CA2100391A1 - Method for crimp closure of coin cell batteries - Google Patents
Method for crimp closure of coin cell batteriesInfo
- Publication number
- CA2100391A1 CA2100391A1 CA002100391A CA2100391A CA2100391A1 CA 2100391 A1 CA2100391 A1 CA 2100391A1 CA 002100391 A CA002100391 A CA 002100391A CA 2100391 A CA2100391 A CA 2100391A CA 2100391 A1 CA2100391 A1 CA 2100391A1
- Authority
- CA
- Canada
- Prior art keywords
- case
- cell
- cap
- coin cell
- periphery
- 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.)
- Abandoned
Links
- 238000000034 method Methods 0.000 title claims abstract description 22
- 238000002788 crimping Methods 0.000 claims description 23
- 238000010276 construction Methods 0.000 claims description 15
- 238000010348 incorporation Methods 0.000 abstract 1
- 230000000052 comparative effect Effects 0.000 description 5
- 239000003792 electrolyte Substances 0.000 description 4
- 239000000203 mixture Substances 0.000 description 4
- 238000007789 sealing Methods 0.000 description 4
- 239000011230 binding agent Substances 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- -1 ethy-lene propylene diene Chemical class 0.000 description 3
- 239000007773 negative electrode material Substances 0.000 description 3
- 239000004033 plastic Substances 0.000 description 3
- 239000007774 positive electrode material Substances 0.000 description 3
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 239000006229 carbon black Substances 0.000 description 2
- 229910052744 lithium Inorganic materials 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 239000010935 stainless steel Substances 0.000 description 2
- 229910001220 stainless steel Inorganic materials 0.000 description 2
- 239000010963 304 stainless steel Substances 0.000 description 1
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- XTHFKEDIFFGKHM-UHFFFAOYSA-N Dimethoxyethane Chemical compound COCCOC XTHFKEDIFFGKHM-UHFFFAOYSA-N 0.000 description 1
- 229920002943 EPDM rubber Polymers 0.000 description 1
- 229910011259 LiCoOz Inorganic materials 0.000 description 1
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910000589 SAE 304 stainless steel Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 239000003125 aqueous solvent Substances 0.000 description 1
- 239000010426 asphalt Substances 0.000 description 1
- 230000000712 assembly Effects 0.000 description 1
- 238000000429 assembly Methods 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000003575 carbonaceous material Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 229920001971 elastomer Polymers 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000012212 insulator Substances 0.000 description 1
- 229910001416 lithium ion Inorganic materials 0.000 description 1
- 229910003002 lithium salt Inorganic materials 0.000 description 1
- 159000000002 lithium salts Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000000178 monomer Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229920000098 polyolefin Polymers 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 230000004224 protection Effects 0.000 description 1
- 239000000565 sealant Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 229910000314 transition metal oxide Inorganic materials 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/10—Primary casings; Jackets or wrappings
- H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
- H01M50/109—Primary casings; Jackets or wrappings characterised by their shape or physical structure of button or coin shape
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Sealing Battery Cases Or Jackets (AREA)
Abstract
IMPROVED METHOD FOR CRIMP CLOSURE
OF COIN CELL BATTERIES
ABSTRACT
A novel coin cell battery container which maintains its dimensions when radial forces are applied during crimp closure on assembly. A method of achieving a satisfactory axial seal with minimal bulging of the container is ach-ieved by incorporation of a weak section in the cell case prior to assembly.
OF COIN CELL BATTERIES
ABSTRACT
A novel coin cell battery container which maintains its dimensions when radial forces are applied during crimp closure on assembly. A method of achieving a satisfactory axial seal with minimal bulging of the container is ach-ieved by incorporation of a weak section in the cell case prior to assembly.
Description
2 ~ 9 1 IMPROVED METHOD FOR CRINP CLOSURE :~
OF COIN CEL~ BATTERIES
FIELD OF THE INVENTION
This invention pertains to a novel coin cell battery and a method of making the battery. More particularly, the invention relates to a novel coin cell battery which resists bulging during crimp closure.
BACRGROUND OF THE INVENTION
As electronics devices shrink in size and thickness in particular, the demand for small, thin batteries i5 con-stantly increasing. Coin cells (small batteries shaped like pucks) are typically used for memory backup and other similar low drain rate applications. The size of such batteries is indicated by convention using a 4-digit designation where the first two digits represent the diameter in mm and the last two digits represent the height times 10 in mm. (ie; a 2320 coin cell is 23 mm in diameter and 2.0 mm high). As the trend towards thin devices continues, so does the trend towards coin cell products with high aspect ratios (defined as the diameter/height).
