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 battery element includes a first electrode, a second electrode, and an electrolyte. The container has a first end including a crimped portion and a second end located opposite the first end in a first direction, and houses the battery element. The lid is attached to the crimped portion via a gasket. The lid has a lid member including a first flange and a valve member including a second flange facing the first flange in a first direction and located between the lid member and the battery element in a first direction. The first flange and the second flange are welded to each other to form a laminate. The laminate is sandwiched in a first direction by the crimped portion via a gasket and includes a weld mark formed to straddle the interface between the first flange and the second flange in a first direction.

Description

【Technical Field】 【0001】 The present 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 such 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 the 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 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 battery element includes a first electrode, a second electrode, and an electrolyte. The container has a first end including a crimped portion 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 crimped portion via a gasket. The lid has a lid member including a first flange and a valve member including a second flange facing the first flange in a first direction and located between the lid member and the battery element in a first direction. The first flange and the second flange are welded to each other to form a laminate. The laminate is sandwiched in a first direction by the crimped portion via a gasket. The laminate includes a weld mark formed so as to straddle the interface between the first flange and the second flange in a first direction. [Effects of the Invention] 【0008】 In one embodiment of the secondary battery of this disclosure, a laminated portion formed by welding a first flange of a lid member and a second flange of a valve member is sandwiched in a first direction via a gasket by a crimped portion provided at the first end of the container. Therefore, leakage of the electrolyte contained in the battery element to the outside through the gap between the container and the lid member can be prevented. 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 disclosure 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] Figure 2 is a partially cross-sectional view showing an enlarged example of the upper part of the secondary battery shown in Figure 1. [Figure 3] Figure 3 is an enlarged cross-sectional view showing an example of the configuration of the safety valve mechanism of the secondary battery shown in Figure 1. [Figure 4] Figure 4 is an exploded perspective view of the safety valve mechanism shown in Figure 3. [Figure 5] FIG. 5 is a partial cross-sectional view showing an enlarged configuration example of a bent 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 a bent portion of the secondary battery as a first modification example and its vicinity. [Figure 10] FIG. 10 is a block diagram showing the configuration of an application example (battery pack) of the secondary battery. [Figure 11] FIG. 11 is a partial cross-sectional view showing an enlarged configuration example of a bent portion of the secondary battery as Comparative Example 1 and its vicinity. [Figure 12] FIG. 12 is a partial cross-sectional view showing an enlarged configuration example of a bent portion of the secondary battery as Comparative Example 2 and its vicinity. [Figure 13] FIG. 13 is a partial cross-sectional view showing an enlarged configuration example of a bent portion of the secondary battery as Comparative Example 3 and its vicinity. [Figure 14] FIG. 14 is a partial cross-sectional view showing an enlarged configuration example of a bent portion of the secondary battery as Comparative Example 4 and its vicinity. 【BEST MODE FOR CARRYING OUT THE INVENTION】 【0011】 Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the drawings. 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 rechargeable batteries 【0012】 <1. Secondary battery> First, a secondary battery according to one embodiment of this disclosure will be described. 【0013】 The charging and discharging principles of secondary batteries described here are not particularly limited, but the following explanation will focus on cases where battery capacity is obtained by utilizing the intercalation and deintercalation of electrode reactants. 【0014】 A rechargeable battery comprises an electrolyte along with a positive electrode and a negative electrode. In this rechargeable battery, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode; that is, the electrochemical capacity per unit area of ​​the negative electrode is greater than the electrochemical capacity per unit area of ​​the positive electrode. This is to prevent the deposition of electrode reactants on the surface of the negative electrode during charging. 【0015】 The types of electrode reactants are not particularly limited, but specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium. 【0016】 In the following example, we will consider the case where lithium is the electrode reactant. A secondary battery that obtains battery capacity by utilizing the intercalation and deintercalation of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is intercalated and deintercalated 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, for example, by 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. 