Nonaqueous electrolyte secondary battery

Abstract

A nonaqueous electrolyte secondary battery (10) according to one embodiment of the present disclosure is characterized by being provided with: a cylindrical outer can package (20) which has a bottom part (21) at one end and an opening part (24) at the other end; an electrode body (14) and a nonaqueous electrolyte which are housed in a body part (22) of the outer can package (20); and a sealing body (30) which closes the opening part (24). The nonaqueous electrolyte secondary battery (10) is also characterized in that: an annular groove (23), in which the diameter of the outer package can (20) is smaller than that in the body part (22), is formed between the opening part (24) and the body part (22); a ring-shaped protective member (40) is provided between the electrode body (14) and the annular groove (23); and the protective member (40) has a planar base material part and a first protruding part that protrudes in the direction of the electrode body at the outer peripheral edge of the base material part.

Description

Non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a nonaqueous electrolyte secondary battery, and more particularly to a cylindrical nonaqueous electrolyte secondary battery having an annular groove formed in an outer can.

[0002] A non-aqueous electrolyte secondary battery has been known that includes a cylindrical outer can with a bottom, an electrode assembly and a non-aqueous electrolyte housed in the body of the outer can, and a sealing member that closes the opening of the outer can. An annular groove having a diameter smaller than that of the body is formed in the side of the outer can between the opening and the body, and an insulating plate is disposed between the annular groove and the electrode assembly.

[0003] Patent Document 1 discloses an insulating plate in which a metal plate such as iron or stainless steel is coated with an insulating material to improve strength.

[0004] JP 2008-103131 A

[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 research 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. Therefore, it is an important issue to prevent damage to the annular groove when an abnormality occurs in the battery. The technology described in Patent Document 1 does not consider preventing damage to the annular groove, and there is still room for improvement.

[0007] A non-aqueous electrolyte secondary battery according to one aspect 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 non-aqueous electrolyte housed in a body of the outer can, and a sealing body that closes the opening, wherein an annular groove is formed between the opening and the body, and the outer can has a diameter smaller than that of the body, and a ring-shaped protective member is provided between the electrode assembly and the annular groove, and the protective member has a flat substrate and a first protrusion that protrudes from the outer periphery of the substrate toward the electrode assembly.

[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] 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention; 2 is a perspective view of a protective member constituting the nonaqueous electrolyte secondary battery according to an embodiment of the present invention; 3 is an enlarged view of the axial cross-section of a protective member constituting the nonaqueous electrolyte secondary battery according to an embodiment of the present invention;

[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 earthy graphite, and graphite such as lump artificial graphite and artificial graphite such as 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 has a cylindrical shape and has a bottom 21 at one end and an opening 24 at the other end. The electrode assembly 14 and a non-aqueous electrolyte are accommodated in a body 22 of the exterior can 20. An annular groove 23 is formed between the body 22 and the opening 24, and the diameter of the exterior can 20 is smaller than that of the body 22.

[0026] The annular groove 23 is a portion of the side surface of the outer can 20 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 of the outer can 20 radially inward to form a ring shape recessed 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.

[0027] The opening 24 is an area of ​​the side surface of the outer can 20 above the annular groove 23, and forms the opening of the outer can 20. The vicinity of the opening edge is bent radially inward, and the sealing body 30 is fixed to the outer can 20 by crimping.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The external terminal plate 33 forms 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 between the open end of the outer can 20 and the annular groove 23 via a gasket 34.

[0032] 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.

[0033] 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.

[0034] 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).

[0035] The nonaqueous electrolyte secondary battery 10 includes a ring-shaped protective member 40 between the electrode body 14 and the annular groove 23. As will be described later, by disposing the protective member 40 having a predetermined shape between the electrode body 14 and the annular groove 23, damage to the annular groove 23 in the event of a battery abnormality can be suppressed. In the example shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes the protective member 40 between the insulating plate 16 and the annular groove 23, but is not limited to this example. For example, the nonaqueous electrolyte secondary battery 10 may not include the insulating plate 16, and the protective member 40 may be disposed so as to contact the electrode body 14.

[0036] Next, the protective member 40 will be described in detail with reference to Figures 2 and 3. Figure 2 is a perspective view of an example of the protective member 40. Figure 3 is an enlarged view of an axial cross section of an example of the protective member 40, i.e., an enlarged view of the protective member in Figure 1.

[0037] 2 , the protective member 40 has a flat substrate portion 41, a first protrusion 42 that protrudes from the outer peripheral edge of the substrate portion 41 toward the electrode body 14, and a second protrusion 43 that protrudes from the inner peripheral edge of the substrate portion 41 toward the sealing body 30. This makes it possible to suppress damage to the annular groove 23 in the event of a battery abnormality. The substrate portion 41, the first protrusion 42, and the second protrusion 43 all have a ring shape.

