Nonflammable, Low-Cost, and Fluorine-Free Solvent for Liquid Electrolyte of Rechargeable Lithium Metal Batteries

Rechargeable metallic lithium batteries are considered as promising candidates for next-generation energy storage due to their high energy densities. However, safety concerns associated with electrolyte flammability and dendrite growth hinder their practical applications. Nonflammable liquid electrolytes have attracted significant attention recently, but they are mainly based on expensive ionic liquids, fluorinated solvents, or with highly concentrated salt. Here we design a novel trisalt electrolyte composed of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-lithium bis(oxalato)borate (LiBOB)-LiPF₆ in EC/PC solvent, which is not flammable even in contact with fire. Moreover, it creates unique protection of solid electrolyte interphase (SEI) film on lithium metal anode that allows 400 cycles of Li/Li(NiMnCo)_1/3O₂ cells with a capacity retention of 97.0% at 0.83 mA cm^-2. This work illustrates that low-cost fluorine-free carbonate solvents can also realize nonflammable electrolyte with high performance, which opens new opportunities to promote safety and energy density of rechargeable lithium batteries simultaneously.