Incombustible solid polymer electrolytes: A critical review and perspective

Since the advent of the solid-state batteries, employing solid polymer electrolytes (SPEs) to replace routine flammable liquid electrolytes is regarded to be one of the most promising solutions in pursing high-energy-density battery systems. SPEs with superior thermal stability, good processability, and high mechanical modulus obtain increasing attentions. However, SPE-based batteries are not impenetrable due to their decomposition and combustibility under extreme conditions. Researchers believe incorporating appropriate flame-retardant additives/solvents/fragments into SPEs can intrinsically reduce their flammability to solve the battery safety issues. In this review, the recent research progress of incombustible SPEs, with special emphasis on flame-retardant structural design, is summarized. Specifically, a brief introduction of flame-retardant mechanism, evaluation index for safety of SPEs, and a detailed overview of the latest advances on diverse-types SPEs in various battery systems are highlighted. The deep insight into thermal runaway process, the free-standing incombustible GPEs, and the rational design of pouch cell structures may be the main directions to motivate revolutionary next-generation for safety batteries.