Flexible Solid Supercapacitor Research Articles

Self-supporting electrodes with in situ built aniline on carbon fibers and reduced graphene oxide covalently for stable flexible supercapacitors

Practical applications of flexible electronics have challenged the stability and cycle performance of flexible supercapacitor under continuous mechanical deformation, thus flexible electrode with stable structure has to be considered to maintain high-quality performance. A covalent modification strategy is present here to improve the stability of electrodes. Graphitized carbon cloth (GCC) and reduced graphene oxide (rGO) that modified with aniline by Suzuki reaction, are covalently bonded together with the polymerization of aniline (PANI). The electrode (GCC-PANI-rGO) modified by covalent bonds is stable enough to remain 97.73 % initial specific capacitance after charge-discharge 15,000 times at 40 mA/cm2. The capacitance retention of asymmetric flexible solid supercapacitor (FSSC) prepared by GCC-PANI-rGO and GCC is 108.78 % after 10,000 times mechanical folding. The electrode formed a π-π conjugation system through Suzuki reaction possesses low charge transfer resistance (0.428 Ω), and exhibits high specific capacitance and energy density that up to 11.825 F/cm2 and 1.642 mWh/cm2 at 1 mA/cm2. The energy density of FSSC is 0.266 mWh/cm2 at 1 mA/cm2 and surpasses most FSSC based on PANI and graphene. This work gives an essential covalently synthetic strategy for flexible supercapacitor with stable electrochemical performance in application.

Flexible Solid Supercapacitors of Novel Nanostructured Electrodes Outperform Most Supercapacitors.

Sustainable and scalable fabrication of electrode materials with high energy and power densities is paramount for the development of future electrochemical energy storage devices. The electrode material of a supercapacitor should have high electrical conductivity, good thermal and chemical stability, and a high surface area per unit volume (or per unit mass). Researchers have made great efforts to use two-dimensional (2D) nanomaterials, but the separated 2D plates are re-stacked during processing for electrode fabrication, impeding the transport of ions and reducing the number of active sites. We developed a novel process for manufacturing thin and flexible electrodes using a 2D material (MXene,Ti3AlC2) and a conducting polymer (poly(3,4-ethylenedioxythiophene), PEDOT). Because the PEDOT layer is electrochemically synthesized, it does not contain the activator poly(styrene sulfonate). The electrospray deposition technique solves the restacking problem and facilitates the infilling of the gel electrolyte by forming a highly porous open structure across the entire electrode. In the PEDOT/MXene multilayered electrode, the double-layer capacitance increased substantially because of a dramatic increase in the number of accessible sites through the MXene layer. Although applied to solid supercapacitors, these new supercapacitors outperform most aqueous electrolyte supercapacitors as well as other solid supercapacitors.

High-performanced flexible solid supercapacitor based on the hierarchical MnCo2O4 micro-flower

Transition metal oxides have attracted much attention in supercapacitors(SCs) research field due to their eco-friendly characteristics and high theoretical specific capacity. However, the slow reaction kinetics process and poor long-cycle performance hinder its potential application. To overcome these shortcomings, MnCo2O4 micro-flowers (MnCo2O4-MF) with hierarchical structure were prepared. The spinel MnCo2O4 has a variety of metal valence states, which can provide more electrochemical active sites compared to mono-metal oxides. Moreover, the unique hierarchical structure of MnCo2O4-MF shortens the transmission distance of ions and electrons, and reduce the volume expansion and structural collapse during the cycles. Benefiting from the crystal phase and structure advantages of MnCo2O4-MF, the reaction kinetics process was accelerated and it showed excellent long-cycle stability. In aqueous alkaline electrolyte, MnCo2O4-MF exhibits an ultra-high specific capacity of 1230 F g−1 at a current density of 1 A g−1. Even after 10,000 cycles at 10 A g−1, the capacity of 102.67% is still maintained. In addition, we constructed the sandwich structured flexible flexible hybrid solid supercapacitor (FHSC) based on MnCo2O4-MF // carbon nanoboxes. The FHSC devices not only expand the working voltage window of SCs, but also show flexibility and excellent electrochemical performance.

