Cylindrical secondary battery

Abstract

A positive electrode (11) has one or more positive electrode core exposed parts (35) which are adjacent to a positive electrode mixture layer (32) in the positive electrode width direction, and in which a positive electrode core (30) is exposed. Positive electrode tabs (20) are bonded one by one to the positive electrode core exposed parts (35). In the positive electrode core exposed parts (35), edges (37) adjacent to the positive electrode mixture layer (32) in the positive electrode width direction include a longitudinally extended edge (37a) extending substantially parallel to the positive electrode longitudinal direction. With regard to at least one of the positive electrode core exposed parts (35), when the elongation rate in the positive electrode longitudinal direction of the longitudinally extended edge (37a) after 100 charge-discharge cycles from a reference time is x%, the distance in the positive electrode width direction between the positive electrode tab (20) and the longitudinally extended edge (37a) is a mm, and the maximum length of the positive electrode core exposed part (35) in the positive electrode width direction is b mm, x ≥ 1% and a / b ≥ 2-3 / (2x) hold.

Description

Cylindrical secondary battery

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

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

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

[0004] Arranging a portion of the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion to which the positive electrode tab is joined in the positive electrode width direction increases capacity and improves battery performance. However, as described in detail below, the present inventors discovered that adopting this configuration makes the positive electrode substrate exposed portion susceptible to damage near the corner of the positive electrode substrate exposed portion on the positive electrode mixture layer side in the positive electrode width direction at the joining point of the positive electrode tab. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can easily achieve high capacity and reliability.

[0005] 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 has a cylindrical portion, and a sealing body that is fixed to an 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, 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 has one or more positive electrode core exposed portions that are adjacent to the positive electrode mixture layer in the positive electrode width direction and at which the positive electrode core is exposed , and positive electrode tabs joined one by one to the positive electrode substrate exposed portions, and the edge of the positive electrode substrate exposed portion adjacent to the positive electrode mixture layer in the positive electrode width direction includes a longitudinally extending edge that extends approximately parallel to the positive electrode longitudinal direction, and for at least one of the positive electrode substrate exposed portions, when the elongation rate in the positive electrode longitudinal direction of the longitudinally extending edge after 100 cycles of charge and discharge from a reference time is x %, the distance between the positive electrode tab and the longitudinally extending edge in the positive electrode width direction is a mm, and the maximum length of the positive electrode substrate exposed portion in the positive electrode width direction is b mm, then x≧1% and a / b≧2−3 / (2x) hold.

[0006] The reference time may be any time after the manufacture of the cylindrical secondary battery, for example, after shipment and before use after a person purchases the battery, or before pre-charging after manufacture, or after completion of pre-charging after manufacture and before shipment. In this specification, the conditions for the cycle are defined as a charge / discharge cycle in which the temperature range of the cylindrical secondary battery is 20°C to 45°C, and the OCV (voltage when no current is flowing through the battery) during charging is 4.1 V or higher and the OCV during discharging is 3.5 V or lower. The current values ​​during charging and discharging may be any values.

[0007] The cylindrical secondary battery according to the present disclosure can easily achieve high capacity and reliability.

[0008] 4 is an axial cross-sectional view of a cylindrical secondary battery according to an embodiment of the present disclosure; FIG. 5 is a perspective view showing a portion of an electrode body and a positive electrode tab; FIG. 6 is a development showing the inner wound surface of a positive electrode, and is a development illustrating the formation position and structure of a positive electrode substrate exposed portion to which a positive electrode tab is joined in the positive electrode; FIG. 7 is an enlarged view of the periphery of one positive electrode substrate exposed portion in FIG. 3; FIG. 8 is an enlarged view corresponding to FIG. 4 of a cylindrical secondary battery of a reference example; FIG. 9 is a diagram illustrating parameters that define the shape of a positive electrode substrate exposed portion; FIG. 10 is an enlarged view corresponding to FIG. 4 of a cylindrical secondary battery of a first modified example; FIG. 11 is an enlarged view corresponding to FIG. 4 of a cylindrical secondary battery of a second modified example.

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

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

[0011] In this specification, the number of revolutions is defined as follows: When viewing a cross section of a cylindrical battery in the axial direction (a cross section including the radial direction of the cylindrical battery), the center of the circle formed by the outer diameter of the outer can is the center of the polar coordinate system, and the position of the inner end of the positive electrode is set to 0 degrees. In this case, if the change in angle when moving from the inner end of the winding along the positive electrode is θ, the number of revolutions is defined as θ÷360. For example, a position 1080 degrees forward is 1080÷360=3.0 revolutions. Furthermore, among the components described below, components not recited in the independent claims representing the superordinate concept are optional components and not essential components.

