Secondary batteries

Abstract

To provide rechargeable batteries with superior safety features. [Solution] This secondary battery comprises a battery element, a container, and a lid. The container has a first end and a second end and houses the battery element. The lid, which is attached to the container via an insulating member, has a lid member including a first flange that extends radially in the direction of the container, and a valve member including a second flange that extends radially so as to overlap the first flange in a first direction and is located between the lid member and the battery element in a first direction. The first flange includes a bottom surface, a top surface, and an end surface. The second flange is folded back so as to continuously cover the first flange from the bottom surface through the end surface to the top surface. The top covering portion of the second flange includes a first portion having a first thickness and a second portion located radially between the first portion and the end surface and having a second thickness that is thinner than the first thickness.

Description

【Technical Field】 【0001】 This technology relates to a secondary battery equipped with a safety valve mechanism. 【Background Art】 【0002】 A variety of electronic devices such as mobile phones are widely popular, and there is a demand for miniaturization, weight reduction, and long life of these electronic devices. Therefore, as a power source, it is small and lightweight. 【0003】 A secondary battery includes an electrolyte together with a positive electrode and a negative electrode. When gas is generated due to a decomposition reaction of the electrolyte or the like, the secondary battery is equipped with a safety valve mechanism that can release gas to the outside as necessary in order to suppress the occurrence of problems caused by the gas (see, for example, Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2007-194167 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 By the way, various studies have been made to improve the performance of secondary batteries. However, there is still room for improvement in the performance of secondary batteries. 【0006】 Therefore, a secondary battery with better safety is desired. 【Means for Solving the Problems】 【0007】 A secondary battery according to one embodiment of the present disclosure comprises a battery element, a container, and a lid. The container has a first end and a second end located opposite to the first end in a first direction, and houses the battery element. The lid is attached to the container via an insulating member. The lid includes a lid member including a first flange extending radially in the container perpendicular to a first direction, and a valve member including a second flange extending radially so as to overlap the first flange in a first direction, and located between the lid member and the battery element in a first direction. The first flange includes a lower surface facing the second flange, an upper surface opposite to the second flange, and an end surface connecting the lower surface and the upper surface. The second flange is folded back to continuously cover from the lower surface through the end surface to the upper surface. The upper covering portion of the second flange that covers the upper surface includes a first portion having a first thickness and a second portion located radially between the first portion and the end surface and having a second thickness that is thinner than the first thickness. [Effects of the Invention] 【0008】 In one embodiment of the secondary battery of this disclosure, the second flange is folded back so as to continuously cover the first flange from its lower surface through its end surface to its upper surface. This ensures a high sealing performance of the container by the lid. Furthermore, the upper covering portion of the second flange that covers the upper surface includes a first portion having a first thickness and a second portion located radially between the first portion and the end surface and having a second thickness that is thinner than the first portion. Therefore, if a short circuit occurs due to the adhesion of saltwater or the like, the progress of the battery reaction is suppressed. Thus, a high level of safety can be ensured. 【0009】 Furthermore, the effects of this disclosure are not necessarily limited to those described herein, but may include any of the series of effects related to this technology described later. [Brief explanation of the drawing] 【0010】 [Figure 1] Figure 1 is a cross-sectional view showing an example of the overall configuration of a secondary battery according to one embodiment of the present disclosure. [Figure 2]FIG. 2 is a partial cross-sectional view showing an enlarged configuration example of the upper part of the secondary battery shown in FIG. 1. [Figure 3] FIG. 3 is an enlarged cross-sectional view showing an enlarged configuration example of the safety valve mechanism of the secondary battery shown in FIG. 1. [Figure 4] FIG. 4 is an exploded perspective view of the safety valve mechanism shown in FIG. 3. [Figure 5] FIG. 5 is a partial cross-sectional view showing an enlarged configuration example of the crimp portion of the secondary battery shown in FIG. 1 and its vicinity. [Figure 6] FIG. 6 is a schematic plan view of the safety valve mechanism shown in FIG. 3. [Figure 7] FIG. 7 is a cross-sectional view showing an enlarged part of the configuration of the battery element shown in FIG. 1. [Figure 8] FIG. 8 is a cross-sectional view for explaining the operation of the secondary battery. [Figure 9] FIG. 9 is a partial cross-sectional view showing an enlarged configuration example of the crimp portion of the secondary battery as a first modification and its vicinity. [Figure 10] FIG. 10 is a partial cross-sectional view showing an enlarged configuration example of the crimp portion of the secondary battery as a second modification and its vicinity. [Figure 11] FIG. 11 is a partial cross-sectional view showing an enlarged configuration example of the crimp portion of the secondary battery as a third modification and its vicinity. [Figure 12] FIG. 12 is a partial cross-sectional view showing an enlarged configuration example of the crimp portion of the secondary battery as a fourth modification and its vicinity. [Figure 13] FIG. 13 is a block diagram showing the configuration of an application example (battery pack) of the secondary battery. [Figure 14] FIG. 14 is an explanatory diagram for explaining the procedure of the voltage drop confirmation test in the embodiment. [Figure 15] FIG. 15 is a schematic plan view of the safety valve mechanism of the secondary battery as a fifth modification. 【MODE FOR CARRYING OUT THE INVENTION】 【0011】 Hereinafter, with reference to the drawings, a detailed description will be given of an embodiment of the present disclosure. The order of description is as follows. 1. Secondary battery 1-1. Overall configuration 1-2. Detailed configuration of the safety valve mechanism 1-3. Detailed configuration of the battery element 1-4. Operation 1-5. Manufacturing method 1-6. Action and effect 2. Modification example 3. Applications of the secondary battery 【0012】 <1. Secondary battery> First, a secondary battery according to an embodiment of the present disclosure will be described. 【0013】 The charge-discharge principle of the secondary battery described here is not particularly limited. Hereinafter, the case where the battery capacity is obtained by utilizing the occlusion and release of the electrode reactant will be described. 【0014】 The secondary battery includes an electrolyte together with a positive electrode and a negative electrode. In this secondary battery, the charging capacity of the negative electrode is larger than the discharging capacity of the positive electrode, that is, the electrochemical capacity per unit area of the negative electrode is larger than the electrochemical capacity per unit area of the positive electrode. This is to prevent the deposition of the electrode reactant on the surface of the negative electrode during charging. 【0015】 The type of the electrode reactant is not particularly limited. Specifically, it is a light metal such as an alkali metal and an alkaline earth metal. The alkali metals include lithium, sodium, potassium, etc., and the alkaline earth metals include beryllium, magnesium, calcium, etc. 【0016】 Hereinafter, the case where the electrode reactant is lithium will be taken as an example. A secondary battery in which the battery capacity is obtained by utilizing the occlusion and release of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is occluded and released in an ionic state. 【0017】 <1-1. Overall Structure> Figure 1 shows the cross-sectional configuration of a secondary battery. As shown in Figure 1, this secondary battery is a so-called cylindrical secondary battery in which the battery elements 20 are housed inside a cylindrical battery case 11. The symbol CP represents the central axis of this secondary battery. 【0018】 In the following, the direction in which the battery elements 20 are housed inside the battery can 11, that is, the height direction of the cylindrical battery can 11, is defined as the Z direction, and the radial direction of the cylindrical battery can 11 is defined as the R direction. 【0019】 More specifically, in the secondary battery shown in Figure 1, for example, a pair of insulating plates 12 and 13 and a battery element 20 are housed inside a cylindrical battery case 11. A safety valve mechanism 30 is attached to the battery case 11. The battery case 11 is sealed by, for example, a battery cover 14. However, the secondary battery may further include a thermal resistance element (also called a PTC element) and reinforcing members inside the battery case 11. Also, in the secondary battery shown in Figure 1, the end on the side where the battery cover 14 is provided in the Z direction is sometimes called the upper part, and the end on the opposite side of the battery cover 14 in the Z direction is sometimes called the lower part. The battery can 11 is a specific example corresponding to "container" as one aspect of this disclosure. The battery cover 14 is a specific example corresponding to "lid member" as one aspect of this disclosure. 