U.S. patent application number 12/548287 was filed with the patent office on 2010-03-18 for flat battery.
Invention is credited to Kenji TSUDA, Noriyuki YABUSHITA, Koji YAMAGUCHI, Toshikazu YOSHIBA.
Application Number | 20100068614 12/548287 |
Document ID | / |
Family ID | 42007521 |
Filed Date | 2010-03-18 |
United States Patent
Application |
20100068614 |
Kind Code |
A1 |
YAMAGUCHI; Koji ; et
al. |
March 18, 2010 |
FLAT BATTERY
Abstract
A flat battery of the present invention is a flat battery
including an exterior can and a sealing can with which an opening
of the exterior can is sealed, wherein the exterior can and the
sealing can include a bottom portion and a circumferential wall
extending upright from an outer circumference of the bottom portion
and have a cylindrical shape that is open at one end; a distal end
portion of the circumferential wall of the exterior can is bent
toward a central axis of the sealing can to form a curve, whereby
the exterior can is fixed to the sealing can by crimping; in a
cross-sectional shape of the sealing can in the direction of the
central axis, the circumferential wall of the sealing can is a
single layer wall without being folded back, and the
circumferential wall of the sealing can includes a rectilinear
portion that is connected to the bottom portion via a corner
portion; and the rectilinear portion has a Vickers hardness greater
than the Vickers hardness of the corner portion.
Inventors: |
YAMAGUCHI; Koji; (Osaka,
JP) ; YABUSHITA; Noriyuki; (Osaka, JP) ;
YOSHIBA; Toshikazu; (Osaka, JP) ; TSUDA; Kenji;
(Osaka, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
42007521 |
Appl. No.: |
12/548287 |
Filed: |
August 26, 2009 |
Current U.S.
Class: |
429/162 |
Current CPC
Class: |
H01M 50/171 20210101;
Y10T 29/4911 20150115; H01M 50/166 20210101; H01M 50/131 20210101;
H01M 50/109 20210101; Y02E 60/10 20130101 |
Class at
Publication: |
429/162 |
International
Class: |
H01M 6/46 20060101
H01M006/46 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2008 |
JP |
2008-239353 |
Sep 18, 2008 |
JP |
2008-239354 |
Sep 19, 2008 |
JP |
2008-241247 |
Claims
1. A flat battery comprising an exterior can and a sealing can with
which an opening of the exterior can is sealed, wherein the
exterior can and the sealing can comprise a bottom portion and a
circumferential wall extending upright from an outer circumference
of the bottom portion and have a cylindrical shape that is open at
one end; a distal end portion of the circumferential wall of the
exterior can is bent toward a central axis of the sealing can to
form a curve, whereby the exterior can is fixed to the sealing can
by crimping; in a cross-sectional shape of the sealing can in a
direction of the central axis, the circumferential wall of the
sealing can is a single layer wall without being folded back, and
the circumferential wall of the sealing can comprises a rectilinear
portion that is connected to the bottom portion via a corner
portion; and the rectilinear portion has a Vickers hardness greater
than a Vickers hardness of the corner portion.
2. The flat battery according to claim 1, wherein the Vickers
hardness of the corner portion is 150 or more, and the Vickers
hardness of the rectilinear portion is 200 or more.
3. The flat battery according to claim 1, wherein the Vickers
hardness of the rectilinear portion is 1.05 times or more greater
than the Vickers hardness of the corner portion.
4. The flat battery according to claim 1, wherein the rectilinear
portion is work hardened by processing that causes the rectilinear
portion to be compressed.
5. The flat battery according to claim 1, wherein a gasket is
pressed against the circumferential wall of the sealing can so as
to press the circumferential wall of the sealing can toward the
central axis.
6. The flat battery according to claim 1, wherein the
circumferential wall of the sealing can is stepped at a shoulder
portion, a gasket is interposed between the shoulder portion and
the circumferential wall of the exterior can, and the gasket is
pressed in a height direction of the sealing can.
7. A flat battery comprising an exterior can and a sealing can with
which an opening of the exterior can is sealed, wherein the
exterior can and the sealing can comprise a bottom portion and a
circumferential wall extending upright from an outer circumference
of the bottom portion and have a cylindrical shape that is open at
one end; a distal end portion of the circumferential wall of the
exterior can is bent toward a central axis of the sealing can to
form a curve, whereby the exterior can is fixed to the sealing can
by crimping; in a cross-sectional shape of the sealing can in a
direction of the central axis, the circumferential wall of the
sealing can is a single layer wall without being folded back and is
connected to the bottom portion via a corner portion; an upright
portion, of the circumferential wall of the sealing can, sandwiched
between the curved distal end portion of the circumferential wall
of the exterior can and the bottom portion of the exterior can has
a thickness greater than a thickness of the corner portion; and the
upright portion has a Vickers hardness greater than a Vickers
hardness of the corner portion.
8. The flat battery according to claim 7, wherein throughout the
circumferential wall of the sealing can, the Vickers hardness is
greater than the Vickers hardness of the corner portion.
9. The flat battery according to claim 7, wherein the Vickers
hardness of the corner portion is 150 or more, and the Vickers
hardness of the upright portion is 200 or more.
10. The flat battery according to claim 7, wherein the Vickers
hardness of the upright portion is 1.05 times or more greater than
the Vickers hardness of the corner portion.
11. The flat battery according to claim 7, wherein the upright
portion is work hardened by processing that causes the
circumferential wall of the sealing can to be compressed.
12. The flat battery according to claim 7, wherein a gasket is
pressed against the circumferential wall of the sealing can so as
to press the circumferential wall of the sealing can toward the
central axis.
13. The flat battery according to claim 7, wherein the
circumferential wall of the sealing can is stepped at a shoulder
portion, a gasket is interposed between the shoulder portion and
the circumferential wall of the exterior can, and the gasket is
pressed in a height direction of the sealing can.
14. A flat battery comprising an exterior can and a sealing can
with which an opening of the exterior can is sealed, wherein the
exterior can and the sealing can comprise a bottom portion and a
circumferential wall extending upright from an outer circumference
of the bottom portion and have a cylindrical shape that is open at
one end; a gasket is interposed between an outer circumferential
face of the circumferential wall of the sealing can and an inner
circumferential face of the circumferential wall of the exterior
can; a distal end portion of the circumferential wall of the
exterior can is bent toward a central axis of the sealing can to
form a curve, whereby the exterior can is fixed to the sealing can
by crimping; and in a cross-sectional shape of the sealing can in a
direction of the central axis, the circumferential wall of the
sealing can is a single layer wall without being folded back, the
bottom portion of the sealing can is a planar portion, the
circumferential wall of the sealing can comprises a rectilinear
portion that is connected to the planar portion via a corner
portion, and an angle .theta.1 formed by the planar portion and the
rectilinear portion is greater than 90.degree..
15. The flat battery according to claim 14, wherein the angle
.theta.1 is 90.5.degree. or more.
16. The flat battery according to claim 14, wherein the angle
.theta.1 is 95.degree. or less.
17. The flat battery according to claim 14, wherein the gasket is
pressed against the circumferential wall of the sealing can so as
to press the circumferential wall of the sealing can toward the
central axis.
18. The flat battery according to claim 14, wherein the
circumferential wall of the sealing can is stepped at a shoulder
portion, the gasket is interposed between the shoulder portion and
the circumferential wall of the exterior can, and the gasket is
pressed in a height direction of the sealing can.
19. The flat battery according to claim 14, wherein an angle
.theta.2 formed by the planar portion and the rectilinear portion
at the time when the sealing can is in a separated state before
assembly is 92.degree. or more.
20. The flat battery according to claim 14, wherein when an angle
formed by the planar portion and the rectilinear portion at the
time when the sealing can is in a separated state before assembly
is an angle .theta.2, an angle difference .theta.3 between the
angle .theta.2 and the angle .theta.1 is between 0.5.degree. and
5.degree. inclusive.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a flat battery known as a
coin-shaped battery or a button-shaped battery.
[0003] 2. Description of Related Art
[0004] Flat batteries known as coin-shaped batteries or
button-shaped batteries are used as a power supply, mainly for
memory backup, in information devices, video equipment, and so on.
FIG. 37 shows a perspective view of an example of a conventional
flat battery. A flat battery 100 is constructed by combining an
exterior can 101 serving as a positive electrode can and a sealing
can 102 serving as a negative electrode can.
[0005] FIG. 38 is a cross-sectional view taken along line FF in
FIG. 37. The flat battery 100 houses a power generating element 110
and is filled with a nonaqueous electrolyte. A gasket 103 is
interposed between a circumferential wall 104 of the exterior can
101 and a folded-back portion 107 of a circumferential wall 105 of
the sealing can 102. Sufficient strength of the portion of the
sealing can 102 that is in close contact with the gasket 103 is
ensured by the folded-back portion 107 formed in the sealing can
102.
[0006] A distal end portion 104a of the circumferential wall 104 of
the exterior can 101 is bent toward a central axis 106 of the
sealing can 102 to form a curve, whereby the exterior can 101 is
fixed to the sealing can 102 by crimping. Thus, a gap between the
exterior can 101 and the sealing can 102 is sealed with the gasket
103, and the exterior can 101 and the sealing can 102 having
different polarities are insulated from each other.
[0007] For example, WO 02/013290 and JP 2003-151511A also disclose
flat batteries that include a structure corresponding to the
folded-back portion 107. A configuration in which the folded-back
portion 107 is formed is advantageous in terms of the strength, but
is disadvantageous in increasing the capacity.
[0008] Specifically, the external dimensions of the flat battery
100 are defined as predetermined dimensions. Assuming flat
batteries have the same external dimensions, a corner portion 108
of the sealing can 102 in a configuration with the folded-back
portion 107 is shifted toward the central axis 106 as compared with
that in a configuration without the folded-back portion 107, which
results in an accordingly reduced capacity.
[0009] On the other hand, JP 7-57706A, JP 2003-68254A, JP
4-341756A, and Japanese Patent No. 3399801 disclose configurations
without the folded-back portion 107. These configurations are
advantageous in increasing the capacity.
[0010] However, a configuration without the folded-back portion 107
as proposed by JP 7-57706A, JP 2003-68254A, JP 4-341756A, and
Japanese Patent No. 3399801, though advantageous in increasing the
capacity, is disadvantageous in terms of the strength.
Specifically, referring to FIG. 38, during a crimping process by
which the distal end portion 104a of the circumferential wall 104
of the exterior can 101 is bent toward the central axis 106 to form
a curve, the circumferential wall 105 of the sealing can 102 is
also deformed toward the central axis 106. In other words, the
circumferential wall 105 is deformed in a direction away from an
inner circumferential face of the gasket 103. At this time, in a
configuration without the folded-back portion 107, the adhesion
between the circumferential wall 105 and the gasket 103 is reduced,
which, in some cases, results in an insufficient seal with the
gasket 103.
[0011] JP 7-57706A proposes a configuration for preventing an
insufficient seal as described above, but does not go so far as to
propose compensation for lack of strength. In addition, processing
for changing the plate thickness of the circumferential wall is
necessary.
SUMMARY OF THE INVENTION
[0012] The present invention has been conceived to address the
conventional problems as described above, and it is an object
thereof to provide a flat battery that is advantageous in
increasing the capacity while ensuring the sealing properties.
[0013] In order to achieve this object, a flat battery according to
a first aspect of the present invention is a flat battery including
an exterior can and a sealing can with which an opening of the
exterior can is sealed, wherein the exterior can and the sealing
can include a bottom portion and a circumferential wall extending
upright from an outer circumference of the bottom portion and have
a cylindrical shape that is open at one end; a distal end portion
of the circumferential wall of the exterior can is bent toward a
central axis of the sealing can to form a curve, whereby the
exterior can is fixed to the sealing can by crimping; in a
cross-sectional shape of the sealing can in the direction of the
central axis, the circumferential wall of the sealing can is a
single layer wall without being folded back, and the
circumferential wall of the sealing can includes a rectilinear
portion that is connected to the bottom portion via a corner
portion; and the rectilinear portion has a Vickers hardness greater
than the Vickers hardness of the corner portion.
