Secondary battery

Abstract

A secondary battery (10) is provided with: an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) therebetween; an electrolyte; a bottomed cylindrical outer can (16) that accommodates the electrode body (14) and the electrolyte; a sealing body (17) that closes an open end (16A) of the outer can (16); and an annular gasket (28) that is interposed between the outer can (16) and the sealing body (17). The bottom surface of the gasket (28) is provided with a protrusion (30) that protrudes further outward than the inner circumference of the outer can (16).

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] The secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an electrolyte, a cylindrical outer can with a bottom that contains the electrode assembly and the electrolyte, a sealing body that closes the open end of the outer can, and an annular gasket that is interposed between the outer can and the sealing body (for example, Patent Document 1).

[0003] In the manufacturing process of the secondary battery described above, a groove is formed in the open end of the outer can, an electrolyte is poured into the outer can, and a gasket is inserted into the groove of the outer can. When the gasket is inserted into the groove of the outer can, the electrolyte adhering to the inside of the outer can is scraped off by the gasket.

[0004] International Publication No. 2022 / 196172

[0005] However, due to dimensional variations in the gasket and the outer can, the gasket may not be able to adequately scrape off the electrolyte adhering to the inside of the outer can. If the electrolyte remains above the groove in the outer can, the electrolyte may leak or corrode the sealing cap or the outer can.

[0006] Therefore, an object of the present disclosure is to provide a secondary battery that can reliably scrape off the electrolyte adhering to the inside of the outer can.

[0007] The secondary battery according to the present disclosure is a secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an electrolyte, a cylindrical outer can with a bottom that contains the electrode assembly and the electrolyte, a sealing body that closes the open end of the outer can, and an annular gasket that is interposed between the outer can and the sealing body, and is characterized in that the bottom surface of the gasket is provided with a protrusion that protrudes outward beyond the inner periphery of the outer can.

[0008] According to the sealed secondary battery of the present disclosure, the electrolyte adhering to the inside of the outer can can be reliably scraped off.

[0009] Fig. 1 is a side cross-sectional view showing a secondary battery as an example of an embodiment; Fig. 2 is a side cross-sectional view showing a gasket as an example of an embodiment; Fig. 3 is a flow showing a manufacturing process of a secondary battery as an example of an embodiment; Fig. 4 is a schematic view showing an inserting step of a gasket as an example of an embodiment; Fig. 5 is another schematic view showing an inserting step of a gasket as an example of an embodiment; Fig. 6 is another schematic view showing an inserting step of a gasket as an example of an embodiment.

[0010] An example of an embodiment of the present disclosure will be described in detail below. In the following description, specific shapes, materials, directions, numerical values, etc. are examples for facilitating understanding of the present disclosure, and can be appropriately changed according to the application, purpose, specifications, etc.

[0011] A secondary battery 10 as an example of an embodiment will be described with reference to FIG.

[0012] The secondary battery 10 includes a wound electrode assembly 14, a non-aqueous electrolyte, and an outer can 16 that accommodates the electrode assembly 14 and the non-aqueous electrolyte. The secondary battery 10 is, for example, a lithium-ion secondary battery. The electrode assembly 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is a cylindrical metal container with a bottom and an open end in the direction of the central axis X1. The opening of the outer can 16 is closed by a sealing member 17. For ease of explanation, the sealing member 17 side of the battery will be referred to as the top, and the bottom side of the outer can 16 will be referred to as the bottom.

[0013] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode assembly 14 are all strip-shaped, long bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length direction (longitudinal direction) and width direction (transverse direction). The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11. The electrode assembly 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0014] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be made of a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film with such a metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode core. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.

[0015] Examples of the conductive agent contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. One type of conductive agent may be used alone, or multiple types may be used in combination. The content of the conductive agent is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less with respect to the mass of the positive electrode mixture layer.

[0016] Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the positive electrode mixture layer.

[0017] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode core can be a foil of a metal stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film with such a metal disposed on its surface. The negative electrode mixture layer contains a negative electrode active material and a binder and is preferably provided on both sides of the negative electrode core. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core. Metallic lithium foil can also be used as the negative electrode 12. Alternatively, the negative electrode 12 may be composed only of a negative electrode core, with metallic lithium being deposited on the core surface during battery charging.

