Cylindrical secondary battery

Abstract

A positive electrode (11) has one or more positive-electrode core exposed parts which are each adjacent to a positive electrode mixture layer in the positive electrode width direction and, in each of which, a positive electrode core is exposed. Positive electrode tabs (20) are joined to the positive-electrode core exposed parts one by one. At least a portion of a negative-electrode core body exposed part (43) comes into contact with the inner circumferential surface of an exterior can. A tape is attached to the outermost circumferential surface of an electrode body (14) so as to extend across at least a portion of a winding outer end (12a) of a negative electrode (12). The winding outer end (12a) of the negative electrode (12) is positioned outside a winding outer end (11a) of the positive electrode (11) by a length exceeding one turn.

Description

Cylindrical secondary battery

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

[0002] A conventional cylindrical secondary battery is described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a long positive electrode 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 disposed adjacent to the exposed portion of the positive electrode substrate to which the positive electrode tab is joined in the width direction of the positive electrode, the capacity increases and the battery performance improves. Also, when the outermost periphery of the electrode assembly includes the negative electrode substrate and the outermost negative electrode substrate is brought into contact with the inner circumferential surface of the outer can, the electrical resistance of the battery decreases and the heat dissipation performance improves.

[0005] However, as will be described in detail later, the present inventors have found that adopting these configurations to increase capacity, reduce electrical resistance, and improve heat dissipation can result in the formation of a gap between the outer end of the positive electrode and the opposing negative electrode mixture layer, which can lead to lithium precipitation around the negative electrode mixture layer. Lithium precipitation can damage the separator. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can easily increase capacity, reduce electrical resistance, and suppress lithium precipitation on the outer periphery of the electrode assembly.

[0006] In order to solve the above problems, a cylindrical secondary battery according to the present disclosure 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 that houses the electrode assembly, and a sealing body that is fixed to the opening of the outer can by crimping 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, and the negative electrode has a long negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, and the positive electrode is adjacent to the positive electrode mixture layer in the positive electrode width direction. Both have one or more positive electrode core exposed portions where the positive electrode core is exposed, and are equipped with positive electrode tabs joined one by one to the positive electrode core exposed portions, the negative electrode core exposed portions where the negative electrode core is exposed constitute at least the outermost winding end portion of the electrode body, at least a portion of the negative electrode core exposed portion contacts the inner peripheral surface of the outer can, and are equipped with tape attached to the outermost peripheral surface of the electrode body so as to straddle at least a portion of the outer winding end of the negative electrode, and the outer winding end of the negative electrode is located outside the winding by a length that exceeds one turn of the positive electrode.

[0007] In this specification, the outer winding end of an electrode (positive electrode, negative electrode) is defined as the outer edge of the electrode in the longitudinal direction of the electrode, and the inner winding end of the electrode is defined as the inner edge of the electrode in the longitudinal direction of the electrode.

[0008] The fact that the outer end of the negative electrode is located on the outer side of the outer end of the positive electrode by a length that exceeds one revolution corresponds to the fact that the circumferential length from the first point, which is located on the outermost side of the opposing points on the negative electrode that are radially opposed to the outer end of the positive electrode, to the second point, which is located on the outermost side of the outer end of the negative electrode, is a circumferential length that exceeds one revolution.

[0009] According to the cylindrical secondary battery according to the present disclosure, it is easy to increase the capacity, it is easy to reduce the electrical resistance, and it is also possible to suppress lithium deposition on the outer periphery of the electrode body.

[0010] 1 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure. FIG. 2 is a perspective view showing a portion of an electrode assembly and a positive electrode tab. FIG. 3 is a plan view showing the wound inner surface of a positive electrode. FIG. 4 is a schematic radial cross-sectional view of the electrode assembly α layer corresponding portion of a cylindrical secondary battery of a comparative example before charging. FIG. 5 is a perspective view of an electrode assembly of a cylindrical secondary battery of a comparative example before charging. FIG. 6 is a schematic radial cross-sectional view of the electrode assembly α layer corresponding portion of a cylindrical secondary battery of a comparative example during charging. FIG. 7 is a perspective view of an electrode assembly of a cylindrical secondary battery of a comparative example during charging. FIG. 8 is a schematic radial cross-sectional view of the electrode assembly α layer corresponding portion of a cylindrical secondary battery of a comparative example during discharging. FIG. 9 is a schematic cross-sectional view corresponding to FIG. 8 of a cylindrical secondary battery according to an embodiment. FIG. 10 is a diagram illustrating the structure of an electrode assembly of a cylindrical battery of a comparative example and the electrode assembly of the cylindrical batteries of Examples 1-6.

