Electrode body for secondary battery, secondary battery, and method for manufacturing electrode body for secondary battery

Abstract

In an electrode body (14) for a secondary battery, a positive electrode (11) and a negative electrode (12) are wound with a separator (13) interposed therebetween. One electrode (12) of the negative electrode (12) and the positive electrode (11) has a core body (40) and a lamination part (45) which results from lamination of a mixture layer on at least one surface of the core body (40). Said one electrode (12) has an uncoated portion (44) which is provided at an end positioned closer to one axial side relative to the lamination part (45) and on which no mixture layer is laminated. A leading-end-side section of the uncoated portion (44) is inclined toward the outer circumferential side continuously over the entire circumference.

Description

Electrode assembly for secondary battery, secondary battery, and method for manufacturing electrode assembly for secondary battery

[0001] The present disclosure relates to an electrode assembly for a secondary battery, a secondary battery, and a method for manufacturing an electrode assembly for a secondary battery.

[0002] Conventionally, as described in Patent Document 1, there is known a configuration for a secondary battery in which an uncoated portion where a mixture layer of a core body of a negative electrode is not laminated is projected from an axial end portion of an electrode assembly, and the projected uncoated portion is welded to a current collector plate. In this configuration, in order to facilitate welding, radially extending protrusions are formed at four positions on the end face of the current collector plate or a pressing jig, and the four protrusions are pressed against the tip of the uncoated portion that rises in the axial direction, thereby pushing down four circumferential positions of the uncoated portion toward the inner peripheral side.

[0003] Japanese Patent Application Laid-Open No. 2010-257851

[0004] In the configuration described in Patent Document 1, the uncoated portion at the end of the negative electrode is largely tilted toward the inner peripheral side only at four positions that are greatly spaced apart in the circumferential direction. At this time, there is a portion that does not tilt toward the inner peripheral side in a part of the circumferential direction of the uncoated portion of the negative electrode. With this configuration, a large load is likely to be locally applied to the uncoated portion of the negative electrode. This may cause precipitation of foreign matter due to peeling of the mixture layer from the core body in the vicinity of the uncoated portion of the negative electrode. On the other hand, if the load for pushing down the uncoated portion of the negative electrode is too small, the amount of the entire uncoated portion pushed toward the inner peripheral side becomes small, and the axial length of the electrode assembly increases, which may make it impossible for the electrode assembly to fit entirely into an outer can. Although the inconveniences in the uncoated portion of the negative electrode have been described above, the same inconveniences occur when pushing down the uncoated portion at the end of the positive electrode.

[0005] On the other hand, in the case of the negative and positive electrodes of a wound-type electrode body, a configuration is conceivable in which the uncoated portion protruding axially from the composite layer laminated portion of one of the electrodes is gradually bent from the outer circumference to the inner circumference. However, this may result in a thinner thickness at the innermost part of the uncoated portion, potentially causing damage such as foil tearing at the innermost part. Furthermore, folding the uncoated portion inward at one end of the roughly cylindrical central hole of the electrode body to eliminate the protruding uncoated portion on the inner circumference may lead to a decrease in battery voltage. In addition, the height variation of the end face of the uncoated portion becomes large, so there is room for improvement in terms of improving the welding strength between this end face and the welding material such as the current collector plate.

[0006] Therefore, the object of this disclosure is to provide an electrode body for a secondary battery, a secondary battery, and a method for manufacturing an electrode body for a secondary battery that can prevent the compound layer from peeling off from the core body near the uncoated portion of the electrode, sufficiently increase the amount of radial tilt of the uncoated portion at the end of the electrode, suppress damage and voltage drop at the innermost circumference, and improve the welding strength with the member welded to the end face.

[0007] The electrode body for a secondary battery according to this disclosure is an electrode body for a secondary battery in which a positive electrode and a negative electrode are wound with a separator in between, wherein one of the negative electrode and the positive electrode has a core body and a laminated portion on at least one side of the core body on which a composite layer is laminated, and has an uncoated portion provided at the end located axially to one side of the laminated portion, on which the composite layer is not laminated, and the tip portion of the uncoated portion is continuously bent toward the outer circumference over its entire circumference.

[0008] The secondary battery according to this disclosure comprises an electrode body for the secondary battery according to this disclosure and an outer casing for housing the electrode body, and a current collector plate is attached to the tip of the unpainted portion.

