Flexible Fiber Supercapacitors Research Articles

Aminated silver nanowires as current collectors and binders for the preparation of multilayer graphite loading high-performance silk fiber electrodes

The rapid development of wearable electronic devices has put forward high requirements for their energy storage devices. Currently, fiber supercapacitors have attracted widespread attention owing to their miniature sizes and high flexibility, but an improvement in their electrochemical performance is often limited by the loading of conductive energy storage materials. Herein, a multilayer graphene loading strategy based on amino silver nanowires (NH2-AgNWs) was developed to prepare silk electrodes, wherein NH2-AgNWs were used as current collectors and binders to increase the conductivity of silk electrodes and achieve multilayer loading graphene on silk. The prepared silk electrode exhibited a high specific capacitance of 37.14 mF/cm because of the multilayer loading of the conductive energy storage material. The generality of this method is further demonstrated with a cotton thread substrate electrode, which exhibited a specific capacitance of 69.45 mF/cm. Additionally, a parallel fiber-shaped supercapacitor (PFSS) was assembled, at the maximum power density of 74.48 mW/m2, the energy density reaches 1468.87 mWh/m2. The PFSS exhibited a capacitance retention rate of 93.01 % when the bending degree was 90°. This study proposes a multilayer graphene loading strategy based on NH2-AgNWs for the preparation of fiber electrodes and a flexible fiber supercapacitor was assembled.

High‐Energy‐Density Graphene Hybrid Flexible Fiber Supercapacitors

AbstractGraphene fiber‐based supercapacitors (GFSCs) as flexible energy‐storage devices have achieved much in the wearable electronics. However, the GFSCs still suffer insufficient energy density, and of which desirable balance between mechanical and electrochemical properties has not been realized. Herein, we developed AgI and conductive polymer assisted co‐enhancement strategy to prepare the high‐performance GFSCs with super‐high energy density, favorable mechanical properties, and superior electrochemical properties. The conductive binder polymer, poly(3,4‐ethylenedioxythiophene) (PEDOT) was introduced into the GO spinning solution to enhance RGO fiber strength, conductivity, and electrochemical performance by forming a strong interface with GO in the spinning solution. On the other hand, the synergistic effect of micro‐ and nano‐scale AgI grown on the fiber surface and aqueous gel electrolyte widen the potential window of the GFSC to 1.6 V, which is much higher than that of reported GFSCs, and resulting in a significantly increased energy density. At 0.1 A cm−3, the volumetric capacitance and energy density of the fabricated GFSCs are as high as 166.6 F cm−3 and 29.65 mWh cm−3, respectively. The high strength and flexibility of the hybrid fibers endowed the GFSCs with ∼100 % capacitance retention when bent to 180°. This work opens a new way to design and fabricate high‐performance GFSCs.

Temperature-dependent pseudocapacitive behaviors of polyaniline-based all-solid-state fiber supercapacitors

The work temperatures have a crucial influence on the performance of supercapacitors. However, temperature effects on pseudocapacitive behaviors are rarely studied for flexible high-performance fiber supercapacitors. Herein, we systematically investigated the electrochemical responses of all-solid-state fiber-based supercapacitors composed of carbon nanotube fiber (CNF) electrodes decorated with porous carbon nanotubes (CNTs)/polyaniline (PANI) and gel electrolyte at various ambient temperatures between −5 °C and 55 °C. The results show that the capacitance of the supercapacitor first enhances with the rising temperature under 40 °C and declines at 55 °C. The internal resistance presents a gradual downward trend and the self-discharge behavior accelerates at high operating temperatures. CNTs/PANI-modified flexible fiber supercapacitors are also far from unsatisfactory for cycling stability tests in a high-temperature environment. After experiencing 5000 charge–discharge cycles at 55 °C, the capacitance retains only 43.86 %, far below the counterpart at low temperatures. This study provides a fundamental comprehension of the temperature dependence of pseudocapacitive behaviors of PANI-based fiber supercapacitors.

Electrostatic Interfacial Cross-Linking and Structurally Oriented Fiber Constructed by Surface-Modified 2D MXene for High-Performance Flexible Pseudocapacitive Storage.

