The development of fiber‐based smart electronics has provoked increasing demand for high‐performance and multifunctional fiber materials. Carbon nanotube (CNT) fibers, the 1D macroassembly of CNTs, have extensively been utilized to construct wearable electronics due to their unique integration of high porosity/surface area, desirable mechanical/physical properties, and extraordinary structural flexibility, as well as their novel corrosion/oxidation resistivity. To take full advantage of CNT fibers, it is essential to understand their mechanical and conductive properties. Herein, the recent progress regarding the intrinsic structure–property relationship of CNT fibers, as well as the strategies of enhancing their mechanical and conductive properties are briefly summarized, providing helpful guidance for scouting ideally structured CNT fibers for specific flexible electronic applications.

Carbon nanotube (CNT) fiber is a promising candidate for lightweight cables. The introduction of metal particles on a CNT fiber can effectively improve its electrical conductivity. However, the decrease in strength is observed in CNT-metal composite fibers. Here we demonstrate a continuous process, which combines fiber spinning, CNT anodization and metal deposition, to fabricate lightweight and high-strength CNT-Cu fibers with metal-like conductivities. The composite fiber with anodized CNTs exhibits a conductivity of 4.08 × 10(4)-1.84 × 10(5) S cm(-1) and a mass density of 1.87-3.08 g cm(-3), as the Cu thickness is changed from 1 to 3 μm. It can be 600-811 MPa in strength, as strong as the un-anodized pure CNT fiber (656 MPa). We also find that during the tensile tests there are slips between the inner CNTs and the outer Cu layer, leading to the drops in electrical conductivity. Therefore, there is an effective fiber strength before which the Cu layer is robust. Due to the improved interfacial bonding between the Cu layer and the anodized CNT surfaces, such effective strength is still high, up to 490-570 MPa.

The fabrication of novel superhydrophobic electrodes is described, which have an air-liquid-solid three-phase interface, where oxygen is sufficient and constant. Oxygen is an effective natural electron acceptor for oxidase, and plays a key role in the development of reliable bioassays. Such an electrode allows detection of glucose concentration, linearly from 50 × 10(-9) m to 156 × 10(-3) m with good sensitivity and accuracy without analyte dilution. This strategy offers a unique route to address the gas-deficit problem of many reaction systems.

The rapid development of wearable electronics needs flexible conductive materials that have stable electrical properties, good mechanical reliability, and broad environmental tolerance. Herein, ultralow‐density all‐carbon conductors that show excellent elasticity and high electrical stability when subjected to bending, stretching, and compression at high strains, which are superior to previously reported elastic conductors, are demonstrated. These all‐carbon conductors are fabricated from carbon nanotube forms, with their nanotube joints being selectively welded by amorphous carbon. The joint‐welded foams have a robust 3D nanotube network with fixed nodes and mobile nanotube segments, and thus have excellent electrical and mechanical stabilities. They can readily scale up, presenting a new type of nonmetal elastic conductor for many possible applications.

Stable mesoporous black TiO2 hollow spheres with controllable diameter, wall thickness and narrow bandgap are fabricated via a small amine molecules encircling strategy, showing high solar-driven photocatalytic hydrogen evolution.

Chemical treatment using concentrated nitric acid (16 M) not only induced significant improvement of mechanical and electrical properties of carbon nanotube fibers due to the enhanced interfacial interaction but also allowed much more efficient deposition of polyaniline for developing fiber-shaped supercapacitors. After the 2 h treatment, the acidized fiber had a tensile strength of 1.52 GPa and an electrical conductivity of 1050 S cm(-1), increased by 52% and 128%, respectively, compared with the untreated one. By depositing polyaniline for 10 min around the fiber, the composite fiber had a volumetric capacitance of 239 F cm(-3), 17% higher than that without the acid treatment. For a long time treatment up to 6 h, although the strength and conductivity decreased slightly, the composite fiber had a super high volumetric capacitance up to 299 F cm(-3). The improvement of electrochemical performance is attributed to the increased deposition rate and structural change of polyaniline due to the existence of functional groups on the fiber surface.

Carbon nanotube (CNT) fiber has not shown its advantage as next-generation light-weight conductor due to the large contact resistance between CNTs, as reflected by its low conductivity and ampacity. Coating CNT fiber with a metal layer like Cu has become an effective solution to this problem. However, the weak CNT-Cu interfacial bonding significantly limits the mechanical and electrical performances. Here, we report that a strong CNT-Cu interface can be formed by introducing a Ni nanobuffer layer before depositing the Cu layer. The Ni nanobuffer layer remarkably promotes the load and heat transfer efficiencies between the CNT fiber and Cu layer and improves the quality of the deposited Cu layer. As a result, the new composite fiber with a 2 μm thick Cu layer can exhibit a superhigh effective strength >800 MPa, electrical conductivity >2 × 10 S/m, and ampacity >1 × 10 A/cm. The composite fiber can also sustain 10 000 times of bending and continuously work for 100 h at 90% ampacity.

The introduction of twist during the spinning of carbon nanotubes from their arrays (forests) has been widely applied in making ultrastrong, stiff, and lightweight nanotube fibers. Here, for the first time, an important observation of a double-peak behavior of the tensile properties, as a function of the twist angle, that is different from the single peak of traditional fibers is reported. Raman spectra show that the new peak arises from the collapse of nanotubes, showing a strong "nano" element in applying the ancient draw-and-twist technique, besides the downsizing. A qualitative continuum model is also presented to describe the collapse-induced enhancement as well as traditional fibers. Our combined experimental and theoretical studies indicate the direction of full utilization of the nano element in improving the mechanical properties of nanotube fibers.