CA2099657C - Electrochemical cell and method of manufacturing same - Google Patents
Electrochemical cell and method of manufacturing sameInfo
- Publication number
- CA2099657C CA2099657C CA002099657A CA2099657A CA2099657C CA 2099657 C CA2099657 C CA 2099657C CA 002099657 A CA002099657 A CA 002099657A CA 2099657 A CA2099657 A CA 2099657A CA 2099657 C CA2099657 C CA 2099657C
- Authority
- CA
- Canada
- Prior art keywords
- diaphragm
- conductive plate
- electrically conductive
- electrochemical cell
- housing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- 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
- H01M50/50—Current conducting connections for cells or batteries
- H01M50/572—Means for preventing undesired use or discharge
- H01M50/574—Devices or arrangements for the interruption of current
-
- 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
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- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Gas Exhaust Devices For Batteries (AREA)
- Primary Cells (AREA)
- Connection Of Batteries Or Terminals (AREA)
Abstract
An electrochemical cell comprises a housing having an electrochemical circuit system therein including a cathode, an anode and an electrolyte solution in contact with the anode and the cathode. A
conductive diaphragm is arranged in the top portion of the housing for cutting off current flow between the cathode and the anode, and is adapted for quick movement between a first stable conducting position and a second stable non-conducting position upon direct application of gas pressure generated in the electrochemical circuit system in excess of a first predetermined pressure. The conductive diaphragm is unstable between the first and the second stable positions. A conductive lead extends from the electrochemical circuit system to the conductive diaphragm and is connected to same when the conductive diaphragm is arranged in its first stable conducting position. When the conductive diaphragm moves to its second stable non-conducting position, it is separated from the conductive lead and, thus, an open circuit condition is created between the cathode and the anode.
conductive diaphragm is arranged in the top portion of the housing for cutting off current flow between the cathode and the anode, and is adapted for quick movement between a first stable conducting position and a second stable non-conducting position upon direct application of gas pressure generated in the electrochemical circuit system in excess of a first predetermined pressure. The conductive diaphragm is unstable between the first and the second stable positions. A conductive lead extends from the electrochemical circuit system to the conductive diaphragm and is connected to same when the conductive diaphragm is arranged in its first stable conducting position. When the conductive diaphragm moves to its second stable non-conducting position, it is separated from the conductive lead and, thus, an open circuit condition is created between the cathode and the anode.
Description
.'i ELBCTROCHEMICAL CELL AND METHOD OF MANUFACT~RING 8AMB
FIELD OF THB lNV~ ON
The present invention pertains to an electrochemical cell having current cutoff means for preventing current flow therein and to a method of manufacturing an electrochemical cell. More particularly, the present invention relates to an electrochemical cell having current cutoff means and - burstable vent means for preventing a dangerous explosion from occurring within the cell, and a method of manufacturing same. Still more particularly, the present invention relates to an electrochemical cell, and a method of manufacturing such cell, having current cutoff means operable upon the exertion of a gas pressure in excess of a first predetermined pressure, and burstable vent means operable upon the application of gas pressure exerted directly on the diaphragm in excess of a second predetermined pressure whereby the second predetermined pressure exceeds the first predetermined pressure.
BAC~GROUND OF THE lNV~ ON
The prior art is replete with electrochemical cells including current cutoff switches for cutting off current flow between the anode and the cathode of the cell. Additionally, the prior art discloses numerous electrochemical cells having vent means for permitting gas trapped within a housing of the cell to escape therethrough. However, the prior art attempts to design and manufacture an electrochemical cell having current - 30 cutoff means and vent valve means to prevent an explosion within the cell, have been inadequate in their efforts to develop a current cutoff means which will ensure the occurrence of an open circuit condition upon the application of a consistent internal gas pressure on a diaphragm within the cell. Further, numerous prior art devices provide no means for venting excessive gas pressure from the interior of an electrochemical cell to prevent an explosion in the event that the current cutoff means fail to prevent chemical reactions within the cell from producing additional gas.
Moreover, no known prior art discloses or otherwise teaches a method for manufacturing an s electrochemical cell comprising the steps of assembling a ~header~ including current cutoff means in an ideal environment away from an assembly line and testing the header assembly under ideal conditions, and thereafter assembling the header to a housing of an electrochemical cell including an anode, a cathode, electrolyte solution and an electrical lead extending from the cathode.
U.S. Patent No. 4,943,497 to Oishi et al.
discloses a battery having switch means for disrupting current flow between the header and the anode or cathode of the battery and vent means for permitting gas to be expelled from the battery when the pressure therein exceeds a predetermined limit. The Oishi et al . battery includes a container having anode material, cathode material and an electrolyte solution for forming an electrochemical circuit system therein, and a header electrically connected to the electrochemical circuit system. An electrical lead extends from the electrochemical circuit system and is directly welded to a projection extending downwardly from an otherwise generally flat conductive diaphragm to complete the circuit between the header and the electrochemical circuit system therebelow, all of which is shown in the drawings of the Oishi et al. patent and is duplicated in Fig. 1 of the present application.
The diaphragm is constructed and arranged to pull away from the lead thereby breaking the welded connection therebetween upon application of a sufficient amount of pressure thereto. Once the diaphragm pulls away from the electrical lead, the circuit is opened and current can no longer flow from the header to the electrochemical circuit system. The current cutoff means of the Oishi et al. battery is undesirable because the resulting separation between the diaphragm and the electrical lead is small, thus allowing the diaphragm to recede and cause a short circuit condition by forming a bridge across the small gap if the battery is even slightly leaky. Further, the structure and operation of the diaphragm disclosed in the Oishi et al. battery is such that the disconnect pressure is dependent almost entirely on the weld strength, thereby permitting the disconnect pressure to vary widely depending on the tolerance of the weld strength itself. Finally, as implied in Columns 6-8 of the Oish~ et al.
specification, the structure and operation of the battery requires the weld between the diaphragm and the electrical lead to be made on the assembly line. Thus, the Oishi et al. battery cannot be separately tested, checked and stored before use on the assembly line to assure the highest degree of quality control.
U.S. Patent Nos. 4,025,696 to Tuchoski et al.
and 4,028,478 to Tuchos~i disclose sealed cells having an irreversible switch means for cutting off current flow within an electrochemical cell. The switch means is actuable upon expansion of a cell container above a predetermined limit. The cell expansion may result from gaseous by-products caused by chemical reactions in an electrochemical circuit system within the cell. The switch means comprises an active electrically conductive disk-shaped spring member defining a central opening therethrough and a passive insulating member. The insulating member also includes a centrally disposed opening wherein the opening has a larger diameter than the opening of the active conductive spring member. The passive member is disposed between the active switch member and a conductive plate, and is further arranged with its centrally disposed opening surrounding the central opening of the active switch member. When the cell is in its normal operating state, the active switch member is in electrical conduct with the conductive plate in the vicinity of its centrally disposed opening, and is also in electrical contact with a cell cover at _4 20~99657 its outer periphery. When an overload condition arises, the cell container bulges upwardly in the vicinity of the header which includes the switch means. In response to such upward bulge, the central portion of the conductive active switch member also deflects upwardly toward the cover while the outer perimeter of the disk - member snaps downwardly and engages an insulating passive switch. Thus, the current which would ordinarily flow from the header to the electrochemical circuit system therebelow, during charging of the cell, is cut off.
The aforementioned Tuchoski references do not cause the switch member to open the circuit as a result of gas pressure applied directly to the switch member itself. Further, the Tuchoski references do not disclose any vent means whatsoever to permit excess gas pressure within the cell to flow therefrom should such venting become necessary to prevent an explosion.
U.S. Patent Nos. 4,690,879 to Huhndorff et al.
and 4,871,553 to Huhndorff disclose galvanic cells having switch means for disrupting current flow between a conductive cell cover and an electrochemical circuit system within the cell container. The switch means disclosed in both of these references are not actuable due to the direct application of excessive gas pressure thereto. - Instead, the operation of the batteries disclosed in the Huhndorff references are similar to the operation of the foregoing Tuchoski references wherein the switch means is actuable as a result of the degree of bulging of a container therebelow. Also like the Tuchoski references, the Huhndorff references do not disclose any vent means whatsoever.
U.S. Patent No. 4,788,112 to ~ung discloses a a battery including current cutoff means and vent means.
The current cutoff means of the Rung references is undesirable in that it does not permanéntly create an open circuit condition. Further, the Rung reference does not disclose a burstable vent means.
~5~ 20g9657 Thus, the prior art devices for cutting off current between the anode and the cathode within a battery have several shortcomings which make the need for an improved battery and a method of manufacturing same evident.
8UMMARY OF TH~ lNv~ lON
The present invention solves the aforementioned shortcomings of the prior art, and thus fulfills the needs of the industry by providing an improved electrochemical cell which includes improved current cutoff means, both with and without vent valve means. Further, the present invention provides a new and improved method for manufacturing such an electrochemical cell.
In accordance with a broad aspect of the present invention there is provided an electrochemical cell comprising a housing having a top portion and a bottom portion which includes an electrochemical circuit system therein. The electrochemical circuit system includes an anode, a cathode and an electrolyte solution which permeates the anode and the cathode. A conductive diaphragm means is arranged in the top portion of the housing for cutting off current flow between the anode and the cathode. The diaphragm means is adapted for quick movement between a first stable conducting position and a second stable non-conducting position upon direct application of gas pressure generated in the electrochemical circuit system in excess of a first predetermined pressure, and is unstable between said first and second stable positions. A conductive lead means is provided for electrically connecting the electrochemical circuit system to the diaphragm means when the diaphragm means is in said first stable conducting position, and is remote from the diaphragm means when said diaphragm means is arranged in said second stable non-conducting position.