[0011] 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.

[0012] 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."

[0013] In this specification, the number of revolutions (perimeter) of electrodes (positive electrode, negative electrode) is defined as follows: In a cross section of a cylindrical secondary battery in the radial 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 casing is defined as the center of polar coordinates, and the position of the innermost point at the inner end of the electrode is defined as 0 degrees. In this case, if the change in angle when moving from a reference point on the electrode in the longitudinal direction of the electrode is defined as θ, the number of revolutions is defined as θ÷360. For example, a position 1080 degrees forward is 1080÷360=3.0 revolutions (a perimeter of 3.0 revolutions). Angles at points on the electrode that are at the same position in the longitudinal direction of the electrode are defined as being the same.

[0014] 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.

[0015] 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.

[0016] 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

[0017] 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.).

[0018] 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, and 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.

[0019] The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. 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.

[0020] 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 (lower end in the negative electrode width direction) from the inner winding end to the outer winding end in the negative electrode longitudinal direction of the long negative electrode 12. The axial lower end of the electrode body 14 is constituted by the negative electrode substrate exposed portion 41. Furthermore, the outermost periphery of the electrode body 14 has a negative electrode substrate exposed portion 43 at least at the outer winding end. At least a portion of the negative electrode substrate exposed portion 43 contacts the inner circumferential surface of the outer can 16.

[0021] The outer end 12a of the negative electrode 12, i.e., the outer edge of the negative electrode 12 in the longitudinal direction of the negative electrode, is located outside the outer end 11a of the positive electrode, i.e., the outer edge of the positive electrode 11 in the longitudinal direction of the positive electrode, by a length greater than one circumference. In this embodiment, the outer end 12a of the negative electrode 12, i.e., the outer edge of the negative electrode 12 in the longitudinal direction of the negative electrode, extends entirely in the longitudinal direction of the negative electrode. However, the outer end of the negative electrode (the outer edge of the negative electrode in the longitudinal direction of the negative electrode) may include a portion inclined with respect to the longitudinal direction of the negative electrode. The preferred length from the outer end of the positive electrode to the outer end of the negative electrode and the preferred shape of the outer end of the negative electrode will be described in detail later using FIG. 10 . The negative electrode 12 may constitute the inner end of the electrode body 14. However, in general, the separator 13 extends beyond the inner end of the negative electrode 12 , and the inner end of the separator 13 becomes the inner end of the electrode assembly 14 .

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 3 is a plan view showing the winding inner surface 15 of the positive electrode 11, and is a plan view illustrating the formation 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. The hatched area in FIG. 3 is the arrangement area of ​​the positive electrode mixture layer 32. In this embodiment, a case where the positive electrode tab 20 is joined to the winding inner surface 15 of the positive electrode 11 is described, but the positive electrode tab may also be joined to the winding outer surface of the positive electrode.

[0026] 3 , the positive electrode 11 has one or more positive electrode core exposed portions 35 that are adjacent to the positive electrode mixture layer 32 in the positive electrode width direction and where the positive electrode core 30 is exposed, and in this embodiment, there are eight positive electrode core exposed portions 35. In order to shorten the current collection path on the positive electrode side and effectively reduce electrical resistance, it is preferable that there be six or more positive electrode core exposed portions 35 that are adjacent to the positive electrode mixture layer 32 in the positive electrode width direction and where the positive electrode core 30 is exposed.

