Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery is characterized in that: a first electrode (12) comprises a first electrode core body (40) and a first electrode mixture layer (42) disposed on the first electrode core body (40); the first electrode mixture layer (42) is not disposed on one end in the axial direction of an electrode body in the first electrode (12); there is provided a first electrode core body exposure part (44) where the first electrode core body (40) is exposed; and the surface of the first electrode core body exposure part (44) is provided with a functional layer (50) including a coating layer (52) that covers at least a portion of the first electrode core body exposure part (44), and large-diameter particles (54) that have a volume-basis average particle size which is greater than the average thickness of the coating layer (52).

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 non-aqueous electrolyte secondary batteries, a technique is known in which exposed core portions where the positive electrode core and the negative electrode core are exposed are provided at both axial ends of an electrode body, and the exposed core portions are 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 notches or through holes are provided in the exposed core portions in order to increase the permeability of the non-aqueous electrolyte into the electrode body and improve the cycle characteristics of the battery.

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

[0005] In recent years, with the spread of electric vehicles and other factors, there has been an increasing demand for improved cycle characteristics of non-aqueous electrolyte secondary batteries. Furthermore, from the viewpoint of improving the reliability of non-aqueous electrolyte secondary batteries, it is also required to suppress the occurrence of internal short circuits during repeated charge and discharge. The techniques disclosed in Patent Documents 1 and 2 are unable to achieve both of these goals, and there is still room for improvement.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery comprising an electrode body 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 body 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 surface of the first electrode core exposed portion is provided with a functional layer including a coating layer that covers at least a portion of the first electrode core exposed portion and large-diameter particles whose volume-based average particle size is larger than the average thickness of the coating layer.

[0007] According to a nonaqueous electrolyte secondary battery according to one aspect of the present disclosure, it is possible to suppress the occurrence of internal short circuits during repeated charge and discharge, while achieving improved cycle characteristics.

[0008] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment; Fig. 2 is a perspective view of an electrode body constituting the nonaqueous electrolyte secondary battery according to an embodiment, showing a part of the winding end side in a developed state; Fig. 3 is a plan view showing a negative electrode constituting the nonaqueous electrolyte secondary battery according to an embodiment, in a developed state; Fig. 4 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment, showing an enlarged view of the lower end side of the electrode body;

[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 15 with a bottom that houses the electrode assembly 14 and the nonaqueous electrolyte, and a sealing member 16 that closes the opening of the outer can 15. Hereinafter, for ease of explanation, the sealing member 16 side will be referred to as "top" and the bottom side of the outer can 15 as "bottom." For ease of explanation, a functional layer 50 (see FIG. 3 ), which will be described later, is omitted from FIGS. 1 and 2 .

[0011] As shown in FIGS. 1 and 2 , the electrode assembly 14 has a wound structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound with two strip-shaped separators 13 interposed therebetween. The positive electrode 11 protrudes upward relative to the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes downward relative to the positive electrode 11 and the separator 13. The positive electrode 11 has a positive electrode core exposed portion 34 in which the positive electrode core 30 is exposed and no positive electrode mixture layer 32 is provided, at the upper end in the width direction, from the longitudinal winding start end to the winding end end of the strip-shaped positive electrode 11. The negative electrode 12 has a negative electrode core exposed portion 44 in which the negative electrode core 40 is exposed and no negative electrode mixture layer 42 is provided, at the lower end in the width direction, from the longitudinal winding start end to the winding end end of the strip-shaped negative electrode 12. For this reason, the upper axial end of the electrode body 14 is constituted by a positive electrode core exposed portion 34, and the lower axial end of the electrode body 14 is constituted by a negative electrode core exposed portion 44. The width of the positive electrode core exposed portion 34 (the length along the axial direction of the electrode body 14) is, for example, 2 mm or more and 20 mm or less, and the width of the negative electrode core exposed portion 44 is, for example, 2 mm or more and 20 mm or less. In this embodiment, a case will be described in which the first electrode is the negative electrode 12 and the second electrode is the positive electrode 11; however, the first electrode may be the positive electrode 11 and the second electrode may be the negative electrode 12.

[0012] 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

[0013] The positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 can be made of a metal foil, 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. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., to 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. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30. 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 substrate 30 .

