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Open AccessArticle

Optimized Process Parameters for a Reproducible Distribution of Relaxation Times Analysis of Electrochemical Systems

1
Chair of Electrical Energy Systems, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany
2
Helmholtz-Institute Ulm (HIU), Helmholtzstraße 11, 89081 Ulm, Germany
*
Author to whom correspondence should be addressed.
Batteries 2019, 5(2), 43; https://doi.org/10.3390/batteries5020043
Received: 15 February 2019 / Revised: 4 April 2019 / Accepted: 11 April 2019 / Published: 5 May 2019
The distribution of relaxation times (DRT) analysis offers a model-free approach for a detailed investigation of electrochemical impedance spectra. Typically, the calculation of the distribution function is an ill-posed problem requiring regularization methods which are strongly parameter-dependent. Before statements on measurement data can be made, a process parameter study is crucial for analyzing the impact of the individual parameters on the distribution function. The optimal regularization parameter is determined together with the number of discrete time constants. Furthermore, the regularization term is investigated with respect to its mathematical background. It is revealed that the algorithm and its handling of constraints and the optimization function significantly determine the result of the DRT calculation. With optimized parameters, detailed information on the investigated system can be obtained. As an example of a complex impedance spectrum, a commercial Nickel–Manganese–Cobalt–Oxide (NMC) lithium-ion pouch cell is investigated. The DRT allows the investigation of the SOC dependency of the charge transfer reactions, solid electrolyte interphase (SEI) and the solid state diffusion of both anode and cathode. For the quantification of the single polarization contributions, a peak analysis algorithm based on Gaussian distribution curves is presented and applied. View Full-Text
Keywords: electrochemical impedance spectroscopy; distribution of relaxation times; Tikhonov regularization; Li-ion battery; polarization analysis electrochemical impedance spectroscopy; distribution of relaxation times; Tikhonov regularization; Li-ion battery; polarization analysis
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Hahn, M.; Schindler, S.; Triebs, L.-C.; Danzer, M.A. Optimized Process Parameters for a Reproducible Distribution of Relaxation Times Analysis of Electrochemical Systems. Batteries 2019, 5, 43.

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