Electrochemical impedance spectroscopy investigation of the FeF3/C cathode for lithium-ion batteries

• Published in: Solid state ionics 2012-08, Vol.222-223, p.23-30
• Main Authors: Shi, Yue-Li, Shen, Ming-Fang, Xu, Shou-Dong, Zhuang, Quan-Chao, Jiang, Li, Qiang, Ying-Huai
• Format: Article
• Language: English
• Subjects: Cathodes; Contact; Conversion reactions; Discharge; EIS; Electrochemical impedance spectroscopy; Electrodes; FeF3; Li-ion battery; Lithium batteries; Lithium-ion batteries; Simulation; Spectra
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2012.06.024

The FeF3/C composites were prepared by high energy milling, and its cyclic performance was characterized by discharge–charge measurements. The electrochemical impedance spectra (EIS) of FeF3/C cathode were obtained at different potentials during the initial discharge–charge cycle. The results show that the FeF3/C cathode exhibits an enhanced initial discharge capacity of 710mAh/g (4.5–1.5V) but shows a capacity retention of 40% after 100cycles at room temperature. EIS of the FeF3/C cathode have revealed that the Nyquist plots of the typical EIS consist of two semicircles and one arc in an order of decreasing frequency during lithiation/delithiation. An equivalent circuit was proposed to simulate the experimental EIS data. The kinetic parameters of lithium ion and electron across the porous FeF3/C electrode in the first discharge–charge cycle are discussed in detail, offering some evidence that both the unstable SEI film on the electrode surface and the Schottky contact between metal-fluorides and conductive agents, can eventually affect the cyclic performance. ► We test and analyze the impedance of FeF3/C cathode by EIS. ► EIS consist of three parts (HFS, MFS and LFA). ► HFS is attributed to Li+ transport through the SEI film on the electrode. ► MFS is related to Schottky contact between FeF3 and conductive agents. ► Both SEI film and Schottky contact affect the cyclic performance.