Cylindrical secondary battery

Abstract

A positive electrode (11) has one or more positive electrode core exposed parts (35) that are adjacent to a positive electrode mixture layer (32) in the positive electrode width direction and in which a positive electrode core (30) is exposed. One positive electrode tab (20) is bonded to each positive electrode core exposed part (35). The center (20b) of an innermost peripheral positive electrode tab (20a) in the positive electrode longitudinal direction is located one or more turns outside a winding inner end (11a) of the positive electrode (11) with respect to the positive electrode longitudinal direction. According to the cylindrical secondary battery of the present disclosure, it is easy to increase the capacitance and also easy to reduce the electrical resistance.

Description

Cylindrical secondary battery

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

[0002] Conventionally, a cylindrical secondary battery is described in Patent Document 1. This cylindrical battery includes an electrode assembly in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween, an outer can housing the electrode assembly, and a sealing body closing an opening on one side of the outer can in the height direction. The positive electrode has a long positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, while the negative electrode has a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. One ends of multiple positive electrode tabs are joined to the positive electrode at intervals in the positive electrode longitudinal direction, and the other ends of the multiple positive electrode tabs are joined to the inner surface of the sealing body. In this cylindrical battery, the current path in the positive electrode longitudinal direction is short, thereby reducing electrical resistance.

[0003] Japanese Patent Application Laid-Open No. 2003-7346

[0004] When a portion of the positive electrode mixture layer is positioned adjacent to the exposed portion of the positive electrode substrate to which the positive electrode tab is joined in the positive electrode width direction, the capacity increases and the battery performance improves. However, as will be described in detail later, the present inventors have found that, when the capacity is increased by adopting such a configuration, depending on the joining location of the innermost positive electrode tab, the positive electrode substrate may be damaged, which may increase the electrical resistance of the positive electrode side. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can easily increase the capacity and reduce the electrical resistance.

[0005] In order to solve the above problems, the cylindrical secondary battery of the present disclosure comprises an electrode assembly in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween, an outer can that houses the electrode assembly, and a sealing body that is crimped and fixed to the opening of the outer can via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, the negative electrode has a long negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, the positive electrode has one or more positive electrode core exposed portions that are adjacent to the positive electrode mixture layer in the positive electrode width direction and at which the positive electrode core is exposed, and comprises positive electrode tabs joined to the positive electrode core exposed portions one by one, and the center in the positive electrode longitudinal direction of the innermost positive electrode tab is located one or more turns outside the winding from the inner end of the winding of the positive electrode in the positive electrode longitudinal direction.

[0006] In this specification, the position one turn from the inner winding end of the positive electrode is defined as the position facing the inner winding end of the positive electrode in the radial direction (radial direction of the outer can) and one turn outside the inner winding end.

[0007] According to the cylindrical secondary battery according to the present disclosure, it is easy to increase the capacity and reduce the electrical resistance.