[0014] A flat battery according to a second aspect of the present
invention is a flat battery including an exterior can and a sealing
can with which an opening of the exterior can is sealed, wherein
the exterior can and the sealing can include a bottom portion and a
circumferential wall extending upright from an outer circumference
of the bottom portion and have a cylindrical shape that is open at
one end; a distal end portion of the circumferential wall of the
exterior can is bent toward a central axis of the sealing can to
form a curve, whereby the exterior can is fixed to the sealing can
by crimping; in a cross-sectional shape of the sealing can in the
direction of the central axis, the circumferential wall of the
sealing can is a single layer wall without being folded back and is
connected to the bottom portion via a corner portion; an upright
portion, of the circumferential wall of the sealing can, sandwiched
between the curved distal end portion of the circumferential wall
of the exterior can and the bottom portion of the exterior can has
a thickness greater than the thickness of the corner portion; and
the upright portion has a Vickers hardness greater than the Vickers
hardness of the corner portion.
[0015] A flat battery according to a third aspect of the present
invention is a flat battery including an exterior can and a sealing
can with which an opening of the exterior can is sealed, wherein
the exterior can and the sealing can include a bottom portion and a
circumferential wall extending upright from an outer circumference
of the bottom portion and have a cylindrical shape that is open at
one end; a gasket is interposed between an outer circumferential
face of the circumferential wall of the sealing can and an inner
circumferential face of the circumferential wall of the exterior
can; a distal end portion of the circumferential wall of the
exterior can is bent toward a central axis of the sealing can to
form a curve, whereby the exterior can is fixed to the sealing can
by crimping; and in a cross-sectional shape of the sealing can in
the direction of the central axis, the circumferential wall of the
sealing can is a single layer wall without being folded back, the
bottom portion of the sealing can is a planar portion, the
circumferential wall of the sealing can includes a rectilinear
portion connected to the planar portion via a corner portion, and
an angle .theta.1 formed by the planar portion and the rectilinear
portion is greater than 90.degree..
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a flat battery according to
Embodiment 1 of the present invention.
[0017] FIG. 2 is a cross-sectional view taken along line AA in FIG.
1.
[0018] FIG. 3 is an exploded view of the flat battery 1 shown in
FIG. 2.
[0019] FIG. 4 is a diagram showing a state in which a disk-like
member is blanked from a plate material according to Embodiment 1
of the present invention.
[0020] FIGS. 5A to 5E are diagrams showing the change in the shape
of a workpiece after undergoing each step according to Embodiment 1
of the present invention.
[0021] FIG. 6 is a diagram showing a method for shaping a sealing
can according to a comparative example.
[0022] FIG. 7A is a diagram showing the points of measurement of
the Vickers hardness in Working Example 1.
[0023] FIG. 7B is a diagram showing the points of measurement of
the Vickers hardness in Comparative Example 1.
[0024] FIG. 8 is a graph showing the relationship between the
measuring points and the Vickers hardness for Working Example 1 and
Comparative Example 1.
[0025] FIGS. 9A and 9B are cross-sectional views of the flat
battery according to Embodiment 1 of the present invention in the
middle of assembly, where FIG. 9A is a cross-sectional view showing
a state in which a gasket 4 is installed on a sealing can 3, and
FIG. 9B is a cross-sectional view showing a state in which a power
generating element 10 is housed in the sealing can 3.
[0026] FIG. 10 is a cross-sectional view showing a state in which
an exterior can 2 is fitted on an assembly shown in FIG. 9B.
[0027] FIG. 11 is a cross-sectional view showing a state before
crimping according to Embodiment 1 of the present invention.
[0028] FIG. 12 is a cross-sectional view showing a state after
crimping according to Embodiment 1 of the present invention.
[0029] FIGS. 13A and 13B are cross-sectional views for performing a
comparison between Embodiment 1 of the present invention and a
comparative example, where FIG. 13A is a cross-sectional view of
the comparative example, and FIG. 13B is a cross-sectional view of
Embodiment 1 of the present invention.
[0030] FIG. 14 is a perspective view of a flat battery according to
Embodiment 2 of the present invention.
[0031] FIG. 15 is a cross-sectional view taken along line CC in
FIG. 14.
[0032] FIG. 16 is an exploded view of the flat battery 1 shown in
FIG. 15.
[0033] FIG. 17 is a diagram showing a state in which a disk-like
member is blanked from a plate material according to Embodiment 2
of the present invention.
[0034] FIG. 18 is a diagram showing the change in the shape of a
workpiece after undergoing each step according to Embodiment 2 of
the present invention.
[0035] FIG. 19 is a diagram showing a method for shaping a sealing
can according to a comparative example.
[0036] FIG. 20A is a diagram showing the points of measurement of
the Vickers hardness in Working Example 2.
[0037] FIG. 20B is a diagram showing the points of measurement of
the Vickers hardness in Comparative Example 2.
[0038] FIG. 21 is a graph showing the relationship between the
measuring points and the Vickers hardness and the relationship
between the measuring points and the thickness shrinkage percentage
for Working Example 2 and Comparative Example 2.
[0039] FIGS. 22A and 22B are cross-sectional views of the flat
battery according to Embodiment 2 of the present invention in the
middle of assembly, where FIG. 22A is a cross-sectional view
showing a state in which a gasket 4 is installed on a sealing can
3, and FIG. 22B is a cross-sectional view showing a state in which
a power generating element 10 is housed in the sealing can 3.
[0040] FIG. 23 is a cross-sectional view showing a state in which
an exterior can 2 is fitted on an assembly shown in FIG. 22B.
[0041] FIG. 24 is a cross-sectional view showing a state before
crimping according to Embodiment 2 of the present invention.
[0042] FIG. 25 is a cross-sectional view showing a state after
crimping according to Embodiment 2 of the present invention.
[0043] FIGS. 26A and 26B are cross-sectional views for performing a
comparison between Embodiment 2 of the present invention and a
comparative example, where FIG. 26A is a cross-sectional view of
the comparative example, and FIG. 26B is a cross-sectional view of
Embodiment 2 of the present invention.
[0044] FIG. 27 is a perspective view of a flat battery according to
Embodiment 3 of the present invention.
[0045] FIG. 28 is a cross-sectional view taken along line EE in
FIG. 27.
[0046] FIG. 29 is an exploded view of the flat battery 1 shown in
FIG. 28.
[0047] FIG. 30 is an enlarged view of and around a circumferential
wall 16 of a sealing can 3 shown in FIG. 29.
[0048] FIGS. 31A and 31B are cross-sectional views of the flat
battery according to Embodiment 3 of the present invention in the
middle of assembly, where FIG. 31A is a cross-sectional view
showing a state in which a gasket 4 is installed on the sealing can
3, and FIG. 31B is a cross-sectional view showing a state in which
a power generating element 10 is housed in the sealing can 3.
[0049] FIG. 32 is a cross-sectional view showing a state in which
an exterior can 2 is fitted on an assembly shown in FIG. 31B.
[0050] FIG. 33 is a cross-sectional view showing a state before
crimping according to Embodiment 3 of the present invention.
[0051] FIG. 34 is a cross-sectional view showing a state after
crimping according to Embodiment 3 of the present invention.
[0052] FIG. 35 is a diagram for illustrating the change in an angle
formed by a planar portion and a rectilinear portion between when
the sealing can according to Embodiment 3 of the present invention
is in a separated state and when the sealing can is in an assembled
state.
[0053] FIGS. 36A and 36B are cross-sectional views for performing a
comparison between Embodiment 3 of the present invention and a
comparative example, where FIG. 36A is a cross-sectional view of
the comparative example, and FIG. 36B is a cross-sectional view of
Embodiment 3 of the present invention.
[0054] FIG. 37 is a perspective view of an example of a
conventional flat battery.
[0055] FIG. 38 is a cross-sectional view taken along line FF in
FIG. 37.
DETAILED DESCRIPTION OF THE INVENTION
[0056] According to the flat battery of the first aspect of the
present invention, in the sealing can, the Vickers hardness of the
rectilinear portion is greater than the Vickers hardness of the
corner portion. Therefore, deformation of both the corner portion
and the rectilinear portion is suppressed during a crimping
process, and the sealing properties provided by a gasket are thus
maintained.
[0057] In the flat battery of the first aspect of the present
invention, it is preferable that the Vickers hardness of the corner
portion is 150 or more, and the Vickers hardness of the rectilinear
portion is 200 or more.
[0058] Moreover, it is preferable that the Vickers hardness of the
rectilinear portion is 1.05 times or more greater than the Vickers
hardness of the corner portion.
[0059] Moreover, it is preferable that the rectilinear portion is
work hardened by processing that causes the rectilinear portion to
be compressed.
[0060] Moreover, it is preferable that the gasket is pressed
against the circumferential wall of the sealing can so as to press
the circumferential wall of the sealing can toward the central
axis. This configuration provides good insulation properties and
sealing properties between the exterior can and the sealing can
having different polarities.
[0061] Moreover, it is preferable that the circumferential wall of
the sealing can is stepped at a shoulder portion, the gasket is
interposed between the shoulder portion and the circumferential
wall of the exterior can, and the gasket is pressed in a height
direction of the sealing can. This configuration also provides good
insulation properties and sealing properties between the exterior
can and the sealing can having different polarities.
[0062] According to the flat battery of the second aspect of the
present invention, the upright portion having a greater thickness
and hardness than the corner portion is formed in the
circumferential wall of the sealing can. Therefore, deformation of
the upright portion is suppressed during a crimping process, and
the sealing properties provided by a gasket are thus
maintained.
[0063] In the flat battery of the second aspect of the present
invention, it is preferable that throughout the circumferential
wall of the sealing can, the Vickers hardness is greater than the
Vickers hardness of the corner portion. With this configuration,
deformation of the entire circumferential wall of the sealing can
is suppressed during the crimping process, which is more
advantageous in preventing the sealing properties from
decreasing.
[0064] Moreover, it is preferable that the Vickers hardness of the
corner portion is 150 or more, and the Vickers hardness of the
upright portion is 200 or more.
[0065] Moreover, it is preferable that the Vickers hardness of the
upright portion is 1.05 times or more greater than the Vickers
hardness of the corner portion.
[0066] Moreover, it is preferable that the upright portion is work
hardened by processing that causes the circumferential wall of the
sealing can to be compressed.
[0067] Moreover, it is preferable that the gasket is pressed
against the circumferential wall of the sealing can so as to press
the circumferential wall of the sealing can toward the central
axis. This configuration provides good insulation properties and
sealing properties between the exterior can and the sealing can
having different polarities.
[0068] Moreover, it is preferable that the circumferential wall of
the sealing can is stepped at a shoulder portion, the gasket is
interposed between the shoulder portion and the circumferential
wall of the exterior can, and the gasket is pressed in a height
direction of the sealing can. This configuration also provides good
insulation properties and sealing properties between the exterior
can and the sealing can having different polarities.
[0069] According to the flat battery of the third aspect of the
present invention, the angle .theta.1 formed by the planar portion
and the rectilinear portion of the sealing can is greater than
90.degree.. Therefore, the adhesion in an area of contact between
the circumferential wall of the sealing can and the gasket is
maintained, and the sealing properties provided by the gasket are
thus maintained. Moreover, an effect of improving the sealing
properties through spring-back of the circumferential wall of the
sealing can and an effect of increasing the strength through work
hardening in the vicinity of the corner portion of the sealing can
also can be obtained.
[0070] In the flat battery of the third aspect of the present
invention, it is preferable that the angle .theta.1 is 90.5.degree.
or more. With this configuration, it can be reliably ensured that
the angle .theta.1 is greater than 90.degree..
[0071] Moreover, it is preferable that the angle .theta.1 is
95.degree. or less. With this configuration, the amount of wasted
space in the inner volume can be reduced.
