Cylindrical battery

Abstract

In the present invention, a battery comprises: an electrode body in which a positive electrode and a negative electrode (12) are wound with a separator therebetween; and an outer can that accommodates the electrode body. The negative electrode (12) has a negative electrode core body (40) and a negative electrode mixture layer (42) disposed on the negative electrode core body (40). The negative electrode mixture layer (42) has a recess (70), which is recessed to the center side in the negative-electrode width direction, at one of a total of four corners on the winding-start side and the winding-end side in the negative-electrode longitudinal direction. The length of the recess (70) in the negative-electrode longitudinal direction is 1 / 5 or less of the length of the negative electrode (12) in the negative-electrode longitudinal direction. As a result, it is possible to suppress the generation of a load concentration part in the electrode mixture layer (42), thus allowing to realize a battery that is easy to achieve high capacity.

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] A conventional cylindrical battery is described in Patent Document 1. In this cylindrical battery, the end of the electrode assembly in the axial direction toward the bottom of the outer can is configured as a negative electrode, and this end is pressed against the negative electrode current collector. In this way, a wide longitudinal area of ​​the strip-shaped negative electrode is electrically connected to the negative electrode current collector, thereby shortening the current path on the negative electrode side and reducing the electrical resistance of the cylindrical battery.

[0003] JP 2014-186912 A

[0004] The present inventors have discovered a new problem, which is described below. Specifically, in a cylindrical battery, if one axial end of the electrode body is formed as a negative electrode substrate exposed portion, and this negative electrode substrate exposed portion is welded to a negative electrode current collector plate, and then the negative electrode current collector plate is welded to the bottom of the outer can, a wide longitudinal area of ​​the negative electrode can be reliably and stably electrically connected to the negative electrode current collector plate, the current path on the negative electrode side can be shortened, and the electrical resistance of the cylindrical battery can be reduced.

[0005] Furthermore, referring to the plan view shown in FIG. 11 , by intermittently applying anode mixture slurry to the widthwise central portion of a band-shaped anode core 540 at intervals in the longitudinal direction and then drying or the like, a plurality of anode mixture layers 542 (indicated by diagonal hatching in FIG. 11 ) are arranged in the longitudinal direction on the anode core 540, and then cutting the anode core 540 at the widthwise center C1 and the longitudinal center C2 between adjacent anode mixture layers 542 in the longitudinal direction, a plurality of anodes 512 can be produced efficiently and with good mass productivity.

[0006] However, the present inventors have found that, in the case of efficiently producing a plurality of anodes 512 with good mass productivity using the above-mentioned method of intermittent application of the anode mixture slurry, if the discharge port for the anode mixture slurry is simply fully opened at the start point of the anode mixture slurry and fully closed at the end point of the anode mixture slurry, a convex portion 570 extending in the anode width direction is likely to be formed at the end of the anode mixture layer 542 corresponding to the end on the discharge start side of the anode mixture slurry, as shown in FIG. 11 .

[0007] Furthermore, the inventors of the present invention have also found that when welding one side end 541 a in the negative electrode width direction of the negative electrode core exposed portion 541 to the negative electrode current collector plate, when the one side end 541 a is pressed against the negative electrode current collector plate to crush it in order to ensure the contact required for welding, a load is likely to be concentrated on the convex portion 570, and there is a risk that the area around the convex portion 570 will be deformed.

[0008] The risk of deformation becomes more pronounced when the load applied to press the one-side end 541a against the negative electrode current collector plate is increased in order to reduce the electrode body height in order to achieve a high capacity cylindrical battery. The risk of deformation also arises when welding one side end of the exposed portion of the positive electrode substrate to the positive electrode current collector plate. Therefore, the objective of the present disclosure is to provide a cylindrical battery that can suppress the occurrence of load concentration areas in the electrode mixture layer and facilitates the realization of a high capacity.

[0009] In order to solve the above problems, the cylindrical battery of the present disclosure comprises an electrode body in which a first electrode has a first electrode core and a first electrode mixture layer arranged on the first electrode core, with a first electrode core exposed portion provided at one end in the first electrode width direction and both end ends in the first electrode longitudinal direction, and a second electrode has a second electrode core and a second electrode mixture layer arranged on the second electrode core, the two electrodes being wound together with a separator interposed therebetween, and an outer can that houses the electrode body, wherein the first electrode mixture layer has a recess that is recessed toward the center in the first electrode width direction at one of a total of four corners present at the start and end of winding in the first electrode longitudinal direction, and the length of the recess in the first electrode longitudinal direction is 1 / 5 or less of the length of the first electrode in the first electrode longitudinal direction.

