The effect of incorporating a room temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI), in the polymer electrolyte (PE) based on poly(ethylene oxide)-(lithium bis(trifluoromethanesulfonyl) imide) [PEO-LiTFSI] was investigated. BMITFSI content was varied between 20 and 80 parts by weight (pbw) in 100 pbw of PEO-LiTFSI and the influence on ionic conductivity, electrochemical stability and interfacial properties on lithium electrode was studied. A remarkable increase in ionic conductivity was achieved with BMITFSI addition, the effect being most pronounced at lower temperatures. Compared to PEO-LiTFSI, the PEs containing BMITFSI exhibited well-defined redox peaks corresponding to stripping and deposition of lithium. The PEs containing BMITFSI exhibited good electrochemical stability and significantly low interfacial resistance with the lithium electrode. Good discharge performance with 82% active material utilization and stable cycling property was achieved when the PE containing 60 pbw of BMITFSI was evaluated in Li/LiFePO4 cells at 40 degrees C. (c) 2007 Elsevier B.V. All rights reserved.