Cylindrical battery

Abstract

A cylindrical battery is provided with an electrode body, an electrolyte, a bottomed cylindrical outer can that accommodates the electrode body and the electrolyte, and a sealing body that closes the opening of the outer can. The bottom (68) of the outer can includes two linear engraved grooves (31, 32) having an intersection point (61). An inclined surface (41) is formed at a corner portion sandwiched by the two linear engraved grooves (31, 32) so that the thickness of the bottom portion (68) becomes smaller as the bottom portion approaches the intersection point (61).

Description

Technical Field

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

[0002] In recent years, batteries with higher energy density are required. In addition, corresponding to the high energy density of batteries, the safety of batteries is also increasingly valued. Patent document 1 discloses the following technology: in order to improve the safety of batteries, an engraved groove is provided at the bottom of a cylindrical secondary battery by stamping using an engraved die, and the bottom is broken along the engraved groove in the event of an abnormality.

[0003] Prior Art Literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 06-333548 Summary of the invention

[0006] When the engraved grooves are provided by a stamping process using an engraving die, wall escape occurs from the portion whose thickness is reduced due to the engraving to other portions. Furthermore, when the bottom of the outer can has a plurality of linear engraved grooves with an intersection, wall escape from two engraved grooves is concentrated at a corner sandwiched by the two engraved grooves, and sometimes work hardening due to stress concentration occurs at the corner. In addition, sometimes the wall escape from each engraved groove interferes at the corner, and uneven thickness bulges from the interfering portion. When such work hardening and uneven thickness occur, the safety valve will not open normally, and the deviation of the working pressure of the safety valve becomes larger. To this end, the purpose of the present disclosure is to provide a cylindrical battery in which work hardening and uneven thickness are unlikely to occur at a corner sandwiched by two linear engraved grooves, and the deviation of the working pressure of the safety valve at the bottom of the outer can is small.

[0007] In order to solve the above-mentioned problems, the cylindrical battery involved in the present disclosure comprises an electrode body, an electrolyte, a bottomed cylindrical outer can containing the electrode body and the electrolyte, and a sealing body that seals the opening of the outer can. The bottom of the outer can includes two linear engraved grooves with an intersection, and an inclined surface is formed at the corner sandwiched by the two linear engraved grooves so that the thickness of the bottom decreases as it approaches the intersection.

[0008] In addition, the manufacturing method of the cylindrical battery involved in the present disclosure is a manufacturing method of a cylindrical battery comprising an electrode body, an electrolyte, a bottomed cylindrical outer can containing the electrode body and the electrolyte, and a sealing body that seals the opening of the outer can. In the manufacturing method of the cylindrical battery, the bottom of the outer can is punched to form two linear grooves with an intersection at the bottom, and an inclined surface is formed at the corner sandwiched by the two linear grooves, so that the thickness of the bottom decreases as it approaches the intersection.

[0009] According to the cylindrical battery of the present disclosure, work hardening and thickness unevenness are unlikely to occur at the corner portion sandwiched between two linear engraved grooves, and the variation in the operating pressure of the safety valve at the bottom of the outer can can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a longitudinal cross-sectional view of a cylindrical secondary battery as an example of an embodiment.

[0011] Figure 2 It is a bottom view of the cylindrical secondary battery.

[0012] Figure 3 yes Figure 2 A partial enlarged bottom view of the area indicated by R in FIG.

[0013] Figure 4 yes Figure 3 An enlarged stereoscopic view of the portion around the intersection of the linear grooves in FIG.

[0014] Figure 5 This is a diagram for explaining the inclination angle of the first inclined surface.

[0015] Figure 6 A cylindrical secondary battery of a modified example Figure 2 Corresponding bottom view. DETAILED DESCRIPTION

[0016] Hereinafter, an example of an embodiment of a cylindrical battery involved in the present disclosure is described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, values, directions, etc. are examples for easy understanding of the present invention and can be appropriately changed to meet the specifications of the cylindrical battery. In addition, in the following description, when multiple embodiments and variations are included, it is envisaged from the beginning that these characteristic parts will be appropriately combined for use.

