Elucidating the Influence of Stack Pressure on Anode and Cathode Impedance of All‐Solid‐State Batteries via Three‐Electrode Measurements

The power density of bulk‐type all‐solid‐state batteries (ASSBs) depends on the mechanical contacts between the solid particles inside the battery and is thus strongly influenced by the fabrication pressure of the battery and by the stack pressure during cycling. In order to achieve a better understanding of the electrochemical processes in ASSBs, we combine three‐electrode impedance measurements with a variation of the stack pressure and of the thickness of the composite cathode. The analysis of the thickness‐dependent impedance of the composite cathode in the framework of a transmission‐line model allows for a determination of the pressure‐dependent exchange current density between cathode active material particles and solid‐electrolyte particles. Furthermore, we find that the impedance of the In–Li anode decreases with increasing stack pressure and with increasing degree of lithiation. This is explained in the framework of a heterogeneous interphase model for the anode/separator interface in combination with a solid solution‐type chemical Li diffusion in the In–Li anode close to the interface.