Cylindrical battery

Abstract

A cylindrical battery (10) is provided with a wound electrode body (14), a bottomed cylindrical outer can (15), and a sealing body (30) for closing an opening of the outer can (15), and is configured so that the electrode body (14) can be discharged from the opening of the outer can (15). The sealing body (30) has a central portion (31), an outer peripheral portion (32), and a thin portion (33) positioned between the central portion (31) and the outer peripheral portion (32). The thin portion (33) includes an easily breakable portion (34) formed in an annular shape in the sealing body (30), and an outer thin portion (35) positioned further to the outer peripheral portion (32) side than the easily breakable portion (34).

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] Conventionally, cylindrical batteries have been widely known, including a wound electrode assembly, a bottomed cylindrical outer can housing the electrode assembly, and a sealing body that closes the opening of the outer can. For example, Patent Document 1 discloses a cylindrical battery including a sealing body formed with an easily breakable portion that breaks to allow gas to be released in the event of a battery abnormality. The sealing body disclosed in Patent Document 1 also has multiple thick portions and multiple thin portions extending radially in the radial direction, with the aim of suppressing deformation of the sealing body during the battery manufacturing process and reducing material costs. The multiple thick portions and multiple thin portions are alternately arranged circumferentially around the sealing body. In the cylindrical battery of Patent Document 1, an easily breakable portion is also formed at the bottom of the outer can.

[0003] International Publication No. 2022 / 092020

[0004] When an abnormality occurs in a battery and the battery temperature rises, it is desirable to exhaust gas and the electrode assembly from the outer can to suppress further temperature rise. In a cylindrical battery, for example, an increase in internal pressure causes the bottom or sealing body of the outer can to rupture, forming an opening, through which the gas and the electrode assembly can be exhausted. However, in this case, there are cases where the amount of gas exhausted is insufficient. Furthermore, there are cases where the electrode assembly is clogged in the opening, preventing smooth exhaust.

[0005] A cylindrical battery according to one aspect of the present disclosure is a cylindrical battery comprising a wound electrode body, a bottomed cylindrical outer can that houses the electrode body, and a sealing body that closes the opening of the outer can, and is configured so that the electrode body can be removed from the opening of the outer can, wherein the sealing body has a central portion that is positioned on an extension of the central axis of the electrode body, an outer periphery to which the edge of the opening of the outer can is crimped and fixed, and a thin-walled portion that is positioned between the central portion and the outer periphery and is thinner than the central portion and the outer periphery, and the thin-walled portion includes an easily breakable portion that is formed in an annular shape when viewed from the bottom of the sealing body, and an outer thin-walled portion that is positioned closer to the outer periphery than the easily breakable portion.

[0006] According to the cylindrical battery of the present disclosure, when an abnormality occurs in the battery, the amount of gas discharged from the outer can can be increased, and further, the electrode assembly can be smoothly discharged from the outer can.

[0007] FIG. 2 is a cross-sectional view of a cylindrical battery of a first embodiment. FIG. 3 is an enlarged view of part A in FIG. 1. FIG. 4 is a diagram showing a sealing body of a first embodiment, where (a) is a bottom view of the sealing body, and (b) is a cross-sectional view taken along line BB in (a). FIG. 5 is a diagram showing a sealing body of a second embodiment, where (a) is a bottom view of the sealing body, (b) is a cross-sectional view taken along line CC in (a), and (c) is a cross-sectional view taken along line DD in (a). FIG. 6 is a vertical cross-sectional view of a main part of a sealing body of another example of this embodiment. FIG. 7 is a vertical cross-sectional view of a main part of a sealing body of another example of this embodiment. FIG. 8 is a vertical cross-sectional view of a main part of a sealing body of another example of this embodiment.

[0008] Hereinafter, an example of an embodiment of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. Note that the scope of the present disclosure includes configurations that are formed by selectively combining the respective components of the multiple embodiments and variations described below.

[0009] Fig. 1 is a cross-sectional view of a cylindrical battery 10 according to a first embodiment. As shown in Fig. 1, the cylindrical battery 10 includes a wound electrode assembly 14, a cylindrical outer can 15 with a bottom that houses the electrode assembly 14, and a sealing body 30 that closes the opening of the outer can 15. The cylindrical battery 10 includes an electrolyte, which is housed in the outer can 15 together with the electrode assembly 14. The cylindrical battery 10 also includes a gasket 17 that is interposed between the outer can 15 and the sealing body 30 to ensure that the battery interior is sealed and to prevent electrical contact between the outer can 15 and the sealing body 30.

[0010] As will be described in detail below, the cylindrical battery 10 is configured so that the electrode assembly 14 can be ejected to the outside through an opening in the outer can 15 if an abnormality occurs in the battery and the temperature rises. By ejecting the electrode assembly 14 from the outer can 15, further temperature increases can be suppressed. Because the opening of the outer can 15 is closed by a sealing body 30, the sealing body 30 breaks to form the opening. The sealing body 30 is a disc-shaped metal member and has a thin-walled portion 33 that breaks preferentially when the battery's internal pressure rises. The thin-walled portion 33 includes an easily breakable portion 34 that is formed in an annular shape when viewed from the bottom of the sealing body 30. When the internal pressure of the cylindrical battery 10 exceeds a predetermined value, the easily breakable portion 34 breaks, forming an opening in the sealing body 30, through which the electrode assembly 14 can be ejected.

