Cylindrical secondary battery

Abstract

This battery (10) comprises: an electrode body in which a long positive electrode (11) and a long negative electrode are wound with a separator therebetween; an outer can that houses the electrode body; and a positive electrode lead (20) that is joined to a positive electrode core exposed part (35) in which a positive electrode core (30) is exposed in the positive electrode (11). The positive electrode core (30) is provided with a through-hole (70) that includes a facing part (70a) that faces a tip part (20a) of the positive electrode lead (20) in the thickness direction thereof.

Description

Cylindrical secondary battery

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

[0002] A conventional cylindrical secondary battery is described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a long positive electrode having a positive electrode core and a positive electrode mixture layer and a long negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween; a bottomed cylindrical outer can housing the electrode assembly; a seal body crimped to the opening of the outer can via a gasket; a positive electrode lead electrically connecting the positive electrode to the seal body; and a negative electrode lead electrically connecting the negative electrode to the outer can. One end of the positive electrode lead is joined to a positive electrode core exposed portion of the positive electrode where the positive electrode core is exposed, and the other end of the positive electrode lead is joined to the inner surface of the seal body. One end of the negative electrode lead is joined to a negative electrode core exposed portion of the negative electrode where the negative electrode core is exposed, and the other end of the negative electrode lead is joined to the inner bottom surface of the outer can.

[0003] JP 2013-016328 A

[0004] In cylindrical secondary batteries, the negative electrode expands radially and longitudinally during charging. Furthermore, when the negative electrode expands, the positive electrode receives forces from the negative electrode in the radial and longitudinal directions, causing it to stretch in the longitudinal direction. Against this background, the present inventors discovered that after multiple cycles of a cylindrical secondary battery, a break in the positive electrode core may occur around a corner at one end of a positive electrode lead joined to the positive electrode. Breaks in the positive electrode core result in a decrease in current collection performance on the positive electrode side. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that is less likely to break in the positive electrode core and that is more likely to maintain good current collection performance over a long period of time.

[0005] In order to solve the above problems, the cylindrical secondary battery according to the present disclosure includes an electrode body in which a long positive electrode having a positive electrode core and a positive electrode mixture layer and a long negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween, an outer can that houses the electrode body, and a positive electrode lead that is joined to a positive electrode core exposed portion at which the positive electrode core is exposed in the positive electrode, and the positive electrode core is provided with a through hole that includes an opposing portion that faces a tip portion of the positive electrode lead in the thickness direction.

[0006] The tip portion may be defined as a portion of the positive electrode lead whose length in the width direction of the positive electrode from the tip of the positive electrode lead is within 1.5 mm.

[0007] According to the cylindrical secondary battery according to the present disclosure, breaks are unlikely to occur in the positive electrode substrate, and good current collection performance can be easily maintained over a long period of time.

[0008] 4 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure; FIG. 5 is a perspective view showing a portion of an electrode body and a positive electrode lead; FIG. 6 is a plan view showing the wound inner surface of a positive electrode; FIG. 7 is an enlarged plan view of the peripheral portion of one positive electrode substrate exposed portion; FIG. 8 is an enlarged plan view in which the first and second insulating tapes are omitted from FIG. 4; FIG. 9 is an enlarged plan view corresponding to FIG. 5 of a cylindrical secondary battery of Comparative Example 1; FIG. 10 is an enlarged plan view corresponding to FIG. 5 of a cylindrical secondary battery of Comparative Example 2; FIG. 11 is an enlarged plan view corresponding to FIG. 5 of a cylindrical secondary battery of Comparative Example 4; FIG. 12 is an enlarged plan view corresponding to FIG. 4 of a modified cylindrical secondary battery;

[0009] Hereinafter, an embodiment of a cylindrical battery according to the present disclosure will be described with reference to the drawings. Note that the cylindrical secondary battery according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a nonaqueous electrolyte. Hereinafter, as an embodiment of cylindrical secondary batteries 10 and 110, a cylindrical lithium-ion secondary battery using a nonaqueous electrolyte will be exemplified, but the cylindrical secondary battery according to the present disclosure is not limited thereto.

[0010] When multiple embodiments and variations are included below, it is assumed from the beginning that new embodiments can be constructed by appropriately combining their characteristic features. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations will be omitted. The drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component do not necessarily match between different drawings. In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical secondary battery 10 is referred to as "upper," and the bottom 68 side of the outer can 16 in the axial direction is referred to as "lower."

