Showing papers on "Supercapacitor published in 2001"

Electrochemical Properties of High-Power Supercapacitors Using Single-Walled Carbon Nanotube Electrodes

Abstract: We have investigated the key factors determining the performance of supercapacitors constructed using single-walled carbon nanotube (SWNT) electrodes. Several parameters, such as composition of the binder, annealing temperature, type of current collector, charging time, and discharging current density have been optimized for the best performance of the supercapacitor with respect to energy density and power density. We find a maximum specific capacitance of 180 F/g and a measured power density of 20 kW/kg at energy densities in the range from 7 to 6.5 Wh/kg at 0.9 V in a solution of 7.5 N KOH (the currently available supercapacitors have energy densities in the range 6‐7 Wh/kg and power density in the range 0.2‐5 kW/kg at 2.3 V in non-aqueous solvents).

A supercapacitor-based energy-storage system for elevators with soft commutated interface

Abstract: Power variations and energy criteria have been the main motivations for developing regenerative drive converters for elevators. A better performing solution for power smoothing can be easily found by using a supercapacitor-based storage device, connected to the intermediary circuit of a variable-speed-drive system. In this paper, power and energy considerations are being accounted for in the design of the storage tank and regarding the maximum power demand from the feeding network. For the power-conversion circuit, which is necessary to compensate the voltage variations of the supercapacitors during charge and discharge, a high-efficiency converter, topology is proposed, which allows the bidirectional energy flow under soft-commutation conditions. Additionally it offers a good flexibility for the optimal sizing of the supercapacitor voltage level. The typical behavior of the special converter is given, together with an analysis of the advantages related to the specific application.

Electrochemical Characterization of Polyaniline in Nonaqueous Electrolyte and Its Evaluation as Electrode Material for Electrochemical Supercapacitors

Abstract: In this study, the performance of a polyaniline (PANI) based supercapacitor where electroactive PANI films were prepared on carbon paper electrodes from a nonaqueous solution with an organic acid (CF 3 COOH) as the proton source was investigated. The use of nonaqueous media as electrolyte led to an increase of the electroactivity window from 0.75 V in aqueous media up to 1.0 V. Low frequency capacitance, evaluated by electrochemical impedance spectroscopy, of about 150 F/g is reported. Scanning electron microscopy indicated a highly porous material for deposited charges greater than 1 C/cm 2 . Constant current charge/discharge cycling of a symmetric supercapacitor based on PANI in nonaqueous medium was performed in a two-electrode cell configuration and a loss of about 60% of the discharge capacity was demonstrated after 1000 cycles. Tetramethylammonium methanesulfonate (Me 4 NCF 3 SO 3 ) was also used instead of tetraethylammonium tetrafluoborate (Et 1 NBF 4 ) as supporting electrolyte in acetonitrile for the charge/discharge testing of the PANI-PANI capacitor. Energy and power densities of approximately 3.5 Wh/kg and 1300 W/kg, respectively, were developed by this supercapacitor for a cell voltage of I V and a discharge time of 20 s. On the other hand, an asymmetrical supercapacitor with polypyrrole and polyaniline used as positive and negative electrodes, respectively, displayed slightly improved performance. Indeed, an energy density of 5 Wh/kg and a power density of 1200 W/kg were reported for discharge time of about 20 s with 1 M Me 4 NCF 3 SO 3 /acetonitrile as electrolyte.

Carbon-Poly(3-methylthiophene) Hybrid Supercapacitors

Abstract: The challenge to the use of electronically conducting polymers as electrode active materials in supercapacitors is to outperform high-power, double-layer carbon supercapacitors (DLCSs). The present study demonstrates that a hybrid supercapacitor with p-doped poly(3-methylthiophene) (pMeT) as the positive electrode and an activated carbon as the negative electrode outperforms the specific power of the DLCSs without reduction in specific energy while maintaining good performance cyclability over 10,000 cycles. Impedance spectra and cyclability data of galvanostatic charge-discharge cycles of C//pMeT hybrid supercapacitors are presented and discussed. © 2001 The Electrochemical Society. All rights reserved.

