Cylindrical battery

Abstract

A seal plate (27) of a cylindrical battery (10) has an outer peripheral portion (27b), which is at least partly fixed to an opening of an outer can (16), and an annular thin portion (27c) adjacent to the outer peripheral portion (27b). The thin portion (27c) has a sloping portion (56) sloping radially inward toward the bottom of the outer can (16) in an axial direction. In a cross section of the thin portion (27c) taken in a plane including the radial direction and the axial direction, an inner surface of an adjacent portion (59) adjacent to the outer peripheral portion (27b) of the thin portion (27c) has a curved shape, and the gradient of an outer surface (70) of the thin portion (27c) changes towards the outer peripheral portion (27b) so as to decrease the thickness of the adjacent portion (59).

Description

[Technical Field]

[0001] The present disclosure relates to cylindrical batteries. [Background technology]

[0002] A conventional cylindrical battery is described in Patent Document 1. This cylindrical battery includes a sealing body having a sealing plate, a metal plate serving as an internal terminal plate, and an insulating material interposed between the sealing plate and the metal plate. This cylindrical battery seals the interior by crimping the sealing body to the opening of a bottomed cylindrical outer can via a resin gasket. The sealing plate of this cylindrical battery has a sloped portion that displaces axially outward and continuously decreases in thickness as it moves radially from the inner periphery to the outer periphery. This cylindrical battery has a safety mechanism that activates when the internal pressure increases due to abnormal heat generation. Specifically, when the internal pressure increases due to abnormal heat generation, the sloped portion reverses, interrupting the current path within the battery. Furthermore, when the internal pressure increases further, the sloped portion breaks, allowing gas inside the battery to be released to the outside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 157749 Summary of the Invention [Problem to be solved by the invention]

[0004] In the cylindrical battery of Patent Document 1, the sealing plate is disposed at the outermost part of the sealing body and functions as an external terminal. When a module is formed with multiple cylindrical batteries, an external lead is electrically connected to the external terminal. However, the inner periphery of the top surface of the sealing plate of the cylindrical battery is recessed toward the inside of the battery compared to the shoulder of the bottomed outer can, which can make it difficult to electrically connect the external terminal to the external lead. In this context, if a protrusion protruding toward the outside of the battery is provided in the radial center of the sealing plate to facilitate the electrical connection between the external terminal and the external lead, the protrusion may make it more difficult for the sealing body to invert or break, resulting in increased variation in inversion pressure and vent pressure (breaking pressure). Regardless of whether or not a protrusion is provided on the sealing plate, it is preferable to reduce variation in inversion pressure and vent pressure.

[0005] Therefore, an object of the present disclosure is to provide a cylindrical battery that can reduce variations in the sealing body inversion pressure and vent pressure. [Means for solving the problem]

[0006] In order to solve the above problems, the cylindrical battery according to the present disclosure is a cylindrical battery comprising a bottomed cylindrical outer can and a sealing body that closes the opening of the outer can, wherein the sealing body includes a sealing plate that ruptures to release internal gas to the outside, and the sealing plate has an outer peripheral portion, at least a portion of which is crimped and fixed to the opening of the outer can, and an annular thin-walled portion adjacent to the outer peripheral portion, and the thin-walled portion has an inclined portion that slopes toward the bottom of the outer can in the axial direction as it goes radially inward, and in a cross section when the thin-walled portion is cut along a plane including the radial and axial directions, the inner surface of an adjacent portion of the thin-walled portion that is adjacent to the outer peripheral portion has a curved shape, and the gradient of the outer surface of the thin-walled portion changes toward the outer peripheral portion so that the thickness of the adjacent portion becomes smaller.

