Improvement of electrical performance by surface structure of Ni-material as a high-performance asymmetric supercapacitor electrode

Abstract

Binder-free Ni-material array electrodes on Ni-foam are fabricated using a facile hydrothermal method for high-performance supercapacitors. Instead of a binder, urea is added to increase the adhesion of Ni-foam as both the substrate and electrode material. In this paper, we present the contribution of urea to the formation of the material. The surface characteristics and the electrical properties of the Ni-material array change with the amount of urea. When 2.4 g of urea is added to the sample for the first time, a Ni(HCO3)2 microrod electrode is obtained; it shows large wire growth on the Ni-foam, which can be explained about the abnormal grain growth behavior because there is little energy barrier for atomic attachments with a disordered or rough interface atomic structure. Its specific capacitance is 346 F g−1 at a current density of 3 A g−1. In contrast, when the amount of urea is reduced to 0.8 g, a Ni2(CO3) (OH)2 array electrode is produced; it exhibits a nano-size wire array and a specific capacitance of 833.2 F g−1 at a current density of 3 A g−1. Thus, it is confirmed that the large surface area of Ni2(CO3) (OH)2 exhibits outstanding electrical properties. And, the fabricated asymmetric supercapacitor of Ni2(CO3) (OH)2 composite as the positive electrode and graphene as the negative electrode, which has a high energy density of 22.1 W h kg−1 at a power density of 673.1 W kg−1. In addition, this obtained asymmetric supercapacitor can turn on the LED light.