Non-aqueous electrolyte secondary cell and method for manufacturing non-aqueous electrolyte secondary cell

Abstract

In the present invention, a negative electrode (12) has: a negative electrode mixture layer (41) on both surfaces of an elongated core body (40); and a negative electrode core body exposed part (42) that is provided to both surfaces of the core body (40) so as to extend across the width of a longitudinal center section thereof and that includes an overlapping section (43) of overlap on both surfaces in a thickness direction of the core body (40). The negative electrode mixture layer (41) has a high-density region (41b) provided so as to extend by a predetermined length in a length direction from the edge of the negative electrode mixture layer facing the negative electrode core body exposed section. The negative electrode core body exposed part (42) includes a first negative electrode core body exposed section (42a) formed on the surface of the core body, and a second negative electrode core body exposed section (42b) formed on the rear surface of the core body (40). Either the first negative electrode core body exposed section (42a) or the second negative electrode core body exposed section (42b) includes, in a region opposing, via the core body (40), the negative electrode mixture layer (41) having the high-density region (41b): a non-overlapping portion (44) where the first negative electrode core body exposed section (42a) and the second negative electrode core body exposed section (42b) do not overlap each other in the thickness direction of the core body (40) and extending 0.5-2.0 mm in the length direction of the core body.

Description

Nonaqueous electrolyte secondary battery and method for manufacturing negative electrode for nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery and a method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery, and more particularly to the structure of an electrode in a non-aqueous electrolyte secondary battery.

[0002] In recent years, secondary batteries such as lithium-ion batteries have been widely used in applications requiring high capacity, high durability, rapid charging performance, etc., such as in-vehicle applications and power storage applications. In general, a secondary battery includes a wound electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, an exterior body that houses the electrode assembly, and a sealing body that closes the opening of the exterior body.

[0003] An electrode for a secondary battery has a core made of metal foil and a mixture layer formed on both sides of the core. It is manufactured by applying a mixture slurry containing active material particles to both sides of the core, drying the coating, and compressing it. In this process, the mixture slurry may be applied intermittently to provide a core exposed portion where the surface of the core is exposed. The core exposed portion is, for example, a portion to which an electrode current collecting tab is connected, and is provided in the longitudinal center of the electrode.

[0004] When the core exposed portion is formed by intermittently applying the mixture slurry, a raised portion is formed at the application start end of the mixture slurry when application is resumed after the formation of the core exposed portion, where the mixture layer rises in the thickness direction of the core. The raised portion is a portion formed so that the mixture slurry rises at the application start end. Therefore, when pressure is applied to the electrode, the core may be strongly compressed while sandwiched between the raised portions on both sides, causing the core to become locally thin. Furthermore, when compressed, the raised portion becomes a high-density region compared to other regions.

[0005] A technique has been known in the past in which at least one of both end portions of a mixture layer formed on a core is offset in order to reduce breakdowns such as breakage during the manufacturing process of an electrode (see Patent Document 1). Patent Document 1 describes that by offsetting at least one of both end portions of the mixture layer formed on the core, the problem of electrode breakage due to pressing is improved.

[0006] Japanese Patent Application Laid-Open No. 2007-305598

[0007] As a result of research by the inventors, it was found that the protrusions cause the core to break and wrinkle during the electrode compression process. If the core breaks or wrinkles, problems such as reduced productivity and an increased rate of electrode waste occur, so it is an important issue to prevent the core from breaking and wrinkles caused by the protrusions. After the battery is fabricated, there is a problem of wrinkles occurring due to high-density regions when the negative electrode expands during charging and discharging. The electrode sheet described in Patent Document 1 has a mixture layer formed on the core that is misaligned at at least one of both longitudinal ends of the core, but does not take into consideration deformation of the core caused by the protrusions and high-density regions of the mixture layer facing the negative electrode core exposed portion located in the longitudinal middle of the core, and therefore is unable to solve this problem.

[0008] The nonaqueous electrolyte secondary battery according to the present disclosure includes an electrode assembly having a positive electrode, a negative electrode, and a separator, the electrode assembly being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween, and a nonaqueous electrolyte. The negative electrode includes a long core, negative electrode mixture layers provided on both sides of the core, and negative electrode core exposed portions provided on both sides of the core and across the width direction of a longitudinal intermediate portion, the negative electrode core exposed portions including overlapping portions that overlap in the thickness direction of the core on both sides. The negative electrode further includes a current collecting tab provided on one of both sides of the negative electrode core exposed portion, and a high-density region provided over a predetermined length in the longitudinal direction from the edge of the negative electrode mixture layer facing the negative electrode core exposed portion. The negative electrode core exposed portion includes a first negative electrode core exposed portion formed on the surface of the core and a second negative electrode core exposed portion formed on the back surface of the core. Either the first negative electrode core exposed portion or the second negative electrode core exposed portion is a region that faces the negative electrode mixture layer having the high-density region provided therein via the core, and is characterized in that the first negative electrode core exposed portion and the second negative electrode core exposed portion include a non-overlapping portion that does not overlap in the thickness direction of the core by 0.5 mm or more and 2.0 mm or less in the length direction of the core.

[0009] According to the method for manufacturing a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte negative electrode according to the present disclosure, it is possible to suppress the occurrence of wrinkles due to high-density regions when the negative electrode expands due to charging and discharging, while also suppressing breakage and wrinkles in the core body due to protrusions.

[0010] 2 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; FIG. 3 is a front view of a negative electrode according to an embodiment of the present invention; FIG. 4 is a cross-sectional view of a negative electrode according to an embodiment of the present invention, taken along the line AA in FIG. 2, showing the negative electrode before compression; and FIG. 5 is a cross-sectional view of a negative electrode according to an embodiment of the present invention after compression.