[0018] The negative electrode active material is not particularly limited as long as it reversibly absorbs and releases lithium ions, and generally, carbon materials such as graphite are used. Furthermore, elements that alloy with Li, such as Si and Sn, or materials containing such elements may also be used as the negative electrode active material. Among these, silicon-containing materials containing Si are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. One type of negative electrode active material may be used alone, or multiple types may be used in combination.

[0019] The carbon material functioning as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Among them, it is preferable to use artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, and amorphous graphite, or a mixture thereof. Examples of the silicon-containing material functioning as the negative electrode active material include silicon alloys, silicon compounds, and composite materials containing Si. A suitable silicon-containing material is a composite particle containing an ion-conducting phase and a Si phase dispersed in the ion-conducting phase.

[0020] The binder contained in the negative electrode mixture layer can be, as in the case of the positive electrode 11, fluororesin, olefin resin, PAN, polyimide, polyamide, acrylic resin, etc., but polyvinyl acetate, styrene-butadiene rubber (SBR), etc. may also be used. Among these, SBR is preferable. A single binder may be used, or multiple binders may be used in combination. The negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. These function as thickeners in the negative electrode mixture slurry. The content of the binder is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the negative electrode mixture layer. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0021] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0022] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides and phosphate compounds containing metal elements such as Ti, Al, Si, and Mg. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0023] The non-aqueous electrolyte has ion conductivity (for example, lithium ion conductivity) and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0024] The electrolyte solution includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent that can be used include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms in these solvents are substituted with halogen atoms such as fluorine. Examples of the halogen-substituted compound include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0025] An upper insulating plate 18 and a lower insulating plate 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the upper insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the lower insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0026] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The gasket 28 will be described in detail below. The exterior can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end 16A of the exterior can 16, which is crimped to the sealing body 17.

[0027] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0028] [Gasket] A gasket 28 as an example of an embodiment will be described with reference to Fig. 2. Fig. 2 shows the gasket 28 before it is inserted into the outer can 16.

[0029] As described above, the gasket 28 is interposed between the exterior can 16 and the sealing body 17. The gasket 28 ensures the airtightness of the interior of the secondary battery 10. Furthermore, as will be described in detail later, the gasket 28 makes it possible to reliably scrape off the electrolyte adhering to the inside of the opening end 16A of the exterior can 16 during the manufacturing process of the secondary battery 10. This improves the reliability of the secondary battery 10.

[0030] An elastic insulating resin is used for the gasket 28. Examples of the elastic insulating resin that may be used include polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), perfluoroalkoxy fluororesin (PFA), and nylon.

[0031] The gasket 28 is formed in an annular shape and includes a ring-shaped main body 29 and a protrusion 30 that is provided on the bottom surface of the main body 29 and protrudes outward beyond the inner periphery of the outer can 16, as will be described in detail later.

[0032] The main body 29 is interposed between the sealing body 17 and the upper insulating plate 18. An opening 29A for pouring the electrolyte is formed in the center of the main body 29. After the sealing body 17 is crimped and fixed to the open end 16A of the outer can 16, the main body 29 is formed into a C-shape in a side cross section. A storage portion 29B is formed in the bottom surface of the main body 29.

[0033] The accommodation portion 29B, which will be described in detail later, is a portion in which the protrusion 30 is accommodated after the gasket 28 is inserted into the outer can 16 during the manufacturing process of the secondary battery 10. The accommodation portion 29B is formed in a rectangular shape in a side cross-sectional view, and is formed in a ring shape in a plan view (when the gasket 28 is viewed from below).

[0034] As described above, the protrusion 30 protrudes outward from the inner periphery of the exterior can 16 in a side cross-sectional view. The protrusion 30 is provided on the edge of the bottom surface of the main body 29. The protrusion 30 is formed in a ring shape in a plan view. As will be described in detail later, the protrusion 30 makes it possible to reliably scrape off the electrolyte adhering to the inside of the opening end 16A of the exterior can 16 during the manufacturing process of the secondary battery 10.

[0035] In a side cross-sectional view, the protrusion 30 has a tip end bent and facing inward. More specifically, in a side cross-sectional view, the protrusion 30 has an outward-facing portion 30A formed on the base end side and facing outward, and an inward-facing portion 30B formed on the tip end side and facing inward. The outward-facing portion 30A and the inward-facing portion 30B are continuously formed with an obtuse-angled portion 30C formed therebetween before insertion into the outer can 16.

