Binder-free Flexible Electrode Research Articles

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.

MOF-Derived Zn/N-Doped Porous Carbon Film on a Carbon Nanotube for High-Performance Supercapacitors.

Designing high-performance binder-free electrochemical electrodes is crucially important toward supercapacitors. In this paper, a Zn/N-doped porous carbon film coating on flexible carbon nanotubes (ZIF-8@CT-800) derived from the epitaxial Zn-MOF film growth on cotton textile was successfully fabricated via a combination of the liquid-phase epitaxial (LPE) method and calcination treatments. The ZIF-8@CT-800 serves directly as a self-supported electrode for supercapacitors and exhibits a high areal capacitance of 930 mF·cm-2 at a current density of 1 mA·cm-2 and a good recyclability of 86% after 2000 cycles. The excellent supercapacitor property is ascribed to the unique structural design of ZIF-8@CT-800, which provides appropriate channels for enhanced electronic and ionic transport as well as increased surface area for accessing more electrolyte ions. This work will provide significant guidance for designing MOF-derived porous carbon to construct flexible binder-free electrode materials with high electrochemical performance.

PPy-PdO modified MXene for flexible binder-free electrodes for asymmetric supercapacitors: Insights from experimental and DFT investigations

Binder-free, flexible electrodes of V2C MXene, V2C-PPy, and V2C-PPy-PdO (a ternary composite of vanadium carbide, polypyrrole, and palladium oxide) were fabricated using a simplified, one-step electrodeposition method. A comprehensive assessment has subsequently been conducted on the microstructural and electrochemical attributes of these electrode materials when utilized in supercapacitors with a 1 M H2SO4 electrolyte. Notably, an impressive specific capacitance of 487F g−1 is achieved for V2C-PPy-PdO ternary composite at 1 A/g. This exceptional performance is due to the considerable active surface area and inherent structural stability of the host material. These factors significantly enhanced the electrochemical reaction kinetics and cyclic reversibility. Furthermore, the V2C-PPy-PdO composite demonstrated a notable specific capacitance of 250F g−1 when integrated into an asymmetric coin cell configuration alongside activated porous carbon under a current density of 1 A/g. Remarkably, it maintained an outstanding capacitance retention of 92 % across 10,000 charge–discharge cycles. Our experimental discoveries were additionally substantiated through the Density Functional Theory calculations, which unveiled that the inclusion of PdO within the V2C-PPy-PdO composite led to an augmentation of electronic states near the Fermi level. This increase in electronic states ultimately improved the quantum capacitance, rendering the V2C-PPy-PdO composite a highly promising candidate for supercapacitor applications.

High areal-capacitance based extremely stable flexible supercapacitors using binder-free exfoliated graphite paper electrode

The highly porous and binder-free flexible paper electrodes can enhance the specific capacitance of symmetric supercapacitors (SCs) due to their large surface and effective ion diffusion pathways. We synthesized the exfoliated graphite (ExG) by the thermal exfoliation method of chemically treated graphite flakes and compressed it into a paper-like thin sheet (binder-free) of ∼0.15 mm thickness. The coin cell SCs with copper (Cu) and stainless steel (SS) as current collectors have been fabricated for the electrochemical measurement. The cyclic voltammetry and galvanostatic charge/discharge measurements are investigated at various scan rates and current densities. The SCs with Cu foil as a current collector perform better than SS-based SCs. The Cu current collector-based SCs showed a specific capacitance of 37.08 mF cm−2, whereas it was ∼29.98 mF cm−2 for SS-based SCs at a 0.01 V s−1 scan rate across a 0–0.6 V potential window. Approximately no degradation in charge storage capacity for more than 15 000 cycles at 0.1 V s−1 shows the ultra-stability of the flexible ExG-based binder-free electrodes. A digital watch is powered using the fabricated pouch cell supercapacitor with copper-based current collectors to show the potential of SCs.

Three-Dimensional Graphene-Wrapped CoSe2 Nanowires for High-Performance Asymmetric Supercapacitors

Herein, a three-dimensional graphene (3DG)-coated porous nanowire architecture was developed, which exhibited favorable multiscale and multidimensional porous nanostructures, resulting in an airgel (3DG/CoSe2NWs) with abundant ion transport channels, high specific surface area, and excellent electrical conductivity. This airgel can be used directly as a flexible binder-free electrode with a high specific capacity of 1272 F g–1 at 1 A g–1 and an excellent rate capability of 1156 F g–1 when the current density was increased to 10 A g–1. The prepared asymmetric supercapacitor (3DG/CoSe2NWs//AC) exhibited excellent cycle stability with a coulombic efficiency of 96.19% at 5 A g–1 after 10,000 cycles. The performance of the flexible asymmetric supercapacitor (ASC) device under different bending angles was evaluated, and the discharge stability was confirmed, which indicated its potential in practical applications. Furthermore, two 3DG/CoSe2NWs//AC ASCs (1 cm × 3 cm) connected in series were able to light up an LED lamp, highlighting the promising prospect of the device.

