Improving the cycling stability of LiCoO2 at 4.5 V through co-modification by Mg doping and zirconium oxyfluoride coating

The co-modification by Mg doping and zirconium oxyfluoride (ZrOxFy) coating is employed to improve the cycling stability of LiCoO2 in the voltage range of 3.0–4.5 V. SEM, TEM images and EDS mappings of the modified sample confirm that there is a compact ZrOxFy coating layer on the surface of the cathode particles and the doping element (Mg) distributes uniformly in the modified sample. Electrochemical tests demonstrate that the co-modified sample exhibits obviously enhanced cycling stability in the voltage range of 3.0–4.5 V, which maintains 91.2% of its initial capacity after 100 cycles at 1 C rate. That is much more than 64.4% for the pristine sample. Moreover, EIS, XRD 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 growth of impedance during prolonged cycling.