An overview of aqueous zinc-ion batteries based on conversion-type cathodes

The scarcity of lithium resources and the unsafety of organic electrolytes limit the further application of lithium-ion batteries (LIBs) in electric vehicles and grid-scale energy storage. Aqueous zinc-ion batteries (AZIBs) are potential complements for LIBs for large-scale grid energy storage because of their abundant resources, environmental friendliness, intrinsic safety and low cost. However, current AZIBs are mainly based on intercalation-type cathodes and their energy densities are not competitive with LIBs. Fortunately, conversion-type cathodes, with higher specific capacity and lower price, endow AZIBs with excellent potential for practical applications. In this review, the mechanism of energy storage and the progress in developing AZIBs based on conversion-type cathodes are summarized. Perspectives on critical scientific issues and the potential developmental directions of AZIBs are also proposed.