Fiber supercapacitors are promising power supplies suitable for wearable electronics, but the internally insufficient cross-linking and random structure of fiber electrodes restrict their performance. This study describes how interfacial cross-linking and oriented structure can fabricate an MXene fiber with high flexibility and electrochemical performance. The continuous and highly oriented macroscopic fibers were constructed by 2D MXene sheets via a liquid-crystalline wet-spinning assembly. The oxyanion-enriched terminations of surface-modified MXene in situ could reinforce the interfacial cross-linking by electrostatic interactions while mediating the sheet-to-sheet lamellar structure within the fiber. The resultant MXene fiber exhibits high electrical conductivity (3545 S cm-1) and mechanical strength (205.5 MPa) and high pseudocapacitance charge storage capability up to 1570.5 F cm-3. Notably, the assembled fiber supercapacitor delivers an energy density of 77.6 mWh cm-3 at 401.9 mW cm-3, exceptional flexibility and stability exhibiting ∼99.5% capacitance retention under mechanical deformation, and can be integrated into commercial textiles to power microelectronic devices. This work provides insight into the fabrication of an advanced MXene fiber and the development of high-performance flexible fiber supercapacitors.

Reliable coaxial wet spinning strategy to fabricate flexible MnO2-based fiber supercapacitors

With the rapid development of electronic technique, wearable energy conversion and storage devices are facing huge challenges. Particularly, fiber supercapacitors have advantages of small size, light weight, high flexibility, fast charge/discharge process, high power density, long cycle life and wide operating temperature, showing considerable application prospect in the smart wearable field. This work proposes a strategy to fabricate MnO2, MnO2/PANI and MnO2/GN fiber electrodes via coaxial wet spinning technology, in which the electrochemical active materials could be wrapped into CMC layer perfectly, ensuring the structure stability of fiber electrodes effectively. And a series of MnO2-based parallel fiber supercapacitors are further assembled. After optimization of mixing ratios, the MnO2/PANI fiber supercapacitor with mixing-ratio of 1:1 exhibits specific capacitance of 0.68 μF·cm−1 at 0.25 μA·cm−1, and the MnO2/GN fiber supercapacitor with mixing-ratio of 9:1 presents 1.23 μF·cm−1at the same current density, which are both higher than that of pure MnO2 fiber supercapacitor (0.59 μF·cm−1), proving significant enhancement of electrochemical performance due to the introduced PANI or GN. Therefore, this work provides a reliable guidance for design and application of wearable fiber supercapacitors.

Coaxial fabrication of Ni-Co layered double hydroxide into 3D carbon nanotube networks for high-performance flexible fiber supercapacitors

Asymmetric fiber-shaped supercapacitors (FSCs), especially those using pseudocapacitive materials, have been considered one of the most promising candidates for high-performance electrochemical devices. Herein, we design a flexible, asymmetric FSC consisting of carbon fiber (CF) as the substrate, multiple and alternate Ni-Co layered double hydroxide/mono-dispersed carbon nanotube (CNT) coaxial layers ([Ni-Co LDH-x/CNT-y]@CF) as the positive electrode materials and tremella-derived activated [email protected] (TDC-z@CF) as the negative electrode material. The 3D Ni-Co LDH/mono-dispersed CNT networks enable the high mass loading of active materials, fast electron transfer, efficient ion diffusion, and mechanical stress release. TDC-z possesses large surface areas with hierarchical porous structures, thus demonstrating high capacitive performance. Based on that, the resulting FSC achieves a remarkable energy density of 26.20 Wh kg−1, a power density of 7569.23 W kg−1, and a superior cycling stability of 112.5% over 5000 cycles at a current density of 5 A g−1. Several supercapacitors connected in series can also drive a portable LED device for over 10 min. Furthermore, the assembled device also exhibits excellent mechanical stability under various deformation conditions. These appealing properties make our FSCs an attractive candidate for powering wearable and flexible electronic devices.

Hierarchical layered nickel–iron double hydroxide/carbon nanotube fiber electrode for constructing asymmetric fiber supercapacitor

A flexible fiber supercapacitor assembled using well-matched Ni–Fe LDH@CNTF and RuO2@CNTF fiber electrodes exhibited favorable energy and power combinations, providing a promising solution to the demands for power sources for flexible electronics.

