Chemistry: electrical current producing apparatus – product – and – Having magnetic field feature
Reexamination Certificate
1998-12-18
2002-01-29
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Having magnetic field feature
C429S006000, C429S006000, C429S006000, C429S082000
Reexamination Certificate
active
06342314
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to metal-air power supplies. This invention more particularly pertains to ventilation systems for controlling ambient airflow to the oxygen electrodes of metal-air batteries.
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 aqueous 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.
It is desirable to preserve the efficiency, power and lifetime of a metal-air cell by effectively limiting the transpiration of water vapor between the electrolyte and the atmosphere. Multiple metal-air batteries can be stacked in a common housing to form a battery pack and to isolate the oxygen electrodes. An air mover is used to provide an airflow of ambient air in to the housing of the battery pack to support higher power output. When the air mover is turned on, the air mover circulates ambient air across the oxygen electrodes and forces air through inlet and outlet passageways to refresh the circulating oxygen-depleted air with ambient air, so that oxygen is supplied to the oxygen electrodes. The power output of the battery pack is increased as a result of the flow of ambient air across the metal-air batteries. When the air mover is turned off, airflow across the metal-air batteries is reduced. The reduced airflow amounts to reduced power output.
However, a nominal amount of airflow is still required to maintain an open cell voltage in the battery cells even though power output is no longer desired. During periods of non-use, such as when the battery pack is being stored, the battery pack tends to maintain an equilibrium relative humidity. Thus, if the ambient humidity is greater than the equilibrium humidity within the battery housing, the battery pack will absorb water from the air through the oxygen electrode and fail due to a condition called flooding. On the other hand, if the ambient humidity is less than the equilibrium humidity within the battery housing, the metal-air batteries will release water vapor from the electrolyte through the oxygen electrode and fail due to drying out. Therefore, when the battery pack is not in use, the cells may fail when the level of ambient air humidity differs from the humidity level within the battery housing.
What is needed is a ventilation system for metal-air batteries that keeps water loss or gain to a minimum while also allowing sufficient ambient airflow during discharge so that enough oxygen is present to fuel the electrochemical reaction. For example, 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 a ventilation system for metal-air batteries. In Pedicini, except for the inlet and outlet passageways, the oxygen electrodes of one or more metal-air battery cells are isolated from the ambient air while the battery cells are not operating. The isolation passageways are sized to (i) pass sufficient ambient airflow while the air mover is operating to enable the metal-air battery cells to provide an output current for powering a load, but (ii) restrict ambient airflow to a low level of diffusion of air while the isolation passageways are unsealed and no ambient air is forced therethrough.
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. These isolation passageways may be referred to as “diffusion tubes”, “isolating passageways”, or “diffusion limiting passageways” due to their isolation capabilities. Other exemplary isolation passageways and systems are disclosed in U.S. Pat. No. 5,919,582, the entire disclosure of which is incorporated herein by reference.
In accordance with the above-referenced example from Pedicini, the isolation passageways function to limit the amount of oxygen that can reach the oxygen electrodes, which minimizes the self discharge and leakage or drain current of the metal-air battery cells. Self discharge can be characterized as a chemical reaction within a metal-air battery cell that does not provide a usable electric current, but diminishes the capacity of the metal-air battery cell for providing a usable electric current. Self discharge occurs, for example, when a metal-air cell dries out and the zinc anode is oxidized by the oxygen that seeps into the cell during periods of non-use. Leakage current, which is synonymous with drain current, can be characterized as the electric current that can be provided to a closed circuit by a metal-air cell while the cell is connected to the circuit and air is not provided to the cell by an air mover. The isolation passageways as described above may limit the drain current to an amount smaller than the output current by a factor of at least about 50.
The isolation passageways of the Pedicini patent also minimize the detrimental impact of humidity on the metal-air cells, especially while the air mover is not forcing airflow through the isolation passageways. The isolation passageways limit the transfer of moisture into or out of the metal-air cells while the air mover is off, so that the negative impacts of the ambient humidity level are minimized.
The efficiency of the isolation passageways in terms of the transfer of air and water into and out of a metal-air cell can be described in terms of an “isolation ratio.” 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 isolation passageways of the type described above. In this example, an isolation ratio of more than 100 to 1 should be obtained.
Metal-air cells have found limited commercial use in devices, such as hearing aids, which require a low level of power. In these cells, the air openings which admit air to the oxygen electrode are so small that the cells can operate for some time without flooding or drying out as a result of the typical difference between the outside relative humidity and the wate
Hope Leonard J.
Sieminski Dennis Paul
AER Energy Resources Inc.
Alston & Bird LLP
Kalafut Stephen
LandOfFree
Geometry change diffusion tube for metal-air batteries does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Geometry change diffusion tube for metal-air batteries, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Geometry change diffusion tube for metal-air batteries will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2827696