Supercapacitor and a method of manufacturing such a supercapacitor

Abstract: An electric double layer capacitor including at least one pair of polarizable electrodes connected to current collectors, a separator made of ion-permeable but electron-insulating material interposed between the electrodes in each pair of electrodes, and a liquid electrolyte. According to the invention the electrodes include a layer of carbon particles having a narrow distribution of nanopores therein, the pore sizes of the nanopores being adapted to fit the ion sizes of the electrolyte. The invention also relates to a method of manufacturing such a supercapacitor.

Synthesis and Characterization of Hydrous Ruthenium Oxide-Carbon Supercapacitors

Abstract: It is shown that composite Ru oxide-carbon based supercapacitors possess superior energy and power densities as compared to bare carbon. An electroless deposition process was used to synthesize the ruthenium oxide-carbon composites Ru is dispersed on the carbon matrix as small particles. The effect of electrochemical oxidation and temperature treatment on the material performance has been studied extensively. Increasing the oxidation temperature reduces the proton transport rate and also increases the degree of crystallinity of the deposits. This adversely affects the performance of the composite. Loading a small amount of Ru oxide (9 wt %) on carbon increases the capacitance from 98 to 190 F/g.

Preparation and Electrochemistry of Hydrous Ruthenium Oxide/Active Carbon Electrode Materials for Supercapacitor

Abstract: Amorphous hydrous ruthenium oxide/active carbon (RuO 2 .xH 2 O/C) powders were prepared by a simple procedure based on the sol-gel process. The precursor was obtained hy mixing an aqueous solution of RuCl 3 and active carhon powders at pH 7. When annealing the precursor at 150°C for 7-9.5 h, the RuO 2 .xH 2 O/C powders obtained had the highest specific capacitance. Transmission electron microscopy photographs showed that the RuO 2 .xH 2 O primary particles were about 10-15 nm diam. They adhered to form large porous secondary particles. A modeling capacitor was made with electrodes comprised of RuO 2 .xH 2 O/C powder and 30% H 2 SO 4 electrolyte. At 10-20 wt % ruthenium in the electrodes, the specific capacitance remained almost unchanged at 243 F/g, which included both the electric double-layer capacitance associated with the high surface area of active carbon and redox capacitance associated with ruthenium oxide. About 52% of the RuO 2 in the RuO 2 .xH 2 O/C powders was utilized. More than 50% of the capacitance in the electrode with 12. 1% ruthenium was due to the formation of the double layer, but for the electrode with 21.1% ruthenium, the capacitance attributed to the double layer dropped to 16.8% of the total capacitance. When the electrodes contained ruthenium from 35 wt % to pure RuO 2 .xH 2 O, the specific capacitance increased from 350 to 715 F/g. The specific capacitance was proportional to the mass of the ruthenium in the electrodes. This enabled the specific capacitance to be controlled by changing the mass ratio of RuCl 3 to active carbon in the preparation. Physical properties of the material and electrochemical characteristics of electrodes are also reported along with the capacitor performance.

Synthesis, chemical polymerization and electrochemicalproperties of low band gap conducting polymers for use in supercapacitors

