Non-aqueous electrolyte secondary battery

Abstract

A first electrode (11) has a first electrode core (30) and first electrode mixture layers (31) disposed on both surfaces of the first electrode core (30). The first electrode mixture layer (31) has raised parts (33) rising in the thickness direction of the first electrode (11) in regions on both surfaces of a first electrode core exposed part (32) that are adjacent to a winding-start end (32A), and has an inclined part (35) that decreases in thickness closer to the first electrode core exposed part (32) in regions of both surfaces of the first electrode core exposed part (32) adjacent to a winding-end end (32B).

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been known that include an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween. Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which a positive electrode core is exposed at a longitudinal intermediate portion of the positive electrode, and an electrode tab is joined to the core exposed portion. In addition, from the viewpoint of suppressing the occurrence of an internal short circuit, the electrode tab and the core exposed portion are covered with an insulating protective tape or the like.

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

[0004] Generally, for reasons such as reducing electrical resistance, the thickness of the electrode tab bonded to the exposed core portion is greater than the thickness of one side of the mixture layer disposed on the surface of the core. In other words, the electrode tab protrudes in the thickness direction of the electrode. As a result, stress tends to concentrate around the electrode tab in the electrode assembly. Furthermore, during the fabrication of a nonaqueous electrolyte secondary battery, foreign matter may be mixed into the electrode assembly. In particular, if such foreign matter is mixed around the electrode tab, excessive stress may be applied around the electrode tab, damaging the protective tape or separator around the electrode tab and potentially causing an internal short circuit.

[0005] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including an electrode body in which strip-shaped first and second electrodes having opposite polarities are wound longitudinally with a separator interposed therebetween, the first electrode having a first electrode core and first electrode mixture layers disposed on both sides of the first electrode core, a first electrode core exposed portion in which the first electrode mixture layer is not disposed and both sides of the first electrode core are exposed is provided in an intermediate portion in the longitudinal direction of the first electrode, a first electrode tab is joined to the first electrode core exposed portion, and the first electrode mixture layer has raised portions in the thickness direction of the first electrode in regions adjacent to the winding start ends on both sides of the first electrode core exposed portion, and has sloped portions in which the thickness of the first electrode mixture layer decreases toward the first electrode core exposed portion in regions adjacent to the winding end ends on both sides of the first electrode core exposed portion.

[0006] According to a nonaqueous electrolyte secondary battery according to one aspect of the present disclosure, stress applied to the electrode tab can be alleviated, and as a result, even if foreign matter is mixed in the vicinity of the electrode tab, damage to the protective tape and separator around the electrode tab can be suppressed, and the occurrence of an internal short circuit can be suppressed.

[0007] 2 is an axial cross-sectional view of the nonaqueous electrolyte secondary battery of the first embodiment; FIG. 3 is a front view showing a developed state of a positive electrode included in the nonaqueous electrolyte secondary battery of the first embodiment; FIG. 4 is a cross-sectional view taken along line A-A in FIG. 2; and FIG. 5 is a view corresponding to FIG. 3 of a positive electrode included in the nonaqueous electrolyte secondary battery of the second embodiment.

[0008] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is initially assumed that the characteristic portions thereof will be used in appropriate combination.

[0009] [First Embodiment] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to a first embodiment. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), and an outer can 16 that houses the electrode assembly 14 and the nonaqueous electrolyte. The outer can 16 is a cylindrical metal container that is open on one axial side and has a bottom, and the opening of the outer can 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the nonaqueous electrolyte secondary battery 10 will be referred to as the "top" and the bottom side of the outer can 16 will be referred to as the "bottom."

[0010] The electrode assembly 14 has a structure in which a first electrode and a second electrode, which are strip-shaped and have different polarities, are wound in the longitudinal direction via a separator 13. In the following, a case in which the first electrode is a positive electrode 11 and the second electrode is a negative electrode 12 will be described.

[0011] The positive electrode 11, negative electrode 12, and separator 13 are spirally wound and stacked alternately in the radial direction of the electrode body 14. In the electrode body 14, the longitudinal direction of the positive electrode 11 and negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and negative electrode 12 is the axial direction. The nonaqueous electrolyte secondary battery 10 further includes a positive electrode tab 20 connected to the positive electrode 11 by welding or the like and protruding from the upper end of the electrode body 14, and a negative electrode tab 21 connected to the negative electrode 12 by welding or the like and protruding from the lower end of the electrode body 14.

