Energy storage devices

Abstract

To provide a technology that appropriately ruptures a case when the internal pressure reaches a predetermined pressure. [Solution] The energy storage device 1 disclosed herein comprises a first metal case 10, a second metal piece 60 made of a different metal from the first metal welded to the case 10, and an intermetallic compound between the first metal and the second metal at the weld between the case 10 and the metal piece 60. With this configuration, the case 10 can be appropriately fractured when the internal pressure of the case 10 reaches a predetermined pressure.

Description

Technical Field

[0001] The present disclosure relates to a power storage device.

Background Art

[0002] As an example of a power storage device, a secondary battery such as a lithium-ion secondary battery can be mentioned. In recent years, this type of power storage device has been suitably used, for example, as a power source for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] The lithium-ion secondary battery disclosed in Japanese Patent Application Laid-Open No. 2012-9317 includes a positive electrode plate having an uncoated portion of an active material mixture on one side along the longitudinal direction, and a negative electrode plate having an uncoated portion of an active material mixture on one side along the longitudinal direction. The positive and negative electrode plates are wound through a separator to form a wound electrode group having an oval cross-section such that the uncoated portions of the positive and negative electrode plates are arranged on opposite sides of each other. The wound electrode group is housed in a rectangular battery container such that the winding axis of the wound electrode group is parallel to the longitudinal direction of the bottom surface. A gas discharge valve is provided on the side surface of the battery container. In the wound electrode group, the uncoated portions of the positive and negative electrode plates are joined between the curved portions where the positive and negative electrode plates are wound back, and the curved portions are open at both ends of the winding. At least one gas discharge valve is arranged in a region where the opening of the curved portion is projected onto the side surface of the battery container.

[0004] The same publication describes that with such a configuration, the gas discharge path generated from within the wound electrode group and the gas discharge valve are linearly arranged, and the distance between the gas discharge path and the gas discharge valve is close. Therefore, gas discharge during the operation of the gas discharge valve can be performed smoothly, and a lithium-ion secondary battery having both safety and reliability can be realized.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] The inventors of this invention wanted to ensure that the case would rupture appropriately when the internal pressure reached a predetermined pressure. [Means for solving the problem]

[0007] The energy storage device disclosed herein comprises a first metal case, a second metal piece different from the first metal welded to the case, and an intermetallic compound between the first metal and the second metal at the weld between the case and the metal piece. With this configuration, the case can be appropriately fractured when the internal pressure of the case reaches a predetermined pressure. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a perspective view of the energy storage device 1. [Figure 2] Figure 2 is a perspective view of the energy storage device 1. [Figure 3] Figure 3 is a cross-sectional view taken along line III-III in Figure 1. [Figure 4] Figure 4 is a plan view of the bottom surface 11 and the metal piece 60. [Figure 5] Figure 5 is a schematic diagram of the electrode body 30. [Figure 6] Figure 6 is a plan view of the welded joint 265. [Modes for carrying out the invention]

[0009] An embodiment of the energy storage device disclosed herein is described below. The embodiment described herein is not limited to the technology disclosed herein. Unless otherwise specified, the technology disclosed herein is not limited to the embodiment described herein. The drawings are schematic and do not necessarily reflect the actual objects. Components and parts that perform the same function are appropriately denoted by the same reference numerals, and redundant explanations may be omitted. The reference numerals "X", "Y", and "Z" in the drawings indicate the "first direction", "second direction", and "third direction" in this specification, respectively. The reference numerals "X1", "X2", "Y1", "Y2", "Z1", and "Z2" in the drawings indicate the orientation in the drawings. However, these directions are defined for the convenience of explanation and do not limit the installation method of the energy storage device in any way. The notation "A~B" indicating a numerical range means "A or more and B or less" unless otherwise specified, and also includes the meaning of "greater than A and less than B".

