CA2105911A1 - Coin cell battery employing concave shaped container pieces - Google Patents
Coin cell battery employing concave shaped container piecesInfo
- Publication number
- CA2105911A1 CA2105911A1 CA002105911A CA2105911A CA2105911A1 CA 2105911 A1 CA2105911 A1 CA 2105911A1 CA 002105911 A CA002105911 A CA 002105911A CA 2105911 A CA2105911 A CA 2105911A CA 2105911 A1 CA2105911 A1 CA 2105911A1
- Authority
- CA
- Canada
- Prior art keywords
- battery
- coin cell
- cap
- case
- cathode
- 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
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 of a single cell or a single battery
- H01M50/102—Primary casings, jackets or wrappings of a single cell or a single battery characterised by their shape or physical structure
- H01M50/109—Primary casings, jackets or wrappings of a single cell or a single battery 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
Abstract
COIN CELL BATTERY EMPLOYING
CONCAVE SHAPED CONTAINER PIECES
ABSTRACT OF THE DISCLOSURE
Concave shaped pieces can be employed for coin cell battery containers in order to apply significant preloading pressure to the solid contents of the battery.
The preloading pressure may be effective in counteracting an increase in internal pressure of the battery during operation. In certain lithium ion coin cell batteries, the invention is used to effectively arrest an increase in battery thickness after assembly.
CONCAVE SHAPED CONTAINER PIECES
ABSTRACT OF THE DISCLOSURE
Concave shaped pieces can be employed for coin cell battery containers in order to apply significant preloading pressure to the solid contents of the battery.
The preloading pressure may be effective in counteracting an increase in internal pressure of the battery during operation. In certain lithium ion coin cell batteries, the invention is used to effectively arrest an increase in battery thickness after assembly.
Description
COIN CELL BATT~RY EMPLOYI~G
CONC~VE 8X~PED CONTAINER PIECE~
FIE~D OF THE INVENTION
The invention relates to the field of batteries.
In particular, it relates to coin cell ~ize batteries and the hardware employed for the container of such batteries.
B~ACKGROUND OF THE INVENT ON
, Coin cell batterie~ are small, puck shaped galvanic cells that are used in a variety of commercial electronics applications. Typically, these are low drain rate applications such as memcry back-up, watches, and the like. However, since power requirements ar~ being reduced for high drain rate electronics devices, the demand ~or larger and/or higher drain rate coin cell batteries is incr~asing. It is desirable in most applications that the ~:~power source have a slim pro~ile. Thusl in order to gek ~:high drain rate in a slim container, it is prP~erable to use larger coin cell diameters and smaller coin call thicknesses. A four digit convention is used to designate coin cell size where the first two digits indicate the diameter in mm and the last two digit~ indicate the overall thickness times ten in mm. A typical commercial product is ~:a 2320 coin cell which is therefore 23 mm in diameter and 2.0 mm thick.
In many electronics applications, it is the maximum thickness of the coin cell that determines whether it will fit in the allocated space. Thus, it is preferable that the faces of the coin cell be ~lat in order to 135 maximize the amount of active material contained in the coin cell. Additionally, it is preferable to use the minimum material thickness for the pieces comprising the coin cell container, again to maximize the amount o~ active ~matexial contained therein.
:
~--~ 2 1 0 ~
Generally, some pressure is applied to the coin cell container by the contents. This can be unintended, for example as a result of the generation of gaseous products during operation of the battery. Pressure can also be applied deliberatelyO For example, U.S. Patent No.
2,971,999 discusses a battery wher~in a spring is inserted between a container wall and the cell electrodes in order to maintain electrical contact between the cell electrodes and the container wall even when internal pressure causes the container wall to swell.
The presence of internal pressure in a coin cell battery tends to deform the container. The extent to which this deformation increases the maximum thickness of the coin cell is a function of the coin cell diameter~ the thickness of the pieces comprising the coin cell container, and, of course, the internal pressure. Larger cell diameters and thinner container pieces result in a battery that is morP sensitive to deformation at a given internal pressure.
SUMMARY QF THE INVENTION
The coin cell battery of this invention is one that uses pieces for the container thereof that are concave shaped prior to assembly. ~fter assembly of the pieces into a coin cell battery, the container applies a preloading pressure to the solid contents, hereinafter referred to as the electrode stack, inside the cell.
Furthermore, the concave shape can be chosen such that, after assembly, the pieces of the container are deformed as a result of generation of this preloading pressure such that the faces of the battery are ef~ectively ~lat.
` ~ 2~9 ., Hardware specific to one possible coin cell size is disclosed that, if suitably shaped, allows the practical application of preloading pr~ssures from about zero up to about 40 psi. In addition, a specific coin cell battery example using lithium ion type electrochemistry is disclosed.
