JP2004178820A - Sealing plate for battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a safety valve that breaks by the deformation of a case when the internal pressure of a battery is increased. <P>SOLUTION: A sealing plate for sealing an opening part of the battery case is made of a plate-like material, the sealing plate has the safety valve, the safety valve has a lower surface comprising a thin flat part formed by seat-press working in the plate-like material, and the flat part is broken by tension in the surface direction of the plate-like material caused by the deformation of the case by the deformation of the case when the internal pressure of the battery is increased. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a battery sealing plate that breaks due to deformation of a case when the internal pressure of a battery increases, and a sealed battery using the same.
[0002]
[Prior art]
If a sealed battery is handled under abnormal conditions, gas may be generated inside the battery and the internal pressure may increase. Therefore, in such a case, a safety valve has been developed to prevent the battery internal pressure from excessively increasing. The safety valve operates when the internal pressure of the battery reaches a predetermined value or more, and discharges gas inside the battery to the outside. As such a safety valve, for example, the following has been proposed.
[0003]
First, a safety valve has been developed in which a thin portion having a predetermined contour is formed on a metal plate that seals an opening of a battery case, and the thin portion bulges toward the surface of the metal plate (for example, Patent Documents). 1, 2). Also, a safety valve that forms a thin part along the contour excluding one long side of a rectangle or an oval having a long side and a short side, and that is opened in a hinged manner toward the top due to an increase in internal pressure of the battery. It has been developed (for example, see Patent Document 3).
[0004]
[Patent Document 1]
Japanese Patent No. 3222418 (Claim 1, FIG. 7)
[Patent Document 2]
Japanese Patent Application Laid-Open No. 2001-325934 (Claim 1, FIGS. 1 and 2)
[Patent Document 3]
JP-A-2002-8615 (Claims 1, FIGS. 1 and 2)
[0005]
However, all of the above safety valves are broken by the force of the gas inside the battery pushing up the valve body. These safety valves operate by the gas pressure itself inside the battery. For this reason, the thin portion is designed to bulge or become dome-shaped so that the portion to be broken is easily subjected to upward pressure by gas. However, in such a safety valve, it is necessary to make the thin portion extremely thin, and it is difficult to maintain uniform performance. Therefore, the operating pressure of the safety valve is not stable, and it is difficult to sufficiently prevent an excessive increase in battery internal pressure.
[0006]
[Problems to be solved by the invention]
The present invention provides a safety valve that breaks due to deformation of a case when the internal pressure of a battery rises, and improves the above-described disadvantages of the conventional safety valve.
[0007]
[Means for Solving the Problems]
The present invention is a sealing plate made of a plate-like material for closing an opening of a battery case, wherein the sealing plate has a safety valve, and the safety valve is a lower surface formed by stamping the plate-like material. Is composed of a flat thin portion, and the thin portion has a thinner flat portion formed by push-in processing, and the flat portion is formed of the plate-shaped material by deformation of the case when a battery internal pressure rises. The present invention relates to a battery sealing plate that is broken by a tension in a plane direction.
[0008]
It is preferable that the thickness of the flat portion is 30 to 80 μm.
The width of the flat portion is preferably 0.1 mm or more.
[0009]
The present invention also includes an electrode group, an electrolyte, a prismatic battery case containing the electrode group and the non-aqueous electrolyte, and a sealing plate made of a plate-like material for sealing an opening of the case. It relates to a sealed battery whose plate has the above-mentioned safety valve.
The thickness of the wall material of the case is preferably 1 to 0.1 mm.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
A preferred embodiment of the sealing plate of the present invention and a sealed battery using the same will be described.
The sealing plate of the present invention is made of a plate-like material and has a safety valve. As the plate material, a metal plate is preferably used, and among them, a metal plate made of aluminum, iron, or the like is preferably used. The thickness of the plate-like material is preferably 0.6 to 2 mm. If the plate-shaped material is too thick, the surface tension applied to the thin portion becomes small, and if it is too thin, deformation other than the thin portion becomes large, and stable operation of the safety valve may not be achieved.
[0011]
The safety valve comprises a thin portion having a flat lower surface formed by a stamping process on a plate-like material. In addition, the thin portion has a thinner flat portion (hereinafter, referred to as a flat portion) formed by push-in processing. The thickness of the thin portion other than the flat portion is preferably 50 to 100 μm. If the thin portion other than the flat portion is too thick, the working becomes difficult, and if it is too thin, the break portion of the safety valve is not determined and stable operation may not be achieved.