In one preferred embodiment of the present invention, an insulating means is provided in the top -6- 2~-~9~57 portion of the housing for retaining the electrochemical circuit system in the bottom portion of the housing. An electrically conductive plate having a bottom surface and a top surface and at least one vented area defining vent holes extending therethrough is also preferably arranged in the top portion of the housing above the insulating means so that gaseous by-products resulting from chemical reactions in the electrochemical circuit system can flow through the electrically conductive plate. In this embodiment, the conductive lead means extending from the electrochemical circuit system is directly connected to the electrically conductive plate to create a current flow path between the anode and the cathode of the electrochemical circuit system therebelow. The conductive diaphragm means is releasably and electrically connected directly to the top surface of the electrically conductive plate and completes the circuit between the anode and the cathode of the electrochemical circuit system during normal operating conditions of the electrochemical cell. The conductive diaphragm means is constructed and arranged so that same will invert from a concave shape to a convex shape, thus moving from a conducting position to a non-conducting position, when the pressure directly exerted on the diaphragm by the gas by-products exceeds a first predetermined pressure thereby permanently opening the circuit to cut off current flow between the anode and the cathode of the electrochemical circuit system In another preferred embodiment of the present invention, the cell includes gasket means disposed between the housing and the diaphragm means for forming a hermetic seal and electrically insulating the diaphragm means from the housing. Further, in this preferred arrangement, the gasket means is at least partially disposed between the outer periphery of the electrically conductive plate and the diaphragm means to prevent electrical contact from recurring therebetween ~7~ 209~fi57 after the diaphragm means has inverted, e.g., moved from its conducting position of its non-conducting position.
It is also preferable for the cell of the present invention to comprise a cover arranged above the diaphragm means and connected along its outer perimeter to the outer perimeter of the diaphragm means within the - gasket means in an appropriately sized and shaped area of the top portion of the housing. Most preferably, the diaphragm means according to this aspect of the present invention comprises a truncated-cone shape and includes a central portion being releasably and electrically connected to a centrally located area at the top surface of the electrically conductive plate.
A cell according to this aspect of the present invention will effectively create an open circuit condition to cut off the current flow between the anode and the cathode as the gas by-products formed from chemical reactions in the electrochemical circuit system exer~ a pressure in excess of a first predetermined pressure directly on the diaphragm. The truncated-cone shape of the diaphragm of the present invention ensures that the open circuit condition will consistently occur within the desired predetermined pressure range.
Another aspect of the present invention provides a cell having current cutoff means as described above in combination with burstable vent means for permitting gas to flow out of the cell upon exertion of a second predetermined pressure in excess of the first predetermined pressure range after the current cutoff means has been actuated to create an open circuit condition between the anode and the cathode. The cell according to this aspect of the present invention includes a diaphragm means as described above further comprising at least one area on the diaphragm means which has been weakened so that the weakened area will ~ , burst upon the application of gas pressure in excess of a second predetermined pressure range applied directly to the diaphragm. The second predetermined pressure -8- 20996~7 range being greater than the first predetermined pressure range so that the at least one weakened area on the diaphragm means will burst to create a passageway for the gas to flow therethrough only if the internal pressure continues to rise after the diaphragm means has created an open circuit condition in the electrochemical circuit system.
It is also desirable for the cover of the cell according to this aspect of the present invention to include at least one vented area defining a gas flow path to permit gas to flow therethrough after the gas has caused the weakened area of the diaphragm to burst.
As can be appreciated, a cell according to this aspect of the present invention will ensure that an open circuit condition will result when the diaphragm inverts, thus moving away from its conductive position against the top surface of the conductive plate, and will ensure that the gas can safely be vented out of the cell to---avoid an explosion if the gas pressure should continue to build up within the cell after the open circuit condition has been created.
Another aspect -of the present invention provides a method of manufacturing an electrochemical cell. More particularly, the present method facilitates the assembly of a ~header~ at a location remote from an assembly line so that the header can be assembled and tested in an ideal environment and thereafter, it can be stored prior to being electrically connected to an electrochemical circuit system within the cell.
Preferably, a method according to this aspect of the present invention includes the step of connecting the outer peripheries of a conductive cover and a conductive diaphragm. The connected outer peripheries of the cover and the diaphragm are then press-fitted into an insulating gasket. Most preferably, the central portion of the diaphragm is then electrically connected to a conductive plate. The conductive plate is then attached to a flexible lead which extends from a cathode ~ -9- ~099657 through the open top of the housing of the electrochemical cell. The header, which includes the cover, the diaphragm, the conductive plate and the insulating gasket, is then placed within the open top of the housing by folding the electrical lead and press-fitting the gasket of the header within the top portion of the housing.
A method according to this aspect of the present invention permits the manufacture of the electrochemical cell in a new and improved manner which has not heretofore been possible. Particularly, the present method permits the ~header~ to be assembled and tested off of the assembly line under ideal conditions.
Thereafter, the header can be electrically and physically connected into a housing to complete an electrochemical cell such as the electrochemical cell of the present invention.
These and other aspects of the present invention will be more clearly understood when read in conjunction with the detailed descriptio~ and the accompanying drawings which follow.
BRIEF DE8CRIPTION OF T~E DRAWING8 FIG. 1 is an enlarged partial cross-sectional view of a prior art cell with the diaphragm directly connected to the electrical lead in its conducting position.
FIG. 2 is an enlarged partial cross-sectional view of a prior art cell with the diaphragm disconnected from the conductive lead in its non-conducting position.
FIG. 3 is an enlarged partial cross-sectional view of one embodiment of the cell of the present invention with the diaphragm connected to the conductive plate in its conductive position.
FIG. 4 is an enlarged partial cross-sectional view of the cell shown in FIG. 3 showing internal forces exerted by gas pressure and counteracting forces due to the diaphragm structure and the weld joint between the diaphragm and the conductive plate.
' 20996S7 FIG. 5 is an enlarged partial cross-sectional view of the cell shown in FIG. 3 with the diaphragm disconnected from the conductive plate in its non-conducting position.
5FIG. 6 shows the qualitative characteristics of displacement of the prior art diaphragm shown in FIGS. 1 and 2 as a function of pressure applied thereto.
FIG. 7 shows the qualitative characteristics of the displacement of the present diaphragm shown in 10FIGS. 3 and 5 as a function of pressure applied thereto.
FIG. 8 is an enlarged partial cross-sectional view of one embodiment of the header isolated from the electrochemical cell of the present invention.
FIG. 9 illustrates the step of electrically 15connecting the header to the electrical lead according to one aspect of the present method.
An electrochemical cell generally designated 10 in accordance with a preferred embodiment of the 20present invention includes a generally cylindrical housing having a top portion 12 and a bottom portion 14, including an electrochemical circuit system 60 therein.
The electrochemical circuit system includes anode material (not shown), cathode material (not shown) and 25an electrolyte solution (not shown) in contact with the anode material and the cathode material. The anode is preferably made of a carbon based material such as Spherical Carbon or Carbon Black, while the cathode preferably comprises lithium ions. A conductive lead 54 30extends from the cathode of the electrochemical circuit system through a centrally disposed passageway 52 in an insulating plate 50. Insulating plate 50 is manufactured from any non-conductive and non-reactive material such as polypropylene, and is arranged in the 35electrochemical cell to retain the electrochemical circuit system 60 within the bottom portion 14 of the housing.
Conductive lead 54 includes a lead plate 56 at its uppermost portion and is eleatrically and permanently connected to the bottom surface 48 of a weld plate 36 at a weld joint 58. Weld plate 36 is preferably constructed of 1145 Aluminum or 4000 Series Aluminum, such as 4047 Aluminum; however, it can be made of any suitable metal or alloy compatible with the lead plate 56 and the diaphragm 30 which will be described in detail below.
It is also preferable for the weld plate 36 to include four symmetrically-spaced vent holes arranged about a centrally located area 42 to define a circumferentially arranged vent area 40 to permit gases formed due to chemical reactions in the electrochemical circuit system 60, such as the C02 formed during decomposition of the cathode material and other gases formed due to the reaction between oxygen and lithium ions of the cathode, to flow therethrough and exert an upwardly directed force on the diaphragm 30.
The structure and operation of a preferred embodiment of the present invention will now be discussed with reference to Figs. 3-5. When the electrochemical cell 10 is in its assembled position, a Diaphragm 30 is arranged above the top surface 44 of the weld plate 36 and is desirably laser welded to the centrally located area 42 thereon at weld joint 46.
Diaphragm 30 is preferably constructed of a flexible conductive material such as aluminum; however, it can also be made of any suitable metal or alloy which has sufficient resistance and flexibility characteristics to serve its intended purpose as discussed hereinbelow. Most preferably, the diaphragm 30 comprises a truncated-cone shape and includes a downwardly extending central portion 28 when it is in its conducting position. The truncated-cone shape of diaphragm 30 is a significant improvement over prior art diaphragms, which are often completely flat or generally flat with a centrally located pro;ection extending - 12 - 209965~
downwardly therefrom, in that its current cutoff charac-teristics are greatly enhanced as will be described in detail below. It is also preferable for diaphragm 30 to include a thin-walled grooved area 34 designed to burst upon application of sufficient force thereto. The operation of this "burstable vent" function of the grooved area 34 is described more fully hereinbelow where the operation of the cell 10 is set forth.
A gasket 16 is desirably arranged between the top portion 12 of the housing and the outer periphery 32 of conductive diaphragm 30. The gasket 16 preferably provides a hermetic seal between the electrochemical circuit system 60 beneath the header 10 and the outside environment. Additionally, the gasket 16 electrically insulates the diaphragm 30 from the top portion 12 of the housing. To effectively provide its insulating and sealing functions, the gasket 16 is made from a non-conductive material such as polypropylene and preferably comprises a rubber or tar coating. Suitable coatings have been found to be VISTANEX, Trade-mark, Exxon (a commercially sold rubber) or bitumen (a commercially sold tar). The gasket 16 includes a bottom portion 20 disposed between the outer periphery 38 of the weld plate 36 and a portion of the diaphragm 30 to ensure that no electrical contact occurs at that location.
An electrically conductive cover 22 con-structed of stainless steel or other suitable metal alloy, is preferably included in the cell 10 to complete the construction thereof. The cover 22 includes an outer periphery 26 mounted within the outer periphery 32 of the diaphragm 30 and is electrically insulated from the top portion 12 of the housing by the non-conductive gasket 16. The top portion 18 of the gasket 16 is arranged to wrap around the outer periphery 32 of the diaphragm 30 and the outer periphery 26 of the cover 22, thus effectively insulating the diaphragm 30 and the cover 22 from the top portion 12 of the conductive k'~
-13- 20g96~7 housing. It is preferable for the cover 22 to include a vent hole 24 arranged between the central portion of the cover and the outer periphery 26 thereof. The foregoing description of the cell 10 is clearly illustrated in FIG. 3.