Facile synthesis of polypyrrole/graphene composite aerogel with Alizarin Red S as reactive dopant for high-performance flexible supercapacitor

Polypyrrole (PPy)/graphene composite aerogel with three-dimensional porous network structure is prepared by a facile one-step hydrothermal method using Alizarin Red S (ARS) as crosslinker, oxidant and dopant. Analysis of infrared spectroscopy, ultraviolet spectroscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy confirm the elimination of oxygen functional groups of graphene oxide, the successful polymerization of PPy and the efficient doping effect of ARS. The optimized aerogel electrode (PGA-10) provides outstanding specific capacitance of 461 F/g at a current density of 0.5A/g. The assembled symmetrical flexible solid supercapacitor constructed from two identical PGA-10 electrodes exhibits excellent electrochemical performance, 134 F/g (316.67 mF/cm2) within a wide potential window up to 1.8V, 60.3 W h kg−1 (142.5 μW h cm−2) at power density of 900.7 W kg−1 (900.7 μW cm−2), while maintaining good cycle stability (capacitance retention rate of 84.4% after 10,000 cycles) and excellent flexibility. This work demonstrates that the feature of high flexibility, light-weight and outstanding supercapacitive performances for PGA-10 composite aerogel can provide promising applications in wearable and portable electronics.

Two-dimensional Mg-doped MnO2@ carbon cloth nanosheets for high performance typical flexible solid supercapacitor

Metal doping MnO2 has better electrochemical performance than pure MnO2. We have demonstrated a facile approach for synthesizing Mg-doped MnO2@ carbon cloth via a typical hydrothermal reaction. The intercalation of Mg2+ rapidly increases the operating window to 1.2 V. Compared to other metal ions (Co2+, Fe3+, Bi2+, Al3+, Cr2+) doping, Mg2+ doping further increases the lattice defects of MnO2, achieving more vacancies, and effectively improving the performance of MnO2. As a flexible symmetric solid supercapacitor (FSSSC), the voltage window can be extended to 2.2 V, and the energy density of FSSSC reaches 2.06 mW h/cm3 at 43.94 mW/cm3. The device can illuminate a 2.2 V LED successfully, showing its huge actual application value.

Low-Temperature-Resistant Flexible Solid Supercapacitors Based on Organohydrogel Electrolytes and Microvoid-Incorporated Reduced Graphene Oxide Electrodes.

Maintaining enough flexibility and satisfied electrochemical performance simultaneously at subzero temperatures is still challengeable for flexible solid supercapacitors. In the present work, by adopting an organohydrogel electrolyte and reduced graphene oxide (rGO) films with microvoids serving as electrodes, a supercapacitor, which could be steadily operated down to -60 °C, has been obtained and has shown excellent low-temperature tolerance. The organohydrogel electrolyte consists of LiCl in glycerol/water solution containing polyvinyl alcohol, exhibiting excellent flexibility at -60 °C. Due to the introduction of micropores between rGO sheets, the porous membrane can be folded even in liquid nitrogen. Combining the rGO electrodes with the organohydrogel electrolyte, the maximum voltage of the present supercapacitor could be extended to 2.0 V, and a capacitance of 7.73 F·g-1 at -60 °C could be achieved. After 5000 charge/discharge cycles at -20 °C, the capacitance retention rate is 87.5%. The excellent flexibility and low-temperature resistance of the current supercapacitor pave a novel way for developing compression-resistant electronic samples compatible with a low-temperature environment.