However, the energy density of such batteries in a given application decreases substantially when the height oc-cupied by the battery container increases significantly with respect to the contents.
For mechanical reasons, the pieces comprising such battery containers are typically about 300 micrometers in thickness. Thus, as an example, only 70% of the total height of an ideal 2320 coin cell comprising a container of such thickness is available for the active contents of the battery. Further, if the faces of the container are not flat, then additional energy density is sacrificed. Using the same example, a bulge in each face of the container of only 50 micrometers effectively increases the coin cell ` ~
OF COIN CEL~ BATTERIES
FIELD OF THE INVENTION
This invention pertains to a novel coin cell battery and a method of making the battery. More particularly, the invention relates to a novel coin cell battery which resists bulging during crimp closure.
BACRGROUND OF THE INVENTION
As electronics devices shrink in size and thickness in particular, the demand for small, thin batteries i5 con-stantly increasing. Coin cells (small batteries shaped like pucks) are typically used for memory backup and other similar low drain rate applications. The size of such batteries is indicated by convention using a 4-digit designation where the first two digits represent the diameter in mm and the last two digits represent the height times 10 in mm. (ie; a 2320 coin cell is 23 mm in diameter and 2.0 mm high). As the trend towards thin devices continues, so does the trend towards coin cell products with high aspect ratios (defined as the diameter/height).
However, the energy density of such batteries in a given application decreases substantially when the height oc-cupied by the battery container increases significantly with respect to the contents.
For mechanical reasons, the pieces comprising such battery containers are typically about 300 micrometers in thickness. Thus, as an example, only 70% of the total height of an ideal 2320 coin cell comprising a container of such thickness is available for the active contents of the battery. Further, if the faces of the container are not flat, then additional energy density is sacrificed. Using the same example, a bulge in each face of the container of only 50 micrometers effectively increases the coin cell ` ~
3 ~ ~ ~
.
height by twice that amount. Such a cell now only has 65%
of the total height available for the active contents.
Therefore, in order to maximize energy density in cells of this size or of greater aspect ratios, it is critical not onIy to employ the thinnest containers possible but also to ensure that the container is as flat as is practical.
Bulging of coin cells, wherein the faces of the container adopt a convex shape, can occur for a variety of reasons. A common cause is the presence of internal pressure arising from the mechanical loading applied by the active contents of the battery or from gases generated inside. Additionally, forces generated as a result of cell closure can lead to bulging of the container. Coin cells with large diameter to height ratios are most sensitive to such forces.
Typically, crimp type closure is employed in coin cell construction. In this construction, a plastic gasket is used both as a seal and as an insulator between the two container pieces. The external surfaces of these container pieces serve to act as the battery terminals. The crimping process bends the periphery of one container piece and forces the sealing surface of said piece against the gasket thereby deforming it. By design, after crimping, residual forces exist between the sealing surfaces of both container pieces and the gasket thus effecting a seal. The radial component of these residual forces causes a bulging of the container to an extent determined by the design of the container and of course the magnitude of the radially applied force.
-SUI~M~RY OF THE INVENTION
A method is described for minimizing the bulging of a coin cell container that results from the crimping oper-ation used to close said container. A weak spot is created `
~ 21~3~ ~
in the periphery of the container piece to be crimped such that the edge of said piece can be deformed to apply substantial axial loads to the sealing gasket without applying a significant radial load.
-~
A method of minimizing the radial forces generated during the case crimping closure of a coin cell battery formed of a case and cap which comprises incorporating a weak section into the case periphery prior to cell con-struction, and crimping the case periphery about the cap.
A method as described above wherein the weak sectionis created by reducing the thickness of the cell case at the periphery prior to cell construction. The weak section can be created by stamping a shallow groove of small radius into the inside periphery of the cell case prior to cell construction. The case and cap have a circular shape. In this way, bulging of the coin cell container due to radial forces is minimized.
A coin cell battery comprising a cap and case wherein a ~eak sectlon is incorporated into the periphery of the case prior to cell construction such that a sharp discon-tinuity exists in the bent sidewall of the case after being crimped about the cap.