[0027] A positive electrode tab 20 is bonded to each positive electrode core exposed portion 35. A portion 32a of the positive electrode mixture layer 32 is disposed adjacent to the positive electrode core exposed portion 35 in the positive electrode width direction, thereby increasing the capacity. The center positions of the eight positive electrode core exposed portions 35 in the positive electrode longitudinal direction are preferably disposed at approximately equal intervals in the positive electrode longitudinal direction. The positive electrode tabs 20 are preferably bonded to the positive electrode core exposed portions 35 by ultrasonic welding or the like, with their widthwise center positions approximately aligned with the center positions of the corresponding positive electrode core exposed portions 35 in the positive electrode longitudinal direction. The positive electrode tabs 20 are covered, for example, with insulating tape (not shown), thereby suppressing short circuits between the positive electrode 11 and the negative electrode 12. The insulating tape preferably covers the entire positive electrode core exposed portion 35.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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. Furthermore, as described above, at least a portion of the negative electrode core exposed portion 43 provided on the outermost periphery of the electrode body 14 contacts the inner circumferential surface of the outer can 16. Therefore, the negative electrode core 40 can be brought into contact with the outer can 16 over a wide area on the outermost periphery of the electrode body 14, which also reduces the electrical resistance of the battery 10.

[0037] In the above description, the negative electrode substrate exposed portion 41 is electrically connected to the outer can 16 via the lower current collector plate 52. However, it is sufficient that at least a portion of the negative electrode substrate exposed portion 43 provided on the outermost periphery of the electrode assembly 14 contacts the inner circumferential surface of the outer can 16, and the lower end of the electrode assembly 14 does not have to be configured with a strip-shaped negative electrode substrate exposed portion 41. For example, the negative electrode may have an inner-winding substrate exposed portion where the negative electrode substrate is exposed at the inner-winding end in the longitudinal direction of the negative electrode. One end of the negative electrode lead may be joined to the inner-winding substrate exposed portion, and the other end of the negative electrode lead may be joined to the inner bottom surface of the outer can.

[0038] 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 along 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.

[0039] 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.

[0040] The battery 10 includes a tape (fastening tape) 70 attached to the outermost surface of the electrode assembly 14 so as to straddle at least a portion of the outer winding end 12a (see FIG. 2 ) of the negative electrode 12 that constitutes the outer winding end of the battery 10. The tape 70 is, for example, an insulating tape. The attachment of the tape 70 prevents the electrode assembly 14 from coming apart. The battery 10 includes, for example, two tapes 70 spaced apart in the axial direction. The tape 70 is, for example, attached to the outermost surface of the electrode assembly 14 over the entire circumference of the electrode assembly 14. The tape 70 has a thickness of approximately several tens of μm, and the electrode assembly 14 expands radially outward due to expansion of the negative electrode 12 during charging and discharging. Therefore, even when the tape 70 is attached to the outermost surface of the electrode assembly 14, at least a portion of the negative electrode core exposed portion 43 can be in contact with the inner circumferential surface of the outer can 16.

[0041] 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.

[0042] Next, using Figures 3 to 10, the effects derived from the relative position of the outer winding end 12a of the negative electrode 12 with respect to the outer winding end 11a of the positive electrode 11 will be described. Note that the separator is not shown in the schematic cross-sectional views of the electrode assembly in the following Figures 4, 6, 8, and 9. The present inventors have discovered that in a configuration in which a portion of the positive electrode mixture layer is provided adjacent to a positive electrode core to which a positive electrode lead is bonded in the positive electrode width direction, when charging and discharging is performed, a gap may be generated between the outer winding end of the positive electrode 11 and the opposing portion of the negative electrode mixture layer, and that this gap may lead to lithium precipitation around the negative electrode mixture layer portion. This is presumably due to the following mechanism.

[0043] 3 , the positive electrode 11 has an α layer having a positive electrode substrate exposed portion 35, and a β layer having no positive electrode substrate exposed portion 35 and consisting only of the positive electrode mixture layer 32. Because the α layer has the thin positive electrode substrate exposed portion 35, radial gaps are more likely to occur in the region of the electrode body 14 corresponding to the α layer than in the region of the electrode body 14 corresponding to the β layer.

[0044] In this context, as shown in Fig. 4, that is, a schematic radial cross-sectional view passing through the α layer in the electrode body 414 of the comparative example, the α layer and the β layer are connected in the positive electrode width direction, and therefore are wound at approximately the same radial interval before charge / discharge, and gaps are unlikely to occur between the positive electrode 411 and the negative electrode 412. Furthermore, as shown in Fig. 5, the tape 70 attached so as to straddle the outer wound end 412a of the negative electrode 412 of the electrode body 414 is not deformed.

