Li₁₀Ge(P1–xSbx)₂S₁₂ Lithium-Ion Conductors with Enhanced Atmospheric Stability

Sulfide solid electrolytes have recently attracted significant interest for use in all-solid-state lithium batteries (ASSLBs) due to their high ionic conductivity. However, one of the main challenges associated with the commercialization of sulfide-based electrolytes is their instability toward air/moisture, which leads to complex processing requirements. Herein, we develop a strategy to not only increase ionic conductivity but also obtain high air stability of the Li 10 Ge(P 1– x Sb x ) 2 S 12 electrolyte system with soft acid Sb substitution. Theoretical calculations predict the Sb substitution in (Ge,P)S 4 tetrahedral sites, which is further confirmed by the X-ray diffraction Rietveld refinement and synchrotron X-ray absorption fine structure analysis. Opened channels and increased unit cell volume are achieved with an appropriate amount of Sb substitution, leading to an ultrahigh ionic conductivity of 17.3 ± 0.9 mS cm –1 . The softer acidity of Sb compared to that of P also ensures strong covalent bonding with S in Li 10 Ge(P 1– x Sb x ) 2 S 12, which improves the air stability of the electrolyte. Moreover, the air-exposed samples exhibit high ionic conductivities of 12.1–15.7 mS cm –1 . Bulk-type ASSLBs assembled with either pristine or air-exposed Li 10 Ge(P 1– x Sb x ) 2 S 12 exhibit high initial Coulombic efficiencies of 92.8 and 91.0%, respectively, with excellent cycling performances of over 110 cycles. The observed variations in the structural parameters and bond strengths provide an effective approach toward designing more ionically conductive and stable solid-state electrolytes.