An Intrinsic Flame‐Retardant Organic Electrolyte for Safe Lithium‐Sulfur Batteries

Abstract Safety concerns pose a significant challenge for the large‐scale employment of lithium–sulfur batteries. Extremely flammable conventional electrolytes and dendritic lithium deposition cause severe safety issues. Now, an intrinsic flame‐retardant (IFR) electrolyte is presented consisting of 1.1 m lithium bis(fluorosulfonyl)imide in a solvent mixture of flame‐retardant triethyl phosphate and high flashpoint solvent 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl (1:3, v/v) for safe lithium–sulfur (Li−S) batteries. This electrolyte exhibits favorable flame‐retardant properties and high reversibility of the lithium metal anode (Coulombic efficiency >99 %). This IFR electrolyte enables stable lithium plating/stripping behavior with micro‐sized and dense‐packing lithium deposition at high temperatures. When coupled with a sulfurized pyrolyzed poly(acrylonitrile) cathode, Li−S batteries deliver a high composite capacity (840.1 mAh g −1 ) and high sulfur utilization of 95.6 %.