A new asymmetric supercapacitor (ASC) was fabricated using flower like alpha-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), galvano static 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(-1) and 35.4 Wh kg(-1) respectively was achieved by adding of KI into Li2SO4 electrolyte, while it was only 29 F g(-1) and 10.2 Wh kg(-1) for pristine (Li2SO4) electrolyte used ASC at 1.5 mA cm(-2). (C) 2013 Elsevier Ltd. All rights reserved.