Exterior material for energy storage devices, method for manufacturing the same, and energy storage device

Abstract

To provide an exterior material for a power storage device, which has a heat-sealing resin layer containing polypropylene and polyethylene, and which can suppress the whitening and worsening of an insulating property owing to molding.SOLUTION: An exterior material 10 for a power storage device comprises a laminate having at least a base material layer 1, a barrier layer 3 and a heat-sealing resin layer 4 from outside toward inside in this order. The heat-sealing resin layer 4 contains polypropylene and polyethylene. As to a cross section of a thickness direction in a direction in parallel with TD of the heat-sealing resin layer 4, a sea island structure is observed in a section image taken by a scanning electron microscope. When a total thickness of layers located inside the barrier layer 3 is 100%, the section image is a section image taken within a range from a surface of the heat-sealing resin layer 4 on an opposite side to the barrier layer side to a thickness of 12.5%. In the section image, the percentage of a total number of island portions accounting for an area of no more than 0.02 μm2 to a total number of island portions of the sea island structure is 80.0% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an exterior material for a power storage device, a method for manufacturing the same, and a power storage device.

Background Art

[0002] Conventionally, various types of power storage devices have been developed. In all power storage devices, an exterior material is an essential member for sealing power storage device elements such as electrodes and electrolytes. Conventionally, metal exterior materials have been frequently used as exterior materials for power storage devices.

[0003] On the other hand, in recent years, with the improvement in performance of electric vehicles, hybrid electric vehicles, personal computers, cameras, mobile phones, etc., various shapes are required for power storage devices, and thinning and weight reduction are also demanded. However, conventionally used metal exterior materials for power storage devices have the drawbacks that it is difficult to follow the diversification of shapes and there is also a limit to weight reduction.

[0004] Therefore, in recent years, as an exterior material for a power storage device that can be easily processed into various shapes and can achieve thinning and weight reduction, a film-like laminate in which a base material layer / a barrier layer / a heat-sealable resin layer are sequentially laminated has been proposed (for example, refer to Patent Document 1).

[0005] In such an exterior material for a power storage device, generally, a concave portion is formed by cold forming, power storage device elements such as electrodes and electrolytic solution are arranged in the space formed by the concave portion, and by heat-sealing the heat-sealable resin layer, a power storage device in which the power storage device elements are housed inside the exterior material for a power storage device can be obtained.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

[0007] In the aforementioned film-like exterior materials for energy storage devices, polyolefins such as polypropylene are sometimes used as the material for forming the heat-sealable resin layer. For example, when polypropylene is used to form the heat-sealable resin layer, polyethylene may be used in combination to improve processability and flexibility.

[0008] However, polypropylene and polyethylene do not have high compatibility. For example, when a small amount of polyethylene is added to polypropylene and a heat-fusible resin layer is formed by melt extrusion molding, a sea-island structure is formed in which polyethylene islands are dispersed within the polypropylene seas (to observe this sea-island structure, the cross-section of the heat-fusible resin layer is stained with ruthenium tetroxide, and a cross-sectional image is obtained and observed using a scanning electron microscope). Therefore, when the exterior material for energy storage devices is subjected to the aforementioned cold molding, the stress applied during molding can cause fine cracks to occur at the interface between the polypropylene and polyethylene portions of the heat-fusible resin layer, which can lead to whitening of the heat-fusible resin layer and a decrease in the insulation properties of the exterior material for energy storage devices.

[0009] For example, Patent Document 2 states that when the inner layer of a battery casing material is made of a mixture of polypropylene resin and polyethylene resin, the seal strength between heat-sealed inner layers can be controlled by controlling the size and number of "islands" by controlling the manufacturing conditions of the battery casing material, the thickness of the inner layer, and the mixing ratio of polypropylene resin and polyethylene resin. In a mixture with a sea-island structure, the particle size of the polyethylene resin, which is the size of the "island," is in the range of 0.5 to 5 μm (i.e., 0.196 to 19.6 μm). 2 It is stated that it is preferable that the degree is such.

[0010] However, the inventors have found that, as disclosed in Patent Document 2, conventional battery casing materials, which have polypropylene and polyethylene in the inner layer, have large polyethylene resin particles, and therefore cannot adequately suppress whitening and deterioration of insulation properties due to molding.

[0011] Under these circumstances, the main objective of this disclosure is to provide an exterior material for energy storage devices comprising a heat-fusible resin layer containing polypropylene and polyethylene, which suppresses whitening and deterioration of insulation properties due to molding. [Means for solving the problem]

[0012] The inventors of this disclosure have diligently studied to solve the above-mentioned problems. As a result, they found that the laminate is composed of at least a base layer, a barrier layer, and a heat-fusible resin layer in this order from the outside to the inside, the heat-fusible resin layer contains polypropylene and polyethylene, and a sea-island structure was observed in the cross-sectional image obtained using a scanning electron microscope of the cross-section of the heat-fusible resin layer in the direction parallel to the TD (Transverse Direction) and in the thickness direction, and in the cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm² relative to the total number of island portions. 2We found that exterior materials for energy storage devices in which the total number of the following island-like structures accounts for 80.0% or more suppress whitening and deterioration of insulation due to molding. The cross-sectional image was obtained within a range from the surface opposite the barrier layer to a thickness of 12.5% ​​when the total thickness of the layers located inside the barrier layer is taken as 100%. The direction of the MD and TD of the heat-fusible resin layers laminated in the laminate can generally be determined from the barrier layer described later. In other words, in exterior materials for energy storage devices, the MD and TD of the barrier layer described later can generally be determined during the manufacturing process. For example, when the barrier layer is made of aluminum foil, linear lines called rolling marks are formed on the surface of the aluminum foil in the rolling direction (RD) of the aluminum foil. Since the rolling marks extend along the rolling direction, the rolling direction of the aluminum foil can be determined by observing the surface of the aluminum foil. Furthermore, in the manufacturing process of the laminate, the MD of the laminate and the RD of the aluminum foil generally coincide. Therefore, by observing the surface of the aluminum foil in the laminate and identifying the rolling direction (RD) of the aluminum foil, the MD of the laminate (i.e., the MD of the heat-fusible resin layer) can be determined. In addition, since the TD of the laminate is perpendicular to the MD of the laminate, the TD of the laminate (i.e., the TD of the heat-fusible resin layer) can also be determined.

[0013] This disclosure is the result of further consideration based on these findings. Specifically, this disclosure provides inventions in the following embodiments. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image obtained using a scanning electron microscope of the heat-fusible resin layer in a direction parallel to TD and in the thickness direction. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm² relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more. [Effects of the Invention]

[0014] According to this disclosure, it is possible to provide an exterior material for energy storage devices that comprises a heat-sealable resin layer containing polypropylene and polyethylene, and in which whitening and deterioration of insulation due to molding are suppressed. Furthermore, according to this disclosure, it is also possible to provide a method for manufacturing the exterior material for energy storage devices and an energy storage device. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram showing an example of the cross-sectional structure of the exterior material for the energy storage device of this disclosure. [Figure 2] This is a schematic diagram showing an example of the cross-sectional structure of the exterior material for the energy storage device of this disclosure. [Figure 3] This is a schematic diagram showing an example of the cross-sectional structure of the exterior material for the energy storage device of this disclosure. [Figure 4] This is a schematic diagram showing an example of the cross-sectional structure of the exterior material for the energy storage device of this disclosure. [Modes for carrying out the invention]

[0016] The exterior material for energy storage devices of this disclosure is composed of a laminate comprising, in order from the outside to the inside, at least a base layer, a barrier layer, and a heat-fusible resin layer. The heat-fusible resin layer contains polypropylene and polyethylene. A sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope of the cross-section of the heat-fusible resin layer in a direction parallel to the TD and in the thickness direction. The cross-sectional image is obtained within a range from the surface of the heat-fusible resin layer opposite the barrier layer to a portion with a thickness of 12.5%, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the cross-sectional image, the area of ​​the islands is 0.02 μm² relative to the total number of islands in the sea-island structure. 2 The following characteristic is that the proportion of the total number of island-shaped sections is 80.0% or more. According to the exterior material for energy storage devices of this disclosure, having this configuration suppresses whitening due to molding and a decrease in insulation performance.

[0017] The exterior materials for energy storage devices described herein will be described in detail below. In this specification, numerical ranges indicated by "~" mean "greater than or equal to" and "less than or equal to". For example, the notation 2~15mm means 2mm or more and 15mm or less.

[0018] 1. Laminated structure of exterior material for energy storage devices The exterior material 10 for energy storage devices of this disclosure is composed of a laminate comprising a base layer 1, a barrier layer 3, and a heat-sealable resin layer 4 in that order, as shown in Figure 1, for example. In the exterior material 10 for energy storage devices, the base layer 1 is the outermost layer, and the heat-sealable resin layer 4 is the innermost layer. When assembling an energy storage device using the exterior material 10 and an energy storage device element, the energy storage device element is housed in a space formed by heat-sealing the peripheral edges of the heat-sealable resin layers 4 of the exterior material 10 facing each other.

[0019] The exterior material 10 for the energy storage device may, for example, have an adhesive layer 2 between the base layer 1 and the barrier layer 3, as needed, for the purpose of improving the adhesion between these layers, as shown in Figures 2 to 4. Also, as shown in Figures 3 and 4, an adhesive layer 5 may, as needed, have an adhesive layer 5 between the barrier layer 3 and the heat-fusible resin layer 4, for the purpose of improving the adhesion between these layers. Furthermore, as shown in Figure 4, a surface coating layer 6 or the like may be provided on the outside of the base layer 1 (opposite the heat-fusible resin layer 4 side), as needed.

[0020] The thickness of the laminate constituting the exterior material 10 for energy storage devices is not particularly limited, but from the viewpoint of cost reduction and improvement of energy density, it is preferably about 180 μm or less, about 155 μm or less, or about 120 μm or less. Furthermore, from the viewpoint of maintaining the function of the exterior material for energy storage devices, which is to protect the energy storage device elements, the thickness of the laminate constituting the exterior material 10 for energy storage devices is preferably about 35 μm or more, about 45 μm or more, or about 60 μm or more. Furthermore, as for the preferred range of thickness of the laminate constituting the exterior material 10 for energy storage devices, for example, it is about 35 to 180 μm, about 35 to 155 μm, about 35 to 120 μm, about 45 to 180 μm, about 45 to 155 μm, about 45 to 120 μm, about 60 to 180 μm, about 60 to 155 μm, or about 60 to 120 μm, with about 60 to 155 μm being particularly preferred.

[0021] In the exterior material 10 for energy storage devices, the ratio of the total thickness of the base layer 1, the adhesive layer 2 (optionally provided), the barrier layer 3, the adhesive layer 5 (optionally provided), the heat-fusible resin layer 4, and the surface coating layer 6 (optionally provided) to the thickness (total thickness) of the laminate constituting the exterior material 10 for energy storage devices is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. For example, if the exterior material 10 for energy storage devices of this disclosure includes a base layer 1, an adhesive layer 2, a barrier layer 3, an adhesive layer 5, and a heat-fusible resin layer 4, the ratio of the total thickness of each of these layers to the thickness (total thickness) of the laminate constituting the exterior material 10 for energy storage devices is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more.

[0022] 2. Each layer forming the exterior material for the energy storage device [Base material layer 1] In this disclosure, the base material layer 1 is a layer provided for purposes such as enabling it to function as a base material for the exterior material of an energy storage device. The base material layer 1 is located on the outer layer side of the exterior material for the energy storage device.

[0023] The material forming the base layer 1 is not particularly limited, as long as it has the function of a base material, that is, at least insulating properties. The base layer 1 can be formed using, for example, a resin, and the resin may contain additives described later.

