Binder-free Supercapacitor Electrode Research Articles

Optimized 3D interconnected foam-like NiO@rGO composite as a binder-free electrode for high-performance asymmetric supercapacitor

Bonding of transition metal oxides and highly conductive carbon materials to exploit the synergistic effect of both materials has been proven to be an efficient means to develop high-capacity electrode materials. A unique interconnected foam-like NiO@rGO structure was constructed by loading the NiO nanoparticles onto rGO frameworks as a binder-free supercapacitor electrode via three steps including hydrothermal reaction, electrodeposition and heating treatment. The morphology and crystallinity were tuned by controlling the electrodeposition time and heating temperature, and the electrochemical properties of the NiO@rGO composites were systematically investigated. The optimized NiO@rGO-250 composite showed excellent electrochemical properties (1399 F g−1 at 1 A g−1) and superior cycling stability. Furthermore, an asymmetric supercapacitor using NiO@rGO and active carbon as two electrodes achieved a high specific energy of 40.4 Wh k g−1 at a specific power of 750 W k g−1.

Unidirectional growth of polyaniline on 3D CoO nanowires for aqueous asymmetric supercapacitors

Metal oxide-based binary nanohybrids are a new class of binder-free supercapacitor electrodes. This paper reports the enhanced electrochemical performance of polyaniline (PANI)/CoO nanowires grown on Ni foam for use in aqueous asymmetric supercapacitors (SCs). Several synthetic parameters were optimized for the unidirectional growth of PANI on CoO nanowires. The rationally designed core-shell structured electrode exhibited a high specific capacity of 1113C g−1 (specific capacitance of 2473 F g−1) at a current density of 3 A g−1 and good cycling stability of 86.3 % over 10,000 charge/discharge cycles in a 1 M KOH electrolyte through a substantial synergistic contribution from each component. In addition, an aqueous asymmetric supercapacitor based on these PANI/CoO nanowire arrays exhibited a high specific energy of 35.8 Wh kg−1 and high cycling stability (89.1 % after 5000 cycles). Two aqueous asymmetric supercapacitors connected in series could light up 19 red light-emitting diodes (LEDs). Therefore, this electrode can be considered a superior candidate for the next-generation SC electrodes.

Constructing metal organic framework derived manganese cobalt layered double hydroxide nanosheets on Ni foam as cost-effective binder-free electrodes of high-performance supercapacitors

A vital aspect of energy storage devices is the development of novel materials with excellent electrical conductivity and rational structures. In combination with alkaline electrolytes, the manganese-cobalt layered double hydroxide (MnCo-LDH) cathode material has long been recognized as a highly desirable cathode material. Nevertheless, the synthesis of MnCo-LDH is time-consuming and required high temperatures. Therefore, it is important to find simple routes for the synthesis of MnCo-LDH. Herein, we propose a synthesis of metal organic framework (MOF)-derived MnCo-LDH nanosheets on conductive nickel foam (NF) for the supercapacitor (SC) application. The CoMOF decorated NF was fabricated by simple precipitation method, and then it was converted to MnCo-LDH by etching process at 80 °C for 5 min (MnCo-LDH/80 °C). The MOF-derived MnCo-LDH/80 °C electrode provides large accessible regions for electrolytes, low charge transfer resistance, and rich electroactive sites. Therefore, the MnCo-LDH/80 °C electrode demonstrates preferable energy storage property with a high areal capacitance of 2.62 F/cm2 at 20 mV/s. In this study, an asymmetric supercapacitor (ASC) is constructed using MnCo-LDH/80 °C and activated carbon (AC) on NF as the positive and negative electrodes, respectively. The optimized MnCo-LDH//AC device provides the maximum energy of 0.116 mWh/cm2 at the maximum power density of 2.49 mW/cm2. Added to that, the ASC has excellent cyclic stability with 78% as the capacitance retention and Coulombic efficiency of 94.3% after 5000 charge-discharge cycles.

