JP5301914B2 - Gasket and sealed secondary battery - Google Patents

Description

  The present invention relates to a gasket used for a sealed secondary battery and the like, and a sealed secondary battery using the gasket.

  For power supplies of portable electronic devices such as cellular phones, it is desired to reduce the weight and size as the capacity increases. As power supplies that meet these demands, for example, sealed secondary batteries such as lithium ion secondary batteries are widely known. In general, a sealed secondary battery has a positive electrode plate, a negative electrode plate, a separator disposed between the positive electrode plate and the negative electrode plate, and a power generation element (battery element) including an electrolyte for immersing them, with an upper portion opened. The battery case is housed in a bottomed battery case, and the opening of the battery case is sealed by a sealing body.

  In this sealed secondary battery, a portion electrically connected (conductive) to the positive electrode plate and a portion electrically connected (conductive) to the negative electrode plate, such as between the opening of the battery case and the sealing body These contacts are provided with gaskets for insulation (prevention of short circuit), sealing and prevention of electrolyte leakage. This gasket is required to have resistance to electrolyte (electrolyte resistance), excellent sealing properties (sealing) and insulation, and further overheating due to overcharging and welding between the battery case and the sealing body. There is a demand for excellent heat resistance that can cope with instantaneous heating at times.

  Therefore, as a material constituting the gasket, polyethylene, polypropylene, ethylene polypropylene elastomer, styrene elastomer, olefin elastomer, ethylene propylene rubber, butyl rubber, styrene butadiene rubber, fluoro rubber (Patent Document 1), olefin having a predetermined surface hardness. A mixed material of resin and olefin rubber or fluoro rubber (Patent Document 2) has been proposed.

Patent Document 3 also proposes a gasket using a crosslinked resin that can be injection-molded in order to further improve sealing performance and insulation performance at low cost.
JP 2000-149886 A JP 2001-126684 A JP 2002-289158 A

  Among sealed secondary batteries, lithium ion secondary batteries are chemical batteries that use metallic lithium for the negative electrode, and lithium reacts quickly with moisture to generate hydrogen, so the electrolyte does not contain water. An organic solvent is used. In such a non-aqueous secondary battery, if water is mixed in the electrolytic solution, the composition of the electrolytic solution is adversely affected. Therefore, the gasket is required to have a function of preventing permeation of water vapor in the use environment (atmosphere) into the battery. It is done.

  However, the conventional gasket as described above is not sufficient in the function of preventing the permeation of water vapor (water vapor barrier property), and its improvement has been desired. In particular, the gasket is often molded into a predetermined shape and then incorporated into the battery, and the gasket may be compressed and deformed when incorporated into the battery. Therefore, in the gasket made of resin as exemplified above, water vapor is likely to be dissolved and diffused in the resin, and water vapor permeates into the battery through a minute path between the gasket and the electrode metal interface. It was.

As a method of preventing water vapor permeation, alumina is formed on the gasket surface by plasma CVD using monosilane and oxygen-containing gas as raw materials, vacuum deposition using SiO, SiO ₂ as raw materials, ion plating method, PVD such as sputtering method, etc. A method of forming a vapor deposition layer or a silica vapor deposition layer is conceivable. However, the alumina vapor deposition layer or the silica vapor deposition layer has low adhesion (adhesiveness) to battery members that are in contact with the gasket, for example, battery case openings or sealing metal, resulting in poor sealing performance. Then there was a problem. In addition, the silica vapor deposition layer may be dissolved or cracked when in contact with the electrolytic solution.

  It is an object of the present invention to provide a gasket that is excellent in water vapor barrier properties, is excellent in adhesion to battery members that are in contact with the gasket, and is excellent in sealing properties.

  As a result of diligent research, the present inventor has made the gasket a three-layer structure, and a layer provided on both surfaces, that is, a layer in contact with a battery member is formed of an insulator similar to a conventional gasket and two insulating layers It has been found that the above-mentioned problems can be achieved by providing a water vapor barrier layer between body layers, and the present invention has been completed.

