Effects of sintering temperature on the structure of the layered phase Lix(Ni0.8Co0.2)O2

The structure of the layered phase Lix(Ni0.8Co0.2)O2 was studied extensively by powder X-ray and neutron diffraction, and the relationships between sintering temperature, structure, and electrochemical properties determined. Samples were prepared with a sintering time of 48 h at 600-750 C. They showed the presence of Ni on the Li site, based on structural analysis by the Rietveld method. The sample with the lowest level of Ni (about 2.0%) on the Li site was prepared at 725 C. 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 C. This sample exhibited initial discharge capacities of about 190 mAh/g. All other samples delivered lower capacities, behaviour 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, the role of the Ni/Co site has not been determined. 35 refs.