Nickel, Manganese Compounds/3D Graphene Composites For Supercapacitor Application

With the continuous development of science and technology, as well as the serious environment pollution, the demand for clean energy becomes more urgent. However, clean energy mainly comes from intermittent energy sources, such as solar energy, wind energy, which require the effective energy storage technology. Because the battery can’t meet the request of the input and output of high power, and the supercapacitor can just make up this defect. Even in more areas, supercapacitor has more superior properties and can replace the battery. So, the key research is to prepare the electrode materials with high energy density, high power density, long cycle life and low cost.Graphene is a material with many excellent properties, such as lightweight, high conductivity and mechanics, etc. And it can be used as the electrode material of supercapacitor directly. In addition, nickel and manganese are ideal materials as the electrodes of faradaic pseudocapacitance with the properties of large reserves, environmentally friendly and low cost.The purpose of this paper is to improve the specific capacitance and cycle stability of the electrode material. Design the reasonable structure of the electrode, and prepare the superior capacitor electrode. We prepared the 3D graphene which was used as current collector by CVD method, and then grew active material on its surface by the hydrothermal method to improve the specific capacitance (Cs). The main content of this paper are as the following:(1) The 3D graphene was synthsized by CVD method to use as current collector, and then Ni(OH)2 nanosheets were grown on the surface of 3D graphene by hydrothermal method. The advantage is that there is no need of any inert binder between current collector and Ni(OH)2 nanosheets. The interface resistance was reduced greatly. Ultralight graphene was used as the current collector, which reduced the weight of the electrode. The electrochemical test was carried out on Ni(OH)2 nanosheets/3D graphene. The Cs is ～1606 F/g at a charge/discharge current density of 10 A/g, and reveals a good electrochemical reversibility and the high power capabilities.(2) Because the electrical conductivity of the Ni(OH)2 nanosheets is very poor, Ag nanoparticles were added into the hydrothermal solution based on the above-depicted work of Ni(OH)2 nanosheets/3D graphene. On the basis of the advantage of Ni(OH)2 nanosheets/3D graphene, the electrical conductivity of the Ni(OH)2 nanosheets was improved. The electrochemical test was taken on Ag/Ni(OH)2 nanosheets/3D graphene. The Cs is～2167 F/g at a charge/discharge current density of 10 A/g. After the Ag nanoparticles was added, the Cs has an improvement by～26% compared with Ni(OH)2 nanosheets/3D graphene. This reveals a good electrochemical reversibility and the high power capabilities.(3) Taking the advantage of the structure of Ni(OH)2 nanosheets/3D graphene, we grow nano-sized MnO2 on the surface of 3D graphene by hydrothermal method. The nano-sized MnO2 attached on 3D graphene firmly. Take the electrochemical test on nano-sized MnO2/3D graphene, the results show that the composites has high specific capacitance and good rate capability. An excellent cycling performance of 97% capacitance retention over 1000 cycles.