Lithium ion batteries ~enerally employ lithiated transition metal oxides as the active cathode mat~rial, carbonaceous compounds as the active anode material, and lithium salts dissolved in one or more non-aqueous solven~s as the electrolyte. ~he specific battery disclosed is a 2320 coin cell using LiNio2 as the active cathode material, a coke-like carbon as the active anode material, and lM
LiN(CF3S02)2in ethylene carbonate (EC)/dimethoxyethane (DME) solvants as the electrolyte. ;.
This invention pertains to a general method that can be used to apply preloading pressure to the electrode stack of a coin cell battery. The purpo~e for the application of said preloading pressure can be to prevent expansion of the cell electrodes, to maintain ePfective electrical contact to the electrodes, to counteract gas ; .:
pressure generated a~ a result of operation of the cell, or for any oth~x such reason.
In addition, a method is descri~ed that allows th~ application of preloading pressure in a coin cell battery such that the faces of the battery are effectively ~0 flat after assembly is complete. For a given cell size and a given thickness o~ the container pieces, it is possible to achieve preloading press~lres over a certain range. A
method for achieving a range from zero to about 40 psi specific to a 2320 size coin cell battery with 300 ~m thick ~.ontainer pi~ces is also disclosed.
~, , ~" ~""",~, ~.i~ ~,i!.'.~,'', ~ i ~ ` 2 ~
...
BRIEF DESCRIPTION OF THE D~WINGS
., In drawings which illustrate specific embodiments of the invention, but whi~h should not be construed as restricting the spirit or scope of the invention in any way:
Figure 1 shows a cross-section of a typical coin cell battery.
' 1~
Figure 2 shows a cross-section of the coin cell battery o~ Figure 1 as it would appear i~ deformed due to a uniform increase in internal pressure.
15Figure 3 shows a cross-section of the invention case and cap container hardware for a coin cell battery.
. ~:
Figure 4a shows a two stage die set suitably modified for purposes of crimp closure of the invention coin cell battery~
Figure 4b shows an enlarged cross-sectional view o~ the first stage die set and coin cell assembly during crimp closure.
:
Figure 4c shows an enlarged cross-sectional view of the second stage di~ set and coin cell assembly during crimp closure. -~
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
OF TEIE INVENTION
A typical coin cell battery is depicted in Figure 1. The solids in the cell are inserted in a stack consisting of a cathode 10, a separator 11, and an anods 12~ An electrolyte 13 permeates the pores o~ the separator :~ 11 and, where applicable, the poras of the cathode 10 and anode 12. A housing conslsting of a metal case 14, a gasket 15, and a metal cap 16 are conventionally used as a container. The metal case 14 and metal cap 16 serve additionally as external electrical contacts to the electrodes ~ithin. Conventional cases 14 and caps 16 have flat faces prior to assembly. The housing is sealed by crimping the edge of the case 17 inwards, thereby deforming the gasket and setting a psrmanent load that acts on the edges of both the case 14 and the cap 16 as well as on the gasket 15.
. , If the coin cell as shown in Figure 1 is subjected to a uniform increase in internal pressure, deformation of the container is expected as shown in Figure 2. (The extent of elastic deformation has been exaggerated for purposss of illustration.) Both the case 14 and cap 16 assume a convex shape that is a function of the diameter of the cell, thickness of the case 1~ and cap 16, and the materials of construction. Said deformation, if within the elas~ic limits of the hardware/ is by definition reversible upon removal of the applied pressure and can be calculated by conventional stress/strain methods if the internal pressure is known. The amount of deformation or bulge measur~d at the centre o~ the case 14 and cap 16 has been denoted by arrows X1 and X2 respectively.
The invention battery is on- that employs a case 14 and cap 16 that are concave shaped prior to assembly of the battery. The specific shape employed for a given preloading pressure and given hardware dimensions is the inverse to the convex shape expected from ~lat hardware of the same dimensions subjected to uniform application of the same prelcading pre~sure. Figure 3 shows hardware with a concave shape of the invention. (The extent of the concave shaping has been exag~erated for purposes of illustration.~
The case 14 and cap 16 are shaped such that their centres are an amoun~ indicated by arrows Yl and Y2 respectively ~,x :,. - - ,. - , ~ . : , ::
from the flat. Thus, the~ concave shaped pieces of the invention are the inverse of the convex shaped pieces of Figure 2 if the hardware dimensions are the same and if the respective magnitudes Yl and Y2 are equal to Xl and X2. In order to achieve the goals of the invention, the desired preloading pressure must be small enough so as not to inelastically deform the given hardware. In such a case, the container can be crimped shut such that the desired preload is applied with the resulting faces of the container being effectively flat after assembly.
The invention battery thus differs significantly ~rom that described in U.S. Patent 3,928,077 wherein a practically planar portion of the container is inwardly o~fset in order to maintain efective contact to the internal electrodes and thus to count~ract the effect of internal pressure on the cell container. The planar portion of the container in said patent does not apply uniform pressure over the entire electrode ~tack nor does : 20 it result in a cell with ~aces that are effeotively flat after assembly.
