CA2164132C - Diffusion vent for a rechargeable metal-air cell - Google Patents
Diffusion vent for a rechargeable metal-air cell Download PDFInfo
- Publication number
- CA2164132C CA2164132C CA002164132A CA2164132A CA2164132C CA 2164132 C CA2164132 C CA 2164132C CA 002164132 A CA002164132 A CA 002164132A CA 2164132 A CA2164132 A CA 2164132A CA 2164132 C CA2164132 C CA 2164132C
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- Prior art keywords
- gas
- case
- gas exit
- cell
- recess
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- Expired - Fee Related
Links
- 238000009792 diffusion process Methods 0.000 title description 7
- 239000012528 membrane Substances 0.000 claims abstract description 58
- 230000002209 hydrophobic effect Effects 0.000 claims abstract description 33
- 239000003792 electrolyte Substances 0.000 claims abstract description 25
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 claims abstract description 22
- 229910002092 carbon dioxide Inorganic materials 0.000 claims abstract description 11
- 239000001569 carbon dioxide Substances 0.000 claims abstract description 11
- 239000007788 liquid Substances 0.000 claims description 8
- 239000011148 porous material Substances 0.000 claims description 8
- 239000012530 fluid Substances 0.000 claims description 7
- 230000000717 retained effect Effects 0.000 claims description 6
- 238000013022 venting Methods 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 2
- 229910052751 metal Inorganic materials 0.000 claims description 2
- 230000000903 blocking effect Effects 0.000 claims 1
- 239000007789 gas Substances 0.000 abstract description 152
- 239000000463 material Substances 0.000 abstract description 19
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 abstract description 18
- 238000004519 manufacturing process Methods 0.000 abstract description 7
- 210000004027 cell Anatomy 0.000 description 142
- 239000003570 air Substances 0.000 description 22
- 239000012080 ambient air Substances 0.000 description 14
- 239000004033 plastic Substances 0.000 description 9
- 229920003023 plastic Polymers 0.000 description 9
- -1 hydroxide ions Chemical class 0.000 description 5
- 230000007246 mechanism Effects 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 230000002093 peripheral effect Effects 0.000 description 5
- 241000282346 Meles meles Species 0.000 description 4
- 238000003860 storage Methods 0.000 description 4
- 238000003466 welding Methods 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 238000001035 drying Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000003487 electrochemical reaction Methods 0.000 description 3
- 238000009931 pascalization Methods 0.000 description 3
- 238000009736 wetting Methods 0.000 description 3
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 239000011324 bead Substances 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 235000012489 doughnuts Nutrition 0.000 description 2
- 239000003822 epoxy resin Substances 0.000 description 2
- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 230000005012 migration Effects 0.000 description 2
- 238000013508 migration Methods 0.000 description 2
- 229920000647 polyepoxide Polymers 0.000 description 2
- 229920005672 polyolefin resin Polymers 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 238000007789 sealing Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 229920013683 Celanese Polymers 0.000 description 1
- 229920012485 Plasticized Polyvinyl chloride Polymers 0.000 description 1
- 239000004698 Polyethylene Substances 0.000 description 1
- 208000027418 Wounds and injury Diseases 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 230000002745 absorbent Effects 0.000 description 1
- 239000002250 absorbent Substances 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000003513 alkali Substances 0.000 description 1
- 239000010425 asbestos Substances 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 210000005056 cell body Anatomy 0.000 description 1
- 210000002421 cell wall Anatomy 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 208000014674 injury Diseases 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 229920000573 polyethylene Polymers 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 229920000915 polyvinyl chloride Polymers 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 238000012552 review Methods 0.000 description 1
- 229910052895 riebeckite Inorganic materials 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229920003002 synthetic resin Polymers 0.000 description 1
- 239000000057 synthetic resin Substances 0.000 description 1
- 229920001169 thermoplastic Polymers 0.000 description 1
- 239000004416 thermosoftening plastic Substances 0.000 description 1
- 210000002268 wool Anatomy 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M12/00—Hybrid cells; Manufacture thereof
- H01M12/08—Hybrid cells; Manufacture thereof composed of a half-cell of a fuel-cell type and a half-cell of the secondary-cell type
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/60—Arrangements or processes for filling or topping-up with liquids; Arrangements or processes for draining liquids from casings
- H01M50/668—Means for preventing spilling of liquid or electrolyte, e.g. when the battery is tilted or turned over
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/30—Arrangements for facilitating escape of gases
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/30—Arrangements for facilitating escape of gases
- H01M50/394—Gas-pervious parts or elements
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/172—Arrangements of electric connectors penetrating the casing
- H01M50/174—Arrangements of electric connectors penetrating the casing adapted for the shape of the cells
- H01M50/176—Arrangements of electric connectors penetrating the casing adapted for the shape of the cells for prismatic or rectangular cells
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Gas Exhaust Devices For Batteries (AREA)
- Sealing Battery Cases Or Jackets (AREA)
- Hybrid Cells (AREA)
Abstract
A vent system for exhausting gas generated within a battery case is provided. The vent system exhausts gas from the battery case (12) while maintaining the hermetic seal of the case. The vent system provides a small gas exit hole (16) that is sufficiently small to prevent electrolyte leakage and also intake of excess carbon dioxide or excess water vapor from the atmosphere. Also,various combinations of gas-permeable, hydrophobic membranes (40, 44) and diffuser material (42) may cover the gas exit hole to provide humidity control for the battery while exhausting gases from the battery. A recess (36) may be provided within the case such that the gas exit hole communicates between the atmosphere and the recess. Also, various combinations of gas-permeable, hydrophobic membranes (40, 44) and diffuser (42) material may cover the recess and gas exit hole to provide humidity control for the battery while exhausting gases from the battery case. The present invention also provides a vent system in which gas-permeable, hydrophobic membranes and diffuser material may fill an opening so as to exhaust gas from the case. The present invention also provides an electrode lead (39) which extends along the battery case and through the seam (34) of the battery case in a manner in which a hermetic seal is provided aroundthe lead. The manufacturing process for the seal around the lead is relatively simple.
Description
216~132 94/29gO8 PCTIUS94/06173 DIFFUSION VENT FOR A RECHARGEABLE METAL-AIR CELL
Technical Field This invention relates generally to electrochemical cells and, more particularly, to vent systems for gas generated by 20 an electrochemical cell, such as a metal-air cell.
Background of the Invention During the operation of an electrochemical cell, various gases are released during the electrochemical reaction 25 which may pressurize the case housing the cell. The pressure build-up due to the released gases can hamper cell operation thus making exhaustion of these gases important to cell operation.
Relieving gas pressure is particularly important in metal-air cells.
Metal-air cells include an air permeable cathode and a metallic 30 anode separated by an aqueous electrolyte. For example, during operation of a zinc-air battery, oxygen from the ambient air is converted at the cathode to hydroxide ions, zinc is oxidized at the anode, reacts with hydroxide ions, and water and electrons are ~o 94/29908 216 413 2 PCT/US94/06173 released to provide electrical energy. During this electrochemical reaction, various gases are released within the cell structure and, consequently, gas pressure increases in the structure with continued use. Because the cathode is not usually capable of 5 supporting very high hydrostatic pressures (typically less than 2 psi), the gases generated within the cell case should be vented at low pressures to protect the cathode. While venting the gases is possible through mechanical devices, these devices must open and close and thus reseal after venting. By opening and closing a 0 mechanical seal, the hermeticity of the battery is sacrificed which makes control of electrolyte leakage and equilibrium vapor pressure more difficult. The leakage and equilibrium vapor pressure would vary depending upon the size of the opening as well as the length of time in which the mechanical device was 15 open. The ambient air which enters the cell through the opening may cause the metal-air cell to fail due to a condition called flooding or drying out depending upon the relative humidity of the ambient air. If the relative humidity of the ambient air is high, then the battery may fail due to flooding. However, if the '~0 relative humidity of the ambient air was low, then the battery may fail due to drying out. Also, environmental cont~min~nts, such as carbon dioxide, may enter through an opening with a mechanical sealing mech~ni~m Various structures have been implemented that vent 25 gases generated from within a cell without using a resealing mechanical device. For example, U.S. Patent No. 3,853,629 to Elliot, U.S. Patent No. 3,904,441 to Badger, and U.S. Patent No.
Technical Field This invention relates generally to electrochemical cells and, more particularly, to vent systems for gas generated by 20 an electrochemical cell, such as a metal-air cell.
Background of the Invention During the operation of an electrochemical cell, various gases are released during the electrochemical reaction 25 which may pressurize the case housing the cell. The pressure build-up due to the released gases can hamper cell operation thus making exhaustion of these gases important to cell operation.
Relieving gas pressure is particularly important in metal-air cells.
Metal-air cells include an air permeable cathode and a metallic 30 anode separated by an aqueous electrolyte. For example, during operation of a zinc-air battery, oxygen from the ambient air is converted at the cathode to hydroxide ions, zinc is oxidized at the anode, reacts with hydroxide ions, and water and electrons are ~o 94/29908 216 413 2 PCT/US94/06173 released to provide electrical energy. During this electrochemical reaction, various gases are released within the cell structure and, consequently, gas pressure increases in the structure with continued use. Because the cathode is not usually capable of 5 supporting very high hydrostatic pressures (typically less than 2 psi), the gases generated within the cell case should be vented at low pressures to protect the cathode. While venting the gases is possible through mechanical devices, these devices must open and close and thus reseal after venting. By opening and closing a 0 mechanical seal, the hermeticity of the battery is sacrificed which makes control of electrolyte leakage and equilibrium vapor pressure more difficult. The leakage and equilibrium vapor pressure would vary depending upon the size of the opening as well as the length of time in which the mechanical device was 15 open. The ambient air which enters the cell through the opening may cause the metal-air cell to fail due to a condition called flooding or drying out depending upon the relative humidity of the ambient air. If the relative humidity of the ambient air is high, then the battery may fail due to flooding. However, if the '~0 relative humidity of the ambient air was low, then the battery may fail due to drying out. Also, environmental cont~min~nts, such as carbon dioxide, may enter through an opening with a mechanical sealing mech~ni~m Various structures have been implemented that vent 25 gases generated from within a cell without using a resealing mechanical device. For example, U.S. Patent No. 3,853,629 to Elliot, U.S. Patent No. 3,904,441 to Badger, and U.S. Patent No.
