The present study investigates physicochemical properties of polymer electrolytes and their usage for construction of supercapacitor. The polymer electrolytes (SPE) comprising sulfonated polysulfone (SPSU) as host polymer, Ionic Liquid (1-Ethyl-3-methyl-imidazolium tetrafluoroborate (IL)) as softening agent, and Hexagonal boron nitride (hBN) as nano additive were mixed at various fractions. Different blend formulations were produced and characterized via spectroscopic techniques. The thermal properties of these materials were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Proton conductivity of the nanocomposite polymer electrolytes were analyzed within the temperature range from -20 degrees C to 100 degrees C. The maximum ionic conductivity values of the film containing SPSU/ 0.1 IL and SPSU / %5 hBN / 0.2 IL were measured as 2.5 x 10(-4) and 1.3 x 10(-3) S cm(-1) at 100 degrees C, respectively. The produced membranes have promising dimensional stability, higher conductivity, and better thermal stability. A symmetrical cell of SPSU / %5 hBN/ 0.2 IL sample yielded a maximum specific capacitance of 90.4 F g(-1) at 1 A g(-1). The same electrolyte yielded a maximum energy density in supercapacitor as 43.8 Wh kg(-1) at a power density of 1100 W kg(-1).