Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery comprising: an electrode body in which a belt-like first electrode (12) and a belt-like second electrode are wound in a longitudinal direction via a separator; and a non-aqueous electrolyte. The first electrode (12) has a first electrode core body (40) and a first electrode mixture layer (42) disposed on the first electrode core body (40). At one end of the electrode body of the first electrode (12) in the axial direction, a first electrode core body exposed part (44) is provided, in which the first electrode mixture layer (42) is not disposed and the first electrode core body (40) is exposed. On the surface of the first electrode core body exposed part (44), a plurality of resin layers (50) are disposed at intervals in the longitudinal direction of the first electrode (12).

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 and lower resistance in non-aqueous electrolyte secondary batteries. Furthermore, from the perspective of improving the reliability of non-aqueous electrolyte secondary batteries, it is also required to suppress damage, such as breakage of the exposed portion of the core, 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 strip-shaped first electrode and a strip-shaped second electrode are wound longitudinally 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 body 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 a plurality of resin layers are disposed on the surface of the first electrode core exposed portion at intervals in the longitudinal direction of the first electrode.

[0007] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, it is possible to achieve improved cycle characteristics and low resistance while suppressing damage to the exposed portion of the core when repeatedly charged and discharged.

[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 resin 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 a strip-shaped separator 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 fabricated, 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 produced, 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 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 battery 10 from rising excessively, which could cause the battery 10 to explode, thereby improving the safety of the 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 Figures 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 resin layer 50 (described later) interposed therebetween. The outer winding surface of the folded negative electrode core exposed portion 44 is then joined to 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] As shown in FIG. 3 , the nonaqueous electrolyte secondary battery 10 of this embodiment has a plurality of resin layers 50 arranged at intervals in the longitudinal direction of the negative electrode 12 in the negative electrode substrate exposed portion 44. This forms an uneven shape on the surface of the negative electrode substrate exposed portion 44, making it easier for nonaqueous electrolyte to flow into the electrode assembly 14 through gaps between adjacent resin layers 50. As a result, even after repeated charge and discharge, the amount of nonaqueous electrolyte inside the electrode assembly 14 is ensured, and cycle characteristics can be improved. In other words, if the resin layers 50 are arranged over the entire longitudinal direction of the negative electrode 12, a sufficient amount of nonaqueous electrolyte will not flow into the electrode assembly 14, and cycle characteristics cannot be sufficiently improved.

[0031] Furthermore, by disposing a plurality of resin layers 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, for example, the deformed or damaged negative electrode core exposed portion 44 may break through the separator 13, causing an internal short circuit. In other words, in this embodiment, the resin 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.

[0032] The resin layer 50 is made of a resin material and is a member capable of forming an uneven shape on the surface of the negative electrode substrate exposed portion 44. For example, the resin layer 50 may be a resin tape made of a resin material such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate).

[0033] From the viewpoint of further improving the cycle characteristics, the resin layer 50 preferably has swelling properties with respect to the non-aqueous electrolyte. In the present disclosure, "having swelling properties" means that the resin layer 50 absorbs the non-aqueous electrolyte and swells. When the resin layer 50 has swelling properties with respect to the non-aqueous electrolyte, the non-aqueous electrolyte is retained in the resin layer 50, making it easier for the non-aqueous electrolyte to be supplied to the inside of the electrode assembly 14 during charge and discharge. As a result, even when charge and discharge are repeated, the amount of non-aqueous electrolyte inside the electrode assembly 14 is more secure, and the cycle characteristics can be further improved.

[0034] When the resin layer 50 has swelling properties in a non-aqueous electrolyte, the resin layer 50 contains, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), nitrile-butadiene rubber (NBR), polyimide resin, polyvinyl alcohol (PVA), and polyethylene oxide (PEO), and preferably contains polyvinylidene fluoride (PVDF). The content of the above resin material in the resin layer 50 is, for example, preferably 80% by mass or more, and more preferably 90% by mass or more. The resin layer 50 can be formed, for example, by intermittently applying a resin solution containing the above resin material to the negative electrode substrate exposed portion 44.