Co-Axial Fabrication of Ni-Co Layered Double Hydroxide into 3d Carbon Nanotube Networks for High-Performance Flexible Fiber Supercapacitors

Co-Axial Fabrication of Ni-Co Layered Double Hydroxide into 3d Carbon Nanotube Networks for High-Performance Flexible Fiber Supercapacitors

High voltage output/energy density flexible asymmetric fiber supercapacitors based on a tree-like topology

Fiber supercapacitors have attracted significant attention because of the relevance for textile electronics. However, the key challenge is to achieve high output voltage and performance of fiber supercapacitors while maintaining the high flexibility of the fibers. Here, we present a fiber supercapacitor, based on an overlaid tree topology configuration, by braiding sub-fiber supercapacitor units in an asymmetrical series connection. The tree-like topology-based asymmetric fiber supercapacitors (TTAFSCs) achieve a high energy density (0.022 Wh cm −3 at a power density of 0.444 W cm −3 ) with an extendable high voltage output (>9.6 V) while maintaining outstanding mechanical properties (>1,000 bending cycles, capable of loading an object of ∼200 g). TTAFSCs of ∼8 cm in length are capable of lighting light-emitting diodes, driving a watch, and powering a display, even in a bent and twisted state. TTAFSCs based on bionic design principles are proposed TTAFSCs have high voltage output/energy density and notable mechanical properties A strategy for preparing coaxial fiber supercapacitors is developed Based on bionic design principles, Shao et al. fabricate tree-like topology-based asymmetric fiber supercapacitors. The fiber supercapacitors are designed to have high output voltage and high energy density and maintain useful mechanical properties.

Full‐Temperature All‐Solid‐State Ti3C2Tx/Aramid Fiber Supercapacitor with Optimal Balance of Capacitive Performance and Flexibility

AbstractFull‐temperature all‐solid‐state flexible symmetrical fiber supercapacitors (FSCs) are assembled by using montmorillonite flake/polyvinyl alcohol organic hydrogel (F‐MMT/PVA OHGE) as the electrolyte and separator and Ti3C2Tx/ANF‐5% (T/A‐5) fiber as the electrode, in which T/A‐5 fiber is prepared by using delaminated Ti3C2Tx nanosheets as assembled units and 5% of aramid nanofiber (ANF) as the functional additive using a wet spinning method in a coagulated bath with 0.5 m FeCl2 solution. The T/A‐5 hybrid fiber exhibits a specific capacity of 807 F cm−3 in 3 m H2SO4 electrolyte, a superior mechanical strength of 104 MPa, and a high conductivity of 1025 S cm−1. The assembled F‐MMT/PVA OHGE T/A‐5 FSC not only shows a specific capacitance of 295 F cm−3 and a capacitance retention of 91% at a current density of 5 A cm−3 after 10 000 charging/discharging cycles, but also a maximum volumetric energy density of 26.2 mWh cm−3. Meanwhile, the assembled device displays good flexibility and excellent capacitance in a wide temperature range of −40 to 80 °C, the electrochemical performance of the FSC is maintained under varying degrees of bending. This study provides an effective strategy for designing and assembling of full‐temperature all‐solid‐state symmetrical flexible FSCs with the optimal balance of capacitive performance and flexibility.

High Voltage Output/Energy Density Flexible Asymmetric Fiber Supercapacitors Based on Tree-Like Topology

Fiber supercapacitors have attracted significant attention owing to the relevancy in textile electronics. However, the key challenge is to achieve a high output voltage and performance in fiber supercapacitors, while maintaining the high flexibility as fibers. Here, we present a particular type of fiber supercapacitors, based on an overlaid tree topological configuration, by braiding sub-fiber supercapacitor units in an asymmetrical series connection. The tree-like topology-based asymmetric fiber supercapacitors (TTAFSCs) simultaneously achieved a high energy density (22 mWh cm-3 at a power density of 444 mW cm-3) and voltage output, while maintaining outstanding mechanical properties (>1000 bending cycles, capable of loading an object of ~200 g). By continuous braiding of a 6-unit TTAFSC (28 cm length), we were able to achieve a tunable output voltage as high as 9.6 V, which is superior to that achieved by most state-of-the-art fiber supercapacitors. Furthermore, TTAFSCs of ~8 cm long are capable of lightening light-emitting diodes, driving a watch, and powering a display, even at the bent and twisted state. The design of TTAFSCs and fabrication technology acquired represent a genuine breakthrough in textile electronics.

