Characterization of solid-state synthesized pure and doped lithium nickel cobalt oxides

The effects of solid-state synthesized pure, anion F-doped and cation Mg-doped lithium nickel cobalt oxide were studied on their electrochemical impedance spectroscopy (EIS), lithium-ion diffusion, cyclability and Fourier transform infrared (FTIR). Their chemical diffusion coefficients are in the same order, 10(-11) cm(2)/s, and decrease with increasing state of charge. The cyclabilities of doped materials are somewhat better. The EIS results show charge transfer resistance increases with cycling; however, the resistance of solid-electrolyte interface (SEI) is random, and it could be the periodical deterioration and reformation process on SEI Different functional groups are found on the cathode materials through FTIR investigation after cycling tests, and their patterns are almost the same. (c) 2005 Elsevier B.V. All rights reserved.