Secondary batteries

Abstract

To provide a highly reliable secondary battery which can be manufactured efficiently.SOLUTION: A secondary battery 1 includes a case 100. The case 100 accommodates an electrode assembly. The case 100 includes a case body 110. The case body 110 includes a pair of first wall portions 111. The pair of first wall portions 111 face each other in a second direction orthogonal to a first direction. In one first wall portion 111A of the pair of first wall portions, a joining portion 115 extending from a first opening 113 to a second opening 114 is formed. A part of the joining portion 115 is provided with a vulnerable part 150 that, when internal pressure of the case 100 becomes equal to or more than a predetermined value, is fractured to discharge gas in the case 100 to outside of the case 100.SELECTED DRAWING: Figure 15

Description

[Technical Field]

[0001] The present technology relates to a secondary battery. [Background technology]

[0002] A prior art document disclosing a nonaqueous electrolyte secondary battery is JP 8-148184 A (Patent Document 1). The nonaqueous electrolyte secondary battery described in Patent Document 1 has grooves extending in multiple directions formed on the side of a flat prismatic battery case that is not parallel to the positive and negative electrodes.

[0003] A prior art document disclosing a secondary battery is Japanese Patent No. 5821605 (Patent Document 2). In the secondary battery described in Patent Document 2, a thin-walled portion that is thinner than the other metal plate portions of the case is formed as a safety valve at the location where the edges of the metal plates are welded together. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-148184 [Patent Document 2] Patent No. 5821605 Summary of the Invention [Problem to be solved by the invention]

[0005] From the viewpoint of reliability of secondary batteries, the secondary batteries described in Patent Documents 1 and 2 have room for efficient production of highly reliable secondary batteries.

[0006] The present technology has been made to solve the above-mentioned problems, and has an object to provide a highly reliable secondary battery that can be manufactured efficiently. [Means for solving the problem]

[0007] A secondary battery based on the present technology includes an electrode assembly and a case. The electrode assembly includes a first electrode and a second electrode having a polarity opposite to that of the first electrode. The case accommodates the electrode assembly. The case includes a case body, a first sealing plate, and a second sealing plate. The case body has a first opening located at an end of a first side in a first direction and a second opening located at an end of a second side opposite the first side in the first direction. The first sealing plate seals the first opening. The second sealing plate seals the second opening. The case body has a pair of first wall portions. The pair of first wall portions face each other in a second direction perpendicular to the first direction. One of the pair of first wall portions has a joint extending from the first opening to the second opening. A weak portion is provided in a part of the joint that breaks when the internal pressure of the case reaches a predetermined value or higher, thereby releasing gas inside the case to the outside. [Effects of the Invention]

[0008] According to the present technology, it is possible to provide a highly reliable secondary battery that can be manufactured efficiently. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a front view showing a configuration of a secondary battery according to a first embodiment of the present technology. [Figure 2] 2 is a diagram showing the secondary battery shown in FIG. 1 as viewed from the direction of arrow II. [Figure 3] 3 is a diagram showing the secondary battery shown in FIG. 1 as viewed from the direction of arrow III. [Figure 4] 4 is a diagram showing the secondary battery shown in FIG. 1 as viewed from the direction of arrow IV. FIG. [Figure 5] 2 is a diagram showing the secondary battery shown in FIG. 1 as viewed from the direction of arrow V. FIG. [Figure 6] FIG. 2 is a front cross-sectional view of the secondary battery shown in FIG. [Figure 7] FIG. 2 is a front view showing a negative electrode blank before being formed into a negative electrode plate. [Figure 8] 8 is a cross-sectional view taken along the line VIII-VIII of the negative electrode plate shown in FIG. 7. [Figure 9]FIG. 2 is a front view showing a negative electrode plate formed from a negative electrode original plate. [Figure 10] FIG. 2 is a front view showing a positive electrode plate before it is formed into a positive electrode plate. [Figure 11] 11 is a cross-sectional view of the positive electrode plate taken along the line XI-XI in FIG. 10. [Figure 12] FIG. 2 is a front view showing a positive electrode plate formed from a positive electrode original plate. [Figure 13] 3A and 3B are diagrams showing plate-shaped members that constitute the case main body. [Figure 14] 14 is a diagram showing a state in which the plate-like member shown in FIG. 13 is bent. FIG. [Figure 15] FIG. 4 is a perspective view showing the arrangement of weak portions in a case body. [Figure 16] 16 is a cross-sectional view of the case body shown in FIG. 15 taken along line XVI-XVI. [Figure 17] 17 is a cross-sectional view of the case body shown in FIG. 16 taken along the line XVII-XVII. [Figure 18] 18 is a cross-sectional view of the case body shown in FIG. 16 taken along the line XVIII-XVIII. [Figure 19] 10 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to a second embodiment. FIG. [Figure 20] FIG. 10 is a top view showing the configuration of a secondary battery according to a third embodiment. [Figure 21] FIG. 10 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to a third embodiment. [Figure 22] FIG. 10 is a perspective view showing the configuration of a secondary battery according to a fourth embodiment. [Figure 23] FIG. 10 is a front view showing the configuration of a secondary battery according to a fourth embodiment. [Figure 24] FIG. 10 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to a fifth embodiment. [Figure 25] 13 is a top view showing the configuration of a case body included in a secondary battery according to a sixth embodiment. FIG. [Figure 26] 26 is a cross-sectional view of the case body shown in FIG. 25 taken along the line XXVI-XXVI. [Figure 27] FIG. 13 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to a seventh embodiment. [Figure 28] 13 is a top view showing the configuration of a case body included in a secondary battery according to an eighth embodiment. FIG. [Figure 29] 29 is a cross-sectional view of the case body shown in FIG. 28 taken along the line XXIX-XXIX. [Figure 30] 13 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to a ninth embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present technology will be described. Note that the same or corresponding parts are denoted by the same reference characters, and description thereof may not be repeated.

[0011] In the embodiments described below, when numbers, amounts, etc. are mentioned, the scope of the present technology is not necessarily limited to those numbers, amounts, etc., unless otherwise specified. Furthermore, in the following embodiments, each component is not necessarily essential to the present technology, unless otherwise specified. Furthermore, the present technology is not necessarily limited to those that achieve all of the effects and advantages mentioned in the present embodiments.

[0012] In this specification, the terms "comprise," "include," and "have" are open-ended. That is, when a certain feature is included, other features may or may not be included.

