Preparation and structure of amorphous solid electrolytes based on lithium sulfide

Structure of amorphous solid electrolytes in the system Li2S-SiS2-Li4SiO4, prepared by twin-roller quenching and mechanical milling, was investigated using nuclear magnetic resonance and X-ray photoelectron spectroscopies (XPS). These spectra revealed that the structure unit comprising two silicon atoms coordinated with three non-bridging sulfur atoms and one bridging oxygen atom was mainly present in the quenched 95(0.6Li(2)S.0.4SiS(2)).5Li(4)SiO(4) glass. The glass with 5 mol% Li4SiO4 had the largest conductivity at room temperature. Amorphous solid electrolytes in the system Li2S-SiS2-Li4SiO4 were also successfully prepared from a mixture of Li2S, SiS2 and Li4SiO4 crystals using a mechanical milling technique at room temperature. The conductivities of the oxysulfide powders, mechanically milled for 20 h, were greater than or equal to 10(-4) S cm(-1) at room temperature, which were comparable to the conductivities of the corresponding glasses prepared by quenching. As the period of mechanical milling treatment was increased from 0 to 20 h, the structure of the milled powders became similar to that of the glasses prepared by quenching. Such a structure change brought about an increase of conductivity in the resultant powders from 10(-9) to 10(-4) S cm(-1). In the case of mechanochemical preparation, the reactivity of the starting materials affected the structure and formation process of the oxysulfide solid electrolytes. (C) 2000 Elsevier Science B.V. All rights reserved.