Progress in flame-retardant solid-state electrolytes for battery safety and sustainability

The widespread adoption of batteries is hampered by persistent safety concerns, which primarily stem from the flammability of conventional organic liquid electrolytes, although common solid-state electrolytes also carry risks of thermal runaway. Flame-retardant solid-state electrolytes (FR-SSEs) represent a promising solution, replacing flammable liquids with non-flammable or flame-retardant solid conductors. In this review, we outline the role of FR-SSEs in aligning safety with sustainability for next-generation batteries. We analyze the specific mechanisms of different FR-SSEs, detailing how they interrupt thermal runaway through radical scavenging, physical heat barriers, and catalytic charring. On the basis of achieving flame retardancy while maintaining battery performance, we emphasize the sustainable advantages of FR-SSEs, such as the use of eco-friendly materials, low-energy production processes, and electrochemical stability, along with associated sustainability challenges. Finally, to tackle end-of-life challenges, we discuss closed-loop recycling approaches and green, solvent-free manufacturing guided by life cycle assessment (LCA).