[0013] Furthermore, when geometric terms and terms expressing positional and directional relationships are used in this specification, such as "parallel," "orthogonal," "45° diagonal," "coaxial," and "along," these terms allow for manufacturing errors and slight variations. When terms expressing relative positional relationships, such as "upper side" and "lower side," are used in this specification, these terms are used to indicate relative positional relationships in a single state, and the relative positional relationships can be reversed or rotated to any angle depending on the installation direction of each mechanism (for example, by turning the entire mechanism upside down).

[0014] In this specification, the term "secondary battery" is not limited to lithium ion batteries, but may include other secondary batteries such as nickel-metal hydride batteries and sodium ion batteries. In this specification, the term "electrode" may collectively refer to a positive electrode and a negative electrode.

[0015] In the drawings, the direction along the winding axis of the electrode body of the secondary battery is the X direction, the shorter side of the case as viewed from the X direction is the Y direction, and the longer side of the case as viewed from the X direction is the Z direction. To facilitate understanding of the present technology, the dimensions of each component in the drawings may be altered from their actual dimensions. Also, the drawings may not show the sealing plate joint between the case body and the sealing plate.

[0016] Furthermore, in this specification, the X direction is the first direction in which the first opening and the second opening of the case body are aligned, the Y direction is the third direction in which the first plate-shaped portion and the second plate-shaped portion of one of the pair of first wall portions (first side portions) are aligned, and the Z direction is the second direction in which the pair of first wall portions (first side portions) are aligned.

[0017] (Embodiment 1) (Overall battery configuration) Fig. 1 is a front view of a secondary battery 1 according to the present embodiment. Figs. 2 to 5 are views of the secondary battery 1 shown in Fig. 1 as viewed from the directions of arrows II, III, IV, and V, respectively. Fig. 6 is a front cross-sectional view of the secondary battery 1 shown in Fig. 1.

[0018] The secondary battery 1 can be mounted in an electric vehicle (BEV: Battery Electric Vehicle), a plug-in hybrid electric vehicle (PHEV: Plug-in Hybrid Electric Vehicle), a hybrid electric vehicle (HEV: Hybrid Electric Vehicle), etc. However, the use of the secondary battery 1 is not limited to being mounted in a vehicle.

[0019] As shown in FIGS. 1 to 6, the secondary battery 1 includes a case 100, an electrode assembly 200, an electrode terminal 300, and a current collector 400.

[0020] When configuring a battery pack including the secondary batteries 1, multiple secondary batteries 1 are stacked in the Y direction. The stacked secondary batteries 1 may be constrained in the stacking direction (Y direction) by a constraining member to form a battery module, or the battery pack may be directly supported on the side surface of the battery pack case without using a constraining member.

[0021] The case 100 houses the electrode assembly 200. The case 100 includes a case body 110, a first sealing plate 120, and a second sealing plate .

[0022] The case body 110 is made of a cylindrical, preferably rectangular, member. This results in a rectangular secondary battery 1. The case body 110 is made of metal. Specifically, the case body 110 is made of aluminum, an aluminum alloy, iron, an iron alloy, or the like. When the case body 110 is made of iron or an iron alloy, the case body 110 may be plated with nickel, tin, zinc, or the like.

[0023] 1 and 2, a first sealing plate 120 and a second sealing plate 130 are provided at both ends of the case body. The case body 110 can be formed into a rectangular tube shape, for example, by abutting the edges of bent plate-like members (at joint 115 shown in FIG. 5) and joining them together (by laser welding, for example). The corners of the "rectangular tube" may be rounded.

[0024] In this embodiment, the case body 110 is formed so that it is longer in the X direction of the secondary battery 1 than in the Y and Z directions of the secondary battery 1. The dimension of the case body 110 in the X direction is preferably about 30 cm or more. This allows for the construction of a relatively large (high-capacity) secondary battery 1. The dimension of the case body 110 in the Z direction is preferably about 20 cm or less, more preferably about 15 cm or less, and even more preferably about 10 cm or less. This allows for the construction of a relatively low-height secondary battery 1, which improves the mountability in a vehicle, for example.

[0025] The case body 110 includes a pair of first side surface portions 111 (a pair of first wall portions) and a pair of second side surface portions 112 (a pair of second wall portions). The pair of first side surface portions 111 face each other in a second direction (Z direction) perpendicular to the first direction (X direction). The pair of first side surface portions 111 form the bottom surface and the top surface of the case 100.

[0026] The pair of second side surface portions 112 face each other in a third direction (Y direction) that is perpendicular to the first direction (X direction) and the second direction (Z direction). The pair of second side surface portions 112 constitute part of the side surfaces of the case 100.

[0027] The pair of first side surface portions 111 and the pair of second side surface portions 112 are arranged to intersect with each other. The pair of first side surface portions 111 and the pair of second side surface portions 112 are connected at their respective ends. As in the present embodiment, it is desirable that the area of ​​each of the pair of first side surface portions 111 be smaller than the area of ​​each of the pair of second side surface portions 112.

[0028] 5, one 111A of the pair of first side surface portions is formed with a joint 115. The joint 115 extends from the first opening 113 to the second opening 114. That is, the joint 115 extends in the X direction of the secondary battery 1. At the joint 115, the edges of the plate-like members that make up the case body 110 are joined together.

[0029] A fragile portion 150 is provided in a part of the joint 115. The fragile portion 150 breaks when the internal pressure of the case 100 reaches or exceeds a predetermined value, and discharges gas inside the case 100 to the outside of the case 100. Details of the joint 115 and the fragile portion 150 will be described later.

[0030] 3, a first opening 113 is provided at an end of a first side in a first direction (X direction) of case body 110. First opening 113 is sealed by first sealing plate 120. A sealing plate joint 125 is formed in first opening 113 to seal first opening 113. First opening 113 and first sealing plate 120 have a substantially rectangular shape with the Y direction as the short side direction and the Z direction as the long side direction.

[0031] A negative electrode terminal 301 (first electrode terminal) is provided on first sealing plate 120. In the present embodiment, negative electrode terminal 301 is located approximately in the center of first sealing plate 120 in both the Y direction and the Z direction. The position of negative electrode terminal 301 can be changed as appropriate.

