Chemistry: electrical current producing apparatus – product – and – Having specified venting – feeding or circulation structure – Venting structure
Reexamination Certificate
1999-07-01
2002-04-02
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having specified venting, feeding or circulation structure
Venting structure
C429S072000, C429S083000
Reexamination Certificate
active
06365296
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to metal-air cells. This invention more particularly pertains to facilitating heat-driven convective airflow in metal-air cells that incorporate air manager technology.
BACKGROUND OF THE INVENTION
Metal-air cells have been recognized as a desirable means for powering portable electronic equipment, such as personal computers, camcorders and telephones, because such battery cells have a relatively high power output with relatively low weight as compared to other types of electrochemical battery cells. Metal-air batteries include an air permeable cathode, commonly referred to as an oxygen electrode, and a metallic anode separated by an electrolyte. Electrical energy is created with a metal-air battery by an electrochemical reaction.
Metal-air battery cells utilize oxygen from the ambient air as a reactant in the electrochemical process. During discharge of a metal-air battery, such as a zinc-air battery, oxygen from the ambient air is converted at the oxygen electrode to hydroxide, zinc is oxidized at the anode by the hydroxide, and water and electrons are released to provide electrical energy. Metal-air cells utilize oxygen from the ambient air as a reactant, rather than utilizing a heavier material, such as a metal or metallic composition. To operate a metal-air battery, it is therefore necessary to provide a supply of oxygen to the oxygen electrode of the battery.
To preserve the efficiency, power and lifetime of a metal-air cell, it is desirable to effectively isolate the oxygen electrodes and anode of the metal-air cell from the ambient air while the cell is not operating. There are ventilation systems designed to provide the dual functions of providing air to a metal-air cell for power output and isolating the cells during non-use. These known ventilation systems are referred to as air managers. Some air managers only provide air doors that open when power is drawn from the cells and close to attempt to seal the cell housing when the cells are not in use. An important component of successful air managers has been an air mover, such as a fan or an air pump. However, such air movers used in metal-air batteries have been bulky and expensive relative to the volume and cost of the metal-air cells.
While a key advantage of metal-air cells is their high energy density resulting from the low weight of the oxygen electrode, this advantage is compromised by the space and weight required by an effective air mover. Space that could otherwise be used for battery chemistry to prolong the life of the battery must be used to accommodate an air mover. This loss of space can be critical to 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. Also, the air mover uses up energy stored in the cells.
U.S. Pat. No. 5,691,074 to Pedicini, entitled “DIFFUSION CONTROLLED AIR VENT FOR A METAL-AIR BATTERY”, the entire disclosure of which is incorporated herein by reference, discloses systems for controlling the isolation of one or more metal-air cells from the ambient air while the cells are not operating. In accordance with one example disclosed by Pedicini, a group of metal-air cells are isolated from the ambient air, except for an inlet passageway and an outlet passageway. These passageways may be, for example, elongate tubes. An air moving device circulates air across the oxygen electrodes and forces air through the inlet and outlet passageways to refresh the circulating air with ambient air, so that oxygen is supplied to the oxygen electrodes. The passageways are sized to (i) pass sufficient airflow while the air moving device is operating to enable the metal-air cells to provided an output current for powering a load, but (ii) restrict airflow while the passageways are unsealed and no air is forced therethrough by the air moving device, so that a limited amount of air diffuses through the passageways.
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 oxygen exposure. The oxygen electrodes are sufficiently isolated from the ambient air by the water vapor such that the cells have long “shelf life” without sealing the passageways with a mechanical door. The passageways may be referred to as “isolating passageways” or “diffusion limiting passageways” due to their isolating capabilities.
Referring in detail to the isolating passageways described above, these isolating passageways are preferably constructed and arranged to allow a sufficient amount of airflow therethrough while the air moving device is operating so that a sufficient output current, typically at least 50 ma, and preferably at least 130 ma can be obtained from the metal-air cells. In addition, the isolating passageways are preferably constructed to limit the airflow and diffusion therethrough such that the drain current that the metal-air cells are capable of providing to a load while the air moving device is not forcing airflow through the isolating passageways is less than 1 ma per square cm of oxygen electrode surface. Thus, the drain current may be limited to an amount that is smaller than the output current by a factor of at least about 50. In addition, the isolating passageways are preferably constructed to provide an “isolation ratio” of more than 50 to 1.
The “isolation ratio” is the ratio of the rate of water loss or gain by a cell while its oxygen electrodes are fully exposed to the ambient air, as compared to the rate of the water loss or gain of the cell while its oxygen electrodes are isolated from the ambient air, except through one or more limited openings. For example, given identical metal-air cells having electrolyte solutions of approximately thirty-five percent (35%) KOH in water, an internal relative humidity of approximately fifty percent (50%), the ambient air having a relative humidity of approximately ten percent (10%), and no fan-forced circulation, the water loss from a cell having an oxygen electrode fully exposed to the ambient air should be more than 100 times greater than the water loss from a cell having an oxygen electrode that is isolated from the ambient air, except through one or more isolating passageways of the type described above. In this example, an isolation ratio of more than 100 to 1 should be obtained.
More specifically, each of the isolating passageways preferably has a width that is generally perpendicular to the direction of flow therethrough, and a length that is generally parallel to the direction of flow therethrough. The length and the width are selected to substantially eliminate airflow and diffusion through the isolating passageways while the air moving device is not forcing airflow through the isolating passageways. The length is greater than the width, and more preferably the length is greater than about twice the width. The use of larger ratios between length and width are preferred. Depending upon the nature of the metal-air cells, the ratio can be more than 200 to 1. However, the preferred ratio of length to width is about 10 to 1.
The isolating passageways could form only a portion of the path air must take between the ambient environment and the oxygen electrodes. Each of the isolating passageways may be defined through the thickness of the battery housing or cell case, but preferably they are in the form of tubes as described above. In either case, the isolating passageways may be cylindrical, and for some applications each can have a length of about 0.3 to 2.5 inches (about 0.7 to 6.4 cm) or longer, with about 0.88 to 1.0 inches (about 2.24 to 2.54 cm) preferred, and an inside diameter of about 0.03 to 0.3 inches (about 0.07 to 0.7 cm), with about 0.09 to 0.19 inches (about 0.23 to 0.48 cm) preferred. The total open area of each isolating passageway for such applications, measured perpendicular to the direction of flow therethrough, is therefore about
AER Energy Resources Inc.
Alston & Bird LLP
Kalafut Stephen
Mercado Julian A.
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