[0011] 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. Note that configurations obtained by selectively combining the respective components of the multiple embodiments and variations described below are included within the scope of the present disclosure.

[0012] The following describes an example of a nonaqueous electrolyte secondary battery 10, which is a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical outer can 16 with a bottom, but the outer can of the battery is not limited to a cylindrical outer can. Other embodiments of the nonaqueous electrolyte secondary battery according to the present disclosure include, for example, a prismatic battery with a prismatic outer can, a coin-shaped battery with a coin-shaped outer can, and a pouch-shaped battery with an outer can made of a laminate sheet including a metal layer and a resin layer. However, the configuration of the present disclosure is particularly effective when applied to a cylindrical battery.

[0013] FIG. 1 is a schematic diagram illustrating an axial cross section of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte (not shown), and a bottomed, cylindrical outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 16 is a bottomed, cylindrical metal container that is open on one axial side, and the opening of the outer can 16 is closed by a sealing member 17. Hereinafter, for convenience of explanation, the sealing member 17 side of the nonaqueous electrolyte secondary battery 10 is referred to as the top, and the bottom side of the outer can 16 is referred to as the bottom.

[0014] The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes 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. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0015] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0016] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the length direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11. The nonaqueous electrolyte secondary battery 10 includes insulating plates 18 and 19 arranged above and below the electrode assembly 14, respectively.

[0017] The electrode assembly 14 has a positive electrode current collecting tab 20 connected to the positive electrode 11 by welding or the like, and a negative electrode current collecting tab 21 connected to the negative electrode 12 by welding or the like. In this embodiment, the positive electrode current collecting tab 20 is connected to the longitudinal center of the positive electrode 11, and the negative electrode current collecting tab 21 is similarly connected to the longitudinal center of the negative electrode 12. The positive electrode current collecting tab 20 is connected to the lower surface of an internal terminal plate 23, which is the bottom plate of the sealing body 17, and the negative electrode current collecting tab 21 is connected to the inner surface of the can bottom of the outer can 16. Therefore, the sealing body 17 serves as a positive electrode external terminal, and the outer can 16 serves as a negative electrode external terminal. The current collection structure of the positive electrode 11 is not particularly limited, and multiple positive electrode current collecting tabs 20 may be connected to the positive electrode 11.

[0018] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film having a surface layer made of such a metal. The thickness of the positive electrode core is preferably 5 μm to 25 μm, more preferably 10 μm to 20 μm. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode core. The thickness of the positive electrode mixture layer is greater than the thickness of the positive electrode core, and is, for example, 60 μm to 120 μm on one side of the positive electrode core.

[0019] The positive electrode active material uses a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn. Examples of metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. One type of lithium transition metal composite oxide may be used alone, or multiple types may be used in combination.

[0020] Examples of conductive agents contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like.

[0021] The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto a positive electrode core, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core. The positive electrode 11, which has a core exposed portion at the center in the longitudinal direction to which the positive electrode current collector tab 20 is connected, is produced by intermittently applying the positive electrode mixture slurry and pausing the application of the slurry midway, with the portion not coated becoming the core exposed portion. For example, N-methyl-2-pyrrolidone (NMP) is used as the dispersion medium for the positive electrode mixture slurry.

[0022] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode core can be a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film having a surface layer made of such a metal. The negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core. The negative electrode 12 can be produced, as in the case of the positive electrode 11, by applying a negative electrode mixture slurry to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0023] The thickness of the negative electrode 12 is, for example, 90 μm or more and 210 μm or less. In this embodiment, the thickness of the negative electrode 12 is substantially constant except for a negative electrode core exposed portion described later. The thickness of the negative electrode core is, for example, 5 μm or more and 15 μm or less. The thickness of the negative electrode mixture layer is, for example, 40 μm or more and 110 μm or less on one side of the negative electrode core.

[0024] The negative electrode active material is not particularly limited as long as it reversibly absorbs and releases lithium ions, and generally, carbon materials such as graphite are used. Furthermore, elements that alloy with Li, such as Si and Sn, or materials containing such elements may also be used as the negative electrode active material. Among these, silicon-containing materials containing Si are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. One type of negative electrode active material may be used alone, or multiple types may be used in combination.

[0025] The negative electrode active material contains, for example, graphite particles having a 20% compressive strength of 20 MPa to 35 MPa. When the negative electrode 12 is made of the graphite particles, the strength of the negative electrode 12 can be improved and wrinkles can be effectively suppressed.

[0026] In the present disclosure, the compressive strength of graphite particles means the compressive force (MPa) when a load is applied toward the center of the graphite particles at room temperature at a predetermined load application rate, causing the graphite particles to deform until the particle diameter (volume average particle diameter) is displaced by 20%. The compressive strength of graphite particles may be measured using a known compression testing device, for example, a microcompression testing machine (MCT-211, manufactured by Shimadzu Corporation).

[0027] The graphite particles according to this embodiment may be any graphite-based material that has conventionally been used as a negative electrode active material for non-aqueous electrolyte secondary batteries. For example, natural graphite such as block graphite and amorphous graphite, as well as artificial graphite such as block artificial graphite and graphitized mesophase carbon microbeads, may be used.

