Electrochemical properties of a poly(ethylene carbonate)-LiTFSI electrolyte containing a pyrrolidinium-based ionic liquid

A novel polymer electrolyte membrane comprising poly(ethylene carbonate) (PEC), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and N-n-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) ionic liquid is prepared by a solvent-free procedure, combining annealing and hot-pressing. The electrochemical properties of the electrolyte are investigated in terms of ionic conductivity, Li transference number (t Li+), and electrochemical stability by a combined study involving electrochemical impedance spectroscopy (EIS), chronoamperometry, and voltammetry. The thermal characteristics are assessed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results reveal an ionic conductivity of a PEC-Pyr14TFSI-LiTFSI electrolyte of the order of 10−5 S cm−1 at 80 °C and t Li+ as high as 0.66 with the intrinsic amorphous nature of the PEC matrix. Furthermore, a Li polymer cell coupling LiFePO4 cathode and the electrolyte is assembled and galvanostatically cycled. The result of this charge-discharge test demonstrates a 3.5-V battery which can be used at 80 °C and a current rate of C/20, delivering a reversible capacity of the order of 150 mAh g−1.