Capturing failure mechanisms toward the rational design of reversible vanadium oxide-based zinc batteries

Aqueous zinc ion batteries (ZIBs) have attracted increasing attention as alternative energy storage technologies due to their safety and low cost. However, the continuous dissolution of active materials in vanadium oxide-based ZIBs has posed an unavoidable challenge. Here, we systematically investigate the dissolution mechanism driven by chemical and electrochemical processes using both ex situ and in situ techniques. Experimental and theoretical analyses revealed an excessive reduction in the vanadium valency following H⁺ insertion at potentials above 1.0 V (vs. Zn²⁺/Zn), contributing to vanadium dissolution rather than Zn²⁺ insertion. Protons preferentially form monodentate coordination with oxygen, increasing local electron density around V atoms and facilitating 1s to higher-energy 3d electron transitions. This leads to a pronounced reduction in V-valency and V–O bond breakage. Specifically, interlayer-inserted H⁺ exhibits the highest dissolution energy due to its significant binding energy compared to Zn²⁺ and surface-insertion. As a proof of concept, without additives or cathode modifications, improvements in Zn/NH₄V₄O₁₀ and Zn/V₂O₅ batteries were achieved by reducing the cut-off voltage or increasing the current density at high voltage to directly inhibit H⁺ insertion or promote the favorable surface-dominant H⁺ insertion. Further evidence is substituted by H⁺-substituting cations (Na⁺ and Li⁺), which deliver sustained cycling stability at 0.2 A g⁻¹ and extended cycling up to 5000 cycles at 5 A g⁻¹ in both battery systems. We contend that understanding failure mechanisms is imperative for the development of strategies rooted in fundamental principles.