U.S. patent application number 09/828895 was filed with the patent office on 2001-08-30 for sealed battery and method of manufacturing the same.
Invention is credited to Kida, Yoshinori, Nishio, Koji, Nohma, Toshiyuki, Ohshita, Ryuji, Yoshida, Toshikazu.
Application Number | 20010016979 09/828895 |
Document ID | / |
Family ID | 13929416 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010016979 |
Kind Code |
A1 |
Kida, Yoshinori ; et
al. |
August 30, 2001 |
Sealed battery and method of manufacturing the same
Abstract
The opening to be sealed in a battery is sealed with an
electrical insulating sealant S by placing an electrical insulating
sealing material C, including a first sealing material A that is
soften by heat applied for sealing and a second sealing material B
that is more difficult to soften by the heat applied for sealing
than the first sealing material A, and by heating and successively
cooling the electrical insulating sealing material C. Thus, a
sealed battery with few defectives such as a sealing failure and a
short-circuit can be manufactured in a high yield rate.
Inventors: |
Kida, Yoshinori; (Osaka,
JP) ; Yoshida, Toshikazu; (Osaka, JP) ;
Ohshita, Ryuji; (Osaka, JP) ; Nohma, Toshiyuki;
(Osaka, JP) ; Nishio, Koji; (Osaka, JP) |
Correspondence
Address: |
KUBOVCIK & KUBOVCIK
SUITE 710
900 17TH STREET NW
WASHINGTON
DC
20006
|
Family ID: |
13929416 |
Appl. No.: |
09/828895 |
Filed: |
April 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09828895 |
Apr 10, 2001 |
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09268314 |
Mar 16, 1999 |
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6248139 |
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Current U.S.
Class: |
29/623.2 ;
429/185 |
Current CPC
Class: |
H01M 50/186 20210101;
Y02E 60/10 20130101; H01M 10/0525 20130101; H01M 50/548 20210101;
H01M 50/191 20210101; H01M 10/052 20130101; Y02P 70/50 20151101;
Y10T 29/4911 20150115; H01M 50/193 20210101; H01M 50/183 20210101;
H01M 50/557 20210101; H01M 50/195 20210101; H01M 50/562
20210101 |
Class at
Publication: |
29/623.2 ;
429/185 |
International
Class: |
H01M 002/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 1998 |
JP |
10-87959 |
Claims
What is claimed is:
1. A method of manufacturing a sealed battery comprising a step of
forming an electrical insulating sealant S for sealing an opening
by placing an electrical insulating sealing material C, including a
first sealing material A that is molten by heat applied for sealing
and a second sealing material B that is more difficult to soften by
the heat applied for sealing than the first sealing material A, on
the opening and by heating and successively cooling the electrical
insulating sealing material C.
2. The method of manufacturing a sealed battery according to claim
1, wherein the first sealing material A is polyolefin, and the
second sealing material B is poly(ethylene terephthalate), alumina
or silica.
3. The method of manufacturing a sealed battery according to claim
1, wherein the first sealing material A is polyethylene or
polypropylene having a melting point of 110.degree. C. through
170.degree. C., and the second sealing material B is poly(ethylene
terephthalate).
4. The method of manufacturing a sealed battery according to claim
1, wherein the second sealing material B is in the form of a mesh
or a powder.
5. The method of manufacturing a sealed battery according to claim
1, wherein the second sealing material B is in the form of a
mesh.
6. The method of manufacturing a sealed battery according to claim
1, wherein there is a difference of 50.degree. C. or more between a
melting point of the first sealing material A and a softening point
of the second sealing material B.
7. The method of manufacturing a sealed battery according to claim
1, wherein the electrical insulating sealing material C is heated
at a temperature where the second sealing material B is
substantially not softened.
8. A sealed battery comprising an electrical insulating sealant S
for sealing an opening, the electrical insulating sealant S
including a first sealing material A that is molten by heat applied
for sealing and a second sealing material B that is more difficult
to soften by the heat applied for sealing than the first sealing
material A.
9. The sealed battery according to claim 8, wherein the first
sealing material A is polyolefin, and the second sealing material B
is poly(ethylene terephthalate), alumina or silica.
