Cylindrical battery

Abstract

Provided is a cylindrical battery comprising: an electrode body in which a positive electrode and a negative electrode are wound with a separator therebetween; a cylindrical outer can (20) that has a bottom part (21) and accommodates the electrode body; and a sealing body that closes an opening in the outer can (20). The cylindrical battery is characterized in that the surface area of an outer surface (21A) of the bottom part (21) is 1.2 times or more the projection area of the outer surface (21A) of the bottom part (21).

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] In general, a cylindrical battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a cylindrical outer can that houses the electrode assembly, and a disk-shaped sealing body that closes the opening of the outer can. Patent Document 1 discloses a cylindrical battery in which an engraving is provided on the outer surface of the bottom of the outer can. Patent Document 1 also describes that by providing an engraving on the outer surface of the bottom of the outer can, the engraving breaks at the location of the engraving when the internal pressure inside the battery increases, allowing gas inside the battery to be vented.

[0003] Japanese Patent Application Publication No. 11-144705

[0004] However, as the capacity of batteries has increased in recent years, the amount of heat generated during use has also increased. If the amount of heat generated increases and the temperature inside the battery rises, there is a risk that the battery performance will deteriorate. Therefore, improving the heat dissipation ability of batteries is an important issue.

[0005] A cylindrical battery according to one aspect of the present disclosure is a cylindrical battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a cylindrical outer can having a bottom and housing the electrode assembly, and a sealing body that closes the opening of the outer can, wherein the surface area of ​​the outer surface of the bottom is 1.2 times or more the projected area of ​​the outer surface of the bottom.

[0006] According to a cylindrical battery according to one aspect of the present disclosure, heat dissipation can be improved, which in turn suppresses temperature rise during battery use and makes it easier to ensure battery performance.

[0007] Fig. 1 is an axial cross-sectional view of a cylindrical battery that is an example of an embodiment; Fig. 2 is a plan view of the bottom of a cylindrical battery that is an example of an embodiment; Fig. 3 is an axial cross-sectional view of the bottom of a cylindrical battery that is an example of an embodiment; Fig. 4 is a plan view of the bottom of a cylindrical battery that is another example of an embodiment; Fig. 5 is a plan view of the bottom of a cylindrical battery that is another example of an embodiment.

[0008] Hereinafter, an example of an embodiment of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure also includes configurations obtained by selectively combining the components of the embodiments described below.

[0009] [First Embodiment] Fig. 1 is a schematic diagram showing a cross section of a cylindrical battery 10 according to a first embodiment. As shown in Fig. 1, the cylindrical battery 10 includes an electrode assembly 14, an electrolyte (not shown), and an outer can 20 that accommodates the electrode assembly 14 and the electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and is configured such that the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 20 is a cylindrical metal container with a bottom and an opening on one axial side, and the opening of the outer can 20 is closed by a sealing body 19. Hereinafter, the sealing body 19 side in the axial direction (height direction) of the cylindrical battery 10 is referred to as "upper," and the bottom 21 side of the outer can 20 in the axial direction is referred to as "lower."

[0010] The electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0011] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0012] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0013] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11. The cylindrical battery 10 includes insulating plates 15 and 16 arranged above and below the electrode assembly 14, respectively.

[0014] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. The positive electrode core can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode core, excluding the exposed portion of the positive electrode core (not shown) to which the positive electrode lead 17 is welded. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.

[0015] The positive electrode mixture layer contains particulate lithium metal composite oxide as a positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium metal composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among them, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0016] Examples of conductive agents contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0017] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and, if necessary, a conductive agent, and is preferably formed on both sides of the negative electrode core, excluding the exposed portion of the negative electrode core (not shown) to which the negative electrode lead 18 is welded. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0018] The negative electrode mixture layer generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, as the negative electrode active material, a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element may be used. Among these, a composite material containing Si is preferred.

[0019] A suitable example of a composite material containing Si is SiO ２ Examples of the composite material include a material in which Si fine particles are dispersed in a silicate phase such as lithium silicate, or a material in which Si fine particles are dispersed in an amorphous carbon phase. A conductive layer such as a carbon coating is formed on the particle surface of the composite material. The combined use of a carbon material and a Si-containing composite material as the negative electrode active material is preferred from the viewpoint of achieving both high capacity and high durability of the battery.

[0020] As in the case of the positive electrode mixture layer, the binder contained in the negative electrode mixture layer can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene-butadiene rubber (SBR) is preferably used. The negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer may contain a conductive agent such as CNT.