[0009] The method for manufacturing an electrode body for a secondary battery according to this disclosure includes a step in which, while holding the electrode body in a holding part, the electrode body is rotated around an axis extending in the vertical direction, the holding part is moved along a horizontal linear path, and as the holding part moves, a hemispherical pressing part, which is previously supported on the upper side of the linear path, is pressed from the inner circumference side against an uncoated part extending in the vertical direction, and the uncoated part is pushed down toward the outer circumference, and in the pushing down step, the contact point between the uncoated part and the pressing part is moved in a spiral shape from the inside to the outside at the upper end of the uncoated part.

[0010] According to this disclosure, in an electrode body for a secondary battery, the tip portion of the uncoated area at the end of the electrode is continuously tilted outward along its entire circumference. This allows for a sufficiently large amount of radial tilting of the uncoated area without applying large localized loads at multiple widely separated positions in the circumferential direction to the tip portion of the uncoated area, thereby preventing it from tilting inward. As a result, peeling of the composite layer from the core body near the uncoated area of ​​the electrode can be prevented, and the amount of radial tilting of the uncoated area at the end of the electrode can be sufficiently large. Furthermore, since the thickness of the innermost part of the uncoated area can be prevented, damage such as foil tearing can be suppressed at the innermost part. In addition, since the uncoated area can be prevented from protruding inward at one end of the central hole of the electrode body, there is no need to push the uncoated area into the inside of the central hole, and a voltage drop in the battery can be suppressed. Furthermore, since the height variation of the end face of the uncoated area can be reduced, the welding strength between this end face and the welding member such as the current collector plate can be improved.

[0011] This is an axial cross-sectional view of a secondary battery according to one embodiment of the present disclosure. This is a perspective view showing a portion of the electrode body for a secondary battery of the embodiment unfolded before both axial ends are pushed down. This is an enlarged view corresponding to part A in Figure 1 before the negative electrode current collector plate is joined to the electrode body for a secondary battery of the embodiment. This is a diagram showing the electrode body for a secondary battery removed from Figure 1 and viewed from below. This is a schematic diagram showing the electrode body for a secondary battery viewed from below. This is a schematic perspective view showing the state when one circumferential portion of a part of the electrode body for a secondary battery is pushed down to the outer circumference in the embodiment. This is a perspective view of a processing device for pushing down the uncoated portion of the negative electrode to the outer circumference in the manufacturing method of the electrode body for a secondary battery of the embodiment. This is a schematic diagram showing the state of the processing device shown in Figure 7 before the movement of the holding portion that holds the electrode body begins. This is a schematic diagram showing the state after the holding portion is moved while the electrode body is rotated using the processing device shown in Figure 7, and the uncoated portion of the negative electrode is pushed down to the outer circumference by the pressing portion. This figure shows an example of the results of measuring the height variation when the electrode body for the secondary battery of the embodiment is removed and viewed from below. This figure shows an example of the results of measuring the height variation when the electrode body for the secondary battery of the comparative example is removed and viewed from below.

[0012] Hereinafter, embodiments of the electrode body for secondary batteries, secondary batteries, and methods for manufacturing the electrode body for secondary batteries according to this disclosure will be described in detail with reference to the drawings. The 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 non-aqueous electrolyte secondary battery will be described as an embodiment of the secondary battery, but the secondary battery of this disclosure can employ various configurations as long as it is a secondary battery equipped with a wound electrode body.

[0013] It is intended from the outset that new embodiments can be constructed by appropriately combining the characteristic features of the embodiments and modifications described below. In the following embodiments, the same reference numerals are used for the same components in the drawings, and redundant explanations are omitted. In addition, 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 axial opening side of the outer casing 15 of the cylindrical secondary battery 10 is referred to as "upper," and the axial bottom side is referred to as "lower." That is, the bottom of the outer casing 15 is described as the lower end. The secondary batteries of this disclosure are not necessarily limited to those in which the bottom of the outer casing is located vertically below when in use. For example, the bottom of the outer casing may be configured to be vertically above the opening of the outer casing when in use. Furthermore, this disclosure is not limited to the embodiments and modifications described below, and various improvements and changes are possible within the scope of the claims of this application and their equivalents.

[0014] Figure 1 is an axial cross-sectional view of the secondary battery 10 of the embodiment. Figure 2 is a perspective view showing a portion of the electrode body 14 for the secondary battery of the embodiment in an unfolded state before both axial ends are pushed down. Figure 3 is an enlarged view corresponding to part A in Figure 1 of the electrode body 14 for the secondary battery before the negative electrode current collector plate 17 is joined. Hereafter, the electrode body 14 for the secondary battery will be referred to as electrode body 14.