[0010] In this specification, "energy storage device" refers to a device in which charging and discharging occur through the movement of a charge carrier between a pair of electrodes (positive and negative electrodes) via an electrolyte. Energy storage devices include secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium-ion capacitors and electric double-layer capacitors. An energy storage device may be, for example, a lithium-ion secondary battery.

[0011] Figures 1 and 2 are perspective views of the energy storage device 1. Figure 1 shows the energy storage device 1 with the Z1 side as the upper side in the drawing. In Figure 1, the top surface 12 of the energy storage device 1 is positioned at the top of the drawing. Figure 2 shows the energy storage device 1 with the Z2 side as the upper side in the drawing. In Figure 2, the bottom surface 11 of the energy storage device 1 is positioned at the top of the drawing. Figure 3 is a cross-sectional view taken along line III-III in Figure 1. Figure 3 shows the cross-sectional structure of the energy storage device 1 with one of the first side surfaces 13 (here, the first side surface 13 on the Y1 side) positioned as the front.

[0012] As shown in Figures 1 to 3, the energy storage device 1 comprises a case 10, a positive electrode terminal 22, a negative electrode terminal 24, an electrode body 30, a spacer 40, a resin film 50, and an electrolyte (not shown). In this case, the energy storage device 1 is a lithium-ion secondary battery.

[0013] As shown in Figures 1 to 3, the case 10 has a bottom surface 11, a top surface 12, a pair of opposing first sides 13, and a pair of opposing second sides 14. In this embodiment, the case 10 is hexahedral. In this embodiment, the bottom surface 11 and the top surface 12 are rectangular and face each other. In the configurations shown in Figures 1 and 2, the pair of opposing first sides 13 extend from a pair of opposing long sides 11a on the bottom surface 11 and have a relatively large area. The pair of opposing second sides 14 extend from a pair of opposing short sides 11b on the bottom surface 11 and have a relatively small area.

[0014] As shown in Figures 1 to 3, the case 10 comprises a main body 10A, a first sealing plate 10B, and a second sealing plate 10C. The case 10 main body 10A is, for example, rectangular and has a bottom surface 11, a top surface 12, and a pair of opposing first sides 13. In this embodiment, the portion of the main body 10A enclosed by the bottom surface 11, the top surface 12, and the pair of opposing first sides 13 is an opening. As shown in Figure 3, the energy storage device 1 has two openings 15.

[0015] The main body 10A can be manufactured, for example, by bending a single metal plate to form a cylindrical shape and joining the joint (for example, by welding). Therefore, as shown in Figure 1, the main body 10A has a joint portion 16 on its upper surface 12 that extends along the first direction X.

[0016] The main body 10A is made of a first metal. The first metal may be, for example, aluminum, aluminum alloy, iron, iron alloy (e.g., stainless steel), or it may be work-hardened H material made of aluminum, aluminum alloy, iron, iron alloy, etc. In this specification, "alloy" means a metallic material containing metal A and other metals B and / or nonmetals different from metal A, and does not include intermetallic compounds as described later. In this specification, aluminum alloy is an alloy containing 50% by mass or more and 95% or less of aluminum in the whole. In this specification, iron alloy is an alloy containing 50% by mass or more and 95% or less of iron in the whole. In this specification, copper alloy is an alloy containing 50% by mass or more and 95% or less of copper in the whole.

[0017] As shown in Figure 2, the main body 10A has a metal piece 60. The main body 10A has a metal piece 60 on the outside of the case 10. In this embodiment, the main body 10A has a metal piece 60 on the bottom surface 11. The metal piece 60 is plate-shaped. The metal piece 60 is, in this case, a second metal. The second metal is a different metal from the first metal. The second metal may be, for example, copper, copper alloy, iron, iron alloy, aluminum, aluminum alloy, etc.

