Packaging material for power storage device, method for producing the same, and power storage device

Abstract

To provide a packaging material for a power storage device that includes a heat-fusible resin layer containing polypropylene and polyethylene, in which whitening and deterioration in insulation properties due to molding are suppressed.SOLUTION: A packaging material for a power storage device is constituted of a laminate comprising at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from an outer side to an inner side. The heat-sealable resin layer contains polypropylene and polyethylene. A sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope with respect to a cross section in a thickness direction parallel to a TD of the heat-sealable resin layer. The cross-sectional image is obtained within a range of 12.5% of a thickness from a surface opposite a barrier layer side of the heat-sealable resin layer when a total thickness of a layer located closer to the inner side than the barrier layer is taken as 100%. In the cross-sectional image, a ratio of a total number of island portions having an area of 0.02 μm2 or less among the island portions to a total number of island portions of the sea-island structure is 80.0% or more.SELECTED DRAWING: None

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 any power storage device, 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 have been required for power storage devices, and thinning and weight reduction have been demanded. However, conventionally frequently used metal exterior materials for power storage devices have the disadvantages 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 (see, for example, Patent Document 1).

[0005] In such an exterior material for a power storage device, generally, a recess is formed by cold forming, power storage device elements such as electrodes and electrolytic solutions are arranged in the space formed by the recess, 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

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] In the above-described film-shaped exterior material for a power storage device, polyolefins such as polypropylene may be used as a material for forming the heat-sealable resin layer. For example, when polypropylene is used for forming the heat-sealable resin layer, polyethylene may be used in combination in order to improve workability 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-sealable resin layer is formed by melt extrusion molding, a sea-island structure in which islands of polyethylene are dispersed in the sea portion of polypropylene is formed (note that in order to observe the sea-island structure, the cross-section of the heat-sealable resin layer is stained with ruthenium tetroxide or the like, and a cross-sectional image is obtained and observed using a scanning electron microscope). Therefore, when the exterior material for a power storage device is subjected to the above-described cold forming, due to the stress applied during forming, fine cracks are generated at the interface between the polypropylene portion and the polyethylene portion of the heat-sealable resin layer, which may cause whitening of the heat-sealable resin layer and a decrease in the insulation of the exterior material for a power storage device.

[0009] For example, Patent Document 2 describes that when the inner layer of an exterior material for a battery is made of a mixture of a polypropylene resin and a polyethylene resin, by controlling the manufacturing conditions of the exterior material for a battery, the thickness of the inner layer, the mixing ratio of the polypropylene resin and the polyethylene resin, etc. to control the size and number of "islands", the seal strength between the heat-sealed inner layers can be controlled. In a mixture having a sea-island structure, the particle size of the polyethylene resin, which is the size of the "island", is preferably in the range of 0.5 to 5 μm (that is, about 0.196 to 19.6 μm). 2 is described.

[0010] However, as a result of the inventor's study, it has been found that in the conventional exterior material for a battery in which polypropylene and polyethylene are blended in the inner layer as disclosed in Patent Document 2, the particle size of the polyethylene resin is large, and whitening due to molding and a decrease in insulation cannot be sufficiently suppressed.

[0011] Under such circumstances, the main object of the present disclosure is to provide an exterior material for a power storage device including a heat-sealable resin layer containing polypropylene and polyethylene, in which whitening due to molding and a decrease in insulation are suppressed.

Means for Solving the Problems

[0012] The inventors of the present disclosure have conducted intensive studies to solve the above problems. As a result, it is composed of a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside. The heat-sealable resin layer contains polypropylene and polyethylene. Regarding a cross-section in a direction parallel to the TD (Transverse Direction) of the heat-sealable resin layer and in the thickness direction, a sea-island structure is observed in the cross-sectional image obtained using a scanning electron microscope. In the cross-sectional image, the ratio of the total number of the following island portions to the total number of the island portions of the sea-island structure is 80.0% or more. The power storage 2 device It has been found that the exterior material for the vice is suppressed from whitening and reducing insulation due to molding. The cross-sectional image was obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion having a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is taken as 100%. Incidentally, regarding the MD direction and TD direction of the heat-sealable resin layer laminated on the laminate, generally, it can be discriminated from the barrier layer described later. That is, in the exterior material for the power storage device, regarding the barrier layer described later, generally, the MD and TD in the manufacturing process thereof can be discriminated. For example, when the barrier layer is composed of an aluminum foil, linear streaks called so-called rolling marks are formed on the surface of the aluminum foil in the rolling direction (RD: Rolling Direction) of the aluminum foil. Since the rolling marks extend along the rolling direction, the rolling direction of the aluminum foil can be grasped by observing the surface of the aluminum foil. Further, in the manufacturing process of the laminate, generally, since the MD of the laminate coincides with the RD of the aluminum foil, by observing the surface of the aluminum foil of the laminate and specifying the rolling direction (RD) of the aluminum foil, the MD of the laminate (that is, the MD of the heat-sealable resin layer) can be specified. Further, since the TD of the laminate is perpendicular to the MD of the laminate, the TD of the laminate (that is, the TD of the heat-sealable resin layer) can also be specified.

[0013] Based on these findings, the present disclosure has been completed through further study. That is, the present disclosure provides an invention in the following aspects. Composed of a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside, The heat-sealable resin layer contains polypropylene and polyethylene, Regarding the cross-section in the direction parallel to the TD of the heat-sealable resin layer and in the thickness direction, an island structure is observed in the cross-sectional image obtained using a scanning electron microscope, The cross-sectional image is a cross-sectional image obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion having a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is taken as 100%. In the cross-sectional image, the ratio of the total number of island portions having an area of 0.02 μm 2 or less among the island portions to the total number of the island portions of the sea-island structure is 80.0% or more. An exterior material for a power storage device.

Advantages of the Invention

[0014] According to the present disclosure, it is possible to provide an exterior material for a power storage device including a heat-sealable resin layer containing polypropylene and polyethylene, in which whitening due to molding and a decrease in insulation properties are suppressed. Further, according to the present disclosure, it is also possible to provide a method for manufacturing an exterior material for a power storage device and a power storage device.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0016] The exterior material for a power storage device of the present disclosure is composed of a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside. The heat-sealable resin layer contains polypropylene and polyethylene. For a cross-section in a direction parallel to TD and in the thickness direction of the heat-sealable resin layer, a sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope. The cross-sectional image is a cross-sectional image obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion having a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is taken as 100%. In the cross-sectional image, the ratio of the total number of the following island portions to the total number of island portions of the sea-island structure is 80.0% or more. According to the exterior material for a power storage device of the present disclosure, by having the above configuration, whitening due to molding and a decrease in insulation are suppressed. 2 It is characterized in that the ratio of the total number of the following island portions is 80.0% or more. According to the exterior material for a power storage device of the present disclosure, by having the above configuration, whitening due to molding and a decrease in insulation are suppressed.

[0017] Hereinafter, the exterior material for a power storage device of the present disclosure will be described in detail. In this specification, the numerical range indicated by "~" means "above" and "below". For example, the notation of 2~15 mm means 2 mm or more and 15 mm or less.

[0018] 1. Laminated structure of the exterior material for the power storage device The exterior material 10 for a power storage device of the present disclosure is composed of a laminate including a base material layer 1, a barrier layer 3, and a heat-sealable resin layer 4 in this order, as shown in FIG. 1 for example. In the exterior material 10 for a power storage device, the base material layer 1 is on the outermost layer side, and the heat-sealable resin layer 4 is on the innermost layer. When assembling a power storage device using the exterior material 10 for a power storage device and a power storage device element, the power storage device element is accommodated in a space formed by heat-sealing the peripheral portions in a state where the heat-sealable resin layers 4 of the exterior material 10 for a power storage device face each other.

[0019] As shown in FIGS. 2 to 4, for example, the exterior material 10 for a power storage device may have an adhesive layer 2 between the base material layer 1 and the barrier layer 3 as needed for the purpose of enhancing the adhesiveness between these layers. Also, as shown in FIGS. 3 and 4, for example, an adhesive layer 5 may be provided between the barrier layer 3 and the heat-sealable resin layer 4 as needed for the purpose of enhancing the adhesiveness between these layers. Further, as shown in FIG. 4, a surface coating layer 6 or the like may be provided on the outer side of the base material layer 1 (the side opposite to the heat-sealable resin layer 4) as needed.

[0020] The thickness of the laminate constituting the exterior material 10 for a power storage device is not particularly limited. However, from the viewpoints of cost reduction, improvement of energy density, etc., it is preferably about 180 μm or less, about 155 μm or less, about 120 μm or less. Also, from the viewpoint of maintaining the function of the exterior material for a power storage device of protecting the power storage device element, the thickness of the laminate constituting the exterior material 10 for a power storage device is preferably about 35 μm or more, about 45 μm or more, about 60 μm or more. Also, regarding the preferable range of the thickness of the laminate constituting the exterior material 10 for a power storage device, for example, 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, about 60 to 120 μm can be mentioned, and particularly about 60 to 155 μm is preferable.

[0021] In the exterior material 10 for a power storage device, the ratio of the total thickness of the base material layer 1, the adhesive layer 2 provided as necessary, the barrier layer 3, the adhesive layer 5 provided as necessary, the heat-sealable resin layer 4, and the surface coating layer 6 provided as necessary to the thickness (total thickness) of the laminate constituting the exterior material 10 for a power storage device is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. As a specific example, when the exterior material 10 for a power storage device of the present disclosure includes the base material layer 1, the adhesive layer 2, the barrier layer 3, the adhesive layer 5, and the heat-sealable resin layer 4, the ratio of the total thickness of these layers to the thickness (total thickness) of the laminate constituting the exterior material 10 for a power storage device 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 power storage device [Base material layer 1] In the present disclosure, the base material layer 1 is a layer provided for the purpose of, for example, exerting the function as a base material of the exterior material for a power storage device. The base material layer 1 is located on the outer layer side of the exterior material for a power storage device.

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

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

[0025] Examples of the resin for forming the base material layer 1 include resins such as polyester, polyamide, polyolefin, epoxy resin, acrylic resin, fluororesin, polyurethane, silicone resin, and phenol resin, and modified products of these resins. Further, the resin for forming the base material layer 1 may be a copolymer of these resins, a modified product of the copolymer, or a mixture of these resins.

[0026] Among these, the resins preferably used for forming the base material layer 1 are polyester and polyamide.

[0027] Specific examples of the polyester include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, and copolyester. Examples of the copolyester include copolyesters having ethylene terephthalate as the main repeating unit. Specifically, copolyester polyesters obtained by polymerizing ethylene isophthalate with 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), polyethylene (terephthalate / decanedicarboxylate), etc. These polyesters may be used alone or in combination of two or more.