[0011] The tip portions 20a, 120a of the positive electrode leads 20, 120 described below may be defined as portions of the positive electrode leads 20, 120 whose length in the positive electrode width direction from the tip of the positive electrode lead is within 1.5 mm. Among the components described below, components that are not recited in the independent claims representing the superordinate concept are optional components and are not essential components. Furthermore, the present disclosure is not limited to the following embodiments and their variations, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0012] Fig. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment of the present disclosure. As shown in Fig. 1, the cylindrical secondary battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17 that is crimped and fixed to the opening of the outer can 16 via a gasket 28.

[0013] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes 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. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0014] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0015] Fig. 2 is a perspective view showing a portion of the electrode body 14 and the positive electrode lead 20. As shown in Fig. 2, the electrode body 14 has a long positive electrode 11, a long negative electrode 12, and two long separators 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. One or more positive electrode leads 20 are joined to the positive electrode 11, and preferably six or more positive electrode leads 20 are joined, and in this embodiment, eight positive electrode leads 20 are joined to the positive electrode 11 at intervals from one another in the longitudinal direction of the positive electrode.

[0016] The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium precipitation. The negative electrode 12 is formed to be longer than the positive electrode 11 in the winding direction and axial direction. Two separators 13 are formed to be slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separator 13 protrudes upward beyond the positive electrode 11 and the negative electrode 12, and the negative electrode 12 protrudes downward beyond the positive electrode 11 and the separator 13.

[0017] The negative electrode 12 has a negative electrode substrate exposed portion 41, where the negative electrode mixture layer 42 is not provided on the negative electrode substrate 40, at the axial lower end from the inner winding end to the outer winding end in the negative electrode longitudinal direction of the negative electrode 12. Therefore, the axial lower end of the electrode body 14 is constituted by the negative electrode substrate exposed portion 41. The negative electrode 12 may constitute the inner winding end of the electrode body 14. However, typically, the separator 13 extends beyond the inner winding end of the negative electrode 12, and the inner winding end of the separator 13 becomes the inner winding end of the electrode body 14.

[0018] The positive electrode 11 has a positive electrode core 30 (see FIG. 3 ) and positive electrode mixture layers 32 (see FIG. 3 ) formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil, 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 32 contains a positive electrode active material, a conductive agent, and a binder. 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 30, drying the coating, and then compressing it to form the positive electrode mixture layers 32 on both sides of the positive electrode core 30.

[0019] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0020] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black such as acetylene black and ketjen black, and carbon materials such as graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, and polyethylene oxide (PEO). To increase capacity, the length of the positive electrode 11 in the longitudinal direction of the positive electrode is preferably 3000 mm or more.

[0021] 3 is a plan view showing the inner winding surface 15 of the positive electrode 11, and is a plan view illustrating the position and structure of the positive electrode substrate exposed portion 35 to which the positive electrode lead 20 is joined in the positive electrode 11. The hatched area in FIG. 3 is the area where the positive electrode mixture layer 32 is disposed. In this embodiment, a case will be described in which the positive electrode lead 20 is joined to the inner winding surface 15 of the positive electrode 11, but the positive electrode lead may also be joined to the outer winding surface of the positive electrode.

[0022] As shown in FIG. 3 , the positive electrode 11 has one or more positive electrode core exposed portions 35 where the positive electrode core 30 is exposed. In this embodiment, the positive electrode 11 has eight positive electrode core exposed portions 35 arranged at intervals in the positive electrode width direction. Positive electrode leads 20 are joined to the positive electrode core exposed portions 35 one by one by ultrasonic welding or the like. The positive electrode mixture layer 32 has a core adjacent portion 32 a arranged adjacent to the positive electrode core exposed portion 35 in the positive electrode width direction. Because the positive electrode mixture layer 32 has the core adjacent portion 32 a, the arrangement area of ​​the positive electrode mixture layer 32 is increased, resulting in increased capacity. Effectively shortening the positive electrode side current collection path greatly reduces electrical resistance, so it is preferable that the center positions of the eight positive electrode leads 20 in the positive electrode longitudinal direction be arranged at approximately equal intervals in the positive electrode longitudinal direction.

[0023] As shown in FIG. 2 , the negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. In FIG. 2 , the positive electrode mixture layer 32 of the positive electrode 11 is indicated by diagonal hatching, and the negative electrode mixture layer 42 of the negative electrode 12 is indicated by diagonal hatching. The negative electrode core 40 can be made of a metal foil, 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 layer. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40.

