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

Abstract

Safety concern poses a significant challenge for the large‐scale employment of lithium‐sulfur batteries. Extreme flammable conventional electrolyte and dendritic lithium deposition cause severe safety issues. Herein, we report an intrinsic flame‐retardant (IFR) electrolyte consisting of 1.1 M lithium bis(fluorosulfonyl)imide in a solvent mixture of flame‐retardant triethyl phosphate and high flash point 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 property and high reversibility of lithium metal anode (Coulombic efficiency >99%). Importantly, this IFR electrolyte enables stable lithium plating/stripping behavior with micro‐sized and dense‐packing lithium deposition at high temperatures. When coupled with sulfurized pyrolyzed poly(acrylonitrile) cathode (sulfur content: 52.6 wt%), Li‐S batteries deliver high composite capacity (840.1 mAh g‐1) and high sulfur utilization of 95.6%. More advantages of this system are its enhanced energy conversion efficiency and energy density under high temperature operation.