U.S. patent application number 09/949079 was filed with the patent office on 2002-02-21 for method of fabricating an electrochemical cell battery and an improved cell package.
This patent application is currently assigned to ALCATEL. Invention is credited to Olsen, Ib Ingemann, Pasquier, Eric Michel.
Application Number | 20020022180 09/949079 |
Document ID | / |
Family ID | 23119362 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020022180 |
Kind Code |
A1 |
Olsen, Ib Ingemann ; et
al. |
February 21, 2002 |
Method of fabricating an electrochemical cell battery and an
improved cell package
Abstract
A method of manufacturing an electrochemical battery where the
electrolyte is introduced into the cell stack with minimal or no
loss of electrolyte. The method of fabricating the battery,
comprises the steps of separately forming an electrode cell stack
and a sealed electrolyte pouch, placing the cell stack and the
electrolyte pouch together into a cell package, applying a vacuum
to the cell package, sealing the cell package, and rupturing the
pouch to release the electrolyte into the cell stack. The pouch is
ruptured by squeezing the pouch until the electrolyte squirts out
of the pouch. Also, the cell package is sealed by heat sealing.
With this fabrication technique there is little or no electrolyte
loss. In particular, since the electrolyte is injected into the
electrode cell stack after the package has been sealed,
substantially all of the electrolyte is suctioned into the
electrode cell stack without any of the electrolyte escaping from
the package. In addition, since the electrolyte is not poured into
the cell stack during the manufacturing of the cell stack, the cell
manufacturing machine does not have to provide a glove box
environment. Also, contamination of the cell stack manufacturing
machine is avoided. The cell package is made of a laminate of
polyester, aluminum and polypropylene to allow the heat sealing of
the polypropylene layers to each other even when the cell package
is contaminated with electrolyte. Accordingly, it is not necessary
to transfer the cell stack to an uncontaminated cell package.
Inventors: |
Olsen, Ib Ingemann;
(Hickory, NC) ; Pasquier, Eric Michel; (Hickory,
NC) |
Correspondence
Address: |
Brian W. Hannon
SUGHRUE MION ZINN MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, NW
Washington
DC
20037-3213
US
|
Assignee: |
ALCATEL
|
Family ID: |
23119362 |
Appl. No.: |
09/949079 |
Filed: |
September 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09949079 |
Sep 10, 2001 |
|
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|
09291212 |
Apr 14, 1999 |
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Current U.S.
Class: |
429/176 ;
29/623.1; 29/623.2; 429/185; 429/52 |
Current CPC
Class: |
H01M 50/119 20210101;
Y10T 29/4911 20150115; H01M 50/133 20210101; H01M 50/129 20210101;
H01M 50/557 20210101; Y02E 60/10 20130101; H01M 50/121 20210101;
Y02P 70/50 20151101; H01M 50/55 20210101; H01M 50/60 20210101; Y10T
29/49108 20150115; H01M 50/116 20210101 |
Class at
Publication: |
429/176 ;
29/623.1; 29/623.2; 429/185; 429/52 |
International
Class: |
H01M 002/02; H01M
002/08; H01M 010/04; H01M 006/32 |
Claims
What is claimed is:
1. A method of fabricating an electrochemical battery, comprising
the following steps: forming an electrode cell stack and an
enclosure; placing said cell stack and a sealed electrolyte pouch
together into said enclosure; applying a vacuum to said enclosure;
sealing said enclosure; and rupturing said pouch to release said
electrolyte into said cell stack.
2. The method of fabricating an electrochemical battery according
to claim 1, wherein said step of forming said enclosure includes
the step of forming a cell package.
3. The method of fabricating an electrochemical battery according
to claim 2, wherein said sealing step includes the step of heat
sealing said cell package.
4. The method of fabricating an electrochemical battery according
to claim 2, wherein said step of forming said cell package
comprises the step of forming first and second parts each
comprising a laminate of polyester, aluminum and polypropylene, and
wherein said sealing step includes the step of heat sealing said
polypropylene layers of said first and second parts to one
another.