Increased di~ficulty in cell assembly results from the use of concave shapsd pieces for the container.
~he electrode stack is conventionally created by stacking one component at a time on top of either a gasket 15 - case 14 subassembly or a gasket 15 - cap 16 subassembly. The concave shape of the container does not allow the electrode stack to lie flat and thus the stack may be more easily disturbed during assembly. In addition, the case 14 and cap 16 must be manipulated into their final respective positions during the crimping closure process, rather than prior to the crimping process. To accomplish this, only minor modifications to conventional coin cell crimping dies ¦ 35 are required.
Figure 4a shows a conventional two stage coin cell crimping die set 20. The first stage die 21 consists of a base 22 and a precrimper 23. Figure 4b shows an enlarged cross~sectional view of the first stage die and coin cell assembly during crimping. The bottom surface 24 of the precrimper 23 is shaped to effect a partial crimp closure of the coin cell. An uncrimped coin cell 2S is placed in the base 22, oriented with the cap 16 upwards as shown. The precrimper 23 is then brought down vertically~
The crimping begins when the shaped bottom surface 24 of the precrimper 23 contacts the perimeter of the case 14.
The design of the shaped bottom surface 24 is such that some limited loading is applied to perimeter of the cap face 26 during this process. The first stage crimping i~
complete once the faces of the precrimper 23 and base 22 contact each other. The components of the partially crimped coin cell (not shown) are now reasonably fixed in place.
Final crimping of the partially crimped coin cell takes place in the second stage die 29. The construction and operation of the second stage die 29 are similar to that of the first stage die 21. Figure 4c shows an enlarged cross-sectional view of the second stage die and partially crimped coin cell 25a during crimping. Similar items are identified with a number corresponding to those used in the ~irst stage with a suffix "a" (ie. second stage base is 22a). The surface 24a of the cximper 23a is shaped to effect the final desired shape of the assembled coin cell. The design o~ the surface 24a is such that increased loading is applied to the cap face ~7a as the crimper 23a travels downwards. Thus, the cap 16 is manipulated into its final position concurrent with the final crimping of the perimeter of the case 14.
The invention has been employed succ ssfully in the construction of certain coin cell batteries employing lithium ion type electrochemistry. In this instance, a signi~icant internal pressure existed during the normal operation of said batteries. The examples to follow are presented to illustrate the application of the invention in this specific case but should not be construed as limiting the scope or spirit of the invention in any way.
COMPARATIVE EX~MPL~ -It was considered desirable to fabricate 2320 size coin cell batteries as shown in Figure 1 using a speci~ic lithium ion type electrochemistry comprising use of LiNio2 as the active cathode material, ~oke like carbon as the active anode material and a lM solution of LiN(CF3So2)2 salt dissolved in equal volumes of ethylene carbonate ~EC) and dimethoxyethane (DME) solvents as the electrolyte.
Cathodes were fabricated in the ~ollowing manner.
A cathoda slurry was prepared using LiNio2 powder as the active material, Super S carbon black (trade-mark of Ensagri) as a conductive dilutant, ethylene propylene diene monomer (EPDM) rubber as a bind4r, and cyclohexane as a solvent for the binder. After blending, the cyclohexane was evaporated away to create a cathode powder blend in which the ratio of the components LiNio2- Super S: EPDM by weight was 100:10:2. Us.ing this dry powder blend, tablets were formed in a press in a size close to that desired for 2320 cells.
1:
In a similar manner, anode tablets were prepared using Conoco XP coke (product of Conoco Inc.) as the active material in which the ratio of the components coke: Super S: EPDM by weight was 100~5:2.
In the ~atteries of this example, Celgard 2502 ~trade-mark of Hoechst-Celanese) was used as a separator material~ Conventional 2320 cap and case hardware with -~ 2 1 ~
g flat faces prior to assembly were used. The cap material was annealed 304 stainless steel and the case material was a special corrosion resistant grade of stainless steel known as Shomac 30-2 (trade~mark). The thickness of the material in both instances was 300 ~m. Coin cells were fabricated as described in a conventional manner without a significant intended preloading pressure. Some slight inter~erence (of order of 50 ~m or less) between the container pieces and the electrode stack was intended to ensure electrical contact was maintained with the cathode and anode tablets. ~fter assembly to this point, the coin cell faces are effectively flat.
As constructed, this type of lithium ion cell is in the discharged statel Upon recharging, there is a net expansion in the total volume occupied by the solids inside. Additionally, gas can be generated inside as a result o~ certain chemical reactions that take place during this process. For these reasons, additional internal pressure is applied to the cell container on recharge and consequently an increase in overall cell thickness is expected.
