Lithium ion conducting Li 4−2 xGe 1− xS xO 4 solid electrolytes

Abstract

A range of stable solid solutions with γ-LISICON type structure forms in the system Li 4−2 x Ge 1− x S x O 4 for 0.08 < x<0.42. This phase has high lithium ion conductivity with a maximum value (bulk) of ∼1.85×10 −5 S cm −1 for x=0.20 at 27° C. The net pellet conductivity for this compositions is ∼1.00×10 −5 S cm −1 at 27°C, rising to ∼0.04 S cm −1 at 300°C. Conductivity Arrhenius plots for different compositions in the γ-solid solution range exhibit markedly non-linear behaviour above ∼ 300°C. The activation energies below ∼ 300°C are in the range 0.50-0.60 eV. The γ-solid solutions are structurally related to orthorhombic γ-Li 3PO 4 and contain interstitial Li + ions; for x=0.20, a=6.253(2) A ̊ , b=10.828(3) A ̊ , c=5.114(2) A ̊ , at room temperature. An approximate phase diagram for the Li 4GeO 4Li 2SO 4 binary system is presented, together with lattice parameter data on the γ-solid solutions.