Ionic Liquid-Based Electrolytes for High-Temperature Lithium-Metal Batteries

Licentiate thesis, 2025

Lithium metal batteries are promising candidates for high-energy-density electrochemical energy storage systems due to the low redox potential and high theoretical capacity of Li metal anodes. However, their practical application, especially at high temperatures, is hindered by unstable Li deposition, dendrite growth, side reactions, and rapid interfacial degradation, which compromise Coulombic efficiency, cycle life, and safety. These challenges are closely linked to the interfacial processes governing Li⁺ transport, desolvation, structure of the electric double layer, solid electrolyte interphase (SEI), and nucleation/growth of Li-metal at the surface. In this thesis, two electrolyte engineering strategies were used to address these issues by tuning the Li⁺ solvation structure, ionic transport, and interfacial processes. First, a novel ionic liquid electrolyte (NS-DAIL) was designed by incorporating LiNO₃ and sulfolane into a dual-anion ionic liquid electrolyte, which weakens the Li⁺-anion coordination, reduces the desolvation barrier, and enhances Li⁺ transfer kinetics, enabling uniform Li plating and improved rate performance at high temperature. Second, by introducing an ionic liquid (Pyr14FSI) as an additive into a conventional carbonate electrolyte, the electrode-electrolyte interface is modified, delaying Li+ depletion at the interface during plating, which mitigates dendrite growth. These two studies elucidate the interplay between solvation structure, ionic transfer kinetics, SEI properties, and suppression of dendrite growth, providing mechanistic insights and practical strategies for achieving safe, high-performance, high-temperature lithium metal batteries.