[0015] As shown in Figures 1 to 3, the secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), and an outer casing 15 and a sealing body 16, which are metal cans. The wound electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, with the positive electrode 11 and the negative electrode 12 wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all in the shape of a roughly rectangular, elongated strip. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0016] In the electrode body 14, as shown in Figure 2, the positive electrode 11 protrudes above the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes below the positive electrode 11 and the separator 13.

[0017] As shown in Figure 2, the positive electrode 11 has an uncoated positive electrode portion 34 in which the positive electrode core 30 is exposed without a positive electrode mixture layer 32. The uncoated positive electrode portion 34 is located at the upper end, which is one end in the winding axis direction (hereinafter sometimes referred to as the axis direction) from the winding start end to the winding end in the longitudinal direction of the electrode plate of the positive electrode 11. The longitudinal direction of the electrode plate is the direction corresponding to the winding direction in the wound state of the positive electrode 11 or negative electrode 12, and is the longitudinal direction of the elongated rectangle when the positive electrode 11 or negative electrode 12 is viewed in the thickness direction when the positive electrode 11 or negative electrode 12 is unfolded along a plane.

[0018] The negative electrode 12 has an uncoated negative electrode portion 44 in which the negative electrode core body 40 (Figure 2) is exposed without a negative electrode mixture layer 42 (Figure 2). The uncoated negative electrode portion 44 is located at the lower end, which is the other end in the axial direction, from the beginning end to the end end in the longitudinal direction of the electrode plate of the negative electrode 12. Therefore, the upper end in the axial direction of the electrode body 14 is composed of the uncoated positive electrode portion 34, and the lower end in the axial direction of the electrode body 14 is composed of the uncoated negative electrode portion 44.

[0019] The non-aqueous electrolyte has ionic conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (non-aqueous electrolyte solution), but may also be a solid electrolyte using a gel-like polymer or the like. The secondary battery 10 is preferably a lithium-ion battery. The electrolyte salt may be, for example, LiBF ４ LiPF ６ Lithium salts such as the above are used. Non-aqueous solvents include, for example, esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0020] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). In terms of suppressing the deterioration of the charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries or improving the input characteristics, the non-aqueous electrolyte preferably contains 5% by mass or more of FEC relative to the mass of the non-aqueous electrolyte, and more preferably contains 5% to 15% by mass of FEC.

[0021] 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.

[0022] 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 thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. 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 film, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm to 150 μm on one side of the positive electrode core 30.

[0023] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. A preferred example of a lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0024] Examples of conductive agents included in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, Ketjen black, and 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.

[0025] On both sides of the upper end of the positive electrode core 30, a positive electrode protective layer may be provided between the positive electrode mixture layer 32 and the uncoated positive electrode portion 34. The positive electrode protective layer can be an inorganic filler protective layer composed of, for example, an inorganic material additive such as alumina, a resin such as a water-insoluble polymer such as polyvinylidene fluoride (PVdF), and a conductive additive such as acetylene black (AB) or carbon black (CB) in a predetermined ratio.

[0026] 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 thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm. 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. The negative electrode mixture layer 42 may be formed on only one side of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm to 150 μm on one side of the negative electrode core 40.

[0027] Generally, carbon materials that reversibly intercalate and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphite such as natural graphite such as flake graphite, lump graphite, and earthy graphite, and artificial graphite such as lump graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. In addition, metals other than Si that alloy with lithium, alloys containing such metals, compounds containing such metals, etc., may be used as the negative electrode active material.

[0028] 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.

[0029] A porous sheet having ion permeability and insulating properties is used for the separator 13. 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.

[0030] As shown in Figure 1, the secondary battery 10 has a negative electrode current collector plate 17 made of metal such as nickel or a nickel alloy on the axial lower side of the electrode body 14. The negative electrode current collector plate 17 can be cross-shaped or disc-shaped, etc. An unpainted negative electrode portion 44 protruding from the electrode body 14 is joined to the negative electrode current collector plate 17, and the negative electrode current collector plate 17 is joined to the inner surface of the bottom plate of the outer casing 15. The outer casing 15, to which the unpainted negative electrode portion 44 is electrically connected via the negative electrode current collector plate 17, becomes the negative electrode terminal.

[0031] The secondary battery 10 has a positive electrode current collector plate 18 located inside the outer casing 15. The positive electrode current collector plate 18 is a metal disc made of aluminum or an aluminum alloy, etc., and is located above the electrode body 14 in the axial direction. When the positive electrode current collector plate 18 is disc-shaped, a through hole is formed to allow gas generated in the electrode body to escape upward. The unpainted positive electrode portion 34 protruding from the electrode body 14 is joined to the positive electrode current collector plate 18 in a state where it is pushed inward in at least a part of its circumferential direction. As a result, the positive electrode current collector plate 18 is fixed to the upper end of the electrode body 14 in the axial direction and electrically connected. The secondary battery 10 has an annular insulating plate 19 above the positive electrode current collector plate 18 in the axial direction.

