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. image