2,452,066 to Murphy, disclose such systems. Elliot discloses wrapper members which enclose battery cells. The wrapper 30 members are made of an inner layer which is pervious to gases generated by the cell and an outer layer which is impervious to liquids and which is less pervious than the inner layer to gases generated by the cell. The inner and outer layers are l~min~ted vo 94/29908 2 1 6 41 3 2 PCT/US94/06173 together except for a portion between the layers that serves as a passageway to vent gases generated in the interior of the battery.
The inner layer serves as a mechanism to dissolve or diffuse gas in the layer. The unl~min~ted gas passageway is shown to open to the atmosphere at opposite exterior edges of the battery. The unl~min~ted gas passageway may vary in width, length and configuration depending on the application. While Elliot discloses a membrane in which gases dissolve or diffuse before exiting the cell through an Iml~min~ted passageway, Elliot's gas exit passageway has a large surface area which exposes the inner wrapper to relatively large amounts of outside air.
Badger discloses a battery vent system particularly for use in automotive type storage batteries. Badger discloses a battery cover that has a plurality of openings which are covered by a microporous filter material. The microporous filter material is then covered by a guard member such that gas may pass laterally through the filter material to the atmosphere. In one embodiment, the gas passes up through the filter material into an elongate chamber open at both ends. Badger also exposes large areas of the filter material to the atmosphere.
Murphy discloses a gas diffusion device for storage batteries. The storage battery is made of several battery cells which each have a vent to allow the passage of gas through a porous diffusion member which may be made of sheet asbestos or sheet wool. A supplementary cover extends for some distance beyond an opening on all sides and serves to protect the diffusion member from accidental mechanical injury or deposit of dirt or other foreign matter. Murphy also exposes the diffusion member to large amounts of ambient air.
Providing a hermetic seal around leads which extend through a battery case is also important in reducing the effects that ambient air may have on a battery. In plastic cell cases, it is ..., .~
often a difficult manufacturing task to extend an electrode lead wo 94/29908 2 1 6 ~ 13 2 PCT/US94/06173 through an opening in the plastic case in a manner that provides a leak proof seal around the electrode. This is especially true when the case is formed in two parts joined at a seam, and one of the two electrodes of the cell is located within the battery case in a plane that is spaced from the plane in which the seam lies. In battery cells that have electrodes placed in this manner, a hole may be provided in the cell case near the electrode that is farthest from the seam of the battery case. However, it is difficult to pass the lead through the opening and provide a hermetic seal.
o Various prior art structures disclose cathode leads which pass through the seam of a cell case. The cases are manufactured in a manner which provides a hermetic seal around the electrode lead. U.S. Patent No. 3,026,365 to Hughes et al.
discloses electric primary cells with cathode supports consisting of expanded or perforated nickel sheet. Each support has an outwardly directed pigtail or lead from the anode or cathode.
The casing for the cell consists of pressed thermo-plastic sheets which may be polyvinyl chloride or other impermeable alkali-resistant material. The cathode is placed in a cathode casing section with its lead extending beyond the casing. Similarly, the anode with its extending lead is placed in an anode casing section.
Both the cathode and anode casings have flanges around the periphery of the casing. A highly plasticized polyvinyl chloride is placed between the cathode and anode assemblies. Even pressure is imposed to the flanges of the two casing sections to form a fluid-tight and hermetically sealed assembly with the leads extended beyond the casing. Migration of the plasticizer from the membrane placed between the anode and cathode permits the flanges of the anode and cathode casing to be welded together.
The flanges of the casing are then cut near the outwardly directed leads. While Hughes discloses an electrode lead extending through the seam of the cell case, Hughes does not deal with the problem of an electrode lead that is not aligned with a seam.
'~0 94/29908 2 1 6 4 1 3 2 PCT/US94/06173 -Furthermore, Hughes requires flanges to be provided which must be cut after heating, as well as requiring a plasticized membrane between the casing sections to obtain the hermetic seal.
U.S. Patent No. 4,664,994 to Koike et al. discloses an enclosed lead storage battery having a positive plate, negative plates and a separator and electrolyte held in position by a plate assembly. Leads for the battery assembly are coated with an epoxy resin which is then dried. A polyolefin resin having an excellent adhesiveness to epoxy resin is injection molded around the lead post so as to form a fitted doughnut shaped structure around the lead. The leads are then welded to their respective positive or negative plate. A jacket made of various kinds of synthetic resin is then heat sealed around the plate assembly and the extending leads. The jacket encloses the leads around the fitted doughnut shaped structures formed around the leads. While Koike discloses an electrode lead extending through the seam of the cell case, Koike requires that a polyolefin resin be molded around the electrode leads before se~ling the leads with the case.
Hughes and Koike require material additional to the casing to provide a seal around the outwardly directed leads of the cell.
Thus there is a need in the art for a vent system for an electrochemical cell which exposes the cell only to a small amount of ambient air while venting gases in a manner which maintains the hermeticity of the cell. There is also a need in the art for a cell case in which the manufacturing of a hermetically sealed electrode lead is straightforward and reliable.
Snmm~ry of the Invention Generally described, the present invention provides a system for venting gas from within a case housing an electrochemical cell. A cell case constructed according to the present invention has at least one gas exit hole defined from the WO 94/29908 2 ~ 6 413 ~ PCT/US94/06173 exterior of the case to the interior of the case, the gas exit hole being sufficiently small to prevent excessive carbon dioxide intake from the atmosphere and to prevent excessive water loss from the battery, and a gas collection area defined by a recess formed in 5 the case wall or by a gas diffuser attached to the case.
More particularly, the cross-sectional area of the gas exit hole is preferably 0.0008 square inches. In connection with the gas diffuser embodiment, the present invention may further provide a gas-permeable, hydrophobic membrane attached to the lo interior surface of the case so as to cover the gas diffuser thereby defining a boundary for the gas collection area. The present invention may further provide a second gas-permeable, hydrophobic membrane located between the gas diffuser and the interior surface of the case. Preferably, the pore size of pores in lS the gas diffuser range approximately from 1-20 microns. The gas exit hole is preferably located at the geometric center of the gas diffuser and preferably the perimeter of the gas diffuser is circular in shape.
Another embodiment of the present invention 20 provides at least one recess defined on the interior surface of the case, the recess extending towards the exterior surface of the case so as to define a gas collection area, and at least one gas exit hole communicating with the atmosphere, having a smaller cross-sectional area than the cross-sectional area of the recess and 25 extending from the exterior surface of the case to the recess. The present invention may further provide a gas-permeable, hydrophobic membrane attached to the interior surface of the case so as to cover the recess thereby defining a boundary of the gas collection area or may provide a gas-permeable membrane 30 within the recess so as to cover the gas exit hole. The present invention may further utilize a gas diffuser which is retained or attached within the recess so as to cover the gas exit hole. The gas diffuser may be made of a material that will provide ~o s4/2sso8 ~ 1 6 413 2 PCT/US94/06173 structural support to the case. Preferably, the diameter of the pores of the gas diffuser range approximately from 1-20 microns.
In the preferred embodiment of the present invention a gas-permeable, hydrophobic membrane is attached to the interior 5 surface of the case and covers the gas diffuser and a second gas-permeable, hydrophobic membrane covers the gas exit hole and is located between the gas diffuser and the gas exit hole. The gas exit hole is preferably located at the geometric center of the recess, and preferably, the perimeter of the recess is circular in o shape. Preferably, the cross-sectional area is at least approximately 0.4 square inches.
Another embodiment of the vent system of the present invention provides an opening defined in the case and a gas diffuser positioned to fill the opening. The present invention also provides a gas-permeable, hydrophobic membrane which covers the diffuser interior surface to help maintain the humidity within the case. The membrane covering the interior surface of the gas diffuser may also extend to cover the peripheral surfaces of the gas diffuser which fits into the opening, or the entire 20 diffuser surface. The diameter of the pores of the diffuser range approximately from 1-20 microns. Preferably, the cross-sectional area of the opening is approximately 0.4 square inches.
The present invention may provide spaced apart gas exit holes to insure that gas may be exhausted from the case when 25 the case is oriented in varying positions. An electrolyte partially fills the volume of the case and thereby defines a fluid volume and a gas volume within the case. The case may have an initial horizontal position which is defined by the position in which the gas exit holes, located on a surface of the case, face upward. The 30 plurality of gas exit holes are spaced apart such that when the case is tilted to a 90 orientation from the horizontal position at least one of the gas exit holes is located above the maximum fluid level .. ~, for that position and communicates with the gas volume. Each of wo 94nggo8 2 ~ ~ ~13 2 PCT/US94/06173 the gas exit holes may be covered by a gas-permeable, hydrophobic membrane attached to the case. The case may comprise a plurality of case sections sealed together thereby defining a closed cell case, and in which at least one of the gas 5 exit holes extends through at least one of the case sections. The gas exit holes are preferably aligned in a diagonal array from one corner of the perimeter of the case to an oppositely opposed corner of the case. Also, the gas exit holes may be positioned near the corners of the perimeter of the case, preferably with an o exit hole also near the center of the case.
According to another aspect of the invention, a hermetically sealed air cathode lead is provided. The lead extends from the air cathode along a side wall to a seam of the cell case, - and then out of the cell at the seam, which is welded to form a 1S seal around the lead. Preferably the lead is perforated and plastic material is bonded through the openings in the lead.