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 extending 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. 【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 a bent portion 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, it is preferable that the battery cover 14 contains an iron-based material such as stainless steel. This is because the physical strength of the crimping structure 11R is ensured in accordance with the physical strength of the battery cover 14, thereby suppressing the detachment of the battery cover 14 and leakage of electrolyte even when the internal pressure of the battery can 11 rises. 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 portion of the battery cover 14 other than the center, that is, the portion surrounding the protrusion 14T, is a flange 14F. The flange 14F of the battery cover 14 is joined to the flange 31F of the safety cover 31 of the safety valve mechanism 30, facing it in the Z direction. The portion where flange 14F and flange 31F are welded together is called the laminated portion SS. 【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 outward 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 lower surface 14BS of the battery cover 14 in the Z direction. 【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. Furthermore, flange 32F is a specific example corresponding to the "second flange" as one aspect of this disclosure. 【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) 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 6B, 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 the gasket 15. The laminated portion SS includes a weld mark WM formed so as to straddle the interface KS between the flange 14F and 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, which constitutes the battery cover 14, and the second material, such as aluminum or an aluminum alloy, which constitutes the safety cover 31, are in solid solution. The bent portion 11P includes a first portion 11P1, a second portion 11P2, and a third portion 11P3. The first portion 11P1 is the portion that includes the open end 11N and extends in the R direction. The second part 11P2 is the part that faces the first part 11P1 in the Z direction, with the laminated part SS in between via the gasket 15. The third part 11P3 is the part that connects the first part 11P1 and the second part 11P2. 【0051】 Flange 14F includes a lower surface 14BS facing flange 31F, an upper surface 14US opposite to interface KS, and an end surface 14ES connecting the lower surface 14BS and the upper surface 14US and provided along the outer edge of flange 14F. Flange 31F includes an upper surface 31US facing flange 14F, a lower surface 31BS opposite to interface KS, and an end surface 31ES connecting the upper surface 31US and the lower surface 31BS and provided along the outer edge of flange 31F. The lower surface 14BS and the upper surface 31US abut each other to form interface KS. The bent portion 11P continuously covers the upper surface 14US, the end surface 14ES, the end surface 31ES, and the lower surface 31BS via a gasket 15. The upper surface 14US is a specific example corresponding to the "first surface" as an embodiment of this disclosure. The end surface 14ES is a specific example corresponding to the "first end surface" as an embodiment of this disclosure. The lower surface 31BS is a specific example corresponding to the "second surface" as an embodiment of this disclosure. The end surface 31ES is a specific example corresponding to the "second end surface" as an embodiment of this disclosure. 【0052】 In this secondary battery, it is desirable that the end face 14ES and the end face 31ES substantially coincide in the in-plane direction (R direction) perpendicular to the Z direction. This is because it reduces the gap between the gasket 15 and the flange 14F and the gap between the gasket 15 and the flange 31F, thereby improving the sealing performance between the battery can 11, the battery cover 14, and the safety valve mechanism 30 by the crimping structure 11R. Note that "substantially coincide" means that a deviation of a manufacturing tolerance (for example, a deviation of about 1% between the external dimensions of the battery cover 14 and the external dimensions of the safety cover 31) is acceptable. 【0053】 As shown in Figure 5, it is preferable that all parts of the weld mark WM exposed on the lower surface 31BS overlap with the bent portion 11P in the Z direction. That is, it is preferable that all parts of the weld mark WM be located in the region 11out outside the position K11 of the tip of the bent portion 11P in the R direction. This is because it is possible to avoid corrosion of the weld mark WM due to exposure to the outside air, and consequently corrosion of the battery cover 14 and the safety cover 31. 【0054】 Furthermore, it is preferable that all parts of the weld marks WM exposed on the lower surface 31BS be covered by the gasket 15. This is because it adequately protects the weld marks WM and prevents them from being exposed to the outside air. 【0055】 Furthermore, it is preferable that the weld mark WM extends, for example, from the lower surface 31BS, through the interface KS, to a position just before reaching the upper surface 14US. By forming the weld mark WM so as to straddle the interface KS between flange 14F and flange 31F in the Z direction, flange 14F and flange 31F are firmly joined. Moreover, by extending from the lower surface 14BS to partway up to the upper surface 14US without penetrating flange 14F, the flatness of the upper surface 14US can be maintained. In addition, since it is not necessary to irradiate with energy rays of high energy intensity that penetrate the weld mark WM, that is, the irradiation energy of the irradiated energy rays can be kept low, the flatness of the surface of the weld mark WS can be improved. Therefore, the sealing performance of the secondary battery is improved, and the possibility of the electrolyte contained in the battery element 20 leaking to the outside through the gap between the battery can 11, the battery cover 14 and the safety valve mechanism 30 can be sufficiently reduced. 