Coin Cell Supercapacitors Research Articles

Activated carbon from agave wastes (agave tequilana) for supercapacitors via potentiostatic floating test

To prepare an efficient supercapacitor, an activated carbon from agave wastes was prepared and their electrochemical performance was evaluated as a novel electrode for supercapacitor. The carbon was prepared by two thermal pyrolysis processes under nitrogen atmosphere. The first pyrolysis was achieved at 500 °C until the charring of the bagasse; in the second pyrolysis step, the char was impregnated with different mass ratios of KOH (1:2–1:4) and thermally treated at 800 or 900 °C, for 1 h under N2 flow. The textural analysis showed that the activated carbon had a specific surface area of 1462 m2 g−1 and depicted a type I isotherm (IUPAC) characteristic of a microporous carbon. Raman spectroscopy and XRD measurements confirm that the activated carbon contains a small graphitization degree and a disordered structure. The electrochemical study of the symmetric carbon supercapacitor was carried out in 1 M Li2SO4 solution as the electrolyte. The electrochemical performance of the coin cell supercapacitor was evaluated under an accelerated aging floating test consisting of potentiostatic steps at different voltages (1.5, 1.6 and 1.8 V) for 10 h followed by galvanostatic charge/discharge sequences, and the overall procedure summarized a floating time up to 200 h. The highest capacitance was observed at a floating voltage of 1.5 V, with a large initial specific capacitance of 297 F g−1.

Phytoremediation of Nickel via Water Hyacinth for Biocarbon‐Derived Supercapacitor Applications

Water hyacinth (Eichhornia crassipes, WH) is cultivated in a hydroponic system containing various concentrations of Ni2+ to demonstrate phytoremediation techniques as a facile, low‐cost, and sustainable method for synthesizing high‐performance biocarbon electrode materials. A high specific capacitance of 541 F g−1 in 2 m potassium hydroxide (KOH) is achieved for WH‐5 biocarbon with an energy density of 30.5 Wh kg−1. Materials are assembled into a coin cell supercapacitor capable of lasting 10 000 cycles with 100% capacitance retention. Surface area characterizations support these results with an SBET of 3429 m2 g−1, a VBET of 2.13 cm3 g−1, and an Sp avg of 2.5 nm, indicating enhanced pore formation and functional group cleaving. Raman spectroscopy, attenuated total reflectance Fourier transform IR (ATR‐FTIR), and X‐ray diffraction (XRD) give further insight into physical characteristics of the biocarbon that lead to improved electrochemical performance. This work describes an optimal concentration of preabsorbed Ni2+ catalyst (5 ppm in H2O) capable of achieving 98% of theoretical capacitance and value‐added environmental cleanup associated with synergistic remedial techniques.

Graphitic Carbon with MnO/Mn7 C3 Prepared by Laser-Scribing of MOF for Versatile Supercapacitor Electrodes.

Pseudocapacitive materials encapsulated in conductive carbon matrix are of paramount importance to develop energy storage devices with high performance and long lifespan. Here, via simple laser-scribing, the Mn-based metal-organic framework [EG-MOF-74(Mn)] is transformed into pseudocapacitive hybrid MnO/Mn7 C3 encapsulated in highly conductive graphitic carbon. It is revealed that the rapid carbothermic reduction of MnO (C + MnO → C' + Mn7 C3 + CO) leads to the formation of the intermediate pseudocapacitive MnO/Mn7 C3 and the concurrent catalytic graphitization of disordered carbon. This reaction produces a new type of pseudocapacitive material in the form of MnO/Mn7 C3 fully embedded in highly conductive graphitic carbon. Thanks to the synergistic effect of the MnO/Mn7 C3 nanoparticles and the graphitic carbon, the composite exhibits a high specific capacitance of 403Fg-1 with excellent stability. Asymmetric coin-cell supercapacitors based on the composite demonstrate high energy (29.2Whkg-1 ) and power densities (8000Wkg-1 ) with a long lifespan. Prototypes of flexible paper-based supercapacitors made of the composite also show great potential toward applications of flexible electronics.

