Cylindrical battery

Abstract

This cylindrical battery (10) has a structure in which an opening edge part (18) of an exterior can (15) is caulked and fixed to a sealing body (30) via a gasket (17), and the exterior can (15) and the sealing body (30) function as an external terminal pair. The sealing body (30) has an annular thin-walled part (33) including an easily breakable portion (34) that breaks when the internal pressure of the battery reaches a predetermined value. The easily breakable portion (34) is formed along the outer peripheral edge of the thin-walled part (33), and an axial cross-section of the battery cut along a plane including the central axis (α) of the exterior can (15) includes an asymmetric cross-section in which the shape of the thin-walled part (33) is laterally asymmetric with respect to the central axis (α).

Description

Cylindrical battery

[0001] The present disclosure relates to a cylindrical battery.

[0002] Conventionally, a cylindrical battery including an electrode body, a bottomed cylindrical outer can for housing the electrode body, and a sealing body for closing the opening of the outer can has been widely known (see, for example, Patent Documents 1 and 2). The cylindrical battery has, for example, a structure in which the opening edge of the outer can is caulked and fixed to the sealing body via a gasket, and the outer can and the sealing body function as an external terminal pair. Patent Document 1 discloses a cylindrical battery having a cylindrical battery case having openings at both axial ends and electrode caps attached to the respective openings of the case and functioning as safety valves. Further, Patent Document 2 discloses a cylindrical battery having a diaphragm in which a cleavage groove that breaks when the internal pressure of the battery reaches a predetermined value is formed.

[0003] Japanese Patent Application Laid-Open No. 2003-115285, Japanese Patent Application Laid-Open No. 2006-338981

[0004] By the way, when an abnormality occurs in the battery and the temperature of the battery rises, it is desirable to smoothly discharge gas from the outer can and also discharge the electrode body to suppress further temperature rise. In a cylindrical battery, for example, due to an increase in internal pressure, the bottom or the sealing body of the outer can breaks to form an opening, and gas and the electrode body are discharged from the opening. However, it is also assumed that the electrode body is not smoothly discharged. In this case, the higher the electrical energy of the electrode body, the greater the temperature rise of the battery.

[0005] The cylindrical battery according to this disclosure comprises a wound electrode body, a bottomed cylindrical outer casing for housing the electrode body, a sealing body for closing the opening of the outer casing, and a gasket interposed between the outer casing and the sealing body, wherein the opening edge of the outer casing is crimped and fixed to the sealing body via the gasket, and the outer casing and the sealing body function as an external terminal pair, wherein the sealing body has an annular thin-walled portion including an easily breakable portion that breaks when the internal pressure of the battery reaches a predetermined value, and a central portion surrounded by the thin-walled portion and formed to be thicker than the thin-walled portion, wherein the easily breakable portion is formed along the outer edge of the thin-walled portion, and the axial cross-section of the battery cut by a plane including the central axis of the outer casing includes an asymmetric cross-section in which the shape of the thin-walled portion is asymmetrical with respect to the central axis.

[0006] According to the cylindrical battery of this disclosure, if a malfunction occurs in the battery and the sealing body opens, the temperature rise of the battery can be effectively suppressed. In the cylindrical battery of this disclosure, the sealing body breaks at the easily breakable portion, forming an opening. At this time, the portion of the sealing body surrounded by the easily breakable portion rotates in a specific direction and opens, contacting the opening edge of the outer casing and causing a short circuit. As a result, the electrical energy of the electrode body can be reduced, and even if the electrode body is not smoothly discharged from the outer casing, the temperature rise of the battery can be suppressed.

[0007] This is a cross-sectional view of a cylindrical battery, which is one example of an embodiment. This is a diagram showing a sealing body, which is one example of an embodiment, where (a) is a bottom view of the sealing body, (b) is a cross-sectional view along line AA in (a), and (c) is a cross-sectional view along line BB in (a). This is a cross-sectional view showing a state in which the easily breakable part of the sealing body, which is one example of an embodiment, has broken and an opening has been formed. This is a diagram showing a sealing body, which is another example of an embodiment, where (a) is a bottom view of the sealing body, (b) is a cross-sectional view along line CC in (a), and (c) is a cross-sectional view along line DD in (a). This is a diagram showing a sealing body, which is yet another example of an embodiment, where (a) is a bottom view of the sealing body, (b) is a cross-sectional view along line EE in (a), and (c) is a cross-sectional view along line FF in (a).