[0028] As in the case of the positive electrode 11, the binder contained in the negative electrode mixture layer can be a fluororesin, an olefin resin, PAN, a polyimide, a polyamide, an acrylic resin, or the like. However, polyvinyl acetate, styrene-butadiene rubber (SBR), or the like may also be used. Among these, SBR is preferably used. One type of binder may be used alone, or multiple types may be used in combination. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0029] The density of the negative electrode mixture layer is, for example, 1.60 g / cm ３ 1.75g / cm or more ３ The density of the negative electrode mixture layer is, for example, the average density of the negative electrode mixture layer. When the average density of the negative electrode mixture layer is within the above range, it is possible to maintain peel strength while suppressing cutting and wrinkling of the negative electrode core 40.

[0030] In the present disclosure, the density of the negative electrode mixture layer can be measured, for example, by the following method. For a negative electrode 12 composed of a negative electrode core and a negative electrode mixture layer, the thickness of the negative electrode mixture layer is measured using a known measuring means. The negative electrode mixture layer is then scraped off using a cutting tool, ultrasonic waves, or the like, and the mass of the negative electrode mixture layer is measured. The above measurement is performed at multiple locations, and the average density of the negative electrode mixture layer is calculated from these measurement results.

[0031] The density of the negative electrode mixture layer can be adjusted, for example, in the production of the negative electrode 12, by adjusting the viscosity of the negative electrode mixture slurry, the contents of the negative electrode active material, the conductive agent, and the binder in the negative electrode mixture slurry, the amount of the negative electrode mixture slurry applied, the pressure during rolling, etc.

[0032] As described above, the negative electrode mixture layer is formed by applying a negative electrode mixture slurry to the negative electrode core. Here, the density of the negative electrode mixture layer may be different between the front and back surfaces of the negative electrode core. For example, one of the front and back surfaces of the negative electrode core may have a density that is 105% of the density of the negative electrode mixture layer on the other surface. The density of the negative electrode mixture layer can be adjusted by changing the amount of negative electrode mixture slurry applied on the front and back surfaces of the negative electrode core.

[0033] Specifically, in the case of a wound-type electrode body 14, the core has an inner winding surface on the inner winding side (diametrically central side) of the electrode body 14 and an outer winding surface on the outer winding side (diametrically outer side) of the electrode body 14. In this electrode body 14, when comparing the negative electrode mixture layer on the inner winding side of the negative electrode core with the positive electrode mixture layer on the outer winding side of the positive electrode core facing each other via a separator, the negative electrode mixture layer located relatively on the outer winding side has a larger amount of mixture slurry applied. On the other hand, when comparing the negative electrode mixture layer on the outer winding side of the negative electrode core with the positive electrode mixture layer on the inner winding side of the positive electrode core facing each other via a separator, the negative electrode mixture layer located relatively on the inner winding side has a smaller amount of mixture slurry applied. Therefore, from the viewpoints of maintaining the NP ratio of the battery and safety, it is preferable that the density of the negative electrode mixture layer on the outer winding side of the negative electrode core be approximately 105% of the density of the negative electrode mixture layer on the inner winding side.

[0034] 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. A highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0035] As described above, the outer can 16 is a cylindrical metal container with a bottom and an opening on one axial side. A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure sealing of the battery interior and insulation between the outer can 16 and the sealing body 17. The outer can 16 has a groove 22 formed by a portion of the side surface protruding inward. The groove 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the outer can 16 by the groove 22 and the open end of the outer can 16, which is crimped to the sealing body 17.

[0036] 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. If an abnormality occurs in the battery and the internal pressure increases, 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. If the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0037] The configuration of the negative electrode 12 will be described in further detail below with reference to Figures 2 and 3. Figure 2 is a front view of the negative electrode 12. Figure 3 is a cross-sectional view taken along line A-A in Figure 2, showing the negative electrode before compression. The protruding portion 41a is omitted from Figure 2.

[0038] 2 and 3 , the negative electrode 12 has a structure including a long negative electrode core 40 and a negative electrode mixture layer 41 provided on both sides of the negative electrode core 40, and a negative electrode core exposed portion 42 that is provided on both sides of the negative electrode core 40 across the width direction of the longitudinal middle portion and includes an overlapping portion 43 that overlaps on both sides of the negative electrode core 40 in the thickness direction of the negative electrode core 40. In detail, the negative electrode core 40 has a first surface 40a and a second surface 40b.

[0039] A negative electrode mixture layer 41 is provided on each of the first surface 40a and the second surface 40b, and a negative electrode core exposed portion 42 is formed in the longitudinal intermediate portion of the negative electrode core 40, where the negative electrode core 40 is exposed across the entire width of the negative electrode core 40. In the present embodiment, the negative electrode core exposed portion 42 includes a first negative electrode core exposed portion 42a formed on the first surface 40a and a second negative electrode core exposed portion 42b formed on the second surface 40b, and is formed in the longitudinal central portion of the negative electrode core 40. In this specification, the intermediate portion refers to a region other than both longitudinal end portions of the negative electrode core 40, and the central portion refers to a region within ±10% of the 50% position in the longitudinal direction of the negative electrode core 40.

[0040] The first surface 40a may face either the outside or the inside of the winding, but in this embodiment, the first surface 40a is the outside surface (front surface) facing the outside of the winding of the electrode body 14, and the second surface 40b is the inside surface (back surface) facing the inside of the winding. The negative electrode current collecting tab 21 is provided on either the negative electrode substrate exposed portion 42 provided on the first surface 40a or the second surface 40b. As will be described in detail later, the negative electrode current collecting tab 21 is, for example, laser welded to the overlapping portion 43 of the first negative electrode substrate exposed portion 42a.