Hybrid supercapacitors using electrodes from fibers comprising polymer blend–metal oxide composites with polymethacrylic acid as chelating agent

Hybrid supercapacitors (SCs) made of carbon–metal oxide composites are devices which combine the advantages of electric double layer capacitors and pseudocapacitors viz high energy density, high power density and high cyclability. This is best achieved when the pseudocapacitive components are uniform in size and distribution on the conducting carbon support. Electrodes mats, fabricated from carbonized electrospun fibers generated from solutions of polyacrylonitrile (PAN) as the carbon source, cobalt (III) acetylacetonate as a metal oxide precursor, and polymethacrylic acid (PMAA) as a metal oxide precursor carrier were utilized in coin cell SCs. Fibers without the PMMA carrier were prepared for comparison. XRD and TGA showed conversion of the cobalt precursor to a mixture of cobalt and cobalt oxide (Co3O4). When the PMAA carrier was used, specific capacitance increased from 68 F g−1 in PAN-Co3O4 to 125 F g−1 in PAN-PMAA-Co3O4. The addition of PMAA to the system results in better uniformity, accessibility and dispersion of metal and metal oxide particles. Due to the relatively low surface area of carbonized samples, Co3O4 nanoparticles are the primary contributors to charge storage. The fabricated fibers show an energy density of 8.9 at 750 W kg−1, which is twice that of the fibers made without PMAA.

High energy density supercapacitors with hierarchical nitrogen-doped porous carbon as active material obtained from bio-waste

Supercapacitors (SCs) is a promising energy storage approach to solve the intermittent problems of most renewable energy sources. N-doped hierarchically activated porous carbon materials (ACBS) for supercapacitor applicaitons are obtained by pre-carbonization and KOH activation of N-rich sword bean shells. ACBS containing 1–2% of N show hierarchical porosity, very high surface area and pore volume (equal to 2917 m2/g and 1.73 cm3/g, respectively). These materials are incorporated into supercapacitors. The device containing ACBS obtained using 700 °C as a post-treatment temperature shows a very high specific capacity (equal to 264 F/g at 1 A/g), which remains high (∼180 F/g) even at 20 A/g current density. Corresponding symmetric coin-cell supercapacitor demonstrats 12.5 Wh/kg energy density at 100 W/kg power density. This cell is capable of maintaining its energy density at the 11.1 Wh/kg level at 5000 W/kg power density and demonstrats almost 100% capacity retention after one thousand 1 A/g charge/discharge cycles. Such superior electrochemical performance of devices fabricated using ACBS as active materials is possible because of synergy between electrical double-layer capacitance and faradaic pseudocapacitance, which strongly depend on the surface area, pore volume and size distribution as well as dopant of heteroatoams.

High-Performance and High-Voltage Supercapacitors Based on N-Doped Mesoporous Activated Carbon Derived from Dragon Fruit Peels.

Designing the mesopore-dominated activated carbon electrodes has witnessed a significant breakthrough in enhancing the electrolyte breakdown voltage and energy density of supercapacitors. Herein, we designed N-doped mesoporous-dominated hierarchical activated carbon (N-dfAC) from the dragon fruit peel, an abundant biomass precursor, under the synergetic effect of KOH as the activating agent and melamine as the dopant. The electrode with the optimum N-doping content (3.4 at. %) exhibits the highest specific capacitance of 427 F g–1 at 5 mA cm–2 and cyclic stability of 123% capacitance retention until 50000 charge–discharge cycles at 500 mA cm–2 in aqueous 6 M KOH electrolytes. We designed a 4 V symmetric coin cell supercapacitor cell, which exhibits a remarkable specific energy and specific power of 112 W h kg–1 and 3214 W kg–1, respectively, in organic electrolytes. The cell also exhibits a significantly higher cycle life (109% capacitance retention) after 5000 GCD cycles at the working voltage of ≥3.5 V than commercial YP-50 AC (∼60% capacitance retention). The larger Debye length of the diffuse ion layer permitted by the mesopores can explain the higher voltage window, and the polar N-doped species in the dfAC enhance capacitance and ion transport. The results endow a new path to design high-capacity and high-working voltage EDLCs from eco-friendly and sustainable biomass materials by properly tuning their pore structures.