Several coin cell batteries were fabricated and ~5 recharged as described in the preceding. The overall thickn~ss at the centre of several cells was measured after final crimp closure. Each cell was then recharged fully and measured again. The increase in overall thickness of each cell was roughly ~00 ~m. This corresponded to a calculated total internal pressure increase of about 35 psi. The coin cell at this point had pronounced convex shaped or domed faces.
This example demonstrates that the internal ¦35 pressure o~ this specific coin cell is significantly higher ¦during operation than it is immediately after initial crimp IclosureO The increase in pressure during operation created ~ 5 9 ~ ~
significant distortion of the coin cell container.
INVENTIVE EXAMPLE
Further testing on cells similar to those of the Comparative Example demonstrated that the maximum increase in coin cell th.ickness after repeated charge-discharge cycles was approximately 250 ~m. This increase corresponded to a calculated total pressure increase of about 45 psi. Additionally, in special laboratory cells (described in Effects of Physical Constraints on Lithium Cyclability by D.P. Wilkinson et al, 5th International Meeting on Lithium Batteries, Beijing, China, 1990), it was demonstrated that the increase in thickness of such coin cells could be arrested by preloading the el~ctrode stack to a similar pressure value.
Coin cells were then constructed usiny concave shaped cases and caps which were designed to apply a preloading pressure of 40 psi. With reference to Figure 3, the magnitudes of Yl and Y2 llsed for the concave case and cap respectively were determined by calcl71ating the bulges Xl and X2 in the eguivalent pieces of Figure 2 assuming the internal pressure applied to the equivalent pieces was 40 ~j25 pSin Thu~, after crimp closure, the container of this :inventive ex~mple was expected to interfere with the electrode stack an amount Yl + Y2 more than that of the container in the Comparative example. This interference was expected to create a preloading pressure of 40 psi in such a case.
It was additionally necessary to tailor the components of the cell such that the thicknesses of the electrodes under the desired preload pressure were suitable for the final as~embled cell thickness. To achieve this result, the cathode used was about 310 mg by weight, approximately 19 mm in diameter and 570 ~m thick. The - 11 2~
anode used was about 230 mg by weight, approximately 19 mm in diameter and 680 ~m thick. :
., Coin cells were constructed and recharged as describad in the foregoing disclosure. The overall thicknesses of the cells increased only slightly (of order of 50 ~m or less~ after recharging. Upon repeated charge-discharge cycling, no significant increa es in overall thicknass occurred.
' 10 Calculations also indicated that greater values for Y1 could be employed without exceeding the elastic limit of the case material. The maximum equivalent preloading pressure achievable within the elastic limit for the case was determined to be 70 psi. For the cap however, the maximum equi~alent preloading pressure was determined to be only 41 p~i as a consequence of using annealed material for construction. Use of a harder grade of stainless steel for the cap would increase the maximum possible preloading pre~sure achievable. Thus, if reguired, greater preloading pressure could be achieved in a slightly modiPied constructionO
This example illustrates the effectiveness of the ~ 25 invention and additionally indicates a possible method for : its practical use.
As will be apparent to those skilled in the art in light of the foregoing disclosure, many alterati.ons and modi~ications are possible in the practice of this invention without departing from the spirit or scope t,hereof. While the examples in the foregoing disclosure applied only to lithium ion coin cell batteries and the need for preloading to prevent electrode expansion, ths hardware and methods described equally can be used ~or . other battery chemistries with other requirements for preloading such as a need to counteract the ePfects of gas ~ `
generation. Accordingly, the scope of the invention is to be construed in accordance with the ~ubstance defined by the following claims.
:
CONC~VE 8X~PED CONTAINER PIECE~
FIE~D OF THE INVENTION
The invention relates to the field of batteries.
In particular, it relates to coin cell ~ize batteries and the hardware employed for the container of such batteries.
B~ACKGROUND OF THE INVENT ON
, Coin cell batterie~ are small, puck shaped galvanic cells that are used in a variety of commercial electronics applications. Typically, these are low drain rate applications such as memcry back-up, watches, and the like. However, since power requirements ar~ being reduced for high drain rate electronics devices, the demand ~or larger and/or higher drain rate coin cell batteries is incr~asing. It is desirable in most applications that the ~:~power source have a slim pro~ile. Thusl in order to gek ~:high drain rate in a slim container, it is prP~erable to use larger coin cell diameters and smaller coin call thicknesses. A four digit convention is used to designate coin cell size where the first two digits indicate the diameter in mm and the last two digit~ indicate the overall thickness times ten in mm. A typical commercial product is ~:a 2320 coin cell which is therefore 23 mm in diameter and 2.0 mm thick.
In many electronics applications, it is the maximum thickness of the coin cell that determines whether it will fit in the allocated space. Thus, it is preferable that the faces of the coin cell be ~lat in order to 135 maximize the amount of active material contained in the coin cell. Additionally, it is preferable to use the minimum material thickness for the pieces comprising the coin cell container, again to maximize the amount o~ active ~matexial contained therein.
