K ⁺ ‐Triggered Defect Engineering and Proton‐Coupled Storage in V ₂ O ₅ ·nH ₂ O for Advanced Zn‐Ion Thin‐Film and Microbatteries

ABSTRACT The increasing demand for wearable electronics, point‐of‐care diagnostics, and integrated microsystems necessitates thin‐film and microbatteries that combine high energy density, fast kinetics, and intrinsic safety. In this work, we develop Zn‐based thin‐film batteries (Zn‐TFBs) and microbatteries (Zn‐MBs) using K ⁺ ‐pre‐intercalated V ₂ O ₅ ·nH ₂ O cathodes and reveal a fundamentally distinct charge‐storage mechanism. Contrary to the conventional paradigm where metal‐ion pre‐intercalation merely enlarges interlayer spacing, K ⁺ incorporation induces interlayer contraction accompanied by substantial oxygen‐vacancy generation and mixed‐valence (V ^{4 +} /V ^{5 +} ) formation. These coupled lattice and electronic modulations activate proton‐dominated transport pathways, enabling cooperative H ⁺ /Zn ^{2 +} co‐storage and markedly accelerated reaction kinetics. Density functional theory calculations further confirm that the enhanced electrochemical behavior cannot be explained by interlayer expansion alone, but originates from defect‐mediated proton conduction and vacancy‐stabilized redox centers. Benefiting from this defect‐engineered proton‐Zn ^{2 +} synergistic storage, the K ⁺ ‐modified V ₂ O ₅ ·nH ₂ O cathode delivers an areal capacity of 200.9 µAh cm ^{− 2} and an areal energy of 150 µWh cm ^{− 2} at 50 µA cm ^{− 2} in Zn‐TFBs, together with a high areal capacity of 49 µAh cm ^{− 2} in Zn‐MBs. This study establishes K ⁺ ‐triggered defect and valence‐state engineering as a powerful strategy to regulate proton‐coupled charge storage in hydrated vanadium oxides, opening a viable pathway toward high‐energy Zn‐based energy‐storage systems.