Non-aqueous electrolyte secondary battery

Abstract

The present invention provides a non-aqueous electrolyte secondary battery characterized by comprising an electrode body (14) in which a strip-shaped positive electrode (11) and a strip-shaped negative electrode (12) are wound along the longitudinal direction with a separator (13) in between, wherein the positive electrode (11) has a positive electrode current collector exposed portion where a positive electrode compound layer (31) is not disposed and a positive electrode current collector (30) is exposed, a positive electrode tab (20) is joined to the positive electrode current collector exposed portion, the negative electrode (12) has a negative electrode current collector exposed portion where a negative electrode compound layer (41) is not disposed and a negative electrode current collector (40) is exposed, a negative electrode tab (21) is joined to the negative electrode current collector exposed portion, the positive electrode tab (20) and the negative electrode tab (21) are provided with a gap formed in the axial direction of the electrode body (14), and said gap is located at a position that does not overlap with the axial center of the electrode body (14).

Description

Nonaqueous electrolyte secondary battery

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

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been known that include an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an outer can that houses the electrode assembly. Patent Document 1 discloses a non-aqueous electrolyte secondary battery in which a positive electrode tab joined to the positive electrode and a negative electrode tab joined to the negative electrode are provided at approximately the center in the radial direction of the electrode assembly.

[0003] US Patent Application Publication No. 2021 / 023044

[0004] However, when an external load is applied to a non-aqueous electrolyte secondary battery, the axial center of the battery tends to deform more easily than both axial end portions of the battery. In the non-aqueous electrolyte secondary battery disclosed in Patent Document 1, the positive electrode tab and the negative electrode tab are arranged only in a limited range at both axial ends of the electrode assembly. Therefore, the axial center of the battery is not strong enough, and the axial center of the battery is easily deformed when an external load is applied.

[0005] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure is a nonaqueous electrolyte secondary battery including an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound lengthwise with a separator interposed therebetween, and a bottomed cylindrical outer can that houses the electrode assembly, wherein the positive electrode has a positive electrode current collector exposed portion where no positive electrode mixture layer is disposed and the positive electrode current collector is exposed, and the negative electrode has a negative electrode current collector exposed portion where no negative electrode mixture layer is disposed and the negative electrode current collector is exposed, and the positive electrode current collector exposed portion has a protruding portion that protrudes from one of both axial ends of the electrode assembly. a positive electrode tab protruding from the other end of each end in the axial direction of the electrode body is joined to the negative electrode current collector exposed portion, and a negative electrode tab protruding from the other end of each end in the axial direction of the electrode body is joined to the negative electrode current collector exposed portion, the negative electrode current collector exposed portion is provided in a region of the negative electrode that at least partially overlaps in the width direction of the negative electrode with an opposing region that faces the positive electrode current collector exposed portion via the separator, and the positive electrode tab and the negative electrode tab are provided with a gap in the axial direction of the electrode body when viewed in the radial direction of the electrode body, and the gap is located at a position that does not overlap with the axial center of the electrode body.

[0006] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, deformation of the battery due to an external load can be suppressed.

[0007] Fig. 2 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery that is an example of an embodiment; Fig. 3 is a front view showing a positive electrode and a negative electrode provided in the nonaqueous electrolyte secondary battery that is an example of an embodiment in an expanded state; Fig. 4 is a cross-sectional view taken along line AA in Fig. 1, showing an enlarged view of the vicinity of a positive electrode tab; Fig. 5 is a cross-sectional view taken along line BB in Fig. 1, showing an enlarged view of the vicinity of a negative electrode tab; Fig. 6 is a front view showing a positive electrode and a negative electrode provided in a nonaqueous electrolyte secondary battery that is another example of an embodiment in an expanded state;

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

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

[0010] The electrode assembly 14 has a structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound longitudinally with a separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are spirally wound so that they are alternately stacked in the radial direction of the electrode assembly 14. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the width direction of the positive electrode 11 and the negative electrode 12 is the axial direction. The nonaqueous electrolyte secondary battery 10 further includes a positive electrode tab 20 connected to the positive electrode 11 by welding or the like and protruding from the upper end of the electrode assembly 14, and a negative electrode tab 21 connected to the negative electrode 12 by welding or the like and protruding from the lower end of the electrode assembly 14.

