Observation of Li2s-P2S5 Crystalline Glass By Transmission Electron Microscopy

Abstract

Sulfide solid electrolytes are electrochemically stable in a wide potential window and exhibit high lithium ion conductivities of more than 10-4 S cm-1 at room temperature. In particular, the Li2S-P2S5 glasses, which are served as the solid electrolyte, have been reported to crystallize above 473 K in the heating process from room temperature. Noted that lithium ion conductivities depend strongly on precipitated crystalline phases [1, 2]. In this study we have investigated microstructures of the Li2S-P2S5 glasses by transmission electron microscopy (TEM). Figure 1 shows the high-resolution (HR) TEM image of the 75Li2S-25P2S5 glass at room temperature, together with the corresponding electron diffraction (ED) pattern. Although a halo pattern due to the amorphous structure was observed in the ED pattern, crystalline nanoparticles with approximately 5x5 nm2 were found to be randomly distributed in the amorphous state, as indicated by dotted circle regions (Fig. 1). Furthermore, in-situ TEM observation in the 75Li2S-25P2S5 glasses revealed that the crystallization started at approximately 473 K and gradually proceeded as temperature increased from 473 K. [1] F. Mizuno et al, Adv. Mater. 17 (2005) 918-921. [2] F. Mizuno et al, Solid State Ionics 177 (2006) 2721-2725. Figure 1