A coin cell battery as described above wherein the weak section comprises a shallow groove of small radius stamped into the inside periphery of the case. In the coin 30 cell battery, the case can have a dish shape and the cap `~
can have a disk shape.
`:
BRIEF DESCRIPTION OF TI~E DRAWINGS ~:
The following drawings illustrate specific embodi-ments of the invention but should not be construed as 2 ~
.
height by twice that amount. Such a cell now only has 65%
of the total height available for the active contents.
Therefore, in order to maximize energy density in cells of this size or of greater aspect ratios, it is critical not onIy to employ the thinnest containers possible but also to ensure that the container is as flat as is practical.
Bulging of coin cells, wherein the faces of the container adopt a convex shape, can occur for a variety of reasons. A common cause is the presence of internal pressure arising from the mechanical loading applied by the active contents of the battery or from gases generated inside. Additionally, forces generated as a result of cell closure can lead to bulging of the container. Coin cells with large diameter to height ratios are most sensitive to such forces.
Typically, crimp type closure is employed in coin cell construction. In this construction, a plastic gasket is used both as a seal and as an insulator between the two container pieces. The external surfaces of these container pieces serve to act as the battery terminals. The crimping process bends the periphery of one container piece and forces the sealing surface of said piece against the gasket thereby deforming it. By design, after crimping, residual forces exist between the sealing surfaces of both container pieces and the gasket thus effecting a seal. The radial component of these residual forces causes a bulging of the container to an extent determined by the design of the container and of course the magnitude of the radially applied force.
-SUI~M~RY OF THE INVENTION
A method is described for minimizing the bulging of a coin cell container that results from the crimping oper-ation used to close said container. A weak spot is created `
~ 21~3~ ~
in the periphery of the container piece to be crimped such that the edge of said piece can be deformed to apply substantial axial loads to the sealing gasket without applying a significant radial load.
-~
A method of minimizing the radial forces generated during the case crimping closure of a coin cell battery formed of a case and cap which comprises incorporating a weak section into the case periphery prior to cell con-struction, and crimping the case periphery about the cap.
A method as described above wherein the weak sectionis created by reducing the thickness of the cell case at the periphery prior to cell construction. The weak section can be created by stamping a shallow groove of small radius into the inside periphery of the cell case prior to cell construction. The case and cap have a circular shape. In this way, bulging of the coin cell container due to radial forces is minimized.
A coin cell battery comprising a cap and case wherein a ~eak sectlon is incorporated into the periphery of the case prior to cell construction such that a sharp discon-tinuity exists in the bent sidewall of the case after being crimped about the cap.
A coin cell battery as described above wherein the weak section comprises a shallow groove of small radius stamped into the inside periphery of the case. In the coin 30 cell battery, the case can have a dish shape and the cap `~
can have a disk shape.
`:
BRIEF DESCRIPTION OF TI~E DRAWINGS ~:
The following drawings illustrate specific embodi-ments of the invention but should not be construed as 2 ~
restricting or limiting the scope of the claims or protec-tion in any way:
Figure 1 illustrates a cross~sectional view of a coin cell battery of typical construction.
Figure 2a illustrates an enlarged cross-sectional view of the seal area of a typical coin cell battery prior to crimping.
Figure 2b illustrates an enlarged cross-sectional view of the seal area of a typical coin cell battery after crimping.
15Figure 3 illustrates a cross-sectional view of a coin cell battery case part in which a shallow circular groove in the periphery is incorporated prior to forming the case sidewall of the battery.
20Figure 4a illustrates an enlarged cross-sectional view of the seal area of a coin cell battery of a first conven- `
tional construction. -'"
Figure 4b illustrates an en]arged cross-sectional view of the seal area of a coin cell battery of a second conven-tional construction.
Figure 4c illustrates an enlarged cross-sectional view ;-of the seal area of a coin cell battery according to the 30 invention. -~
DETAILED DESCRIPTION OF SPECIFIC
EMBODIMENTS OF THE INVENTION
35Coin cell batteries are generally constructed as shown in Figure 1 which illustrates a cross-sectional view of a coin cell battery of typical construction. A cathode `~ 2~3~ :
Figure 1 illustrates a cross~sectional view of a coin cell battery of typical construction.
Figure 2a illustrates an enlarged cross-sectional view of the seal area of a typical coin cell battery prior to crimping.
