Kinetic Investigation of LiCoO₂ by Electrochemical Impedance Spectroscopy (EIS)

摘要

Electrochemical impedance spectroscopy (EIS) is employed to investigate the electrochemicalproperties of LiCoO2 cathode. At initial state, the Nyquist plots consist of one compressed semicirclein high and intermediate frequency ranges that reflect charge transfer resistance and a straight lineinclined at a constant angle to the real axis in lower frequency range that reflects the diffusionproperties of lithium ion in solid materials. When the cell was charged for several hours, the Nyquistplots consist of two compressed semicircles alike in appearance of a half ellipse at high andintermediate frequency ranges and an anomalous line at lower frequency range, and the shape of thesecond semicircle is a half ellipse in appearance almost. The information of electrolyte resistance,surface film resistance and charge transfer resistance have been obtained by modeling with twodifferent equivalent circuits according with the Nyquist plots with different shape. It can be speculatedthat both the passivating film on the surface of LiCoO2 cathode and the channels for lithium iontransfer in LiCoO2 cathode are mostly formed during the first charge/discharge process. Both diffusioncoefficient of lithium ion in LiCoO2 cathode and exchange current density are in accord with theanalysis of the Nyquist plots of electrochemical impedance spectra, indicating the rationality of thespeculation.