Cylindrical battery and method for manufacturing positive electrode for cylindrical battery

Abstract

In one example of an embodiment of the present invention, this cylindrical battery comprises: a positive electrode (11); a negative electrode; and a separator. The positive electrode (11) of the cylindrical battery includes: a positive electrode core (30); positive electrode mixture layers (31) disposed over the positive electrode core (30); and a positive electrode tab (20) joined to positive electrode core exposed sections (32). The positive electrode (11) of the cylindrical battery is provided with insulating tape (50) which is attached to the positive electrode mixture layers (31) positioned at either end of the positive electrode core exposed part (32) in the positive electrode length direction. The positive electrode mixture layers (31) adjacent to the positive electrode core exposed sections (32) in the positive electrode long direction thereof satisfy the condition that the difference between the maximum thickness of a first end having a raised section (33) and the maximum thickness of a second end not having the raised section (33) at a predetermined length is less than or equal to a predetermined value, and the condition that the peel strength between the positive electrode core (30) and the positive electrode mixture layers (31) is greater than or equal to a predetermined value.

Description

Cylindrical battery and method for manufacturing positive electrode for cylindrical battery

[0001] The present disclosure relates to a cylindrical battery and a method for manufacturing a positive electrode for a cylindrical battery.

[0002] Conventionally, batteries including a wound electrode assembly in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween have been widely known. Patent Document 1 discloses a battery in which a positive electrode has a core exposed portion in the longitudinal middle of the positive electrode, where the positive electrode core is exposed, and an electrode tab is joined to the core exposed portion. In addition, in order to prevent the occurrence of an internal short circuit, insulating tape is attached to the electrode tab and the core exposed portion.

[0003] Japanese Patent Application Laid-Open No. 2004-311282

[0004] The core exposed portion for joining the electrode tab is formed, for example, by intermittently applying a mixture slurry. Specifically, in the application process, the discharge of the mixture slurry onto the conveyed strip-shaped core is temporarily stopped and then resumed, thereby creating a core exposed portion where no mixture layer exists on the core. The mixture slurry has a certain viscosity, and the starting end of the application of the mixture slurry inevitably rises compared to the intermediate portion of the application, etc. The core exposed portion formed by intermittent application is adjacent to the end having this raised portion, and the insulating tape covering the core exposed portion is applied so as to overlap the raised portion.

[0005] When winding the electrode plate to create an electrode body, compressive stress is applied to the inner circumferential mixture layer arranged on the inner circumferential side of the core body, and tensile stress is applied to the outer circumferential mixture layer arranged on the outer circumferential side of the core body due to the difference in curvature. The inventors have found that when winding the electrode plate, stress is concentrated at the end of the insulating tape that overlaps the protrusion, which places a load on the mixture layer, causing the mixture layer to peel off from the core body.

[0006] The cylindrical battery according to the present disclosure is a cylindrical battery in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, the positive electrode including a positive electrode core, a positive electrode mixture layer disposed on the positive electrode core, and a positive electrode tab joined to a positive electrode core exposed portion, the positive electrode including insulating tape attached to the positive electrode mixture layer located at both ends of the positive electrode core exposed portion in the positive electrode longitudinal direction, and characterized in that any one of the following conditions (1) to (3) is satisfied: (1) In the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness over a predetermined length of a second end not having the raised portion is 9 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of the first end having the raised portion and the maximum thickness of the second end not having the raised portion in a predetermined length is 4 μm or less, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of the first end having the raised portion and the maximum thickness of the second end not having the raised portion in a predetermined length is 9 μm or less, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 8.5 N / m or more.

[0007] The method for manufacturing a cylindrical battery positive electrode according to the present disclosure includes the steps of intermittently applying a positive electrode slurry to the surface of a positive electrode core so as to form a positive electrode core exposed portion where the positive electrode core is exposed, and drying and rolling the coating to form a positive electrode mixture layer on the positive electrode core, and is characterized in that any of the following conditions (1) to (3) is satisfied: (1) In the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness over a predetermined length of a second end not having a raised portion is 7 μm or more and 24 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of the first end having the raised portion and the maximum thickness of the second end not having the raised portion in a predetermined length is 7 μm to 10 μm, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of the first end having the raised portion and the maximum thickness of the second end not having the raised portion in a predetermined length is 7 μm to 24 μm, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 8.5 N / m or more.

[0008] According to one aspect of the present disclosure, a cylindrical battery can be provided in which peeling of the positive electrode mixture layer during electrode plate winding is suppressed. The cylindrical battery according to the present disclosure has stable battery performance.

[0009] Fig. 2 is an axial cross-sectional view of a cylindrical battery according to an example of an embodiment; Fig. 3 is a front view of a positive electrode according to an example of an embodiment; Fig. 4 is a cross-sectional view taken along line AA in Fig. 2; Fig. 5 is a cross-sectional view of a positive electrode according to an example of an embodiment when wound; Fig. 6 is a cross-sectional view of a positive electrode according to another example of an embodiment.

[0010] With regard to the peeling of the mixture layer, no prior art documents have focused on the raised portions at the end of the mixture layer, and the relationship between the peeling of the mixture layer and the raised portions has not been considered at all until now. In prior art documents, the mixture layer is often illustrated as flat, as if it does not have raised portions, but these are merely schematic diagrams, and the ends of the mixture layer formed by applying the mixture slurry will always be raised. Although the raised portions at the end of the mixture layer are unavoidable, the fact that the end of the mixture layer has been depicted as flat in the schematic diagrams in prior art documents confirms that the raised portions have not been considered in relation to the peeling of the mixture layer. Therefore, the inventors' focus on the relationship between the peeling of the mixture layer and the raised portions at the end can be said to provide a completely new problem.

