Secondary battery

Abstract

The present application relates to a secondary battery for shortening the length of an electrode terminal engaged with a wound electrode body. A secondary battery (100) includes a flat wound electrode body in which an electrode sheet (80) is wound about a winding axis W in a winding direction (D11), and an electrode terminal (40). The electrode sheet includes a current collector (82), an electrode active material layer (84) formed on a surface of the current collector and including an electrode active material, and an unformed portion (82a) configured to be arranged with the electrode active material layer in a direction (D12) of the winding axis and in which the electrode active material layer is not formed on the surface of the current collector. The wound electrode body includes a first end portion (21) in which a circular arc is formed. A first slit (91) is formed in the unformed portion of the first end portion in the winding direction. A flat portion for engagement with the electrode terminal is provided in a portion of the unformed portion of the first end portion that is located at a position opposite the electrode active material layer from the first slit.

Description

TECHNICAL FIELD

[0001] The present application relates to a secondary battery. BACKGROUND

[0002] For example, in Patent Literature 1, a secondary battery provided with a battery container and a flat-shaped wound electrode body housed in the battery container is disclosed. The wound electrode body has, for example, a positive electrode plate, and an unformed portion in which an active material is not formed is formed at one end portion of the positive electrode plate in a winding axis direction. An electrode terminal is connected to the unformed portion of the positive electrode plate. The electrode terminal has an internal terminal portion (referred to as a current collector in Patent Literature 1) disposed inside the battery container, and the internal terminal portion of the electrode terminal is engaged with the unformed portion inside the battery container. In addition, in the secondary battery disclosed in Patent Literature 1, a plurality of slits extending in the winding axis direction are formed at both end portions of the positive electrode plate at equal intervals, and electrolyte solution easily permeates from the slits to the inside of the wound electrode body.

[0003] In addition, in Patent Literature 2, a wound electrode body having a positive electrode plate, a negative electrode plate, and a separator is disclosed. The positive electrode plate has a coated portion in which a positive electrode active material layer is formed and an uncoated portion in which the positive electrode active material layer is not formed. Near the boundary between the coated portion and the uncoated portion, a plurality of slits are formed at equal intervals along the winding direction of the wound electrode body. Thus, occurrence of wrinkles that can be generated near the boundary and breakage of the positive electrode plate can be prevented.

[0004] Patent Literature 1: Japanese Patent Application Publication No. 2013-218804

[0005] Patent Literature 2: Japanese Patent Application Publication No. 2013-98026

[0006] In the secondary battery disclosed in Patent Literature 1, the electrode terminal is connected to the unformed portion located at the central portion in the length direction of the wound electrode body. As a result, the internal terminal portion of the electrode terminal is relatively long inside the battery container. From the viewpoint of material cost, it is preferable that the electrode terminal be short. SUMMARY

[0007] The secondary battery according to the present application includes a flat wound electrode body in which an electrode sheet of a positive electrode or a negative electrode is wound around a winding axis in a prescribed winding direction; a battery case that houses the wound electrode body; and an electrode terminal. The electrode terminal has an external terminal portion disposed outside the battery case and an internal terminal portion disposed inside the battery case. The electrode sheet has a current collector; an electrode active material layer extending in the winding direction and formed on a surface of the current collector and including an electrode active material; and an unformed portion extending in the winding direction and disposed at a position at which the electrode active material layer is not formed on the surface of the current collector. The wound electrode body has a flat portion having two flat surfaces extending in a length direction orthogonal to the winding axis direction; a first end portion provided at one side in the length direction of the flat portion and formed with a circular arc; and a second end portion provided at the other side in the length direction of the flat portion and formed with a circular arc. A first slit is formed in the unformed portion at the first end portion along the winding direction. A flat portion to which the internal terminal portion of the electrode terminal is joined is provided in the unformed portion at the first end portion at a position opposite the electrode active material layer from the first slit.

