Cylindrical battery

Abstract

A cylindrical battery (10) comprising an outer can (20) of a bottomed cylinder shape having a bottom part (21) and a side wall part (22), an electrode body (14), and a sealing body (30) blocking the opening of the outer can (20), said cylindrical battery (10) being characterized in that: the side wall part (22) includes a grooved part (23) that is recessed inward in the radial direction, and a barrel part (24) that is a portion more on an other side in the axial direction than the grooved part (23); the grooved part (23) includes a most-diameter-reduced part (26) that is most recessed inward in the radial direction and a groove lower part (27) that connects the most-diameter-reduced part (26) and the trunk part 24; and the maximum thickness t1 of the groove lower part (27) is greater than the thickness t2 of the trunk part (24) at an axial-direction center part thereof and the thickness t3 of the most-diameter-reduced part (26).

Description

Cylindrical battery

[0001] The present disclosure relates to a cylindrical battery.

[0002] Conventionally, a cylindrical battery including an outer can that houses an electrode body and a sealing body that closes the opening of the outer can has been widely known. As disclosed in Patent Document 1, a cylindrical battery is manufactured by forming a groove portion in the side wall portion of an outer can that houses an electrode body, caulking and fixing a sealing body between the groove portion and the open end, and then pressing the battery from above to compress the groove portion. By pressing the battery from above and compressing the groove portion, for example, the sealing performance of the battery can be improved, and the height of the battery can be adjusted to a predetermined height.

[0003] Japanese Unexamined Patent Application Publication No. 2018-018575

[0004] As a result of the study by the present inventors, it has been found that, for example, when the outer can has a uniform thickness throughout, when the battery is pressed from above and the groove portion is compressed, the groove portion may collapse toward the electrode body side. When the groove portion collapses toward the electrode body side, the electrode body is likely to be pressed by the groove portion, which is not preferable from the viewpoint of ensuring the reliability of the battery.

[0005] A cylindrical battery according to one aspect of the present disclosure includes a bottomed cylindrical outer can having a bottom portion and a side wall portion extending axially from the outer peripheral edge of the bottom portion, an electrode body housed in the outer can, and a sealing body that closes the opening of the outer can. The side wall portion includes a groove portion that is recessed inward in the radial direction, and a body portion that is a portion on the other side in the axial direction than the groove portion. The groove portion includes a most contracted diameter portion that is most recessed inward in the radial direction, and a groove lower portion that connects the most contracted diameter portion and the body portion. In an axial cross-sectional view of the outer can, the maximum thickness t1 of the groove lower portion is larger than the thickness t2 of the body portion at the axial center portion of the body portion and the thickness t3 of the most contracted diameter portion.

[0006] According to the cylindrical battery according to one aspect of the present disclosure, when the battery is pressed axially to compress the groove portion, it is possible to suppress the groove portion from collapsing toward the electrode body side. As a result, a cylindrical battery with excellent reliability can be provided.

[0007] This is an axial cross-sectional view of a cylindrical battery, which is one example of an embodiment. This is an axial cross-sectional view of an outer casing, which is one example of an embodiment, showing an enlarged view of the vicinity of the grooved portion. This is a schematic diagram showing the manufacturing process of the outer casing of a cylindrical battery, which is one example of an embodiment. This is an axial cross-sectional view of an outer casing, which is another example of an embodiment, showing an enlarged view of the vicinity of the grooved portion. This is an axial cross-sectional view of an outer casing, which is another example of an embodiment, showing an enlarged view of the vicinity of the grooved portion.

[0008] Hereinafter, an example of an embodiment of the cylindrical battery according to this disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and this disclosure is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in this disclosure.

[0009] Figure 1 is an axial cross-sectional view of a cylindrical battery 10, which is an example of an embodiment. As shown in Figure 1, the cylindrical battery 10 comprises an electrode body 14, a non-aqueous electrolyte (not shown), and an outer casing 20 that houses the electrode body 14 and the non-aqueous electrolyte. The outer casing 20 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 20 is sealed by a sealing body 30. The cylindrical battery 10 further comprises a gasket 40 interposed between the outer casing 20 and the sealing body 30 to ensure airtightness inside the battery and to prevent electrical contact between the outer casing 20 and the sealing body 30. Hereinafter, the side of the cylindrical battery 10 with the sealing body 30 in the axial direction (up and down direction) will be referred to as "up," and the side of the outer casing 20 with the bottom 21 in the axial direction will be referred to as "down."

