A Wire-Shaped Supercapacitor in Micrometer Size Based on Fe_3O_4 Nanosheet Arrays on Fe Wire

One-dimensional(1D, wire-and fiber-shaped)supercapacitors have recently attracted interest due to their roll-up, micrometer size and potential applications in portable or wearable electronics. Herein, a 1D wireshaped electrode was developed based on Fe_3O_4 nanosheet arrays connected on the Fe wire, which was prepared via oxidation of Fe wire in 0.1 M KCl solution(pH 3) with O2-rich environment under 70 °C. The obtained Fe_3O_4 nanosheet arrays displayed a high specific capacitance(20.8 m F cm^(-1) at 10 mV s^(-1)) and long cycling lifespan(91.7% retention after 2500 cycles). Theexcellent performance may attribute to the connected nanosheet structure with abundant open spaces and the intimate contact between the Fe_3O_4 and iron substrate. In addition, a wire-shaped asymmetric supercapacitor was fabricated and had excellent capacitive properties with a high energy density(9 l Wh cm^(-2)) at power density of 532.7 l W cm^(-2) and remarkable long-term cycling performance(99% capacitance retention after 2000 cycles).Considering low cost and earth-abundant electrode material, as well as outstanding electrochemical properties, the assembled supercapacitor will possess enormous potential for practical applications in portable electronic device.

High loading carbon nanotubes deposited onto porous nickel yarns by solution imbibition as flexible wire-shaped supercapacitor electrodes

The deposition of active materials directly onto metal wires is a general strategy to prepare wire-shaped electrodes for flexible and wearable energy storage devices. However, it is still a critical challenge to coat active materials onto the aimed metal wires because of their smooth surface and small specific surface area. In this work, high porous nickel yarns（PNYs） was fabricated using commercial nylon yarns as templates through step-wise electroless plating, electroplating and calcination processes. The PNYs are composed of multiplied fibers with hollow tubular structure of 5–10 μm in diameter, allowing the imbibition of carbon nanotubes（CNTs） solution by a facile capillary action process. The prepared CNTs/PNY electrodes showed a typical electrochemical double layer capacitive performance and the constructed allsolid flexible wire-shaped symmetric supercapacitors provided a specific capacitance of 4.67 F/cm3 with good cycling stability at a current density of 0.6 A/cm3.

Wire-Shaped 3D-Hybrid Supercapacitors as Substitutes for Batteries

We report a wire-shaped three-dimensional(3D)-hybrid supercapacitor with high volumetric capacitance and high energy density due to an interconnected 3D-configuration of the electrode allowing for large number of electrochemical active sites,easy access of electrolyte ions,and facile charge transport for flexible wearable applications.The interconnected and compact electrode delivers a high volumetric capacitance(gravimetric capacitance)of 73 F cm−3(2446 F g−1),excellent rate capability,and cycle stability.The 3D-nickel cobalt-layered double hydroxide onto 3D-nickel wire(NiCo LDH/3D-Ni)//the 3D-manganese oxide onto 3D-nickel wire(Mn3O4/3D-Ni)hybrid supercapacitor exhibits energy density of 153.3 Wh kg−1 and power density of 8810 W kg−1.The red lightemitting diode powered by the as-prepared hybrid supercapacitor can operate for 80 min after being charged for tens of seconds and exhibit excellent electrochemical stability under various deformation conditions.The results verify that such wire-shaped 3D-hybrid supercapacitors are promising alternatives for batteries with long charge–discharge times,for smart wearable and implantable devices.

An efficient chemical reduction-induced assembly of Fe_(3)O_(4)@graphene fiber for wire-shaped supercapacitors with ultrahigh volumetric energy density

Benefiting from high flexibility and weavability,the wire-shaped supercapacitors(SCs)arouse tremendous interests for the applications in wearable/portable electronics.Graphene fiber(GF)is considered as a promising linear electrode for wire-shaped SCs.However,the bottleneck is how to develop the GF-based linear electrode with facile fabrication process while wellmaintaining satisfactory electrochemical performance.Herein,a novel Fe_(3)O_(4)@GF composite linear electrode is proposed via a chemical reduction-induced assembly approach,in which the GO and Fe_(3)O_(4) nanoparticles(NPs)realize the efficient selfassembly owing to the electrostatic and van der Waals interactions,as well as the sufficient reduction of GO during the preparation process.The resultant fiber-shaped architecture shows boosted charge-transfer kinetics,high flexibility and structural integrity.Such Fe_(3)O_(4)@GF linear electrode exhibits excellent electrochemical behaviors including a large volumetric specific capacitance(~250.75 F cm^(−3)),remarkable rate capability and favorable electrochemical kinetics in aqueous electrolyte,superior than previously reported GF-based linear electrodes.For real application,a high-performance wire-shaped SC with excellent flexibility and weavability is fabricated based on such Fe_(3)O_(4)@GF linear electrode and gel electrolyte,demonstrating ultrahigh volumetric energy density(18.8 mWh cm^(−3)),power density(4000 mW cm^(−3))and strong durability(~93.5%retention after 10000 cycles).Prospectively,the fabricated wire-shaped SC can maintain reliable electrochemical behaviors in various deformation states,showing its potentials in future portable and wearable devices.