High-performance Flexible Supercapacitor Electrode Research Articles

Deposition of MnO2 on KOH-activated laser-produced graphene for a flexible planar micro-supercapacitor

The rapid development of flexible supercapacitors has been impeded by the difficulty of preparing flexible electrodes. We report the fabrication of a highly flexible and conductive microporous graphene-based substrate obtained by direct laser writing combined with KOH activation, which we call activated laser-produced graphene (a-LPG), which is then decorated with electrochemically deposited MnO2 to form a flexible a-LIG/MnO2 thin-film electrode. This hybrid electrode has a high areal capacitance of 304.61 mF/cm2 at a current density of 1 mA/cm2 in a 1 mol/L Na2SO4 aqueous electrolyte. A flexible asymmetric supercapacitor with a-LIG/MnO2 as the anode, a-LIG as the cathode and PVA/ H3PO4 as a gel electrolyte was assembled, giving an areal energy density of 2.61 μWh/cm2 at a power density of 260.28 μW/cm2 and an ultra-high areal capacitance of 18.82 mF/cm2 at 0.2 mA/cm2 with 90.28% capacitance retained after 5 000 cycles. It also has an excellent electrochemical performance even in the bent state. This work provides an easy and scalable method to design high-performance flexible supercapacitor electrodes and may open a new way for their large-scale fabrication.

A morphology control engineered strategy of Ti3C2Tx/sulfated cellulose nanofibril composite film towards high-performance flexible supercapacitor electrode

2D Ti3C2Tx MXene is an ideal material for fabricating supercapacitor electrodes due to its excellent physical-chemical properties. However, the inherent self-stacking, narrow interlayer spacing, and low general mechanical strength limit its application in flexible supercapacitors. Herein, facile structural engineering strategies by drying (vacuum drying, freeze drying, and spin drying) were proposed to fabricate 3D high-performance Ti3C2Tx/sulfated cellulose nanofibril (SCNF) self-supporting film supercapacitor electrodes. Compared with other composite films, the freeze-dried Ti3C2Tx/SCNF composite film exhibited a looser interlayer structure with more space which was conducive to charge storage and ion transport in the electrolyte. Therefore, the freeze-dried Ti3C2Tx/SCNF composite film exhibited a higher specific capacitance (220 F/g) compared to the vacuum-dried Ti3C2Tx/SCNF composite film (191 F/g) and the spin-dried Ti3C2Tx/SCNF composite film (211 F/g). After 5000 cycles, the capacitance retention rate of the freeze-dried Ti3C2Tx/SCNF film electrode was close to 100 %, showing excellent cycle performance. Meanwhile, the tensile strength of freeze-dried Ti3C2Tx/SCNF composite film (13.7 MPa) was much greater than that of the pure film (7.4 MPa). This work demonstrated a facile strategy for control of Ti3C2Tx/SCNF composite film interlayer structure by drying for fabricating well-designed structured flexible and free-standing supercapacitor electrodes.

Cellulose Nanomaterials Based Flexible Electrodes for All-Solid-State Supercapacitors

Abstract: In recent years, flexible all-solid-state supercapacitors have been widely used as the energy storage devices for various smart and wearable electronic devices. However, the design and fabrication of high-performance flexible supercapacitor electrodes is still challenging since most of the active materials used for supercapacitor electrodes lack the ability to form flexible and mechanically stable structures. Recently, cellulose nanomaterials (mainly include cellulose nanocrystals and cellulose nanofibrils) have gained extensive interests due to their large specific surface areas, versatile surface chemistry, high mechanical strength, and the ability to form mechanically stable structures (e.g., films, aerogels). These days, the design of flexible supercapacitor electrodes by combining cellulose nanomaterials with different active materials gradually attracted the attention of scholars. The main objective of this review is to give an overview of recent developments in the preparation of cellulose nanomaterials based flexible all-solid-state supercapacitor electrodes. The fabrication approach, structure characterization, and electrochemical performance of the invented cellulose nanomaterials based flexible supercapacitor are elaborated. Also, the current challenges and future outlook for the design and fabrication of cellulose nanomaterials based flexible all-solid-state supercapacitor are proposed.