[0041] 3 , the negative electrode 12 has a protruding portion 41a that protrudes in the thickness direction of the negative electrode core 40 at an end of the negative electrode mixture layer 41 that faces the negative electrode core exposed portion 42. The negative electrode 12 having the negative electrode core exposed portion 42 at the center in the longitudinal direction is formed, for example, by intermittently applying a negative electrode mixture slurry to the negative electrode core 40. The protruding portion 41a is formed, for example, at the application start end after the application of the negative electrode mixture slurry is temporarily stopped during intermittent application to form the negative electrode core exposed portion 42.

[0042] The raised portion 41 a is generated by the negative electrode mixture layer 41 rising in the thickness direction of the negative electrode core 40 at the application start end of the intermittent application as described above. That is, when intermittent application is performed on both sides, the raised portion 41 a is formed at the application start end of both the first surface 40 a and the second surface 40 b. Generally, in the step of applying the negative electrode mixture slurry to the negative electrode core, application is performed in the same direction on the first surface and the second surface, and therefore, raised portions are formed on the first surface and the second surface at the same position across the negative electrode core.

[0043] The protruding portion 41 a is formed across the entire width of the negative electrode mixture layer 41, and has a dimension of 15 μm to 60 μm in the thickness direction of the negative electrode core 40 as viewed from the negative electrode mixture layer 41. Furthermore, the protruding portion 41 a has a dimension of 100 μm to 5000 μm in the length direction from the edge of the negative electrode mixture layer 41 facing the negative electrode core exposed portion 42.

[0044] As described above, the negative electrode 12 can be produced by applying the negative electrode mixture slurry to the negative electrode core 40, drying the coating, and then compressing it to form negative electrode mixture layers on both sides of the negative electrode core. Hereinafter, the high-density region 41b formed by compressing the raised portion 41a of the negative electrode mixture layer 41 will be described.

[0045] The high-density region 41b is a region formed by compressing the protruding portion 41a formed in the negative electrode mixture layer 41 as described above. The high-density region 41b has a density that is 105% or more and 120% or less of the density of a region where the protruding portion 41a is not formed in the negative electrode mixture layer 41. The high-density region 41b has a dimension of, for example, 1000 μm or more and 5000 μm or less in the length direction from the edge of the negative electrode mixture layer 41 that faces the negative electrode core exposed portion 42.

[0046] As shown in Fig. 3 , the negative electrode core exposed portion 42 has a non-overlapping portion 44 where the negative electrode core exposed portion 42 does not overlap in the thickness direction of the negative electrode core 40 in a region facing the negative electrode mixture layer 41 on which the protrusion 41a is provided, across the negative electrode core 40, on either one of the two surfaces of the negative electrode core 40. Furthermore, after the negative electrode 12 is compressed, as shown in Fig. 4 , the negative electrode core exposed portion 42 has a non-overlapping portion 44 where the negative electrode core exposed portion 42 does not overlap in the thickness direction of the negative electrode core 40, in a region facing the negative electrode mixture layer 41 on which the high-density region 41b is provided, across the negative electrode core 40. That is, either the first negative electrode core exposed portion 42a or the second negative electrode core exposed portion 42b has a non-overlapping portion 44 where the first negative electrode core exposed portion 42a and the second negative electrode core exposed portion 42b do not overlap, in a region facing the negative electrode mixture layer 41 on which the high-density region 41b is provided, across the negative electrode core 40. The non-overlapping portion 44 is formed in the first negative electrode substrate exposed portion 42a, for example, as shown in FIGS.

[0047] 4, the non-overlapping portion 44 is formed by misaligning the edges of the negative electrode mixture layer 41 that face the negative electrode core exposed portion 42 in a region facing the high-density region 41b via the negative electrode core 40. In this way, the negative electrode core exposed portion 42 and the negative electrode mixture layer 41 are formed so that the raised portions 41a (high-density regions 41b) formed on the first surface 40a and the second surface 40b do not overlap.

[0048] 3 and 4 , the non-overlapping portion 44 is provided contiguous with the overlapping portion 43. In the present embodiment, the overlapping portion 43 and the non-overlapping portion 44 are formed across the entire width of the negative electrode core 40. The non-overlapping portion 44 is preferably formed to have a length of 0.5 mm or more and 2.0 mm or less in the length direction of the negative electrode core 40. The non-overlapping portion 44 is more preferably formed to have a length of 1.0 mm or more and 2.0 mm or less in the length direction of the negative electrode core 40, and particularly preferably to have a length of 1.5 mm or more and 2.0 mm or less in the length direction of the negative electrode core 40.

[0049] If the non-overlapping portion 44 is formed with a dimension of less than 0.5 mm in the length direction of the negative electrode core 40, wrinkles cannot be effectively suppressed. If the non-overlapping portion 44 is formed with a dimension of more than 2.0 mm in the length direction of the negative electrode core 40, the width of the negative electrode core exposed portion 42 including the non-overlapping portion 44 increases, and the area of ​​the negative electrode mixture layer 41 decreases, which causes a decrease in battery capacity.

[0050] The non-overlapping portion 44 prevents the negative electrode core 40 from being cut or wrinkled due to compression of the protruding portion 41 a during a compression process after the negative electrode mixture slurry is applied to the negative electrode core 40. In the compression process, for example, two rollers are used to compress the negative electrode core 40 coated with the negative electrode mixture slurry from both sides. In the example shown in FIG. 3 , the non-overlapping portion 44 is provided in the region facing the protruding portion 41 a and the negative electrode core 40, thereby reducing the pressure applied to the negative electrode core 40 during compression and preventing the negative electrode core 40 from being cut or wrinkled. Furthermore, after the non-aqueous electrolyte secondary battery 10 is fabricated, the non-overlapping portion 44 prevents wrinkles from occurring due to high-density regions when the negative electrode expands due to charge and discharge.