That is, the present invention provides, as claim 1, a gasket characterized by having two insulator layers provided on both surfaces and a low-water-vapor barrier layer provided between the insulator layers. The gasket of the present invention is characterized by having a barrier layer having low water vapor permeability between two insulator layers on the front surface side and the back surface side. Since it has a barrier layer having low water vapor permeability, excellent water vapor barrier properties can be achieved. Here, the low water vapor permeability means that the water vapor transmission rate measured by the barrier layer alone is 0.8 g / m ² · day or less at 24 ° C. The water vapor transmission rate is 24 hours when the layer thickness is 0.1 mm, the relative humidity of the air on one side of the layer is kept at 90%, and the relative humidity of the air on the other side is kept at 0%. It is represented by the mass per unit area (m ² ) of water vapor that passes through

  The invention according to claim 2 is the gasket according to claim 1, wherein the barrier layer is an alumina deposited layer or a silica deposited layer. The alumina vapor-deposited layer or silica vapor-deposited layer can be preferably cited as a barrier layer because it has low water vapor permeability and can achieve excellent water vapor barrier properties. The alumina vapor deposition layer or the silica vapor deposition layer has low adhesion (adhesiveness) with the opening of the battery case or the metal of the sealing body, and as a result, there is a problem that the sealing performance is lowered. The alumina vapor-deposited layer or the silica vapor-deposited layer is provided between the insulator layers, and does not come into contact with the opening of the battery case or the metal of the sealing body.

The gasket having the alumina deposited layer or the silica deposited layer can be formed, for example, by the following method. First, two resin layers to be insulator layers are manufactured, and at least one of the two insulator layers is formed on one surface thereof by a known method, for example, plasma CVD using monosilane and oxygen-containing gas as raw materials, An alumina vapor deposition layer or a silica vapor deposition layer is formed by PVD such as a vacuum vapor deposition method, an ion plating method, or a sputtering method using SiO and SiO ₂ as raw materials. The two resin layers are bonded so that the formed alumina vapor deposition layer or silica vapor deposition layer is in contact with the other resin layer (or the alumina vapor deposition layer or silica vapor deposition layer formed thereon). The gasket according to claim 2 can be obtained by forming the three-layer structure thus obtained into a predetermined shape.

  Or after manufacturing resin layers other than the resin layer used as an insulator layer and forming an alumina vapor deposition layer or a silica vapor deposition layer in the surface of at least one of the said resin layer, the said resin layer is used as an insulator layer 2 It can also be formed by a method of bonding so as to be sandwiched between two resin layers.

  The continuity of the alumina vapor deposition layer or silica vapor deposition layer formed in this way may be lost by caulking when the gasket is incorporated in the battery, but even in this case, the water vapor transmission is reduced due to the maze effect. Can do.

  The invention according to claim 3 is the gasket according to claim 1, wherein the barrier layer is a resin layer made of a water vapor low permeability resin. As the barrier layer, a resin layer made of water vapor low permeability resin can also be used. This gasket is produced by, for example, manufacturing a resin layer made of a low-vapor-permeable resin by a known method, and combining a resin layer of the low-vapor-permeable resin and two resin layers serving as an insulator layer with a low-vapor-permeable resin. It can be formed by a method of bonding or three-layer extrusion so that the resin layer is sandwiched between the other two layers.

The low water vapor permeable resin refers to a resin having a water vapor permeability of 0.8 g / m ² · day or less. That is, a sheet having a thickness of 0.1 mm is prepared from the resin, the relative humidity of air on one side of the sheet is kept at 90%, the relative humidity of air on the other side is kept at 0%, The mass of water vapor that permeates the sheet over time is measured, and the value obtained by dividing the mass by the sheet area (m ² ) is 0.8 g or less.

As such a water vapor low permeability resin, polypropylene (d = 0.907: water vapor transmission rate is 0.75 g / m ² · day), high density polyethylene (HDPE: d = 0.954: water vapor transmission rate 0) .26 g / m ² · day), cyclic polyolefin and the like. On the other hand, the low-density polyethylene (LDPE) has a water vapor transmission rate of 0.90 g / m ² · day, and does not correspond to a water vapor low-permeability resin. Among the low water vapor permeable resins, cyclic polyolefin is preferable because it has excellent adhesion to the resin of the insulator layer and has chemical resistance to the electrolyte solution of the lithium ion battery. The invention according to claim 4 is the gasket according to claim 3, wherein the water vapor low permeability resin layer is a cyclic polyolefin.

