All solid-state batteries (ASSBs) are an interesting candidate to exceed conventional lithium-ion battery performance. They promise enhanced safety as well as significantly increased energy density by enabling lithium metal as an anode. Nevertheless, the technology still needs to overcome some fundamental challenges. One of these concerns the C-rate performance and cycling stability of the composite cathode. The cathode typically consists of active material (CAM) and a solid electrolyte (SE) forming a complex 3D transport network. The properties and pathways of the transport network can change dynamically during cycling. For example, the CAM undergoes volume changes during cycling due to the insertion and extraction of lithium, which can cause localized stress peaks as well as contact loss between particles. Transport bottlenecks within the structure can then reduce utilization as well as cycle life of the cathode. It is therefore crucial to detect such bottlenecks and understand their origin for the development of improved composite cathode structures. In this work, we conduct operando energy dispersive X-ray diffraction (EDXRD) experiments on ASSB composite cathodes consisting of NMC811 as CAM and Li3InCl5.4F0.6 as SE. The method allows to measure the average degree of lithiation in through-direction during a full charge-discharge-cycle. The utilization of the CAM can therefore be observed directly revealing potential bottlenecks within the cathode structure, which are dynamically influenced by local conditions during cycling. By complementary electrochemical simulations using a homogenized battery model [1], links between the observed lithiation dynamics and properties of the composite cathode can be established. Varying hypotheses on the implications of material properties on the chemo-mechanical response within a composite cathode and the impact on transport pathways and capacity are examined. The results of the simulations are also applicable to other typical CAM chemistries. REFERENCES [1] T. F. Fuller, M. Doyle and J. Newman. Simulation and Optimization of the Dual Lithium Ion Insertion Cell. Journal of The Electrochemical Society, 141, 1 (1994).