[0072] Moreover, it is preferable that the gasket is pressed
against the circumferential wall of the sealing can so as to press
the circumferential wall of the sealing can toward the central
axis. This configuration provides good insulation properties and
sealing properties between the exterior can and the sealing can
having different polarities.
[0073] Moreover, it is preferable that the circumferential wall of
the sealing can is stepped at a shoulder portion, the gasket is
interposed between the shoulder portion and the circumferential
wall of the exterior can, and the gasket is pressed in a height
direction of the sealing can. This configuration also provides good
insulation properties and sealing properties between the exterior
can and the sealing can having different polarities.
[0074] Moreover, it is preferable that an angle .theta.2 formed by
the planar portion and the rectilinear portion at the time when the
sealing can is in a separated state before assembly is 92.degree.
or more. With this configuration, it can be more reliably ensured
that the angle .theta.1 at the time when the flat battery is in a
completed state will be greater than 90.degree..
[0075] Moreover, it is preferable that when an angle formed by the
planar portion and the rectilinear portion at the time when the
sealing can is in a separated state before assembly is an angle
.theta.2, an angle difference .theta.3 between the angle .theta.2
and the angle .theta.1 is between 0.5.degree. and 5.degree.
inclusive. With this configuration, manufacturing is facilitated
and, at the same time, the effect of improving the sealing
properties through spring-back of the circumferential wall of the
sealing can and the effect of increasing the strength through work
hardening in the vicinity of the corner portion of the sealing can
also can be obtained.
[0076] Hereinafter, embodiments of the present invention will be
described in detail with reference to the drawings. Although
Embodiments 2 and 3 partly overlap with Embodiment 1, the
overlapping parts will be described again in Embodiments 2 and 3
for the convenience of description.
Embodiment 1
[0077] FIG. 1 shows a perspective view of a flat battery according
to Embodiment 1 of the present invention. A flat battery 1 is
constructed by combining an exterior can 2 serving as a positive
electrode can and a sealing can 3 serving as a negative electrode
can. An example of the flat battery 1 has an external diameter
dimension (dimension D in FIG. 2) of 20.0 mm and a thickness of 5
mm.
[0078] FIG. 2 is a cross-sectional view taken along line AA in FIG.
1. The exterior can 2 includes a bottom portion 11 and a
circumferential wall 12 extending upright from an outer
circumference of the bottom portion 11 and has a cylindrical shape
that is open at one end. The sealing can 3 includes a bottom
portion 15 and a circumferential wall 16 extending upright from an
outer circumference of the bottom portion 15 and has a cylindrical
shape that is open at one end. A gasket 4 is interposed between an
inner circumferential face of the circumferential wall 12 of the
exterior can 2 and an outer circumferential face of the
circumferential wall 16 of the sealing can 3.
[0079] A distal end portion 12a of the circumferential wall 12 of
the exterior can 2 is bent toward a central axis 9 of the sealing
can 3 to form a curve, whereby the exterior can 2 is fixed to the
sealing can 3 by crimping. Thus, a gap between the exterior can 2
and the sealing can 3 is sealed with the gasket 4, and the exterior
can 2 and the sealing can 3 having different polarities are
insulated from each other.
[0080] The flat battery 1 houses a power generating element 10 and
is filled with a nonaqueous electrolyte. The power generating
element 10 includes a positive electrode material (electrode
material) 5 made of a positive electrode active material and the
like pressed into the shape of a disk, a negative electrode
material (electrode material) 6 made of metallic lithium or an
lithium alloy, which are negative electrode active materials,
formed into the shape of a disk, and a non-woven fabric separator
7. The separator 7 is disposed between the positive electrode
material 5 and the negative electrode material 6. A positive
electrode ring 8 formed of stainless steel or the like is installed
on an outer face of the positive electrode material 5.
[0081] FIG. 3 shows an exploded view of the flat battery 1 shown in
FIG. 2. As described above, the exterior can 2 and the sealing can
3 have cylindrical shapes that are open at one end. These cans can
be shaped by, for example, press forming a stainless steel
material. The circumferential wall portion 16 of the sealing can 3
includes a rectilinear portion 17, and a corner portion 18 is
formed at the intersection of the bottom portion 15 and the
rectilinear portion 17. Furthermore, the circumferential wall
portion 16 is stepped at a shoulder portion 19.
[0082] The gasket 4 is a resin molded article and is made by
molding a resin composition containing, for example, polyphenylene
sulfide (PPS) as a main ingredient and an olefin elastomer. The
gasket 4 is a ring-like member and includes a base portion 20 and
inner and outer walls 21 and 22 extending upwardly from the base
portion 20. A gap 23 is formed between the inner wall 21 and the
outer wall 22. The circumferential wall 16 of the sealing can 3 can
be inserted into this gap 23.
[0083] The positive electrode material 5 is made by shaping the
positive electrode active material integrally with the positive
electrode ring 8 into the shape of a disk. Examples of the positive
electrode active material include those obtained by shaping a
positive electrode mixture prepared by mixing, for example,
graphite, a tetrafluoroethylene-hexafluoropropylene copolymer, and
hydroxypropylcellulose into manganese dioxide.
[0084] The separator 7 is formed of a non-woven fabric, and the
material for the non-woven fabric is, for example, a fiber made of
polybutylene terephthalate.
[0085] The separator 7 is impregnated with a nonaqueous
electrolyte. For example, a solution of LiClO.sub.4 dissolved in a
solvent prepared by mixing propylene carbonite with
1,2-dimethoxyethane can be used as the nonaqueous electrolyte. The
separator 7 has a thickness of, for example, about 0.3 to 0.4
mm.
[0086] The configuration of the flat battery 1 is schematically
described above. However, the flat battery 1 according to
Embodiment 1 is characterized by the distribution of hardness in
the sealing can 3. Specifically, in the sealing can 3 shown in FIG.
3, the Vickers hardness of the rectilinear portion 17 is greater
than the Vickers hardness of the corner portion 18. As will be
described later in detail, the purpose of this is to suppress
deformation of the rectilinear portion 17 of the sealing can 3
during a crimping process by which the distal end portion 12a of
the circumferential wall 12 of the exterior can 2 is bent into a
curve and thereby ensuring the sealing properties provided by the
gasket 4.
[0087] Here, the Vickers hardness is a hardness that is measured in
conformity with JIS Z 2244. In such a measurement, the surface of a
test piece is indented using a diamond indenter having the shape of
a quadrangular pyramid with an angle of 136.degree. between
opposite faces, and the surface area of the resulting permanent
indentation is calculated from the diagonal length of the permanent
indentation. The Vickers hardness is obtained from a value
calculated by dividing the test load applied to the indenter when
the indentation is made by the surface area of the permanent
indentation.
[0088] Hereinafter, a shaping method for achieving a distribution
of hardness in the sealing can 3 as above will be described with
reference to FIGS. 4 and 5A to 5E. FIG. 4 shows a state in which a
disk-like member 41 is blanked from a plate material 40 that is the
raw material for the sealing can 3. A transfer press is used to
process the disk-like member 41. The transfer press is a press
machine including dies corresponding to individual steps of
multiple steps and a transfer mechanism that transfers a workpiece
to the subsequent step. The disk-like member 41 is processed using
the dies corresponding to the individual steps and formed into the
shape shown in FIG. 3.
[0089] FIGS. 5A to 5E show the change in the shape of the workpiece
after undergoing each step. Each of FIGS. 5A to 5E shows a plan
view and a cross-sectional view. FIG. 5A shows the disk-like member
41. As described above, the disk-like member 41 is blanked from the
plate material 40 as shown in FIG. 4. In FIG. 5B, the disk-like
member 41 is drawn into a cylindrical shape that includes a bottom
portion 42 and a circumferential wall 43 extending upright from an
outer circumference of the bottom portion 42.
[0090] FIG. 5C shows a state of the workpiece after undergoing a
beating step. In the state of FIG. 5C, the workpiece still has a
cylindrical shape, but the height of the circumferential wall 43 is
adjusted by beating the circumferential wall 43.
[0091] This height adjustment causes the circumferential wall 43 to
be deformed under compression and work hardened. As described
above, in the sealing can 3 according to Embodiment 1, the Vickers
hardness of the rectilinear portion 17 is greater than the Vickers
hardness of the corner portion 18. This is due to work hardening
during the beating step. FIG. 5D shows a state in which a shoulder
portion 45 is formed by processing a corner portion 44 of the
workpiece shown in FIG. 5C. FIG. 5E shows a completed state after
finishing.
[0092] The completed sealing can has the same shape as the sealing
can 3 shown in FIG. 3. As described above, since the sealing can
has undergone the beating step, the Vickers hardness of the
rectilinear portion 17 is greater than the Vickers hardness of the
corner portion 18.
[0093] On the other hand, the sealing can 3 shown in FIG. 3 also
can be shaped by press working using a progressive die. However, a
beating step cannot be included in this processing method, and so a
sealing can 3 in which the Vickers hardness of the rectilinear
portion 17 is greater than the Vickers hardness of the corner
portion 18 cannot be obtained.
[0094] Hereinafter, a method for shaping a sealing can using a
progressive die will be described as a comparative example. FIG. 6
shows a plan view of a coil material 50 that is being processed
using a progressive die. FIG. 6 also shows cross-sectional views of
workpieces. Each of the cross-sectional views is a cross-sectional
view of the coil material 50 taken in a width direction
(cross-sectional view taken along line BB), but the cross-sectional
views are arranged laterally for the convenience of
illustration.
[0095] In FIG. 6, each workpiece at A, B, or C is fed to the next
station at a position B, C, or D by moving the coil material 50
forward by a distance corresponding to the interval between
stations (in the direction of arrow a). In this state, the
workpieces are processed into the shapes of the cross-sectional
views at respective positions, in a single press stroke. That is to
say, each time the coil material 50 is moved forward by a distance
corresponding to the interval between stations, press operations at
multiple stations are performed simultaneously.
[0096] A disk-like member 51 at A is processed into a drawn shape
at B. A corner portion 52 of a workpiece having the drawn shape at
B is processed so as to have the shape at C, in which a shoulder
portion 53 is formed. At D, the workpiece processed into the shape
at C is blanked along a dashed line and cut off from the coil
material 50. An upper end portion 54 of the workpiece cut off from
the coil material 50 is folded back as shown at E to form a shape
corresponding to the folded-back portion 107 in FIG. 38. It is also
possible to omit the operation at E and configure a circumferential
wall as a single layer wall without a folded-back portion.
[0097] In the shaping method shown in FIG. 6, the workpiece remains
integral with the coil material 50 while processing is proceeding.
This shaping method is the same as the shaping method shown in
FIGS. 5A to 5E in that the corner portion 52 can be work hardened
by a bending process.
[0098] However, the shaping method shown in FIG. 6 does not include
a step of compressing a circumferential wall of a cylindrical
member. Accordingly, in the case where the sealing can 3 shown in
FIG. 3 is shaped using the shaping method shown in FIG. 6, the
Vickers hardness of the rectilinear portion 17 is smaller than the
Vickers hardness of the corner portion 18. This relationship in the
magnitude of the Vickers hardness is the opposite to that of the
sealing can 3 that is shaped using the shaping method shown in
FIGS. 5A to 5E.
[0099] This will be described below with reference to the results
of an experiment. FIGS. 7A and 7B show the points of measurement of
the Vickers hardness in Working Example 1 and Comparative Example
1. FIG. 7A shows a relevant part of a sealing can 3 according to
Working Example 1. Points A to H are the measuring points. Working
Example 1 is a sealing can for a coin-shaped battery having a
diameter of 20 mm and a height of 5 mm. The sealing can 3 of
Working Example 1 has the same configuration as the sealing can 3
shown in FIG. 3, and a side wall portion 16 is a single layer wall
without a folded-back portion. Moreover, the sealing can of Working
Example 1 is shaped using the shaping method shown in FIGS. 5A to
5E, where processing is performed on a disk-like workpiece that has
been blanked.
