Fabricating a high-energy-density supercapacitor with asymmetric aqueous redox additive electrolytes and free-standing activated-carbon-felt electrodes

By Tian, Meng; Wu, Jiawen; Li, Ruihan; Chen, Youlin; Long, Donghui
Published in Chemical Engineering Journal 2019

Abstract

Aqueous carbon-based supercapacitors are now reaching the energy density limits set by electric double layer mechanism and water decomposition voltage window. Here, we construct a high-energy-density carbon-based supercapacitor with a new strategy of asymmetric electrolyte design by adding K3[Fe(CN)6] and 2,6-dihydroxyanthraquinone (2,6-DHAQ) as positive and negative redox additives in 2 M KOH solution respectively. Modified activated carbon felt (ACF) serves as low-cost free-standing electrodes with no binders and conductive additives, porous structure of which facilitates excellent electrolyte permeability and fast ion transport. And it shows great potential for large-scale energy storage due to unique flexible and scalable properties. The corresponding supercapacitor integrating the advantages of redox activity of K3[Fe(CN)6] in positive potential and 2,6-DHAQ in negative potential achieves higher ion utilization, extended operation window to 2 V, high cell capacitance of 79 F g?1 and excellent cycling performance with 84% capacitance retention after 5000 cycles. Most importantly, it delivers high energy density of 39.1 Wh kg?1 maintaining superior power density, much higher than those of previously reported supercapacitors with symmetric aqueous redox electrolytes. The asymmetric redox additives in aqueous electrolytes for ACF-based supercapacitors may represent a new approach to high-performance energy storage.

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