5. The method of fabricating an electrochemical battery according
to claim 1, wherein said rupturing step includes the step of
squeezing said pouch.
6. The method of fabricating an electrochemical battery according
to claim 1, wherein said sealing step includes the step of heat
sealing said enclosure.
7. A method of fabricating an electrochemical battery, comprising
the following steps: forming an electrode cell stack; injecting an
electrolyte into a pouch through an open end; sealing said open end
of said pouch in a vacuum state; placing said sealed pouch and said
electrode cell stack into an enclosure; applying a vacuum to said
enclosure; and rupturing said pouch to release said electrolyte
into said electrode cell stack.
8. The method of fabricating an electrochemical battery according
to claim 7, wherein said enclosure is a cell package.
9. The method of fabricating an electrochemical battery according
to claim 7, wherein said rupturing step includes the step of
squeezing said pouch.
10. The method of fabricating an electrochemical battery according
to claim 7, wherein said sealing step includes the step of heat
sealing said enclosure.
11. The method of fabricating an electrochemical battery according
to claim 8, wherein said sealing step includes the step of heat
sealing said cell package.
12. The method of fabricating an electrochemical battery,
comprising the following steps: forming an electrode cell stack;
placing said cell stack and a sealed electrode pouch into a vacuum
enclosure; and rupturing said pouch to fill said electrode cell
stack with electrolyte.
13. The method of fabricating an electrochemical battery according
to claim 12, wherein said sealed electrode pouch is a vacuum
pouch.
14. A method of fabrication an electrochemical battery, comprising
the following steps: forming a cell package having first and second
enclosures and including a tube communicating between said first
and second enclosures; placing a cell stack in said first enclosure
with leads of said cell stack protruding from said first enclosure
and sealing and evacuating said first enclosure; placing an
evacuated electrolyte pouch in said second enclosure and sealing
and evacuating said enclosure; rupturing said pouch such that
electrolyte flows from said pouch, through said tube and into said
cell stack; and sealing said tube.
15. The method of claim 14, further comprising the step of removing
said second enclosure after said sealing step.
16. The method of claim 15, further comprising, after said
rupturing step and before said sealing step, the steps of
subjecting said cell package to formation and thereafter puncturing
said second enclosure and applying a vacuum to said second
enclosure to degas said first enclosure.
17. A method of fabrication an electrochemical battery, comprising
the following steps: forming a cell package having an enclosure and
including a tube having one end communicating with said enclosure
and an opposite end extending from said cell package; placing a
cell stack in said enclosure with leads of said cell stack
protruding from said enclosure and sealing and evacuating said
first enclosure; introducing electrolyte into said opposite end of
said tube such that said electrolyte enters said enclosure and said
cell stack; and sealing said tube.
18. An electrochemical cell comprising: a casing; and an electrode
cell stack contained within said casing along with an electrolyte,
wherein said casing includes first and second parts each comprising
a laminate having an outer layer, an inner layer and a barrier
layer interposed between said inner and outer layers, said first
and second parts having their inner layers adhered to one another,
said inner layer being a polypropylene layer, wherein said inner
layer and said barrier layer are adhered together with an adhesive,
said adhesive being one of a thermoset polyurethane adhesive or an
organosol type modified polypropylene dispersion adhesive.
19. The electrochemical cell of claim 18, wherein said outer layer
is a polyester layer and said barrier layer is an aluminum
layer.
20. The electrochemical cell of claim 18, wherein said
polypropylene inner layers are heat sealed to each other.
21. The electrochemical cell of claim 19, wherein said
polypropylene inner layers are heat sealed to each other.
22. The electrochemical cell of claim 18, wherein said first and
second parts are unitary with each other.
23. The electrochemical cell of claim 18, wherein said first and
second parts are initially independent of each other and are heat
sealed to each other around the entire periphery thereof.