[0018] In this embodiment, the metal piece 60 is welded to the main body 10A at the bottom surface 11. As a welding method between the metal piece 60 and the main body 10A, laser welding or resistance welding can be preferably used, for example, from the viewpoint of appropriately forming an intermetallic compound at the welded joint between the two.

[0019] FIG. 4 is a plan view of the bottom surface 11 and the metal piece 60. As shown in FIG. 4, the welded portion 65 between the main body 10A and the metal piece 60 has two first welding lines 61a, 61b and a second welding line 62. The first welding lines 61a, 61b are V-shaped here. Therefore, the first welding lines 61a, 61b and the second welding line 62 extend in different directions from each other and intersect at the vertices 61c, 61d. In the metal piece 60, one first welding line 61a is arranged on the X1 side in the first direction X such that the vertex 61c is inside the metal piece 60. In the metal piece 60, the other first welding line 61b is arranged on the X2 side in the first direction X such that the vertex 61d is inside the metal piece 60. The second welding line 62 is linear and intersects one first welding line 61a at the vertex 61c and intersects the other first welding line 61b at the vertex 61d.

[0020] In this embodiment, an intermetallic compound of the first metal and the second metal is formed at the welded portion 65 between the case 10 (here, the main body 10A) and the metal piece 60. The type of the intermetallic compound depends on the types of the first metal and the second metal. In this specification, the "intermetallic compound" is a solid substance composed of at least two or more metal elements, and refers to a compound having a structure and properties clearly different from those of the constituent metals, and does not include the alloys described above. For example, when the first metal is aluminum or an aluminum alloy and the second metal is copper or a copper alloy, an intermetallic compound of aluminum and copper (for example, Al4Cu9, Al2Cu, etc.) may occur as the intermetallic compound. When the first metal is aluminum or an aluminum alloy and the second metal is iron or an iron alloy, an intermetallic compound of aluminum and iron (for example, Fe3Al, FeAl, FeAl2, Fe2Al5, FeAl3, etc.) may occur as the intermetallic compound. When the first metal is iron or an iron alloy and the second metal is aluminum or an aluminum alloy, the above-described intermetallic compound of aluminum and iron may occur as the intermetallic compound. When the first metal is iron or an iron alloy and the second metal is copper or a copper alloy, an intermetallic compound of iron and copper may occur as the intermetallic compound.

[0021] The timing for providing the welding portion 65 is not particularly limited. For example, before bending the metal plate constituting the main body 10A, the metal piece 60 may be placed on the metal plate and the welding portion 65 may be provided. In this case, the metal plate provided with the welding portion 65 may be bent to obtain the cylindrical main body 10A. Alternatively, after bending the metal plate to obtain the cylindrical main body 10A, the metal piece 60 may be placed on the main body 10A and the welding portion 65 may be provided.

[0022] In this embodiment, the welding portion 65 functions as the gas discharge portion of the case 10. The gas discharge portion is a portion designed to break when the internal pressure of the case 10 reaches a predetermined value and release the internal pressure. For this reason, the welding portion 65 breaks when the internal pressure of the case 10 reaches a predetermined value. The internal pressure of the case 10 when the welding portion 65 breaks may be, for example, 1.0 MPa, but may be lower or higher than this value as required. Although not particularly limited, for example, by appropriately adjusting the welding depth in the welding portion 65, the internal pressure of the case 10 at which the welding portion 65 can break can be set. Note that the gas discharge portion does not necessarily have to be provided on the bottom surface 11. In other embodiments, the gas discharge portion may be provided on the upper surface 12 or the first side surface 13.

[0023] The first sealing plate 10B is, for example, a member that seals one opening 15. The first sealing plate 10B is, for example, a substantially rectangular plate-like member. In this embodiment, the first sealing plate 10B is fitted into one opening 15 and joined by welding (for example, laser welding). As shown in FIGS. 1 and 3, the positive electrode terminal 22 is attached to the first sealing plate 10B.

