Flexible Symmetric Supercapacitor Research Articles

A high-frequency flexible symmetric supercapacitor prepared by the laser-defocused ablation of MnO2 on a carbon cloth

The rapid development of flexible electronics has produced an enormous demand for supercapacitors. Compared to batteries, supercapacitors have great advantages in terms of power density and cycling stability. They can also respond well on a time scale of seconds, but most have a poor frequency response, and behave more like pure resistors when used at high frequencies (e.g., above 100 Hz). It is therefore challenging to develop supercapacitors that work at a frequency of over 100 Hz. We report a high-frequency flexible symmetrical supercapacitor composed of a MnO2@carbon cloth hybrid electrode (CC@MnO2), which is synthesized by the defocused-laser ablation method. This CC@MnO2-based symmetric supercapacitor has an excellent specific areal capacitance of 1.53 mF cm−2 at a frequency of 120 Hz and has good cycling stability with over 92.10% capacitance retention after 100 000 cycles at 100 V s−1. This remarkable electrochemical performance is attributed to the combined effect of the high conductivity of the 3D structure of the carbon cloth and the exceptional pseudo-capacitance of the laser-produced MnO2 nanosheets. The defocused laser ablation method can be used for large-scale production using roll-to-roll technology, which is promising for the wide use of the supercapacitor in high-frequency electronic devices.

Direct growth of porous vanadium nitride on carbon cloth with commercial-level mass loading for solid-state supercapacitors

Mass production of wearable devices with effective three-dimensional (3D) structure is a vital prerequisite for practical energy storage. Vanadium nitride (VN) has been identified as a promising supercapacitor electrode due to its wide negative potential working window, high specific capacitance and outstanding electrical conductivity, Herein, porous VN is grown on carbon cloth (CC) by a dip-coating and nitridation method. Such a VN/CC electrode provides effective 3D structure is beneficial for high mass loading (up to 28.3 mg cm−2) with high specific capacitance. Consequently, the as-prepared VN/CC electrode can achieve high areal capacitance of 3.34 F cm−2 at 5 mA cm−2. As a result, the flexible symmetric supercapacitor shows robust cycling stability (96% retention over 10,000 cycles) with PVA/KOH gel electrolyte. In addition, high energy/power density (0.341 mWh cm−2 at 1.92 mW cm−2) and excellent cycling performance (87% retention over 8000 cycles) are achieved in the assembled solid-state asymmetric supercapacitor cell with Zn−Ni−Co ternary oxides (ZNCO)/NF cathode and VN/CC anode. The results provide a simple route to prepare high mass loading porous VN-based electrodes with outstanding areal capacitance. It is believed that this strategy will favor the development of other transition metal nitride electrodes for commercial use in the future.

Design and realization of binder-free electrodes with leaf-like structure based on Fe-Co binary oxides/graphene enabling efficient energy storage of flexible solid-state supercapacitors

High performance and efficient preparation of electrodes are prerequisites for energy storage devices to adapt to complex usage scenarios in the future. In this work, flexible binder-free electrodes with unique leaf-like structure were designed and prepared based on Fe-Co binary oxides nanoparticles/graphene coated on carbon cloth, which can be directly used in supercapacitors without any subsequent operations or additives. Morphological characterization demonstrates that the structure of the electrodes is similar to that of a leaf, including veins (carbon fibers), blades (graphene layers), and mesophyll cells (evenly distributed CoO particles of 60–80 nm and Fe3O4 particles less than 10 nm). Electrochemical characterization confirms that the electrode exhibits high specific capacitance of 458 F g−1 at 1 A g−1 under a wide operating potential window of 1.45 V. After assembled into a flexible solid-state symmetric supercapacitor with aqueous KOH/PVA as the gel electrolyte, the device exhibits good energy density (20.2 Wh kg−1), ameliorated power density (8910 W kg−1), and excellent cycling stability (capacitance retention of 87% after 3000 continuous cycles at 1 A g−1). Furthermore, after being bent at 60°, 120°, 180° and finally restored to the original state, its cyclic voltammetry curve remains almost unchanged in both shape and area, indicative of its remarkable flexibility and structural stability. All the results prove that this work is promising to further promote the development of supercapacitors.

