Nonaqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery having excellent safety when subjected to an impact from the outside. A non-aqueous electrolyte secondary battery according to one aspect of the present invention is provided with: an electrode body in which a belt-shaped positive electrode and a belt-shaped negative electrode are wound with a separator interposed therebetween; a non-aqueous electrolyte; and an outer case that houses the electrode body and the non-aqueous electrolyte, in which the positive electrode has a positive electrode current collector and positive electrode mixture layers formed on both surfaces of the positive electrode current collector, and the positive electrode has, in the vicinity of the winding inner end portion, a wedge-shaped portion that becomes thinner toward the winding inner end portion from the surface of the positive electrode mixture layer on one side to the positive electrode current collector.

Description

Technical Field

[0001] The present invention relates to a nonaqueous electrolyte secondary battery. Background Art

[0002] A non-aqueous electrolyte secondary battery having a wound electrode body formed by winding a positive electrode and a negative electrode (electrode) with a separator interposed therebetween is widely used. Patent Documents 1 and 2 disclose the following technology: by making the inner end of the wound inner side of the electrode mixture layer thin-walled, peeling of the mixture layer and breaking of the electrode are prevented near the winding axis of the electrode body having a small curvature radius of the electrode.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-134916

[0006] Patent Document 2: Japanese Patent Application Publication No. 2011-198483 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] In recent years, the high capacity and high output of non-aqueous electrolyte secondary batteries used in electric vehicles, power storage devices, etc. have been continuously developed. Due to the high capacity and high output of the battery, the heat generated when the battery has an internal short circuit becomes larger, and it is required to reduce the risk of internal short circuit. The inventors have conducted in-depth research and found that when the battery is deformed due to an impact from the outside, there is a possibility that the inner end of the winding of the positive electrode breaks the separator and an internal short circuit occurs at the broken part. In the technology described in Patent Documents 1 and 2, there is no research on the impact of the battery under the impact from the outside, and there is room for improvement.

[0009] An object of the present invention is to provide a nonaqueous electrolyte secondary battery having excellent safety when subjected to external impact.

[0010] A technical solution of the present invention provides a non-aqueous electrolyte secondary battery, comprising: an electrode body, which is formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator in between; a non-aqueous electrolyte; and an outer shell, which accommodates the electrode body and the non-aqueous electrolyte, and is characterized in that the positive electrode has a positive electrode collector and a positive electrode mixture layer formed on two surfaces of the positive electrode collector, and the positive electrode has a wedge-shaped portion near the inner end of the winding, the wall of which becomes thinner as it approaches the inner end of the winding from the surface of the positive electrode mixture layer on one side to the positive electrode collector.

[0011] According to a secondary battery of one aspect of the present invention, safety can be improved, and in particular, heat generation during an impact test can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is an axial cross-sectional view of a cylindrical secondary battery as an example of an embodiment.

[0013] Figure 2 yes Figure 1 The illustrated secondary battery is a perspective view of a wound electrode assembly.

[0014] Figure 3 It is a front view showing a positive electrode and a negative electrode constituting an electrode body as an example of an embodiment in a developed state. DETAILED DESCRIPTION

[0015] Hereinafter, an example of an embodiment of a cylindrical secondary battery of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for easy understanding of the present invention and can be appropriately changed according to the specifications of the cylindrical secondary battery. In addition, in the following description, when multiple embodiments and variations are included, it is envisaged from the beginning that their characteristic parts can be appropriately combined and used.

[0016] Figure 1 FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 as an example of an embodiment. Figure 1 In the secondary battery 10 shown, the electrode body 14 and the non-aqueous electrolyte (not shown) are accommodated in the outer shell 15. The electrode body 14 has a winding structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound across a separator 13. As a non-aqueous solvent (organic solvent) of a non-aqueous electrolyte, carbonates, lactones, ethers, ketones, esters, etc. can be used, and these solvents can be mixed with two or more. In the case of mixing two or more solvents, a mixed solvent containing cyclic carbonates and chain carbonates is preferably used. For example, as a cyclic carbonate, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used, and as a chain carbonate, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), etc. can be used. As an electrolyte salt of a non-aqueous electrolyte, LiPF6, LiBF4, LiCF3SO3, etc. and their mixtures can be used. The amount of the electrolyte salt dissolved in the nonaqueous solvent can be, for example, 0.5 mol / L to 2.0 mol / L. In the following, for convenience of description, the sealing body 16 side is referred to as "upper" and the bottom side of the outer shell 15 is referred to as "lower".

