Lithium Argyrodite Sulfide Electrolytes with High Ionic Conductivity and Air Stability for All-Solid-State Li-Ion Batteries

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 Li6.5Sb0.5Ge0.5S5I, 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. Li6.5Sb0.5Ge0.5S5I shows good compatibility with LiNi0.5Co0.2Mn0.3O2-based all-solid-state batteries (ASSBs) after applying Li3YCl6 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.