Lid, power storage device, and peripheral member

Abstract

Provided is a lid used with a casing of a power storage device, wherein the lid includes a heat-fusible resin layer the main material of which is an olefin-based copolymer.

Description

Lid, electricity storage device, peripheral member

[0001] The present invention relates to a lid, an electricity storage device, and a peripheral member.

[0002] Patent Document 1 discloses an example of an electricity storage device. This electricity storage device includes an electrode assembly and an exterior body that seals the electrode assembly. The exterior body includes an exterior film that encases the electrode assembly and a lid that is joined to the exterior film.

[0003] Japanese Patent Application Laid-Open No. 2022-123686

[0004] In the above-described electricity storage device, if the exterior film and the lid are not sufficiently joined, a gap may be formed between the outer film and the lid, leaving room for improvement in terms of properly sealing the electrode assembly with the exterior film.

[0005] An object of the present invention is to provide an electricity storage device in which an electrode assembly can be suitably sealed with an exterior body, a lid body used in this electricity storage device, and a peripheral member constituting this lid body.

[0006] A lid according to a first aspect of the present invention is a lid used as an exterior body for an electricity storage device, and the lid includes a heat-sealable resin layer whose main material is an olefin-based copolymer.

[0007] A lid body according to a second aspect of the present invention is a lid body used as an outer casing for an electricity storage device, the lid body including a lid main body and a peripheral member joined to at least a portion of the peripheral edge of the lid main body, and the peripheral member including a heat-sealable resin layer whose main material is an olefin-based copolymer.

[0008] A lid according to a third aspect of the present invention is the lid according to the second aspect, wherein the peripheral member is an adhesive film bonded to the lid body.

[0009] A lid body according to a fourth aspect of the present invention is the lid body according to the second aspect, wherein the peripheral member is a frame body joined to the lid main body.

[0010] A lid according to a fifth aspect of the present invention is the lid according to any one of the first to third aspects, wherein the olefin copolymer is an olefin random copolymer.

[0011] A lid body according to a sixth aspect of the present invention is a lid body according to any one of the first to fifth aspects, wherein the lid body comprises a lid seal portion that is sealed to an exterior film that constitutes the exterior body, and a protrusion that protrudes from the lid seal portion.

[0012] A lid according to a seventh aspect of the present invention is the lid according to any one of the first to sixth aspects, wherein the heat-fusible resin layer contains a fatty acid amide-based lubricant.

[0013] A lid according to an eighth aspect of the present invention is the lid according to the seventh aspect, wherein there are multiple types of fatty acid amide-based lubricants, and at least one of the fatty acid amide-based lubricants is a saturated fatty acid amide.

[0014] A lid according to a ninth aspect of the present invention is the lid according to the eighth aspect, wherein the plurality of types of fatty acid amide-based lubricants further include an unsaturated fatty acid amide.

[0015] A lid according to a tenth aspect of the present invention is the lid according to the eighth or ninth aspect, wherein the saturated fatty acid amide has 18 or more carbon atoms.

[0016] A lid according to an eleventh aspect of the present invention is the lid according to any one of the eighth to tenth aspects, in which the saturated fatty acid amide is behenic acid amide.

[0017] A lid according to a twelfth aspect of the present invention is the lid according to the ninth aspect, wherein the unsaturated fatty acid amide is erucic acid amide.

[0018] A lid according to a thirteenth aspect of the present invention is the lid according to any one of the first to fourth aspects, wherein the heat-sealable resin layer is made of any one of an acid-modified polyolefin resin, an unsaturated carboxylic acid-grafted polyolefin resin, a polypropylene resin, a metal ion-crosslinked polyethylene, a copolymer resin of ethylene and an acrylic acid derivative, and a copolymer resin of ethylene and a methacrylic acid derivative.

[0019] A lid according to a fourteenth aspect of the present invention is the lid according to any one of the first to fourth aspects, wherein the heat-fusible resin layer contains a propylene-based elastomer resin having a melting point higher than 150°C.

[0020] The energy storage device according to a fifteenth aspect of the present invention comprises an electrode body and an exterior body that seals the electrode body, the exterior body including an exterior film that wraps the electrode body and a lid body that is joined to the exterior film, and the lid body including a heat-sealable resin layer whose main material is an olefin-based copolymer.

[0021] The energy storage device according to a sixteenth aspect of the present invention comprises an electrode body and an outer casing that seals the electrode body, the outer casing including an outer casing film that wraps the electrode body and a lid body that is joined to the outer casing film, the lid body including a lid main body and a peripheral member that is joined to at least a portion of the peripheral edge of the lid main body, and the peripheral member including a heat-sealable resin layer whose main material is an olefin-based copolymer.

[0022] A peripheral member according to a seventeenth aspect of the present invention is a peripheral member constituting a lid body used in an outer casing of an electricity storage device, the lid body including a lid main body and the peripheral member joined to at least a portion of the peripheral edge of the lid main body, and the peripheral member including a heat-sealable resin layer whose main material is an olefin-based copolymer.

[0023] A peripheral member according to an eighteenth aspect of the present invention is the peripheral member according to the seventeenth aspect, which is an adhesive film bonded to the lid main body.

[0024] A peripheral member according to a nineteenth aspect of the present invention is the peripheral member according to the seventeenth aspect, which is a frame body joined to the lid body.

[0025] A lid according to a twentieth aspect of the present invention is a lid used in an exterior packaging for an electricity storage device, the lid including a heat-sealable resin layer, wherein the heat-sealable resin layer is measured for temperature differences T1 and T2 by the following method, and the value obtained by dividing the temperature difference T2 by the temperature difference T1 is 0.60 or greater. Differential scanning calorimetry is used to measure the temperature difference T1 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-sealable resin layer. The heat-sealable resin layer is left to stand for 72 hours in an 85°C environment in an electrolyte solution that is a solution containing lithium hexafluorophosphate at a concentration of 1 mol / L and a 1:1:1 volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate, and then dried. Differential scanning calorimetry is used to measure the temperature difference T2 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-sealable resin layer after drying.

[0026] A lid according to a twenty-first aspect of the present invention is a lid used in an exterior body of an electricity storage device, the lid including a heat-sealable resin layer, the lid including a lid seal portion that is sealed to an exterior film that constitutes the exterior body, a sea-island structure being observed in a cross-sectional image of a cross section in the thickness direction of the lid seal portion obtained using a field emission scanning electron microscope, and the area ratio of the island portions of the sea-island structure being 0.1% or more and 50% or less in the cross-sectional image.

[0027] A twenty-second aspect of the present invention provides a peripheral member constituting a lid used in an exterior packaging for an electricity storage device, the lid including a lid main body and the peripheral member joined to at least a portion of the peripheral edge of the lid main body, the peripheral member including a heat-sealable resin layer. The heat-sealable resin layer is measured by the following method to measure a temperature difference T1 and a temperature difference T2, and a value obtained by dividing the temperature difference T2 by the temperature difference T1 is 0.60 or more. The temperature difference T1 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-sealable resin layer is measured by differential scanning calorimetry. The heat-sealable resin layer is left to stand for 72 hours in an 85°C environment in an electrolyte solution containing lithium hexafluorophosphate at a concentration of 1 mol / L and containing ethylene carbonate, diethyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1, and then dried. The temperature difference T2 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-fusible resin layer after drying is measured by differential scanning calorimetry.

[0028] A peripheral member according to a twenty-third aspect of the present invention is a peripheral member constituting a lid used in an exterior body of an electricity storage device, the lid body including a lid main body and the peripheral member joined to at least a portion of the peripheral edge of the lid main body, the peripheral member having a peripheral member seal portion that is sealed to an exterior film that constitutes the exterior body, a sea-island structure being observed in a cross-sectional image of a cross section in the thickness direction of the peripheral member seal portion obtained using a field emission scanning electron microscope, and in the cross-sectional image, the area ratio of the island portions of the sea-island structure is 0.1% or more and 50% or less.

[0029] The electricity storage device, lid, and peripheral member according to the present invention can contribute to the electrode assembly being suitably sealed by the exterior body.

[0030] 1A . A perspective view of an electricity storage device according to an embodiment. A diagram relating to a method for measuring the seal strength of a second sealed portion of the electricity storage device of FIG. 1A. A cross-sectional view showing the layer structure of an exterior film included in the electricity storage device of FIG. 1A. A diagram of the exterior film included in the electricity storage device of FIG. 1A in an unfolded state. A cross-sectional view taken along line D4-D4 of FIG. 1A. A side view of a lid body in a state where the exterior film of FIG. 4 is omitted. A plan view of the lid body in a state where the exterior film of FIG. 4 is omitted. A flowchart showing an example of a manufacturing process for the electricity storage device of FIG. 1A. A cross-sectional view of a lid body included in an electricity storage device of a second modified example. A cross-sectional view of a lid body included in an electricity storage device of a third modified example. A cross-sectional view of a lid body included in an electricity storage device of a fourth modified example. A cross-sectional view showing an example of the layer structure of the peripheral member of FIG. 10. A cross-sectional view of a lid body included in an electricity storage device of a tenth modified example. A cross-sectional view of a lid body included in another electricity storage device of the tenth modified example. A cross-sectional view showing an example of the layer structure of a peripheral member included in yet another electricity storage device of the tenth modified example. 17 is a cross-sectional view showing an example of the layer structure of a peripheral member included in an electricity storage device of an eleventh modified example. 18 is a cross-sectional view of a lid included in an electricity storage device of a twelfth modified example. 19 is a cross-sectional view of an electricity storage device 10 of a fourteenth modified example. 20 is a cross-sectional view of the lid and its periphery in Figure 17. 21 is a cross-sectional view showing an example of the layer structure of the barrier film in Figure 17. 22 is a cross-sectional view showing another example of the layer structure of the barrier film in Figure 17.

[0031] Hereinafter, an electricity storage device according to one embodiment of the present invention will be described with reference to the drawings. In this specification, a numerical range indicated by "to" means "greater than or equal to" or "less than or equal to." For example, the expression "2 to 15 mm" means 2 mm or more and 15 mm or less.

[0032] [Embodiments] <1-1. Configuration of Electricity Storage Device> FIG. 1A is a plan view schematically illustrating an electricity storage device 10 according to a first embodiment. FIG. 1B is a diagram illustrating a method for measuring the seal strength of a second sealed portion 80 of the electricity storage device 10 of FIG. 1A. FIG. 2 is a cross-sectional view illustrating the layer configuration of an exterior film 50 included in the electricity storage device 10 of FIG. 1A. FIG. 3 is a diagram illustrating the exterior film 50 included in the electricity storage device 10 of FIG. 1A in an unfolded state. FIG. 4 is a cross-sectional view taken along line D4-D4 in FIG. 1A. FIG. 5 is a side view of a lid body 60 included in the electricity storage device 10 of FIG. 1A. FIG. 6 is a plan view of the lid body 60 of FIG. 5. In FIGS. 1A , 4 to 6 , 8 , and 9 , the direction of arrow UD indicates the thickness direction of the electricity storage device 10, the direction of arrow LR indicates the width direction of the electricity storage device 10, and the direction of arrow FB indicates the depth direction of the electricity storage device 10. The directions indicated by the arrows UDLRFB are the same in the subsequent drawings.

[0033] The energy storage device 10 includes an electrode body 20, an electrode terminal 30, and an exterior body 40. The electrode body 20 includes electrodes (positive and negative electrodes) constituting an energy storage member such as a lithium-ion battery, a capacitor, an all-solid-state battery, a semi-solid battery, a quasi-solid battery, a polymer battery, an all-resin battery, a lead-acid battery, a nickel-metal hydride battery, a nickel-cadmium battery, a nickel-iron battery, a nickel-zinc battery, a silver oxide-zinc battery, a metal-air battery, a polyvalent cation battery, or a capacitor, as well as a separator. In this embodiment, the shape of the electrode body 20 is approximately rectangular. Note that the term "approximately rectangular" includes not only a perfect rectangular parallelepiped, but also a solid that can be considered a rectangular parallelepiped by modifying the shape of a portion of its outer surface, for example. The shape of the electrode body 20 may be, for example, a cylinder or a polygonal prism.

[0034] In this embodiment, the power storage device 10 includes two electrode terminals 30. The electrode terminals 30 are metal terminals used for inputting and outputting electric power to and from the electrode body 20. One end of the electrode terminal 30 is electrically connected to an electrode (positive electrode or negative electrode) included in the electrode body 20. The other end of the electrode terminal 30 protrudes outward from, for example, an edge of the exterior body 40. Note that the electrode terminals 30 only need to be capable of inputting and outputting electric power to and from the electrode body 20, and may not, for example, protrude from the exterior body 40. When the lid body 60 described below is made of, for example, metal, the lid body 60 may also function as the electrode terminals 30. In this case, the lid body 60, which functions as an electrode terminal, may or may not protrude from the exterior body 40.

