Physical and electrochemical characteristics of nanostructured nickel hydroxide powder

Nanostructured nickel hydroxide powder has been synthesized by a chemical precipitation method with the aid of ultrasound radiation, and the physical properties of the synthesized material were characterized by scanning electron microscopy, specific surface area, X-ray diffraction and differential scanning calorimetry. It was found that nanostructured nickel hydroxide was crystalline β-Ni(OH)₂ with a nanocrystalline and nanoporous surface structure. The crystallite sizes of nanostructured β-Ni(OH)₂ along the c- and a-axis were 2.5 and 2.3 nm, respectively, as calculated from (001) and (100) X-ray diffraction peaks. In comparison with spherical β-Ni(OH)₂ which has now been widely used as the active material for pasted nickel electrodes, nanostructured β-Ni(OH)₂ possessed a smaller crystallite size, more structural defects, a larger lattice parameter of c₀, a higher specific surface area and lower thermal decomposition temperature. These physical characteristics were advantageous to the improvement of electrochemical activity of the nanostructured nickel hydroxide powder. Studies indicated that the filling property and flowability of nanostructured β-Ni(OH)₂, which were characterized by the measurements of tapping density and angle of repose, were inferior to those of spherical β-Ni(OH)₂. Pasted nickel electrodes with a porous nickel-foam substrate were prepared using a mixture of the nanostructured and spherical Ni(OH)₂ powders as the active material. Charge/discharge tests showed that the addition of an appropriate amount of nanostructured Ni(OH)₂ powder to spherical Ni(OH)₂ powder could enhance the specific discharge capacity and high-rate capability of the pasted nickel electrodes. This enhancement could be attributed to a lowered electrochemical reaction impedance for the nickel electrode with the addition of nanostructured Ni(OH)₂ relative to the electrode without nanostructured Ni(OH) ₂.