[0012]
The flat part is broken by the tension in the surface direction of the plate-like material due to the deformation of the case when the internal pressure of the battery rises. According to the tension in the plane direction, even if the flat portion is somewhat thick, it can be relatively easily broken. Therefore, the flat portion of the safety valve according to the present invention can be made thicker than the broken portion of the safety valve which breaks due to the conventional upward force. For example, in the case of a conventional safety valve that is broken by an upward force, the thickness of the broken portion needs to be 20 μm or less. On the other hand, the thickness of the flat portion of the safety valve of the present invention can be 30 to 80 μm, and more preferably 35 to 50 μm.
[0013]
Since the safety valve of the present invention can make the break portion thicker than before, even if there is a slight variation in thickness, the variation has little effect on the operating pressure, and as a result, the operating pressure of the safety valve is stabilized. . In addition, although it depends on the size of the sealing plate, the width of the flat portion is preferably 0.1 mm or more, more preferably 1 mm or more, from the viewpoint of further stabilizing the operating pressure. To some extent, the wider the flat portion, the more stable the operating pressure.
[0014]
Hereinafter, a sealing plate having a preferable flat portion will be exemplified.
Embodiment 1
FIG. 1 shows a top view of the sealing plate according to the present embodiment. FIG. 2 is an enlarged sectional view taken along the line II-II of the sealing plate shown in FIG. 1, and FIG. 3 is an enlarged partial sectional view taken along the line III-III of the sealing plate.
As shown in FIGS. 1 to 3, the safety valve of the sealing plate according to the present embodiment includes a thin portion 11 having a flat lower surface formed by stamping a plate-shaped material 12. In FIG. 1, the thin portion 11 has a substantially elliptical outline 10, but the outline of the thin portion is not particularly limited. In the thin portion 11, a groove-shaped flat portion 13 is formed along a substantially oval contour having a pair of parallel straight portions. The groove-shaped flat portion 13 may have a shape along a rectangular outline other than such a substantially elliptical shape. A terminal hole 14a for inserting an electrode terminal is provided at the center of the sealing plate, and a concave portion 14b for fitting an insulating material for insulating the electrode terminal and the sealing plate is provided around the terminal hole 14a. Have been. Further, at the other end of the sealing plate without the safety valve, an injection hole 15a for injecting the electrolyte is provided, and around the opening, a concave portion 15b for fitting a plug is provided. .
[0015]
As described above, the groove width is preferably 0.1 mm or more, and particularly preferably 1 mm or less. The depth (B1) of the groove is determined by the thickness (A1) of the thin portion 11 and the thickness (C1) of the flat portion. In the case of such a groove-shaped flat portion, the thickness (C1) of the flat portion is particularly preferably 30 to 80 μm. Although the depth of the groove is preferably constant as shown in FIGS. 2 and 3, the depth of the groove may be partially changed. The wall surface of the groove may be tapered.
[0016]
The length (L1) of the substantially oval straight portion is preferably 0.5 to 10 mm, but the straight portion may be longer than 10 mm. The longer the straight portion, the thicker the flat portion can be. If the length of the straight portion is too short, the flat portion is less likely to break due to the tension when the case expands and tension is generated in the surface direction. The linear portion is preferably parallel or substantially parallel to the longitudinal direction of the sealing plate so that the flat portion 13 is easily broken when the case is expanded. Further, the distance (W1) between the straight portions is preferably 1.5 to 8 mm. If this distance is too short, the opening due to the break will be small and the ability to release gas will be insufficient even when the safety valve is activated.
[0017]
Although it depends on the size of the sealing plate, from the viewpoint of maintaining the strength of the sealing plate, it is preferable that the area of the safety valve including the thin portion is small. On the other hand, from the viewpoint of enhancing the function of the safety valve to release gas, it is preferable that the area of the break portion of the safety valve is large. Accordingly, a safety valve that is smaller and produces multiple breaks during operation is most preferred. The safety valve according to the present embodiment has an excellent exhaust capability as compared with the safety valves according to Embodiments 2 and 3 described below, and is suitable for a sealing plate of a high-capacity battery.