[0021] The separator 13 is a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0022] A positive electrode lead 17 is connected to the positive electrode 11, and a negative electrode lead 18 is connected to the winding end side of the negative electrode 12. The positive electrode lead 17 passes through a through hole in the insulating plate 15 and extends toward the sealing body 19, and the negative electrode lead 18 passes outside the insulating plate 16 and extends toward the bottom 21 of the outer can 20. The positive electrode lead 17 is connected to the underside of an internal terminal plate 24 of the sealing body 19 by welding or the like, and the sealing body 19 serves as a positive electrode terminal. The negative electrode lead 18 is connected to the inner surface of the bottom 21 of the metal outer can 20 by welding or the like, and the outer can 20 serves as a negative electrode terminal.

[0023] The outer can 20 is a cylindrical metal container that is open at the top in the axial direction. From the viewpoint of achieving both workability and heat dissipation, the outer can 20 is made of a material, for example, a metal whose main component is iron. The outer can 20 has a bottom 21 and a side wall 22. As will be described in detail later, a plurality of first protrusions 30 each having a substantially annular shape are formed on the outer surface 21A of the bottom 21, and the surface area of ​​the outer surface 21A of the bottom 21 is 1.2 times or more the projected area of ​​the outer surface 21A of the bottom 21.

[0024] A gasket 27 is provided between the exterior can 20 and the sealing body 19, ensuring sealing of the interior of the battery and insulation between the exterior can 20 and the sealing body 19. The exterior can 20 has a grooved portion 23 formed by a portion of the side wall 22 protruding inward to support the sealing body 19. The grooved portion 23 is preferably formed in an annular shape along the circumferential direction of the exterior can 20, and supports the sealing body 19 on its top surface. The sealing body 19 is fixed to the top of the exterior can 20 by the grooved portion 23 and the open end of the exterior can 20, which is crimped to the sealing body 19.

[0025] The sealing body 19 is a disc-shaped member equipped with a safety valve. The sealing body 19 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 24, an insulating member 25, and an external terminal plate 26 are stacked. The internal terminal plate 24 is a metal plate including a thick outer peripheral portion 24A to which the positive electrode lead 17 is connected, and a thin central portion 24B that is cut off from the outer peripheral portion 24A when the internal pressure of the battery exceeds a predetermined threshold. A plurality of vent holes 24C are formed in the outer peripheral portion 24A.

[0026] The external terminal plate 26 is disposed opposite the internal terminal plate 24 with the insulating member 25 sandwiched therebetween. The insulating member 25 has an opening 25A formed in its radial center, and an air vent 25B formed in a portion overlapping the air vent 24C of the internal terminal plate 24. The external terminal plate 26 has a valve portion 26A that ruptures when the internal pressure of the cylindrical battery 10 exceeds a predetermined threshold, and the valve portion 26A is connected to the central portion 24B of the internal terminal plate 24 by welding or other means. The insulating member 25 insulates portions other than the connection between the central portion 24B and the valve portion 26A. Furthermore, the outer peripheral portion surrounding the valve portion 26A of the external terminal plate 26 is held, via a gasket 27, between a crimped portion formed by bending the opening of the exterior can 20 inward and the grooved portion 23.

[0027] The valve portion 26A is formed in the radial center of the external terminal plate 26, including a joint located in the radial center and protruding toward the inside of the battery, and a thin-walled portion formed around the joint. The joint of the valve portion 26A passes through the opening 25A of the insulating member 25 and joins with the central portion 24B. When an abnormality occurs in the cylindrical battery 10 and the internal pressure rises, the generated high-temperature gas pushes the external terminal plate 26 upward, causing the internal terminal plate 24 to break, separating the central portion 24B from the outer peripheral portion 24A, and deforming the valve portion 26A so that it protrudes toward the outside of the battery. This interrupts the current path in the sealing body 19. If the internal pressure of the cylindrical battery 10 continues to rise after the current path is interrupted, the thin-walled portion of the valve portion 26A breaks, forming a gas outlet in the external terminal plate 26.

[0028] The structure of sealing body 19 is not limited to the structure shown in Fig. 1. Sealing body 19 may have a laminated structure including two valve bodies, or may have a convex sealing body cap that covers the valve bodies.