[0007] The outer surface may have a polygonal line shape formed by connecting two or more straight lines with different gradients in the cross section, or may include a curve. Here, if the outer surface includes a polygonal line portion in the cross section, the gradient of the outer surface at the connecting point of the polygonal lines is defined as the same gradient as the gradient of the line located radially inward of the two straight lines. Furthermore, if the outer surface includes a curved line in the cross section, the gradient of the outer surface at the curved point is defined as the gradient of the tangent to the curve. [Effects of the Invention]

[0008] The cylindrical battery according to the present disclosure can reduce variations in the sealing body inversion pressure and vent pressure. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an axial cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view of an electrode body of the cylindrical battery. [Figure 3] FIG. 2 is an enlarged cross-sectional view of the periphery of the sealing body of the cylindrical battery. [Figure 4] FIG. 2 is a cross-sectional view of a cylindrical battery according to a modified example, corresponding to FIG. 1. [Figure 5A] 2 is a cross-sectional view of the sealing plate taken along an axial direction thereof, the cross-sectional view being obtained by cutting the sealing plate along a plane including its axial and radial directions. FIG. [Figure 5B] FIG. 5B is an enlarged view of the R1 region of FIG. 5A. [Figure 6A] FIG. 4B is a cross-sectional view of a sealing plate of a comparative example, corresponding to FIG. 4A. [Figure 6B] FIG. 6B is an enlarged view of the R2 region of FIG. 6A. [Figure 7] FIG. 2 is a schematic diagram for explaining an outline of a method for measuring the inversion pressure and vent pressure of the sealing plate. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. The cylindrical battery according to the present disclosure may be a primary battery or a secondary battery. It may also be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a non-aqueous electrolyte secondary battery (lithium ion battery) using a non-aqueous electrolyte will be exemplified as a cylindrical battery 10 according to one embodiment, but the cylindrical battery according to the present disclosure is not limited thereto.

[0011] When multiple embodiments and variations are included below, it is anticipated from the beginning that new embodiments can be constructed by appropriately combining their characteristic features. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match. The axial direction of the cylindrical battery 10 coincides with the height direction of the cylindrical battery 10, but for convenience of explanation, the side of the sealing body 17 in the axial direction will be referred to as "upper" and the bottom side of the outer can 16 in the axial direction will be referred to as "lower." Among the components described below, those not recited in the independent claims representing the highest concepts are optional and not required.

[0012] FIG. 1 is an axial cross-sectional view of a cylindrical battery 10 according to one embodiment of the present disclosure, and FIG. 2 is a perspective view of an electrode assembly 14 of the cylindrical battery 10. As shown in FIG. 1, the cylindrical battery 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), and a battery case 15 that accommodates the electrode assembly 14 and the non-aqueous electrolyte. As shown in FIG. 2, the electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13 interposed between the positive electrode 11 and the negative electrode 12, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The battery case 15 is composed of a cylindrical outer can 16 with a bottom and a sealing member 17 that closes the opening of the outer can 16. The cylindrical battery 10 also includes a resin gasket 28 that is disposed between the outer can 16 and the sealing member 17.

[0013] The non-aqueous electrolyte includes 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 mixtures of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The non-aqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel polymer or the like. The electrolyte salt is a lithium salt such as LiPF6.

[0014] As shown in Fig. 2, the electrode assembly 14 has a long positive electrode 11, a long negative electrode 12, and two long separators 13. The electrode assembly 14 also has a positive electrode lead 20 joined to the positive electrode 11 and a negative electrode lead 21 joined to the negative electrode 12. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to suppress lithium deposition, and is formed to be longer than the positive electrode 11 in the longitudinal direction and width direction (short direction). The two separators 13 are also formed to be at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11, for example.

[0015] The positive electrode 11 has a positive electrode current collector and a positive electrode mixture layer formed on both sides of the current collector. The positive electrode current collector can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode current collector, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the current collector.

[0016] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0017] Examples of conductive agents contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of binders contained in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO).

[0018] The negative electrode 12 has a negative electrode current collector and a negative electrode mixture layer formed on both sides of the current collector. The negative electrode current collector can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface layer. The negative electrode mixture layer contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the binder onto the negative electrode current collector, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the current collector.