Electrodeposited coral-like bimetallic NiCo-MOFs on Ni foam as binder-free electrodes for high performance all solid-state asymmetric supercapacitors

The rational design of electrode materials is greatly significant for improving the performance of the supercapacitor. In this work, high mass loading coral-like bimetallic nickel/cobalt-based metal-organic frameworks are in-situ constructed on cobalt-modified nickel foam (NiCo-MOFs/NF) via a facile cathodic electrodeposition process as binder-free electrodes for supercapacitors. Such electrodes with optimized Ni/Co molar ratios, high specific surface area and unique hierarchical structure with open channels provide abundant reaction active sites and fast ion transfer kinetics, and the three-dimensional porous Ni foam (NF) offers successive pathways for fast electron transportation. As a result, an ultrahigh areal specific capacitance of over 9300 mF cm−2 with a high-capacity retention of over 87% is achieved at 10 mA cm−2. And the NiCo-MOFs/NF with Ni/Co molar ratio of 1:3 presents a favorable stability of retaining its 73% original specific capacitance after a long-term cycling of 10,000 cycles. Moreover, the assembled all solid-state asymmetric supercapacitors (ASSCs) device performs an energy density of 617.2 mWh cm−2 at a power density of 7506.9 mW cm−2.

Controllable synthesis of MnSe2/Co0.85Se nanosheets as a binder-free electrode for high-performance asymmetric supercapacitors

With the increasingly serious environmental pollution and depletion of natural resources, it is necessary to develop efficient and environmentally friendly energy storage equipments to alleviate the problem of resource shortage. In this study, a novel MnSe2/Co0.85Se (MCSe) electrode was successfully prepared using a simple, green and environmentally friendly electrodeposition method. The MCSe electrode exhibited good electrochemical performance, and possesses a high specific capacity (Cs) of 1380C/g at a current density (CD) of 1 A/g. An asymmetric supercapacitor (ASC) assembled using a positive electrode (the MCSe electrode) and a negative electrode (active carbon (AC) electrode) delivered a high specific energy density (Es) of 49.63 Wh/kg at a specific power density (Ps) of 750 W/kg. Hence, this study provides a new approach for designing metal selenides for energy storage and conversion.

Electrodeposition Synthesis of Coral-like MnCo Selenide Binder-Free Electrodes for Aqueous Asymmetric Supercapacitors.

Bimetallic selenide compounds show great potential as supercapacitor electrode materials in energy storage and conversion applications. In this work, a coral-like MnCo selenide was grown on nickel foam using a facile electrodeposition method to prepare binder-free supercapacitor electrodes. The heating temperature was varied to tune the morphology and crystal phase of these electrodes. Excellent electrochemical performance was achieved due to the unique coral-like, dendritic- dispersed structure and a bimetallic synergistic effect, including high specific capacitance (509 C g-1 at 1 A g-1) and outstanding cycling stability (94.3% capacity retention after 5000 cycles). Furthermore, an asymmetric supercapacitor assembled with MnCo selenide as the anode and active carbon as the cathode achieved a high specific energy of 46.2 Wh kg-1 at 800 W kg-1. The work demonstrates that the prepared coral-like MnCo selenide is a highly promising energy storage material.

Three-dimensional nitrogen-doped graphene quantum dots/reduced graphene oxide composite hydrogels as binder-free electrodes for symmetric supercapacitors

Herein, nitrogen-doped graphene quantum dots/reduced graphene oxide composite hydrogels (N-GQDs/rGOs) were prepared via a hydrothermal approach from graphene oxide (GO) aqueous solution. During the preparation of the samples, ammonia water was used as reducing agent, pH regulator and nitrogen dopant, and graphene quantum dots (GQDs) were used as spacer between graphene sheets. Benefiting from their three-dimensional porous structures, large specific surface area, large number of heteroatom functional groups (N, O) on the surface, and the synergistic effect between GQDs and graphene sheets, the synthesized samples exhibit excellent electrochemical performance. Particularly, the N-GQDs/rGO-20 sample based binder-free symmetric supercapacitor show a high specific capacitance of 277.8 F g−1 at 0.3 A g−1, and this value can still maintain at 220.9 F g−1 even at 10 A g−1 in 6 M KOH electrolyte. Moreover, the capacitance retention rate of the symmetric supercapacitor can reach 92.7% after 10,000 cycles at 10 A g−1, indicating its excellent cycle stability.

