Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1999-07-07
2002-04-16
Dunn, Tom (Department: 1725)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S006000, C029S623100, C428S679000
Reexamination Certificate
active
06372381
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to air depolarized alkaline electrochemical cells. Typically, such cells have metal-containing anode materials, and air cathodes, and are commonly known as metal-air cells. More particularly, this invention relates to the composition and structure of cathode cans utilized in such cells, and in general to the cells, themselves. The invention addresses especially the tendency of cathode cans of air depolarized cells to corrode in high humidity environments. The invention particularly addresses structures and methods for attenuating susceptibility of such cans to corrode at edges of the cans which are cut during can fabrication, exposing a corrosion-susceptible interior layer of the metal sheet material from which such cans are fabricated. The invention specifically addresses improvements in can-making technology which facilitate changeover between assembling cells of pre-plated cans bearing no post-coating protection and cells wherein the cans bear a post-coated protective coating at edges of the cans cut during dimensional fabrication of the cans, including fabrication of air ports when the cans are to be used in air depolarized cells.
BACKGROUND
As used herein, “post-plated” cans and “post-coated” cans refer to any can which is subjected to a plating or other metal-coating process after dimensional fabrication of the can has been substantially completed.
As used herein, a “pre-plated” can refers to a metal coating which is applied before dimensional fabrication of the can is substantially completed, including all methods of applying such layers, such as electroplating, electroless plating, and cladding.
As used herein, “unplated” and “uncoated” metal sheet or can refers to material which is not coated or plated with nickel or another corrosion-inhibiting metal before dimensional fabrication of the can has been substantially completed, and which material is subsequently coated onto the metal sheet after fabrication of the can has been substantially completed.
As used herein, a “fully coated” can refers to a can having no uncoated, corrosion-susceptible layers, although coating thickness can be different at different locations on a given can.
As used herein, unless otherwise specifically stated, the term “outer surface” as referring to metal strip or a cathode can made therefrom, means all surfaces of the sheet or can which are exposed to an environment external to the respective sheet or can.
Growth in use of small and very small electrically-powered devices has fueled corresponding growth in demand for small and very small metal-air electrochemical cells. Such cells are known, for example, by the size designations “PR41,” “PR44, “PR48,” and “PR70,” as well as size “5.” Metal-air cells have gained significant popularity because only the anode reaction material need be packaged as an electroactive chemical in the cell. The corresponding cathode reaction material is oxygen, which is drawn from the surrounding ambient environment.
Such small and very small cells are usually disc-like or pellet-like in appearance, and are about the sizes of garment buttons. These cells generally have diameters ranging from less than 6 millimeters to about 25 millimeters, and heights ranging from about 2.0 millimeters or less up to about 15 millimeters.
Such metal-air cells take in atmospheric oxygen, and convert the oxygen to hydroxyl ions in the air cathode by interaction with aqueous alkaline electrolyte. The hydroxyl ions then migrate to the anode, where they cause the metal contained in the anode to oxidize. Usually the active anode material in such cells comprises zinc, although a variety of other operable anode materials are well known to those skilled in the art.
More particularly, the desired reaction in the air cathode of a metal-air cell involves the reduction of oxygen, the consumption of electrons, and the production of hydroxyl ions. The hydroxyl ions migrate through the aqueous alkaline electrolyte toward the anode, where oxidation occurs, forming zinc oxide.
In typical metal-air cells, air enters the cell through one or more air ports in the bottom the cathode can. The port or ports extend through the bottom wall of the cathode can, and may be disposed immediately adjacent the cathode assembly, or may preferably be separated from the cathode assembly by an air reservoir, which is typically occupied at least in part by an air diffusion member.
In such arrangements, the air port facilitates movement of air through the bottom wall of the cathode can and to the cathode assembly. At the cathode assembly, oxygen in the air reacts with water in the electrolyte as a chemically reactive participant in the electrochemical reaction of the cell, and thereby forms the hydroxyl ions.
Typical cathode cans used in air depolarized cells are fabricated from metal sheet having a core layer of steel, and layers of nickel on opposing sides of the steel core layer. Can fabrication comprises a series of punching, pressing, and/or otherwise dimensionally forming steps, including punching out the air ports, and cutting the cans from a continuous strip of the metal sheet. In the process, the core steel layer is exposed at severed edges of the so-created air ports and at severed edges formed when the cans are separated from the continuous strip of metal sheet.
This invention focuses on apparatus, methods, and materials for providing improved cathode cans, including providing improved protection of severed edges from corrosion while generally maintaining the dimensional can specifications which are related to pre-plated cans not having the severed edge protection.
One can to select from a variety of known materials for use in making e.g. pre-plated or post-plated cathode cans. The respective different materials may have different dimensional specifications, different chemical compositions, or different chemical or physical properties, or any combination of these.
Changing material selection affects the ability to fabricate the can, or the method by which the cathode can is fabricated, and the corresponding ability of the can to support fabrication and use of the cell. Thus, starting from a given set of metal strip specifications, where thicker or thinner, or harder or softer, metal sheet, or metal strip having different layer structuring, is contemplated for use to form cathode cans, there is the prospect that the actual structures and properties of cans resulting from dimensional and structural fabrication of such metal sheet, and absent changes in the can fabrication process, will be dependent in part on the specifications of the metal sheet from which the cans are fabricated.
Accordingly, using known pre-plated cans as a reference, any change in selection of material from which the cans are to be made, or change in physical dimensions of such material, or changes in set-up of machines or other equipment for can fabrication, must be balanced against the fabrication characteristics associated with such material and set-up as the material is used to fabricate the respective cans; as well as the characteristics associated with fabrication and use of a cell utilizing such cans.
Any change of material must, of course, be compatible with the chemical environment within which the cell operates. Typically, air depolarized cells operate in an alkaline environment, and so any material used in such cells must be compatible with such environment to the extent such material is exposed to the alkaline environment. Similarly, where the cells are to be used in high humidity climates, any material exposed to the ambient environment should have a suitably high degree of resistance to being corroded by water vapor during the contemplated use lives of the cans and respective cells.
Air depolarized cells are used in the full range of inhabited climates. The cathode cans of typical air depolarized cells are made using metal sheet comprising a core layer of steel, coated on opposing sides with respective first and second layers of nickel.
Fabrication of cathode cans for use in air depo
Armour David Matthew
Park Sang-Keun
Springstead John Claude
Dunn Tom
Edmondson L.
Quarles & Brady LLP
Rayovac Corporation
LandOfFree
Duplex-coated cathode cans, and electrochemical cells made... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Duplex-coated cathode cans, and electrochemical cells made..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Duplex-coated cathode cans, and electrochemical cells made... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2895420