[0011] The positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 31 disposed on the positive electrode current collector 30. The positive electrode current collector 30 can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode current collector 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode current collector 30.

[0012] The positive electrode mixture layer 31 contains a particulate lithium-containing composite oxide as a positive electrode active material. The lithium-containing composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium-containing composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, Al, and Mn. Examples of suitable composite oxides include a lithium-containing composite oxide containing Ni, Co, and Mn, and a lithium-containing composite oxide containing Ni, Co, and Al.

[0013] Examples of the conductive agent contained in the positive electrode mixture layer 31 include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of the binder contained in the positive electrode mixture layer 31 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0014] The negative electrode 12 has a negative electrode current collector 40 and a negative electrode mixture layer 41 disposed on the negative electrode current collector 40. The negative electrode current collector 40 can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on its surface. The negative electrode mixture layer 41 contains a negative electrode active material, a binder, and, if necessary, a conductive agent. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing the negative electrode active material and the binder to the surface of the negative electrode current collector 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode current collector 40.

[0015] The negative electrode mixture layer 41 generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, as the negative electrode active material, a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element may be used. Among these, a composite material containing Si is preferred.

[0016] As in the case of the positive electrode mixture layer 31, the binder contained in the negative electrode mixture layer 41 can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene butadiene rubber (SBR) is preferably used. The negative electrode mixture layer 41 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer 41 may also contain a conductive agent such as CNT.

[0017] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. Furthermore, a highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13.

[0018] On the outer peripheral surface of the electrode body 14, the negative electrode mixture layer 41 is not formed, so that the negative electrode current collector 40 is exposed, and a contact portion 43 that abuts against the inner surface of the outer can 16 is arranged. By providing the negative electrode tab 21 and arranging the contact portion 43 on the outer peripheral surface of the electrode body 14, it is possible to further reduce the internal resistance of the nonaqueous electrolyte secondary battery 10. Note that the separator 13 may be arranged on the outer peripheral surface of the electrode body 14 without arranging the contact portion 43.

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

[0020] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0021] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0022] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode tab 20 passes through a through-hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode tab 21 passes through a through-hole in the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode tab 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode tab 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0023] As described above, the outer can 16 is a cylindrical metal container with a bottom and an opening at one axial end, and the opening of the outer can 16 is closed by a sealing body 17 .

[0024] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0025] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the battery increases due to abnormal heat generation, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged through a vent hole in the cap 27.

[0026] Next, the positive electrode 11 and the negative electrode 12 will be described in detail with further reference to Figures 2 to 4. Figure 2 is a front view showing the positive electrode 11 and the negative electrode 12 in a developed state, Figure 3 is a cross-sectional view taken along line AA in Figure 1, showing an enlarged view of the vicinity of the positive electrode tab 20, and Figure 4 is a cross-sectional view taken along line BB in Figure 1, showing an enlarged view of the vicinity of the negative electrode tab 21. In Figure 2, (a) is a plan view of the inner surface of the wound positive electrode 11, (b) is a plan view of the outer surface of the wound positive electrode 11, (c) is a plan view of the inner surface of the wound negative electrode 12, and (d) is a plan view of the outer surface of the wound negative electrode 12.

[0027] 2, the positive electrode 11 has a positive electrode current collector exposed portion 32 where the positive electrode mixture layer 31 is not disposed and the positive electrode current collector 30 (see FIG. 1) is exposed. In this embodiment, the positive electrode current collector exposed portion 32 includes a first positive electrode current collector exposed portion 33 and a second positive electrode current collector exposed portion 35. The positive electrode current collector exposed portion 32 can be formed, for example, by intermittent application in which the positive electrode mixture slurry is not applied to a portion of the positive electrode current collector 30.

