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This work exploits the advantage of asymmetric configuration over symmetric supercapacitor in designing high energy density flexible devices from two active electrode materials–keratin‐based renewable‐resource hierarchically porous carbon and hydrous ruthenium oxide (RuO2). The asymmetric device exhibits significantly high capacitance. Conventional estimation of energy storage parameters, however, cannot be applied for devices with a Faradaic energy storage contribution via redox charge transfer mechanism. Therefore, this work applies a precise measurement of pseudocapacitance contribution at various scan rates to correct the device data that reveals effective capacitance of 120 F g−1 with the energy density of 37 W h kg−1 at 776 W kg−1. It also retains excellent rate capability, >74% at high current density 25 A g−1. The charge storage activity and device stability can be further enhanced by introducing redox‐active electrolytes that improve specific capacitance, but the rate capabilities deteriorate at high current densities. Further, the principle of asymmetric electrode design is applied to fabricate a bending‐tolerant, flexible device by depositing active electrode material on wire‐shaped current collector followed by coupling those separated with polyvinyl alcohol gel containing redox electrolyte; it yields 36.8 mF cm−1 specific capacitance at a 0.2 mA cm−1 current density. [ABSTRACT FROM AUTHOR]

• Chemical-free synthesis technique was employed for the synthesis of the composite. • Waste keratin fibers were used as a carbon precursor. • ROKF-2 delivers excellent true specific capacitance of 2556 F g−1 at 2 A g−1. • In double hybridization assembly, the device depicts a true capacitance of 238 F g−1 at 1 A g−1. • In K 3 Fe(CN) 6 redox mediator electrolyte, the device shows an energy density of 265 Wh Kg−1 at a power density of 1000 W kg−1. • The flexible device delivers 142 mF cm−1 at a scan rate of 10 mV s−1. The present study exploits a chemical-free, low-cost, simple, scalable, and facile synthesis technique using an in-situ methodology to prepare composite electrodes. The as-synthesized composite is utilized as a hybrid electrode for supercapacitor application. The hydrous RuO 2 and keratin fiber-derived carbon (ROKF-2) show excellent specific capacitance of 3542 F g−1 at 2 A g−1. However, true analysis reveals that the actual capacitance is 2556 F g−1. It focuses on delivering the actual performance of the hybrid device by eliminating the use of conventional equations. In symmetric assembly, the excellent device capacitance of 121 F g−1 at 1 A g-1 is achieved while maintaining its coulombic efficiency above 90% throughout the applied current. The double hybridization assembly shows the broadening of working potential with an outstanding energy density of 226 Wh kg−1 at 1000 W Kg−1. Upon introducing redox additives, the performance increases, suggesting their effective contribution to the charge storage process. In the presence of K 3 Fe(CN) 6 , the device delivers a remarkable rate capability of 50% till 5 A g−1, whereas, in the KI environment, the device efficiency gets enhanced ∼45%. The wire-shaped flexible device shows a specific capacitance of 142 mF cm−1 at a scan rate of 10 mV s−1 with an energy density of 0.03 mWh cm−1 at 33 W cm−1. The process approaches a chemical-free process for the composite synthesis, which can be utilized in various hybridization modes. The study eliminates the traditional equations to minimize the overestimated electrochemical performance. The prepared composites pave a new path in hybrid energy storage systems. [Display omitted] [ABSTRACT FROM AUTHOR]