【0056】 The weld marks WM are formed such that, for example, their width decreases from the lower surface 31BS towards the upper surface 14US. 【0057】 Furthermore, it is preferable that the weld marks WM be provided continuously and without gaps in a ring-shaped pattern in a plane perpendicular to the Z direction, as shown in Figure 6, for example. This is because it improves the bonding strength between the battery cover 14 and the safety cover 31, and also improves the sealing performance of the secondary battery. Figure 6 is a schematic plan view of the safety cover 31, showing the safety cover 31 as viewed from the battery element 20 side. 【0058】 {1-3. Detailed configuration of battery elements} 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. 【0059】 [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. 【0060】 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. 【0061】 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. 【0062】 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. 【0063】 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. 【0064】 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. 【0065】 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. 【0066】 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. 【0067】 [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. 【0068】 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. 【0069】 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). 【0070】 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。 【0071】 [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. 【0072】 [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. 【0073】 {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. 【0074】 [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. 【0075】 [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. 【0076】 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. 【0077】 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. 【0078】 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. 【0079】 {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. 【0080】 [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. 【0081】 [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. 【0082】 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. 【0083】 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. After that, 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. 【0084】 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. 【0085】 [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. 【0086】 <1-6. Mechanism and Effects> In the secondary battery of this embodiment, the flange 14F of the battery cover 14 and the flange 31F of the safety cover 31 of the safety valve mechanism 30 are welded to each other to form a laminated portion SS. 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. In this way, the laminated portion SS is sandwiched by the bent portion 11P, which acts as a crimp, so that even if iron-based materials are used for the battery cover 14 and the safety cover 31, the weld marks WM do not come into contact with the outside air. Therefore, corrosion of the battery cover 14 and the safety cover 31 can be avoided. In addition, since the bent portion 11P sandwiches the laminated portion SS via the gasket 15, 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. 【0087】 In the secondary battery of this embodiment, if the end face 14ES and the end face 31ES substantially coincide in the in-plane direction (R direction) perpendicular to the Z direction, the sealing performance between the battery can 11, the battery cover 14, and the safety valve mechanism 30 by the crimping structure 11R can be improved. This is because the gap between the gasket 15 and the flange 14F and the gap between the gasket 15 and the flange 31F can be reduced. 【0088】 In the secondary battery of this embodiment, by positioning the welded joint WM such that all parts of the welded joint WM overlap with the bent portion 11P in the Z direction, the possibility of the welded joint WM being exposed to the outside air is sufficiently reduced, and corrosion of the battery cover 14 and safety cover 31 can be sufficiently avoided. Furthermore, if all parts of the welded joint WM exposed on the lower surface 31BS are covered by the gasket 15, the welded joint WM is sufficiently protected, and corrosion of the battery cover 14 and safety cover 31 can be sufficiently avoided. 【0089】 Furthermore, in this embodiment, since the surface of the welded mark WM is exposed to the lower surface 31BS of the safety cover 31, the sealing performance between the battery can 11, the battery cover 14, and the safety valve mechanism 30 can be improved compared to the embodiment in which the surface of the welded mark WM is exposed to the upper surface US of the battery cover 14. In this secondary battery structure, the biasing force on the lower surface 31BS by the second part P2 of the bent part 11P is stronger than the biasing force on the upper surface 14US by the first part P1 of the bent part 11P, so the adhesion force of the gasket 15 to the lower surface 31BS is stronger than the adhesion force of the gasket 15 to the upper surface 14US. Therefore, when the surface of the welded mark WM, which often has a fine uneven shape, is on the lower surface 31BS rather than on the upper surface 14US, the surface of the welded mark WM and the gasket 15 can be adhered to each other without gaps and in good contact. 