[0051] 3 and 4, the non-overlapping portion 44 is provided in the first negative electrode substrate exposed portion 42a on the first surface 40a, but may also be provided in the second negative electrode substrate exposed portion 42b on the second surface 40b. That is, the non-overlapping portion 44 may be provided on either the radially inner side (winding inner side) or the radially outer side (winding outer side) of the negative electrode substrate 40.

[0052] As described above, the density of the negative electrode mixture layer 41 may be different on the front and back surfaces of the negative electrode core 40. That is, the amount of negative electrode mixture slurry applied may be different on the front and back surfaces of the negative electrode core 40. The negative electrode mixture layer 41 is formed, for example, so that the density of the negative electrode mixture layer 41 on the second surface 40b is greater than the density of the negative electrode mixture layer 41 on the first surface 40a. In this case, because the high-density negative electrode mixture layer 41 applies a large pressure to the negative electrode core 40 during compression, the non-overlapping portion 44 of the negative electrode core exposed portion 42 is preferably provided on the first surface 40a. That is, the non-overlapping portion 44 is preferably provided on the surface of the negative electrode mixture layer 41 with a low density. As a result, the non-overlapping portion 44 reduces the pressure applied to the negative electrode core 40 by the high-density negative electrode mixture layer 41, thereby more effectively suppressing the occurrence of cutting and wrinkling of the negative electrode core 40.

[0053] The edge of the negative electrode mixture layer 41 on which the protrusion 41a is not formed, facing the negative electrode core exposed portion 42, may be misaligned or may coincide on the first surface 40a and the second surface 40b in the length direction of the negative electrode core 40. It is preferable that the edge of the negative electrode mixture layer 41 on which the protrusion 41a is not provided, facing the negative electrode core exposed portion 42, substantially coincide on the first surface 40a and the second surface 40b. Substantial coincidence includes, for example, a misalignment of 5 μm or less in the length direction of the negative electrode core 40.

[0054] The negative electrode core exposed portion 42 has dimensions that allow the negative electrode current collector tab 21 to be arranged without overlapping with the negative electrode mixture layer 41. In this embodiment, the negative electrode core exposed portion 42 is longer in the width direction than in the length direction of the negative electrode core 40 and is formed across the entire width of the negative electrode core 40. The width of the negative electrode core exposed portion 42 (the length in the length direction of the negative electrode core 40) is preferably, for example, 6.0 mm or more and 10.0 mm or less. This makes it possible to arrange the negative electrode current collector tab 21 so as not to overlap with the negative electrode mixture layer 41 while ensuring the capacity of the battery. Furthermore, the negative electrode core exposed portion 42 preferably falls within the above dimensions even when a non-overlapping portion 44 is formed.

[0055] The negative electrode current collecting tab 21 is preferably provided in the overlapping portion 43. As described above, the negative electrode current collecting tab 21 is provided by laser welding to either the first surface 40a or the second surface 40b of the negative electrode core exposed portion 42. In this case, since welding is performed by irradiating a laser from the backside of the surface on which the negative electrode current collecting tab 21 is provided, it is preferable that the negative electrode mixture layer 41 is not present in the region facing the negative electrode current collecting tab 21 and the negative electrode core 40 interposed therebetween.

[0056] 3 and 4, the negative electrode current collecting tab 21 is provided in the overlapping portion 43 of the first negative electrode core exposed portion 42a provided on the front surface of the negative electrode core 40, but may also be provided in the overlapping portion 43 of the second negative electrode core exposed portion 42b provided on the back surface of the negative electrode core 40. Furthermore, the negative electrode current collecting tab 21 and the non-overlapping portion 44 may be provided on the same surface as shown in FIGS. 3 and 4, or may be provided on different surfaces.

[0057] The overlapping portion 43 preferably has a dimension of 5.0 mm or more and 8.0 mm or less. By having the overlapping portion 43 have the above dimension, the negative electrode current collector tab 21 can be disposed so as not to come into contact with the negative electrode mixture layer 41. For example, the width of the negative electrode current collector tab 21 is 3.0 mm, and the overlapping portion 43 has a width of 5.0 mm, and is disposed at a distance of 1.0 mm from the negative electrode mixture layer 41.

[0058] The negative electrode core exposed portion 42 is formed by intermittently applying the negative electrode mixture slurry to the negative electrode core 40 as described above. The intermittent application is performed using, for example, a die coater. The widths of the negative electrode core exposed portion 42, the overlapping portion 43, and the non-overlapping portion 44 can be adjusted, for example, by controlling the length for which application of the negative electrode mixture slurry is temporarily stopped on the first surface 40 a and the second surface 40 b during the intermittent application.

[0059] As described above, the nonaqueous electrolyte secondary battery 10 having the negative electrode 12 configured as described above can prevent the negative electrode substrate 40 from being cut or wrinkled due to the protrusion 41a.

[0060] In the above embodiment, a case has been described in which the negative electrode core exposed portion 42 is formed across the entire width of the central portion in the length direction of the negative electrode 12, but a plurality of negative electrode core exposed portions 42 may be formed, and may not be formed across the entire width of the negative electrode 12. For example, when a plurality of negative electrode core exposed portions 42 are provided in the negative electrode 12, an overlapping portion 43 and a non-overlapping portion 44 may be provided in each of the negative electrode core exposed portions 42.

