Electrochemically Driven Phase Transition in LiCoO 2 Cathode.

Lithium cobalt oxide (LiCoO₂), which has been successfully applied in commercial lithium-ion batteries for portable devices, possesses a theoretical specific capacity of 274 mAh g⁻¹. However, its actual capacity is only half of the theoretical specific capacity, because the charging voltage is restricted below 4.2 V. If a higher charging voltage is applied, an irreversible phase transition of LiCoO₂ during delithiation would occur, resulting in severe capacity fading. Therefore, it is essential to investigate the electrochemically driven phase transition of LiCoO₂ cathode material to approach its theoretical capacity. In this work, it was observed that LiCoO₂ partially degraded to Co₃O₄ after 150 charging-discharging cycles. From the perspective of crystallography, the conventional cell of LiCoO₂ was rebuilt to an orthonormal coordinate, and the transition path from layered LiCoO₂ to cubic Co₃O₄ proposed. The theoretical analysis indicated that the electrochemically driven phase transition from LiCoO₂ to Co₃O₄ underwent several stages. Based on this, an experimental verification was made by doping LiCoO₂ with Al, In, Mg, and Zr, respectively. The doped samples theoretically predicted behavior. The findings in this study provide insights into the electrochemically driven phase transition in LiCoO₂, and the phase transition can be eliminated to improve the capacity of LiCoO₂ to its theoretical value. [ABSTRACT FROM AUTHOR]