[0024] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. To facilitate increased capacity, the negative electrode active material of the negative electrode mixture layer 42 preferably contains a silicon (Si) material containing silicon particles, and the mass ratio of Si element in the negative electrode mixture layer 42 is preferably 5% by mass or more. Furthermore, it is preferred that 3.0% by mass or more of the negative electrode mixture layer be composed of silicon oxide. The negative electrode active material may also include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0025] As in the case of the positive electrode 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer 42, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. The negative electrode mixture layer 42 may contain, in addition to SBR or the like, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0026] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0027] As shown in Figure 1, the battery 10 includes an annular insulating plate 18 on the upper side of the electrode body 14. A positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17. The sealing body 17 includes an upper current collector plate 50 and a terminal cap 27. The upper current collector plate 50 is a metal annular plate member and has a through-hole 50a in its radial center.

[0028] The terminal cap 27 is a metal plate-like member without a through hole and is located axially above the sealing body 17. The axially upper end face of the terminal cap 27 is exposed to the outside except for the outer edge, and this exposed portion forms the positive electrode terminal. The sealing body 17 further has a metal plate 51. The metal plate 51 is a metal annular member with a through hole.

[0029] Each positive electrode lead 20 is bent from the positive electrode 11 through the through hole 50a of the upper current collector plate 50 so as to fit along the upper surface of the upper current collector plate 50. The tip of each positive electrode lead 20 is sandwiched between the upper surface of the upper current collector plate 50 and the lower surface of the metal plate 51. Each positive electrode lead 20 is bonded to the upper surface of the upper current collector plate 50. The upper current collector plate 50 and the metal plate 51 are also bonded, and each positive electrode lead 20 and the metal plate 51 are also bonded. These bonds can be achieved, for example, by laser welding the tip of each positive electrode lead 20 sandwiched between the upper current collector plate 50 and the metal plate 51 by irradiating the metal plate 51 with a laser beam in the axial direction from above. By laser welding the tip of the positive electrode lead 20 sandwiched between the upper current collector plate 50 and the metal plate 51, the positive electrode lead 20 can be reliably and easily welded and bonded to the upper current collector plate 50.

[0030] The sealing body 17 has a laminated portion 60 on its outer periphery, in which the terminal cap 27 and the upper current collector plate 50 are laminated. By irradiating the laminated portion 60 with a laser beam from above, the terminal cap 27 and the upper current collector plate 50 are laser-welded and electrically connected. The annular upper surface of the upper current collector plate 50 has an annular recess 65 radially inward from the laminated portion 60. Because the upper surface of the upper current collector plate 50 has the recess 65 recessed downward, a space is provided between the terminal cap 27 and the recess 65 of the upper current collector plate 50. Each positive electrode lead 20 is joined to the upper current collector plate 50 within the recess 65. The upper current collector plate 50 does not need to be joined to the metal plate 51, and the positive electrode lead 20 does not need to be joined to the metal plate 51. The battery does not need to have a metal plate 51. The positive electrode lead 20 may also be joined to the lower surface of the upper current collector plate 50.

[0031] The battery 10 includes a metal lower current collector plate 52 on the axially lower side of the electrode assembly 14. Referring to FIGS. 1 and 2 , the electrode assembly 14 is pressed against the upper surface of the lower current collector plate 52 so as to tilt the elongated negative electrode substrate exposed portion 41 radially inward. Laser light is irradiated from the lower surface of the lower current collector plate 52, thereby laser-welding and joining the negative electrode substrate exposed portion 41 over a wide area to the upper surface of the lower current collector plate 52. Laser light is also irradiated from the lower side of the outer can 16, thereby laser-welding the bottom 68 of the outer can 16 to the lower current collector plate 52. This electrically connects the negative electrode 12 of the electrode assembly 14 to the outer can 16 via the lower current collector plate 52. By joining the negative electrode substrate exposed portion 41 over a wide area to the upper surface of the lower current collector plate 52, it is possible to prevent current from flowing long distances along the longitudinal direction of the elongated negative electrode 12, thereby reducing the electrical resistance of the battery 10.

