Characterization of LiCoO 2 coated Li 1.05Ni 0.35Co 0.25Mn 0.4O 2 cathode material for lithium secondary cells

Abstract

In this study, nano-crystalline LiCoO 2 was coated onto the surface of Li 1.05Ni 0.35Co 0.25Mn 0.4O 2 powders via sol–gel method. The influence of the coating on the electrochemical behavior of Li 1.05Ni 0.35Co 0.25Mn 0.4O 2 is discussed. The surface morphology was characterized by transmission electron microscopy (TEM). Nano-crystallized LiCoO 2 was clearly observed on the surfaces of Li 1.05Ni 0.35Co 0.25Mn 0.4O 2. 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 LiCoO 2 coated Li 1.05Ni 0.35Co 0.25Mn 0.4O 2 cathode material exhibited distinct surface morphology and lattice constants. Cyclic voltammetry (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.% LiCoO 2 coating. This behavior implies that LiCoO 2 inhibits structural change of Li 1.05Ni 0.35Co 0.25Mn 0.4O 2 or reaction with the electrolyte on cycling. In addition, the LiCoO 2 coating on Li 1.05Ni 0.35Co 0.25Mn 0.4O 2 significantly improves the rate capability over the range 0.1–4.0 C. Comparative data for the coated and uncoated materials are presented and discussed.