Direct growth of AC@NiCo2S4 composite on nickel foam as binder-free electrodes for supercapacitors

In this study, folded nanotubes were directly grown on Ni foam by two-step hydrothermal method to form activated carbon (AC) and NiCo2S4 composite material with a unique structure like nano-urchin. In addition, the morphology and structure can be controlled by the time of hydrothermal reaction. The resulting samples were characterized by means of XRD, XPS, EDS and SEM. The electrochemical test results show that compared with the 6 h and 24 h hydrothermal composites, the 12 h hydrothermal composites (AC@NiCo2S4–2) form a complete folded nanotube structure, provide a large number of reactive sites, and show better electrochemical properties. And compared with the capacitance of NiCo2S4 (456.14 C g−1), the AC@NiCo2S4–2 exhibited a high specific capacitance of 653.9 C g−1 at a current density of 1 A g−1. In addition, after combination with AC, AC@NiCo2S4 has better electrochemical performance and cycle stability, the capacitance retention rate at 10 A g−1 is 62.84 % of 1 A g−1, and can still maintain 84.96 % of the initial capacitance after 3000 cycles. Moreover, the fabricated hybrid supercapacitor (HSC) based on AC@NiCo2S4–2 and AC electrodes achieved a high energy density of 29.75 Wh kg−1 at the power density of 700 W kg−1 and still maintain the energy density of 16.86 Wh kg−1 at the high power density of 7000 W kg−1.

The Morphology-Controllable Synthesis of Ni–Co–O Nanosheets on a 3D Porous Ni Template as a Binder-Free Electrode for a Solid-State Symmetric Supercapacitor

In this work, a porous Ni template (Ni–Co–O@3D Ni) with Ni–Co oxide nanosheets (Ni–Co–O)@3D was synthesized by incorporating Ni–Co oxide nanosheets within a 3D porous Ni template as a binder-free electrode for a supercapacitor. The 3D Ni template was synthesized with hydrogen bubble templates that possessed different applied voltages that marked differences in terms of physicochemical properties, as well as factors that affect the subsequent growth of Ni–Co–O nanosheets. Then, Ni and Co metal ion sources were introduced to produce the morphology adjustment of Ni–Co–O@3D Ni with a multiple hierarchical architecture with a hydrothermal process. Field emission scanning electron microscopy (FESEM), X-ray absorption spectroscopy (XAS), and an electrochemical analysis were employed to investigate the morphological, structural, and electrochemical characteristics. FESEM and XAS results evidenced that Ni–Co–O@3D Ni consists of a 3D, well-designed hierarchical interconnected network, and the local electronic structure change has a great influence on the capacitive performance. The electrochemical results of Ni–Co–O@3D Ni displayed an excellent electrochemical performance due to the synergistic effect of Ni and Co on Ni–Co–O@3D Ni, which possessed multiple oxidation states to enable various reversible Faradaic redox reactions. Remarkably, the solid-state symmetric supercapacitor fabricated with Ni–Co–O@3D Ni exhibited excellent capacitive behaviour at a wide operating voltage window and cycling performance. Also, the as-assembled solid-state symmetric supercapacitor (two devices in series) can successfully illuminate a desired parallel pattern consisting of 36 red LED lights, demonstrating its practical application as a supercapacitor.

