Cylindrical non-aqueous electrolyte secondary battery

Abstract

Provided is a secondary battery in which corrosion of an exterior body is stably suppressed.　A non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure comprises: an exterior body having a bottomed cylindrical shape and having a grooving portion (21) in an opening portion (15a); an electrode body and a non-aqueous electrolyte housed in the exterior body; and a sealed body (16) caulked and fixed between the grooving portion (21) and an opening end (15b) in the opening (15a), wherein in a portion from the grooving portion (21) of the inner surface of the exterior body to the open end portion (15b), a powder of at least one among compounds selected from the group consisting of hydroxides, oxides, and carbonates is present.

Description

[Technical Field]

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

[0002] A cylindrical nonaqueous electrolyte secondary battery houses an electrode assembly and a nonaqueous electrolyte in a cylindrical exterior body with a bottom, and a sealing member is crimped and fixed between a groove and the open edge of the exterior body to seal the interior. However, during battery manufacturing, nonaqueous electrolyte injected into the exterior body may remain attached to the opening of the exterior body. If nonaqueous electrolyte remains in the area where the sealing member is crimped and fixed above the groove of the exterior body, the nonaqueous electrolyte may react with moisture that has entered from the outside to produce hydrofluoric acid, which may corrode the exterior body. Patent Document 1 discloses a technology for improving the sealing properties of a battery by applying a sealant made by adding an alkaline compound having an amino group to pitch to the inner surface of the exterior body above the groove. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-151516 Summary of the Invention [Problem to be solved by the invention]

[0004] However, alkaline compounds such as butylamine are prone to volatilization, making it difficult to obtain a stable effect, and the technology disclosed in Patent Document 1 still needs further investigation.

[0005] Therefore, an object of the present disclosure is to provide a secondary battery in which corrosion of the exterior body is stably suppressed. [Means for solving the problem]

[0006] A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure comprises a cylindrical, bottomed exterior housing having a grooved opening, an electrode assembly and a nonaqueous electrolyte housed in the exterior housing, and a sealing body that is crimped and fixed between the grooved opening and the open edge of the opening, and is characterized in that a powder of one or more compounds selected from the group consisting of hydroxides, oxides, and carbonates is present in a region on the inner surface of the exterior housing from the grooved opening to the open edge. [Effects of the Invention]

[0007] According to the nonaqueous electrolyte secondary battery according to the present disclosure, corrosion of the exterior body can be stably suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a longitudinal cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery according to an embodiment of the present invention; [Figure 2] 2 is an enlarged view of the vicinity of the opening of the exterior body in FIG. 1. FIG. DETAILED DESCRIPTION OF THE INVENTION

[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 non-aqueous electrolyte (not shown) are housed in an exterior body 15. For ease of explanation, the following description will refer to the sealing body 16 side as "top" and the bottom side of the exterior body 15 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 having such a metal disposed on its surface.

[0012] The positive electrode mixture layer is produced by applying a positive electrode mixture slurry containing 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 its salts, polyacrylic acid or its salts, 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] The nonaqueous solvent (organic solvent) for the nonaqueous electrolyte contained in the exterior body 15 can be carbonates, lactones, ethers, ketones, esters, etc., and two or more of these solvents can be mixed. When two or more solvents are mixed, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. 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. The electrolyte salt for the nonaqueous electrolyte can be LiPF6, LiBF4, LiCF3SO3, etc., or a mixture thereof. The amount of electrolyte salt dissolved in the nonaqueous solvent can be, for example, 0.5 to 2.0 mol / L.

[0017] The opening of the exterior body 15 is closed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 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 through a through hole in the insulating plate 18 to the bottom side of the exterior body 15 and is welded to the inner surface of the bottom of the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal.

[0018] The exterior body 15 has a cylindrical shape with a bottom, and has a grooved portion 21 at the opening 15a. The exterior body 15 is made of, for example, metal. As will be described later, the grooved portion 21 supports the sealing body 16 on its upper surface. The electrode assembly 14 and non-aqueous electrolyte are accommodated in the portion of the exterior body 15 below the grooved portion 21. The grooved portion 21 is preferably present in an annular shape along the circumferential direction of the exterior body 15. The grooved portion 21 can be formed, for example, by pressing the side portion of the exterior body 15 from the outside.