[0011] 4 , one end of the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 has a raised portion 33. The insulating tape 50, which is applied so as to cover the positive electrode tab 20 and the like joined to the positive electrode substrate exposed portion 32, is also applied so as to overlap the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32. At this time, the insulating tape 50, which is applied so as to overlap the first end having the raised portion 33, rises along the raised portion 33.

[0012] The present inventors conducted extensive research into the prevention of material mix layer peeling in cylindrical battery positive electrodes, and as a result, they focused on the protrusions at the ends of the insulating tape and discovered that, in the positive electrode material mix layer adjacent to the positive electrode substrate exposed portion in the longitudinal direction of the positive electrode, peeling of the material mix layer can be significantly prevented by setting the difference between the maximum thickness of the first end having the protrusion and the maximum thickness of the second end without the protrusion to a predetermined value or less. If the difference in thickness of the material mix layer adjacent to the substrate exposed portion is greater than the predetermined value, the effect of preventing material mix layer peeling cannot be obtained.

[0013] When the electrode plate is wound, a mixture bending reaction force is applied to the outer peripheral mixture layer, and a tape bending reaction force is applied to the insulating tape attached to the outer peripheral mixture layer so as to cover the outer peripheral exposed portion of the core.

[0014] The inventors of the present invention have focused on the fact that peeling of the mixture layer occurs when the sum of the mixture bending reaction force and the tape bending reaction force exceeds the peel strength, which indicates the adhesive strength between the core and the mixture layer, and have succeeded in suppressing peeling of the mixture layer by suppressing these bending reaction forces. Specifically, they have discovered that by reducing the thickness of the mixture layer, particularly the height of the protrusion at the first end that overlaps with the location where the insulating tape is attached and that inevitably occurs when the mixture slurry is applied, it is possible to suppress the mixture bending reaction force that acts in the direction that peels the mixture layer, and thereby suppress peeling of the mixture layer.

[0015] After further investigation, the inventors found that reducing the viscosity of the mixture slurry when it is applied to reduce the height of the protrusion at the first end increases the amount of organic solvent contained in the slurry, thereby reducing the peel strength between the core and the mixture layer and ultimately leading to peeling of the mixture layer. Based on this, they found that peeling of the mixture layer can be suppressed by setting the peel strength between the core and the mixture layer to a predetermined value or greater in accordance with a predetermined value indicating the difference in thickness of the mixture layer adjacent to the core exposed portion. Even if the difference in thickness of the mixture layer adjacent to the core exposed portion is equal to or less than the predetermined value, the effect of suppressing peeling of the mixture layer cannot be obtained if the peel strength is less than the predetermined value.

[0016] Hereinafter, an example of an embodiment of a cylindrical battery and a method for manufacturing a positive electrode for the cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. Note that the scope of the present disclosure includes configurations that selectively combine the respective components of the multiple embodiments and modifications described below.

[0017] FIG. 1 is a cross-sectional view of a cylindrical battery 10 according to an embodiment. As shown in FIG. 1 , the cylindrical battery 10 includes a wound electrode assembly 14, an electrolyte, and an outer can 16 that houses the electrode assembly 14 and the electrolyte. The cylindrical battery 10 is, for example, a lithium-ion secondary battery. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is a cylindrical metal container with a bottom and an open end in the axial direction. The opening of the outer can 16 is closed by a sealing member 17. Hereinafter, for convenience of explanation, the sealing member 17 side of the battery is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom.

[0018] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium precipitation. That is, the negative electrode 12 is formed to be longer in the length direction and width direction than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11. The electrode assembly 14 has a positive electrode tab 20 connected to the positive electrode 11 by welding or the like, and a negative electrode tab 21 connected to the negative electrode 12 by welding or the like.

[0019] The electrolyte may be an aqueous electrolyte, but in this embodiment, a non-aqueous electrolyte is used. The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, and preferably a lithium ion battery.

[0020] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0021] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0022] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode tab 20 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode tab 21 passes outside the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode tab 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode tab 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0023] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0024] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0025] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode assembly 14, with the positive electrode 11 being particularly described in detail below.

[0026] [Positive Electrode] Fig. 2 is a front view of the positive electrode 11. As shown in Fig. 2, the positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 provided on the positive electrode core 30. For the positive electrode core 30, a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film with such a metal disposed on the surface layer can be used. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode core 30.

[0027] The positive electrode 11 has a positive electrode core exposed portion 32 where the surface of the positive electrode core 30 is exposed. The positive electrode core exposed portion 32 has a predetermined width in the longitudinal direction of the positive electrode 11 and is formed in a strip shape extending parallel to the width direction of the positive electrode 11. The positive electrode core exposed portion 32 is a portion to which the positive electrode tab 20 is connected, and is provided by not forming a positive electrode mixture layer 31 on the positive electrode core 30. The positive electrode 11 can be produced, for example, by applying a positive electrode slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the positive electrode core 30, leaving the portion that will become the positive electrode core exposed portion 32, drying the coating, and then compressing it to form a positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0028] 2 , the positive electrode core exposed portion 32 is formed in only a portion of the width direction of the positive electrode 11. More specifically, the positive electrode core exposed portion 32 is formed in the width direction from one end of the positive electrode 11 in the width direction, with a length of 50% or less of the entire width of the positive electrode core 30. The length of the positive electrode core exposed portion 32 along the width direction of the positive electrode 11 is preferably 17% or more and 50% or less, or 20% or more and 40% or less, of the entire width of the positive electrode core 30.

