## 3 Results and Discussion
### He-Pycnometry  
To measure the skeletal density, \(\rho_{shel}\), of the electrodes and the AM powder, He-pycnometry measurements were performed. By comparing \(\rho_{shel}\) with \(\rho_{stal}\), the closed porosity \(\varepsilon_{mac}\) could be determined. Closed pores, as shown in Figure 5(c2), can be located in AM secondary particles, in CBD agglomerates, between CBD and AM particles, or between AM particles. The latter could occur especially after strong calendering in combination with particle cracking. The results for \(\rho_{shel}\) ranged between 4.27 g cm\({}^{-3}\) for the uncalendered electrode and 4.31 g cm\({}^{-3}\) for the lowest porosity electrode. As the uncertainty was up to \(\pm\)0.01 g cm\({}^{-3}\), the difference with regard to \(\rho_{shel}\) for the variation in porosities can be considered to be insignificant. Comparing \(\rho_{shel}\) with \(\rho_{stal}\) (4.436 g cm\({}^{-3}\)) provides the amount of closed pores inside the solid volume of the electrode, which was between 3.7% and 2.8% (highest to lowest porosity). This amount agrees with the measurement of \(\rho_{shel}\) (4.61 g cm\({}^{-3}\)) and \(\rho_{stal}\) (4.76 g cm\({}^{-3}\)) of the pristine AM powder. Here, the void space inside the AM particles was determined to be 3.2%. To some extent, the polycrystallinity of the AM also decreased its density in comparison to \(\rho_{stal}\). The main contribution of the difference between \(\rho_{shel}\) and \(\rho_{stal}\) of the AM remains the pores inside the AM particles as visualized in the SEM cross-sections (see Figure 3). By He-pycnometry, the pores in the AM can be quantified. The increase in \(\rho_{shel}\) with lower porosity could be due to the particle cracking of the AM. With this, the He-gas obtains access to originally closed pores. A counteracting effect could be the creation of new closed pores due to the intense calendering, especially within the CBD. However, due to the high amount of particle cracking at low total porosity identified in the SEM images, this was assumed to be the dominant effect for changes in \(\rho_{shel}\). The results for \(\rho_{skel}\) ranged between 4.27 g cm\({}^{-3}\) for the uncalendered electrode and 4.31 g cm\({}^{-3}\) for the lowest porosity electrode. As the uncertainty was up to \(\pm\)0.01 g cm\({}^{-3}\), the difference with regard to \(\rho_{skel}\) for the variation in porosities can be considered to be insignificant. Comparing \(\rho_{skel}\) with \(\rho_{xtal}\) (4.436 g cm\({}^{-3}\)) provides the amount of closed pores inside the solid volume of the electrode, which was between 3.7% and 2.8% (highest to lowest porosity). This amount agrees with the measurement of \(\rho_{skel}\) (4.61 g cm\({}^{-3}\)) and \(\rho_{xtal}\) (4.76 g cm\({}^{-3}\)) of the pristine AM powder. Here, the void space inside the AM particles was determined to be 3.2%. To some extent, the polycrystallinity of the AM also decreased its density in comparison to \(\rho_{xtal}\). The main contribution of the difference between \(\rho_{skel}\) and \(\rho_{xtal}\) of the AM remains the pores inside the AM particles as visualized in the SEM cross-sections (see Figure 3). By He-pycnometry, the pores in the AM can be quantified. The increase in \(\rho_{skel}\) with lower porosity could be due to the particle cracking of the AM. With this, the He-gas obtains access to originally closed pores. A counteracting effect could be the creation of new closed pores due to the intense calendering, especially within the CBD. However, due to the high amount of particle cracking at low total porosity identified in the SEM images, this was assumed to be the dominant effect for changes in \(\rho_{skel}\). Figure 5: MIP results: (**a**) intruded/extruded specific Hg-volume, \(\
u_{\text{Hg}}\), during pressure increase/decrease.