Cylindrical secondary battery

Abstract

This positive electrode 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. The positive electrode leads are joined one by one to the positive electrode core body exposed parts. When a positive electrode width direction region of the positive electrode in which the positive electrode core body exposed part is present is referred to as an α layer, and a positive electrode width direction region of the positive electrode in which the positive electrode core body exposed part is not present is referred to as a β layer, the average expansion coefficient of a first region (70) of the negative electrode mixture layer (42) radially facing the α layer is greater than the average expansion coefficient of a second region (80) of the negative electrode mixture layer (42) radially facing the β layer.

Description

Cylindrical secondary battery

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

[0002] Conventionally, as a cylindrical secondary battery, there is one described in Patent Document 1. This cylindrical secondary battery includes an electrode body in which a long positive electrode having a positive electrode core and a positive electrode mixture layer and a long negative electrode having a negative electrode core and a negative electrode mixture layer are wound with a separator interposed therebetween, a bottomed cylindrical outer can that houses the electrode body, and a sealing body caulked and fixed to the opening of the outer can through a gasket, a positive electrode lead that electrically connects the positive electrode and the sealing body, and a negative electrode lead that electrically connects the negative electrode and the outer can. One end of the positive electrode lead is joined to the positive electrode core exposed portion where the positive electrode core is exposed in the positive electrode, and the other end of the positive electrode lead is joined to the inner surface of the sealing body. One end of the negative electrode lead is joined to the negative electrode core exposed portion where the negative electrode core is exposed in the negative electrode, and the other end of the negative electrode lead is joined to the inner surface of the bottom of the outer can.

[0003] Japanese Patent Application Laid-Open No. 2013-016328

[0004] When a part of the positive electrode mixture layer is arranged adjacent in the positive electrode width direction to the positive electrode core exposed portion to which the positive electrode lead is joined, the capacity increases and the battery performance improves. However, as will be described in detail later, the present inventor has found that when such a configuration is adopted, a radial gap is likely to occur in the electrode body on the sealing body side in the axial direction and radially inward in the wound electrode body after a number of cycles. When a radial gap occurs in the electrode body, the reliability and battery performance of the battery are likely to deteriorate. Therefore, an object of the present disclosure is to provide a cylindrical secondary battery that can suppress the occurrence of a radial gap on the radially inner side of the electrode body and is likely to maintain high reliability and high performance over a long period of time.

[0005] To solve the above problems, the cylindrical secondary battery according to this disclosure comprises an electrode body in which a long positive electrode and a long negative electrode are wound with a separator in between, an outer can containing the electrode body, and a sealing body crimped and fixed to the opening of the outer can via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer 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, and the positive electrode is adjacent to the positive electrode mixture layer in the positive electrode width direction and The negative electrode mixture layer has one or more positive electrode core exposed portions in which the positive electrode core is exposed, and is provided with positive electrode leads joined one to each of the positive electrode core exposed portions, and the positive electrode widthwise region in which the positive electrode core exposed portions exist is referred to as the α layer, and the positive electrode widthwise region in which the positive electrode core exposed portions do not exist is referred to as the β layer, the average expansion rate of the first region of the negative electrode mixture layer radially facing the α layer is greater than the average expansion rate of the second region of the negative electrode mixture layer radially facing the β layer.

[0006] The cylindrical secondary battery according to this disclosure can suppress the generation of radial gaps on the radially inward side of the electrode body, making it easier to maintain high reliability and high performance over a long period of time.

[0007] This is an axial cross-sectional view of a cylindrical secondary battery according to one embodiment of the present disclosure. This is a perspective view showing a portion of the electrode body and the positive electrode lead. This is a schematic plan view of a portion of the inner surface of the winding of the elongated positive electrode as seen from the outside in the positive electrode thickness direction. (a) is a schematic plan view of the outer surface of the winding of the elongated negative electrode as seen from the outside in the negative electrode thickness direction, and (b) is a schematic plan view of the inner surface of the winding of the elongated negative electrode as seen from the outside in the negative electrode thickness direction. (a) is a schematic plan view corresponding to Figure 4(a) in the cylindrical battery of the reference example, and (b) is a schematic plan view corresponding to Figure 4(b) in the cylindrical battery of the reference example. (a) is a schematic cross-sectional view of the cylindrical battery of the reference example along line B-B in Figure 5(a) during discharge, and (b) is a schematic cross-sectional view of the cylindrical battery of the reference example along line B-B in Figure 5(a) during charging. This is a schematic axial cross-sectional view of the electrode body illustrating the problems of the cylindrical secondary battery in the reference example. (a) is a schematic cross-sectional view of the cylindrical battery of one embodiment along the line A-A in Figure 4(a) during discharge, and (b) is a schematic cross-sectional view of the cylindrical battery of one embodiment along the line A-A in Figure 4(a) during charging. This is a schematic diagram illustrating several parameters in the cylindrical battery of the experimental example. This is a schematic diagram illustrating several other parameters in the cylindrical battery of the experimental example.

