CF3-Substituted Ethylene Carbonates for High-Voltage/High-Energy Rechargeable Lithium Metal-LiNi0.8Co0.1Mn0.1O2 Batteries.

Abstract

The development of advanced liquid electrolytes for high-voltage/high-energy rechargeable Li metal batteries is an important strategy to attain an effective protective surface film on both the Li metal anode and the high-voltage composite cathode. Herein, we report a study of two CF3-substituted ethylene carbonates as components of the electrolyte solutions for Li metal|NCM811 cells. We evaluated trifluoromethyl ethylene carbonate (CF3-EC) and trans-ditrifluoromethylethylene carbonate Di-(CF3)-EC as cosolvents and additives to the electrolyte solutions. Using CF3-substituted ethylene carbonates as additives to a fluoroethylene carbonate (FEC)-based electrolyte solution enables improved capacity retention of high-power Li metal|NCM811 cells. The composition of the products from the transformations of CF3-EC and Di-(CF3)-EC in Li|NCM811 cells was studied by FTIR, XPS, and 19F NMR spectroscopy. We concluded that fluorinated Li alkyl carbonates are the main reaction products formed from these cyclic carbonates during the cycling of Li|NCM 811 cells, and fragmentation of the ring with the formation of CO2, CO, or olefins is not characteristic of CF3-substituted ethylene carbonates. The NCM 811 cathodes and Li metal anodes were characterized by X-ray diffraction, SEM, XPS, and FTIR spectroscopy. The role of CF3-substituted ethylene carbonate additives in stabilizing high energy density secondary batteries based on Li metal anodes was discussed. A bright horizon for developing sustainable rechargeable batteries with the highest possible energy density is demonstrated.