Nonaqueous electrolyte secondary battery

Abstract

Provided is a nonaqueous electrolyte secondary battery which comprises an electrode body in which a first electrode and a second electrode are wound with a separator (13) interposed therebetween. The nonaqueous electrolyte secondary battery is characterized in that: the first electrode has a first electrode core body and a first electrode mixture layer; one end portion of the first electrode in the axial direction of the electrode body is provided with a first electrode core body exposed portion in which the first electrode mixture layer is not disposed and the first electrode core body is exposed; the separator (13) has a base material layer (50) and a filler layer (52) that is disposed on at least one surface of the base material layer (50); and the filler layer (52) includes inorganic particles and resin particles (54) which have a larger average particle diameter than the inorganic particles, and has protrusion portions (56) which are formed by the resin particles projecting from an inorganic particle layer (58) that is formed of the inorganic particles.

Description

Nonaqueous electrolyte secondary battery

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

[0002] 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. Generally, the positive electrode is formed by disposing a positive electrode mixture layer on a positive electrode core, and the negative electrode is formed by disposing a negative electrode mixture layer on a negative electrode core.

[0003] From the viewpoint of improving the output characteristics of a non-aqueous electrolyte secondary battery, a technique is known in which a core exposed portion where a positive electrode core or a negative electrode core is exposed is provided at an axial end of an electrode body, and the core exposed portion is joined to a current collector plate or an outer can (see, for example, Patent Document 1). Furthermore, Patent Documents 1 and 2 disclose techniques in which a cut or a through hole is provided in the core exposed portion from the viewpoint of increasing the permeability of a non-aqueous electrolyte into the inside of the electrode body and improving the cycle characteristics of the battery.

[0004] JP 2000-77054 A JP 2015-103420 A

[0005] As a result of investigations by the present inventors, it was found that in nonaqueous electrolyte secondary batteries in which the exposed core portion is bonded to a current collector plate or an outer can, lithium deposition may occur in the negative electrode during repeated charge and discharge. This is presumably because the exposed core portion blocks the flow path of the nonaqueous electrolyte, and the amount of nonaqueous electrolyte inside the electrode assembly decreases with repeated charge and discharge. From the viewpoint of ensuring the cycle characteristics of nonaqueous electrolyte secondary batteries, the deposition of lithium in the negative electrode is undesirable.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including an electrode assembly in which a first electrode and a second electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the first electrode has a first electrode core and a first electrode mixture layer disposed on the first electrode core, and one axial end of the first electrode is provided with a first electrode core exposed portion where the first electrode mixture layer is not disposed and the first electrode core is exposed, and the separator has a base layer and a filler layer disposed on at least one surface of the base layer, and the filler layer contains inorganic particles and resin particles having an average particle size larger than that of the inorganic particles, and has convex portions formed by the resin particles protruding from the inorganic particle layer formed by the inorganic particles.

[0007] According to a nonaqueous electrolyte secondary battery according to one aspect of the present disclosure, lithium deposition can be suppressed, and as a result, a nonaqueous electrolyte secondary battery with excellent cycle characteristics can be provided.

[0008] 1 is a cross-sectional view of a separator of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention; 2 is a perspective view of an electrode assembly of the non-aqueous electrolyte secondary battery according to an embodiment of the present invention, the electrode assembly being partially unfolded; 3 is a cross-sectional view of a separator of the non-aqueous electrolyte secondary battery according to an embodiment of the present invention;

[0009] 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.

[0010] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment of the present disclosure, and Fig. 2 is a perspective view illustrating the structure of an electrode assembly 14. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the nonaqueous electrolyte, and a sealing member 17 that closes the opening of the outer can 16. For ease of explanation, the sealing member 17 side will be referred to as the "top" and the bottom 16A side of the outer can 16 will be referred to as the "bottom."

[0011] 1 and 2 , the electrode assembly 14 has a structure in which a strip-shaped first electrode and a second electrode having different polarities are wound longitudinally with a separator 13 interposed therebetween. In the following, a case will be described in which the first electrode is a negative electrode 12 and the second electrode is a positive electrode 11. However, the first electrode may be a positive electrode 11 and the second electrode may be a negative electrode 12.

[0012] The positive electrode 11, the negative electrode 12, and the separator 13 are spirally wound and alternately stacked in the radial direction of the electrode body 14. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the axial direction. 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 longitudinal direction and width direction than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0013] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 32 formed on the positive electrode core 30. The positive electrode core 30 can be made of 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 the surface layer. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less.