[0035] The metal material constituting the electrode terminal 30 is, for example, aluminum, nickel, copper, etc. For example, when the electrode body 20 is a lithium ion battery, the electrode terminal 30 connected to the positive electrode is usually made of aluminum, etc., and the electrode terminal 30 connected to the negative electrode is usually made of copper, nickel, etc. The outermost layer of the electrode body 20 does not necessarily have to be an electrode, and may be, for example, a protective tape or a separator.

[0036] The exterior body 40 seals the electrode body 20. The exterior body 40 includes an exterior film 50 and a lid 60. The exterior film 50 wraps the electrode body 20 so as to have an opening 40A. In this embodiment, the exterior film 50 is wrapped around the electrode body 20 so as to have the opening 40A. The lid 60 is disposed on the side of the electrode body 20 so as to close the opening 40A. Note that the electrode body 20 may be housed inside the exterior film 50 that is configured in a cylindrical shape so as to form the opening 40A, and the opening 40A may be closed by the lid 60.

[0037] For example, there is a method of forming a storage portion (recess) in the exterior film 50 through cold forming to accommodate the electrode assembly 20. However, it is not necessarily easy to form a deep storage portion using such a method. Attempting to form a deep storage portion (recess) by cold forming (for example, a forming depth of 15 mm) increases the likelihood of pinholes or cracks occurring in the exterior film 50, resulting in a decrease in battery performance. On the other hand, the exterior body 40 seals the electrode assembly 20 by wrapping the exterior film 50 around the electrode assembly 20, and therefore can easily seal the electrode assembly 20 regardless of the thickness of the electrode assembly 20. Note that in order to reduce the dead space between the electrode assembly 20 and the exterior film 50 and improve the volumetric energy density of the power storage device 10, it is preferable that the exterior film 50 be wrapped so as to contact the outer surface of the electrode assembly 20. Furthermore, in all-solid-state batteries, it is necessary to apply a high pressure uniformly from the outer surface of the battery to exhibit battery performance, so it is necessary to eliminate the space between the electrode assembly 20 and the exterior film 50. Therefore, it is preferable that the exterior film 50 be wrapped so as to contact the outer surface of the electrode assembly 20.

[0038] As shown in FIG. 2 , the exterior film 50 is a laminate (laminate film) having, for example, a base material layer 51, a barrier layer 52, and a heat-sealable resin layer 53 in this order. It is not necessary for the exterior film 50 to include all of these layers; for example, it may not include the barrier layer 52. That is, the exterior film 50 may be made of any material that is flexible and easily bendable, and may be made of, for example, a resin film. It is preferable that the exterior film 50 is heat-sealable. The innermost and outermost layers of the exterior film 50 may be heat-sealable resin layers 53. In this case, the exterior film 50 may encase the electrode body 20 and the lid body 60 by joining the outermost and innermost layers.

[0039] The substrate layer 51 included in the exterior film 50 is a layer that imparts heat resistance to the exterior film 50 and suppresses the occurrence of pinholes that may occur during processing or distribution. The substrate layer 51 is composed of, for example, at least one layer of a stretched polyester resin layer and a stretched polyamide resin layer. For example, by including at least one layer of a stretched polyester resin layer and a stretched polyamide resin layer in the substrate layer 51, the barrier layer 52 can be protected during processing of the exterior film 50 and breakage of the exterior film 50 can be suppressed. Furthermore, from the viewpoint of increasing the tensile elongation of the exterior film 50, the stretched polyester resin layer is preferably a biaxially stretched polyester resin layer, and the stretched polyamide resin layer is preferably a biaxially stretched polyamide resin layer. Furthermore, from the viewpoint of excellent puncture strength or impact strength, the stretched polyester resin layer is more preferably a biaxially stretched polyethylene terephthalate (PET) film, and the stretched polyamide resin layer is more preferably a biaxially stretched nylon (ONy) film. The substrate layer 51 may be composed of both a stretched polyester resin layer and a stretched polyamide resin layer. From the viewpoint of film strength, the thickness of the substrate layer 51 is preferably, for example, 5 to 300 μm, and more preferably 5 to 150 μm.

[0040] The barrier layer 52 is a layer that prevents at least moisture penetration. The barrier layer 52 is bonded to the substrate layer 51 via, for example, an adhesive layer 54. Examples of the barrier layer 52 include metal foils, vapor-deposited films, and resin layers with barrier properties. Vapor-deposited films include metal vapor-deposited films, inorganic oxide vapor-deposited films, and carbon-containing inorganic oxide vapor-deposited films. Resin layers include fluorine-containing resins such as polyvinylidene chloride, polymers based on chlorotrifluoroethylene (CTFE), polymers based on tetrafluoroethylene (TFE), polymers having fluoroalkyl groups, and polymers based on fluoroalkyl units, as well as ethylene-vinyl alcohol copolymers. The barrier layer 52 may also be a resin film having at least one of these vapor-deposited films and resin layers. The barrier layer 52 may be formed of multiple layers. The barrier layer 52 preferably includes a layer made of a metal material. Specific examples of the metal material constituting the barrier layer 52 include aluminum alloys, stainless steel, titanium steel, and steel plates. When used as a metal foil, it is preferable that the metal material contains at least one of an aluminum alloy foil and a stainless steel foil.

[0041] In the barrier layer 52, the layer made of the aforementioned metal material may contain recycled metal material. Examples of recycled metal material include recycled aluminum alloy, stainless steel, titanium steel, and steel plate. These recycled materials can be obtained by known methods. Recycled aluminum alloy material can be obtained, for example, by the manufacturing method described in International Publication No. 2022 / 092231. The barrier layer 52 may be made of recycled material alone, or may be made of a mixture of recycled and virgin material. Note that recycled metal material refers to metal material that has been made reusable by collecting, isolating, and refining various products used in the market or waste from manufacturing processes. Furthermore, virgin metal material refers to new metal material refined from natural metal resources (raw materials) and is not recycled material.

[0042] From the viewpoint of improving the formability or conformability of the exterior film 50, the aluminum alloy foil is preferably a soft aluminum alloy foil made of, for example, an annealed aluminum alloy. From the viewpoint of further improving the formability or conformability, an iron-containing aluminum alloy foil is preferred. In the iron-containing aluminum alloy foil (100% by mass), the iron content is preferably 0.1 to 9.0% by mass, more preferably 0.5 to 2.0% by mass. By having an iron content of 0.1% by mass or more, an exterior film 50 with better formability can be obtained. By having an iron content of 9.0% by mass or less, an exterior film 50 with better flexibility can be obtained. Furthermore, silicon, magnesium, copper, manganese, etc. may be added as necessary. Furthermore, softening can be achieved by annealing or the like. From the viewpoint of improving the mechanical strength of the exterior film 50, the aluminum alloy foil is more preferably a hard aluminum alloy foil made of, for example, a work-hardened aluminum alloy.

[0043] Examples of the stainless steel foil include austenitic, ferritic, austenitic-ferritic, martensitic, and precipitation hardened stainless steel foils. Furthermore, from the viewpoint of providing an exterior film 50 with excellent formability, the stainless steel foil is preferably made of austenitic stainless steel.

[0044] Specific examples of austenitic stainless steels that form the stainless steel foil include SUS304, SUS301, and SUS316L, with SUS304 being particularly preferred.

[0045] In the case of a metal foil, the thickness of the barrier layer 52 should be sufficient to at least function as a barrier layer that prevents moisture penetration, and may be, for example, approximately 5 to 200 μm. The thickness of the barrier layer 52 is preferably approximately 85 μm or less, more preferably approximately 50 μm or less, even more preferably approximately 40 μm or less, and particularly preferably approximately 35 μm or less. The thickness of the barrier layer 52 is preferably approximately 9.0 μm or more, more preferably approximately 20 μm or more, and more preferably approximately 25 μm or more. Preferred ranges for the thickness of the barrier layer 52 include about 9.0 to 85 μm, about 9.0 to 50 μm, about 9.0 to 40 μm, about 9.0 to 35 μm, about 20 to 85 μm, about 20 to 50 μm, about 20 to 40 μm, about 20 to 35 μm, about 25 to 85 μm, about 25 to 50 μm, about 25 to 40 μm, and about 25 to 35 μm. When the barrier layer 52 is made of aluminum alloy foil, the above-mentioned ranges are particularly preferred. From the viewpoint of imparting high formability and high rigidity to the exterior film 50, the thickness of the barrier layer 52 is preferably about 35 μm or more, more preferably about 45 μm or more, even more preferably about 50 μm or more, and even more preferably about 55 μm or more, and is preferably about 200 μm or less, more preferably about 85 μm or less, even more preferably about 75 μm or less, and even more preferably about 70 μm or less. Preferred ranges are approximately 35 to 200 μm, approximately 35 to 85 μm, approximately 35 to 75 μm, approximately 35 to 70 μm, approximately 45 to 200 μm, approximately 45 to 85 μm, approximately 45 to 75 μm, approximately 45 to 70 μm, approximately 50 to 200 μm, approximately 50 to 85 μm, approximately 50 to 75 μm, approximately 50 to 70 μm, approximately 55 to 200 μm, approximately 55 to 85 μm, approximately 55 to 75 μm, and approximately 55 to 70 μm. The high formability of the exterior film 50 facilitates deep drawing, which can contribute to increasing the capacity of the electricity storage device. Furthermore, while increasing the capacity of the electricity storage device increases the weight of the electricity storage device, increasing the rigidity of the exterior film 50 can contribute to high sealing performance of the electricity storage device.In particular, when the barrier layer 52 is made of stainless steel foil, the thickness of the stainless steel foil is preferably about 60 μm or less, more preferably about 50 μm or less, even more preferably about 40 μm or less, even more preferably about 30 μm or less, and particularly preferably about 25 μm or less. The thickness of the stainless steel foil is preferably about 10 μm or more, more preferably about 15 μm or more. Preferred ranges for the thickness of the stainless steel foil include about 10 to 60 μm, about 10 to 50 μm, about 10 to 40 μm, about 10 to 30 μm, about 10 to 25 μm, about 15 to 60 μm, about 15 to 50 μm, about 15 to 40 μm, about 15 to 30 μm, and about 15 to 25 μm.

[0046] Furthermore, when the barrier layer 52 is an aluminum foil, it is preferable that a corrosion-resistant coating be provided on at least the surface opposite the substrate layer 51 to prevent dissolution and corrosion. The barrier layer 52 may be provided with a corrosion-resistant coating on both sides. Here, the corrosion-resistant coating refers to a thin film that is provided with corrosion resistance (e.g., acid resistance, alkali resistance, etc.) by performing, for example, a hydrothermal conversion treatment such as boehmite treatment, a chemical conversion treatment, an anodizing treatment, a plating treatment of nickel or chromium, or a corrosion prevention treatment such as applying a coating agent on the surface of the barrier layer 52. Specifically, the corrosion-resistant coating refers to a coating that improves the acid resistance of the barrier layer 52 (acid-resistant coating), a coating that improves the alkali resistance of the barrier layer 52 (alkali-resistant coating), or the like. The corrosion-resistant coating may be formed by one type of treatment or a combination of two or more types. Furthermore, the barrier layer 52 may be formed not only as a single layer but also as a multi-layer. Furthermore, among these treatments, hydrothermal conversion treatment and anodizing treatment are treatments in which the surface of the metal foil is dissolved with a treatment agent to form a metal compound with excellent corrosion resistance. Note that these treatments may also be included in the definition of chemical conversion treatment. Furthermore, if the barrier layer 52 has a corrosion-resistant coating, the corrosion-resistant coating is also included in the barrier layer 52.

[0047] The corrosion-resistant coating prevents delamination between the barrier layer 52 (e.g., aluminum alloy foil) and the substrate layer 51 during molding of the exterior film 50, prevents dissolution and corrosion of the surface of the barrier layer 52 due to hydrogen fluoride produced by a reaction between an electrolyte and water, and in particular prevents dissolution and corrosion of aluminum oxide present on the surface of the barrier layer 52 when the barrier layer 52 is an aluminum alloy foil, and also improves the adhesion (wettability) of the surface of the barrier layer 52, thereby preventing delamination between the substrate layer 51 and the barrier layer 52 during heat sealing and between the substrate layer 51 and the barrier layer 52 during molding.

