Secondary battery and positive electrode for secondary battery

Abstract

A cylindrical battery (10) comprises an electrode body (14) in which a positive electrode (11) and a negative electrode (12) are wound with a separator (13) therebetween. A first tape (51) and a second tape (52) are affixed to the positive electrode (11) so as to cover a positive electrode start end (11x) positioned on the winding start side of the electrode body (14). The second tape (52) has an adhesive layer (54) that adheres to a second positive electrode mixture layer (31B) positioned on the winding inner surface of the positive electrode (11), whereas the first tape (51) does not substantially have an adhesive layer that adheres to a first positive electrode mixture layer (31A) positioned on the winding outer surface of the positive electrode (11).

Description

Secondary battery and positive electrode for secondary battery

[0001] The present disclosure relates to a secondary battery and a positive electrode for a secondary battery, and more particularly to a secondary battery provided with a wound electrode body and a positive electrode for a secondary battery used in a wound electrode body.

[0002] Some secondary batteries such as cylindrical batteries include a wound electrode body having a structure in which a positive electrode and a negative electrode are wound in a spiral shape with a separator interposed therebetween. In a wound electrode body, generally, at the winding start side of the electrode body, the negative electrode start end, which is the end of the negative electrode, extends closer to the winding center side than the positive electrode start end, which is the end of the positive electrode, and the positive electrode start end is sandwiched between the negative electrodes through a separator.

[0003] The electrodes constituting the wound electrode body have a long core body and a mixture layer provided on the core body, and are manufactured by cutting the long core body to a desired length. At this time, cut burrs may occur at the longitudinal ends of the electrodes. Cut burrs are protrusions of an unintended shape, and if these penetrate the separator, there is a risk of internal short circuit of the battery. In particular, since the positive electrode start end is sandwiched between the negative electrodes, the risk of short circuit due to cut burrs is high at the positive electrode start end.

[0004] Patent Document 1 discloses a wound electrode body provided with a protective tape adhered to the longitudinal end of an electrode for the purpose of preventing the occurrence of a short circuit caused by the above cut burrs. Patent Document 2 also discloses a wound electrode body provided with a core body exposed portion formed at the positive electrode start end and a protective tape adhered from the exposed portion over the positive electrode mixture layer.

[0005] JP 2002-42881 A International Publication No. 2024 / 135586

[0006] The protective tape of Patent Document 2 is also adhered on the positive electrode mixture layer. In the electrode body of Patent Document 2, a core body exposed portion is formed at the positive electrode start end. However, when the ends of the positive electrode core body and the positive electrode mixture layer coincide, the protective tape will be adhered on the positive electrode mixture layer. Adhering a tape to the positive electrode start end can suppress the influence of cut burrs, but as a result of the study by the present inventors, it has been found that cracks are likely to occur in the positive electrode mixture layer due to the tape adhered to the positive electrode mixture layer.

[0007] The purpose of this disclosure is to address cracks in the positive electrode mixture layer while suppressing the effects of cut burrs at the positive electrode starting point. When cracks occur in the positive electrode mixture layer, for example, the battery reaction becomes non-uniform, leading to a decrease in charge-discharge cycle characteristics.

[0008] The secondary battery according to this disclosure comprises a positive electrode, a negative electrode, and a separator, and is an electrode body in which the positive electrode and the negative electrode are wound around the separator, wherein a tape is attached to the positive electrode so as to cover the positive electrode start end, which is the end of the positive electrode at the starting side of the winding of the electrode body, and the tape comprises a first tape that covers a first positive electrode mixture layer located on the outer surface of the winding of the positive electrode facing radially outward of the electrode body, and a second tape that covers a second positive electrode mixture layer located on the inner surface of the winding of the positive electrode facing radially inward of the electrode body, wherein the first tape substantially does not have an adhesive layer that adheres to the first positive electrode mixture layer, and the second tape has an adhesive layer that adheres to the second positive electrode mixture layer.