:
~--~ 2 1 0 ~
Generally, some pressure is applied to the coin cell container by the contents. This can be unintended, for example as a result of the generation of gaseous products during operation of the battery. Pressure can also be applied deliberatelyO For example, U.S. Patent No.
2,971,999 discusses a battery wher~in a spring is inserted between a container wall and the cell electrodes in order to maintain electrical contact between the cell electrodes and the container wall even when internal pressure causes the container wall to swell.
The presence of internal pressure in a coin cell battery tends to deform the container. The extent to which this deformation increases the maximum thickness of the coin cell is a function of the coin cell diameter~ the thickness of the pieces comprising the coin cell container, and, of course, the internal pressure. Larger cell diameters and thinner container pieces result in a battery that is morP sensitive to deformation at a given internal pressure.
SUMMARY QF THE INVENTION
The coin cell battery of this invention is one that uses pieces for the container thereof that are concave shaped prior to assembly. ~fter assembly of the pieces into a coin cell battery, the container applies a preloading pressure to the solid contents, hereinafter referred to as the electrode stack, inside the cell.
Furthermore, the concave shape can be chosen such that, after assembly, the pieces of the container are deformed as a result of generation of this preloading pressure such that the faces of the battery are ef~ectively ~lat.
` ~ 2~9 ., Hardware specific to one possible coin cell size is disclosed that, if suitably shaped, allows the practical application of preloading pr~ssures from about zero up to about 40 psi. In addition, a specific coin cell battery example using lithium ion type electrochemistry is disclosed.
Lithium ion batteries ~enerally employ lithiated transition metal oxides as the active cathode mat~rial, carbonaceous compounds as the active anode material, and lithium salts dissolved in one or more non-aqueous solven~s as the electrolyte. ~he specific battery disclosed is a 2320 coin cell using LiNio2 as the active cathode material, a coke-like carbon as the active anode material, and lM
LiN(CF3S02)2in ethylene carbonate (EC)/dimethoxyethane (DME) solvants as the electrolyte. ;.
This invention pertains to a general method that can be used to apply preloading pressure to the electrode stack of a coin cell battery. The purpo~e for the application of said preloading pressure can be to prevent expansion of the cell electrodes, to maintain ePfective electrical contact to the electrodes, to counteract gas ; .:
pressure generated a~ a result of operation of the cell, or for any oth~x such reason.
In addition, a method is descri~ed that allows th~ application of preloading pressure in a coin cell battery such that the faces of the battery are effectively ~0 flat after assembly is complete. For a given cell size and a given thickness o~ the container pieces, it is possible to achieve preloading press~lres over a certain range. A
method for achieving a range from zero to about 40 psi specific to a 2320 size coin cell battery with 300 ~m thick ~.ontainer pi~ces is also disclosed.
~, , ~" ~""",~, ~.i~ ~,i!.'.~,'', ~ i ~ ` 2 ~
...
BRIEF DESCRIPTION OF THE D~WINGS
., In drawings which illustrate specific embodiments of the invention, but whi~h should not be construed as restricting the spirit or scope of the invention in any way:
Figure 1 shows a cross-section of a typical coin cell battery.
' 1~
Figure 2 shows a cross-section of the coin cell battery o~ Figure 1 as it would appear i~ deformed due to a uniform increase in internal pressure.
15Figure 3 shows a cross-section of the invention case and cap container hardware for a coin cell battery.
. ~:
Figure 4a shows a two stage die set suitably modified for purposes of crimp closure of the invention coin cell battery~
Figure 4b shows an enlarged cross-sectional view o~ the first stage die set and coin cell assembly during crimp closure.
:
Figure 4c shows an enlarged cross-sectional view of the second stage di~ set and coin cell assembly during crimp closure. -~
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
OF TEIE INVENTION
A typical coin cell battery is depicted in Figure 1. The solids in the cell are inserted in a stack consisting of a cathode 10, a separator 11, and an anods 12~ An electrolyte 13 permeates the pores o~ the separator :~ 11 and, where applicable, the poras of the cathode 10 and anode 12. A housing conslsting of a metal case 14, a gasket 15, and a metal cap 16 are conventionally used as a container. The metal case 14 and metal cap 16 serve additionally as external electrical contacts to the electrodes ~ithin. Conventional cases 14 and caps 16 have flat faces prior to assembly. The housing is sealed by crimping the edge of the case 17 inwards, thereby deforming the gasket and setting a psrmanent load that acts on the edges of both the case 14 and the cap 16 as well as on the gasket 15.
