Granular Creep and Its Role in Optimizing Solid Electrolyte Fabrication for All-Solid-State Batteries

The densification of solid electrolyte (SE) materials is crucial for improving the performance and stability of all-solid-state batteries (ASSBs). In this study, the role of granular creep in SE densification is investigated using numerical simulations and experimental validation on Li₆PS₅Cl separators. Using discrete element method simulations, we analyze the influence of strain rate and cohesion on force chain evolution, particle rearrangement, and porosity reduction. Our results indicate that low strain rates promote granular creep, allowing for gradual particle reorientation and stress relaxation, leading to higher packing density and lower residual porosity. To validate these findings, we also performed experiments at different strain rates, where X-ray computed tomography and scanning electron microscopy confirm that low strain rates produce a more homogeneous microstructure. Furthermore, critical current density (CCD) tests on lithium symmetric cells reveal that samples processed at the lowest strain rate exhibit a CCD of $\backsim 3$ mA cm^-2, three times higher than samples processed at faster strain rates, highlighting the direct correlation between granular creep, densification, and ionic transport enhancement. These findings underscore the importance of strain-rate-controlled processing in optimizing SE microstructure, mechanical, and electrochemical performance, offering insights into the fabrication of high-density, high-performance separators for next-generation ASSBs.