[0009] The positive electrode for a secondary battery according to this disclosure is a positive electrode for a secondary battery used in a wound electrode body, and comprises a tape that is attached so as to cover one longitudinal end of the positive electrode at the winding start side of the electrode body, wherein the tape includes a first tape that covers a first positive electrode mixture layer which is the outer surface of the winding of the positive electrode facing radially outward of the electrode body, and a second tape that covers a second positive electrode mixture layer which is the inner surface of the winding of the positive electrode facing radially inward of the electrode body, wherein the first tape substantially does not have an adhesive layer that adheres to the first positive electrode mixture layer, and the second tape has an adhesive layer that adheres to the second positive electrode mixture layer.

[0010] The positive electrode and secondary battery according to this disclosure can suppress cracks in the positive electrode mixture layer while suppressing the effect of cut burrs at the positive electrode starting end, thereby reducing the risk of short circuits caused by cut burrs, for example.

[0011] This is a cross-sectional view of a cylindrical battery, which is one example of an embodiment. This is a diagram showing a part of the radial cross-section of an electrode body, which is one example of an embodiment. This is a front view of a positive electrode, which is one example of an embodiment, with the starting end of the positive electrode and its vicinity shown in detail. This is a cross-sectional view along line AA in Figure 3. This is a front view of a positive electrode, which is another example of an embodiment, with the starting end of the positive electrode and its vicinity shown in detail.

[0012] Hereinafter, an example of an embodiment of the secondary battery according to this disclosure will be described in detail with reference to the drawings. Note that the secondary battery according to this disclosure is not limited to the embodiments described below. Configurations obtained by appropriately combining the configurations of the multiple embodiments and modified examples described below are included in this disclosure.

[0013] In the following, a cylindrical battery 10 in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 16 is given as an example, but the battery's outer casing is not limited to a cylindrical outer casing. The secondary battery according to this disclosure only needs to have a wound electrode body, and other embodiments include, for example, a rectangular battery with a rectangular outer casing, and a pouch-type battery with an outer casing made of a laminate sheet including a metal layer and a resin layer.

[0014] Figure 1 is a schematic diagram showing the axial and radial cross-sections of a cylindrical battery 10, which is an example of an embodiment. As shown in Figure 1, the cylindrical battery 10 includes a positive electrode 11, a negative electrode 12, and a separator 13, and comprises an electrode body 14 in which the positive electrode 11 and the negative electrode 12 are wound around the separator 13, and a bottomed cylindrical outer casing 16 that houses the electrode body 14. The cylindrical battery 10 also includes an electrolyte housed in the outer casing 16 and a sealing body 17 that closes the opening of the outer casing 16. The outer casing 16 has grooves 22 formed in its side wall, and the sealing body 17 is supported by the grooves 22 and closes the opening of the outer casing 16. In the following description, for convenience, the side of the cylindrical battery 10 with the sealing body 17 will be considered the top, and the bottom side of the outer casing 16 will be considered the bottom.

[0015] As will be explained in more detail later, a tape is attached to the positive electrode 11 so as to cover the positive electrode start end 11x (see Figure 2, etc., described later), which is the end of the positive electrode 11 at the winding start side of the electrode body 14. Note that the tape is not shown in Figure 1. This tape is a protective tape to suppress the effects of cut burrs on the positive electrode start end 11x.

[0016] 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 (electrolyte solution) or a solid electrolyte. The cylindrical battery 10 is, for example, a non-aqueous electrolyte secondary battery, and among these, a lithium-ion battery is preferred.

[0017] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0018] 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, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0019] As described above, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound in a spiral shape via a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger in dimensions than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0020] The positive electrode 11 comprises a long positive electrode core 30 and a positive electrode mixture layer 31 provided on the positive electrode core 30. The positive electrode core 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film with the metal arranged on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode core 30. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc., can be used as the positive electrode active material.