Figure 2b illustrates an enlarged cross-sectional view of the seal area of a typical coin cell battery after crimping.
15Figure 3 illustrates a cross-sectional view of a coin cell battery case part in which a shallow circular groove in the periphery is incorporated prior to forming the case sidewall of the battery.
20Figure 4a illustrates an enlarged cross-sectional view of the seal area of a coin cell battery of a first conven- `
tional construction. -'"
Figure 4b illustrates an en]arged cross-sectional view of the seal area of a coin cell battery of a second conven-tional construction.
Figure 4c illustrates an enlarged cross-sectional view ;-of the seal area of a coin cell battery according to the 30 invention. -~
DETAILED DESCRIPTION OF SPECIFIC
EMBODIMENTS OF THE INVENTION
35Coin cell batteries are generally constructed as shown in Figure 1 which illustrates a cross-sectional view of a coin cell battery of typical construction. A cathode `~ 2~3~ :
electrode 1 and an anode electrode 2 form the active elements of the coin cell. A porous separator 3 is in-serted between the two electrodes 1 and 2. An electrolyte 4 is added to fill the porous spaces in the cathode 1, anode 2, and separator 3. The cap 5 and case 6 serve both as a container and as electrical terminals for the battery.
A plastic gasket 7 serves to isolate the cap 5 and case 6 electrically and to act as a seal. Typically, a sealant 8, normally bitumen, is used on the sealing surfaces to fill leak paths that result from minor imperfections in the parts.
A preferred embodiment of coin cell is that of a lithium ion-type rechargeable coin cell. In such a cell, a lithiated transition metal oxide such as LiCoOz, LiNio2, or the like, is used as the active positive electrode material. A tablet is pressed using a mixture of said positive electrode material, a binder such as EPDM (ethy-lene propylene diene monomer) rubber, and a conductive dilutant, normally carbon black, to create the cathode 1.
A graphitic or pseudo graphitic carbonaceous material is used as the active negative electrode material.
In a like manner, a tablet is pressed using a mixture of said negative electrode material, a binder, and an optional conductive dilutant to create the anode 2. A thin micro-porous polyolefin film such as Celgard 2502, is normally used as the separator 3. The electrolyte 4 normally comprises one or more lithium salts dissolved in a mixture of non-aqueous solvents.
The preferred choice of materials and amounts thereof will depend on the specific application requirements.
Lithium ion-type cells generally operate at high voltages (> 3 V). For this reason, special oxidation resistant grades of stainless steel are employed for the case 6 (the - :-; : ~ ~ ., .
`~ 21~{~3~
positive terminal). A Ni-plated mild steel or stainless steel cap 5 and polypropylene gasket 7 complete the assem-bly.
The cell is normally constructed in inverted configur-ation from that shown in Figure 1. Starting with the cap 5, components are stacked sequentially with electrolyte 4 added drop-wise to each porous component after stacking.
With the case 6 in place, crimping of the case on the cap is performed which completes the construction.
Figure 2a illustrates an enlarged cross-sectional view of the seal area of a typical cell prior to the crimping stage. Figure 2b depicts an enlarged cross-sectional view of the same seal area after crimping. Ideally, the plastic gasket 7 is crimped (compressed) at areas R and S in Figure 2b with the seal being effected at S. The bent segment 9 of the case sidewall 10 exerts an axial load indicated by a vertical arrow in this ideal case. For ease of assembly prior to crimping, the case sidewall 10 is tapered (shown in Figure 2a) creating a slight positive angle e with respect to the vertical side of the gasket 7.
;;, During crimping, it is desirable to close the case sidewall 10 in towards the gasket 7 thereby reducing or eliminating the angle ~. If the case sidewall 10 is closed excessively, then a significant radial load can be created that pushes on the cap sidewall 11. The direction of this radial load is indicated by a horizontal arrow in Figure 2b. Bending all or part of the case sidewall 10, such that it compresses the gasket 7 anywhere along its vertical side, can generate such significant radial force. Thus, ideally, a sharp discontinuous bend appears at point x in Figure 2b.
On certain conventional crimping apparatus using certain typical supplies of hardware, crimp closures can be 3 i3 ~
obtained that result in adequate application of axial load without associated excessive application of radial load.
However, it is not possible to achieve such results with all supplies of hardware as will be demonstrated in the examples to follow. In such cases, the hardware and closure process are not as robust or tolerant of variation as would be desired.
