Electrochemical impedance spectroscopy (EIS) is a powerful technique for partitioning a system’s performance into contributions from individual physicochemical processes via their characteristic frequencies.¹ Typically, analysis of experimental EIS spectra aims to extract meaningful information by fitting an equivalent circuit analog composed of ideal circuit elements representing different physicochemical phenomena within the cell. While fitting an equivalent circuit to experimental data is easily accomplished using nonlinear least squares regression, the lumped nature and lack of direct physical interpretation of the resulting parameters can limit the information content of the analysis.²

An alternative approach for extracting meaningful parameters from the data is to directly fit physics-based mathematical models of the electrochemical systems. In fact, many decades of electrochemical modeling research have laid the groundwork for the physics-based modeling of impedance in a wide variety of fields including corrosion,³ hydrodynamic systems,⁴ fuel cells,⁵ and lithium ion batteries.⁶However, despite the important role and wide acceptance of these physics-based models, their impact in experimental impedance analysis has been limited by their complexity – these models often contain many coupled partial differential equations representing the different physicochemical processes.

Here we present an open-source, web-based tool for the in-depth analysis of experimental EIS spectra. We show that building a large database of simulated spectra across a wide range of parameters enables deeper insight into the electrochemical system under study. As a demonstration, we present an analysis of experimental lithium ion battery data using the widely utilized pseudo 2-dimensional (P2D) battery model.

References:

1. M. E. Orazem and B. Tribollet, Electrochemical impedance spectroscopy, p. 523, Wiley, Hoboken, N.J, (2008).

2. S. Fletcher, J. Electrochem. Soc., 141, 1823–1826 (1994).

3. D. D. Macdonald, S. Real, S. I. Smedley, and M. Urquidi‐Macdonald, J. Electrochem. Soc., 135, 2410–2414 (1988).

4. D. T. Schwartz, P. Stroeve, and B. G. Higgins, J. Electrochem. Soc., 136, 1755–1764 (1989).

5. J. R. Wilson, D. T. Schwartz, and S. B. Adler, Electrochimica Acta, 51, 1389–1402 (2006).

6. M. Doyle, J. P. Meyers, and J. Newman, J. Electrochem. Soc., 147, 99–110 (2000).