Asymmetric Fire-Retardant Quasi-Solid Electrolytes for Safe and Stable High-Voltage Lithium Metal Battery

Lithium metal batteries (LMBs) with high energy density show substantial promise as advanced electrochemical energy storage solutions, although they encounter persistent challenges pertaining to cycling stability and safety performance. Conventional homogeneous electrolytes widely employed in LMBs are inherently flammable, possessing a limited electrochemical window, thereby presenting obstacles to meeting the stringent safety and cycling criteria. In this investigation, we devised an asymmetric fire-retardant quasi-solid polymer electrolyte to mitigate thermal runaway risks and chemical/electrochemical instability at the electrolyte–electrode interface in LMBs. Specifically, on the cathode side, a poly(vinylidene fluoride-co-hexafluoropropylene gel electrolyte incorporating flame-retarded organophosphates exhibited remarkable compatibility and heightened thermal stability when paired with high-voltage Ni-rich layered materials. Simultaneously, a thin yet resilient polyether gel electrolyte was in-situ synthesized on lithium metal anodes, expanding the applicability of fire-retardant electrolytes to lithium metal anodes while suppressing the formation of lithium dendrites. Consequently, high-voltage LMBs utilizing asymmetric fire-retardant electrolytes demonstrated a substantial enhancement in safety performance and cycling stability. This research delineates a viable pathway toward realizing secure and consistent cycling in high-energy-density energy storage systems.