[0038] Because the annular groove 23 is formed by recessing the side surface of the outer can 20 radially inward, it is believed that the annular groove 23 is susceptible to damage when gases or flames generated in the event of a battery abnormality strike the annular groove 23. The area near the connection between the annular groove 23 and the body portion 22 is thinner than other areas and is particularly susceptible to damage in the event of a battery abnormality. The first protrusion 42 protruding downward from the outer circumferential edge of the base portion 41 protects the area near the connection between the annular groove 23 and the body portion 22, thereby improving battery safety. Furthermore, the protective member 40 further includes a second protrusion 43 protruding upward from the inner circumferential edge of the base portion 41, thereby protecting the radially inner tip portion of the annular groove 23, further improving battery safety.

[0039] The shape of the protective member 40 is not limited to the example shown in Fig. 2. In the protective member 40, the first protruding portion 42 is an essential component, but the second protruding portion 43 is an optional component. For example, the protective member 40 may have a flat base portion 41 and the first protruding portion 42, but not the second protruding portion 43. Note that an embodiment in which the protective member 40 has the first protruding portion 42 and the second protruding portion 43 is more effective in suppressing damage to the annular groove than an embodiment in which the protective member 40 has only the first protruding portion 42.

[0040] The material of the protective member 40 is not particularly limited, but is preferably one having high strength and high heat resistance. The protective member 40 contains, for example, at least one selected from the group consisting of metal materials, ceramic materials, and resin materials. These may be used alone or in combination of two or more. Examples of metal materials include metals such as copper, zinc, tin, iron, and aluminum, and alloys such as stainless steel. Examples of ceramic materials include alumina, titania, zirconia, magnesium oxide, silicon nitride, aluminum nitride, boron nitride, and silicon carbide. Examples of resin materials include polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), and polyamide (PA). When the protective member 40 contains a metal material, the nonaqueous electrolyte secondary battery 10 preferably includes an insulating plate 16.

[0041] An example of the protective member 40 has a cross-sectional shape as shown in FIG.

[0042] The thickness A of the substrate 41 is, for example, 1.5 mm or less, and is preferably 0.05 mm or more and 1 mm or less, and more preferably 0.1 mm or more and 0.5 mm or less.

[0043] The height B of the first protrusion 42 is, for example, 10 mm or less. The height B of the first protrusion 42 is preferably 0.1 mm or more and 5 mm or less, and more preferably 0.3 mm or more and 2 mm or less.

[0044] The height C of the second protrusion 43 is, for example, 1.5 mm or less. The height C of the second protrusion 43 is preferably 0.1 mm or more and 1 mm or less, and more preferably 0.3 mm or more and 0.7 mm or less.

[0045] The width X of the protective member 40 is, for example, greater than the distance L (see FIG. 1 ) from the inner surface of the body 22 to the tip of the annular groove 23 in the radial direction of the outer can 20, in other words, the depth (radial length) of the annular groove. The width X of the protective member 40 is, for example, 7.5 mm or less. The width X of the protective member 40 is preferably 0.5 mm or more and 5 mm or less, and more preferably 1 mm or more and 3 mm or less.

[0046] The width Y of the first protrusion 42 is, for example, 1 mm or less. The width Y of the first protrusion 42 is preferably 0.05 mm or more and 0.5 mm or less, and more preferably 0.1 mm or more and 0.3 mm or less.

[0047] The width Z of the second protrusion 43 is, for example, 1 mm or less. The width Z of the second protrusion 43 is preferably 0.05 mm or more and 0.5 mm or less, and more preferably 0.1 mm or more and 0.3 mm or less.

[0048] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0049] <Example 1> [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 core 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 core 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 core exposed portion by ultrasonic welding.

[0050] [Negative Electrode Preparation] 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 core made of copper foil, dried, cut to a predetermined electrode size, and rolled using a roller to obtain a strip-shaped negative electrode. Furthermore, a negative electrode core exposed portion 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 negative electrode core exposed portion by ultrasonic welding.

[0051] [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.

[0052] [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.

[0053] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A metal can made of steel and shaped like a cylinder with a bottom, having a diameter of 21 mm and a height of 70 mm, was used as the outer can. Insulating plates with a thickness of 0.3 mm were placed on the top and bottom of the electrode body, and a protective member was placed on the insulator placed on the electrode body. The shape of the protective member is as shown in Figures 1 to 3, and is as follows: Thickness A of base portion 41: 0.3 mm Height B of first protrusion 42: 0.3 mm Height C of second protrusion 43: 0.3 mm Width X of protective member 40: 2 mm Width Y of first protrusion 42: 0.2 mm Width Z of second protrusion 43: 0.2 mm

[0054] In this state, the electrode assembly was housed in an outer can, and then the negative electrode lead was 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 distance from the inner surface of the body 22 to the tip of the annular groove 23 was 1.5 mm. Next, an internal terminal plate was placed on the annular groove via a gasket, and the positive electrode lead was ultrasonically welded to the top surface of the internal terminal plate. After degassing under reduced pressure, an external terminal plate was placed on the internal terminal plate, and the external terminal plate and the internal terminal plate were welded together. The top end of the outer can was then crimped to secure the sealing body to the top of the outer can.

