Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Tape or flexible-type cell including tape fuel cells or...
Reexamination Certificate
1999-03-05
2002-10-08
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Tape or flexible-type cell including tape fuel cells or...
C429S185000, C429S006000
Reexamination Certificate
active
06461761
ABSTRACT:
BACKGROUND
This invention relates to air depolarized electrochemical cells. This invention is relates 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, an 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 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 electrochemical cell wherein a stop ledge in a top grommet faces a stop groove in a cathode can, preventing the grommet from being pushed too far inwardly into the cell.
It is another object to provide a cell wherein the cathode assembly can extend into a slot at an outer edge of the top grommet.
Another object of the invention is to provide a top grommet having an upwardly extending leg overlain by a top closure member.
Yet another object is to provide a tubular air depolarized cell wherein the air diffusion member controls the rate of entry of air to the reaction surface, for example as a function of density of the air diffusion member, whereby the air diffusion member controls the limiting current of the cell.
Still another object of the invention is to provide an air depolarized cell which is free from adhesive bonding of the separator to the cathode assembly.
It is yet another object to provide an air depolarized cell wherein the bottom of the cathode current collector is in a bottom slot, in a path of flow of current between a reaction surface of the cathode assembly and a positive electrode terminal.
A yet further object is to provide a method of fabricating cells, including crimping a top washer and an outer leg of a top grommet at the same time, including closing a slot defined between legs of the grommet.
In a first family of embodiments, the invention comprehends a tubular air depolarized electrochemical cell, having a length, a top and a bottom. The cell comprises a cathode, including a cathode can and a tubular air cathode assembly extending along the length of the cell; an anode, including electroactive anode material in an anode chamber disposed inwardly, of the cathode assembly, in the cell; a separator between the anode material and the cathode assembly; electrolyte dispersed in the anode, cathode, and separator; bottom closure structure closing the bottom of the cell; and top closure structure closing the top of the cell. The top closure structure can comprise a top grommet having an outwardly extending step having a downwardly directed surface disposed about a perimeter of the top grommet, and an inwardly extending ledge on the cathode can having an upwardly directed surface disposed about a perimeter of the cathode can. The downwardly directed surface of the outwardly extending step abuts the upwardly directed surface of the inwardly directed ledge. The abutment of the step and the ledge cooperatively prevents movement of the top grommet, from the described location, downwardly toward the bottom closure structure.
Some embodiments include a seal extending into a slot between the grommet and a top closure member of the cell. The air cathode assembly, for example a cathode current collector or air diffusion member, or both, can extending into the slot, the seal being disposed between the grommet and the cathode assembly. The air diffusion member can extend into the slot from an outer surface of the cathode assembly, extending about an upper edge of the cathode current collector, and downwardly toward an inner surface of the cathode assembly such as toward the cathode current collector.
In some embodiments, the air cathode assembly extends into the slot along a longitudinally-extending length of the slot, the seal extending, in the slot, along substantially the entirety of the length of the slot occupied by the cathode current collector.
In some embodiments, the s
Dopp Robert Brian
Moy Gregory Scott
Oltman John Edward
Passaniti Joseph Lynn
Ward Michael Andrew
Chaney Carol
Quarles & Brady LLP
Rayovac Corporation
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