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

Abstract 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.