[0008] Hereinafter, embodiments of the cylindrical secondary battery according to this disclosure will be described with reference to the drawings. The cylindrical secondary battery of this disclosure may be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. In the following, a cylindrical lithium-ion secondary battery using a non-aqueous electrolyte will be given as an example of one embodiment of the cylindrical secondary battery 10, but the cylindrical secondary battery of this disclosure may be a cylindrical secondary battery other than a cylindrical lithium-ion secondary battery.

[0009] Where multiple embodiments and modifications are included below, it is anticipated from the outset that new embodiments may be constructed by appropriately combining their characteristic features. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. Multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. In this specification, the side of the cylindrical secondary battery 10 with the sealing body 17 in the axial direction (height direction) is referred to as "upper," and the side of the outer casing 16 with the bottom 68 in the axial direction is referred to as "lower." Also, when the radial direction is referred to in the following description, that radial direction is the radial direction of the cylindrical secondary battery 10 and coincides with the radial direction of the outer casing 16.

[0010] Furthermore, in the following explanation, the expansion rate is the plate thickness V at a constant current discharge of 0.05C and 2.5V. discharge In contrast, the plate thickness V when constant current constant voltage charging is performed at 0.3C, 4.2V, and 0.02C cut-off. charge Ratio V charge / V discharge It is defined as follows. Of the components described below, those not described in the independent claim representing the highest-level concept are optional and not essential components. Furthermore, this disclosure is not limited to the embodiments and their modifications described below, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0011] Figure 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to one embodiment of the present disclosure. As shown in Figure 1, the cylindrical secondary battery (hereinafter simply referred to as "battery") 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), a bottomed cylindrical metal outer casing 16 that houses the electrode body 14 and the non-aqueous electrolyte, and a sealing body 17 crimped and fixed to the opening of the outer casing 16 via a gasket 28. The outer casing may have openings at both ends in the vertical direction in the axial direction, and the battery may have a configuration in which these two openings are closed.

[0012] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes. Liquid electrolytes (electrolytes) contain a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. Non-aqueous solvents may contain halogen-substituted compounds (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in these solvents are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0013] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0014] Figure 2 is a perspective view showing a portion of the electrode body 14 and the positive electrode lead (positive electrode tab) 20. In Figure 2, the positive electrode mixture layer 32 and the negative electrode mixture layer 42 are shown with diagonal hatching. As shown in Figure 2, the electrode body 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 around the separator 13. One or more positive electrode leads 20 are joined to the positive electrode 11, preferably six or more positive electrode leads 20 are joined, and in this embodiment, eight positive electrode leads 20 are joined to the positive electrode 11 at intervals from each other in the longitudinal direction of the positive electrode.

[0015] The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. The negative electrode 12 is formed to be longer than the positive electrode 11 in the winding direction and axial direction. The two separators 13 are formed to be slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separators 13 protrude above the positive electrode 11 and the negative electrode 12, and the negative electrode 12 protrudes below the positive electrode 11 and the separators 13.

[0016] The negative electrode 12 has a negative electrode core body exposed portion 41 at its lower axial end, extending from the inner end to the outer end in the longitudinal direction of the negative electrode, where the negative electrode mixture layer 42 is not provided in the negative electrode core body 40. Therefore, the lower axial end of the electrode body 14 is composed of at least a part of the negative electrode core body exposed portion 41. The negative electrode 12 may constitute the inner end of the electrode body 14. However, generally, 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 body 14.

[0017] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, or a film with the metal arranged on its 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 manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30.

[0018] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. A preferred example of a lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0019] Examples of conductive agents included 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 binders included 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 carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc. To increase capacity, it is preferable that the longitudinal length of the positive electrode 11 is 3000 mm or more.

[0020] Figure 3 is a schematic plan view of a portion of the inner surface 15 of the winding of the positive electrode 11, which is unfolded in a long, strip-like shape, as viewed from the outside in the thickness direction of the positive electrode. This plan view explains the formation position and structure of the positive electrode core exposed portion 35 to which the positive electrode lead 20 is joined in the positive electrode 11. In Figure 3, the area hatched with diagonal lines is the arrangement area of ​​the positive electrode mixture layer 32. In this embodiment, the case in which the positive electrode lead 20 is joined to the inner surface 15 of the winding of the positive electrode 11 is described, but the positive electrode lead may also be joined to the outer surface of the winding of the positive electrode.