[0010] According to the cylindrical battery according to the present disclosure, it is possible to prevent the occurrence of load concentration portions in the first electrode mixture layer, and it is easy to achieve a high capacity.

[0011] FIG. 1 is an 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 body and a positive electrode lead. FIG. 3 is a perspective view of a negative electrode current collector. FIG. 4 is a plan view of the negative electrode current collector as viewed from below. FIG. 5 is a plan view of the inner winding surface of the negative electrode when developed into a strip shape. FIG. 6 is a plan view of the corresponding surface of the inner winding surface of a negative electrode in the middle of manufacture when developed into a strip shape. FIG. 7 is a schematic view of the negative electrode of the first reference example developed into a long shape. FIG. 8 is a schematic view of the negative electrode of the second reference example developed into a long shape. FIG. 9 is a schematic view of the negative electrode of the third reference example developed into a long shape. 6A is a schematic cross-sectional view of a negative electrode of a modified example developed into a long strip, cut along a plane that passes through the negative electrode mixture layer and includes the negative electrode longitudinal direction and the negative electrode thickness direction, (b) is a plan view of the negative electrode of the modified example as viewed from the outside in the thickness direction of the negative electrode indicated by arrow A in (a), (c) is a cross-sectional view of line A-A in (a), which is a schematic cross-sectional view of a first layer cut along a plane perpendicular to the thickness direction of the negative electrode, and (d) is a cross-sectional view of line B-B in (a), which is a schematic cross-sectional view of a negative electrode of a fourth reference example during production.

[0012] Hereinafter, a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. Hereinafter, a cylindrical lithium-ion battery having a nonaqueous electrolyte will be described as an example of a cylindrical battery, but the cylindrical battery according to the present disclosure is not limited to this. The cylindrical battery according to the present disclosure may be a primary battery or a secondary battery. Furthermore, the cylindrical battery according to the present disclosure is not limited to a battery having a nonaqueous electrolyte, and may also be a battery having an aqueous electrolyte.

[0013] When multiple embodiments and variations are included below, it is anticipated from the beginning that new embodiments can be constructed by appropriately combining their characteristic features. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple 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 side of the sealing body 17 in the axial direction (height direction) is referred to as the upper side, and the side of the bottom 68 of the outer can 16 in the axial direction is referred to as the lower side. Furthermore, in the following description, the radial direction refers to the radial direction of the outer can 16, which coincides with the radial direction of the cylindrical battery 10. Furthermore, the circumferential direction refers to the circumferential direction of the outer can 16, which coincides with the circumferential direction of the cylindrical battery 10. Furthermore, among the components described below, components not recited in the independent claims representing the highest concepts are optional components and not required components.

[0014] Fig. 1 is an axial cross-sectional view of a cylindrical battery 10 according to one embodiment of the present disclosure. As shown in Fig. 1, the cylindrical battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical outer can 16 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17 that seals the opening of the outer can 16 via a gasket 28.

[0015] FIG. 2 is a perspective view showing a portion of the electrode assembly 14 and the positive electrode lead 20. Note that in FIG. 2, the positive electrode mixture layer 32 and the negative electrode mixture layer 42 are indicated by diagonal hatching. 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. In this embodiment, the negative electrode 12 constitutes a first electrode, and the positive electrode 11 constitutes a second electrode. 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. In this embodiment, eight positive electrode leads 20 are joined to the positive electrode 11 at intervals from one another in the longitudinal direction of the positive electrode.

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

[0017] A negative electrode core exposed portion 41, where the negative electrode mixture layer 42 is not disposed on the negative electrode core 40, is provided at the lower end of the negative electrode 12 in the negative electrode width direction from the winding start end to the winding end in the negative electrode longitudinal direction, and at both ends in the negative electrode longitudinal direction. The negative electrode core 40 is an example of a first electrode core, and the negative electrode mixture layer 42 is an example of a first electrode mixture layer. The negative electrode core exposed portion 41 is an example of a first electrode core exposed portion, and the negative electrode width direction is an example of a first electrode width direction. The negative electrode longitudinal direction is an example of a first electrode longitudinal direction. The axial lower end of the electrode assembly 14 is formed by a part of the negative electrode core exposed portion 41. The negative electrode 12 may form the winding start end of the electrode assembly 14. However, typically, the separator 13 extends beyond the winding start end of the negative electrode 12, and the winding start end of the separator 13 becomes the winding start end of the electrode assembly 14.

