Competitive Dynamics between Deposition–Dissolution and Embedding–Detachment Induced by Aluminum in Zn-MnO2 Batteries

The rechargeable aqueous Zn-MnO2 batteries have attracted significant attention due to their high safety, environmental friendliness, and low cost. However, the complex reaction mechanisms of MnO2 cathodes present challenges for practical applications. Specifically, the MnO2/Mn2+ deposition–dissolution reaction, while offering a high theoretical capacity (616 mAh g–1), requires further investigation into the conditions under which it occurs and the factors influencing it. This study introduces Al3+ into sulfate-based electrolytes to explore their regulatory effects on the performance of Zn-MnO2 batteries. The deposition–dissolution reaction occurring within the battery is visually demonstrated through the use of an electrochemical quartz crystal microbalance (EQCM). Research reveals that Al3+ not only serves as a dynamic pH regulator for the electrolyte but also integrates into the MnO2 structure as dopant atoms, affecting Mn–O bonds and significantly enhancing the reversibility of the MnO2/Mn2+ deposition–dissolution process. Using characterization techniques such as in situ XRD and in situ Raman spectroscopy, the study reveals the impact of Al3+ on the energy storage mechanism dominated by the deposition–dissolution reaction, achieving high-performance Zn-MnO2 batteries.