[0036] When the gasket 28 is placed on the open end 16A of the outer can 16 so that the central axis X2 of the gasket 28 is aligned with the central axis X1 of the outer can 16 immediately before insertion into the outer can 16, the tip of the outward portion 30A (obtuse-angled portion 30C) protrudes outward beyond the inner periphery of the outer can 16 in a side cross-sectional view. As will be described in detail later, the obtuse-angled portion 30C makes it possible to reliably scrape off the electrolyte adhering to the inside of the open end 16A of the outer can 16 during the manufacturing process of the secondary battery 10.

[0037] When the gasket 28 is placed on the open end 16A of the outer can 16 so that the central axis X2 of the gasket 28 is aligned with the central axis X1 of the outer can 16 immediately before insertion into the outer can 16, the tip of the inward portion 30B (the tip of the protrusion 30) is located inside the inner periphery of the outer can 16 in a side cross-sectional view. The length of the inward portion 30B is longer than the length of the outward portion 30A in a side cross-sectional view. As will be described in detail later, the inward portion 30B allows the protrusion 30 to be guided inside the open end 16A of the outer can 16 when inserting the gasket 28 into the outer can 16 in a manufacturing process of the secondary battery 10, making it easy to insert the gasket 28 into the outer can 16.

[0038] [Secondary Battery Manufacturing Process] A manufacturing process of the secondary battery 10 as an example of the embodiment will be described with reference to FIG.

[0039] In step S11, the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween to produce an electrode assembly 14. In step S12, the electrode assembly 14, together with a lower insulating plate 19, is inserted into a cylindrical outer can 16 with a bottom made by drawing a steel plate. In step S13, the inner surface of the bottom of the outer can 16 and the negative electrode lead 21 are welded.

[0040] In step S14, the upper insulating plate 18 is inserted into the outer can 16. In step S15, a groove is machined on the upper side of the upper insulating plate 18 at the open end 16A of the outer can 16 to form a grooved portion 22. In step S16, an electrolyte is injected into the outer can 16. In step S17 (insertion step S17, described in detail below), a gasket 28 is inserted into the grooved portion 22. In step S18, the sealing body 17 and the positive electrode lead 20 are welded together. In step S19, the sealing body 17 is inserted into the open end 16A of the outer can 16. In step S20, the sealing body 17 is crimped and fixed to the open end 16A of the outer can 16 via the gasket 28. Note that in this embodiment, as shown in steps S17 to S19 in FIG. 3 , the gasket 28 is inserted into the outer can 18 and then the sealing body 17 is inserted, but the order is not limited to this. For example, after the gasket 28 and the sealing body 17 are integrated, the sealing body 17 and the positive electrode lead 20 may be welded, and then the gasket 28 integrated with the sealing body 17 may be inserted into the outer can 16 .

[0041] [Gasket Insertion Step] The step S17 of inserting the gasket 28, which is an example of an embodiment, will be described with reference to FIGS. 4 to 6. FIG.

[0042] In the insertion step S17, as described above, the gasket 28 is inserted into the grooved portion 22 of the outer can 16. In the insertion step S17, as will be described in detail later, the protrusion 30 of the gasket 28 can reliably scrape off the electrolyte adhering to the inside of the opening end 16A of the outer can 16 (the inner wall portion 16B and the grooved upper portion 16C). Note that the inner wall portion 16B is the inner wall portion above the grooved portion 22 of the outer can 16.

[0043] 4 , in the insertion step S17, first, the gasket 28 is inserted into the opening edge 16A of the outer can 16. At this time, as described above, the tip of the protrusion 30 of the gasket 28 (the tip of the inward-facing portion 30B) is located inside the opening edge 16A of the outer can 16 in a side cross-sectional view, and therefore the tip of the inward-facing portion 30B of the protrusion 30 of the gasket 28 is guided into the opening edge 16A of the outer can 16, and the gasket 28 can be easily inserted into the outer can 16.

[0044] 5 , in the insertion step S17, the gasket 28 is then pressed downward along the inner wall portion 16B of the outer can 16. At this time, as described above, the tip of the outward-facing portion 30A of the protrusion 30 of the gasket 28 (outside the obtuse-angled portion 30C) is positioned outside the inner wall portion 16B of the outer can 16 in a side cross-sectional view, and therefore the obtuse-angled portion 30C reliably abuts against the inner wall portion 16B of the outer can 16. In this state, by pressing the gasket 28 downward along the inner wall portion 16B of the outer can 16, the obtuse-angled portion 30C can reliably scrape off the electrolyte adhering to the inner wall portion 16B.

