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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Renewable Energy, Sustainability and the Environment
- Surfaces, Coatings and Films
- Materials Chemistry