Non-flammable gel polymer electrolytes with stable dual-interface compatibility for safe and high-voltage lithium metal batteries.

Enhancing the intrinsic safety of high-performance lithium metal batteries through flame-retardant solvents is a promising strategy, yet their high reactivity often destabilizes electrode interfaces. Engineering the solvation structure and introducing gel polymer frameworks provides effective pathways to overcome this challenge. Here, we report an in situ polymerized high-voltage gel polymer electrolyte (GPE) with a localized high-concentration electrolyte (LHCE) structure dominated by flame-retardant solvents. Strong polar interactions between the PO groups of trimethyl phosphate (TMP) and the acrylate polymer matrix immobilize TMP molecules, mitigating their parasitic reactivity while maintaining flame-retardant functionality. This confined solvation environment further induces anion-rich coordination, thereby promoting the formation of inorganic-rich dual interfaces between solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers. As a result, Li||LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) cells deliver a high capacity of 197.9 mAh g-1 at 4.5 V and retain 86.5% of their capacity after 300 cycles at 0.5C. This work highlights a generalizable strategy for designing non-flammable, high-voltage GPEs compatible with lithium metal anodes.