Characterization of LiCoO2 coated Li1.05Ni0.35Co0.25Mn0.4O2 cathode material for lithium secondary cells

In this study, nano-crystalline LiCoO2 was coated onto the surface of Li1.05Ni0.35Co0.25Mn0.4O2 powders via sol-gel method. The influence of the coating on the electrochemical behavior of Li1.05Ni0.35Co0.25Mn0.4O2 is discussed. The surface morphology was characterized by transmission electron microscopy (TEM). Nano-crystallized LiCoO2 was clearly observed on the surfaces of Li1.05M0.35Co0.25Mn0.4O2. The phase and structural changes of the cathode materials before and after coating were revealed by X-ray diffraction spectroscopy (XRD). It was found that LiCoO2 coated Li1.05Ni0.35Co0.25Mn0.4O2 cathode material exhibited distinct surface morphology and lattice constants. Cyclic voltarnmetry (2.8-4.6 V versus Li/Li+) shows that the characteristic voltage transitions on cycling exhibited by the uncoated material are suppressed by the 7 wt.% LiCoO2 coating. This behavior implies that LiCoO2 inhibits structural change of Li1.05M0.35Co0.25Mn0.4O2 or reaction with the electrolyte on cycling. In addition, the LiCoO2 coating on Li1.05M0.35Co0.25Mn0.4O2 significantly improves the rate capability over the range 0.1-4.0C. Comparative data for the coated and uncoated materials are presented and discussed. (c) 2007 Published by Elsevier B.V.