【0020】 [Battery can] The battery can 11 is a hollow container that extends in the Z direction, with a first end in the Z direction being open and a second end opposite to the first end in the Z direction being closed. The first end of the battery can 11 in the Z direction is the open end 11N. The battery can 11 contains one or more types of metallic materials, such as iron, aluminum, and their alloys. The surface of the battery can 11 may be plated with one or more types of metallic materials, such as nickel. In particular, it is preferable that the battery can 11 contains an iron-based material containing iron (Fe), such as stainless steel. This is because the physical strength of the battery can 11 is ensured, and even if the internal pressure of the battery can 11 rises, the detachment of the battery lid 14 and leakage of the electrolyte are suppressed. Specific examples of stainless steel include SUS304 and SUS430. 【0021】 [insulating board] The pair of insulating plates 12 and 13 are arranged to sandwich the battery element 20 in the Z direction and to extend along a plane perpendicular to the Z direction. 【0022】 [Crimped structure] The open end 11N of the battery can 11 is crimped to the battery cover 14 and the safety valve mechanism 30 via a gasket 15. The battery can 11 has a bent portion 11P that defines the open end 11N. 【0023】 With the battery elements 20 and the like housed inside the battery can 11, the open end 11N of the battery can 11 is sealed by the battery cover 14. The battery can 11 has a crimping structure 11R formed near the open end 11N. The crimping structure 11R is a structure in which the 11P defining the open end 11N, the battery cover 14 and the safety valve mechanism 30 are crimped together via a gasket 15. Between the bent portion 11P and the insulating plate 12, there is a constricted portion 11S in which a part of the battery can 11 protrudes inward. The bent portion 11P is a specific example corresponding to the "crimped portion" as one aspect of this disclosure. The crimping structure 11R is also called the crimped structure. 【0024】 [Battery cover] The battery cover 14 is a cover member that closes the open end 11N of the battery can 11. The battery cover 14 is attached to the bent portion 11P via a gasket 15 so as to close the open end 11N. The battery cover 14 together with the safety cover 31 (described later) constitutes the cover portion. The battery cover 14 may be made of the same material as the forming material of the battery can 11. However, the battery cover 14 may contain a different forming material than the forming material of the battery can 11. 【0025】 In particular, the battery cover 14 is preferably made of an iron-based material containing iron (Fe), such as stainless steel. This is because the physical strength of the crimped structure 11R is ensured by the physical strength of the battery cover 14, and even if the internal pressure of the battery can 11 rises, the battery cover 14 will not fall off and the electrolyte will not leak. Specific examples of stainless steel include SUS304 and SUS430. 【0026】 The battery cover 14 has a protrusion 14T in the center that extends away from the battery element 20 (in the +Z direction). The part of the battery cover 14 other than the center, that is, the part surrounding the protrusion 14T, is a flange 14F. The flange 14F of the battery cover 14 is joined to the flange 31F (described later) of the safety cover 31 of the safety valve mechanism 30, facing it in the Z direction. The part where flange 14F and flange 31F are welded together is called the laminated section SS. Flange 14F is a specific example corresponding to the "first flange" as one aspect of this disclosure. 【0027】 [gasket] The gasket 15 is a sealing member that seals the gap between the bent portion 11P and the battery cover 14. The gasket 15 is interposed between the bent portion 11P of the battery can 11 and the battery cover 14. 【0028】 The gasket 15 contains one or more insulating materials, and specific examples of these insulating materials are polymer materials such as polybutylene terephthalate (PBT) and polypropylene (PP). In particular, the gasket 15 preferably contains polypropylene. This is because the battery can 11 and the battery cover 14 are electrically isolated from each other, while the gap between the folded portion 11P and the battery cover 14 is sufficiently sealed. 【0029】 [Safety valve mechanism] The safety valve mechanism 30 is located inside the battery cover 14 in the Z direction. The safety valve mechanism 30 is a mechanism that releases the internal pressure of the battery can 11 by releasing the sealed state of the battery can 11 as needed when the internal pressure of the battery can 11 rises. The cause of the rise in internal pressure of the battery can 11 is gas generated due to the decomposition reaction of the electrolyte during charging and discharging. The detailed configuration of the safety valve mechanism 30 will be described later (see Figures 2-5 below). 【0030】 [Battery element] The battery element 20 is housed inside the battery case 11 and contains an electrolyte, which is a liquid electrolyte, along with the positive electrode 21 and the negative electrode 22. The electrolyte is not limited to a liquid form; for example, it may be a gel-type electrolyte. 【0031】 Here, the battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are stacked with a separator 23 in between, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound together. The electrolyte is impregnated into the positive electrode 21, the negative electrode 22, and the separator 23, respectively. 【0032】 At the center of the battery element 20, a space is formed, i.e., a central space 20C, which is created when winding the positive electrode 21, negative electrode 22, and separator 23. A center pin 24 is inserted into the central space 20C. However, the center pin 24 may be omitted. 【0033】 A positive electrode lead 25 is connected to the positive electrode 21. A negative electrode lead 26 is connected to the negative electrode 22. The positive electrode lead 25 contains one or more types of conductive materials, such as metal materials. A specific example of the metal material constituting the positive electrode lead 25 is aluminum. The positive electrode lead 25 is electrically connected to the battery cover 14 via a safety valve mechanism 30. The negative electrode lead 26 contains one or more types of conductive materials, such as metal materials. A specific example of the metal material constituting the negative electrode lead 26 is nickel. The negative electrode lead 26 is electrically connected to the battery can 11. 【0034】 The detailed configuration of the battery element 20, namely the positive electrode 21, negative electrode 22, separator 23, and electrolyte, will be described later (see Figure 7). 【0035】 <1-2. Detailed Configuration of the Safety Valve Mechanism> Figure 2 shows a portion of the cross-sectional configuration of the secondary battery shown in Figure 1, more specifically the safety valve mechanism 30 and its vicinity. Figure 3 is an enlarged cross-sectional view showing an example of the configuration of the safety valve mechanism 30. 【0036】 As shown in Figure 2, the safety valve mechanism 30 includes, for example, a safety cover 31, a disc holder 32, a stripper disc 33, and a sub-disc 34. The safety cover 31 and the stripper disc 33 are fixed together via the disc holder 32. The safety cover 31 and the stripper disc 33 are electrically insulated from each other by the disc holder 32, except for the connecting portion in their central regions. The stripper disc 33 is located on the battery element 20 side when viewed from the safety cover 31. That is, the safety cover 31 is provided between the stripper disc 33 and the battery cover 14. Furthermore, the sub-disc 34 is located furthest from the battery element 20 side of the safety valve mechanism 30. That is, the sub-disc 34 is provided between the stripper disc 33 and the battery element 20 and is connected to the positive electrode lead 25. 【0037】 Figure 4 is an exploded perspective view of the safety valve mechanism 30. 【0038】 [Safety cover] As shown in Figure 2, the safety cover 31 is provided so as to face the lower surface 14BS of the battery cover 14. The safety cover 31 is partially detachable in response to an increase in the internal pressure of the battery can 11. As shown in Figure 3, for example, the safety cover 31 includes a valve portion 31V in the central region AR1 of the safety valve mechanism 30 that is detachable in response to an increase in the internal pressure of the battery can 11. When the safety cover 31 detaches, the valve portion 31V may be partially detached, or the entire valve portion 31V may be ruptured. The safety cover 31 is a specific example corresponding to a "valve member" as one aspect of this disclosure. 【0039】 In the peripheral region AR2 of the safety valve mechanism 30, the safety cover 31 further includes an annular projection 31Z that extends to surround the valve portion 31V. The annular projection 31Z has an end face 31ZS on its outer side in the R direction, which is the radial direction of the secondary battery. As will be described later, the end face 31ZS faces the end face 332S of the stripper disc 33, with the annular wall portion 32W of the disc holder 32 in between. A central projection 31T is provided at the center of the valve portion 31V, i.e., at a position that coincides with the central axis CP. The central projection 31T protrudes downward from the valve portion 31V toward the battery element 20, is inserted through the through hole 33H (described later), and is in contact with the upper surface of the sub-disk 34. 