Flexible Supercapacitor Electrodes Research Articles

Co1-xS/N, S-codoped carbon loaded porous carbon cloth as flexible electrode for high performance supercapacitors

The capacitive performances of flexible electrodes highly depend on their architectures and redox activity. In this work, Co1-xS/N, S-codoped carbon (NSC) loaded porous carbon cloth (p-CC) was prepared through an etching procedure and a followed repeated-sulfurization process. Since the porous CC could accommodate more Co1-xS nanoparticles and the phase structure of Co1-xS was well controlled by the repeated-sulfurization process, the obtained p-CC/Co1-xS/NSC electrode with optimized composition and architecture exhibits high areal capacitances of 1263.8 mF cm−2 at 1 mA cm−2 and 858.6 mF cm−2 at 50 mA cm−2. The deposited NSC on Co1-xS could effectively prevent their slipping and agglomeration, and thus make the electrode exhibit high capacitance retention of 99.7 % after 20,000 charge–discharge tests. The all-solid-state symmetric supercapacitor assembled by the formed electrodes and ionic liquid/gel electrolyte shows a maximum energy density of 1.34 mWh cm−3 at the power density of 9.55 mW cm−3. These results present a new strategy for the construction of cobalt-sulfide/carbon based flexible electrode with high capacitive performances.

Flexible supercapacitors based on in-situ synthesis of composite nickel manganite@reduced graphene oxide nanosheets cathode: An integration of high mechanical flexibility and energy storage

Supercapacitors have attracted considerable attention in the context of electric vehicles, renewable energy storage, and industrial equipment. Nevertheless, further work is required to enhance the energy storage performance and improve the adaptability of supercapacitors under mechanical loads. To address these challenges, we propose a novel design strategy for composite micro-nano structures of reduced graphene oxide coated in situ growth of nickel manganite nanoarrays on the carbon fiber surface (CF@NiMn2O4@rGO). This design enables the fabrication of flexible supercapacitor electrodes with optimised electrochemical and mechanical properties. The CF@NiMn2O4@rGO cathode exhibits a synergistic effect that enhances energy storage, as evidenced by a high specific capacitance of 1003.35 F g−1 (at 10 mA cm−2) and exceptional cycling stability over more than 4000 cycles. Furthermore, the flexible carbon fiber (CF) and in-situ grown nickel manganite@reduced graphene oxide (NiMn2O4@rGO) contribute to improved mechanical properties of the electrode. The assembled supercapacitor exhibits both high energy density and cycling stability. Notably, the flexible bending angle ranging from 0° to 180° has minimal impact on the energy storage performance of this flexible supercapacitor. Even under a bending angle of 180°, it successfully powers a small light bulb. This novel nanostructured material presents an innovative approach for designing flexible supercapacitors.

Citric acid induced enhancement in capacitive performances of polyaniline/graphene gel electrode for flexible supercapacitors

Abstract A composite hydrogel electrode for a flexible supercapacitor was fabricated by dispersing polyaniline/graphene composite into a polyvinyl alcohol gel network in the presence of citric acid. It was found that the introduction of citric acid could greatly promote the capacitive performances of composite gel electrodes. The assembled flexible supercapacitor could exhibit a maximum specific capacitance of 321.3 F g−1 at 1 A g−1 with a capacitance retention rate of 76.0% (from 1 A g−1 to 20 A g−1). Furthermore, even after enduring 5000 cycles at 20 A g−1, the supercapacitor maintained 86.8% of its initial capacitance, demonstrating excellent cycling stability. This work indicated that the introduction of multifunctional organic acid offered a more efficient pore structure for facilitating charge transport and dextral charge storage for gel electrodes, as a result, significant enhancement in capacitive performances.

