The single phase of LiCo0.3-x,GaxNi0.7O2 (x = 0, 0.05) was synthesized by a sol-gel method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical performance. The powders are homogeneous and have a good-layered structure. The synthesized LiCo0.25Ga0.05Ni0.7O2 exhibits better electrochemical performance with an initial discharge capacity of 180.0mAh g(-1) and a capacity retention of 95.2% after 50 cycles between 2.8 and 4.4 V at 0.2C rate. The study on the structural evolution of the material during the cycling shows that Ga-doping improves the structure stability of LiCo0.3Ni0.7O2, at ambient temperature and 55 degrees C. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo0.3Ni0.7O2 but also promotes the Li+ diffusion in LiCo0.3Ni0.7O2. Furthermore, thermal stability of the charged LiCo0.25Ga0.05Ni0.7O2 is improved, which may be attributed to the retard of O-2 evolution in LiCo0.3Ni0.70O2 and the suppression of electrolyte oxidation during cycling by Ga-doping. (c) 2005 Elsevier B.V. All rights reserved.