  In the invention according to claim 5, the insulator layer is selected from the group consisting of polyolefin resin, polyolefin elastomer, polyethylene terephthalate resin, polyester elastomer, polyphenylene sulfide resin, polyarylate resin, polyamide resin, polyamide elastomer, fluororesin and fluoroelastomer. The gasket according to any one of claims 1 to 4, comprising a cross-linked product of at least one selected resin.

  Since the insulator layer constituting the gasket of the present invention is a part in contact with the outside, excellent electrolytic solution resistance and sealing properties are desired, and excellent insulating properties and heat resistance are also desired. Here, as the heat resistance, excellent heat resistance that can cope with overheating due to overcharging and instantaneous heating during welding of the battery case and the sealing body is required. Moreover, in order to achieve excellent sealing properties, excellent hardness, strength, elasticity and the like are required. By using the above-exemplified crosslinked resin, it becomes easy to satisfy these requirements.

  The invention according to claim 6 is characterized in that the insulator layer is a copolymer of an olefin and a monomer having a polar group and contains a crosslinked resin. It is a gasket given in any 1 paragraph.

  Here, the olefin may include ethylene and α-olefin, and the monomer having a polar group may be a monomer having an ionic functional group such as a carboxyl group or a sulfo group, such as acrylic acid, Examples thereof include a monomer having a hydroxyl group and maleic anhydride. Among these, a polymer composed of a polymer (ionomer molecule) containing a structural unit having an ionic functional group and / or an ionizable group, so-called ionomer is preferable. In particular, when the barrier layer having low water vapor permeability is an alumina vapor deposition layer and is provided in contact with the insulator layer, if an ionomer is used as the insulator layer, the adhesion between the insulator layer and the alumina vapor deposition layer is excellent and preferable. .

  If the resin constituting the insulator layer is a copolymer of an olefin and a monomer having a polar group and contains a crosslinked resin, particularly a crosslinked ionomer, excellent electrolyte resistance and In addition to obtaining insulation, the shape maintenance temperature can be increased while maintaining its elasticity. That is, the heat resistance can be improved while maintaining the sealing performance of the gasket, and the instantaneous heat resistance can also be improved.

  Furthermore, a resin that is a copolymer of an olefin and a monomer having a polar group and is crosslinked has, for example, adhesion to a metal (for example, aluminum) that forms a battery case of a sealed secondary battery. A metal copolymer and a gasket are firmly bonded by bonding an insulating layer formed of a cross-linked resin, which is a high copolymer of olefin and a monomer having a polar group, by heating and pressing. be able to.

  Since the gasket of the present invention is excellent in water vapor barrier properties, a sealed secondary battery, in particular, a lithium ion secondary battery whose characteristics are greatly affected by permeation of water vapor in the environment of use (atmosphere) into the battery, etc. It is suitably used for non-aqueous secondary batteries. The present invention also provides a sealed secondary battery using the gasket of the present invention, in which the influence of water vapor in the use environment (atmosphere) on the battery characteristics is suppressed.

That is, the present invention is as claim 7,
Bottomed battery case with an open top,
A power generation element comprising a positive electrode plate, a negative electrode plate, a separator disposed between the positive electrode plate and the negative electrode plate, and an electrolyte, and housed in the battery case,
A sealing body that seals the opening of the battery case, and a sealed secondary battery comprising the gasket according to any one of claims 1 to 6.

  The sealed secondary battery of the present invention is characterized in that the gasket according to any one of claims 1 to 6 is used as a gasket, but other components, that is, a battery case, a positive electrode plate, and a negative electrode plate As the separator, the electrolytic solution, and the sealing body, the same type as that of a sealed secondary battery that is normally used as a power source of a portable electronic device or the like can be used. Further, its shape and structure, and its manufacturing method are the same as those of a normally used sealed secondary battery.

  The gasket for the sealed secondary battery of the present invention is excellent in water vapor barrier property, excellent in adhesion to a battery member that the gasket contacts, and excellent in sealing properties. Therefore, the sealed secondary battery of the present invention using this gasket is suitably used even in an environment with high humidity because the influence of water vapor in the use environment (atmosphere) on the characteristics of the battery is small.

  Next, the best mode for carrying out the present invention will be described with reference to the drawings. In addition, this invention is not limited to the form described here, The change to another form is also possible, unless the meaning of this invention is impaired.