[0024] When the base layer 1 is formed of resin, the base layer 1 may be, for example, a resin film formed of resin, or a film formed by coating with resin. The resin film may be an unstretched film or a stretched film. Examples of stretched films include uniaxially stretched films and biaxially stretched films, with biaxially stretched films being preferred. Examples of stretching methods for forming a biaxially stretched film include sequential biaxial stretching, inflation stretching, and simultaneous biaxial stretching. Examples of resin coating methods include roll coating, gravure coating, and extrusion coating.

[0025] Examples of resins that form the base layer 1 include polyester, polyamide, polyolefin, epoxy resin, acrylic resin, fluororesin, polyurethane, silicon resin, phenolic resin, and modified versions of these resins. Furthermore, the resin forming the base layer 1 may be a copolymer of these resins, or a modified version of such copolymer. It may also be a mixture of these resins.

[0026] Among these, polyester and polyamide are preferred as resins for forming the base layer 1.

[0027] Examples of polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, and copolymerized polyesters. Examples of copolymerized polyesters include copolymerized polyesters with ethylene terephthalate as the main repeating unit. Specifically, examples include copolymerized polyesters polymerized with ethylene isophthalate using ethylene terephthalate as the main repeating unit (hereinafter abbreviated as polyethylene(terephthalate / isophthalate)), polyethylene(terephthalate / adipate), polyethylene(terephthalate / sodium sulfoisophthalate), polyethylene(terephthalate / sodium isophthalate), polyethylene(terephthalate / phenyl-dicarboxylate), and polyethylene(terephthalate / decanedicarboxylate). These polyesters may be used individually or in combination of two or more types.

[0028] Furthermore, specific examples of polyamides include aliphatic polyamides such as nylon 6, nylon 66, nylon 610, nylon 12, nylon 46, and copolymers of nylon 6 and nylon 66; hexamethylenediamine-isophthalic acid-terephthalic acid copolymer polyamides such as nylon 6I, nylon 6T, nylon 6IT, and nylon 6I6T (where I represents isophthalic acid and T represents terephthalic acid), which contain constituent units derived from terephthalic acid and / or isophthalic acid; aromatic polyamides such as polyamide MXD6 (polymetaxylylene adipamide); alicyclic polyamides such as polyamide PACM6 (polybis(4-aminocyclohexyl)methaneadipamide); polyamides copolymerized with lactam components or isocyanate components such as 4,4'-diphenylmethane-diisocyanate; polyesteramide copolymers and polyether esteramide copolymers, which are copolymers of copolymerized polyamides with polyester or polyalkylene ether glycol; and other polymers of these polyamides. These polyamides may be used individually or in combination of two or more types.

[0029] The base layer 1 preferably contains at least one of polyester film, polyamide film, and polyolefin film, preferably at least one of stretched polyester film, stretched polyamide film, and stretched polyolefin film, more preferably at least one of stretched polyethylene terephthalate film, stretched polybutylene terephthalate film, stretched nylon film, and stretched polypropylene film, and even more preferably at least one of biaxially oriented polyethylene terephthalate film, biaxially oriented polybutylene terephthalate film, biaxially oriented nylon film, and biaxially oriented polypropylene film.

[0030] The base layer 1 may be a single layer or may consist of two or more layers. If the base layer 1 consists of two or more layers, the base layer 1 may be a laminate formed by laminating resin films with an adhesive, or it may be a laminate of two or more resin films formed by co-extruding resin. Furthermore, the laminate of two or more resin films formed by co-extruding resin may be used as the base layer 1 in its unstretched state, or it may be used as the base layer 1 after uniaxial stretching or biaxial stretching.

[0031] Specific examples of a laminate of two or more resin films in the base layer 1 include a laminate of polyester film and nylon film, a laminate of two or more nylon films, and a laminate of two or more polyester films. Preferably, a laminate of stretched nylon film and stretched polyester film, a laminate of two or more stretched nylon films, and a laminate of two or more stretched polyester films are preferred. For example, when the base layer 1 is a laminate of two resin films, a laminate of polyester resin film and polyester resin film, a laminate of polyamide resin film and polyamide resin film, or a laminate of polyester resin film and polyamide resin film is preferred, and a laminate of polyethylene terephthalate film and polyethylene terephthalate film, a laminate of nylon film and nylon film, or a laminate of polyethylene terephthalate film and nylon film is more preferred. Furthermore, since polyester resin is less likely to discolor when an electrolyte adheres to its surface, for example, when the base layer 1 is a laminate of two or more resin films, it is preferable that the polyester resin film be located in the outermost layer of the base layer 1.

[0032] If the base layer 1 is a laminate of two or more resin films, the two or more resin films may be laminated with an adhesive in between. Preferred adhesives include those similar to those exemplified in adhesive layer 2 described later. The method for laminating the two or more resin films is not particularly limited, and known methods can be used, such as dry lamination, sandwich lamination, extrusion lamination, and thermal lamination, with dry lamination being preferred. When laminating by dry lamination, it is preferable to use a polyurethane adhesive. In this case, the thickness of the adhesive is, for example, about 2 to 5 μm. Alternatively, an anchor coat layer may be formed on the resin film and then laminated. The anchor coat layer is similar to the adhesive exemplified in adhesive layer 2 described later. In this case, the thickness of the anchor coat layer is, for example, about 0.01 to 1.0 μm.

[0033] Furthermore, at least one of the surface and interior of the base layer 1 may contain additives such as lubricants, flame retardants, antiblocking agents, antioxidants, light stabilizers, tackifiers, and antistatic agents. Only one type of additive may be used, or two or more types may be mixed and used.

[0034] In this disclosure, from the viewpoint of improving the moldability of the exterior material for energy storage devices, it is preferable that a lubricant be present on the surface of the base layer 1. The lubricant is not particularly limited, but amide lubricants are preferred. Specific examples of amide lubricants include saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides, and aromatic bisamides. Specific examples of saturated fatty acid amides include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide. Specific examples of unsaturated fatty acid amides include oleic acid amide and erucic acid amide. Specific examples of substituted amides include N-oleyl palmitic acid amide, N-stearyl stearate amide, N-stearyl oleic acid amide, N-oleyl stearate amide, and N-stearyl erucic acid amide. Specific examples of methylolamides include methylol stearate amide. Specific examples of saturated fatty acid bisamides include methylenebisstearate, ethylenebiscaprate, ethylenebislaurate, ethylenebisstearate, ethylenebishydroxystearate, ethylenebisbehenamide, hexamethylenebisstearate, hexamethylenebisbehenamide, hexamethylenehydroxystearate, N,N'-distearyladipamide, and N,N'-distearylsebacinamide. Specific examples of unsaturated fatty acid bisamides include ethylenebisoleamide, ethylenebiserucamide, hexamethylenebisoleamide, N,N'-dioleyladipamide, and N,N'-dioleylsebacinamide. Specific examples of fatty acid ester amides include stearamidoethylstearate. Specific examples of aromatic bisamides include m-xylylenebisstearate, m-xylylenebishydroxystearate, and N,N'-distearyl isophthalamide. The lubricant may be used alone or in combination of two or more types.

[0035] If a lubricant is present on the surface of the substrate layer 1, the amount present is not particularly limited, but preferably about 3 mg / m². 2 More preferably 4-15 mg / m² 2 To a certain extent, more preferably 5-14 mg / m² 2 The degree can be described as follows.

[0036] The lubricant present on the surface of the base layer 1 may be a lubricant contained in the resin constituting the base layer 1 that has seeped out, or a lubricant may be applied to the surface of the base layer 1.

[0037] The thickness of the base layer 1 is not particularly limited as long as it performs its function as a base material, but for example, it can be about 3 to 50 μm, preferably about 10 to 35 μm. If the base layer 1 is a laminate of two or more resin films, the thickness of each resin film constituting each layer can be preferably about 2 to 25 μm.

[0038] [Adhesive layer 2] In the exterior material for energy storage devices of this disclosure, the adhesive layer 2 is a layer provided between the substrate layer 1 and the barrier layer 3 as needed, for the purpose of improving the adhesion between them.

[0039] The adhesive layer 2 is formed by an adhesive capable of bonding the substrate layer 1 and the barrier layer 3. The adhesive used to form the adhesive layer 2 is not limited, but may be a chemical reaction type, solvent evaporation type, heat melt type, hot pressure type, etc. It may also be a two-component curing adhesive (two-part adhesive), a one-component curing adhesive (one-part adhesive), or a resin that does not undergo a curing reaction. Furthermore, the adhesive layer 2 may be a single layer or a multi-layer layer.

[0040] Specifically, adhesive components included in adhesives include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, copolymerized polyester; polyethers; polyurethanes; epoxy resins; phenolic resins; polyamides such as nylon 6, nylon 66, nylon 12, copolymerized polyamides; polyolefin resins such as polyolefins, cyclic polyolefins, acid-modified polyolefins, and acid-modified cyclic polyolefins; polyvinyl acetate; cellulose; (meth)acrylic resins; polyimides; polycarbonates; amino resins such as urea resins and melamine resins; rubbers such as chloroprene rubber, nitrile rubber, and styrene-butadiene rubber; and silicone resins. These adhesive components may be used individually or in combination of two or more. Among these adhesive components, polyurethane adhesives are particularly preferred. Furthermore, the adhesive strength of these adhesive resins can be increased by using an appropriate curing agent. The curing agent is selected appropriately from polyisocyanates, polyfunctional epoxy resins, oxazoline group-containing polymers, polyamine resins, acid anhydrides, etc., depending on the functional groups of the adhesive components.

[0041] Examples of polyurethane adhesives include polyurethane adhesives comprising a main component containing a polyol compound and a curing agent containing an isocyanate compound. Preferably, a two-component curing type polyurethane adhesive is used, in which a polyol such as polyester polyol, polyether polyol, and acrylic polyol is the main component and an aromatic or aliphatic polyisocyanate is the curing agent. Furthermore, as the polyol compound, it is preferable to use a polyester polyol that has hydroxyl groups not only at the ends of the repeating units but also in the side chains. Because the adhesive layer 2 is formed of a polyurethane adhesive, the exterior material for the energy storage device is given excellent electrolyte resistance, and peeling of the base material layer 1 is suppressed even if electrolyte adheres to the side surface.

[0042] Furthermore, the adhesive layer 2 may contain other components as long as they do not impair adhesion, and may include colorants, thermoplastic elastomers, tackifiers, fillers, etc. The inclusion of a colorant in the adhesive layer 2 allows for the coloring of the exterior material for energy storage devices. Known colorants such as pigments and dyes can be used. Additionally, only one type of colorant may be used, or two or more types may be mixed.

[0043] The type of pigment is not particularly limited, as long as it does not impair the adhesion of adhesive layer 2. Examples of organic pigments include azo, phthalocyanine, quinacridone, anthraquinone, dioxazine, indigothioindigo, perinone-perylene, isoindorenine, and benzimidazolon pigments. Examples of inorganic pigments include carbon black, titanium dioxide, cadmium, lead, chromium oxide, and iron pigments. Other examples include fine mica powder and fish scale foil.

[0044] Among colorants, carbon black is preferred for, for example, to give the exterior material of an energy storage device a black appearance.

[0045] The average particle size of the pigment is not particularly limited, but for example, it can be about 0.05 to 5 μm, preferably about 0.08 to 2 μm. The average particle size of the pigment is the median diameter measured by a laser diffraction / scattering particle size distribution analyzer.

[0046] The pigment content in the adhesive layer 2 is not particularly limited as long as the exterior material for the energy storage device is colored, and for example, it is about 5 to 60% by mass, preferably 10 to 40% by mass.

[0047] The thickness of the adhesive layer 2 is not particularly limited as long as it can bond the substrate layer 1 and the barrier layer 3, but for example, it is about 1 μm or more and about 2 μm or more. Alternatively, the thickness of the adhesive layer 2 is about 10 μm or less and about 5 μm or less. Preferred ranges for the thickness of the adhesive layer 2 include about 1 to 10 μm, about 1 to 5 μm, about 2 to 10 μm, and about 2 to 5 μm.