[0028] Also, examples of the polyamide specifically 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) that contain structural units derived from terephthalic acid and / or isophthalic acid, and polyamides containing aromatics such as polyamide MXD6 (polymetaxylylene adipamide); alicyclic polyamides such as polyamide PACM6 (poly-bis(4-aminocyclohexyl)methane adipamide); furthermore, polyamides copolymerized with a lactam component or an isocyanate component such as 4,4'-diphenylmethane-diisocyanate, and polyester amide copolymers and polyether ester amide copolymers that are copolymers of a copolymer polyamide with a polyester or a polyalkylene ether glycol; polyamides such as these copolymers and the like are included. These polyamides may be used alone or in combination of two or more.

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

[0030] The base material layer 1 may be a single layer or may be composed of two or more layers. When the base material layer 1 is composed of two or more layers, the base material layer 1 may be a laminate obtained by laminating resin films with an adhesive or the like, or may be a laminate of resin films formed by co-extruding resin into two or more layers. Further, the laminate of resin films formed by co-extruding resin into two or more layers may be used as the base material layer 1 without stretching, or may be used as the base material layer 1 after uniaxial stretching or biaxial stretching.

[0031] In the base material layer 1, specific examples of the laminate of two or more resin films include a laminate of a polyester film and a nylon film, a laminate of two or more nylon films, a laminate of two or more polyester films, etc. Preferably, a laminate of a stretched nylon film and a 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 material layer 1 is a laminate of two resin films, a laminate of a polyester resin film and a polyester resin film, a laminate of a polyamide resin film and a polyamide resin film, or a laminate of a polyester resin film and a polyamide resin film is preferred, and a laminate of a polyethylene terephthalate film and a polyethylene terephthalate film, a laminate of nylon films, or a laminate of a polyethylene terephthalate film and a nylon film is more preferred. Further, since the polyester resin is less likely to change color when, for example, an electrolytic solution adheres to the surface, when the base material layer 1 is a laminate of two or more resin films, it is preferred that the polyester resin film is located in the outermost layer of the base material layer 1.

[0032] When the base material layer 1 is a laminate of two or more resin films, the two or more resin films may be laminated via an adhesive. Preferred adhesives include the same ones as those exemplified for the adhesive layer 2 described below. The method for laminating two or more resin films is not particularly limited, and known methods can be adopted. For example, dry lamination method, sandwich lamination method, extrusion lamination method, thermal lamination method, etc. can be mentioned, and preferably the dry lamination method can be mentioned. When laminating by the dry lamination method, it is preferable to use a polyurethane adhesive as the adhesive. At this time, the thickness of the adhesive is, for example, about 2 to 5 μm. Also, an anchor coat layer may be formed on and laminated to the resin film. The anchor coat layer includes the same ones as those exemplified for the adhesive layer 2 described below. At this time, the thickness of the anchor coat layer is, for example, about 0.01 to 1.0 μm.

[0033] In addition, additives such as lubricants, flame retardants, antiblocking agents, antioxidants, light stabilizers, tackifiers, antistatic agents, etc. may be present on at least one of the surface and the inside of the base material layer 1. Only one type of additive may be used, or two or more types may be mixed and used.

[0034] In the present disclosure, from the viewpoint of enhancing the moldability of the exterior material for the power storage device, it is preferable that a lubricant is present on the surface of the base material layer 1. The lubricant is not particularly limited, but preferably an amide-based lubricant. Specific examples of the amide-based lubricant include, for example, saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylol amides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides, aromatic bisamides, and the like. Specific examples of the saturated fatty acid amides include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, hydroxystearic acid amide, and the like. Specific examples of the unsaturated fatty acid amides include oleic acid amide, erucic acid amide, and the like. Specific examples of the substituted amides include N-oleyl palmitic acid amide, N-stearyl stearic acid amide, N-stearyl oleic acid amide, N-oleyl stearic acid amide, N-stearyl erucic acid amide, and the like. Further, specific examples of the methylol amides include methylol stearic acid amide, and the like. Specific examples of the saturated fatty acid bisamides include methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbehenic acid amide, hexamethylene bisstearic acid amide, hexamethylene bisbehenic acid amide, hexamethylene hydroxystearic acid amide, N,N'-distearyl adipic acid amide, N,N'-distearyl sebacic acid amide, and the like. Specific examples of the unsaturated fatty acid bisamides include ethylene bisoleic acid amide, ethylene biserucic acid amide, hexamethylene bisoleic acid amide, N,N'-dioleyl adipic acid amide, N,N'-dioleyl sebacic acid amide, and the like. Specific examples of the fatty acid ester amides include stearoamide ethyl stearate, and the like. Further, specific examples of the aromatic bisamides include m-xylylene bisstearic acid amide, m-xylylene bishydroxystearic acid amide, N,N'-distearyl isophthalic acid amide, and the like. The lubricant may be used alone or in combination of two or more kinds.

[0035] When a lubricant is present on the surface of the base material layer 1, its amount of presence is not particularly limited, but preferably about 3 mg / m 2 or more, more preferably 4 - 15 mg / m 2 or so, even more preferably 5 - 14 mg / m 2 or so.

[0036] The lubricant present on the surface of the base material layer 1 may be one obtained by exuding the lubricant contained in the resin constituting the base material layer 1, or may be one obtained by applying a lubricant to the surface of the base material layer 1.

[0037] Regarding the thickness of the base material layer 1, it is not particularly limited as long as it exhibits the function as a base material. For example, it may be about 3 - 50 μm, preferably about 10 - 35 μm. When the base material layer 1 is a laminate of two or more resin films, the thickness of each resin film constituting each layer is preferably about 2 - 25 μm, respectively.

[0038] [Adhesive layer 2] In the exterior material for a power storage device of the present disclosure, the adhesive layer 2 is a layer provided between the base material layer 1 and the barrier layer 3 as needed for the purpose of enhancing the adhesiveness therebetween.

[0039] The adhesive layer 2 is formed of an adhesive capable of adhering the base material layer 1 and the barrier layer 3. The adhesive used for forming the adhesive layer 2 is not limited, and it may be any of a chemical reaction type, a solvent volatilization type, a hot melt type, a hot press type, etc. Also, it may be a two - component curing adhesive (two - component adhesive), a one - component curing adhesive (one - component adhesive), or a resin without a curing reaction. Further, the adhesive layer 2 may be a single layer or a multilayer.

[0040] Specific examples of the adhesive component contained in the adhesive include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, and copolyester; polyethers; polyurethanes; epoxy resins; phenolic resins; polyamides such as nylon 6, nylon 66, nylon 12, and copolyamide; polyolefin resins such as polyolefin, cyclic polyolefin, acid-modified polyolefin, and acid-modified cyclic polyolefin; polyvinyl acetate; cellulose; (meth)acrylic resins; polyimides; polycarbonates; amino resins such as urea resin and melamine resin; rubbers such as chloroprene rubber, nitrile rubber, and styrene-butadiene rubber; and silicone resins. These adhesive components may be used alone or in combination of two or more. Among these adhesive components, a polyurethane adhesive is preferably mentioned. Also, the resin serving as these adhesive components can enhance the adhesive strength by using an appropriate curing agent in combination. The curing agent is appropriately selected from polyisocyanate, polyfunctional epoxy resin, oxazoline group-containing polymer, polyamine resin, acid anhydride, etc., according to the functional group of the adhesive component.

[0041] Examples of the polyurethane adhesive include a polyurethane adhesive containing a main agent containing a polyol compound and a curing agent containing an isocyanate compound. Preferably, a two-component curing type polyurethane adhesive using a polyol such as polyester polyol, polyether polyol, and acrylic polyol as the main agent and an aromatic or aliphatic polyisocyanate as the curing agent is mentioned. Also, as the polyol compound, it is preferable to use a polyester polyol having a hydroxyl group not only at the terminal of the repeating unit but also in the side chain. By forming the adhesive layer 2 with a polyurethane adhesive, excellent electrolyte resistance is imparted to the exterior material for the power storage device, and even when the electrolyte adheres to the side surface, peeling of the base material layer 1 is suppressed.

[0042] In addition, as long as the adhesiveness is not inhibited, the addition of other components is permitted in the adhesive layer 2, and it may contain a colorant, a thermoplastic elastomer, a tackifier, a filler, and the like. Since the adhesive layer 2 contains a colorant, the exterior material for the power storage device can be colored. As the colorant, known ones such as pigments and dyes can be used. Further, only one type of colorant may be used, or two or more types may be mixed and used.

[0043] The type of the pigment is not particularly limited as long as it does not impair the adhesiveness of the adhesive layer 2. Examples of the organic pigment include pigments such as azo-based, phthalocyanine-based, quinacridone-based, anthraquinone-based, dioxazine-based, indigothioindigo-based, perinone-perylene-based, isoindolenine-based, and benzimidazolone-based pigments. Examples of the inorganic pigment include pigments such as carbon black-based, titanium oxide-based, cadmium-based, lead-based, chromium oxide-based, and iron-based pigments. In addition, fine powders of mica (muscovite), fish scale foil, and the like can be mentioned.

[0044] Among the colorants, for example, in order to make the appearance of the exterior material for the power storage device black, carbon black is preferable.

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

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

[0047] The thickness of the adhesive layer 2 is not particularly limited as long as the base material layer 1 and the barrier layer 3 can be adhered, but for example, it is about 1 μm or more, about 2 μm or more. Further, the thickness of the adhesive layer 2 is, for example, about 10 μm or less, 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] [Coloring layer] The coloring layer is a layer provided between the base material layer 1 and the barrier layer 3 as needed (omitted in the illustration). When having the adhesive layer 2, the coloring layer may be provided between the base material layer 1 and the adhesive layer 2, and between the adhesive layer 2 and the barrier layer 3. Also, the coloring layer may be provided outside the base material layer 1. By providing the coloring layer, the exterior material for the power storage device can be colored.

[0049] The coloring layer can be formed, for example, by applying ink containing a colorant to the surface of the base material layer 1 or the surface of the barrier layer 3. As the colorant, known ones such as pigments and dyes can be used. Also, only one type of colorant may be used, or two or more types may be mixed and used.

[0050] Specific examples of the colorant contained in the coloring layer are the same as those exemplified in the column of [adhesive layer 2].

[0051] [Barrier layer 3] In the exterior material for the power storage device, the barrier layer 3 is a layer that at least suppresses the intrusion of moisture.

[0052] Examples of the barrier layer 3 include a metal foil having barrier properties, a vapor deposition film, a resin layer, and the like. Examples of the vapor deposition film include a metal vapor deposition film, an inorganic oxide vapor deposition film, a carbon-containing inorganic oxide vapor deposition film, and the like. Examples of the resin layer include fluorine-containing resins such as polyvinylidene chloride, polymers mainly composed of chlorotrifluoroethylene (CTFE), polymers mainly composed of tetrafluoroethylene (TFE), polymers having a fluoroalkyl group, and polymers mainly composed of fluoroalkyl units, ethylene-vinyl alcohol copolymers, and the like. Further, examples of the barrier layer 3 also include a resin film provided with at least one of these vapor deposition films and resin layers. A plurality of barrier layers 3 may be provided. The barrier layer 3 preferably includes a layer made of a metal material. Specific examples of the metal material constituting the barrier layer 3 include aluminum alloy, stainless steel, titanium steel, steel sheet, and the like. When used as a metal foil, it preferably includes at least one of an aluminum alloy foil and a stainless steel foil.