Morphologically controlled synthesis of MnCo2O4 arrays on ACF as binder-free electrode for asymmetric supercapacitor

MnCo2O4 with a unique spinel structure has great potential as advanced electrode materials for supercapacitors. In this work, MnCo2O4 nano-arrays with controllable morphologies were pleasingly deposited on the surface of ACF by a simple hydrothermal route followed by an annealing process. The MnCo2O4@ACF binder-free electrode with nanowire morphology exhibited the most excellent electrochemical performance: specific capacitance of 1.58 mAh·cm−2 at 1 mA.cm−2 and 89.13% capacity retention after 1000 cycles at 5 A.g−1. Asymmetric supercapacitor devices were assembled to further investigate the performance of the composite electrodes. A high energy density of 47.83 Wh.kg−1 was obtained at 1.0 A.g−1 with a power density of 2623.45 W.kg−1. In the light of the above results, active layers with controllable morphology and fabrication of binder-free composite electrode systems may provide feasible design ideas for advanced electrode materials of high-performance supercapacitors.

Graphene sheets assembled into three-dimensional networks of carbon nanofibers: A nano-engineering approach for binder-free supercapacitor electrodes

The design and synthesis of flexible and free-standing carbon nanofibers membrane with good electrochemical properties have recently attracted much attention in energy storage applications. Herein, we fabricated graphene sheets-incorporated three-dimensional carbon nanofibers membrane (3D-GCNFs) as effective electrode materials for supercapacitors. The electrospun two-dimensional (2D) graphene oxide sheets-incorporated polyacrylonitrile nanofibers (GO/PAN NFs) were transformed into 3D membrane by a gas-forming technique using sodium borohydride. Subsequent thermal treatment converted the 2D-assembled GO/PAN NFs membrane into the low-density 3D-GCNFs membrane. The morphology and electrochemical performances of the as-prepared 3D membrane were systematically investigated using state-of-the-art techniques. It was found that the electrochemical performance of the as-obtained 3D-GCNFs membrane was greatly improved compared to the 2D counterparts. As a binder-free electrode, the materials exhibited a high areal capacitance of 318 mF/cm2 at a current density of 1 mA/cm2 and good cyclic stability of up to 98.5% after 5000 cycles. In addition, a symmetrical supercapacitor was constructed using the 3D-GCNFs membrane as both negative and positive electrodes. The device exhibited areal capacitance of 240 mF/cm2 at a current density of 1 mA/cm2, an energy density of 33.33 mWh/cm2, a power density of 1000 mW/cm2, and capacitance retention of 103% after 5000 cycles. The improved performance of the 3D-GCNFs membrane was attributed to its high electrical conductivity due to the absence of binders, high porosity, and conductive networks that form efficient channels for electrolyte penetration and effectively shorten the transmission distance. We believe that this study not only provides a reference for the introduction of 3D CNFs-based composite membranes, but also demonstrates their great potential for energy storage applications.

Fabrication of NiCo Layered Double Hydroxide on Carbon Fiber Paper as High Performance Binder-free Electrode for Supercapacitors

Design of binder-free electrode with high performance exhibits great glamour for energy storage devices recently. Herein, nickel cobalt layered double hydroxide (NiCo LDH) has been directly grown on carbon fiber paper (CFP) by an electrodeposition method. Thanks to the porous nanosheet-like morphology of the deposits, the high conductivity of carbon fibers, as well as the strong connection between the deposits and the substrate, the optimized electrode, labeled as NiCo LDH-2/CFP can deliver a discharge specific capacitance of 878.4 F g−1 at 1 A g−1, which can increase to 1080.0 F g−1 at 20 A g−1, exhibiting excellent rate performance. Moreover, after cycled at 5 A g−1 for 5000 cycles, the capacitance of the electrode can retain 96.1%, manifesting unique cyclic stability. This work provides a new strategy for preparing high performance binder-fee electrodes for supercapacitors, lithium batteries and catalytes.

