The tortuosity τ is an important parameter for characterizing transport properties of complex electrodes, as it describes the influence of the morphology on its effective transport properties. Thus it is of special interest in a broad range of applications, such as lithium-ion batteries or fuel cells.
One of the most accurate ways to determine the tortuosity is to use microstructural data from reconstructions based on X-ray or FIB-SEM tomography . The calculation of τ uses the effective conductivity through the structure which is typically obtained by a finite element method (FEM) or a finite volume method (FVM) simulation on the reconstruction as model geometry. Thus, the calculation of the tortuosity is also a prototypical example to show and discuss problems arising from 3D simulations based on detailed tomography data.
In this contribution, a discussion of critical points arising during the 3D simulation based on tomography data is given. This will cover the geometry and the mesh together with the resolution of the tomography data, as well as the boundary conditions applied for the simulation.
Moreover, the approach by FEM simulations is compared to FVM simulations and other common methods to estimate tortuosity [2,3]. This includes the well-known Bruggemann equation and related approaches, as well as estimations based on geometrical quantities. Also a comparison to measurements will be given. Finally, the importance of the derived values for modeling using homogenized electrode models will be discussed.
1. M. Ender, J. Joos, T. Carraro and E. Ivers-Tiffée, J. Electrochem. Soc., 159 (7), p. A972 (2012).
2. L. Holzer, D. Wiedenmann, B. Münch, L. Keller, M. Prestat, P. Gasser, I. Robertson and B. Grobéty, J. of Materials Science, p. 1 (2012).
3. D. Chung, M. Ebner, D. Ely, V. Wood and R. E. García, Model. Simulat. Mater. Sci. Eng., 21, (2014).