Characterization of solvent-free polymer electrolytes consisting of ternary PEO-LiTFSI-PYR14 TFSI

The physical properties and electrochemical performance of solvent-free polymer electrolytes, consisting of poly(ethylene oxide) [P(EO)] with Li+ and N-butyl-N-methylpyrrolidinium (PYR14+) salts of bis(trifluoromethanesulfonyl)imide (TFSI), are reported. The addition of the PYR14TFSI room-temperature molten salt to the conventional P(EO)(10)LiTFSI polymer electrolyte results in a significant enhancement of the ionic conductivity (to 2.6x10(-4) S/cm at 20 degrees C). Li metal/LiFePO4 batteries making use of this new family of solid polymer electrolytes have shown a very promising low-temperature cycle life. It was found that a Li metal/LiFePO4 cell at 20 degrees C can deliver 138 mAh/g during the first discharge, corresponding to 90% of the nominal specific capacity (154 mAh/g), and a promisingly low capacity fading of about 0.2%/cycle over 500 cycles.