[0029] Next, the structure of the outer can 20 will be described in detail with further reference to Figures 2 and 3. Figure 2 is a plan view of the outer surface 21A of the bottom 21 of the outer can 20, and Figure 3 is a cross-sectional view taken along line AA in Figure 2, which is an axial cross-sectional view of the bottom 21 of the outer can 20. Note that in Figure 2, the region where the first protrusion 30 is provided is indicated by hatching.

[0030] As shown in FIG. 2 , the outer surface 21A of the bottom portion 21 is provided with multiple first protrusions 30 having a generally annular shape. This allows the surface area of ​​the outer surface 21A of the bottom portion 21 to be at least 1.2 times the projected area of ​​the outer surface 21A of the bottom portion 21. Research by the inventors has revealed that the surface area of ​​the outer surface 21A of the bottom portion 21 significantly affects the heat dissipation performance of the cylindrical battery 10. By making the surface area of ​​the outer surface 21A of the bottom portion 21 at least 1.2 times the projected area of ​​the outer surface 21A of the bottom portion 21, the area of ​​the outer can 20 exposed to the outside air is increased, allowing more heat from inside the battery to be released to the outside air through the outer can 20. As a result, temperature increases during battery use are suppressed, making it easier to ensure battery performance. In other words, if the surface area of ​​the outer surface 21A of the bottom portion 21 is less than 1.2 times the projected area of ​​the outer surface 21A of the bottom portion 21, the heat dissipation performance of the cylindrical battery 10 cannot be sufficiently improved. The first protrusion 30 can be formed by, for example, pressing the bottom portion 21 .

[0031] The number of first protrusions 30 can be set as appropriate within a range that allows the surface area of ​​the outer surface 21A of the bottom 21 to be 1.2 times or more the projected area of ​​the outer surface 21A of the bottom 21, but is preferably 3 or more, and more preferably 5 or more. In this embodiment, 10 first protrusions 30 are provided on the outer surface 21A of the bottom 21 at intervals in the radial direction.

[0032] In this specification, the term "first protrusion 30 having a substantially annular shape" includes not only first protrusions 30 having an annular shape, but also first protrusions 30 having a shape in which some parts are discontinuous. For example, the first protrusions 30 may be discontinuous at one or more points in the annular shape. When the total circumferential length of the annular shape is taken as 100, the total length of the continuous parts of the first protrusions 30 is preferably 70 or more, more preferably 80 or more, and even more preferably 90 or more.

[0033] The surface area of ​​the outer surface 21A of the bottom 21 may be at least 1.2 times the projected area of ​​the outer surface 21A of the bottom 21, but is preferably at least 1.5 times, more preferably at least 2.0 times, and even more preferably at least 2.5 times. By making the surface area of ​​the outer surface 21A of the bottom 21 at least 1.5 times the projected area of ​​the outer surface 21A of the bottom 21, the area of ​​the outer can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the outer can 20. Furthermore, the upper limit of the surface area of ​​the outer surface 21A of the bottom 21 is, for example, 10 times the projected area of ​​the outer surface 21A of the bottom 21. If the surface area of ​​the outer surface 21A of the bottom 21 exceeds 10 times the projected area of ​​the outer surface 21A of the bottom 21, the strength of the outer can 20 decreases, and the bottom 21 may deform when the internal pressure of the cylindrical battery 10 increases excessively. Therefore, the surface area of ​​the outer surface 21A of the bottom 21 is preferably 1.5 to 10 times, more preferably 2.0 to 10 times, and even more preferably 2.5 to 10 times the projected area of ​​the outer surface 21A of the bottom 21. The projected area of ​​the outer surface 21A of the bottom 21 means the area of ​​the outer surface 21A of the bottom 21 when viewed from above in a plan view along the axial direction of the outer can 20.

[0034] When the outer surface 21A of the bottom 21 is viewed from above in a plan view, the ratio of the area occupied by the first convex portions 30 to the area of ​​the outer surface 21A of the bottom 21 is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. Setting the ratio of the area occupied by the first convex portions 30 to the area of ​​the outer surface 21A of the bottom 21 to 20% or more facilitates increasing the surface area of ​​the outer surface 21A of the bottom 21. As a result, the area of ​​the outer can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the outer can 20. Furthermore, when the outer surface 21A of the bottom 21 is viewed from above in a plan view, the ratio of the area occupied by the first convex portions 30 to the area of ​​the outer surface 21A of the bottom 21 is preferably 50% or less, from the viewpoint of increasing the surface area of ​​the outer surface 21A of the bottom 21 while ensuring the strength of the outer can 20. Therefore, the ratio of the area occupied by the first convex portion 30 to the area of ​​the outer surface 21A of the bottom portion 21 is preferably 20% or more and 50% or less, more preferably 25% or more and 50% or less, and even more preferably 30% or more and 50% or less.