10. The sealed battery according to claim 8, wherein the first
sealing material A is polyethylene or polypropylene having a
melting point of 110.degree. C. through 170.degree. C., and the
second sealing material B is poly(ethylene terephthalate).
11. The sealed battery according to claim 8, wherein the second
sealing material B is in the form of a mesh or a powder.
12. The sealed battery according to claim 8, wherein the second
sealing material B is in the form of a mesh.
13. The sealed battery according to claim 8, wherein there is a
difference of 50.degree. C. or more between a melting point of the
first sealing material A and a softening point of the second
sealing material B.
14. The sealed battery according to claim 8, wherein the second
sealing material B is substantially not softened by the heat
applied for sealing.
Description
BACKGROUND OF THE INVENTION
[0001] This application claims the priority of Japanese Patent
Application No. 10-87959 filed on Mar. 16, 1998, which is
incorporated herein by reference.
[0002] The present invention relates to a sealed battery and a
method of manufacturing the sealed battery.
[0003] Sealing of a battery for preventing leakage of the
electrolyte solution and protecting a water reactive active
material used therein is conventionally conducted by placing a
sealing material on the opening of the housing of the battery, and
melting and then cooling the sealing material thereon.
[0004] In this sealing process, when the opening of the battery
requires prevention of a short-circuit, a sealing material with an
electrical insulating property is particularly used.
[0005] Therefore, any of electrical insulating materials, such as
polyethylene and polypropylene, that can be adhered to the housing
when thermally molten by heat applied for sealing was used as the
conventional sealing material.
[0006] However, such a conventional heat-melting adhesive sealing
material can easily flow out of the opening during the sealing
process, and hence, the sealing tends to be incomplete. Such
incomplete sealing can result in leakage of the electrolyte
solution and a short life of the battery. Also, in the case where
the sealing material also serving as the electrical insulating
material flows out, a short-circuit can be easily caused when the
housing is slightly deformed by the sealing heat, resulting in
decreasing the yield rate of batteries.
SUMMARY OF THE INVENTION
[0007] In consideration of the aforementioned conventional
disadvantages, an object of the invention is providing a sealed
battery with few defectives such as a sealing failure and a
short-circuit and a method of manufacturing the sealed battery in a
high yield rate.
[0008] The method of manufacturing a sealed battery of this
invention comprises a step of forming an electrically insulating
sealant S for sealing an opening by placing an electrical
insulating sealing material C, including a first sealing material A
that is molten by heat applied for sealing and a second sealing
material B that is more difficult to soften by the heat applied for
sealing than the first sealing material A, on the opening and by
heating and successively cooling the electrical insulating sealing
material C.
[0009] Alternatively, the sealed battery of this invention
comprises an electrical insulating sealant S for sealing an
opening, and the electrical insulating sealant S includes a first
sealing material A that is molten by heat applied for sealing and a
second sealing material B that is more difficult to soften by the
heat applied for sealing than the first sealing material A.
[0010] In this manner, the invention provides a sealed battery with
few defectives such as a sealing failure and a short-circuit and a
method of manufacturing the sealed battery in a high yield
rate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same become better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0012] FIG. 1 is a perspective view for showing procedures adopted
in an example of the invention; and
[0013] FIG. 2 is a sectional view of a lithium secondary battery
manufactured in the example of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] According to a method of manufacturing a sealed battery of
the invention, in sealing an opening with an electrical insulating
sealant S, an electrical insulating sealing material C including a
first sealing material A that is molten by heat applied for sealing
and a second sealing material B that is more difficult to soften by
the heat applied for sealing than the first sealing material A is
placed on the opening. This sealing material C is heated and then
cooled on the opening, so as to form the electrical insulating
sealant S.
[0015] A sealed battery according to the invention comprises an
electrical insulating sealant S for sealing an opening including a
first sealing material A that is molten by heat applied for sealing
and a second sealing material B that is more difficult to soften by
the heat applied for sealing than the first sealing material A.