One-step rapid prototyping of recyclable ultrathin CNF/MWCNT/Fe-based spinel oxide asymmetric interdigital nanopaper electrodes for high performance flexible supercapacitors

Flexible asymmetric supercapacitors (FASCs) are potential energy storage devices for wearable electronics, considering that these have a wide operating voltage window, high specific capacity, and high energy density. However, achieving high energy density through the optimization of structure and electrode remains a challenge. Herein, two electrode inks with exceptional homogeneity nature and stability are prepared by using in-situ grown Fe-based spinel oxide (MFe2O4 = Fe3O4/MnFe2O4) on multi-walled carbon nanotubes (MWCNT) combined with eco-friendly and renewable cellulose nanofiber (CNF). Meanwhile, ultrathin flexible asymmetric interdigital nanopaper electrodes (NFT@MnFe and NFT@Fe) with customized patterns are fabricated through a one-step mask-assisted vacuum filtration strategy by using the obtained electrode inks. The planar interdigital FASC device based on the NFT@MnFe cathode and the NFT@Fe anode has excellent area specific capacity (309.8 mF cm−2), energy density (110.2 μW h cm−2), and power density (0.47 mW cm−2). The FASC maintain over 95 % of the original capacity after 5000 charge/discharge cycles. Noteworthy, a stacked interdigital FASC can be achieved with an energy density of up to 273.8 μW h cm−2 at 0.47 mW cm−2 power density, combining the structural benefits of planar interdigital and sandwich-type devices.

Ultrafast reaction kinetic of polyaniline in flexible hydrogel electrodes facilitated by graphene ribbons

Abstract By loading energy storage active materials on hydrogel which is inherently flexible, the flexibility of electrode materials can be simply realized, thereby achieving the flexibility of energy storage devices. However, the polymer network that constructs the three-dimensional skeleton of the hydrogel is not conductive, which inhibits the redox ability of the active material. If a high speed conductive structure can be added to the colloidal phase, the performance of the flexible electrode material can be greatly improved. Here, we introduce redox graphene ribbons into the polyvinyl alcohol hydrogel loaded with polyaniline. The in situ three-dimensional conductive graphene network greatly enhanced the conductivity of the hydrogel electrode, thus increasing the specific capacitance to as high as 1117 F g−1 at 2 mg cm−2 mass loading, with a retention ratio of 66.96% from 0.5 A g−1 to 20 A g−1. These highlighted properties enable the PRP hydrogel as an electrode for flexible supercapacitors, which provides a promising possibility for the practical application of wearable electronics.

The design of binder-free self-supporting carbon paper electrode based on biomass derived hierarchical porous carbon/cellulose nanofibers for sustainable flexible supercapacitors

The design and synthesis of advanced electrodes with high conductivity and flexibility are the key to the development of wearable energy storage devices. Herein, a strategy for preparing conductive carbon paper electrode for flexible supercapacitors is reported by vacuum filtration of a mixture of biomass hierarchical porous carbon materials (HPC), cellulose nanofibers (CNFs) from polysaccharide cellulose of plant origin and silver nanowire (AgNWs), in which CNFs serve as substrates for dispersion and crosslinking of HPC. The prepared self-supporting electrode showed multi-scale pore structure and excellent conductivity (14.1 S cm−1). The electrode exhibited the highest specific capacitance of 383 F g−1 at 0.5 A g−1. Even after 10,000 charge and discharge cycles, 95 % of the original capacitance was remained, which means excellent cyclic stability. High strength and flexibility of the as-assembled flexible supercapacitor make the electrochemical performance of this device remain unchanged when bent at any angle. The present research delineates a simple and convenient method to prepare green, efficient and low-cost flexible supercapacitor.

