Recent progress in aqueous zinc-ion batteries based on conversion-type cathodes

Developing advanced secondary batteries with low cost and high safety has attracted increasing research interests across the world. In particular, the aqueous zinc-ion battery (AZIB) has been regarded as a promising candidate owing to the high abundance and capacity of Zn metal. Currently, manganese-based and vanadium-based oxides are most common choices for cathode materials used in AZIBs, but they unfortunately show a moderate cell voltage and limited rate performance induced by slow intercalation-extraction kinetics of Zn²⁺ ions. To address these issues, alternative cathode systems with tunable redox potentials and intrinsic fast kinetics have been exploited. In the past few years, conversion-type cathodes of I₂ and S have become the most illustrative examples to match or even surpass the performance of conventional metal oxide cathodes in AZIBs. Herein, we sum up most recent progress in conversion-type cathodes and focus on novel ideas and concepts in designing/modifying cathodes for AZIBs with high voltage/capacity. Additionally, potential directions and future efforts are tentatively proposed for further development of conversion-type cathodes, aiming to speed up the practical application of AZIBs.