[0061] Fabrication of a negative electrode, which is one example of an embodiment, includes, for example, the following steps: (1) a first coating step of intermittently applying a negative electrode mixture slurry to a first surface of the negative electrode core to form a first negative electrode core exposed portion where the negative electrode core is exposed at a longitudinal intermediate portion of the negative electrode core, thereby forming a first coating layer; (2) a second coating step of intermittently applying the negative electrode mixture slurry to a second surface of the negative electrode core to form a second negative electrode core exposed portion that includes an overlapping portion that overlaps with the first negative electrode core exposed portion via the negative electrode core, and a non-overlapping portion that does not overlap with the first negative electrode core exposed portion in the thickness direction of the negative electrode core, thereby forming a second coating layer; (4) a drying step of drying the coating layer formed on the negative electrode core to form a negative electrode mixture layer; and (3) a rolling step of rolling the negative electrode mixture layer using rolling means such as a pressure roll.

[0062] In detail, in the first and second application steps, as described above, application of the negative electrode mixture slurry is temporarily stopped when forming the negative electrode substrate exposed portion, and a raised portion is formed at the application start point when application is resumed. Therefore, in the second application step, it is preferable that a non-overlapping portion is formed in a region that faces the raised portion across the negative electrode substrate.

[0063] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited thereto.

[0064] Example 1 [Preparation of Negative Electrode] Graphite particles with a 20% compressive strength of 30 MPa were used as the negative electrode active material. The 20% compressive strength of the graphite particles was measured using the above-mentioned measurement method. This negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 100:1:1, and a negative electrode mixture slurry was prepared using water as a dispersion medium. Next, the negative electrode mixture slurry was intermittently applied to both sides (first and second sides) of a negative electrode core made of copper foil with a thickness of 8 μm, and the coating was dried. The amount of negative electrode mixture slurry applied was adjusted so that the density of the negative electrode mixture layer formed on the first side of the negative electrode core was 105% of the density of the negative electrode mixture layer formed on the second side of the negative electrode core.

[0065] In the intermittent application of the negative electrode mixture slurry, first and second negative electrode core exposed portions, where the negative electrode mixture layer was not present, were provided on both sides of the negative electrode core and across the entire width of the center portion in the longitudinal direction, as shown in Fig. 2. Furthermore, the negative electrode core exposed portions were provided with overlapping portions that overlapped in the thickness direction of the negative electrode core on both sides, and non-overlapping portions in which the negative electrode core exposed portion did not face the negative electrode core via the negative electrode core in a region on the first surface of the negative electrode core that faced the negative electrode mixture layer on the second surface on which the protrusion was formed, via the negative electrode core. The width of the first negative electrode core exposed portion was 7.0 mm, the width of the second negative electrode core exposed portion was 6.5 mm, the width of the overlapping portion was 6.5 mm, and the width of the non-overlapping portion of the first negative electrode core exposed portion was 0.5 mm.

[0066] Next, the coating film was rolled with a rolling roller and cut to a predetermined electrode size to prepare a negative electrode. As a result, a non-overlapping portion was formed in which the first negative electrode substrate exposed portion and the second negative electrode substrate exposed portion did not overlap in the thickness direction of the substrate in a region facing the negative electrode mixture layer, in which a high-density region formed by compressing the protrusions was provided, via the substrate. At this time, according to the above measurement method, the average density of the negative electrode mixture layer was 1.70 g / cm ３ It was.

[0067] Example 2 A negative electrode was produced in the same manner as in Example 1, except that the width of the first negative electrode substrate exposed portion was set to 6.5 mm and the width of the second negative electrode substrate exposed portion was set to 7.0 mm.

[0068] Example 3 A negative electrode was produced in the same manner as in Example 1, except that the width of the second negative electrode substrate exposed portion was 6.0 mm, the width of the overlapping portion was 6.0 mm, and the width of the non-overlapping portion of the first negative electrode substrate exposed portion was 1.0 mm.

[0069] <Example 4> A negative electrode was produced in the same manner as in Example 1, except that the width of the first negative electrode core exposed portion was 6.0 mm, the width of the second negative electrode core exposed portion was 7.0 mm, the width of the overlapping portion was 6.0 mm, and the width of the non-overlapping portion of the first negative electrode core exposed portion was 1.0 mm.

[0070] Example 5 A negative electrode was produced in the same manner as in Example 1, except that the width of the second negative electrode substrate exposed portion was 5.0 mm, the width of the overlapping portion was 5.0 mm, and the width of the non-overlapping portion of the first negative electrode substrate exposed portion was 2.0 mm.

[0071] <Example 6> A negative electrode was produced in the same manner as in Example 1, except that the width of the first negative electrode core exposed portion was 5.0 mm, the width of the second negative electrode core exposed portion was 7.0 mm, the width of the overlapping portion was 5.0 mm, and the width of the non-overlapping portion of the second negative electrode core exposed portion was 2.0 mm.

[0072] <Example 7> A negative electrode was produced in the same manner as in Example 1, except that the width of the first negative electrode core exposed portion was 10.0 mm, the width of the second negative electrode core exposed portion was 8.0 mm, the width of the overlapping portion was 8.0 mm, and the width of the non-overlapping portion of the first negative electrode core exposed portion was 2.0 mm.

[0073] <Example 8> A negative electrode was produced in the same manner as in Example 1, except that the width of the first negative electrode core exposed portion was 8.0 mm, the width of the second negative electrode core exposed portion was 10.0 mm, the width of the overlapping portion was 8.0 mm, and the width of the non-overlapping portion of the second negative electrode core exposed portion was 2.0 mm.

