Stabilized Phase Transition Process of Layered NaxCoO2 via Ca-Substitution

We investigated the suppressed capacity fading of a Ca-substituted P3-type NaxCoO2 during the charge/discharge process. The Ca-substituted NaxCoO2 shows similar phase transition behavior to the Ca free one, with an expanded P ' 3 phase region. The capacity fading of the NaxCoO2 is highly correlated with the phase transition at 4.0 V of P ' 3-O3 ' phase transition and at 2.7 V of O ' 3-P ' 3 phase transition. The amount of Co3O4 observed in the cycled electrodes corresponds to the capacity loss during the cycling test. Thus, the migration of the Co3+/4+ ions during the phase transition process causes the capacity fading. The decomposition of the electrolyte solution also accelerates the migration of the Co3+/4+ ions. Though the Ca-substitution does not prevent the phase transition, the Ca-substituted NaxCoO2 shows improved capacity retention.

Automated summary

The study found that Ca substitution in NaxCoO2 affects its capacity fading during charge and discharge cycles, mainly due to the migration of Co3+/4+ ions. Although Ca substitution does not completely prevent phase transitions, it does improve capacity retention.