Tortuosity of Battery Electrodes: Validation of Impedance-Derived Values and Critical Comparison with 3D Tomography
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Date
2018
Publication Type
Journal Article
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yes
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Abstract
Tortuosity values of porous battery electrodes determined using electrochemical impedance spectroscopy in symmetric cells with a non-intercalating electrolyte are typically higher than those values based on numerical analysis of 3D tomographic reconstructions. The electrochemical approach assumes that the electronic resistance in the porous coating is negligible and that the tortuosity of the porous electrode can be calculated from the ionic resistance determined by fitting a transmission line equivalent circuit model to the experimental data. In this work, we validate the assumptions behind the electrochemical approach. First, we experimentally and theoretically investigate the influence of the electronic resistance of the porous electrode on the extracted ionic resistances using a general transmission line model, and provide a convenient method to determine whether the electronic resistance is sufficiently low for the model to be correctly applied. Second, using a macroscopic setup with known tortuosity, we prove that the ionic resistance quantified by the transmission line model indeed yields the true tortuosity of a porous medium. Based on our findings, we analyze the tortuosities of porous electrodes using both X-ray tomography and electrochemical impedance spectroscopy on electrodes from the same coating and conclude that the distribution of the polymeric binder phase, which is not imaged in most tomographic experiments, is a key reason for the underestimated tortuosity values calculated from 3D reconstructions of electrode microstructures.
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published
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Journal / series
Volume
165 (3)
Pages / Article No.
Publisher
The Electrochemical Society
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Subject
Electronic resistance; Impedance spectroscopy; Tortuosity
Organisational unit
03895 - Wood, Vanessa / Wood, Vanessa
00002 - ETH Zürich
Notes
Funding
680070 - Development of Quantitative Metrologies to Guide Lithium Ion Battery Manufacturing (EC)