Interface Effects on Crystal Growth and Li Ion Dynamics in Sulfide Glass-Ceramics

Glass-ceramics are promising materials for use as solid electrolytes in all-solid-state batteries because of their high Li⁺ conductivity. This study investigated an interfacial model for glass-ceramics consisting of 75Li₂S–25P₂S₅ glass and β-Li₃PS₄ with seven different β-Li₃PS₄ planes using molecular dynamics simulations. The equilibrated structure at 300 K and crystal growth at 500 K were analyzed in terms of interfacial enthalpy and crystallization rates. A novel method for identifying PS₄^3– units as either glassy or crystalline was established based on the rotational motion of PS₄^3– units. The rotational motion of PS₄^3– units in the interfacial model was quantitatively indexed using sulfur trajectories within a 100 ps time window. The crystallization rate calculated using crystal growth simulations was found to depend on the crystalline plane forming the interface. The predicted crystal shape, derived from the interfacial enthalpy and growth rate, was analyzed using Wulff’s theorem. The Li⁺ diffusivity in the crystalline, glassy, and interfacial regions of the interfacial model was evaluated through the time integration of velocity–velocity autocorrelation functions. Notably, the Li⁺ diffusivity in the crystalline regions varied depending on the interfacial model and differed from that of bulk β-Li₃PS₄. This variation was attributed to differences in the degree of PS₄^3– rotational motion in the crystalline regions of the interfacial model. The analytical methodologies developed in this study and the insights into the effects of interfaces on PS₄^3– rotational motion, make valuable contributions to the understanding and design of glass-ceramics with interfaces.