Preparation and ionic conductivity of (100−x)(0.8Li2S·0.2P2S5)·xLiI glass–ceramic electrolytes

Abstract

The glass–ceramic electrolytes of (100−x)(0.8Li2S·0.2P2S5)·xLiI (in mole percent; x = 0, 2, 5, 10, 15, 20, and 30) were prepared by mechanical milling and subsequent heat treatment. Crystalline phases analogous to the thio-LISICON region II or III in the Li2S–GeS2–P2S5 system were precipitated. The thio-LISICON III analog phase was mainly precipitated at the composition x = 0, and the thio-LISICON II analog phase was precipitated in the composition range from x = 2 to 15. The X-ray diffraction peaks of the thio-LISICON II analog phase shifted to the lower diffraction angle side with increasing the LiI content. High conductivities above 2 × 10−3 S cm−1 at room temperature were observed in the glass–ceramics at the wide composition range from x = 2 to 15. The glass–ceramic electrolyte at x = 5 with the highest conductivity of 2.7 × 10−3 S cm−1 showed a wide electrochemical window of about 10 V. The addition of LiI to the 80Li2S·20P2S5 (in mole percent) glass was effective in crystallizing the thio-LISICON II analog phase with high conductivity from the glass.