High-Capacity LiNi0.8Co0.1Mn0.1O2 Positive-Electrodes in the Nearly Saturated and Fluorinated Acetate-Diluted Electrolyte Solutions

Six kinds of acetic acid esters substituted with a different number of fluorine atoms were systematically investigated as a diluent for the nearly saturated LiBF4-based electrolyte solutions. Of these, only one fluorinated acetic acid ester was found to be suitable for the dilution and to greatly improve the charge–discharge cycle performance of LiNi0.8Co0.1Mn0.1O2 (NCM811) electrodes. The charging voltage was raised to 4.6 V to increase the discharge capacities. The structure and thermal stability of the diluted electrolyte solutions, as well as the surface of the NCM811 electrodes after repeated charge/discharge cycles, were analyzed to elucidate the mechanism for the improved performance.