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||LiNi1/3Mn1/3Co1/3O2 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.