In operation, the electrochemical cell 10 is arranged to receive a charging current from an outside source to recharge the electrochemical circuit system 60 therein. Thus, during charging operations, current is permitted to flow through the passageway -created by cover 22, diaphragm 30, weld plate 36 and conductive lead 54 of header 10 and into the electrochemical cell therebelow. If an overcharged condition should result, the cathode material in the electrochemical circuit system 60 would begin to decompose, thus emitting gaseous by-products, such as CO2, therefrom. So long as the anode and the cathode are electrically connected, the generation of gas will continue. Thus, the internal gas pr_ ~ure within the housing will continuously increase. Under such circumstances, it is most desirable to cut off ~ current flow to the electrochemical circuit s~stem so that the chemical reactions therein will stop forming gaseous by-products before an explosion occurs.
As shown in FIG. 4, as the internal gas pressure builds up, a force is exerted upwardly through the circumferentially arranged vented area 40 in the weld plate 36 directly upon the diaphragm 30 and a counter force is exerted downwardly due to the combination of the inherent strength of the truncated-cone shape of the diaphragm 30 and the weld location 46 to retain the diaphragm in contact with the top surface 44 of the weld plate 36 as illustrated in FIG. 3.
However, when the upwardly exerted gas pressure exceeds a pressure within a predetermined range, e.g., approximately 150-200 psi, it overbears the counteracting forces shown in FIG. 4 and the diaphragm becomes ~inverted~ as it quickly snaps away from its ' -14- 2099657 conducting position on the weld plate 36 thereby breaking the electrical connection at the weld joint 46, all of which is clearly shown in FIG. 5. As will be discussed more fully below, the truncated-cone shape of the diaphragm 30 ensures that the pressure required to invert it is substantially constant because any variation in the disconnect pressure is due to variations in the weld strength, which is a small percentage of the overall disconnect pressure.
When the diaphragm 30 i8 in its ~inverted~
position as shown in FIG. 5, an open circuit condition exists; thus, the charging current between the diaphragm 30 and the electrochemical circuit system 60 is cut off.
Preferably this open circuit condition will prevent the formation of significant amounts of additional gases due to chemical reactions in the electrochemical circuit system. The now increased internal gas pressure continues to exert an upwardly directed pressure through the vent area 40 against the undersurface of the diaphragm 30. The top surface 44 of the weld plate 36 remains flush against the bottom portion 20 of the gasket 16 at all times. Thus, as shown in FIG. 5, the combination of the gasket 16 and the weld joint 58 between the lead plate 56 and the bottom surface 48 of the weld plate 36 effectively prevents any possibility of electrical contact from occurring between the top surface 44 of the weld plate 36 and the diaphragm 30 when the diaphragm 30 is in its inverted position.
Also, as clearly shown in FIG. 5, the distance between the diaphragm 30 and the top surface 44 of the weld plate 36 is relatively large compared to prior art ~disconnect distances~, and is preferably between about .50 and 1.0 mm, and typically is about .75 mm. Thus, the large ~disconnect distance~ of the present invention eliminates or at least greatly minimizes the possibility of a short circuit condition from occurring between the diaphragm 30 and the top surface 44 of the weld plate 36 - 15 - 2 0 ~ 9 6 5 7 after the diaphragm 30 has snapped to its inverted position, even if the cell becomes leaky.
Thus, as evident from the aforementioned current cutoff aspect of the present invention, the 5 charging current can be disconnected before the internal gas pressure rises to such a level as to cause an explosion. Ideally, the range of disconnect pressures of about 150-200 psi and more preferably of about 170 psi, in the foregoing example should be sufficient to create an open circuit condition as described above before the venting aspect of the present invention is actuated. However, under certain extreme overcharge conditions, the internal gas pressure will continue to rise after the diaphragm 30 has separated from the weld 15 plate 36. Under these circumstances, weakened areas such as a circumferentially arranged groove (not shown) in diaphragm 30 are designed to burst when the internal gas pressure reaches between about 250-500 psi and preferably between about 350-450 psi, so that the gas 20 by-products can flow out of the newly created vent area at the groove 34 and can continue to flow out of header 10 through a vent hole 24 in the cover 22 and into the outside environment. Thus, the burstable venting feature of the present invention permits gas pressure to 25 be let out of the electrochemical cell before a danger-ous explosion results. As can be appreciated, the present invention is not limited to any particular range of disconnect pressures. Indeed, the disconnect pres-sure can be varied for use in various types of cells by 30 changing the thickness of the diaphragm 30. Further-more, the disconnect pressure can be changed by changing the configuration of the truncated cone-shaped diaphragm 30. For example, if a higher disconnect pressure range is required, such as 240-260 psi, the cone configuration 35 of the diaphragm 30 can be exaggerated.
According to one preferred embodiment, the truncated-cone shape of the diaphragm 30 will permit the , ' ~ -16- 20'996S7 diaphragm to remain in its normal downwardly extending state against the top surface 44 of the weld plate 36 until about 115 psi in the absence of the weld joint 46.
The presence of the center weld 46 raises the pressure required to invert the diaphragm, as shown in FIG. 5, to approximately 170 psi. FIG. 6 qualitatively illustrates an example of the displacement of the center portion of the diaphragm 30 as a function of the internal pressure exerted thereon, both with and without the presence of the weld joint 46. Significantly, the truncated-cone design of the diaphragm 30 contributes greater than two-thirds of the overall resistance strength against displacement of the diaphragm. This is due to the novel shape of the burstable diaphragm 30 which includes inherent forces acting downwardly against the internal gas pressure to resist displacement and inversion of the diaphragm. As can be appreciated, the anti-displacement and inversion characteristics of the present truncated-cone shaped diaphragm 30 are far superior to the generally flat prior art diaphragms, such as the diaphragm disclosed in the Oishi et al. header, which rely almost entirely upon the strength of a weld joint, such as weld joint 46, to prevent displacement of the diaphragm. As discussed above, the presence of the weld joint 46 between the downwardly extending central portion 28 of the conical diaphragm 30 and the top surface 44 of the weld plate 36 increases the displacement strength of the diaphragm 30 by only about 30%.
FIG. 1 illustrates a prior out battery having a generally flat diaphragm 70 having a center projection 72 extending downwardly therefrom, in contrast to the truncated-cone shaped diaphragm of the present invention. The projection 72 of the generally flat diaphragm 70 is welded to a lead plate 74 at a weld joint 76. When internal pressure caused by gaseous by-products as described above, is exerted directly upon the diaphragm 70, the projection 72 is forced upwardly s, -17- 2099657 and pulls away from the weld joint 76 thereby creating an open circuit between the diaphragm 70 and the lead plate 74, as shown in FIG. 2. As can be appreciated, the distance between the lowermost portion of the projection 72 and the lead plate 74, after the internal gas pressure has caused a separation therebetween, is very small in comparison to the large permanent gap between the conical diaphragm 30 and the weld plate 36 of the present invention, when the diaphragm 30 is in its inverted position, as shown in FIG. 5. If the electrochemical cell becomes leaky (i.e. gases are permitted to escape from the housing), as is often the case when the cell is greatly overcharged, the al~eady small disconnect distance between the projection 72 of the diaphragm 70 and the lead plate 74 may diminish until an electrical connection is again created therebetween. The small disconnect distance as described above is largely a result of the generally flat construction of the prior art diaphragms.
Furthermore, an additional shortcoming of this prior art design is due to "burrs", i.e., rough edges, which may form on the projection 72 and the lead plate 74 after they have become separated, as discussed above. The burrs can facilitate the reoccurrence of the electrical connection between the projection 72 of the diaphragm 70 and the lead plate 74 and are thus, a drawback of the prior art diaphragms.
From a pressure-strength standpoint, the generally flat prior art diaphragm functions essentially as a flat plate regardless of the presence of a central projection extending therefrom. As discussed above, the pressure required to raise the prior art diaphragm, shown in FIGS. 1 and 2, away from its connection with the lead plate 74 is minimal without the presence of the weld joint 76. Thus, in prior art diaphragms, the weld joint 76 provides an extremely large percentage of the -overall disconnect strength as compared with the weld joint 44 between the truncated-cone shaped diaphragm 30 '~ -18- 2099657 and the top surface 44 of the weld plate 36 of the present invention. The qualitative relationship between the displacement of projection 72 of the prior art diaphragm 70 from the weld plate 74 as a function of s internal gas pressure applied thereto is illustrated in FIG. 7. An analysis of the qualitative relationship illustrated in FIG. 7 clearly shows that the structure of the prior art diaphragm contributes very little to the forces which counteract the internal gas pressure to keep electrical contact between the diaphragm and the electrical lead. The inadequacy of the prior art design is more evident when the prlor art diaphragm displacement versus internal pressure relationship, as shown in FIG. 7, is directly compared with the same qualitative relationship of the truncated-cone shaped diaphragm of the present invention as shown in FIG. 6.
According to the present method of manufacturing an electrochemical cell, the diaphragm 30 can be laser welded, or electrically connected according to other known methods, to the top surface 44 of the weld plate 36 in an environment away from the general assembly line which permits the welded parts to be tested, checked and stored before insertion into the electrochemical cell 10 on the assembly line.
The present - method of manufacturing an electrochemical cell is a significant improvement over prior art methods. The improvement is clear when viewed in light of the method of manufacturing batteries as taught in the prior art. In particular, prior art cap assemblies, such as the cap assembly comprising a weldable diaphragm in the Oishi et al. reference discussed above, required the cap assembly, and in particular the ~critical weld~ between the diaphragm and an electrical lead to be made on an assembly line under less than ideal conditions. Additionally, all testing of the ~disconnect pressure~ in prior art batteries (e.g., the pressure required to separate the diaphragm from the electrical lead) must be conducted with the cap -19- 2099~S7 assembly integrally formed as part of the electrochemical cell. Thus, the cap assembly of the Oishi et al. reference cannot be manufactured or tested in an ideal environment off of the assembly line.
s Additionally, the prior art cap assemblies cannot be stored as an integral unit prior to assembly into the battery.
In contrast to the method of manufacturing electrochemical cells, including a ~critical weld~, as taught in the prior art, the present method of manufacturing an electrochemical cell permits the separate components of a header 11 to be assembled ~off-line~ under ideal working conditions. As clearly shown in FIG. 8, the components of the header 11 of the present invention include the cover 22, the diaphragm 30, the gasket 16 and the electrically conductive plate 36.