[0017] The open end of the outer shell 15 is blocked by the sealing body 16, so that the interior of the secondary battery 10 is sealed. An insulating plate 17 and an insulating plate 18 are provided above and below the electrode body 14, respectively. The positive lead 19 extends upward through the through hole of the insulating plate 17 and is welded to the lower surface of the filter 22 which is the bottom plate of the sealing body 16. In the secondary battery 10, the cover 26 which is the top plate of the sealing body 16 and is electrically connected to the filter 22 becomes the positive terminal. On the other hand, the negative lead 20 extends to the bottom side of the outer shell 15 through the through hole of the insulating plate 18 and is welded to the bottom inner surface of the outer shell 15. In the secondary battery 10, the outer shell 15 becomes the negative terminal. In addition, when the negative lead 20 is provided at the outer end of the winding, the negative lead 20 extends to the bottom side of the outer shell 15 through the outside of the insulating plate 18 and is welded to the bottom inner surface of the outer shell 15.

[0018] The outer shell 15 is, for example, a metal outer shell can in a bottomed cylindrical shape. A gasket 27 is provided between the outer shell 15 and the sealing body 16 to ensure the airtightness of the interior of the secondary battery 10. The outer shell 15 has a groove portion 21 formed, for example, by pressurizing the side surface from the outside to support the sealing body 16. The groove portion 21 is preferably formed in an annular shape along the circumference of the outer shell 15, and the sealing body 16 is supported by the upper surface of the groove portion 21.

[0019] The sealing body 16 has a filter 22, a lower valve core 23, an insulating member 24, an upper valve core 25 and a cover 26 stacked in order from the electrode body 14 side. The components constituting the sealing body 16 have, for example, a disc shape or a ring shape, and the components except the insulating member 24 are electrically connected to each other. The lower valve core 23 and the upper valve core 25 are connected to each other at their respective central portions, and the insulating member 24 is interposed between the peripheral portion of the lower valve core 23 and the peripheral portion of the upper valve core 25. When the internal pressure of the battery rises due to abnormal heat, for example, the lower valve core 23 breaks, whereby the upper valve core 25 bulges toward the cover 26 side and leaves the lower valve core 23, thereby cutting off the electrical connection between the two. When the internal pressure rises further, the upper valve core 25 breaks, and the gas is discharged from the opening 26a of the cover 26.

[0020] Next, refer to Figure 2 The electrode body 14 will be described. Figure 2It is a three-dimensional diagram of the electrode body 14. As described above, the electrode body 14 has a winding structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12 and the separator 13 are all formed in a strip shape and are wound in a spiral shape around a winding core arranged along the winding axis 28, thereby being alternately stacked in the radial direction of the electrode body 14. In the radial direction, the side of the winding axis 28 is called the inner peripheral side, and the opposite side is called the outer peripheral side. In the electrode body 14, the long side direction of the positive electrode 11 and the negative electrode 12 becomes the winding direction, and the short side direction of the positive electrode 11 and the negative electrode 12 becomes the axial direction. The positive electrode lead 19 extends axially from the upper end of the electrode body 14, approximately in the center of the radial direction between the center and the outermost periphery. In addition, the negative electrode lead 20 extends axially from the vicinity of the winding axis 28 at the lower end of the electrode body 14.

[0021] For the separator 13, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous membranes, woven fabrics, nonwoven fabrics, etc. As the material of the separator 13, olefin resins such as polyethylene and polypropylene are preferred. The thickness of the separator 13 is, for example, 10 μm to 50 μm. The separator 13 tends to be thinner as the battery has a higher capacity and a higher output.

[0022] The puncture strength of the separator 13 is preferably 0.1N or more. If the puncture strength of the separator 13 is less than 0.1N, there is a case where the separator 13 breaks when the electrode body 14 is wound. The puncture strength of the separator 13 is preferably 15N or less. If the puncture strength of the separator 13 is greater than 15N, the porosity of the separator 13 becomes smaller, and therefore, there is a case where the electrolyte resistance of the secondary battery 10 increases. The puncture strength of the separator 13 may also be greater than 0.5N, or greater than 1N, or greater than 2N, or greater than 3N. In addition, the puncture strength of the separator 13 may also be less than 10N, or less than 8N, or less than 7N, or less than 5N.

