Non-aqueous electrolyte secondary battery

Abstract

A negative electrode (12) has a non-facing part (43) wound in a state of not facing a positive electrode (11) across a separator on the winding start side of an electrode body (14). The non-facing part (43) has a first mixture layer formation part (44), a first mixture layer non-formation part (45), a second mixture layer formation part (46), and a second mixture layer non-formation part (47) in the stated order from a winding end (43Y) of the non-facing part (43) to the winding start side. The second mixture layer non-formation part (47) has a lead connection part (48) in which a negative electrode lead (21) is joined to at least one surface of the negative electrode core body (40). A reinforcement layer (50) is positioned on the surface of the lead connection part (48), the reinforcement layer (50) being positioned straddling a winding start end (46X) of the second mixture layer formation part (46). The first mixture layer non-formation part (45) includes an exposed region (49) in which both surfaces of the negative electrode core body (40) are not covered by the reinforcement layer (50) and both surfaces of the negative electrode core body (40) are exposed.

Description

Nonaqueous electrolyte secondary battery

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

[0002] Conventionally, nonaqueous 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 a bottomed cylindrical outer can that houses the electrode assembly (see, for example, Patent Document 1). The negative electrode in Patent Document 1 has a mixture layer forming portion in which a negative electrode mixture layer is formed on at least one surface of a negative electrode core from a position facing the winding start end of the positive electrode, with the separator interposed, toward the winding start side of the electrode assembly. In addition, an exposed region in which both surfaces of the negative electrode core are exposed is formed in a longitudinal intermediate portion of the mixture layer forming portion.

[0003] International Publication No. 2023 / 145674

[0004] As the capacity of non-aqueous electrolyte secondary batteries has increased in recent years, the volume change of the negative electrode during charge and discharge has become larger. As a result of studies by the present inventors, it has become clear that with the technology disclosed in Patent Document 1, when the volume change of the negative electrode during charge and discharge becomes large, the negative electrode is more likely to deform near the winding start end of the positive electrode. Deformation of the negative electrode near the winding start end of the positive electrode may cause an internal short circuit.

[0005] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes 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 negative electrode has a non-facing portion at the winding start side of the electrode assembly where the negative electrode is wound so as not to face the positive electrode with the separator interposed therebetween, and the non-facing portion is formed, in order from the winding end end of the non-facing portion toward the winding start side, with a first mixture layer forming portion in which a negative electrode mixture layer is formed on at least one surface of a negative electrode core, and a first mixture layer non-forming portion in which a negative electrode mixture layer is not formed on both surfaces of the negative electrode core. a negative electrode mixture layer forming portion, a second mixture layer forming portion in which a negative electrode mixture layer is formed on at least one surface of the negative electrode core, and a second mixture layer non-forming portion in which a negative electrode mixture layer is not formed on either surface of the negative electrode core, the second mixture layer non-forming portion having a lead connection portion to which a negative electrode lead is joined on at least one surface of the negative electrode core, a reinforcing layer being disposed on the surface of the lead connection portion, the reinforcing layer being disposed so as to straddle the winding start end of the second mixture layer forming portion, and the first mixture layer non-forming portion including an exposed region in which both surfaces of the negative electrode core are exposed without being covered by the reinforcing layer.

[0006] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, deformation of the negative electrode near the winding start end of the positive electrode can be suppressed, and as a result, the occurrence of an internal short circuit can be suppressed.

[0007] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment; Fig. 2 is a diagram showing a portion of a radial cross-section of an electrode body according to an embodiment; Fig. 3 is a plan view of the winding start side of the outer surface of a roll in a state in which a positive electrode and a negative electrode according to an embodiment are unfolded; Fig. 4 is a plan view of the winding start side of the outer surface of a roll in a state in which a positive electrode and a negative electrode of a nonaqueous electrolyte secondary battery according to a comparative example are unfolded.

[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. Note that the nonaqueous electrolyte secondary battery according to the present disclosure is not limited to the embodiment described below.

