A thermostable ionic liquid-methacrylate-based polymer electrolyte for energy storage application

Abstract

In recent years, gel polymer electrolytes (GPEs) incorporating ionic liquids (ILs) have been explored extensively for lithium-ion batteries due to their favourable thermal stability and high ionic conductivity. Gel polymer electrolytes can also improve the safety of lithium-ion batteries by eliminating the flammable organic solvents which are often used in traditional electrolyte systems. Herein, we report an efficient synthesis of a thermostable ionic liquid-methacrylate-based polymer gel electrolyte via a photo-initiated phase separation (PIPS) process in an inert environment. Anionic liquid phase of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI), coupled with a low molecular weight polyethylene glycol dimethyl ether (PEGDME), was combined with a solid phase of bisphenol A ethoxylate dimethacrylate (BEMA) at varying solid to liquid ratios to produce a thermally stable gel electrolyte. The highest ionic conductivity of 1.9 × 10−3 S cm−1 (at 30 °C) was achieved for the electrolyte with a solid-to-liquid ratio of 1:3 by weight. The Lithium metal cells utilizing these electrolytes and LiFePO4 as cathode active material exhibited the initial discharge capacity of 144 mAh g−1 with capacity retention of 85 % over 100 cycles in ambient temperature. The thermal stability of the cells was significantly improved upon increasing the EMIMTFSI content. This study illustrates the potential application of the IL-methacrylate gel polymer electrolyte system in enhancing the safety of Li-ion batteries through careful tuning of the composition. Their versatile properties also make them suitable for quasi-solid-state batteries with high energy density and safety.