[0021] The thickness of the positive electrode 11 is, for example, 160 μm to 200 μm. In this embodiment, the thickness of the positive electrode 11 is substantially constant except for the core body exposed portion to which the positive electrode lead 20 is connected. The thickness of the positive electrode core body 30 is, for example, 10 μm to 30 μm. The thickness of the positive electrode mixture layer 31 is, for example, 70 μm to 100 μm on one side of the positive electrode core body 30. The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core body 30, drying the coating film, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core body 30.

[0022] The negative electrode 12 comprises a long negative electrode core 40 and a negative electrode mixture layer 41 provided on the negative electrode core 40. The negative electrode core 40 can be made of a metal foil that is 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 the metal arranged on its surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode core 40. Examples of negative electrode active materials include graphite and Si-containing materials.

[0023] The thickness of the negative electrode 12 is, for example, 170 μm to 210 μm. In this embodiment, the thickness of the negative electrode 12 is substantially constant, except for the core body exposed portion described later. The thickness of the negative electrode core body 40 is, for example, 5 μm to 15 μm. The thickness of the negative electrode mixture layer 41 is, for example, 70 μm to 110 μm on one side of the negative electrode core body 40. The negative electrode 12 can be manufactured in the same way as the positive electrode 11 by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core body 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core body 40.

[0024] The electrode body 14 has a positive electrode lead 20 connected to a positive electrode 11 and a negative electrode lead 21 connected to a negative electrode 12. In this embodiment, the positive electrode mixture layer 31 is absent in the longitudinal center of the positive electrode 11, and a core exposed portion is formed where the surface of the positive electrode core 30 is exposed, to which the positive electrode lead 20 is connected. On the other hand, the negative electrode lead 21 is provided at one longitudinal end of the negative electrode 12, which is located on the winding start side of the electrode body 14. At one longitudinal end of the negative electrode 12, the negative electrode mixture layer 41 is absent, and a first core exposed portion 42 (see Figure 2 described later) is formed where the surface of the negative electrode core 40 is exposed, to which the negative electrode lead 21 is connected.

[0025] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends through a through-hole in the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0026] A negative electrode 12 is positioned on the outermost surface of the electrode body 14, and a second core exposure portion 43 is provided where the surface of the negative electrode core body 40 is exposed. The core exposure portion 43 is in contact with the inner surface of the outer casing 16. By the core exposure portion 43 contacting the inner surface of the outer casing 16, both longitudinal ends of the negative electrode 12 and the outer casing 16 are electrically connected, ensuring good current collection. The core exposure portion 43 may be provided on a part of the outermost surface of the electrode body 14, but preferably it is provided over the entire outermost surface. Note that a winding stopper tape may be attached to the outermost surface of the electrode body 14.

[0027] The outer casing 16 is a bottomed cylindrical metal container. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to seal the inside of the battery. The outer casing 16 has a grooved portion 22 that supports the sealing body 17, which is formed, for example, by pressing the side surface from the outside. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The upper end of the outer casing 16 is bent inward and crimped to the peripheral edge of the sealing body 17.

[0028] The sealing body 17 has a structure in which 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 in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except 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, with the insulating member 25 interposed between their respective peripheries. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0029] The electrode body 14, and in particular the protective tape attached to the positive electrode 11, will be described in detail below with reference to Figures 2 to 5. Figure 2 is a radial cross-sectional view of the electrode body 14 at the winding start end. In Figure 2, the separator 13 is omitted for clarity. Figure 3 is a front view of the positive electrode 11, showing the positive electrode start end 11x and its vicinity in an enlarged view. Figure 4 is a cross-sectional view taken along line AA in Figure 3.

[0030] As shown in Figure 2, the electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are alternately arranged in the radial direction of the electrode body 14 via a separator 13. The negative electrode 12 is longer than the positive electrode 11, and a portion of the negative electrode 12 overlaps the electrode body 14 radially without the positive electrode 11 passing between them. The negative electrode 12 extends towards the beginning of the winding of the electrode body 14 beyond the position facing the positive electrode start end 11x, which is the end of the positive electrode 11 at the beginning of the winding of the electrode body 14. As a result, the positive electrode start end 11x is sandwiched between the negative electrode 12 via the separator 13. On the beginning of the winding of the negative electrode 12, there is a non-opposing region that has been wound one or more times without facing the positive electrode 11.