[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 an electrode assembly 14 in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween, and a cylindrical outer can 16 with a bottom that houses the electrode assembly 14. The nonaqueous electrolyte secondary battery 10 also includes a nonaqueous electrolyte housed in the outer can 16, and a sealing member 17 that closes the opening of the outer can 16. Hereinafter, for convenience of explanation, the sealing member 17 side of the nonaqueous electrolyte secondary battery 10 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 non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0011] 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

[0012] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0013] The electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long strips that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the length direction and width direction than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0014] The positive electrode 11 has a long positive electrode core 30 and a positive electrode mixture layer 31 disposed on the positive electrode core 30. The positive electrode core 30 can be a foil of a metal that is stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film with such a metal disposed on the surface layer. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode core 30. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, or the like is used as the positive electrode active material.

[0015] The thickness of the positive electrode 11 is, for example, 160 μm or more and 220 μm or less. In this embodiment, the thickness of the positive electrode 11 is substantially constant except for the core exposed portion to which the positive electrode lead 20 is connected. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The thickness of the positive electrode mixture layer 31 is, for example, 70 μm or more and 100 μm or less on one side of the positive electrode core 30. The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 31 on both sides of the positive electrode core 30.

[0016] The negative electrode 12 has a long negative electrode core 40 and a negative electrode mixture layer 41 disposed on the negative electrode core 40. The negative electrode core 40 can be made of a foil of a metal that is stable within the potential range of the negative electrode 12, such as copper, a copper alloy, stainless steel, nickel, or a nickel alloy, or a film having such a metal disposed on its surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and is preferably formed on both sides of the negative electrode core 40.

[0017] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite such as flake graphite, massive graphite, and amorphous graphite, and artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB).

[0018] Furthermore, it is preferable to use a silicon-containing material for the negative electrode active material. Using a silicon-containing material for the negative electrode active material facilitates achieving high capacity. Furthermore, silicon-containing materials undergo a larger volume change during charge and discharge than carbon materials. Therefore, when a silicon-containing material is used for the negative electrode active material, deformation of the negative electrode 12 is likely to occur near the winding start end 11X (see FIG. 2) of the positive electrode 11. In other words, when a silicon-containing material is used for the negative electrode active material, the effect of suppressing deformation of the negative electrode 12, described below, is significant. The content of the silicon-containing material may be, for example, 3% by mass or more and 30% by mass or less, or 5% by mass or more and 25% by mass or less, of the total mass of the negative electrode active material.

[0019] The silicon-containing material may be any material containing Si, and examples thereof include silicon alloys, silicon compounds, and composite materials containing Si. Among the silicon-containing materials, composite materials containing Si are preferred. A suitable example of a composite material containing Si is SiO ２ Examples of such composite materials include a material in which Si fine particles are dispersed in a silicon dioxide phase, a silicate phase such as lithium silicate, or an amorphous carbon phase. A conductive layer such as a carbon coating may be formed on the particle surface of the composite material.

[0020] The thickness of the negative electrode 12 is, for example, 150 μm or more and 230 μm or less. In the present embodiment, the thickness of the negative electrode 12 is substantially constant except for an outer peripheral exposed portion 42, a first mixture layer non-forming portion 45 (see FIG. 2), and a second mixture layer non-forming portion 47 (see FIG. 2), which will be described later. The thickness of the negative electrode core 40 is, for example, 5 μm or more and 15 μm or less. The thickness of the negative electrode mixture layer 41 is, for example, 70 μm or more and 110 μm or less on one side of the negative electrode core 40. The negative electrode 12 can be produced, similar to the positive electrode 11, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0021] The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 and a negative electrode lead 21 connected to the negative electrode 12. In this embodiment, a core exposed portion where the positive electrode mixture layer 31 is not present and the surface of the positive electrode core 30 is exposed is formed in the center of the positive electrode 11 in the longitudinal direction, and the positive electrode lead 20 is connected to this core exposed portion. In addition, the negative electrode lead 21 is connected to one end of the negative electrode 12 in the longitudinal direction, which is located at the start side of winding of the electrode body 14.