[0017] Figure 1 1 is a longitudinal cross-sectional view of a cylindrical secondary battery 10 as an example of an embodiment. The cylindrical secondary battery 10 includes an electrode body 14, an electrolyte (not shown), a bottomed cylindrical outer can 15 that accommodates the electrode body 14 and the electrolyte, and a sealing body 16 that seals the opening of the outer can 15. In the following, the sealing body 16 side of the outer can 15 in the axial direction is referred to as the upper side, and the bottom 68 side of the outer can 15 in the axial direction is referred to as the lower side. In addition, the direction perpendicular to the axial direction of the outer can 15 is referred to as the radial direction, the radial center side of the outer can 15 is referred to as the inner side, and the radial outer side is referred to as the outer side.

[0018] The electrode body 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The electrode body 14 is not limited to the wound type, and may also be a stacked type. The positive electrode 11, for example, has a strip-shaped positive electrode collector and a positive electrode composite layer formed on both sides of the positive electrode collector. For the positive electrode collector, for example, a foil of a metal such as aluminum, a film obtained by arranging the metal on the surface, and the like are used. The positive electrode composite layer contains at least a positive electrode active material, and may also contain a conductive agent, an adhesive, and the like. As the positive electrode active material, lithium-containing transition metal oxides containing transition metal elements such as Ni and the like can be exemplified. After applying a positive electrode composite slurry obtained by dispersing the positive electrode active material and the like in a solvent to both sides of the positive electrode collector, the positive electrode composite layer is dried and rolled, thereby making the positive electrode 11.

[0019] The negative electrode 12 has, for example, a strip-shaped negative electrode current collector and a negative electrode composite layer formed on both sides of the negative electrode current collector. For the negative electrode current collector, for example, a foil of a metal such as copper, a film obtained by disposing the metal on the surface layer, etc. is used. The negative electrode composite layer contains at least a negative electrode active material, and may also contain a binder, etc. As the negative electrode active material, carbon materials such as natural graphite and artificial graphite, metal compounds such as silicon-based compounds, etc. can be exemplified. After applying a negative electrode composite slurry obtained by dispersing the negative electrode active material, etc. in a solvent to both sides of the negative electrode current collector, the negative electrode composite layer is dried and rolled, thereby making the negative electrode 12.

[0020] A porous sheet having ion permeability and insulation can be used as the separator 13. Specific examples of the porous sheet include microporous films, woven fabrics, nonwoven fabrics, etc. The material of the separator 13 is preferably an olefin resin such as polyethylene or polypropylene.

[0021] An upper insulating plate 17 and a lower insulating plate 18 are arranged above and below the electrode body 14, respectively. The positive lead 19 extends upward through the through hole of the upper insulating plate 17 and is welded to the bottom plate of the sealing body 16, that is, the lower surface of the filter plate 22. In the cylindrical secondary battery 10, the top plate of the sealing body 16, that is, the cover 26, which is electrically connected to the filter plate 22, becomes the positive terminal. On the other hand, the negative lead 20 extends to the bottom side of the outer can 15 through the through hole of the lower insulating plate 18 and is welded to the bottom inner surface of the outer can 15. In the cylindrical secondary battery 10, the outer can 15 becomes the negative terminal.

[0022] The outer can 15 is a metal outer can with a bottomed cylindrical shape. The outer can 15 has a bottom 68 and a side wall portion 69 that is erected on the periphery of the bottom 68. The bottom 68 of the outer can 15 has a disc-shaped thin-walled portion 29 in the central portion on the radial inner side. The thin-walled portion 29 includes engraved grooves 31 and 32 formed by stamping using an engraving mold. When the cylindrical secondary battery 10 generates abnormal heat and the internal pressure rises, the engraved grooves 31 and 32 break, and high-temperature gas is discharged from the broken parts. A groove portion 21 is formed in the side wall portion 69 of the outer can 15. The groove portion 21 supports the sealing body 16 from the lower side. The groove portion 21 is preferably formed in an annular shape along the circumference of the outer can 15.

