Br3]– anion, while in the spectrum of the mixture with two equivalents of Br2 bands of [Br5]– are

accompanied by the appearance of bands attributed to the presence of [Br3]– and [Br7]–. These

assignments are based on the work of Chen et al.[15], who systematically analysed the Raman spectra

of anions present in mixtures of [NEt4]Br with 1 to 5 equivalents of bromine with the aid of computed

spectra. They made similar observations of several anions being present in the equilibrium for a specific

stoichiometric ratio.

On addition of SnBr4 to the ILs composed of [HMIM]Br and one or two equivalents of bromine, the

equilibrium is shifted towards larger polybromide anions. The bands of [Br3]– are not present in any of

the synthesized bulk mixtures containing both SnBr4 and Br2. Instead a broad signal is observed

between 255 and 285 cm–1. For [HMIM]Br + 2 Br2 + 0.4 SnBr4 the maximum is observed at a frequency

of 275 cm–1, which is similar in frequency to the broad band attributed to [Br7]– by Chen et al.[15]. For

all other mixtures, the maximum is shifted to even higher values, which could indicate the presence of

a mixture of the [Br9]– and the [Br11]–[30] anion.

When comparing the two mixtures containing one equivalent of SnBr4 and either one or two

equivalents of Br2, it can be seen that the equilibrium for the different tin species is shifted from

[SnBr5]– towards higher concentrations of SnBr4 with increasing bromine content. This tendency can

also be seen when comparing the spectra of the pure SnBr4/[HMIM]Br mixtures, shown in light grey

lines where applicable, with the spectra after addition of bromine.


114

Summarizing, the equilibrium for the complexation of bromide anions in competition of SnBr4 and Br2

lies on the side of the formation of [SnBr5]– in mixtures with [HMIM]Br, but it can be shifted in favour

of the formation of polybromides by increasing the amount of bromine in the mixtures. Only very little

[SnBr6]2– appears to be present in the mixtures.

a) b)

Figure 38: Raman spectra for binary mixtures of [HMIM]Br and Br2 and ternary mixtures containing additionally SnBr4. a) Mixture of [HMIM]Br with one equivalent of Br2 and also with 1.0 or 1.5 equivalents of SnBr4 added to the mixture. b) Mixture of [HMIM]Br with two equivalents of Br2 and with additional 0.4 or 1.0 equivalents of SnBr4.


115

Table 18: Raman bands of binary mixtures containing [HMIM]Br and either one or two equivalents of Br2 and ternary mixtures containing an additional 0.4 to 1.5 equivalents of SnBr4.

Characteristic Raman bands of named complexes Experimental Raman spectra of synthesized bulk mixtures

[SnBr6]2– a) [SnBr5]– a) SnBr4a) [Br3]–

[15] [Br5]–[15] [Br7]–[15] [Br9]–[15] [Br11][30] [HMIM]

[Br3] [HMIM]Br + 2 Br2

[HMIM]Br + Br2 + SnBr4

[HMIM]Br + Br2 + 1.5 SnBr4

[HMIM]Br + 2 Br2 + 0.4 SnBr4

[HMIM]Br + 2 Br2 + SnBr4

88 (m) 87 (w) 87 (m) 87 (m)

99 (w) 99 (w, sh) 102 (w) 102 (m) 103 (m) 100 (w) 102 (m)

148 (w) 145 (vw) 147 (vw)

152 (vw) 149 (vw) 149 (vw)

163 162 (vs) 162 (w) 184 (vs) 183 (w) 185 (vw) 183 (w) 184 (w) 198 196 (w, sh)

198 (vs) 198 (vs) 198 (vs) 198 (w) 198 (s)

210 211 (w, sh) 221 (vs) 220 (w) 220 (s) 223 (w, sh) 221 (m)

253 (vw) 253 260 (vs)b) 257

258 (w, sh) 258 (w, sh)

255 (w, sh) 264 269 270 260 (vs)b) 275 (vs, b)

278 (vw) 276

284 (s) 285 (m)

282 (vs) 286 a) Assigned based on Raman bands observed in own measurements, see Table 17; b) this band is interpreted as a superposition of two bands originating from the [Br5]– and the [Br7]– anion.


116

D.2.2.3 NMR Spectroscopy

As for the binary mixtures, only one 119Sn-NMR signal is obtained in the spectra of the ternary mixtures,

despite the presence of a mixture of complexes as observed via Raman spectroscopy. To retrieve

information about the nature of the tin complexes in the mixtures from the coalescence signal, the

linear relationship between the average number y of complexed Br– anions in complexes [SnBr4+y]y–

and the 119Sn signal of the binary mixtures with known composition can be employed. To this end, a

linear regression was performed on the experimental 119Sn-NMR chemical shifts obtained from the

binary mixtures under the assumption that every available bromide anion is complexed by SnBr4 and

that, depending on the stoichiometric ratio, only SnBr4 and [SnBr5]– or [SnBr5]– and [SnBr6]2– are present

simultaneously in any of the mixtures. The used data points are listed in Table 19. As has been

discussed before, the signal of the mixture with two equivalents of SnBr4 is excluded from the fit, due

to the large amount of undissolved SnBr4. Since the residual amount of undissolved SnBr4 in the x = 1.5

mixture at room temperature is very small, its composition is assumed to be exactly as the

stoichiometric ratio of the starting materials.

Equations (20) and (21) were used to calculate the slope ? and the y-intercept > using the individual

measurement points @l, .l.and the total number of measurement points �.

? = ∑ @l.l − �@̅.o∑ @l0 − �@l@²q (20)

> = .o ∑ @l0 − @̅ ∑ @l.l∑ @l0 − �@l@²q (21)

The standard deviation for the data points is calculated using Equation (22).

r = s 1� – 2 vS.l– ?@l − >U²wlx� (22)

Fro these calculations, the linear Equation (23) is obtained.

y = –1.40 ∙ 10–3 – 0.948 (23)

The standard deviation for the data points is 0.08 regarding the average number y in complexes

[SnBr4+y]y–, which is considered sufficient for the purpose of this investigation.


117

Table 19: Data points used for the linear regression to determine the numeric relationship between 119Sn-NMR chemical shifts (x) and the average number of complexed bromide anions per SnBr4 (y).

SnBr4 [HMIM]Br + 1.5 SnBr4

[HMIM]Br + 1.0 SnBr4

[HMIM]2[SnBr6]

average y in [SnBr4+y]y– 0 0.67 1.0 2.0 119Sn-NMR chem. shift / ppm (x) –636 –1198 –1432 –2073

Using the linear equation, values y for the bulk ternary mixtures were calculated from their

experimentally determined 119Sn-NMR chemical shifts. The uncertainty of the calculated data points is

assumed to be equal to the standard deviation of the original measurement points.

The results shown in Figure 39 confirm the conclusions derived from the Raman spectra, namely, that

y decreases, when the amount of Br2 is increased in the mixtures. The two mixtures which are not

homogeneous outside of NMR-tubes at room temperature also show the highest y value, which

indicates, that the equilibrium is shifted towards the formation of [SnBr5]– and even [SnBr6]2–.

Figure 39: Average number y of complexed Br– anions per SnBr4 plotted against the 119Sn-NMR Chemical shift of binary and ternary mixtures. A linear regression was performed on the experimental data for the binary mixtures of [HMIM]Br and SnBr4. The linear equation has a slope of –1.40 ∙ 10–3 and a y-intercept of –0.948. With these parameters, the approximate values y were calculated for the ternary mixtures of [HMIM]Br, SnBr4 and Br2 from their respective 119Sn-NMR chemical shift.

D.2.2.4 Conductivity of Exemplary Mixtures

The conductivity of the electrolyte influences a battery’s inner resistance and contributes, if the

conductivity is high, positively to the power density and the energy efficiency of the device. Since for

flow batteries, the active material is part of the liquid electrolyte, its conductivity has an even stronger

influence on the cell characteristics. The construction of the cell stack has to be adopted according to

the electrolytes conductivity to allow for a small area specific resistance (ASR). For IL-RFBs, the active

mass is the main part of the electrolyte, thus, as has been discussed earlier in this work, its composition

changes strongly with the SOC.


118

Figure 40: Temperature dependent conductivities y of binary and ternary mixtures of [HMIM]Br, Br2 and SnBr4. Conductivities of [HMIM][Br9] are literature values[19] measured with the same equipment as used for [HMIM]Br + 2 Br2 and [HMIM]Br + 2 Br2 + SnBr4. The uncertainty in the temperature for the measured values of [HMIM]Br sat. with SnBr4 is 2 K.

To get an idea on the conductivity of the membrane-free Sn/Br2 Hyb-IL-RFB, exemplary conductivities

for a battery utilizing [HMIM][Br9] in its fully charged state have been measured. The temperature

dependent conductivity for [HMIM][Br9][19] (SOC 100 %), a mixture of [HMIM]Br, two eq. of Br2 and one

eq. of SnBr4 (SOC 50 %) and of [HMIM]Br saturated with SnBr4 (ionic phase at SOC 0 %) is shown in

Figure 40. When comparing the respective conductivities at 50 °C, it becomes clear, that the value

drops drastically from 88 to 12.9 to 2.7 mS cm–1 for SOCs 100 %, 50 % and 0 %. The cell design should

therefore be oriented at the properties of the electrolyte at lower SOCs, since the drop in conductivity

from SOC 100 % to SOC 50 % is much larger than the drop from SOC 50 % to an SOC of 0 %. Extremely

low states of charge should probably be avoided.

To explain the high conductivities of polybromide ionic liquids, a Grotthus[19] type mechanism has been

discussed. It could be, that the mechanism that leads to these high conductivities is hindered, when a

large fraction of Br– is complexed by SnBr4. An additional factor is certainly the increased viscosity that

is observed on the addition of SnBr4. The negative effect of SnBr4 is seen more clearly when comparing

the conductivities of [HMIM]Br + 2.0 Br2 with and without the addition of 1.0 SnBr4: the conductivity

drops by a factor of three, even though, as determined by Raman Spectroscopy, [Br9]– is probably one

of the dominant polybromide species present in the ternary mixture.


119

Electrochemical Measurements on the System Sn/[HMIM]Br/Br2/SnBr4

All battery measurements were performed using the cell and insets described in detail in Section F.1.

For some measurements, a magnetic stir bar was placed inside the cell, with its rotation axis being

identical to the axis of the screw of the battery cell.

D.2.3.1 Battery Experiments Starting from SOC 100 % Using Sn/TF6 Electrodes

The first test of a membrane-free Sn/Br2 Hyb-IL-RFB at a SOC of 100 % can be considered a risky

endeavour. It involves bringing an IL, which consists mostly of bromine, in direct contact with a tin

metal electrode. If the formation of a protective layer does not take place as envisioned, a violent

direct reaction of the two chemicals would be expected.

To estimate the risk of encountering this undesired reaction, small pieces of tin (131 mg, 262 mg,

268 mg) were placed into screw lid glasses, which contained approximately 0.25 mL of a mixture of

[HMIM]Br and 2, 3 or 4 eq. of Br2. While no reaction was observed with the polybromide IL containing

2 eq. of Br2, the mixture with 3 eq. of Br2 felt warm to the touch. A violent reaction under emission of

light, boiling of the ionic liquid and the formation of bromine fumes took place in the mixture with 4

eq. of Br2. However, when the test with the mixture of [HMIM]Br and 4 eq. Br2 was repeated, no violent

reaction was observed, even when the mixture was heated with a heat gun.

On one hand, it might be, that the violent reaction in the first test was due to a different sample

preparation of the tin piece. In the first case, it was cut from a plate of tin with a dull knife, which

resulted in a rough and comparatively large surface area. For all other tests, the tin was cut with a pair

of pincers, which resulted in a smooth surface area. On the other hand, this behaviour can be

understood based on the experiments on the ternary mixtures of [HMIM]Br, SnBr4, and Br2 and the

diagram in Figure 37. The lower the bromine content of the employed polybromide IL, the higher is

the SOC at which a formation of solid [HMIM]2[SnBr6] takes place. This is true both for the

electrochemical and the chemical reaction. Additionally, if the components of the battery heat up due

to an unhindered reaction, the formation of any solid protective layer grows less likely, but instead,

liquids are obtained.

As a safety measure, batteries were set up based on mixtures of [HMIM]Br with 2, 3 and 3.5 eq. of Br2

(from here on referred to as battery 1, 2 and 3) but not with 4 eq. of Br2. The cells were set up in a

desiccator using insets 9 in combination with the expanded graphite electrodes 10 shown in Figure 71

and a tin electrode. This setup resulted in a comparatively small electrode distance of 2 mm and a

surface area of 7.07 cm2.


120

The results of the measurements are shown in Figure 41, Figure 42 and Figure 43 for battery 1, 2 and

3, respectively. The measurement of the OCV was typically started prior to filling the cell with the

polybromide and stabilized once the cell was filled with the liquid. For battery 3, the OCV measurement

was halted shortly after the attempted filling, since part of the liquid was spilled and the cell was

cleaned in a half-filled state and only then filled completely. This variation in the procedure could have

influenced the measured values for this battery.

OCV Values of 1.10 V, 1.13 V and 1.16 V were measured for batteries 1,2 and 3 respectively. After 20

to 30 min, the maximum discharge current was determined by setting a potential of 0 V. To avoid

excessive heating of the battery, these measurements were aborted after less than 1 min. The

obtained maximum currents in this short measurement period were 61 mA (8.5 mA cm–2), 499 mA

(71 mA cm–2) and 214 mA (30 mA cm–2). Even though the current was measured only for a very brief

moment, all values are remarkably high when compared to all other battery measurements performed

on IL-RFBs in our work group.

Battery 1 was then discharged at a current of 5 mA for 30 min. Afterwards, discharging at a current of

10 mA was attempted, though the lower limiting potential of 0 V was reached already after 10 min.

The OCV measured afterwards stabilized again to a value of 1.10 V, which was sustained for 65 h.

Charging of the battery was attempted with a limiting potential of up to 2.5 V, but the achieved

currents were only around 1 mA.

After the previously described short discharge, battery 2 was discharged at a current of 20 mA for

30 min. The observed potential during the discharge operation decreases significantly over this period

of time, though intermediate OCV measurements still showed a value of 1.13 V. The next

measurement performed was a discharge at a potential of 0 V. The maximum current obtained at the

beginning of the measurement was 46 mA but dropped below 10 mA in less than 20 min, at which

point the OCV had also dropped to 1.0 V. Charging was attempted at a potential of 2.5 V and after

charging for 20 min at a maximum current of 0.61 mA, the OCV was raised to 1.12 V. However, the

currents obtained dropped from this point onwards, and so did the measured OCV.

A similar behaviour was observed for battery 3, though the potential dropped even quicker during the

discharge for 30 min with 20 mA and quickly dropped to almost 0 on trying to discharge the battery

further. The OCV measured at the end of the third discharge attempt was 1.08 V.


121

Figure 41: Electrochemical measurements performed on battery 1 (electrolyte: [HMIM]Br + 2 eq. Br2). The heavy oscillation at the beginning is due to the test having been started before filling the cell with electrolyte.

Figure 42: Electrochemical measurements for battery 2 (electrolyte: [HMIM]Br + 3 eq. Br2). The fluctuation of the potential at the beginning of the measurement is due to the measurement having been started prior to filling the cell with electrolyte. The indicated signal at 0.35 h corresponds to the first discharge at 0 V.

Figure 43: Electrochemical measurements for battery 3 (electrolyte: [HMIM]Br + 3 eq. Br2). Due to a spill of part of the electrolyte, there is no data for the beginning of the measurement, as the cell needed to be cleaned and filled with additional electrolyte.


122

Table 20: ASR values calculated for the first discharge and for the end of the following 30 min discharge operation. The values are calculated based on the difference of the potential ∆� between the last measured open circuit voltage �� and the potential �� at the first measurement point of the discharge and the obtained current � at this point.

Battery �� ∆� ASR

V V mA V Ω cm2 1 1.10 0.00 –51.7 –1.10 151

1.11 0.83 –5.0 –0.28 395 1.10 2.50 1.2 1.40 8116

2 1.13 0.00 –491.3 –1.13 16

1.13 0.86 –20.0 –0.27 95 0.99 2.50 0.2 1.51 55124

3 1.16 0.00 –213.5 –1.16 38

1.14 0.43 –20.0 –0.71 252

ASR values were calculated, in the manner set out in detail in the introduction, for the first discharge

at a potential of 0 V, for the end of the 30 min discharge period with a current depending on the

specific battery, and, for battery 1 and 2, for the attempted charging. All values are summarized in

Table 20. The ASRs measured at the beginning of the experiments are not as low as they are desired

for a practical battery, but they are much closer to practical values than the values obtained after the

30 min discharge and especially for the attempted charging. The increased inner resistance is a sign of

a decreased conductivity in the electrolyte and/or the formation of solids.

Figure 44 shows the batteries upon opening after all experiments were finished and the residual liquid

electrolyte removed with a syringe prior to opening. The amount of solid clearly decreases from

battery 1 to battery 2 and 3, which is the expected result based on the prior experiments. Additionally,

the formerly smooth tin electrode had gained a rough surface.


123

battery 1 battery 2 battery 3

Figure 44: Disassembled membrane-free Sn/Br2 IL-Bs after discharge, the tin electrode is shown at the bottom.

The yellow solid obtained from battery 1 showed the typical bands of the [SnBr6]2- anion, and to a

lesser extent those of [SnBr5]– and SnBr4. A similar spectrum was obtained for the yellow to orange

solid/liquid mixture found in battery 2, though the intensity of the bands of SnBr4 and [SnBr5]– is

increased. For battery 3, a red solid, a red liquid, an orange solid and an orange liquid were obtained

and analysed. The respective Raman spectra are shown in Figure 45. It seems, that besides the solid

liquid phase separation, an additional phase separation between two liquids had taken place, the

orange one being composed of SnBr4 and the red one being a mixture of [HMIM]Br, Br2 and a large

amount of SnBr4. Consulting the diagram in Figure 37, this is the expected result for batteries starting

from a mixture of [HMIM]Br and 3.5 eq. of Br2 at lower SOCs, since the resulting bromostannate IL has

a stoichiometric ratio of x = 1.75, which corresponds to a content of SnBr4 for which a phase separation

is expected based on the results discussed earlier.

Based on the volume of the polybromide used in the batteries and the difference in mass of the

electrode between the beginning and the end of the experiment, an estimate on the discharge capacity

was calculated. All values are listed in Table 21. From the obtained calculated capacity values for tin

and the polybromide, it seems, that most of the polybromide has reacted with the tin electrode. In all


124

Figure 45: Raman spectra for the solids and liquids retrieved from battery 3 after discharge. In the red phases, the bands associated with polybromides can be identified. The most intense band for the solid compounds is attributed to the [SnBr6]2– anion.

cases, only a few percent of the charge were transferred via the external circuit. It could be, that a

large amount of tin reacted during the period of 30 min OCV measurement at the beginning of the

experiment, however, the chemical reaction might also have been induced during the first discharge

and proceeded subsequently much faster than the electrochemical reaction. To clarify this matter, a

similar battery could be set up and discharged immediately at the highest possible rate to evaluate

and compare the efficiency. Then again, this could potentially result in a violent reaction and should,

if attempted at all, probably be first tried with a polybromide of low bromine concentration.

The main issue at this point seemed, that charging the battery had not been possible in the

experiments performed. For this reason, further batteries were set up at an intermediate SOC.

Table 21: Estimation on the efficiency of the first tests of a membrane-free Sn/Br2 Hyb-IL-RFB based on the comparison of the amount of charge � transferred in the chemical reaction vs. the amount of charge transferred vie the external electronic circuit. The calculation of the chemically transferred charge is based on the amount of bromine present in the battery at the beginning of the measurement and the mass difference ∆� of the tin electrode at the end of the measurement compared to its starting value, and the number of charges 7 transferred per atom/molecule.

Battery [HMIM]Br + x Br2

est. a) � $ �(Br2) �(Br2) 7(Br2) �(Br2) ∆�(Sn) �(Sn) 7(Sn) �(Sn) �(disch.)

g mL–1 g mol-1 ml g mmol 103 C g mmol 103 C 103 C

1 2.15 1.96 592 1.41 2.77 10.1 2 1.9 0.49 4.1 4 1.6 0.017

2 3.10 2.27 743 1.41 3.19 13.3 2 2.6 0.73 6.1 4 2.4 0.064

3 3.48 2.39 803 1.41 3.36 14.6 2 2.8 0.59 5.0 4 1.9 0.050 a) Estimated density based on the measured density of [HMIM][Br3] (1.6 g mL–1)[31] and the crystallographic density of [HMIM][Br9] (2.55 g mL–1)[19] using a linear relationship between the density and the bromine content.


125

D.2.3.2 Battery Experiments Starting from Intermediate SOCs using TF6 Electrodes

To investigate, whether charging from a ternary mixture would be possible, two cells with two TF6

electrodes each (produced by SGL Carbon, composite made from expanded graphite and a fluoro

polymer) and filled with two different electrolytes were set up. The electrolytes were the mixtures

[HMIM]Br + Br2 + SnBr4 and [HMIM]Br + Br2 + 1.5 SnBr4, which are two of the mixtures which were

described and analysed in the previous sections. These electrolytes correspond to a SOC of 33 % for a

battery starting from [HMIM]Br + 3 Br2 (SOC 100 %) and an SOC of 25 % for a battery starting from

[HMIM]Br + 4 Br2 (SOC 100 %), respectively. Since a small amount of solid was present in the [HMIM]Br

+ Br2 + SnBr4 mixture, only the liquid phase was transferred to the battery. Therefore, the stoichiometry

of the mixture is not exactly as indicated. However, the fact that the mixture was saturated in respect

to the precipitation of [HMIM]2[SnBr6], was considered beneficial for the formation of a protective

layer on the desired tin deposit.

By using two TF6 electrodes instead of a tin and a graphite electrode as in the prior experiments, it

was ensured that the SOC could not drop below the starting values, since no additional tin was

available. Therefore, no undesired precipitation of [HMIM]2[SnBr6] was expected. As a further

measure, a magnetic stir bar was included in the cell (2mm x 20 mm) and a magnetic stirrer placed at

the flat side of the test cell opposite of the screw and directly behind the positive electrode. The

intention was to have a homogeneous liquid at all times, so that no major amount of solid could built

up due to locally varying concentrations of the components of the mixture.

The first measurement performed on the batteries was the linear sweep voltammogram shown in

Figure 46. It shows an almost linear relationship between potential and current, which means that the

a) b)

Figure 46: Linear sweep experiment performed after setting up the batteries with electrolytes a) [HMIM]Br + Br2 + SnBr4 and b) [HMIM]Br + Br2 + 1.5 SnBr4.The experiment shown was measured without stirring but the same result was obtained when measured under stirring at 100 rpm.


126

electrolyte behaves more like an ohmic resistor than like a redox active chemical system, for which an

increase in the current is expected only as soon as the threshold value of the respective oxidation or

reduction potential is reached. This behaviour was also observed by Haller in her investigation of the

[HMIM][Br9] IL.[32] Stirring at 100 rpm had no significant effect on the results obtained.

After this first experiment, charging was attempted at several different voltages with and without

stirring for several days. Though an OCV of up to 0.9 V was observed after charging for several hours,

both the OCV and the discharge currents dropped to 0 very quickly compared with the long charging

times. Stirring at lower speeds and not stirring at all lead to only slightly higher OCVs but otherwise,

no significant change in the electrochemical behaviour was observed. The performance is represented

in the excerpts of the charging and discharging experiments shown in Figure 47 for the [HMIM]Br + Br2

+ SnBr4 and Figure 48 for the [HMIM]Br + Br2 + 1.5 SnBr4 electrolyte.

On dismantling the cells, the [HMIM]Br + Br2 + SnBr4 electrolyte had a basically unchanged Raman

spectrum. For the cell containing the [HMIM]Br + Br2 + 1.5 SnBr4 electrolyte, a liquid and a small

amount of solid liquid mixture were obtained. While the liquid seemed to be mostly composed of SnBr4

based on its Raman spectrum, the solid showed the expected bands of polybromides and the [SnBr6]2–

anion.

Figure 47: Exemplary charging test performed on a [HMIM]Br + Br2 + SnBr4 electrolyte. The experiment on the left shows clearly that, even though a large charging current is obtained even at a potential of 2 V, almost no discharging current is retrieved. In the experiment shown on the right, the ratio of charging and discharging current is still not good, though at least a moderate OCV of 0.6 to 0.8 V can be observed in the intermediate measurements. Again, stirring at different speeds does not influence the measurement significantly.


127

Figure 48: Exemplary charging test performed on a [HMIM]Br + Br2 + 1.5 SnBr4 electrolyte. Charging at different voltages and with different stirring frequencies did not make a major difference. When charging for extended periods of time, a similar OCV as in the experiment with the [HMIM]Br + Br2 + 1.5 SnBr4 electrolyte is observed.

Concluding from these results, charging seems not to be possible using the described setup and

electrolytes. It might be, that the high conductivities of the polybromides lead to a kind of short

circuiting of the electrodes, thus preventing the formation of potential sufficient to reduce the

contained SnBr4. The experimental setup was consequently changed to try and create conditions,

through which successful charging could be accomplished.

D.2.3.3 Battery Experiments Starting from Intermediate SOC with Experimental Variations

The first variation made to the experimental setup in order to succeed in charging the membrane free

Sn/Br2 Hyb-IL-RFB battery, was to vary the temperature of operation. The reasoning behind this was,

that metal deposition could in general benefit from elevated temperatures, and, that by controlling

the temperature, the phase equilibrium for the formation and dissolution of [HMIM]2[SnBr6] could be

controlled.

For this reason, the electrolyte [HMIM]Br + 2 Br2 + 0.4 SnBr4 was heated, to form a homogeneous

liquid, and then filled in a test cell preheated to 60 °C and placed into the preheated apparatus shown

in Figure 73 in Section F.1.

The plan was to first keep the temperature at a level high enough to keep all components of the

electrolyte liquid and then slowly drop the temperature to see if a sudden change in the

electrochemical behaviour would be observed.


128

Figure 49: Charging experiment with two TF6 electrodes and a [HMIM]Br + 2 Br2 + 0.4 SnBr4 electrolyte at temperatures between 51 and 17 °C. The mark for 41 °C is shown as an exemplary intermediate temperature. The dotted blue line at around 0.2 V represents intermediate OCV measurements. Due to the high conductivity of the electrolyte, the current limit of 100 mA is reached at the beginning of the measurement, leading to the SMU lowering the voltage accordingly. The measurement was performed under continuous stirring at approximately 40 rpm.

Again, the first experiment performed was a linear sweep, which showed the same, linear behaviour

observed in the other experiments with two graphite electrodes, although the maximal current

obtained was much higher (approximately 80 mA at 2 V). This is most likely due to the higher bromine

content of the electrolyte and also the elevated ambient temperatures compared to the previous

measurements.

A charging experiment was then started at a charging potential of 3 V and an ambient temperature of

50 °C inside the Styrofoam box. The current limit was set to 100 mA, and looking at the experimental

data shown in Figure 49, it was reached a couple of hours after the beginning of the test, which resulted

in the SMU lowering the potential. A possible explanation is, that the electrolyte had reached a stable

temperature at this point, and that the cell temperature had decreased to a temperature below 51 °C

during its filling with electrolyte. The temperature was then lowered stepwise over the next 11 days

to a minimum temperature of 17 °C. Despite the decreasing current corresponding to decreasing

temperatures, no effect on the intermediately measured OCV was observed.

On disassembling the battery at room temperature, a solid and a liquid were retrieved from the

battery. Both showed the well-known Raman bands for bromostannates and polybromides with the

expected ratio for the intensities of the relevant bands.

At this point, it was considered, that the deposition of tin at the TF6 electrode might be the problematic

step for the charging. To investigate this possibility, a cell with a [HMIM]Br + 2 Br2 + SnBr4 electrolyte

and a tin and a graphite electrode was set up. This corresponds to an SOC of 50 % for a battery starting


129

a) b)

Figure 50: Beginning of the experiment for a cell utilizing a tin and a TF6 electrode and a [HMIM]Br + 2 Br2 + SnBr4 electrolyte. The measurement was conducted at room temperature for the first 17 hours. a) Filling of the cell at a terminal voltage of 1.3 V, short OCV, linear sweep and subsequently charging attempts at 2.0 V. b) Linear sweep experiment conducted shortly after filling the cell.

from an electrolyte composed of [HMIM]Br + 4 Br2. In contrast to the experiments starting from SOC

100 %, the electrolyte was stirred to have a homogeneous electrolyte during the whole test. The

distance of the electrodes was increased to 8 mm, because it would increase the inner resistance of

the cell, and therefore help in building a potential gradient instead of being “short circuited” through

the high conductivity of the polybromides.

To hinder immediate self-discharge, the cell was filled, while applying a constant potential of 1.3 V.

This resulted in a small charging current as soon as the electrolyte was filled in the cell, as shown in

Figure 50 a). The linear sweep experiment, which was conducted shortly after filling the cell (Figure 50

b)), again, shows a linear dependency between current and potential. Since, in contrast to the charging

experiments up to this point, a tin electrode was used, a discharging current of approximately 10 mA

was obtained at 0 V and at a current 0 mA, the OCV can be determined to 1.18 V. Calculating from

these values, an ASR of 182 Ω cm2 is obtained. This value is not directly comparable to the ones

obtained for the cells tested at SOC 100 %, since the distance of the electrodes in these tests was 4

times smaller.

Charging was attempted at a potential of 2 V from this point onwards, but the obtained

currents dropped to almost zero within the first 6 hours, whereas the OCV only dropped to 1.14 V. The

temperature of the cell was then raised to 46 °C, which resulted in the current increasing again.

However, intermediately performed, short discharge pulses did not reach the values observed at the


130

Figure 51: Charging experiment using one tin and one TF6 electrode and a [HMIM]Br + 2 Br2 + SnBr4 electrolyte at temperatures between 25 and 51 °C. The dotted blue line between values of 1.1 and 0 V represents intermediate OCV measurements. The measurement was performed under continuous stirring at approximately 40 rpm. From day 8 onwards, spikes in the observed current up to the current limit of 100 mA are seen.

beginning of the measurement. This indicates, that the inner resistance of the cell had increased, most

likely due to self-discharge, despite the applied potential of 2 V. The whole experiment, which lasted

12 days, is shown in Figure 51.

Discharging was attempted two days after starting the experiment but resulted only in very low

currents and a drop in the OCV to 0.58 V. A stable OCV significantly above this value could not be

reached for the rest of the experiment. On attempting to charge the battery at a temperature of 51 °C

and a potential of 3 V, a sudden increase in the current to values above 40 mA and later to the current

limit of 100 mA was observed.

On opening the cell, a grey and a yellow solid were obtained (Figure 52). It was suspected, that the

grey powder might be elemental tin, which would explain the sudden increase of the current as a short

circuiting inside the cell through the metallic powder. However, a pXRD measurement did not yield

any signals and the composition of the powder remains unclear to this point. Raman spectra show the

major signal of the yellow substance being an unfamiliar one at 140 cm–1, which is also the most

intense band observed for SnBr2.[3] The spectrum is shown in Figure 55 in comparison with results

obtained in a battery measurement with membrane, where a similar signal is found in the spectrum

of a solid found on the tin electrode. Since a large amount of a yellow substance was found in the

battery, it remains unclear, if the entire substance is indeed composed of SnBr2, as is the mechanism

of its formation.

The natural explanation for the apparent lack of bromine in the products found in the cell, would be

that all bromine has reacted with the tin electrode under self-discharge, and the complete electrolyte


131

was transformed to a bromostannate(IV) IL. Starting from this point, the electrochemical formation of

a large amount of SnBr2 would demand the formation of some oxidized product, which is not observed.

An alternative would be the comproportionation of Sn(0) and Sn(IV) to form Sn(II). This reaction is

typical for Pb(0) and Pb(IV), however, it is untypical for the lighter homologues of group 14.[1] Further

experiments need to be performed to clarify this matter.

The last variation of the test setup was the use of a FAPQ-375-PP anion exchange membrane in

combination with a tin and a TF6 electrode. This was to meant to test, whether or not charging would

be possible, if bromine and tin were in contact only with one electrode. [HMIM]Br saturated with SnBr4

was chosen as the anolyte, and [HMIM]Br + 2 Br2 as catholyte. The cell was operated at an ambient

temperature of 57 °C inside a Styrofoam box to ensure, that the anolyte would stay a homogeneous

liquid for the whole measurement. The complete measurement is shown in Figure 53.

Figure 52: Pictures taken while disassembling the battery with a [HMIM]Br + 2 Br2 + SnBr4 starting electrolyte. From left to right: visibly degraded tin electrode, yellow solid, grey solid and white magnetic stir bar, only slightly degraded TF6 electrode.

Figure 53: Overview for all experiments performed on the battery utilizing a tin and a TF6 electrode in combination with a membrane. The spikes in the current and voltage are due to polarization measurements performed throughout the experiment.


132

Figure 54: Pictures taken while disassembling the Sn/Br2 IL battery. From left to right: anolyte, catholyte, membrane, tin electrode with O-ring sealing and a yellow solid, tin electrode after some cleaning, almost unaltered TF6 electrode.

Over the course of the first 24 h after setting up the battery, the ASR decreased from over

900 000 Ω cm2 to a value around 6000 Ω cm2. Similar observations were made for other IL batteries

using the FAPQ-375-PP.[31] At this point, the OCV had stabilized to a value of 1.15 V. The battery was

then discharged for 3 days, during which the ASR in respect to charging lowered to values between

1600 and 2000 Ω cm2. Charging was then attempted at 2, 2.5 and 3 V, however, the ASR rose from this

point onwards and reached values of around 12 000 Ω cm2 for both charging an discharging when the

battery was disassembled. The charge balance was almost back to its starting value at this point.

A yellow solid (Figure 54) was found adhering strongly to the tin electrode and showed the bands of

the [SnBr6]2–anion in the Raman spectrum. A band at 140 cm–1 was found as well, though with less

intensity than in the charging experiment utilizing a tin electrode without a membrane. For the

catholyte, a slight shift to larger polybromides was found. Since the state of charge was not increased,

a) b)

Figure 55: Raman spectra of compounds before and after the electrochemical testing of the Sn/Br2 IL battery with membrane and, in comparison, the solid found after the charging experiment in a membrane-free battery with tin electrode. a) Compounds found in the anodic half-cell and the membrane-free cell. Concluding from the Raman bands, it might be that by the time of the measurement, the yellow liquid in the NMR tube had solidified. b) Liquid polybromide IL filled into and retrieved from the cathodic half-cell.


133

as judged by the coulombic balance of the measurement, this could mean that [HMIM]Br was

transferred through the membrane. This could be seen in conjunction with the formation of solid

[HMIM]2[SnBr6] in the anolyte, which lowers the formal concentration of [HMIM]Br in the anodic half-

cell and could lead to an increased drag of [HMIM]Br from the cathodic half-cell through the

membrane.

D.2.3.4 Cyclic Voltammetry of [HMIM]Br Saturated with SnBr4

In a last attempt to shed some light on the electrochemical processes occurring within the studied

Bromostannate-ILs, cyclic voltammetry was performed on [HMIM]Br saturated with SnBr4 at 60 °C. As

a first experiment, the a cyclic voltammogram was recorded using a glassy carbon UME as work

electrode, a tin wire as reference electrode and a TF6 counter electrode in a small glass vial placed in

an oil bath inside a glove box. The setup is shown in Figure 56.

