Chemistry: electrical current producing apparatus – product – and – With pressure equalizing means for liquid immersion operation
Reexamination Certificate
2000-05-18
2003-12-09
Maples, John S. (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
With pressure equalizing means for liquid immersion operation
C429S006000
Reexamination Certificate
active
06660418
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to batteries, and more particularly relates to air managers for metal-air cells.
BACKGROUND OF THE INVENTION
Metal-air cells have been recognized as a desirable means for powering portable electronic equipment such as personal computers and camcorders because such cells have a relatively high power output with relatively low weight as compared to other types of electrochemical cells. Metal-air cells utilize oxygen from the ambient air as a reactant in the electrochemical process rather than a heavier material, such as a metal or metallic composition.
Metal-air cells use one or more oxygen electrodes separated from a metallic anode by an aqueous electrolyte. During the operation of a metal-air cell, such as a zinc-air cell, oxygen from the ambient air and water from the electrolyte are converted at the oxygen electrode to hydroxide ions and zinc is oxidized at the anode and reacts with the hydroxide ions, such that water and electrons are released to provide electric energy.
Metal-air cells are often arranged in multiple cell battery packs within a common housing to provide a sufficient amount of electrical power. The result is a relatively light-weight battery. A supply of air must be supplied to the oxygen electrodes of the battery pack in order for the battery pack to supply electricity. Some prior systems sweep a continuous flow of fresh air from the ambient environment across the oxygen electrodes at a flow rate sufficient to achieve the desired power output. Such an arrangement is shown in U.S. Pat. No. 4,913,983 to Cheiky. Cheiky uses a fan within air from the ambient environment to the oxygen the battery housing to supply the flow of 1 electrodes. When the Cheiky battery is turned on an air inlet and an air outlet, which are closed by one or more “air doors” while the battery is turned off, are opened and the fan is operated to create the flow of air into, through, and out of the housing. Thus, the air doors are closed when the battery is turned off to isolate the cells from the environment. Although the mechanical air doors may limit the transfer of oxygen, water vapor, and contaminates into and out of the housing, such mechanical air doors add complexity to the battery housing itself and, inevitably, increase the size and cost of the overall battery pack.
In contrast to the nonrecirculating arrangement of Cheiky, U.S. Pat. No. 5,691,074 to Pedicini discloses a system in which a fan recirculates air across the oxygen electrodes of metal-air battery. The fan also forces air through one or more openings to refresh the recirculating air. The cells provide an output current while the fan is operating but experience minimal discharge while the fan is not operating and the opening or openings remain unsealed. That is, the Pedicini metal-air battery has a long shelf life without requiring operation of air doors, or the like, to open and close the opening or openings. The opening or openings are sized to restrict air flow therethrough while the opening or openings are unsealed and the fan is off.
The restrictive air openings of Pedicini, as well as the air doors of Cheiky, function to substantially isolate the metal-air cells from the ambient environment while the battery is not operating. Isolating the metal-air cells from the ambient environment while the battery is not operating increases the shelf life of the battery and also decreases the detrimental impact of the ambient humidity level on the metal-air cells. Exposed metal-air cells may absorb water from the air through the oxygen electrode and fail due to a condition called flooding, or they may release water vapor from the electrolyte through the oxygen electrode and fall due to drying.
Typically metal-air cells are designed to have a relatively large oxygen electrode surface, so that the largest power output possible can be obtained from a cell of a given volume and weight. Once air is introduced into a metal-air battery housing, the oxygen-bearing air is distributed to all oxygen electrode surfaces. However, in multiple cell systems it is common for an air distribution path to extend from a fan for a lengthy distance and sequentially across oxygen electrode surfaces. Oxygen may be depleted from the air stream flowing along the distribution path so that the oxygen concentration at the end of the distribution path falls below a level desired for optimal power production from all the cells. As a result of the nonuniform air flow distribution, each of the cells may operate at a different current (when the cells are arranged in parallel) and voltage (when the cells are arranged in series), which is not optimal.
If one uses such an air distribution path or paths with a flow through system as in Cheiky, the oxygen depletion problem may be overcome by moving a large volume of air through the battery housing so that the amount of oxygen removed from the air flow in the upstream portions of the distribution path has a negligible impact on the oxygen concentration in downstream portions of the distribution path. However, using such a large volume of fresh air may subject the battery to the flooding or drying problems described above. Pedicini at least partially resolves the flooding or drying out problems by recirculating air within the battery housing and continuously replenishing a portion of the recirculated air. Pedicini may nonetheless experience some oxygen depletion problems if using an air distribution path that extends from a fan for a lengthy distance and sequentially across oxygen electrode surfaces.
One drawback with the current design of metal-air cells is that the cells tend to be somewhat larger in size than conventional electrochemical power sources. This size constraint is caused, in part, by the requirements of having an anode, a cathode, an electrolyte, a cell casing of some sort, and an air manager or an air passageway of some sort to provide the reactant air to the cell. These elements all take up a certain amount of valuable space.
In attempting to design smaller metal-air cells and batteries, one concern is to provide a sufficient amount of air to operate the cells at their desired capability while also preventing too much air from reaching the cells during periods of non-use. A vast improvement in air manager technology is found in the above-mentioned U.S. Pat. No. 5,691,074, entitled “Diffusion Controlled Air Vent for a Metal-Air Battery” to Pedicini, which is incorporated herein by reference. Pedicini discloses, in one embodiment, a group of metal-air cells isolated from the ambient air except for an inlet and an outlet passageway. These passageways may be, for example, elongate tubes. An air-moving device positioned within the housing forces air through the inlet and outlet passageways to circulate the air across the oxygen electrodes and to refresh the circulating air with ambient air. The passageways are sized to allow sufficient airflow therethrough while the air mover is operating but also to restrict the passage of water vapor therethrough while the passageways are unsealed and the air mover is not operating.
When the air mover is off and the humidity level within the cell is relatively constant, only a very limited amount of air diffuses through the passageways. The water vapor within the cell protects the oxygen electrodes from exposure to oxygen. The oxygen electrodes are sufficiently isolated from the ambient air by the water vapor such that the cells have a long “shelf life” without sealing the passageways with a mechanical air door. These passageways may be referred to as “diffusion tubes”, “isolating passageways”, or “diffusion limiting passageways” due to their isolating capabilities.
The isolating passageways act to minimize the detrimental impact of humidity on the metal-air cells, especially while the air-moving device is off. A metal-air cell that is exposed to ambient air having a high humidity level may absorb too much water through its oxygen electrode and fail due to a condition referred to as “flooding.” Alternatively, a me
Tinker Lawrence A.
Witzigreuter John D.
AER Energy Resources Inc.
Alston & Bird LLP
Maples John S.
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