FeSe and Fe3Se4 encapsulated in mesoporous carbon for flexible solid-state supercapacitor

Metal selenides have been developed as promising alternatives of metal oxides in energy storage field due to their high conductivity and low bandgap. However, the synthesis of selenides usually suffers from the low melting point and strong volatility of selenium at temperatures higher than 217 ℃. Herein, a facile strategy was developed to prepare iron selenides using a template of Se-contained MOF gel, which could in situ immobilize Se powder due to the fast gelation process, resulting a porous, uniform and tight precursor. By adjusting the mole ratio of Fe and Se in the precursor, FeSe@C and Fe3Se4@C were controllably synthesized with rich mesopores and excellent carbon-encapsulation structure. The kinetics analysis indicates that these unique structures are beneficial for improving electrode kinetics, charge/ion-transfer resistance and electrochemical stability. FeSe@C and Fe3Se4@C exhibit significant capacitances (611.0F g−1 and 569.0F g−1 at 1 A g−1), and excellent cycling properties (94.22% and 93.28% retention after 2000 charge–discharge cycles at 5 A g−1). When estimated in practical application, the flexible solid-state symmetric supercapacitor of FeSe@C//Fe3Se4@C delivers a high Csp of 160.1F g−1, the superior energy density of 32.1 W h kg−1 and a high specific power density of 5998 W kg−1 with 89.5% capacitance retention after 5000 cycles, and the outstanding flexibility.

Facile Preparation of a 3D Porous Aligned Graphene-Based Wall Network Architecture by Confined Self-Assembly with Shape Memory for Artificial Muscle, Pressure Sensor, and Flexible Supercapacitor.

The development of a novel preparation strategy for 3D porous network structures with an aligned channel or wall is always in challenge. Herein, a 3D porous network composed of an aligned graphene-based wall is fabricated by a confined self-assembly strategy in which holey reduced graphene oxide (HrGO)/lignin sulfonate (Lig) composites are orientedly anchored on the framework of the Lig/single-wall carbon nanotube (Lig/SWCNT) hydrogel by vacuum-assisted filtration accompanied with confined self-assembly and followed with hydrothermal treatment. After freeze drying, the obtained ultralight Lig/SWCNT/HrGOal aerogel exhibits excellent shape memory properties and can roll back to the original shape even if suffering from a high compressive strain of 86.2%. Furthermore, the as-prepared aerogel used as a water-driven artificial muscle shows powerful driving force and can lift ultrahigh weight cargo that is 1030.6 times its own weight. When the prepared Lig/SWCNT/HrGOal aerogel is used as a pressure sensor, it also exhibits high sensitivity (2.28 kPa-1) and a wide detection region of 0.27-14.1 kPa. Additionally, the symmetric flexible supercapacitor assembled with as-prepared aerogel films shows superior stored energy performance that can tolerate 5000 cycles of bending. The present work not only fabricates a high-performance multifunctional material but also develops a new strategy for the preparation a wood-like 3D porous aligned wall network structure.

Three-dimensional ordered and porous Ti3C2Tx@Chitosan film enabled by self-assembly strategy for high-rate pseudocapacitive energy storage

MXenes with outstanding electric conductivity and surface chemistry are promising materials for future energy storage. However, processing MXenes into free-standing films can lead to restacking and aggregation of the 2D nanosheets, which limits the ionic kinetics within materials. Current solutions are difficult for films to satisfy both rate performance and flexibility. Herein, we propose a novel chitosan-induced self-assembly strategy to construct MXene into flexible Ti3C2Tx@Chitosan films with 3D ordered and porous structure. The interconnected 3D network provides fast transport channels for electrons and electrolyte ions. Therefore, the film exhibits excellent rate capability and low mass-loading dependence. The Ti3C2Tx@Chitosan film with a high mass loading of 4 mg−2 delivers a capacitance of 245.2F g−1 at 2 V s−1, which demonstrates 57.1% capacitance retention with 400-fold scan rate increase. The crosslinked chitosan is interconnected and interwoven with MXene nanosheets, resulting in enhanced mechanical strength and flexibility for Ti3C2Tx@Chitosan. Furthermore, by applying Ti3C2Tx@Chitosan film to assemble flexible symmetrical supercapacitors, an ultra-high power density of 143.2 μWh cm−2 can be attained. This work develops a simple route for assembling 2D MXene into 3D high-flexible porous films as state-of-the-art electrodes for high-rate pseudocapacitive energy storage.