[0024] In this embodiment, the first sealing plate 10B has a liquid injection portion 19. The liquid injection portion 19 has a liquid injection hole 19A and a sealing plug 19B. The liquid injection hole 19A is, here, a portion for injecting an electrolytic solution into the case 10 in the manufacturing process of the power storage device 1. In this embodiment, the liquid injection hole 19A is provided in the first sealing plate 10B close to the upper surface 12. The sealing plug 19B is, here, a member that closes the liquid injection hole 19A.

[0025] The second sealing plate 10C is, for example, a member that seals the other opening 15. The second sealing plate 10C is, for example, a substantially rectangular plate-shaped member. In this embodiment, the second sealing plate 10C is fitted into the other opening 15 and joined by welding (for example, laser welding). As shown in Figures 2 and 3, a negative electrode terminal 24 is attached to the second sealing plate 10C.

[0026] In the configurations shown in Figures 1 to 3, the first sealing plate 10B and the second sealing plate 10C constitute a pair of opposing second sides 14. Preferably, both the first sealing plate 10B and the second sealing plate 10C are made of the same metal material (in this case, the first metal) as the metal material that constitutes the main body 10A.

[0027] The positive terminal 22 is electrically connected to, for example, the positive electrode 32 of the electrode body 30 (see Figure 5). As shown in Figures 1 and 3, the positive terminal 22 is attached to the first sealing plate 10B. As shown in Figure 3, the positive terminal 22 is electrically connected to the positive electrode tab 33 of the electrode body 30 via the positive electrode current collector 23. The positive terminal 22 is made of, for example, metal, preferably aluminum or an aluminum alloy. The positive terminal 22 may also constitute the positive electrode current collector 23.

[0028] The negative electrode terminal 24 is electrically connected to, for example, the negative electrode 34 of the electrode body 30 (see Figure 5). As shown in Figures 2 and 3, the negative electrode terminal 24 is attached to the second sealing plate 10C. As shown in Figure 3, the negative electrode terminal 24 is electrically connected to the negative electrode tab 35 of the electrode body 30 via the negative electrode current collector 25. The negative electrode terminal 24 is made of, for example, metal, preferably copper or a copper alloy. The negative electrode terminal 24 may also constitute the negative electrode current collector 25.

[0029] The electrode body 30 is, for example, a power generation element in the energy storage device 1. As shown in Figure 3, the electrode body 30 is housed in the case 10. Figure 5 is a schematic diagram of the electrode body 30. As shown in Figure 5, the electrode body 30 comprises a positive electrode 32, a negative electrode 34, and a separator 36 interposed between the positive electrode 32 and the negative electrode 34. In this embodiment, the electrode body 30 is a flat-shaped wound electrode body in which a long sheet-like positive electrode 32 and a long sheet-like negative electrode 34 are stacked with a long sheet-like separator 36 interposed between them, and wound in the longitudinal direction of the sheet. The symbol "WL" in Figure 5 is the winding axis in the electrode body 30.

[0030] As shown in Figures 3 and 5, the electrode body 30 has a first end face 30A at one end in the direction along the winding axis WL (first direction X in Figures 3 and 5) and a second end face 30B at the other end in the same direction. In this embodiment, the first end face 30A and the second end face 30B are the laminated surfaces of the electrode and the separator 36, and are open surfaces that open outwards toward the outside of the electrode body 30. As shown in Figure 3, the first end face 30A faces the first sealing plate 10B. The second end face 30B faces the second sealing plate 10C.

[0031] In the configurations shown in Figures 3 and 5, the electrode body 30 has a positive electrode tab 33 connected to a positive electrode 32 on its first end face 30A. The electrode body 30 has a negative electrode tab 35 connected to a negative electrode 34 on its second end face 30B. The positive electrode tabs 33 are provided on each positive electrode 32 included in the electrode body 30. The positive electrode tabs 33 provided on each positive electrode 32 (multiple positive electrode tabs 33) can be stacked, for example, to form a group of positive electrode tabs. The negative electrode tabs 35 are provided on each negative electrode 34 included in the electrode body 30. The negative electrode tabs 35 provided on each negative electrode 34 (multiple negative electrode tabs 35) can be stacked, for example, to form a group of negative electrode tabs.

