A Ca3Co3FeO9 electrode exhibiting enhanced cycle-life performance compared to that of Co3O4 was presented in this study. In order to examine the mechanism of the improved capacity retention in the Ca3Co3FeO9 electrode, the cycling-induced variation of electrode kinetics was observed using electrochemical impedance spectroscopy. The separable electrochemical reactions using the appropriate equivalent circuit and the goodness-of-fit results demonstrated the superior charge-transfer kinetics of Ca3Co3FeO9, compared to Co3O4, during prolonged cycling. These results clearly demonstrated the benefits of the inactive CaO matrix that is spontaneously formed in Ca3Co3FeO9 during the first discharge process.