[0031] A negative electrode mixture layer 41 may be formed in the non-opposing region of the negative electrode 12, but in this embodiment, most of the non-opposing region, excluding the vicinity of the positive electrode start end 11x, is the core body exposed portion 42. A negative electrode lead 21 is connected to the core body exposed portion 42 near the negative electrode start end 12x, which is the end of the negative electrode 12 that starts winding. In the example shown in Figure 2, the negative electrode lead 21 is welded to the outer surface of the core body exposed portion 42, but it may also be welded to the inner surface of the core body exposed portion 42. In this specification, the surface of the electrode body 14 facing radially outward is referred to as the "outer surface of the winding," and the surface of the electrode body 14 facing radially inward is referred to as the "inner surface of the winding."

[0032] As shown in Figures 2 to 4, a first tape 51 and a second tape 52 are attached to the positive electrode 11 as tapes covering the positive electrode start end 11x. As described above, the positive electrode 11 is manufactured by cutting a long positive electrode core 30 to the desired length, but at this time, cut burrs, which are unintended protrusions, may occur at the longitudinal end of the positive electrode 11. Since the positive electrode start end 11x is sandwiched between the negative electrode 12, cut burrs on the positive electrode start end 11x increase the risk of short circuits. The first and second tapes 51 and 52 are protective tapes that cover the positive electrode start end 11x and reduce the risk of short circuits caused by cut burrs.

[0033] The protective tape includes a first tape 51 covering the first positive electrode mixture layer 31A located on the outer surface of the winding of the positive electrode 11, and a second tape 52 covering the second positive electrode mixture layer 31B located on the inner surface of the winding of the positive electrode 11, sandwiching the positive electrode start end 11x where cut burrs may occur. In this embodiment, the winding lengths of the first and second tapes 51 and 52 are substantially the same, and the areas of the positive electrode mixture layers 31A and 31B covered by each tape are also substantially the same. The winding length can be rephrased as the length along the longitudinal direction of the positive electrode 11, or the length along the circumferential direction of the electrode body 14. Furthermore, the lengths of the first and second tapes 51 and 52 along the width direction of the positive electrode 11 are also the same, and the ends of each tape coincide with each other.

[0034] The second tape 52 has a tape base material 53 and an adhesive layer 54 provided on one side of the tape base material 53, and is attached to the positive electrode mixture layer 31B on the inner surface of the roll via the adhesive layer 54. The adhesive layer 54 is formed, for example, by coating one side of the tape base material 53 with adhesive. On the other hand, the first tape 51 has substantially no adhesive layer that adheres to the positive electrode mixture layer 31A. The first tape 51 is composed, for example, only of a tape base material. As will be described in detail later, by not adhering the first tape 51 to the positive electrode mixture layer 31A, cracks in the positive electrode mixture layer 31A are effectively suppressed.

[0035] Here, "the first tape 51 substantially does not have an adhesive layer that adheres to the positive electrode mixture layer 31A" means that there is no adhesive layer at all, and that there is no adhesive layer in a manner that is deemed to be substantially absent, specifically, that there is no adhesive layer in more than 95% of the portion facing the positive electrode mixture layer 31A.

[0036] The first and second tapes 51 and 52 extend beyond the positive electrode start end 11x toward the winding start side of the electrode body 14, and also extend in the width direction from both ends of the positive electrode 11 in the width direction. The extended portions of the first and second tapes 51 and 52 are joined to each other via the adhesive layer 54 of the second tape 52. In this embodiment, the positive electrode start end 11x is wrapped by the two protective tapes, which more effectively reduces the risk of short circuits caused by cut burrs. The first tape 51 does not have an adhesive layer, but the portion of the first tape 51 that extends from the end of the positive electrode 11 is joined to the second tape 52, so that the two tapes are formed in a bag-like shape.

