The T#2-Li2\3Co2\3Mn1\3O2 System. 2. Its Electrochemical Behavior

Electrochemical lithium deintercalation from the metastable T#2-Li2\3Co2\3Mn1\3O2 system has been investigated. The single-phase domains that separate the voltage plateaus observed on the cycling curve have been characterized by in situ and ex situ X-ray diffraction. T#2, T#2ʹ, and O61 phases are formed during the first charge and then O61, T#2ʹ, T#2, and O62 during the first discharge, and the O62 structure is finally maintained for the whole composition range during the next cycles. The T#2 stacking, also reported for the T2-Li2\3Ni1\3Mn2\3O2 phase by Dahn et al. and for the T#2-LixCoO2 phase (0.52 < x 0.72) by Carlier et al., is characterized by oxygen ions that do not occupy the positions of a same triangular lattice and by very distorted tetrahedral sites for lithium ions. The O6 stacking is observed for small and large lithium compositions, corresponding to O61 and O62 phases, respectively. Because the formation of the O62 phase is irreversible, it is assumed to be different from the O61 and from the O6-LixCoO2 (0.33 < x 0.42) previously reported.