Thermotolerant and fireproof gel polymer electrolyte toward high-performance and safe lithium-ion battery

Poly(ethylene oxide) (PEO) and its derivatives based gel polymer electrolytes (GPEs) are severely limited in advanced and safe lithium-ion batteries (LIBs) owing to the intrinsically high flammability of liquid electrolytes and PEO. Directly adding flame retardants to the GPEs can suppress their flammability and thus improve the safety of LIBs, but results in deteriorative electrochemical performance. Herein, a novel GPE with chemically bonded flame retardant (i.e. diethyl vinylphosphonate) in cross-linked polyethylene glycol diacrylate matrix, featuring both high-safety and high-performance, is designed. This as-prepared GPE storing the commercial 1 mol L−1 LiPF6 electrolyte resists high temperature of 200 °C and cannot be ignited as well as possesses a high ionic conductivity (0.60 mS cm−1) and good compatibility with lithium. Notably, the LiFePO4/Li battery with this GPE delivers a satisfactory capacity of 142.2 mA h g−1 and a superior cycling performance with a capacity retention of 96.3% and a coulombic efficiency of close to 100% for 350 cycles at 0.2 C under ambient temperature. Furthermore, the battery can achieve steady charge–discharge for 100 cycles with a coulombic efficiency of 99.5% at 1 C under 80 °C and run normally even at a high temperature of 150 °C or under the exposure to butane flame. Differential scanning calorimetry manifests significantly improved battery safety compared to commercial battery systems. This work provides a new pathway for developing next-generation advanced LIBs with enhanced performance and high safety.