[0010] The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strips, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in both the longitudinal and width (short direction). The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators are arranged so as to sandwich the positive electrode 11. The cylindrical battery 10 also includes insulating plates 16 and 17 arranged above and below the electrode body 14, respectively.

[0011] The positive electrode 11 comprises a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. The positive electrode core can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its 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 to which the positive electrode lead 18 is welded. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core, drying the coating, and then compressing it to form the positive electrode mixture layer on both sides of the positive electrode core.

[0012] The positive electrode composite layer contains particulate lithium metal composite oxide as the 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 elements constituting the lithium metal composite oxide are, 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 these, 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.

[0013] Examples of conductive agents included in the positive electrode mixture layer include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0014] The negative electrode 12 comprises a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core can be made of a metal foil that is stable within the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both sides of the negative electrode core, excluding the exposed portion of the negative electrode core to which the negative electrode lead 19 is welded. The negative electrode 12 can be manufactured 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 the negative electrode mixture layer on both sides of the negative electrode core.

[0015] The negative electrode composite layer generally contains a carbon material that reversibly intercepts and releases lithium ions as the negative electrode active material. Suitable examples of carbon materials include natural graphite such as flake graphite, lumpy graphite, and clay graphite, as well as artificial graphite such as lumpy artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). In addition, 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 as the negative electrode active material. Among these, composite materials containing Si are preferred.

[0016] A preferred example of a composite material containing Si is SiO ２ Examples include materials in which Si nanoparticles are dispersed in a phase or a silicate phase such as lithium silicate, or materials in which Si nanoparticles are dispersed in an amorphous carbon phase. A conductive layer, such as a carbon film, is formed on the particle surface of the composite material.

[0017] The binder in the negative electrode mixture layer may be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., similar to the positive electrode mixture layer, but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, a combination of SBR and CMC or a salt thereof, PAA or a salt thereof is preferred. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0018] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as 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.

[0019] A positive lead 18 is connected to the positive electrode 11, and a negative lead 19 is connected to the end of the winding of the negative electrode 12. The positive lead 18 extends towards the sealing body 30 through a through hole in the insulating plate 16, and the negative lead 19 extends towards the bottom 21 of the outer casing 20 through the outside of the insulating plate 17. The positive lead 18 is connected to the lower surface of the sealing body 30 by welding or the like, so that the sealing body 30 becomes the positive terminal. The negative lead 19 is connected to the inner surface of the bottom 21 of the metal outer casing 20 by welding or the like, so that the outer casing 20 becomes the negative terminal. Note that the current collection configuration of the positive electrode 11 and the negative electrode 12 is not limited to this.

[0020] The non-aqueous electrolyte contained in the outer container 20 is lithium ion conductive. The non-aqueous electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0021] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0022] 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, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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 a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0023] The outer container 20 is a bottomed cylindrical metal container having a bottom 21 and side walls 22 extending upward from the outer edge of the bottom 21. The outer container 20 is made of a material mainly composed of iron, such as carbon steel or stainless steel. The opening of the outer container 20 is sealed by a sealing body 30.

[0024] In this embodiment, the sealing body 30 is made of a single disc-shaped metal member. The sealing body 30 has a circular shape when viewed from above, and is crimped and fixed to the outer can 20 with its outer edge sandwiched between the gasket 40. The constituent material of the sealing body 30 is not particularly limited, but examples of preferred constituent materials include aluminum or an aluminum alloy. The structure of the sealing body 30 is not limited to this, and the sealing body 30 may have a structure in which multiple members are stacked.

[0025] The sealing body 30 forms the upper surface of the cylindrical battery 10. The sealing body 30 has a central portion 31 formed in the radial center of the sealing body 30, an outer peripheral portion 32 that forms the outer edge of the sealing body 30, and a thin-walled portion 33 that is thinner than the central portion 31 and the outer peripheral portion 32. The thin-walled portion 33 is located between the central portion 31 and the outer peripheral portion 32 and is formed in an annular shape.

