Flexible supercapacitors based on 3D conductive network electrodes of poly(3,4-ethylenedioxythiophene)/non-woven fabric composites

Abstract

We design a flexible supercapacitor with poly(3,4-ethylenedioxythiophene) nanowire-coated non-woven fabrics (PEDOT/NW) as the electrode material via a simple and low-cost chemical polymerization synthesis. PEDOT nanowires depositing on non-woven fabrics form a conductively and mechanically robust composite that is utilized directly as an electrode without introducing organic binders or conducting additives. The PEDOT/NW electrodes are characterized by scanning electron microscopy (SEM) that confirms the porous morphology of PEDOT/NW at the nanoscale. The capacitive characteristics of the supercapacitor are evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The PEDOT/NW composites afford a high-efficient and stable electrode for a supercapacitor showing high specific capacitance of 169 F g⁻¹ and excellent energy density of 21.1 W h kg⁻¹ as well as good long-term cycling stability with 90% specific capacitance retained after 1000 cycles. Therefore, this conductively porous PEDOT/NW electrode holds considerable promise as a flexible, low-cost and high-efficient electrode material.

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Introduction

Flexible energy storage devices are getting more and more attractive nowadays due to their excellent performances of lightweight and wearable power conversation and long cycle lifetime.^1–4 Among the energy storage devices, supercapacitors are considered to be very attractive flexible and wearable electronics for their high electrochemical performances, such as higher power density than batteries and higher energy density than conventional dielectric capacitors.^5–9 Therefore great attention has focused on the development of flexible supercapacitors with high performances.¹⁰ The preparation of flexible electrodes with high capacitive properties and good mechanical strength has already been a critical challenge. Carbon materials are used most commonly to prepare the flexible electrodes, such as carbon nanotubes (CNTs), carbon nanofibres, activated carbon and graphene,^8,11–16 and show good electrochemical performances. However, the elaborate fabrication procedures and high cost of carbon materials could restrict their further application in large-area synthesis.

Conducting polymers have been widely investigated and applied in various electronic devices. Poly(3,4-ethylenedioxythiophene) (PEDOT) affords an ideal prototypical conductive polymer for supercapacitors owing to its excellent capacitive performances, highly electric conductivity, low cost, easy preparation as well as good environmental and conductive stability.^17–20 In addition, the specific capacitance of PEDOT is larger than that of conventional carbon materials using double layer charge storage. Because conducting polymers can proceed additional faradic pseudocapacitance apart from the pure electrostatic attraction of ions which occurs in electric double layer.⁵ Liu et al. reported the electrode materials based on MnO₂/PEDOT coaxial nanowires²¹ and MnO₂ nanoparticle enrichment in PEDOT nanowires²² presented excellent electrochemical capacitive performances with the specific capacitance over 200 F g⁻¹ and fast charge–discharge performances. Despite of excellent capacitive performances of the PEDOT-based materials, the electrochemical deposition on the metal substrate would have great limitations to the formation of flexible electrodes. To obtain flexible electrodes, commercial supercapacitor separator (CSS) membranes were used as the supporting substrate for the synthesis of graphite/PEDOT/MnO₂ ternary composites. A flexible asymmetric supercapacitor based on this ternary composite electrode and activated carbon electrode exhibited high energy density (31.4 W h kg⁻¹) and power density (90 W kg⁻¹) as well as an acceptable cycling performance of 81.1% retention after 2000 cycles, as reported by Zhang et al.¹⁸ Jia et al. synthesized MnO₂/poly(3,4-ethylenedioxythiophene)/multiwalled carbon nanotubes hybrid nanocomposite and investigated their electrochemical properties as a flexible micro-supercapacitor. This micro-supercapacitor presented a specific capacitance of 110 F g⁻¹ at a current density of 2 A g⁻¹.²³ Hammond et al. reported a freestanding film of high aspect ratio PEDOT nanofibres prepared by vapour-phase polymerization (VPP). A flexible supercapacitor based on the electrodes of PEDOT nanofibres deposited on a carbon fibre paper showed excellent capacitive performances, e.g. a gravimetric capacitance of 175 F g⁻¹ and 94% capacitance retention after 1000 cycles.²⁴ Laforgue also reported PEDOT nanofibres synthesized by the combination of electrospinning and vapour-phase polymerization. The highly conductive PEDOT nanofibres were incorporated into all-textile flexible supercapacitors that demonstrated stable performances with a capacitance of 20 F g⁻¹ of active materials, the positive and negative electrodes reaching values of 75 F g⁻¹ and 85 F g⁻¹, respectively.¹⁹ The literatures developed various PEDOT-based electrodes as flexible supercapacitors possessing good electrochemical performances. However, most of the approaches to the fabrication of PEDOT are complicated (e.g. high temperature required for VPP method) to operate and limited to the large-area synthesis (e.g. electrochemical polymerization approach). Additionally, most of the previous reports lack control over the morphology of PEDOT. Electrochemical charge storage in PEDOT is a surface phenomenon that is significantly determined by the conductivity and surface area of the polymer electrode. Three-dimensional (3D) PEDOT nanostructures are considered as high-performance electrode materials due to their high conductivity and large specific surface area that are favourable for ion transportation. Therefore, creating the flexible 3D-structured PEDOT composites still remains a challenge, which allows highly efficient utilization of PEDOT for charge storage with facilitated transport of ions and good cycle stability. In our previous work, a novel 3D flowerlike PEDOT nanomaterial was synthesized by adjusting the molar ratio of water to surfactant in a ternary phase system.²⁵ This 3D flowerlike PEDOT applied as electrode material on stainless steel substrate showed much higher capacitive performances (111 F g⁻¹)²⁶ than that of 1D PEDOT nanofibres (73 F g⁻¹).²⁷ That is due to the fact that this outstanding morphology can greatly assist in the penetration of electrolyte and reactants into the whole electrode matrix to accelerate the charge–discharge reactions of ions and reduce the diffusion resistance of electrolyte.

