A high-performance flexible and weavable asymmetric fiber-shaped solid-state supercapacitor enhanced by surface modifications of carbon fibers with carbon nanotubes

Abstract

To meet the demands of high energy storage and low productive cost as well as the ability to be incorporated into wearable electronics, we developed a flexible and weavable asymmetric fiber-shaped solid-state supercapacitor (a-FSSC) based on carbon fiber bundle@CNT–NiCo(OH)_x (CF@CNC) and carbon fiber bundle@activated carbon (CF@AC) electrodes with increased operating voltage (1.4–1.6 V) and capacitance. For the positive electrode of CF@CNC, great electrochemical performance enhancement brought about by surface modifications with air plasma and carbon nanotube (CNT) coating is demonstrated. For the negative electrode of CF@AC, a facile and effective way of incorporating activated carbon into carbon fiber bundles is developed. The resultant assembled a-FSSC showed an areal energy and power density of 33.0 μW h cm⁻² and 0.75 mW cm⁻² at 1.6 V, which are better than those of most of the present fiber-shaped supercapacitors. The volumetric energy and power density of 0.84 mW h cm⁻³ and 19.1 mW cm⁻³ are also comparable to the reported results. Its long cycle life (100% capacitance retention after 8000 charge–discharge cycles) reveals its high electrochemical stability. High capacitance retention in the repeated bending (20% decay after 1000 bending times) and torsion (107% retention after 1000 twisting times) tests demonstrated the great flexibility, structural stability and potential utilization of the a-FSSC in wearable electronics. As a demonstration, a woolen fabric woven with three a-FSSCs connected in series can light a blue LED and be worn on the arm.