LiCoO2, Mg-doped LiCoO2, and Zr doped LiCoO2, are manufactured by a sol–gel method, and are used as cathode active materials for lithium rechargeable batteries. The structural characteristics of the synthesized electrodes are analyzed by X-ray diffraction. The materials have a layered structure with the space gropu R 3 ¯ m of hexagonal systems. LiCoO2 prepared by sol–gel method shows a capacity decay over 4.3V but LiCoO2 doped with Mg and Zr give an improvement in charge–discharge cycling performance. This effect may attribute to the fact that Mg2+ and Zr4+ ions have the same size as the Li+ ion and they locate at the inter-slab space. Therefore, they provide a pathway for the intercalation–deintercalation of Li+ during the charge and the discharge processes and prevent distortion of the structure. Also, the formation of a solid solution on the surface of the electrode acts as the buffer to phase transition and the structure becomes very stable.