Cylindrical secondary battery

Abstract

A battery (10) is provided with: a positive electrode lead (20) having a joint part (75) joined to a positive electrode core body-exposing part (35) where a positive electrode core body (30) is exposed in a positive electrode (11); and a tape (70) that is attached closer to the tip-end of the positive electrode lead (29) than the joint part (75), and includes a core body-side covering part positioned between the positive electrode lead (29) and the positive electrode core body-exposing part (35). The positive electrode lead (20) has a protrusion (75) that protrudes from the tape (70) in the positive electrode width direction.

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 may occur in the positive electrode core around a corner at one end of a positive electrode lead joined to the positive electrode. Breaks in the positive electrode core reduce the current collection performance of the positive electrode. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that is less likely to break around the corner of the positive electrode lead in the positive electrode core, making it easier 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; a positive electrode lead having a joint joined to a positive electrode core exposed portion where the positive electrode core is exposed in the positive electrode; and a tape that is affixed to the positive electrode lead closer to the tip than the joint and includes a core side covering portion located between the positive electrode lead and the positive electrode core exposed portion, and the positive electrode lead has a protrusion that protrudes from the tape in the positive electrode width direction.

[0006] In the cylindrical secondary battery according to the present disclosure, breaks are less likely to occur around the portion of the positive electrode substrate that faces the corner portion of the positive electrode lead, making it easier to maintain good current collection performance over a long period of time.

[0007] 1 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure; FIG. 2 is a perspective view showing a portion of an electrode body and a positive electrode lead; FIG. 3 is a plan view showing the wound inner surface of a positive electrode; FIG. 4 is an enlarged plan view of the peripheral portion of one positive electrode substrate exposed portion; FIG. 5 is a cross-sectional view of a portion of a positive electrode lead, a tape, and a positive electrode substrate cut along a plane including the width direction and thickness direction of the positive electrode lead; FIG. 6 is an enlarged plan view of a cylindrical secondary battery of a modified example, corresponding to FIG. 4 ;

[0008] 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 non-aqueous electrolyte. Hereinafter, a cylindrical lithium-ion secondary battery using a non-aqueous electrolyte will be exemplified as a cylindrical secondary battery 10 according to one embodiment, but the cylindrical secondary battery according to the present disclosure is not limited thereto.

[0009] 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."

[0010] Among the components described below, those not recited in the independent claims showing the highest concepts are optional components and are not essential components. Furthermore, the present disclosure is not limited to the following embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0011] 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.

[0012] 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, LiPF６ Lithium salts such as

[0013] 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.).

[0014] Fig. 2 is a perspective view showing a portion of the electrode assembly 14 and a positive electrode lead (positive electrode tab) 20. As shown in Fig. 2, the electrode assembly 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and 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.

[0020] 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.

[0021] 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.

[0022] In order to prevent a short circuit between the positive electrode 11 and the negative electrode 12, it is preferable that 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 be covered with insulating tape (not shown), and it is preferable that the insulating tape cover the entire positive electrode core exposed portion 35. Furthermore, in order to prevent a short circuit between the positive electrode 11 and the negative electrode 12, it is preferable that insulating tape 55 be attached around the entire periphery of the base portion of the extension portion that extends from the positive electrode 11 in the positive electrode lead 20. These insulating tapes 55 are made of an insulating material, and for example, the base material may be made of a polyimide film and the adhesive material may be made of silicone.

[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 negative electrode longitudinal direction, and a second negative electrode substrate exposed portion where the negative electrode substrate is exposed at the outer end of the winding in the negative electrode longitudinal direction. The second negative electrode substrate exposed portion may have an outermost surface portion included in the outermost surface of the electrode assembly. One end of the negative electrode lead (negative electrode tab) 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. The outermost surface portion may also be in contact with 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] Fig. 4 is an enlarged plan view of the peripheral portion of one positive electrode core exposed portion 35. In Fig. 4, the area hatched with dots 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. As shown in Fig. 4, the battery 10 has a tape 70 attached to the positive electrode lead 20 on the tip side of the joint portion 75. The tape 70 is preferably an insulating tape, for example, a tape having a base material made of polyimide film and an adhesive material made of silicone, but may also be a non-insulating tape.

[0038] 5 is a cross-sectional view of the positive electrode lead 20, the tape 70, and a portion of the positive electrode core 30 cut along a plane including the width direction and thickness direction of the positive electrode lead 20. As shown in Fig. 5, the tape 70 is attached only to the positive electrode lead 20 so as to cover the entire periphery of the positive electrode lead 20. The tape 70 includes a core-side covering portion 70a located between the positive electrode lead 20 and the positive electrode core exposed portion 35.

