In the present work, we investigated physical properties as well as supercapacitor application of nanocomposite polymer gel electrolytes. The polymer electrolyte (PE) consists of Ionic Liquid, (1-Ethyl-3-methyl-imidazolium tetrafluoroborate (IL)) as a softening agent, aluminum oxide (Al2O3) as a nano additive and sulfonated polysulfone (SPSU) as the main polymer. The resulting nanocomposite gel polymer electrolyte structure was characterized using spectroscopic methods. Thermal characteristic properties of polymeric nanocomposites were investigated by performing differential scanning calorimetry (DSC) and terhmogravimetric analysis (TGA). Conductivity measurements of the materials were obtained between -20 degrees C and 100 degrees C at varying temperature intervals. The highest ionic conductivity values were obtained from the SPSU / 0.1 IL and SPSU / 5% Al2O3 / 0.2 IL polymer electrolyte structures as 2.5 x10(-4) and 2.06 x10(-3) S cm(-1) at 100 degrees C, respectively. The maximum specific capacitance value of 144 F g(-1) was obtained from SPSU / 5% Al2O3 / 0.2 IL polymer electrolyte based system at a current density of 1 A g(-1). The supercapacitor reached an energy density of 20 Wh kg(-1) at a power density of 1028 W kg(-1). In addition, the supercapacitor has shown a remarkable capacitance retention with a performance loss of only about 10% after 5000 cycles.