[0008] Hereinafter, an example of an embodiment of the cylindrical battery according to this disclosure will be described in detail with reference to the drawings. Note that the configurations obtained by selectively combining the various embodiments and modified components described below are included within the scope of this disclosure.

[0009] Figure 1 is a cross-sectional view of a cylindrical battery 10, which is an example of an embodiment, and is an axial cross-sectional view of the cylindrical battery 10 cut along a plane containing the central axis α of the outer casing 15. As shown in Figure 1, the cylindrical battery 10 comprises a wound electrode body 14, a bottomed cylindrical outer casing 15 that houses the electrode body 14, and a sealing body 30 that closes the opening of the outer casing 15. The outer casing 15 and the sealing body 30 function as an external terminal pair. The cylindrical battery 10 also includes an electrolyte, which is housed in the outer casing 15 together with the electrode body 14. The cylindrical battery 10 further includes a gasket 17. The gasket 17 is interposed between the outer casing 15 and the sealing body 30 to ensure airtightness inside the battery and to prevent electrical contact between the outer casing 15 and the sealing body 30, which function as an external terminal pair.

[0010] As will be described in more detail later, the sealing body 30 has an annular thin-walled portion 33 that includes an easily breakable portion 34 that breaks when the internal pressure of the battery reaches a predetermined value. Furthermore, the axial cross-section of the battery, when cut by a plane containing the central axis α of the outer casing 15, includes an asymmetrical cross-section in which the shape of the thin-walled portion 33 is asymmetrical with respect to the central axis α. Figure 1 shows this asymmetrical cross-section. When an abnormality occurs in the battery and the internal pressure rises, the easily breakable portion 34 breaks and the sealing body 30 opens. At this time, due to the shape of the thin-walled portion 33 including the asymmetrical cross-section, the portion surrounded by the easily breakable portion 34 rotates in a specific direction and comes into contact with the outer casing 15, causing a short circuit. This reduces the electrical energy of the electrode body 14 and suppresses the temperature rise of the battery.

[0011] The electrode body 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 wound in a spiral shape via the separator 13. In this embodiment, the central axis of the electrode body 14 and the central axis α of the outer casing 15 coincide, and the central axis α can be said to be the central axis of the cylindrical battery 10. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in dimensions 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 the width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger in dimensions than the positive electrode 11, and two separators are arranged so as to sandwich the positive electrode 11.

[0012] The outer casing 15 is a metal container that houses the electrode body 14 and the electrolyte. The outer casing 15 has a grooved portion 16 formed on its side, which protrudes inward in part of its surface, supporting the sealing body 30. For the sake of explanation, the sealing body 30 side of the cylindrical battery 10 will be considered the top, and the bottom side of the outer casing 15 will be considered the bottom. The grooved portion 16 is preferably formed in an annular shape along the circumferential direction of the outer casing 15, and its upper surface supports the sealing body 30. The sealing body 30 is fixed to the upper part of the outer casing 15 by the grooved portion 16 and the opening edge portion 18 of the outer casing 15, which is crimped and fixed to the sealing body 30 via a gasket 17. The opening of the outer casing 15 is circular in plan view, and the sealing body 30 is similarly 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 (electrolyte solution) or a solid electrolyte. The cylindrical battery 10 is a non-aqueous electrolyte secondary battery, and among these, a lithium-ion battery is preferred.

[0014] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0015] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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 a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyethers, etc.

[0016] The positive electrode 11 comprises a long positive electrode core and a positive electrode mixture layer provided on the positive electrode core. The positive electrode core can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film with the metal arranged on its 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 later is connected. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, etc., can be used as the positive electrode active material.

[0017] The negative electrode 12 comprises 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 metal foil that is 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 the metal arranged 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 later is connected. For example, graphite or a Si-containing material can be 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 porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 (porous sheet) include polyethylene, polyolefins such as 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 aramid resin, may be formed on the surface of the separator 13, and 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.

[0019] The electrode body 14 further includes 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. In addition, insulating plates 22 and 23 are arranged above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends towards the sealing body 30 through a through hole in the insulating plate 22, and the negative electrode lead 21 extends towards the bottom of the outer can 15 through the outside of the insulating plate 23. In this embodiment, the positive electrode lead 20 is connected to the inner surface of the central part 31 of the sealing body 30 by welding or the like, so that the sealing body 30 becomes the 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 becomes the negative electrode external terminal.