[0045] When charging is then performed, the negative electrode 412 expands radially outward as indicated by arrow A in Fig. 6 , and the tape 70 is subjected to a radially outward force. Then, as shown in region R in Fig. 7 , at least a portion of the tape 70 undergoes plastic deformation so as to extend in the circumferential direction. Plastic deformation of the tape 70 is likely to occur near the outer winding end of the electrode body 414, i.e., the outer winding end 412a of the negative electrode 412.

[0046] When discharge is then performed, the negative electrode 412 contracts radially inward as indicated by arrow B in Fig. 8. However, since the electrode body 14 expands due to plastic deformation of the tape 70, it is presumed that a gap S is likely to occur in the region of the electrode body 14 corresponding to the α layer, particularly at the outer end of the winding where the positive electrode 411 has a high degree of freedom of movement in the radial direction, as shown in Fig. 8.

[0047] If radial gaps occur in the electrode body 414, the lithium ion concentration in the gaps increases, making lithium deposition more likely to occur and potentially damaging the separator. The present inventors have discovered that the occurrence of such gaps can be suppressed by taking the following measures.

[0048] Specifically, as shown in Fig. 8 , the gap S between the positive electrode 411 and the negative electrode 412 becomes smaller toward the inner side of the winding. In other words, the positive electrode 411 becomes less likely to move radially as it moves away from the outer winding end 412a toward the inner side of the winding. Therefore, as shown in Fig. 9 , by positioning the outer winding end 11a of the positive electrode 11 on the inner side of the winding by at least a predetermined distance from the outer winding end 12a of the negative electrode 12, the gap that occurs between the outer winding end of the positive electrode 11 and the opposing portion of the negative electrode mixture layer can be reduced to a size that makes lithium deposition less likely to occur.

[0049] The present inventors experimentally found a length from the outer winding end 11a of the positive electrode 11 to the outer winding end 12a of the negative electrode 12 that is less likely to cause lithium deposition on the outer periphery of the electrode assembly. Below, the batteries of Examples 1-6 and Comparative Example, as well as the test contents and test results, are described using FIG. 10 . In FIG. 10 , (a) is a plan view showing the inner winding surface of the positive electrode 11, and (b)-(h) are plan views showing the outer winding surfaces of the negative electrodes 12, 112, 212, and 312. The hatched area in (a) is the area where the positive electrode mixture layer is disposed, and the hatched area in (b)-(h) is the area where the negative electrode mixture device is disposed.

[0050] <Comparative Example> As shown in Figures 10(a) and (b) , in comparison with the battery having eight positive electrode tabs described in Figures 1 to 3 , the battery used as the comparative example is one that differs in that the outer winding end 412a of the negative electrode 412 is located one turn outside the outer winding end 11a of the positive electrode 11.

[0051] Example 1 As shown in FIGS. 10( a) and 10(c), the battery of Example 1 was a battery having the eight positive electrode tabs described in FIGS. 1 to 3, in which the outer winding end 12a of the negative electrode 12 was positioned 5 / 4 turns outside the outer winding end 11a of the positive electrode 11.

[0052] Example 2 As shown in FIGS. 10( a) and 10(d), the battery of Example 2 was a battery having eight positive electrode tabs as described with reference to FIGS. 1 to 3, in which the outer winding end 12 a of the negative electrode 12 was positioned 3 / 2 turns outside the outer winding end 11 a of the positive electrode 11.

[0053] Example 3 As shown in FIGS. 10( a) and 10(e), the battery of Example 3 was a battery having the eight positive electrode tabs described in FIGS. 1 to 3, in which the outer winding end 12a of the negative electrode 12 was positioned two turns outside the outer winding end 11a of the positive electrode 11.

[0054] Example 4 As shown in Figures 10(a) and 10(f), the battery of Example 4 differs from the battery with eight positive electrode tabs described in Figures 1 to 3 in that it uses a negative electrode 112 with a different shape of the outer winding end 112a. Specifically, in the battery of Example 4, a first end 133 of the outer winding end 112a of the negative electrode 112, which is closer to the exposed portion 35 of the positive electrode substrate in the negative electrode width direction, is positioned three-and-a-half turns outward from the outer winding end 11a of the positive electrode 11. Furthermore, a second end 134 of the outer winding end 112a of the negative electrode 112, which is opposite to the exposed portion 35 of the positive electrode substrate in the negative electrode width direction, is positioned one turn outward from the outer winding end 11a of the positive electrode 11. Furthermore, the outer winding end 112a is inclined inward from the first end 133 to the second end 134.