[0012] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 disposed on the positive electrode core 30. The positive electrode core 30 can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0013] The positive electrode mixture layer 31 contains a particulate lithium-containing composite oxide as a positive electrode active material. The lithium-containing composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium-containing composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, Al, and Mn. Examples of suitable composite oxides include a lithium-containing composite oxide containing Ni, Co, and Mn, and a lithium-containing composite oxide containing Ni, Co, and Al.

[0014] Examples of the conductive agent contained in the positive electrode mixture layer 31 include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of the binder contained in the positive electrode mixture layer 31 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0015] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 41 disposed on the negative electrode core 40. The negative electrode core 40 can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on its surface. The negative electrode mixture layer 41 contains a negative electrode active material, a binder, and, if necessary, a conductive agent. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing the negative electrode active material and the binder to the surface of the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0016] The negative electrode mixture layer 41 generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite, such as flake graphite, massive graphite, and amorphous graphite, and artificial graphite, such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, the negative electrode active material may include a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element.

[0017] As in the case of the positive electrode mixture layer 31, the binder contained in the negative electrode mixture layer 41 can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene butadiene rubber (SBR) is preferably used. The negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0018] 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.

[0019] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[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 the 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 through a through-hole in 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] As described above, the outer can 16 is a cylindrical metal container with a bottom and an opening at one axial end, and the opening of the outer can 16 is closed by a sealing body 17 .

[0024] 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.

[0025] 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 abnormal heat generation causes an increase in the internal pressure of the battery, 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 through a vent hole in the cap 27.

[0026] Next, the positive electrode 11 will be described in detail with reference to Figures 2 and 3. Figure 2 is a front view showing the positive electrode 11 in a developed state, and Figure 3 is a cross-sectional view taken along line AA in Figure 2.

[0027] As shown in FIGS. 2 and 3 , the positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 31 disposed on each of both sides of the positive electrode core 30. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. Hereinafter, for convenience of explanation, as shown in FIG. 3 , the positive electrode mixture layer 31 disposed 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 disposed 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, excluding the protruding portion 33 and the inclined portion 35 described below, are, for example, 50 μm or more and 100 μm or less, respectively.

[0028] A positive electrode core exposed portion 32 is provided in the longitudinal middle portion of the positive electrode 11, where the positive electrode mixture layer 31 is not disposed and both surfaces of the positive electrode core 30 are 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 positioned so as to overlap each other in the thickness direction of the positive electrode 11. 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 and does not contact the lower end 11Y of the positive electrode 11 in the width direction. Furthermore, the positive electrode mixture layer 31 is disposed on the surface of the positive electrode core 30 in a region that overlaps the positive electrode core exposed portion 32 and the positive electrode 11 in the width direction. This allows the area of ​​the positive electrode mixture layer 31 to be increased, facilitating the increase in capacity of the nonaqueous electrolyte secondary battery 10. 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 substrate exposed portion 32 can be produced by intermittent application in which the positive electrode mixture slurry is not applied to a portion of the positive electrode substrate 30 .

[0029] 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 a first surface 11A of the positive electrode 11. Note that the first surface A 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 wound electrode body 14.

[0030] 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 is configured to protrude 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.

[0031] An insulating protective tape 50 is provided on the surface of the positive electrode 11, covering the positive electrode core exposed portion 32. The protective tape 50 covers the entire surface of the positive electrode core exposed portion 32, a portion of the positive electrode tab 20, and the positive electrode mixture layer 31 around the positive electrode core exposed portion 32. By providing the protective 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.

[0032] The protective 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.

[0033] The adhesive layer is a portion for adhering the protective 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 protective tape 50 to the surface of the positive electrode 11. The adhesive layer may further contain, for example, a silicone-based polymer.

