Menghe Miao

Core-spun carbon nanotube yarn supercapacitors for wearable electronic textiles

Linear (fiber or yarn) supercapacitors have demonstrated remarkable cyclic electrochemical performance as power source for wearable electronic textiles. The challenges are, first, to scale up the linear supercapacitors to a length that is suitable for textile manufacturing while their electrochemical performance is maintained or preferably further improved and, second, to develop practical, continuous production technology for these linear supercapacitors. Here, we present a core/sheath structured carbon nanotube yarn architecture and a method for one-step continuous spinning of the core/sheath yarn that can be made into long linear supercapacitors. In the core/sheath structured yarn, the carbon nanotubes form a thin surface layer around a highly conductive metal filament core, which serves as current collector so that charges produced on the active materials along the length of the supercapacitor are transported efficiently, resulting in significant improvement in electrochemical performance and scale up of the supercapacitor length. The long, strong, and flexible threadlike supercapacitor is suitable for production of large-size fabrics for wearable electronic applications.

High‐Performance Two‐Ply Yarn Supercapacitors Based on Carbon Nanotube Yarns Dotted with Co3O4 and NiO Nanoparticles

Yarn supercapacitors are promising power sources for flexible electronic applications that require conventional fabric-like durability and wearer comfort. Carbon nanotube (CNT) yarn is an attractive choice for constructing yarn supercapacitors used in wearable textiles because of its high strength and flexibility. However, low capacitance and energy density limits the use of pure CNT yarn in wearable high-energy density devices. Here, transitional metal oxide pseudocapacitive materials NiO and Co3 O4 are deposited on as-spun CNT yarn surface using a simple electrodeposition process. The Co3 O4 deposited on the CNT yarn surface forms a uniform hybridized CNT@Co3 O4 layer. The two-ply supercapacitors formed from the CNT@Co3 O4 composite yarns display excellent electrochemical properties with very high capacitance of 52.6 mF cm(-2) and energy density of 1.10 μWh cm(-2) . The high performance two-ply CNT@Co3 O4 yarn supercapacitors are mechanically and electrochemically robust to meet the high performance requirements of power sources for wearable electronics.

Gamma-Irradiated Carbon Nanotube Yarn As Substrate for High-Performance Fiber Supercapacitors

As an electrical double layer capacitor, dry-spun carbon nanotube yarn possesses relatively low specific capacitance. This can be significantly increased as a result of the pseudocapacitance of functional groups on the carbon nanotubes developed by oxidation using a gamma irradiation treatment in the presence of air. When coated with high-performance polyaniline nanowires, the gamma-irradiated carbon nanotube yarn acts as a high-strength reinforcement and a high-efficiency current collector in two-ply yarn supercapacitors for transporting charges generated along the long electrodes. The resulting supercapacitors demonstrate excellent electrochemical performance, cycle stability, and resistance to folding-unfolding that are required in wearable electronic textiles.

High Performance Carbon Nanotube Yarn Supercapacitors with a Surface-Oxidized Copper Current Collector.

Threadlike linear supercapacitors have demonstrated high potential for constructing fabrics to power electronic textiles (eTextiles). To improve the cyclic electrochemical performance and to produce power fabrics large enough for practical applications, a current collector has been introduced into the linear supercapcitors to transport charges produced by active materials along the length of the supercapacitor with high efficiency. Here, we first screened six candidate metal filaments (Pt, Au, Ag, AuAg, PtCu, and Cu) as current collectors for carbon nanotube (CNT) yarn-based linear supercapacitors. Although all of the metal filaments significantly improved the electrochemical performance of the linear supercapacitor, two supercapacitors constructed from Cu and PtCu filaments, respectively, demonstrate far better electrochemical performance than the other four supercapacitors. Further investigation shows that the surfaces of the two Cu-containing filaments are oxidized by the surrounding polymer electrolyte in the electrode. While the unoxidized core of the Cu-containing filaments remains highly conductive and functions as a current collector, the resulting CuO on the surface is an electrochemically active material. The linear supercapacitor architecture incorporating dual active materials CNT + Cu extends the potential window from 1.0 to 1.4 V, leading to significant improvement to the energy density and power density.

Flexible Asymmetric Threadlike Supercapacitors Based on NiCo2Se4Nanosheet and NiCo2O4/Polypyrrole Electrodes

Flexible threadlike supercapacitors with improved performance are needed for many wearable electronics applications. Here, we report a high performance flexible asymmetric all-solid-state threadlike supercapacitor with a NiCo2 Se4 positive electrode and a NiCo2 O4 @PPy (PPy: polypyrrole) negative electrode. The as-prepared electrodes display outstanding volume specific capacitance (14.2 F cm-3 ) and excellent cycling performance (94 % retention after 5000 cycles at 0.6 mA) owing to their nanosheet and nanosphere structures. The asymmetric all-solid-state threadlike supercapacitor expanded the stability voltage window from 0-1.0 V to 0-1.7 V and exhibits high volume energy density (5.18 mWh cm-3 ) and superior flexibility under different bending conditions. This study provides a scalable method for fabricating high performance flexible supercapacitors from easily available materials for use in wearable and portable electronics.

Self-assembly of amido-ended hyperbranched polyester films with a highly ordered dendritic structure.