• Concentric core-shell design for wire-shaped lithium-ion capacitor (WSLIC) • All-solid-state WSLIC using a solid polymer electrolyte. • Helically wrapped current collectors provide structural support like spring. • Comparable volumetric energy density with other wire-shaped lithium-ion battery. • Highly bendable WSLIC without degradation in electrochemical performances. Flexible wire shaped energy storage devices grab tremendous attention due to the emergence of wearable and portable electronics markets. Herein, the design principles (fabrication and assembly process) and device performance (electrochemical performance in static and bending conditions) of the lithium-ion capacitor in core-shell wire topology are described. The wire shaped lithium-ion capacitor (WSLIC) assembly consists of multi-walled carbon nanotubes coated carbon fibers (CNT-CFs) core electrode, polymer electrolytes, lithium titanium oxide (LTO) composite outer electrode, helically wrapped current collectors and protective outer covering. This 2.7 V device exhibits a maximum energy density of 1.85 mWh/cm3, comparable to the energy densities of other reported wire-shaped batteries. WSLIC exhibits excellent safety at a high temperature of 60 °C due to plasticized polymer electrolytes of non-volatile composition, challenges may arise if flammable organic electrolytes were employed. The device also exhibits excellent electrochemical performance under different deforming and repeated bending conditions, attributed to unique properties of CNT-CF core electrode and helically wrapped current collectors. Therefore, WSLIC has excellent potential for implementation in wearable applications. [ABSTRACT FROM AUTHOR]

Heteroatom-doped graphene and its derived layered materials play a substantial role in several emerging science fields, demonstrating great potential for implementation in new devices and for improving the performance of existing technologies. A wide variety of strategies have been applied for the controlled synthesis and for achieving the intended doping/co-doping levels in the carbon network of graphene-based materials. Precise and reproducible doping is crucial for altering the Fermi energy level and to tune the band gap according to the desired device/application. Heteroatom-doped and co-doped graphene-based materials (n-type and p-type doping) have been synthesized for devices in energy-related applications using various chemical and physical routes. In this review article, we survey the most recent research works on the synthesis of heteroatom-doped graphene materials such as reduced graphene oxide, graphene oxide, graphene quantum dots and graphene nanoribbons. Applications of these materials in energy storage/conversion devices (supercapacitors, batteries, fuel cells, water splitting and solar cells) are also reviewed. Finally, the challenges and future perspectives for heteroatom-doped graphene materials are briefly discussed. We hope this article offers a useful starting point for researchers entering the field, providing an overview of synthesis approaches and energy applications. [ABSTRACT FROM AUTHOR]

Solid polymer electrolytes (SPEs) have wide-scale applications in the fields of energy storage (capacitors and batteries), power conversion (fuel cells), electrochemical sensing etc. In the present work, poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) based SPEs with varying concentration of lithium triflate and composite solid polymer electrolytes (CSPEs) composed of BaTiO 3 in addition to the optimised loading of lithium triflate in PVDF-HFP matrix are synthesized by solution casting technique. SPE with 10 wt.% lithium triflate shows highest DC conductivity of 2.19 × 10 −6 S cm −1 at 300 K, which enhances to 8.89 × 10 −6 S cm −1 by adding 4 wt.% of BaTiO 3 . X-Ray diffraction (XRD) and scanning electron microscopy (SEM) analysis shows that the reduction in crystallite size of the polymeric matrix assists in enhancing the conductivity. Hence, the crystallite size, by altering the arrangement of the non-conducting polymeric chains, affects the ionic conductivity of the composites significantly. [ABSTRACT FROM AUTHOR]

Laser-based methodologies for synthesis, reduction, modification and assembly of graphene-based materials are highly demanded for energy-related electrodes and devices for portable electronics. Laser technologies for graphene synthesis and modification exhibit several advantages when compared to alternative methods. They are fast, low-cost and energy saving, allowing selective heating and programmable processing, with controlled manipulation over the main experimental parameters. In this review, we summarize the most recent studies on laser-assisted synthesis of graphene-based materials, as well as their modification and application as electrodes for supercapacitor and battery applications. After a brief introduction to the physical properties of graphene and a discussion of the different types of laser processing operations, the practical uses of laser techniques for the fabrication of electrode materials are discussed in detail. Finally, the review is concluded with a brief discussion of some of the outstanding problems and possible directions for research in the area of laser-based graphene materials for energy storage devices. [ABSTRACT FROM AUTHOR]