Vanadium-based cathodes for aqueous zinc-ion batteries: Mechanism, design strategies and challenges

Although lithium-ion batteries (LIBs) have many advantages like high energy density, high average operating voltage, low self-discharge, and long-cycle performance, it cannot meet the practical demand of large-scale energy storage devices due to the shortage of lithium resources and potential safety hazards. Aqueous zinc-ion batteries (AZIBs) are being considered as a potential alternative to LIBs owing to their advantages of low cost, high safety, abundant natural zinc resources, and high gravimetric energy density. However, developing high-performance cathode materials for AZIBs is still a great challenge because the current cathode materials of AZIBs often suffer from low conductivity, and the energy storage mechanism is relatively complex. Compared to other cathode materials, vanadium-based materials have the advantages of low cost, high capacity, high power density, and long cycle life. In this review, the latest progress in vanadium-based cathodes for AZIBs is summarized, and several energy storage mechanisms (Zn2+intercalation/extraction, H+/Zn2+co-insertion/extraction, and conversion reaction) are presented. Meanwhile, the relationship between the material structure and electrochemical activity is briefly discussed by summarizing the materials structures (including layered, tunnel, NASICON-type, spinel structures) and the design strategies (such as the ion intercalation, the molecular intercalation, the ion/molecule co-intercalation, the vacancy defects intercalation, and introduction of conductive carbon materials). Finally, this review also addresses the challenges in vanadium-based cathode materials for AZIBs and the perspectives for future development of vanadium-based cathode materials.