[0019] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0020] The binder contained in the negative electrode mixture layer may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like, as in the case of the positive electrode 11. Preferably, styrene-butadiene rubber (SBR) or a modified product thereof is used. The negative electrode mixture layer may contain, in addition to SBR, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0021] The separator 13 is a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13. The negative electrode 12 may form the winding start end of the electrode assembly 14, but typically the separator 13 extends beyond the winding start end of the negative electrode 12, and the winding start end of the separator 13 becomes the winding start end of the electrode assembly 14.

[0022] In the example shown in FIGS. 1 and 2 , the positive electrode lead 20 is electrically connected to an intermediate portion, such as the center portion, of the positive electrode core in the winding direction, and the negative electrode lead 21 is electrically connected to the end of the negative electrode core in the winding direction. However, the negative electrode lead may be electrically connected to the end of the negative electrode core in the winding direction where the winding begins. Alternatively, the electrode body may have two negative electrode leads, one of which is electrically connected to the end of the negative electrode core in the winding direction where the winding begins, and the other negative electrode lead is electrically connected to the end of the negative electrode core in the winding direction. Alternatively, the end of the negative electrode core in the winding direction on the winding side may be abutted against the inner surface of the outer can, thereby electrically connecting the negative electrode and the outer can.

[0023] As shown in FIG. 1 , the cylindrical battery 10 further includes an insulating plate 18 disposed above the electrode assembly 14 and an insulating plate 19 disposed below the electrode assembly 14. In the example shown in FIG. 1 , a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside the insulating plate 19 and extends toward the bottom 68 of the outer can 16. The positive electrode lead 20 is connected to the underside of a terminal plate 23, which is the bottom plate of the sealing body 17, by welding or the like, and the sealing plate 27, which is the top plate of the sealing body 17 and is electrically connected to the terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 68 of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0024] The outer can 16 is a metal container having a cylindrical portion with a bottom. The space between the outer can 16 and the sealing body 17 is sealed with an annular gasket 28, thereby hermetically sealing the internal space of the battery case 15. The gasket 28 also includes a clamping portion 32 that is sandwiched between the outer can 16 and the sealing body 17, and insulates the sealing body 17 from the outer can 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to prevent short-circuiting between the outer can 16 and the sealing body 17.

[0025] The outer can 16 has an annular grooved portion 35 along a portion of the cylindrical outer surface in the height direction. The grooved portion 35 can be formed, for example, by spinning a portion of the cylindrical outer surface radially inward to create a recess in the radial direction. The outer can 16 has a bottomed tubular portion 30 including the grooved portion 35 and an annular shoulder portion 33. The bottomed tubular portion 30 accommodates the electrode assembly 14 and the nonaqueous electrolyte, and the shoulder portion 33 is bent radially inward from the end of the open side of the bottomed tubular portion 30 and extends inward. The shoulder portion 33 is formed when the upper end of the outer can 16 is bent inward and crimped to the peripheral edge 31 of the sealing body 17. The sealing body 17 is clamped between the shoulder portion 33 and the grooved portion 35 via a gasket 28 by this crimping, and is fixed to the outer can 16.

[0026] Next, the structure, current interruption operation, and gas release operation of the sealing body 17 will be described. Figure 3 is an enlarged cross-sectional view of the sealing body periphery of the cylindrical battery 10. As shown in Figure 3, the sealing body 17 has a structure in which, starting from the electrode body 14, a terminal plate 23, an annular insulating plate 25, and a sealing plate 27 are stacked. Each component of the sealing body 17 has a disk or ring shape, and all components except the insulating plate 25 are electrically connected. The terminal plate 23 forms the bottom plate of the sealing body 17 and has a circular upper surface 23a located on a substantially coplanar surface. The terminal plate 23 has an annular thick portion 23b located on the radially outer side and a disk-shaped thin portion 23c that is connected to the annular end of the thick portion 23b on the radially inner side and is thinner than the thick portion 23b. The positive electrode lead 20 is connected to the underside of the thick portion 23b of the terminal plate 23 by welding or the like. The sealing body 17 may be composed of only the sealing plate 27. In this case, the positive electrode lead 20 is connected to a sealing plate 27 as shown in FIG.