[0032] As shown in Figure 5, the positive electrode 32 has a long, strip-shaped positive electrode current collector foil 32a and a positive electrode active material layer 32b provided on the surface of the positive electrode current collector foil 32a. The positive electrode current collector foil 32a has a plurality of positive electrode tabs 33 intermittently arranged along its longitudinal direction at one end in the short direction. The positive electrode tabs 33 are, in this case, the exposed portion of the positive electrode current collector foil 32a. The positive electrode current collector foil 32a may be made of, for example, aluminum or an aluminum alloy. The positive electrode active material layer 32b is a layer containing positive electrode active material and other optional components (e.g., binder, conductive material, etc.). In this embodiment, the positive electrode current collector foil 32a has a protective layer 32p extending along its longitudinal direction at the other end in the short direction. The protective layer 32p may be, for example, a layer containing an inorganic filler and a resin binder. Furthermore, the constituent material of the positive electrode 32 can be any material used for the positive electrode of this type of energy storage device without any particular limitations.

[0033] As shown in Figure 5, the negative electrode 34 comprises a long, strip-shaped negative electrode current collector foil 34a and a negative electrode active material layer 34b provided on the surface of the negative electrode current collector foil 34a. The negative electrode current collector foil 34a has a plurality of negative electrode tabs 35 intermittently arranged along its longitudinal direction at one end in the short direction. The negative electrode tabs 35 are the exposed portions of the negative electrode current collector foil 34a. The negative electrode current collector foil 34a may be made of copper or a copper alloy, for example. The negative electrode active material layer 34b is a layer containing a negative electrode active material and other optional components (e.g., binder, conductive additive, thickener, etc.). The constituent material of the negative electrode 34 can be any material used for the negative electrode of this type of energy storage device without particular limitations.

[0034] As the separator 36, for example, a separator from this type of energy storage device can be used without particular limitation. The separator 36 may be a single-layer structure, or it may be a structure of two or more layers with different properties and characteristics (thickness, porosity, etc.), for example, a three-layer structure. The separator 36 is made of resin, for example, and is preferably made of polyolefin resin. The polyolefin resin may be polyethylene, polypropylene, or a mixture thereof.

[0035] As the electrolyte, for example, the electrolyte used in this type of energy storage device can be used without particular limitation. The electrolyte is, for example, a non-aqueous electrolyte containing a non-aqueous solvent (organic solvent) and a supporting salt. Examples of non-aqueous solvents include carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorine-containing lithium salts such as lithium hexafluoride phosphate (LiPF6).

[0036] The spacer 40 is a component that is placed, for example, between the case 10 and the electrode body 30. In the configuration shown in Figure 3, the spacer 40 is placed between the case 10 and the first end face 30A of the electrode body 30. As shown in Figure 3, the spacer 40 is placed between the first sealing plate 10B and the electrode body 30 (first end face 30A on the X1 side), and between the second sealing plate 10C and the electrode body 30 (first end face 30A on the X2 side). The spacer 40 may be made of an insulating resin (for example, polyamide resin, etc.) that has been conventionally used in this type of energy storage device.

[0037] The resin film 50 is, for example, a component that insulates the case 10 from the electrode body 30. As shown in Figure 3, the resin film 50 is arranged to surround the outer circumference of the electrode body 30. In this embodiment, the resin film 50 is cylindrical and houses the electrode body 30 inside. As the resin material constituting the resin film 50, for example, the resin material constituting the resin film included in this type of energy storage device may be used. Such resin materials may be, for example, polyamide resin, polyolefin resin (polyethylene, polypropylene, etc.).