Ti3C2Tx MXene as a growth template for amorphous RuOx in carbon nanofiber-based flexible electrodes for enhanced pseudocapacitive energy storage

A noble surface engineering method was developed to create a binder-free flexible electrode comprising Ti3C2Tx MXene/carbon nanofibers (MCNFs) covered by amorphous RuOx with a combined electrospinning and hydrothermal process. Utilizing the hydrophilicity of the MXene on/in the MCNFs, RuOx was easily coated on the surfaces of the MCNFs through oxygen-mediated chemical bonding between the functional groups of the MXene and Ru ions. A structural analysis revealed that the MXene acted as a growth template for RuOx and that the formed RuOx had an amorphous and disordered state in the composite electrode, which impacted the electrochemical performance. The electrochemical tests showed that these composite electrodes improved the electrochemical performance, with a two-fold increase in the gravimetric capacitance (279.4 F/g at 2 mV/s) relative to that of pristine MCNFs, a wide potential window (from 0.7 to 1 V) providing a superior energy density of 8.5 Wh/kg at a power density of 85.8 W/kg, as well as long-term cycling stability (99% after 10,000 cycles). The synergetic effect of the RuOx and MXene in the composite electrodes was attributed to an enhanced pseudocapacitive reaction. Our novel electrodes and fabrication method confirm the great potential of CNF-based composites for the development of high-performance binder-free electrodes for supercapacitors.

Preparation of N/S co-doped graphene/polypyrrole composites for binder-free flexible supercapacitors

Flexible electrodes have been extensively studied and developed, but how to maintain flexibility and increase capacitance at the same time is still challenging. In this work, nitrogen/sulfur co-doped reduced graphene oxide (RGO) and a series of polypyrrole (PPy) composite (RGP-i, i = 1, 2, 3, 4, 5, 6) aerogel materials are prepared by adjusting the mass ratio of graphene oxide (GO) and PPy and using thiourea (CS(NH2)2) as a reducing agent. Binder-free flexible electrodes are assembled by using carbon cloth (CC) as substrates. Among these samples, RGP-5 prepared with the ratio of m(GO):m(PPy) = 1:1 exhibits excellent comprehensive electrochemical performance, with high specific capacitance (394 F g−1 at 1 A g−1) and high capacitance retention (55.4% from 1 to 20 A g−1) simultaneously. The assembled RGP-5//RGP-5 flexible quasi-solid symmetric supercapacitor shows an energy density of 6.25 Wh kg−1 at a power density of 500 W kg−1, and a power density of 2501 W kg−1 at an energy density of 4.37 Wh kg−1. After 1000 cycles of charging and discharging, its capacitance can maintain 80%. The specific capacitance of RGP-5//RGP-5 under different bending angles is almost unchanged, indicating that it shows good flexibility.

MOFs-derived niobium oxide nanoparticles/carbon nanofiber hybrid paper as flexible binder-free electrode for solid-state asymmetric supercapacitors

For the first time, a bottom-up approach was adopted to prepare free-standing orthorhombic Nb2O5-anchored carbon nanofibers (Nb2O5 @CNFs) hybrid paper via in-situ solvothermal synthesis of Nb-metal organic framework@CNFs hybrid and subsequent pyrolysis process. The nanocrystalline Nb2O5 decorated on the CNF surfaces improved the charge storage performance through synergistic effect between porous CNFs (EDLC) and Nb2O5 (pseudocapacitance). Moreover, the high surface area and core-shell structure of Nb2O5 @CNF hybrid reduce diffusion limitations and facilitate ionic transport. The Nb2O5 @CNF hybrid paper as a binder-free electrode delivered greater specific capacitance of 633.6 F/g (975.7 F/cm3) in 1 M H2SO4, compared to Li2SO4 electrolyte (524.3 F/g) at 0.5 A/g. However, the Nb2O5 @CNF electrode showed better cycling stability in neutral Li2SO4 electrolyte than in acidic H2SO4 electrolyte. The solid-state asymmetric supercapacitor (ASC) based on Nb2O5 @CNF paper and activated carbon (AC) electrodes delivered higher energy density of 62.1 Wh kg−1 at 292.7 W kg−1 in Li2SO4 electrolyte due to a wider working potential window (0–1.5 V), compared to H2SO4 electrolyte (55 Wh kg−1). The Li2SO4-based ASC cell is also capable of producing an energy density of up to 45.6 Wh kg−1, even at a high-power density of up to 5853.6 W kg−1. The as-assembled ASC demonstrated low self-discharge rate as well as excellent bending stability, indicating its excellent prospects in real-life applications.