[0014] The positive electrode mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder, and is formed on both sides of the positive electrode core 30 except for a positive electrode core exposed portion (not shown) to which a positive electrode lead 20 (described later) is welded. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm or more and 150 μm or less on one side of the positive electrode core 30. 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, etc. onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30.

[0015] The positive electrode mixture layer 32 contains particulate lithium metal composite oxide as a positive electrode active material. The lithium metal 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 metal 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, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, or lithium metal composite oxides containing Ni, Co, and Al.

[0016] Examples of the conductive agent contained in the positive electrode mixture layer 32 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 32 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.

[0017] The negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 42 formed 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 the surface layer. The negative electrode mixture layer 42 contains a negative electrode active material, a binder, and, if necessary, a conductive agent, and is formed on both sides of the negative electrode core 40 except for a negative electrode core exposed portion 44 described below. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40.

[0018] The negative electrode mixture layer 42 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, lump 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. Among these, a composite material containing Si is preferred.

[0019] A suitable example of a composite material containing Si is SiO ２ Examples of such composite materials include a material in which Si fine particles are dispersed in a silicate phase such as lithium silicate, or a material in which Si fine particles are dispersed in an amorphous carbon phase. A conductive layer such as a carbon coating is formed on the particle surfaces of the composite material. The combined use of a carbon material and a Si-containing composite material as the negative electrode active material is preferred from the viewpoint of achieving both high capacity and high durability of the battery.

[0020] As in the case of the positive electrode mixture layer 32, the binder contained in the negative electrode mixture layer 42 can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but preferably styrene-butadiene rubber (SBR) is used. The negative electrode mixture layer 42 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 a combination of SBR with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer 42 may contain a conductive agent such as CNT.

[0021] 1 and 2 , the negative electrode 12 has a negative electrode core exposed portion 44 at the end (lower end) on the bottom 16A side of both widthwise ends of the negative electrode 12, where the negative electrode mixture layer 42 is not provided and the negative electrode core 40 is exposed. Therefore, the lower end in the axial direction of the electrode body 14 is formed by the negative electrode core exposed portion 44. The negative electrode core exposed portion 44 is formed, for example, from the winding start end to the winding end end in the longitudinal direction of the strip-shaped negative electrode 12.

[0022] When the nonaqueous electrolyte secondary battery 10 is assembled, the negative electrode substrate exposed portion 44 is bent at the bending point 44A toward the radially inner side of the electrode body 14. For example, a portion of the bent negative electrode substrate exposed portion 44 may be arranged so as to overlap another adjacent negative electrode substrate exposed portion 44 on the radially inner side. The outer winding surface of the bent negative electrode substrate exposed portion 44 is then joined to the upper surface of the current collecting member 18 described below. The negative electrode substrate exposed portion 44 is preferably bent toward the radially inner side of the electrode body 14 at an angle of 30° or more and 90° or less with respect to the winding axis direction of the electrode body 14. Note that the negative electrode substrate exposed portion 44 may extend linearly to the current collecting member 18, with the tip of the negative electrode substrate exposed portion 44 joined to the current collecting member 18.

[0023] The axial length of the negative electrode substrate exposed portion 44 is preferably 5 mm or more, and more preferably 7 mm or more. By making the axial length of the negative electrode substrate exposed portion 44 5 mm or more, it becomes easier to join the negative electrode substrate exposed portion 44 to the current collecting member 18. Furthermore, the axial length of the negative electrode substrate exposed portion 44 is preferably 20 mm or less, and more preferably 18 mm or less. By making the axial length of the negative electrode substrate exposed portion 44 20 mm or less, the non-aqueous electrolyte can easily enter the inside of the electrode body 14, and the effects of the present disclosure can be more significantly exhibited. Therefore, the axial length of the negative electrode substrate exposed portion 44 is preferably 5 mm or more and 20 mm or less, and more preferably 7 mm or more and 18 mm or less. Note that the axial length of the negative electrode substrate exposed portion 44 refers to the length along the axial direction in a state before the negative electrode substrate exposed portion 44 is bent at the bending point 44A.

[0024] Furthermore, the negative electrode core exposed portion 44 is not provided with a notch or through-hole as disclosed in the above-mentioned Patent Document 1 or Patent Document 2. If a notch or through-hole is provided in the negative electrode core exposed portion 44, the non-aqueous electrolyte will more easily flow into the electrode assembly 14, but an internal short circuit will more easily occur during repeated charge and discharge. Specifically, during repeated charge and discharge, deformation (e.g., breakage or bending) or damage (e.g., cutting) of the negative electrode core exposed portion 44 may occur starting from the notch or through-hole provided in the negative electrode core exposed portion 44. The deformed or damaged negative electrode core exposed portion 44 may then break through the separator 13 or come into contact with the positive electrode 11, causing an internal short circuit.