[0023] Next, refer to Figure 3 The positive electrode 11 and the negative electrode 12 of this embodiment will be described. Figure 3 FIG. 1 is a front view of the positive electrode 11 and the negative electrode 12 constituting the electrode body 14. Figure 3 In FIG. 1 , the positive electrode 11 and the negative electrode 12 are shown in an unfolded state. Figure 3As illustrated, in the electrode body 14, in order to prevent the precipitation of lithium at the negative electrode 12, the negative electrode 12 is formed larger than the positive electrode 11. Specifically, the length of the short side direction of the negative electrode 12 is larger than the length of the short side direction of the positive electrode 11. In addition, the length of the long side direction of the negative electrode 12 is larger than the length of the long side direction of the positive electrode 11. Therefore, when the electrode body 14 is wound, at least the portion of the positive electrode 11 where the positive electrode mixture layer 32 is formed is arranged opposite to the portion of the negative electrode 12 where the negative electrode mixture layer 42 is formed, with the separator 13 interposed therebetween.

[0024] The negative electrode 12 includes a strip-shaped negative electrode collector 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode collector 40. The negative electrode mixture layer 42 is formed on both the inner and outer sides of the negative electrode collector 40, and is preferably formed on the entire area of ​​both surfaces of the negative electrode collector 40 except for the negative electrode exposed portion 44 described later. For example, a foil of a metal such as copper, a film having the metal disposed on the surface layer, etc. can be used for the negative electrode collector 40. The thickness of the negative electrode collector 40 is, for example, 5 μm to 30 μm.

[0025] The negative electrode mixture layer 42 includes, for example, a negative electrode active material and a binder. The negative electrode mixture layer 42 can be manufactured by, for example, applying a negative electrode mixture slurry including a negative electrode active material, a conductive agent, a binder, and a solvent such as water to both surfaces of the negative electrode current collector 40, drying the slurry, and then rolling the slurry.

[0026] exist Figure 3 In the example shown, a negative electrode exposed portion 44 is provided near the inner end of the winding in the long side direction of the negative electrode 12 over the entire length of the collector in the short side direction. The negative electrode exposed portion 44 is a portion to which the negative electrode lead 20 is connected, and is a portion of the surface of the negative electrode collector 40 that is not covered by the negative electrode mixture layer 42. The negative electrode exposed portion 44 is formed wider than the width of the negative electrode lead 20 in the long side direction. The negative electrode exposed portion 44 is preferably provided on both surfaces of the negative electrode 12 in a manner overlapping in the thickness direction of the negative electrode 12. The negative electrode lead 20 is joined to the negative electrode exposed portion 44 by, for example, ultrasonic welding. When wound into the electrode body 14, the negative electrode lead 20 protrudes downward from the end surface in the short side direction.

[0027] The arrangement position of the negative electrode lead 20 is not limited to Figure 3 In the example shown, the negative electrode lead 20 may be provided only at the outer end of the winding of the negative electrode 12. Alternatively, the negative electrode lead 20 may be provided at both the inner end and the outer end of the winding of the negative electrode 12. In this case, the current collection performance is improved. It is also possible to connect the negative electrode exposed portion 44 at the outer end of the winding of the negative electrode 12 to the outer shell 15 (see Figure 1), so that the wound outer end of the negative electrode 12 is electrically connected to the outer shell 15 without using the negative electrode lead 20 at the wound outer end. The negative electrode exposed portion 44 is provided, for example, by intermittent coating of the negative electrode mixture slurry without coating a part of the negative electrode current collector 40.