[0026] If a malfunction occurs in the battery and the internal pressure exceeds a predetermined value, the thin-walled portion 33 ruptures, and an opening is formed in the area surrounded by the thin-walled portion 33. In the cylindrical battery 10, gas is released to the outside through this opening, and the electrode body 14 is also discharged. The cylindrical battery 10 is designed so that no opening is formed in the bottom 21 of the outer casing 20, and gas is released to the outside and the electrode body 14 is discharged only through the opening of the sealing body 30. In this case, for example, in a battery module equipped with multiple cylindrical batteries 10, the structure of the exhaust duct can be simplified, and the battery module can be made smaller.

[0027] The gasket 40 is a sealing material interposed between the sealing body 30 and the outer casing 20. By providing the gasket 40, the gap between the sealing body 30 and the outer casing 20 is sealed, ensuring airtightness inside the cylindrical battery 10. In other words, the gasket 40 is required to seal the gap between the sealing body 30 and the outer casing 20. The gasket 40 clamps the outer periphery 32 of the sealing body 30.

[0028] The gasket 40 is made of, for example, a polyolefin resin such as polypropylene (PP), a fluorinated resin such as tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), or a resin material such as polyphenylene sulfide (PPS).

[0029] Next, the outer can 20 will be described in detail with further reference to Figure 2. Figure 2 is an axial cross-sectional view of the outer can 20, showing an enlarged view of the vicinity of the grooved portion 23.

[0030] As shown in Figures 1 and 2, the outer container 20 has a bottom portion 21 and side wall portions 22. The bottom portion 21 has a disc shape and a uniform thickness across its surface. In this embodiment, the thickness of the bottom portion 21 is the same as the thickness t2 of the body portion 24, which will be described later. The thickness of the bottom portion 21 is not particularly limited.

[0031] The side wall portion 22 extends upward from the outer peripheral edge of the bottom portion 21 and forms the outer peripheral surface of the cylindrical battery 10. The side wall portion 22 includes a grooved portion 23 that is recessed radially inward, a body portion 24 which is the part below the grooved portion 23, and an opening 25 which is the part above the grooved portion 23. In other words, the side wall portion 22 is bent radially inward at the boundary between the grooved portion 23 and the body portion 24, and at the boundary between the grooved portion 23 and the opening 25. As will be described in detail later, the thickness of the side wall portion 22 in this embodiment differs in the axial direction.

[0032] The grooved portion 23 includes the smallest diameter portion 26, which is the most recessed part in the radial direction. In other words, the inner surface of the smallest diameter portion 26 constitutes the radial inner end of the grooved portion 23. The grooved portion 23 also includes a lower groove portion 27 that connects the smallest diameter portion 26 to the body portion 24, and an upper groove portion 28 that connects the smallest diameter portion 26 to the opening 25.

[0033] A sealing body 30 is positioned above the upper part 28 of the groove via a gasket 40. The sealing body 30 is then fixed to the opening 25 by crimping the open end 20X of the outer casing 20, thereby ensuring airtightness inside the cylindrical battery 10.

[0034] In the manufacturing process of the cylindrical battery 10, as shown in Figure 3 described later, a groove 23 is formed in the side wall 22, and after the sealing body 30 is crimped and fixed, the cylindrical battery 10 is pressed from above to compress the groove 23 in order to adjust the battery height to a predetermined height. As a result of the inventors' investigations, it was found that when the side wall 22 has a uniform thickness in the axial direction, the lower part 27 of the groove may collapse downward when the groove 23 is compressed. When the lower part 27 of the groove collapses downward, the electrode body 14 is more likely to be compressed by the groove 23, which may reduce the reliability of the battery.

[0035] Therefore, in this embodiment, as shown in Figure 2, in an axial cross-sectional view of the outer can 20, the maximum thickness t1 of the groove lower part 27 is greater than the thickness t2 of the body 24 at the axial center of the body 24, and greater than the thickness t3 of the smallest diameter portion 26. When t1, t2, and t3 satisfy the above relationship, the rigidity near the boundary between the groove lower part 27 and the body 24 can be increased, and the rigidity of the smallest diameter portion 26 can be decreased. As a result, when the grooved portion 23 is compressed, the area near the smallest diameter portion 26 is preferentially crushed, and the downward collapse of the groove lower part 27 is suppressed. As a result, the electrode body 14 is suppressed from being compressed by the grooved portion 23, and the reliability of the battery can be improved.