[0011] 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 positive electrode 11, the negative electrode 12, and the separator 13 are all long, strip-shaped bodies, and are spirally wound so that they are 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 in the longitudinal direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11.

[0012] The outer can 15 is a metal container that houses the electrode assembly 14 and the electrolyte. The outer can 15 has a grooved portion 16 formed on its side that protrudes inward and supports the sealing body 30. For ease of explanation, the sealing body 30 side of the cylindrical battery 10 will be referred to as the top, and the bottom side of the outer can 15 as the bottom. The grooved portion 16 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and its upper surface supports the sealing body 30. The sealing body 30 is fixed to the top of the outer can 15 by the grooved portion 16 and the open end of the outer can 15 that is crimped to the sealing body 30. The opening of the outer can 15 is circular in plan view, and the sealing body 30 is also circular in plan view.

[0013] The electrolyte may be an aqueous electrolyte, but in this embodiment, a non-aqueous electrolyte is used. The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The cylindrical battery 10 is a non-aqueous electrolyte secondary battery, and preferably a lithium ion battery.

[0014] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0015] As the solid electrolyte, for example, a solid or gel polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether, etc. can be used.

[0016] The positive electrode 11 has a long positive electrode core and a positive electrode mixture layer provided on the positive electrode core. The positive electrode core can be a foil of a metal 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 such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode core except for the portion to which the positive electrode lead 20 described below is connected. The positive electrode active material can be, for example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like.

[0017] The negative electrode 12 has a long negative electrode core and a negative electrode mixture layer provided on the negative electrode core. The negative electrode core can be made of a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a 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 such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode core except for the portion to which the negative electrode lead 21 described below is connected. For example, graphite, a Si-containing material, or the like is used as the negative electrode active material.

[0018] 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 (porous sheet) 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.

[0019] The electrode body 14 further has a positive electrode lead 20 connected to the core of the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the core of the negative electrode 12 by welding or the like. Insulating plates 22, 23 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 insulating plate 22 and extends toward the sealing body 30, and the negative electrode lead 21 passes outside the insulating plate 23 and extends toward the bottom of the outer can 15. In this embodiment, the positive electrode lead 20 is connected to the inner surface of a central portion 31 of the sealing body 30 by welding or the like, so that the sealing body 30 serves as a positive electrode external terminal, and the negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 15 by welding or the like, so that the outer can 15 serves as a negative electrode external terminal.

[0020] The outer can 15 is a cylindrical metal container with a bottom and an open axial end, and the opening of the outer can 15 is closed by a sealing body 30 via a gasket 17. The material of which the outer can 15 is made is not particularly limited, but an example of a suitable material is stainless steel. Furthermore, the bottom of the outer can 15 does not have a portion that would preferentially break when the internal pressure of the battery increases, such as a locally thin portion like the thin-walled portion 33 of the sealing body 30. In other words, the bottom of the outer can 15 does not have an opening that would allow the electrode assembly 14 to be discharged to the outside.

[0021] As described above, the sealing body 30 is fixed to the upper end of the outer can 15 by the grooved portion 16 of the outer can 15 and the crimped portion 18 at the opening edge of the outer can 15 that is crimped to the sealing body 30. The crimped portion 18 is formed by bending the opening edge of the outer can 15 radially inward, and together with the grooved portion 16, it clamps the outer peripheral portion 32 of the sealing body 30 from both sides in the thickness direction. The length of the crimped portion 18 along the radial direction of the outer can 15 is preferably shorter than the length of the grooved portion 16 along the radial direction of the outer can 15. In other words, the tip position of the grooved portion 16 is located radially inward of the outer can 15 relative to the tip position of the crimped portion 18.

[0022] The sealing body 30 of the first embodiment will be described in detail below with reference to Figures 2 and 3. Figure 2 is an enlarged view of part A in Figure 1. Figure 3 shows the sealing body 30, where (a) is a bottom view of the sealing body 30 and (b) is a cross-sectional view taken along line BB in (a).

[0023] 2 and 3 , the sealing body 30 has a central portion 31 located on an extension of the central axis α of the electrode body 14 (see FIG. 2 ), an outer peripheral portion 32 to which the opening edge of the grooved portion 16 is fixed by crimping, and a thin-walled portion 33 that is thinner than the central portion 31 and the outer peripheral portion 32. The thin-walled portion 33 is located between the central portion 31 and the outer peripheral portion 32 and is preferably formed in an annular shape when viewed from the bottom of the sealing body 30. Note that the bottom view of the sealing body 30 refers to the inner surface of the sealing body 30 facing the inside of the cylindrical battery 10, viewed from a direction perpendicular to the inner surface. The thin-walled portion 33 preferably surrounds the central portion 31 and has a constant width (length along the radial direction of the sealing body 30) around the entire circumference.