[0008] For example, if the first slit is not formed in the unformed portion at the first end portion, the unformed portion at the first end portion is formed with a circular arc, and it is difficult to join the electrode terminal to the unformed portion at the first end portion. However, according to the secondary battery according to the present application, the first slit is formed in the unformed portion, and thus the unformed portion at the first end portion is easily crushed, and the flat portion is easily provided in the unformed portion. Therefore, the electrode terminal can be reliably joined to the unformed portion at the first end portion, and as a result, the length of the electrode terminal can be shortened compared to conventional secondary batteries.

[0009] In the secondary battery according to the present application, a second slit can be formed in the unformed portion at the first end portion, the second slit being disposed at a position opposite the electrode active material layer from the first slit and extending in the winding axis direction. In addition, the second slit can be formed at a position farthest from the winding axis in the unformed portion at the first end portion.

[0010] In the secondary battery according to the present application, the interval between the second slits when the electrode sheet is unwound can decrease toward the winding start side in the winding direction. In addition, the interval between the first slits when the electrode sheet is unwound can decrease toward the winding start side in the winding direction.

[0011] In the secondary battery according to the present application, the length of the first slit can decrease as the first slit approaches the winding axis. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1is a cross-sectional view schematically showing an internal configuration of a secondary battery to which the embodiment is applied.

[0013] Figure 2 is a schematic view showing a structure of a jelly-roll electrode body of a secondary battery to which the embodiment is applied, and is a partially expanded view.

[0014] Figure 3 is a view schematically showing a jelly-roll electrode body in a rolled state.

[0015] Figure 4 is a view schematically showing a battery case and a jelly-roll electrode body, and is a view observed from a jelly-roll axis direction.

[0016] Figure 5 is a view schematically showing a state in which an electrode sheet to which the embodiment is applied is expanded.

[0017] Figure 6 is a view schematically showing a state in which an electrode sheet to which a modification example is applied is expanded. Description of Reference Numerals:

[0018] 20... jelly-roll electrode body; 21... first end portion; 22... second end portion; 23... flat portion; 24... flat surface; 40... electrode terminal; 50... positive electrode sheet; 60... negative electrode sheet; 80... electrode sheet; 82... current collector; 82a... unformed portion; 84... electrode active material layer; 90... planar portion; 91... first slit; 92... second slit; 100... secondary battery; D11... rolling direction; D12... jelly-roll axis direction. DETAILED DESCRIPTION

[0019] Hereinafter, one embodiment of a secondary battery disclosed herein will be described with reference to the drawings. For the cases required for implementation in the cases other than the matters specifically mentioned in the present specification, it can be understood as matters of design by those skilled in the art based on the existing technology in the field. The present application can be implemented based on the content disclosed in the present specification and the technical common sense in the field. Among them, in the following drawings, the components that play the same role are denoted by the same reference numerals to be described. In addition, the dimensional relationship (length, width, thickness, etc.) in each drawing does not reflect the actual dimensional relationship.

[0020] In the present specification, "battery" is a general term for power storage devices from which electric power can be taken out, and is a concept including primary batteries and secondary batteries. "Secondary battery" is a general term for power storage devices that can be repeatedly charged and discharged, and includes so-called accumulators such as lithium secondary batteries, nickel-hydrogen batteries, and nickel-cadmium batteries. Hereinafter, a lithium-ion secondary battery, which is one kind of secondary batteries, will be exemplified to describe the secondary battery disclosed herein in detail. However, the secondary battery disclosed herein is not limited to the embodiment described here.

[0021] Figure 1 is a cross-sectional view schematically showing an internal configuration of the secondary battery 100 according to the present embodiment. As shown in Figure 1 , the secondary battery 100 according to the present embodiment is a lithium ion secondary battery of a sealed type provided with a battery case 30, an electrode terminal 40, a wound electrode body 20, and a nonaqueous electrolyte solution 10.