[0014] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0015] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0016] The negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. The negative electrode core 40 can be made of a metal foil, 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. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 30 μm or less. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be fabricated, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to 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. The negative electrode mixture layer 42 may be formed on only one side of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode substrate 40 .

[0017] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0018] As in the case of the positive electrode 11, the binder contained in the negative electrode mixture layer 42 may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like, but is preferably styrene-butadiene rubber (SBR) or a modified product thereof. The negative electrode mixture layer 42 may contain, in addition to SBR or the like, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0019] 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. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0020] 1 , the nonaqueous electrolyte secondary battery 10 has a metallic negative electrode current collector 17 made of nickel, a nickel alloy, or the like, on the axially lower side of the electrode body 14. A negative electrode substrate exposed portion 44 protruding from the electrode body 14 is joined to the upper surface of the negative electrode current collector 17, and the negative electrode current collector 17 is joined to the inner surface of the bottom plate of an outer can 15. In other words, the outer can 15, which is electrically connected to the negative electrode substrate exposed portion 44 via the negative electrode current collector 17, serves as the negative electrode terminal. By joining the negative electrode substrate exposed portion 44 to the negative electrode current collector 17, the contact area can be increased, making it easier to achieve low resistance in the nonaqueous electrolyte secondary battery 10.

[0021] The nonaqueous electrolyte secondary battery 10 has a metallic positive electrode current collector 18 made of aluminum, aluminum alloy, or the like, above the electrode body 14 in the axial direction. A positive electrode substrate exposed portion 34 protruding from the electrode body 14 is joined to the underside of the positive electrode current collector 18. Joining the positive electrode substrate exposed portion 34 to the positive electrode current collector 18 makes it easier to achieve low resistance in the nonaqueous electrolyte secondary battery 10. The nonaqueous electrolyte secondary battery 10 has a circular insulating plate 19 above the positive electrode current collector 18 in the axial direction.

[0022] The nonaqueous electrolyte secondary battery 10 further includes a positive electrode lead 20 made of a metal such as aluminum or an aluminum alloy. The lower end of the positive electrode lead 20 is joined to the upper surface of the positive electrode current collector plate 18 by welding or the like. The positive electrode lead 20 passes through a through-hole in the insulating plate 19 and extends toward the sealing body 16, and the upper end of the positive electrode lead 20 is connected to the lower surface of a filter 22 of the sealing body 16 by welding or the like. A cap 26 constituting the top plate of the sealing body 16 is electrically connected to the filter 22, and the cap 26 serves as a positive electrode terminal.

[0023] The outer can 15 is a cylindrical metal container with a bottom and an open axial end, and the opening of the outer can 15 is closed by a sealing body 16 .

[0024] A gasket 27 is provided between the exterior can 15 and the sealing body 16 to ensure airtightness inside the battery. The exterior can 15 has a grooved portion 21 formed on its side surface that protrudes inward and supports the sealing body 16. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior can 15, and supports the sealing body 16 on its top surface. The sealing body 16 is fixed to the top of the exterior can 15 by the grooved portion 21 and the open end of the exterior can 15 that is crimped to the sealing body 16.

[0025] The sealing body 16 has a structure in which, in order from the electrode body 14 side, a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each member constituting the sealing body 16 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.

[0026] When the nonaqueous electrolyte secondary battery 10 generates abnormal heat and the internal pressure of the nonaqueous electrolyte secondary 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 from the through-hole 26a of the cap 26. This gas discharge prevents the internal pressure of the nonaqueous electrolyte secondary battery 10 from rising excessively, which could cause the nonaqueous electrolyte secondary battery 10 to explode, thereby improving the safety of the nonaqueous electrolyte secondary battery 10.

[0027] Next, the configuration of the negative electrode 12 and the vicinity of the negative electrode substrate exposed portion 44 will be described with further reference to Figures 3 and 4. Figure 3 is a plan view showing the negative electrode 12 in an unfolded state, illustrating the inner surface of the wound negative electrode 12. Figure 4 is an axial cross-sectional view of the nonaqueous electrolyte secondary battery 10, illustrating an enlarged view of the vicinity of the lower end of the electrode body 14.