[0039] In this embodiment, the tape 70 is arranged to surround the positive electrode lead 20 all around so that both end faces of the band-shaped tape 70 are in contact with each other. However, the tape 70 may be attached around the positive electrode lead 20 all around so that both end portions of the band-shaped tape 70 slightly overlap. The tape 70 need only be attached to the positive electrode lead 20 so that the core-side covering portion 70a is located between the positive electrode lead 20 and the positive electrode core exposed portion 35, and does not have to be attached all around the positive electrode lead 20. The tape 70 may be composed of only the core-side covering portion 70a. Furthermore, when the tape 70 is composed of only the core-side covering portion 70a, the core-side covering portion 70a may be located between the entire width direction of the positive electrode lead 20 and the positive electrode core exposed portion 35, or may be located between a partial width direction region of the positive electrode lead 20 and the positive electrode core exposed portion 35. As shown in FIG. 4, the positive electrode lead 20 has a protruding portion 77 that protrudes from the tape 70 in the positive electrode width direction.

[0040] Next, we will explain the effects obtained by attaching the tape 70, which has a substrate-side covering portion 70a located between the positive electrode lead 20 and the positive electrode substrate exposed portion 35, to the positive electrode lead 20. 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 in the radial direction and the longitudinal direction of the positive electrode from the negative electrode, causing it to stretch in the longitudinal direction of the positive electrode. The present inventors have found that in conventional cylindrical secondary batteries, there is a risk of the positive electrode substrate breaking around the corners of the positive electrode lead joined to the positive electrode after multiple cycles.

[0041] 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.

[0042] In light of this background, according to the battery 10 of the present disclosure, the core-side covering portion 70a is present between the location between the joint portion 75 and the protruding portion 77 in the positive electrode lead 20 and the positive electrode core exposed portion 35. Therefore, the protruding portion 77, including the corner portion of the positive electrode lead 20, receives a force from the core-side covering portion 70a that moves it away from the positive electrode core exposed portion 35 (a force that lifts it up from the positive electrode core exposed portion 35). This reduces the force that the periphery of the corner portion of the positive electrode lead 20 in the positive electrode core exposed portion 35 receives from the corner portion, thereby preventing the positive electrode core 30 from breaking.

[0043] Since a force can be effectively applied to the protrusion 77, including the corner portion of the positive electrode lead 20, to move away from the positive electrode core exposed portion 35, it is preferable that the core side covering portion 70a be present between the entire width of the positive electrode lead 20 and the positive electrode core exposed portion 35, and for example, it is preferable that the tape 70 covers the entire circumference of the positive electrode lead 20.

[0044] Since it is easy to adjust the force that the protrusion 77 applies to the positive electrode core exposed portion 35, when the tape 70 is attached around the entire circumference of the positive electrode lead 20, it is preferable that the end faces that are the mating surfaces of the tape 70 and the end ends that constitute the overlapping portion are located on the opposite side of the positive electrode lead 20 from the positive electrode core 30 side in the thickness direction of the positive electrode lead 20.

[0045] Example 1 In the battery 10 of the above embodiment, insulating tape was attached around the entire circumference of the positive electrode lead 20, as shown in Fig. 5, so that the core-side covering portion 70a was present. In addition, the tab protrusion (lead protrusion), which is the distance of the protrusion 77 in the positive electrode longitudinal direction, was set to 0.3 µm. The tab protrusion is the length indicated by t in Fig. 4.

[0046] Example 2 A battery of Example 2 was prepared by comparing it with the battery of Example 1 in that the tab protrusion was set to 0.5 μm.

[0047] Example 3 A battery of Example 3 was prepared by comparing it with the battery of Example 1 in that the tab protrusion was set to 0.8 μm.

[0048] Comparative Example 1 In comparison with the battery of Example 1, a battery without insulating tape was used as the battery of Comparative Example 1.

[0049] Comparative Example 2 A battery different from the battery of Example 1 in that it does not have the protrusion 77, in other words, a battery with a tab protrusion of 0 μm, was used as the battery of Comparative Example 2.

[0050] 6 , that is, a cross-sectional view of the positive electrode lead 20, the tape 270, and a portion of the positive electrode core 30 cut along a plane including the width direction and thickness direction of the positive electrode lead 20, a tape 270 without a core-side covering portion was attached to the positive electrode lead 20. The tape 270 was affixed so that no protruding portion 77 was present and the tab protrusion margin was 0 μm.

[0051] Comparative Example 4 In comparison with the battery of Comparative Example 3, the difference was that the tab protrusion was 0.3 μm.

[0052] (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.

[0053] The test results are shown in Table 1. As shown in Table 1, breakage of the positive electrode substrate was confirmed in the battery of Comparative Example 1 in which no tape was attached to the positive electrode lead, the battery of Comparative Example 2 in which a substrate-side covering portion was provided but no tab protrusion allowance was provided, and the batteries of Comparative Examples 3 and 4 in which tape was attached that was not provided with a substrate-side covering portion.

[0054] In the batteries of Comparative Examples 1, 3, and 4, there was no substrate side covering portion, and therefore no force existed to separate the corner of the positive electrode lead from the exposed portion of the positive electrode substrate, and it is presumed that the force from the corner caused the positive electrode substrate to break.

[0055] In addition, in the battery of Comparative Example 2, the substrate-side covering was attached so as to overlap the corner of the positive electrode lead, and it is presumed that the force from the corner of the positive electrode lead was amplified by the presence of the substrate-side covering and transmitted to the positive electrode substrate, resulting in localized stress concentration in the positive electrode substrate, which is thought to have caused the positive electrode substrate to break.

