Cylindrical nonaqueous electrolyte secondary battery

Abstract

Provided is a nonaqueous electrolyte secondary battery in which the risk of breakage of an outer can is reduced. A cylindrical nonaqueous electrolyte secondary battery according to an embodiment comprises: an outer can having a cylindrical shape and including a bottom portion at one end and an opening portion at the other end; an electrode body and a nonaqueous electrolyte that are stored in a body portion of the outer can; and a sealing body that closes the opening portion. A grooved portion having a diameter smaller than that of the body portion of the outer can is formed between the opening portion and the body portion. The thickness t1 of an upper groove portion, which is located on the opening portion side relative to a minimum diameter portion in the grooved portion, is greater than the thickness t2 of the opening portion.

Description

Cylindrical non-aqueous electrolyte secondary battery

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

[0002] A cylindrical nonaqueous electrolyte secondary battery contains a wound electrode assembly and a nonaqueous electrolyte in a cylindrical outer can with a bottom, and a sealing member is crimped and fixed between a grooved portion and the open end of the outer can via a gasket, thereby sealing the interior. Generally, the grooved portion is formed by pressing a predetermined position on the wall of the rotating outer can inward with a roller and stretching it, so the wall thickness of the grooved portion is thinner than the rest of the wall of the outer can.

[0003] Patent document 1 discloses a technology in which the lower part of the groove, which is located closer to the bottom than the narrowest diameter part of the grooved part, is made thicker than the body part in order to prevent damage to the grooved part when gas is generated inside the battery.

[0004] International Publication No. 2018 / 173453

[0005] In recent years, there has been an increasing demand for lightweight secondary batteries. While weight reduction can be achieved by reducing the thickness of the exterior can, it is also necessary to prevent damage to the exterior can and ensure the safety of the secondary battery.

[0006] During the manufacture of secondary batteries, depending on the clearance between the inner diameter of the outer can and the outer diameter of the sealing body, the sealing body may be forced into the opening of the outer can, which may cause deformation of the upper part of the groove located closer to the opening than the narrowest part of the groove insertion portion and, in the worst case, damage to the sealing body. Also, if strong pressure is applied to the sealing body in the secondary battery state, the upper part of the groove may deform and cause damage.

[0007] An object of the present disclosure is to provide a cylindrical nonaqueous electrolyte secondary battery that reduces the risk of damage to the outer can.

[0008] The cylindrical nonaqueous electrolyte secondary battery according to the present disclosure comprises a cylindrical outer can having a bottom at one end and an opening at the other end, an electrode assembly and nonaqueous electrolyte housed in a body of the outer can, and a sealing body that closes the opening, wherein a grooved portion is formed between the opening and the body, and the diameter of the outer can is smaller than that of the body, and the thickness t1 of an upper portion of the groove located closer to the opening than the narrowest diameter part of the grooved portion is greater than the thickness t2 of the opening.

[0009] The cylindrical nonaqueous electrolyte secondary battery according to the present disclosure has a reduced risk of damage to the outer can and is therefore excellent in safety.

[0010] 1 is an axial cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[0011] Hereinafter, an example of an embodiment of a cylindrical nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure also includes embodiments obtained by selectively combining the components of the embodiments described below.

[0012] Fig. 1 is a longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery 10 according to an embodiment. In the cylindrical nonaqueous electrolyte secondary battery 10 shown in Fig. 1, an electrode assembly 14 and a nonaqueous electrolyte (not shown) are housed in a body 15a of an outer can 15. For ease of explanation, the following description will refer to the sealing body 16 side as the "top" and the bottom side of the outer can 15 as the "bottom."

[0013] The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. The positive electrode 11 has a strip-shaped positive electrode current collector and positive electrode mixture layers formed on both sides of the positive electrode current collector. The positive electrode current collector may be, for example, a foil of a metal such as aluminum, or a film with the metal disposed on its surface.

[0014] The positive electrode mixture layer is produced by applying a positive electrode mixture slurry containing, for example, a positive electrode active material, a conductive agent, a binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of a positive electrode current collector, followed by drying and compression. Examples of the positive electrode active material include lithium transition metal composite oxides containing transition metal elements such as Co, Mn, and Ni. Examples of the conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins.

