Secondary battery

Abstract

The invention relates to a secondary battery. This secondary battery is provided with: a wound electrode body in which a positive electrode sheet in which a positive electrode active material layer is formed excluding a positive electrode collector foil exposed portion along one long side of a positive electrode collector foil, and a negative electrode sheet in which a negative electrode active material layer is formed are wound with a separator interposed therebetween; a negative electrode active material layer is formed on the negative electrode sheet except a negative electrode exposed part along one long side of the negative electrode current collector foil; a battery case accommodating the wound electrode body and an electrolyte; a positive electrode collector terminal electrically connected to a positive electrode collector foil portion formed by converging the positive electrode collector foil exposed portions; a negative electrode collector terminal electrically connected to a negative electrode collector foil portion formed by gathering the negative electrode collector foil exposed portions; and an insulating layer formed in at least one of a region of the exposed positive electrode collector foil portion other than the positive electrode collector foil portion and a region of the exposed negative electrode collector foil portion other than the negative electrode collector foil portion.

Description

Technical Field

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

[0002] In Japanese Patent Publication No. 2023-089639, a secondary battery having a wound electrode body formed by winding a positive electrode sheet and a negative electrode sheet with a separator is disclosed. The positive electrode sheet extends from the separator on the first side in the winding axis direction, and the positive electrode collector is joined to this part. The outermost periphery of the negative electrode sheet is wound on the outer peripheral side than the outermost periphery of the positive electrode sheet. The part of the separator that is wound on the outer peripheral side than the outermost periphery of the negative electrode sheet extends along the first side and stops at the part where the positive electrode collector is joined to the positive electrode sheet. Thus, the situation where foreign matter enters the gap between the outermost positive electrode sheet and the negative electrode sheet is reduced. Summary of the invention

[0003] In Japanese Patent Application Laid-Open No. 2023-089639, the outermost separator is stretched and joined to the positive electrode collector together with the positive electrode sheet, thereby preventing a short circuit at the gap between the outermost positive electrode sheet and the negative electrode sheet. However, Japanese Patent Application Laid-Open No. 2023-089639 does not consider the impregnation of the wound electrode body when injecting the electrolyte, and the impregnation of the electrolyte sometimes decreases.

[0004] The present invention has been made in view of the above problems. An object of the present invention is to provide a secondary battery that can prevent a short circuit in a gap between a positive electrode sheet and a negative electrode sheet with a separator interposed therebetween and suppress a decrease in the permeability of an electrolyte solution to a wound electrode body.

[0005] A secondary battery according to one embodiment includes:

[0006] A wound electrode body, formed by winding a positive electrode sheet and a negative electrode sheet with a strip-shaped separator, wherein the positive electrode sheet has a positive electrode active material layer formed except for the positive electrode current collector foil exposed along one long side of the strip-shaped positive electrode current collector foil, and the negative electrode sheet has a negative electrode active material layer formed except for the negative electrode current collector foil exposed along one long side of the strip-shaped negative electrode current collector foil;

[0007] A battery box, containing the wound electrode body and the electrolyte;

[0008] A positive electrode current collector terminal electrically connected to a positive electrode current collector foil portion formed by gathering the exposed portions of the positive electrode current collector foil;

[0009] a negative electrode current collector terminal electrically connected to a negative electrode current collector foil portion formed by collecting the exposed portions of the negative electrode current collector foil; and

[0010] The insulating layer is formed in at least one of a region of the positive electrode current collector foil exposed portion excluding the positive electrode current collector foil portion and a region of the negative electrode current collector foil exposed portion excluding the negative electrode current collector foil portion.

[0011] According to the present invention, it is possible to prevent a short circuit in the gap between the positive electrode sheet and the negative electrode sheet via the separator, and suppress a decrease in the permeability of the electrolyte solution to the wound electrode body. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like symbols represent like elements, and in which:

[0013] Figure 1 It is a diagram showing the external appearance of a secondary battery according to an embodiment.

[0014] Figure 2 Yes Description Figure 1 Diagram of the internal structure of a secondary battery.

[0015] Figure 3 It is an exploded view illustrating the structure of the wound electrode body.

[0016] Figure 4 This is a diagram of a wound electrode body as viewed from the side.

[0017] Figure 5 Yes Figure 4 FIG. 1 is an enlarged view of a portion of a cross section of the wound electrode body at a cutting line V. FIG.

