Flexible Solid-state Symmetric Supercapacitor Research Articles

First report on binder-free boehmite (AlOOH) based prototype, flexible, high-energy and high-power density solid-state symmetric supercapacitor

Supercapacitor has potential to accomplish the world-wide growing demand for clean and sustainable energy. It has virtue of both the battery and the conventional capacitor. The proper selection of electrode material is one of the deterministic factors for the excellent performance of supercapacitor. This work presents the first report on the boehmite phase of a polymorph of earth abundant and inexpensive aluminum based oxy hydroxide for energy storage application. The binder-free synthesis of AlOOH electrode has been carried out by the simple, user-friendly, and low-cost successive ionic layer adsorption and reaction (SILAR) technique at 300 K. The X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy characterizations are performed for the knowledge of crystal structure, chemical bonds, oxidation states, morphology and elements present in the sample, respectively. The electrochemical activities of electrode as well as fabricated solid-state symmetric device are disclosed by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The maximum specific capacitance of 726.5 F g−1 @ 5 mV s−1 has been achieved for AlOOH electrode with ~67 % cyclic stability for 6500 cycles. The assembled device exhibits an excellent specific capacitance of 314 F g−1 @ 5 mV s−1, energy density of 242 Wh Kg−1 and power density of 4701 W Kg−1 with ~80 % stability up to 6500 cycles. The device has ability to glow red, green, blue and white coloured light emitting diodes (LEDs) for 50, 52, 27 and 21 min respectively. Also, the fabricated device is successful for glowing a panel ‘MNNIT’ made up by 56 red coloured LEDs. These results indicate that this work can be beneficial for fulfilling the energy demand of future generation.

Performance of solid-state symmetric supercapacitors based on Dy2S3 electrodes

Rare earth metal sulfides show good capacitance retention and better charge discharge performance. Dysprosium based materials could be a promising candidate for the utilization in supercapacitors due to it's multiple transition states. The dysprosium sulfide (Dy2S3) thin films were deposited on stainless steel (SS) substrate using facile successive ionic layer adsorption and reaction (SILAR) method. The films exhibits orthorhombic crystal structure and spherical nanoparticles morphology. The electrochemical supercapacitive performance of Dy2S3 film showed maximum specific capacitance (Cs) of 273 F g−1 at a scan rate of 5 mV s−1 with excellent (83 %) cycling performance over 2000 cycles in 1 M Na2SO4 electrolyte. The industrial application of SILAR deposited Dy2S3 thin film was examined by fabricating flexible solid-state symmetric supercapacitor (FSS-SSC) device with configuration Dy2S3/PVA-Na2SO4/Dy2S3. It exhibited Cs of 26 F g−1 with specific energy of 17 Wh kg−1 and specific power of 520 W kg−1. A good cyclic stability was observed with capacitive retention of 79 % at the scan rate of 100 mV s−1 after 5000 cyclic voltammetry (CV) cycles. This study highlights the potential application of Dy2S3 for supercapacitor application.

A green approach for synthesis of an efficient nano pebbles-like BiVO4@C electrode for supercapacitor application

A simple, sustainable, cost-effective, and environmentally benign BiVO4@C electrode is developed via an in-situ bio-mediated green SILAR approach. The optimized synthesis and electrochemical characterization of a BiVO4@C and BiVO4 electrode are reported. The in-situ incorporation of carbon in the BiVO4 (BiVO4@C) was determined by Raman, XPS, and FTIR spectroscopy. The BiVO4@C electrode demonstrates a large specific surface area (106.7 m2 g−1), higher charge storage, superior capacitive performance, longer discharge time, and excellent cycling stability when compared to BiVO4. The flexible solid-state symmetric supercapacitor (SSC) device using BiVO4@C electrode material with PVA/KOH electrolyte gel delivered maximum specific capacitance (Csp) (154.6 F g−1) and energy density of 42.0 Wh kg−1 at a power density of 571.6 W kg−1. Moreover, the symmetric device exhibited cycle stability of 5000 cycles with 97.4 % capacitance retention paving the way for developing sustainable supercapacitors for commercial application.