[0034] 3 , the positive electrode mixture layer 31 has a protruding portion 33 that protrudes in the thickness direction of the positive electrode 11 in a region adjacent to each winding start end 32A on both sides of the positive electrode substrate exposed portion 32. The protruding portion 33 includes a first protruding portion 33A provided on the first surface 11A of the positive electrode 11 and a second protruding portion 33B provided on the second surface 11B of the positive electrode 11. That is, the first positive electrode mixture layer 31A has the first protruding portion 33A, and the second positive electrode mixture layer 31B has the second protruding portion 33B. A flat portion 34 where the thickness of the positive electrode mixture layer 31 is approximately constant is provided in a region of the positive electrode mixture layer 31 closer to the winding start side than the protruding portion 33.

[0035] As described above, the positive electrodes 11 and negative electrodes 12 are alternately stacked in the radial direction of the electrode body 14 with the separators 13 interposed therebetween. Therefore, stress tends to concentrate on the positive electrode tabs 20 that protrude from the surfaces of the positive electrodes 11 in the thickness direction of the positive electrodes 11. In particular, if foreign matter is mixed in the vicinity of the positive electrode tabs 20, excessive stress is applied to the positive electrode tabs 20 from the foreign matter. This may also apply excessive stress to the protective tape 50 and separator 13 around the positive electrode tabs 20, causing damage such as breakage to the protective tape 50 and separator 13. If the protective tape 50 or separator 13 is damaged, the positive electrode tabs 20 may come into contact with the negative electrodes 12, resulting in an internal short circuit.

[0036] In this embodiment, by providing the protruding portions 33 on both sides of the positive electrode mixture layer 31 closer to the winding start side than the positive electrode substrate exposed portion 32, stress concentration on the positive electrode tab 20 is alleviated even if foreign matter is mixed in the periphery of the positive electrode tab 20. As a result, damage to the protective tape 50 and separator 13 around the positive electrode tab 20 is suppressed, and the occurrence of an internal short circuit can be suppressed.

[0037] If the protruding portion 33 is provided closer to the winding end side than the positive electrode substrate exposed portion 32, it is not possible to sufficiently alleviate the stress applied to the positive electrode tab 20, as will be shown in the results of examples described later. As a result, the protective tape 50 and the separator 13 around the positive electrode tab 20 may be damaged. This is presumably because, in a nonaqueous electrolyte secondary battery 10 in which the positive electrode substrate exposed portion 32 is provided in the middle portion of the positive electrode 11 in the longitudinal direction, stress is concentrated more at the winding start side of the positive electrode substrate exposed portion 32 than at the winding end side.

[0038] Furthermore, even when the protrusion 33 is provided on only one of the first surface 11A and the second surface 11B of the positive electrode 11 in the region closer to the winding start side than the positive electrode substrate exposed portion 32, it is not possible to sufficiently alleviate the stress applied to the positive electrode tab 20. This is presumably because when the protrusion 33 is provided on only one of the surfaces of the positive electrode 11, the thickness of the positive electrode mixture layer 31 in the region closer to the winding start side of the positive electrode substrate exposed portion 32 is not sufficiently ensured.

[0039] As shown in FIG. 3 , the protruding portion 33 is formed in the positive electrode mixture layer 31 from the end adjacent to the winding start end 32A of the positive electrode substrate exposed portion 32 to the flat portion 34. The thickness of the protruding portion 33 gradually increases from the end adjacent to the winding start end 32A of the positive electrode substrate exposed portion 32 toward the winding start side. The protruding portion 33 is thickest at a position a predetermined distance away from the end adjacent to the winding start end 32A of the positive electrode substrate exposed portion 32. The maximum thickness of the protruding portion 33 at this position is, for example, 1.1 to 2.5 times the thickness of the flat portion 34, or may be 1.2 to 2.0 times the thickness of the flat portion 34. The thickness of the protruding portion 33 gradually decreases from the position where the thickness is greatest toward the winding start side. The length of the protruding portion 33 along the longitudinal direction of the positive electrode 11 is, for example, 2 mm to 5 mm. In this embodiment, the first mound portion 33A and the second mound portion 33B have substantially the same shape. However, the first mound portion 33A and the second mound portion 33B may have different shapes.

[0040] It is preferable that at least a portion of the first mound 33A is provided in a position where it overlaps with the second mound 33B in the thickness direction of the positive electrode 11. In this case, the thickness of the positive electrode mixture layer 31 can be increased in the region where the first mound 33A and the second mound 33B overlap in the thickness direction of the positive electrode 11. This can further reduce the stress applied to the positive electrode tab 20.