[0024] As described above, the sealing body 30 is a disc-shaped metal member, and the thin-walled portion 33 is configured to rupture preferentially when the internal pressure of the battery increases. While the material of the sealing body 30 is not particularly limited, a suitable example of a material is aluminum or an aluminum alloy. When an abnormality occurs in the battery and the internal pressure exceeds a predetermined value, the thin-walled portion 33 ruptures, forming an opening in the area surrounded by the thin-walled portion 33. In the cylindrical battery 10, gas is released to the outside through this opening, and the electrode assembly 14 is also discharged. The cylindrical battery 10 is designed so that no opening is formed in the bottom of the outer can 15, and gas is released to the outside and the electrode assembly 14 is discharged only through the opening in the sealing body 30. In this case, for example, in a battery module including multiple cylindrical batteries 10, the exhaust duct structure can be simplified, allowing the battery module to be made more compact.

[0025] As will be described in more detail below, the sealing body 30 is configured so that the opening diameter expands in stages. This allows the electrode body 14 to be smoothly ejected through the opening of the sealing body 30 in the event of a battery abnormality. The thin-walled portion 33 includes an easily breakable portion 34 that is formed in an annular shape when viewed from the bottom of the sealing body 30, and an outer thin-walled portion 35 that is located closer to the outer periphery 32 than the easily breakable portion 34. When the internal pressure of the battery exceeds a predetermined value, the easily breakable portion 34 breaks, forming an opening. If the electrode body 14 clogs the opening and cannot be properly ejected, for example, gas release is hindered, further increasing the internal pressure. In this case, the outer thin-walled portion 35 bends outward (upward) from the battery, expanding the opening diameter.

[0026] It is conceivable to increase the diameter of the easily breakable portion 34 of the sealing body 30 to form a large opening from the beginning, but in this case, the pressure required to eject the electrode body 14 would decrease, and it may be impossible to eject the electrode body 14. For this reason, a configuration in which the opening of the sealing body 30 is gradually enlarged is effective for smoothly ejecting the electrode body 14 from the outer can 15. Furthermore, if the opening of the sealing body 30 widens radially outward from the outer can, problems such as damage to the side surface of the outer can are expected. Therefore, a design in which the opening diameter is enlarged when the electrode body 14 becomes clogged in the opening, as in the present embodiment, is preferable. Note that, because the opening diameter of the sealing body 30 is smaller than the diameter of the electrode body 14, the electrode body 14 is ejected to the outside while its wound structure unwinds.

[0027] The central portion 31 is formed in the radial center of the sealing body 30 and is positioned opposite the winding core portion of the electrode body 14. The central portion 31 has a circular shape when viewed from the bottom of the sealing body 30, and the center β of the circle of the central portion 31 (see FIG. 3( a)) is preferably located on an extension of the central axis α of the electrode body 14. A hollow portion is formed in the winding core of the electrode body 14, and this hollow portion functions as a gas exhaust path in the event of a battery abnormality. The central portion 31 is positioned opposite the entire hollow portion in the vertical direction of the cylindrical battery 10 and receives gas exhausted from the electrode body 14 through the hollow portion. The diameter of the central portion 31 is, for example, 25% to 55% or 30% to 50% of the diameter of the sealing body 30.

[0028] The central portion 31 is a portion to which the positive electrode lead 20 is welded. Furthermore, since the sealing body 30 functions as a positive electrode external terminal, an external lead on the positive electrode side is welded to the outer surface of the central portion 31. Furthermore, the central portion 31 is directly hit by gas discharged from the electrode body 14 in the event of an abnormality. For this reason, the central portion 31 preferably has excellent mechanical strength, and is formed with a large thickness. The thickness of the central portion 31 is the largest in the sealing body 30, and is, for example, 0.8 mm or more and 2 mm or less. The thickness of the central portion 31 may vary slightly, but in this embodiment, it is substantially constant throughout the entire area.

[0029] The outer peripheral portion 32 is formed radially outward of the sealing body 30 and is sandwiched between the grooved portion 16 and the crimped portion 18 via the gasket 17. The outer peripheral portion 32 is formed in an annular shape when viewed from the bottom of the sealing body 30 and surrounds the thin-walled portion 33. The outer peripheral portion 32 is formed with a constant width around the entire circumference. The width of the outer peripheral portion 32 is, for example, 3% to 15% or 5% to 10% of the diameter of the sealing body 30. The thickness of the outer peripheral portion 32 is smaller than the thickness of the central portion 31 and larger than the outer thin-walled portion 35 and the inner thin-walled portion 36 (described later) of the thin-walled portion 33. The thickness of the outer peripheral portion 32 is, for example, 40% to 80% or 50% to 70% of the thickness of the central portion 31.

[0030] As described above, the thin-walled portion 33 includes the easily breakable portion 34 and the outer thin-walled portion 35, and is formed in an annular shape between the central portion 31 and the outer peripheral portion 32. The thin-walled portion 33 further includes an inner thin-walled portion 36 located closer to the central portion 31 than the easily breakable portion 34. If the inner thin-walled portion 36 were not present, a steep difference in thickness would be formed between the central portion 31 and the easily breakable portion 34, which could lead to problems such as difficulty in machining the thin-walled portion 33 and difficulty in gradually increasing the opening diameter due to the increased mass of the portion that would be blown away in the event of an abnormality. For this reason, it is preferable to provide the inner thin-walled portion 36.