[0028] The negative electrode active material contained in the negative electrode mixture layer 42 is not particularly limited as long as it is a material that can reversibly absorb and release Li ions, and carbon materials such as graphite are generally used. Graphite can be any of natural graphites such as flaky graphite, blocky graphite, and earthy graphite, blocky artificial graphite, and artificial graphites such as graphitized mesophase carbon microbeads. In addition, as the negative electrode active material, metals such as Si and Sn that can be alloyed with Li, metal compounds containing Si, Sn, etc., lithium-titanium composite oxides, etc. can also be used. For example, SiO x (x is 0.5 to 1.6) represented by silicon oxide, in the presence of Li 2y SiO (2+y) A silicon-containing material in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2), a silicon-containing material in which fine particles of Si are dispersed in a carbon phase, or the like.

[0029] As the binder included in the negative electrode mixture layer 42, for example, styrene-butadiene rubber (SBR), nitrile rubber (NBR), carboxymethyl cellulose (CMC) or its salt (which may be CMC-Na, CMC-K, CMC-NH4, etc., or a partially neutralized salt), polyacrylic acid (PAA) or its salt (which may be PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0030] The positive electrode 11 has a strip-shaped positive electrode collector 30 and a positive electrode mixture layer 32 formed on the surface of the positive electrode collector 30. The positive electrode mixture layer 32 is formed on both the inner and outer sides of the positive electrode collector 30, and is preferably formed on the entire area of ​​both surfaces of the positive electrode collector 30 except for the positive electrode exposed portion 34 described later. The winding inner end 11a is the end of the positive electrode 11 on the winding axis 28 side in the long side direction, and the winding outer end 11b is the end of the positive electrode 11 on the outer shell 15 side in the long side direction. Figure 3 In the illustrated example, the positive electrode mixture layer 32 is formed on both surfaces of the positive electrode current collector 30 at the winding inner end portion 11 a .

[0031] For example, a foil of a metal such as aluminum, a film having the metal disposed on the surface layer, etc. can be used as the positive electrode current collector 30. The thickness of the positive electrode current collector 30 is, for example, 10 μm to 30 μm.

[0032] The positive electrode mixture layer 32 includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture layer 32 can be manufactured, for example, by applying a positive electrode mixture slurry including a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both surfaces of the positive electrode collector 30 and drying the mixture, followed by rolling.

[0033] The positive electrode 11 is provided with a positive electrode exposed portion 34 formed by exposing the surface of the positive electrode collector 30. The positive electrode exposed portion 34 is a portion to which the positive electrode lead 19 is connected, and is a portion of the surface of the positive electrode collector 30 that is not covered by the positive electrode mixture layer 32. The positive electrode exposed portion 34 is formed wider than the positive electrode lead 19 in the longitudinal direction. The positive electrode exposed portion 34 is preferably provided on both surfaces of the positive electrode 11 in a manner overlapping in the thickness direction of the positive electrode 11. The positive electrode lead 19 is joined to the positive electrode exposed portion 34 by, for example, ultrasonic welding.

[0034] exist Figure 3 In the example shown, a positive electrode exposure portion 34 is provided at approximately the center of the long side direction of the positive electrode 11 over the entire length in the short side direction. The position of the positive electrode exposure portion 34 is not limited to this example. From the viewpoint of current collection, the positive electrode exposure portion 34 is preferably provided at a position where the distance from the winding inner end 11a and the distance from the winding outer end 11b are approximately equal. By connecting the positive electrode lead 19 to the positive electrode exposure portion 34 provided at such a position, the positive electrode lead 19 is arranged to protrude upward from the end surface in the short side direction at approximately the center in the radial direction of the electrode body 14 when the electrode body 14 is wound. The positive electrode exposure portion 34 is provided, for example, by intermittent coating of the positive electrode mixture slurry without coating a part of the positive electrode current collector 30.

[0035] As the positive electrode active material contained in the positive electrode mixture layer 32, lithium transition metal composite oxides containing metal elements such as Ni, Co, and Mn can be exemplified. As the positive electrode active material, NCA-based lithium transition metal composite oxides containing Ni, Co, and Al, NCM-based lithium transition metal composite oxides containing Ni, Co, and Mn, etc. can be exemplified. They can be used alone or in combination. NCA-based lithium transition metal composite oxides are, for example, composed of the general formula Li a Ni b Co c Al d M1 e O2 (0.8≤a≤1.2, 0.6≤b≤0.95, 0.01≤c≤0.2, 0.01≤d≤0.2, 0≤e≤0.1, b+c+d+e=1, M1 is at least one element selected from the group consisting of W, Nb, Mg, Ti and Mo). NCM-based lithium transition metal composite oxides are, for example, represented by the general formula Li f Ni gCo h Mn i M2 j O2 (0.8≤f≤1.2, 0.6≤g≤0.95, 0.01≤h≤0.2, 0.01≤i≤0.2, 0≤j≤0.1, g+h+i+j=1, M2 is at least one element selected from the group consisting of W, Nb, Mg, Ti and Mo).

