Non-aqueous electrolyte secondary battery

Abstract

A non-aqueous electrolyte secondary battery (10) is provided with: an electrode body (14); a bottomed cylindrical outer can (20) that contains a first metal material; and a sealing body (30) that closes an opening (24) of the outer can (20). The non-aqueous electrolyte secondary battery (10) is characterized in that the side surface of the outer can (20) on the opening (24) side is provided with an annular groove (23) that is recessed inward in the radial direction of the outer can, inside the annular groove (23), there is a protective member (40) that abuts at least a portion of the surface of the annular groove (23) and contains a second metal material, and the melting point of the second metal material is lower than the melting point of the first metal material and is 500°C or lower.

Description

Nonaqueous electrolyte secondary battery

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

[0002] A nonaqueous electrolyte secondary battery has been known that includes an electrode assembly having a positive electrode and a negative electrode, a cylindrical outer can with a bottom that houses the electrode assembly, and a sealing body that closes the opening of the outer can. The sealing body is supported on the upper surface of an annular groove provided in the side surface of the outer can and is fixed to the top of the outer can by being crimped to the opening of the outer can.

[0003] Patent Document 1 discloses a nonaqueous electrolyte secondary battery in which an insulating coating layer is provided on the entire side surface of the outer can, including the inside of the annular groove. Patent Document 1 also describes that providing the coating layer can suppress the occurrence of short circuits caused by dust from the metal material that constitutes the outer can during the manufacturing process.

[0004] Japanese Patent Application Laid-Open No. 2005-071710

[0005] In a nonaqueous electrolyte secondary battery, for example, if an external short circuit occurs while the battery is being charged, a large current may be applied to the electrode body, causing the electrode body to overheat abnormally. This may result in gas generation inside the battery, increasing the internal pressure of the battery and damaging the outer can. If the outer can is damaged, gas may be ejected from the damaged area, which is undesirable from the viewpoint of ensuring the safety of the battery.

[0006] Furthermore, as a result of investigations by the present inventors, it was found that damage to the outer can when an abnormality occurs in the battery may occur in the annular groove provided in the outer can, and therefore it is an important issue to prevent damage to the annular groove when an abnormality occurs in the battery.

[0007] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure is a nonaqueous electrolyte secondary battery including: an electrode assembly having a positive electrode and a negative electrode; a nonaqueous electrolyte; a cylindrical outer can with a bottom that houses the electrode assembly and the nonaqueous electrolyte and contains a first metal material; and a sealing member that closes an opening of the outer can; the side surface of the outer can is provided with an annular groove recessed radially inward of the outer can; a protective member that abuts at least a portion of the surface of the annular groove and contains a second metal material is provided inside the annular groove; and the melting point of the second metal material is lower than the melting point of the first metal material and is 500°C or lower.

[0008] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, damage to the annular groove in the event of a battery abnormality can be suppressed, and as a result, a highly safe nonaqueous electrolyte secondary battery can be provided.

[0009] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment; Fig. 2 is an enlarged view of the vicinity of an annular groove provided in an outer can in Fig. 1; Fig. 3 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to another embodiment, showing an enlarged view of the vicinity of an annular groove provided in an outer can; Fig. 4 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to another embodiment, showing an enlarged view of the vicinity of an annular groove provided in an outer can.

[0010] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. 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.

[0011] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte (not shown), and an outer can 20 that houses the electrode assembly 14 and the nonaqueous electrolyte. The outer can 20 is a cylindrical metal container that is open on one axial side and has a bottom, and an opening 24 of the outer can 20 is closed by a sealing body 30. Hereinafter, the side of the sealing body 30 in the axial direction (height direction) of the nonaqueous electrolyte secondary battery 10 will be referred to as "upper," and the side of the bottom 21 of the outer can 20 in the axial direction will be referred to as "lower."

[0012] The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11. The nonaqueous electrolyte secondary battery 10 includes insulating plates 16 and 17 arranged above and below the electrode assembly 14, respectively.

