Superionic Conductors: Li10+δ[SnySi1–y]1+δP2−δS₁₂ with a Li₁₀GeP₂S₁₂-type Structure in the Li₃PS₄–Li₄SnS₄–Li₄SiS₄ Quasi-ternary System

Solid solutions of Sn–Si derivatives with an LGPS (Li 10 GeP 2 S 12 )-type structure are synthesized by a solid-state reaction in the Li 3 PS 4 –Li 4 SnS 4 –Li 4 SiS 4 quasi-ternary system. The monophasic region of the LGPS-type structure deviates from the tie line between Li 10 SiP 2 S 12 and Li 10 SnP 2 S 12, and the composition of the solid solution is determined to be −0.1 ≤ δ ≤ 0.5 and 0 ≤ y ≤ 1.0 in Li 10+δ [Sn y Si 1– y ] 1+δ P 2−δ S 12 (0.50 ≤ x ≤ 0.7 and 0 ≤ y ≤ 1.0 in Li 4– x [Sn y Si 1– y ] 1– x P x S 4 ). The solid solution is formed by a double substitution that changes the Sn/Si ratio and the M 4+ (Sn 4+ and Si 4+ )/P 5+ ratio, which adjusts the sizes of the lithium conduction tunnels and the lithium concentration, and contributes to the optimal conductivity value. The highest ionic conductivity value of 1.1 × 10 –2 S cm –1 is achieved for the composition of Li 10.35 [Sn 0.27 Si 1.08 ]P 1.65 S 12 (Li 3.45 [Sn 0.09 Si 0.36 ]P 0.55 S 4 ) at 298 K, which is close to the value for the original LGPS compound (1.2 × 10 –2 S cm –1 ). The Ge-free solid electrolyte could be suitable for practical applications in all-solid-state batteries.