[0031] The thin-walled portion 33 is provided by forming a groove on the inner surface of the sealing body 30. Therefore, the portion of the inner surface of the sealing body 30 where the thin-walled portion 33 is formed is recessed. In this embodiment, the portion of the outer surface of the sealing body 30 where the thin-walled portion 33 is formed protrudes slightly outward. The inner thin-walled portion 36, the easily breakable portion 34, and the outer thin-walled portion 35 are all formed in annular shapes and are arranged in this order from the central portion 31 side. It is preferable that the inner thin-walled portion 36, the easily breakable portion 34, and the outer thin-walled portion 35 are formed on concentric circles centered on the center β of the central portion 31. In this case, when the internal pressure of the battery reaches a predetermined value, an opening in the sealing body 30 is stably formed, allowing the electrode body 14 to be ejected more smoothly.

[0032] The easily breakable portion 34 has the smallest thickness among the thin-walled portions 33 and is the portion that will break preferentially when the internal pressure of the battery exceeds a predetermined value. When viewed from the bottom of the sealing body 30, the easily breakable portion 34 is formed in an annular shape that surrounds the inner thin-walled portion 36 and has a constant thickness around the entire circumference. The thickness of the easily breakable portion 34 is not limited to a specific thickness as long as it does not break during use but breaks when the internal pressure of the battery reaches a predetermined value, but an example of a suitable thickness is 5% to 30% or 10% to 25% of the thickness of the central portion 31.

[0033] The easily breakable portion 34 is formed in the deepest part of the annular groove that forms the thin-walled portion 33, and is the portion of the sealing body 30 that protrudes furthest outward from the battery. The easily breakable portion 34 is preferably formed in a thin line shape when viewed from the bottom of the sealing body 30. Furthermore, when viewed in cross section of the sealing body 30, the easily breakable portion 34 can be said to be formed at the intersection of the outer thin-walled portion 35 and the inner thin-walled portion 36, and is located at the apex of a substantially V-shape formed by the inner surfaces of the outer thin-walled portion 35 and the inner thin-walled portion 36. In this case, when the internal pressure of the battery exceeds a predetermined value, the sealing body 30 is likely to break along the easily breakable portion 34, and an opening is stably formed in the portion surrounded by the easily breakable portion 34. The outer thin-walled portion 35 and the inner thin-walled portion 36 may have bent portions as long as their respective functions are not impaired.

[0034] The outer thin-walled portion 35 is a thin-walled portion located between the outer peripheral portion 32 and the easily breakable portion 34, and its thickness is smaller than the thicknesses of the central portion 31 and the outer peripheral portion 32 and larger than the thickness of the easily breakable portion 34. Furthermore, as will be described in detail later, the thickness of the outer thin-walled portion 35 is preferably smaller than the thickness of the inner thin-walled portion 36. The outer thin-walled portion 35 is formed in a circular ring shape surrounding the easily breakable portion 34 and the inner thin-walled portion 36 in a bottom view of the sealing body 30, and has a constant width around the entire circumference. The outer thin-walled portion 35 is formed point-symmetrically with respect to the center β of the central portion 31 (a position on an extension of the central axis α of the electrode body 14). When the easily breakable portion 34 breaks to form an opening, the outer thin-walled portion 35 remains in the battery as the periphery of the opening.

[0035] The outer thin-walled portion 35 is inclined at a predetermined angle relative to the radial direction of the sealing body 30, and both the outer and inner surfaces of the outer thin-walled portion 35 are inclined so as to gradually decrease in size from the easily breakable portion 34 toward the outer periphery 32. Therefore, when the electrode body 14 is ejected from the opening in the sealing body 30 formed by the breakage of the easily breakable portion 34, the electrode body 14 is less likely to get caught on the periphery of the opening. However, because the diameter of the opening in the sealing body 30 is smaller than the diameter of the electrode body 14, if the electrode body 14 is not properly unraveled and ejected, the electrode body 14 may become stuck in the opening. As described above, the outer thin-walled portion 35 has the function of deforming outward from the battery to expand the opening diameter when the electrode body 14 becomes stuck in the opening of the sealing body 30.

[0036] The thickness of the outer thin portion 35 gradually increases from the easily breakable portion 34 toward the outer peripheral portion 32. In a cross-sectional view of the sealing body 30, both the outer surface and the inner surface of the outer thin portion 35 are formed linearly, and the inclination angle with respect to the radial direction of the sealing body 30 is larger on the inner surface than on the outer surface. This results in a difference in thickness between the tip side of the outer thin portion 35, which is on the easily breakable portion 34 side, and the base side of the outer thin portion 35, which is on the outer peripheral portion 32 side. The minimum thickness of the outer thin portion 35 is, for example, 25% to 75% or 35% to 65% of the maximum thickness of the outer thin portion 35. Furthermore, the maximum thickness of the outer thin portion 35 is preferably 105% to 800% of the thickness of the easily breakable portion 34.