Abstract: A set of nine monomers derived from diaryl-cyanovinylene, -carboxyvinylene and -cyanobutadiene were synthesized as were the corresponding polymers resulting from the chemical polymerization of the monomers in the presence of an almost quantitative amount of FeCl3 in chloroform. The aim of this work was to investigate the effect of the chemical structure of the polymers on their charge capacitance and stability upon galvanostatic charge/discharge cycling. The electrochemical performances of composite electrodes based on polymer, acetylene black and PTFE have been investigated in acetonitrile containing 1 M Et4NBF4 using cyclic voltammetry and galvanostatic charge/discharge cycling experiments. The best performances in terms of charge capacitance for both the p- and n-doping processes were demonstrated with poly(7) (2E,4E)-2,5-di-2-thienylpenta-2,4-dienenitrile and poly(9) (2E)-3-(2,2′-bithienyl-5-yl)-2-(2-thienyl)prop-2-enenitrile since values as high as 245 C g−1 were obtained with poly(7) in its n-doped state and 325 C g−1 with p-doped poly(9). The energy density (68 Wh kg−1) and power density (24 kW kg−1) delivered by a poly(9) capacitor are in good agreement with those expected from cyclic voltammetry and galvanostatic charge/discharge experiments performed with single electrodes. Unfortunately, a capacitance loss was observed upon cycling and was ascribed exclusively to the n-doping process occurring at the negative electrode since the capacitance of the positive electrode remained almost unchanged during these experiments.

Supercapacitor using electrode of new material and method of manufacturing the same

Abstract: A supercapacitor using an electrode formed of a new material is provided. The supercapacitor includes two electrodes facing each other, the electrodes being composed of carbon nanotubes, an electrolyte provided between the two electrodes, and a separator for separating the electrolyte between the two electrodes.

Carbon cloth-reinforced and activated aerogel films for supercapacitors

Abstract: The incorporation of carbon cloth into resorcinol formaldehyde (RF) aerogel precursors allows the manufacture of flexible, mechanically stable monolithic carbon aerogel electrodes with thicknesses in the 100 μm range. These were used to build button cell supercapacitors (diameter: 22 mm, thickness: 6 mm) with a capacitance of about 11 F and a serial resistance of about 170 mΩ. These cells were characterized by cyclic voltammetry (CV) and impedance spectroscopy (IS). A fit function for CV data was developed and confirmed with IS. Self discharge properties and long-term stability of these cells were investigated and compared to cells made with Maxsorb carbon black binder electrodes and activated Kynol fiber cloth electrodes. In these tests the carbon aerogel showed significantly better results than the commercial materials. Activation tests on carbon aerogel electrodes were performed with promising results.

A power supply

Abstract: A power supply (1) for a pulsed load (2) includes a first energy storage device in the form of a battery (3) which is in parallel with a second energy storage device in the form of a supercapacitor (4). Battery (3) and supercapacitor (4) are respectively modelled as: an ideal battery (7) in series with an internal resistance (8); and an ideal capacitor (9) in series with an equivalent series resistance (ESR) (10). Through use of a supercapacitor (4) having a low ESR with respect to the resistance (8), the power supply (1) facilitates continuity of supply to load (2). That is, during peak demand more of the load current will be supplied by supercapacitor (4) due to the lower ESR. Moreover, during times of lower load current demands the battery recharges the supercapacitor. This reduces the peak current needed to be provided by the battery and thereby improves battery longevity.

Preparation and Modification of Polyacrylonitrile Microcellular Foam Films for Use as Electrodes in Supercapacitors

Abstract: Considerable effort has been devoted to the development and characterization of new electrode materials with improved performance for applications in energy storage devices such as electrochemical supercapacitors. 1-3 Supercapacitors are unique devices exhibiting 20 to 200 times greater capacitance than conventional capacitors mainly due to the high surface area of the electrodes used or to highly functionalized surfaces. 5-7 The large capacitance exhibited by these systems arises from double layer (dl) capacitance (i.e., from charge separation across the electrode/electrolyte interfacial dl) often in combination with pseudocapacitance. This pseudocapacitance is associated with redox-type reactions due to the presence of surface chemical groups and/or to participation of adsorbed species on its surface. 5-7 Studies currently in progress in this area include materials such as carbons, metal oxides, and conducting polymers. For industrial use, these electrode materials must be easy to produce and inexpensive, and exhibit high energy and power densities, high cycle life, and good stability. Carbon materials meet the majority of the requirements mentioned above. They are available in a variety of structures (powder,