[0035] As shown in Figure 2, the outer surface 21A of the bottom 21 has four slits 31 arranged along the radial direction, dividing the first protrusion 30 in the circumferential direction. By providing the slits 31, outside air stagnating on the outside of the bottom 21 flows through the slits 31 toward the center of the bottom 21. As a result, heat from the center of the bottom 21 is more easily released to the outside air. Therefore, providing the slits 31 on the outer surface 21A of the bottom 21 can further improve the heat dissipation performance of the cylindrical battery 10.

[0036] The slits 31 are preferably provided at equal angular intervals in the circumferential direction. By providing the slits 31 at equal angular intervals in the circumferential direction, the flow of outside air near the outer surface 21A of the bottom portion 21 becomes smoother. As a result, heat from the bottom portion 21 is more easily released into the outside air.

[0037] In this embodiment, four slits 31 are provided, but the number of slits 31 is not limited to this. The number of slits 31 may be three or less, or five or more. From the viewpoint of smoothing the flow of outside air through the slits 31, the number of slits 31 is preferably four or more. Furthermore, from the viewpoint of ensuring the surface area of ​​the outer surface 21A of the bottom 21, the number of slits 31 is preferably eight or less. Therefore, the number of slits 31 is preferably four or more and eight or less.

[0038] The circumferential length (width) of the slits 31 is not particularly limited, but is, for example, 0.1 mm or more and 5.0 mm or less. The circumferential length of the slits 31 may be constant in the radial direction or may vary in the radial direction. For example, the circumferential length of the slits 31 may become smaller as it moves radially inward. Although the slits 31 preferably divide all of the first protrusions 30 in the circumferential direction, some of the first protrusions 30 may not necessarily be divided in the circumferential direction. In other words, some of the first protrusions 30 may have a continuous annular shape in the circumferential direction.

[0039] As shown in FIG. 2 , a flat region 32 where the first protrusion 30 is not provided is provided in the center of the outer surface 21A of the bottom 21. The flat region 32 has a perfect circular shape when the outer surface 21A of the bottom 21 is viewed from above in a plan view. The negative electrode lead 18 is joined to the center of the inner surface of the bottom 21 by welding or the like. Therefore, providing the flat region 32 in the center of the outer surface 21A of the bottom 21 facilitates welding work and improves productivity. The diameter of the flat region 32 is not particularly limited, but is, for example, 20% to 60% of the diameter of the outer surface 21A of the bottom 21.

[0040] As shown in FIG. 3 , the height of the first protrusion 30 is preferably 0.01 mm or more, more preferably 0.1 mm or more, and even more preferably 0.3 mm or more. Setting the height of the first protrusion 30 to 0.01 mm or more facilitates increasing the surface area of ​​the outer surface 21A of the bottom 21. As a result, the area of ​​the exterior can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the exterior can 20. The upper limit of the height of the first protrusion 30 is, for example, 5.0 mm. Therefore, the height of the first protrusion 30 is preferably 0.01 mm or more and 5.0 mm or less, more preferably 0.1 mm or more and 5.0 mm or less, and even more preferably 0.3 mm or more and 5.0 mm or less. The height of the first protrusion 30 refers to the length along the axial direction of the exterior can 20 from the outer surface 21A of the bottom 21 to the top of the first protrusion 30.

[0041] In this embodiment, the height of all the first protrusions 30 is approximately uniform, but the height of the first protrusions 30 may vary within the plane. For example, the height of the first protrusions 30 provided on the radially inner side may be greater than the height of the first protrusions 30 provided on the radially outer side. In this case, outside air is more likely to flow toward the center of the bottom 21.

[0042] The radial length (width) of the first protrusions 30 is preferably 0.01 mm or more. By making the radial length of the first protrusions 30 0.01 mm or more, it becomes easier to ensure the strength of the first protrusions 30. Furthermore, the radial length of the first protrusions 30 is preferably 5.0 mm or less. If the radial length of the first protrusions 30 exceeds 5.0 mm, it becomes difficult to provide a sufficient number of first protrusions 30 on the outer surface 21A of the bottom portion 21. As a result, it becomes difficult to increase the surface area of ​​the outer surface 21A of the bottom portion 21. Therefore, the radial length of the first protrusions 30 is preferably 0.01 mm or more and 5.0 mm or less.