[0053] From the viewpoint of improving the formability of the exterior material for the power storage device, 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 the formability, it is preferably an aluminum alloy foil containing iron. In the aluminum alloy foil containing iron (100% by mass), the content of iron is preferably 0.1 to 9.0% by mass, and more preferably 0.5 to 2.0% by mass. When the content of iron is 0.1% by mass or more, an exterior material for the power storage device having more excellent formability can be obtained. When the content of iron is 9.0% by mass or less, an exterior material for the power storage device having more excellent flexibility can be obtained. Examples of the soft aluminum alloy foil include aluminum alloy foils having a composition defined by JIS H4160:1994 A8021H-O, JIS H4160:1994 A8079H-O, JIS H4000:2014 A8021P-O, or JIS H4000:2014 A8079P-O. Also, silicon, magnesium, copper, manganese, etc. may be added as necessary. The softening can be performed by annealing treatment or the like.

[0054] In addition, examples of the stainless steel foil include austenitic, ferritic, austenitic-ferritic, martensitic, and precipitation hardening stainless steel foils. Further, from the viewpoint of providing an exterior material for the power storage device having excellent formability, the stainless steel foil is preferably composed of an austenitic stainless steel.

[0055] Specific examples of the austenitic stainless steel constituting the stainless steel foil include SUS304, SUS301, SUS316L, etc. Among these, SUS304 is particularly preferred.

[0056] In the case of a metal foil, the thickness of the barrier layer 3 only needs to exhibit a function as a barrier layer that at least suppresses the intrusion of moisture. For example, it can be 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, still 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, still more preferably about 20 μm or more, and more preferably about 25 μm or more. Preferred ranges of such 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 composed of an aluminum alloy foil, the above-described ranges are particularly preferred. Also, particularly when the barrier layer 3 is composed of a stainless steel foil, the thickness of the stainless steel foil is preferably about 60 μm or less, more preferably about 50 μm or less, still more preferably about 40 μm or less, still more preferably about 30 μm or less, and particularly preferably about 25 μm or less. Also, the thickness of the stainless steel foil is preferably about 10 μm or more, and more preferably about 15 μm or more. Also, preferred ranges of the thickness of the stainless steel foil include about 10 to 60 μm, about 10 to 50 μm, about 10 to 40 μm, about 10 to 30 μm, about 10 to 25 μm, about 15 to 60 μm, about 15 to 50 μm, about 15 to 40 μm, about 15 to 30 μm, and about 15 to 25 μm.

[0057] Also, when the barrier layer 3 is a metal foil, it is preferably provided with a corrosion-resistant film on at least the surface opposite to the base material layer in order to prevent dissolution and corrosion. The barrier layer 3 may be provided with corrosion-resistant films on both sides. Here, the corrosion-resistant film refers to, for example, a thin film that is formed by performing a hydrothermal transformation treatment such as boehmite treatment, a chemical conversion treatment, an anodizing treatment, a plating treatment such as nickel or chromium, or a corrosion prevention treatment of applying a coating agent on the surface of the barrier layer to impart corrosion resistance to the barrier layer. As the treatment for forming the corrosion-resistant film, one type may be performed, or two or more types may be combined. Further, not only a single layer but also a multilayer structure can be formed. Furthermore, among these treatments, the hydrothermal transformation treatment and the anodizing treatment are treatments that dissolve the surface of the metal foil with a treatment agent and form a metal compound having excellent corrosion resistance. Note that these treatments may be included in the definition of the chemical conversion treatment. Also, when the barrier layer 3 is provided with a corrosion-resistant film, the barrier layer 3 includes the corrosion-resistant film.

[0058] The corrosion-resistant film prevents delamination between the barrier layer (for example, an aluminum alloy foil) and the base material layer during the molding of the exterior material for the power storage device, and prevents dissolution and corrosion of the surface of the barrier layer due to hydrogen fluoride generated by the reaction of the electrolyte and moisture. In particular, when the barrier layer is an aluminum alloy foil, it prevents dissolution and corrosion of aluminum oxide present on the surface of the barrier layer, and improves the adhesiveness (wettability) of the surface of the barrier layer, showing the effect of preventing delamination between the base material layer and the barrier layer during heat sealing and preventing delamination between the base material layer and the barrier layer during molding.

[0059] As the corrosion-resistant film formed by chemical conversion treatment, various types are known, and mainly include corrosion-resistant films containing at least one of phosphates, chromates, fluorides, triazine thiol compounds, and rare earth oxides. Examples of chemical conversion treatments using phosphates and chromates include chromic acid chromate treatment, phosphoric acid chromate treatment, phosphoric acid-chromate treatment, chromate treatment, etc. Examples of chromium compounds used in these treatments include chromium nitrate, chromium fluoride, chromium sulfate, chromium acetate, chromium oxalate, chromium metaphosphate, acetylacetate chromium, chromium chloride, potassium chromium sulfate, etc. Examples of phosphorus compounds used in these treatments include sodium phosphate, potassium phosphate, ammonium phosphate, polyphosphoric acid, etc. Examples of chromate treatments include etching chromate treatment, electrolytic chromate treatment, coating-type chromate treatment, etc., and coating-type chromate treatment is preferred. This coating-type chromate treatment involves first degreasing at least the inner layer side surface of the barrier layer (e.g., aluminum alloy foil) by well-known treatment methods such as alkaline immersion method, electrolytic cleaning method, acid cleaning method, electrolytic acid cleaning method, acid activation method, etc. Then, a treatment liquid mainly composed of metal phosphates such as chromium (Cr) phosphate, titanium (Ti) phosphate, zirconium (Zr) phosphate, zinc (Zn) phosphate, etc. and mixtures of these metal salts, or a treatment liquid mainly composed of non-metal phosphates and mixtures of these non-metal salts, or a treatment liquid composed of a mixture of these and synthetic resin, etc. is applied by well-known coating methods such as roll coating method, gravure printing method, immersion method, etc. and dried. As the treatment liquid, various solvents such as water, alcohol-based solvents, hydrocarbon-based solvents, ketone-based solvents, ester-based solvents, ether-based solvents, etc. can be used, and water is preferred. Examples of resin components used at this time include polymers such as phenolic resins and acrylic resins, and chromate treatment using an aminated phenol polymer having repeating units represented by the following general formulas (1) to (4) can be mentioned. In the aminated phenol polymer, the repeating units represented by the following general formulas (1) to (4) may be included alone 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 a sodium salt, ammonium salt, amine salt, etc. of these. In particular, derivatives of polyacrylic acid such as ammonium salt, sodium salt, or amine salt of polyacrylic acid are preferred. In the present disclosure, polyacrylic acid means a polymer of acrylic acid. Further, the acrylic resin is preferably a copolymer of acrylic acid and a dicarboxylic acid or dicarboxylic anhydride, and is also preferably an ammonium salt, sodium salt, or amine salt of a copolymer of acrylic acid and a dicarboxylic acid or dicarboxylic anhydride. Only one type of acrylic resin may be used, or two or more types may be mixed and used.

[0060]

Chemical formula

[0061]

Chemical formula

[0062]

Chemical formula

[0063]

Chemical formula

[0064] In general formulas (1) to (4), X represents a hydrogen atom, a hydroxy group, an alkyl group, a hydroxyalkyl group, an allyl group, or a benzyl group. Also, R 1 and R 2 each independently represent a hydroxy group, an alkyl group, or a hydroxyalkyl group, which may be the same or different. In general formulas (1) to (4), X, R 1 and R 2Examples of the alkyl group represented by [alkyl group] include linear or branched alkyl groups having 1 to 4 carbon atoms such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, etc. Also, X, R 1 and R 2 Examples of the hydroxyalkyl group represented by [hydroxyalkyl group] include linear or branched alkyl groups having 1 to 4 carbon atoms with one hydroxy 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, 4-hydroxybutyl group, etc. In General Formulas (1) to (4), the alkyl groups and hydroxyalkyl groups represented by X, R 1 and R 2 may be the same or different from each other. In General Formulas (1) to (4), X is preferably a hydrogen atom, a hydroxy group or a hydroxyalkyl group. The number average molecular weight of the aminated phenol polymer having a repeating unit represented by General Formulas (1) to (4) is preferably about 500 to 1,000,000, more preferably about 1,000 to 20,000. The aminated phenol polymer is produced, for example, by polycondensing a phenol compound or a naphthol compound and formaldehyde to produce a polymer composed of the repeating unit represented by the above General Formula (1) or General Formula (3), and then introducing a functional group (-CH2NR 1 R 2 ) into the polymer obtained above using formaldehyde and an amine (R 1 R 2 NH). The aminated phenol polymer is used alone or in a mixture of two or more.

[0065] As another example of the corrosion-resistant film, there is a thin film formed by a coating-type corrosion prevention treatment in which a coating agent containing at least one selected from the group consisting of rare earth element oxides sols, anionic polymers, and cationic polymers is applied. The coating agent may further contain phosphoric acid or a phosphate, and a crosslinking agent for crosslinking the polymer. In the rare earth element oxide sol, fine particles of a rare earth element oxide (for example, particles having an average particle diameter of 100 nm or less) are dispersed in a liquid dispersion medium. Examples of the rare earth element oxide include cerium oxide, yttrium oxide, neodymium oxide, lanthanum oxide, etc., and cerium oxide is preferable from the viewpoint of further improving the adhesion. The rare earth element oxide contained in the corrosion-resistant film can be used alone or in combination of two or more. As the liquid dispersion medium of the rare earth element oxide sol, for example, various solvents such as water, alcohol-based solvents, hydrocarbon-based solvents, ketone-based solvents, ester-based solvents, and ether-based solvents can be used, and water is preferable. Examples of the cationic polymer include polyethyleneimine, an ion polymer complex composed of polyethyleneimine and a polymer having a carboxylic acid, a primary amine graft acrylic resin obtained by graft polymerizing a primary amine to an acrylic main skeleton, polyallylamine or its derivative, and aminophenol. Further, as the anionic polymer, it is preferably poly(meth)acrylic acid or its salt, or a copolymer mainly composed of (meth)acrylic acid or its salt. Further, it is preferable that the crosslinking agent is at least one selected from the group consisting of a compound having any functional group of an isocyanate group, a glycidyl group, a carboxyl group, and an oxazoline group and a silane coupling agent. Further, it is preferable that the phosphoric acid or the phosphate is condensed phosphoric acid or a condensed phosphate.