Flexible ultracapacitor device fabricated with an organic electrode material- naphthalene diimide nitrile/reduced graphene oxide

In this work, we have demonstrated a high-performance flexible supercapacitor electrode based on reduced graphene oxide (rGO) and naphthalene diimide nitrile (NDI-CN) composite. The rGO/NDI-CN composite was prepared by a simple approach. This composite was well characterized using various techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) etc. Besides, the π -π stacking of NDI-CN on rGO surface was confirmed using UV–vis and FTIR techniques. As fabricated rGO/NDI-CN composite was examined as an electrode material for the supercapacitor applications. The rGO/NDI-CN electrode has delivered an excellent specific capacitance (Csp) of 336 F g−1 at 0.5 A g−1current density. The fabricated supercapacitor (SC) displays robustness with 80 % capacitance retention over 10,000 cycles at higher current density of 10 A g−1. To further explore the real-world application of electrode materials, the corresponding flexible supercapacitor was designed and examined. The flexible device exhibited an energy density of 9.54μWh cm−2 at a power density of 0.3 mWcm−2. These results confirmed that the rGO/NDI-CN electrode material has good potential as an energy storage device. Furthermore, the facile construction and fabrication of flexible device displayed operation of LED when fully charged. The assembled flexible supercapacitor device could be bent and twisted, signifying the potential to be used in practical applications in various high-performance electrochemical devices.

Redox-active conjugated microporous anthraquinonylamine-based polymer network grafted with activated graphene toward high-performance flexible asymmetric supercapacitor electrodes

Conjugated microporous polymer (CMP) networks with multi-dimensional structure and excellent physicochemical stability with tunable porosity are receiving increased interest. Herein, we report a composite of anthraquinonylamine-based CMP network and activated graphene (CMAP@AG hybrid) via facile Buchwald-Hartwig coupling. The hybrid composites are made via chemical grafting of CMAP onto AG samples prepared with varied activation treatment times. The grafting of CMAP with AG provides a good hybrid morphology, and its structural properties are tuned by controlling the activation step of AG since both porosity and flake size of the AG sample depend on the etching conditions. The optimized CMAP@AG hybrid exhibits a large surface area of 498 m2 g−1 and low sheet resistance of 278 Ω sq−1, and it can be directly used as an electrode material for supercapacitors. The CMAP@AG hybrid electrode shows a three-electrode specific capacitance of 751 F g−1 at a current density of 1 A g−1 with a good rate capability. A quasi-solid-state CMAP@AG//AG asymmetric supercapacitor (ASC) displays a high energy density of 76.6 Wh kg−1, a power density of 27,634 W kg−1, and good cycle stability with mechanical flexibility. These investigations offer insight into a rational design of CMP-based activated graphene composite for energy storage devices.

Morphology modulation of NiCo2S4 arrays in-situ growth on carbon cloth for high performance flexible supercapacitor electrode

NiCo2S4 has been extensively researched as a promising pseudocapacitor material. In this work, NiCo2S4 with three different morphologies (nanoneedles, nanosheets and hexahedrons) were synthesized in-situ grown on the surface of carbon cloth by two-step hydrothermal method with adding different dosage of NH4F. The NH4F plays a key role in controlling the morphology of NiCo2S4 and the mechanisms for the effects of different dosage of NH4F on the morphology of NiCo2S4 are proposed. The electrochemical results show that NiCo2S4 nanosheets delivers the best performance with specific capacitance of 2.98 F cm−2 at 1 mA cm−2 and good cycling stability (82% retention at 20 mA cm−2 after 1000 cycles). In addition, the flexible supercapacitor fabricated with NiCo2S4 nanosheet and activated carbon possesses an energy density of 21.4 Wh kg−1 at a power density of 662.98 W kg−1. All these results indicate that NiCo2S4 nanosheet is an ideal potential electrode material for supercapacitors.

