New ionic liquids with an asymmetric anion, fluorosulfonyl-(trifluoromethanesulfonyl)imide (FTFSI), were prepared and their chemical-physical properties were investigated. The ionic liquids based on N-methyl-N-propylpyrrolidinium, PYR(13), N-butyl-N-methylpyrrolidinium, PYR(14), and N-methoxyethyl-N-methylpyrrolidinium, PYR(12O1), exhibit high electrochemical stability (>5.5 V on platinum) and thermal stability (>250 °C in N(2) and >200 °C in O(2)). Due to the highly asymmetric anion, the prepared ionic liquids do not crystallize down to -150 °C while maintaining ionic conductivity above 10(-4) S cm(-1) even at -40 °C. Conductivity and viscosity values at 20 °C are in the range 3.5-5.0 mS cm(-1) and 30-60 mPa s respectively. PFG-NMR measurements showed high self-diffusion coefficients of cations and the anion.