Effects of Methyl Acetate as a Co-Solvent in Carbonate-Based Electrolytes for Improved Lithium Metal Batteries

In lithium metal batteries (LMBs), electrolytes composed of salts and organic solvents play a significant role in transporting Li⁺ ions and creating the surface film on Li-metal anodes. Herein, the effect of methyl acetate (MA) as a co-solvent is reported, which enables the facilitated Li⁺ transport and formation of a robust solid electrolyte interphase (SEI) on the Li-metal anode. The symmetrical Li//Li cell tests show remarkable cycle stability of MA-based electrolytes at 3 mA/cm² without obvious voltage fluctuation. At 5 mA/cm², the Li//Li cells in MA-based electrolytes can still run up to 110 h with lower overpotential, compared to the cell cycled with MA-free electrolytes. Furthermore, the LMBs consisting of the Li anode and LiNi_0.8Co_0.15Al_0.05O₂ (NCA) cathode deliver the high capacity (∼200 mA h/g), good cycling stability up to 300 cycles, excellent rate capability (10 C), and low self-discharging rates (8.5%) with MA-based electrolytes. Especially, the capacity of the Li//NCA cells with MA30 electrolytes at -35 °C is as high as 144 mA h/g, which is higher than that of the cells in MA-free electrolytes. It demonstrates that the MA is beneficial for the LMB operation at high rate and low temperature.