Structural instability of LiCoO2 can be improved by sol-gel coating of Al2O3 and subsequent heat-treatments. While Al2O3 phase does not exist after heat-treatments. solid solution LiCo1-xAlxO2 that has discretely higher Al concentration was formed at the surface, up to similar to 500 Angstrom inside the particle. However, heat-treatment to 700 degreesC results in the presence of the solid solution beyond similar to 500 Angstrom. The different Al concentration at the surface significantly affects the structural stability of the materials during cycling, and those prepared at 400 degreesC do not show a phase transition from hexagonal to monoclinic phase, Disappearance of such a phase transition improves capacity retention of the cathode. Moreover, cathodes prepared at 400 and 500 degreesC show improved layered characteristics with cation order.