Preparation and characterization of gel polymer electrolytes containing N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide ionic liquid for lithium ion batteries

Gel polymer electrolytes containing N-butyl-N-methylpyrrolidinum bis(trifluoromethanesulfonyl) imide (PYR₁₄TFSI) ionic liquid are prepared by the solution casting method. Thermal and electrochemical properties have been determined for these gel polymer electrolytes. The electrical properties are investigated in detail by the linear sweep voltammetry, cyclic voltammetry and impedance spectroscopy with the aid of the equivalent circuit fitting of the impedance spectra. The results show that the studied electrolytes have good self-standing characteristics, and also a sufficient level of thermal stability and a good electrochemical window. The conductivity increases with increasing amount of mixture, and for the studied system, the highest value of the conductivity measured at room temperature is 4.0 × 10^-4 S cm^-1. The lithium ions transference number reaches the maximum value when the gel electrolyte contains 33.3 wt% PYR₁₄TFSI ionic liquid. Based on the experiments, measurements and fitting, the models describing the lithium ion transmission and the properties of electrolyte/electrode interface are developed.