Biomass modified carbon nanofibers use for flexible supercapacitor electrodes with thermal conductive performances

The advancement of flexible electrode with excellent energy storage is essential for supercapacitors. Herein, a porous biomass-doped carbon nanofiber@bimetallic oxide composite (B-CNF@NiO/Co3O4) has been prepared as a binder-free flexible electrode. The heteroatoms form biomass not only offer pseudocapacitance but also a multitude of active sites for the grow of bimetallic oxides. The well-grown B-CNF@NiO/Co3O4 shows a high specific capacitance (629.5 F g−1) and the asymmetric flexible supercapacitor (ASC) has an energy density of 31.5 Wh kg−1 at a power density of 757.4 W kg−1. The properties of bimetallic oxides and 3D networks facilitate transportation of interlayer ion, providing a straightforward approach to fabricate non-adhesive flexible electrode with dual functionalities of energy storage. In addition, the thermal conductive experiment demonstrated a favorable thermal conductivity (TC) of 1.06 W m−1 K−1.

Eu-viologen based bimetal–organic frameworks nanosheets with Mn atoms anchored on Eu-µ-O skeletons as high-performance negative electrode for flexible asymmetric supercapacitors

Exploring advanced negative electrode materials is imperative to develop high-performance asymmetric supercapacitors for breaking through current energy density limits of supercapacitors, but remains challenging. Herein, a strategy is proposed to create a novel negative electrode by anchoring Mn single-atoms on Eu-viologen metal–organic frameworks (EV-Mn MOFs) nanosheets flowery architectures that self-supported on oxidized carbon cloths (OCC). Such EV-Mn/OCC achieves a negative broadened voltage window (−1 ∼ 0 V) and boosted areal capacitance (840.82 mF cm−2), which is four folds of the isostructural EV/OCC without Mn atoms and surpasses most of currently reported negative electrodes. Also, the EV-Mn/OCC manifests good cycling stability (∼80 % retention for 10,000 cycles). As deduced by the thorough studies of X-ray absorption fine spectra and X-ray photoelectron spectroscopies, the enhanced pseudocapacitance of EV-Mn/OCC definitely correlates to the valence modulation of Mn and Eu through internal electron transfer via Eu-O-Mn bonds on Eu-µ-O skeleton in EV-Mn MOFs. Subsequently, the constructed flexible all-solid-state symmetric supercapacitors employing EV-Mn/OCC as negative electrode can deliver a high energy density (86.89 μWh cm−2) at 1600 μW cm−2, outperforming many asymmetric devices based on traditional negative electrode materials. This work can spur the development of single-atom metallic electronic-modulation strategy for MOFs negative electrode material (MOFs-NEM), and accelerate their applications in flexible energy conversion and storage devices.

Melamine foam scaffolded 3D porous polyaniline/reduced graphene oxide composite electrode for flexible supercapacitor

Graphene composite foam with enhanced mechanical and electrochemical properties holds great promise for flexible supercapacitors. This work developed a cost-effective method for massive production of three-dimensional (3D) porous graphene composite using melamine foam (MF) as a flexible scaffold. The MF was coated reduced graphene oxide (RGO) to form an interconnected conductive layer by dip-coating and vapor reduction, and loaded with polyaniline (PANI) by in-situ polymerization. The resulted PANI/RGO/MF, as self-supporting electrode, exhibits extraordinary mechanical flexibility and a high specific capacitance of 806.2 mF cm−2 at 0.5 mA cm−2. Furthermore, the assembled solid-state supercapacitor exhibits an outstanding capacity of 299.1 mF cm−2 at 0.5 mA cm−2, a high energy density of 26.6 μWh cm−2 at 200 μW cm−2, nearly 100 % capacitance retention at 0°–180°, and good cycling stability. This study provides a scalable strategy for fabricating graphene composite foam suitable for flexible energy storage application.