The cyclic voltammogram is shown for the oxidative and the reductive region in Figure 57. While in the

oxidative region, an increase in current is obtained starting at 1.35 V, the situation for the reductive

region seems more complicated. Though a reductive current starts to appear at around –0.2 V and

increases strongly at around –0.8 V, the signal is very unstable. During repeated attempts to further

analyse this region, the signal got more and more erratic, which could indicate the formation of an

obstructing solid on the electrode. This interpretation is further supported by the results obtained

from the chronoamperometric experiment shown in Figure 58. It was performed using a TF6 electrode,

a) b)

Figure 56: Experimental setup for cyclic voltammetry (CV) and chrono amperometry (CA) measurements performed on [HMIM]Br saturated with SnBr4. a) Left to right: glass vessel, alligator crimp used to hold and contact the electrodes, TF6 counter electrode, TF6 work electrode for CA measurement, Sn wire used as reference, Sn wire used as counter electrode for CA measurement. b) Setup inside the glove box with manual and digital thermometer and the glassy carbon UME in use.


134

and two tin wires as reference and counter electrode. In trying to deposit metallic tin, the potential

was set to –0.5 V vs. Sn and the current recorded over a period of several minutes. Again, the current

did fluctuate, and was also influenced by stirring the solution, though no clear relationship could be

found. After this period, a yellow solid had formed on the TF6 electrode, of which a picture is shown

in Figure 58 b). On attempting to clean the deposit from residual IL with MeCN, the solid dissolved

completely. One interpretation of this finding is, that SnBr2 is formed in the reductive region. This

would lead to two bromide ions being released. At the surface of the negatively charged cathode, a

a) b)

Figure 58: a) Chronoamperometric experiment on [HMIM]Br saturated with SnBr4. The current was not stable and fluctuated heavily, potentially influenced by stirring the solution, but no clear relationship could be identified. b) Picture of the the reference electrode (left), the counter electrode (center) and the TF6 working electrode with a solid on the part of the surface which was submerged in the liquid during the experiment.

Figure 57: First cycle of cyclic voltammograms measured in oxidative and reductive direction on [HMIM]Br saturated with SnBr4. On the reductive side, no stable signal could be obtained. Both voltammograms were recorded at a sweep rate of 100 mV s–1.


135

layer of [HMIM]+ cations is most likely adsorbed as a Helmholtz or a diffuse double layer.[33] If SnBr4 is

now transported towards the cathode via diffusion, the conditions are ideal for the formation of solid

[SnBr6]– due to the high local concentration of [HMIM]Br. In sum, the formation of a “protective layer”

is observed, but most likely directly on the carbon electrode and not on top of deposited tin, as it would

be needed for a functional battery.


136

D.3 Conclusion and Outlook

137

D.3 Conclusion and Outlook

The phase behaviour of mixtures of SnBr4 and [HMIM]Br were systematically analysed both in the bulk

and via synthesis in DSC crucibles. The different bromostannate species present in these mixtures were

analysed by Raman and NMR spectroscopy both for the solid and the liquid state. The extremes of the

melting points are observed for [HMIM]2[SnBr6] (165 °C) and a phase containing a mixture of [HMIM]Br

saturated with SnBr4, for which a homogenisation in the bulk was observed around 40 °C. In the solid

state at room temperature, [HMIM]2[SnBr6] and SnBr4 are the dominating compounds. The

dismutation of [HMIM][SnBr5] on cooling the liquid to room temperature, was explored in more depth

by calculating a thermodynamic cycle and concluding, that the lattice enthalpy for the formation of

solid [HMIM]2[SnBr6] is the energetic driving force.

An overview over possible compositions for a ternary electrolyte based on [HMIM]Br, SnBr4 and Br2

and the anionic complexes present in these mixtures, was obtained by analysing experimental mixtures

via Raman and NMR spectroscopy. The conductivity of these samples decreased significantly on an

increase of the SnBr4 content.

Discharging experiments for the first membrane-free Sn/Br2 IL battery showed promising ASR values,

though the observed efficiencies were poor for all studied electrolytes. Charging experiments were

performed under variation of the electrolyte, electrode materials and operating temperature. None of

these variations led to successful charging of the membrane free Sn/Br2 IL battery. Charging was even

impossible when using a membrane to separate the anodic and the cathodic half-cell in a further

experiment. The observation of a band at 140 cm–1 in the Raman spectra obtained on solids found in

the cells after charging experiments which utilized a tin electrode, suggests the presence of SnBr2.

The problem of a poor discharge efficiency might be overcome when moving from static cells to a flow

setup. In these flow-cells, the electrolyte should be kept saturated with an [cat]2[SnBr6] salt, thus

ensuring that a protective layer would be stable over the whole SOC range. Such a setup was already

depicted in Figure 9 in Chapter B.1.2.1. The cost of the electrolyte could be reduced by utilizing a salt

which is less soluble in the electrolyte than [HMIM]Br.

The major problem of the envisioned battery is the fact that successful charging was not achieved

during the course of this work. It might be, that the formation of Sn(II) species play a role in preventing

a tin deposition. However, no firm conclusions can be drawn from the exploratory charging


138

experiments and neither from the cyclic voltammetry experiment. A systematic study of the charging

behaviour of the membrane-free Sn/Br2 IL battery should therefore be the next step in the course of

this research.

D.4 Experimental

139

D.4 Experimental

General: If not stated otherwise, all reactions were performed under argon inert atmosphere using

standard Schlenk techniques and a vacuum of < 3 × 10-2 mbar. MBraun Labmaster sp glove boxes were

used with H2O and O2 contents < 0.1 ppm. Glassware was cleaned using iPrOH/KOH (over night) and

HCl (> 30 min) baths with subsequent rinsing using deionised water. Prior to the use for inert reactions,

apparatuses were heated with a heat gun (650 °C) under vacuum.

Chemicals: The manufacturer and grade of purity of the chemicals used are listed in Table 22.


manufacturer purity purification [HMIM]Br IoLiTec GmbH 99 % dryinga) SnBr4 Sigma Aldrich 99 % distillation Br2 Sigma Aldrich >99 % dryingb) Sn Alfa Aeser 99.85 % – a) Heated to 80 °C under vacuum for 24 h by Dipl.-Chem. M. Hog and stored in a glove box; b) transferred to a Schlenk flask and stored over P4O10.

pXRD: Powder diffraction was measured using a StoeStadiP diffractometer combined with a Mythen

1K area sensitive detector, Mo-Kα radiation (λ = 0.71073 Å), and a Ge(111)-monochromator in glass

capilaries.

scXRD: Single crystals were coated with perfluoroether oil, mounted on a micromount at room

temperature and measured after shock-cooling the crystals to 100 K. Data was collected using a Bruker

SMART APEX2 CCD area detector and Mo-Kα radiation. SAINT was used for data reduction and scaling

and absorption correction was performed by SADABS-2014/3 respectively.[34] The structures were

solved by intrinsic phasing using SHELXT[35] and were refined by full matrix least squares minimization

on F2 using all reflections with SHELXL[36] in the ShelXle GUI[37]. Idealized positions of all hydrogen atoms

were calculated using a riding model, and all graphical representations of the crystal structures were

prepared using Ortep-3 for Windows[38].

Conductivity: A Mettler Toledo inLab 710 was used to measure conductivities of samples in a

temperature controlled glass vessel under inert argon atmosphere. Calibration was performed using

Merck Certipur aqueous KCl standards (1.41 and 12.8 mS cm–1). A Metrohm 712 conductometer was

used to measure conductivities in a glove box, where sample temperature was controlled by an oil

bath with an estimated uncertainty of ± 2 °C.


140


operating at 1064 nm was used to record the spectra from 0 to 4000 cm–1 and a resolution of 4 cm–1.

Intensities were assigned letters according to their relative intensities and appearance (very strong (vs)

> 0.8, strong (s) > 0.6, medium (m) > 0.4, weak (w) > 0.2, very weak < 0.2 (vw), shoulder (sh), broad

(br)). Bands at and below 80 cm–1 were ignored due to a strong signal inherent to the spectrometer

used and the baseline was manually corrected if a strong base intensity was found.

F-IR Spectra: Spectra were recorded on a Nicolet 760 Magna IR using a diamond ATR unit and

processed using the baseline correction and advanced ATR correction of Omnic 7.2 (Thermo Electron

Corporation).

NMR Spectra: Liquid phases of neat samples were analysed in flame sealed 3mm NMR-tubes with and

without external lock on toluene. Spectra were recorded on a Bruker Avance DPX 200 Mhz, a Bruker

Avance III 300 MHz NMR or a BRUKER Avance II+ 400 MHz and were calibrated according to a chemical

shift of 3.88 ppm for the N-Me group of the [HMIM]+ cation obtained for [HMIM]2[SnBr6] in MeCN-d3

solution. Signals from solvents providing external lock are ommitted in the listing of the signals. The

shift of the spectrum reference frequency (SR) for hetero nuclei was calculated from the 1H-NMR SR

value using the respective spectrometer frequencies (SF) in Equation (24).

��Sdz{U = ��Sdz{U ∙ ��S d� U��S d� U (24)

Elementary analysis: A VarioEL (Elementaranalysensysteme GmbH) was used for elemental analysis.

Viscosity: A Brookfield RVDV-III UCP rotational viscosimeter was used for all viscosity measurements

and was operated in a self-built glove box operating with dry air (relative humidity <0.1 %). The

temperature was controlled by an external cryostat (± 0.1 °C).

DSC: A Setaram DSC 131 differential scanning calorimeter was used in combination with a FTS Systems

SP-Scientific Flexi-Cool system to perform all DSC measurements, which were analysed using the

software SetSoft 2000.

Cyclic Voltammetry: Measurements were performed in a glove box using a Biologic SP-300

potentiostat and analysed using EC-Lab (V10.44). The Glassy Carbon circular disk UME was polished

prior to its use as working electrode.

D.4 Experimental

141

Battery Measurement: The cell described in Section F.1 with aluminium or copper current collectors

was used for the battery measurement and performed using an Agilent B2901A Source Measure Unit

in conjunction with the bbat software (see Section F.2). All parts of the cell, including the PTFE insets,

were stored at 60 °C prior to use.

Theoretical Methods

D.4.1.1 Quantum-Chemical Calculations

Quantum chemical calculations were performed with the Turbomole program package V6.4 [39,40] and

7.1[40,41]. For geometry optimisations, RI-DFT[42,42,43] (BP86, B3LYP-D3BJ, PBE0) and RI-MP2[44,45]

methods were used on def2-TZVPP[46] basis sets. Geometry optimizations were performed using a DFT

functional and starting with the highest possible symmetry. The symmetry was then reduced stepwise

until no imaginary frequencies were found in the calculated vibrational spectra, which were

determined analytically (aoforce[45]) for RI-DFT and numerically (numforce) for RI-MP2 calculations.

Thermodynamic functions at room temperature and a pressure of 1 bar were calculated using the tool

freeh (default symmetry, scaling factor 1) provided with Turbomole based on frequencies obtained

from BP86/def2-TZVPP calculations. It provides thermodynamic values for the molar Internal Energy �, from which the molar Enthalpy d can be calculated following Equation (18).

d = � / � ∙ e (25)

D.4.1.2 Lattice Enthalpies

Lattice energies �8|� were calculated from molecular volumes $}, the charges of cation 7~ and anion 7–, and the total number of ions per molecule using Equation (26) as proposed by Jenkins et al.[28]

�8|� = |7~||7–| N � ��$}� / �� (26)

All values used in the calculation of the lattice enthalpy including the parameters � and � Table 25.

Comparative results were obtained using the formula proposed by Kapustinskii,[47] which is given in

Equation (27) and was converted using a factor of 1 cal = 4.227 J.

�8|� = 121400 |7~||7–| N�b / �� 1 − 34.5�b / �� (27)


142

The cation radius �b anion radius �� were approximated by calculation from the molecular volumes of

the respective ions.

The lattice enthalpy ∆#"��d is obtained following Equation (28) for a salt MpXq and a value of � = 6 for

polyatomic nonlinear ions.[28]

∆#"��d = �8|� / �� b2 − 2� / � ��2 − 2�� e (28)

The results are summarized in Figure 36.

Bromostannate Ionic Liquids

D.4.2.1 Synthesis of the Bulk Mixtures

For the synthesis of all bulk mixtures [HMIM][Br] + x [SnBr4] (x = 0.5, 1.0, 1.5, 2.0) dry SnBr4 was

condensed into a reaction vessel and the transferred amount determined gravimetrically. The

appropriate amount of dry [HMIM]Br for the desired stoichiometric ratio was weighed into a second

vessel in a Glovebox. The SnBr4 of the first vessel was then sublimed on to the organic salt at

approximately −50 °C under static vacuum. The mixture was slowly warmed in an oil bath until a

homogeneous liquid was obtained. After cooling down to room temperature, the obtained product

was weighed again and then slowly heated in order to observe bulk phase transitions.

SnBr4: SnBr4 was distilled prior to use.

119Sn-NMR (111.94 MHz, CDCl3, 300 K): δ = –636 ppm.

FT-Raman (RT, liquid): NO = 88(w), 222(m), 281 (vw) cm–1.

Table 23: Parameters and results for the calculation of lattice enthalpies ∆#"��d° and lattice energies �8|�.using Equations (26), (27) and (28).

Jenkins Kapus-tinskii

∆#"��d° �8|� �8|� � � 7~ 7^ N � � $} $~ $̂ �~ �̂

kJ mol–1 kJ nm mol–1 kJ mol–1 nm3 nm [HMIM] [SnBr5]

421 406 304 1 1 1 1 2 117.3 51.9 0.467a) 0.249b) 0.218c) 0.390 0.373

[HMIM]2

[SnBr6] 1266 1239 879 1 2 2 1 3 133.5 60.9 0.771d) 0.249b) 0.274e) 0.390 0.403

a) Sum of cation and anion volumes; b) derived value using volume of [SnBr6]2–[28] and scXRD volume of [HMIM]2[SnBr6]; c) approximated by substracting volume of Br–[28] from [SnBr6]2–[28]; d) from scXRD measurement; e) published value[28].

D.4 Experimental

143

[HMIM]2[SnBr6]: The mixture of [HMIM]Br (5.472 g, 22.14 mmol) and SnBr4 (4.810 g, 10.97 mmol,

0.495 eq) partly melted on heating to 160 °C and formed a brown homogeneous liquid at (185 ± 10)◦C

oil bath temperature.

1H-NMR (300.18 MHz, CD3CN, 300 K): δ = 0.84 – 0.93 (m, 3H), 1.23 – 1.39 (m, 6H), 1.77 – 1.91 (m, 2H),

2.21 (s, 1.38H, H2O), 3.88 (s, 3H), 4.18 (t, 3J H,H = 7.32Hz, 2H), 7.32 – 7.43 (m, 2H), 8.64 (b, 1H) ppm.

119Sn-NMR (111.94 MHz, CD3CN, 300 K): δ = 2073 ppm.

FT-Raman (RT, solid): NO = 99 (w), 140 (vw, sh), 148 (w), 184 (vs), 200 (vw, sh), 600 (vw), 1021 (vw),

1106 (vw), 1332 (vw), 1381 (vw), 1411 (vw), 1431 (vw), 1882 (vw), 2869 (vw), 2898 (vw), 2932 (vw),

2954 (vw), 3080 (vw), 3131 (vw), 3154 (vw) cm−1.

ATR-IR (RT, solid): NO = 108, 185, 197 cm−1.

EA: Anal. calculated for C20H38Br6N4Sn: C, 25.75; H, 4.11; N, 6.01. Found: C, 25.93; H, 4.13; N, 6.10.

[HMIM]Br + 1.0 SnBr4: The mixture of [HMIM]Br (5.162 g, 20.9 mmol) and SnBr4 (9.131 g, 20.8 mmol,

1.00 eq) partly melted on heating from RT and formed a hazy yellow liquid at (70 ± 5)◦C that clarified

to be homogeneous at (85 ± 5)◦C.

1H-NMR (300.18 MHz, 300 K): δ = 0.49 - 0.73 (m, 3H), 0.94 - 1.28 (m, 6H), 1.62 - 1.89 (m, 2H), 3.88 (s,

3H), 4.01 - 4.20 (m, 2H), 7.27 - 7.45 (m, 2H), 8.51 - 8.68 (b, 1H), ppm.

119Sn-NMR (111.94 MHz, 300 K): δ = –1432 ppm.

119Sn-NMR (149.23 MHz, 353 K): δ = –1451 ppm.

FT-Raman (RT, liquid): NO = 102 (w), 152 (vw), 183 (vw), 198 (vs), 220 (vw), 253 (vw), 414 (vw), 561 (vw),


(vw) cm−1.

FT-Raman (RT, solid): NO = 88 (w, sh), 98 (w), 142 (w, sh), 148 (w), 184 (vs), 198 (vw, sh), 221 (vw), 409

(vw), 442 (vw), 528 (vw), 598 (vw), 1021 (vw), 1104 (vw), 1332 (vw), 1408 (vw), 1448 (vw), 2906 (vw),

2954 (vw), 2989 (vw), 3079 (vw), 3133 (vw), 3154 (vw) cm−1.

ATR-IR (RT, solid): ν˜ = 108, 182, 196 cm−1.

[HMIM]Br + 1.5 SnBr4: The mixture of [HMIM]Br (2.63 g, 10.6 mmol) and SnBr4 (6.98 g, 15.9 mmol,

1.50eq) partly melted on heating from RT and formed a pale yellow homogeneous liquid at (52 ± 5)◦C.

A sample of the heated liquid was transferred into a 3 mm NMR-tube and flame-sealed. At room

temperature, a small amount of a transparent liquid formed next to the main liquid, yellow phase. The

phase separation could be reversed by storing the tube at 60 °C for several hours.


144

1H-NMR (300.18 MHz, 300 K): δ = 0.56 - 0.78 (m, 3H), 1.03 - 1.35 (m, 6H), 1.63 - 1.90 (m, 2H), 3.88 (s,

3H), 4.09 (t, 3JH,H = 7.31 Hz, 2H), 7.25 - 7.42 (m, 2H), 8.40 - 8.58 (b, 1H) ppm.

119Sn-NMR (111.94 MHz, 300 K): δ = –1198 ppm.

119Sn-NMR (149.23 MHz, 353 K): δ = –1201 ppm.

FT-Raman (RT, liquid yellow): NO = 87 (w), 102 (w), 152 (vw), 183 (vw, sh), 198 (vs), 220 (w), 253 (vw),

280 (vw), 622 (vw), 1023 (vw), 1414 (vw), 1438 (vw), 2862 (vw), 2931 (vw), 2954 (vw) cm−1.

FT-Raman (RT, solid): NO = 87 (vs), 98 (vw, sh), 140 (vw, sh), 149 (vw), 184 (m), 200 (vw), 220 (vs), 276


(vw), 2925 (vw), 2956 (vw), 3971 (vw) cm−1.

FT-Raman (RT, liquid transp.): NO = 88 (m), 135 (vw), 152 (vw), 198 (vw), 221 (vs), 279 (vw), 287 (vw,

sh), 1023 (vw), 1415 (vw), 2859 (vw), 2954 (vw) cm−1.

ATR-IR (RT, solid): NO = 85, 112, 182, 200, 274 cm−1.

[HMIM]Br + 2.0 [SnBr4]: The mixture of [HMIM]Br (0.508 g, 2.06 mmol) and SnBr4 (1.82 g, 4.14 mmol,

2.01eq) partly melted on heating from RT and formed a liquid brown phase at (48 ± 5)◦C. A sample of

the heated liquid was transferred into a 3 mm NMR-tube and flame-sealed. At room temperature, a

small amount of a transparent liquid formed next to the main liquid, yellow phase. The transparent

phase was reduced in amount by storing the tube at 60 °C for several hours, but did not dissolve

completely.

1H-NMR (300.18 MHz, 300 K): δ = 0.61 - 0.73 (m, 3H) 1.01 - 1.29 (m, 6H) 1.65 - 1.89 (m, 2H) 3.88 (s, 3H)

4.09 (t, 3JH,H = 7.31 Hz, 2H) 7.27 - 7.41 (m, 2H) 8.44 - 8.55 (b, 1H) ppm.

119Sn-NMR (111.94 MHz, 300 K): δ = –1202 ppm.

119Sn-NMR (149.23 MHz, 353 K): δ = –1172 ppm.

FT-Raman (RT, liquid yellow): NO = 87 (w), 102 (w), 152 (vw), 183 (vw, sh), 198 (vs), 220 (m), 254 (vw),

281 (vw), 887 (vw), 1415 (vw), 1916 (vw), 2859 (vw), 2897 (vw), 2924 (vw), 2954 (vw) cm−1.

FT-Raman (RT, liquid trasp.): NO = 70 (w), 88 (m), 198 (vw), 221 (vs), 278 (vw), 287 (vw, sh) cm−1.

FT-Raman (RT, solid): NO = 87 (vs), 100 (w), 149 (vw), 184 (m), 199 (w), 220 (vs), 251 (vw), 276 (vw), 285



(vw), 3157 (vw) cm−1.

ATR-IR (RT): NO = 83, 108, 200, 250, 274 cm−1.

[HMIM]Br saturated with SnBr4: SnBr4 (6.67 g, 15.2 mmol) was mixed with solid [HMIM]2[SnBr6]

(4.73 g, 5.07 mmol, 0.33 eq) in a glove box and stirred for 2 h at 60 °C. Two liquid phases were obtained

D.4 Experimental

145

(11.39 g, 100 %). The lower phase was transparent, the upper identical in color to the solid

[HMIM]2[SnBr6] used (brown). A sample of the upper phase was taken at 60 °C and the dynamic

viscosity measured in the temperature range from 50 to 65 °C (see Table 24). The conductivity of the

upper phase was measured in the glove box between 40 and 65 °C (see Table 27).

FT-Raman (40 °C, upper liquid phase): NO = 102 (w), 152 (vw), 198 (vs), 220 (m), 253 (vw), 280 (vw), 476

(vw), 624 (vw), 1415 (vw), 2851 (vw), 2881 (vw), 2919 (vw), 2934 (vw), 2955 (vw) cm−1.

D.4.2.2 Viscosity Measurements

The dynamic viscosity of SnBr4 was measured from 35 °C to 80 °C, and of [HMIM]Br saturated with

SnBr4 from 45 to 60 °C. All values are listed in Table 24.

Table 24: Dynamic viscosities ƞ for SnBr4 and a saturated solution of SnBr4 in [HMIM]Br. Data was measured consecutively for rising temperatures and again during cooling down.

T SnBr4 sat. sol. of SnBr4 in [HMIM]Br

ƞheating ƞcooling ƞmean est. error ƞheating ƞcooling ƞmean est. error

°C Pa s Pa s 35 1.67 – 1.67 0.05 – – – 40 1.60 1.61 1.61 0.05 – – – 45 1.56 – 1.56 0.08 – 42.9 42.9 1.5 50 1.41 1.50 1.45 0.08 34.0 35.7 34.9 1.5 55 1.37 – 1.37 0.08 28.9 29.9 29.5 1.5 60 1.26 1.22 1.24 0.08 24.9 – 24.9 1.5 65 1.11 – 1.1 0.1 – – – 70 1.05 0.95 1.0 0.1 – – – 75 1.02 – 1.0 0.15 – – – 80 0.99 0.85 0.9 0.15 – – –

D.4.2.3 DSC Analysis

The parameters used for the DSC measurements are summarized in Table 25, whereas the observed

signals for the first and fourth heating are listed in Table 26. All samples were prepared in a glove box

in aluminium crucibles using either standard lids or crimped lids which are resistant to an internal

pressure of up to 3 bars. [HMIM]2[SnBr6] was ground before use, and SnBr4 warmed above its melting

point for the transfer. To ensure procedural accuracy, the weight of the crucible was noted before

filling with the substance, then the scale was tared, the sample transferred and its weight noted, and

the mass of the crucible including the substance noted again. Additionally, crucibles were weighed

before and after transfer to and from the glove box.

Each measurement was started from room temperature and the sample heated to the respective

maximum temperature for four times. All samples were tempered at the respective high measurement

temperature for 5 min and at the lower temperature for 20 min.


146

Table 25: Experimental details for the DSC measurements performed. The lids used are abbreviated with c for crimped lids s for the standard lid.

SnBr4/[HMIM]Br x (SnBr4) m(SnBr4) m([HMIM2SnBr6]) temperature range

scan rate

mg °C K min–1 lid 0.50 0.333 - 21.0 RT 185 2 s 0.67 0.401 2.9 18.3 –40 180 1 c 0.80 0.445 8.3 29.3 –40 180 1 c 0.90 0.474 8.0 21.5 –40 120 1 c 0.98 0.494 11.4 25.4 –40 120 1 c 1.24 0.553 14.7 21.2 –40 110 1 c 1.34 0.573 19.3 24.4 –20 80 1 c 1.43 0.589 15.3 17.5 –40 90 1 c 1.51 0.602 23.4 24.6 –40 90 1 c 2.00 0.667 31.6 22.4 –40 80 1 c 2.01 0.668 30.7 21.6 –40 80 1 c 2.38 0.704 38.4 21.7 –20 80 1 s 3.03 0.752 51.5 21.7 –20 80 1 s 3.90 0.796 69.7 21.8 –20 80 1 c 4.05 0.802 65.7 19.7 –20 80 1 s 8.10 0.890 81.5 11.4 –20 80 1 s 9.02 0.900 165.0 20.6 –20 80 1 c

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147

Table 26: Observed transitions on the first and the fourth heating of samples analysed by DSC. The grouping of the transitions is intended to make the representation clearer, but does not imply chemical similarity of the transitions.

x (SnBr4) 1st heatinga) 4th heating transition 1 transition 2 transition 3 transition 1 transition 2 transition 3 transition 4 Tonset Tpeak ΔH Tonset Tpeak ΔH Tonset Tpeak ΔH Tonset Tpeak ΔH Tonset Tpeak ΔH Tonset Tpeak ΔH Tonset Tpeak ΔH

°C J g–1 °C J g–1 °C J g–1 °C J g–1 °C J g–1 °C J g–1 °C J g–1 0.33 165 168 63 – – – 165c) 168 62 0.40 28 28 9 38 41 11 75b) –202 – – 9 9 2 – 0.45 28 28 17 38 41 34 71 87 –443 – – 6 7 1 – 0.47 28 30 17 38 42 33 79 84 –416 – – – – 0.49 28 29 26 39 43 56 103 116 –448 – – – – 0.55 28 28 33 37 41 41 73 71 –50 – – – – 0.57 28 29 35 35 40 37 74 76 –51 – –4 –1 –17 15 25 57 – 0.59 28 29 41 39 42 47 – –20 –19 9 – – 10 10 2 0.60 28 29 42 39 42 59 – –22 –19 10 –3 1 –10 17 26 39 – 0.67 28 29 54 39 42 38 – – –3 0 –9 –d) 28 29 66 0.67 28 31 51 39 42 31 – –22 –20 2 –5 –2 –7 19 23 13 28 29 22 0.70 28 29 30 39 41 15 – – –4 –1 –6.4 –d) 28 29 61 0.75 28 29 46 39 41 13 – – –2 0 –7.2 –d) 28 29 62 0.80 28 29 68 39 42 19 – – – – 29 30 47 0.80 28 29 51 39 41 11 – – – – 28 29 50 0.89 28 29 53 36 41 9 – – – – 28 29 38 0.90 28 31 82 39 42 10 – – – – 29 31 74 a)Minor signals below 28 °C and with enthalpies smaller than 3 J g–1 are not included; b)broad transition with two peaks; c) preceding small endothermic transition merged to main transition; d)the sharp signal at 29 °C is preceded by a broad signal, which can not be evaluated separately.


148

Mixtures of [HMIM]Br, Br2, and SnBr4

D.4.3.1 Synthesis of Polybromide ILs used for Battery Measurements at SOC 100 %

For the following syntheses, bromine was used as received and not dried over P4O10.

[HMIM]Br + 4.07 Br2: [HMIM][Br] (5.53 g, 22.4 mmol) was transferred to a Schlenk RBF in a glove box.

Br2 (14.57 g, 91.2 mmol, 4.07 eq) was added via a syringe over a period of 25 min and under cooling

with a water bath. After stirring over night, a brown vapour was visible over the brown liquid (20.11 g,

100 %).

[HMIM]Br + 2.15 Br2: [HMIM][Br] (6.02 g, 24.4 mmol) was transferred to a Schlenk RBF in a glove box.

Br2 (8.39 g, 52.5 mmol, 2.15 eq) was added via a syringe over a period of 15 min and under cooling with

a water bath. After stirring overnight, a dark red liquid was obtained (14.42 g, 100 %).

[HMIM]Br + 3.10 Br2: [HMIM]Br + 4.07 Br2 (2.65 g, 2.95 mmol) was added to a mixture of [HMIM]Br +

2.15 Br2 (1.80 g, 3.04 mmol) in an RFB. After stirring overnight, a pale brown vapour was visible over a

dark red liquid (4.45 g, 100 %).

[HMIM]Br + 3.48 Br2: [HMIM]Br + 4.07 Br2 (3.89 g, 4.33 mmol) was added to a mixture of [HMIM]Br +

2.15 Br2 (1.15 g, 1.95 mmol) in an RFB. After stirring overnight, a pale brown vapour was visible over a

dark red liquid (4.45 g, 100 %).

D.4.3.2 Synthesis of Polybromides ILs Used for the Preparation of Bulk Mixtures with SnBr4

Bromine was dried over P4O10 prior to its use in the following syntheses. In a typical procedure, bromine

was condensed into Schlenk tube at –70 °C and weighed. The appropriate amount of [HMIM]Br was

then weighed into a second Schlenk tube in a glove box. The vessel was subsequently cooled to –70 °C

and the bromine condensed on top of the frozen [HMIM]Br. A reaction occurred upon slowly allowing

the mixture to reach room temperature.

[HMIM][Br3]: Br2 (9.39 g, 58.8 mmol, 1.00 eq) was condensed on [HMIM]Br (14.46 g, 58.50 mmol) at

–70 . The mixture was allowed to reach room temperature over a period of 50 min. A red liquid

(23.85 g, 100 %) was obtained after stirring overnight.

FT-Raman (RT): NO = 162 (vs), 196 (w, sh), 347 (vw), 603 (vw), 621 (vw), 696 (vw), 1023 (vw), 1106 (vw),


D.4 Experimental

149

3108 (vw), 3161 (vw) cm–1.

1H–NMR (300.18 MHz, neat, 300 K): P = 0.55-0.71 (m, 3 H, (CH2)5CH3), 0.98-1.27 (m, 6 H,

(CH2)2(CH2)3CH3), 1.67-1.84 (m, 2 H, CH2CH2(CH2)3CH3), 3.88 (s, 3 H, NCH3), 4.05-4.22 (m, 2 H,

CH2(CH2)4CH3), 7.37-7.50 (m, 2 H, NCHCHN), 8.67-8.76 (b, 1 H, NCHN) ppm.

[HMIM] + 2 Br2: Br2 (22.13 g, 179.2 mmol, 2.00 eq) was condensed on [HMIM]Br (22.13 g, 89.5 mmol)

at –79 °C. The mixture was allowed to reach room temperature over a period of 40 min. A dark red

liquid (50.76 g, 100 %) was obtained after stirring overnight.

The temperature dependent conductivity was measured and is listed in Table 27.


(CH2)2(CH2)3CH3), 1.75-1.84 (m, 2 H, CH2CH2(CH2)3CH3), 3.88 (s, 3 H, NCH3), 4.12 (t, 3JH,H = 7.49 Hz, 2 H,


FT-Raman (RT): NO = 99 (w, sh), 162 (w), 211 (w, sh), 260 (vs), 620 (vw), 736 (vw), 845 (vw), 1023 (vw),


2868 (vw), 2932 (vw), 2953 (vw), 3116 (vw), 3164 (vw) cm–1.

D.4.3.3 Synthesis of Mixtures of [HMIM]Br, SnBr4, and Br2

In a typical procedure, a polybromide IL was transferred to a Schlenk RBF and weighed. The appropriate

amount of SnBr4 was then weighed into a Schlenk tube in a glove box and subsequently condensed on

top of the cooled polybromide IL at –70 °C. A reaction occurred upon slowly allowing the mixture to

reach room temperature.

[HMIM]Br + Br2 + SnBr4: SnBr4 (3.67 g, 8.37 mmol, 1.01 eq) was condensed on [HMIM][Br3 (3.43 g,

8.42 mmol) at –79 °C. The mixture was allowed to reach room temperature. Since the dark red mixture

(7.10 g, 100 % ) was not completely clear after reaching room temperature, the mixture was heated to

40 °C, and turned into a homogeneous liquid. Upon cooling to room temperature, a precipitation was

observed again.



CH2(CH2)4CH3), 7.28-7.35 (b, 2 H, NCHCHN), 8.45-8.53 (b, 1 H, NCHN) ppm.

119Sn-NMR (111.94 MHz, neat, 300 K): δ = –1291 ppm.

FT-Raman (RT): NO = 87 (w), 102 (m), 149 (vw), 183 (w), 198 (vs), 220 (w), 258 (w, sh), 284 (s), 599 (vw),


(vw), 2869 (vw), 2934 (vw), 2954 (vw), 3165 (vw) cm–1.


150

[HMIM]Br + Br2 + 1.5 SnBr4: SnBr4 (4.22 g, 9.62 mmol, 1.52 eq) was condensed on [HMIM][Br3 (2.58 g,

6.34 mmol) at –79 °C. The mixture was allowed to reach room temperature over 1 h. A dark red liquid

(7.10 g, 100 %) was obtained after stirring over night at room temperature.



CH2(CH2)4CH3), 7.27-7.35 (b, 2 H, NCHCHN), 8.43-8.50 (b, 1 H, NCHN) ppm.


FT-Raman (RT): NO = 87 (m), 103 (m), 149 (vw), 185 (vw), 198 (vs), 220 (s), 258 (w, sh), 285 (m), 597

(vw), 620 (vw), 657 (vw), 744 (vw), 890 (vw), 1023 (vw), 1083 (vw), 1106 (vw), 1336 (vw), 1387 (vw),


3166 (vw) cm–1.

[HMIM]Br + 2 Br2 + SnBr4: SnBr4 (8.491 g, 19.37 mmol, 1.00 eq) was condensed on [HMIM]Br + 2 Br2

(2.58 g, 6.34 mmol) at –79 °C. The mixture was allowed to reach room temperature over 3 h. A dark

red liquid (19.29 g, 19.32 mmol, 100 %) was obtained.





FT-Raman (RT): NO = 87 (m), 102 (m), 147 (vw), 184 (w), 198 (s), 221 (m), 255 (w, sh), 282 (vs), 621 (vw),


(vw), 2869 (vw), 2933 (vw), 2955 (vw), 3167 (vw) cm–1.

[HMIM]Br + 2 Br2 + 0.4 SnBr4: SnBr4 (1.015 g, 2.316 mmol, 0.387 eq) was condensed on [HMIM]Br + 2

Br2 (3.390 g, 5.981 mmol) at –79 °C. The mixture was allowed to reach room temperature. A dark red

suspension (4.405 g, 5.981 mmol, 100 %) was obtained, which could be liquefied at 44 °C, but turned

inhomogeneous upon cooling to room temperature again.

1H–NMR (300.18 MHz, neat, metastable liquid, 300 K): P =0.59-0.69 (m, 3 H, (CH2)5CH3), 1.00-1.26 (m,

6 H, (CH2)2(CH2)3CH3), 1.69-1.82 (m, 2 H, CH2CH2(CH2)3CH3), 3.88 (s, 3 H, NCH3), 4.09 (t, 3JH,H = 7.40 Hz,

2 H, CH2(CH2)4CH3), 7.27-7.33 (m, 2 H, NCHCHN), 8.51-8.55 (b, 1 H, NCHN) ppm.


FT-Raman (RT): NO = 100 (w), 145 (vw), 183 (w), 198 (w), 223 (w, sh), 275 (vs, b), 613 (vw), 857 (vw),


2954 (vw), 3171 (vw) cm–1.