[0048] [Colored layer] The colored layer is a layer provided between the base layer 1 and the barrier layer 3 as needed (not shown in the figure). If an adhesive layer 2 is present, the colored layer may be provided between the base layer 1 and the adhesive layer 2, and between the adhesive layer 2 and the barrier layer 3. Alternatively, the colored layer may be provided on the outside of the base layer 1. By providing a colored layer, the exterior material for the energy storage device can be colored.

[0049] The colored layer can be formed, for example, by applying an ink containing a coloring agent to the surface of the substrate layer 1 or the surface of the barrier layer 3. Known coloring agents such as pigments and dyes can be used. In addition, only one type of coloring agent may be used, or two or more types may be mixed and used.

[0050] Specific examples of colorants included in the colored layer are the same as those exemplified in the [Adhesive Layer 2] section.

[0051] [Barrier layer 3] In the exterior material for energy storage devices, the barrier layer 3 is a layer that at least prevents the intrusion of moisture.

[0052] Examples of barrier layer 3 include metal foil, vapor-deposited film, and resin layer with barrier properties. Examples of vapor-deposited films include metal vapor-deposited films, inorganic oxide vapor-deposited films, and carbon-containing inorganic oxide vapor-deposited films. Examples of resin layers include fluorine-containing resins such as polymers mainly composed of polyvinylidene chloride, chlorotrifluoroethylene (CTFE), polymers mainly composed of tetrafluoroethylene (TFE), polymers having fluoroalkyl groups, and polymers mainly composed of fluoroalkyl units, as well as ethylene vinyl alcohol copolymers. In addition, a resin film having at least one of these vapor-deposited films and resin layers can also be provided as barrier layer 3. Multiple layers of barrier layer 3 may be provided. It is preferable that barrier layer 3 includes a layer made of a metal material. Specific examples of metal materials constituting barrier layer 3 include aluminum alloy, stainless steel, titanium steel, and steel plates. When used as a metal foil, it is preferable that it includes at least one of aluminum alloy foil and stainless steel foil.

[0053] From the viewpoint of improving the formability of the exterior material for energy storage devices, the aluminum alloy foil is more preferably a soft aluminum alloy foil composed of, for example, an annealed aluminum alloy, and from the viewpoint of further improving formability, it is more preferably an aluminum alloy foil containing iron. In an iron-containing aluminum alloy foil (100% by mass), the iron content is preferably 0.1 to 9.0% by mass, and more preferably 0.5 to 2.0% by mass. By having an iron content of 0.1% by mass or more, an exterior material for energy storage devices with better formability can be obtained. By having an iron content of 9.0% by mass or less, an exterior material for energy storage devices with better flexibility can be obtained. Examples of soft aluminum alloy foils include aluminum alloy foils having compositions specified in JIS H4160:1994 A8021H-O, JIS H4160:1994 A8079H-O, JIS H4000:2014 A8021P-O, or JIS H4000:2014 A8079P-O. Silicon, magnesium, copper, manganese, etc., may also be added as needed. Softening can be achieved through annealing or other treatments.

[0054] Furthermore, examples of stainless steel foils include austenitic, ferritic, austenitic-ferritic, martensitic, and precipitation-hardening stainless steel foils. Moreover, from the viewpoint of providing an exterior material for energy storage devices with excellent formability, it is preferable that the stainless steel foil be made of austenitic stainless steel.

[0055] Specific examples of austenitic stainless steels that make up stainless steel foil include SUS304, SUS301, and SUS316L, with SUS304 being particularly preferred among these.

[0056] In the case of metal foil, the thickness of the barrier layer 3 should at least function as a barrier layer that prevents moisture from penetrating, for example, about 9 to 200 μm. The thickness of the barrier layer 3 is preferably about 85 μm or less, more preferably about 50 μm or less, even more preferably about 40 μm or less, and particularly preferably about 35 μm or less. Also, the thickness of the barrier layer 3 is preferably about 10 μm or more, even more preferably about 20 μm or more, and more preferably about 25 μm or more. Preferred ranges for the thickness include about 10 to 85 μm, about 10 to 50 μm, about 10 to 40 μm, about 10 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 3 is made of aluminum alloy foil, the above range is particularly preferred. Furthermore, when the barrier layer 3 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. Furthermore, the thickness of the stainless steel foil is preferably about 10 μm or more, more preferably about 15 μm or more. Furthermore, preferred thickness ranges for 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.

[0057] Furthermore, if the barrier layer 3 is a metal foil, it is preferable to provide a corrosion-resistant coating on at least the side opposite to the substrate layer to prevent dissolution and corrosion. The barrier layer 3 may also have a corrosion-resistant coating on both sides. Here, a corrosion-resistant coating refers to a thin film that provides corrosion resistance to the barrier layer by performing a corrosion prevention treatment on the surface of the barrier layer, such as a hot water modification treatment like boehmite treatment, a chemical conversion treatment, anodizing treatment, plating treatment with nickel or chromium, or coating agent application. One type of treatment may be performed to form the corrosion-resistant coating, or two or more types may be combined. In addition, it is possible to have multiple layers instead of just one. Furthermore, among these treatments, hot water modification treatment and anodizing treatment are treatments that dissolve the surface of the metal foil with a treatment agent and form a metal compound with excellent corrosion resistance. Note that these treatments may also be included in the definition of chemical conversion treatment. Also, if the barrier layer 3 has a corrosion-resistant coating, the barrier layer 3 includes the corrosion-resistant coating.

[0058] The corrosion-resistant coating prevents delamination between the barrier layer (e.g., aluminum alloy foil) and the base layer during the molding of exterior materials for energy storage devices. It also prevents dissolution and corrosion of the barrier layer surface due to hydrogen fluoride generated by the reaction of electrolyte and water, particularly the dissolution and corrosion of aluminum oxide present on the barrier layer surface when the barrier layer is aluminum alloy foil. Furthermore, it improves the adhesion (wettability) of the barrier layer surface, preventing delamination between the base layer and the barrier layer during heat sealing and molding.

[0059] Various corrosion-resistant coatings are known to be formed by chemical conversion treatments, mainly including corrosion-resistant coatings containing at least one of the following: phosphates, chromates, fluorides, triazinethiol compounds, and rare earth oxides. Examples of chemical conversion treatments using phosphates and chromates include chromate treatment, phosphate chromate treatment, phosphate-chromate treatment, and chromate treatment. Examples of chromium compounds used in these treatments include chromium nitrate, chromium fluoride, chromium sulfate, chromium acetate, chromium oxalate, chromium biphosphate, acetyl acetate chromate, chromium chloride, and potassium chromium sulfate. Examples of phosphorus compounds used in these treatments include sodium phosphate, potassium phosphate, ammonium phosphate, and polyphosphate. Examples of chromate treatments include etching chromate treatment, electrolytic chromate treatment, and coating-type chromate treatment, with coating-type chromate treatment being preferred. This coating-type chromate treatment involves first degreasing at least the inner surface of a barrier layer (e.g., aluminum alloy foil) using a well-known treatment method such as alkaline immersion, electrolytic cleaning, acid cleaning, electrolytic acid cleaning, or acid activation. Then, a treatment solution mainly composed of metal phosphate salts such as chromium phosphate, titanium phosphate, zirconium phosphate, and zinc phosphate, or mixtures thereof, or a treatment solution mainly composed of nonmetallic phosphates and mixtures thereof, or a treatment solution consisting of a mixture of these with synthetic resins, etc., is applied to the degreased surface using a well-known coating method such as roll coating, gravure printing, or immersion, and then dried. Various solvents can be used as the treatment solution, such as water, alcohol-based solvents, hydrocarbon-based solvents, ketone-based solvents, ester-based solvents, and ether-based solvents, with water being preferred. Furthermore, examples of resin components used in this process include polymers such as phenolic resins and acrylic resins, and examples of chromate treatment using an amination phenol polymer having repeating units represented by the following general formulas (1) to (4). In this amination phenol polymer, the repeating units represented by the following general formulas (1) to (4) may be included individually or in any combination of two or more types.The acrylic resin is preferably a derivative such as polyacrylic acid, an acrylic acid-methacrylic acid ester copolymer, an acrylic acid-maleic acid copolymer, an acrylic acid-styrene copolymer, or their sodium salts, ammonium salts, amine salts, etc. In particular, derivatives of polyacrylic acid such as ammonium salts, sodium salts, or amine salts of polyacrylic acid are preferred. In the present disclosure, polyacrylic acid means a polymer of acrylic acid. Further, the acrylic resin is also preferably a copolymer of acrylic acid and a dicarboxylic acid or a dicarboxylic anhydride, and is also preferably an ammonium salt, a sodium salt, or an amine salt of a copolymer of acrylic acid and a dicarboxylic acid or a dicarboxylic anhydride. The acrylic resin may be used alone or in combination of two or more kinds.

[0060]

Chemical formula

[0061]

Chemical formula

[0062]

Chemical formula

[0063]

Chemical formula

[0064] ​​​​​​​​​Examples of alkyl groups represented by include linear or branched alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, and tert-butyl groups. Also, X, R 1 and R 2 Examples of hydroxyalkyl groups represented by include linear or branched alkyl groups having 1 to 4 carbon atoms with one hydroxyl group substituted, such as hydroxymethyl group, 1-hydroxyethyl group, 2-hydroxyethyl group, 1-hydroxypropyl group, 2-hydroxypropyl group, 3-hydroxypropyl group, 1-hydroxybutyl group, 2-hydroxybutyl group, 3-hydroxybutyl group, and 4-hydroxybutyl group. In general formulas (1) to (4), X and R 1 and R 2 The alkyl group and hydroxyalkyl group shown may be the same or different. In general formulas (1) to (4), X is preferably a hydrogen atom, a hydroxyl group, or a hydroxyalkyl group. The number-average molecular weight of the amination phenol polymer having repeating units represented by general formulas (1) to (4) is preferably about 500 to 1,000,000, and more preferably about 1,000 to 20,000. The amination phenol polymer is produced, for example, by polycondensing a phenol compound or naphthol compound with formaldehyde to produce a polymer consisting of repeating units represented by the above general formula (1) or general formula (3), and then adding formaldehyde and amine (R 1 R 2 Using NH) the functional group (-CH2NR 1 R 2 It is produced by introducing ) into the polymer obtained above. The amination phenol polymer can be used alone or in a mixture of two or more types.

[0065] Another example of a corrosion-resistant coating is a thin film formed by a coating-type corrosion prevention treatment, which involves applying a coating agent containing at least one selected from the group consisting of rare earth element oxide sols, anionic polymers, and cationic polymers. The coating agent may further contain phosphoric acid or phosphate, and a crosslinking agent for crosslinking the polymer. In the rare earth element oxide sol, fine particles of rare earth element oxides (for example, particles with an average particle size of 100 nm or less) are dispersed in a liquid dispersion medium. Examples of rare earth element oxides include cerium oxide, yttrium oxide, neodymium oxide, and lanthanum oxide, with cerium oxide being preferred from the viewpoint of further improving adhesion. The rare earth element oxides contained in the corrosion-resistant coating can be used individually or in combination of two or more. Various solvents can be used as the liquid dispersion medium for the rare earth element oxide sol, such as water, alcohol-based solvents, hydrocarbon-based solvents, ketone-based solvents, ester-based solvents, and ether-based solvents, with water being preferred. Preferred cationic polymers include, for example, polyethyleneimine, ionic polymer complexes comprising polyethyleneimine and a polymer having a carboxylic acid, primary amine-grafted acrylic resins obtained by graft polymerization of a primary amine onto an acrylic main skeleton, polyallylamine or its derivatives, and amination phenols. Preferred anionic polymers are poly(meth)acrylic acid or its salts, or copolymers mainly composed of (meth)acrylic acid or its salts. Furthermore, the crosslinking agent is preferably at least one selected from the group consisting of a compound having one of the functional groups of isocyanate, glycidyl, carboxyl, or oxazoline, and a silane coupling agent. Additionally, the phosphoric acid or phosphate is preferably condensed phosphoric acid or condensed phosphate.