Hollow 1D carbon tube core anchored in Co3O4@SnS2 multiple shells for constructing binder-free electrodes of flexible supercapacitors

The design of the core@multi-shell metal sulfide hollow tube is of great importance for various supercapacitor electrodes. Herein, a hollow carbon tube (HCT) core@multi-shell with rich pores is developed for constructing the binder-free flexible electrodes (HCT-x@Co3O4@SnS2). The inner core–shell is derived from the zeolitic imidazole framework (ZIF)-8@ZIF-67 porous carbon tube and is engineered with vertically aligned SnS2 nanosheets. The unique inner core–shell and the outer-shell SnS2 contribute to the excellent characteristics, including abundant pores and channels for the rapid ion transport and storage, high specific surface area, improved electrical conductivity, and additional electroactive sites for the faradaic reaction. Thanks to the synergies between the unique 1D porous hollow structure and the different components, the as-fabricated HCT-2@Co3O4@SnS2 electrode exhibits a high specific capacitance of 439 F/g at 1 A/g. Moreover, the assembled flexible supercapacitor also demonstrates a remarkable energy density of 40.22 Wh kg−1, the corresponding power densities of 750.22 W kg−1, and long cycle life. In addition, no structural deformation and capacitance loss are observed in the bended devices. The developed approach provides a facile structure design route for the flexible binder-free electrode preparation of flexible energy storage applications.

In situ preparation of nitrogen-doped carbon nanotubes on carbon cloth surface as binder-free flexible electrode materials for supercapacitors

In situ preparation of nitrogen-doped carbon nanotubes on carbon cloth surface as binder-free flexible electrode materials for supercapacitors

Sulfur-doped carbonized bacterial cellulose as a flexible binder-free 3D anode for improved sodium ion storage.

Carbon-based materials have received wide attention as electrodes for energy storage and conversion owing to their rapid mass transfer processes, outstanding electronic conductivities, and high stabilities. Here, sulfur-doped carbonized bacterial cellulose (S-CBC) was prepared as a high-performance anode for sodium-ion batteries (SIBs) by simultaneous carbonization and sulfidation using the bacterial cellulose membrane produced by microbial fermentation as the precursor. Doping sublimed sulfur powder into CBC results in a greater degree of disorder and defects, buffering the volume expansion during the cycle. Significantly, the three-dimensional (3D) network structure of bacterial cellulose endows S-CBC with flexible self-support. As an anode for sodium ion batteries, S-CBC exhibits a high specific capacity of 302.9 mA h g-1 at 100 mA g-1 after 50 cycles and 177.6 mA h g-1 at 2 A g-1 after 1000 cycles. Compared with the CBC electrode, the S-CBC electrode also exhibits enhanced rate performance in sodium storage. Moreover, theoretical simulations reveal that Na+ has good adsorption stability and a faster diffusion rate in S-CBC. The doping of the S element introduces defects that enlarge the interlayer distance, and the synergies of adsorption and bonding are the main reasons for its high performance. These results indicate the potential application prospects of S-CBC as a flexible binder-free electrode for high-performance SIBs.

Hierarchical ZnO arrays engineered hollow carbon nanofibers derived from metal-organic frameworks for flexible supercapacitors

Carbon nanofibers (CNFs) have been playing an essential role in addressing the challenges of the flexibility in energy storage devices. However, the unsatisfactory electrochemical performance and poor electrical conductivity are often caused by insufficient physical contact points of CNFs. The design and implementation of unique electrodes are expected to overcome these issues. Here, the N-doped hierarchical porous carbon nanofibers (NCNFs) hollow framework derived from metal-organic frameworks (MOFs) is fabricated, which is decorated with high conductive reduced graphene oxide rGO and single-crystal ZnO nanorod for engineering the binder-free flexible electrodes NCNF@rGO-x@ZnO. The obtained NCNF@rGO-7@ZnO electrode exhibits the desired specific capacitance of 473 F g-1. An assembled hybrid supercapacitor exhibits the high energy density of 35.16 Wh kg-1 at the power density of 747.2 W kg-1, and superior cycling life. Given these advantages, the NCNF@rGO-7@ZnO is selected as the electrode in a flexible and foldable supercapacitor. There is exceptional flexibility and no visible capacitance loss when the supercapacitor bending at different angles. Furthermore, a timer is successfully driven by two supercapacitor devices connected in series. Hence, a flexible binder-free electrode with excellent electrochemical performance can be obtained by engineering the structure into a hollow interconnected architecture and the rational design of materials.