[0100] FIG. 7B shows a relevant part of a sealing can 102 according
to Comparative Example 1. Points A, A', and B to J are the
measuring points. Comparative Example 1 is a sealing can for a
coin-shaped battery having a diameter of 24.5 mm and a height of 5
mm. The sealing can 102 of Comparative Example 1 has the same
configuration as the sealing can 102 shown in FIG. 38, and a
folded-back portion 107 is formed in a side wall portion 105.
Moreover, the sealing can of Comparative Example 1 is shaped using
the shaping method shown in FIG. 6, where processing is performed
on a workpiece that is integral with the coil material 50.
[0101] FIG. 8 shows the relationship between the measuring points
and the Vickers hardness for Working Example 1 and Comparative
Example 1. A solid line 60 represents Working Example 1, and a
dashed line 61 represents Comparative Example 1. For both of
Working Example 1 and Comparative Example 1, the hardness at a
point B (corner portion) is a higher value than the hardness at a
point A or A' (bottom portion). This can be considered to be a
result of work hardening of the corner portion due to the bending
process. This also applies to points D and F, which are corner
portions of Working Example 1 and Comparative Example 1, and a
point H, which is a folded portion, of Comparative Example 1.
[0102] Here, work hardening occurs not only in a bent portion but
also in the vicinity thereof. Thus, in Working Example 1, it is
considered that work hardening also occurs at the points C, E, and
G in the vicinity of the corner portions. Moreover, in Working
Example 1, the entire circumferential wall is work hardened by the
beating step, so that work hardening occurs even at the point H
distant from the corner portions.
[0103] In Comparative Example 1, work hardening also occurs at the
points C and E in the vicinity of the corner portions and even at
the point G in the vicinity of both the corner portion (point F)
and the folded portion (point H).
[0104] Therefore, in both of Working Example 1 and Comparative
Example 1, a high value of hardness is maintained between the point
B and the point H.
[0105] Meanwhile, between the point B and the point H, a comparison
between Working Example 1 and Comparative Example 1 indicates that
the hardness of Working Example 1 (solid line 60) is greater than
the hardness of Comparative Example 1 (dashed line 61) in almost
the entire range between the point B and the point H. In
particular, the hardness at the point C (rectilinear portion 111)
is lower than the hardness at the point B (corner portion 108) in
Comparative Example 1 (dashed line 61), whereas the hardness at the
point C (rectilinear portion 17) is a higher value than the
hardness at the point B (corner portion 18) in Working Example 1
(solid line 60).
[0106] This can be considered to be a result of the difference
between the shaping methods of Working Example 1 and Comparative
Example 1. In other words, it can be considered that the difference
in the relationship of the magnitude of hardness between the points
B and C between Working Example 1 and Comparative Example 1 results
from the fact that, as described above, work hardening due to the
beating step shown in FIG. 5C can be obtained in Working Example 1,
whereas a step corresponding to the beating step is not performed
in Comparative Example 1.
[0107] Here, in FIG. 2, the distal end portion 12a of the
circumferential wall 12 of the exterior can 2 is bent in a
direction toward the central axis 9 to form a curve. The exterior
can 2 is thus fixed to the sealing can 3 by crimping. When the
hardness at the point C (rectilinear portion 17) is higher than the
hardness at the point B (corner portion 18) as in Working Example
1, deformation of the rectilinear portion 17 of the sealing can 3
is suppressed, which is advantageous in ensuring the sealing
properties provided by the gasket 4. This will be described in
detail with reference to FIGS. 2, 13A and 13B after the following
description of a manufacturing process with reference to FIGS. 9 to
12.
[0108] During assembly of the components shown in FIG. 3, assembly
is advanced with the components being turned upside down from the
orientation shown in FIG. 3. FIGS. 9A and 9B show cross-sectional
views of a state in the middle of assembly. FIG. 9A is a
cross-sectional view showing a state in which the gasket 4 is
installed on the sealing can 3. The circumferential wall 16 of the
sealing can 3 is inserted into the gap 23 of the gasket 4, thereby
installing the gasket 4 on the sealing can 3.
[0109] FIG. 9B shows a state in which the power generating element
10 is housed in the sealing can 3. The negative electrode material
6 is fixed to the sealing can 3 with a conductive adhesive or the
like. The separator 7 and the positive electrode material 5 are
laid on top of the negative electrode material 6. Then, the
nonaqueous electrolyte is injected into the sealing can 3.
[0110] FIG. 10 is a cross-sectional view showing a state in which
the exterior can 2 is fitted on an assembly shown in FIG. 9B. In
this state, an outer circumferential face of the gasket 4 is fitted
against the inner circumferential face of the circumferential wall
12 of the exterior can 2. The components are assembled into the
state shown in FIG. 10 before the process proceeds to a crimping
step. In the crimping step, the distal end portion 12a of the
circumferential wall 12 of the exterior can 2 is bent toward the
central axis 9 of the sealing can 3 to form a curve.
[0111] FIG. 11 is a cross-sectional view showing a state before
crimping. The flat battery 1 shown in FIG. 10 is sandwiched between
a knockout pin 30 and a punch 31. A die face of a sealing die 32
fits over an outer circumferential face of the circumferential wall
12 so as to surround the circumferential wall 12 of the exterior
can 2. In this state, the knockout pin 30 and the punch 31 are
moved down. Thus, the distal end portion 12a of the circumferential
wall 12 of the exterior can 2 is bent along a curved face of the
sealing die 32 toward the central axis 9 of the sealing can 3.
[0112] FIG. 12 is a cross-sectional view showing a state in which
the downward movement of the knockout pin 30 and the punch 31 is
completed. In this state, the gasket 4 is sandwiched between the
inner circumferential face of the circumferential wall 12 of the
exterior can 2 and the outer circumferential face of the
circumferential wall 16 of the sealing can 3.
[0113] Furthermore, an end portion of the gasket 4 is pressed
against the circumferential wall 16 of the sealing can 3 so as to
press the circumferential wall 16 toward the central axis 9. This
provides good insulation properties and sealing properties between
the exterior can 2 and the sealing can 3 having different
polarities.
[0114] Moreover, between the shoulder portion 19 of the sealing can
3 and the distal end portion 12a of the circumferential wall 12 of
the exterior can 2, the gasket 4 is pressed in a height direction
of the sealing can 3. This also provides good insulation and
sealing properties between the exterior can 2 and the sealing can
3.
[0115] In a finished product state after the crimping process shown
in FIG. 2, the distal end portion 12a of the circumferential wall
12 of the exterior can 2 is bent toward the central axis 9 of the
sealing can 3. During bending, an external force that acts to
deform the circumferential wall 16 toward the central axis 9 is
applied to the circumferential wall 16 of the sealing can 3. When
the circumferential wall 16 is deformed toward the central axis 9,
the circumferential wall 16 is displaced away from the gasket 4.
This results in a decrease in the sealing properties provided by
the gasket 4.
[0116] In Comparative Example 1, as shown in FIG. 38, the
folded-back portion 107 is formed to increase the strength, thereby
preventing the sealing properties from decreasing. On the other
hand, in the case of a circumferential wall that is a single layer
wall without the folded-back portion 107, the entire
circumferential wall is displaced toward the central axis, which is
disadvantageous in ensuring the sealing properties.
[0117] Specifically, in the configuration shown in FIG. 2, the
corner portion 18 can be work hardened by the bending process. Even
in the case where the corner portion 18 with an increased hardness
is not deformed during the crimping process, if the rectilinear
portion 17 is deformed, the entire circumferential wall 16, which
is a single layer wall, is displaced toward the central axis 9,
resulting in a disadvantage in ensuring the sealing properties
provided by the gasket 4.
[0118] On the other hand, in the configuration shown in FIG. 2,
when not only the corner portion 18 of the sealing can 3 but also
the rectilinear portion 17 of the circumferential wall 16 has an
increased hardness, displacement of the entire circumferential wall
16 toward the central axis 9 is suppressed even in the case where
the circumferential wall 16 is a single layer wall, and the sealing
properties thus can be prevented from decreasing.
[0119] As described above, in Working Example 1, the hardness of
the rectilinear portion 17 is greater than the hardness of the
corner portion 18. In other words, the sealing can 3 according to
Embodiment 1 satisfies the relationship of an expression (1) below,
where the Vickers hardness of the corner portion 18 of the sealing
can 3 is Hv1, and the Vickers hardness of the rectilinear portion
17 is Hv2.
Hv1<Hv2 Expression (1)
[0120] With this configuration, the corner portion 18 has an
increased hardness due to work hardening as a result of the bending
process, and the rectilinear portion 17 has a higher hardness than
the corner portion 18. Therefore, during the crimping process,
deformation of both the corner portion 18 and the rectilinear
portion 17 is suppressed, and the sealing properties also can be
prevented from decreasing.
[0121] To make the effect obtained by satisfying the expression (1)
more certain, preferably, the relationship of an expression (2)
below is satisfied. Referring to FIG. 8, in Working Example 1, the
value at the point C (rectilinear portion 17) is about 1.15 times
higher than the value at the point B (corner portion 18), and the
sealing properties are ensured. When this is taken into account,
the range of an expression (3) below is more preferable.
1.05.ltoreq.Hv2/Hv1 Expression (2)
1.10.ltoreq.Hv2/Hv1 Expression (3)
[0122] Meanwhile, when the limit of work hardening achieved by the
beating process is taken into account, Hv2/Hv1 is preferably within
the range of an expression (4) below.
Hv2/Hv1.ltoreq.1.6 Expression (4)
[0123] Numerical examples of the ratio between Hv1 and Hv2 are
described above, and preferred numerical ranges of Hv1 and Hv2 are
as described below. A stainless steel material such as SUS430 is
usually used as the material for the sealing can 3, and the
numerical ranges below are derived from the extent of work
hardening caused by bending of the corner portion and the extent of
work hardening caused by the beating process, in the case of
SUS430.
[0124] The Vickers hardness Hv1 of the corner portion 18 is
preferably within the range of an expression (5) below, more
preferably within the range of an expression (6) below, and even
more preferably within the range of an expression (7) below.
150.ltoreq.Hv1 Expression (5)
170.ltoreq.Hv1 Expression (6)
190.ltoreq.Hv1 Expression (7)
[0125] The Vickers hardness Hv2 of the rectilinear portion 17 is
preferably within the range of an expression (8) below, more
preferably within the range of an expression (9) below, and even
more preferably within the range of an expression (10) below.
200.ltoreq.Hv2 Expression (8)
210.ltoreq.Hv2 Expression (9)
220.ltoreq.Hv2 Expression (10)
[0126] Meanwhile, processing for increasing the hardness of the
corner portion 18 is difficult, and an excessively high hardness of
the corner portion 18 also makes it difficult to increase the
hardness of the rectilinear portion 17 to a higher level than the
hardness of the corner portion 18. For this reason, the hardness of
the corner portion 18 is preferably within the range of an
expression (11) below and more preferably within the range of an
expression (12) below.
Hv1.ltoreq.210 Expression (11)
Hv1.ltoreq.200 Expression (12)
[0127] Next, Embodiment 1 will be compared with a comparative
example with reference to FIGS. 13A and 13B. FIG. 13A is a
cross-sectional view of a relevant part of a flat battery 100
according to the comparative example. FIG. 13A shows the same
configuration as the conventional example shown in FIG. 38. FIG.
13B is a cross-sectional view of a relevant part of the flat
battery 1 according to Embodiment 1. FIG. 13B shows the same
configuration as the flat battery 1 shown in FIG. 2.
[0128] Both the flat battery 100 and the flat battery 1 have the
same external dimension D. A folded-back portion 107 is formed in a
sealing can 102 of the flat battery 100, whereas the
circumferential wall 16 of the flat battery 1 is a single layer
wall without being folded back.
[0129] Even when the folded-back portion 107 is omitted from the
sealing can 102, the amount of engagement between a shoulder
portion 109 of a circumferential wall 105 and a gasket 103 is not
changed. In this case, the entire circumferential wall 105 of the
sealing can 102 can be shifted toward a circumferential wall 104 of
an exterior can 101 by an amount corresponding to the folded-back
portion 107 that has been omitted.
