While the market for supercapacitors is rapidly growing due to their high power density, their low energy density compared to batteries represents a great barrier for the future of this technology. The poorly understood chemistry of electrode-electrolyte interfaces implies that there is substantial room for improvement through a careful design of the materials involved. Here we present a unique approach for improving the energy density of supercapacitors through redox additive-assisted electrocatalytic in situ regeneration of the electrode active materials. By utilizing a quinone-based redox electrolyte and a nanostructured conjugated polyaniline electrode, we continually regenerate the reactants, resulting in a redox supercapacitor having an extremely high energy density of 1091Whkg−1 (based on the total mass of the electrode active materials and the redox additive) and a high power density up to 196kWkg−1. Considering the other outstanding properties of the polyaniline-naphthoquinone system, such as extreme flexibility (96% capacity retention after bending at an angle of 180° for 1000 cycles), non-flammability, and excellent cycling stability (84% capacity retention after 7000 cycles at 35Ag−1), such a well designed in situ regeneration of the electrode active materials makes this method a very promising approach towards the development of state-of-the-art energy storage devices.