High-Fluorinated Electrolytes for Li-S Batteries

Rechargeable Li-S batteries are regarded as one of the most promising next-generation energy-storage systems. However, the inevitable formation of Li dendrites and the shuttle effect of lithium polysulfides significantly weakens electrochemical performance, preventing its practical application. Herein, a new class of localized high-concentration electrolyte (LHCE) enabled by adding inert fluoroalkyl ether of 1H, 1H, 5H-octafluoropentyl-1,1,2,2- tetrafluoroethyl ether into highly-concentrated electrolytes (HCE) lithium bis(fluorosulfonyl) imide/dimethoxyether (DME) system is reported to suppress Li dendrite formation and minimize the solubility of the high-order polysulfides in electrolytes, thus reducing the amount of electrolyte in cells. Such a unique LHCE can achieve a high coulombic efficiency of Li plating/ stripping up to 99.3% and completely suppressing the shuttling effect, thus maintaining a S cathode capacity of 775 mAh g(-1) for 150 cycles with a lean electrolyte of 4.56 g A(-1) h(-1). The LHCE reduces the solubility of lithium polysulfides, allowing the Li/S cell to achieve super performance in a lean electrolyte. This conception of using inert diluents in a highly concentrated electrolyte can accelerate commercialization of Li-S battery technology.