Invited Presentation: Impedance Analysis of Lithium-Ion Battery for Future

Batteries have become one of the most important devices because green vehicles, such as hybrid electric vehicles, battery electric vehicles, and even fuel cell electric vehicles, mount batteries. Also, solar power and wind power plants require batteries, in which the power leveling are demanded to stabilize electrical power systems. In order to operate the batteries in those systems, an understanding of the state of batteries, such as the state of charge and state of health of batteries, is very important for effective and safe operation of the batteries. Therefore, a non-destructive analysis of the condition is in high demand for the premonitory diagnosis of the on-board batteries of electric vehicles, and of installed batteries in load leveling systems. Electrochemical impedance spectroscopy (EIS), in which a small-amplitude sinusoidal potential perturbation is applied to a cell, is one of the most powerful tools for the non-destructive analysis of energy devices such as lithium-ion batteries (LIB) ^1-4]and fuel cells ^5,6. However, the capacity and the internal resistance of large-scale LIBs become higher and lower, respectively, for the application to electric vehicles and large-scale power storage systems: EIS using conventional frequency response analyzer (FRA) – potentiostat systems is not easy to measure the impedance of the LIB because of its low internal resistance. In this situation, we focused on the power controller of LIB system to create a signal for analyzing the battery health. In the present study, application of square wave potential/current for input signals of EIS was investigated firstly in simple electrochemical reaction to verify a new technique called “Square-potential/current electrochemical impedance spectroscopy (SP-EIS, SC-EIS)” which is a method for EIS without using FRA systems. And then, we applied SC-EIS to evaluate a degradation of commercial LIB with the charge­discharge cycling.

Firstly, a redox reaction of Fe(Ⅱ)/(Ⅲ) was investigated as a simple electrochemical reaction. On the basis of the technique of fourier transform in ref. ^{7, 8}, EIS was carried out using square potential input. Figure 1A shows Nyqust plots of [Fe(CN)₆]^4-/[Fe(CN)₆]^3- electrolyte using square potential input generated by potentiostat. The value of frequency response as ten times higher than that of input frequency was successfully obtained. The value was as almost same as that was obtained by the FRA system. From Fig.1B, applying this method to LIB, we successfully obtained frequency response using several square current inputs generated by a power controller.

A commercially available laminated LIB with a nominal capacity of 5 Ah for an electric power assisted bicycle was also evaluated. As the results, fine Nyquist plots could be obtained by means of SC-EIS as well as that by means of the FRA system even in the case of degraded LIBs. Specifically, there was a good accordance between Nyquist plots obtained by SC-EIS on an LIB cell and those obtained by EIS using the FRA system with the error of each plot being less than 3% in the range of 1 kHz – 1 Hz. Therefore, the SC-EIS must be a method of great promise for widespread use in society.

References

[1]                   T. Osaka, et al., J. Power Sources, 205 (2012) 483.

[2]                   T. Momma, et al., J. Power Sources, 216 (2012) 304.

[3]                   D. Mukoyama, et al., Chem. Lett., 41 (2012) 444.

[4]                   T. Hang, et al., J. Power Sources, 222 (2013) 442.

[5]                   H. Nara, et al., J. Electrochem. Soc., 158 (2011) B1184.

[6]                   H. Nara, et al., Electrochim. Acta, 113 (2013) 720.

[7]                  T. Osaka, et al., Bull. Chem, Soc. Jpn., 55 (1982) 36.

[8]                  T. Osaka, et al., DENKI KAGAKU, 50, (1982) 295.