[0028] As shown in FIGS. 3 and 4 , a negative electrode core exposed portion 44 is provided on the lower end portion 12Y side of the negative electrode 12, where the negative electrode mixture layer 42 is not disposed and the negative electrode core 40 is exposed. The negative electrode core exposed portion 44 is provided from the winding start end 12A to the winding end end 12B of the negative electrode 12. When the nonaqueous electrolyte secondary battery 10 is assembled, the negative electrode core exposed portion 44 is folded toward the radially inner side of the electrode body 14 at the bending point R. In this embodiment, a portion of the folded negative electrode core exposed portion 44 is arranged to overlap another adjacent negative electrode core exposed portion 44 on the radially inner side, with a functional layer 50 (described later) interposed therebetween. The outer winding surface of the folded negative electrode core exposed portion 44 is then joined to the upper surface of the negative electrode current collector plate 17. The negative electrode substrate exposed portion 44 is preferably bent radially inward 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 negative electrode current collector plate 17, and the tip of the negative electrode substrate exposed portion 44 may be joined to the negative electrode current collector plate 17.

[0029] As a result of investigations by the present inventors, it was found that the cycle characteristics are likely to deteriorate in a nonaqueous electrolyte secondary battery 10 in which a negative electrode substrate exposed portion 44 is provided at one axial end of the electrode assembly 14 as described above and the negative electrode substrate exposed portion 44 is joined to the negative electrode current collector plate 17. 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, making it difficult for the nonaqueous electrolyte that is pushed out of the electrode assembly 14 as the electrode assembly 14 expands during charging to flow back into the electrode assembly 14 when the electrode assembly 14 contracts during discharging. Therefore, the amount of nonaqueous electrolyte inside the electrode assembly 14 decreases as charging and discharging are repeated, resulting in a deterioration in the cycle characteristics.

[0030] Furthermore, as shown in the results of the examples described below, when a slit or through-hole is provided in the negative electrode substrate exposed portion 44 as disclosed in Patent Document 1 or Patent Document 2, and a flow path for the non-aqueous electrolyte is secured, the cycle characteristics are improved, but an internal short circuit is likely to occur during repeated charge and discharge. This is because, during repeated charge and discharge, deformation (e.g., breakage or bending) or damage (e.g., cuts) of the negative electrode substrate exposed portion 44 occurs starting from the slit or through-hole provided in the negative electrode substrate exposed portion 44. It is presumed that the deformed or damaged negative electrode substrate exposed portion 44 then breaks through the separator 13, causing an internal short circuit.

[0031] 4 , a functional layer 50 is provided on the surface of the negative electrode substrate exposed portion 44 of this embodiment, and the functional layer 50 includes a coating layer 52 that covers at least a portion of the negative electrode substrate exposed portion 44 and large-diameter particles 54 whose volume-based average particle size is larger than the average thickness of the coating layer 52. As a result, an uneven shape caused by the large-diameter particles 54 is formed on the surface of the negative electrode substrate exposed portion 44, and non-aqueous electrolyte easily flows into the electrode body 14 through gaps between the large-diameter particles 54. As a result, even when charge and discharge are repeated, the amount of non-aqueous electrolyte inside the electrode body 14 is secured, and cycle characteristics can be improved.

[0032] Furthermore, by disposing the functional layer 50 on the negative electrode core exposed portion 44, the strength of the negative electrode core exposed portion 44 can be increased. As a result, even if uneven stress is applied to the negative electrode core exposed portion 44 due to movement of the electrode body 14 associated with charge and discharge, deformation (e.g., breakage or bending) or damage (e.g., cutting) of the negative electrode core exposed portion 44 is suppressed. If the negative electrode core exposed portion 44 is deformed or damaged, as described above, the deformed or damaged negative electrode core exposed portion 44 may break through the separator, causing an internal short circuit. In other words, in this embodiment, the functional layer 50 suppresses deformation and damage to the negative electrode core exposed portion 44, thereby suppressing the occurrence of an internal short circuit associated with charge and discharge.

