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Electrochemical impedance spectroscopy (EIS) is powerful tool to evaluate a performance of lithium-ion battery because time constants in electrochemical signals can be distinguished with no damage to the electrode. 1,2 Separation of time constants of anode and cathode is desired in the interpretation of impedance spectra of a lithium-ion battery. Multi -EIS measurement is an analysis method in which simultaneous measurements of three impedance spectra (cathode-reference electrode, anode-reference electrode and anode-cathode) are carried out using a suitable reference electrode. The time-constants of anode and cathode from full cell impedance spectra can be separated by using Multi-EIS measurement. On the other hand, in the case of in-situ EIS measurements for lithium-ion battery, impedance spectra were measured successively during charge or discharge sequence. The in-situ EIS measurement is very useful for monitoring the degradation process of lithium-ion battery during the charge-discharge cycles. 3 In the present study, we developed a multi-in-situ EIS measurement system in which simultaneous measurements of three impedance spectra were carried out during the charge-discharge cycle. The system is based on a newly developed potentiostat which has an integrated high-performance frequency response analyser and data processing software. The electrode reactions in rechargeable batteries do not satisfy the time stability during the charge–discharge cycles and the low frequency components of the impedance might contain significant errors due to the time variation. In order to compensate the impedance spectrum deviated by the variation of reaction resistance in the charge or discharge, the impedance spectra were measured successively and plotted on the three-dimensional (3D) complex diagram, which has a time axis. The plots were connected by the spline under tension function at each frequency. The cross-section of 3D impedance shell perpendicular to the time axis gives the instantaneous impedance at an arbitrary time, which can be given automatically by using the software. We investigated the influence of SOC and C-rate on impedance spectra of both cathode and anode. Acknowledgement This work was supported by JST A-STEP (AS2421666K). References 1. M. Itagaki, in Nanoscale Technology for Advanced Lithium Batteries, T. Osaka and Z. Ogumi, Editor, p.123, Springer Science+Business Media, New York (2014). 2. T. Osaka, T. Momma, D. Mukoyama, H. Nara, J. Power Souces 205 (2012) 483. 3. M. Itagaki, N. Kobari, S. Yotsuda, K. Watanabe, S. Kinoshita, M. Ue, J. Power Souces 148 (2005) 78. |
