Controllable Morphology Synthesis of MnO ₂ and Structure–Activity Relationship Study on its Electrochemical Performance in Supercapacitor

The morphological structure is of great significance for supercapacitors. Designing materials with diverse morphologies have attracted considerable attention, as it can achieve impressive electrochemical performance in energy storage technologies. Therefore, in this paper, two differentiated hydrothermal synthesis methods were employed to successfully prepare nanoflowers and nanosphere MnO 2 . Characterization results revealed that both MnO 2 samples with distinct morphologies possessed the same crystal structure. However, the nanosphere MnO 2 exhibited a higher specific surface area and a wider pore size distribution, thereby demonstrating better electrochemical performance. Specifically, in 1[Formula: see text]M Na 2 SO 4 electrolyte, the specific capacitance of nanosphere MnO 2 reached 162[Formula: see text]F[Formula: see text]g[Formula: see text], while that of nanoflowers MnO 2 was only 113[Formula: see text]F[Formula: see text]g[Formula: see text]. An asymmetric supercapacitor was assembled using the nanosphere MnO 2 as the positive electrode and activated carbon as the negative electrode in 3[Formula: see text]M KOH electrolyte. After 5000 charge–discharge cycles at a current density of 5[Formula: see text]A[Formula: see text]g[Formula: see text], the device still maintained a high capacity retention rate of 95%, exhibiting outstanding cycling stability.