[0018] Figure 6 Yes Figure 4 FIG. 1 is an enlarged view of a portion of the cross section of the wound electrode body taken along cutting line VI. DETAILED DESCRIPTION

[0019] Hereinafter, the present embodiment will be described with reference to the accompanying drawings. In addition, the following embodiments are not intended to limit the technology disclosed herein. For the purpose of clear description, the following description and the accompanying drawings are appropriately omitted and simplified. The dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. In addition, in each of the accompanying drawings, the same symbols are attached to the same elements, and repeated descriptions are omitted as needed.

[0020] The embodiment relates to, for example, a secondary battery used as a driving power source for a battery electric vehicle, etc. In this specification, "secondary battery" refers to a common storage device that can be repeatedly charged and discharged, including so-called storage batteries, double-layer capacitors and other storage elements. Here, the embodiment is described in detail by taking a flat square lithium-ion secondary battery as an example. "Lithium secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and realizes charging and discharging by the movement of charges accompanied by lithium ions between positive and negative electrodes.

[0021] Figure 1 It is a diagram showing the external appearance of a secondary battery 10 according to the embodiment. Figure 2 Yes Description Figure 1 FIG. 1 is a diagram of the internal structure of the secondary battery 10. Figure 1 , 2 As shown, the secondary battery 10 has a structure in which a wound electrode body 20 and an electrolyte (not shown) are accommodated in a battery case 11. W in the figure represents the width direction of the battery case 11. H in the figure represents the height direction of the battery case 11. In addition, the direction orthogonal to the width direction W and the height direction H is set as the thickness direction D of the battery case 11. In addition, these directions do not limit the arrangement method of the secondary battery 10.

[0022] The battery case 11 is a square container having an internal space and a substantially rectangular outer shape. As the battery case 11, a metal material such as aluminum or stainless steel (SUS) which is light and has good thermal conductivity is used. The battery case 11 includes a main body 12 having an opening portion opening upward and a cover body 13 blocking the opening portion. The main body 12 has a substantially rectangular bottom surface, a pair of wide surfaces, and a narrow surface disposed between the pair of wide surfaces. Figure 1 In the embodiment, a pair of wide width surfaces extend upward from the front end and the rear end of the bottom surface, respectively. In addition, a pair of narrow width surfaces extend upward from the left end and the right end of the bottom surface, respectively. The edge of the opening of the main body 12 and the outer edge of the cover 13 are laser welded to make the battery box 11 airtight.

[0023] The cover 13 of the battery case 11 is provided with a positive external terminal 14 and a negative external terminal 15. In addition, the cover 13 is provided with a liquid injection port (not shown) for injecting electrolyte. The liquid injection port can be provided, for example, between the positive external terminal 14 and the negative external terminal 15 of the cover 13. Figure 2 As shown, a part of the positive electrode external terminal 14 and the negative electrode external terminal 15 are connected to the positive electrode current collecting terminal 16 and the negative electrode current collecting terminal 17 , respectively, inside the battery case 11 .

[0024] The wound electrode body 20 is accommodated in a space surrounded by the body 12 and the lid 13 . Figure 3 It is an exploded view illustrating the structure of the wound electrode body 20 . Figure 4 This is a diagram of the wound electrode body 20 as viewed from the side. Figure 4 In the figure, it is shown that Figure 3 The dotted line indicates the side surface of the wound electrode body 20 to which the positive electrode current collector terminal 16 is connected.

[0025] like Figure 3As shown, the wound electrode body 20 includes a strip-shaped first separator 1, a second separator 2, a positive electrode sheet 3, and a negative electrode sheet 4. The length direction of the first separator 1, the second separator 2, the positive electrode sheet 3, and the negative electrode sheet 4 is set as the long side direction, and the width direction is set as the short side direction. The first separator 1, the positive electrode sheet 3, the second separator 2, and the negative electrode sheet 4 are aligned and overlapped in the long side direction in sequence, and are wound around the winding axis X. In this embodiment, the direction of the winding axis X of the wound electrode body 20 is consistent with the width direction W of the secondary battery 10. As shown Figure 4 As shown, the cross section of the wound electrode body 20 is elliptical.

[0026] The positive electrode sheet 3 includes a positive electrode collector foil 30 and a positive electrode active material layer 31. The positive electrode collector foil 30 is a supporting member for the positive electrode active material layer 31 and is a conductive member for extracting charge from the positive electrode active material layer 31. A positive electrode collector foil exposed portion 32 is provided in a region along one long side of the strip-shaped positive electrode collector foil 30. The positive electrode active material layer 31 is formed in a region other than the positive electrode collector foil exposed portion 32 on the positive electrode collector foil 30. The positive electrode active material layer 31 is formed in a strip shape along the other long side of the positive electrode collector foil 30. The positive electrode active material layer 31 may be formed on one side or both sides of the positive electrode collector foil 30. Here, the positive electrode active material layer 31 is formed on both sides of the positive electrode collector foil 30. That is, the positive electrode sheet 3 is in a long strip shape and is arranged in a manner that a wide positive electrode active material layer 31 and a narrow positive electrode collector foil exposed portion 32 are arranged in the width direction.

