Gel polymer electrolyte for lithium-ion batteries using triethyl phosphate solvent and ionic liquid with LiTFSI/LiTDI salts

Batteries are used in daily basis throughout our modern society. Solid-state and semi-solid electrolytes offer optimistic candidate for battery materials by replacing the conventionally used toxic and highly flammable liquid electrolytes. Gel polymer electrolytes (GPE) provide batteries a safe option and mechanical flexibility. GPEs can work without redundant use of rare earth metals like in brittle inorganic solid electrolytes. Ionic liquids and polar aprotic solvents are known to reduce polymer crystallinity, thereby enhancing ionic conductivity (IC) and ion diffusion in polymer electrolytes. In this study, the addition of 1-methyl-1-propylpyrrolidinium 4,5-dicyano-2-(trifluoromethyl) imidazolate (MPPyrTDI) and various polar processing solvents was investigated using Daikin NEOFLON VT-475 fluoropolymer and poly (vinylidene fluoride- co -hexafluoropropylene), (PVDF-HFP). The resulting GPE membranes exhibited a highly amorphous and polar structure, facilitating efficient ion transport. The membranes demonstrated IC values exceeding 1 mS/cm. When implemented in lithium-ion batteries, the membranes showed stable electrochemical performance of 75 cycles with a capacity of 95 mAh/g, indicating good compatibility with electrode interfaces. These results demonstrate that the developed GPE membranes can serve as safe and efficient alternatives to conventional liquid electrolytes in lithium-ion batteries.