[0032] 4, a second opening 114 is provided at the end of a second side of case body 110 opposite the first side in the first direction (X direction). That is, second opening 114 is located at the end opposite first opening 113. Second opening 114 is sealed by second sealing plate 130. A sealing plate joint 135 is formed in second opening 114 to seal second opening 114. Second opening 114 and second sealing plate 130 have a substantially rectangular shape with the Y direction as the short side direction and the Z direction as the long side direction.

[0033] A positive electrode terminal 302 (second electrode terminal) and a liquid injection hole 134 are provided on the second sealing plate 130. In the present embodiment, the positive electrode terminal 302 is located approximately in the center of the second sealing plate 130 in both the Y direction and the Z direction. The positions of the positive electrode terminal 302 and the liquid injection hole 134 can be changed as appropriate.

[0034] The first sealing plate 120 and the second sealing plate 130 are made of metal. Specifically, the first sealing plate 120 and the second sealing plate 130 are made of aluminum, an aluminum alloy, iron, an iron alloy, etc. When the first sealing plate 120 and the second sealing plate 130 are made of iron or an iron alloy, the first sealing plate 120 and the second sealing plate 130 may be plated with nickel, tin, zinc, or the like.

[0035] The negative electrode terminal 301 is electrically connected to the negative electrode (first electrode) of the electrode body 200. The negative electrode terminal 301 is attached to the first sealing plate 120, that is, the case 100.

[0036] The positive electrode terminal 302 is electrically connected to the positive electrode (second electrode) of the electrode body 200. The positive electrode terminal 302 is attached to the second sealing plate 130, that is, the case 100.

[0037] The negative electrode terminal 301 is made of a conductive material (more specifically, a metal), and may be made of, for example, copper or a copper alloy. The outer surface of the negative electrode terminal 301 may be provided with a portion or layer made of aluminum or an aluminum alloy.

[0038] The positive terminal 302 is made of a conductive material (more specifically, a metal), and may be made of, for example, aluminum or an aluminum alloy.

[0039] The liquid inlet hole 134 is sealed with a sealing member (not shown), which may be, for example, a blind rivet or other metal member.

[0040] The electrode assembly 200 is a flat-shaped electrode assembly having positive and negative electrode plates, as described below. Specifically, the electrode assembly 200 is a wound-type electrode assembly in which a strip-shaped positive electrode plate and a strip-shaped negative electrode plate are wound together via a strip-shaped separator (not shown). However, in this specification, the term "electrode assembly" is not limited to a wound-type electrode assembly and may also be a stacked-type electrode assembly in which multiple positive electrode plates and multiple negative electrode plates are alternately stacked. The strip-shaped separator may be formed, for example, of a polyolefin microporous membrane. The electrode assembly may include multiple positive electrode plates and multiple negative electrode plates, and the positive electrode tabs provided on each positive electrode plate may be stacked to form a positive electrode tab group, or the negative electrode tabs provided on each negative electrode plate may be stacked to form a negative electrode tab group. The electrode assembly 200 may include multiple wound-type electrode bodies or multiple stacked-type electrode bodies.

[0041] 6, case 100 houses electrode assembly 200. Electrode assembly 200 is housed in case 100 so that its winding axis is parallel to the X direction.

[0042] Specifically, one or more wound electrode bodies are housed inside an insulating sheet (not shown) arranged inside the case 100, together with an electrolytic solution (electrolyte) (not shown). The electrolytic solution (nonaqueous electrolytic solution) can be, for example, a nonaqueous solvent made by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio (25°C) of 30:30:40, in which LiPF6 is dissolved at a concentration of 1.2 mol / L. Note that a solid electrolyte may be used instead of the electrolytic solution.

[0043] The electrode body 200 includes a main body portion (a portion where positive electrode plates and negative electrode plates are stacked with a separator interposed therebetween), a first electrode tab group 220 (negative electrode tab group), and a second electrode tab group 250 (positive electrode tab group).

[0044] The main body is composed of a negative electrode plate 210 (first electrode) and a positive electrode plate 240 (second electrode), which will be described later. The first electrode tab group 220 is located at the end of the main body on the first sealing plate 120 side in the X direction. The second electrode tab group 250 is located at the end of the main body on the second sealing plate 130 side in the first direction (X direction).

[0045] The first electrode tab group 220 and the second electrode tab group 250 are formed so as to protrude from the center portion of the electrode body 200 toward the first sealing plate 120 or the second sealing plate 130, respectively.

[0046] The current collectors 400 include a negative electrode current collector 400A and a positive electrode current collector 400B. The negative electrode current collector 400A and the positive electrode current collector 400B are each made of a plate-shaped member. The electrode assembly 200 is electrically connected to a negative electrode terminal 301 and a positive electrode terminal 302 via the current collectors 400.

[0047] The negative electrode current collector 400A is disposed on the first sealing plate 120 via a resin insulating member. The negative electrode current collector 400A is electrically connected to the first electrode tab group 220 and the negative electrode terminal 301. The negative electrode current collector 400A is made of a conductive material (more specifically, a metal), and may be made of, for example, copper or a copper alloy.

[0048] The positive electrode current collector 400B is disposed on the second sealing plate 130 via a resin insulating member. The positive electrode current collector 400B is electrically connected to the second electrode tab group 250 and the positive electrode terminal 302. The positive electrode current collector 400B is made of a conductive material (more specifically, a metal), such as aluminum or an aluminum alloy. The second electrode tab group 250 may be electrically connected to the second sealing plate 130 directly or via the positive electrode current collector 400B. In this case, the second sealing plate 130 may serve as the positive electrode terminal 302.

[0049] (Configuration of electrode body 200) FIG. 7 is a front view showing the negative electrode plate 210S before the negative electrode plate 210 is formed, FIG. 8 is a cross-sectional view taken along line VIII-VIII of the negative electrode plate 210S shown in FIG. 7, and FIG. 9 is a front view showing the negative electrode plate 210 formed from the negative electrode plate 210S.

[0050] The negative electrode plate 210 is manufactured by processing a negative electrode original plate 210S. As shown in Figures 7 and 8, the negative electrode original plate 210S includes a negative electrode core 211 and a negative electrode active material layer 212. The negative electrode core 211 is a copper foil or a copper alloy foil.

[0051] A negative electrode active material layer 212 is formed on both surfaces of the negative electrode substrate 211 except for one end portion. The negative electrode active material layer 212 is formed by applying a negative electrode active material layer slurry using a die coater.

[0052] The negative electrode active material layer slurry is prepared by kneading graphite as the negative electrode active material, styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) as binders, and water as a dispersion medium so that the mass ratio of graphite:SBR:CMC is approximately 98:1:1.

