A Localized High-Concentration Electrolyte with Optimized Solvents and Lithium Difluoro(oxalate)borate Additive for Stable Lithium Metal Batteries

We report a carbonate-based localized high-concentration electrolyte (LHCE) with a fluorinated ether as a diluent for 4-V class lithium metal batteries (LMBs), which enables dendrite-free Li deposition with a high Li Coulombic efficiency (∼98.5%) and much better cycling stability for Li metal anodes than previously reported dimethyl carbonate-based LHCEs at lean electrolyte conditions. This electrolyte consists of 1.2 M lithium bis(fluorosulfonyl)imide (LiFSI) in a cosolvent mixture of ethylene carbonate (EC)/ethyl methyl carbonate (EMC) with bis(2,2,2-trifluoroethyl) ether (BTFE) as the diluent and 0.15 M lithium difluoro(oxalate)borate (LiDFOB) as an additive. A Li||LiNi_1/3Mn_1/3Co_1/3O₂ battery with a high areal loading of 3.8 mAh cm^-2 maintains 84% of its initial capacity after 100 cycles. The enhanced stability can be attributed to the robust solid-electrolyte interface (SEI) layer formed on the Li metal anode, arising from the preferential decomposition of LiDFOB salt and EC solvent molecules.