Flexible interdigitated symmetric solid-state micro-supercapacitors with higher energy density for wearable electronics

Planar interdigitated solid-state supercapacitors are one of the most promising energy storage devices as they offer the merit of fast ionic transportation with minimal charge transfer resistance due to the narrow gap between the interdigitated isolated electrode fingers. This study focuses on fabricating flexible symmetric solid-state supercapacitor devices with high energy and power densities. Specifically, a symmetric SnO2‖PVA-LiClO4‖SnO2 solid-state supercapacitor (SSC) device was fabricated using the electron beam evaporation (e-beam) technique on thin, flexible electrodes in interdigitated (ISSC) and stacked (SSSC) configurations and their electrochemical performances were compared. The ISSC exhibiting pseudo-capacitive behavior achieved a maximum volumetric capacitance of 439.5 F cm−3 at a scan rate of 5 mV S−1. Quantitative calculation of the device's charge storage dynamics reveals that the diffusion-limited Lithium insertion processes predominantly contribute to the capacitance of ISSC. Comparatively, the ISSC outperformed the SSSC with a diffusion coefficient of 2.55 × 10−13 m2s−1 and ac conductivity of 2.2 × 10−2 S m−1, demonstrating excellent energy density and power density values. Furthermore, the ISSC with no adverse effect on its capacitance even when bent at various angles suggesting its suitability for flexible wearable electronic devices.

Construction of highly transparent, flexible, and robust solid-state symmetric supercapacitors using NiO electrodes roughened by conformal atomic layer deposition

Transparent flexible supercapacitors (TFSCs) have received significant attention as a power source for modern high-tech wearable electronic gadgets. Although carbon nanomaterials have been employed to manufacture TFSCs, unsatisfactory electrochemical performance and poor optical transparency have restricted their commercial use. In the present study, a TFSC device with large areal capacitance, excellent cyclic stability, and high optical transparency was developed by enhancing the electronic conductivity of the pseudocapacitive material using atomic layer deposition (ALD). In this method, a conformal nickel oxide (NiO) layer whose roughness was readjusted according to its thickness was successfully fabricated on a flexible substrate. The NiO film exhibited a high areal capacitance of 1.51 mF cm−2 at an optical transparency of > 81 % when employed as a TFSC electrode, and it outperformed other state-of-the-art TFSC electrodes. The symmetric solid-state TFSC fabricated via the complete integration of these layers exhibited scalable areal capacitance and cyclic stability at a transmittance of 76 %. These findings demonstrate the potential of ALD-based NiO electrodes for use in sustainable and integrated supercapacitor applications.

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.

FeSe and Fe3Se4 encapsulated in mesoporous carbon for flexible solid-state supercapacitor

Metal selenides have been developed as promising alternatives of metal oxides in energy storage field due to their high conductivity and low bandgap. However, the synthesis of selenides usually suffers from the low melting point and strong volatility of selenium at temperatures higher than 217 ℃. Herein, a facile strategy was developed to prepare iron selenides using a template of Se-contained MOF gel, which could in situ immobilize Se powder due to the fast gelation process, resulting a porous, uniform and tight precursor. By adjusting the mole ratio of Fe and Se in the precursor, FeSe@C and Fe3Se4@C were controllably synthesized with rich mesopores and excellent carbon-encapsulation structure. The kinetics analysis indicates that these unique structures are beneficial for improving electrode kinetics, charge/ion-transfer resistance and electrochemical stability. FeSe@C and Fe3Se4@C exhibit significant capacitances (611.0F g−1 and 569.0F g−1 at 1 A g−1), and excellent cycling properties (94.22% and 93.28% retention after 2000 charge–discharge cycles at 5 A g−1). When estimated in practical application, the flexible solid-state symmetric supercapacitor of FeSe@C//Fe3Se4@C delivers a high Csp of 160.1F g−1, the superior energy density of 32.1 W h kg−1 and a high specific power density of 5998 W kg−1 with 89.5% capacitance retention after 5000 cycles, and the outstanding flexibility.