Hierarchically decorated ZnO/CoOx nanoparticles on carbon fabric for high energy–density and flexible supercapacitors

Exploring the electrochemical performance of metal/metal oxide nanoparticle composites is vital for enhancing the charge storage capability of supercapacitors. Herein, electrodes coated with ZnO/CoOx are fabricated by soaking cotton fabric seeded with 2-methylimidiazole in an ethylene glycol–based solution containing Zn and Co salts. The use of cotton fabric can reduce textile industrial waste while achieving high capacitance and sustainable energy for wearable electronics. In addition, the three-dimensional network of conductive flexible carbon derived from cotton fabric facilitates rapid ion transport kinetics at interlayers. The concentrations of Zn and Co salts are varied to produce ZnO/CoOx samples and determine the optimal salt ratio for superior electrochemical performance. The optimal sample exhibits a capacitance of 1.95 F cm−2 at 5 mA cm−2 and an energy density of 725 μWh·cm−2 over a wide potential window of 1.6 V. The long-term stability test results of the symmetric cells indicate 94 % capacitance retention after 12,000 charge–discharge cycles, emphasizing the advantages of mixed metallic oxides with cellulose-derived carbon fabric for supercapacitor electrodes. This study offers valuable insights into the fabrication of high-performance, flexible, and binder-free supercapacitor electrodes as a scalable alternative for practical applications.

One-pot preparation of one-dimensional hierarchically porous carbon@SnO2 nanocomposites for flexible fabric-based supercapacitor electrodes

The design of functional energy storage materials with superior performances has become the focus topic with the growing energy crisis in recent years. Herein, porous carbon nanofibers@tin dioxide (PCNFs@SnO2) composites are prepared by one-pot electrospinning and followed by carbonization. The PCNFs@SnO2 possesses a hierarchically porous structure containing mesopores and micropores. The specific surface area is as high as ∼ 559.4 m2 g−1, and the total pore volume can reach 0.28 cm3 g−1. Meanwhile, the nonwoven fabric surface is coated with a silver layer through the screen printing technique to obtain silver-coated nonwoven fabric (SNF). Importantly, PCNFs@SnO2 and SNF are combined to obtain flexible fabric-based functional materials. As a primary energy application, the prepared PCNFs@SnO2/SNF electrode has a high mass specific capacitance of 583.1 F g−1 at 1 A g−1, a high area specific capacitance of 933 mF cm−2 at 1 mA cm−2, and a good rate capability (70 % at 10 A g−1). The supercapacitor device with two PCNFs@SnO2/SNF electrodes also shows outstanding cycling durability, capacitor retention is as high as ∼ 91.52 %, after 10000 charging/discharging cycles. In brief, our study may provide an innovative route for designing hierarchically porous one-dimensional carbon nanocomposites for supercapacitors with high performances.

Ti2TaC2: A novel out-of-plane ordered MXene towards flexible and cytocompatible supercapacitors

Exploring biocompatible and flexible supercapacitor electrode material is crucial for expanding the development of health monitoring bioelectronics. MXene films, due to their low cost, high conductivity, and excellent durability under different deformation conditions, are highly competitive in bioelectronic device applications compared with traditional carbon-based materials. Herein, a novel out-of-plane ordered double transition metal MXene (Ti2TaC2) is elaborately designed and originally synthesized, where Ti atoms preferentially reside in the outer transition metal layer and Ta atoms occupy in the middle layer. Theoretical calculations prove that the introduction of Ta species into Ti3C2 MXene enlarges the work function, raises the d-band center close to Fermi level and increases the density of states of d-orbital. Consequently, the Ti2TaC2 film delivers high specific capacitance of 313 F g−1 at 2 mV s−1 and excellent cycling stability without capacitance loss after 10,000 cycles at 10 A/g. Furthermore, the safety and cytotoxicity of Ti2TaC2 material are innovatively evaluated in vitro multiple cell lines (e.g., 293T, bEnd.3, PC-12, BV2 and HUVEC cells) and implanted into the subcutaneous tissue of mice, proving its good biosafety and cytocompatibility. The results suggest that flexible Ti2TaC2 MXene film may be a promising cytocompatible electrode material for long-term health monitoring bioelectronics.

