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Calcium ion batteries (CIBs) are considered as an important candidate for post‐lithium energy storage devices due to their abundance of resources and low cost. However, CIBs still suffer from slow kinetics due to the large solvation structure and high desolvation energy of Ca2+ ions. Here, a solvation regulation strategy based on donor number (DN) is reported to achieve easy‐desolvation and rapid storage of Ca2+ in sodium vanadate (Na2V6O16·2H2O, NVO). Specially, the solvent with a low DN, represented by propylene carbonate (PC), forms the first solvation shell of calcium ions with weak binding energy and small shell structure, which facilitates the migration of Ca2+ in the electrolyte. More importantly, the low DN solvent is preferentially desolvated at the cathode/electrolyte interface, promoting the insertion of Ca2+ into the NVO electrode. Mechanism studies further confirm the highly reversible uptake/release of Ca2+ in the NVO cathode, along with the VO distance change in the coordination structure. Therefore, the NVO cathode achieves high capacity (376 mAh g−1 at 0.3 A g−1) and high‐rate performance (151 mAh g−1 at 5 A g−1). The weak solvation effect strategy further improves the electrochemical performance and provides great importance for the design of the long‐term development of CIBs. [ABSTRACT FROM AUTHOR]

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, V2O5 pre‐intercalated with various transition metal ions M2+ (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 M2+ 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 VOx polyhedron and local electronic structure. Furthermore, NiVO cathode materials with the smallest layer spacing shows higher redox voltage and better rate/cycling performance for Ca2+ 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 Ca2+. 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. [ABSTRACT FROM AUTHOR]

Metal nitrides and quasi‐metallic compounds have been extensively employed as sulfur hosts for confining polysulfide shuttling and improving the electronic conductivity. Their electronic structures and surface chemical bonds significantly determine the adsorption and catalytic abilities for polysulfide. However, the surface compositions of the reported metal nitrides and their sulfur anchoring mechanisms are still controversial. Herein, the authors demonstrate the anion‐substituted mechanism from vanadium oxide, oxynitride to nitride during ammonia‐annealing process and systematically unravel the long‐range disorder rock‐salt structure of vanadium oxynitride with abundant vanadium (V) and nitrogen (N) vacancies by synchrotron X‐ray absorption spectra, atomic pair distribution function, and density functional theory calculation. The defect‐rich vanadium oxynitride that is previously considered as vanadium nitride possesses the enhanced electron delocalization of V, N, and oxygen (O) atoms. It strengthens the polar LiN/O and VS bonds, especially near V vacancy, resulting in a strong polar adsorption for polysulfide. Meanwhile, the vanadium oxynitride effectively catalyzes the breaking and conversion of polysulfide, improving the reduction kinetics during discharge process. The bifunctional effects render the excellent cycling and rate performances. This work deeply understands the sulfur redox mechanisms on vanadium oxynitride and nitride and promotes the developments of the quasi‐metallic compounds/sulfur cathodes in Lithium‐sulfur battery. [ABSTRACT FROM AUTHOR]