Solid electrolytes (SEs) are promising candidates for enhancing the energy density and safety of conventional lithium-ion batteries. Recently, lithium thioantimonate iodide argyrodites have been regarded as promising SEs because of their high ionic conductivities and air-stability. In this study, we utilized high-energy ball milling to synthesize Ge-substituted thioantimonate argyrodites and achieved an ionic conductivity of 16.1 mS cm –1 for Li 6.5 Sb 0.5 Ge 0.5 S 5 I, which is the highest value among the reported cold-pressed SE pellets. First-principles calculations reveal that concerted Li-ion migrations through the inter-cage paths substantially improve the ionic conductivity. Li 6.5 Sb 0.5 Ge 0.5 S 5 I shows good compatibility with LiNi 0.5 Co 0.2 Mn 0.3 O 2 -based all-solid-state batteries (ASSBs) after applying Li 3 YCl 6 as a catholyte, which exhibits a high discharge capacity of 164 mAh g –1 and good cycle stability. Ge-substituted thioantimonate argyrodites exhibit excellent air-stability, which facilitates reducing the synthesis and fabrication costs of ASSBs with hygroscopic P-based sulfide SEs. The superionic conductors with high air-stability reported in this study demonstrate substantial promise for the development of ASSBs.