[0020] The outer casing 15 is a bottomed cylindrical metal container with one end open in the axial direction, and the opening of the outer casing 15 is sealed by a sealing body 30. The constituent material of the outer casing 15 is not particularly limited, but stainless steel is one example of a preferred constituent material. Furthermore, there is no part at the bottom of the outer casing 15 that is likely to break preferentially when the internal pressure of the battery increases, such as a locally thinned part like the easily breakable portion 34 of the sealing body 30. In other words, no opening is formed at the bottom of the outer casing 15 that would allow the electrode body 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 opening edge portion 18 of the outer can 15 which is crimped to the sealing body 30 via the gasket 17. The opening edge portion 18 is bent radially inward of the outer can 15 and, together with the grooved portion 16, clamps the outer circumference 32 of the sealing body 30 from both sides in the thickness direction. In this embodiment, the length of the opening edge portion 18 along the radial direction of the outer can 15 is longer than the length of the grooved portion 16 along the radial direction of the outer can 15, and the tip position of the opening edge portion 18 is located radially inward of the outer can 15 than the tip position of the grooved portion 16.

[0022] Hereinafter, an example of an embodiment, the sealing body 30, will be described in detail with reference to Figures 2 and 3. Figure 2(a) is a bottom view of the sealing body 30, (b) is a cross-sectional view along line AA in (a), and (c) is a cross-sectional view along line BB in (a). Figure 3 shows the state in which the easily breakable portion 34 of the sealing body 30 breaks to form an opening 100, and the sealing body 30 comes into contact with the opening edge 18 of the outer casing 16, causing a short circuit between the external terminals. The bottom view of the sealing body 30 refers to the view of the inner surface of the sealing body 30 facing the inside of the cylindrical battery 10, viewed from a direction perpendicular to that inner surface.

[0023] As shown in Figure 2, the sealing body 30 has a central portion 31 positioned on the central axis α of the outer can 15, an outer peripheral portion 32 sandwiched between the grooved portion 16 and the opening edge portion 18 of the outer can 15 via a gasket 17, and an annular thin-walled portion 33 including an easily breakable portion 34. The central portion 31 is the part surrounded by the thin-walled portion 33 and is formed to be thicker than the thin-walled portion 33. The thin-walled portion 33 is located between the central portion 31 and the outer peripheral portion 32. The easily breakable portion 34 is the part that breaks when the internal pressure of the battery reaches a predetermined value and is formed along the outer peripheral edge of the thin-walled portion 33.

[0024] The sealing body 30 is a disc-shaped metal component. The constituent material of the sealing body 30 is not particularly limited, but examples of preferred constituent materials include aluminum or an aluminum alloy. When an abnormality occurs in the battery and the internal pressure reaches a predetermined value, the easily breakable portion 34 breaks, and an opening 100 is formed in the area surrounded by the easily breakable portion 34. The cylindrical battery 10 is designed so that no opening is formed at the bottom of the outer casing 15, and gas and the electrode body 14 are discharged only from the opening 100 of the sealing body 30. In this case, for example, in a battery module equipped with multiple cylindrical batteries 10, the structure of the exhaust duct can be simplified, and the battery module can be made smaller.

[0025] As will be described in more detail later, the axial cross-section of the cylindrical battery 10, cut along a plane containing the central axis α of the outer casing 15, includes an asymmetrical cross-section where the shape of the thin-walled portion 33 is asymmetrical with respect to the central axis α. The axial cross-section also includes a symmetrical cross-section where the shape of the thin-walled portion 33 is symmetrical with respect to the central axis α. The cross-section shown in Figure 2(b) is the asymmetrical cross-section, and the cross-section shown in Figure 2(c) is the symmetrical cross-section. As shown in Figure 3, when the easily breakable portion 34 of the sealing body 30 breaks, the valve portion 36, which is the part surrounded by the easily breakable portion 34, rotates in a specific direction and opens, forming an opening 100.

[0026] The central portion 31 is located on the central axis α of the outer casing 15 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. A hollow portion is formed in the winding core of the electrode body 14, and in the event of a battery malfunction, this hollow portion functions as a gas exhaust path. The central portion 31 may be positioned opposite the entire area of ​​the hollow portion in the vertical direction of the cylindrical battery 10 and receives the gas discharged 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.

