Sodium–Sulfur Cells with a Sulfurized Polyacrylonitrile Cathode and a Localized High Concentration Electrolyte with Toluene as a Nonfluorinated Diluent

Room‐temperature sodium–sulfur (Na–S) batteries are recognized as promising candidates for next‐generation scalable energy storage systems due to their high energy density and cost‐effectiveness. However, several challenges persist, including the shuttle effect of polysulfide and the compatibility of sodium metal with electrolytes. Herein, the study presents a novel type of localized high‐concentration electrolyte (LHCE), utilizing a cost‐effective, low‐density nonfluorinated diluent, toluene, in contrast to the conventional fluorinated diluents. Based on density functional theory calculations and sodium stripping/plating behavior, toluene demonstrates better reduction stability than other aromatic solvents with different substitutions. Also, compared to the 1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl‐ether (TTE) diluent, toluene exhibits enhanced compatibility with sodium metal. Furthermore, it modifies the solvation structure by favoring anion‐dominated species, which contributes to the formation of a robust inorganic‐rich solid‐electrolyte interphase (SEI) with better Na‐ion transport. Consequently, Na–S cells featuring sulfurized polyacrylonitrile (SPAN) cathode with the developed LHCE exhibit good cycling stability with high capacity. The work presents a promising strategy for developing low‐cost practical Na–S batteries. Sodium‐SPAN batteries with a localized high‐concentration electrolyte with a nonfluorinated diluent toluene exhibit good electrochemical performance as the electrolyte enables a solvation structure facilitating anion‐dominated species, inhibits shuttle effect, and demonstrates good compatibility with sodium metal anode.