[0048] The heat-sealable resin layer 53 is bonded to the barrier layer 52 via, for example, an adhesive layer 55. The heat-sealable resin layer 53 included in the exterior film 50 is a layer that provides heat-sealing properties to the exterior film 50. Examples of the heat-sealable resin layer 53 include resin films made of polyester resins such as polyethylene terephthalate resins and polybutylene terephthalate resins, polyolefin resins such as polyethylene resins and polypropylene resins, or acid-modified polyolefin resins obtained by graft-modifying these polyolefin resins with an acid such as maleic anhydride. From the standpoints of sealability and strength, the thickness of the heat-sealable resin layer 53 is preferably, for example, 20 to 300 μm, and more preferably 40 to 150 μm.

[0049] The exterior film 50 preferably has one or more layers having a buffer function (hereinafter referred to as "buffer layer") outside the heat-sealable resin layer 53, more preferably outside the barrier layer 52. The buffer layer may be laminated on the outside of the base material layer 51, or the base material layer 51 may also function as a buffer layer. When the exterior film 50 has multiple buffer layers, the multiple buffer layers may be adjacent to each other, or may be laminated with the base material layer 51, the barrier layer 52, or the like interposed therebetween.

[0050] The material constituting the buffer layer can be arbitrarily selected from materials having cushioning properties. Examples of the material having cushioning properties include rubber, nonwoven fabric, and foam sheet. Examples of rubber include natural rubber, fluororubber, and silicone rubber. The rubber hardness is preferably about 20 to 90. The material constituting the nonwoven fabric is preferably a material having excellent heat resistance. When the buffer layer is made of nonwoven fabric, the lower limit of the thickness of the buffer layer is preferably 100 μm, more preferably 200 μm, and even more preferably 1000 μm. When the buffer layer is made of nonwoven fabric, the upper limit of the thickness of the buffer layer is preferably 5000 μm, and even more preferably 3000 μm. The thickness of the buffer layer is preferably in the range of 100 μm to 5000 μm, 100 μm to 3000 μm, 200 μm to 5000 μm, 200 μm to 3000 μm, 1000 μm to 5000 μm, or 1000 μm to 3000 μm, with the most preferred range being 1000 μm to 3000 μm.

[0051] When the buffer layer is made of rubber, the lower limit of the thickness of the buffer layer is preferably 0.5 mm. When the buffer layer is made of rubber, the upper limit of the thickness of the buffer layer is preferably 10 mm, more preferably 5 mm, and even more preferably 2 mm. When the buffer layer is made of rubber, the preferred range of the thickness of the buffer layer is 0.5 mm to 10 mm, 0.5 mm to 5 mm, or 0.5 mm to 2 mm.

[0052] When the exterior film 50 has a buffer layer, the buffer layer functions as a cushion, thereby preventing the exterior film 50 from being damaged by impact when the energy storage device 10 is dropped or by handling during manufacturing of the energy storage device 10.

[0053] The lid body 60 has, for example, a rectangular parallelepiped shape and is made of, for example, a resin material. The lid body 60 may be formed by, for example, cold-forming the exterior film 50, or may be a metal molded product. If the lid body 60 is a metal molded product, it preferably has the corrosion-resistant coating described in the barrier layer 52. The lid body 60 has a lid main body 60A. The lid main body 60A has a first surface 61, a second surface 62, and a lid seal portion 63. The first surface 61 faces the electrode assembly 20. The second surface 62 is the surface opposite the first surface 61. The lid seal portion 63 is connected to the first surface 61 and the second surface 62 and is heat-sealed to the heat-sealable resin layer 53 of the exterior film 50. The lid seal portion 63 includes a first seal surface 63A, a second seal surface 63B, a third seal surface 63C, and a fourth seal surface 63D. The first sealing surface 63A constitutes the upper surface of the lid body 60. The first sealing surface 63A extends in a first direction (in the present embodiment, the LR direction) when viewed from the front of the lid body 60. The second sealing surface 63B and the third sealing surface 63C are connected to the first sealing surface 63A and constitute the side surfaces of the lid body 60. The second sealing surface 63B and the third sealing surface 63C extend in a second direction (in the present embodiment, the UD direction) that intersects with the first direction when viewed from the front of the lid body 60. In the present embodiment, the first direction and the second direction are orthogonal when viewed from the front of the lid body 60. The first direction and the second direction do not have to be orthogonal when viewed from the front of the lid body 60. The fourth sealing surface 63D constitutes the lower surface of the lid body 60. The fourth sealing surface 63D extends in a first direction (in the present embodiment, the LR direction) when viewed from the front of the lid body 60.

[0054] When the lid body 60 is plate-shaped, it is preferable that the lid body 60 have a certain thickness so that deformation of the exterior body 40 is suppressed even when the power storage device 10 is placed on top of it. From another perspective, when the lid body 60 is plate-shaped, it is preferable that the lid seal portion 63 of the lid body 60 have a certain thickness so that the lid seal portion 63 of the lid body 60 and the exterior film 50 can be heat-sealed appropriately when forming the second sealing portion 80 described below. The minimum thickness of the lid seal portion 63 of the lid body 60 is, for example, 1.0 mm, more preferably 3.0 mm, and even more preferably 4.0 mm. The maximum thickness of the lid seal portion 63 of the lid body 60 is, for example, 20 mm, more preferably 15 mm, and even more preferably 10 mm. The maximum thickness of the lid seal portion 63 of the lid body 60 may be 20 mm or more. Preferred ranges for the thickness of the lid seal portion 63 of the lid body 60 are 1.0 mm to 20 mm, 1.0 mm to 15 mm, 1.0 mm to 10 mm, 3.0 mm to 20 mm, 3.0 mm to 15 mm, 3.0 mm to 10 mm, 4.0 mm to 20 mm, 4.0 mm to 15 mm, and 4.0 mm to 10 mm. In this embodiment, when the lid body 60 is described as plate-shaped, this does not include embodiments in which the lid body 60 is composed solely of a film as defined by the JIS (Japanese Industrial Standards) [Packaging Terminology] standard. Note that the thickness of the lid seal portion 63 of the lid body 60 may vary depending on the region of the lid body 60. When the thickness of the lid seal portion 63 of the lid body 60 varies depending on the region, the thickness of the lid seal portion 63 of the lid body 60 is the thickness of the thickest portion.

[0055] The lid seal portion 63 further includes boundaries 64, 65, 66, and 67. The boundary 64 is the boundary between the first seal surface 63A and the second seal surface 63B. The boundary 65 is the boundary between the first seal surface 63A and the third seal surface 63C. The boundary 66 is the boundary between the fourth seal surface 63D and the second seal surface 63B. The boundary 67 is the boundary between the fourth seal surface 63D and the third seal surface 63C. The shapes of the boundaries 64 to 67 may be angular, or may be rounded by applying a rounding process. In this embodiment, the boundaries 64 to 67 are angular.

[0056] From the viewpoint of appropriately heat-sealing the lid body 60 and the exterior film 50, it is preferable that the material constituting the lid body 60 and the material constituting the heat-sealable resin layer 53 of the exterior film 50 are mainly made of the same material. In this embodiment, the material constituting the lid body 60 and the material constituting the heat-sealable resin layer 53 are mainly made of polypropylene. Note that the main material refers to, for example, a material that accounts for 50% or more of the materials contained in the constituent elements.

[0057] In this embodiment, the lid 60 includes a heat-sealable resin layer 60Z whose main material is an olefin-based copolymer. In this embodiment, the entire lid 60 is made of the heat-sealable resin layer 60Z. It is sufficient that at least the portion of the lid 60 including the lid seal portion 63 is made of the heat-sealable resin layer 60Z. The main material making up the heat-sealable resin layer 60Z is preferably an olefin-based random copolymer.

[0058] The thermally adhesive resin layer 60Z contains a polyolefin skeleton such as polyolefin or acid-modified polyolefin. The presence of a polyolefin skeleton in the resin constituting the thermally adhesive resin layer 60Z can be determined by, for example, infrared spectroscopy, gas chromatography mass spectrometry, or the like. Furthermore, when the resin constituting the thermally adhesive resin layer 60Z is analyzed by infrared spectroscopy, a peak derived from maleic anhydride is preferably detected. For example, when maleic anhydride-modified polyolefin is measured by infrared spectroscopy, a peak derived from maleic anhydride is detected at a wavenumber of 1760 cm. -1 Nearby and wave number 1780 cm -1 A peak derived from maleic anhydride is detected around . When the thermally adhesive resin layer 60Z is a layer made of maleic anhydride-modified polyolefin, a peak derived from maleic anhydride is detected when measured by infrared spectroscopy. However, if the degree of acid modification is low, the peak becomes small and may not be detected. In such cases, analysis can be performed by nuclear magnetic resonance spectroscopy.

[0059] The heat-sealable resin layer 60Z preferably contains a resin containing a polyolefin skeleton as a main component, more preferably a polyolefin as a main component, and even more preferably polypropylene as a main component. Here, "main component" refers to a resin component whose content of the resin components contained in the heat-sealable resin layer 60Z is, for example, 35% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more. For example, "the heat-sealable resin layer 60Z contains polypropylene as a main component" refers to a resin component whose content of polypropylene is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, even more preferably 98% by mass or more, and even more preferably 99% by mass or more.

[0060] Specific examples of polyolefins include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; ethylene-α-olefin copolymers; polypropylenes such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymers of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymers of propylene and ethylene); propylene-α-olefin copolymers; and ethylene-butene-propylene terpolymers. Among these, polypropylene is preferred. When the polyolefin resin is a copolymer, it may be a block copolymer or a random copolymer. These polyolefin resins may be used alone or in combination of two or more.

[0061] The polyolefin may also be a cyclic polyolefin. Cyclic polyolefins are copolymers of olefins and cyclic monomers, and examples of olefins constituting the cyclic polyolefins include ethylene, propylene, 4-methyl-1-pentene, styrene, butadiene, and isoprene. Examples of cyclic monomers constituting the cyclic polyolefins include cyclic alkenes such as norbornene; and cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Among these, cyclic alkenes are preferred, and norbornene is more preferred.

[0062] The polyolefin may also be an acid-modified polyolefin. An acid-modified polyolefin is a polymer modified by block polymerization or graft polymerization of a polyolefin with an acid component. Examples of the acid-modified polyolefin include the above-mentioned polyolefins, copolymers of the above-mentioned polyolefins with polar molecules such as acrylic acid or methacrylic acid, and polymers such as crosslinked polyolefins. Examples of the acid component used for acid modification include carboxylic acids or anhydrides thereof, such as maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride.

[0063] The acid-modified polyolefin may be an acid-modified cyclic polyolefin. The acid-modified cyclic polyolefin is a polymer obtained by copolymerizing a part of the monomers constituting the cyclic polyolefin by replacing it with an acid component, or by block polymerizing or graft polymerizing an acid component onto the cyclic polyolefin. The acid-modified cyclic polyolefin is the same as described above. The acid component used for the acid modification is the same as the acid component used for the modification of the polyolefin.

[0064] Preferred acid-modified polyolefins include polyolefins modified with carboxylic acid or its anhydride, polypropylenes modified with carboxylic acid or its anhydride, maleic anhydride-modified polyolefins, and maleic anhydride-modified polypropylenes.

[0065] It is preferable that multiple types of amide-based lubricants are present in the heat-sealable resin layer 60Z. When the lid 60 is molded in the manufacture of the electricity storage device 10, the amide-based lubricants are present on the surface of the heat-sealable resin layer 60Z. This improves the slipperiness of the surface of the heat-sealable resin layer 60Z, thereby enhancing the moldability of the lid 60.

[0066] Methods for making the heat-sealable resin layer 60Z contain an amide-based lubricant include coating the surface of the heat-sealable resin layer 60Z of the lid 60 with the amide-based lubricant or blending the amide-based lubricant into the polyolefin resin or the like that forms the heat-sealable resin layer 60Z. Even when blending an amide-based lubricant into the polyolefin resin or the like that forms the heat-sealable resin layer 60Z, the amide-based lubricant can be made to exist on the surface of the heat-sealable resin layer 60Z by causing the amide-based lubricant to bleed out onto the surface of the heat-sealable resin layer 60Z. On the other hand, even when coating the surface of the heat-sealable resin layer 60Z of the lid 60 with the amide-based lubricant, a portion of the amide-based lubricant migrates from the surface to the interior, thereby making the amide-based lubricant present inside the heat-sealable resin layer 60Z. In addition, a common method for causing the amide-based lubricant to bleed out onto the surface of the heat-sealable resin layer 60Z is to mature the lid body 60 at a slightly high temperature of approximately 30 to 50°C for several hours to three days to accelerate the bleeding. However, as the temperature approaches the melting point of the amide-based lubricant, the saturated lubrication amount into the heat-sealable resin layer 60Z increases, so care must be taken with the amount added and the maturing temperature.