[0027] In addition, although Figure 3 Although not shown in the figure, the negative electrode sheet 4 includes a negative electrode current collector foil 40, a negative electrode active material layer 41 (see Figure 5 ). The negative electrode collector foil 40 is a supporting member for the negative electrode active material layer 41, and is a conductive member for extracting charge from the negative electrode active material layer 41. A negative electrode collector foil exposed portion is provided in an area along one long side of the strip-shaped negative electrode collector foil 40. The negative electrode active material layer 41 is formed in an area other than the negative electrode collector foil exposed portion on the negative electrode collector foil 40. The negative electrode active material layer 41 is formed in a strip shape along the other long side of the negative electrode collector foil 40. The negative electrode active material layer 41 can be formed on one side or both sides of the negative electrode collector foil 40. Here, the negative electrode active material layer 41 is formed on both sides of the negative electrode collector foil 40. That is, the negative electrode sheet 4 is in the shape of a long strip, and is arranged in a manner such that a wide negative electrode active material layer 41 and a narrow negative electrode collector foil exposed portion are arranged in the width direction.

[0028] As the members and materials constituting the secondary battery 10 , the same members and materials as those used for widely known lithium ion secondary batteries can be used, and the present invention is not particularly limited. An example of the members and materials constituting the secondary battery 10 is shown below.

[0029] Examples of the positive electrode current collector foil 30 constituting the positive electrode sheet 3 include aluminum (including aluminum alloy) foil. Examples of the positive electrode active material contained in the positive electrode active material layer 31 include lithium transition metal oxides (e.g., LiNi 1 / 3 Co 1 / 3Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.), lithium transition metal phosphorus oxides (e.g., LiFePO4, etc.). The positive electrode active material layer 31 may contain components other than the active material, such as a conductive material, a binder, etc. As the conductive material, for example, carbon black such as acetylene black (AB) or other carbon materials (e.g., graphite, etc.) may be used. As the binder, for example, polyvinylidene fluoride (PVdF) may be used.

[0030] As the negative electrode collector foil 40 constituting the negative electrode sheet 4, for example, copper foil or the like can be cited. As the negative electrode active material contained in the negative electrode active material layer 41, for example, carbon materials such as graphite, hard carbon, and soft carbon can be used. In the case of using graphite as the negative electrode active material, the negative electrode active material can be either natural graphite or artificial graphite, or it can be coated with an amorphous carbon material. The negative electrode active material layer 41 may contain components other than the active material, such as a binder, a thickener, and the like. As a binder, for example, styrene-butadiene rubber (SBR) or the like can be used. As a thickener, for example, carboxymethyl cellulose (CMC) or the like can be used.

[0031] The first separator 1 and the second separator 2 insulate the positive electrode sheet 3 from the negative electrode sheet 4 and provide a path for the charge carrier to move between the positive electrode active material layer 31 and the negative electrode active material layer 41. As the first separator 1 and the second separator 2, a porous sheet (film) made of polyolefins such as polyethylene (PE) and polypropylene (PP) can be used. Such a porous sheet can be a single-layer structure or a stacked structure of two or more layers (for example, a three-layer structure with PP layers stacked on both sides of the PE layer). A heat-resistant layer (HRL) can also be provided on the surface of the first separator 1 and the second separator 2.

[0032] The electrolyte typically includes a non-aqueous solvent and a supporting salt. As the non-aqueous solvent, a known solvent used as a non-aqueous solvent for an electrolyte for a lithium ion secondary battery can be used. For example, as a non-aqueous solvent, carbonates, ethers, esters, nitriles, sulfones, lactones, etc. can be cited. As examples of carbonates, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. can be cited. Such a non-aqueous solvent can be used alone or in combination of two or more.

[0033] As supporting salt, for example, lithium salts such as LiPF6, LiBF4, LiClO4 (preferably LiPF6) are appropriately used. The electrolyte may also contain other components. Examples of other components include gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB), film forming agents, dispersants, thickeners, etc.