  FIG. 2 shows an example of the gasket of the sealed secondary battery of the present invention. Specifically, a gasket (a gasket 20 described later) provided between the opening of the battery case of the sealed secondary battery represented in FIG. The battery case of the sealed secondary battery shown in FIG. 3 has a cylindrical shape. Therefore, the gasket has an annular shape, but FIG. 2 passes through the diameter of the annular ring and is cut by a plane perpendicular to the circle. It is sectional drawing. This gasket is composed of two insulator layers provided on both surfaces and a barrier layer having a low water vapor permeability provided between the two insulator layers. These are shown in FIG. 1 and shown in detail in FIG. Such a structure is not shown.

  FIG. 1 is an enlarged cross-sectional view enlarging a part of FIG. 2 (inside A in the figure), and shows an example of the gasket of the present invention. As shown in FIG. 1, this gasket is composed of two layers of an insulator layer 1 and an insulator layer 2 and a barrier layer 3 having a low water vapor permeability, and the barrier layer 3 includes the insulator layer 1 and the insulator. It is sandwiched between the layers 2.

  The barrier layer 3 is, for example, a silica vapor deposition layer or an alumina vapor deposition layer. A silica vapor deposition layer or an alumina vapor deposition layer is formed, for example, by vapor-depositing silica or alumina on a substrate used for forming an insulator layer. As described above, as a method of vapor deposition, physical vapor deposition is used. Method (PVD) or chemical vapor deposition (CVD) may be used. The silica vapor deposition layer or the alumina vapor deposition layer may be one in which silica and alumina are vapor-deposited. As for the thickness of an alumina vapor deposition layer or a silica vapor deposition layer, 0.1-1 micrometer is preferable. If the vapor deposition layer is thicker than the above range, it may be difficult to process the shape when the gasket is incorporated into the battery. On the other hand, if it is thinner than the above range, the effect of reducing the water vapor transmission (barrier property) is not good. May be sufficient.

  The barrier layer 3 may be a resin layer made of, for example, a water vapor low permeability resin. Further, in order to improve the water vapor barrier property, a silica vapor deposition layer or an alumina vapor deposition layer may be formed on a resin layer made of a water vapor low permeability resin. The thickness of the low water vapor permeable resin layer is preferably 1 to 10 μm. When the water vapor low-permeability resin layer is thicker than the above range, it may be difficult to shape the gasket when it is installed in the battery, and the elasticity of the gasket may be reduced, resulting in insufficient sealing performance. There is. On the other hand, if it is thinner than the above range, the effect of reducing the permeation of water vapor (barrier property) may be insufficient.

  The cyclic polyolefin used as the water vapor low permeability resin is a polyolefin resin obtained by polymerizing a monomer containing a cyclic olefin monomer. The cyclic olefin monomer is known from JP-A-8-20692, and preferred examples include cyclopentene, 2-norbornene, and tetracyclododecene compounds.

  The monomer used for the polymerization reaction for producing the cyclic polyolefin-based resin may contain a monomer other than the cyclic olefin monomer. As the monomer other than the cyclic olefin monomer, a monomer having an unsaturated group copolymerizable with the cyclic olefin monomer is used. Specifically, α-olefins such as ethylene and propylene, acrylic Examples thereof include unsaturated carboxylic acids such as acids, acrylic acid esters and methacrylic acid esters, unsaturated dicarboxylic acid diesters, unsaturated carboxylic acid anhydrides, vinyl esters, and styrenes.

  Examples of the insulator constituting the insulator layer include a cross-linked body of the resin exemplified above. Sealed secondary battery gaskets are required to have sealing properties, insulating properties, heat resistance, electrolytic solution resistance, etc. In the gasket of the present invention, these properties can be achieved mainly by an insulator layer. Desirably, therefore, the resin constituting the insulator layer is required to have a sealing property, an insulating property, a heat resistance, an electrolytic solution resistance, and the like. Here, in order to obtain an excellent sealing property, the hardness, strength, elasticity and the like of the resin are required. Therefore, these properties are also required for the crosslinked body of the resin constituting the insulator layer. The insulator layers on both surfaces do not necessarily need to be made of the same material, and the two insulator layers may be made of different materials as long as the above properties are satisfied.

  Examples of the crosslinking method for producing a crosslinked resin include radiation crosslinking and chemical crosslinking. Radiation crosslinking is preferred in terms of easy control. Examples of radiation cross-linking include electron beam cross-linking, X-ray cross-linking, and γ-ray cross-linking. However, since an electron beam generator is relatively inexpensive and can provide a high-power electron beam, electron beam cross-linking using an electron beam is possible. However, it is industrially preferable.

