• • The H2V3O8@Ppy cathode delivers an initial discharge capacity of 405 mA h g−1 at 100 mA g−1, exceeding the theoretical capacity of conventional vanadium oxides (e.g., V2O5 ~294 mA h g−1), enabling higher energy density for grid-scale storage.
• • Capacity retention of nearly 100% after 800 cycles at 2 A g−1 demonstrates exceptional cycling stability, addressing the rapid capacity fade (often >30% after 500 cycles) of uncoated H2V3O8 due to vanadium dissolution.
• • DFT calculations show a binding energy difference of 1.765 eV between HVO3 (−1.97 eV) and hydrated Zn2+ (−0.205 eV) on polypyrrole, providing a thermodynamic basis for ion-selective transport that suppresses active material loss while maintaining Zn2+ mobility.
• • In situ XRD reveals a two-step phase transformation mechanism during discharge/charge, offering mechanistic insights that can guide the rational design of vanadium-based cathodes with controlled phase transitions for enhanced reversibility.