[0032] The case where the negative electrode substrate exposed portion 41 is electrically connected to the outer can 16 via the lower current collector plate 52 has been described. However, the negative electrode may have a first negative electrode substrate exposed portion where the negative electrode substrate is exposed at the inner end of the winding in the longitudinal direction of the negative electrode, and a second negative electrode substrate exposed portion where the negative electrode substrate is exposed at the outer end of the winding in the longitudinal direction of the negative electrode. Furthermore, the second negative electrode substrate exposed portion may have an outermost surface portion included in the outermost surface of the electrode assembly. Furthermore, one end of the negative electrode lead may be joined to the first negative electrode substrate exposed portion, and the other end of the negative electrode lead may be joined to the inner bottom surface of the outer can. Furthermore, the outermost surface portion may contact the inner circumferential surface of the outer can.

[0033] Alternatively, two negative electrode leads may be joined to the electrode body, with one end of one negative electrode lead electrically connected to the inner end of the negative electrode core in the negative electrode longitudinal direction, and one end of the other negative electrode lead electrically connected to the outer end of the negative electrode core in the negative electrode longitudinal direction. The other end of each negative electrode lead may be electrically connected to the bottom of the outer can. Alternatively, the negative electrode and the outer can may be electrically connected via a single negative electrode lead.

[0034] The outer can 16 has a cylindrical portion 39 and a bottom 68. The cylindrical portion 39 includes an annular grooved portion 22 and an annular shoulder portion 29. The grooved portion 22 is formed by spinning a portion of the cylindrical portion 39 to recess it radially inward around the entire circumferential direction. The sealing body 17 is placed on the grooved portion 22 and is fixed to the opening of the outer can 16 by crimping via a resin gasket 28. The shoulder portion 29 is formed when the upper end of the cylindrical portion 39 is bent radially inward and crimped to the outer edge of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 39.

[0035] The space between the outer can 16 and the sealing body 17 is sealed with an annular gasket 28, thereby sealing the internal space of the battery 10. The gasket 28 is sandwiched between the outer can 16 and the sealing body 17 and insulates the sealing body 17 from the outer can 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer can 16 from the sealing body 17. The terminal cap 27 electrically connected to the positive electrode lead 20 serves as a positive electrode terminal, and the outer can 16 electrically connected to the negative electrode core exposed portion 41 via the lower current collector plate 52 serves as a negative electrode terminal.

[0036] The battery 10 has a thin, easily breakable portion 68a on the bottom 68 of the exterior can 16. The easily breakable portion 68a is formed, for example, by stamping a circle or a C-shape on the underside of the bottom 68. If the bottom 68 has the easily breakable portion 68a, when the battery 10 abnormally heats up, the easily breakable portion 68a breaks, allowing high-temperature gas inside the battery 10 to be discharged to the outside, thereby increasing the safety of the battery 10. The thin, easily breakable portion may also be provided on the terminal cap.

[0037] In the above description, the sealing body 17 does not have a rupture plate, and an easily breakable portion 68a is provided on the bottom 68 of the outer can. However, the bottom of the outer can does not have to have an easily breakable portion. The sealing body may have two rupture plates (a lower valve body and an upper valve body) and a convex terminal cap that covers the rupture plate. Alternatively, the sealing body may be composed of only a rupture plate, or may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are stacked in this order from the electrode body side.

[0038] FIG. 4 is an enlarged plan view of the periphery of one positive electrode core exposed portion 35. FIG. 5 is an enlarged plan view of FIG. 4 , with the first and second insulating tapes 53, 54 omitted. In FIGS. 4 and 5 , the dotted hatched area indicates a joint portion 75 of the positive electrode lead 20 that is joined to the positive electrode core exposed portion 35 by ultrasonic welding or the like. The dotted hatched area indicates the tip portion 20a of the positive electrode lead 20. As shown in FIG. 5 , a through hole 70 is provided in the positive electrode core 30 at a location that overlaps the positive electrode core exposed portion 35 in the positive electrode thickness direction. In the positive electrode width direction, the through hole 70 is located closer to the tip of the positive electrode lead 20 than the joint portion 75 and is spaced apart from the joint portion 75. The through-hole 70 includes a facing portion (facing region) 70 a facing the tip portion 20 a of the positive electrode lead 20 in the thickness direction of the tip portion 20 a (thickness direction of the positive electrode core 30 ).

[0039] When viewed from the thickness direction of the positive electrode core 30, the tip portion 20a fits into the through hole 70. When viewed from the thickness direction of the positive electrode core 30, the tip portion 20a is located inside the annular edge 71 of the through hole 70 and is spaced apart from the annular edge 71. In this embodiment, the through hole 70 has a substantially rectangular opening. The edge of the through hole 70 includes a pair of first edge portions 72a, 72b extending substantially in the positive electrode width direction and a pair of second edge portions 73a, 73b extending substantially in the positive electrode longitudinal direction. One first edge portion 72a is located on a first side in the positive electrode longitudinal direction relative to the tip portion 20a, and the other first edge portion 72b is located on a second side in the positive electrode longitudinal direction relative to the tip portion 20a. One second edge portion 73a is located at a distance from the positive electrode lead 20 in the positive electrode width direction.