24. The electrochemical cell of claim 21, wherein said casing
initially includes a first portion in which said cell stack is
located and a removable second portion in which an electrolyte
pouch is receivable for impregnating said electrodes with said
electrolyte upon the bursting of said pouch.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of fabricating an
electrochemical battery and, more particularly, to a method of
injecting the electrolyte into the cell stack of the battery by
first placing the electrolyte in a sealed pouch that is placed
together with the cell stack into a cell package. The invention
also relates to a cell package which can be heat sealed even after
it has been contaminated during the process of introducing the
electrolyte into the cell stack.
[0003] 2. Background
[0004] A important consideration in the manufacturing of
electrochemical batteries is the manner in which the electrolyte is
introduced into the cell stack. A current technique includes the
steps of pouring the electrolyte into the cell stack during the
manufacturing of the cell stack in a machine, placing the
electrolyte impregnated cell stack into the cell package,
evacuating the cell package and heat sealing the package.
[0005] This technique suffers from many disadvantages. The first
problem is the loss of electrolyte during the step of pouring the
electrolyte into the cell stack and the subsequent step of
evacuating the package. It is estimated that between 10 and 30% of
the electrolyte is lost during these steps. The electrolyte is a
relatively expensive component of the electrochemical cell. Thus,
the loss of electrolyte increases the overall cost of manufacturing
the battery. Further, since the amount of lost electrolyte cannot
be gauged, the final volume of electrolyte that remains in the cell
stack is unknown.
[0006] A second problem is that the electrolyte that is naturally
suctioned from the cell stack during the evacuating step
contaminates the inside of the package. Such contamination of the
package makes it difficult to securely seal the package. As such,
subsequent leakage of the electrolyte from the sealed package may
result. A further problem is that the pouring step must be
performed in a glove box environment (i.e., dry and inert
atmosphere) . Since this step is an intermediate step in the
manufacturing of the cell stack, the machine which manufactures the
cell stack must consequently have a glove box environment, thus
driving up the cost of the machine. In addition, when the
electrolyte is poured into the cell stack, the electrolyte
contaminates the machine thus requiring that it be cleaned on a
regular basis. In addition, the vacuum that is applied to the cell
stack during the evacuating step may change the solvent ratio of
the impregnated electrolyte.
[0007] The current cell package is formed of a laminate of a
polyester outer layer, an aluminum barrier layer and a polyethylene
acrylic acid (EAA) inner layer. The polyester layer provides,
strength, the aluminum layer prevents water from penetrating the
cell package and the inner layer allows for the heat sealing of the
cell package. Specifically, generally, the cell package includes
two parts that are bonded together around their periphery by
heating sealing the EAA inner layers to each other. The problem
with this laminate is that once contaminated with electrolyte, the
EAA inner layers cannot form a secure heat seal. This makes
degassing and resealing of the cell package a problem. Also, the
current material has a relatively high permeability to water
necessitating the use of wider heat sealing areas in order to
ensure a long shelf life. Finally, the current laminate will absorb
electrolyte at elevated temperatures which can interact with the
adhesive layer between the EAA inner layer and the aluminum barrier
layer.
SUMMARY OF THE INVENTION
[0008] It is an object of the invention to provide a method of
manufacturing an electrochemical battery which overcomes the above
problems. In particular, an object of the invention is to provide a
method of manufacturing a battery where the electrolyte is
introduced into the cell stack with minimal or no loss of
electrolyte. Another object of the invention is to provide a method
in which the electrolyte filling step is performed after the cell
stack is manufactured so that the cell stack manufacturing machine
does not have to maintain a glove box environment and contamination
of the machine is eliminated.
[0009] These and other objects are achieved by a method of
fabricating an electrochemical battery, comprising the steps of
separately forming an electrode cell stack and a sealed electrolyte
pouch, placing the cell stack and the electrolyte pouch together
into a cell package, applying a vacuum to the cell package, sealing
the cell package, and rupturing the pouch to release the
electrolyte into the cell stack. The rupturing step includes the
step of squeezing the pouch until the electrolyte squirts out of
the pouch. Further, the sealing step includes the step of heat
sealing the cell package.