[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 lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 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 lead 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 lead 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] The negative electrode 12 is disposed on the outermost peripheral surface of the electrode assembly 14, and an outer peripheral exposed portion 42 is provided where the surface of the negative electrode core 40 is exposed. At least a portion of the outer peripheral exposed portion 42 abuts against the inner peripheral surface of the outer can 16. By abutting the outer peripheral exposed portion 42 against the inner peripheral surface of the outer can 16, both longitudinal ends of the negative electrode 12 and the outer can 16 are electrically connected, ensuring good current collection. The outer peripheral exposed portion 42 may be provided on a portion of the outermost peripheral surface of the electrode assembly 14, but is preferably provided over the entire outermost peripheral surface of the electrode assembly 14. A separator 13 may be disposed on the outermost peripheral surface of the electrode assembly 14.

[0024] The outer can 16 is a cylindrical metal container with a bottom. A gasket 28 is provided between the outer can 16 and the sealing body 17, sealing the inside of the battery. The outer can 16 has a groove 22 formed, for example, by pressing the side surface from the outside. The groove 22 is preferably formed in an annular shape along the circumferential direction of the outer can 16, and supports the sealing body 17 on its top surface. The upper end of the outer can 16 is bent inward and crimped to the periphery of 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 component constituting the sealing body 17 has, for example, a disk or ring shape, and all components except for the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective radial centers, with the insulating member 25 interposed between their respective peripheral edges. When abnormal heat generation causes an increase in the internal pressure of the battery, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27. This interrupts 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 ruptures, and gas is discharged from the opening of the cap 27.

[0026] The electrode assembly 14 will be described in detail below with reference to Figures 2 and 3. Figure 2 is a radial cross-sectional view of the winding start side of the electrode assembly 14, and Figure 3 is a plan view showing the winding start side of the outer surface of the winding in a state in which the positive electrode 11 and negative electrode 12 are unfolded. Note that in Figure 2, the separator 13, positive electrode core 30, and positive electrode mixture layer 31 are omitted for clarity.

[0027] 2 and 3 , the negative electrode 12 constituting the electrode assembly 14 has a non-facing portion 43 at the winding start side of the electrode assembly 14 where the negative electrode 12 is wound without facing the positive electrode 11 via the separator 13. In other words, the negative electrode 12 extends toward the winding start side of the electrode assembly 14 beyond the position where it faces the winding start end 11X of the positive electrode 11 via the separator 13.

[0028] The non-facing portion 43 has a first mixture layer forming portion 44 in which the negative electrode mixture layer 41 is formed on at least one surface of the negative electrode core 40, extending from the winding end 43Y of the non-facing portion 43 toward the winding start side. The non-facing portion 43 also has a first mixture layer non-forming portion 45 in which the negative electrode mixture layer 41 is not formed on either surface of the negative electrode core 40, extending from the winding start end 44X of the first mixture layer forming portion 44 toward the winding start side. The non-facing portion 43 also has a second mixture layer forming portion 46 in which the negative electrode mixture layer 41 is formed on at least one surface of the negative electrode core 40, extending from the winding start end 45X of the first mixture layer non-forming portion 45 toward the winding start side. The non-facing portion 43 also has a second mixture layer non-forming portion 47 in which the negative electrode mixture layer 41 is not formed on either surface of the negative electrode core 40, extending from the winding start end 46X of the second mixture layer forming portion 46 toward the winding start side. In other words, the non-opposing portion 43 has, in order from the winding end 43Y of the non-opposing portion 43 toward the winding start side, a first mixture layer forming portion 44, a first mixture layer non-forming portion 45, a second mixture layer forming portion 46, and a second mixture layer non-forming portion 47.

