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
2002-08-20
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S006000, C429S164000, C429S171000
Reexamination Certificate
active
06436571
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 provides 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 an depolarized electrochemical cell having a cathode extending along the length of the cell, and having a bottom electrically insulating seal member extending across the bottom of the anode cavity between the anode cavity and the bottom wall of the cell.
It is another object of the invention to provide an air depolarized cell wherein the bottom seal member comprises a melt plug.
It is a further object to provide such a cell having such a melt plug by melting one or more solid particles of electrically insulating thermoplastic seal material inside the anode cavity.
It is a yet further object to provide a cell having such a melt plug by melting such solid particles by driving heat through the bottom wall of the cell.
Still another object is to provide a cell having such a melt plug by melting such solid particles by applying heat to the solid particles by applying heat through the top of the cell.
Another object is to provide a cell having such a melt plug by spray-applying a melted such thermoplastic electrically-insulating material into the bottom of the otherwise-empty anode cavity.
Another object is to provide a cell wherein the bottom seal member comprises an isolation cup extending generally across the bottom of the anode cavity and separating the anode material from the bottom wall.
A yet further object is to provide a cell wherein the bottom seal member comprises a combination of an isolation cup between the bottom wall and a melt plug.
A still further object is for the separator to extend below the top of the bottom seal member at the joint between the bottom seal member and the separator, and to terminate above the bottom of the cathode current collector.
It is yet another object to provide a method of fabricating an elongate air depolarized cell, including melting one or more particles of an electrically insulating thermoplastic seal material in situ in the bottom of the anode cavity, and subsequently to solidify the melt plug material, thereby to provide an insulating melt plug between the positively-charged bottom wall and the negatively-charged anode material.
In a first family of embodiments, the invention comprehends an elongate air depolarized electrochemical cell. The cell has a top and a bottom, and a transverse cross-section disposed along a length of the cell. The cell comprises a cathode, including an air cathode assembly extending along the length of the cell; an anode, including an anode cavity and electroactive anode material in the anode cavity, the anode cavity having a top and a bottom; and a separator, having an inner side wall thereof defining a side wall of the anode cavity between the anode material and the cathode assembly. Electrolyte is dispersed in the anode, the cathode, and the separator. A bottom closure member is electrically connected to the cathode assembly and forms a bottom wall of the air depolarized electrochemical cell. An electrically insulating bottom seal member extends generally across that portion of the transverse cross-section which spans the anode cavity at the bottom of the anode cavity. The bottom seal member separates the electroactive anode material from the bottom wall, and provides a seal about the side wall of the anode cavity at the separator.
In preferred embodiments, the bottom seal member comprises a melt plug extending generally across the bottom of the anode cavity, electrically separating the electroactive anode mate
Dopp Robert Brian
Launder Susan Jean
Moy Gregory Scott
Oltman John Edward
Passaniti Joseph Lynn
Chaney Carol
Quarles & Brady LLP
Rayovac Corporation
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