3d-Orbital Regulation of Transition Metal Intercalated Vanadate as Optimized Cathodes for Calcium-Ion Batteries

Vanadate materials are feasible cathodes for metal–ion batteries due to their stable layered structure, abundant valence states, and high capacity. However, much uncertainty still exists about precisely modulating intercalants to facilitate ion storage. Here, V 2 O 5 pre-intercalated with various transition metal ions M 2+ (M═Ni, Co, Mn) are developed as model materials to analyze the coupling effect between guest ions and host material. Through density functional theory simulations, it is found that M 2+ interacts with V–O chain via M 3d-O 2p covalent bonds, and extended X-ray absorption fine structure reveals the Ni─O interatomic distance at 1.56 Å shorter than Co─O (1.60 Å) and Mn─O (1.72 Å), suggesting the M–O band type with different covalency degree can optimize VO x polyhedron and local electronic structure. Furthermore, NiVO cathode materials with the smallest layer spacing shows higher redox voltage and better rate/cycling performance for Ca 2+ storage than CoVO/MnVO, elucidating that Ni has stronger tendency to attract electrons and bonds with V–O layer tightly, thus supplying a reliable ion diffusion channel for Ca 2+ . Through ions pre-intercalated techniques, this work highlights both layer spacing and physicochemical properties of intercalants affect electrochemical process, which is significant for developing high-performance vanadate cathode materials.