[0038] The energy storage device 1 can be used for various purposes, but it is particularly suitable for use as a power source (driving power supply) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, but preferred examples include plug-in hybrid vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0039] As described above, the energy storage device 1 comprises a case 10 and a metal piece 60. The case 10 is made of a first metal. The metal piece 60 is welded to the case 10 and is made of a second metal different from the first metal. The energy storage device 1 includes an intermetallic compound between the first metal and the second metal at the welded joint 65 between the case 10 and the metal piece 60.

[0040] In other words, in the energy storage device 1, the case 10 has an intermetallic compound formed at the weld joint 65 with the metal piece 60, resulting from the welding of two different metals, a first metal and a second metal. The area containing the intermetallic compound is a weak point in the case 10. Therefore, when the internal pressure of the case 10 rises and reaches a predetermined value, this weak point (i.e., the area containing the intermetallic compound) fractures. This releases the internal pressure of the case 10, allowing the energy storage device 1 to be used more safely.

[0041] The case 10 may be equipped with a welded section 65 as a gas outlet. This eliminates the need to form the gas outlet using, for example, press working. Therefore, a gas outlet can be provided in the case 10 more easily. This effect can be more preferably achieved, for example, when forming a gas outlet in a case 10 made of a material, shape, or structure that is difficult to press work.

[0042] The welded joint 65 may be configured to rupture when the internal pressure of the case 10 reaches 1.0 MPa. This can further enhance safety in the use of the energy storage device 1.

[0043] In a plan view, the welded portion 65 may include linear portions (here, first weld lines 61a, 61b and second weld line 62). As a result, the intermetallic compound is provided linearly in the case 10, and therefore the weak portion is provided linearly. When the internal pressure of the case 10 rises and the case 10 expands, and the internal pressure reaches a predetermined value, the stress due to the expansion on the case 10 causes the weak portion to fracture. Here, if the weak portion is linear, it fractures more easily and the fractured portion tends to spread. Therefore, the effects of the technology disclosed herein can be better realized and the safety of using the energy storage device 1 can be further improved.

[0044] In a plan view, the welded joint 65 may include a first weld line 61a, 61b and a second weld line 62. The first weld lines 61a, 61b and the second weld line 62 extend in different directions and may intersect at least one point (here, vertices 61c and 61d). In this case, the welded joint 65 has an intermetallic compound along the first weld lines 61a, 61b and the second weld line 62. In other words, the case 10 has a weak area along the first weld lines 61a, 61b and the second weld line 62. The shape of the welded joint 65 described above is set to make the case 10 more prone to fracture when stress is applied due to expansion. Therefore, the effects of the technology disclosed herein can be better realized, and the safety of using the energy storage device 1 can be further improved.

[0045] The energy storage device 1 may have a metal piece 60 on the outside of the case 10. This makes it easier to create a welded joint 65. Although not particularly limited, in this case, the metal piece 60 is preferably in the form of a plate, for example. This is preferable because it allows for space saving, for example when constructing an energy storage module.

[0046] The case 10 may include a cylindrical body 10A having openings 15 at both ends, and a pair of sealing plates (here, a first sealing plate 10B and a second sealing plate 10C) that seal the openings 15. The welded portion 65 may be provided on the body 10A. It is difficult to provide a gas discharge portion on a cylindrical body 10A by press working or the like. However, since the welded portion 65 is provided, for example, by overlapping a metal piece 60 on the body 10A and welding the two together, a gas discharge portion can be provided more easily even on a cylindrical body 10A.

[0047] The first metal may be aluminum or an aluminum alloy. The second metal may be copper or a copper alloy. Welding aluminum and copper tends to produce brittle intermetallic compounds. Therefore, the effects of the techniques disclosed herein can be better realized in such combinations of first and second metals.