[0130] The state after shifting corresponds to FIG. 13B. In the
flat battery 1 shown in FIG. 13B, the inner circumferential face of
the sealing can 3 is shifted outward by a dimension A as compared
with the flat battery 100 shown in FIG. 13A. Accordingly, the flat
battery 1 can have a larger capacity than the flat battery 100 even
though the flat battery 1 has the same external dimension D as the
flat battery 100.
[0131] Moreover, formation of the rectilinear portion 17 also
provides an advantage in ensuring sufficient capacity. In FIG. 13B,
an increase in the radius of the corner portion 18 causes the
rectilinear portion 17 to become a part of the corner portion 18.
With this configuration, the corner portion 18 is displaced toward
the central axis 9, which is disadvantageous in ensuring sufficient
capacity. In other words, the smaller the radius of the corner
portion 18 and the greater the length of the rectilinear portion
17, the larger the capacity can be.
[0132] Meanwhile, as described above, the flat battery 1 satisfies
the relationship of the expression (1), and so the corner portion
18 has an increased hardness due to work hardening as a result of
the bending process, and the rectilinear portion 17 has a higher
hardness than the corner portion 18.
[0133] Therefore, according to Embodiment 1, even though the
circumferential wall 16 of the sealing can 3 is a single layer
wall, deformation of both the corner portion 18 and the rectilinear
portion 17 can be suppressed during the crimping process, and the
sealing properties provided by the gasket 4 can be ensured.
[0134] In other words, it can be said that Embodiment 1 has an
advantageous configuration that ensures the sealing properties
provided by the gasket 4 while employing a single layer wall
without being folded back for the circumferential wall 16 of the
sealing can 3, which is an advantageous structure in increasing the
capacity.
[0135] It should be noted that in the sealing can 3 according to
Embodiment 1, the rectilinear portion 17 is formed in the
cross-sectional shape of the circumferential wall 16 both before
and after crimping Meanwhile, an external force is applied to the
circumferential wall 16 by the crimping process. Thus, in some
cases, the perfectly rectilinear shape of the rectilinear portion
17 cannot be maintained after the crimping process. Even with such
a configuration, the effect of increasing the sealing properties
provided by the gasket 4 still can be obtained.
[0136] Therefore, the shape of the rectilinear portion 17 includes
not only a perfect straight line but also a curved line that has a
large radius of curvature and can be regarded as a straight line.
More specifically, it should be construed that the shape of the
rectilinear portion 17 includes a curved line having a radius of
curvature of 5 mm or more or a curved line having a radius of
curvature that is 20 times or more greater than the radius of the
corner portion 18.
[0137] Moreover, although the dimensions of the flat battery 1 and
the materials for the components thereof are described using FIGS.
1 to 3, these dimensions and materials are described by way of
example. The flat battery 1 may have dimensions different from
those described above, and materials different from those described
above may be used.
Embodiment 2
[0138] FIG. 14 shows a perspective view of a flat battery according
to Embodiment 2 of the present invention. A flat battery 1 is
constructed by combining an exterior can 2 serving as a positive
electrode can and a sealing can 3 serving as a negative electrode
can. An example of the flat battery 1 has an external diameter
dimension (dimension D in FIG. 2) of 20.0 mm and a thickness of 5
mm.
[0139] FIG. 15 is a cross-sectional view taken along line CC in
FIG. 14. The exterior can 2 includes a bottom portion 11 and a
circumferential wall 12 extending upright from an outer
circumference of the bottom portion 11 and has a cylindrical shape
that is open at one end. The sealing can 3 includes a bottom
portion 15 and a circumferential wall 16 extending upright from an
outer circumference of the bottom portion 15 and has a cylindrical
shape that is open at one end. A gasket 4 is interposed between an
inner circumferential face of the circumferential wall 12 of the
exterior can 2 and an outer circumferential face of the
circumferential wall 16 of the sealing can 3.
[0140] A distal end portion 12a of the circumferential wall 12 of
the exterior can 2 is bent toward a central axis 9 of the sealing
can 3 to form a curve, whereby the exterior can 2 is fixed to the
sealing can 3 by crimping. Thus, a gap between the exterior can 2
and the sealing can 3 is sealed with the gasket 4, and the exterior
can 2 and the sealing can 3 having different polarities are
insulated from each other.
[0141] The flat battery 1 houses a power generating element 10 and
is filled with a nonaqueous electrolyte. The power generating
element 10 includes a positive electrode material (electrode
material) 5 made of a positive electrode active material and the
like pressed into the shape of a disk, a negative electrode
material (electrode material) 6 made of metallic lithium or an
lithium alloy, which are negative electrode active materials,
formed into the shape of a disk, and a non-woven fabric separator
7. The separator 7 is disposed between the positive electrode
material 5 and the negative electrode material 6. A positive
electrode ring 8 formed of stainless steel or the like is installed
on an outer face of the positive electrode material 5.
[0142] FIG. 16 shows an exploded view of the flat battery 1 shown
in FIG. 15. As described above, the exterior can 2 and the sealing
can 3 have cylindrical shapes that are open at one end. These cans
can be shaped by, for example, press forming a stainless steel
material. The circumferential wall portion 16 of the sealing can 3
includes a rectilinear portion 17, and a corner portion 18 is
formed at the intersection of the bottom portion 15 and the
rectilinear portion 17. Furthermore, the circumferential wall
portion 16 is stepped at a shoulder portion 19.
[0143] The gasket 4 is a resin molded article and is made by
molding a resin composition containing, for example, polyphenylene
sulfide (PPS) as a main ingredient and an olefin elastomer. The
gasket 4 is a ring-like member and includes a base portion 20 and
inner and outer walls 21 and 22 extending upwardly from the base
portion 20. A gap 23 is formed between the inner wall 21 and the
outer wall 22. The circumferential wall 16 of the sealing can 3 can
be inserted into this gap 23.
[0144] The positive electrode material 5 is made by shaping the
positive electrode active material integrally with the positive
electrode ring 8 into the shape of a disk. Examples of the positive
electrode active material include those obtained by shaping a
positive electrode mixture prepared by mixing, for example,
graphite, a tetrafluoroethylene-hexafluoropropylene copolymer, and
hydroxypropylcellulose into manganese dioxide.
[0145] The separator 7 is formed of a non-woven fabric, and the
material for the non-woven fabric is, for example, a fiber made of
polybutylene terephthalate.
[0146] The separator 7 is impregnated with a nonaqueous
electrolyte. For example, a solution of LiClO.sub.4 dissolved in a
solvent prepared by mixing propylene carbonite with
1,2-dimethoxyethane can be used as the nonaqueous electrolyte. The
separator 7 has a thickness of, for example, about 0.3 to 0.4
mm.
[0147] The configuration of the flat battery 1 is schematically
described above. However, the flat battery 1 according to
Embodiment 2 is characterized by the distribution of hardness and
thickness in the sealing can 3. Specifically, an upright portion
13, of the circumferential wall 16 of the sealing can 3 shown in
FIG. 15, has a greater thickness than the thickness of the corner
portion 18. Furthermore, the Vickers hardness of the upright
portion 13 is greater than the Vickers hardness of the corner
portion 18.
[0148] The upright portion 13 is a portion sandwiched between the
curved distal end portion 12a of the circumferential wall 12 of the
exterior can 2 and the bottom portion 11 of the exterior can 2. In
the shoulder portion 19, a part outside of a line 14 extending from
an inner face of the upright portion 13 is included in the upright
portion 13.
[0149] As will be described later in detail, the purpose of forming
the upright portion 13 having a greater hardness and thickness is
to suppress deformation of the circumferential wall 16 of the
sealing can 3 during a crimping process by which the distal end
portion 12a of the circumferential wall 12 of the exterior can 2 is
bent into a curve and thereby ensuring the sealing properties
provided by the gasket 4.
[0150] Here, the Vickers hardness is a hardness that is measured in
conformity with JIS Z 2244. In such a measurement, the surface of a
test piece is indented using a diamond indenter having the shape of
a quadrangular pyramid with an angle of 136.degree. between
opposite faces, and the surface area of the resulting permanent
indentation is calculated from the diagonal length of the permanent
indentation. The Vickers hardness is obtained from a value
calculated by dividing the test load applied to the indenter when
the indentation is made by the surface area of the permanent
indentation.
[0151] Hereinafter, a shaping method for obtaining the upright
portion 13 of the sealing can 3 as above will be described with
reference to FIGS. 17 and 18A to 18E. FIG. 17 shows a state in
which a disk-like member 41 is blanked from a plate material 40
that is the raw material for the sealing can 3. A transfer press is
used to process the disk-like member 41. The transfer press is a
press machine including dies corresponding to individual steps of
multiple steps and a transfer mechanism that transfers a workpiece
to the subsequent step. The disk-like member 41 is processed using
the dies corresponding to the individual steps and formed into the
shape shown in FIG. 16.
[0152] FIGS. 18A to 18E show the change in the shape of the
workpiece after undergoing each step. Each of FIGS. 18A to 18E
shows a plan view and a cross-sectional view. FIG. 18A shows the
disk-like member 41. As described above, the disk-like member 41 is
blanked from the plate material 40 as shown in FIG. 17. In FIG.
18B, the disk-like member 41 is drawn into a cylindrical shape that
includes a bottom portion 42 and a circumferential wall 43
extending upright from an outer circumference of the bottom portion
42.
[0153] FIG. 18C shows a state of the workpiece after undergoing a
beating step. In the state of FIG. 18C, the workpiece still has a
cylindrical shape, but the height of the circumferential wall 43 is
adjusted by beating the circumferential wall 43.
[0154] This height adjustment causes the circumferential wall 43 to
be deformed under compression and work hardened. As described
above, the thickness and Vickers hardness of the upright portion 13
of the circumferential wall 16 of the sealing can 3 are increased
through deformation under compression during the beating step and
work hardening associated with the deformation.
[0155] FIG. 18D shows a state in which a shoulder portion 45 is
formed by processing a corner portion 44 of the workpiece shown in
FIG. 18C. FIG. 18E shows a completed state after finishing. The
completed sealing can has the same shape as the sealing can 3 shown
in FIG. 16.
[0156] On the other hand, the sealing can 3 shown in FIG. 16 also
can be shaped by press working using a progressive die. However, a
beating step cannot be included in this processing method, and so
the thickness and hardness of the upright portion 13 (FIG. 15) of
the circumferential wall 16 cannot be made greater than those of
the corner portion 18.
[0157] Hereinafter, a method for shaping the sealing can 3 using a
progressive die will be described as a comparative example. FIG. 19
shows a plan view of a coil material 50 that is being processed
using a progressive die. FIG. 19 also shows cross-sectional views
of workpieces. Each of the cross-sectional views is a
cross-sectional view of the coil material 50 taken in a width
direction (cross-sectional view taken along line DD), but the
cross-sectional views are arranged laterally for the convenience of
illustration.
[0158] In the state shown in FIG. 19, each workpiece at A, B, or C
is fed to the next station at a position B, C, or D by moving the
coil material 50 forward by a distance corresponding to the
interval between stations (in the direction of arrow a). In this
state, the workpieces are processed into the shapes of the
cross-sectional views at respective positions, in a single press
stroke. That is to say, each time the coil material 50 is moved
forward by a distance corresponding to the interval between
stations, press operations at multiple stations are performed
simultaneously.
[0159] A disk-like member 51 at A is processed into a drawn shape
at B. A corner portion 52 of a workpiece having the drawn shape at
B is processed so as to have the shape at C, in which a shoulder
portion 53 is formed. At D, the workpiece processed into the shape
at C is blanked along a dashed line and cut off from the coil
material 50. An upper end portion 54 of the workpiece cut off from
the coil material 50 is folded back as shown at E to form a shape
corresponding to the folded-back portion 107 in FIG. 15. It is also
possible to omit the operation at E and configure a circumferential
wall as a single layer wall without a folded-back portion.
