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

Abstract

Continuous densification procedures such as calendering are crucial for sulfide‐based solid‐state batteries to realize industry‐relevant processing. Therefore, this study investigates the impact of line load, roller circumferential speed and roll temperature on slurry‐based Li3PS4 and Li6PS5Cl separators compressed by a lab‐calender installed in an argon‐gas filled glovebox. While Li3PS4 layer become fragile in compressed state, the tested Li6PS5Cl separator is more suitable for calendering due to better mechanical stability. Next to basic analysis of, for example, density, length expansion, pore size distribution and specific ionic conductivity, 3D structures are generated based on images obtained by synchrotron tomography. All calendered separators showed particle breakage of the Li6PS5Cl. A slight decrease of the specific ionic conductivity with increased applied line load or pressure, respectively, is observed for both calendering and uniaxial pressing. However, expected increase of the conductivity was obtained for an increase of the stack pressure. Next to poorer contacting at low stack pressure, it is assumed that springback effect after densification could affect negatively the microstructure of the separator. These results highlight the opportunities and challenges in terms of calendering of sulfide‐based separators, as well as the complex correlations between densification, stack pressure and choice of material.

Atmospheric Influences on Li6PS5Cl Separators and the Resulting Ionic Conductivity for All-Solid-State Batteries

“…24 Moreover, any discrepancies can also be attributed to the applied pressure during the EIS, as an increase in pressure has been demonstrated to enhance conductivity. 32 However, unlike the previous research by Chen et al, cell assembly at a dew point of −45 °C is only possible with very short processing times. This is suggested to be related to variations in the sulfide material used or different binder materials.…”

“…Sample production.-Separator processing was performed as described in previous studies by Scharmann et al as well as Heck et al 31,32 The layers consist of 95.7 wt% LPSCl (NEI Corporation) as electrolyte material and 4.3 wt% acrylate-based binder. The powder was dissolved (Dispermat CV3-PLUS, VMA Getzmann GmbH) in p-xylene at a peripheral velocity of 1 m s −1 for 30 min to a solids content of 63.5 wt% followed by an increase of the peripheral velocity to 3 m s −1 for 60 min.…”