[0037] The thickness of the first and second tapes 51 and 52 is such that the cut burrs do not penetrate the tape, for example, 15 μm to 70 μm, preferably 20 μm to 50 μm. The thickness of the tape substrate is greater than the thickness of the adhesive layer, for example, 10 μm to 65 μm, or 15 μm to 45 μm. Since the first tape 51 does not have an adhesive layer, the thickness of the first tape 51 is, for example, less than the thickness of the second tape 52 by the thickness of the adhesive layer.

[0038] The tape substrate is composed of a single-layer or multi-layer resin substrate. Examples of resins that make up the tape substrate include polyester such as polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polyphenylene sulfide (PPS), polyetherimide (PEI), and polyamide. The first and second tapes 51 and 52 may contain inorganic particles such as titania, alumina, silica, and zirconia, and a layer containing inorganic particles may be provided separately from the tape substrate and adhesive layer. Different substrate compositions may be used for each tape, for example, if the tape substrate of the first tape 51 is made of polyimide and the tape substrate 53 of the second tape 52 is made of polypropylene.

[0039] The adhesive constituting the adhesive layer 54 may be a hot-melt type that exhibits adhesive properties upon heating or a thermosetting type that hardens upon heating, but from the viewpoint of productivity, it is preferable to have adhesive properties at room temperature. Examples of adhesives include acrylic adhesives and synthetic rubber adhesives. An example of the thickness of the adhesive layer 54 is 5 μm to 30 μm. The adhesive layer 54 can be provided on only a part of one side of the tape substrate 53, but in this embodiment, it is provided over the entire area of ​​one side of the tape substrate 53.

[0040] The second tape 52 includes a portion that is attached to the second positive electrode mixture layer 31B located on the inner surface of the winding of the positive electrode 11. In this embodiment, the positive electrode mixture layer 31B is formed over the entire inner surface of the winding of the positive electrode core 30, excluding the core body exposed portion to which the positive electrode lead 20 is connected. The portion of the second tape 52 that is attached to the positive electrode mixture layer 31B extends for a predetermined length from the positive electrode start end 11x toward the winding end of the electrode body 14 and spans the entire width of the positive electrode 11. As described above, the second tape 52 extends from the positive electrode start end 11x toward the winding end of the electrode body 14 and extends from both ends in the width direction of the positive electrode 11. That is, the second tape 52 includes a portion that is attached to the positive electrode mixture layer 31B and a portion that extends from the end of the positive electrode 11.

[0041] The first tape 51 includes a portion that covers the first positive electrode mixture layer 31A located on the outer surface of the winding of the positive electrode 11. The portion of the first tape 51 that covers the positive electrode mixture layer 31A extends for a predetermined length from the positive electrode start end 11x toward the winding end of the electrode body 14 and spans the entire width of the positive electrode 11, similar to the second tape 52. The first tape 51 is similar to the second tape 52 in that it extends beyond the positive electrode start end 11x toward the winding start of the electrode body 14, extends from both ends in the width direction of the positive electrode 11 and includes a portion that covers the positive electrode mixture layer 31A and a portion that extends from the end of the positive electrode 11.

[0042] The protective tape covering the positive electrode start end 11x effectively suppresses the effects of cut burrs, but it also makes the positive electrode mixture layer more susceptible to cracking. The tape acts on the positive electrode mixture layer, causing stress and making it more prone to cracking. Our investigations have shown that cracks in the positive electrode mixture layer do not occur uniformly on the outer and inner surfaces of the winding, but rather occur more frequently on the outer surface. Near the positive electrode start end 11x, the winding radius is small and the difference in circumference between the outer and inner surfaces is large. Therefore, the stress acting on the positive electrode mixture layer 31A on the outer surface of the winding is particularly large, making it more prone to cracking.