. , If the coin cell as shown in Figure 1 is subjected to a uniform increase in internal pressure, deformation of the container is expected as shown in Figure 2. (The extent of elastic deformation has been exaggerated for purposss of illustration.) Both the case 14 and cap 16 assume a convex shape that is a function of the diameter of the cell, thickness of the case 1~ and cap 16, and the materials of construction. Said deformation, if within the elas~ic limits of the hardware/ is by definition reversible upon removal of the applied pressure and can be calculated by conventional stress/strain methods if the internal pressure is known. The amount of deformation or bulge measur~d at the centre o~ the case 14 and cap 16 has been denoted by arrows X1 and X2 respectively.
The invention battery is on- that employs a case 14 and cap 16 that are concave shaped prior to assembly of the battery. The specific shape employed for a given preloading pressure and given hardware dimensions is the inverse to the convex shape expected from ~lat hardware of the same dimensions subjected to uniform application of the same prelcading pre~sure. Figure 3 shows hardware with a concave shape of the invention. (The extent of the concave shaping has been exag~erated for purposes of illustration.~
The case 14 and cap 16 are shaped such that their centres are an amoun~ indicated by arrows Yl and Y2 respectively ~,x :,. - - ,. - , ~ . : , ::
from the flat. Thus, the~ concave shaped pieces of the invention are the inverse of the convex shaped pieces of Figure 2 if the hardware dimensions are the same and if the respective magnitudes Yl and Y2 are equal to Xl and X2. In order to achieve the goals of the invention, the desired preloading pressure must be small enough so as not to inelastically deform the given hardware. In such a case, the container can be crimped shut such that the desired preload is applied with the resulting faces of the container being effectively flat after assembly.
The invention battery thus differs significantly ~rom that described in U.S. Patent 3,928,077 wherein a practically planar portion of the container is inwardly o~fset in order to maintain efective contact to the internal electrodes and thus to count~ract the effect of internal pressure on the cell container. The planar portion of the container in said patent does not apply uniform pressure over the entire electrode ~tack nor does : 20 it result in a cell with ~aces that are effeotively flat after assembly.
Increased di~ficulty in cell assembly results from the use of concave shapsd pieces for the container.
~he electrode stack is conventionally created by stacking one component at a time on top of either a gasket 15 - case 14 subassembly or a gasket 15 - cap 16 subassembly. The concave shape of the container does not allow the electrode stack to lie flat and thus the stack may be more easily disturbed during assembly. In addition, the case 14 and cap 16 must be manipulated into their final respective positions during the crimping closure process, rather than prior to the crimping process. To accomplish this, only minor modifications to conventional coin cell crimping dies ¦ 35 are required.
Figure 4a shows a conventional two stage coin cell crimping die set 20. The first stage die 21 consists of a base 22 and a precrimper 23. Figure 4b shows an enlarged cross~sectional view of the first stage die and coin cell assembly during crimping. The bottom surface 24 of the precrimper 23 is shaped to effect a partial crimp closure of the coin cell. An uncrimped coin cell 2S is placed in the base 22, oriented with the cap 16 upwards as shown. The precrimper 23 is then brought down vertically~
The crimping begins when the shaped bottom surface 24 of the precrimper 23 contacts the perimeter of the case 14.
The design of the shaped bottom surface 24 is such that some limited loading is applied to perimeter of the cap face 26 during this process. The first stage crimping i~
complete once the faces of the precrimper 23 and base 22 contact each other. The components of the partially crimped coin cell (not shown) are now reasonably fixed in place.
Final crimping of the partially crimped coin cell takes place in the second stage die 29. The construction and operation of the second stage die 29 are similar to that of the first stage die 21. Figure 4c shows an enlarged cross-sectional view of the second stage die and partially crimped coin cell 25a during crimping. Similar items are identified with a number corresponding to those used in the ~irst stage with a suffix "a" (ie. second stage base is 22a). The surface 24a of the cximper 23a is shaped to effect the final desired shape of the assembled coin cell. The design o~ the surface 24a is such that increased loading is applied to the cap face ~7a as the crimper 23a travels downwards. Thus, the cap 16 is manipulated into its final position concurrent with the final crimping of the perimeter of the case 14.
The invention has been employed succ ssfully in the construction of certain coin cell batteries employing lithium ion type electrochemistry. In this instance, a signi~icant internal pressure existed during the normal operation of said batteries. The examples to follow are presented to illustrate the application of the invention in this specific case but should not be construed as limiting the scope or spirit of the invention in any way.
COMPARATIVE EX~MPL~ -It was considered desirable to fabricate 2320 size coin cell batteries as shown in Figure 1 using a speci~ic lithium ion type electrochemistry comprising use of LiNio2 as the active cathode material, ~oke like carbon as the active anode material and a lM solution of LiN(CF3So2)2 salt dissolved in equal volumes of ethylene carbonate ~EC) and dimethoxyethane (DME) solvents as the electrolyte.
Cathodes were fabricated in the ~ollowing manner.