[0021] As shown in Figure 3, the positive electrode 11 has one or more positive electrode core exposed portions 35 in which the positive electrode core 30 is exposed. In this embodiment, there are eight positive electrode core exposed portions 35 that are spaced apart in the positive electrode width direction. One positive electrode lead 20 is joined to each positive electrode core exposed portion 35 by ultrasonic welding or the like. The positive electrode mixture layer 32 has core adjacent portions 32a that are positioned adjacent to the positive electrode core exposed portions 35 in the positive electrode width direction. Because the positive electrode mixture layer 32 has core adjacent portions 32a, the arrangement area of ​​the positive electrode mixture layer 32 is increased, and the capacitance is increased. Since the reduction in electrical resistance is increased by effectively shortening the positive electrode side current path, it is preferable that the center positions of the eight positive electrode leads 20 in the positive electrode longitudinal direction are arranged at approximately equal intervals in the positive electrode longitudinal direction.

[0022] To suppress short circuits between the positive electrode 11 and the negative electrode 12, it is preferable that at least a portion of the overlapping portion of the positive electrode lead 20 that overlaps the positive electrode core exposed portion 35 in the positive electrode thickness direction is covered with a first insulating tape (not shown), and it is preferable that the insulating tape covers the entire positive electrode core exposed portion 35. Furthermore, to suppress short circuits between the positive electrode 11 and the negative electrode 12, it is preferable that a second insulating tape (a headband-shaped insulating tape: not shown) is applied around the entire circumference of the base portion of the extension portion extending from the positive electrode 11 in the positive electrode lead 20. The first and second insulating tapes are made of insulating materials, for example, a polyimide film may be used as the base material and silicone as the adhesive.

[0023] As shown in Figure 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 that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40.

[0024] Generally, carbon materials that reversibly intercept and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphites such as natural graphite such as flake graphite, lump graphite, and clay graphite, and artificial graphite such as lump graphite and graphitized mesophase carbon microbeads. Since it is easy to increase the capacity, it is preferable that the negative electrode active material of the negative electrode mixture layer 42 contains a Si material containing silicon (Si) particles, and it is preferable that the mass ratio of Si elements in the negative electrode mixture layer 42 is 5% by mass or more. It is also preferable that 3.0% by mass or more of the negative electrode mixture layer is composed of silicon oxide. Other metals that alloy with lithium besides Si, alloys containing such metals, compounds containing such metals, etc., may also be used as the negative electrode active material.

[0025] The binder contained in the negative electrode mixture layer 42 may be fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, etc., as in the case of the positive electrode 11, but preferably styrene-butadiene rubber (SBR) or a modified version thereof is used. In addition to SBR, the negative electrode mixture layer 42 may also contain CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0026] Figure 4(a) is a schematic plan view of the outer surface 75 of the rolled-up negative electrode 12, which is unfolded in a long shape, as seen from the outside in the direction of the negative electrode thickness. Figure 4(b) is a schematic plan view of the inner surface 85 of the rolled-up negative electrode 12, which is unfolded in a long shape, as seen from the outside in the direction of the negative electrode thickness. In Figures 4(a) and (b), the negative electrode mixture layer 42 is hatched with dots.

[0027] As shown in Figure 3, the region in the positive electrode width direction of the positive electrode 11 where the positive electrode core exposed portion 35 exists is referred to as the α layer, and the region in the positive electrode width direction of the positive electrode 11 where the positive electrode core exposed portion 35 does not exist is referred to as the β layer. In this case, referring to Figure 4, the average expansion rate of the first region (α layer opposing region) 70 of the negative electrode mixture layer 42 that is radially opposite to the α layer is greater than the average expansion rate of the second region (β layer opposing region) 80 of the negative electrode mixture layer 42 that is radially opposite to the β layer.

[0028] More specifically, in this embodiment, referring to Figure 4(a), the average expansion rate of the first outer winding portion 72 located on the outer winding surface 40a of the negative electrode core body 40 within the first region 70 is greater than the average expansion rate of the second outer winding portion 82 located on the outer winding surface 40a of the negative electrode core body 40 within the second region 80. Also, referring to Figure 4(b), the average expansion rate of the first inner winding portion 74 located on the inner winding surface 40b of the negative electrode core body 40 within the first region 70 is greater than the average expansion rate of the second inner winding portion 84 located on the inner winding surface 40b of the negative electrode core body 40 within the second region 80.