[0066] As an example of the corrosion-resistant film, there is one formed by applying, to the surface of a barrier layer, a material in which fine particles of metal oxides such as aluminum oxide, titanium oxide, cerium oxide, and tin oxide and barium sulfate are dispersed in phosphoric acid, and performing a baking treatment at 150 °C or higher.

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

[0068] Note that the analysis of the composition of the corrosion-resistant film can be carried out, for example, using time-of-flight secondary ion mass spectrometry.

[0069] The amount of the corrosion-resistant film formed on the surface of the barrier layer 3 in the chemical conversion treatment is not particularly limited. For example, in the case of performing a coating-type chromate treatment, per 1 m2 of the surface of the barrier layer 3, 2 the chromic acid compound is preferably about 0.5 to 50 mg, more preferably about 1.0 to 40 mg in terms of chromium conversion, the phosphorus compound is preferably about 0.5 to 50 mg, more preferably about 1.0 to 40 mg in terms of phosphorus conversion, and the aminophenol polymer is preferably about 1.0 to 200 mg, more preferably about 5.0 to 150 mg. .0~40mg in terms of phosphorus conversion, and the aminophenol polymer is preferably contained in a proportion of about 1.0 to 200 mg, more preferably about 5.0 to 150 mg.

[0070] The thickness of the corrosion-resistant film is not particularly limited. From the viewpoints of the cohesion of the film and the adhesion to the barrier layer or 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 film 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 energy loss spectroscopy. By analyzing the composition of the corrosion-resistant film using time-of-flight secondary ion mass spectrometry, for example, peaks derived from secondary ions composed of Ce, P, and O (for example, at least one of Ce2PO4 + , C ePO4 - etc.) and secondary ions composed of, for example, Cr, P, and O (for example, at least one of CrPO2 + , CrPO4 - etc.) are detected.

[0071] The chemical conversion treatment is carried out by applying a solution containing a compound used for forming a corrosion-resistant film onto the surface of the barrier layer by means such as a bar coating method, a roll coating method, a gravure coating method, a dipping method, etc., and then heating the barrier layer so that its temperature reaches about 70 to 200 °C. Also, before applying the chemical conversion treatment to the barrier layer, the barrier layer may be preliminarily subjected to a degreasing treatment by means such as an alkali dipping method, an electrolytic cleaning method, an acid cleaning method, an electrolytic acid cleaning method, etc. By performing such a degreasing treatment, it becomes possible to perform the chemical conversion treatment on the surface of the barrier layer more efficiently. Further, by using an acid degreasing agent in which a fluorine-containing compound is dissolved in an inorganic acid for the degreasing treatment, it is possible to form not only a degreasing effect on the metal foil but also a fluoride of a passive metal. In such a case, only the degreasing treatment may be performed.

[0072] [Heat-sealable resin layer 4] In the exterior material for a power storage device of the present disclosure, the heat-sealable resin layer 4 corresponds to the innermost layer and is a layer (sealant layer) that exhibits a function of heat-sealing the heat-sealable resin layers with each other during the assembly of the power storage device to seal the power storage device element.

[0073] The heat-sealable resin layer 4 contains polypropylene and polyethylene. In the exterior material for a power storage device of the present disclosure, a sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope for a cross-section in the direction parallel to TD of the heat-sealable resin layer 4 and in the thickness direction y. The cross-sectional image is, for example, a cross-sectional image obtained within a range from the surface on the side opposite to the barrier layer 3 side of the heat-sealable resin layer 4 to the portion having a thickness of 12.5% (the region surrounded by the broken line in FIG. 3) when the total thickness of the layers located inside the barrier layer 3 is taken as 100% as shown in the schematic diagram of FIG. 3. The surface on the side opposite to the barrier layer 3 side of the heat-sealable resin layer 4 has a thickness of 0%. To explain with a specific example, for example, in the exterior material for a power storage device in which a base material layer (including the adhesive, 30 μm thick) / adhesive layer (3 μm) / barrier layer (40 μm) / adhesive layer (40 μm) / heat-sealable resin layer (40 μm) are laminated in this order as in Examples 1 and 2 described later, the layers located inside the barrier layer 3 are the adhesive layer (40 μm) and the heat-sealable resin layer (40 μm), and the total thickness of these, 80 μm, is taken as 100%. Also, the position of the surface on the side opposite to the barrier layer 3 side of the heat-sealable resin layer 4 is, that is, the inner surface (inner face) of the exterior material 10 for a power storage device, and the thickness at this position is taken as 0%. Then, within the range from the said surface (thickness 0%) to the position having a thickness of 12.5% (that is, taking 80 μm in total as 100%, the position having a thickness of 12.5% is the position having a thickness of 10 μm from the surface on the side opposite to the barrier layer 3 side of the heat-sealable resin layer 4 toward the barrier layer 3 side), a cross-sectional image is obtained using a scanning electron microscope.

[0074] That a sea-island structure is observed in the cross-sectional image means that a sea portion (sea part) and an island portion (island part) are observed in the cross-sectional image. As described above, when a small amount of polyethylene is added to polypropylene and a heat-sealable resin layer is formed by melt extrusion molding, a sea-island structure in which island portions of polyethylene are dispersed in the sea portion of polypropylene is formed. In addition, to observe the said sea-island structure, as described later, the cross-section of the heat-sealable resin layer is stained with ruthenium tetroxide or the like, and a cross-sectional image is obtained and observed using a scanning electron microscope.

[0075] In the exterior material for a power storage device of the present disclosure, in the cross-sectional image of the heat-sealable resin layer 4, with respect to the total number of island portions of the sea-island structure, among the island portions, the area is 0.02 μm 2 The ratio of the total number of the following island portions is 80.0% or more. The exterior material for a power storage device of the present invention has such characteristics, whereby whitening of the heat-sealable resin layer due to cold forming of the exterior material for a power storage device and a decrease in the insulation of the exterior material for a power storage device are suppressed. That is, in the exterior material for a power storage device of the present disclosure, in the heat-sealable resin layer 4 containing polypropylene and polyethylene, among all the island portions, the area is 0.02 μm 2 The ratio occupied by the very fine island portions of being set high effectively suppresses the generation of fine cracks at the interface between the polypropylene portion and the polyethylene portion of the heat-sealable resin layer. As a result, it is considered that whitening of the heat-sealable resin layer 4 due to cold forming of the exterior material for a power storage device and a decrease in the insulation of the exterior material for a power storage device are suppressed.

[0076] In the cross-sectional image of the heat-sealable resin layer 4, with respect to the total number of island portions of the sea-island structure, among the island portions, the area is 0.02 μm 2 The ratio of the total number of the following island portions (total number of island portions with an area of 0.02 μm 2 or less / total number of all island portions) only needs to be 80.0% or more. From the viewpoint of more effectively suppressing the aforementioned whitening and decrease in insulation, it is preferably 90.0% or more, more preferably 95.0% or more. Note that the ratio of the total number is, for example, 100.0% or less, 99.0% or less, 98.0% or less. Preferred ranges for the ratio of the total number include, for example, about 80.0 to 100.0%, about 80.0 to 99.0%, about 80.0 to 98.0%, about 90.0 to 100.0%, about 90.0 to 99.0%, about 90.0 to 98.0%, about 95.0 to 100.0%, about 95.0 to 99.0%, about 95.0 to 98.0%.

[0077] Further, from the viewpoint of more effectively suppressing the aforementioned whitening and reduction in insulation properties, in the cross-sectional image of the heat-sealable resin layer 4, with respect to the total number of island portions of the sea-island structure, among the island portions, the area is 0.01 μm 2 The ratio of the total number of the following island portions (the total number of island portions of 0.01 μm 2 or less / the total number of all island portions) is preferably 50.0% or more, more preferably 55.0% or more, still more preferably 60.0% or more. Note that the ratio of the total number is, for example, 80.0% or less, 75.0% or less, 70.0% or less, etc. The preferable range of the ratio of the total number is, for example, about 50.0 to 80.0%, about 50.0 to 75.0%, about 50.0 to 70.0%, about 55.0 to 80.0%, about 55.0 to 75.0%, about 55.0 to 70.0%, about 60.0 to 80.0%, about 60.0 to 75.0%, about 60.0 to 70.0%.

[0078] Further, from the viewpoint of more effectively suppressing the aforementioned whitening and reduction in insulation properties, in the cross-sectional image of the heat-sealable resin layer 4, with respect to the total number of island portions of the sea-island structure, among the island portions, the area is 0.03 μm 2 The ratio of the total number of the following island portions (the total number of island portions of 0.03 μm 2 or less / the total number of all island portions) is preferably 90.0% or more, more preferably 95.0% or more, still more preferably 97.0% or more. Note that the ratio of the total number is, for example, 100.0% or less, 99.0% or less, 98.0% or less, etc. The preferable range of the ratio of the total number is, for example, about 90.0 to 100.0%, about 90.0 to 99.0%, about 90.0 to 98.0%, about 95.0 to 100.0%, about 95.0 to 99.0%, about 95.0 to 98.0%, about 97.0 to 100.0%, about 97.0 to 99.0%, about 97.0 to 98.0%.

[0079] Further, from the viewpoint of more effectively suppressing the aforementioned whitening and reduction in insulation properties, in the cross-sectional image of the heat-sealable resin layer 4, with respect to the total number of island portions of the sea-island structure, among the island portions, the area is 0.30 μm 2 The ratio of the total number of the following island portions (the total number of island portions of 0.30 μm 2(The total number of the above island parts / the total number of all island parts) is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.1% or less. Note that the ratio of the total number is, for example, 0.0% or more.

[0080] Furthermore, from the viewpoint of more effectively suppressing the above-mentioned whitening and reduction in insulation properties, in the cross-sectional image of the heat-sealable resin layer 4, with respect to the total number of island parts of the sea-island structure, among the island parts, the area is 0.15 μm 2 The ratio of the total number of island parts with an area of 0.15 μm or more (the total number of island parts with an area of 0.15 μm or more / the total number of all island parts) is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.1% or less. Note that the ratio of the total number is, for example, 0.0% or more. 2 (The total number of the above island parts / the total number of all island parts) is preferably 1.0% or less, more preferably 0.5% or less, and still more preferably 0.1% or less. Note that the ratio of the total number is, for example, 0.0% or more.

[0081] Also, from the viewpoint of more effectively suppressing the above-mentioned whitening and reduction in insulation properties, in the cross-sectional image of the heat-sealable resin layer 4, the ratio of the total area of the island parts of the sea-island structure to the area of the measurement range of the cross-sectional image (the total area of the island parts / the area of the measurement range of the cross-sectional image) is preferably 12.0% or less, more preferably 5.0% or less, and still more preferably 1.0% or less. For the ratio of the total area, for example, 0.1% or more can be mentioned. Preferred ranges for the ratio of the total area include, for example, about 0.1 to 12.0%, about 0.1 to 5.0%, and about 0.1 to 1.0%.

