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For the fabrication of high-energy and high-power all-solidstate batteries (ASSBs), easily synthesizable solid electrolytes are needed, which enable fast ion transport inside the composite cathode as well as good contacts between cathode active material and solid electrolyte particles. Regarding the latter, the size ratio of the particles inside the composite cathode has to be optimized. Here, we use a wet ball milling process for the synthesis of agyrodite-type Li 5.5 PS 4.5 Cl 1.5 solid electrolyte par-ticles and study the influence of milling time on particle size and ionic conductivity. With longer milling time, both the solid electrolyte particle size and the ionic conductivity decrease, which exert an opposing influence on the cathode performance. We show that a milling time of approximately 2 h leads to an optimum cathode performance, as this time is sufficient for a favorable particle size ratio, while a strong drop of the ionic conductivity of Li 5.5 PS 4.5 Cl 1.5 is avoided.

The morphology of the electrolyte‐filled pore space in lithium‐ion batteries is determined by the solid microstructure formed by μm‐sized active material particles and the smaller‐featured carbon binder domain (CBD). Tomographic reconstructions have largely neglected the CBD, resulting in inadequately defined pore space morphologies at odds with experimental ionic tortuosity values. We present a three‐phase reconstruction of a LiCoO2 composite cathode by focused ion‐beam scanning electron microscopy tomography. Morphological analysis proves that the reconstruction, which combines an unprecedented volume (20 μm minimum edge length) with the hitherto highest resolution (13.9×13.9×20 nm3 voxel size), represents the cathode's pore space morphology. Pore‐scale diffusion simulations show consideration of the resolved CBD as indispensable to reproduce ionic tortuosity values from electrochemical impedance spectroscopy. Our results reveal the CBD as a convoluted network that dominates the pore space morphology and limits Li+ transport through tortuous and constricted diffusion pathways.