[0066] An example of a corrosion-resistant coating is one formed by dispersing metal oxides such as aluminum oxide, titanium oxide, cerium oxide, and tin oxide, or fine particles of barium sulfate, in phosphoric acid, applying this mixture to the surface of a barrier layer, and then baking it at a temperature of 150°C or higher.

[0067] The corrosion-resistant coating may, if necessary, be a laminated structure in which at least one of a cationic polymer and an anionic polymer is further laminated. Examples of cationic and anionic polymers include those mentioned above.

[0068] Furthermore, the composition of the corrosion-resistant coating can be analyzed, for example, using time-of-flight secondary ion mass spectrometry.

[0069] The amount of corrosion-resistant film to be formed on the surface of the barrier layer 3 in the chemical conversion treatment is not particularly limited, but for example, in the case of coating-type chromate treatment, the surface of the barrier layer 3 is 1 m 2 It is desirable that the product contains, for example, about 0.5 to 50 mg of chromium-based chromium, preferably about 1.0 to 40 mg of phosphorus-based chromium

[0070] The thickness of the corrosion-resistant coating is not particularly limited, but from the viewpoint of the cohesive force of the coating and the adhesion force with the barrier layer and the heat-fusible resin layer, it is preferably about 1 nm to 20 μm, more preferably about 1 nm to 100 nm, and even more preferably about 1 nm to 50 nm. The thickness of the corrosion-resistant coating can be measured by observation with a transmission electron microscope, or by a combination of observation with a transmission electron microscope and energy-dispersive X-ray spectroscopy or electron beam energy loss spectroscopy. By analyzing the composition of the corrosion-resistant coating using time-of-flight secondary ion mass spectrometry, for example, secondary ions consisting of Ce, P, and O (e.g., Ce2PO4) can be identified. + CePO4 - (at least one of the above), or, for example, a secondary ion consisting of Cr, P, and O (e.g., CrPO2) + , CrPO4 - Peaks originating from at least one of the following are detected.

[0071] The chemical conversion treatment is carried out by applying a solution containing compounds used to form a corrosion-resistant film to the surface of the barrier layer using methods such as bar coating, roll coating, gravure coating, or immersion, and then heating the barrier layer to a temperature of approximately 70-200°C. Alternatively, before applying the chemical conversion treatment to the barrier layer, it may be subjected to a degreasing treatment using methods such as alkaline immersion, electrolytic cleaning, acid cleaning, or electrolytic acid cleaning. This degreasing treatment makes it possible to perform the chemical conversion treatment on the surface of the barrier layer more efficiently. Furthermore, by using an acid degreasing agent, which is a fluorine-containing compound dissolved in an inorganic acid, it is possible to not only degrease the metal foil but also form a fluoride of the passive metal; in such cases, only the degreasing treatment may be performed.

[0072] [Thermal adhesive resin layer 4] In the exterior material for energy storage devices of this disclosure, the heat-sealable resin layer 4 is the innermost layer and is a layer (sealant layer) that performs the function of sealing the energy storage device elements by heat-sealing the heat-sealable resin layers together during the assembly of the energy storage device.

[0073] The heat-fusible resin layer 4 contains polypropylene and polyethylene. In the exterior material for energy storage devices of this disclosure, a sea-island structure is observed in the cross-sectional image obtained using a scanning electron microscope of the cross-section of the heat-fusible resin layer 4 in a direction parallel to TD and in the thickness direction y. The cross-sectional image is obtained within the range from the surface of the heat-fusible resin layer 4 opposite to the barrier layer 3 to a thickness of 12.5% ​​(the area enclosed by the dashed line in Figure 3), assuming that the total thickness of the layers located inside the barrier layer 3 is 100%. The surface of the heat-fusible resin layer 4 opposite to the barrier layer 3 has a thickness of 0%. To explain with a specific example, as in Examples 1 and 2 described later, if the exterior material for an energy storage device is constructed by laminating a base layer (30 μm thick including the adhesive) / adhesive layer (3 μm) / barrier layer (40 μm) / adhesive layer (40 μm) / heat-fusible resin layer (40 μm) in that order, then the layers located inside the barrier layer 3 are the adhesive layer (40 μm) and the heat-fusible resin layer (40 μm), and their combined thickness of 80 μm is considered 100%. Furthermore, the position of the heat-fusible resin layer 4 on the surface opposite to the barrier layer 3 is the inner surface (inner surface) of the exterior material for the energy storage device 10, and the thickness at this position is considered 0%. Then, a cross-sectional image is acquired using a scanning electron microscope within the range from the surface (0% thickness) to the position where the thickness is 12.5% ​​(i.e., with a total thickness of 80 μm as 100%, the position where the thickness is 10 μm from the surface of the heat-fusible resin layer 4 opposite to the barrier layer 3 side toward the barrier layer 3 side).

[0074] The observation of a sea-island structure in a cross-sectional image means that the cross-sectional image shows both a sea portion and an island portion. As mentioned above, when a small amount of polyethylene is added to polypropylene and a heat-fusible resin layer is formed by melt extrusion molding, a sea-island structure is formed in which polyethylene islands are dispersed within the polypropylene sea portion. To observe this sea-island structure, as described below, the cross-section of the heat-fusible resin layer is stained with ruthenium tetroxide or the like, and a cross-sectional image is acquired and observed using a scanning electron microscope.

[0075] In the exterior material for energy storage devices of this disclosure, in the cross-sectional image of the heat-fusible resin layer 4, the area of ​​the island portion is 0.02 μm relative to the total number of island portions of the sea-island structure. 2 The proportion of the total number of the following island areas is 80.0% or more. The exterior material for energy storage devices of the present invention has these characteristics, thereby suppressing whitening of the heat-fusible resin layer due to cold forming of the exterior material for energy storage devices and a decrease in the insulation properties of the exterior material for energy storage devices. In other words, in the exterior material for energy storage devices of the present disclosure, in the heat-fusible resin layer 4 containing polypropylene and polyethylene, of all island areas, the area is 0.02 μm 2 By setting a high proportion of the extremely fine island-like areas, the occurrence of fine cracks at the interface between the polypropylene and polyethylene portions of the heat-fusible resin layer is effectively suppressed. As a result, it is believed that whitening of the heat-fusible resin layer 4 due to cold forming of the exterior material for energy storage devices and a decrease in the insulation properties of the exterior material for energy storage devices are suppressed.

[0076] In the cross-sectional image of the heat-fusible resin layer 4, the area of ​​the island portion is 0.02 μm relative to the total number of island portions in the sea-island structure. 2 The percentage of the total number of island areas (0.02 μm) 2 The ratio of the total number of islands (total number of islands / total number of all islands) should be 80.0% or more, but from the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulation performance, it is preferably 90.0% or more, more preferably 95.0% or more. The ratio of the total number can be, for example, 100.0% or less, 99.0% or less, or 98.0% or less. A preferred range for the ratio of the total number can be, for example, around 80.0-100.0%, 80.0-99.0%, 80.0-98.0%, 90.0-100.0%, 90.0-99.0%, 90.0-98.0%, 95.0-100.0%, 95.0-99.0%, or 95.0-98.0%.

[0077] Furthermore, from the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulating properties, in the cross-sectional image of the heat-fusible resin layer 4, the area of ​​the island portion of the sea-island structure is 0.01 μm² relative to the total number of island portions.2 The percentage of the total number of island areas (0.01 μm) 2 The ratio of the total number of islands (total number of islands) is preferably 50.0% or more, more preferably 55.0% or more, and even more preferably 60.0% or more. The percentage of the total number is, for example, 80.0% or less, 75.0% or less, 70.0% or less, etc. A preferred range for the percentage of the total number is, for example, around 50.0-80.0%, around 50.0-75.0%, around 50.0-70.0%, around 55.0-80.0%, around 55.0-75.0%, around 55.0-70.0%, around 60.0-80.0%, around 60.0-75.0%, and around 60.0-70.0%.

[0078] Furthermore, from the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulating properties, in the cross-sectional image of the heat-fusible resin layer 4, the area of ​​the island portion of the island portion relative to the total number of island portions of the sea-island structure is 0.03 μm². 2 The percentage of the total number of the following island areas (0.03 μm) 2 The ratio of the total number of islands (total number of islands / total number of all islands) is preferably 90.0% or more, more preferably 95.0% or more, and even more preferably 97.0% or more. The percentage of the total number is, for example, 100.0% or less, 99.0% or less, 98.0% or less, etc. A preferred range for the percentage of the total number is, for example, around 90.0-100.0%, around 90.0-99.0%, around 90.0-98.0%, around 95.0-100.0%, around 95.0-99.0%, around 95.0-98.0%, around 97.0-100.0%, around 97.0-99.0%, and around 97.0-98.0%.

[0079] Furthermore, from the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulating properties, in the cross-sectional image of the heat-fusible resin layer 4, the area of ​​the island portion of the island portion relative to the total number of island portions of the sea-island structure is 0.30 μm². 2 The percentage of the total number of the above island areas (0.30 μm 2The ratio of the above-mentioned island units (total number of island units / total number of all island units) is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less. The percentage of this total number is, for example, 0.0% or more.

[0080] Furthermore, from the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulating properties, in the cross-sectional image of the heat-fusible resin layer 4, the area of ​​the island portion of the island portion relative to the total number of island portions of the sea-island structure is 0.15 μm². 2 The percentage of the total number of the above island areas (0.15 μm) 2 The ratio of the above-mentioned island units (total number of island units / total number of all island units) is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less. The percentage of this total number is, for example, 0.0% or more.

[0081] Furthermore, from the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulating properties, in the cross-sectional image of the heat-fusible resin layer 4, the ratio of the total area of ​​the island portion of the sea-island structure to the area of ​​the measurement range of the cross-sectional image (total area of ​​the island portion / area of ​​the measurement range of the cross-sectional image) is preferably 12.0% or less, more preferably 5.0% or less, and even more preferably 1.0% or less. Examples of the ratio of the total area include 0.1% or more. Examples of a preferred range for the ratio of the total area include approximately 0.1 to 12.0%, approximately 0.1 to 5.0%, and approximately 0.1 to 1.0%.

[0082] The ratio of the total area of ​​the island portions of each area can be determined by adjusting the conditions for forming the heat-fusible resin layer 4, in addition to the blending ratio of polypropylene and polyethylene contained in the heat-fusible resin layer 4 (for example, if the heat-fusible resin layer 4 is formed by melt extrusion molding as described later, the cooling conditions of the heat-fusible resin layer by the cooling roll should be set to rapid cooling conditions (for example, setting the difference in surface temperature between the melt-extruded heat-fusible resin layer and the cooling roll to 70°C or higher) to suppress the crystal growth of polyethylene in the polypropylene).

