Sodium metal batteries (NMBs) are among the most promising alternatives to lithium-ion batteries. However, the thermal instability, potential leakage, and dendrite growth typical of NMBs with organic liquid electrolytes still pose severe limitations to this technology. These challenges can be overcome by replacing the organic liquid electrolytes with solids or gels. In this study, a hybrid dual-salt polymer electrolyte (DSPE), comprising sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) and sodium difluoro(oxalate)borate (NaDFOB) salts is reported. The two salts work synergistically: NaTFSI enhances ionic conductivity and thermal stability, while NaDFOB extends the electrochemical window and inhibits the corrosion of the Al current collectors caused by NaTFSI. Furthermore, the DSPE with a NaDFOB/NaTFSI optimized molar ratio of 20% delivers a high ionic conductivity of 0.31 mS cm⁻¹ at 23 °C. At this temperature, the NMB with a Na₃V₂(PO₄)₃@carbon positive electrode has excellent cycling performance (104.0 mAh g ^− 1 at 1 C with 92.4% capacity retention over 300 cycles) and rate capability (93.5 mAh g ^− 1 at 5 C). X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) characterizations, together with ab initio calculations reveal that stable battery performance is linked to the formation of a Na_xBO_yF_z-containing protective cathode-electrolyte interphase layer. Leveraging the synergistic combination of two salts, this new DSPE formulation opens a new path for next-generation, high-performance NMBs.

钠金属电池（NMB）是锂离子电池最有前途的替代品之一。然而，具有有机液体电解质的 NMB 典型的热不稳定性、潜在泄漏和枝晶生长仍然对该技术构成严重限制。这些挑战可以通过用固体或凝胶代替有机液体电解质来克服。在这项研究中，报道了一种混合双盐聚合物电解质（DSPE），包括双（三氟甲基磺酰基）亚胺钠（NaTFSI）和二氟（草酸）硼酸钠（NaDFOB）盐。这两种盐协同工作：NaTFSI 增强了离子电导率和热稳定性，而 NaDFOB 扩展了电化学窗口并抑制了由 NaTFSI 引起的铝集流体的腐蚀。此外，^-1在 23 °C。在此温度下，具有 Na ₃ V ₂ (PO ₄ ) ₃ @carbon 正极的 NMB 具有出色的循环性能（104.0 mAh g  ^{-  1}在 1 C 下，300 次循环后容量保持率为 92.4%）和倍率性能（93.5 mAh g  ^{-  1}在 5 C)。X 射线光电子能谱 (XPS) 和飞行时间二次离子质谱 (ToF-SIMS) 表征以及从头算计算表明，稳定的电池性能与 Na _x BO _y F _{z的形成有关}-含有保护性阴极-电解质界面层。利用两种盐的协同组合，这种新的 DSPE 配方为下一代高性能 NMB 开辟了一条新途径。