Intercalation of Ca into a Highly Defective Manganese Oxide at Room Temperature

The utilization of oxide frameworks as intercalation cathodes for nonaqueous Ca-ion batteries potentially unlocks a new energy-storage system that delivers high energy density. However, the slow kinetics of Ca2+ in oxide electrodes strongly handicaps their activity and reversibility at room temperature. Herein, nanocrystals of layered MnOx containing a high concentration of atomic defects and lattice water are shown to have remarkable electrochemical activity toward Ca2+, amounting to a capacity of ∼130 mAh/g at room temperature. Multimodal characterization revealed the notable degree of intercalation by probing the structural, compositional, and redox changes undertaken by the defective MnOx nanocrystals. The results suggest that the existence of atomic defects and lattice water played a role in improving Ca2+ diffusivity in the oxide. These outcomes reaffirm the prospects for functional Ca-ion batteries using oxide cathodes under moderate conditions.