In order to elucidate the structural change of LixCoO2 with temperature (T), powder X-ray diffraction measurements have been carried out using a synchrotron radiation source in the T range between 300 and 90 K for the samples with x = 1.02, 0.60, 0.56, and 0.53. The samples with x < 1.02 were prepared by an electrochemical reaction in a non-aqueous lithium cell. The x = 1.02 and 0.60 samples are in a rhombohedral phase (R<(3)over bar>m) in the whole T range measured. On the other hand, the x = 0.56 and 0.53 samples exhibit a structural transition around 140 K, although the both samples are in a monoclinic phase (C2/m) down to 90 K. That is, the angle between a(M)- and c(M)-axis (beta(M)) increases monotonically down to 150 K, then increases more rapidly with further lowering T. The values of Delta beta and a(M)/b(M), which are parameters to characterize a monoclinic distortion from the hexagonal symmetry, are Delta beta > + 0.6 degrees and a(M)/b(M) < 1.732 above 140 K, while Delta beta < + 0.6 degrees and a(M)/b(M) approximate to 1.732 below 140 K. This suggests that the monoclinic distortion below 140 K is mainly caused by a gliding along the basal plane. (C) 2009 Elsevier B.V. All rights reserved.