It is an-object of the present invention to provide a vent system which exhausts gases generated within a battery case.
It is a further object of the present invention to 20 provide a vent system which exhausts gases generated within a battery while m~int~ining the herrnetic seal of the battery.
It is a further object of the present invention to provide a vent system which exhausts gases generated within a battery while preventing excess water loss or gain within the 25 battery.
It is a further object of the present invention to provide a vent system which exhausts gases generated within a battery while minimi7in~ carbon dioxide intake.
It is a further object of the present invention to 30 provide an arrangement of gas exit holes which communicates with the gas volume within a battery case regardless of the orientation of the case.
~4132 VO 94nggo8 ~CT/US94/06173 It is a further object of the present invention to provide an electrode lead which is hermetically sealed and simple to manufacture.
Other objects, features, and advantages of the present s invention will become apparent upon review of the following detailed description of preferred embodiments of the invention, when taken in conjunction with the drawing and the appended claims.
10 Brief Description of the Drawings Fig. 1 shows a top view of a cell case section embodying the vent arrangement of the preferred embodiment of the present invention.
1S Fig. 2 shows a cross-sectional view of a metal-air cell embodying the preferred embodiment of the vent system of the present invention.
Fig. 3 shows an exploded cross-sectional view of a portion of the cell wall shown in Fig. 1, showing the vent system of the present invention.
Fig. 4 shows the metal-air cell shown in Fig. 2 oriented at an angled position.
Fig. S shows the metal-air cell shown in Fig. 2 oriented in a vertical position.
2s Figs. 6-8 show cross-sectional views of alternate embodiments of the vent system of the present invention.
Fig. 9a shows an exploded cross-sectional view of an alternate embodiment of the present invention.
Fig. 9b shows an assembled view of the alternate embodiment of Fig. 9.
Fig. 10a shows an exploded cross-sectional view of another alternate embodiment of the present invention.
WO 94/29908 2 1 ~ 4 1 3 ~ PCT/US94/06173 Fig. 10b shows an assembled view of the alternate embodiment of Fig. 10a.
Fig. 1 la shows an exploded cross-sectional view of another embodiment of the present invention.
s Fig. llb shows an assembled view of the alternate embodiment of Fig. 11.
Fig. 12 shows a top view of a cell case embodying the vent arrangement of any of the alternate embodiments of the present invention shown in Figs. 9-11.
0 Fig. 13 shows a partial cross-sectional view of an alternate embodiment of the present invention.
D~tailed Description of the Invention Referring to the drawings, in which like numerals 1S represent like parts throughout the several views, Fig. 1 and Fig.
2 show the preferred embodiment of the vent system 10 embodied in a cell case 12 for a metal-air cell 14. One or more vent systems 10 provide for exhausting excess gas generated by the cell 14 from within the cell case 12 in order to prevent excess pressure from building within the cell case 12. A gas exit hole 16 associated with each vent 10 extends through the cell case to provide a means for exhausting gases generated during operation of the metal-air cell 14.
Depicted in Fig. 2 are the various components of the 2s metal-air cell 14. The cell case 12 includes a case body 18 consisting of a horizontal grid 19 defining a plurality of openings 20, and an upwardly extending peripheral side wall 21. An air cathode 22 is disposed within the cell case body 18, along the bottom of the cell case body 21. The openings 20 expose the cathode 22 to the atmosphere. A gas-permeable, hydrophobic membrane 23 extends along the interior of the cell case 12 between the cathode 22 and the openings 20 and along the sidewall 21 to prevent electrolyte leakage and/or moisture from ~vo 94/2g908 ~ 1 G 41 3 2 PCT/US94/06173 exiting the cell 14, while allowing air to pass through for reaction at the cathode 22. A cathode support 28 secures the cathode 22 in position in the cell case body 18 as well as containing and supporting: an anode screen 30; an absorbent separator material s 31; and an electrolyte 32. A cell lid 24 encloses the cell body 18 and meets the body 18 along a seam 34. An electrode lead 33 extends from the cathode 22 along the side wall 21 and through the seam 34, between the lid 24 and the cell side wall 21. The aqueous electrolyte 32 partially fills the cell case 12 thereby 10 defining a liquid volume within the cell case 12. The rem~ining non-solid volume defines a gas volume that may change positions within the cell case 12 depending upon the volume of the cell case 12 filled by the aqueous electrolyte 32. The aqueous electrolyte 32 preferably fills approximately three quarters of the non-solid 15 volume of the cell case 12. In Fig. 2, the liquid level is indicated by a dashed lines 35.
During operation of cell 14, the reaction that occurs with the ambient air and cathode 22, the electrolyte 32, and the anode screen 30 release various gases within the metal-air cell 20 case 12. Consequently, the cell case 12 becomes pressurized and very high hydrostatic pressures may build. Typically, the air-permeable cathode is not usually capable of supporting very high hydrostatic pressures, which makes the venting of excessive gases important to the operation of the metal-air cell 14. While it is 25 possible to vent gases from within a cell case by opening and resealing a portion of a cell case, the hermeticity of the cell would sacrificed.
Referring to Fig. 3, an exploded view of the preferred embodiment of the vent system 10 is illustrated. The 30 preferred embodiment of the vent system 10 shown embodied in the cell lid 24 comprises: a small gas exit hole 16; a recess 36 within the cell case section; a gas-permeable, hydrophobic membrane 40; a porous gas diffuser 42; and a gas-permeable, -hydrophobic membrane 44. Within the recess 36, the gas-permeable hydrophobic membrane 40 is attached to the surface of the recess 36 such that the membrane 40 covers the gas exit hole 16. The recess 36 is preferably circular in shape. A gas diffuser 42 having a plurality of pores is placed adjacent to the membrane 40 within the recess 36 so as to cover the gas exit hole 16. The other membrane 44 may be attached to the interior surface of the cell case 12 so as to cover the recess 36 and the gas diffuser 42 which is fitted within the recess 36.
o The membrane 40 is preferably attached to the recess 36 at weld points 46 by ultrasonic welding techniques. A suitable membrane which has characteristics suitable for ultrasonic welding is a polypropylene membrane sold under the trademark Celgard 4599 which is available from Hoechet Celanese Corporation in Charlotte, North Carolina. The membrane preferably has a wetting angle of 90. With a 90 wetting angle, liquid beads more readily than with a smaller wetting angle. The beading of liquid on the membrane allows gases generated in the cell to pass through the membrane. If the liquid did not bead on the membrane, a liquid layer could form across the membrane and thus prevent gas from exiting the cell. The membrane 44 may be a polypropylene material such as Celgard 2400 from the same suppller.
The porous diffuser 42 may be held within the recess 2s 36 by the membrane 44 which is also ultrasonically welded to the interior surface of the cell case 12 at weld points 47. Rather than being retained within the recess 36 by the membrane 44 the porous diffuser 42 may be also attached to the recess 36 by ultrasonic welding techniques. A gas diffuser suitable for use with the present invention is made of polyethylene and is available under the trademark Porex from Porex` Corporation in Fairburn, Georgia. It should be appreciated that the membranes 40, 44 and the gas diffuser 42 may be retained or attached within the recess WO 94/29908 ~ 13 2 PCT/US94/06173 -by other welding techniques known to those skilled in the art, or may be retained by adhesives, bonding materials, clamps or fasteners known by those skilled in the art.
The vent system 10 of the present invention has a two 5 fold function: to exhaust excess gas from the cell case 12; and to maintain the hermetic seal of the case 12 so that cont~min~nts do not enter the cell and so that electrolyte is retained within the cell 14 during exhaustion of gas. This purpose is facilitated by the relatively large ratio of the gas collection area to the exit hole 10 area for each vent. The embodiment of the present invention which utilizes a recess provides a gas collection area which may be defined by a membrane without a diffuser. When a diffuser is used within the recess, the thin portion of the cell lid that results from the recess may be structurally supported or strengthened by 1S the use of the diffuser. An important aspect of the preferred embodiment of the present invention is that the vent system 10 uses hydrophobic material to m~int~in the hermeticity of the case 14.
During the electrochemical reaction of the cell 14, 20 hydrogen is released and becomes pressurized within the cell 14.
While it is desirable to release the hydrogen generated during operation of the cell 14, it is undesirable to vent the water vapor - generated as the cell 14 could dry out. The gas-permeable, hydrophobic membrane 44 passes hydrogen gas but substantially 25 prevents the water vapor from exiting the cell 14. For any small amount of water vapor that passes through the gas-permeable, hydrophobic membrane 44, the gas diffuser further impedes the migration of such water vapor from the cell 14. The diameter of the pores of the gas diffuser 42 preferably ranges from 1-20 30 microns. By using a gas diffuser 42 with a large surface area, a large gas collection area is provided which also provides a greater distance of impedance through which water vapor must pass, thereby retaining more water vapor within the cell than is WO 94129908 2 1 G ~ 13 2 PCT/US94/06173 -otherwise possible with gas-permeable, hydrophobic membranes 40 and 44 alone. The gas-permeable, hydrophobic membrane 40 located within the recess 36 immediately covering the gas exit hole 16 provides a further means for preventing electrolyte s leakage from the cell 14 as well as being a barrier to prevent water and contaminants from entering the cell 14 from the atmosphere.
While it is desirable to prevent electrolyte or water from within the cell from exiting the cell 14, it is also important 0 that an excessive amount of water vapor or carbon dioxide from the atmosphere does not enter the cell case 12 through the gas exit hole 16. Carbon dioxide is undesirable because it neutralizes the electrolyte within the cell. The gas exit hole 16 extends from the exterior surface of the case 12 to the recess 36 so as to 15 communicate with the atmosphere. Because the gas exit hole 16 is in constant communication with the atmosphere and because the water vapor pressure and the contents of the atmosphere are not easily controlled, the vent system 10 provides mech~ni~m.s to limit potential adverse effects of a gas exit hole which openly 20 communicates with the atmosphere. The small size of the exit hole 16 and the hydrophobic membranes 40 and 44 prevent excess water and carbon dioxide from entering the cell 14 in the same manner as they prevents excess water from exiting the cell case 12, as discussed above. If excess water vapor were allowed to 2s enter the cell case 12, then the metal-air cell 14 could fail due to flooding.
