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 MnO x 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 MnO x 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.