[0032] One end of the positive electrode connection lead 20 is joined to the upper surface of the positive electrode current collector plate 18 by welding or the like. The positive electrode connection lead 20 extends through a through-hole in the insulating plate 19 towards the sealing body 16, and the other end of the positive electrode connection lead 20 is connected to the lower surface of the internal terminal plate 22 of the sealing body 16 by welding or the like. The cap 26 that forms the top plate of the sealing body 16 is electrically connected to the internal terminal plate 22. As a result, the positive electrode current collector plate 18 is electrically connected to the cap 26, and the cap 26 becomes the positive electrode terminal. The positive electrode connection lead 20 is a conductive member made of a metal mainly composed of aluminum.

[0033] The secondary battery 10 further includes a resin gasket 27 positioned between the outer casing 15 and the sealing body 16. The gasket 27 is sandwiched between the outer casing 15 and the sealing body 16, insulating the sealing body 16 from the outer casing 15. The gasket 27 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer casing 15 from the sealing body 16. The outer casing 15 has an annular groove 21 in a part of its axial direction.

[0034] The grooved portion 21 can be formed, for example, by spinning a part of the side surface radially inward to create a recess in the radial direction. The outer casing 15 has a bottomed cylindrical portion including the grooved portion 21 and an annular shoulder portion. The bottomed cylindrical portion houses the electrode body 14 and the non-aqueous electrolyte, and the shoulder portion is bent radially inward from the opening end of the bottomed cylindrical portion and extends inward. The shoulder portion is formed when the upper end of the outer casing 15 is bent inward and crimped to the periphery of the sealing body 16. The sealing body 16 is crimped and fixed to the outer casing 15 via a gasket 27 between the shoulder portion and the grooved portion 21. In this way, the internal space of the secondary battery 10 is sealed.

[0035] The sealing body 16 has a structure in which an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The internal terminal plate 22 has at least one through hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges.

[0036] On the other hand, a central hole 52 having a substantially cylindrical inner surface is provided in the center of the electrode body 14, extending in the axial direction. The central hole 52 functions as an exhaust passage that allows gas generated inside the electrode body 14 to escape upward through holes (not shown) formed in the positive electrode current collector plate 18.

[0037] When the secondary battery 10 overheats abnormally and its internal pressure rises to a predetermined value, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 towards the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further and reaches a predetermined value, the upper valve body 25 ruptures, and gas is discharged from the through-hole 26a of the cap 26. This gas discharge prevents the secondary battery 10 from deforming or rupturing due to an excessive rise in internal pressure, thereby improving the safety of the secondary battery 10. Furthermore, it can suppress the impact on adjacent components (not shown) due to deformation or rupture of the secondary battery 10.

[0038] In this example, the configuration of the present disclosure is applied to a configuration in which gas generated inside the secondary battery 10 is exhausted to the outside through a through hole 26a in the upper cap 26. On the other hand, the configuration of the present disclosure is not limited to applying to such a secondary battery, and for example, an annular or C-shaped thin-walled portion may be formed at the bottom of the outer casing, and this thin-walled portion may form an easily breakable portion. In this case, when the internal pressure of the secondary battery rises and reaches a predetermined value, the gas is discharged from the bottom of the outer casing by the breakage of the thin-walled portion, thereby suppressing the rise in the internal pressure of the secondary battery.

[0039] Next, with reference to Figures 1 to 6, the peripheral configuration of the junction between the electrode body 14 and the negative electrode current collector plate 17 at the lower part of the secondary battery 10, and the configuration of the negative electrode 12 will be explained. Figure 4 is a diagram showing the electrode body 14 removed from Figure 1 and viewed from below. Figure 5 is a schematic diagram showing the electrode body 14 viewed from below. Figure 6 is a schematic perspective view showing the state when one side of the circumferential portion of the electrode body 14 is pushed down toward the outer circumference.

