High-nickel ternary LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode materials modified by Na-doping and MgF2 coating are synthesized by high-temperature solid-phase method. The morphology and structure of the materials are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performances test shows that the initial discharge specific capacity of the pristine NCM811 sample is 173 mAh/g at 0.5C, and the discharge specific capacity after 100 cycles is 131 mAh/g. However, when the doping amount of sodium ion is 0.05, 0.1, 0.15 respectively (NCM811-0.05Na, NCM811-0.1Na, NCM811-0.15Na), the corresponding initial discharge specific capacity of the sample is 187, 191, 179 mAh/g, and the corresponding discharge specific capacity after 100 cycles is 140, 158, 119 mAh/g. Discharged at 0.1, 0.5, 1, 2, 5 and 10C rate, the discharge specific capacity for the pristine NCM811 samples is 193, 170, 156, 138, 106 and 79 mAh/g respectively, while the corresponding value for NCM811-0.1Na samples is 203, 191, 180, 165, 137 and 105 mAh/g respectively. And for the sample modified by Na-doping and MgF2 coating (NCM811-Na@MgF2), the corresponding discharge specific capacity is 210, 196, 183, 172, 146 and 126 mAh/g respectively. It can be seen that the synergistic modification by Na-doping and MgF2 coating is beneficial to the improvement of electrochemical performances of high nickel ternary NCM811 cathode material. (C) 2019 The Electrochemical Society.