## 3 Results and Discussion
### Focused Ion Beam/Scanning Electron Microscopy Tomography  
The results of the previous methods can be verified using FIB/SEM tomography combined with a digital 3D model applying the GeoDict2020 software to gain further insights into the electrode microstructure. For this purpose, the electrode with the lowestporosity (18%) was investigated. Highly densified electrodes are rarely investigated in the literature, even though the low porosities are required to achieve high energy densities of the battery cell. Intense calendering results in extensive changes to AM particles in terms of cracking and distortion, whereby a 3D instead of 2D visualization is beneficial for a comprehensive understanding of microstructural properties. Figure 7 shows a FIB-prepared cross-section with its microstructural features. It verifies the results regarding the presence of closed pores in AM particles, AM particle cracking predominantly at the electrode surface, and that most of the space between the AM particles was filled with CBD. The cracking of large AM particles (e.g., at the left border of the FIB cross-section) could result in theoretical access (e.g., He-gas) to originally closed pores. Pore sizes from small mesopores inside the CBD to macroopes in the lower parts of the electrode could be detected. The larger macroopre depicted in Figure 7 illustrates the limitations of the previous methods. With MIP, the actual macroopre would be measured at smaller pore sizes due to the small pore entry. For N\({}_{2}\)-physisorption, the pore size was above the detection limit, and in an embedded cross-section, the epoxy resin would reduce the contrast between CBD and pore. To finalize the results of the previous methods and to create a 3D model using tomography in the next step, the focus of the FIB/SEM experiments was on the microstructure and porosity of the electrode. Therefore, the measurement parameters were optimized for the visualization of the AM, the AM particle cracking, and the closed pores within the AM. In this work, an FIB current of 2 nA was used for visualizing a larger tomography volume, and the CBD was simulated in the void space between AM particles for 3D reconstruction. To resolve the CBD structure and the according mesopores, the required FIB preparation parameters led to a tradeoff between a longer measurement time and smaller tomography volume. Only using low FIB currents (e.g., 20 pA [27]) for the cross-section preparation of CBD could preserve the according structure. Otherwise, melting effects occur and result in preparational structural changes such as clogging of pores within the CBD. Therefore, in literature FIB/SEM tomography is typically combined with simulations [27; 52; 53]. Figure 7: FIB/SEM tomography of a positive electrode with a porosity \(<20\%\). All significant microstructural features are marked. Comparing the structure of the electrode in this study with the results in the literature, significantly higher electrode total porosities, where \(\varepsilon\) was at least 31% [36] and often higher [27; 52; 53] than in this study (\(\varepsilon=18\%\)), have to be considered. Stronger calendering as applied herein resulted in more AM particle cracking and in a different, more densified CBD structure. The conductive agent-to-binder ratio was set herein to 2:3, whereas in the literature, it was often 1:1, which changes the binder-to-surface area ratio and, therefore, the CBD structure. Since there are also electrode materials behind the sectional plane visible in Figure 7, an automatized discrimination of the phases (i.e., AM, CBD, pores) is challenging. To transfer the tomography data of the electrode to a 3D model, a high contrast for the microstructural features (AM, particle cracking, and closed pores) within the sectional plane was used (Figure 8b). A digital 3D model can be created based on the FIB-prepared cross-sectional micrographs applying the GeoDict2020 software. The results are shown in Figure 8, with an example of an FIB-prepared cross-section and the same position in the digital model.