The densification of separators for solid-state batteries is a key requirement for achieving high energy densities, improved ionic conductivities, and defined microstructures. In this study, fundamental investigations of the densification of Li6PS5Cl- and Li3PS4-based separators by uniaxial pressing and calendering were conducted. Separator slurries based on p-xylene as solvent and a hydrogenated nitrile butadiene rubber type material as binder were produced using a dissolver and coated on a substrate foil by doctor blading.

The Li3PS4-based samples were analyzed regarding the ionic conductivity and density of the manufactured separators as a function of fabrication pressures up to 200 MPa, as well as a stepwise compaction up to 1.5 GPa under “in die” measurement conditions, revealing structural changes in the crystal lattice under high-pressure application. To interpret the results obtained by electrochemical impedance spectroscopy in further detail, binder migration by FTIR-analysis, the cell body, and elastic deformation after stress release were taken into account. It was found that separators with 4.3 wt% binder exhibit an average elastic recovery of 10 % after compaction at a loading speed of 1 mm min⁻¹ and a pressure of 640 MPa. However, while separators containing Li3PS4 have brittle characteristics in a compacted state and show lower ionic conductivity, Li6PS5Cl-layers are more suitable for industrial-relevant calendering. In this study, the porosity of the layers was reduced from 38 % to 11 %. Ionic conductivity, as well as tensile strength, and other properties, were investigated for different line loads, roll temperatures, and roller circumferential speeds. Overall, the obtained knowledge in these studies can contribute to the establishment of scale-up processing of sulfide-based solid-state batteries addressing opportunities and challenges of the densification procedure.