[0010] With this fabrication technique there is no electrolyte
loss. In particular, since the electrolyte is injected into the
electrode cell stack after the package has been sealed,
substantially all of the electrolyte is suctioned into the
electrode cell stack without any of the electrolyte escaping from
the package. In addition, since the electrolyte is not poured into
the cell stack during the manufacturing of the cell stack, the cell
manufacturing machine does not have to provide a glove box
environment. Also, contamination of the machine is avoided.
Accordingly, all of the disadvantages discussed above with respect
to the current technique are overcome.
[0011] Another aspect of the invention is to form the cell package
so that it includes two separate enclosures with a tube extending
between the two enclosures such that they communicate with each
other through the tube. The cell stack is placed in a first one of
the enclosures which is then evacuated. The sealed electrolyte
pouch is placed in the second enclosure which is also evacuated
after the pouch is inserted. Thereafter, as with the previous
embodiment, the pouch is ruptured to release the electrolyte from
the pouch such that it flows through the tube and into the cell
stack contained in the first enclosure. The tube is then sealed and
the second enclosure is removed.
[0012] Also, with this technique, after formation it is possible to
degas the first enclosure. The formation is naturally done after
the electrolyte has been released into the cell stack. The
degassing step is performed by puncturing the second enclosure and
applying a vacuum thereto so that the first enclosure is degassed
via the tube. The tube is then sealed and the second enclosure is
removed.
[0013] It is a further object of the invention to provide a cell
package made of a laminate which can be heat sealed even when the
cell package is contaminated with electrolyte. This is achieved by
a laminate which includes a polyester outer layer, an aluminum
barrier layer and a polypropylene inner layer which are adhered
together using a unique adhesive which does not break down when
contaminated with electrolyte. It has been discovered that the
polypropylene layers associated with the overlapped portions of the
cell package can be securely heat sealed to each other even when
contaminated with electrolyte.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and other objects, features and advantages of the
present invention will be better understood from the following
specification when read in conjunction with the accompanying
drawings in which:
[0015] FIG. 1 is a plan view showing the pouch filled with
electrolyte according to a first embodiment of the invention;
[0016] FIG. 2 is a sectional view taken along line 2-2 of FIG. 1
showing the electrolyte pouch;
[0017] FIG. 3 is a plan view showing the partially sealed cell
package with cell stack located therein, according to the
embodiment of FIG. 1;
[0018] FIG. 4 is a plan view showing the completely sealed cell
package with both the cell stack and the electrolyte pouch
contained therein, according to the embodiment of FIG. 1;
[0019] FIG. 5 is a plan view showing the cell package after the
electrolyte package has been ruptured and the electrolyte released
inside the cell stack, according to the embodiment of FIG. 1;
[0020] FIG. 6 is a plan view showing the cell package having a tube
interconnecting the cell stack enclosure and the pouch enclosure,
according to a second embodiment of the invention;
[0021] FIG. 7 is a plan view showing cell package of FIG. 6 with
the tube sealed after the introduction of the electrolyte into the
cell stack enclosure;
[0022] FIG. 8 is a plan view showing the cell package of FIG. 6
with the pouch enclosure portion having been removed;
[0023] FIG. 9 is a side elevational view showing the tube;
[0024] FIG. 10 is a plan view showing the cell package where the
tube is connected to an external electrolyte source, according to
another embodiment of the invention;
[0025] FIG. 11 is a perspective view showing the preferred
construction of the cell package; and
[0026] FIG. 12 is an exploded sectional view showing the sealed
portion of the cell package.
DETAILED DESCRIPTION OF THE INVENTION
[0027] Referring to FIGS. 1-4, according to a first embodiment of
the invention, an electrolyte 8 is first introduced into a pouch 10
and the pouch is evacuated and sealed. The sealed pouch is then
placed along with a pre-manufactured cell stack 12 inside a cell
package 14 which is then evacuated and sealed. Thereafter, the
sealed pouch 10 is ruptured so that the electrolyte is released
from the open end 16 of the pouch and impregnated inside the cell
stack 12.