[0082] Regarding the ratio of the total area of the island parts with each area, in addition to the blending ratio of polypropylene and polyethylene contained in the heat-sealable resin layer 4, by further adjusting the conditions when forming the heat-sealable resin layer 4, the above values can be obtained (for example, as described later, in the case of forming the heat-sealable resin layer 4 by melt extrusion molding or the like, the cooling condition of the heat-sealable resin layer by the cooling roll is set to a rapid cooling condition (for example, setting the difference in surface temperature between the melt-extruded heat-sealable resin layer and the cooling roll to 70 °C or more) to suppress the crystal growth of polyethylene in polypropylene, etc.).

[0083] Regarding the cross-sectional image of the heat-sealing resin layer 4, the method for measuring the ratio of the area of the island part in the sea-island structure is as follows.

[0084] <Measurement of the Ratio of the Area and Number of Island Parts in the Sea-Island Structure> An exterior material for a power storage device is embedded in a thermosetting epoxy resin and cured. A commercially available rotary microtome (for example, EM UC6 manufactured by LEICA) and a glass knife are used to prepare a cross-section in a direction parallel to TD and in the thickness direction y. At this time, the cross-section is prepared using a normal temperature microtome. The heat-sealable resin layer of the exterior material for the power storage device is stained with ruthenium tetroxide together with the embedding resin for 3 hours. When stained, the resin expands and the sea-island structure cannot be confirmed near the cross-section, so the expanded part is trimmed with a microtome. Then, a stained section about 100 nm thick, collected using a diamond knife from the cross-section after advancing about 1 to 2 μm, is observed as follows. For the stained section, a cross-sectional image is acquired using a field emission scanning electron microscope (for example, S-4800 manufactured by Hitachi High-Technologies Corporation). As described above, the cross-sectional image is an image acquired within the range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to the portion with a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is set to 100%. When using, for example, S-4800 manufactured by Hitachi High-Technologies Corporation as the field emission scanning electron microscope, the measurement conditions are: acceleration voltage: 30 kV, emission current: 10 μA, detector: transmission detector, tilt: none (0°), observation magnification: 5000 times. Next, using image processing software capable of binarizing the cross-sectional image (for example, the image analysis software attached to the Keyence electron microscope VHX-5000), the island part and the sea part of the sea-island structure are binarized for the cross-sectional image. When using, for example, the image analysis software attached to the Keyence electron microscope VHX-5000 as the image processing software, specifically, the measurement is started under the condition of the brightness (standard) of the image analysis software, the extraction area (measurement range) is rectangular (vertical 7 μm, horizontal 13 μm), the imaging size is standard (1600×1200), the tilt angle is 0 degrees, the shooting mode is normal shooting, and the extraction target is the "dark area". Also, by automatic measurement, the missing extraction parts and extra extraction locations are corrected, and the total area and total number of the extracted locations (island parts) are measured. At this time, the area and number of all island parts existing in the extraction area are measured respectively.Using the acquired data, the ratio of the total area of all island portions to the area of the measurement range of the cross-sectional image (total area of island portions / area of the measurement range of the cross-sectional image), and among all the island portions, the area is 0.01 μm each. 2 The following ratio of the total number of island portions (0.01 μm 2 The following total number of island portions / total number of all island portions), 0.02 μm 2 The following ratio of the total number of island portions (0.02 μm 2 The following total number of island portions / total number of all island portions), 0.03 μm 2 The following ratio of the total number of island portions (0.03 μm 2 The following total number of island portions / total number of all island portions), 0.30 μm 2 The following ratio of the total number of island portions (0.30 μm 2 The following total number of island portions / total number of all island portions), 0.15 μm 2 The following ratio of the total number of island portions (0.15 μm 2 The following total number of island portions / total number of all island portions) is calculated.

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

[0086] The heat-sealable resin layer 4 is preferably formed of a polypropylene resin composition containing 45% by mass or less of polyethylene. In the heat-sealable resin layer 4, the content of polyethylene is adjusted such that, in the cross-sectional image described above, the ratio of the total number of island portions having an area of 0.02 μm 2 or less to the total number of island portions of the sea-island structure is 80.0% or more. The content of polyethylene 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 is preferably about 5% by mass or more, more preferably about 10% by mass or more. Preferred ranges include about 5 to 45% by mass, about 5 to 30% by mass, about 5 to 20% by mass, about 10 to 45% by mass, about 10 to 30% by mass, and about 10 to 20% by mass. Also, the content of polypropylene is, for example, 95% by mass or less, 90% by mass or less. Also, the content of polypropylene is, for example, 55% by mass or more, 70% by mass or more, 80% by mass or more. Preferred ranges for the content of polypropylene include about 55 to 95% by mass, about 70 to 95% by mass, about 80 to 95% by mass, about 55 to 90% by mass, about 70 to 90% by mass, and about 80 to 90% by mass. Also, as the mass ratio of polypropylene to polyethylene in the polypropylene resin composition, with 100 parts by mass of polypropylene, polyethylene 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.

[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] An acid-modified polyolefin is a polymer obtained by modifying a polyolefin by block polymerization or graft polymerization with an acid component.

[0089] Examples of the polyolefin to be acid-modified include, specifically, 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 copolymers of propylene and ethylene), random copolymers of polypropylene (e.g., random copolymers of propylene and ethylene); propylene-α-olefin copolymers; and terpolymers of ethylene-butene-propylene. Among these, polypropylene is preferred. The polyolefin resin in the case of a copolymer may be a block copolymer or a random copolymer. These polyolefin-based resins may be used alone or in combination of two or more.

[0090] In addition, as the acid-modified polyolefin, a copolymer obtained by copolymerizing a polar molecule such as acrylic acid or methacrylic acid with the above polyolefin, or a polymer such as a crosslinked polyolefin can also be used. Examples of the acid component used for acid modification include carboxylic acids such as maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, and itaconic anhydride, or their anhydrides.

[0091] The acid-modified polyolefin may be an acid-modified cyclic polyolefin. The acid-modified cyclic polyolefin is a polymer obtained by copolymerizing a part of the monomers constituting the cyclic polyolefin by replacing it with an acid component, or by block polymerization or graft polymerization of an acid component onto the cyclic polyolefin. The cyclic polyolefin to be acid-modified is the same as described above. Also, the acid component used for acid modification is the same as the acid component used for the modification of the above polyolefin.

[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 of only one layer, or may be formed of two or more layers of the same or different resins.

[0094] Also, the heat-sealable resin layer 4 may contain a lubricant or the like as necessary. When the heat-sealable resin layer 4 contains a lubricant, the moldability of the exterior material for the power 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.

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

[0096] When a lubricant is present on the surface of the heat-sealable resin layer 4, the amount thereof is not particularly limited, but from the viewpoint of improving the moldability of the exterior material for the power storage device, it is preferably about 10 to 50 mg / m 2 and more preferably about 15 to 40 mg / m 2 .

[0097] The lubricant present on the surface of the heat-sealable resin layer 4 may be one obtained by exuding the lubricant contained in the resin constituting the heat-sealable resin layer 4, or may be one obtained by applying a lubricant to the surface of the heat-sealable resin layer 4.

[0098] Moreover, the thickness of the heat-sealable resin layer 4 is not particularly limited as long as the heat-sealable resin layers can exhibit the function of heat-sealing to seal the power storage device element. For example, it can be about 100 μm or less, preferably about 85 μm or less, and more preferably about 15 to 85 μm. In addition, for example, when the thickness of the adhesive layer 5 described later is 10 μm or more, the thickness of the heat-sealable resin layer 4 is preferably about 85 μm or less, and more preferably about 15 to 45 μm. For example, when the thickness of the adhesive layer 5 described later is less than 10 μm or when the adhesive layer 5 is not provided, the thickness of the heat-sealable resin layer 4 is preferably about 20 μm or more, and more preferably about 35 to 85 μm.

[0099] The heat-sealable resin layer 4 is preferably formed by melt extrusion molding. Further, when having the adhesive layer 5 described later, it is preferable that the adhesive layer 5 and the heat-sealable resin layer 4 are formed by melt co-extrusion molding. In the present disclosure, it is preferable to set the cooling condition of the molten resin forming the heat-sealable resin layer 4 to a rapid cooling condition to suppress the crystal growth of polyethylene in polypropylene. Thereby, in the cross-sectional image, with respect to the total number of island portions of the sea-island structure, the ratio of the total number of island portions having an area of 0.02 μm 2 or less to the total number of island portions is 80. 0% or more can be adjusted. For example, as described above, while appropriately adjusting the blending ratio of polypropylene and polyethylene contained in the heat-sealable resin layer 4, when forming the heat-sealable resin layer 4 by melt extrusion molding or the like, the cooling condition of the molten resin (the molten resin forming the heat-sealable resin layer) by a cooling roll (a roll that cools while conveying a sheet formed from the molten resin) is set to a rapid cooling condition (for example, setting the temperature difference between the surface temperature of the melt-extruded heat-sealable resin layer and the cooling roll to 70 ° C or more). By suppressing the crystal growth of polyethylene in polypropylene, in the cross-sectional image, with respect to the total number of island portions of the sea-island structure, the ratio of the total number of island portions having an area of 0.02 μm 2It can be adjusted so that the ratio of the total number of the following island portions is 80.0% or more. When the adhesive layer 5 and the heat-sealable resin layer 4 are formed by melt coextrusion molding, it is preferable that the thickness of the adhesive layer 5 is 15 to 45 μm and the thickness of the heat-sealable resin layer 4 is 15 to 45 μm.

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

[0101] The adhesive layer 5 is formed of a resin capable of bonding the barrier layer 3 and the heat-sealable resin layer 4. As the resin used for forming the adhesive layer 5, for example, the same adhesives as those exemplified in the adhesive layer 2 can be used. In addition, the resin used for forming the adhesive layer 5 preferably contains a polyolefin backbone, and examples thereof include the polyolefins and acid-modified polyolefins exemplified in the aforementioned heat-sealable resin layer 4. That the resin constituting the adhesive layer 5 contains a polyolefin backbone can be analyzed by, for example, infrared spectroscopy, gas chromatography-mass spectrometry, etc., and the analysis method is not particularly limited. Further, when the resin constituting the adhesive layer 5 is analyzed by infrared spectroscopy, it is preferable that a peak derived from maleic anhydride is detected. For example, when measuring maleic anhydride-modified polyolefin by infrared spectroscopy, peaks derived from maleic anhydride are detected in the vicinity of a wave number of 1760 cm -1 in the vicinity and a wave number of 1780 cm -1 in the vicinity. However, if the degree of acid modification is low, the peak may become small and not be detected. In that case, it can be analyzed by nuclear magnetic resonance spectroscopy.