[0083] The method for measuring the proportion of the island area in a sea-island structure from a cross-sectional image of the heat-fusible resin layer 4 is as follows:

[0084] <Measurement of the ratio of island area and number of islands in a sea-island structure> The exterior material for the energy storage device is embedded in a thermosetting epoxy resin and cured. A cross-section parallel to the TD and in the thickness direction y is prepared using a commercially available rotary microtome (e.g., LEICA EM UC6) and a glass knife, and the cross-section is prepared at room temperature using the microtome. The thermosealable resin layer of the energy storage device exterior material, along with the embedding resin, is stained with ruthenium tetroxide for 3 hours. After staining, the resin expands, making it impossible to observe the sea-island structure near the cross-section, so the expanded portion is trimmed with the microtome. Then, a stained section about 100 nm thick is taken from the cross-section after cutting about 1 μm to 2 μm using a diamond knife and observed as follows. Cross-sectional images of the stained section are obtained using a field emission scanning electron microscope (e.g., Hitachi High-Technologies Corporation S-4800). As mentioned above, the cross-sectional image was obtained within a range from the surface opposite the barrier layer of the heat-fusible resin layer to a point with a thickness of 12.5% ​​when the total thickness of the layers located inside the barrier layer is taken as 100%. If a field emission scanning electron microscope, such as the Hitachi High-Technologies S-4800, is used, the measurement conditions are as follows: acceleration voltage: 30kV, emission current: 10μA, detector: transmission detector, tilt: none (0°), and observation magnification: 5000x. Next, using image processing software capable of binarizing cross-sectional images (for example, the image analysis software included with the Keyence VHX-5000 electron microscope), the island portion and the sea portion of the sea-island structure were binarized in the cross-sectional image. If using image processing software, for example, the image analysis software included with the Keyence VHX-5000 electron microscope, the measurement would start under the brightness (standard) setting of the image analysis software, with the extraction area (measurement range) set to rectangular (7 μm vertically, 13 μm horizontally), the imaging size to standard (1600 × 1200), the tilt angle to 0 degrees, the shooting mode to normal shooting, and the extraction target to "dark areas". Automatic measurement would then correct for any missing or extra areas, and the total area and number of extracted areas (islands) would be measured. At this time, the area and number of all islands present in the extraction area would be measured, respectively.Using the acquired data, the ratio of the total area of ​​all islands to the area of ​​the measurement range of the cross-sectional image (total area of ​​islands / area of ​​the measurement range of the cross-sectional image), and the area of ​​each island being 0.01 μm are calculated. 2 The percentage of the total number of island areas (0.01 μm) 2 (Total number of islands / Total number of all islands), 0.02 μm 2 The percentage of the total number of island areas (0.02 μm) 2 (Total number of islands / Total number of all islands), 0.03 μm 2 The percentage of the total number of the following island areas (0.03 μm) 2 (Total number of islands / Total number of all islands), 0.30 μm 2 The percentage of the total number of the above island areas (0.30 μm 2 (Total number of islands / Total number of all islands), 0.15 μm 2 The percentage of the total number of the above island areas (0.15 μm) 2 Calculate the total number of islands (as shown above) / the total number of all islands.

[0085] Examples of propylene include homopolypropylene, polypropylene block copolymers (e.g., propylene-ethylene block copolymer, propylene-butene block copolymer, propylene-ethylene-butene block copolymer, preferably propylene-ethylene block copolymer), polypropylene random copolymer (e.g., propylene-ethylene random copolymer, propylene-butene random copolymer, propylene-ethylene-butene random copolymer, preferably propylene-ethylene random copolymer), and propylene-α-olefin copolymer. Examples of ethylene include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ethylene-α-olefin copolymer. The polypropylene and polyethylene contained in the heat-fusible resin layer 4 may be one type or two or more types.

[0086] The heat-fusible resin layer 4 is preferably formed from a polypropylene resin composition containing 45% by mass or less of polyethylene. The polyethylene content in the heat-fusible resin layer 4 is such that, in the cross-sectional image, the area of ​​the island portion of the island is 0.02 μm² relative to the total number of island portions of the sea-island structure. 2 The proportion of the total number of island parts is adjusted to be 80.0% or more. The polyethylene content is, for example, about 45% by mass or less, preferably about 30% by mass or less, more preferably about 20% by mass or less, and also preferably about 5% by mass or more, more preferably about 10% by mass or more. Preferred ranges include about 5-45% by mass, about 5-30% by mass, about 5-20% by mass, about 10-45% by mass, about 10-30% by mass, and about 10-20% by mass. The polypropylene content is, for example, 95% by mass or less, and 90% by mass or less. The polypropylene content is, for example, 55% by mass or more, 70% by mass or more, and 80% by mass or more. Preferred ranges for the polypropylene content include about 55-95% by mass, about 70-95% by mass, about 80-95% by mass, about 55-90% by mass, about 70-90% by mass, and about 80-90% by mass. Furthermore, the mass ratio of polypropylene to polyethylene in the polypropylene resin composition is preferably about 5 to 80 parts by mass, more preferably about 5 to 45 parts by mass, and even more preferably about 10 to 30 parts by mass of polyethylene per 100 parts by mass of polypropylene.

[0087] The heat-sealable resin layer 4 may contain other resins in addition to polypropylene and polyethylene. Examples of other resins include acid-modified polyolefins.

[0088] Acid-modified polyolefins are polymers that have been modified by block polymerization or graft polymerization of polyolefins with an acid component.

[0089] Examples of polyolefins that can be acid-modified include polyethylene such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; ethylene-α-olefin copolymers; polypropylene such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymer of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymer 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 individually or in combination of two or more.

[0090] Furthermore, acid-modified polyolefins can also be copolymers obtained by copolymerizing the aforementioned polyolefin with polar molecules such as acrylic acid or methacrylic acid, or polymers such as crosslinked polyolefins. Examples of acid components used for acid modification include carboxylic acids or their anhydrides, such as maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride.

[0091] Acid-modified polyolefins may also be acid-modified cyclic polyolefins. Acid-modified cyclic polyolefins are polymers obtained by copolymerizing a portion of the monomers constituting a cyclic polyolefin with an acid component, or by block polymerization or graft polymerization of an acid component to a cyclic polyolefin. The cyclic polyolefin to be acid-modified is the same as described above. Furthermore, the acid component used for acid modification is the same as the acid component used for modifying the polyolefin described above.

[0092] Preferred acid-modified polyolefins include polyolefins modified with carboxylic acids or their anhydrides, polypropylenes modified with carboxylic acids or their anhydrides, maleic anhydride-modified polyolefins, and maleic anhydride-modified polypropylenes.

[0093] The heat-sealable resin layer 4 may be formed as a single layer, or it may be formed as two or more layers of the same or different resins.

[0094] Furthermore, the heat-fusible resin layer 4 may contain a lubricant or the like as needed. When the heat-fusible resin layer 4 contains a lubricant, the moldability of the exterior material for the energy storage device can be improved. The lubricant is not particularly limited, and known lubricants can be used. The lubricant may be used alone or in combination of two or more types.

[0095] The lubricant is not particularly limited, but amide-based lubricants are preferred. Specific examples of lubricants include those exemplified in base layer 1. The lubricant may be used alone or in combination of two or more types.

[0096] When a lubricant is present on the surface of the heat-fusible resin layer 4, the amount present is not particularly limited, but from the viewpoint of improving the moldability of the exterior material for energy storage devices, it is preferably 10 to 50 mg / m². 2 To a certain extent, more preferably 15-40 mg / m² 2 The degree can be described as follows.

[0097] The lubricant present on the surface of the heat-fusible resin layer 4 may be a lubricant contained in the resin constituting the heat-fusible resin layer 4 that has seeped out, or a lubricant may be applied to the surface of the heat-fusible resin layer 4.

[0098] Furthermore, the thickness of the heat-fusible resin layer 4 is not particularly limited as long as the heat-fusible resin layers heat-fuse together to seal the energy storage device elements, but for example, it can be about 100 μm or less, preferably about 85 μm or less, and more preferably about 15 to 85 μm. For example, if the thickness of the adhesive layer 5 described later is 10 μm or more, the thickness of the heat-fusible resin layer 4 can be preferably about 85 μm or less, and more preferably about 15 to 45 μm. For example, if the thickness of the adhesive layer 5 described later is less than 10 μm or if the adhesive layer 5 is not provided, the thickness of the heat-fusible resin layer 4 can be preferably about 20 μm or more, and more preferably about 35 to 85 μm.

[0099] The heat-fusible resin layer 4 is preferably formed by melt extrusion molding. Furthermore, if there is an adhesive layer 5 described later, it is preferable that the adhesive layer 5 and the heat-fusible resin layer 4 are formed by melt co-extrusion molding. In this disclosure, it is preferable to suppress the crystal growth of polyethylene in polypropylene by using rapid cooling conditions for the cooling of the molten resin forming the heat-fusible resin layer 4, thereby reducing the area of ​​the islands in the cross-sectional image to 0.02 μm² relative to the total number of islands in the sea-island structure. 2 The proportion of the total number of island portions described below can be adjusted to be 80.0% or more. For example, as described above, while appropriately adjusting the mixing ratio of polypropylene and polyethylene contained in the heat-fusible resin layer 4, when forming the heat-fusible resin layer 4 by melt extrusion molding, the cooling conditions of the molten resin (molten resin forming the heat-fusible resin layer) by the cooling roll (a roll that cools the sheet formed from the molten resin while transporting it) can be set to rapid cooling conditions (for example, setting the difference in surface temperature between the melt-extruded heat-fusible resin layer and the cooling roll to 70°C or more) to suppress the crystal growth of polyethylene in polypropylene. As a result, in the cross-sectional image described above, the proportion of the island portions with an area of ​​0.02 μm² relative to the total number of island portions in the sea-island structure can be adjusted. 2 The proportion of the total number of the following island areas can be adjusted to be 80.0% or more. When the adhesive layer 5 and the heat-fusible resin layer 4 are formed by melt co-extrusion molding, it is preferable that the thickness of the adhesive layer 5 be 15 to 45 μm and the thickness of the heat-fusible resin layer 4 be 15 to 45 μm.

[0100] [Adhesive layer 5] In the exterior material for energy storage devices of this disclosure, the adhesive layer 5 is a layer provided as necessary between the barrier layer 3 (or acid-resistant film) and the heat-fusible resin layer 4 in order to firmly bond them together.

[0101] The adhesive layer 5 is formed of a resin capable of bonding the barrier layer 3 and the heat-fusible resin layer 4. The resin used to form the adhesive layer 5 can be the same as the adhesive exemplified in the adhesive layer 2. Preferably, the resin used to form the adhesive layer 5 contains a polyolefin skeleton, such as the polyolefin and acid-modified polyolefin exemplified in the heat-fusible resin layer 4. The presence of a polyolefin skeleton in the resin constituting the adhesive layer 5 can be analyzed by methods such as infrared spectroscopy and gas chromatography-mass spectrometry, and the analytical method is not particularly limited. Furthermore, when the resin constituting the adhesive layer 5 is analyzed by infrared spectroscopy, it is preferable to detect a peak originating from maleic anhydride. For example, when maleic anhydride-modified polyolefin is measured by infrared spectroscopy, a peak originating from maleic anhydride is detected at wavenumber 1760 cm⁻¹. -1 Nearby wave frequency 1780cm -1 A peak originating from maleic anhydride is detected in the vicinity. However, if the degree of acid denaturation is low, the peak may become small and not be detected. In that case, analysis is possible by nuclear magnetic resonance spectroscopy.

[0102] From the viewpoint of firmly bonding the barrier layer 3 and the heat-fusible resin layer 4, the adhesive layer 5 preferably contains an acid-modified polyolefin. Particularly preferred as the acid-modified polyolefin are polyolefins modified with a carboxylic acid or its anhydride, polypropylenes modified with a carboxylic acid or its anhydride, maleic anhydride-modified polyolefins, and maleic anhydride-modified polypropylenes.

[0103] Furthermore, from the viewpoint of reducing the thickness of the exterior material for energy storage devices while providing excellent shape stability after molding, it is more preferable that the adhesive layer 5 is a cured product of a resin composition containing an acid-modified polyolefin and a curing agent. Examples of acid-modified polyolefins include those mentioned above.