[0028] In more detail, the electrolyte pouch 10 is illustrated in
FIGS. 1 and 2. The pouch is made of a polyethylene film or the like
having, for example, a thickness of 50.mu., and is formed by
folding the film in half and heat sealing the two longitudinal
sides 18 to form heat sealed seams 19. The bottom end 20 of the
pouch is closed by virtue of the fold while the top end of the
pouch 22 is initially open (FIG. 1 shows the pouch after the
electrolyte has been inserted and the pouch completely sealed).
There are, of course, alternative techniques for forming the pouch.
For example, the pouch can be formed by folding the film along the
length of the film and heat sealing the longitudinal side opposite
the fold and the bottom. Also, the pouch can be formed so it is
seamless with an open top. Alternatively, the pouch can be formed
of two separate sheets which are heat sealed together.
[0029] The next step is to fill the pouch 10 with a predetermined
amount of electrolyte. This step is preferably conducted in a glove
box having a dry and inert atmosphere and using a dropper. After
the pouch 10 is filled, the top 22 of the pouch 10 is heat sealed
in a condition that there are no air bubbles inside the pouch. One
technique to accomplish this is to seal the pouch just below the
top level of the electrolyte, although the invention is no so
limited. This ensures that all of the air is removed from the pouch
prior to sealing. After the top 22 of the pouch 10 is heat sealed,
the excess portion of the pouch (i.e., above the seal) is removed
by cutting the pouch just above the seal. Thereafter, the top edge
is cleaned to remove the electrolyte on the outside of the pouch so
as to avoid subsequent contamination. The electrolyte pouch 10 is
now ready to be inserted into the cell package 14.
[0030] Referring to FIG. 3, the cell stack 12 is positioned inside
the cell package 14 with its leads 24 extending outside the package
14. Like the pouch, the package can be formed by folding the film
in either the longitudinal or transverse direction and heat sealing
two of the remaining three sides to leave one end open. Since the
leads must be accessible from the exterior of the cell package, the
cell package should be folded and heat sealed around the cell
stack. In the illustrated embodiment, the cell package has been
formed by folding the film along a longitudinal side 26 to cover
the cell stack and thereafter heat sealing the opposite
longitudinal side 28 and the top end 30 around the leads 24. This
leaves the bottom end 32 of the cell package open. Alternatively,
the cell package can be formed from two separate sheets 31 which
are heat sealed together, as shown in FIG. 11, and discussed in
greater detail below.
[0031] Referring to FIG. 4, after the cell package 14 has been
formed, the pouch 10 is inserted into the cell package 14 through
the open bottom end 32. It is preferred that the pouch 10 be
positioned so that a sealed end (e.g., the top end 22) of the pouch
is closest to the cell stack, as shown. The cell package 14 is then
evacuated and the open bottom end 32 of the package 14 is heat
sealed, as designated by reference numeral 34. This results in an
evacuated cell package 14 with the cell stack 12 and the
electrolyte pouch 10 located inside.
[0032] Referring to FIG. 5, the pouch 10 is then ruptured to
release the electrolyte from the pouch. Since the cell package 14
is evacuated, the released electrolyte is suctioned inside the cell
package to activate the cell stack 12. A preferred technique for
rupturing the pouch is to apply a sufficient pressure to the pouch
to burst the pouch. It is important that the technique used for
rupturing the cell does not rupture the package. In the illustrated
embodiment, the top, heat sealed, end 22 of the pouch, closest to
the cell stack, is ruptured. This is achieved by rolling a roller
(not shown) along the pouch starting from the bottom end 20 and
proceeding toward the top end 22 or by applying a mechanical shock
to the pouch.
[0033] After the cell stack is impregnated with the electrolyte, it
is desirable to keep the cell stack in the cell package, instead of
transferring the cell stack to another uncontaminated cell package,
although the invention is not limited in this respect. This can be
done by heat sealing the cell package along seam line 36 extend
transversely between the cell stack 12 and the electrolyte pouch
10. This involves heat sealing the cell package when it is
contaminated with electrolyte. The preferred cell package material
is discussed below, although it is understood that the invention is
not limited to the particular type of cell package material.
