Effects of sintering temperature on the structure of the layered phase Li-x(Ni0.8Co0.2)O-2

The structure of the layered phase Li-x(Ni0.8Co0.2)O-2 was studied extensiv ely by powder X-ray and neutron diffraction, and the relationships between the sintering temperature, structure, and electrochemical properties were d etermined. 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 l owest level of Ni (similar to2.0%) on the Li site was prepared at 725 degre esC. Structural analysis also indicated that the occupancy of the Ni/Co lay er 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 be st sample in terms of electrochemical properties was that prepared at 725 d egreesC. This sample exhibited initial discharge capacities of similar to 1 90 mAh/g. All other samples delivered lower capacities, behavior which corr elates with the degree of Li site disordering. These results clearly show t he role of 3a site disorder on the electrochemical properties of these mate rials. However, we have not determined the role of the Ni/Co site, in parti cular, the disorder on electrochemical properties. (C) 2000 The Electrochem ical Society. S0013-4651(00)05-010-2. All rights reserved.