Tuning interlayer water content for optimized stability and mechanistic insights in bilayered V2O5∙nH2O cathode material for Zinc (Magnesium)-ion batteries: A DFT and AIMD study

Abstract

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.