All-solid-state batteries (ASSBs) are candidates for the next-generation of battery electric vehicles. They potentially enable the use of lithium metal as an anode material thereby highly improving the energy density of the battery. Among the most promising candidates for solid electrolytes are polycrystalline materials such as LLZO, due to their high ionic conductivity and chemical stability. Lithium dendrites form above a critical current density (CDC) of as low as 0.6 mA/cm² [1], however. While some explanations where suggested, the underlying mechanisms are not yet understood. In a recent paper a more viable CDC of 5 mA/cm² was reported, which was achieved by protonating the interfaces and grain boundaries [2], this shows that understanding both external and internal interfaces is crucial for the successful development of ASSBs. One often used tool in battery analysis is Electrochemical Impedance Spectroscopy (EIS). We developed a continuum scale model [3] in order to compare experimental impedance data with simulated impedances for a range of possible interface configurations. Space charge layers and their effects are resolved in the model and material properties are informed by atomistic simulations. In our contribution we simulate impedances at ASSB internal and external interfaces. The comparison to experiment helps us validate the model while better understanding the effect that different interface configurations have on resistance and capacitance. The gained understanding can inform the development and manufacturing of future ASSBs. Acknowledgements This work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm-Karlsruhe). The authors thank the German Ministry of Education and Research (BMBF) for funding of the project CatSE II under grant number 03XP0223E. Han, F., Westover, A. S. et al. Nature Energy 2019, 4(3), 187-196. DOI: 1038/s41560-018-0312-z Kim, S., Kim, J. S. et al. Nature Commun 2022, 13(1), 1-12. DOI: 10.1038/s41467-022-29531-x Becker-Steinberger, K., Schardt, S. et al. arXiv 2021 DOI: 10.48550/arXiv.2101.10294