[0018] 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

[0019] 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.).

[0020] As shown in FIG. 2 , the positive electrode 11 includes a positive electrode core 30 and positive electrode mixture layers 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 is an example of a second electrode core, and the positive electrode mixture layers 32 are an example of a second electrode mixture layer. 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 includes 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, and the like onto 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, polyethylene oxide (PEO), and the like.

[0023] The positive electrode 11 has one or more positive electrode core exposed portions (not shown) where the positive electrode core is exposed, and in this embodiment, the positive electrode 11 has eight positive electrode core exposed portions arranged at intervals in the longitudinal direction of the positive electrode. Positive electrode leads 20 are joined to the positive electrode core exposed portions one by one by ultrasonic welding or the like. Effectively shortening the positive electrode side current path increases the reduction in electrical resistance, so it is preferable that the center positions of the eight positive electrode leads 20 in the longitudinal direction of the positive electrode be arranged at approximately equal intervals in the longitudinal direction of the positive electrode.

[0024] 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. For the negative electrode core 40, 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, can be used. 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, etc., onto 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.

[0025] 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 5.0 mass% or more. Furthermore, it is preferable that 3.0 mass% or more of the negative electrode mixture layer 42 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.

[0026] 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.

[0027] 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.

[0028] 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 a positive electrode current collector 26 and a terminal cap 27. The positive electrode current collector 26 is a metal annular plate member with a through-hole 26a in its radial center.

[0029] Terminal cap 27 is a metal plate-like member without a through hole and is located axially above sealing body 17. The axially upper end face of terminal cap 27 is exposed to the outside except for the outer edge, and this exposed portion forms the positive electrode terminal. Sealing body 17 further has a metal plate 25. Metal plate 25 is a metal annular member with a through hole.

[0030] Each positive electrode lead 20 is bent from the positive electrode 11 through the through hole 26a of the positive electrode collector plate 26 so as to fit along the upper surface of the positive electrode collector plate 26. The tip of each positive electrode lead 20 is sandwiched between the upper surface of the positive electrode collector plate 26 and the lower surface of the metal plate 25. Each positive electrode lead 20 is joined to the upper surface of the positive electrode collector plate 26. The positive electrode collector plate 26 and the metal plate 25 are also joined, and each positive electrode lead 20 and the metal plate 25 are also joined. These joints can be achieved, for example, by laser welding the tip of each positive electrode lead 20 sandwiched between the positive electrode collector plate 26 and the metal plate 25 by irradiating the metal plate 25 with a laser beam in the axial direction from above. By laser welding the tip of the positive electrode lead 20 sandwiched between the positive electrode collector plate 26 and the metal plate 25, the positive electrode lead 20 can be reliably and easily welded and joined to the positive electrode collector plate 26.

[0031] The sealing body 17 has a laminated portion 35 on its outer periphery, in which a terminal cap 27 and a positive current collector plate 26 are laminated. By irradiating the laminated portion 35 with a laser beam from above, the terminal cap 27 and the positive current collector plate 26 are laser-welded and electrically connected. The annular upper surface of the positive current collector plate 26 has an annular recess 31 radially inward from the laminated portion 35. Because the upper surface of the positive current collector plate 26 has the recess 31 recessed downward, a space is provided between the terminal cap 27 and the recess 31 of the positive current collector plate 26. Each positive electrode lead 20 is joined to the positive current collector plate 26 within the recess 31. The positive electrode collector plate 26 does not have to be joined to the metal plate 25, and the positive electrode lead 20 does not have to be joined to the metal plate 25. The battery does not have to include the metal plate 25. The positive electrode lead 20 may also be joined to the lower surface of the positive current collector plate 26.

[0032] The battery 10 has a metal negative current collector 19 axially below the electrode body 14. FIG. 3 is a perspective view of the negative current collector 19, and FIG. 4 is a plan view of the negative current collector 19 as viewed from below. As shown in FIGS. 3 and 4 , the negative current collector 19 has a flat plate portion 51 that is approximately circular in plan view in the radial center. The flat plate portion 51 may have any flat plate shape other than a circular shape, such as a rectangular shape. The negative current collector 19 also has multiple radially extending portions 53 connected to the flat plate portion 51. In this embodiment, the negative current collector 19 has four radially extending portions 53. The radially extending portions 53 have a columnar shape and extend in the radial direction. Preferably, the multiple radially extending portions 53 are arranged at equal intervals in the circumferential direction.

