Non-aqueous electrolyte secondary battery

Abstract

This nonaqueous electrolyte secondary battery comprises: an electrode body; a nonaqueous electrolyte; a bottomed cylindrical outer can (20) that accommodates the electrode body and the nonaqueous electrolyte; and a sealing body (30) that closes an opening of the outer can (20). The nonaqueous electrolyte secondary battery is characterized in that an annular groove (23) recessed inward in the radial direction of the outer can (20) is provided on a side surface of the outer can (20), and a protective member (40) containing an endothermic material that causes an endothermic reaction is provided inside the annular groove (23).

Description

Non-aqueous electrolyte secondary battery

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

[0002] Conventionally, a non-aqueous electrolyte secondary battery including an electrode body having a positive electrode and a negative electrode, a bottomed cylindrical outer can that houses the electrode body, and a sealing body that closes the opening of the outer can is known. The sealing body is fixed to the upper part of the outer can by being caulked and fixed to the opening of the outer can while being supported on the upper surface of an annular groove provided on the side surface of the outer can.

[0003] Patent Document 1 discloses a non-aqueous electrolyte secondary battery provided with an insulating coating layer on the entire side surface of the outer can including the inside of the annular groove. Further, Patent Document 1 describes that by providing the coating layer, it is possible to suppress the occurrence of a short circuit caused by dust of the metal material constituting the outer can during the manufacturing process.

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

[0005] By the way, in a non-aqueous electrolyte secondary battery, for example, when an external short circuit occurs in a charged state of the battery, a large current may be applied to the electrode body and the electrode body may abnormally generate heat. Then, gas is generated inside the battery, increasing the internal pressure of the battery, and the outer can may be damaged. When the outer can is damaged, gas is ejected from the damaged portion, which is not preferable from the viewpoint of ensuring the safety of the battery.

[0006] Further, as a result of the study by the present inventors, it has been found that the damage of the outer can at the time of the above-mentioned battery abnormality may occur in the annular groove provided in the outer can. Therefore, suppressing the damage of the annular groove at the time of battery abnormality is an important issue.

[0007] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including an electrode body having a positive electrode and a negative electrode, a non-aqueous electrolyte, a bottomed cylindrical outer can that houses the electrode body and the non-aqueous electrolyte, and a sealing body that closes the opening of the outer can, wherein an annular groove recessed inward in the radial direction of the outer can is provided on the side surface of the outer can, and a protective member including a heat-absorbing material that causes a heat-absorbing reaction is provided inside the annular groove.

[0008] According to a non-aqueous electrolyte secondary battery as described in this disclosure, damage to the annular groove in the event of a battery malfunction can be suppressed. As a result, a highly safe non-aqueous electrolyte secondary battery can be provided.

[0009] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is one example of an embodiment. This is an enlarged view of the vicinity of the annular groove provided in the outer casing in Figure 1. This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is another example of an embodiment, and this is an enlarged view of the vicinity of the annular groove provided in the outer casing. This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is another example of an embodiment, and this is an enlarged view of the vicinity of the annular groove provided in the outer casing. This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is another example of an embodiment, and this is an enlarged view of the vicinity of the annular groove provided in the outer casing.

[0010] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and this disclosure is not limited to the embodiments described below. Furthermore, forms obtained by selectively combining each component of the embodiments described below are included in this disclosure.

[0011] Figure 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises an electrode body 14, a non-aqueous electrolyte (not shown), and an outer container 20 that houses the electrode body 14 and the non-aqueous electrolyte. The outer container 20 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening 24 of the outer container 20 is sealed by a sealing body 30. Hereinafter, the side of the non-aqueous electrolyte secondary battery 10 with the sealing body 30 in the axial direction (height direction) will be referred to as "up," and the side of the outer container 20 with the bottom 21 in the axial direction will be referred to as "down."