D.4 Experimental

151

Electrochemistry

D.4.4.1 Conductivities

Table 27: Conductivity σ for binary and ternary mixtures of [HMIM]Br, SnBr4 and Br2. More details on the measurement are given in the methods part at the beginning of the experimental section.

T [HMIM]Br sat. with SnBr4 [HMIM]Br + 2 Br2 + SnBr4 [HMIM]Br + 2 Br2

σ a) est. error σ est. error σ est. error °C mS cm–1 mS cm–1 mS cm–1 20 – – 4.2 0.1 17.3 0.2 25 – – 5.3 0.1 21.1 0.2 30 – – 6.6 0.1 24.0 0.2 35 – – 8.0 0.1 28.1 0.2 40 1.92 0.10 9.6 0.1 32.5 0.2 45 2.31 0.10 11.2 0.2 37.0 0.5 50 2.7 0.2 12.9 0.3 41.7 0.8 55 3.1 0.2 14.6 0.3 46.8 0.8 60 3.4 0.2 – – – – 65 3.6 0.3 – – – – a) Mean value from two or more measurements, uncertainty of the temperature ±2 °C.

D.4.4.2 Safety Pretest for the Membrane-Free Battery Experiments

Sn + [HMIM]Br + 4.07 Br2: A piece of tin (268.74 mg, 2.26 mmol) was placed in a small screw lid glass

and a mixture of [HMIM]Br + 4.07 Br2 (0.4 mL) added. A vigorous reaction under emission of light and

brown fumes was observed.

Sn + [HMIM]Br + 2.16 Br2: A piece of tin (131.81 mg, 1.11 mmol) was placed in a small screw lid glass

and a mixture of [HMIM]Br + 2.16 Br2 (0.25 mL) added. No visible reaction occurred.

Sn + [HMIM]Br + 3.5 Br2: A piece of tin (262.27 mg, 2.21 mmol) was added to a mixture of [HMIM]Br

+ 2.16 Br2 (0.17 ml) and [HMIM]Br + 4.07 Br2 (0.26 ml) in a small screw lid. A limited evolution of

brown vapours was observed along with a slight warming of the reaction vessel.

D.4.4.3 Sn/Br2 IL Battery Experiments.

All parameters for the battery measurements are summarized in Table 17. Additional information, like

Raman spectra of the electrolyte after the measurement, are listed on the following pages for each

experiment individually.


152

Table 28: Summary for the experimental setup of the performed battery tests.

battery number

starting electrolyte Anode Cathode inset number

stir bar

tempered current collector

further information

1 [HMIM]Br + 2 Br2 Sn BMA5 9/10 no no Al – 2 [HMIM]Br + 3 Br2 Sn BMA5 9/10 no no Al – 3 [HMIM]Br + 3.5 Br2 Sn BMA5 9/10 no no Al – 4 [HMIM]Br + Br2

+ 1.5 SnBr4 TF6 TF6 11 yes no Al –

5 [HMIM]Br + Br2

+ SnBr4 TF6 TF6 11 yes no Al –

6 [HMIM]Br + 2 Br2 + 0.4 SnBr4

TF6 TF6 11 yes yes Al –

7 [HMIM]Br + 2 Br2 + SnBr4

Sn TF6 2*12 yes yes Al –

8 [HMIM]Br sat. SnBr4 | [HMIM]Br + 2 Br2

Sn TF6 2*16 yes yes Cu membrane: FAPQ-375-PP

Battery 1, [HMIM]Br + 2 Br2:

FT-Raman (RT, solid): NO = 99 (w), 142 (w, sh), 150 (w), 184 (vs), 198 (w), 221 (w), 249 (vw), 279 (vw),

287 (vw, sh), 599 (vw), 1021 (vw), 1105 (vw), 1333 (vw), 1411 (vw), 1431 (vw), 2857 (vw), 2955 (vw),

3082 (vw), 3154 (vw) cm–1.

Battery 2, [HMIM]Br + 3 Br2:

FT-Raman (RT, solid/liquid): NO = 88 (m), 99 (m), 143 (w, sh), 150 (w), 184 (vs), 198 (m), 220 (m), 280

(vw), 287 (vw, sh), 576 (vw), 1083 (vw), 1309 (vw), 1383 (vw), 1439 (vw), 2856 (vw), 2870 (vw), 2911

(vw), 2935 (w), 3117 (vw), 3132 (vw) cm–1.

Battery 3, [HMIM]Br + 3.5 Br2:

FT-Raman (RT, solid, orange): NO = 99 (w), 142 (vw, sh), 150 (w), 184 (vs), 198 (w), 220 (vw), 254 (vw),

280 (vw), 599 (vw), 699 (vw), 817 (vw), 869 (vw), 956 (vw), 1021 (vw), 1064 (vw), 1105 (vw), 1308 (vw),


2933 (vw), 2955 (w), 2989 (vw), 3082 (vw), 3132 (vw), 3155 (vw) cm–1.

FT-Raman (RT, solid, red): NO = 88 (m), 100 (m), 142 (w, sh), 150 (w), 184 (vs), 198 (s), 220 (m), 252 (vw,

sh), 262 (vw, sh), 286 (w), 599 (vw), 819 (vw), 890 (vw), 1021 (vw), 1077 (vw), 1106 (vw), 1311 (vw),


2898 (vw), 2935 (vw), 2955 (w), 2988 (vw), 3082 (vw), 3131 (vw), 3155 (vw) cm–1.

FT-Raman (RT, liquid, orange): NO = 88 (m), 221 (vs), 279 (vw) cm–1.

FT-Raman (RT, liquid, red): NO = 87 (m), 102 (w), 150 (vw), 184 (w), 198 (vs), 220 (s), 256 (vw), 284 (w),


D.4 Experimental

153


(vw) cm–1.

Battery 4, [HMIM]Br + Br2 + 1.5 SnBr4:

Disassembling: graphite corroded on one side, slimy substance at bottom of cell, liquid on top.

FT-Raman (RT, liquid) NO = 71 (vw), 88 (m), 221 (vs), 279 (vw), 313 (vw) cm–1.

FT-Raman (RT, solid/liquid mixture, red-brown,) NO = 99 (s), 142 (w, sh), 150 (w), 150 (w), 184 (vs), 198

(m), 278 (vs), 599 (vw), 816 (vw), 1021 (vw), 1106 (vw), 1334 (vw), 1382 (vw), 1413 (vw), 1413 (vw),


3156 (vw) cm–1.

Battery 5, [HMIM]Br + Br2 + SnBr4:

Disassembling: Small amount of solid at screw, otherwise completely liquid. No major change at

graphite electrodes.

FT-Raman (RT, liquid) NO = 86 (vs, sh), 102 (vw), 150 (vw), 183 (s), 198 (vw), 220 (vw), 248 (s, sh), 258

(vw), 285 (vw) cm–1.

Battery 6, [HMIM]Br + 2 Br2 + 0.4 SnBr4:

FT-Raman (RT, solid) NO = 98 (m), 141 (w, sh), 150 (m, sh), 161 (m), 183 (vs), 183 (vs), 197 (m), 261 (s),


2870 (w), 2897 (w), 2910 (w), 2918 (w), 2935 (w), 2955 (w), 2989 (vw), 3117 (w), 3152 (w) cm–1.

FT-Raman (RT, liquid) NO = 99 (m), 144 (w), 183 (w), 198 (m), 221 (m), 276 (vs), 1023 (vw), 1374 (vw),

1415 (vw), 2869 (vw), 2897 (vw), 2915 (vw), 2932 (vw), 2955 (vw) cm–1.

Battery 7, [HMIM]Br + 2 Br2 + SnBr4:

FT-Raman (RT, solid, yellow): NO = 90 (vs, sh), 99 (vs), 142 (vs), 146 (vs, sh), 165 (w), 184 (s), 198 (w),


(vw), 1413 (vw), 1441 (vw), 2856 (vw), 2870 (vw), 2894 (vw), 2930 (vw), 2954 (vw), 2990 (vw) cm–1.

FT-Raman (RT, solid, grey): NO = 87 (vs), 140 (s), 221 (w) cm–1.

Battery 8, Catholyte [HMIM]Br + 2 Br2, Anolyte [HMIM]Br saturated with SnBr4:

FT-Raman (RT, liquid, red, catholyte): NO = 100 (w, sh), 161 (w), 214 (w, sh), 264 (vs), 1024 (vw), 1340

(vw), 1414 (vw), 2868 (vw), 2932 (vw), 2954 (vw) cm–1.


154

FT-Raman (RT, liquid, yellow, anolyte): NO = 88 (s), 149 (w), 184 (vs), 200 (vw, sh), 221 (vs), 279 (vw),


2933 (vw), 2954 (vw), 3081 (vw), 3133 (vw), 3155 (vw) cm–1.

FT-Raman (RT, solid, yellow, anode): NO = 92 (vs, sh), 99 (vs), 142 (vs), 149 (s, sh), 167 (w, sh), 185 (vs),

198 (m), 221 (w), 251 (vw), 279 (vw), 463 (vw), 494 (vw), 1022 (vw), 1038 (vw), 1059 (vw), 1107 (vw),


2931 (vw), 2955 (vw), 3086 (vw), 3121 (vw), 3155 (vw) cm–1.

D.4 Experimental

155

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158

D.5 Appendix

Crystallographic data for [HMIM]2[SnBr6]

Table 29: Crystal data and structure refinement for [HMIM]2[SnBr6]

Empirical formula C20H38N4SnBr6 Formula weight 932.69 Temperature/K 100(2) K Crystal system Orthorhombic Space group Pmn21 a/Å 13.2078(6) b/Å 8.8520(6) c/Å 13.1963(4) Volume/Å3 1542.85(14) Z 2 ρcalc / g cm–3 2.008

μ / mm-1 8.613 mm-1 F(000) 892 Crystal size/mm3 0.070 x 0.070 x 0.060 Radiation Mo-Kα (λ = 0.71073) 2Θ range for data collection /° 1.542 to 32.358 Index ranges –18 ≤ h ≤ 19, –13 ≤ k ≤ 13, –19 ≤ l ≤ 19 Reflections collected 32796 Independent reflections 5693 [Rint = 0.0277] Data/restraints/parameters 5693 / 604 / 190 Goodness-of-fit on F2 1.076 Final R indexes [I >= 2σ (I)] R1 = 0.0298, wR2 = 0.0658 Final R indexes [all data] R1 = 0.0356, wR2 = 0.0677 Largest diff. peak/hole / e Å-3 1.689 / –0.978

D.5 Appendix

159

Table 30: Selected bond lengths and bond angles for [HMIM]2[SnBr6].

bond length bond angle Å °

Sn(1)–Br(4) 2.5852(13) Br(4)–Sn(1)–Br(3) 90.55(4) Sn(1)–Br(3) 2.5890(8) Br(4)–Sn(1)–Br(5) 179.29(4) Sn(1)–Br(5) 2.5910(13) Br(3)–Sn(1)–Br(5) 90.15(4) Sn(1)–Br(2_#1)a) 2.5973(6) Br(4)–Sn(1)–Br(2_#1) a) 90.65(3) Sn(1)–Br(2) 2.5973(6) Br(3)–Sn(1)–Br(2_#1) a) 90.58(2) Sn(1)–Br(1) 2.6159(8) Br(5)–Sn(1)–Br(2_#1) a) 89.35(3) N(1)–C(4) 1.337(8) Br(4)–Sn(1)–Br(2) 90.65(3) N(1)–C(3) 1.374(9) Br(3)–Sn(1)–Br(2) 90.58(2) N(1)–C(5) 1.458(9) Br(5)–Sn(1)–Br(2) 89.35(3) N(2)–C(4) 1.311(9) Br(2_#1) a)–Sn(1)–Br(2) 178.26(6) N(2)–C(2) 1.394(8) Br(4)–Sn(1)–Br(1) 88.44(4) N(2)–C(1C) 1.507(17) Br(3)–Sn(1)–Br(1) 178.99(5) N(2)–C(1B) 1.539(18) Br(5)–Sn(1)–Br(1) 90.85(4) N(2)–C(1A) 1.540(15) Br(2_#1) a)–Sn(1)–Br(1) 89.43(2) C(2)–C(3) 1.343(12) Br(2)–Sn(1)–Br(1) 89.43(2) C(1A)–C(2A) 1.512(17) C(4)–N(1)–C(3) 106.4(6) C(2A)–C(3A) 1.415(17) C(4)–N(1)–C(5) 126.9(6) C(3A)–C(4A) 1.362(19) C(3)–N(1)–C(5) 126.7(6) C(3A)–C(5A) 1.93(3) C(4)–N(2)–C(2) 109.4(6) C(4A)–C(5A) 1.449(19) C(4)–N(2)–C(1C) 128.8(13) C(5A)–C(6A) 1.44(2) C(2)–N(2)–C(1C) 118.3(13) C(1B)–C(2B) 1.496(19) C(4)–N(2)–C(1B) 114.5(13) C(2B)–C(3B) 1.447(19) C(2)–N(2)–C(1B) 127.4(13) C(3B)–C(4B) 1.45(2) C(4)–N(2)–C(1A) 125.2(9) C(4B)–C(5B) 1.48(2) C(2)–N(2)–C(1A) 123.5(9) C(5B)–C(6B) 1.46(2) C(2)–C(3)–N(1) 109.9(6) C(1C)–C(2C) 1.487(19) N(2)–C(4)–N(1) 109.6(6) C(2C)–C(3C) 1.451(19) C(2A)–C(1A)–N(2) 119.5(14) C(3C)–C(4C) 1.470(19) C(3A)–C(2A)–C(1A) 110.8(16) C(4C)–C(5C) 1.460(19) C(4A)–C(3A)–C(2A) 124(2) C(5C)–C(6C) 1.46(2) C(4A)–C(3A)–C(5A) 48.6(10) C(2A)–C(3A)–C(5A) 120.5(17) C(3A)–C(4A)–C(5A) 86.6(17) C(6A)–C(5A)–C(4A) 91.1(19) C(6A)–C(5A)–C(3A) 93.4(19) C(4A)–C(5A)–C(3A) 44.8(10) C(2B)–C(1B)–N(2) 129(2) C(3B)–C(2B)–C(1B) 120(2) C(2B)–C(3B)–C(4B) 117(2) C(3B)–C(4B)–C(5B) 113(3) C(6B)–C(5B)–C(4B) 116(3) C(2C)–C(1C)–N(2) 116.0(18) C(3C)–C(2C)–C(1C) 116(2) C(2C)–C(3C)–C(4C) 112(2) C(5C)–C(4C)–C(3C) 110(2) C(4C)–C(5C)–C(6C) 117(3) C(4C)–C(5C)–C(6C) 117(3) a) –x+1,y,z


160

Table 31: Fractional Atomic Coordinates (×104) and Equivalent Isotropic Displacement Parameters (Å2×103) for [HMIM]2[SnBr6]. Ueq is defined as 1/3 of the trace of the orthogonalised UIJ tensor.

Atom x y z U(eq)

Sn(1) 5000 8838(1) 6204(1) 11(1) Br(1) 5000 5888(1) 6315(1) 15(1) Br(2) 3034(1) 8807(1) 6183(1) 25(1) Br(3) 5000 11761(1) 6130(1) 17(1) Br(4) 5000 8922(1) 8163(1) 26(1) Br(5) 5000 8719(1) 4243(1) 22(1) N(1) 2770(6) 3135(6) 3880(7) 36(1) N(2) 2377(6) 5411(6) 3427(6) 38(1) C(2) 3119(8) 5554(10) 4170(7) 40(2) C(3) 3347(10) 4128(10) 4433(9) 50(3) C(4) 2175(8) 3976(7) 3284(9) 36(1) C(5) 2822(12) 1491(8) 3910(12) 62(3) C(1A) 2073(15) 6701(19) 2705(13) 28(2) C(2A) 2669(13) 6950(30) 1741(14) 40(2) C(3A) 3673(13) 7400(30) 1961(17) 48(3) C(4A) 4503(16) 6870(30) 1464(18) 63(4) C(5A) 4511(18) 8290(30) 925(17) 61(3) C(6A) 3930(20) 7650(40) 113(19) 73(5) C(1B) 1480(18) 6480(30) 3220(20) 28(2) C(2B) 564(18) 6780(40) 3860(18) 40(2) C(3B) 680(20) 7340(40) 4883(19) 48(3) C(4B) -230(20) 7790(50) 5420(20) 63(4) C(5B) -10(60) 8460(30) 6427(18) 61(3) C(6B) 300(50) 7400(60) 7210(30) 73(5) C(1C) 1732(18) 6770(20) 3180(20) 28(2) C(2C) 1061(19) 7310(30) 4010(20) 40(2) C(3C) 341(19) 6220(30) 4410(20) 48(3) C(4C) -290(20) 6870(50) 5220(20) 63(4) C(5C) 270(20) 6880(40) 6180(20) 61(3) C(6C) -310(40) 7220(70) 7090(30) 73(5)

E.1 Introduction

161

E Investigation Towards an All-Mn Hybrid IL-RFB

The concept for an All-Mn Hyb-IL-RFB, as described in the introduction, was developed by myself in

spring 2014 and it was subsequently included in the application for funds for the IL-RFB project. The

experiments described in the following chapter were performed by Maximilian Schmucker and are part

of his master thesis, which he conducted under my direct supervision.

The crystal structure of [NEt4]4[MnCl5][MnCl4] was solved and refined by M.Sc. Phillipe Weiss and the

simulated CVs created by Dr. Valentin Radke. pXRD measurements and analysis were carried out by

Dr. Thilo Ludwig.

E.1 Introduction

Three challenges present themselves, when trying to establish a working chemistry for an All-Mn Hyb-

IL-RFB. The first is to create liquid compounds, the second to stabilize manganese in the oxidation state

+III or +IV to be used in the catholyte, and the third, to electrodeposit elemental manganese from the

anolyte.

Chloromanganate Salts and Ionic Liquids

As has been described in the introduction to this thesis, a common type of IL is synthesized by using

[cat]X salts in conjunction with metal halides to form halometallate anions. When considering the

quest to stabilize higher oxidation states of manganese, it becomes clear that for this approach, salts

of heavier homologues to chlorine are not suitable, since even chloride is oxidized by Managnese(III)

at –40 °C.[1] Manganese(IV)fluoride is the only known binary manganese(IV) halide, however, it

decomposes at room temperature under evolution of fluorine gas.[1] Since the metal fluorides also

bear the immanent risk of releasing hydrofluoric acid by contact with humidity and organochloride

salts are much easier to obtain than the respective fluoride salts, fluoride was not considered as a

ligand for this preliminary study.

The limited stability of the binary manganese chloride salts in respect to the chlorine elimination for

oxidation states higher than +II, can be expanded when utilizing negatively charged chloromanganates.

So in a sense, the quest to obtain liquid compounds and the quest to stabilize manganese(III)/(IV)

species, can be combined and comes down to identifying suitable chloromanganate complexes – and

cations which allow their formation.


162

Table 32: Examples for known binary manganese chlorides and chloromanganate salts. The chloromanganate salts are listed as combinations of manganese chlorides in different oxidation states with 0.25 to 2 equivalents of various chloride salts.

[cat]Cl : Mn(X)Clx X

II III IV 1 : 0.25 / 4 : 1 (C6H10N2)2[MnCl6]∙2H2O[2] – – 1 : 0.33 / 3 : 1 – [Co(pn)3][MnCl6][3],c) – 1 : 0.5 / 2 : 1 [N1111]2[MnCl4][4] [bipyH2][MnCl5][5] K2[MnCl6][6] 1 : 1 [N1111][MnCl3][4] – – 1 : 1.5 K3Mn2Cl7[7],b) – – 1 : 2 NaMn2Cl5[7],b) – – ∞ MnCl2 MnCl3a) – a) Decomposition at –40 °C[1]; b) compound melts incongruently; c) pn = 1,2-diaminopropane.

Typically, the tendency to eliminate chlorine should be decreased with every negative charge added

to a manganate complex of a fixed oxidation state, this is to say with every added chloride ligand. For

example, [MnIIICl5]2– would be expected to be more stable than [MnIIICl4]–. However, lower charged

anions tend to form lower melting ionic liquids. This means, that a middle ground has to be found for

the number of overall negative charges per anion to accomplish both tasks simultaneously.

Table 32 gives examples for known chloromanganate salts. While chloromanganate(II) salts are known

for a large variety of stochiometric ratios, the diversity decreases significantly when moving to

oxidation states +III and +IV.

MnCl2 crystalizes in a CdCl2 type structure, forming layers of manganese(II) cations octahedrally

coordinated by chloride anions.[1] In chloromangante(II) salts of the stoichiometric ratio 1 : 1,

manganese(II) is still coordinated octahedrally, though in this case, the coordination polyhedra are

linked to form infinite chains composed of [MnIICl3]– units.[4] When moving up to stoichiometries

1 : 0.5, and 1 : 0.25, structures with isolated tetrahedra[4] and isolated octahedra[2] are known,

respectively. The former has also been identified by UV/Vis and vibrational spectroscopy in the only

known chloromanganate RTIL [HMIM]2[MnCl4][8] and the latter is probably unsuitable for the synthesis

of ILs, due to the three fold negative charge.

Chloromanganate(III) salts in a stoichiometric ratio of 1 : 1 are unknown. Considering the fact that

MnCl3 is not a particular stable compound, it is probable that enriching the complexation sphere by

one chloride ligand and its associated negative charge, is not enough to reduce the oxidative power of

manganese(III) to the extent of allowing stable compounds to form. In fact, even salts of the

stoichiometry 1 : 0.5 have been noted for their self-destructive behaviour: recrystallization of shiny

black plates of [bipyH2][MnIIICl5] ([bipyH2]2+= 2,2’-dihydro-2,2’-bipyridinium) was not possible and

attributed to the occurrence of internal redox reactions.[5] Nevertheless, the crystals were analysed via

E.1 Introduction

163

scXRD and isolated anions of quadratic pyramidal structure were identified.

Only very scarce reports exist for chloromanganate(IV) salts, even though the most investigated

compound, K2[MnCl6], has been described as early as 1899.[9] It has been characterized by vibrational

spectroscopy and pXRD.[6] Analogue compounds, like Cs2[MnCl6], Rb2[MnCl6], [NH4]2[MnCl6] and even

[NMe4]2[MnCl6] were prepared as well, but were less well characterized.[6]

A typical procedure to obtain chloromanganates both in oxidation states +III and +IV is the combination

of either Ca[MnO4]2 or K[MnO4] with a chloride salt in concentrated hydrochloric acid.[10] The following

equation was proposed for the synthesis of K2[MnIVCl6] through this route.[6]

2 K[MnVIIO4](s) + 16 HCl → K2[MnIVCl6](s) + 4 Cl2(g) + 8 H2O + Mn2+ + 2 Cl– (29)

The stabilization of chloromanganates in oxidation states higher than +II using cations typically utilized

for the synthesis of ILs has, to the best of my knowledge, not yet been attempted.

Manganese Deposition from Ionic Liquids

Despite a negative potential of –1.18 V vs. SHE, manganese can be deposited from aqueous

electrolytes.[11] In fact, it is the least noble metal to be obtained in this way on a technical scale, with

9 % of the world wide annually available manganese ore being used for the production of electrolytic

manganese.[11] However, coulombic efficiency is limited by simultaneous hydrogen evolution and

reaches values between 65 and 90 % depending on electrolyte impurities and the use of suitable

additives.[11]

Only few reports on the deposition of manganese[12,13] or manganese alloys (Al-Mn[14], Al-Mo-Mn[15],

Al-W-Mn[16], Zn-Mn[17], Cu-Mn[18]) from non-aqueous electrolytes exist. Manganese coatings were

obtained from the ILs [N1444][NTf2][17] and [BMP][NTf2][12] at a potential of approximately –2 V vs. Fc/Fc+

and coulombic efficiencies of >99 % were reported. Morphology was found to depend on the

temperature and the potential applied for the deposition, with compact spherical particles obtained

at 50 °C and a potential of –2.2 V vs. Fc/Fc+.[13] In these studies, manganese(II) ions were introduced in

the solution by anodic dissolution of elemental manganese prior to the experiment. There are no

reports on electrodeposition of manganese from chloromanganates in non-aqueous electrolytes.


164

Manganese and Manganese Salts in Batteries

Manganese(IV)oxide has found widespread application in primary (Zinc–carbon Battery, Alkaline

Battery, Lithium Manganese Dioxide Battery) as well as secondary batteries (Rechargeable Alkaline

Battery).[19] A lithiated derivate is found in Lithium Manganese Oxide Batteries (LiMn2O4).[19] In all of

these cases, the industrial use of manganese is helped by its low price, it’s the availability across the

globe and its low toxicity. Since the working principle of the named batteries is very different from the

envisioned All-Mn Hyb-IL-RFB, they will not be discussed in detail.

Recently, the concept of fluoride ion batteries (FIBs) has been studied by Hörmann et al.[20] In these

batteries, a metallic anode is oxidized, resulting in the formation of the respective fluoride salt. On the

cathode, a fluoride salt is reduced to elemental metal. A wide range of metals has been studied,

including a manganese anode in combination with AlF3 or TiF4 as positive active material. The batteries

were assembled in the charged state and only discharged once; charging was not possible and this

observation attributed to the formation of a fluoridic passivation layer on the anode. As one would

expect when trying to utilize aluminium or titanium salts as oxidizing agents, the OCV was only

between 0.2 and 0.4 V. Except for this report, to the best of my knowledge, there is no battery known

to date that utilizes elemental manganese or chloromanganates as their active material.

E.2 Results and Discussion

165


Chloromanganate(II) Ionic Liquids

E.2.1.1 Attempted Synthesis of Chloromanganate(II) Ionic Liquids

To establish whether or not isolated complexes like [MnIICl3]– or [MnII2Cl5]– could be stabilized in ionic

liquids, and if more than the known [MnIICl4]2– ILs are accessible, [BMP]Cl, [HMIM]Cl and [P666 14]Cl were

combined with 0.5, 1.0 and 2.0 equivalents of MnCl2. [BMP]Cl is a well investigated cation in IL

chemistry, is therefore readily available, and also does not have a C-C double bond like [HMIM]Cl,

which could be incompatible with the oxidative nature of chloromanganates in higher oxidation states.

Nevertheless, experiments were conducted with [HMIM]Cl as well, since it is the only cation for which

RTILs with MnCl2 were known and it is liquid itself at room temperature. [P666 14]Cl was chosen since it

is aliphatic like [BMP]Cl, but also liquid at room temperature and could therefore combine the benefits

of [HMIM]Cl and [BMP]Cl, though at the cost of an increased viscosity compared to [HMIM]Cl.

The organo chloride salts were combined with MnCl2 at room temperature and then stored at 60 °C

for several hours. For [BMP]Cl, no reaction was observed, so the temperature was raised to 200 °C, at

which point the mixtures turned liquid.

Unfortunately, RTILs were only obtained for the mixture [HMIM]Cl : MnCl2 = 1 : 0.5. The same

stoichiometric ratio with [P666 14]Cl still contained a small amount of a pink solid, though the reaction

was later repeated and a homogeneous liquid was obtained. It might be, that in this first attempt, the

reactions temperature or time had been too low or too short, respectively. All mixtures with [BMP]Cl

turned solid at room temperature and all Raman spectra had a very poor noise to signal ratio. Only for

mixtures of [BMP]Cl with 0.5 MnCl2 could bands be identified, namely the bands corresponding to the

[MnIICl4]2– dianion.

The Raman spectra of the reactions with [HMIM]Cl are shown in Figure 9 and are discussed exemplarily

for all reactions. While only the characteristic signals of [MnIICl4]2– are observed in the 1 : 0.5

stoichiometry, both stoichiometries with higher MnCl2 content show bands around 224 cm–1, which

are similar in frequency to a band observed in pristine MnCl2 at 235 cm–1 and respective literature

values (228 cm–1)[21].


166

Figure 59: Raman spectra of mixtures of [HMIM]Cl with 0.5, 1.0 and 2.0 equivalents of MnCl2 as well as the spectrum of pure MnCl2.

E.2.1.2 [P666 14]2[MnCl4] Cyclic Voltammetry

To investigate the electrochemical behaviour of [MnIICl4]2– anions, a 3.36 mM solution of

[P666 14]2[MnCl4] in MeCN was analysed via cyclic voltammetry (CV) using a platinum disk

Ultramicroelectrode (UME) of 10 µm diameter. Because of its small diameter, the diffusion field of a

UME allows for the investigation of reactions with very fast kinetics at high scan rates and enters a so

called steady state at lower rates.[22] [NBu4][BF4] was used as supporting electrolyte to increase the

conductivity of the solution. Since elemental manganese is available only at very high prices, a platinum

wire was used as a quasi-reference and a reference CV of Ferrocene dissolved in a sample of the

analyte solution was recorded (see Figure 69 of the Appendix).

A CV was recorded of the solution in oxidative direction up to a limiting potential of 2.7 V and is shown

in Figure 60. Two distinct steps are observed. After reaching a maximum at 2.3 V, the current drops,

until the direction of the potential sweep is reversed. This is not the common behaviour observed

when using an UME. Typically, the current reaches a plateau, a steady state at which the current is

constant and limited by the diffusion of the analyte to the electrode. The fact that the current

decreases, could be a sign that the electrode surface becomes partially blocked by reaction products.


167

Figure 60: Cyclic voltammogram of [P666 14]2[MnCl4] in MeCN recorded using a scan rate of 0.1 V s–1. The CV has been corrected with the blank shown in light grey and a simulation has been fitted which suggests an EEE mechanism, meaning three consecutive electrochemical reactions, with the second and third step occurring almost at the same potential.

To investigate the potential steps further, a simulation has been fitted to the observed data and is

shown along with the recorded CV in Figure 60. The best fit is obtained for a simulation based on three

consecutive electrochemical oxidations at the electrode surface, a so called EEE mechanism. This

means that no intermediate chemical reaction step takes place, which would for example be the case

for an ECE or ECCEE mechanism.[23] All simulation parameters are listed in Table 33. Since the potentials

of the second and the third step are very similar, only one oxidation wave is observed for this two-step

process.

Table 33: Parameters for the simulation fitted to the experimental CV of [P666 14]2[MnCl4] using a platinum UME. E0 refers to the standard reduction potential of the respective reaction step, k0 to the reaction rate constant, and α to the charge transfer coefficient. The diffusion coefficient was set to 1.22 ∙ 10-5 cm2 s–1, the electrode radius to 6 µm and the temperature to 298.2 K.

Reaction step E0 vs. q-Pt E0 vs. Fc/Fc+ α k0 V V cm s–1

1 1.58 0.665 0.5 1.2 ∙ 10–3 2 2.025 1.11 0.6 3.0 ∙ 10–2 3 2.108 1.193 0.65 2.5 ∙ 10–2

The first step is very likely the oxidation of manganese(II) to manganese(III) corresponding to the

complexes [MnIICl4]2– and [MnIIICl4]–, respectively. The next steps could be the oxidation to

manganese(IV), and a subsequent oxidation of a chloride ligand to form elemental chlorine. This could


168

Figure 61: Cyclic voltammogram of [P666 14]2[MnCl4] in MeCN for the reductive and oxidative direction recorded using a scan rate of 0.1 V s–1. For the reductive region, only the sweep in negative direction but not the reverse sweep is shown. Due to the fast increase in current the chosen measurement range was exceeded, rendering the rest of the measurement invalid.

explain the drop in current, since the electrode surface could be blocked by the gaseous Cl2. However,

the electrode could also be blocked by the formation of solid products. Additional experiments are

necessary to better understand this electrochemical behaviour.

Figure 61 shows a cyclic voltammogram for the oxidative region up to a potential of 4 V and the

reductive region to a potential of –2.5 V. Additional waves are observed for the oxidation above 2.7 V,

which could be further oxidations of manganese to even higher oxidation states considering the high

potentials applied. In the reductive region, the current drops very quickly at potentials below –2.3 V.

In the blank curve, a decomposition process is already observed in the reductive region at potentials

lower than –1.8 V. To better understand this behaviour, the experiments should be repeated using a

suitable reference electrode instead of the quasi reference. A deposition and subsequent dissolution

of manganese is not observed, possibly because MeCN decomposes before a reduction of [MnCl4]2–

can occur.


169

Attempted Synthesis of Chloromanganate(IV) ILs

Three routes were investigated for the synthesis of chloromanganate(IV) ILs: The reduction of KMnO4

in presence of hydrochloric acid, metathesis reaction from K2[MnCl6] and the oxidation of

chloromanganate(II) salts using elemental chlorine.

E.2.2.1 Attempted Synthesis of Chloromanganate(IV) ILs through the Reduction of KMnO4

The first step in this approach was the synthesis of K2MnCl6 according to a procedure described by

Moews.[6] The intention was to see if the procedure could be reproduced in our laboratory and at the

same time obtain a pure and stable starting material for the metathesis reactions. Only the drying

procedure was altered and the black solid dried under vacuum. The purity of the product was

confirmed by pXRD (see Figure 70 in the Appendix), with K2MnCl4 as an expected but minor

contaminant. As expected for the octahedral structure of [MnIVCl6]2–, a Raman spectrum with three

intense signals was obtained. The observed frequencies of 310, 244 and 190 cm–1 complement the

literature known IR spectrum for K2[MnCl6] with bands at 358, 200 and 102 cm–1 [24]. They are also

coherent with the frequencies observed for [MnIVF6]2–[25], as listed in Figure 4 in the introduction.

In the next reaction, [BMP]Cl was dissolved in concentrated hydrochloric acid prior to the addition of

K2MnCl6. The reaction did only yield K2[MnCl6], though this might be the result of an error in the

calculation of the stoichiometric ratio due to which only 0.5 equivalents of [BMP]Cl were utilized. This

is unfortunate, because on the basis of the negative result, no further experiments using this route

were conducted.

If, in the future, further experiments are conducted, it might be productive to use an excess of [BMP]Cl

or even a concentrated solution in hydrochloric acid. This might help to shift the equilibrium to yield

crystalline [BMP]2[MnCl6] instead of K2[MnCl6].

E.2.2.2 Attempted Synthesis of Chloromanganate(IV) ILs through Metathesis Reaction

[P666 14]Cl, [BMP]Cl and [NEt4]Cl were dissolved in either MeCN, DCM or acetone after which 0.5

equivalents of K2[MnCl6] were added. The principal idea was that in solvents less polar than water, the

targeted organic salts of [MnIVCl6]2– were expected to be more soluble than KCl, which was hoped to

precipitate quantitatively. This approach is utilized widely in chemical reactions and in particular for

the synthesis of ionic liquids when an exchange of halogen anions to larger, non-halogen anions is

desired.


170

a) b)

Figure 62: Crystal structure of [NEt4]4[MnCl4][MnCl5] with hydrogen atoms omitted for clarity and thermal ellipsoids at 50 % probability. a) Constituent ions, [NEt4]+ disordered over two positions, symmetry equivalent chlorine atoms are not labelled separately. b) Unit cell viewed in a direction showing the layered structure of the two different anions and cations.

Though the general principle does seem to work, the products obtained were either chloromanganates

in the oxidation state +III or +II or mixtures thereof. [MnIIICl5]2– ions could be identified in green solids

and solutions through their literature known[3] and intense Raman band at around 290 cm–1, though

the targeted [MnIVCl6]2– salts stayed elusive. Details on the results of the reactions are included in the

experimental part, but since no pure product was obtained through any of the routes, the results will

not be discussed in detail here.

