Dual pseudocapacitive electrode/redox electrolyte systems for asymmetric supercabatteries

Supercabatteries refer to those supercapacitors with supercapacitor-like high power density and battery-like high energy density. In this work, dual pseudocapacitive electrode/redox electrolyte systems, namely MnO2@carbon cloth/Na2SO4 + KI and Fe2O3@carbon cloth/Na2SO4 + ethyl viologen dibromide, have been designed and developed. As the cathodic and anodic systems, they are employed for the construction of asymmetric supercabatteries. The different working potential windows of two systems lead to a cell voltage of as high as 2.0 V. The synergistic effect of two redox species on the electrode and in the electrolyte results in an enlarged capacitance of 509.1 mF cm−2 at a current density of 10 mA cm−2. The supercabattery device delivers a maximal energy of 6.6 Wh L−1 and a maximal power density of 357.6 W L−1. They are higher than those of most of reported manganese oxide//iron oxide based asymmetric supercapacitor devices, and meanwhile comparable to those of some rechargeable batteries. The integration of pseudocapacitive electrodes with redox electrolytes is thus an efficient approach to construct energy storage devices such as supercapacitors with both high power- and energy-densities.