Arafumi Kimura
(Research and Development Department, Chemicoat Co., Ltd., 1-14 Okayamadai, Togane-city, Chiba 283-0826, Japan)
Abstract: This paper is aimed to present a clean, inexpensive and sustainable method to synthesize high purity lithium sulfide (Li2S) powder through hydrogen reduction of lithium sulfate (Li2SO4). A three-step reduction process has been successfully developed to synthesize well-crystallized and single-phase Li2S powder by investigating the melting, sintering and reduction behavior of the mixtures of Li2SO4-Li2S. High purity alumina was found to be the most suitable crucible material for producing high purity Li2S, because it was not attacked by the Li2SO4-Li2S melt during heating, as compared with other materials, such as carbon, mullite, quartz, boron nitride and stainless steel. The use of synthesized Li2S resulted in higher purity and substantially higher room temperature ionic conductivity (2.77 mS·cm−1) for the argyrodite sulfide electrolyte Li6PS5Cl than commercial Li2S (1.12 mS·cm−1). This novel method offers a great opportunity to produce battery grade Li2S for sulfide solid electrolyte applications.
Key words: lithium sulfide；lithium sulfate；hydrogen reduction；sulfide solid electrolyte；all-solid-state lithium-ion battery