Interfacial modification for heightening the interaction between PEDOT and substrate towards enhanced flexible solid supercapacitor performance

Poly(3,4-ethylene-dioxythiophene) (PEDOT) was reported to be an organic electrode material for supercapacitor. But poor stability and small capacitance restrict its further application. Here, we fabricate a new PEDOT-based supercapacitor device where the working electrode is prepared by depositing trace of Ni-rich oxide on the interface between PEDOT and substrate (named as PEDOT-Ni2+/NiO-SS). This PEDOT-Ni2+/NiO-SS half-electrode obtained a higher specific capacitance of 236 F/g, good rate capability and superior cycling stability (99% capacitance retention after 2500 cycles) than those of untreated PEDOT. Subsequently, a flexible all-solid-state asymmetric supercapacitor (ASC) device was fabricated by using PEDOT-Ni2+/NiO-carbon cloth as positive electrode and untreated PEDOT-carbon cloth as negative electrode. An ASC cell presented higher energy density (40.15 Ah/Kg) and power density (1.32 kW/Kg) than the symmetrical supercapacitor device composed of untreated PEDOT. PEDOT-Ni2+/NiO-SS structure could facilitate the insertion of ions from electrolytes into electrode material, achieve long cyclic lifetime and high electrochemical stability. The electrochemical deposition method to modify electrode interface using metal oxide could be a promising strategy and pave the way for the preparation of other supercapacitor electrodes.

Synthesis of Starch-<i>g</i>-PAN Polymer Electrolyte Membrane and Its Application to Flexible Solid Supercapacitors

Synthesis of Starch-<i>g</i>-PAN Polymer Electrolyte Membrane and Its Application to Flexible Solid Supercapacitors

Flexible solid supercapacitor, based on reduction oxidized graphene polymerization (3, 4-ethylenedioxythiophene)

In this case, RGO (graphene reduced load) aggregates (3, 4-ethylenedioxythiophene) were used to prepare basic films by chemical deposition method. Optimize electrochemical deposition (3, 4-ethylene dioxide) and rGO voltage Windows and electrolytes. SEM observation confirmed that PEDOT/rGO did synthesize the necessary composites. Electrochemical tests showed that the electrochemical performance of PEDOT electrode was improved by adding rGO. The mixed PEDOT/rGO electrode has a high specific capacitance (134 F/g, 0.8 mA/cm2).

High-voltage flexible solid state supercapacitor based on neutral hydrogel/carbon nanotube arrays

As a new energy storage device, supercapacitor (or electrochemical capacitor) has an ultra-long cycle life, extremely high power density and enhanced energy density. It fills the gap in the energy-power spectrum between traditional capacitor and battery. In general, the traditional energy storage and conversion device cannot have a perfect trade-off between high energy density and high power density. With the rapid development of modern society, developing light, portable, safe and environmentally friendly high-performance energy storage devices has become increasingly vital. Therefore, there are numerous researches of flexible solid supercapacitors emerging at this historic moment. The selection of flexible electrode materials and that of electrolytes are crucial factors in designing the flexible solid state supercapacitors, which have been the research hotspots in recent years. Carbon nanotube array has been widely used in electrode material of super capacitors due to its excellent electrical conductivity, large specific surface area and super high chemical stability. But in assembly process, carbon nanotube array easily collapses and breaks its neat orientation because of its poor mechanical strength. In consideration of environmental contamination and practical demands, in this paper the neutral gel electrolyte is adopted to embed carbon nanotube array to form flexible composite film electrode. Besides the fact that we use hydrophilic flexible carbon cloth as current collector and neutral gel electrolyte as separator to prepare flexible devices, we compare the electrochemical properties among different devices by changing the electrolyte salt added in gel electrolyte. Meanwhile, after continuous bending and folding, the properties of flexible devices have not been significantly damaged, indicating good flexibility and mechanical stability. The specific capacity of the whole device with PVA-NaCl used as gel electrolyte increases up to 104.5 mF·cm<sup>–3</sup>, which is much higher than the specific capacity of the composite device formed by organic ionic gels with carbon nanotube array and that of the composite device formed by commercial short carbon nanotubes with hydrogels. A maximum energy density of 0.034 mW·h·cm<sup>–3</sup> is obtained at the same time. In addition, it has good rate performance, cycling stability, suppressing self-discharge property, and good chemical stability at a high voltage of 1.6 V. Neutral gel/carbon nanotube array composite devices not only meet the needs of the era of green safety, flexible and portable folding, but also open up the future application prospects of medical implants.

