Tailoring Composite Microstructure Through Milling for Dry-Processed Sulfide-Based Solid-State Battery Cathodes

While the effects of new solid electrolytes and active materials in cathode composites for solid-state batteries are being intensively researched, little is known about the influence of mechanical processing on the properties of these composites. Here, the influence of mechanical process parameters on the production of Li₆PS₅Cl and LiNi_0.83Co_0.11Mn_0.06O₂ composite cathodes applying a planetary ball milling process is systematically investigated. It is shown that the milling process has a significant influence on the microstructure of the composite by affecting the solid electrolyte particle size and the formation of electrolyte-active material aggregates. The combination of experimental results with discrete element simulations shows that changes in microstructure with increasing energy input result in an increase in the density of heterocontacts, which improves the electrochemical performance. However, if the energy input is too high, a decrease in the crystallite size of Li₆PS₅Cl and an increase in strain in LiNi_0.83Co_0.11Mn_0.06O₂ have a negative impact on the electrochemical performance. Subsequent dry film production of the pre-milled composites reveals that a non-optimized composite can be partially compensated by the high shear stresses acting during dry film production. Overall, the paramount importance of precisely controlling the milling process for the production of cathode composites is demonstrated.