Mg doping and zirconium oxyfluoride (ZrOxFy) coating are introduced simultaneously to improve the high-voltage performance of LiCoO2 cathode material. XRD, TEM and XPS analysis confirm that the doping element (Mg) is incorporated into the lattices of the modified samples and there is a compact ZrOxFy coating layer on the surface of the co-modified sample. In addition, DSC results indicate that the modified samples show better thermal stability at the charged state. Electrochemical tests demonstrate that the cycling capability of co-modified sample is enhanced apparently, which maintains 76.3% of its initial capacity after 100 cycles at 1 C in the voltage range of 3.0-4.6 V. That is much more than 19.5% for the pristine sample. Moreover, EIS, XRD, TEM and Co dissolution tests of the cycled electrodes reveal that Mg-doping stabilizes the crystal structure of LiCoO2 and ZrOxFy-coating alleviates unwanted interfacial side reactions between the cathode and electrolyte, thereby suppressing Co dissolution and the impedance growth during prolonged cycling.