[0022] The battery case 30 houses the wound electrode body 20 and the nonaqueous electrolyte solution 10 in a state of being sealed inside. In the present embodiment, the battery case 30 is in a cuboid shape, and is flat and square. The battery case 30 is provided with a main body 31 and a lid 32. The main body 31 is a square hollow member having an opening portion (not shown) at one end (for example, the upper end). The lid 32 is a plate-like member that seals the opening portion of the main body 31. The lid 32 is attached to the main body 31.

[0023] A safety valve 36 is provided in the lid 32. The safety valve 36 is used to release the internal pressure of the battery case 30 in the case where the internal pressure rises to a prescribed pressure or more. In addition, an injection port (not shown) for injecting the nonaqueous electrolyte solution 10 into the main body 31 is provided in the battery case 30. The material of the battery case 30 is not particularly limited, but for example, a light and highly thermally conductive metal material such as aluminum can be used as the material of the battery case 30.

[0024] The electrode terminal 40 is a long and flat member composed of an electrically conductive material such as aluminum. The electrode terminal 40 is provided in the lid 32 of the battery case 30. The electrode terminal 40 has an external terminal portion 40a disposed outside the battery case 30 and an internal terminal portion 40b disposed inside the battery case 30. The external terminal portion 40a is exposed to the outside of the battery case 30 from the lid 32. The external terminal portion 40a is configured to be connected to other batteries, external devices, and the like. In the present embodiment, the electrode terminal 40 of the positive electrode is referred to as a positive electrode terminal 42, and the electrode terminal 40 of the negative electrode is referred to as a negative electrode terminal 44.

[0025] Figure 2 is a schematic view showing the structure of the wound electrode body 20 of the secondary battery 100 according to the present embodiment, and is a partially expanded view. As shown in Figure 2 , the wound electrode body 20 has an electrode sheet 80 of a long strip shape of the positive electrode or the negative electrode and a separator 70 of a long strip shape. In the present embodiment, the electrode sheet 80 is composed of a positive electrode sheet 50 of the positive electrode and a negative electrode sheet 60 of the negative electrode. The separator 70 has a first separator 71 and a second separator 72, and is composed of two separators. Here, the wound electrode body 20 is such that the positive electrode sheet 50, the negative electrode sheet 60, and the separator 70 are overlapped and wound around a winding axis W in a winding direction D11 (refer to Figure 4) flat structure wound. In the present embodiment, the positive electrode sheet 50, the first separator 71, the negative electrode sheet 60, and the second separator 72 are overlaid in this order.

[0026] In the present embodiment, the electrode sheet 80 has a current collector 82, an electrode active material layer 84 including an electrode active material, and an unformed portion 82a. The current collector 82 is in a long strip shape. The electrode active material layer 84 is formed on one face or both faces (both faces in the present embodiment) of the current collector 82 in a manner extending in a winding direction D11 (refer to FIG. 1). The unformed portion 82a refers to a portion of the current collector 82 in which the electrode active material layer 84 is not formed. The unformed portion 82a extends in the winding direction D11 (refer to FIG. 1) and is disposed at a position aligned with the electrode active material layer 84 in a direction in which the winding axis W extends (hereinafter referred to as winding axis direction) D12. Figure 4 Figure 4 In the present embodiment, the current collector 82, the electrode active material layer 84, and the unformed portion 82a in the positive electrode sheet 50 are respectively referred to as a positive electrode current collector 52, a positive electrode active material layer 54, and a positive electrode unformed portion 52a. The positive electrode active material layer 54 includes a positive electrode active material as one example of an electrode active material. The positive electrode unformed portion 52a is formed at an end portion of the positive electrode current collector 52 on the one end side (left end side in the present embodiment) in the winding axis direction D12.

