How Particle Size Affects Consolidation Behavior, Strain and Properties of Li₆ PS₅ Cl Fast Ionic Conductors

Solid-state battery fabrication requires the densification of solid electrolytes to achieve optimal cycling performance and high energy density. However, the underlying compaction mechanisms of these electrolytes remain poorly understood. Here, we investigate the effect of pressure consolidation on the ionic conductor Li₆PS₅Cl with particle size distributions (PSD) ranging from 4 to 40 µm. Heckel analysis reveals that samples with smaller PSDs exhibit higher compressibility at lower pressures. X-ray diffraction peak profiling shows that applied pressure induces lattice strain, leading to peak broadening, while pair distribution function analysis demonstrates a reduction in coherence length upon pressing. Dark-field X-ray microscopy further provides spatially resolved orientation maps, uncovering intragranular structural variations within individual Li₆PS₅Cl agglomerates after compression. To better understand the origin of stress fluctuations, we performed discrete element method simulations using the experimental PSDs. The results indicate that smaller particles and broader PSDs experience higher stresses, whereas monodisperse systems do not exhibit significant stress fluctuations with position or particle size. This suggests that the high strain observed cannot be attributed solely to smaller particles, but rather to size inhomogeneity. Overall, these findings highlight that both particle size and its distribution play a critical role in processing solid electrolytes for solid-state batteries.