Phase transition mechanisms in LixCoO2 (0.25 ≤ x ≤ 1) based on group-subgroup transformations

Hamdi Ben Yahia, Masahiro Shikano, Hironori Kobayashi

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The basic structural chemistry of O3-LixCoO2 (0.25 ≤ x ≤ 1) oxides is reviewed. Crystal chemical details of selected compositions and group-subgroup schemes are discussed with respect to phase transitions upon electrochemical or chemical deintercalation of the lithium atoms. Furthermore, the theoretical crystal structures of LixCoO 2 supercells (x = 0.75, 0.5, 0.33, and 0.25) are reported for the first time based on the combination of transmission electron microscopy (TEM) and X-ray (XRD) or neutron diffraction (ND) experiments. Li 0.75CoO2 and Li0.25CoO2 supercells crystallize with the space group R3Ì...m, a4 = 5.6234 Å and 5.624 Å, and c4 = 14.2863 Å and 14.26 Å, respectively, whereas the Li0.5CoO2 supercell crystallizes with the space group P21/m, a7 = 4.865 Å, b 7 = 2.809 Å, c7 = 9.728 Å, and β7 = 99.59. The Li0.33CoO2 supercell may crystallize in different unit cells (hexagonal or orthorhombic or monoclinic). For Li0.75CoO2, the TEM superstructure reflections are due to only one type of lithium and vacancy ordering within the lithium layers; however, for x = 0.5, the superstructure reflections are due to an intergrowth of two Li0.5CoO2 monoclinic structures (P2/m, a 5 = 4.865(3) Å, b5 = 2.809(3) Å, c5 = 5.063(3) Å, β5 = 108.68(5)) with the lithium and vacancies alternating the 1g and 1f atomic positions, in two successive layers, along the c direction. For Li0.33CoO2, in most cases, the Li and vacancy ordering are similar to Li and Mn ordering in the Li 2MnO3 structure. The phase transition mechanisms from O3-LiCoO2 to O3-Li0.25CoO2 and from O3-LiCoO2 to spinel-Li0.5CoO2 have been determined, and the structural relationship between O3-LiCoO2 and Li2MnO3 has been discussed in detail.

Original languageEnglish
Pages (from-to)3687-3701
Number of pages15
JournalChemistry of Materials
Issue number18
Publication statusPublished - 24 Sep 2013



  • O3-LiCoO system
  • group-subgroup schemes
  • lithium battery
  • phase transition

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

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