Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
1998-12-18
2002-08-20
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000, C429S062000, C429S082000, C383S045000, C383S103000
Reexamination Certificate
active
06436564
ABSTRACT:
RELATED APPLICATION
The following patent applications for related subject matter,
“CYLINDRICAL METAL-AIR BATTERY WITH A CYLINDRICAL PERIPHERAL AIR CATHODE” U.S. patent application Ser. No. 09/215,820; now U.S. Pat. No. 6,274,261;
“AIR MANAGER SYSTEMS FOR METAL-AIR BATTERIES UTILIZING A DIAPHRAGM OR BELLOWS” U.S. patent application Ser. No. 09/216,026 pending,
“DIFFUSION CONTROLLED AIR VENT WITH AN INTERIOR FAN” U.S. patent application No. 09/215,879 pending,
“UNIFORM SHELL FOR A METAL-AIR BATTERY” U.S. patent application No. 09/216,114, now U.S. Pat. No. 6,235,418;
“LOAD RESPONSIVE AIR DOOR FOR A METAL-AIR CELL” U.S. patent application Ser. No. 09/216,115, now U.S. Pat. No. 6,350,537;
“Geometry Change Diffusion Tube For Metal-Air Batteries” U.S. patent application No. 09/216,273, now U.S. Pat. No. 6,342,314;
“AIR-MANAGING SYSTEM FOR METAL-AIR BATTERY USING RESEALABLE SEPTUM” U.S. patent Ser. No. 09/216,343, now U.S. Pat. No. 6,168,877; and
“AIR DELIVERY SYSTEM WITH VOLUME-CHANGEABLE PLENUM OF METAL-AIR BATTERY” U.S. patent application No. 09/216,660, now U.S. Pat. No. 6,346,341;
all of which are incorporated herein by reference, have been filed concurrently with the present application.
TECHNICAL FIELD
The present invention relates to metal-air batteries of the type that are supplied with reactive gas by an active air moving device, and more particularly relates to an air mover mechanism located in the cathode plenum space of one or more metal-air cells.
BACKGROUND OF THE INVENTION
Generally described, a metal-air cell, such as a zinc-air cell, uses one or more air permeable cathodes separated from a metallic zinc anode by an aqueous electrolyte. During operation of the cell, oxygen from the ambient air is converted at the one or more cathodes to produce hydroxide ions. The metallic zinc anode is then oxidized by the hydroxide ions. Water and electrons are released in this electrochemical reaction to provide electrical power.
Initially, metal-air cells found limited commercial use in devices, such as hearing aids, which required a low level of power. In these cells, the air openings which admitted air to the air cathode were so small that the cells could operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the water vapor pressure within the cell. However, the power output of such cells was too low to operate devices such as camcorders, cellular phones, or laptop computers. Furthermore, enlarging the air openings of a typical “button cell” was not practical because it would lead to premature failure as a result of flooding or drying out.
In order to increase the power output of metal-air cells so that they could be used to operate devices such as camcorders, cellular phones, or laptop computers, air managers were developed with a view to providing a flow of reactive air to the air cathodes of one or more metal-air cells while isolating the cells from environmental air and humidity when no output is required. As compared to conventional electrochemical power sources, metal-air cells containing air managers provide relatively high power output and long lifetime with relatively low weight. These advantages are due in part to the fact that metal-air cells utilize oxygen from the ambient air as the reactant in the electrochemical process as opposed to a heavier material such as a metal or a metallic composition. Examples of air managers are shown in U.S. Pat. Nos. 4,913,983, 5,356,729, and 5,691,074.
A disadvantage of most air managers, however, is that they distribute air within a plenum adjacent to the air electrode, and the plenum requires an empty volume of space. Furthermore, an important component of a successful air manager is an air moving device, typically a fan or an air pump. In the past, air moving devices used in metal-air batteries have been bulky relative to the volume of the metal-air cells. As a result, space that could otherwise be used for battery chemistry to prolong the life of the battery must be used to create a plenum adjacent to the air electrode and to accommodate an air moving device. This loss of space presents a particular challenge in attempts to provide a practical metal-air cell in small enclosures such as the “AA” cylindrical size now used as a standard in many electronic devices.
In addition to being bulky, air moving devices used in metal-air batteries also consume energy stored in the metal-air cells that might otherwise be delivered as power output to a load. Therefore, while a key advantage of metal-air cells is their high energy density resulting from the low weight of the air electrode, this advantage is compromised by the space and power required for an effective air manager.
As stated previously, air managers have been developed with a view to isolating the metal-air cells from ambient air when no output is required. A factor contributing to the problem of isolating metal-air cells from the ambient air is the porosity of inexpensive plastics typically used for molding cases for containing components of the cells. The amount of water vapor that seeps through plastic walls of a cell can be on the same order of magnitude as the amount of water vapor that passes into the cell through one or two diffusion limiting isolation tubes. Utilizing less porous materials or coating the plastic walls to reduce transmission of gases would add significant expense to the cost of each cell.
Therefore, there has been a need in the art for an air manager incorporating an air moving device that occupies less of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal-air cell, and consumes a relatively low amount of power. Also, there is a further need in the art of metal-air cells to reduce the significance of case wall porosity.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved air moving device for metal-air cells that occupies a minimal amount of the volume available for battery chemistry, is usable with advanced systems for isolating the air electrodes when power is not being drawn from the metal air cell, and consumes a relatively low amount of power.
In accordance with the invention, this object is accomplished by providing an air-moving device for supplying ambient air to the air electrodes of a metal-air cell which includes a variable volume enclosure surrounding a plenum adjacent to the air electrode, means for varying the volume of this enclosure, and one or more air passageways which allow air flow into and out of the enclosure while its volume is changing. The variable volume enclosure serves to isolate the electrode from the ambient air except through the air passageways and operates so that air flows into the enclosure when its volume is increasing (as a result of a decrease in pressure inside the enclosure) and out of the enclosure when its volume is decreasing increasing (as a result of an increase in pressure inside the enclosure). Thus, the air moving device brings in new ambient air and distributes it across the surface of the air electrode during operation of the metal-air cell.
In one embodiment of the invention, the air passageways comprise diffusion limiting passageways. The variable volume enclosure may be a rigid plate connected to a deformable wall that extends to the frame surrounding the electrodes of one or more cells. The air passageways may extend through the rigid plate or the deformable wall. In this embodiment, the volume of the enclosure is varied by alternately moving the rigid plate toward and away from the air electrode. The means for alternately moving the rigid plate toward the air electrode may be a linear actuator such as a line engaging the rigid plate and a fixed member below the rigid plate and means for selectively pulling the rigid plate toward the fixed member using the line. The means for alternately moving the rigid plate away from the air electrode may be a line engaging the rigid plate and the outer casing of
Witzigreuter John D.
Young Jeffrey E.
AER Energy Resources Inc.
Alston & Bird LLP
Kalafut Stephen
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