[0008] 1 is a schematic axial cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure; FIG. 2 is a perspective view showing a portion of an electrode assembly and a positive electrode tab; FIG. 3 is a plan view showing the inner surface of the wound positive electrode, illustrating the position and structure of a positive electrode substrate exposed portion to which the positive electrode tab is joined in the positive electrode; FIG. 4 is a schematic top view of the inner surface of the wound electrode assembly as viewed from above in the axial direction; FIG. 5 is a schematic developed view of the positive electrode illustrating a positive electrode tab arrangement that easily shortens the current collection path on the positive electrode side when the number of positive electrode tabs is three; FIG. 6(a) is a schematic top view of the positive electrode α layer on the inner surface of the wound electrode assembly as viewed from above in the axial direction during pre-discharge of a cycle in the battery of the first reference example; and FIG. 7(b) is a schematic top view of the positive electrode β layer on the inner surface of the wound electrode assembly as viewed from above in the axial direction during pre-discharge of a cycle in the battery of the first reference example. (a) is a schematic top view of the positive electrode α layer on the inside of the electrode body winding of the battery of Reference Example 1 when viewed from the axial top during in-cycle charging, and (b) is a schematic top view of the positive electrode β layer on the inside of the electrode body winding of the battery of Reference Example 1 when viewed from the axial top during in-cycle charging. (a) is a schematic top view of the positive electrode α layer on the inside of the electrode body winding of the battery of Reference Example 1 when viewed from the axial top during post-cycle discharging, and (b) is a schematic top view of the positive electrode β layer on the inside of the electrode body winding of the battery of Reference Example 1 when viewed from the axial top during post-cycle discharging. (a) is a schematic top view of the inside of the electrode body winding of the battery of Reference Example 2 before cycling when viewed from the axial top, and (b) is a schematic top view of the inside of the electrode body winding of the battery of Reference Example 2 after cycling when viewed from the axial top. 1A is a schematic top view of the inner surface of the electrode body wound of the battery of the third reference example before cycling, as viewed from above in the axial direction, and FIG. 1B is a schematic top view of the inner surface of the electrode body wound of the battery of the third reference example after cycling, as viewed from above in the axial direction. 1B is a schematic development of the inner surface of the positive electrode wound of the fourth reference example when the inner surface is unwound, and is a schematic development explaining the problems of the battery of the fourth reference example. 1C is a schematic development of the inner surface of the positive electrode wound of the battery that can improve the problems of the fourth reference example when the inner surface is unwound.

[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 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.

[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] In this specification, the number of revolutions is defined as follows: When viewing a cross section of a cylindrical battery in the axial direction (a cross section including the radial direction of the cylindrical battery), the center of the circle formed by the outer diameter of the outer can is set as the center of the polar coordinates, and the position of the inner winding end of the positive electrode is set as 0 degrees. In this case, if the change in angle when moving from the inner winding end of the positive electrode along the positive electrode is set as θ, the number of revolutions is defined as θ÷360. For example, a position 1080 degrees forward is 1080÷360=3.0 revolutions.

[0012] In this specification, when the longitudinal position of the positive electrode substrate exposed portion is expressed as the number of turns (winding position), this is expressed as the center position of the positive electrode substrate exposed portion in the longitudinal direction of the positive electrode. For example, when the position of the positive electrode substrate exposed portion in the longitudinal direction of the positive electrode is the 6.5th turn, this means that the center of the positive electrode substrate exposed portion in the longitudinal direction of the positive electrode is located at the 6.5th turn. Furthermore, when the position of the positive electrode tab in the longitudinal direction of the positive electrode is expressed as the number of turns (winding position), this is expressed as the center position of the positive electrode tab in the width direction (the center position of the positive electrode tab in the longitudinal direction of the positive electrode). For example, when the position of the positive electrode tab in the longitudinal direction of the positive electrode is the 4.5th turn, this means that the center of the positive electrode tab in the width direction (the center of the positive electrode tab in the longitudinal direction of the positive electrode) is located at the 4.5th turn.

[0013] 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.

[0014] 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.

[0015] 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

[0016] 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.).

[0017] Fig. 2 is a perspective view showing a portion of the electrode assembly 14 and the 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 tabs 20 are joined to the positive electrode 11, and preferably six or more positive electrode tabs 20 are joined thereto. In this embodiment, eight positive electrode tabs 20 are joined to the positive electrode 11 at intervals from one another in the longitudinal direction of the positive electrode.

[0018] 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.

[0019] 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 portion from the inner winding end to the outer winding end in the negative electrode longitudinal direction of the long negative electrode 12. Therefore, the axial lower end portion of the electrode assembly 14 is formed by the negative electrode substrate exposed portion 41. The negative electrode 12 may form the inner winding end of the electrode assembly 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 assembly 14.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] FIG. 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 a positive electrode substrate exposed portion 35 to which a positive electrode tab 20 is joined in the positive electrode 11. FIG. 4 is a schematic top view of the inner winding surface of the electrode assembly 14 as viewed from above in the axial direction. The hatched area in FIG. 3 is the area where the positive electrode mixture layer 32 is disposed. In FIG. 4, the separator 13 is not shown. Note that, although the present embodiment describes a case where the positive electrode tab 20 is joined to the inner winding surface 15 of the positive electrode 11, the positive electrode tab may also be joined to the outer winding surface of the positive electrode.

