Preparation and characterization of lithium ion conducting Li2S–P2S5–GeS2 glasses and glass-ceramics

Glasses and glass-ceramics in the system Li2S–P2S5–GeS2 with the following three compositions of Li7 + xP3 − xGexS11, Li7P3 − yGeyS11 − y/2, and (100 − z)(70Li2S·30P2S5)·zGeS2, were prepared by using a mechanical milling technique. At the compositions of Li7 + xP3 − xGexS11 and Li7P3 − yGeyS11 − y/2, conductivity decreased monotonically with an increase in x or y. The conductivity decrease was due to the increase of lithium ion concentration around ortho thio-phosphate which led to the precipitation of the Li3.2P0.96S4 crystal. At the composition of (100 − z)(70Li2S·30P2S5)·zGeS2, conductivity was enhanced with an increase in z (up to z = 2), and the glass-ceramic with 2 mol% of GeS2 showed the highest conductivity of 5.4 ± 0.1 × 10− 3 S cm− 1 at room temperature. From the XRD pattern, germanium would not be incorporated into the Li7P3S11 crystal. One possible reason for the conductivity enhancement is the increase of the crystallinity of Li7P3S11 crystal.