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Highly flexible freestanding carbon nanofibers were electroplated with silver for use in supercapacitor applications. The brittle carbon nanofibers were encased within bendable silver shells to provide superior flexibility and resilience of the supercapacitors. The enhanced electrical conductivity derived from the silver shell structure dramatically increased the capacitance of the supercapacitor. The silver shell also conferred structural stability to the carbon core, thus furnishing stable, long-term electrode performance. Nearly 100% of the specific capacitance was retained after N  = 10,000 galvanostatic charge-discharge cycles. The mechanical endurance or stability of the fabricated electrode was evaluated using 1,000 bending cycles, demonstrating that the electrode performance remained unchanged. Cyclic voltammetry and galvanostatic discharge curves were measured at various scan rates and current densities. The fabricated electrodes were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy, which clearly illustrated the carbon-core and silver-shell structure. [ABSTRACT FROM AUTHOR]

Transparent conducting films (TCFs) and transparent heaters (THs) are of interest for a wide variety of applications, from displays to window defrosters. Here, we demonstrate production of highly flexible, conducting, and transparent nickel (Ni) electrodes suitable for use not only in TCFs and THs but also in some other engineering applications. The merging of fibers at their intersections (i.e. self-junctioning) minimizes contact resistance in these films. The Ni electrodes exhibited a remarkably low sheet resistance of 0.73 Ω sq −1 at an optical transmittance of 93%. This low sheet resistance allows them to serve as low-voltage heaters, achieving a heating temperature of 373 °C at an applied voltage of 2 V. The innate corrosion resistance of Ni allows these electrodes to be used in air at temperatures exceeding 200 °C, and it is expected to help the electrodes to find wide use in a range of industrial applications requiring long-term electrode service. Furthermore, we fabricated perfectly core-shell-structured Cu/Ni electrodes, which exhibited both the excellent electrical properties of Cu and the high corrosion resistance of Ni. [ABSTRACT FROM AUTHOR]

• The review focuses on potential of flexible, freestanding binder-free nanofiber electrodes for real time applications. • The advancement of the hollow/porous composite nanofibers, and process parameters are presented. • Morphology engineering over composite nanofibers for enhancing electrochemical performance is reviewed. • Current challenges and future prospect of binder free composite nanofibers for flexible SCs are suggested. The versatile electrospinning technique is scalable and suitable to fabricate highly conducting freestanding carbon nanofiber composite electrodes for energy storage devices. Freestanding/flexible electrodes hold enormous potential for use in wearable electronic devices. Carbon-yielding polymers and the optimal use of sacrificial polymers, metal oxides, and sulfides retain the flexibility and enhance the surface area and pseudocapacitance of electrodes. Both as-prepared electrospun fibers and carbonized nanofibers are compatible with surface decoration via various chemical and electrochemical routes. Metal oxides/sulfides with various morphologies, such as nanocones and nanosheets, can be grown on the carbon nanofibers or on the as-prepared electrospun fibers using chemical synthesis methods such as electrodeposition, hydrothermal processes, and chemical impregnation to enhance the pseudocapacitance of the electrodes. Similarly, the deposition of metal organic frameworks on as-prepared electrospun fibers embellishes these fibers with nanostructures of specific morphologies such as dodecahedral and spindle-shaped structures. Under optimal conditions, these morphologies do not hamper the flexibility of the fibers, and binders are not required to retain them or maintain the electrode integrity. The engineering of electrodes with various morphologies and process parameters is presented systematically. Electrospinning-derived electrodes that have demonstrated significant electrochemical performance are highlighted and critically analyzed, and the energy storage mechanisms of these supercapacitors are described in detail. [ABSTRACT FROM AUTHOR]

• Flexible, freestanding, binder-free nanofiber electrodes for lithium-ion batteries are introduced. • Significance and limitations of electrospinning for fabrication of freestanding electrodes are discussed. • Parameters and polymers for the design of porous and core–shell nanofibers are analyzed. • Feasibility of decorating fibers with nanosheets, nanocones, and polyhedra of active materials is discussed. Carbon nanofibers derived from electrospun precursors show great promise for electronic applications owing to their flexibility, conductivity, high surface area, and open structure. The integration of metal oxides and sulfides in carbon nanofibers, rather than using them with other binders, eliminates many problems caused by poor adhesion, nanomaterial agglomeration, excess mass contributed by inactive binders, and low conductivity of embedded active materials. The engineering of electrospun fibers with novel morphologies, such as core–shell, hollow, or porous structures, and the use of decorated carbon nanofibers (e.g. , by electrodeposition or co-precipitation) are discussed in this review. Representative schematic illustrations of the lithium-storage mechanism for these binder-free electrodes are presented. We describe how the electrospinning technique can offer a cost-effective strategy for fabrication of lightweight lithium-ion batteries with high capacity and excellent bendability. This review presents the fascinating morphologies of these specially designed carbon nanofiber electrodes, which enhance the electrochemical performance of metal oxides and sulfides, illustrating their enormous potential for use in wearable electronic devices and hybrid electric vehicles. [ABSTRACT FROM AUTHOR]