[0041] The length along the longitudinal direction of the positive electrode 11 from the position where the sum of the thicknesses of the first protrusion 33A and the second protrusion 33B is greatest to the winding start end of the positive electrode tab 20 is preferably 8 mm or less, and more preferably 5 mm or less. In this case, the stress applied to the positive electrode tab 20 can be further alleviated.

[0042] In this embodiment, the position where the first protuberance 33A has the greatest thickness and the position where the second protuberance 33B has the greatest thickness are located at positions that overlap in the thickness direction of the positive electrode 11. In other words, the positions where the sum of the thicknesses of the first protuberance 33A and the second protuberance 33B is greatest coincide with the positions where the thickness of the first protuberance 33A is the greatest and the positions where the thickness of the second protuberance 33B is the greatest in the longitudinal direction of the positive electrode 11, respectively.

[0043] At the position where the sum of the thicknesses of the first protruding portion 33A and the second protruding portion 33B is greatest, the sum of the thicknesses of the first protruding portion 33A and the second protruding portion 33B is preferably greater than the thickness of the positive electrode tab 20. In this case, it is possible to further reduce the stress applied to the positive electrode tab 20. At the position where the sum of the thicknesses of the first protruding portion 33A and the second protruding portion 33B is greatest, the sum of the thicknesses of the first protruding portion 33A and the second protruding portion 33B is preferably greater than the thickness of the positive electrode tab 20 by, for example, 20 μm or more, and more preferably 30 μm or more.

[0044] As shown in FIG. 3 , the positive electrode mixture layer 31 has inclined portions 35 whose thickness decreases toward the positive electrode substrate exposed portion 32 in regions adjacent to the winding end ends 32B on both sides of the positive electrode substrate exposed portion 32. The inclined portions 35 include a first inclined portion 35A provided on the first surface 11A of the positive electrode 11 and a second inclined portion 35B provided on the second surface 11B of the positive electrode 11. That is, the first positive electrode mixture layer 31A has the first inclined portion 35A, and the second positive electrode mixture layer 31B has the second inclined portion 35B. A flat portion 36 in which the thickness of the positive electrode mixture layer 31 is substantially constant is provided in a region of the positive electrode mixture layer 31 closer to the winding end side than the inclined portion 35. The flat portion 36 generally has the same thickness as the flat portion 34.

[0045] The inclined portion 35 may be formed continuously along the width direction of the positive electrode 11 or may be formed in a comb shape in a plan view of the positive electrode 11. The length of the inclined portion 35 along the longitudinal direction of the positive electrode 11 is, for example, 2 mm or more and 5 mm or less.

[0046] In this embodiment, the first inclined portion 35A and the second inclined portion 35B have substantially the same shape. Note that the first inclined portion 35A and the second inclined portion 35B may have different shapes. In this embodiment, the first inclined portion 35A is provided at a position overlapping the second inclined portion 35B in the thickness direction of the positive electrode 11.

[0047] The raised portion 33 and the inclined portion 35 are formed, for example, as follows. The hoop-shaped positive electrode core 30 is unwound by a drive roll, thereby transporting the positive electrode core 30 to one side in the longitudinal direction at a predetermined speed. At this time, the positive electrode core 30 is transported below a first discharge unit and a second discharge unit that discharge positive electrode mixture slurry. The first discharge unit discharges the positive electrode mixture slurry to a region of the positive electrode 11 that overlaps in the longitudinal direction with the region where the positive electrode core exposed portion 32 is to be formed, and the second discharge unit discharges the positive electrode mixture slurry to a region of the positive electrode 11 that does not overlap in the longitudinal direction with the region where the positive electrode core exposed portion 32 is to be formed. In other words, the first discharge unit intermittently discharges the positive electrode mixture slurry so as to form the positive electrode core exposed portion 32, and the second discharge unit continuously discharges the positive electrode mixture slurry.

[0048] When the discharge of the positive electrode mixture slurry from the first discharge part is interrupted due to the formation of the positive electrode substrate exposed part 32, an inclined part 35 where the thickness of the positive electrode mixture layer 31 gradually decreases is formed at the end of the positive electrode mixture layer 31. Furthermore, when the discharge of the positive electrode mixture slurry from the first discharge part is resumed after the formation of the positive electrode substrate exposed part 32, the amount of positive electrode mixture slurry initially discharged from the first discharge part is generally greater than that of other regions. This is because the pressure inside the first discharge part increases when the discharge of the positive electrode mixture slurry is resumed. Therefore, a raised part 33 is formed at the end of the positive electrode mixture layer 31 adjacent to the positive electrode substrate exposed part 32.