[0043] The first tape 51 covers the positive electrode 11 in the same way as the second tape 52, but differs from the second tape 52 in that it substantially does not have an adhesive layer and is not substantially adhered to the positive electrode mixture layer 31A. Because the first tape 51 is not adhered to the positive electrode mixture layer 31A, the stress acting on the positive electrode mixture layer 31A is greatly reduced, and as a result, cracks in the positive electrode mixture layer 31A are effectively suppressed. Although the first tape 51 is not adhered to the positive electrode mixture layer 31A, the portion of the first tape 51 that extends beyond the positive electrode 11 is joined to the second tape 52, and together with the second tape 52 it is formed into a bag-like shape, thereby protecting the positive electrode start end 11x without coming off the positive electrode 11.

[0044] In this embodiment, the first tape 51 is composed only of a tape base material, but a very small part of the first tape 51 may be adhered to the positive electrode active material layer 31A as long as the object of the present disclosure is not impaired. The first tape 51 may be adhered, for example, to a region having a predetermined width along the end of the positive electrode active material layer 31A. That is, the first tape 51 may have an adhesive layer only in a portion that faces a region having a predetermined width along the end of the positive electrode active material layer 31A, in other words, a portion that faces the positive electrode active material layer 31A and covers the positive electrode active material layer 31A. The predetermined width is, for example, 1.0 mm or less.

[0045] For example, in a portion of the first tape 51 that covers the positive electrode active material layer 31A, the first tape 51 may not have an adhesive layer over its entire area or in a range excluding a portion that faces a region having a predetermined width from the end of the positive electrode active material layer 31A. It is preferable that the first tape 51 does not have an adhesive layer in a range exceeding 95% of the portion that covers the positive electrode active material layer 31A. It is assumed that an adhesive that constitutes the adhesive layer 54 of the second tape 52 adheres to the end of the portion of the first tape 51 that covers the positive electrode active material layer 31A to form an adhesive layer.

[0046] The first and second tapes 51 and 52 have a winding direction length of one turn or less from the positive electrode start end 11x to the winding end side of the electrode body 14, more preferably 0.5 turns or less, and particularly preferably 0.3 turns or less. That is, the above-mentioned predetermined length of the portion overlapping the positive electrode active material layers 31A and 31B is preferably one turn or less, more preferably 0.5 turns or less, and particularly preferably 0.3 turns or less from the positive electrode start end 11x. In this case, the capacity reduction caused by the protective tape does not substantially become a problem.

[0047] On the other hand, if the first and second tapes 51 and 52 are too short, problems such as difficulty in attaching them to the positive electrode 11 and easy peeling of the tapes from the positive electrode 11 are assumed. Therefore, the first and second tapes 51 and 52 preferably have a winding direction length of at least 0.1 turn or at least 0.5 mm from the positive electrode start end 11x to the winding end side of the electrode body 14. In addition, from the viewpoint of improving productivity and the like, the total length of the first and second tapes 51 and 52 is preferably 1.5 mm or more, or 2.0 mm or more. The width of the first and second tapes 51 and 52 is preferably larger than the width of the positive electrode 11 and smaller than the width of the separator 13.

[0048] The winding direction length of the portions of the first and second tapes 51 and 52 that cover the positive electrode active material layers 31A and 31B varies somewhat depending on the size of the electrode body 14 and the like, but is preferably 1.0 mm or more and 8.0 mm or less, more preferably 1.5 mm or more and 5.0 mm or less, or 2.0 mm or more and 3.5 mm or less. If the winding direction length of the portions covering the positive electrode active material layers 31A and 31B is within this range, while preventing capacity reduction and tape peeling, the crack suppression effect of the positive electrode active material layers 31A and 31B becomes more prominent. On the other hand, even if the winding direction length of the portions covering the positive electrode active material layers 31A and 31B is within this range, when the tape is attached to the positive electrode active material layer 31A, the cracks in the positive electrode active material layer 31A cannot be sufficiently suppressed.

