LiCoO[sub 2] Cathode Material That Does Not Show a Phase Transition from Hexagonal to Monoclinic Phase

Structural instability of can be improved by sol-gel coating of and subsequent heat-treatments. While phase does not exist after heat-treatments, solid solution that has discretely higher Al concentration was formed at the surface up to ∼500 Å inside the particle. However, heat-treatment to 700°C results in the presence of the solid solution beyond ∼500 Å. The different Al concentration at the surface significantly affects the structural stability of the materials during cycling, and those prepared at 400°C 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°C show improved layered characteristics with cation order. © 2001 The Electrochemical Society. All rights reserved.