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 electrodes^1-4—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 (𝜏_T-P) and in-plane (𝜏_I-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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