[0036] The maximum thickness t1 of the lower groove 27 is, for example, 0.3 mm to 0.5 mm. The thickness t2 of the body portion 24 is, for example, 0.20 mm to 0.3 mm. The thickness t3 of the smallest diameter portion 26 is, for example, 0.20 mm to 0.4 mm.

[0037] In this embodiment, the body portion 24 has a uniform thickness along the axial direction. Furthermore, the groove lower portion 27 has an increased thickness near the boundary with the body portion 24 and has a substantially uniform thickness extending to the thin-walled portion 27A, which will be described later.

[0038] The ratio of t1 to t2 (t1 / t2) is preferably 1.2 or greater, and more preferably 1.3 or greater. When t1 / t2 is 1.2 or greater, the rigidity near the boundary between the lower groove portion 27 and the body portion 24 can be further improved, and when the grooved portion 23 is compressed, the downward collapse of the lower groove portion 27 can be further suppressed. The upper limit of t1 / t2 is not particularly limited, and is, for example, 2.0.

[0039] Furthermore, the ratio of t1 to t3 (t1 / t3) is preferably 1.1 or greater, and more preferably 1.2 or greater. When t1 / t3 is 1.1 or greater, when the grooved portion 23 is compressed, the area near the smallest diameter portion 26 is more likely to collapse preferentially, and the downward collapse of the lower part of the groove 27 can be further suppressed. The upper limit of t1 / t3 is not particularly limited, and is, for example, 2.0.

[0040] Note that t3 may be the same as t2 or smaller than t2. When t3 is smaller than t2, when the groove insertion part 23 is compressed, the vicinity of the minimum diameter part 26 is more likely to be crushed preferentially, and it is possible to further suppress the lower part 27 of the groove from falling downward. The ratio (t3 / t2) of t3 to t2 is, for example, 0.95 or less, and may be 0.90 or less.

[0041] The maximum thickness t1 of the lower part 27 of the groove is preferably substantially uniform over the entire circumference. In this case, it is possible to further improve the rigidity in the vicinity of the boundary between the lower part 27 of the groove and the body part 24 over the entire circumference, and when the groove insertion part 23 is compressed, it is possible to further suppress the lower part 27 of the groove from falling downward. Note that being substantially uniform over the entire circumference means that the difference between the maximum value and the minimum value of t1 in the circumferential direction is 0.03 mm or less.

[0042] The lower part 27 of the groove has a thin part 27A with a thickness that gradually decreases as it approaches the minimum diameter part 26 in the radially inner region. By providing the thin part 27A, when the groove insertion part 23 is compressed, the vicinity of the minimum diameter part 26 is more likely to be crushed preferentially, and it is possible to further suppress the lower part 27 of the groove from falling downward.

[0043] Also, in the present embodiment, the minimum thickness t4 of the upper part 28 of the groove is configured to be smaller than the thickness t3 of the minimum diameter part 26. The ratio (t1 / t4) of t1 to the minimum thickness t4 of the upper part 28 of the groove is preferably 1.2 or more, and more preferably 1.3 or more. When t1 / t4 is 1.4 or more, when the groove insertion part 23 is compressed, the groove insertion part 23 collapses so that the radially outer region of the upper part 28 of the groove falls downward. As a result, the stress applied to the lower part 27 of the groove decreases, and it is possible to further suppress the lower part 27 of the groove from falling downward. Also, the ratio (t4 / t3) of t4 to t3 is, for example, 0.95 or less, and may be 0.90 or less. Note that the minimum thickness t4 of the upper part 28 of the groove and the thickness t3 of the minimum diameter part 26 may be the same.

[0044] Next, while referring to FIG. 3, the processing steps of the outer can 20 in the manufacturing method of the cylindrical battery 10 will be described. FIG. 3 is a diagram schematically showing the processing steps of the outer can 20 of the present embodiment. In FIG. 3, among the constituent members of the cylindrical battery 10, illustration of constituent members other than the electrode body 14, the outer can 20, the sealing body 30, and the gasket 40 is omitted.

