Unraveling the Dynamic Correlations between Transition Metal Migration and the Oxygen Dimer Formation in the Highly Delithiated Li x CoO 2 Cathode.

The voltage-window expansion can increase the practical capacity of Li x CoO 2 cathodes, but it would lead to serious structural degradations and oxygen release induced by transition metal (TM) migration. Therefore, it is crucial to understand the dynamic correlations between the TM migration and the oxygen dimer formation. Here, machine-learning-potential-assisted molecular dynamics simulations combined with enhanced sampling techniques are performed to resolve the above question using a representative CoO 2 model. Our results show that the occurrence of the Co migration exhibits local characteristics. The formation of the Co vacancy cluster is necessary for the oxygen dimer generation. 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. Our work reveals atomic-scale dynamic correlations between the TM migration and the oxygen sublattice's instability and provides insights about the dopant's promotion of the structural stability.