[0027] In the present embodiment, the current collector 82, the electrode active material layer 84, and the unformed portion 82a in the positive electrode sheet 50 are respectively referred to as a positive electrode current collector 52, a positive electrode active material layer 54, and a positive electrode unformed portion 52a. The positive electrode active material layer 54 includes a positive electrode active material as one example of an electrode active material. The positive electrode unformed portion 52a is formed at an end portion of the positive electrode current collector 52 on the one end side (left end side in the present embodiment) in the winding axis direction D12. Figure 2 As shown in FIG. 2, the internal terminal portion 40b of the positive electrode terminal 42 is joined to the positive electrode unformed portion 52a. Figure 1

[0028] In the present embodiment, the positive electrode current collector 52 can use a configuration that can be used as a positive electrode current collector of such a secondary battery and is not particularly limited. As the positive electrode current collector 52, a metal-made positive electrode current collector having good electrical conductivity is preferably used. As the positive electrode current collector 52, for example, a metal material such as aluminum, nickel, titanium, or stainless steel can be adopted. In particular, aluminum (for example, aluminum foil) is preferably used as the positive electrode current collector 52.

[0029] As the positive electrode active material included in the positive electrode active material layer 54, for example, a lithium complex metal oxide (for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 ​​O4, LiCrMnO4, LiFePO4, etc.). By dispersing the positive electrode active material and materials used as needed (e.g., conductive materials, adhesives, etc.) in a suitable solvent (e.g., N-methyl-2-pyrrolidone: NMP), adjusting the composition to a paste (or slurry) state, applying an appropriate amount of the composition to the surface of the positive electrode current collector 52, and drying, a positive electrode active material layer 54 can be formed.

[0030] like Figure 2 As shown, in the negative electrode sheet 60, the current collector 82, the electrode active material layer 84, and the unformed portion 82a are respectively referred to as the negative electrode current collector 62, the negative electrode active material layer 64, and the negative electrode unformed portion 62a. The negative electrode active material layer 64 includes a negative electrode active material as an example of an electrode active material. The negative electrode unformed portion 62a is formed on the other end side of the negative electrode current collector 62 in the winding axis direction D12 (in Figure 2 The middle part (right end). For example... Figure 1 As shown, the internal terminal portion 40b of the negative electrode 44 is joined in the negative electrode unformed portion 62a.

[0031] In this embodiment, the negative current collector 62 can be constructed using a structure suitable for use as a negative current collector in such a secondary battery, and is not particularly limited. As the negative current collector 62, a metal negative current collector with good conductivity is preferably used. For example, a copper (e.g., copper foil) or a copper-based alloy can be used as the negative current collector 62.

[0032] The negative electrode active material included in the negative electrode active material layer 64 can be exemplified by, at least in part, particulate (or spherical, flake-like) carbon materials with a graphite structure (e.g., layered structure), and lithium transition metal composite oxides (e.g., Li4Ti5O). 12 Examples of lithium-titanium composite oxides and lithium transition metal composite nitrides include lithium-titanium composite oxides and lithium-transition metal composite nitrides. By dispersing the negative electrode active material and materials used as needed (such as binders) in a suitable solvent (such as deionized water), adjusting the composition to a paste (or slurry) state, applying an appropriate amount of the composition to the surface of the negative electrode current collector 62, and drying it, a negative electrode active material layer 64 can be formed.

[0033] like Figure 2As shown, the separators 70 (specifically, the first separator 71 and the second separator 72) can be made of porous sheets as is commonly known, without particular limitation. Examples of separators 70 include porous sheets (e.g., membranes, nonwoven fabrics) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. These porous sheets can be single-layered or have multiple layers (e.g., a three-layered structure with PP layers laminated on both sides of a PE layer). Alternatively, the porous sheet may have a porous heat-resistant layer on one or both sides. This heat-resistant layer can be, for example, a layer including inorganic fillers and adhesives (e.g., a filler layer). For example, alumina, boehmite, and silica are preferred as inorganic fillers.