[0160] In the shaping method shown in FIG. 19, the workpiece
remains integral with the coil material 50 while processing is
proceeding. This shaping method is the same as the shaping method
shown in FIGS. 18A to 18E in that the corner portion 52 can be work
hardened by a bending process.
[0161] However, the shaping method shown in FIG. 19 does not
include a step of compressing a circumferential wall of a
cylindrical member, so processing that increases the thickness and
hardness of the upright portion 13 (FIG. 15) to a higher level than
those of the corner portion 18 cannot be performed.
[0162] This will be described below with reference to the results
of an experiment. FIGS. 20A and 20B show the points of measurement
of the thickness and Vickers hardness in Working Example 2 and
Comparative Example 2. FIG. 20A shows a relevant part of a sealing
can 3 according to Working Example 2. Points A to H are the
measuring points. The range of the upright portion 13 shown in FIG.
15 is shown in FIG. 20A. As described above, a part outside of the
line 14 extending from the inner circumferential face of the
upright portion 13 is included in the upright portion 13. Thus, the
points F, G, and H are the measuring points within the upright
portion 13.
[0163] Working Example 2 is a sealing can for a coin-shaped battery
having a diameter of 20 mm and a height of 5 mm. The sealing can 3
of Working Example 2 has the same configuration as the sealing can
3 shown in FIG. 16, and a side wall portion 16 is a single layer
wall without a folded-back portion. Moreover, the sealing can of
Working Example 2 is shaped using the shaping method shown in FIGS.
18A to 18E, where processing is performed on a disk-like workpiece
that has been blanked.
[0164] FIG. 20B shows a relevant part of a sealing can 102
according to Comparative Example 2. Points A, A', and B to J are
the measuring points. Comparative Example 2 is a sealing can for a
coin-shaped battery having a diameter of 24.5 mm and a height of 5
mm. The sealing can 102 of Comparative Example 2 has the same
configuration as the sealing can 102 shown in FIG. 38, and a
folded-back portion 107 is formed in a side wall portion 105.
Moreover, the sealing can of Comparative Example 2 is shaped using
the shaping method shown in FIG. 19, where processing is performed
on a workpiece that is integral with the coil material 50.
[0165] FIG. 21 shows the relationship between the measuring points
and the Vickers hardness and the relationship between the measuring
points and the thickness shrinkage percentage for Working Example 2
and Comparative Example 2. A solid line 60 represents the Vickers
hardness of Working Example 2, and a dashed line 61 represents the
Vickers hardness of Comparative Example 2.
[0166] A solid line 70 represents the thickness shrinkage
percentage of Working Example 2, and a dashed line 71 represents
the thickness shrinkage percentage of Comparative Example 2. The
thickness shrinkage percentage indicates the extent of shrinkage
relative to the original thickness and is calculated using an
expression (13) below. It is seen from the expression (13) that the
greater the thickness shrinkage percentage, the thinner the
thickness.
Thickness shrinkage percentage (%)=[(original thickness-measurement
value)/original thickness].times.100 Expression (13)
[0167] First, a comparison between the solid line 60 and the dashed
line 61, which represent the Vickers hardness, is performed. For
both of Working Example 2 and Comparative Example 2, the hardness
at the point B (corner portion) is a higher value than the hardness
at the point A or A' (bottom portion). This can be considered to be
a result of work hardening of the corner portion due to the bending
process. This also applies to the points D and F, which are corner
portions of Working Example 2 and Comparative Example 2, and the
point H, which is a folded portion, of Comparative Example 2.
[0168] Here, work hardening occurs not only in a bent portion but
also in the vicinity thereof. Thus, in Working Example 2, it is
considered that work hardening also occurs at the points C, E, and
G in the vicinity of the corner portions. Moreover, in Working
Example 2, the entire circumferential wall 16 is work hardened by
the beating step, so that work hardening occurs even at the point H
distant from the corner portion (point F).
[0169] In Comparative Example 2, work hardening also occurs at the
points C and E in the vicinity of the corner portions, and work
hardening occurs even at the point G in the vicinity of both the
corner portion (point F) and the folded portion (point H).
[0170] Therefore, in both of Working Example 2 and Comparative
Example 2, a high value of hardness is maintained between the point
B and the point H.
[0171] Meanwhile, between the point B and the point H, a comparison
between Working Example 2 and Comparative Example 2 indicates that
the hardness of Working Example 2 (solid line 60) is greater than
the hardness of Comparative Example 2 (dashed line 61) in almost
the entire range between the point B and the point H. In
particular, the hardness at the point C (rectilinear portion 111)
is lower than the hardness at the point B (corner portion 108) in
Comparative Example 2 (dashed line 61), whereas the hardness at the
point C (rectilinear portion 17) is a higher value than the
hardness at the point B (corner portion 18) in Working Example 2
(solid line 60).
[0172] This can be considered to be a result of the difference
between the shaping methods of Working Example 2 and Comparative
Example 2. In other words, it can be considered that the difference
in the relationship of the magnitude of hardness between the points
B and C between Working Example 2 and Comparative Example 2 results
from the fact that, as described above, work hardening due to the
beating step shown in FIG. 18C can be obtained in Working Example
2, whereas a step corresponding to the beating step is not
performed in Comparative Example 2.
[0173] Next, in FIG. 21, a comparison between the solid line 70 and
the dashed line 71, which represent the thickness shrinkage
percentage (%), is performed. The scale of the thickness shrinkage
percentage (%) is shown on the right side of FIG. 21. The thickness
shrinkage percentage of Working Example 2 (solid line 70) is
smaller than the thickness shrinkage percentage of Comparative
Example 2 (dashed line 71) in the entire range between the points F
and H corresponding to the upright portion 13 in FIG. 20A.
[0174] Meanwhile, the thickness shrinkage percentage of Working
Example 2 (solid line 70) at the points F to H is smaller than the
thickness shrinkage percentage at the point B (corner portion 18).
That is to say, in Working Example 2, the thickness at the points F
to H corresponding to the upright portion 13 is greater than the
thickness at the point B (corner portion 18). In contrast, the
value at the point F of Comparative Example 2 (dashed line 71)
exceeds the value at the point B (corner portion 108), so the
thickness at the point F is smaller than that at the point B
(corner portion 108).
[0175] As described above, in Working Example 2, both the hardness
and the thickness of the upright portion 13 are greater than those
of the corner portion 18 in FIG. 21A. Such an upright portion 13
can be formed because, as described above, the shaping method of
Working Example 2 includes a beating step, which is not included in
the shaping method of Comparative Example 2.
[0176] Here, in FIG. 15, the distal end portion 12a of the
circumferential wall 12 of the exterior can 2 is bent in a
direction toward the central axis 9 to form a curve. The exterior
can 2 is thus fixed to the sealing can 3 by crimping. In the
upright portion 13 having a greater hardness and thickness than the
corner portion 18 as in Working Example 2, deformation is
suppressed, which is advantageous in ensuring the sealing
properties provided by the gasket 4. This will be described in
detail with reference to FIGS. 15, 26A, and 26B after the following
description of a manufacturing process with reference to FIGS. 22
to 25.
[0177] During assembly of the components shown in FIG. 16, assembly
is advanced with the components being turned upside down from the
orientation shown in FIG. 16. FIGS. 22A and 22B show
cross-sectional views of a state in the middle of assembly. FIG.
22A is a cross-sectional view showing a state in which the gasket 4
is installed on the sealing can 3. The circumferential wall 16 of
the sealing can 3 is inserted into the gap 23 of the gasket 4,
thereby installing the gasket 4 on the sealing can 3.
[0178] FIG. 22B shows a state in which the power generating element
10 is housed in the sealing can 3. The negative electrode material
6 is fixed to the sealing can 3 with a conductive adhesive or the
like. The separator 7 and the positive electrode material 5 are
laid on top of the negative electrode material 6. Then, a
nonaqueous electrolyte is injected into the sealing can 3.
[0179] FIG. 23 is a cross-sectional view showing a state in which
the exterior can 2 is fitted on an assembly shown in FIG. 22B. In
this state, an outer circumferential face of the gasket 4 is fitted
against the inner circumferential face of the circumferential wall
12 of the exterior can 2. The components are assembled into the
state shown in FIG. 23 before the process proceeds to a crimping
step. In the crimping step, the distal end portion 12a of the
circumferential wall 12 of the exterior can 2 is bent toward the
central axis 9 of the sealing can 3.
[0180] FIG. 24 is a cross-sectional view showing a state before
crimping. The flat battery 1 shown in FIG. 23 is sandwiched between
a knockout pin 30 and a punch 31. A die face of a sealing die 32
fits over an outer circumferential face of the circumferential wall
12 so as to surround the circumferential wall 12 of the exterior
can 2. In this state, the knockout pin 30 and the punch 31 are
moved down. Thus, the distal end portion 12a of the circumferential
wall 12 of the exterior can 2 is bent along a curved face of the
sealing die 32 toward the central axis 9 of the sealing can 3.
[0181] FIG. 25 is a cross-sectional view showing a state in which
the downward movement of the knockout pin 30 and the punch 31 is
completed. In this state, the gasket 4 is sandwiched between the
inner circumferential face of the circumferential wall 12 of the
exterior can 2 and the outer circumferential face of the
circumferential wall 16 of the sealing can 3.
[0182] Furthermore, an end portion of the gasket 4 is pressed
against the circumferential wall 16 of the sealing can 3 so as to
press the circumferential wall 16 toward the central axis 9. This
provides good insulation properties and sealing properties between
the exterior can 2 and the sealing can 3 having different
polarities.
[0183] Moreover, between the shoulder portion 19 of the sealing can
3 and the distal end portion 12a of the circumferential wall 12 of
the exterior can 2, the gasket 4 is pressed in a height direction
of the sealing can 3. This also results in good insulation and
sealing properties between the exterior can 2 and the sealing can
3.
[0184] In a finished product state after the crimping process shown
in FIG. 25, the distal end portion 12a of the circumferential wall
12 of the exterior can 2 is bent toward the central axis 9 of the
sealing can 3. During bending, if the circumferential wall 16 of
the sealing can 3 is deformed, there is a possibility that the
sealing properties provided by the gasket 4 may decrease.
[0185] In Comparative Example 2, as shown in FIG. 38, the
folded-back portion 107 is formed to increase the strength, thereby
preventing the sealing properties from decreasing. In contrast, in
Embodiment 2, the upright portion 13 that is a single layer wall
with an increased thickness and hardness is formed instead of the
folded-back portion 107, thereby preventing the sealing properties
from decreasing.
[0186] As described above, according to Working Example 2, in FIG.
20A, the thickness of the upright portion 13 is greater than that
of the corner portion 18. In other words, the sealing can 3
according to Embodiment 2 satisfies the relationship of an
expression (14) below, where the thickness of the corner portion 18
of the sealing can 3 is t1, and the thickness of the upright
portion 13 is t2.
t1<t2 Expression (14)
[0187] Furthermore, as described above, according to Working
Example 2, in FIG. 20A, the hardness of the upright portion 13 is a
higher value than that of the corner portion 18. In other words,
the sealing can 3 according to Embodiment 2 satisfies the
relationship of an expression (15) below, where the Vickers
hardness of the corner portion 18 of the sealing can 3 is Hv1, and
the Vickers hardness of the upright portion 13 is Hv2.
Hv1<Hv2 Expression (15)
[0188] With this configuration, the corner portion 18 has an
increased hardness due to work hardening as a result of the bending
process, and the upright portion 13 has a greater hardness and also
a greater thickness than the corner portion 18. Therefore, during
the crimping process, deformation of the upright portion 13 is
suppressed, and the sealing properties also can be prevented from
decreasing.
[0189] To make the effect obtained by satisfying the expression
(14) more certain, preferably, the relationship of an expression
(16) below is satisfied, and more preferably, the relationship of
an expression (17) below is satisfied.