[0034] The positive electrode active material layer 31 and the negative electrode active material layer 41 are stacked in the center of the winding axis X direction of the wound electrode body 20 to form a core portion for charge and discharge reactions. Figure 3 The positive electrode current collector foil laminated portion 33 is formed by laminating the positive electrode current collector foil exposed portion 32 with the positive electrode current collector foil exposed portion 32 protruding from the negative electrode sheet 4. In addition, in the wound electrode body 20, at the other end in the winding axis X direction (not shown, it is Figure 3 At the right end portion of the positive electrode sheet 3, there is a negative electrode collector foil stacking portion, which is stacked in a state where the exposed portion of the negative electrode collector foil protrudes from the positive electrode sheet 3.

[0035] like Figure 4 As shown, the positive electrode current collector foil exposed portion 32 (hereinafter referred to as “collector foil”) is gathered at the center portion in the height direction H of the positive electrode current collector foil stacked portion 33 to form a positive electrode current collector foil portion 34 . Figure 5 Yes Figure 4 A partially enlarged view of the cross section of the wound electrode body at the cutting line V. Figure 5 , the vicinity of the positive electrode foil collecting portion 34 at the cutting line V is shown when viewed from the upper side (the hollow arrow side). Figure 4 As shown, the positive electrode current collector terminal 16 is electrically connected to the positive electrode foil collecting portion 34 by ultrasonic welding or the like. Figure 5 As shown, in the positive electrode current collecting foil portion 34 , the adjacent positive electrode current collecting foils 30 are collected, so that foreign matter does not enter between the positive electrode sheet 3 and the negative electrode sheet 4 .

[0036] Similarly, the negative electrode current collector foil exposed portion is gathered at the central portion of the negative electrode current collector foil stacking portion in the height direction H to form a negative electrode current collector foil portion. The negative electrode current collector terminal 17 is electrically connected to the negative electrode current collector foil portion. In the negative electrode current collector foil portion, the adjacent negative electrode current collector foils are collected, so foreign matter does not invade between the positive electrode sheet 3 and the negative electrode sheet 4.

[0037] An insulating layer 35 is formed on at least one of the region of the positive electrode current collector foil exposed portion 32 excluding the positive electrode current collector foil portion 34 and the region of the negative electrode current collector foil exposed portion excluding the negative electrode current collector foil portion. The insulating layer 35 is preferably formed on both the region of the positive electrode current collector foil exposed portion 32 excluding the positive electrode current collector foil portion 34 and the region of the negative electrode current collector foil exposed portion excluding the negative electrode current collector foil portion.

[0038] The insulating layer 35 formed on the exposed portion 32 of the positive electrode collector foil is described in detail below. In addition, the insulating layer 35 is also formed on the exposed portion of the negative electrode collector foil in the same manner as the exposed portion 32 of the positive electrode collector foil, so the description is omitted. The insulating layer 35 is, for example, a solidified body of a liquid insulating paste. The insulating paste may contain, for example, an inorganic substance having insulating properties, a solvent for the insulating paste, and a resin component. The inorganic substance may be at least one of powdered aluminum oxide, boehmite, and titanium dioxide. The solvent for the insulating paste uses an NMP solution as an example of an organic solvent. The resin component functions as an adhesive in the insulating layer 35. The resin component may be at least one selected from a group including PVDF, PVA, and propylene, which are polymer materials soluble in NMP. The insulating layer 35 preferably has flexibility when the exposed portion 32 of the positive electrode collector foil is collected.

[0039] like Figure 3 As shown in FIG. 1 , the insulating layer 35 is formed at a predetermined interval along the long side direction of the positive electrode current collector foil exposed portion 32. The "predetermined interval" for forming the insulating layer 35 is preferably a spacing at which the insulating layer 35 is formed over the entire area of ​​the positive electrode current collector foil exposed portion 32 except for the positive electrode current collector foil portion 34 when the positive electrode sheet 3 is wound. In addition, the insulating layer 35 is formed on both sides of the positive electrode current collector foil exposed portion 32. Thus, when the positive electrode sheet 3 is wound to form the wound electrode body 20, the positive electrode current collector foil 30 is exposed only at the positive electrode current collector foil portion 34.

[0040] Figure 6 Yes Figure 4 A partially enlarged view of a cross section of the wound electrode body at the cutting line VI. Figure 6 , the vicinity of the positive electrode current collector foil stacking portion 33 at the cutting line VI is shown when viewed from the upper side (the hollow arrow side). Figure 6 As shown, in the positive electrode current collector foil stacked portion 33 , insulating layers 35 are formed on both surfaces of the positive electrode current collector foil exposed portion 32 .