[0034] like Figure 1 As shown, the non-aqueous electrolyte 10, housed together with the wound electrode body 20 in the battery casing 30, contains a salt in a suitable non-aqueous solvent. Conventionally known non-aqueous electrolytes can be used without particular limitation. Examples of non-aqueous solvents include ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). Additionally, lithium salts (e.g., LiBOB, LiPF6, etc.) can be suitably used as the salt. In this embodiment, LiBOB is used as the salt. In this case, it is preferable that the LiBOB content in the non-aqueous electrolyte 10 is 0.3 wt% to 0.6 wt%.

[0035] Next, the structure of the wound electrode body 20 according to this embodiment will be described in more detail. Figure 4 As shown, the wound electrode body 20 has a first end portion 21, a second end portion 22, and a flat portion 23. Among them, in Figure 4 The diagram shows the outer periphery of the wound electrode body 20, but the wound state is omitted. The first end portion 21 is the part of the wound electrode body 20 that forms an arc when viewed from the winding axis direction D12. The first end portion 21 constitutes one end of the wound electrode body 20 in the longitudinal direction D13, which is orthogonal to the winding axis W. The second end portion 22 is opposite the first end portion 21 across the winding axis W, and is the part of the wound electrode body 20 that forms an arc when viewed from the winding axis direction D12. The second end portion 22 constitutes the other end of the wound electrode body 20 in the longitudinal direction D13, which is orthogonal to the winding axis W. In this embodiment, when the wound electrode body 20 is housed in the battery casing 30, the first end portion 21 is positioned closer to the cover 32 of the battery casing 30 than the second end portion 22; in other words, it is positioned closer to the outer terminal portion 40a of the electrode terminal 40. Here, the first end 21 and the second end 22 include the outer peripheral surface of the wound electrode body 20 with an arc and the interior of the outer peripheral surface with an arc.

[0036] A flat portion 23 is disposed between the first end portion 21 and the second end portion, and has two flat surfaces 24. That is, the first end portion 21 is provided on one side of the flat portion 23 in the longitudinal direction D13, and the second end portion 22 is provided on the other side of the flat portion 23 in the longitudinal direction D13. The flat surfaces 24 are flat surfaces extending along the longitudinal direction D13. The two flat surfaces 24 are opposite each other. In this embodiment, when the wound electrode body 20 is housed in the battery housing 30, the wound electrode body 20 is configured such that the first end portion 21, the flat portion 23, and the second end portion 22 are arranged sequentially from the side closest to the cover 32.

[0037] In this embodiment, such as Figure 1 As shown, an internal terminal portion 40b of electrode terminals 40 (e.g., positive terminal 42 and negative terminal 44) is connected to an unformed portion 82a (e.g., positive electrode unformed portion 52a and negative electrode unformed portion 62a) located at the first end 21 of the wound electrode body 20. Preferably, the portion of the wound electrode body 20 connecting the electrode terminals 40 is a flat surface. By engaging the electrode terminals 40 on this flat surface, the electrode terminals 40 can be more reliably connected to the wound electrode body 20. Therefore, in this embodiment, as... Figure 4 As shown, in order to more reliably connect the electrode terminal 40 to the unformed portion 82a located at the first end 21, a flat portion 90 with a flat surface is provided in the unformed portion 82a located at the first end 21.

[0038] In order to provide a planar portion 90 in the unformed portion 82a (e.g., the positive electrode unformed portion 52a and the negative electrode unformed portion 62a) located at the first end 21, such as Figure 3 As shown, a first slit 91 and a second slit 92 are formed in the unformed portion 82a. The first slit 91 is formed in the portion of the unformed portion 82a located at the first end 21, along the winding direction D11 (see reference). Figure 4 A first slit 91 is formed in the unformed portion 82a at a position corresponding to the first end 21 around the winding axis W. In this embodiment, the end furthest from the winding axis W in the unformed portion 82a of the first end 21 is referred to as the tip 21a. The tip 21a refers to the end on the cover 32 side of the unformed portion 82a. The first slit 91 is formed in the unformed portion 82a through the tip 21a. The first slit 91 is formed such that a portion of the unformed portion 82a located at the first end 21 on the side of one of the two flat surfaces 24 of the winding electrode body 20 extends through the tip 21a to the portion of the unformed portion 82a located at the first end 21 on the side of the other flat surface 24. In this embodiment, as Figure 2As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70.