Herein, we demonstrate 3D conductive PEDOT/non-woven fabric composites on the basis of a ternary phase system mentioned above. It is advantageous to maintain the flowerlike morphology of PEDOT in a ternary phase polymerization system. Due to its flexibility and good mechanical properties, non-woven fabric was selected to play both the roles of a template and a flexible substrate to support the deposition of PEDOT nanowires. The flexible supercapacitors assembled from these flexible electrodes exhibited superior capacitive performances. The PEDOT/non-woven fabric electrode for flexible supercapacitors showed an enhanced specific capacitance (169 F g⁻¹) and cyclic stability in comparison to the electrodes based on pure 3D flowerlike PEDOT reported by us before.

Experimental

Materials

3,4-Ethylenedioxythiophene monomer (EDOT, ≥99.7%) was purchased from Aldrich. Sodium bis(2-ethylhexyl)sulfosuccinate (AOT, 96%) was supplied by Acros Organics. Ferric chloride (FeCl₃), lithium perchlorate (LiClO₄) and other regents were obtained from Chemical Regent Company in Beijing. All of the regents were used as received without further purification.

Synthesis of PEDOT/NW composite

The PEDOT/NW composite was synthesized by in situ chemically oxidative polymerization on the basis of a ternary phase system. A piece of non-woven fabric (no. 609, Shenzhen Kingclean Clean Technology Co., Ltd., China) was washed by a mixture of water and ethanol (1 : 1, v/v) under a table concentrator (PSE-T150A, STIK (Shanghai) Co., LTD). Then the cleaned non-woven fabric was dried at 60 °C for 12 h and weighed out by a balance. As shown in Scheme 1, in a typical synthesis, the surfactant AOT was dissolved in 20 mL p-xylene at the concentration of 1.5 mol L⁻¹ and stirred for 20 min under ultrasonic irradiation until they were mixed together uniformly. 8.1 mL aqueous FeCl₃ solution (7 mol L⁻¹) was progressively added in the well-dispersed suspensions and kept being stirred about 30 min. The cleaned non-woven fabric was absolutely dipped into the above solution for 30 min. After that, the monomer of EDOT was introduced into the polymerization system. 0.4 mL of the EDOT monomer was slowly dripped into this system whilst stirring and then the reaction proceeded for 24 h at ambient temperature. Subsequently, the resultant dark non-woven fabric coated with PEDOT was taken out of the polymerization system and washed firstly with ethanol, and then by the mixture of water and ethanol (1 : 1 v/v) several times to remove the residual reagents until the mixture solution was colourless and transparent. Afterwards, the resultant dark PEDOT/NW fabrics were put into a conical flask and washed for 1 h under a table concentrator with a rotate speed of 180 rpm. Finally, this resultant samples were dried under vacuum at 60 °C for 8 h.

Scheme 1 Schematic illustration of the one-step fabrication process of the flexible PEDOT/NW electrode.

