Thermally Adaptive PVDF‐HFP/Ionic Liquid Electrolyte Enabling Stable SEI/CEI Formation in Sodium Metal Batteries

Abstract Sodium‐metal batteries (SMBs) offer exceptional energy density but face persistent interfacial instability and electrolyte degradation challenges. Herein, to address these limitations, an adaptive polymer electrolyte membrane (EM) is developed from poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) integrated with 1‐ethyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [EMPYR][TFSI] ionic liquid (IL). The membrane exhibits a smart thermal response, functioning as a solid electrolyte at 55 °C while forming a gel electrolyte at 25 °C upon incorporation of a conventional liquid electrolyte. This reversible transition effectively mitigates cathode‐electrolyte side reactions at elevated…