The argyrodite family, Li6PS5X (X=Cl, Br) is one of the more promising candidates for the development of all-solid-state lithium batteries. The high ionic conductivities (>10-3 S cm-1 at RT) and good mechanical properties render this class of solid-electrolyte a feasible choice for next generation battery cells [1,2]. Nevertheless, a prevailing challenge is still hindering the use of this technology:
How to form a dense, thin (<20 µm) and flexible film without impeding the ionic conductivity and shear modulus?
Dry- and wet- chemical processing is eligible for the preparation of thin electrolyte sheets. The latter is preferred, though, as it is more aligned with currently established processing technologies in lithium-ion battery industry. Thus, developed methods for solid electrolytes can be easily adopted and scaled to meaningful size without a significant change in the currently available production lines [3].
In a typical wet-chemical process, the Li6PS5X powder is mixed with a suitable polymeric binder and solvent and further cast onto a substrate. After drying, a thin and flexible film forms. The high reactivity of the argyrodite-electrolytes with polar materials, however, limits the choice of eligible binders and solvents. The established materials (PVdF, NMP) thus cannot be readily adopted from conventional lithium-ion processing methods. Therefore, non-polar binders like synthetic rubbers (e.g. NBR) are used [4]. Unfortunately, it is reported that these materials are inducing a significant decrease in the ionic conductivity compared to the pristine materials [5]. Therefore, a lot of recent reports focus on finding suitable alternatives to enable the production of thin Li6PS5X sheets without significant impact on the electrochemical properties.
In this work we followed a different approach. Rather than changing the binder, we investigated different solvents to modify the conformation of the binder in solution. Thus, the obtained micro-structure of the cast films and the distribution of the binder in-between the electrolyte particles could be changed. In addition, utilization of different solvents, especially the combination of solvents and non-solvents, enabled processes adopted from polymer industry, e.g. non-solvent induced phase separation (NIPS) or self-organized precipitation (SORP). Subsequently the physical and electro-chemical properties of the different films have been characterized and compared.

References
[1] C. Yu, F. Zhao, J. Luo, L. Zhang, X. Sun, Nano Energy, 83, 105858 (2021)
[2] D.K. Singh, A. Henss, B. Mogwitz, A. Gautam, J. Horn, T. Krauskopf, S. Burkhardt, J. Sann, F.H. Richter, J. Janek, Cell Reports Physical Science, 3, 101043 (2022)
[3] J. Schnell, T. Günther, T. Knoche, C. Vieider, L. Köhler, A. Just, M. Keller, S. Passerini, G. Reinhart, Journal of Power Sources, 382, 160-175 (2018)
[4] Y-T. Chen, M. Duquesnoy, D.H.S. Tan, J-M. Doux, H. Yang, G. Deysher, P. Ridley, A.A. Franco, Y.S. Meng, Z. Chen, ACS Energy Letters, 6, 1639-1648 (2021)
[5] N. Riphaus, P. Strobl, B. Stiaszny, T. Zinkevich, M. Yavuz, J. Schnell, S. Indris, H.A. Gasteiger, S.J. Sedlmaier, Journal of The Electrochemical Society, 165, A3993-A3999 (2018)