[0049] Here, when the positive electrode mixture slurry is applied to the first surface 11A of the positive electrode 11, it is applied along the application direction α shown in FIG. 3 . Then, when the positive electrode mixture slurry is applied to the second surface 11B of the positive electrode 11, it is applied along the application direction β shown in FIG. 3 . As a result, on both surfaces of the positive electrode 11, a protruding portion 33 can be formed on one side of the positive electrode substrate exposed portion 32, and an inclined portion 35 can be formed on the other side of the positive electrode substrate exposed portion 32. Then, when winding the electrode body 14, the protruding portion 33 is positioned closer to the start of winding than the positive electrode substrate exposed portion 32, thereby fabricating a nonaqueous electrolyte secondary battery 10 having the configuration of this embodiment.

[0050] As described above, on both sides of the positive electrode 11, the raised portion 33 that protrudes in the thickness direction of the positive electrode 11 is provided in a region adjacent to the winding start end 32A of the positive electrode substrate exposed portion 32, and the inclined portion 35 that decreases in thickness toward the positive electrode substrate exposed portion 32 is provided in a region adjacent to the winding end end 32B of the positive electrode substrate exposed portion 32, thereby alleviating the stress applied to the positive electrode tab 20. As a result, even if foreign matter is mixed in the vicinity of the positive electrode tab 20, damage to the protective tape 50 and separator 13 due to stress concentration on the positive electrode tab 20 is suppressed, and the occurrence of an internal short circuit can be suppressed.

[0051] The above embodiment can be modified as appropriate without departing from the scope of the present disclosure. For example, in the above embodiment, the positive electrode substrate exposed portion 32 contacts only the upper end 11X of the positive electrode 11 in the width direction and does not contact the lower end 11Y of the positive electrode 11 in the width direction. However, the positive electrode substrate exposed portion 32 may be formed across the entire width of the positive electrode 11. When the positive electrode substrate exposed portion 32 contacts only one width direction end of the positive electrode 11 as in the above embodiment, the positive electrode mixture layer 31 is disposed in a region that overlaps with the positive electrode substrate exposed portion 32 in the width direction. The positive electrode mixture layer 31 disposed in the region that overlaps with the positive electrode substrate exposed portion 32 in the width direction acts to relieve stress applied to the positive electrode tab 20. Therefore, when the positive electrode substrate exposed portion 32 contacts only one width direction end of the positive electrode 11, stress applied to the positive electrode tab 20 can be further relieved.

[0052] Furthermore, in the above embodiment, the positive electrode 11 has one positive electrode substrate exposed portion 32 , but may have two or more positive electrode substrate exposed portions 32 .

[0053] In addition, in the above embodiment, the first electrode is a positive electrode 11 and the second electrode is a negative electrode 12, but the first electrode may be a negative electrode 12 and the second electrode may be a positive electrode 11.

[0054] Second Embodiment Next, a positive electrode 11 constituting a nonaqueous electrolyte secondary battery 10 according to a second embodiment will be described in detail with reference to Fig. 4. Fig. 4 is a view of the positive electrode 11 according to the second embodiment, corresponding to Fig. 3. Below, the same reference numerals are used for components common to the first embodiment, and redundant explanations are omitted, and differences from the first embodiment will be mainly described.

[0055] As shown in FIG. 4 , the positive electrode 11 of the second embodiment differs from the positive electrode 11 of the first embodiment in that a resin layer 60 containing a resin material is disposed on the surface of the inclined portion 35. By disposing the resin layer 60 on the surface of the inclined portion 35, the thickness of the positive electrode 11 in the region adjacent to the winding end 32B of the positive electrode substrate exposed portion 32 can be increased, and the resin layer 60 acts to relieve stress applied to the positive electrode tab 20. Note that a portion of the resin layer 60 may be disposed on the surface of the positive electrode substrate exposed portion 32 or the flat portion 36. Furthermore, the resin layer 60 may cover the entire surface of the inclined portion 35, or may cover only a portion of the surface of the inclined portion 35.