[0029] The average expansion rate of the outer portion 72 of the first volume is approximately the same as the average expansion rate of the inner portion 74 of the first volume, and the average expansion rate of the outer portion 82 of the second volume is approximately the same as the average expansion rate of the inner portion 84 of the second volume. The expansion rate of the negative electrode mixture layer increases as the mass ratio of Si element increases. In this embodiment, the average expansion rate of the first region 70 is made greater than that of the second region 80 by making the mass ratio of Si element in the first region 70 greater than that of the second region 80.

[0030] Referring again to Figures 1 and 2, the separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the separator 13 is preferably polyethylene, polyolefin resins such as polypropylene, or 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.

[0031] As shown in Figure 1, the battery 10 is equipped with an annular insulating plate 18 on the upper side of the electrode body 14. The positive electrode lead 20 attached to the positive electrode 11 extends towards the sealing body 17 through a through hole in the insulating plate 18. The sealing body 17 has 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 the radial center.

[0032] 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 constitutes the positive terminal. The sealing body 17 further has a metal plate 51. The metal plate 51 is a metal annular member and has a through hole.

[0033] Each positive electrode lead 20 is bent from the positive electrode 11 through the through hole 50a of the upper current collector plate 50 so as to follow the upper surface of the upper current collector plate 50. The tip of each positive electrode lead 20 is sandwiched between the upper surface of the upper current collector plate 50 and the lower surface of the metal plate 51. Each positive electrode lead 20 is joined to the upper surface of the upper current collector plate 50. The upper current collector plate 50 and the metal plate 51 are also joined, and each positive electrode lead 20 is also joined to the metal plate 51. These joining can be achieved, for example, by laser welding by irradiating the metal plate 51 from above with laser light in the axial direction while the tip of each positive electrode lead 20 is sandwiched between the upper current collector plate 50 and the metal plate 51. By laser welding the tip of the positive electrode lead 20 while it is sandwiched between the upper current collector plate 50 and the metal plate 51, the positive electrode lead 20 can be reliably and easily welded and joined to the upper current collector plate 50.

[0034] The sealing body 17 has a laminated portion 60 on its outer edge in which the terminal cap 27 and the upper current collector plate 50 are stacked. By irradiating the laminated portion 60 from above with laser light, 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 53 that is radially inward from the laminated portion 60. Because the upper surface of the upper current collector plate 50 has a recess 53 that is recessed downward, a space is provided between the terminal cap 27 and the recess 53 of the upper current collector plate 50. Each positive electrode lead 20 is joined to the upper current collector plate 50 within the recess 53. The upper current collector plate 50 does not have to be joined to the metal plate 51, and the positive electrode leads 20 do not have to be joined to the metal plate 51. Also, the battery does not have to have the metal plate 51. Also, the positive electrode leads 20 may be joined to the lower surface of the upper current collector plate 50.

[0035] The battery 10 is equipped with a metal lower current collector plate 52 on the axially lower side of the electrode body 14. Referring to Figures 1 and 2, the electrode body 14 is pressed against the upper surface of the lower current collector plate 52 so that the elongated negative electrode core exposed portion 41 is tilted radially inward, and a laser beam is irradiated from the lower side of the lower current collector plate 52 to join the negative electrode core exposed portion 41 to the upper surface of the lower current collector plate 52 over a wide area by laser welding. In addition, by irradiating the bottom 68 of the outer casing 16 from the lower side of the outer casing 16, the bottom 68 of the outer casing 16 is joined to the lower current collector plate 52 by laser welding. As a result, the negative electrode 12 of the electrode body 14 is electrically connected to the outer casing 16 via the lower current collector plate 52. By joining the negative electrode core exposed portion 41 to the upper surface of the lower current collector plate 52 over a wide area, it is possible to suppress the flow of current over a long distance along the longitudinal direction of the elongated negative electrode 12, thereby reducing the electrical resistance of the battery 10.

[0036] The case in which the negative electrode core exposed portion 41 is electrically connected to the outer casing 16 via the lower current collector plate 52 has been described. However, the negative electrode may have a first negative electrode core exposed portion where the negative electrode core is exposed at the inner end of the winding in the longitudinal direction of the negative electrode, and a second negative electrode core exposed portion where the negative electrode core is exposed at the outer end of the winding in the longitudinal direction of the negative electrode. Furthermore, the second negative electrode core exposed portion may have an outermost surface portion included in the outermost surface of the electrode body. In addition, one end of the negative electrode lead (negative electrode tab) may be joined to the first negative electrode core exposed portion, and the other end of the negative electrode lead may be joined to the inner surface of the bottom of the outer casing casing. Furthermore, the outermost surface portion may be in contact with the inner surface of the outer casing casing casing.

