Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
1999-01-19
2001-01-30
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S504000, C361S508000
Reexamination Certificate
active
06181546
ABSTRACT:
TECHNICAL FIELD
The present invention relates to electrical engineering and, more specifically to electrical double layer capacitors that can be used in various power supply systems such as power sources for electrical vehicles and means for reliable internal combustion engine starting.
BACKGROUND ART
Double-layer capacitors with liquid electrolyte and electrodes made of various materials having large specific surface are known in the art (e.g. U.S. Pat. No. 4,313,084 of 1982 and FRG Patent 3,210,420 of 1983). Best results are attained when using various activated carbons as the material of electrodes. Specific capacity of such capacitors exceed 2 F/cu.cm, while use of aprotic electrolytes enables their working voltage to be increased up to 2 or 3 V (see U.S. Pat. No. 4,697,224 of 1987; Nat. Tech. Report, 1980, 26 # 2, pp. 220-230).
However, use of carbonic materials and organic solvents ensures against obtaining high power characteristics of double-layer capacitors that are sometimes necessary, due to high internal resistance caused by low conductance of carbon and electrolyte. Increased charge/discharge current values of double-layer capacitors is attained by further improvements in construction of capacitor electrodes due to, e.g., the use of electrically conducting binder additives and of fibrous carbonic materials (see Carbon, 1990, 28 # 4, pp. 477-482; Radio-Fernsehen-Elektron, 1990, 39 # 2, pp. 77-800).
The most closely pertinent to the present invention in terms of its technical essence and the attainable effect is a double-layer capacitor having two polarizable electrodes made of activated carbon fiber (see W. Hallop et al. Low Cost Supercapacitors. Third International Seminar on double-layer capacitors and similar energy storage devices. Florida, 1993).
However, the electrical energy that can be stored by such capacitors are not sufficient for such applications as power sources for electric vehicles.
DISCLOSURE OF THE INVENTION
The present invention provides a novel double layer capacitor which allows a large amount of electric energy to be stored due to combining a polarizable electrode with a non-polarizable electrode.
Conventional double layer capacitors use polarizable electrodes as both positive and negative electrodes. During discharge of a double electric layer capacitor with two polarizable electrodes, potentials at both electrodes change in opposite directions. As a result, the voltage at the capacitor reduces twice as fast as the potential at each of the electrodes. If the capacitances of the electrodes are equal, the capacitance of the capacitor is about half the capacitance of each electrode.
In accordance with the present invention, the double layer capacitor uses a polarizable negative electrode, whereas its positive electrode comprising nickel hydroxide is non-polarizable.
During discharge, potential at the nickel hydroxide electrode remains practically unchanged. Thus, the capacity of the capacitor is approximately equal to the capacity of the polarizable electrode. As a result, the capacity of the present capacitor is nearly twice as large as the capacitance of a conventional capacitor with two polarizable electrodes. Accordingly, energy that may be accumulated by the capacitor of the present invention is substantially larger than the energy of conventional capacitors having two polarizable electrodes.
Moreover, the mass and volume of the nickel hydroxide electrode may be much smaller than the mass and volume of the polarizable electrode having similar characteristics. This allows the specific energy to be further increased.
Also, the use of the nickel hydroxide electrode in a combination with a polarizable electrode allows the maximum voltage of the capacitor to be increased. As a result, the specific energy may be further increased.
In accordance with a first aspect of the invention, a double layer electrical capacitor for storing electrical energy comprises a combination of polarizable electrode and a non-polarizable electrode reacting with each other in an alkaline electrolyte.
In a preferred embodiment of the invention, the polarizable electrode may be made of carbon material, and the non-polarizable electrode may comprise nickel hydroxide as active material. The polarizable electrode and the non-polarizable electrode may react with each other in the electrolyte comprising aqueous solution of a compound selected from the group consisting of alkali metal carbonate, alkali metal hydroxide and compositions thereof.
The carbon material may be metallized by nickel, silver or copper. The polarizable electrode may be provided with a current collector made of copper or silver. Alternatively, the current collector may be made of nickel covered with silver, gold or carbon.
In accordance with another aspect of the present invention, a capacitor-based module for storing electrical energy is composed of a plurality of capacitor cells electrically connected with each other. Each capacitor cell comprises a negative electrode made of carbon material and a nickel hydroxide positive electrode reacting with each other in electrolyte comprising an aqueous solution of a compound selected from the group consisting of alkali metal carbonate, alkali metal hydroxide, and compositions thereof.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
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Hahn, G., et al, “Elektrische Doppelschichtkondensatoren fur die Speicherpufferung”Radio Fernsehen Elektronik, Berlin 39 (1990), pp. 77-80.
Halliop, Wojtek and John Stannard, “Low Cost Supercapacitors,”Third International Seminar on Double Layer Capacitors and Similar Energy Storage Devices, Dec. 6-8, 1993 (7 pages).
Sekiso, Satoshi, et al. “Liquid Electrolyte Double-Layer Capacitor ‘Gold Capacitor’”,National Technical Report, vol. 26, No. 2, Apr. 1980, pp. 220-230.
Klementov Arkadi D.
Menukhov Vladimir V.
Stepanov Aleksei B.
Varakin Igor N.
Aktsionernoe Obschestvo Zakrytogo Tipa "Elton"
Dinkins Anthony
McDermott & Will & Emery
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