A simple means o* achieving the desired features of a satisfactory coin cell closure is illustrated in Figure 3.
During preparation of the case 6, a circular grooved weak section 13 is incorporated into the inside periphery before forming the case sidewall 10 (not shown in this Figure).
Preferably the weak section 13 comprises a shallow groove of small radius in profile which does not overly or unduly lessen the strength of the case 6. The groove 13 can be easily formed in the case 6 using conventional metal stamping methods. The groove-shaped weak section 13 is located in the inner surface of the case 6 at a radius equivalent to point x shown in Figure 2b.
The presence of a suitably weakened section at point x increases the robustness or tolerance of the crimping process to variations in supplied parts or to the crimping apparatus employed, by ensuring that minimal radial forces are created during crimping.
Comparative Example 1 -A ~320 lithium ion type rechargeable coin cell was fabricated as described previously in association with Figure 1. LiNio2 powder was used as the active positive electrode material and a coke-like carbon (from Conoco Inc.) was used as the active negative electrode material.
EPDM rubber and Super S~ carbon black (from Chemetals) were used as binder and conductive dilutant respectively for both electrodes. Celgard ~ 2502 was used as a separator and .,.,; .. : .. . - - - .. : , --- - - . , , . . ,:- . , -::: . . - -:
:- ` 2 ~3~
the electrolyte used was a solution of lM LiN(CF3So2)z in an equivolume mixture of propylene carbonate and dimethoxye-thane solvents. The container pieces consisted of a case made of Shomac 30-2~ alloy and a 304 stainless steel can both 300 micrometers in thickness. The case sidewall was however appreciably thinner than 300 micrometers due to stretching of the material during the forming operation of the part.
10The coin cell was assembled as described previously using a conventional progressive two step crimping process.
The height specification for this cell was 1.95 (+ 0.05, -0.10) mm. This cell fell within the appropriate specifica-tion limit. A cross-section of this cell was obtained. An enlarged cross-sectional view of the seal area of this coin cell is shown in the sketch of Figure 4a. As desired, a sharp discontinuous bend was created at point x which roughly coincides with the point where stretching and thinning of the case commenced as a result of the case ~
20 forming operation. ~;
.
Comparative Example 2 A 2320 coin cell similar to that of Comparative Example 1 was prepared except that no significant stretch-ing, and hence thinning, of the case sidewall occurred during the forming operation of the case. After assembly using the same crimping process, the height of the cell significantly exceeded the upper specification limit of 2.0 mm. A cross-section of the c211 was obtained. An enlarged cross-sectional view of the seal area of this coin cell is shown in Figure 4b. In this case, a sharp discontinuous bend has not been created as desired. As a consequence, significant undesirable compression of the gasket has occurred at point y. There are significant axial and radial forces applied by the case sidewall in this example, 0 ~
resulting in a cell with an adequate seal but also one with excessive bulging of the container.
A theoretical analysis was performed to estimate the possible bulging that could arise due to excessive radial forces. The compressive strength of polypropylene is of the order of 5000 psi. The area presented by the cap sidewall is of the order of 0.04 square inches. If the crimping process compresses the gasket over all of this effective area, total radial forces acting on the cap of the order of 220 lbs would be created. Finite element analyses performed for this cap design showed that bulging of the order of 110 micrometers at the centre of the cap would be expected if such forces were uniformly applied over the cap sidewall.
These two comparative examples demonstrate that it is possible to obtain an effective seal without excessive bulging due to the application of excessive radial force on such a coin cell using a typical set of hardware and a typical crimping process. However, the process is not robust or tolerant in that a similar result was not ob-.: :
tained when using a case part of uniform thickness.Furthermore, it is clearly possible that excessive radial force can result in significant bulging of the cap.
Invention Example ~ :~
A 2320 coin cell similar to that of Comparative Example 2 was prepared except that, prior to forming the sidewall of the case, a shallow groove 13 was stamped into the case blank at a radius equivalent to that of point x in Figure 2b. The groove profile radius was 0.1 mm and penetrated the case approximately .05 mm. After assembly using the same crimping process, the cell height was within that required by the specification. Again, a cross-section of the cell was obtained. An enlarged cross-sectional view ,,. ~ ~ .. ,- : -1 . ~ : . i ., ~ .. .. -. ~, . - :
, ,. .... ~
- ~ 2 ~
of the seal area of this coin cell is shown in Figure 4c.