[0102] From the viewpoint of firmly bonding the barrier layer 3 and the heat-sealable resin layer 4, the adhesive layer 5 preferably contains an acid-modified polyolefin. As the acid-modified polyolefin, polyolefin modified with a carboxylic acid or its anhydride, polypropylene modified with a carboxylic acid or its anhydride, maleic anhydride-modified polyolefin, and maleic anhydride-modified polypropylene are particularly preferable.

[0103] Furthermore, from the viewpoint of making the exterior material for a power storage device excellent in shape stability after molding while reducing the thickness of the exterior material for a power storage device, the adhesive layer 5 is more preferably a cured product of a resin composition containing an acid-modified polyolefin and a curing agent. Examples of the acid-modified polyolefin preferably include those described above.

[0104] Also, the adhesive layer 5 is preferably a cured product of a resin composition containing an acid-modified polyolefin and at least one selected from the group consisting of a compound having an isocyanate group, a compound having an oxazoline group, and a compound having an epoxy group, and particularly preferably a cured product of a resin composition containing an acid-modified polyolefin and at least one selected from the group consisting of a compound having an isocyanate group and a compound having an epoxy group. Further, 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 the polyester, for example, an amide ester resin is preferable. The 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 containing at least one of these resins and the acid-modified polyolefin. When unreacted substances of curing agents such as a compound having an isocyanate group, a compound having an oxazoline group, and an epoxy resin remain in the adhesive layer 5, the presence of the unreacted substances can be confirmed by a method selected from, for example, infrared spectroscopy, Raman spectroscopy, time-of-flight secondary ion mass spectrometry (TOF-SIMS), and the like.

[0105] Further, from the viewpoint of further enhancing the adhesion between the barrier layer 3 and the adhesive layer 5, the adhesive layer 5 is preferably a cured product of a resin composition containing a curing agent having at least one selected from the group consisting of an oxygen atom, a heterocyclic ring, a C═N bond, and a C—O—C bond. Examples of the curing agent having a heterocyclic ring include a curing agent having an oxazoline group, a curing agent having an epoxy group, and the like. Examples of the curing agent having a C═N bond include a curing agent having an oxazoline group, a curing agent having an isocyanate group, and the like. Examples of the curing agent having a C—O—C bond include a curing agent having an oxazoline group, a curing agent having an epoxy group, polyurethane, and the like. Whether 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] The compound having an isocyanate group is not particularly limited, but from the viewpoint of effectively enhancing the adhesion between the barrier layer 3 and the adhesive layer 5, a polyfunctional isocyanate compound is preferably used. The polyfunctional isocyanate compound is not particularly limited as long as it has two or more isocyanate groups. Specific examples of the polyfunctional isocyanate-based curing agent include pentane diisocyanate (PDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), those obtained by polymerizing or nurating these, mixtures thereof, and copolymers with other polymers. Further, adducts, burettes, isocyanurates, and the like can be mentioned.

[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, more preferably in the range of 0.5 to 40% by mass, in the resin composition constituting the adhesive layer 5. Thereby, the adhesion between the barrier layer 3 and the adhesive layer 5 can be effectively enhanced.

[0108] The compound having an oxazoline group is not particularly limited as long as it is a compound having an oxazoline skeleton. Specific examples of the compound having an oxazoline group include those having a polystyrene main chain and those having an acrylic main chain. Commercially available products include, for example, the Epocros 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, more preferably in the range of 0.5 to 40% by mass, in the resin composition constituting the adhesive layer 5. Thereby, the adhesion between the barrier layer 3 and the adhesive layer 5 can be effectively enhanced.

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

[0111] Specific examples of the epoxy resin include glycidyl ether derivatives of trimethylolpropane, bisphenol A diglycidyl ether, modified bisphenol A diglycidyl ether, novolak glycidyl ether, glycerin polyglycidyl ether, polyglycerin polyglycidyl ether, and the like. The epoxy resin may be used alone or in combination of two or more.

[0112] Regarding the proportion of the epoxy resin in the adhesive layer 5, it 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 in the resin composition constituting the adhesive layer 5. Thereby, the adhesion between the barrier layer 3 and the adhesive layer 5 can be effectively enhanced.

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

[0114] Regarding the proportion of the polyurethane in the adhesive layer 5, it 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 in the resin composition constituting the adhesive layer 5. Thereby, the adhesion between the barrier layer 3 and the adhesive layer 5 can be effectively enhanced in an atmosphere where components that induce corrosion of the barrier layer such as an electrolytic solution are present.

[0115] In addition, when the adhesive layer 5 is a cured product of a resin composition containing at least one selected from the group consisting of a compound having an isocyanate group, a compound having an oxazoline group, and an epoxy resin, and the acid-modified polyolefin, the acid-modified polyolefin functions as a main component, and the compound having an isocyanate group, the compound having an oxazoline group, and the compound having an epoxy group each function as a curing agent.

[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, about 5 μm or less. Also, 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, about 15 μm or more. As the range of the thickness, preferably, it is about 0.1 to 50 μm, about 0.1 to 45 μm, about 0.1 to 30 μm, about 0.1 to 20 μm, about 0.1 to 5 μm, about 0.5 to 50 μm, about 0.5 to 45 μm, about 0.5 to 30 μm, about 0.5 to 20 μm, about 0.5 to 5 μm, about 5 to 50 μm, about 5 to 45 μm, about 5 to 30 μm, about 5 to 20 μm, about 10 to 50 μm, about 10 to 45 μm, about 10 to 30 μm, about 10 to 20 μm, about 15 to 50 μm, about 15 to 45 μm, about 15 to 30 μm, about 15 to 20 μm, etc.

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

[0118] [Surface coating layer 6] The exterior material for the power storage device of the present disclosure may be provided with a surface coating layer 6, if necessary, on the upper side of the base material layer 1 (the side opposite to the barrier layer 3 of the base material layer 1), for the purpose of improving at least one of design, electrolyte resistance, scratch resistance, moldability, etc. The surface coating layer 6 is a layer located on the outermost layer side of the exterior material for the power storage device when the power storage device is assembled using the exterior material for the power storage device.

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

[0120] When the resin forming the surface coating layer 6 is a curable resin, the resin may be either a one-component curable type or a two-component curable type, but preferably a two-component curable type. Examples of the two-component curable resin include two-component curable polyurethane, two-component curable polyester, two-component curable epoxy resin, etc. Among these, two-component curable polyurethane is preferable.

[0121] Examples of the two-component curable polyurethane include polyurethane containing a main agent containing a polyol compound and a curing agent containing an isocyanate compound. Preferably, a two-component curable polyurethane using a polyol such as polyester polyol, polyether polyol, and acrylic polyol as the main agent and an aromatic or aliphatic polyisocyanate as the curing agent can be mentioned. In addition, as the polyol compound, it is preferable to use a polyester polyol having a hydroxyl group not only at the terminal of the repeating unit but also in the side chain. Since the surface coating layer 6 is formed of polyurethane, excellent electrolyte resistance is imparted to the exterior material for the power storage device.

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

[0123] The additives may be either inorganic or organic substances. Also, the shape of the additives is not particularly limited, and examples include spherical, fibrous, plate-like, amorphous, scaly, etc.

[0124] Specific examples of the 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 nanotube, high melting point nylon, acrylate resin, crosslinked acrylic, crosslinked styrene, crosslinked polyethylene, benzoguanamine, gold, aluminum, copper, nickel, etc. The additives may be used alone or in combination of two or more. Among these additives, silica, barium sulfate, and titanium oxide are preferably mentioned from the viewpoints of dispersion stability and cost. Also, various surface treatments such as insulation treatment and high dispersibility treatment may be performed on the surface of the additives.

[0125] The method for forming the surface coating layer 6 is not particularly limited, and examples include a method of applying a resin for forming the surface coating layer 6. When adding additives to the surface coating layer 6, a resin mixed with the additives may be applied.

[0126] The thickness of the surface coating layer 6 is not particularly limited as long as the above-described functions of the surface coating layer 6 are exhibited. For example, it is about 0.5 to 10 μm, preferably about 1 to 5 μm.

[0127] 3. Manufacturing method of the exterior material for the power storage device The manufacturing method of the exterior material for a power storage device is not particularly limited as long as a laminate in which each layer included in the exterior material for a power storage device of the present invention is laminated can be obtained. For example, a method including a step of laminating at least a base material layer 1, a barrier layer 3, and a heat-sealable resin layer 4 in this order from the outside to the inside can be mentioned. Specifically, it includes a step of laminating at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order to obtain a laminate. The heat-sealable resin layer contains polypropylene and polyethylene. Regarding a cross-section in a direction parallel to TD of the heat-sealable resin layer and in the thickness direction y, a sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope. In the cross-sectional image, the ratio of the total number of the following island portions to the total number of the island portions of the sea-island structure is 80.0% or more. This is a manufacturing method of an exterior material for a power storage device. 2 The manufacturing method of the exterior material for a power storage device is as follows. As an example, first, a laminate (hereinafter, sometimes referred to as "laminate A") in which a base material layer 1, an adhesive layer 2, and a barrier layer 3 are laminated in this order is formed. The formation of laminate A can be specifically performed by applying an adhesive used for forming the adhesive layer 2 on the base material layer 1 or on the barrier layer 3 whose surface is chemically converted as necessary by a coating method such as a gravure coating method or a roll coating method, drying, and then laminating the barrier layer 3 or the base material layer 1 and curing the adhesive layer 2 by a dry lamination method.

[0128] As an example of the manufacturing method of the exterior material for a power storage device of the present invention, it is as follows. First, a laminate (hereinafter, sometimes referred to as "laminate A") in which a base material layer 1, an adhesive layer 2, and a barrier layer 3 are laminated in this order is formed. The formation of laminate A can be specifically performed by applying an adhesive used for forming the adhesive layer 2 on the base material layer 1 or on the barrier layer 3 whose surface is chemically converted as necessary by a coating method such as a gravure coating method or a roll coating method, drying, and then laminating the barrier layer 3 or the base material layer 1 and curing the adhesive layer 2 by a dry lamination method.

[0129] Next, a heat-sealable resin layer 4 is laminated on the barrier layer 3 of the laminate A. When directly laminating the heat-sealable resin layer 4 on the barrier layer 3, it may be laminated on the barrier layer 3 of the laminate A by methods such as the thermal lamination method or the extrusion lamination method. When an adhesive layer 5 is provided between the barrier layer 3 and the heat-sealable resin layer 4, for example, (1) a method of laminating by extruding the adhesive layer 5 and the heat-sealable resin layer 4 on the barrier layer 3 of the laminate A (co-extrusion lamination method, tandem lamination method), (2) separately forming a laminate in which the adhesive layer 5 and the heat-sealable resin layer 4 are laminated, and laminating this on the barrier layer 3 of the laminate A by the thermal lamination method, or forming a laminate in which the adhesive layer 5 is laminated on the barrier layer 3 of the laminate A and laminating this with the heat-sealable resin layer 4 by the thermal lamination method, (3) a method of bonding the laminate A and the heat-sealable resin layer 4 through the adhesive layer 5 while pouring the molten adhesive layer 5 between the barrier layer 3 of the laminate A and the heat-sealable resin layer 4 previously formed in a sheet shape (sandwich lamination method), (4) a method of laminating by solution coating and drying an adhesive for forming the adhesive layer 5 on the barrier layer 3 of the laminate A, and further by baking or the like, and laminating the heat-sealable resin layer 4 previously formed in a sheet shape on this adhesive layer 5 can be mentioned.