[0018]
Embodiment 2
FIG. 4 shows a top view of the sealing plate according to the present embodiment. FIG. 5 is an enlarged sectional view taken along line VV of the sealing plate shown in FIG. 4, and FIG. 6 is an enlarged partial sectional view taken along line VI-VI of the sealing plate.
As shown in FIG. 4, the safety valve of the sealing plate according to the present embodiment has a pair of parallel flat straight grooves 20. Other structures are the same as in the first embodiment. The groove width is preferably 0.1 mm or more, and more preferably 1 mm or less. In the case of such a groove-shaped flat portion, the thickness (C2) of the flat portion is particularly preferably 30 to 50 μm. The depth (B2) of the groove is determined by the thickness (A2) of the thin portion 21 and the thickness (C2) of the flat portion. Although the depth of the groove is preferably constant as shown in FIG. 4, the depth of the groove may be partially changed.
[0019]
The length (L2) of the straight portion is preferably 0.5 to 10 mm, but the straight portion may be longer than 10 mm. If the length of the straight portion is too short, the flat portion is less likely to break due to the tension when the case expands and tension is generated in the surface direction. The straight portion is preferably parallel or substantially parallel to the longitudinal direction of the sealing plate so that the flat portion 20 is easily broken when the case is expanded. Further, the distance (W2) between the straight portions is preferably 1.5 to 8 mm. If this distance is too short, the opening due to the break will be small and the ability to release gas will be insufficient even when the safety valve is activated. .
[0020]
Embodiment 3
FIG. 7 shows a top view of the sealing plate according to the present embodiment. FIG. 8 is an enlarged sectional view taken along line VIII-VIII of the sealing plate shown in FIG. 7, and FIG. 9 is an enlarged partial sectional view taken along line IX-IX.
As shown in FIG. 7, the safety valve of the sealing plate according to the present embodiment also has the thin portion 31 and the groove-shaped flat portion 30 along a pair of parallel straight lines. The same structure as that of the sealing plate of the second embodiment except that a plurality of small flat portions 32 are provided intermittently along an R-shaped contour connecting between opposed ends of a pair of straight lines. Have. The thickness (C3 ′) of the plurality of small flat portions 32 may be larger than the thickness (C3) of the groove-shaped flat portion 30 along the straight line.
[0021]
Embodiment 4
FIG. 10 shows a top view of the sealing plate according to the present embodiment. FIG. 11 is an enlarged sectional view taken along line XI-XI of the sealing plate shown in FIG. 10, and FIG. 12 is an enlarged partial sectional view taken along line XII-XII of the sealing plate. As shown in FIGS. 10 to 12, the safety valve of the sealing plate according to the present embodiment has a flat portion 40 including a concave portion surrounded by a substantially oval outline. Other structures are the same as in the first embodiment. Again, the generally oval contour has a pair of parallel straight sections. In addition to such a substantially elliptical shape, a flat portion composed of a concave portion surrounded by a rectangular outline may be used.
[0022]
The length (L4) of the substantially oval straight portion is preferably 0.5 to 10 mm, but the straight portion may be longer than 10 mm. If the length of the straight portion is too short, the flat portion is less likely to break due to the tension when the case expands and tension is generated in the surface direction. The straight portion is preferably parallel or almost parallel to the longitudinal direction of the sealing plate so that the flat portion 40 is easily broken when the case is expanded.
[0023]
The distance (W4) between the linear portions is preferably 1.5 to 8 mm. If this distance is too short, the opening due to the break will be small and the ability to release gas will be insufficient even when the safety valve is activated. The depth (B4) of the concave portion is determined by the thickness (A4) of the thin portion and the thickness (C4) of the flat portion. In the case of such a flat portion, the thickness (C4) of the flat portion is particularly preferably 30 to 80 μm. The depth of the recess is preferably constant as shown in FIGS. 11 and 12, but the depth may be partially changed.
[0024]
The sealing plate as described above can be obtained, for example, by subjecting a flat plate-shaped material to a stamping process (a press process for forming a flat surface) using a press die having a predetermined uneven shape. it can. According to the push-in process, a safety valve having a thin portion with a flat lower surface can be easily obtained. In the case where a thin portion having a flat lower surface is formed on a plate-like material, variations in products are reduced and processing conditions are easily managed. An example of such a method will be specifically described below, taking the sealing plate of Embodiment 1 as an example.