[0027] The sealing plate 27 has a circular shape in a plan view. The sealing plate 27 can be fabricated, for example, by pressing a sheet of aluminum or an aluminum alloy. Aluminum and aluminum alloys are preferred materials for the sealing plate 27, which functions as an explosion-proof valve, due to their excellent flexibility. The sealing plate 27 has a central portion 27a located at the radial center, an annular outer peripheral portion 27b located radially outward, and a thin-walled portion 27c connecting the central portion 27a and the outer peripheral portion 27b. The central portion of the lower surface of the central portion 27a has a substantially circular shape in a plan view and extends in a direction substantially perpendicular to the height direction. The upper surface of the thin-walled portion 23c of the terminal plate 23 and the central portion of the lower surface of the central portion 27a of the sealing plate 27 are joined by metallurgical joining, for example, laser welding. Forming the terminal plate 23 from aluminum or an aluminum alloy, like the sealing plate 27, facilitates joining the sealing plate 27 and the terminal plate 23.

[0028] The central portion 27a has a protrusion 55 that is connected to the radially inner end of the thin-walled portion 27c and protrudes axially outward (upward in the height direction) from that end. The top surface 55a of the protrusion 55 is located axially outward of the axially outermost point 33a of the shoulder portion 33. The outer peripheral end of the outer peripheral portion 27b of the sealing plate 27 is sandwiched between the shoulder portion 33 and the grooved portion 35 via the gasket 28. This secures the sealing plate 27 to the opening of the outer can 16. The axial thickness of the thin-walled portion 27c is thinner than the axial thickness of the outer peripheral portion 27b, which is also thinner than the axial thickness of the central portion 27a. The thin-walled portion 27c has an inclined portion 56 that slopes axially downward as it extends radially inward. The axial thickness of annular adjacent portion 59 of thin-walled portion 27c adjacent to outer circumferential portion 27b is thinner than the axial thickness of other portions of thin-walled portion 27c. The shape of thin-walled portion 27c will be described in detail later with reference to Figures 5A and 5B.

[0029] Sealing plate 27 has a protrusion 57 that protrudes downward from its lower axial end. Insulating plate 25 is press-fitted and fixed onto the outer peripheral surface 29 of protrusion 57. Insulating plate 25 has an annular protrusion 25a that bends downward in the height direction on the radially outward side, and thick portion 23b of terminal plate 23 is press-fitted and fixed onto the inner peripheral surface of annular protrusion 25a, for example. Insulating plate 25 is provided to ensure insulation and prevents thick portion 23b of terminal plate 23 from being electrically connected to sealing plate 27.

[0030] The insulating plate 25 is preferably made of a material that does not affect the battery characteristics. Examples of materials for the insulating plate 25 include polymer resins, such as polypropylene (PP) resin and polybutylene terephthalate (PBT) resin. The outer peripheral surface of the insulating plate 25 abuts against the inner peripheral surface of the sealing plate 27, which is located axially below the outer peripheral portion 27b. A portion of the lower surface of the sealing plate 27, including the lower surface of the thin-walled portion 27c, and the upper surface of the insulating plate 25 combine to define an annular space 58. The insulating plate 25 has one or more vent holes 25b that penetrate in the axial direction and communicate with the space 58, and the terminal plate 23 has one or more vent holes 23d that penetrate in the axial direction and communicate with the vent holes 25b.

[0031] In the above configuration, if the cylindrical battery 10 generates abnormal heat and the internal pressure of the cylindrical battery 10 reaches a predetermined value, the sealing body 17 performs a current interruption operation and gas release operation as follows. Specifically, when the internal pressure of the cylindrical battery 10 reaches a predetermined value, the central portion 27a and thin-walled portion 27c of the sealing plate 27 flip upward in the axial direction, using the annular adjacent portion 59, which is thin and has low rigidity, as a fulcrum. Simultaneously with this flip, the thin-walled portion 23c of the terminal plate 23 breaks, separating the portion connected to the sealing plate 27 from the terminal plate 23, or disengaging the weld between the terminal plate 23 and the sealing plate 27. This action interrupts the current path between the terminal plate 23 and the sealing plate 27. Furthermore, if the internal pressure increases, the adjacent portion 59 of the thin-walled portion 27c breaks, and gas inside the battery is released from the broken portion of the sealing plate 27 to the outside via the vent holes 23d and 25b. This prevents the battery from exploding even if the internal pressure of the cylindrical battery 10 increases, minimizing the impact on the device in which the cylindrical battery 10 is installed, thereby improving safety. The thin-walled portion 27c of the sealing plate acts as a rupture portion that releases internal gas to the outside when ruptured.