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

[0013] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

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

[0015] FIG. 2 is a perspective view showing a portion of the electrode 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. It is preferable that a plurality of positive electrode tabs are joined to the positive electrode 11 at intervals in the positive electrode longitudinal direction, and it is more preferable that six or more positive electrode tabs 20 are joined to the positive electrode 11 at intervals in the positive electrode longitudinal direction. In this embodiment, eight positive electrode tabs 20 are joined to the positive electrode 11 at intervals from one another in the longitudinal direction.

[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 the axial direction. Two separators 13 are formed to be slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separator 13 protrudes upward beyond the positive electrode 11 and the negative electrode 12, and the negative electrode 12 protrudes downward beyond the positive electrode 11 and the separator 13.

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

[0018] The positive electrode 11 has a positive electrode core 30 (see FIG. 3 ) and positive electrode mixture layers 32 (see FIG. 3 ) formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The positive electrode mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layers 32 on both sides of the positive electrode core 30.

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

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

[0021] 3 is a development showing the winding inner surface 15 of the positive electrode 11, and is a development illustrating the formation position and structure of a positive electrode substrate exposed portion 35 to which the positive electrode tab 20 is joined in the positive electrode 11. The hatched area in FIGS. 3 to 8 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.

[0022] As shown in FIG. 3 , the positive electrode 11 has one or more positive electrode core exposed portions 35 adjacent to the positive electrode mixture layer 32 in the positive electrode width direction and where the positive electrode core 30 is exposed; in this embodiment, there are eight positive electrode core exposed portions 35. A positive electrode tab 20 is joined to each positive electrode core exposed portion 35. Since a portion of the positive electrode mixture layer 32 is arranged adjacent to the positive electrode core exposed portion 35 in the positive electrode width direction, the capacity is increased. To facilitate shortening the current collection path, it is preferable that the longitudinal center positions of the eight positive electrode core exposed portions 35 be arranged at approximately equal intervals in the positive electrode longitudinal direction.

[0023] The positive electrode tab 20 is joined to the positive electrode core exposed portion 35 by ultrasonic welding or the like, with its widthwise center position substantially coinciding with the longitudinal center position of the corresponding positive electrode core exposed portion 35. The positive electrode tab 20 is covered, for example, with insulating tape (not shown), thereby suppressing short-circuiting between the positive electrode 11 and the negative electrode 12. It is preferable that the insulating tape cover the entire positive electrode core exposed portion 35.

[0024] 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.

[0025] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials are graphites such as natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as 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, and the mass ratio of Si element in the negative electrode mixture layer 42 is preferably 5 mass% or more. The negative electrode active material may also be 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 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The case where the negative electrode substrate exposed portion 41 is electrically connected to the outer can 16 via the lower current collector plate 52 has been described. However, the negative electrode may have a first negative electrode substrate exposed portion where the negative electrode substrate is exposed at the inner end of the winding in the longitudinal direction of the negative electrode, and a second negative electrode substrate exposed portion where the negative electrode substrate is exposed at the outer end of the winding in the longitudinal direction of the negative electrode. Furthermore, the second negative electrode substrate exposed portion may have an outermost surface portion included in the outermost surface of the electrode assembly. Furthermore, one end of the negative electrode lead may be joined to the first negative electrode substrate exposed portion, and the other end of the negative electrode lead may be joined to the inner bottom surface of the outer can. Furthermore, the outermost surface portion may contact the inner circumferential surface of the outer can.

[0034] Alternatively, two negative electrode leads may be joined to the electrode body, with one end of one negative electrode lead electrically connected to the inner end of the negative electrode core in the negative electrode longitudinal direction, and one end of the other negative electrode lead electrically connected to the outer end of the negative electrode core in the negative electrode longitudinal direction. The other end of each negative electrode lead may then be electrically connected to the bottom of the outer can. Alternatively, the negative electrode and the outer can may be electrically connected via a single negative electrode tab.

