A new asymmetric supercapacitor (ASC) was fabricated using flower like  _-Bi2O3as negative and bio-waste derived activated carbon (AC) as positive electrodes with Li2SO4as electrolyte. Here, the fabricated ASC was operated over the potential range of 0-1.6 V and evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycle life. Further to improve the performance of ASC, KI was used as electrolyte redox additive with pristine (Li2SO4) electrolyte due to their possible redox reactions of iodine ions. Remarkably, a nearly threefold improved specific capacitance and energy density of 99.5 F g⁻¹and 35.4 Wh kg⁻¹respectively was achieved by adding of KI into Li₂SO₄ electrolyte, while it was only 29 F g⁻¹and 10.2 Wh kg⁻¹for pristine (Li2O4)electrolyte used ASC at 1.5 mA cm⁻².