[0029] In this embodiment, the positive electrode core exposed portion 32 contacts only the upper end 11X of the positive electrode 11 in the width direction, but not the lower end 11Y of the positive electrode 11 in the width direction. A positive electrode mixture layer 31 is disposed on the surface of the region of the positive electrode core 30 adjacent to the positive electrode core exposed portion 32 in the width direction of the positive electrode 11. This allows the area of ​​the positive electrode mixture layer 31 to be increased, facilitating the achievement of a high capacity cylindrical battery 10. The positive electrode mixture layer 31 includes a first region aligned with the positive electrode core exposed portion 32 in the longitudinal direction of the positive electrode 11, and a second region aligned with the positive electrode core exposed portion 32 and the first region in the width direction of the positive electrode 11. The capacity of each region can be varied by changing the type and composition ratio of the positive electrode active material contained in the first region and the second region. As will be described in detail later with reference to FIG. 3 , an insulating tape 50 covering the positive electrode core exposed portion 32 is provided on the surface of the positive electrode 11.

[0030] Examples of binders contained in the positive electrode mixture layer 31 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF); olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer; and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. One type of binder may be used alone, or multiple types may be used in combination. The content of the binder is not particularly limited, but is, for example, 0.1% by mass to 5% by mass, preferably 0.8% by mass to 1% by mass, relative to the total weight of the positive electrode active material. In this case, the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is increased, which is effective in suppressing peeling of the positive electrode mixture layer 31.

[0031] The positive electrode mixture layer 31 contains at least acetylene black (hereinafter referred to as AB) as a conductive agent. The positive electrode mixture layer 31 may also contain a conductive agent other than AB, for example, carbon black such as ketjen black, graphite, carbon nanotubes (hereinafter referred to as CNT), carbon nanofibers, graphene, or other carbon fibers. However, from the viewpoint of cost, the main component of the conductive agent is preferably AB, and the positive electrode mixture layer 31 may contain substantially only AB as the conductive agent.

[0032] 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 lithium-containing metal composite oxide is a composite oxide containing Ni, Co, Mn, and Al. The positive electrode active material is, for example, a lithium-containing metal composite oxide having a composition formula of Li ａ Ni ｂ Co （１－ｂ－ｃ―ｄ） Mn ｃ Al ｄ O ｅ(0.9<a≦1.1, 0.87≦b≦0.93, 0<c<0.08, 0<d≦0.08, 1.9≦e≦2.1).

[0033] The positive electrode active material contains Mn as an essential component. Mn stabilizes the crystalline structure of the composite oxide. The positive electrode active material also contains Co and Al as other essential components. While such a positive electrode active material tends to have low peel strength, it can achieve high capacity.

[0034] Next, the configuration of the positive electrode mixture layer 31 will be described in more detail with reference to Figures 3 and 4. Figure 3 is a cross-sectional view taken along line AA in Figure 2. Figure 4 is a cross-sectional view of a wound positive electrode according to an embodiment.

[0035] As shown in FIG. 3 , the thickness of the positive electrode core 30 after rolling is preferably 5 μm to 25 μm, more preferably 10 μm to 20 μm. Hereinafter, for convenience of explanation, as shown in FIG. 3 , the positive electrode mixture layer 31 arranged on the first surface 11A of the positive electrode 11 will be referred to as the first positive electrode mixture layer 31A, and the positive electrode mixture layer 31 arranged on the second surface 11B of the positive electrode 11 will be referred to as the second positive electrode mixture layer 31B. The first positive electrode mixture layer 31A and the second positive electrode mixture layer 31B have, for example, approximately the same thickness. The thicknesses of the first positive electrode mixture layer 31A and the second positive electrode mixture layer 31B are each greater than the thickness of the positive electrode core 30 and, excluding the protruding portion 33 described below, are, for example, 80 μm to 150 μm after rolling.

[0036] The positive electrode 11 has a positive electrode core exposed portion 32 where the positive electrode mixture layer 31 is not disposed and the positive electrode core 30 is exposed. The positive electrode core exposed portions 32 provided on the first surface 11A and the second surface 11B of the positive electrode 11 are disposed in positions where they overlap each other in the thickness direction of the positive electrode 11. The length of the positive electrode core exposed portion 32 along the longitudinal direction of the positive electrode 11 is, for example, 5 mm or more and 50 mm or less. The positive electrode core exposed portion 32 can be formed by intermittent application in which the positive electrode mixture slurry is not applied to a portion of the positive electrode core 30. A plurality of positive electrode core exposed portions 32 may be provided in the longitudinal direction of the positive electrode 11.

[0037] A positive electrode tab 20 is joined to at least one surface of the positive electrode substrate exposed portion 32. In this embodiment, the positive electrode tab 20 is joined to the first surface 11A of the positive electrode 11. When a plurality of positive electrode substrate exposed portions 32 are provided in the longitudinal direction of the positive electrode 11, the positive electrode tabs 20 are joined to each of the plurality of positive electrode substrate exposed portions 32. Note that the first surface 11A of the positive electrode 11 to which the positive electrode tab 20 is joined may be located on either the outer surface side or the inner surface side of the electrode body 14, but in this embodiment, the first surface 11A of the positive electrode 11 is located on the outer surface side (see FIG. 4 ).

[0038] The positive electrode tab 20 is made of, for example, a metal containing aluminum as a main component. The thickness of the positive electrode tab 20 is generally greater than the thicknesses of the first positive electrode mixture layer 31A and the second positive electrode mixture layer 31B for reasons such as reducing electrical resistance. In other words, the positive electrode tab 20 protrudes from the surface of the positive electrode 11 in the thickness direction of the positive electrode 11. The thickness of the positive electrode tab 20 is, for example, 100 μm or more and 200 μm or less. The width of the positive electrode tab 20 is, for example, 3 mm or more and 6 mm or less.

