Structure and transport properties in the pseudo-binary phase system Li4SiS4-Li4SnS4

Balzat, L.; Li, Y.; Dums, S.; Moudrakovski, I.; Gjorgjevikj, K.; Schulz, A.; Li, Y.; Krause, S.; Canepa, P.; Lotsch, B.

doi:10.1021/acs.chemmater.5c00358

Structure and transport properties in the pseudo-binary phase system Li₄SiS₄-Li₄SnS₄

L. Balzat, Y. Li, S. Dums, I. Moudrakovski, K. Gjorgjevikj, A. Schulz, Y. Li, S. Krause, P. Canepa, and B. Lotsch; Chem. Mater. 37, 6127–6139 (2025).

BibTeX

@article{Balzat2025structure,
  author  = {Balzat, L. and Li, Y. and Dums, S. and Moudrakovski, I. and Gjorgjevikj, K. and Schulz, A. and Li, Y. and Krause, S. and Canepa, P. and Lotsch, B.},
  title   = {{Structure and transport properties in the pseudo-binary phase system Li$_{4}$SiS$_{4}$-Li$_{4}$SnS$_{4}$}},
  journal = {Chemistry of Materials},
  volume  = {37},
  pages   = {6127--6139},
  year    = {2025},
  doi     = {10.1021/acs.chemmater.5c00358}
}

Abstract

Thio-lithium superionic conductors (thio-LISICONs) are a family of promising solid electrolyte materials for potential applications in solid-state batteries. The orthorhombic polymorph of the thio-LISICON Li₄SiS₄ (o-Li₄SiS₄) has been known for decades, but its complete crystal structure has been reported only recently. Here, using single-crystal X-ray diffraction, we reevaluated the crystal structure of o-Li₄SiS₄ and showed that o-Li₄SiS₄ crystallizes in space group Pmn2₁ (no. 31, a = 7.7694(15) Å, b= 13.731(3) Å, and c = 6.1413(12) Å). The crystal structure of o-Li₄SiS₄ consists of isolated SiS₄ tetrahedra arranged in a zigzag-type manner, whereas Li atoms are coordinated both tetrahedrally and octahedrally by sulfur atoms of the SiS₄ groups. Structures identified by first-principles calculations support the lower symmetry solution presented here, with the Pmn2₁ polymorph being more stable at room temperature than a higher symmetry phase. By knowing the accurate crystal structure of o-Li₄SiS₄, we investigated the solid solution behavior with another group IV thio-LISICON, Li₄SnS₄. Rietveld refinements of powder X-ray diffraction data revealed the solid solution Li₄Si_1-xSn_xS₄ (0 ≤ x ≤ 1, Δx = 0.1), which shows a nearly ideal Vegard-type behavior for all silicon-containing samples. ²⁹Si and ¹¹⁹Sn magic-angle-spinning solid-state NMR and Raman spectroscopy showed the presence of SiS₄ and SnS₄ tetrahedral moieties, with the spectra showing expected behavior consistent with the silicon−tin ratio in the materials. Electrochemical impedance spectroscopy revealed the highest ionic conductivity of 8.4x10⁻⁶ S cm⁻¹ at 25 ℃ for Li₄Si_0.5Sn_0.5S₄, accompanied by the lowest migration barrier of ~0.37 eV.