Abstract Cation distribution in Li 1-xNi 1+xO 2 was studied by Rietvelt analysis of XRD data. The occupancy levels of 3a and 3b sites by Ni and Li atoms approach as x increases, leading to a statistical distribution for x ≥ 0.4. Acid treatment of these oxides causes the solid to be partly dissolved. The remaining oxide shows divergences in chemical composition and XRD patterns which can be associated with lithium deintercalation. This process is accompanied by a decrease in the rhombohedral angle, α. The thermal behaviour of acid-treated samples is characterized by the occurrence of a spinel phase at ca. 270°C.