[0028] The positive electrode current collector exposed portion 32 is provided across the entire width of the positive electrode 11. In other words, the positive electrode current collector exposed portion 32 contacts the upper end 11A and the lower end 11B of the positive electrode 11, respectively. The first positive electrode current collector exposed portion 33 and the second positive electrode current collector exposed portion 35 are provided on the inner and outer winding surfaces of the positive electrode 11, respectively, so as to overlap each other in the thickness direction of the positive electrode 11. In this embodiment, a positive electrode tab 20 protruding from the upper end of the electrode assembly 14 is joined to the first positive electrode current collector exposed portion 33. The positive electrode tab 20 may be joined to either the inner winding surface or the outer winding surface of the first positive electrode current collector exposed portion 33.

[0029] The first positive electrode current collector exposed portion 33 to which the positive electrode tab 20 is joined is preferably provided in approximately the center in the longitudinal direction of the positive electrode 11. By providing the first positive electrode current collector exposed portion 33 in approximately the center in the longitudinal direction of the positive electrode 11, the internal resistance of the positive electrode 11 can be reduced.

[0030] As shown in FIG. 3 , the first positive electrode current collector exposed portion 33 to which the positive electrode tab 20 is joined faces the negative electrode current collector exposed portion 42 with the separator 13 interposed therebetween. As will be described in detail later, the negative electrode tab 21 is joined to the negative electrode current collector exposed portion 42. By arranging the first positive electrode current collector exposed portion 33 to which the positive electrode tab 20 is joined so as to face the negative electrode current collector exposed portion 42 to which the negative electrode tab 21 is joined with the separator 13 interposed therebetween in this manner, it is possible to suppress winding misalignment of the electrode body 14 and to suppress lithium deposition in the negative electrode current collector exposed portion 42 during charging. Because the negative electrode current collector 40 is exposed not only on the outer surface of the negative electrode current collector exposed portion 42 but also on the inner surface of the winding, it is preferable that the second positive electrode current collector exposed portion 35 be arranged to face the inner surface of the negative electrode current collector exposed portion 42 with the separator 13 interposed therebetween. In this case, the positive electrode current collector 30 may be exposed only on the outer surface of the second positive electrode current collector exposed portion 35. Note that, because it is possible to suppress lithium deposition on the negative electrode current collector exposed portion 42 during charging using an insulating member 50 or the like, the second positive electrode current collector exposed portion 35 to which the positive electrode tab 20 is not joined is not necessarily required. The length of the positive electrode current collector exposed portion 32 along the longitudinal direction of the positive electrode 11 is, for example, 120% or more, and may be 150% or more, of the length of the negative electrode current collector exposed portion 42 along the longitudinal direction of the negative electrode 12. The length of the positive electrode current collector exposed portion 32 along the longitudinal direction of the positive electrode 11 is, for example, 5 mm or more and 50 mm or less. Note that the lengths of the positive electrode current collector exposed portions 32 along the longitudinal direction of the positive electrode 11 may be the same or different from each other.

[0031] 2 and 3 , an insulating member 50 covering the positive electrode current collector exposed portion 32 is provided on the surface of the positive electrode 11. The insulating member 50 covers the entire positive electrode current collector exposed portion 32, a portion of the positive electrode tab 20, and the positive electrode mixture layer 31 around the positive electrode current collector exposed portion 32. By providing the insulating member 50, if the separator 13 is damaged, contact between the positive electrode current collector exposed portion 32 and the positive electrode tab 20 and the negative electrode 12 can be suppressed. As a result, an internal short circuit can be suppressed.

[0032] The insulating member 50 is, for example, an adhesive tape having a substrate and an adhesive portion formed on one surface of the substrate. A heat-resistant layer containing inorganic particles such as metal oxide may be provided between the substrate and the adhesive portion. The substrate may be made of any insulating resin, such as PPS (polyphenylene sulfide), PEEK (polyether ether ketone), PI (polyimide), PP (polypropylene), PET (polyethylene terephthalate), or PBT (polybutylene terephthalate). The thickness of the substrate is, for example, 5 μm or more and 50 μm or less, and preferably 10 μm or more and 30 μm or less.

[0033] The adhesive portion is a portion for adhering the insulating member 50 to the surface of the positive electrode 11. The thickness of the adhesive portion is, for example, 1 μm or more and 30 μm or less, and preferably 5 μm or more and 25 μm or less. The adhesive portion may contain at least one of a rubber-based polymer and an acrylic-based polymer. The rubber-based polymer and the acrylic-based polymer have adhesive properties, and therefore can adhere the insulating member 50 to the surface of the positive electrode 11. The adhesive portion may further contain, for example, a silicone-based polymer.

