NaDFOB-Based Single-Salt Polymer Electrolyte for Long-Lifespan and Wide-Temperature Sodium–Metal Batteries

Solid polymer electrolytes are pivotal to safe, high-energy sodium–metal batteries but suffer from low ionic conductivity and poor interfacial stability. Here we pioneer a single-salt quasi-solid polymer electrolyte (PSDF) using NaDFOB, where dissolution is driven by interaction with C–O–C bonds rather than C═O groups. Together with succinonitrile-optimized solvation, PSDF achieves an ionic conductivity of 0.89 mS cm–1, a Na+ transference number of 0.58, and an oxidation potential of 5.1 V (vs Na+/Na). DFOB– preferentially forms B/F-rich interphases on both anode and cathode, enabling good interfacial stability. This allows the Na||PSDF||Na3V2(PO4)3 cell to retain 98.2% capacity after 3500 cycles, while operating effectively across a wide temperature range (−10 to 90 °C). Impressively, the cell respectively maintains 98 and 81.2% of its room-temperature capacity at 0 and −10 °C, and retains capacity retention >85% after 500 cycles at 80 and 90 °C. Besides, the Na||PSDF||Na3V2(PO4)3 pouch cells also show decent electrochemical performance and safety.