| In this paper, based on the review of the research and development of Ni(OH)2, nanometer Ni(OH)2 and NiO were synthesized by micro-emulsion method and micro-emulsion/solvent-thermal method. The morphology and structure of the products were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared absorption spectroscopy (IR) and thermo-gravimetry (TG). The growth mechanism of Ni(OH)2 was investigated preliminarily, the electrochemical properties of Ni(OH)2 in the MH/Ni and NiO in the AC/NiO capacitor were also studied.The hexagonalβ-Ni(OH)2, which had irregular morphology and poor crystallinity, was prepared in micro-emulsion solution formed by TX-100/n-hexanol/ n-heptane/water. Whenω=10, the Ni(OH)2 electrode exhibited the maximum discharge specific capacity 196.5 mAh·g-1 at 0.2C, and the specific capacity reached to 234.6 mAh·g-1 after doping CoO with the content of 7%. The electrochemical properties were superior to Ni(OH)2 prepared by co-precipitation and coated with Co(OH)2. When hydrothermally treated for 1 h at 140℃, the discharge specific capacity of the Ni(OH)2 electrode was 259.2 mAh·g-1, the capacity retention of C1C/C0.2C and 100 cycles at 1C were 89.8% and 81.2% respectively. After solvent-thermal reaction, the crystallinity and diameter of the Ni(OH)2, which had flake, rod and spindle morphologies, were increased, and the law betweenωvalues and discharge specific capacity was not changed. As the time of solvent-thermal reaction was prolonged, the high-rate discharge ability of the Ni(OH)2 electrode was improved. When the solvent-thermal reaction was 18 h at 140℃, the Ni(OH)2 electrode showed the maximum discharge specific capacity 279 mAh·g-1 at 0.2C, and was enhanced by 44.4 mAh·g-1. CV and EIS tests indicated that the Ni(OH)2 electrode had the best reversibility, the highest diffusion coefficient and the lowest charge transfer resistance.The hexagonalβ-Ni(OH)2, whose morphology was needle with the diameter of 20-40 run, was prepared in micro-emulsion solution formed by CTAB/n-butanol /n-heptane/water. Whenω=28, the Ni(OH)2 electrode exhibited the maximum discharge specific capacity 222.6 mAh·g-1 at 0.2C, and increased to 285.3 mAh·g-1after doping CoO with the content of 7%. The electrochemical properties was superior to Ni(OH)2 prepared by co-precipitation and coated with Co(OH)2. The crystallinity of the Ni(OH)2 was increased after solvent-thermal reaction. The diameter of flake and rod Ni(OH)2 was 80-100 nm and 100-160 nm, respectively. The regularity betweenωvalues and discharge specific capacity was not changed, but the discharge specific capacity was decreased significantly. When solvent-thermal reaction was 12 h at 140℃, the Ni(OH)2 electrode exhibited the maximum discharge specific capacity 234.6 mAh·g-1 at 0.2C, and was decreased by 50.7 mAh·g-1. CV and EIS tests showed that the Ni(OH)2 electrode had the highest diffusion coefficient and the lowest charge transfer resistance, the electrode was controlled by charge transfer resistance. The growth mechanism of Ni(OH)2 was investigated. And we inferred the structure of rod and flake Ni(OH)2 was formed by the induction of surfactant and self-assemble.NiO with cubic crystalline and irregular shape was prepared by calcining Ni(OH)2 at 300℃. The Ni(OH)2 was made by micro-emulsion method using TX-100/n-hexanol/n-heptane/water. As the calcination temperature was increased, the diameter of NiO increased gradually. The activation energy for nanocrystallite growth was 10.72 kJ·mol-1. The TG curve was divided into three segments, which corresponded to the loss of adsorbed water, residual surfactant and crystal water of Ni(OH)2, respectively. The result of DSC curve showed that the thermal decomposition temperature was 258℃.The specific capacitance, power and energy of AC/NiO capacitor were 104.4 F·g-1, 75 W·kg-1 and 65.3 Wh·kg-1 and the capacity retention was 87.7% after 200 cycles. AC/NiO capacitor exhibited excellent capacitance performance with the potential range from 0 to 1.5 V. The EIS result indicated that the NiO electrode had lower charge transfer resistance and better electrochemical capacitance performance. |
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