[0039] As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 5 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 2 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 4 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 5 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70.

[0040] As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70.

[0041] As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 5 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 6 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 5 As shown, the unformed portion 82a partially overlaps the partition 70. Thus, the first slit 91 is formed at a position of the unformed portion 82a that does not overlap the partition 70. Figure 2When the electrode sheet 80 is unwound, the spacing between adjacent first slits 91 in the winding direction D11 decreases as it moves toward the winding start side in the winding direction D11. Similarly, when the electrode sheet 80 is unwound, the spacing between adjacent second slits 92 in the winding direction D11 decreases as it moves toward the winding start side in the winding direction D11. In other words, when the electrode sheet 80 is unwound, the spacing between adjacent first slits 91 in the winding direction D11 and the spacing between adjacent second slits 92 in the winding direction D11 decrease as they move from the winding end of the electrode sheet 80 toward the winding start end.

[0042] Furthermore, the length of the first slit 91 (specifically, the length in the winding direction D11) decreases as it approaches the winding axis W. In other words, when the electrode sheet 80 is unrolled, the length of the first slit 91 decreases towards the winding start side in the winding direction D11 (e.g., towards the end of the electrode sheet 80 where winding begins). In this embodiment, the lengths of the plurality of second slits 92 are each the same, but they may also be different.

[0043] Furthermore, in this embodiment, the plurality of first slits 91 are slit-like structures, and the width of each of the plurality of first slits 91 (in other words, the length of the groove of the first slit 91 in the winding axis direction D12) is the same. Similarly, in this embodiment, as Figure 5 As shown, the multiple second slits 92 are also slit-like structures, and the width of each of the multiple second slits 92 (in other words, the length of the groove of the second slit 92 in the winding direction D11) is the same. However, the width of the second slit 92 can also be as follows: Figure 6 As shown in the modified example, the width of the second slit 92 increases as it moves away from the starting end of the winding of the electrode sheet 80 toward the ending end. In other words, the width of the second slit 92 can increase as it moves away from the winding axis W.

[0044] Furthermore, the timing and method of forming the first slit 91 and the second slit 92 in the unformed portion 82a of the electrode sheet 80 are not particularly limited. In this embodiment, as... Figure 2 As shown, the wound electrode body 20 is manufactured by winding the electrode sheet 80 (e.g., positive electrode sheet 50 and negative electrode sheet 60) with the separator 70 using a so-called winding machine (not shown). For example, a cutter linked to the winding machine is used to automatically form the first slit 91 and the second slit 92 in the unformed portion 82a. For example, when the winding machine is used to wind the electrode sheet 80 with the separator 70 overlapping, the cutter can be used to form the first slit 91 and the second slit 92 in the unformed portion 82a at a predetermined time (e.g., when the portion of the unformed portion 82a located at the first end 21 is the working area where the cutter forms the slits 91 and 92).

[0045] In the present embodiment, by forming the first slit 91 and the second slit 92 in the unformed portion 82a located at the first end portion 21, a cut can be introduced at the positions of the first slit 91 and the second slit 92. Thus, it is possible to crush the portion of the wound electrode body 20 in the unformed portion 82a located at the first end portion 21, which is on the end portion side of the unformed portion 82a in the winding axis direction D12 than the first slit 91. As a result, as shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 3 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 4 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking.

[0046] As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 3 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 1 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking.

