Improving thermal and electrochemical performances of LiCoO2 cathode at high cut-off charge potentials by MF3 (M=Ce, Al) coating

Abstract

Surface coating of LiCoO2 remained one of the efficient methods to enhance its electrochemical and thermal performances, especially at high cut-off potential. In this work, MF3 (M=Ce, Al) coated LiCoO2 was synthesized via co-precipitation method followed by a solid state reaction at 400°C. The morphology and structure of the modified cathode material were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the fluoride compound MF3 is successfully coated on the surface of LiCoO2 cathode particles with an average layer thickness about 12nm and 40nm for AlF3 and CeF3, respectively.The electrochemical tests show that the AlF3-coating layer significantly enhances the cycling performance of LiCoO2 cathode material, even at high cut-off potential. While the bare LiCoO2 cathode displays fast fading at 4.6V vs. Li+/Li cutoff potential, the surface-modified electrode exhibits the great capacity of 160mAhg−1 with excellent capacity retention on several cycles.We concluded that the electrochemical and the thermal enhancement at high potential are ascribed to the presence of MF3 coating layer which prevent the side reaction during the charge discharge process, alleviate the attack by the acidic electrolyte and reduce the damage of electrode structure.