## 3 Results and Discussion
### Focused Ion Beam/Scanning Electron Microscopy Tomography
Regardless of the model, the observation considering larger pores isolated within the highly densified electrode, which are only measured at higher pressures in the MIP experiment, is confirmed in Figure 7.  
The digital model of the electrode showed a lower total porosity than in the gauge measurement (16.1% instead of 18%) and, therefore, resulted in a slightly higher electrode density of 3.72 g cm\({}^{-3}\) compared to 3.65 g cm\({}^{-3}\). In addition, \(\epsilon_{inacc}\) had a value of 0.5%, more than four times smaller in the model compared to the value determined with He-pycnometry. Therefore, \(\epsilon_{acc}\) was also slightly smaller compared to the MIP experiments. However, the localization, which was not possible to detect with He-pycnometry, and quantification of closed pores (marked green in Figures 8a and S3) within the AM is an advantage of the 3D reconstruction, as it is important for simulation of ionic transport in AM secondary particles and their mechanical properties, which is often neglected in the literature [54]. The closed pores were distributed within the AM secondary particles and not only in the particle center as assumed from the results of the embedded cross-sections. One reason for the difference in total porosity of up to 2 percentage points is the lower limit of the pore size in the model. The batch size in the simulation was chosen to be the voxel length of 37.2 nm. Therefore, in the MIP simulation, pore throat diameters smaller than 18.6 nm were not covered, while the experiment covered pore throats down to 3.7 nm. For the strongest calendered electrode, 3.7% of \(\epsilon_{acc}\) were in this range in the MIP experiment. Hence, 0.6 percentage points must be added to \(\epsilon_{acc}\) from the simulation (now 16.2%) to be comparable to the experiment. Since the depth of the prepared cross-section for FIB/SEM tomography was not covering the overall electrode thickness, the extracted electrode section for the simulation was from the top third (close to the surface) of the electrode. To some extent, more particle cracking was observed at this surface-near position compared to parts closer to the current collector. This resulted in a slightly denser electrode and a lower total porosity of the investigated electrode section. This effect could be amplified by a heterogenous distribution of the CBD within the electrode, as only the ratio of AM to CBD from the electrode recipe was applied in the model. Binder migration during the drying process or a segregation during calendering could lead to higher and lower amounts of CBD at some positions in the electrode [42; 55]. Contradicting this, embedded SEM cross-sections in Figures 4 and S1 suggest a homogeneous distribution of all components. The major difference between the experiments and the digital model was in the amount of \(\epsilon_{inacc}\), which was more than four times smaller in the model. Here, the absolute accuracy and the made assumptions (e.g., \(\rho_{theo}\) of AM is \(\rho_{xtd}\)) of all the experimental methods have to be considered, as they can lead to large relative errors for the small values of \(\epsilon_{inacc}\). A similar effect could originate from the comparatively small electrode, thus sample section investigated by FIB/SEM tomography. More particle cracking of secondary particles resulted in more access points to originally closed pores in AM in the model. As stated, the CBD model did not include nanoporosity with diameters smaller than 37.2 nm and no closed pores associated with the CBD. For the segmentation of the FIB/SEM 3D image data, a non-local means filter was applied besides others, and the threshold for segmentation between active material and pore was chosen manually. These two factors might lead to small errors during segmentation, especially regarding small pores and cracks in the active material.