Room-temperature chemical reconfiguration enables oxygen-deficient KVO for ultrafast and durable zinc-ion storage

Aqueous zinc-ion batteries are considered ideal candidates for large-scale energy storage, yet the sluggish kinetics of vanadium-based cathodes severely limit their electrochemical performance. Here, we propose a room-temperature spontaneous chemical reconstruction strategy grounded in the hard–soft acid–base theory, achieving a phase transition from V2O5 to oxygen-deficient KV3O8via a facile coprecipitation method. We reveal that the strong interaction between K+, acting as a mild Lewis acid, and lattice oxygen not only enables K+ intercalation to construct structural pillars but also thermodynamically induces spontaneous lattice oxygen loss, thereby introducing oxygen vacancies and establishing a V4+/V5+ mixed-valence system. This dual effect simultaneously enhances intrinsic electronic conductivity, widens interlayer ion-transport channels, and lowers diffusion barriers, yielding ultrafast Zn2+ diffusion kinetics with a diffusion coefficient of 1.3 × 10−10 cm2 s−1. Consequently, the KV3O8 cathode delivers a high specific capacity of 342.4 mAh g−1 at 0.3 A g−1 and retains 81.1% capacity after 5830 cycles at 5 A g−1. Moreover, a flexible pouch cell assembled with this cathode exhibits exceptional voltage stability and capacity retention under severe mechanical bending. This work reinterprets ion pre-intercalation from the perspective of lattice oxygen chemistry, offering new design principles for next-generation layered electrode materials in aqueous batteries.