High-Efficiency Lithium Metal Batteries with Fire-Retardant Electrolytes

Rechargeable lithium metal batteries are regarded as the “holy grail” of energy storage systems, but their practical applications have long been hindered by poor cyclability and severe safety concerns. In this work, we report a fire-retardant localized high-concentration electrolyte consisting of 1.2 M lithium bis(fluorosulfonyl)imide in a mixture of flame-retardant triethyl phosphate/bis(2,2,2-trifluoroethyl) ether (1:3 by mol) for 4-V class lithium metal batteries. This electrolyte enables stable, dendrite-free cycling of lithium metal anodes with high Coulombic efficiency of up to 99.2%. Moreover, it exhibits excellent anodic stability even up to 5.0 V and greatly enhances the cycling performance of lithium metal batteries. A Li||LiNi0.6Mn0.2Co0.2O2 battery using this electrolyte can retain >97% capacity after 600 cycles at 1 C rate (ca. 1.6 mA cm−2), corresponding to a negligible capacity decay of <0.005% per cycle. Therefore, this new electrolyte can enable safe operation of high-energy lithium metal batteries for practical applications.