Ni-doped α-MnO2 nanosheets coupled carbontubes for highly efficient Na+ ions capacity storage

Manganese dioxide (MnO2) has been broadly investigated as electrode material candidate for supercapacitors due to its high theoretical capacity and environmental protection. However, MnO2 also suffer from poor electrical conductivity. Herein, nickel-doped MnO2 coupled carbontubes (Ni-MnO2@CTs) material is prepared by one-step hydrothermal method and carbonization processes. Compared with undoped MnO2, Ni-doped MnO2 can improve the electrical conductivity and expand the voltage window of supercapacitors. This is because Ni doping can introduce additional charge states and regulate the reaction kinetics, changing the energy storage mechanism of the material. Additionally, the carbontubes substrate can enhance both the electrical conductivity and surface area of the material. Based on these advantages, Ni-MnO2@CTs can extend the voltage window of the positive to 0-1 V with high specific capacitance of 366 F g-1 at 1 A g-1. To explore the practical application of the materials, the asymmetric supercapacitor is fabricated with Ni-MnO2@CTs positive and Fe3O4/CTs negative (NiMnO2@CTs//Fe3O4/CTs) in a wide voltage window of 2 V. The supercapacitor displays excellent rate capability and cycle performance, while also possessing a high energy density of 44.5 Wh kg- 1. These results suggest that the materials utilized in this study have the potential to be used in the development of wide-voltage aqueous asymmetric supercapacitors, which can further enhance their energy density.