[0032] Next, the detailed structure of the thin-walled portion 27c of the sealing plate 27 will be explained, and the effects that can be obtained by the cylindrical battery 10 that employs the thin-walled portion 27c will be explained by comparing the sealing plate 27 with a comparative sealing plate 127 (see Figures 6A and 6B).

[0033] FIG. 5A is an axial cross-sectional view of sealing plate 27, taken along a plane including the axial and radial directions. FIG. 5B is an enlarged view of region R1 in FIG. 5A, showing the radially outer portion of sealing plate 27. As shown in FIG. 5B, thin-walled portion 27c has an annular adjacent portion 59 adjacent to outer peripheral portion 27b, and the inner surface of adjacent portion 59 has a curved shape. That is, the inner surface of adjacent portion 59 forms an annular curved surface 59a. As shown in FIG. 5B, the gradient of outer surface 70 of thin-walled portion 27c changes toward outer peripheral portion 27b so that the axial thickness of adjacent portion 59 decreases.

[0034] 5B, the outer surface 70 of the thin-walled portion 27c includes a conical inner circumferential surface 70a that shifts axially outward as it extends radially outward, and an annular flat surface 70b that connects to the radially outer end of the conical inner circumferential surface 70a and extends in a direction substantially perpendicular to the axial direction. The conical inner circumferential surface 70a is located radially inward of the adjacent portion 59. The flat surface 70b includes an opposing surface 70c that axially faces the curved surface 59a on the outer surface 70. The opposing surface 70c corresponds to the outer surface of the adjacent portion 59.

[0035] 5B, the outer surface 70 has a polygonal line shape and includes a first linear portion 60a that displaces axially outward as it extends radially outward, and a second linear portion 60b that extends from an outer end 71 on the radially outer side of the first linear portion 60a in a direction substantially perpendicular to the axial direction. The outer end 71 is located radially inward relative to the adjacent portion 59. The gradient of the outer surface 70 of the thin-walled portion 27c changes such that the axial thickness of the adjacent portion 59 becomes smaller at the outer end 71, which is the gradient change point. The outer surface 70 of the thin-walled portion 27c inclines toward the inner surface 80 of the thin-walled portion 27c as it moves from the radially inner side to the radially outer side.

[0036] The inner surface 80 of the thin-walled portion 27c includes the curved surface 59a and an annular inclined surface 81 connected to the radially inward end of the curved surface 59a. The inclined surface 81 forms a conical outer peripheral surface that shifts axially downward as it extends radially inward. As shown in FIG. 5A, the lower surface of the central portion 27a has a conical outer peripheral surface portion 82 that extends radially outward to the inclined surface 81 and is located on the same conical outer peripheral surface as the inclined surface 81. Note that, as shown in FIG. 5B, in this embodiment, the conical inner peripheral surface 70a is substantially parallel to the inclined surface 81, and the axial thickness of the inclined portion 56 is substantially constant regardless of radial position. However, the axial thickness of the inclined portion located radially inward of the thin-walled portion may gradually increase radially inward. [Example]

[0037] The sealing bodies of the examples and comparative examples, and the test methods will be described below.

[0038] [Example sealing body] As the sealing body of the embodiment, sealing plate 27 described in detail using Figures 5A and 5B was used, that is, a sealing plate in which the gradient of outer surface 70 of thin-walled portion 27c changes so that the axial thickness of adjacent portion 59 becomes smaller toward outer peripheral portion 27b, as shown in Figure 5B.