[0055] Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that a protective member having only a base portion and a first protrusion and not a second protrusion was used. The dimensions A, B, X, and Y of the protective member were the same as those in Example 1.

[0056] Comparative Example 1 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.

[0057] Comparative Example 2 A nonaqueous electrolyte secondary battery was fabricated in the same manner as in Example 1, except that an insulating plate formed by sandwiching a SUS304 metal plate between polypropylene (PP) layers was used as the insulating plate placed on the electrode assembly, and no protective member was provided. The thickness of the SUS304 metal plate was 0.3 mm, the thickness of the PP was 0.3 mm, and the total thickness of the insulating plate was 0.9 mm.

[0058] [Evaluation of Battery Heating Test] Ten batteries each of the Example and Comparative Example were prepared, and each was placed in an oven at 500°C and heated for 10 minutes, after which the heating was stopped. Damage to the annular groove of the outer can was visually evaluated, and each battery was classified into "× (major damage)", "△ (minor damage)", or "◯ (no damage)" based on the following evaluation criteria, and the number of batteries that fell into each category was counted. The evaluation results of the Example and Comparative Example are shown in Table 1. × (major damage): Area is 4 mm ２ Damage is more than 4mm ２ There is less than 100% damage. ○ (No damage): There is no damage.

[0059]

[0060] As shown in Table 1, the batteries of the comparative example suffered from significant damage rated as "x (severe damage)," whereas none of the batteries of the example suffered from significant damage rated as "x (severe damage)." In particular, 9 out of 10 batteries of example 1 were rated as "○ (no damage)." This demonstrates that the safety of the battery can be improved by providing a protective member between the electrode body and the annular groove, the protective member having a ring-shaped, flat base material and a first protrusion that protrudes toward the electrode body from the outer periphery of the base material.

[0061] 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 nonaqueous electrolyte housed in a body of the outer can; and a sealing member closing the opening, wherein an annular groove is formed between the opening and the body, the diameter of the outer can being smaller than that of the body; and a ring-shaped protective member is provided between the electrode assembly and the annular groove, the protective member having a flat base portion and a first protrusion protruding from the outer periphery of the base portion toward the electrode assembly. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, further comprising an insulating plate between the protective member and the electrode assembly. Aspect 3: The nonaqueous electrolyte secondary battery according to Aspect 1 or 2, wherein the thickness of the base portion is 1.5 mm or less. Aspect 4: The nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 3, wherein the height of the first protrusion is 10 mm or less. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the width of the protective member is greater than the distance from the inner surface of the body portion to the tip of the annular groove in the radial direction of the outer can.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the width of the first protrusion is 1 mm or less.Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the protective member has a second protrusion that protrudes toward the sealing body at the inner peripheral edge of the base portion.Configuration 8: The nonaqueous electrolyte secondary battery according to Configuration 7, wherein the height of the second protrusion is 1.5 mm or less.Configuration 9: The nonaqueous electrolyte secondary battery according to Configuration 7 or 8, wherein the width of the second protrusion is 1 mm or less.

[0062] 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 Body, 23 Annular groove, 24 Opening, 30 Sealing body, 31 Internal terminal plate, 31A Thick portion, 31B Center, 31C Ventilation hole, 32 Insulating member, 32A Opening, 32B Ventilation hole, 33 External terminal plate, 33A Thin portion, 34 Gasket, 40 Protective member, 41 Base member, 42 First protrusion, 43 Second protrusion

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 member that closes the opening; wherein an annular 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 ring-shaped protective member is provided between the electrode assembly and the annular groove, and the protective member has a flat base member and a first protrusion that protrudes from the outer periphery of the base member toward the electrode assembly.

2. The nonaqueous electrolyte secondary battery according to claim 1, further comprising an insulating plate between the protective member and the electrode assembly.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the thickness of the substrate is 1.5 mm or less.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the height of the first protrusion is 10 mm or less.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the width of said protective member is greater than the distance from the inner surface of said body portion to the tip of said annular groove in the radial direction of said outer can.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the width of the first protrusion is 1 mm or less.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the protective member has a second protrusion that protrudes from the inner peripheral edge of the base member toward the sealing member.

8. The nonaqueous electrolyte secondary battery according to claim 7, wherein the height of the second protrusion is 1.5 mm or less.

9. The nonaqueous electrolyte secondary battery according to claim 7, wherein the width of the second protrusion is 1 mm or less.

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