[0033] The effects of the present disclosure can be achieved as long as the functional layer 50 is provided on at least one surface of the negative electrode substrate exposed portion 44, but it is preferable that the functional layer 50 be provided on the inner winding surface of the negative electrode substrate exposed portion 44. As described above, the outer winding surface of the negative electrode substrate exposed portion 44 is joined to the negative electrode current collector plate 17. Therefore, by providing the functional layer 50 only on the inner winding surface of the negative electrode substrate exposed portion 44, it becomes easier to join the negative electrode substrate exposed portion 44 and the negative electrode current collector plate 17. Furthermore, by providing the functional layer 50 only on the inner winding surface of the negative electrode substrate exposed portion 44, electrical continuity between the negative electrode substrate exposed portion 44 and the negative electrode current collector plate 17 is more easily ensured, and the resistance of the nonaqueous electrolyte secondary battery 10 can be reduced.

[0034] The functional layer 50 is preferably provided in a region of the negative electrode core exposed portion 44 from the bending point R to the lower end 44Y of the negative electrode core exposed portion 44. In this case, the non-aqueous electrolyte more easily flows into the inside of the electrode assembly 14. Furthermore, the functional layer 50 more preferably abuts against the lower end 44Y of the negative electrode core exposed portion 44. In this case, the non-aqueous electrolyte more easily flows into the inside of the electrode assembly 14, and the cycle characteristics can be further improved. Note that the functional layer 50 may be provided in a region from the bending point R to the upper end 44X of the negative electrode core exposed portion 44, in addition to or instead of the region from the bending point R to the lower end 44Y.

[0035] 4 , the functional layer 50 includes a coating layer 52 and large-diameter particles 54. The volume-based average particle size of the large-diameter particles 54 is larger than the average thickness of the coating layer 52. That is, some of the large-diameter particles 54 protrude from the surface of the coating layer 52, forming convex portions on the surface of the functional layer 50. By providing the functional layer 50 on the surface of the negative electrode substrate exposed portion 44, as described above, the nonaqueous electrolyte can more easily flow into the electrode body 14 through the gaps between the large-diameter particles 54.

[0036] The coating layer 52 contains, for example, inorganic particles having a diameter smaller than that of the large-diameter particles 54 and a binder, and has a structure in which the inorganic particles are stacked in layers. The average thickness of the coating layer 52 may be smaller than the volume-based average particle size of the large-diameter particles 54, and is, for example, 0.5 μm or more and 5 μm or less. The average thickness of the coating layer 52 is determined by image analysis using a scanning electron microscope (SEM). Specifically, the average thickness of the coating layer 52 is determined by observing the cross-sectional profile of the coating layer 52 with the SEM, measuring the thickness at any 10 points, and calculating the arithmetic average of the measured values.

[0037] Examples of inorganic particles contained in the coating layer 52 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, examples of 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.

[0038] The volume-based average particle size of the inorganic particles contained in the coating layer 52 is, for example, 0.05 μm or more and 2 μm or less. The volume-based average particle size of the inorganic particles (as well as the large-diameter particles 54) refers to the particle size at which the cumulative frequency of the smallest particle size in the volume-based particle size distribution is 50%, 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 analyzer (e.g., MT3000II manufactured by Microtrac-Bell) using water as a dispersion medium.

[0039] The binder contained in the coating layer 52 functions to bond the individual inorganic particles contained in the coating layer 52 to each other and to bond the inorganic particles to the negative electrode substrate exposed portion 44. The binder contained in the coating layer 52 also functions to bond the large-diameter particles 54 to the coating layer 52. The binder is preferably a polymer material, and examples of the binder 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 types.

[0040] As described above, the large-diameter particles 54 have a volume-based average particle size greater than the average thickness of the coating layer 52 and protrude from the surface of the coating layer 52. The volume-based average particle size of the large-diameter particles 54 is preferably 1.0 μm or greater, and more preferably 2.0 μm or greater. In this case, nonaqueous electrolyte is more likely to flow into the electrode body 14 through gaps between the large-diameter particles 54. The upper limit of the volume-based average particle size of the large-diameter particles 54 is, for example, 20 μm, from the viewpoint of preventing the large-diameter particles 54 from falling off the coating layer 52 and from the viewpoint of easily bending the negative electrode substrate exposed portion 44 during manufacturing. Therefore, the volume-based average particle size of the large-diameter particles 54 is preferably 1.0 μm or greater and 20 μm or less, and more preferably 2.0 μm or greater and 20 μm or less.

