## 3 Results and Discussion
### Scanning Electron and Laser Microscopy  
To evaluate the influence of calendering on the microstructure of electrodes in the cross-sectional and surface profiles, the results for uncalendered electrodes and for electrodes with the lowest porosity of 18% are discussed. Figure 4 shows the SEM cross-sections and CLSM top view of these two electrodes (44% and 18% porosity). With the same height scale in the CLSM images, a significantly smoother surface of the calendered sample is visible. The compression to 18% porosity resulted in a decrease in the electrode surface roughness (root mean square) by a factor of 3.5 from 2.59 \(\pm\) 0.12 \(\upmu\)m for 44% porosity to 0.74 \(\pm\) 0.04 \(\upmu\)m for 18% porosity. Considering the lateral resolution of the CLSM method, a 50% reduction in the effective surface area can be observed when the porosity was decreased from 44% to 18% porosity. While the smoothening of the electrode surface could result in a more homogeneous current distribution at the electrode surface, it can also negatively influence the Li-ion mobility on the surface of the porous electrode structure by reducing electrolyte accessibility and rate capability as well as the electrolyte wetting behavior of the electrodes during cell production. The speed of electrolyte uptake decreases with smaller and fewer access areas for the electrolyte, since some closing of the surface pores occurs with high electrode compression [42]. Beyond that, low porosities lead to an increased tortuosity which cause prolonged Li-ion migration/diffusion pathways that can reduce the electrode rate capability. Thus, depending on the application and the operating conditions, the advantages or drawbacks of a denser electrode surface predominate in terms of increasedenergy density and homogeneous current distribution or reduced accessibility and rate capability, respectively. The SEM images of the uncalendered electrode showed almost no cracking or deformation of the AM secondary particles. Few exceptions can originate from AM production or electrode paste processing. The mean particle size of the AM was 10 \(\upmu\)m with a range from 1 to 20 \(\upmu\)m in diameter. The homogenous distribution of CBD and the differentiation between CBD and pores are shown in the Supplementary Material (Figure S1). A few AM secondary particles show voids, which can be assigned to closed pores or to some extent to material removal by sample preparation. Figure 4: SEM cross-sections and CLSM top views (**a**–**d**) of positive electrodes with the highest (44%) (**a**–**c**), and lowest (18%) (**d**–**f**), porosity. Decreasing the porosity to 18%, the thickness of the electrode was reduced from 94 to 64 \(\upmu\)m (without an aluminum current collector, visible at the bottom of Figure 4e). Due to the high calendering pressure, the AM particles were pressed into the metal foil, which improves the adhesion and decreases the electronic contact resistance between the composite electrode and current collector [23]. Approximately half of the AM secondary particles were cracked to achieve the high density of the electrode, while at the surface, nearly all particles were deformed/cracked. Pore sizes were mostly below 1 \(\upmu\)m, considering that CBD filled most of the voids between the AM particles (see Figure S1). Both electrodes had a homogenous distribution of AM and particle sizes as well as a uniform densification in the case of the calendered electrode. At some positions, the higher thickness values of the cross-section compared to gauge measurements can be explained as follows. Firstly, charging effects of the epoxy resin in the electron beam can lead to drifting effects due to the electrostatic deflection of the beam during SEM characterization. Secondly, the cutting angle can deviate from 90 degrees with respect to the electrode within the resin block, leading to a misinterpretation considering the electrode thickness. Thus, sample preparation can be considered as the main source of error for the SEM cross-sectional measurement.