[0019] 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 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may break, and gas may be released from the opening 26a of the cap 26.

[0020] Next, the sealed state of the opening 15a of the secondary battery 10 will be described with reference to Fig. 2. Fig. 2 is an enlarged view of the vicinity of the opening 15a of the exterior body 15.

[0021] The sealing body 16 is fixed by crimping between the grooved portion 21 and the opening edge 15b at the opening 15a of the exterior body 15. That is, the sealing body 16 is compressed and fixed between the grooved portion 21 and the opening edge 15b, which is the upper end of the inwardly bent exterior body 15, via a gasket 27. The gasket 27 is a flexible insulating member that electrically isolates the sealing body 16, which is the positive electrode terminal, from the exterior body 15, which is the negative electrode terminal, while being compressed in the vertical direction to ensure the internal sealing of the secondary battery 10. The material of the gasket 27 is not particularly limited as long as it is a compressible insulating material, and examples of materials that can be used include polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyamide (PA).

[0022] A powder of one or more compounds (hereinafter referred to as the compound) selected from the group consisting of hydroxides, oxides, and carbonates is present in a region of the inner surface of the exterior body 15 from the grooved portion 21 to the opening end 15b (hereinafter referred to as the opening upper region 30). As a result, even if a non-aqueous electrolyte adheres to the inner surface of the opening 15a and reacts with moisture that has entered through the opening end 15b to generate hydrofluoric acid, the hydrofluoric acid is neutralized by the compound present in the opening upper region 30, thereby suppressing corrosion of the exterior body 15. Furthermore, the compound does not volatilize even during long-term storage, so corrosion of the exterior body can be stably suppressed.

[0023] In the compound, it is preferable that (molecular weight) / (total valence of cations) is 60 or less. This makes it possible to reduce the required amount (mass) of the compound present in the upper opening region 30. Here, the total valence of cations is the sum of the valences of all cations constituting the compound. For example, the total valence of cations in Al2O3 is Al 3+ Since it contains two, the total is 6.

[0024] The compound preferably contains any one of aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), aluminum oxide (Al2O3), magnesium oxide (MgO), lithium carbonate (Li2CO3), and sodium carbonate (Na2CO3). These have low volatility and low toxicity, making them suitable for use in the secondary battery 10. The compound particularly preferably contains Al(OH)3 or Mg(OH)2. Since Al(OH)3 or Mg(OH)2 has a small specific gravity, it does not settle when preparing a coating liquid containing the compound, as will be described later, and is easy to handle.

[0025] The required amount of compound present in the opening upper region 30 can be calculated by estimating the amount of hydrofluoric acid generated from the amount of non-aqueous electrolyte expected to adhere to the opening 15a of the exterior body 15. For example, in an exterior body 15 having a cylindrical shape with a bottom and a diameter of φ18 mm and a height of 65 mm, preferably 0.5 mg to 40 mg, more preferably 1 mg to 20 mg, and particularly preferably 3 mg to 14 mg of compound is present in the opening, thereby neutralizing the hydrofluoric acid and suppressing corrosion of the exterior body 15.

[0026] To allow the compound to be present in the upper opening region 30, for example, a coating liquid containing the compound may be applied to the upper opening region 30. The coating liquid is a mixture of the compound and a solvent, and examples of the solvent include xylene, ethylbenzene, and toluene. Furthermore, additives such as rubber-based polymers, such as 1,2-polybutadiene, which have traditionally been used as sealants, pitch, asphalt, vinyl-based, silicone-based, acrylic-based, urethane-based, and fluorine-based polymers, may also be used in the coating liquid, or a combination of two or more of these may also be used. The proportion of the compound in the coating liquid is, for example, preferably 0.5% to 20% by mass, more preferably 1% to 10% by mass, and particularly preferably 3% to 7% by mass. Within this range, the coating liquid can be appropriately applied to the upper opening region 30. The proportion of the compound in the coating liquid is particularly preferably about 5% by mass from the viewpoints of viscosity, sedimentation, and coating amount, as well as improved workability. After application, the coating liquid may be dried by heat treatment. The heat treatment can be carried out, for example, by holding the film in an environment of 100°C to 200°C for 30 minutes to 300 minutes.