Construction of 3D interconnected NiCo2S4/bio-carbon coated Ni foam as binder-free electrode for high-performance supercapacitor

Although transition metal hydroxides/sulfides are considered as promising potential electrode materials for supercapacitors due to their excellent electrochemical activity, the low electrical conductivity, easy agglomeration of nanomaterials and poor rate performance seriously hinder their practical applications. Herein, we construct 3D interconnected binder-free electrode NiCo2S4/bio-carbon coated nickel foam (NiCo2S4/GRCNF) by growing NiCo2S4 nanosheets on the surface of low-cost and highly conductive GRCNF substrate via a simple hydrothermal reaction followed with subsequent sulfidation. As suggested by systematic characterizations, the advantages of obtained NiCo2S4/GRCNF include that the ultrathin 3D interconnected network of NiCo2S4 can furnish massive electrochemically active sites for faradic reaction, and the highly conductive GRCNF substrate promotes electron transfer and meanwhile prevents the aggregation of NiCo2S4 nanosheets. With a high specific capacitance of 7.71 F cm−2 at 3 mA cm−2, NiCo2S4/GRCNF has a huge application advantage over the contrast samples Ni-Co LDH/NF (3.29 F cm−2) and Ni-Co LDH/GRCNF (5.97 F cm−2). In addition, NiCo2S4/GRCNF shows a much higher rate performance (82.1%) than Ni-Co LDH/NF (44.5%) and Ni-Co LDH/GRCNF (66.4%). Furthermore, hybrid supercapacitor NiCo2S4/GRCNF//GNPC which is assembled with NiCo2S4/GRCNF as the anode possesses an impressive energy density of 0.429 mWh cm−2 at a power density of 7.023 mW cm−2 and good cycling stability (82.3% over 5000 cycles). The outstanding electrochemical performance of NiCo2S4/GRCNF suggests that the reported strategy provides new inspiration for the design and preparation of new binder-free composite electrodes for electrochemical energy storage.

Electrodeposition of polypyrrole as binder-free and high mass-loading electrodes for flexible supercapacitors

Flexible or bendable energy storage devices have drawn great attention recently due to the great demand for the development of soft portable equipment. Conducting polymers (polypyrrole, polyaniline, polythiophene) are particularly interesting powder form candidates for active materials in such devices. A traditional slurry-based technology with low mass loadings (1 mg/cm2) is usually used. However, poor interparticle or particle-substrate connections influence the performance of devices during bending. Furthermore, increasing the mass loading (10 mg/cm2) of commercial-level electrode materials often has the problems of poor electrical and ionic conductivity, which will hinder their practical applications. The electrodeposition process of conducting polymers provides an alternate useful method to synthesize uniform and binder-free electrodes with high mass loadings. Here, electrochemically synthesized polypyrrole is proposed and investigated to increase the energy storage performance with high mass loadings. The electrodeposition polypyrrole electrode with a mass loading of 10 mg/cm2 demonstrates a competitive gravimetric capacitance of 265 F/g at a current density of 1 A/g. In the case of a symmetrical supercapacitor with E-PPy, the differences in the capacitance obtained with different electrode masses are insignificant (59.1 F/g for 2.4 mg/cm2 and 54.9 F/g for 10 mg/cm2). The assembled supercapacitor also possesses outstanding flexibility (as high as 96.3% capacitance retention at 2 A/g) upon bending to 140° for 10 cycles.

Large-scale vertical graphene on nickel foil as a binder-free electrode for high performance battery-like supercapacitor with an aqueous redox electrolyte

Due to the special three-dimensional structures and excellent physicochemical properties, vertical graphene (VG) has been extensively investigated as potential material for supercapacitors. However, achieving VG-based supercapacitors with high-energy density and high-power density is a still tremendous challenge. Here we attempt to synthesize large-scale VG films on flexible substrates and design a novel battery-like supercapacitor (BSCs) with the VG on Ni foil (VG@Ni) as a binder-free electrode operating in the KOH electrolyte with the redox additives of K3Fe(CN)6 and/or K4Fe(CN)6. The VG@Ni electrodes demonstrate an ultrahigh areal capacitance of 1453 mF cm−2 at 5 mA cm−2 in 1 M KOH electrolyte with adding 0.07 M K3Fe(CN)6 and 0.07 M K4Fe(CN)6, coulombic efficiency greater than 90%, and long-life cycling stability (capacitance retention is 99.3% after 20000 charge-discharge cycles). The BSCs, which are assembled with two identical VG@Ni electrodes, deliver the areal capacitance of 231 mF cm−2 with energy density of 32 μWh cm−2 and power density of 2498 μW cm−2 at 1 mA cm−2. These outstanding performances can be ascribed to the special feature and excellent properties of VG materials, high electronic conductivity of binder-free VG@Ni electrode, faradaic properties of redox electrolyte, and synergistic effects between the VG film and redox electrolyte.