【0040】 In the peripheral region AR2, the safety cover 31 further includes a flange 31F. The flange 31F is an annular portion located on the outside in the R direction when viewed from the annular projection 31Z and extending along a horizontal plane perpendicular to the Z direction. The flange 31F overlaps with the flange 14F of the battery cover 14 in the Z direction and together with the flange 14F constitutes a laminated portion SS. Furthermore, flange 31F is a specific example corresponding to the "second flange" as one aspect of this disclosure. 【0041】 The safety cover 31 contains one or more types of conductive materials, such as metal materials, and specific examples of such metal materials include aluminum and aluminum alloys. The planar shape of the safety cover 31 is not particularly limited, but specifically it is circular, for example. This "planar shape" refers to a shape along a horizontal plane perpendicular to the Z direction, and the definition of planar shape described here will be the same hereafter. 【0042】 [Disk holder] The disc holder 32 is an interposed component between the safety cover 31 and the stripper disc 33, which aligns the stripper disc 33 with respect to the safety cover 31 and securely holds the stripper disc 33 to the safety cover 31. The disc holder 32 contains one or more types of insulating materials, such as polymer materials, and specific examples of these polymer materials include polypropylene (PP) and polybutylene terephthalate (PBT). 【0043】 The planar shape of the disk holder 32 is not particularly limited, but specifically it is circular, for example. The disk holder 32 has an opening 32K that penetrates in the Z direction at a position occupying the central region AR1. The opening 32K is a vent for releasing gas generated inside the battery can 11 to the outside. The planar shape of the opening 32K is not particularly limited, but specifically it is circular, for example. In the peripheral region AR2, the disk holder 32 has an annular wall portion 32W that surrounds the annular projection portion 31Z along a horizontal plane perpendicular to the Z direction. 【0044】 As shown in Figures 3 and 4, the disc holder 32 further includes a flange 32F. The flange 32F is an annular portion extending along a horizontal plane perpendicular to the Z direction. In the Z direction, the flange 32F is sandwiched between the flange 31F of the safety cover 31 and the flange 331F of the stripper disc 33. 【0045】 [Stripper Disc] The stripper disc 33 is a component that releases gas generated inside the battery can 11. The stripper disc 33 is also in a state where it can conduct electricity with the valve portion 31V of the safety cover 31 via the sub-disc 34. When the internal pressure of the secondary battery rises, the safety cover 31 separates from the sub-disc 34. When the valve portion 31V of the safety cover 31 separates from the sub-disc 34, the conductivity between the safety cover 31 and the stripper disc 33 and sub-disc 34 is released, and the current inside the secondary battery is interrupted. The stripper disc 33 contains one or more types of conductive materials such as metal materials, and specific examples of such metal materials include aluminum and aluminum alloys. 【0046】 The stripper disc 33 includes a main body 331 and a claw member 332. The claw member 332 is provided between the main body 331 and the disc holder 32. The main body 331 and the claw member 332 are joined to each other by various methods such as laser welding, resistance welding, or ultrasonic welding. The stripper disc 33 is spaced apart from the flange 31F of the safety cover 31, and the flange 32F of the disc holder 32 is sandwiched in the gap between the stripper disc 33 and the flange 31F. 【0047】 (Main body) The planar shape of the main body 331 is not particularly limited, but specifically it is circular. The main body 331 has a disc-shaped central part 331C that occupies the central region AR1, and an annular flange 331F provided in the peripheral region AR2 so as to surround the central part 331C along the horizontal plane. A through hole 33H is provided at the center of the central part 331C, penetrating in the Z direction. The central projection 31T is inserted through the through hole 33H. Furthermore, an opening 331K is formed in the central part 331C, penetrating in the Z direction around the through hole 33H. The opening 331K is provided at a position that overlaps with the valve part 31V in the Z direction. The opening 331K, like the opening 32K, is a vent for releasing gas generated inside the battery can 11 to the outside. Therefore, as shown in Figure 3 and other figures, the opening 331K is not blocked by the disk holder 32 and is in communication with the opening 32K. In other words, the main body 331 of the stripper disc 33 is provided to occupy all areas that overlap with the disc holder 32 in the Z direction. With this configuration, even if the disc holder 32 softens due to heating, the disc holder 32 can be kept in a predetermined position. Furthermore, it is desirable to provide multiple openings 331K. This is because gas generated inside the battery can be quickly released to the outside, ensuring a high level of safety. The number of openings 331K is not particularly limited, but it is preferable to have 6 to 8. This is because having 6 or more openings 331K allows gas generated inside the battery can 11 to be released to the outside more efficiently, ensuring a higher level of safety. Also, having 8 or fewer openings 331K ensures sufficient mechanical strength and further reduces variations in the safety valve operating pressure. 【0048】 (Claw member 332) The planar shape of the claw member 332 is not particularly limited, but specifically it is annular in shape. The claw member 332 has a claw portion 332A and an annular support portion 332B that supports the claw portion 332A. The annular support portion 332B is joined to the flange 331F so as to overlap in the Z direction. It is preferable that multiple claw portions 332A are provided along the horizontal plane so as to surround the annular projection 31Z of the safety cover 31. This is because providing multiple claw portions 332A along the direction that circumfers the central axis CP reduces variations in the mechanical strength of the safety valve mechanism 30 due to differences in position in the horizontal plane. As shown in Figure 4, the claw portion 332A is provided inside the annular support portion 332B and protrudes toward the central axis CP. The end face 332S of the tip of the claw portion 332A faces the end face 31ZS of the annular projection 31Z via the annular wall portion 32W of the disc holder 32. The number of claws 332A is not particularly limited, but it is preferable that it be between 6 and 9. This is because having 6 or more claws 332A can further reduce variations in the mechanical strength of the safety valve mechanism 30 due to differences in position within the horizontal plane. Also, having 9 or fewer claws 332A ensures machining accuracy and ease of machining of the claws 332A. 【0049】 The sub-disk 34 is an interposed component between the safety cover 31 and the positive electrode lead 25, thereby electrically connecting the central projection 31T of the safety cover 31 to the positive electrode lead 25. The sub-disk 34 contains one or more types of conductive materials, such as metal materials, and specific examples of such metal materials include aluminum and aluminum alloys. The planar shape of the sub-disk 34 is not particularly limited, but specifically, it is circular, for example. 【0050】 Figure 5 is a partially cross-sectional view showing an enlarged example of the configuration of the bent portion 11P and its vicinity. As shown in Figure 5, the flange 14F of the battery cover 14 and the flange 31F of the safety cover 31 are welded to each other to form a laminated portion SS. The laminated portion SS is sandwiched in the Z direction by the bent portion 11P via a gasket 15. That is, the battery cover 14 and the safety cover 31 of the safety valve mechanism 30 are attached to the bent portion 11P via a gasket 15. The laminated portion SS includes a weld mark WM formed so as to straddle the interface KS between the upper surface 14US of the flange 14F and the upper surface covering portion F3 (described later) of the flange 31F in the Z direction. The weld mark WM is formed by irradiation with an energy ray such as a laser or electron beam. The weld mark WM is a portion where the first material, such as nickel-plated stainless steel that constitutes the battery cover 14, and the second material, such as aluminum or aluminum alloy that constitutes the safety cover 31, have solid-solved together. The bent portion 11P includes a lower surface facing portion 11P1, an end surface facing portion 11P2, and an upper surface facing portion 11P3. The lower surface facing portion 11P1 is the portion facing the lower surface 14BS of the flange 14F. The lower surface facing portion 11P1 sandwiches the gasket 15 and the lower surface covering portion F1 (described later) of the flange 31F in the Z direction between itself and the lower surface 14BS of the flange 14F. The end surface facing portion 11P2 is the portion facing the end surface 14ES of the flange 14F. The end surface facing portion 11P2 sandwiches the gasket 15 and the end surface covering portion F2 (described later) of the flange 31F in the R direction between itself and the end surface 14ES of the flange 14F. The end surface facing portion 11P2 is the portion connecting the lower surface facing portion 11P1 and the upper surface facing portion 11P3, and extends approximately in the Z direction. The upper facing portion 11P3 includes the open end 11N and extends approximately in the R direction. The upper facing portion 11P3 faces the upper surface 14US of the flange 14F. The upper facing portion 11P3 sandwiches the gasket 15 and the upper covering portion F3 of the flange 31F in the Z direction between itself and the upper surface 14US of the flange 14F. Furthermore, the upper facing portion 11P3 is the portion that faces the lower facing portion 11P1 in the Z direction, sandwiching the laminated portion SS via the gasket 15.Therefore, in the crimping structure 11R, in the Z direction, the upper surface facing portion 11P3, the gasket 15, the upper surface covering portion F3 of the flange 31F, the flange 14F, the lower surface covering portion F1 of the flange 31F, and the lower surface facing portion 11P1 are arranged in that order from the top to the bottom of the secondary battery. 