[0039] [Comparative Example Sealing Body] A sealing plate 127 shown in FIGS. 6A and 6B was used as a sealing body of the comparative example. FIG. 6A is a cross-sectional view of the sealing plate 127 of the comparative example corresponding to FIG. 6A , and FIG. 6B is an enlarged view of region R2 in FIG. 6A , showing the radially outer portion of the sealing plate 127 of the comparative example. As shown in FIG. 6B , the sealing plate 127 differs from the sealing plate 27 of the example in that the outer surface 170 of the thin-walled portion 127c is displaced axially outward (upward in the height direction) as it moves radially outward, and the gradient of the outer surface 170 is constant. The sealing plate 127 also differs from the sealing plate 27 of the example in that a gradient change point 171, where the gradient of the outer surface 170 changes from the constant gradient at the point on the outer surface 170, is present in the outer peripheral portion 127b, and the gradient change point 171 is located radially outward in the thin-walled portion 127c relative to an adjacent portion 159 adjacent to the outer peripheral portion 127b.

[0040] Other configurations of sealing plate 127 are substantially the same as the corresponding configurations of sealing plate 27. For example, central portion 127a has convex portion 155 that protrudes axially outward (axially upward) from the radially inner end of thin-walled portion 127c, and adjacent portion 159 has a curved shape, with the inner surface of adjacent portion 159 being curved surface 159a, which are the same as sealing plate 27. Also, inner surface 180 of thin-walled portion 127c has inclined surface 181 that connects to the radially inner end of curved surface 159a and that displaces axially downward as it moves axially inward, which is the same as sealing plate 27.

[0041] [Measurement of sealing plate reversal pressure and vent pressure] The reversal pressure and vent pressure of each sealing plate 27, 127 were measured using the same device as follows. Below, the method for measuring the reversal pressure and vent pressure of sealing plate 27 will be described, and the method for measuring the reversal pressure and vent pressure of sealing plate 127 will not be described. As shown in FIG. 7 , sealing plate 27 was fixed to a fixture 50 having a clamping portion 51 and a receiving portion 52. Clamping portion 51 and receiving portion 52 were made of a transparent material, such as acrylic or tempered glass. A measuring device was connected to receiving portion 52, and pressure was applied from above to clamping portion 51 with an air cylinder (not shown), thereby ensuring airtightness of space S surrounded by sealing plate 27 and receiving portion 52. Gas was supplied to this space S at a constant rate from a gas cylinder 54 filled with gas via a regulator 53. Reversal or rupture of sealing plate 27 was then visually confirmed, and the air pressure in space S when reversal or rupture was confirmed was defined as the reversal pressure and vent pressure, respectively. Measurements of inversion pressure and vent pressure were carried out using 20 samples for each of the examples and comparative examples.

[0042] [Test Results] The test results are shown in Table 1. [Table 1]

[0043] The above test results confirmed that the sealing plates of the Example had smaller variations in operating pressure for both reversal and rupture than the sealing plates of the Comparative Example. The inventors speculate as follows why the sealing plates of the Comparative Example had larger variations in reversal pressure and vent pressure than the sealing plates of the Example.

[0044] Specifically, in the case of sealing plate 127 of the comparative example, as shown in FIG. 6B, outer surface 170 is displaced axially outward at a constant gradient as it goes radially outward, and the portion of inner surface 180 other than adjacent portion 159 is also displaced axially outward at a constant gradient as it goes radially outward. outside6B, that is, in a direction inclined at an acute angle radially inward relative to the axially upper side, and as a result, adjacent portion 159 is less likely to bend. The inventors of the present application therefore speculate that the reversal action becomes more dependent on chance, increasing uncertainty in the timing at which reversal or rupture begins and increasing the variability in reversal pressure and vent pressure.

[0045] In contrast, in the case of sealing plate 27 of the embodiment, as shown in Fig. 5B, the gradient of outer surface 70 of thin-walled portion 27c changes so that the axial thickness of adjacent portion 59 decreases, causing the plane of opposing surface 70c, the outer surface of adjacent portion 59 where reversal or rupture occurs, to extend closer to a plane perpendicular to the axial direction. As a result, the axial force indicated by arrow A in Fig. 5B is more likely to act on adjacent portion 59 of thin-walled portion 27c, presumably reducing variations in the reversal pressure and vent pressure of thin-walled portion 27c.

