Hydrofluoroether Diluted Dual-Salts-Based Electrolytes for Lithium-Sulfur Batteries with Enhanced Lithium Anode Protection.

Abstract

With a high energy density, lithium-sulfur batteries (LSB) are regarded as one of the promising next-generation energy storage systems. However, many challenges hinder the practical applications of LSB, such as the dendrite formations/parasitic reactions on the Li metal anode and the "shuttle effect" of lithium polysulfides of the LSB cathode. Herein, a novel diluted medium-concentrated electrolyte (DMCE) is developed by adding 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) into a dual salt medium-concentrated electrolyte (MCE) consisting of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-lithium bis(fluorosulfonyl)imide (LiFSI)/tetrahydrofuran (THF)-dipropyl ether (DPE). The optimized DMCE electrolyte is capable of protecting the Li metal anode and suppresses the dissolution of polysulfides and the "shuttle effect", delivering a high coulombic efficiency (CE) of Li plating-stripping up to 99.6% even at a low concentration of Li salt (1.0-2.0m). Impressively, compared with the cells cycled in the MCE electrolyte, the LiS cells with the DMCE-2.0m electrolyte have delivered an enhanced initial capacity of 682 mAh g-1 with an excellent capacity retention of 92% for 500 cycles. This strategy of using fluorinated ether as diluent solvent in a medium-concentrated electrolyte can accelerate the commercialization of LSB.