The structure of the layered phase Li-x(Ni0.8Co0.2)O-2 was studied extensively by powder X-ray and neutron diffraction, and the relationships between the sintering temperature, structure, and electrochemical properties were determined. Samples in this study were prepared with a sintering time of 48 h at 600-750 degreesC, and all indicated the presence of Ni on the Li site, based on structural analysis by the Rietveld method. The sample with the lowest level of Ni (similar to2.0%) on the Li site was prepared at 725 degreesC. Structural analysis also indicated that the occupancy of the Ni/Co layer varied as a function of the sintering temperature, but as the sintering temperature was increased, the deviation from the expected value decreased. Electrochemical measurements were carried out on these samples, and the best sample in terms of electrochemical properties was that prepared at 725 degreesC. This sample exhibited initial discharge capacities of similar to 190 mAh/g. All other samples delivered lower capacities, behavior which correlates with the degree of Li site disordering. These results clearly show the role of 3a site disorder on the electrochemical properties of these materials. However, we have not determined the role of the Ni/Co site, in particular, the disorder on electrochemical properties.