Herein we report a comparative study of quaternary polymer electrolyte membranes, comprising polyethylene oxide (PEO), lithium bis(trifluoromethanesulfonyl)imide, LiTFSI(salt), SiO2-filler and N-methyl-N-butyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr1,4TFSI) ionic liquid. The membranes are developed in view of an efficient application in polymeric lithium battery. The study shows improvement of the ionic conductivity and the stability of the lithium interphase by increasing the Pyr1,4TFSI content up to 20% wt, as revealed by Arrhenius conductivity plots, electrochemical impedance spectroscopy as well as by cyclic test in symmetrical lithium cell. This trend is directly reflected in enhanced behavior of lithium polymer cell using LiFePO4, in terms of delivered capacity. Furthermore, the measurement indicated that setting up a proper amount of added IL is a key requirement for an optimal behavior of the electrolyte in battery.