[0037] If the thickness of outer thin portion 35 were constant, for example, a large step would be formed at the boundary with easy-to-break portion 34, making it difficult to process thin portion 33, or outer thin portion 35 would become too thin, reducing the strength on the outer periphery of sealing body 30. By gradually increasing the thickness of outer thin portion 35 from the tip side toward the base side, in other words, by gradually decreasing the thickness from the base side toward the tip side, outer thin portion 35 can be more smoothly deformed when electrode body 14 gets stuck in the opening while maintaining the strength of sealing body 30.

[0038] The outer thin-walled portion 35 further has a notch 37 formed on the base side, away from the fragile portion 34. The notch 37 is a cutout formed on the inner surface of the outer thin-walled portion 35, and is preferably formed in an annular shape along the circumferential direction of the outer thin-walled portion 35. The notch 37 can be considered an annular groove, and is preferably formed at the base of the outer thin-walled portion 35 adjacent to the outer peripheral portion 32. The notch 37 forms a thin portion at the base of the outer thin-walled portion 35, making the base of the outer thin-walled portion 35 more likely to bend when the electrode body 14 gets stuck in the opening and a strong force acts on the outer thin-walled portion 35. The outer thin-walled portion 35 bends at the base and deforms outward, thereby more effectively enlarging the opening diameter.

[0039] The outer thin-walled portion 35 is formed radially inward of the tip of the grooved portion 16 of the outer can 15. Furthermore, since the tip of the crimped portion 18 is located radially outward of the outer can 15 from the tip of the grooved portion 16, the outer thin-walled portion 35 is formed radially inward of the outer can 15 from the tip of the crimped portion 18. Because a large force is likely to act on the portion supported by the grooved portion 16 and pressed by the crimped portion 18, it is preferable not to form a thin-walled portion that would preferentially cause rupture or deformation of the sealing body 30 when the internal pressure of the battery increases radially outward of the tip of the grooved portion 16 and the crimped portion 18 on the outer can 15.

[0040] The inner thin-walled portion 36 is a thin-walled portion located between the central portion 31 and the easily breakable portion 34, and its thickness is smaller than the thicknesses of the central portion 31 and the outer peripheral portion 32, but larger than the thickness of the easily breakable portion 34. The thickness of the inner thin-walled portion 36 is preferably larger than the thickness of the outer thin-walled portion 35. Like the outer thin-walled portion 35, the inner thin-walled portion 36 is formed in a circular ring shape surrounding the central portion 31 in a bottom view of the sealing body 30, and has a constant width around the entire circumference. When the easily breakable portion 34 breaks and an opening is formed, the inner thin-walled portion 36 is separated from the battery together with the central portion 31. In other words, the central portion 31 and the inner thin-walled portion 36 are blown away, forming an opening where the central portion 31 and the inner thin-walled portion 36 were previously located.

[0041] The inner thin portion 36 is inclined at a predetermined angle relative to the radial direction of the sealing body 30, and both the outer surface and the inner surface of the inner thin portion 36 are inclined so as to gradually decrease in size from the easily breakable portion 34 toward the central portion 31. The inner thin portion 36 also gradually increases in thickness from the easily breakable portion 34 toward the central portion 31. In a cross-sectional view of the sealing body 30, both the outer surface and the inner surface of the inner thin portion 36 are linear, and the angle of inclination relative to the radial direction of the sealing body 30 is greater on the inner surface than on the outer surface. This results in a difference in thickness between the easily breakable portion 34 side of the inner thin portion 36 and the central portion 31 side. The minimum thickness of the inner thin portion 36 is, for example, 25% to 75% or 35% to 65% of the maximum thickness of the inner thin portion 36.

[0042] The thickness of the inner thin portion 36 is preferably greater than the thickness of the outer thin portion 35. By forming the inner thin portion 36 thicker than the outer thin portion 35, when the internal pressure of the battery exceeds a predetermined value, the inner thin portion 36 is deformed, and the sealing body 30 is prevented from inverting, which would cause the central portion 31 to become convex upward. If the sealing body 30 does not invert when the internal pressure reaches a predetermined value but instead ruptures at the easy-to-rupture portion 34, an opening is formed more stably and the electrode body 14 can be ejected more smoothly. It is preferable that both the maximum thickness and the average thickness of the inner thin portion 36 be greater than that of the outer thin portion 35.

[0043] The width of the inner thin portion 36 is preferably greater than the width of the outer thin portion 35. Here, the width of each thin portion refers to the length along the radial direction of the sealing body 30. The width of the inner thin portion 36 is, for example, 1.1 to 2.5 times, or 1.3 to 2.0 times, the width of the outer thin portion 35. Furthermore, as described above, when the inner surfaces of the outer thin portion 35 and the inner thin portion 36 form a substantially V-shape in a cross-sectional view of the sealing body 30, the angle formed by the inner surfaces of the thin portions is, for example, 100° to 150°, or 110° to 140°. In this case, an opening is more likely to be formed when the internal pressure of the battery reaches a predetermined value, allowing for smoother removal of the electrode body 14.