Synthesis, characterization and supercapacitive application of nanocauliflower-like cobalt tungstate thin films by successive ionic layer adsorption and reaction (SILAR) method

For the first time, cobalt tungstate (CoWO4) thin films were synthesized by successive ionic layer adsorption and reaction (SILAR) method. The monoclinic crystal structure of CoWO4 film was confirmed from X-ray diffraction (XRD) technique. The elemental, surface morphological, structural, and electrical analyses were executed using Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray analysis (EDAX), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET), two point probe method, and contact angle measurement techniques. The surface morphology of CoWO4 thin film consisted of islands of agglomerated cauliflower-like spherical nanoparticles with hydrophilic nature. The specific surface area of 60 m2 g−1 with an average pore size of 1.10 nm. The CoWO4 thin film electrode exhibited specific capacitance of 1436.5 F g−1 at a scan rate of 2 mV s−1 in 1 M KOH as well as capacitance retention of 94% over 3000 galvanostatic charge discharge (GCD) cycles. Furthermore, flexible solid-state symmetric supercapacitor (FSS-SSC) device assembled using CoWO4 thin films, showed specific capacitance of 101.32 F g−1, specific energy of 14.07 Wh kg−1 and specific power of 1225.25 W kg−1. This work highlights simplistic preparation of CoWO4 thin films for energy storage application.

High performance flexible carbon cloth-based solid-state supercapacitors with redox-mediated gel electrolytes

The electrochemical performance of supercapacitors is mainly determined by both the electrodes and electrolytes. By integration of the flexible electrodes with redox-mediated gel electrolytes, high performance solid state supercapacitors were designed in the present work. The flexible carbon cloth (CC)-based electrodes were prepared by covalent immobilization of tetraaniline (TA) onto the oxidized carbon cloth (OCC). Hydroquinone (HQ) and p-phenylenediamine (PPD) were used as redox additive respectively to enhance the electrochemical property of the PVA-H2SO4 gel electrolyte. After optimization, high performance flexible solid-state symmetric supercapacitors (SSSCs) were obtained with specific capacitance of 834.0 mF/cm2, retention of 93.69% after 10,000 CV cycles and 108.5% after 500 cycles of 180°-bending, and energy density of 74.2 mWh/cm2 at power density of 405.3 mW/cm2. Such outstanding comprehensive performance makes them promising potential for practical application.

Enhanced Pseudocapacitive Performance of Symmetric Polypyrrole-MnO2 Electrode and Polymer Gel Electrolyte.

Herein, the nanostructured polypyrrole-coated MnO2 nanofibers growth on carbon cloth (PPy-MnO2-CC) to serve as the electrodes used in conjunction with a quasi-ionic liquid-based polymer gel electrolyte (urea-LiClO4-PVA) for solid-state symmetric supercapacitors (SSCs). The resultant PPy-MnO2-CC solid-state SSCs exhibited a high specific capacitance of 270 F/g at 1.0 A/g in a stable and wide potential window of 2.1 V with a high energy/power density (165.3 Wh/kg at 1.0 kW/kg and 21.0 kW/kg at 86.4 Wh/kg) along with great cycling stability (capacitance retention of 92.1% retention after 3000 cycles) and rate capability (141 F/g at 20 A/g), exceeding most of the previously reported SSCs. The outstanding performance of the studied 2.1 V PPy-MnO2-CC flexible SSCs could be attributed to the nanostructured PPy-coated MnO2 composite electrode and the urea-LiClO4-PVA polymer gel electrolyte design. In addition, the PPy-MnO2-CC solid-state SSCs could effectively retain their electrochemical performance at various bending angles, demonstrating their huge potential as power sources for flexible and lightweight electronic devices. This work offers an easy way to design and achieve light weight and high-performance SSCs with enhanced energy/power density.