[0035] The outer can 16 has a cylindrical portion 39 and a bottom 68. The cylindrical portion 39 includes an annular grooved portion 22 and an annular shoulder portion 29. The grooved portion 22 is formed by spinning a portion of the cylindrical portion 39 to recess it radially inward around the entire circumferential direction. The sealing body 17 is placed on the grooved portion 22 and is fixed to the opening of the outer can 16 by crimping via a resin gasket 28. The shoulder portion 29 is formed when the upper end of the cylindrical portion 39 is bent radially inward and crimped to the outer edge of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 39.

[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 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.

[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 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.

[0038] Next, the joining structure of the positive electrode tab 20 to the positive electrode substrate exposed portion 35 will be described in detail with reference to Fig. 4. Fig. 4 is an enlarged view of the periphery of one positive electrode substrate exposed portion in Fig. 3. As shown in Fig. 4, an edge 37 of the positive electrode substrate exposed portion 35 adjacent to the positive electrode mixture layer 32 in the positive electrode width direction includes a longitudinally extending edge 37a that extends approximately parallel to the longitudinal direction of the positive electrode.

[0039] With respect to at least one of the positive electrode substrate exposed portions 35 to which the positive electrode tab 20 is joined, when the elongation rate in the positive electrode longitudinal direction of the longitudinally extending edge 37a after 100 cycles of charge and discharge from a reference time is x%, the distance in the positive electrode width direction between the positive electrode tab 20 and the longitudinally extending edge 37a is a mm, and the maximum length in the positive electrode width direction of the positive electrode substrate exposed portion 35 is b mm, then x≧1% and a / b≧2−3 / (2x) are satisfied.

[0040] The reference time may be any time after the manufacture of the cylindrical secondary battery, for example, after shipment and before use of the battery after purchase, or before pre-charging after manufacture, or after completion of pre-charging after manufacture and before shipment. The cycle is defined as a charge / discharge cycle in which the temperature range of the cylindrical secondary battery is 20°C to 45°C, and the OCV (the voltage when no current is flowing through the battery) during charging is 4.1 V or higher and the OCV during discharging is 3.5 V or lower. With respect to the positive electrode substrate exposed portion 35 to which the positive electrode tab 20 is joined, the positive electrode tab 20 is joined from the inner end of the positive electrode 11 to the outer side of the winding number of turns of the positive electrode 11 × 0.35, it is preferable that x ≥ 1% and a / b ≥ 2-3 / (2x) be satisfied.

[0041] Next, the effects of the battery 10 of the present disclosure will be described. Fig. 5 is an enlarged view corresponding to Fig. 4 of a cylindrical secondary battery 310 of a reference example. In a configuration as shown in Fig. 5 in which the positive electrode mixture layer 332 includes an adjacent mixture layer 332a adjacent in the positive electrode width direction to the positive electrode core exposed portion 335 to which the positive electrode tab 320 is joined, during charging, the positive electrode mixture layer 332 expands in the positive electrode longitudinal direction so as to be pulled by the expansion in the negative electrode longitudinal direction of the negative electrode mixture layer opposite in the radial direction, while the positive electrode core exposed portion 335 does not expand in the positive electrode longitudinal direction.

[0042] Therefore, the elongation rate in the positive electrode longitudinal direction of the positive electrode core exposed portion 335 is greatest at the edge 335a that contacts the adjacent mixture layer 332a in the positive electrode width direction, gradually decreases as it moves away from the adjacent mixture layer 332a in the positive electrode width direction, and is smallest at the edge 335b on the opposite side from the adjacent mixture layer 332a in the positive electrode width direction.

[0043] Therefore, when the tip side of the positive electrode tab 320 is joined to the adjacent region of the adjacent mixture layer 332a as in the battery 310 of the reference example, excessive stress in the positive electrode longitudinal direction is likely to act on the adjacent region, where elongation in the positive electrode longitudinal direction is hindered by the joining of the positive electrode tab 320. Furthermore, damage is likely to occur in the positive electrode core exposed portion 335 near a corner 339 on the positive electrode core exposed portion 335's side in the positive electrode width direction, at the joining point of the positive electrode tab 320.

[0044] In contrast, as shown in Figure 4, in the battery 10 of the present disclosure, the positive electrode tab 20 is only joined in a range that satisfies a / b ≥ 2 - 3 / (2x), and is therefore less likely to be joined to a region of the positive electrode substrate exposed portion 35 where the elongation rate in the positive electrode longitudinal direction is large. For example, when x is 1%, a / b ≥ 0.5, and the positive electrode tab 20 can only be joined above half of the positive electrode width direction range of the positive electrode substrate exposed portion 35. Therefore, not only is it easy to increase the capacity, but the positive electrode substrate exposed portion 35 is less likely to be damaged, making it possible to produce a highly reliable battery 10.

