Ion-Selective Polypyrrole Coating Enhances H2V3O8 Cathode Stability in Aqueous Zinc-Ion Batteries
Aqueous zinc-ion batteries (AZIBs) are promising for grid-scale energy storage, but the H2V3O8 cathode suffers from poor electrical conductivity, vanadium dissolution, and structural instability, limiting rate performance and cycling stability. A polypyrrole-coated H2V3O8 composite (H2V3O8@Ppy) was developed. Density functional theory calculations reveal that Ppy interacts with HVO3 species with a binding energy of −1.97 eV, significantly stronger than with hydrated Zn2+ ions (−0.205 eV). This selective interaction enables the Ppy coating to capture dissolved HVO3 while permitting efficient transport of solvated Zn2+ ion clusters, thereby preventing structural degradation. The optimized H2V3O8@Ppy cathode delivers an initial capacity of 405 mA h g−1 at 100 mA g−1 and maintains nearly 100% capacity retention after 800 cycles at 2 A g−1. A quasi-solid-state AZIB incorporating this cathode exhibits excellent mechanical flexibility and superior long-term cycling performance. In situ XRD analysis reveals 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.