Electrochemical Properties of Olivine-Type LiFePO4/C Cathode Material for Lithium Ion Batteries

摘要

Although olivine LiFePO4 has been widely utilized as a cathode material for lithium ion batteries,there is still debate regarding the interpretation of the Nyquist plots of LiFePO4 electrodes in theliterature. In the present paper, the impedance spectra for lithium ion de-insertion and insertion inLiFePO4 electrodes, with different percentages of graphite material serving as the conductive additive,were obtained at different potentials during the first charge-discharge cycle. The results reveal that thecharacteristic Nyquist plot of LiFePO4 electrodes is strongly influenced by the content of theconductive additive. With increasing conductive content in the LiFePO4 electrode, the characteristicNyquist plot changes from a semicircle and an inclined line to two semicircles and an inclined line.The fundamental reason for this new phenomenon and the ascription of the time constants in theNyquist plots of the LiFePO4 electrodes are analyzed in detail based on simulated results of theexperimental EIS data.