The aim of this paper is to characterise the compounds formed by the ageing of α NI(OH)2 in 5 M KOH at 70 °C. The final product of this treatment is known as the β Ni(OH)2 phase, but with the ageing period, a progressive change of electrochemical reactivity as well as a textural and structural evolution are observed. The products obtained are stable in time once the ageing is stopped and are not a mere mixture of α and β but single phase nickel hydroxides whose properties are intermediate between those of α and β Ni (OH)2. Intermediate forms of nickel hydroxide, whose specific features seem to be the crystallites size and the quantity of absorbed nitrate ions, will be called “badly crystallised β” or βbc as proposed by Delmas et al.