Synthesis and characterization of LiCo_(0.3-x)Ga_xNi_(0.7)O_2 (x = 0, 0.05) as a cathode material for lithium ion battery

摘要

The single phase of LiCo_(0.3-x)Ga_xNi_(0.7)O_2 (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 LiCo_(0.25)Ga_(0.05)Ni_(0.7)O_2 exhibits better electrochemical performance with an initial discharge capacity of 180.0 mAhg~(-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 LiCo_(0.3)Ni_(0.7)O_2 at ambient temperature and 55℃. Meanwhile, Ga-doping not only suppresses the alternating current (AC) impedance of LiCo_(0.3)Ni_(0.7)O_2 but also promotes the Li~+ diffusion in LiCo_(0.3)Ni_(0.7)O_2. Furthermore, thermal stability of the charged LiCo_(0.25)Ga_(0.05)Ni_(0.7)O_2 is improved, which may be attributed to the retard of O_2 evolution in LiCo_(0.3)Ni_(0.7)O_2 and the suppression of electrolyte oxidation during cycling by Ga-doping.