Dimethylsulfamoyl Fluoride‐Based Electrolyte With Dual Cathodic‐Anodic Stability for Sodium‐Ion and Sodium‐Metal Batteries

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ABSTRACT Sodium‐based batteries are attractive low‐cost alternatives to lithium‐ion systems; however, their practical deployment is limited by the insufficient electrochemical stability of conventional electrolytes. Here, we introduce a high‐performance electrolyte comprising sodium bis(fluorosulfonyl)imide (NaFSI) dissolved in N,N ‐dimethylsulfamoyl fluoride (DMSF), a fluorosulfonamide solvent. DMSF is synthesized via a sulfur fluoride exchange (SuFEx) click reaction under ambient conditions. Compared with conventional ether‐based electrolytes, the NaFSI/DMSF delivers improved electrochemical performance derived from its enhanced reductive and oxidative stabilities, affording higher coulombic efficiency and superior cycling stability for both sodium metal and hard carbon anodes, along with stable capacity retention of high‐voltage NaNi 0.6 Fe 0.2 Mn 0.2 O 2 cathodes. Comprehensive physicochemical analyses reveal that DMSF induces a distinct Na + solvation structure dominated by aggregate ion associations. This increases Na + activity, thereby positively shifting the Na/Na + redox potential. The solvation environment of DMSF promotes the formation of inorganic‐rich solid electrolyte interphases, suppressing electrolyte decomposition. A positive correlation between the Na/Na + redox potential and coulombic efficiency is consistently observed across different electrolytes. In addition, the solvation structure and the associated Na + transport mechanism are investigated by density‐functional theory calculations and molecular dynamics simulations. These findings provide critical insight into a promising electrolyte design platform for achieving stable and high‐efficiency sodium‐based batteries.