Enhancing Cycling Stability of Li Metal Batteries by a Bifunctional Fluorinated Ether

Passivation of both anode and cathode surfaces by the inorganic-rich solid electrolyte interphases (SEI) is a very efficient approach to extent the cycle life of rechargeable high-voltage lithium (Li) metal batteries (LMBs). In this work, a fluorinated ether with weakly-solvating ability, termed DB, was used as a diluent as well as a co-solvent in the localized high-concentration electrolyte (LHCE) system, which contains LiFSI salt, 1,2-dimethoxyethane solvent, and DB. Dissimilar to most reported inert diluents, DB is demonstrated to form an anion-rich solvation sheath and partially participate in the solvation structure as well, resulting in the relatively weakened FSI--Li+ coordination, which significantly enhanced anion decomposition kinetics at the Li metal surface, promoting the formation of inorganic-rich SEI. With an optimized electrolyte, the SEIs of both the anode and cathode consist of inorganic-rich components with F, N, S, and O-containing species. Consequently, the full-cell with Li metal and NMC811 cathode at 4.4 V achieved long cycle life of 478 cycles at 80% capacity retention, which provides new perspective toward practical high-voltage battery systems.