[0043] In this embodiment, the radial lengths of all the first protrusions 30 are substantially uniform, but the radial lengths of the first protrusions 30 may vary within the plane. For example, the radial length of the first protrusions 30 provided on the radially inner side may be greater than the radial length of the first protrusions 30 provided on the radially outer side. Furthermore, first protrusions 30 with a large radial length and first protrusions 30 with a small radial length may be alternately arranged at intervals in the radial direction.

[0044] 3, the first protrusion 30 has a substantially rectangular shape in an axial cross section. That is, the inclined surface 33 of the first protrusion 30 extends along the axial direction. Here, the substantially rectangular shape also includes a shape in which the corners of the first protrusion 30 are rounded.

[0045] The shape of the first protrusions 30 is not limited to this. The shape of the first protrusions 30 may be, for example, a substantially triangular shape when viewed in cross section in the axial direction. That is, the inclined surfaces 33 of the first protrusions 30 may extend in a direction inclined with respect to the axial direction. Furthermore, when the cross section of the first protrusions 30 has a triangular shape, the first protrusions 30 may be provided adjacent to each other without any gaps in the radial direction.

[0046] 3, the inner surface of the bottom portion 21 is substantially flat, but is not limited to this. For example, the inner surface of the bottom portion 21 may have a recess formed at a position corresponding to the first protrusion 30.

[0047] Second Embodiment A cylindrical battery 10 according to a second embodiment will be described with reference to Figure 4. Figure 4 is a plan view of the outer surface 21A of the bottom 21 of the outer can 20. Note that in Figure 4, the area where the second protrusion 40 is provided is indicated by hatching. Below, the same reference numerals are used for components common to the first embodiment, and redundant explanations will be omitted. Differences from the first embodiment will be mainly described.

[0048] 4, a plurality of second protrusions 40 are scattered on the outer surface 21A of the bottom portion 21. This allows the surface area of ​​the outer surface 21A of the bottom portion 21 to be 1.2 times or more the projected area of ​​the outer surface 21A of the bottom portion 21. Similar to the first protrusions 30, the second protrusions 40 can be formed by, for example, pressing the bottom portion 21.

[0049] The second protrusions 40 are preferably arranged periodically. In this embodiment, when the outer surface 21A of the bottom 21 is viewed from above in a plan view, the second protrusions 40 are arranged on the lattice points of a square lattice. By arranging the second protrusions 40 periodically, the flow of outside air near the bottom 21 becomes smoother, making it easier for heat from the bottom 21 to be released into the outside air. Note that the second protrusions 40 may also be arranged on the lattice points of a triangular lattice or a hexagonal lattice.

[0050] 4 , the second convex portions 40 are provided over substantially the entire outer surface 21A of the bottom portion 21, but are not limited to this. The second convex portions 40 may be provided only in a partial area of ​​the outer surface 21A of the bottom portion 21, as long as the surface area of ​​the outer surface 21A of the bottom portion 21 is at least 1.2 times the projected area of ​​the outer surface 21A of the bottom portion 21. For example, a flat area where the second convex portions 40 are not provided may be provided in the center of the outer surface 21A of the bottom portion 21.

[0051] When viewed from above and in a plan view of the outer surface 21A of the bottom portion 21, the second convex portion 40 has a substantially rectangular shape. The second convex portion 40 may have a substantially circular shape. The second convex portion 40 may also have a tapered shape in which the cross-sectional area decreases toward the tip of the second convex portion 40, i.e., toward the lower side in the axial direction.

[0052] When the outer surface 21A of the bottom 21 is viewed from above in a plan view, the ratio of the area occupied by the second convex portions 40 to the area of ​​the outer surface 21A of the bottom 21 is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. Setting the ratio of the area occupied by the second convex portions 40 to the area of ​​the outer surface 21A of the bottom 21 to 20% or more facilitates increasing the surface area of ​​the outer surface 21A of the bottom 21. As a result, the area of ​​the outer can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the outer can 20. Furthermore, when the outer surface 21A of the bottom 21 is viewed from above in a plan view, the ratio of the area occupied by the second convex portions 40 to the area of ​​the outer surface 21A of the bottom 21 is preferably 50% or less, from the viewpoint of increasing the surface area of ​​the outer surface 21A of the bottom 21 while ensuring the strength of the outer can 20. Therefore, it is preferable that the ratio of the area occupied by the second convex portion 40 to the area of ​​the outer surface 21A of the bottom portion 21 is 20% or more and 50% or less, more preferably 25% or more and 50% or less, and even more preferably 30% or more and 50% or less.

