Synthesis of Core‐Shell Structured MnO ₂ Petal Nanosheet@Carbon Sphere Composites and Their Application as Supercapacitor Electrodes

A novel MnO 2 petal nanosheet@carbon sphere core‐shell structure was successfully fabricated by adjusting the quantity of the KMnO 4 precursor employed during the in situ growth of MnO 2 on the surface of carbon spheres via a facile hydrothermal method. In the presence of low KMnO 4 contents, only MnOOH was generated. In contrast, upon increasing the quantity of KMnO 4 , δ‐MnO 2 nanorods and petal nanosheets were obtained, thereby allowing the formation of the core‐shell structured δ‐MnO 2 petal nanosheet@carbon sphere composites. However, beyond a certain point, further increases in the KMnO 4 content were unfavorable. Although, prepared MnO 2 /carbon sphere composites of different morphologies can be used for supercapacitors (SCs) electrode materials, we found that the core‐shell structured MnO 2 petal nanosheet@carbon sphere composites exhibited the optimal capacitance performances in all the composites. These composites exhibited an excellent specific capacitance of 231 F⋅g −1 under a current density of 0.5 A⋅g −1 . Furthermore, they also demonstrated an impressive cycling stability. Indeed, after 1,000 cycles at 10 A⋅g −1 , the MnO 2 petal nanosheet@carbon spheres exhibited 96% of their initial capacitance in a 1 M Na 2 SO 4 aqueous electrolyte. The synergistic effect between δ‐MnO 2 and the porous carbon spheres in the unique core‐shell structured is responsible for the excellent cycle life.