Thus, according to a preferred method of the present invention, the sequence of steps during the assembly of an electrochemical cell, such as electrochemical cell 10 described above, includes the step of placing the outer periphery 26 of the conductive cover 22 within the outer periphery 32 of the conductive diaphragm 30. The outer periphery 32 of the diaphragm 30 is then crimped to secure the outer periphery 26 of the cover 22 therein. Most preferably, the diaphragm 30 and the cover 22 will be arranged so that the central portion of the diaphragm 30 comprises a concave shape with respect to the cover 22.
The now unitary cover 22 and diaphragm 30 is then press-fitted into the insulating gasket 16 between the top portion 18 and the bottom portion 20 thereof.
The friction-fit between the crimped cover 22 and the diaphragm 30 and the gasket 16 is sufficiently secure to retain the cover 22 and the diaphragm 30 therein.
Preferably, the now secured cover 22 and diaphragm 30 are arranged so that the central portion of the diaphragm 30 abuts the top surface 44 of the weld plate 36 at the centrally located area 42. As shown in FIG. 8, it is preferable for the diaphragm 30 to include a convex shape with respect to the top surface 44 of the weld plate 36. The diaphragm 30 is then welded thereto by any suitable welding technique, such as laser welding, to form the weld joint 46. The weld formed during this welding operation is a ~critical weld,~
since it must break upon application of a predetermined pressure, and can be performed according to the method of the present invention in an ideal environment to assure that the weld is precisely formed within a predetermined tolerance.
After the foregoing welding operation is completed, the header 11 can be tested apart from the rest of the electrochemical cell 10 under ideal conditions. Additionally, the header 11 comprising the cover 22, the diaphragm 30, the weld plate 36 and the gasket 16 can now be stored until it is desirable to electrically connect same to the top portion 56 of the electrical lead 54 which extends through the open top 12 of an electrochemical cell as shown in FIG. 9.
It is desirable, according to the method of the present invention, for the bottom surface 48 of the conductive plate 36 to be welded to the electrical lead on the assembly line. The weld joint 58 formed between bottom surface 48 of the conductive plate 36 and top portion 56 of the electrical lead 54 is a ~non-criticaln weld joint. The non-critical weld joint 58 need not be made under ideal conditions because the weld joint 58 is not designed to break at a predetermined pressure, as is the critical weld joint 46. After this non-critical welding operation occurs, it is preferable for electrical lead 54 to be folded by a specially designed folding apparatus (not shown) so that the lead plate portion 56 will be arranged between the electrochemical circuit system (i.e., the anode, the cathode and the electrolyte solution) and the electrically conductive plate 36 when the header 11 is placed within the open -21- 2~99657 top portion 12 of the electrochemical cell 10. Finally, the top portion 12 of the cell is crimped into position to secure the cell into assembled position.
It is most desirable to place the header 11 into the top portion 12 of the housing in a manner such that the gasket 16 forms an insulating seal between the header 11 and the top portion of the housing 12 as clearly shown in FIG. 1.
As can be appreciated, the structure of the components, and especially diaphragm 30, of the present electrochemical cell 10 facilitates the foregoing advantageous sequence of assembly steps resulting in the manufacturing advantage as discussed above. Such a manufacturing advantage (i.e., the ~off-line~ assembly, testing and storage of the components of the header 11 of the present invention) has not heretofore been achieved.
While the foregoing description and figures are directed toward the preferred embodiment and method of the present invention, it should be appreciated that numerous modifications can be made to each of the individual components of the entire apparatus and the steps in the method as discussed above, and are indeed encouraged to be made in the materials, structure and arrangement of the disclosed method and embodiment without departing from the spirit and scope of the present invention. Thus, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the present invention as described by the claims set forth below.
FIELD OF THB lNV~ ON
The present invention pertains to an electrochemical cell having current cutoff means for preventing current flow therein and to a method of manufacturing an electrochemical cell. More particularly, the present invention relates to an electrochemical cell having current cutoff means and - burstable vent means for preventing a dangerous explosion from occurring within the cell, and a method of manufacturing same. Still more particularly, the present invention relates to an electrochemical cell, and a method of manufacturing such cell, having current cutoff means operable upon the exertion of a gas pressure in excess of a first predetermined pressure, and burstable vent means operable upon the application of gas pressure exerted directly on the diaphragm in excess of a second predetermined pressure whereby the second predetermined pressure exceeds the first predetermined pressure.
BAC~GROUND OF THE lNV~ ON
The prior art is replete with electrochemical cells including current cutoff switches for cutting off current flow between the anode and the cathode of the cell. Additionally, the prior art discloses numerous electrochemical cells having vent means for permitting gas trapped within a housing of the cell to escape therethrough. However, the prior art attempts to design and manufacture an electrochemical cell having current - 30 cutoff means and vent valve means to prevent an explosion within the cell, have been inadequate in their efforts to develop a current cutoff means which will ensure the occurrence of an open circuit condition upon the application of a consistent internal gas pressure on a diaphragm within the cell. Further, numerous prior art devices provide no means for venting excessive gas pressure from the interior of an electrochemical cell to prevent an explosion in the event that the current cutoff means fail to prevent chemical reactions within the cell from producing additional gas.
Moreover, no known prior art discloses or otherwise teaches a method for manufacturing an s electrochemical cell comprising the steps of assembling a ~header~ including current cutoff means in an ideal environment away from an assembly line and testing the header assembly under ideal conditions, and thereafter assembling the header to a housing of an electrochemical cell including an anode, a cathode, electrolyte solution and an electrical lead extending from the cathode.
U.S. Patent No. 4,943,497 to Oishi et al.
discloses a battery having switch means for disrupting current flow between the header and the anode or cathode of the battery and vent means for permitting gas to be expelled from the battery when the pressure therein exceeds a predetermined limit. The Oishi et al . battery includes a container having anode material, cathode material and an electrolyte solution for forming an electrochemical circuit system therein, and a header electrically connected to the electrochemical circuit system. An electrical lead extends from the electrochemical circuit system and is directly welded to a projection extending downwardly from an otherwise generally flat conductive diaphragm to complete the circuit between the header and the electrochemical circuit system therebelow, all of which is shown in the drawings of the Oishi et al. patent and is duplicated in Fig. 1 of the present application.
The diaphragm is constructed and arranged to pull away from the lead thereby breaking the welded connection therebetween upon application of a sufficient amount of pressure thereto. Once the diaphragm pulls away from the electrical lead, the circuit is opened and current can no longer flow from the header to the electrochemical circuit system. The current cutoff means of the Oishi et al. battery is undesirable because the resulting separation between the diaphragm and the electrical lead is small, thus allowing the diaphragm to recede and cause a short circuit condition by forming a bridge across the small gap if the battery is even slightly leaky. Further, the structure and operation of the diaphragm disclosed in the Oishi et al. battery is such that the disconnect pressure is dependent almost entirely on the weld strength, thereby permitting the disconnect pressure to vary widely depending on the tolerance of the weld strength itself. Finally, as implied in Columns 6-8 of the Oish~ et al.
specification, the structure and operation of the battery requires the weld between the diaphragm and the electrical lead to be made on the assembly line. Thus, the Oishi et al. battery cannot be separately tested, checked and stored before use on the assembly line to assure the highest degree of quality control.
U.S. Patent Nos. 4,025,696 to Tuchoski et al.
and 4,028,478 to Tuchos~i disclose sealed cells having an irreversible switch means for cutting off current flow within an electrochemical cell. The switch means is actuable upon expansion of a cell container above a predetermined limit. The cell expansion may result from gaseous by-products caused by chemical reactions in an electrochemical circuit system within the cell. The switch means comprises an active electrically conductive disk-shaped spring member defining a central opening therethrough and a passive insulating member. The insulating member also includes a centrally disposed opening wherein the opening has a larger diameter than the opening of the active conductive spring member. The passive member is disposed between the active switch member and a conductive plate, and is further arranged with its centrally disposed opening surrounding the central opening of the active switch member. When the cell is in its normal operating state, the active switch member is in electrical conduct with the conductive plate in the vicinity of its centrally disposed opening, and is also in electrical contact with a cell cover at _4 20~99657 its outer periphery. When an overload condition arises, the cell container bulges upwardly in the vicinity of the header which includes the switch means. In response to such upward bulge, the central portion of the conductive active switch member also deflects upwardly toward the cover while the outer perimeter of the disk - member snaps downwardly and engages an insulating passive switch. Thus, the current which would ordinarily flow from the header to the electrochemical circuit system therebelow, during charging of the cell, is cut off.
The aforementioned Tuchoski references do not cause the switch member to open the circuit as a result of gas pressure applied directly to the switch member itself. Further, the Tuchoski references do not disclose any vent means whatsoever to permit excess gas pressure within the cell to flow therefrom should such venting become necessary to prevent an explosion.
U.S. Patent Nos. 4,690,879 to Huhndorff et al.
and 4,871,553 to Huhndorff disclose galvanic cells having switch means for disrupting current flow between a conductive cell cover and an electrochemical circuit system within the cell container. The switch means disclosed in both of these references are not actuable due to the direct application of excessive gas pressure thereto. - Instead, the operation of the batteries disclosed in the Huhndorff references are similar to the operation of the foregoing Tuchoski references wherein the switch means is actuable as a result of the degree of bulging of a container therebelow. Also like the Tuchoski references, the Huhndorff references do not disclose any vent means whatsoever.
U.S. Patent No. 4,788,112 to ~ung discloses a a battery including current cutoff means and vent means.
The current cutoff means of the Rung references is undesirable in that it does not permanéntly create an open circuit condition. Further, the Rung reference does not disclose a burstable vent means.
~5~ 20g9657 Thus, the prior art devices for cutting off current between the anode and the cathode within a battery have several shortcomings which make the need for an improved battery and a method of manufacturing same evident.
8UMMARY OF TH~ lNv~ lON
The present invention solves the aforementioned shortcomings of the prior art, and thus fulfills the needs of the industry by providing an improved electrochemical cell which includes improved current cutoff means, both with and without vent valve means. Further, the present invention provides a new and improved method for manufacturing such an electrochemical cell.