[0025] The non-aqueous electrolyte has lithium ion conductivity. The non-aqueous electrolyte 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

[0026] The nonaqueous electrolyte secondary battery 10 includes a metal current collecting member 18 made of nickel, nickel alloy, or the like, on the axially lower side of the electrode assembly 14. A negative electrode substrate exposed portion 44 protruding from the electrode assembly 14 is joined to the upper surface of the current collecting member 18, and the current collecting member 18 is joined to the inner surface of the bottom 16A of the outer can 16. As a result, the outer can 16 electrically connected to the negative electrode substrate exposed portion 44 via the current collecting member 18 serves as the negative electrode terminal. Joining the negative electrode substrate exposed portion 44 to the current collecting member 18 increases the contact area, making it easier to achieve low resistance in the nonaqueous electrolyte secondary battery 10. Note that the nonaqueous electrolyte secondary battery 10 may not include the current collecting member 18, and the negative electrode substrate exposed portion 44 may be joined directly to the inner surface of the bottom 16A of the outer can 16.

[0027] An insulating plate 19 is disposed above the electrode body 14. The insulating plate 19 has a circular shape in a plan view. A through hole is provided in the radial center of the insulating plate 19. The thickness of the insulating plate 19 is, for example, 0.5 mm or more and 5 mm or less.

[0028] The nonaqueous electrolyte secondary battery 10 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like. The number of positive electrode leads 20 may be one or more. Increasing the number of positive electrode leads 20 can reduce the electrical resistance of the nonaqueous electrolyte secondary battery 10. The positive electrode lead 20 passes through a through-hole in the insulating plate 19 and extends toward the sealing body 17, and the upper end of the positive electrode lead 20 is connected to the lower surface of the filter 22 of the sealing body 17 by welding or the like. A cap 26 constituting the top plate of the sealing body 17 is electrically connected to the filter 22, and the cap 26 serves as a positive electrode terminal.

[0029] The outer can 16 is a cylindrical metal container having a bottom 16A and an open end in the axial direction. The opening of the outer can 16 is closed by a sealing body 17.

[0030] A gasket 27 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 21 formed on its side surface that protrudes radially inward and supports the sealing body 17. The grooved portion 21 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 21 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0031] The sealing body 17 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. However, the configuration of the sealing body 17 is not limited to this.

[0032] When the nonaqueous electrolyte secondary battery 10 generates abnormal heat and the internal pressure of the battery 10 rises, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures and gas is discharged through the vent hole 26a of the cap 26. This gas discharge prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby improving the safety of the battery 10.

[0033] Next, the separator 13 will be described in detail with reference to Fig. 3. Fig. 3 is a diagram schematically showing a cross section of the separator 13.

[0034] As shown in Fig. 3 , the separator 13 has a substrate layer 50 and a filler layer 52 disposed on at least one surface of the substrate layer 50. In this embodiment, the filler layer 52 is disposed on only one surface of the substrate layer 50, with the filler layer 52 facing the positive electrode 11 and the substrate layer 50 facing the negative electrode 12. Note that the configuration of the separator 13 is not limited to the example shown in Fig. 3 , and the filler layer 52 may face the negative electrode 12 and the substrate layer 50 may face the positive electrode 11. Furthermore, the filler layer 52 may be disposed on both surfaces of the substrate layer 50.

[0035] The substrate layer 50 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. The material of the substrate layer 50 is not particularly limited, but examples include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyesters, cellulose, polyimides, polyphenylene sulfide, polyether ether ketones, and fluororesins. The substrate layer 50 may have a single-layer structure or a multi-layer structure.

[0036] The thickness of the base layer 50 is preferably 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.

[0037] The porosity of the substrate layer 50 is preferably, for example, 30% or more and 70% or less in order to ensure ionic conductivity during charging and discharging of the battery. The porosity of the substrate layer 50 is measured by the following method. (1) Ten circular pieces with a diameter of 2 cm are punched out of the substrate layer 50, and the thickness h and mass w of the center of each of the punched pieces of the substrate layer 50 are measured. (2) The volume V and mass W of the 10 pieces are determined from the thickness h and mass w, and the porosity ε is calculated using the following formula: Porosity ε (%) = ((ρV - W) / (ρV)) × 100, where ρ is the density of the material constituting the substrate.

