Structurally Coordinated Water Enhances Structural Stability of Tunnel‐Type Co(VO ₃ ) ₂ ·2H ₂ O Cathodes for Aqueous Zinc‐Ion Batteries

ABSTRACT Tunnel‐type cobalt vanadate dihydrate (Co(VO ₃ ) ₂ ·2H ₂ O, CoVO) is first demonstrated as a robust cathode for aqueous Zn‐ion batteries. The orthorhombic framework, built from CoO ₆ octahedra and VO ₄ tetrahedra, incorporates two structural water molecules directly coordinated to Co ²⁺ . These structural waters serve critical functions: 1) forming hydrogen‐bond networks that buffer local strain, 2) shielding electrostatic repulsion between Zn ²⁺ and the polyanionic framework, and 3) creating secondary diffusion channels that accelerate H ⁺ /Zn ²⁺ transport. Owing to this cooperative effect, CoVO delivers 83.6 mAh/g at 0.5C and retains 90.6% capacity after 1000 cycles at 3C. Ex situ XRD and Rietveld refinements confirm a topotactic, zero‐strain intercalation mechanism (ΔV = 0.17%) without bulk decomposition, while bond valence sum analysis reveals dual‐ion pathways with low migration barriers. The synergy between tunnel topology and structural water coordination underpins the exceptional rate capability, minimal impedance growth, and long‐term stability, establishing a general design strategy for advanced multivalent‐ion battery cathodes.