[0037] 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 longitudinal direction, and the other end of the negative electrode lead electrically connected to the outer end of the negative electrode core in the longitudinal direction. The other end of each negative electrode lead may be electrically connected to the bottom of the outer casing. Alternatively, the negative electrode and the outer casing may be electrically connected via a single negative electrode lead.

[0038] 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 part of the cylindrical portion 39 to create a recess radially inward along its entire circumference. The sealing body 17 is placed on the grooved portion 22 and is crimped and fixed to the opening of the outer can 16 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 internal space of the battery 10 is sealed by an annular gasket 28 that seals the space between the outer casing 16 and the sealing body 17. The gasket 28 is sandwiched between the outer casing 16 and the sealing body 17, insulating the sealing body 17 from the outer casing 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer casing 16 and the sealing body 17. The terminal cap 27 electrically connected to the positive electrode lead 20 becomes the positive electrode terminal, and the outer casing 16 electrically connected to the negative electrode core exposed portion 41 via the lower current collector plate 52 becomes the negative electrode terminal.

[0040] The battery 10 has a thin, easily breakable portion 68a at the bottom 68 of the outer casing 16. The easily breakable portion 68a is formed, for example, by marking the lower surface of the bottom 68 with a circular or C-shaped mark. Providing an easily breakable portion 68a at the bottom 68 enhances the safety of the battery 10. When the battery 10 overheats abnormally, the easily breakable portion 68a breaks, allowing the high-temperature gas inside the battery 10 to be released to the outside. The thin, easily breakable portion may also be provided on the terminal cap.

[0041] Next, the effects of the battery 10 of this disclosure will be described. Figure 5(a) is a schematic plan view of the cylindrical battery (hereinafter simply referred to as "battery") 110 of the reference example, corresponding to Figure 4(a), and Figure 5(b) is a schematic plan view of the battery 110, corresponding to Figure 4(b). Figure 6(a) is a schematic cross-sectional view of the battery 110 during discharge along the line B-B in Figure 5(a), and is a schematic cross-sectional view of the cross-section including the negative electrode width direction and the negative electrode thickness direction. Figure 6(b) is a schematic cross-sectional view of the battery 110 during charging along the line B-B in Figure 5(a).

[0042] As shown in FIGS. 5(a) and 5(b), in the negative electrode 112 of the battery 110, a negative electrode mixture layer 142 having an average expansion rate substantially the same as that of the second region 80 of the battery 10 is disposed on the negative electrode core 40. The average expansion rate of the negative electrode mixture layer 142 is substantially constant throughout the region, and the arrangement region of the negative electrode mixture layer 142 on the negative electrode core 40 is substantially the same as the arrangement region of the negative electrode mixture layer 42 on the negative electrode core 40. The configuration other than the negative electrode of the battery 110 is the same as the configuration other than the negative electrode of the battery 10. In this case, as shown in FIGS. 6(a) and 6(b), the expansion rate of the negative electrode mixture layer 142 is substantially the same throughout the region of the negative electrode mixture layer 142.

[0043] The inventor has found that the following problem may occur in the battery 110 of the reference example. Specifically, as shown in FIG. 3, in a cylindrical secondary battery, when a positive electrode core exposed portion 35 is provided so that the positive electrode mixture layer 32 has a core adjacent portion 32a in order to increase the capacity, as shown in FIG. 7, it has been found that when a large number of cycles are passed, a radial gap is likely to occur in the electrode body on the sealing body side in the axial direction and inward in the radial direction of the electrode body.

[0044] The reason for this is that when the positive electrode core exposed portion 35 is provided so that the positive electrode mixture layer 32 has the core adjacent portion 32a, while the core adjacent portion 32a is involved in expansion and contraction, the positive electrode core exposed portion 35 is not involved in expansion and contraction. Therefore, it is presumed that when the electrode body contracts, the portion where the positive electrode core exposed portion 35 exists in the height direction of the electrode body is difficult to contract, and a radial gap is likely to occur. Also, it is presumed that a radial gap is particularly likely to occur on the hollow portion side of the electrode body, that is, on the inner side in the radial direction, where it is difficult to generate a force outward in the radial direction.