Electrochemical Performance of an Asymmetric Coin Cell Supercapacitor Based on Marshmallow-like MnO2/Carbon Cloth in Neutral and Alkaline Electrolytes

As a new energy-storage device, a supercapacitor has attracted great attention, but its low power density limits its wide application. The key to develop high-performance supercapacitors is to find...

Fabrication of high-performance symmetrical coin cell supercapacitors by using one step and green synthesis sulfur doped graphene powders

In this work, symmetrical supercapacitors in the form of coin cell types were produced by using S-doped graphene powders.

Oxygen vacancy-rich doped CDs@graphite felt-600 heterostructures for high-performance supercapacitor electrodes.

Carbon dots (CDs) have attracted much attention owing to their distinctive 0D chemical structure, ultra-small size, and intrinsic surface/edge defects, and have been widely used in many kinds of research fields. In this work, a facile method to synthesize an oxygen vacancy-rich doped CDs@graphite felt-600 heterostructure with outstanding electrochemical properties is presented. The electron spin resonance (ESR) provides clear evidence for the existence of abundant oxygen vacancies in the CDs@graphite felt-600 heterostructure. The as-synthesized CDs@graphite felt-600 shows superior areal specific capacitance (5.99 F cm-2), due to abundant oxygen vacancies and extensive surface/edge defects in the heterostructure. In addition, a home-made coin cell supercapacitor (SC) with CDs@graphite felt-600 as the electrode delivers a large areal energy density of 20.7 μW h cm-2 at a power density of 150.0 μW cm-2. To determine the charge storage mechanism at the interface of CDs@graphite felt-600, the binding energies between the CDs and graphite felt are calculated by density functional theory (DFT).

Commonalities of Atomic Layer Deposition of Oxide Coatings on Activated Carbons for 3.5 V Electric Double Layer Supercapacitors

High voltage electric double layer capacitors with reliable cycling performance are in high demand for energy storage applications. In this research, studies of the process-structure-property relations of commercial activated carbon (AC) electrode modified with atomic layer deposition (ALD) have been performed in terms of coating of various oxide compounds. These investigations have yielded similar enhancements of cycling performance at high voltages (3.5V) enabled by the ALD coating of oxides on AC surfaces. The commonalities are the phenomenal increase in capacitance retention of coin cell supercapacitors after 1000 charge/discharge cycles regardless of the electric nature of ALD deposited oxides. Minor differences in coating morphologies and uniformities were observed between the aluminum oxide, titanium oxide, and manganese-cobalt oxide. ALD coating of these oxides of about 20-growth cycle (1-2 nm in thickness) was found to effectively result in reliable cycling performance, lower impedance, and significantly low leakage current. The authors proposed a modified Gouy-Chapman-Stern model to explain the remarkable increase in operating voltage and cycling performance by the increased Stern layer thickness due to the ALD oxide coating. These results demonstrate that the ALD oxide coating has excellent potential for activated carbons for high operating voltage and energy density supercapacitor.

Promising carbon nanosheets decorated by self-assembled MoO2 nanoparticles: Controllable synthesis, boosting performance and application in symmetric coin cell supercapacitors

A composite containing self-assembled MoO2 nanoparticles and functional carbon nanosheets was obtained via a facile and controllable strategy. Two-dimensional functional carbon nanosheets as matrices have close contact with MoO2 nanoparticles, which assists in the improvement of electronic conductivity, provides efficient pathways and accelerates electron transfer. The carbon nanosheets have functional groups on the surface, which could serve as the nucleation sites for MoO2. The MC-0.12 composite shows optimal specific capacitance (190.9 F g-1 at 1 A g-1) and excellent cycle stability between monomers and composites with different constituents. The assembled symmetrical coin cell supercapacitor using MC-0.12 possesses the maximum energy density of 10.3 Wh kg-1 at a power density of 378 W kg-1 and still maintains the energy density of 7.9 Wh kg-1 at 1682 W kg-1 with a larger potential window. The capacitance retention (92%) of the assembled device is maintained after 2000 cycles, showing outstanding cycle life. Therefore, the integration of self-assembled MoO2 nanoparticles with 2D functional carbon nanosheets provides the composite superior electrochemical performance for supercapacitor applications.

