Cylindrical nonaqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises: a cylindrical outer can having a bottom section at one end and an opening at the other end; an electrode body and a nonaqueous electrolyte accommodated in a body section of the outer can; and a sealing body that blocks the opening via a gasket. A groove section where the diameter of the outer can is smaller than that of the body section is formed between the opening and the body section, and a functional layer containing a compound to which calcium ions are bonded is disposed in at least part of a region comprising the groove section and the opening on the inner surface of the outer can.

Description

Cylindrical non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a cylindrical non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery with improved reliability.

[0002] A cylindrical nonaqueous electrolyte secondary battery contains an electrode assembly and a nonaqueous electrolyte in a cylindrical outer can with a bottom, and a sealing member is crimped and fixed between the grooved portion and the open end of the outer can via a gasket, thereby sealing the interior. Patent Document 1 describes that hydrofluoric acid may be generated by a reaction between water and the nonaqueous electrolyte remaining during battery manufacturing. Hydrofluoric acid may chemically react with the outer can, potentially reducing the stability of the quality of the outer can. Patent Document 1 also discloses a technology for solving the above problem, in which a basic compound is present as a neutralizing agent on the inner surface of the opening.

[0003] International Publication No. 2022 / 080175

[0004] The invention described in Patent Document 1 neutralizes the generated hydrofluoric acid to suppress the corrosive effect of hydrofluoric acid on the exterior can, but in order to further improve the stability of the quality of the exterior can, it is preferable to suppress the generation of acidic compounds such as hydrofluoric acid.The inventors of the present invention have conducted extensive research and found that the stability of the quality of the exterior can can be improved by capturing fluoride ions and phosphate ions generated by the reaction between the nonaqueous electrolyte and water before they form compounds with the metal components of the exterior can.

[0005] An object of the present disclosure is to provide a secondary battery with improved stability of the quality of the outer can.

[0006] A cylindrical nonaqueous electrolyte secondary battery according to one embodiment of 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 a nonaqueous electrolyte solution housed in a body of the outer can, and a sealing body that closes the opening via a gasket, wherein a grooved portion is formed between the opening and the body, and the outer can has a diameter smaller than that of the body, and a functional layer containing a compound to which calcium ions are bound is disposed in at least a portion of a region on the inner surface of the outer can that is formed by the grooved portion and the opening.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure improves the reliability of the battery.

[0008] Fig. 1 is a longitudinal sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment. Fig. 2 is an enlarged view of the vicinity of an opening and a grooved portion of an outer can in Fig. 1. Fig. 3 is a view corresponding to Fig. 2 in another embodiment. Fig. 4 is a view corresponding to Fig. 2 in another embodiment. Fig. 5 is a view corresponding to Fig. 2 in another embodiment. Fig. 6 is a view corresponding to Fig. 2 in another embodiment. Fig. 7 is a view corresponding to Fig. 2 in another embodiment.

[0009] An example of an embodiment of a cylindrical secondary battery according to the present disclosure will be described in detail below with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the cylindrical secondary battery. Furthermore, when multiple embodiments and variations are included in the following description, it is assumed from the outset that the characteristic features of these embodiments and variations can be appropriately combined and used.

[0010] Fig. 1 is a longitudinal cross-sectional view of a secondary battery 10 according to an embodiment. In the secondary battery 10 shown in Fig. 1, an electrode assembly 14 and a nonaqueous electrolyte (not shown) are housed in an outer can 15. For ease of explanation, the following description will be given with the sealing body 16 side referred to as "top" and the bottom side of the outer can 15 referred to as "bottom."

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] As the nonaqueous solvent (organic solvent) of the nonaqueous electrolyte solution contained in the outer can 15, carbonates, lactones, ethers, ketones, esters, etc. can be used, and two or more of these solvents can be mixed and used. When two or more solvents are mixed and used, it is preferable to use a mixed solvent containing a cyclic carbonate and a chain carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. can be used as the chain carbonate. As the electrolyte salt of the nonaqueous electrolyte solution, LiPF ６ , LiBF ４ , LiCF ３ SO ３ The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol / L.

[0017] The opening of the outer can 15 is closed with the sealing body 16, thereby sealing the interior of the secondary battery 10. 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 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 downward through a through hole in the insulating plate 18 and is welded to the inner surface of the bottom 15a of the outer can 15. In the secondary battery 10, the outer can 15 serves as the negative electrode terminal.

[0018] The outer can 15 is cylindrical and has a bottom 15a at one end and an opening 15b at the other end. The electrode assembly 14 and a non-aqueous electrolyte are accommodated in a body 15c of the outer can 15. A groove 15d is formed between the opening 15b and the body 15c, and the diameter of the outer can 15 is smaller than that of the body 15c.

