In this study, excellent performance and wide operating voltage are obtained with an aqueous electrolyte. Aqueous electrolytes are attracted more attention than other electrolytes (such as organic solvents, ionic liquids) in supercapacitor applications because of their safety, low cost, nontoxicity. Polypyrrole (PPy), aniline 2-sulfonic acid (ASA) modified electrodes are hydrothermal synthesized on carbon felt (CFt) for supercapacitor applications. We investigate the presence of the concentration of ASA on the polymerization of the PPy. Furthermore, a high operating voltage of 3.0 V asymmetric supercapacitor (ASC) with graphite plate is assembled 3 M KCI. CFt/PPy/ASA(0.02)//GP exhibits a high specific capacitance value of 902.9 F g(-1) at 5 mV s(-1) and after 5000 cycle-life testing 93.6% capacitance retention at a scan rate of 1000 mV s(-1). The assembled ASC has an ultrahigh-energy density of 1005 Wh kg(-1) while delivering a power density of 3000 W kg(-1) at a current density of 2 A g(-1). The effect of ASA concentration on the supercapacitor performance has been observed.