Influence of Solvent Nature and Binder Presence on Argyrodite (Li₆PS₅Cl) Slurry Properties

There is an increasing need to better understand the behavior of solid electrolytes during solution-based processing for all-solid-state batteries in order to improve the performance of these devices. Among the most promising candidates for this application are thiophosphate-based solid electrolytes, which are known to be sensitive to the physicochemical properties of the solvents and binders used in slurry formulation. This sensitivity is usually studied from the perspective of performance or degradation. In this study, the solvation and the rheological behavior of a slurry containing Li6PS5Cl (LPSCl) were studied to better understand the particle–particle and particle–solvent interactions. For that, the Hansen solubility parameter (HSP) model was employed as a predictive tool to differentiate between “good” and “bad” solvents for LPSCl. This approach was also extended to identify a set of solvents compatible with both the LPSCl particles and the binder, marking the first application of this methodology in the sulfide solid electrolyte field. Raman and IR spectroscopies were utilized to investigate solvent-particle and particle–particle interactions providing deeper insight into the physicochemical properties of the LPSCl-based slurries. These analyses enabled the construction of Hansen solubility and dispersibility spheres specific to LPSCl, which were then used to guide solvent selection. Sedimentation tests were implemented to obtain insights into solvent–LPSCl interactions. The agglomeration or dispersibility of LPSCl particles directly influences the slurry rheology, and the processability of LPSCl-based slurries. In this regard, a comprehensive investigation of the rheological behavior of LPSCl in various solvents─both those promoting agglomeration and dispersion was conducted. Dispersion of argyrodite particles in different inert solvents led to either a deagglomerated and compact slurry or a loosely agglomerated suspension. These dispersions exhibited two different rheological behaviors: (i) well-dispersed slurries where frictional properties dominated and (ii) agglomerated suspensions were cohesive interactions governed. Moreover, the incorporation of styrene-ethylene-butylene-styrene (SEBS) as a binder appeared to modify the particle–particle contacts, reducing both frictional and cohesive interactions. This effect was demonstrated through sedimentation and rheological measurements.