Supercapacitors for peak-power demand in fuel-cell-driven cars

Abstract: A downscaled drive train with a 6.5 kW fuel cell and a 10 kW supercapacitor module was realized and tested. The voltage levels and the energy flow between fuel cell and supercapacitor were controlled by an electronic unit. The combined fuel-cell/supercapacitor drive train was tested with a modified New European Driving Cycle (NEDC). The 60 V, 60 F supercapacitor module consisted of 2 x 24 capacitors in series having a capacitance of 800 F each. The capacitors had a max. specific energy of 2.75 Wh/kg and a max. specific power of 6.5 kW/kg. An active electronic unit managed voltage balancing among the 24 capacitors in series. The capacitor module had a max. total energy of 30 Wh and a total max. power of 45 kW and could deliver 10 kW over a period of 6 seconds. It was demonstrated that a supercapacitor is an energy storage device that can be used efficiently in vehicle applications for recuperating braking energy and boosting peak power.

Nanostructure lithium titanate electrode for high cycle rate rechargeable electrochemical cell

Abstract: Rechargeable electrochemical cells, such as lithium batteries and asymmetric hybrid battery/supercapacitor systems, exhibiting exceptional specific capacity levels and stability over extended high-rate recharge cycling comprise nanostructure zero strain Li 4 Ti 5 O 12 intercalation electrode material synthesized in a short duration process of annealing mixed TiO 2 and Li-source precursor compounds at about 800° C. for a time of about 15–30 min which is not substantially longer than that required to effect maximum available reaction between the precursors, thereby substantially eliminating the growth of synthesized Li 4 Ti 5 O 12 particles beyond nanostructure size. The process reduces by order of magnitude the time and energy required for synthesis of the active electrode material and fabrication of utilizing cell devices, and provides such nanostructure material which enables repeated, high-rate recharge cycling without loss of cell capacity or efficiency.

Supercapacitors and method for fabricating the same

Abstract: Using thin-films of iron oxide as the active material of electrodes, supercapacitors are fabricated on various substrates in different shapes. By chemical oxidation the iron-oxide film is formed directly and conformably on the substrates in a short period of cooking. The iron oxide has a chemical composition of Fe x O y H z , where 1.0≦x≦3.0, 0.0≦y≦4.0, and 0.0≦z≦1.0. Substrates, as the current collector, tested includes Al, Ti, Fe, Cu and Ni. Measurements by cyclic voltammetry indicates that the iron-oxide electrodes in a selected electrolyte can store charges as high as 0.5 F/cm 2 or 417 F/g of the electrode materials. Supercapacitors as prepared are economical and can be used as enclosure housings for portable electronics, power tools, and batteries. The supercapacitors can also be integrated with the frames and chassis of electric vehicles.

Synthesis and Characterization of Sb-Doped SnO2 Xerogel Electrochemical Capacitor

Abstract: The performance of electrochemical capacitors made of Sb (6 mol %)-doped SnO 2 xerogel electrodes and nonacidic aqueous electrolyte solutions, including 0.1-2 M KOH and Na 2 SO 4 , has been studied as a function of the thermal history of the xerogel. With increasing calcination temperature, the capacitance per unit weight was found first to increase, due to improved crystallinity, and then to decrease after 500°C due to surface loss. The fully crystallized xerogel exhibited capacitance behaviors consistent with the space-charge model of a semiconductor, showing an average capacitance per unit real surface area of 8 and 16 μF/cm 2 within ± 1.0 V for calcination in air and in vacuum (0.1 Torr). respectively. Composite electrode using the xerogel as a substrate for highly dispersed RuO 2 particles has been constructed, showing a capacitance of 670 F/g RuO 2 with a base (1 M KOH) electrolyte solution.