[0039] An insulating tape 50 covering the positive electrode core exposed portion 32 is provided on the surface of the positive electrode 11. On the first surface 11A of the positive electrode 11 having the positive electrode tab 20, the insulating tape 50 covers the entire positive electrode core exposed portion 32, a portion of the positive electrode tab 20, and the first positive electrode mixture layer 31A around the positive electrode core exposed portion 32. On the second surface 11B of the positive electrode 11 not having the positive electrode tab 20, the insulating tape 50 covers the entire positive electrode core exposed portion 32 and the second positive electrode mixture layer 31B around the positive electrode core exposed portion 32. The overlapping portion of the insulating tape 50 and the positive electrode mixture layer 31 has a width of, for example, 4 mm. By providing the insulating tape 50, contact between the positive electrode core exposed portion 32 or the positive electrode tab 20 and the negative electrode 12 can be suppressed if the separator 13 is damaged.

[0040] The insulating tape 50 is, for example, an adhesive tape having a base layer and an adhesive layer formed on one surface of the base layer. A heat-resistant layer containing inorganic particles such as metal oxide may be provided between the base layer and the adhesive layer. The base layer may be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate). The thickness of the base layer is, for example, 5 μm or more and 50 μm or less, and preferably 10 μm or more and 30 μm or less.

[0041] The adhesive layer is a portion for adhering the insulating tape 50 to the surface of the positive electrode 11. The thickness of the adhesive layer is, for example, 1 μm or more and 30 μm or less, and preferably 5 μm or more and 25 μm or less. The adhesive portion may contain at least one of a rubber-based polymer and an acrylic-based polymer. The rubber-based polymer and the acrylic-based polymer have adhesive properties, and therefore can adhere the insulating tape 50 to the surface of the positive electrode 11. The adhesive layer may further contain, for example, a silicone-based polymer.

[0042] The positive electrode mixture layer 31 has a raised portion 33 that rises in the thickness direction of the positive electrode 11 in one of the regions adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction. For ease of explanation, the side of the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 that has the raised portion 33 is referred to as a first end, and the side that does not have the raised portion 33 is referred to as a second end. The first end of the positive electrode mixture layer 31 is the application start end side when intermittently applying the positive electrode slurry, and the second end is the application end side.

[0043] The raised portion 33 is formed over the length of the first end of the positive electrode mixture layer 31 in the positive electrode width direction, and raised in the thickness direction of the positive electrode mixture layer 31. The raised portion 33 has a dimension of, for example, 1 mm or more and 6 mm or less in the longitudinal direction of the positive electrode 11 from the edge of the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 (w in FIG. 3 ).

[0044] In the present embodiment, in the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, the difference (h in FIG. 3 ) between the maximum thickness of the first end having the protrusion 33 and the maximum thickness in a predetermined length of the second end not having the protrusion 33 is set to 9 μm or less, thereby mitigating the tape bending reaction force and the mixture bending reaction force when winding the electrode plate. In the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, when the difference between the maximum thickness of the first end having the protrusion 33 and the maximum thickness in a predetermined length of the second end not having the protrusion 33 is 9 μm or less and the peel strength between the positive electrode substrate 30 and the positive electrode mixture layer 31 is 9 N / m or more, peeling of the positive electrode mixture layer 31 from the positive electrode substrate 30 can be suppressed.

[0045] The composite slurry is a viscous mixture, and the coating film formed by applying the composite slurry has a shape that includes some irregularities even after rolling. The difference between the maximum thickness of the first end having the raised portion 33 and the maximum thickness over a predetermined length of the second end not having the raised portion 33 is a numerical representation of the protrusion on the first end side having the raised portion 33, based on the maximum thickness over a predetermined length of the second end, which is the end of the composite slurry application. The predetermined length for measuring the maximum thickness of the second end is not particularly limited, but is preferably at least the length of the portion overlapping with the insulating tape 50, for example, 4 mm.

[0046] In addition to the above conditions, in the positive electrode mixture layer 31 adjacent to the positive electrode core exposed portion 32 in the positive electrode longitudinal direction, if the difference (h in FIG. 3 ) between the maximum thickness of the first end having the raised portion 33 and the maximum thickness over a predetermined length of the second end not having the raised portion 33 is 4 μm or less, and if the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is 4 N / m or more, the tape bending reaction force and the mixture bending reaction force during winding of the electrode plate are alleviated, and peeling of the positive electrode mixture layer 31 from the positive electrode core 30 can be suppressed.

[0047] As another condition, when the positive electrode mixture layer 31 contains CNTs, and in the positive electrode mixture layer 31 adjacent to the positive electrode core exposed portion 32 in the positive electrode longitudinal direction, the difference (h in FIG. 3 ) between the maximum thickness of the first end having the raised portion and the maximum thickness over a predetermined length of the second end not having the raised portion is 9 μm or less, and the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is 8.5 N / m or more, the tape bending reaction force and the mixture bending reaction force during winding of the electrode plate can also be reduced, and peeling of the positive electrode mixture layer 31 from the positive electrode core 30 can be suppressed.

[0048] The CNT contained in the positive electrode active material as a conductive agent has a so-called anchor effect, and it is presumed that peeling of the positive electrode mixture layer 31 can be suppressed if the peel strength is 8.5 N / m or more.