[0029] In the present embodiment, the first mixture layer forming portion 44 and the second mixture layer forming portion 46 have the negative electrode mixture layer 41 formed on both sides of the negative electrode core 40. This can further increase the rigidity of the first mixture layer forming portion 44 and the second mixture layer forming portion 46, making it easier to achieve the effects of the present disclosure described below. Note that at least one of the first mixture layer forming portion 44 and the second mixture layer forming portion 46 may have the negative electrode mixture layer 41 formed on one side of the negative electrode core 40.

[0030] The portion 47 without the second mixture layer has a lead connection portion 48 to which the negative electrode lead 21 is joined on at least one surface of the negative electrode core 40. In the present embodiment, the negative electrode lead 21 is joined to the outer winding surface of the portion 47 without the second mixture layer. Note that the negative electrode lead 21 may also be joined to the inner winding surface of the portion 47 without the second mixture layer.

[0031] 2 and 3 , a reinforcing layer 50 is disposed on at least one surface of the lead connection portion 48. The reinforcing layer 50 has, for example, a rectangular shape in a plan view. The thickness of the reinforcing layer 50 is, for example, 10 μm or more and 70 μm or less, and preferably 20 μm or more and 60 μm or less. By disposing the reinforcing layer 50, the rigidity of the region of the negative electrode 12 where the reinforcing layer 50 is disposed can be improved.

[0032] The reinforcing layer 50 is preferably a flexible insulating material. An example of the reinforcing layer 50 is insulating tape, which is attached to at least the surface of the lead connection portion 48. The insulating tape includes, for example, a base layer and an adhesive layer formed on one surface of the base layer. A layer containing inorganic particles such as metal oxide may be provided between the base layer and the adhesive layer. The base layer may be made of any insulating resin, such as polypropylene (PP), polyethylene terephthalate (PET), polyimide (PI), polyphenylene sulfide (PPS), or polyamide (PA). These resins may be used alone or in combination of two or more. The thickness of the base layer is, for example, 5 μm or more and 50 μm or less, preferably 10 μm or more and 30 μm or less.

[0033] The adhesive layer is a portion for adhering the insulating tape serving as the reinforcing layer 50 to the surface of the lead connection portion 48 or the like. The adhesive layer contains, for example, 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, allowing the insulating tape to adhere to the surface of the lead connection portion 48 or the like. The adhesive layer may further contain a silicone-based polymer. The thickness of the adhesive layer is, for example, 1 μm or more and 30 μm or less, and preferably 5 μm or more and 25 μm or less.

[0034] The reinforcing layer 50 is not limited to the insulating tape described above. The reinforcing layer 50 may be, for example, a coating layer formed by applying a resin solution to the surface of the lead connection portion 48 or the like and drying the coating. Examples of resin materials contained in the coating layer include synthetic resins such as epoxy resin, melamine resin, phenolic resin, polyolefin resin, and polyimide resin. These resins may be used alone or in combination of two or more.

[0035] Here, the reinforcing layer 50 is disposed so as to straddle the winding start end 46X of the second mixture layer forming portion 46. In other words, in the region of the second mixture layer not forming portion 47 that is closer to the winding end side than the lead connection portion 48, there is no region in which both surfaces of the negative electrode core 40 are exposed across the width direction of the second mixture layer not forming portion 47.

[0036] Furthermore, the reinforcing layer 50 is arranged so as not to straddle the winding start end 44X of the first mixture layer forming portion 44. As a result, in the first mixture layer non-forming portion 45, both surfaces of the negative electrode core 40 are not covered with the reinforcing layer 50 across the width direction of the first mixture layer non-forming portion 45, and an exposed region 49 is formed in which both surfaces of the negative electrode core 40 are exposed.

[0037] 2 , there is a gap near winding start end 11X of positive electrode 11 that is not occupied by negative electrode 12 and separator 13. Therefore, when the volume of positive electrode 11 and negative electrode 12 changes due to repeated charge and discharge, stress concentration occurs near winding start end 11X of positive electrode 11, making negative electrode 12 particularly prone to bending and deformation.