[0104] Furthermore, the adhesive layer 5 is preferably a cured product of a resin composition comprising an acid-modified polyolefin and at least one selected from the group consisting of compounds having isocyanate groups, compounds having oxazoline groups, and compounds having epoxy groups, and is particularly preferably a cured product of a resin composition comprising an acid-modified polyolefin and at least one selected from the group consisting of compounds having isocyanate groups and compounds having epoxy groups. Furthermore, the adhesive layer 5 preferably contains at least one selected from the group consisting of polyurethane, polyester, and epoxy resin, and more preferably contains polyurethane and epoxy resin. As polyester, for example, amide ester resin is preferred. Amide ester resin is generally produced by the reaction of a carboxyl group and an oxazoline group. The adhesive layer 5 is more preferably a cured product of a resin composition comprising at least one of these resins and the acid-modified polyolefin. Furthermore, if unreacted compounds containing isocyanate groups, compounds containing oxazoline groups, or curing agents such as epoxy resin remain in the adhesive layer 5, the presence of these unreacted compounds can be confirmed by methods selected from, for example, infrared spectroscopy, Raman spectroscopy, or time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0105] Furthermore, from the viewpoint of further improving the adhesion between the barrier layer 3 and the adhesive layer 5, it is preferable that the adhesive layer 5 is a cured product of a resin composition containing a curing agent having at least one selected from the group consisting of oxygen atoms, heterocyclic rings, C=N bonds, and COC bonds. Examples of curing agents having heterocyclic rings include curing agents having oxazoline groups and curing agents having epoxy groups. Examples of curing agents having C=N bonds include curing agents having oxazoline groups and curing agents having isocyanate groups. Examples of curing agents having COC bonds include curing agents having oxazoline groups, curing agents having epoxy groups, and polyurethane. The fact that the adhesive layer 5 is a cured product of a resin composition containing these curing agents can be confirmed by methods such as gas chromatography-mass spectrometry (GCMS), infrared spectroscopy (IR), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and X-ray photoelectron spectroscopy (XPS).

[0106] While there are no particular limitations on the compound having an isocyanate group, polyfunctional isocyanate compounds are preferred from the viewpoint of effectively improving the adhesion between the barrier layer 3 and the adhesive layer 5. The polyfunctional isocyanate compound is not particularly limited as long as it is a compound having two or more isocyanate groups. Specific examples of polyfunctional isocyanate curing agents include pentane diisocyanate (PDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), polymerized or nurated versions thereof, mixtures thereof, and copolymers with other polymers. Adducts, burettes, and isocyanurates are also examples.

[0107] The content of the compound having an isocyanate group in the adhesive layer 5 is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, of the resin composition constituting the adhesive layer 5. This effectively enhances the adhesion between the barrier layer 3 and the adhesive layer 5.

[0108] Compounds containing an oxazoline group are not particularly limited as long as they have an oxazoline skeleton. Specific examples of compounds containing an oxazoline group include those with a polystyrene main chain and those with an acrylic main chain. Commercially available examples include the Epocross series manufactured by Nippon Shokubai Co., Ltd.

[0109] The proportion of the compound having an oxazoline group in the adhesive layer 5 is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, of the resin composition constituting the adhesive layer 5. This effectively enhances the adhesion between the barrier layer 3 and the adhesive layer 5.

[0110] Examples of compounds having epoxy groups include epoxy resins. The epoxy resin is not particularly limited as long as it is capable of forming a crosslinked structure by the epoxy groups present in the molecule; known epoxy resins can be used. The weight-average molecular weight of the epoxy resin is preferably around 50 to 2000, more preferably around 100 to 1000, and even more preferably around 200 to 800. In the first disclosure, the weight-average molecular weight of the epoxy resin is the value measured by gel permeation chromatography (GPC) under conditions using polystyrene as a standard sample.

[0111] Specific examples of epoxy resins include glycidyl ether derivatives of trimethylolpropane, bisphenol A diglycidyl ether, modified bisphenol A diglycidyl ether, novolac glycidyl ether, glycerin polyglycidyl ether, and polyglycerin polyglycidyl ether. Epoxy resins may be used individually or in combination of two or more types.

[0112] The proportion of epoxy resin in the adhesive layer 5 is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, of the resin composition constituting the adhesive layer 5. This effectively enhances the adhesion between the barrier layer 3 and the adhesive layer 5.

[0113] The polyurethane is not particularly limited, and any known polyurethane can be used. The adhesive layer 5 may be, for example, a cured product of a two-component polyurethane.

[0114] The proportion of polyurethane in the adhesive layer 5 is preferably in the range of 0.1 to 50% by mass, and more preferably in the range of 0.5 to 40% by mass, of the resin composition constituting the adhesive layer 5. This effectively enhances the adhesion between the barrier layer 3 and the adhesive layer 5 in an atmosphere where components that induce corrosion of the barrier layer, such as electrolytes, are present.

[0115] Furthermore, if the adhesive layer 5 is a cured product of a resin composition containing at least one compound selected from the group consisting of compounds having isocyanate groups, compounds having oxazoline groups, and epoxy resins, and the acid-modified polyolefin, the acid-modified polyolefin functions as the main agent, and the compounds having isocyanate groups, compounds having oxazoline groups, and compounds having epoxy groups each function as curing agents.

[0116] The thickness of the adhesive layer 5 is preferably about 50 μm or less, about 45 μm or less, about 30 μm or less, about 20 μm or less, or about 5 μm or less. Alternatively, the thickness of the adhesive layer 5 is preferably about 0.1 μm or more, about 0.5 μm or more, about 5 μm or more, about 10 μm or more, or about 15 μm or more. Preferably, the thickness range includes approximately 0.1 to 50 μm, 0.1 to 45 μm, 0.1 to 30 μm, 0.1 to 20 μm, 0.1 to 5 μm, 0.5 to 50 μm, 0.5 to 45 μm, 0.5 to 30 μm, 0.5 to 20 μm, 0.5 to 5 μm, 5 to 50 μm, 5 to 45 μm, 5 to 30 μm, 5 to 20 μm, 10 to 50 μm, 10 to 45 μm, 10 to 30 μm, 10 to 20 μm, 15 to 50 μm, 15 to 45 μm, 15 to 30 μm, and 15 to 20 μm.

[0117] More specifically, in the case of adhesives exemplified in adhesive layer 2, or cured products of acid-modified polyolefin and a curing agent, the thickness is preferably about 1 to 10 μm, more preferably about 1 to 5 μm. In particular, when using resins exemplified in heat-fusible resin layer 4 (such as acid-modified polyolefin), the thickness is preferably about 5 to 50 μm, 5 to 45 μm, 10 to 50 μm, 10 to 45 μm, 15 to 50 μm, or 15 to 45 μm. When adhesive layer 5 is an adhesive exemplified in adhesive layer 2, or a cured product of a resin composition containing acid-modified polyolefin and a curing agent, for example, adhesive layer 5 can be formed by applying the resin composition and curing it by heating or the like. When using resins exemplified in heat-fusible resin layer 4, for example, it can be suitably formed by melt co-extrusion molding of heat-fusible resin layer 4 and adhesive layer 5.

[0118] [Surface coating layer 6] The exterior material for energy storage devices of this disclosure may optionally include a surface coating layer 6 on the base layer 1 (on the side opposite to the barrier layer 3 of the base layer 1) for the purpose of improving at least one of the following: aesthetics, electrolyte resistance, scratch resistance, and moldability. The surface coating layer 6 is the outermost layer of the exterior material for energy storage devices when the energy storage device is assembled using the exterior material for energy storage devices.

[0119] The surface coating layer 6 can be formed from a resin such as polyvinylidene chloride, polyester, polyurethane, acrylic resin, or epoxy resin.

[0120] If the resin forming the surface coating layer 6 is a curable resin, it may be either a one-component curable resin or a two-component curable resin, but is preferably a two-component curable resin. Examples of two-component curable resins include two-component curable polyurethane, two-component curable polyester, and two-component curable epoxy resin. Among these, two-component curable polyurethane is preferred.

[0121] Examples of two-component curable polyurethanes include polyurethanes comprising a main component containing a polyol compound and a curing agent containing an isocyanate compound. Preferably, two-component curable polyurethanes are used with a polyol such as polyester polyol, polyether polyol, and acrylic polyol as the main component and an aromatic or aliphatic polyisocyanate as the curing agent. Furthermore, it is preferable to use a polyester polyol as the polyol compound, which has hydroxyl groups not only at the terminals of the repeating units but also in the side chains. The surface coating layer 6 being formed of polyurethane provides excellent electrolyte resistance to the exterior material for energy storage devices.

[0122] The surface coating layer 6 may contain, as necessary, additives such as the aforementioned lubricants, antiblocking agents, matting agents, flame retardants, antioxidants, tackifiers, and antistatic agents in at least one of its surface and interior, depending on the functionality to be provided to the surface coating layer 6 and its surface. Examples of additives include fine particles with an average particle size of about 0.5 nm to 5 μm. The average particle size of the additive is the median diameter measured by a laser diffraction / scattering particle size distribution analyzer.

[0123] The additive may be either inorganic or organic. Furthermore, there are no particular restrictions on the shape of the additive; examples include spherical, fibrous, plate-like, amorphous, or flaky forms.

[0124] Specific examples of additives include talc, silica, graphite, kaolin, montmorillonite, mica, hydrotalcite, silica gel, zeolite, aluminum hydroxide, magnesium hydroxide, zinc oxide, magnesium oxide, aluminum oxide, neodymium oxide, antimony oxide, titanium oxide, cerium oxide, calcium sulfate, barium sulfate, calcium carbonate, calcium silicate, lithium carbonate, calcium benzoate, calcium oxalate, magnesium stearate, alumina, carbon black, carbon nanotubes, high-melting-point nylon, acrylate resin, cross-linked acrylic, cross-linked styrene, cross-linked polyethylene, benzoguanamine, gold, aluminum, copper, and nickel. Additives may be used individually or in combination of two or more. Among these additives, silica, barium sulfate, and titanium oxide are preferred from the viewpoint of dispersion stability and cost. In addition, various surface treatments such as insulation treatment and high-dispersibility treatment may be applied to the surface of the additives.

[0125] The method for forming the surface coating layer 6 is not particularly limited, and for example, a method of applying a resin to form the surface coating layer 6 can be used. If an additive is to be incorporated into the surface coating layer 6, the resin mixed with the additive can be applied.

[0126] The thickness of the surface coating layer 6 is not particularly limited as long as it performs the above-mentioned functions as a surface coating layer 6, and for example, it can be about 0.5 to 10 μm, preferably about 1 to 5 μm.

[0127] 3. Method for manufacturing exterior materials for energy storage devices The method for manufacturing the exterior material for energy storage devices is not particularly limited as long as a laminate is obtained by laminating each layer of the exterior material for energy storage devices of the present invention, and includes a step of laminating the base layer 1, barrier layer 3, and heat-fusible resin layer 4 in this order from the outside to the inside. Specifically, the method includes a step of obtaining a laminate by laminating the base layer, barrier layer, and heat-fusible resin layer in this order, wherein the heat-fusible resin layer contains polypropylene and polyethylene, and a sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope of the cross-section of the heat-fusible resin layer in a direction parallel to TD and in the thickness direction y, and in the cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm² relative to the total number of island portions of the sea-island structure. 2 A method for manufacturing exterior material for energy storage devices, wherein the proportion of the total number of the following island-shaped sections is 80.0% or more.

[0128] An example of a method for manufacturing the exterior material for energy storage devices of the present invention is as follows. First, a laminate (hereinafter sometimes referred to as "laminated body A") is formed by sequentially laminating a base material layer 1, an adhesive layer 2, and a barrier layer 3. Specifically, laminate A can be formed by a dry lamination method in which the adhesive used to form the adhesive layer 2 is applied to the base material layer 1 or, if necessary, to the barrier layer 3 whose surface has been chemically treated, using a coating method such as gravure coating or roll coating, and after drying, the barrier layer 3 or base material layer 1 is laminated and the adhesive layer 2 is cured.