[0024] As shown in Fig. 3, the positive electrode 11 has one or more positive electrode core exposed portions 35 adjacent to the positive electrode mixture layer 32 in the positive electrode width direction and at which the positive electrode core 30 is exposed; in this embodiment, there are eight positive electrode core exposed portions 35. A positive electrode tab 20 is bonded to each positive electrode core exposed portion 35. Since a portion 32a of the positive electrode mixture layer 32 is arranged adjacent to the positive electrode core exposed portion 35 in the positive electrode width direction, the capacity is increased. It is preferable that the center positions of the eight positive electrode core exposed portions 35 in the positive electrode longitudinal direction are arranged at approximately equal intervals in the positive electrode longitudinal direction.

[0025] The positive electrode tab 20 is joined to the positive electrode core exposed portion 35 by ultrasonic welding or the like, with its widthwise center position substantially coinciding with the center position in the positive electrode longitudinal direction of the corresponding positive electrode core exposed portion 35. As shown in Figure 4, the center 20b in the positive electrode longitudinal direction of the innermost peripheral positive electrode tab 20a is located one or more turns outside the inner winding end 11a of the positive electrode 11 in the positive electrode winding direction.

[0026] As will be described in detail later, it is preferable that the center 20b of the innermost positive electrode tab 20a be located between one turn and seven turns away from the inner winding end 11a, and more preferably between one turn and two turns away from the inner winding end 11a, as in the present embodiment.

[0027] Furthermore, when N is a natural number and there are N positive electrode tabs 20, it is preferable that the center 20b of the innermost peripheral positive electrode tab 20a be located in the positive electrode longitudinal direction range from a position one turn outside the inner winding end 11a to L / (2N), where L is the total length in the positive electrode longitudinal direction. Fig. 5 is a schematic development of the positive electrode illustrating a positive electrode tab arrangement that makes it easy to shorten the current collection path on the positive electrode side when the number of positive electrode tabs 20 is three (when N is 3).

[0028] As shown in FIG. 5 , when the positive electrode tabs are arranged such that the distance x from each end to the center of the end positive electrode tab 120 is L / (2N) and the center-to-center distance 2x of two adjacent positive electrode tabs 120 is L / N, the longitudinal distance from any position on the positive electrode 111 to the closest positive electrode tab 120 is less than x, i.e., L / (2N). This tends to shorten the current collection path, minimizing electrical resistance. Therefore, when the center 20b of the innermost positive electrode tab 20a is located in the positive electrode longitudinal range from the inner winding end 11a to a position one turn outside, where L is the total length of the positive electrode longitudinal direction, this tends to shorten the current collection path on the positive electrode side, and reduces electrical resistance.

[0029] The effects derived from the arrangement of the positive electrode tab 20 according to the present disclosure will be described in detail later with reference to Figures 6 to 12. The positive electrode tab 20 is covered with, for example, insulating tape (not shown), thereby suppressing short circuits between the positive electrode 11 and the negative electrode 12. It is preferable that the insulating tape cover the entire positive electrode core exposed portion 35.

[0030] As shown in FIG. 2 , the negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. 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.

[0031] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include graphite, such as natural graphite (e.g., flake graphite, lump graphite, and amorphous graphite), and artificial graphite (e.g., lump artificial graphite and graphitized mesophase carbon microbeads). The negative electrode active material of the negative electrode mixture layer 42 preferably contains a Si material containing silicon (Si) particles. Furthermore, 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.

[0032] 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.

[0033] 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.

[0034] As shown in Figure 1, the battery 10 includes an annular insulating plate 18 on the upper side of the electrode assembly 14. A positive electrode tab 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.

