Two pyrrolidinium-based ionic liquids (ILs) with ether groups, and namely N-methoxyethyl-N-methylpyrrolidinium bis-trifluoromethanesulfonimide (PYRA1,2O1) and 1-(2-(2-(2-methoxyethoxy) ethoxy)ethyl)-1-methylpyrrolidinium bis-trifluoromethanesulfonide (PYRA1,2(O2)2O1), were used as plasticizers for the PEO20–LiTFSI solid polymer electrolyte. The ionic liquids differ for the number of oxygens and lateral chain length. The properties of the plasticized polymer electrolytes were investigated by means of thermal analysis, impedance spectroscopy, XRD, FTIR spectroscopy and voltammetry. Both the ILs enhanced the conductivity of PEO20–LiTFSI of about one order of magnitude at 40°C. The polymer electrolyte plasticized with PYRA1,2O1 showed a higher transport number, and a wider electrochemical window.