Sodium‐Difluoro(oxalato)Borate‐Based Electrolytes for Long‐Term Cycle Life and Enhanced Low‐Temperature Sodium‐Ion Batteries

Abstract Sodium‐ion batteries (SIBs) are emerging as a promising alternative for next‐generation energy storage solutions, driven by the economic and environmental benefits of abundant sodium resources. A pivotal aspect of SIB advancement is the development of advanced electrolytes, which remains a formidable challenge. Herein, a facile and scalable synthesis method for low‐cost sodium‐difluoro(oxalato)borate (NaDFOB) is reported and explored its application as a standalone electrolyte salt for SIBs. The NaDFOB‐based ether electrolyte demonstrates exceptional electrochemical stability, solvent compatibility, and the unique capacity to form a dense, robust solid‐electrolyte interphase layer on electrode surfaces. As a result, the Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 (NFPP) cathode with NaDFOB‐based electrolyte exhibits ultrahigh cycling stability with a remarkable capacity retention of 98.7% after 1000 cycles. Furthermore, an Ah‐level hard carbon (HC)//NFPP pouch cell using NaDFOB‐based ether electrolyte shows an impressive cycle life of 500 cycles, coupled with an average Coulombic efficiency of 99.9%. The pouch cells also maintain superior electrochemical performance across a broad temperature range from −40 to 60 °C, showcasing the electrolyte's versatility. This work contributes significant insights into the strategic design and application of innovative salts, paving the way for longer‐lasting SIBs with enhanced electrochemical performance.