Unsaturated Coordination Oxygen in Zn─V─O Vacancy Clusters Enables Superb Zinc Storage Capability

Vanadates have been extensively applied in aqueous zinc-ion batteries (AZIBs) for the enlarged interlayer spacing and rich active sites induced by the pre-intercalation of metal or ammonium ions. However, the strong electrostatic interaction between Zn²⁺ ions and guest cations always results in finite insertion ability of Zn²⁺ ions and low specific capacity. Herein, Zn₃(VO₄)₂ with Zn─V─O vacancy clusters (Zn₃(VO₄)₂-V_ZVO) is innovatively prepared as cathode material for AZIBs. Based on the ab initio molecular dynamics (AIMD) simulations and comprehensive characterizations, the Zn─V─O vacancy clusters are demonstrated to effectively capture most of free Zn²⁺ and H⁺ ions, reduce the inherent electrostatic interaction, and contribute the dominative capacity through abundant unsaturated coordination oxygen atoms. Additionally, part of adsorbed Zn²⁺ ions can reversibly intercalate Zn₃(VO₄)₂-V_ZVO and transform into Zn₃V₂O₇(OH)₂·2H₂O to contribute the remaining capacity. Consequently, the optimized Zn₃(VO₄)₂-V_ZVO cathode delivers high reversible capacity of 410 mAh g^-1 at 1.0 A g^-1 and satisfying capacity retention of 94.1% after 800 cycles at 0.1 A g^-1. This study not only reveals the formation and action mechanism of unsaturated coordination oxygen sites in Zn₃(VO₄)₂-V_ZVO cathode, but also offers new insight to design high-performance cathode materials for AZIBs.