Concluding from these results, it seems that the [MnIVCl6]2– anion is not stable in solution. One step in

the decomposition process was captured in the obtained crystal structure of [NEt4]4[MnCl4][MnCl5]. A

section of the crystal structure and the unit cell are shown in Figure 62, while more crystallographic

details are given in the Appendix. The structure includes tetrahedral and square pyramidal

chloromanganates in the oxidation states +II and +III respectively. The Mn–Cl bond lengths are

234.58(8) pm for manganese(II) whereas the chlorine atom at the tip and the atoms at the base of the

square pyramid are located at a distance of 240.3(2) pm and 229.77(9) pm from the central

manganese(III). These values are in the expected range compared to other salts of these anions.[26][5]

The [MnIICl4]2– tetrahedron is slightly distorted along the twofold axes in c direction with Cl–Mn–Cl

opening angles in this direction of 112.08(4)°. [MnIIICl5]2– shows Cl–Mn–Cl angles of 88.17(1)° between

the four symmetry equivalent chlorine atoms and of 100.28(4) to the chlorine atom located on the 4-

fold axis. The different types of anions form separate layers interspersed with a cationic layers in c

direction.


171

Since no stable products were obtained utilizing 0.5 equivalents of K2[MnCl6] and salts containing the

anion [MnIVCl5]– are expected to be even less stable, no reactions using one equivalent of K2[MnCl6]

were carried out.

E.2.2.3 Attempted Synthesis of [NEt4]2[MnCl6] Through the Oxidation of [NEt4]2[MnCl4]

The final attempt to stabilize an organic salt of [MnIVCl6]2– was the oxidation of [Net4]2[MnCl4] with

elemental chlorine. The [NEt4]+ cation was chosen, since the conclusion from the results obtained up

to this point suggested, that the [MnIVCl6]2– anion would most likely only be stable in the solid state,

and crystallisation is facilitated by using a symmetrically substituted ammonium salt. The apparatus

used is shown in Figure 18. Chlorine was not only passed through the solution, but liquefied using a

gas condenser cooled to temperatures below –40 °C and refluxed back into the solution. The

decreased temperatures and excess of chlorine were supposed to reduce the tendency of possible

products to eliminate chlorine and to shift the equilibrium towards their formation.

Unfortunately, neither chlorination in MeCN, concentrated hydrochloric acid or in pure liquid chlorine

yielded chloromanganates(IV), though, again, a green solution was obtained for the reaction in MeCN.

In a last attempt, o-DFB was added to the unchanged solid from the attempted oxidation with pure

liquid chlorine. When no visible change occurred during chlorine reflux, a small amount of MeCN was

added in the hope, that part of the salt would dissolve, and that the targeted product, [NEt4]2[MnCl6]

would precipitate. Only on heating to 50 °C under continuous chlorine reflux, a change in the solution’s

colour to dark green was observed, and on cooling to room temperature, a green solid precipitated.

The Raman spectrum shows the characteristic band of [MnIIICl5]2– at 288 cm–1, though, when measured

with a laser power of 100 mW instead of 3 mW, the additional band of [MnIICl4]2– at 258 cm–1 is

observed, and the green powder turns white at the spot of the measurement.

In conclusion, it seems possible to oxidize the [MnIICl4]2– anion to form [MnIIICl5]2– with elemental

chlorine, though the procedure still needs to be refined and the product should be analysed by pXRD

to confirm its purity. However, the oxidation to chloromanganates(IV) does not seem possible through

this route, at least not in combination with the [NEt4]+ cation.

All-Mn Hybrid Ionic Liquid Battery Tests

[P666 14]2[MnCl4] was chosen as electrolyte for a first All-Mn Hyb-IL battery test, since it seemed to be

able to stabilize chloromanganate(III) anions at least for a short period of time. A membrane-free cell

setup was chosen, since the viscosity of this specific ionic liquid was expected to limit self discharge to

a tolerable rate and in this way, any influence of the membrane chemistry could be avoided. Two inert


172

po

ten

tia

l /

V

cu

rre

nt

/ m

A,

ch

arg

e /

10

−1 C

time / s

potentialcurrentcharge

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0.0 100.0 200.0 300.0 400.0 500.0 600.0

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

TF6 insets served as inert electrodes with the intension of depositing elemental manganese on one

side and electrochemically synthesizing manganese(III) or manganese (IV) on the opposing side. To

allow for an easier filling of the cell, MeCN (8 wt%) was added, reducing the viscosity dramatically from

similar to honey to similar to olive oil according to visual inspection. This was also intended to decrease

the inner resistance of the cell. Further experimental details are given in the experimental section.

E.2.3.1 Polarisation at SOC 0 %

Since the battery was set up in its discharged state, the first measurement performed was a charge

polarisation. It was conducted using current pulses alternating with OCV measurements in 15 s

intervals and the result is depicted in Figure 4. The limit for the charging current was set to 3.5 V and

was reached at currents as low as 0.2 mA. The recorded OCV, however, was encouragingly high and

reached values up to 3 V. The OCV prior to the polarisation measurement was just below 2 V, which

was unexpected due to the assumed SOC of 0 %, but could be due to a built-up of static electricity.

Figure 63: Polarisation measurement performed at an SOC of 0 %. Current pulses and OCV measurements alternate in 15 s intervals.

E.2.3.2 Cycling

After some experiments to determine appropriate charging voltages and currents, the battery was

cycled in a limited SOC range for 15 charge and discharge cycles (Figure 64). The battery was charged

at a constant current of 0.1 mA (0.065 mA cm–2) up to a limiting potential of 3.8 V. At this point, an

OCV was measured for 2 minutes and the battery discharged at 0 V until the discharging current

reached –0.02 mA.


173

pote

ntial / V

curr

ent / m

A, charg

e / C

time / h


−1.0

0.0

1.0

2.0

3.0

4.0

0.0 5.0 10.0 15.0 20.0 25.0

−0.5

0.0

0.5

1.0

1.5

2.0

Figure 64: Charge-discharge cycling for the All-Mn Hyb-IL battery . Charging is performed galvanostatically up to a limiting potential of 3.8 V, discharging is performed at 0 V. As coulombic efficiency is less than 100 %, the value for the total charge rises during the operation.

Typically, the OCV was 3.3 V after charging and dropped to 3.1 V within two minutes. The initial

discharging current was approximately –0.75 mA (0.49 mA cm–2), after which the OCV stabilized to

reach values between 1.4 and 1.7 V. The time needed for a complete cycle, as defined by the charging

voltage limit and the limit for the discharge current, decreased for the first cycles and reached a steady

state of 85 +- 2 minutes for the last seven cycles. The coulombic efficiency for the last cycle of this

measurement was calculated to 65 %. The change in SOC during the charging of the cycle was 0.44 %

assuming a two electron process at both electrodes, and 0.59 % assuming a one electron process at

the cathode.

The limited coulombic efficiency could be due to a decomposition of the oxidative species, an

irreversible deposition process at the cathode, to diffusion of the charged species away from the

electrode, self-discharge or other decomposition processes in the electrolyte caused by the potential

of 3.8 V. Further experiments need to be conducted, but the fact that a cycling is possible at all is a

promising result considering that this was the first experiment on an All-Mn Hyb-IL battery.


174

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ten

tia

l /

V

cu

rre

nt

/ m

A,

ch

arg

e /

10

−1 C

time / h


−1.0

0.0

1.0

2.0

3.0

4.0

0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

−0.5

0.0

0.5

1.0

1.5

2.0

E.2.3.3 Polarisation at Medium SOC and ASR

To gain further insight into the electrochemical behaviour of the battery, it was charged up to a limiting

potential of 3.8 V and allowed to self-discharge until an OCV of 2.5 V was reached. At this point a

polarisation with positive and negative currents of up to 0.3 mA (0.19 mA cm–2) was measured. The

current pulses were of 15 s duration and alternated with 45 s of OCV measurement as suggested by

our collaboration partner Kolja Bromberger. From the obtained data, the ASR plot shown in Figure 66

was created. The ASR of 6600 Ω cm2 is very high compared to commercial aqueous redox flow

batteries, which typically exhibit ASRs of less than 1 Ω cm2. This is certainly due to the high viscosity

and therefore low electronic conductivity of the electrolyte as well as the low surface area of the planar

TF6 electrodes compared to the felt electrodes utilized in aqueous redox flow batteries. The ASR is

almost constant over the investigated current range. This means, that almost no overpotential is

observed at the applied current densities and that the electrolyte behaves more or less like an ohmic

resistor.

Figure 65: Polarisation at a medium SOC defined by an OCV of 2.5 V. Current pulses of 15 s duration are alternated with 45 s OCV measurements.


175

Figure 66: Area specific resistance (ASR) for current densities up to 0.2 mA cm–2 at a medium SOC defined by an OCV of 2.5 V. The potential difference on the y-axes was calculated from the last point of the OCV measurement to the first point of the current pulse 0.5 seconds later.

E.2.3.4 Dismantling of the Battery in the Charged State

To investigate the charged species formed in the electrolyte and on the anode, the battery was charged

for 50 hours, reaching a state of charge of 32 % assuming a two and 42 % assuming a one electron

process at the cathode. The colour of the electrolyte had changed from a pale yellow to brown (see

Figure 67 a), but the Raman spectrum was identical to the spectrum of the starting material. A black

solid was found on the anode (see Figure 67 b) and analysed via pXRD, but no reflexes were observed.

It could be, that the deposited material was amorphous manganese, as has been observed for the

deposition from [BMP][NTf2].[12] EDX measurements need to be performed to clarify this matter.

a) b)

Figure 67: a) PTFE inset with residual electrolyte after the dismantling of the All-Mn Hyb-IL battery. b) Anode with deposited solid. Parts of the deposit were removed to reveal an optically unaltered TF6 electrode.


176

E.3 Conclusion and Outlook

177

E.3 Conclusion and Outlook

In conclusion, this preliminary assessment shows that the development of an All-Mn Hyb-IL-RFB might

be feasible and should be further investigated. The finding is based on results gained through

electrochemical experiments on a mixture of the RTIL [P666 14]2[MnCl4] with MeCN. Ionic liquids of the

desired [MnIICl3]– or [MnII2Cl5]– anion could not be obtained with [P666 14]+, [BMP]+ or [HMIM]+. The

stability of the double-bond containing imidazolium cation in [HMIM]2[MnCl4] when applied in an All-

Mn Hyb-IL battery, is questionable considering the observed elimination reactions of dichlorine from

manganese in oxidation states greater than +II.

The first results for the measurements on an All-Mn Hyb-IL battery are encouraging, especially because

of the high OCV and the fact that cycling is possible, though coulombic efficiency has to be increased.

No indication for a kinetic limitation on the electrode reactions were observed. The battery

measurements also suggest, that an electrochemical oxidation and reduction of [MnIICl4]2– is possible,

though the reaction products could so far not be identified.

Since the stabilisation of chloromanganates(IV) in ILs was not achieved through chemical oxidation,

reduction or metathesis reaction and the extent of the stability of the obtained manganese(III) salts

needs yet to be better understood, the nature of the species produced by electrochemical oxidation

remains unclear. Cyclic voltammetry, in combination with simulations, indicate that the oxidation of

[MnIICl4]2– in MeCN proceeds via an EEE mechanism given high enough potentials. It might be possible

that chlorine or polychloride anions are formed through direct oxidation of chloride anions or through

the decomposition of chloromanganates in the oxidation state +III or +IV. Reversible reduction of

[MnIICl4]2– was not observed in the CV experiment and further analysis is required to identify the

composition of the black solid obtained during the battery measurement.

Further research is needed to find suitable liquid electrolytes of improved conductivity. Alternative

cations need to be considered since [P666 14]+ is not an ideal option due to its high viscosity and high

molecular weight. Other asymmetrically substituted phosphonium salts or ammonium salts could be

an alternative and their solubility in electrochemically suitable solvents like MeCN or PC should be

investigated. If, for example, [N2225][MnCl4] could be used, the resulting specific energy, energy density,

and cost per stored energy would be approximately 100 Wh kg–1, 170 Wh L–1, 200 € KWh–1

respectively. These numbers are based on the assumed formation of Mn(III) at the cathode on charging

and do not include the use of a solvent in the calculation. For polar solvents like PC, it might be feasible

to even use K2[MnCl4] as a cheap and robust alternative to [cat]X salts, which would drop the price per

stored energy significantly. It might be fruitful to investigate the use of fluoride, cyanide or other non-


178

halogen ligands for the use in the All-Mn Hyb-IL-RFB since this could allow for the stabilization of

manganese(IV) complexes.

The metal deposition process needs to be studied in detail to yield reversible plating of elemental

manganese without the formation of dendrites. In this respect, the combination of [BMP]2[MnCl4] and

[BMP][NTf2] might be promising, since the electroplating of manganese from ILs containing the [NTf2]–

anion has been demonstrated with high coulombic efficiency and good morphology. An increase in

electrode surface, for example by employing graphite felts, should be considered as soon as the plating

process is optimized and better understood.

E.4 Experimental

179

E.4 Experimental

General: If not stated otherwise, all reactions were performed under argon inert atmosphere using

standard Schlenk techniques and a vacuum of < 3 × 10-2 mbar. MBraun Labmaster sp glove boxes were

used with H2O and O2 contents < 0.1 ppm. Glassware was cleaned using iPrOH/KOH (over night) and

HCl (> 30 min) baths with subsequent rinsing using deionised water. Prior to the use for inert reactions,

apparatuses were heated with a heat gun (650 °C) under vacuum.

Chemicals: The manufacturer and grade of purity of the chemicals used are listed in Table 34.


manufacturer purity purification [NEt4]Cl Acros 98+ % dryinga) [BMP]Cl IoLiTec GmbH 99 % dryingb) [HMIM]Cl IoLiTec GmbH 99 % – [P666 14]Cl IoLiTec GmbH > 95 % dryingc) [N4444][BF4] available in working group – dryingd) Ferrocene available in working group – – Cl2 Linde – passing through conc. H2SO4 KMnO4 available in working group – – MnCl2 Acros 99+% dried using SOCl2

e) SOCl2 Merck > 99 % distillation DCM Grubbs facility of institute – – MeCN Grubbs facility of institute – for CV: dryingf) degassingg) Alumina B-Super ICN – activation in muffle furnaceh) a) Dissolved in DCM with CaH2 and stirred for 72h at room temperature, stored in glove box after removal of residual solid and solvent; b) heated to 120 °C under vacuum for 10 h, ground in a mortar (glove box); procedure repeated three times; c) heated to 80 °C under vacuum for 24 h and stored in a glove box; d) dried under vacuum at room temperature; e) dried by stirring for 72 h in freshly distilled SOCl2, which was then removed under reduced pressure. FT-Raman: 235, 144 cm–1; f)the solvent was stirred over activated alumina in a glove box; g) vacuum applied to the frozen solvent (liquid nitrogen), the solvent was allowed to reach room temperature under static vacuum and the procedure repeated until static and dynamic vacuum reached the same value; h) the powder was heated to 500 °C for 24 h in a muffle furnace and stored in a glove box.


operating at 1064 nm was used to record the spectra from 0 to 4000 cm–1 and a resolution of 4 cm–1.

Intensities were assigned letters according to their relative intensities and appearance (very strong (vs)

> 0.8, strong (s) > 0.6, medium (m) > 0.4, weak (w) > 0.2, very weak < 0.2 (vw), shoulder (sh), broad

(br)). Bands at and below 90 cm–1 were ignored due a strong signal inherent to the spectrometer used.

pXRD: Powder diffraction was measured using a StoeStadiP diffractometer combined with a Mythen

1K area sensitive detector, Mo-Kα radiation (λ = 0.71073 Å) and a Ge(111)-monochromator in glass

capilaries.


180

Cyclic Voltammetry: Measurements were performed in a glove box using a Biologic SP-300

potentiostat and analysed using EC-Lab (V10.44). Platinum circular disk electrodes were polished prior

to use as working electrode. Simulated CVs were produced with DigiElch Professional 7.

Battery Measurement: The cell described in Section F.1 with aluminium current collectors was used

for the battery measurement and performed using an Agilent B2901A Source Measure Unit in

conjunction with bbat v.2.2.1 (see Section F.2). All parts of the cell, including the PTFE insets, were

stored at 60 °C prior to use.

Synthesis of Chloromanganat(II) Ionic Liquids

E.4.1.1 Screening Reactions of [BMP]Cl, [HMIM]Cl and [P666 14] with 0.5, 1 and 2 eq. of MnCl2

In a typical procedure, an organic chloride salt was mixed with dry MnCl2 and held at elevated

temperatures for a limited time. The exact masses and employed stoichiometries are given in

Table 35. Additional procedural details and spectroscopic data are given for each reaction individually.

Table 35: Stochiometric ratios and masses employed for neat reactions of organic chloride salts and manganese(II) chloride.

[cat]Cl MnCl2

� � � � eq. g mmol g mmol

[BMP]Cl 130 0.73 184 1.46 2.0

184 1.03 130 1.03 1.0

327 1.84 115 0.91 0.50

[HMIM]Cl 144 0.710 179 1.42 2.0

184 0.908 114 0.91 1.0

178 0.878 055 0.44 0.50

[P666 14]Cl 164 0.316 080 0.63 2.0

207 0.399 050 0.40 1.0

167 0.322 020 0.16 0.50

[BMP]Cl + x MnCl2: The mixtures were heated to 120 °C in evacuated Schlenk tubes and stirred at

120 °C for 6 h without visual change. At 200 °C, all mixtures were liquid and were stirred for 6 h. Upon

cooling to room temperature, all liquids solidified again. Due to fluorescence in the other mixtures, a

Raman spectrum could only be obtained for the mixture of [BMP]Cl with 0.5 equivalents of MnCl2.

FT-Raman ([BMP]Cl + 0.5 MnCl2): NO = 114 (w), 256 (vw), 301 (vw), 903 (m), 1452 (s), 2878 (m), 2921

(m), 2940 (s), 2960 (vs), 3008 (s), 3033 (m) cm–1.

E.4 Experimental

181

[HMIM]Cl + x MnCl2: The starting materials were mixed under atmospheric conditions in small screw

lid glasses which were subsequently closed and tempered for 12 h at 60 °C. Stochiometric ratios of 1:2,

1:1 and 1:0.5 of [HMIM]Cl : MnCl2 yielded a pale pink solid, a mixture of a solid and a viscous liquid,

and a pale yellow, viscous liquid, respectively.

FT-Raman ([HMIM]Cl + 2.0 MnCl2): NO = 225 (m), 415 (vw), 599 (vw), 623 (vw), 660 (vw), 698 (vw), 726

(vw), 766 (vw), 816 (vw), 850 (vw), 869 (vw), 892 (vw), 965 (vw), 1022 (m), 1087 (vw), 1105 (w), 1163

(vw), 1278 (vw), 1309 (w), 1339 (w), 1385 (w), 1422 (m), 1443 (m), 1567 (vw), 2732 (vw), 2756 (vw),

2872 (vs), 2914 (vs), 2937 (vs), 2961 (vs), 3023 (vw), 3100 (vw), 3157 (vw) cm–1.

FT-Raman ([HMIM]Cl + 1.0 MnCl2): NO = 224 (w), 254 (w), 414 (vw), 600 (vw), 623 (vw), 660 (vw), 697

(vw), 737 (vw), 762 (vw), 815 (vw), 869 (vw), 892 (vw), 1022 (m), 1080 (vw), 1105 (w), 1308 (vw), 1338

(w), 1386 (w), 1417 (m), 1442 (m), 1566 (vw), 2733 (vw), 2872 (vs), 2912 (vs), 2937 (vs), 2958 (vs), 3101

(vw), 3155 (vw) cm–1.

FT-Raman ([HMIM]Cl + 0.5 MnCl2): NO = 255 (w), 413 (vw), 600 (vw), 624 (vw), 660 (vw), 698 (vw), 735

(vw), 767 (vw), 818 (vw), 870 (vw), 892 (vw), 1023 (m), 1080 (w), 1120 (w), 1164 (vw), 1308 (w), 1338

(w), 1387 (w), 1417 (m), 1442 (m), 1566 (vw), 2733 (vw), 2872 (s), 2904 (vs), 2936 (vs), 2957 (vs), 3104

(vw), 3158 (vw) cm–1.

[P666 14]Cl + MnCl2: The starting materials were mixed under atmospheric conditions in small screw lid

glasses which were subsequently closed and tempered over night at 60 °C. Stochiometric ratios of 1:2,

1:1 and 1:0.5 of P[P666 14]Cl : MnCl2 yielded a mixture of a pale pink solid and a viscous liquid, a mixture

of a little less solid and a viscous liquid, and a mixture of a small amount of a pale pink solid and a

yellow, viscous liquid, respectively.

FT-Raman ([P666 14]Cl + 2.0 MnCl2): NO = 167 (vs), 235 (vs), 568 (vs), 787 (w), 1092 (vs), 1302 (vw), 1438

(w), 1907 (w), 2857 (w), 2900 (m), 2900 (m), 2900 (m), 2900 (m), 2934 (w, sh) cm–1.

FT-Raman ([P666 14]Cl + 1.0 MnCl2): NO = 118 (vw, sh), 168 (vw), 250 (vw), 410 (vw), 670 (vw), 737 (vw),


(vw), 1217 (vw), 1305 (vw), 1369 (vw), 1411 (vw), 1441 (w), 2729 (vw), 2854 (vs), 2874 (vs), 2897 (vs)

cm–1.

FT-Raman ([P666 14]Cl + 0.5 MnCl2): NO = 115 (m, sh), 168 (vw), 249 (vw), 409 (vw), 670 (vw), 775 (vw),


(vw), 2729 (vw), 2854 (s), 2874 (s), 2896 (s) cm–1.


182

E.4.1.2 Synthesis of [P666 14]2[MnCl4]

[P666 14]Cl (4.38 g, 8.44 mmol) and [MnCl2] (0.531 g, 4.22 mmol, 0.50 eq) were combined in a Schlenk

tube inside a glove box. The mixture was then heated to 60 °C and stirred until a homogeneous liquid

had formed.

FT-Raman (RT): NO = 115 (w, sh), 184 (w), 250 (w), 407 (w), 670 (w), 848 (vw), 891 (vw), 967 (vw), 1007

(vw), 1077 (vw), 1114 (vw), 1306 (w), 1410 (vw), 1441 (w), 2729 (vw), 2854 (s), 2873 (s),

2899 (vs) cm–1.

Attempted Synthesis of Chloromanganats(IV)

E.4.2.1 Reduction of K2MnO4

Synthesis of K2[MnCl6]: The synthetic procedure was adopted from the literature.[6] KMnO4 (3.0 g, 19

mmol) was added to concentrated hydrochloric acid at 0 °C. A black precipitate formed under

simultaneous evolution of a yellow gas. The suspension was allowed to reach room temperature while

stirring for 3 h. The precipitate was filtered off the suspension and washed with glacial acetic acid

(150 mL) and, in addition to the described procedure, dried over P4O10 and under vacuum. The product

was obtained as a black powder (1.06 g, 3.05 mmol, 16 %).

The powder diffractogram is depicted in Figure 70 of the Appendix and shows only a minor

contamination of K2[MnCl4].

FT-Raman (RT): NO = 190 (m), 245 (s), 311 (vs) cm–1.

Attempted Synthesis of [BMP]2[MnCl6]: A solution of [BMP]Cl (200 mg, 1.13 mmol) in conc.

hydrochloric acid (10 mL) was cooled to 0 °C and KMnO4 (389 mg, 2.46 mmol, 2.2 eq) added. A black

precipitate formed under simultaneous evolution of a yellow gas. The precipitate was filtered off the

suspension, washed with glacial acetic acid and dried over P4O10 and under vacuum. A black powder

(207 mg) was obtained.

FT-Raman: NO = 190 (m), 245 (s), 311 (vs) cm–1.

E.4.2.2 Metathesis Reactions of K2[MnCl6] with Neat [cat]Cl salts

In a typical procedure, a liquid organo chloride salt and K2[MnCl6] were mixed under atmospheric

conditions in a small screw lid glass which was subsequently tempered at 60 °C for 48 h. The exact

masses of the starting materials along with the employed stoichiometries are given in Table 36.

Additional procedural details and spectroscopic data are given for each reaction individually.

E.4 Experimental

183

Table 36: Stochiometric ratios and masses employed for neat reactions of organic chloride salts and K2[MnCl6].

[cat]Cl K2[MnCl6]

� � � � eq. mg mmol mg mmol

[HMIM]Cl 138 0.681 118 0.340 0.50

149 0.735 254 0.745 1.00

[P666 14]Cl 148 0.285 049 0.14 0.50

141 0.272 094 0.27 1.00

[P666 14]Cl + x K2[MnCl6]: The mixtures turned dark green after 30 min. After 48 h, the colour of the

viscous liquid had faded to pale green and a white solid had formed.

FT-Raman ([P666 14]Cl + 0.5 K2[MnCl6]): NO = 167 (w), 224 (w), 250 (w), 669 (w), 848 (w), 875 (w), 892 (w),

968 (w), 1077 (w), 1113 (w), 1306 (w), 1411 (w), 1441 (m), 2729 (vw), 2856 (s), 2873 (s),

2900 (vs) cm–1.

FT-Raman ([P666 14]Cl + 1.0 K2[MnCl6]): NO = 106 (s), 168 (s), 228 (s), 350 (s), 639 (vs), 805 (vs), 891 (vs),

1076 (vs), 1113 (vs), 1195 (vs), 1305 (vs), 1443 (vs), 2857 (s), 2873 (s), 2901 (s), 2928 (s) cm–1.

[HMIM]Cl + x K2[MnCl6]: The mixtures turned dark green after 30 min. After 48 h, the colour of the

viscous liquid had faded to pale green and a white solid had formed.

FT-Raman ([HMIM]Cl + 0.5 K2[MnCl6]): NO = 166 (sh), 224 (vs), 254 (vs), 348 (s), 411 (s), 559 (s), 600 (s),

623 (s), 852 (w), 869 (w), 892 (w), 1023 (s), 1081 (m), 1109 (m), 1308 (w), 1338 (m), 1386 (w), 1417 (s),

1441 (m), 1566 (w), 1790 (vw), 1822 (w), 2730 (vw), 2872 (vs), 2936 (vs), 2957 (vs), 3101 (w), 3158 (w)

cm–1.

FT-Raman ([HMIM]Cl + 1.0 K2[MnCl6]): NO = 166 (s), 224 (m), 254 (m), 339 (w), 407 (w), 459 (w), 487

(w), 600 (w), 624 (w), 697 (vw), 732 (vw), 764 (vw), 818 (vw), 868 (w), 892 (vw), 1023 (m), 1079 (w),

1119 (w), 1308 (w), 1338 (w), 1386 (w), 1416 (m), 1441 (m), 1566 (vw), 1779 (vw), 1820 (vw), 2732

(vw), 2872 (vs), 2936 (vs), 2957 (vs), 3102 (w), 3156 (vw) cm–1.

E.4.2.3 Metathesis reactions of K2[MnCl6] with [cat]Cl salts in solution

In a typical reaction, the starting materials were dissolved in a solvent and the solution turned green

immediately. It was stirred at room temperature for several hours, after which a white precipitate was

filtered off. The solutions were then stored at 6, –4 and –25 °C in order to obtain crystalline compounds

or the solvent was removed under reduced pressure. In these cases a pale yellow colour was

observable in the cold trap.


184

Table 37: Stochiometric ratios, employed masses, type and volume of solvents for reactions of organic chloride salts and K2[MnCl6] in solution.

[cat]Cl K2[MnCl6] solvent condition

� � � � eq. V type mg mmol mg mmol mL

[P666 14]Cl 313 0.603 104 0.301 0.50 02 DCM atmospheric

[BMP]Cl 103 0.578 100 0.289 0.50 05 MeCN inert

206 1.15 200 0.578 0.50 10 DCM inert

[NEt4]Cl 105 0.634 110 0.317 0.50 10 acetone atmospheric

047.9 0.289 050.0 0.145 0.50 00.5 MeCN inert

192 1.15 200 0.578 0.50 10 MeCN inert

The exact masses and the stoichiometries as well as the type and amount of solvent are given in

Table 37. Additional procedural details and spectroscopic data are given for each reaction individually.

[P666 14]Cl + 0.5 K2[MnCl6] in DCM: The green reaction mixture was stirred for 48 h at room

temperature. After the white solid was removed, a Raman spectrum of the viscous green liquid was

recorded (see below). While removing the solvent under reduced pressure, the green colour

disappeared.

FT-Raman: NO = 167 (vw), 288 (s), 386 (w), 578 (vw), 704 (s), 734 (vs), 1085 (vw), 1216 (vw), 1301 (vw),

1382 (w), 1423 (vw), 1885 (vw), 2297 (vw), 2526 (vw), 2759 (vw), 2909 (vw), 2933 (vw), 2988 (w), 3053

(vw) cm–1.

[BMP]Cl + 0.5 K2[MnCl6] in MeCN: After removal of the white precipitate, a Raman spectrum was

recorded of the green solution.

FT-Raman: NO = 116 (s), 256 (vs), 300 (vs), 351 (vs), 419 (vs), 480 (vs), 561 (vs), 636 (vs), 724 (vs), 816

(vs), 903 (vs), 939 (vs), 1091 (vs), 1314 (vs), 1380 (vs), 1450 (vs), 1580 (vs), 2061 (s), 2077 (s), 2874 (m),

2960 (m) cm–1.

[BMP]Cl + 0.5 K2[MnCl6] in DCM: The solvent was removed under reduced pressure and a pale green

solid was obtained, which was analysed by Raman spectroscopy. Though several attempts were made,

no crystals could be obtained from solutions of the solvent in MeCN at –25 °C.

FT-Raman: NO = 115 (w), 167 (vw), 256 (vw), 295 (w), 375 (vw), 446 (vw), 630 (vw), 821 (vw), 903 (w),

930 (vw), 967 (vw), 1022 (vw), 1051 (w), 1122 (vw), 1239 (vw), 1314 (w), 1451 (m), 2044 (w), 2129 (w),

2757 (s), 2875 (s), 2939 (vs), 2963 (vs) cm–1.

E.4 Experimental

185

[N2222]Cl + 0.5 K2[MnCl6] in Acetone: A green precipitate in a colourless solution was obtained after 5 h

of stirring at room temperature. The solvent was removed by filtration and the solid analysed by

Raman Spectroscopy directly after synthesis and after three month of storage (see below). A solution

of the solid (50 mg) in MeCN (1 mL) was stored at –25 °C resulting in crystals suitable for scXRD,

through which the structure of [NEt4]4[MnCl4][MnCl5] was obtained.

FT-Raman: NO = 119 (vw), 166 (vw), 188 (vw), 262 (vw), 288 (w), 664 (vw), 791 (vw), 896 (vw), 1031 (vw),

1072 (vw), 1464 (w), 1489 (w), 1504 (w), 1911 (m), 2077 (m), 2139 (m), 2757 (vs), 2911 (vs), 2938 (vs),

2990 (vs) cm–1.

FT-Raman (3 months): NO = 118 (m), 167 (w), 258 (w), 289 (w), 309 (w), 389 (w), 430 (w), 469 (w), 663

(w), 797 (vw), 895 (vw), 1012 (vw), 1035 (vw), 1072 (w), 1120 (vw), 1184 (vw), 1302 (vw), 1359 (vw),

1461 (w), 2138 (w), 2757 (m), 2945 (vs), 2990 (vs), 3433 (vw), 3495 (vw) cm–1.

[N2222]Cl + 0.5 K2[MnCl6] in MeCN (0.5 mL): Crystals were obtained from a dark green filtrate at –6 °C

and were analysed by scXRD to yield the structure of [NEt4]4[MnCl4][MnCl5] (details are given in the

Appendix).

FT-Raman: NO = 118 (w), 167 (vw), 187 (vw), 228 (vw), 260 (vw), 288 (w), 390 (vw), 469 (vw), 664 (vw),

796 (vw), 896 (vw), 1072 (vw), 1302 (vw), 1462 (w), 2146 (m), 2756 (s), 2891 (s), 2946 (vs),

2990 (vs) cm–1.

[N2222]Cl + 0.5 K2[MnCl6] in MeCN (10 mL): No crystals could be obtained from the solution. A colourless

solid formed while removing the solvent under reduced pressure and was discarded.

E.4.2.4 Oxidation of Chloromanganats(II) with Cl2

For the following reactions, chlorine gas was passed through a gas washing flask filled with

concentrated sulfuric acid and then through the reaction mixture via a gas inlet tube. The reaction

vessel had a gas condenser attached, which was filled with a cooling mixture of iPrOH and dry ice. The

temperature of the condenser was held below –40 °C to allowed for the refluxing of liquid chlorine.

Argon was added to the gas flow during the reaction to counterbalance any over- or underpressure in

the apparatus that would have led to liquids being pressed or sucked from their original containers. At

the end of the reaction time, the apparatus was flushed with argon and all residual chlorine gas was

absorbed in the terminal gas-washing bottle, which was filled with an aqueous solution of Ca[OH]2.

Empty gas-washing flasks were used as a safety precaution at appropriate places and the whole

apparatus is shown in Figure 68.


186

Figure 68: Apparatus used for the oxidation of organic chloromanganates(II) under reflux of elemental chlorine.

Attempted Oxidation in MeCN: In a glove box, [NEt4]Cl (658 mg, 3.97 mmol) and MnCl2 (250 mg, 1.99

mmol, 0.50 eq) were dissolved in MeCN (50 mL) and the reaction vessel then connected to the

chlorination apparatus. After 15 min of chlorine reflux, the colour of the solution had changed to a

dark green. The reaction was terminated after 1 h. Raman measurements on the reaction mixture did

not yield usable results and no crystals were obtained through storage of the solution at –25 °C.

Attempted Oxidation in HCl: [NEt4]Cl (553 mg, 3.34 mmol) and MnCl2 (210 mg, 1.67 mmol, 0.50 eq)

were dissolved in conc. hydrochloric acid (10 mL). After 30 min of chlorine reflux, the colour of the

solution had only changed from transparent to pale yellow and the reaction was therefore aborted.

Attempted Oxidation in liquid Cl2: In a glove box, [NEt4]Cl (329 mg, 1.99 mmol) and MnCl2 (125 mg,

0.99 mmol, 0.50 eq) were dissolved in MeCN (10 mL) and the mixture stirred for 2 h. The MeCN was

removed under reduced pressure and the reaction vessel then connected to the chlorination

apparatus. Cl2 was condensed on the solid and stirred under reflux for 30 min. After removal of the

residual chlorine, only a small portion of the white solid had turned green.

E.4 Experimental

187

Oxidation in o-DFB/MeCN: In this reaction the residue left in the apparatus from the attempted

oxidation in elemental chlorine was reused. o-DFB (20 mL) was added to the white solid and chlorine

passed through the suspension and refluxed. The solution turned yellow and was stirred for 3 h, after

which MeCN (2 mL) was added. After 1.5 h, additional MeCN (2.5 mL) was added and the colour of the

liquid phase turned pale green. The reaction mixture was heated to 50 °C, while passing chlorine

through the suspension and stirred under chlorine reflux for 4 h. During this time, the white solid

disappeared and the solution turned dark green. After cooling to RT and evaporation of the residual

chlorine, a green precipitate had formed in a transparent liquid phase. The solvent was decanted and

the product washed with pentane and dried under a weak argon flow.

FT-Raman (100mW): NO = 118 (w), 258 (vw), 288 (vw), 469 (vw), 555 (vw), 663 (w), 794 (vw), 895 (vw),

1034 (vw), 1072 (w), 1120 (vw), 1184 (vw), 1302 (vw), 1358 (vw), 1395 (vw), 1462 (w), 2147 (w), 2756

(m), 2891 (s), 2946 (vs), 2990 (vs) cm–1.