[0041] The average height of the protruding portions of the large-diameter particles 54 protruding from the coating layer 52 is preferably 0.5 μm or more, and more preferably 0.7 μm or more. In this case, nonaqueous electrolyte is more likely to flow into the electrode body 14 through gaps between the large-diameter particles 54. The upper limit of the average height of the protruding portions of the large-diameter particles 54 protruding from the coating layer 52 is, for example, 20 μm, from the viewpoint of preventing the large-diameter particles 54 from falling off the coating layer 52 and from the viewpoint of easily bending the negative electrode substrate exposed portion 44 during manufacturing. Therefore, the average height of the protruding portions of the large-diameter particles 54 protruding from the coating layer 52 is preferably 0.5 μm or more and 20 μm or less, and more preferably 0.7 μm or more and 20 μm or less. The average height of the protruding portions is determined by image analysis using a SEM. Specifically, the average height of the protruding portions is determined by observing the cross-sectional profile of the functional layer 50 with a SEM, randomly selecting 50 large-diameter particles 54, measuring the heights of the protruding portions, and arithmetically averaging the measured values.

[0042] The large-diameter particles 54 are, for example, particulate polymers containing inorganic particles. In this case, deformation of the large-diameter particles 54 is suppressed even when charging and discharging are repeated, thereby further improving cycle characteristics. The inorganic particles contained in the coating layer 52 described above can be used as the inorganic particles constituting the large-diameter particles 54. Note that the large-diameter particles 54 may contain resin particles made of an acrylic resin or the like in addition to or instead of the inorganic particles.

[0043] The arithmetic mean height of the functional layer 50 is preferably 0.10 μm or more, and more preferably 0.15 μm or more. In this case, the nonaqueous electrolyte is more likely to flow into the electrode body 14 through the gaps between the large-diameter particles 54. The upper limit of the arithmetic mean height of the functional layer 50 is not particularly limited, but is, for example, 0.50 μm. The arithmetic mean height of the functional layer 50 is measured according to the method specified in ISO 25178 (Surface Texture (Surface Roughness Measurement)).

[0044] When viewed from the surface of the functional layer 50, the ratio of the area of ​​the large diameter particles 54 to the area of ​​the surface of the functional layer 50 is, for example, 5% or more and 50% or less, and may be 10% or more and 45% or less. In this case, an appropriate uneven shape is formed on the surface of the negative electrode substrate exposed portion 44 while ensuring electrical continuity between the negative electrode substrate exposed portion 44 and the negative electrode current collector plate 17, making it easier for the non-aqueous electrolyte to flow into the inside of the electrode body 14.

[0045] As described above, by providing the functional layer 50 on the surface of the negative electrode substrate exposed portion 44, it is possible to form an uneven shape on the surface of the negative electrode substrate exposed portion 44. This makes it easier for the non-aqueous electrolyte to flow into the electrode body 14, ensuring the amount of non-aqueous electrolyte inside the electrode body 14 and improving the cycle characteristics.

[0046] The above embodiment can be modified as appropriate within the scope of the objectives of the present disclosure. For example, in the above embodiment, the functional layer 50 is disposed on the surface of the negative electrode substrate exposed portion 44 provided on the lower end side of the electrode assembly 14. However, the functional layer 50 may be disposed on the surface of the positive electrode substrate exposed portion 34 in addition to or instead of the surface of the negative electrode substrate exposed portion 44. During charge and discharge, the nonaqueous electrolyte also flows into the electrode assembly 14 from the upper end side. Therefore, by providing the functional layer 50 on the positive electrode substrate exposed portion 34 provided on the upper end side of the electrode assembly 14, the nonaqueous electrolyte can more easily flow into the electrode assembly 14. As a result, even when charge and discharge are repeated, the amount of nonaqueous electrolyte inside the electrode assembly 14 is maintained, and cycle characteristics can be improved.

[0047] Furthermore, in the above embodiment, the nonaqueous electrolyte secondary battery 10 includes the negative electrode current collector 17, but the nonaqueous electrolyte secondary battery 10 does not necessarily need to include the negative electrode current collector 17. In that case, the negative electrode core exposed portion 44 is directly joined to the bottom of the outer can 15.