[0067] In this embodiment, it is preferable that the heat-sealable resin layer 60Z contains multiple types of fatty acid amide lubricants, and at least one of the fatty acid amide lubricants is a saturated fatty acid amide. The heat-sealable resin layer 60Z may contain only one type of fatty acid amide lubricant.

[0068] The saturated fatty acid amide may be used alone or in combination of two or more. The saturated fatty acid amide is not particularly limited, but from the viewpoint of further improving moldability and continuous productivity of the electricity storage device 10, preferably, saturated fatty acid amides having 18 or more carbon atoms, more preferably, stearic acid amide, behenic acid amide, arachidic acid amide, etc., are used, and particularly preferably, behenic acid amide is used.

[0069] In this embodiment, the amide-based lubricant other than the saturated fatty acid amide is not particularly limited, and examples thereof include saturated fatty acid amides other than the saturated fatty acid amides exemplified above, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, etc. Specific examples of other saturated fatty acid amides include lauric acid amide, palmitic acid amide, stearic acid amide, hydroxystearic acid amide, etc. Specific examples of unsaturated fatty acid amides include oleic acid amide, erucic acid amide, etc. Specific examples of substituted amides include N-oleyl palmitic acid amide, N-stearyl stearic acid amide, N-stearyl oleic acid amide, N-oleyl stearic acid amide, N-stearyl erucic acid amide, etc. Specific examples of methylolamides include methylol stearic acid amide, etc. Specific examples of saturated fatty acid bisamides include methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene hydroxystearic acid amide, N,N'-distearyl adipamide, N,N'-distearyl sebacic acid amide, etc. Specific examples of unsaturated fatty acid bisamides include ethylene bisoleic acid amide, ethylene biserucic acid amide, hexamethylene bisoleic acid amide, N,N'-dioleyl adipamide, N,N'-dioleyl sebacic acid amide, etc. Specific examples of fatty acid ester amides include stearamidoethyl stearate, etc. Specific examples of aromatic bisamides include m-xylylene bisstearic acid amide, m-xylylene bishydroxystearic acid amide, N,N'-cystearyl isophthalic acid amide, etc. These amide lubricants may be used alone or in combination of two or more.

[0070] In this embodiment, it is preferable that the multiple types of amide-based lubricants further contain an unsaturated fatty acid amide in addition to the saturated fatty acid amide. This can further improve moldability and continuous productivity of the electricity storage device 10 when the lid 60 is not exposed to high temperatures. While the details of this mechanism are unclear, it can be thought of, for example, as follows. That is, unsaturated fatty acid amides have double bonds in their molecular structure, and when the molecules form an association, the olefin chains take on a folded structure. Therefore, unsaturated fatty acid amides are relatively mobile within the heat-sealable resin layer 60Z, easily bleed onto the surface of the heat-sealable resin layer 60Z, and easily exhibit slipperiness. On the other hand, saturated fatty acid amides do not have double bonds in their molecular structure, are linear, and take on a bulky structure when the molecules form an association (especially when the number of carbon atoms is 18 or more). Therefore, they are less likely to bleed onto the surface of the heat-sealable resin layer 60Z even during high-temperature storage, and are less likely to exhibit slipperiness. One hypothesis is that the association of the unsaturated fatty acid amide and the saturated fatty acid amide forms an association that provides appropriate bleeding and slip properties. Another hypothesis is that the unsaturated fatty acid bleeds first to form a first layer on the surface of the heat-fusible resin layer 60Z, and then the bled saturated fatty acid forms a second layer between the first layer and the heat-fusible resin layer 60Z, thereby suppressing further bleeding of the unsaturated fatty acid, which causes the problem of white powder.

[0071] Regarding the carbon number of the saturated fatty acid amide, if the carbon number is less than 18, the weight loss upon heating in the temperature range of about 230 to 280°C when the resin (such as polypropylene) forming the heat-sealable resin layer 60Z is melt-extruded reaches about 50% or more. From the viewpoint of content control, a carbon number of 18 or more is desirable. Furthermore, as described above, saturated fatty acids (regardless of the above speculation) suppress excessive bleeding of the lubricant, so a carbon number of about 22, such as behenic acid amide, is desirable. From the viewpoint of further improving moldability and continuous productivity of the electricity storage device 10, erucic acid amide is particularly preferred as the unsaturated fatty acid amide. One type of unsaturated fatty acid amide may be used alone, or two or more types may be used in combination.

[0072] In another example, the heat-sealable resin layer 60Z may be made of any of an acid-modified polyolefin resin, an unsaturated carboxylic acid grafted polyolefin resin, a polypropylene resin, a metal ion cross-linked polyethylene, a copolymer resin of ethylene and an acrylic acid derivative, and a copolymer resin of ethylene and a methacrylic acid derivative.

[0073] In yet another example, the heat-sealable resin layer 60Z may be made of a polyolefin resin to which a propylene-based elastomer having a melting point higher than 150° C. has been added. Compared to a polyolefin resin to which a propylene-based elastomer having a melting point higher than 150° C. has not been added, the adhesive strength between the heat-sealable resin layer 60Z and the heat-sealable resin layer 53 of the exterior film 50 in an environment of around 150° C. is stable. This is because the heat-sealable resin layer 60Z is formed in a state in which the propylene-based elastomer resin having a melting point higher than 150° C. is uniformly dispersed in the polyolefin resin, and the high-melting-point propylene-based elastomer resin remains uniformly dispersed in the polyolefin resin even after heat sealing (e.g., sealing temperature 190° C., surface pressure 1.0 MPa, sealing time 3.0 seconds). This prevents the portion where the heat-sealable resin layer 60Z and the heat-sealable resin layer 53 are sealed, i.e., the second sealing portion 80 described below, from melting and softening even in a high-temperature environment of around 150°C.

[0074] The heat-sealable resin layer 60Z is characterized by having at least one layer having an elastic modulus of 1300 MPa or more, measured at an indentation load of 100 μN in the FB direction. Because the heat-sealable resin layer 60Z has an elastic modulus of 1300 MPa or more, it can exhibit high insulating properties even when minute foreign matter is present in the heat-sealed portion of the heat-sealable resin layer 60Z. Because the heat-sealable resin layer 60Z has at least one layer having a high elastic modulus of 1300 MPa or more, it can effectively prevent the heat-sealable resin layer 60Z from becoming thin, even when heat-sealed in a location where minute foreign matter is present.

[0075] From the viewpoint of further improving the insulating properties, the elastic modulus is preferably 1500 MPa or more, more preferably 1800 MPa or more, and even more preferably 2000 MPa or more. Also, preferably 3000 MPa or less, more preferably 2800 MPa or less, and even more preferably 2500 MPa or less. Preferred ranges include about 1300 to 3000 MPa, about 1300 to 2800 MPa, about 1300 to 2500 MPa, about 1500 to 3000 MPa, about 1500 to 2800 MPa, about 1500 to 2500 MPa, about 1800 to 3000 MPa, about 1800 to 2800 MPa, about 1800 to 2500 MPa, about 2000 to 3000 MPa, about 2000 to 2800 MPa, and about 2000 to 2600 MPa. More specifically, when the thermal adhesive resin layer 60Z is a layer having a modulus of elasticity of 1300 MPa or more, the above-mentioned modulus of elasticity is preferable.

[0076] The elastic modulus of the thermally adhesive resin layer 60Z is measured by the indentation method as follows. The elastic modulus is measured using a nanoindenter (HYSITRON Corporation's TriboIndenter TI950). A regular triangular pyramid (Berkovich type) indenter with a diamond tip (HYSITRON Corporation's TI-0039) is used in the nanoindenter. At room temperature (25°C), the thermally adhesive resin layer 60Z is cut to expose a cross section of the thermally adhesive resin layer 60Z. Next, the nanoindenter is used to measure the elastic modulus when the indenter is pressed perpendicularly against the cross section of the layer of the thermally adhesive resin layer 60Z to be measured. The measurement conditions were a load control method, with the indentation load being a constant 100 μN (load was applied from 0 to 100 μN in 10 seconds, 100 μN was maintained for 5 seconds, and the load was removed from 100 to 0 μN in 10 seconds).

[0077] The heat-fusible resin layer 60Z preferably has a logarithmic decrement ΔE of 0.50 or less at 120° C. in a rigid pendulum measurement. When the logarithmic decrement ΔE is 0.50 or less at 120° C., collapse of the heat-fusible resin layer 60Z when heat-fused is effectively suppressed.

[0078] The logarithmic attenuation at 120°C in rigid pendulum measurements is an index of the hardness of a resin in a high-temperature environment of 120°C, with a smaller logarithmic attenuation indicating a higher resin hardness. The temperature when heat-sealing the heat-sealing resin layer 60Z is high, and in the heat-sealed portion formed by heat-sealing the heat-sealing resin layer 60Z, the heat-sealing resin layer 60Z may significantly protrude into the heat-sealed portion (the space where the electrode body 20 is housed) inside the heat-sealed portion. If the heat-sealing resin layer 60Z significantly protrudes into the heat-sealed portion, cracks (so-called polymer pools) may form in the heat-sealed resin layer 60Z, potentially reducing its insulating properties. Therefore, if the heat-sealing resin layer 60Z significantly protrudes into the heat-sealed portion, cracks may form in the heat-sealed resin layer 60Z, reducing its insulating properties. For this reason, it is important to control the shape of the heat-sealed portion, and the hardness of the heat-sealing resin layer 60Z at high temperatures is important for this purpose. Therefore, in this embodiment, the logarithmic attenuation rate at a high temperature of 120°C is used. In rigid pendulum measurements, the attenuation rate of a pendulum is measured as the temperature of a resin is increased from a low temperature to a high temperature. In rigid pendulum measurements, the edge of the measurement object is generally brought into contact with the surface of the measurement object and the object is caused to vibrate by swinging in a left-right direction. In this embodiment, the lid 60 is made of a hard heat-sealable resin layer 60Z having a logarithmic attenuation rate of 0.50 or less in a high-temperature environment of 120°C. This prevents the heat-sealable resin layer 60Z from collapsing (thinning) during heat fusion of the lid 60. By preventing the heat-sealable resin layer 60Z from collapsing too much inward at the heat-sealed portion formed by heat fusion of the heat-sealable resin layer 60Z, the heat-sealable resin layer 60Z is prevented from protruding too much into the heat-sealed portion, effectively preventing a decrease in the insulating properties of the lid 60 due to heat fusion.

[0079] The logarithmic decrement ΔE is calculated by the following formula: ΔE=[ln(A1 / A2)+ln(A2 / A3)+...ln(An / An+1)] / n, where A is the amplitude and n is the wave number.

[0080] From the viewpoint of effectively suppressing the collapse of the heat-sealable resin layer 60Z when the heat-sealable resin layer 60Z is heat-sealed, the logarithmic decrement ΔE at 120°C is preferably about 0.10 or more, more preferably about 0.11 or more, and even more preferably about 0.12 or more, and is also preferably about 0.50 or less, more preferably about 0.30 or less, even more preferably about 0.22 or less, and even more preferably 0.16 or less. Preferred ranges of the logarithmic decrement ΔE include about 0.10 to 0.50, about 0.10 to 0.30, about 0.10 to 0.22, about 0.10 to 0.16, about 0.11 to 0.50, about 0.11 to 0.30, about 0.11 to 0.22, about 0.11 to 0.16, about 0.12 to 0.50, about 0.12 to 0.30, about 0.12 to 0.22, and about 0.12 to 0.16.

[0081] The logarithmic decrement ΔE of the heat-sealable resin layer 60Z can be adjusted by, for example, the melt mass flow rate (MFR), molecular weight, melting point, softening point, molecular weight distribution, and crystallinity of the resin constituting the heat-sealable resin layer 60Z.

[0082] In measuring the logarithmic decrement ΔE, a commercially available rigid pendulum type physical property tester is used, and a rigid pendulum physical property test is performed on the heat-sealable resin layer 60Z under the conditions of a cylindrical cylinder edge as the edge portion pressed against the heat-sealable resin layer 60Z, an initial amplitude of 0.3 degrees, a temperature range of 30°C to 200°C, and a temperature rise rate of 3°C / min.

[0083] The melt mass flow rate of the heat-fusible resin layer 60Z at 230° C. is preferably in the range of 1 g / 10 min to 80 g / 10 min, and more preferably in the range of 5 g / 10 min to 60 g / 10 min. The melt mass flow rate is measured in accordance with JIS K7210-1:2014.

