Ionic liquid electrolytes based on multi-methoxyethyl substituted ammoniums and perfluorinated sulfonimides: Preparation, characterization, and properties

New functionalized ionic liquids (ILs), comprised of multi-methoxyethyl substituted quaternary ammonium cations (i.e. [N(CH2CH2OCH3)4−n(R)n]+; n = 1, R = CH3OCH2CH2; n = 1, R = CH3, CH2CH3; n = 2, R = CH3CH2), and two representative perfluorinated sulfonimide anions (i.e. bis(fluorosulfonyl)imide (FSI−) and bis(trifluoromethanesulfonyl)imide (TFSI−)), were prepared. Their fundamental properties, including phase transition, thermal stability, viscosity, density, specific conductivity and electrochemical window, were extensively characterized. These multi-ether functionalized ionic liquids exhibit good capability of dissolving lithium salts. Their binary electrolytes containing high concentration of the corresponding lithium salt ([Li+] >1.6 mol kg−1) show Li+ ion transference number (tLi+tLi+) as high as 0.6–0.7. Their electrochemical stability allows Li deposition/stripping realized at room temperature. The desired properties of these multi-ether functionalized ionic liquids make them potential electrolytes for Li (or Li-ion) batteries.

Graphical abstractNew functionalized ionic liquids based on multi-methoxyethyl substituted quaternary ammonium cations and perfluorinated sulfonimide anions are introduced.Figure optionsDownload full-size imageDownload as PowerPoint slide