[0035] 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.

[0036] Each positive electrode tab 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 tab 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 tab 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 tab 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 tab 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 tab 20 sandwiched between the upper current collector plate 50 and the metal plate 51, the positive electrode tab 20 can be reliably and easily welded and bonded to the upper current collector plate 50.

[0037] 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 tab 20 is bonded to the upper current collector plate 50 within the recess 65. The upper current collector plate 50 does not need to be bonded to the metal plate 51, and the positive electrode tab 20 does not need to be bonded to the metal plate 51. The battery does not need to have a metal plate 51. The positive electrode tab 20 may also be bonded to the lower surface of the upper current collector plate 50.

[0038] 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.

[0039] 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 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 contact the inner circumferential surface of the outer can.

[0040] 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 then 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 tab.

[0041] 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.

[0042] 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 sealant 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 tab 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.

[0043] 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.

[0044] Next, the effects derived from the positive electrode tab arrangement of the present disclosure will be described using Figures 6 to 12. The present inventors have discovered that in a configuration in which a portion of the positive electrode mixture layer is provided adjacent to the positive electrode core to which the positive electrode lead is joined in the positive electrode width direction, as the number of cycles increases, radial gaps are more likely to occur on the inner side of the wound electrode assembly. This is thought to be due to the following mechanism.

[0045] That is, the positive electrode has an α layer having a positive electrode substrate exposed portion and a β layer having no positive electrode substrate exposed portion and consisting only of a negative electrode mixture layer, as shown in Fig. 3. In this context, during discharge in the initial state before cycling, the α layer and the β layer are connected in the positive electrode width direction, and are therefore wound at the same radial intervals as shown in Fig. 6.

[0046] However, the exposed core portion of the α layer is thin and does not react during charging, while the β layer has a positive electrode mixture layer adjacent to the exposed core portion in the positive electrode width direction, resulting in a high surface pressure during charging. In other words, the exposed core portion of the α layer experiences a lower surface pressure than the β layer during charging, when the negative electrode expands. Therefore, as shown in Figure 7 , due to this surface pressure difference, the α layer is more likely to move toward the hollow portion of the electrode body where no electrode is present (the radial inner side of the winding) than the β layer. As a result, during discharge after multiple cycles, as shown in Figure 8 , it is presumed that the radial gap c is particularly likely to occur in the α layer due to the movement of the α layer toward the inner side of the winding during charging.

[0047] If radial gaps occur in the electrode body, it becomes difficult for reactions to occur in the vicinity, resulting in a decrease in capacity and an increase in electrical resistance. The present inventors thought that the occurrence of such gaps could be suppressed by taking the following measures.

[0048] Specifically, when the innermost circumferential positive electrode tab 220a is joined to a location away from the inner winding end in the longitudinal direction of the positive electrode, as shown in FIG. 9(a), the inner winding end 211b of the positive electrode 211 tends to move freely radially inward, and as a result, the inner circumferential end 211a of the positive electrode protrudes toward the inner circumferential side, as shown in FIG. 9(b), and a radial gap is generated.

[0049] Therefore, it was inferred that if, as shown in FIG. 10( a), the innermost circumferential positive electrode tab 320 a is fixed to the inner-winding end 311 b of the positive electrode 311 and the inner-winding end 311 b is restrained by the innermost circumferential positive electrode tab 320 a, thereby suppressing radially inward movement of the inner-winding end 311 a of the positive electrode 311, this would result in suppressing the generation of radial gaps as shown in FIG. 10( b).

[0050] However, the closer to the innermost end of the positive electrode, the greater the amount of movement of the positive electrode toward the inner side of the winding during charging. Therefore, in this configuration, the inner end of the positive electrode, which is most likely to move toward the inner side, is restrained, and as shown in Figure 11, there is a concern that the inner side of the innermost circumferential positive electrode tab 320a of the positive electrode 311 will be pulled toward the inner side of the winding and damaged. This damage may result in a decrease in current collection performance and an increase in resistance.

