For preparation of the pellets for impedance analysis, 50 mg of the desired electrolyte powder were weighted out and placed directly in the cavity formed by the PEEK alignment tube and a steel current collector pin. Before pressing with a hydraulic cylinder, a piece of carbon coated aluminum foil was placed on each side of the hand-compacted powder to ensure good contact between steel pins and electrolyte with the possibly uneven surfaces. The pellet was then compacted in the setup for subsequent pressure-dependent impedance analysis and the pellet was not extracted from the PEEK alignment tube before measurement.