Lithium and Vacancy Ordering in T#2−LixCoO2 Derived from O2-Type LiCoO2

Electron diffraction revealed evidence of commensurate and incommensurate superstructures in an unusual phase, T # 2, derived from O2-type layered LiCoO 2 upon lithium deintercalation. 2 a orth. × 2 b orth. × 2 c orth., 2 a orth. × b orth. × c orth., and incommensurate with q = (γ = 0.23 and 0.36) superstructures were found. It is believed that lithium and vacancy ordering is the most probable cause for the presence of these superstructures. Lithium ordering configurations were discussed in detail with respect to the superstructures observed. It is believed that the presence of various lithium and vacancy ordering configurations improves the stability of the T # 2 structure over a range of lithium compositions. Nevertheless, it should be mentioned that the nature of superstructures present and possible lithium ordering configurations in T # 2−Li x CoO 2 were complex and further investigations are needed. In addition, it is of significance to point out that a combination of transmission electron microscopy and electron diffraction showed that three T # 2 variants could coexist in different regions within one T # 2 crystal, which led to the development of a domain (mazed) microstructure.