Fabrication of Poly(vinyl alcohol)-Polyaniline Nanofiber/Graphene Hydrogel for High-Performance Coin Cell Supercapacitor.

Electroactive polymer hydrogel offers several advantages for electrical devices, including straightforward synthesis, high conductivity, excellent redox behavior, structural robustness, and outstanding mechanical properties. Here, we report an efficient strategy for generating polyvinyl alcohol–polyaniline–multilayer graphene hydrogels (PVA–PANI–MLG HDGs) with excellent scalability and significantly improved mechanical, electrical, and electrochemical properties; the hydrogels were then utilized in coin cell supercapacitors. Production can proceed through the simple formation of boronate (–O–B–O–) bonds between PANI and PVA chains; strong intermolecular interactions between MLG, PANI, and PVA chains contribute to stronger and more rigid HDGs. We identified the optimal amount of PVA (5 wt.%) that produces a nanofiber-like PVA–PANI HDG with better charge transport properties than PANI HDGs produced by earlier approaches. The PVA–PANI–MLG HDG demonstrated superior tensile strength (8.10 MPa) and higher specific capacitance (498.9 F/cm2, 166.3 F/cm3, and 304.0 F/g) than PVA–PANI HDGs without MLG. The remarkable reliability of the PVA–PANI–MLG HDG was demonstrated by 92.6% retention after 3000 cycles of galvanostatic charge–discharge. The advantages of this HDG mean that a coin cell supercapacitor assembled using it is a promising energy storage device for mobile and miniaturized electronics.

A facile route to synthesize Ag decorated MoO3 nanocomposite for symmetric supercapacitor

Specific surface area and electrical conductivity are two decisive factors affecting materials properties. As a potential energy material, MoO3 is still limited in research and application due to its inherent defects. Ag nanoparticles with good electrical conductivity and unique small-size effect are predicted to have more hopeful prospects in energy storage. Ag@MoO3 composites with different Ag content were successfully prepared by a simple liquid-phase reduction method. The results show that the Ag@MoO3 composite has good morphology and the maximum capacitance (225 F/g) when the content of Ag is 8%. Notably, the internal resistance and Warberg resistance of the composite compared with that of MoO3 have been greatly reduced. It is mainly due to the high ion conductivity and small-size effect of Ag nanoparticles, which effectively improve the diffusion efficiency of ions between electrolyte and active materials. Practical application feasibility of Ag@MoO3 electrode was tested in the two-electrode system. Symmetrical coin cell supercapacitor using 8% Ag@MoO3 as electrodes has superior performance. Our work has potential reference value for the combination and characterization of energy storage materials.

Decorating carbon nanosheets with copper oxide nanoparticles for boosting the electrochemical performance of symmetric coin cell supercapacitor with different electrolytes

The synergetic combination of double-layer capacitor carbon nanosheets and pseudocapacitive CuO particles with enhanced electrochemical properties had been proposed. Herein, CuO/carbon nanosheets electrode material with outstanding electrochemistry performance was successfully synthesized via a low-cost and controllable strategy. Such rational architecture integrates high-conductivity carbon nanosheets with rich-chemical-activity CuO particles. The surface-functional carbon nanosheets serve as a conductive substrate, provide an efficient pathway and accelerate the fast diffusion of electrons. This electrode material depicts high specific capacitance up to 183.9 and 371.1 F g−1 at 1 A g−1 in Na2SO4 and KOH electrolyte using three-electrode tests, respectively. Moreover, two symmetric devices using this CuO/carbon nanosheets electrode material were assembled with different electrolytes. The as-fabricated device with KOH electrolyte delivers remarkable energy density of 19.36 W h kg−1 at power density of 355.6 W kg−1 and still maintains 12.06 W h kg−1 at 1750.7 W kg−1. The as-fabricated device with Na2SO4 electrolyte achieves the maximum energy density of 12.46 W h kg−1 at 355.6 W kg−1. The capacitance retention rate is maintained at 94.4% after 2000 cycles in the as-fabricated coin cell supercapacitor with Na2SO4 electrolyte, showing outstanding long-cycling life. Herein, the strategic integration of CuO particles with two-dimensional functional carbon nanosheets as the electrode material provides superior electrochemical performance for supercapacitors.