[0045] As shown in FIG. 3(a), the side wall portion 22 of the outer can 20 has different thicknesses in the axial direction in the state before processing. Specifically, the thickness of the region where the groove bottom portion 27 is finally formed is larger than the thickness of the body portion 24. Also, in the vicinity of the region where the minimum diameter portion 26 is finally formed, the thickness gradually decreases upward.

[0046] Then, as shown in FIG. 3(b), after accommodating the electrode body 14 and the like inside the outer can 20, a part of the side wall portion 22 is recessed inward in the radial direction to form an annular groove insertion portion 23. The groove insertion portion 23 can be formed, for example, by spinning. In the example shown in FIG. 3(b), the groove bottom portion 27 extends along a direction inclined upward with respect to the radial direction toward the minimum diameter portion 26, and the groove upper portion 28 extends along the radial direction. Note that the shapes of the groove bottom portion 27 and the groove upper portion 28 during the formation of the groove insertion portion 23 are not limited to this.

[0047] Next, as shown in FIG. 3(c), the sealing body 30 is disposed via the gasket 40 above the groove upper portion 28, and the open end 20X of the outer can 20 is caulked. Thereby, the sealing body 30 is fixed to the opening portion 25 via the gasket 40.

[0048] Finally, as shown in FIG. 3(d), the cylindrical battery 10 is pressed axially from above to compress the groove insertion portion 23. At this time, as described above, since the maximum thickness t1 of the groove bottom portion 27 is larger than the thickness t2 of the body portion 24 and the thickness t3 of the minimum diameter portion 26, it becomes difficult for the groove bottom portion 27 to fall downward.

[0049] Next, while referring to FIGS. 4 and 5, a modified example of the outer can 20 of the present embodiment will be described. FIGS. 4 and 5 are axial cross-sectional views of the modified outer can 20 and are corresponding views to FIG. 2.

[0050] The outer can 20 shown in Figures 4 and 5 differs from the outer can 20 shown in Figure 2 in that the thickness of the body portion 24 differs in the axial direction. Specifically, the outer can 20 shown in Figures 4 and 5 has a thick-walled portion 24A in which the thickness of the body portion 24 increases as it approaches the grooved portion 23 side.

[0051] In the example shown in Figure 4, the thickened portion 24A is formed by the inner surface of the body portion 24 bulging inward, while in the example shown in Figure 5, the thickened portion 24A is formed by the outer surface of the body portion 24 bulging outward. When the thickened portion 24A is formed by the inner surface of the body portion 24 protruding inward, an increase in battery size can be suppressed.

[0052] By providing the thickened portion 24A, the rigidity near the boundary between the lower groove portion 27 and the body portion 24 can be further improved. As a result, when the grooved portion 23 is compressed, the downward tilting of the lower groove portion 27 can be further suppressed.

[0053] The ratio of the maximum thickness t5 of the thickened portion 24A to the thickness t2 of the body portion 24 at the axial center of the body portion 24 (t5 / t2) is preferably 1.2 or more, and more preferably 1.3 or more. By setting t5 / t2 to 1.2 or more, the rigidity near the boundary between the groove lower portion 27 and the body portion 24 can be further improved, and the downward tilting of the groove lower portion 27 can be further suppressed.

[0054] Furthermore, as shown in Figure 4, when the inner surface of the body portion 24 bulges inward to form a thickened portion 24A, it is preferable that the thickened portion 24A and the electrode body 14 do not overlap radially, from the viewpoint of securing the internal volume of the battery.

[0055] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0056] <Example 1> [Fabrication of the positive electrode] LiNi as the positive electrode active material ０．８ Co ０．１５ Al ０．０５ O ２A positive electrode slurry was prepared by mixing 100 parts by mass of positive electrode active material, 1.7 parts by mass of polyvinylidene fluoride, and 2.5 parts by mass of acetylene black, and using N-methyl-2-pyrrolidone as a dispersion medium. The prepared positive electrode slurry was then applied to both sides of a positive electrode core made of aluminum foil, excluding the connection portion of the positive electrode lead. The coating was dried, and then compressed to a predetermined thickness to obtain the positive electrode. This positive electrode was cut to a predetermined size, and the positive electrode lead was connected to the exposed portion of the core by ultrasonic welding.

