Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Cell enclosure structure – e.g. – housing – casing – container,...
Reexamination Certificate
1998-11-05
2001-07-24
Brouillette, Gabrielle (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Cell enclosure structure, e.g., housing, casing, container,...
C429S163000, C429S176000
Reexamination Certificate
active
06265102
ABSTRACT:
The present invention relates to prismatic metal-air, primarily zinc-air, electrochemical cells.
Currently, the major commercial application for zinc-air cells is in hearing aids, whereby the cell shape is button-like. These cells are usually manufactured from metal and closed by crimping. This method of sealing is successful and electrolyte, usually KOH, leakage does not occur. The success of this method is due to the circular shape of the cell which ensures a uniform distribution of forces around the cell's circumference and along its joint(s).
As is known and as described, e.g., in U.S. Pat. No. 5,733,676, metal-air cells convert atmospheric oxygen to hydroxyl ions in the air cathode. 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.
More particularly, the desired reaction in a metal-air cell air cathode involves the reduction of oxygen, the consumption of electrons, and the production of hydroxyl ions. The hydroxyl ions migrate through the electrolyte to the anode, where oxidation of zinc occurs, forming zinc oxide, and liberating electrons.
Electrolyte leaks in zinc-air cells are the result of several factors. First, the zinc anode expands when oxidized to zinc oxide during the course of discharge. Because of the lower density of the oxide, volume increases ranging from 17 to 60% have been reported. When a cell's anode compartment expands, the walls of the cell casing distort causing electrolyte leakage at the joints.
Hydrogen gas, when not permitted to vent at a reasonable rate, is also a source of internal cell pressure. Hydrogen is produced by the parasitic reaction of zinc with the cell's alkaline electrolyte and occurs even when the cell is dormant. Galvanic reactions between contaminant metals, such as nickel, iron and chromium and the electrolyte are another source of hydrogen gas generation.
Another factor in electrolyte leakage is the phenomenon of KOH “creep”. It is well documented that KOH flows easily over many types of surfaces, especially metal surfaces. It is difficult to control this flow which occurs even in a contra-gravitational direction.
Many different solutions to these expansion/leakage problems have been suggested for zinc-air button cells. As mentioned previously, crimping is an acceptable solution for circular and cylindrical cells where uniform radial forces exist. However, preventing electrolyte leakage from prismatic (rectangular) cells is much more difficult. Conventional crimping techniques and cell designs are usually unsuccessful in controlling KOH leakage because of the non-uniform distribution of forces operating along the cell's perimeter. Even the use of rounded corners, fails to produce a leak-proof cell due to the changing compressive forces between the rounded corners and the straight side-walls.
In order to solve this problem, according to the present invention, there is now provided a metal-air electrochemical cell, having a leak-proof, metal prismatic casing comprising a pair of interfacing interengaging rectangular tray-like casing components, a first substantially rectangular tray-like casing component having a first major surface and contiguous side walls for encompassing a cathode of said cell and a second inverted substantially tray-like casing component having a second major surface and contiguous depending side walls for encompassing an anode of said cell, the side walls of one of said casing components being of a height to facilitate the curling and crimping of an upper portion thereof over a peripheral edge area of the major surface of the other casing component to form a leak-proof, closed prismatic casing.
As will be realized, in contradistinction to the prior art button-like metal-air cells, the interaction of forces between said upper portion of the side walls of said one casing component and the peripheral edge area of the major surface of the other casing component, upon curling and crimping to form a closed casing, are axial.
In preferred embodiments of the present invention there is provided a prismatic metal-air electrochemical cell, having a leak-proof, metal prismatic casing comprising a pair of interfacing interengaging rectangular tray-like casing components, a first substantially rectangular tray-like casing component having a first major surface and contiguous side walls for encompassing a cathode of said cell and a second inverted substantially tray-like casing component having a second major surface and contiguous depending side walls for encompassing an anode of said cell, the side walls of one of said casing components being of a height to facilitate the curling and crimping of an upper portion thereof over a peripheral edge area of the major surface of the other casing component to form a leak-proof, closed prismatic casing.
In especially preferred embodiments of the present invention there is provided a metal-air electrochemical cell, having a leak-proof, metal prismatic casing comprising a pair of interfacing interengaging rectangular tray-like casing components, a first substantially rectangular tray-like casing component having a first major surface and contiguous side walls for encompassing a cathode of said cell and a second inverted substantially tray-like casing component having a second major surface and contiguous depending side walls for encompassing an anode of said cell, wherein one of said major surfaces is provided with a groove adjacent a peripheral edge thereof forming a peripheral rim therewith, the side walls of the other casing component being of a height to facilitate the curling and crimping of an upper portion thereof over the surface of said rim and toward and into said peripheral groove upon assembly of said components to form a closed casing.
In the most preferred embodiments of the present invention there is provided a metal-air electrochemical cell, having a leak-proof, metal prismatic casing comprising a pair of interfacing interengaging rectangular tray-like casing components, a first substantially rectangular tray-like casing component having a first major surface and contiguous side walls for encompassing a cathode of said cell and a second inverted substantially tray-like casing component having a second major surface and contiguous depending side walls for encompassing an anode of said cell, wherein said second major surface is provided with a groove adjacent said depending side walls forming a peripheral rim therewith, the side walls of said first casing component being of a height to facilitate the curling and crimping of an upper portion thereof over the surface of said rim and toward and into said peripheral groove upon assembly of said components to form a closed casing.
In order to increase the interaction of forces between the interengaging casing components and in order to allow for applied axial forces to operate over a greater surface area there is provided according to the present invention a metal-air electrochemical cell, having a leak-proof, metal prismatic casing comprising a pair of interfacing interengaging rectangular tray-like casing components, a first substantially rectangular tray-like casing component having a first major surface and contiguous side walls for encompassing a cathode of said cell and a second inverted substantially tray-like casing component having a second major surface and contiguous depending side walls for encompassing an anode of said cell, wherein said depending side walls are provided with a terminal outwardly extending peripheral flange, and said second major surface is provided with a groove adjacent said depending side walls forming a peripheral rim therewith, the side walls of said first casing component being of a height to facilitate the curling and crimping of an upper portion thereof over the surface of said rim and toward and into said peripheral groove upon assembly of said components to form a closed casing.
Preferably said flange is bent at an angle of about 90° from the p
Abramson Mariano
Dopp Robert B.
Shrim Yaron
Brouillette Gabrielle
Electric Fuel Limited (E.F.L.)
Helfgott & Karas P.C.
Wills M.
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