[0038] In the present embodiment, when the reinforcing layer 50 is disposed on the winding start side of the negative electrode 12 and an exposed region 49 in which both surfaces of the negative electrode core 40 are exposed is provided between the first mixture layer forming portion 44 and the second mixture layer forming portion 46, the exposed region 49 deforms preferentially when volume changes occur in the positive electrode 11 and the negative electrode 12 during repeated charge and discharge. This is because the exposed region 49 has no negative electrode mixture layer 41 or reinforcing layer 50 disposed on its surface and is therefore less rigid than the surrounding areas. The preferential deformation of the exposed region 49, which has the lowest rigidity among the non-facing portions 43, alleviates stress concentration near the winding start end 11X of the positive electrode 11, thereby suppressing deformation of the negative electrode 12 near the winding start end 11X of the positive electrode 11. As a result, the occurrence of an internal short circuit can be suppressed.

[0039] As described above, the exposed region 49 is provided in the non-facing portion 43 that does not face the positive electrode 11 via the separator 13. Therefore, even if the exposed region 49 is deformed, an internal short circuit due to the deformation of the exposed region 49 does not occur.

[0040] When the reinforcing layer 50 is positioned so as not to straddle the winding start end 46X of the second mixture layer forming portion 46, the exposed region 49 tends to be less likely to deform preferentially when volume changes occur in the positive electrode 11 and the negative electrode 12 due to repeated charge and discharge. When the reinforcing layer 50 is positioned so as not to straddle the winding start end 46X of the second mixture layer forming portion 46, a region in which both surfaces of the negative electrode core 40 are exposed across the width of the second mixture layer non-forming portion 47 is formed in a region of the second mixture layer non-forming portion 47 closer to the winding end than the lead connection portion 48. Like the exposed region 49, this region has a lower rigidity than the surrounding area because the negative electrode mixture layer 41 and the reinforcing layer 50 are not disposed on the surface. Although the detailed mechanism is unclear, if a region with lower rigidity than the surrounding area is formed between the lead connection portion 48 and the second mixture layer forming portion 46 in addition to the exposed region 49, the stress that deforms the exposed region 49 is dispersed, and the exposed region 49 is less likely to deform preferentially. If exposed region 49 does not deform, stress concentration near winding start end 11X of positive electrode 11 will not be alleviated, resulting in deformation of negative electrode 12 near winding start end 11X of positive electrode 11. Therefore, in order to preferentially deform exposed region 49, reinforcing layer 50 needs to be disposed so as to straddle winding start end 46X of second mixture layer forming portion 46.

[0041] In this embodiment, the reinforcing layer 50 is not disposed on the surface of the first mixture layer non-forming portion 45. That is, the entire area of ​​the first mixture layer non-forming portion 45 corresponds to the exposed region 49. If the reinforcing layer 50 is not disposed on the surface of the first mixture layer non-forming portion 45 and the winding end of the reinforcing layer 50 is disposed in a position overlapping with the second mixture layer forming portion 46, the exposed region 49 becomes more likely to deform.

[0042] The length of exposed region 49 is preferably 1 mm or more, and more preferably 2 mm or more, in the longitudinal direction of negative electrode 12. By making the length of exposed region 49 1 mm or more, the amount of deformation of exposed region 49 can be increased, and stress concentration near winding start end 11X of positive electrode 11 can be further alleviated. As a result, the occurrence of an internal short circuit due to deformation of negative electrode 12 near winding start end 11X of positive electrode 11 can be further suppressed.

[0043] Furthermore, exposed region 49 is preferably wound 0.5 turns or less, and more preferably 0.45 turns or less. When exposed region 49 is wound 0.5 turns or less, when charge and discharge are repeated and volume changes occur in positive electrode 11 and negative electrode 12, exposed region 49 tends to deform preferentially. In other words, when exposed region 49 is wound more than 0.5 turns, stress applied to exposed region 49 is dispersed, and exposed region 49 may become less likely to deform.

