Capturing Failure Mechanisms in Vanadium Oxide Cathodes for Aqueous Zinc Batteries

Aqueous zinc ion batteries (ZIBs) attract increasing attention as alternative energy storage technologies due to their merits of safety and low cost. However, the continuous dissolution of active materials in vanadium oxide-based ZIBs has posed an unavoidable challenge. Here, we systematically analyzed the dissolution mechanism using both ex-situ and in-situ methods. Experimental and theoretical analyses revealed an excessive reduction in vanadium valence following H ⁺ insertion at potentials above 1.0 V ( vs. Zn ²⁺ /Zn), primarily contributing to vanadium dissolution rather than Zn ²⁺ insertion. Protons preferentially form monodentate coordination with oxygen, increasing local electron density around V atoms and facilitating more electron transitions from 1 s to higher-energy 3 d states. This leads to a pronounced reduction in V-valence and V-O bond breakage. Specifically, interlayer-inserted H ⁺ exhibits the highest dissolution energy due to its significant binding energy compared to Zn ²⁺ and surface-inserted H ⁺ . As a proof of concept, without additives or cathode modifications, electrochemical improvements in Zn/NH ₄ V ₄ O ₁₀ and Zn/V ₂ O ₅ batteries were achieved by reducing the cut-off voltage or increasing current density at high voltage to directly inhibit H ⁺ insertion or promote the favorable surface-dominant H ⁺ insertion. We contend that understanding the chemistry and electrochemistry-related failure mechanisms are crucial for designing Adv. Mater. and their applications.