Dotted Mn3O4-Decorated MnO2 Composites: Fabrication, Interfacial Characteristics, and Multivalent Mn Charge-Storage Behavior

To address the issues of insufficient conductivity, slow reaction kinetics, and limited cycling stability associated with pure MnO2 electrode materials, this study used MnO2 as a precursor to prepare MnO2/Mn3O4 composite electrode materials through a subsequent compositing process and investigated their supercapacitor performance. The results show that M2@M4-30, prepared with an optimized reaction time, exhibits the best electrochemical performance, with a specific capacitance of 212.5 F g–1 at 0.2 A g–1 and 175.0 F g–1 at 10 A g–1, corresponding to a capacitance retention of approximately 82.4%. After 10,000 cycles, the electrode retained 92.86% of its initial capacitance. The performance enhancement is primarily attributed to the dotted loading of Mn3O4 on the MnO2 surface, the formation of the MnO2/Mn3O4 heterointerface, and the multivalent environment of Mn2+, Mn3+, and Mn4+. Specifically, the dotted loading structure helps keep the active areas exposed, the heterointerface promotes interfacial charge transfer, and the multivalent Mn states endow the composite system with richer reversible redox activity. The assembled M2@M4-30//AC asymmetric supercapacitor achieves an energy density of 31.6 Wh kg–1 at a power density of 180.0 W kg–1, demonstrating significant application potential.