[0016] The first sealing material A is not herein specified and can
be any electrical insulating sealing materials as far as a part of
or all the material can be thermally molten to be adhered onto a
material of a housing or the like in the opening. Preferable
examples of the first sealing material A include polyolefins such
as polyethylene, polypropylene and polybutene, among which
polyethylene and polypropylene having a melting point of
110.degree. C. through 170.degree. C. are more preferred.
[0017] The second sealing material B can be any of electrical
insulating sealing materials that are more difficult to soften by
the sealing heat than the first sealing material A. Specific
examples include poly(ethylene terephthalate), alumina and silica,
among which poly(ethylene terephthalate) is preferred. In the case
where a material with a significantly low melting point, such as
polyethylene, is used as the first sealing material A,
polypropylene that has a higher melting point and is more difficult
to soften can be used as the second sealing material B. As the
second sealing material B, a material that is not substantially
softened by the sealing heat is preferably used. In order that the
first sealing material A alone is molten but the second sealing
material B is not substantially softened during the sealing
process, it is preferred, from a view point of sealing workability,
that the second sealing material B has a softening point higher by
50.degree. C. or more than the melting point of the first sealing
material A. Means for applying the sealing heat is not herein
specified. For example, external heating means such as a heater or
magnetic induction heating means can be used.
[0018] The first sealing material A is not specified in its shape
because it is molten in the sealing process. In contrast, the
second sealing material B should retain its original shape after
the sealing process so as to provide the sealed portion of the
housing with the electrical insulting property, and therefore is
preferably in the form of a mesh or a powder. More preferably, the
second sealing material B is in the form of a mesh which can be
entangled with the molten first sealing material A during the
sealing process so as to exhibit an effect of suppressing the first
sealing material A from flowing out of the opening to be
sealed.
[0019] The first sealing material A functions not only as a part of
the electrical insulating sealant S after the sealing process but
also as an adhesive with being partly or entirely molten during the
sealing process. In a conventional method of manufacturing a sealed
battery, the battery is sealed with this first sealing material A
alone. Therefore, the sealing material can flow out of the opening
during the sealing process, resulting in occasionally causing a
sealing failure. In contrast, according to the method of the
invention, the second sealing material B is used in addition to the
first sealing material A. The second sealing material B functions
as a part of the electrical insulating sealant S after the sealing
process similarly to the first sealing material A. In addition, the
second sealing material B is more difficult to soften by the
sealing heat than the first sealing material A, and hence is more
difficult to flow out of the opening to be sealed during the
sealing process. Accordingly, when the present method is adopted,
even if the housing or the like of the battery is slightly deformed
by the sealing heat, a sealing failure and a short-circuit can be
avoided.
[0020] Other features of the invention will become more apparent in
the course of the following descriptions of exemplary embodiments
which are given for illustration of the invention and not intended
to be limiting thereof.
[0021] Various kinds of card type sealed lithium secondary
batteries, respectively using different sealants in their openings,
were manufactured as follows, so as to examine the incidence of a
short-circuit and the capacity degradation ratio during
charge-discharge cycles.
Manufacture of Batteries A1 Through A6
[0022] Preparation of Positive Electrode
[0023] A mixture including LiCoO.sub.2 serving as a positive
electrode active material, artificial graphite serving as a
conducting agent, and poly(vinylidene fluoride) serving as a binder
in a ratio by weight of 8:1:1 and N-methyl-2-pyrollidone were
kneaded to give a slurry. The slurry was applied on one surface of
an aluminum foil serving as a collector by a doctor blade method,
and the resultant foil was dried under vacuum at a temperature of
150.degree. C. for 2 hours. In this manner, a plate-shaped positive
electrode (with a size of 6.4 cm.times.2.4 cm.times.0.15 cm) was
prepared.
[0024] Preparation of Negative Electrode
[0025] A mixture including a natural graphite powder (having a
lattice spacing d.sub.002 between lattice planes (002) of 3.35
.ANG. and an Lc, a crystallite size in the c-axis direction,
exceeding 1000 .ANG.) serving as a lithium ion intercalating agent
and poly(vinylidene fluoride) serving as a binder in a ratio by
weight of 9:1 and N-methyl-2-pyrollidone were kneaded to give a
slurry. The slurry was applied on one surface of a copper foil
serving as a collector by the doctor blade method, and the
resultant foil was dried under vacuum at a temperature of
150.degree. C. for 2 hours. In this manner, a plate-shaped negative
electrode (with a size of 6.6 cm.times.2.6 cm.times.0.15 cm) was
prepared.
