Mechanical properties of sulfide glasses in all-solid-state batteries

Abstract

Sulfide glasses are considered to be promising electrolytes for all-solid-state batteries because of their high ionic conductivities and favorable mechanical properties. In this paper, comprehensive studies of the mechanical properties of sulfide glasses were carried out based on the Li2SP2S5 system, and we evaluated the effects of changing the glass former and modifier on the elastic moduli and formability of these glasses. Young’s moduli of Li2SP2S5 glasses increased when the glass former P was replaced with Ge or Si. Moreover, the Young’s moduli of Li2SP2S5 glasses also increased when substituting S with O. Irrespective of the glass modifier, the Young’s moduli of RxSyP2S5 glasses (R = Li, Na, Ag, Mg, or Sn) increased with the increase in content of each modifier. The measured Young’s moduli are correlated with the mean atomic volumes of the glasses. We evaluated the formability of the sulfide glasses in powder-compaction tests at room temperature. Sulfide glasses with lower bonding energy, larger free volume, and more isolated structure exhibited higher densification ability. Pugh’s ratio (B/G) (B is the bulk and G the shear modulus) was used to evaluate the ductile-brittle property of materials. The glasses with a larger B/G ratio, meaning higher ductility, tended to show a higher relative density. It is suggested that plastic deformation contributes to the densification. This study will provide valuable results for glass science, and will be useful for developing all-solid-state batteries.