Chelate Effects in Glyme/Lithium Bis(trifluoromethanesulfonyl)amide Solvate Ionic Liquids. I. Stability of Solvate Cations and Correlation with Electrolyte Properties

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• 作者：Ce Zhang ; Kazuhide Ueno ; Azusa Yamazaki ; Kazuki Yoshida ; Heejoon Moon ; Toshihiko Mandai ; Yasuhiro Umebayashi ; Kaoru Dokko ; Masayoshi Watanabe
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：May 15, 2014
• 年：2014
• 卷：118
• 期：19
• 页码：5144-5153
• 全文大小：438K
• 年卷期：v.118,no.19(May 15, 2014)
• ISSN：1520-5207

文摘

To develop a basic understanding of a new class of ionic liquids (ILs), 鈥渟olvate鈥?ILs, the transport properties of binary mixtures of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) and oligoethers (tetraglyme (G4), triglyme (G3), diglyme (G2), and monoglyme (G1)) or tetrahydrofuran (THF) were studied. The self-diffusion coefficient ratio of the solvents and Li⁺ ions (D_sol/D_Li) was a good metric for evaluating the stability of the complex cations consisting of Li⁺ and the solvent(s). When the molar ratio of Li⁺ ions and solvent oxygen atoms ([O]/[Li⁺]) was adjusted to 4 or 5, D_sol/D_Li always exceeded unity for THF and G1-based mixtures even at the high concentrations, indicating the presence of uncoordinating or highly exchangeable solvents. In contrast, long-lived complex cations were evidenced by a D_sol/D_Li 1 for the longer G3 and G4. The binary mixtures studied were categorized into two different classes of liquids: concentrated solutions and solvate ILs, based on D_sol/D_Li. Mixtures with G2 exhibited intermediate behavior and are likely the borderline dividing the two categories. The effect of chelation on the formation of solvate ILs also strongly correlated with electrolyte properties; the solvate ILs showed improved thermal and electrochemical stability. The ionicity (螞_imp/螞_NMR) of [Li(glyme or THF)_x][TFSA] exhibited a maximum at an [O]/[Li⁺] ratio of 4 or 5.