Conducting Polymer Hydrogel Driven By Sodium Chloride as High Performance Flexible Supercapacitor Electrode

With the rapid development of the wearable devices and flexible supercapacitors (FSCs), urgent demand for electrodes with high specific capacitance and excellent flexibility have been put forward. Herein, a self-standing conducting polymer hydrogel electrode has been successfully synthesized by in situ polymerization of aniline (ANI) in aqueous solution of polyvinyl alcohol (PVA), phytic acid (PA) and sodium chloride (NaCl). The prepared PANI/PVA/NaCl (PPN) hydrogel electrode shows high specific capacitance (1544 mF cm−2 at current density of 1 mA cm−2), good flexibility (elongation at fracture of 110%), satisfactory electrochemical stability (92% capacitance retention after 500 repeated bending cycles) and excellent cycling stability (78.2% capacitance retention after 10000 cycles) due to the uniform 3D interconnected structure driven by NaCl pseudo template. In order to further explore the potential application prospects of the synthesized hydrogel in flexible devices, a series of all-hydrogel-state FSCs are assembled based on the prepared PPN hydrogel electrodes and typical PVA/H2SO4 electrolyte. The assembled FSCs exhibit high energy density of 51.1 μWh cm−2 at power density of 250 μW cm−2 and long-life stability of 81.10% capacitance retention after 10000 charge/discharge cycles. This work provides a new synthesis strategy for the high performance energy storage electrodes and devices.

Fabrication of High-Performance Flexible Supercapacitor Electrodes with Poly(3,4-ethylenedioxythiophene) (PEDOT) Grown on Carbon-Deposited Polyurethane Sponge

Composite porous supercapacitor electrodes were prepared by growing poly(3,4-ethylenedioxythiophene) (PEDOT) on graphite nanoplatelet- or graphene nanoplatelet-deposited open-cell polyurethane (PU) sponges via a vapor phase polymerization (VPP) method. The resulting composite supercapacitor electrodes exhibited great capacitive performance, with PEDOT acting as both the conductive binder and the active material. The chemical composition was characterized by Raman spectroscopy and the surface morphology was characterized by scanning electron microscopy (SEM). Cyclic voltammetry (CV), charge-discharge (CD) tests and electrochemical impedance spectroscopy were utilized to study the electrical performance of the composite electrodes produced in symmetrically configured supercapacitor cells. The carbon material deposited on PU substrates and the polymerization temperature of PEDOT affected significantly the PEDOT morphology and the electrical properties of the resulting composite sponges. The highest areal specific capacitance 798.2 mF cm−2 was obtained with the composite sponge fabricated by VPP of PEDOT at 110 °C with graphene nanoplatelet-deposited PU sponge substrate. The capacitance retention of this composite electrode was 101.0% after 10,000 charging–discharging cycles. The high flexibility, high areal specific capacitance, excellent long-term cycling stability and low cost make these composite sponges promising electrode materials for supercapacitors.

Polypyrrole decorated cobalt carbonate hydroxide on carbon cloth for high performance flexible supercapacitor electrodes

Polypyrrole decorated cobalt carbonate hydroxide on carbon cloth (PPy@CoCH/CC) has been synthesized by a simple and cost-effective hydrothermal method. The prepared PPy@CoCH/CC exhibits unique 3D hierarchical nanostructure, showing uniform decoration of PPy nanoparticles on CoCH nanosheets. The PPy@CoCH/CC composites exhibit enhanced electrochemical performances due to the enhanced electrical conductivity, pseudocapcitive behavior, and efficient ion transport of PPy. Specifically, The PPy@CoCH/CC composites show high specific capacitance of 1217 F·g−1 at a current density of 1 A·g−1 and a good cycling performance of 89% capacity retention after 8000 cycles. In addition, a symmetric supercapacitor is fabricated using the PPy@CoCH/CC composites as both positive and negative electrode. The prepared symmetric supercapacitors deliver a high energy density of 47.36 Wh·kg−1 at a power density of 1600 W·kg−1.