[0036] Examples of the conductive agent included in the positive electrode mixture layer 32 include carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), graphene, graphite and other carbon particles, etc. These may be used alone or in combination of two or more.

[0037] Examples of the binder included in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyimide-based resins, acrylic resins, polyolefin-based resins, and polyacrylonitrile (PAN). These may be used alone or in combination of two or more.

[0038] The positive electrode 11 has a wedge-shaped portion 36 near the winding inner end 11a, which becomes thinner as it approaches the winding inner end 11a from the surface of the positive electrode mixture layer 32 on one side to the positive electrode current collector 30. Thus, when the battery is deformed due to an external impact, the winding inner end 11a of the positive electrode 11 can be prevented from breaking the separator, thereby improving the safety of the battery.

[0039] Preferably, the positive electrode 11 has a wedge-shaped portion 36 at the winding inner end 11a, which is thinner as the surface of the positive electrode mixture layer 32 on the inner circumference side reaches the positive electrode current collector 30 closer to the winding inner end 11a. That is, the inclined surface of the wedge-shaped portion 36 is preferably oriented toward the inner circumference. The separator 13 located on the inner side of the positive electrode 11 is easily broken near the winding axis 28 of the electrode body 14, so by making the inclined surface of the wedge-shaped portion 36 oriented toward the inner circumference, the safety of the battery can be further improved.

[0040] The length L of the wedge-shaped portion 36 in the long side direction of the positive electrode 11 is preferably within 1 mm. When the length L of the wedge-shaped portion 36 exceeds 1 mm, the effect of the wedge-shaped portion 36 may be reduced. The lower limit of the length L of the wedge-shaped portion 36 is, for example, 0.05 mm. The thickness D of the positive electrode 11 is, for example, greater than 170 μm. The upper limit of the thickness D of the positive electrode 11 is, for example, 500 μm. The length L of the wedge-shaped portion in the long side direction of the positive electrode 11 and the thickness D of the positive electrode preferably satisfy L / D≤6. The lower limit of L / D is, for example, 0.1. By making the length L of the wedge-shaped portion 36 and the thickness D of the positive electrode 11 satisfy the above relationship, the safety of the battery can be further improved.

[0041] In the cross section along the long side direction of the positive electrode 11, the inclined surface of the wedge-shaped portion 36 may be continuously inclined or intermittently inclined. That is, the inclination of the inclined surface of the wedge-shaped portion 36 may be constant or variable from the surface of the positive electrode mixture layer 32 on the inner circumference to the positive electrode collector 30. In the cross section along the long side direction of the positive electrode 11, the inclined surface of the wedge-shaped portion 36 is preferably continuous and has no steps. In the cross section along the long side direction of the positive electrode 11, the inclined surface of the wedge-shaped portion 36 may be linearly inclined, curved, or stepped, for example. In addition, the end of the wedge-shaped portion 36 may be pointed or chamfered.

[0042] The method for making the wedge-shaped portion 36 is not particularly limited. The wedge-shaped portion 36 may be made by grinding the winding inner end 11a from one side of the positive electrode 11 after forming the positive electrode mixture layer 32 on both sides of the positive electrode current collector 30. Alternatively, the wedge-shaped portion 36 may be made by reducing the amount of positive electrode mixture slurry applied near the winding inner end 11a when forming the positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0043] The breakage of the separator 13 is also affected by the compressive Young's modulus of the positive electrode 11. By increasing the compressive Young's modulus of the positive electrode 11, the active material density of the positive electrode mixture layer 32 is increased, and the battery capacity is improved. However, the shape change of the positive electrode 11 when the secondary battery 10 is impacted becomes smaller, so the separator 13 is easily broken. By reducing the compressive Young's modulus of the positive electrode 11, the shape change of the positive electrode 11 when the secondary battery 10 is impacted can be increased, and the shear stress acting on the separator 13 can be reduced. Therefore, it is not easy to cause the separator 13 to break, but the battery capacity will decrease.