[0044] In the non-facing portion 43, the region where the first mixture layer forming portion 44, the first mixture layer non-forming portion 45, and the second mixture layer forming portion 46 are arranged is preferably wound a total of 0.5 turns or more, more preferably 0.75 turns or more. In this case, the shape of the winding core portion can be easily maintained, and in the event of abnormal heat generation in the battery, gas generated inside the battery can be easily vented to the outside of the battery via the winding core portion.

[0045] Furthermore, the region of the non-facing portion 43 where the first mixture layer forming portion 44, the first mixture layer non-forming portion 45, and the second mixture layer forming portion 46 are arranged is preferably wound a total of 2.0 turns or less, more preferably 1.75 turns or less. The regions where the first mixture layer forming portion 44, the first mixture layer non-forming portion 45, and the second mixture layer forming portion 46 are arranged are regions where no charge / discharge reaction occurs. Therefore, when the region of the non-facing portion 43 where the first mixture layer forming portion 44, the first mixture layer non-forming portion 45, and the second mixture layer forming portion 46 are arranged is wound a total of 2.0 turns or less, the energy density of the non-aqueous electrolyte secondary battery 10 can be increased. Therefore, it is preferable that the area of ​​the non-facing portion 43 in which the first mixture layer forming portion 44, the first mixture layer non-forming portion 45, and the second mixture layer forming portion 46 are arranged is wound a total of 0.5 to 2.0 revolutions, and it is more preferable that it is wound a total of 0.75 to 1.75 revolutions.

[0046] 2 and 3 , the reinforcing layer 50 is disposed on the surface of the negative electrode 12 to which the negative electrode lead 21 is bonded (outer winding surface) and is disposed so as to cover the surface of the negative electrode lead 21, but the arrangement of the reinforcing layer 50 is not limited to this. The reinforcing layer 50 may also be disposed on the surface of the negative electrode 12 opposite to the surface to which the negative electrode lead 21 is bonded (outer winding surface). In this case, the reinforcing layer 50 is not disposed on the surface of the negative electrode lead 21. Alternatively, the reinforcing layer 50 may be disposed on both surfaces of the negative electrode 12.

[0047] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0048] <Examples> [Fabrication of Positive Electrode] Aluminum-containing lithium nickel cobalt oxide (LiNi) was used as the positive electrode active material. ０．８８ Co ０．０９ Al ０．０３ O ２) was used. 100 parts by mass of this positive electrode active material, 1 part by mass of acetylene black (AB) as a conductive additive, and 0.9 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. This positive electrode mixture slurry was uniformly applied to both sides of a positive electrode core made of aluminum foil with a thickness of 15 μm. At this time, an exposed core portion for attaching a positive electrode lead was provided. Next, heat treatment was performed in a heated dryer to remove the NMP, and then compressed using a roll press. The compressed positive electrode was then brought into contact with a heated roll and heat treated, and cut to a thickness of 0.179 mm, a width of 62.6 mm, and a length of 703 mm to prepare a positive electrode. An aluminum positive electrode lead was then attached to the exposed core portion of the positive electrode.

[0049] [Preparation of Negative Electrode] A mixture of 95 parts by mass of graphite and 5 parts by mass of silicon oxide was used as the negative electrode active material. 100 parts by mass of this negative electrode active material was mixed with 1 part by mass of carboxymethyl cellulose (CMC) as a thickener and 1 part by mass of styrene-butadiene rubber (SBR) as a binder, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to both sides of a negative electrode core made of copper foil with a thickness of 8 μm to form a negative electrode mixture layer as shown in FIG.

[0050] Next, the negative electrode mixture layer was dried, and then compressed with a compression roller so that the negative electrode thickness was 0.192 mm, and cut to a width of 64 mm and a length of 816 mm to prepare a negative electrode. Then, a nickel-copper negative electrode lead was attached to the portion of the negative electrode where the second mixture layer was not formed. Then, a 30 μm thick insulating tape containing polyimide (PI) as a substrate layer was attached as a reinforcing layer so as to cover the negative electrode lead. At this time, the insulating tape was attached so as to straddle the winding start end of the portion where the second mixture layer was formed, and was attached so as not to cover the portion where the first mixture layer was not formed. In other words, both surfaces of the negative electrode core were exposed throughout the entire area of ​​the portion where the first mixture layer was not formed.