[0038] The filler layer 52 contains inorganic particles and resin particles 54 having an average particle size larger than that of the inorganic particles. The filler layer 52 also has protrusions 56 formed by the resin particles 54. The protrusions 56 protrude from an inorganic particle layer 58 of the filler layer 52 formed by the inorganic particles and a binder. In other words, the protrusions 56 are regions of the resin particles 54 that protrude from the inorganic particle layer 58.

[0039] As a result of investigations by the present inventors, it was found that in a nonaqueous electrolyte secondary battery 10 in which a negative electrode substrate exposed portion 44 is provided at the axial end of the electrode assembly 14 and the negative electrode substrate exposed portion 44 is joined to a current collecting member 18 or the like as described above, lithium deposition may occur in the negative electrode 12. In particular, lithium deposition tends to occur more easily at the lower end side of the negative electrode 12 where the negative electrode substrate exposed portion 44 is formed. This is presumably because the negative electrode substrate exposed portion 44 blocks the flow path of the nonaqueous electrolyte at the lower end side of the electrode assembly 14. For example, the electrode assembly 14 expands during charge, and the nonaqueous electrolyte is pushed out of the electrode assembly 14, making it difficult for the nonaqueous electrolyte to flow back into the electrode assembly 14 when the electrode assembly 14 contracts during discharge. As a result, the amount of nonaqueous electrolyte inside the electrode assembly 14 decreases with repeated charge and discharge.

[0040] 3, the surface of the separator 13 in this embodiment has an uneven shape. This creates an appropriate gap between the positive electrode 11 and the separator 13, allowing the non-aqueous electrolyte to flow through the gap. As a result, even after repeated charge and discharge, the amount of non-aqueous electrolyte inside the electrode assembly 14 is maintained, and lithium deposition on the negative electrode 12 can be suppressed.

[0041] The average protrusion height of the protrusions 56 is preferably 1.2 μm or more, and more preferably 1.5 μm or more. By making the average protrusion height of the protrusions 56 1.2 μm or more, a larger gap can be formed between the positive electrode 11 and the separator 13, and the amount of non-aqueous electrolyte that flows into the electrode body 14 can be increased. As a result, lithium deposition in the negative electrode 12 can be further suppressed.

[0042] Furthermore, the average protrusion height of the protrusions 56 is preferably 3.5 μm or less, and more preferably 3.0 μm or less. By setting the average protrusion height of the protrusions 56 to 3.5 μm or less, an increase in the inter-electrode distance between the positive electrode 11 and the negative electrode 12 can be suppressed, and lithium precipitation in the negative electrode 12 can be further suppressed. In other words, if the average protrusion height of the protrusions 56 exceeds 3.5 μm, smooth lithium movement between the positive electrode 11 and the negative electrode 12 may be hindered, which may cause lithium precipitation in the negative electrode 12. Furthermore, if the average protrusion height of the protrusions 56 exceeds 3.5 μm, the resin particles 54 may be more likely to fall off from the filler layer 52. Therefore, the average protrusion height of the protrusions 56 is preferably 1.2 μm or more and 3.5 μm or less, and more preferably 1.5 μm or more and 3.0 μm or less. The average protrusion height of the protrusions 56 is determined by image analysis of the cross-sectional shape of the separator 13. Specifically, the average protrusion height of the protrusions 56 is determined by arbitrarily selecting 100 protrusions 56 (resin particles 54), measuring the protrusion height, which is the length along the thickness direction of the separator 13 from the surface of the inorganic particle layer 58 to the top of the resin particle 54, and calculating the arithmetic mean of the measured values. The cross-sectional shape of the separator 13 can be measured using, for example, a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation).

[0043] When viewed from the surface of the filler layer 52, the ratio of the area of ​​the protrusions 56 (resin particles 54) to the surface area of ​​the filler layer 52 is preferably 12% or more, and more preferably 14% or more. By making the ratio of the area of ​​the protrusions 56 to the surface area of ​​the filler layer 52 12% or more, a larger gap can be formed between the positive electrode 11 and the separator 13, and the amount of non-aqueous electrolyte that flows into the electrode assembly 14 can be increased. As a result, lithium precipitation in the negative electrode 12 can be further suppressed.

[0044] Furthermore, when viewed from the surface of the filler layer 52, the ratio of the area of ​​the protrusions 56 (resin particles 54) to the surface area of ​​the filler layer 52 is preferably 20% or less, and more preferably 18% or less. When viewed from the surface of the filler layer 52, if the ratio of the area of ​​the protrusions 56 to the surface area of ​​the filler layer 52 exceeds 20%, the ionic conductivity of the separator 13 may decrease. This may result in impeded smooth movement of lithium between the positive electrode 11 and the negative electrode 12, and lithium precipitation may occur in the negative electrode 12. Therefore, when viewed from the surface of the filler layer 52, the ratio of the area of ​​the protrusions 56 (resin particles 54) to the surface area of ​​the filler layer 52 is preferably 12% or more and 20% or less, and more preferably 14% or more and 18% or less.