[0012] The electrode body 14 has 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 wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies, and are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in dimensions 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 the width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger in dimensions than the positive electrode 11, and two separators are arranged so as to sandwich the positive electrode 11. The non-aqueous electrolyte secondary battery 10 includes insulating plates 16 and 17 arranged above and below the electrode body 14, respectively.

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

[0014] The positive electrode composite layer contains particulate lithium metal composite oxide as the 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 elements constituting the lithium metal composite oxide are, 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 these, 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 included in the positive electrode mixture layer include carbon black such as acetylene black and Ketjenblack, graphite, carbon nanotubes (CNTs), carbon nanofibers, and graphene. Examples of binders included in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resins, and polyolefins. In addition, these resins may be used in combination with carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0016] The negative electrode 12 comprises a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film with the metal arranged on its surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and optionally a conductive agent, and is preferably formed on both sides of the negative electrode core, excluding the exposed portion (not shown) of the negative electrode core to which the negative electrode lead 19 is welded. The negative electrode 12 can be manufactured 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 the negative electrode mixture layer on both sides of the negative electrode core.

[0017] The negative electrode composite layer generally contains a carbon material that reversibly intercepts and releases lithium ions as the negative electrode active material. Suitable examples of carbon materials include natural graphite such as flake graphite, lumpy graphite, and clay graphite, as well as artificial graphite such as lumpy artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). In addition, 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 as the negative electrode active material. Among these, composite materials containing Si are preferred.

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

[0019] The binder in the negative electrode mixture layer may be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., similar to the positive electrode mixture layer, but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, a combination of SBR and CMC or a salt thereof, PAA or a salt thereof is preferred. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0020] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A heat-resistant resin layer, such as 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 lead 18 is connected to the positive electrode 11, and a negative lead 19 is connected to the end of the winding of the negative electrode 12. The positive lead 18 extends towards the sealing body 30 through a through hole in the insulating plate 16, and the negative lead 19 extends towards the bottom 21 of the outer can 20 through the outside of the insulating plate 17. The positive lead 18 is connected to the lower surface of the internal terminal plate 31 of the sealing body 30 by welding or the like, so that the sealing body 30 becomes the positive terminal. The negative lead 19 is connected to the inner surface of the bottom 21 of the metal outer can 20 by welding or the like, so that the outer can 20 becomes the negative terminal.

[0022] Non-aqueous electrolytes are lithium ion conductive. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0023] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[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, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, 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 a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0025] The outer container 20 is a bottomed cylindrical container with an opening on one side in the axial direction. The outer container 20 has a bottom portion 21 and a side portion 22 that forms the side surface of the non-aqueous electrolyte secondary battery 10. The side portion 22 is the part of the outer container 20 excluding the bottom portion 21 and includes an annular groove 23 and an opening 24, which will be described later.

[0026] The outer container 20 contains a metallic material. Examples of metallic materials include iron, stainless steel, aluminum, aluminum alloy, and nickel. In this embodiment, the outer container 20 is made of steel with iron as the main component.

[0027] The annular groove 23 is a portion of the side surface 22 that is recessed radially inward, and is provided in an annular 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 create an annular recess toward the radially inward side. The width (axial length) of the annular groove 23 is not particularly limited, but for example, it is 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 for example, it is 0.5 mm or more and 5.0 mm or less. As will be described in more detail later, a protective member 40 is provided inside the annular groove 23.

[0028] The opening 24 is the region of the side portion 22 above the annular groove 23, and forms the opening of 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 forms an opening side portion 25 that forms part of the side of the non-aqueous electrolyte secondary battery 10 and covers the outer circumferential surface of the gasket 34, and a crimped portion 26 that forms part of the upper surface of the non-aqueous electrolyte secondary battery 10 and extends radially inward. In this embodiment, the radial inner end of the crimped portion 26 is located radially outward from the radial inner end of the gasket 34. That is, a part of the upper 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 order from the electrode body 14 side.