1.01.ltoreq.t2/t1 Expression (16)
1.05.ltoreq.t2/t1 Expression (17)
[0190] Meanwhile, when the limit of compression achieved by the
beating process is taken into account, t2/t1 is preferably within
the range of an expression (18) below.
t2/t1.ltoreq.1.30 Expression (18)
[0191] Moreover, to make the effect obtained by satisfying the
expression (15) more certain, preferably, the relationship of an
expression (19) below is satisfied, and more preferably, the
relationship of an expression (20) below is satisfied.
1.05.ltoreq.Hv2/Hv1 Expression (19)
1.10.ltoreq.Hv2/Hv1 Expression (20)
[0192] Meanwhile, when the limit of work hardening achieved by the
beating process is taken into account, Hv2/Hv1 is preferably within
the range of an expression (21) below.
Hv2/Hv1.ltoreq.1.6 Expression (21)
[0193] Preferred numerical ranges of Hv1 and Hv2 are as described
below. A stainless steel material such as SUS430 is usually used as
the material for the sealing can 3, and the numerical ranges below
are derived from the extent of work hardening caused by bending of
the corner portion and the extent of work hardening caused by the
beating process, in the case of SUS430.
[0194] The Vickers hardness Hv1 of the corner portion 18 is
preferably within the range of an expression (22) below, more
preferably within the range of an expression (23) below, and even
more preferably within the range of an expression (24) below.
150.ltoreq.Hv1 Expression (22)
170.ltoreq.Hv1 Expression (23)
190<Hv1 Expression (24)
[0195] The Vickers hardness Hv2 of the upright portion 13 is
preferably within the range of an expression (25) below, more
preferably within the range of an expression (26) below, and even
more preferably within the range of an expression (27) below.
200.ltoreq.Hv2 Expression (25)
210.ltoreq.Hv2 Expression (26)
220<Hv2 Expression (27)
[0196] Meanwhile, processing for increasing the hardness of the
corner portion 18 is difficult, and an excessively high hardness of
the corner portion 18 also makes it difficult to increase the
hardness of the upright portion 13 to a higher level than the
hardness of the corner portion 18. For this reason, the hardness of
the corner portion 18 is preferably within the range of an
expression (28) below and more preferably within the range of an
expression (29) below.
Hv1.ltoreq.210 Expression (28)
Hv1.ltoreq.200 Expression (29)
[0197] Here, as shown by the solid line 60 in FIG. 21, in Working
Example 2, the Vickers hardness of not only the upright portion 13
(points F to H) but the entire circumferential wall 16 (points C to
H) is greater than that of the corner portion 18 (point B). With
this configuration, the corner portion 18 has an increased hardness
due to work hardening as a result of the bending process, and the
entire circumferential wall 16 has a higher hardness than the
corner portion 18. In this case, deformation of the corner portion
18 and the entire circumferential wall 16 is suppressed during the
crimping process, which is more advantageous in preventing the
sealing properties from decreasing.
[0198] It should be noted that the bottom portion 15 (FIG. 15) that
is a planar portion of the sealing can 3 is also required to have a
certain level of hardness in order to prevent swelling of the
battery and the like, though this is not directly related to the
prevention of a decrease in the sealing properties. Thus, the
Vickers hardness of the bottom portion 15 is preferably 130 or more
and more preferably 140 or more.
[0199] Next, Embodiment 2 will be compared with a comparative
example with reference to FIGS. 26A and 26B. FIG. 26A is a
cross-sectional view of a relevant part of a flat battery 100
according to the comparative example. FIG. 26A shows the same
configuration as the conventional example shown in FIG. 38. FIG.
26B is a cross-sectional view of a relevant part of the flat
battery 1 according to Embodiment 2. FIG. 26B shows the same
configuration as the flat battery 1 shown in FIG. 15.
[0200] Both the flat battery 100 and the flat battery 1 have the
same external dimension D. A folded-back portion 107 is formed in a
sealing can 102 of the flat battery 100, whereas the
circumferential wall 16 of the flat battery 1 is a single layer
wall without being folded back.
[0201] Even when the folded-back portion 107 is omitted from the
sealing can 102, the amount of engagement between a shoulder
portion 109 of a circumferential wall 105 and a gasket 103 is not
changed. In this case, the entire circumferential wall 105 of the
sealing can 102 can be shifted toward a circumferential wall 104 of
an exterior can 101 by an amount corresponding to the folded-back
portion 107 that has been omitted.
[0202] The state after shifting corresponds to FIG. 26B. In the
flat battery 1 shown in FIG. 26B, the inner circumferential face of
the sealing can 3 is shifted outward by a dimension A as compared
with the flat battery 100 shown in FIG. 26A. Accordingly, the flat
battery 1 can have a larger capacity than the flat battery 100 even
though the flat battery 1 has the same external dimension D as the
flat battery 100.
[0203] Moreover, formation of the rectilinear portion 17 also
provides an advantage in ensuring sufficient capacity. In FIG. 26B,
an increase in the radius of the corner portion 18 causes the
rectilinear portion 17 to become a part of the corner portion 18.
With this configuration, the corner portion 18 is displaced toward
the central axis 9, which is disadvantageous in ensuring sufficient
capacity. In other words, the smaller the radius of the corner
portion 18 and the greater the length of the rectilinear portion
17, the larger the capacity can be.
[0204] Meanwhile, as described above, in the flat battery 1, an
upright portion 13 that satisfies the expressions (14) and (15) is
formed, so during the crimping process, deformation of the upright
portion 13 is suppressed, and the sealing properties also can be
prevented from decreasing.
[0205] In other words, it can be said that Embodiment 2 has an
advantageous configuration that ensures the sealing properties
provided by the gasket 4 while employing a single layer wall
without being folded back for the circumferential wall 16 of the
sealing can 3, which is an advantageous structure in increasing the
capacity.
[0206] It should be noted that although the sealing can 3 according
to Embodiment 2 is described using an example in which the
rectilinear portion 17 is formed in the cross-sectional shape of
the circumferential wall 16, the sealing can 3 may have a
configuration in which the rectilinear portion 17 is not formed. On
the other hand, in the case where the rectilinear portion 17 is
formed, the rectilinear portion 17 is present in the
cross-sectional shape of the circumferential wall 16 after the
crimping process. However, an external force is applied to the
circumferential wall 16 by the crimping process, and so, in some
cases, the perfectly rectilinear shape of the rectilinear portion
17 cannot be maintained after the crimping process. Even such a
configuration is still advantageous in ensuring sufficient
capacity.
[0207] Therefore, the shape of the rectilinear portion 17 includes
not only a perfect straight line but also a curved line that has a
large radius of curvature and can be regarded as a straight line.
More specifically, it should be construed that the shape of the
rectilinear portion 17 includes a curved line having a radius of
curvature of 5 mm or more or a curved line having a radius of
curvature that is 20 times or more greater than the radius of the
corner portion 18.
[0208] Moreover, although the dimensions of the flat battery 1 and
the materials for the components thereof are described using FIGS.
14 to 16, these dimensions and materials are described by way of
example. The flat battery 1 may have dimensions different from
those described above, and materials different from those described
above may be used.
Embodiment 3
[0209] FIG. 27 shows a perspective view of a flat battery according
to Embodiment 3 of the present invention. A flat battery 1 is
constructed by combining an exterior can 2 serving as a positive
electrode can and a sealing can 3 serving as a negative electrode
can. An example of the flat battery 1 has an external diameter
dimension (dimension D in FIG. 28) of 20.0 nm and a thickness of 5
mm.
[0210] FIG. 28 is a cross-sectional view taken along line EE in
FIG. 27. The exterior can 2 includes a bottom portion 11 and a
circumferential wall 12 extending upright from an outer
circumference of the bottom portion 11 and has a cylindrical shape
that is open at one end. The sealing can 3 includes a planar
portion 15 serving as a bottom portion and a circumferential wall
16 extending upright from an outer circumference of the planar
portion 15 and has a cylindrical shape that is open at one end. A
gasket 4 is interposed between an inner circumferential face of the
circumferential wall 12 of the exterior can 2 and an outer
circumferential face of the circumferential wall 16 of the sealing
can 3.
[0211] A distal end portion 12a of the circumferential wall 12 of
the exterior can 2 is bent toward a central axis 9 of the sealing
can 3 to form a curve, whereby the exterior can 2 is fixed to the
sealing can 3 by crimping. Thus, a gap between the exterior can 2
and the sealing can 3 is sealed with the gasket 4, and the exterior
can 2 and the sealing can 3 having different polarities are
insulated from each other.
[0212] The flat battery 1 houses a power generating element 10 and
is filled with a nonaqueous electrolyte. The power generating
element 10 includes a positive electrode material (electrode
material) 5 made of a positive electrode active material and the
like pressed into the shape of a disk, a negative electrode
material (electrode material) 6 made of metallic lithium or an
lithium alloy, which are negative electrode active materials,
formed into the shape of a disk, and a non-woven fabric separator
7. The separator 7 is disposed between the positive electrode
material 5 and the negative electrode material 6. A positive
electrode ring 8 formed of stainless steel or the like is installed
on an outer face of the positive electrode material 5.
[0213] FIG. 29 shows an exploded view of the flat battery 1 shown
in FIG. 28. As described above, the exterior can 2 and the sealing
can 3 have cylindrical shapes that are open at one end. These cans
can be shaped by, for example, press forming a stainless steel
material. The circumferential wall portion 16 of the sealing can 3
includes a rectilinear portion 17, and a corner portion 18 is
formed at the intersection of the planar portion 15 and the
rectilinear portion 17. Furthermore, the circumferential wall
portion 16 is stepped at a shoulder portion 19.
[0214] The gasket 4 is a resin molded article and is made by
molding a resin composition containing, for example, polyphenylene
sulfide (PPS) as a main ingredient and an olefin elastomer. The
gasket 4 is a ring-like member and includes a base portion 20 and
inner and outer walls 21 and 22 extending upwardly from the base
portion 20. A gap 23 is formed between the inner wall 21 and the
outer wall 22. The circumferential wall 16 of the sealing can 3 can
be inserted into this gap 23.
[0215] The positive electrode material 5 is made by shaping the
positive electrode active material integrally with the positive
electrode ring 8 into the shape of a disk. Examples of the positive
electrode active material include those obtained by shaping a
positive electrode mixture prepared by mixing, for example,
graphite, a tetrafluoroethylene-hexafluoropropylene copolymer, and
hydroxypropylcellulose into manganese dioxide.
[0216] The separator 7 is formed of a non-woven fabric, and the
material for the non-woven fabric is, for example, a fiber made of
polybutylene terephthalate.
[0217] The separator 7 is impregnated with a nonaqueous
electrolyte. For example, a solution of LiClO.sub.4 dissolved in a
solvent prepared by mixing propylene carbonite with
1,2-dimethoxyethane can be used as the nonaqueous electrolyte. The
separator 7 has a thickness of for example, about 0.3 to 0.4
mm.
[0218] FIG. 30 shows an enlarged view of and around the
circumferential wall 16 of the sealing can 3 shown in FIG. 29. An
angle .theta.2 is an angle formed by the planar portion 15 and the
rectilinear portion 17 when the sealing can 3 is in a separated
state. The angle .theta.2 is greater than 90.degree.. Thus, the
farther from the corner portion 18 and closer to a distal end 16a
of the circumferential wall portion 16, the larger the inner
diameter of the sealing can 3.
[0219] During assembly of the components shown in FIG. 29, assembly
is advanced with the components being turned upside down from the
orientation shown in FIG. 29. FIGS. 31A and 31B show
cross-sectional views of a state in the middle of assembly. FIG.
31A is a cross-sectional view showing a state in which the gasket 4
is installed on the sealing can 3. The circumferential wall 16 of
the sealing can 3 is inserted into the gap 23 of the gasket 4,
thereby installing the gasket 4 on the sealing can 4.