[0027] The central portion 31 is the part to which the positive electrode lead 20 is welded. Furthermore, since the sealing body 30 functions as an external positive electrode terminal, the lead member is welded to the outer surface of the central portion 31. Additionally, the central portion 31 is directly hit by gas released from the electrode body 14 when a battery malfunction occurs. For this reason, the central portion 31 preferably has excellent mechanical strength, and is formed thicker than other parts. The thickness of the central portion 31 is the largest in the sealing body 30, for example, 0.8 mm to 2.0 mm. The thickness of the central portion 31 may vary slightly, but in this embodiment, it is substantially constant throughout.

[0028] The outer periphery 32 surrounds the thin-walled portion 33 and is formed with a constant width in the circumferential direction. In this embodiment, an annular, easily breakable portion 34, where the thickness of the sealing body 30 is minimized, is formed at the boundary between the outer periphery 32 and the thin-walled portion 33. The inner surface of the outer periphery 32 is formed to be substantially flat, but the thickness of the outer periphery 32 is smaller on the outer side than on the radially inner side, and a slope exists on the outer surface of the outer periphery 32. The portion sandwiched between the grooved portion 16 and the opening edge portion 18 is substantially flat. The thickness of the outer periphery 32 is, for example, 40% to 80% or 50% to 70% of the thickness of the central portion 31 in the portion sandwiched between the grooved portion 16 and the opening edge portion 18.

[0029] As described above, the thin-walled portion 33 is formed in an annular shape between the central portion 31 and the outer peripheral portion 32, and has an easily breakable portion 34 formed along its outer peripheral edge, that is, along the boundary with the outer peripheral portion 32. In this embodiment, the thin-walled portion 33 is provided by forming an annular groove 35 on the inner surface of the sealing body 30. The depth of the groove 35 changes in the radial direction of the sealing body 30, gradually becoming deeper from the radially inner side to the radially outer side. In addition, the outer surface of the sealing body 30 is inclined such that the portion where the thin-walled portion 33 is formed is gradually positioned upward toward the radially outer side of the sealing body 30.

[0030] The thickness of the thin-walled portion 33 gradually decreases from the central portion 31 towards the outer peripheral portion 32, reaching its minimum at the easily breakable portion 34. As described above, the easily breakable portion 34 is the part that preferentially breaks when the internal pressure of the battery reaches a predetermined value, and the valve portion 36, which is the part surrounded by the easily breakable portion 34, opens to form an opening 100. The thickness of the easily breakable portion 34 does not need to be any thickness that breaks when the internal pressure reaches a predetermined value and does not break during normal use of the battery, and is not limited to a specific thickness, but an example of a suitable thickness is 5% to 30% or 10% to 25% of the thickness of the central portion 31.

[0031] In this embodiment, the thickness of the easily breakable portion 34 is constant along the circumferential direction of the sealing body 30 (easily breakable portion 34). Furthermore, the easily breakable portion 34 is formed in a circular shape with respect to point Z, through which the central axis α of the outer can 15 passes, when viewed from the bottom of the sealing body 30. That is, the easily breakable portion 34 is formed in an annular shape with a constant distance from the central axis α. On the other hand, the distance from the center 31z of the central portion 31 to the easily breakable portion 34 is not constant, and the central portion 31 is biased to one side in the radial direction of the sealing body 30. And, since the central portion 31 has a circular shape when viewed from the bottom, the width of the annular thin-walled portion 33 surrounding the central portion 31 changes along the circumferential direction.

[0032] Preferably, the thin-walled portion 33 has a maximum width portion 33a where the width is greatest and a minimum width portion 33b where the width is least greatest. The axial cross-section of the cylindrical battery 10 cut by a plane containing the central axis α of the outer casing 15 (hereinafter simply referred to as the "axial cross-section") includes an asymmetric cross-section in which the shape of the thin-walled portion 33 is asymmetric with respect to the central axis α, as shown in Figure 2(b). In this asymmetric cross-section, there is a maximum width portion 33a and a minimum width portion 33b. Hereafter, the cross-section including the maximum width portion 33a and the minimum width portion 33b will be referred to as the "asymmetric cross-section S1". Furthermore, the axial cross-section of the cylindrical battery 10 includes a symmetric cross-section S2 in which the shape of the thin-walled portion 33 is asymmetric with respect to the central axis α, as shown in Figure 2(c).