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

[0031] The insulating member 32 insulates the portion of the internal terminal plate 31 and the external terminal plate 33 other than the connection portion. The insulating member 32 has an opening 32A in its radial center, and a ventilation hole 32B is formed in the portion that overlaps with the ventilation hole 31C of the internal terminal plate 31.

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

[0033] When an abnormality occurs in the non-aqueous electrolyte secondary battery 10 and the internal pressure rises, the high-temperature gas generated pushes the internal terminal plate 31 upward, causing it to rupture and the central portion 31B to separate from the thick portion 31A, and the external terminal plate 33 to deform so that it protrudes outward from the battery. This interrupts the current path in the sealing body 30. Then, if the internal pressure of the non-aqueous electrolyte secondary battery 10 rises further after the current path has been interrupted, the thin portion 33A of the external terminal plate 33 ruptures, forming a gas outlet in the external terminal plate 33.

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

[0035] The gasket 34 is a flexible insulating member that electrically isolates the sealing body 30, which is the positive terminal, from the outer can 20, which is the negative terminal, while ensuring airtightness inside the outer can 20 by being compressed vertically. The material of the gasket 34 is not particularly limited as long as it is a compressible insulating material, and for example, polypropylene (PP), polyphenylene sulfide (PPS), polyethylene (PE), polybutylene terephthalate (PBT), perfluoroalkoxyalkane (PFA), polytetrafluoroethylene (PTFE), polyamide (PA), etc. can be used.

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

[0037] As shown in Figure 2, a protective member 40 containing a heat-absorbing material that generates an endothermic reaction is provided inside the annular groove 23. In the example shown in Figure 2, the protective member 40 fills almost the entire interior of the annular groove 23. That is, the protective member 40 is in contact with the upper surface 23A and the lower surface 23B, which are the surfaces on both sides of the annular groove 23 in the width direction.

[0038] As a result of the inventors' investigations, it has become clear that when the electrode body 14 overheats abnormally, gas is generated inside the battery, and when the internal pressure of the battery increases, damage to the outer casing 20 may occur in the region where the annular groove 23 is formed. Although the detailed mechanism is not clear, it is thought that when the electrode body 14 overheats abnormally, sparks generated on the outer circumference of the electrode body 14 may strike the annular groove 23, causing the temperature near the annular groove 23 to rise excessively, resulting in damage to the outer casing 20 in the region where the annular groove 23 is formed.

[0039] Here, the protective member 40 includes a heat-absorbing material that generates an endothermic reaction. Because the protective member 40 includes a heat-absorbing material, when the electrode body 14 overheats abnormally and the temperature near the annular groove 23 rises excessively, the endothermic reaction of the heat-absorbing material suppresses the temperature rise near the annular groove 23. As a result, damage to the annular groove 23 in the event of a battery malfunction can be suppressed. It is preferable that the protective member 40 has a heat-absorbing material as its main component. Here, the main component means the component with the highest mass ratio among the materials constituting the protective member 40. It is more preferable that the protective member 40 contains 80% by mass or more of the heat-absorbing material. In this embodiment, the protective member 40 is substantially composed of only a heat-absorbing material.

[0040] The heat-absorbing material preferably undergoes an endothermic reaction at 200°C or higher. Generally, when a spark generated on the outer peripheral side of the electrode body 14 hits the annular groove 23 during abnormal heat generation of the electrode body 14, the temperature of the annular groove 23 becomes 200°C or higher. Therefore, when the heat-absorbing material undergoes an endothermic reaction at 200°C or higher, the temperature rise in the vicinity of the annular groove 23 can be effectively suppressed. Further, the heat-absorbing material preferably undergoes an endothermic reaction below the melting point of the metallic material constituting the outer can 20, and preferably undergoes an endothermic reaction at 1500°C or lower, more preferably at 1000°C or lower. In this case, damage to the outer can 20 in the region where the annular groove 23 is formed can be suppressed. Thus, the heat-absorbing material preferably undergoes an endothermic reaction at 200°C or higher and 1500°C or lower, more preferably at 200°C or higher and 1000°C or lower. The endothermic reaction temperature of the heat-absorbing material can be determined by TG-DTA (thermogravimetry-differential thermal analysis) or DSC (differential scanning calorimetry).

