Lithium deintercalation from Li0.98Ni1.02O2 leads at high voltage to two almost complete deintercalated phases: R3 and H4. The first one presents the O3-type oxygen packing while the second one exhibits the CdI2-type structure (O1 oxygen packing). For both materials, the broadening of some diffraction lines shows the existence of stacking faults. The experimental diffraction patterns have been successfully simulated using the DIFFaX program. At high potential, part of the H4 phase is irreversibly transformed in a new phase (called R'3) through Ni3+ ion migration in the interslab space. This behaviour has been related to fluctuations in composition at the crystallite scale. The presence of a significant amount of extra-nickel ions (z greater than or equal to 0.07) in Li1-zNi1+zO2 prevents the formation of the Ol-type packing. (C) 2000 Elsevier Science B.V. All rights reserved.