[0074] Example 9: The density of the negative electrode mixture layer is 1.55 g / cm ３ A negative electrode was prepared in the same manner as in Example 1, except that:

[0075] Example 10 A negative electrode was fabricated in the same manner as in Example 1, except that graphite particles having a 20% compressive strength of 10 MPa were used as the negative electrode active material.

[0076] <Comparative Example 1> A negative electrode was produced in the same manner as in Example 1, except that the width of the second negative electrode substrate exposed portion was 7.0 mm, the width of the overlapping portion was 7.0 mm, and the non-overlapping portion was eliminated.

[0077] <Comparative Example 2> A negative electrode was produced in the same manner as in Example 1, except that the width of the second negative electrode substrate exposed portion was 7.0 mm, the width of the overlapping portion was 7.0 mm, there was no non-overlapping portion, and graphite particles having a 20% compressive strength of 10 MPa were used as the negative electrode active material.

[0078] Each negative electrode in the examples and comparative examples was evaluated by the following method, and the evaluation results are shown in Table 1. Breaking of the negative electrode core was judged visually, and the number of negative electrode cores for which breakage was confirmed was counted. Evaluation was performed on 100,000 negative electrodes, and the following was indicated: ◯ if no breakage of the negative electrode core occurred; △ if breakage of more than 0 but less than 10 negative electrode cores (more than 0% but less than 0.01%) occurred; and × if breakage of more than 10 negative electrode cores (0.01% or more) occurred. Core breakage was confirmed in 0 negative electrodes in Examples 1 to 9, 6 in Example 10, 23 in Comparative Example 1, and 12 in Comparative Example 2.

[0079] [Wrinkle Height Measurement] The negative electrode was cut in the length direction, and the cross section was photographed with a field emission scanning electron microscope (FE-SEM). The cross-sectional image was taken using a Hitachi High-Technologies Corporation SU8200, with an acceleration voltage of 10 kV and a magnification of 10,000 times. The wrinkle height was measured from the cross-sectional image taken by the above method. In detail, using the cross-sectional image, the height from the surface where the non-overlapping portion was formed, which is the region where the negative electrode mixture layer was formed on both sides of the negative electrode core, to the part where the negative electrode core was most raised in the thickness direction was measured as the wrinkle height. As shown in Table 1, the wrinkle height of the negative electrode of Example 1 was 22 μm, and the wrinkle height of Comparative Example 1 was 70 μm, and it can be confirmed that wrinkles were suppressed in the negative electrode of Example 1.

[0080] [Peel Strength Measurement] The surface of the negative electrode (surface of the negative electrode mixture layer) was attached to a plastic plate using double-sided tape (tape width 5 mm), and the negative electrode was peeled off in a direction perpendicular to the plastic plate using a peel tester to measure the peel strength of the negative electrode mixture layer. The peel strength indexes for Examples 1 to 10 and Comparative Examples 1 and 2 shown in Table 1 are relative values, with the peel strength of Example 1 set to 100.

[0081]

[0082] As shown in Table 1, no improvement in cutting and wrinkle height of the negative electrode core was observed in Comparative Examples 1 and 2, but improvements in cutting and wrinkle height of the negative electrode core were confirmed in Examples 1 to 10. That is, suppression of cutting and wrinkles of the negative electrode core was confirmed in Examples 1 to 10. Furthermore, more significant suppression of cutting and wrinkles of the negative electrode core was confirmed in Examples 6 to 8. That is, by having a non-overlapping portion in the region where the negative electrode core exposed portion faces the negative electrode mixture layer including the protruding portion via the negative electrode core, cutting and wrinkles of the negative electrode core are suppressed. Note that, by positioning the negative electrode mixture layer in the region where the protruding portion faces the negative electrode core via the negative electrode core, when the negative electrode is compressed, the negative electrode core sandwiched between the protruding portion and the negative electrode mixture layer is subjected to a large localized compressive force, causing cutting and wrinkles. Therefore, it is believed that by providing a non-overlapping portion and positioning the negative electrode substrate exposed portion in a position opposite the raised portion, the compressive force caused by the raised portion is reduced and cutting and wrinkling of the negative electrode substrate exposed portion are sufficiently suppressed.

[0083] In the negative electrode shown in Example 9, the occurrence of breakage of the negative electrode core was suppressed by providing a non-overlapping portion, and the wrinkle height was suppressed, but it was confirmed that the peel strength of the negative electrode mixture layer was reduced compared to Example 1. If the peel strength is low, there is a possibility that the negative electrode mixture layer will peel off from the negative electrode core during the winding process. ３ 1.70g / cm or more ３ By using the following negative electrode, the peel strength of the negative electrode mixture layer can be maintained.

[0084] The negative electrode shown in Example 10 has a non-overlapping portion similar to Example 1, but uses graphite with a 20% compressive strength of 10 MPa as the negative electrode active material, and thus exhibits relatively more wrinkling than Example 1. Because a material with low compressive strength is used as the negative electrode active material, even if a non-overlapping portion is provided, cutting and wrinkling of the negative electrode core cannot be sufficiently suppressed. By including graphite with a 20% compressive strength of 20 MPa or more and 35 MPa or less in the negative electrode active material, cutting and wrinkling of the negative electrode core can be more effectively suppressed.

