Tailoring layered transition metal compounds for high-performance aqueous zinc-ion batteries

The development of cathodes is critical for achieving high-performance aqueous Zn-ion batteries (ZIBs). To date, it remains a great challenge to find cathode materials with high operating potential, excellent electrochemical activity, and good structural stability. Layered transition metal compounds have received extensive attention for widespread applications in energy storage and conversion owing to their two-dimensional ion diffusion channels, superior mechanical flexibility, and highly adjustable layered structure. However, a critical bottleneck that hinders their application in aqueous ZIBs is the sluggish reaction kinetics due to the slow desolvation process at the cathode/electrolyte interface and the strong electrostatic interaction between the anion sublattice of host materials and divalent Zn2+. In this review, we comprehensively scrutinize the latest progresses and encountered challenges in the development of layered transition metal compounds as cathodes for aqueous ZIBs. Some dichalcogenides, carbides and nitrides, phosphates, and vanadates are also introduced, and their energy storage mechanisms are clarified. Much efforts and progress regarding the interlayer, defect and composite engineering to achieve high electrical conductivity, fast ion diffusion kinetics and stable structure of layered transition metal compounds are summarized.