Stable Lithium Metal Plating/Stripping in a Localized High-Concentration Cyclic Carbonate-Based Electrolyte (Supporting Information)

Li metal is the ultimate anode material for rechargeable Li batteries because of its high capacity and low electrochemical potential. However, Li metal anodes suffer from low Coulombic efficiency and poor cycling stability owing to the growth of Li dendrites. In this study, we report that a localized high-concentration electrolyte comprising lithium bis(fluorosulfonyl)imide (LiFSI), ethylene carbonate (EC), propylene carbonate (PC), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) achieves stable Li plating/stripping cycling with a Coulombic efficiency of >98 %. In contrast to LiFSI/EC : PC electrolytes, this electrolyte shows good wettability on a polypropylene separator. Li metal deposited in this electrolyte displays a large, granular, and dense morphology. Spectroscopic analyses confirm strong FSI⁻–Li⁺ coordination in this electrolyte, leading to the formation of a solid electrolyte interphase (SEI) layer enriched with LiF and sulfurous compounds derived from FSI⁻. These results indicate that the SEI layer facilitates the deposition of compact Li and effectively prevents Li loss owing to electrolyte decomposition and dead Li formation, resulting in highly reversible Li plating/stripping cycling. This electrolyte design can be an effective strategy for developing high-energy-density Li metal batteries.