Anti-swelling gel polymer electrolyte membrane for high-performance lithium-ion battery

Gel polymer electrolyte (GPE) represents an effective and advanced substitution of polyolefin separator in high-rate lithium-ion rechargeable batteries. We here develop a novel pyridine ionic liquid (IL)-based GPE membrane for that purpose via a one-step reactive vapor-induced phase separation (RVIPS) method. Casting mixture solution of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and 1-butylpyridinium hexafluorophosphate ([C₄Py]PF₆) to evaporate solvent in ammonia water vapor, the IL-based membrane was successfully prepared in one step. The effects of the IL content on the membrane microstructure were investigated in detail. Our results demonstrate that the pyridine IL plays a role as plasticizer to suppress crystallization of the polymer, while the RVIPS process can induce dehydrofluorination-crosslinking of PVDF-HFP to greatly reduce swelling of the membrane in liquid electrolyte. Based on those, the GPE from the membrane containing 10 % [C₄Py]PF₆ exhibits the best electrochemical properties (ionic conductivity of 1.48 mS cm⁻¹, Li⁺ transference number of 0.66, and electrochemical stable window of 5.2V), though it uptakes a moderate amount of liquid electrolyte. Moreover, the long-term interfacial stability of the GPE with the metal anodes was checked to indicate its suitability as excellent GPE. According to the battery tests, the GPE exhibits superior discharge capacities at high C-rates, achieving 129.7 mAh g⁻¹ at 3C and 115.5 mAh g⁻¹ at 5C, while remains a low capacity decay of 0.014 % per cycle over 300 cycles at 3C. Therefore, our work provides a facile strategy of one-step RVIPS to prepare pyridine ionic liquid-based GPE, which demonstrates promising potential for high-performance rechargeable lithium-ion battery.