Characterization of Surface of LiCoO₂Modified by Zr Oxides Using Analytical Transmission Electron Microscopy

To understand the effect of surface modification on the degradation of battery materials, analytical transmission electron microscopy (TEM), which provides fine structure and chemical state with high spatial resolution, was applied. To address current issues about the artificial damage around the surface region of cathodic oxide particles from sample preparation, such as ion milling, LiCoO 2 submicron particles were synthesized by using the Pechini method; LiCoO 2 particles modified by the oxides of Zr were prepared by using the evaporation and dryness method. Smaller Zr-oxide particles with a diameter of about 10 nm and partial coverage were deposited on LiCoO 2 to explore the effect of coating. The cycling properties of a cell containing LiCoO 2 were improved by coating with Zr oxides even in the inhomogeneous coverage. Capacity retention was found to be virtually the same as that of cells containing LiCoO 2 coated with 5 wt% and 10 wt% oxides of Zr. Our TEM results revealed a thin Li-Zr oxide overlayer on the LiCoO 2 surface, where Zr-oxide particles were not deposited. It is suggested that this thin overlayer can provide an effective improvement of the electrochemical performance.