Screening with first-principles calculations, we analyze the thermodynamic chemical compatibility of an extensive range of inorganic materials, including oxide and sulfide SEs as anolytes and ternary halide SEs (chlorides and fluorides) as catholytes, for their potential use as bilayer separators in ASSBs. We find that Li 3 PS 4 and Li 3 PO 4 are the least reactive anolytes when in contact with halide catholytes. We identify a few bilayer interfaces that are thermodynamically stable upon contact. The Li 3 PO 4 /Li 3 InCl 6 combination is examined experimentally for these few SE pairings that are predicted to be stable. Results from solid-state nuclear magnetic resonance (ssNMR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy suggest the excellent chemical compatibility of the Li 3 PO 4 /Li 3 InCl 6 bilayer.