[0053] The height of the second convex portion 40, like the height of the first convex portion 30, is preferably 0.01 mm or more, more preferably 0.1 mm or more, and even more preferably 0.3 mm or more. Setting the height of the second convex portion 40 to 0.01 mm or more facilitates increasing the surface area of ​​the outer surface 21A of the bottom portion 21. As a result, the area of ​​the exterior can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the exterior can 20. The upper limit of the height of the second convex portion 40 is, for example, 5.0 mm. Therefore, the height of the second convex portion 40 is preferably 0.01 mm or more and 5.0 mm or less, more preferably 0.1 mm or more and 5.0 mm or less, and even more preferably 0.3 mm or more and 5.0 mm or less.

[0054] Third Embodiment A cylindrical battery 10 according to a third embodiment will be described with reference to Figure 5. Figure 5 is a plan view of the outer surface 21A of the bottom 21 of the outer can 20. Note that in Figure 5, the area where the third protrusion 50 is provided is indicated by hatching. Below, the same reference numerals are used for components common to the first and second embodiments, and redundant explanations are omitted. Differences from the first and second embodiments will be mainly described.

[0055] As shown in FIG. 5 , the outer surface 21A of the bottom portion 21 has a plurality of third protrusions 50 extending along an arbitrary first direction. When the outer surface 21A of the bottom portion 21 is viewed from above in a plan view, the third protrusions 50 are arranged at predetermined intervals in a second direction perpendicular to the first direction. This results in a plurality of first slits 51 extending along the second direction being formed between adjacent third protrusions 50. By providing a plurality of third protrusions 50 on the outer surface 21A of the bottom portion 21, the surface area of ​​the outer surface 21A of the bottom portion 21 can be made 1.2 times or more the projected area of ​​the outer surface 21A of the bottom portion 21. The third protrusions 50 can be formed, for example, by press-forming the bottom portion 21, similar to the first protrusions 30 and the second protrusions 40.

[0056] The spacing between the third protrusions 50 in the second direction, i.e., the second-direction length (width) of the first slits 51, can be set appropriately within a range that allows the surface area of ​​the outer surface 21A of the bottom 21 to be at least 1.2 times the projected area of ​​the outer surface 21A of the bottom 21. The second-direction length of the first slits 51 is, for example, 0.1 mm or more and 5.0 mm or less. The second-direction length of the first slits 51 may be uniform across substantially the entire outer surface 21A of the bottom 21 or may vary within the plane. For example, the second-direction length of the first slits 51 provided on the central side of the bottom 21 may be shorter than the second-direction length of the first slits 51 provided on the outer periphery of the bottom 21. That is, more third protrusions 50 may be arranged on the central side of the bottom 21 than on the outer periphery of the bottom 21.

[0057] When the outer surface 21A of the bottom 21 is viewed from above in a plan view, the ratio of the area occupied by the third convex portions 50 to the area of ​​the outer surface 21A of the bottom 21 is preferably 20% or more, more preferably 25% or more, and even more preferably 30% or more. Setting the ratio of the area occupied by the third convex portions 50 to the area of ​​the outer surface 21A of the bottom 21 to 20% or more facilitates increasing the surface area of ​​the outer surface 21A of the bottom 21. As a result, the area of ​​the outer can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the outer can 20. Furthermore, when the outer surface 21A of the bottom 21 is viewed from above in a plan view, the ratio of the area occupied by the third convex portions 50 to the area of ​​the outer surface 21A of the bottom 21 is preferably 50% or less, from the viewpoint of increasing the surface area of ​​the outer surface 21A of the bottom 21 while ensuring the strength of the outer can 20. Therefore, it is preferable that the ratio of the area occupied by the third convex portion 50 to the area of ​​the outer surface 21A of the bottom portion 21 is 20% or more and 50% or less, more preferably 25% or more and 50% or less, and even more preferably 30% or more and 50% or less.

[0058] In this embodiment, second slits 52 extending along the first direction are formed on the outer surface 21A of the bottom 21. That is, the third protrusion 50 is divided by the second slits 52. By providing the second slits 52, outside air stagnating on the outside of the bottom 21 flows through the second slits 52 toward the center of the bottom 21. As a result, heat from the center of the bottom 21 is more easily released to the outside air. Therefore, providing the second slits 52 on the outer surface 21A of the bottom 21 can further improve the heat dissipation performance of the cylindrical battery 10.

