Succinonitrile‐Modulated Polymer Electrolyte for Ultra‐Long Lifespan and High Voltage Sodium Metal Batteries

Abstract Gel polymer electrolytes (GPEs) are promising for solid‐state sodium metal batteries owing to their attractive room‐temperature ionic conductivity and good flexibility. However, achieving good stability at high voltages and temperatures remains a great challenge. Herein, a novel thin gel polymer electrolyte (36 µm) consisting of succinonitrile (SN), poly (ethylene glycol) methyl ether methacrylate (PEGDMA), and sodium‐difluoro(oxalato)borate (NaDFOB) for a long lifespan and high voltage SMBs at multiple scenarios is designed. The well construction of the GPE and the generated robust electrolyte interface films not only ensure the Na || Na cells display good stability up to 6000 h, but also endow the Na || Na ₃ V ₂ (PO4) ₃ with stable cycling of 1000 cycles at 60 °C. Even at 4.7 V, a capacity retention ratio of 94.34% after 1000 cycles with a high CE of 99.71% is achieved, displaying superior oxidative toleration and good compatibility with the high‐voltage cathode.