Current-accumulator module comprising batteries and capacitors, in particular, supercapacitors

Abstract: To charge/discharge energy accumulators (1a, 1b ... 1n), preferably supercapacitors, said supercapacitors are connected in parallel by means of their own AC/DC converters (20) to an alternating-current power circuit (4). Said circuit can also act as a compensating circuit, if the accumulators are connected in series.

New energy storage devices for an improved load managing on distribution level

Abstract: For a few years, problems regarding power quality issues in general have become of increasing interest. They have their own negative influence on several aspects of modern society. The problems in industry have been addressed for a longer period of time. However, home and nonmanufacturing industries also suffer from a lack of power quality. Besides the visual disadvantages, such as flicker, electronic equipment and domotic systems are very sensitive to deviations in mains voltage. To avoid these problems, one can use power supplies which are redundant during normal mains supply, but become active in the case of voltage sags or in cases of total loss of power. All these systems are based on the storage of energy. During recent years, more powerful techniques like superconducting magnetic storage systems (SMES) and systems with supercapacitors, as alternatives for the conventional solutions, have become attractive. Recently, redox flow batteries gave another alternative. A literature study is carried out to present an overview of the advantages and drawbacks of these new storage systems against the existing systems, and to study their usefulness in the distribution grid.

Achieving a high pulse power system through engineering the battery-capacitor combination

Abstract: The advancing technology of thin, lightweight, and high power ultracapacitors has been one of the most exciting and important developments in electronic components. The technology provides a new dimension for engineers and designers to manage the power and energy used in electronic products. The batteries will not have to be oversized to accommodate a peak power demand. A combination of battery and ultracapacitor (hybrid power system) can improve the battery capability for power peaks and also extend battery lifetime. This paper discusses results of an ultra-thin hydro-amorphous ruthenium oxide ultracapacitor. The unique electrochemical characteristics of this ultracapacitor allows it to provide a much higher pulse current capability over the battery-only system. The ultracapacitor is 0.1 cm thick, 14 cm/sup 2/ in area, and weighing 2.6 g has the capability to deliver over 30 W pulse peaks. By combination of an ultracapacitor with the battery, the pulse performance of traditional alkaline primary battery can be significantly improved.

Electric double layer capacitor, electrolytic solution therefore and method for suppressing self-discharge in electronic component

Abstract: Electric double layer capacitors having improved stability of electrochemical properties and improved retention of residual voltage, imparted by using an electrolytic solution containing a polymer, such as acrylonitrile/stryrene copolymer, giving an increased electrolyte ion difusion resistance are provided The capacitors are useful for electro-storage devices, such as back-up power source for real time clocks The polymer is useful for suppressing self discharge in electronic components, such as electric double layer capacitor, aluminum electrolytic capacitors, electro-chemical capacitor and secondary batteries

Serial stage power supply combination for emergency auxiliary charging apparatus

Abstract: An improved emergency auxiliary power supply comprised of a rechargeable secondary battery, a super capacitor or any other type of storage with the capacity equal to or smaller than the load voltage to function as an emergency charging source; a conduction train, an optional charging control circuit and another optional first storage unit comprised of a diode on the output side to prevent inverse voltage and connected to a second storage in the load coupled to the output are provided to comprise a lighter, easy to carry, and for emergency use DC power supply system allowing flexible combination with at least two stages for serial stage power supply.

Manufacturing method for a metal oxide electrode for supercapacitor

Abstract: A metal oxide electrode for a supercapacitor and a manufacturing method thereof are disclosed Potassium permanganate is absorbed on a conductive material, such as carbon or activated carbon, and mixed with a solution including manganese acetate so as to form amorphous manganese oxide Amorphous manganese oxide powder is grounded to a powder which is mixed with binder to form an electrode having a predetermined shape The electrode reduces equivalent serial resistance and enhances high frequency characteristics since the contact area and the adhesion strength between the manganese oxide and the conductive carbon are improved Also, the electrode has high capacitance suitable for a supercapacitor, which is manufactured therefrom at a greatly reduced cost