High voltage stability and enhanced electrochemical performances of LiCoO2 by CeF3 coating

Surface coating of LiCoO
₂
remained one of the efficient methods to enhance its electrochemical and thermal performances, especially at high cut-off potential. For several years, REMINEX research center has worked on the development of cathode materials for lithium batteries. Recently, a patent was published on a new cathode materials based on Ce doped-LiCoO
₂
. Based on previous works and our know-how on cerium chemistry, we developed LiCoO
₂
coating using Ce-based compounds. In this work, CeF
₃
coated LiCoO
₂
was synthesized via solid state reaction of cobalt oxide and lithium carbonates followed by precipitation of CeF
₃
in presence of lithium cobalt oxide powder. 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 the disappearance of the Hexagonal-Monoclinic transition around 4.1V by coating. This transition contributes indeed in the structural instability of bare-LiCoO
₂
. the fluoride compound CeF
₃
is successfully coated on the surface of LiCoO
₂
cathode particles with an average layer thickness about 40 nm. The electrochemical tests show that the CeF
₃
-coating layer significantly enhances the cycling performance of LiCoO
₂
cathode material, even at high cut-off potential. While the bare LiCoO
₂
cathode displays fast fading at 4.6 V vs. Li
⁺
/Li cutoff potential, the surface-modified electrode exhibits the great capacity of 160 mAh/g with an excellent capacity retention on several cycles. The thermal stability of coated LiCoO
₂
was also improved by the surface modification. We concluded that the electrochemical and the thermal enhancement at high potential are ascribed to the presence of CeF
₃
coating layer which prevents the side reaction during the charge discharge process, alleviate the attack by the acidic electrolyte and reduce the damage of electrode structure.