Biowaste-derived electrode and electrolyte materials for flexible supercapacitors

One of the key challenges in the development of energy storage devices relates to material sourcing in harmony with clean technologies. Herein, cellulose nanocrystals (CNC) extracted from brewery residues are used as transparent hydrogel electrolyte after physical cross-linking with aluminum ions (Al3+). The hydrogel electrolyte (Al-CNC) exhibits an ultrahigh ionic conductivity (∼24.9 mS cm−1), high optical transmittance (∼92.9% at 550 nm wavelength), outstanding compression strength (3.9 MPa at a 70% strain), and tolerates to various deformations (e.g., twisting, folding, rolling). Meanwhile, animal bone biowaste is used to synthesize porous carbon (PC) electrodes (∼879 m2 g−1) that are effective in delivering an outstanding specific capacitance (∼804 F g−1 at 1 A g−1). A fully renewable flexible symmetric supercapacitor is assembled by sandwiching the Al-CNC hydrogel between two bone-derived PC electrodes (PC//Al-CNC//PC). The obtained flexible device displays a high energy density (18.2 Wh kg−1 at 1 425 W kg−1), exceptional power density (20 833 W kg−1 at 7.1 Wh kg−1), and ∼92% capacitance retention after 6 000 cycles at 5 A g−1. We further demonstrated the biowaste-derived high-performance flexible supercapacitors for their mechanical durability and reliable electrochemical performance under bending cycles. All combined, the devices are shown to be ideally suited for renewable energy storage applications.

Three-Dimensional ZnCo-MOF Modified Graphene Sponge: Flexible Electrode Material for Symmetric Supercapacitor

Developing flexible, lightweight, and portable energy storage systems have become a necessity with the advent of wearable electronic devices in modern society. We report a novel, easy, and low-cost way to fabricate flexible bimetallic metal–organic framework (MOF) doped graphene sponge (GS) free-standing materials (ZnCo-MOF/GS). The electrochemical behavior of the flexible ZnCo-MOF/GS was probed via galvanostatic charge–discharge, electrochemical impedance spectroscopy, and cyclic voltammetry. The morphological and structural studies of this material were performed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectrometry. ZnCo-MOF/GS exhibited a high specific capacitance of 695 F/g at 1.0 A/g and excellent cyclic stability with 78% retention after a 7500 cycle test in 3.0 M KOH. Furthermore, a ZnCo-MOF/GS based symmetric supercapacitor (SC) was fabricated, and this flexible device displayed a specific capacitance of 302 F/g at 1.0 A/g, an energy density of 108 W h/kg, and a power density of 5037 W/kg. Moreover, this flexible SC kept its excellent performance at severe bending conditions. We believe that our electrode with its outstanding electrochemical performance has a great potential in energy storage applications, especially for lightweight and flexible electronics.

Synthesis, characterization and supercapacitive application of nanocauliflower-like cobalt tungstate thin films by successive ionic layer adsorption and reaction (SILAR) method

For the first time, cobalt tungstate (CoWO4) thin films were synthesized by successive ionic layer adsorption and reaction (SILAR) method. The monoclinic crystal structure of CoWO4 film was confirmed from X-ray diffraction (XRD) technique. The elemental, surface morphological, structural, and electrical analyses were executed using Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), two point probe method, and contact angle measurement techniques. The surface morphology of CoWO4 thin film consisted of islands of agglomerated cauliflower-like spherical nanoparticles with hydrophilic nature. The specific surface area of 60 m2 g−1 with an average pore size of 1.10 nm. The CoWO4 thin film electrode exhibited specific capacitance of 1436.5 F g−1 at a scan rate of 2 mV s−1 in 1 M KOH as well as capacitance retention of 94% over 3000 galvanostatic charge discharge (GCD) cycles. Furthermore, flexible solid-state symmetric supercapacitor (FSS-SSC) device assembled using CoWO4 thin films, showed specific capacitance of 101.32 F g−1, specific energy of 14.07 Wh kg−1 and specific power of 1225.25 W kg−1. This work highlights simplistic preparation of CoWO4 thin films for energy storage application.

High performance flexible carbon cloth-based solid-state supercapacitors with redox-mediated gel electrolytes

The electrochemical performance of supercapacitors is mainly determined by both the electrodes and electrolytes. By integration of the flexible electrodes with redox-mediated gel electrolytes, high performance solid state supercapacitors were designed in the present work. The flexible carbon cloth (CC)-based electrodes were prepared by covalent immobilization of tetraaniline (TA) onto the oxidized carbon cloth (OCC). Hydroquinone (HQ) and p-phenylenediamine (PPD) were used as redox additive respectively to enhance the electrochemical property of the PVA-H2SO4 gel electrolyte. After optimization, high performance flexible solid-state symmetric supercapacitors (SSSCs) were obtained with specific capacitance of 834.0 mF/cm2, retention of 93.69% after 10,000 CV cycles and 108.5% after 500 cycles of 180°-bending, and energy density of 74.2 mWh/cm2 at power density of 405.3 mW/cm2. Such outstanding comprehensive performance makes them promising potential for practical application.

