Flexible Asymmetric Solid-state Supercapacitor Research Articles

In situ growth of binder-free CoNi0.5-MOF/CC electrode for high-performance flexible solid-state supercapacitor application.

Metal organic frameworks (MOFs) with binder-free electrodes have shown promise for portable electrochemical energy storage applications. However, their low specific capacitance and challenges associated with the attachment of active materials to the substrate constrain their practical utility. In this research, we prepared a CoNi0.5-MOF/CC electrode by in situ growth of CoNi0.5-MOF on an H2O2-pretreated carbon cloth (CC) without using any binder. It exhibits a higher specific capacitance of 1337.5 F g-1 than that of CoNi0.5-MOF (∼578 F g-1) at a current density of 1 A g-1 and an excellent rate ability of 88% specific capacitance retention at a current density of 10 A g-1 after 6000 cycles. The as-assembled flexible asymmetric solid-state supercapacitor based on the CoNi0.5-MOF/CC positive electrode and a nitrogen-doped graphene (N-Gr) negative electrode exhibits an energy density of 61.46 W h kg-1 at a power density of 1244.56 W kg-1 and holds a stable capacitance of ∼125 F g-1 at 1 A g-1 when the flexible supercapacitor is bent, showing great potential for flexible electronics application. The H2O2 is indicated to play an important role, enhancing the adhesion of CoNi0.5-MOF on CC and reducing its charge transfer resistance by functionalizing the carbon fiber during the pretreatment of the CC matrix. The results provide a great way to prepare a flexible asymmetric solid-state supercapacitor with both high power density and high energy density for practical application.

Facile synthesis of layered reduced graphene oxide/polyaniline (rGO/PANI) composite electrode for flexible asymmetric solid-state supercapacitor

For supercapacitors, composite electrodes with a combination of reduced graphene oxide and polyaniline (rGO/PANI) have gained a lot of attention due to their synergistic effects. In this study, rGO-PANI composite thin films were deposited on a stainless steel substrate with various mass loadings by successive ionic layer adsorption and reaction (SILAR) method. The specific surface area rises from 13 m2 g−1 to 30 m2 g−1 with the introduction of rGO. Due to the composition modification and specific surface area enhancement, the specific capacitance (capacity) of 1348 F g−1 (1255C g−1) was obtained at 0.89 mg cm−2 mass deposition. Additionally, rGO/PANI/PVA-H2SO4/AC flexible asymmetric solid-state supercapacitor (ASSS) showed specific energy of 20 Wh kg−1 at specific power of 1198 W kg−1. The device maintained almost 96 % of Cs at bending angle of 160° and 75 % over 5000 cycles. This work illustrates a simple way to improve the capacity and stability of PANI via rGO composition for supercapacitor applications.

Self-supported heterojunction nanofibrous membranes for high-performance flexible asymmetric capacitors

Rational design of an electrode material with high flexibility and electrochemical performance is the key to wearable energy storage devices. Herein, a facile and productive needleless electrospinning method was introduced to prepare self-supported and flexible nanofibrous electrode materials for asymmetric capacitor. The MnO2 nanoclusters and ZIF67-derived Co3O4 nano-sheets were sequentially deposited on the surface of N, B-doped carbon nanofibers (hetero-junction MnO2/Co3O4/NB-PCNF). Attributing to the constructed multi-pathway for redox reactions on electrode, the specific capacitance of NB-PCNF and MnO2/Co3O4/NB-PCNF can reach up to 204.2F/g and 141.43F/g at a small current density of 0.1 A/g, respectively. In long-term cycling tests, the electrode materials exhibited excellent cycling stability and good rate capability. The electrodes were assembled with Potassium-ion hydrogel electrolyte to form a flexible asymmetric solid-state supercapacitor (FASS-SC). FASS-SC can reach a voltage window of 1.6 V. It provided 28.2 W h/kg at an energy density of 600 W/kg and a specific capacitance retention of 94.18 % after 10,000 cycles. The FASS-SC offers new research ideas for future flexible devices and wearable technologies.

