Alkoxyethyl Acetate Electrolytes for High-Voltage Lithium Metal Batteries.

High-energy-density lithium metal batteries (LMBs) require electrolytes that can simultaneously support stable lithium metal anodes and high-voltage cathodes such as NMC811 operated up to 4.5 V. Here, a molecular engineering strategy is introduced in which a carbonyl group and a trifluoromethyl group are incorporated into a glycol-ether-type backbone to produce a fluorinated alkoxyethyl acetate solvent, 2-(2,2,2-trifluoroethoxy)ethyl acetate (TFE-EA), used as the main solvent in LiFSI-TFE-EA-FEC electrolytes. This design breaks the symmetric bidentate solvation typical of ether solvents, establishes carbonyl-dominant solvation, and depresses the solvating ability and oxidation reactivity of the ethereal oxygen, as revealed by combined DFT, NMR, FTIR, Raman, and AIMD analyses. The resulting TFE-EA-based electrolyte exhibits enhanced oxidative stability, improved lithium plating/stripping efficiency, dense and uniform lithium deposition, and robust cathode-electrolyte interphases in Li||NMC811 cells cycled to 4.5 V, delivering markedly superior capacity retention and Coulombic efficiency compared with ethereal counterparts. Parallel studies on the non-fluorinated alkoxyethyl acetate MEA and its ether analog EME confirm that ester introduction alone improves oxidative stability and cycling, while fluorination further amplifies these benefits. This work establishes alkoxyethyl acetates, exemplified by TFE-EA, as a promising solvent platform for practical, high-voltage LMB electrolytes.