Layered Li[Li0.3Cr0.1Mn0.6]O-2 cathode material with a hexagonal structure was synthesized by a solid-state reaction. The structural changes of this material were studied using a synchrotron-based in situ X-ray diffraction (XRD) technique during charge/discharge cycles. The results of in situ X-ray diffraction indicated that the layer structure and the hexagonal symmetry of this material were preserved through the phase transition between H1 and H2 during the charge/discharge cycling. When cycled in the voltage range of 2.0-4.5 V, the changes in lattice parameters a and c are smaller than those for the LiNiO2, layered material. When charged to a high voltage at 5.1 V, the hexagonal phase H3, which is commonly formed at voltages higher than 4.3 V in LiNiO2 with a very short c-axis, is not observed in the Li[Li0.3Cr0.1Mn0.6]O-2 cathode, indicating a possible high thermal stability in the fully charged state. Cyclic voltammograms show a single pair of oxidation and reduction peaks, consistent with a reversible phase transition between H1 and H2 observed from the in situ X-ray diffraction data. (C) 2004 Elsevier B.V All rights reserved.