[0049] On the other hand, because the use of CNTs is very costly, cylindrical batteries that do not substantially contain CNTs may be produced from the perspective of cost reduction. In this case, it is preferable that, in the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, the difference between the maximum thickness of the first end having the protrusion 33 and the maximum thickness of the second end not having the protrusion 33 in a predetermined length is 9 μm or less, and the peel strength between the positive electrode substrate 30 and the positive electrode mixture layer 31 is 9 N / m or more, or, in the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, the difference between the maximum thickness of the first end having the protrusion 33 and the maximum thickness of the second end not having the protrusion 33 in a predetermined length is 4 μm or less, and the peel strength between the positive electrode substrate 30 and the positive electrode mixture layer 31 is 4 N / m or more.

[0050] Even if the difference between the maximum thickness of the first end having the raised portion 33 and the maximum thickness of the second end in a predetermined length without the raised portion 33 is 9 μm or less, peeling of the positive electrode mixture layer 31 cannot be sufficiently suppressed if the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is less than 9 N / m, as shown in the results of the examples described below. This is because even if the difference between the maximum thickness of the first end having the raised portion 33 and the maximum thickness of the second end in a predetermined length without the raised portion 33 is kept to a predetermined value or less to suppress the mixture bending reaction force and the tape bending reaction force, the bending reaction force still exceeds the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31. This also applies when the difference between the maximum thickness of the first end having the raised portion 33 and the maximum thickness of the second end in a predetermined length without the raised portion 33 is 4 μm or less but the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is less than 4 N / m.

[0051] The peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 depends not only on the binder content in the positive electrode active material but also on the drying rate of the positive electrode slurry. Specifically, the binder content is preferably 0.8 mass % or more and 1 mass % or less, relative to the total weight of the positive electrode active material. In this case, a higher peel strength is obtained between the positive electrode core 30 and the positive electrode mixture layer 31, compared to a case in which the positive electrode slurry contains less than 0.8 mass % of the binder relative to the total weight of the positive electrode active material and is dried at a similar slurry drying rate.

[0052] If the drying rate of the positive electrode slurry is fast, the solvent contained in the slurry evaporates rapidly. At this time, the binder migrates to the upper layer of the positive electrode slurry along with the evaporated solvent and becomes unevenly distributed, a phenomenon known as migration. Since the effect of the binder is not fully obtained, the peel strength between the positive electrode mixture layer 31 and the positive electrode core 30 where migration has occurred tends to be low. For this reason, in order to ensure the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31, it is preferable to include a predetermined amount of binder and dry the positive electrode slurry at a rate that minimizes the occurrence of migration.

[0053] The manufacturing process of the positive electrode 11 includes the following steps (a) and (b), and satisfies any one of the conditions (1) to (3): (a) a step of intermittently applying a positive electrode slurry to the surface of a positive electrode core so as to form a positive electrode core exposed portion where the positive electrode core is exposed; (b) a step of drying the coating and rolling the coating to form a positive electrode mixture layer on the positive electrode core; (1) in the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness over a predetermined length of a second end not having a raised portion is 7 μm or more and 24 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 7 μm to 10 μm, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 7 μm to 24 μm, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 8.5 N / m or more.

[0054] The positive electrode slurry will be described in detail below. The dispersion medium disperses the positive electrode active material and the conductive agent and dissolves the binder, for example. Depending on the type of binder, water, lower alcohols such as ethanol, etc. can be used as the dispersion medium, but generally, aprotic polar solvents are used. Examples of the dispersion medium include NMP, methyl ethyl ketone, and dimethylformamide. Among these, NMP is preferably used.

[0055] A conventionally known mixer or the like can be used to mix (knead) the positive electrode active material, conductive agent, binder, and dispersion medium. Examples of mixers include a planetary mixer, homomixer, pin mixer, high-speed mixer, disperser, roll mill, ball mill, jet mill, kneader, etc. Among these, it is preferable to use a planetary mixer. A planetary mixer is a rotation-revolution type agitation mixer that can impart a strong shear force to the slurry by planetary motion of blades.

[0056] In the present embodiment, in the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of the first end having the protruding portion 33 and the maximum thickness in a predetermined length of the second end not having the protruding portion 33 is set to 7 μm or more and 24 μm or less, thereby alleviating the tape bending reaction force and the mixture bending reaction force during winding of the electrode plate. In the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, when the difference before rolling between the maximum thickness of the first end having the protruding portion 33 and the maximum thickness in a predetermined length of the second end not having the protruding portion 33 is 7 μm or more and 24 μm or less, and when the peel strength between the positive electrode substrate 30 and the positive electrode mixture layer 31 is 9 N / m or more, peeling of the positive electrode mixture layer 31 from the positive electrode substrate 30 can be suppressed.

[0057] The composite slurry is a viscous mixture, and the coating film after application has a shape that includes some irregularities. The difference between the maximum thickness of the first end having the raised portion 33 and the maximum thickness in a predetermined length of the second end without the raised portion 33 before rolling is a numerical representation of the protrusion before rolling on the first end side having the raised portion 33, based on the maximum thickness in a predetermined length of the second end, which is the terminal side of the composite slurry application. The predetermined length for measuring the maximum thickness of the second end is not particularly limited, but is preferably at least the length of the portion overlapping with the insulating tape 50, for example, 4 mm.

[0058] When preparing a mixture slurry so that the difference between the maximum thickness of the first end of the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction and the maximum thickness of the second end at a predetermined length before rolling is less than 7 μm, the viscosity of the mixture slurry must be reduced. However, a mixture slurry with low viscosity exhibits poor drainage during application and is unsuitable for intermittent application. Furthermore, when the viscosity of the mixture slurry is reduced, the mixture slurry contains a large amount of organic solvent, which reduces the peel strength between the substrate and the mixture layer and makes the mixture layer more likely to peel. For this reason, it is preferable that the difference between the maximum thickness of the first end of the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction and the maximum thickness of the second end at a predetermined length before rolling be 7 μm or more.