Characterization of the materials and the electrodes

Scanning electron microscope (SEM) images of the non-woven and PEDOT/NW fabric composite were obtained in an S-4800 (Japan) operated at 5 kV. The surface resistance was carried out by a two-probe method at room temperature by a resistance meter (America Desco Industries) with a potential of 3 V DC. The mass of the active material was determined by weight measurements before and after polymerization process.

Electrochemical measurement

The flexible supercapacitor was assembled to measure the device properties. In detail, PEDOT/NW (area of around 1 cm by 1.5 cm) with a mass loading of around 0.7 mg cm⁻² was put on the polyethylene glycol terephthalate (PET) membrane as both electrodes. Two pieces of these sheets were assembled with a separator of TF-3040 (pore size: ∼0.45 μm) sandwiched in between to produce a symmetric supercapacitor (Fig. 2). Two pieces of platinum were embedded and connected to the edge of the electrode on each side to enable a good electrical contract with an electrochemical measurement instrument. The electrolyte used in all of the measurements was a 1 mol L⁻¹ LiClO₄ aqueous solution, which was sealed by epoxy resin.

Electrochemical tests, including cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge–discharge, were performed in two-electrode system by CHI 660C instrument (Shanghai Chenhua Instrument Co. Ltd.). The electrochemical impedance spectroscopy measurements were performed over a frequency range from 10⁵ to 10⁻² Hz with an AC perturbation of 5 mV. The specific capacitance derived from galvanostatic discharge curves was calculated based on the following equation:^2,4

C_m = 2(I × t)/(m × ΔV) (1)

where C_m is the specific capacitance of the electrode (F g⁻¹), I is the discharge current, t is the time for a full discharge, m is the mass of one electrode, and ΔV stands for the potential window after a full discharge. The energy density (E, W h kg⁻¹) and power density (P, W kg⁻¹) of the supercapacitor depicted in the Ragone plots were calculated by using the equations:^2,4

E = C_m × ΔV²/2 (2)

P = E/t (3)

where C_m is the specific capacitance derived from galvanostatic discharge curves e, ΔV is the potential window, and t is the time for a full discharge.

Results and discussion

In order to make a flexible electrode, a non-woven fabric cloth was selected as a flexible substrate owing to its various advantages, e.g. low-cost, softness, highly adsorbing ability to the electrolyte and electrochemical stability. However, as an electrode, the non-woven fabric also possesses a drawback that it is insulating. To avoid the insulating feature, CNTs were loaded on the surfaces of the cloth to increase the conductivity of the cloth. Afterwards, polyaniline (PANI) was deposited on the surface of the obtained CNT/cloth substrate. The PANI/CNT/cloth electrode exhibited enhanced capacitive properties in comparison to PANI/cloth electrode.²⁸ That is due to the fact that PANI possesses poor conductivity, as a result of poor electrochemical performances of PANI/cloth. Despite of an enhancement of capacitive properties, the processing to prepare the composite electrodes is complicated. For the case of PEDOT, we proposed a simple approach that the EDOT monomer polymerized directly on the surface of the non-woven fabrics because PEDOT has higher conductivity than that of other conducting polymers, e.g. PANI. This facile approach will not only simplify the operation to prepare the composite electrodes, but also reduce the cost to fabricate a flexible supercapacitor.

In our experiment, the non-woven fabrics served as substrates were immersed into a ternary phase system and PEDOT was in situ deposited on their surfaces to obtain the PEDOT/NW composite electrodes. The digital camera (a and d) and SEM images of the non-woven fabrics without and with PEDOT are shown Fig. 1. From the digital images, after polymerization the colour of the non-woven fabric changes from white (Fig. 1a) to black (Fig. 1d), indicating an obvious difference in the morphology or structure for the non-woven fabric before and after polymerization. According to SEM images, more details of non-woven fabrics with and without PEDOT can be obtained. Before polymerization, Fig. 1b and c reveal that the bare non-woven fabrics show layer-by-layer structure that consists of overlapped fibres. But after the polymerization of EDOT monomer each fibre of non-woven fabrics was coated with PEDOT (Fig. 1e). Therefore, the colour of the non-woven fabrics changed from white to black. The magnified image of a fibre coated with PEDOT is shown in Fig. 1f. It is worth noting that PEDOT nanowires with diameters of around 50 nm wrapped around the fibre surface of non-woven fabrics, as a result of the widening of the pristine non-woven fabrics. The resultant PEDOT nanowires entangled together to form a porous network nanostructure (Fig. 1f). Thus a 3D conductive PEDOT/NW network was achieved. This morphology could be favourable for the ion and electron transport between the electrodes and the active materials, which may lead to highly capacitive performances of supercapacitors. The results of surface resistance of PEDOT/NW electrodes reveal that the insulating feature of the non-woven fabrics was overcome after the deposition of PEDOT nanowires. The PEDOT/NW electrode becomes conductive and its surface resistance is around 275 Ω sq⁻¹. Additionally, there is a change in the thickness after the deposition of PEDOT nanowires. The PEDOT/NW electrode has an enhanced thickness of 0.32 mm in comparison to 0.26 mm of the non-woven fabric substrate.