[0023] The opening of the upper part of the outer can 15 is blocked by the sealing body 16 through the gasket 27, ensuring the airtightness of the interior of the cylindrical secondary battery 10. The sealing body 16 has a filter plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25 and a cover 26 stacked in sequence from the electrode body 14 side. The components constituting the sealing body 16 have, for example, a disc shape or a ring shape, and the components except the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective central parts, and the insulating member 24 is between their respective peripheral parts. During abnormal heating, if the internal pressure of the cylindrical secondary battery 10 rises, for example, the lower valve body 23 breaks, so that the upper valve body 25 expands to the cover 26 side and separates from the lower valve body 23, thereby blocking the electrical connection between the two. If the internal pressure rises further, the upper valve body 25 breaks, and the gas is discharged from the opening 26a of the cover 26. The bottom 68 of the outer can 15 and the sealing body 16 both function as safety valves (explosion-proof valves). There is no particular limitation on which one opens first, and the design can be appropriately performed.

[0024] In addition to the electrode body 14, the outer can 15 also contains an electrolyte. As an electrolyte, for example, an aqueous electrolyte and a non-aqueous electrolyte can be used, but a non-aqueous electrolyte is preferably used. As a non-aqueous solvent (organic solvent) of the non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc. can be exemplified. These solvents can be used by mixing two or more. When two or more solvents are mixed for use, a mixed solvent containing cyclic carbonates and chain carbonates is preferably used. As cyclic carbonates, ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) can be used. As chain carbonates, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) can be used. As esters, carbonates such as methyl acetate (MA) and methyl propionate (MP) are preferably used. The non-aqueous solvent may also contain a halogen substituted product obtained by replacing at least a part of the hydrogen atoms of these solvents with halogen atoms such as fluorine. As the halogen-substituted substance, for example, fluoroethylene carbonate (FEC) and methyl fluoropropionate (FMP) are preferably used.

[0025] As the electrolyte salt of the non-aqueous electrolyte, LiPF6, LiBF4, LiCF3SO3, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, etc. and mixtures thereof can be used. The amount of the electrolyte salt dissolved in the non-aqueous solvent is, for example, 0.5 mol / L to 2.0 mol / L. In addition, vinylene carbonate (VC) and propane sultone-based additives may be further added.

[0026] Figure 2 FIG. 1 is a bottom view of a cylindrical secondary battery 10. Figure 2 As shown, the bottom 68 of the outer can 15 has a plurality of linear first engraved grooves 31 that are combined to form a polygon, and a plurality of linear second engraved grooves 32 that extend outward from a plurality of vertices of the polygon. The polygon formed by the plurality of first engraved grooves 31 is, for example, a regular polygon. The polygon formed by the first engraved grooves 31 can be recognized as a polygon by the naked eye, and the first engraved grooves 31 are not limited to straight lines, but may also be curved lines.

[0027] exist Figure 2 In the example shown, the polygon is a triangle surrounded by three identical first engraved grooves 31 protruding outward. Thus, when the plurality of first engraved grooves defining the polygon are curved, each first engraved groove preferably protrudes outward. The number of engraved grooves is determined by taking the portion surrounded by the intersection or the portion surrounded by the intersection and the end as one unit. Figure 2 In the example shown, the number of the first engraved groove 31 and the number of the second engraved groove 32 are both 3. In addition, in the cylindrical battery disclosed in the present invention, the bottom of the outer can only need to include two linear engraved grooves having an intersection, and the number of linear engraved grooves is not particularly limited. In addition, the bottom of the outer can does not have to have a polygonal shape consisting of a plurality of engraved grooves.

[0028] The depth of the engraved grooves 31 and 32 is, for example, 0.1 mm to 0.5 mm, and the width of the engraved grooves 31 and 32 is, for example, 0.1 mm to 1.0 mm. The cross-sectional shape of the engraved grooves 31 and 32 is not particularly limited, and is, for example, an isosceles trapezoidal shape or a V-shape. In addition, the depth, width, and cross-sectional shape of the engraved grooves 31 and 32 may also vary in the extension direction. In this case, the depth and width of the engraved grooves 31 and 32 are respectively represented by the average value in the extension direction.