[0033] As shown in FIG. 1 , the radially extending portion 53 is connected to the flat portion 51 via a step portion 54, and the bottom surface of the flat portion 51 is located below the bottom surface of the radially extending portion 53. This allows the bottom surface of the flat portion 51 to be tightly attached to the inner surface of the bottom portion 68 of the outer can 16 when the flat portion 51 is joined to the bottom portion 68, as described below, without any gaps, making it easier to achieve good joining of the flat portion 51. As shown in FIG. 3 , the radially extending portion 53 has a protrusion 56 on its upper side. The protrusion 56 is provided at the widthwise center of the radially extending portion 53 and protrudes in the thickness direction. The protrusion 56 extends radially. A groove 57 extending radially is provided on the lower surface of the radially extending portion 53 at a location overlapping the protrusion 56 in the thickness direction. The widthwise center of the lower surface of the radially extending portion 53 is pressed upward in the thickness direction by a predetermined radial distance. By this press working, the protrusions 56 and the grooves 57 are formed.

[0034] A lower portion (lower end) 41a (see FIG. 2 ) constituting the lower end of the electrode assembly 14 in the negative electrode core exposed portion 41 is joined to the protrusion 56. Specifically, with the lower portion 41a pressed against the protrusion 56, a laser beam is irradiated from below toward the bottom of the groove 57. This laser beam irradiates the lower portion 41a to the protrusion 56 by laser welding over a wide radial area. Then, with a presser rod (not shown) inserted from above into the hollow portion 14a (see FIG. 1 ) of the electrode assembly 14 pressing the upper surface of the flat portion 51 against the inner surface of the bottom 68 of the outer can 16, a laser beam is irradiated from below the outer can 16, thereby laser welding the bottom 68 to the negative electrode current collector plate 19. This electrically connects the negative electrode 12 of the electrode assembly 14 to the outer can 16 via the negative electrode current collector plate 19. By joining the lower portion 41 a to the upper surface of the negative electrode current collector plate 19 over a wide area in the negative electrode longitudinal direction, it is possible to prevent current from flowing long distances in the negative electrode longitudinal direction of the negative electrode 12, thereby reducing the electrical resistance of the battery 10. The lower portion 41 a is an example of one side portion of the first electrode core exposed portion.

[0035] As shown in FIG. 1 , the outer can 16 has a cylindrical portion 39 and a bottom portion 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.

[0036] 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 insulator 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 lower portion 41 a via the negative electrode current collector plate 19 serves as a negative electrode terminal.

[0037] 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 provided, for example, by stamping a circle or a C-shape on the underside of the bottom 68. If the easily breakable portion 68a is provided on the bottom 68, 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 improving the safety of the battery 10. The thin, easily breakable portion may also be provided on the terminal cap.

[0038] In the above description, the sealing body 17 does not have a rupture plate, and an easy-to-break 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 easy-to-break 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. Alternatively, the sealing body 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.

[0039] Next, the structure of the negative electrode mixture layer 42 of the battery 10 will be described in detail using Figures 5, 6, and 11. Figure 5 is a plan view of the inner winding surface 12a of the negative electrode 12 when it is unfolded into a strip shape. In Figure 5, the negative electrode mixture layer 42 is indicated by diagonal hatching. As shown in Figure 5, the inner winding surface 12a of the negative electrode 12 has negative electrode substrate exposed portions 41 at the lower end in the negative electrode longitudinal direction and at both ends in the negative electrode longitudinal direction.

[0040] The negative electrode mixture layer 42 on the inner surface 12a of the winding has a recess 70 recessed toward the center in the negative electrode width direction at one of four corners present at the winding start and end sides in the negative electrode longitudinal direction. In this embodiment, the negative electrode mixture layer 42 has a recess 70 recessed toward the center in the negative electrode width direction at the winding start end in the negative electrode longitudinal direction, at a position adjacent to the lower portion 41a. In a plan view when the negative electrode 12 is unfolded into a strip shape, the edge of the recess 70 may have any shape, such as a right angle, an inclined shape, or a curved shape. The edge of the recess 70 may have a quadratic curve shape, such as a circular arc, a hyperbolic shape, or a parabolic shape. The length of the recess 70 in the negative electrode longitudinal direction is ⅕ or less of the length of the negative electrode 12 in the negative electrode longitudinal direction.

[0041] The outer surface of the negative electrode 12 may have a negative electrode mixture layer 42 formed in the longitudinal direction of the negative electrode that is the same as or different from the inner surface 12a of the winding, but like the inner surface 12a, the outer surface of the negative electrode 12 also has a negative electrode substrate exposed portion at the lower end and both ends in the longitudinal direction of the negative electrode. The outer surface of the negative electrode 12 also has a recess recessed toward the center in the width direction of the negative electrode at one of a total of four corners that exist on the winding start side and winding end side in the longitudinal direction of the negative electrode.

