Design of Hindered Amine-Based Gel Electrolytes through Molecular Grafting Engineering for High-Voltage and Fire-Resistant Lithium Batteries

In situ polymerized gel electrolytes have attracted widespread attention for the high ionic conductivity and leakage-free risk. However, conventional polyether-based polymerized gel electrolytes (GPEs) suffer from residual ether solvents prone to decomposition at high voltages, limiting energy density. Moreover, the high flammability of polyether molecular chains fails to fundamentally resolve the fire safety risks of batteries. Herein, a novel flame-retardant in situ gel electrolyte with excellent high-voltage stability has been innovatively synthesized via molecular grafting engineering, incorporating hindered amines as multifunctional additives that act as both radical scavengers and high-voltage film-forming agents. As a result, benefiting from the preferential formation of a cathode electrolyte interphase layer enriched with Li³N and LiF, which ensures high ionic conductivity, PTF-GPE exhibits outstanding cycling stability in NCM811//Li cells, delivering a capacity of 135.59 mAh/g with 81.07% retention after 200 cycles. Furthermore, the combined radical-trapping effect of hindered amine monomers and the condensed-phase char formation mechanism of the phosphorus-rich 3-dimensional gel framework endow PTF-GPE with self-extinguishing behavior. Compared with polyether-based GPEs, PTF-GPE reduces the peak thermal runaway temperature and the total heat release of NCM811//graphite pouch cells by 106.7 °C and 88.62%, respectively, without visible flame throughout the process, thereby substantially enhancing fire safety.