[0045] Furthermore, when the surface of the filler layer 52 is observed with a scanning electron microscope (SEM, for example, SU8220 manufactured by Hitachi High-Technologies Corporation), it is preferable that 40 to 300 convex portions 56 are detected in an area of ​​100 μm × 100 μm, and it is more preferable that 60 to 250 convex portions 56 are detected. In this case, the amount of nonaqueous electrolyte inside the electrode body 14 increases, and lithium deposition in the negative electrode 12 can be further suppressed.

[0046] The resin particles 54 are non-conductive particles, and are made of, for example, an acrylic resin made of an ethylenically unsaturated carboxylic acid alkyl ester such as methyl acrylate, butyl acrylate, ethyl acrylate, or 2-ethylhexyl acrylate, a resin made of a cyano group-containing ethylenically unsaturated monomer such as acrylonitrile, or a resin made of an ethylenically unsaturated carboxylic acid or a salt thereof such as acrylic acid, methacrylic acid, or maleic acid. These may be used alone or in combination of two or more types.

[0047] The volume-based average particle size (D50) of the resin particles 54 is larger than the volume-based average particle size (D50) of the inorganic particles. The volume-based average particle size (D50) of the resin particles 54 is, for example, 0.5 μm or more and 20.0 μm or less, and preferably 2.0 μm or more and 10.0 μm or less. The volume-based average particle size (D50) of the resin particles 54 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the resin particles 54 can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell) using water as a dispersion medium.

[0048] The resin particles 54 preferably have adhesive properties. The resin particles 54 have adhesive properties with the positive electrode 11, for example, and may be adhered to the positive electrode 11 in the nonaqueous electrolyte secondary battery 10. The resin particles 54 may also exhibit adhesive properties to the positive electrode 11 when holding a nonaqueous electrolyte. Here, having adhesive properties means that when the separator 13 and the positive electrode 11 are laminated and pressed together, the surface of the positive electrode 11 and the surface of the separator 13 can be in contact with each other and cannot be separated.

[0049] The inorganic particle layer 58 contains inorganic particles and a binder, and is a layer in which the inorganic particles are stacked in the thickness direction. The thickness of the inorganic particle layer 58 is preferably smaller than the thickness of the base layer 50, for example, 0.5 μm or more and 10.0 μm or less, and preferably 1.0 μm or more and 5.0 μm or less.

[0050] Examples of inorganic particles 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, 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.

[0051] The volume-based average particle size (D50) of the inorganic particles is smaller than the volume-based average particle size (D50) of the resin particles 54, and is, for example, 0.05 μm or more and 2 μm or less. Note that, like the volume-based average particle size (D50) of the resin particles 54, the volume-based average particle size (D50) of the inorganic particles refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the inorganic particles can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac-Bell) using water as the dispersion medium.

[0052] The content of inorganic particles in the filler layer 52 is, for example, 70% by mass or more and 99% by mass or less, preferably 80% by mass or more and 99% by mass or less, and more preferably 85% by mass or more and 99% by mass or less, relative to the total mass of the filler layer 52.

[0053] The binder contained in the filler layer 52 functions to bond the inorganic particles to each other and to bond the inorganic particles to the base material layer 50. The binder 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 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.

[0054] A method for forming the filler layer 52 containing inorganic particles and resin particles 54 on the surface of the base layer 50 includes preparing a dispersion liquid in which the inorganic particles and resin particles 54 are dispersed, applying the dispersion liquid to the surface of the base layer 50, and drying the dispersion liquid. Examples of methods for applying the dispersion liquid to the surface of the base layer 50 include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing, and among these, gravure coating is preferred.

[0055] 3, a portion of the resin particles 54 is present inside the inorganic particle layer 58, but the entire resin particles 54 may protrude from the inorganic particle layer 58 to form the protrusions 56. Alternatively, a portion of the resin particles 54 may not protrude from the inorganic particle layer 58 but may be embedded in the inorganic particle layer 58.

[0056] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0057] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, LiNi ０．８８ Co０．０９ Al ０．０３ O ２ An aluminum-containing lithium nickel cobalt oxide represented by the formula (I) was used. The above positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a solids mass ratio of 100:1:0.9, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a strip-shaped positive electrode core made of aluminum foil with a thickness of 15 μm, dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode core. Then, a positive electrode core exposed portion in which no positive electrode mixture layer was present and the positive electrode core surface was exposed was provided in the longitudinal middle portion of the positive electrode. In addition, an aluminum positive electrode lead was welded to the positive electrode core exposed portion.

