As an alternative to lithium-ion batteries (LIB), sodium-ion batteries (SIB) are considered as a promising and more sustainable technology. In order to improve the performance of SIB, the concept of hierarchically structured active materials--known from LIB [1,2]--is applied, which advantageously leads to shorter diffusion paths and an increased stress resistance in the electrode. In this talk, we combine experiments, 3D imaging and statistical image analysis to quantify the impact of calendering on the morphology of cathode materials, consisting of nanostructured $\mathrm{Na}_3\mathrm{V}_2 (\mathrm{PO}_4)_3/\mathrm{C}$-composite-particles as active material, additives and mesopores. The data basis of our study are synchrotron measurements representing the microstructure of three differently calendered and one uncalendered reference cathode at the electrode scale, \emph{i.e.}, the nanopores are not resolved. As done for compressed electrodes in LIB [3], we use methods from spatial statistics to compute the morphological descriptors mean geodesic tortuosity and constrictivity for active material, additives and pores. These descriptors quantify the length and quality of transportation paths and allow for a prediction of effective transport properties [4]. Doing so, we quantify the impact of mechanical compression induced by calendering on effective transport properties in the electrode, which are--in turn--crucial quantities for the performance of the cell.

References

[1] M. Neumann, N. Bohn, A. Wagner, M. Osenberg, A. Hilger, I. Manke, J. Binder, and V. Schmidt. Characterization of hierarchically structured electrodes with
different thicknesses by means of experiments and image analysis. Materials Characterization, 155:109778, 2019.

[2] M. Müller, L. Schneider, N. Bohn, J.R. Binder and W. Bauer. Effect of Nanostructured and Open-Porous Particle Morphology on Electrode Processing and Electrochemical Performance of Li-Ion Batteries. ACS Applied Energy Materials, 4:1993–2003, 2021.

[3] K. Kuchler, B. Prifling, D. Schmidt, H. Markötter, I. Manke, T. Bernthaler, V. Knoblauch, and V. Schmidt. Analysis of the 3D microstructure of experimental cathode films for lithium-ion batteries under increasing compaction. Journal of Microscopy, 272:96–110, 2018.

[4] M. Neumann, O. Stenzel, F. Willot, L. Holzer, and V. Schmidt. Quantifying the influence of microstructure on effective conductivity and permeability: virtual
materials testing. International Journal of Solid and Structures, 184:211–220, 2020.