K⁺-Triggered Defect Engineering and Proton-Coupled Storage in V₂O₅·nH₂O for Advanced Zn-Ion Thin-Film and...

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 V₂O₅·nH₂O 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 V₂O₅·nH₂O 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.