[0058] [Preparation of Negative Electrode] Graphite, Si oxide (SiO), carboxymethyl cellulose sodium (CMC-Na), and styrene butadiene rubber (SBR) were mixed in a solids mass ratio of 88:12:1:1, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil with a thickness of 19 μm so that a negative electrode core exposed portion with a width of 11 mm was formed over the entire longitudinal direction. This coating was dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode core.

[0059] [Preparation of separator] Alumina (α-Al) was used as inorganic particles having an average particle size (D50) of 0.7 μm. ２ O ３ ) particles, acrylic resin particles as resin particles having a D50 of 3.0 μm, and an acrylic acid ester-based binder emulsion were mixed in a solid content mass ratio of 100:8:3, and then an appropriate amount of water was added to give a solid content concentration of 10 mass % to prepare a first dispersion.

[0060] A porous polyethylene substrate having a thickness of 11 μm was used as the substrate layer. The first dispersion was applied to one side of the porous substrate serving as the substrate layer. The coating was then dried in an oven at 50°C for 4 hours to produce a filler layer in which resin particles protruded from the surface of a 2.5 μm-thick inorganic particle layer formed from the binder.

[0061] The cross section of the filler layer was observed with a laser microscope (Keyence VK-X3000), and the average protrusion height of the convex portions was calculated to be 1.5 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (Hitachi High-Tech SU8220), the ratio of the area of ​​the convex portions to the area of ​​the surface of the filler layer (hereinafter referred to as the "area ratio of the convex portions") was 16%. Furthermore, when the surface of the filler layer was observed with the scanning electron microscope (Hitachi High-Tech SU8220), 160 resin particles were detected in an area of ​​100 μm × 100 μm.

[0062] [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.

[0063] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A wound electrode assembly was fabricated by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween. At this time, the filler layer of the separator faced the positive electrode. A current collecting member was placed under the fabricated electrode assembly, and the exposed portion of the negative electrode substrate at the lower end of the electrode assembly was bent radially inward and welded to the current collecting member. The electrode assembly was then housed in a bottomed cylindrical outer can, the current collecting member was welded to the bottom of the bottomed cylindrical outer can, and the positive electrode lead was welded to a sealing member. A groove was then formed in the opening of the outer can by pressing. After pouring a non-aqueous electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket, resulting in the fabrication of a cylindrical non-aqueous electrolyte secondary battery.

[0064] [Evaluation of Lithium Deposition] The fabricated nonaqueous electrolyte secondary battery was charged to 4.2 V at a constant current of 0.7 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 1-hour rest, the battery was discharged to 2.5 V at a constant current of 0.3 C. This constituted one cycle, and 100 cycles were performed. Thereafter, the nonaqueous electrolyte secondary battery was disassembled, and the area of ​​lithium deposited on the surface of the negative electrode was measured. The lithium deposition area ratio was calculated using the following formula: Li deposition area ratio [%] = (area of ​​lithium deposited on the surface of the negative electrode) / (surface area of ​​the negative electrode) × 100

[0065] Example 2 In the production of a separator, alumina (α-Al ２ O ３ A second dispersion was prepared by mixing inorganic particles, acrylic resin particles having a D50 of 5.0 μm, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:8:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the second dispersion was applied to one surface of a porous substrate serving as a base layer and dried to form a filler layer in which resin particles protruded from the surface of a 2.5 μm-thick inorganic particle layer.

[0066] The cross section of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), and the average protrusion height of the convex portions was calculated to be 2.0 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), the area ratio of the convex portions was found to be 16%. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 160 resin particles were detected in an area of ​​100 μm × 100 μm.

[0067] Example 3 In the production of a separator, alumina (α-Al) was used as inorganic particles having an average particle size (D50) of 0.7 μm. ２ O ３A third dispersion was prepared by mixing inorganic particles, acrylic resin particles having a D50 of 7.0 μm, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:8:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the third dispersion was applied to one side of a porous substrate serving as a substrate layer and dried to form a filler layer in which resin particles protruded from the surface of an inorganic particle layer having a thickness of 2.5 μm.

[0068] The cross section of the filler layer was observed with a laser microscope (Keyence VK-X3000), and the average protrusion height of the convex portions was calculated to be 2.6 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (Hitachi High-Tech SU8220), the area ratio of the convex portions was found to be 16%. Furthermore, when the surface of the filler layer was observed with the scanning electron microscope (Hitachi High-Tech SU8220), 160 resin particles were detected in an area of ​​100 μm × 100 μm.