[0045] In contrast, in the battery 10 of the present disclosure, the average expansion rate of the first region 70 that faces the α layer in the radial direction in the negative electrode mixture layer 42 is larger than the average expansion rate of the second region 80 that faces the β layer in the radial direction in the negative electrode mixture layer 42. Therefore, as shown in FIGS. 8(a) and 8(b), during charging (expansion), the first region 70 bulges more in the negative electrode thickness direction than the second region 80, so the α layer can be strongly compressed in the radial direction. Thus, during discharging (contraction), the α layer can be contracted so as to follow the first region 70, so the generation of radial gaps can be suppressed, and it is easy to maintain high reliability and high performance over a long period of time.

[0046] <Cylindrical Batteries of Experimental Examples 1-11> When an insulating tape is not attached to the exposed portion of the positive electrode core, the non-reactive portion of the mixture is defined as the same region as the exposed portion of the positive electrode core. When an insulating tape is attached to at least a part of the exposed portion of the positive electrode core, the non-reactive portion of the mixture is defined as the region of the sum of the exposed portion of the positive electrode core and the portion of the negative electrode mixture layer to which the insulating tape is attached. At this time, as shown in FIG. 9, when the total length in the longitudinal direction of the positive electrode of one or more non-reactive portions of the mixture is Lα, Lα = Lα1 + Lα2 + Lα3 +... + Lαn. Also, the length in the longitudinal direction of the positive electrode of the β layer is Lβ, and (Lα / Lβ) × 100 is defined as A. Further, as shown in FIG. 10, the expansion rate of the α layer is Vα, the expansion rate of the β layer is Vβ, and (Vα / Vβ - 1) × 100 is defined as B. At this time, for each of the cylindrical batteries of Experimental Examples 1-11, A, B, the relationship between A and B, the mass ratio of the Si element in the negative electrode mixture layer, and the negative electrode coating amount were set to the values shown in Table 1. Here, the negative electrode coating amount was calculated as the weight of the negative electrode mixture per unit area excluding the weight of the core material.

[0047] In Table 1, regarding the mass ratio of the Si element in the negative electrode mixture layer and the negative electrode coating amount, the value in the region of the negative electrode mixture layer that faces the α layer in the radial direction is denoted as α, and the value in the region of the negative electrode mixture layer that faces the β layer in the radial direction is denoted as β.

[0048] <Test to confirm the presence or absence of radial gap formation> In each experimental example, a test was conducted to confirm the presence or absence of radial gap formation in multiple samples. Specifically, the batteries of each experimental example were charged at a constant current of 0.3C in a 25°C environment until the voltage reached 4.2V, and then charged again at a constant voltage of 4.2V until the current reached 0.02C. After that, they were left for 20 minutes, and then discharged at a constant current of 0.5C until the voltage reached 2.85V. This charge-discharge cycle was considered one cycle, and the charge-discharge cycle was repeated 500 times. After that, it was confirmed whether or not a radial gap (gap between electrodes) larger than the threshold had occurred based on the CT (computed tomography) image of the electrode cross-section of each battery.

[0049] In Table 1, for each experimental example, "good" was indicated if the radial gap was below the threshold for all samples, and "bad" was indicated if the radial gap was above the threshold for all samples. Experiments in which some samples had radial gaps below the threshold and others had radial gaps above the threshold were indicated as "fair."

[0050]

[0051] As shown in Table 1, for the batteries in Experimental Examples 1 and 2, in which the expansion rate of the negative electrode mixture layer region (first region) radially opposite the positive electrode α layer was the same as the expansion rate of the negative electrode mixture layer region (second region) radially opposite the positive electrode β layer, in the battery of Experimental Example 1, where the positive electrode width direction length of the exposed positive electrode core was very small, the gap between the electrode plates was acceptable in all samples. On the other hand, when the positive electrode width direction length of the exposed positive electrode core was increased, as in the batteries of Experimental Examples 2-3, an inappropriate radial gap was observed in all samples.

[0052] In the battery of Experimental Example 4-10, the mass ratio of Si element to the negative electrode mixture layer in the negative electrode mixture layer region (first region) radially opposite the positive electrode α layer was made greater than the mass ratio of Si element to the negative electrode mixture layer in the negative electrode mixture layer region (second region) radially opposite the positive electrode β layer, so that the average expansion rate of the first region was higher than the average expansion rate of the second region.

[0053] More specifically, in the battery of Experimental Example 4-8, the average expansion rate of the outer region of the first region was set to be higher than the average expansion rate of the outer region of the second region, and the average expansion rate of the inner region of the first region was set to be higher than the average expansion rate of the inner region of the second region.