[0042] The negative electrode 12 is fabricated, for example, as follows. FIG. 6 is a plan view of the surface corresponding to the winding inner surface 12a of the negative electrode 12 during production, when the surface is developed into a band shape. Note that in FIG. 6, the negative electrode mixture layer 42 is indicated by diagonal hatching. Referring to FIG. 6, the negative electrode mixture slurry is intermittently applied to the central portion in the negative electrode width direction of the band-shaped negative electrode core 40 at intervals in the longitudinal direction. During this intermittent application, when the discharge of the negative electrode mixture slurry starts, the opening of the nozzle from which the negative electrode mixture slurry is discharged is gradually widened so that the discharge amount of the negative electrode mixture slurry per unit time at the start of the discharge of the negative electrode mixture slurry is smaller than the discharge amount of the negative electrode mixture slurry per unit time when the nozzle opening is fully open.

[0043] Thereafter, drying or the like is performed to arrange a plurality of negative electrode mixture layers 42 at intervals in the negative electrode longitudinal direction of the negative electrode core 40, and then the negative electrode core 40 is cut at the widthwise center K1 and the longitudinal center K2 between adjacent negative electrode mixture layers 42 in the longitudinal direction, thereby producing a plurality of negative electrodes 12. By discharging the negative electrode mixture slurry in this manner, recesses 70 can be formed at the ends of the negative electrode mixture layers 42 in the negative electrode longitudinal direction that correspond to the start of discharging the negative electrode mixture slurry. In this method of producing the negative electrode 12, cutting the negative electrode core 40 at the widthwise center K1 produces a set of a negative electrode 12 in which the recesses 70 exist at the winding start end in the negative electrode longitudinal direction and a negative electrode 12 in which the recesses 70 exist at the winding end end in the negative electrode longitudinal direction.

[0044] Next, the effects of the battery 10 will be described. As described with reference to FIG. 11 , the present inventors have discovered that, when intermittently applying a negative electrode mixture slurry, fully opening the discharge port for the negative electrode mixture slurry at the start of application of the negative electrode mixture slurry and fully closing the discharge port at the end of application of the negative electrode mixture slurry easily results in a convex portion 570 protruding in the negative electrode width direction at a corner of the negative electrode mixture layer 542 corresponding to the end where application of the negative electrode mixture slurry began. Furthermore, the present inventors have also discovered that, when welding one side end 541 a of the negative electrode substrate exposed portion 541 in the negative electrode width direction (the portion corresponding to the lower portion 41 a in this embodiment) to the negative electrode current collector plate, pressing the one side end 541 a against the negative electrode current collector plate to ensure the necessary contact for welding tends to concentrate a load on the convex portion 570 protruding in the negative electrode width direction, posing a risk of deformation around the convex portion 570.

[0045] In contrast, in the battery 10 of the present disclosure, the negative electrode mixture layer 42 does not have any protrusions protruding in the negative electrode width direction at any of the four corners present at the start and end of the winding in the negative electrode longitudinal direction. Therefore, even if the lower portion 41 a of the negative electrode core exposed portion is pressed against the negative electrode current collector plate when welding the lower portion 41 a, excessive stress is not generated around the corners of the negative electrode mixture layer 42. This prevents deformation around the corners of the negative electrode mixture layer 42, thereby improving battery quality. Furthermore, the negative electrode longitudinal length (first electrode longitudinal length) d1 of the recess 70 is equal to or less than one-fifth the negative electrode longitudinal length d2 of the negative electrode 12, allowing the negative electrode mixture layer 42 to be effectively used for reaction, facilitating increased battery capacity. In this embodiment, when the length of the negative electrode mixture layer 42 in the negative electrode longitudinal direction is d3 and the length of a region of the negative electrode mixture layer 42 in the negative electrode longitudinal direction where no recess 70 exists is d4, the length d1 of the recess 70 in the negative electrode longitudinal direction is the value obtained by subtracting d4 from d3.

[0046] Since deformation of the lower portion 41 a can be effectively suppressed, the negative electrode width direction length (first electrode width direction length) d5 of the recess 70 is preferably 1 mm or more. As described above, this can suppress the formation of convex portions that protrude in the negative electrode width direction, and can suppress excessive stress from occurring around the corners of the negative electrode mixture layer 42.

