Effect of mold pressure on compaction and ion conductivity of all-solid-state batteries revealed by the discrete element method

Abstract

All-solid-state batteries (ASSBs) have enabled the development of compact and safer batteries with solid and non-flammable electrolytes. However, their practical applications are limited due to the difficulty associated with solid electrolytes (SEs) in forming a connected network for ionic transport and sufficient contact area on the active material (AM). Lithium-phosphate sulfides (LPS) are promising materials for SEs in ASSBs because they can plastically deform and form a close contact with AM. Herein, we develop and numerically implement a discrete element model for cold pressing that considers plastic deformation. Particle compaction proceeds in three steps, i.e., breakage of aggregates, particle rearrangement, and particle consolidation by plastic deformation. In addition, localized stresses easily deform the SE particles, thereby resulting in a force concentration between the AM particles. A higher mold pressure increases the relative density and contact area between the AM and SE. The relative density and ionic conductivity results agree well with the experimental results. We demonstrate a new correlation for ionic conductivity based on percolation theory from our observation of poor connectivity between SE aggregates. We believe that this research will help us understand the interactions during fabrication that can guide the development of future ASSBs. • We simulated a battery electrode using the discrete element method. • In the cold press, we simulated aggregate destruction and particle consolidation. • The highest stresses build up in the less ductile active material particles. • Aggregates from ball milling cause a significant ionic percolation threshold.