In accordance with a broad aspect of the present invention there is provided an electrochemical cell comprising a housing having a top portion and a bottom portion which includes an electrochemical circuit system therein. The electrochemical circuit system includes an anode, a cathode and an electrolyte solution which permeates the anode and the cathode. A conductive diaphragm means is arranged in the top portion of the housing for cutting off current flow between the anode and the cathode. The diaphragm means is adapted for quick movement between a first stable conducting position and a second stable non-conducting position upon direct application of gas pressure generated in the electrochemical circuit system in excess of a first predetermined pressure, and is unstable between said first and second stable positions. A conductive lead means is provided for electrically connecting the electrochemical circuit system to the diaphragm means when the diaphragm means is in said first stable conducting position, and is remote from the diaphragm means when said diaphragm means is arranged in said second stable non-conducting position.
In one preferred embodiment of the present invention, an insulating means is provided in the top -6- 2~-~9~57 portion of the housing for retaining the electrochemical circuit system in the bottom portion of the housing. An electrically conductive plate having a bottom surface and a top surface and at least one vented area defining vent holes extending therethrough is also preferably arranged in the top portion of the housing above the insulating means so that gaseous by-products resulting from chemical reactions in the electrochemical circuit system can flow through the electrically conductive plate. In this embodiment, the conductive lead means extending from the electrochemical circuit system is directly connected to the electrically conductive plate to create a current flow path between the anode and the cathode of the electrochemical circuit system therebelow. The conductive diaphragm means is releasably and electrically connected directly to the top surface of the electrically conductive plate and completes the circuit between the anode and the cathode of the electrochemical circuit system during normal operating conditions of the electrochemical cell. The conductive diaphragm means is constructed and arranged so that same will invert from a concave shape to a convex shape, thus moving from a conducting position to a non-conducting position, when the pressure directly exerted on the diaphragm by the gas by-products exceeds a first predetermined pressure thereby permanently opening the circuit to cut off current flow between the anode and the cathode of the electrochemical circuit system In another preferred embodiment of the present invention, the cell includes gasket means disposed between the housing and the diaphragm means for forming a hermetic seal and electrically insulating the diaphragm means from the housing. Further, in this preferred arrangement, the gasket means is at least partially disposed between the outer periphery of the electrically conductive plate and the diaphragm means to prevent electrical contact from recurring therebetween ~7~ 209~fi57 after the diaphragm means has inverted, e.g., moved from its conducting position of its non-conducting position.
It is also preferable for the cell of the present invention to comprise a cover arranged above the diaphragm means and connected along its outer perimeter to the outer perimeter of the diaphragm means within the - gasket means in an appropriately sized and shaped area of the top portion of the housing. Most preferably, the diaphragm means according to this aspect of the present invention comprises a truncated-cone shape and includes a central portion being releasably and electrically connected to a centrally located area at the top surface of the electrically conductive plate.
A cell according to this aspect of the present invention will effectively create an open circuit condition to cut off the current flow between the anode and the cathode as the gas by-products formed from chemical reactions in the electrochemical circuit system exer~ a pressure in excess of a first predetermined pressure directly on the diaphragm. The truncated-cone shape of the diaphragm of the present invention ensures that the open circuit condition will consistently occur within the desired predetermined pressure range.
Another aspect of the present invention provides a cell having current cutoff means as described above in combination with burstable vent means for permitting gas to flow out of the cell upon exertion of a second predetermined pressure in excess of the first predetermined pressure range after the current cutoff means has been actuated to create an open circuit condition between the anode and the cathode. The cell according to this aspect of the present invention includes a diaphragm means as described above further comprising at least one area on the diaphragm means which has been weakened so that the weakened area will ~ , burst upon the application of gas pressure in excess of a second predetermined pressure range applied directly to the diaphragm. The second predetermined pressure -8- 20996~7 range being greater than the first predetermined pressure range so that the at least one weakened area on the diaphragm means will burst to create a passageway for the gas to flow therethrough only if the internal pressure continues to rise after the diaphragm means has created an open circuit condition in the electrochemical circuit system.
It is also desirable for the cover of the cell according to this aspect of the present invention to include at least one vented area defining a gas flow path to permit gas to flow therethrough after the gas has caused the weakened area of the diaphragm to burst.
As can be appreciated, a cell according to this aspect of the present invention will ensure that an open circuit condition will result when the diaphragm inverts, thus moving away from its conductive position against the top surface of the conductive plate, and will ensure that the gas can safely be vented out of the cell to---avoid an explosion if the gas pressure should continue to build up within the cell after the open circuit condition has been created.
Another aspect -of the present invention provides a method of manufacturing an electrochemical cell. More particularly, the present method facilitates the assembly of a ~header~ at a location remote from an assembly line so that the header can be assembled and tested in an ideal environment and thereafter, it can be stored prior to being electrically connected to an electrochemical circuit system within the cell.
Preferably, a method according to this aspect of the present invention includes the step of connecting the outer peripheries of a conductive cover and a conductive diaphragm. The connected outer peripheries of the cover and the diaphragm are then press-fitted into an insulating gasket. Most preferably, the central portion of the diaphragm is then electrically connected to a conductive plate. The conductive plate is then attached to a flexible lead which extends from a cathode ~ -9- ~099657 through the open top of the housing of the electrochemical cell. The header, which includes the cover, the diaphragm, the conductive plate and the insulating gasket, is then placed within the open top of the housing by folding the electrical lead and press-fitting the gasket of the header within the top portion of the housing.
A method according to this aspect of the present invention permits the manufacture of the electrochemical cell in a new and improved manner which has not heretofore been possible. Particularly, the present method permits the ~header~ to be assembled and tested off of the assembly line under ideal conditions.
Thereafter, the header can be electrically and physically connected into a housing to complete an electrochemical cell such as the electrochemical cell of the present invention.
These and other aspects of the present invention will be more clearly understood when read in conjunction with the detailed descriptio~ and the accompanying drawings which follow.
BRIEF DE8CRIPTION OF T~E DRAWING8 FIG. 1 is an enlarged partial cross-sectional view of a prior art cell with the diaphragm directly connected to the electrical lead in its conducting position.
FIG. 2 is an enlarged partial cross-sectional view of a prior art cell with the diaphragm disconnected from the conductive lead in its non-conducting position.
FIG. 3 is an enlarged partial cross-sectional view of one embodiment of the cell of the present invention with the diaphragm connected to the conductive plate in its conductive position.
FIG. 4 is an enlarged partial cross-sectional view of the cell shown in FIG. 3 showing internal forces exerted by gas pressure and counteracting forces due to the diaphragm structure and the weld joint between the diaphragm and the conductive plate.
' 20996S7 FIG. 5 is an enlarged partial cross-sectional view of the cell shown in FIG. 3 with the diaphragm disconnected from the conductive plate in its non-conducting position.
5FIG. 6 shows the qualitative characteristics of displacement of the prior art diaphragm shown in FIGS. 1 and 2 as a function of pressure applied thereto.
FIG. 7 shows the qualitative characteristics of the displacement of the present diaphragm shown in 10FIGS. 3 and 5 as a function of pressure applied thereto.
FIG. 8 is an enlarged partial cross-sectional view of one embodiment of the header isolated from the electrochemical cell of the present invention.
FIG. 9 illustrates the step of electrically 15connecting the header to the electrical lead according to one aspect of the present method.
An electrochemical cell generally designated 10 in accordance with a preferred embodiment of the 20present invention includes a generally cylindrical housing having a top portion 12 and a bottom portion 14, including an electrochemical circuit system 60 therein.
The electrochemical circuit system includes anode material (not shown), cathode material (not shown) and 25an electrolyte solution (not shown) in contact with the anode material and the cathode material. The anode is preferably made of a carbon based material such as Spherical Carbon or Carbon Black, while the cathode preferably comprises lithium ions. A conductive lead 54 30extends from the cathode of the electrochemical circuit system through a centrally disposed passageway 52 in an insulating plate 50. Insulating plate 50 is manufactured from any non-conductive and non-reactive material such as polypropylene, and is arranged in the 35electrochemical cell to retain the electrochemical circuit system 60 within the bottom portion 14 of the housing.
Conductive lead 54 includes a lead plate 56 at its uppermost portion and is eleatrically and permanently connected to the bottom surface 48 of a weld plate 36 at a weld joint 58. Weld plate 36 is preferably constructed of 1145 Aluminum or 4000 Series Aluminum, such as 4047 Aluminum; however, it can be made of any suitable metal or alloy compatible with the lead plate 56 and the diaphragm 30 which will be described in detail below.
It is also preferable for the weld plate 36 to include four symmetrically-spaced vent holes arranged about a centrally located area 42 to define a circumferentially arranged vent area 40 to permit gases formed due to chemical reactions in the electrochemical circuit system 60, such as the C02 formed during decomposition of the cathode material and other gases formed due to the reaction between oxygen and lithium ions of the cathode, to flow therethrough and exert an upwardly directed force on the diaphragm 30.
The structure and operation of a preferred embodiment of the present invention will now be discussed with reference to Figs. 3-5. When the electrochemical cell 10 is in its assembled position, a Diaphragm 30 is arranged above the top surface 44 of the weld plate 36 and is desirably laser welded to the centrally located area 42 thereon at weld joint 46.
Diaphragm 30 is preferably constructed of a flexible conductive material such as aluminum; however, it can also be made of any suitable metal or alloy which has sufficient resistance and flexibility characteristics to serve its intended purpose as discussed hereinbelow. Most preferably, the diaphragm 30 comprises a truncated-cone shape and includes a downwardly extending central portion 28 when it is in its conducting position. The truncated-cone shape of diaphragm 30 is a significant improvement over prior art diaphragms, which are often completely flat or generally flat with a centrally located pro;ection extending - 12 - 209965~
downwardly therefrom, in that its current cutoff charac-teristics are greatly enhanced as will be described in detail below. It is also preferable for diaphragm 30 to include a thin-walled grooved area 34 designed to burst upon application of sufficient force thereto. The operation of this "burstable vent" function of the grooved area 34 is described more fully hereinbelow where the operation of the cell 10 is set forth.