[0047] If the negative electrode width direction length d5 ​​of the recess 70 is excessively large, the negative electrode longitudinal direction length (i.e., the length d1 of the recess 70) required for the negative electrode width direction length of the negative electrode mixture layer 42 to return to its original negative electrode width direction length d6 (the negative electrode width direction length of the negative electrode mixture layer 42 at a location where the recess 70 is not present) tends to be long, and the battery capacity tends to be small. Since this makes it easier to increase the battery capacity, the negative electrode width direction length d5 ​​of the recess 70 is preferably 20 mm or less. Note that in this embodiment, when the negative electrode width direction length of a region where the recess 70 is not present in the negative electrode width direction is d7, the negative electrode width direction length d5 ​​of the recess 70 is the value obtained by subtracting d7 from d6.

[0048] In order to effectively suppress lithium dendrites, it is preferable that the recess 70 does not face the positive electrode mixture layer 32 in the radial direction of the outer can 16. Furthermore, it is preferable that the thickness of an edge 77 that defines the recess 70 in the negative electrode mixture layer 42 is thinner than the thickness of a region of the negative electrode mixture layer 42 in the longitudinal direction where the recess 70 is not present. In other words, it is preferable that the thickness of the edge 77 that defines the recess 70 in the negative electrode mixture layer 42 is thinner than the thickness of a portion 78 of the negative electrode mixture layer 42 that is spaced apart from the recess 70 in the longitudinal direction of the negative electrode. This prevents the electrode body 14 from having a locally increased radial thickness, allowing the electrode body 14 to be wound up smoothly and efficiently. Furthermore, the circularity of the electrode body 14 is likely to be high, which facilitates uniform reactions, thereby improving battery performance and effectively suppressing, for example, capacity degradation.

[0049] Fig. 7 is a schematic diagram of the negative electrode 212 of the first reference example developed into a long shape, Fig. 8 is a schematic diagram of the negative electrode 312 of the second reference example developed into a long shape, and Fig. 9 is a schematic diagram of the negative electrode 412 of the third reference example developed into a long shape. The hatched areas in Figs. 7 to 9 are areas where the negative electrode mixture layers 242, 342, and 442 are arranged.

[0050] As shown in FIG. 7 , in the negative electrode 212 of the first reference example, the lower portions (lower ends) 241 a of the negative electrode substrate exposed portion 241 are spaced apart in the negative electrode longitudinal direction. Also, as shown in FIG. 8 , in the negative electrode 312 of the second reference example, the lower portions (lower ends) 341 a of the negative electrode substrate exposed portion 341 are not present at both ends in the negative electrode longitudinal direction. Also, as shown in FIG. 9 , in the negative electrode 412 of the third reference example, a notch 441 b is formed in the lower portion (lower end) 441 a of the negative electrode substrate exposed portion 441. In these cases, the rigidity of the lower portions 241 a, 341 a, 441 a is reduced, making the lower portions 241 a, 341 a, 441 a more easily crushed in the axial direction (height direction) of the electrode body. This reduces the load applied to the electrode body when welding the lower portions 241 a, 341 a, 441 a to the negative electrode current collector plate 19.

[0051] 2 , in this embodiment, the lower portion 41a of the negative electrode substrate exposed portion 41 has a band shape that extends from the winding start end to the winding end end in the longitudinal direction of the negative electrode 12, and the lower portion 41a does not have any notches. Therefore, the lower portion 41a has high rigidity and is less likely to be crushed in the axial direction, and the load that presses the lower portion 41a in the axial direction when the lower portion 41a is welded to the negative electrode current collector plate 19 is large. Therefore, the effect of the present disclosure, that is, deformation around the corners of the negative electrode mixture layer 42 can be suppressed, becomes remarkable.

[0052] The present disclosure is not limited to the above-described embodiment and its variations. Various improvements and modifications are possible within the scope of the claims of the present application and their equivalents. For example, in the above-described embodiment, the first electrode mixture layer is the negative electrode mixture layer 42, the negative electrode mixture layer 42 includes a corner having a recess 70, and the lower portion 41 a of the negative electrode core exposed portion 41 is welded to the negative electrode current collector plate 19. However, in a cylindrical battery in which one end of the positive electrode core exposed portion in the positive electrode width direction is welded to the positive electrode current collector plate, the first electrode mixture layer may be a positive electrode mixture layer, and the positive electrode mixture layer may include a corner having a recess. Note that the negative electrode mixture layer may include a corner having a recess, and the positive electrode mixture layer may also include a corner having a recess, and deformation around the corner of the negative electrode may be suppressed, and deformation around the corner of the positive electrode may also be suppressed.