[0130] When providing the surface coating layer 6, the surface coating layer 6 is laminated on the surface of the base material layer 1 opposite to the barrier layer 3. The surface coating layer 6 can be formed, for example, by applying the above resin for forming the surface coating layer 6 to the surface of the base material layer 1. The order of the step of laminating the barrier layer 3 on the surface of the base material layer 1 and the step of laminating the surface coating layer 6 on the surface of the base material layer 1 is not particularly limited. For example, after forming the surface coating layer 6 on the surface of the base material layer 1, the barrier layer 3 may be formed on the surface of the base material layer 1 opposite to the surface coating layer 6.

[0131] As described above, a laminate is formed which comprises, in this order, a surface coating layer 6 provided as necessary / a base material layer 1 / an adhesive layer 2 provided as necessary / a barrier layer 3 / an adhesive layer 5 provided as necessary / a heat-sealable resin layer 4. However, in order to strengthen the adhesiveness of the adhesive layer 2 and the adhesive layer 5 provided as necessary, it may be further subjected to heat treatment.

[0132] In the exterior material for a power storage device, each layer constituting the laminate may be subjected to a surface activation treatment such as corona treatment, blasting treatment, oxidation treatment, ozone treatment, etc. as necessary to improve the processability. For example, by subjecting the surface of the base material layer 1 on the side opposite to the barrier layer 3 to corona treatment, the printability of the ink on the surface of the base material layer 1 can be improved.

[0133] 4. Use of the exterior material for the power storage device The exterior material for a power storage device of the present disclosure is used for a package for sealing and housing power storage device elements such as a positive electrode, a negative electrode, and an electrolyte. That is, a power storage device can be formed by housing a power storage device element including at least a positive electrode, a negative electrode, and an electrolyte in a package formed by the exterior material for a power storage device of the present disclosure.

[0134] Specifically, a power storage device element including at least a positive electrode, a negative electrode, and an electrolyte is covered with the exterior material for a power storage device of the present disclosure in a state where metal terminals connected to each of the positive electrode and the negative electrode protrude outward so that a flange portion (a region where the heat-sealable resin layers contact each other) can be formed at the periphery of the power storage device element, and the heat-sealable resin layers of the flange portion are heat-sealed and sealed, thereby providing a power storage device using the exterior material for a power storage device. When housing a power storage device element in a package formed by the exterior material for a power storage device of the present disclosure, the package is formed such that the heat-sealable resin portion of the exterior material for a power storage device of the present disclosure is on the inner side (the surface in contact with the power storage device element).

[0135] The exterior material for a power storage device of the present disclosure can be suitably used for power storage devices such as batteries (including capacitors, condensers, etc.). Further, the exterior material for a power storage device of the present disclosure can be used for either a primary battery or a secondary battery, but is preferably a secondary battery. There is no particular limitation on the type of secondary battery to which the exterior material for a power storage device of the present disclosure is applied. For example, 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, condensers, etc. can be mentioned. Among these secondary batteries, lithium-ion batteries and lithium-ion polymer batteries can be mentioned as suitable application targets for the exterior material for a power storage device of the present disclosure.

Examples

[0136] Examples and comparative examples are shown below to explain the present disclosure in detail. However, the present disclosure is not limited to the examples.

[0137] <Manufacture of exterior material for power storage device> Examples 1, 2 and Comparative Examples 1, 2 A polyethylene terephthalate (PET) film (thickness 12 μm) and a stretched nylon (ONy) film (thickness 15 μm) were prepared. A two-component urethane adhesive (a polyol compound and an aromatic isocyanate compound) was applied to the PET film (3 μm), and it was adhered to the ONy film to form a base material layer. Also, as a barrier layer, an aluminum alloy foil (JIS H4160:1994 A8021H-O (thickness 40 μm)) was prepared. Next, a two-component urethane adhesive (a polyol compound and an aromatic isocyanate compound) was applied to one surface of the aluminum alloy foil, and an adhesive layer (thickness 3 μm) was formed on the barrier layer. Then, after laminating the adhesive layer on the barrier layer and the base material layer (ONy film side) by the dry lamination method, an aging treatment was carried out to produce a laminate of the base material layer / adhesive layer / barrier layer. Chemical conversion treatment was performed on both surfaces of the aluminum alloy foil. The chemical conversion treatment of the aluminum alloy foil was carried out by applying a treatment liquid composed of a phenol resin, a chromium fluoride compound, and phosphoric acid to both surfaces of the aluminum alloy foil by the roll coating method so that the coating amount of chromium was 10 mg / m 2 (dry mass), and baking was performed.

[0138] Next, maleic anhydride-modified polypropylene as an adhesive layer (thickness 40 μm) and random polypropylene (a composition of random polypropylene and polyethylene) as a heat-sealable resin layer (thickness 40 μm) were melt coextruded onto the barrier layer of each laminate obtained above, and the heat-sealable resin layer side was brought into contact with a cooling roll for cooling (each of the cooling conditions A or B described later). As a result, an adhesive layer / heat-sealable resin layer was laminated on the barrier layer, and an exterior material for a power storage device (total thickness 153 μm) in which a base material layer (including the adhesive, thickness 30 μm) / adhesive layer (3 μm) / barrier layer (40 μm) / adhesive layer (40 μm) / heat-sealable resin layer (40 μm) were laminated in order was obtained. In Example 2, the content of polyethylene contained in the heat-sealable resin layer was decreased compared with Example 1. Comparative Example 1 had an increased content of polyethylene contained in the heat-sealable resin layer compared with Example 1. Comparative Example 2 had the same composition as Example 1 for the heat-sealable resin layer and employed cooling condition B.

[0139] (Cooling conditions) The conditions for cooling by bringing the side of the heat-sealing resin layer into contact with the cooling roll are as follows. Table 1 shows the cooling conditions adopted in the examples and comparative examples. Cooling condition A: A condition for rapidly cooling the molten resin to form a heat-sealing resin layer (a condition for suppressing the crystal growth of polyethylene) by setting the difference between the temperature of the melt-extruded molten resin (the molten resin forming the heat-sealing resin layer) and the surface temperature of the cooling roll to 70°C or more. Cooling condition B: A condition for gently cooling the molten resin to form a heat-sealing resin layer by setting the difference between the temperature of the melt-extruded molten resin (the molten resin forming the heat-sealing resin layer) and the surface temperature of the cooling roll to 50°C or less.

[0140] (Measurement of the area and ratio of the number of island parts in the sea-island structure) An exterior material for a power storage device was embedded in a thermosetting epoxy resin and cured. Using a commercially available rotary microtome (LEICA EM UC6) and a glass knife, cross-sections were prepared in a direction parallel to TD and in the thickness direction. At this time, the cross-sections were prepared using a normal-temperature microtome. The heat-sealing resin layer of the exterior material for the power storage device was stained with ruthenium tetroxide for 3 hours together with the embedding resin. When staining, the resin expands and the sea-island structure cannot be confirmed near the cross-section, so the expanded part is trimmed with a microtome. Then, a stained section about 100 nm thick, taken from the cross-section after advancing about 1 to 2 μm, was observed as follows. For the stained section, a cross-sectional image was obtained using a field emission scanning electron microscope (S-4800 manufactured by Hitachi High-Technologies Corporation). The cross-sectional image was obtained within the range from the surface on the side opposite to the barrier layer side of the heat-sealing resin layer to the part with a thickness of 12.5% when the total thickness of the layers located inside the barrier layer was taken as 100%. The measurement conditions were an acceleration voltage of 30 kV, an emission current of 10 μA, a detector of a transmission detector, an inclination of no (0°), and an observation magnification of 5000 times. Next, using image processing software (image analysis software attached to the KEYENCE electron microscope VHX-5000) that can binarize the cross-sectional image, the island part and the sea part of the sea-island structure were binarized for the cross-sectional image. Specifically, the measurement was started under the condition of the brightness (standard) of the image analysis software. The extraction area (measurement range) was rectangular (7 μm in length and 13 μm in width), the imaging size was standard (1600×1200), the inclination angle was 0 degrees, the shooting mode was normal shooting, and the extraction target was the "dark area". Also, by automatic measurement, the missing extraction parts and the extra extraction parts were corrected, and the total area and the total number of the extracted parts (island parts) were measured. At this time, the area and the number of all the island parts existing in the extraction area were measured respectively. Using the obtained data, the ratio of the total area of all the island parts to the area of the measurement range of the cross-sectional image (total area of the island parts / area of the measurement range of the cross-sectional image), among all the island parts, the area is 2 The following ratio of the total number of island parts (0.01 μm 2 The following ratio of the total number of island parts / the total number of all the island parts), 0.02 μm 2 The following ratio of the total number of island parts (0.02 μm2 The ratio of the total number of the following island parts / the total number of all island parts), 0.03 μm 2 The ratio of the total number of the following island parts (0.03 μm 2 The ratio of the total number of the following island parts / the total number of all island parts), 0.30 μm 2 The ratio of the total number of the above island parts (0.30 μm 2 The ratio of the total number of the above island parts / the total number of all island parts), 0.15 μm 2 The ratio of the total number of the above island parts (0.15 μm 2 The ratio of the total number of the above island parts / the total number of all island parts) was calculated. Each result is shown in Table 1.

[0141] <Whitening due to molding> The exterior material for each power storage device was cut into a rectangle with a length (MD: Machine Direction) of 90 mm and a width (TD) of 150 mm to obtain test samples. The MD of the exterior material for the power storage device corresponds to the rolling direction (RD) of the aluminum alloy foil, and the TD of the exterior material for the power storage device corresponds to the TD of the aluminum alloy foil. This test sample was placed in an environment at 25°C and cold-formed (one-step drawing forming) with a pressing pressure (surface pressure) of 0.1 MPa so that the forming depth was 6.0 mm using a rectangular forming die (female die, the surface has a maximum height roughness (Rz nominal value) of 3.2 μm as specified in Table 2 of the reference surface roughness standard piece attached to JIS B 0659-1:2002. Corner R 2.0 mm, edge line R 1.0 mm) and a corresponding forming die (male die, the surface of the edge line part has a maximum height roughness (Rz nominal value) of 1.6 μm as specified in Table 2 of the reference surface roughness standard piece attached to JIS B 0659-1:2002, and the surface other than the edge line part has a maximum height roughness (Rz nominal value) of 3.2 μm as specified in Table 2 of the reference surface roughness standard piece attached to JIS B 0659-1:2002. Corner R 2.0 mm, edge line R 1.0 mm). At this time, the above test sample was placed on the female die for forming so that the heat-sealable resin layer side was located on the male die side. Also, the clearance between the male die and the female die was set to 0.3 mm. The heat-sealable resin layer of the test sample after forming was visually observed to confirm the presence or absence of whitening. Those without whitening were evaluated as A, those with slight whitening were evaluated as B, and those with clear whitening were evaluated as C. The results are shown in Table 1. Note that the part where whitening occurs is mainly around the side wall on the short side of the formed part.