Fig. 1 Top-view digital camera and SEM images of the non-woven fabrics (a–c) and the as-prepared PEDOT/NW composites (d–f).

3D conductive network electrodes based on the PEDOT/NW composites were selected to assemble a symmetric supercapacitor with a sandwich structure (Fig. 2a). Two pieces of the flexible PEDOT/NW electrodes with the same area were put on PET membranes as both electrodes, and were assembled with a separator of TF-3040 sandwiched in between to produce a symmetric supercapacitor structure. Two pieces of platinum were embedded and connected to the edge of the electrode on each side to enable a good electrical contract with an electrochemical measurement instrument. Fig. 2b shows an assembled supercapacitor that possesses good flexibility. Notably, PEDOT/NW composites are mechanically robust and are utilized directly as the electrodes of supercapacitors without the introduction for organic binders or conductive additives generally used in conventional supercapacitors.

Fig. 2 A schematic diagram of the structure of an assembled flexible supercapacitor (a) and a digital camera image (b) of the flexible supercapacitor. The scale is 1 cm in (b).

To explore the advantages of PEDOT/NW composites, we investigated the electrochemical properties of PEDOT/NW composite toward flexible supercapacitor application in two-electrode system. Cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) of the PEDOT/NW electrodes were investigated (Fig. 3). Fig. 3a reveals that PEDOT/NW presents a near ideal rectangular cyclic voltammetry profile with the potential range from −0.4 to +0.6 V (vs. SCE) at a scan rate of 10 mV s⁻¹ in 1 M LiClO₄ aqueous solution, indicating excellent capacitive behaviour and low resistance of materials.²⁹ That is due to the fact that facile ion and electron transport kinetics lead to fast electrochemical switching and highly reversible doping/de-doping reactions that result in a PEDOT pseudocapacitor to exhibit capacitive behaviour.^30–33 Galvanostatic charge–discharge behaviour of the PEDOT/NW composite is depicted between 0 and 1 V at the current density of 0.2 A g⁻¹ (Fig. 3b). As expected, the galvanostatic measurement agrees well with the CV study: the PEDOT/NW supercapacitor shows a typical triangular curve with only a small voltage drop at the beginning of the discharge curve, which again confirms superior capacitive behaviour of this flexible electrode. This linear and symmetric charge–discharge curve is characteristic of PEDOT pseudocapacitors that have high Coulombic efficiency and excellent reversibility.^19,32,33 The specific capacitance of the PEDOT/NW electrode was calculated according to the eqn (1). The calculated result shows that PEDOT/NW electrode possesses excellent specific capacitance of 169 F g⁻¹ that is around 85% of the theoretical specific capacitance of PEDOT (∼200 F g⁻¹), which is evaluated by the molecular weight of polymer (142 g mol⁻¹) and the doping level of counter-ions (0.3).^33,34 The specific capacitance of 3D conductively porous PEDOT/NW is greatly higher than previous reports.^{26,27,30,32,33} It is worth noting that the flexible PEDOT/NW composite electrodes present not only the superior nanostructures but also the superior capacitive properties due to the flexible substrates. A PEDOT nanowire coating on a three-dimensional non-woven fabric substrate as a conductively porous current collector enhances material utilization, maximizes surface area of electrochemical interaction, and results in a higher capacitance. In addition, the non-woven fabrics can adsorb more electrolyte solutions, thereby leading to the fast transport of ions and electrons during charge–discharge process of PEDOT nanowires.

Fig. 3 Electrochemical curves of the flexible supercapacitor based on PEDOT/NW electrodes (1 M LiClO₄): (a) CV curve at the scan rate of 10 mV s⁻¹ and the potential window −0.4 to +0.6 V. (b) Galvanostatic charge–discharge test at the current density of 0.2 A g⁻¹. (c) Nyquist plot at a frequency from 100 kHz to 10 mHz.

