Modified Imidazolium-Based Ionic Liquids With Improved Chemical Stability Against Lithium Metal

Chemical instability against metallic lithium of imidazolium cation-based ionic liquids (ILs) such as 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide ([C4MIm] TFSI) has been reported in literature previously. In this work, modified imidazolium cation-based ionic liquids are shown, in which the acidic proton at the C-2 position of the imidazolium ring is replaced by methyl groups. 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl) imide ([C4MMIm] TFSI) and 1-butyl-2,3,4,5-tetramethylimidazolium bis(trifluoromethanesulfonyl) imide ([C44MIm] TFSI) are found to prevent the formation of N-heterocyclic carbenes and thus improve the electrochemical performance of electrolytes including these ILs. Furthermore, possible decomposition products of the modified imidazolium cations are characterized.