Lithium bis(fluorosulfonyl)imide (LiFSI) in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) was successfully tested as an electrolyte for graphite composite anodes at elevated temperature of 55 degrees C. The graphite anode showed a good cyclability during the galvanostatic testing at C/10 rate and 55 degrees C with the capacity close to theoretical. The formation of SEI in different electrolytes was the subject of study using impedance spectroscopy on symmetrical cells containing two lithium electrodes. The 0.7m LiFSI in PYR14TFSI exhibits a good ionic conductivity (5.9 mS cm(-1) at 55 degrees C) along with high electrochemical stability and high thermal stability. These properties allow their potential application in large-scale lithium ion batteries with improved safety. (C) 2011 Elsevier B.V. All rights reserved.