[0040] As shown in FIG. 3, the negative electrode 12 includes a stacked portion 45 in which negative electrode mixture layers 42 are stacked on both surfaces of a negative electrode core 40, and a negative electrode uncoated portion 44 provided at an end portion located on the lower side (one axial side) that is closer to the negative electrode current collector plate 17 than the stacked portion 45. The negative electrode uncoated portion 44 has an axially extending portion 47 extending substantially parallel to the axial direction of the electrode body 14, and an outer peripheral side fallen portion 48 that is fallen toward the outer peripheral side from the lower end of the axially extending portion 47. The outer peripheral side fallen portion 48 is welded to the upper surface of the negative electrode current collector plate 17. Accordingly, the negative electrode uncoated portion 44 is provided at the axial lower end of the negative electrode 12 on the negative electrode current collector plate 17 side, and no negative electrode mixture layer is stacked thereon.

[0041] As shown in FIGS. 3, 4 and 5, in the present example, the distal end side portion of the negative electrode uncoated portion 44 is continuously fallen toward the outer peripheral side over the entire circumference. As a result, as will be described later, peeling of the negative electrode mixture layer 42 from the negative electrode core 40 at the end portion of the negative electrode 12 can be prevented, and the amount of the negative electrode uncoated portion 44 pushed down in the radial direction can be made sufficiently large.

[0042] More specifically, in the present example, as shown in FIGS. 3 and 4, when the negative electrode uncoated portion 44 is viewed from the lower side that is one axial side, the entire portion from the inner peripheral end to the outer peripheral end is fallen toward the outer peripheral side such that the distal end of the negative electrode uncoated portion 44 is arranged in a spiral shape whose curvature increases toward the outer periphery.

[0043] It should be noted that the negative electrode uncoated portion 44 may be configured such that, when viewed from the lower side, only a part from the inner peripheral end to between the inner peripheral end and the outer peripheral end is fallen toward the outer peripheral side such that the distal end of the negative electrode uncoated portion 44 is arranged in a spiral shape whose curvature increases toward the outer periphery.

[0044] Furthermore, as shown in the schematic diagrams of FIGS. 5 and 6, in the present example, the negative electrode uncoated portion 44 has a plurality of unit elements 49 that are stacked in the radial direction at a part in the circumferential direction and are integrally displaced in the circumferential direction, and the plurality of unit elements 49 are spirally arranged. A folded portion 50 is formed when some of the unit elements 49 fall toward the outer peripheral side in a state where ends of a part in the circumferential direction overlap in the radial direction so as to enter the outer peripheral side with respect to another unit element 49 adjacent to one side in the circumferential direction, and the folded portions 50 are repeated in the spiral direction together with the unit elements 49.

[0045] For example, in the examples shown in FIGS. 5 and 6, the negative electrode uncoated portion 44 is collapsed in a spiral shape in the direction of arrow A1. In this case, from the state of FIG. 6(a), the unit element 49 indicated by B1, which is a part in the circumferential direction, is adjacent to the left side of FIG. 5 (the right side of FIG. 6(b)), which is one side in the circumferential direction, and with respect to the unit element 49 indicated by B2, the end of the circumferential part B1 overlaps in the radial direction so as to enter the outer peripheral side, and the circumferential part B1 collapses toward the outer peripheral side, whereby folded portions 50 are formed, and the folded portions 50 are repeated in the spiral direction. As a result, when the negative electrode uncoated portion 44 collapses toward the outer peripheral side, the excess portion generated in the portion including the tip edge is absorbed by the folded portions 50, and the tip portion of the negative electrode uncoated portion 44 can be continuously collapsed toward the outer peripheral side along the spiral direction.

[0046] Next, with reference to FIGS. 7 to 8B, a method of collapsing the negative electrode uncoated portion 44 toward the outer peripheral side in the method for manufacturing the electrode body 14 will be described more specifically. FIG. 7 is a perspective view of a processing apparatus 90 that pushes the negative electrode uncoated portion 44 toward the outer peripheral side in the method for manufacturing the electrode body 14 according to the embodiment. The processing apparatus 90 includes: a guide member 91 having a horizontal linear path such as a rail on an upper side thereof; a moving part 92 movably provided along the linear path; a motor 93 fixed to an upper side of the moving part 92; a holding part 94 placed and supported on an upper side of a motor case of the motor 93 and holding the electrode body 14 on an upper side thereof; and a columnar first support part 95 provided to stand upright integrally with the guide member 91.

[0047] The moving part 92 moves along the linear path by a robot cylinder mechanism or the like. The holding part 94 protrudes above the motor case, is fixed to a vertically extending rotating shaft (not shown), and is rotatable. The rotating shaft is rotationally driven by the motor 93. The electrode body 14 is held by the holding part 94 such that the axial direction thereof extends vertically, and the axially extending negative electrode uncoated portion 44 is disposed at the upper end portion. The axial direction of the electrode body 14 is located on an extension line of the rotating shaft.