In this case, it is noted that a sharp discontinuous bend has been created at point x, corresponding to the location of the weakening groove. No significant radial compression of the gasket is evident yet a significant axial compres-sion occurred. This coin cell was leak tight.
This Example demonstrates the effectiveness of intro-ducing a weak section in the case of a coin cell for the purpose of obtaining an adequate seal with minimal bulging of the container as a result of crimp closure. -As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this inven-tion without departing from the spirit or scope thereof.
While the example in the foregoing disclosure demonstrated only one preferred option for introducing a desirable weak section in the case, many other satisfactory alternatives should be apparent to those skilled in the art. According-ly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
A plastic gasket 7 serves to isolate the cap 5 and case 6 electrically and to act as a seal. Typically, a sealant 8, normally bitumen, is used on the sealing surfaces to fill leak paths that result from minor imperfections in the parts.
A preferred embodiment of coin cell is that of a lithium ion-type rechargeable coin cell. In such a cell, a lithiated transition metal oxide such as LiCoOz, LiNio2, or the like, is used as the active positive electrode material. A tablet is pressed using a mixture of said positive electrode material, a binder such as EPDM (ethy-lene propylene diene monomer) rubber, and a conductive dilutant, normally carbon black, to create the cathode 1.
A graphitic or pseudo graphitic carbonaceous material is used as the active negative electrode material.
In a like manner, a tablet is pressed using a mixture of said negative electrode material, a binder, and an optional conductive dilutant to create the anode 2. A thin micro-porous polyolefin film such as Celgard 2502, is normally used as the separator 3. The electrolyte 4 normally comprises one or more lithium salts dissolved in a mixture of non-aqueous solvents.
The preferred choice of materials and amounts thereof will depend on the specific application requirements.
Lithium ion-type cells generally operate at high voltages (> 3 V). For this reason, special oxidation resistant grades of stainless steel are employed for the case 6 (the - :-; : ~ ~ ., .
`~ 21~{~3~
positive terminal). A Ni-plated mild steel or stainless steel cap 5 and polypropylene gasket 7 complete the assem-bly.
The cell is normally constructed in inverted configur-ation from that shown in Figure 1. Starting with the cap 5, components are stacked sequentially with electrolyte 4 added drop-wise to each porous component after stacking.
With the case 6 in place, crimping of the case on the cap is performed which completes the construction.
Figure 2a illustrates an enlarged cross-sectional view of the seal area of a typical cell prior to the crimping stage. Figure 2b depicts an enlarged cross-sectional view of the same seal area after crimping. Ideally, the plastic gasket 7 is crimped (compressed) at areas R and S in Figure 2b with the seal being effected at S. The bent segment 9 of the case sidewall 10 exerts an axial load indicated by a vertical arrow in this ideal case. For ease of assembly prior to crimping, the case sidewall 10 is tapered (shown in Figure 2a) creating a slight positive angle e with respect to the vertical side of the gasket 7.
;;, During crimping, it is desirable to close the case sidewall 10 in towards the gasket 7 thereby reducing or eliminating the angle ~. If the case sidewall 10 is closed excessively, then a significant radial load can be created that pushes on the cap sidewall 11. The direction of this radial load is indicated by a horizontal arrow in Figure 2b. Bending all or part of the case sidewall 10, such that it compresses the gasket 7 anywhere along its vertical side, can generate such significant radial force. Thus, ideally, a sharp discontinuous bend appears at point x in Figure 2b.
On certain conventional crimping apparatus using certain typical supplies of hardware, crimp closures can be 3 i3 ~
obtained that result in adequate application of axial load without associated excessive application of radial load.
However, it is not possible to achieve such results with all supplies of hardware as will be demonstrated in the examples to follow. In such cases, the hardware and closure process are not as robust or tolerant of variation as would be desired.
A simple means o* achieving the desired features of a satisfactory coin cell closure is illustrated in Figure 3.
During preparation of the case 6, a circular grooved weak section 13 is incorporated into the inside periphery before forming the case sidewall 10 (not shown in this Figure).
Preferably the weak section 13 comprises a shallow groove of small radius in profile which does not overly or unduly lessen the strength of the case 6. The groove 13 can be easily formed in the case 6 using conventional metal stamping methods. The groove-shaped weak section 13 is located in the inner surface of the case 6 at a radius equivalent to point x shown in Figure 2b.