Low Temperature Tolerant Organohydrogel Electrolytes for Flexible Solid‐State Supercapacitors

AbstractGel electrolytes are attracting growing interest in the field of flexible solid supercapacitors. So far, hydrogel electrolytes have been widely investigated, and high performance flexible supercapacitors based on these electrolytes have been realized. However, conventional hydrogel electrolytes contain massive solvent water, inevitably freeze and restrict ion transport at subzero temperatures, which fundamentally limits the utilization of supercapacitors in extreme low temperatures. A new organohydrogel electrolyte that successfully brings the advantages of outstanding flexibility and ionic conductivity at low temperatures by using H2O/ethylene glycol as a dispersion medium is reported here. When applying the antifreezing organohydrogel electrolyte, the flexible solid supercapacitor with carbon nanotube paper electrodes (≈0.5 × 2.2 cm2) exhibits stable electrochemical performance (70.6% capacitance retained at −40 °C) and excellent cycling stability (only 11.7% capacitance decay over 5000 charge/discharge cycles at −20 °C.) at low temperatures, representing the excellent low temperature tolerance. Meanwhile, the supercapacitor devices offer remarkable flexible performance under consecutive bending conditions. It is anticipated that the low temperature tolerant organohydrogel electrolyte may be a promising gel electrolyte for the next generation of flexible solid supercapacitors for using at low temperature environments.

High energy flexible supercapacitors formed via bottom-up infilling of gel electrolytes into thick porous electrodes

Formation of thick, high energy density, flexible solid supercapacitors is challenging because of difficulties infilling gel electrolytes into porous electrodes. Incomplete infilling results in a low capacitance and poor mechanical properties. Here we report a bottom-up infilling method to overcome these challenges. Electrodes up to 500 μm thick, formed from multi-walled carbon nanotubes and a composite of poly(3,4-ethylenedioxythiophene), polystyrene sulfonate and multi-walled carbon nanotubes are successfully infilled with a polyvinyl alcohol/phosphoric acid gel electrolyte. The exceptional mechanical properties of the multi-walled carbon nanotube-based electrode enable it to be rolled into a radius of curvature as small as 0.5 mm without cracking and retain 95% of its initial capacitance after 5000 bending cycles. The areal capacitance of our 500 μm thick poly(3,4-ethylenedioxythiophene), polystyrene sulfonate, multi-walled carbon nanotube-based flexible solid supercapacitor is 2662 mF cm–2 at 2 mV s–1, at least five times greater than current flexible supercapacitors.

Flexible solid-state supercapacitors based on shrunk high-density aligned carbon nanotube arrays

Nowadays flexible solid-state supercapacitors (FSCs) have received more and more attention than conventional capacitors due to the good operability and flexible fabrication process as well as high specific/volumetric energy density. In general, carbon based materials including amorphous carbon, carbon nanotube, grapheme, etc. can be used to fabricate electrolytic double-layer capacitance (EDLC)-type FSCs due to its extraordinary cyclic stability at high current density. Aligned carbon nanotube (ACNT) arrays are one of the ideal electrode candidates for energy storage due to their good capacity, highly efficient charge transfer rate, excellent rate performance and long cycle life compared with those of other carbon-based materials carbon nanotubes. However, the low density and the weak interaction between the carbon tubes cause the CNT arrays to tend to easily collapse during processing and transferring. Thus pure carbon nanotube arrays are unable to be directly used to assemble flexible electronic devices. In this paper, we use ethyl alcohol to shrink the CNT array to increase the density and mechanical strength. At the same time we embed the conductive polyvingle alcohol (PVA) gel into the carbon nanotube array to fabricate a flexible solid supercapacitor. Hydrogel-based solid electrolytes have been long considered to be used to prepare FSCs, because this method possesses obvious advantages including low cost, good environmental compatibility and simple manufacturing process. The ACNT/PVA complex can maintain good mechanical stability and flexibility during its folding and bending, and can also keep the high orientation of carbon nanotubes. The maximum capacitance of the hybrid flexible device can reach 458 mFcm-3 at a current density of 10 mAcm-3, which is much higher than the capacitance reported in the literature. After 5000 charging-discharging cycles, a capacity still keeps nearly 100%. The maximum energy density of CNTs/gel composite device can reach 0.04 mWhcm-3 with an average power density of 3.7 mWcm-3. The capacitance can be further increased to 618 mFcm-3 by a simple in-situ electrochemical oxidation treatment. The energy density can be further increased to 0.07 mWhcm-3 by the electro-oxidation treatment. The electrochemical performance of the device is far superior to that of EDLC-typed FSC reported in the literature. Additionally the equivalent series resistance (RESR) of the devices decreases from 120 to 30 and also the charge transfer resistance declines from 90 to 10 . This is mainly due to the effect of pseudo capacitance and electro-wetting effect caused by electro-oxidation. This easy-to-assemble hybrid devices thus potentially pave the way for manufacturing wearable devices and implantable medical devices.