[0035] The thickness of the resin layer 50 is preferably 5 μm or more, and more preferably 10 μm or more. In this case, the gap formed on the surface of the negative electrode substrate exposed portion 44 can be made larger, making it easier for the non-aqueous electrolyte to flow into the inside of the electrode body 14. Furthermore, the thickness of the resin layer 50 is preferably 100 μm or less, and more preferably 90 μm or less. In this case, good bonding between the negative electrode substrate exposed portion 44 and the negative electrode current collector plate 17 can be ensured, making it easier to achieve low resistance. Therefore, the thickness of the resin layer 50 is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 90 μm or less.

[0036] The resin layers 50 have, for example, a generally rectangular shape in a plan view. The shapes and sizes of the resin layers 50 may be the same or different. The length of each resin layer 50 in the longitudinal direction of the negative electrode 12 can be appropriately set depending on the size of the nonaqueous electrolyte secondary battery 10, and is, for example, 1 mm or more and 50 mm or less.

[0037] 3, the resin layers 50 are arranged at approximately equal intervals in the longitudinal direction of the negative electrode 12, but the arrangement of the resin layers 50 is not limited to this. The resin layers 50 may be arranged, for example, so that the intervals between them increase toward the end of the winding of the negative electrode 12. The intervals between adjacent resin layers 50 in the longitudinal direction of the negative electrode 12 can be set appropriately depending on the size of the nonaqueous electrolyte secondary battery 10, for example, and are 1 mm or more and 50 mm or less.

[0038] 3 , in the longitudinal direction of the negative electrode 12, the ratio of the total length of the resin layer 50 to the length from the winding start end 44A to the winding end end 44B of the negative electrode substrate exposed portion 44 is preferably 20% or more and 90% or less, and more preferably 50% or more and 80% or less. In this case, an appropriate uneven shape is formed on the surface of the negative electrode substrate exposed portion 44, making it easier to ensure the amount of non-aqueous electrolyte inside the electrode body 14. Furthermore, if the resin layer 50 has swelling properties with respect to non-aqueous electrolyte, setting the length of the resin layer 50 within the above range allows a sufficient amount of non-aqueous electrolyte to be retained in the resin layer 50, thereby further improving cycle characteristics.

[0039] The resin layer 50 is preferably disposed 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 disposing the resin layer 50 on the inner winding surface of the negative electrode substrate exposed portion 44, joining of the negative electrode substrate exposed portion 44 and the negative electrode current collector plate 17 is facilitated. Furthermore, by disposing the resin layer 50 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, thereby realizing low resistance of the nonaqueous electrolyte secondary battery 10. Note that the resin layer 50 may be disposed on the outer winding surface of the negative electrode substrate exposed portion 44 in addition to or instead of the inner winding surface of the negative electrode substrate exposed portion 44.

[0040] 3 and 4 , the resin layer 50 is preferably disposed in a region of the negative electrode substrate exposed portion 44 from the bending point R to the lower end 44Y. In this case, the nonaqueous electrolyte is more likely to flow into the electrode assembly 14. In the width direction of the negative electrode 12, the length of the resin layer 50 is, for example, 30% to 100%, or may be 50% to 95%, of the length from the bending point R to the lower end 44Y. Note that the resin layer 50 may be disposed in a region from the bending point R to the upper end 44X in addition to or instead of the region from the bending point R to the lower end 44Y.

[0041] Furthermore, it is more preferable that the resin layer 50 abuts against the lower end 44Y of the negative electrode substrate exposed portion 44. In this case, the nonaqueous electrolyte can more easily flow into the inside of the electrode body 14, thereby further improving the cycle characteristics.

[0042] As described above, by arranging a plurality of resin layers 50 at intervals in the longitudinal direction of the negative electrode 12 in the negative electrode core exposed portion 44, it is possible to form an uneven shape on the surface of the negative electrode core 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.