MnO2 nanoneedles loaded on silicon oxycarbide-derived hierarchically porous carbon for supercapacitor electrodes with enhanced electrochemical performance

Manganese oxide nanoneedle/carbide-derived carbon (MnO2/CDC) composite electrodes with hierarchically porous structure for supercapacitors have been obtained by a convenient hydrothermal technology. MnO2 nanoneedles are homogeneously grown on the surface of CDC obtained by etching silicon oxycarbide (SiOC) using sodium hydroxide (NaOH) according to a self-limiting reaction. The as-prepared MnO2/CDC composites possess large specific surface area of 1749.3 m2 g−1, and facilitate to the enhancement of some certain pseudocapacitance. The MnO2/CDC composite electrodes show a high specific capacitance (255.8 F g−1 at 1 A g−1) in a three-electrode system. Additionally, MnO2/CDC electrodes are used to fabricate a symmetrical coin cell supercapacitor. The device delivers the remarkable energy density of 12.6 Wh kg−1 at a power density of 3997.7 W kg−1 and still maintain 92.2% of the capacitance after 2000 cycles. The electrode materials prepared by combining CDC with transition metal oxide have great potential in supercapacitor applications.

Binder free carbon nanofiber electrodes derived from polyacrylonitrile-lignin blends for high performance supercapacitors

Lignin was blended with polyacrylonitrile (PAN) in different ratios and fabricated into carbon nanofiber electrodes by electrospinning followed by thermal stabilization, carbonization and subsequent activation by CO2 of the carbonized mats. These carbon fiber electrodes exhibit high surface area, high mesoporosity, high graphitic content and high electrical conductivity. Activated carbon nanofiber mats derived from PAN:Lignin 70:30 blends display a surface area of 2370 m2 g−1 with 0.635 cm3 g−1 mesopore volume. These results are due to the selective partial removal of carbonized lignin during the activation step. Coin cell supercapacitors employing these electrodes exhibit 128 Fg−1 specific capacitance, 59 Wh kg−1 energy density and a 15 kW kg−1 power density when operated at 3.5 V using an ionic liquid electrolyte. Since lignin is an inexpensive, abundant, and green polymer, incorporating it into carbon blends enhances the scalability of such materials in energy storage applications.

Water-dispersible graphene–wrapped MnO2 nanospheres and their applications in coin cell supercapacitors

A highly stable and more water-dispersible graphene (WDG) was synthesized using microwave-assisted ball milling technique. The WDG-wrapped MnO2 nanocomposites were prepared for two mass ratios of nanospheres and graphene sheets using reflux method. Comprehensive characterization of the prepared WDG-Mn1 and WDG-Mn2 hybrid nanocomposites was carried out to explore the electrochemical capacitance behaviors. The WDG-Mn1 and WDG-Mn2 electrodes showed capacitance performance of 130 F g−1 at 0.5 A g−1 and 178 F g−1 at 0.5 A g−1, respectively. The WDG-Mn2 electrode revealed enhanced capacitance performance, that is, 84% of its initial capacitance was retained even after repeating the cyclic voltammetry test for 3000 cycles. This study reveals the enhanced capacity performance in WDG-Mn2 nanocomposite hybrid materials for supercapacitors.