Electrodeposition of Graphene/Polypyrrole Electrode for Flexible Supercapacitor with Large Areal Capacitance

Electrodeposition of Graphene/Polypyrrole Electrode for Flexible Supercapacitor with Large Areal Capacitance

Tailoring the ion storage of MXene by aramid nanofibers towards self-standing electrodes for flexible solid-state supercapacitors

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) are a class of 2D nanomaterials that can offer excellent properties for high-performance supercapacitors. Nevertheless, irreversible restacking of MXene sheets decreases the interlayer spacing, which inhibits the ion intercalation between the MXene nanosheets and finally deteriorates the electrochemical performance of supercapacitors. Herein, aramid nanofibers (ANFs) are mixed with Ti3C2T x MXene to prepare MXene/ANFs composite films. The restacking of MXene sheets is inhibited by the electrostatic repulsion between ANFs and MXene. The ANFs act as intercalation agents to increase the interlayer spacing of the composite films, which can improve the ion storage ability of supercapacitors. Furthermore, the ANFs enhance the mechanical strength of the composite films due to the strong hydrogen bonding interaction and nanomechanical interlocking between ANFs and MXene, endowing the composite films with self-standing property. The resultant composite films are used as electrodes for flexible solid-state supercapacitors to achieve high specific capacitance (996.5 mF cm−2 at 5 mV s−1) and outstanding cycling stability. Thus, this work provides a potential strategy to regulate the properties of 2D nanomaterials, which may expand the application of them in energy storage, ionic separation, osmotic energy conversion and beyond.

Single‐Step One‐Pot Synthesis of NiCo2O4/Molybdate Nanocomposites for Flexible Supercapacitor Electrodes

Energy storage technology plays a critical role in integrating variable energy sources into the grid and ensuring energy consistency. Electrochemical supercapacitors are one of the most promising energy storage devices, as they present multiple advantages of high power density, rapid charge/discharge characteristics, and long‐term cycle stability. Herein, the NiCo2O4/molybdate nanocomposites are developed as electrode materials for supercapacitor applications. The NiCo2O4/molybdate nanocomposites are synthesized by a facile single‐pot hydrothermal method and are coated on a carbon cloth substrate to form flexible supercapacitor electrodes. The structures, chemical compositions, morphologies, and textural properties of these materials are carefully studied by X‐Ray diffraction, X‐Ray absorption spectroscopy, scanning electron microscopy/energy‐dispersive X‐Ray spectroscopy mapping, and N2 adsorption–desorption isotherms. The formation of spinel NiCo2O4 nanorods decorated with molybdate (AMoO4, A = Co, Ni) particles is confirmed for all samples. The NiCo2O4/CoMoO4 electrode exhibits pseudocapacitive behavior and provides the highest specific capacitance (287.28 F g−1 at current density 6 A g−1), about 5.5 times as high as that of NiCo2O4, with excellent cycle stability (107% specific capacitance retention after 1000 charge/discharge cycles at 1 A g−1). Therefore, the NiCo2O4/CoMoO4 composites can be considered as a promising pseudocapacitor electrode material.

Self-healable and Robust Film Based on Electroactive Polymer Brush as Electrode for Flexible Supercapacitor

Self-healable and Robust Film Based on Electroactive Polymer Brush as Electrode for Flexible Supercapacitor

Highly stable MXene/g-PPy@sulfonated cellulose composite electrodes for flexible supercapacitors

Traditional two-dimensional transition metal carbides/nitrides (MXene) have gained much academic concern due to their excellent physicochemical properties, but their susceptibility to self-stacking leads to poor cyclic stability. In this paper, an MXene-based electrode active material was successfully prepared. The generated modified PPy (g-PPy) increases the active site, increases the accessibility of ions, and can give full play to the pseudocapacitance. By the combination of modified PPy (g-PPy) nanoparticles with pseudocapacitive behavior polymerized in situ on sulfonated cellulose (SC) and MXene, not only the electrochemical performance was improved by exploiting the synergy between different electrode materials and different energy storage mechanisms, but also the MXene as a skeleton limited the volume expansion and contraction of PPy during charge/discharge cycles and the g-PPy and SC composites (g-PPy@SC) as a spacer supported the MXene layer, resulting in much higher cycle stability. Cycle stability of 98.4 % even after 10,000 cycle tests. In addition, a symmetric supercapacitor assembled from this electrode material maintains a stability of 84.4 % under 10,000 cycles at a low temperature of −40 °C. Therefore, this study provides a feasible method for the preparation of MXene-based electrodes with high cycling stability.