[0025]
FIG. 13 illustrates a manufacturing process of the sealing plate of the first embodiment, and a black arrow indicates a flow of the process. First, a plate-like material 50 having a size that can be easily processed is prepared. Here, sectional views of the plate-like material in the lateral direction are shown in A1 to D1, and sectional views in the longitudinal direction are shown in A2 to D2.
The safety valve can be formed by two-stage pressing. In the first-stage press working, as shown by A1 and A2, pressure is applied in the direction indicated by the white arrow by the upper mold 51a and the lower mold 51b to form a thin portion 52 as shown by B1 and B2. I do.
At this time, as shown in B2, the terminal hole 54 and the liquid injection hole 55 may be formed simultaneously with the formation of the thin portion 52.
[0026]
Next, the second stage of press working (spotting) is performed using the upper mold 53 and the lower mold 53b. On the lower surface of the upper mold 53, a rib 53a having a flat top is formed along a substantially elliptical outline, and a flat portion 56 as shown by C1 and C2 is formed along the rib 53a.
Finally, a sealing plate having a safety valve according to the first embodiment can be obtained by cutting out a sealing plate having a predetermined shape from a plate-like material with a cutting blade 57 having an opening having a predetermined shape. Next, in order to remove distortion from the obtained sealing plate, it is preferable to anneal the cut-out sealing plate. Annealing may be performed, for example, at 100 to 300 ° C.
[0027]
Next, an example of a battery case combined with the above-described sealing plate will be described.
FIG. 14 shows a longitudinal sectional view of an example of a prismatic battery case 60 used for a sealed battery. Here, in order to facilitate understanding of the structure of the case and the sealing plate, a diagram in which the opening of the battery case 60 is closed with the sealing plate 61 of the above-described first embodiment is shown. The opening of the case is closed after the positive electrode, the negative electrode and the separator are stacked and the wound electrode group is accommodated. An electrode terminal 63 is inserted into the terminal hole at the center of the sealing plate via an insulating material 62. On both sides of the electrode terminal 63, a safety valve 64 and an electrolyte injection hole are provided, and the injection hole is closed by a plug 65. The peripheral edge of the sealing plate and the opening end of the battery case, and the liquid injection hole and the plug are respectively joined by laser welding or the like.
[0028]
The following correlation exists between the swellability of the case and the dimensions of the battery case. The ratio of the width (X) to the thickness of the battery case, that is, the ratio of the length in the longitudinal direction to the length in the short direction of the sealing plate is preferably 3 to 17, and the height relative to the thickness of the battery case. The ratio of (Y) is preferably from 3 to 35. Further, the ratio of X to Y: X / Y is preferably 0.3 to 1.5.
[0029]
As the material of the battery case, a metal is preferably used, and among them, aluminum, iron and the like are preferably used. The thickness of the wider side wall of the battery case is preferably smaller than that of the related art in order to enhance the operation stability of the safety valve, and for example, is preferably 0.1 to 0.3 mm. If the thickness of the side wall is too large, deformation of the case when the internal pressure of the battery rises is hindered, and the safety valve becomes difficult to operate. On the other hand, if the thickness of the side wall is too small, it is difficult to sufficiently secure the strength of the battery case.
[0030]
When gas is generated in the battery case and the battery case swells in the thickness direction, tension in the short direction acts on the sealing plate. When the tension exceeds a certain value, the thinnest flat portion of the safety valve is broken, and the gas inside the battery is released to the outside.
The present invention can be applied to a non-aqueous electrolyte secondary battery, an alkaline storage battery, and various primary batteries. In the following examples, a non-aqueous electrolyte secondary battery will be described as an example.
[0031]
【Example】
<< Example 1 >>
(A) Production of sealing plates Using an aluminum plate having a thickness of 1 mm as a plate-like material and a press die having a predetermined uneven shape, the following sealing plates A, B and C were produced. The dimensions of each sealing plate were 34 mm in length and 4.5 mm in width in accordance with the size of the opening of the battery case described below.
First, a thin part having an approximately elliptical outline with a major axis of 3.6 mm and a minor axis of 2.4 mm and a thickness of 80 μm was formed on an aluminum plate having a predetermined shape by countersinking. Next, a predetermined flat portion was formed by further pressing the thin portion. The thickness of the flat part was 50 μm in each sealing plate.
[0032]
The flat portion of the sealing plate A is the same as that shown in FIGS. 1 to 3 and has a groove shape along a substantially elliptical contour having a pair of parallel linear portions. The groove width (width of the flat portion) was 0.1 mm. The length (L1) of the straight portion was 1.2 mm, and the distance (W1) between the straight portions was 3.2 mm.