[0053] Furthermore, the first electrode mixture layer may include a first layer disposed on the first electrode core and a second layer disposed on the first layer, the recess may include a first recess provided in the first layer and a second recess provided in the second layer, and the first recess may overlap at least a portion of the second recess in the thickness direction of the first electrode.

[0054] Next, this configuration will be described using Fig. 10 as an example in which the first electrode mixture layer is a negative electrode mixture layer 142. Fig. 10(a) is a schematic cross-sectional view of a modified negative electrode 112 developed into a long strip, cut along a plane that passes through the negative electrode mixture layer 142 and includes the negative electrode longitudinal direction and the negative electrode thickness direction. Fig. 10(b) is a plan view of the negative electrode 112 as viewed from the outside in the thickness direction of the negative electrode 112, as indicated by arrow A in Fig. 10(a).

[0055] Figure 10(c) is a cross-sectional view taken along line A-A in Figure 10(a) and is a schematic cross-sectional view of the first layer 146 cut along a plane perpendicular to the thickness direction of the negative electrode 112. Figure 10(d) is a cross-sectional view taken along line B-B in Figure 10(a) and is a schematic cross-sectional view of the second layer 147 cut along a plane perpendicular to the thickness direction of the negative electrode 112. In Figure 10, the first layer 146 is indicated by diagonal hatching, and the second layer 147 is indicated by dot hatching.

[0056] As shown in FIG. 10( a), the negative electrode 112 includes a negative electrode core 140 and a negative electrode mixture layer 142 disposed on the negative electrode core 140. The negative electrode mixture layer 142 has a first layer 146 disposed on the negative electrode core 140 and a second layer 147 disposed on the first layer 146. The first layer 146 and the second layer 147 have different ratios of conductive material and active material and have different physical properties. The first layer 146 has better adhesion than the second layer 147 and is less likely to peel off from the negative electrode core 140. On the other hand, the second layer 147 has better liquid absorption than the first layer 146, and the second layer 147 is easily impregnated with a nonaqueous electrolyte, allowing the reaction to occur efficiently.

[0057] As shown in FIG. 10( b), the negative electrode mixture layer 142 has a recess 170 recessed toward the center in the negative electrode width direction at one of four corners located at the winding start and winding end in the negative electrode longitudinal direction. In this embodiment, the recess 170 is recessed toward the center in the negative electrode width direction at the winding start end in the negative electrode longitudinal direction. The length of the recess 170 in the negative electrode longitudinal direction is ⅕ or less of the length of the negative electrode 112 in the negative electrode longitudinal direction. As shown in FIG. 10( c), the first layer 146 has a first recess 170a recessed toward the center in the negative electrode width direction at the winding start end in the negative electrode longitudinal direction. As shown in FIG. 10( d), the second layer 147 has a second recess 170b recessed toward the center in the negative electrode width direction at the winding start end in the negative electrode longitudinal direction.

[0058] The recesses 170 include a first recess 170a provided in the first layer 146 and a second recess 170b provided in the second layer 147, and the first recess 170a overlaps at least a portion of the second recess 170b in the thickness direction of the negative electrode 112. In the present embodiment, all of the first recesses 170a overlap substantially all of the second recesses 170b in the thickness direction of the negative electrode 112. Even when the modified negative electrode 112 is used, it is possible to prevent load concentration portions from occurring in the negative electrode mixture layer 142, making it easier to achieve a high capacity.