[0054] On the other hand, in the battery of Experimental Example 9, the average expansion rate of the inner region of the first region was made higher than the average expansion rate of the inner region of the second region, while the average expansion rate of the outer region of the first region was made the same as the average expansion rate of the outer region of the second region. Conversely, in the battery of Experimental Example 10, the average expansion rate of the outer region of the first region was made higher than the average expansion rate of the outer region of the second region, while the average expansion rate of the inner region of the first region was made the same as the average expansion rate of the inner region of the second region.

[0055] Furthermore, in the battery of Experimental Example 11, the mass ratio of Si elements to the negative electrode mixture layer in the negative electrode mixture layer region (first region) radially opposite the positive electrode α layer was made the same as the mass ratio of Si elements to the negative electrode mixture layer in the negative electrode mixture layer region (second region) radially opposite the positive electrode β layer. On the other hand, both on the outer side of the negative electrode core and on the inner side of the negative electrode core, the coating amount per unit area in the first region was made greater than the coating amount per unit area in the second region. In this way, the average expansion rate of the first region was made higher than the average expansion rate of the second region. As a method for making the coating amount per unit area of ​​the first region greater than the coating amount per unit area of ​​the second region, one method is to make the material and density of the first region approximately the same as the material and density of the second region, while making the thickness of the first region greater than the thickness of the second region. Alternatively, as a method to increase the coating amount per unit area of ​​the first region compared to the coating amount per unit area of ​​the second region, the material and thickness of the first region are made approximately the same as those of the second region, while the density of the first region is made higher than that of the second region.

[0056] As shown in Table 1, in the battery of experimental example 4-11, the evaluation of the gap between the electrode plates was either "fair" or "good," confirming that the occurrence of an inappropriate gap between the electrode plates could be suppressed. Therefore, it was confirmed that the occurrence of an inappropriate gap between the electrode plates could be suppressed by making the average expansion rate of the first region higher than the average expansion rate of the second region.

[0057] Furthermore, in the battery of Experimental Example 6-11, which satisfies A ≥ 2.5 and A ≤ B ≤ A × 1.75, the evaluation of the inter-plate gap was good in all samples, indicating that the inter-plate gap was acceptable. Therefore, it was confirmed that by fabricating a battery that satisfies A ≥ 2.5 and A ≤ B ≤ A × 1.75, the occurrence of inappropriate inter-plate gaps can be significantly suppressed.

[0058] In the battery of Experimental Example 11, the coating amount per unit area of ​​the first region was greater than the coating amount per unit area of ​​the second region, both on the outer side of the negative electrode core and on the inner side of the negative electrode core. However, even if the coating amount per unit area of ​​the first region is greater than the coating amount per unit area of ​​the second region in either the outer side of the negative electrode core or the inner side of the negative electrode core, the occurrence of an inappropriate gap between the electrode plates can be suppressed.

[0059] Furthermore, the cylindrical secondary battery of this disclosure may also have the following configuration: Configuration 1: comprising an electrode body in which a long positive electrode and a long negative electrode are wound with a separator in between, an outer casing for housing the electrode body, and a sealing body crimped and fixed to the opening of the outer casing 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, and the positive electrode has one or more adjacent to the positive electrode mixture layer in the positive electrode width direction and the positive electrode core is exposed A cylindrical secondary battery having a positive electrode core exposed portion and positive electrode leads joined one by one to the positive electrode core exposed portion, wherein the positive electrode widthwise region in which the positive electrode core exposed portion exists is referred to as the α layer, and the positive electrode widthwise region in which the positive electrode core exposed portion does not exist is referred to as the β layer, the average expansion rate of the first region of the negative electrode mixture layer radially facing the α layer is greater than the average expansion rate of the second region of the negative electrode mixture layer radially facing the β layer. Configuration 2: The cylindrical secondary battery according to Configuration 1, wherein the non-reacting portion of the mixture is defined as the same region as the exposed portion of the positive electrode core when insulating tape is not applied to the exposed portion of the positive electrode core, and as the sum of the exposed portion of the positive electrode core and the portion of the positive electrode mixture layer to which insulating tape is applied when insulating tape is applied to at least a part of the exposed portion of the positive electrode core, the sum of the longitudinal lengths of one or more non-reacting portions of the mixture is Lα, the longitudinal length of the positive electrode of the β layer is Lβ, the expansion rate of the α layer is Vα, the expansion rate of the β layer is Vβ, (Lα / Lβ) × 100 is A, and (Vα / Vβ-1) × 100 is B, such that A ≥ 2.5 and A ≤ B ≤ A × 1.75. Configuration 3: The cylindrical secondary battery according to Configuration 1 or 2, wherein the mass ratio of Si element in the first region is greater than the mass ratio of Si element in the second region. Configuration 4: A cylindrical secondary battery according to Configuration 1 or 2, wherein in at least one of the areas outside the negative electrode core and the area inside the negative electrode core, the amount of coating per unit area of ​​the first region is greater than the amount of coating per unit area of ​​the second region.Configuration 5: A cylindrical secondary battery according to any one of Configurations 1 to 4, wherein the average expansion rate of the first outer winding portion located on the outer winding surface of the negative electrode core in the first region is greater than the average expansion rate of the second outer winding portion located on the outer winding surface of the negative electrode core in the second region, and the average expansion rate of the first inner winding portion located on the inner winding surface of the negative electrode core in the first region is greater than the average expansion rate of the second inner winding portion located on the inner winding surface of the negative electrode core in the second region.

