Unveiling the reaction mechanism of capacity reactivation in silver vanadate cathodes for aqueous zinc-ion batteries

Abstract

Aqueous zinc-ion batteries are regarded as promising candidates for future energy storage devices because of their high safety. Due to the dissolution in the aqueous electrolytes, most vanadate-based zinc-ion batteries suffer from continuous capacity fading. In some cases, a capacity reactivation process can be observed in vanadate-based cathodes after capacity decay. Herein, we employed electrochemical methods and characterization techniques to study the reaction mechanism of capacity reactivation in Ag_0.33V₂O₅ cathodes. Our preliminary results suggested that the reactivation is due to an in situ crystalline structure evolution in the cathode materials. Under the electrochemical condition, a new phase Zn₃(OH)₂V₂O₇·2H₂O irreversibly formed on the initial cathodes, which prevented the dissolution of vanadate and further resulted in the capacity increase. Moreover, we confirmed the unique intercalation pseudocapacitive behavior in the reconstructed Zn₃(OH)₂V₂O₇·2H₂O, which provided fast ionic diffusion to facilitate electrochemical performance. Accordingly, our study offers a new understanding of the capacity change of the vanadate-based cathode materials and provides a more general explanation of the capacity reactivation in aqueous zinc-ion batteries.