The presence of a suitably weakened section at point x increases the robustness or tolerance of the crimping process to variations in supplied parts or to the crimping apparatus employed, by ensuring that minimal radial forces are created during crimping.
Comparative Example 1 -A ~320 lithium ion type rechargeable coin cell was fabricated as described previously in association with Figure 1. LiNio2 powder was used as the active positive electrode material and a coke-like carbon (from Conoco Inc.) was used as the active negative electrode material.
EPDM rubber and Super S~ carbon black (from Chemetals) were used as binder and conductive dilutant respectively for both electrodes. Celgard ~ 2502 was used as a separator and .,.,; .. : .. . - - - .. : , --- - - . , , . . ,:- . , -::: . . - -:
:- ` 2 ~3~
the electrolyte used was a solution of lM LiN(CF3So2)z in an equivolume mixture of propylene carbonate and dimethoxye-thane solvents. The container pieces consisted of a case made of Shomac 30-2~ alloy and a 304 stainless steel can both 300 micrometers in thickness. The case sidewall was however appreciably thinner than 300 micrometers due to stretching of the material during the forming operation of the part.
10The coin cell was assembled as described previously using a conventional progressive two step crimping process.
The height specification for this cell was 1.95 (+ 0.05, -0.10) mm. This cell fell within the appropriate specifica-tion limit. A cross-section of this cell was obtained. An enlarged cross-sectional view of the seal area of this coin cell is shown in the sketch of Figure 4a. As desired, a sharp discontinuous bend was created at point x which roughly coincides with the point where stretching and thinning of the case commenced as a result of the case ~
20 forming operation. ~;
.
Comparative Example 2 A 2320 coin cell similar to that of Comparative Example 1 was prepared except that no significant stretch-ing, and hence thinning, of the case sidewall occurred during the forming operation of the case. After assembly using the same crimping process, the height of the cell significantly exceeded the upper specification limit of 2.0 mm. A cross-section of the c211 was obtained. An enlarged cross-sectional view of the seal area of this coin cell is shown in Figure 4b. In this case, a sharp discontinuous bend has not been created as desired. As a consequence, significant undesirable compression of the gasket has occurred at point y. There are significant axial and radial forces applied by the case sidewall in this example, 0 ~
resulting in a cell with an adequate seal but also one with excessive bulging of the container.
A theoretical analysis was performed to estimate the possible bulging that could arise due to excessive radial forces. The compressive strength of polypropylene is of the order of 5000 psi. The area presented by the cap sidewall is of the order of 0.04 square inches. If the crimping process compresses the gasket over all of this effective area, total radial forces acting on the cap of the order of 220 lbs would be created. Finite element analyses performed for this cap design showed that bulging of the order of 110 micrometers at the centre of the cap would be expected if such forces were uniformly applied over the cap sidewall.
These two comparative examples demonstrate that it is possible to obtain an effective seal without excessive bulging due to the application of excessive radial force on such a coin cell using a typical set of hardware and a typical crimping process. However, the process is not robust or tolerant in that a similar result was not ob-.: :
tained when using a case part of uniform thickness.Furthermore, it is clearly possible that excessive radial force can result in significant bulging of the cap.
Invention Example ~ :~
A 2320 coin cell similar to that of Comparative Example 2 was prepared except that, prior to forming the sidewall of the case, a shallow groove 13 was stamped into the case blank at a radius equivalent to that of point x in Figure 2b. The groove profile radius was 0.1 mm and penetrated the case approximately .05 mm. After assembly using the same crimping process, the cell height was within that required by the specification. Again, a cross-section of the cell was obtained. An enlarged cross-sectional view ,,. ~ ~ .. ,- : -1 . ~ : . i ., ~ .. .. -. ~, . - :
, ,. .... ~
- ~ 2 ~
of the seal area of this coin cell is shown in Figure 4c.
In this case, it is noted that a sharp discontinuous bend has been created at point x, corresponding to the location of the weakening groove. No significant radial compression of the gasket is evident yet a significant axial compres-sion occurred. This coin cell was leak tight.
This Example demonstrates the effectiveness of intro-ducing a weak section in the case of a coin cell for the purpose of obtaining an adequate seal with minimal bulging of the container as a result of crimp closure. -As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this inven-tion without departing from the spirit or scope thereof.
