where i = iion + ie is the total applied current density, ne is the number of electrons partaking in the reaction and L is the thickness of the electrode. The dimensionless current density describes the relative ratio of Ohmic potential losses in the cathode to limitations by (slow) reaction kinetics. For low values of δ ≲ 1, the reaction current density distribution is uniform and the kinetics of the reaction, i.e., the exchange current density, limit the system. This is the case for high effective conductivities and σion ≈ σe low applied current densities and in thin electrode configuration (red line in Figure ultimately leads to reaction fronts that have been experimentally shown to exist in both lithium-sulfur and NCM-based solid-state batteries. Considering that both, the thickness and the applied current density are desired to be high to improve energy density and enable fast charging, the conductivity term is the free composite design parameter for achieving low values of δ. The δ-parameter as a function of both effective conductivities is shown in Figure for an exemplary thickness of 200 μm and a current density of 5 mA•cm -2 . It shows that the δ-parameter is low, and reaction rates are uniform, when both conductivities are high and equal (diagonal in Figure ). When one effective conductivity is significantly lower than its counterpart, 𝛿 is high (lower and left boundaries in Figure ). With that, the uniformity of the reaction rate distribution, inversely proportional to δ, is limited by the lower conductivity. Exemplarily, this means that changing σe in the situation σion ≪ σe, while keeping σion constant, does not lead to significant changes in δ until the condition σion ≈ σe is reached (staying on the contour lines in Figure ). Opposed to that, changing σion in the same case has drastic influences ("moving" perpendicular to contour lines in Figure ). By changing the volume fractions of electrolyte and active material or the microstructure of the composite, both conductivities of the porous electrode change simultaneously, complicating this assessment. In this work, we consider the δ-parameter as stated by Newman and Tobias. Nonetheless, similar descriptors are derived by Wagner, Again, all spectra and fits are shown in the Supporting Information (Figure ).