In addition to the protection provided by the hydrophobic membranes 40 and 44, the cross-sectional area of the gas exit hole 16 is smaller than the cross-sectional area of the 30 recess 36. Further, the gas exit hole 16 is preferably very small so that carbon dioxide intake from the atmosphere is minimi7ed as well as diffusion of water vapor from the atmosphere.
Preferably, the gas exit hole is approximately 0.0008 square 70 94/29908 216 ~1~ 3 2 PCT/US94/06173 inches but may range from 0.0003 to 0.008 square inches and is preferably located at the geometric center of the recess 36.
Preferably, the cross-sectional area of the recess 36 is approximately 0.2 square inches and circular in shape. Gas 5 within the cell may collect in the recess 36 from a relatively large area and then escape through the small exit hole 16. It should be appreciated by those skilled in the art that the size of the gas exit hole 16 may be varied according to level of sensitivity of the battery components to atmospheric cont~min~nts. Thereby, the 10 vent system 10 of the preferred embodiment of the present invention provides multiple mechanisms within the one system to maintain optimum operating conditions within the cell 14 while exhausting the gases generated within the cell 14.
Referring again to Fig. 1, a top view of the preferred 15 embodiment of the vent system of the present invention is shown.
The gas exit holes 16 are shown at spaced apart locations along the cell lid 24. The case may have an initial horizontal position which is defined by the position in which the gas exit holes, located on a surface of the case, face upward. Because the 20 electrolyte 32 partially fills the cell case 12, the gas exit holes 16 are preferably spaced apart in a manner such that if the cell case 12 is oriented or positioned such that the electrolyte covers one of the gas exit holes 16, another gas exit hole 16 will be free to communicate with the gas volume defined within the cell case 12.
2s That is, because gas vapor rises above the electrolyte 32, at least one gas exit hole 16 will be positioned to communicate with the gas volume such that at least one gas exit hole 16 is above the maximum fluid level of the electrolyte fluid volume for the positions of orientation of the cell case 12 at least up to a 90 30 vertical orientation of the case from the horizontal position. Figs.
4 and 5 show different orientations of the cell 14.
Depending upon the shape of the cell case 12, the position of the gas exit holes 16 may vary for a given amount of WO 94t29908 21 6 ~13 2 PCTIUS94/06173 -electrolyte 32. Preferably, the gas exit holes 16 are aligned in a diagonal array as shown in Fig. 1 but may also be positioned near the edges or corners of the cell case 12. It should be appreciated that the number of gas exit holes 16 and the position of gas exit holes 16 may vary depending upon the amount of electrolyte 32 used within the cell case 12 and depending upon the shape and contents of the cell case 12. Also, the number of gas exit holes 16 may vary according to the cross-sectional area of the gas exit holes 16. As the cross-sectional area of the gas exit holes 16 decrease, more gas exit holes 16 may be needed to exhaust a given amount of gas generated within the cell case 12.
As shown in Fig. 13, when no diffuser member 42 is placed in the recess 36 between the membranes 40 and 44, a plurality of posts 45 integrally molded with the case lid 24 may be provided. The posts 45 extend to support the membrane 44 against the pressure of the electrolyte 32 within the cell. The posts 45 may be arranged within the recess 36 to allow flow of gas to the exit hole 16 and so as not to block too much surface area of the membrane 44.
Referring to Fig. 6, an alternate embodiment of the present invention is shown. The vent system 48 shown in Fig. 6 comprises a gas exit hole 16; a recess 36; one gas-permeable, hydrophobic membrane 40 located within the recess 36, and a porous gas diffuser 42 attached within the recess 36 by the methods of ret~ining the diffuser 42 discussed above.
Referring to Fig. 7, another embodiment of a vent system 49 comprises a gas exit hole 16 communicating between the atmosphere and the recess 36, the gas diffuser 42 located within the recess 36, and the gas-permeable, hydrophobic membrane 44 attached to the interior surface of the cell case 12 and covering the gas diffuser 42 and recèss 36.
Referring to Fig. 8, another embodiment of a vent system 51 is illustrated without the recess 36. In Fig. 6, gas exit 21~132 ~0 94/29908 PCT/US94tO6173 hole 16 extends from the exterior surface of the cell case 12 to the interior surface of the cell case 12 so as to communicate with the gas-permeable, hydrophobic membrane 40 which is attached to the interior surface of the cell case 12 and covers the gas exit 5 hole 16. The porous gas diffuser 42 is placed adjacent to the gas-permeable, hydrophobic membrane 40 so as to cover the gas exit hole 16. Another gas-permeable, hydrophobic membrane 44 may be attached to the interior surface of the cell case 12 so as to cover gas diffuser 42 as shown.
It should be appreciated that the embodiments shown in Figs. 6-8 and 13 provide similar cell vent control mechanisms, as discussed above, through the use of various combinations and structures of the gas-permeable, hydrophobic membranes, gas exit holes, recesses, diffuser materials, and cell case sections. The 15 moisture control for any given structure will vary depending upon the combination of, number of, or size of the various components used as part of the vent system 10. The embodiments illustrated are given by way of example, and many variations may be readily discerned by those skilled in the art and fall within the 20 scope of the present invention.
Referring to Fig. 9a, another embodiment of a vent system 52 of the present invention is shown. In Fig. 9a, an opening S0 is defined in the cell case 12 and extends through the exterior surface of the cell case 12 to the interior surface of the 25 cell case 12. The gas diffuser 42 has a diffuser exterior surface 54 and a diffuser interior surface 56 connected by a diffuser peripheral surface 58 therebetween so as to define the volume of the diffuser 42. The diffuser 42 may be positioned to fill the opening 50 such that the diffuser exterior surface 54 30 communicates with the atmosphere. A gas-permeable, hydrophobic membrane 40 covers the diffuser peripheral surface 58 and the diffuser interior surface 56 so as to help maintain the equilibrium vapor pressure of the cell 14. The diffuser 42 may WO 94/29908 2 ~ 6 4 1 3 2 PCT/US94/06173 be tightly fitted within the opening 50 so as to fill opening 50 with the diffuser exterior surface 54 substantially parallel with the cell lid 24 or substantially within the same plane as the cell lid 24. The diffuser 42 may thereby enclose the opening 50 so as to S become an integral part of the cell case 12. Fig. 9b depicts an assembled view of the embodiment shown in Fig. 9.
Referring to Fig. lOa, another embodiment of a vent system 59 is shown which is similar to the vent construction illustrated in Fig. 9. The vent system 59 illustrated in Fig. lOa 0 differs from the vent system illustrated in Fig. 9 in that a gas-permeable, hydrophobic membrane covers the diffuser exterior surface 54 of the gas diffuser 42 rather than the interior surface 56 of the gas diffuser 42 as shown in Fig. 9. Fig. lOb depicts an assembled view of the embodiment shown in Fig. lOa. Referring 1S to Fig. lla, a vent system 61 is similar in construction to the embodiments illustrated in Fig. 9 and Fig. 10 except that the entire surface of the diffuser 42 is covered by the gas-perrneable, hydrophobic membrane 40. Fig. 1 lb depicts an assembled view of the embodiment shown in Fig. 1 1 a. In each of the 20 embodiments of Fig. 9, Fig. 10 and Fig. 11, the diffuser may be snugly positioned or fitted within the opening 50 by pressing the diffuser into the opening in the direction indicated by the direction arrows 60. Referring to Fig. 12, a top view of any of the embodiments of the vent system 58, 59, or 61 illustrated in 2s Figs. 9-11 is shown. The embodiment depicts the vents in a diagonal array as discussed above.
It should be appreciated that the embodiments shown in Figs. 9-11 provide similar cell vent control mechanisms, as discussed above, through the use of various combinations and 30 structures of the gas-permeable, hydrophobic membranes, openings, diffuser materials, and cell case sections. The embodiments shown in Figs. 9-11, however, allow more carbon dioxide to enter the cell than the embodiments shown in Figs. 2, ~'VO 94/2g908 21 6 4 1 3 2 PCT/US94/06173 -3, and 6-8. The moisture control for any given structure will vary depending upon the combination of, number of, or size of the various components used as part of the vent system 10. The embodiments illustrated are given by way of example, and many variations may be readily discerned by those skilled in the art and fall within the scope of the present invention.
In contrast to the present invention, mechanisms which open and close to vent gases from a cell may allow electrolyte to escape from the cell or may allow cont~rnin~nts O such as carbon dioxide to enter the cell. The equilibrium vapor pressure of the cell could also vary depending upon the length of time in which the mechanical devices were opened and upon the relative humidity of the atmosphere. The ambient air which enters the cell during such a process may cause the metal-air cell to fail. If the equilibrium vapor pressure of the ambient air is high, then the battery may fail due to flooding. If the e~uilibrium vapor pressure of the ambient air is low, then the battery may fail due to a condition called drying out. With optimum control of the hermeticity of the cell during exhaustion of gases, failure or performance losses due to the ambient air or electrolyte leakage may be better controlled. The vent system of the present invention exhausts gases generated by the cell while minimi7ing the above discussed effects of exposure to an excessive amount of ambient air.
Referring again to Fig. 2, electrode lead 33 is attached to and extends up from the cathode 22 along the peripheral side wall 21 of the case body 18 to fit through the seam 34 between the case body 18 and the case lid 24. The arrangement of the electrode lid 33 of the present invention provides the advantage of yielding a hermetically sealed case for a battery structure in which the electrodes of the cell are spaced at varying distances from the seam 34 of the case 12.