A cathoda slurry was prepared using LiNio2 powder as the active material, Super S carbon black (trade-mark of Ensagri) as a conductive dilutant, ethylene propylene diene monomer (EPDM) rubber as a bind4r, and cyclohexane as a solvent for the binder. After blending, the cyclohexane was evaporated away to create a cathode powder blend in which the ratio of the components LiNio2- Super S: EPDM by weight was 100:10:2. Us.ing this dry powder blend, tablets were formed in a press in a size close to that desired for 2320 cells.
1:
In a similar manner, anode tablets were prepared using Conoco XP coke (product of Conoco Inc.) as the active material in which the ratio of the components coke: Super S: EPDM by weight was 100~5:2.
In the ~atteries of this example, Celgard 2502 ~trade-mark of Hoechst-Celanese) was used as a separator material~ Conventional 2320 cap and case hardware with -~ 2 1 ~
g flat faces prior to assembly were used. The cap material was annealed 304 stainless steel and the case material was a special corrosion resistant grade of stainless steel known as Shomac 30-2 (trade~mark). The thickness of the material in both instances was 300 ~m. Coin cells were fabricated as described in a conventional manner without a significant intended preloading pressure. Some slight inter~erence (of order of 50 ~m or less) between the container pieces and the electrode stack was intended to ensure electrical contact was maintained with the cathode and anode tablets. ~fter assembly to this point, the coin cell faces are effectively flat.
As constructed, this type of lithium ion cell is in the discharged statel Upon recharging, there is a net expansion in the total volume occupied by the solids inside. Additionally, gas can be generated inside as a result o~ certain chemical reactions that take place during this process. For these reasons, additional internal pressure is applied to the cell container on recharge and consequently an increase in overall cell thickness is expected.
Several coin cell batteries were fabricated and ~5 recharged as described in the preceding. The overall thickn~ss at the centre of several cells was measured after final crimp closure. Each cell was then recharged fully and measured again. The increase in overall thickness of each cell was roughly ~00 ~m. This corresponded to a calculated total internal pressure increase of about 35 psi. The coin cell at this point had pronounced convex shaped or domed faces.
This example demonstrates that the internal ¦35 pressure o~ this specific coin cell is significantly higher ¦during operation than it is immediately after initial crimp IclosureO The increase in pressure during operation created ~ 5 9 ~ ~
significant distortion of the coin cell container.
INVENTIVE EXAMPLE
Further testing on cells similar to those of the Comparative Example demonstrated that the maximum increase in coin cell th.ickness after repeated charge-discharge cycles was approximately 250 ~m. This increase corresponded to a calculated total pressure increase of about 45 psi. Additionally, in special laboratory cells (described in Effects of Physical Constraints on Lithium Cyclability by D.P. Wilkinson et al, 5th International Meeting on Lithium Batteries, Beijing, China, 1990), it was demonstrated that the increase in thickness of such coin cells could be arrested by preloading the el~ctrode stack to a similar pressure value.
Coin cells were then constructed usiny concave shaped cases and caps which were designed to apply a preloading pressure of 40 psi. With reference to Figure 3, the magnitudes of Yl and Y2 llsed for the concave case and cap respectively were determined by calcl71ating the bulges Xl and X2 in the eguivalent pieces of Figure 2 assuming the internal pressure applied to the equivalent pieces was 40 ~j25 pSin Thu~, after crimp closure, the container of this :inventive ex~mple was expected to interfere with the electrode stack an amount Yl + Y2 more than that of the container in the Comparative example. This interference was expected to create a preloading pressure of 40 psi in such a case.
It was additionally necessary to tailor the components of the cell such that the thicknesses of the electrodes under the desired preload pressure were suitable for the final as~embled cell thickness. To achieve this result, the cathode used was about 310 mg by weight, approximately 19 mm in diameter and 570 ~m thick. The - 11 2~
anode used was about 230 mg by weight, approximately 19 mm in diameter and 680 ~m thick. :
., Coin cells were constructed and recharged as describad in the foregoing disclosure. The overall thicknesses of the cells increased only slightly (of order of 50 ~m or less~ after recharging. Upon repeated charge-discharge cycling, no significant increa es in overall thicknass occurred.
' 10 Calculations also indicated that greater values for Y1 could be employed without exceeding the elastic limit of the case material. The maximum equivalent preloading pressure achievable within the elastic limit for the case was determined to be 70 psi. For the cap however, the maximum equi~alent preloading pressure was determined to be only 41 p~i as a consequence of using annealed material for construction. Use of a harder grade of stainless steel for the cap would increase the maximum possible preloading pre~sure achievable. Thus, if reguired, greater preloading pressure could be achieved in a slightly modiPied constructionO
This example illustrates the effectiveness of the ~ 25 invention and additionally indicates a possible method for : its practical use.