[0059] The number of second slits 52 is not limited to one, and may be multiple. When multiple second slits 52 are provided on the outer surface 21A of the bottom 21, the second slits 52 are preferably provided at equal intervals in the second direction.

[0060] The length (width) of the second slits 52 in the first direction is not particularly limited, but is, for example, 0.1 mm or more and 5.0 mm or less. The length of the second slits 52 in the first direction may be constant throughout the second direction or may vary in the second direction. For example, the length of the slits 31 in the first direction may become smaller toward the center of the bottom 21. The second slits 52 preferably cross all of the third protrusions 50, but may not cross some of the third protrusions 50. In other words, some of the third protrusions 50 may extend continuously in the first direction.

[0061] The height of the third protrusion 50, like the heights of the first protrusion 30 and the second protrusion 40, is preferably 0.01 mm or more, more preferably 0.1 mm or more, and even more preferably 0.3 mm or more. Setting the height of the third protrusion 50 to 0.01 mm or more facilitates increasing the surface area of ​​the outer surface 21A of the bottom 21. As a result, the area of ​​the exterior can 20 exposed to the outside air is further increased, making it easier for heat inside the battery to be released to the outside air through the exterior can 20. The upper limit of the height of the third protrusion 50 is, for example, 5.0 mm. Therefore, the height of the third protrusion 50 is preferably 0.01 mm or more and 5.0 mm or less, more preferably 0.1 mm or more and 5.0 mm or less, and even more preferably 0.3 mm or more and 5.0 mm or less.

[0062] The length (width) in the second direction of the third protrusion 50 can be set appropriately within a range that allows the surface area of ​​the outer surface 21A of the bottom 21 to be 1.2 times or more the projected area of ​​the outer surface 21A of the bottom 21. The length (width) in the second direction of the third protrusion 50 is, for example, 0.01 mm or more and 5.0 mm or less.

[0063] The above-described embodiments can be modified as appropriate within the scope of the present disclosure. For example, in the first to third embodiments, the outer surface 21A of the bottom 21 is provided with a convex portion, thereby making the surface area of ​​the outer surface 21A of the bottom 21 at least 1.2 times the projected area of ​​the outer surface 21A of the bottom 21. However, this is not limited to this. For example, the outer surface 21A of the bottom 21 may be provided with a concave portion, thereby making the surface area of ​​the outer surface 21A of the bottom 21 at least 1.2 times the projected area of ​​the outer surface 21A of the bottom 21. In this case, when the outer surface 21A of the bottom 21 is viewed from above in a plan view, the area of ​​the concave portion relative to the area of ​​the outer surface 21A of the bottom 21 is preferably 20% to 50%, more preferably 25% to 50%, and even more preferably 30% to 50%.

[0064] The present disclosure is further described by the following embodiments. Aspect 1: A cylindrical battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a cylindrical outer can having a bottom and housing the electrode assembly, and a sealing body closing an opening of the outer can, wherein the surface area of ​​the outer surface of the bottom is 1.2 times or more the projected area of ​​the outer surface of the bottom. Aspect 2: The cylindrical battery according to Aspect 1, wherein the outer surface of the bottom is provided with a plurality of first protrusions having a substantially annular shape. Aspect 3: The cylindrical battery according to Aspect 2, wherein the outer surface of the bottom is provided with slits extending along the radial direction and dividing the first protrusions in the circumferential direction. Aspect 4: The cylindrical battery according to Aspect 3, wherein the outer surface of the bottom is provided with a plurality of slits, the slits being arranged at equal angular intervals from one another in the circumferential direction. Aspect 5: The cylindrical battery according to any one of Aspects 2 to 4, wherein the height of the first protrusions is 0.01 mm or more and 5.0 mm or less. Configuration 6: The cylindrical battery according to any one of Configurations 2 to 5, wherein the radial length of the first protrusions is 0.01 mm or more and 5.0 mm or less. Configuration 7: The cylindrical battery according to any one of Configurations 2 to 6, wherein, when the outer surface of the bottom is viewed in a plan view from above, the ratio of the area occupied by the first protrusions to the area of ​​the outer surface of the bottom is 20% or more and 50% or less. Configuration 8: The cylindrical battery according to Configuration 1, wherein a plurality of second protrusions are scattered on the outer surface of the bottom. Configuration 9: The cylindrical battery according to Configuration 8, wherein, when the outer surface of the bottom is viewed in a plan view from above, the plurality of second protrusions are arranged on lattice points of a triangular lattice, a square lattice, or a hexagonal lattice. Configuration 10: The cylindrical battery according to Configuration 8 or 9, wherein the height of the second protrusions is 0.01 mm or more and 5.0 mm or less. The cylindrical battery of any one of the preceding embodiments, wherein the outer surface of the bottom is provided with a plurality of third protrusions extending along a first direction, the third protrusions being spaced apart in a second direction perpendicular to the first direction when viewed from above in a plan view of the outer surface of the bottom.Aspect 13: The cylindrical battery according to Aspect 12, wherein the height of the third convex portion is 0.01 mm or more and 5.0 mm or less. Aspect 14: The cylindrical battery according to Aspect 12 or 13, wherein, when the outer surface of the bottom portion is viewed from above in a plan view, the ratio of the area occupied by the third convex portion to the area of ​​the outer surface of the bottom portion is 20% or more and 50% or less.

