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## Synthesis and characterization of polymer electrolytes involving imidazolium ionic liquids for application in lithium-ion batteries

### Anna Puczyłowska

#### Abstract

Introduction Lithium-ion batteries are characterized by high energy density, high efficiency and a lack of memory effect. They are mainly used in portable devices such as cell phones and laptops [1]. However, increasing demands on the safety of their use are forcing scientists to conduct further research into improving them. They are trying to completely eliminate liquid flammable solvents from the battery which can cause an explosion. Promising solution seems to be using, instead of them, ionic liquids, which have unique properties at room temperature, they are: nonvolatile, nonflammable, thermally and chemically stable with a high ionic conductivity and wide potential window [2]. Previous studies show that the following properties of the electrolyte can be improved: ionic conductivity, electrochemical, thermal and mechanical stability through the introduction of ceramic fillers, such as: Al2O3, SiO2, ZrO2, ZnO and TiO2 [3]. Main goal of the thesis was to carry out studies to determine the effect of additive ceramic filler, colloidal silica on the properties of electrolytes based on imidazolium ionic liquids substituted by oligooxyethylene groups with a varying number of EO monomeric units at position 2 in the imidazole ring. C C N N + C H9C4 CH3 H2C OH H H BF4 - C C N N + C H9C4 CH3 H2C O H H CH2CH2 OH BF4 - 3 C C N N + C H9C4 CH3 H2C O H H CH2CH2 OH BF4 - 7 Results and discussion The ionic liquids selected for testing in this thesis were characterized using magnetic resonance 1H NMR and MALDI ToF spectroscopy, which allowed to determine average number of OE units substituted at C-2 in the imidazole ring. Using impedance spectroscopy the ionic conductivity of the selected systems containing ionic liquids, colloidal silica and lithium salt was determined. It was shown that the addition of ceramic filler at certain concentrations may increase the ionic conductivity of the examined electrolyte. It was determined that ionic conductivity is decreasing with increased lithium salt content in the system - this is due to the increased viscosity of the electrolyte. The study has also shown that the structure of the imidazole cation has the greatest impact on the value of the ionic conductivity. It plays a more important role than the concentration of salt used and the addition of silica. Using chronowoltamperometry was analyzed electrochemical stability of ionic liquids and composites with silica and lithium salt. This experiment gives us a proof that more important for electrochemical stability is the structure of imidazole cation than the additives. A significant addition of silica (20 wt%) contributed to the shift of the potential window toward higher potentials. This relationship was not observed at low concentration of SiO2 in the analyzed electrolytes. The prepared electrolytes were also thermally analyzed by the DSC technique. It was determined that all studied systems are amorphous and their glass transition temperature ranges from -43oC to -70oC. In systems based on ionic liquids containing in their structure EO 73 monomeric units, glass transition occurred at higher temperature. Increase in Tg value was observed also with the increasing participation of lithium salt in the analyzed system. In electrolytes containing silica an interesting property was observed – their Tg temperature with increasing SiO2 content underwent cyclic changes. The results of thermal analysis was compared with ionic conductivity. Changes in both parameters are consistent, the increase in Tg reduces the ionic conductivity of systems and conversely, decrease in Tg is accompanied by increase in ionic conductivity. The characterization of electrolytes containing analyzed ionic liquids also included the determination of lithium transference numbers (t+). The studies were performed by the electrochemical method of Bruce and Vincent, for the following systems: ionic liquid (0 EO and 3 EO) + SiO2 + lithium salt (LiBF4 or LiN(CF3SO2)2). The obtained values of t+ are low, which is characteristic for ionic liquids, and are similar to the concentration of lithium cations in the electrolyte (xLi) both for systems consisting of ionic liquid + lithium salt as well as containing ionic liquid + lithium salt and silica as an additive. It indicates that the mobility of lithium cations in the studied electrolytes is proportional to their concentration. Conclusions It was shown that the use of a ceramic filler - colloidal silica may result in improvement of electrochemical properties of studied systems: ionic conductivity and electrochemical stability. Properties of analyzed electrolytes depend mainly on the structure of the ionic liquid imidazolium cation, that is the presence of substituent - oligooxyethylene group.
Record ID
WUTb2987016d9a340dc8e2f55927aae5ef2
Diploma type
Master of Science
Author
Anna Puczyłowska Anna Puczyłowska,, Undefined Affiliation
Title in Polish
Synteza i badanie właściwości elektrolitów polimerowychz z udziałem imidazoliowych cieczy jonowych do zastosowania w akumulatorach litowo-jonowych
Supervisor
Ewa Zygadło-Monikowska (FC/CPCT) Ewa Zygadło-Monikowska,, Chair Of Polymer Chemistry And Technology (FC/CPCT)Faculty of Chemistry (FC)
Certifying unit
Faculty of Chemistry (FC)
Affiliation unit
Chair Of Polymer Chemistry And Technology (FC/CPCT)
Study subject / specialization
, Technologia Chemiczna
Language
(pl) Polish
Status
Finished
Defense Date
12-07-2012
Issue date (year)
2012
Keywords in Polish
-
Keywords in English
-
Abstract in Polish
File
• File: 1
praca magisterska Alicja Puczyłowska.pdf
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Uniform Resource Identifier
https://repo.pw.edu.pl/info/master/WUTb2987016d9a340dc8e2f55927aae5ef2/
URN
urn:pw-repo:WUTb2987016d9a340dc8e2f55927aae5ef2

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