【0051】 The flange 14F includes a lower surface 14BS, an upper surface 14US, and an end surface 14ES. The lower surface 14BS is the surface facing the flange 31F. The upper surface 14US is the surface opposite to the interface KS, i.e., the surface opposite to the flange 31F. The end surface 14ES is the surface that connects the lower surface 14BS and the upper surface 14US and is provided along the outer edge of the flange 14F. The flange 31F has a folded structure that continuously covers the flange 14F from the lower surface 14BS through the end surface 14ES to the upper surface 14US. Specifically, the flange 31F has a lower surface covering portion F1 that covers the lower surface 14BS, an end surface covering portion F2 that covers the end surface 14ES, and an upper surface covering portion F3 that covers the upper surface 14US. Here, the upper covering portion F3 of the flange 31F includes a first portion R1 having a first thickness H1 and a second portion R2 having a second thickness H2. The first thickness H1 is the maximum thickness of the first portion R1. The second portion R2 is located between the first portion R1 and the end face 14ES in the radial direction (R direction). The second thickness H2 is thinner than the first thickness H1 (H1 > H2). The second thickness H2 is the maximum thickness of the second portion R2. The first thickness H1 may be, for example, 120% or less of the second thickness H2. The bent portion 11P continuously covers the lower covering portion F1, the end face covering portion F2, and the upper covering portion F3 via the gasket 15. However, at least a part of the first portion R1 is exposed and not covered by the gasket 15. 【0052】 In the flange 31F, the second portion R2 of the upper surface covering portion F3 is sandwiched in the Z direction between the open end 11N, which is the tip of the upper surface opposing portion 11P3 of the bent portion 11P, and the upper surface 14US of the flange 14F. 【0053】 Figure 6 is a schematic plan view of the safety cover 31, showing the safety cover 31 viewed in the Z direction from the opposite side of the battery element 20. As shown in Figure 6, in a plan view of the safety cover 31 in the Z direction, the first part R1 and the second part R2 are each provided in an annular shape, and the first part R1 is provided inside the second part R2. 【0054】 As shown in Figure 5, the first portion R1 of the upper covering portion F3 may include, for example, the tip portion 31FT of the upper covering portion F3. Furthermore, it is preferable that at least a part of the tip portion 31FT of the upper covering portion F3 is joined to the upper surface 14US of the flange 14F. For example, the weld marks WM are provided discretely along the tip portion 31FT in a plane perpendicular to the Z direction. Figure 6 illustrates a case where weld marks WM are provided in three locations. That is, in the example in Figure 6, the tip portion 31FT of the upper covering portion F3 and the upper surface 14US of the flange 14F are joined at three locations. 【0055】 Furthermore, as shown in Figure 3, the ratio of the width L in the R direction of the upper covering portion F3 to the diameter D14 of the battery cover 14 (L / D14) should be, for example, 6.36% or more and 10.98% or less. 【0056】 <1-3. Detailed Configuration of Battery Components> Figure 7 shows a magnified view of a portion of the cross-sectional configuration of the battery element 20 shown in Figure 1. As described above, the battery element 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte. 【0057】 [Positive electrode] As shown in Figure 7, the positive electrode 21 includes a positive electrode current collector 21A and a positive electrode active material layer 21B. 【0058】 The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is provided. The positive electrode current collector 21A contains a conductive material such as a metal material, a specific example of which is aluminum. 【0059】 In the example shown in Figure 7, the positive electrode active material layer 21B is provided on both sides of the positive electrode current collector 21A. The positive electrode active material layer 21B contains one or more types of positive electrode active materials capable of intercalating and deintercalating lithium. However, the positive electrode active material layer 21B may be provided on only one side of the positive electrode current collector 21A on the side where the positive electrode 21 faces the negative electrode 22. Furthermore, the positive electrode active material layer 21B may also contain a positive electrode binder and a positive electrode conductive agent. The method for forming the positive electrode active material layer 21B is not particularly limited, but specifically, it may be a coating method. 【0060】 The positive electrode active material contains a lithium compound. This lithium compound is a compound that contains lithium as a constituent element, and more specifically, a compound that contains lithium along with one or more transition metal elements as constituent elements. This is because a high energy density can be obtained. However, the lithium compound may also contain one or more other elements, i.e., elements other than lithium and the transition metal elements. 【0061】 The types of lithium compounds are not particularly limited, but specifically include lithium composite oxides having a layered rock salt crystal structure, lithium composite oxides having a spinel crystal structure, and lithium phosphate compounds having an olivine crystal structure. A specific example of a lithium composite oxide having a layered rock salt crystal structure is LiNiO 2 、 LiRing 0.8 Co 0.15 Al 0.05 Examples include LiCoO2. A specific example of a lithium composite oxide having a spinel-type crystal structure is LiMn2O4. Specific examples of lithium phosphate compounds having an olivine-type crystal structure are LiFePO4 and LiMnPO4. 【0062】 In particular, the positive electrode active material preferably contains a lithium phosphate compound having an olivine-type crystal structure. This is because the crystal structure of lithium phosphate compounds having an olivine-type crystal structure is thermally stable, making it less likely for thermal runaway caused by overcharging and internal short circuits to occur in secondary batteries. Furthermore, because the crystal structure of lithium phosphate compounds having an olivine-type crystal structure is robust, the battery capacity does not easily decrease even after repeated charging and discharging of secondary batteries. 【0063】 The positive electrode binder contains one or more of the following: synthetic rubber and polymer compounds. Synthetic rubber is styrene-butadiene rubber, while polymer compounds are polyvinylidene fluoride. 【0064】 The positive electrode conductive agent contains one or more types of conductive materials, such as carbon materials, and the carbon materials include graphite, carbon black, acetylene black, and Ketjenblack. However, the conductive materials may also be metallic materials and polymer compounds. 【0065】 [Negative electrode] As shown in Figure 7, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B. 【0066】 The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is provided. The negative electrode current collector 22A contains a conductive material such as a metal material, a specific example of which is copper. 【0067】 Here, the negative electrode active material layer 22B is provided on both sides of the negative electrode current collector 22A and contains one or more types of negative electrode active materials capable of intercalating and deintercalating lithium. However, the negative electrode active material layer 22B may be provided on only one side of the negative electrode current collector 22A on the side where the negative electrode 22 faces the positive electrode 21. Furthermore, the negative electrode active material layer 22B may further contain a negative electrode binder and a negative electrode conductive agent. Details regarding the negative electrode binder and negative electrode conductive agent are the same as the details regarding the positive electrode binder and positive electrode conductive agent. The method for forming the negative electrode active material layer 22B is not particularly limited, but specifically, it may be one or more types from among coating, gas phase, liquid phase, thermal spraying, and firing (sintering). 【0068】 The negative electrode active material includes one or both of the following: carbon materials and metallic materials. This is because a high energy density can be obtained. Carbon materials include easily graphitizable carbon, poorly graphitizable carbon, and graphite (natural graphite and artificial graphite). Metallic materials are materials that contain one or more metallic elements and metalloid elements capable of forming alloys with lithium as constituent elements. Specific examples of these metallic and metalloid elements include one or both of silicon and tin. However, metallic materials may be elements, alloys, compounds, mixtures of two or more of these, or materials containing two or more of these phases. Specific examples of metallic materials are TiSi2 and SiO2. x (0 <x≦2または0.2<x<1.4)などである。 