Laser-assisted fabrication of flexible monofilament fiber supercapacitors

A laser-assisted method for the fabrication of a flexible fiber supercapacitor (SC) and serially connected SCs within a seamless monofilament unit.

High-performance wearable supercapacitors based on PANI/N-CNT@CNT fiber with a designed hierarchical core-sheath structure

A hierarchical core-sheath structured PANI/N-CNT@CNT fiber is designed to modify the rate capability and cycling stability of flexible fiber supercapacitors.

Joule Heating-Induced Carbon Fibers for Flexible Fiber Supercapacitor Electrodes.

Microscale fiber-based supercapacitors have become increasingly important for the needs of flexible, wearable, and lightweight portable electronics. Fiber electrodes without pre-existing cores enable a wider selection of materials and geometries than is possible through core-containing electrodes. The carbonization of fibrous precursors using an electrically driven route, different from a conventional high-temperature process, is particularly promising for achieving this structure. Here, we present a facile and low-cost process for producing high-performance microfiber supercapacitor electrodes based on carbonaceous materials without cores. Fibrous carbon nanotubes-agarose composite hydrogels, formed by an extrusion process, are converted to a composite fiber consisting of carbon nanotubes (CNTs) surrounded by an amorphous carbon (aC) matrix via Joule heating. When assembled into symmetrical two-electrode cells, the composite fiber (aC-CNTs) supercapacitor electrodes deliver a volumetric capacitance of 5.1 F cm−3 even at a high current density of 118 mA cm−3. Based on electrochemical impedance spectroscopy analysis, it is revealed that high electrochemical properties are attributed to fast response kinetics with a characteristic time constant of 2.5 s. The aC-CNTs fiber electrodes exhibit a 94% capacitance retention at 14 mA cm−3 for at least 10,000 charge-discharge cycles even when deformed (90° bend), which is essentially the same as that (96%) when not deformed. The aC-CNTs fiber electrodes also demonstrate excellent storage performance under mechanical deformation—for example, 1000 bending-straightening cycles.

Flexible and freestanding MoS2/rGO/CNT hybrid fibers for high-capacity all-solid supercapacitors

Flexible fiber supercapacitors (FSCs) have been considered as a promising energy supply for wearable and portable electronics due to their easy integration with fabrics. However, it is challenging to fabricate high-capacity FSCs without compromising their flexibility. Here, an FSCs with both high capacity and flexibility were fabricated by coating electroactive molybdenum disulfide (MoS2) nanoflakes on a CNT fiber backbone with rGO as the adhesion layer. The as-prepared MoS2/rGO/CNT FSC exhibited a high areal capacitance of 93.2 mF cm−2 and an 85% capacitance retention rate after continuous 5000 cycling. Moreover, the MoS2/rGO/CNT FSC was highly flexible and no performance decay was observed after 1000 cyclic bending. The MoS2/rGO/CNT FSC provides a promising candidate to supply wearable and portable electronics.

Alternately Dipping Method to Prepare Graphene Fiber Electrodes for Ultra-high-Capacitance Fiber Supercapacitors.

SummaryFlexible fiber supercapacitors are promising candidate for power supply of wearable electronics. Fabrication of high-performance fibers is in progress yet challenging. The currently available graphene fibers made from wet-spinning or electro-deposition technologies are far away from practical applications due to their unsatisfactory capacitance. Here we report a facile alternately dipping (AD) method to coat graphene on wire-like substrates. The excellent mechanical properties of the substrate with greatly diverse choices can be carried over to the fiber supercapacitors. Under such guideline, the graphene fiber with a titanium core made by our AD method (AD:Ti@RGO) shows an ultra-high specific capacitance of up to 1,722.1 mF cm−2, which is ∼1,000 times that of wet-spinning- and electro-deposition-fabricated neat graphene fibers and presents the highest specific capacitance to date. With excellent mechanical properties and striking electrochemical performances, the AD:Ti@RGO-based supercapacitors light the path to the next-generation technologies for wearable devices.

