Enhancing vanadium pentoxide-based (VO) cathodes for high-performance aqueous zinc-ion batteries: optimization of interlayer spacing, ion kinetics, voltage window.

The urgent need for safe, affordable, and environmentally responsible energy storage has placed rechargeable aqueous zinc-ion batteries (AZIBs) at the centre of next-generation research. While earlier reviews surveyed VO cathodes in broad terms, none has yet unified the latest insights on interlayer engineering, electrolyte coordination, and diagnostics into a coherent design framework. Focusing on progress from 2019 to mid-2025, this review offers three distinctive contributions. First, it correlates the crystallographic evolution of VO, captured by synchrotron X-ray, TEM, and Raman studies, with voltage plateaus and capacity decay, providing a mechanistic map of Zn/HO co-intercalation and phase transitions. Second, it compares emerging synthesis routes (sol-gel, hydrothermal, solid-state, and electrochemical deposition) through a quantitative lens, linking specific surface area, defect chemistry, and conductivity (10 to 10 S cm) to rate capability and long-term retention. Third, it surveys interlayer-expansion strategies, metal-ion pre-intercalation, organic pillar insertion, conductive-polymer hybrids, and hierarchical nanostructuring, showing how each modulates Zn diffusivity, lattice strain (<5% with water co-insertion), and dissolution resistance. By integrating experimental advances with density-functional-theory, molecular-dynamics, and machine-learning predictions, the review distils actionable design principles and a forward roadmap for achieving >400 mAh g capacities and >90% retention beyond 2000 cycles. These new perspectives position VO not merely as a promising cathode, but as a model system for understanding and optimizing layered hosts in aqueous multivalent batteries.