【0069】 [Separator] As shown in Figure 7, the separator 23 is an insulating porous membrane interposed between the positive electrode 21 and the negative electrode 22. The separator 23 allows lithium ions to pass through while preventing a short circuit between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene. 【0070】 [Electrolyte] The electrolyte is an electrolyte solution containing a solvent and an electrolyte salt. The solvent contains one or more non-aqueous solvents (organic solvents) such as carbonate ester compounds, carboxylic acid ester compounds, and lactone compounds, and the electrolyte solution containing such a non-aqueous solvent is a so-called non-aqueous electrolyte solution. However, the solvent may also be an aqueous solvent. The electrolyte salt contains one or more light metal salts such as lithium salts. The content of the electrolyte salt is not particularly limited, but it is preferably 0.3 mol / kg to 3 mol / kg relative to the solvent, because high ionic conductivity can be obtained. 【0071】 <1-4. Operation> Figure 8 is an explanatory diagram illustrating the operation of the secondary battery in this embodiment, specifically its behavior when the internal pressure rises, and shows the cross-sectional configuration corresponding to Figure 2. Below, the operation during charging and discharging will be described, followed by the operation when the internal pressure rises. In this case, Figure 2 will be referred to along with Figure 8 as needed. 【0072】 [Operation during charging and discharging] During charging, lithium is released from the positive electrode 21 of the battery element 20, and this lithium is absorbed into the negative electrode 22 via the electrolyte. Conversely, during discharging, lithium is released from the negative electrode 22 of the battery element 20, and this lithium is absorbed into the positive electrode 21 via the electrolyte. During both charging and discharging, lithium is absorbed and released in an ionic state. 【0073】 [Operation when internal pressure rises] During charging and discharging of the secondary battery, if the internal pressure of the battery case 11 rises, the safety valve mechanism 30 is activated to prevent the secondary battery from rupturing or being damaged. 【0074】 Specifically, during normal operation of the secondary battery, the valve portion 31V of the safety cover 31 is not yet open, as shown in Figure 2. Therefore, the opening 332K of the stripper disc 33 is blocked by the safety cover 31. 【0075】 In contrast, if gas is generated inside the battery can 11 due to side reactions such as the decomposition reaction of the electrolyte, this gas accumulates inside the battery can 11, causing the internal pressure of the battery can 11 to rise. When the internal pressure of the battery can 11 reaches a certain level, the valve portion 31V of the safety cover 31 partially ruptures, as shown in Figure 8. This creates an opening 31K in the safety cover 31, opening the gas release path using the openings 332K, 32K, and 31K. Therefore, the gas generated inside the battery can 11 is released through the openings 332K, 32K, and 31K. Also, the valve portion 31V of the safety cover 31 separates from the sub-disk 34. As a result, the electrical connection between the sub-disk 34 and the stripper disc 33 and the safety cover 31 is released, and the current inside the secondary battery is interrupted. 【0076】 Furthermore, depending on the magnitude of the internal pressure of the secondary battery, the bent portion 11P may deform, causing the crimped structure 11R to break. As a result, the battery cover 14 will detach from the battery case 11, and gas will be released to the outside of the secondary battery. 【0077】 <1-5. Manufacturing method> [Fabrication of the positive electrode] First, a positive electrode mixture is prepared by mixing the positive electrode active material with a positive electrode binder and a positive electrode conductive agent as needed. Next, the positive electrode mixture is dispersed in a solvent to prepare a paste-like positive electrode mixture slurry. The type of solvent is not particularly limited and may be an aqueous solvent or a non-aqueous solvent (organic solvent). Subsequently, the positive electrode mixture slurry is applied to both sides of the positive electrode current collector 21A to form a positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B is compressed and molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or the compression molding of the positive electrode active material layer 21B may be repeated multiple times. As a result, a positive electrode active material layer 21B is formed on both sides of the positive electrode current collector 21A, and the positive electrode 21 is manufactured. 【0078】 [Fabrication of the negative electrode] A negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A using the same procedure as described above for the positive electrode 21. Specifically, a negative electrode mixture is formed by mixing the negative electrode active material with a negative-positive electrode binder and a negative electrode conductive agent. Then, the negative electrode mixture is dispersed in a solvent to form a paste-like negative electrode mixture slurry. Details regarding the solvent are as described above. Next, the negative electrode active material layer 22B is formed by applying the negative electrode mixture slurry to both sides of the negative electrode current collector 22A. Finally, the negative electrode active material layer 22B is compressed and molded using a roll press or the like. Details regarding the compression molding are as described above. As a result, a negative electrode active material layer 22B is formed on both sides of the negative electrode current collector 22A, and the negative electrode 22 is manufactured. 【0079】 [Assembly of rechargeable batteries] First, the positive electrode lead 25 is connected to the positive electrode current collector 21A of the positive electrode 21 using a welding method or the like. Similarly, the negative electrode lead 26 is connected to the negative electrode current collector 22A of the negative electrode 22 using a welding method or the like. Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 to form a laminate, and then the resulting laminate is wound to form a wound body having a central space 20C. This wound body has the same configuration as the battery element 20, except that the positive electrode 21, the negative electrode 22, and the separator 23 are not impregnated with electrolyte. Next, a center pin 24 is inserted into the central space 20C of the wound body. 【0080】 Next, after preparing the battery can 11, the winding body is placed inside the battery can 11 together with the insulating plates 12 and 13, with the insulating plates 12 and 13 facing each other via the winding body. In this case, the positive electrode lead 25 is connected to the safety valve mechanism 30 using a welding method or the like, and the negative electrode lead 26 is connected to the battery can 11 using a welding method or the like. 【0081】 Next, electrolyte is injected into the battery can 11, impregnating the wound material with the electrolyte. This impregnates the positive electrode 21, negative electrode 22, and separator 23 with the electrolyte, thus creating the battery element 20. Next, the safety valve mechanism 30 is fabricated by stacking the safety cover 31, disc holder 32, stripper disc 33, and sub-disc 34 in order, as shown in Figure 4. Furthermore, the battery cover 14 is placed over the safety cover 31, and then the flange 31F of the safety cover 31 is folded back to cover the flange 14F of the battery cover 14, forming a stacked section SS. After that, the upper covering portion F3 of the flange 31F of the safety cover 31 is welded to the flange 14F of the battery cover 14 by laser irradiation. Subsequently, the battery cover 14 and the safety valve mechanism 30 are housed inside the battery can 11 together with the gasket 15. 【0082】 Finally, as shown in Figure 1, the open end 11N of the battery can 11 is crimped to the battery cover 14 and the safety valve mechanism 30 via the gasket 15. This forms the bent portion 11P and the crimped structure 11R. As a result, the battery can 11 is closed by the battery cover 14, and the assembly of the secondary battery is completed. 【0083】 [Stabilization of secondary batteries] The assembled secondary battery is then charged and discharged. Various conditions such as ambient temperature, number of charge / discharge cycles, and charge / discharge conditions can be set arbitrarily. This causes a film to form on the surface of the negative electrode 22, etc., and the state of the secondary battery is electrochemically stabilized. As a result, a cylindrical secondary battery with the battery elements 20 and other components sealed inside the battery case 11 is completed. 【0084】 <1-6. Mechanism and Effects> In the secondary battery of this embodiment, the flange 31F of the safety cover 31 is folded back to continuously cover the flange 14F of the battery cover 14 from the lower surface 14BS through the end surface 14ES to the upper surface 14US, forming a laminated portion SS. Furthermore, the laminated portion SS is sandwiched in the Z direction via a gasket 15 by a bent portion 11P provided at the open end 11N of the battery can 11. As a result, the secondary battery of this embodiment has high sealing performance. That is, it is possible to prevent the electrolyte contained in the battery element 20 from leaking out to the outside through the gap between the battery can 11, the battery cover 14 and the safety valve mechanism 30. 