[0085] The present disclosure will be further described by the following embodiments. Configuration 1: An electrode assembly having a positive electrode, a negative electrode, and a separator, the electrode assembly being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween, and a non-aqueous electrolyte, wherein the negative electrode comprises a long core body, a negative electrode mixture layer provided on both sides of the core body, a negative electrode core exposed portion provided on both sides of the core body across the width direction of a longitudinal intermediate portion thereof and including overlapping portions that overlap the core body in the thickness direction on both sides, a current collecting tab provided on one of both sides of the negative electrode core exposed portion, and a current collecting tab extending longitudinally from an edge of the negative electrode mixture layer facing the negative electrode core exposed portion. a high-density region provided over a predetermined length, the negative electrode core exposed portion including a first negative electrode core exposed portion formed on the surface of the core and a second negative electrode core exposed portion formed on the back surface of the core, either the first negative electrode core exposed portion or the second negative electrode core exposed portion being a region facing the negative electrode mixture layer in which the high-density region is provided, via the core, the first negative electrode core exposed portion and the second negative electrode core exposed portion including a non-overlapping portion that does not overlap in the thickness direction of the core by 0.5 mm to 2.0 mm in the length direction of the core. A nonaqueous electrolyte secondary battery according to Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein the high-density region of the negative electrode mixture layer has a density that is 105% to 120% of the density of the remaining region. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein the predetermined length is 1.0 mm to 3.0 mm from the edge of the negative electrode mixture layer that faces the negative electrode core. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the current collecting tab is provided at the overlapping portion. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the negative electrode substrate exposed portion has a width of 6.0 mm to 10.0 mm in the length direction of the substrate. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the negative electrode mixture layer contains, as a negative electrode active material, graphite particles having a 20% compressive strength of 20 MPa to 35 MPa. Configuration 7: The negative electrode mixture layer has a density of 1.60 g / cm ３ 1.75g / cm or more ３The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, which is as follows: Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, which is provided with a cylindrical outer can with a bottom; Configuration 9: A method for manufacturing a negative electrode for a nonaqueous electrolyte secondary battery, comprising: a first coating step of intermittently applying a negative electrode mixture slurry to a first surface of a negative electrode core so as to form a first negative electrode core exposed portion in which the negative electrode core is exposed at a longitudinal intermediate portion of the negative electrode core, thereby forming a first coating layer; and a second coating step of intermittently applying the negative electrode mixture slurry to a second surface of the negative electrode core so as to form a second negative electrode core exposed portion that includes an overlapping portion that overlaps with the first negative electrode core exposed portion via the negative electrode core and a non-overlapping portion that does not overlap with the first negative electrode core exposed portion in the thickness direction of the negative electrode core.

[0086] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 16 Outer can 17 Sealing body 18, 19 Insulating plate 20 Positive electrode current collecting tab 21 Negative electrode current collecting tab 22 Grooved portion 23 Internal terminal plate 24 Lower valve body 25 Insulating member 26 Upper valve body 27 Cap 28 Gasket 40 Negative electrode core 40a First surface 40b Second surface 41 Negative electrode mixture layer 41a Raised portion 41b High-density region 42 Negative electrode core exposed portion 42a First negative electrode core exposed portion 42b Second negative electrode core exposed portion 43 Overlapping portion 44 Non-overlapping portion

Claims

1. An electrode assembly having a positive electrode, a negative electrode, and a separator, the electrode assembly being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween; and a non-aqueous electrolyte, wherein the negative electrode comprises a long core body, a negative electrode mixture layer provided on both sides of the core body, a negative electrode core exposed portion provided on both sides of the core body across the width direction of a longitudinal intermediate portion, the negative electrode core exposed portion including overlapping portions that overlap in the thickness direction of the core body on both sides, a current collecting tab provided on one of both sides of the negative electrode core exposed portion, and a high density region provided over a predetermined length in the longitudinal direction from an edge of the negative electrode mixture layer facing the negative electrode core exposed portion, wherein the negative electrode core exposed portion includes a first negative electrode core exposed portion formed on the surface of the core body and a second negative electrode core exposed portion formed on the back surface of the core body, a non-aqueous electrolyte secondary battery, wherein either the first negative electrode core exposed portion or the second negative electrode core exposed portion is a region that faces the negative electrode mixture layer in which the high-density region is provided, via the core, and the first negative electrode core exposed portion and the second negative electrode core exposed portion include a non-overlapping portion that does not overlap in a thickness direction of the core by 0.5 mm or more and 2.0 mm or less in a length direction of the core.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the high-density region of the negative electrode mixture layer has a density that is 105% or more and 120% or less of the density of the remaining region.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the predetermined length is 1.0 mm or more and 3.0 mm or less from the edge of the negative electrode mixture layer facing the exposed portion of the negative electrode substrate.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the current collecting tab is provided in the overlapping portion.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode substrate exposed portion has a width of 6.0 mm or more and 10.0 mm or less in the length direction of the substrate.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode mixture layer contains graphite particles having a 20% compressive strength of 20 MPa or more and 35 MPa or less as a negative electrode active material.

7. The density of the negative electrode mixture layer is 1.60 g / cm ３ 1.75g / cm or more ３ 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein:

8. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 7, comprising a cylindrical outer can with a bottom.

9. A method for manufacturing a negative electrode for a non-aqueous electrolyte secondary battery, comprising: a first coating step of intermittently applying a negative electrode mixture slurry to a first surface of a negative electrode core so as to form a first negative electrode core exposed portion where the negative electrode core is exposed at a longitudinal intermediate portion of the negative electrode core, thereby forming a first coating layer; and a second coating step of intermittently applying the negative electrode mixture slurry to a second surface of the negative electrode core so as to form a second negative electrode core exposed portion that includes an overlapping portion that overlaps with the first negative electrode core exposed portion via the negative electrode core, and a non-overlapping portion that does not overlap with the first negative electrode core exposed portion in the thickness direction of the negative electrode core, thereby forming a second coating layer.

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