[0015] The negative electrode 12 includes a strip-shaped negative electrode current collector and a negative electrode mixture layer formed on both sides of the negative electrode current collector. Examples of the negative electrode current collector include a foil of a metal such as copper, and a film having such a metal disposed on its surface.

[0016] The negative electrode mixture layer is produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, water, etc. to both sides of a negative electrode current collector, followed by drying and compression. Examples of the negative electrode active material include carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys and oxides containing these. Examples of the binder include styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, etc.

[0017] A porous sheet having ion permeability and insulating properties is used as the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. The separator is preferably made of an olefin resin such as polyethylene or polypropylene.

[0018] The nonaqueous electrolyte contained in the outer can 15 has ion conductivity (e.g., lithium ion conductivity). The nonaqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. Examples of the nonaqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the nonaqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The nonaqueous 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

[0019] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0020] The outer can 15 is made of metal and has a cylindrical shape, a bottom 15b at one end, and an opening 15c at the other end. Here, the bottom 15b is a disk-shaped portion located below the body 15a, which rises substantially vertically in the up-down direction. The opening 15c is a cylindrical portion located above the body 15a. A grooved portion 21, in which a portion of the side surface protrudes inward, is formed between the opening 15c and the body 15a. As described below, the grooved portion 21 supports the sealing body 16 on its upper surface. The grooved portion 21 is provided along the circumferential direction of the outer can 15 and may be formed, for example, in an annular shape around the entire circumference of the outer can 15. The grooved portion 21 can be formed, for example, by pressing the side surface of the outer can 15 from the outside.

[0021] The opening 15c of the outer can 15 is closed by the sealing body 16, sealing the inside of the cylindrical nonaqueous electrolyte secondary battery 10. In this embodiment, the sealing body 16 is fixed by crimping between the grooved portion 21 and the open end 15e of the outer can 15 via a gasket 27.

[0022] Insulating plates 17, 18 are provided above and below the electrode body 14. The positive electrode lead 19 extends upward through a through hole in the insulating plate 17 and is welded to the underside of a filter 22, which is the bottom plate of the sealing body 16. In the cylindrical nonaqueous electrolyte secondary battery 10, a cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode lead 20 extends through a through hole in the insulating plate 18 to the bottom side of the outer can 15 and is welded to the inner bottom surface of the outer can 15. In the cylindrical nonaqueous electrolyte secondary battery 10, the outer can 15 serves as the negative electrode terminal.

[0023] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may break, causing the upper valve body 25 to swell toward the cap 26 and separate from the lower valve body 23, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may break, allowing gas to be released through the opening 26a in the cap 26.

[0024] Next, the outer can 15 will be described in detail with reference to Fig. 2. Fig. 2 is an enlarged view of the vicinity of the grooved portion 21 of the outer can 15 in Fig. 1.

[0025] As described above, groove portion 21 is formed between opening 15c and body portion 15a, and the diameter of outer can 15 at groove portion 21 is smaller than that of body portion 15a. Groove portion 21 has narrowest diameter portion 21a located closest to the inside of the battery, and can be divided into upper groove portion 21u located closer to opening 15c than narrowest diameter portion 21a, and lower groove portion 21d located closer to bottom portion 15b than narrowest diameter portion 21a. In the example shown in Fig. 2, narrowest diameter portion 21a is located approximately in the center of groove portion 21 in the up-down direction, but this example is not limiting.

[0026] The thickness t1 of the groove upper portion 21u is greater than the thickness t2 of the opening 15c. This reduces the risk of damage to the outer can 15. That is, the grooved portion 21 having such a shape can withstand the pressure applied when the sealing body 16 is pressed into the opening 15c of the outer can 15 during battery manufacturing. Furthermore, the grooved portion 21 having such a shape can withstand strong pressure applied to the sealing body in the battery state.

[0027] The thickness t1 of the groove upper portion 21u is the thickness of the thickest portion of the groove upper portion 21u observed in a cross section taken along the axial direction of the cylindrical nonaqueous electrolyte secondary battery 10. The thickness t2 of the opening 15c is the thickness at a position half the vertical height of the opening 15c in a cross section taken along the axial direction of the cylindrical nonaqueous electrolyte secondary battery 10.

[0028] The thickness t1 of the groove upper portion 21u and the thickness t2 of the opening 15c preferably satisfy the relationship t1 / t2≧1.2. This more significantly reduces the risk of breakage of the outer can 15. The upper limit of t1 / t2 is, for example, 2 times. It is more preferable that t1 and t2 satisfy the relationship 1.4≦t1 / t2≦1.6.