Rational Design of Electrochemical Iodine-Based Redox Mediators for Water-Proofed Flexible Fiber Supercapacitors

Flexible supercapacitors based on electrostatic double-layer capacitors as next-generation energy storage systems hold great promise for wearable and flexible electronic devices owing to their high flexibility and electrochemical cyclability. However, the challenge of low charge-storing ability still remains, as electronic devices require a high charge storage capability. As one of the advanced strategies for enhancing charge-storing ability in flexible supercapacitors, the introduction of a redox mediator (RM) into a gel electrolyte has recently attracted great interest. Here, we present a fiber-based flexible energy storage system (f-FESS) integrated with iodine-based chemical species as a novel RM, carbon fiber-based electrodes, and a solid-state polymer-gel electrolyte so as to enhance the charge storage capability of flexible supercapacitors. The as-prepared f-FESS-RM exhibits enhanced charge storage capabilities of up to 461.8 F L–1 and 64.14 mWh L–1, which are 3.6 times higher than those of f-FESS without RM. The enhanced capacitive properties of f-FESS-RM are attributed to their additional Faradic redox reaction of iodine-based chemical species in the electrolyte as well as electrical double-layer capacitive behavior. Also, the f-FESS-RM shows remarkably superior mechanical robustness under various bending, winding, knotting, and weaving conditions. Furthermore, we have demonstrated that the f-FESS-RM is stably workable under deionized water and base electrolytes. In combination, these outcomes provide a novel advanced strategy to enhance the charge-storing ability with strong mechanical robustness in flexible supercapacitors.

Laser-induced bi-metal sulfide/graphene nanoribbon hybrid frameworks for high-performance all-in-one fiber supercapacitors

High-performance yet flexible all-in-one fiber supercapacitors (FSCs) hold a great potential in powering the next-generation wearable/portable electronics. Rational design and scalable construction of unique three-dimensional structures are challenging for assembling these types of FSCs. Here, we demonstrate a unique laser-induced bi-metal sulfide/graphene nanoribbon (GR) hybrid framework for high-performance all-in-one flexible FSCs. The bi-metal sulfide/GR hybrid framework performs a superior electrochemical performance to both of GR and single-metal sulfide/GR hybrid frameworks. In addition, the as-assembled all-in-one flexible FSCs based on laser-induced molybdenum disulfide/manganese sulfide/GR (MoS2/MnS/GR) hybrid frameworks exhibit a high areal specific capacitance of 58.3 mF/cm2 at 50 μA/cm2, a high areal energy density of 7.0 μWh/cm2 at 50 μA/cm2, a high areal power density of 49.9 μW/cm2 at 50 μA/cm2, as well as a high cycling stability (93.6%, 10000 cycles). It's proposed that the synergistic effects of bi-metal sulfide as well as the unique laser-induced three-dimensional frameworks account for the excellent electrochemical performances of the as-designed framework electrodes. The concept of designing this laser-induced three-dimensional hybrid structure based on bi-metallic pseudocapacitive material and capacitive GR can provide an insight for assembling high-performance flexible fiber supercapacitors and show promising for integrating and powering portable and wearable electronics.

Hierarchical construction of high-performance all-carbon flexible fiber supercapacitors with graphene hydrogel and nitrogen-doped graphene quantum dots

Carbon-based flexible fiber-based supercapacitors (FFSCs) are promising power sources for portable and wearable electronics, but their applications are limited by low energy density due to a lower specific capacitance of common carbon materials. We fabricated ternary all-carbon fiber electrodes (N-GQD/GH/CF) with improved electrochemical performance. In this structure, graphene hydrogel (GH) was grown on carbon fibers (CFs) to form a 3D interconnected porous network (GH/CF), and nitrogen-doped graphene quantum dots (N-GQDs) with high pseudocapacitive activity were electrodeposited into the GH/CF network. The ternary N-GQD/GH/CF hybrid electrode delivered a volumetric capacitance of 93.7 F cm−3 at 20 mA cm−3, which was around 7 times higher than that of the GH/CF, while the capacitance retention after 5000 cycles reached 87.9%, which was only a little lower than that of the GH/CF electrode (90.2%). It indicates the introduction of N-GQDs drastically improves the capacitance of the FFSCs without sacrificing the cycle stability. All-carbon asymmetric FFSCs were assembled using N-GQD/GH/CF as positive electrode and GH/CF as negative electrode. The assembled FFSCs exhibited a high energy density of 3.6 mW h cm−3 at power density of 35.6 mW cm−3 owing to the wider potential window (2 V) and the higher volumetric capacitance as well as excellent flexibility and cycling stability.