【0085】 Furthermore, in the secondary battery of this embodiment, the upper covering portion F3 of the flange 31F includes a first portion R1 having a first thickness H1 and a second portion R2 located between the first portion R1 and the end face 14ES in the R direction and having a second thickness H2. Here, the first thickness H1 is thicker than the second thickness H2. For this reason, for example, if the battery can 11 is made of a metal material containing iron (Fe) and the safety cover 31 is made of a metal material containing aluminum (Al), even if a short circuit occurs due to saltwater or the like adhering across the bent portion 11P of the battery can 11 and the safety cover 31, the progress of the battery reaction is suppressed. Thus, a high level of safety can be ensured. 【0086】 The following provides a more detailed explanation. When saltwater or the like adheres to the open end 11N of the bent portion 11P of the secondary battery and the upper surface covering portion F3 of the safety cover 31, the positive electrode 21 and the negative electrode 22 are short-circuited externally. This is because the safety cover 31 is electrically connected to the positive electrode 21 and the battery can 11 is electrically connected to the negative electrode 22, and the safety cover 31 and the battery can 11 become electrically connected via the saltwater containing the electrolyte. In such a short-circuit state, the aluminum that makes up the safety cover 31, which is the positive electrode, and the iron that makes up the battery can 11, which is the negative electrode, dissolve. After that, when the saltwater is removed by evaporation or drying, the aluminum becomes an oxide or hydroxide, and the iron becomes an oxide or hydroxide. A mixture of these aluminum oxides or aluminum hydroxides and iron oxides or iron hydroxides may adhere continuously from the open end 11N to the upper surface covering portion F3. In this embodiment, the thickness of the first portion R1 of the upper surface covering portion F3 is greater than the thickness of the second portion R2. Therefore, the proportion of aluminum oxide and aluminum hydroxide in the above mixture becomes large. The insulation resistance of aluminum oxide and aluminum hydroxide is greater than that of iron oxide and iron hydroxide. Consequently, compared to, for example, the case where the thickness of the first part R1 and the thickness of the second part R2 are the same, the resistance between the positive and negative electrodes through the adhering mixture becomes relatively larger. As a result, in the secondary battery of this embodiment, even if an external short circuit occurs due to the adhesion of salt water or the like, the generation of heat and smoke can be suppressed. 【0087】 Furthermore, in the secondary battery of this embodiment, if the positive electrode 21 contains a lithium phosphate compound having an olivine-type crystal structure, thermal runaway of the secondary battery becomes less likely to occur, and the battery capacity does not decrease easily even after repeated charging and discharging, thus achieving higher operational reliability. If the positive electrode 21 contains a nickel-cobalt composite oxide with a layered rock salt-type crystal structure, a battery with an excellent balance between high power output characteristics and energy density can be obtained. 【0088】 Furthermore, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing lithium intercalation and deintercalation, thus achieving higher operational reliability. 【0089】 <2. Variant> The configuration of the secondary battery can be modified as appropriate, as described below. However, any two or more of the variations described below may be combined with each other. 【0090】 [First variation] In the secondary battery of the above embodiment, the first portion R1 includes the tip portion 31FT. However, in the secondary battery of this disclosure, the first portion R1 may be positioned further back than the tip portion 31FT, as in the secondary battery as the first modified example shown in Figure 9. 【0091】 [Second variation] Furthermore, the secondary battery of this disclosure may be formed in which the first portion R1 is formed by bending the tip portion 31FT of the upper surface covering portion F3 upward, as shown in the second modified secondary battery in Figure 10. 【0092】 [Third variation] Furthermore, the secondary battery of this disclosure may be formed by further folding the tip portion 31FT of the upper covering portion F3 outwards, as shown in the third modified secondary battery in Figure 11. 【0093】 [Fourth variation] In the secondary battery of the above embodiment, the entire first portion R1 is exposed without being covered by the gasket 15. However, in the secondary battery of this disclosure, as in the fourth modified secondary battery shown in Figure 12, a portion of the first portion R1 may be covered by the gasket 15. 【0094】 Furthermore, in the above embodiment, an electrolyte solution, which is a liquid electrolyte, was used. However, the secondary battery of this disclosure may use an electrolyte layer, which is a gel-like electrolyte, instead of an electrolyte solution. 【0095】 In the battery element 20 using an electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked on top of each other via a separator 23 and the electrolyte layer, and the positive electrode 21, negative electrode 22, separator 23, and electrolyte layer are wound together. This electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also between the negative electrode 22 and the separator 23. 【0096】 Specifically, the electrolyte layer contains a polymer compound along with the electrolyte, and the electrolyte is held in place by the polymer compound within the electrolyte layer. This prevents leakage of the electrolyte. The composition of the electrolyte is as described above. The polymer compound includes polyvinylidene fluoride, etc. When forming the electrolyte layer, a precursor solution containing the electrolyte, polymer compound, and organic solvent is prepared, and then the precursor solution is applied to one or both sides of the positive electrode 21 and the negative electrode 22, respectively. 【0097】 Even when this electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, so the same effect can be obtained. 【0098】 <3. Applications of rechargeable batteries> Next, I will explain the applications (examples of use) of the secondary batteries mentioned above. 【0099】 The uses of secondary batteries are not particularly limited. Secondary batteries used as power sources are the primary or auxiliary power sources for electronic devices and electric vehicles. A primary power source is a power source that is used preferentially regardless of the availability of other power sources. An auxiliary power source is a power source used in place of the primary power source, or a power source that can be switched to from the primary power source. 【0100】 Specific examples of secondary battery applications are as follows: Electronic devices such as video cameras, digital still cameras, mobile phones, notebook computers, headphone stereos, portable radios, and portable information terminals; backup power supplies and storage devices such as memory cards; power tools such as electric drills and electric saws; battery packs installed in electronic devices; medical electronic devices such as pacemakers and hearing aids; electric vehicles (including hybrid vehicles); and power storage systems such as household or industrial battery systems that store power in preparation for emergencies. In these applications, one secondary battery may be used, or multiple secondary batteries may be used. 【0101】 The battery pack may use individual cells or a battery pack. An electric vehicle is a vehicle that operates (drives) using a secondary battery as its power source, and may also be a hybrid vehicle equipped with a power source other than the secondary battery. In a household power storage system, household electrical appliances can be used by utilizing the electricity stored in the secondary battery, which is the power storage source. 【0102】 Here, we will specifically explain one example of a secondary battery application. The configuration of the application example described below is merely an example and can be modified as needed. 【0103】 Figure 13 shows the block configuration of the battery pack. The battery pack described here is a single rechargeable battery pack (a so-called soft pack) and is installed in electronic devices such as smartphones. 【0104】 As shown in Figure 10, this battery pack comprises a power supply 51 and a circuit board 52. The circuit board 52 is connected to the power supply 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55. 【0105】 The power supply 51 includes one rechargeable battery. In this rechargeable battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since the power supply 51 can be connected to the outside via the positive terminal 53 and the negative terminal 54, it can be charged and discharged. The circuit board 52 includes a control unit 56, a switch 57, a thermal resistance element (PTC element) 58, and a temperature detection unit 59. However, the PTC element 58 may be omitted. 【0106】 The control unit 56 includes a central processing unit (CPU) and memory, and controls the operation of the entire battery pack. This control unit 56 detects and controls the usage status of the power supply 51 as needed. 【0107】 Furthermore, when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or over-discharge detection voltage, the control unit 56 disconnects the switch 57 to prevent charging current from flowing through the current path of the power supply 51. For example, the overcharge detection voltage is 4.2V ± 0.05V, and the over-discharge detection voltage is 2.4V ± 0.1V. 