As will be apparent to those skilled in the art in light of the foregoing disclosure, many alterati.ons and modi~ications are possible in the practice of this invention without departing from the spirit or scope t,hereof. While the examples in the foregoing disclosure applied only to lithium ion coin cell batteries and the need for preloading to prevent electrode expansion, ths hardware and methods described equally can be used ~or . other battery chemistries with other requirements for preloading such as a need to counteract the ePfects of gas ~ `
generation. Accordingly, the scope of the invention is to be construed in accordance with the ~ubstance defined by the following claims.
:
Claims (15)
1. A coin cell battery comprising a cathode, an anode, a separator and an electrolyte housed in a case and cap container wherein the case and cap pieces comprising the container prior to assembly are concave shaped towards one another.
2. A battery as claimed in claim 1 wherein the case and cap pieces comprising the container apply a preloading pressure to the electrode stack comprising said cathode, anode, and separator after assembly.
3. A battery as claimed in claim 2 wherein the faces of the case and cap of the assembled battery are flat.
4. A battery as claimed in claim 2 wherein the preloading pressure is in the range from greater than zero to less than about 40 psi.
5. A battery as claimed in claim 3 wherein the preloading pressure is in the range from greater than zero to less than about 40 psi.
6. A battery as claimed in claim 5 wherein active material of the cathode comprises lithiated transition metal oxides, active material of the anode comprises carbonaceous material, the separator comprises porous polyolefin film, and the electrolyte comprises lithium salts dissolved in one or more non-aqueous solvents.
7. A battery as claimed in claim 6 wherein the active material of the cathode is LiNiO2, the active material of the anode is a coke-like carbon, and the electrolyte is lM LiN(CF3SO2)2 in a solvent mixture containing ethylene carbonate (EC) and dimethoxyethane (DME) solvents.
8. A method of applying preloading pressure to an electrode stack of a coin cell battery wherein case and cap pieces comprising the battery container prior to assembly are concave shaped when viewed externally.
9. A method as claimed in claim 8 wherein the case and cap faces of the battery are effectively flat after assembly.
10. A method as claimed in claim 9 wherein preloading pressure of the battery is in the range from greater than zero to less than about 40 psi.
11. A coin cell battery comprising the following pre-crimp components:
(a) a concave metal cap;
(b) an anode;
(c) a separator;
(d) a cathode;
(e) an electrolyte permeating pores of the anode, separator and cathode; and (f) a concave metal case, the concave cap and concave case being flat after crimping and preloading internal pressure.
(a) a concave metal cap;
(b) an anode;
(c) a separator;
(d) a cathode;
(e) an electrolyte permeating pores of the anode, separator and cathode; and (f) a concave metal case, the concave cap and concave case being flat after crimping and preloading internal pressure.
12. A battery as claimed in claim 11 wherein the case and cap comprising the battery container apply a preloading pressure to the electrode stack comprising the cathode, anode, and separator after assembly.
13. A battery as claimed in claim 12 wherein the internal preloading pressure is in the range from greater than zero to less than about 40 psi.
14. A battery as claimed in claim 11 wherein active material of the cathode comprises lithiated transition metal oxides, active material of the anode comprises carbonaceous material, the separator comprises porous polyolefin film, and the electrolyte comprises lithium salts dissolved in one or more non-aqueous solvents.
15. A battery as claimed in claim 14 wherein the active material of the cathode is LiNiO2, the active material of the anode is a coke-like carbon, and the electrolyte is lM LiN(CF3SO2)2 in a solvent mixture containing ethylene carbonate (EC) and dimethoxyethane (DME) solvents.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002105911A CA2105911A1 (en) | 1993-09-10 | 1993-09-10 | Coin cell battery employing concave shaped container pieces |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002105911A CA2105911A1 (en) | 1993-09-10 | 1993-09-10 | Coin cell battery employing concave shaped container pieces |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2105911A1 true CA2105911A1 (en) | 1995-03-11 |
Family
ID=4152294
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002105911A Abandoned CA2105911A1 (en) | 1993-09-10 | 1993-09-10 | Coin cell battery employing concave shaped container pieces |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2105911A1 (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1997014187A1 (en) * | 1995-10-11 | 1997-04-17 | Micron Communications, Inc. | Method of producing button-type batteries and spring-biased concave button-type battery |
| 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 |
| US6248463B1 (en) | 1997-05-05 | 2001-06-19 | Rayovac Corporation | Metal-air cathode can and electrochemical cell made therewith |
-
1993
- 1993-09-10 CA CA002105911A patent/CA2105911A1/en not_active Abandoned
Cited By (5)
| 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 |
| US6042957A (en) * | 1995-05-05 | 2000-03-28 | Rayovac Corporation | Thin walled electrochemical cell |
| WO1997014187A1 (en) * | 1995-10-11 | 1997-04-17 | Micron Communications, Inc. | Method of producing button-type batteries and spring-biased concave button-type battery |
| US6248463B1 (en) | 1997-05-05 | 2001-06-19 | Rayovac Corporation | Metal-air cathode can and electrochemical cell made therewith |
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