[0084] From the viewpoint of effectively suppressing misalignment of the second sealing portion 80, which will be described later, the melting point Tm1 of the heat-sealable resin layer 60Z is preferably 90° C. or higher and 245° C. or lower, and more preferably 100° C. or higher and 220° C. or lower. From the same viewpoint, the softening point Ts1 of the heat-sealable resin layer 60Z is preferably 70° C. or higher and 180° C. or lower, and more preferably 80° C. or higher and 150° C. or lower.

[0085] Here, the melting point Tm1 of the heat-sealable resin layer 60Z is a value obtained by measuring the melting points of the resin components constituting the heat-sealable resin layer 60Z by a DSC method in accordance with JIS K6921-2 (ISO1873-2.2:95). When the heat-sealable resin layer 60Z is formed of a blend resin containing multiple resin components, the melting point Tm1 can be calculated by determining the melting points of the individual resins as described above and averaging them by weight based on their mass ratios.

[0086] The softening point Ts1 of the thermally adhesive resin layer 60Z is a value measured by a thermo-mechanical analyzer (TMA). When the thermally adhesive resin layer 60Z is made of a blend resin containing multiple resin components, the softening point Ts1 can be calculated by determining the softening points of the individual resins as described above and averaging them by weight based on their mass ratios.

[0087] The number average molecular weight (Mn) of the resin constituting the heat-sealable resin layer 60Z is preferably 70,000 or more and 80,000 or less, the weight average molecular weight (Mw) is preferably 320,000 or more and 370,000 or less, and the dispersity (Mw / Mn) is preferably 4.5 or more and 5.5 or less.

[0088] Furthermore, although the details of the mechanism by which the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of the resin constituting the heat-fusible resin layer 60Z falling within the above-mentioned ranges can impart high insulating properties and heat-sealing properties to the lid 60 are not necessarily clear, it can be considered, for example, as follows. That is, if the number-average molecular weight (Mn) is less than 70,000, the amount of low-molecular-weight components is high, resulting in a large amount of crushing due to pressure during heat sealing, and thus a decrease in insulating properties. On the other hand, if the number-average molecular weight (Mn) is greater than 80,000, the amount of low-molecular-weight components is low, which may result in a decrease in MFR and a decrease in film-formability. Furthermore, if the weight-average molecular weight (Mw) is less than 320,000, the overall amount of high-molecular-weight components is low, resulting in a large amount of crushing due to pressure during heat sealing, and thus a decrease in insulating properties. On the other hand, if the weight-average molecular weight (Mw) is greater than 370,000, the overall amount of high-molecular-weight components is high, which may result in a decrease in MFR and a decrease in film-formability. Furthermore, although the details of the mechanism by which the polydispersity (Mw / Mn) of the resin constituting the heat-fusible resin layer 60Z within the above range can impart high insulating properties and heat-sealing properties to the lid 60 are not necessarily clear, it can be considered, for example, as follows. That is, if the polydispersity (Mw / Mn) is less than 4.5, the molecular weight distribution is narrow, which may cause necking during extrusion and result in a decrease in film-forming properties. On the other hand, if the polydispersity (Mw / Mn) is greater than 5.5, the molecular weight distribution is broadened and the amount of low-molecular-weight components increases, resulting in a large amount of crushing due to pressure during heat sealing and a decrease in insulating properties.

[0089] In the present embodiment, the lid body 60 has a through hole 60X formed therein, into which the electrode terminal 30 is inserted. The through hole 60X penetrates the first surface 61 and the second surface 62. When the electrode body 20 is stored, the electrode terminal 30 passes through the through hole 60X formed in the lid body 60 and protrudes to the outside of the exterior body 40. A small gap between the through hole 60X of the lid body 60 and the electrode terminal 30 is filled with, for example, resin. Note that, in the energy storage device 10, the position from which the electrode terminal 30 protrudes to the outside can be selected arbitrarily. For example, the electrode terminal 30 may protrude to the outside from a hole formed in any one of the six surfaces of the exterior body 40. In this case, a small gap between the exterior body 40 and the electrode terminal 30 is filled with, for example, resin. In the energy storage device 10, the lid body 60 and the electrode terminal 30 are provided as separate bodies; however, the lid body 60 and the electrode terminal 30 may be integrally formed. If the electrode terminals 30 do not protrude from the edge of the exterior body 40, the lid body 60 does not need to have the through-holes 60X formed therein.

[0090] In this embodiment, the first sealing portion 70 is formed by wrapping the exterior film 50 around the electrode body 20 so as to have an opening 40A, and then heat-sealing the opposing surfaces of the exterior film 50 (heat-fusible resin layer 53) together.

[0091] The first sealed portion 70 is formed by heat-sealing a portion of the exterior film 50 including the first edge 50A and a portion of the exterior film 50 including the second edge 50B shown in FIG. 3 . The first sealed portion 70 extends in the longitudinal direction of the exterior body 40. The position at which the first sealed portion 70 is formed on the exterior body 40 can be selected arbitrarily. In this embodiment, the base 70X of the first sealed portion 70 is preferably located on the edge 43 at the boundary between the first surface 41 and the second surface 42 of the exterior body 40. The first surface 41 has a larger area than the second surface 42. The base 70X of the first sealed portion 70 may be located on any surface of the exterior body 40. In this embodiment, the first sealed portion 70 protrudes outward beyond the electrode body 20 in a plan view. The first sealed portion 70 may be folded, for example, toward the second surface 42 or the first surface 41 of the exterior body 40.

[0092] In this embodiment, the second sealing portion 80 is formed by heat-sealing the heat-fusible resin layer 53 of the exterior film 50 and the lid seal portion 63 of the lid body 60. Hereinafter, the seal strength between the heat-fusible resin layer 53 of the exterior film 50 and the lid seal portion 63 of the lid body 60 may be referred to as the seal strength of the second sealing portion 80. Note that the seal strength of the second sealing portion 80 is the seal strength between the heat-fusible resin layer 53 and the lid body 60 at the long side portion of the lid seal portion 63, i.e., the lid seal portion 63 extending in the LR (width) direction in FIG. 1A .

[0093] The seal strength of the second sealing portion 80 is measured as follows. First, a slit is formed in the portion of the exterior film 50 that constitutes the first surface 41 of the exterior body 40, forming three strip-shaped members 41X, 41Y, and 41Z aligned in the LR direction (see the two-dot chain lines in FIG. 1B ). The width of the three strip-shaped members 41X, 41Y, and 41Z in the LR direction is 15 mm. The ends of the strip-shaped members 41X, 41Y, and 41Z are joined to the lid body 60 at the second sealing portion 80. The length of the lid body 60 in the LR direction is 45 mm or more. Next, the end of each of the strip-shaped members 41X, 41Y, and 41Z opposite the end joined to the lid body 60 is pulled upward in the UD direction (away from the first surface 41B), thereby measuring the seal strength of each of the strip-shaped members 41X, 41Y, and 41Z. In this embodiment, the seal strength of the second sealing portion 80 is the average value of the seal strengths of the strip-shaped members 41X, 41Y, and 41Z. When the lid body 60 has a length in the LR direction of less than 45 mm, three strip-shaped members with an arbitrary width X mm, less than 15 mm, are formed, and the seal strengths of the three strip-shaped members are measured in the same manner as when the lid body 60 has a length in the LR direction of 45 mm or more. The obtained seal strengths are each divided by the arbitrary width X mm and multiplied by 15 to convert them to the seal strengths of the three strip-shaped members in a 15 mm width. The seal strength of the second sealing portion 80 is the average value of the seal strengths of the three strip-shaped members converted to a 15 mm width. Note that when the lid body 60 is divided into multiple parts including long and short sides, the seal strength of the second sealing portion 80 is the seal strength of the long sides of the lid seal portions 63 of the multiple parts.

[0094] From the viewpoint of suitably maintaining the state in which the electrode assembly 20 is sealed by the exterior body 40, the seal strength of the second sealing unit 80 is preferably 40 N / 15 mm or more, more preferably 50 N / 15 mm or more, even more preferably 60 N / 15 mm or more, even more preferably 70 N / 15 mm or more, and even more preferably 85 N / 15 mm or more. When the seal strength of the second sealing unit 80 is 40 N / 15 mm or more, the state in which the electrode assembly 20 is sealed by the exterior body 40 is suitably maintained even after the power storage device 10 has been used for, for example, several years (less than 10 years). When the seal strength of the second sealing unit 80 is 85 N / 15 mm or more, the state in which the electrode assembly 20 is sealed by the exterior body 40 is suitably maintained even after the power storage device 10 has been used for, for example, 10 years or more. The seal strength of the second sealing unit 80 is preferably 300 N / 15 mm or less. A preferred range for the seal strength of the second sealing portion 80 is 40N / 15mm to 300N / 15mm, 50N / 15mm to 300N / 15mm, 60N / 15mm to 300N / 15mm, 70N / 15mm to 300N / 15mm, or 85N / 15mm to 300N / 15mm.

[0095] In this embodiment, the lid body 60 preferably has a protrusion 68 protruding from the lid seal portion 63 to prevent gaps from forming between the exterior film 50 and the lid body 60. The protrusion 68 may be formed integrally with the lid main body 60A, or may be formed separately from the lid main body 60A and joined to the lid main body 60A. In this embodiment, the protrusion 68 is formed integrally with the lid main body 60A. The position at which the protrusion 68 is formed in the lid seal portion 63 can be selected arbitrarily. A gap between the exterior film 50 and the lid body 60 is likely to form, for example, between the base 70X of the first sealing portion 70 and the lid body 60. In particular, when the base 70X of the first sealing portion 70 is located between the boundary 64 and boundary 67 of the lid body 60, the resin filling ability between the base 70X of the first sealing portion 70 and the lid body 60 is likely to decrease. For this reason, the protrusion 68 is preferably formed in the lid seal portion 63 at the location where the base 70X of the first sealing portion 70 is located. In this embodiment, the base 70X of the first sealing portion 70 is located at the boundary 64 of the lid body 60. For this reason, the protrusion 68 is preferably formed at the boundary 64 in the lid seal portion 63. In this embodiment, the first sealing portion 70 is sealed with the protrusion 68 sandwiched between them. Note that the protrusion 68 may be formed on at least one of the first seal surface 63A, the second seal surface 63B, the third seal surface 63C, the fourth seal surface 63D, the boundary 65, the boundary 66, and the boundary 67.

[0096] The shape of the protrusion 68 can be selected arbitrarily. In this embodiment, the shape of the protrusion 68 is plate-like. The thickness of the protrusion 68 can be selected arbitrarily. In this embodiment, the thickness of the protrusion 68 becomes thinner as it moves away from the boundary 64. In other words, the protrusion 68 has a tapered shape as it moves away from the boundary 64. The thickness of the protrusion 68 may be constant, or may become thicker as it moves away from the boundary 64.

[0097] The direction in which the protrusion 68 extends can be selected arbitrarily. In this embodiment, the protrusion 68 extends along a first direction (in this embodiment, the LR direction). The protrusion 68 may also extend along a second direction (in this embodiment, the UD direction).

[0098] The length of the protrusion 68 can be selected arbitrarily within a range equal to or less than the length of the first sealing portion 70. For example, the length of the protrusion 68 may be substantially equal to the length of the first sealing portion 70, or may be 30% to 50% of the length of the first sealing portion 70.

[0099] 7 is a flowchart showing an example of a method for manufacturing the power storage device 10. The method for manufacturing the power storage device 10 includes, for example, a first step, a second step, a third step, and a fourth step. The first step to the fourth step are performed by, for example, a manufacturing apparatus for the power storage device 10.

[0100] In the first process of step S11, the manufacturing apparatus places the lid body 60 with the electrode terminals 30 attached to both ends of the electrode body 20. Completion of the first process electrically connects the electrode terminals 30 to the electrodes of the electrode body 20. Note that in the first process, the lid body 60 may be connected to the electrode terminals 30 that are electrically connected to the electrode body 20.

[0101] The second step of step S12 is performed after the first step. In the second step, the manufacturing apparatus winds the exterior film 50 around the electrode assembly 20 and the lid body 60 while tension is applied to the exterior film 50, while restricting the movement of the electrode assembly 20 and the lid body 60 using a restricting means. The restricting means is, for example, a groove into which the electrode assembly 20 and the lid body 60 are fitted. The restricting means may be a device that applies an external force to the electrode assembly 20 and the lid body 60 to prevent the electrode assembly 20 and the lid body 60 from moving. The restricting means may be a device that applies a force to the electrode assembly 20 and the lid body 60 in a direction opposite to the direction in which the exterior film 50 is pulled. The restricting means may include a roller that runs on the exterior film 50 while the exterior film 50 is being pulled, in order to remove wrinkles in the exterior film 50.