[0013] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. The positive electrode core can be a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably formed on both sides of the positive electrode core, excluding the exposed portion of the positive electrode core (not shown) to which the positive electrode lead 18 is welded. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.

[0014] The positive electrode mixture layer contains particulate lithium metal composite oxide as a positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium metal composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among them, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0015] Examples of conductive agents contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0016] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and, if necessary, a conductive agent, and is preferably formed on both sides of the negative electrode core, excluding the exposed portion of the negative electrode core (not shown) to which the negative electrode lead 19 is welded. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0017] The negative electrode mixture layer generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, as the negative electrode active material, a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element may be used. Among these, a composite material containing Si is preferred.

[0018] A suitable example of a composite material containing Si is SiO ２ Examples of such composite materials include a material in which Si fine particles are dispersed in a silicate phase such as lithium silicate, or a material in which Si fine particles are dispersed in an amorphous carbon phase. A conductive layer such as a carbon coating is formed on the particle surfaces of the composite material.

[0019] As in the case of the positive electrode mixture layer, the binder contained in the negative electrode mixture layer can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene-butadiene rubber (SBR) is preferably used. The negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer may contain a conductive agent such as CNT.

[0020] The separator 13 is a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0021] A positive electrode lead 18 is connected to the positive electrode 11, and a negative electrode lead 19 is connected to the winding end side of the negative electrode 12. The positive electrode lead 18 passes through a through hole in the insulating plate 16 and extends toward the sealing body 30, and the negative electrode lead 19 passes outside the insulating plate 17 and extends toward the bottom 21 of the outer can 20. The positive electrode lead 18 is connected to the underside of an internal terminal plate 31 of the sealing body 30 by welding or the like, and the sealing body 30 serves as a positive electrode terminal. The negative electrode lead 19 is connected to the inner surface of the bottom 21 of the metal outer can 20 by welding or the like, and the outer can 20 serves as a negative electrode terminal.

[0022] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0023] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0024] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0025] The exterior can 20 is a cylindrical container with a bottom that is open on one axial side. The exterior can 20 has a bottom 21 and a side surface 22 that forms the side surface of the nonaqueous electrolyte secondary battery 10. The side surface 22 is the portion of the exterior can 20 excluding the bottom 21, and includes an annular groove 23 and an opening 24, which will be described later.

[0026] The exterior can 20 contains a metal material (first metal material). Examples of the first metal material include iron, stainless steel, aluminum, an aluminum alloy, and nickel. In this embodiment, the exterior can 20 is made of a steel material containing iron as a main component.

[0027] The annular groove 23 is a portion of the side surface 22 recessed radially inward, and is provided in a ring shape along the circumferential direction of the outer can 20. The annular groove 23 supports the sealing body 30 on its upper surface. The annular groove 23 can be formed, for example, by spinning a portion of the side surface 22 radially inward to recess the annular groove radially inward. The width (axial length) of the annular groove 23 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 annular groove 23 is also not particularly limited, but is, for example, 0.5 mm or more and 5.0 mm or less. As will be described in detail later, a protective member 40 is provided inside the annular groove 23.

[0028] The opening 24 is a region of the side surface portion 22 that is above the annular groove 23 and forms an opening in the outer can 20. The opening 24 is bent radially inward when the sealing body 30 is crimped and fixed to the outer can 20. As a result, the opening 24 is formed with an opening side surface portion 25 that forms part of the side surface of the nonaqueous electrolyte secondary battery 10 and covers the outer peripheral surface of the gasket 34, and a crimped portion 26 that forms part of the top surface of the nonaqueous electrolyte secondary battery 10 and extends radially inward. In this embodiment, the radially inner end of the crimped portion 26 is located radially outward of the radially inner end of the gasket 34. In other words, part of the top surface of the gasket 34 is not covered by the crimped portion 26.

[0029] The sealing body 30 is a disc-shaped member equipped with a safety valve. The sealing body 30 has a structure in which an internal terminal plate 31, an insulating member 32, and an external terminal plate 33 are stacked in this order from the electrode body 14 side.