Facial electrosynthesis of hydrophilic poly(aniline-co-p-phenylenediamine) nanostructures for high performance supercapacitor electrodes

A high-rate, coin cell (CR2023) supercapacitor (SC) with excellent charge storage performances was fabricated using hydrophilic poly(aniline-co-p-phenylenediamine) nanofiber-decorated nitrogen-doped reduced graphene oxide (referred to as P(ANi-co-pPDA)@N-rGO) as a redox electrode material and 25 mM Fe(CN)64+/Fe(CN)63+ in 1 M H2SO4 as a redox-active electrolyte. P(ANi-co-pPDA)@N-rGOs were synthesized by co-electropolymerization using different co-monomer feeding ratios in 0.5 M H2SO4. From electrochemical measurements, P(ANi-co-pPDA)@N-rGO) with 4% pPDA ratio (noted as [email protected]) showed a high specific capacity of 350 Cg−1 (413 Cg−1 at 10 mV/s), which was 2.2 and 4.5 times as high as those of [email protected] and N-rGO, respectively. Moreover, [email protected] exhibited an improved specific energy of 35.4 Whkg−1 with a specific power of 969 Wkg−1 at 0.5 Ag−1, a good capacity retention of 85% after 1000 cycles at 6 Ag−1 and a low equivalent series resistance of 2.83 Ω. The excellent SC performances can be attributed to its high electrical conductivity, highly hydrophilic nature and excellent electrochemical properties leading to a synergistic effect between co-polymer/N-rGO electrodes and Fe(CN)64+/Fe(CN)63+ redox electrolytes. Thus, the P(ANi-co-pPDA)@N-rGO) SCs produced by the simple cyclic-co-electropolymerization method were highly potential for advanced energy storage applications.

High performance supercapacitors using lignin based electrospun carbon nanofiber electrodes in ionic liquid electrolytes

Flexible, free standing and binder-free electrodes were fabricated by electrospinning from a series of lignin: polyvinyl alcohol (PVA) polymer blends, followed by heat treatment. PVA has the dual function of facilitating the electrospinning of lignin and acting as a sacrificial polymer. Upon stabilization, carbonization and CO2 activation, carbon nanofibers (ACNF) derived from the lignin:PVA 80:20 blend displayed a high surface area of 2170 m2 g−1 and a mesopore volume of 0.365 cm3 g−1. ACNFs derived from all the compositions show high degrees of graphitization based on Raman analysis. Pyr14TFSI ionic liquid (IL), modified by mixing with propylene carbonate and ethylene carbonate to reduce the viscosity and increase the ionic conductivity, was used as a high-performance electrolyte. The resulting IL mixture exhibited a four-fold increase in ionic conductivity compared to the neat IL Coin cell supercapacitors using electrodes derived from lignin:PVA 80:20 blends and this electrolyte displayed 87 F g−1 specific capacitance and 38 Wh kg−1 energy density which is the highest reported energy density for lignin:PVA blends to date.

Insights into the electrochemical capacitor performance of transition metal-vertical graphene nanosheet hybrid electrodes.

Vertical graphene nanosheets (VGN) are envisioned as supercapacitor (SC) electrode materials due to their distinct geometry and remarkable properties. Of late, the hybrid structures of graphene-transition metal (TM) or oxides were found to exhibit enhanced charge storage capacity. Herein, we report the charge storage performance of VGN-transition metal nanoparticle (Au, Ag, Cu, and Ni) hybrid electrodes. Amongst them, Ni-decorated VGN exhibited the highest enhancement, up to 3.04 mF cm-2 (121.6 F g-1) compared to 0.16 mF cm-2 (6.4 F g-1) for as-grown VGN. Further, this was corroborated by the improved electrical as well as ionic conductivity of the metal-decorated VGN structures. Additionally, the presence of metal-oxygen-carbon bonding ensured a contribution of pseudocapacitance. Ab initio calculations elucidated the extent as well as the nature of charge (e-) transfer in TM nanoparticle-VGN hybrid structures. These findings are well corroborated with the charge storage performance. A combined effect from charge transfer and pseudocapacitance on the charge storage performance of TM nanoparticle-VGN hybrid electrodes is demonstrated. A symmetric coin-cell supercapacitor device using Ni/VGN electrodes was fabricated and the sustained performance tested over 10 000 charge-discharge cycles.