[0102] The third step of step S13 is performed after the second step. In the third step, the manufacturing apparatus forms a first sealing portion 70 by heat-sealing the heat-sealable resin layer 53 in a portion including the first edge 50A of the exterior film 50 and the heat-sealable resin layer 53 in a portion including the second edge 50B while restricting movement of the electrode body 20 and the lid body 60 and applying tension to the exterior film 50, so that the protruding portion 68 of the lid body 60 is sandwiched between the exterior film 50. Note that the third step corresponds to the step of forming the first sealing portion 70.

[0103] The fourth step of step S14 is carried out after the third step. The manufacturing apparatus heat-seals the exterior film 50 and the lid 60 to form the second sealed portion 80.

[0104] <1-3. Functions and Effects of the Electricity Storage Device> According to the electricity storage device 10, the lid body 60 is configured with the heat-sealable resin layer 60Z, and is therefore suitably heat-sealed to the heat-sealable resin layer 53 of the exterior film 50. Therefore, the electrode body 20 can be suitably sealed by the exterior body 40.

[0105] [2. Modifications] The above-described embodiments are examples of possible forms of the lid, electricity storage device, and peripheral member of the present invention, and are not intended to limit the forms. The lid, electricity storage device, and peripheral member of the present invention may take forms different from those exemplified in the embodiments. Examples include forms in which part of the configuration of the embodiment is replaced, modified, or omitted, or forms in which a new configuration is added to the embodiment. Below are some examples of modifications of the embodiments. Note that the following modifications can be combined with each other as long as there is no technical contradiction.

[0106] <2-1. First Modification> In the electricity storage device 10 of the above embodiment, the lid 60 does not have to have the protrusion 68. Note that the first modification can also be similarly applied to the following second to fourteenth modifications.

[0107] 2-2. Second Modification In the power storage device 10 of the above embodiment, the direction in which the protrusion 68 extends can be changed as desired. For example, as shown in Fig. 8 , the protrusion 68 may extend in a third direction that intersects with the first direction (in the embodiment, the LR direction) and the second direction (in the embodiment, the UD direction) in a front view of the lid 60.

[0108] 2-3. Third Modification In the power storage device 10 of the above embodiment, the configuration of the lid body 60 can be modified as desired. As shown in FIG. 9 , the lid body 60 may include a peripheral member 60B joined to at least a portion of the peripheral edge of the lid main body 60A. In the third modification, the peripheral member 60B is a frame that covers the entire peripheral edge of the lid main body 60A. In this modification, the lid main body 60A may be made of any material, such as metal or resin. The peripheral member 60B is made of a thermally adhesive resin layer 60BZ. The specifications of the thermally adhesive resin layer 60BZ can be applied to the specifications of the thermally adhesive resin layer 60Z. In the third modification, the lid seal portion 63 and the protrusion 68 of the lid body 60 are formed on the peripheral member 60B. In the third modification, the lid main body 60A and the peripheral member 60B may be formed as separate bodies and joined to each other. In the third modified example, the lid main body 60A and the peripheral member 60B may be integrally formed by two-color molding or insert molding.

[0109] In a third modification, the power storage device 10 may include at least one of an adhesive film and an adhesive layer between the lid main body 60A and the peripheral member 60B to suitably bond them together. The adhesive film or adhesive layer may be a single layer or a multilayer, and preferably contains at least a resin material having a polar group. The adhesive layer can be formed by dip coating, a dispenser, inkjet printing, spraying, screen printing, or the like. From the viewpoint of suitably bonding the lid main body 60A and the peripheral member 60B, it is preferable that the surface of at least the lid seal portion 63 of the lid main body 60A be subjected to a roughening treatment.

[0110] In the third modified example, the lid seal portion 63 of the peripheral member 60B preferably has a certain thickness so that deformation of the exterior body 40 is suppressed even when the power storage devices 10 are stacked. From another perspective, the lid seal portion 63 of the peripheral member 60B preferably has a certain thickness so that the lid seal portion 63 of the peripheral member 60B and the exterior film 50 can be heat-sealed appropriately when the second sealing portion 80 is formed. The minimum thickness of the lid seal portion 63 of the peripheral member 60B is, for example, 1.0 mm, more preferably 3.0 mm, and even more preferably 4.0 mm. The maximum thickness of the lid seal portion 63 of the peripheral member 60B is, for example, 20 mm, more preferably 15 mm, and even more preferably 10 mm. The maximum thickness of the lid seal portion 63 of the peripheral member 60B may be 20 mm or more. Preferred ranges for the thickness of the lid seal portion 63 of the peripheral member 60B are 1.0 mm to 20 mm, 1.0 mm to 15 mm, 1.0 mm to 10 mm, 3.0 mm to 20 mm, 3.0 mm to 15 mm, 3.0 mm to 10 mm, 4.0 mm to 20 mm, 4.0 mm to 15 mm, and 4.0 mm to 10 mm.

[0111] 2-4. Fourth Modification In the electricity storage device 10 of the above embodiment, the specific method for forming the protrusion 68 of the lid body 60 can be changed as desired. For example, the protrusion 68 may be formed by an adhesive film or the like that is bonded to the lid seal portion 63 of the lid main body 60A. In this modification, for example, the protrusion 68 may be formed by bonding a plurality of adhesive films to the lid seal portion 63 in an overlapping manner, or the protrusion 68 may be formed by bonding an adhesive film to the lid seal portion 63 in a flap shape.

[0112] 2-5. Fifth Modification The power storage device 10 of the above embodiment may have a peripheral member 60C disposed between the exterior film 50 and the lid body 60A, as shown in FIG. 10 , in order to suitably bond the exterior film 50 and the lid body 60. In the fifth modification, the peripheral member 60C is an adhesive film bonded to the peripheral portion (lid seal portion 63) of the lid body 60A. In the fifth modification, for example, the material constituting the lid body 60A may be any material, such as metal or resin. In the fifth modification, the peripheral member 60C is bonded to substantially the entire lid seal portion 63 of the lid body 60A. Note that the peripheral member 60C may be bonded to at least a portion of the first surface 61 and at least a portion of the second surface 62 of the lid body 60.

[0113] In the fifth modified example, for example, the lid body 60 with the peripheral member 60C adhered thereto is attached to the openings 40A at both ends of the exterior body 40, and then the second sealing portion 80 is formed. For example, the peripheral member 60C may be wrapped around the lid body 60 so as to cover the entire surface of the lid seal portion 63 of the lid body 60. It is preferable that the peripheral member 60C is configured to be wider overall than the lid seal portion 63 of the lid body 60. In this case, the peripheral member 60C can be easily adhered to the lid body 60. Furthermore, because the boundaries 64 to 67 of the lid seal portion 63 are covered by the peripheral member 60C, the adhesion between the lid body 60 and the peripheral member 60C is improved.

[0114] FIG. 11 is a cross-sectional view showing an example of the layer structure of the peripheral member 60C. The peripheral member 60C is a film capable of bonding the exterior film 50 and the lid 60. The peripheral member 60C preferably has a heat-sealable resin layer 60CA at least in the portion that is bonded to the heat-sealable resin layer 53 of the exterior film 50. In the example shown in FIG. 11, the peripheral member 60C is a laminate (laminate film) having at least the heat-sealable resin layer 60CA, the barrier layer 60CB, and the heat-sealable resin layer 60CC, in this order. The peripheral member 60C may have a single-layer structure of the heat-sealable resin layer 60CA. The specifications of the heat-sealable resin layers 60CA and 60CC of the peripheral member 60C are the same as those of the heat-sealable resin layer 60Z. The specifications of the barrier layer 60CB are the same as those of the barrier layer 52 of the exterior film 50. The peripheral member 60C may have a heat-sealable resin layer instead of the heat-sealable resin layer 60CC on the side of the peripheral member 60C that is bonded to the lid body 60. The material constituting the heat-sealable resin layer is preferably an acid-modified polyolefin resin graft-modified with an acid such as maleic anhydride. The material constituting the heat-sealable resin layer 60CC of the peripheral member 60C can be selected arbitrarily as long as it can be bonded to the lid body 60A.

[0115] The peripheral member 60C may have a heat-resistant base layer instead of or in addition to the barrier layer 60CB. The heat-resistant base layer may be any film made of a heat-resistant resin, such as a non-stretched or stretched film of polyethylene terephthalate, polyethylene naphthalate, polyphenylene sulfide, polymethylpentene (registered trademark), polyacetal cyclic polyolefin, polyethylene, or polypropylene. Polyethylene terephthalate is particularly preferable because it is inexpensive and strong.

[0116] The peripheral member 60C preferably has adhesive properties. When the peripheral member 60C has adhesive properties, the peripheral member 60C is less likely to shift position relative to the lid body 60 and the lid body 60 when the second sealing portion 80 is formed with the peripheral member 60C disposed between the lid body 60 and the lid body 60. Adhesion can be imparted to the peripheral member 60C by incorporating a tackifying resin into the heat-sealable resin layers 60CA, 60CC of the peripheral member 60C. Examples of the tackifying resin include amorphous polyolefins. Examples of amorphous polyolefins include amorphous polypropylene and copolymers of amorphous propylene and other α-olefins. The content of the tackifying resin relative to the base material constituting the heat-sealable resin is preferably 10 to 20% by weight or less.

[0117] 2-6. Sixth Modification In the above embodiment, it is possible to arbitrarily select the position at which the electrode terminal 30 is disposed. For example, the electrode terminal 30 may protrude from the first sealing portion 70.

[0118] <2-7. Seventh Modification> In the above embodiment, the exterior film 50 of the power storage device 10 may protrude outward in the FB direction beyond at least one of the two lid bodies 60. The electrode body 20 is sealed by closing the portion of the exterior film 50 that protrudes outward beyond the lid body 60. The portion of the exterior film 50 that protrudes beyond the lid body 60 may be folded like a Goebel-top pouch or a brick pouch.

[0119] <2-8. Eighth Modification> In the above embodiment, the exterior body 40 may not have one of the two lid bodies 60. In this modification, in the FB direction, in the portion of the exterior body 40 where the lid body 60 is omitted, the electrode body 20 is sealed by closing the portion of the exterior film 50 that protrudes outward beyond the electrode body 20. In this modification, the portion of the exterior film 50 that protrudes outward beyond the electrode body 20 may be folded like a Goebel-top pouch or a brick pouch.

[0120] 2-9. Ninth Modification In the above embodiment, it is possible to arbitrarily change the outer shape of the exterior body 40. The outer shape of the exterior body 40 may be a cylinder, a prism, or a cube.

[0121] 2-10. Tenth Modification In the above embodiment, the lid 60 may be configured to include a heat-sealable resin layer 160Z as shown in FIG. 12 instead of the heat-sealable resin layer 60Z shown in FIG. 4. In a third modification, the peripheral member 60B may be configured to include a heat-sealable resin layer 160ZB as shown in FIG. 13 instead of the heat-sealable resin layer 60BZ shown in FIG. 9. In a fifth modification, the peripheral member 60C may be configured to include a heat-sealable resin layer 160CA as shown in FIG. 14 instead of the heat-sealable resin layer 60CA shown in FIG. 11. Hereinafter, when no particular distinction is made between the heat-sealable resin layer 160Z, the heat-sealable resin layer 160ZB, and the heat-sealable resin layer 160CA, they may be simply referred to as heat-sealable resin layers.

[0122] In the tenth variant, the heat-sealable resin layer is characterized in that, when the temperature difference T1 and the temperature difference T2 are measured by the following method, the value obtained by dividing the temperature difference T2 by the temperature difference T1 (ratio T2 / T1) is 0.60 or more.

[0123] (Measurement of temperature difference T1) According to the provisions of JIS K7121:2012, a DSC curve is obtained for the heat-fusible resin layer by differential scanning calorimetry (DSC). From the obtained DSC curve, the temperature difference T1 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-fusible resin layer is measured. Note that, unlike the measurement of the temperature difference T2 described below, the measurement of the temperature difference T1 is performed on a heat-fusible resin layer that has not been subjected to treatment such as immersion in an electrolyte solution.

[0124] (Measurement of temperature difference T2) In an environment of 85 ° C, the heat-fusible resin layer is left standing for 72 hours in an electrolyte solution of 1 mol / L lithium hexafluorophosphate and a volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate of 1:1:1, and then dried. Next, in accordance with the provisions of JIS K7121:2012, a DSC curve is obtained for the heat-fusible resin layer after drying by differential scanning calorimetry (DSC). From the obtained DSC curve, the temperature difference T2 between the extrapolated melting start temperature and the extrapolated melting end temperature of the heat-fusible resin layer is measured.