[0044] The sealing body 40 of the second embodiment will be described in detail below with reference to Fig. 4. Fig. 4 shows the sealing body 40, where (a) is a bottom view of the sealing body 40, (b) is a cross-sectional view taken along line CC in (a), and (c) is a cross-sectional view taken along line DD in (a). Below, overlapping descriptions of content common to the sealing body 30 of the first embodiment will be omitted, and differences from the sealing body 30 will be mainly described.

[0045] As shown in FIG. 4 , the sealing body 40 is similar to the sealing body 30 in that it has a central portion 41, an outer peripheral portion 42, and a thin-walled portion 43 that is thinner than the central portion 41 and the outer peripheral portion 42. Similarly to the thin-walled portion 33 of the sealing body 30, the thin-walled portion 43 of the sealing body 40 includes an easily breakable portion 44 that is formed in an annular shape in a bottom view of the sealing body 40, an outer thin-walled portion 45 located closer to the outer peripheral portion 42 than the easily breakable portion 44, and an inner thin-walled portion 46 located closer to the central portion 41 than the easily breakable portion 44. However, the sealing body 40 differs from the sealing body 30 in that the outer thin-walled portion 45 includes a second region 49 that is formed as two or more straight lines aligned in the radial direction of the sealing body 40 in a bottom view of the sealing body 40. The thickness of the sealing body 40 is thinnest at the intersection of the easily breakable portion 44 and the second region 49.

[0046] The outer thin-walled portion 45 is similar to the outer thin-walled portion 35 of the sealing body 30 in that it includes a first region 48 formed in an annular shape surrounding the fragile portion 44. However, it differs from the outer thin-walled portion 35 in that it includes a second region 49 within the first region 48 that is thinner than the other portions of the first region 48. As shown in FIG. 4( b ), the radial cross-sectional shape of the sealing body 40 in the portion where the second region 49 does not exist (i.e., the other portions of the first region 48) is the same as the radial cross-sectional shape of the sealing body 30. Note that the radial cross-sectional shape of the sealing body 30 is the same throughout the entire circumference. On the other hand, as shown in FIG. 4( c ), the thickness of the outer thin-walled portion 45 is further reduced in the portion where the second region 49 is formed.

[0047] The second region 49 of the outer thin-walled portion 45 breaks preferentially, for example, when the electrode body 14 fills the opening formed by the breakage of the easily breakable portion 44 and a large force acts on the outer thin-walled portion 45, and a notch extending radially of the sealing body 30 is made in the outer thin-walled portion 45. As a result, the outer thin-walled portion 45 is more likely to deform outward, and the opening expands more smoothly. In other words, by forming the second region 49, which is even thinner, in part of the annular first region 48, sufficient strength can be ensured during normal use while promoting deformation of the outer thin-walled portion 45 when an abnormality occurs.

[0048] The first region 48 and the second region 49 of the outer thin portion 45 are each formed point-symmetrically with respect to the center β of the central portion 41 (a position on an extension of the central axis α of the electrode body 14). The second regions 49 are formed by narrow grooves extending radially on the inner surface of the sealing body 40, and multiple second regions 49 are arranged at intervals around the circumferential direction of the first region 48. For example, four second regions 49 are arranged at equal intervals, and each second region 49 is aligned with another second region 49 in the radial direction of the sealing body 40. That is, in a bottom view of the sealing body 40, one second region 49 is arranged on the extension line of each second region 49, and the extension lines of the second regions 49 intersect at right angles at the center β of the central portion 41, forming a cross shape. In this case, the cuts are made at equal intervals around the circumferential direction of the outer thin portion 45, and the effect of providing the second regions 49 is more pronounced.

[0049] The second region 49 extends from the easily breakable portion 44 to the outer peripheral portion 42 along the radial direction of the sealing body 40. The second region 49 is formed to a length that does not extend beyond the first region 48. The number of second regions 49 may be two, but three or more is preferable, and four or more is particularly preferable. As described above, the four second regions 49 are arranged at equal intervals in the circumferential direction of the first region 48, and each preferably has the same width, length, and thickness. Note that when there are three second regions 49, they are not lined up in the radial direction of the sealing body 40, but even in this case, the second regions 49 are preferably arranged at equal intervals in the circumferential direction of the first region 48.

[0050] A notch 47 is preferably formed at the base of the outer thin-walled portion 45, similar to the outer thin-walled portion 35. In this embodiment, the notch 47 is formed annularly around the entire circumference of the outer thin-walled portion 45, including the second region 49. The second region 49 may be formed radially from the easily breakable portion 44, with the center β of the central portion 41 as the center. In this specification, the formation of five or more second regions 49 is defined as a radial formation. Furthermore, the second region formed within the annular first region 48 may be formed spirally from the easily breakable portion 44.