[0034] 2, the negative electrode 12 has a negative electrode current collector exposed portion 42 where the negative electrode mixture layer 41 is not disposed and the negative electrode current collector 40 (see FIG. 1) is exposed. The negative electrode current collector exposed portion 42 can be produced, for example, by intermittent application in which the negative electrode mixture slurry is not applied to a part of the negative electrode current collector 40.

[0035] The negative electrode current collector exposed portion 42 is provided across the entire width of the negative electrode 12. In other words, the negative electrode current collector exposed portion 42 is in contact with each of the upper end 12A and the lower end 12B of the negative electrode 12. The negative electrode current collector exposed portion 42 is provided on the inner and outer winding surfaces of the negative electrode 12 so as to overlap each other in the thickness direction of the negative electrode 12. In this embodiment, a negative electrode tab 21 protruding from the lower end of the electrode assembly 14 is joined to the outer winding surface of the negative electrode current collector exposed portion 42. Note that the negative electrode tab 21 may also be joined to the inner winding surface of the negative electrode 12.

[0036] The negative electrode current collector exposed portion 42 to which the negative electrode tab 21 is joined is preferably provided at approximately the center in the longitudinal direction of the negative electrode 12. Providing the negative electrode current collector exposed portion 42 at approximately the center in the longitudinal direction of the negative electrode 12 can reduce the internal resistance of the negative electrode 12. A negative electrode current collector exposed portion may be provided in a region that does not face the positive electrode current collector exposed portion 32 across the separator 13, such as at the winding start end of the negative electrode 12, and the negative electrode tab may be joined to that negative electrode current collector exposed portion.

[0037] 2 and 4 , the negative electrode current collector exposed portion 42 is provided in a region (facing region) facing the first positive electrode current collector exposed portion 33 to which the positive electrode tab 20 is joined, with the separator 13 interposed therebetween. As described above, if the positive electrode mixture layer 31 faces the negative electrode current collector exposed portion 42 with the separator 13 interposed therebetween, lithium deposition may occur in the negative electrode current collector exposed portion 42 during charging. Therefore, from the viewpoint of preventing the positive electrode mixture layer 31 and the negative electrode current collector exposed portion 42 from facing each other with the separator 13 interposed therebetween, it is preferable to arrange the first positive electrode current collector exposed portion 33 provided for joining the positive electrode tab 20 so as to face the negative electrode current collector exposed portion 42 with the separator 13 interposed therebetween. As in the present embodiment, the first positive electrode current collector exposed portion 33 to which the positive electrode tab 20 is joined and the negative electrode current collector exposed portion 42 to which the negative electrode tab 21 is joined are arranged to face each other with the separator interposed therebetween, thereby suppressing lithium deposition on the negative electrode 12 during charging while avoiding a decrease in capacity of the nonaqueous electrolyte secondary battery 10. Note that the negative electrode current collector exposed portion 42 may also be covered with an insulating member 50, similar to the positive electrode current collector exposed portion 32.

[0038] 1 and 2 , the positive electrode tab 20 and the negative electrode tab 21 are provided with a gap in the axial direction of the electrode body 14 when viewed from the radial direction of the electrode body 14. The gap is located at a position that does not overlap with the axial center of the electrode body 14. In other words, one of the positive electrode tab 20 and the negative electrode tab 21 is located at a position that overlaps with the axial center of the electrode body 14.

[0039] When an external load is applied to the nonaqueous electrolyte secondary battery 10, the axial center of the battery is more likely to deform than both axial ends of the battery. In particular, when the positive electrode tab 20 and the negative electrode tab 21 are provided at both axial ends of the electrode assembly 14, the axial center of the battery tends to deform more easily due to the external load. As in this embodiment, by shifting the gap between the positive electrode tab 20 and the negative electrode tab 21 from the axial center of the electrode assembly 14 and arranging the positive electrode tab 20 or the negative electrode tab 21 at the axial center of the electrode assembly 14, the strength of the axial center of the electrode assembly 14 can be increased. As a result, deformation of the axial center of the battery due to the external load can be suppressed.