[0045] 6 , in the insertion step S17, the gasket 28 is then brought into contact with the grooved upper portion 16C of the outer can 16. At this time, the protrusion 30 of the gasket 28 is pressed against the main body 29 and folded and accommodated in the accommodation portion 29B. When the protrusion 30 of the gasket 28 is folded, the electrolyte adhering to the grooved upper portion 16C can be reliably scraped off. Furthermore, by folding the protrusion 30 and accommodating it in the accommodation portion 29B, the adhesion between the gasket 28 and the outer can 16 can be improved.

[0046] [Summary] The present disclosure will be further described by the following embodiments. Configuration 1: A secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an electrolyte, a cylindrical outer can with a bottom that houses the electrode assembly and the electrolyte, a sealing body that closes the open end of the outer can, and an annular gasket that is interposed between the outer can and the sealing body, wherein a protrusion that protrudes outward beyond the inner periphery of the outer can is provided on the bottom surface of the gasket. Configuration 2: The secondary battery according to Configuration 1, wherein a tip side of the protrusion is bent and faces inward. Configuration 3: The secondary battery according to Configuration 2, wherein a tip of the protrusion is located inside the inner periphery of the outer can. Configuration 4: The secondary battery according to Configuration 3, wherein the protrusion is provided on an edge of the bottom surface. Configuration 5: The secondary battery according to configuration 4, wherein the protrusion has an outward portion formed on the base end side facing outward, and an inward portion formed on the tip end side facing inward.Configuration 6: The secondary battery according to configuration 5, wherein the tip of the outward portion protrudes outward beyond the inner periphery of the outer can.Configuration 7: The secondary battery according to configuration 5, wherein the tip of the inward portion is located inside the inner periphery of the outer can.Configuration 8: The secondary battery according to configuration 5, wherein the outward portion and the inward portion are formed continuously, forming an obtuse angle.Configuration 7: The secondary battery according to configuration 5, wherein the inward portion is longer than the outward portion.Configuration 8: The secondary battery according to configurations 1 to 9, wherein the bottom surface of the gasket is provided with a receiving portion that receives the protrusion after the gasket is inserted into the outer can.

[0047] It should be noted that the present disclosure is not limited to the above-described embodiment and its modifications, and it goes without saying that various modifications and improvements are possible within the scope of the matters described in the claims of the present application.

[0048] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 16 outer can, 16A opening end, 16B inner wall portion, 16C grooved upper portion, 17 sealing body, 18 upper insulating plate, 19 lower insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 grooved portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket, 29 main body, 29A opening, 29B storage portion, 30 protrusion, 30A outward portion, 30B inward portion, 30C obtuse angle portion

Claims

1. A secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; an electrolyte; a cylindrical outer can with a bottom that contains the electrode assembly and the electrolyte; a sealing body that closes the open end of the outer can; and an annular gasket that is interposed between the outer can and the sealing body, wherein the bottom surface of the gasket is provided with a protrusion that protrudes outward beyond the inner circumference of the outer can.

2. A secondary battery according to claim 1, wherein the tip of the protrusion is bent to face inward.

3. A secondary battery according to claim 2, wherein the tip of the protrusion is located inside the inner periphery of the outer can.

4. A secondary battery according to claim 3, wherein the protrusion is provided on the edge of the bottom surface.

5. A secondary battery according to claim 4, wherein the protrusion has an outward facing portion formed on the base end side and facing outward, and an inward facing portion formed on the tip end side and facing inward.

6. A secondary battery according to claim 5, wherein the tip of the outward-facing portion protrudes outward beyond the inner periphery of the outer can.

7. A secondary battery according to claim 5, wherein the tip of the inward-facing portion is located inside the inner periphery of the outer can.

8. A secondary battery according to claim 5, wherein the outward facing portion and the inward facing portion are formed continuously and form an obtuse angle.

9. A secondary battery according to claim 5, wherein the inward-facing portion is longer than the outward-facing portion.

10. A secondary battery according to any one of claims 1 to 9, wherein the bottom surface of the gasket is provided with a receiving portion in which the protrusion is received after the gasket is inserted into the outer can.

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