【0090】 Furthermore, in the secondary battery of this embodiment, the safety valve mechanism 30 further includes a conductive sub-disk 34 provided between the positive electrode lead 25 and the valve portion 31V of the safety cover 31, so that the valve portion 31V is electrically connected to the positive electrode lead 25 via the sub-disk 34. As a result, the positive electrode lead 25 can be stably and easily connected to the sub-disk 34, a stable conductive state can be obtained between the positive electrode lead 25 and the safety cover 31, and high reliability can be obtained. 【0091】 Furthermore, 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, 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. 【0092】 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. 【0093】 <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. 【0094】 [First variation] In the secondary battery of the above embodiment, the weld mark WM is exposed only on the lower surface 31BS, and not exposed on the upper surface 14US. However, in the secondary battery of this disclosure, the weld mark WM may be exposed only on the upper surface 14US, and not exposed on the lower surface 31BS. That is, as shown in Figure 9, the weld mark WM may extend from the upper surface 14US through the interface KS to a position just before reaching the lower surface 31BS, as in the secondary battery as the first modified example. 【0095】 [Second variation] 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. 【0096】 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. 【0097】 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. 【0098】 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. 【0099】 <3. Applications of rechargeable batteries> Next, I will explain the applications (examples of use) of the secondary batteries mentioned above. 【0100】 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. 【0101】 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. 【0102】 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. 【0103】 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. 【0104】 Figure 10 shows the block configuration of the battery pack. The battery pack described here is a battery pack (so-called soft pack) that uses a single rechargeable battery and is installed in electronic devices such as smartphones. 【0105】 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. 【0106】 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. 【0107】 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. 【0108】 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. 【0109】 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. 【0110】 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] 【0111】 Examples of the present disclosure will be described below. 【0112】 <Example 1> After fabricating a secondary battery as described below, its battery characteristics were evaluated. 【0113】 [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. 【0114】 (Fabrication of the positive electrode) First, the positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05A 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. 【0115】 (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. 【0116】 (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. 【0117】 (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. 【0118】 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, 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 5, the laser irradiation was performed from the lower surface 31BS of the flange 31F to form a weld mark WM that extended from the lower surface 31BS through the interface KS to partway up to the upper surface 14US. In addition, as shown in Figure 6, a continuous annular weld mark WM was formed. Furthermore, the weld mark WM was formed so that all parts of the weld mark WM overlapped with the bent portion 11P in the Z direction. 【0119】 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. 【0120】 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. 【0121】 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. 【0122】 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. 【0123】 (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. 【0124】 As a result, the state of the secondary battery was electrochemically stabilized, leading to the completion of a cylindrical lithium-ion secondary battery. 【0125】 [Evaluation of battery characteristics] The fabricated secondary batteries underwent corrosion resistance and electrolyte leakage resistance evaluations according to the procedure described below, and the results shown in Table 1 were obtained. It should be noted that the corrosion resistance and electrolyte leakage resistance evaluations conducted here were performed under extremely harsh conditions compared to the normal operating environment of secondary batteries. Therefore, even if rust formation or electrolyte leakage occurs during the corrosion resistance and electrolyte leakage evaluations, this does not mean that problems will occur under normal operating conditions. 