[0040] As shown in Fig. 4, the battery 10 includes a first insulating tape 53 attached to the inner winding surface 15 of the positive electrode 11 and a second insulating tape 54 attached to the outer winding surface (not shown) of the positive electrode 11. To prevent short-circuiting between the positive electrode 11 and the negative electrode 12, the first insulating tape 53 covers at least a portion of the overlapping portion of the positive electrode lead 20 that overlaps the positive electrode core exposed portion 35 in the positive electrode thickness direction. The first insulating tape 53 is arranged so as to close the opening of the through hole 70 on the first side in the positive electrode thickness direction. It is preferable that the first insulating tape 53 cover the entire positive electrode core exposed portion 35.

[0041] The second insulating tape 54 has a facing portion that faces the first insulating tape 53 in the positive electrode thickness direction. The second insulating tape 54 is arranged so as to close the opening of the through hole 70 on the second side in the positive electrode thickness direction. Both sides of the through hole 70 are closed with the first insulating tape 53 and the second insulating tape 54, and both sides in the thickness direction of the tip portion 20a of the positive electrode lead 20 are covered with the first insulating tape 53 and the second insulating tape 54. Therefore, no short circuit will occur due to the provision of the through hole 70 in the positive electrode core 30.

[0042] The first insulating tape 53 and the second insulating tape 54 preferably have protruding portions 53a, 54a that protrude from the positive electrode 11 in the positive electrode width direction. The protruding portions 53a, 54a preferably have a bonding portion where they are bonded to each other. In order to prevent a short circuit between the positive electrode 11 and the negative electrode 12, an insulating tape 55 is preferably attached around the entire periphery of the base portion of the extension portion of the positive electrode lead 20 that extends from the positive electrode 11. These insulating tapes 53, 54, 55 are made of an insulating material; for example, the base material is made of a polyimide film and the adhesive material is made of silicone.

[0043] 4 and 5, the case where the through hole 70 has a substantially rectangular opening has been described, but the through hole may have an opening of any shape. Even if the through hole has an opening that is not substantially rectangular, the tip end of the positive electrode lead is arranged to fit into the through hole when viewed from the thickness direction of the positive electrode core. Even if the through hole has an opening that is not substantially rectangular, the tip end of the positive electrode lead is preferably located inside the annular edge of the through hole when viewed from the thickness direction of the positive electrode core, and is preferably located at a distance from the annular edge.

[0044] Next, we will explain the effects obtained by providing the positive electrode core 30 with a through-hole 70 including an opposing portion 70a that faces the tip portion 20a of the positive electrode lead 20 in the thickness direction. In a cylindrical secondary battery, the negative electrode expands in the radial direction of the electrode body and in the longitudinal direction of the negative electrode during charging. Furthermore, when the negative electrode expands, the positive electrode receives forces from the negative electrode in the radial direction and in the longitudinal direction of the positive electrode, causing it to elongate in the longitudinal direction of the positive electrode. The present inventors have discovered that in conventional cylindrical secondary batteries, after multiple cycles, there is a risk of the positive electrode core breaking around the corner of the positive electrode lead joined to the positive electrode.

[0045] When a cut occurs in the positive electrode core, the current collection performance of the positive electrode side deteriorates. It is presumed that this cut in the positive electrode core is caused by a large strain (stress) occurring around a corner of the exposed portion of the positive electrode core that is susceptible to excessive force from the sharp corner of the positive electrode lead, due to additional force being applied in the longitudinal direction of the positive electrode.

[0046] In view of this background, according to the battery 10 of the present disclosure, the positive electrode core 30 does not have an opposing portion that faces the tip portion 20a of the positive electrode lead 20 in the thickness direction of the tip portion 20a. In other words, the positive electrode core 30 does not have an opposing portion that is likely to receive excessive force from the sharp corners of the positive electrode lead 20 and cause large distortion. Therefore, distortion that occurs in the positive electrode 11 due to expansion and contraction of the negative electrode 12 during charge and discharge can be alleviated, thereby suppressing breakage of the positive electrode core.

