Studies on conductivity, structural and thermal properties of PEO-LiTFSI polymer electrolytes doped with EMImTFSI ionic liquid

Abstract

In this work, Poly (ethylene oxide) (PEO) is used as polymer host, Lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) as doping salt and 1-Ethyl-3-methyl bis (trifluoromethanesulfonyl) imide (EMIm-TFSI) ionic liquid as plasticizer to prepare plasticized PEO-based polymer electrolytes. All samples were prepared using solution cast technique and were characterised by Impedance Spectroscopy (IS), X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The ionic conductivity of pure PEO film at ambient temperature was found to be 1.43 × 10−8 Scm−1. When LiTFSI was added, the ionic conductivity was enhanced and was optimized at 30 wt. % of LiTFSI with value of 3.54 × 10−5 Scm−1. Further enhancement of the ionic conductivity occurred when 8 wt. % of EMImTFSI was added into the polymer electrolyte system with value of 1.15 × 10−4 Scm−1. The increase in ionic conductivity is due to increasing number of charge carriers in the system attributed to ion dissociation. The increase in ionic conductivity at room temperature is also attributed to the plasticization effects of ionic liquid as well as decrease in glass transition temperature (Tg) and increase in amorphous nature as evidenced by DSC and XRD respectively.