Rational Optimization of Cathode Composites for Sulfide-Based All-Solid-State Batteries

All-solid-state lithium-ion batteries with argyrodite solid electrolytes have been developed to attain high conductivities of 10^-3 S cm^-1 in studies aiming at fast ionic conductivity of electrolytes. However, no matter how high the ionic conductivity of the electrolyte, the design of the cathode composite is often the bottleneck for high performance. Thus, optimization of the composite cathode formulation is of utmost importance. Unfortunately, many reports limit their studies to only a few parameters of the whole electrode formulation. In addition, different measurement setups and testing conditions employed for all-solid-state batteries make a comparison of results from mutually independent studies quite difficult. Therefore, a detailed investigation on different key parameters for preparation of cathodes employed in all-solid-state batteries is presented here. Employing a rational approach for optimization of composite cathodes using solid sulfide electrolytes elucidated the influence of different parameters on the cycling performance. First, powder electrodes made without binders are investigated to optimize several parameters, including the active materials' particle morphology, the nature and amount of the conductive additive, the particle size of the solid electrolyte, as well as the active material-to-solid electrolyte ratio. Finally, cast electrodes are examined to determine the influence of a binder on cycling performance.