A gasket 16 is desirably arranged between the top portion 12 of the housing and the outer periphery 32 of conductive diaphragm 30. The gasket 16 preferably provides a hermetic seal between the electrochemical circuit system 60 beneath the header 10 and the outside environment. Additionally, the gasket 16 electrically insulates the diaphragm 30 from the top portion 12 of the housing. To effectively provide its insulating and sealing functions, the gasket 16 is made from a non-conductive material such as polypropylene and preferably comprises a rubber or tar coating. Suitable coatings have been found to be VISTANEX, Trade-mark, Exxon (a commercially sold rubber) or bitumen (a commercially sold tar). The gasket 16 includes a bottom portion 20 disposed between the outer periphery 38 of the weld plate 36 and a portion of the diaphragm 30 to ensure that no electrical contact occurs at that location.
An electrically conductive cover 22 con-structed of stainless steel or other suitable metal alloy, is preferably included in the cell 10 to complete the construction thereof. The cover 22 includes an outer periphery 26 mounted within the outer periphery 32 of the diaphragm 30 and is electrically insulated from the top portion 12 of the housing by the non-conductive gasket 16. The top portion 18 of the gasket 16 is arranged to wrap around the outer periphery 32 of the diaphragm 30 and the outer periphery 26 of the cover 22, thus effectively insulating the diaphragm 30 and the cover 22 from the top portion 12 of the conductive k'~
-13- 20g96~7 housing. It is preferable for the cover 22 to include a vent hole 24 arranged between the central portion of the cover and the outer periphery 26 thereof. The foregoing description of the cell 10 is clearly illustrated in FIG. 3.
In operation, the electrochemical cell 10 is arranged to receive a charging current from an outside source to recharge the electrochemical circuit system 60 therein. Thus, during charging operations, current is permitted to flow through the passageway -created by cover 22, diaphragm 30, weld plate 36 and conductive lead 54 of header 10 and into the electrochemical cell therebelow. If an overcharged condition should result, the cathode material in the electrochemical circuit system 60 would begin to decompose, thus emitting gaseous by-products, such as CO2, therefrom. So long as the anode and the cathode are electrically connected, the generation of gas will continue. Thus, the internal gas pr_ ~ure within the housing will continuously increase. Under such circumstances, it is most desirable to cut off ~ current flow to the electrochemical circuit s~stem so that the chemical reactions therein will stop forming gaseous by-products before an explosion occurs.
As shown in FIG. 4, as the internal gas pressure builds up, a force is exerted upwardly through the circumferentially arranged vented area 40 in the weld plate 36 directly upon the diaphragm 30 and a counter force is exerted downwardly due to the combination of the inherent strength of the truncated-cone shape of the diaphragm 30 and the weld location 46 to retain the diaphragm in contact with the top surface 44 of the weld plate 36 as illustrated in FIG. 3.
However, when the upwardly exerted gas pressure exceeds a pressure within a predetermined range, e.g., approximately 150-200 psi, it overbears the counteracting forces shown in FIG. 4 and the diaphragm becomes ~inverted~ as it quickly snaps away from its ' -14- 2099657 conducting position on the weld plate 36 thereby breaking the electrical connection at the weld joint 46, all of which is clearly shown in FIG. 5. As will be discussed more fully below, the truncated-cone shape of the diaphragm 30 ensures that the pressure required to invert it is substantially constant because any variation in the disconnect pressure is due to variations in the weld strength, which is a small percentage of the overall disconnect pressure.
When the diaphragm 30 i8 in its ~inverted~
position as shown in FIG. 5, an open circuit condition exists; thus, the charging current between the diaphragm 30 and the electrochemical circuit system 60 is cut off.
Preferably this open circuit condition will prevent the formation of significant amounts of additional gases due to chemical reactions in the electrochemical circuit system. The now increased internal gas pressure continues to exert an upwardly directed pressure through the vent area 40 against the undersurface of the diaphragm 30. The top surface 44 of the weld plate 36 remains flush against the bottom portion 20 of the gasket 16 at all times. Thus, as shown in FIG. 5, the combination of the gasket 16 and the weld joint 58 between the lead plate 56 and the bottom surface 48 of the weld plate 36 effectively prevents any possibility of electrical contact from occurring between the top surface 44 of the weld plate 36 and the diaphragm 30 when the diaphragm 30 is in its inverted position.
Also, as clearly shown in FIG. 5, the distance between the diaphragm 30 and the top surface 44 of the weld plate 36 is relatively large compared to prior art ~disconnect distances~, and is preferably between about .50 and 1.0 mm, and typically is about .75 mm. Thus, the large ~disconnect distance~ of the present invention eliminates or at least greatly minimizes the possibility of a short circuit condition from occurring between the diaphragm 30 and the top surface 44 of the weld plate 36 - 15 - 2 0 ~ 9 6 5 7 after the diaphragm 30 has snapped to its inverted position, even if the cell becomes leaky.
Thus, as evident from the aforementioned current cutoff aspect of the present invention, the 5 charging current can be disconnected before the internal gas pressure rises to such a level as to cause an explosion. Ideally, the range of disconnect pressures of about 150-200 psi and more preferably of about 170 psi, in the foregoing example should be sufficient to create an open circuit condition as described above before the venting aspect of the present invention is actuated. However, under certain extreme overcharge conditions, the internal gas pressure will continue to rise after the diaphragm 30 has separated from the weld 15 plate 36. Under these circumstances, weakened areas such as a circumferentially arranged groove (not shown) in diaphragm 30 are designed to burst when the internal gas pressure reaches between about 250-500 psi and preferably between about 350-450 psi, so that the gas 20 by-products can flow out of the newly created vent area at the groove 34 and can continue to flow out of header 10 through a vent hole 24 in the cover 22 and into the outside environment. Thus, the burstable venting feature of the present invention permits gas pressure to 25 be let out of the electrochemical cell before a danger-ous explosion results. As can be appreciated, the present invention is not limited to any particular range of disconnect pressures. Indeed, the disconnect pres-sure can be varied for use in various types of cells by 30 changing the thickness of the diaphragm 30. Further-more, the disconnect pressure can be changed by changing the configuration of the truncated cone-shaped diaphragm 30. For example, if a higher disconnect pressure range is required, such as 240-260 psi, the cone configuration 35 of the diaphragm 30 can be exaggerated.
According to one preferred embodiment, the truncated-cone shape of the diaphragm 30 will permit the , ' ~ -16- 20'996S7 diaphragm to remain in its normal downwardly extending state against the top surface 44 of the weld plate 36 until about 115 psi in the absence of the weld joint 46.
The presence of the center weld 46 raises the pressure required to invert the diaphragm, as shown in FIG. 5, to approximately 170 psi. FIG. 6 qualitatively illustrates an example of the displacement of the center portion of the diaphragm 30 as a function of the internal pressure exerted thereon, both with and without the presence of the weld joint 46. Significantly, the truncated-cone design of the diaphragm 30 contributes greater than two-thirds of the overall resistance strength against displacement of the diaphragm. This is due to the novel shape of the burstable diaphragm 30 which includes inherent forces acting downwardly against the internal gas pressure to resist displacement and inversion of the diaphragm. As can be appreciated, the anti-displacement and inversion characteristics of the present truncated-cone shaped diaphragm 30 are far superior to the generally flat prior art diaphragms, such as the diaphragm disclosed in the Oishi et al. header, which rely almost entirely upon the strength of a weld joint, such as weld joint 46, to prevent displacement of the diaphragm. As discussed above, the presence of the weld joint 46 between the downwardly extending central portion 28 of the conical diaphragm 30 and the top surface 44 of the weld plate 36 increases the displacement strength of the diaphragm 30 by only about 30%.
FIG. 1 illustrates a prior out battery having a generally flat diaphragm 70 having a center projection 72 extending downwardly therefrom, in contrast to the truncated-cone shaped diaphragm of the present invention. The projection 72 of the generally flat diaphragm 70 is welded to a lead plate 74 at a weld joint 76. When internal pressure caused by gaseous by-products as described above, is exerted directly upon the diaphragm 70, the projection 72 is forced upwardly s, -17- 2099657 and pulls away from the weld joint 76 thereby creating an open circuit between the diaphragm 70 and the lead plate 74, as shown in FIG. 2. As can be appreciated, the distance between the lowermost portion of the projection 72 and the lead plate 74, after the internal gas pressure has caused a separation therebetween, is very small in comparison to the large permanent gap between the conical diaphragm 30 and the weld plate 36 of the present invention, when the diaphragm 30 is in its inverted position, as shown in FIG. 5. If the electrochemical cell becomes leaky (i.e. gases are permitted to escape from the housing), as is often the case when the cell is greatly overcharged, the al~eady small disconnect distance between the projection 72 of the diaphragm 70 and the lead plate 74 may diminish until an electrical connection is again created therebetween. The small disconnect distance as described above is largely a result of the generally flat construction of the prior art diaphragms.
Furthermore, an additional shortcoming of this prior art design is due to "burrs", i.e., rough edges, which may form on the projection 72 and the lead plate 74 after they have become separated, as discussed above. The burrs can facilitate the reoccurrence of the electrical connection between the projection 72 of the diaphragm 70 and the lead plate 74 and are thus, a drawback of the prior art diaphragms.
From a pressure-strength standpoint, the generally flat prior art diaphragm functions essentially as a flat plate regardless of the presence of a central projection extending therefrom. As discussed above, the pressure required to raise the prior art diaphragm, shown in FIGS. 1 and 2, away from its connection with the lead plate 74 is minimal without the presence of the weld joint 76. Thus, in prior art diaphragms, the weld joint 76 provides an extremely large percentage of the -overall disconnect strength as compared with the weld joint 44 between the truncated-cone shaped diaphragm 30 '~ -18- 2099657 and the top surface 44 of the weld plate 36 of the present invention. The qualitative relationship between the displacement of projection 72 of the prior art diaphragm 70 from the weld plate 74 as a function of s internal gas pressure applied thereto is illustrated in FIG. 7. An analysis of the qualitative relationship illustrated in FIG. 7 clearly shows that the structure of the prior art diaphragm contributes very little to the forces which counteract the internal gas pressure to keep electrical contact between the diaphragm and the electrical lead. The inadequacy of the prior art design is more evident when the prlor art diaphragm displacement versus internal pressure relationship, as shown in FIG. 7, is directly compared with the same qualitative relationship of the truncated-cone shaped diaphragm of the present invention as shown in FIG. 6.
