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Establishment of an extrusion process for the scalable production of sulfide-based SSBs

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The focus of this work lies on the establishment of scalable solvent-based processing routes to produce sulfide solid-state cathodes and separators. Sulfide-based solid-state batteries are predicted to have several advantages compared to conventional lithium ion batteries, e.g. in the aspects of energy density, electrochemical stability and safety. These are faced with challenges regarding the formation of percolation networks for ions and electrons as well as the large scale processing under inert gas atmosphere. To meet these requirements, we carried out a systematic formulation variation based on a discontinuous process route. Binder type and proportion besides solid electrolyte material and content of the separators were varied. For processing the cathodes, type and proportion of the active material as well as the conductive additive fraction were added. After evaluating the adhesion, conductivities and cycling, the best recipes were selected and used for the following continuous process. The discontinuous route includes a dry mixing step (for cathodes), wet dispersion in a dissolver, coating and drying and compaction in a laboratory press. On the continuous route, an extruder is used instead of the dissolver and a calender replaces the press. Finally, the coatings are electrochemically analyzed in measuring cells. The formulation variation reveals some interesting results: the substitution of coarse by fine solid electrolyte particles shows different adhesive strength and particularly higher ionic conductivities, which can be explained by various porosities and particle interactions. Also the relation of the ionic conductivity between coatings and pure powder can be seen. In the production of cathode layers, there is an almost linear correlation between binder content, adhesion and resistivity. The change in the conductive additive content reveals on the one hand the formation of a percolation network, on the other hand the negative impact of carbon black on the ionic conductivity. This is caused by the blocking of the solid electrolyte pathways, which can be seen in the SEM image. The cycling of a cell with the best separator and cathode layer shows an improvement in impedance with increasing pressure, which is, however, limited, in the case of large-format pouch cells. Also, the decrease in specific capacity with increasing number of cycles by a factor of two is visible. The extrusion results reveal the high potential of this process step: First, the conductivity of the separator layers is three times higher than for the dissolver layers; second, comparatively well dispersed cathode layers can be produced. In conclusion, fine solid electrolyte particles, only as much binder and carbon black as necessary and the lowest possible operating pressures should be used. In addition, the great potential of the extrusion process was pointed out. For a more detailed discussion of my work, I am looking forward to welcoming you at my poster P1-028.

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