The conditions for radiation crosslinking are not particularly limited because they are appropriately set according to the type of radiation, the thickness of the gasket, etc. In general, the radiation dose is preferably 10 to 1.
000 kGy, more preferably 100 to 500 kGy. If the radiation dose is too high, the elasticity of the insulator layer and thus the gasket may be impaired, and the sealing performance may be reduced.If the radiation dose is too low, the heat resistance of the gasket, especially the instantaneous heat resistance, may be reduced. It may be insufficient.

Examples of the chemical crosslinking include so-called peroxide crosslinking using a peroxide as a crosslinking agent. Examples of the peroxide as the crosslinking agent include dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, and the like. In order to facilitate molding, the crosslinking is preferably performed after molding.

  As described above, a crosslinked ionomer is preferably used as the insulator constituting the insulator layer, and examples of the ionomer include a polyolefin ionomer and a fluorine ionomer. When the ionomer is a polyolefin ionomer, the balance between elasticity and heat resistance (shape maintaining property) after crosslinking is good. When the ionomer is a fluorinated ionomer, the durability of the gasket is good, and the gasket is more suitable for use at high temperatures.

  Examples of the polyolefin ionomer include the product name “Admer (registered trademark)” series (modified polyolefin) manufactured by Mitsui Chemicals, and the fluorine ionomer includes, for example, the product name “Nafion (registered trademark)” manufactured by Dubon. Trademark) ”series (perfluorosulfonic acid-tetrafluoroethylene copolymer), trade name“ Neofluon ETFE ”series (tetrafluoroethylene-ethylene copolymer (ETFE)) manufactured by Daikin Industries, Ltd. Is mentioned.

  FIG. 3 is a cross-sectional view showing an example of a sealed secondary battery using the gasket of the present invention, that is, an example of a sealed secondary battery of the present invention. The sealed secondary battery of FIG. 3 accommodates an electrode 6 and an electrolyte solution 7 in a bottomed cylindrical metal battery case 5, and the opening 8 of the battery case 5 is interposed via the gasket 20 of the present invention. The battery is closed with a metal sealing body 9 (lid). In the example of FIG. 3, the battery case 5 has a cylindrical shape, but may have other shapes such as a square shape and a flat shape.

  The electrode 6 includes a positive electrode 11 and a negative electrode 12. As the positive electrode 11 and the negative electrode 12, those obtained by applying an active material kneaded with a binder or the like to both surfaces of a belt-like current collector can be used. Between the positive electrode 11 and the negative electrode 12, a belt-like separator 13 that holds the electrolyte solution 7 is sandwiched between the positive electrode 11 and the negative electrode 12, and those wound are accommodated in the battery case 5.

  The positive electrode 11 is electrically connected to the inner lid 14, and further, a metal sealing body via a spring body 15 provided to stably hold the electrode 6 in the battery case 5. 9 is conducted. On the other hand, the negative electrode 12 is electrically connected to the inner lid 16, and is further connected to the battery case 5 via the inner lid 16.

  The gasket 20 of the present invention is interposed between the sealing body 9 electrically connected to the positive electrode 11 and the battery case 5 electrically connected to the negative electrode 12 to insulate between the two and seal between them. The inside of the battery is sealed.

  As shown in FIG. 3, the battery case 5 is folded in the vicinity of the opening 8 to form a gasket housing portion 21, and the gasket 20 is fitted into the gasket housing portion 21.

  FIG. 2 shows a cross section of the gasket 20 before being fitted into the gasket housing portion 21. The gasket 20 is formed by forming a sealing body storage portion 23 on the opening 22 and forming a folded portion 24 having a diameter larger than that of the opening 22 thereon. The opening 22 has a size and a shape that match the gasket storage portion 21 of the battery case 5.

  When manufacturing the battery, the electrode 6, the electrolyte solution 7, and the like are stored in the battery case 5, and the inner lid 14 is placed on the electrode 6, and then the opening 22 of the gasket 20 is fitted into the gasket storage portion 21. It is. Further, the sealing body 9 provided with the spring body 15 is fitted into the sealing body housing part 23 of the gasket 20, and then the folded part 24 of the gasket 20 is folded back as shown by the arrow in FIG. Sealed and fixed.