[0049] The first and second tapes 51 and 52 are arranged so as not to overlap the negative electrode lead 21 in the radial direction from the winding center Z of the electrode body 14. The first and second tapes 51 and 52 have a winding direction length of 0.5 turns or less, or 0.3 turns or less from the positive electrode start end 11x to the winding end side of the electrode body 14, and are arranged opposite to the negative electrode lead 21 in the radial direction of the electrode body 14 with the winding center Z interposed therebetween. The winding direction length of the negative electrode lead 21 is 0.5 turns or less of the electrode body 14. If the negative electrode lead 21 and the first and second tapes 51 and 52 overlap in the radial direction, the step becomes large and defects such as electrode plate deformation are likely to occur. By arranging the first and second tapes 51 and 52 on the side opposite to the negative electrode lead 21 with the winding center Z of the electrode body 14 interposed therebetween, defects such as electrode plate deformation can be suppressed.

[0050] As described above, the first and second tapes 51 and 52 are arranged to cover the positive electrode 11 over the entire width of the positive electrode start end 11x and to extend beyond both ends of the positive electrode 11 in the width direction. However, if there is a part of the positive electrode start end 11x where cut burrs are likely to occur, it is also possible to provide tape to cover only that part of the positive electrode start end 11x. In this case, it is easier to suppress capacity reduction, cracks in the positive electrode mixture layers 31A and 31B, etc., and the effects of cut burrs can be suppressed efficiently. However, it is preferable that each tape extends beyond the positive electrode start end 11x toward the winding start side of the electrode body 14, extends from at least one end of the positive electrode 11 in the width direction, and that the portion of the first tape 51 that extends beyond the positive electrode 11 is joined to the second tape 52.

[0051] Figure 5 shows modified examples of the first and second tapes 51 and 52. As shown in Figure 5, it is preferable to make the winding length (A) of the first tape 51 longer than the winding length (B) of the second tape 52. In this case, the entire area facing the second tape 52 in the winding direction can be covered by the first tape 51, preventing exposure of the adhesive layer 54. By preventing exposure of the adhesive layer 54, it is possible to prevent the adhesive layer 54 from adhering to other parts. The winding length (A) of the first tape 51 is, for example, 105% to 120% of the winding length (B) of the second tape 52.

[0052] Furthermore, the length of the first tape 51 along the width direction of the positive electrode 11 may be longer than the length of the second tape 52 along the width direction of the positive electrode 11. For example, the first tape 51 is slightly larger than the second tape 52, and the portion of the second tape 52 that extends beyond the end of the positive electrode 11 is positioned opposite the first tape 51 over its entire length.

[0053] The positive electrode 11 having the above configuration is manufactured by attaching a protective tape so as to cover one longitudinal end which becomes the positive electrode starting end 11x. The protective tape includes, as described above, a first tape 51 which covers the first positive electrode mixture layer 31A which is the outer surface of the winding of the positive electrode 11 and substantially does not have an adhesive layer that adheres to the positive electrode mixture layer 31A, and a second tape 52 which covers the second positive electrode mixture layer 31B which is the inner surface of the winding of the positive electrode 11 and has an adhesive layer 54 that adheres to the positive electrode mixture layer 31B. Since the first tape 51 does not have an adhesive layer, it is joined to the portion of the second tape 52 that protrudes from the end of the positive electrode 11, thereby forming a bag shape between the two tapes.

[0054] As described above, the cylindrical battery 10 equipped with a positive electrode 11 can suppress cracks in the positive electrode mixture layers 31A and 31B while suppressing the effect of cut burrs at the positive electrode starting end 11x, thereby reducing the risk of short circuits caused by cut burrs, for example.