[0027] Next, an example of a method for manufacturing the secondary battery 10 will be described. First, insulating plates 17 and 18 are placed above and below the electrode assembly 14, and the electrode assembly 14 is housed in the exterior housing 15. Next, the negative electrode lead 20 is welded to the bottom of the exterior housing 15, and a grooved portion 21 is formed in the opening 15a of the exterior housing 15 by pressing. Then, a coating liquid is applied above the grooved portion 21. After leaving the assembly at room temperature for 30 minutes, a gasket 27 is housed above the grooved portion 21. Next, the sealing member 16 is welded to the positive electrode lead 19, and heat treatment is performed in a 110°C environment for 150 minutes. Next, an appropriate amount of nonaqueous electrolyte is injected into the interior of the exterior housing 15, and the sealing member 16 is crimped and fixed between the opening end 15b of the exterior housing 15 and the grooved portion 21 via the gasket 27, thereby producing a cylindrical nonaqueous electrolyte secondary battery. [Example]

[0028] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0029] Example 1 [Preparation of positive electrode] Lithium cobalt oxide (LiCoO2) was used as the positive electrode active material. 100 parts by weight of this positive electrode active material was mixed with 1 part by weight of acetylene black (AB) as a conductive agent and 1 part by weight of polyvinylidene fluoride (PVDF) as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. Next, this positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil, dried in a dryer, cut to the specified electrode size, and rolled using a roller to obtain a strip-shaped positive electrode. In addition, a plain section without active material was formed at one end of the positive electrode in the longitudinal direction, and an aluminum positive electrode lead was fixed to this plain section by ultrasonic welding.

[0030] [Preparation of negative electrode] Natural graphite powder was used as the negative electrode active material. 100 parts by mass of this negative electrode active material was mixed with 1 part by mass of styrene-butadiene rubber (SBR) as a binder and 1 part by mass of carboxymethyl cellulose (CMC) as a thickener, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to both sides of a negative electrode current collector made of copper foil, dried in a dryer, cut to a predetermined electrode size, and rolled using a roller to obtain a strip-shaped positive electrode. In addition, a plain section without active material was formed at one end of the negative electrode in the longitudinal direction, and a nickel negative electrode lead was fixed to this plain section by ultrasonic welding.

[0031] [Preparation of electrode body] The prepared positive and negative electrodes were spirally wound with a separator between them to prepare a wound electrode assembly. At this time, one end of the positive electrode connected to the positive electrode lead was located on the inner periphery (the winding start side), and one end of the negative electrode connected to the negative electrode lead was located on the outer periphery (the winding end side). The separator used was a polyethylene microporous membrane with a heat-resistant layer formed on one side, in which polyamide and alumina fillers were dispersed.

[0032] [Preparation of non-aqueous electrolyte] A non-aqueous electrolyte solution was prepared by adding LiPF6 to a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DMC = 3:3:4 to give a concentration of 1 mol / L.

[0033] [Preparation of coating solution] A coating solution was prepared by mixing 5 g of aluminum hydroxide (Al(OH)3) powder with a solvent consisting of 90 g of xylene and 5 g of 1,2-polybutadiene.

[0034] [Secondary battery production] The exterior was a cylindrical metal can with a bottom and a diameter of 18 mm and a height of 65 mm. Insulating plates were placed on the top and bottom of the electrode assembly, respectively. After the electrode assembly was housed in the exterior, the negative electrode lead was welded to the bottom of the exterior. A groove was formed in the opening of the exterior by pressing, and then a coating solution was applied above the groove. After holding the assembly at room temperature for 30 minutes, a gasket was housed above the groove. A sealing cap was welded to the positive electrode lead, and heat treatment was performed in a 110°C environment for 150 minutes. 6.5 g of nonaqueous electrolyte was then poured into the exterior. The opening of the exterior was then sealed by crimping the sealing cap via a gasket, resulting in a cylindrical nonaqueous electrolyte secondary battery. The secondary battery had a nominal voltage of 4.2 V and a rated capacity of 1950 mAh. Five secondary batteries were produced in this manner.