Highly stretchable and flexible supercapacitors based on electrospun PEDOT:SSEBS electrodes

Highly stretchable and flexible symmetrical supercapacitors are constructed from conductive polymer-infused electrospun microfibers and freeze/thawed PVA-H2SO4 gel electrolyte.

Nanostructured Zig-Zag Γ-Mo2n Thin Films Produced by Glancing Angle Deposition for Flexible Symmetrical Solid-State Supercapacitors

Nanostructured Zig-Zag Γ-Mo2n Thin Films Produced by Glancing Angle Deposition for Flexible Symmetrical Solid-State Supercapacitors

Synthesis of Highly Dispersed Nb2o5-Graphene Heterojunction Composite Using Edta and Boron-Functionalized Graphene Quantum Dot for Flexible Symmetrical Supercapacitors with Ultrahigh Energy Density

Synthesis of Highly Dispersed Nb2o5-Graphene Heterojunction Composite Using Edta and Boron-Functionalized Graphene Quantum Dot for Flexible Symmetrical Supercapacitors with Ultrahigh Energy Density

One pot synthesis of tungsten oxide nanomaterial and application in the field of flexible symmetric supercapacitor energy storage device

At present, electronic markets aim to develop new energy storage devices which are lightweight, portable, and flexible. In the present study, a flexible as well as a light weight energy storage device has been fabricated using tungsten oxide material. By a simple and effective hydrothermal technique, highly crystalline monoclinic tungsten oxide nanomaterial has been synthesised and the electrochemical performance of this material for supercapacitor energy storage application were analysed. Structural, optical and morphological studies were conducted using X-ray diffraction technique, Raman spectroscopy, Fourier transform infrared spectroscopy, and FESEM analysis. The electrochemical performance studies are carried out in two electrode set up. The supercapacitor device exhibits a specific capacitance of 64 F g -1 at 5 mV s−1.

Functional Graphene Quantum Dot-Mediated Synthesis of Heterojunction Nb2o5-Graphene Composite for Flexible Symmetrical Supercapacitors with High Energy Density and Wide Voltage Window of 2 V

Functional Graphene Quantum Dot-Mediated Synthesis of Heterojunction Nb2o5-Graphene Composite for Flexible Symmetrical Supercapacitors with High Energy Density and Wide Voltage Window of 2 V

A quasi-solid-state supercapacitor based on waste surgical masks with high flexibility and designable shape

A quasi-solid-state flexible symmetric supercapacitor (QFSSC) based on waste surgical masks (WSMs) with high electrochemical performance and high flexibility has been designed. The WSMs with three-layer construction have been fully utilized to fabricate the QFSSC. The two outer layers are served as the flexible substrate to achieve flexible electrodes by loading polypyrrole (PPy) microcones via electropolymerization, while the interlayer is immersed into hydrogel electrolyte to play the role as separator. The unique three-dimensional porous network of WSMs provides sufficient sites to load the active substance and endows the electrodes with numerous electron/ion transmission channels. The influences of electropolymerization time on the morphology of the PPy and electrochemical performance of the electrodes have been comprehensively studied. The as-prepared QFSSC shows the maximum specific capacitance of 219.1 mF cm−2 at 1 mA cm−2, energy density of 19.48 μWh cm−2 at 219.2 μW cm−2, and power density of 3.3 mW cm−2 at 15.2 μWh cm−2, as well as good cycling stability and excellent flexibility. The QFSSC even keeps high capacitance retention of 92.1% and 88.3% after 10,000 charge/discharge cycles and 100,000 bending cycles, respectively. Moreover, the electrode/device can be cut into designable shapes to meet the need of practical application. In addition, the as-prepared QFSSC displays a satisfactory self-discharge property. This work demonstrates an economical and environmental way to recycle the WSMs produced in large quantities, which may make a great contribution to the circular sustainability.

One-pot temperature-controlled hydrothermal synthesis of α-MnO2 nanoparticles decorated thermally reduced graphene oxide composite as high-performance flexible aqueous symmetric supercapacitors