[0129] Next, a heat-fusible resin layer 4 is laminated onto the barrier layer 3 of laminate A. When the heat-fusible resin layer 4 is directly laminated onto the barrier layer 3, the heat-fusible resin layer 4 can be laminated onto the barrier layer 3 of laminate A by methods such as thermal lamination or extrusion lamination. When an adhesive layer 5 is provided between the barrier layer 3 and the heat-fusible resin layer 4, for example, (1) a method of laminating the adhesive layer 5 and the heat-fusible resin layer 4 by extrusion onto the barrier layer 3 of laminate A (co-extrusion lamination method, tandem lamination method), (2) a method of forming a laminate in which the adhesive layer 5 and the heat-fusible resin layer 4 are laminated separately, and then laminating this onto the barrier layer 3 of laminate A by thermal lamination, or a method of forming a laminate in which the adhesive layer 5 is laminated onto the barrier layer 3 of laminate A, and then laminating this with the heat-fusible resin layer 4 by thermal lamination. (3) A method of lamination by pouring a molten adhesive layer 5 between the barrier layer 3 of the laminate A and the heat-fusible resin layer 4 which has been previously formed into a sheet, thereby bonding the laminate A and the heat-fusible resin layer 4 via the adhesive layer 5 (sandwich lamination method); (4) A method of lamination by applying an adhesive solution to the barrier layer 3 of the laminate A to form the adhesive layer 5, drying it, or even baking it, and then laminating the heat-fusible resin layer 4 which has been previously formed into a sheet, onto this adhesive layer 5.

[0130] When a surface coating layer 6 is provided, the surface coating layer 6 is laminated on the surface of the base layer 1 opposite to the barrier layer 3. The surface coating layer 6 can be formed, for example, by applying the resin used to form the surface coating layer 6 to the surface of the base layer 1. The order of the steps of laminating the barrier layer 3 to the surface of the base layer 1 and laminating the surface coating layer 6 to the surface of the base layer 1 is not particularly limited. For example, the surface coating layer 6 may be formed on the surface of the base layer 1, and then the barrier layer 3 may be formed on the surface of the base layer 1 opposite to the surface coating layer 6.

[0131] As described above, a laminate is formed comprising, as necessary, a surface coating layer 6, a base material layer 1, an adhesive layer 2 as necessary, a barrier layer 3, an adhesive layer 5 as necessary, and a heat-fusible resin layer 4 in this order. In order to strengthen the adhesion of the adhesive layer 2 and adhesive layer 5 as necessary, the laminate may be subjected to further heat treatment.

[0132] In exterior materials for energy storage devices, the processability of each layer constituting the laminate may be improved by subjecting it to surface activation treatments such as corona treatment, blast treatment, oxidation treatment, or ozone treatment, as needed. For example, by applying corona treatment to the surface of the substrate layer 1 opposite to the barrier layer 3, the printability of ink on the surface of the substrate layer 1 can be improved.

[0133] 4. Applications of exterior materials for energy storage devices The exterior material for energy storage devices of this disclosure is used in packaging for sealing and housing energy storage device elements such as a positive electrode, a negative electrode, and an electrolyte. That is, an energy storage device can be formed by housing energy storage device elements, which include at least a positive electrode, a negative electrode, and an electrolyte, in packaging formed from the exterior material for energy storage devices of this disclosure.

[0134] Specifically, an energy storage device is provided by covering an energy storage device element, which comprises at least a positive electrode, a negative electrode, and an electrolyte, with the energy storage device exterior material of this disclosure, such that a flange portion (a region where heat-sealable resin layers come into contact) is formed around the periphery of the energy storage device element, with the metal terminals connected to the positive electrode and negative electrode respectively protruding outward, and then heat-sealing the heat-sealable resin layers of the flange portion to seal it. When housing the energy storage device element in a package formed from the energy storage device exterior material of this disclosure, the package is formed such that the heat-sealable resin portion of the energy storage device exterior material of this disclosure faces inward (the surface in contact with the energy storage device element).

[0135] The casing material for energy storage devices disclosed herein can be suitably used in energy storage devices such as batteries (including capacitors, capacitors, etc.). Furthermore, the casing material for energy storage devices disclosed herein can be used in either primary batteries or secondary batteries, but is preferably used in secondary batteries. The type of secondary battery to which the casing material for energy storage devices disclosed herein can be applied is not particularly limited, and examples include lithium-ion batteries, lithium-ion polymer batteries, all-solid-state batteries, lead-acid batteries, nickel-metal hydride batteries, nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, silver oxide-zinc batteries, metal-air batteries, polyvalent cation batteries, capacitors, capacitors, etc. Among these secondary batteries, lithium-ion batteries and lithium-ion polymer batteries are particularly suitable applications for the casing material for energy storage devices disclosed herein. [Examples]

[0136] The present disclosure will be described in detail below with reference to examples and comparative examples. However, the present disclosure is not limited to the examples.

[0137] <Manufacturing of exterior materials for energy storage devices> Examples 1 and 2 and Comparative Examples 1 and 2 Polyethylene terephthalate (PET) film (12 μm thick) and stretched nylon (ONy) film (15 μm thick) were prepared. A two-component urethane adhesive (polyol compound and aromatic isocyanate compound) was applied to the PET film (3 μm thick) and bonded to the ONy film to form the base layer. Aluminum alloy foil (JIS H4160:1994 A8021H-O (40 μm thick)) was prepared as a barrier layer. Next, the two-component urethane adhesive (polyol compound and aromatic isocyanate compound) was applied to one side of the aluminum alloy foil to form an adhesive layer (3 μm thick) on the barrier layer. Subsequently, the adhesive layer on the barrier layer and the base layer (ONy film side) were laminated using a dry lamination method, and then an aging treatment was performed to create a laminate of base layer / adhesive layer / barrier layer. Both sides of the aluminum alloy foil were treated with chemical conversion treatment. The chemical conversion treatment of aluminum alloy foil involves a treatment solution consisting of phenolic resin, chromium fluoride compound, and phosphoric acid, with a chromium coating amount of 10 mg / m². 2 This was achieved by applying the coating to both sides of the aluminum alloy foil using the roll coating method and then baking it to achieve the desired (dry mass).

[0138] Next, maleic anhydride-modified polypropylene as an adhesive layer (40 μm thick) and random polypropylene (a composition of random polypropylene and polyethylene) as a heat-fusible resin layer (40 μm thick) were melt-extruded onto the barrier layer of each laminate obtained above. The heat-fusible resin layer side was then cooled by contacting it with a cooling roll (using cooling conditions A or B described later), thereby laminating the adhesive layer and heat-fusible resin layer on the barrier layer. This resulted in an exterior material for energy storage devices (total thickness 153 μm) in which a base layer (30 μm thick including adhesive) / adhesive layer (3 μm) / barrier layer (40 μm) / adhesive layer (40 μm) / heat-fusible resin layer (40 μm) were laminated in that order. Example 2 had a lower polyethylene content in the heat-fusible resin layer compared to Example 1. Comparative Example 1 had a higher polyethylene content in the heat-fusible resin layer compared to Example 1. Comparative Example 2 used the same composition of the heat-fusible resin layer as in Example 1, and adopted cooling condition B.

[0139] (Cooling conditions) The conditions for cooling the heat-fusible resin layer by bringing it into contact with a cooling roll are as follows. Table 1 shows the cooling conditions used in the examples and comparative examples. Cooling condition A: The temperature difference between the molten resin (the molten resin that forms the heat-fusible resin layer) obtained by molten co-extrusion and the surface temperature of the cooling roll is set to 70°C or more, and the molten resin is rapidly cooled to form the heat-fusible resin layer (conditions that suppress the crystal growth of polyethylene). Cooling condition B: The temperature difference between the molten resin (the molten resin forming the heat-fusible resin layer) obtained by molten co-extrusion and the surface temperature of the cooling roll is set to 50°C or less, allowing the molten resin to be cooled slowly to form the heat-fusible resin layer.

[0140] <Measurement of the ratio of island area and number of islands in a sea-island structure> An outer casing material for an energy storage device was embedded in a thermosetting epoxy resin and cured. A cross-section parallel to the TD and in the thickness direction was prepared using a commercially available rotary microtome (LEICA EM UC6) and a glass knife, with the cross-section preparation performed at room temperature. The thermosealable resin layer of the energy storage device outer casing material, along with the embedding resin, was stained with ruthenium tetroxide for 3 hours. Upon staining, the resin expanded, making it impossible to observe the sea-island structure near the cross-section, so the expanded portion was trimmed with the microtome. Then, a stained section approximately 100 nm thick was taken from the cross-section after cutting by 1 μm to 2 μm using a diamond knife and observed as follows. Cross-sectional images of the stained section were acquired using a field emission scanning electron microscope (Hitachi High-Technologies Corporation S-4800). The cross-sectional image was obtained within a range from the surface opposite the barrier layer to a point 12.5% ​​thick, assuming the total thickness of the layers located inside the barrier layer is 100%. The measurement conditions were: acceleration voltage: 30kV, emission current: 10μA, detector: transmission detector, tilt: none (0°), and observation magnification: 5000x. Next, using image processing software capable of binarizing cross-sectional images (image analysis software included with the Keyence VHX-5000 electron microscope), the island and sea portions of the sea-island structure were binarized in the cross-sectional image. Specifically, measurement was started with the brightness (standard) setting of the image analysis software, the extraction area (measurement range) was set to rectangular (7μm vertical, 13μm horizontal), the imaging size to standard (1600×1200), the tilt angle to 0 degrees, the shooting mode to normal shooting, and the extraction target to "dark areas". Furthermore, automatic measurement was used to correct for any missing or extra extracted areas, and the total area and number of extracted areas (islands) were measured. At this time, the area and number of all islands present in the extracted region were measured, respectively. Using the acquired data, the ratio of the total area of ​​all islands to the area of ​​the measurement range of the cross-sectional image (total area of ​​islands / area of ​​the measurement range of the cross-sectional image), and the area of ​​all islands, were calculated to be 0.01 μm. 2 The percentage of the total number of island areas (0.01 μm) 2 (Total number of islands / Total number of all islands), 0.02 μm 2 The percentage of the total number of island areas (0.02 μm)2 (Total number of islands / Total number of all islands), 0.03 μm 2 The percentage of the total number of the following island areas (0.03 μm) 2 (Total number of islands / Total number of all islands), 0.30 μm 2 The percentage of the total number of the above island areas (0.30 μm 2 (Total number of islands / Total number of all islands), 0.15 μm 2 The percentage of the total number of the above island areas (0.15 μm) 2 The total number of islands (as shown above / total number of all islands) was calculated. The results are shown in Table 1.

[0141] <Whitening due to molding> Each exterior material for the energy storage device was cut into a rectangle with a length (MD: Machine Direction) of 90 mm and a width (TD) of 150 mm to serve as a test sample. The MD of the exterior material for the energy storage device corresponds to the rolling direction (RD) of the aluminum alloy foil, and the TD of the exterior material for the energy storage device corresponds to the TD of the aluminum alloy foil. This test sample was subjected to the following conditions at 25°C: a rectangular molding die (female mold, surface has a maximum height roughness (nominal value Rz) of 3.2 μm, as specified in Table 2 of the comparative surface roughness standard specimens in Annex 1 (Reference) of JIS B 0659-1:2002; corner radius 2.0 mm, edge radius 1.0 mm) and a corresponding molding die (male mold, surface of the edge has a maximum height roughness (nominal value Rz) of 1.6 μm, as specified in Table 2 of the comparative surface roughness standard specimens in Annex 1 (Reference) of JIS B 0659-1:2002; surface other than the edge has a maximum height roughness (nominal value Rz) of 1.6 μm. The maximum height roughness (nominal value of Rz) is 3.2 μm, as specified in Table 2 of the comparative surface roughness standard specimens. Cold forming (single-stage pull-in forming) was performed with a pressing pressure (surface pressure) of 0.1 MPa to achieve a molding depth of 6.0 mm using corner radius R2.0 mm and edge radius R1.0 mm. At this time, the test sample was placed on the female mold so that the heat-fusible resin layer side was located on the male mold side, and forming was performed. The clearance between the male and female molds was set to 0.3 mm. The heat-fusible resin layer of the molded test sample was visually observed to check for whitening. Samples with no whitening were rated A, those with slight whitening were rated B, and those with clear whitening were rated C. The results are shown in Table 1. Note that the areas where whitening occurred were mainly around the side walls on the short side of the molded part.