[0019] The grooved portion 15d is a portion of the side surface of the outer can 15 recessed radially inward, and is provided in an annular shape along the circumferential direction of the outer can 15. The grooved portion 15d supports the sealing body 16 on its upper surface. The grooved portion 15d can be formed, for example, by spinning a portion of the side surface of the outer can 15 radially inward to form an annular recess radially inward. The width (axial length) of the grooved portion 15d is not particularly limited, but is, for example, 0.1 mm or more and 2.0 mm or less. The depth (radial length) of the grooved portion 15d is also not particularly limited, but is, for example, 0.5 mm or more and 5.0 mm or less.

[0020] Opening 15b is an area of ​​the side surface of outer can 15 above grooved portion 15d, and forms an opening of outer can 15. An upper end 15e of opening 15b is bent radially inward, and sealing body 16 is crimped and fixed to outer can 15 via gasket 27.

[0021] The exterior can 15 is made of metal, and the main component of the exterior can 15 is, for example, iron. Here, the main component refers to the component with the highest mass ratio.

[0022] The sealing body 16 is a disc-shaped member equipped with a safety valve. The sealing body 16 has a structure in which, in order from the electrode body 14 side, a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each component constituting the sealing body 16 has, for example, a disc 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 breaks, 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 further increases, the upper valve body 25 breaks, and gas is released through the opening 26a of the cap 26.

[0023] Gasket 27 is a flexible insulating member that electrically isolates sealing body 16, which is the positive electrode terminal, from outer can 15, which is the negative electrode terminal, while being compressed in the vertical direction to ensure the airtightness of the interior of outer can 15. The material of gasket 27 is not particularly limited as long as it is a compressible insulating material, and examples that can be used include polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyamide (PA).

[0024] Next, the functional layer 30 provided above the grooved portion 15d of the secondary battery 10 will be described with reference to Fig. 2 and Fig. 3A to Fig. 3E. Fig. 2 is an enlarged view of the vicinity of the opening 15b and the grooved portion 15d of the exterior can 15. Fig. 3A to Fig. 3E are views corresponding to Fig. 2 in another example of the embodiment.

[0025] LiPF as electrolyte salt ６ dissociates as shown in the following chemical formulas (1) and (2).

[0026] LiPF ６ When a non-aqueous electrolyte containing the above reacts with water, it reacts as shown in the following chemical formulas (3) to (6) to produce acidic compounds such as hydrofluoric acid and phosphoric acid.

[0027] A functional layer 30 containing a compound with calcium ions bonded thereto is disposed in at least a portion of the region defined by the grooved portion 15d and the opening 15b on the inner surface of the outer can 15. In other words, the functional layer 30 containing a compound with calcium ions bonded thereto is disposed in at least a portion of the region of the inner surface of the outer can 15 above the boundary between the body portion 15c and the grooved portion 15d. The calcium ions contained in the compound capture fluoride ions and phosphate ions generated by the reaction between the nonaqueous electrolyte and water, thereby suppressing the reaction of the fluoride ions and phosphate ions with the metal components of the outer can, thereby improving the quality stability of the outer can. The calcium ions react with the fluoride ions and phosphate ions to generate sparingly soluble compounds. The content of the compound with calcium ions bonded thereto in the functional layer 30 is, for example, 10 ppm by mass or more and 10% by mass or less. The compound with calcium ions contained in the functional layer 30 does not contain calcium fluoride.

[0028] In the example shown in FIG. 2 , a functional layer 30 containing a compound with calcium ions bonded thereto is disposed over the entire area of ​​the inner surface of the outer can 15, which is defined by the grooved portion 15 d and the opening 15 b. This further improves the stability of the outer can's quality. Water present outside the battery may penetrate into the battery, for example, between the outer can 15 and the gasket 27 or through the inside of the gasket 27. Furthermore, nonaqueous electrolyte remaining in the opening 15 b during electrolyte injection, and nonaqueous electrolyte contained in the body portion 15 c that has reached the opening 15 b, may travel between the outer can 15 and the gasket 27 by capillary action and reach the vicinity of the opening end 15 f. Thus, acidic compounds such as hydrofluoric acid and phosphoric acid may be generated between the outer can 15 and the gasket 27. By disposing the functional layer 30 between the outer can 15 and the gasket 27, the reaction of fluoride ions and phosphate ions with the metal components of the outer can can be suppressed. Furthermore, by arranging the functional layer 30 on the inner surface of the grooved portion 15d that is not in contact with the gasket 27, even if water enters the inside of the battery between the outer can 15 and the gasket 27 or through the inside of the gasket 27, the reaction between fluoride ions or phosphate ions and the metal components of the outer can can be suppressed.

