Unveiling Mo doping effects in hydrated vanadium oxide cathodes for high-energy zinc-ion batteries: Evidence from operando synchrotron X-ray and DFT analysis

Aqueous zinc-ion batteries (AZIBs) offer strong potential for grid-scale energy storage, yet their performance is often constrained by sluggish Zn²⁺ diffusion and insufficiently stable cathode hosts. In this work, we develop a Mo-doped hydrated vanadium oxide (MoVOH/VOH) cathode designed to overcome these limitations. Using operando X-ray diffraction, operando XANES, and extended X-ray absorption fine structure (EXAFS) analysis combined with density functional theory (DFT) calculations, we not only elucidate the Zn²⁺ storage mechanism but also resolve the previously controversial structural position of Mo within the VOH framework. Our results demonstrate that high-oxidation-state Mo ions are predominantly incorporated substitutionally within the V-O layers, rather than occupying interlayer sites. This substitution significantly improves electronic conductivity, accelerates Zn²⁺ transport, and stabilizes the VOH lattice during repeated cycling. Consequently, the MoVOH/VOH cathode delivers a high capacity of 405 mAh g⁻¹ at 0.1 A g⁻¹, excellent rate capability, and 82% capacity retention after 300 cycles at 5 A g⁻¹, and an energy density of ∼284 Wh kg⁻¹ at 71 W kg⁻¹. These findings demonstrate that Mo doping is an effective strategy for tailoring vanadium-based hosts for high-performance AZIBs and provide direct experimental and theoretical insight into the local structural role of Mo, addressing a key unresolved issue in hydrated vanadium oxides.