Porous electrodes in (solid-state) batteries. Extensive work has been done in the past to theoretically describe the electrochemical behavior of electrodes that consist of a porous, electron conducting active material (matrix) infiltrated by ion conducting liquid electrolyte. The theory of porous electrodes aims to describe the spatial distribution of current densities and reaction rates throughout the electrode that depend on the electrode geometry, the effective electronic and ionic conductivity, and the polarization behavior of the active material. These distributions, if nonuniform, can be considered the underlying reason for cathode underutilization, or the creation of stateof-charge gradients over the electrode. Not considered specifically in the porous electrode theory, the approximations commonly made to the solvent-based electrolyte, e.g., no concentration gradients, neglecting electrochemical double-layer formation and dismissing convection, are fulfilled in SE. Consequently, the results of the porous electrode theory should persist to the solid-state configuration.