High-voltage Li metal batteries enabled by a nonflammable amphiphilic electrolyte

Ether-based solvents generally have low oxidative stability and high flammability, which have hindered their application in practical high-voltage lithium metal batteries. Herein, we report an amphiphilic ether-based electrolyte whose solvent contains a lithiophilic epoxy functional group and a lithiophobic carbon-fluorine chain segment to address these critical challenges. The electrolyte of 1.5 M LiFSI/FEO presents a special core-shell solvation structure in a self-assembled form, leading to the increased Li+ transference number. Moreover, it is flame-retardant and enables the formation of stable F-rich SEI on the Li metal anode and CEI on the NCM811 cathode. As a result, the Li||Cu cell demonstrates a high Li Coulombic efficiency of 99.1 %, and the Li||NCM811 cell exhibits outstanding cycling stability with high capacity retention of more than 80 % over 200 cycles at an upper-limit voltage of 4.5 V. This research confirms that ether electrolytes are competent in lithium metal batteries with high energy density, long lifetime, and high safety.