We report an investigation on quaternary, polyethylene oxide (PEO)-based electrolytes as separators for lithium polymer batteries. The target is the development of Li+ conducting membranes, containing large fraction of the N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid, able to combine fast ion transport properties with improved electrochemical stability. The PEO electrolytes, prepared through a fully-dry solvent-free procedure, exhibited good aging resistance and conductivity values equal to 3.46×10−4 and 2.43×10−3 Scm−1 at −20 and 20°C, respectively, combined with an anodic stability up to 4.5V (vs. Li°/Li+). These results represent the best performance, in terms of ion transport properties and electrochemical stability, reported till now for PEO electrolytes.