[0026] Preparation of Electrolyte Solution
[0027] An electrolyte solution was prepared by dissolving, in a
concentration of 1 mole per liter, LiPF.sub.6 in a mixed solvent
including ethylene carbonate and diethyl carbonate in a ratio by
volume of 1:1.
[0028] Manufacture of Batteries
[0029] Card type sealed lithium secondary batteries were
manufactured by using the aforementioned positive and negative
electrodes and electrolyte solution. The manufacturing procedures
for these sealed batteries will now be described with reference to
the accompanying drawings.
[0030] With regard to each battery, an electrode body 1 was
fabricated by successively stacking the positive electrode, a
separator impregnated with the electrolyte solution and the
negative electrode. Also, two sheets of a first sealing material A
each with a length of 9 cm, a width of 5 cm and a thickness of 100
.mu.m were respectively cut, at the centers thereof, into a size
with a length of 7 cm and a width of 3 cm. Thus, two sheets of the
first sealing material A to be used in each battery were obtained.
Then, a 30-mesh sheet of a second sealing material B was cut, at
the center thereof, into a size with a length of 7 cm and a width
of 3 cm. Thus, the second sealing material B to be used in each
battery was obtained. The second sealing material B was sandwiched
between the two sheets of the first sealing material A, thereby
preparing an electrical insulating sealing material C for each
battery. However, in batteries A5 and A6, another type of
electrical insulating sealing material C obtained as follows was
used: 0.1 g of a powder (of the second sealing material B) with an
average particle size of 20 .mu.m was sandwiched between two sheets
(of the first sealing material A) each with a length of 9 cm, a
width of 5 cm and a thickness of 100 .mu.m. The resultant sheets
were pressed at a pressure of 100 kgf/cm.sup.2, thereby obtaining a
sheet with a thickness of 230 .mu.m. This sheet was cut, at the
center thereof, into a size with a length of 7 cm and a width of 3
cm, which was used as the electrical insulating sealing material C
for these batteries.
[0031] Next, as is shown in FIG. 1, a negative electrode housing
member 2a of a stainless foil (SUS 304) was placed on a support M.
The electrode body 1 was placed at the center of the negative
electrode housing member 2a, and the sealing material C (not shown)
was placed in the periphery of the negative electrode housing
member 2a. Thereafter, a positive electrode housing member 2b of an
aluminum foil was placed on top.
[0032] Then, an elevation type mold W for sealing (with a frame
having a thickness of 1 cm) connected with a heater (not shown) was
lowered. With a pressure of 5 kgf/cm.sup.2 applied to the positive
electrode housing member 2b, the mold W was heated to a temperature
of 140.degree. C. (whereas 170.degree. C. and 215.degree. C. in
manufacture of batteries A3 and A4, respectively) by turning the
heater on, and the temperature was retained for 5 seconds, thereby
melting the first sealing material A. Thereafter, the heater was
turned off so as to decrease the temperature of the mold W, and
thus, the negative electrode housing member 2a and the positive
electrode housing member 2b were adhered to the electrical
insulating sealing material C. In this manner, each of batteries A1
through A6 was manufactured. These batteries are present batteries
manufactured in accordance with the invention. FIG. 2 is a
schematic sectional view of the present battery thus manufactured.
The present battery X of FIG. 2 comprises a positive electrode 5, a
negative electrode 6, a separator 7, the negative electrode housing
member 2a, the positive electrode housing member 2b and the sealant
S. The sealant S includes the first sealing material A that is
molten by the heat applied for sealing and the second sealing
material B (in the form of a mesh in FIG. 2) that is more difficult
to soften by the heat applied for sealing than the first sealing
material A, and the sealant S has an electrical insulating
property. Since the present battery X thus comprises the sealant S
including the second sealing material B that is difficult to soften
by the heat applied for sealing, the battery has less fear of
short-circuit. In addition, there is less fear of a sealing
failure, and hence, the capacity scarcely decreases through
repeated charge-discharge cycles.
