Unveiling the Reversibility and Stability Origin of the Aqueous V₂O₅–Zn Batteries with a ZnCl₂ “Water-in-Salt” Electrolyte

Aqueous V₂O₅–Zn batteries, an alternative chemistry format that is inherently safer to operate than lithium-based batteries, illuminates the low-cost deployment of the stationary energy storage devices. However, the cathode structure collapse caused by H₂O co-insertion in aqueous solution dramatically deteriorates the electrochemical performance and hampers the operation reliability of V₂O₅–Zn batteries. The real-time phase tracking and the density functional theory (DFT) calculation prove the high energy barrier that inhibits the Zn²⁺ diffusion into the bulk V₂O₅, instead the ZnCl₂ “water-in-salt electrolyte” (WiSE) can enable the dominant proton insertion with negligible lattice strain or particle fragment. Thus, ZnCl₂ WiSE enables the enhanced reversibility and extended shelf life of the V₂O₅–Zn battery upon the high temperature storage. The improved electrochemical performance also benefits by the inhibition of vanadium cation dissolution, enlarged voltage window, as well as the suppression of the Zn dendrite protrusion. This study comprehensively elucidates the pivotal role of a concentrated ZnCl₂ electrolyte to stabilize the aqueous batteries at both the static storage and dynamic operation scenarios.