[0048] A second support portion 96 is provided above the first support portion 95, which is movable in the vertical direction and fixed in position by a screw (not shown). The second support portion 96 has a plate portion 97 that protrudes laterally from its lower end, and a hemispherical pressing portion 98 is supported below the plate portion 97. The pressing portion 98 can rotate freely around an axis in the vertical direction relative to the plate portion 97. As a result, the pressing portion 98 is supported in advance on the upper side of the straight path.

[0049] As shown in Figure 7, the uncoated negative electrode portion 44 of the electrode body 14 is flat with no irregularities along its entire tip edge when it is in an axially upright position before being bent outward. This suppresses an increase in electrical resistance, unlike the case where the tip edge of the uncoated negative electrode portion 44 has a shape with repeated irregularities along the longitudinal direction of the electrode plate, which is the winding direction, in order to make it easier to bend the tip portion of the uncoated negative electrode portion 44, which is in an axially upright position, outward.

[0050] The manufacturing method of the electrode body 14 in this example includes a pushing step. In the pushing step, with the electrode body 14 held in the holding part 94, the electrode body 14 is rotated around an axis along the vertical direction by the drive of the motor 93. While the electrode body 14 is rotating in this way, the holding part 94 is moved along a horizontal straight path by the moving part 92. As the holding part 94 moves, the hemispherical pressing part 98, which is supported in advance on the upper side of the straight path, is pressed from the inner circumference to the outer circumference at the tip of the unpainted negative electrode portion 44 that extends in the vertical direction, pushing the unpainted negative electrode portion 44 toward the outer circumference. At this time, in the pushing step, the contact point between the unpainted negative electrode portion 44 and the pressing part 98 is moved in a spiral shape from the inside to the outside at the upper end of the unpainted negative electrode portion 44.

[0051] Figure 8A is a schematic diagram showing the state of the holding part 94 that holds the electrode body 14 in the processing apparatus 90 before movement begins. Figure 8B is a schematic diagram showing the state after the holding part 94 is moved while the electrode body 14 is rotated using the processing apparatus 90, and the uncoated negative electrode portion 44 is tilted outward by the pressing part 98.

[0052] When processing the uncoated negative electrode portion 44 to tilt it toward the outer circumference using the processing device 90, as shown in Figure 8A, the lower center end of the pressing portion 98 is positioned on the extension of the center line of the central hole 52 (Figure 1) of the electrode body 14. With the pressing portion 98 lowered, the electrode body 14 held by the holding portion 94 is rotated around an axis along the vertical direction by the rotation of the motor 93. While rotating the electrode body 14, the holding portion 94 is moved along a straight path together with the moving portion 92. At this time, the moving portion 92 is moved at a constant speed in the horizontal direction. As the holding portion 94 moves, the hemispherical pressing portion 98, which has been supported in advance on the upper side of the straight path, is pressed from the inner circumference side against the uncoated negative electrode portion 44 that extends in the vertical direction, performing a pushing-down step that pushes the uncoated negative electrode portion 44 toward the outer circumference. In this pushing-down step, the uncoated portion 44 of the negative electrode is pressed by the pressing portion 98 for, for example, two or three or more turns. This causes the contact point between the uncoated portion 44 of the negative electrode and the pressing portion 98 to move in a spiral motion from the inside to the outside at the upper end of the uncoated portion 44 of the negative electrode. As a result, the amount of deformation of the uncoated portion 44 of the negative electrode caused by the pressing portion 98 in one turn is kept small, while the uncoated portion 44 of the negative electrode can be tilted significantly towards the outer circumference.

[0053] As a result, as shown in Figures 4 and 5, an electrode body 14 can be obtained in which the uncoated negative electrode portion 44 is continuously tilted outward along its entire circumference, and when viewed from one axial side of the uncoated negative electrode portion 44, the tip of the uncoated negative electrode portion 44 is arranged in a spiral shape.

[0054] According to the electrode body 14 and its manufacturing method described above, the tip portion of the uncoated negative electrode portion 44 at the end of the negative electrode 12 is continuously tilted toward the outer circumference along its entire circumference. This allows for a sufficiently large amount of radial tilting of the uncoated negative electrode portion 44 without applying large localized loads to the tip portion of the uncoated negative electrode portion 44 at multiple positions far apart in the circumferential direction, thereby preventing it from tilting significantly toward the inner circumference. As a result, peeling of the negative electrode mixture layer 42 from the negative electrode core body 40 near the uncoated negative electrode portion 44 of the negative electrode 12 can be prevented, and the amount of radial tilting of the uncoated negative electrode portion 44 can be sufficiently large.