While the example in the foregoing disclosure demonstrated only one preferred option for introducing a desirable weak section in the case, many other satisfactory alternatives should be apparent to those skilled in the art. According-ly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
Claims (8)
1. A method of minimizing the radial forces generated during the case crimping closure of a coin cell battery formed of a case and cap which comprises incorporating a weak section into the case periphery prior to cell con-struction, and crimping the case periphery about the cap.
2. A method as claimed in claim 1 wherein the weak section is created by reducing the thickness of the cell case at the periphery prior to cell construction.
3. A method as claimed in claim 2 wherein the weak section is created by stamping a shallow groove of small radius into the inside periphery of the cell case prior to cell construction.
4. A method as claimed in claim 2 wherein the case and cap are circular, and the case is formed to have a dish shape before being crimped on the circular cap.
5. A method as in claim 1, 2, 3 or 4 wherein bulging of the coin cell container due to said radial forces is minimized.
6. A coin cell battery comprising a cap and case wherein a weak section is incorporated into the periphery of the case prior to cell construction such that a sharp discon-tinuity exists in the bent sidewall of said case after being crimped about the cap.
7. A coin cell battery as claimed in claim 6 wherein the weak section comprises a shallow groove of small radius stamped into the inside periphery of the case.
8. A coin cell battery as claimed in claim 7 wherein the case has a circular dish shape, and the cap has a dish shape.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002100391A CA2100391A1 (en) | 1993-07-13 | 1993-07-13 | Method for crimp closure of coin cell batteries |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
CA002100391A CA2100391A1 (en) | 1993-07-13 | 1993-07-13 | Method for crimp closure of coin cell batteries |
Publications (1)
Publication Number | Publication Date |
---|---|
CA2100391A1 true CA2100391A1 (en) | 1995-01-14 |
Family
ID=4151924
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002100391A Abandoned CA2100391A1 (en) | 1993-07-13 | 1993-07-13 | Method for crimp closure of coin cell batteries |
Country Status (1)
Country | Link |
---|---|
CA (1) | CA2100391A1 (en) |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5804327A (en) * | 1995-05-05 | 1998-09-08 | Rayovac Corporation | Thin walled electrochemical cell |
US5904998A (en) * | 1995-05-05 | 1999-05-18 | Rayovac Corporation | Metal-air cathode can and electrochemical cell made therewith |
US5945234A (en) * | 1995-05-05 | 1999-08-31 | Rayovac Corporation | Metal-air cathode can having reduced corner radius and electrochemical cells made therewith |
US6205831B1 (en) | 1998-10-08 | 2001-03-27 | Rayovac Corporation | Method for making a cathode can from metal strip |
US6248463B1 (en) | 1997-05-05 | 2001-06-19 | Rayovac Corporation | Metal-air cathode can and electrochemical cell made therewith |
CN104779360A (en) * | 2014-01-14 | 2015-07-15 | 福特全球技术公司 | Electric vehicle battery cell having conductive case |
-
1993
- 1993-07-13 CA CA002100391A patent/CA2100391A1/en not_active Abandoned
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5804327A (en) * | 1995-05-05 | 1998-09-08 | Rayovac Corporation | Thin walled electrochemical cell |
US5904998A (en) * | 1995-05-05 | 1999-05-18 | Rayovac Corporation | Metal-air cathode can and electrochemical cell made therewith |
US5945234A (en) * | 1995-05-05 | 1999-08-31 | Rayovac Corporation | Metal-air cathode can having reduced corner radius and electrochemical cells made therewith |
US6042957A (en) * | 1995-05-05 | 2000-03-28 | Rayovac Corporation | Thin walled electrochemical cell |
US6280876B1 (en) | 1995-05-05 | 2001-08-28 | Rayovac Corporation | Metal-air cathode can having reduced corner and electrochemical cells made therewith |
US6248463B1 (en) | 1997-05-05 | 2001-06-19 | Rayovac Corporation | Metal-air cathode can and electrochemical cell made therewith |
US6205831B1 (en) | 1998-10-08 | 2001-03-27 | Rayovac Corporation | Method for making a cathode can from metal strip |
CN104779360A (en) * | 2014-01-14 | 2015-07-15 | 福特全球技术公司 | Electric vehicle battery cell having conductive case |
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