[0040] If no gap is formed between the positive electrode tab 20 and the negative electrode tab 21, i.e., if the positive electrode tab 20 and the negative electrode tab 21 are arranged to overlap in the radial direction of the electrode assembly 14, the outer diameter of the electrode assembly 14 will increase excessively in the region where the positive electrode tab 20 and the negative electrode tab 21 overlap. As a result, stress will concentrate in the region where the positive electrode tab 20 and the negative electrode tab 21 overlap, causing damage to the electrode assembly 14. By forming a gap between the positive electrode tab 20 and the negative electrode tab 21 and arranging the positive electrode tab 20 and the negative electrode tab 21 so that they do not overlap in the radial direction of the electrode assembly 14 as in this embodiment, it is possible to suppress deformation of the axial center side of the battery due to an external load while suppressing damage to the electrode assembly 14.

[0041] In this embodiment, the positive electrode tab 20 extends from the upper end of the electrode body 14 to a position beyond the axial center of the electrode body 14, and the negative electrode tab 21 extends from the lower end of the electrode body 14 to a position not beyond the axial center of the electrode body 14. Therefore, the gap between the positive electrode tab 20 and the negative electrode tab 21 is formed below the axial center of the electrode body 14. In general, the material used for the positive electrode tab 20 is cheaper than the material used for the negative electrode tab 21, so making the length of the positive electrode tab 20 longer than the length of the negative electrode tab 21 makes it easy to reduce the manufacturing costs of the battery.

[0042] The relative positions of the positive electrode tab 20 and the negative electrode tab 21 are not limited to those shown in Fig. 1 and Fig. 2. For example, the positive electrode tab 20 may extend from the upper end of the electrode body 14 to a position not exceeding the axial center of the electrode body 14, and the negative electrode tab 21 may extend from the lower end of the electrode body 14 to a position exceeding the axial center of the electrode body 14. In other words, the gap between the positive electrode tab 20 and the negative electrode tab 21 in the axial direction of the electrode body 14 may be formed above the axial center of the electrode body 14.

[0043] The gap between the positive electrode tab 20 and the negative electrode tab 21 in the axial direction of the electrode assembly 14 is preferably provided within a range of 20% or more and less than 50% of the axial length of the electrode assembly 14 from both axial ends of the electrode assembly 14, and more preferably within a range of 25% or more and 45% or less. In this case, the strength of the axial center side of the electrode assembly 14 is increased, and it becomes easy to join the positive electrode tab 20 and the negative electrode tab 21 to the positive electrode current collector exposed portion 32 and the negative electrode current collector exposed portion 42, respectively. Note that the axial length of the electrode assembly 14 refers to the length along the axial direction of the electrode assembly 14 from the upper end of the electrode assembly 14 to the lower end of the electrode assembly 14. In this embodiment, it refers to the length along the axial direction of the electrode assembly 14 from the upper end of the separator 13 to the lower end of the separator 13.

[0044] The length of the gap between the positive electrode tab 20 and the negative electrode tab 21 along the axial direction of the electrode assembly 14 is preferably 3% or more, and more preferably 5% or more, of the axial length of the electrode assembly 14. In this case, the occurrence of an internal short circuit due to contact between the positive electrode tab 20 and the negative electrode tab 21 can be suppressed. Furthermore, the length of the gap between the positive electrode tab 20 and the negative electrode tab 21 along the axial direction of the electrode assembly 14 is preferably 30% or less, and more preferably 25% or less, of the axial length of the electrode assembly 14. In this case, the area in which the positive electrode tab 20 and the negative electrode tab 21 are disposed is increased, thereby further increasing the strength of the electrode assembly 14. Therefore, the length of the gap between the positive electrode tab 20 and the negative electrode tab 21 along the axial direction of the electrode assembly 14 is preferably 3% or more and 30% or less, and more preferably 5% or more and 25% or less, of the axial length of the electrode assembly 14.

