Glass Electrolytes with High Ion Conductivity and High Chemical Stability in the System LiI-Li2O-Li2S-P2S5

The Li2O-Li2S-P2S5 glasses, which were prepared by a reaction of the Li2S-P2S5 glass and Li2O, hardly generated H2S gas in air. These glasses showed relatively high ion conductivities about 10−4 S cm−1 at room temperature. However, these conductivities were lower than those of original sulfide glasses. In this study, an addition of LiI to the Li2O-Li2S-P2S5 glasses was examined in order to improve ion conductivities. The 30LiI·70(0.07Li2O·0.68Li2S·0.25P2S5) glass showed high ion conductivity of 1.3 × 10−3 S cm−1 at room temperature, and hardly generated H2S gas in air. On the other hand, the 30LiI·70(0.07Li2O·0.68Li2S·0.25P2S5) glass was electrochemically stable in the potential range of 0–10 V. Moreover, the all-solid-state C/LiCoO2 cell using the 30LiI·70(0.07Li2O·0.68Li2S·0.25P2S5) glass as solid electrolytes worked as lithium secondary batteries at room temperature, and exhibited a good cycle performance. Therefore, the 30LiI·70(0.07Li2O·0.68Li2S·0.25P2S5) glass was a suitable electrolyte for all-solid-state cells because the glass had high conductivity, wide electrochemical window and high chemical stability to moisture.