Graphene oxide/polypyrrole/polyaniline composite hydrogel synthesized by vapor-liquid interfacial method for supercapacitors

The main research about the preparation of the conducting polymer/graphene composite hydrogel has been focused on the hydrothermal synthesis or the external gel accelerator. Herein, the composite hydrogel based on graphene oxide (GO) and polypyrrole (PPy) and polyaniline (PANI) is fabricated via vapor-liquid interfacial synthesis. FeCl 3 and GO are dispersed in an aqueous solution. Then, the polymerization of pyrrole and aniline occurs on the interface between their vapor and the above aqueous solution. The effect of FeCl 3 and GO on formation, morphology and performance of composite hydrogel of GO/PPy/PANI is investigated. Furthermore, the specific capacitance of hydrogel is larger than that of composite film obtained without the addition of GO. After 2000 electrochemical cycles at a scan rate of 1 A g −1 , about 91% of the specific capacitance of GO/PPy/PANI composite hydrogel is kept, indicating the enhanced cyclic stability of composite hydrogel. Moreover, graphite paper can be coated by GO/PPy/PANI composite hydrogels and used as binder-free electrodes to construct a flexible solid-state symmetric supercapacitor with excellent cyclic stability and rate capability. This work reveals an easy, efficient, and scalable route for the preparation of the conducting composite hydrogel with improved electrochemical performance. • GO/PPy/PANI composite hydrogel is fabricated by vapor-liquid interfacial synthesis. • The effect of GO and FeCl 3 on the composite hydrogel is investigated. • The specific capacitance of composite hydrogel is improved. • The composite hydrogels are further used to construct a flexible supercapacitor.

Enhanced specific energy of silver-doped MnO2/graphene oxide electrodes as facile fabrication symmetric supercapacitor device

The present work is about the preparation of silver (Ag)-doped manganese oxide (MnO2)/graphene oxide (GO) composite thin films are deposited by a facile and binder-free successive ionic layer adsorption and reaction (SILAR) method for the first time. The Brunauer-Emmett-Teller (BET) study revealed the nanosheets of MnO2–Ag3/GO exhibit high specific surface area of 192 m2 g−1. The tailored flower-like morphology and interconnected nanosheets of MnO2–Ag3/GO electrodes achieved high electrochemical performance. The maximum specific capacitance (Cs) of 877 F g−1 at the scan rate of 5 mV s−1 is obtained for MnO2–Ag3/GO electrode tested in 1 M sodium sulfate (Na2SO4) electrolyte with capacity retention of 94.57% after 5000 cycling stability. The MnO2–Ag3/GO composite-based flexible solid state symmetric supercapacitor (FSS-SSC) device delivered Cs as 164 F g−1 with specific energy of 57 Wh kg−1 at specific power of 1.6 kW kg−1 and capacitive retention of 94% after 10,000 cycles.

The role of uniformly distributed ZnO nanoparticles on cellulose nanofibers in flexible solid state symmetric supercapacitors

Paper—a flexible, foldable, and cost-effective substrate made of one-dimensional cellulose nanofibers (1D-CNF)—is being extensively investigated as a promising aspirant for wearable as well as foldable energy storage appliances.

Combined electrochemical and DFT investigations of iron selenide: a mechanically bendable solid-state symmetric supercapacitor

Graphene analogous nanoflakes morphology of iron selenide for advanced flexible solid-state symmetric supercapacitor.

