The superb mechanical and physical properties of individual carbon nanotubes (CNTs) have provided the impetus for researchers in developing high-performance continuous fibers based upon CNTs. The reported high specific strength, specific stiffness and electrical conductivity of CNT fibers demonstrate the potential of their wide application in many fields. In this review paper, we assess the state of the art advances in CNT-based continuous fibers in terms of their fabrication methods, characterization and modeling of mechanical and physical properties, and applications. The opportunities and challenges in CNT fiber research are also discussed.

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While the emerging wire-shaped supercapacitors (WSS) have been demonstrated as promising energy storage devices to be implemented in smart textiles, challenges in achieving the combination of both high mechanical stretchability and excellent electrochemical performance still exist. Here, an asymmetric configuration is applied to the WSS, extending the potential window from 0.8 to 1.5 V, achieving tripled energy density and doubled power density compared to its asymmetric counterpart while accomplishing stretchability of up to 100% through the prestrainning-then-buckling approach. The stretchable asymmetric WSS constituted of MnO2/CNT hybrid fiber positive electrode, aerogel CNT fiber negative electrode and KOH-PVA electrolyte possesses a high specific capacitance of around 157.53 μF cm(-1) at 50 mV s(-1) and a high energy density varying from 17.26 to 46.59 nWh cm(-1) with the corresponding power density changing from 7.63 to 61.55 μW cm(-1). Remarkably, a cyclic tensile strain of up to 100% exerts negligible effects on the electrochemical performance of the stretchable asymmetric WSS. Moreover, after 10,000 galvanostatic charge-discharge cycles, the specific capacitance retains over 99%, demonstrating a long cyclic stability.

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Due to their exceptional flexibility and transparency, CVD graphene films have been regarded as an ideal replacement of indium tin oxide for transparent electrodes, especially in applications where electronic devices may be subjected to large tensile strain. However, the search for a desirable combination of stretchability and electrochemical performance of such devices remains a huge challenge. Here, we demonstrate the implementation of a laminated ultrathin CVD graphene film as a stretchable and transparent electrode for supercapacitors. Transferred and buckled on PDMS substrates by a prestraininig-then-buckling strategy, the four-layer graphene film maintained its outstanding quality, as evidenced by Raman spectra. Optical transmittance of up to 72.9% at a wavelength of 550 nm and stretchability of 40% were achieved. As the tensile strain increased up to 40%, the specific capacitance showed no degradation and even increased slightly. Furthermore, the supercapacitor demonstrated excellent frequency capability with small time constants under stretching.

Motivated by their unique structure and excellent properties, significant progress has been made in recent years in the development of graphene-based fibers (GBFs). Potential applications of GBFs can be found, for instance, in conducting wires, energy storage and conversion devices, actuators, field emitters, solid-phase microextraction, springs, and catalysis. In contrast to graphene-based aerogels (GBAs) and membranes (GBMs), GBFs demonstrate remarkable mechanical and electrical properties and can be bent, knotted, or woven into flexible electronic textiles. In this review, the state-of-the-art of GBFs is summarized, focusing on their synthesis, performance, and applications. Future directions of GBF research are also proposed.

conventional 3D and 2D types when used for miniaturized electronic devices, textile electronics, and implantable medical devices. [1,2] However, compared with other energy storage devices such as batteries, the much lower stored specific energy of 1D supercapacitors limited their practical applications. Since the energy stored in a supercapacitor is proportional to CV 2 (E = 1/2 CV 2 , where C is the capacitance of the device and V is the operating voltage), enhancements in energy density can be achieved by increasing the specific capacitance (C) or widening the operating voltage range (V). [3] Specific capacitance can be improved by the incorporation of electrochemically active nanomaterials (e.g., metal oxides or conducting polymers) into the base electrode materials, such as carbon nanotube (CNT) or graphene assemblies. In comparison, insufficient attention has been paid to improve the voltage range of flexible supercapacitors. This is especially true in fiber-shaped supercapacitors (FSSs), which usually show ideal capacitive behavior only in a relatively small potential window (0.8-1.0 V), [4][5][6][7][8][9][10][11][12][13][14] and consequently deliver limited energy or power densities. An effective approach for addressing this issue is the strategy of asymmetric electrode configuration by coupling different positive and negative electrode materials with well-separated potential windows for achieving a high operating voltage. [15][16][17][18] So far, several papers addressing asymmetric FSS can be found in the literature. A fiber-based flexible all-solid state asymmetric supercapacitor using molybdenum disulfide (MoS 2 )-reduced graphene oxide (rGO)/multiwalled carbon nanotube (MWCNT) and rGO/MWCNT fibers has accomplished a potential window of 1.4 V with high Coulombic efficiency and improved energy density. [19] Cheng et al. reported an asymmetric fiber-shaped supercapacitor based on MnO 2 /conducting polymer/CNT fiber and ordered microporous carbon/ CNT hybrid fiber as positive and negative electrode, respectively, which produced a high energy density of 11.3 mW h cm −3 . [20] Yang et al. fabricated a fiber-shaped asymmetric supercapacitor by using porous NiO/Ni(OH) 2 /PEDOT/contra wire electrode as the positive electrode, and the ordered mesoporous carbon fiber as the negative electrode. The supercapacitor exhibited an output voltage of 1.5 V. [21] Wang et al. used titanium wire/cobalt oxide (Co 3 O 4 ) nanowires and carbon fibers/graphene electrodes to fabricate an asymmetric supercapacitor, which enhanced both stored energy and delivered power by at least 1860% compared with that of the supercapacitor with a potential window The emerging fiber-shaped supercapacitors (FSSs) have motivated tremendous research interest in energy storage devices. However, challenges still exist in the pursuit of combination of excellent electrochemical performance and mechanical stretchability. Here, a core-sheath asymmetric FSS is first made by wrapping gel electrolyte coated carbon nanotube (CNT)@MnO 2 core fiber with CNT@...

The emergence of stretchable electronic devices has attracted intensive attention. However, most of the existing stretchable electronic devices can generally be stretched only in one specific direction and show limited specific capacitance and energy density. Here, we report a stretchable isotropic buckled carbon nanotube (CNT) film, which is used as electrodes for supercapacitors with low sheet resistance, high omnidirectional stretchability, and electro-mechanical stability under repeated stretching. After acid treatment of the CNT film followed by electrochemical deposition of polyaniline (PANI), the resulting isotropic buckled acid treated CNT@PANI electrode exhibits high specific capacitance of 1147.12 mF cm(-2) at 10 mV s(-1). The supercapacitor possesses high energy density from 31.56 to 50.98 μWh cm(-2) and corresponding power density changing from 2.294 to 28.404 mW cm(-2) at the scan rate from 10 to 200 mV s(-1). Also, the supercapacitor can sustain an omnidirectional strain of 200%, which is twice the maximum strain of biaxially stretchable supercapacitors based on CNT assemblies reported in the literature. Moreover, the capacitive performance is even enhanced to 1160.43-1230.61 mF cm(-2) during uniaxial, biaxial, and omnidirectional elongations.