Electricity: electrical systems and devices – Electrolytic systems or devices – Double layer electrolytic capacitor
Reexamination Certificate
2001-08-06
2003-07-15
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Double layer electrolytic capacitor
C361S503000
Reexamination Certificate
active
06594138
ABSTRACT:
This application claims priority of Russian Patent Application No. 98120015 filed Nov. 11, 1998.
FIELD OF THE ART
The present invention relates to high-capacity electric capacitors for storing electric energy and to methods of their manufacture, and more particularly to an electrochemical capacitor and to a method of manufacturing thereof.
STATE OF THE ART
Known in the art is a design of a capacitor with a double electric layer (U.S. Pat. No. 3,356,963), comprising a bank of storage sections arranged one on the other, connected in series and provided with insulators and current leadouts, each section having two porous electrodes impregnated with an aqueous electrolyte, said electrodes containing activated carbon particles and being separated by an electron-insulating porous separator. Each storage section has electron-conducting current-leading plates impervious for and inert to the electrolyte, encompassing the electrodes and connected with the separator over the periphery of the section with the help of a sealing layer.
The electrodes are made paste-like from a mixture of activated carbon particles and the electrolyte, the electron-insulating ion-conducting separator contacting the electrodes. The electrodes have a consistency of a viscous paste and consist of activated carbon particles having a surface area of 1000 to 2000 m
2
/g, mixed with the electrolyte. As the activated carbon use is made of materials prepared from charcoal, coal and coke. As the electrolyte use is made of aqueous solutions of acids, salts or bases, as well as of nonaqueous electrolytes. The separator is made from a highly porous material in the form of an ion-exchange membrane, and is impregnated with the electrolyte. Each storage section has two electron-conducting electron-impervious plates inert to the electrolyte, encompassing the electrodes. Each plate contacts the surface of the corresponding electrode, it functions as a current collector, and separates neighboring storage sections with respect to the electrolyte. As the plate material use is made of carbon, lead, iron, nickel, titanium or other material inert to the chosen electrolyte. The plates are connected with the separator over the periphery of the storage section with the help of a sealing layer made as a flexible gasket whose main function is to retain the paste-like electrolyte and preclude its spreading beyond the section when mounting in a compressed state in the capacitor body. Storage sections are arranged in the bank one atop the other and connected in series. Electric contact between the sections is ensured over the surface of contacting plates. The bank is installed in the capacitor body made as a chamber from polymethyl methacrylate, provided with current leadouts in the form of wires passing through openings in an insulation disk.
The structure nearest in its technical essence to the one proposed in the present invention is a structure of an electric capacitor comprising a body, at least one bank of elements arranged therein and current leadouts connected with said bank, the bank of elements consisting of series-connected end and internal elements containing porous electrodes with activated carbon particles and a bulk collector, electron-insulating separators and an electron-conducting collector, the separators and the electrodes being impregnated with an electrolyte (WO, A1 92/12521), each electrode is made solid, additionally comprises a disperse electrode and a binder, and has an ion-conducting support integrally connected therewith, the separator is provided with an integral bearing frame from a hard dielectric material, extending beyond the periphery of the electrodes and the plates made from a plastic metallic sheet, whose edges are profiled and hermetically connected with the bearing framer of the separator, and a bank of storage sections is arranged between flat current-leading plates connected with switching current taps of the storage sections and the leadouts of the body which is made as a tight enclosure from an elastic metallic sheet, tightly connected with power plates, the surfaces of the switching current taps, the profiled edges of the capacitor plates, and the bearing frames of the separators of each storage section, as well as the internal surface of the body enclosure which faces them and is at a prescribed distance therefrom, making up a cavity, whose internal volume is filled with a dielectric having a high adhesion to at least the materials of the capacitor plates, bearing frame, and insulators of the capacitor body, said dielectric together with the bank of sections and the body enclosure making up a single unit.
Though the above-described designs on the whole provide for the realization of a new method of storing electric energy in electrochemical capacitors in their double electric layer on the developed surface of the electrodes, they suffer from a number of technical and economic limitations:
paste-like electrodes connected with the separator by means of a flexible gasket, comprised in the banks of elements arranged in a rigid body may peel off the capacitor plate in the course of their service, which leads to an increase of contact resistance between the electrode and, in its turn, increases the internal resistance of the elements and the capacitor comprising the bank of elements;
during long-term service the electric contact between the activated carbon particles in the paste-like electrode inevitably deteriorates, and this also leads to an increase of the internal resistance of the capacitor and to a decrease of its electric capacity;
the use of the paste-like electrode involves serious difficulties in making a section having a large area, so that the field of application of this design is limited to small-size capacitors having a low power capacity (less than 10-100 J); the solid electrode is brittle and breaks easily;
the presence in the designs of a flexible gasket which connects the capacitor plate with the separator over the periphery of the banks does not rule out the possibility of the liquid electrolyte to be squeezed out of the banks beyond them, electrolyte bridges being thus formed between the adjacent banks. This leads to an increase of the leakage current and to the formation of gases owing to electrolysis of the released electrolyte, whereby the capacitor service life is shortened and its reliability is impaired.
The design of an electrochemical capacitor intended for being charged with a high voltage, comprising a large number (hundreds) of elements in a bank, must meet enhanced requirements to the mechanical strength of the capacitor body and electrical insulation between the current-leading parts, the leadout elements and the capacitor body. The capacitor design known heretofore fails to meet this requirement.
The known method of making capacitors (U.S. Pat No. 3,536,963) comprises preparing an electrode mass and making electrodes therefrom, making a separator and capacitor plates, impregnating the electrodes with an electrolyte, assembling the electrodes and capacitor plates into elements, sealing thereof, assembling with leadouts into a bank, and mounting said bank into a body.
This prior art method involves appreciable difficulties in automating the process and requires the use of costly corrosion-resistant materials for carrying out the processes of drying, proportioning the components and paste, and their transportation; the electrochemical capacitor cannot be manufactured using one production line.
The method of shaping an electrode does not ensure introducing the same amount of activated carbon particles into the electrode, therefore the capacity of the bank of elements comprised in the capacitor features an appreciable spread, this leading to an appreciable voltage redistribution in the bank when charging the block of series-connected elements. This calls for arranging an additional number of elements in the barn for lowering the mean charging voltage per element, whereby the capacitor mass and internal resistance become increased.
In addition to the above-stated reasons
Alekhin Viktor G.
Belyakov Alexei I.
Bryntsev Alexander M.
Khodyrevskaya Nelya V.
Zvyagintsev Michail S.
Dinkins Anthony
McDermott & Will & Emery
Thomas Eric
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