## 3 Results and Discussion  
### Comparison of Porosity Investigation Methods  
In Figure 2, the characterization methods for the microstructures of the positive electrodes are summarized and sorted according to the required sample amount for an accurate measurement. Therein, the comparatively large sample volume for the different methods, except SEM, has the advantage of yielding representative results by analyzing a complete electrode sheet with a size of approximately 150 cm\({}^{2}\). The width of the bars represents the range of pore sizes that can be investigated with the corresponding technique. Most of them are physically limited (e.g., by the size of the N\({}_{2}\)-molecule or the pressure range of MIP), while the upper and lower limits of the FIB/SEM tomography technique were determined by a combination of desired resolution, sample volume, and measurement time. He-pycnometry does not directly measure the pores within the electrode, but helium gas penetrates all accessible pores (>kinetic diameter of He), and by measuring \(\rho_{skel}\) and comparing with \(\rho_{xtal}\), it allows the determination of the amount of closed pores. This method has no upper pore size limit. \begin{table}
\begin{tabular}{c c c} \hline  & **NMC622** & **CB** & **PVdF** \\ \hline Weight-Percentage (\%) & 95 & 2 & 3 \\ \hline Solid-Volume-Percentage (\%) & 88.54 & 3.94 11.46 (CBD) 7.52 \\ \hline Density (g/cm\({}^{3}\)) & 4.76 & 2.25 1.935 (CBD) 1.77 \\ \hline \end{tabular}
\end{table} 
Table 1: Composition of the positive electrodes and the used densities for AM, CB, and binder. The CB and binder were combined to the CBD. As an example, for the investigated microstructural features in dependence of the respective methods, Figure 3 shows an embedded cross-section of a positive electrode. The CBD (not visible) fills most of the voids between the AM particles. With the gauge, only the highest electrode thickness value can be measured, including the current collector. The compaction of the electrode to 30% porosity resulted in the cracking of several AM secondary particles. This led to an increase in the inner surface area and created pores  
Figure 3: Cross-section of a positive electrode with a porosity of 30% embedded in epoxy resin. At the bottom, the aluminum current collector is visible. The measurement methods were assigned to their corresponding microstructural features. Figure 2: Overview of porosity investigation methods used in this work: The required sample volume is small for FIB/SEM and much larger for the other analysis techniques. The \(x\)-axis shows the measurable pore sizes of the methods. The gas physisorption and expansion methods have lower limits determined by the size of the gas molecules. The N\({}_{2}\) molecular cross-sectional area was 0.162 nm\({}^{2}\) and the He kinetic diameter is 0.26 nm [14; 40]. MIP was simply limited in both directions by the pressure range of the device (see experimental part), where the pore range of the last two methods based on SEM depends on the setup, operation conditions, and the sample properties. in the nanometer range, which can be measured by N\({}_{2}\)-physisorption. Particle cracking at the surface and clogging of surface pores with CBD caused a densification of the electrode surface, which can be identified by SEM or quantified via CLSM. The closing of surface pores with CBD is also described by [PERSON] et al. and [PERSON] et al. as an effect of high densification of the electrodes [41; 42]. The closed pores inside the AM secondary particles led to a difference between \(\rho_{shel}\) and \(\rho_{stal}\) that can be measured by He-pycnometry. Most of the accessible pores within the composite electrode were in the measurable range of MIP. To verify all of the described microstructural features and effects, FIB/SEM tomography was necessary to create a 3D model of the electrode. As a reference measurement for all further methods, the thicknesses of the electrodes determined with a gauge were used to calculate the total porosity.