Binder-free polypyrrole/fluorinated graphene nanocomposite hydrogel as a novel electrode material for highly efficient supercapacitors

Nowadays, many scientific communities and researchers are disparate towards the development of new and advanced energy storage/conversion devices to fulfill the increasing energy demands. Supercapacitors have considered as attractive energy storage devices because of their tremendous features. But their low conductivity creates a barrier to their practical applications, which is a consequence of the presence of binder in the formation of electrode material. Herein, a binder-free flexible supercapacitor electrode based on polypyrrole/fluorinated graphene (PFG) nanocomposite hydrogel on carbon cloth has been designed using in-situ oxidative polymerization. The resultant composite hydrogel possessed excellent electrochemical performance with a high specific capacitance of 1372 F/g in 1 M H2SO4 at a current density of 0.5 A/g. The maximum specific energy and specific power were estimated to be 20.13 Wh/kg and 176 W/kg, respectively. The outstanding electrochemical performance may be attributed to the combined effect of polypyrrole, fluorinated graphene as well as porous morphology of hydrogel. The resultant flexible and binder-free supercapacitor electrode with outstanding electrochemical performance will play a significant role in the field of wearable electronics, touch screens, electronic papers and roll up displays.

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

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

Electrochemical Properties of Iron Oxide Decorated Activated Carbon Cloth as a Binder-Free Flexible Electrode

The oxidation and deposition of transition metal oxides on porous carbon precursor materials strongly influence the final performance of supercapacitor electrodes. Thus, the influence of oxidation time combined with simple iron oxide deposition was evaluated on a flexible carbon fiber cloth electrode oxidized at three different times and exposed to spontaneous iron oxide deposition. The 140 minutes oxidation time increased by two times the iron quantity deposited on the activated carbon fiber cloth (ACC) and also increased the crystallinity of the carbon matrix. The iron oxide deposition improved the contribution of anions to store energy, enhancing the pseudocapacitive effect in the samples. The optimal oxidation time of the ACC140_Fe sample with the greater iron oxide deposition achieves 116.8 F g-1. The binder-free flexible electrode presents a successful design through pre-oxidation and spontaneous iron oxide deposition on the carbon matrix without expensive and environmentally unfriendly chemical treatments.

Highly hydrophilic electrodeposited NiS/Ni3S2 interlaced nanosheets with surface-enriched Ni3+ sites as binder-free flexible cathodes for high-rate hybrid supercapacitors

In this study, nanostructured nickel sulfides (NiS, Ni3S2 and NiS/Ni3S2) were fabricated directly on the surface of flexible carbon fiber cloths by simply modifying the deposition parameters of pulse-reversal (PR) electrodeposition method and utilized as binder-free flexible electrodes for aqueous hybrid supercapacitors (SCs). X-ray photoelectron spectroscopy and contact angle measurement studies verifies that the surface of heterostructure NiS/Ni3S2 electrode has enriched Ni3+ sites and highly hydrophilic nature. Consequently, the heterostructure NiS/Ni3S2 electrode demonstrated superior rate capability than that of both single phase NiS and Ni3S2 electrodes. Additionally, the hybrid SC device based on the flexible NiS/Ni3S2 electrode delivered a capacity of 40.4 mAh g−1 at a current density of 2 A g−1 and representing a maximum energy density of 32.3 Wh kg−1 at an impressive power density of 1.6 kW kg−1. Furthermore, the device provided excellent electrochemical stability with a capacity retention of 86.2%, even after a 120-h floating test. Hence, the heterostructure NiS/Ni3S2 with interlaced nanosheets morphology should be considered as promising binder-free flexible electrode materials for next-generation energy storage applications.

