Hybrid diluents enable localized high-concentration electrolyte with balanced performance for high-voltage lithium-metal batteries

Localized high-concentration electrolytes (LHCE) have shown good compatibility with high-voltage lithium (Li)-metal batteries, but their practicality is yet to be proved in terms of cost and safety. Here we develop a hybrid-LHCE with favorable integrated properties by combining the merits of two representative diluents, fluorobenzene (FB) and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFE). Specifically, the extremely cheap and lightweight FB significantly reduces the cost and density of electrolyte, while the fire-retardant TFE circumvents the flammable nature of FB and thus greatly improves the safety of electrolyte. Moreover, the FB–TFE mixture enhances the thermodynamic stability of hybrid-LHCE and renders a controllable defluorination of FB, contributing to the formation of a thin and durable inorganic-rich solid electrolyte interphase (SEI) with rapid ion-transport kinetics. Benefiting from the designed hybrid-LHCE, a Li|NCM523 battery demonstrates excellent cycling performance (215 cycles, 91% capacity retention) under challenging conditions of thin Li-anode (30 µm) and high cathode loading (3.5 mAh/cm2).