[0047] When 3.0 mass % or more of the negative electrode mixture layer 42 is composed of silicon oxide, the negative electrode 12 tends to stretch in the negative electrode longitudinal direction during charging, and concomitantly, the positive electrode 11 also tends to stretch in the positive electrode longitudinal direction. Therefore, the effect of suppressing damage to the positive electrode core 30 that can be obtained by adopting the configuration of the battery 10 of the present disclosure tends to be significant.

[0048] Furthermore, if the positive electrode mixture layer 32 includes a substrate adjacent portion 32a adjacent to the positive electrode substrate exposed portion 35 in the positive electrode width direction, the positive electrode substrate exposed portion 35 is likely to extend in the positive electrode longitudinal direction due to expansion of the portion of the negative electrode mixture layer facing the substrate adjacent portion 32a during charging. Therefore, in this case as well, the effect of suppressing damage to the positive electrode substrate 30 that can be obtained by adopting the configuration of the battery 10 of the present disclosure is likely to be significant.

[0049] Furthermore, in large-diameter batteries having a total length in the positive electrode longitudinal direction of 3000 mm or more, large-diameter batteries having a distance of 5 mm or more between the inner end of the negative electrode in the electrode assembly and the central axis of the outer can, and large-diameter batteries having six or more positive electrode substrate exposed portions (six or more positive electrode leads) joined to the positive electrode at intervals in the positive electrode longitudinal direction, the negative electrode tends to stretch in the negative electrode longitudinal direction during charging, and the positive electrode also tends to stretch in the positive electrode longitudinal direction. Therefore, even in these batteries, the effect of suppressing damage to the positive electrode substrate that can be obtained by adopting the battery configuration of the present disclosure is likely to be significant.

[0050] 1 to 5 was fabricated. The opening shape of the through-hole 70 was rectangular. The through-hole 70 was formed by laser cutting a part of the positive electrode substrate 30.

[0051] <Comparative Example 1> As shown in Figure 6, that is, an enlarged plan view of battery 210 of Comparative Example 1 corresponding to Figure 5, battery 210 was produced, which differs from battery 10 of Example 1 in that a positive electrode core 230 without through-holes 70 was used.

[0052] Comparative Example 2 As shown in FIG. 7 , an enlarged plan view of a battery 310 of Comparative Example 2 corresponding to FIG. 5 , a battery 310 was fabricated that differed from the battery 10 of Example 1 in that it used a positive electrode core 330 on which a linear cut portion (notch) 370 was formed. The linear cut portion 370 was formed by laser cutting a portion of the positive electrode core 330. The linear cut portion 370 had an overlapping portion 370a that substantially overlapped the tip surface of the positive electrode lead 20 in the thickness direction of the positive electrode 311. The length of the linear cut portion 370 was made longer than the width of the positive electrode lead 20. The center of the linear cut portion 370 in the positive electrode longitudinal direction was aligned with the center of the positive electrode lead 20 in the positive electrode longitudinal direction.

[0053] Comparative Example 3 A battery (cylindrical secondary battery) was produced that differed from the battery 10 of Example 1 in that it used a positive electrode core on which a linear cut portion (notch) was formed. The linear cut portion was formed by laser cutting a portion of the positive electrode core. The linear cut portion was made to substantially overlap the tip surface of the positive electrode lead in the thickness direction of the positive electrode. The length of the linear cut portion was made shorter than the width of the positive electrode lead. The center of the linear cut portion in the positive electrode longitudinal direction was aligned with the center of the positive electrode lead in the positive electrode longitudinal direction.

[0054] Comparative Example 4 As shown in FIG. 8 , that is, an enlarged plan view of a battery 410 of Comparative Example 4 corresponding to FIG. 5 , a battery 410 was produced that differed from the battery of Example 1 in that it used a positive electrode core 430 having a through hole 470 formed therein, the length of the substantially rectangular opening in the positive electrode longitudinal direction being smaller than the width of the positive electrode lead 20. The through hole 470 was formed by laser cutting a portion of the positive electrode core 430. The center of the through hole 470 in the positive electrode longitudinal direction was aligned with the center of the positive electrode lead 20 in the positive electrode longitudinal direction.

[0055] (Inspection of Positive Electrode Core Breakage) Each of the fabricated batteries was charged at a constant current of 0.3 C in a 25°C environment until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.02 C. Subsequently, the battery was discharged at a constant current of 0.5 C until the voltage reached 2.5 V. This charge / discharge cycle was counted as one cycle, and the charge / discharge cycle was repeated 300 times. Thereafter, each battery was destroyed, and light was irradiated onto the positive electrode from the side opposite the positive electrode lead bonding side. If the positive electrode had broken, light would leak from the broken area. The presence or absence of light leakage was visually confirmed to inspect the positive electrode core for breakage.

