Synthesis of Hydrophobic Ionic Liquids for Electrochemical Applications

Abstract

In this work is described an improved synthesis of hydrophobic room-temperature ionic liquids (RTIL) composed of NN -methyl- NN -alkylpyrrolidinium (or piperidinium) cations and (perfluoroalkylsulfonyl)imide, [(CnF2n+1SO2)(CmF2m+1SO2)N−][(CnF2n+1SO2)(CmF2m+1SO2)N−] , anions. The procedure described allows the synthesis of hydrophobic ionic liquids with the purity required for electrochemical applications such as high-voltage supercapacitors and lithium batteries. This new synthesis does not require the use of environmentally unfriendly solvents such as acetone, acetonitrile, and alogen-containing solvents that are not suitable for industrial applications. Only water and ethyl acetate are used throughout the entire process. The effect of the reaction temperature, time, and stoichiometry in the various steps of the synthesis has been investigated. With an iterative purification step performed at the end of the synthesis, ultrapure, clear, colorless, inodorous RTILs were obtained. The final vacuum drying at 120°C120°C gave RTILs with a moisture content below 10ppm10ppm . Details for the synthesis of N-butyl-N-methylpyrrolidinium bis(trifluoromethansulfonyl)imide (PYR14TFSI)(PYR14TFSI) are reported. The overall yield for the synthesis of this ionic liquid was above 86wt%86wt% . Electrochemical tests performed on this material are also reported.