Interfacial engineering of hydrated vanadate to promote the fast and highly reversible H+/Zn2+ co-insertion processes for high-performance aqueous rechargeable batteries

Layered hydrated vanadates have been regarded as promising cathode materials for Zn-ion batteries due to their high capacities. Nevertheless, the strong Coulombic interaction of Zn2+ with the host structure and the large de-solvation penalty of Zn2+, together with the vanadium dissolution and the poor electronic conductivity, significantly constrain their electrochemical performances and hinder their practical applications. Herein, this work reveals that the rational interfacial engineering based on phytic acid/polypyrrole coating can modulate the charge storage mechanism and effectively optimize the electrochemical performances of a typical hydrated vanadate cathode Ca0.24V2O5·H2O. Specifically, through in-situ and ex-situ characterizations backed with first-principle calculations, the coating strategy is found to offer a favorable interfacial environment, which intriguingly promotes the highly reversible H+/Zn2+ co-insertion processes. This, plus the beneficial effects of the coating layer in facilitating the de-solvation process of Zn2+ at the interface, boosts the ion diffusion kinetics of the coated cathode and gives rise to pseudocapacitive charge storage behaviors. In addition, the coating layer protects the cathode against dissolution in the electrolyte and promotes the electronic conduction, which collectively lead to enhanced rate and cycling performances. Accordingly, this study suggests that the interfacial environment is of vital importance in influencing the charge storage mechanisms and electrochemical performances of hydrated vanadate cathode materials, which indicates that the rational interfacial engineering may offer an avenue to further optimizing the performances of vanadium-based and even other Zn-ion battery cathode materials.