[0048] Furthermore, in the above embodiment, the nonaqueous electrolyte secondary battery 10 includes the positive electrode current collector 18 and the positive electrode lead 20, but the nonaqueous electrolyte secondary battery 10 does not necessarily have to include the positive electrode current collector 18 and the positive electrode lead 20. In this case, the positive electrode substrate exposed portion 34 is directly joined to the lower surface of the sealing body 16.

[0049] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0050] Example 1 Preparation of Positive Electrode 100 parts by mass of a positive electrode active material, 1 part by mass of acetylene black (AB), and 0.9 parts by mass of polyvinylidene fluoride (PVDF) were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. ０．８８ Co ０．０９ Al ０．０３ O ２ An aluminum-containing lithium nickel cobalt oxide represented by the formula (1) was used. Next, the positive electrode mixture slurry was applied to both sides of the aluminum foil so as to form the above-mentioned exposed portion of the positive electrode substrate. This coating was 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 substrate.

[0051] [Preparation of Negative Electrode] 95 parts by mass of graphite, 5 parts by mass of silicon oxide (SiO), 1 part by mass of sodium carboxymethyl cellulose (CMC-Na), and 1 part by mass of styrene butadiene rubber (SBR) were mixed, 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 the copper foil so that a negative electrode core exposed portion having a width of 5 mm was formed. 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.

[0052] Alumina (α-Al) with a volume-based average particle size of 0.5 μm ２ O ３ ) particles and alumina (α-Al) particles as large particles with a volume-based average particle size of 1.1 μm. ２ O ３) particles and an acrylic acid ester-based binder emulsion were mixed in a solid content mass ratio of 100:10:3, and then an appropriate amount of water was added to make the solid content concentration 10 mass % to prepare a dispersion. The dispersion was then applied to the inner surface of the wound negative electrode substrate exposed portion to form a functional layer. Furthermore, as shown in Figure 3, the dispersion was applied only to the region below the bending point when the negative electrode substrate exposed portion was bent. After fabricating the negative electrode, the cross-sectional profile of the functional layer was observed by SEM, and it was found that the functional layer was composed of alumina (α-Al) particles with a volume-based average particle size of 0.5 μm. ２ O ３ A structure in which large particles protruded from the surface of the coating layer formed by the ) particles was confirmed. Furthermore, the average thickness of the coating layer and the arithmetic mean height of the functional layer were measured using the above-mentioned measurement method, and were found to be 1.0 μm and 0.11 μm, respectively.

[0053] [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.

[0054] [Preparation of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] A wound electrode assembly was prepared by spirally winding a positive electrode and a negative electrode with a polyethylene microporous membrane separator interposed therebetween. A positive electrode current collector and a negative electrode current collector were placed on the top and bottom of the electrode assembly, respectively. The exposed positive electrode core at the top end of the electrode assembly and the exposed negative electrode core at the bottom end were bent inward and welded to the positive electrode current collector and the negative electrode current collector, respectively. The electrode assembly was then placed in a bottomed cylindrical outer can, and the negative electrode current collector was welded to the bottom of the bottomed cylindrical outer can. The positive electrode current collector and the seal were connected with a positive electrode lead. After pouring a non-aqueous electrolyte into the outer can, the opening of the outer can was sealed with a seal via a gasket to prepare a cylindrical test cell.

[0055] [Evaluation of Capacity Retention Rate] In an environment of 25°C, the battery was charged at a constant current of 0.7 C until the battery voltage reached 4.2 V, and then discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V without a break. This charge / discharge cycle was counted as one cycle, and 500 cycles were performed. The capacity retention rate was calculated using the following formula: Capacity retention rate [%] = (discharge capacity at 500th cycle / initial discharge capacity) × 100

[0056] [Evaluation of Internal Short Circuits] In an environment of 25°C, 200 test cells were charged at a constant current of 0.5C to a battery voltage of 4.2V, and then at a constant voltage of 4.2V, the cells were charged at a constant current of 0.5C to a battery voltage of 4.2V until the current value reached 0.01C. Subsequently, the cells were discharged at a constant current of 0.5C to 2.5V, and this cycle of charging and discharging was repeated for 5 cycles. After the sixth cycle of constant current / constant voltage charging, each test cell in the charged state was placed in a thermostatic chamber at 60°C and left to stand for 12 hours, at which time it was subjected to high-temperature storage. The amount of change in voltage was determined from the battery voltage of the test cell in the charged state before and after high-temperature storage, and test cells in which the change in voltage was 0.1V or more were determined to have experienced an internal short circuit.

