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Hydrated vanadium pentoxide, V2O5·1.75H2O has emerged as a promising cathode material for multivalent ion batteries due to its tunable layered structure and enhanced ion transport properties. In this study, density functional theory (DFT) simulations are applied to investigate bilayer V2O5·nH2O material, focusing on how water content (n = 0, 1, 1.75, 2 and 2.25) influences its structural stability, electronic properties and ion intercalation behavior. Structural water forms hydrogen-bonded networks and pentameric clusters that expand the interlayer spacing, preserve VO5 coordination, and create efficient diffusion pathways for Zn2+ and Mg2+ ions. Electronic structure analysis reveals that water intercalation narrows the band gap and increases electronic conductivity, while charge redistribution around vanadyl oxygen sites enhances cation–host interactions. The results indicate that the interlayer spacing expands from 2.44 Å (n = 0) to 7.94 Å (n = 2.25), with an optimal water ratio of approximately 1.75. This value is close to the experimentally observed value of 1.8. Moreover, it is found that V2O5·1.75H2O exhibits the lowest bandgap (0.21 eV), which is beneficial for enhancing electronic conductivity and contributes to improved rate capability. However, excessive water content (n = 2.25) leads to reduced charge density and increased bandgap, highlighting the importance of interlayer spacing optimization. Overall, V2O5·1.75H2O provides an optimal balance between structural robustness, ion transport, and electrochemical performance, exhibiting a moderate volume expansion (ΔV/V₀ ≈ 0–3%), a low band gap of 0.21 eV for enhanced electronic conductivity, and reversible Zn2+ and Mg2+ insertion capacities of 251.06 and 188 mAh g⁻¹, respectively, making it a highly promising cathode for aqueous Zn-ion and Mg-ion batteries. These findings provide critical insights into the role of structural water in multivalent ion intercalation and offer a rational strategy for designing high-performance hydrated vanadium oxide electrodes.
Nguyen et al. (Wed,) studied this question.