[0057] [Preparation of the negative electrode] Graphite was used as the negative electrode active material. 100 parts by mass of the negative electrode active material, 0.6 parts by mass of polyvinylidene fluoride, and 1 part by mass of carboxymethylcellulose were mixed, and water was used as the dispersion medium to obtain a negative electrode mixture slurry. The prepared negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, excluding the connection parts of the negative electrode leads. The coating was dried, and then compressed to a predetermined thickness to obtain the negative electrode. This negative electrode was cut to predetermined dimensions, and the negative electrode leads were connected to the exposed parts of the core by ultrasonic welding.

[0058] [Preparation of non-aqueous electrolyte] A mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) is mixed with lithium hexafluorophosphate (LiPF). ６ A non-aqueous electrolyte was prepared by dissolving the solution to a concentration of 1.0 mol / L.

[0059] [Creation of Cylindrical Battery] A bottomed cylindrical container made of carbon steel with side walls of different thicknesses in the axial direction was used as the outer casing. After the electrode body, in which the positive and negative electrodes were wound with a separator in between, was placed inside the outer casing, a groove was formed by spinning at a height of 4 mm from the opening end of the outer casing. Then, after pouring in a non-aqueous electrolyte, a sealing body was inserted into the outer casing, and a bending process was performed starting at a height of 2 mm from the opening end of the outer casing, and the sealing body was crimped and fixed to the opening of the outer casing.

[0060] Subsequently, the battery was pressed from the top along the axial direction to compress the grooved portion. Observation of the cross-section of the compressed cylindrical battery revealed that the maximum thickness t1 at the bottom of the groove was 0.35 mm, the thickness t2 of the body at the axial center of the body was 0.25 mm, the thickness t3 at the smallest diameter was 0.28 mm, and the minimum thickness t4 at the top of the groove was 0.25 mm. Furthermore, the lower part of the groove in the outer casing of Example 1 after compression extended radially and did not collapse downwards.

[0061] <Example 2> A cylindrical battery was created in the same manner as in Example 1, except that a bottomed cylindrical container was used as the outer casing, in which the thickness of the side walls differed in the axial direction and a thickened section was provided in the body where the thickness increased as it approached the grooved section. The cross-section was then observed. The thickened section was formed by bulging the outer surface of the body outward, as shown in Figure 5.

[0062] Observation of the cross-section of the compressed cylindrical battery revealed that the maximum thickness t1 at the bottom of the groove was 0.35 mm, the thickness t2 of the body at the axial center of the body was 0.25 mm, the thickness t3 at the smallest diameter was 0.28 mm, the minimum thickness t4 at the top of the groove was 0.25 mm, and the maximum thickness t5 at the thickest part was 0.35 mm. Furthermore, the lower part of the groove in the outer can of Example 2 after compression of the grooved portion extended radially and did not collapse downwards.

[0063] <Comparative Example 1> A cylindrical battery was prepared in the same manner as in Example 1, except that a bottomed cylindrical container with a uniform thickness of the side walls along the axial direction was used as the outer casing, and the cross-section was observed.

[0064] Upon observing the cross-section of the compressed cylindrical battery, t1 to t4 were all found to be 0.25 mm. Furthermore, the lower part of the groove in the outer can of Comparative Example 1, after the grooved portion was compressed, extended along a direction that was inclined downward in the radial direction toward the smallest diameter side, and was bent downward.

[0065] Based on the above, it can be said that by making the maximum thickness t1 of the lower part of the groove greater than the thickness t2 of the body portion 24 and the thickness t3 of the smallest diameter portion 26, it is possible to suppress the entire grooved portion from tilting towards the electrode body. As a result, the electrode body is suppressed from being compressed by the grooved portion, and a cylindrical battery with excellent reliability can be provided.