[0033] The thin-walled portion 33 has a bottom view shape in which the width gradually decreases from the widest portion 33a to the narrowest portion 33b. Strictly speaking, the axial cross-section of the cylindrical battery 10 includes one symmetrical cross-section S2, and all other cross-sections are asymmetrical. Furthermore, the asymmetrical cross-section S1 and the symmetrical cross-section S2 are orthogonal to each other. As will be described in detail later, in this case, when the internal pressure of the battery increases, the easily breakable portion 34 of the widest portion 33a becomes the starting point for rupture, and the valve portion 36 opens with the easily breakable portion 34 of the narrowest portion 33b or its vicinity as the center of rotation. That is, by providing the asymmetrical cross-section S1, it becomes possible to control the rotation direction of the valve portion 36 in a specific direction.

[0034] In the asymmetric cross-section S1, the first distance D1 between the first inner periphery 33c of the thin-walled portion 33 and the central axis α is smaller than the second distance D2 between the second inner periphery 33d of the thin-walled portion 33 and the central axis α. In the asymmetric cross-section S1, the portion located between the first inner periphery 33c and the easily fractured portion 34 is the maximum width portion 33a, and the portion located between the second inner periphery 33d and the easily fractured portion 34 is the minimum width portion 33b. Since the inner periphery of the thin-walled portion 33 is the outer periphery of the central portion 31, it can be said that the central portion 31 is off-center to one side in the radial direction of the sealing body 30 from the central axis α.

[0035] In the asymmetrical cross-section S1, the difference between the first distance D1 and the second distance D2 is preferably 0.2 mm or more. In other words, the difference between the maximum width and minimum width of the thin-walled portion 33 is 0.2 mm or more. In this case, it becomes easier to control the rotational direction of the valve portion 36.

[0036] In this embodiment, since the thickness of the easily breakable portion 34 is constant along the circumferential direction, the thickness of the thin-walled portion 33 changes more abruptly at the minimum width portion 33b than at the maximum width portion 33a. Furthermore, the thickness of the thin-walled portion 33 at the second inner circumferential edge 33d is greater than the thickness at the first inner circumferential edge 33c. The thickness along the inner circumferential edge of the thin-walled portion 33 gradually increases from the maximum width portion 33a to the minimum width portion 33b. It is preferable that the width and thickness of the thin-walled portion 33 change continuously from the maximum width portion 33a to the minimum width portion 33b.

[0037] As shown in Figure 3, when the internal pressure of the cylindrical battery 10 exceeds a predetermined value and the easily ruptured portion 34 ruptures, the valve portion 36 rotates in a specific direction and opens, forming an opening 100 in the sealing body 30. Gas is discharged from the opening 100, and the electrode body 14 is discharged as the winding structure unravels. At this time, the valve portion 36 rotates with a part of it connected to the outer circumference 32 and comes into contact with the opening edge 18 of the outer casing 15. Since the sealing body 30 functions as the positive electrode external terminal and the outer casing 15 functions as the negative electrode external terminal, a short circuit occurs due to the contact between the valve portion 36 and the opening edge 18.

[0038] In the cylindrical battery 10, the electrical energy of the electrode body 14 can be reduced by short-circuiting the sealing body 30 and the outer casing 15. Therefore, even if the electrode body 14 is not smoothly discharged from the outer casing 15, the temperature rise of the battery is effectively suppressed. Although a large current flows and heat is generated at the short-circuit point, this heat does not affect the electrode body 14 because it is located away from the electrode body 14. In other words, the cylindrical battery 10 is designed so that the valve body 36 is rotated in a specific direction while the valve body 36 is not completely separated from the outer circumference 32, bringing the valve body 36 into contact with the opening edge 18 and intentionally causing a short circuit between the pairs of external terminals.

[0039] When an abnormality occurs in the cylindrical battery 10 and the internal pressure reaches a predetermined value, as described above, the easily breakable portion 34 of the widest portion 33a in the asymmetrical cross-section S1 becomes the starting point for fracture. The thickness of the easily breakable portion 34 is constant along the circumferential direction, but a large force acts on the easily breakable portion 34 of the widest portion 33a, which is far from the inner peripheral edge 33c. The easily breakable portion 34 fractures from the widest portion 33a, which is the starting point of the fracture, toward the narrowest portion 33b, but the valve portion 36 rotates with the vicinity of the narrowest portion 33b as the pivot point before the easily breakable portion 34 completely fractures. As a result, with a part of the valve portion 36 connected to the outer peripheral portion 32, it is possible to rotate the valve portion 36 in a specific direction to intentionally cause a short circuit. No members that would hinder rotation are placed on the outside of the valve portion 36, and the outer surface of the valve portion 36 is the outermost surface.

