Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1999-03-05
2001-03-06
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S164000, C429S171000, C429S185000, C429S006000, C429S006000
Reexamination Certificate
active
06197445
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, 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 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 elongate air depolarized electrochemical cell having a novel bottom structures and bottom closures for the cell.
It is another object of the invention to provide an air depolarized electrochemical cell wherein an elongate cathode extends into a slot between outer and inner side walls of a bottom closure member, including optionally a bottom portion of a cathode can.
A further object of the invention is to provide an air depolarized electrochemical cell wherein an air permeable diffusion member extends downwardly into a slot between the cathode assembly and an outer side wall of the bottom closure member.
A still further object is to provide an air depolarized electrochemical cell having a crimp extending about a circumference of the outer side wall of the bottom closure member of the cell.
It is yet another object to provide a method of fabricating an air depolarized electrochemical cell including running a crimping tool against a circumference of the outer side wall of the bottom closure member while backing up the crimping tool with a back-up tool disposed against the inner side wall, and thereby crimping the outer side wall against the combination of the cathode assembly and the inner side wall.
It is a still further object to so develop a crimp bias crimping the outer side wall of the bottom closure member, optionally a cathode can, along a height of the outer side wall corresponding to substantially the full height of the inner side wall.
The invention comprehends an air depolarized electrochemical cell, having a length, a top, and a bottom. The cell comprises a cathode, including an air cathode assembly, extending along the length of the cell; an anode, including electroactive anode material disposed inwardly, in the cell, of the cathode assembly; a separator between the anode and the cathode assembly; electrolyte dispersed in the anode, the cathode, and the separator; a top closure member closing the top of the cell; and a bottom closure member closing the bottom of the cell, the bottom closure member having an outer side wall, a lowest extremity of the bottom closure member, and an inner side wall extending upwardly from the lowest extremity, defining a slot between the outer and inner side walls, the outer side walls applying a crimping bias against the cathode assembly and thereby developing a friction fit holding the cathode assembly in the slot between the outer and inner side walls.
In preferred embodiments, the crimping bias on the outer side wall extends about the bottom closure member along substantially the full height of the inner side wall.
In preferred embodiments, a cavity is defined inwardly of the inner side wall. The cavity has a bottom opening at the lowermost extremity and a closed top, a bottom wall at an upwardly disposed portion of the bottom closure member, the crimping bias in the outer side wall being located on the outer side wall mid-way between the closed top and the bottom opening of the cavity as measured on the opposing inner side wall.
In some embodiments, the bottom closure member further comprises an arcuate bottom wall disposed inwardly of said inner side wall and applying a bias urging the inner side wall against the cathode assembly. Optionally, the arcuate bottom wall extends downwardly from the inner side wall, at an acute angle, toward a central portion of the bottom wall.
In preferred embodiments, the cell includes a liquid-tight seal in the slo
Dopp Robert Brian
Moy Gregory Scott
Oltman John Edward
Passaniti Joseph Lynn
Ward Michael Andrew
Kalafut Stephen
Martin Angela J.
Rayovac Corporation
Wilhelm Thomas D.
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