[0142] <Insulating properties> The exterior material for the energy storage device was cut into sheet pieces measuring 160mm in length (MD) x 90mm in width (TD). Next, these sheet pieces were subjected to a 25°C environment using a rectangular molding die (female mold, surface has a maximum height roughness (nominal value of Rz) of 3.2 μm, as specified in Table 2 of the comparative surface roughness standard specimens in Annex 1 (Reference) of JIS B 0659-1:2002, corner R2.0 mm, ridge R1.0 mm) and a corresponding molding die (male mold, surface of the ridge has a maximum height roughness (nominal value of Rz) of 1.6 μm, as specified in Table 2 of the comparative surface roughness standard specimens in Annex 1 (Reference) of JIS B 0659-1:2002, and the surface other than the ridge has a maximum height roughness (nominal value of Rz) of 1.6 μm, as specified in Annex 1 (Reference) of JIS B 0659-1:2002 The maximum height roughness (nominal value of Rz) is 3.2 μm, as specified in Table 2 of the comparative surface roughness standard specimens. Cold forming (single-stage pull-in forming) was performed with a pressing pressure (surface pressure) of 0.1 MPa to achieve a molding depth of 3.0 mm using corner radius (R2.0 mm) and edge radius (R1.0 mm). Next, the molded sample piece was folded in half in the MD direction so that the heat-fusible resin layers faced each other, and the molded body was obtained by cutting the end on the MD side from the molded part to a width of 3 mm. The position of the molded part was such that the distance between the molded part and both ends of the TD of the sheet piece was 25 mm and 32 mm, respectively.

[0143] Next, a polyethylene terephthalate sheet (PET sheet) with a thickness of 3.0 mm, a length (MD) of 30.0 mm, and a width (TD) of 52.5 mm, and an aluminum terminal with a thickness of 70 μm, a length (MD) of 55 mm, and a width (TD) of 5 mm were prepared. A tab film (formed from maleic anhydride-modified polypropylene) with a thickness of 100 μm and a width of 10 mm was wrapped around the center of the aluminum terminal. Using paper tape, the aluminum terminal was attached to the MD end of the PET sheet, and the PET sheet was inserted into the molded part of the molded body as described above. At this time, the aluminum terminal protruded from the molded part to the outside of the molded body, and the tab film was positioned between the heat-sealable resin layers of the molded body. In this state, the edge of the molded body from which the aluminum terminal protruded was heat-sealed under the conditions of a width of 3 mm, a surface pressure of 4.0 MPa, a sealing temperature of 170°C, and a sealing time of 3.0 seconds. Next, one end perpendicular to the heat-sealed end was heat-sealed under the conditions of a width of 3 mm, a surface pressure of 1.0 MPa, a sealing temperature of 170°C, and a sealing time of 3.0 seconds to form a bag-like structure. Then, the bag-shaped molded body was stored in a dry room for one day. An electrolyte (prepared by mixing lithium hexafluoride phosphate to a concentration of 1 mol / L in a solution of ethylene carbonate:diethyl carbonate:dimethyl carbonate in a volume ratio of 1:1:1) was poured through the remaining open end (opening), and the opening was heat-sealed under the conditions of a width of 3 mm, a surface pressure of 1.0 MPa, a sealing temperature of 170°C, and a sealing time of 3.0 seconds to seal the electrolyte inside the molded body. Finally, with the heat-sealed end facing upwards, the molded body was stored in a 60°C environment for 6 hours. Next, between the last heat-sealed edge and the molded portion, heat-sealable resin layers were heat-sealed together along the molded portion under the conditions of a width of 3 mm, a surface pressure of 1.0 MPa, a sealing temperature of 170°C, and a sealing time of 3.0 seconds, to create a test sample in which the electrolyte was sealed into the molded portion.

[0144] Next, the insulation between the barrier layer of the test sample and the aluminum terminal was evaluated using a tester (HIOKI 3154 insulation resistance tester). First, 10 test samples were prepared. Next, one terminal of the tester was connected to the aluminum terminal of the test sample, and the other terminal was connected to the barrier layer of the exterior material for the energy storage device using alligator clips. Next, a voltage of 25V was applied between the testers, and samples with a resistance value of 200MΩ or more after 10 seconds were judged as pass (OK), and samples with a resistance value of less than 200MΩ after 10 seconds were judged as fail (NG). The number of failing (NG) test samples out of 10 test samples is shown in Table 1.

[0145] [Table 1]

[0146] In Table 1, "PE" stands for polyethylene.

[0147] As is clear from the description in Table 1, the exterior material for the energy storage device in Examples 1 and 2, in the cross-sectional image of the heat-sealable resin layer containing polypropylene and polyethylene, has an island structure where the area of ​​the island portion is 0.02 μm² relative to the total number of island portions. 2 The proportion of the total number of the following island-like structures is 80.0% or more, indicating that whitening and a decrease in insulation performance due to molding are effectively suppressed.

[0148] As described above, this disclosure provides inventions in the following embodiments. Item 1. The laminate comprises, from the outside to the inside, at least a base layer, a barrier layer, and a heat-fusible resin layer in this order. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image obtained using a scanning electron microscope of the heat-fusible resin layer in a direction parallel to TD and in the thickness direction. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm² relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more. Item 2. The exterior material for an energy storage device according to Item 1, wherein in the cross-sectional image of the heat-fusible resin layer, the ratio of the total area of ​​the island portion of the sea-island structure to the area of ​​the measurement range of the cross-sectional image is 12.0% or less. Item 3. In the cross-sectional image of the heat-fusible resin layer, the area of ​​the island portion of the sea-island structure is 0.03 μm² relative to the total number of island portions of the sea-island structure. 2 An exterior material for an energy storage device as described in item 1 or 2, wherein the proportion of the total number of the following island sections is 90.0% or more. Item 4. In the cross-sectional image of the heat-fusible resin layer, the area of ​​the island portion of the sea-island structure is 0.01 μm² relative to the total number of island portions of the sea-island structure. 2 An exterior material for an energy storage device as described in any one of items 1 to 3, wherein the proportion of the total number of the following island sections is 50.0% or more. Item 5. In the cross-sectional image of the heat-fusible resin layer, the area of ​​the island portion of the sea-island structure is 0.30 μm² relative to the total number of island portions of the sea-island structure. 2 An exterior material for an energy storage device as described in any one of items 1 to 4, wherein the proportion of the total number of the above-mentioned island portions is 1.0% or less. Item 6. An exterior material for an energy storage device according to any one of items 1 to 5, comprising an adhesive layer between the barrier layer and the heat-fusible resin layer. Item 7. An exterior material for an energy storage device according to Item 6, wherein the thickness of the adhesive layer is 5 μm or more. Item 8. A step of obtaining a laminate by laminating a base material layer, a barrier layer, and a heat-fusible resin layer in this order from the outside to the inside, The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image obtained using a scanning electron microscope of the heat-fusible resin layer in a direction parallel to TD and in the thickness direction. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm² relative to the total number of island portions of the sea-island structure. 2 A method for manufacturing exterior material for energy storage devices, wherein the proportion of the total number of the following island-shaped sections is 80.0% or more. Item 9. An energy storage device in which an energy storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte is housed in a package formed from an outer casing material for an energy storage device as described in any one of items 1 to 7. [Explanation of Symbols]

[0149] 1 Base material layer 2 Adhesive layer 3. Barrier layer 4 Heat-fusible resin layer 5 Adhesive layer 6 Surface coating layer 10. Exterior materials for energy storage devices

Claims

1. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The substrate layer includes a laminate of polyester film and polyamide film, a laminate of polyester film and polyester film, or a laminate of polyamide film and polyamide film. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

2. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. At least one of the surface and interior of the substrate layer contains two or more types of lubricants. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

3. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. At least two types selected from the group consisting of saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides, and aromatic bisamides are present on the surface and inside of the substrate layer. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

4. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The barrier layer comprises at least one of an aluminum alloy foil and a stainless steel foil. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

5. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The thickness of the barrier layer is 9 μm or more and 200 μm or less. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

6. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The heat-fusible resin layer is formed of two or more layers of the same or different resins. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

7. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. At least one of the surface and interior of the heat-fusible resin layer contains two or more types of lubricants. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

8. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. At least two types selected from the group consisting of saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides, and aromatic bisamides are present on the surface and interior of the heat-fusible resin layer. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

9. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The laminate is colored, The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the cross-sectional image, the ratio of the total number of island portions of the sea-island structure to the total number of island portions having an area of 0.02 μm 2 or less among the island portions is 80.0% or more. An exterior material for a power storage device.

10. It is composed of a laminate comprising, in order from the outside to the inside, at least a base layer, an adhesive layer, a barrier layer, and a heat-fusible resin layer. The adhesive layer contains a coloring agent, The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

11. The laminate is composed of, from the outside inward, at least a base layer, a colored layer, a barrier layer, and a heat-sealable resin layer, in this order. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

12. It is composed of a laminate comprising, in order from the outside to the inside, at least a surface coating layer, a base material layer, a barrier layer, and a heat-fusible resin layer. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

13. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The thickness of the laminate is 35 μm or more and 180 μm or less. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

14. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The thickness of the substrate layer is 3 μm or more and 50 μm or less. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

15. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. An adhesive layer is provided between the barrier layer and the heat-fusible resin layer. The thickness of the adhesive layer is 0.1 μm or more and 50 μm or less. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

16. It is composed of a laminate comprising, from the outside to the inside, at least a base layer, a barrier layer, and a heat-sealable resin layer in this order. The heat-fusible resin layer is formed of two or more layers of the same or different resins. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure was observed in the cross-sectional image of the heat-fusible resin layer in the direction parallel to TD and in the thickness direction, obtained using a scanning electron microscope. The aforementioned cross-sectional image is obtained within a range of 12.5% ​​thickness from the surface of the heat-fusible resin layer opposite to the barrier layer, assuming that the total thickness of the layers located inside the barrier layer is 100%. In the aforementioned cross-sectional image, the area of ​​the island portion of the sea-island structure is 0.02 μm, relative to the total number of island portions of the sea-island structure. 2 Exterior material for energy storage devices in which the total number of the following island-shaped sections accounts for 80.0% or more.

17. The exterior material for an energy storage device according to any one of claims 1 to 16, wherein in the cross-sectional image of the heat-fusible resin layer, the ratio of the total area of ​​the island portion of the sea-island structure to the area of ​​the measurement range of the cross-sectional image is 12.0% or less.

18. In the cross-sectional image of the heat-fusible resin layer, the area of ​​the island portion of the sea-island structure is 0.03 μm. 2 An exterior material for an energy storage device according to any one of claims 1 to 17, wherein the proportion of the total number of the following island portions is 90.0% or more.

19. In the cross-sectional image of the heat-fusible resin layer, the area of ​​the island portion of the sea-island structure is 0.01 μm² relative to the total number of island portions. 2 An exterior material for an energy storage device according to any one of claims 1 to 18, wherein the proportion of the total number of the following island portions is 50.0% or more.

20. In the cross-sectional image of the heat-fusible resin layer, the area of ​​the island portion of the sea-island structure is 0.30 μm² relative to the total number of island portions. 2 The exterior material for an energy storage device according to any one of claims 1 to 19, wherein the proportion of the total number of the above-mentioned island portions is 1.0% or less.

21. An energy storage device in which an energy storage device element comprising at least a positive electrode, a negative electrode, and an electrolyte is housed in a package formed from an outer material for an energy storage device according to any one of claims 1 to 20.

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