[0040] The cylindrical battery 10 may be configured to facilitate a short circuit between the outer casing 15 and the sealing body 30 when a malfunction occurs in the battery and the sealing body 30 opens. In this embodiment, the opening edge 18 of the outer casing 15 extends radially inward beyond the tip position of the grooved portion 16, and the inner circumference of the opening edge 18 coincides with the inner circumference of the gasket 17. In this case, the valve portion 36 is more likely to come into contact with the opening edge 18 when it rotates. In conventional cylindrical batteries, the inner circumference of the gasket is located radially inward of the sealing body than the inner circumference of the opening edge.

[0041] The opening edge 18 of the outer can 15 is formed to be the same length all around, for example, and its inner edge coincides with the inner edge of the gasket 17 along its entire length. The portion of the opening edge 18 that is located in the direction in which the valve portion 36 opens may be locally made longer. Here, the state in which the inner edges coincide includes a state in which they are considered to be substantially coincide. A specific example is when the distance between the inner edges of the gasket 17 and the opening edge 18 along the radial direction of the outer can 15 is 0.1 mm or less.

[0042] The melting temperature of the gasket 17 may be lowered to make it easier for the outer can 15 and the sealing body 30 to short-circuit. The melting temperature of the gasket 17 is set, for example, to 120°C or higher and 140°C or lower, or 130°C or higher and 140°C or lower. When an abnormality occurs in the battery and the sealing body 30 opens, the temperature of the outer can 15 becomes about 140°C. Therefore, if the melting temperature of the gasket 17 is within this range, while ensuring the heat resistance of the gasket 17 during normal use of the battery, the gasket 17 can be melted during an abnormality to short-circuit the outer can 15 and the sealing body 30.

[0043] The melting temperature of the gasket 17 is measured by a differential scanning calorimeter (DSC). The melting temperature of the gasket 17 can be set to 120°C or higher and 140°C or lower, for example, by adjusting the composition of the resin constituting the gasket 17. The resin constituting the gasket 17 is not particularly limited, but examples include polyolefins such as polyethylene and ethylene-propylene copolymers. Also, the melting temperature of the gasket 17 can be adjusted by adding insulating inorganic fillers such as silica, alumina, and mica.

[0044] FIG. 4 is a view showing the sealing body 40 according to the second embodiment. FIG. 4(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). Hereinafter, the differences from the sealing body 30 will be mainly described in detail.

[0045] As shown in FIG. 4, the sealing body 40 has a central portion 41, an outer peripheral portion 42, and a thin portion 43, which is common to the sealing body 30. On the other hand, the center 41z of the central portion 41 coincides with the point Z through which the central axis α of the outer can 15 passes, and the width of the annular thin portion 43 surrounding the central portion 41 is constant along the circumferential direction, which is different from the sealing body 30 in which the width of the thin portion 33 changes. Also, the easily breakable portion 44 includes a thinnest portion 44a having the minimum thickness in the sealing body 40 and a thick portion 44b having a thickness 18% or more greater than the thickness of the thinnest portion 44a, which is different from the sealing body 30 in which the thickness of the easily breakable portion 34 is constant.

[0046] In the sealing body 40 as well, the axial cross-section of the battery includes an asymmetric cross-section in which the shape of the thin-walled portion 43 is asymmetric with respect to the central axis α. The axial cross-section of the battery further includes a symmetric cross-section in which the thicknesses of the easily breakable portions 44 are the same and the shape of the thin-walled portion 43 is symmetric with respect to the central axis α. Note that the cross-section shown in FIG. 4(b) is the asymmetric cross-section, and the cross-section shown in FIG. 4(c) is the symmetric cross-section. Also in the case of the sealing body 40, with a part of the valve portion 46 connected to the outer peripheral portion 42, the valve portion 46 rotates and opens in a specific direction. As a result, the valve portion 46 and the outer can 15 come into contact with each other and short-circuit, and the electric energy possessed by the electrode body 14 can be reduced.

[0047] In the present embodiment, the thickness of the easily breakable portion 44 changes in the circumferential direction and increases from the thinnest portion 44a toward the thick-walled portion 44b. Strictly speaking, the axial cross-section of the battery includes one symmetric cross-section, and the cross-sections other than the symmetric cross-section are asymmetric cross-sections. The asymmetric cross-section including the thinnest portion 44a and the thick-walled portion 44b where the thickness is maximum in the easily breakable portion 44 and the symmetric cross-section are orthogonal to each other. As a result of the study by the present inventors, for example, when the thick-walled portion 44b has a thickness 18% or more larger than that of the thinnest portion 44a, the thinnest portion 44a serves as a breakage starting point, and the thick-walled portion 44b or the vicinity thereof serves as a fulcrum, facilitating the rotation of the valve portion 46.

