Indexed on: 01 May '87Published on: 01 May '87Published in: Journal of Applied Electrochemistry
The textural and structural modifications involved in electrochemical redox cycling of turbostratic nickel (II) hydroxide has been investigated using X-ray diffraction and electron microscopy methods. It was found that during the first cycles, different phenomena compete: redox reactions which occur in the solid state, and ageing reactions via the solution. For the first galvanostatic charge performed at the C/5 rate in 4.5 N KOH, the direct oxidation of α(II) to γ(III) and the ageing of α(II) to β(II) via the solution followed by the oxidation to γ(III) are in competition. The study of the discharge mechanism shows that the direct reduction γ(III)→β(II) is parallel to the reduction γ(III)→α(II) and the ageing of the turbostratic hydroxide via the solution. After the first cycle it was established that the alpha-generated β(II) active phase consisted of a mixture of two kinds of particles, the oxidation of which follows two paths: β(II)/β(III) for the thicker particles and for the thinner β(II)/γ(III), but these latter β(II) particles aged via the solution by Oswald ripening and the β(II)/γ(III) couples swung to β(II)/β(III).