[0056]

[0057] The test results are shown in Table 1. As shown in Table 1, breakage of the positive electrode core was confirmed in the battery 210 of Comparative Example 1, which used a positive electrode core 230 without a through-hole, the batteries 310 of Comparative Examples 2 and 3, which were provided with the linear cut portion 370, and the battery 410 of Comparative Example 4, which used a positive electrode core 430 that was provided with the through-hole 470 but had an opposing portion 430a (see FIG. 8 ) that opposed the corner 20b (see FIG. 8 ) on the tip side of the positive electrode lead 20.

[0058] In the batteries of Comparative Examples 1 and 4, the positive electrode core 230, 430 has an opposing portion 430a that faces the corner of the positive electrode lead 20, and it is presumed that the force that the opposing portion 430a received from the corner caused strain concentration (stress concentration) around the opposing portion 430a, resulting in the positive electrode core breaking.

[0059] Furthermore, in the batteries of Comparative Examples 2 and 3, the positive electrode core 330 was provided with a linear cut portion 370, and therefore it is presumed that the force that the positive electrode core 330 received from the corner portion could not be sufficiently reduced, resulting in the positive electrode core breaking.

[0060] In contrast, no positive electrode breakage was observed in the battery 10 of Example 1, in which the positive electrode core 30 was provided with a through-hole 70 including a facing portion 70a facing the tip end 20a of the positive electrode lead 20 in the thickness direction. This demonstrates that when the positive electrode core 30 is provided with a through-hole 70 including a facing portion 70a facing the tip end 20a of the positive electrode lead 20 in the thickness direction, the positive electrode core 30 is not subjected to excessive force from the sharp corners of the positive electrode lead 20, and it is possible to effectively reduce stress generated in the positive electrode core 30 due to expansion and contraction of the negative electrode 12 during charge and discharge.

[0061] The present disclosure is not limited to the above-described embodiment and its modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0062] For example, in the above embodiment, the positive electrode mixture layer 32 includes a substrate adjacent portion 32a adjacent in the positive electrode width direction to the positive electrode substrate exposed portion 35. However, as shown in Fig. 9, that is, an enlarged plan view of a modified battery 110 corresponding to Fig. 4, the positive electrode substrate exposed portion 135 to which the positive electrode lead 120 is joined may be present over the entire area in the positive electrode width direction, and the positive electrode mixture layer 132 may not have a substrate adjacent portion adjacent in the positive electrode width direction to the positive electrode substrate exposed portion 135.

[0063] Even in this case, the positive electrode lead 120 is joined to the positive electrode core exposed portion 135 at one or more joints 175. The joints 175 are areas indicated by dotted hatching, and in the example shown in Fig. 9, three joints 175 are present at intervals in the positive electrode width direction. A through hole 170 is provided in the positive electrode core 130 at a location that overlaps the positive electrode core exposed portion 135 in the positive electrode thickness direction. In the positive electrode width direction, the through hole 170 is located closer to the tip of the positive electrode lead 120 than the joint 175, and is located at an interval from the joint 175.

[0064] The through hole 170 includes a facing portion (facing region) 170a that faces the tip portion 120a of the positive electrode lead 120 in the thickness direction of the tip portion 120a (thickness direction of the positive electrode core 130). The tip portion 120a is the region indicated by dotted hatching. When viewed from the thickness direction of the positive electrode core 130, the tip portion 120a fits into the through hole 170. When viewed from the thickness direction of the positive electrode core 130, the tip portion 120a is located inside a ring-shaped edge 171 of the through hole 170 and is spaced apart from the ring-shaped edge 171. The battery 110 includes a first insulating tape 153 attached to the inner winding surface 115 of the positive electrode 111 and a second insulating tape 154 attached to the outer winding surface (not shown) of the positive electrode 111. The first insulating tape 153 is attached to the inner winding surface 115 so as to close the through-hole 170, and the second insulating tape 154 is attached to the outer winding surface so as to close the through-hole 170. In the battery 110 of the modified example, the stress generated in the positive electrode core due to the expansion and contraction of the negative electrode that accompanies charging and discharging can also be effectively reduced, and the positive electrode core can be effectively prevented from breaking.