[0045] The first positive electrode current collector exposed portion 33 and the negative electrode current collector exposed portion 42, which face each other with the separator 13 interposed therebetween, may be provided at a plurality of positions on the positive electrode 11 and the negative electrode 12. Furthermore, the positive electrode 11 may have a positive electrode current collector exposed portion other than the positive electrode current collector exposed portion 32, and the negative electrode 12 may have a negative electrode current collector exposed portion other than the negative electrode current collector exposed portion 42. For example, a negative electrode current collector exposed portion that does not face the positive electrode current collector exposed portion with the separator 13 interposed therebetween may be provided at the winding start end of the negative electrode 12, and a negative electrode tab may be joined to that negative electrode current collector exposed portion.

[0046] Next, another example of an embodiment of the nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to Fig. 5. Fig. 5 is a front view showing the positive electrode 11 and the negative electrode 12 in a developed state. In Fig. 5, (a) is a plan view of the inner surface of the wound positive electrode 11, (b) is a plan view of the outer surface of the wound positive electrode 11, (c) is a plan view of the inner surface of the wound negative electrode 12, and (d) is a plan view of the outer surface of the wound negative electrode 12.

[0047] 5 , the positive electrode current collector exposed portion 32 of this embodiment includes a third positive electrode current collector exposed portion 37 in addition to a first positive electrode current collector exposed portion 33 and a second positive electrode current collector exposed portion 35. The third positive electrode current collector exposed portion 37 is provided on the inner and outer winding surfaces of the positive electrode 11 so as to overlap each other in the thickness direction of the positive electrode 11. Like the other positive electrode current collector exposed portions 32, the third positive electrode current collector exposed portion 37 is covered with an insulating member 50.

[0048] Furthermore, the positive electrode current collector exposed portion 32 of this embodiment is not provided across the entire width of the positive electrode 11. Specifically, the first positive electrode current collector exposed portion 33 contacts only the upper end 11A of the positive electrode 11, and the second positive electrode current collector exposed portion 35 and the third positive electrode current collector exposed portion 37 contact only the lower end 11B of the positive electrode 11. By having the positive electrode current collector exposed portion 32 contact only one of both widthwise end portions of the positive electrode 11, the volume of the positive electrode mixture layer 31 can be increased, making it easier to achieve a high capacity nonaqueous electrolyte secondary battery 10.

[0049] The negative electrode current collector exposed portion 42 in this embodiment is not provided across the entire width of the negative electrode 12, but is in contact only with the lower end 12B of the negative electrode 12. Therefore, unlike the embodiments shown in FIGS. 2 to 4 , the negative electrode current collector exposed portion 42 to which the negative electrode tab 21 is joined does not face the first positive electrode current collector exposed portion 33, which is joined via the separator 13, across the separator 13. However, the negative electrode current collector exposed portion 42 is provided in a region of the negative electrode 12 that faces the first positive electrode current collector exposed portion 33 across the separator 13 (facing region) and overlaps with the negative electrode 12 in the width direction. This suppresses winding misalignment in this embodiment. Note that it is sufficient that the negative electrode current collector exposed portion 42 is provided in a region that at least partially overlaps with the facing region in the width direction of the negative electrode 12. In order to suppress lithium deposition in the negative electrode current collector exposed portion 42 during charging, the third positive electrode current collector exposed portion 37 is disposed to face the negative electrode current collector exposed portion 42 across the separator 13. As with the second positive electrode current collector exposed portion 35, the third positive electrode current collector exposed portion 37 does not necessarily have to be provided.

[0050] 5 , the positive electrode tab 20 extends from the upper end of the electrode body 14 to a position that exceeds the axial center of the electrode body 14, and the negative electrode tab 21 extends from the lower end of the electrode body 14 to a position that does not exceed the axial center of the electrode body 14. Therefore, the first positive electrode current collector exposed portion 33 extends from the upper end 11A of the positive electrode 11 to a position that exceeds the widthwise center of the positive electrode 11, and the second positive electrode current collector exposed portion 35 and the third positive electrode current collector exposed portion 37 extend from the lower end 11B of the positive electrode 11 to positions that do not exceed the widthwise center of the positive electrode 11.