A novel and facile step-by-step hydrothermal fabrication of peony-like Ni0.4Co0.6(OH)2 supported on carbon fiber cloth as flexible electrodes for advanced electrochemical energy storage

Nickel/Cobalt double hydroxide has attracted increasing attention as promising electrode material in supercapacitor field, but its poor adhesion in most conductive substrates largely thwarts the capacitance and cycling stability performance. In this work, an effective strategy was developed to synthesis Ni0.4Co0.6(OH)2 onto carbon fiber cloth (CFC) and obtained a flexible peony-like electrode (Ni0.4Co0.6(OH)2/CFC) by a simple step-by-step hydrothermal method without any adscititious alkali source and oxidant. Electrochemical studies showed that this type of Ni0.4Co0.6(OH)2/CFC exhibited an extraordinary capacitance of 1816Fg−1 (605Fcm−2) at the current density of 1.0Ag−1 and excellent cycling stability with capacitance retention of 98.3% after 5000 charge/discharge cycles. After assembled to be a symmetric flexible solid supercapacitor, its electrochemical performances remained stability under flat, folded, twisted and rolled states. The remarkable electrochemical and flexible properties of Ni0.4Co0.6(OH)2/CFC developed in this study are obviously superior to those previously reported Ni0.4Co0.6(OH)2-based supercapacitors.

High Performance All-solid Supercapacitors Based on the Network of Ultralong Manganese dioxide/Polyaniline Coaxial Nanowires

In recent years, thin, lightweight and flexible solid supercapacitors are of considerable interest as energy storage devices. Here we demonstrated all-solid supercapacitors (SSCs) with high electrochemical properties, low self-discharge characteristics based on manganese dioxide/polyaniline (MNW/PANI) coaxial nanowire networks. The synergistic effect of MnO2/PANI plus the unique coaxial nanostructure of the ultralong nanowires with a highly interconnected network effectively enhance the conductivity and capacitive performance of the SSCs device. The MNW/PANI composite with 62.5% MnO2 exhibits an outstanding areal specific capacitance reaching 346 mF/cm2 at 5 mV s−1 which is significant higher than most previously reported solid supercapacitors (15.3 mF/cm2–109 mF/cm2) and is close to the that of the best graphene films solid state supercapacitors (372 mF/cm2). In contrast, only 190 mF/cm2 of areal specific capacitance was obtained for the pure MnO2 NW network. The supercapacitors also exhibited low leakage current as small as 20.1 μA, which demonstrated that the MNW/PANI SSCs have great potential for practical applications.

Novel scalable synthesis of highly conducting and robust PEDOT paper for a high performance flexible solid supercapacitor

A scalable method to produce flexible PEDOT/cellulose paper by surfactant-free interfacial polymerization is developed and its application is demonstrated for a flexible solid-state supercapacitor.