FT-Raman (3mW): NO = 123 (vw), 168 (vw), 189 (vw), 221 (vw), 259 (vw), 288 (vw), 664 (vw), 722 (vw),

2138 (m), 2758 (vs), 2792 (s), 2817 (s), 2847 (s), 2912 (vs), 2938 (vs), 2990 (s), 3124 (m),

3143 (m) cm–1.

Electrochemical Measurements on Solutions of [P666 14]2[MnCl4] in MeCN

E.4.3.1 Cyclic voltammetry

An electrolyte was prepared by dissolving [NBu4][BF4] (659 mg, 2.00 mmol, 100 mM) in dried and

degassed MeCN (20 mL). In a part of the electrolyte (13 mL), [P666 14]2[MnCl4] (51 mg, 0.044 mmol,

3.36 mM) was dissolved and analysed using a platinum circular disc electrode (diameter 10µm) as

working electrodes and platinum wires as quasi reference and as counter electrode. After addition of

ferrocene (10 mg, 0.054 mmol, 27 mM) to part of the solution (2 mL), the measurement was repeated

and is shown in Figure 69 in the Appendix.

E.4.3.2 Battery Measurements

[P666 14]2[MnCl4] (4.9 g, 4.2 mmol) and MeCN (0.42 g, 0.54 mL, 2.4 eq, 8 wt%) were combined in a glove

and the mixture stirred for 30 min. A cylindrical cell with circular SGL Carbon TF6 Electrodes (electrode

distance: 0.4 cm, surface area per electrode: 1.53 cm2, volume: 0.612 mL, inset 12 in Figure 71) was

filled with the mixture (590 mg, 0.467 mmol [P666 14]2[MnCl4]) inside the glove box and hermetically

sealed using appropriate screws. The cell was transferred to a desiccator and all electronic

measurements were performed under a slight argon flux. The electrolyte was removed and analysed

via Raman spectroscopy prior to dismantling the cell. A black solid was discovered on dismantling the


188

cell at an SOC of approximately 32 % for a one and 42 % assuming a two electron process at the

cathode. A pXRD measurement of the black solid did not yield any reflexes.

FT-Raman (prior to battery measurement): NO = 251 (vw), 381 (vw), 669 (vw), 749 (vw), 920 (vw), 1078

(vw), 1115 (vw), 1308 (vw), 1375 (vw), 1444 (vw), 2204 (vw), 2253 (s), 2293 (vw), 2733 (vw), 2877 (vw),

2943 (vs), 3001 (vw) cm–1.

FT-Raman (after battery measurement): NO = 184 (m), 250 (m), 379 (m), 407 (m), 669 (m), 848 (m), 873

(m), 891 (m), 919 (m), 967 (m), 1008 (m), 1077 (m), 1114 (m), 1306 (m), 1372 (m), 1410 (m), 1441 (s),

2061 (w), 2077 (w), 2158 (w), 2185 (w), 2221 (w), 2250 (w), 2284 (w), 2729 (w), 2856 (vs), 2873 (vs),

2900 (vs), 2932 (vs) cm–1.

E.4 Experimental

189

References



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[6] P. C. Moews Jr, Inorg. Chem. 1966, 5, 5.

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4447.

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Electrochem. Soc. 2015, 162, D405-D411.

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[18] P.-Y. Chen, M.-J. Deng, D.-X. Zhuang, Electrochim. Acta 2009, 54, 6935.

[19] C. Daniel, J. O. Besenhard (Eds.) Handbook of Battery Materials, Wiley-VCH, 2011.

[20] F. Gschwind, G. Rodriguez-Garcia, D. J. S. Sandbeck, A. Gross, M. Weil, M. Fichtner, N. Hörmann,

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190

[22] J. Heinze, Angew. Chem. 1993, 105, 1327.

[23] J. Heinze, Angew. Chem. 1984, 96, 823.

[24] D. M. Adams, D. M. Morris, J. Chem. Soc. A 1968, 694.

[25] C. D. Flint, Journal of Molecular Spectroscopy 1971, 37, 414.

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E.5 Appendix

191

E.5 Appendix

Crystallographic data for [NEt4]4[MnCl4][MnCl5]

Table 38: Crystal data and structure refinement for [NEt4]4[MnCl4][MnCl5]

Empirical formula C32H80N4Cl9Mn2 Formula weight 949.93 Temperature/K 100.0 Crystal system tetragonal Space group P4/n a/Å 14.0370(4) b/Å 14.0370(4) c/Å 12.1648(4) α/° 90 β/° 90 γ/° 90 Volume/Å3 2396.92(16) Z 2 ρcalc / g cm–3 1.316 μ / mm-1 1.055 F(000) 1006.0 Crystal size/mm3 0.16 × 0.16 × 0.13 Radiation Mo-Kα (λ = 0.71073) 2Θ range for data collection /° 3.348 to 56.568 Index ranges -18 ≤ h ≤ 18, -18 ≤ k ≤ 18, -16 ≤ l ≤ 16 Reflections collected 59198 Independent reflections 2993 [Rint = 0.0297, Rsigma = 0.0120] Data/restraints/parameters 2993/84/165 Goodness-of-fit on F2 1.076 Final R indexes [I >= 2σ (I)] R1 = 0.0577, wR2 = 0.1415 Final R indexes [all data] R1 = 0.0637, wR2 = 0.1455 Largest diff. peak/hole / e Å-3 1.21/-0.98

Table 39: Selected bond lengths and bond angles for [NEt4]4[MnCl4][MnCl5].

bond length bond angle Å °

Mn01 Cl04 2.3458(8) Cl04c) Mn01 Cl042 108.181(19) Mn01 Cl04a) 2.3459(8) Cl05d) Mn02 Cl03 100.28(4) Mn01 Cl04b) 2.3459(8) Cl05e) Mn02 Cl03 100.28(4) Mn01 Cl04c) 2.3459(8) Cl05f) Mn02 Cl03 100.28(4) Mn02 Cl03 2.4025(17) Cl05 Mn02 Cl03 100.28(4) Mn02 Cl05 2.2977(9) Cl054 Mn02 Cl056 88.174(13) Mn02 Cl05d) 2.2977(9) Cl055 Mn02 Cl05 88.174(13) Mn02 Cl05e) 2.2977(9) Cl055 Mn02 Cl056 88.174(13) Mn02 Cl05f) 2.2977(9) a)1/2-X, 3/2-Y, +Z; b)1-Y, 1/2+X, 2-Z; c)-1/2+Y, 1-X, 2-Z; d)1/2-Y, +X, +Z; e)1/2-X, 1/2-Y, +Z; f)+Y, 1/2-X, +Z.


192

Table 40: Fractional Atomic Coordinates (×104) and Equivalent Isotropic Displacement Parameters (Å2×103) for [NEt4]4[MnCl4][MnCl5]. Ueq is defined as 1/3 of the trace of the orthogonalised UIJ tensor.

Atom x y z U(eq)

Mn01 2500 7500 10000 32.8(2) Mn02 2500 2500 4918.4(9) 44.5(3) Cl03 2500 2500 6893.3(11) 32.0(3) Cl04 1550.7(7) 6489.9(6) 8922.8(6) 46.8(2) Cl05 945.1(7) 2919.9(6) 4581.2(8) 54.0(3) N1 -465.7(15) 4404.2(15) 7483.9(18) 28.7(5) C1 -999(3) 4279(3) 6346(3) 30.9(9) C2 -1788(14) 3576(16) 6368(13) 42.8(14) C1 -1220(5) 3635(5) 7508(7) 30.7(16) C2 -1810(30) 3610(30) 6450(20) 42.8(14) C1 171(3) 5272(3) 7294(4) 33.3(9) C2 1021(5) 5091(5) 6550(9) 37.0(17) C1 277(5) 4192(5) 6652(6) 28.7(16) C2 1148(9) 4832(11) 6638(18) 37.0(17) C1 -1189(3) 4635(3) 8349(3) 31.7(9) C2 -1809(6) 5490(7) 8167(11) 39(2) C1 -822(5) 5381(4) 7482(6) 27.0(15) C2 -1638(14) 5629(15) 8250(20) 39(2) C1 57(3) 3523(3) 7727(4) 32.6(9) C2 642(10) 3569(7) 8808(11) 44(2) C1 39(5) 4288(5) 8676(5) 27.3(15) C2 540(20) 3371(15) 8830(20) 44(2)

Cyclic Voltammetry

Figure 69: Cyclic voltammogram of ferrocene in a solution of [P666 14]2[MnCl4] and [NBu4][BF4] in MeCN using an UME of 10 µm diameter and a sweep rate of 0.1 V s–1.

E.5 Appendix

193

32-0810 (Q) - Potassium Manganese Chloride - K2MnCl4 - Y: 3.84 % - d x by: 1. - WL: 0.7093 -

71-1074 (C) - Potassium Manganese Chloride - K2MnCl6 - Y: 93.75 % - d x by: 1. - WL: 0.7093 - Cubic - a 9.64450 - b 9.64450 - c 9.64450 - alpha 90.000 - beta 90.000 - gamma 90.000 - Face-centred - Fm-3

Operations: Import

File: MS_1_eva.raw - Type: 2Th/Th locked - Start: 5.000 ° - End: 49.990 ° - Step: 0.010 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 5.000 ° - Theta: 2.500 ° - Phi: 0.00 ° - Aux1: 0.0 -

Lin

(C

oun

ts)

0

1000

2000

3000

4000

2-Theta - Scale

5 10 20 30 40

Powder Diffractogram of K2[MnCl6]

Figure 70: Powder diffractogram of K2[MnCl6.]. The observed reflexes are in good agreement with literature values (red lines) and only a minor contamination of K2[MnCl4] is found (blue lines).


194

F.1 Hardware I: Battery Test Setup for Static Liquid Active Materials

195

F Development of a Battery Test Setup


Test Cell

The test cell shown in Figure 71 was used for battery tests on static liquid active materials. I developed

the design based on a central screw with self-sealing insets (Figure 71, number 5) during my diploma

thesis.[1] The advantage compared to other designs is the possibility to use easily producible and flat

electrodes with a clearly defined surface area and a constant distance between anode and cathode to

allow for the accurate determination of current densities. Additionally, it offers superior sealing

compared to typical designs utilizing several screws surrounding the electrodes, since the central screw

applies pressure more evenly, and is much easier to assemble reproducibly. The insets are machined

from PTFE and offer excellent chemical stability. No other materials needs to be in contact with the

liquid active materials, except, of course, for the electrodes and, as described below, O-rings when the

cell is used with a membrane.

During this doctorate the insets were further refined to allow the use of smaller volumes of active

material and a smaller distance of the electrodes. Details on dimensions, resulting electrode surfaces,

and cell volumes are given in Table 41. Screws were used to allow for hermetic sealing of the test cells

and O-rings were added as suggested by Kolja Bromberger to improve sealing when testing cells with

a membrane. One O-ring is used on each side of the membrane and the diameter differs by a few

millimetres so that the membrane is pressed against the opposing inset from both sides. This improved

the sealing significantly, as tested by Michael Hog. A typical configuration and an assembled test cell

is shown in Figure 72.


196

Figure 71: Overview over the parts used for battery measurements during the doctorate. The numbered insets are inserted in the casing A and compressed with the central screw B (see Figure 72). A detailed description of the inset dimensions is given in Table 41.

Table 41: Details for the inner parts of the test cell depicted in Figure 71. The outer diameter of all insets is 4 cm, ri = inner radius, d = thickness, A = residual electrode surface, V = volume excluding shaft.

description ri d A V mm mm cm2 mL

1 current collector made from aluminium – – – – 2 current collector made from copper – – – – 3 exemplary metal electrode used for hybrid cells – – – – 4 electrode cut from TF6 (SGL Carbon, expanded graphite) – – – – 5 first version of the insets, no O-rings 10 8 3.14 2.51 6 spacer used when very thin insets are used in the casing A – – – – 7 thin inset closed loosely with a triangular flat sheet of PTFE 10 1 3.14 0.31 8 one half of an inset consisting of two 2 mm PTFE sheets, half of the drill

hole is shown 10 4 3.14 1.26

9 fitted to electrode 10, which reduces the effective thickness to 2mm 15 2 7.07 1.41 10 electrode made from BMA5 (SGL Carbon, expanded graphite) 15 – 7.07 – 11 one half of an inset consisting of two 2 mm PTFE sheets, sealing surface

reduced for increased pressure 10 4 3.14 1.26

12 small inset with reduced sealing surface for increased pressure 7 4 1.54 0.62 13 O-rings on both sides, two different diameters for enhanced membrane

sealing 10 8 3.14 2.51

14 identical to inset 13, shown from the other side 10 8 3.14 2.51 15 similar to inset 13, but decreased overall thickness and thinner O-rings 10 4 3.14 1.26 16 identical to inset 15, shown from the other side 10 4 3.14 1.26


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a) b)

Figure 72: a) Typical order of insets for measurement of a hybrid battery with membrane (from back to front): current collector, TF6 inert electrode, PTFE inset with two O-rings, membrane, PTFE inset with two O-rings, metal electrode, current collector. b) Insets assembled in the casing and compressed with the central screw. Additionally, a spacer was inserted and can be seen at the right side.

Source Measure Unit, Temperature Control, Environmental Sealing

A Keysight B2901A Source Measure Unit was used for all experiments. The device can work as a source

and a sink, allows for the simultaneous recording of voltage and current (up to 3 A), supports 4-wire

sensing, and is programmable using the SCPI[2] language. All measurements were controlled by the

software bbat, which is described in Section F.2.

To protect the battery from moisture and oxygen, the cells were in some cases measured inside a

specially prepared desiccator shown in Figure 73 a). This was, for example, the case for some

measurements of membrane-free cells, when a hermetic sealing with a screw was intentionally

avoided to allow for pressure to be relieved that could have resulted from an unintended direct

reaction of the battery components. Some batteries were measured at elevated temperatures in a

styrofoam box because the melting point of the corresponding ILs was above room temperature for

some states of charge (see Figure 73 b)). In this case, the batteries were sealed hermetically with

screws. Additionally, a magnetic stir bar could be added to the cell to allow for stirring inside the

battery via a strong permanent magnet.


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a) b)

Figure 73: a) Battery measurement in a desiccator with inert gas connection. b) Setup for measurement at elevated temperatures achieved by environmental heating with a spiral copper tube and a connected thermostat. The motor to the right in combination with a large permanent magnet attached to the head can be used to stir the liquid inside a test cell via an included magnetic stir bar.

F.2 Software: bbat

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F.2 Software: bbat

The bbat program has been created to provide a software interface to perform standard battery testing

with the Source Measure Unit Keysight B2901A. The key goal in the design was to build a highly

customizable tool which would allow the user to create a reproducible test environment by providing

a reliable and comfortable interface and documenting both test results and conditions transparently.

bbat uses text files to store its source code, to define the tests performed, to save the measured data

and to save the files logging the test records. These text files are UTF-8 encoded, which has become

the accepted standard for the source code of websites, and are therefore readable by any graphical or

command line editor. This ensure transparency and accessibility throughout the program and also

means that the data produced during a test will be accessible even if bbat is not available or executable

at some point in the future.

The software runs under Linux and can therefore be easily transferred to a single-board computer like

the Raspberry Pi.[3] The Raspberry Pi in particular is supported by a large community which provides

valuable support. The program can be accessed via network through default SSH clients, which are

available for all common operating systems. Since the Keysight B2901A uses the standardised SCPI

(Standard Commands for Programmable Instrumentation)[2] commands, bbat should in principle be

adaptable to other devices which implement SCPI.

To help and encourage the user to understand and possibly modify the software, an extensive

documentation has been created. One part of this documentation is the source code itself, which

includes many comments to explain its inner workings.

Figure 74 gives an overview of the folders and files contained within the program folder. Since the

source code of bbat and the included documentation are designed to “speak” for themselves, the

following sections are structured according to the inner file structure of bbat. These sections are only

intended to help in getting an overview over the project and will mainly reference the documentation

and source code included in the Appendix of this chapter.

If one were to explain to an interested person the clockwork of a mechanical watch, it would be a good idea to first tell the person how to correctly tell the time from such a device. He or she would then be familiar with the purpose and the names of the different hands and the crown, which would be helpful to grasp the point behind the parts which constitute the clockwork of the watch. In the same manner,


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Figure 74: Overview over the inner file and folder structure of bbat.

F.2 Software: bbat

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the next section will deal with the way a user can define and execute a battery test, before diving into

the inner workings of bbat in Section F.2.3.

Throughout the following chapter, names of folders and scripts as well as specific terms will be set in

quotes whenever it is considered helpful for the reader’s understanding of the matter.

Documentation

F.2.1.1 user_manual.txt and installation_readme.txt

The user manual (Section F.4.1.1) gives detailed instructions on how to operate bbat, starting with the

creation of a folder for the experiment via a command line terminal and setting up bbat inside. All

steps necessary to set up software requirements are explained in detail in the installation readme

(Section F.4.1.2).

The terms “experiment”, “subexperiment”, “test”, “subtest” and “SCPI Program” have a specific

meaning within bbat. An “experiment” refers to all actions performed on one battery, a

“subexperiment” to a specific run of a “test” performed on the battery. A “test” is a collection of

“subtests”, each defined by one line of an instructions file called "runlist". Each subtest is connected

to a “SCPI Program”, which is a set of commands stored in a file.

The commands of a “SCPI Program” are instructions defining settings and limits for the SMU. For

example, the SMU could be set to discharge the battery at a constant current for one hour. A limit

could be defined to report a “fail” as soon as the voltage drops below a certain value during this

discharge operation. An example for this “SCPI Program” is given in Section F.4.2.2 of the Appendix.

A “SCPI Program” combined with instructions on how many times to run it, what to do after it is

completed and what to do if a “fail” of a limit is detected is called a “subtest”. It is defined by one line

in the “runlist”.

Section F.4.2.1 contains an example “runlist” for a cycling test. The lines, or “subtests”, in the runlist

define in their sum the logic behind the “test” and are discussed in detail in the user manual starting

in line 104. Samples for a cycling test (Section F.4.2.1), an OCV measurement, and a polarisation

(Section F.4.2.4) are included in the bbat default test library.

The results of each run of a test, called a “subexperiment”, are stored in a “subexperiment folder”. An

overview of its contents after the conclusion of the “subexperiment” is given in Figure 75. To complete


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Figure 75: Overview over the inner file and folder structure of a subexperiment after its conclusion. The locks on the folders “rawdata”, “script” and “test” as well as the “logfile” represent withdrawn writing permissions to prevent accidental modification or deletion.

the documentation, it contains not only the measured data, but also a copy of the script folder and a

copy of the “test” used.

F.2.1.2 coding_guidelines.txt and coding_style.txt

The document coding_style.txt, which is given in Section F.4.1.3, lays down standards according to

which the source code of bbat has been formatted. A consistent formatting helps tremendously in

understanding the logical structure of program code and also simplifies debugging. Common practices

have been adopted where applicable and are referenced throughout the file.[4]

The document coding_guidelines.txt (see Section F.4.1.4) is partly based on the same references and

is concerned with good practices in structuring programs. For example, it is a good idea not to have

one large file that contains all the code of the program, but to split the code in smaller portions of

code, each serving a specific and well defined purpose. These smaller portions of code can be capsuled

into so called “functions”, stored in separate files called “libraries”, and called from the main program

file whenever their functionality is needed.

F.2 Software: bbat

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User Interaction: pcontrol and extras

The script “pcontrol” (see Section F.4.3.1) is the script a user executes whenever he or she wishes to

start, change, or look at the current status of a subexperiment. When executed, “pcontrol” will first

check whether or not a subexperiment is already in progress. If this is the case, then the user can

choose to either abort the subexperiment, change to a different subtest, or execute the “datahandler”

(see Section F.4.4.3), which will convert and plot all data that has already been transferred to the

controlling computer. If no subexperiment is running, it will instead start the script “script/wrapper”,

which will set the whole program in motion (see next section).

The “extras” script is not a control tool for subexperiments but provides two features to evaluate them

(see Section F.4.3.2). The first is an option to call the script “script/create_overview” (see Section

F.4.4.4), which will create an overview plot displaying all subexperiments on a single time axis, with

the starting time of each subexperiment shown relative to the first subexperiment. The second feature

is an option to produce ASR plots from polarisation measurements. The script will accept user input

on experiment specific data like the surface area of the electrodes or the number of data points for

each polarisation step.

Inner Workings: script Folder

The “script” folder contains the core of the bbat program. If a user executes the “pcontrol” script while

no other subexperiment is running, the first script to be called is the “wrapper” script. It will create

directories for the subexperiment and check if a test and all corresponding programs can be found in

the “run_this_test” folder. During this process, the folder “script” is copied to the subexperiment

folder, and within this copy, the “mainscript” is then called. The “mainscript” contains the part of the

program that communicates with the SMU and switches between subtests according to the rules

dictated by the runlist. This includes considering whether or not predefined limits are failed during a

subtest. Only when the subexperiment is finished will the “mainscript” be left, and the “wrapper” script

takes over again. It will then call the “datahandler” (see Section F.4.4.3) which will convert the received

data files and create default plots. The last action of the wrapper script is to withdraw writing

permissions on the “rawdata”, “script”, and “test” folder as well as the “logfile”.

F.2.3.1 Script/lib

To do its work, bbat uses multiple “global” variables and constants. Unlike their “local” counterparts,

they are accessible throughout a script and not only in the block of code confined by a “function”. This


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property has several advantages but has the disadvantage that the values of these “global” variables

can be changed from everywhere in the script, thus making debugging more difficult.

To restrict the use of global variables to the minimal amount necessary and also to have a clear

overview on what they are and what they are supposed to do, there is a file in the bbat library called

“globvars.sh” (see Section F.4.5.1). It is called at the beginning of every script and contains a list of all

global variables and constants even if they are not assigned at the very beginning but during the

runtime of the script. These “runtime” variables, like, for example, the name of the subexperiment

which is defined by the user, will be written to a file called “runtimeglobvars.sh” in the “script/tmp”

folder as soon as they are assigned. There are a number of variables which depend on the values of

these global runtime variables. These “dependent runtime global variables” are stored in the file

“script/lib/dep_runtimeglobvars.sh” and are loaded after the “global runtime variables” variables are

set (see Section F.4.5.2).

The last file containing constants is “SCPImessages.sh” (Section F.4.5.4). The constants defined in this

file contain command strings in the SCPI language and are sent to the SMU to control a subtest or to

pull data from it.

As mentioned before, it is a good idea to split the code of a program to form smaller blocks of code

called functions, which have a specific purpose and can be called whenever needed. For this reason,

the largest file of bbat is “script/lib/functions.sh” (see Section F.4.5.3) in the “lib” folder. It contains all

functions defined and used in bbat.

F.2.3.2 Script/gnuplot

bbat employs gnuplot[5] for the plotting of measured data. In the “gnuplot” folder a script

“GnuPlottingScript” is contained (Section F.4.6.1). It will merge the templates

“SP_template_bbat.head” (see Section F.4.6.2), containing all settings for the appearance of the plot,

“SP_template_bbat.body”, which contains links to the location of the data files, and

“SP_template_bbat.tail”, which contains instructions to produce cropped *.pdf and *.eps files, to form

a *.plt file, which it will then plot using gnuplot.

F.2.3.3 Script/Vxi11 Recompile

The creation of bbat would not have been possible without Steve D. Sharples'

([email protected]) program “VXI11 Ethernet Protocol for Linux”, which he published

under the GNU General Public License Version 2.[6] His “vxi11_cmd” utility is used in bbat to

communicate with the SMU. It has been modified only slightly to allow for longer data messages to be

F.2 Software: bbat

205

transmitted. See the “vxi11_readme.txt” for details (Section F.4.1.5). The utility has been compiled

both for x86 and ARM CPU architectures and is provided in both versions with bbat.


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F.3 Hardware II: Progress Towards a Flow-Battery Test Setup

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An extension of the static battery test setup to allow for thermally controlled flow battery testing has

been planned during and will be realised subsequent to the completion of this dissertation. A short

description of the selected compounds and the reasoning behind their selection will be given in the

following chapter.

All prices for components stated in this section are given as approximate values at the time of writing

and may not reflect the current prices.

Flow Test Cell

Following the results of the static battery tests, and due to the high price of the ionic liquids at least at

the research state, it was decided during the project meeting in November 2016 that the flow test cell

should be smaller in dimension than originally envisioned. I suggested to use a similar concept to the

one of the static test cell, possibly with fluid connections opposite of the central screw. Further

development of the flow cell based on this idea was then carried out in collaboration with our

cooperation partner Fraunhofer ISE. Prithiv Mohan, as part of his master thesis supervised by Kolja

Bromberger, designed the test cell shown in Figure 76.[7] A crossectional view is given in Figure 77. The

cell has been found to provide adequate and evenly distributed sealing pressure and has been tested

with pressurized air up to a pressure of 2 bar.[7]

For the first experiments an inset with a flow channel reduced to 1 cm in width was designed, so that

the inner volume of the cell is only 3.1 mL compared to 8.9 mL for the full-sized flow field. The two

different insets and the dimensions of the smaller inset are given in Figure 78.


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a)

b)

Figure 76: a) Schematic drawing of the inner components of the flow battery test cell. Picture created based on a file provided by Prithiv Mohan. b) Picture of the cell fitted with one inset.

Figure 77: Cross section of the flow test cell at the plane “A” showing three insets which are intended for the use without a membrane. Four of the six fluid connection ports are not used in this setup. The picture was created based on files provided by Prithiv Mohan.


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Figure 78: Dimensions of the small inset and comparison to the full-sized inset. Picture fabricated based on files provided by Prithiv Mohan.

Process Engineering

All components providing the supporting functions surrounding the flow cell have been selected in

terms of their physicochemical compatibility with the employed active materials and their

compatibility with respect to the requirements for software control. The intention is to use a Raspberry

Pi as a local controlling computer, connected to the instruments via serial (USB/DE-9) or LAN (RJ-45)

port.

F.3.2.1 Pumps and Tubing

Several types of positive displacement pumps have been considered. Diaphragm pumps were

considered ill-suited due to their inherent dead volume and because they are hard to clean reliably.

Rotary piston pump heads available from Fluid Metering Inc. do not share the problem of a large dead

volume but the moving piston protrudes from the housing cylinder on every pumping cycle and may

carry a thin film of the pumped medium.[8] Though there are variants of pump heads which provide

the possibility for a cleansing solvent or inert gas to be applied to the lower part of the piston, this

would mean having an additional part in the setup to maintain and monitor.


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Peristaltic pumps offer advantages in terms of environmental sealing, dead volume and cleanability.

Their drawback is a limited life span of the section of tube inside the pump head, but for the battery

flow test stand, the lifetime of a pumping tube should in general outlast the time span of an

experiment.

At the time of writing and to the best of my knowledge, there are only two combinations of pump

heads and tubes available that provide adequate flow rates in the range of mL min–1 and can withstand

the harsh chemicals used in our IL-RFBs.

The first option is to use a standard pump head (e.g. Masterflex L/S Easy-Load II Pump Heads for

Precision Tubing, 390 €)[9] in combination with Masterflex “Solve-Flex” tubing, which consists of an

outer layer of a thermoplastic polymer and an inner lining of PTFE.[10] The tube is chemically resistant

to all relevant media and the maximum applicable pressure is 1.7 bar for the combination of tube head

and tube, which should, according to calculations of our cooperation partners Prithiv Mohan and Kolja

Bromberger, be sufficient even for the comparably high viscosities encountered with ILs. At the time

of writing, the price was 760 € per pack (3.8 m, 210 € m–1) for the smallest available inner diameter of

1/8“ (3.2 mm), which would lead to an inner volume of 4.0 mL for an assumed total tube length of 0.5

m per half-cell and allow for a maximum flow rate of 240 mL min–1 at 300 rpm. The manufacturer

stated the lifetime to be 3700 hours at 100 rpm and a pressure of 0.7 bar and 360 hours at 100 rpm

and 1.4 bar, corresponding to a flow rate of 80 mL min–1. Two tube heads can be mounted on one

pump drive.

The second option is the use of a Masterflex “L/S Rigid PTFE-Tubing Pump Head” (1000 €)[11] with

“Masterflex PTFE-tubing” produced specifically for this pump head. The pump head can deliver

pumping pressures of up to 6.9 bar with these PTFE tubes, and the tube is compatible with all media

used in IL-RFBs. There are two tubing diameters available with either 2/4 mm[12] or 4/6 mm[13] inner

and outer diameter, allowing for a maximum flow rate of 17 and 65 mL min–1 at 300 rpm respectively.

Assuming a total tube length of 0.5 meters per half-cell, this would result in 1.6 and 6.3 mL inner tube

volume per half-cell, respectively. The manufacturer states the tube lifetime to be 300 hours at 0 bar

and 100 hours at 0.7 bar with no specification on revolutions per minute. The price per tube is 36 €

(0.38 m, 95 € m–1) for the 2/4 mm version.

Considering all factors mentioned, the Solve-Flex tube in combination with the Masterflex L/S Easy-

Load II Pump Head offers a lower entry price and a lower total life time cost. The produced pressures

are sufficient even for viscous ILs, and the greater price and inner volume will be counteracted by using

the smallest piece of Solve-Flex tube possible and using adapters to connect it to a PTFE tube of 2/4


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mm inner/outer diameter. Assuming a minimum 0.2 m of Solve-Flex tube and an additional 0.3 m of

2/4 mm PTFE tube per half-cell, the total inner volume of the tubing setup would be 2.55 mL for one

half-cell.

There are computer controllable pump drives available from Masterflex (L/S Computer-Compatible

Digital Drive, 0.1 – 600 rpm)[14] and ISMATEC (MCP Standard, 1 – 240 rpm)[15], which are both

compatible with the Masterflex pump heads specified above. Both utilise the RS-323 interface via a

DE-9 connector. The MCP Standard’s signalling language was considered more flexible and better

documented than the one used for the Masterflex pump drives, but in the end the Masterflex Drive

was chosen because it offered a wider range of revolutions especially at the low end.

F.3.2.2 Cryostats

To control the temperature of the flow setup and allow for a setup like the concept depicted in

Figure 73 b), cryostats of the manufacturers Huber, Lauda, and Julapo were compared. The Huber

Ministat 240[16] was chosen, since it offers a competitive price and is equipped with the Huber Pilot

One controller, which is accessible via LAN, USB and RS-232 interface. Additionally, there are very well

documented Python sample programs to communicate with this controller.[17]

F.3.2.3 Thermal Sensors

To monitor the temperature at different points of the test cell as well as the tanks of the electrolyte, a

Pico TC-08 thermocouple data logger was chosen.[18] It supports monitoring 8 thermocouples, which

are available in PTFE mantled versions and is supplied with a Linux driver. Sample programs exist for

the Raspberry Pi.


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References

[1] S. B. Burgenmeister, University of Freiburg, Freiburg, Germany, 2013.

[2] “SCPI. Standard Commands for Programmable Instrumentation”, can be found under

http://www.ivifoundation.org/scpi/, 2017.

[3] “Raspberry Pi - Teach, Learn, and Make with Raspberry Pi”, can be found under

https://www.raspberrypi.org/, 2017.

[4] a) The kernel development community, “Linux kernel coding style”, can be found under

https://kernel.org/doc/html/latest/_sources/process/coding-style.txt, 2016; b) G. van Rossum,

B. Warsaw, N. Coghlan, “PEP 8 -- Style Guide for Python Code. Python.org”, can be found under

https://www.python.org/dev/peps/pep-0008/, 2016; c) P. Armstrong, “Google Shell Style

Guide”, can be found under https://google.github.io/styleguide/shell.xml, 2016.

[5] T. Williams, C. Kelley, gnuplot 4.6, An Interactive Plotting Program, 2014.

[6] S. D. Sharples, “VXI11 Ethernet Protocol for Linux”, can be found under

http://optics.eee.nottingham.ac.uk/vxi11/, 2016.

[7] P. Mohan, Master’s thesis, Fraunhofer ISE, Freiburg, Germany, 2017.

[8] Fluid Metering, Inc., Pump Heads, can be found under

http://fluidmetering.com/pumpheads.html.

[9] “Masterflex L/S Easy-Load II Head with Adjustable Occlusion for Precision Tubing, GZ-77201-60”,

can be found under https://www.coleparmer.com/i/masterflex-l-s-easy-load-ii-head-w-adj-

occlusion-for-precision-tubing/7720160.

[10] “Masterflex Solve-Flex Pump Tubing, L/S 16, 12 ft, GZ-96446-16”, can be found under

https://www.coleparmer.com/i/masterflex-solve-flex-pump-tubing-l-s-16-12-ft/9644616#eb-

item-specification.

[11] “Masterflex L/S Rigid PTFE-Tubing Pump Head, GZ-77390-00”, can be found under

https://www.coleparmer.com/i/masterflex-l-s-rigid-ptfe-tubing-pump-

head/7739000?searchterm=Masterflex+L%2fS+Rigid+PTFE-Tubing+Pump+Head.

[12] “Masterflex PTFE-tubing sets, 2mm ID, 4mm OD, GZ-77390-50”, can be found under

https://www.coleparmer.com/i/masterflex-ptfe-tubing-sets-2mm-id-4mm-od-set-of-

two/7739050.

[13] “Masterflex PTFE-tubing sets, 4mm ID, 6mm OD, GZ-77390-60”, can be found under


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https://www.coleparmer.com/i/masterflex-ptfe-tubing-sets-4mm-id-6mm-od-set-of-

two/7739060.

[14] “Masterflex L/S Computer-Compatible Digital Drive, HV-07551-20”, can be found under

https://www.masterflex.com/i/masterflex-l-s-computer-compatible-digital-drive-0-1-to-600-

rpm-115-230-vac/0755120, 2017.

[15] “Ismatec MCP Standard, ISM 404”, can be found under

http://www.ismatec.com/int_e/pumps/t_mcp_bvp/mcp_stan.htm.

[16] “Huber Ministat 240 Compact cooling bath circulation thermostat, 2016.0005.01”, can be found

under http://www.huber-online.com/en/product_datasheet.aspx?no=2016.0005.01.

[17] Huber AG, pySoftcheck Operation Manual, 2013.

[18] “TC-08 Thermocouple data logger, Pico Technology”, can be found under

https://www.picotech.com/data-logger/tc-08/thermocouple-data-logger

F.4 Appendix: bbat Source Code and Documentation user_manual.txt

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F.4 Appendix: bbat Source Code and Documentation

This chapter includes both the documenting and the source code files for bbat. To increase readability,

the name of the file will also appear in the header of this section.

documentation

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###############################################################################

### User manual for bbat v0.3.0.0 (01/2017) ###

### by Benedikt Burgenmeister, [email protected] ###

###############################################################################

### Table of Contents ###

* Abbreviations

* General remarks

* Performing a measurement

* "extras" - overview and ASR plots

* Miscellaneous

* Footnotes

* Appendix

###############################################################################

### Abbreviations ###

ASR Area Specific Resistance a value characterizing the electronic

resistance of a specific battery

OCV Open Circuit Voltage Voltage of a battery without external load

SCPI Standard Commands for standardized command set for the

Programmable Instruments communication from a computer to a

measurement device

SMU source measure unit the electronic device which is used to

perform measurements on the battery

###############################################################################

### General remarks ###

This user manual will not document the inner workings of bbat, but instead

supply you with the basic knowledge necessary to perform measurements on a

battery. Sometimes detailed explanations are referenced by a number, e.g. (1),

and can be found in the "Footnotes" section.