[0056] In this embodiment, the resin layer 60 is disposed on each of the first surface 11A and the second surface 11B of the positive electrode 11. In this case, it is possible to further reduce the stress applied to the positive electrode tab 20. Note that the resin layer 60 may be disposed on only one of the first surface 11A and the second surface 11B of the positive electrode 11.

[0057] The resin layer 60 preferably has a thickness such that the maximum sum of the thickness of the inclined portion 35 and the thickness of the resin layer 60 is equal to or greater than the thickness of the flat portion 36. In this case, the thickness of the positive electrode 11 in the region adjacent to the winding end end 32B of the positive electrode substrate exposed portion 32 can be increased, thereby further reducing the stress applied to the positive electrode tab 20. As described above, the thickness of the inclined portion 35 decreases as it approaches the positive electrode substrate exposed portion 32. Therefore, it is preferable that the resin layer 60 has a shape that bulges in the thickness direction of the positive electrode 11 on the inclined portion 35, as shown in FIG. 4 .

[0058] The resin layer 60 is a layer containing at least a resin material. The resin layer 60 may be, for example, a layer containing a resin material and inorganic particles. Examples of inorganic particles contained in the resin layer 60 include metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles. Examples of metal oxide particles include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide. Examples of metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of metal carbide particles include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. Furthermore, the inorganic particles include zeolite (M ２／ｎ O.Al ２ O ３ xSiO ２ ・yH ２ O, M is a metal element, n is the valence of M, x≧2, y≧0), porous aluminosilicates such as talc (Mg ３ Si ４ O １０ (OH) ２ ), layered silicates such as barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ These may be used alone or in combination of two or more.

[0059] The content of inorganic particles in the resin layer 60 is, for example, 50% by mass or more and 95% by mass or less, preferably 60% by mass or more and 95% by mass or less, and more preferably 70% by mass or more and 90% by mass or less, relative to the total mass of the resin layer 60.

[0060] The resin material contained in the resin layer 60 functions as a binder that bonds the individual inorganic particles together and between the inorganic particles and the inclined portion 35. The resin material is preferably a polymer material, and examples thereof include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), polyimide-based resins, polyamide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0061] The resin layer 60 can be produced by applying a coating liquid containing dispersed inorganic particles to the surface of the inclined portion 35. The coating liquid is produced by mixing the inorganic particles and a resin material and then adding an appropriate amount of water or the like. The solids concentration of the coating liquid is, for example, 3% by mass or more and 50% by mass or less. Examples of methods for applying the coating liquid include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing. The produced coating film may also be subjected to a drying process to remove the solvent. The drying method is not particularly limited, and may be, for example, natural drying, ventilation drying using warm air or the like, heat drying, reduced pressure / vacuum drying, or a combination thereof.

[0062] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0063] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, lithium nickel oxide (LiNi) containing cobalt and aluminum was used. ０．８８ Co ０．０９ Al ０．０３ O２ ) was used. 100 parts by mass of this positive electrode active material, 1 part by mass of acetylene black (AB) as a conductive agent, and 1 part by mass of polyvinylidene fluoride (PVDF) as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to both sides of a positive electrode core made of aluminum foil with a thickness of 15 μm along the application direction α and application direction β shown in FIG. 3, respectively, and the coating was dried. After that, it was cut into a predetermined electrode size and rolled using a roller to obtain a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode core.

[0064] Furthermore, one positive electrode core exposed portion, where no positive electrode mixture layer was formed on either side of the positive electrode core, was provided in the longitudinal center of the positive electrode, and a 120 μm-thick aluminum positive electrode tab was fixed to the positive electrode core exposed portion by ultrasonic welding.

[0065] When the cross section of the fabricated positive electrode was examined, it was confirmed that a protruding portion was formed in a region adjacent to one longitudinal end of each of both surfaces of the positive electrode substrate exposed portion, and an inclined portion was formed in a region adjacent to the other longitudinal end of each of both surfaces of the positive electrode substrate exposed portion, as shown in Figure 3. The thickness of the positive electrode mixture layer was 50 μm on one side of the flat portion. The sum of the thicknesses of the first protruding portion and the second protruding portion at the position where the sum of the thicknesses of the first protruding portion and the second protruding portion was greatest was 140 μm.