[0035] <Example 2> A battery was fabricated in the same manner as in Example 1, except that in applying the compound to the exterior body, a coating solution was prepared using magnesium hydroxide (Mg(OH)2) powder instead of Al(OH)3 powder.

[0036] Example 3 A battery was fabricated in the same manner as in Example 1, except that in applying the compound to the exterior body, aluminum oxide (Al2O3) powder was used instead of Al(OH)3 powder to prepare the coating solution.

[0037] Example 4 A battery was fabricated in the same manner as in Example 1, except that in applying the compound to the exterior body, a coating solution was prepared using magnesium oxide (MgO) powder instead of Al(OH)3 powder.

[0038] <Example 5> A battery was fabricated in the same manner as in Example 1, except that in applying the compound to the exterior body, a coating solution was prepared using lithium carbonate (Li2CO3) powder instead of Al(OH)3 powder.

[0039] Example 6 A battery was fabricated in the same manner as in Example 1, except that in applying the compound to the exterior body, a coating solution was prepared using sodium carbonate (Na2CO3) powder instead of Al(OH)3 powder.

[0040] <Comparative Example 1> A battery was fabricated in the same manner as in Example 1, except that when coating the compound on the exterior body, no Al(OH)3 powder was mixed into the coating solution, and only 95 g of xylene and 5 g of polybutadiene were mixed to prepare the coating solution.

[0041] <Comparative Example 2> When applying the compound to the exterior body, butylamine (C4H 11 N) Using liquid, C4H 11 A battery was fabricated in the same manner as in Example 1, except that the coating solution was prepared by mixing 10 g of N, 85 g of xylene, and 5 g of polybutadiene.

[0042] [Evaluation of corrosion occurrence through accelerated testing] The batteries of the examples and comparative examples were charged at a constant current of 0.3 C in a 25°C environment until the battery voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current value reached 0.02 C. The batteries were then held in an environment of 75°C and 90% humidity for 30 days to conduct an accelerated corrosion test for the exterior body. After the accelerated test, 360° cross-sections of the batteries were observed using an X-ray CT (Computed Tomography) device to confirm the presence or absence of corrosion of the exterior body above the grooved portion. Evaluation was based on the number of batteries in which corrosion occurred.

[0043] The evaluation results of the examples and comparative examples are shown in Table 1. Table 1 also shows the type of compound mixed in the coating liquid, the molecular weight, the total valence of the cations, and (molecular weight) / (total valence of the cations).

[0044] [Table 1]

[0045] Corrosion occurred in all the batteries in Comparative Examples 1 and 2, but no corrosion occurred in Examples 1 to 6. In Comparative Example 2, the compound (C4H 11 Although no effect was observed even when the proportion of C4H) was 10% by mass, in Examples 1 to 6, the effect was observed when the compound was contained at half the amount, 5% by mass. 11 N exhibits monovalent alkalinity by coordinating one proton to the amino group, but because it has a large molecular weight, a large amount is required to neutralize hydrofluoric acid, and because it is volatile, the amount added was reduced, and it is thought that the amount added this time was not sufficient to neutralize hydrofluoric acid. [Explanation of symbols]

[0046] 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 exterior body, 15a opening, 15b opening edge, 16 sealing body, 17, 18 insulating plate, 19 positive electrode lead, 20 negative electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a opening hole, 27 gasket, 30 upper opening region

Claims

1. an exterior body having a bottomed cylindrical shape and a grooved portion at an opening; an electrode assembly and a non-aqueous electrolyte housed in the exterior housing; a sealing body that is fixed by crimping between the grooved portion and the opening edge in the opening, a cylindrical nonaqueous electrolyte secondary battery, wherein one or more hydroxide powders are present in a region from the grooved portion to the open end of the inner surface of the exterior body;

2. 2. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the hydroxide has a molecular weight / total valence of cations of 60 or less.

3. 3. The cylindrical nonaqueous electrolyte secondary battery according to claim 1, wherein the hydroxide includes either aluminum hydroxide or magnesium hydroxide.

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