[0051] As described above, in a cylindrical battery equipped with the sealing body 30 or 40, in the event of a battery abnormality, the electrode body 14 and gas are smoothly discharged through an opening formed by the rupture of the thin-walled portion of the sealing body. As a result, further temperature increases in the cylindrical battery are suppressed. When a battery abnormality occurs and the internal pressure exceeds a predetermined value, the easily breakable portions 34, 44 rupture, forming an opening in the sealing body 30, 40. Gas is released to the outside through this opening, and the electrode body 14 is discharged. However, the electrode body 14 may become clogged in the opening. In such a case, in a cylindrical battery equipped with the sealing body 30 or 40, the outer thin-walled portions 35, 45 function to expand the opening, thereby eliminating the clog of the electrode body 14 and enabling the electrode body 14 to be more reliably discharged to the outside. Furthermore, regardless of the discharge of the electrode body 14, the expanded opening diameter increases the amount of gas discharged.

[0052] The above-mentioned effects are more pronounced when the thin-walled portions 33, 43 of the sealing bodies 30, 40 have the above-mentioned preferred configuration. For example, gradually reducing the thickness of the outer thin-walled portion from the outer periphery of the sealing body toward the easily breakable portion can ensure sufficient strength of the sealing body during normal use while facilitating deformation of the outer thin-walled portion when the electrode body 14 becomes lodged in the opening. Similarly, a notch formed at the base of the outer thin-walled portion also facilitates deformation of the outer thin-walled portion when the electrode body 14 becomes lodged in the opening.

[0053] The above-described embodiments can be modified as needed without sacrificing the purpose of the present disclosure. For example, although the sealing bodies 30, 40 of the above-described embodiments have the inner thin-walled portions 36, 46, they can also be configured without the inner thin-walled portions 36, 46. In this case, an easily breakable portion is formed adjacent to the center of the sealing body. However, in this case, the above-described function of the inner thin-walled portions 36, 46 would be lost, so it is desirable to provide the inner thin-walled portions.

[0054] Furthermore, in the gasket 40, a thin-line second region 49 is formed radially of the gasket 40 within the annular first region 48. However, it is also possible to form only the thin-line second region 49 without forming the annular first region 48. The outer thin-walled portion may be formed, for example, in a spiral shape, a radial shape, or two or more straight lines aligned radially from the fragile portion when viewed from the bottom of the gasket. In this case, too, the radially or linearly formed outer thin-walled portion is preferably formed point-symmetrically with respect to a position on an extension of the central axis of the electrode assembly. However, if an annular outer thin-walled portion is not provided, the peripheral edge of the opening formed by the fracture of the fragile portion is less likely to deform than if an annular outer thin-walled portion is present.

[0055] In a cross-sectional view of the sealing bodies 30 and 40, both the outer and inner surfaces of the outer thin-walled portions 35 and 45 are linear, but this is not limiting. Figures 5 to 7 are vertical cross-sectional views of essential portions of sealing bodies 50, 60, and 70, showing the essential portions of a cross section passing through the central axis of the electrode assembly. Each sealing body 50, 60, and 70 has a central portion 51, 61, and 71, an outer peripheral portion 52, 62, and 62, a thin-walled portion 53, 63, and 73, a fragile portion 54, 64, and 74, and an outer thin-walled portion 55, 65, and 75. As shown in Figure 5, the inner surface of the outer thin-walled portion 55 may be stepped. Alternatively, as shown in Figure 6, the outer thin-walled portion 65 may have a curved inner surface with a concave center. Furthermore, as shown in Figure 7, the outer thin-walled portion 75 may have a curved inner surface with a convex center.

[0056] Furthermore, in the above embodiment, the easily breakable portions 34, 44, 54, 64, and 74 are described as being formed in a circular ring shape when viewed from the bottom of the sealing body, but the outer shape of the easily breakable portions 34, 44, 54, 64, and 74 may be a ring formed by a wavy line, or may have a geometric shape.

[0057] The present disclosure is further described by the following embodiments. Configuration 1: A cylindrical battery comprising a wound electrode assembly, a bottomed cylindrical outer can housing the electrode assembly, and a sealing body closing the opening of the outer can, the battery being configured so that the electrode assembly can be removed from the opening of the outer can, wherein the sealing body has a central portion located on an extension of the central axis of the electrode assembly, an outer periphery to which an edge of the opening of the outer can is crimped, and a thin-walled portion located between the central portion and the outer periphery and thinner than the central portion and the outer periphery, the thin-walled portion including an easily breakable portion formed in an annular shape in a bottom view of the sealing body, and an outer thin-walled portion located closer to the outer periphery than the easily breakable portion. Configuration 2: The cylindrical battery according to Configuration 1, wherein the thin-walled portion further includes an inner thin-walled portion located closer to the central portion than the easily breakable portion. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein the outer thin-walled portion gradually increases in thickness from the easily breakable portion toward the outer periphery. The cylindrical battery of any one of Configurations 1 to 3, wherein the outer thin-walled portion includes a first region that is formed in a spiral shape, a radial shape, or two or more straight lines aligned in a radial direction of the sealing body from the easily breakable portion, or a ring shape surrounding the easily breakable portion, or a ring shape surrounding the easily breakable portion, and a second region that is formed in the first region in a spiral shape, a radial shape, or two or more straight lines aligned in a radial direction of the sealing body and is thinner than the rest of the first region. Configuration 5: The cylindrical battery of any one of Configurations 1 to 3, wherein the outer thin-walled portion includes a first region that is formed in a ring shape, or a ring shape surrounding the easily breakable portion, or a ring shape surrounding the easily breakable portion, and a second region that is formed in the first region in a spiral shape, a radial shape, or two or more straight lines aligned in a radial direction of the sealing body and is thinner than the rest of the first region. The cylindrical battery of any one of the preceding embodiments, wherein the outer thin-walled portion is formed point-symmetrically with respect to a position on an extension line of the central axis of the electrode body. The cylindrical battery of any one of the preceding embodiments, wherein the outer thin-walled portion further has a notch formed on a base side away from the fragile portion.Configuration 8: The cylindrical battery according to any one of Configurations 1 to 7, wherein the thin-walled portion further includes an inner thin-walled portion located closer to the center than the fragile portion, and wherein the length of the inner thin-walled portion along the radial direction of the sealing body is longer than the length of the outer thin-walled portion along the radial direction of the sealing body.Configuration 9: The cylindrical battery according to any one of Configurations 1 to 8, wherein the thin-walled portion further includes an inner thin-walled portion located closer to the center than the fragile portion, and wherein the maximum thickness of the inner thin-walled portion is greater than the maximum thickness of the outer thin-walled portion.Configuration 10: The cylindrical battery according to any one of Configurations 1 to 9, wherein the bottom of the outer can does not have a portion that will preferentially break when the battery internal pressure increases.Configuration 11: The cylindrical battery according to any one of Configurations 1 to 10, wherein the outer can has a grooved portion that supports the sealing body, and the outer thin-walled portion is formed radially inward of the outer can relative to the tip of the grooved portion.