The flat portion of the sealing plate B is the same as that shown in FIGS. 4 to 6 and has a groove shape along a pair of parallel straight lines. The groove width (width of the flat portion) was 0.1 mm. The length (L2) of the straight portion was 1.2 mm, and the distance (W2) between the straight portions was 3.2 mm.
The flat portion of the sealing plate C is the same as that shown in FIGS. 10 to 12 and has a concave shape surrounded by a substantially elliptical outline having a pair of parallel linear portions. The length (L4) of the straight portion was 1.2 mm, and the distance (W4) between the straight portions was 3.2 mm.
[0033]
(B) Preparation of positive electrode In 100 parts by weight of a positive electrode active material (LiCoO ₂ ), 3 parts by weight of acetylene black as a conductive material, 7 parts by weight of polytetrafluoroethylene as a binder, and 1% by weight of carboxymethyl cellulose. And 100 parts by weight of the resulting aqueous solution, and the mixture was stirred and mixed to obtain a paste-like positive electrode mixture. This positive electrode mixture was applied to both sides of a 20 μm-thick aluminum foil serving as a current collector, dried, rolled, and cut into predetermined dimensions to obtain a positive electrode.
[0034]
(C) Preparation of negative electrode 100 parts by weight of flaky graphite pulverized and classified so that the average particle diameter becomes about 20 μm, containing 3 parts by weight of styrene / butadiene rubber as a binder and 1% by weight of carboxymethyl cellulose. 100 parts by weight of an aqueous solution were added, and the mixture was stirred and mixed to obtain a paste-like negative electrode mixture. This negative electrode mixture was applied to both surfaces of a copper foil having a thickness of 15 μm as a current collector, dried, rolled, and cut into predetermined dimensions to obtain a negative electrode.
[0035]
(D) Battery assembly Using the above positive electrode and negative electrode, a predetermined sealing plate and an aluminum square battery case (aluminum material having a thickness of 0.3 mm) having the shape shown in FIG. A secondary battery (thickness 5 mm, width 34 mm, height 50 mm) was assembled. FIG. 15 is a partial perspective view in which a part of the manufactured battery is cut away.
First, the positive electrode and the negative electrode were wound via a 25 μm-thick microporous polyethylene resin separator to form an electrode group 70. An aluminum positive electrode lead 71 and a nickel negative electrode lead 72 were welded to the positive electrode and the negative electrode, respectively. An insulating plate 73 made of polyethylene resin was mounted on the upper part of the electrode group, and housed in a battery case 74. The other end of the positive electrode lead was spot-welded to the lower surface of a sealing plate 78 having a predetermined safety valve 77 described below. The other end of the negative electrode lead was electrically connected to a lower part of a nickel negative electrode terminal 75 inserted into a terminal hole at the center of the sealing plate via an insulating material 76.
[0036]
After the opening end of the battery case and the peripheral edge of the sealing plate were laser-welded, a predetermined amount of non-aqueous electrolyte was injected from an injection hole provided in the sealing plate. Finally, the injection hole was closed with an aluminum stopper 79, and the injection hole was sealed by laser welding to complete the battery. As the non-aqueous electrolyte, one obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / L in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 3 was used.
In addition, ten batteries each using the sealing plates A to C were produced.
[0037]
(E) Battery evaluation At constant temperature of 25 ° C., constant-current charging is performed until the voltage of each battery reaches 4.2 V, and after the voltage reaches 4.2 V, the total charging time is 3 hours. Was charged at a constant voltage. Thereafter, each battery was placed on a hot plate at 250 ° C., and a safety valve tear test was performed.
After the test, the batteries were observed. As a result, the safety valves of 10 out of 10 batteries were activated, and the batteries did not rupture or ignite at all. From this, according to the present invention, it was confirmed that the safety valve operates stably even though the thickness of the break portion of the safety valve is 50 μm thicker than before.
[0038]
【The invention's effect】
As described above, according to the present invention, the safety valve is relatively easy to manufacture because a safety valve that breaks due to deformation of the case when the internal pressure of the battery rises is employed. The safety of the rechargeable battery can be improved.
[Brief description of the drawings]
FIG. 1 is a top view of a sealing plate according to a first embodiment.
