Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Plural housing having spacing means or channels for air...
Reexamination Certificate
1999-04-15
2003-02-11
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Plural housing having spacing means or channels for air...
C429S159000
Reexamination Certificate
active
06517967
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to disposable battery packs containing electrochemical cells. More particularly, the present invention has features relating to such packs that are disposable and which contain at least one cell that requires a gas exchange with ambient atmosphere.
BACKGROUND OF THE INVENTION
Most high-drain portable electronic devices are powered by secondary or rechargeable batteries. Examples of such high-drain devices are cellular telephones, notebook computers, camcorders, and cordless hand-tools. The reason primary batteries are unattractive in such applications is that the life-span of a typical primary or single-use batteries is so short, and the cost so high, that they ultimately prove too costly for long-term use. In addition, their weight alone would discourage a person from carrying enough primary batteries for a long-term operation of the device. For example, a cellular telephone with alkaline batteries would last about as long as a single charge of a nickel-metal-hydride battery, but in the long term, cost far more per unit energy. A nickel-metal hydride battery, though initially expensive, costs only pennies to recharge.
New primary battery technologies have emerged that have, in principle at least, the ability to offer sufficient energy and power at a sufficiently low cost to make these batteries attractive for high-drain portable devices. One such technology is metal-air batteries, for example zinc-air batteries. In a zinc-air battery, one of the electrodes of the battery uses oxygen that can be supplied by ambient oxygen. Since oxygen is available everywhere, a zinc-air battery need house only one consumable electrode. Because of this, the energy capacity per unit weight is magnified greatly. Unfortunately, the intrinsic benefits of electrochemical cells that use air as an electrode are attended by some serious technical problems.
Typical zinc-air cells, such as those in hearing aid batteries, have holes in their casings to admit air. These holes permit oxygen to diffuse into the cell and also permit water vapor to escape. For larger batteries with high power capacity, multiple cells must be used. In such large combinations, the exchange of these gases becomes a real problem as discussed below.
Although zinc-air batteries have high energy densities, they are moderately low on power. To increase their power, large amounts of oxygen must be supplied. This creates some obvious design problems for hand-held consumer devices. Many small portable electronic devices have battery compartments that are narrow with a small opening for exchanging the batteries when they are depleted. These configurations provide little area for the exchange of air gases with the outside. A typical zinc-air battery for use in a hearing aid would require a total surface area of approximately 200 cm
2
to generate sufficient power to operate a typical digital telephone. To expose such a large area to the outside would require a dramatic rethinking of the way batteries are housed by appliances.
One solution is to pump air into and through the battery pack. So called active air management systems can pump large amounts of air through a small opening. However, these systems usually require an air pump that can be difficult to fit into the cost and volume constraints of a disposable battery.
An additional problem with metal-air batteries is the fact that, because oxygen must enter the battery, water vapor can leave the battery. As such, metal-air batteries are susceptible to desiccation in low humidity environments, which can destroy their ability to function.
Leakage of water between or onto metal-air batteries is also a concern. Water from a multitude of sources can potentially enter the battery pack. Intruding water can then contact the metal-air battery cells and cause electrical shorts. Sources of such water include sweat from the person handling the device, moisture from speaking near or into the device, or simply from water spilled onto the device.
Finally, portable electronic devices place constraints on battery weight and volume. The battery cell must be sized to deliver, cost effectively, required power while also conforming to the various shapes, sizes, voltages, amperages, etc. of cellular telephones, notebook computers, camcorders, and cordless hand-tools.
SUMMARY OF THE INVENTION
A battery pack, in at least one embodiment of the invention, contains at least one battery cell that uses an air electrode. One of the goals of the invention is to improve the passive exchange of air gases with electrochemical cells housed in the pack. The embodiments described below provide compact configurations that are compatible with small portable high current electronic devices. Further, design strategies and guidelines are provided for applications other than those discussed herein.
A paradigmatic use of the invention is as a primary battery for cellular or mobile telephones. The battery pack is capable of replacing or supplementing existing, commonly used, secondary (rechargeable) power supplies such as a nickel-metal hydride battery.
Typically, metal-air battery cells include an outer case wall having one or more holes to permit diffusion of oxygen from ambient air. The metal-air battery cell generates power through electrochemical reactions. To generate power, an oxygen-reducing catalyst, in an air cathode inside the battery cell, catalyzes the conversion of oxygen to hydroxyl ions. The hydroxyl ions then migrate to the anode where the anode metal oxidizes. Electrons are liberated by the anode and pumped through the load to offset the deficit generated by the oxygen reduction in the cathode. A preferable metal for the anode in these types of battery cells, is zinc.
For metal-air batteries to provide high power, large amounts of oxygen must pass into the metal-air battery cells (up to 0.0032 cc/sec/cm
2
). This creates some obvious design problems for hand-held consumer electronic devices. Small portable electronic devices provide little surface area for air access through the battery pack case. Moreover, the metal-air battery cells themselves must be designed so as to insure adequate oxygen delivery through the cell.
The battery pack is designed in accord with the goal of delivering an adequate supply of oxygen to generate enough current to power computers and cell phones while optimally balancing the sometimes competing goals of improving the efficiency of supplying oxygen to the cathode and minimizing moisture loss. In addition, the design is in accord with the goals of providing a compact and flexible mechanical configuration, reducing the cost and complexity of the pack, and increasing the energy density of the pack.
Most of the battery pack features discussed herein stem from the advantages and constraints of a prism-shaped cell design.
At the cell level, the total area, the placement, and the size of each hole on the battery cell reflect an optimization of the needs of manufacturability, efficient oxygen supply to the cathode, and minimal moisture loss as discussed in the applications mentioned above.
To support the cell's demand for oxygen, an ideal scenario would be for each cell to be continuously immersed in fresh, oxygen rich air. In that case, the driving gradient of oxygen is maximized. The pack designs described herein employ various principles in combination to provide oxygen delivery at a rate that is compatible with the high current demands of the above-noted applications.
When arranging cells inside the case, as many cells as possible should be oriented so that their gas-exchange walls face an external wall of the housing. (Note that a single cell may have more than one gas-exchange wall) The external wall of the housing is populated with holes. The short distance between the gas-exchange walls and the ambient air coupled with the abundance of holes on the housing ensure that oxygen can passively diffuse at a rate adequate to satisfy the oxygen requirements of the cells. The number of cells needed to generate the necessary level of cu
Abramson Mariano
Givon Menachem
Goldstein Jonathan
Naimer Neal
Rosenberg Tzvi
Electric Fuel Limited
Lyon & Lyon LLP
Ryan Patrick
Wills M.
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