[0034] According to another embodiment of the invention, a method
is used which does not require the sealing of the cell package
after it becomes contaminated. This method will be described in
detail with reference to FIGS. 6-9. According to this aspect of the
invention, the cell package 14 is formed so that it includes two
enclosure that are separated from each other. A first enclosure 50
has a cell stack cup 52 which is sized to receive the cell stack 12
and the second enclosure 54 has a pouch cup 56 which is sized to
receive the electrolyte pouch 10, discussed above. The cell package
14 is vacuum heat sealed along seams 58, as shown in FIGS. 6 and 7
and discussed further below, so as to form the two enclosures. A
tube 60 is provided inside the cell package 14 so that one end
communicates with the cell stack cup 52 and the other end
communicates with the pouch cup 56. As a result, the two cups are
in fluid communication with each other. A window 62 is provided in
the cell package 14 between the two enclosures such that a portion
64 of the tube is exposed to the outside of the cell package to
allow the tube to be ultra-sonically welded without interfering
with the package.
[0035] In the illustrated embodiment, the cell package 14 is formed
from two sheets of packaging material that are heat sealed together
along the seams 58 in a conventional manner. Prior to sealing the
transverse seams 66, the tube is positioned between the sheets with
respective ends in communication with the cell stack cup 52 and the
pouch cup 56. Thereafter, the package is heat sealed to form the
transverse seams. It is noted that the tube 60 is made of an
annealed metal, preferably nickel, copper, aluminum or any other
material that is electrochemically compatible and weldable.
Further, it is preferable that the tube be no thicker than the
leads. The tube can be circular, oval or the like. Since the tube
is made of metal, as discussed below, the heat sealing of the cell
package does not cause the tube to be sealed.
[0036] As shown in FIG. 6, the cell stack 12 is provided in the
cell stack cup 52 such that its leads extend to the exterior of the
cell package 14. Thus, the cell package 14 is sealed around the
leads 24 and evacuated, as discussed above. Similarly, the
electrolyte pouch 10 is provided in the pouch cup 56 in the second
enclosure 54 and the second enclosure is evacuated. As with the
previous embodiment, the cell package 14 is completely sealed
without the presence of free electrolyte. Therefore, the cell
package is not contaminated with the electrolyte when it is
sealed.
[0037] After the cell package 14 has been sealed and the two
enclosures 50, 54 have been evacuated, the electrolyte pouch 10 is
then ruptured in the manner discussed above. Thus, the electrolyte
is released from the pouch 10, flows through the tube 60, and
becomes impregnated in the cell stack 12 to thereby activate the
cell.
[0038] The cell stack 14 is then subjected to formation which
causes gases to develop inside the first and second enclosures 50,
54 and the cell stack cup 52 and pouch cup 56, which communicate
with each other. To degas the enclosures, the second enclosure 54
containing the burst electrolyte pouch is punctured to form hole 68
and evacuated by drawing a vacuum as designated by arrow V in FIG.
7. Thus, the electrolyte gasses are evacuated from the enclosures.
After degassing, the tube is sealed at seam 70 in the window 62.
Preferably, the tube 60 is ultrasonically welded so that
contaminants are removed from the weld area. Of course, the
invention is not to be limited in this respect, it being understood
that any convention welding technique would suffice.
[0039] Referring to FIG. 8, after degassing, the cell package is
trimmed to remove the second enclosure portion. The tube 60 is then
folded back over the side of the cell package 14 so that it does
not protrude from the package.
[0040] FIG. 9 illustrates one technique for forming the tube 60. As
noted above, the tube 60 is formed by a thin metallic sheet. The
sheet is folded such that the inside surfaces of the sheet contact
each other and are welded together at weld area 72. Although a
description has been provided of one technique for forming the
tube, it is understood that the invention is not limited to this
arrangement. For example, the tube could be formed by injection
molding or the like so that it is seamless, much like a hollow
needle.