Metal phthalocyanine-based conjugated microporous polymer/carbon nanotube composites as flexible electrodes for supercapacitors

Conjugated microporous polymers with active functional groups have attracted more and more attentions in energy conversion systems. However, their low electrical conductivity results in low capacitance, thus limiting their practical application. Herein, conjugated microporous polymer with triphenylamine aldehyde linked to metal phthalocyanines (MNC) is synthesized and then compounded with high-conductivity carbon nanotubes (CNTs) (denoted as CoNCCs) by vacuum filtration. Moreover, CoNCCs exhibit flexibility, which could be served as a self-standing and binder-free flexible electrode of supercapacitors. As a result, the optimized CoNCCs as the flexible electrode show high specific capacitance of 213.4 F g−1 at 0.5 A g−1. In addition, the higher capacity retention rate 85.3% can be retained after 1750 cycles at 20 A g−1. The good electrochemical properties can be attributed to the synergistic effect and strong dual-phase interaction between MNC and CNTs. This work opens the way to develop high-performance and low environmental footprint organic electrode materials for SCs.

Design and synthesis of polyaniline/MWCNT composite hydrogel as a binder-free flexible supercapacitor electrode

The novel polyaniline/MWCNT composite hydrogel has been successfully synthesized on carbon cloth using in situ oxidative polymerization of aniline in the presence of MWCNT and phytic acid which can further be used as a binder-free electrode for supercapacitor. The use of electrode without binder is an effective approach to get better electrochemical behavior, which makes the ions move quicker. The supercapacitor cell has been built in a Teflon Swagelok assembly by sandwiching a separator impregnated with 1 M H2SO4 electrolyte between two symmetrical hydrogel electrodes and used further for electrochemical characterization. The electrochemical behavior of supercapacitor electrodes has been explored in a two-electrode cell configuration using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) measurements. The electrochemical results reveal that in 1 M H2SO4 aqueous solution, polyaniline/MWCNT composite hydrogel possesses a high specific capacitance (Cs) value of 277.59 F/g as compared to Cs value of 142.24 F/g for polyaniline hydrogel at 0.25 A/g. The polyaniline/MWCNT electrode shows superior rate capability and outstanding cyclic stability up to 5000 consecutive cycles. The electrochemical performance of composite hydrogel may be attributed to its well-designed nanostructure and the collective effect of both components. It may be concluded that as prepared composite hydrogel serves as a favorable electrode material for highly capable flexible energy storage system.

Metal-organic framework derived porous flakes of cobalt chalcogenides (CoX, X = O, S, Se and Te) rooted in carbon fibers as flexible electrode materials for pseudocapacitive energy storage

The development of binder-free flexible electrode materials with high surface area and high electrical conductivity is desirable but remains a serious challenge for pseudocapacitive energy storage. In this work, a universal method is developed for synthesizing porous cobalt chalcogenides flakes uniformly grown on carbon fibers (CF@CoX, X = O, S, Se and Te) by a one-step process of annealing four composites of cotton cloth and leaf-like zeolitic imidazolate frameworks. The as-synthesized CF@CoXs have favorable features, including large surface area, high electrical conductivity, and flexible three-dimensional network architectures, which promote the performance of active materials to a greater extent in their energy-storage applications. Used as flexible electrode materials for pseudocapacitive energy storage, the capacitive performance of CF@CoX is comparable superior. Especially for CF@CoS, it shows a high areal specific capacitance of 3576.0 mF cm−2 at a current density of 5.0 mA cm−2 in a three-electrode configuration. Furthermore, an asymmetric flexible supercapacitor assembled using CF@CoS as a positive electrode and active carbon cloth as a negative electrode exhibits a high areal energy density of 149.4 µWh cm−2 at a power density of 4.3 mW cm−2.

Metal phthalocyanine-linked conjugated microporous polymer hybridized with carbon nanotubes as a high-performance flexible electrode for supercapacitors

Metal phthalocyanine-linked conjugated microporous polymers (MPc-CMPs) have huge potential applications in energy conversion and storage systems. However, the inherent low conductivity limits their practical application. Herein, the MPc-CMPs are hybridized with highly conductive carbon nanotubes (CNTs) via the easy vacuum filtration method. Interestingly, the composite (denoted as CoPc-CMP/CNTs) shows the flexible feature, which can be served as the flexible binder-free electrode for supercapacitors (SCs). As expected, the flexible CoPc-CMP/CNTs exhibits a high specific capacitance of 289.1 F g−1 at a current density of 1 A g−1 and good capacity retention of 82.4% over 1350 cycles at a high current density of 10 A g−1. Furthermore, First-principle calculations are used to elucidate the superiority of CoPc-CMP to other analogues. The good electrochemical performance could be attributed to the synergistic effect from the high pseudocapacitance and good conductivity of CoPc-CMP as well as the capacitive contribution and good conductivity of CNTs. Our strategy provides a new avenue to develop the high-performance SCs via rational integration of MPc-CMPs with highly conductive CNTs.