Opportunities and Challenges of Calendering Sulfide‐Based Separators for Solid‐State Batteries

Abstract

AbstractContinuous densification procedures such as calendering are crucial for sulfide‐based solid‐state batteries to realize industry‐relevant processing. Therefore, in this study, the impact of line load, roller circumferential speed and roll temperature on slurry‐based Li3PS4 and Li6PS5Cl separators compacted by a lab‐calender installed in an argon‐gas‐filled glovebox was investigated. While the Li3PS4 layers became fragile in calendered state, the tested Li6PS5Cl separators were more suitable for calendering due to better mechanical stability. Besides basic analysis of, for example, density, length expansion, pore size distribution and specific ionic conductivity of the Li6PS5Cl separators, 3D images of the structures were generated based on images obtained by synchrotron tomography. Here, all calendered separators showed particle breakage of the Li6PS5Cl. A slight decrease of the specific ionic conductivity with increased applied line load or pressure was observed for calendering and uniaxial pressing, respectively. However, an increase in the conductivity was obtained for an increase in the stack pressure. In addition to poorer contact with the metal current collectors at low stack pressure, it is assumed that a spring back effect after densification could negatively affect the microstructure of the separator. These results highlight that a densification of binder‐based Li6PS5Cl separators does not necessarily result in improved ionic conductivity probably due to the individual deformation behavior of the materials used.