Structural characterisation of new metastable NiO2 phases

Lithium deintercalation from Li0.98Ni1.02O2 leads at high voltage to two al most complete deintercalated phases: R3 and H4. The first one presents the O3-type oxygen packing while the second one exhibits the CdI2-type structur e (O1 oxygen packing). For both materials, the broadening of some diffracti on lines shows the existence of stacking faults. The experimental diffracti on patterns have been successfully simulated using the DIFFaX program. At h igh potential, part of the H4 phase is irreversibly transformed in a new ph ase (called R'3) through Ni3+ ion migration in the interslab space. This be haviour 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-ty pe packing. (C) 2000 Elsevier Science B.V. All rights reserved.