[0065] The cylindrical secondary battery of the present disclosure may also have the following configurations: Configuration 1: A cylindrical secondary battery including: an electrode assembly in which a long positive electrode having a positive electrode core and a positive electrode mixture layer and a long negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween, an outer can that houses the electrode assembly, and a positive electrode lead that is joined to a positive electrode core exposed portion at which the positive electrode core is exposed in the positive electrode, wherein the positive electrode core is provided with a through hole that includes an opposing portion at a tip end of the positive electrode lead that faces the tip end in a thickness direction. Aspect 2: The cylindrical secondary battery according to Aspect 1, wherein the through hole has a substantially rectangular opening, and the annular edge of the through hole includes a pair of first edge portions extending substantially in the positive electrode width direction and a pair of second edge portions extending substantially in the positive electrode longitudinal direction, one of the first edge portions being located on a first side in the positive electrode longitudinal direction relative to the tip portion and the other of the first edge portions being located on a second side in the positive electrode longitudinal direction relative to the tip portion, and one of the second edge portions being located at a distance in the positive electrode width direction relative to the positive electrode lead. Aspect 3: The cylindrical secondary battery according to Aspect 1 or 2, comprising: a first insulating tape attached to an inner winding surface of the positive electrode so as to close the through hole; and a second insulating tape attached to an outer winding surface of the positive electrode so as to close the through hole. Aspect 4: The cylindrical secondary battery according to any one of Aspects 1 to 3, wherein the positive electrode mixture layer includes a substrate adjacent portion adjacent to the positive electrode substrate exposed portion in the positive electrode width direction. Configuration 5: The cylindrical secondary battery according to any one of Configurations 1 to 4, wherein 3.0 mass % or more of the negative electrode mixture layer is composed of silicon oxide.

[0066] 10,110 Battery, 11,111 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15,115 Inner surface of winding, 16 Outer can, 17 Sealing body, 18 Insulating plate, 20,120 Positive electrode lead, 20a,120a Tip portion, 20b Corner portion, 22 Grooved portion, 27 Terminal cap, 28 Gasket, 29 Shoulder portion, 30,130 Positive electrode core, 32,132 Positive electrode mixture layer, 32a Core adjacent portion, 35,135 Positive electrode core exposed portion, 39 Cylindrical portion, 40 Negative electrode core, 41 Negative electrode core exposed portion, 42 Negative electrode mixture layer, 50 Upper current collector plate, 51 Metal plate, 52 Lower current collecting plate; 53, 153 First insulating tape; 54, 154 Second insulating tape; 60 Lamination portion; 65 Recess; 68 Bottom; 68a Easy-to-break portion; 70, 170 Through hole; 70a, 170a Opposing portion; 71, 171 Annular edge; 72a, 72b First edge portion; 73a, 73b Second edge portion; 75, 175 Joint portion.

Claims

1. A cylindrical secondary battery comprising: an electrode assembly in which a long positive electrode having a positive electrode core and a positive electrode mixture layer, and a long negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween; an outer can that houses the electrode assembly; and a positive electrode lead joined to a positive electrode core exposed portion at which the positive electrode core is exposed in the positive electrode, wherein the positive electrode core is provided with a through hole including an opposing portion that faces the tip of the positive electrode lead in the thickness direction.

2. The cylindrical secondary battery according to claim 1, wherein the through hole has a substantially rectangular opening, the annular edge of the through hole includes a pair of first edge portions extending substantially in the width direction of the positive electrode and a pair of second edge portions extending substantially in the longitudinal direction of the positive electrode, one of the first edge portions being located on a first side in the longitudinal direction of the positive electrode relative to the tip portion and the other of the first edge portions being located on a second side in the longitudinal direction of the positive electrode relative to the tip portion, and one of the second edge portions being located at a distance from the positive electrode lead in the width direction of the positive electrode.

3. The cylindrical secondary battery according to claim 1 or 2, comprising: a first insulating tape attached to the inner surface of the wound positive electrode so as to close the through-hole; and a second insulating tape attached to the outer surface of the wound positive electrode so as to close the through-hole.

4. The cylindrical secondary battery according to claim 1 or 2, wherein the positive electrode mixture layer includes a substrate adjacent portion adjacent to the positive electrode substrate exposed portion in the positive electrode width direction.

5. The cylindrical secondary battery according to claim 1 or 2, wherein 3.0 mass % or more of the negative electrode mixture layer is composed of silicon oxide.

Images