Self-assemblies fabricated from dendrimers and amphiphilic polymers have demonstrated remarkable performances and a wide range of applications. Direct self-assembly of hyperbranched polymers into highly ordered macrostructures with heat-resistance remains a big challenge due to the weak amphiphilicity of the polymers. Here, we report the self-assembly of amphiphilic amido-ended hyperbranched polyester (HTDA-2) into millimeter-size dendritic films using combined hydrogen bond interaction and solvent induction. The self-assembly process and mechanism have been studied. Hydrogen bond interaction between amido-ended groups assists the aggregation of inner and outer chains of the HTDA-2, resulting in phase separation and micelle formation. Some micelles attach to and grow on the glass substrate like seedlings. Other micelles move to the seedlings and connect with their branches via solvent induction and hydrogen bond interaction, leading to the fabrication of highly ordered crystalline dendritic films that show high heat-resistance. HTDA-2 can further self-assemble into sheet crystals on the dendritic films.

Synthesis of a Degradable High-Performance Epoxy-Ended Hyperbranched Polyester

Degradation and recycling of cured thermosetting epoxy resins are major challenges to the industry. Here, a low-viscosity, degradable epoxy-ended hyperbranched polyester (DEHP) is synthesized by a reaction between epichlorohydrin and a carboxyl-ended hyperbranched polyester (DCHP) obtained from an esterification between citric acid and maleic anhydride. The chemical structures of DCHP and DEHP were characterized by Fourier transform infrared and 1H NMR. DEHP has a positive effect on reinforcing and toughening of the diglycidyl ether of bisphenol-A (DGEBA). With an increase in the content and molecular weight of DEHP, the mechanical performances of the cured DEHP/DGEBA composites, including the tensile, flexural, and impact strengths, increase first and then decrease. The improvements on the tensile, flexural, and impact strengths were 34.2–43.4%, 35.6–48.1%, and 117.9–137.8%, respectively. Moreover, the DEHP also promotes degradation of the cured DEHP/DGEBA composites. The degree of degradation of the cured DEHP/DGEBA composites increases with an increase of the DEHP content and molecular weight. The composites containing 12 wt % DEHP can be degraded completely in only about 2 h at about 90 °C, compared with the degradation degree (35%) of cured DGEBA, indicating good degradation and recycling properties of the DEHP.

Novel core/shell CoSe2@PPy nanoflowers for high-performance fiber asymmetric supercapacitors

Nanostructured CoSe2 chrysanthemum flower are synthesized via a simple hydrothermal route. The highly hierarchical and electrochemically active material is electrodeposited with PPy to produce high performance CoSe2@PPy core/shell structured electrodes. A flexible fiber asymmetric supercapacitor (FASC) assembled from a CoSe2@PPy core/shell positive electrode and an electrochemically activated carbon fiber (EACF) negative electrode exhibits high volumetric energy density, superior flexibility and long lifespan. The resulting FASC has been used to power a mini-scale flexible photodetector, demonstrating great potential for the development of high performance energy storage devices.

Wearable supercapacitors based on conductive cotton yarns

High-performance fiber- and yarn-shaped supercapacitors based on commonly available fiber materials and production technologies are needed to meet the fast developing electronic textile market. In this investigation, natural cotton and stainless steel fibers (SSFs) are blended to form a conductive yarn for constructing novel high-performance two-ply yarn supercapacitors. The supercapacitors show very high areal capacitance, energy density, flexibility and electrochemical stability. The excellent performance is attributed to the high porosity, high conductivity and distributive metal fiber network formed in the blended yarn, coupled with the high electrochemical efficiency of the nanostructured polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT:PSS) pseudocapacitance materials. The SSF-cotton blended yarn is economic to produce and retains the flexibility of a normal cotton yarn that is commonly used in apparel textiles. This greatly facilitates the integration of the two-ply yarn supercapacitor into electronic textiles.

Influence of vinyl-terminated hyperbranched polyester on performance of films obtained by UV-initiated thiol–ene click reaction of A 2 + B 3 system

UV curing technology has become an efficient method to fabricate films with desirable properties, although it is susceptible to oxygen inhibition, resulting in low conversion of double bonds and poor mechanical performance. Thiol–ene click reaction can overcome the shortcomings of common UV curing techniques. In this paper, the vinyl-terminated hyperbranched polyester (VTDP) was incorporated into the curing system of di-ene (A2) and trithiol (B3). Trithiols, including 1,3,5-tris(2-hydroxyethyl)isocyanurate tris(3-mercaptopropionate) (THMP) and trimethylolpropane tris(3-mercaptopropionate) (TMMP), were synthesized by an esterification between 3-mercaptopropionic acid and 1,3,5-tris(2-hydroxyethyl) isocyanurate, and tri(hydroxymethyl)propane, respectively. The UV-initiated thiol–ene click reaction between 1,4-butanediol diacrylate (BDDA) and trithiols (TMMP and THMP) was researched by adjusting different VTDP content. FTIR spectral analysis showed that the thiol–ene reactions proceeded smoothly and the conversion degree of acrylic groups was higher than that of thiol groups. The pencil hardness and abrasion resistance of the cured film increased first and then decreased with the increase in VTDP content, but both their flexibility and adhesion had little change. Their glass transition temperatures increased slightly with the increase in VTDP content. THMP has better positive effect than TMMP on the pencil hardness, abrasion resistance and thermal performance of the cured film.