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High Li-Ion Conductive Molecular Crystal and Its Application for All-Solid-State Li-Ion Battery

 On October 29, 2020, Shizuoka University and Tokyo Institute of Technology announced that high lithium (Li) ion conductive organic molecular crystal with novel ion conduction mechanism was developed and its potential application in all-solid-state Li-batteries was confirmed by the research group led by Lecturer Makoto Moriya at Faculty of Science - Department of Chemistry, Shizuoka University and Professor Taro Hitosugi at School of Materials and Chemical Technology, Tokyo Institute of Technology. The work was supported by research grants from JSPS and JST, and the results were published in Nano Letters*.

 In order to make ignition-safe all solid-state Li-ion battery, which is seemed to be the key device for the realization of the sustainable society, various solid electrolytes are under development. In the previous studies, solid electrolytes are classified into three types as ceramics, inorganic glass and organic polymer. The research group challenged to develop organic molecular crystal Li(FSA)(SN)2, short for Li{N(SO2F)2}(NCCH2CH2CN)2, as a novel type of the solid electrolyte. The organic molecular crystal is expected to possess advantages of both ceramics and organic polymers. Li(FSA)(SN)2 crystal is synthesized by melt mixing LiFSA and SN at 70℃ then cooled to room temperature. Spatial arrangement of these molecules in the crystal makes the Li-ion path. The Li-ion conductivity is 1×10-4 Scm-1 at 30℃ and 1×10-5 Scm-1 at -20℃, with an activation energy 28 kJmol-1. Li-ion conductivity of Li(FSA)(SN)2 is as high as those of sulfide ceramics. This high Li-ion conductivity is available in a wide temperature range and two orders higher compared with previously reported molecular crystals at -20℃.

 Li(FSA)(SN)2 crystal melts at 59.5℃ and when cooled to solid, its crystal structure and high Li-ion conductivity are recovered. All solid-state Li-ion battery was fabricated by utilizing a molten state of Li(FSA)(SN)2. The battery made by putting the molten Li(FSA)(SN)2 on LiCoO2 thin film anode maintained 90% of the initial capacity after 100 charge-discharge cycles.

*Kenjiro Tanaka, Yusuke Tago, Mitsuru Kondo, Yuki Watanabe, Kazunori Nishio, Taro Hitosugi, and Makoto Moriya, "High Li-Ion Conductivity in Li{N(SO2F)2}(NCCH2CH2CN)2 Molecular Crystal", Nano Letters, 2020, DOI:10.1021/acs.nanolett.0c03313; Publication Date: October 28, 2020