ZnO@NiCo-LDH core-shell nanostructures grown on carbon cloth for high-performance flexible supercapacitor electrodes

ABSTRACT The ZnO@NiCo-LDH core-shell nanostructures on carbon cloth (CC) are synthesised by a combination of hydrothermal and electrochemical deposition method. The effects of deposition times on the morphology, structure and electrochemical properties of the product are studied. The results show that deposition times at 300 s NiCo-LDH sheets are anchored onto the surface of ZnO NRs, forming a three-dimensional (3D) interconnected thin-walled network structure. ZnO@NiCo-LDH300s electrode shows excellent electrochemical performance, such as areal capacitance of 667.3 mF cm−2 at 1 mA cm−2, and good cycle stability (86.78% capacitance retention after 2000 cycles), which may be attributed to the larger contact area and rich active sites between electrode provided by the NiCo-LDH grown on ZnO NRs. Furthermore, the asymmetric supercapacitor (ASC) is assembled with the ZnO@NiCo-LDH300s and active carbon (AC) as the electrodes, which exhibits an energy density of 0.044 mWh cm−2 at 1.17 mW cm−2.

In situ hybridization of polyaniline on Mn oxide for high-performance supercapacitor

• in situ polymerization of aniline on the surface of oxidative MnO x particles. • MnO x /PANI hybrid electrode displays the capacitance of 647 F g −1 at 1 A g −1 . • A flexible all-solid-state symmetric supercapacitor shows 37 Wh kg −1 at 800 W kg −1 . Effective hybridization of Mn oxide with polyaniline (PANI) have exhibited promising potential in improving the electrochemical performances of supercapacitors. Herein, MnO x /PANI hybrid electrode is fabricated by in situ polymerization of aniline on the oxidative MnO x particles via a facile immersion process. The hybrid electrode delivers a high specific capacitance of 647 F g −1 at a current density of 1 A g −1 , which is higher than that of MnO x electrode (56.0 F g −1 at 1 A g −1 ). Moreover, the hybrid electrode shows high rate capability and long-term cycling stability. Such excellent energy storage characteristics are attributed to the unique electrode structure, in which the porous network integrated by short PANI nanorod arrays facilitates the electrolyte access, and in situ polymerization enhances effectively the interaction between MnO x and PANI. A flexible all-solid-state symmetric supercapacitor based on the hybrid electrode was then assembled, which delivered a specific energy of 37 Wh kg −1 at a specific power of 800 W kg −1 , and excellent cycling ability. This work provides an effective approach for building a high-performance flexible supercapacitor electrode.

Setaria Viridis-Inspired Electrode with Polyaniline Decorated on Porous Heteroatom-Doped Carbon Nanofibers for Flexible Supercapacitors.

Carbon nanofibers are promising as primary electrode materials for supercapacitors on account of high specific surface area, lightweight, superior physicochemical stability, rich resource, and renewability. However, constructing porous and flexible carbon electrode materials with high capacitance for practical applications remains challenging. Here, heteroatom-decorated hierarchical porous carbon nanofiber composites containing phosphazene [N3P3(p-OC6H4-p-CHO)6, HAPCP], polymethyl methacrylate (PMMA), and graphene oxide (GO) are prepared through one-step electrospinning and subsequent thermal treatment. The alternant phosphorus-nitrogen structure links to the carbon backbones to improve flexibility and electrochemical performance. Inspired by a biomimetic Setaria viridis-like structure, the polyaniline (PANI)-decorated porous hybrid electrodes are prepared. The PANI@GO/PMMA/HAPCP/PAN carbon nanofibers (400P@0.1GPHCNFs) covered by PANI nanofibers as a novel free-standing flexible electrode exhibit an excellent electrochemical performance of 680.8 F g-1 at 0.5 A g-1 with a good capacitance retention of 93.5% after 3000 cycles. Moreover, the symmetric flexible all-solid-state supercapacitor assembled by the novel and delicate electrodes exhibits a high energy density of 27.70 W h kg-1 (at a power density of 231.08 W kg-1) and favorable cycling stability (84.50% retention of the capacitance after 1000 charge-discharge cycles), which indicates that the 400P@0.1GPHCNFs have great potential as a high-performance flexible supercapacitor electrode.