[0055] Furthermore, by tilting the uncoated negative electrode portion 44 toward the outer circumference, it is possible to prevent the thickness of the uncoated negative electrode portion 44 from becoming thinner at its innermost circumference, thereby suppressing damage such as foil tearing at the innermost circumference. In addition, it is possible to prevent the uncoated negative electrode portion 44 from protruding toward the inner circumference at one end of the central hole 52 of the electrode body 14, eliminating the need to push the uncoated negative electrode portion 44 into the inside of the central hole 52. This suppresses voltage drop in the secondary battery 10.

[0056] Furthermore, when the unpainted portion 44 of the negative electrode is bent outward, unlike when it is bent inward, the excess portion due to bending can be more easily released to the outer circumference where the circumferential length is greater. This reduces the height variation of the end face of the unpainted portion 44 of the negative electrode. This improves the welding strength between this end face and the negative electrode current collector plate 17, which is the component welded to this end face.

[0057] Figure 9 shows an example of the results of measuring the height variation when the electrode body 14 of the embodiment is removed and viewed from below. In Figure 9, the pattern shown on the end face of the uncoated negative electrode portion 44 indicates that the same pattern is used for portions at approximately the same height. The coarsest sandy area indicates the lowest portion of the end face, the finest sandy area indicates the highest portion of the end face, and the sandy area of ​​intermediate coarseness indicates the portion at an intermediate height on the end face. As shown in Figure 9, the electrode body of the embodiment can reduce the height variation on the end face of the uncoated negative electrode portion 44.

[0058] Figure 10 shows an example of the results of measuring the height variation when the electrode body 14a of the comparative example is removed and viewed from below. Unlike the embodiment, the electrode body 14a of the comparative example has the tip portion of the uncoated negative electrode portion 44 continuously bent in a spiral shape toward the inner circumference around its entire circumference. The meaning of the pattern shown on the end face of the uncoated negative electrode portion 44 in Figure 10 is the same as in Figure 9, but the plain portion indicates that the height is even lower than the coarsest sandy area.

[0059] As shown in Figure 10, in the comparative example, the height of the uncoated negative electrode portion 44 is lowest near the inner circumference of the end face and at multiple circumferential positions, and highest at multiple other circumferential positions. As a result, there is a large variation in the height of the end face. In addition, in the comparative example, the uncoated negative electrode portion 44 protrudes towards the inner circumference of the central hole 52 at one end of the central hole 52, so in order to ensure a large gas passage for the electrode body 14a, it may be necessary to push the uncoated negative electrode portion 44 into the inner side of the central hole 52 with a pin-shaped jig. Furthermore, the inner circumference of the uncoated negative electrode portion 44 has a reduced thickness, and when tilted inward, the excess portion is prone to wrinkles and unevenness due to pressing against each other on the inner circumference side where the circumferential length is smaller. This makes it easier for damage such as foil tearing to occur.

[0060] In the above embodiment, the configuration of the portion that pushes the uncoated portion of the negative electrode 12 toward the outer circumference and the method for obtaining that configuration were described. However, the uncoated portion of the positive electrode 11 can also be pushed toward the outer circumference together with the negative electrode 12, or instead of the negative electrode 12. In that case, the configuration of the portion that pushes the uncoated portion of the positive electrode 11 toward the outer circumference and the method for obtaining that configuration can be configured in the same way as in the case of the uncoated portion of the negative electrode 12. At this time, the configuration of the above embodiment can be applied to the configuration of the portion that pushes the uncoated portions of one or both of the positive and negative electrodes toward the outer circumference.