【0126】 [Table 1] 【0127】 (Corrosion resistance evaluation) To evaluate corrosion resistance, a corrosion resistance test was conducted according to the following procedure and conditions. The corrosion resistance test was performed using the "JIS Z 2371 Neutral Salt Spray Test". The test duration was 48 hours, and the evaluation was performed on the secondary battery. The battery cover 14 and safety valve mechanism 30 were removed from the secondary battery that underwent the "JIS Z 2371 Neutral Salt Spray Test", and the number of samples in which iron rust (red rust) occurred on the laser-welded flange 14F or aluminum rust (white discoloration) occurred on the flange 31F was counted. The corrosion resistance test was performed on 30 secondary batteries as samples. 【0128】 (Leak resistance evaluation) For leakage resistance evaluation, drop tests and vibration tests were conducted according to the following procedures and conditions. The drop tests and vibration tests were performed on 30 secondary batteries as samples. 【0129】 (Drop test) Sample: A rechargeable battery with a battery voltage of 4.4V was used. Test method: The object was dropped 10 times from a height of 1 meter onto a concrete surface. 【0130】 (Vibration test) Sample: A rechargeable battery in a completely discharged state (discharged to 2.5V with a constant current of 4.0A in an atmosphere of 2°C) was used. Test method: The system was swept over a 15-minute period in the order of frequencies 7Hz → 200Hz → 7Hz, and this was performed 12 times for each of the three mutually orthogonal axis directions. 【0131】 (Judgment criteria) After the drop test, a vibration test was conducted, and the presence or absence of electrolyte leakage from the outside of the secondary battery was visually checked. 【0132】 <Example 2> When welding the flange 31F of the safety cover 31 to the flange 14F of the battery cover 14 by laser irradiation, as shown in Figure 9, the laser irradiation was performed from the upper surface US, and a weld mark WM was formed that extended from the upper surface US through the interface KS to partway down to the lower surface 31BS. Except for this point, the secondary battery of Example 2 was manufactured in the same manner as in Example 1, and the same battery characteristics evaluation as in Example 1 was performed. The results are also shown in Table 1. In Example 2, as in Example 1, the weld mark WM was formed so that all parts of the weld mark WM overlapped with the bent portion 11P in the Z direction. Also in Example 2, as in Example 1, a continuous annular weld mark WM was formed. 【0133】 <Example 3> When welding the flange 31F of the safety cover 31 to the flange 14F of the battery cover 14 by laser irradiation, as shown in Figure 9, the laser irradiation was performed from the upper surface US, and a weld mark WM was formed that extended from the upper surface US through the interface KS to partway down to the lower surface 31BS. In addition, in Example 3, a discontinuous weld mark WM with a part of the annular shape missing was formed. Except for these points, the secondary battery of Example 3 was manufactured 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. In Example 3, as in Example 1, the weld mark WM was formed so that all parts of the weld mark WM overlapped with the bent portion 11P in the Z direction. 【0134】 <Comparative Example 1> When welding the flange 31F of the safety cover 31 to the flange 14F of the battery cover 14 by laser irradiation, as shown in Figure 11, the welding mark WM was formed such that a portion of it overlapped in the Z direction with the tip of the bent portion 11P, which serves as the crimp portion, i.e., the open end 11N. Aside from this point, the secondary battery of Comparative Example 1 was manufactured in the same manner as in Example 1, and the same battery characteristics evaluation as in Example 1 was performed. The results are also shown in Table 1. In Comparative Example 1, as in Example 1, a continuous, annular welding mark WM was formed. 【0135】 <Comparative Example 2> When welding the flange 31F of the safety cover 31 to the flange 14F of the battery cover 14 by laser irradiation, as shown in Figure 12, the welding mark WM was formed so that a portion of it overlapped in the Z direction with the tip of the bent portion 11P, which serves as the crimp portion, i.e., the open end 11N. In addition, laser irradiation was performed from the upper surface US to form a welding mark WM that extended from the upper surface US through the interface KS to partway down to the lower surface 31BS. Except for these points, the secondary battery of Comparative Example 2 was manufactured 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. In Comparative Example 2, as in Example 1, a continuous annular welding mark WM was formed. 【0136】 <Comparative Example 3> When welding the flange 31F of the safety cover 31 to the flange 14F of the battery cover 14 by laser irradiation, as shown in Figure 13, the welding mark WM was formed such that all parts of the welding mark WM were located closer to the center of the secondary battery than the open end 11N, which is the tip of the bent portion 11P that serves as the crimp portion. Except for this point, the secondary battery of Comparative Example 3 was manufactured in the same manner as in Example 1, and the same evaluation of the battery characteristics as in Example 1 was performed. The results are also shown in Table 1. In Comparative Example 3, as in Example 1, a continuous annular welding mark WM was formed. 