Precise Interfacial Regulation Achieving High‐Rate and Long‐Life Polymer Solid‐State Sodium Metal Batteries

Abstract Poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP)‐based polymer electrolytes have attracted significant attention due to their high dielectric constant, excellent ionic conductivity, and outstanding mechanical flexibility. However, the high reactivity of sodium metal leads to persistent side reactions with various components in the electrolyte membrane. In this study, a precise interfacial regulation strategy is proposed onto the surface of sodium metal. When the mass ratio of fluoroethylene carbonate (FEC) to residual dimethylformamide (DMF) is optimized at 1:1, a synergistic effect between FEC and DMF is achieved at the interface. This synergy leads to the formation of a solid electrolyte interphase (SEI) which exhibits a multilayered gradient structure enriched with NaF, Na 3 N and Na x S. As a result, the solid‐state sodium metal batteries (SSMBs) with Na 3 V 2 (PO 4 ) 3 delivers a high capacity of 93.8 mAh g −1 at 15C, and maintains 93.3% capacity retention after 1000 cycles at 1C. Notably, excellent low‐temperature performance is achieved, with 94.7% capacity retention after 350 cycles at −20 °C. Importantly, a 12 V bipolar configuration is demonstrated. This work not only provides an innovative solution for stabilizing PVDF‐HFP‐based solid electrolytes in SSMBs but also reveals the critical role of precise interfacial engineering in advancing high‐performance polymer SSMBs for the first time.