21 ~4 ~ 32 In plastic battery cases, it is often a difficult manufacturing task to extend an electrode contact through an opening in the battery case in a manner that provides a leak proof seal around the electrode as it passes through the hole in the case.
5 The present invention provides an electrode lead for an electrode that is displaced a distance from the plane between the two case sections in which the seam 34 is formed. The seal around the cathode lead 33 of the present invention is leak proof and simple to manufacture. The electrode lead is made of a conducting 0 material that may be a wire mesh or a perforated tab. It may be an integral extension of a conductive cathode current collector screen. Instead of providing the plastic case 12 that houses the battery cell with an opening so that the electrode lead may pass directly out of the case in the plane of the electrode 32, the 15 electrode lead 33 is extended from the electrode 22 to pass through the seam 34. The electrode lead 33 is first attached to or formed integrally with the electrode 22. Then the lead is extended along the cell side wall 21 and is bent out of the case at the seam 34. The plastic lid 24 of the case 12 is welded to the 20 lower section 18 of the case, and the heated plastic extrudes through the perforated holes of the electrode lead. When the plastic cools, it contracts around the metal causing an injection molded type metal-to-plastic seal which is highly resistant to leakage. By sealing and constructing the cathode lead 33 as 25 described above, the manufacture of a leak proof seal around the electrode lead 33 is provided.
The foregoing relates only to the preferred embodiment of the present invention, and many changes may be made therein without departing from the scope of the invention as 30 defined by the following claims.
The inner layer serves as a mechanism to dissolve or diffuse gas in the layer. The unl~min~ted gas passageway is shown to open to the atmosphere at opposite exterior edges of the battery. The unl~min~ted gas passageway may vary in width, length and configuration depending on the application. While Elliot discloses a membrane in which gases dissolve or diffuse before exiting the cell through an Iml~min~ted passageway, Elliot's gas exit passageway has a large surface area which exposes the inner wrapper to relatively large amounts of outside air.
Badger discloses a battery vent system particularly for use in automotive type storage batteries. Badger discloses a battery cover that has a plurality of openings which are covered by a microporous filter material. The microporous filter material is then covered by a guard member such that gas may pass laterally through the filter material to the atmosphere. In one embodiment, the gas passes up through the filter material into an elongate chamber open at both ends. Badger also exposes large areas of the filter material to the atmosphere.
Murphy discloses a gas diffusion device for storage batteries. The storage battery is made of several battery cells which each have a vent to allow the passage of gas through a porous diffusion member which may be made of sheet asbestos or sheet wool. A supplementary cover extends for some distance beyond an opening on all sides and serves to protect the diffusion member from accidental mechanical injury or deposit of dirt or other foreign matter. Murphy also exposes the diffusion member to large amounts of ambient air.
Providing a hermetic seal around leads which extend through a battery case is also important in reducing the effects that ambient air may have on a battery. In plastic cell cases, it is ..., .~
often a difficult manufacturing task to extend an electrode lead wo 94/29908 2 1 6 ~ 13 2 PCT/US94/06173 through an opening in the plastic case in a manner that provides a leak proof seal around the electrode. This is especially true when the case is formed in two parts joined at a seam, and one of the two electrodes of the cell is located within the battery case in a plane that is spaced from the plane in which the seam lies. In battery cells that have electrodes placed in this manner, a hole may be provided in the cell case near the electrode that is farthest from the seam of the battery case. However, it is difficult to pass the lead through the opening and provide a hermetic seal.
o Various prior art structures disclose cathode leads which pass through the seam of a cell case. The cases are manufactured in a manner which provides a hermetic seal around the electrode lead. U.S. Patent No. 3,026,365 to Hughes et al.
discloses electric primary cells with cathode supports consisting of expanded or perforated nickel sheet. Each support has an outwardly directed pigtail or lead from the anode or cathode.
The casing for the cell consists of pressed thermo-plastic sheets which may be polyvinyl chloride or other impermeable alkali-resistant material. The cathode is placed in a cathode casing section with its lead extending beyond the casing. Similarly, the anode with its extending lead is placed in an anode casing section.
Both the cathode and anode casings have flanges around the periphery of the casing. A highly plasticized polyvinyl chloride is placed between the cathode and anode assemblies. Even pressure is imposed to the flanges of the two casing sections to form a fluid-tight and hermetically sealed assembly with the leads extended beyond the casing. Migration of the plasticizer from the membrane placed between the anode and cathode permits the flanges of the anode and cathode casing to be welded together.
The flanges of the casing are then cut near the outwardly directed leads. While Hughes discloses an electrode lead extending through the seam of the cell case, Hughes does not deal with the problem of an electrode lead that is not aligned with a seam.
'~0 94/29908 2 1 6 4 1 3 2 PCT/US94/06173 -Furthermore, Hughes requires flanges to be provided which must be cut after heating, as well as requiring a plasticized membrane between the casing sections to obtain the hermetic seal.
U.S. Patent No. 4,664,994 to Koike et al. discloses an enclosed lead storage battery having a positive plate, negative plates and a separator and electrolyte held in position by a plate assembly. Leads for the battery assembly are coated with an epoxy resin which is then dried. A polyolefin resin having an excellent adhesiveness to epoxy resin is injection molded around the lead post so as to form a fitted doughnut shaped structure around the lead. The leads are then welded to their respective positive or negative plate. A jacket made of various kinds of synthetic resin is then heat sealed around the plate assembly and the extending leads. The jacket encloses the leads around the fitted doughnut shaped structures formed around the leads. While Koike discloses an electrode lead extending through the seam of the cell case, Koike requires that a polyolefin resin be molded around the electrode leads before se~ling the leads with the case.
Hughes and Koike require material additional to the casing to provide a seal around the outwardly directed leads of the cell.
Thus there is a need in the art for a vent system for an electrochemical cell which exposes the cell only to a small amount of ambient air while venting gases in a manner which maintains the hermeticity of the cell. There is also a need in the art for a cell case in which the manufacturing of a hermetically sealed electrode lead is straightforward and reliable.
Snmm~ry of the Invention Generally described, the present invention provides a system for venting gas from within a case housing an electrochemical cell. A cell case constructed according to the present invention has at least one gas exit hole defined from the WO 94/29908 2 ~ 6 413 ~ PCT/US94/06173 exterior of the case to the interior of the case, the gas exit hole being sufficiently small to prevent excessive carbon dioxide intake from the atmosphere and to prevent excessive water loss from the battery, and a gas collection area defined by a recess formed in 5 the case wall or by a gas diffuser attached to the case.
More particularly, the cross-sectional area of the gas exit hole is preferably 0.0008 square inches. In connection with the gas diffuser embodiment, the present invention may further provide a gas-permeable, hydrophobic membrane attached to the lo interior surface of the case so as to cover the gas diffuser thereby defining a boundary for the gas collection area. The present invention may further provide a second gas-permeable, hydrophobic membrane located between the gas diffuser and the interior surface of the case. Preferably, the pore size of pores in lS the gas diffuser range approximately from 1-20 microns. The gas exit hole is preferably located at the geometric center of the gas diffuser and preferably the perimeter of the gas diffuser is circular in shape.
Another embodiment of the present invention 20 provides at least one recess defined on the interior surface of the case, the recess extending towards the exterior surface of the case so as to define a gas collection area, and at least one gas exit hole communicating with the atmosphere, having a smaller cross-sectional area than the cross-sectional area of the recess and 25 extending from the exterior surface of the case to the recess. The present invention may further provide a gas-permeable, hydrophobic membrane attached to the interior surface of the case so as to cover the recess thereby defining a boundary of the gas collection area or may provide a gas-permeable membrane 30 within the recess so as to cover the gas exit hole. The present invention may further utilize a gas diffuser which is retained or attached within the recess so as to cover the gas exit hole. The gas diffuser may be made of a material that will provide ~o s4/2sso8 ~ 1 6 413 2 PCT/US94/06173 structural support to the case. Preferably, the diameter of the pores of the gas diffuser range approximately from 1-20 microns.
In the preferred embodiment of the present invention a gas-permeable, hydrophobic membrane is attached to the interior 5 surface of the case and covers the gas diffuser and a second gas-permeable, hydrophobic membrane covers the gas exit hole and is located between the gas diffuser and the gas exit hole. The gas exit hole is preferably located at the geometric center of the recess, and preferably, the perimeter of the recess is circular in o shape. Preferably, the cross-sectional area is at least approximately 0.4 square inches.
Another embodiment of the vent system of the present invention provides an opening defined in the case and a gas diffuser positioned to fill the opening. The present invention also provides a gas-permeable, hydrophobic membrane which covers the diffuser interior surface to help maintain the humidity within the case. The membrane covering the interior surface of the gas diffuser may also extend to cover the peripheral surfaces of the gas diffuser which fits into the opening, or the entire 20 diffuser surface. The diameter of the pores of the diffuser range approximately from 1-20 microns. Preferably, the cross-sectional area of the opening is approximately 0.4 square inches.
The present invention may provide spaced apart gas exit holes to insure that gas may be exhausted from the case when 25 the case is oriented in varying positions. An electrolyte partially fills the volume of the case and thereby defines a fluid volume and a gas volume within the case. The case may have an initial horizontal position which is defined by the position in which the gas exit holes, located on a surface of the case, face upward. The 30 plurality of gas exit holes are spaced apart such that when the case is tilted to a 90 orientation from the horizontal position at least one of the gas exit holes is located above the maximum fluid level .. ~, for that position and communicates with the gas volume. Each of wo 94nggo8 2 ~ ~ ~13 2 PCT/US94/06173 the gas exit holes may be covered by a gas-permeable, hydrophobic membrane attached to the case. The case may comprise a plurality of case sections sealed together thereby defining a closed cell case, and in which at least one of the gas 5 exit holes extends through at least one of the case sections. The gas exit holes are preferably aligned in a diagonal array from one corner of the perimeter of the case to an oppositely opposed corner of the case. Also, the gas exit holes may be positioned near the corners of the perimeter of the case, preferably with an o exit hole also near the center of the case.