[0057] Example 2 In the production of a negative electrode, alumina (α-Al) having a volume-based average particle size of 2.1 μm was used as the large-diameter particles. ２ O ３ A test cell was prepared and evaluated in the same manner as in Example 1, except that the dispersion was applied using ) particles so that the average thickness of the coating layer was 2.0 μm. After preparing the negative electrode, the cross-sectional profile of the functional layer was observed using an SEM, and a structure in which large-diameter particles protruded from the surface of the coating layer was confirmed. Furthermore, the arithmetic mean height of the functional layer was measured using the above-mentioned measurement method and was found to be 0.13 μm.

[0058] Example 3 In the production of a negative electrode, alumina (α-Al) having a volume-based average particle size of 2.5 μm was used as the large-diameter particles. ２ O ３A test cell was prepared and evaluated in the same manner as in Example 1, except that the dispersion was applied using ) particles so that the average thickness of the coating layer was 2.0 μm. After preparing the negative electrode, the cross-sectional profile of the functional layer was observed using an SEM, and a structure in which large-diameter particles protruded from the surface of the coating layer was confirmed. Furthermore, the arithmetic mean height of the functional layer was measured using the above-mentioned measurement method and was found to be 0.18 μm.

[0059] Example 4 In the production of a negative electrode, alumina (α-Al) having a volume-based average particle size of 3.5 μm was used as the large-diameter particles. ２ O ３ A test cell was prepared and evaluated in the same manner as in Example 1, except that the dispersion was applied using ) particles so that the average thickness of the coating layer was 2.5 μm. After preparing the negative electrode, the cross-sectional profile of the functional layer was observed using an SEM, and a structure in which large-diameter particles protruded from the surface of the coating layer was confirmed. Furthermore, the arithmetic mean height of the functional layer was measured using the above-mentioned measurement method and was found to be 0.21 μm.

[0060] Example 5 In the production of a negative electrode, alumina (α-Al) having a volume-based average particle size of 4.0 μm was used as the large-diameter particles. ２ O ３ A test cell was prepared and evaluated in the same manner as in Example 1, except that the dispersion was applied using ) particles so that the average thickness of the coating layer was 2.5 μm. After preparing the negative electrode, the cross-sectional profile of the functional layer was observed using an SEM, and a structure in which large-diameter particles protruded from the surface of the coating layer was confirmed. Furthermore, the arithmetic mean height of the functional layer was measured using the above-mentioned measurement method and was found to be 0.28 μm.

[0061] Comparative Example 1 A test cell was produced and evaluated in the same manner as in Example 1, except that in the production of the negative electrode, no functional layer was formed on the exposed portion of the negative electrode substrate.

[0062] <Comparative Example 2> A test cell was produced in the same manner as in Example 1, except that in producing the negative electrode, no functional layer was formed on the exposed portion of the negative electrode substrate, and multiple linear cut portions (see Patent Document 1) were formed on the exposed portion of the negative electrode substrate.

[0063] Comparative Example 3 In the production of the negative electrode, alumina (α-Al) having an average particle size of 0.5 μm on a volume basis was used.２ O ３ A test cell was fabricated and evaluated in the same manner as in Example 1, except that the acrylic ester-based binder emulsion and the acrylic ester-based particles were mixed at a solids mass ratio of 100:3, and then an appropriate amount of water was added to prepare a dispersion having a solids concentration of 10 mass%. That is, a functional layer having only a coating layer was provided on the surface of the negative electrode substrate exposed portion 44 of Comparative Example 3. The arithmetic mean height of the functional layer was measured using the above-mentioned measurement method and was found to be 0.07 μm.

[0064] Comparative Example 4 In the production of the negative electrode, alumina (α-Al) having a volume-based average particle size of 0.5 μm was used as the large-diameter particles. ２ O ３ A test cell was prepared and evaluated in the same manner as in Example 1, except that the dispersion was applied using 1.0 μm of large-diameter particles so that the average thickness of the coating layer was 1.0 μm. After preparing the negative electrode, the cross-sectional profile of the functional layer was observed using an SEM, and a structure in which most of the large-diameter particles were embedded inside the coating layer was confirmed. Furthermore, the arithmetic mean height of the functional layer was measured using the above-mentioned measurement method and found to be 0.09 μm.