FIG. 2 is an enlarged sectional view taken along line II-II of the sealing plate shown in FIG.
FIG. 3 is an enlarged partial cross-sectional view of the sealing plate shown in FIG. 1, taken along the line III-III.
FIG. 4 is a top view of a sealing plate according to a second embodiment.
FIG. 5 is an enlarged sectional view taken along line VV of the sealing plate shown in FIG.
6 is an enlarged partial cross-sectional view of the sealing plate shown in FIG. 4, taken along the line VI-VI.
FIG. 7 is a top view of a sealing plate according to a third embodiment.
FIG. 8 is an enlarged sectional view taken along line VIII-VIII of the sealing plate shown in FIG. 7;
9 is an IX-IX line enlarged partial sectional view of the sealing plate shown in FIG. 7;
FIG. 10 is a top view of a sealing plate according to a fourth embodiment.
FIG. 11 is an enlarged cross-sectional view taken along line XI-XI of the sealing plate shown in FIG.
12 is an enlarged partial cross-sectional view of the sealing plate shown in FIG. 11, taken along the line XII-XII.
FIG. 13 is a manufacturing process diagram of the sealing plate according to the first embodiment.
FIG. 14 is a longitudinal sectional view of an example of a prismatic battery case used for a sealed battery.
FIG. 15 is a partial perspective view of the nonaqueous electrolyte secondary battery according to the present invention, with a portion cut away.
[Explanation of symbols]
10 Oval outline 11, 21, 31, 52 Thin part 12, 50 Plate material 13, 20, 30, 32, 40, 56 Flat part 14a Terminal hole 14b Concave part 15a around terminal hole Injection hole 15b Injection Recesses 51a, 53 around the hole Upper mold 51b, 53b Lower mold 53a Rib 54 Terminal hole 55 Liquid injection hole 57 Cutting blade 60, 74 Square battery case 61, 78 Sealing plate 62, 76 Insulating material 63 Electrode terminal 64, 77 Safety valve 65, 79 Seal 70 Electrode group 71 Positive lead 72 Negative lead 73 Insulating plate 75 Negative terminal

Claims (13)

A sealing plate made of a plate-like material for closing an opening of the battery case,
The sealing plate has a safety valve,
The safety valve comprises a flat thin portion formed on the lower surface of the plate-like material by buckling,
The thin portion has a thinner flat portion formed by a push process,
The sealing plate for a battery, wherein the flat portion is broken by a tension in a surface direction of the plate-shaped material due to deformation of the case when a battery internal pressure rises. The battery sealing plate according to claim 1, wherein the flat portion has a thickness of 30 to 80 m. 3. The battery sealing plate according to claim 1, wherein the width of the flat portion is 0.1 mm or more. The battery sealing plate according to any one of claims 1 to 3, wherein the flat portion forms a groove along a rectangular outline or a substantially oval outline having a pair of parallel linear portions. The battery sealing plate according to any one of claims 1 to 3, wherein the flat portion has a groove formed along a pair of parallel straight lines. The battery sealing plate according to any one of claims 1 to 3, wherein the flat portion forms a concave portion surrounded by a rectangular outline or a substantially oval outline having a pair of parallel linear portions. An electrode group, an electrolyte, a prismatic battery case containing the electrode group and the non-aqueous electrolyte, and a sealing plate made of a plate-like material for sealing an opening of the case,
The sealing plate has a safety valve, the safety valve is formed of a thin portion having a flat bottom surface formed by pressing the plate-shaped material,
The thin portion has a thinner flat portion formed by a push process,
A sealed battery in which the flat portion is broken by a tension in a plane direction of the plate-like material due to deformation of the case when a battery internal pressure increases. The sealed battery according to claim 7, wherein the flat portion has a thickness of 30 to 80 m. 9. The sealed battery according to claim 7, wherein the thickness of the wall material of the case is 1 to 0.1 mm. The sealed battery according to any one of claims 7 to 9, wherein the width of the flat portion is 0.1 mm or more. The sealed battery according to any one of claims 7 to 10, wherein the flat portion forms a groove along a rectangular outline or a substantially oval outline having a pair of parallel linear portions. The sealed battery according to claim 7, wherein the flat portion forms a groove along a pair of parallel straight lines. The sealed battery according to any one of claims 7 to 12, wherein the flat portion forms a concave surface having a rectangular outline or a substantially oval outline having a pair of parallel linear portions.

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