[0125] The resin component used in the heat-sealable resin layer is not particularly limited as long as it is heat-sealable, and examples thereof include polyolefins, cyclic polyolefins, acid-modified polyolefins, and acid-modified cyclic polyolefins. That is, the heat-sealable resin layer may contain a polyolefin skeleton, and preferably contains a polyolefin skeleton. The presence of a polyolefin skeleton in the heat-sealable resin layer can be determined by, for example, infrared spectroscopy, gas chromatography mass spectrometry, or the like, and the analysis method is not particularly limited. For example, when maleic anhydride-modified polyolefin is measured by infrared spectroscopy, the wavelength is 1760 cm. -1 Nearby and wave number 1780 cm -1 A peak derived from maleic anhydride is detected around this point. However, if the degree of acid modification is low, the peak may be small and not be detected. In this case, analysis can be performed using nuclear magnetic resonance spectroscopy.

[0126] Specific examples of the polyolefin include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; polypropylenes such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymers of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymers of propylene and ethylene); and ethylene-butene-propylene terpolymers. Of these polyolefins, polyethylene and polypropylene are preferred.

[0127] The cyclic polyolefin is a copolymer of an olefin and a cyclic monomer, and examples of the olefin constituting the cyclic polyolefin include ethylene, propylene, 4-methyl-1-pentene, butadiene, and isoprene. Examples of the cyclic monomer constituting the cyclic polyolefin include cyclic alkenes such as norbornene; specifically, cyclic dienes such as cyclopentadiene, dicyclopentadiene, cyclohexadiene, and norbornadiene. Among these polyolefins, preferred are cyclic alkenes, and more preferred are norbornene.

[0128] The acid-modified polyolefin is a polymer obtained by modifying the polyolefin by block polymerization or graft polymerization with an acid component such as a carboxylic acid. Examples of the acid component used for modification include carboxylic acids and anhydrides thereof, such as maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride.

[0129] The acid-modified cyclic polyolefin is a polymer obtained by copolymerizing a cyclic polyolefin by substituting an α,β-unsaturated carboxylic acid or an anhydride thereof for some of the monomers constituting the cyclic polyolefin, or by block or graft polymerizing an α,β-unsaturated carboxylic acid or an anhydride thereof onto a cyclic polyolefin. The carboxylic acid-modified cyclic polyolefin is the same as described above. The carboxylic acid used for the modification is the same as the acid component used for the modification of the polyolefin.

[0130] Among these resin components, polyolefins such as polypropylene and carboxylic acid-modified polyolefins are preferred; polypropylene and acid-modified polypropylene are more preferred.

[0131] The heat-fusible resin layer may be formed of one type of resin component alone, or may be formed of a blend polymer of two or more types of resin components.Furthermore, the heat-fusible resin layer may be formed of only one layer, or may be formed of two or more layers of the same or different resin components.

[0132] The heat-fusible resin layer may contain a lubricant. The lubricant present on the surface of the heat-fusible resin layer may be a lubricant exuded from the resin constituting the heat-fusible resin layer, or a lubricant applied to the surface of the heat-fusible resin layer.

[0133] More specifically, as can be seen from the measurement of the temperature differences T1 and T2 below, the closer the ratio T2 / T1 is to the upper limit of 1.0, the smaller the change in the width between the start point (extrapolated melting onset temperature) and end point (extrapolated melting end temperature) of the melting peak before and after contact with the electrolytic solution. That is, the value of the temperature difference T2 is usually equal to or less than the value of the temperature difference T1. One factor that causes a large change in the width between the extrapolated melting onset temperature and the extrapolated melting end temperature of the melting peak is that the low molecular weight resin contained in the resin constituting the heat-fusible resin layer dissolves into the electrolytic solution upon contact with the electrolytic solution, and the width between the extrapolated melting onset temperature and the extrapolated melting end temperature of the melting peak of the heat-fusible resin layer after contact with the electrolytic solution becomes smaller than before contact with the electrolytic solution. One method for reducing the change in the width between the extrapolated melting onset temperature and the extrapolated melting end temperature of the melting peak is to adjust the proportion of low molecular weight resin contained in the resin constituting the heat-fusible resin layer.

[0134] A commercially available differential scanning calorimeter can be used to measure the extrapolated melting onset temperature and extrapolated melting end temperature of the melting peak temperature. The DSC curve used is a curve obtained by holding a test sample at -50°C for 10 minutes, then heating it to 200°C at a heating rate of 10°C / min (first time), holding it at 200°C for 10 minutes, then cooling it to -50°C at a heating rate of -10°C / min, holding it at -50°C for 10 minutes, then heating it to 200°C at a heating rate of 10°C / min (second time), holding it at 200°C for 10 minutes, and then heating it to 200°C for the second time. When measuring the temperature difference T1 and the temperature difference T2, the melting peak appearing in the range of 120 to 160°C in each DSC curve, with the largest difference in thermal energy input, is analyzed. Even if two or more overlapping peaks exist, only the melting peak with the largest difference in thermal energy input is analyzed.

[0135] The extrapolated melting onset temperature refers to the start point of the melting peak temperature and is the temperature at the intersection of a line extending the low-temperature (65-75°C) baseline toward the high-temperature side with a tangent drawn at the point where the gradient is maximum on the curve on the low-temperature side of the melting peak where the difference in thermal energy input is maximum. The extrapolated melting end temperature refers to the end point of the melting peak temperature and is the temperature at the intersection of a line extending the high-temperature (170°C) baseline toward the low-temperature side with a tangent drawn at the point where the gradient is maximum on the curve on the high-temperature side of the melting peak where the difference in thermal energy input is maximum.

[0136] Even when an electrolytic solution contacts the heat-sealable resin layer in a high-temperature environment and the heat-sealable resin layers are heat-sealed together with the electrolytic solution adhering to the heat-sealable resin layer, the value obtained by dividing the temperature difference T2 by the temperature difference T1 (ratio T2 / T1) is preferably 0.70 or more, more preferably 0.75 or more, with preferred ranges being about 0.70 to 1.0, or about 0.75 to 1.0. The upper limit is, for example, 1.0. To achieve such a ratio T2 / T1, for example, the type, composition, molecular weight, etc. of the resin constituting the heat-sealable resin layer can be adjusted.

[0137] <2-11. Eleventh Modification> In the fifth modification, the peripheral member 60C may be configured to include a heat-sealable resin layer 260CA as shown in FIG. 15, instead of the heat-sealable resin layer 60CA shown in FIG. 11. That is, in the eleventh modification, the peripheral member 60C is configured from a laminate including at least a barrier layer 60CB and a heat-sealable resin layer 260CA, in this order, from the inside (the lid 60 side) to the outside (the exterior film 50 side). Note that it is sufficient for the peripheral member 60C to include at least the heat-sealable resin layer 260CA. The peripheral member 60C includes a peripheral member seal portion that is sealed to the exterior film 50 that constitutes the exterior body 40. In the eleventh modification, a sea-island structure is observed in a cross-sectional image of a thickness direction cross section of the peripheral member seal portion obtained using a field emission scanning electron microscope, and in the cross-sectional image, the area ratio of the island portions of the sea-island structure is 0.1% or more and 50% or less. Note that the thermally adhesive resin layer 260CA corresponds to the peripheral member seal portion. In the cross-sectional image, the area ratio RA of the island portions of the sea-island structure is preferably 5% or more and 50% or less, more preferably 10% or more and 50% or less, and even more preferably 25% or more and 35% or less.

[0138] The primary material constituting the thermally adhesive resin layer 260CA can be any material as long as the ratio RA is between 5% and 50%. The primary material constituting the thermally adhesive resin layer 260CA is preferably an olefin copolymer, and more preferably an olefin random copolymer. In the eleventh modification, when a cross section of the thermally adhesive resin layer 260CA arranged on the first seal surface 63A or the fourth seal surface 63D is cut along a plane perpendicular to the FB direction and a plane perpendicular to the LR direction and observed using a scanning electron microscope, the cross section with an average aspect ratio of the island shape closest to 1 is defined as the TD cross section. When a cross section of the thermally adhesive resin layer 260CA arranged on the second seal surface 63B or the third seal surface 63C is cut along a plane perpendicular to the FB direction and a plane perpendicular to the UD direction and observed using a scanning electron microscope, the cross section with an average aspect ratio of the island shape closest to 1 is defined as the TD cross section.

[0139] Observing a sea-island structure in a cross-sectional image means that a sea portion (sea portion) and an island portion (island portion) are observed in the cross-sectional image. When a small amount of polyethylene is added to polypropylene and a heat-sealable resin layer is formed by melt extrusion molding, a sea-island structure is formed in which polyethylene island portions are dispersed in a sea portion of polypropylene. To observe the sea-island structure, as described below, the cross section of the heat-sealable resin layer is stained with ruthenium tetroxide or the like, and a cross-sectional image is obtained and observed using a scanning electron microscope. The specifications for the eleventh modified example can also be applied to the peripheral member 60B (frame body) shown in FIG. 9. The portion of the peripheral member 60B including the lid seal portion 63 corresponds to the peripheral member seal portion.

[0140] 2-12. Twelfth Modification In the above embodiment, the lid 60 may include a heat-sealable resin layer 260Z as shown in FIG. 16 instead of the heat-sealable resin layer 60Z shown in FIG. 4 . A sea-island structure is observed in a cross-sectional image of the lid seal portion 63 of the lid 60 taken in the thickness direction using a field emission scanning electron microscope, and the area ratio RB of the islands in the sea-island structure in the cross-sectional image is 0.1% to 50%, preferably 5% to 50%, more preferably 10% to 50%, and even more preferably 25% to 35%. In the twelfth modification, it is sufficient that at least a portion of the lid 60 including the lid seal portion 63 is formed of the heat-sealable resin layer 260Z. The main material constituting the heat-sealable resin layer 260Z may be selected from any material as long as the ratio RB is 0.1% to 50%. The main material constituting the heat-fusible resin layer 260Z is preferably an olefin copolymer, and more preferably an olefin random copolymer.

[0141] "A sea-island structure is observed in a cross-sectional image" means that a sea portion (sea part) and an island portion (island part) are observed in the cross-sectional image. When a small amount of polyethylene is added to polypropylene and a heat-sealable resin layer is formed by melt extrusion molding, a sea-island structure is formed in which polyethylene island parts are dispersed in a sea portion of polypropylene. To observe the sea-island structure, the cross-section of the heat-sealable resin layer 260Z is stained with ruthenium tetroxide or the like, and a cross-sectional image is obtained and observed using a scanning electron microscope.

[0142] <2-13. Thirteenth Modification> In the fifth modification, the peripheral member 60C as an adhesive film may be made of cast polypropylene having necessary physical properties such as heat resistance and moisture resistance.

[0143] 2-14. Fourteenth Modification FIG. 17 is a cross-sectional view of the electricity storage device 10 of the fourteenth modification. FIG. 18 is a cross-sectional view of the lid 60 and its periphery in FIG. 17. As shown in FIGS. 17 and 18, a barrier film 90 may be bonded to the lid 60 from the viewpoint of preventing at least one of moisture and gas from penetrating into the interior of the exterior body 40. In this embodiment, the barrier film 90 prevents moisture and gas from penetrating into the interior of the exterior body 40. The barrier film 90 may be bonded to the lid 60 at a position where it can be bonded to the exterior film 50. In the example shown in FIGS. 17 and 18, the barrier film 90 covers the entire lid seal portion 63, the second surface 62, and the inside of the through-hole 60X of the lid 60. The barrier film 90 may cover the boundaries 64 to 67. The barrier film 90 covers the second surface 62 and the inside of the through-hole 60X in addition to the lid seal portion 63 and the boundaries 64 to 67, thereby preventing moisture from penetrating into the exterior body 40 from between the electrode terminal 30 and the through-hole 60X. The barrier film 90 may be formed from a single film, or, for example, the portion covering the lid seal portion 63 and the portion covering the second surface 62 may be formed separately. In other words, the barrier film 90 may be formed from a plurality of divided films.

[0144] The position of the end 90A of the portion of the barrier film 90 that covers the lid seal portion 63 and the position of the end 90B of the portion that covers the inside of the through-hole 60X of the lid body 60 can be selected arbitrarily. When the electricity storage device 10 is a battery that contains an electrolyte solution, such as a lithium ion battery, the ends 90A and 90B of the barrier film 90 may come into contact with gas such as hydrogen fluoride generated from the electrolyte solution, which may corrode a barrier layer 91 provided in the barrier film 90, which will be described later.