Impacts of Mn Content and Mass Loading on the Performance of Flexible Asymmetric Solid-State Supercapacitors Using Mixed-Phase MnO2/N-Containing Graphene Composites as Cathode Materials

MnO2/nitrogen-containing graphene (x-NGM) composites with varying contents of Mn were used as the electrode materials for flexible asymmetric solid-state supercapacitors. The MnO2 was a two-phase mixture of γ- and α-MnO2. The combination of nitrogen-containing graphene and MnO2 improved reversible Faraday reactions and charge transfer. However, excessive MnO2 reduced conductivity, hindering ion diffusion and charge transfer. Overloading the electrode with active materials also negatively affected conductivity. Both the mass loading and MnO2 content were crucial to electrochemical performance. x-NGM composites served as cathode materials, while graphene acted as the anode material. Operating by two charge storage mechanisms enabled a synergistic effect, resulting in better charge storage purposes. Among the supercapacitors, the 3-NGM1//G1 exhibited the highest conductivity, efficient charge transfer, and superior capacitive characteristics. It showed a superior specific capacitance of 579 F·g−1, leading to high energy density and power density. Flexible solid-state supercapacitors using x-NGM composites demonstrated good cycle stability, with a high capacitance retention rate of 86.7% after 2000 bending cycles.

3D hetero-nanostructured electrode constructed on carbon fiber paper with 2D 1T-MoS2/1D Cu(OH)2 for flexible asymmetric solid-state supercapacitors

One-dimensional Cu(OH)2 nanorods and two-dimensional 1T-MoS2 nanosheets have attracted attention due to their attractive electrochemical properties. However, 1T-MoS2 nanosheets tend to agglomerate and transform to 2H-MoS2, resulting in a decrease in electrochemical performance. In this study, flexible electrodes with 3D hetero-nanostructures are constructed by growing Cu(OH)2 nanorod arrays and loading 1T-MoS2 nanosheets on carbon fiber paper made of chopped carbon fibers as a conductive flexible substrate. The flower-shaped 1T-MoS2 nanosheets with increased interlayer spacing are conducive to the rapid diffusion and insertion of electrolyte, while the conductive copper hydroxide nanorod array and carbon fiber paper can facilitate electron transport. The 1T-MoS2/Cu(OH)2@CFP based electrode has a high areal capacitance of 1124.0 mF cm−2 at 1 mA cm−2 and excellent cycle stability (with 98.3% capacitance retention after 10000 charge-discharge cycles). Furthermore, a flexible asymmetric solid-state supercapacitor (FASSC) device based on the as-prepared 1T-MoS2/Cu(OH)2@CFP electrode exhibits an energy density of 0.130 mWh cm−2 at a power density of 0.375 mW cm−2. The capacitance of FASSC device remains 90.8% of the initial value after 20000 cycles. In addition, the CFP substrate can be bent at a large angle and folded into different shapes, which makes 1T-MoS2/Cu(OH)2@CFP based electrodes suitable for flexible and portable electronics.

Flexible asymmetric solid-state supercapacitor of boron doped reduced graphene for high energy density and power density in energy storage device

Environment safe, cost-effective, reusable and portable asymmetric solid-state supercapacitor (ASSC) device, working at higher operating potential with high energy density was the challenging criteria for practical application. To satisfy all these we fabricated the ASSC device with boron doped reduced graphene (BRG) as positive and reduced graphene oxide as negative electrode with H2SO4/PVA solid gel electrolyte. Using three different precursors at different weight ratio of boric acid (HBG), boron powder (BG) and boron trioxide (BTG) boron doped reduced graphene oxide was prepared by hydrothermal treatment followed by pyrolysis at 1000 °C in CVD for 2 h. All electrode material exhibits a EDLC and pseudocapacitance in CV and GCD with high capacitance, HBG exhibits 225 Fg−1, BG shows 216 Fg−1 and BTG exhibits 266 Fg−1. Our BTG2//rGO ASSC device exhibits the specific capacitance of 122 Fg−1 with an energy density of 67.8 Wh Kg−1, also exerts an excellent stability of 94% capacitance retention with 99% of coulombic efficiency even after 5000 cycles. Using the device 5 mm red light emitting diode (LED) and DC motors was demonstrated for potential applications.

