High-performance MnO2-based cathodes for aqueous zinc-ion batteries: Challenges, strategies, and perspectives

Aqueous zinc-ion batteries (AZIBs) have been identified as ideal candidates for large-scale energy storage due to their high safety, low cost, and environmental friendliness. Due to its high theoretical capacity, abundant resources, and multi-electron redox characteristics, MnO 2 has attracted widespread attention among cathode materials for AZIBs. However, the practical application of MnO 2 -based cathodes still faces numerous challenges, including structural distortion caused by the Jahn–Teller effect, low intrinsic electrical conductivity, slow Zn 2+ diffusion kinetics, insufficient active sites, and irreversible phase transitions. This article systematically reviews the recent research progress on the energy storage mechanisms of MnO 2 , including multiple mechanisms such as Zn 2+ insertion/extraction, H + /Zn 2+ co-insertion/extraction, the conversion reaction, dissolution–deposition, and hybrid mechanisms, as well as the effects of various crystal structures on Zn storage behavior. Thus, it outlines the role and mechanisms of various modification strategies in improving MnO 2 ’s electrical conductivity, ion diffusion capability, and structural stability, including defect engineering, doping engineering, intercalation engineering, composite materials, and low- dimensionalization. We also explore Zn-MnO 2 pouch batteries constructed using modified MnO 2 cathodes, whose effective application has been verified in scenarios such as high-capacity commercial energy storage, flexible electronics, and portable device power supply, further confirming their practical value. The paper concludes by proposing future research directions from the perspectives of multi-mechanism synergistic regulation, interface optimization, structural design, and large-scale preparation, providing theoretical references and technical ideas for the development of high-performance MnO 2 -based cathode materials in AZIBs. • The diverse energy storage mechanisms of MnO 2 -based cathodes in AZIBs and their influencing factors are clarified. • The key issues of MnO 2 -based cathodes and mechanisms of performance optimization strategies are explored in detail. • The future research directions of high-performance MnO 2 -based cathodes and theoretical-technical supports are proposed.