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

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 %.