Regulating Functional Groups Enhances the Performance of Flexible Microporous MXene/Bacterial Cellulose Electrodes in Supercapacitors.

Ultrathin MXene-based films exhibit superior conductivity and high capacitance, showing promise as electrodes for flexible supercapacitors. This work describes a simple method to enhance the performance of MXene-based supercapacitors by expanding and stabilizing the interlayer space between MXene flakes while controlling the functional groups to improve the conductivity. Ti3C2Tx MXene flakes are treated with bacterial cellulose (BC) and NaOH to form a composite MXene/BC (A-M/BC) electrode with a microporous interlayer and high surface area (62.47 m2 g-1). Annealing the films at low temperature partially carbonizes BC, increasing the overall electrical conductivity of the films. Improvement in conductivity is also attributed to the reduction of -F, -Cl, and -OH functional groups, leaving -Na and -O functional groups on the surface. As a result, the A-M/BC electrode demonstrates a capacitance of 594 F g-1 at a current density of 1 A g-1 in 3 M H2SO4, which represents a ∼2× increase over similarly processed films without BC (309 F g-1) or pure MXene (298 F g-1). The corresponding device has an energy density of 9.63 Wh kg-1 at a power density of 250 W kg-1. BC is inexpensive and enhances the overall performance of MXene-based film electrodes in electronic devices. This method underscores the importance of functional group regulation in enhancing MXene-based materials for energy storage.

Flexible Supercapacitor Electrodes Based on Nitrogen-Doped Carbon Derived from Polyimide/Graphene

Flexible Supercapacitor Electrodes Based on Nitrogen-Doped Carbon Derived from Polyimide/Graphene

Scalable one-step synthesis of reduced graphene oxide: Towards flexible transparent conductive films and active supercapacitor electrodes

The reduced graphene oxide (rGO) thin films have attracted much attention in flexible electronic devices and supercapacitors (SCs). However, the chemical reduction mechanism of GO needs to be clarified, and the one-step process at low temperatures for preparing high-quality rGO thin films from GO dispersions is still blank in the research field. Here, we propose a one-step operation to spray GO dispersions onto substrate or current collector under a hydroiodic acid (HI) atmosphere while simultaneously achieving the preparation of rGO thin films. This pioneering metal-free, transfer-free, fast, low-temperature, environmentally friendly, and scalable spraying technology enables large-scale production of high-quality rGO. This method realizes the preparation of highly conductive and high transmittance rGO thin films on flexible polyimide and polyethylene terephthalate substrates, as well as the preparation of rGO thin films on current collectors as SCs electrodes. Density functional theory calculations show that oxygen-containing functional groups on the surface of GO exhibit a stronger adsorption energy for HI, and have a low energy barrier during reduction by HI. Ab initio molecular dynamics simulated the possible reduction reaction path between GO and HI at 90 °C, demonstrating that HI molecules can effectively reduce GO. Furthermore, the sheet resistance of the transparent conductive film created using the method developed in this study reaches approximately 1000 Ω/sq (80 % transparency), and the specific capacitance of the SCs electrode film created in this method is 433.2 F/g (5 mV/s, 1 M H2SO4). Our study not only validates the efficacy of the one-step synthesis method for rGO thin films but also provides theoretical insights into the underlying reaction mechanism. This work holds significant promise for advancing applications in various electronics by facilitating large-scale production of high-quality rGO thin films.