Low‐Cost Sodium‐Antimony Rechargeable Battery in Bis(fluorosulfonyl)imide Molten Salt Electrolyte

ABSTRACT Molten salt sodium (Na) rechargeable batteries, such as Na‐S, Na‐NiCl 2 , and liquid‐metal configurations, are promising candidates for grid‐scale energy storage due to their inherent reliability and low cost. However, most conventional systems require ultra‐high operating temperatures, which demand complex thermal management and accelerate the corrosion of cell components, thereby limiting widespread adoption. Here, we report a sodium‐antimony (Na||Sb) molten salt rechargeable battery that operates at 95°C. By integrating a micro‐sized Sb particle cathode and an all‐bis(fluorosulfonyl)imide‐based electrolyte (denoted as NaKFSA), the Na||Sb cell achieves a discharge specific capacity of 651.7 mAh g Sb − 1 with an average operating voltage of 0.61 V at 95°C and C/2 rate. Remarkably, the Na||Sb cell exhibits outstanding rate capability, delivering 300.0 mAh g Sb −1 at 60 C, corresponding to 46.8% of the capacity obtained at 1 C. In situ synchrotron X‐ray characterization reveals that Sb transforms into a stable Na 3 Sb phase during cycling, enabling stable (de)sodiation of micron‐sized Sb particles. This work presents a Na||Sb molten salt rechargeable battery operating at 95°C, providing a potentially low‐cost, moderate‐temperature candidate for next‐generation grid‐scale energy storage.