In this study, manganese dioxide (MnO2)/thermally reduced graphene oxide (rGO) symmetric supercapacitors were fabricated. The (MnO2/rGO@X) composites with varying reaction temperatures (100, 120, and 140 °C) were prepared from a one-pot hydrothermal approach. First, we optimize the reaction temperature as 120 °C for the MnO2/rGO composite on its electrochemical behaviour in a two-electrode cell. Then, pure MnO2nanoparticles were synthesized at the same reaction temperature. X-ray diffraction (XRD) analysis revealed the presence of α-MnO2 produced through hydrothermal synthesis. The MnO2/rGO composite formation was confirmed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The scanning electron microscope (SEM) image of the MnO2/rGO@120 composite showed that the rGO surface was decorated with flakes-like MnO2 nanoparticles. The electrochemical properties of pure MnO2@120 and the MnO2/rGO@120 composite were evaluated using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge measurements. In a two-electrode symmetric cell configuration, the MnO2/rGO@120 exhibits a much larger specific capacitance of 413 Fg−1 at a current 1 mA and delivers maximum specific energy 14.3 Wh kg−1 with a specific power of 260 W kg−1. Moreover, the 99.7% efficiency exhibited by this composite symmetric supercapacitor was found to retain after 5000 charge/discharge cycles at 3 mA current. The excellent supercapacitive performance of our MnO2/rGO composite electrode material prepared via one-pot hydrothermal treatment at a reaction temperature of 120 °C has potential applications for energy storage applications.

Phase engineering of Mo1-xWxS2 nanosheets for flexible supercapacitors

Considering the atomic size mismatch between Mo and W, a large compressive microstrain is introduced and phase engineering may be achieved in MoS2. A simple one-step hydrothermal method as a facile method is employed to synthesize 1T-Mo0.71W0.29S2. 1T-Mo0.71W0.29S2 doping Co element and then growing on carbon cloth are the effective way to improve the supercapacitor performance. Benefitting from the outstanding conductivity of 1T-Mo0.71W0.29S2 and carbon cloth, the more active sites by doping Co, the electrode of Co-(1T-Mo0.71W0.29S2)-1% on carbon cloth exhibits high specific capacity of 1235 mF cm−2 at 2 mA cm−2. Flexible symmetric supercapacitors constructed by Co-(1T-Mo0.71W0.29S2)-1% on carbon cloth show high energy density (22.7 μWh cm−2), strong flexibility and stability (88.7% at 20 mA cm−2). The simple strategy provides a facile route for easy phase engineering and improvement on performance of transition metal dichalcogenides (TMDs).

Flexible, Transparent and Highly Conductive Polymer Film Electrodes for All-Solid-State Transparent Supercapacitor Applications.

Lightweight energy storage devices with high mechanical flexibility, superior electrochemical properties and good optical transparency are highly desired for next-generation smart wearable electronics. The development of high-performance flexible and transparent electrodes for supercapacitor applications is thus attracting great attention. In this work, we successfully developed flexible, transparent and highly conductive film electrodes based on a conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The PEDOT:PSS film electrodes were prepared via a simple spin-coating approach followed by a post-treatment with a salt solution. After treatment, the film electrodes achieved a high areal specific capacitance (3.92 mF/cm2 at 1 mA/cm2) and long cycling lifetime (capacitance retention >90% after 3000 cycles) with high transmittance (>60% at 550 nm). Owing to their good optoelectronic and electrochemical properties, the as-assembled all-solid-state device for which the PEDOT:PSS film electrodes were utilized as both the active electrode materials and current collectors also exhibited superior energy storage performance over other PEDOT-based flexible and transparent symmetric supercapacitors in the literature. This work provides an effective approach for producing high-performance, flexible and transparent polymer electrodes for supercapacitor applications. The as-obtained polymer film electrodes can also be highly promising for future flexible transparent portable electronics.

Flexible and High‐Performance MXene/MnO2 Film Electrodes Fabricated by Inkjet Printing: Toward a New Generation Supercapacitive Application

AbstractWith the deepening of the commercialization of flexible electronic products, it is urgently needed to develop a handleable solution for the applications of printing high‐performance and wearable energy storage devices. Herein, flexible, low‐cost, and high‐performance MXene/manganese dioxide (MnO2) composite film electrodes are reported to meet this urgent expectation. The MXene‐based composite film electrodes with different MnO2 content are prepared by inkjet printing using MXene/MnO2 ink. Characterization and test results show that there is a synergistic effect between MXene and MnO2, which can effectively achieve faster electron transfer and shorter diffusion path, thus improving the overall electrochemical performance of the composite. The inkjet‐printed MXene/10 wt% MnO2 composite film electrode, with an excellent conductivity of 3400 S m−1, exhibits an ultrahigh volumetric capacitance of 312 F cm−3 and retains 130.8% of the initial capacitance after 5000 charge/discharge cycles. Moreover, the fabricated flexible symmetrical supercapacitor shows a superior areal energy density of 0.51 μWh cm−2 at a power density of 12.5 μW cm−2. Taken together, inkjet printing technology provides a low‐cost, large‐area manufacturing route for different MXene‐based composites, which are expected to promote the development of novel energy storage technologies that exploit the attractions of MXene.