Ion-selective polypyrrole coating enhances H₂V₃O₈ cathode stability in aqueous zinc-ion batteries

Aqueous zinc-ion batteries have emerged as promising candidates for large-scale energy storage. Despite its potential as a cathode material for AZIBs, H₂V₃O₈ suffers from poor electrical conductivity, vanadium dissolution, and structural instability, which severely compromises its rate performance and cycling stability. To address these limitations, we have developed a polypyrrole-coated H₂V₃O₈ composite (H₂V₃O₈@Ppy). Density functional theory calculations demonstrate that Ppy exhibits substantially stronger interactions with HVO₃ (−1.97 eV) compared to hydrated Zn²⁺ ions (−0.205 eV). This selective interaction enables the Ppy coating to effectively capture dissolved HVO₃ species while maintaining efficient transport of solvated Zn²⁺ ion clusters, thereby preventing structural degradation of the cathode. The optimized H₂V₃O₈@Ppy cathode delivers an impressive initial capacity of 405 mA h g⁻¹ at 100 mA g⁻¹ and demonstrates exceptional cycling stability, maintaining nearly 100% capacity retention after 800 cycles at 2 A g⁻¹. Furthermore, a quasi-solid-state zinc-ion battery incorporating H₂V₃O₈@Ppy cathode exhibits excellent mechanical flexibility and superior long-term cycling performance. Notably, in situ XRD analysis reveals for the first time a two-step phase transformation mechanism of H₂V₃O₈ during discharge/charge processes. This study presents an effective strategy for enhancing the structural stability of H₂V₃O₈ cathodes in aqueous zinc-ion batteries. (Figure presented.)