Lee, Tommy Hoong Wy
(2025)
Thermophysical and electrochemical properties measurements of novel choline-based ionic liquids.
PhD thesis, University of Nottingham Malaysia.
Abstract
The urgent need for sustainable energy storage propels the search for advanced battery technologies. Traditional lithium-ion batteries with liquid electrolytes pose safety risks like flammability and leakage. Choline-based ionic liquids (ILs) incorporated into gel polymer electrolytes (GPEs) offer a promising solution with the potential to enhance safety, cost-effectiveness, and environmental sustainability. This thesis focuses on the development and optimization of choline-based IL GPEs specifically for lithium battery applications.
Choline is a vital water-soluble nutrient that plays a crucial role in numerous physiological processes including neurotransmitter synthesis, cell membrane integrity, and lipid transport. Its versatility extends to diverse fields like aquaculture and beef production, highlighting its potential for large-scale applications. Although the versatility of choline is very broad, research on its usage in lithium-ion batteries is very limited. Choline-based ionic liquids inherit properties like biocompatibility, biodegradability, and cost effectiveness while offering the tunability needed to tailor electrochemical characteristics. These properties make them promising candidates for electrolytes in advanced battery technologies.
A series of novel choline-ester ILs were synthesized using facile methods, including an acid-base reaction to produce choline hydroxide and subsequent esterification with selected carboxylic acids. Their structures were confirmed by NMR and FTIR. These choline ester ILs exhibited high thermal stability (up to 300°C), non-flammability, high ionic conductivities (up to 60.92 mScm-2), high oxidative stability (up to 4.76 V), and impressive lithium-ion transference numbers (up to 0.94). GPEs were fabricated by incorporating these ILs into a PVDF-HFP matrix using a solution casting technique. The fabricated GPEs demonstrated significant safety improvements compared to traditional liquid electrolytes while maintaining electrochemical performance comparable to other ILGPEs systems. The structure-property relationships uncovered, particularly the effect of alkyl chain length on ionic conductivity, offer valuable guidance for further optimization.
This work underscores the potential of choline based ILs as a versatile electrolyte platform. It also highlights the advantages of GPEs for creating safer, high-performance lithium-ion batteries. Further research exploring other choline derivatives, advanced GPE architectures, and detailed battery testing could unlock even greater breakthroughs in energy storage technology. These future research directions could include investigations into bio-derived polymers, the inclusion of fillers for enhanced mechanical and electrochemical properties, and the development of solid-state electrolytes based on choline chemistries.
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