【0108】 Switch 57 includes a charge control switch, a discharge control switch, a charging diode, and a discharging diode, and switches the connection between the power supply 51 and external equipment according to the instructions of the control unit 56. This switch 57 includes a field-effect transistor (MOSFET) using a metal oxide semiconductor, and the charge / discharge current is detected based on the ON resistance of switch 57. 【0109】 The temperature detection unit 59 includes a temperature detection element such as a thermistor and measures the temperature of the power supply 51 using the temperature detection terminal 55, and outputs the temperature measurement result to the control unit 56. The temperature measurement result measured by the temperature detection unit 59 is used when the control unit 56 performs charge / discharge control in the event of abnormal heat generation, and when the control unit 56 performs correction processing when calculating the remaining capacity. [Examples] 【0110】 Examples of the present disclosure will be described below. 【0111】 <Example 1> After fabricating a secondary battery as described below, its battery characteristics were evaluated. 【0112】 [Manufacturing of secondary batteries] A cylindrical lithium-ion secondary battery (diameter = outer diameter 21 mm and length 70 mm) shown in Figure 1 was fabricated using the procedure described below. 【0113】 (Fabrication of the positive electrode) First, the positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 A positive electrode mixture was prepared by mixing 94 parts by mass of (a, 3 parts by mass of a positive electrode binder (polyvinylidene fluoride) and 3 parts by mass of a positive electrode conductive agent (graphite). Next, the positive electrode mixture was added to a solvent (an organic solvent, N-methyl-2-pyrrolidone), and the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both sides of the positive electrode current collector 21A (a strip of aluminum foil with a thickness of 15 μm) using a coating apparatus, and the positive electrode mixture slurry was dried to form the positive electrode active material layer 21B. Finally, the positive electrode active material layer 21B was compressed and molded using a roll press. 【0114】 (Fabrication of the negative electrode) First, a negative electrode mixture was prepared by mixing 95 parts by mass of negative electrode active material (graphite), 3 parts by mass of negative electrode binder (styrene-butadiene rubber (SBR)), and 2 parts by mass of negative electrode conductive agent (carbon black). Next, the negative electrode mixture was added to a solvent (water), and the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Subsequently, the negative electrode mixture slurry was applied to both sides of the negative electrode current collector 22A (a strip of copper foil with a thickness of 15 μm) using a coating apparatus, and the negative electrode mixture slurry was dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compressed and molded using a roll press. 【0115】 (Preparation of electrolyte solution) An electrolyte salt (LiPF6) was added to a solvent (ethylene carbonate, ethylmethyl carbonate, and dimethyl carbonate), and the solvent was then stirred. In this case, the solvent mixing ratio (by weight) was ethylene carbonate:ethylmethyl carbonate:dimethyl carbonate = 20:20:60, and the electrolyte salt content was 1 mol / kg relative to the solvent. 【0116】 (Assembly of secondary batteries) First, an aluminum positive electrode lead 25 was welded to the positive electrode 21 (positive electrode current collector 21A), and a nickel negative electrode lead 26 was welded to the negative electrode 22 (negative electrode current collector 22A). Next, the positive electrode 21 and the negative electrode 22 were stacked on top of each other via a separator 23 (a porous polyethylene film with a thickness of 16 μm), and then the positive electrode 21, the negative electrode 22, and the separator 23 were wound together to create a wound body with a central space 20C. Subsequently, a center pin 24 was inserted into the central space 20C of the wound body. 【0117】 Next, a safety valve mechanism 30 was prepared, which included an aluminum safety cover 31, a polybutylene terephthalate (PBT) disc holder 32, and an aluminum stripper disc 33. Furthermore, after placing the battery cover 14 over the safety cover 31, the flange 31F of the safety cover 31 was folded over to cover the flange 14F of the battery cover 14, forming a laminated section SS. Here, the outer diameter D14 of the battery cover 14 and the width L of the upper covering section F3 were the values ​​shown in Table 1 below. The first thickness H1 of the first section R1 and the second thickness H2 of the second section R2 were also the values ​​shown in Table 1. After that, the upper covering section F3 of the flange 31F of the safety cover 31 was welded to the flange 14F of the battery cover 14 by laser irradiation. At that time, as shown in Figure 6 for example, welding was performed at three locations so that they were at approximately equal intervals in a plan view, forming weld marks WM. 【0118】 Next, the winding body was placed inside the nickel-plated iron battery case 11 along with a pair of insulating plates 12 and 13. The positive electrode lead 25 was welded to the stripper disc 33 of the safety valve mechanism 30, and the negative electrode lead 26 was welded to the battery case 11. Subsequently, electrolyte was injected into the battery case 11 using a reduced pressure method, and the electrolyte was impregnated into the winding body. 【0119】 Next, asphalt was added to the solvent (ethylcyclohexane, an organic solvent), and the solvent was stirred to prepare a coating solution. After that, the coating solution was applied to a polypropylene gasket 15. 【0120】 Finally, a crimped structure 11R was formed by crimping the open end 11N of the battery can 11, the battery cover 14, and the safety valve mechanism 30 together via a polypropylene gasket 15. 【0121】 As a result, the open end 11N of the battery can 11 is closed by the battery cover 14, and battery elements and other components are housed inside the battery can 11, thus assembling a cylindrical lithium-ion secondary battery. 【0122】 (Stabilization of secondary batteries) A secondary battery was subjected to one charge-discharge cycle in a normal temperature environment (temperature = 23°C). During charging, constant current charging was performed at a current of 0.1C until the voltage reached 4.2V, and then constant voltage charging was performed at that voltage of 4.2V until the current reached 0.05C. During discharging, constant current discharge was performed at a current of 0.1C until the voltage reached 3.0V. 0.1C is the current value required to completely discharge a battery with a theoretical capacity of 4000mAh in 10 hours, and 0.05C is the current value required to completely discharge a battery with a theoretical capacity of 4000mAh in 20 hours. 【0123】 As a result, the state of the secondary battery was electrochemically stabilized, leading to the completion of a cylindrical lithium-ion secondary battery. 【0124】 [Evaluation of battery characteristics] The fabricated secondary batteries were subjected to water resistance evaluation according to the procedure described below, and the results shown in Table 1 were obtained. Specifically, water resistance was evaluated by conducting a voltage drop confirmation test. 【0125】 (Voltage drop verification test) First, the open-circuit voltage Vs of the sample secondary battery was measured (Procedure 1). Next, as shown in Figure 14, for example, cellophane tape was wrapped around the outer surface of the crimped structure 11R at least once to form a cylindrical wall portion 61 that stands upright in the Z direction along the outer edge of the battery cover 14 (Procedure 2). Next, a 1% salt solution was placed in the space 61V enclosed by the battery cover 14 and the wall portion 61 and left for 2 hours (Procedure 3). After that, the cellophane tape was removed from the secondary battery, and the secondary battery was turned upside down with the top surface 14US of the battery cover 14 facing vertically downwards and left for 3 hours or more to air dry (Procedure 4). After drying, the open-circuit voltage Ve of the secondary battery was measured (Procedure 5). The voltage drop rate [%] was calculated using the following equation (1) with the open-circuit voltage Vs before salt water immersion and the open-circuit voltage Ve after salt water immersion. The number of samples was 5, and the average value was calculated. 【0126】 {(Vs-Ve) / Vs}×100[%] ……(1) 【0127】 The open-circuit voltages Vs and Ve were measured using a battery tester with a constant AC current at a measurement frequency of 1 kHz and an AC voltmeter. The batteries were discharged to 2.5V with a constant current of 4.0A under an atmosphere of 23±2℃. The obtained voltage drop rates [%] are shown in Table 1. 【0128】 [Table 1] 【0129】 <Examples 2-4> Except for changing the second thickness H2 of the upper coating portion F3 as shown in Table 1, secondary batteries for Examples 2 to 4 were manufactured in the same manner as in Example 1, and the same battery characteristics were evaluated as in Example 1. The results are also shown in Table 1. 【0130】 <Examples 5-8> Except for changing the width L of the upper covering portion F3 as shown in Table 1, secondary batteries for Examples 5 to 8 were manufactured in the same manner as in Example 1, and the same battery characteristics were evaluated as in Example 1. The results are also shown in Table 1. 【0131】 <Comparative Examples 1-2> Except for changing the second thickness H2 of the upper coating portion F3 as shown in Table 1, the secondary batteries of Comparative Examples 1 and 2 were fabricated in the same manner as in Example 1, and the battery characteristics were evaluated in the same manner as in Example 1. The results are also shown in Table 1. 