Critical issues and optimization strategies of vanadium dioxide-based cathodes towards high-performance aqueous Zn-ion batteries.

Aqueous zinc-ion batteries (AZIBs) are gaining significant attention due to their excellent safety, cost-effectiveness, and environmental friendliness, making them highly competitive energy storage solutions. Despite these advantages, the commercial application of AZIBs faces substantial challenges, particularly those related to performance limitations of cathode materials. Among potential candidates, vanadium dioxide (VO) stands out due to its exceptional electrochemical properties and unique crystal structure, rendering it a promising cathode material for AZIB applications. The review summarizes the recent research progress on VO in AZIBs, analyzes its crystal structures (tetragonal VO(A), monoclinic VO(B, D, M), and rutile VO(R)), morphology and energy storage mechanisms (Zn insertion/extraction, H/Zn co-insertion/extraction, and chemical reaction mechanism), and discusses the relationship between the structure and performance. The review also addresses key challenges associated with VO as a cathode material, including dissolution, by-product formation, and limited ion diffusion kinetics. To overcome these issues, various optimization strategies are systematically discussed, such as ion/molecule pre-intercalation, composite material fabrication, defect engineering, and elemental doping. Finally, potential research directions and strategies to further enhance the performance and commercial viability of VO-based cathodes are proposed.