Assembly of Co3S4-encapsulated reduced graphene oxide nanosheets on Ni foam for binder-free supercapacitor electrode with boosted cycling stability

Assembly of Co3S4-encapsulated reduced graphene oxide nanosheets on Ni foam for binder-free supercapacitor electrode with boosted cycling stability

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.

Salts-assistant synthesis of g-C3N4/Prussian-blue analogue/nickel foam with hierarchical structures as binder-free electrodes for supercapacitors

The exploitation of high-performance electrode materials is significant to develop supercapacitors with satisfied energy and power output properties. In this study, a g-C3N4/Prussian-blue analogue (PBA)/Nickel foam (NF) with hierarchical micro/nano structures was developed by a simple salts-directed self-assembly approach. In this synthetic strategy, NF acted as both 3D macroporous conductive substrate and Ni source for PBA formation. Moreover, the incidental salt in molten salt-synthesized g-C3N4 nanosheets could regulate the combination mode between g-C3N4 and PBA to generate interactive networks of g-C3N4 nanosheets-covered PBA nano-protuberances on NF surfaces, which further expended the electrode/electrolyte interfaces. Based on the merits from this unique hierarchical structure and the synergy effect of PBA and g-C3N4, the optimized g-C3N4/PBA/NF electrode exhibited a maximum areal capacitance of 3366 mF cm−2 at current of 2 mA cm−2, as well as 2118 mF cm−2 even under large current of 20 mA cm−2. The solid-state asymmetric supercapacitor using g-C3N4/PBA/NF electrode possessed an extended working potential window of 1.8 V, prominent energy density of 0.195 mWh cm−2 and power density of 27.06 mW cm−2. Compared to the device with pure NiFe-PBA electrode, a better cyclic stability with capacitance retention rate of 80% after 5000 cycles was also achieved due to the protective effect of g-C3N4 shells on the etching of PBA nano-protuberances in electrolyte. This work not only builds a promising electrode material for supercapacitors, but also provide an effective way to apply molten salt-synthesized g-C3N4 nanosheet without purification.

Self-supporting NiO-coated activated carbon nanofibers based on atomic layer deposition for supercapacitor

The rapid development of consumer electronics, electric vehicles, and smart meters demands high-performance energy storage devices. By now, supercapacitors are expected to become one of the most promising energy devices for future energy technology. In this work, NiO nanoparticles supported on activated carbon nanofibers (NiO/ACNFs) have been synthesized by atomic layer deposition technique, which is directly used as self-supporting binder-free electrodes for supercapacitors. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman results show that NiO nanoparticles (3.1 nm) are uniformly coated on ACNFs. The NiO/ACNFs-600 electrodes demonstrate a specific capacitance of 870 F·g−1 (1 A·g−1) and good rate capability (remain 67% at 10 A·g−1). The asymmetric supercapacitor devices with NiO/ACNFs-600//ACNFs electrodes yield a fairly high energy density of 39.85 Wh·kg−1 at 2000 W·kg−1 and excellent capacitance retention of 87% after 10,000 cycles. The excellent electrochemical capacitance performance for NiO/ACNFs is attributed to the high conductivity and large specific surface area of ACNFs, high capacity, small size, and even dispersion of NiO as well as the synergistic effect between them. These results demonstrate that NiO/ACNFs can serve as excellent electrode materials for high-performance asymmetric supercapacitors.

Polyaniline combining with ultrathin manganese dioxide nanosheets on carbon nanofibers as effective binder-free supercapacitor electrode

Polyaniline combining with ultrathin manganese dioxide nanosheets on carbon nanofibers as effective binder-free supercapacitor electrode