[0047] As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 4 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 2 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking. Figure 5 As shown in FIG. 1, a flat portion 90 can be provided in the portion of the unformed portion 82a located at the first end portion 21, which is on the end portion side in the winding axis direction D12 than the first slit 91. Moreover, as shown in FIG. 1, the electrode terminal 40 (specifically, the internal terminal portion 40b) can be joined to the flat portion 90. Furthermore, the method of joining the electrode terminal 40 to the flat portion 90 is not particularly limited. For example, the electrode terminal 40 can be joined to the flat portion 90 by ultrasonic welding, resistance welding, laser welding, or so-called caulking.Figure 4 As shown, the wound electrode body 20 has a flat portion 23 having two flat surfaces 24 extending in the length direction D13, a first end portion 21 provided on one side in the length direction D13 of the flat portion 23 and formed with a circular arc, and a second end portion 22 provided on the other side in the length direction D13 of the flat portion 23 and formed with a circular arc. As shown in FIG. 1, the flat portion 23 is formed by cutting the flat surfaces 24 of the wound electrode body 20. Figure 3 As shown, the first slit 91 is formed in the portion of the unformed portion 82a of the first end portion 21 along the winding direction D11 (see FIG. 1). A flat portion 90 for connecting the inner terminal portion 40b (see FIG. 1) of the electrode terminal 40 is provided in the portion of the unformed portion 82a of the first end portion 21 opposite the first slit 91 from the electrode active material layer 84. Figure 4 Figure 4

[0048] For example, if the first slit 91 is not formed in the portion of the unformed portion 82a of the first end portion 21, the unformed portion 82a becomes a state in which a circular arc is formed, and it is difficult to connect the electrode terminal 40 in the portion of the unformed portion 82a of the first end portion 21. However, in the present embodiment, by forming the first slit 91 as shown, the portion of the unformed portion 82a of the first end portion 21 is easily crushed, and the flat portion 90 is easily provided in the unformed portion 82a. Therefore, the electrode terminal 40 can be reliably joined to the portion of the unformed portion 82a of the first end portion 21, and as a result, the length of the electrode terminal 40 (more specifically, the length of the inner terminal portion 40b) can be shortened compared to the past. Figure 4

[0049] In the present embodiment, as shown, the second slit 92 is formed in the unformed portion 82a of the first end portion 21, the second slit 92 being disposed at a position opposite the electrode active material layer 84 from the first slit 91 and extending along the winding axis direction D12. In this way, by forming the second slit 92 in the unformed portion 82a, the portion of the unformed portion 82a of the first end portion 21 that can be formed into a circular arc is separated. Therefore, the portion of the unformed portion 82a of the first end portion 21 is easily crushed, and the flat portion 90 is easily provided in the portion of the unformed portion 82a of the first end portion 21. Figure 3

[0050] In the present embodiment, as shown, the second slit 92 is formed in the unformed portion 82a of the first end portion 21, the second slit 92 being disposed at a position opposite the electrode active material layer 84 from the first slit 91 and extending along the winding axis direction D12. In this way, by forming the second slit 92 in the unformed portion 82a, the portion of the unformed portion 82a of the first end portion 21 that can be formed into a circular arc is separated. Therefore, the portion of the unformed portion 82a of the first end portion 21 is easily crushed, and the flat portion 90 is easily provided in the portion of the unformed portion 82a of the first end portion 21. Figure 4 ​​​​As shown, the second slit 92 is formed at the position furthest from the top end 21a of the unformed portion 82a at the first end 21 from the top end 21. The portion of the unformed portion 82a at this top end 21a is a position where an arc can be formed. Therefore, by forming the second slit 92 at the top end 21a, the portion of the unformed portion 82a at the first end 21 that can be formed into an arc can be separated more reliably. Therefore, it is easier to crush the portion of the unformed portion 82a at the first end 21, and it is easier to provide a flat portion 90 on the portion of the unformed portion 82a at the first end 21.