[0060] 10 Battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Inner surface of positive electrode winding, 16 Outer can, 17 Sealing body, 18 Insulating plate, 20 Positive electrode lead, 22 Grooved section, 27 Terminal cap, 28 Gasket, 29 Shoulder section, 30 Positive electrode core body, 32 Positive electrode mixture layer, 32a Core body adjacent section, 35 Positive electrode core body exposed section, 39 Cylindrical section, 40 Negative electrode core body, 40a Negative electrode core body winding outer surface, 40b Negative electrode core body winding inner surface, 41 Negative electrode core body exposed section, 42 Negative electrode mixture layer, 50 Upper current collector plate, 50a Through hole, 51 Metal plate, 52 Lower current collector plate, 53 Recessed portion, 60 Laminated portion, 68 Bottom portion, 68a Easily breakable portion, 70 First region, 72 First winding outer portion, 74 First winding inner portion, 75 Outer surface of the negative electrode winding, 80 Second region, 82 Second winding outer portion, 84 Second winding inner portion, 85 Inner surface of the negative electrode winding.

Claims

1. The electrode comprises an electrode body in which a long positive electrode and a long negative electrode are wound around a separator, an outer container for housing the electrode body, and a sealing body crimped and fixed to the opening of the outer container via a gasket, wherein the positive electrode has a long positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, the negative electrode has a long negative electrode core and a negative electrode mixture layer disposed on the negative electrode core, the positive electrode has one or more positive electrode core exposed portions adjacent to the positive electrode mixture layer in the positive electrode width direction and in which the positive electrode core is exposed, and positive electrode leads are bonded one to each of the positive electrode core exposed portions. A cylindrical secondary battery in which, when the region in the width direction of the positive electrode where the positive electrode core is exposed is referred to as the α layer, and the region in the width direction of the positive electrode where the positive electrode core is not exposed is referred to as the β layer, the average expansion rate of the first region of the negative electrode mixture layer radially opposite the α layer is greater than the average expansion rate of the second region of the negative electrode mixture layer radially opposite the β layer.

2. The cylindrical secondary battery according to claim 1, wherein the non-reacting portion of the mixture is defined as the same region as the exposed portion of the positive electrode core when insulating tape is not applied to the exposed portion of the positive electrode core, and as the sum of the exposed portion of the positive electrode core and the portion of the positive electrode mixture layer to which insulating tape is applied when insulating tape is applied to at least a part of the exposed portion of the positive electrode core, the sum of the longitudinal lengths of one or more non-reacting portions of the mixture in the positive electrode direction is Lα, the longitudinal length of the β layer in the positive electrode direction is Lβ, the expansion rate of the α layer is Vα, the expansion rate of the β layer is Vβ, (Lα / Lβ) × 100 is A, and (Vα / Vβ-1) × 100 is B, such that A ≥ 2.5 and A ≤ B ≤ A × 1.

75.

3. The cylindrical secondary battery according to claim 1 or 2, wherein the mass ratio of Si elements in the first region is greater than the mass ratio of Si elements in the second region.

4. The cylindrical secondary battery according to claim 1 or 2, wherein in at least one of the areas outside the negative electrode core and the area inside the negative electrode core, the amount of coating per unit area of ​​the first region is greater than the amount of coating per unit area of ​​the second region.

5. The cylindrical secondary battery according to claim 1 or 2, wherein the average expansion rate of the first outer winding portion located on the outer winding surface of the negative electrode core in the first region is greater than the average expansion rate of the second outer winding portion located on the outer winding surface of the negative electrode core in the second region, and the average expansion rate of the first inner winding portion located on the inner winding surface of the negative electrode core in the first region is greater than the average expansion rate of the second inner winding portion located on the inner winding surface of the negative electrode core in the second region.

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