A nonflammable electrolyte for ultrahigh-voltage (4.8 V-class) Li||NCM811 cells with a wide temperature range of 100 °C

Abstract

The development of ultrahigh-voltage lithium metal batteries is one of the most promising ways to increase the energy density. However, commercial ethylene carbonate (EC)-based electrolytes have poor compatibility with both lithium metal anodes and cathodes at ultrahigh voltages. We report a high-voltage resistant electrolyte (HV electrolyte) produced by the fluorination of commercial solvents with the guidance of theoretical calculations. These designed solvents, with low energy levels of the lowest unoccupied molecular orbital (LUMO), can be preferably reduced at the lithium metal anode, suppressing lithium dendrite growth because of the formation of a LiF-rich solid–electrolyte interphase (SEI). Fluorination also decreases the energy levels of the highest occupied molecular orbital (HOMO), resulting in improved anodic stability at ultrahigh voltages. The low binding energies between fluorinated solvents in the HV electrolyte and Li⁺ accelerate the desolvation of Li⁺, leading to excellent electrochemical kinetics. As a result, Li||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cells, which can work in a wide operating temperature range from −30 to 70 °C, have capacity retentions of 95.1% after 160 cycles and 85.7% after 100 cycles at ultrahigh cut-off voltages of 4.7 and 4.8 V, respectively. Li||NCM811 cells with a thin (50 μm) lithium metal anode and a lean electrolyte were constructed, and had a capacity retention of 89.2% after 150 cycles, demonstrating high potential in practical use as high energy density batteries.