Characterization of an ultrafine β-nickel hydroxide from supersonic co-precipitation method

Nickel hydroxide is a well known electrode active material for nickel-based batteries. Compared with a commercial spherical Ni(OH)2, characteristics of an ultrafine Ni(OH)2 made from supersonic co-precipitation method were studied. SEM showed that the prepared Ni(OH)2 exhibited a worm-like structure, compared to the ball-like shape of spherical Ni(OH)2. By XRD, the sample was found to be β-type Ni(OH)2, with more structure distortion due to a shortening in Ni–Ni distances and a prolongation in distances between NiO2 layers as the lattice constants for the sample are a = 3.123 Å, c = 4.655 Å. XANES testified a severe structure distortion for the prepared Ni(OH)2, and EXAFS showed expansion in Ni–O and contraction in Ni–Ni distances when compared to perfect crystal Ni(OH)2. Electrochemical impedance spectroscopy (EIS) determined that proton diffusion coefficient of the ultrafine powder (6.0 × 10−16 cm2 s−1) was about two orders larger than that of spherical Ni(OH)2 (5.6 × 10−18 cm2 s−1). The badly crystallized ultrafine Ni(OH)2 may have more electrochemical activities and thus could be applied in nickel-based batteries.