Biotemplate synthesis of polypyrrole@bacterial cellulose/MXene nanocomposites with synergistically enhanced electrochemical performance

Polypyrrole (PPy) has received extensive attention in supercapacitor electrodes due to its promising electrochemical activity, while the poor cycling stability and densely packed structure limited its electrochemical performance. Herein, we demonstrate the fabrication of flexible and freestanding PPy@bacterial cellulose (BC)/MXene composite film with significantly enhanced electrochemical performance. PPy nanoparticles were uniformly deposited on BC nanofibers via in situ polymerization, and assembled with highly conductive MXene (Ti3C2Tx) nanoflakes through strong interfacial interactions. BC as a biological template can effectively disperse PPy nanoparticles. The intercalation of PPy@BC nanofibers into Ti3C2Tx layers constructs hierarchically packed nanofibrous structure, which provides extensive accessible electrochemical active sites. Freestanding PPy@BC/Ti3C2Tx (PBM) electrode exhibits superior specific capacitance (gravimetric and areal capacitance of up to 550 F g−1 and 879 mF cm−2, respectively) and excellent capacitance retention of 83.5% after 10,000 cycles. In addition, the symmetric supercapacitor assembled by PBM papers present a high energy density of 33.1 W h kg−1 (power density of 243 W kg−1) and excellent capacitance retention. The elaborately designed nanostructure and PPy-Ti3C2Tx hybridization make great contribution to the enhanced electrochemical performance, which provide a feasible method for the fabrication of conductive polymer-based high-performance flexible supercapacitor electrodes.

Interface guide: In-situ integrating MoS2 nanosheets into highly ordered polypyrrole film for high performance flexible supercapacitor electrodes

Self-standing film with desirable properties is a promising candidate for flexible electronic applications. Conducting polymers (CP) have intrinsic film forming and pseudocapacitive characteristics. However, pure CP films are rarely applied in energy storage devices due to their disordered molecular structure which would result in insufficient utilization of the supported active materials and apparent volumetric effect. The specific lamellar structure of 2D nanosheets is an ideal platform for CP growing into self-standing film with desirable structure. Herein, a facile interface engineering strategy is proposed for in-situ integrating 2D MoS2 nanosheets into 3D polypyrrole (PPy) framework, in which dodecylbenzene sulfonate (DBS−) anions intercalate into MoS2 nanosheets and guide PPy to grow into ordered molecular structure. The resultant self-standing films with PPy chains in a high degree of ordering can deliver a high area capacitance of 1200 mF/cm2 and a high volumetric capacitance of 325 F/cm3, which are significantly superior to pure PPy films and show a great potential for high performance flexible supercapacitor application.

Electrospun Core-Shell Nanofibrous Membranes with Nanocellulose-Stabilized Carbon Nanotubes for Use as High-Performance Flexible Supercapacitor Electrodes with Enhanced Water Resistance, Thermal Stability, and Mechanical Toughness.

A high-performance flexible supercapacitor electrode with a core-shell structure is successfully developed from cellulose nanocrystal (CNC)-stabilized carbon nanotubes (CNTs). By incorporating poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA), a cross-linked nanofibrous membrane (CNT-CNC/PVA-PAA) is prepared as the core material via directional electrospinning, followed by a thermal treatment. The flexible supercapacitor electrodes are eventually fabricated via the in situ polymerization of polyaniline (PANI), which was used as the coating shell material, on the aligned electrospun nanofibers. By taking advantage of the thermally induced esterification cross-linking that occurs among PVA, PAA, and the CNT-CNC nanohybrids, the membranes present with enhanced water resistance, mechanical strength, and thermal stability. After the surface coating of the PANI shell, the optimized PANI@CNT-CNC/PVA-PAA nanofibrous membranes exhibit a large porosity, an enhanced specific surface area, a superior tensile strength of ∼54.8 MPa, and a favorable electroconductivity of ∼0.44 S m-1. As expected, the nanofibrous electrodes with a specific capacitance of 164.6 F g-1 can maintain 91% of the original capacitance after 2000 cycles. The symmetrical solid-state supercapacitor assembled by the nanofibrous electrodes shows an excellent capacitance of 155.5 F g-1 and a remarkable capacitance retention of 92, 90, and 89% after 2000 cycles under flat, bending, and twisting deformations, respectively.