[0061] This disclosure is further illustrated by the following embodiments. Configuration 1: An electrode body for a secondary battery in which a positive electrode and a negative electrode are wound with a separator in between, wherein one of the negative electrode and the positive electrode has a core body and a laminated portion in which a composite layer is laminated on at least one side of the core body, and an uncoated portion provided at an end located axially to one side of the laminated portion, in which the composite layer is not laminated, and the tip portion of the uncoated portion is continuously bent outward over its entire circumference. Configuration 2: The electrode body for a secondary battery according to Configuration 1, wherein the uncoated portion is bent outward over at least a portion of it so that when viewed from the axial side, the tip of the uncoated portion is arranged in a spiral shape with increasing curvature towards the outer circumference. Configuration 3: The electrode body for a secondary battery according to Configuration 2, wherein the uncoated portion is bent outward over its entire length from the inner end to the outer end so that when viewed from the axial side, the tip of the uncoated portion is arranged in a spiral shape. Configuration 4: A secondary battery electrode body according to Configuration 2, wherein a portion of the circumferential direction of the unpainted portion is folded outward in a radial direction so that the end of the portion of the circumferential direction overlaps with the portion adjacent to one side in the circumferential direction, and the folded portion is repeated in a spiral direction. Configuration 5: A secondary battery electrode body according to any one of Configurations 1 to 4, wherein one of the electrodes is the negative electrode. Configuration 6: A secondary battery electrode body according to any one of Configurations 1 to 5, wherein the unpainted portion is flat with no irregularities throughout its tip edge when it is standing upright in the axial direction before being folded outward. Configuration 7: A secondary battery comprising a secondary battery electrode body according to any one of Configurations 1 to 6 and an outer casing for housing the electrode body, wherein a current collector plate is joined to the tip of the unpainted portion.Configuration 8: A method for manufacturing an electrode body for a secondary battery as described in Configuration 1, comprising: holding the electrode body in a holding part, rotating the electrode body around an axis extending in the vertical direction, moving the holding part along a horizontal straight path, and, as the holding part moves, pressing a hemispherical pressing part, which has been previously supported on the upper side of the straight path, against the unpainted part extending in the vertical direction from the inner circumference, thereby pushing the unpainted part toward the outer circumference, wherein in the pushing step, the contact point between the unpainted part and the pressing part is moved in a spiral shape from the inside to the outside at the upper end of the unpainted part.

[0062] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14, 14a Electrode body for secondary battery (electrode body), 15 Outer can, 16 Sealing body, 17 Negative electrode current collector plate, 18 Positive electrode current collector plate, 19 Insulating plate, 20 Positive electrode connection lead, 21 Grooved section, 22 Internal terminal plate, 23 Lower valve body, 24 Insulating member, 25 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 30 Positive electrode core body, 32 Positive electrode mixture layer, 34 Positive electrode uncoated section, 40 Negative electrode core body, 42 Negative electrode mixture layer, 44 Negative electrode uncoated section, 45 Laminated section, 47 Axial extension section, 48 Outer peripheral tilted section, 49 Unit element, 50 Folded section, 52 Center hole, 90 Processing device, 91 Guide member, 92 moving part, 93 motor, 94 holding part, 95 first support part, 96 second support part, 97 plate part, 98 pressing part.

Claims

1. An electrode body for a secondary battery in which a positive electrode and a negative electrode are wound with a separator in between, wherein one of the negative electrode and the positive electrode has a core body and a laminated portion on at least one side of the core body on which a composite material layer is laminated, and has an uncoated portion provided at an end located axially to one side of the laminated portion, on which the composite material layer is not laminated, and the tip portion of the uncoated portion is continuously bent toward the outer circumference over its entire circumference.

2. The electrode body for a secondary battery according to claim 1, wherein, when viewed from one side in the axial direction, at least a portion of the uncoated portion is tilted outward so that the tip of the uncoated portion is arranged in a spiral shape with increasing curvature towards the outer circumference.

3. The electrode body for a secondary battery according to claim 2, wherein the uncoated portion is tilted outward so that, when viewed from one side in the axial direction, the tip of the uncoated portion is arranged spirally from the inner end to the outer end.

4. The electrode body for a secondary battery according to claim 2, wherein a portion of the uncoated portion in the circumferential direction folds outward in a radial direction, with the ends of the portion overlapping, so as to extend outward with respect to a portion adjacent to one side in the circumferential direction, thereby forming a folded portion, and the folded portion is repeated in a spiral direction.

5. The electrode body for a secondary battery according to claim 1, wherein one of the electrodes is the negative electrode.

6. The electrode body for a secondary battery according to claim 1, wherein the uncoated portion, when in an axially upright state before being bent toward the outer circumference, has a flat surface with no irregularities throughout its tip edge.

7. A secondary battery comprising an electrode body for a secondary battery as described in claim 1, and an outer casing for housing the electrode body, wherein a current collector plate is joined to the tip of the unpainted portion.

8. A method for manufacturing an electrode body for a secondary battery according to claim 1, comprising: holding the electrode body in a holding part, rotating the electrode body around an axis in the vertical direction while moving the holding part along a horizontal straight path, and, as the holding part moves, pressing a hemispherical pressing part, which has been previously supported on the upper side of the straight path, against the unpainted part extending in the vertical direction from the inner circumference, thereby pushing the unpainted part toward the outer circumference, wherein in the pushing step, the contact point between the unpainted part and the pressing part is moved in a spiral shape from the inside to the outside at the upper end of the unpainted part.

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