[0053] The negative electrode substrate 211 coated with the negative electrode active material layer slurry is dried to remove water contained in the negative electrode active material layer slurry, thereby forming the negative electrode active material layer 212. The negative electrode active material layer 212 is then compressed to form a negative electrode base plate 210S including the negative electrode substrate 211 and the negative electrode active material layer 212. The negative electrode base plate 210S is cut into a predetermined shape to form the negative electrode plate 210. The negative electrode base plate 210S can be cut by laser processing using energy beam irradiation, mold processing, cutter processing, or the like.

[0054] As shown in FIG. 9, a plurality of negative electrode tabs 230 each made of a negative electrode core 211 are provided at one end in the width direction of a negative electrode plate 210 formed from a negative electrode original plate 210S. When the negative electrode plate 210 is wound, the plurality of negative electrode tabs 230 are stacked to form a first electrode tab group 220. As a result, the first electrode tab group 220 is connected to the negative electrode plate 210 (first electrode). The position and length in the protruding direction of each of the plurality of negative electrode tabs 230 are appropriately adjusted taking into consideration the state in which the first electrode tab group 220 is connected to the negative electrode current collector 400A. The shape of the negative electrode tab 230 is not limited to the example shown in FIG. 8.

[0055] FIG. 10 is a front view showing a positive electrode plate 240S before the positive electrode plate 240 is formed, FIG. 11 is a cross-sectional view taken along line XI-XI of the positive electrode plate 240S shown in FIG. 10, and FIG. 12 is a front view showing a positive electrode plate 240 formed from the positive electrode plate 240S.

[0056] The positive electrode plate 240, which is the second electrode, has a polarity different from that of the negative electrode plate 210, which is the first electrode. The positive electrode plate 240 is manufactured by processing a positive electrode base plate 240S. As shown in FIGS. 10 and 11, the positive electrode base plate 240S includes a positive electrode core 241, a positive electrode active material layer 242, and a positive electrode protective layer 243. The positive electrode core 241 is an aluminum foil or an aluminum alloy foil.

[0057] A positive electrode active material layer 242 is formed on both surfaces of the positive electrode core 241 except for one end portion. The positive electrode active material layer 242 is formed on the positive electrode core 241 by applying a positive electrode active material layer slurry using a die coater.

[0058] The positive electrode active material layer slurry is prepared by kneading lithium nickel cobalt manganese composite oxide as the positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, a carbon material as a conductive material, and N-methyl-2-pyrrolidone (NMP) as a dispersion medium so that the mass ratio of lithium nickel cobalt manganese composite oxide:PVdF:carbon material is approximately 97.5:1:1.5.

[0059] The positive electrode protective layer 243 is in contact with the positive electrode core 241 and is formed on one end of the positive electrode active material layer 242 in the width direction. The positive electrode protective layer 243 is formed on the positive electrode core 241 by applying a positive electrode protective layer slurry using a die coater. The positive electrode protective layer 243 has a larger electrical resistance than the positive electrode active material layer 242.

[0060] The positive electrode protective layer slurry is prepared by kneading alumina powder, a carbon material as a conductive material, PVdF as a binder, and NMP as a dispersion medium so that the mass ratio of alumina powder:carbon material:PVdF is approximately 83:3:14.

[0061] The positive electrode substrate 241 coated with the positive electrode active material layer slurry and the positive electrode protective layer slurry is dried, and the NMP contained in the positive electrode active material layer slurry and the positive electrode protective layer slurry is removed, thereby forming the positive electrode active material layer 242 and the positive electrode protective layer 243. The positive electrode active material layer 242 is then compressed to form a positive electrode base plate 240S including the positive electrode substrate 241, the positive electrode active material layer 242, and the positive electrode protective layer 243. The positive electrode base plate 240S is cut into a predetermined shape to form the positive electrode plate 240. The positive electrode base plate 240S can be cut by laser processing using energy beam irradiation, mold processing, cutter processing, or the like.

[0062] As shown in FIG. 12, a plurality of positive electrode tabs 260 each made of a positive electrode core 241 are provided at one end in the width direction of a positive electrode plate 240 formed from a positive electrode original plate 240S. When the positive electrode plate 240 is wound, the plurality of positive electrode tabs 260 are stacked to form a second electrode tab group 250. As a result, the second electrode tab group 250 is connected to the positive electrode plate 240 (second electrode). The position and length in the protruding direction of each of the plurality of positive electrode tabs 260 are appropriately adjusted taking into consideration the state in which the second electrode tab group 250 is connected to the positive electrode current collector 400B. The shape of the positive electrode tab 260 is not limited to the example shown in FIG. 12.

[0063] A positive electrode protective layer 243 is provided at the base of each of the positive electrode tabs 260. The positive electrode protective layer 243 does not necessarily have to be provided at the base of the positive electrode tab 260.

[0064] In a typical example, the thickness of the negative electrode tab 230 (one piece) is smaller than the thickness of the positive electrode tab 260 (one piece). In this case, the thickness of the first electrode tab group 220 is smaller than the thickness of the second electrode tab group 250.

[0065] (Production of the case body 110) Fig. 13 is a view showing a plate-like member that constitutes the case main body, and Fig. 14 is a view showing a state in which the plate-like member shown in Fig. 13 is folded.

[0066] As shown in Fig. 13, the case body 110 is formed by bending one plate-shaped member. The plate-shaped member 11 is bent along the bending portion 12. As a result, a tubular shape having a pair of first side surfaces 111 is formed as shown in Fig. 14. Here, the portion where two end sides 13 parallel to the bending portion 12 butt together forms the joint portion 115. The vicinity of the two end sides 13 may be overlapped and joined in the thickness direction of the plate-shaped member 11.

[0067] (Structure of joint 115 and fragile portion 150) Fig. 15 is a perspective view showing the arrangement of weak portions in the case body, and Fig. 16 is a cross-sectional view taken along line XVI-XVI of the case body shown in Fig. 15.

[0068] 15 and 16, one 111A of the pair of first side surface portions is provided with a joint 115. The joint 115 is a portion where the plate-like member of the case body 110 is melted and then solidified.

[0069] The joints 115 are formed by, for example, laser irradiation. Note that the method for forming the joints 115 is not limited to laser irradiation, and they may be formed using other high-energy rays such as arc welding, or may be resistance welding that uses heat transfer when a voltage is applied to the plate-like members of the case body 110.