[0066] This disclosure is further illustrated by the following embodiments. Configuration 1: A cylindrical battery comprising a bottomed cylindrical outer casing having a bottom and a side wall portion extending axially from the outer peripheral edge of the bottom, an electrode body housed in the outer casing, and a sealing body that closes the opening of the outer casing, wherein the side wall portion includes a grooved portion recessed radially inward and a body portion which is the other axial side of the grooved portion, the grooved portion includes a smallest diameter portion which is most recessed radially inward and a groove lower portion connecting the smallest diameter portion and the body portion, and in an axial cross-sectional view of the outer casing, the maximum thickness t1 of the groove lower portion is greater than the thickness t2 of the body portion at the axial center of the body portion and the thickness t3 of the smallest diameter portion. Configuration 2: The cylindrical battery according to Configuration 1, wherein the ratio of t1 to t2 (t1 / t2) is 1.2 or more. Configuration 3: A cylindrical battery according to Configuration 1 or 2, wherein the ratio of t1 to t3 (t1 / t3) is 1.1 or greater. Configuration 4: A cylindrical battery according to any one of Configurations 1 to 3, wherein the lower part of the groove has a thin-walled portion whose thickness decreases as it approaches the smallest diameter portion. Configuration 5: A cylindrical battery according to any one of Configurations 1 to 4, wherein the side wall portion includes an opening which is a part on one side in the axial direction from the grooved portion, the grooved portion includes the upper part of the groove connecting the smallest diameter portion and the opening, and the ratio of t1 to the minimum thickness t4 of the upper part of the groove (t1 / t4) is 1.2 or greater. Configuration 6: A cylindrical battery according to any one of Configurations 1 to 5, wherein the body portion has a thick-walled portion whose thickness increases as it approaches the grooved portion side. Configuration 7: A cylindrical battery according to Configuration 6, wherein the ratio of the maximum thickness t5 of the thick-walled portion to t2 (t5 / t2) is 1.2 or greater. Configuration 8: A cylindrical battery according to any one of Configurations 1 to 7, wherein the maximum thickness t1 of the lower part of the groove is substantially uniform around the entire circumference.

[0067] 10 Cylindrical battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16, 17 Insulating plate, 18 Positive electrode lead, 19 Negative electrode lead, 20 Outer casing, 20X Open end, 21 Bottom, 22 Side wall, 23 Grooved section, 24 Body, 24A Thick-walled section, 25 Opening, 26 Smallest diameter section, 27 Lower groove, 28 Upper groove, 30 Sealing body, 31 Center section, 32 Outer circumference, 33 Thin-walled section, 40 Gasket

Claims

1. A cylindrical battery comprising: a bottomed cylindrical outer casing having a bottom and a side wall portion extending axially from the outer peripheral edge of the bottom; an electrode body housed in the outer casing; and a sealing body that closes the opening of the outer casing, wherein the side wall portion includes a grooved portion recessed radially inward and a body portion which is the other axial side of the grooved portion, the grooved portion includes a smallest diameter portion which is most recessed radially inward and a groove lower portion connecting the smallest diameter portion and the body portion, and in an axial cross-sectional view of the outer casing, the maximum thickness t1 of the groove lower portion is greater than the thickness t2 of the body portion at the axial center of the body portion and the thickness t3 of the smallest diameter portion.

2. The cylindrical battery according to claim 1, wherein the ratio of t1 to t2 (t1 / t2) is 1.2 or more.

3. The cylindrical battery according to claim 1, wherein the ratio of t1 to t3 (t1 / t3) is 1.1 or greater.

4. The cylindrical battery according to claim 1, wherein the lower part of the groove has a thin-walled portion in which the thickness decreases as it approaches the smallest diameter portion.

5. The cylindrical battery according to claim 1, wherein the side wall portion includes an opening which is a portion on one side in the axial direction from the grooved portion, the grooved portion includes the upper part of the groove connecting the smallest diameter portion and the opening, and the ratio of t1 to the minimum thickness t4 of the upper part of the groove (t1 / t4) is 1.2 or more.

6. The cylindrical battery according to claim 1, wherein the body portion has a thickened portion that increases in thickness as it approaches the grooved portion.

7. The cylindrical battery according to claim 6, wherein the ratio of the maximum thickness t5 of the thickened portion to t2 (t5 / t2) is 1.2 or more.

8. The cylindrical battery according to claim 1, wherein the maximum thickness t1 of the lower part of the groove is substantially uniform around the entire circumference.

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