Chemical and structural changes of 70Li2S-30P2S5 solid electrolyte during heat treatment

• Published in: Solid state ionics Vol. 310; pp. 50 - 55
• Main Authors: Aoki, Yasuhito, Ogawa, Kengo, Nakagawa, Takeshi, Hasegawa, Yuichi, Sakiyama, Yoko, Kojima, Toshikatsu, Tabuchi, Mitsuharu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2017
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2017.08.006

To elucidate the chemical and structural changes of sulfide solid electrolyte during heat treatment, in situ outgas (TPD-MS), Raman, and XRD analyses were applied for a 70Li2S-30P2S5 glass sample. A sulfide solid electrolyte was constructed from the PS43− and P2S74− anions, together with a small amount of P2S64− anions. In the course of the structural change from glass to glass-ceramic through heat treatment, the fraction of PS43− anion decreased and P2S74− anion increased at 210°C. Sulfur compounds were detected as outgas at about 240°C, which suggests thermal decomposition of PS43− anion to produce P2S74− and sulfur compounds as by-product. The thermal treatment temperature should be higher than 240°C to eliminate sulfur compounds generated as the reaction by-product. In the same temperature region, crystallization of Li7P3S11 was also detected using in situ XRD. The ionic conductivity increased from 1.0×10−4Scm−1 to 8.4×10−4Scm−1 after heat treatment at 270°C. Therefore, the partial compositional change of PS43− to P2S74− anions and crystallization of Li7P3S11 are key factors producing higher ionic conductivity. By combining these experimental techniques implemented in this study, it is possible to detect the temperature at which the chemical and structural changes proceed. One can also ascertain the suitable heat treatment temperature for production of by-product free and high-quality sulfide-based solid electrolyte.
•In situ analyses were conducted during heat treatment for sulfide solid electrolyte.•Thermal decomposition of PS43− to P2S74− and sulfur as by-product were detected.•Generation of P2S64− is unfavorable for ionic conduction detected over 300°C.•Heat treatment should be conducted at 240–270°C for better ion conductivity.