[0055] 10( a) and 10(g), the battery of Example 5 was a battery that differed from the battery having eight positive electrode tabs described in FIGS. 1 to 3 in that it used a negative electrode 212 having a different shape of the outer winding end 212a. Specifically, in the battery of Example 5, the negative electrode portion located closer to the positive electrode substrate exposed portion 35 in the negative electrode width direction than the negative electrode width direction position radially opposed to the positive electrode width direction position of the end 11b of the positive electrode substrate exposed portion 35 on the positive electrode mixture layer 32 side in the positive electrode width direction was designated as a first portion 240. In addition, the negative electrode portion of the negative electrode 212 other than the first portion 240 was designated as a second portion 250.

[0056] The first outer winding end 240a of the first portion 240 was positioned three-and-a-half turns outside the outer winding end 11a of the positive electrode 11. Furthermore, a first end 233 on the opposite side of the second outer winding end 250a of the second portion 250 from the first portion 240 side was positioned one turn outside the outer winding end 11a of the positive electrode 11. Furthermore, the outer winding end 212a of the negative electrode 212 was inclined inward from the second end 234 on the second portion 250 side of the first outer winding end 240a of the first portion 240 toward the first end 233.

[0057] Example 6 As shown in FIGS. 10( a) and 10(h), the battery of Example 6 differed from the battery with eight positive electrode tabs described in FIGS. 1 to 3 in that it used a negative electrode 312 with a different shape of outer winding end 312a. Specifically, in the battery of Example 6, the negative electrode portion located closer to the positive electrode substrate exposed portion 35 in the negative electrode width direction than the negative electrode width direction position radially opposite the positive electrode width direction position of the end 11b of the positive electrode substrate exposed portion 35 on the positive electrode mixture layer 32 side in the positive electrode width direction was designated as the first portion 340. The negative electrode portion of the negative electrode 312 other than the first portion 340 was designated as the second portion 350. The first outer winding end 340a of the first portion 340 was positioned three-and-a-half turns outward from the outer winding end 11a of the positive electrode 11. The second outer winding end 350a of the second portion 350 was positioned one turn outward from the outer winding end 11a of the positive electrode 11.

[0058] (Presence or absence of lithium deposition) For each battery, 10 samples were prepared, and each sample was subjected to constant voltage charging at an ambient temperature of 25° C. at a constant current of 0.3 C until the voltage reached 4.2 V, and then constant voltage charging at a voltage of 4.2 V until the current value reached 0.02 C. Thereafter, constant current discharging was performed at a constant current of 0.2 C until the battery voltage reached 2.3 V. After discharge, each sample battery was disassembled, and the presence or absence of lithium deposition was visually confirmed around the portion of the negative electrode mixture layer facing the outer end of the positive electrode in the radial direction.

[0059] (Resistance Measurement) Resistance was measured for one sample of each battery. Specifically, at an ambient temperature of 25°C, the battery was charged at a constant current of 0.3 C up to 3.75 V, and then at a constant voltage of 3.75 V down to 0.002 C. After a two-hour rest, the battery was discharged at a constant current of 0.5 C for 30 seconds. The resistance was calculated according to the following formula (1) using the voltage V0 after the two-hour rest and the voltage V1 after 10 seconds of 0.5 C discharge. The resistance was evaluated as a relative value when the resistance of the comparative battery was set to 100. Resistance = (V0 - V1) / 1.0 C (1)

[0060] Table 1 shows the test results for each battery. As shown in Table 1, the resistance values ​​were the same for all batteries. Furthermore, lithium deposition was confirmed in all samples of the comparative battery in which the length of the negative electrode (the length of the negative electrode from the outer end of the positive electrode winding) from the opposing portion of the outer end of the positive electrode winding was one turn. On the other hand, lithium deposition was confirmed in two samples of the battery of Example 1 in which the length of the negative electrode from the outer end of the positive electrode winding was 5 / 4 turns, but the lithium deposition confirmed was slight enough to cause unevenness in the negative electrode mixture layer. Furthermore, lithium deposition was not confirmed in the battery of Example 2-6 in which the length of the negative electrode from the outer end of the positive electrode winding was 3 / 2 turns or more.

