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

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 || Na₃V₂(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.