[0066] [Preparation of Negative Electrode] A mixture of graphite and a Si-containing material in a mass ratio of 95:5 was used as the negative electrode active material. 100 parts by mass of this negative electrode active material, 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and 1 part by mass of carboxymethyl cellulose (CMC) as a thickener were mixed, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil, dried, cut to a predetermined electrode size, and rolled using a roller to obtain a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode core. In addition, a negative electrode core exposed portion where a negative electrode mixture layer was not formed on both sides of the negative electrode core was formed at one end in the longitudinal direction of the negative electrode, and a nickel negative electrode tab was fixed to the negative electrode core exposed portion by ultrasonic welding.

[0067] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / L of ammonium hydroxide in water.

[0068] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A wound electrode assembly was fabricated by spirally winding the positive electrode and negative electrode with a separator interposed therebetween. The protruding portion of the positive electrode mixture layer was positioned closer to the start of the winding than the exposed portion of the positive electrode substrate. Insulating plates were placed on the top and bottom of the electrode assembly, and the electrode assembly was housed in an outer can. The negative electrode tab was welded to the bottom of the cylindrical outer can with a bottom, and the positive electrode tab was welded to a sealing member. After the non-aqueous electrolyte was poured into the outer can, the opening of the outer can was sealed with a sealing member via a gasket, completing the fabrication of a non-aqueous electrolyte secondary battery.

[0069] [Evaluation of Stress Applied to Positive Electrode Tab] The fabricated nonaqueous electrolyte secondary battery was charged to 4.2 V at a constant current of 0.3 C in a temperature environment of 25 ° C, and then charged at a constant voltage of 4.2 V until the current value reached 0.01 C. After a one-hour rest, the battery was discharged to 2.5 V at a constant current of 0.3 C. This constituted one cycle, and 1,500 cycles were performed. X-ray CT images of the nonaqueous electrolyte secondary battery after cycling were then taken using an inspeXio SMX-255CT FPD HR manufactured by Shimadzu Corporation. In the X-ray CT images, the distance from the surface of the positive electrode tab to the surface of the negative electrode core of the negative electrode facing the positive electrode tab via the separator was measured, and the stress applied to the positive electrode tab was evaluated from the measured distance. As the stress applied to the positive electrode tab increased, the separator interposed between the positive electrode tab and the negative electrode was compressed, thereby reducing the distance from the surface of the positive electrode tab to the surface of the negative electrode core.

[0070] Example 2 A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that in the fabrication of the positive electrode, a resin layer prepared by the following method was formed on the surface of the inclined portion as shown in FIG.

[0071] [Preparation of Resin Layer] Titania (TiO) was used as inorganic particles having an average particle size of 1 μm. ２ The sintered body particles and polyvinylidene fluoride (PVDF) resin material were mixed in a solids mass ratio of 80:20, and then an appropriate amount of NMP was added to obtain a solids concentration of 30% by mass to prepare a coating solution. The resulting coating solution was then applied to substantially the entire surface of the inclined portion and dried to form a resin layer. When the cross section of the prepared positive electrode was examined, the maximum sum of the thickness of the inclined portion and the thickness of the resin layer was 60 μm.

[0072] Comparative Example A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the positive electrode was wound so that the protruding portion was positioned closer to the winding end side than the exposed portion of the positive electrode substrate.

[0073] Table 1 shows the distance from the surface of the positive electrode tab to the surface of the negative electrode core after cycling for the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples. The distance from the surface of the positive electrode tab to the surface of the negative electrode core shown in Table 1 is expressed as a relative value, with the distance from the surface of the positive electrode tab to the surface of the negative electrode core of the Comparative Example being set at 100. As described above, the greater the stress applied to the positive electrode tab, the smaller the distance from the surface of the positive electrode tab to the surface of the negative electrode core.