[0046] [Essential configurations of the cylindrical battery of the present disclosure and their effects] As described above, the cylindrical battery 10 of the present disclosure includes a bottomed, cylindrical outer can 16 and a sealing body 17 that closes the opening of the outer can 16. The sealing body 17 includes a sealing plate 27 that ruptures to release internal gas to the outside. The sealing plate 27 has an outer peripheral portion 27b, at least a portion of which is crimped to the opening of the outer can 16, and an annular thin-walled portion 27c adjacent to the outer peripheral portion 27b. The thin-walled portion 27c has a sloped portion 56 that slopes radially inward toward the bottom of the outer can 16 in the axial direction. The inner surface of an adjacent portion 59 of the thin-walled portion 27c adjacent to the outer peripheral portion 27b forms a curved surface 59a. When the thin-walled portion 27c is cut along a plane including the radial and axial directions, the gradient of the outer surface 70 of the thin-walled portion 27c changes toward the outer peripheral portion 27b so that the thickness of the adjacent portion 59 decreases.

[0047] Therefore, the plane on which the facing surface 70c of the adjacent portion 59 extends can be made closer to a plane perpendicular to the axial direction, and the force that the adjacent portion 59, which is the fracture portion, receives from the internal gas can be made closer to a force parallel to the axial direction. As a result, when the cylindrical battery 10 generates abnormal heat, the variation in the force that the adjacent portion 59 receives from the gas inside the battery can be reduced, and the variation in the reversal pressure and vent pressure can be reduced.

[0048] [Preferable cylindrical battery configurations and their effects] Furthermore, the outer surface 70 may extend in a direction substantially perpendicular to the axial direction at the adjacent portion 59. In other words, an opposing surface 70c of the outer surface 70 that faces the curved surface 59a in the axial direction may extend in a direction substantially perpendicular to the axial direction, or may be substantially parallel to a plane perpendicular to the axial direction.

[0049] The above configuration allows the force that the adjacent portion 59 receives from the internal gas to be parallel to the axial direction, which makes it easier to further suppress the variation in the force that the adjacent portion 59 receives from the gas inside the battery when the cylindrical battery 10 generates abnormal heat, and further reduces the variation in reversal pressure and vent pressure.

[0050] Furthermore, the sealing plate 27 may have a protrusion 55 at the center in the radial direction that protrudes outward in the axial direction.

[0051] As explained in the section on problems, in the cylindrical battery of the conventional configuration disclosed in Patent Document 1, if a convex portion that protrudes outward from the battery in the radial center of the sealing plate is provided to facilitate electrical connection between the external terminal and the external lead, there is a risk that the convex portion will make it more difficult for the sealing body to invert or break, resulting in greater variation in inversion pressure and vent pressure.

[0052] In contrast, in the cylindrical battery 10 of the present disclosure, variations in reversal pressure and vent pressure are less likely to occur, so even if a protrusion 55 that protrudes axially outward is provided at the radial center of the sealing plate 27 to facilitate electrical connection between the external terminal and external lead, the sealing plate 27 can be easily reversed or broken at the desired operating pressure. Therefore, a cylindrical battery 10 can be realized that not only facilitates electrical connection between the external terminal and external lead, but also reduces variations in reversal pressure and vent pressure.

[0053] Furthermore, the top surface 55 a of the protrusion 55 may be located axially outward from the shoulder 33 of the outer can 16 .

[0054] According to the above configuration, the outer can 16 is less likely to become an obstacle when electrically connecting the top surface 55a of the protrusion 55 constituting the external terminal to the external lead, and the top surface 55a of the protrusion 55 can be connected to the external lead more smoothly.