[0051] In this embodiment, such as Figure 5 As shown, the spacing between the first slits 91 when the electrode sheet 80 is unfolded decreases towards the winding start side in the winding direction D11. Similarly, the spacing between the second slits 92 when the electrode sheet 80 is unfolded decreases towards the winding start side in the winding direction D11. Here, the fewer the number of turns of the electrode body 20, the shorter the length of the electrode sheet 80 required for one turn. Therefore, by reducing the spacing between the first slits 91 and the second slits 92 towards the winding start side in accordance with the length of the electrode sheet 80 required for one turn, the first slits 91 and the second slits 92 can be formed in the unformed portion 82a located at the first end 21.

[0052] In this embodiment, the length of the first slit 91 increases as it approaches the winding axis W (refer to...). Figure 4 The shorter the number of turns of the winding electrode body 20, the shorter the length of the winding direction D11 of the unformed portion 82a at the first end 21. Therefore, by shortening the length of the first slit 91 as it approaches the winding axis W in accordance with the length of the winding direction D11 of the unformed portion 82a at the first end 21, it is easy to make multiple first slits 91 overlap. As a result, it is easy to crush the portion of the unformed portion 82a at the first end 21, and it is easy to provide a planar portion 90 in the portion of the unformed portion 82a at the first end 21.

[0053] In this embodiment, although a first slit 91 and a second slit 92 are formed in the unformed portion 82a located at the first end 21, the second slit 92 can be omitted. Even in this case, since the first slit 91 is formed in the unformed portion 82a, a greater force is required compared to the case where the second slit 92 is formed, but it is still possible to crush the unformed portion 82a located at the first end 21. Therefore, even if the second slit 92 is omitted, a planar portion 90 can still be provided in the unformed portion 82a located at the first end 21.

Claims

1. A secondary battery, wherein, Possessing: a flat wound electrode body in which an electrode sheet of a positive electrode or a negative electrode is wound along a prescribed winding direction around a winding axis; a battery case that houses the wound electrode body; and an electrode terminal having an external terminal portion disposed outside the battery case and an internal terminal portion disposed inside the battery case, the electrode sheet has: a current collector; an electrode active material layer that extends in the winding direction, is formed on a surface of the current collector, and includes an electrode active material; and an unformed portion that extends in the winding direction, is disposed at a position at which the electrode active material layer is arranged in the winding axis direction, and is not formed with the electrode active material layer on the surface of the current collector, the wound electrode body has: a flat portion having two flat surfaces that extend in a length direction orthogonal to the winding axis direction; a first end portion disposed on one side in the length direction in the flat portion and formed with a circular arc; and a second end portion disposed on the other side in the length direction in the flat portion and formed with a circular arc, a first slit is formed in a portion of the unformed portion at the first end portion along the winding direction, a flat portion in which the internal terminal portion of the electrode terminal is engaged is provided in a portion of the unformed portion at the first end portion that is located on the opposite side to the electrode active material layer from the first slit, the length of the first slit becomes shorter as it approaches the winding axis, the flat portion is provided by crushing the portion of the unformed portion at the first end portion, the internal terminal portion of the electrode terminal is joined to the flat portion from the outside without being inserted into the first slit.

2. The secondary battery according to claim 1, wherein a second slit is formed in the unformed portion at the first end portion, the second slit being disposed on the opposite side to the electrode active material layer from the first slit and extending in the winding axis direction.

3. The secondary battery according to claim 2, wherein the second slit is formed at a position in the unformed portion at the first end portion that is farthest from the winding axis.

4. The secondary battery according to claim 2 or 3, wherein the interval between the second slits when the electrode sheet is unfolded becomes smaller as it approaches the winding start side in the winding direction.

5. The secondary battery according to any one of claims 1 to 3, wherein the interval between the first slits when the electrode sheet is unfolded becomes smaller as it approaches the winding start side in the winding direction.

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