In the following, there is a difference between the words

- experiment (all actions performed on one battery)

- subexperiment (a specific test run on the battery)

- test (a collection of SCPI programs and a corresponding instructions file

called "runlist")

- subtest (one of several run during a "test")

- (SCPI) program (a set of commands sent to the SMU which specify the settings

of the SMU during the test)

. Since bbat depends on certain programs, for the following it is


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assumed that all requirements given in the file

bbat/documentation/installation_readme.txt are met.

Please note that when the manual asks you to type "something", you are not

supposed to type the quotes. Whenever a line starts with a "$", it means that

these commands are supposed to be run in a shell. The "$" is preceded by

the current working directory. The "~" sign is the common abbreviation for the

home directory. So if you see a "~$", this means the following command is

supposed to be typed in the home directory. For this manual, it is assumed that

you are starting your experiment in the home directory and that you are either

logged into a shell remotely via SSH or you are using your local machine. If

the working directory is too long, it will be abbreviated and the missing parts

replaced by "...".

A basic knowledge of commands (e.g. ls, cp -r, cd ...) and the general use of a

linux shell (3) is assumed.

###############################################################################

### Performing an experiment ###

### Preparations ###

For each experiment, you should create a new folder.

~$ mkdir 201701_sample_battery_experiment

This folder will be called the "experiment folder" from now on.

For ease of use, bbat is usually supplied as a compressed *.tar.gz file.(2)

Prepare your experiment by extracting the compressed file into your new

experiment directory, replacing the here indicated "version" with the actual

version provided to you.

~$ tar -xzf bbat_version.tar.gz -C 201701_sample_battery_experiment/

You can now change to the bbat folder by typing

~$ cd 201701_sample_battery_experiment/bbat_version

This folder will from now on be called the "bbat folder".

If you have not done so already, you need to let bbat know the IP address of

your SMU by entering it into the file "bbat_version/script/settings/ip".

~/201701_battery_experiment/bbat_version$ nano script/settings/ip

### Preparing a subexperiment ###

Usually testing a battery means running several subexperiments over the course

of hours or days. In every subexperiment, a "test" is run. A "test" consists

of several subtests and a "runlist" which defines the logical order of these

subtests.

The test which is to be used in a subexperiment has to be copied to

the folder "bbat_version/run_this_test". You can find several examples of such

tests within the folder "bbat_version/testlibrary".

.../bbat_version$ cp -r testlibrary/default/cycling run_this_test/

.../bbat_version$ cd run_this_test/cycling

For each subtest, there must be an SCPI program in the folder "progs" within

the test folder (in this example called "cycling"). Each "program" specifies

settings which are sent to the SMU. You can find an elaborately commented

version of an SCPI example file in Appendix b) to this manual.

Every line in a "runlist" corresponds to a subtest which is supposed to be run.


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An exemplary runlist can be found in Appendix b) of this manual. For now you

can simply open the "runlist" to have a look at it.

.../bbat_version/run_this_test/cycling$ nano runlist

Lets look at the second subtest, which looks like this:

#0 1 2 3 4 5 6 # this is just the key

#

2 dcharge dchrg1 1 3 5 0

The value under "0" just lets you know which line you are in. The first or "1"

value the name of the subtest, the second the name of the file in the folder

"progs" that is supposed to be sent to the SMU. The third tells bbat how many

times this program is supposed to be run, the fourth which line to go to next.

Within the programs you can specify limits for the measured values. If these

limits are failed, the fifth value specifies which subtest to go to next. You

can also specify how many times you want this "go to on fail" operation to take

place in the sixth value. If this value is exceeded, bbat will go to the last

line in the runlist. It is important to note this fact as it may not be

intuitive. (4) If you take a closer look at the logic set up by the six lines

found in the runlist, you will find that this test consists of charging and

discharging, with intermediate OCV measurements.

### Starting and controlling a subexperiment ###

To start bbat and to actually perform measurements, we need to change to the

bbat folder.

~$ cd ~/201701_sample_battery_experiment/bbat_version

~/201701_battery_experiment/bbat_version$

Now start bbat by typing "./pcontrol"

~/201701_battery_experiment/bbat_version$ ./pcontrol

Every interaction you will have with the program while the experiment is

running will be through this script. For the evaluation of measurements, there

is also the "extras" script within the same folder, which will be covered later

in this manual.

If no subexperiment is running, a "screen" session will be started. "screen"

is a neat program which allows you to log off from the program/your shell and

resuming it later. You can even log off from your SSH connection. To resume a

session, simply execute "./pcontrol" again.

From now on the program itself will guide you through the necessary steps to

start the experiment. It will also ask you to name the subexperiment. A

corresponding folder will be created in the folder "subexperiments" within your

experiments folder. In our case, since we already prepared a cycling test by

copying it into the "run_this_test" folder, we will call the subexperiment

"cycling_01". The date and time will be added and a folder

~/201701_battery_experiment/subexperiments/20170113_1536_cycling_01

will be created. As soon as the subexperiment is running, the screen session

can be left by pressing "Ctrl + a" followed by "d" (not "Ctrl + a + d"). When

"./pcontrol" is called again, you will have several options to control your

subexperiment. In short, you can abort the test, jump to a different subtest

within the test and call the datahandler (will be covered in the next section).


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This is all you need to edit, start and control a test.

### Documentation and plotting of a subexperiment ###

The plotting of the measured data is performed by a script called

"datahandler". It will automatically be called at the end of an experiment, but

if you want to sneak a peak at the experimental data, you can execute it

manually during a subexperiment by executing the script "./pcontrol" and

selecting the appropriate option.

After a subexperiment is complete, there will be the subfolders

rawdata

convdata

gnuplot

script

test

within every subexperiment folder along with a file named "logfile". All

relevant information on when certain subtests were started, on user interaction

or return values of the SMU, are stored within this file. All data received

from the SMU is first stored in the "rawdata" folder, and then converted and

stored in the convdata folder. The files are then used to create plots within

the "gnuplot" folder. By default, three plots in three timescales will be

prepared. Plots in days, hours and seconds are saved to the folders "plot0_d",

"plot0_h" and "plot0_s" respectively. A default plot will be prepared in the

"gnuplot/timescale/default" folder and you can modify a copy of this plot

within the "gnuplot/timescale/editable" folder. Plotting is performed by the

program gnuplot (5), which is called through the "GnuPlottingScript", a copy of

which is present inside every folder containing a plot. All parameters of the

plot, including axes scaling, colour and shape of plotted lines, can be edited

in the file "*.head". The edited plot is then created within the plot folder by

executing the "GnuPlottingScript".

.../20170105_subexp_1/gnuplot/plot0_h/editable$ nano SP_template_bbat.head

.../20170105_subexp_1/gnuplot/plot0_h/editable$ ./GnuPlottingScript

The folder "script" contains a copy of the original folder

"bbat_version/script". During a subexperiment, all scripts and programs are

executed from within this folder. It is kept after the subexperiment for the

sake of documentation. The folder "test" contains a copy of the test performed

during the subexperiment. At the end of a subexperiment, bbat will revoke

writing rights on the folders "rawdata", "script" and "test" as well as the

"logfile" to prevent accidental modifications or deletion.

###############################################################################

### "extras" - overview and ASR plots ###

You can plot an overview plot, which includes all subexperiments with a

timeline starting from the first subexperiment performed, and an ASR (Area

Specific Resistance) plot by executing the "extras script", which is located

alongside the "pcontrol" script inside the "bbat_version" folder.

~/201701_battery_experiment/bbat_version$ ./extras

You can then choose either option and the script will guide you.

###############################################################################

### Miscellaneous ###


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### gnuplot templates

If the default gnuplotting templates do not match your needs, you can change

them inside the folder bbat_version/gnuplot.

### lost raw data

If you lose raw data on the controlling computer (e.g. a Raspberry Pi), they

might still be on the USB-Stick connected to the SMU.

To retrieve the data, copy the relevant files to the "rawdata" folder of your

subexperiment, then, to translate the files to a format that is readable by the

datahandler, change to the "rawdata" folder and paste the following line.

for file in *; do tail $file -n +2 > ${file}_new; mv ${file}_new $file; done

Change to the "script" folder within the subexperiment folder and execute the

datahandler by typing "./datahandler". Your data should now be converted and

plotted as usual.

### copying folders

Please be aware that there is a subtle difference between the command

~$ cp -r sample_folder sample_2/

, which will result in a structure like this

~/sample_folder/content_of_sample_folder

~/sample_2/sample_folder/content_of_sample_folder

, and the command without the trailing "/"

~$ cp -r sample_folder sample_2

, which will result in a copy of the folder "sample_directory" named "sample_2"

~/sample_folder/content_of_sample_folder

~/sample_2/content_of_sample_folder

. The lesson to remember: if you specify a folder with

a trailing "/", you are addressing its content, and otherwise, without a

trailing

"/", you are addressing the folder itself.

###############################################################################

### Footnotes ###

1) This was only an example for the notation of footnotes.

2) This method ensures that appropriate execution rights for the included

files are maintained.

3) To be more precise: a bash shell.

4) The intention behind this behaviour is that you could decide to cycle a

battery five times, a full or empty battery being defined by failing a limit

test, and then go on to a different subtest.

5) At the time of writing, gunplot 4.6 is used:

Thomas Williams, Colin Kelley and many others, gnuplot 4.6, An Interactive

Plotting Program, 2014, http://sourceforge.net/projects/gnuplot.

###############################################################################

### Appendix ###


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a) Commented sample runlist

The start and end of the file is signalled with a whole line of "-".

-------------------------------------------------------------------------------

###############################################################################

### runlist for a bbat battery cycling test ###

# General remarks

# - do not use blanks neither in subtest names nor in program names

# - though not mandatory, the standard distance between values is 8 characters,

# filled with white spaces

# - you must not have empty lines in this file

# - subtest numbers must start with 1 and must not skip numbers

# - whenever an "a" is inserted into a "goto" instruction, the subexperiment

# will be aborted

# - a value of "0" is treated equal to infinity

###############################################################################

#

### key

# 0: subtest number

# 1: subtest name

# 2: program name (must be present in folder "progs")

# 3: "runtimes": times to run the program consecutively

# 4: "goto": subtest to go to after the subtest is finished

# 5: "gotoonfail": subtest to go to when a "fail" is received from the SMU

# 6: "gototimes": how many times to go to the subtest specified in "gotoonfail"

#

### runlist

#

### Before anything else is done: measure the o(pen) c(ircuit) v(oltage).

#0 1 2 3 4 5 6

#

1 ocv_beg ocv1 1 2 a 0

#

### Cycling starts with discharge and includes intermediate ocv measurements.

#0 1 2 3 4 5 6

#


3 d_ocv docv1 1 2 4 0

4 charge chrg1 1 5 3 0

5 c_ocv cocv1 1 4 2 0

#

### At the end of the test, an ocv measurement is performed and repeated until

# an abort signal is received.

#0 1 2 3 4 5 6

#

6 ocv_end ocv2 1 6 a 0

#

### end of runlist ###

###############################################################################

-------------------------------------------------------------------------------

b) Commented SCPI program file

The following file is an elaborately commented version of an ocv measurement

program. The start and end of the file is signalled with a whole line of "-".

-------------------------------------------------------------------------------

### Commented SCPI program file ###


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# This file contains the settings which are to be applied to the SMU unit. The

# whole file will be processed by bbat into the format needed for the SMU unit.

# The first line ( #!/bin/bash ) has the sole intention of enabling syntax

# highlighting in the editor.

# Only Comments with hash tags (#) at the very beginning of the line are

# allowed and will be interpreted as comments. Do not (!) start comments in the

# middle of a line.

# Comments framed by three lines with three leading hash tags (###) section are

# of a general sort, comments directly above commands are specific to this file

# and can be modified by the user describe his intentions.

### SCPI language ###

# SCPI stands for "Standard Commands for Programmable Instruments" and is a

# standard defining commands through which a computer can communicate with a

# programmable measurement device. Your SCPI capable device should come with an

# appropriate manual, so explanations will be kept brief in this file.

# This file represents a working configuration for the Keysight B2901A/B2902A

# devices, and all information regarding these devices is taken from:

#

# Just one general remark: a leading ":" in the SCPI language specifies, that

# the command is given in its whole. If the leading ":" is missing, the stem of

# the prior command is used. For example:

# :SOUR1:CURR 10;RANG: 2

# and

# :SOUR1:CURR 10;:SOUR1:RANG: 2

# are interpreted completely analogue.

###############################################################################

### Basic Settings ###

# The commands in this section usually do not need to be modified.

# Four point sensing is the default for our measurements and is turned on

# with the remote sensing option.

###

:SENS1:REM ON

###

# We could turn the output on manually, but usually AUTO mode

# is just fine.

###

:OUTP1:ON:AUTO ON

:OUTP1:OFF:AUTO ON

###

# Usually we do not want to define any WAIT times before our measurements

# start.

###

:SOUR1:WAIT OFF

:SENS1:WAIT OFF

###############################################################################

### Mode of operation and ranges ###

# The SMU can either work in CURRent controlled or in VOLTage controlled mode.

# If one is the SOURce, the other as to be set as SENS. For SOURce you will set

# your desired value, which will result in a value for the other entity, that

# depends on the properties of the device under testing and can only be

# measured (SENSed).

# Measurement is more consistent with the RANGe AUTO feature turned off and

# specific values set for SOURce and SENSe.

###

# For the OCV measurement, the current range should be small, since a desired

# current of 0 should be met very closely.

:SOUR1:CURR:RANG 0.00001;RANG:AUTO OFF

:SENS1:VOLT:RANG 2;RANG:AUTO OFF


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###############################################################################

### SOURce ###

# Setting up the shape of the desired output of the SMU

# FUNCtion:MODE: CURR or VOLT (see above)

# FUNCtion - defines the shape, e.g. PULSE or DC

# MODE - e.g. FIX, LIST, SWEEP

###

# We want a FIXed value of a DC current and we want it to be 0 for the OCV

# measurement.

:SOUR1:FUNC:MODE CURR

:SOUR1:FUNC DC;

:SOUR1:CURR:MODE FIX

###

# Setting the SOURce value before a TRIGger is received (see below)

###

:SOUR1:CURR 0

###

# Setting the SOURce value when a TRIGger event takes place (see below)

###

:SOUR1:CURR:TRIG 0

###############################################################################

### SENSe ###

# For SENSe, you can set a maximum allowable value. The value set in SOURce

# will be adjusted accordingly on the fly.

###

# There is no need for a limit in the OCV measurement, it is set here to the

# value of the measurement range.

:SENS1:VOLT:PROT 2

###############################################################################

### ARM and TRIGger ###

# To perform any measurement, the SMU has to enter the ARMed state.

# To actually perform a measurements or change the SOURce output,

# these events have to be TRIGered.

# If TRANsient is triggered, the value for SOURce defined above will be set.

# If ACQire is triggered, the SMU performs a SENSe measurement.

# If ALL is set, then both ACQire and TRANsient will be triggered

# simultaneously.

# There can be various TRIGger SOURces, here we will only use a TIMer.

# TIM specifies the interval in seconds between two TRIGger events, COUN the

# total amount of TRIGger events initiated. A DELay before the first Trigger

# is sent, can also be set.

# APERture time is the time over which the measured value will be integrated.

# The maximum value is 2 seconds for the Keysight B2901A and is common for both

# CURR and VOLT, so it does not matter which is specified.

###

# It is enough to ARM once, so COUN should be 1 and the TIM value is irrelevant

# here.

:ARM1:ALL:COUN 1;DEL 0;SOUR TIM;TIM 5

# :ARM1:ACQ:COUN 1;DEL 0; SOUR TIM; TIM 5

# :ARM1:TRAN:COUN 1;DEL 0; SOUR TIM; TIM 5

# We would like to SENSe a value every second, 60 times, so the total program

# duration will be 1 minute.

:TRIG1:ALL:DEL 0;SOUR TIM;TIM 1;COUN 60

# :TRIG1:TRAN:DEL 0;SOUR TIM; TIM 0.5;COUN 200

# :TRIG1:ACQ:DEL 0;SOUR TIM; TIM 0.5;COUN 200

# Setting APERture time to 1 second as well.

:SENS1:CURR:DC:APER 1

###############################################################################

F.4 Appendix: bbat Source Code and Documentation installation_readme.txt

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### LIMit ###

# You can turn off the limit tests completely by changing ON to OFF in the

# following line.

###

:CALC1:CLIM:STAT ON

###

# The following values will be the same for all types of measurement - see the

# SCPI programming guide for details.

###

:CALC1:CLIM:MODE GRAD

:CALC1:CLIM:UPD IMM

:CALC1:LIM:FUNC LIM

:CALC1:CLIM:CLE:AUTO OFF

:CALC1:LIM1:STAT ON

###

# FEED defines which of the available values is taken for the LIMit test.

# The default behaviour is to report a "fail" when the measured value is

# outside of the range defined by the upper and lower limit.

###

# Let us assume, that for the current battery, something is definitely wrong

# if the OCV value is not between 0 and 2 Volts.

:CALC1:FEED VOLT

:CALC1:LIM1:LOW 0

:CALC1:LIM1:UPP 2

### End of program. ###

###############################################################################

-------------------------------------------------------------------------------

F.4.1.2 installation_readme.txt

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###############################################################################

### Installation readme for bbat v0.3.0.0 (01/2017) ###

### by Benedikt Burgenmeister, [email protected] ###

###############################################################################

### Table of content ###

* General Remarks

* Installation instructions for bbat

* Configuration of Raspbian

* Footnotes

###############################################################################

### General Remarks ###

The instructions in this readme have been tested on a raspberry pi 1/2/3 (1)

with Raspbian (2). They should, however, work on any Debian (3) based linux

distribution.

###############################################################################

### Installation instructions for bbat ###

If you have a working Raspbian/Debian linux environment the bbat scripts

themselves need Python 3 installed but otherwise have no special requirements.

To enjoy the benefits of plotted data both in *.pdf, *.eps and cropped and

uncropped versions, you need to install the programs


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texlive-font-utils (provides epstopdf)

epstool

pdfcrop

gnuplot

. To install the packages copy the following line in a terminal:

sudo apt-get install texlive-font-utils epstool pdfcrop gnuplot

Though plotting the data is not mandatory, I wouldn't guarantee that the

script in total will work fine without these tools.

bbat will usually be supplied to you as a compressed *.tar.gz file. You can

extract it by typing

tar xzf bbat_version.tar.gz

In order for bbat to function correctly, the SMU must have a static IP address.

It has to be made known to bbat by writing it to the file

bbat_version/script/settings/ip

. The program has been thoroughly tested on on a raspberry pi 1/2/3 with

different Raspbian images (last on Raspbian Jessie, released in September

2016).

Everything from here on onwards is described in the user manual.

###############################################################################

### Configuration of Raspbian ###

The installation of Raspbian onto an microSD card is covered in detail on the

Raspberry Pi website.(4) We will go through all the steps for a working

configuration (for ssh access) after you have inserted your microSD card in the

Raspberry Pi. The instructions will be kept very brief, as always google or a

different search engine of you choice will be your friend.

If you are starting the Raspberry Pi for the first time, make sure you have a

keyboard and a monitor connected to it. The Raspberry Pi will boot into a

graphic desktop environment, you can enter a terminal by pressing

"Ctrl + alt + F1".

### raspi-config ###

~$ sudo raspi-config

* "Internationalisation Options" - change local, timezone, keyboard layout

* change administrator password

* "Advanced Setup" - enable SSH

* boot options - enable boot to console

### network ###

~$ sudo nano /etc/network/interfaces

* now you have to change the settings for eth0 (assuming you are connected to

your local lan by ethernet cable)

* Example configuration - fill in the appropriate numbers for your

F.4 Appendix: bbat Source Code and Documentation installation_readme.txt

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configuration

auto eth0

allow-hotplug eth0

iface eth0 inet static

address 10.6.13.16

netmask 255.255.255.0

gateway 10.6.13.254

dns-nameservers 132.230.200.200 132.230.200.111

iDHCP needs to be disabled.

~$ sudo service dhcpcd stop

~$ sudo systemctl disable dhcpcdi

It is recommended to reboot now and check if you can log into your Raspberry Pi

via ssh. If it works, you can do the rest of the steps via ssh.

### Enabling time synchronisation ###

The Raspberry PI does not have an integrated battery and will loose the current

time if you disconnect the power supply. Time synchronisation via ethernet is

recommended, find out a suitable ntp time-server for your organisation by (e.g.

time.uni-freiburg.de).

~$ sudo timedatectl set-timezone Europe/Berlin

~$ sudo timedatectl set-time "2016-10-28 18:37"

~$ sudo timedatectl set-ntp true

~$ sudo nano /etc/systemd/timesyncd.conf

* add your time server

Servers=time.uni-freiburg.de

A reboot is strongly recommended now. Check for the correct time and enabled

ntp.

~$ sudo timedatectl

### Adding users ###

It is recomended to perform experiments not from the administrators account

(pi) but from a standard user account.

~$ sudo adduser sample-user-name-please-replace-by-your-name

###############################################################################

### Footnotes ###

1) Visit https://www.raspberrypi.org/ for more information.

2) Visit https://www.raspbian.org/ for more information.

3) Visit https://www.debian.org/ for more information.

4) Installation instructions can be found on

https://www.raspberrypi.org/documentation/installation/installing-

images/README.md


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F.4.1.3 coding_style.txt

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###############################################################################

### Coding style used for bbat ###

###############################################################################

# last updated: 2016.01.16

# version: 0.1.0

The coding style summarized in this document lays down specification for the

formatting of the bbat code. It is a mix of own specifications and the ones in

the documents given as references [1,2,3]. Whenever concepts are adopted

without modification from these sources or literal quotes are made, they will

be referenced.

References

[1] https://www.python.org/dev/peps/pep-0008 (accessed 19.12.2016)

[2] https://www.kernel.org/doc/Documentation/CodingStyle (accessed 19.12.2016)

[3] https://google.github.io/styleguide/shell.xml (accessed 19.12.2016)

### Line width

Lines should not exceed 79 characters to comply with established coding

standards and to increase readability. A good summary of reasons is given in

[1].

Python code in brackets can be split in several lines without any further

modification. For some statements it is necessary to mark the continuation of

a line with a "\".

The python coding style also demands longer flowing text to be formated to a

width of 72 Characters, which is not the rule adopted forthis style guide.

As stated in the linux kernel coding style:

"However, never break user-visible strings such as

printk messages, because that breaks the ability to grep for them." [2]

### Indentation

In accordance with recommendation for python in [1], all indentations, even

for

bash should be four whitespaces for each indentation level. Wherever you still

may find tabs instead of spaces: replace them.

Closing bracket on multi-line code should line up under the first non-

whitespace

character of the last line of the embraced code:

# bash example for a function

functionname () {

###

# General use of the function

# Globals:

# Dependencies on global functions or variables

# Parameters:

# description of parameters

# Returns:

# description of return values

###

function content

code code code

}

### Functions

F.4 Appendix: bbat Source Code and Documentation coding_style.txt

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As you can see in the description above, functions should also be described by

at least the mentioned four lines, which is partly taken from [3].

Different funtions should be separated by empty lines. Different groups of

functions my be separated by several lines. For everything else see "Comments

and Structuring".

# Comments and Structuring

It is good sense to assume that nothing is obvious and that a comment is always

justified. Some quotes on this matter:

"Comment tricky, non-obvious, interesting or important parts of your code."[3]

"Generally, you want your comments to tell WHAT your code does, not HOW."[2]

"Use TODO comments for code that is temporary, a short-term solution, or

good-enough but not perfect."[3]

Bigger blocks of code may be separated by a full line of hashes with a hanging

description enclosed by two blocks of three hash tags and a full line of

hashes again.

###############################################################################

### example level 1 ###

###############################################################################

. You can omit the last line of hashes to get to level 2:

###############################################################################

### example level 2 ###

. The next level is three leading hashes:

### example level 3

. An even smaller level is:

# example level 4

. And if you want to comment something on a very small level, you can simply

put

a comment in the same line as the code:

variable="foobar" # this is an example for an inline comment

other_variable=1 # make sure, that successive comments line up.

### File encoding

All files must use UTF-8 encoding. Period.

Python style guide recommends function names to be lower case only and to use

an underscore as separator.[1] Generally I recommend sicking to this guide

line, but as long as it is readable anything else is fine too.

### Variables and function naming

"... while mixed-case names are frowned upon, descriptive names for

global variables are a must. To call a global function ``foo`` is a

shooting offense." [2]

Leading underscores should be used for local variables of functions.

"Use one leading underscore only for non-public methods and instance

variables." [1]


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"LOCAL variable names should be short, and to the point. If you have

some random integer loop counter, it should probably be called ``i``."[2]

### Constants

Will be nameed in CAPITAL_LETTERS and with underscores as separator. [1]

### if/do/while statement

For an if statement in bash, always use 4 whitespaces as indentation and have

the "then" statement in the same line as the "if", separated by a semicolon.

"else" and "elif" are on the same logical level as "if" and should

therefore be at the same indentation as should be the closing fi.

if [ $blub = $blub ]; then

echo "la la la"

exit 3

else

echo

elif [ $blub ]; then

echo "lui lui lui"

fi

### Case statements [3]

For bash, alternatives of case statements are indented once, the commands

starting with two indentations one line below. The closing semicolons ";;"

should be on the same indentation as the commands. If the commands are short

and simple, you may skip the new lines and indentation.

F.4.1.4 coding_guidelines.txt

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###############################################################################

### Coding guidelines used for bbat ###

###############################################################################

# last updated: 2016.01.16

# version: 0.1.0

This document is intended to summarize a view guiding principles which have

been adhered or should be adhered to for further programming of bbat.

References

[1] https://www.python.org/dev/peps/pep-0008 (accessed 19.12.2016)

[2] https://www.kernel.org/doc/Documentation/CodingStyle (accesssed 19.12.2016)

[3] https://google.github.io/styleguide/shell.xml (accessed 19.12.2016)

### Variables

All global constants and variables used in bbat must (!) appear in the file

lib/globvars.sh or dep_runtimeglobvars.sh. The point behind this is to have a

central

file, where the use of the variables is explained, and also, since the program

consists of several separate scripts, to not have to declare them separately

for every script. It is fine to set the value of constants somewhere inside a

script, but an explanation must (!) appear in the globvars.sh file.

"GLOBAL variables (to be used only if you **really** need them) need to

have descriptive names, as do global functions."[2]

F.4 Appendix: bbat Source Code and Documentation coding_guidelines.txt

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CONSTANTS should be made readonly explicitly to avoid bugs.

"Use readonly or declare -r to ensure they're read only." [3]

The following seems to avoid things I do not completely understand.

"Declare function-specific variables with local. Declaration and assignment

should be on different lines." [3]

"Always quote strings containing variables, command substitutions, spaces or

shell meta characters, unless careful unquoted expansion is required.

Prefer quoting strings that are "words" (as opposed to command options or

path names). Never quote literal integers." [3]

### Using bash and the scope of this project

"If you are writing a script that is more than 100 lines long, you should

probably be writing it in Python instead. Bear in mind that scripts grow.

Rewrite your script in another language early to avoid a time-consuming rewrite

at a later date." [3]

I probably should have taken this advice. It is clear, that this script should

be rewritten in python... at some point.

### Libraries

All functions and classes should be stored in libraries which should sit in a

folder called lib.

"Executables should have no extension (strongly preferred) or a .sh extension.

Libraries must have a .sh extension and should not be executable. " [3]

### eval in bash

"eval should be avoided."[3]

### Test, [ and [[ and empty strings

The following two Google recommends have not been followed in the coding of

bbat, but it may be a good idea to change this, or even better, rewrite bbat

in Python.

"[[ ... ]] reduces errors as no pathname expansion or word splitting takes

place between [[ and ]] and [[ ... ]] allows for regular expression matching

where [ ... ] does not." [3]

"# -z (string length is zero) and -n (string length is not zero) are

# preferred over testing for an empty string

if [[ -z "${my_var}" ]]; then

do_something

fi

" [3]

### Functions

"Functions should be short and sweet, and do just one thing. They should

fit on one or two screenfuls of text (the ISO/ANSI screen size is 80x24,

as we all know), and do one thing and do that well."[2]

"Another measure of the function is the number of local variables. They

shouldn't exceed 5-10, or you're doing something wrong. Re-think the

function, and split it into smaller pieces." [2]

### Builtin Commands vs. External Commands


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For bash:

"Given the choice between invoking a shell builtin and invoking a separate

process, choose the builtin." [3]

### bash return values and error handling

The following needs to be invoked still and would be very helpful:

"Always check return values and give informative return values."[3]

This can be done by:

"A function to print out error messages along with other status information is

recommended.

err() {

echo "[$(date +'%Y-%m-%dT%H:%M:%S%z')]: $@" >&2

}

if ! do_something; then

err "Unable to do_something"

exit "${E_DID_NOTHING}"

fi

"[3]

F.4.1.5 vxi11_readme.txt

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###############################################################################

### Readme regarding the modifications on vxi11_cmd utillity (16.01.2017) ###

### Benedikt Burgenmeister, [email protected] ###

###############################################################################

Steve D. Sharples'([email protected]) program is "VXI11 Ethernet

Protocol for Linux" is used in bbat. It was published under the GNU GENERAL

PUBLIC LICENSE Version 2. Version 1.10, released on 9/09/2010 was obtained from

http://optics.eee.nottingham.ac.uk/vxi11/ on 2013/10/17.

The site has now moved to https://github.com/applied-optics/vxi11 (2016/06/15).

The source code for his vxi11_cmd utility has been modifiedi (vxi11_cmd.cc and

vxi11_user.h) slightly and according to the GNU GENERAL PUBLIC LICENCE VERSION

2, prominent notice has been given in the source code to specify these

modifications.

This slightly modified version is released under the same licensing terms and

conditions as the original version of Steve D. Sharples, especially noting:

This program is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

GNU General Public License for more details.

The original source code is supplied within the folder

bbat/vxi11_recompile/original_vxi11_1.10 , the modified version under

bbat/vxi11_recompile/modified_vxi11_1.10 .

F.4 Appendix: bbat Source Code and Documentation cycling – runlist

231

testlibrary

F.4.2.1 cycling – runlist

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###############################################################################

### runlist for a bbat cycling test ###

# General remarks

# - do not use blanks neither in subtest names nor in program names



# - you must not have empty lines in this file


# - whenever an "a" is inserted into a "goto" instruction, the sub experiment

# will be aborted


###############################################################################

#

### key

# 0: subtest number

# 1: subtest name






#

### runlist

#

### Before anything else is done: measure the o(pen) c(ircuit) v(oltage).

#0 1 2 3 4 5 6

#

1 ocv_beg ocv1 1 2 a 0

#

### Cycling starts with discharge and includes intermediate ocv measurements.

#0 1 2 3 4 5 6

#


3 d_ocv docv1 1 2 4 0

4 charge chrg1 1 5 3 0

5 c_ocv cocv1 1 4 2 0

#

### At the end of the test, an ocv measurement is performed and repeated until

# an abort signal is received.

#

#0 1 2 3 4 5 6

6 ocv_end ocv2 1 6 a 0

#


###############################################################################

F.4.2.2 cycling – dischrg1

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#!/bin/bash

###############################################################################





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# middle of a line.

###############################################################################



:SENS1:REM ON

# Turn the output on AUTOmatically.

:OUTP1:ON:AUTO ON

:OUTP1:OFF:AUTO ON

# We do not want to define any WAIT times before our measurement.

:SOUR1:WAIT OFF

:SENS1:WAIT OFF

###############################################################################


# We will discharge with a constant current, so we are setting it as source.

# You could also specify a Voltage and discharge potentiostatic mode.



###############################################################################

### SOURce ###

# We want a FIXed DC current.

# measurement.


:SOUR1:FUNC DC;


# We will discharge (negative current) with 1 mA, or 0.001 A.

:SOUR1:CURR -0.001

:SOUR1:CURR:TRIG -0.001

###############################################################################

### SENSe ###

# We will set a fail limit at the end of the program, a protect limit is not

# necessary at this point.

:SENS1:VOLT:PROT 2

###############################################################################



# here.




# We would like to TRIGger SENSe and source every second for 3600 times, so the

# total program duration will be one hour if no error occurs






###############################################################################

### LIMit ###

# Switching test ON

:CALC1:CLIM:STAT ON

# Default values


:CALC1:CLIM:UPD IMM

:CALC1:LIM:FUNC LIM

F.4 Appendix: bbat Source Code and Documentation cycling – docv1

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:CALC1:LIM1:STAT ON

# Let us assume, that for the current battery, we do not want to go below 0.5

# Volts during discharge. The upper limit is irrelevant at this point.

:CALC1:FEED VOLT

:CALC1:LIM1:LOW 0.5

:CALC1:LIM1:UPP 2


###############################################################################

F.4.2.3 cycling – docv1

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#!/bin/bash

###############################################################################








# middle of a line.

###############################################################################



:SENS1:REM ON


:OUTP1:ON:AUTO ON

:OUTP1:OFF:AUTO ON


:SOUR1:WAIT OFF

:SENS1:WAIT OFF

###############################################################################


# For the OCV measurement, the current range should be small, since a desired

# current of 0 should be met very closely.



###############################################################################

### SOURce ###

# We want a FIXed value of a DC current and we want it to be 0 for the OCV

# measurement.


:SOUR1:FUNC DC;


# Setting the SOURce value to 0 before a TRIGger is received (see below)

:SOUR1:CURR 0

# Setting the SOURce value when a TRIGger event takes place (see below)

:SOUR1:CURR:TRIG 0

###############################################################################

### SENSe ###

# There is no need for a limit in the OCV measurement, it is set here to the

# value of the measurement range.

:SENS1:VOLT:PROT 2

###############################################################################



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# here.