[0055] The present disclosure is not limited to the above-described embodiment and its modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0056] For example, in the above embodiment, the opposing surface 70c of the adjacent portion 59 extends substantially parallel to a plane perpendicular to the axial direction. However, the opposing surface, which is the outer surface of the adjacent portion, does not have to extend substantially parallel to a plane perpendicular to the axial direction, and may be, for example, an inclined surface that slopes outward in the axial direction as it extends radially outward relative to the plane perpendicular to the axial direction.

[0057] In addition, the sealing plate 27 has a protrusion 55 protruding axially outward in its radial center, and the top surface 55a of the protrusion 55 is located axially outward from the shoulder 33 of the outer can 16. However, the top surface of the protrusion protruding axially outward in the radial center of the sealing plate may be located closer to the electrode body in the axial direction than the outermost axial position of the shoulder of the outer can. Alternatively, the sealing plate does not need to have a protrusion protruding axially outward.

[0058] Also, the case has been described where the outer surface 70 of the thin-walled portion 27c in a cross section when the thin-walled portion 27c is cut along a plane including the radial and axial directions has a broken line shape in which the gradient changes at only one location (the outer end 71). However, the shape of the outer surface of the thin-walled portion in a cross section when the thin-walled portion is cut along a plane including the radial and axial directions may be any shape as long as the gradient of the outer surface changes so that the thickness of the adjacent portion becomes smaller.

[0059] For example, the outer surface of the thin-walled portion in a cross section when the thin-walled portion is cut along a plane including the radial and axial directions may have a broken line shape with a gradient that changes at multiple locations, and the gradient of the outer surface may gradually incline toward the inner surface of the thin-walled portion in multiple steps as the outer surface moves radially outward. Alternatively, the outer surface of the thin-walled portion in a cross section when the thin-walled portion is cut along a plane including the radial and axial directions may include a curve, and the gradient of the tangent to the curve may gradually incline toward the inner surface of the thin-walled portion as it moves toward the adjacent portion of the thin-walled portion. [Explanation of symbols]

[0060] 10 cylindrical battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 battery case, 16 outer can, 17 sealing body, 20 positive electrode lead, 21 negative electrode lead, 23 terminal plate, 25 insulating plate, 27 sealing plate, 27a central portion, 27b outer peripheral portion, 27c thin-walled portion, 28 gasket, 30 bottomed cylindrical portion, 33 shoulder portion, 50 fixing jig, 51 pressing portion, 52 receiving portion, 53 regulator, 54 gas cylinder, 55 convex portion, 55a top surface of convex portion, 56 inclined portion, 59 adjacent portion, 59a curved surface, 70 outer surface of thin-walled portion, 70a conical inner surface, 70b Flat side, 70c opposite side.

Claims

1. A cylindrical battery comprising a bottomed cylindrical outer can and a sealing body that closes an opening of the outer can, the sealing body includes a sealing plate that is broken to release internal gas to the outside, the sealing plate has an outer circumferential portion at least a portion of which is fixed to the opening of the outer can by crimping, and an annular thin-walled portion adjacent to the outer circumferential portion, and also has a convex portion at a radial center thereof that protrudes outward in the axial direction, the thin-walled portion has an inclined portion that inclines toward the bottom side of the outer can in the axial direction as it goes inward in the radial direction, In a cross section of the thin-walled portion cut along a plane including the radial direction and the axial direction, an inner surface of an adjacent portion of the thin-walled portion that is adjacent to the outer periphery and serves as a starting point for inversion and fracture of the thin-walled portion has a curved shape, and an inner surface of the thin-walled portion on the radially inner side of the adjacent portion has an inclined structure that inclins toward the bottom side of the outer can in the axial direction as it goes inward in the radial direction, and the gradient of the outer surface of the thin-walled portion changes toward the outer periphery so as to approach a direction perpendicular to the axial direction. Cylindrical battery.

2. The cylindrical battery according to claim 1 , wherein the outer surface extends in a direction substantially perpendicular to the axial direction at the adjacent portion.

3. The cylindrical battery according to claim 1 or 2, wherein a top surface of the protrusion is located further outward in the axial direction than a shoulder portion of the outer can.

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