Notably, in the case of the nanostructures, the capacitors based on the nanostructures displayed morphology-dependent capacitance values. PEDOT thin films synthesized by electrochemical polymerization exhibited higher specific capacitance (ca. 100 F g⁻¹)³⁵ than those of PEDOT tracked blocks (<20 F g⁻¹), nanoparticles (<60 F g⁻¹) as well as micro/nanorods (<100 F g⁻¹).^36–38 But such thin films could hardly find any application for energy storage.³⁵ Recently, to improve the capacitive performances, the vapor-phase polymerization method is widely utilized to fabricate PEDOT nanofabrillars (20–175 F g⁻¹).^19,24,32 For example, recent vapor-phase research efforts result in PEDOT nanofibres deposited on hard carbon fibre paper, a supercapacitor with specific capacitance of 175 F g⁻¹, and high conductivity of 130 S cm⁻¹.²⁴ Although the nanofibres showed good capacitive performances, the vapour-phase polymerization strategy is more complicated in comparison to in situ chemical polymerization method. Obviously, the work shows not only a facile route to fabricate the PEDOT/NW composite, but also assembles a flexible supercapacitor based on the PEDOT/NW electrode, possessing superior specific capacitance of 169 F g⁻¹.

The electrochemical impedance spectroscopy has been utilized to characterize the electrochemical process of the electrode materials. As shown in Fig. 3c, a typical Nyquist plot of the EIS measurement was performed at the open circuit potential in a frequency range of 100 kHz to 10 mHz, using a perturbation amplitude of 5 mV. At the high frequency region, a semicircle is observed, which is indicative of the charge transfer phenomena of a faradic redox process.³⁹ The diameter of the semicircle stands for the charge transfer resistance in the electrochemical system. The relative low diffusion resistance of the composite reveals that: the 3D conductively porous network can promote the electrolyte ions fast penetrating between the PEDOT nanowires. In the intermediate frequency region, the 45° line indicates the characterization of Warburg diffusion, owing to the semi-infinite diffusion of ions into the interface between 3D porous materials and electrolyte. The Warburg curve is quite short which manifests the short diffusion path. It facilitates the efficient access of electrolyte ions to the electrode surface. The lines are almost vertical to the real axis in the imaginary part of the impedance in the low frequency region. This ideal capacitive behaviour is attributed to the Faradic pseudo-capacitance of the composite electrode.⁴⁰

The electrochemical impedance spectroscopy results can be further confirmed by the measurements of cyclic voltammetry at various scan rates (Fig. 4a) and galvanostatic charge–discharge at various current densities (Fig. 4b). In Fig. 4a, when the scan rates increase from 5 to 20 mV s⁻¹, the near ideal rectangular curves can still be maintained. The scan rate reaches as high as 50 mV s⁻¹, there is only a small deformation of the rectangular curve. The similar behaviour is observed for galvanostatic charge–discharge curves in Fig. 4b. Although the discharge time decreased with the current density increasing from 0.5 A g⁻¹ to 5 A g⁻¹, the PEDOT/NW supercapacitor still shows a typical triangular curve. Both the cyclic voltammetry and galvanostatic charge–discharge results indicate a high rate property of the supercapacitor. Fig. 4c presents the specific capacitance originated from charge–discharge curves at various current densities. The capacitance was calculated by eqn (1) based on the active material weight coated on the now-woven fabrics. At the current density of 0.2 A g⁻¹, the specific capacitance of the PEDOT/NW composite is 169 F g⁻¹. Furthermore, a PEDOT supercapacitor can be operated at charge–discharge rates that are 10 times faster, while maintaining more than 70% of its full capacity. The high rate capacity of the PEDOT/NW supercapacitor can be explained by the short ionic diffusion pathway during the charge–discharge processes, which is derived from 3D conductively porous network of the composite. Now-woven fabrics are served as substrates that are homogeneously coated by PEDOT nanowires to form a 3D conductively porous network. The 3D highly conductive architecture of PEDOT/NW thereby facilitates to collect the current during the faradic redox reaction of PEDOT and maximizes interfacial contact area for efficient supercapacitors. On the other hand, the non-woven fabric plays an important role of the container for the electrolyte storage. Both of the factors facilitate ion transport kinetics. Consequently, a fast charge–discharge performance and high charge storage capacity can be achieved with a PEDOT/NW supercapacitor.

Fig. 4 The electrochemical curves of the flexible supercapacitor based on PEDOT/NW electrodes (1 M LiClO₄): (a) CV curves of the supercapacitor at different scan rates of 5, 10, 20, 50 mV s⁻¹, respectively; (b) galvanostatic charge–discharge tests at different current densities; (c) the specific capacitance plot with various current densities; (d) Ragone plot of the supercapacitor at diverse current densities.

