Structural characterisation of new metastable NiO2 phases

Lithium deintercalation from Li 0.98 Ni 1.02 O 2 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 CdI 2 -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 Ni 3+ 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 ≥0.07) in Li 1− z Ni 1+ z O 2 prevents the formation of the O1-type packing.