[0051] [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, to prepare a non-aqueous electrolyte solution containing lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / L of ammonium hydroxide in water.

[0052] [Fabrication of a Non-Aqueous Electrolyte Secondary Battery] A wound electrode assembly was fabricated by winding a positive electrode and a negative electrode with a polyethylene separator interposed therebetween. The first mixture layer-forming portion was wound 0.4 turns, the first mixture layer-non-forming portion was wound 0.4 turns, and the second mixture layer-forming portion was wound 0.6 turns. An outer peripheral exposed portion, in which the surface of the negative electrode core was exposed, was disposed on the outermost peripheral surface of the electrode assembly 14. Insulating plates were placed above and below the electrode assembly, and the electrode assembly was housed in an outer can. The negative electrode lead was welded to the bottom of a cylindrical outer can with a bottom, and the positive electrode lead was welded to a sealing member. After the non-aqueous electrolyte was poured into the outer can, the opening of the outer can was sealed with a sealing member via a gasket to fabricate a non-aqueous electrolyte secondary battery.

[0053] [Evaluation of Deformation of Negative Electrode After Cycle Testing] The fabricated nonaqueous electrolyte secondary battery was charged at a constant current of 0.3 It in a 45°C environment until it reached 4.2 V, then subjected to constant voltage charging with a cut-off current of 0.02 It at 4.2 V, followed by a 20-minute pause, followed by constant current discharge at a discharge current of 1 It, followed by a 20-minute pause. This charge-discharge cycle was repeated 500 times. Then, for the nonaqueous electrolyte secondary battery after 500 cycles, the vicinity of the winding start side of the electrode body was observed using an X-ray CT device (Shimadzu Corporation, SMX-225CT FPD HR) to confirm the presence or absence of deformation of the negative electrode near the winding start end of the positive electrode.

[0054] Comparative Example A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, and the presence or absence of deformation of the negative electrode was confirmed, except that in fabricating the negative electrode, an insulating tape serving as a reinforcing layer was attached so as not to straddle the winding start end of the second mixture layer-forming portion, as shown in Fig. 4. That is, in the nonaqueous electrolyte secondary battery of the comparative example, a region in which both surfaces of the negative electrode core were exposed across the width direction was formed in a region of the second mixture layer-not-forming portion closer to the winding end side than the lead connection portion.

[0055] Table 1 shows the evaluation results of the nonaqueous electrolyte secondary batteries of Examples and Comparative Examples.

[0056]

[0057] As shown in Table 1, in the nonaqueous electrolyte secondary batteries of the examples, no deformation of the negative electrode occurred near the winding start end of the positive electrode. On the other hand, in the nonaqueous electrolyte secondary batteries of the comparative examples, deformation of the negative electrode occurred near the winding start end of the positive electrode. Therefore, it can be said that by disposing a reinforcing layer on the winding start side of the negative electrode and providing an exposed region in which both surfaces of the negative electrode core are exposed between the first mixture layer forming portion and the second mixture layer forming portion, deformation of the negative electrode near the winding start end of the positive electrode can be suppressed.