[0029] The functional layer 30 may further include a sealant. Examples of sealants that can be used include conventionally used rubber polymers such as 1,2-polybutadiene, pitch, asphalt, and the like. In its raw state, the sealant is dissolved in a solvent such as xylene or ethylbenzene. The term "the functional layer 30 includes a sealant" includes a state in which the functional layer 30 and the sealant are mixed together, and a state in which the functional layer 30 also serves as the sealant.

[0030] There is no particular limitation on the method for disposing the functional layer 30 on the inner surface of the battery. The functional layer 30 can be formed, for example, by applying a slurry containing a compound to which calcium ions are bound to the inner surface of the outer can 15 and drying the slurry. There is no particular limitation on the thickness of the functional layer 30, but it is, for example, 1 μm or more and 1000 μm or less.

[0031] The compound to which calcium ions are bound, which is contained in the functional layer 30, includes, for example, a calcium salt of an inorganic compound, a calcium salt of an organic acid, or a polymer to which calcium ions are bound.

[0032] The calcium salt of the inorganic compound contained in the functional layer 30 includes, for example, one or more compounds selected from the group consisting of calcium carbonate, calcium hydroxide, calcium silicate, calcium bicarbonate, calcium peroxide, and calcium bicarbonate. These compounds have high affinity with battery materials and have little effect on the battery reaction even when present in the non-aqueous electrolyte.

[0033] The calcium salt of an organic acid refers to an organic compound in which a calcium ion is bound to a functional group. Examples of calcium salts of organic acids include calcium acetate, calcium propionate, calcium citrate, calcium ascorbate, calcium stearate, and calcium lactate. Calcium salts of organic acids are easily soluble in the solvent contained in the raw material of the sealant, improving the dispersibility of the calcium salt and sealant in the slurry and improving the uniformity of the functional layer 30. Calcium stearate, which has particularly good solubility in solvents, is preferred as the calcium salt of an organic acid.

[0034] The term "polymers with calcium ions bound to them" refers to polymers whose base is a polymer and whose calcium ions are bound to functional groups in the main chain or side chain. Examples of polymers with calcium ions bound to them include calcium pectate, calcium salts of carboxymethylcellulose (CMC), and calcium polyacrylate.

[0035] The functional layer 30 shown in each of Figures 3A to 3E differs from the example shown in Figure 2 in terms of the position where it is arranged. Note that the functional layer 30 shown in each of Figures 3A to 3E may be the same as the example shown in Figure 2 in terms of the configuration other than the position where it is arranged.

[0036] In the example shown in FIG. 3A , the functional layer 30 is disposed between the outer can 15 and the gasket 27. This prevents fluoride ions and phosphate ions from reacting with metal components of the outer can when acidic compounds such as hydrofluoric acid and phosphoric acid are generated between the outer can 15 and the gasket 27. The functional layer 30 may be disposed over the entire surface between the outer can 15 and the gasket 27, or over at least a portion of the surface between the outer can 15 and the gasket 27. From the viewpoint of productivity, the functional layer 30 is preferably disposed near the boundary between the grooved portion 15 d and the opening 15 b. For example, the functional layer 30 may be disposed only on the upper portion of the grooved portion 15 d and the L-shaped portion at the lower end of the opening 15 b (within the dotted-line frame E1 shown in FIG. 3A ) connecting the upper portion of the grooved portion 15 d. When the functional layer 30 contains an inorganic compound, it is preferable that the functional layer 30 not also function as the gasket 27 but be disposed independently of the gasket 27. This is because the inclusion of an inorganic compound in the gasket 27 may reduce processability during crimping.

[0037] In the example shown in Figure 3B, the functional layer 30 is disposed at the tip of the grooved portion 15d. This prevents fluoride ions and phosphate ions from reacting with the metal components of the outer can even when water enters the battery. Here, the tip of the grooved portion 15d refers to the curved portion of the grooved portion 15d near the portion that is most recessed radially inward. The functional layer 30 may be disposed over the entire tip of the grooved portion 15d, or may be disposed over only a portion of the tip of the grooved portion 15d.

[0038] 3C , the functional layer 30 is disposed on the upper and lower portions of the grooved portion 15d. This prevents fluoride ions and phosphate ions from reacting with the metal components of the outer can even when water enters the battery. Here, the upper portion of the grooved portion 15d refers to a substantially flat portion of the grooved portion 15d facing the sealing body 16, and the lower portion of the grooved portion 15d refers to a substantially flat portion of the grooved portion 15d facing the electrode body 14. The functional layer 30 may be disposed on the entire upper and lower portions of the grooved portion 15d, or may be disposed on only a portion of the upper and lower portions of the grooved portion 15d.

