Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1999-03-05
2001-10-02
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S047000, C429S101000, C429S166000, C429S231800
Reexamination Certificate
active
06296961
ABSTRACT:
BACKGROUND
This invention relates to air depolarized electrochemical cells. This invention is related specifically to metal-air, air depolarized electrochemical cells, especially elongate cylindrical cells. Elongate cells are described herein with respect to cells having the size generally known as “AA.”
Button cells, also illustrated herein, are commercially produced in smaller sizes having lesser height-to-diameter ratios, and are generally directed toward use in hearing aids and computer applications. Such button cells generally feature overall contained cell volume of less than 2 cm
3
, and for the hearing aid cells less than 1 cm
3
.
The advantages of air depolarized cells have been known as far back as the 19th century. Generally, an air depolarized cell draws oxygen from air of the ambient environment, for use as the cathode active material. Because the cathode active material need not be carried in the cell, the space in the cell that would have otherwise been required for carrying cathode active material can, in general, be utilized for containing anode active material.
Accordingly, the amount of anode active material which can be contained in an air depolarized cell is generally significantly greater than the amount of anode active material which can be contained in a 2-electrode cell of the same overall size. By “2-electrode” cell, we mean an electrochemical cell wherein the entire charge of both anode active material and cathode active material are contained inside the cell structure when the cell is received by the consumer.
Generally, for a given cell size, and similar mass, and air depolarized cell can provide a significantly greater number of watt-hours of electromotive force than can a similarly sized, and similar mass, 2-electrode cell using the same, or a similar, material as the anode electroactive material.
Several attempts have been made to develop and market commercial applications of metal-air cells. However, until about the 1970's, such cells were prone to leakage, and other types of failure.
In the 1970's, metal-air button cells were successfully introduced for use in hearing aids, as replacement for 2-electrode cells. The cells so introduced were generally reliable, and the incidence of leakage had generally been controlled to an extent sufficient to make such cells commercially acceptable.
By the mid 1980's, zinc-air cells became the standard for hearing aid use. Since that time significant effort has been made toward improving metal-air hearing aid cells. Such effort has been directed toward a number of issues. For example, efforts have been directed toward increasing electrochemical capacity of the cell, toward consistency of performance from cell to cell, toward control of electrolyte leakage, toward providing higher voltages desired for newer hearing aid appliance technology, toward higher limiting current, and toward controlling movement of moisture into and out of the cell, and the like.
An important factor in button cell performance is the ability to consistently control movement of the central portion of the cathode assembly away from the bottom wall of the cathode can during final cell assembly. Such movement of the central portion of the cathode assembly is commonly known as “doming.”
Another important factor in button cell performance is the electrical contact between the cathode current collector and the cathode can or other cathode terminal. Conventional cathode current collectors comprise woven wire screen structure wherein ends of such wires provide the electrical contact between the cathode current collector and the inner surface of the cathode can.
While metal-air button cells have found wide-spread use in hearing appliances, and some use as back-up batteries in computers, air depolarized cells have, historically, not had wide-spread commercial application for other end uses, or in other than small button cell sizes.
The air depolarized button cells readily available as items of commerce for use in hearing aid appliances are generally limited to sizes of no more than 0.6 cm
3
overall volume. In view of the superior ratio of “watt-hour capacity/mass” of air depolarized cells, it would be desirable to provide air depolarized electrochemical cells in additional sizes and configurations, and for other applications. It would especially be desirable to provide air depolarized electrochemical cells which are relatively much larger than button cells. For example, it would be desirable to provide such cells in “AA” size as well as in the standard button cell sizes.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an air depolarized button cell having structure enabling improved control of doming.
It is another object of the invention to provide an air depolarized cell having improved electrical contact between the cathode current collector and the cathode terminal or cathode can.
It is yet another object of the invention to provide an air depolarized cell which is relatively larger than a hearing aid button cell and which has a greater overall discharge cycle capacity than a similarly-sized alkaline manganese dioxide cell.
It is another object to provide an air depolarized cell which is relatively larger than a hearing air button cell, which has an overall discharge capacity at least as great as a similarly-sized alkaline manganese dioxide cell, and wherein the energy/mass ratio of such cell is significantly greater than the energy/mass ratio of a similarly-sized alkaline manganese dioxide cell.
The invention comprehends a cathode assembly precursor, and cathode assembly made therefrom, for use in an elongate air depolarized electrochemical cell. The cathode assembly precursor comprises a closed-loop elongate cathode current collector having a side wall extending along a length thereof, and having a thickness, a top and a top edge, a bottom, a first outer surface and a first inner surface, and an array of perforations extending through the thickness of the side wall, from the outer surface of the side wall to the inner surface of the side wall; and a catalytically active carbon composition mounted on the side wall of the cathode current collector and extending into the perforations in the cathode current collector. The resulting cathode assembly precursor has a second outer surface and a second inner surface.
In some embodiments, the cathode current collector comprises a cylindrical cathode current collector free from longitudinal jointing along the length of the cathode current collector.
In other embodiments, the cathode current collector comprises a longitudinally-extending joint, preferably free from overlap of elements of the side wall at the joint, optionally interdigitated elements of the side wall joined to each other and thereby forming a longitudinally-extending joint on the side wall.
Preferably, the cathode current collector comprises an imperforate edge region at at least one of the top and bottom, left edge or right edge.
Preferably, any imperforate top and bottom edge regions together extend along no more than 20 percent, preferably 5 to 15 percent, of the length of the cathode current collector.
The array of perforations defines a perforated area of the side wall, the array defining an open fraction of the side wall, of about 45 percent to about 70 percent, preferably about 49 percent to about 65 percent of the perforated area.
In preferred embodiments, respective ones of the perforations have perimeters defining corners therein, the corners being effective to assist in holding the carbon composition securely mounted to the cathode current collector.
Typical composition of the catalytically active carbon composition generally comprises carbon, polymeric binder, and manganese(II) moieties. In general, the catalytically active carbon composition comprises a layer of the carbon composition disposed on one of the first inner and first outer surfaces of the cathode current collector, and extending into the perforations.
In preferred embodiments, the catalytically active carbon composition compr
Dopp Robert Brian
Loch Robert Brian
Moy Gregory Scott
Oltman John Edward
Passaniti Joseph Lynn
Dunn Tom
Quarles & Brady LLP
Rayovac Corporation
Stoner Kiley
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