[0041] Also, the heat-absorbing material is preferably a material that undergoes an endothermic reaction by dehydration decomposition. When an endothermic reaction occurs by dehydration decomposition, the amount of heat absorbed can be increased, so that the temperature rise in the vicinity of the annular groove 23 during abnormal heat generation of the electrode body 14 can be further suppressed.

[0042] From the perspective of increasing the heat absorption amount, the heat-absorbing material is preferably an inorganic substance. Examples of inorganic substances include hydroxides such as aluminum hydroxide, magnesium hydroxide, and calcium hydroxide, carbonates such as calcium carbonate, hydrogen carbonates such as sodium hydrogen carbonate, and hydrates of sulfates such as calcium sulfate dihydrate and magnesium sulfate heptahydrate. These may be used alone or in combination of two or more. Note that although ammonium nitrate, potassium chloride, potassium chlorate, etc. require caution in handling and are not preferably used as the heat-absorbing material in this embodiment, they are included in the heat-absorbing material because they exhibit an endothermic reaction when dissolved in water. Also, the heat-absorbing material may be an organic substance such as polyethylene (PE) or polypropylene (PP). Such an organic substance exhibits a phase change from solid to liquid in a temperature range below 200°C and causes an endothermic reaction.

[0043] From the perspective of increasing the heat absorption amount more, the heat-absorbing material is preferably a hydroxide or a carbonate, and more preferably contains at least one selected from the group consisting of aluminum hydroxide and magnesium hydroxide. Aluminum hydroxide generally undergoes an endothermic reaction at 200°C or higher and 350°C or lower, and magnesium hydroxide generally undergoes an endothermic reaction at 350°C or higher and 450°C or lower.

[0044] As described above, the protective member 40 is filled in substantially the entire area inside the annular groove 23. That is, in the axial cross-sectional view of the outer can 20, the ratio of the area of the protective member 40 inside the annular groove 23 to the area of the space of the annular groove 23 is 20% or more. By setting the ratio of the area of the protective member 40 to the area of the space of the annular groove 23 to 20% or more, the volume of the protective member 40 can be ensured, and the heat absorption effect of the protective member 40 during abnormal heat generation of the electrode body 14 can be improved. As a result, the temperature rise in the vicinity of the annular groove 23 can be further suppressed, and damage to the annular groove 23 during abnormal occurrence of the battery can be further suppressed. Note that the area of the space of the annular groove 23 in the axial cross-sectional view of the outer can 20 means the area of the region surrounded by the virtual line α along the outer surface of the side portion 22 of the outer can 20 and the wall surface of the annular groove 23.

[0045] In an axial cross-sectional view of the outer can 20, the ratio of the area of ​​the protective member 40 inside the annular groove 23 to the area of ​​the annular groove 23 space is more preferably 40% or more, and even more preferably 60% or more. By increasing the ratio of the area of ​​the protective member 40 inside the annular groove 23, the heat absorption effect of the protective member 40 when the electrode body 14 overheats abnormally can be further improved. Also, as shown in Figure 2, the ratio of the area of ​​the protective member 40 to the area of ​​the annular groove 23 space may be substantially 100%, that is, the protective member 40 may be arranged to fill the entire annular groove 23.

[0046] Next, a modified example of the protective member 40 will be described with reference to Figures 3 to 5. Figures 3 to 5 show modified examples of the protective member 40 and correspond to Figure 2.

[0047] In the example shown in Figure 3, the protective member 40 is provided in a portion of the interior of the annular groove 23. The protective member 40 is in contact with the upper surface 23A and the lower surface 23B, which are the surfaces on both sides of the annular groove 23 in the width direction. When the protective member 40 is in contact with the upper surface 23A and the lower surface 23B of the annular groove 23, the heat absorption effect of the protective member 40 when the electrode body 14 overheats abnormally can be improved. As a result, the temperature rise near the annular groove 23 is further suppressed, and damage to the annular groove 23 when a battery malfunction occurs can be further suppressed.

