Design strategy towards flame-retardant gel polymer electrolytes for safe lithium metal batteries

The emergence of lithium metal batteries (LMBs) as a promising technology in energy storage devices is attributed to their high energy density. However, the inherent flammability and leakage of the internal liquid organic electrolyte pose serious safety risks when exposed to heat. In response to this challenge, gel polymer electrolytes (GPEs) have been developed to mitigate leakage and enhance nonflammability by incorporating flame-retardant groups, thereby improving the safety of LMBs. This review commences with a brief analysis of the thermal runaway mechanism specific to LMBs, emphasizing its distinctions from that of lithium-ion batteries. Following this, the various methods employed to assess the safety of LMBs are discussed, including flammability, thermal stability, and abuse assessment. The following section categorizes recent research on safe GPEs according to different flame retardancy levels providing a concise overview of each category. Finally, the review explores current advancements in developing safety-oriented GPEs and considers potential future research directions.