[0051] On the other hand, as shown in FIG. 12 , when the innermost positive electrode tab 420 a is joined at a position away from the inner end of the positive electrode 411 in the longitudinal direction of the positive electrode, the amount of movement of the inner end of the positive electrode 411 toward the inner side of the winding is not hindered, and therefore there is less concern that the inner side of the innermost positive electrode tab 420 a will be damaged.

[0052] The present inventors experimentally found a joining position for the innermost circumferential positive electrode tab 20a that can suppress damage to the inner side of the winding of the innermost circumferential positive electrode tab 20a. Furthermore, the present inventors experimentally found a joining position for the innermost circumferential positive electrode tab 20a that can not only suppress damage to the inner side of the winding of the innermost circumferential positive electrode tab 20a, but also effectively suppress the occurrence of radial gaps after multiple cycles. Below, the batteries of Examples 1-5 and Comparative Examples 1 and 2, the test contents, and the test results are described.

[0053] Example 1 In the battery having eight positive electrode tabs described with reference to FIGS. 1 to 4 , the center in the positive electrode longitudinal direction of the innermost positive electrode tab 20 a was joined to a position one turn outward from the inner winding end 11 a of the positive electrode 11, and the centers in the positive electrode longitudinal direction of the other seven positive electrode tabs 20 were joined to positions where the current collection path was short, as described with reference to FIG. 5 , to form battery 10 of Example 1.

[0054] Example 2 The battery 10 of Example 2 differs from that of Example 1 in that the center of the innermost circumferential positive electrode tab 20a in the positive electrode longitudinal direction was joined to a position two turns outside from the inner winding end 11a of the positive electrode 11.

[0055] Example 3 The battery 10 of Example 3 differs from that of Example 1 in that the center of the innermost circumferential positive electrode tab 20a in the positive electrode longitudinal direction was joined to a position three turns outside from the inner winding end 11a of the positive electrode 11.

[0056] Example 4 The battery 10 of Example 4 differs from that of Example 1 in that the center of the innermost positive electrode tab 20a in the positive electrode longitudinal direction was joined to a position seven turns outside from the inner winding end 11a of the positive electrode 11.

[0057] Example 5 The battery 10 of Example 5 differs from that of Example 1 in that the center of the innermost circumferential positive electrode tab 20a in the positive electrode longitudinal direction was joined to a position 10 turns outside from the inner winding end 11a of the positive electrode 11.

[0058] Comparative Example 1 The battery of Comparative Example 1 differed from Example 1 in that the center of the innermost circumferential positive electrode tab in the longitudinal direction of the positive electrode was joined to the inner end of the wound positive electrode.

[0059] Comparative Example 2 The battery of Comparative Example 2 differed from Example 1 in that the center of the innermost positive electrode tab in the longitudinal direction of the positive electrode was joined to a position 0.5 turns outward from the inner end of the positive electrode winding.

[0060] (Measurement of the movement angle of the inner winding end of the positive electrode) For each battery, in an air-cooled environment at 45°C, constant voltage charging was performed at a constant current of 0.3 C until the battery voltage reached 4.2 V, followed by constant voltage charging at a voltage of 4.2 V until the current value reached 0.02 C, and then constant current discharging at a constant current of 0.5 C until the battery voltage reached 2.85 V. This charge-discharge cycle was repeated 600 times. The movement angle was then measured based on a computed tomography (CT) image of a cross section of the electrode body in the radial direction. The movement angle is the angle between a line segment connecting the inner winding end of the positive electrode and the center of the outer can before the cycle test and a line segment connecting the inner winding end of the positive electrode and the center of the outer can after the cycle test. The larger the movement angle, the greater the amount of movement of the inner winding end toward the inside of the winding.

[0061] (Presence or absence of damage to the positive electrode core near the inner side of the innermost positive electrode tab) After the above cycle test, each battery was visually inspected to determine whether or not damage had occurred to the positive electrode core near the inner side of the innermost positive electrode tab.