According to another aspect of the invention, a hermetically sealed air cathode lead is provided. The lead extends from the air cathode along a side wall to a seam of the cell case, - and then out of the cell at the seam, which is welded to form a 1S seal around the lead. Preferably the lead is perforated and plastic material is bonded through the openings in the lead.
It is an-object of the present invention to provide a vent system which exhausts gases generated within a battery case.
It is a further object of the present invention to 20 provide a vent system which exhausts gases generated within a battery while m~int~ining the herrnetic seal of the battery.
It is a further object of the present invention to provide a vent system which exhausts gases generated within a battery while preventing excess water loss or gain within the 25 battery.
It is a further object of the present invention to provide a vent system which exhausts gases generated within a battery while minimi7in~ carbon dioxide intake.
It is a further object of the present invention to 30 provide an arrangement of gas exit holes which communicates with the gas volume within a battery case regardless of the orientation of the case.
~4132 VO 94nggo8 ~CT/US94/06173 It is a further object of the present invention to provide an electrode lead which is hermetically sealed and simple to manufacture.
Other objects, features, and advantages of the present s invention will become apparent upon review of the following detailed description of preferred embodiments of the invention, when taken in conjunction with the drawing and the appended claims.
10 Brief Description of the Drawings Fig. 1 shows a top view of a cell case section embodying the vent arrangement of the preferred embodiment of the present invention.
1S Fig. 2 shows a cross-sectional view of a metal-air cell embodying the preferred embodiment of the vent system of the present invention.
Fig. 3 shows an exploded cross-sectional view of a portion of the cell wall shown in Fig. 1, showing the vent system of the present invention.
Fig. 4 shows the metal-air cell shown in Fig. 2 oriented at an angled position.
Fig. S shows the metal-air cell shown in Fig. 2 oriented in a vertical position.
2s Figs. 6-8 show cross-sectional views of alternate embodiments of the vent system of the present invention.
Fig. 9a shows an exploded cross-sectional view of an alternate embodiment of the present invention.
Fig. 9b shows an assembled view of the alternate embodiment of Fig. 9.
Fig. 10a shows an exploded cross-sectional view of another alternate embodiment of the present invention.
WO 94/29908 2 1 ~ 4 1 3 ~ PCT/US94/06173 Fig. 10b shows an assembled view of the alternate embodiment of Fig. 10a.
Fig. 1 la shows an exploded cross-sectional view of another embodiment of the present invention.
s Fig. llb shows an assembled view of the alternate embodiment of Fig. 11.
Fig. 12 shows a top view of a cell case embodying the vent arrangement of any of the alternate embodiments of the present invention shown in Figs. 9-11.
0 Fig. 13 shows a partial cross-sectional view of an alternate embodiment of the present invention.
D~tailed Description of the Invention Referring to the drawings, in which like numerals 1S represent like parts throughout the several views, Fig. 1 and Fig.
2 show the preferred embodiment of the vent system 10 embodied in a cell case 12 for a metal-air cell 14. One or more vent systems 10 provide for exhausting excess gas generated by the cell 14 from within the cell case 12 in order to prevent excess pressure from building within the cell case 12. A gas exit hole 16 associated with each vent 10 extends through the cell case to provide a means for exhausting gases generated during operation of the metal-air cell 14.
Depicted in Fig. 2 are the various components of the 2s metal-air cell 14. The cell case 12 includes a case body 18 consisting of a horizontal grid 19 defining a plurality of openings 20, and an upwardly extending peripheral side wall 21. An air cathode 22 is disposed within the cell case body 18, along the bottom of the cell case body 21. The openings 20 expose the cathode 22 to the atmosphere. A gas-permeable, hydrophobic membrane 23 extends along the interior of the cell case 12 between the cathode 22 and the openings 20 and along the sidewall 21 to prevent electrolyte leakage and/or moisture from ~vo 94/2g908 ~ 1 G 41 3 2 PCT/US94/06173 exiting the cell 14, while allowing air to pass through for reaction at the cathode 22. A cathode support 28 secures the cathode 22 in position in the cell case body 18 as well as containing and supporting: an anode screen 30; an absorbent separator material s 31; and an electrolyte 32. A cell lid 24 encloses the cell body 18 and meets the body 18 along a seam 34. An electrode lead 33 extends from the cathode 22 along the side wall 21 and through the seam 34, between the lid 24 and the cell side wall 21. The aqueous electrolyte 32 partially fills the cell case 12 thereby 10 defining a liquid volume within the cell case 12. The rem~ining non-solid volume defines a gas volume that may change positions within the cell case 12 depending upon the volume of the cell case 12 filled by the aqueous electrolyte 32. The aqueous electrolyte 32 preferably fills approximately three quarters of the non-solid 15 volume of the cell case 12. In Fig. 2, the liquid level is indicated by a dashed lines 35.
During operation of cell 14, the reaction that occurs with the ambient air and cathode 22, the electrolyte 32, and the anode screen 30 release various gases within the metal-air cell 20 case 12. Consequently, the cell case 12 becomes pressurized and very high hydrostatic pressures may build. Typically, the air-permeable cathode is not usually capable of supporting very high hydrostatic pressures, which makes the venting of excessive gases important to the operation of the metal-air cell 14. While it is 25 possible to vent gases from within a cell case by opening and resealing a portion of a cell case, the hermeticity of the cell would sacrificed.
Referring to Fig. 3, an exploded view of the preferred embodiment of the vent system 10 is illustrated. The 30 preferred embodiment of the vent system 10 shown embodied in the cell lid 24 comprises: a small gas exit hole 16; a recess 36 within the cell case section; a gas-permeable, hydrophobic membrane 40; a porous gas diffuser 42; and a gas-permeable, -hydrophobic membrane 44. Within the recess 36, the gas-permeable hydrophobic membrane 40 is attached to the surface of the recess 36 such that the membrane 40 covers the gas exit hole 16. The recess 36 is preferably circular in shape. A gas diffuser 42 having a plurality of pores is placed adjacent to the membrane 40 within the recess 36 so as to cover the gas exit hole 16. The other membrane 44 may be attached to the interior surface of the cell case 12 so as to cover the recess 36 and the gas diffuser 42 which is fitted within the recess 36.
o The membrane 40 is preferably attached to the recess 36 at weld points 46 by ultrasonic welding techniques. A suitable membrane which has characteristics suitable for ultrasonic welding is a polypropylene membrane sold under the trademark Celgard 4599 which is available from Hoechet Celanese Corporation in Charlotte, North Carolina. The membrane preferably has a wetting angle of 90. With a 90 wetting angle, liquid beads more readily than with a smaller wetting angle. The beading of liquid on the membrane allows gases generated in the cell to pass through the membrane. If the liquid did not bead on the membrane, a liquid layer could form across the membrane and thus prevent gas from exiting the cell. The membrane 44 may be a polypropylene material such as Celgard 2400 from the same suppller.
The porous diffuser 42 may be held within the recess 2s 36 by the membrane 44 which is also ultrasonically welded to the interior surface of the cell case 12 at weld points 47. Rather than being retained within the recess 36 by the membrane 44 the porous diffuser 42 may be also attached to the recess 36 by ultrasonic welding techniques. A gas diffuser suitable for use with the present invention is made of polyethylene and is available under the trademark Porex from Porex` Corporation in Fairburn, Georgia. It should be appreciated that the membranes 40, 44 and the gas diffuser 42 may be retained or attached within the recess WO 94/29908 ~ 13 2 PCT/US94/06173 -by other welding techniques known to those skilled in the art, or may be retained by adhesives, bonding materials, clamps or fasteners known by those skilled in the art.
The vent system 10 of the present invention has a two 5 fold function: to exhaust excess gas from the cell case 12; and to maintain the hermetic seal of the case 12 so that cont~min~nts do not enter the cell and so that electrolyte is retained within the cell 14 during exhaustion of gas. This purpose is facilitated by the relatively large ratio of the gas collection area to the exit hole 10 area for each vent. The embodiment of the present invention which utilizes a recess provides a gas collection area which may be defined by a membrane without a diffuser. When a diffuser is used within the recess, the thin portion of the cell lid that results from the recess may be structurally supported or strengthened by 1S the use of the diffuser. An important aspect of the preferred embodiment of the present invention is that the vent system 10 uses hydrophobic material to m~int~in the hermeticity of the case 14.
During the electrochemical reaction of the cell 14, 20 hydrogen is released and becomes pressurized within the cell 14.
While it is desirable to release the hydrogen generated during operation of the cell 14, it is undesirable to vent the water vapor - generated as the cell 14 could dry out. The gas-permeable, hydrophobic membrane 44 passes hydrogen gas but substantially 25 prevents the water vapor from exiting the cell 14. For any small amount of water vapor that passes through the gas-permeable, hydrophobic membrane 44, the gas diffuser further impedes the migration of such water vapor from the cell 14. The diameter of the pores of the gas diffuser 42 preferably ranges from 1-20 30 microns. By using a gas diffuser 42 with a large surface area, a large gas collection area is provided which also provides a greater distance of impedance through which water vapor must pass, thereby retaining more water vapor within the cell than is WO 94129908 2 1 G ~ 13 2 PCT/US94/06173 -otherwise possible with gas-permeable, hydrophobic membranes 40 and 44 alone. The gas-permeable, hydrophobic membrane 40 located within the recess 36 immediately covering the gas exit hole 16 provides a further means for preventing electrolyte s leakage from the cell 14 as well as being a barrier to prevent water and contaminants from entering the cell 14 from the atmosphere.