[0030] The internal terminal plate 31 is a metal plate including a thick portion 31A to which the positive electrode lead 18 is connected and a thin central portion 31B that is separated from the thick portion 31A when the internal pressure of the battery exceeds a predetermined threshold. A plurality of vent holes 31C are formed in the thick portion 31A.

[0031] The insulating member 32 insulates the portions other than the connection portion between the internal terminal plate 31 and the external terminal plate 33. The insulating member 32 has an opening 32A formed in the radial center thereof, and an air vent 32B formed in a portion overlapping with the air vent 31C of the internal terminal plate 31.

[0032] The external terminal plate 33 forms a part of the upper surface of the nonaqueous electrolyte secondary battery 10 and is disposed opposite the internal terminal plate 31 with the insulating member 32 sandwiched therebetween. The external terminal plate 33 has a thin-walled portion 33A that breaks when the internal pressure of the nonaqueous electrolyte secondary battery 10 exceeds a predetermined threshold. The external terminal plate 33 is connected at its radial center to a central portion 31B of the internal terminal plate 31 by welding or the like. The radial outer side of the external terminal plate 33 is sandwiched, via a gasket 34, between the annular groove 23 and a crimping portion 26 formed by bending the opening of the outer can 20 inward.

[0033] When an abnormality occurs in the nonaqueous electrolyte secondary battery 10 and the internal pressure rises, the generated high-temperature gas pushes the internal terminal plate 31 upward, causing the internal terminal plate 31 to break, separating the central portion 31B from the thick portion 31A, and deforming the external terminal plate 33 so that it protrudes toward the outside of the battery, thereby interrupting the current path in the sealing body 30. Then, when the internal pressure of the nonaqueous electrolyte secondary battery 10 rises further after the current path is interrupted, the thin portion 33A of the external terminal plate 33 breaks, forming a gas outlet in the external terminal plate 33.

[0034] The structure of sealing body 30 is not limited to the structure shown in Fig. 1. Sealing body 30 may have, for example, a convex cap that covers external terminal board 33.

[0035] The gasket 34 is a flexible insulating member that electrically isolates the sealing body 30, which is the positive electrode terminal, from the outer can 20, which is the negative electrode terminal, while being compressed in the vertical direction to ensure the airtightness of the interior of the outer can 20. The material of the gasket 34 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).

[0036] Next, the protective member 40 will be described in detail with further reference to Figures 2 and 3. Figure 2 is an enlarged view of the vicinity of the annular groove 23 in Figure 1, and is a view schematically showing the shape of the protective member 40.

[0037] 2 , a protective member 40 made of a metal material is provided inside the annular groove 23. In this embodiment, the protective member 40 has a wire shape and extends along the circumferential direction of the outer casing 20. The protective member 40 is wound around the annular groove 23 multiple times, thereby occupying substantially the entire interior of the annular groove 23 and abutting against the upper surface 23A and the lower surface 23B of the annular groove 23.

[0038] As a result of investigations by the present inventors, it has become clear that when abnormal heat generation occurs in the electrode body 14, gas is generated inside the battery, and when the internal pressure of the battery increases, damage to the outer can 20 may occur in the area where the annular groove 23 is formed. Although the detailed mechanism is not clear, it is thought that when abnormal heat generation occurs in the electrode body 14, sparks generated on the outer periphery of the electrode body 14 may hit the annular groove 23, causing the temperature near the annular groove 23 to rise excessively, resulting in damage to the outer can 20 in the area where the annular groove 23 is formed.

[0039] The protective member 40 contains a metal material (second metal material) different from the first metal material (steel in this embodiment) constituting the outer can 20 and is disposed so as to abut against the upper surface 23A and the lower surface 23B of the annular groove 23. The melting point of the second metal material constituting the protective member 40 is lower than the melting point of the first metal material constituting the outer can 20 and is 500°C or less. By including the second metal material in the protective member 40, the second metal material preferentially melts when the temperature near the annular groove 23 rises excessively during abnormal heat generation in the electrode body 14. As a result, the heat absorption effect caused by melting suppresses the temperature rise near the annular groove 23, thereby preventing damage to the annular groove 23 in the event of a battery abnormality. The protective member 40 preferably contains the second metal material as its main component. Here, "main component" refers to the component with the highest mass ratio among the materials constituting the protective member 40. More preferably, the protective member 40 contains 80 mass% or more of the second metal material. In this embodiment, the protective member 40 is composed solely of the second metal material.