Manufacture of Battery C1
[0033] A battery C1 was manufactured in the same manner as
described above with regard to the battery A1 (sealed at a
temperature of 140.degree. C.) except that two sheets of
polyethylene (i.e., the first sealing material A) alone were
stacked to obtain the electrical insulating sealing material. The
battery C1 is a comparative battery manufactured by a conventional
method.
[0034] Table 1 lists the first sealing materials A and the second
sealing materials B used in the respective batteries, whereas a
softening point of Table 1 is a vicat softening temperature.
1TABLE 1 Battery First sealing material A Second sealing material B
A1 polyethylene poly(ethylene terephthalate) (melting point:
135.degree. C.) (mesh) (softening point: 255.degree. C.) A2
polyethylene polypropylene (melting point: 135.degree. C.) (mesh)
(softening point: 150.degree. C.) A3 polypropylene poly(ethylene
terephthalate) (melting point: 165.degree. C.) (mesh) (softening
point: 255.degree. C.) A4 polybutene poly(ethylene terephthalate)
(melting point: 210.degree. C.) (mesh) (softening point:
255.degree. C.) A5 polyethylene poly(ethylene terephthalate)
(melting point: 135.degree. C.) (powder with average particle size
of 20 .mu.m) (softening point: 255.degree. C.) A6 polyethylene
alumina (melting point: 135.degree. C.) (powder with average
particle size of 20 .mu.m) (not softened at 300.degree. C. or
lower) C1 polyethylene not used (melting point: 135.degree. C.)
[0035] Short-Circuit Test
[0036] Internal resistances of 100 batteries were measured with
regard to each of the aforementioned kinds of batteries so as to
examine the incidence (%) of a short-circuit battery. A battery
having an internal resistance of 1 .OMEGA. or less at 1 kHz was
determined to be a short-circuit battery. The thus obtained
incidence is shown in Table 2:
2 TABLE 2 Battery Incidence of short-circuit (%) A1 1 A2 4 A3 1 A4
3 A5 1 A6 1 C1 11
[0037] As is shown in Table 2, the incidence of short-circuit in
the present batteries A1 through A6 is much lower than that in the
comparative battery C1 manufactured by the conventional method. In
particular, the incidence of short-circuit is as low as merely 1%
in the batteries A1, A3, A5 and A6, in which a difference between
the melting point of the first sealing material A and the softening
point of the second sealing material B is 50.degree. C. or
more.
[0038] Capacity Degradation Ratio
[0039] With regard to twenty batteries of each kind where no
short-circuit was caused, 200 charge-discharge cycles were run, in
which each battery was charged at 50 mA to 4.1 V and discharged at
50 mA to 2.8 V. Thus, an average capacity degradation ratio per
cycle (%/cycle) up to the 200th cycle defined by the following
formula was obtained. The thus obtained ratios are shown in Table
3, wherein the capacity degradation ratio is an average of those
obtained in the twenty batteries of each kind.
Capacity degradation ratio={(discharge capacity in 1st
cycle-discharge capacity in 200th cycle)/discharge capacity in 1st
cycle}.div.199 (cycles).times.100
[0040]
3 TABLE 3 Battery Discharge degradation ratio (%/cycle) A1 0.07 A2
0.10 A3 0.07 A4 0.09 A5 0.07 A6 0.14 C1 0.22
[0041] As is shown in Table 3, the capacity degradation ratios of
the present batteries A1 through A6 manufactured by the present
method are much lower than that of the comparative battery C1
manufactured by the conventional method. Furthermore, the capacity
degradation ratio is particularly low in the batteries A1 and A3
through A5 which include poly(ethylene terephthalate) as the second
sealing material B. This seems because entanglement (integration)
between poly(ethylene terephthalate) and polyolefin is so good that
a sealing failure scarcely occurs.
[0042] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described herein.
* * * * *