[0051] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0052] Example: [Fabrication of Positive Electrode] Aluminum-containing lithium nickel cobalt oxide was used as the positive electrode active material. This positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 100:2:1, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil with a thickness of 15 μm, and the coating was dried. The coating was rolled using a rolling roller and cut to a predetermined electrode size to prepare a positive electrode. In this case, as shown in FIG. 2, first to fourth positive electrode current collector exposed portions were provided, each exposing the surface of the positive electrode current collector, and an aluminum positive electrode tab was welded to the first positive electrode current collector exposed portion. The positive electrode tab was joined to an area extending beyond the center of the positive electrode in the width direction.

[0053] [Preparation of Negative Electrode] As the negative electrode active material, a mixture of artificial graphite and a silicon-carbon composite material (SiC) in a mass ratio of 90:10 was used. This negative electrode active material, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 100:1:1, and a negative electrode mixture slurry was prepared using water as a dispersion medium. Next, the negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil with a thickness of 8 μm, and the coating was dried. The coating was rolled using a rolling roller and cut to a predetermined electrode size to prepare a negative electrode. At this time, as shown in FIG. 2, first and second negative electrode current collector exposed portions where the surface of the negative electrode current collector was exposed were respectively provided, and a nickel negative electrode tab was welded to the first negative electrode current collector exposed portion. The negative electrode tab was joined in a range that did not extend beyond the widthwise center of the negative electrode and that was positioned with a gap in the axial direction from the positive electrode tab when the electrode body was fabricated. In addition, as shown in Figure 2, a contact portion where the surface of the negative electrode current collector was exposed was provided at one longitudinal end of the negative electrode 12.

[0054] [Fabrication of Electrode Assembly] The electrode assembly was fabricated by spirally winding the positive and negative electrodes with a 14 μm thick polyethylene separator interposed therebetween, with the gap between the positive and negative electrode tabs extending from the bottom end of the electrode assembly to 25% to 35% of the axial length of the electrode assembly.

[0055] [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 1.3 mol / L of ammonium hydroxide in water.

[0056] [Fabrication of a Non-Aqueous Electrolyte Secondary Battery] Insulating plates were placed on the top and bottom of the fabricated electrode assembly, and the electrode assembly was housed inside an outer can. A cylindrical steel can with a diameter of 21 mm and a height of 70 mm was used as the outer can. The negative electrode tab was welded to the bottom of the outer can, and the positive electrode tab was welded to a sealing member. The contact portion of the outer peripheral surface of the electrode assembly 14 was in contact with the inner surface of the outer can. After injecting a non-aqueous electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket, thereby fabricating a non-aqueous electrolyte secondary battery.

[0057] A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that the positive electrode tab was joined to an area not extending beyond the widthwise center of the positive electrode, and the negative electrode tab was joined to an area not extending beyond the widthwise center of the negative electrode. In this case, the gap between the positive electrode tab and the negative electrode tab overlapped the axial center of the electrode assembly, and was formed over a range of 45% to 55% of the axial length of the electrode assembly from the upper end (lower end) of the electrode assembly.

[0058] [Crash Test] The fabricated nonaqueous electrolyte secondary batteries were charged to 50% SOC at a constant current of 0.3 C in an environment of 25°C. Next, a test was conducted in accordance with the T6 crash test under UN transportation test conditions. Specifically, a metal round bar with a diameter of 15.8 mm was placed at the axial center of the nonaqueous electrolyte secondary battery, and a 9.1 kg weight was dropped from a height of 70 cm. The nonaqueous electrolyte secondary battery was then disassembled, and the presence or absence of damage to the electrode assembly was confirmed. Those without damage were judged to be OK. Ten nonaqueous electrolyte secondary batteries of the examples and comparative examples were tested, and the number of batteries judged to be OK was used for evaluation. The weight drop height specified in the T6 crash test was 61 cm.

[0059] As a result, 10 out of 10 nonaqueous electrolyte secondary batteries of the example were OK, whereas 6 out of 10 nonaqueous electrolyte secondary batteries of the comparative example were OK. From these results, it can be said that by shifting the gap between the positive electrode tab and the negative electrode tab from the axial center of the electrode body and arranging the positive electrode tab or the negative electrode tab in the axial center of the electrode body, the strength of the axial center side of the electrode body can be increased and deformation of the axial center side of the battery due to an external load can be suppressed.

