## 3 Results and Discussion
### He-Pycnometry
The shape of the curves during decreasing pressure contains information about the pore shape with less trapped mercury for lower porosities; (**b**) PSD: a shift in the mean pore size to smaller values and an increase in pore volume for pores < 100 nm for lower porosity; (**c**) schematic representation of a porous electrode during He-pycnometry and MIP and the corresponding densities and porosities that can be measured/calculated. MIP is shown as a 3 step process with wetting, intrusion, and extrusion in addition to the resulting Hg-entrapment. In contrast to calculating closed pores inside the solid volume, calculating \(\varepsilon_{inacc}\) also took the void volume inside the electrodes into consideration, which then resulted in closed porosities of 2.2%/2.1%/2.6%/2.3%/2.4% (highest to lowest total porosity \(\varepsilon\)). The highest value for \(\varepsilon_{inacc}\) was calculated for electrodes with \(\varepsilon=30\%\). This was confirmed by reference electrodes with \(\varepsilon=28\%\) and \(\varepsilon_{inacc}=2.6\%\). Considering the margin of error of \(\rho_{skel}\), the uncertainty for \(\varepsilon_{inacc}\) was 0.2 percentage points. Thus, the difference in \(\varepsilon_{inacc}\) among the different porous electrodes was not significant. As a consequence of the calculation of \(\varepsilon_{inacc}\), the accessible porosity, \(\varepsilon_{acc}\), was for all electrodes more than two percentage points lower than \(\varepsilon\), which affected the pore volume in the electrode that could be filled by electrolyte. In addition to the rational results for \(\rho_{skd}\), errors in the measurement technique should be considered. The measured sample volume increased during the first two measurement steps (procedure described in Section 2) and stabilized afterwards. [PERSON] et al. studied ideal measurement conditions for different material classes (e.g., nonporous silicon and porous zeolite material) and the influence of activation (=drying) of the samples, the number of cycles, and percentage fill volumes (sample volume compared to volume of the measuring chamber) [40]. Since the electrodes in our study were dried during sample preparation for N\({}_{2}\)-physisorption measurements, the amount of residual moisture within the porous electrode structure was expected to be negligible. Before starting the pycnometry measurement, the samples were briefly exposed to the lab atmosphere during sample transfer (sample preparation in a dry room), possibly causing deviations during the first measurement cycles. The small kinetic diameter of He of 0.26 nm enables diffusion of the gas into the different electrode materials, especially into the CBD [40]. However, changing to a larger or even non-inert gas molecule, such as N\({}_{2}\), would result in larger errors. The annulus volume, which is the volume between the surface of the electrode materials and the closest distance at which the gas molecules approach it, would increase and the ad-/desorption of N\({}_{2}\) by the sample would result in incorrect pressure readings [40]. Another source of inaccuracy is the subtraction of the volume of the aluminum current collector, which was determined in a separate measurement. This additional measurement was performed with pristine foil. The pycnometry measurement was necessary to calculate \(\varepsilon_{acc}\), which describes the maximum pore volume that can be filled with electrolytes. According to the results of this study, 2-3% less electrolyte was needed than expected from the total pore volume within the electrodes. In addition, the closed pores within the solid phase could influence the mechanical properties of the electrodes (e.g., volume expansion of AM during de-/lithiation), and measuring a variation of these pores for differently compressed electrodes could be a sign of structural changes such as particle cracking of the AM.