Micro-Flexible-Surface Probe for Determining Spatially Heterogeneous Electronic Conductivity of Lithium-Ion Battery Electrode Films

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Heterogeneity of MacMullin number within battery electrodes is a key metric affecting cell performance. To characterize this heterogeneity, an aperture probe was developed. This probe, coupled with a newly developed transmission-line model, allows for measurements of tortuosity, represented by the MacMullin number, on millimeter length scales. Local MacMullin number values of seven electrodes were measured, and the ionic resistance profiles of these electrodes are given through contour maps of the MacMullin number. The method is validated by comparing the average MacMullin number to the value obtained through other measurement methods. The results show significant local MacMullin number variation in such electrodes on a millimeter length scale. This method will allow battery manufacturers and researchers to better quantify sources of heterogeneity and improve electrode quality.

“…A planned avenue for future exploration is to compare localized ionic transport with localized electronic transport 41 or other properties such as state of charge or state of health.…”

Section: Discussionmentioning

confidence: 99%

Section: Aperture Probe and Experimentsmentioning

confidence: 99%

Heterogeneity in MacMullin Number of Li-Ion Battery Electrodes Studied by Means of an Aperture Probe

Liu

Prugue

Nikpour

et al. 2022

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“…The electrode thickness and the electrolyte bulk conductivity were chosen according to practical experiments. The electrical conductivity of the solid-phase was in the range of values measured using the micro-flexible surface probe developed by Vogel et al 35 With a low ratio of the ionic conductivity to the electronic conductivity of the electrode, the resistance of the solid phase in the transmission-line model becomes negligible, 36 and the impedance depends only on changes in the ionic resistance. Faradaic resistance is set to be large enough to assume that the electrolyte behaves as a "blocking electrolyte," meaning that very little charge-transfer reaction occurs at the solidliquid interface.…”

Section: Virtual Experiments Using Comsol Multiphysicsmentioning

confidence: 97%

Direct Measurements of Ionic Transport Behavior of Dual-Layer Porous Electrodes

Liu

James

Hamedi

et al. 2023

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To improve power and cycling performance of lithium-ion batteries, dual-layer or porosity-gradient electrodes have been proposed. By using a higher porosity close to the separator, the intention is to improve ion transport where it is most needed. Here, MacMullin numbers of two dual-layer anode samples are tested using an impedance measurement technique developed previously. To characterize the microstructure of each layer independently, we developed an improved transmission-line model that accounts for each layer's properties. Virtual experiments in which impedance measurements were simulated using COMSOL Multiphysics were used to examine and improve the accuracy of experimental inversion process. The results for the two dual-layer anodes studied show that MacMullin numbers follow expected trends, though the anodes are quite different from each other.

“…To address this potential use of the peel test to estimate electrical properties, in this work we quantitatively test the hypothesis that the peel test is an accurate indicator of electrode contact resistance. Our method will be to take measured electrical contact resistance, as estimated by a derivative of the micro-four-point method, 32 namely a micro-flexible-surface probe (μFSP), and explicitly compare with peel test values, namely areal force.…”

mentioning

confidence: 99%

“…In previous work, we have shown that a μFSP can be employed to accurately estimate the contact resistance and bulk electronic conductivity of a thin battery electrode film. 32 Previous iterations of this device have allowed us to accurate estimate electronic properties z E-mail: bmazzeo@byu.edu…”

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confidence: 99%

Li-Ion Battery Electrode Contact Resistance Estimation by Mechanical Peel Test

Vogel¹,

Sederholm²,

Shumway³

et al. 2022

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Li-ion battery electrode electronic properties, including bulk conductivity and contact resistance, are critical parameters affecting cell performance and fast-charge capability. Contact resistance between the coating and current collector is often the largest electronic resistance in an electrode and is affected by chemical, microstructural, and interfacial variations. Direct measurements of contact resistance and bulk conductivity have proven to be challenging. In their absence, a mechanical electrode peel test is often used to compare adhesion and electrical contact resistance. However, using a micro-flexible-surface probe, contact resistance can be directly determined. This work compares contact resistance and mechanical peel strength of multiple commercial-grade HE5050 and NCM523 cathodes and graphite and silicon anodes. It was found that peel strength correlates well with contact resistance in a carefully curated data set (p < 0.05) and in some situations may be a good metric to estimate electrical properties. However, there were distinct outliers in the data set, indicating that peel strength may not accurately reflect electrical properties when there is significant variation in electrode composition. These results illustrate the value of the micro-flexible-surface probe in quantifying contact resistance and bulk conductivity to better understand how battery composition and processing steps affect microstructure and resulting cell performance.