Energy density and power density are the two key factors for evaluating the power applications of electrochemical supercapacitors. A highly electrical conductivity and a high surface area of the electrode material as well as electrolyte solutions are the significant factors to ensure high energy density and power density.⁴¹ The nanostructures and mechanical properties allow to form an electrode with an accessible electrode–electrolyte interface for efficient charge propagation and fast faradic redox reactions that enable the high energy and power densities.⁴² Fig. 4d depicts a Ragone plot for a comparison of the energy density and power density of the tested PEDOT/NW supercapacitors, calculated by eqn (2) and (3). The PEDOT/NW composite shows much higher energy density of 21.1 W h kg⁻¹ in comparison to the literatures (around 7 W h kg⁻¹).^30,33 With the current densities increasing the energy density decreases slowly, while the power density increases. The energy density of the PEDOT/NW composite can still maintain above 14.8 W h kg⁻¹ as the power density reaches highly as 4750 W kg⁻¹. The well-maintained energy density even at high current density is owing to the 3D conductively porous nanostructure and good electrochemical properties. It is worth noting that the PEDOT/NW composite could be used as an excellent supercapacitor electrode material working at a high charge–discharge current density.

The flexibility is one of significant parameters for flexible devices. Hence the capacitive property of the flexible supercapacitor was investigated under different strains as shown in Fig. 5a. The specific capacitances of the supercapacitor were calculated from the galvanostatic charge–discharge measurements (Fig. 5b). Compared with the normal condition (160.9 F g⁻¹), the specific capacitance showed slight decrease when the supercapacitor was bended over 90° (153 F g⁻¹). That is probably due to the fact that the resistance of the supercapacitor increased because the amount of electrolyte solution adsorbed in the electrodes would be reduced upon flex, especially when folded (150 F g⁻¹). Thus the ion and electron diffusion could be slowed down during the redox reaction of PEDOT/NW electrode, resulting in the decrease of specific capacitance of the supercapacitor.

Fig. 5 The specific capacitance of flexible supercapacitors with different mechanical deformation (a) was measured by galvanostatic charge–discharge tests at the current density of 0.5 A g⁻¹ (b).

Cycling stability of electrode materials is another important requirement for supercapacitor applications. The cycling stability tests (in normal condition) over 1000 cycles for the PEDOT/NW composite at a current density of 1 A g⁻¹ was carried out using constant-current galvanostatic charge–discharge cycling techniques in the potential window ranging from 0 to 1 V. Fig. 6 presents the specific capacitance of the PEDOT/NW composite as a function of charge–discharge cycling numbers. It is worth nothing that the specific capacitance decreased slightly. That is due to the fact that the swelling and shrinkage of conducting polymers could often lead to the degradation of specific capacitance during the doping/de-doping process of the dopants in the polymer backbone. However, its discharge specific capacitance can still retain above 90% of its original value (150 F g⁻¹) after 1000 consecutive charge–discharge cycles, illustrating the excellent long-term cyclability of the PEDOT/NW flexible supercapacitor.

Fig. 6 Cycling stability of the flexible supercapacitor based on PEDOT/NW electrodes working at 1 A g⁻¹.

Conclusion

In summary, a facile and cost-effective approach is developed to prepare PEDOT-coated non-woven fabric composite that leads to highly efficient electrodes showing high specific capacitance (169 F g⁻¹), high energy density (21.1 W h kg⁻¹), good rate capability and long-term cycling life (maintaining 90% after 1000 cycles). That is due to fact that now-woven fabrics are served as substrates that are homogeneously coated by PEDOT nanowires to form a 3D conductively porous network, which facilitates to accumulate the current during the charge–discharge process of PEDOT electrode.

Additionally, the non-woven fabric plays an important role of the container for the electrolyte storage. As a result, a PEDOT nanowire coating on a 3D non-woven fabric substrate as a conductively porous current collector facilitates effectively ion transport kinetics, improves material utilization, maximizes surface area of electrochemical interaction, and thereby leads to a flexible supercapacitor with superior capacitive performances. In view of its simplicity and low preparation cost, the homogeneous and highly conductive PEDOT/NW nanoarchitectures have certain advantages over conventional electrode materials in energy storage of supercapacitors.

Acknowledgements

This work was supported by the National Natural Science Foundation of China grants (no. 20874112) and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, TIPC, CAS.

Notes and references

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