While it is desirable to prevent electrolyte or water from within the cell from exiting the cell 14, it is also important 0 that an excessive amount of water vapor or carbon dioxide from the atmosphere does not enter the cell case 12 through the gas exit hole 16. Carbon dioxide is undesirable because it neutralizes the electrolyte within the cell. The gas exit hole 16 extends from the exterior surface of the case 12 to the recess 36 so as to 15 communicate with the atmosphere. Because the gas exit hole 16 is in constant communication with the atmosphere and because the water vapor pressure and the contents of the atmosphere are not easily controlled, the vent system 10 provides mech~ni~m.s to limit potential adverse effects of a gas exit hole which openly 20 communicates with the atmosphere. The small size of the exit hole 16 and the hydrophobic membranes 40 and 44 prevent excess water and carbon dioxide from entering the cell 14 in the same manner as they prevents excess water from exiting the cell case 12, as discussed above. If excess water vapor were allowed to 2s enter the cell case 12, then the metal-air cell 14 could fail due to flooding.
In addition to the protection provided by the hydrophobic membranes 40 and 44, the cross-sectional area of the gas exit hole 16 is smaller than the cross-sectional area of the 30 recess 36. Further, the gas exit hole 16 is preferably very small so that carbon dioxide intake from the atmosphere is minimi7ed as well as diffusion of water vapor from the atmosphere.
Preferably, the gas exit hole is approximately 0.0008 square 70 94/29908 216 ~1~ 3 2 PCT/US94/06173 inches but may range from 0.0003 to 0.008 square inches and is preferably located at the geometric center of the recess 36.
Preferably, the cross-sectional area of the recess 36 is approximately 0.2 square inches and circular in shape. Gas 5 within the cell may collect in the recess 36 from a relatively large area and then escape through the small exit hole 16. It should be appreciated by those skilled in the art that the size of the gas exit hole 16 may be varied according to level of sensitivity of the battery components to atmospheric cont~min~nts. Thereby, the 10 vent system 10 of the preferred embodiment of the present invention provides multiple mechanisms within the one system to maintain optimum operating conditions within the cell 14 while exhausting the gases generated within the cell 14.
Referring again to Fig. 1, a top view of the preferred 15 embodiment of the vent system of the present invention is shown.
The gas exit holes 16 are shown at spaced apart locations along the cell lid 24. The case may have an initial horizontal position which is defined by the position in which the gas exit holes, located on a surface of the case, face upward. Because the 20 electrolyte 32 partially fills the cell case 12, the gas exit holes 16 are preferably spaced apart in a manner such that if the cell case 12 is oriented or positioned such that the electrolyte covers one of the gas exit holes 16, another gas exit hole 16 will be free to communicate with the gas volume defined within the cell case 12.
2s That is, because gas vapor rises above the electrolyte 32, at least one gas exit hole 16 will be positioned to communicate with the gas volume such that at least one gas exit hole 16 is above the maximum fluid level of the electrolyte fluid volume for the positions of orientation of the cell case 12 at least up to a 90 30 vertical orientation of the case from the horizontal position. Figs.
4 and 5 show different orientations of the cell 14.
Depending upon the shape of the cell case 12, the position of the gas exit holes 16 may vary for a given amount of WO 94t29908 21 6 ~13 2 PCTIUS94/06173 -electrolyte 32. Preferably, the gas exit holes 16 are aligned in a diagonal array as shown in Fig. 1 but may also be positioned near the edges or corners of the cell case 12. It should be appreciated that the number of gas exit holes 16 and the position of gas exit holes 16 may vary depending upon the amount of electrolyte 32 used within the cell case 12 and depending upon the shape and contents of the cell case 12. Also, the number of gas exit holes 16 may vary according to the cross-sectional area of the gas exit holes 16. As the cross-sectional area of the gas exit holes 16 decrease, more gas exit holes 16 may be needed to exhaust a given amount of gas generated within the cell case 12.
As shown in Fig. 13, when no diffuser member 42 is placed in the recess 36 between the membranes 40 and 44, a plurality of posts 45 integrally molded with the case lid 24 may be provided. The posts 45 extend to support the membrane 44 against the pressure of the electrolyte 32 within the cell. The posts 45 may be arranged within the recess 36 to allow flow of gas to the exit hole 16 and so as not to block too much surface area of the membrane 44.
Referring to Fig. 6, an alternate embodiment of the present invention is shown. The vent system 48 shown in Fig. 6 comprises a gas exit hole 16; a recess 36; one gas-permeable, hydrophobic membrane 40 located within the recess 36, and a porous gas diffuser 42 attached within the recess 36 by the methods of ret~ining the diffuser 42 discussed above.
Referring to Fig. 7, another embodiment of a vent system 49 comprises a gas exit hole 16 communicating between the atmosphere and the recess 36, the gas diffuser 42 located within the recess 36, and the gas-permeable, hydrophobic membrane 44 attached to the interior surface of the cell case 12 and covering the gas diffuser 42 and recèss 36.
Referring to Fig. 8, another embodiment of a vent system 51 is illustrated without the recess 36. In Fig. 6, gas exit 21~132 ~0 94/29908 PCT/US94tO6173 hole 16 extends from the exterior surface of the cell case 12 to the interior surface of the cell case 12 so as to communicate with the gas-permeable, hydrophobic membrane 40 which is attached to the interior surface of the cell case 12 and covers the gas exit 5 hole 16. The porous gas diffuser 42 is placed adjacent to the gas-permeable, hydrophobic membrane 40 so as to cover the gas exit hole 16. Another gas-permeable, hydrophobic membrane 44 may be attached to the interior surface of the cell case 12 so as to cover gas diffuser 42 as shown.
It should be appreciated that the embodiments shown in Figs. 6-8 and 13 provide similar cell vent control mechanisms, as discussed above, through the use of various combinations and structures of the gas-permeable, hydrophobic membranes, gas exit holes, recesses, diffuser materials, and cell case sections. The 15 moisture control for any given structure will vary depending upon the combination of, number of, or size of the various components used as part of the vent system 10. The embodiments illustrated are given by way of example, and many variations may be readily discerned by those skilled in the art and fall within the 20 scope of the present invention.
Referring to Fig. 9a, another embodiment of a vent system 52 of the present invention is shown. In Fig. 9a, an opening S0 is defined in the cell case 12 and extends through the exterior surface of the cell case 12 to the interior surface of the 25 cell case 12. The gas diffuser 42 has a diffuser exterior surface 54 and a diffuser interior surface 56 connected by a diffuser peripheral surface 58 therebetween so as to define the volume of the diffuser 42. The diffuser 42 may be positioned to fill the opening 50 such that the diffuser exterior surface 54 30 communicates with the atmosphere. A gas-permeable, hydrophobic membrane 40 covers the diffuser peripheral surface 58 and the diffuser interior surface 56 so as to help maintain the equilibrium vapor pressure of the cell 14. The diffuser 42 may WO 94/29908 2 ~ 6 4 1 3 2 PCT/US94/06173 be tightly fitted within the opening 50 so as to fill opening 50 with the diffuser exterior surface 54 substantially parallel with the cell lid 24 or substantially within the same plane as the cell lid 24. The diffuser 42 may thereby enclose the opening 50 so as to S become an integral part of the cell case 12. Fig. 9b depicts an assembled view of the embodiment shown in Fig. 9.
Referring to Fig. lOa, another embodiment of a vent system 59 is shown which is similar to the vent construction illustrated in Fig. 9. The vent system 59 illustrated in Fig. lOa 0 differs from the vent system illustrated in Fig. 9 in that a gas-permeable, hydrophobic membrane covers the diffuser exterior surface 54 of the gas diffuser 42 rather than the interior surface 56 of the gas diffuser 42 as shown in Fig. 9. Fig. lOb depicts an assembled view of the embodiment shown in Fig. lOa. Referring 1S to Fig. lla, a vent system 61 is similar in construction to the embodiments illustrated in Fig. 9 and Fig. 10 except that the entire surface of the diffuser 42 is covered by the gas-perrneable, hydrophobic membrane 40. Fig. 1 lb depicts an assembled view of the embodiment shown in Fig. 1 1 a. In each of the 20 embodiments of Fig. 9, Fig. 10 and Fig. 11, the diffuser may be snugly positioned or fitted within the opening 50 by pressing the diffuser into the opening in the direction indicated by the direction arrows 60. Referring to Fig. 12, a top view of any of the embodiments of the vent system 58, 59, or 61 illustrated in 2s Figs. 9-11 is shown. The embodiment depicts the vents in a diagonal array as discussed above.
It should be appreciated that the embodiments shown in Figs. 9-11 provide similar cell vent control mechanisms, as discussed above, through the use of various combinations and 30 structures of the gas-permeable, hydrophobic membranes, openings, diffuser materials, and cell case sections. The embodiments shown in Figs. 9-11, however, allow more carbon dioxide to enter the cell than the embodiments shown in Figs. 2, ~'VO 94/2g908 21 6 4 1 3 2 PCT/US94/06173 -3, and 6-8. The moisture control for any given structure will vary depending upon the combination of, number of, or size of the various components used as part of the vent system 10. The embodiments illustrated are given by way of example, and many variations may be readily discerned by those skilled in the art and fall within the scope of the present invention.
In contrast to the present invention, mechanisms which open and close to vent gases from a cell may allow electrolyte to escape from the cell or may allow cont~rnin~nts O such as carbon dioxide to enter the cell. The equilibrium vapor pressure of the cell could also vary depending upon the length of time in which the mechanical devices were opened and upon the relative humidity of the atmosphere. The ambient air which enters the cell during such a process may cause the metal-air cell to fail. If the equilibrium vapor pressure of the ambient air is high, then the battery may fail due to flooding. If the e~uilibrium vapor pressure of the ambient air is low, then the battery may fail due to a condition called drying out. With optimum control of the hermeticity of the cell during exhaustion of gases, failure or performance losses due to the ambient air or electrolyte leakage may be better controlled. The vent system of the present invention exhausts gases generated by the cell while minimi7ing the above discussed effects of exposure to an excessive amount of ambient air.
