Determining the Parameters Influencing the in-Plane Tortuosity of Porous Anodes in Lithium-Ion Batteries

The anisotropic nature of the porous electrodes in lithium-ion batteries, necessitates the determination of both in-plane (τ ip ) and through-plane tortuosity (τ tp ) for the optimal design of 3D-structured electrodes. 1,2 Recent research has also shown that in-plane transport resistance is a parameter of interest in the phenomena of electrolyte motion 3 induced salt inhomogeneity 4 where significant concentration gradients has been observed in large cylindrical cells along the length of the jelly roll. This concentration gradient in the in-plane direction leads to inhomogeneous utilization of the electrode, which in turn could result in lithium plating at the top and bottom of the jellyroll. Moreover, experimentally obtained in-plane tortuosity values play a crucial role in validating the in-plane tortuosity values from numerical simulations based on imaging data. 5 Electrochemical impedance spectroscopy (EIS) based techniques 6 are extensively used in determining the through-plane tortuosity of battery electrodes along its dependence on various factors such as binder content, particle shape, porosity, etc.,. 6,7 However, in contrast, studies on in-plane tortuosity remain relatively limited and unexplored. In this presentation, the effect of electrodes having various porosities, particle shapes, and binder weight percentages on in-plane tortuosity are determined by using the impedance-based method with blocking electrolyte developed by Suthar et al. 8 The key finding of this work was observed when the electrodes were calendered sequentially to investigate the effect of porosity wherein we found that the in-plane tortuosity decreases as the porosity decreases, while through-plane tortuosity increases as shown in Figure 1. A comparison of through-plane and in-plane tortuosity for flake-like graphite electrodes at varying porosities is shown in Figure 1, with green triangles representing through-plane and orange circles representing in-plane values. It also shows how the in-plane tortuosity varies with varying porosity according to the relation developed by 3D-simulation studies (purple line) by using FIB-SEM data, which is in contrast with the experimental findings. This presentation will also highlight the impact of particle shape on the anisotropic transport properties of porous graphite electrodes. Lastly, the influence of binder weight percentages was studied where an increase in binder content leads to a corresponding increase in in-plane tortuosity, consistent with the trend observed in the through-plane tortuosity. Acknowledgments: The authors acknowledge funding from the Science and Engineering Research Board, DST, Government of India (Project No. CRG/2020/005571), as well as prior support at the Technical University of Munich, Germany. We thank Prof. Hubert A. Gasteiger, Dr. Robert Morasch, and Lennart Reuter for their valuable discussions and for access to experimental facilities at the TEC lab. We are also grateful to our group members for their constructive feedback. References Y. Sterzl and W. Pfleging, Batteries , 10 (2024). J. Keilhofer et al., Energy Technology , 2200869 (2023). C. P. Aiken et al., Journal of the Electrochemical Society , 170 , 040529 (2023). S. Solchenbach et al., Energy and Environmental Science , 17 , 7294–7317 (2024). M. Ebner, D. W. Chung, R. E. García, and V. Wood, Advanced Energy Materials , 4 , 1–6 (2014). J. Landesfeind, J. Hattendorff, A. Ehrl, W. A. Wall, and H. A. Gasteiger, Journal of the Electrochemical Society , 163 , A1373–A1387 (2016). J. Landesfeind, A. Eldiven, and H. A. Gasteiger, Journal of the Electrochemical Society , 165 , A1122–A1128 (2018). B. Suthar, J. Landesfeind, A. Eldiven, and H. A. Gasteiger, Journal of the Electrochemical Society , 165 , A2008–A2018 (2018). Figure 1