[0048] In the example shown in Figure 4, the protective member 40 is provided in layers so as to cover the upper surface 23A and the lower surface 23B of the annular groove 23. In the example shown in Figure 5, the protective member 40 is provided in layers so as to cover the lower surface 23B of the annular groove 23.

[0049] Furthermore, if the protective member 40 is positioned to cover at least a portion of the surface of the annular groove 23, it is preferable that the protective member 40 covers 25% or more of the surface of the annular groove 23, and more preferably that it covers 50% or more of the surface of the annular groove 23. By having the protective member 40 cover 25% or more of the surface of the annular groove 23, it becomes easier to suppress the temperature rise near the annular groove 23 when the battery overheats abnormally.

[0050] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0051] <Example 1> [Preparation of positive electrode] Lithium nickel cobalt oxide (LiNi) containing aluminum was used as the positive electrode active material. ０．８８ Co ０．０９ Al ０．０３ O ２ A positive electrode slurry was prepared by mixing 100 parts by mass of 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 in an N-methylpyrrolidone (NMP) dispersion medium. Next, this positive electrode slurry was applied to both sides of a positive electrode current collector made of aluminum foil, dried, cut to a predetermined electrode size, and rolled using a roller to obtain a strip-shaped positive electrode. Furthermore, an exposed portion of the positive electrode current collector was formed in a part of the length direction of the positive electrode where the positive electrode slurry layer was not formed, and an aluminum positive electrode lead was fixed to this exposed portion of the positive electrode current collector by ultrasonic welding.

[0052] [Fabrication of the negative electrode] A mixture of 90 parts by mass of graphite powder and 10 parts by mass of Si oxide was used as the negative electrode active material. A negative electrode slurry was prepared by mixing 100 parts by mass of the negative electrode active material, 1 part by mass of CMC as a thickener, and 1 part by mass of styrene-butadiene rubber as a binder in water. Next, this negative electrode 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, a negative electrode current collector exposed portion without a negative electrode slurry layer was formed at one end in the longitudinal direction of the negative electrode, and a nickel negative electrode lead was fixed to this exposed portion by ultrasonic welding.

[0053] [Electrode Fabrication] A wound electrode body was fabricated by winding the fabricated positive and negative electrodes in a spiral shape via a separator. 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.

[0054] [Preparation of Non-Aqueous Electrolyte] A mixed solvent is prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 3:3:4 (at 25°C), to which LiPF is added. ６ A non-aqueous electrolyte was prepared by dissolving it at a concentration of 1.2 mol / L.

[0055] [Fabrication of a Non-Aqueous Electrolyte Secondary Battery] A metal can made of steel with a bottomed cylindrical shape, φ21 mm in diameter and 70 mm in height, was used as the outer casing. After placing insulating plates above and below the electrode body and housing the electrode body in the outer casing, the negative electrode lead was welded to the bottom of the outer casing. Subsequently, the outer casing was spun to form an annular groove. The width (axial length) of the annular groove was set to 0.4 mm, and the depth (radial length) of the annular groove was set to 2.0 mm. 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 degassing under reduced pressure, an external terminal plate was placed on the internal terminal plate, and after welding the external terminal plate and the internal terminal plate, the sealing body was fixed to the top of the outer casing by crimping the upper end of the outer casing.

[0056] Next, a coating solution was prepared by mixing aluminum hydroxide powder as a heat-absorbing material with water in a mass ratio of 2:1, and this coating solution was filled into the entire interior of the annular groove. After that, it was left at room temperature (25°C) for 12 hours to evaporate the water, and the entire interior of the annular groove was filled with a protective member made of aluminum hydroxide. The endothermic peak of the aluminum hydroxide used was measured by TG-DTA, and an endothermic peak was confirmed at 302.8°C.

