Structural and electronic descriptors for atmospheric instability of Li-thiophosphate using density functional theory

Abstract

We investigated the structural and electronic descriptors for atmospheric instability of Li-thiophosphates (β-Li3PS4) using density functional theory. Based on thermodynamic and crystallographic considerations, four stable surfaces such as (111), (101), (001), and (100) were identified in β-Li3PS4 using the equilibrium crystal shape according to Gibbs-Wulff theorem. As such, the p-band center of the S-ion (∆Ep) and segregation energy of S vacancy (EVS∙∙, seg) were utilized as electronic and structural descriptors to evaluate the atmospheric instability of β-Li3PS4. It was determined that the (110) and (111) surfaces led to high surface instability among the four surfaces. Furthermore, it was observed that the p-band center and the segregation energy of S have a linear relationship (i.e., ∆Ep increased as EVS∙∙, seg decreased), which could be used as simple descriptors to evaluate the atmospheric instability of sulfide-based Li-ion conductors.