Synthesis of layered copper selenide on reduced graphene oxide sheets via SILAR method for flexible asymmetric solid-state supercapacitor

Along with growing use of electrochemical energy storage systems, there is a requirement for investigating electrode materials which assure applications in portable and wearable electrical energy storage devices. In this study, facile successive ionic layer adsorption and reaction (SILAR) method was employed to composite CuSe2 with reduced graphene oxide (rGO). The X-ray diffraction study showed orientation of CuSe2 nanoparticles from (200) to (221) plane with rGO composition. The field emission-scanning electron microscope images showed that CuSe2 nanoparticles are uniformly anchored onto the surface of rGO sheets. The composite CuSe2@rGO material offered a higher specific surface area (84 m2 g−1) compared to CuSe2 (24 m2 g−1) with the specific capacitance (Cs) of 612 F g−1 at a scan rate of 2 mV s−1. Moreover, the flexible solid-state asymmetric supercapacitor (ASC) fabricated with configuration CuSe2@rGO/PVA-KOH/CuS exhibited specific energy of 28.3 Wh kg−1 at the specific power of 1538 W kg−1. The device retained about 89% of the initial Cs at a bending angle of 165°. For practical manifestation, two series connected ASC devices charged with 2.8 V delivered 19.6 mW cm−2 of initial power and illuminated LED panel made of 211 red LED’s for 150 s

Fabrication of iron oxide-CNT based flexible asymmetric solid state supercapacitor device with high cyclic stability

Integration of high surface area nanostructures with conducting and deformable electrodes at large scale are of significant importance for flexible supercapacitors with high cyclic stability and low cost. Here, we report water assisted meter scale growth of aligned iron oxide and CNT 1D nanostructures on flexible stainless steel mesh for asymmetric supercapacitor device applications. Electron microscopic investigations revealed the uniform coverage of both iron oxide and CNT forest nanostructures over one meter length of SS mesh. Both iron oxide and CNT nanostructures were tested for supercapacitor electrode material in neutral electrolytes. Further, asymmetric solid state devices were fabricated and connected in serial fashion to demonstrate glowing of LEDs as well as rotation of 5 V micro fan. In addition, at bending angle of 90°, device showed 68% increase whereas, at 180° it showed 13% decrease in capacitance. The calculated specific capacitance for single device is found to be 14.4 mF cm−2. Corresponding energy density and power density are found to be 3 μW-hr cm−2 and 0.74 mW cm−2 respectively. The device showed remarkable capacitance retention of 87% over 25 000 charge discharge cycles. The flexible nature with remarkable cyclic stability of solid state iron oxide/CNT device is suitable for low cost flexible and wearable supercapacitor applications.

Enhanced energy density of flexible asymmetric solid state supercapacitor device fabricated with amorphous thin film electrode materials

Supercapacitors have recently received immense interest in scientific community, as a complementary technology to batteries, to meet the various requirements for energy usage in practice. Amorphous MnO2 and CuS thin films are prepared on stainless steel-304 (SS) substrate by chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR) methods, respectively. Asymmetric flexible solid state supercapacitor fabricated with configuration of SS/A-MnO2/Polyvinyl acetate (PVA)-Na2SO4/A-CuS/SS delivered an impressive specific energy of 57.4 Wh kg−1 at specific power 317 W kg−1 and excellent cycling stability over 10,000 cycles with capacitive retention of 84%. Moreover, series configuration of two asymmetric devices shows the capability of powering 211 red LEDs for ~150 s after charging for 30 s.

Correction: Dual-defect surface engineering of bimetallic sulfide nanotubes towards flexible asymmetric solid-state supercapacitors

Correction for ‘Dual-defect surface engineering of bimetallic sulfide nanotubes towards flexible asymmetric solid-state supercapacitors’ by Ling Kang et al., J. Mater. Chem. A, 2020, DOI: 10.1039/d0ta08979f.

Dual-defect surface engineering of bimetallic sulfide nanotubes towards flexible asymmetric solid-state supercapacitors

Nickel cobalt sulfide (NiCo2S4) is a promising battery-type material for electrochemical energy storage.

Enhancing the capacity of activated carbon electrodes by a redox mediator pair for the fabrication of flexible asymmetric solid-state supercapacitors

We use a redox mediator pair - hydroquinone (for positive electrode) and sodium anthraquinone-2-sulfonate (for negative electrode) - to treat the activated carbon electrodes for fabricating asymmetric supercapacitors. This simple adsorption-based treatment improves the specific capacity of the activated carbon electrode from 69.3 mAh g−1 to 300.4 mAh g−1 (negative electrode) and 63.5 mAh g−1 to 301.1 mAh g−1 (positive electrode). The charge balance between the two electrodes is achieved by synchronous potential measurements on redox reaction of hydroquinone and anthraquinone-2-sulfonate. Under 5 A g−1, the asymmetric supercapacitor delivers a high energy density of 37.1 Wh kg−1 with the power density of 2087 W kg−1. Meanwhile, the asymmetric supercapacitor demonstrates excellent cycling stability, capable of retaining 81.8% of its capacity after 20000 cycles at 10 A g−1. A flexible solid-state asymmetric supercapacitor is fabricated with the treated electrode-pair and exhibits excellent flexing stability, high volumetric energy density (2.20 mWh cm−3 at 0.017 W cm−3), and good cycling stability (>91% capacity retention after 3000 cycles), which holds great potential for application in wearable electronics.