[0048] The thickness of the easily breakable portion 44 preferably changes continuously from the thinnest portion 44a toward the thick-walled portion 44b. In this case, the rotation of the valve portion 46 becomes smoother. Also, in the asymmetric cross-section including the thinnest portion 44a and the thick-walled portion 44b, the thickness of the thin-walled portion 43 may be constant from the inner peripheral edge of the thin-walled portion 43 to the thick-walled portion 44b. The thickness of the thinnest portion 44a is set to a thickness that does not break during normal use of the battery, but breaks when an abnormality occurs in the battery and the internal pressure reaches a predetermined value.

[0049] FIG. 5 is a diagram showing a sealing body 50 according to the third embodiment. FIG. 5(a) is a bottom view of the sealing body 50, (b) is a cross-sectional view taken along line EE in (a), and (c) is a cross-sectional view taken along line FF in (a).

[0050] As shown in Figure 5, the sealing body 50 includes a central portion 51, an outer peripheral portion 52, and a thin-walled portion 53, and is similar to the sealing body 30 in that the central portion 51 is biased to one side in the radial direction of the sealing body 50, and the width of the annular thin-walled portion 53 surrounding the central portion 51 changes along the circumferential direction. The sealing body 50 is also similar to the sealing body 40 in that the thickness of the easily breakable portion 54 is not constant along the circumferential direction, and includes a thinnest portion 54a in the sealing body 50 where the thickness is smallest, and a thick-walled portion 54b which has a thickness of 18% or more greater than the thickness of the thinnest portion 54a.

[0051] In other words, the sealing body 50 differs from the sealing bodies 30 and 40 in that the shape of the thin-walled portion 53 is asymmetrical with respect to the central axis α of the outer can 15, and has an asymmetrical cross-section including the widest portion 53a, the narrowest portion 53b, the thinnest portion 54a, and the thickest portion 54b. The cross-section shown in Figure 5(b) is the asymmetrical cross-section, and the cross-section shown in Figure 5(c) is a symmetrical cross-section in which the shape of the thin-walled portion 53 is symmetrical with respect to the central axis α. In this case as well, the thinnest portion 54a becomes the starting point for fracture, and the thickest portion 54b or its vicinity becomes the fulcrum, causing the valve portion 56 to rotate.

[0052] As described above, in a cylindrical battery equipped with any of the sealing bodies 30, 40, or 50, if a malfunction occurs in the battery and the sealing body opens, the valve portion, which is the part surrounded by the easily breakable portion, rotates in a specific direction and opens, contacting the opening edge 18 of the outer casing 15 and causing a short circuit. As a result, the electrical energy of the electrode body 14 can be reduced, and even if the electrode body 14 is not smoothly discharged from the outer casing 15, the temperature rise of the battery is effectively suppressed. However, if the shape of the thin-walled portion is symmetrical with respect to the central axis of the outer casing around the entire circumference, for example, it is difficult to intentionally cause a short circuit by completely breaking the easily breakable portion and separating the valve portion from the outer circumference.

[0053] Furthermore, by aligning the inner edge of the opening edge 18 of the outer casing 15 with the inner edge of the gasket 17, or by using a gasket 17 with a melting temperature of 140°C or lower, or by applying both, the sealing body and the outer casing 15 can more easily come into contact when a battery malfunction occurs. In other words, the pairs of external terminals can be short-circuited more smoothly.

[0054] The above embodiments can be modified as appropriate without impairing the purpose of this disclosure. For example, in the above embodiments, the central part of the sealing body has a circular shape when viewed from the bottom, but the central part may have a polygonal shape when viewed from the bottom. In addition, in a battery pack configured using cylindrical batteries according to this disclosure, lead members for electrically connecting the batteries may be placed at the opening edge of the outer casing, which is located in the direction in which the valve of the sealing body opens. In this case, the negative electrode external terminal protrudes upward by the thickness of the lead member, so contact with the valve becomes easier, similar to when the opening edge is made longer.

