Li+ Solvation and Ionic Transport in Lithium Solvate Ionic Liquids Diluted by Molecular Solvents
Li+ Solvation and Ionic Transport in Lithium Solvate Ionic Liquids Diluted by Molecular Solvents
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DOI：
10.1021/acs.jpcc.5b11642
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发表时间：
2016-07-28
影响因子：
3.7
通讯作者：
Watanabe, Masayoshi
中科院分区：
文献类型：
--
作者：
Ueno, Kazuhide;Murai, Junichi;Watanabe, Masayoshi
锂二（三氟甲烷磺酰）酰胺（Li[TFSA]）和三甘油酯（G3）或四甘油酯（G4）的等摩尔混合物产生稳定的熔融配合物：[Li(G3)][TFSA]和[Li(G4)][TFSA]。这些被称为溶剂离子液体（SILs）。glyme基SILs具有热学和电化学性能，有利于用作锂电池中的锂导电电解质。然而，它们固有的高粘度和低离子电导率阻碍了实际应用。因此，我们用分子溶剂稀释SILs，以提高其离子电导率。为了确定络合阳离子在稀释SILs中的稳定性，测量了它们的电导率、粘度、自扩散系数和拉曼光谱。[Li(G3)]（+）和[Li(G4)]（+）在非极性溶剂中稳定，即甲苯、碳酸二乙酯和氢氟醚（HFE）；然而，当使用极性溶剂，即水和碳酸丙烯酯时，glyme和溶剂之间会发生配体交换。在乙腈（AN）混合溶剂中形成了[Li(G3)(AN)]（+）和[Li(G4)(AN)]（+）络合阳离子。当用非极性溶剂稀释[Li(G4)][TFSA]时，[Li(G3)][TFSA]的导电性优于[Li(G3)][TFSA]，这是由于[Li(G4)][TFSA]混合物中的离子解离性更大。考虑到Li-glyme配合物阳离子的稳定性，离子电导率的增强，以及稀释溶剂的固有电化学稳定性，[Li(G4)][TFSA]可以被甲苯或HFE稀释，作为替代电池电解质的候选物。
An equimolar mixture of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) and either triglyme (G3) or tetraglyme (G4) yielded stable molten complexes: [Li(G3)][TFSA] and [Li(G4)][TFSA]. These are known as solvate ionic liquids (SILs). Glyme-based SILs have thermal and electrochemical properties favorable for use as lithium-conducting electrolytes in lithium batteries. However, their intrinsically high viscosities and low ionic conductivities prevent practical application. Therefore, we diluted SILs with molecular solvents in order to enhance their ionic conductivities. To determine the stabilities of the complex cations in diluted SILs, their conductivity and viscosity, the self-diffusion coefficients, and Raman spectra were measured. [Li(G3)](+) and [Li(G4)](+) were stable in nonpolar solvents, that is, toluene, diethyl carbonate, and a hydrofluoroether (HFE); however, ligand exchange took place between glyme and solvent when polar solvents, that is, water and propylene carbonate, were used. In acetonitrile (AN) mixed solvent complex cations [Li(G3)(AN)](+) and [Li(G4)(AN)](+) were formed. [Li(G4)][TFSA] was more conductive than [Li(G3)][TFSA] when diluted with nonpolar solvents due to the greater ionic dissociativity in [Li(G4)][TFSA] mixtures. In view of the stability of the Li-glyme complex cations, the enhanced ionic conductivities, and the intrinsic electrochemical stabilities of the diluting solvents, [Li(G4)][TFSA] diluted by toluene or HFE, can be a candidate for an alternative battery electrolyte.