Solid-state lithium-ion batteries with the superionic conductor Li6PS5Cl (LPSCl, Argyrodite) are regarded as one promising next-generation battery technology. They have shown outstanding performance in lab-scale cells, and the next step is to achieve practical operation in large-scale pouch cells. One of the key components in such pouch cells are LPSCl membranes, which as solid electrolyte separator, conduct Li+-ions but block electron transport between cathode and anode. Our work employs a slurry casting method to fabricate freestanding LPSCl thin membranes. Various processing parameters such as LPSCl particle sizes, binder types and contents, and solid loading, were evaluated with regards to reproducibility, ionic conductivity, and critical current densities. The results emphasize the necessity of a binder suited for the material processed to retain sufficient ionic conductivity and with it, sufficient electrochemical performance. This developed process will be further investigated and implemented for the upscaling production of LPSCl membranes as well as pouch cells thereof in the Innovation Labs of FFB PreFab.