[0062] (Measurement of Electrical Resistance of Battery Before and After Cycle Test) The electrical resistance of each battery before the cycle test and the electrical resistance of each battery after the cycle test were measured. The resistance value was evaluated as a relative value when the resistance value of the battery of Example 4 before the cycle test was set to 100.

[0063] Table 1 shows the test results for each battery. As shown in Table 1, in the batteries of Comparative Examples 1 and 2, in which the innermost positive electrode tab was joined within 0.5 turns from the inner end of the positive electrode winding, damage was confirmed to have occurred in the positive electrode substrate on the inner side of the innermost positive electrode tab after the cycle test. Furthermore, due to this damage, the resistance values ​​after the cycle test were significantly higher in the batteries of Comparative Examples 1 and 2. Therefore, it was confirmed that it is difficult to manufacture a highly reliable battery when the innermost positive electrode tab is joined within 0.5 turns from the inner end of the positive electrode winding.

[0064] On the other hand, in the battery in which the innermost positive electrode tab was joined at a position one or more turns from the inner end of the positive electrode winding, no damage to the positive electrode core on the inner side of the innermost positive electrode tab was confirmed after the cycle test, and the resistance value after the cycle was also smaller than those of the batteries of Comparative Examples 1 and 2. Therefore, it was confirmed that a highly reliable battery can be manufactured by joining the innermost positive electrode tab at a position one or more turns from the inner end of the positive electrode winding.

[0065] Furthermore, it was confirmed that the post-cycling resistance value decreased as the number of turns from the inner end of the positive electrode at the joining position of the innermost positive electrode tab decreased from 10 turns. It was also confirmed that when the innermost positive electrode tab was joined to a position 7 turns from the inner end of the positive electrode, the post-cycling resistance could be reduced to 121, and when the innermost positive electrode tab was joined to a position 2 turns from the inner end of the positive electrode, the post-cycling resistance could be rapidly reduced to 116. Furthermore, when the innermost positive electrode tab was joined to a position 1 turn from the inner end of the positive electrode, the post-cycling resistance was the smallest at 115.

[0066] From this, it was confirmed that when the innermost positive electrode tab is joined at a position between one and two turns from the inner end of the positive electrode, both gap generation and damage to the positive electrode core can be suppressed, and a battery with both excellent reliability and performance can be produced. Furthermore, when the innermost positive electrode tab is joined at a position between two and seven turns from the inner end of the positive electrode, there is a risk of a small radial gap occurring after multiple cycles, but it was confirmed that a battery with high reliability and good performance can be produced. Furthermore, it was confirmed that when the innermost positive electrode tab is joined at a position between one and two turns from the inner end of the positive electrode, damage to the positive electrode core can be suppressed, and a highly reliable battery can be produced.

[0067] In large-diameter batteries with a total length in the longitudinal direction of the positive electrode of 3000 mm or more, or in large-diameter batteries with a distance between the inner end of the negative electrode in the electrode assembly and the central axis of the outer can of 5 mm or more, the radial stress of the battery due to expansion of the negative electrode during charging tends to be large. Therefore, by adopting the battery configuration of the present disclosure, the resistance reduction effect after multiple cycles can be made significant. Furthermore, when the negative electrode contains Si, the negative electrode expands significantly during charging. Therefore, even in this case, by adopting the battery configuration of the present disclosure, the resistance reduction effect after multiple cycles can be made significant.

