The study of the ageing of the manganese-substituted nickel hydroxides with α-structure in the KOH electrolytic medium of Ni/Cd batteries has given evidence of a new type of structure interstratification. This behaviour is due to spontaneous oxidation of the manganese ions, which are trivalent in the starting phases, to the tetravalent state in the aged materials. According to the infrared and chemical analysis results, the structure of the interstratified aged materials consists of a distribution of α-, β(II)- and β(III)-interslab spaces directly related to fluctuations of the manganese distribution within the slabs.