Fluorinated co-solvent promises Li-S batteries under lean-electrolyte conditions

Abstract

Practical lithium-sulfur batteries stipulate the use of a lean-electrolyte and a high Coulombic efficiency of the lithium metal anode. Herein, we employ 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether as a co-solvent in the electrolyte of Li-S batteries to meet the demands. The co-solvent fosters the formation of a LiF-rich solid electrolyte interphase on lithium metal anode, as revealed by Ab initio molecular dynamics and Femtosecond Stimulated Raman spectroscopy. The co-solvent results in an average Coulombic efficiency of 99.4% for lithium plating/stripping cycles. Full cells with a capacity ratio of 2 between lithium anode and the S@PAN cathode (3?mgs?cm−2) exhibited a stable cycle life over 100 cycles at an electrolyte/sulfur ratio of 2 µL?mg−1, validating the high Coulombic efficiency of the lithium anode and demonstrating the compatibility of the electrolyte with both electrodes. To enhance the energy density, we prepared a hybrid cathode composed of 45?wt.% VS2 mixed with ZnS-coated Li2S@graphene as the cathode. Based on the mass of both electrodes and the electrolyte, the full cell delivers an energy density of 483?Wh?kg−1, which demonstrates viable Li-S batteries with the lean-electrolyte.

https://doi.org/10.1016/j.mattod.2020.06.007