[0057] <Example 2> A non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1, except that magnesium hydroxide was used instead of aluminum hydroxide as the heat-absorbing material. When the endothermic peak of the magnesium hydroxide used was measured by TG-DTA, an endothermic peak was confirmed at 415.7°C.

[0058] <Comparative Example 1> A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1, except that a protective member was not provided.

[0059] Four batteries each were prepared for Examples 1 and 2, and five batteries were prepared for Comparative Example 1. Each was heated in a 500°C oven for 10 minutes, after which heating was stopped. The presence or absence of perforation in the annular groove (presence or absence of gas injection from the annular groove) was evaluated by observing the appearance of the outer casing. The evaluation results for Examples 1 and 2 and Comparative Example 1 are shown in Table 1.

[0060] As shown in Table 1, the non-aqueous electrolyte secondary batteries of Examples 1 and 2, which were equipped with protective members, showed a significantly reduced rate of porosity compared to the non-aqueous electrolyte secondary battery of Comparative Example 1, which was not equipped with protective members. This is presumed to be because the temperature rise near the annular groove was suppressed when a battery malfunction occurred by providing protective members in the annular groove.

[0061] This disclosure is further illustrated by the following embodiments. Configuration 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 container housing the electrode body and the non-aqueous electrolyte, and a sealing body closing the opening of the outer container, wherein an annular groove recessed radially inward is provided on the side surface of the outer container, and a protective member containing a heat-absorbing material that causes an endothermic reaction is provided inside the annular groove. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the heat-absorbing material causes an endothermic reaction at 200°C or higher and 1500°C or lower. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the heat-absorbing material causes an endothermic reaction by dehydration decomposition. Configuration 4: The non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the heat-absorbing material is an inorganic material. Configuration 5: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the heat-absorbing material is a hydroxide or a carbonate. Configuration 6: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the heat-absorbing material includes at least one selected from the group consisting of aluminum hydroxide and magnesium hydroxide. Configuration 7: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the protective member abuts against the surfaces on both sides in the width direction of the annular groove. Configuration 8: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein in an axial cross-sectional view of the outer casing, the ratio of the area of ​​the protective member inside the annular groove to the area of ​​the space of the annular groove is 20% or more. Configuration 9: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 8, wherein the protective member covers an area of ​​25% or more of the surface of the annular groove.

[0062] 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, 23 Annular groove, 23A Top, 23B Bottom, 24 Opening, 25 Opening side, 26 Crimping part, 30 Sealing body, 31 Internal terminal plate, 31A Thick part, 31B Center part, 31C Ventilation hole, 32 Insulating member, 32A Opening, 32B Ventilation hole, 33 External terminal plate, 33A Thin part, 34 Gasket, 40 Protective member, α Imaginary 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 container housing the electrode body and the non-aqueous electrolyte; and a sealing body closing the opening of the outer container, wherein an annular groove recessed toward the radially inward side of the outer container is provided on the side surface of the outer container, and a protective member containing a heat-absorbing material that causes an endothermic reaction is provided inside the annular groove.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-absorbing material undergoes an endothermic reaction at a temperature of 200°C or higher and 1500°C or lower.

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-absorbing material produces an endothermic reaction by dehydration decomposition.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-absorbing material is an inorganic material.

5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-absorbing material is a hydroxide or a carbonate.

6. The non-aqueous electrolyte secondary battery according to claim 1, wherein the heat-absorbing material comprises at least one selected from the group consisting of aluminum hydroxide and magnesium hydroxide.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective member is in contact with the surfaces on both sides in the width direction of the annular groove.

8. In an axial cross-sectional view of the outer casing, the ratio of the area of ​​the protective member inside the annular groove to the area of ​​the space in the annular groove is 20% or more, as described in claim 1.

9. The non-aqueous electrolyte secondary battery according to claim 1, wherein the protective member covers an area of ​​25% or more of the surface of the annular groove.

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