[0070] The joint portion 115 includes a first joint portion 116, a second joint portion 117, and a fragile portion 150. The fragile portion 150 is located between the first joint portion 116 and the second joint portion 117 in the first direction (X direction).

[0071] The fragile portion 150 is preferably provided at two or less locations of the joint portion 115. It is more preferable that the fragile portion 150 is provided at one location of the joint portion 115. In the present embodiment, the fragile portion 150 is provided at one location of the joint portion 115.

[0072] When gas is generated inside case 100, the central portion of one 111A of the pair of first side surface portions in the first direction (X direction) is the portion of case 100 that is most susceptible to deformation. The central portion refers not only to a single point in the center of one 111A of the pair of first side surface portions in the X direction, but also to a range that includes the periphery of the center. Fragile portion 150 is located in the central portion of one 111A of the pair of first side surface portions in the first direction (X direction).

[0073] As shown in FIG. 15, the fragile portion 150 is preferably arranged so that the ratio of the length L1 of the first joint portion 116 to the length L2 of the second joint portion 117 in the first direction (X direction) satisfies the relationship L1 / L2=0.8 to 1.2.

[0074] In the first direction (X direction), the length of the fragile portion 150 is preferably ⅓ or less of the length of the joint portion 115. This makes it easier to concentrate the gas pressure at the fragile portion 150 when gas is generated inside the case 100.

[0075] Fig. 17 is a cross-sectional view of the case body taken along line XVII-XVII of Fig. 16. Fig. 18 is a cross-sectional view of the case body taken along line XVIII-XVIII of Fig. 16.

[0076] One 111A of the pair of first side surface portions has a first plate-shaped portion 118 and a second plate-shaped portion 119. In this embodiment, the thicknesses of the first plate-shaped portion 118 and the second plate-shaped portion 119 in the second direction (Z direction) are substantially the same at the position where the joint 115 is formed and at other positions. Specifically, the thicknesses of the first plate-shaped portion 118 and the second plate-shaped portion 119 in the second direction (Z direction) have a thickness ratio of 0.9 or more and 1.1 or less at the position where the joint 115 is formed and at other positions.

[0077] The first plate-shaped portion 118 and the second plate-shaped portion 119 are joined to each other at a joint 115. In this embodiment, the first plate-shaped portion 118 and the second plate-shaped portion 119 face each other in a third direction (Y direction) that is perpendicular to the first direction (X direction) and the second direction (Z direction). The first plate-shaped portion 118 and the second plate-shaped portion 119 are butt-joined to each other (butt-welded in this embodiment) at the joint 115. Note that when the first plate-shaped portion 118 and the second plate-shaped portion 119 are butt-welded, a gap may be formed between them.

[0078] The fragile portion 150 is a joining portion along a region R where the first plate-shaped portion 118 and the second plate-shaped portion 119 come into contact with each other in the second direction (Z direction).

[0079] The joint 115 is formed so that the dimension in the second direction (Z direction) in the fragile portion 150 is smaller than the dimension in the other portions of the fragile portion 150. As a result, the joint 115 is formed shallower (thicker) in the second direction (Z direction) in the fragile portion 150 than the other portions of the fragile portion (the first joint 116 and the second joint 117).

[0080] In the bonding portion 115 of the present embodiment, the maximum depth at the fragile portion 150 is shallower than the maximum depth at portions other than the fragile portion 150. Specifically, the bonding portion 115 is formed so that the depth D2 in the second direction (Z direction) at the fragile portion 150 is smaller than the depth D1 in the second direction (Z direction) at the first bonding portion 116 and the second bonding portion 117 other than the fragile portion 150.

[0081] The depth D2 of the bonding portion 115 in the fragile portion 150 is preferably 90% or less, and more preferably 80% or less, of the depth D1 of the bonding portion 115 in the first bonding portion 116 and the second bonding portion 117 other than the fragile portion 150. Furthermore, the depth D2 is preferably 30% or more, and more preferably 40% or more, of the depth D1.

[0082] When laser welding, which uses high-energy rays, is used to form the joint 115, the depth of the joint 115 can be changed by adjusting the trajectory, speed, or output of the laser.

[0083] By forming a portion with a shallow bonding depth such as fragile portion 150 in part of bonding portion 115, it is possible to form a portion with weak bonding strength between first plate-shaped portion 118 and second plate-shaped portion 119. As a result, if gas is generated inside case 100, fragile portion 150 will break when the internal pressure of case 100 reaches or exceeds a predetermined value, and the gas inside case 100 will be discharged to the outside of case 100.

[0084] In the secondary battery 1 according to the first embodiment of the present technology, a fragile portion 150 is provided in a part of the joint 115 that joins the case body 110. By forming the fragile portion 150 in a part of the joint 115, the joint 115 and the fragile portion 150 can be formed in the same process, compared to when a fragile portion such as a groove is provided separately from the formation of the joint, and therefore the number of processing steps can be reduced and the fragile portion 150 can be efficiently provided. As a result, the secondary battery 1 can be efficiently manufactured by forming the fragile portion 150 in a part of the joint 115, and the fragile portion 150 serves to release gas, making it possible to provide a highly reliable secondary battery 1.

[0085] In the secondary battery 1 according to embodiment 1 of the present technology, when gas is generated inside the case 100, by providing a fragile portion 150 on the first side surface portion 111 (first wall portion) side, which has a smaller area than the second side surface portion 112, rather than on the second side surface portion 112 (second wall portion) side where multiple secondary batteries 1 are stacked and adjacent to each other, the generated gas can be easily discharged to the outside without interfering with adjacent secondary batteries 1.

[0086] In the secondary battery 1 according to embodiment 1 of the present technology, when the joint 115 is formed by butt joining (butt welding), the depth D2 of the joint 115 in the second direction (Z direction) at the fragile portion 150 is formed to be shallower than the depth D1 of the joint 115 at other than the fragile portion 150, thereby allowing the fragile portion 150 to be fractured preferentially relative to other than the fragile portion 150.

[0087] In the secondary battery 1 according to the first embodiment of the present technology, when the internal pressure of the case 100 increases, the fragile portion 150 can be easily broken by arranging the fragile portion 150 in the center in the first direction (X direction) of the first side surface portion 111, which is the portion of the case 100 that is most susceptible to deformation. Note that it is preferable that at least a part of the fragile portion 150 is arranged on the center in the X direction of one 111A of the pair of first side surface portions.