Designed mesoporous hollow sphere architecture metal (Mn, Co, Ni) silicate: A potential electrode material for flexible all solid-state asymmetric supercapacitor

The high performance of a supercapacitor device relies largely on the nanoarchitectures scrupulous designed and electrode material used. In this work, by utilizing Stöber method-prepared SiO2 sphere as a template, porous hollow spherical nanostructured metal silicates (MnSi, CoSi and NiSi) were synthesized by a hydrothermal method. When MnSi, CoSi and NiSi were used as effective positive materials for asymmetric supercapacitor, they exhibited a battery-type redox behavior and a relatively high charge storage property (517.0, 452.8, 66.7 F g−1 at 0.5 A g−1) in an aqueous alkaline electrolyte. The excellent electrochemical performance is mainly based on the large surface area of metal silicates, and the porous hollow spherical structure facilitates fast electrolyte ions and electrons transportation. More importantly from the practical applications, three high capacity performance, flexible asymmetric solid-state supercapacitor devices were assembled by employing metal silicates as an effective positive electrode and activated carbon as negative material in PVA-KOH gel electrolyte. The MnSi//AC, CoSi//AC and NiSi//AC device showed an areal capacitance of 1048.3, 375.5 and 120.9 F cm−2, corresponding to a high energy density of 4.6, 2.6 and 0.93 mWh cm−3, respectively. The detailed formation mechanism and electrochemical mechanism of metal silicate is performed experimentally and theoretically. The results reveal that MnSi, CoSi and NiSi have a potential application in energy storage.

Mixed-Phase MnO₂/N-Containing Graphene Composites Applied as Electrode Active Materials for Flexible Asymmetric Solid-State Supercapacitors.

MnO2/N-containing graphene composites with various contents of Mn were fabricated and used as active materials for the electrodes of flexible solid-state asymmetric supercapacitors. By scanning electron microscopes (SEM), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectrometer (XPS), fourier-transform infrared spectroscopy (FTIR) and Raman spectra, the presence of MnO2 and N-containing graphene was verified. The MnO2 nanostructures decorated on the N-containing graphene were of α- and γ-mixed phases. N-containing graphene was found to reduce the charge transfer impedance in the high-frequency region at the electrode/electrolyte interface (RCT) due to its good conductivity. The co-existence of MnO2 and N-containing graphene led to a more reduced RCT and improved charge transfer. Both the mass loading and content of Mn in an active material electrode were crucial. Excess Mn caused reduced contacts between the electrode and electrolyte ions, leading to increased RCT, and suppressed ionic diffusion. When the optimized mass loading and Mn content were used, the 3-NGM1 electrode exhibiting the smallest RCT and a lower ionic diffusion impedance was obtained. It also showed a high specific capacitance of 638 F·g−1 by calculation from the cyclic voltammetry (CV) curves. The corresponding energy and power densities were 372.7 Wh·kg−1 and 4731.1 W·kg−1, respectively. The superior capacitance property arising from the synergistic effect of mixed-phase MnO2 and N-containing graphene had permitted the composites promising active materials for flexible solid-state asymmetric supercapacitors. Moreover, the increase of specific capacitance was found to be more significant by the pseudocapacitive MnO2 than N-containing graphene.