【0132】 [Table 2] 【0133】 Furthermore, the internal resistance of the secondary battery of Example 2 was measured. The resistance was measured when a constant AC current at a measurement frequency of 1 kHz was applied. The results are shown in Table 2. In addition, the secondary battery of Example 9 was manufactured in the same manner as in Example 2, except that the upper surface covering portion F3 of the flange 31F was not welded to the upper surface 14US of the battery cover 14, and the internal resistance was measured in the same manner as in Example 2. The results are also shown in Table 2. 【0134】 [result] As shown in Table 1, in all of Examples 1 to 8, the voltage drop rate was smaller than that of Comparative Examples 1 to 2. In other words, in Examples 1 to 8, the progress of the battery reaction was slowed down compared to Comparative Examples 1 to 2. Therefore, it was confirmed that higher reliability can be obtained according to the present invention. 【0135】 Furthermore, from the results of Examples 1 to 4, it was found that the larger the ratio H1 / H2 of the first thickness to the second thickness H2, the smaller the voltage drop rate could be kept. However, in Example 4, since the ratio (H1 / H2) exceeded 120%, it was confirmed that defects were likely to occur in the welding of the upper surface covering portion F3 of the flange 31F to the upper surface 14US of the battery cover 14. Also, in Example 7, the ratio (L / D14) of the width L of the upper surface covering portion F3 to the outer diameter D14 of the battery cover 14 was larger than in the other examples, so the voltage drop rate could be kept small. However, in Example 7, it was confirmed that defects were likely to occur in the welding of the upper surface covering portion F3 of the flange 31F to the upper surface 14US of the battery cover 14. 【0136】 Although the present disclosure has been described above with reference to one embodiment and one example, the configuration of the present disclosure is not limited to the configuration described in the one embodiment and one example, and can be modified in various ways. 【0137】 Specifically, the explanation described the case where the element structure of the battery element is a wound type, but the element structure of the battery element is not particularly limited, and other element structures such as a stacked type in which the electrodes (positive electrode and negative electrode) are stacked, and a zigzag-fold type in which the electrodes (positive electrode and negative electrode) are folded are also acceptable. 【0138】 Furthermore, while we have described the case where the electrode reactant is lithium, the electrode reactant is not particularly limited. Therefore, as mentioned above, the electrode reactant may be other alkali metals such as sodium and potassium, or alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reactant may be other light metals such as aluminum. 【0139】 Furthermore, in the above embodiment, the upper surface covering portion F3 of the flange 31F includes an annular first portion R1, but the disclosure is not limited to this embodiment. For example, as in the secondary battery as a fifth modified example shown in Figure 15, the tip portion 31FT of the upper surface covering portion F3, which is provided in an annular shape in plan view, may selectively include the first portion R1 and the third portion R3 in its extending direction. Figure 15 is a schematic plan view of the safety valve mechanism of the secondary battery as a fifth modified example. The third portion R3 has a third thickness that is thinner than the first thickness H1. It is preferable that the third thickness is equal to or greater than the second thickness H2. It is also preferable that the third portion R3 of the tip portion 31FT is welded to the upper surface 14US of the flange 14F. In this modified example, by joining the third portion R3 to the upper surface 14US of the flange 14F, it can be welded well by irradiation with an energy ray (such as a laser or electron beam) having lower energy than when the first portion R1 is joined to the upper surface 14US of the flange 14F. On the other hand, by providing the first portion R1, which has a relatively large thickness, it becomes easier to stop the progress of the battery reaction due to external short circuits caused by the adhesion of saltwater, etc. 【0140】 The effects described herein are illustrative only, and therefore the effects of this disclosure are not limited to those described herein. Accordingly, other effects may be obtained with respect to this disclosure. [Explanation of Symbols] 【0141】 11...Battery can, 11N...Open end, 11P...Bent part, 11P1...Bottom opposing part, 11P2...End opposing part, 11P3...Top opposing part, 11R...Crimped structure, 12,13...Insulating plate, 14...Battery cover, 14US...Top surface, 14BS...Bottom surface, 14ES...End surface, 14F...Flange, 15...Gasket, 20...Battery element, 20C...Center space, 21...Positive electrode, 22...Negative electrode, 23...Separator, 24...Center Turpin, 25... Positive lead, 26... Negative lead, 30... Safety valve mechanism, 31... Safety cover, 31F... Flange, F1... Bottom cover, F2... End cover, F3... Top cover, 31US... Top surface, 31V... Valve section, 31BS... Bottom surface, 31ES... End face, 32... Disc holder, 33... Stripper disc, AR1... Central region, AR2... Peripheral region, KS... Interface, SS... Laminated section, WS... Weld marks.

Claims

[Claim 1] Battery element and A container for housing the battery element, having a first end and a second end located opposite to the first end in a first direction, The lid attached to the container via an insulating member and Equipped with, The lid portion includes a lid member including a first flange that extends radially in the direction of the container perpendicular to the first direction, and a valve member including a second flange that extends radially so as to overlap with the first flange in the first direction and is located between the lid member and the battery element in the first direction. The first flange includes a lower surface facing the second flange, an upper surface opposite to the second flange, and an end surface connecting the lower surface and the upper surface. The second flange is folded back so as to continuously cover from the lower surface through the end surface to the upper surface. The upper covering portion of the second flange that covers the upper surface includes a first portion having a first thickness and a second portion that is located between the first portion and the end face in the radial direction and has a second thickness that is thinner than the first thickness. Secondary battery. [Claim 2] The first end of the container includes a crimped portion. The lid portion is attached to the crimped portion via a gasket. The secondary battery according to claim 1. [Claim 3] The crimped portion sandwiches the laminated portion, which is formed by stacking the first flange and the second flange, in the first direction via the gasket. The secondary battery according to claim 2. [Claim 4] At least a portion of the first part is exposed and not covered by the gasket. The secondary battery according to claim 3. [Claim 5] The crimped portion is, The lower surface facing portion of the first flange that is facing the lower surface, sandwiching the gasket and the second flange, The end face facing portion of the first flange that is facing the end face of the first flange, sandwiching the gasket and the second flange, The upper surface facing portion of the first flange that is facing the upper surface, sandwiching the gasket and the second flange. has A secondary battery according to any one of claims 2 to 4. [Claim 6] The second portion of the upper covering portion is sandwiched in the first direction between the tip of the upper surface-facing portion of the crimp portion and the upper surface of the first flange. The secondary battery according to claim 5. [Claim 7] In a plan view of the lid in the first direction, the first portion and the second portion are each provided in an annular shape, and the first portion is provided inside the second portion. A secondary battery according to any one of claims 1 to 6. [Claim 8] The first portion of the upper covering portion includes the tip portion of the upper covering portion. The secondary battery according to claim 7. [Claim 9] At least a portion of the tip of the upper covering portion is joined to the upper surface of the first flange. The secondary battery according to claim 8. [Claim 10] The first thickness is 120% or less of the second thickness. A secondary battery according to any one of claims 1 to 9. [Claim 11] The ratio of the radial width of the upper covering portion to the diameter of the lid member is 6.36% or more and 10.98% or less. A secondary battery according to any one of claims 1 to 9. [Claim 12] The upper covering portion has an annular tip portion in a plan view when the lid portion is viewed in the first direction, The tip portion includes the first portion and a third portion having a third thickness that is thinner than the first portion. The third portion of the tip is joined to the upper surface of the first flange. The secondary battery according to claim 1. [Claim 13] The valve member is made of a metallic material containing aluminum (Al), The aforementioned container is made of a metallic material containing iron (Fe). A secondary battery according to any one of claims 1 to 12. [Claim 14] The aforementioned battery element has a first electrode and a second electrode, The cover portion is electrically connected to the first electrode, The container is electrically connected to the second electrode. A secondary battery according to any one of claims 1 to 13.

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