[0040] The melting point of the second metal material contained in protective member 40 is lower than the melting point of the first metal material contained in outer can 20 and may be 500° C. or lower, preferably 400° C. or lower, and more preferably 300° C. or lower. By lowering the melting point of the second metal material contained in protective member 40, it is possible to further suppress the temperature rise in the vicinity of annular groove 23 when an abnormality occurs in the battery.

[0041] The second metal material contained in the protective member 40 preferably contains at least one selected from the group consisting of tin, lead, and zinc. By containing at least one selected from the group consisting of tin, lead, and zinc, it becomes easy to set the melting point of the second metal material to 500°C or less. The second metal material may be an alloy containing at least two selected from the group consisting of tin, lead, and zinc. An example of the second metal material constituting the protective member 40 is an alloy material such as solder.

[0042] As described above, the protective member 40 has a wire shape. In this embodiment, the protective member 40 has a generally circular cross-sectional shape. The size of the protective member 40 is not particularly limited as long as it can be inserted into the annular groove 23, but for example, the diameter of the wire is 0.1 mm or more and 2.0 mm or less. The cross-sectional shape of the protective member 40 is not limited to a circular shape, and may be an elliptical shape or a rectangular shape.

[0043] In this embodiment, the protective member 40 is disposed over substantially the entire interior of the annular groove 23. In other words, the ratio of the area of ​​the protective member 40 inside the annular groove 23 to the area of ​​the space within the annular groove 23 is 80% or more. By setting the ratio of the area of ​​the protective member 40 to the area of ​​the space within the annular groove 23 to be 80% or more, the volume of the protective member 40 can be secured, and the heat absorption effect due to melting of the protective member 40 in the event of abnormal heat generation in the electrode assembly 14 can be improved. As a result, the temperature rise near the annular groove 23 can be further suppressed, and damage to the annular groove 23 in the event of a battery abnormality can be further suppressed. The area of ​​the space within the annular groove 23 in the axial cross-section of the outer can 20 refers to the area of ​​the region surrounded by the imaginary line α along the outer surface of the side surface portion 22 of the outer can 20 and the wall surface of the annular groove 23.

[0044] The ratio of the area of ​​the protective member 40 to the area of ​​the space in the annular groove 23 in an axial cross-sectional view of the outer can 20 is preferably 85% or more, and more preferably 90% or more. Increasing the ratio of the area of ​​the protective member 40 to the area of ​​the space in the annular groove 23 can further improve the heat absorption effect caused by melting of the protective member 40 in the event of abnormal heat generation in the electrode body 14. Furthermore, the ratio of the area of ​​the protective member 40 to the area of ​​the space in the annular groove 23 may be substantially 100%, i.e., the protective member 40 may be disposed so as to fill the entire annular groove 23.

[0045] The above-described embodiment may be modified as appropriate within the scope of the present disclosure. For example, in the above-described embodiment, the protective member 40 has a wire shape, but the shape of the protective member 40 is not limited thereto as long as it abuts at least a portion of the surface of the annular groove. The protective member 40 may also be a plate-like member having a circular ring shape or an arc shape in a plan view. The protective member 40 may be composed of, for example, two plate-like members having a semicircular shape in a plan view, and may be fixed to the annular groove 23 by being fitted into the annular groove 23 from the radially outer side of the outer can 20.