[0142] <Insulativity> The exterior material for the energy storage device was cut into sheet pieces with a length (MD) of 160 mm and a width (TD) of 90 mm. Next, in an environment at 25°C, these sheet pieces were formed using a rectangular forming die (female die) with a diameter of 31.6 mm (MD) × 54.5 mm (TD). The surface has a maximum height roughness (the nominal value of Rz) of 3.2 μm as defined in Table 2 of the surface roughness standard piece for comparison in Annex 1 of JIS B 0659-1:2002. The corner has an R of 2.0 mm and the ridge line has an R of 1.0 mm. Corresponding to this, a forming die (male die) was used. The surface of the ridge line part has a maximum height roughness (the nominal value of Rz) of 1.6 μm as defined in Table 2 of the surface roughness standard piece for comparison in Annex 1 of JIS B 0659-1:2002. The surfaces other than the ridge line part have a maximum height roughness (the nominal value of Rz) of 3.2 μm as defined in Table 2 of the surface roughness standard piece for comparison in Annex 1 of JIS B 0659-1:2002. The corner has an R of 2.0 mm and the ridge line has an R of 1.0 mm. Cold forming (one-step drawing forming) was carried out with a pressing pressure (surface pressure) of 0.1 MPa so that the forming depth became 3.0 mm. Next, the formed sample pieces were folded in half twice in the MD direction so that the heat-sealable resin layers faced each other, and were cut so that the width from the forming part to the end on the MD side became 3 mm to obtain a formed body. The position of the forming part was set so that the distances between the forming part and both end sides in the TD of the sheet piece were 25 mm and 32 mm, respectively.

[0143] Next, a polyethylene terephthalate plate (PET plate) 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 of maleic anhydride-modified polypropylene) with a thickness of 100 μm and a width of 10 mm was wound around the central portion of the aluminum terminal. Using paper tape, the aluminum terminal was attached to the MD end of the PET plate, and the PET plate was inserted into the molding portion of the above-described molded body. At this time, the aluminum terminal protruded outside the molded body from the molding portion, and the tab film was positioned between the heat-fusible resin layers of the molded body. In this state, the edge of the molded body where the aluminum terminal protruded was heat-sealed under the conditions of a width of 3 mm, a surface pressure of 4.0 MPa, a seal temperature of 170 °C, and a seal time of 3.0 seconds. Next, one edge perpendicular to the heat-sealed edge was heat-sealed under the conditions of a width of 3 mm, a surface pressure of 1.0 MPa, a seal temperature of 170 °C, and a seal time of 3.0 seconds to form the molded body into a bag shape. Next, the bag-shaped molded body was stored in a dry room for one day, and an electrolytic solution (a solution obtained by mixing lithium hexafluorophosphate to a concentration of 1 mol / L in a solution mixed at a volume ratio of ethylene carbonate:diethyl carbonate:dimethyl carbonate = 1:1:1) was poured in from the remaining one open edge (opening), and the opening was heat-sealed under the conditions of a width of 3 mm, a surface pressure of 1.0 MPa, a seal temperature of 170 °C, and a seal time of 3.0 seconds to seal the electrolytic solution inside the molded body. Finally, with the heat-sealed edge on top, the molded body was stored in an environment at 60 °C for 6 hours. Next, between the last heat-sealed edge and the molding portion, along the molding portion, the heat-fusible resin layers were heat-sealed under the conditions of a width of 3 mm, a surface pressure of 1.0 MPa, a seal temperature of 170 °C, and a seal time of 3.0 seconds to obtain a test sample with the electrolytic solution sealed in the molding portion.

[0144] Next, for the obtained test samples, the insulation between the barrier layer of the test sample and the aluminum terminal was evaluated using a tester (Insulation Resistance Tester 3154 manufactured by Hioki Electric Co., Ltd.). First, 10 test samples were prepared respectively. 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 power storage device using alligator clips so as to be in contact. Next, a voltage of 25 V was applied between the testers, and those with a resistance value of 200 MΩ or more after 10 seconds were considered qualified (OK), and those with a resistance value of less than 200 MΩ after 10 seconds were considered unqualified (NG). Table 1 shows the number of unqualified (NG) test samples among the 10 test samples.

[0145]

Table 1

[0146] In Table 1, "PE" means polyethylene.

[0147] As is clear from the description in Table 1, for the exterior materials for power storage devices of Examples 1 and 2, in the cross-sectional image of the heat-sealable resin layer containing polypropylene and polyethylene, the ratio of the total number of island parts to the number of island parts among which the area is 0.02 μm 2 of the following total number of island parts is 80. 0% or more, and whitening due to molding and reduction in insulation are effectively suppressed.

[0148] As described above, the present disclosure provides an invention in the following aspects. Item 1. It is composed of a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside, the heat-sealable resin layer contains polypropylene and polyethylene, for the cross-section in the direction parallel to TD and the thickness direction of the heat-sealable resin layer, an island structure is observed in the cross-sectional image obtained using a scanning electron microscope, The cross-sectional image is a cross-sectional image obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion having a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is taken as 100%. In the cross-sectional image, the ratio of the total number of the island portions of the sea-island structure to the total number of the island portions having an area of 0.02 μm 2 The following ratio of the total number of the island portions is 80.0% or more. An exterior material for a power storage device. Item 2. In the cross-sectional image of the heat-sealable resin layer, the ratio of the total area of the island portions of the sea-island structure to the area of the measurement range of the cross-sectional image is 12.0% or less. The exterior material for a power storage device according to Item 1. Item 3. In the cross-sectional image of the heat-sealable resin layer, the ratio of the total number of the island portions of the sea-island structure to the total number of the island portions having an area of 0.03 μm 2 The following ratio of the total number of the island portions is 90.0% or more. The exterior material for a power storage device according to Item 1 or 2. Item 4. In the cross-sectional image of the heat-sealable resin layer, the ratio of the total number of the island portions of the sea-island structure to the total number of the island portions having an area of 0.01 μm 2 The following ratio of the total number of the island portions is 50.0% or more. The exterior material for a power storage device according to any one of Items 1 to 3. Item 5. In the cross-sectional image of the heat-sealable resin layer, the ratio of the total number of the island portions of the sea-island structure to the total number of the island portions having an area of 0.30 μm 2 The following ratio of the total number of the island portions is 1.0% or less. The exterior material for a power storage device according to any one of Items 1 to 4. Item 6. An adhesive layer is provided between the barrier layer and the heat-sealable resin layer. The exterior material for a power storage device according to any one of Items 1 to 5. Item 7. The thickness of the adhesive layer is 5 μm or more. The exterior material for a power storage device according to Item 6. Item 8. A step of obtaining a laminate by laminating at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside is provided. The heat-sealable resin layer contains polypropylene and polyethylene. In the cross-section parallel to TD of the heat-sealable resin layer and in the thickness direction, an island structure was observed in the cross-sectional image obtained using a scanning electron microscope. The cross-sectional image was obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion with a thickness of 12.5% when the total thickness of the layers located inside the barrier layer was taken as 100%. In the cross-sectional image, the ratio of the total number of the following island portions to the total number of island portions in the island structure, where the area of the island portion is 0.02 μm 2 A method for manufacturing an exterior material for a power storage device, wherein the ratio is 80.0% or more. Item 9. A power storage device, wherein a power storage device element including at least a positive electrode, a negative electrode, and an electrolyte is housed in a package formed of the exterior material for a power storage device according to any one of Items 1 to 7.

Explanation of Reference Numerals

[0149] 1 Substrate layer 2 Adhesive layer 3 Barrier layer 4 Heat-sealable resin layer 5 Adhesive layer 6 Surface coating layer 10 Exterior material for a power storage device

Claims

1. It is composed of a laminate including at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside, the heat-sealable resin layer contains polypropylene and polyethylene, a sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope for a cross-section in a direction parallel to the TD of the heat-sealable resin layer and in the thickness direction, the cross-sectional image is a cross-sectional image obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion with a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is taken as 100%, In the cross-sectional image, the ratio of the total number of island portions having an area of 0.02 μm 2 or less among the island portions to the total number of the island portions of the sea-island structure is 80.0% or more. An exterior material for a power storage device.

2. The exterior material for a power storage device according to claim 1, wherein in the cross-sectional image of the heat-sealable resin layer, the ratio of the total area of the island portions of the sea-island structure to the area of the measurement range of the cross-sectional image is 12.0% or less.

3. In the cross-sectional image of the heat-sealing resin layer, the ratio of the total number of the island portions of the sea-island structure to the total number of the island portions having an area of 0.03 μm 2 The exterior material for a power storage device according to claim 1 or 2, wherein the ratio of the total number of the following island portions is 90.0% or more.

4. In the cross-sectional image of the heat-fusible resin layer, 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 0.01 μm 2 The exterior material for a power storage device according to any one of claims 1 to 3, wherein the ratio of the total number of the following island portions is 50.0% or more.

5. In the cross-sectional image of the heat-sealing resin layer, the ratio of the total number of island portions having an area of 0.30 μm 2 or more to the total number of island portions in the sea-island structure is 1.0% or less. The exterior material for a power storage device according to any one of claims 1 to 4.

6. The exterior material for a power storage device according to any one of claims 1 to 5, further comprising an adhesive layer between the barrier layer and the heat-sealable resin layer.

7. The exterior material for a power storage device according to claim 6, wherein the thickness of the adhesive layer is 5 μm or more.

8. It includes a step of obtaining a laminate by laminating at least a base material layer, a barrier layer, and a heat-sealable resin layer in this order from the outside to the inside, the heat-sealable resin layer contains polypropylene and polyethylene, a sea-island structure is observed in a cross-sectional image obtained using a scanning electron microscope for a cross-section in a direction parallel to the TD of the heat-sealable resin layer and in the thickness direction, the cross-sectional image is a cross-sectional image obtained within a range from the surface on the side opposite to the barrier layer side of the heat-sealable resin layer to a portion with a thickness of 12.5% when the total thickness of the layers located inside the barrier layer is taken as 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 is 80.0% or more. A method for manufacturing an exterior material for a power storage device.

9. A power storage device, wherein a power storage device element including at least a positive electrode, a negative electrode, and an electrolyte is housed in a package formed of the exterior material for a power storage device according to any one of claims 1 to 7.

Images