A strategy to prepare activated carbon fiber membranes for flexible solid-state supercapacitor applications

The development of flexible supercapacitors is highly desired for electrode materials with good flexibility and a high specific surface area. The electrospun carbon fiber membranes (CFMs) have the possibility of being used as flexible electrodes due to their one-dimensional fiber structure. The pristine CFMs generally have poor porosity, and the activation process is of the essence. However, the conventional blending activation process will produce an uneven pore distribution and destroy the fiber membrane structure, which is not conducive to maintaining the flexibility of CFMs and hindering the application in flexible supercapacitors. Herein, by treating the electrospun CFMs with KOH impregnation activation process, we have succeeded in making the activation of CFMs more uniform and avoiding the occurrence of local over-activation. On the premise of ensuring that the fiber structure of CFMs is not damaged, the specific surface area of activated CFMs (ACFMs) was increased to 2408 m2 g−1, and the mechanical flexibility of CFMs was well maintained. As a result, the optimal ACFMs delivers a specific capacitance of 289.2 F g−1 at a current density of 0.5 A g−1 in aqueous electrolyte and an energy density of 14.8 Wh kg−1 in neutral electrolyte. In addition, the flexible solid-state symmetric supercapacitor also shows excellent electrochemical performance, making it have great potential in energy storage applications for wearable, foldable, and portable electronic devices.

Na3PO4 assistant dispersion of nano-CaCO3 template to enhance electrochemical interface: N/O/P co-doped porous carbon hybrids towards high-performance flexible supercapacitors

Recently porous carbon hybrids have attracted ever-increasing attention as electrode materials for supercapacitors, but it remains a great challenge to simultaneously control their pore structure and element composition with optimal electrochemical performances. Herein, Na3PO4 assistant dispersion of nano-CaCO3 template in egg white was proposed to fabricate nitrogen/oxygen/phosphorus (N/O/P) co-doped 3D hierarchical porous carbon hybrids. The as-prepared carbon exhibited a high surface area (2576 m2 g−1), well-balanced pore size distribution with a large micropore volume (0.77 cm3 g−1) and multi-heteroatoms doped carbon skeleton (3.9% of N, 12.2% of O and 4.1% of P). These physicochemical advantages were synergistically beneficial to supercapacitive performances: an ultrahigh capacitance of 452 F g−1 at 0.5 A g−1 in 6 M KOH electrolyte and excellent stability of 92.4% capacitance retention after 10000 cycles at 10 A g−1. The energy density was 22.6 Wh kg−1 at the power density of 225.0 W kg−1 in the neutral electrolyte of 1 M Li2SO4. Especially, a flexible symmetric solid-state supercapacitor was assembled, which delivered a high capacitance (166 F g−1) and excellent flexibility (86.3% capacitance retention) with bending angles to 180°. Thus, this work provides a cost-effective strategy to fabricate multi-element co-doped 3D hierarchical porous carbon and expand its application for flexible energy storage devices.

Single-pot hydrothermal synthesis of manganese phosphate microrods as a cathode material for highly stable flexible solid-state symmetric supercapacitors

Here, we report a binder-free synthesis of microrods-like manganese phosphate thin film over stainless steel substrate by a facile, single-pot hydrothermal method. The XRD analysis reveals that, the formation of manganese phosphate [Mn3(PO4)2] material of a monoclinic crystal structure. From SEM images observed microrods like morphology of manganese phosphate with an average width of ∼25 μm. The manganese phosphate electrode shows a better electrochemical performance with a specific capacitance of 145 F g−1 at 0.2 mA cm-2 current density in 1.0 M Na2SO4 electrolyte. Moreover, the flexible solid-state symmetric electrochemical energy storage device was assembled with PVA-Na2SO4 solid gel-electrolyte consists of manganese phosphate as anode and cathode electrode. The corresponding symmetric supercapacitor achieves a high energy density of 11.7 Wh kg−1 at a high power density of 1.41 kW kg−1 with an excellent specific capacitance of 37 F g−1 at 0.1 mA cm-2 current density. Manganese phosphate shows long-term electrochemical cyclic stability at a current density of 0.8 mA cm-2 for 9000 galvanostatic charge-discharge cycles with excellent capacitance retention (99 %). This excellent capacitive performance confirms that the manganese phosphate is promising material and fabricated flexible solid-state symmetric supercapacitor has high potential in the field of portable and bendable energy storage devices.