[0041] The following is a description of yet another embodiment of
the invention illustrated in FIG. 10. Instead of providing two
enclosures in the cell package, it is possible to provide just a
single enclosure 50 for receiving the cell stack 14 and supply the
electrolyte from an external source through the tube 60 which
communicates with the single enclosure 50. In more detail,
according to this aspect of the invention, one end of the tube
extends into the cell stack cup 52 in the first enclosure 50 and
the other end of the tube 60 extends outside the cell package so as
to be exposed. The exposed end of the tube 60 may then be connected
to an electrolyte reservoir 80 via a three-way pump 82 which allows
the enclosure to first be evacuated and then filled with the
electrolyte. After the enclosure is filled, the tube is sealed and
the cell is then subjected to formation. After formation, the tube
is cut to allow for degassing by drawing a vacuum through the tube.
After degassing, the tube is US welded a second time. The tube is
then folded over the cell package.
[0042] FIGS. 11 and 12 show the construction of the preferred cell
package 14, although the above methods are not limited to the use
of this particular package. One of the sheets 31 has a cavity
corresponding to the cell stack cup 52. The material of the sheets
31 includes a polyester layer 37, an Al (Aluminum) foil layer 38
and a polypropylene heat seal layer 40. The polyester layer 37 is
adhered to the Al foil layer 38 by adhesive 42 and the heat seal
layer 40 is adhered to the Al foil layer using thermoset adhesive
44. The polyester layer 37 provides mechanical strength, the Al
foil layer 38 acts as a moisture barrier to prevent moisture from
entering into the cell package and the heat seal layer 40 seals the
cell package.
[0043] The thickness of the heat seal layer is between 25.mu. and
100.mu., and preferably between 50.mu. and 75.mu.. The primary
purpose of the heat seal layer is to seal the cell package after
the electrolyte has been impregnated into the cell stack 12.
Polypropylene has a good compatibility with the electrolyte so that
it can be heat sealed even when the cell package is contaminated
with the electrolyte.
[0044] Referring to FIG. 12 showing the heat sealed edge 46 of the
cell package, the edge does not have an Al foil layer 38 to act as
a barrier. Thus, it is important that the heat seal layer 40 have
low permeability for both water and the electrolyte to ensure a
long shelf life. Because of the non-polar nature of polypropylene
it has a lower moisture permeability than the polyethylene,
polyethylene acrylic acid (EAA) and Surlyn.TM., which, as discussed
above, are current packaging materials for lithium polymer
batteries. Also, polypropylene is more resistant to organic
solvents than these materials.
[0045] Potential disadvantages associated with polypropylene is
that is has a higher sealing temperature than the conventional
materials (approximately 140.degree. C. v. 100-120.degree. C.) and
cannot be sealed directly to the metal leads of the battery. The
former problem can be addressed by using packaging equipment that
is capable of heat sealing at this higher temperature. The latter
problem can be overcome by coating the leads 24 with a suitable
hotmelt EAA glue or EAA film in advance.
[0046] Any convention adhesive can be used as the adhesive 42,
i.e., aqueous or solvent based adhesive. On the other hand, the
adhesive 44 is preferably a thermoset polyurethane adhesive or an
organosol type modified polypropylene dispersion adhesive
(Morprime.RTM.10B), both available from Morton International, Inc.
These adhesives are advantageous in that they will not break down
in the event the electrolyte penetrates through the polypropylene
heat seal layer 40 during extended use or storage of the battery. A
conventional water or solvent based adhesive can be attacked by the
electrolyte.
[0047] The following test results demonstrate the improved strength
associated with these adhesives 44. Specifically, a test was
conducted to compare the seal strength of the cell package of the
present invention (in both the uncontaminated state and the
contaminated state) with the current cell package.
[0048] The following is a description of the test.