[0055] The present disclosure is further illustrated by the following embodiments. Configuration 1: A secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are wound around the separator, and a tape is attached to the positive electrode so as to cover the positive electrode start end, which is the end of the positive electrode at the starting end of the electrode body, and the tape comprises a first tape covering a first positive electrode mixture layer located on the outer surface of the winding of the positive electrode facing radially outward of the electrode body, and a second tape covering a second positive electrode mixture layer located on the inner surface of the winding of the positive electrode facing radially inward of the electrode body, wherein the first tape substantially does not have an adhesive layer that adheres to the first positive electrode mixture layer, and the second tape has an adhesive layer that adheres to the second positive electrode mixture layer. Configuration 2: The secondary battery according to Configuration 1, wherein the winding length of the first tape is longer than the winding length of the second tape. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the tape has a base material made of polyimide or polypropylene. Configuration 4: The secondary battery according to any one of Configurations 1 to 3, wherein the tape has a winding length of one turn or less from the positive electrode start end to the winding end side of the electrode body. Configuration 5: The secondary battery according to any one of Configurations 1 to 3, wherein the tape has a winding length of 0.5 turns or less from the positive electrode start end to the winding end side of the electrode body. Configuration 6: The secondary battery according to any one of Configurations 1 to 5, wherein the electrode body has a lead connected to the negative electrode at the winding start end of the electrode body, and the tape is arranged radially from the winding center of the electrode body so as not to overlap with the lead. Configuration 7: A positive electrode for a secondary battery used in a wound electrode body, comprising a tape attached so as to cover one longitudinal end of the positive electrode at the winding start side of the electrode body, wherein the tape includes a first tape that covers a first positive electrode mixture layer which is the outer surface of the winding of the positive electrode facing radially outward of the electrode body, and a second tape that covers a second positive electrode mixture layer which is the inner surface of the winding of the positive electrode facing radially inward of the electrode body, wherein the first tape substantially does not have an adhesive layer that adheres to the first positive electrode mixture layer, and the second tape has an adhesive layer that adheres to the second positive electrode mixture layer.

[0056] 10 Cylindrical battery, 11 Positive electrode, 11x Positive electrode start end, 12 Negative electrode, 12x Negative electrode start end, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18 Upper insulating plate, 19 Lower insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode core body, 31 Positive electrode mixture layer, 40 Negative electrode core body, 41 Negative electrode mixture layer, 42, 43 Core body exposed section, 51 First tape, 52 Second tape, 53 Tape base material, 54 Adhesive layer, Z Winding center

Claims

1. A secondary battery comprising an electrode body including a positive electrode, a negative electrode, and a separator, wherein the positive electrode and the negative electrode are wound around the separator, wherein a tape is attached to the positive electrode so as to cover the positive electrode start end, which is the end of the positive electrode at the starting end of the winding of the electrode body, and the tape comprises a first tape covering a first positive electrode mixture layer located on the outer surface of the winding of the positive electrode facing radially outward of the electrode body, and a second tape covering a second positive electrode mixture layer located on the inner surface of the winding of the positive electrode facing radially inward of the electrode body, wherein the first tape substantially does not have an adhesive layer that adheres to the first positive electrode mixture layer, and the second tape has an adhesive layer that adheres to the second positive electrode mixture layer.

2. The secondary battery according to claim 1, wherein the winding length of the first tape is longer than the winding length of the second tape.

3. The secondary battery according to claim 1 or 2, wherein the tape has a base material made of polyimide or polypropylene.

4. The secondary battery according to claim 1 or 2, wherein the tape has a winding length of one turn or less from the positive electrode starting end to the end of the electrode body winding.

5. The secondary battery according to claim 1 or 2, wherein the tape has a winding length of 0.5 turns or less from the positive electrode starting end to the end of the electrode body winding.

6. The secondary battery according to claim 1 or 2, wherein the electrode body has a lead connected to the negative electrode at a point closer to the winding start end of the electrode body than to the positive electrode start end, and the tape is arranged radially from the winding center of the electrode body so as not to overlap with the lead.

7. A positive electrode for a secondary battery used in a wound electrode body, comprising a tape attached so as to cover one longitudinal end of the positive electrode at the winding start side of the electrode body, wherein the tape includes a first tape covering a first positive electrode mixture layer which is the outer surface of the winding of the positive electrode facing radially outward of the electrode body, and a second tape covering a second positive electrode mixture layer which is the inner surface of the winding of the positive electrode facing radially inward of the electrode body, wherein the first tape substantially does not have an adhesive layer that adheres to the first positive electrode mixture layer, and the second tape has an adhesive layer that adheres to the second positive electrode mixture layer.

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