[0043] 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 resin 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 resin 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 flows into the electrode assembly 14 from the upper end side of the electrode assembly 14 as well. Therefore, by arranging multiple resin layers 50 at intervals in the longitudinal direction of the positive electrode 11 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.

[0044] 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.

[0045] 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.

[0046] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0047] 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.

[0048] [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 as to form a negative electrode core exposed portion having a width of 5 mm. 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.

[0049] A resin solution containing 2% by mass of polyvinylidene fluoride (PVDF) was applied to the inner surface of the wound negative electrode substrate exposed portion and dried to form a resin layer. In this case, resin layers having a generally rectangular shape in plan view were formed at approximately equal intervals in the longitudinal direction of the negative electrode so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end of the negative electrode substrate exposed portion was 10%. The resin solution was applied only to the region below the bending point when the negative electrode substrate exposed portion was bent. The resin solution was applied so that the thickness of the resin layer was 10 μm.

[0050] [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.

[0051] [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.

[0052] [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 200 cycles were performed. The capacity retention rate was calculated using the following formula: Capacity retention rate [%] = (discharge capacity at 200th cycle / initial discharge capacity) × 100

[0053] [Evaluation of Shape of Exposed Negative Electrode Substrate Portion] 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. Then, using an X-ray CT scanner (Shimadzu Corporation, SMX-225CT FPD HR), the presence or absence of damage (for example, cuts) in the exposed negative electrode substrate portion was confirmed.

[0054] [Evaluation of Reaction Resistance (AC-IR)] The reaction resistance at a 30% state of charge (SOC 30%) was determined by AC impedance measurement in a 25°C environment. Specifically, using a Solartron 1255B (manufactured by Solartron Corporation), the AC impedance of the test cell was measured at an applied voltage of 10 mV and a measurement frequency range of 0.01 Hz to 200 kHz. A Nyquist diagram was plotted from the measurement data, and the reaction resistance was determined from the size of the arc between 10 Hz and 0.1 Hz.

[0055] Example 2 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode substrate in the longitudinal direction of the negative electrode was 20%.

[0056] Example 3 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode substrate in the longitudinal direction of the negative electrode was 40%.

[0057] Example 4 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode core in the longitudinal direction of the negative electrode was 50%.

[0058] Example 5 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode core in the longitudinal direction of the negative electrode was 80%.

[0059] Example 6 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode core in the longitudinal direction of the negative electrode was 90%.

[0060] Example 7 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode core in the longitudinal direction of the negative electrode was 5%.

[0061] Example 8 A test cell was produced and evaluated in the same manner as in Example 1, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode core in the longitudinal direction of the negative electrode was 95%.

[0062] Example 9 A test cell was produced and evaluated in the same manner as in Example 4, except that in the production of the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied only to a region above the bending point when the negative electrode substrate exposed portion was bent.

[0063] Example 10 A test cell was produced and evaluated in the same manner as in Example 4, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied to the outer surface of the wound negative electrode substrate exposed portion.

[0064] Example 11 A test cell was fabricated and evaluated in the same manner as in Example 4, except that a resin tape made of PI (polyimide) was used as the resin layer in the fabrication of the negative electrode. The resin tape had a rectangular shape in a plan view and was attached at approximately equal intervals to the inner surface of the wound negative electrode substrate exposed portion. The thickness of the resin tape was 10 μm.

[0065] Example 12 A test cell was produced and evaluated in the same manner as in Example 4, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the resin layer had a thickness of 110 μm.

[0066] Example 13 A test cell was produced and evaluated in the same manner as in Example 4, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the resin layer had a thickness of 100 μm.

[0067] Example 14 A test cell was produced and evaluated in the same manner as in Example 4, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the resin layer had a thickness of 50 μm.

[0068] Example 15 A test cell was produced and evaluated in the same manner as in Example 4, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the resin layer had a thickness of 5 μm.