[0045] The present inventors investigated the elongation rate in the positive electrode longitudinal direction of the longitudinally extending edge 37a and the presence or absence of foil tears in the positive electrode core after 100 cycles of charge and discharge for 10 samples each of the cylindrical secondary batteries of Examples 1-7 and Comparative Examples 1-5, which were varied in various dimensions of the positive electrode core exposed portion, the dimensions of the insulating tape attachment area, and the dimensions of the positive electrode tab bonding area in the positive electrode core exposed portion.

[0046] <Cylindrical Secondary Batteries of Examples 1-7 and Comparative Examples 1-5> Referring to FIG. 6 , in addition to the above-mentioned a mm and b mm, the length c mm in the positive electrode width direction at the inner end 435a of the positive electrode substrate exposed portion 435, the length d mm in the positive electrode width direction at the outer end 435b of the positive electrode substrate exposed portion 435, and the maximum length em mm in the positive electrode width direction of the rectangular insulating tape 450 applied so as to cover the entire positive electrode substrate exposed portion 435 were changed to fabricate cylindrical secondary batteries of Examples 1-7 and Comparative Examples 1-5. Each cylindrical secondary battery was fabricated by changing a, b, c, d, and e in the cylindrical secondary battery described using FIGS. 1 to 4 . The dimensions of the cylindrical secondary batteries of Examples 1-7 and Comparative Examples 1-5 are shown in Table 1 below.

[0047] <Measurement of Positive Electrode Substrate Elongation Percentage x> For each of the batteries of Examples 1-7 and Comparative Examples 1-5, a charge-discharge cycle was repeated 100 times over a temperature range of 20°C to 45°C, where the OCV (the voltage when no current is flowing through the battery) during charge was 4.1 V or higher and the OCV during discharge was 3.5 V or lower. More specifically, in an air-cooled environment at 45°C, after reaching 4.2 V at a constant current of 0.3 C, constant voltage charging was performed at a voltage of 4.2 V until the current value reached 0.02 C, and then constant current discharging was performed at a constant current of 0.5 C until the battery voltage reached 2.85 V. This charge-discharge cycle was repeated 100 times. The positive electrode substrate elongation percentage x was calculated by measuring the length of the longitudinally extending edge in CT (computed tomography) images of a cross-section perpendicular to the axial direction of the electrode body before and after 100 charge-discharge cycles. The positive electrode substrate elongation percentages x of the cylindrical secondary batteries of Examples 1-7 and Comparative Examples 1-5 are shown in Table 1.

[0048] The positive electrode substrate elongation rate x can be adjusted with high precision, for example, by adjusting the average aluminum crystal grain size of the aluminum foil constituting the positive electrode substrate. The average aluminum crystal grain size can also be adjusted with high precision by adjusting the heat treatment temperature of the positive electrode substrate or by adjusting the impurities mixed into the constituent material of the positive electrode substrate. The elongation rate of the longitudinally extending edge can be determined by actually performing 100 cycles of charge and discharge once the material of the positive electrode substrate and the material of the positive electrode mixture layer have been determined.

[0049] <Confirmation of Positive Electrode Core Breakage> After the 100 charge / discharge cycles described above, the presence or absence of foil breakage in the positive electrode core was visually confirmed based on CT images of a cross section perpendicular to the axial direction of the electrode assembly, that is, a CT image of the area around the lower end of the positive electrode tab. The percentage of samples in which foil breakage in the positive electrode core occurred was determined among 10 samples for each battery. The percentages are shown in Table 1.

[0050] As shown in Table 1, it was confirmed that the batteries of Example 1-7, in which positive electrode substrate breakage hardly occurred, had x≧1% and all a / b values ​​were greater than 2-3 / (2x). On the other hand, it was confirmed that the batteries of Comparative Example 1-5, in which positive electrode substrate breakage frequently occurred with a probability of 60% or more, all a / b values ​​were smaller than 2-3 / (2x). Therefore, when a / b≧2-3 / (2x) is produced, the capacity is likely to be large and damage is less likely to occur.