[0029] The thickness t3 of the groove lower portion 21d located closer to the bottom 15b than the narrowest diameter portion 21a in the groove insertion portion 21, the thickness t1 of the groove upper portion 21u, and the thickness t2 of the opening 15c preferably satisfy the relationship t2 < t3 < t1. This further improves the durability of the groove insertion portion 21 against pressure from above the battery, thereby more significantly reducing the risk of damage to the outer can 15. Here, the thickness t3 of the groove lower portion 21d is the thickness of the thickest portion of the groove lower portion 21d observed in a cross section along the axial direction of the cylindrical nonaqueous electrolyte secondary battery 10.

[0030] The thickness t4 of the body portion 15a and the thickness t2 of the opening 15c may satisfy the relationship 0.6≦t2 / t4≦1.5, and may be 0.8≦t2 / t4≦1.2, for example. The thickness t4 of the body portion 15a and the thickness t2 of the opening 15c may be substantially the same. Here, the thickness t4 of the body portion 15a is the thickness at a position halfway through the vertical height of the body portion 15a in a cross section taken along the axial direction of the cylindrical nonaqueous electrolyte secondary battery 10.

[0031] There are no particular limitations on the method for making the thickness t1 of the groove upper portion 21u greater than the thickness t2 of the opening 15c in the outer can 15, but for example, before forming the groove upper portion 21u, the thickness of the portion of the outer can 15 corresponding to the groove upper portion 21u can be increased to make t1 > t3. Also, the thickness t3 of the groove lower portion 21d can be increased in the same manner as above.

[0032] As described above, by increasing the thickness of the groove upper portion 21u of the grooved portion 21, the safety of the cylindrical nonaqueous electrolyte secondary battery 10 can be improved.

[0033] The present disclosure is further described by the following embodiments. Configuration 1: A cylindrical nonaqueous electrolyte secondary battery comprising: a cylindrical outer can having a bottom at one end and an opening at the other end; an electrode assembly and nonaqueous electrolyte housed in a body of the outer can; and a sealing member closing the opening, wherein a grooved portion is formed between the opening and the body, the diameter of the outer can being smaller than that of the body, and a thickness t1 of an upper portion of the groove located closer to the opening than the narrowest diameter portion of the grooved portion is greater than a thickness t2 of the opening. Configuration 2: The cylindrical nonaqueous electrolyte secondary battery according to Configuration 1, wherein the grooved portion is formed in an annular shape around the entire circumference of the outer can. Configuration 3: The cylindrical nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein t1 and t2 satisfy the relationship t1 / t2≧1.2. A cylindrical nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 3, wherein a thickness t3 of a lower portion of the groove located closer to the bottom than the narrowest diameter portion in the groove insertion portion, the thickness t1, and the thickness t2 satisfy the relationship t2<t3<t1. A cylindrical nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 4, wherein a thickness t4 of the body portion and the thickness t2 satisfy the relationship 0.6≦t2 / t4≦1.5.

[0034] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 15a body, 15b bottom, 15c opening, 15e opening end, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion, 21a narrowest diameter portion, 21u groove upper portion, 21d groove bottom portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening hole, 27 gasket

Claims

1. A cylindrical non-aqueous electrolyte secondary battery comprising: a cylindrical outer can having a bottom at one end and an opening at the other end; an electrode assembly and non-aqueous electrolyte housed in a body of the outer can; and a sealing body that closes the opening, wherein a grooved portion is formed between the opening and the body, and the diameter of the outer can is smaller than that of the body, and a thickness t1 of an upper portion of the groove located closer to the opening than the narrowest diameter part of the grooved portion is greater than a thickness t2 of the opening.

2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the grooved portion is formed in an annular shape around the entire circumference of the outer can.

3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein t1 and t2 satisfy the relationship t1 / t2≧1.

2.

4. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein a thickness t3 of a lower portion of the groove located closer to the bottom than the narrowest diameter portion in the groove insertion portion, t1, and t2 satisfy the relationship t2<t3<t1.

5. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the thickness t4 of the body portion and the thickness t2 satisfy the relationship 0.6≦t2 / t4≦1.5.

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