Influence of Post‐Synthesis Processing on the Structure, Transport, and Performance of the Solid Electrolyte Li5.5PS4.5Cl1.5 in All‐Solid‐State Batteries

Post-synthesis processing affects the microstructure and crystallinity of the solid electrolyte Li_5.5PS_4.5Cl_1.5. While a reduction in particle size after short ball milling times improves the tortuosity in cathode composites, longer ball milling times decrease the coherence and the ionic conductivity of the solid electrolyte. The specific energy input of the milling method is the decisive influence as simulations reveal.

Abstract

While post-synthesis processing steps are frequently applied in the preparation of cathode composites for solid-state batteries to ensure homogeneous mixing and good contact with the cathode active material, little is known about the processes that occur during milling and how they influence structure and transport of solid electrolytes. Here, an extensive set of experimental methods and simulations are used to study the effects of post-synthesis milling by a frequency and planetary ball mill on the highly conducting chloride-rich argyrodite Li_5.5PS_4.5Cl_1.5. Structural analyses show that processing can reduce the coherence length and increase the disorder. The reduced crystallite size correlates with a decrease in ionic conductivity in the post-processed solid electrolytes. Simulating the ball milling processes by the discrete element method provides fundamental understanding and reveals the correlation of the loss in coherence with the specific energy input and the numbers of stressing events during the milling process. An observed decrease in particle size in ball milled samples leads to lower tortuosity in the cathode composites. As the loss in coherence and decrease in particle size have opposite effects on the performance, optimizing these processing conditions will play a significant role on the road to highly performing solid-state batteries.