Li₁₀Ge(P_1–<i>x</i>Sb<i>_x</i>)₂S₁₂ Lithium-Ion Conductors with Enhanced Atmospheric Stability

Abstract

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 Li10Ge(P1–xSbx)2S12 electrolyte system with soft acid Sb substitution. Theoretical calculations predict the Sb substitution in (Ge,P)S4 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 Li10Ge(P1–xSbx)2S12, 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 Li10Ge(P1–xSbx)2S12 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.