Thermal, electrical and electrochemical properties of ionic liquid-doped poly(ethylene oxide)-LiTDI polymer electrolytes for Li-ion batteries

In the present study, we report the synthesis and characterisation of solid polymer electrolytes (SPEs) based on polymer poly(ethylene oxide) (PEO), salt lithium 4,5-dicyano-2-(trifluoromethyl)imidazole (LiTDI) and different amounts of added ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) via a solution casting technique, and we investigate the use of these electrolytes in solid-state Li-ion batteries (LIBs). Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), complex impedance spectroscopy, linear sweep voltammetry (LSV) and electrochemical studies exhibit promising characteristics of the prepared SPEs suitable for application in LIBs. The optimum conducting composition (OCC) PEO20-LiTDI-40 wt% EMImTFSI SPEs shows high thermal stability (i.e., up to 300 degrees C), high ionic conductivity (similar to 1.78 x 10(-4) S/cm at 60 degrees C) and a high electrochemical stability window (similar to 4.2 V). The Li/PEO20-LiTDI-40 wt% EMImTFSI/LiFePO4 coin-type cell cycled at 0.1 C shows initial discharge capacity of about 161 mAh g(-1), and retains capacity of 144.5 mAh g(-1) on the 50th cycle. The above results suggest that PEO20-LiTDI-40 wt% EMImTFSI SPE is a suitable separator for LIBs.