LiNi1−y Co y O2 samples are prepared by a sol–gel method at various cobalt concentrations (y-value) by sintering at 800°C for a period of 10h. An X-ray diffraction technique is used to examine the structural properties of the samples. The sample with a y-value of 0.25 has the largest initial discharge capacity and shows the best cycling performance. It is concluded that this performance results from better hexagonal ordering, crystallinity, and smaller particle size with good particle-size distribution compared with other samples. Li x Ni0.75Co0.25O2 samples with different lithium content are also prepared and it is found that Li1.05Ni0.75CO0.25O2 shows the best electrochemical performance. This suggests that the presence of excess lithium prevents the exchange of Ni2+ ions at lithium sites.