According to the present method of manufacturing an electrochemical cell, the diaphragm 30 can be laser welded, or electrically connected according to other known methods, to the top surface 44 of the weld plate 36 in an environment away from the general assembly line which permits the welded parts to be tested, checked and stored before insertion into the electrochemical cell 10 on the assembly line.
The present - method of manufacturing an electrochemical cell is a significant improvement over prior art methods. The improvement is clear when viewed in light of the method of manufacturing batteries as taught in the prior art. In particular, prior art cap assemblies, such as the cap assembly comprising a weldable diaphragm in the Oishi et al. reference discussed above, required the cap assembly, and in particular the ~critical weld~ between the diaphragm and an electrical lead to be made on an assembly line under less than ideal conditions. Additionally, all testing of the ~disconnect pressure~ in prior art batteries (e.g., the pressure required to separate the diaphragm from the electrical lead) must be conducted with the cap -19- 2099~S7 assembly integrally formed as part of the electrochemical cell. Thus, the cap assembly of the Oishi et al. reference cannot be manufactured or tested in an ideal environment off of the assembly line.
s Additionally, the prior art cap assemblies cannot be stored as an integral unit prior to assembly into the battery.
In contrast to the method of manufacturing electrochemical cells, including a ~critical weld~, as taught in the prior art, the present method of manufacturing an electrochemical cell permits the separate components of a header 11 to be assembled ~off-line~ under ideal working conditions. As clearly shown in FIG. 8, the components of the header 11 of the present invention include the cover 22, the diaphragm 30, the gasket 16 and the electrically conductive plate 36.
Thus, according to a preferred method of the present invention, the sequence of steps during the assembly of an electrochemical cell, such as electrochemical cell 10 described above, includes the step of placing the outer periphery 26 of the conductive cover 22 within the outer periphery 32 of the conductive diaphragm 30. The outer periphery 32 of the diaphragm 30 is then crimped to secure the outer periphery 26 of the cover 22 therein. Most preferably, the diaphragm 30 and the cover 22 will be arranged so that the central portion of the diaphragm 30 comprises a concave shape with respect to the cover 22.
The now unitary cover 22 and diaphragm 30 is then press-fitted into the insulating gasket 16 between the top portion 18 and the bottom portion 20 thereof.
The friction-fit between the crimped cover 22 and the diaphragm 30 and the gasket 16 is sufficiently secure to retain the cover 22 and the diaphragm 30 therein.
Preferably, the now secured cover 22 and diaphragm 30 are arranged so that the central portion of the diaphragm 30 abuts the top surface 44 of the weld plate 36 at the centrally located area 42. As shown in FIG. 8, it is preferable for the diaphragm 30 to include a convex shape with respect to the top surface 44 of the weld plate 36. The diaphragm 30 is then welded thereto by any suitable welding technique, such as laser welding, to form the weld joint 46. The weld formed during this welding operation is a ~critical weld,~
since it must break upon application of a predetermined pressure, and can be performed according to the method of the present invention in an ideal environment to assure that the weld is precisely formed within a predetermined tolerance.
After the foregoing welding operation is completed, the header 11 can be tested apart from the rest of the electrochemical cell 10 under ideal conditions. Additionally, the header 11 comprising the cover 22, the diaphragm 30, the weld plate 36 and the gasket 16 can now be stored until it is desirable to electrically connect same to the top portion 56 of the electrical lead 54 which extends through the open top 12 of an electrochemical cell as shown in FIG. 9.
It is desirable, according to the method of the present invention, for the bottom surface 48 of the conductive plate 36 to be welded to the electrical lead on the assembly line. The weld joint 58 formed between bottom surface 48 of the conductive plate 36 and top portion 56 of the electrical lead 54 is a ~non-criticaln weld joint. The non-critical weld joint 58 need not be made under ideal conditions because the weld joint 58 is not designed to break at a predetermined pressure, as is the critical weld joint 46. After this non-critical welding operation occurs, it is preferable for electrical lead 54 to be folded by a specially designed folding apparatus (not shown) so that the lead plate portion 56 will be arranged between the electrochemical circuit system (i.e., the anode, the cathode and the electrolyte solution) and the electrically conductive plate 36 when the header 11 is placed within the open -21- 2~99657 top portion 12 of the electrochemical cell 10. Finally, the top portion 12 of the cell is crimped into position to secure the cell into assembled position.
It is most desirable to place the header 11 into the top portion 12 of the housing in a manner such that the gasket 16 forms an insulating seal between the header 11 and the top portion of the housing 12 as clearly shown in FIG. 1.
As can be appreciated, the structure of the components, and especially diaphragm 30, of the present electrochemical cell 10 facilitates the foregoing advantageous sequence of assembly steps resulting in the manufacturing advantage as discussed above. Such a manufacturing advantage (i.e., the ~off-line~ assembly, testing and storage of the components of the header 11 of the present invention) has not heretofore been achieved.
While the foregoing description and figures are directed toward the preferred embodiment and method of the present invention, it should be appreciated that numerous modifications can be made to each of the individual components of the entire apparatus and the steps in the method as discussed above, and are indeed encouraged to be made in the materials, structure and arrangement of the disclosed method and embodiment without departing from the spirit and scope of the present invention. Thus, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by way of limitation of the present invention as described by the claims set forth below.
Claims (40)
1. A electrochemical cell comprising:
a housing having a top portion and a bottom portion, said bottom portion including an electrochemical circuit system therein, said electrochemical circuit system including cathode means for forming a positive electrode, anode means for forming a negative electrode and an electrolyte solution in contact with said anode means and said cathode means;
conductive diaphragm means arranged in said top portion of said housing for cutting off current flow between said anode means and said cathode means, said diaphragm means being adapted for quick movement between a first stable conducting position and a second stable non-conducting position upon direct application of gas pressure generated in said electrochemical circuit system in excess of a first predetermined pressure, and being unstable between said first and second stable positions; and conductive lead means for electrically connecting said electrochemical circuit system to said diaphragm means when said diaphragm means is in said first stable conducting position, and being remote from said diaphragm means when said diaphragm means is arranged in said second stable non-conducting position.
a housing having a top portion and a bottom portion, said bottom portion including an electrochemical circuit system therein, said electrochemical circuit system including cathode means for forming a positive electrode, anode means for forming a negative electrode and an electrolyte solution in contact with said anode means and said cathode means;
conductive diaphragm means arranged in said top portion of said housing for cutting off current flow between said anode means and said cathode means, said diaphragm means being adapted for quick movement between a first stable conducting position and a second stable non-conducting position upon direct application of gas pressure generated in said electrochemical circuit system in excess of a first predetermined pressure, and being unstable between said first and second stable positions; and conductive lead means for electrically connecting said electrochemical circuit system to said diaphragm means when said diaphragm means is in said first stable conducting position, and being remote from said diaphragm means when said diaphragm means is arranged in said second stable non-conducting position.
2. The electrochemical cell of Claim 1, further comprising an electrically conductive plate having a bottom surface and a top surface and at least one vented area defining at least one passageway extending therethrough, said conductive plate being arranged in said top portion of said housing below said conductive diaphragm means, said conductive lead means being directly connected to said electrically conductive plate and said diaphragm means being electrically connected directly to said electrically conductive plate when said diaphragm means is in said first stable conducting position and being disconnected from said electrically conductive plate when said diaphragm means is in said second stable non-conducting position.
3. The electrochemical cell of Claim 2, further comprising gasket means arranged in said top portion of said housing for sealing and electrically insulating said diaphragm means with respect to said top portion of said housing.
4. The electrochemical cell of Claim 3, wherein said electrically conductive plate includes an outer periphery and a central portion, said gasket means being at least partially disposed between the outer periphery of said electrically conductive plate and said diaphragm means to prevent electrical contact therebetween.
5. The electrochemical cell of Claim 1, wherein said diaphragm means includes a convex shape with respect to said electrochemical circuit system when arranged in said first stable conducting position and a concave shape with respect to said electrochemical circuit system when arranged in said second stable non-conducting position.
6. The electrochemical cell of Claim 1, wherein said diaphragm means includes burstable vent means for permitting gas to flow therethrough.
7. The electrochemical cell of Claim 6, wherein said burstable vent means comprises at least one area on said conductive diaphragm means which has been weakened so that said at least one area will burst upon application of gas pressure in excess of a second predetermined pressure applied directly to said diaphragm means, said second predetermined pressure being greater than said first predetermined pressure required to move said diaphragm means from said first conductive position to said second non-conductive position.
8. The electrochemical cell of Claim 2, wherein said diaphragm means provides a first predetermined resistance to counteract said gas pressure exerted thereto, and wherein said connection between said diaphragm means and said electrically conductive plate provides a second predetermined resistance to counteract said gas pressure exerted on said diaphragm means, said first predetermined resistance being greater than said second predetermined resistance.
9. The electrochemical cell of claim 8, wherein said first predetermined resistance is at least two times greater than said second predetermined resistance.
10. An electrochemical cell comprising:
a housing having a top portion and a bottom portion, said bottom portion including an electrochemical circuit system therein, said electrochemical circuit system including cathode means for forming a positive electrode, anode means for forming a negative electrode and an electrolyte solution in contact with said anode means and said cathode means;
a conductive diaphragm having an outer periphery and a central portion, said diaphragm being arranged in said top portion of said housing and being quickly movable from a conducting position to a non-conducting position on direct application of gas pressure thereto generated by chemical reactions in said electrochemical circuit system in excess of a first predetermined pressure, said diaphragm being unstable between said conducting position and said non-conducting position, said diaphragm having a convex shape with respect to said electrochemical circuit system when arranged in said conducting position and having a concave shape with respect to said electrochemical circuit system when arranged in said non-conducting position, said diaphragm including burstable vent means for permitting gas to flow therethrough upon exertion of a gas pressure thereto in excess of a second predetermined pressure, said second predetermined pressure being greater than said first predetermined pressure; and conductive lead means for electrically connecting said electrochemical circuit system to said diaphragm means when said diaphragm means is in said conducting position, and said diaphragm means being remote from said conductive lead means when said diaphragm means is arranged in said non-conducting position.
a housing having a top portion and a bottom portion, said bottom portion including an electrochemical circuit system therein, said electrochemical circuit system including cathode means for forming a positive electrode, anode means for forming a negative electrode and an electrolyte solution in contact with said anode means and said cathode means;
a conductive diaphragm having an outer periphery and a central portion, said diaphragm being arranged in said top portion of said housing and being quickly movable from a conducting position to a non-conducting position on direct application of gas pressure thereto generated by chemical reactions in said electrochemical circuit system in excess of a first predetermined pressure, said diaphragm being unstable between said conducting position and said non-conducting position, said diaphragm having a convex shape with respect to said electrochemical circuit system when arranged in said conducting position and having a concave shape with respect to said electrochemical circuit system when arranged in said non-conducting position, said diaphragm including burstable vent means for permitting gas to flow therethrough upon exertion of a gas pressure thereto in excess of a second predetermined pressure, said second predetermined pressure being greater than said first predetermined pressure; and conductive lead means for electrically connecting said electrochemical circuit system to said diaphragm means when said diaphragm means is in said conducting position, and said diaphragm means being remote from said conductive lead means when said diaphragm means is arranged in said non-conducting position.