【0137】 <Comparative Example 4> When welding the flange 31F of the safety cover 31 to the flange 14F of the battery cover 14 by laser irradiation, as shown in Figure 14, the welding mark WM was formed such that all parts of the welding mark WM were located closer to the center of the secondary battery than the open end 11N, which is the tip of the bent portion 11P that serves as the crimp portion. In addition, laser irradiation was performed from the upper surface US to form a welding mark WM that extends from the upper surface US through the interface KS to partway down to the lower surface 31BS. Except for these points, the secondary battery of Comparative Example 4 was manufactured in the same manner as in Example 1, and the same battery characteristics evaluation as in Example 1 was performed. The results are also shown in Table 1. In Comparative Example 4, as in Example 1, a continuous annular welding mark WM was formed. 【0138】 As shown in Table 1, no samples exhibiting rust or electrolyte leakage were observed in Example 1. In Examples 2 and 3, some samples exhibiting rust or electrolyte leakage were observed, but the number of samples exhibiting rust or electrolyte leakage was significantly smaller compared to Comparative Examples 1 to 4. From the above, it was found that, according to the present invention, since the laminated portion SS is sandwiched by the bent portion 11P as a crimped portion, corrosion of the battery cover 14 and safety cover 31 can be avoided even when iron-based materials are used for the battery cover 14 and safety cover 31. Furthermore, since the bent portion 11P sandwiches the laminated portion SS via the gasket 15, it was found that the electrolyte contained in the battery element 20 is prevented from leaking out to the outside through the gap between the battery can 11, the battery cover 14, and the safety valve mechanism 30. Therefore, it was confirmed that higher reliability can be obtained according to the present invention. 【0139】 Although the present technology has been described above with reference to one embodiment and one example, the configuration of the present technology is not limited to the configuration described in the one embodiment and one example, and can be modified in various ways. 【0140】 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. 【0141】 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. 【0142】 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] 【0143】 11...Battery can, 11N...Open end, 11P...Bent section, 11R...Crimped structure, 12,13...Insulating plate, 14...Battery cover, 14US...Top surface, 14BS...Bottom surface, 14ES...End face, 14F...Flange, 15...Gasket, 20...Battery element, 20C...Center space, 21...Positive electrode, 22...Negative electrode, 23...Separator, 24...Center pin, 25...Positive electrode lead, 26...Negative electrode lead, 30...Safety valve mechanism, 31...Safety cover, 31F...Flange, 31US...Top surface, 31BS...Bottom surface, 31ES...End face, 32...Disc holder, 33...Stripper disc, KS...Interface, SS...Laminated section, WS...Welding marks.

Claims

[Claim 1] A battery element comprising a first electrode, a second electrode, and an electrolyte, A container for housing the battery element, having a first end including a crimped portion and a second end located opposite to the first end in a first direction, A lid portion attached to the crimped portion via a gasket and Equipped with, The lid portion includes a lid member including a first flange, and a valve member including a second flange facing the first flange in the first direction and located between the lid member and the battery element in the first direction. The first flange and the second flange are welded to each other to form a laminated section. The laminated portion is sandwiched in the first direction by the crimped portion via the gasket, The laminated portion includes a weld mark formed so as to straddle the interface between the first flange and the second flange in the first direction. The welding marks are positioned such that all parts of the welding marks overlap with the crimped portion in the first direction. Secondary battery. [Claim 2] The first flange includes a first surface opposite to the interface and a first end face that connects the interface and the first surface and is provided along the outer edge of the first flange. The second flange includes a second surface opposite to the interface and a second end face that connects the interface and the second surface and is provided along the outer edge of the second flange. The crimped portion continuously covers the first surface, the first end face, the second end face, and the second surface via the gasket. The secondary battery according to claim 1. [Claim 3] In the in-plane direction perpendicular to the first direction, the first end face and the second end face coincide. The secondary battery according to claim 2. [Claim 4] The aforementioned weld marks are covered by the gasket. The secondary battery according to claim 2 or claim 3. [Claim 5] The welding marks extend from the second surface, through the interface, to a position just before reaching the first surface. A secondary battery according to any one of claims 2 to 4. [Claim 6] The welding marks have a width that decreases as you move from the second surface towards the first surface. The secondary battery according to claim 5. [Claim 7] The lid member is made of the first material, The valve member is made of a second material, The aforementioned weld marks are the areas where the first material and the second material have solid-solved together. A secondary battery according to any one of claims 1 to 6. [Claim 8] The aforementioned welding marks were formed by laser irradiation or electron beam irradiation. A secondary battery according to any one of claims 1 to 7. [Claim 9] The welding marks are arranged in an annular shape in a plane perpendicular to the first direction. A secondary battery according to any one of claims 1 to 8.

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