[0046] In the above embodiment, the protective member 40 is disposed so as to abut against the upper surface 23A and the lower surface 23B of the annular groove 23, but the protective member 40 may be in contact with only one of the upper surface 23A or the lower surface 23B of the annular groove 23. Note that, when the battery abnormally generates heat, the temperature of the lower surface 23B of the annular groove 23 is more likely to rise than that of the upper surface 23A. Therefore, it is preferable that the protective member 40 abut against at least the lower surface 23B of the annular groove 23.

[0047] 3 and 4, the protective member 40 may be disposed so as to cover at least a portion of the surface of the annular groove 23. In the example shown in Fig. 3, the protective member 40 is disposed so as to cover substantially the entire surface of the annular groove 23, and in the example shown in Fig. 4, the protective member 40 is disposed so as to cover the lower surface 23B of the annular groove 23.

[0048] When the protective member 40 is disposed so as to cover at least a portion of the surface of the annular groove 23, the protective member 40 preferably covers 25% or more of the surface area of ​​the annular groove 23, and more preferably covers 50% or more of the surface area of ​​the annular groove 23. By having the protective member 40 cover 25% or more of the surface area of ​​the annular groove 23, it becomes easier to suppress a temperature rise in the vicinity of the annular groove 23 when the battery abnormally heats up.

[0049] In the above embodiment, the protective member 40 provided in the annular groove 23 is made of only the second metal material having a melting point of 500°C or less, but the protective member 40 may contain a material other than the second metal material. Examples of the material other than the second metal material include a metal material or a resin material having a melting point higher than 500°C.

[0050] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0051] <Examples> [Fabrication of Positive Electrode] Aluminum-containing lithium nickel cobalt oxide (LiNi) was used as the positive electrode active material. ０．８８ Co ０．０９ Al ０．０３ O ２ ) was used. 100 parts by mass of the positive electrode active material, 1.0 part by mass of acetylene black as a conductive agent, and 0.9 parts by mass of polyvinylidene fluoride (PVDF) as a binder were mixed in a dispersion medium of N-methylpyrrolidone (NMP) 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, and then cut to a predetermined electrode size and rolled using a roller to obtain a strip-shaped positive electrode. In addition, a positive electrode current collector exposed portion where no positive electrode mixture layer was formed was formed in a portion of the positive electrode in the longitudinal direction, and an aluminum positive electrode lead was fixed to the positive electrode current collector exposed portion by ultrasonic welding.

[0052] [Negative Electrode Fabrication] A mixture of 90 parts by weight of graphite powder and 10 parts by weight of silicon oxide was used as the negative electrode active material. 100 parts by weight of the negative electrode active material, 1 part by weight of CMC as a thickener, and 1 part by weight of styrene-butadiene rubber as a binder were mixed in water 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, cut to a predetermined electrode size, and rolled using a roller to obtain a strip-shaped negative electrode. Furthermore, an exposed portion of the negative electrode current collector where the negative electrode mixture layer was not formed was formed at one end of the negative electrode in the longitudinal direction, and a nickel negative electrode lead was fixed to the exposed portion of the negative electrode current collector by ultrasonic welding.

[0053] [Fabrication of Electrode Assembly] The fabricated positive and negative electrodes were spirally wound with a separator interposed therebetween to fabricate a wound electrode assembly. The separator was a polyethylene microporous membrane with a heat-resistant layer formed on one side with a polyamide and alumina filler dispersed therein.

[0054] [Preparation of non-aqueous electrolyte] LiPF 6 was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4 (25°C). ６ was dissolved in the solution at a concentration of 1.2 mol / L to prepare a non-aqueous electrolyte.

[0055] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A cylindrical steel metal can with a diameter of 21 mm and a height of 70 mm was used as the outer can. The electrode assembly was housed in the outer can with insulating plates placed on the top and bottom of the electrode assembly, and the negative electrode lead was then welded to the bottom of the outer can. The outer can was then spun to form an annular groove. The width (axial length) of the annular groove was 0.4 mm, and the depth (radial length) of the annular groove was 2.0 mm.