[0048] The first metal may be aluminum or an aluminum alloy of grade H. For example, grade H is difficult to press-form due to its high hardness. Therefore, the effects of the technology disclosed herein can be better realized for a case 10 made of the first metal being aluminum or an aluminum alloy of grade H.

[0049] While embodiments of the technology disclosed herein have been described above, these embodiments are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes, for example, various modifications and changes to the above embodiments.

[0050] For example, in the above embodiment, the weld 65 has the shape shown in Figure 4. However, the shape of the weld between the case 10 and the metal piece 60 is not limited to this shape. The shapes exemplified below as weld shapes and other shapes are preferred for realizing the effects of the technology disclosed herein. Figure 6 is a plan view of the weld 265. As shown in Figure 6, the weld 265 has a first weld line 261 and a second weld line 262. The first weld line 261 and the second weld line 262 extend in different directions from each other and intersect at an intersection point 265c. In the embodiment shown in Figure 6, the angle between the first weld line 261 and the second weld line 262 is obtuse or acute. The first weld line 261 and the second weld line 262 form an X shape. The "X shape" here includes a cross shape where the two weld lines are perpendicular to each other.

[0051] The technologies disclosed herein may include the technologies described in the following sections. Section 1: First, a metal case, A metal piece made of a second metal different from the first metal is welded to the case, In the welded joint between the case and the metal piece, the intermetallic compound between the first metal and the second metal, A power storage device equipped with the following features. Section 2: The case is provided with the welded section as a gas discharge section. The energy storage device described in item 1. Section 3: The welded joint is configured to rupture when the internal pressure of the case reaches 1.0 MPa. A power storage device as described in item 1 or 2. Section 4: In a plan view, the welded portion includes a linear portion. A power storage device described in any one of items 1 to 3. Section 5: In a plan view, the welded portion includes a first weld line and a second weld line. The first weld line and the second weld line extend in different directions from each other and intersect at least one point. A power storage device described in any one of items 1 to 4. Item 6: The metal piece is provided on the outside of the case. A power storage device described in any one of items 1 to 5. Section 7: The case comprises a cylindrical body having openings at both ends, and a pair of sealing plates that seal the openings. The aforementioned welded portion is provided on the main body, A power storage device as described in any one of items 1 to 6. Section 8: The first metal is aluminum or an aluminum alloy, and the second metal is copper or a copper alloy. A power storage device described in any one of items 1 through 7. Section 9: The first metal is aluminum or an aluminum alloy of material H. A power storage device described in any one of items 1 to 8. [Explanation of symbols]

[0052] 1. Energy storage device 10 cases 30 Electrode body 40 Spacers 50 resin film 60 metal pieces 61a, 61b First weld line 62. Second weld line 65 Welded section WL winding shaft

Claims

1. First, a metal case, A metal piece made of a second metal different from the first metal is welded to the case, In the welded joint between the case and the metal piece, the intermetallic compound between the first metal and the second metal, A power storage device equipped with [a specific feature].

2. The case is provided with the welded section as a gas discharge section. The energy storage device according to claim 1.

3. The welded joint is configured to rupture when the internal pressure of the case reaches 1.0 MPa. The energy storage device according to claim 2.

4. In a plan view, the welded portion includes a linear portion. The energy storage device according to claim 1.

5. In a plan view, the welded portion includes a first weld line and a second weld line. The first weld line and the second weld line extend in different directions from each other and intersect at least one point. The energy storage device according to claim 4.

6. The metal piece is provided on the outside of the case. The energy storage device according to any one of claims 1 to 5.

7. The case comprises a cylindrical body having openings at both ends, and a pair of sealing plates that seal the openings. The aforementioned welded portion is provided on the main body, The energy storage device according to any one of claims 1 to 5.

8. The first metal is aluminum or an aluminum alloy, and the second metal is copper or a copper alloy. The energy storage device according to any one of claims 1 to 5.

9. The first metal is aluminum or an aluminum alloy of material H. The energy storage device according to claim 8.

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