Document Type
Dissertation
Degree
Doctor of Philosophy (PhD)
Major/Program
Materials Science and Engineering
First Advisor's Name
Bilal El-Zahab
First Advisor's Committee Title
Committee Chair
Second Advisor's Name
Norman Munroe
Second Advisor's Committee Title
Committee Member
Third Advisor's Name
Chunlei Wang
Third Advisor's Committee Title
Committee Member
Fourth Advisor's Name
Yu Zhong
Fourth Advisor's Committee Title
Committee Member
Fifth Advisor's Name
Irene Calizo
Fifth Advisor's Committee Title
Committee Member
Keywords
Poly Ionic Liquid, Gel Polymer Electrolyte, Composite Gel Electrolyte, Electrochemical Impedance Spectroscopy, Lithium Metal Battery, Lithium Sulfur Battery
Date of Defense
5-14-2018
Abstract
The demand for electric vehicles is increasing rapidly as the world is preparing for a fossil fuel-free future in the automotive field. Lithium battery technologies are the most effective options to replace fossil fuels due to their higher energy densities. However, safety remains a major concern in using lithium as the anode, and the development of non-volatile, non-flammable, high conductivity electrolytes is of great importance. In this dissertation, a gel polymer electrolyte (GPE) consisting of ionic liquid, lithium salt, and a polymer has been developed for their application in lithium batteries. A comparative study between GPE and ionic liquid electrolyte (ILE) containing batteries shows a superior cyclic performance up to 5C rate and a better rate capability for 40 cycles for cells with GPE at room temperature. The improvement is attributed to GPE’s improved stability voltage window against lithium as well as higher lithium transference number. The performance of the GPE in lithium-sulfur battery system using sulfur-CNT cathodes shows superior rate capability for the GPE versus ILE for up to 1C rates. Also, GPE containing batteries had higher capacity retention versus ILE when cycled for 500 cycles vii at C/2 rate. Electrochemical impedance spectroscopy (EIS) studies reveal interfacial impedances for ILE containing batteries grew faster than in GPE batteries. The accumulation of insoluble Li2S2/Li2S on the electrodes decreases the active material thus contributes to capacity fading. SEM imaging of cycled cathodes reveals cracks on the surface of cathode recovered from ILE batteries. On the other hand, the improved electrochemical performance of GPE batteries indicates better and more stable passivation layer formation on the surface of the electrodes. Composite GPE (cGPE) containing micro glass fillers were studied to determine their electrochemical performance in Li batteries. GPE with 1 wt% micro fillers show superior rate capability for up to 7C and also cyclic stability for 300 cycles at C/2 rate. In situ, EIS also reveals a rapid increase in charge transfer resistance in GPE batteries, responsible for lowering the capacity during cycling. Improved ion transport properties due to ion-complex formations in the presence of the micro fillers, is evidenced by improved lithium transference number, ionic conduction, and ion-pair dissociation detected using Raman spectroscopy.
Identifier
FIDC006891
ORCID
Recommended Citation
Safa, Meer N., "Poly (Ionic Liquid) Based Electrolyte for Lithium Battery Application" (2018). FIU Electronic Theses and Dissertations. 3746.
https://digitalcommons.fiu.edu/etd/3746
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