[0044] The compressive Young's modulus of the positive electrode 11 is preferably 3000 MPa or less. If the compressive Young's modulus of the positive electrode 11 exceeds 3000 MPa, the active material density of the positive electrode mixture layer 32 becomes extremely high, and there is a possibility that cracks may occur in the positive electrode active material, resulting in a decrease in battery capacity.

[0045] The compressive Young's modulus of the positive electrode 11 is preferably 1200 MPa or more. If the compressive Young's modulus of the positive electrode 11 is less than 1200 MPa, the active material density of the positive electrode mixture layer 32 is reduced, so the battery capacity may be reduced.

[0046] By setting the compressive Young's modulus of the positive electrode 11 to the above range, the battery capacity can be increased and the safety of the battery can be further improved. The compressive Young's modulus of the positive electrode 11 can also be 2500 MPa or less. In addition, the compressive Young's modulus of the positive electrode 11 can also be 1500 MPa or more.

[0047] The compressive Young's modulus of the positive electrode 11 can be calculated from data of a linear region representing elastic deformation obtained by compressing the positive electrode 11 taken out after disassembling the secondary battery 10 charged to SOC 100% using a universal testing machine and measuring the relationship between stress and strain of the positive electrode 11 .

[0048] Example

[0049] Hereinafter, the present invention will be further described by way of examples, but the present invention is not limited to these examples.

[0050] [Production of positive electrode]

[0051] 95 parts by mass of LiNi 0.91 Co 0.05 Al 0.04 O2, 2.5 parts by mass of acetylene black (AB), and 2.5 parts by mass of polyvinylidene fluoride (PVdF) with an average molecular weight of 1.1 million are mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is added to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry is applied to the two surfaces of a strip-shaped positive electrode collector composed of aluminum foil, and the coating is dried and rolled, and then cut according to the specified electrode size to produce a positive electrode with a positive electrode mixture layer formed on both surfaces of the positive electrode collector. The thickness D of the positive electrode is 170μm. In the approximate center of the long side direction of the positive electrode, a positive electrode exposure portion is provided where there is no mixture layer and the surface of the collector is exposed, and an aluminum positive electrode lead is welded to the positive electrode exposure portion. In addition, at one end of the long side direction of the positive electrode, a wedge-shaped portion is provided by grinding the positive electrode mixture layer formed on the surface of one side of the positive electrode current collector, and the wedge-shaped portion has a cross-sectional shape such that the wall becomes thinner as it approaches the inner end of the winding from the surface of the positive electrode mixture layer on the inner circumference to the positive electrode current collector. The length L of the wedge-shaped portion is 0.2 mm.

[0052] [Production of negative electrode]

[0053] 100 parts by mass of artificial graphite, 1 part by mass of sodium carboxymethyl cellulose (CMC-Na) and 1.2 parts by mass of styrene-butadiene rubber (SBR) were mixed and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a strip-shaped negative electrode collector composed of copper foil, and after the coating was dried and rolled, it was cut according to a specified electrode size to produce a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode collector. A negative electrode exposure portion in which there is no mixture layer and the collector surface is exposed is provided at the inner end of the winding in the long side direction of the negative electrode, and a negative electrode lead made of nickel is welded to the negative electrode exposure portion.

[0054] [Preparation of non-aqueous electrolyte]

[0055] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC=1:3 by volume ratio), and LiPF6 was dissolved in the mixed solvent to a concentration of 1 mol / L, thereby preparing a non-aqueous electrolyte.