[0061] This confirmed that lithium deposition was suppressed when the outer end of the negative electrode was positioned more than one turn outward from the outer end of the positive electrode, and that lithium deposition was effectively suppressed when the outer end of the negative electrode was positioned more than 5 / 4 of a turn outward from the outer end of the positive electrode. It was also confirmed that lithium deposition could be substantially prevented when the outer end of the negative electrode was positioned more than 3 / 2 of a turn outward from the outer end of the positive electrode.

[0062] Gaps on the outer periphery of the electrode assembly are likely to occur in the α layer-corresponding portion of the electrode assembly. Therefore, the occurrence of such gaps can be suppressed by increasing the longitudinal length of the α layer-corresponding side of the negative electrode. Therefore, as in the batteries of Examples 4-6, even if the longitudinal length of the α layer-corresponding side of the negative electrodes 112, 212, and 312 is made longer than the minimum longitudinal length of the β layer-corresponding side of the negative electrodes 112, 212, and 312, the occurrence of such gaps can be suppressed. Adopting such a configuration not only suppresses the occurrence of gaps on the outer periphery of the electrode assembly, but also reduces the cost of negative electrode materials, thereby reducing the manufacturing cost of the battery.

[0063] In large-diameter batteries in which the total length of the positive electrode in the longitudinal direction is 3000 mm or more, or in which 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, the radial stress of the battery due to the expansion of the negative electrode during charging tends to be large. Therefore, the lithium deposition suppression effect obtained by adopting the battery configuration of the present disclosure can be made significant. Furthermore, when the negative electrode contains Si, the negative electrode expands significantly during charging. Therefore, even in this case, the lithium deposition suppression effect obtained by adopting the battery configuration of the present disclosure can be made significant.

[0064] The cylindrical secondary battery of the present disclosure may have the following configurations: Configuration 1: An electrode assembly in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween; a cylindrical secondary battery comprising: an outer can that accommodates the electrode assembly; and a sealing body that is fixed to an opening of the outer can by crimping via a gasket; 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 that expose the positive electrode core; and positive electrode tabs are joined to the positive electrode core exposed portions, respectively; the negative electrode core exposed portions that expose the negative electrode core constitute at least an outer winding end portion of the outermost periphery of the electrode assembly; at least a part of the negative electrode core exposed portion contacts an inner circumferential surface of the outer can; and tape is attached to the outermost peripheral surface of the electrode assembly so as to straddle at least a part of the outer winding end of the negative electrode; and the outer winding end of the negative electrode is located outside the outer winding end of the positive electrode by a length that exceeds one full turn. A cylindrical secondary battery according to Aspect 2, wherein the outer end of the negative electrode is positioned at a distance of at least 3 / 2 turns outward from the outer end of the positive electrode. A cylindrical secondary battery according to Aspect 3, wherein a first end of the outer end of the negative electrode on the side of the exposed portion of the positive electrode substrate in the negative electrode width direction is positioned at a distance of at least 3 / 2 turns outward from the outer end of the positive electrode, and a second end of the outer end of the negative electrode on the opposite side to the exposed portion of the positive electrode substrate in the negative electrode width direction is positioned at a distance of at least one turn outward from the outer end of the positive electrode, and the outer end of the negative electrode is inclined inward from the first end to the second end. Configuration 4: When a negative electrode portion located closer to the positive electrode substrate exposed portion in the negative electrode width direction than a negative electrode width direction position that is radially opposed to a positive electrode width direction position of an end of the positive electrode substrate exposed portion on the positive electrode mixture layer side in the positive electrode width direction is defined as a first portion, and a negative electrode portion of the negative electrode other than the first portion is defined as a second portion, a first outer winding end of the first portion is located at a winding outer side of the positive electrode by at least three-half turns, a first end of a second outer winding end of the second portion that is opposite to the first portion side is located at a winding outer side of the positive electrode by at least one turn, and the outer winding end of the negative electrode is inclined inward from a second end of the first outer winding end of the first portion on the second portion sideConfiguration 5: The cylindrical secondary battery according to Configuration 1, wherein a first portion is a negative electrode portion located closer to the positive electrode substrate exposed portion in the negative electrode width direction than a negative electrode width direction position radially opposite to a positive electrode width direction position of an end of the positive electrode substrate exposed portion on the positive electrode mixture layer side in the positive electrode width direction, and a second portion is a negative electrode portion of the negative electrode other than the first portion. The first outer winding end of the first portion is located at a winding outer side of the outer winding end of the positive electrode by at least 3 / 2 turns, and the second outer winding end of the second portion is located at a winding outer side of the outer winding end of the positive electrode by at least 1 turn. Configuration 6: The cylindrical secondary battery according to any one of Configurations 1 to 5, wherein the length of the positive electrode in the positive electrode longitudinal direction 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 winding 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.

