Understanding the Dissolution and Phase Transformation Mechanisms in Aqueous Zn/α-V2O5 Batteries

Anhydrous α-V2O5 was the first class of cathodes studied for rechargeable aqueous zinc-ion batteries (AZIBs), mainly due to its layered structure and high theoretical capacity. However, the poor cycle life of Zn/α-V2O5 prevents it from being used as a practical cathode. A critical need for the advancement of high-capacity aqueous Zn/α-V2O5 batteries is a better understanding of the degradation mechanisms in an α-V2O5 cathode. Through a combined experimental and theoretical approach, we here report that the stability of an α-V2O5 cathode in aqueous Zn/α-V2O5 batteries is fundamentally controlled by its dissolution mechanisms in water and concurrent phase transition to a hydrated V2O5·1.75H2O (H-V2O5) xerogel. We show that α-V2O5 partially dissolves as [V10O26(OH)2]4– into aqueous ZnSO4 but precipitates out as Zn3(OH)2V2O7·2H2O in aqueous Zn(CF3SO3)2, while its majority is transformed into H-V2O5. We provide evidence that H-V2O5 is the active material for the storage of Zn2+/H+ due to its favorable gallery spacing for intercalation chemistry. Overall, presented experimental evidence and gained fundamental insights by this study contribute to the advancement of high-capacity aqueous Zn/α-V2O5 batteries.