[0059] In addition to the above conditions, in the positive electrode mixture layer 31 adjacent to the positive electrode core exposed portion 32 in the positive electrode longitudinal direction, if the difference before rolling between the maximum thickness of the first end having the raised portion 33 and the maximum thickness over a predetermined length of the second end not having the raised portion 33 is 7 μm or more and 10 μm or less, and if the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is 4 N / m or more, the tape bending reaction force and the mixture bending reaction force during winding of the electrode plate are alleviated, and peeling of the positive electrode mixture layer 31 from the positive electrode core 30 can be suppressed.

[0060] As another condition, when the positive electrode mixture layer 31 contains CNTs, and in the positive electrode mixture layer 31 adjacent to the positive electrode core exposed portion 32 in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of the first end having the raised portion 33 and the maximum thickness over a predetermined length of the second end not having the raised portion 33 is 7 μm or more and 24 μm or less, and the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is 8.5 N / m or more, the tape bending reaction force and the mixture bending reaction force during winding of the electrode plate can also be reduced, and peeling of the positive electrode mixture layer 31 from the positive electrode core 30 can be suppressed.

[0061] The CNT contained in the positive electrode active material as a conductive agent has a so-called anchor effect, and it is presumed that peeling of the positive electrode mixture layer 31 can be suppressed if the peel strength is 8.5 N / m or more.

[0062] On the other hand, because the use of CNTs is very costly, cylindrical batteries that do not substantially contain CNTs may be produced from the perspective of cost reduction. In this case, it is preferable that, in the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of the first end having the raised portion 33 and the maximum thickness of the second end not having the raised portion 33 in a predetermined length is 7 μm to 24 μm, and the peel strength between the positive electrode substrate 30 and the positive electrode mixture layer 31 is 9 N / m or more, or, in the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed portion 32 in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of the first end having the raised portion 33 and the maximum thickness of the second end not having the raised portion 33 in a predetermined length is 7 μm to 10 μm, and the peel strength between the positive electrode substrate 30 and the positive electrode mixture layer 31 is 4 N / m or more.

[0063] Even if the difference before rolling between the maximum thickness of the first end having the raised portion 33 and the maximum thickness in a predetermined length of the second end not having the raised portion 33 is 24 μm or less, if the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31 is less than 9 N / m, peeling of the positive electrode mixture layer 31 cannot be sufficiently suppressed, as shown in the results of the Examples described later. This is because even if the difference before rolling between the maximum thickness of the first end having the raised portion 33 and the maximum thickness in a predetermined length of the second end not having the raised portion 33 is suppressed to a predetermined value or less, thereby suppressing the mixture bending reaction force and the tape bending reaction force, the bending reaction force still exceeds the peel strength between the positive electrode core 30 and the positive electrode mixture layer 31.

[0064] [Negative Electrode] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode core can be a foil of a metal stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film with such a metal disposed on its surface. The negative electrode mixture layer contains a negative electrode active material and a binder and is preferably provided on both sides of the negative electrode core. The negative electrode 12 can be fabricated, for example, by applying a negative electrode slurry containing a negative electrode active material and a binder to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core. Metallic lithium foil can also be used as the negative electrode 12. Alternatively, the negative electrode 12 may be composed only of a negative electrode core, with metallic lithium being deposited on the core surface during battery charging.

[0065] The negative electrode active material is not particularly limited as long as it reversibly absorbs and releases lithium ions, and typically, carbon materials such as graphite are used. Furthermore, elements that alloy with Li, such as Si and Sn, or materials containing such elements, may also be used as the negative electrode active material. Among these, silicon-containing materials containing Si are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. One type of negative electrode active material may be used alone, or multiple types may be used in combination.

[0066] The carbon material functioning as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Among these, it is preferable to use artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, and amorphous graphite, or a mixture thereof. Examples of silicon-containing materials functioning as the negative electrode active material include silicon alloys, silicon compounds, and composite materials containing Si. A suitable silicon-containing material is a composite particle containing an ion-conducting phase and a Si phase dispersed in the ion-conducting phase.

[0067] As with the positive electrode 11, the binder contained in the negative electrode mixture layer can be a fluororesin, an olefin resin, PAN, a polyimide, a polyamide, an acrylic resin, or the like. However, polyvinyl acetate, styrene-butadiene rubber (SBR), or the like may also be used. Among these, SBR is preferably used. A single binder may be used, or multiple binders may be used in combination. The negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. These function as thickeners in the negative electrode slurry. The content of the binder is not particularly limited, but is, for example, 0.1% by mass or more and 5% by mass or less, relative to the mass of the negative electrode mixture layer. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0068] [Separator] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0069] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphate compounds. The filler layer can be formed by applying a slurry containing the filler to the surface of the positive electrode 11, the negative electrode 12, or the separator 13.

[0070] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0071] Example 1 Preparation of Positive Electrode Slurry A positive electrode active material having the composition formula LiNi ０．９ Co ０．０４ Mn ０．０５ Al ０．０１ O ２A composite oxide represented by the formula: 100 (mass ratio) of the positive electrode active material, 0.80 (mass ratio) of AB as a conductive agent, and 0.82 (mass ratio) of polyvinylidene fluoride (PVdF) as a binder were added to a liquid component (NMP) and kneaded to obtain a positive electrode slurry containing the positive electrode active material, the conductive agent, and the binder.

[0072] [Preparation of Positive Electrode] The above positive electrode slurry was applied to both sides of a positive electrode core (total width: 750 mm) made of aluminum foil, and the coating was dried and compressed. The positive electrode core was then cut to a predetermined electrode size to obtain a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode core. At this time, a positive electrode core exposed portion was provided at the longitudinal center of the positive electrode, extending 20 mm in the width direction (33% of the electrode plate width) from one end of the positive electrode core in the width direction, where the core surface was exposed. The width (electrode plate width) of the positive electrode core (positive electrode) after cutting was 60 mm.