Referring again to Fig. 2, electrode lead 33 is attached to and extends up from the cathode 22 along the peripheral side wall 21 of the case body 18 to fit through the seam 34 between the case body 18 and the case lid 24. The arrangement of the electrode lid 33 of the present invention provides the advantage of yielding a hermetically sealed case for a battery structure in which the electrodes of the cell are spaced at varying distances from the seam 34 of the case 12.
21 ~4 ~ 32 In plastic battery cases, it is often a difficult manufacturing task to extend an electrode contact through an opening in the battery case in a manner that provides a leak proof seal around the electrode as it passes through the hole in the case.
5 The present invention provides an electrode lead for an electrode that is displaced a distance from the plane between the two case sections in which the seam 34 is formed. The seal around the cathode lead 33 of the present invention is leak proof and simple to manufacture. The electrode lead is made of a conducting 0 material that may be a wire mesh or a perforated tab. It may be an integral extension of a conductive cathode current collector screen. Instead of providing the plastic case 12 that houses the battery cell with an opening so that the electrode lead may pass directly out of the case in the plane of the electrode 32, the 15 electrode lead 33 is extended from the electrode 22 to pass through the seam 34. The electrode lead 33 is first attached to or formed integrally with the electrode 22. Then the lead is extended along the cell side wall 21 and is bent out of the case at the seam 34. The plastic lid 24 of the case 12 is welded to the 20 lower section 18 of the case, and the heated plastic extrudes through the perforated holes of the electrode lead. When the plastic cools, it contracts around the metal causing an injection molded type metal-to-plastic seal which is highly resistant to leakage. By sealing and constructing the cathode lead 33 as 25 described above, the manufacture of a leak proof seal around the electrode lead 33 is provided.
The foregoing relates only to the preferred embodiment of the present invention, and many changes may be made therein without departing from the scope of the invention as 30 defined by the following claims.
Claims (23)
1. An electrochemical cell having an anode and a cathode with a separator positioned therebetween, said cell enclosed within a case, said case having an interior surface and an exterior surface and said case having a gas exit hole therein, characterized by:
said electrochemical cell being a metal air cell having an anode and an air cathode;
said separator dividing said case and effectively blocking any gas path from the anode side of said separator to said air cathode; and said gas exit hole communicating with a recess defined on the interior surface of said case on the anode side of said separator, said recess extending towards the exterior surface of said case, so as to define a gas collection area and said gas exit hole communicating with the atmosphere, having a smaller cross-sectional area than the cross-sectional area of said recess, and extending from the exterior surface of said case on the anode side of said separator to said recess.
said electrochemical cell being a metal air cell having an anode and an air cathode;
said separator dividing said case and effectively blocking any gas path from the anode side of said separator to said air cathode; and said gas exit hole communicating with a recess defined on the interior surface of said case on the anode side of said separator, said recess extending towards the exterior surface of said case, so as to define a gas collection area and said gas exit hole communicating with the atmosphere, having a smaller cross-sectional area than the cross-sectional area of said recess, and extending from the exterior surface of said case on the anode side of said separator to said recess.
2. The apparatus of Claim 1 further characterized by, a gas-permeable, hydrophobic membrane attached to said interior surface of said case so as to cover said recess thereby defining a boundary of said gas collection area.
3. The apparatus of Claim 1 further characterized by a gas diffuser having a plurality of pores, located within said gas collection area covering said gas exit hale and retained within said recess.
4. The apparatus of Claim 3 wherein said gas diffuser is positioned within said recess to provide structural support to said case.
5. The apparatus of Claim 3 wherein the diameter of said pores of said gas diffuser range approximately from 1-20 microns.
6. The apparatus of Claim 3 further characterized by a second gas-permeable, hydrophobic membrane covering said gas exit hole and located between said gas diffuser and said gas exit hole.
7. The apparatus of Claim 1 wherein said recess has a geometric center and wherein said gas exit hole is located at the geometric center of said recess.
8. The apparatus of Claim 7 wherein the perimeter of said recess is circular in shape.
9. The apparatus of Claim 1 wherein the cross-sectional area of said recess is approximately 0.4 square inches.
10. The apparatus of Claim 9 wherein the cross-sectional area of said gas exit hole ranges approximately from 0.0003 to 0.008 square inches.
11. The apparatus of Claim 1 wherein said size of said gas exit hole is sufficiently small to prevent excessive carbon dioxide intake from the atmosphere.
12. The apparatus of Claim 1 wherein said size of said exit hole is sufficiently small to prevent excess liquid loss from said battery.
13. The apparatus of Claim 1 wherein said cross-sectional area of said gas exit hole ranges approximately from 0.0003 to 0.008 square inches.
14. The apparatus of Claim 2 wherein said gas collection area projects inwardly from said interior surface of said case and further comprising a gas permeable structure supporting said membrane.
15. A system for venting gas from within a case housing an electrochemical cell, said case having an interior surface and exterior surface and said case defining a volume, comprising:
an electrolyte partially filling the volume of said case, thereby defining a fluid volume and a gas volume within said case;
a plurality of gas exit holes, communicating with the atmosphere, defined from the exterior of said case to the interior of said case so as to exhaust gas from said gas volume, said case having an initial horizontal position defined by the position in which said gas exit holes located on a surface of said case face upward, said exit holes being spaced apart such that at least one of said gas exit holes is located above the maximum fluid level of said fluid volume for any position of orientation of said case from said horizontal position to at least a 90° vertical orientation of said case so that at least said one of said gas exit holes communicates with said gas volume, and each of said gas exit holes being covered by a gas-permeable, hydrophobic membrane attached to said case.
an electrolyte partially filling the volume of said case, thereby defining a fluid volume and a gas volume within said case;
a plurality of gas exit holes, communicating with the atmosphere, defined from the exterior of said case to the interior of said case so as to exhaust gas from said gas volume, said case having an initial horizontal position defined by the position in which said gas exit holes located on a surface of said case face upward, said exit holes being spaced apart such that at least one of said gas exit holes is located above the maximum fluid level of said fluid volume for any position of orientation of said case from said horizontal position to at least a 90° vertical orientation of said case so that at least said one of said gas exit holes communicates with said gas volume, and each of said gas exit holes being covered by a gas-permeable, hydrophobic membrane attached to said case.
16. The apparatus of Claim 15 wherein said case comprises a plurality of case sections sealed together, thereby defining a closed cell case, and wherein said at least one of said gas exit holes extends through at least one of said case sections.
17. The apparatus of Claim 16 wherein said plurality of gas exit holes each extend through the same case section.
18. The apparatus of Claim 17 wherein the perimeter of at least one of said case sections is polygonal in shape.
19. The apparatus of Claim 18 wherein said plurality of gas exit holes are aligned in a diagonal array from one corner o said perimeter to the oppositely opposed corner of said perimeter.
20. The apparatus of Claim 18 wherein said gas exit holes are aligned from one corner of said perimeter to the oppositely opposed side of said perimeter.
21. The apparatus of Claim 18 wherein a plurality of said gas exit holes are positioned near the corners of said perimeter.
22. The apparatus of Claim 21 wherein at least one of said gas exit holes is positioned in a center portion of one of said case section.
23. The apparatus of Claim 16 wherein at least one of said gas exit holes is positioned in a center portion of said one case section.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/071,844 US5362577A (en) | 1993-06-04 | 1993-06-04 | Diffusion vent for a rechargeable metal-air cell |
| US071,844 | 1993-06-04 | ||
| PCT/US1994/006173 WO1994029908A2 (en) | 1993-06-04 | 1994-06-02 | Diffusion vent for a rechargeable metal-air cell |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2164132A1 CA2164132A1 (en) | 1994-12-22 |
| CA2164132C true CA2164132C (en) | 2000-11-07 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002164132A Expired - Fee Related CA2164132C (en) | 1993-06-04 | 1994-06-02 | Diffusion vent for a rechargeable metal-air cell |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5362577A (en) |
| EP (1) | EP0708988B1 (en) |
| JP (1) | JP2865424B2 (en) |
| AT (1) | ATE162908T1 (en) |
| AU (1) | AU6920294A (en) |
| CA (1) | CA2164132C (en) |
| DE (1) | DE69408324T2 (en) |
| WO (1) | WO1994029908A2 (en) |
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-
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- 1993-06-04 US US08/071,844 patent/US5362577A/en not_active Expired - Fee Related
-
1994
- 1994-06-02 WO PCT/US1994/006173 patent/WO1994029908A2/en not_active Ceased
- 1994-06-02 DE DE69408324T patent/DE69408324T2/en not_active Expired - Fee Related
- 1994-06-02 CA CA002164132A patent/CA2164132C/en not_active Expired - Fee Related
- 1994-06-02 JP JP7501919A patent/JP2865424B2/en not_active Expired - Lifetime
- 1994-06-02 EP EP94917505A patent/EP0708988B1/en not_active Expired - Lifetime
- 1994-06-02 AU AU69202/94A patent/AU6920294A/en not_active Abandoned
- 1994-06-02 AT AT94917505T patent/ATE162908T1/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0708988B1 (en) | 1998-01-28 |
| EP0708988A1 (en) | 1996-05-01 |
| DE69408324T2 (en) | 1998-05-14 |
| JP2865424B2 (en) | 1999-03-08 |
| AU6920294A (en) | 1995-01-03 |
| WO1994029908A3 (en) | 1995-03-30 |
| DE69408324D1 (en) | 1998-03-05 |
| WO1994029908A2 (en) | 1994-12-22 |
| ATE162908T1 (en) | 1998-02-15 |
| CA2164132A1 (en) | 1994-12-22 |
| JPH09500480A (en) | 1997-01-14 |
| US5362577A (en) | 1994-11-08 |
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| EEER | Examination request | ||
| MKLA | Lapsed |