[0029] Figure 3 yes Figure 2 A partial enlarged bottom view of the area indicated by R in FIG. Figure 4 yes Figure 3 The enlarged stereoscopic view of the part around the intersection 61 of the linear engraved grooves 31 and 32. Figure 3 as well as Figure 4As shown, the two first engraved grooves 31 and the second engraved groove 32 have an intersection 61 intersecting each other. A first inclined surface 41 is formed at a corner portion sandwiched by the first engraved groove 31 and the second engraved groove 32, and the first inclined surface 41 is formed so that the thickness of the bottom 68 decreases as it approaches the intersection 61. Furthermore, a second inclined surface 42 is formed at a corner portion sandwiched by the two first engraved grooves 31 so that the thickness of the bottom 68 decreases as it approaches the intersection 61.

[0030] In this specification, the intersection of two linear engraved grooves can be determined as the point where the bottoms of the two linear engraved grooves intersect each other. In addition, the angle of the corner can be determined based on the bottoms of the two linear engraved grooves in a top view when the bottom surface of the outer can is observed from the axial lower side. In the case where the engraved groove extending from the intersection is curved, the intersection of the corner can be determined based on the tangent line at the intersection of the engraved grooves. In the case where the bottom of the engraved groove has a given width, the angle of the corner can be determined based on the center position of the bottom in the width direction.

[0031] exist Figure 3 In the figure, the tangent lines of the first engraved groove 31 and the second engraved groove 32 at the intersection 61 are shown by straight lines A and B. The angle θ1 of the corner sandwiched by the first engraved groove 31 and the second engraved groove 32 is an acute angle smaller than 90°. On the other hand, the angle θ2 of the corner sandwiched by the two first engraved grooves 31 is an obtuse angle larger than 90°. In the case where multiple corners are adjacent to the intersection 61, it is sufficient to form an inclined surface at at least one corner. In the case where the angle of the corner is an acute angle, work hardening and uneven thickness are likely to occur at the corner, so it is preferred to form an inclined surface at the acute corner. From the viewpoint of ease of manufacturing, the angle of the corner is preferably greater than 30°.

[0032] Figure 5 3 is a diagram for explaining the inclination angle θ3 of the first inclined surface 41. Figure 5 In FIG. 7 , the plane 71 is a plane extending in the radial direction of the cylindrical secondary battery 10. The inclination angle θ3 of the first inclined surface 41 is the angle formed by the first inclined surface 41 relative to the bottom 68 of the outer can 15. In other words, Figure 5 As shown, the inclination angle θ3 of the first inclined surface 41 is the inclination angle of the first inclined surface 41 relative to the plane 71 extending in the radial direction, which is less than 90°. The inclined surfaces 41 and 42 are formed by punching the bottom surface 68a of the bottom 68 of the outer can 15. For the punching, an engraving mold is used, which includes a punching surface having convex portions corresponding to all the engraved grooves 31 and 32 and inclined surfaces corresponding to all the inclined surfaces 41 and 42.

[0033] The inclination angle θ3 of the inclined surfaces 41 and 42 (see Figure 5) is preferably greater than 40° and less than 80°, and further preferably greater than 50° and less than 70°. As long as the inclination angle of the inclined surface is less than 80°, the wall from the engraved groove can effectively escape to the side away from the corner. Therefore, it is possible to effectively suppress the work hardening and uneven thickness around the corner, and the deviation of the working pressure of the safety valve can be effectively reduced. In addition, as long as the inclination angle of the inclined surface is greater than 40°, high-precision stamping can be easily performed. The inclined surface does not need to be a flat surface in the entire range. For example, the portion of the inclined surface separated from the intersection can also be a curved surface.