NiCo-LDH nanowires@nanosheets core-shell structure grown on carbon fiber cloth for high performance flexible supercapacitor electrode

In this paper, a facile two-step method was adopted to in-situ develop a flexible electrode with NiCo-LDH nanowires@NiCo-LDH nanosheets core-shell structure on carbon fiber cloth (CFC). The electrochemical properties of the composite materials with different Ni/Co molar ratios nanosheets were systematically studied. It is found that the NiCo-LDH nanowires@Ni2Co1-LDH nanosheets (NiCo@Ni2Co1) composite material achieves a high areal capacitance of 9.67 F/cm2 at 5 mA/cm2 and a good cycling stability (75% capacitance retention after 2000 cycles). The excellent performance benefits from the distinct core-shell structure and the synergistic effect of NiCo-LDH nanosheets and NiCo-LDH nanowires. Moreover, a solid-state flexible asymmetric supercapacitor (ASC) assembled with NiCo@Ni2Co1/CFC as positive electrode and activated carbon on CFC as negative electrode can work stably at a voltage of 1.6 V. This ASC displays a high areal energy density of 298.6 uWh/cm2 at a current density of 1 mA/cm2 and with a corresponding areal power density of 0.80 mW/cm2.

Functional graphene film macroscopic assemblies for flexible supercapacitor application

The ever-increasing demand for flexible/wearable electronic devices has stimulated the rapid development of flexible supercapacitors with enhanced electrochemical performance and mechanical flexibility. Graphene-based materials are promising candidates for high-performance flexible supercapacitor electrodes due to their large surface area, high conductivity, low weight and superior mechanical flexibility. In this review, after a brief introduction, we mainly discuss different strategies to enhance performances of graphene-based electrode in recent years. Their fabrication process and electrochemical performances are discussed and compared. Then two types of flexible supercapacitors, namely, fiber-type supercapacitor and micro-supercapacitor, are also discussed in detail. We also present our point of view in our discussion.

A core–shell MnO2@Au nanofiber network as a high-performance flexible transparent supercapacitor electrode

A highly transparent core–shell MnO2@AuNF network electrode is fabricated for a flexible portable energy storage device

A high-performance flexible supercapacitor electrode material based on nano-flowers-like FeS2/NSG hybrid nanocomposites

Novel FeS2/nitrogen-sulfur double doped graphene (NSG) flexible hybrids electrode materials have been successfully prepared via a rapid microwave method followed by tube furnace heating process. Small size nano-flower-like structure of FeS2 uniformly supported on multi-fold NSG, which promote electron transport and electrochemical reaction. The material shows good electrochemical performance in a three-electrode system, such as high specific capacitance (528.7 F g−1 at the current density of 1 A g−1), excellent charge/discharge stability and long-term cycling life (89% of capacitance retention after 10,000 cycles at 10 A g−1). These results demonstrate great potential of FeS2/NSG flexible hybrid nanocomposites for supercapacitor application.

Core-Shell Composite Fibers for High-Performance Flexible Supercapacitor Electrodes.

Core-shell nanofibers containing poly(acrylic acid) (PAA) and manganese oxide nanoparticles as the core and polypyrrole (PPy) as the shell were fabricated through electrospinning the solution of PAA and manganese ions (PAA/Mn2+). The obtained nanofibers were stabilized by Fe3+ through the interaction between Fe3+ ions and carboxylate groups. Subsequent oxidation of Mn2+ by KMnO4 produced uniform manganese dioxide (MnO2) nanoparticles in the fibers. A PPy shell was created on the fibers by immersing the fibers in a pyrrole solution where the Fe3+ ions in the fiber polymerized the pyrrole on the fiber surfaces. In the MnO2@PAA/PPy core-shell composite fibers, MnO2 nanoparticles function as high-capacity materials, while the PPy shell prevents the loss of MnO2 during the charge/discharge process. Such a unique structure makes the composite fibers efficient electrode materials for supercapacitors. The gravimetric specific capacity of the MnO2@PAA/PPy core-shell composite fibers was 564 F/g based on cyclic voltammetry curves at 10 mV/s and 580 F/g based on galvanostatic charge/discharge studies at 5 A/g. The MnO2@PAA/PPy core-shell composite fibers also present stable cycling performance with 100% capacitance retention after 5000 cycles.