Latest advances in supercapacitors: From new electrode materials to novel device designs

Due to the global warming and energy depletion issues, developing sustainable and renewable energy resources has become a critical concern among researchers. The constantly growing demand for energy has urged researchers to develop highly improved energy storage devices. In relation to relevant energy storage systems, supercapacitor technology has drawn burgeoning interest in recent years owing to its environmentally safe and cost effective advantages. Especially, its high power density (>10 kW/kg), fast charge/discharge characteristics, and excellent cycle stability are highly beneficial in storing renewable energy. Currently, the rapid development of portable electronic devices and the expanding renewable energy systems have paved the way for energy storage systems to play an important role in human society. Many significant breakthroughs for the next-generation supercapacitors have been achieved in terms of material synthesis, device innovations, and multifunctional device designs. Therefore, this paper summarizes the latest progress on new materials and novel device assemblies. First, to fully assess the effect of device assembly on supercapacitor performance, five types of supercapacitor structures and their assembly principles are discussed in detail, including the three-electrode (also known as semi-battery) device, two-electrode supercapacitor, flexible solid-state supercapacitor, fiber supercapacitor, and planar (micro-) supercapacitor. Among them, the three-electrode system and the two-electrode device are still the most widely used types at present. The three-electrode cell is suitable for characterizing electrode materials or investigating the electrochemical storage processes. The structure of a two-electrode system is closer to an actual supercapacitor. Other specially designed cells, which are fabricated with the aim of meeting the requirements of flexible and lightweight energy sources, have also been proposed in recent years. The results indicate that the structural innovative design could provide a fascinating way to enhance the energy density of devices while also holding huge potential to enhance the compatibility between supercapacitor component and various portable or wearable electronic devices. A careful interpretation and rigorous scrutiny of the electrochemical characteristics of every supercapacitor is also conducted in this work. Moreover, the design principles for enhancing the supercapacitor performance are highlighted through a comprehensive analysis of the literature. The main challenges in the structural innovations for enhancing the electrochemical performance are analyzed. The solutions to overcome these challenges are proposed. Second, supercapacitors still suffer from a lower energy density compared with Li-ion batteries. Among various efforts to build high-performance supercapacitors in recent years, major improvements have been made in electrode materials with rational designs. This review article also examines the latest methodologies and performance evaluation metrics for several emerging electrode materials in terms of their improved electrochemical properties, including carbon materials, binary transition metal oxides (NiCo2O4, Ni3V2O8, and Co3V2O8, among others), transition metal chalcogenides/selenide/phosphide positive electrodes, and VN, Fe2O3 negative electrode materials. This paper also highlights the electrode material design principle, which is the fundamental understanding of the relationships between structural design, structural properties and components of electrode materials and their electrochemical performances. Moreover, we also summarized the latest contributions and progress in multifunctional supercapacitors, which include the transparent flexible supercapacitor, self-healable supercapacitor, piezoelectric supercapacitors, self-charging supercapacitors, and so on. Several methods to realize the abilities of transparent, folded, wearable, self-healable, and even self-chargeable supercapacitors with almost no performance degradation are discussed. This paper also analyzes the compatibility of a multifunctional supercapacitor with industrial manufacturing, and offers a paradigm for developing portable and wearable energy storage devices and systems. Furthermore, the operating principles, system design/engineering, and the rational optimization of the multifunctional supercapacitors are also analyzed in this review. Finally, the major challenges faced by next-generation supercapacitors, along with the future research prospects, are discussed at the end of the paper.