[0069] Example 4 In the production of a separator, alumina (α-Al ２ O ３ A fourth dispersion was prepared by mixing inorganic particles, acrylic resin particles having a D50 of 10.0 μm, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:8:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the fourth dispersion was applied to one side of a porous substrate serving as a base layer and dried to form a filler layer in which resin particles protruded from the surface of an inorganic particle layer having a thickness of 2.5 μm.

[0070] The cross section of the filler layer was observed with a laser microscope (Keyence VK-X3000), and the average protrusion height of the convex portions was calculated to be 3.4 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (Hitachi High-Tech SU8220), the area ratio of the convex portions was found to be 16%. Furthermore, when the surface of the filler layer was observed with the scanning electron microscope (Hitachi High-Tech SU8220), 160 resin particles were detected in an area of ​​100 μm × 100 μm.

[0071] Example 5 In the production of a separator, alumina (α-Al) was used as inorganic particles having an average particle size (D50) of 0.7 μm. ２ O ３ A fifth dispersion was prepared by mixing inorganic particles, acrylic resin particles having a D50 of 3.0 μm, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:3.5:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the fifth dispersion was applied to one surface of a porous substrate serving as a base layer and dried to form a filler layer in which resin particles protruded from the surface of an inorganic particle layer having a thickness of 2.5 μm.

[0072] The cross section of the filler layer was observed with a laser microscope (Keyence VK-X3000), and the average protrusion height of the convex portions was calculated to be 1.5 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (Hitachi High-Tech SU8220), the area ratio of the convex portions was found to be 10%. Furthermore, when the surface of the filler layer was observed with the scanning electron microscope (Hitachi High-Tech SU8220), 40 resin particles were detected in an area of ​​100 μm × 100 μm.

[0073] Example 6 In the production of a separator, alumina (α-Al ２ O ３A sixth dispersion was prepared by mixing inorganic particles, acrylic resin particles having a D50 of 1.0 μm, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:8:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the sixth dispersion was applied to one surface of a porous substrate serving as a base layer and dried to form a filler layer in which resin particles protruded from the surface of an inorganic particle layer having a thickness of 2.5 μm.

[0074] The cross section of the filler layer was observed with a laser microscope (Keyence VK-X3000), and the average protrusion height of the convex portions was calculated to be 1.0 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (Hitachi High-Tech SU8220), the area ratio of the convex portions was found to be 16%. Furthermore, when the surface of the filler layer was observed with the scanning electron microscope (Hitachi High-Tech SU8220), 160 resin particles were detected in an area of ​​100 μm × 100 μm.

[0075] Example 7 In the production of a separator, alumina (α-Al ２ O ３ A seventh dispersion was prepared by mixing inorganic particles, acrylic resin particles having a D50 of 12.0 μm as resin particles, and an acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:8:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the seventh dispersion was applied to one surface of a porous substrate serving as a base layer and dried to form a filler layer in which resin particles protruded from the surface of a 2.5 μm-thick inorganic particle layer.

[0076] The cross section of the filler layer was observed with a laser microscope (Keyence VK-X3000), and the average protrusion height of the convex portions was calculated to be 3.9 μm. Furthermore, when the surface of the filler layer was observed with a scanning electron microscope (Hitachi High-Tech SU8220), the area ratio of the convex portions was found to be 16%. Furthermore, when the surface of the filler layer was observed with the scanning electron microscope (Hitachi High-Tech SU8220), 160 resin particles were detected in an area of ​​100 μm × 100 μm.

[0077] Comparative Example 1 In the production of a separator, alumina (α-Al ２ O ３ The eighth dispersion was prepared by mixing inorganic particles and an acrylic ester-based binder emulsion at a solids mass ratio of 100:3, and then adding an appropriate amount of water to adjust the solids concentration to 10 mass%. The eighth dispersion was then applied to one side of a porous substrate serving as a substrate layer, followed by drying to prepare a filler layer having an inorganic particle layer with a thickness of 2.5 μm. A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1. In other words, the filler layer of Comparative Example 1 did not contain resin particles.

[0078] The evaluation results of lithium deposition in the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples are shown in Table 1. Table 1 also shows the average protrusion height, area ratio, and number of detected protrusions in a 100 μm × 100 μm area of ​​each separator.