[0055] The present disclosure is further illustrated by the following embodiments. Configuration 1: A cylindrical battery comprising a wound electrode body, a bottomed cylindrical outer can housing the electrode body, a sealing body closing the opening of the outer can, and a gasket interposed between the outer can and the sealing body, wherein the opening edge of the outer can is crimped and fixed to the sealing body via the gasket, and the outer can and the sealing body function as an external terminal pair, wherein the sealing body has an annular thin-walled portion including an easily breakable portion that breaks when the internal pressure of the battery reaches a predetermined value, and a central portion surrounded by the thin-walled portion and formed to be thicker than the thin-walled portion, wherein the easily breakable portion is formed along the outer edge of the thin-walled portion, and the axial cross-section of the battery cut by a plane including the central axis of the outer can includes an asymmetric cross-section in which the shape of the thin-walled portion is asymmetrical with respect to the central axis. Configuration 2: The cylindrical battery according to Configuration 1, wherein the easily breakable portion is formed in an annular shape at a constant distance from the central axis. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein the easily breakable portion includes a thinnest portion having the minimum thickness in the sealing body and a thick portion having a thickness 18% or more greater than the thickness of the thinnest portion. Configuration 4: The cylindrical battery according to Configuration 3, wherein the thickness of the easily breakable portion changes in the circumferential direction and increases from the thinnest portion toward the thick portion. Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein in the asymmetrical cross-section, the first distance between the first inner circumferential edge of the thin portion and the central axis is smaller than the second distance between the second inner circumferential edge of the thin portion and the central axis. Configuration 6: The cylindrical battery according to Configuration 5, wherein the difference between the first distance and the second distance is 0.2 mm or more. Configuration 7: The cylindrical battery according to any one of Configurations 1 to 6, wherein the inner circumferential edge of the opening edge of the outer casing coincides with the inner circumferential edge of the gasket. Configuration 8: A cylindrical battery according to any one of Configurations 1 to 7, wherein the melting temperature of the gasket is 120°C or higher and 140°C or lower.

[0056] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer casing, 16 Grooved section, 17 Gasket, 18 Opening edge, 20 Positive electrode lead, 21 Negative electrode lead, 22, 23 Insulating plate, 30, 40, 50 Sealing body, 31, 41, 51 Center section, 31z, 41z Center, 32, 42, 52 Outer periphery, 33, 43, 53 Thin-walled section, 33a, 53a Maximum width section, 33b, 53b Minimum width section, 33c First inner periphery, 33d Second inner periphery, 34, 44, 54 Easily breakable section, 35 Groove, 36, 46, 56 Valve section, 44a, 54a Thinnest section, 44b, 54b Thick-walled section, 100 Opening, α (central axis of the outer can), Z (point through which the central axis α passes).

Claims

1. A cylindrical battery comprising a wound electrode body, a bottomed cylindrical outer can housing the electrode body, a sealing body that closes the opening of the outer can, and a gasket interposed between the outer can and the sealing body, wherein the opening edge of the outer can is crimped and fixed to the sealing body via the gasket, and the outer can and the sealing body function as an external terminal pair, wherein the sealing body has an annular thin-walled portion including an easily breakable portion that breaks when the internal pressure of the battery reaches a predetermined value, and a central portion surrounded by the thin-walled portion and formed to be thicker than the thin-walled portion, wherein the easily breakable portion is formed along the outer edge of the thin-walled portion, and the axial cross-section of the battery cut by a plane including the central axis of the outer can includes an asymmetric cross-section in which the shape of the thin-walled portion is asymmetrical with respect to the central axis.

2. The cylindrical battery according to claim 1, wherein the easily breakable portion is formed in an annular shape at a constant distance from the central axis.

3. The cylindrical battery according to claim 2, wherein the easily breakable portion includes the thinnest portion having the minimum thickness in the sealing body and the thicker portion having a thickness of 18% or more greater than the thickness of the thinnest portion.

4. The cylindrical battery according to claim 3, wherein the thickness of the easily breakable portion changes in the circumferential direction and increases from the thinnest portion toward the thickest portion.

5. The cylindrical battery according to claim 2, wherein in the asymmetrical cross-section, the first distance between the first inner periphery of the thin-walled portion and the central axis is smaller than the second distance between the second inner periphery of the thin-walled portion and the central axis.

6. The cylindrical battery according to claim 5, wherein the difference between the first distance and the second distance is 0.2 mm or more.

7. The cylindrical battery according to any one of claims 1 to 6, wherein the inner periphery of the opening edge of the outer casing coincides with the inner periphery of the gasket.

8. The cylindrical battery according to any one of claims 1 to 6, wherein the melting temperature of the gasket is 120°C or higher and 140°C or lower.

Images