[0074]

[0075] As shown in Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 and 2 have a larger distance from the surface of the positive electrode tab to the surface of the negative electrode substrate after cycling than the nonaqueous electrolyte secondary battery of the comparative example, and the stress applied to the positive electrode tab is reduced. Therefore, it can be said that by providing a protruding portion in a region adjacent to the winding start end of the positive electrode substrate exposed portion and providing an inclined portion in a region adjacent to the winding end end of the positive electrode substrate exposed portion on both sides of the positive electrode, the stress applied to the positive electrode tab can be reduced. Furthermore, the nonaqueous electrolyte secondary battery of Example 2, in which a resin layer is provided on the inclined portion, has a reduced stress applied to the positive electrode tab after cycling compared to the nonaqueous electrolyte secondary battery of Example 1, in which a resin layer is not provided on the inclined portion.

[0076] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including an electrode assembly in which strip-shaped first and second electrodes having opposite polarities are wound longitudinally with a separator interposed therebetween, the first electrode having a first electrode core and a first electrode mixture layer disposed on each of both sides of the first electrode core, a first electrode core exposed portion where the first electrode core is exposed and the first electrode mixture layer is not disposed is provided in a longitudinally intermediate portion of the first electrode, a first electrode tab is joined to the first electrode core exposed portion, the first electrode mixture layer has raised portions where the first electrode mixture layer bulges in the thickness direction of the first electrode in regions adjacent to the winding start ends on each of both sides of the first electrode core exposed portion, and has sloped portions where the thickness of the first electrode mixture layer decreases toward the first electrode core exposed portion in regions adjacent to the winding end ends on each of both sides of the first electrode core exposed portion. Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the protruding portion includes a first protruding portion provided on a first surface of the first electrode and a second protruding portion provided on a second surface of the first electrode, and at least a portion of the first protruding portion is provided at a position overlapping the second protruding portion in the thickness direction of the first electrode. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 2, wherein the length along the longitudinal direction of the first electrode from the position where the sum of the thicknesses of the first protruding portion and the second protruding portion is greatest to the winding start end of the first electrode tab is 8 mm or less. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the first electrode core exposed portion contacts only one widthwise end of the first electrode, and the first electrode mixture layer is disposed on the surface of a region of the first electrode core that overlaps the first electrode core exposed portion in the width direction of the first electrode. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the first electrode has a resin layer disposed on the surface of the inclined portion. Aspect 6: The nonaqueous electrolyte secondary battery according to any one of aspects 1 to 5, wherein the first electrode is a positive electrode.

[0077] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode (first electrode), 11A first surface, 11B second surface, 11X upper end, 11Y lower end, 12 negative electrode (second electrode), 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18 insulating plate, 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, 31A first positive electrode mixture layer, 31B second positive electrode mixture layer, 32 positive electrode core exposed portion, 32A winding start end, 32B winding end end, 33 protruding portion, 33A first protruding portion, 33B second protruding portion, 34 Flat portion, 35 inclined portion, 35A first inclined portion, 35B second inclined portion, 36 flat portion, 40 negative electrode substrate, 41 negative electrode mixture layer, 50 protective tape, 60 resin layer.

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which strip-shaped first and second electrodes of opposite polarity are wound longitudinally with a separator interposed therebetween, wherein the first electrode has a first electrode core and a first electrode mixture layer disposed on each side of the first electrode core, a first electrode core exposed portion is provided in an intermediate portion of the first electrode in the longitudinal direction, where the first electrode mixture layer is not disposed and both sides of the first electrode core are exposed, a first electrode tab is joined to the first electrode core exposed portion, and the first electrode mixture layer has raised portions in the thickness direction of the first electrode in regions adjacent to the winding start ends on each side of the first electrode core exposed portion, and has sloped portions in which the thickness of the first electrode mixture layer decreases toward the first electrode core exposed portion in regions adjacent to the winding end ends on each side of the first electrode core exposed portion.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the protruding portion includes a first protruding portion provided on a first surface of the first electrode and a second protruding portion provided on a second surface of the first electrode, and at least a portion of the first protruding portion is provided at a position overlapping the second protruding portion in the thickness direction of the first electrode.

3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the length along the longitudinal direction of the first electrode from the position where the sum of the thickness of the first protruding portion and the thickness of the second protruding portion is greatest to the winding start end of the first electrode tab is 8 mm or less.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode core exposed portion contacts only one widthwise end of the first electrode, and the first electrode mixture layer is disposed on the surface of the first electrode core in an area that overlaps the first electrode core exposed portion and the first electrode in the widthwise direction.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode has a resin layer disposed on the surface of the inclined portion.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode is a positive electrode.

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