The Negative Role of Proton Insertion on the Lifetime of Vanadium-Based Aqueous Zinc Batteries

Abstract

Vanadium oxides are attracted cathodes for aqueous zinc batteries owing to their high capacity. However, the limited cyclability of vanadium-based oxide cathodes, especially at low current densities, impedes their practical application. Here, it is revealed that proton insertion is responsible for the limited lifetime of vanadium oxides. Proton insertion promotes the dissolution of vanadium oxides, deteriorating electrochemical performance. Propylene carbonate (PC) is introduced into Zn(CF₃SO₃)₂ electrolyte to regulate the coordination environment of water, forming PC-coordinated Zn²⁺ solvation structure and [H₂O-CF₃SO₃⁻-PC] complex. The optimized coordination environment of water weakens the adsorption energy between water molecules and vanadium oxides, inhibiting proton insertion. As a result, vanadium-based oxides cathode without proton insertion can maintain the stability of crystal structure and avoid the dissolution of V. Taking CaV₈O₂₀·nH₂O as cathode, Zn||CaV₈O₂₀·nH₂O battery without proton insertion performs enhanced cycling performance. This work not only reveals the negative effect of proton insertion on the lifetime of vanadium-based oxides cathode but also provides an effective strategy to modulate proton insertion.