Method to Determine in-Plane Tortuosity of Battery Electrodes and Its Dependence on Particle Shape, Binder Content, and Porosity
Authors: Suthar Bharatkumar , Landesfeind Johannes , Morasch Robert , Eldiven Askin , Gasteiger Hubert A. 
Published: February 2020

One of the critical parameters that affect the performance of a commercial lithium-ion battery is the through-plane tortuosity. The shape and size distribution of electrode particles, binder content, and preparation method, may affect the tortuosity of an electrode. The design optimization of novel 3-dimensional battery architectures like patterned electrodes1-4—where the transport of lithium-ions within the electrode is not restricted to the through-plane direction alone—will require quantitative values for both the in-plane and the through-plane tortuosity.5 While methods to determine through-plane tortuosity are established in the literature and summarized by Landesfeind et al.,6, 7 in-plane tortuosity values are rarely reported and so far are only accessible by modeling the transport in 3D reconstructed electrodes.8

In this presentation, we outline an experimental setup that enables us to extract the in-plane tortuosity of a battery electrode. The mathematical analysis is performed using the blocking-conditionransmission line model. The precise measurements of in-plane tortuosity along with the through-plane tortuosity will be very critical for simulating and optimizing the above mentioned 3-dimensional electrode architectures and for gaining insights into the quality of electrode preparation methods. The combined use of through-plane and in-plane tortuosity will act as an indispensable tool to design better electrodes and validate numerical models for electrodes.9 Figure 1 shows comparison of through-plane (𝜏T-P) and in-plane (𝜏I-P) tortuosity of two different electrodes consisting of mesoporous carbon microbeads MCMB (spherical) and flake-like graphite materials obtained using the proposed method.

Figure 1: and of MCMB based electrodes (MCMB 97%wt, PVDF 3%wt, porosity ~48%) and Flake-like graphite based electrode (Graphite 94%wt, PVDF 6%wt, porosity ~55%). The error bars represent the standard deviation from 2 measurements. SEM images of MCMB and flake-like graphite based electrodes are also shown.

After having outlined our method to determine the in-plane tortuosity of electrodes, we will also show its dependence on various factors, such as particle shape, binder content, binder layer thickness, and electrode porosity.

Acknowledgements: This work is supported by the BMBF (Federal Ministry of Education and Research, Germany) for its financial support under the auspices of the ExZellTUM II project (grant number 03XP0081).

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Figure 1