[0051] In a large-diameter battery having a total length in the positive electrode longitudinal direction of 3000 mm or more, or in a large-diameter battery having six or more exposed positive electrode core portions (six or more positive electrode tabs) joined to the positive electrode at intervals in the positive electrode longitudinal direction, the negative electrode tends to stretch in the negative electrode longitudinal direction during charging, and the positive electrode also tends to stretch in the positive electrode longitudinal direction. Therefore, the effect of suppressing damage to the positive electrode core that can be obtained by adopting the battery configuration of the present disclosure is likely to be significant.

[0052] When the mass ratio of Si element in the negative electrode mixture layer is 5 mass% or more, the negative electrode expands significantly during charging. Therefore, even in this case, the effect of suppressing damage to the positive electrode core, which can be obtained by adopting the battery configuration of the present disclosure, is likely to be significant.

[0053] The positive electrode does not elongate evenly in the longitudinal direction of the positive electrode, but is more severe on the outer side of the winding, where the space allowing for the positive electrode elongation is larger than on the inner side. Therefore, damage to the positive electrode core is more likely to occur on the outer side of the winding. Therefore, with regard to the exposed portion of the positive electrode core to which the positive electrode tab is joined, the number of turns from the inner end of the positive electrode winding to the outer side of the winding is greater than 0.35 times the total number of turns of the positive electrode, if x ≧ 1% and a / b ≧ 2-3 / (2x) are satisfied, damage to the positive electrode core can be effectively suppressed.

[0054] The present disclosure is not limited to the above-described embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0055] For example, in the above embodiment, the positive electrode substrate exposed portion 35 has a rectangular shape. However, as in the batteries of Examples 3 and 4, even if the maximum length of the positive electrode substrate exposed portion in the positive electrode width direction is longer than the length of at least one end of the positive electrode in the positive electrode longitudinal direction in the positive electrode width direction, damage to the positive electrode substrate can be effectively suppressed.

[0056] 7, that is, an enlarged view of a cylindrical secondary battery 110 of a first modified example corresponding to FIG. 4, the positive electrode substrate exposed portion 135 of the positive electrode 111 may have a rectangular first region 135a and a rectangular second region 135b that protrudes downward (toward the bottom of the can) from the longitudinal center of the first region 135a and has a longitudinal width greater than the width of the positive electrode tab 120. The boundary between the positive electrode substrate exposed portion 135 and the positive electrode mixture layer 132 may have a stepped shape.

[0057] Alternatively, as shown in FIG. 8 , that is, an enlarged view corresponding to FIG. 4 of a cylindrical secondary battery 210 of a second modified example, an edge (boundary) 237 between the positive electrode 211 and the positive electrode mixture layer 232 in the core exposed portion 235 to which the positive electrode tab 220 is joined may include, in addition to a longitudinally extending edge 237 a that is substantially parallel to the longitudinal direction of the positive electrode, at least one of an inclined edge 237 b that inclines upward (toward the sealing body) as it approaches the inside of the winding in the longitudinal direction of the positive electrode, and an inclined edge 237 c that inclines upward (toward the sealing body) as it approaches the outside of the winding in the longitudinal direction of the positive electrode.

[0058] In this way, the cylindrical secondary battery may include one or more positive electrode substrate exposed portions in which the maximum length in the positive electrode width direction within the range in the positive electrode longitudinal direction to which the positive electrode tab is joined is longer than the length in the positive electrode width direction at at least one of both ends in the positive electrode longitudinal direction. According to these battery variations, the coating area of ​​the positive electrode mixture layer 132, 232 can be widened, thereby increasing the battery capacity.