[0060] The present disclosure will be further described by the following embodiments. Configuration 1: A nonaqueous electrolyte secondary battery including an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound in the longitudinal direction with a separator interposed therebetween, and a bottomed cylindrical outer can that houses the electrode assembly, wherein the positive electrode has a positive electrode current collector exposed portion where a positive electrode mixture layer is not disposed and the positive electrode current collector is exposed, the negative electrode has a negative electrode current collector exposed portion where a negative electrode mixture layer is not disposed and the negative electrode current collector is exposed, a positive electrode tab protruding from one end of both axial ends of the electrode assembly is joined to the positive electrode current collector exposed portion, and a negative electrode tab protruding from the other end of each axial end of the electrode assembly is joined to the protruding portion, the negative electrode current collector exposed portion being provided in a region of the negative electrode that at least partially overlaps in the width direction of the negative electrode with a facing region of the negative electrode that faces the positive electrode current collector exposed portion across the separator, the positive electrode tab and the negative electrode tab being provided with a gap in the axial direction of the electrode assembly when viewed in the radial direction of the electrode assembly, and the gap being located at a position that does not overlap with the axial center of the electrode assembly. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein the gap is provided within a range of 20% or more and less than 50% of the axial length of the electrode assembly from both axial end portions of the electrode assembly. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein a region of the positive electrode that faces the negative electrode current collector exposed portion across the separator is covered with an insulating member. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the positive electrode current collector exposed portion is provided across the width direction of the positive electrode, and the negative electrode current collector exposed portion is provided across the width direction of the negative electrode.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the positive electrode current collector exposed portion is in contact with only one of both width direction end portions of the positive electrode, and the negative electrode current collector exposed portion is in contact with only the other width direction end portion of the negative electrode.

[0061] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 11A upper end, 11B lower end, 12 negative electrode, 12A upper end, 12B lower end, 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode tab, 21 negative electrode tab, 22 grooved portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket, 30 positive electrode current collector, 31 positive electrode mixture layer, 32 positive electrode current collector exposed portion, 33 first positive electrode current collector exposed portion, 35 second positive electrode current collector exposed portion, 37 third positive electrode current collector exposed portion, 40 negative electrode current collector, 41 negative electrode mixture layer, 42 negative electrode current collector exposed portion, 43 contact portion, 50 Insulating materials

Claims

1. A nonaqueous electrolyte secondary battery comprising: an electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound lengthwise with a separator interposed therebetween; and a bottomed cylindrical outer can that houses the electrode assembly, wherein the positive electrode has a positive electrode current collector exposed portion where a positive electrode mixture layer is not disposed and the positive electrode current collector is exposed, the negative electrode has a negative electrode current collector exposed portion where a negative electrode mixture layer is not disposed and the negative electrode current collector is exposed, a positive electrode tab protruding from one end of both axial ends of the electrode assembly is joined to the positive electrode current collector exposed portion, and a negative electrode tab protruding from the other end of both axial ends of the electrode assembly is joined to the negative electrode current collector exposed portion, the negative electrode current collector exposed portion is provided in a region of the negative electrode that at least partially overlaps with a region of the negative electrode that faces the positive electrode current collector exposed portion with the separator interposed therebetween, and the positive electrode tab and the negative electrode tab are provided with a gap in the axial direction of the electrode assembly when viewed in the radial direction of the electrode assembly, the gap is disposed at a position that does not overlap with the axial center of the electrode assembly.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the gap is provided within a range of 20% or more and less than 50% of the axial length of the electrode body from both axial ends of the electrode body.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein a region of said positive electrode facing said exposed portion of said negative electrode current collector with said separator interposed therebetween is covered with an insulating member.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode current collector exposed portion is provided across the width of the positive electrode, and the negative electrode current collector exposed portion is provided across the width of the negative electrode.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode current collector exposed portion contacts only one of both widthwise end portions of the positive electrode, and the negative electrode current collector exposed portion contacts only the other widthwise end portion of the negative electrode.

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