Unraveling the Dynamic Correlations between Transition Metal Migrations and the Oxygen Dimer Formation in the Layered LiCoO2 Cathode

Expanding the voltage window is a common approach for increasing the practical capacity of the LiCoO2 cathode. However, it brings serious concerns such as structural degradations and the associated oxygen release induced by the transition metal (TM) cation migrations at a highly delithiated state. Therefore, it is crucial to understand the dynamic correlations between the TM cation migrations and the oxygen dimer formation. In this work, machine-learning-potential-assisted molecular dynamics simulations combined with enhanced sampling techniques are performed to resolve the above question using a representative CoO2 model. Our results show that the occurrence of the Co migrations exhibits local characteristics. The formation of two adjacent Co vacancies (the Co vacancy cluster) is necessary for the oxygen dimer generation. We further show that the introduction of the Ti dopant can significantly increase the kinetic barrier of the Co ion migration and thus effectively suppress the formation of the Co vacancy cluster. Overall, our work reveals the atomic-scale dynamic correlations between the TM migrations and the instability of the oxygen sublattice in the cathode material, and provides insights about the mechanism of the dopants promotion on the stability of cathode materials.