The influence of the annealing temperature on the degree of cation-disordering in the layered structures was examined for three different compositions of LiNiyCo1-yO2, (y = 0.2, 0.66 and 0.75, respectively). A minimum in cation-disorder is found for annealing temperatures between 700 and 800 degrees C for y = 0.75, between 750 and 810 degrees C for y = 0.66 and a less pronounced minimum between 795 and 870 degrees C for y = 0.2. One optimum annealed sample with y = 0.75 was used for an in situ characterisation using synchrotron radiation. The obtained structural data correlate well with the electrochemical data. The known phase transition occurring during the first cycle was closely observed by ADXRD (angular dispersive X-ray diffraction). The two states of the material during the first cycle could be distinguished and the obtained data were processed by Rietveld refinement. (c) 2005 Elsevier B.V All rights reserved.