[0039] In the example shown in Figure 3D, the functional layer 30 is disposed on the upper part of the grooved portion 15d and on the upper end 15e of the opening 15b. Non-aqueous electrolyte from inside the battery can easily reach the upper part of the grooved portion 15d, while water from outside the battery can easily reach the upper end 15e of the opening 15b. By disposing the functional layer 30 on the upper part of the grooved portion 15d and on the upper end 15e, it is possible to more efficiently suppress the reaction between fluoride ions and phosphate ions and the metal components of the outer can. The functional layer 30 may be disposed on the entire upper part of the grooved portion 15d and the upper end 15e of the opening 15b, or may be disposed on only a part of the upper part of the grooved portion 15d and the upper end 15e of the opening 15b.

[0040] 3E , the functional layer 30 may be further disposed between the sealing body 16 and the gasket 27. The functional layer 30 may be disposed over the entire surface between the sealing body 16 and the gasket 27, or may be disposed over a portion of the surface between the sealing body 16 and the gasket 27. The functional layer 30 may be disposed, for example, near the lower end of the outer periphery of the sealing body 16.

[0041] As described above, in the nonaqueous electrolyte secondary battery of the present disclosure, a functional layer containing a compound to which calcium ions are bound is disposed in at least a part of the region consisting of the grooved portion and the opening on the inner surface of the outer can, thereby improving the stability of the quality of the outer can and improving the reliability of the battery.

[0042] The present disclosure is further described by the following embodiments. Aspect 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 a nonaqueous electrolyte solution housed in a body of the outer can; and a sealing member closing the opening via a gasket, wherein a groove is formed between the opening and the body, the diameter of the outer can being smaller than that of the body, and a functional layer containing a compound to which calcium ions are bound is disposed in at least a portion of a region on the inner surface of the outer can defined by the groove and the opening. Aspect 2: The cylindrical nonaqueous electrolyte secondary battery according to Aspect 1, wherein the compound includes a calcium salt of an inorganic compound, a calcium salt of an organic acid, or a polymer to which calcium ions are bound. Aspect 3: The cylindrical nonaqueous electrolyte secondary battery according to Aspect 2, wherein the calcium salt of an organic acid is calcium stearate. Configuration 4: The cylindrical nonaqueous electrolyte secondary battery according to Configurations 2 or 3, wherein the calcium salt of an inorganic compound includes one or more compounds selected from the group consisting of calcium carbonate, calcium hydroxide, calcium silicate, calcium bicarbonate, calcium peroxide, and calcium bicarbonate.Configuration 5: The cylindrical nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the functional layer further includes a sealant.Configuration 6: The cylindrical nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the functional layer is disposed between the outer can and the gasket.Configuration 7: The cylindrical nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the functional layer is disposed at an end portion of the grooved portion.Configuration 8: The cylindrical nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the functional layer is disposed at an upper and lower portion of the grooved portion.Configuration 9: The cylindrical nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the functional layer is disposed at an upper portion of the grooved portion and at an upper end of the opening. Configuration 10: The cylindrical nonaqueous electrolyte secondary battery according to any one of configurations 1 to 5, wherein the functional layer is disposed on an upper portion of the grooved portion and on a lower end of the opening connected to the upper portion of the grooved portion.

[0043] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 15a bottom, 15b opening, 15c body, 15d grooved portion, 15e upper end, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening hole, 27 gasket, 30 functional layer

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 via a gasket, wherein a groove is formed between the opening and the body, and the diameter of the outer can is smaller than that of the body, and a functional layer containing a compound to which calcium ions are bound is disposed in at least a part of the region on the inner surface of the outer can formed by the groove and the opening.

2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the compound includes a calcium salt of an inorganic compound, a calcium salt of an organic acid, or a polymer to which calcium ions are bound.

3. The cylindrical nonaqueous electrolyte secondary battery according to claim 2, wherein the calcium salt of an organic acid is calcium stearate.

4. The cylindrical nonaqueous electrolyte secondary battery according to claim 2, wherein the calcium salt of an inorganic compound includes one or more compounds selected from the group consisting of calcium carbonate, calcium hydroxide, calcium silicate, calcium bicarbonate, calcium peroxide, and calcium bicarbonate.

5. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer further contains a sealant.

6. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer is disposed between the outer can and the gasket.

7. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer is disposed at the tip of the groove.

8. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layers are disposed above and below the grooved portion.

9. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer is disposed on top of the groove and on the upper end of the opening.

10. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the functional layer is disposed on an upper portion of the grooved portion and on a lower end of the opening that is connected to the upper portion of the grooved portion.

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