Recent progress and perspectives on energy storage mechanisms for rechargeable Zn//MnO2 batteries

Zn//MnO2 batteries has gained widespread attention for large-scale energy storage owing to their unparalleled safety and eco-friendliness. However, the energy storage mechanism is a pressing concern restricting the progress of Zn//MnO2 batteries. Recently, great efforts have been made to uncovering the energy storage mechanism of MnO2 for Zn-ion batteries. To achieve an insightful and systematic understanding of these energy storage mechanism, it is necessary to categorize and summarize the energy storage mechanism of Zn//MnO2 batteries timely. In this review, the in-depth discussion and comprehensive summary of the progress of Zn//MnO2 batteries with various energy storage mechanisms is offered, which can be classified into four categories: 1) Zn2+ insertion; 2) H+/Zn2+ co-insertion; 3) Dissolution/deposition; 4) Chemical conversion reaction. The dominating problems and solutions of different energy storage mechanisms are discussed, and overall guidance is provided for the construction and exploitation of high-performance Zn//MnO2 batteries.