First-principles identification of spinel CaCo2O4 as a promising cathode material for Ca-ion batteries

The search for potential cathode materials is essential for the development of Ca-ion-based batteries, which are a cheap alternative to Li-ion batteries. In this work, we report a first-principles investigation into the feasibility of using spinel CaCo2O4 as a cathode for Ca-ion batteries. The results show that the spinel CaCo2O4 structure is stable, indicating that the synthesis of this compound should be feasible. The predicted voltage is consistently above 3.0 V at any Ca concentration, which is interesting for a cathode. Electronic structure analysis shows that the extracted spinel CaxCo2O4 compounds are metallic, which is indicative of good electronic conduction properties. The calculated activation energy barriers for Ca2+ migration are 0.58 and 0.22 eV at 100% Ca and 0% Ca concentrations, respectively, which suggest favorable electrode kinetics. Overall, the demonstrated structural stability, high average voltage, good electronic conductivity and excellent Ca2+ mobility highlight the promising potential of spinel CaCo2O4 as a cathode for Ca-ion batteries. The new fundamental insights presented here should stimulate further work on spinel CaCo2O4 cathodes for Ca-ion batteries.