Unusual Li+ Ion Solvation Structure in Bis(fluorosulfonyl)amide Based Ionic Liquid

被引:140
作者
Fujii, Kenta [1 ]
Hamano, Hiroshi [2 ]
Doi, Hiroyuki [8 ]
Song, Xuedan [3 ]
Tsuzuki, Seiji [4 ]
Hayamizu, Kikuko [4 ]
Seki, Shiro [5 ]
Kameda, Yasuo [6 ]
Dokko, Kaoru [7 ]
Watanabe, Masayoshi [7 ]
Umebayashi, Yasuhiro [8 ]
机构
[1] Univ Tokyo, Inst Solid State Phys, Neutron Sci Labolatory, Kashiwa, Chiba 2778581, Japan
[2] Kyushu Univ, Fac Sci, Dept Chem, Higashi Ku, Fukuoka 8128581, Japan
[3] Dalian Univ Technol, State Key Lab Fine Chem, Dalian 116024, Peoples R China
[4] Tsukuba Ctr, Natl Inst Adv Ind Sci & Technol AIST, Tsukuba, Ibaraki 3058565, Japan
[5] Cent Res Inst Elect Power Ind, Mat Sci Res Lab, Tokyo 2018511, Japan
[6] Yamagata Univ, Fac Sci, Dept Mat & Biol Chem, Yamagata 9908560, Japan
[7] Yokohama Natl Univ, Dept Chem & Biotechnol, Hodogaya Ku, Yokohama, Kanagawa 2408501, Japan
[8] Niigata Univ, Grad Sch Sci & Technol, Nishi Ku, Niigata 9502181, Japan
基金
日本科学技术振兴机构;
关键词
MOLECULAR-FORCE FIELD; LITHIUM SECONDARY BATTERIES; X-RAY-DIFFRACTION; BIS(TRIFLUOROMETHANESULFONYL) IMIDE ANION; SALT BINARY ELECTROLYTES; ELECTROCHEMICAL PROPERTIES; RAMAN-SPECTROSCOPY; CRYSTAL-STRUCTURE; LI/LICOO2; CELL; GRAPHITE;
D O I
10.1021/jp4053264
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Raman spectra of 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)amide [C(2)mIm(+)] [FSA(-)] ionic liquid solutions dissolving LiFSA salt of various concentrations were measured at 298 K. FSA(-) ((FSO2)(2)N-) is an analogue anion of bis(trifluoromethanesulfonyl)amide ((CF3SO2)(2)N-; TFSA(-)). We found that a solvation number of the Li+ ion in [C(2)mIm(+)] [FSA(-)] is 3, though it has been well established that Li+ ion is solvated by two TFSA(-) anions in the corresponding ionic liquids below the Li+ ion mole fraction of x(Li+) < 0.2. To yield further insight into larger solvation numbers, Raman spectra were measured at higher temperatures up to 364 K. The Li+ ion solvation number in [C(2)mIm][FSA(-)] evidently decreased when the temperature was elevated. Temperature dependence of the Li+ ion salvation number was analyzed assuming an equilibrium between [Li(FSA)(2)](-) and [Li(FSA)(3)](2-), and the enthalpy Delta H degrees and the temperature multiplied entropy T Delta S degrees for one FSA(-) liberation toward a bulk ionic liquid were successfully evaluated to be 35(2) kJ mol(-1) and 29(2) kJ mol(-1), respectively. The Delta H degrees and Delta S degrees suggest that the Li+ ion is coordinated by one of bidentate and two of monodentate FSA(-) at 298 K, and that the more weakly solvated monodentate FSA(-) is liberated at higher temperatures. The high-energy X-ray diffraction (HEXRD) experiments of these systems were carried out and were analyzed with the aid of molecular dynamics (MD) simulations. In radial-distribution functions evaluated with HEXRD, a peak at about 1.94 angstrom appeared and was attributable to the Li+-O(FSA(-)) correlations. The longer Li+-O(FSA(-)) distance than that for the Li+-O(TFSA(-)) of 1.86 angstrom strongly supports the larger solvation number of the Li+ ions in the FSA(-) based ionic liquids. MD simulations at least qualitatively reproduced the Raman and HEXRD experiments.
引用
收藏
页码:19314 / 19324
页数:11
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