[0059] The cylindrical battery of the present disclosure may also have the following configurations: Configuration 1: A cylindrical battery comprising: an electrode assembly in which a first electrode having a first electrode core and a first electrode mixture layer disposed on the first electrode core, the first electrode core having first electrode core exposed portions at one end in the first electrode width direction and both end ends in the first electrode longitudinal direction, and a second electrode having a second electrode core and a second electrode mixture layer disposed on the second electrode core, are wound together with a separator interposed therebetween; and an outer can that houses the electrode assembly, wherein the first electrode mixture layer has a recess recessed toward the center in the first electrode width direction at one of a total of four corners present at the start and end of winding in the first electrode longitudinal direction, and the length of the recess in the first electrode longitudinal direction is one-fifth or less of the length of the first electrode in the first electrode longitudinal direction. Configuration 2: The cylindrical battery according to Configuration 1, in which the length of the recess in the first electrode width direction is 1 mm or more. Configuration 3: The cylindrical battery according to Configuration 1 or 2, wherein the length of the recess in the first electrode width direction is 20 mm or less.Configuration 4: The cylindrical battery according to any one of Configurations 1 to 3, wherein the length of the recess in the first electrode longitudinal direction is 20 mm or less.Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein the recess does not face the second electrode mixture layer in the radial direction of the outer can.Configuration 6: The cylindrical battery according to any one of Configurations 1 to 5, wherein the thickness of an edge defining the recess in the first electrode mixture layer is thinner than the thickness of a portion of the first electrode mixture layer spaced apart from the recess in the first electrode longitudinal direction.Configuration 7: The cylindrical battery according to any one of Configurations 1 to 6, wherein the edge of the recess is right-angled, inclined, or arc-shaped. The cylindrical battery of any one of configurations 1 to 7, wherein the first electrode core exposed portion has a band shape extending from a winding start end to a winding end end in the longitudinal direction of the first electrode of the first electrode, and the one side portion has no notch. The cylindrical battery of any one of configurations 1 to 8, wherein the first electrode mixture layer includes a first layer disposed on the first electrode core and a second layer disposed on the first layer, the recesses include a first recess provided in the first layer and a second recess provided in the second layer, and the first recess overlaps at least a portion of the second recess in the thickness direction of the first electrode.

[0060] REFERENCE SIGNS LIST 10 Battery, 11 Positive electrode, 12, 112 Negative electrode, 12a Winding inner surface, 13 Separator, 14 Electrode body, 14a Hollow portion, 16 Outer can, 17 Sealing body, 18 Insulating plate, 19 Negative electrode current collector, 20 Positive electrode lead, 22 Grooved portion, 25 Metal plate, 26 Positive electrode current collector, 26a Through hole, 27 Terminal cap, 28 Gasket, 29 Shoulder portion, 30 Positive electrode core, 31 Recess, 32 Positive electrode mixture layer, 35 Laminated portion, 39 Cylindrical portion, 40, 140 Negative electrode core, 41 Negative electrode core exposed portion, 41a Lower portion of negative electrode core exposed portion, 42, 142 Negative electrode mixture layer, 51 Flat plate portion, 53 radially extending portion, 54 step portion, 56 ridge portion, 57 groove portion, 68 bottom portion, 68a easily breakable portion, 70, 170 recess portion, 146 first layer, 147 second layer, 170a first recess portion, 170b second recess portion.

Claims

1. A cylindrical battery comprising: an electrode assembly in which a first electrode having a first electrode core and a first electrode mixture layer disposed on the first electrode core, with a first electrode core exposed portion provided at one end in the first electrode width direction and both ends in the first electrode longitudinal direction, and a second electrode having a second electrode core and a second electrode mixture layer disposed on the second electrode core, are wound together with a separator interposed therebetween; and an outer can that houses the electrode assembly, wherein the first electrode mixture layer has a recess that is recessed toward the center in the first electrode width direction at one of a total of four corners present at the start and end of winding in the first electrode longitudinal direction, and the length of the recess in the first electrode longitudinal direction is 1 / 5 or less of the length of the first electrode in the first electrode longitudinal direction.

2. The cylindrical battery according to claim 1, wherein the length of the recess in the width direction of the first electrode is 1 mm or more.

3. The cylindrical battery according to claim 1 or 2, wherein the length of the recess in the width direction of the first electrode is 20 mm or less.

4. The cylindrical battery according to claim 1 or 2, wherein the length of the recess in the longitudinal direction of the first electrode is 20 mm or less.

5. The cylindrical battery according to claim 1 or 2, wherein the recess does not face the second electrode mixture layer in the radial direction of the outer can.

6. A cylindrical battery as described in claim 1 or 2, wherein the thickness of the edge defining the recess in the first electrode mixture layer is thinner than the thickness of a portion of the first electrode mixture layer that is spaced apart from the recess in the longitudinal direction of the first electrode.

7. The cylindrical battery according to claim 1 or 2, wherein the edge of the recess is a right angle, an inclined shape, or an arc shape.

8. A cylindrical battery as described in claim 1 or 2, wherein one side portion of the first electrode core exposed portion constituting the one side end has a band shape extending from the winding start end to the winding end end in the longitudinal direction of the first electrode, and the one side portion does not have a notch.

9. The cylindrical battery according to claim 1 or 2, wherein the first electrode mixture layer includes a first layer disposed on the first electrode core and a second layer disposed on the first layer, the recesses include a first recess provided in the first layer and a second recess provided in the second layer, and the first recess overlaps at least a portion of the second recess in the thickness direction of the first electrode.

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