[0056] [Manufacturing of Secondary Batteries]

[0057] The positive electrode and the negative electrode are wound with a separator made of polyethylene to produce an electrode body. The puncture strength of the separator is 4N. At this time, the positive electrode is arranged in a manner that the wedge-shaped portion faces the inner circumference at the inner end of the winding. After that, the insulating plates are arranged on the upper and lower sides of the electrode body, and the electrode body is placed in an outer can with a bottom cylindrical shape of 21mm in diameter and 70mm in height. Next, the negative electrode lead is welded to the bottom of the outer can, and the positive electrode lead is welded to the sealing body. After that, a non-aqueous electrolyte is injected into the interior of the outer can by decompression, and then the open end of the outer can is sealed by fastening it to the sealing body through a gasket, thereby producing a secondary battery. In addition, after the secondary battery produced is charged to SOC100%, it is disassembled, and after the positive electrode plate is cut out to a specified size, the positive electrode plate is compressed using a universal testing machine and the relationship between stress and strain is measured. The slope was determined from the data of the linear region of elastic deformation among the obtained data, and the compressive Young's modulus of the positive electrode was derived. The compressive Young's modulus of the positive electrode was 2000 MPa.

[0058] <Example 2>

[0059] A secondary battery was produced in the same manner as in Example 1 except that a wedge-shaped portion was produced so that the length L was 1 mm during the production of the positive electrode.

[0060] <Example 3>

[0061] In the process of manufacturing the secondary battery, a secondary battery was manufactured in the same manner as in Example 1 except that the positive electrode was arranged so that the wedge-shaped portion faced the outer peripheral side at the inner end of the winding.

[0062] <Example 4>

[0063] A secondary battery was produced in the same manner as in Example 1 except that the wedge-shaped portion was produced so as to have a length L of 1 mm during the production of the positive electrode and the positive electrode was arranged so that the wedge-shaped portion faced the outer peripheral side at the inner end of the winding during the production of the secondary battery.

[0064] <Comparative Example 1>

[0065] A secondary battery was produced in the same manner as in Example 1 except that the positive electrode mixture layer was not polished and the wedge-shaped portion was not formed during the production of the positive electrode.

[0066] <Comparative Example 2>

[0067] During the process of manufacturing the positive electrode, the positive electrode mixture layers formed on both surfaces of the positive electrode collector were ground to provide a wedge-shaped portion having a cross-section from the surface of the positive electrode mixture layers on each of the inner and outer sides to the positive electrode collector, where the wall becomes thinner as it approaches the inner end of the winding. The length L of the wedge-shaped portion is 1 mm. Other than this, a secondary battery was manufactured in the same manner as in Example 1.

[0068] <Comparative Example 3>

[0069] During the process of making the positive electrode, the positive electrode mixture layers formed on both surfaces of the positive electrode collector were ground to provide a wedge-shaped portion having a cross-section from the surface of the positive electrode mixture layers on each of the inner and outer sides to the positive electrode collector, where the wall becomes thinner as it approaches the inner end of the winding. The length L of the wedge-shaped portion is 10 mm. Other than this, a secondary battery was manufactured in the same manner as in Example 1.

[0070] [Impact test]

[0071] A collision test was carried out using the manufactured secondary battery. It was charged to 4.2V at a constant current of 0.3C in an atmosphere of 25°C. Afterwards, a T6 collision test based on the UN transport test conditions was carried out. Specifically, a metal round bar with a diameter of 15.8mm was placed in the center of the secondary battery, and a weight of 9.1kg was dropped from three levels of 61cm, 70cm, and 80cm, and the temperature of the side of the secondary battery was measured using a thermocouple. In addition, the drop height of the weight set in the T6 collision test was 61cm.

[0072] The evaluation results of the impact test of the secondary batteries of the examples and comparative examples are summarized in Table 1. In addition, Table 1 also shows the position of the wedge-shaped portion, the length L, and the value of L / D.

[0073] [Table 1]

[0074]

[0075] No temperature rise was observed in the secondary battery of the comparative example under the condition of a weight height of 61 cm, but when the weight height was increased to 70 cm and 80 cm, the temperature of the side rose to above 50°C. On the other hand, in the secondary batteries of Examples 1 to 4, even if the weight height was increased to 80 cm, the temperature of the side was suppressed to below 40°C. In particular, in Examples 1 and 2, no temperature rise was observed under any conditions. Therefore, it can be seen that the safety is improved by using a secondary battery having a positive electrode with a prescribed wedge-shaped portion. In addition, in Comparative Example 2 in which a wedge-shaped portion is provided on both sides of the positive electrode, the temperature of the side rises compared with Examples 2 and 4 in which a wedge-shaped portion is provided only on one side of the positive electrode. Although the details of the mechanism are unclear, it is speculated that in Comparative Example 2, the acute angle around the positive electrode collector at the inner end of the winding causes an adverse effect.

