Abstract
The cycle life of LiCoO2 cathodes cycled at a high cutoff voltage can be largely improved by surface modification with ZnO coating. The bright-field transmission electron microscopy (TEM) images and selected area diffraction patterns of as-coated LiCoO2 particles reveal the existence of continuous ZnO films with a 10-nm thickness deposited on LiCoO2 surfaces, indicating a Li-Zn-O phase formed on the surface region. Besides high-voltage cycleability, cycle-life degradation caused by inappropriate conductive carbon can also be moderated by ZnO coating. Furthermore, the rate capability at high current density can also be notably improved. The role ZnO coating played in the charge-discharge process is discussed from the viewpoint of surface chemistry with the aid of data from scanning electron microscopy, TEM, energy-dispersive X-ray, and impedance spectra. Moreover, the correlation between electrochemical performance and surface properties of ZnO-coated LiCoO2 is explored.