Flexible supercapacitor with superior length and volumetric capacitance enabled by a single strand of ultra-thick carbon nanotube fiber

Abstract

Fiber-shaped supercapacitors (FSSCs) based on next-generation carbon-based fibers are widely recognized as the most promising power supplies for wearable devices; however, achieving a high capacitance in weight, volume, and length simultaneously with a single fiber, which is necessary to realize practical FSSCs, has rarely been reported. Here, we show for the first time that a single ultra-thick carbon nanotube fiber (UCNTF, 10 tex) with high linear density can function as a practical electrode material in FSSCs. A series of sonochemical treatments is used to modify the internal structure and physical properties of pristine UCNTFs and to further synthesize pseudocapacitive active materials (i.e., polyaniline (PANI)). PANI in its most electrochemically useful state uniformly incorporated into purified UCNTFs with a controlled morphology and functional groups, facilitating the penetration of ions and promoting a reversible redox reaction between the electrolyte ions and the fiber. A symmetric FSSC fabricated using the prepared PANI-incorporated UCNTF exhibits a high specific capacitance of 335F/g at 1 A/g, an excellent volumetric capacitance of 523.3F cm−3, and an outstanding length capacitance of 96.5 mF cm−1 without additional fibers being added. In addition, the FSSC exhibits high flexibility (98.4 % at a bending angle of 90°) and high stability (80.1 % after 20,000 bending cycles). We believe that this first report of the preparation of an FSSC using a single CNTF, which can be conducted on an industrial scale, will open new opportunities for commercializing wearable energy storage devices.