[0079]

[0080] As shown in Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 7 had a significantly reduced lithium deposition area compared to the nonaqueous electrolyte secondary battery of Comparative Example 1. This is presumably because the provision of protrusions formed of resin particles on the surface of the separator created an appropriate gap between the positive electrode and the separator, making it easier for the nonaqueous electrolyte to flow into the electrode assembly through this gap.

[0081] Furthermore, the nonaqueous electrolyte secondary batteries of Examples 1 to 5, in which the average protruding height of the convex portions is 1.2 μm or more and 3.5 μm or less, have a significantly reduced lithium deposition area compared to the nonaqueous electrolyte secondary batteries of Examples 6 and 7, in which the average protruding height of the convex portions is less than 1.2 μm or more than 3.5 μm. Therefore, it can be said that lithium deposition in the negative electrode can be further suppressed by controlling the average protruding height of the convex portions to a limited range of 1.2 μm or more and 3.5 μm or less.

[0082] The present disclosure is further described by the following embodiments. Aspect 1: A non-aqueous electrolyte secondary battery including an electrode assembly in which a first electrode and a second electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the first electrode has a first electrode core and a first electrode mixture layer disposed on the first electrode core, and one axial end of the first electrode is free of the first electrode mixture layer and has a first electrode core exposed portion where the first electrode core is exposed, and the separator has a base layer and a filler layer disposed on at least one surface of the base layer, and the filler layer contains inorganic particles and resin particles having an average particle size larger than that of the inorganic particles, and has convex portions formed by the resin particles protruding from the inorganic particle layer formed by the inorganic particles. Aspect 2: The non-aqueous electrolyte secondary battery according to Aspect 1, wherein the convex portions have an average protrusion height of 1.2 μm or more and 3.5 μm or less. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the average protrusion height of the convex portions is 1.5 μm or more and 3.0 μm or less.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein, in a surface view of the filler layer, the ratio of the area of ​​the convex portions to the area of ​​the surface of the filler layer is 12% or more and 20% or less.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein, when the surface of the filler layer is observed with a scanning electron microscope, 40 to 300 convex portions are detected in an area of ​​100 μm × 100 μm.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the resin particles have adhesive properties.Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the resin particles are non-conductive particles. Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the first electrode core exposed portion has a bending point and is bent from the bending point toward the radially inward direction of the electrode body.Configuration 9: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the first electrode core exposed portion is not provided with a notch or a through-hole.Configuration 10: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 9, wherein the axial length of the first electrode core exposed portion is 5 mm or more and 20 mm or less.Configuration 11: The nonaqueous electrolyte secondary battery according to any one of configurations 1 to 10, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

[0083] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode (second electrode), 12 negative electrode (first electrode), 13 separator, 14 electrode body, 16 outer can, 16A bottom, 17 sealing body, 18 current collecting member, 19 insulating plate, 20 positive electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a ventilation hole, 27 gasket, 30 positive electrode core, 32 positive electrode mixture layer, 40 negative electrode core (first electrode core), 42 negative electrode mixture layer (first electrode mixture layer), 44 negative electrode core exposed portion (first electrode core exposed portion), 44A bending point, 50 substrate layer, 52 filler layer, 54 resin particles, 56 convex portion, 58 inorganic particle layer

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a first electrode and a second electrode are wound with a separator interposed therebetween; and a non-aqueous electrolyte, wherein the first electrode has a first electrode core and a first electrode mixture layer disposed on the first electrode core, and one axial end of the first electrode assembly is provided with a first electrode core exposed portion where the first electrode mixture layer is not disposed and the first electrode core is exposed, and the separator has a base layer and a filler layer disposed on at least one surface of the base layer, and the filler layer contains inorganic particles and resin particles having an average particle size larger than that of the inorganic particles, and has convex portions formed by the resin particles protruding from the inorganic particle layer formed by the inorganic particles.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the average protrusion height of said convex portions is 1.2 μm or more and 3.5 μm or less.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the average protrusion height of the convex portions is 1.5 μm or more and 3.0 μm or less.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the proportion of the area of ​​the protrusions to the area of ​​the surface of the filler layer when viewed from the surface of the filler layer is 12% or more and 20% or less.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein when the surface of said filler layer is observed with a scanning electron microscope, 40 to 300 of said convex portions are detected in an area of ​​100 μm×100 μm.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the resin particles have adhesive properties.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin particles are non-conductive particles.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode substrate exposed portion has a bending point and is bent from the bending point toward the inside in the radial direction of the electrode body.

9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode substrate exposed portion has no notch or through-hole.

10. The nonaqueous electrolyte secondary battery according to claim 1, wherein the axial length of the first electrode substrate exposed portion is 5 mm or more and 20 mm or less.

11. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

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