[0088] In the secondary battery 1 according to embodiment 1 of the present technology, by butt-joining (butt welding) the first plate-shaped portion 118 and the second plate-shaped portion 119 to form the joint 115 including the fragile portion 150, it is possible to form the joint 115 including the fragile portion 150 regardless of the planar accuracy of the abutting surfaces of the first plate-shaped portion 118 and the second plate-shaped portion 119, or even if there is a gap between them.

[0089] Secondary batteries according to embodiments 2 to 9 will be described below. The secondary batteries according to these embodiments differ from secondary battery 1 according to embodiment 1 of the present technology in the configuration of the joint of the case body, and therefore, the description of the configuration that is the same as secondary battery 1 according to embodiment 1 of the present technology will not be repeated.

[0090] (Embodiment 2) Fig. 19 is a cross-sectional view showing the configuration of a fragile portion of the secondary battery according to embodiment 2. As shown in Fig. 19, the secondary battery according to embodiment 2 includes a case main body 110A.

[0091] The case body 110A is provided with a joint 115A that joins the first plate-shaped portion 118A and the second plate-shaped portion 119A. A fragile portion 150A is formed in a part of the joint 115A.

[0092] Case body 110A in this embodiment has recess 155A in fragile portion 150A. Recess 155A faces the inside of case body 110A.

[0093] The recess 155A is formed by providing a chamfered portion on both the first plate-shaped portion 118A and the second plate-shaped portion 119A. The recess 155A may also be formed by providing a chamfered portion on one of the first plate-shaped portion 118A and the second plate-shaped portion 119A. The depth of the recess 155A in the second direction (Z direction) is preferably, for example, between ⅓ and ½ of the thickness of the first plate-shaped portion 118A and the second plate-shaped portion 119A. By forming the recess 155A, the plate thickness of the case body 110A in the second direction (Z direction) at the fragile portion 150A becomes thinner than other portions of the case body 110A.

[0094] The fragile portion 150A is a joint portion from the position of the maximum depth of the recess 155A in the second direction (Z direction) to the outer surface of the case body 110A along the second direction (Z direction). By forming the recess 155A, the depth D3 in the second direction (Z direction) of the joint portion 115A in the fragile portion 150A is shallower than the depth in the second direction (Z direction) of the joint portion 115A other than the fragile portion 150A. This makes it possible to form a portion where the joint strength between the first plate-shaped portion 118 and the second plate-shaped portion 119 is weak.

[0095] In the secondary battery according to the second embodiment of the present technology, by providing a recess 155A on the inner side of the case body 110A in the fragile portion 150A, it is possible to easily control the depth D3 of the fragile portion 150A.

[0096] In the secondary battery according to embodiment 2 of the present technology, when forming the fragile portion 150A, there is no need to adjust the laser irradiation conditions, such as weakening them more than other portions than the fragile portion 150A, making it easier to manufacture the case body 110A and improving yield.

[0097] (Embodiment 3) Fig. 20 is a top view showing the configuration of a secondary battery according to embodiment 3. Fig. 21 is a cross-sectional view showing the configuration of a fragile portion of the secondary battery according to embodiment 3.

[0098] As shown in FIGS. 20 and 21, a secondary battery 1B in the third embodiment includes a case body 110B.

[0099] Case body 110B is provided with a joint 115B that joins first plate-shaped portion 118B and second plate-shaped portion 119B. A fragile portion 150B is formed in a part of joint 115B. Fragile portion 150B is continuous with first joint portion 116B and second joint portion 117B other than fragile portion 150B.

[0100] When viewed from the first direction (X direction), i.e., in a cross section perpendicular to the first direction (X direction), the centers of the joints 115B in the weak portion 150B and in the portions other than the weak portion 150B are arranged offset from each other in the third direction (Y direction).

[0101] Specifically, the center C of the joint 115B in the fragile portion 150B is offset in the Y direction from the contact position of the first plate-shaped portion 118B and the second plate-shaped portion 119B. On the other hand, the centers of the first joint 116B and the second joint 117B other than the fragile portion 150B are not offset from the contact position of the first plate-shaped portion 118B and the second plate-shaped portion 119B. The centers of the first joint 116B and the second joint 117B other than the fragile portion 150B may be offset from the contact position of the first plate-shaped portion 118B and the second plate-shaped portion 119B to a lesser extent than the center C of the joint 115B in the fragile portion 150B. The center C of the joint 115B and the center of the second joint 117B are the deepest parts (thickest parts) of the joints, respectively.

[0102] The center C of the joint 115B in the fragile portion 150B is shifted in the third direction (Y direction) by ⅓ or more of the width dimension of the joint 115B on the outer surface of the case body 110B.

[0103] The maximum depth D4 of the joint 115B in the second direction (Z direction) is substantially the same for the weak portion 150B and the first joint 116B and the second joint 117B other than the weak portion 150B. In the second direction (Z direction), the depth D5 of the joint portion constituting the weak portion 150B of the joint 115B is shallower than the maximum depth D4. The ratio of the depth D5 to the maximum depth D4 is preferably 50% or more and 80% or less.

[0104] The weakened portion 150B is formed, for example, by shifting the trajectory of the laser that forms the joint portion 115B in the third direction (Y direction) relative to portions other than the weakened portion 150B.

[0105] In the secondary battery 1B according to the third embodiment of the present technology, the centers of the joints 115B in the weak portion 150B and the portions other than the weak portion 150B are shifted in the third direction (Y direction) in which the first plate-shaped portion 118B and the second plate-shaped portion 119B are butted together. This eliminates the need to adjust the laser irradiation conditions, such as weakening them, when forming the weak portion 150B, making it easier to manufacture the case body 110B and improving the yield.

[0106] When joining portion 115B is formed by resistance welding using heat transfer, if the joining depth of joining portion 115B is shallow, problems such as the generation of unjoined portions occur. In secondary battery 1B according to embodiment 3 of the present technology, when the entire joining portion 115B is shallowly joined, it is not necessary to change the joining conditions by simply shifting the positions of the heat generation points in fragile portion 150B and other portions than fragile portion 150B, so that fragile portion 150B can be formed while suppressing the generation of unjoined portions in joining portion 115B.