[0145] For this reason, from the viewpoint of suppressing corrosion of the barrier layer 91, it is preferable that the end 90A be located closer to the second surface 62 than to the boundary between the lid seal portion 63 and the first surface 61. From the same viewpoint, it is preferable that the end 90B be located closer to the opening of the through-hole 60X on the second surface 62 side than to the opening of the through-hole 60X on the first surface 61 side. Note that the end 90A may be located at the boundary between the lid seal portion 63 and the first surface 61, or may extend to a position closer to the electrode body 20 than the lid body 60. The end 90B may be located near the opening of the through-hole 60X on the first surface 61 side, or may extend to a position closer to the electrode body 20 than the lid body 60.

[0146] 19 and 20 are cross-sectional views showing an example of the layer structure of a barrier film 90. As shown in Fig. 19, the barrier film 90 may include a barrier layer 91 and a heat-sealable resin layer 92 laminated on the surface of the barrier layer 91 opposite to the surface bonded to the lid 60. The specifications of the barrier layer 91 can be the same as those of the barrier layer 52.

[0147] The heat-sealable resin layer 92 is heat-sealed to the heat-sealable resin layer 53 of the exterior film 50. The specifications of the heat-sealable resin layer 92 can be the same as those of the heat-sealable resin layers 60Z, 60BZ, 60CA, 60CC, 160Z, 160BZ, 160CA, 260CA, and 260Z. The heat-sealable resin layer 92 may be thinner than the heat-sealable resin layer 53. The thickness of the heat-sealable resin layer 92 may be, for example, 5 to 20 μm.

[0148] 20 , the barrier film 90 may include a heat-sealable resin layer 93 laminated on the surface of the barrier layer 91 that is to be bonded to the lid 60. The specifications of the heat-sealable resin layer 93 are the same as those of the heat-sealable resin layer 92. The heat-sealable resin layer 93 may be thinner than the heat-sealable resin layer 53. The thickness of the heat-sealable resin layer 93 may be, for example, 5 to 20 μm. When the barrier film 90 includes the heat-sealable resin layer 93, the barrier film 90 and the lid 60 can be suitably bonded together by heat fusion. The barrier layer 91 and the heat-sealable resin layer 93 may be bonded together by an adhesive layer 55.

[0149] In the fourteenth modification, the barrier film 90 may be bonded to only at least a portion of the second surface 62 of the lid 60. In this configuration, as in the seventh modification, the electrode body 20 may be sealed by heat-sealing the heat-fusible resin layer 53 of the portion of the exterior film 50 that protrudes outward beyond the lid 60 and the heat-fusible resin layer 92 of the barrier film 90.

[0150] The fourteenth modification discloses the following technical idea: (A) A lid used for an exterior body of an electricity storage device, the lid including: a lid main body; and a barrier film joined to the lid main body at a position where it can be joined to an exterior film constituting the exterior body, and the barrier film includes a heat-sealable resin layer whose main material is an olefin copolymer.

[0151] (B) An electricity storage device comprising: an electrode body; and an exterior body sealing the electrode body, wherein the exterior body includes an exterior film wrapping the electrode body; and a lid body joined to the exterior film, and the lid body includes a lid main body; and a barrier film joined to a position of the lid main body where it can be joined to the exterior film constituting the exterior body, and the barrier film includes a heat-sealable resin layer whose main material is an olefin-based copolymer.

[0152] (C) A barrier film constituting a lid used in an exterior packaging for an electricity storage device, the lid including: a lid main body; and a barrier film joined to the lid main body at a position where it can be joined to an exterior film constituting the exterior packaging, and the barrier film includes a heat-sealable resin layer whose main material is an olefin copolymer.

[0153] (D) A barrier film constituting a lid used in an exterior packaging for an electricity storage device, the lid comprising: a lid main body; and the barrier film joined to a position of the lid main body where it can be joined to an exterior film constituting the exterior packaging, the barrier film comprising a heat-sealable resin layer, wherein the heat-sealable resin layer is a barrier film in which a temperature difference T1 and a temperature difference T2 are measured by the following method, and the value obtained by dividing the temperature difference T2 by the temperature difference T1 is 0.60 or more. (Measurement of Temperature Difference T1) The temperature difference T1 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-sealable resin layer is measured by differential scanning calorimetry. (Measurement of Temperature Difference T2) In an environment of 85° C., the heat-fusible resin layer is left to stand for 72 hours in an electrolyte solution that is a solution of lithium hexafluorophosphate with a concentration of 1 mol / L and a volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate of 1:1:1, and then dried. The temperature difference T2 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-fusible resin layer after drying is measured by differential scanning calorimetry.

[0154] (E) A barrier film constituting a lid used in an exterior packaging for an electricity storage device, the lid including: a lid body; and the barrier film joined to the lid body at a position where it can be joined to an exterior film constituting the exterior packaging, the barrier film having a heat-sealable resin layer sealed to the exterior film, a sea-island structure being observed in a cross-sectional image of a cross section in the thickness direction of the heat-sealable resin layer obtained using a field emission scanning electron microscope, and in the cross-sectional image, the area ratio of the island portions of the sea-island structure is 0.1% or more and 50% or less, preferably 5% or more and 50% or less, more preferably 10% or more and 50% or less, and even more preferably 25% or more and 35% or less.

[0155] 10: Electricity storage device 20: Electrode body 40: Exterior body 50: Exterior film 60: Lid body 60B: Peripheral member (frame body) 60C: Peripheral member (adhesive film) 60Z, 60BZ, 60CA, 60CC, 160Z, 160BZ, 160CA, 260CA, 260Z: Heat-sealable resin layer 60CB: Barrier layer

Claims

1. A lid body used for an exterior body of an electricity storage device, The lid body is The thermal adhesive resin layer is made of an olefin copolymer as a main material. It is a resin molded product having a lid seal part of a thickness that allows it to be joined to the exterior film that constitutes the exterior body. Lid body.

2. A lid body used for an exterior body of an electricity storage device, The lid body is The lid body and a peripheral member joined to at least a portion of the peripheral portion of the lid body; The peripheral member is The thermal adhesive resin layer is made of an olefin copolymer as a main material. A frame body joined to the lid body, The frame is a resin molded product having a lid seal portion thick enough to be joined to the exterior film that constitutes the exterior body. Lid body.

3. A lid for use in an exterior body of an electricity storage device, comprising: The lid body is The thermal adhesive resin layer is made of an olefin copolymer as a main material. A lid seal portion that is sealed to an exterior film that constitutes the exterior body; A protrusion protruding from the lid seal portion. Lid body.

4. The olefin copolymer is an olefin random copolymer. The lid according to any one of claims 1 to 3.

5. The lid body is A protrusion protruding from the lid seal portion. The lid according to claim 1 or 2.

6. The heat-sealable resin layer contains a fatty acid amide-based lubricant. The lid according to any one of claims 1 to 3.

7. There are multiple types of fatty acid amide lubricants, At least one of the fatty acid amide-based lubricants is a saturated fatty acid amide. The lid according to claim 6.

8. The plurality of fatty acid amide-based lubricants further include an unsaturated fatty acid amide. The lid according to claim 7.

9. The saturated fatty acid amide has 18 or more carbon atoms. The lid according to claim 7.

10. The saturated fatty acid amide is behenic acid amide. The lid according to claim 7.

11. The unsaturated fatty acid amide is erucic acid amide. The lid according to claim 8.

12. The heat-sealable resin layer is made of any one of an acid-modified polyolefin resin, an unsaturated carboxylic acid-grafted polyolefin resin, a polypropylene resin, a metal ion-crosslinked polyethylene, a copolymer resin of ethylene and an acrylic acid derivative, and an ethylene and a methacrylic acid derivative. The lid according to any one of claims 1 to 3.

13. The heat-sealable resin layer contains a propylene-based elastomer resin having a melting point of more than 150° C. The lid according to any one of claims 1 to 3.

14. An electrode body; and an exterior body that seals the electrode body, The exterior body is An exterior film that wraps the electrode body; A lid body joined to the exterior film, The lid body is The thermal adhesive resin layer is made of an olefin copolymer as a main material. It is a resin molded product having a lid seal part thick enough to be bonded to the exterior film. Energy storage device.

15. An electrode body; and an exterior body that seals the electrode body, The exterior body is An exterior film that wraps the electrode body; A lid body joined to the exterior film, The lid body is The lid body and a peripheral member joined to at least a portion of the peripheral portion of the lid body; The peripheral member is The thermal adhesive resin layer is made of an olefin copolymer as a main material. A frame body joined to the lid body, The frame is a resin molded product having a lid seal portion thick enough to be bonded to the exterior film. Energy storage device.

16. An electrode body; and an exterior body that seals the electrode body, The exterior body is An exterior film that wraps the electrode body; A lid body joined to the exterior film, The lid body is The thermal adhesive resin layer is made of an olefin copolymer as a main material. A lid seal portion that is sealed to the exterior film; A protrusion protruding from the lid seal portion. Energy storage device.

17. A peripheral member constituting a lid used for an exterior body of an electricity storage device, The lid body is The lid body and The peripheral member is joined to at least a portion of the peripheral portion of the lid body, the peripheral member includes a heat-sealable resin layer whose main material is an olefin-based copolymer, A resin molded frame body having a lid seal part that is joined to the lid body and has a thickness that allows it to be joined to the exterior film that constitutes the exterior body. Peripheral parts.

18. A lid body used for an exterior body of an electricity storage device, A resin molded product including a heat-sealable resin layer and a lid seal portion having a thickness sufficient to be bonded to an exterior film constituting the exterior body, The heat-sealable resin layer has a temperature difference T1 and a temperature difference T2 measured by the following method, and the value obtained by dividing the temperature difference T2 by the temperature difference T1 is 0.60 or more. (Measurement of temperature difference T1) A temperature difference T1 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-fusible resin layer is measured by differential scanning calorimetry. (Measurement of temperature difference T2) The heat-sealable resin layer is left to stand for 72 hours in an electrolyte solution having a lithium hexafluorophosphate concentration of 1 mol / L and a volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate of 1:1:1 in an environment at a temperature of 85° C., and then dried. A temperature difference T2 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-sealable resin layer after drying is measured by differential scanning calorimetry.

19. A lid body used for an exterior body of an electricity storage device, A resin molded product including a heat-sealable resin layer and a lid seal portion having a thickness sufficient to be bonded to an exterior film constituting the exterior body, A sea-island structure is observed in a cross-sectional image of a cross section in the thickness direction of the lid seal portion obtained using a field emission scanning electron microscope, and the area ratio of the island portions of the sea-island structure in the cross-sectional image is 0.1% or more and 50% or less. Lid body.

20. A peripheral member constituting a lid used for an exterior body of an electricity storage device, The lid body is The lid body and The peripheral member is joined to at least a portion of the peripheral portion of the lid body, the peripheral member is a resin molded frame including a heat-sealable resin layer, joined to the lid body, and having a lid seal portion having a thickness sufficient to be joined to an exterior film constituting the exterior body; The heat-sealable resin layer has a temperature difference T1 and a temperature difference T2 measured by the following method, and the value obtained by dividing the temperature difference T2 by the temperature difference T1 is 0.60 or more. (Measurement of temperature difference T1) A temperature difference T1 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-fusible resin layer is measured by differential scanning calorimetry. (Measurement of temperature difference T2) The heat-sealable resin layer is left to stand for 72 hours in an electrolyte solution having a lithium hexafluorophosphate concentration of 1 mol / L and a volume ratio of ethylene carbonate, diethyl carbonate, and dimethyl carbonate of 1:1:1 in an environment at a temperature of 85° C., and then dried. A temperature difference T2 between the extrapolated melting start temperature and the extrapolated melting end temperature of the melting peak temperature of the heat-sealable resin layer after drying is measured by differential scanning calorimetry.

21. A peripheral member constituting a lid used for an exterior body of an electricity storage device, The lid body is The lid body and The peripheral member is joined to at least a portion of the peripheral portion of the lid body, the peripheral member is a resin molded frame body that is joined to the lid body and has a lid seal portion that is thick enough to be joined to an exterior film that constitutes the exterior body, A sea-island structure is observed in a cross-sectional image of a cross section of the lid seal portion in the thickness direction, the cross-sectional image being obtained using a field emission scanning electron microscope, and the area ratio of the island portions of the sea-island structure in the cross-sectional image is 0.1% or more and 50% or less. Peripheral parts.