[0073] [Fabrication of Negative Electrode] Graphite was used as the negative electrode active material. The negative electrode active material, a dispersion of styrene butadiene rubber (SBR), and a sodium salt of carboxymethyl cellulose (CMC-Na) were mixed in a solids mass ratio of 98:1:1, and water was used as the dispersion medium to prepare a negative electrode slurry. Next, the negative electrode slurry was applied to both sides of a negative electrode core made of copper foil, leaving a predetermined exposed portion. The coating was then dried and compressed, and the negative electrode core was cut to a predetermined electrode size to obtain a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode core.

[0074] [Preparation of non-aqueous electrolyte] LiPF 6 was dissolved in a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 3:7 (25°C) at a concentration of 1.2 mol / L. ６ was dissolved to obtain a non-aqueous electrolyte solution.

[0075] [Preparation of Test Cell] The positive electrode with an aluminum tab welded to its exposed portion and insulating tape attached, and the negative electrode with a nickel tab welded to its exposed portion and insulating tape attached were spirally wound together with a separator interposed therebetween to prepare a wound electrode assembly. This electrode assembly was placed in a cylindrical outer can with a bottom, the nonaqueous electrolyte was poured into it, and the opening of the outer can was sealed with a sealing member via a gasket to obtain a test cell (cylindrical battery) X1.

[0076] Examples 2 to 4 In the preparation of the positive electrodes, positive electrodes and test cells X2 to X4 were obtained in the same manner as in Example 1, except that the discharge pressure during intermittent application and the slurry drying speed were adjusted.

[0077] Example 5 A positive electrode and a test cell X5 were obtained in the same manner as in Example 1, except that in the preparation of the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent, and the binder was changed to 100:0.90:0.92, and in the production of the positive electrode, the discharge pressure during intermittent application and the drying speed of the slurry were adjusted.

[0078] Examples 6 to 9 In the preparation of the positive electrodes, positive electrodes and test cells X6 to X9 were obtained in the same manner as in Example 5, except that the discharge pressure during intermittent application and the slurry drying speed were adjusted.

[0079] Example 10 A positive electrode and a test cell X10 were obtained in the same manner as in Example 1, except that in preparing the positive electrode slurry, CNT was used as a conductive agent, and the positive electrode active material, the conductive agent (CNT), and the binder were kneaded so that the mass ratio was 100:0.40:0.65, and in producing the positive electrode, the discharge pressure during intermittent application and the drying speed of the slurry were adjusted.

[0080] Comparative Examples 1 to 6 Positive electrodes and test cells Y1 to Y6 were obtained in the same manner as in Example 1, except that the discharge pressure during intermittent application and the slurry drying speed were adjusted in the preparation of the positive electrodes.

[0081] Comparative Example 7 A positive electrode and a test cell Y7 were obtained in the same manner as in Example 5, except that in the preparation of the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent, and the binder was changed to 100:0.90:0.92, and the discharge pressure during intermittent application and the drying speed of the slurry were adjusted.

[0082] <Comparative Examples 8 to 10> Positive electrodes and test cells Y8 to 10 were obtained in the same manner as in Example 1, except that in the preparation of the positive electrode slurry, the mass ratio of the positive electrode active material, the conductive agent, and the binder was changed to 100:0.75:0.60, and in the production of the positive electrode, the discharge pressure during intermittent application and the slurry drying speed were adjusted.

[0083] Each test cell in the examples and comparative examples was evaluated using the following method, and the peel strength between the positive electrode core and the positive electrode mixture layer was also measured. Furthermore, the maximum thickness of the positive electrode mixture layer at the first end and the maximum thickness at a predetermined length at the second end were measured after applying the positive electrode slurry and after rolling, and the difference in thickness was calculated. The evaluation results and measurement results are shown in Table 1. Peeling of the positive electrode mixture layer was determined by cross-sectional observation using an X-ray CT scanner. Test cells in which no distortion was observed at the end of the insulating tape were evaluated as "(peel) not present," and test cells in which distortion was observed at the end of the insulating tape were evaluated as "(peel) present."

[0084] [Evaluation of Peeling of Positive Electrode Mixture Layer] After winding the positive and negative electrodes and separator, the cross section was observed using an X-ray CT device to evaluate whether or not the positive electrode mixture layer had peeled off near the end of the adhesive layer of the protective tape.

[0085] [Measurement of Peel Strength] The peel strength between the positive electrode mixture layer and the positive electrode current collector was measured by peeling the positive electrode current collector (aluminum foil) in a direction 90° from the positive electrode surface of each Example and Comparative Example using a Minebia (TGJ2kN, manufactured by Minebia Mitsumi Inc.) The peel strength was measured twice on both sides of each Example and Comparative Example, and the average was taken as the peel strength.

[0086]

[0087] As shown in Table 1, peeling of the positive electrode mixture layer was not observed in any of the test cells X1 to X10 of the example. In contrast, in the test cells Y1, Y2, Y7, and Y9 of the comparative example, in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of the first end having the raised portion and the maximum thickness of the second end without the raised portion in a predetermined length was greater than 9 μm, and peeling of the positive electrode mixture layer was confirmed. In the test cells Y3 to Y6, Y8, and Y10 of the comparative example, although the difference between the maximum thickness of the first end having the raised portion and the maximum thickness of the second end without the raised portion in a predetermined length was 9 μm or less in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the peel strength between the positive electrode substrate and the positive electrode mixture layer was less than 9 N / m, resulting in peeling of the positive electrode mixture layer.