[0065] The evaluation results of the capacity retention rate and the incidence rate of internal short circuits for the test cells of the examples and comparative examples are shown in Table 1. Table 1 also shows the average thickness of the coating layer, the volume-based average particle size of the large-diameter particles, the arithmetic mean height of the functional layer, and the presence or absence of cut portions.

[0066]

[0067] As shown in Table 1, the test cells of the examples have improved capacity retention rates while suppressing the occurrence of internal short circuits compared to the test cells of the comparative examples. Furthermore, in the test cells of the examples, the capacity retention rates improve as the arithmetic mean height of the functional layer increases. This suggests that providing a functional layer on the surface of the negative electrode substrate exposed portion and forming an uneven shape on the surface of the negative electrode substrate exposed portion facilitates the flow of nonaqueous electrolyte into the electrode assembly.

[0068] Furthermore, the test cell of Comparative Example 2, in which a cut was provided in the negative electrode substrate exposed portion, achieved improved cycle characteristics, but the incidence of internal short circuits significantly increased. Furthermore, when the inside of the test cell of Comparative Example 2 was observed, damage to the negative electrode substrate exposed portion originating from the cut was found after cycling. Therefore, it is presumed that damage to the negative electrode substrate exposed portion occurred, and the damaged negative electrode substrate exposed portion broke through the separator, causing an internal short circuit.

[0069] 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 electrode assembly of the first electrode is free of the first electrode mixture layer, providing a first electrode core exposed portion where the first electrode core is exposed, and a functional layer is provided on the surface of the first electrode core exposed portion, the functional layer including a coating layer covering at least a portion of the first electrode core exposed portion and large-diameter particles having a volume-based average particle size larger than an average thickness of the coating layer. Aspect 2: The non-aqueous electrolyte secondary battery according to Aspect 1, wherein the large-diameter particles include inorganic particles. Aspect 3: The non-aqueous electrolyte secondary battery according to Aspect 1 or Aspect 2, wherein the large-diameter particles have a volume-based average particle size of 1.0 μm or more. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the arithmetic mean height of the functional layer is 0.10 μm or more.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the average height of the protruding portions of the large-diameter particles protruding from the coating layer is 0.5 μm or more.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the functional layer is provided only on the inner winding surface of the first electrode core exposed portion.Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the first electrode core exposed portion has a bending point and is bent from the bending point toward the radially inward side of the electrode body, and the functional layer is provided in a region of the first electrode core exposed portion from the bending point to the one end.Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the first electrode core exposed portion is free of a notch or a through-hole. Configuration 9: The nonaqueous electrolyte secondary battery according to any one of configurations 1 to 8, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

[0070] REFERENCE SIGNS LIST 10 nonaqueous electrolyte secondary battery, 11 positive electrode (second electrode), 12 negative electrode (first electrode), 12A winding start end, 12B winding end end, 12Y lower end, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17 negative electrode current collector plate, 18 positive electrode current collector plate, 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 through hole, 27 gasket, 30 positive electrode core, 32 positive electrode mixture layer, 34 positive electrode core exposed portion, 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), 44X upper end, 44Y Lower end, 50 functional layer, 52 coating layer, 54 large diameter particle, R bending point

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; one axial end of the electrode assembly of the first electrode is free from the first electrode mixture layer and has a first electrode core exposed portion where the first electrode core is exposed; and the surface of the first electrode core exposed portion is provided with a coating layer that covers at least a portion of the first electrode core exposed portion, and a functional layer that includes large-diameter particles whose volume-based average particle size is larger than the average thickness of the coating layer.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the large-diameter particles include inorganic particles.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the large-diameter particles have a volume-based average particle size of 1.0 μm or more.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer has an arithmetic mean height of 0.10 μm or more.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the large-diameter particles have protruding portions protruding from the coating layer with an average height of 0.5 μm or more.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer is provided only on the inner surface of the first electrode substrate exposed portion.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the first electrode core exposed portion has a bending point and is bent from the bending point toward the inside in the radial direction of the electrode body, and the functional layer is provided in a region of the first electrode core exposed portion from the bending point to the one end.

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

9. 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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