[0069] Example 16 A test cell was produced and evaluated in the same manner as in Example 4, except that in producing the negative electrode, a resin solution containing polyvinylidene fluoride (PVDF) was applied so that the resin layer had a thickness of 3 μm.

[0070] 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 resin layer was formed on the exposed portion of the negative electrode substrate.

[0071] Comparative Example 2 A test cell was produced and evaluated in the same manner as in Example 1, except that a resin solution containing polyvinylidene fluoride (PVDF) was applied to the exposed portion of the negative electrode substrate over the entire longitudinal direction of the negative electrode. That is, the resin solution was applied so that the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed portion of the negative electrode substrate in the longitudinal direction of the negative electrode was 100%.

[0072] <Comparative Example 3> A test cell was produced in the same manner as in Example 1, except that in the production of the negative electrode, no resin 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.

[0073] Table 1 shows the evaluation results of the capacity retention rate, the presence or absence of damage to the negative electrode substrate exposed portion, and the reaction resistance of the test cells of the examples and comparative examples. The capacity retention rate and reaction resistance were classified as ◎, ◯, △, and × based on the following evaluation criteria. Table 1 also shows the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the negative electrode substrate exposed portion (resin layer ratio), the position where the resin layer is formed, the surface where the resin layer is formed, the material of the resin layer, the thickness of the resin layer, and the presence or absence of cut portions. <Capacity retention rate> ◎: 92% or more ◯: 90% or more, less than 92% △: 85% or more, less than 90% ×: less than 85% <Reaction resistance> ◎: 2.1 mΩ or less ◯: More than 2.1 mΩ, 2.3 mΩ or less △: More than 2.3 mΩ, 2.5 mΩ or less ×: More than 2.5 mΩ

[0074]

[0075] As shown in Table 1, the test cells of the examples were able to achieve improved cycle characteristics and low resistance while suppressing damage to the exposed negative electrode substrate portion. Furthermore, the test cells of Examples 2 to 6, in which the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the exposed negative electrode substrate portion in the longitudinal direction of the negative electrode (resin layer ratio) was 20% or more and 90% or less, exhibited improved capacity retention rates compared to Examples 1, 7, and 8, in which the resin layer ratio was less than 20% or more than 90%. This is presumably because, by setting the resin layer ratio to 20% or more and 90% or less, appropriate irregularities are formed on the surface of the exposed negative electrode substrate portion, making it easier for the nonaqueous electrolyte to flow into the electrode assembly.

[0076] Furthermore, the test cell of Example 4, in which a resin layer was formed below the bending point of the negative electrode substrate exposed portion, had an improved capacity retention rate compared to the test cell of Example 9, in which a resin layer was formed above the bending point of the negative electrode substrate exposed portion. This is presumably because forming a resin layer below the bending point of the negative electrode substrate exposed portion makes it easier for the nonaqueous electrolyte to flow from the lower end side of the electrode body into the interior of the electrode body.

[0077] Furthermore, the test cell of Example 4, in which a resin layer was formed on the inner winding surface of the negative electrode substrate exposed portion, had a reduced reaction resistance compared to the test cell of Example 10, in which a resin layer was formed on the outer winding surface of the negative electrode substrate exposed portion. This is presumably because forming a resin layer on the inner winding surface of the negative electrode substrate exposed portion makes it easier to ensure electrical continuity between the negative electrode substrate exposed portion and the negative electrode current collector plate.

[0078] Furthermore, the test cell of Example 4, which used PVDF, which has swelling properties in non-aqueous electrolytes, for the resin layer, had an improved capacity retention rate compared to Example 11, which used PI, which does not have swelling properties in non-aqueous electrolytes, for the resin layer. This is presumably because the use of a material, which has swelling properties in non-aqueous electrolytes, for the resin layer allows the non-aqueous electrolyte to be retained in the resin layer, making it easier for the non-aqueous electrolyte to be supplied to the inside of the electrode assembly.