[0034] As described above, the bottom surface 68a of the bottom 68 of the cylindrical secondary battery 10 has inclined surfaces 41 and 42 at the corner portion sandwiched by the two linear engraved grooves 31 and 32 (or 31 and 31), and the inclined surfaces 41 and 42 are formed so that the thickness of the bottom 68 decreases as it approaches the intersection 61. Therefore, the wall from the two linear engraved grooves 31 and 32 (or 31 and 31) can escape to the side away from the corner portion, and the wall will not escape to the intersection 61 side which becomes the starting point of the fracture, and the work hardening and uneven thickness at the corner portion can be suppressed. Therefore, the deviation of the working pressure of the safety valve can be reduced.

[0035] <Example>

[0036] [Production of outer cans]

[0037] After the housing made of the plate material is stretched, the engraved groove and the inclined surface described in the above embodiment are formed. The inclination angle of the inclined surface is set to 60 degrees or less.

[0038] [Production of positive electrode]

[0039] As the positive electrode active material, LiNi 0.8 Co 0.15 Al 0.05 O2. 100 parts by mass of positive electrode active material, 1.7 parts by mass of polyvinylidene fluoride as a binder, and 2.5 parts by mass of acetylene black as a conductive agent are mixed in a dispersion medium to prepare a positive electrode composite slurry. The positive electrode composite slurry is applied to both sides of a positive electrode collector composed of aluminum foil, dried except for the connecting portion of the positive electrode tab, and then rolled to a given thickness to obtain a positive electrode. The positive electrode is cut to a given size, and the positive electrode tab (collector lead) made of Al is connected to the exposed portion of the collector by ultrasonic welding.

[0040] [Production of negative electrode]

[0041] As the negative electrode active material, graphitizable carbon is used. 100 parts by mass of the negative electrode active material, 0.6 parts by mass of polyvinylidene fluoride as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener are mixed in water to prepare a negative electrode composite slurry. The negative electrode composite slurry is applied to both sides of a negative electrode collector composed of copper foil, dried except for the connecting portion of the negative electrode tab, and then rolled to a given thickness to obtain a negative electrode. The negative electrode is cut to a given size, and a negative electrode tab (collector lead) composed of a Ni-Cu-Ni cladding material is connected to the exposed portion of the collector by ultrasonic welding.

[0042] [Preparation of non-aqueous electrolyte]

[0043] In a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), lithium hexafluorophosphate (LiPF6) was dissolved as an electrolyte salt to a concentration of 1.0 mol / L, thereby preparing a non-aqueous electrolyte solution.

[0044] [Assembly of cylindrical batteries]

[0045] The positive electrode and the negative electrode are wound into a spiral shape with a microporous film made of a polyolefin resin as a separator to produce an electrode body. The electrode body is inserted into the outer can through a disc-shaped bottom insulating plate, and the negative electrode tab connected to the negative electrode is connected to the bottom of the outer can by welding. After that, the positive electrode tab connected to the positive electrode is connected to the sealing plate by welding, and the opening of the outer can is sealed by the sealing plate.

[0046] <Comparative Example>

[0047] In comparison with the cylindrical battery of the example, a cylindrical battery was produced which differed only in that the above-mentioned inclined surface was not formed.

[0048] [Determination of working pressure]

[0049] The working pressure of the safety valve at the bottom of the outer can was measured in the cylindrical batteries of the multiple examples and the cylindrical batteries of the multiple comparative examples. Specifically, in each cylindrical battery, a through hole was provided in the sealing plate, and nitrogen was injected into the interior of the outer can through the through hole to increase the pressure inside the battery until the safety valve at the bottom of the outer can formed by the engraved groove was operated, and the working pressure of the safety valve was measured. Through this measurement, it was confirmed that the deviation of the working pressure of the safety valve in the cylindrical battery of the example was smaller than the deviation of the working pressure of the safety valve in the cylindrical battery of the comparative example.