[0107] (Fourth embodiment) Fig. 22 is a perspective view showing the configuration of a secondary battery according to embodiment 4. Fig. 23 is a front view showing the configuration of a secondary battery according to embodiment 4. Note that in Figs. 22 and 23, the current collector, the insulating member disposed between the sealing plate and the current collector, etc. are not shown, but the configuration can be the same as in embodiment 1.

[0108] 22 and 23, a joint 115C in a case 100C of a secondary battery 1C of the present embodiment is provided with a fragile portion 150C. The fragile portion 150C has a first fragile portion 151C and a second fragile portion 152C.

[0109] The first weak portion 151C is located near the end on the first sealing plate 120 side. The second weak portion 152C is spaced apart from the first weak portion 151C and located near the end on the second sealing plate 130 side. The first weak portion 151C and the second weak portion 152C sandwich the central joint portion 116C between them. It is preferable that at least a portion of the first weak portion 151C is arranged to overlap with the region between the end of the first sealing plate 120 of the main body portion of the electrode assembly 200 and the first sealing plate 120. It is also preferable that at least a portion of the second weak portion 152C is arranged to overlap with the region between the end of the second sealing plate 130 of the main body portion of the electrode assembly 200 and the second sealing plate 130. This makes it easier for gas generated inside the electrode assembly 200 to reach each weak portion through the spaces between each sealing plate and the electrode assembly 200, and each weak portion is ruptured reliably.

[0110] It is desirable that first weak portion 151C is spaced apart from the end on the side of first sealing plate 120. It is desirable that second weak portion 152C is spaced apart from the end on the side of second sealing plate 130. If first weak portion 151C or second weak portion 152C breaks, it will cause a chain reaction of breakage of the joint between first sealing plate 120 and case body 110 or the joint between second sealing plate 130 and case body 110, thereby preventing gas from being discharged from unintended areas.

[0111] For example, the length in the X direction of each of first weak portion 151C and second weak portion 152C is preferably about 1 / 20 to 1 / 4 of the length in the X direction of case 100. Furthermore, for example, if the length in the X direction of case 100 is 20 cm or more, the length in the first direction of each of first weak portion 151C and second weak portion 152C is preferably 1 cm or more, and more preferably 2 cm or more. Note that, although not particularly limited, the length in the first direction of each of first weak portion 151C and second weak portion 152C is preferably 5 cm or less, and more preferably 4 cm or less.

[0112] The height H2 in the Z direction of the second electrode tab group 250 is preferably equal to or less than half the height H1 in the Z direction of the electrode body 200. This makes it easier to ensure a space S in the portion of the case 100 where the second electrode tab group 250 is disposed. Note that the height H2 is the maximum height of the second electrode tab group 250.

[0113] The second weak portion 152C is provided so that the second weak portion 152C and the second electrode tab group 250 are aligned in the Z direction. This allows the second weak portion 152C to be provided adjacent to the space S around the second electrode tab group 250. Note that although the configuration on the second weak portion 152C side is illustrated in Figures 22 and 23, the first weak portion 151C side may also have a similar configuration to the second weak portion 152C.

[0114] In the secondary battery 1C according to embodiment 4 of the present technology, by providing two weak parts 150, a first weak part 151C and a second weak part 152C, at the joint 115C, the gas inside the case 100 can be dispersed, and high-pressure gas can be prevented from being sprayed onto adjacent secondary batteries, compared to when a weak part is provided at one location at the joint.

[0115] In the secondary battery according to the fourth embodiment of the present technology, in a configuration in which the electrode body 200 has an electrode tab group, by providing a fragile portion 150C around the electrode tab group, the space S around the electrode tab group can be used as a gas exhaust path, thereby making it easier to secure a gas exhaust path.

[0116] (Embodiment 5) Fig. 24 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to embodiment 5. As shown in Fig. 24, the first plate-shaped portion 118D and the second plate-shaped portion 119D of a case body 110D each have an uneven surface shape that comes into contact with each other. When the first plate-shaped portion 118D and the second plate-shaped portion 119D are butt-joined (butt-welded), the uneven surfaces are engaged with each other. The engagement of the uneven surfaces makes it easy to position the first plate-shaped portion 118D and the second plate-shaped portion 119D relative to each other.

[0117] In the secondary battery according to the fifth embodiment of the present technology, the joint 115D of the fragile portion 150D is shallower in the second direction (Z direction) than the joint 115D other than the fragile portion 150D, so that the fragile portion 150D can be broken preferentially.

[0118] (Embodiment 6) Fig. 25 is a top view showing the configuration of a case body included in a secondary battery according to Embodiment 6. Fig. 26 is a cross-sectional view taken along line XXVI-XXVI of the case body shown in Fig. 25.

[0119] 25 and 26, a case body 110E in this embodiment includes a first plate-shaped portion 118E and a second plate-shaped portion 119E. A portion of each of the first plate-shaped portion 118E and the second plate-shaped portion 119E faces each other in the second direction (Z direction).

[0120] The first plate-shaped portion 118E and the second plate-shaped portion 119E are welded together at a joint 115E. The joint 115E is formed in the second direction (Z direction) so as to extend from the outer surface of the second plate-shaped portion 119E through the second plate-shaped portion 119E and reach the first plate-shaped portion 118E.

[0121] The fragile portion 150E is a joining portion along a region R where the first plate-shaped portion 118E and the second plate-shaped portion 119E face each other in the third direction (Y direction).

[0122] The joint 115E is formed such that the width dimension W1 in the third direction (Y direction) at the fragile portion 150E is smaller than the width dimensions at the first joint 116E and the second joint 117E other than the fragile portion 150E. In addition, in this embodiment, when viewed from the first direction (X direction), the joint depth in the second direction (Z direction) of the joint 115E at the fragile portion 150E is shallower than the joint depth in the second direction (Z direction) of the joint 115E other than the fragile portion 150E.

[0123] In the secondary battery according to embodiment 6 of the present technology, when the joint 115E is formed by through-hole welding, the width dimension W1 of the joint 115E in the third direction (Y direction) at the fragile portion 150E is formed to be shallower than the width dimension of the joint 115E in the third direction (Y direction) at other than the fragile portion 150E, thereby allowing the fragile portion 150 to be preferentially fractured.

[0124] (Embodiment 7) Fig. 27 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to embodiment 7. As shown in Fig. 27, the first plate-shaped portion 118F and the second plate-shaped portion 119F of the case body 110F each have an uneven surface shape where they come into contact. When the first plate-shaped portion 118F and the second plate-shaped portion 119F are welded together, the uneven surfaces are fitted together. This fitting of the uneven surfaces makes it easy to position the first plate-shaped portion 118F and the second plate-shaped portion 119F relative to each other.

