Crystallinity-Dependent Behavior of MnO2 Cathodes for Aqueous Zinc-Ion Batteries

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Abstract
Manganese dioxide (MnO2) is a promising cathode material for aqueous zinc-ion batteries (AZIBs) owing to its low cost and high theoretical capacity. However, its practical application is hindered by sluggish reaction kinetics and structural instability arising from Mn dissolution and irreversible phase transitions during repeated cycling. In this study, an amorphous–crystalline MnO2 (AMC-MnO2) heterostructure is constructed to address these limitations, in which amorphous MnO2 (AM-MnO2) provides abundant active sites and structural flexibility, while crystalline MnO2 (C-MnO2) offers continuous ion diffusion pathways and structural robustness. The heterointerface promotes interfacial charge redistribution, thereby improving the charge-transfer kinetics and structural stability through a buffering effect. Electrochemical analyses revealed that AMC-MnO2 exhibited faster H+ diffusion kinetics than AM-MnO2 and C-MnO2 while maintaining comparable Zn2+ diffusion behavior. Consequently, the AMC-MnO2 electrode delivered enhanced rate capability and superior cycling stability compared with AM-MnO2 and C-MnO2. These findings demonstrate that amorphous–crystalline heterostructure engineering effectively regulates Zn2+/H+ storage behavior and provides a rational strategy for developing high-performance MnO2 cathodes for aqueous zinc-ion batteries.

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