# We would like to SENSe a value every second, 60 times, so the total program

# duration will be 1 minute.






###############################################################################

### LIMit ###

# Switching test ON

:CALC1:CLIM:STAT ON

# Default values


:CALC1:CLIM:UPD IMM

:CALC1:LIM:FUNC LIM


:CALC1:LIM1:STAT ON

# Since this is the OCV measurement performed in between to discharge

# operations, we would like to stop discharging and return a "fail" when the

# OCV value drops below 0.8 Volts.

:CALC1:FEED VOLT

:CALC1:LIM1:LOW 0.8

:CALC1:LIM1:UPP 2


###############################################################################

F.4.2.4 cycling – chrg1

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#!/bin/bash

###############################################################################








# middle of a line.

###############################################################################



:SENS1:REM ON


:OUTP1:ON:AUTO ON

:OUTP1:OFF:AUTO ON


:SOUR1:WAIT OFF

:SENS1:WAIT OFF

###############################################################################


# Let us assume we want to charge in potentiostatic mode but we will limit the

# current to 5 mA later.

F.4 Appendix: bbat Source Code and Documentation cycling – chrg1

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:SOUR1:VOLT:RANG 2;RANG:AUTO OFF

:SENS1:CURR:RANG 0.01;RANG:AUTO OFF

###############################################################################

### SOURce ###

# We want a FIXed DC VOLTage.

# measurement.

:SOUR1:FUNC:MODE VOLT

:SOUR1:FUNC DC;

:SOUR1:VOLT:MODE FIX

# We will charge with a potential of 1.9 V.

:SOUR1:VOLT 1.9

:SOUR1:VOLT:TRIG 1.9

###############################################################################

### SENSe ###

# We will set a fail limit for a minimal current later, but we also want the

# current not to go higher than 5 mA.

:SENS1:CURR:PROT 0.005

###############################################################################



# here.




# We would like to TRIGger SENSe and source every second for 3600 times, so the

# total program duration will be one hour if no error occurs






###############################################################################

### LIMIT ###

# Switching test ON

:CALC1:CLIM:STAT ON

# Default values


:CALC1:CLIM:UPD IMM

:CALC1:LIM:FUNC LIM


:CALC1:LIM1:STAT ON

# We will assume the battery under testing fully charged, when the current

# drops below a value of 1mA. The upper limit is set so to not interfere with

# our measurement.

:CALC1:FEED CURR

:CALC1:LIM1:LOW 0.001

:CALC1:LIM1:UPP 0.01


###############################################################################


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F.4.2.5 polarisation – runlist

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###############################################################################

### runlist for a bbat polarisation test ###

# General remarks

# - do not use blanks neither in subtest names nor in program names.



# - you must not have leave empty lines in this file


# - whenever an "a" is inserted in a "goto" instruction, the sub experiment

# will be aborted


###############################################################################

#

### key

# 0: subtest number

# 1: subtest name






#

### runlist

#

### Make an o(pen) c(ircuit) v(oltage) measurement at the beginning.

#0 1 2 3 4 5 6

#

1 ocv ocv1 1 2 a 0

#

### Then do the polarisation and go back to the ocv measurement.

#0 1 2 3 4 5 6

#

2 pol50 pol50 1 1 5 0

#


###############################################################################

F.4.2.6 polarisation – pol50

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#!/bin/bash

###############################################################################








# middle of a line.

###############################################################################



:SENS1:REM ON


:OUTP1:ON:AUTO ON

:OUTP1:OFF:AUTO ON

F.4 Appendix: bbat Source Code and Documentation polarisation – pol50

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:SOUR1:WAIT OFF

:SENS1:WAIT OFF

###############################################################################


# For a polarisation, we would like to set specific current values between 0.1

# and 5 mA.



###############################################################################

### SOURce ###

# We want to have current PULSes which are of 15 second WIDTh and have

# currents according to values in a LIST. In between we want OCV measurements,

# which means a current of 0.

# A.


:SOUR1:CURR:MODE LIST

:SOUR1:FUNC PULS;

:SOUR1:PULS:WIDT 15

# SOURce value set to 0 in between two TRANsient actions (see below)

:SOUR1:CURR 0

# The number of items in a LIST is limited to 2500 for the Keysight

# 2901A/2902A. We are starting the list with a value of 0.

:SOUR1:LIST:CURR 0.0

# Values can be APPended to a previously defined list.

# If the list spans a very wide range of currents, you may want to split the

# program in two parts and apply a different measurement range.

:SOUR1:LIST:CURR:APP 0.0005,-0.0005,0.0010,-0.0010,0.0015,-0.0015



###############################################################################

### SENSe ###

# The maximum Voltage we would like to apply is 5 V.

:SENS1:VOLT:PROT 5

###############################################################################



# here.




# 19 values have been added to the LIST above, so we need to TRIGger 19

# TRANsient events initiating 19 PULSes. A TIMer of 60 seconds with a PULSe

# WIDTh of 15 seconds will lead to a ocv break of 45 seconds.

:TRIG1:TRAN:DEL 0;SOUR TIM; TIM 60;COUN 19

# Additionally we would like to ACQuire a measurement point every 0.5 seconds.

# In total we need a COUNt of

# ((60 s) * 19) / 0.5 s/point) = 2280 points

:TRIG1:ACQ:DEL 0;SOUR TIM; TIM 0.5;COUN 2280

# :TRIG1:ALL:DEL 0;SOUR TIM;TIM 1;COUN 60

# Setting APERture time to 0.5 second as well.

:SENS1:CURR:DC:APER 0.5

###############################################################################

### LIMit ###

# TODO Switching test OFF - it can for now not be used with a PULSe program.

# The reason is, that a limit test can only be performed once per TRANsient

# action and not on every ACQuire action.

# A workaround would be to define 30 LIST values triggering 30 0.5 second


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# PULSes for every desired current value.

:CALC1:CLIM:STAT OFF

# Default values


:CALC1:CLIM:UPD IMM

:CALC1:LIM:FUNC LIM


:CALC1:LIM1:STAT ON

# Let us assume, that for the current battery, something is definitely wrong

# if the OCV value is not between 0.1 and 2 Volts.

:CALC1:FEED VOLT

:CALC1:LIM1:LOW 0.1

:CALC1:LIM1:UPP 2


###############################################################################

pcontrol & extras

F.4.3.1 pcontrol

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#!/bin/bash

###############################################################################

### pcontrol ###

# This script is used for all user interaction with bbat. This means:

# start and abort of a subexperiments, but also jumping to certain subtests.

###############################################################################

### Header

# assigning and loading variables

# The PDIR variable must be assigned fist, because many of the functions and

# other variables depend on its value.

PDIR=$(pwd)

VERSION=$(cat script/version)

source script/lib/globvars.sh

# loading relevant functions

source script/lib/functions.sh

###############################################################################

### Checking current status ###

# Is there an active screen session which was initiated by bbat?

# the following doesn't work if its in the [] of an if condition some how

_screentest="$(screen -ls | grep "$SCREENSESSIONNAME")"

# checking for running subexperiments

if [ -e subexp_running ]; then

# reading path of subexperiment in variable, skipping the rest of the tests

# and moving on to the control part of this script.

SUBEXPDIR=$(cat subexp_running)

# No subexperiment - but maybe still a screen session?

elif ! [ "$_screentest" = "" ]; then

printf "There seems to be no experiment but a screen session

$SCREENSESSIONNAME running.\n"

read -p "Press enter to resume it."

resumescreen

exit 0

F.4 Appendix: bbat Source Code and Documentation pcontrol

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# no subexperiment, no screen session - a new subexperiment will be started

else

printf "There seems to be no experiment and no screen\

session $SCREENSESSIONNAME running.\n"

printf "Starting wrapper script within a new screen session."

createscreen # creating screen session

# starting wrapper script within screen session

screen -S $SCREENSESSIONNAME -X stuff "script/wrapper $PDIR\n"

# entering screen session

resumescreen

# this is all the script should do on startup

exit 0

fi

###############################################################################

### Subexperiment control ###

# Header

# reading rest of relevant variables

source $SUBEXPDIR/script/tmp/runtimeglobvars.sh

source $SUBEXPDIR/script/lib/dep_runtimeglobvars.sh

source $SCRIPTDIR/lib/SCPImessages.sh

greetingsofbender # printing license information etc.

answer=""

read -p "Hello, an experiment is running, want to control something? What?

r: resume the screen session to see what's going on

0: execute datahandler

1: jump to a specific subtest immediately

2: jump to a specific subtest after the current run of the current subtest

3: abort sub experiment immediately

4: abort sub experiment after the current subtest is completed

5: hm... I'd rather keep everything the way it is

" answer

case "$answer" in

r)

resumescreen

;;

0)

$SCRIPTDIR/datahandler "$PDIR" "$SUBEXPDIR"

;;

1)

printf "Which subtest (= which line in the runlist) would you like to

go to?\n"

read answer_two

echo "$answer_two" > $SCRIPTDIR/jumpto_imm

;;

2)

printf "Which subtest (= which line in the runlist) would you like to

go to?\n"

read answer_two

echo "$answer" > $SCRIPTDIR/jumpto_aoper

;;

3)

echo "1" > $SCRIPTDIR/abort_imm

;;

4)


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echo "1" > $SCRIPTDIR/abort_aoper

;;

5)

echo "Very well, bender will do nothing as requested."

;;

*)

echo "No valid option selected."

exit 0

;;

esac

F.4.3.2 extras

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#!/bin/bash

###############################################################################

### Extras script ###

# This script supply's tools which can be used to process the acquired data for

# a specific or all subexperiments independently of the currently running

# subexperiments and even after the complete experiment is finished.

###############################################################################

### Header ###


PDIR="$(pwd)"

PSCRIPTDIR="$PDIR/script"

source $PSCRIPTDIR/lib/globvars.sh

# The dependent variables should not be loaded, since they are meant for normal

# operation and do not work as they should in this script. If any of the

# variables may be necessary in this script, they will be assigned explicitly

# below this text.

# source $PSCRIPTDIR/script/lib/dep_runtimeglobvars.sh

source $PSCRIPTDIR/lib/functions.sh

source $PSCRIPTDIR/lib/SCPImessages.sh

EXPDIR="$PDIR/../$EXPDIR_NAME"

GNUPLOTDIR="$PSCRIPTDIR/gnuplot"

###############################################################################

### Extras ###

# checking weather or not there is an experiment folder

# which is to say weather or not the script is run from the correct location

checkexpfolder

greetingsofbender # That's always fun.

read -p "This is the extras script. Which extra would you like to see done?

1: create an overview plot for all subexperiments

2: create an ASR plot for a specific polarisation subtest

" answer

### Overview plotting ###

if [ "$answer" == "1" ]; then

cd $PSCRIPTDIR # will not work otherwise

./create_overview

exit 0

fi

### ASR plotting ###

F.4 Appendix: bbat Source Code and Documentation extras

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# TODO The following should be put into a function

if [ "$answer" == "2" ]

then

# listing all experiment folders, j and i variables are needed because

# we do not want to start our displayed list with 0

_folders=($(ls $EXPDIR))

_i=0

_j=1

_length=${#_folders[@]}

echo "The following folders were found:"

while [ $_j -le $_length ]

do

echo "$_j: ${_folders[$_i]}"

(( _i++ ))

(( _j++ ))

done

_answer=""

printf "Please enter the number of the folder you would like to use\n"

read _answer

_number=$( expr $_answer - 1 )

_FOLDER="${_folders[$_number]}"

echo $_FOLDER

# reading all files in the specified folder

_files=($(ls $EXPDIR/$_FOLDER/$CONVDATADIR_NAME/*.conv))

if [ "$_files" == "" ]; then

echo "No converted data files were found in the folder. You may need to

run datahandler first."

exit 0

fi

_i=0

_j=1

_length=${#_files[@]} # getting the number of items in the array

echo "The following files were found:"

while [ $_j -le $_length ]; do

echo "$_j: $( basename ${_files[$_i]})"

(( _i++ ))

(( _j++ ))

done

_answer=""

printf "Please enter the number of the file you would like to use\n"

read _answer

_number=$( expr $_answer - 1 )

_FILE="${_files[$_number]}"

# making directory for plot and copying templates

_ASR_PLOT_FOLDER="$EXPDIR/$_FOLDER/gnuplot/ASR_plot_$(basename $_FILE)"

# checking for existing plots

_answer=""

if [ -d $_ASR_PLOT_FOLDER ]; then

printf "There seems to be an existing plot for this datafile. Press

Enter to overwrite or input a suffix for the new plot (no spaces!).\n"

read _answer

fi

_ASR_PLOT_FOLDER="${_ASR_PLOT_FOLDER}$_answer"

mkdir -p $_ASR_PLOT_FOLDER

cp $GNUPLOTDIR/ASR/* $_ASR_PLOT_FOLDER

# making data directory and copying data file

mkdir -p $_ASR_PLOT_FOLDER/data

cp $_FILE $_ASR_PLOT_FOLDER/data/


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cd $_ASR_PLOT_FOLDER/data

# Now let's do some numbers crunching with python

# TODO This especially should go into a function.

# TODO The python code has not yet been formatted according to the coding

# style guidelines

python3 -c "import sys

import os

import glob

import csv

# Asking for user input

points = input(\"How many data points between two voltage jumps (default =

120)?\\n\")

lastocv = input(\"At which data point is the last OCV data point before the

first voltage jump? (default = 120)?\\n\")

datagap = input(\"How many data points later do you want to evaluate the

voltage? (default=1) \\n\")

area = input(\"Please input area size of electrode in cm^2 with a point as

separator (default = 3.1416).\\n\")

datasets = input(\"How many datasets are there? An input of 2 means both

positive and negative current values (default = 2).\\n\")

# Checking inputs, correcting variable type

if not points:

points = int(120)

else:

points = int(points)

if not lastocv:

lastocv = int(120)

else:

lastocv =int(lastocv)

if not datagap:

datagap = int(1)

else:

datagap =int(datagap)

if not area:

area = float(3.1416)

else:

area = float(area)

if not datasets:

datasets = int(2)

else:

datasets =int(datasets)

# reading filename

file = glob.glob(\"*.conv\") # returns a list

# defining outputfile

polaris = \"polaris.dat\"

# opening files for reading and writing

with open(file[0], \"r\") as infile, open(polaris, \"w\") as oufile:

# print(file)

dataarray = csv.reader(infile, delimiter='\t')

i = 0 # current row

j = 0 # rows since last jump

k = 0 # counting datasets.

voltagebefore = 0 # voltage before jump

voltageafter = 0 # voltage at jump

current = [] # current at jump

for row in dataarray:

i += 1

F.4 Appendix: bbat Source Code and Documentation wrapper

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if i >= ( lastocv ):

j += 1

# defining starting point for row counting

if i == ( lastocv ):

j = int(points)

# everytime the rowcount reaches the points value, you have found

the point before a jump.

if j == points:

voltagebefore = float(row[0])

j = 0

# So now we want to take the voltage after the voltage jump.

datagap defines how many lines we skip.

if j == datagap:

voltageafter = float(row[0])

current = float(row[1])

# to make sure the current density is positive

currentdensity = abs(( current / area ))

jump = ( voltageafter - voltagebefore )

# and asr should be poitive aswell...

asr = abs(( jump / currentdensity ))

k += 1

if k == 1:

jumpone = jump

curdensone = currentdensity

asrone = asr

if k == datasets:

# if only one dataset is present, then this will lead to identical

points and printing them one over the other - not pretty but works.

oufile.write (str(curdensone) + \"\\t\" + str(currentdensity) +

\"\\t\" + str(jumpone) + \"\\t\" + str(jump) + \"\\t\" + str(asrone) + \"\\t\"

+ str(asr) + \"\\n\")

k = 0

"

cd ../

./GnuPlotingScript

### Any other option chosen ###

else echo "No valid Option selected."

fi

script

F.4.4.1 wrapper

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#!/bin/bash

###############################################################################

### Wrapper script ###

# This script is called at the beginning of a subexperiment and will setup the

# necessary environment like folders, names etc. After the test is done, it

# will also call the datahandler and clean up.

###############################################################################

###############################################################################

### Header ###


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# Assigning parameters and loading variables

PDIR="$1"


source script/lib/globvars.sh

# loading relevant functions

source script/lib/functions.sh

# printing general information on this program and license information for

# the vxi11_cmd utility.

greetingsofbender

read -p "Please press Enter to continue."

newline

###############################################################################

### Setting up subexperiment environment ###

cleartmp # clearing tmp directory

checkrunthis # checking if there is only one test in the runthis folder

createsubexpdir # creating a subexperiment folders and copying files

# creating a folders in the subexperiment folder

createsubsubexpdir "test"

createsubsubexpdir "rawdata"

createsubsubexpdir "script"

cp -r $PDIR/script/* $SCRIPTDIR # Copying program to subexperiment folder. It

# will be run from there.

cp -r $PDIR/run_this_test/* $TESTDIR # copying test to the subexperiment

folder.

newline

logger "Logfile created." # Creating logfile.

###############################################################################

### Calling mainscript ###

logger "Mainscript is being started."

newline

$SCRIPTDIR/mainscript $PDIR $SUBEXPDIR

###############################################################################

### data handling an cleanup ###

# calling datahandler which will convert data and plot standard diagrams

$SCRIPTDIR/datahandler $PDIR $SUBEXPDIR

# removing writing permissions on appropriate folders of the subexperiment

logger "Making files of experiments read only. End of experiment."

chmod -R oug-w $SCRIPTDIR $RAWDATADIR $TESTDIR $SUBEXPDIR/logfile

# cleaning up

cleartmp

rm $PDIR/subexp_running

printf "

###############################################################################

### Subexperiment complete. ###

### You can close the screen session now. (Ctrl + A , \\)

###

"

F.4 Appendix: bbat Source Code and Documentation mainscript

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F.4.4.2 mainscript

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#!/bin/bash

###############################################################################

### Main script ###

# This is the main script, which is called as soon as the actual test is

# started.

# It is not started in the original folder, but in the experiment

# folder.

###

#

###############################################################################

### Header ###

# Reading Parameters and assigning variables

PDIR=$1 # Others depend on this variable - assign first

SUBEXPDIR=$2 # dito - assign second

source $SUBEXPDIR/script/lib/globvars.sh




# loading functions

source $SCRIPTDIR/lib/functions.sh

###############################################################################

### Pretesting ###

printf "

###############################################################################

### Reading test ###

\n"

echo " "

# reading the runlist, writing lines to disk, reading first line into array.

echo "The following runlist was read."

readwriterunlist

newline

# checking whether or not all programs are there

checkprogramms

newline

# any doubts?

read -p "Press enter to start the test"

# writing the path to the subexperiment folder to a file which also signals

# that a subexperiment is running.

echo "$SUBEXPDIR" > $PDIR/subexp_running

###############################################################################

### Preparing SMU

printf "

###############################################################################

### Preparing $TESTNAME \n\n"

echo "Testing for error messages."

sendtoDerGeraet "$ASK_ERROR"

echo "Resetting the SMU."

sendtoDerGeraet "$DO_RESET" > /dev/null

# sendtoDerGeraet "$ASK_ERROR" # Uncomment this line for debugging

echo "Deleting all existing programs on the SMU."

sendtoDerGeraet "$PROG_DEL"> /dev/null


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# sendtoDerGeraet "$ASK_ERROR" # Uncomment this line for debugging

echo "Create folder for experiment"

sendtoDerGeraet "$SCPI_MAKE_DIR" > /dev/null

echo "Translating and sending programs."

progtranssend

newline


###############################################################################

### Starting test ###

printf "

###############################################################################

### $(echotime) Starting $TESTNAME !\n\n"

###############################################################################

### Starting the subtest loop ###

# This loop will control the order of the subtests according to the logic of

# the runlist and the limits set within each subtest (if applicable). It will

# also contain checks for user input (aborts or jumps). This is the logical

# core of the program.

# TODO When this program is rewritten in Python, there should be a subtest

# class with subtest objects for each subtest.

### ###

while true; do

### defining the runlinearray

# This is the array which contains one line of the runlist corresponding to and

# defining a particular subtest. Additionally it holds the history of this

# subtest during this experiment.

# reading file on the disk which contains the data for the subtest to be run

readrunlinearray "$crunnumber"

# st stands for subtest. The following values are defined by one line of the

# runlist

_st_runnumber="${runlinearray[0]}" # identical to line number

_st_runname="${runlinearray[1]}" # name of the subtest

_st_progname="${runlinearray[2]}" # program to be called for subtest

_st_runtimes="${runlinearray[3]}" # times the subtest is run consecutively

_st_gotonumber="${runlinearray[4]}" # which subtest is next?

_st_gotoonfail="${runlinearray[5]}" # which subtest to got to on fail?

_st_gototimes="${runlinearray[6]}" # number of times to go to a diff.

# subtest after a fail

# c stands for the current values of these variables which describe the history

# of the subtest during this subexperiment. For description see the file

# script/lib/globvars.sh

cfailtimes="${runlinearray[7]}"

ctotalruntimes="${runlinearray[8]}"

crtsincefail="${runlinearray[9]}"

cruntimes="${runlinearray[10]}"

cgototimes="${runlinearray[11]}"

inccruntimes # increases the cruntimes

# creating the filename to store the data of this run of the subtest

nameandincdata "$_st_runname"

F.4 Appendix: bbat Source Code and Documentation mainscript

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### Initiating subtest ###

printf "

###############################################################################

### $(echotime) $_st_progname $cruntimes, total runtimes $ctotalruntimes, \

total subtest #${datanumber}\n\n"

newline

sendtoDerGeraet "$DO_RESET" > /dev/null

# sendtoDerGeraet "$ASK_ERROR" # uncomment this line for debugging

dergeraet_progexec "$_st_progname" > /dev/null


sendtoDerGeraet "$INIT" > /dev/null


logger "Init for $_st_progname $cruntimes was sent, writing to file $dataname."

newline

### Control loop ###

# controlloop checks every four seconds for fail or abort_imm

controlloop

# if the controlloop is left, then it means that the subtest should be aborted.

sendtoDerGeraet "$ABORT_ALL"


### Saving data ###

# unfortunately combining an *OPC? or *WAI command with a save command does

# not work.

if savetoDerGeraet > /dev/null; then

logger "Data has been stored on USB-Drive on SMU."

fi

### Transferring data

###

if sendtoDerGeraet "$ASK_SENS_DATA" > $RAWDATADIR/$dataname; then

logger "Data was transferred to PC."

fi


### deciding what to do next ###

# TODO This should all go into a simplified function named nexttestdecider

# which would decide which test to go to

# Priority one: Did the user request an abort of the subexperiment?

if ! [ "$abort" = "0" ]; then

break

# Priority two: Checking if the user decided to jump to a certain line.

elif ! [ "$jumpto" = "0" ]; then

case "$jumpto" in

imm)

crunnumber=$(cat jumpto_imm)

jumpto=0

rm jumpto_imm

cruntimes="0" # resetting cruntimes for this subtest

;;

aoper)

crunnumber=$(cat jumpto_aoper)

jumpto=0

rm jumpto_aoper


;;


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*)

;;

esac

# Priority three: Was a fail detected during the subtest?

elif [ "$fail" = "+1" ]; then

inccfailtimes # increasing cfailtimes

crtsincefail="0" # resetting number of runs since last fail


# checking if the gototimes are exceeded or alternatively if the there is

# no limit for the gototimes

if [ $cgototimes -lt $_st_gototimes ] || [ $_st_gototimes = 0 ]; then

inccgototimes # increases the cgototimes

crunnumber="$_st_gotoonfail" # preparing for jump to a different

# subtest

echo "Detected fail -> going to subtest $crunnumber"

# if the limit is exceeded, the test will go to the last line in the

# runlist.

else

logger " cgototimes is equal to tgototimes -> going to last line."

crunnumber="$TOTAL_RUNLINES"

fi

# Priority four: checking if the limit for consequtive runs of the subtest is

# reached

elif [ "$cruntimes" -eq "$_st_runtimes" ]; then

crunnumber="$_st_gotonumber"


fi

# Priority five: If none of the above matches - then we should simply continue

# with this subtest.

### writing runlinearray to disk ###

# transferring variables with current values to runlinearry and saving to disk

runlinearray[7]="$cfailtimes"

runlinearray[8]="$ctotalruntimes"

runlinearray[9]="$crtsincefail"

runlinearray[10]="$cruntimes"

runlinearray[11]="$cgototimes"

writerunlinearray "$_st_runnumber"

done

F.4.4.3 datahandler

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#!/bin/bash

###############################################################################

### Create Overview ###

# This script will convert raw data and then plot the default plots in three

# timescales (days, hours, seconds).

#

###############################################################################

### Header ###

PDIR=$1 # must be the first line otherwise nothing will work.

SUBEXPDIR=$2 # must be the second line otherwise nothing will work.

# checking for empty parameter - if so, then assuming the datahandler is not

F.4 Appendix: bbat Source Code and Documentation datahandler

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# called from the mainscript or not during the experiment at all.

if [ "$SUBEXPDIR" = "" ]; then

SUBEXPDIR=$(cd ..; pwd)

else

# if there was a SUBEXPDIR supplied, there should also be runtimeglobvars


fi

source $SUBEXPDIR/script/lib/globvars.sh



source $SCRIPTDIR/lib/functions.sh

###############################################################################

### Conversion and integration of data ###

printf "

###############################################################################

### Converting, integrating and plotting data ###

"

# Creating data directory for converted files

mkdir -p $CONVDATADIR

convdata # converting raw files

intcurr # integrating current

write_sum_time_chrg $CONVDATADIR # writing a file with times and charges

# needed correct files for plotting

###############################################################################

### Setting up plot environment ###

# Assigning which template to use for gnuplotting

# TODO automatic detection would be best, so for now it will not be moved to

the

# global variables.

GNUPLOTTEMPLATE=SP_template_bbat

### Setting up timescales ###

# the following while loop will run three times, one time for every timescale

# to be plotted.

# setting variables for different timescales

_timeletter=(d h s)

_timescale=(86400 3600 1)

# $_i will determine the timescale

_i=0

while [ $_i -le 2 ]; do


# function setupplotenv will create appropriate folder, copy and modify

# templates to fit the timescale supplied by the parameter

# Will also return the path to the default and the editable plotdirectory

_plotdirs=($(setupplotenv ${_timeletter[$_i]} $GNUPLOTDIR))

_plotdir_def=${_plotdirs[0]}

_plotdir_edit=${_plotdirs[1]}

# Plotting starting line of data body file

### writing body file ###

echo "

### Plot ###

plot \\" > $_plotdir_def/$GNUPLOTTEMPLATE.body

# reading addtimefile to find out individual start times and charges

while read _line ; do


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_addfileline=($_line)

# when the summarizing line is reached, you should skip it

if ! [ "${_addfileline[0]}" = "total" ] ; then

_datafilepath="../../../$CONVDATADIR_NAME/${_addfileline[0]}"

_starttime="${_addfileline[1]}"

_startcharge="${_addfileline[2]}"

writelineplotbody "$_datafilepath" "$_starttime" \

"${_timescale[$_i]}" "$_startcharge" \

"$_plotdir_def/$GNUPLOTTEMPLATE.body"

fi

done < $CONVDATADIR/$ADD_FILE_NAME

# deleting comma and backslash in last line of body files

sed -i '$ s/,\\//g' $_plotdir_def/$GNUPLOTTEMPLATE.body

# joining files to form .plt file

cd $_plotdir_def

cat $GNUPLOTTEMPLATE.head $GNUPLOTTEMPLATE.body $GNUPLOTTEMPLATE.tail \

> $GNUPLOTTEMPLATE.plt

### plotting freshly created .plt file ###

printf "Creating overview plot in [${_timeletter[$_i]}]\n"

cd $_plotdir_def

./GnuPlotingScript $GNUPLOTTEMPLATE

(( _i++ ))

done

echo "End of datahandler."

F.4.4.4 create_overview

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#!/bin/bash

###############################################################################

### Create overview ###

# This script will plot an overview for all subexperiments in one plot.

###############################################################################

### Header ###

# creating variables for directories with absolute paths

PDIR="$(pwd)/../" # gets parent directory of script.

PSCRIPTDIR="$PDIR/script"

source $PSCRIPTDIR/lib/globvars.sh

# The dependent variables should not be loaded, since they are meant for normal

# operation and do not work as they should in this script. If any of the

# variables may be necessary in this script, they will be assigned explicitly

# below.

# source $PSCRIPTDIR/script/lib/dep_runtimeglobvars.sh

source $PSCRIPTDIR/lib/SCPImessages.sh

source $PSCRIPTDIR/lib/functions.sh

GNUPLOT_DEFAULT="$PSCRIPTDIR/gnuplot/default" # path to default

OVERVIEWDIR="$PDIR../overview"

EXPDIR="$PDIR/../$EXPDIR_NAME"

# Checking for folder $EXPDIR

if ! [ -d $EXPDIR ]; then

echo "There does not seem to be a $EXPDIR_NAME folder."

echo "Are you coming from an older version of bbat and need to rename?"

exit 3

F.4 Appendix: bbat Source Code and Documentation create_overview

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fi

###############################################################################

### Creating data body ###

# Assigning wich template to use for gnuplotting

# TODO automatic detection would be best, so for now it will not be moved to

# the global variables.

GNUPLOTTEMPLATE=SP_template_bbat

### defining variables for overview plotting ###

_zerodate=0 # starting time relative to the first subexperiment

_lastcharge=0 # starting value of the charge for a subexperiment

### Setting up timescales ###

# The following while loop will run three times, one time for every

# timescale to be plotted.

# setting variables for different timescales

_timeletter=(d h s)

_timescale=(86400 3600 1)

# $_i will determine the timescale

_i=0

while [ $_i -le 2 ]; do


# function setupplotenv will create appropriate folder, copy and modfy

# templates to fit the timescale supplied by the parameter

# Will also return the path to the default and the editable plotdirectory

_plotdirs=($(setupplotenv ${_timeletter[$_i]} $OVERVIEWDIR))

_plotdir_def=${_plotdirs[0]}

_plotdir_edit=${_plotdirs[1]}

### writing body file ###

# Plotting starting line of data body file

printf "

### Plot ###

plot \\

" > $_plotdir_def/$GNUPLOTTEMPLATE.body

cd $EXPDIR

### Starting loop 1 - looping over subexperiment folders ###

echo "Determining experiment starting times and writing .body files"

for _folder in 20* ; do

### Subexperiment starting times ###

# determining differences between start of first subexperiment and all

# other sub experiments

# TODO this could be done once and written to a file instead of doing

# it for every time scale separately.

# substring extraction in bash: ${variable:offset:length}

_epocht="$(date -d "$(echo "${_folder:0:13}" | tr '_' ' ')" +%s)"

_newdate="$_epocht"

if [ "$_zerodate" = "0" ]; then

_zerodate="$_newdate" # on the first run timediff is 0

fi

_timediff=$(expr $_newdate - $_zerodate)

### Starting loop 2 - looping over .conv files ###

# Checking for folder with converted data files

if [ -d $_folder/$CONVDATADIR_NAME ] ; then

cd $_folder/$CONVDATADIR_NAME

else

newline


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echo "No folder $CONVDATADIR_NAME in $_folder. Did you execute

datahandler?"

exit 3

fi

# reading addtimefile to find out individual start times and charges

if ! [ -e $ADD_FILE_NAME ]; then

# read the files and write the summed up charges and times

write_sum_time_chrg "$(pwd)"

fi


_addfileline=($_line)

# Adding additional subexperiment starting time and charge

_datafilepath="../../../$EXPDIR_NAME/$_folder/$CONVDATADIR_NAME/

${_addfileline[0]}"

_starttime="( $_timediff + ${_addfileline[1]} )"

_startcharge="($_lastcharge + ${_addfileline[2]})"

# checking for the summarizing last line, which can not be plotted

if ! [ "${_addfileline[0]}" = "total" ] ; then

writelineplotbody "$_datafilepath" "$_starttime" \

"${_timescale[$_i]}" "$_startcharge" \

"$_plotdir_def/$GNUPLOTTEMPLATE.body"

else

# if you reached the final line, then we need to assign the

# final and unused startcharge to the _lastcharge variable used

# as the lastcharge value for the next subesperiment folder.

# TODO this is confusing ;)

_lastcharge=$(python -c "print ($_startcharge)")

fi

done < $ADD_FILE_NAME

cd $EXPDIR

done

# deleting komma and backslash in last line of body files

sed -i '$ s/,\\//g' $_plotdir_def/$GNUPLOTTEMPLATE.body

# joining files to form .plt file

cd $_plotdir_def

cat $GNUPLOTTEMPLATE.head $GNUPLOTTEMPLATE.body $GNUPLOTTEMPLATE.tail \

> $GNUPLOTTEMPLATE.plt

### plotting freshly created .plt file ###

printf "Creating overview plot in [${_timeletter[$_i]}]\n"

./GnuPlotingScript $GNUPLOTTEMPLATE

(( _i++ ))

done

echo "End of overview script."

script/lib

F.4.5.1 globvars.sh

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###############################################################################

### Global Variables

# This file contains (hopefully) all global variables and constants used in

# the program and which do not depend on the values of other variables. These

# variables are listed instead in script/lib/dep_runtimeglobvars.sh

# Some CONSTANTS and variables are preassigned in this file, some will be

F.4 Appendix: bbat Source Code and Documentation globvars.sh

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# assigned during runtime and are commented out here, so that they will not be

# overwritten on calling this file. If constants are assigned during runtime,

# they will be made read-only then.

###############################################################################

### preassigned ###

# variables

fail="+0" # variable for fail status, preassigned to "no fail detected"

stat="1152" # variable for status of der Geraet, preassigned to "busy"

# subtest variables

runlinearray=() # array which stores the instructions read from the runlist

crunnumber="1" # runnnumber, the line with which to start

cfailtimes="0" # number of times this Test has failed

ctotalruntimes="0" # how many times has the actual line been run in total?

crtsincefail="0" # How many times did this line run since it last failed

cruntimes="0" # How many times has this line been run consecutively?

cgototimes="0" # How many times did this test go to a different line?

abort="0" # abort test?

jumpto="0" # jumpto instruction given?

# variables for file names to which the data is written

dataname=""

datanumber=""

# misc

sophiasaid="" # adds an s to corrects output to singular or plural

# CONSTANTS

readonly SCREENSESSIONNAME="bbat_session" # screen session name

readonly DIGITS="4" # for leading number in file names

readonly EXPDIR_NAME="subexperiments" # name for folder of subexperiments

readonly RAWDATADIR_NAME="rawdata" # name for folder of raw data files

readonly CONVDATADIR_NAME="convdata" # name of the folder for converted

# data files

# name of the file that contains the starting times and charges for plotting

# data files

readonly ADD_FILE_NAME="sum_time_chrg.bbatplot"

###############################################################################

### assigned during runtime ###

#

### CONSTANTS

# Given as parameter at the beginning of a script

# PDIR="" # absolute path to bbat folder within the experiment folder

# SUBEXPDIR="" # absolute path to the folder containing all subexperiments

# PSCRIPTDIR="$PDIR/script" # scriptdir in parent working directory

# Read from specific file

# VERSION="" # version of bbat, read from file script/version

#

# stored in /tmp/runtimevars.sh

# SUBEXP_NAME="" # name of the current subexperiment

# SUBEXPDIR_NAME="" # name of the subexperiment director

# TESTNAME="" # name of the test(sequence) to be run.

# PROGDIR="" # absolute path to the folder where all progs are found

# TOTAL_RUNLINES="0" # total (run)lines in the test


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F.4.5.2 dep_runtimeglobvars.sh

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###############################################################################

### Dependent Global Runtime Variables ###

# This file contains variables and constants that have to be set during

# runtime.

# This is mostly because the absolute experiment and script directory and the

# corresponding variables can only be known after the startup process.

# This means that variables needed for the assignment have to be assign prior

# to calling this file, either by means of parameters or by means of the file

# /tmp/runtimevars.sh created during runtime.

###

# misc CONSTANTS

readonly SCRIPTDIR="$SUBEXPDIR/script" # should be first, has dependent vars

readonly SETTINGSDIR="$SCRIPTDIR/settings"

readonly CONVDATADIR="$SUBEXPDIR/$CONVDATADIR_NAME"

readonly RAWDATADIR="$SUBEXPDIR/$RAWDATADIR_NAME"

readonly GNUPLOTDIR="$SUBEXPDIR/gnuplot"

readonly GNUPLOT_DEFAULT="$SCRIPTDIR/gnuplot/default" # path to default

# printing template

readonly TESTDIR="$SUBEXPDIR/test"

readonly TMPDIR="$SCRIPTDIR/tmp"

readonly IP=$(cat $SETTINGSDIR/ip) # IP-address of der one and only

readonly DER_GERAET="$SCRIPTDIR/vxi11_cmd $IP" # der one and only Geraet

# SCPI message to create the experiment folder on der one and only Geraet

readonly SCPI_MAKE_DIR=":MMEM:MDIR \"USB:\\$EXPDIR_NAME\";:MMEM:MDIR

\"USB:\\$EXPDIR_NAME\\$SUBEXPDIR_NAME\";:MMEM:MDIR

\"USB:\\$EXPDIR_NAME\\$SUBEXPDIR_NAME\\rawdata\";*OPC?

q

"

F.4 Appendix: bbat Source Code and Documentation functions.sh

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F.4.5.3 functions.sh

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###############################################################################

### Bash Functions ###

# Put the following descriptor at the first line inside every function... well

# at least if the function contains something that corresponds to any of the

# fields.

###


# Globals:


# Parameters:


# Returns:


###

###############################################################################

### General functions ###

greetingsofbender() {

printf "

###############################################################################

### bbat v. $VERSION ###

### by Benedikt Burgenmeister - [email protected] ###

###############################################################################

() Additional credit to Steve D. Sharples,

|| [email protected].