[0220] FIG. 31B shows a state in which the power generating element
10 is housed in the sealing can 3. The negative electrode material
6 is fixed to the sealing can 3 with a conductive adhesive or the
like. The separator 7 and the positive electrode material 5 are
laid on top of the negative electrode material 6. Then, the
nonaqueous electrolyte is injected into the sealing can 3.
[0221] FIG. 32 is a cross-sectional view showing a state in which
the exterior can 2 is fitted on an assembly shown in FIG. 31B. In
this state, an outer circumferential face of the gasket 4 is fitted
against the inner circumferential face of the circumferential wall
12 of the exterior can 2. The components are assembled into the
state shown in FIG. 32 before the process proceeds to a crimping
step. In the crimping step, the distal end portion 12a of the
circumferential wall 12 of the exterior can 2 is bent toward the
central axis 9 of the sealing can 3.
[0222] FIG. 33 is a cross-sectional view showing a state before
crimping. The flat battery 1 shown in FIG. 32 is sandwiched between
a knockout pin 30 and a punch 31. A die face of a sealing die 32
fits over an outer circumferential face of the circumferential wall
12 so as to surround the circumferential wall 12 of the exterior
can 2. In this state, the knockout pin 30 and the punch 31 are
moved down. Thus, the circumferential wall 12 of the exterior can 2
is bent along a curved face of the sealing die 32 toward the
central axis 9 of the sealing can 3.
[0223] FIG. 34 is a cross-sectional view showing a state in which
the downward movement of the knockout pin 30 and the punch 31 is
completed. In this state, the gasket 4 is sandwiched between the
inner circumferential face of the circumferential wall 12 of the
exterior can 2 and the outer circumferential face of the
circumferential wall 16 of the sealing can 3.
[0224] Furthermore, an end portion of the gasket 4 is pressed
against the circumferential wall 16 of the sealing can 3 so as to
press the circumferential wall 16 toward the central axis 9. This
provides good insulation properties and sealing properties between
the exterior can 2 and the sealing can 3 having different
polarities.
[0225] Moreover, between the shoulder portion 19 of the sealing can
3 and the distal end portion 12a of the circumferential wall 12 of
the exterior can 2, the gasket 4 is pressed in a height direction
of the sealing can 3. This also provides good insulation and
sealing properties between the exterior can 2 and the sealing can
3.
[0226] The flat battery 1 is removed from the state shown in FIG.
34. FIG. 28 shows the flat battery 1 after being removed from the
state shown in FIG. 34 and turned upside down. In this state, the
circumferential wall 16 of the sealing can 3 has also been deformed
due to the crimping process of the circumferential wall 12 of the
exterior can 2.
[0227] As shown in FIG. 30, when the sealing can 3 is in a
separated state before assembly, an angle formed by the planar
portion 15 and the rectilinear portion 17 is .theta.2, and the
angle .theta.2 is greater than 90.degree.. In the state after the
crimping process shown in FIG. 28, the angle .theta.2 has become an
angle .theta.1 smaller than the angle .theta.2. This will be
described with reference to FIG. 35.
[0228] FIG. 35 is a cross-sectional view for illustrating a change
in the angle formed by the planar portion 15 and the rectilinear
portion 17 between when the sealing can 3 is in a separated state
and when the sealing can 3 is in an assembled state. The angle
.theta.2 in FIG. 35 is the same as the angle .theta.2 in FIG. 30
and indicates the angle formed by the planar portion 15 and the
rectilinear portion 17 when the sealing can is in a separated state
before assembly.
[0229] Along dashed double-short dashed line in FIG. 35 indicates
the circumferential wall 16 after fixation by crimping, and the
circumferential wall 16 has been deformed toward the central axis
9. Thus, the angle formed by the planar portion 15 and the
rectilinear portion 17 has changed from the angle .theta.2 to an
angle .theta.1 that is smaller than the angle .theta.2.
[0230] The angle .theta.1 after fixation by crimping remains
greater than 90.degree.. Therefore, in FIG. 28, the adhesion in an
area of contact between the circumferential wall 16 of the sealing
can 3 and the gasket 4 is maintained, and the sealing properties
provided by the gasket 4 are maintained.
[0231] Moreover, after the crimping process, a spring-back effect
caused by the recovery of the circumferential wall 16 of the
sealing can 3 to its original state can be obtained. Thus, the
circumferential wall 16 presses the gasket 4. This is also useful
in ensuring the sealing properties provided by the gasket 4.
[0232] Meanwhile, to maintain the state in which the
circumferential wall 16 presses the gasket 4, sufficient strength
is required in the vicinity of the corner portion 18 where the
stress is concentrated. Due to the bending process by which the
angle .theta.2 is changed to the angle .theta.1, work hardening is
obtained in the vicinity of the corner portion 18. Thus, the
strength in the vicinity of the corner portion 18 can be
increased.
[0233] Next, numerical ranges of the angles .theta.1 and .theta.2
will be described. The angle 61 after fixation by crimping is a
value greater than 90.degree. and satisfies an expression (30)
below. In order to reliably ensure that the angle .theta.1 is
greater than 90.degree., preferably, an expression (31) is
satisfied.
90.degree.<.theta.1 Expression (30)
90.5.degree..ltoreq..theta.1 Expression (31)
[0234] Moreover, when the ensuring of a sufficient inner volume is
taken into account, the angle .theta.1 is preferably within the
range of an expression (32) below and more preferably within the
range of an expression (33).
90.degree.<.theta.1.ltoreq.95.degree. Expression (32)
90.5.degree..ltoreq..theta.1.ltoreq.93.degree. Expression (33)
[0235] In the expression (32), the upper limit value is set to
95.degree. because the greater the angle .theta.1, the larger the
amount of wasted space in the inner volume. Specifically, referring
to FIG. 28, it is necessary to maintain the external dimension D of
the flat battery 1. If the angle .theta.1 is increased with the
external dimension D being fixed, the corner portion 18 is
displaced toward the central axis 9, resulting in a decrease in the
inner volume.
[0236] Moreover, an angle difference .theta.3 (.theta.2-.theta.1)
between the angle .theta.2 at the time when the sealing can 3 is in
a separated state and the angle .theta.1 after fixation by crimping
is preferably within the range of an expression (34) below and more
preferably within the range of an expression (35).
0.5.degree..ltoreq..theta.3.ltoreq.5.degree. Expression (34)
1.degree..ltoreq..theta.3.ltoreq.3.degree. Expression (35)
[0237] An excessively large angle difference .theta.3 causes
difficulty in the insertion of the gasket 4 shown in FIG. 3A or the
fitting of the exterior can 2 shown in FIG. 32. An angle difference
.theta.3 within the range of the expression (34) or (35)
facilitates manufacturing and, at the same time, makes it possible
to obtain an effect that the sealing properties are improved by
spring-back and an effect that the strength is increased by work
hardening in the vicinity of the corner portion 18.
[0238] It should be noted that although the spring-back effect or
the extent of work hardening decreases in the vicinity of the lower
limit value of the expression (34) or (35), the sealing properties
provided by the gasket 4 are still maintained as long as the angle
.theta.1 after fixation by crimping is maintained so as to be
greater than 90.degree..
[0239] Next, in order for the angle .theta.1 to be greater than
90.degree. as described above, preferably, the angle .theta.2 at
the time when the sealing can 3 is in a separated state satisfies
an expression (36) below.
92.degree..ltoreq..theta.2 Expression (36)
[0240] On the other hand, when consideration is given to the
expressions (32) and (33) for ensuring a sufficient inner volume
and the expressions (34) and (35) for balancing the ease of
manufacture and the effect of work hardening or spring-back, the
angle .theta.2 is preferably within the range of an expression (37)
below and more preferably within the range of an expression
(38).
92.degree..ltoreq..theta.2.ltoreq.98.degree. Expression (37)
93.degree..ltoreq..theta.2.ltoreq.95.degree. Expression (38)
[0241] In a working example in which the angles .theta.1, .theta.2,
and .theta.3 are within the above-described numerical ranges, the
angle .theta.1 of the sealing can 3 after fixation by crimping is
90.9.degree., the angle .theta.2 at the time when the sealing can 3
is in a separated state is 93.8.degree., and the angle difference
.theta.3 is 2.9.degree..
[0242] Next, Embodiment 3 will be compared with a comparative
example with reference to FIGS. 36A and 36B. FIG. 36A is a
cross-sectional view of a relevant part of a flat battery 100
according to a comparative example. FIG. 36A shows the same
configuration as the conventional example shown in FIG. 38. FIG.
36B is a cross-sectional view of a relevant part of the flat
battery 1 according to Embodiment 3. FIG. 36B shows the same
configuration as the flat battery 1 shown in FIG. 28.
[0243] Both the flat battery 100 and the flat battery 1 have the
same external dimension D. A folded-back portion 107 is formed in a
sealing can 102 of the flat battery 100, whereas the
circumferential wall 16 of the flat battery 1 is a single layer
wall without being folded back.
[0244] Even when the folded-back portion 107 is omitted from the
sealing can 102, the amount of engagement between a shoulder
portion 109 of a circumferential wall 105 and a gasket 103 is not
changed. In this case, the entire circumferential wall 105 of the
sealing can 102 can be shifted toward a circumferential wall 104 of
an exterior can 101 by an amount corresponding to the folded-back
portion 107 that has been omitted.
[0245] The state after shifting corresponds to FIG. 36B. In the
flat battery 1 shown in FIG. 36B, the inner circumferential face of
the sealing can 3 is shifted outward by a dimension A as compared
with the flat battery 100 shown in FIG. 36A. Accordingly, the flat
battery 1 can have a larger capacity than the flat battery 100 even
though the flat battery 1 has the same external dimension D as the
flat battery 100.
[0246] Moreover, formation of the rectilinear portion 17 also
provides an advantage in ensuring sufficient capacity. In FIG. 36B,
an increase in the radius of the corner portion 18 causes the
rectilinear portion 17 to become a part of the corner portion 18.
With this configuration, the corner portion 18 is displaced toward
the central axis 9, which is disadvantageous in ensuring sufficient
capacity. In other words, the smaller the radius of the corner
portion 18 and the greater the length of the rectilinear portion
17, the larger the capacity can be.
[0247] Meanwhile, as described above, since the angle .theta.1 of
the flat battery 1 is greater than 90.degree., the sealing
properties provided by the gasket 4 can be ensured. Moreover, due
to the spring-back effect, the sealing properties can be improved
even more, and a lack of strength also can be compensated for by
work hardening.
[0248] In other words, it can be said that Embodiment 3 has an
advantageous configuration that ensures the sealing properties
provided by the gasket 4 while employing a single layer wall
without being folded back for the circumferential wall 16 of the
sealing can 3, which is an advantageous structure in increasing the
capacity.
[0249] It should be noted that in the sealing can 3 according to
Embodiment 3, the rectilinear portion 17 is formed in the
cross-sectional shape of the circumferential wall 16 both before
and after the crimping process. Meanwhile, an external force is
applied to the circumferential wall 16 by the crimping process.
Thus, in some cases, the perfectly rectilinear shape of the
rectilinear portion 17 cannot be maintained after the crimping
process. Even with such a configuration, the effect of increasing
the sealing properties provided by the gasket 4 still can be
obtained.
[0250] Therefore, the shape of the rectilinear portion 17 includes
not only a perfect straight line but also a curved line that has a
large radius of curvature and can be regarded as a straight line.
More specifically, it should be construed that the shape of the
rectilinear portion 17 includes a curved line having a radius of
curvature of 5 mm or more or a curved line having a radius of
curvature that is 20 times or more greater than the radius of the
corner portion 18.
[0251] Moreover, although the dimensions of the flat battery 1 and
the materials for the components thereof are described using FIGS.
27 to 29, these dimensions and materials are described by way of
example. The flat battery 1 may have dimensions different from
those described above, and materials different from those described
above may be used.
[0252] The embodiments described above are solely intended to
illustrate the technological content of the present invention, and
the present invention is not limited to or by these specific
examples alone. Various modifications are possible within the
spirit of the invention and the scope of the claims, and the
present invention should be interpreted broadly.
* * * * *