The first question we need to answer is that whether it is reasonable to apply the bias on Co ions. In other words, why we can presume that the Co cross-layer migration in CoO2 is more likely to occur ahead of a direct oxygen dimer formation? We therefore employ the CI-NEB method to compare the barrier of the Co cross-layer migration with a perfect oxygen sublattice to the barrier of the oxygen dimer combination with all the TM ions located in the stable octahedral sites in the TM layer. Visualizations of the above processes and the corresponding barriers are displayed in Figure . The results show that the Co ion migration in the absence of oxygen dimers exhibits a lower barrier.