Electricity: electrical systems and devices – Electrolytic systems or devices – Liquid electrolytic capacitor
Reexamination Certificate
1998-12-07
2001-04-24
Dinkins, Anthony (Department: 2831)
Electricity: electrical systems and devices
Electrolytic systems or devices
Liquid electrolytic capacitor
C361S502000, C361S523000
Reexamination Certificate
active
06222723
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to capacitors for storing electrical energy. More particularly, the invention relates to capacitors which store energy by electrochemical means and methods of making such capacitors.
BACKGROUND OF THE PRIOR ART
Capacitors are widely used devices for storing electrical energy. Among the various types of capacitors are electrochemical capacitors and electrolytic capacitors.
Electrolytic capacitors consist of series combinations of two capacitors (e.g. foil electrodes or plates), separated by an electrolyte, and between which a dielectric oxide film is formed adjacent to the surface of one or both of the electrodes.
Electrochemical capacitors consist of a series combination of at least two capacitors separated by an electrolyte. Each capacitor is formed by electrochemical processes (double layer charge storage or Faradaic pseudocapacitance charge storage) across an interface, such as the interface between an electrolyte and an electrode. Such capacitors rely on charge accumulation at the interface in order to store energy. Such capacitors do not rely on a dielectric oxide film for charge storage.
It is well known to produce electrochemical capacitors with electrodes made of carbon materials, with an electrolyte between the electrodes.
An important parameter in selection of capacitors is energy density. The energy density of a capacitor is the amount of energy stored per unit volume or mass of the capacitor. Among the desirable characteristics of capacitors is high energy density, since high energy density capacitors result in decreased capacitor mass and volume required for a given task.
Various approaches have been investigated to increase the energy density of electrochemical capacitors, while still allowing them to provide high power performance. One such approach has been to use non-aqueous electrolytes, which can increase operating voltage and thus energy density. However, non-aqueous electrolytes have low conductivity compared to aqueous electrolytes and thus lower power performance. Further, such electrolytes can be expensive, unstable, and prone to contamination by water and/or air.
From the foregoing is clear that a need exists for improved capacitor having large energy density and long service life.
SUMMARY OF THE INVENTION
An asymmetric electrochemical capacitor has at least a larger capacitance electrode and a smaller capacitance electrode, with an electrolyte therebetween. The larger capacitance electrode has a larger absolute capacitance than the smaller capacitance electrode. The capacitor thus has an overall capacitance which is approximately the absolute capacitance of the smaller capacitance electrode. The electrodes are made of different materials, with the larger capacitance electrode made of the material having a larger specific capacitance. The larger capacitance electrode may thus be the same physical size as or smaller than the smaller capacitance electrode. Such cells may be series connected.
According to one aspect of the invention, an asymmetric electrochemical capacitor includes a first electrode and a second electrode with an electrolyte therebetween, the first electrode being made of a different material than the second electrode, wherein the absolute capacitance of the first electrode has at least three times the absolute capacitance of the second electrode.
According to a particular embodiment of the invention, one of the electrodes uses a Faradaic process and the other electrode uses a non-Faradaic process. The electrode using a Faradaic pseudocapacitive process is made from a material selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, cobalt, manganese, iron, platinum, tantalum, molybdenum, lead, tungsten, vanadium, electrically-conductive alloys, oxides, hydroxides, nitrides, and carbides of the same, metal hydride materials of AB
2
or AB
5
type, doped polymers, and combinations of the foregoing. The other electrode of the capacitor is made of a carbon material.
According to another aspect of the invention, a bipolar capacitance device includes two or more asymmetric electrochemical capacitor cells stacked together in series and bipolar conducting plates between adjacent pairs of the cells. Each of the capacitor cells includes a first electrode and a second electrode with an electrolyte therebetween, the first electrode being made of a different material than the second electrode, wherein the absolute capacitance of the first electrode has at least three times the absolute capacitance of the second electrode.
According to yet another aspect of the invention, a method of storing energy includes the steps of storing energy in a capacitor using an electrochemical process at a first electrode of the capacitor in contact with an aqueous electrolyte; and simultaneously storing energy in the capacitor using an electrochemical process at a second electrode of the capacitor in contact with the electrolyte, the second electrode being a different material than the first electrode, and the absolute capacitance of the first electrode being at least three times the absolute capacitance of the second electrode.
According to a further aspect of the invention, a method of creating a capacitor, comprising the steps of identifying a group of materials which are electrically conducting, which are able to reversibly store charge, and which have a capacitance per unit mass of at least 200 F/g; selecting a first material from the group of materials for use as a first electrode; selecting an electrolyte such that the first electrode is electrochemically stable in the electrolyte; and combining in a capacitor the first electrode made of the first material and a second electrode made of a carbon material, with the electrolyte therebetween, the first electrode having an absolute capacitance which is at least three times the absolute capacitance of the second electrode.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
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Beliakov Alexey
Klementov Arkadi
Litvinenko Serguei
Razoumov Serguei
Dinkins Anthony
Joint Stock Company “Elton”
Renner , Otto, Boisselle & Sklar, LLP
Thomas Eric
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