[0068] The cylindrical secondary battery according to 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 and a long negative electrode are wound with a separator interposed therebetween, an outer can housing the electrode assembly, and a sealing body that is crimped and fixed to an opening of the outer can via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, the negative electrode has a long negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, the positive electrode has one or more positive electrode core exposed portions that are adjacent to the positive electrode mixture layer in the positive electrode width direction and at which the positive electrode core is exposed, and positive electrode tabs are joined to the positive electrode core exposed portions one by one, and the center of the positive electrode longitudinal direction of the innermost positive electrode tab is located one or more turns outward from the inner end of the positive electrode in the positive electrode longitudinal direction. Configuration 2: The cylindrical secondary battery according to Configuration 1, wherein the positive electrode has two or more positive electrode substrate exposed portions arranged at intervals in the longitudinal direction of the positive electrode.Configuration 3: The cylindrical secondary battery according to Configuration 1 or 2, wherein the battery includes N positive electrode tabs, where N is a natural number, and wherein the center of the innermost positive electrode tab is located in a range in the longitudinal direction of the positive electrode from a position one turn outward from the inner end of winding to L / (2N), where L is the total length of the positive electrode in the longitudinal direction of the positive electrode.Configuration 4: The cylindrical secondary battery according to Configuration 1 or 2, wherein the center of the innermost positive electrode tab is located in a range from one turn outward to seven turns outward from the inner end of winding.Configuration 5: The cylindrical secondary battery according to Configuration 4, wherein the center of the innermost positive electrode tab is located in a range from one turn outward to two turns outward from the inner end of winding. Configuration 6: The cylindrical secondary battery according to any one of Configurations 1 to 5, wherein the total length of the positive electrode in the longitudinal direction of the positive electrode is 3000 mm or more. Configuration 7: The cylindrical secondary battery according to any one of Configurations 1 to 6, wherein the distance between the inner end of the negative electrode in the electrode assembly and the central axis of the outer can is 5 mm or more. Configuration 8: The cylindrical secondary battery according to any one of Configurations 1 to 7, wherein the negative electrode contains Si.

[0069] REFERENCE SIGNS LIST 10 Battery, 11 Positive electrode, 11a Inner end of positive electrode winding, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Inner surface of positive electrode winding, 16 Outer can, 17 Sealing body, 18 Insulating plate, 20 Positive electrode tab, 20a Innermost positive electrode tab, 20b Width direction center of positive electrode tab, 22 Grooved portion, 27 Terminal cap, 28 Gasket, 29 Shoulder portion, 30 Positive electrode core, 32 Positive electrode mixture layer, 35 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 Laminated portion, 65 recessed portion, 68 bottom portion, 68a easily breakable portion, c radial gap of electrode body.

Claims

1. A cylindrical secondary battery comprising: an electrode body in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween; an exterior can that houses the electrode body; and a sealing body caulked and fixed to an opening of the exterior can via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, the negative electrode has a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the positive electrode has one or more positive electrode core exposed portions adjacent to the positive electrode mixture layer in the positive electrode width direction and exposing the positive electrode core, and the positive electrode has positive electrode tabs respectively joined to the positive electrode core exposed portions, and a center of the innermost positive electrode tab in the positive electrode longitudinal direction is located one or more turns outside the winding inner end of the positive electrode in the positive electrode longitudinal direction.

2. The cylindrical secondary battery according to claim 1, wherein the positive electrode has two or more of the positive electrode core exposed portions spaced apart from each other in the positive electrode longitudinal direction.

3. When N is a natural number and the cylindrical secondary battery includes N positive electrode tabs, and when a total length of the positive electrode in the positive electrode longitudinal direction is L, the center of the innermost positive electrode tab is located in a positive electrode longitudinal direction range from a position one turn outside the winding inner end to L / (2N).

4. The cylindrical secondary battery according to claim 1, wherein the center of the innermost positive electrode tab exists from a position one turn outside the winding inner end to a position seven turns outside the winding outer end.

5. The cylindrical secondary battery according to claim 4, wherein the center of the innermost positive electrode tab exists from a position one turn outside the winding inner end to a position two turns outside the winding outer end.

6. The cylindrical secondary battery according to claim 1, wherein a total length of the positive electrode in the positive electrode longitudinal direction is 3000 mm or more.

7. The cylindrical secondary battery according to claim 1, wherein a distance between a winding inner end of the negative electrode in the electrode body and a central axis of the exterior can is 5 mm or more.

8. The cylindrical secondary battery according to any one of claims 1 to 7, wherein the negative electrode contains Si.

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