[0059] The cylindrical secondary battery of the present disclosure may also have the following configuration: Configuration 1: An electrode assembly in which a long positive electrode and a long negative electrode are wound with a separator interposed therebetween, an outer can housing the electrode assembly, and a sealing body that is crimped and fixed to an opening of the outer can via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer arranged on the positive electrode core, the negative electrode has a long negative electrode core and a negative electrode mixture layer arranged on the negative electrode core, the positive electrode has one or more positive electrode core exposed portions that are adjacent to the positive electrode mixture layer in the positive electrode width direction and where the positive electrode core is exposed, and positive electrode tabs are joined one by one to the positive electrode core exposed portions. a positive electrode tab and the longitudinally extending edge of at least one of the positive electrode substrate exposed portions after 100 charge / discharge cycles from a reference time are defined as x %, a distance between the positive electrode tab and the longitudinally extending edge in the positive electrode width direction is a mm, and a maximum length of the positive electrode substrate exposed portion in the positive electrode width direction is b mm, where x≧1% and a / b≧2−3 / (2x) are satisfied. Configuration 3: The cylindrical secondary battery according to Configuration 1 or 2, wherein a / b≧2−3 / (2x) holds true for the positive electrode substrate exposed portion to which the positive electrode tab is joined, the positive electrode being joined further outward from the inner end of the positive electrode than 0.35 times the total number of windings of the positive electrode.Configuration 4: The cylindrical secondary battery according to any one of Configurations 1 to 3, wherein the length of the positive electrode in the longitudinal direction of the positive electrode is 3000 mm or more.Configuration 5: The cylindrical secondary battery according to any one of Configurations 1 to 4, comprising six or more positive electrode substrate exposed portions arranged at intervals in the longitudinal direction of the positive electrode.Configuration 6: The cylindrical secondary battery according to any one of Configurations 1 to 5, wherein the mass ratio of Si element in the negative electrode mixture layer is 5 mass% or more.Configuration 7: The cylindrical secondary battery according to any one of configurations 1 to 6, comprising one or more positive electrode substrate exposed portions, the maximum length in the positive electrode width direction within a range in the positive electrode longitudinal direction to which the positive electrode tab is joined being longer than the length in the positive electrode width direction at at least one of both ends in the positive electrode longitudinal direction.

[0060] 10,110,210 Battery, 11,111,211 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Inner surface of winding, 16 Outer can, 17 Sealing body, 18 Insulating plate, 20,120,220 Positive electrode tab, 22 Grooved portion, 27 Terminal cap, 28 Gasket, 29 Shoulder portion, 30 Positive electrode core, 32,132,232 Positive electrode mixture layer, 32a Adjacent mixture layer, 35,135,235 Positive electrode core exposed portion, 37a,237a Longitudinal extending edge, 39 Cylindrical portion, 40 Negative electrode core, 41 Negative electrode core exposed portion, 42 Negative electrode mixture layer, 50 Upper current collector plate, 50a: Through hole; 51: Metal plate; 52: Lower current collecting plate; 60: Lamination portion; 65: Recess; 68: Bottom; 68a: Easy-to-break portion; 135a: First region; 135b: Second region; 237b, 237c: Sloped edges.

Claims

1. A cylindrical secondary battery comprising: an electrode body in which a long positive electrode and a long negative electrode are wound with a separator therebetween; an exterior can that houses the electrode body; and a sealing body caulked and fixed to an opening of the exterior can via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, the negative electrode has a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the positive electrode has one or more positive electrode core exposed portions that are adjacent to the positive electrode mixture layer in the positive electrode width direction and in which the positive electrode core is exposed, and includes positive electrode tabs respectively joined to the positive electrode core exposed portions one by one, and a longitudinally extending edge extending substantially parallel to the positive electrode longitudinal direction is included at an edge of the positive electrode mixture layer adjacent to the positive electrode width direction in the positive electrode core exposed portion. For at least one of the positive electrode core exposed portions, when the elongation rate in the positive electrode longitudinal direction of the longitudinally extending edge after 100 charge-discharge cycles from the reference time is x%, the distance in the positive electrode width direction between the positive electrode tab and the longitudinally extending edge is amm, and the maximum length in the positive electrode width direction of the positive electrode core exposed portion is bmm, x≧1% and a / b≧2−3 / (2x) are satisfied.

2. The cylindrical secondary battery according to claim 1, comprising a plurality of the positive electrode core exposed portions arranged at intervals in the positive electrode longitudinal direction.

3. For the positive electrode core exposed portion to which the positive electrode tab joined outside the winding of the positive electrode is joined, at a position more than 0.35 times the total number of winding turns of the positive electrode from the inner end of the winding of the positive electrode, a / b≧2−3 / (2x) is satisfied. The cylindrical secondary battery according to claim 1.

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

5. The cylindrical secondary battery according to claim 1, comprising six or more of the positive electrode core exposed portions arranged at intervals in the positive electrode longitudinal direction.

6. The cylindrical secondary battery according to claim 1, wherein the mass ratio of the Si element in the negative electrode mixture layer is 5 mass% or more.

7. The cylindrical secondary battery according to claim 1, comprising one or more positive electrode core exposed portions in which the maximum length in the positive electrode width direction in the range in the positive electrode longitudinal direction where the positive electrode tab is joined is longer than the length in the positive electrode width direction at at least one of both ends in the positive electrode longitudinal direction.

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