Development and supercapacitor application of ionic liquid-incorporated gel polymer electrolyte films

A new gel polymer electrolyte based on 1-methyl-1-propylpyrrolidinium bis(trifluoromethyl sulfonyl)imide ([PMpyr][NTf₂]) entrapped in poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) is prepared and optimized for flexible solid state supercapacitor applications. The structural, thermal, electrical and electrochemical properties of the ionic liquid gel polymer electrolyte membranes are studied by different characterization techniques. The transparent gel polymer electrolyte membranes exhibit high amorphicity and excellent thermal stability. The 20PVdF-HFP:80[PMpyr][NTf₂] gel polymer electrolyte membrane possesses a high ionic conductivity (1.596 × 10⁻³ S cm⁻¹) and wide electrochemical stability window (4.7 V) at room temperature. It is used as the electrolyte material for the fabrication of flexible electric double layer supercapacitors (EDLCs) with multiwalled carbon nanotube (MWCNT)-added and unadded activated carbon (AC) electrodes. The performances of flexible EDLCs are evaluated using cyclic voltammetry and galvanostatic charge–discharge measurements. The EDLC with MWCNT-added AC electrodes exhibits apparently higher specific capacitance of electrode (156.64 F g⁻¹), specific energy (30.69 Wh kg⁻¹) and specific power (4.13 kW kg⁻¹) than that with AC electrodes. The cyclic stability of the former is still in a good condition at the 2000th charge–discharge cycle and much better than the latter. The present comparative study indicates that the 20PVdF-HFP:80[PMpyr][NTf₂] gel polymer electrolyte is a good candidate for the development of flexible solid-state supercapacitors.