Vanadium-based cathodes for aqueous zinc ion batteries: Structure, mechanism and prospects

As an emerging energy storage device with high-safety aqueous electrolytes, low-cost, environmental benignity and large-reserves, the rechargeable aqueous zinc-ion batteries (AZIBs) have attracted more and more attention. Vanadium-based compounds are also supposed as the potential candidate cathode materials for AZIBs due to their wide variety of phases, variable crystal structures and high theoretical capacity. In this review, the recent progress in the development of vanadium-based materials was summarized, and the relationship between the crystal structure types of active materials and Zn-ion transport mechanism was highlighted. During the charge-discharge process, the different electrostatic repulsion between the cations of vanadium-based compounds with different crystal structures and Zn2+ results in a variety of the Zn-ion storage mechanisms, which can be significant guidance for designing the advanced battery-electrode materials for AZIBs. Furthermore, other factors associated with the storage mechanisms, such as electrolyte components and electrode morphology, are discussed. Finally, the strategies to improve the electrical conductivity, inhibit the dissolution and stabilize the crystal structure of vanadium-based compounds are proposed and the future prospects for developing high-energy-density AZIBs are presented.