[0065] REFERENCE SIGNS LIST 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Insulating plate, 16 Insulating plate, 17 Positive electrode lead, 18 Negative electrode lead, 19 Sealing body, 20 Outer can, 21 Bottom, 21A Outer surface, 22 Side wall portion, 23 Grooved portion, 24 Internal terminal plate, 24A Outer periphery, 24B Central portion, 24C Ventilation hole, 25 Insulating member, 25A Opening, 25B Ventilation hole, 26 External terminal plate, 26A Valve portion, 27 Gasket, 30 First convex portion, 31 Slit, 32 Flat region, 33 Slope, 40 Second convex portion, 50 Third convex portion, 51 First slit, 52 Second slit

Claims

1. A cylindrical battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a cylindrical outer can having a bottom and housing the electrode assembly; and a sealing body that closes the opening of the outer can, wherein the surface area of ​​the outer face of the bottom is 1.2 times or more the projected area of ​​the outer face of the bottom.

2. The cylindrical battery according to claim 1, wherein the outer surface of the bottom portion is provided with a plurality of first protrusions having a substantially annular shape.

3. The cylindrical battery according to claim 2, wherein a slit is provided on the outer surface of the bottom portion along the radial direction and divides the first protrusion in the circumferential direction.

4. A cylindrical battery as set forth in claim 3, wherein a plurality of said slits are provided on the outer surface of said bottom portion, and said plurality of slits are provided at equal angular intervals from each other in the circumferential direction.

5. The cylindrical battery according to claim 2, wherein the height of the first protrusion is not less than 0.01 mm and not more than 5.0 mm.

6. The cylindrical battery according to claim 2, wherein the radial length of the first protrusion is 0.01 mm or more and 5.0 mm or less.

7. The cylindrical battery according to claim 2, wherein when the outer surface of the bottom is viewed in a plan view looking down from above, the ratio of the area occupied by the first convex portion to the area of ​​the outer surface of the bottom is 20% or more and 50% or less.

8. The cylindrical battery according to claim 1, wherein a plurality of second protrusions are dotted on the outer surface of the bottom.

9. The cylindrical battery according to claim 8, wherein, when the outer surface of the bottom is viewed in a plan view looking down from above, the second protrusions are arranged on lattice points of a triangular lattice, a square lattice, or a hexagonal lattice.

10. The cylindrical battery according to claim 8, wherein the height of the second protrusion is equal to or greater than 0.01 mm and equal to or less than 5.0 mm.

11. The cylindrical battery according to claim 8, wherein when the outer surface of the bottom is viewed in a plan view looking down from above, the ratio of the area occupied by the second convex portion to the area of ​​the outer surface of the bottom is 20% or more and 50% or less.

12. A cylindrical battery as described in claim 1, wherein the outer surface of the bottom has a plurality of third protrusions extending along a first direction, and the third protrusions are arranged at intervals in a second direction perpendicular to the first direction when the outer surface of the bottom is viewed in a plan view looking down from above.

13. The cylindrical battery according to claim 12, wherein the height of the third protrusion is 0.01 mm or more and 5.0 mm or less.

14. The cylindrical battery according to claim 12, wherein, when the outer surface of the bottom is viewed in a plan view looking down from above, the ratio of the area occupied by the third convex portion to the area of ​​the outer surface of the bottom is 20% or more and 50% or less.

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