Chemical bath synthesis of NiCo2O4 nanoflowers with nanorods like thin film for flexible supercapacitor application-effect of urea concentration on structural conversion

In a simple chemical bath deposition, the flexible NiCo2O4 thin films with different nanostructures such as nanoflakes, nanoflowers with the surface composed of nanorods have been synthesized on stainless steel by changing the urea concentration of precursor. This study showed that the concentration of urea has a crucial role in the structural conversion of nanostructures. Here, the NiCo2O4 nanoflowers with nanorods like thin film demonstrated superior supercapacitive performance exhibiting a maximum specific capacitance of 702 F g−1 ascribed to the higher electronic conductivity of NiCo2O4 and lower ionic diffusion resistance due to nanoflowers with nanorods like mixed morphology. In further, the higher concentration of urea during synthesis leads to disorientation and overgrowth of the NiCo2O4 nanoflowers which deteriorated its supercapacitive performance. The two flexible solid state symmetric supercapacitor devices have been successfully fabricated using polyvinyl alcohol–KOH and polyvinyl alcohol-LiClO4 gel electrolytes. In comparison, the device with polyvinyl alcohol-LiClO4 gel exhibited superior performance exhibiting a maximum specific capacitance of 132 F g−1 with an energy density of 18.52 Wh kg−1 and a power density of 3.13 kW kg−1.

Hierarchical WS2@NiCo2O4 Core-shell Heterostructure Arrays Supported on Carbon Cloth as High-Performance Electrodes for Symmetric Flexible Supercapacitors.

Nowadays, rationally preparing heterostructure materials can not only make up for the shortage of individual components, but also exert unexpected performance through synergistic interactions between the components. Herein, a core–shell of WS2@NiCo2O4 screw-like heterostructure arrays grown on carbon cloth (CC) was prepared by a two-step solvothermal method for supercapacitors. As a binder-free flexible electrode, a high areal capacitance of 2449.9 mF cm–2 can be achieved for WS2@NiCo2O4/CC at a current density of 1 mA cm–2. Benefiting from the core–shell of the WS2@NiCo2O4 heterostructure, the capacitive property of the flexible WS2@NiCo2O4/CC electrode is better than those of WS2/CC and NiCo2O4/CC electrodes. Based on WS2@NiCo2O4/CC electrodes, the assembled flexible solid-state symmetric supercapacitor (FSS) device shows a high energy density of ∼45.67 W h kg–1 at a power density of 992.83 W kg–1. Meantime, the WS2@NiCo2O4/CC-assembled FSS device also exhibits high cycling stability with an excellent capacity retention of ∼85.59% after 5000 cycles.

3D network of V2O5 for flexible symmetric supercapacitor

The obstacles, faced by flexible lithium-ion batteries (LIB) for its unambiguous synthesis procedure and low power densities for practical applications escalate the position of flexible supercapacitors (SCs) as a new standalone performer in modern energy storage devices. Additionally, some admirable features like supremacy over energy density, cyclic stability and fast response make SCs a vital aspirant among the energy storage devices. Eying on those advantages of SCs, in this work layered oxide V2O5 3D array has been grown on carbon fabric. The prepared electrode exhibits a specific capacitance of 1098 F/g at a scan rate of 5 mV/s in 0.5 M K2SO4 electrolyte at three electrode configurations. Further, a flexible solid-state symmetric supercapacitor (SSSc) has been assembled taking LiCl/PVA gel electrolyte. The fabricated SSSc manifests a maximum energy density of 48.32 Wh/kg at a power density of 0.49 kW/kg. Moreover, the device exhibits 92% capacitance retention at a current density of 15 A/g after 10,000 cyclic performance. Interconnected network morphology with a large number of cavities/pores actually provides swift access of the electrolyte ions which utterly improves the performance of the electrode when it has been used for energy storage purposes.