[0065] REFERENCE SIGNS LIST 10 Battery, 11 Positive electrode, 11a Outer winding end of positive electrode, 12, 112, 212, 312 Negative electrode, 12a, 112a, 212a, 312a Outer winding end of negative electrode, 13 Separator, 14 Electrode body, 15 Inner winding surface, 16 Outer can, 17 Sealing body, 18 Insulating plate, 20 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, 43 Negative electrode core exposed portion, 42 Negative electrode mixture layer, 43 Negative electrode core exposed portion, 50 Upper current collector plate 50a: Through hole, 51: Metal plate, 52: Lower current collecting plate, 60: Lamination portion, 65: Recess, 68: Bottom, 68a: Easily breakable portion, 70: Tape, 240, 340: First portion of negative electrode, 240a, 340a: Outer end of first portion, 250, 350: Second portion, 250a, 350a: Outer end of second portion.

Claims

1. An electrode assembly comprising an elongated positive electrode and an elongated negative electrode wound with a separator interposed therebetween; an outer can housing the electrode assembly; and a sealing body fixed to the opening of the outer can by crimping via a gasket, wherein the positive electrode has an elongated positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, the negative electrode has an elongated 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 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, each of which constitutes the outermost winding end of the electrode assembly, at least a portion of the negative electrode core exposed portion contacts the inner circumferential surface of the outer can, and a tape is attached to the outermost peripheral surface of the electrode assembly so as to straddle at least a portion of the outer winding end of the negative electrode, The cylindrical secondary battery has an outer end of the negative electrode positioned outside the outer end of the positive electrode by a length that exceeds one full turn.

2. The cylindrical secondary battery according to claim 1, wherein the outer end of the negative electrode is positioned at least 3 / 2 turns outside the outer end of the positive electrode.

3. The cylindrical secondary battery according to claim 1, wherein a first end of the outer winding end of the negative electrode on the side of the exposed portion of the positive electrode substrate in the negative electrode width direction is located at least 3 / 2 turns outward from the outer winding end of the positive electrode, a second end of the outer winding end of the negative electrode on the opposite side to the exposed portion of the positive electrode substrate in the negative electrode width direction is located at least one turn outward from the outer winding end of the positive electrode, and the outer winding end of the negative electrode is inclined inward from the first end to the second end.

4. The cylindrical secondary battery according to claim 1, wherein a first portion is a negative electrode portion located closer to the positive electrode substrate exposed portion in the negative electrode width direction than a negative electrode width direction position radially opposite to a positive electrode width direction position of an end of the positive electrode substrate exposed portion on the positive electrode mixture layer side in the positive electrode width direction, and a second portion is a negative electrode portion of the negative electrode other than the first portion, wherein a first outer winding end of the first portion is located at a winding outer side of the positive electrode outer winding end by 3 / 2 turns or more, a first end of the second outer winding end of the second portion opposite to the first portion side is located at a winding outer side of the positive electrode outer winding end by 1 turn or more, and the outer winding end of the negative electrode is inclined inward from a second end of the first outer winding end of the first portion on the second portion side to the first end.

5. The cylindrical secondary battery according to claim 1, wherein a first portion is a negative electrode portion located closer to the positive electrode substrate exposed portion in the negative electrode width direction than a negative electrode width direction position radially opposite to a positive electrode width direction position of an end of the positive electrode substrate exposed portion on the positive electrode mixture layer side in the positive electrode width direction, and a second portion is a negative electrode portion of the negative electrode other than the first portion, wherein a first outer winding end of the first portion is located at a winding outer side of the outer winding end of the positive electrode by at least 3 / 2 turns, and a second outer winding end of the second portion is located at a winding outer side of the outer winding end of the positive electrode by at least one turn.

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

7. The cylindrical secondary battery according to claim 1, 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.

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

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