Electrochemical properties of PEO-based polymer electrolytes blended with different room temperature ionic liquids

Polymer electrolyte (PE) based on poly(ethylene oxide)-lithium bis(trifluoromethane sulfonyl)imide (PEO-LiTFSI) was blended with three room temperature ionic liquids (RTILs), namely 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (BMITFSI), 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and i-butyl-3-methylimidazolium trifluoromethanesulfonate (BMICF3SO3) with a view to enhance the room temperature ionic conductivity to acceptable levels for use in lithium batteries. The incorporation of 80 parts by weight (pbw) of the RTILs in 100 pbw of PEO-LiTFSI resulted in enhanced ionic conductivity, the effect being more pronounced at lower temperatures. Evaluation of electrochemical properties showed that PEs with RTILs exhibit an electrochemical stability window between -1.0 V and 4.5 V vs Li/Li+ and good reversibility of redox reactions on cycling. The optimum results were obtained with the incorporation of BMITFSI in the PE, which exhibited a low and stable interfacial resistance on lithium metal.