[0076] The present invention is further described by the following embodiments.

[0077] Structure 1:

[0078] A non-aqueous electrolyte secondary battery comprises: an electrode body, which is formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator interposed therebetween; a non-aqueous electrolyte; and an outer shell, which accommodates the electrode body and the non-aqueous electrolyte, wherein:

[0079] The positive electrode comprises a positive electrode current collector and positive electrode mixture layers formed on both surfaces of the positive electrode current collector.

[0080] The positive electrode has a wedge-shaped portion near a winding inner end portion, the wall of which becomes thinner as it extends from a surface of the positive electrode mixture layer on one side to the positive electrode current collector toward the winding inner end portion.

[0081] Structure 2:

[0082] The nonaqueous electrolyte secondary battery according to Structure 1, wherein

[0083] The positive electrode has the wedge-shaped portion near the winding inner end portion, the wedge-shaped portion being thinner from the surface of the positive electrode mixture layer on the inner peripheral side to the positive electrode current collector as it approaches the winding inner end portion.

[0084] Structure 3:

[0085] The nonaqueous electrolyte secondary battery according to Structure 1 or 2, wherein

[0086] A length L of the wedge-shaped portion in the longitudinal direction of the positive electrode is within 1 mm.

[0087] Structure 4:

[0088] The nonaqueous electrolyte secondary battery according to any one of Structures 1 to 3, wherein

[0089] The thickness D of the positive electrode is greater than 170 μm.

[0090] Structure 5:

[0091] The nonaqueous electrolyte secondary battery according to any one of Structures 1 to 4, wherein

[0092] A length L of the wedge-shaped portion in the long-side direction of the positive electrode and a thickness D of the positive electrode satisfy L / D≤6.

[0093] Structure 6:

[0094] The nonaqueous electrolyte secondary battery according to any one of Structures 1 to 5,

[0095] The positive electrode mixture layer contains a positive electrode active material.

[0096] The positive electrode active material is an NCA-based lithium transition metal composite oxide or an NCM-based lithium transition metal composite oxide.

[0097] Description of Reference Numerals

[0098] 10. Secondary battery; 11. Positive electrode; 11a. Inner end of winding; 11b. Outer end of winding; 12. Negative electrode; 13. Separator; 14. Electrode body; 15. Outer shell; 16. Sealing body; 17, 18. Insulating plate; 19. Positive electrode lead; 20. Negative electrode lead; 21. Groove; 22. Filter; 23. Lower valve core; 24. Insulating member; 25. Upper valve core; 26. Cover; 26a. Opening; 27. Gasket; 28. Winding axis; 30. Positive electrode collector; 32. Positive electrode mixture layer; 34. Positive electrode exposed portion; 36. Wedge-shaped portion; 40. Negative electrode collector; 42. Negative electrode mixture layer; 44. Negative electrode exposed portion.

Claims

1. A non-aqueous electrolyte secondary battery comprising: An electrode body, which is formed by winding a strip-shaped positive electrode and a strip-shaped negative electrode with a separator interposed therebetween; a non-aqueous electrolyte; and an outer shell, which accommodates the electrode body and the non-aqueous electrolyte, wherein The positive electrode comprises a positive electrode current collector and positive electrode mixture layers formed on both surfaces of the positive electrode current collector. The positive electrode has a wedge-shaped portion near a winding inner end portion, the wall of which becomes thinner as it extends from a surface of the positive electrode mixture layer on one side to the positive electrode current collector toward the winding inner end portion.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein The positive electrode has the wedge-shaped portion near the winding inner end portion, the wedge-shaped portion being thinner from the surface of the positive electrode mixture layer on the inner peripheral side to the positive electrode current collector as it approaches the winding inner end portion.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein A length L of the wedge-shaped portion in the longitudinal direction of the positive electrode is within 1 mm.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein The thickness D of the positive electrode is greater than 170 μm.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein A length L of the wedge-shaped portion in the long-side direction of the positive electrode and a thickness D of the positive electrode satisfy L / D≤6.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material is an NCA-based lithium transition metal composite oxide or an NCM-based lithium transition metal composite oxide.

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