_||_ His \"VXI11 Ethernet Protocol for Linux\" is used in this

/ \\ programm. It was published under the GNU GENERAL PUBLIC

| ______|_ LICENSE Version 2 and obtained from

| (__(.)(.)) http://optics.eee.nottingham.ac.uk/vxi11/

| _____| ~ on 2013/10/17.

| (-|-|-| ~

|________| ||

/__________\\ /_\\

_| _______ |_ _| B|

/_| | | |_\\/_|__|

/ /| | o| |\\_|/ Mr B. says: \"Stop whining and get the test done.\"

###############################################################################

"

}

newline() {

printf "\n"

}

logger() {

###

# logs messages inside the experiment directory.

# Globals:

# $SUBEXPDIR

# Parameters:


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# $1: message to log

# Returns:

# -

###

local _message=$1 # message that should be logged

local _timestamp=$(date +%Y/%m/%d\ \ \ %H\:%M\:%S)

# Checking if the file exists

if ! [ -e $SUBEXPDIR/logfile ]; then

echo "No logfile, creating it."

printf "$SUBEXP_NAME \n\n" > $SUBEXPDIR/logfile

fi

# logging the message

echo "$_timestamp $_message" >> $SUBEXPDIR/logfile

echo "logging:\"$_timestamp $_message\""

}

echotime() {

echo "$(date +%Y/%m/%d\ \ \ %H\:%M\:%S)"

}

###############################################################################

### extras script ###

checkexpfolder() {

###


# Globals:

# $PDIR

# $EXPDIR_NAME

# $EXPFOLDER is assigned

# Parameters:

# -

# Returns:

# -

###

if ! [ -d $PDIR/../$EXPDIR_NAME ]; then

printf "Could not find the ../$EXPDIR_NAME folder.\n"

printf "Did you run the script from within the main folder?\n"

exit 3

fi

}

###############################################################################

### wrapper scrip ###

createscreen() {

###

# create screen session with a specific name

# Globals:

# $SCREENSESSIONNAME

# Parameters:

# -

# Returns:

# -

###

echo "Creating screen session: $SCREENSESSIONNAME"

screen -dmS $SCREENSESSIONNAME -c script/settings/screen/screenrc


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}

resumescreen() {

###

# resume screen session with a specific name

# Globals:

# $SCREENSESSIONNAME

# Parameters:

# -

# Returns:

# -

###

echo "resuming screen session: $SCREENSESSIONNAME"

screen -x "$SCREENSESSIONNAME"

}

checkrunthis() {

###

# See if there is more than one folder/file in runthis.

# Globals:

# $PDIR

# $runthis

# Parameters:


# Returns:


# needs

# assigns $TESTNAME

###

cd $PDIR/run_this_test

local _runthis=($(echo *))

cd $PDIR

if [ "${_runthis[1]}" != "" ]; then

printf "Multiple tests were found (${_runthis[*]}) though only one is

allowed.

Quitting.\n"

exit 0

else

printf "The following test was found: $_runthis \n"

fi

}

createsubexpdir() {

###

# creates subxperiment directory

# Globals:

# rtglobvar()

# $EXPNAME

# $SUBEXPDIR - assigned

# $SUBEXPDIR_NAME - assigned

# $TESTDIR - assigned

# $RAWDATADIR -assigned

# Parameters:

# -

# Returns:

# -

###

echo "Insert a subexperiment name (blanks will produce errors - don't):"


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read SUBEXP_NAME

_date=$(date +%Y%m%d_%H%M)

readonly SUBEXPDIR="$PDIR/../$EXPDIR_NAME/${_date}_$SUBEXP_NAME"

# TODO This doesn't look quite elegant...

local _mkdirsays=$(mkdir -pv $SUBEXPDIR)

if [ "$_mkdirsays" = "" ]; then

echo "Folder exists. Quitting."

exit 3

else

rtglobvar "SUBEXP_NAME" "$SUBEXP_NAME"

rtglobvar "SUBEXPDIR_NAME" "${_date}_$SUBEXP_NAME"

printf "\nFolder ../$EXPDIR_NAME/$SUBEXPDIR_NAME was created.\n"

fi

}

createsubsubexpdir() {

###

# creates a subfolders within the subexperiment folder and assign the global

# variable.

# Globals:

# $SUBEXPDIR

# Parameters:

# $1 name of the directory to be created

# Returns:

# -

###

local _dirname="${1}"

local _dirvar="${1^^}DIR" # ^^ is bash syntax to make the string in the

# variable upper case

local _dirpath="$SUBEXPDIR/$_dirname"

mkdir -p $_dirpath

echo "Folder $_dirname was created."

# assigning varibale with variable name - need to use declare and -g(lobal)

declare -g $_dirvar="$_dirpath"

}

rtglobvar() {

###

# used to define a global variable during runtime and write it to the file

# $SUBEXPDIR/tmp/runtimeglobvars.sh

# Globals:

# -

# Parameters:

# $1=varname

# $2=contentofvar

# $SUBEXPDIR

# Returns:

# -

# checking for $SUBEXPDIR

###

if [ "$SUBEXPDIR" = "" ]; then

printf "Internal error: function rtglobvar was called even though

\$SUBEXPDIR is empty. Quitting.\n"

exit 3

else

# TODO can the global variable TMPDIR be used here?

local _tmpdir="$SUBEXPDIR/script/tmp"

mkdir -p $_tmpdir


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fi

echo "$1=\"$2\"" >> $_tmpdir/runtimeglobvars.sh

source $_tmpdir/runtimeglobvars.sh

}

cleartmp() {

###

# clears the tmp directory

# Globals:

# $PDIR

# Parameters:

# -

# Returns:

# -

###

rm -f $PDIR/script/tmp/*

}

###############################################################################

### mainscript ###

checkprogramms() {

###

# tests if all programs are there

# Globals:

# $TOTAL_RUNLINES

# Parameters:

# -

# Returns:

# -

###

cd $TESTDIR/$TESTNAME/progs

local _i=1

for ((_i=1; _i <= $TOTAL_RUNLINES; _i++ )); do

readrunlinearray "$_i"

local _progname="${runlinearray[2]}"

if ! [ -e $_progname ]; then

echo "Program $_progname is missing, quitting."; exit 3;

fi

done

echo "All programs were found."

cd $SCRIPTDIR

}

readwriterunlist() {

###

# Reads the runlist and writes single lines to files.

# Adds trailing zeros for additional variables cruntimes ... see below

# Globals:

# rtglobvar()

# $SCRIPTDIR

# $TESTDIR

# $TOTAL_RUNLINES assigned

# cfailtimes - ${runlinearray[7]}

# ctotalruntimes - ${runlinearray[8]}

# crtsincefail - ${runlinearray[9]}

# cruntimes - {runlinearray[10]}

# cgototimes - {runlinearray[11]}


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# Parameters:

# -

# Returns:

# -

###

# finding out TESTNAME and assigning variable

cd $TESTDIR

rtglobvar "TESTNAME" "$(echo *)"

cd $SCRIPTDIR

echo "Testname is $TESTNAME."

# reading runlist

declare -A runarray=() #indexed array deffinieren

local _i=0

local _line=""

# reading lines and write to files


# checking for comments

if ! [ "$(echo "$_line" | cut -c1 )" = "#" ]; then

(( _i++ ))

# two zeros for additional variables (see above)

echo "$_line 0 0 0 0 0" > $TMPDIR/line_${_i}

echo "$_line"

(( TOTAL_RUNLINES++ ))

fi

done < $TESTDIR/$TESTNAME/runlist

rtglobvar "TOTAL_RUNLINES" "$TOTAL_RUNLINES"

}

readrunlinearray() {

###

# Reads the line that defines a test. Aborts if the next step is to abort.

# Globals:

# -

# Parameters:

# $1 = line to read, may contain a if the next step is to abbort.

# Returns:

# -

###

if [ "$1" = "a" ]; then

logger "The next step is to abort the test. Aborting."; break;

else

runlinearray=($(cat $TMPDIR/line_$1))

fi

}

writerunlinearray() {

###

# Writes the line that defines a test and the additional variables in the array

# which are modified during runtime.

# Globals:

# -

# Parameters:

# $1 = line to read, may contain a if the next step is to abbort.

# Returns:

# -

###

# needs linenumber

echo ${runlinearray[*]} > $TMPDIR/line_$1


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}

progtranssend() {

###

# Removes comments from program files and translates the lines in SCPI

# commands that der one and only Geraet understands.

# Globals:

# $TESTDIR

# $TESTNAME

# $PROGDIR - assigned

# $PROGRAM_NAMES

# Parameters:

# -

# Returns:

# -

###

cd $TESTDIR/$TESTNAME/progs

local _i=0

rm -f *_transl

local _PROGRAM_NAMES=($(echo *)) # read existing programs

# looping over program files, translating and sending them

while [ -e "${_PROGRAM_NAMES[$_i]}" ] ; do

local _program="${_PROGRAM_NAMES[$_i]}"

(( _i++ ))

# writing SCPI header for program

echo ":PROG:NAME \"$_program\"" > "${_program}_transl"

echo ":PROG:DEF #218:FORMAT:DATA ASCII" >> "${_program}_transl"

# reading lines of file

while read line ; do

# ignoring comments

if [ "$(echo "$line" | cut -c1 )" != "#" ]; then

# counting characters per line

_charperline=$(expr $(expr length "$line") )

_digits=3

# formatting the number of lines to have three digits

_charperline_f=$(printf "%.${_digits}i\n" $_charperline)

# and writing SCPI message to file

echo ":PROG:APP #3$_charperline_f$line" >> "${_program}_transl"

fi

done < $_program

# writing final q which quits the transfer program

echo "q" >> "${_program}_transl"

# sending

sendtoDerGeraet "$(cat ${_program}_transl)"

echo "${_program} was translated and sent."

done

cd $SCRIPTDIR

}

sendtoDerGeraet() {

###

# Notice the exception in the naming of the function for der one and only

# Geraet.

###

# Used to send SCPI messages do der one and only Geraet

# Globals:

# $DER_GERAET

# Parameters:


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# $1 SCPI message for der Geraet

# Returns:

# -

###

echo "$1" | $DER_GERAET

}

dergeraet_progexec() {

###

# Executes a program on der one and only Geraet given by the parameter $1

# Globals:

# sendtoDerGeraet()

# Parameters:

# $1 = name of program stored on der Geraet to be executed

# Returns:


###

sendtoDerGeraet ":PROG:NAME \"$1\";:PROG:EXEC;*OPC?

q

"

}

nameandincdata() {

###

# Assigns the dataname variable and increases the counting for the datafiles.

# Globals:

# see below

# Parameters:

# $1 name of the subtest that is currently running

# Returns:

# -

###

local _testrunname=$1

# the following does not work with ((++)) because of 4 digits format

datanumber=$(expr $datanumber + 1)

# the following works only if $datanumber is not in the 4 digit format already

datanumber=$(printf "%.${DIGITS}i\n" $datanumber)

# calculating the times the battery was charged and discharged

cycltimes=$(expr $cfailtimes + 1)

# TODO This format "might" be confusing

dataname="${datanumber}_${_testrunname}_${cycltimes}_${ctotalruntimes}.

${crtsincefail}.${cruntimes}.dat"

}

inccruntimes() {

###

# Increases all numbers which are counting the current runtimes.

# Globals:


# Parameters:

# -

# Returns:

# -

###

(( ctotalruntimes ++ ))

(( crtsincefail ++ ))

(( cruntimes ++ ))

}


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inccgototimes() {

###

# increases the counter for the times the program was ordered to go to a

# certain line

# Globals:

# see below

# Parameters:

# -

# Returns:

# -

###

(( cgototimes ++ ))

}

function inccfailtimes {

###

# increases the counter for the times a fail was detected

# certain line

# Globals:

# see below

# Parameters:

# -

# Returns:

# -

###

(( cfailtimes ++ ))

}

controlloop() {

###

# controls weather or not a fail was detected and if an abort_imm was detected.

# Globals:

# sophiasays()

#

# Parameters:

# -

# Returns:

# -

###

# Here is a short dictionary what the numbers returned by der one and only

# Geraet are telling us about its status. The values are additional!

# 2 Ch1 Trans Idle

# 16 Ch1 Acquire Idle

# 32 waiting for transition trigger

# 4 waiting for Acquire trigger

# 128 Ch2 Trans Idle

# 1024 Ch2 Acquire Idle

# This means when operating in single channel mode, returning the following

# values, der one and only Geraet is trying to tell us it is:

# 1152 busy

# 1170 idle

# 1188 waiting for something

# So far I have not found other modes.

# If the loop is not paused inbetween, it will run 93 times in 20 s,

# corresponding to a response time of about 0.2 seconds.

# During this test, no influence on the measurement undertaken during that

# moment was observed.

###


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echo "Checking every 3 seconds if limit is failed and if abbort_imm was sent."

local _i=0

while true; do

# waiting for 3 seconds to give der Geraet some resti

# The sleep command is placed at the beginning of the loop to allow

# for an "init" command to take effect prior to checking the status.

sleep 3

# Getting limit status and general status

fail=$(sendtoDerGeraet "$ASK_FAIL_LIM1")

stat=$(sendtoDerGeraet "$ASK_STATREG")

(( _i++ ))

# checking if an abbort was send from the user

if [ -e abort_imm ]; then

logger "Abort_imm was detected."

abort="imm"

break

fi

# TODO I am not sure why this if statement does also check $abort

if [ -e abort_aoper ] && ! [ "$abort" = "aoper" ]; then

echo "abort_aoper was detected."

logger "Abort_aoper was detected."

abort="aoper"

fi

if [ -e jumpto_imm ] ; then

logger "jumpto_imm was detected."

jumpto="imm"

break

fi

# TODO I am not sure why this if statement does also check $jumpto

if [ -e jumpto_aoper ] && ! [ "$jumpto" = "aoper" ]; then

logger "jumpto_aoper was detected."

jumpto="aoper"

fi

if [ "$fail" = "+1" ];

then break

fi

# if der Geraet is

# neither busy, nor idle, nor waiting, something is surely wrong!

if [ "$stat" != "1188" ] && [ "$stat" != "1152" ] && [ "$stat" != "1184" ];

then break;

fi

done

# checking with sophia if we should add an s in the following sentence

sophiasays "$_i"

echo "Limit and status was checked $li time${sophiasaid}."


newline

# logging

logger "Status register bit is $stat, LIM1 Fail is $fail."

}

sophiasays() {

###

# This function has a close eye on grammatical correctness.

# Globals:

# $sophiasaid - assigned

# Parameters:

# $1 - how many objects are described in the concerning sentence.


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# Returns:

# -

###

if [ $1 = "1" ] ; then

sophiasaid=""

else

sophiasaid="s"

fi

}

OPCtestDerGeraet() {

###

# Checking the OPC status of der one and only Geraet.

# TODO describe what the OPC status is telling us.

# Globals:

# sendtoDerGeraet()

# Parameters:

# -

# Returns:

# -

###

# testing if SMU is done.

# needs function sendtoDerGeraet

echo "The SMU was asked to send a signal when all processes are completed."

local _done=0

while [ "$_done" != "1" ] ; do

_done=$(sendtoDerGeraet "$ASK_OPC")

echo "*OPC? answer is: $_done"

done

logger "*OPC? answer is: $_done"

}

savetoDerGeraet() {

###

# Saves the current data on the USB drive connected to der one and only Geraet

# Globals:

# sendtoDerGeraet()

# $dataname

# $RAWDATADIR

# $TMPDIR

# Parameters:

# -

# Returns:

# -

###

# saves files on usb drive at DerGeraet

local _save=":MMEM:CDIR \"USB:\\$EXPDIR_NAME\\$SUBEXPDIR_NAME\\rawdata\";

:MMEM:STOR:DATA:SENS \"$dataname\";*OPC?

q

"

sendtoDerGeraet "$_save" #> $TMPDIR/outputdump


}

###############################################################################

### datahandler ###

convdata() {


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###

# Splits raw data in lines and changes separator from "," to tab

# Globals:

# $RAWDATADIR

# $CONVDATADIR

# Parameters:

# -

# Returns:

# -

###

cd $RAWDATADIR

if [ "$(echo *)" = "*" ]; then

echo "Datahandler: no files found."; exit 3

fi

# splitting raw data in lines and changing separator from "," to tab

local _file=""

for _file in *.dat ; do

if ! [ -e $CONVDATADIR/$_file.conv ]; then

cat $_file | fold -b -w 84 | tr ',' '\t' > $CONVDATADIR/$_file.conv

fi

done

echo "Data was folded and kommas were replaced with blanks."

}

intcurr() {

###

# Integrates the current and saves the charge to a file dataname.conv.int

# Globals:

# $CONVDATADIR

# Parameters:

# -

# Returns:

# -

###

cd $CONVDATADIR

echo "Charge is being integrated

"

# clearing .tmp files which might be left over from an aborted integration

rm -f *.tmp

# Integration was the clear bottleneck in bash and also easier in python

# TODO formatting according to code style guidelines

python3 -c "import sys

import os

import glob

import csv

filelist = glob.glob(\"*.conv\") #returns a list of files

for file in filelist:

if not(os.path.isfile(file + \".int\")): # checking for exiting .int file

tempfilename = file + \"int.tmp\"

intfile = file + \".int\"

lastcharge = 0

lasttime = 0

with open(file, \"r\") as convfile, \

open(tempfilename, \"w\") as tempfile:

dataarray = csv.reader(convfile, delimiter='\t')

for row in dataarray:

time = float(row[3])

current = float(row[1])


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charge = ((time - lasttime) * current + lastcharge)

tempfile.write(str(time) + \"\\t\" + str(charge) + \"\\n\")

lasttime = time

lastcharge = charge

os.rename(tempfilename, intfile)

"

}

setupplotenv() {

###

# Creates directories and copies default templates for gnuplotting

# Globals:

# $GNUPLOTDIR # path to the directory where the prints will go

# $GNUPLOT_DEFAULT # path to the default templates

# Parameters:

# $1 letter to add to directory name

# $2 absolute path to the plotting directory

# Returns:

# 1: _plotdir_def # plot directory "default"

# 2: _plotdir_edit # plot directory "editable"

###

local _plotdir_def="$2/plot0_$1/default"

local _plotdir_edit="$2/plot0_$1/editable"

# creating directories

mkdir -p $_plotdir_def

mkdir -p $_plotdir_edit

# returning paths to default and editable directories

echo "$_plotdir_def $_plotdir_edit"

# copy templates to default

cp $GNUPLOT_DEFAULT/* $_plotdir_def/

# replacing the x label with the appropriate one

local _head="$_plotdir_def/$GNUPLOTTEMPLATE.head"

sed -i "s/will be set by script/time in \[$1\]/g" $_head

# copy templates and link template.body in editable to default

cp -u $GNUPLOT_DEFAULT/* $_plotdir_edit/

echo "here"

ln -sfrT $_plotdir_def/$GNUPLOTTEMPLATE.body \

$_plotdir_edit/$GNUPLOTTEMPLATE.body

local _head="$_plotdir_edit/$GNUPLOTTEMPLATE.head"

sed -i "s/will be set by script/time in \[$1\]/g" $_head

}

write_sum_time_chrg() {

###

# Writes the starting times and the cumulated charges that need to be added to

# each datafile for a subtest to get an overview over the whole subexperiment.

# Globals:

# $ADD_FILE_NAME - the name of the file to be written

# Parameters:

# $1 absolute path to the convdata

# Returns:

# -

###

# saving starting directory

local _startdirectory=$(pwd)

# changing to working directory

cd $1

# removing old add_file


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rm -f $ADD_FILE_NAME

local _file=""

# setting up variables for summed up times and charges

local _sumcharge=0

local _sumtime=0

for _file in *.conv ; do

# writing summed up charges and times to file

printf "$_file\t$_sumtime\t$_sumcharge\n" >> $ADD_FILE_NAME

### determining next sumtime ###

# loading last line of datafile in an array

local _lastlinearray=($(tail -n 1 $_file))

# extractig duration of subtest = last time value of this datafile

local _addtime=$(echo ${_lastlinearray[3]})

# calculating total amount of time to be added to next datafile

# python is much more competent in this discipline

local _sumtime=$(python -c "print (${_sumtime})+(${_addtime})")

# deleting array

unset _lastlinearray

### Determining next sumcharge ###

if [ -e ./$_file.int ]; then

# reading last line of integration file

local _lastlinearray=($(tail -n 1 $_file.int))

# extracting total charge value of this file

local _addcharge=$(echo ${_lastlinearray[1]})

# calculating total amount of charge to be added to next datafile

local _sumcharge=$(python -c "print ($_sumcharge)+($_addcharge)")

# deleting array

unset lastlinearray

else

echo "Could not find $file.int ."

exit 3

fi

done

# adding a final line for the total experiment duration and total experiment

# time

printf "total\t$_sumtime\t$_sumcharge\n" >> $ADD_FILE_NAME

# and changing back to start directory.

cd $_startdirectory

}

writelineplotbody() {

###

# Writes three lines of a body file for gnuplotting of potential, current and

# charge

# Globals:

# $GNUPLOTDIR # path to the directory where the prints will go

# $CONVDATADIR # path to converted data files

# Parameters:

# $1 file path including name

# $2 time to add

# $3 timescale

# $4 charge to add

# $5 out file

# Returns:

# $1 line to print in file

###

# Writing separator

F.4 Appendix: bbat Source Code and Documentation SCPImessages.sh

269

F.4.5.4 SCPImessages.sh

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###############################################################################

### SCPI Messages ###

# This file contains variables which contain an SCPI command with an additional

# "q" to quit the interface program

# Are there any errors?

ASK_ERROR=":SYST:ERR:ALL?

q

"

# Get the status of the current program.

ASK_PROGSTAT=":PROG:STAT?

q

"

# Get data stored in the buffer.

ASK_SENS_DATA=":SENS:DATA?

q

"

# Resetting der Geraet and asking for a signal as soon as all commands are done

DO_RESET="*RST;*OPC?

q

"

# Asking der Geraet to return a number describing its status.

ASK_STATREG=":STAT:OPER:COND?

q

"

# Has the device failed the limit 1 test?

ASK_FAIL_LIM1=":CALC:LIM1:FAIL?

q

"



q

"



q

"

# Send the start signal for channel 1.

INIT=':INIT (@1);

q

'

# Returns 1 if all commands have been processed.

ASK_OPC="*OPC?;

q

"

# Delete all programs stored in der one and only Geraet.

>

804

>

805

>

806

echo "\"$1\" using (( \$4 + $2) / $3 ):1 with lines linestyle 1 axes x1y1,\\"

>> $5

echo "\"$1\" using (( \$4 + $2) / $3 ):2 with lines linestyle 2 axes x1y2,\\"

>> $5

echo "\"$1\" using (( \$1 + $2) / $3 ): (( \$2 + $4 ) * coulscal ) with lines

linestyle 3 axes x1y1,\\" >> $5

}


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PROG_DEL=":PROG:DEL:ALL

q

"

# Abort all measurements immediately.

ABORT_ALL=":ABOR:ALL

q

"

script/gnuplot

F.4.6.1 GnuPlottingScript

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#!/bin/bash

###############################################################################

### GnuPlottingScript ###

# Small script that will assemble a *.plt file from a *.head file containing

# all settings on what the plot will look like, the *.body file, which contains

# all information on the data files, and a *.tail, which will take care of

# producing both .eps and .pdf files both in a cropped and an uncropped

# version. A note for MS Word users: You can put an .eps file directly into

# newer versions of word. It will look crappy in there, because you only see

# the embedded preview. However, on printing or creation of a *.pdf, the

# quality will be much better than for standard bitmaps/jpgs since it is a

# vector based graphic.

TEMPLATE=$1

if [ "$TEMPLATE" = "" ]; then

printf "No template was given as parameter.\n"

printf "Using name of template that was used to create *.plt file within

this directory.\n"

TEMPLATE=$(echo *.plt | sed 's/....$//')

fi

# assembling .plt file

cat $TEMPLATE.head $TEMPLATE.body $TEMPLATE.tail > $TEMPLATE.plt

# and plotting

gnuplot "$TEMPLATE.plt"

F.4.6.2 SP_template

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###############################################################################

### .head file for GnuPlottingScript supplied with bbat ###

# This file contains all settings which determine what the plot will look like.

# For more information see the "GnuPlottingScript".

#

###############################################################################

### Header ###

set encoding utf8

reset # clear all previous settings

outputfile = "overview" # defining a variable for the output

set output outputfile # making gnuplot print to the file

###############################################################################

### Settings ###

F.4 Appendix: bbat Source Code and Documentation SP_template

271

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### Font type and size, size of print

# Please note that somehow in eps graphics, the actual font size will be half

# of what you put here.

set terminal postscript eps enhanced font "Arial,24" size 25cm,16cm color

### margins ###

# You might need to experiment with these values

# set tmargin 2

# set bmargin 1

# set lmargin 1

set rmargin 12 # necessary to not cut numbers in half on the y2 axis

### Graphs - look ###

# Settings style of different lines.

# style 1 is used for the potential

# style 2 is used for the current

# style 3 is used for the charge

set style line 1 linetype 1 linecolor rgb "orange-red" linewidth 4

set style line 2 linetype 1 linecolor rgb "dark-blue" linewidth 4

set style line 3 linetype 3 linecolor rgb "dark-green" linewidth 4

# uncomment and modify to get a key

# set key bottom right

unset key

# showing a grid above all other plotted lines.

set grid front

### Graphs - data representation ###

# Insert Factor for the scaling of the charge plot in coulomb

# please make sure to also adjust the label of the x axes

coulscal = 0.01

### x axis - time

# set xrange [0:8000] # uncomment and modify to plot specific area

set xtics # 100 # you can also set the spacing (!) of tics

set mxtics # 5 # you can also set the number (!) of minor tics

set format x "%.1f" # general style and number of digits after comma

set xlabel "will be set by script" # leave this unchanged and the label

# will be set by the script

### y axis - potential and charge

set yrange [-3:3] # modify to match your needs

set ytics nomirror # 100 # you can also set the spacing (!) of tics

set mytics # 5 # you can also set the number (!) of minor tics

set ylabel "potential [V] and charge [x100 C]" # modify if you changed coulscal

set format y "%.2f" # general style and number of digits after comma

### y2 axis - current

set y2range [-0.003:0.003] # modify to match your needs - I would recommend

# at least having the zero at the same level as on

# the y axis

set y2tics # 100 # you can also set the spacing (!) of tics

set my2tics # 5 # you can also set the number (!) of minor tics

set y2label "current [A]"

set format y2 "%.4f" # general style and number of digits after comma


272

273

G Conclusion and Outlook

In this work, a tool was presented, which gives access to an estimate for the economic potential of

specific battery chemistries. Applied to our IL based batteries and considering only the energy densities

and the cost for the active materials per stored energy, all proposed systems seemed viable, when

considering the all vanadium RFB as an established reference technology.

The results obtained through this tool also revealed the scope of the economic potential of the

membrane-free IL-RFB concept, which is due to a competitive price and a very high theoretical energy

density for both aluminium and tin based systems. The All-Mn Hyb-IL-RFB was also identified to offer

competitive characteristics, however, for all battery systems the price of the [cat]X salt was identified

as the main cost determining factor and should ideally be decreased.

Ionic liquids based on the combination of organic halide salts and I2Cl6 were first investigated in this

work as a possible electrolyte for a membrane-free IL-RFB. However, a battery test revealed iodine as

a reduction product in the discharged state. Based on this finding, it was decided that the well

characterized polybromides would be a better choice for the investigation of an inherently challenging

battery concept.

The chloroiodate compounds were investigated nevertheless, since they still seemed attractive for the

use in other batteries, which led to the finding of experimental evidence for the hitherto unknown

[I2Cl7]– anion. The experimental study included mixtures of [HMIM]Cl, [BMP]Cl and [NEt4]Cl (in

cooperation with Karsten Sonnenberg, AG Riedel, FU Berlin) with 0.5, 1.0 and 1.5 equivalents of I2Cl6

and was supplemented with quantum-chemical calculations both to obtain theoretical Raman spectra

and a deeper insight in the observed instability of the compounds. By calculating minimum structures

for anions containing iodine(I) and iodine(III) in the series [IxClx+y+1]– (x = 1,2,3, y = 0 … 2x), it was found

that the tendency for the elimination of dichlorine increases with the number of iodine and the number

of chlorine atoms contained in the anion. This is in accordance with the observation that [BMP][I2Cl7],

which is a homogeneous liquid at room temperature, is only stable if contained in a gas tight vessel.

Mixtures of [NEt4]Cl with one equivalent of I2Cl6 are liquid as well, despite their symmetrical cation,

which on one hand is a good sign for the intended use in redox flow batteries. On the other hand, the

instability of these compounds might be contradictory with their wide spread use for this application.

The concept for a membrane-free Sn/Br2 Hyb-IL-RFB was investigated starting with the synthesis of

novel bromostannate(IV) ILs, studying their phase behaviour and their mixtures with bromine, and

finally building batteries based on the synthesized ILs. The initially observed discharge currents

G Conclusion and Outlook

274

obtained in cells consisting of polybromide ILs, a tin, and a graphite electrode, were encouraging

despite the low electrochemical efficiency determined for these first experiments. However, all

attempts to charge this type of membrane-free battery, or even a battery set up with the same

chemicals and using a membrane, were unsuccessful. In some of these charging experiments evidence

for the formation of SnBr2 was found via Raman spectroscopy, which could indicate that the reduction

process of bromostannates(IV) to yield a deposit of elemental tin is problematic. Further research is

needed to better understand this behaviour.

The results obtained during in the preliminary assessment of the feasibility of an All-Mn Hyb-IL-RFB

were more promising. Though chemical attempts in synthesizing chloromanganate(IV) ILs were

unsuccessful and yielded at best manganese(III) compounds, the OCV obtained for a first All-Mn

battery was 3.0 V, which encourages further research. Even cycling in a very limited SOC range was

possible.

All battery tests were controlled using a software programmed as part of this thesis. The program was

proven to be reliable in operation and is intended to be the base for the planned integration of pumps

and thermostats in combination with the newly developed flow test-cell.

At the beginning of the work on this thesis, only very basic knowledge on the performance and

chemical characteristics of IL batteries existed, most of which had resulted from the two diploma

theses written on the topic. Through the combined efforts of all members of the IL-RFB project, a far

greater understanding of the potential and the limitations of the technology was achieved. Based on

the knowledge gathered to this point, it seems to me that a shift in the focus of this technology might

be necessary in future research.

In the introduction to this thesis, general considerations in respect to the physical design of flow

batteries in comparison with classical batteries based on solid active materials were laid out. It might

be that flow reactors designed for vanadium chemistry and a flow setup in general are not suited for

the use with ILs. The encountered conductivities of the halometallate ILs are too low to reach

competitive ASR values, even when considering the higher surface area of graphite felts, which might

be used in the future, and assuming that the reversible deposition and dissolution of metal in them

can be achieved. The resistance of the membrane is a problem at this point as well.

The membrane free variant of the setup might be a feasible alternative. However, the challenges

associated with the depositions of tin starting from the oxidation state IV are not likely to be overcome

without a sizeable amount of research or at all. The deposition from tin species in the oxidation state

275

II might be an alternative, though not for a membrane free system, where the respective

halostannate(II) would be oxidized by the halogen right away. Nevertheless, the investigation on the

membrane-free Sn/Br2 IL battery has led to a strongly increased understanding of the general principle

of a membrane free IL battery and on the effects of mixing halometallate ILs with halogens.

A variant of the membrane-free setup could be feasible for other IL chemistries, though. On reaction

of halogens with a metal, the metal halide is formed. If a saturated solution of the respective metal

halide in a polyhalide IL were prepared and kept saturated by keeping it in contact with a certain

amount of the salt in the tank of the RFB, it could be that an initially formed metal halide film on a

metal electrode might work as a separator, or at least limit the self-discharge to a tolerable rate. Since

metal deposition has been demonstrated for zinc from Lewis basic mixtures and it is a cheap, non-toxic

element with a good OCV when combined with bromine, it might be a good starting point for further

investigation in this direction.

For the All-Mn IL battery, the addition of a co-solvent might be feasible to decrease the inner resistance

of a future redox flow battery. A membrane free variant should be studied as well, since the high

observed OCVs combined with the comparatively simple and potentially robust chemical system could

yield flow batteries with both high energy efficiencies and a long cycle life.

However, especially for the All-Mn battery, I suggest the investigation of an additional, alternative

direction. When looking at the lead acid accumulator, which has been invented in the 19th century and

is, despite its shortcomings, still in use today, a similar battery based on manganese and an organic

electrolyte seems viable. The battery could use K2MnCl4 or salts of alternative cations in its discharged

state, and would yield K2MnCl6 and manganese metal on charging. An important design element would

be that the charged species precipitate on the electrodes and are thereby immobilized, which would

hinder any self-discharge. Since the discharged active material, K2MnCl4, is identical for both anode

and cathode reactions and unreactive towards the respective charged states, it could either be

completely dissolved in the electrolyte or be precipitated as well. In the latter case, the working

principle of the battery would be closest to the lead acid battery. In any case, the physical layout of

the battery should be developed with an open mind and creativity to fit this unique and promising

chemical system that might one day be used for the storage of climate neutral energy.

277

Lebenslauf

Simeon Benedikt Burgenmeister Geburtsdatum: 14.04.1986 Geburtsort: Tübingen

Universitäre Ausbildung

09/2013 Promotionsstudium – 05/2017 INSTITUT FÜR ANORGANISCHE UND ANALYTISCHE CHEMIE, ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG

� Entwicklung von Redox-Flow-Batterien auf Basis von ionischen Flüssigkeiten � Kommunikations- und Informationsmanagement für das BMBF-Projekt IL-RFB

10/2006 Studium der Chemie (Diplom) – 05/2013 ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG UND UBC VANCOUVER, KANADA

� Schwerpunkt Anorganische Chemie

10/2008 Studium der Philosophie (Bachelor of Arts, Doppelstudium) – 10/2010 ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG UND UBC VANCOUVER, KANADA

� Wissenstheorie, Logik, Rechts- und Moralphilosophie

10/2008 Studentischer Vertreter Fakultätsrat und Studienkommission Chemie – 08/2009 ALBERT-LUDWIGS-UNIVERSITÄT FREIBURG

Schulische Bildung

09/1996 Allgemeine Hochschulreife – 07/2005 GEORG-BÜCHNER-GYMNASIUM WINNENDEN

� Profilfach: Physik, Neigungsfach: Chemie � Sprachen: Französisch, Englisch

Konferenzbeiträge

07/2016 Posterbeitrag zur Konferenz EuChem Molten Salts and Ionic Liquids 2016 � “Ionic Liquids Derived from Mixtures of Tin(IV) Bromide and

1-Hexyl-3-Methyl-Imidazolium Bromide”

09/2014 Posterbeitrag zur Wöhler Tagung 2014 (GDCh) � “Novel Iodine-Chloride-Anions in ILs?”

07/2014 Posterbeitrag zur Konferenz EuChem Molten Salts and Ionic Liquids 2014 � “Novel Iodine-Chloride-Anions in ILs?”

Publikationen

2017 „From Square-planar [ICl4]– to Novel Chloroiodates(III)? A Systematic Experimental and Theoretical Investigation of their Ionic Liquids“ Benedikt Burgenmeister, Karsten Sonnenberg, Sebastian Riedel und Ingo Krossing Chemistry – A European Journal (Wiley-VCH, 2017)

Investigations of Ionic Liquids Based on Chloroiodates ...

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