Sythesis And Supercapacitive Properties Of Binary Ni-Co Hydroxides/Oxides

α-Ni(OH)2 is a promising electrode materials of supercapacitor with a hydrotalcite-like structure. It has a very high theoretical specific capacitance but a low electrical conductivity, and its rate capability and cycling stability need to be further improved. Meanwhile, α-Co(OH)2 has a high electrical conductivity and similar microstructure to α-Ni(OH)2. Nickel-cobalt binary hydroxide has the advantages of both components, and can acquire a synergistic effect. It can exhibit a higher specific capacitance and better cycling performance than single metal hydroxide.In this work, firstly we synthesized nickel-cobalt binary hydroxide by simple hydrothermal method, and then explored the influence of elementary composition of the material on its electrochemical properties. Compared with that of single metal hydroxide, the layer spacing of binary hydroxidewas larger and that the morphology was not substantially changed. Electrochemical tests demonstrated that the specific capacitance, rate capability and cycling stability of nickel-cobalt binary hydroxide were improved obviously. We chose the sample with the initial reactant Co:Ni= 7:3 and the activated carbon as positive and negative electrode, respectively, to fabricate an asymmetric supercapacitor. The hybrid capacitor had a good rate capability and cycling stability, and could obtain high power density and energy density.Then, we synthesized nickel-cobalt binary oxide with a porous structure by calcinating nickel-cobalt hydroxide precursor and then studied its composition, specific surface area, porous structure and electrochemical properties. The results showed that nickel-cobalt binary oxide had better electrochemical properties than single metal oxide as well. Among these binary oxides, the sample with the initial reactant Co:Ni= 7:3 had the highest specific capacitance of 750 F g-1, good rate capability, and long cycle life. We applied this sample and activated carbon as positive and negative electrode materials, respectively, to assemble an asymmetry capacitor. The electrochemical results showed that the assembled asymmetry capacitor had a very high potential window (1.75 V), high energy density and good cycling stability (capacitance retained 86.4% after 10000 cycles).