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Appl. Sci. 2018, 8(7), 1018; https://doi.org/10.3390/app8071018

Variation of Impedance in Lead-Acid Batteries in the Presence of Acid Stratification

1
Chair for Electrochemical Energy Conversion and Storage Systems, Institute for Power Electronics and Electrical Drives (ISEA), RWTH Aachen University, Jägerstrasse 17-19, 52066 Aachen, Germany
2
BatterieIngenieure GmbH, Huettenstraße 5, 52068 Aachen, Germany
3
Institute for Power Generation and Storage Systems (PGS), E.ON ERC, RWTH Aachen University, Templergraben 55, 52062 Aachen, Germany
4
Jülich Aachen Research Alliance, JARA-Energy, Wilhelm-Johnen-Strasse, 52425 Jülich, Germany
5
Helmholtz Institute Münster (HI MS), IEK-12, Forschungszentrum Jülich, Jägerstrasse 17-19, 52066 Aachen, Germany
*
Author to whom correspondence should be addressed.
Received: 31 May 2018 / Revised: 18 June 2018 / Accepted: 19 June 2018 / Published: 22 June 2018
(This article belongs to the Special Issue Battery Management and State Estimation)
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Abstract

Acid stratification is a common issue in lead-acid batteries. The density of the electrolyte rises from the top to the bottom and causes inhomogeneous current distribution over the electrodes. The consequences are unequal aging processes provoking earlier battery failure. In stationary applications electrolyte circulation pumps are sporadical installed in the battery to mix the acid. For automotive applications passive mixing systems are implemented by some battery manufacturers against stratification. Stratification does not show any distinct voltage-current profile to be recognizable online. However, it increases the voltage and affects the impedance, which both are essential information for diagnostic purpose. Impedance spectra were performed here on lead-acid test cells with adjusted stratification levels to analyze the influence on the impedance in details. It is observed, that the high-frequency impedance is decreased in the stratified cell and that in contrast to this the charge-transfer resistance is increased. Based on simulations with a spatially-resolved equivalent electrical circuit the increased charge-transfer resistance could be explained with an inhomogeneous State-of-Charge resulting in an accumulation of sulfate crystals in the bottom part of the electrodes. These sulfate crystals further affected recorded impedance spectra after the electrolyte was homogenized. View Full-Text
Keywords: electro-chemical impedance spectroscopy; EIS; stratification; lead-acid battery; diagnostic; spatially-resolved modeling; equivalent-electrical circuit electro-chemical impedance spectroscopy; EIS; stratification; lead-acid battery; diagnostic; spatially-resolved modeling; equivalent-electrical circuit
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Kwiecien, M.; Huck, M.; Badeda, J.; Zorer, C.; Komut, K.; Yu, Q.; Sauer, D.U. Variation of Impedance in Lead-Acid Batteries in the Presence of Acid Stratification. Appl. Sci. 2018, 8, 1018.

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