[0058] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer can, 16 Grooved portion, 17 Gasket, 18 Crimped portion, 20 Positive electrode lead, 21 Negative electrode lead, 22, 23 Insulating plate, 30, 40, 50, 60, 70 Sealing body, 31, 41, 51, 61, 71 Central portion, 32, 42, 52, 62, 72 Outer peripheral portion, 33, 43, 53, 63, 73 Thin portion, 34, 44, 54, 64, 74 Easily breakable portion, 35, 45, 55, 65, 75 Outer thin portion, 36, 46, 56, 66, 76 Inner thin portion, 37, 47 Notch, 48 First region, 49 Second region

Claims

1. A cylindrical battery comprising a wound electrode assembly, a cylindrical outer can with a bottom that houses the electrode assembly, and a sealing body that closes the opening of the outer can, wherein the electrode assembly can be removed from the opening of the outer can, wherein the sealing body has a central portion that is positioned on an extension of the central axis of the electrode assembly, an outer periphery to which the edge of the opening of the outer can is crimped, and a thin-walled portion that is positioned between the central portion and the outer periphery and is thinner than the central portion and the outer periphery, and the thin-walled portion includes an easily breakable portion that is formed in an annular shape when viewed from the bottom of the sealing body, and an outer thin-walled portion that is positioned closer to the outer periphery than the easily breakable portion.

2. The cylindrical battery according to claim 1, wherein the thin-walled portion further includes an inner thin-walled portion located closer to the central portion than the easily breakable portion.

3. The cylindrical battery according to claim 2, wherein the thickness of the outer thin-walled portion gradually increases from the easily breakable portion toward the outer periphery.

4. The cylindrical battery described in claim 2, wherein the outer thin portion includes a first region that is formed in a spiral shape, radial shape, or two or more straight lines aligned in the radial direction of the sealing body from the easily breakable portion, or formed in a circular ring shape surrounding the easily breakable portion, or formed in a circular ring shape surrounding the easily breakable portion, when viewed from the bottom of the sealing body, and a second region that is thinner than other parts of the first region and is formed in a spiral shape, radial shape, or two or more straight lines aligned in the radial direction of the sealing body within the first region.

5. A cylindrical battery as described in claim 4, wherein the outer thin-walled portion is formed in a circular ring shape surrounding the easily breakable portion when viewed from the bottom of the sealing body, or includes a first region formed in a circular ring shape surrounding the easily breakable portion, and a second region formed within the first region in a spiral shape, a radial shape, or two or more straight lines aligned in the radial direction of the sealing body, and which is thinner than other parts of the first region.

6. The cylindrical battery according to claim 4, wherein the outer thin-walled portion is formed point-symmetrically with respect to a position on an extension of the central axis of the electrode body.

7. The cylindrical battery according to claim 2, wherein the outer thin-walled portion further has a notch formed on the base side away from the easily breakable portion.

8. The cylindrical battery according to claim 2, wherein the length of the inner thin portion along the radial direction of the sealing body is longer than the length of the outer thin portion along the radial direction of the sealing body.

9. The cylindrical battery according to claim 2, wherein the thickness of the inner thin-walled portion is greater than the thickness of the outer thin-walled portion.

10. A cylindrical battery according to any one of claims 1 to 9, wherein the bottom of the outer can does not have a portion that will preferentially break when the internal pressure of the battery increases.

11. A cylindrical battery according to any one of claims 1 to 9, wherein the outer can has a grooved portion that supports the sealing body, and the outer thin-walled portion is formed radially inward of the outer can relative to the tip of the grooved portion.

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