A new tunnel-type V₄O₉ cathode for high power density aqueous zinc ion batteries

A mixed valence V₄O₉ with a tunnel structure and room temperature metallic properties was prepared via partially reducing vanadium pentoxide. Its unique tunnel structure and metallic characteristics are beneficial for fast zinc ion and electron diffusion. A Zn//V₄O₉ battery displays a high rate performance of 234.4 mA h g⁻¹ at 50C, a large reversible capacity of 420 mA h g⁻¹ at 0.5C, and good cycling stability. The intercalation mechanism of Zn²⁺ and H⁺ is proved by in situ XRD, ex situ XPS, and other characterization techniques, along with density functional theory calculations. This work provides a strategy to improve the electrochemical performance of vanadium oxides through valence regulation.