[0088] From the above results, it can be seen that the test cells X1 to X10 of the example can suppress peeling of the positive electrode mixture layer.

[0089] The above-described embodiment can be appropriately modified in design without impairing the objectives of the present disclosure. As shown in FIG. 5 , the positive electrode 11 may have a terminal end of the positive electrode mixture slurry on the second surface 11B via the positive electrode core 30 so as to face the protruding portion 33 on the first surface 11A, and a protruding portion 33 on the second surface 11B via the positive electrode core 30 so as to face the terminal end of the positive electrode mixture slurry on the first surface 11A. By changing the conveyance direction of the positive electrode core 30 during application of the positive electrode mixture slurry, it is possible to apply the positive electrode mixture slurry so that the protruding portion 33 and the terminal end of the positive electrode mixture slurry face each other via the positive electrode core 30. By arranging the protruding portion 33 on the first surface 11A and the protruding portion 33 on the second surface 11B of the positive electrode so as to be offset, it is possible to reduce the difference in thickness of the positive electrode mixture layer, thereby suppressing peeling of the positive electrode mixture layer.

[0090] The present disclosure is further described by the following embodiments. Configuration 1: A cylindrical battery in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, wherein the positive electrode includes a positive electrode core, a positive electrode mixture layer disposed on the positive electrode core, and a positive electrode tab joined to a positive electrode core exposed portion, and the positive electrode includes insulating tape attached to the positive electrode mixture layer located at both ends of the positive electrode core exposed portion in the positive electrode longitudinal direction, and the cylindrical battery satisfies any of the following conditions (1) to (3): (1) In the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness over a predetermined length of a second end not having a raised portion is 9 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 4 μm or less, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 9 μm or less, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 8.5 N / m or more. Configuration 2: The cylindrical battery according to Configuration 1, wherein the positive electrode mixture layer contains a composite oxide containing Ni, Co, Mn, and Al as a positive electrode active material, and acetylene black as a conductive agent. Configuration 3: The cylindrical battery according to Configuration 1, wherein the positive electrode mixture layer is substantially free of carbon nanotubes.Configuration 4: The cylindrical battery according to Configuration 1, wherein the positive electrode has the positive electrode substrate exposed portion only in a portion in the width direction.Configuration 5: The cylindrical battery according to Configuration 1, wherein a plurality of the positive electrode substrate exposed portions are provided in the longitudinal direction of the positive electrode, and the positive electrode tabs are joined to each of the plurality of positive electrode substrate exposed portions.Configuration 6: A method for manufacturing a positive electrode for a cylindrical battery, comprising: a step of intermittently applying a positive electrode slurry to a surface of a positive electrode substrate so as to form positive electrode substrate exposed portions where the positive electrode substrate is exposed; and a step of drying and rolling the coating to form a positive electrode mixture layer on the positive electrode substrate, wherein the method satisfies any of the following conditions (1) to (3).(1) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 7 μm or more and 24 μm or less, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 7 μm or more and 10 μm or less, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion over a predetermined length is 7 μm or more and 24 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 8.5 N / m or more.

[0091] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode tab, 21 Negative electrode tab, 22 Grooved portion, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core, 31 Positive electrode mixture layer, 32 Positive electrode core exposed portion, 33 Raised portion, 50 Insulating tape

Claims

1. A cylindrical battery in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, the positive electrode including a positive electrode core, a positive electrode mixture layer placed on the positive electrode core, and a positive electrode tab joined to a positive electrode core exposed portion, the positive electrode is provided with insulating tape attached to the positive electrode mixture layer located at both ends of the positive electrode core exposed portion in the positive electrode longitudinal direction, and the cylindrical battery satisfies any of the following conditions (1) to (3): (1) In the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness over a predetermined length of a second end not having a raised portion is 9 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 4 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 9 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 8.5 N / m or more.

2. The cylindrical battery according to claim 1, wherein the positive electrode mixture layer contains a composite oxide containing Ni, Co, Mn, and Al as a positive electrode active material, and acetylene black as a conductive agent.

3. The cylindrical battery according to claim 1, wherein the positive electrode mixture layer is substantially free of carbon nanotubes.

4. The cylindrical battery according to claim 1, wherein the positive electrode has the positive electrode substrate exposed portion only in a portion in the width direction.

5. The cylindrical battery according to claim 1, wherein a plurality of the positive electrode substrate exposed portions are provided in the longitudinal direction of the positive electrode, and the positive electrode tabs are respectively joined to the plurality of positive electrode substrate exposed portions.

6. A method for manufacturing a positive electrode for a cylindrical battery, comprising: a step of intermittently applying a positive electrode slurry to the surface of a positive electrode core so as to form a positive electrode core exposed portion where the positive electrode core is exposed; and a step of drying and rolling the coating to form a positive electrode mixture layer on the positive electrode core, wherein the method satisfies any of the following conditions (1) to (3): (1) In the positive electrode mixture layer adjacent to the positive electrode core exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness over a predetermined length of a second end not having a raised portion is 7 μm or more and 24 μm or less, and the peel strength between the positive electrode core and the positive electrode mixture layer is 9 N / m or more. (2) In the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 7 μm to 10 μm, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 4 N / m or more. (3) The positive electrode mixture layer contains carbon nanotubes, and in the positive electrode mixture layer adjacent to the positive electrode substrate exposed portion in the positive electrode longitudinal direction, the difference before rolling between the maximum thickness of a first end having a raised portion and the maximum thickness of a second end not having a raised portion in a predetermined length is 7 μm to 24 μm, and the peel strength between the positive electrode substrate and the positive electrode mixture layer is 8.5 N / m or more.

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