Rational design of integrated CuO@CoxNi1−x(OH)2 nanowire arrays on copper foam for high-rate and long-life supercapacitors

Rational electrode architectural design, favorable electrode composition, and versatile synthesis approach play a significant role in developing advanced electrodes for high-performance supercapacitor. In this work, we report a facile approach for fabricating 1D hierarchical CuO@CoxNi1−x(OH)2 nanowire arrays grown on 3D highly conductive copper foam. The optimized CuO@Co0.2Ni0.8(OH)2 electrode delivers an ultrahigh specific capacity of 374.7 mAh g−1 at 2 A g−1 with exceptional rate capability (301.7 mAh g−1 at 50 A g−1) and remarkable cycling stability (95.9% after 10 000 cycles at 50 A g−1). A flexible asymmetric solid-state supercapacitor (ASC) is fabricated using the optimized CuO@Co0.2Ni0.8(OH)2 as the positive electrode, activated carbon-coated nickel foam as the negative electrode, and polyvinyl alcohol/KOH gel as electrolyte. The flexible ASC operating with a potential window of 0–1.6 V delivers an energy density of 46.5 Wh kg−1 with a power density of 526.9 W kg−1. The ASC also exhibits excellent cycling stability with a capacity retention of 84.3% after 10 000 cycles at a current density of 7 A g−1.

Flexible Asymmetric Solid-State Supercapacitors by Highly Efficient 3D Nanostructured α-MnO2 and h-CuS Electrodes.

A simplistic and economical chemical way has been used to prepare highly efficient nanostructured, manganese oxide (α-MnO2) and hexagonal copper sulfide (h-CuS) electrodes directly on cheap and flexible stainless steel sheets. Flexible solid-state α-MnO2/flexible stainless steel (FSS)/polyvinyl alcohol (PVA)-LiClO4/h-CuS/FSS asymmetric supercapacitor (ASC) devices have been fabricated using PVA-LiClO4 gel electrolyte. Highly active surface areas of α-MnO2 (75 m2 g-1) and h-CuS (83 m2 g-1) electrodes contribute to more electrochemical reactions at the electrode and electrolyte interface. The ASC device has a prolonged working potential of +1.8 V and accomplishes a capacitance of 109.12 F g-1 at 5 mV s-1, energy density of 18.9 Wh kg-1, and long-term electrochemical cycling with a capacity retention of 93.3% after 5000 cycles. Additionally, ASC devices were successful in glowing seven white-light-emitting diodes for more than 7 min after 30 s of charging. Outstandingly, real practical demonstration suggests "ready-to-sell" products for industries.

Three-Dimensional NiCo2O4@Polypyrrole Coaxial Nanowire Arrays on Carbon Textiles for High-Performance Flexible Asymmetric Solid-State Supercapacitor.

In this article, we report a novel electrode of NiCo2O4 nanowire arrays (NWAs) on carbon textiles with a polypyrrole (PPy) nanosphere shell layer to enhance the pseudocapacitive performance. The merits of highly conductive PPy and short ion transport channels in ordered NiCo2O4 mesoporous nanowire arrays together with the synergistic effect between NiCo2O4 and PPy result in a high specific capacitance of 2244 F g(-1), excellent rate capability, and cycling stability in NiCo2O4/PPy electrode. Moreover, a lightweight and flexible asymmetric supercapacitor (ASC) device is successfully assembled using the hybrid NiCo2O4@PPy NWAs and activated carbon (AC) as electrodes, achieving high energy density (58.8 W h kg(-1) at 365 W kg(-1)), outstanding power density (10.2 kW kg(-1) at 28.4 W h kg(-1)) and excellent cycling stability (∼89.2% retention after 5000 cycles), as well as high flexibility. The three-dimensional coaxial architecture design opens up new opportunities to fabricate a high-performance flexible supercapacitor for future portable and wearable electronic devices.

1D Co2.18Ni0.82Si2O5(OH)4 architectures assembled by ultrathin nanoflakes for high-performance flexible solid-state asymmetric supercapacitors

1D Co2.18Ni0.82Si2O5(OH)4 architectures assembled by ultrathin nanoflakes are synthesized for the first time by a hydrothermal method. We present a self-reacting template method to synthesize 1D Co2.18Ni0.82Si2O5(OH)4 architectures using Ni(SO4)0.3(OH)1.4 nanobelts. A high-performance flexible asymmetric solid-state supercapacitor can be successfully fabricated based on the 1D Co2.18Ni0.82Si2O5(OH)4 architectures and graphene nanosheets. Interestingly, the as-assembled 1D Co2.18Ni0.82Si2O5(OH)4 architectures//Graphene nanosheets asymmetric solid-state supercapacitor can achieve a maximum energy density of 0.496 mWh cm−3, which is higher than most of reported solid state supercapacitors. Additionally, the device shows high cycle stability for 10,000 cycles. These features make the 1D Co2.18Ni0.82Si2O5(OH)4 architectures as one of the most promising candidates for high-performance energy storage devices.