[0079] Furthermore, the results of the test cells of Examples 4 and 12 to 16 showed that when the resin layer thickness was 5 μm or more and 100 μm or less, both improved cycle characteristics and low resistance were achieved at a high level while suppressing damage to the exposed portion of the negative electrode substrate. Furthermore, the test cell of Comparative Example 3, in which a cut was provided in the exposed portion of the negative electrode substrate, achieved improved cycle characteristics and low resistance, but damage to the exposed portion of the negative electrode substrate originating from the cut was confirmed after cycling. Damage to the exposed portion of the negative electrode substrate may cause the damaged exposed portion of the negative electrode substrate to break through the separator, resulting in an internal short circuit. Therefore, the test cell of Comparative Example 3 cannot be considered a highly reliable nonaqueous electrolyte secondary battery.

[0080] 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 strip-shaped first electrode and a strip-shaped second electrode are wound in the longitudinal direction 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 from the first electrode mixture layer and has a first electrode core exposed portion where the first electrode core is exposed, and a plurality of resin layers are disposed on a surface of the first electrode core exposed portion at intervals in the longitudinal direction of the first electrode. Aspect 2: The non-aqueous electrolyte secondary battery according to Aspect 1, wherein the ratio of the total length of the resin layers to the length from the winding start end to the winding end end of the first electrode core exposed portion in the longitudinal direction of the first electrode is 20% or more and 90% or less. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein the ratio of the total length of the resin layer to the length from the winding start end to the winding end end of the first electrode core exposed portion in the longitudinal direction of the first electrode is 50% or more and 80% or less.Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the first electrode core exposed portion has a bending point and is bent from the bending point toward the radially inward side of the electrode body, and the resin layer is disposed in a region of the first electrode core exposed portion from the bending point to the one end.Configuration 5: The nonaqueous electrolyte secondary battery according to Configuration 4, wherein the resin layer abuts against the one end of the first electrode core exposed portion.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the resin layer is disposed 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 resin layer has swelling properties with respect to the nonaqueous electrolyte.Configuration 8: The nonaqueous electrolyte secondary battery of Configuration 7, wherein the resin layer contains at least one selected from the group consisting of carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), nitrile-butadiene rubber (NBR), polyimide resin, polyvinyl alcohol (PVA), and polyethylene oxide (PEO). Configuration 9: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 8, wherein the resin layer has a thickness of 5 μm or more and 100 μm or less. Configuration 10: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 9, wherein the first electrode is a negative electrode and the second electrode is a positive electrode.

[0081] 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), 44A winding start end, 44B End of winding, 44X upper end, 44Y lower end, 50 resin layer, R bending point

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode assembly in which a strip-shaped first electrode and a strip-shaped second electrode are wound in the longitudinal direction 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 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 a plurality of resin layers are disposed on the surface of the first electrode core exposed portion at intervals in the longitudinal direction of the first electrode.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the total length of the resin layers to the length from the winding start end to the winding end end of the first electrode substrate exposed portion in the longitudinal direction of the first electrode is 20% or more and 90% or less.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the total length of the resin layers to the length from the winding start end to the winding end end of the first electrode substrate exposed portion in the longitudinal direction of the first electrode is 50% or more and 80% or less.

4. 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 resin layer is disposed in a region of the first electrode core exposed portion from the bending point to the one end.

5. The nonaqueous electrolyte secondary battery according to claim 4, wherein the resin layer abuts against the one end of the first electrode substrate exposed portion.

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

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the resin layer has swelling properties with respect to the non-aqueous electrolyte.

8. The nonaqueous electrolyte secondary battery according to claim 7, wherein the resin layer contains at least one selected from the group consisting of carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), nitrile-butadiene rubber (NBR), polyimide resin, polyvinyl alcohol (PVA), and polyethylene oxide (PEO).

9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the resin layer has a thickness of 5 μm or more and 100 μm or less.

10. 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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