Zeolitic imidazolate framework-derived carbon and metal oxide composites are promising for applications in lithium-ion batteries due to their morphology and porous structure. Herein, we report freestanding carbon nanofibers grafted with amorphous ZnO where the rhombic dodecahedral morphology of the parent (ZIF8) is maintained. The impacts of ZIF8 loading temperature on particle size after pyrolysis and on the electrochemical properties of these hybrid structures for LIBs are investigated. Polyacrylonitrile nanofiber loaded with ZIF8 at 45 °C exhibits a perfect sodalite topology and optimized particle size. The carbonized freestanding composite fibers have a high specific capacity of 818 mAh·g −1 at a current density of 100 mA·g −1 after 100 cycles. This remarkable performance of ZIF8-derived ZnO is due to its loading and coordination chemistry, which facilitates flexible volume changes and continuity in electrical conductivity through a continuous carbon nanofiber. [ABSTRACT FROM AUTHOR]

Development of high performance electrode materials for energy storage is one of the most important issues for our future society. However, a lack of clear analytical views limits critical understanding of electrode materials. This review covers useful analytical work using X-ray diffraction, X-ray absorption spectroscopy, microscopy and neutron diffraction for ion storage systems. The in situ observation facilitates comprehending real-time ion storage behaviour while the ion storage system is operating, which help us to understand detailed physical and chemical properties. We will discuss how the tools have been used to reveal detailed reaction mechanisms and underlying properties of electrode materials. [ABSTRACT FROM AUTHOR]

The surface framework of LiCoO2 is modified through a surface treatment called phosphidation, which suppressed the unwanted phase transition occurring above 4.2 V. The surface instability of LiCoO2 toward organic electrolytes is simultaneously improved by changing its surface structure from an O2-based framework to a PO4-based framework that can protect against HF attack during cycling. Phosphidated LiCoO2 is successfully synthesized that showed greater stability in its bulk and surface structures. The phosphidated form enables faster Li+ diffusion and prevents irreversible phase transitions, especially when charged above 4.2 V, and consequently demonstrates excellent cycling performance and rate capabilities. The improved kinetics and stability resulting from phosphidation make LiCoO2 highly suitable as a high-voltage cathode material for use in lithium ion batteries. [ABSTRACT FROM AUTHOR]

Highlights: [•] Loosely arranged decahedral particles formed larger bulk particles on fluorine substitution. [•] At high potentials, fluorine coating reduces surface damage and improves lithium diffusion and thereby capacity retention. [•] Fluorine substitution triggers the formation of layered–layered–spinel, which stabilized the electrode structures. [•] Formation of layered-layered-spinel counters voltage decay upon subsequent cycling. [Copyright &y& Elsevier]

Abstract: Lithium iron phosphate–carbon (LiFePO4–C) composites with various amounts of Fe2P are synthesized by ball-milling coupled with microwave heating to serve as cathodes for lithium-ion batteries. LiFePO4–C in which Fe2P is restrained below a critical concentration gives as very high discharge capacity of 165mAhg−1, excellent rate capability (85.4% C/50-rate discharge capacity at 2C) and stable cyclic retention for 250 cycles. Above the critical concentration however, electrochemical performance deterioated. Analysis and debate, based on a comparison of the physical and electrochemical properties among LiFePO4–C composites with the variation of Fe2P, proceeded to the conclusion that below the critical concentration, Fe2P enhanced the conductivity of LiFePO4–C, whereas above the critical concentration, it blocked the one-dimensional Li+ pathways in LiFePO4 and might hinder Li+ movement in LiFePO4. Therefore, in order to obtain a LiFePO4–C composite that enhances electrochemical performance, it is concluded that the amount of Fe2P should be carefully controlled below its critical concentration. [Copyright &y& Elsevier]