[0041] Generally, it is known that metal foreign matter such as welding spatter is generated during battery manufacturing and enters the secondary battery 10 through the liquid injection port. The metal foreign matter entering the secondary battery 10 may cause conduction between the battery case 11 and the wound electrode body 20 or between the positive electrode and the negative electrode in the wound electrode body 20, resulting in a short circuit.

[0042] Normally, during electrolyte impregnation, the electrolyte penetrates from the region of the positive electrode current collector foil stacking portion 33 above and below the positive electrode collector foil portion 34 toward the center of the wound electrode body 20. When a metallic foreign object that has penetrated into the interior of the secondary battery 10 through the liquid injection port causes a short circuit between the positive electrode and the negative electrode in the wound electrode body 20, the path along which the metallic foreign object moves with the flow of the electrolyte that has penetrated into the wound electrode body 20 is considered. As a means of preventing a short circuit based on this path, preventing the metallic foreign object from penetrating between the positive electrode and the negative electrode can be cited.

[0043] In Japanese Patent Application Laid-Open No. 2023-089639, the outermost separator is extended and joined to the positive electrode current collector together with the separator, thereby suppressing the intrusion of metallic foreign matter. However, since the separator is covered, the permeability of the electrolyte may be reduced.

[0044] In contrast, in the embodiment, the insulating layer 35 is formed in the positive electrode current collector foil exposed portion 32 in the region other than the positive electrode current collector foil portion 34. Therefore, when the electrolyte is injected, even if the metallic foreign matter F enters the gap between the positive electrode sheet 3 and the negative electrode sheet 4 of the wound electrode body 20, the occurrence of a short circuit can be suppressed. Figure 6 As shown, in the positive electrode current collector foil laminated portion 33, the positive electrode sheet 3 is not joined to the separator as in Japanese Patent Application Laid-Open No. 2023-089639, so when collecting foil, a gap is generated in the positive electrode current collector foil laminated portion 33 other than the positive electrode current collector foil portion 34. Therefore, the electrolyte can be impregnated into the wound electrode body 20 without changing the electrolyte injection conditions.

[0045] In addition, the present invention is not limited to the above-mentioned embodiment, and can be appropriately modified within a scope not departing from the gist.

Claims

1. A secondary battery comprising: A wound electrode body, formed by winding a positive electrode sheet and a negative electrode sheet with a strip-shaped separator, wherein the positive electrode sheet has a positive electrode active material layer formed except for the positive electrode current collector foil exposed along one long side of the strip-shaped positive electrode current collector foil, and the negative electrode sheet has a negative electrode active material layer formed except for the negative electrode current collector foil exposed along one long side of the strip-shaped negative electrode current collector foil; A battery box, containing the wound electrode body and the electrolyte; A positive electrode current collector terminal electrically connected to a positive electrode current collector foil portion formed by gathering the exposed portions of the positive electrode current collector foil; a negative electrode current collector terminal electrically connected to a negative electrode current collector foil portion formed by collecting the exposed portions of the negative electrode current collector foil; and The insulating layer is formed in at least one of a region of the positive electrode current collector foil exposed portion excluding the positive electrode current collector foil portion and a region of the negative electrode current collector foil exposed portion excluding the negative electrode current collector foil portion.

2. The secondary battery according to claim 1, wherein The insulating layers are formed at predetermined intervals along the long side direction of the positive electrode current collector foil or the negative electrode current collector foil.

3. The secondary battery according to claim 1, wherein The insulating layer is formed on both a region of the positive electrode current collector foil exposed portion excluding the positive electrode current collector foil portion and a region of the negative electrode current collector foil exposed portion excluding the negative electrode current collector foil portion.

4. The secondary battery according to claim 1, wherein The diaphragm includes a first diaphragm and a second diaphragm, The first separator, the positive electrode sheet, the second separator, and the negative electrode sheet are sequentially stacked and aligned in a long-side direction and are wound around a winding axis set along a short-side direction.

5. The secondary battery according to claim 4, wherein The battery box is a square box having a substantially rectangular shape. The wound electrode body has a flat rectangular parallelepiped shape. The positive electrode current collector foil exposed portion is stacked and arranged so as to protrude from the negative electrode sheet at one end portion in the winding axis direction. At the other end in the winding axis direction, the negative electrode current collector foil exposed portion is stacked and arranged so as to protrude from the positive electrode sheet. The wound electrode body is housed in the battery case such that the winding axis direction extends in the width direction of the battery case.

Images