Ambient Cationic Activation-Radical Synergy Yields High-Performance Polymer Electrolytes

Conventional in situ thermal radical polymerization of electrolytes requires elevated temperatures and typically leads to complete monomer and Li-salt consumption, which severely limits ionic transport and results in an unstable solid-electrolyte interphase (SEI) for lithium metal batteries (LMBs). Here, we propose an ambient cationic activation-radical synergy strategy (CIP), in which PF₆^- derived Lewis acidic species selectively activate vinylene carbonate (VC) and trigger polymerization at room temperature through a cationic-induced pathway fundamentally distinct from the traditional thermal-initiated process (TIP). Combined theoretical calculations and in situ spectroscopic analyses indicate that PF₆^- decomposition precedes polymer growth and lowers the activation barrier, enabling controlled polymerization while preserving a fraction of electrochemically active monomers. The resulting gel polymer electrolyte (GPE) exhibits accelerated ionic transport kinetics with an elevated transference number of 0.78 and an ionic conductivity of 6.49 × 10^-3 S cm^-1. When applied in LMBs, this electrolyte promotes the formation of a dense, inorganic-rich, and dynamically reinforced SEI, enabling stable lithium plating/stripping over 2000 h, sustained cycling over 1200 cycles at 0.5 C, and excellent rate capability up to 10 C, demonstrating its promise for high-performance LMBs.