[0056] Then, an internal terminal plate was placed on the annular groove via a gasket, and the positive electrode lead was ultrasonically welded to the upper surface of the internal terminal plate. After that, the external terminal plate was placed on the internal terminal plate after degassing under reduced pressure. The external terminal plate and the internal terminal plate were welded, and then the upper end of the outer can was crimped to fix the sealing body to the top of the outer can. Finally, a solder wire (composition: Sn 99%, Ag 0.3%, Cu 0.7%, melting point: about 230 ° C., manufactured by HOZAN, HS-341) having a generally circular cross section (diameter: 0.3 mm) was wound around the annular groove so as to be positioned throughout the entire annular groove. From the length of the wound solder wire, the ratio of the area of ​​the protective member to the area of ​​the space in the annular groove in the axial cross section of the outer can was calculated, and it was 85%.

[0057] Comparative Example A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that no protective member was provided in the fabrication of the nonaqueous electrolyte secondary battery.

[0058] [Evaluation of Battery Heating Test] Three batteries each of the Example and Comparative Example were fabricated, and each was placed in an oven at 500°C for 10 minutes, after which heating was stopped. The exterior cans were then visually inspected to evaluate the presence or absence of perforations in the annular groove (presence or absence of gas ejection from the annular groove). As a result, no perforations were observed in any of the three Example batteries. On the other hand, perforations were observed in all three Comparative Example batteries. This is presumably because the provision of a protective member in the annular groove suppressed the temperature rise near the annular groove 23 in the event of a battery abnormality.

[0059] The present disclosure is further described by the following embodiments. Aspect 1: A nonaqueous electrolyte secondary battery including an electrode assembly having a positive electrode and a negative electrode, a nonaqueous electrolyte, a cylindrical outer can with a bottom that houses the electrode assembly and the nonaqueous electrolyte and contains a first metal material, and a sealing member that closes an opening of the outer can, wherein a side surface of the outer can is provided with an annular groove recessed radially inward of the outer can, and a protective member is provided inside the annular groove and in contact with at least a portion of the surface of the annular groove and contains a second metal material, the second metal material having a melting point lower than that of the first metal material and not higher than 500°C. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein the second metal material contains at least one selected from the group consisting of tin, lead, and zinc. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein the second metal material is an alloy containing at least two selected from the group consisting of tin, lead, and zinc. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the second metal material is solder.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the protective member has a wire shape and extends along the circumferential direction of the outer can.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the protective member covers 25% or more of the surface area of ​​the annular groove.Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein, in an axial cross-sectional view of the outer can, the ratio of the area of ​​the protective member inside the annular groove to the area of ​​the space in the annular groove is 80% or more.

[0060] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 16, 17 insulating plate, 18 positive electrode lead, 19 negative electrode lead, 20 outer can, 21 bottom, 22 side surface, 23 annular groove, 23A upper surface, 23B lower surface, 24 opening, 25 opening side surface, 26 crimping portion, 30 sealing body, 31 internal terminal plate, 31A thick portion, 31B central portion, 31C ventilation hole, 32 insulating member, 32A opening, 32B ventilation hole, 33 external terminal plate, 33A thin portion, 34 gasket, 40 protective member, α virtual line

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body having a positive electrode and a negative electrode; a non-aqueous electrolyte; a bottomed cylindrical outer can containing the electrode body and the non-aqueous electrolyte and containing a first metal material; and a sealing body for closing an opening of the outer can, wherein an annular groove recessed inward in the radial direction of the outer can is provided on a side surface of the outer can, and a protective member containing a second metal material is provided inside the annular groove and is in contact with at least a part of a surface of the annular groove, and a melting point of the second metal material is lower than a melting point of the first metal material and is 500 °C or lower.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the second metal material contains at least one selected from the group consisting of tin, lead, and zinc.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the second metal material is an alloy containing at least two selected from the group consisting of tin, lead, and zinc.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the second metal material is solder.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective member has a wire shape and extends along a circumferential direction of the outer can.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective member covers a region of 25% or more of a surface of the annular groove.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein a ratio of an area of the protective member inside the annular groove to an area of a space of the annular groove in an axial cross-sectional view of the outer can is 80% or more.