[0125] The joint 115F is formed so that the width dimension W2 in the third direction (Y direction) at the fragile portion 150F is smaller than the width dimension of the joint 115F other than the fragile portion 150F.

[0126] In the secondary battery according to the seventh embodiment of the present technology, the joint portion 115F of the fragile portion 150F is also narrower in width in the third direction (Y direction) than the portions other than the fragile portion 150F, so that the fragile portion 150F can be broken preferentially.

[0127] (Embodiment 8) Fig. 28 is a top view showing the configuration of a case body included in a secondary battery according to Embodiment 8. Fig. 29 is a cross-sectional view taken along line XXIX-XXIX of the case body shown in Fig. 28.

[0128] As shown in FIGS. 28 and 29, the first plate-shaped portion 118G and the second plate-shaped portion 119G of the case body 110G face each other in the second direction (Z direction).

[0129] The first plate-shaped portion 118G and the second plate-shaped portion 119G are fillet-welded at a joint 115G. The joint 115G is formed to connect an edge portion of the second plate-shaped portion 119G to the outer surface of the first plate-shaped portion 118G.

[0130] The joint portion 115G is formed so that the width dimension W3 in the third direction (Y direction) at the fragile portion 150G is smaller than the width dimensions at the first joint portion 116G and the second joint portion 117G other than the fragile portion 150G.

[0131] (Embodiment 9) Fig. 30 is a cross-sectional view showing the configuration of a fragile portion of a secondary battery according to Embodiment 9. As shown in Fig. 30, in a case body 110H, a first plate-shaped portion 118H and a second plate-shaped portion 119H are fillet-welded by a joint portion 115H.

[0132] The joint portion 115H is formed so that the portion on the outer surface side is recessed. In the fragile portion 150H of the present embodiment, a width dimension W4 defined by the shortest distance between the outer surface portion P1 of the fragile portion 150H and the other end P2 in a direction inclined from the third direction (Y direction) is smaller than the width dimensions of the first joint portion 116H and the second joint portion 117H other than the fragile portion 150H.

[0133] In the secondary batteries according to the eighth and ninth embodiments of the present technology, when a joint is formed by fillet welding, the width dimensions W3 and W4 of the joint at the fragile portion are formed to be narrower than the width dimensions of the joint at other than the fragile portion, thereby allowing the fragile portion to be fractured preferentially.

[0134] Although the embodiments of the present technology have been described above, the embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present technology is defined by the claims, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0135] 1, 1B, 1C secondary battery, 11 plate-shaped member, 12 folded portion, 13 edge, 100, 100C case, 110, 110A, 110B, 110D, 110E, 110F, 110G, 110H case body, 111 pair of first side portions (first wall portions), 111A one of the pair of first side portions, 112 pair of second side portions (second wall portions), 113 first opening, 114 second opening, 115, 115A, 115B, 115C, 115D, 115E, 115F, 115G, 115H joint portion, 116, 116B, 116E, 116G, 116H first joint portion, 116C Central joint, 117,117B,117E,117G,117H Second joint, 118,118A,118B,118D,118E,118F,118G,118H First plate-shaped part, 119,119A,119B,119D,119E,119F,119G,119H 2nd plate-shaped part, 120 1st sealing plate, 125,135 Sealing plate joint, 130 2nd sealing plate, 134 Liquid injection hole, 150, 150A, 150B, 150C, 150D, 150E, 150F, 150G, 150H Weak part, 151C 1st weak part, 152C 2nd weak part, 155A Recess, 200 Electrode body, 210 Negative electrode plate, 210S negative electrode base plate, 211 negative electrode core, 212 negative electrode active material layer, 220 first electrode tab group, 230 negative electrode tab, 240 positive electrode plate, 240S positive electrode base plate, 241 positive electrode core, 242 positive electrode active material layer, 243 positive electrode protective layer, 250 second electrode tab group, 260 positive electrode tab, 300 electrode terminal, 301 negative electrode terminal, 302 positive electrode terminal, 400 current collector, 400A negative electrode current collector, 400B positive electrode current collector, C center, P1 outer surface portion, P2 other end, R abutting area, S space.

Claims

1. an electrode body including a first electrode and a second electrode having a polarity different from that of the first electrode; a case that houses the electrode assembly, The case is a case body having a first opening located at an end of a first side in a first direction and a second opening located at an end of a second side opposite to the first side in the first direction; a first sealing plate that seals the first opening; a second sealing plate that seals the second opening, The case body includes: a pair of first walls facing each other in a second direction perpendicular to the first direction; a joint portion extending from the first opening to the second opening is formed in one of the pair of first wall portions, a weakened portion is provided in a part of the joint, the weakened portion being ruptured when the internal pressure of the case reaches or exceeds a predetermined value, thereby discharging gas inside the case to the outside of the case; the electrode body has a first electrode tab group located at an end on the first sealing plate side and a second electrode tab group located at an end on the second sealing plate side, The fragile portion has a first fragile portion located near the end on the first sealing plate side, and a second fragile portion spaced apart from the first fragile portion and located near the end on the second sealing plate side.

2. the case body has a pair of second wall portions facing each other in a third direction perpendicular to the first direction and the second direction, The secondary battery according to claim 1 , wherein an area of ​​each of the pair of first walls is smaller than an area of ​​each of the pair of second walls.

3. one of the pair of first walls has a first plate-shaped portion and a second plate-shaped portion joined to each other at the joint portion, the first plate-shaped portion and the second plate-shaped portion face each other in a third direction perpendicular to the first direction and the second direction, and are butt-joined to each other at the joint portion; The secondary battery according to claim 1 , wherein the joint portion is formed so that the dimension in the second direction at the weak portion is smaller than the dimension at any portion other than the weak portion.

4. The secondary battery according to claim 3 , wherein the joint is formed shallower in the second direction in the weak portion than in the other portion.

5. The secondary battery according to claim 3 , wherein the case body has a recess facing inward at a portion where the fragile portion is formed.

6. The secondary battery according to claim 3 , wherein centers of the joints at the weak portion and at the portion other than the weak portion are arranged to be shifted from each other in the third direction when viewed from the first direction.

7. The secondary battery according to claim 1 , wherein the fragile portion is disposed in a central portion of one of the pair of first walls in the first direction.

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