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 beta-Li3PS4 with seven different beta-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 PS43- units as either glassy or crystalline was established based on the rotational motion of PS43- units. The rotational motion of PS43- 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 beta-Li3PS4. This variation was attributed to differences in the degree of PS43- 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 PS43- rotational motion, make valuable contributions to the understanding and design of glass-ceramics with interfaces.