[0056] In contrast, no positive electrode breakage was observed in the battery of Example 1-3, in which a tape having a substrate-side covering portion was attached to the positive electrode lead and a tab protrusion was provided. This demonstrates that when a tape having a substrate-side covering portion is attached to the positive electrode lead and a tab protrusion is provided, a force can be applied to the corner of the positive electrode lead to separate it from the positive electrode substrate exposed portion, and the force applied by the corner of the positive electrode lead to the positive electrode substrate exposed portion can be reduced.

[0057] As shown in the above test results, the dimension of the protruding portion 77 in the positive electrode width direction is preferably 0.3 μm or more because this can reliably prevent the positive electrode substrate exposed portion 35 from being torn by the force that the positive electrode substrate exposed portion 35 receives from the substrate side covering portion 70 a. Furthermore, the dimension of the protruding portion 77 in the positive electrode width direction is preferably 0.8 μm or less because this can effectively apply a force that moves the protruding portion (tab protrusion) 77, including the corner portion of the positive electrode lead 20, away from the positive electrode substrate exposed portion 35.

[0058] The thickness of the tape 70 (thickness of the core-side covering portion 70a) is preferably 10 μm or more because this effectively reduces the pressing force with which the corners of the positive electrode lead 20 press against the positive electrode core 30 (the pressing force may be zero). Furthermore, the thickness of the tape 70 (thickness of the core-side covering portion 70a) is preferably 30 μm or less because this makes it easier to increase the circularity of the electrode body 14 and to make the reaction occur uniformly.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] For example, in the above embodiment, the case has been described in which the positive electrode mixture layer 32 includes a substrate adjacent portion 32a that is adjacent in the positive electrode width direction to the positive electrode substrate exposed portion 35. However, as shown in Fig. 7, that is, an enlarged plan view corresponding to Fig. 4 of a modified battery (cylindrical secondary battery) 110, 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 that is adjacent in the positive electrode width direction to the positive electrode substrate exposed portion 135.

[0064] Even in this case, the positive electrode lead 120 is joined to the positive electrode substrate exposed portion 135 at one or more joint portions 175. The joint portions 175 are areas indicated by dotted hatching, and in the example shown in FIG. 7 , three joint portions 175 are present at intervals in the positive electrode width direction. The battery 110 is provided with a tape 170 that is attached to the positive electrode lead 120 closer to the tip than the joint portion 175 and includes a substrate side covering portion 170a located between the positive electrode lead 120 and the positive electrode substrate exposed portion 135. The positive electrode lead 120 has a protrusion 177 that protrudes from the tape 170 in the positive electrode width direction.

[0065] 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.

[0066] The cylindrical secondary battery of the present disclosure may also have the following configurations. Configuration 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 accommodating the electrode assembly; a positive electrode lead having a joint joined to a positive electrode core exposed portion where the positive electrode core is exposed in the positive electrode; and a tape attached to the positive electrode lead closer to the tip than the joint and including a core-side covering portion located between the positive electrode lead and the positive electrode core exposed portion, wherein the positive electrode lead has a protrusion protruding from the tape in the positive electrode width direction. Configuration 2: The cylindrical secondary battery according to Configuration 1, in which the dimension of the protrusion in the positive electrode width direction is 0.3 μm or more and 0.8 μm or less. Configuration 3: The cylindrical secondary battery according to Configuration 1 or 2, in which the tape covers the positive electrode lead over the entire circumference. Configuration 4: The cylindrical secondary battery according to any one of Configurations 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.

[0067] 10,110 Battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Inner surface of winding, 16 Outer can, 17 Sealing body, 18 Insulating plate, 20,120 Positive electrode lead, 22 Grooved portion, 27 Terminal cap, 28 Gasket, 29 Shoulder portion, 30 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, 50a Through hole, 51 Metal plate, 52 Lower current collector plate, 60 Lamination portion, 65 Recessed portion, 68 Bottom portion, 68a: easily breakable portion, 70,170: tape, 70a,170a: core side covering portion, 75,175: joint portion, 77,177: protruding 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; a positive electrode lead having a joint joined to a positive electrode core exposed portion where the positive electrode core is exposed in the positive electrode; and a tape that is affixed to the positive electrode lead closer to the tip than the joint and includes a core side covering portion located between the positive electrode lead and the positive electrode core exposed portion, wherein the positive electrode lead has a protrusion that protrudes from the tape in the positive electrode width direction.

2. The cylindrical secondary battery according to claim 1, wherein the dimension of said protrusion in the width direction of the positive electrode is 0.3 μm or more and 0.8 μm or less.

3. The cylindrical secondary battery according to claim 1, wherein the tape covers the entire periphery of the positive electrode lead.

4. The cylindrical secondary battery according to claim 1, 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 any one of claims 1 to 4, wherein 3.0 mass % or more of the negative electrode mixture layer is composed of silicon oxide.

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