1 Conventional packaging material Polyester 23 .mu.m (outer layer)
Adhesive layer aqueous or solvent based Aluminum foil layer 20
.mu.m Adhesive layer aqueous or solvent based Low density PE/Surlyn
.RTM. 70 .mu.m (Heat seal layer) Packaging material according to
invention: Polyester layer 12 .mu.m (outer layer) Adhesive layer
aqueous or solvent based adhesive, or thermoset Aluminum foil layer
13 .mu.m Adhesive layer thermoset polyurethane Polypropylene 100
.mu.m (heat-seal layer)
[0049] Strips were cut of each packaging material and they were
heat sealed together to form pouches. A first group of pouches were
filled with organic electrolyte composed of a mixture of
dimethylcarbonate, diethylcarbonate, ethylenecarbonate, and
LiPF.sub.6. They were subsequent stored for 4 days at 60.degree. C.
20 mm strips were then cut from the pouches so the heat seal area
was in one end. The two pieces of packaging material, which
previously made up the sides of the pouch were then pulled apart at
a 180.degree. angle, and the force and failure mechanism were
determined. A second group of pouches were subjected to the tension
test without being contaminated.
[0050] In all cases the failure mode was delamination of the heat
seal layer from the Aluminum foil, so the test showed the quality
of the adhesive bonding those two layers together. The test results
are shown in the following table.
2 Seal strength of 20 mm wide strips No Electrolyte After 4 days @
60.degree. C. with Contamination Electrolyte Conventional Package
of Conventional Package of Packaging Invention Packaging Invention
Tensile 3.9 kg 9.1 kg 0.0 kg 4.7 kg strength 3.2 kg 10.2 kg 0.0 kg
5.2 kg 4.3 kg 10.9 kg 1.1 kg 9.5 kg 2.1 kg Average 3.8 kg 9.9 kg
0.8 kg 5.0 kg The conventional packaging used a aqueous based
adhesive The package of this invention used a thermoset
polyurethane based adhesive
[0051] As is apparent, the cell package material of the present
invention provides superior strength as compared to the
conventional cell package, both when contaminated with electrolyte
and when uncontaminated.
[0052] The Al foil layer should be thick enough to avoid pinholes,
preferably in the range of 25.mu. to 75.mu.. In the event that the
cell package must be preformed, a formable grade Al foil should be
used.
[0053] As noted above, the outer polyester layer 37 is designed to
provide mechanical strength to the cell package 14. It should be
understood that the invention is not limited to the use of
polyester for this layer. For example, a laminate of PET and PE
could be used as an alternative.
[0054] The methods of the present invention provides the following
important advantages. First, since the cell stack is sealed at the
time that the pouch is ruptured, there is minimal loss of
electrolyte. Also, there is no contamination of the equipment.
Further, since the cell package is evacuated prior to the rupturing
of the electrolyte pouch, electrolyte loss is further eliminate as
it will not be suctioned from the cell stack. Further, the only
step that must be performed in a glove box (i.e., a dry and inert
atmosphere) is the filling of the pouch with electrolyte and the
subsequent sealing of the pouch. The remaining assembly process
steps can be performed in a dry room. Therefore, the equipment used
for manufacturing the cell stack is less costly. Further, since the
vacuum is applied to the package cell under the condition that the
pouch is sealed inside the package, a higher vacuum pressure can be
applied to ensure deep impregnation of the electrolyte into the
cell stack without risking loss of electrolyte.
[0055] In addition, the cell package construction with the
polypropylene heat sealing layer and the special adhesive enables
the cell package to be heat sealed after the impregnation of the
electrolyte, using the first method described above, and retains
its integrity even when contaminated by electrolyte. Therefore,
additional steps associated with transferring the electrode stack
to another, uncontaminated cell package can be eliminated.
[0056] Further, using the tube technique for filling the cell stack
with the electrolyte eliminates altogether the need for heat
sealing a contaminated cell package.
[0057] The foregoing detailed description is illustrative of the
invention, and it is to be understood that additional embodiments
thereof will be obvious to those skilled in the art. The
embodiments disclosed herein together with those additional
embodiments are considered to be within the scope of the invention
as described in the claims appended hereto.
* * * * *