Mg doping and zirconium oxyfluoride coating co-modification to enhance the high-voltage performance of LiCoO₂ for lithium ion battery

Highlights: • Oxyfluoride ZrO_xF_y is investigated as coating material. • First introducing the co-modification of LiCoO₂ by Mg doping and ZrO_xF_y coating. • Co-modified LiCoO₂ exhibits enhanced high-voltage electrochemical performance. • Possible mechanisms of Mg-doping and ZrO_xF_y-coating co-modification are discussed. - Abstract: Mg doping and zirconium oxyfluoride (ZrO_xF_y) 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 ZrO_xF_y 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 ZrO_xF_y-coating alleviates unwanted interfacial side reactions between the cathode and electrolyte, thereby suppressing Co dissolution and the impedance growth during prolonged cycling