  FIG. 4 is an enlarged cross-sectional view showing the vicinity of the gasket 20 in FIG. 3, and shows a state where the folded portion 24 of the gasket 20 is folded and the end portion of the battery case 5 is folded. After the folded portion 24 of the gasket 20 is folded, the end portion of the battery case 5 is folded as shown by the arrow in FIG. 4, whereby a predetermined surface pressure is generated in the gasket 20, and the sealing (sealing) of the sealing body 9 is performed. Fixing is more reliable. 4 represents the end of the battery case 5 and the folded portion of the gasket 20 before folding.

  In conventional gaskets, problems such as water vapor dissolving and diffusing in the resin and water vapor permeating into the battery through a minute path between the gasket and the electrode metal interface are likely to occur. However, since the gasket 20 of the present invention has a barrier layer, such a problem is prevented.

Example 1
Using a multilayer film extruder, 50 μm thick Appel 8008T (cyclic polyolefin, Mitsui Chemicals, water vapor permeability is 0.09 g / between two layers of 100 μm thick Himiran 1706 (polyethylene ionomer, Mitsui DuPont Polychemical Co., Ltd.) A three-layer film in which layers of m ² · day) were sandwiched was formed. Then, it vacuum-molded and stamped and shape | molded and also irradiated the electron beam of 360KGy, and obtained the gasket product. The gasket had a water vapor transmission rate of 0.2 g / m ² · day.

Example 2
Two films of high-milan 1706 having a thickness of 125 μm were prepared by a film extruder. An alumina deposited film having a thickness of 1 μm was formed on one surface of one film by vacuum deposition. On this alumina vapor deposition film, the other film produced above was laminated and bonded by heating. Then, it vacuum-molded and stamped and shape | molded and also irradiated the electron beam of 360KGy, and obtained the gasket product. The gasket had a water vapor transmission rate of 0.38 g / m ² · day.

Comparative Example A film of High Milan 1706 having a thickness of 250 μm was prepared by a film extruder. Thereafter, vacuum forming and punching were performed to form a gasket shape, and further a 360 KGy electron beam was irradiated to obtain a gasket product. The gasket had a water vapor transmission rate of 1.00 g / m ² · day.

  From the above results, the gaskets of the present invention provided with a barrier layer (Examples 1 and 2) were compared with the conventional gasket (Comparative Example 1) which is formed of the same material but does not have a barrier layer. It is shown to be excellent in performance.

It is an expanded sectional view showing a part of an example of a gasket of the present invention. It is sectional drawing which shows an example of the gasket of this invention. It is sectional drawing which shows an example of the sealed secondary battery of this invention. It is an expanded sectional view which shows the gasket vicinity of an example of the sealed secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Insulator layer 3 Barrier layer 5 Battery case 6 Electrode 7 Electrolyte 8 Opening part (battery case) 9 Sealing body 11 Positive electrode 12 Negative electrode 13 Separator 14, 16 Inner lid 15 Spring body 20 Gasket 21 Gasket housing part 22 Opening 23 (of gasket) Sealing body storage 24 Folding part

Claims (5)

Two insulating layers provided on both surfaces, the have a water vapor reduced-permeability barrier layer provided on the insulation layers, the barrier layer, characterized in der Rukoto alumina vapor deposited layer or silica-deposited layer gasket. Possess two an insulator layer provided on both surfaces, water vapor reduced-permeability barrier layer provided on the insulator layer, the barrier layer, wherein the resin layer der Rukoto consisting cyclic polyolefin gasket . The insulator layer is made of at least one resin selected from the group consisting of polyolefin resin, polyolefin elastomer, polyethylene terephthalate resin, polyester elastomer, polyphenylene sulfide resin, polyarylate resin, polyamide resin, polyamide elastomer, fluororesin, and fluoroelastomer. The gasket according to claim 1 or 2 , comprising a crosslinked body. The gasket according to any one of claims 1 to 3, wherein the insulator layer is a copolymer of an olefin and a monomer having a polar group and includes a crosslinked resin. Bottomed battery case with an open top,
A power generation element comprising a positive electrode plate, a negative electrode plate, a separator disposed between the positive electrode plate and the negative electrode plate, and an electrolyte, and housed in the battery case,
A sealing body for sealing the opening of the battery case, and
A sealed secondary battery comprising the gasket according to any one of claims 1 to 4 .

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