[0058] The present disclosure will be further described by the following embodiments. Configuration 1: An electrode assembly including a strip-shaped positive electrode and a strip-shaped negative electrode wound lengthwise with a separator interposed therebetween, and a bottomed cylindrical outer can that houses the electrode assembly, wherein the negative electrode has a non-facing portion wound at the winding start side of the electrode assembly in a state where it does not face the positive electrode with the separator interposed therebetween, and the non-facing portion includes, in order from the winding end end of the non-facing portion toward the winding start side, a first mixture layer formed portion in which a negative electrode mixture layer is formed on at least one surface of a negative electrode core, a first mixture layer non-formed portion in which the negative electrode mixture layer is not formed on both sides of the negative electrode core, and a first mixture layer non-formed portion in which the negative electrode mixture layer is not formed on at least one surface of the negative electrode core. a second mixture layer-forming portion having the negative electrode mixture layer formed on one surface thereof, and a second mixture layer-non-forming portion having the negative electrode mixture layer not formed on either surface of the negative electrode core, the second mixture layer-non-forming portion having a lead connection portion to which a negative electrode lead is joined on at least one surface of the negative electrode core, a reinforcing layer being disposed on the surface of the lead connection portion, the reinforcing layer being disposed so as to straddle a winding start end of the second mixture layer-forming portion, and the first mixture layer-non-forming portion including an exposed region in which both surfaces of the negative electrode core are exposed, whereby both surfaces of the negative electrode core are not covered by the reinforcing layer. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein the length of the exposed region in the longitudinal direction of the negative electrode is 1 mm or more. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein the exposed region is wound 0.5 turns or less. Configuration 4: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the region of the non-facing portion where the first mixture layer forming portion, the first mixture layer non-forming portion, and the second mixture layer forming portion are arranged is wound a total of 0.5 to 2.0 turns. Configuration 5: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the winding end of the reinforcing layer is arranged at a position overlapping the second mixture layer forming portion. Configuration 6: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the second mixture layer forming portion has the negative electrode mixture layer formed on both sides of the negative electrode core. Configuration 7: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the reinforcing layer is an insulating tape.Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material.

[0059] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 11X winding start end, 12 negative electrode, 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18 insulating plate, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 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 core, 31 positive electrode mixture layer, 40 negative electrode core, 41 negative electrode mixture layer, 42 outer periphery exposed portion, 43 non-facing portion, 43Y winding end end, 44 first mixture layer formed portion, 44X winding start end, 45 first mixture layer non-formed portion, 45X winding start end, 46 second mixture layer formed portion, 46X winding start end, 47 Second mixture layer non-forming portion, 48 lead connection portion, 49 exposed region, 50 reinforcing layer.

Claims

1. An electrode assembly comprising a strip-shaped positive electrode and a strip-shaped negative electrode wound lengthwise with a separator interposed therebetween; and a bottomed cylindrical outer can accommodating the electrode assembly, wherein the negative electrode has a non-facing portion wound at the winding start side of the electrode assembly so as not to face the positive electrode with the separator interposed therebetween, and the non-facing portion has, in order from the winding end of the non-facing portion toward the winding start side, a first mixture layer-formed portion in which a negative electrode mixture layer is formed on at least one surface of the negative electrode core, a first mixture layer-non-formed portion in which the negative electrode mixture layer is not formed on either surface of the negative electrode core, a second mixture layer-formed portion in which the negative electrode mixture layer is formed on at least one surface of the negative electrode core, and a second mixture layer-non-formed portion in which the negative electrode mixture layer is not formed on either surface of the negative electrode core, and the second mixture layer-non-formed portion has a lead connection portion to which a negative electrode lead is joined to at least one surface of the negative electrode core, and a reinforcing layer is arranged on the surface of the lead connection portion, the reinforcing layer is disposed so as to straddle a winding start end of the second material mixture layer-forming portion, and the first material mixture layer-not-forming portion includes an exposed region in which both surfaces of the negative electrode core are not covered with the reinforcing layer and both surfaces of the negative electrode core are exposed.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the length of the exposed region in the longitudinal direction of the negative electrode is 1 mm or more.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the exposed region is wound 0.5 turns or less.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the region of the non-facing portion where the first mixture layer forming portion, the first mixture layer non-forming portion, and the second mixture layer forming portion are arranged is wound a total of 0.5 to 2.0 turns.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the winding end of the reinforcing layer is positioned so as to overlap the second mixture layer forming portion.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the second mixture layer forming portion has the negative electrode mixture layer formed on both sides of the negative electrode core.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the reinforcing layer is an insulating tape.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material.

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