11. The electrochemical cell of Claim 10, further comprising an electrically conducting plate having a bottom surface and a top surface and at least one vented area defining at least one passageway extending therethrough, said conducting plate being arranged in said top portion of said housing below said conductive diaphragm means, said conductive lead means being directly connected to said electrically conductive plate and said central portion of said diaphragm being electrically connected directly to said top surface of said electrically conductive plate when said diaphragm is in said conducting position and being disconnected from said electrically conductive plate when said diaphragm means is in said non-conducting position.
12. The electrochemical cell of Claim 11, further comprising a non-conductive gasket arranged between said outer periphery of said diaphragm and said top portion of said housing.
13. The electrochemical cell of Claim 12, wherein said non-conductive gasket is adapted to be at least partially disposed between said outer periphery of said electrically conductive plate and said conductive diaphragm to prevent electrical contact from occurring therebetween.
14. The electrochemical cell of Claim 13, further comprising an insulating plate arranged between said top portion and said bottom portion of said housing, said insulating plate having at least one non-conductive surface and having an opening therein defining a passageway between said bottom portion of said housing and said top portion thereof, said conductive lead extending from said electrochemical circuit system through said passageway of said insulating plate and being electrically connected to said electrically conductive plate.
15. The electrochemical cell of Claim 14, further comprising a conductive cover electrically connected to said conductive diaphragm and being at least partially arranged above said diaphragm in said top portion of said housing, said cover having at least one vented area defining a gas flow path therethrough.
16. The electrochemical cell of Claim 15, wherein said cover includes an outer periphery, said outer periphery of said cover being electrically connected to said outer periphery of said diaphragm, and being arranged within said gasket and said top portion of said housing so that a hermetic seal is formed between said electrochemical circuit system and a location outside of the cell prior to the bursting of said burstable vent means.
17. The electrochemical cell of Claim 10, wherein said anode means comprises carbon.
18. The electrochemical cell of Claim 10, wherein said diaphragm comprises a truncated-cone shape.
19. The electrochemical cell of Claim 10, wherein said diaphragm comprises a semi-spherical shape.
20. The electrochemical cell of Claim 11, wherein said diaphragm provides a first predetermined resistance to counteract said gas pressure exerted thereto, and wherein said connection between said diaphragm and said electrically conductive plate comprises a second predetermined resistance to counteract said gas pressure exerted on said diaphragm, said first predetermined resistance being greater than said second predetermined resistance.
21. The electrochemical cell of Claim 20, wherein said first predetermined resistance is at least two times greater than said second predetermined resistance.
22. A method of manufacturing an electrochemical cell comprising the steps of:
connecting the outer periphery of a conductive cover to the outer periphery of a conductive diaphragm:
arranging the connected outer peripheries of said cover and said diaphragm in an insulating gasket so that said cover, said diaphragm and said gasket are connected to form a unitary device;
providing a housing having an open top and including an electrochemical circuit system therein comprising an anode, a cathode, an electrolyte solution and a flexible electrical lead extending from said cathode;
electrically connecting said diaphragm of said unitary device to said cathode of said electrochemical cell; and placing said formed unitary device within the open top of said housing.
connecting the outer periphery of a conductive cover to the outer periphery of a conductive diaphragm:
arranging the connected outer peripheries of said cover and said diaphragm in an insulating gasket so that said cover, said diaphragm and said gasket are connected to form a unitary device;
providing a housing having an open top and including an electrochemical circuit system therein comprising an anode, a cathode, an electrolyte solution and a flexible electrical lead extending from said cathode;
electrically connecting said diaphragm of said unitary device to said cathode of said electrochemical cell; and placing said formed unitary device within the open top of said housing.
23. The method of Claim 22, further comprising the step of connecting a central portion of said diaphragm to an electrically conductive plate prior to performing the step of electrically connecting said diaphragm to said cathode of said electrochemical cell.
24. The method of Claim 23, wherein the step of electrically connecting diaphragm to said cathode of said electrochemical cell comprises the steps of placing the electrically conductive plate against said flexible electrical lead, and electrically connecting said conductive plate to said electrical lead extending from said cathode prior to placing said unitary device and said electrically conductive plate into the open top of said electrochemical cell.
25. The method of Claim 24, wherein the step of placing said unitary device and said electrically conductive plate into the open top of the electrochemical cell comprises the step of folding said electrical lead so that it is arranged between said electrochemical circuit system and said electrically conductive plate when said unitary device and said electrically conductive plate are placed within the open top of said housing of said electrochemical cell.
26. The method of Claim 25, wherein the step of connecting the outer peripheries of said cover and said diaphragm comprises placing the outer periphery of said cover within the outer periphery of said diaphragm and crimping the outer peripheries together.
27. The method of Claim 22, wherein the step of connecting the outer peripheries of said cover and said diaphragm comprises the step of arranging said diaphragm so that it has a concave shape with respect to said cover prior to connecting the outer peripheries thereof.
28. The method of Claim 22, wherein the step of arranging the connected outer peripheries of said cover and said diaphragm in a gasket comprises the step of press-fitting said cover and said diaphragm into said gasket.
29. The method of Claim 23, wherein the step of connecting the central portion of said diaphragm to an electrically conductive plate comprises the step of welding said diaphragm to a first surface on said electrically conductive plate so that said diaphragm has a convex shape with respect to said electrically conductive plate.
30. The method of Claim 24, wherein the step of placing said unitary device and said electrically conductive plate in said housing of said cell comprises the step of arranging said gasket so that it forms an insulating seal with respect to said housing.
31. The method of Claim 29, wherein the step of welding said diaphragm to said electrically conductive plate comprises the step of arranging said electrically conductive plate so that the outer periphery is adjacent a portion of said gasket.
32. The method of Claim 31, wherein the step of electrically connecting said conductive plate to an electrical lead extending from said cathode comprises the step of welding said electrical lead to a second surface of said electrically conductive plate.
33. The method of Claim 23, wherein the step of connecting the outer peripheries of said cover and said diaphragm comprises the step of arranging said diaphragm so that it has a concave shape with respect to said cover prior to connecting the outer peripheries thereof.
34. The method of Claim 33, wherein the step of connecting the outer peripheries of said cover and said diaphragm comprises the steps of placing the outer periphery of said cover within the outer periphery of said diaphragm and crimping the outer peripheries together.
35. The method of Claim 34, wherein the step of arranging the connected outer peripheries of said cover and said diaphragm in a gasket comprises the step of press-fitting said cover and said diaphragm into the gasket.
36. The method of Claim 35, wherein the step of connecting the central portion of said diaphragm to said electrically conductive plate comprises welding said diaphragm to a first surface of said electrically conductive plate, so that the diaphragm has a convex shape with respect to said electrically conductive plate.
37. The method of Claim 36, wherein the step of welding said diaphragm to said electrically conductive plate comprises the step of arranging said electrically conductive plate so that the outer periphery is adjacent a portion of said gasket.
38. The method of Claim 37, wherein the step of electrically connecting said conductive plate to an electrical lead extending from said cathode comprises the step of welding said electrical lead to a second surface of said electrically conductive plate remote from the first surface thereof.
39. The method of Claim 38, wherein the step of placing said unitary device and said electrically conductive plate in the top of said housing comprises the steps of:
folding said electrical lead so that it is arranged between said electrochemical circuit system and said electrically conductive plate when said unitary device and said electrically conductive plate are placed in the top of said housing; and arranging said gasket so that it forms an insulating seal between said diaphragm and said housing.
folding said electrical lead so that it is arranged between said electrochemical circuit system and said electrically conductive plate when said unitary device and said electrically conductive plate are placed in the top of said housing; and arranging said gasket so that it forms an insulating seal between said diaphragm and said housing.
40. The method of Claim 39 further comprising the step of crimping the top portion of said housing around said gasket after said gasket is arranged to form an insulating seal between said diaphragm and said housing.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US92782492A | 1992-08-10 | 1992-08-10 | |
| US07/927,824 | 1992-08-10 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2099657A1 CA2099657A1 (en) | 1994-02-11 |
| CA2099657C true CA2099657C (en) | 1998-04-07 |
Family
ID=25455307
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002099657A Expired - Lifetime CA2099657C (en) | 1992-08-10 | 1993-06-25 | Electrochemical cell and method of manufacturing same |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPH06196150A (en) |
| CA (1) | CA2099657C (en) |
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| KR102389409B1 (en) * | 2019-02-25 | 2022-04-22 | 주식회사 엘지에너지솔루션 | The Apparatus For Venting |
-
1993
- 1993-06-25 CA CA002099657A patent/CA2099657C/en not_active Expired - Lifetime
- 1993-08-09 JP JP5197050A patent/JPH06196150A/en active Pending
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8679670B2 (en) | 2007-06-22 | 2014-03-25 | Boston-Power, Inc. | CID retention device for Li-ion cell |
| US10020146B2 (en) | 2012-04-12 | 2018-07-10 | Kabushiki Kaisha Toyota Jidoshokki | Current interruption device and electric storage device using same |
| US11978919B2 (en) | 2018-07-13 | 2024-05-07 | HYDRO-QUéBEC | Battery safety vent assembly |
Also Published As
| Publication number | Publication date |
|---|---|
| CA2099657A1 (en) | 1994-02-11 |
| JPH06196150A (en) | 1994-07-15 |
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