[0050] <Modification>

[0051] The present disclosure is not limited to the above-mentioned embodiments and their variations, and various improvements and changes can be made within the scope of the matters recorded in the claims of the present application and their equivalents. For example, in the above-mentioned embodiments, the case where the angle θ2 of the corner portion is greater than 90° is described. However, as described below, the angles of the corner portions formed with the inclined surface can all be less than 90°.

[0052] Figure 6 The cylindrical secondary battery 110 of the modified example is Figure 2 The corresponding bottom view. Figure 6 As shown, in the cylindrical secondary battery 110, the bottom 168 of the outer can has four linear first engraved grooves 131 that are combined to form a square, and four linear second engraved grooves 132 that extend outward from the vertices of the square. The engraved grooves 131 and 132 are formed by punching the bottom surface 168a of the bottom 168 with an engraving die, and the engraved grooves 131 and 132 are formed in the thin-walled portion 129 provided in the radial center portion of the bottom 168. In addition, the first inclined surface 141 is provided at the corner sandwiched by the first engraved groove 131 and the second engraved groove 132, and the second inclined surface 142 is provided at the corner sandwiched by two adjacent first engraved grooves 131 (corner of the inner angle of the square).

[0053] In the cylindrical secondary battery 110, the angle of the corner having the first inclined surface 141 and the angle of the corner having the second inclined surface 142 are both 90°. In the case where the angles of the corners having inclined surfaces are all 90°, it is preferred to provide inclined surfaces at all corners. Thus, it is possible to effectively suppress work hardening and uneven thickness at the portion where the wall escape from the imprinted groove is easier, and it is possible to effectively suppress the deviation of the working pressure at the time of fracture.

[0054] In addition, the bottom of the outer can does not have to have a thin-walled portion. In addition, in the above-mentioned embodiment, the inclined surfaces 41 and 42 are composed of the same plane. However, as long as the inclined surface is a surface provided at a corner portion sandwiched by two linear engraved grooves having an intersection, and is formed so that the thickness of the bottom of the outer can decreases as it approaches the intersection, it can be a surface of any shape. For example, the inclined surface may include two or more planar portions with different inclination angles, may include one or more curved surface portions, or may include one or more planar portions and one or more curved surface portions.

[0055] -Explanation of symbols-

[0056] 10, 110: cylindrical secondary battery; 11: positive electrode; 12: negative electrode; 13: separator; 14: electrode body; 15: outer can; 16: sealing body; 17: upper insulating plate; 18: lower insulating plate; 19: positive electrode lead; 20: negative electrode lead; 21: groove portion; 22: filter plate; 23: lower valve body; 24: insulating member; 25: upper valve body; 26: cover; 26a: opening portion; 27: gasket; 29, 129: thin-walled portion; 31, 131: first engraved groove; 32, 132: second engraved groove; 41, 141: first inclined surface; 42, 142: second inclined surface; 61: intersection; 68, 168: bottom; 68a, 168a: bottom surface; 69: side wall portion; 71: plane extending in the radial direction.

Claims

1. A cylindrical battery comprising an electrode body, an electrolyte, a bottomed cylindrical outer can accommodating the electrode body and the electrolyte, and a sealing body for sealing an opening of the outer can, The bottom of the outer can includes two linear engraved grooves with an intersection. An inclined surface is formed at a corner portion sandwiched between the two linear engraved grooves so that the thickness of the bottom portion decreases as it approaches the intersection.

2. The cylindrical battery according to claim 1, wherein: The angle of the corner is less than 90°.

3. The cylindrical battery according to claim 1 or 2, wherein: The inclination angle of the inclined surface is greater than or equal to 40° and less than or equal to 80° with respect to the bottom portion.

4. A method for manufacturing a cylindrical battery, the cylindrical battery comprising an electrode body, an electrolyte, a bottomed cylindrical outer can accommodating the electrode body and the electrolyte, and a sealing body for sealing an opening of the outer can, The method for manufacturing the cylindrical battery comprises: By punching the bottom of the outer can, two linear engraved grooves with an intersection are formed on the bottom, and an inclined surface is formed at the corner sandwiched by the two linear grooves so that the thickness of the bottom decreases as it approaches the intersection.

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