Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2001-10-12
2004-09-21
Cantelmo, Gregg (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S010000, C429S006000, C429S071000, C429S120000
Reexamination Certificate
active
06794074
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
The present invention relates to air-depolarized power sources having an electrode such as metal-air battery cells and, in particular, relates to an improved method and apparatus for providing an adequate supply of oxygen to air-depolarized cells.
The vast majority of portable electronic devices can be battery operated. The battery or batteries required to operate such devices are typically inserted into a cavity within the device or are attached to an external surface of the device. Of greatest interest in the marketplace today are so-called high current drain portable consumer electronic devices such as cell phones, digital cameras, flash cameras, computers, personal digital assistants, cassette players and compact disc players. In many instances, such devices accept alkaline batteries. However, alkaline batteries are not necessarily efficient energy sources for such devices since the energy available from alkaline batteries decreases as the rate of current drain increases. It thus became advantageous to provide an alternative energy source for such devices. The ability to do so was constrained by the existing cavity or surface configurations which are typically sized for a pre-determined number of cylindrical alkaline cells.
Metal-air battery cells were introduced as an improved alternative to alkaline cells for use in a portable electronic device while providing an energy source more appropriate to the high current drain conditions associated with such devices.
FIG. 1
depicts the available energy of AA premium alkaline and AA zinc-air cells at various power draws. It is apparent from
FIG. 1
that the energy available in the typical power ranges of 100 mW to 1000 mW is much greater in zinc-air cells than in alkaline cells. Accordingly, it is desirable to substitute zinc-air cells in place of standard alkaline cells. For example, a pair of AA alkaline cells in a digital camera have an expected operating life of less than ½ hour. In contrast, zinc-air cells in a digital camera can provide several hours of operation, and can be readily be replaced by the user when discharged.
Metal-air cells include an air permeable cathode and a metallic anode separated by an aqueous electrolyte. For example, in a zinc-air battery, the anode contains zinc, and during discharge, oxygen from the ambient air and water from the electrolyte is converted at the cathode to hydroxide, zinc is oxidized at the anode by the hydroxide, and water and electrons are released to provide electrical energy. Metal-air batteries have a relatively high energy density because the cathode of a metal-air battery utilizes oxygen from ambient air as a reactant in the electrochemical reaction rather than a heavier material such as a metal or metallic composition. Metal-air battery cells are often arranged in multiple cell battery packs within a common housing to provide a sufficient amount of power output. The result is a relatively lightweight battery.
Both primary and secondary metal-air batteries have been developed. A rechargeable metal-air battery is recharged by applying voltage between the anode and cathode of the metal-air battery cell and reversing the electrochemical reaction. Oxygen is discharged into the atmosphere through the air permeable cathode.
One difficulty associated with metal air batteries is that the ambient humidity level can cause the metal-air battery to fail. Equilibrium vapor pressure of the metal-air battery results in an equilibrium relative humidity that is typically about 45%. If ambient humidity is greater than the equilibrium relative humidity value for the metal-air battery, the metal-air battery will absorb water from the air through the cathode and fail due to a condition called flooding, which may cause the battery to leak. If the ambient humidity is less than the equilibrium relative humidity value for the metal-air battery, the metal-air battery will release water vapor from the electrolyte through the air cathode and fail due to drying out. In most environments where a metal-air battery is used, failure occurs from drying out.
The problems caused by ambient humidity are exacerbated in air depolarized cells because the oxygen diffusion electrode (cathode) typically passes water vapor as freely as oxygen due to the similar size and polarization of gaseous water molecules. Thus, as air is supplied to such batteries on discharge, or vented on recharge (in the case of rechargeable batteries), water vapor freely passes through the cathode as well.
Therefore, the art has recognized that an imbalance between the humidity level in the air passing over the air cathode and the humidity level within the cell creates a net transfer of water into or out of the cell, and may lead to the problems outlined above. Furthermore, such problems become more serious when large quantities of new ambient air continuously flow over the cathode.
Another problem associated with supplying a metal-air cell with continuous supplies of fresh air is the transfer of carbon dioxide into the cell, which neutralizes the electrolyte such as potassium hydroxide.
In order to make such cells more useful over longer periods of time, air managers have been developed, which isolate the cells from the environment when they are not in use, but provide air when needed. The system disclosed in U.S. Pat. No. 4,913,983 encloses metal air cells in a housing having an air inlet and outlet. A baffle within the battery housing is used to open or close the air inlet and outlet, limiting air access when the cells are not in use. The system also has a fan to supply a greater flow of ambient air to the cells when needed. This arrangement achieves a continuous flow of new ambient air across the air cathodes at a flow rate sufficient to achieve the desired power output. More advanced air managers have been developed which also include a cell enclosure, and an air mover, such as a fan, but use diffusion tubes rather than a closable baffle to isolate the cells from the environment. In particular, the cell receives open air through the diffusion tubes, which limit the amount of fresh air reaching the cell when it is not in use sufficiently to reduce dryout or flooding, and carbon dioxide absorption, which would further reduce the cell capacity. When the cell is in use, the air mover forces air through the diffusion tubes, bringing fresh air through the enclosure.
Examples of such air manager are disclosed in U.S. Pat. Nos. 5,356,729, 5,560,999, and 5,919,582, the disclosure of each of which is hereby incorporated as if set forth in its entirety herein. In the '729 patent, a housing is typically provided that encloses at least one metal-air cell having at least one ventilation opening that is sized to preferentially diffuse oxygen into the housing upon reduction of the oxygen concentration within the housing caused by operation of the cell or cells. A fan is positioned to circulate and mix gases which are present within the housing. Accordingly, the need of the cell for oxygen is met while maintaining a more stable water vapor and carbon dioxide equilibrium across the air cathode.
The purpose of previous air managers thus has been to isolate the cells from the environment, extending the usable life of the cells. The air manager disclosed in the '729 patent is designed to be used in either open air or in places (such as battery compartments of some electronic devices) where there would be enough fresh air circulation for a metal-air cell to be used at the desired rate without using an air manager. In particular, the air manager is able to only move air within the air manager's internal housing, but can not influence the freshness of the air surrounding the air manager because of the relatively low air flow rate. Accordingly, when the metal-air cell is used inside a battery compartment where an insufficient amount of oxygen is present to support the operation of the cell at the desired rate, the air flow describe
Cheeseman Paul G.
Pedicini Christopher S.
Syvertsen Marc L.
Thompson John A.
Vu Viet H.
Cantelmo Gregg
Quarles & Brady LLP
Rayovac Corporation
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