Battery packaging material with excellent long-term electrolyte resistance

Abstract

Disclosed is a battery packaging material with excellent long-term electrolyte resistance, the material having a laminated structure of an outer layer made of a heat-resistant resin film, a barrier layer including a metal foil, and an inner layer made of a composition comprising a thermoplastic polyolefin, wherein excellent adhesive strength is imparted to an adhesive layer laminated between the barrier layer and the inner layer. The present invention provides the battery packaging material having a laminated structure of an outer layer made of a heat-resistant resin film, a barrier layer including a metal foil, and an inner layer made of a composition comprising a thermoplastic polyolefin, wherein a first adhesive layer is further laminated between the barrier layer and the inner layer, and the first adhesive layer comprises 30-70 wt% of a polypropylene, 20 wt% or less of a polyethylene, 10-45 wt% of a propylene-based elastomer and 1-10 wt% of an acid-modified polypropylene.

Description

Battery packaging material with excellent long-term electrolytic resistance

[0001] The present invention relates to a packaging material for batteries, and more specifically, to a packaging material for batteries having a structure in which an outer layer, a barrier layer including a metal foil, and an inner layer are laminated.

[0002] This application claims priority and interest to Korean Patent Application No. 10-2024-0160918 filed on November 13, 2024, the full text of which is incorporated herein by reference.

[0003] A secondary battery is a device that converts external electrical energy into chemical energy to store electricity, and then converts that chemical energy back into electrical energy to supply it when needed. It typically refers to a lithium-ion battery and is used in fields such as portable terminals like laptops, smartphones, tablet PCs, and video cameras; electric vehicles, including hybrid cars; smart grids for energy storage; robots; and satellites.

[0004] The packaging material used for these secondary batteries is an outer casing that stores internal components and protects battery cells from external shocks, and is an important component material that determines the battery's lifespan characteristics and operational sustainability.

[0005] Conventional packaging materials for secondary batteries include cylindrical (can-type), prismatic, and pouch types, each with its own advantages and disadvantages. First, cylindrical types allow for mass production in standardized sizes and offer cost advantages, but they have low space efficiency when stacked. Second, prismatic types are more space-efficient and lighter than cylindrical types, but they have the disadvantages of difficult thermal management and higher production costs. The pouch type is used due to its advantages, such as shape diversification that allows for flexible battery deformation, lightweight design, high space utilization, and good packaging efficiency.

[0006] A pouch for a secondary battery is, for example, composed mainly of an outer layer, a barrier layer, and an inner layer (heat sealing layer), and has a multilayer structure with a separate adhesive layer interposed between each layer. The inner layer serves as a sealing agent when the multilayer film is manufactured into a pouch form; since it must possess heat sealability, it is a polyolefin-based film layer composed of polyethylene (PE), polypropylene (PP), or copolymers thereof. Additionally, for the barrier layer, aluminum, a metal foil, is mainly used as a substrate to provide not only mechanical strength but also a moisture and oxygen barrier. Furthermore, functional polymer films such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), nylon, and liquid crystal polymer (LCP), which have excellent pinhole resistance, gas barrier properties, heat resistance, and mechanical strength, are used as the film material constituting the outer layer.

[0007] As such, while cell pouches (pouch-shaped packaging materials) offer advantages in terms of shape diversification and lightweight design compared to conventional cylindrical and can types, the use of soft, multi-layer film materials for packaging makes them susceptible to damage from various factors during different manufacturing processes. For instance, during the process of housing the electrode assembly inside the pouch, protruding parts such as electrode tabs or leads can cause damage, such as cracks, to the inner layers of the pouch. Furthermore, heat applied during the sealing (heat sealing) process can cause pinholes or internal damage, leading to cracks. If the aluminum layer is exposed due to such damage, adverse reactions can occur due to its reactivity with the electrolyte. The aluminum layer exposed to the electrolyte can chemically react with oxygen or moisture in the electrolyte that has penetrated or diffused into the battery, leading to corrosion. This results in the generation of corrosive gases, causing a swelling phenomenon that expands the interior of the battery, presenting a significant problem. Specifically, lithium hexafluorophosphate (LiPF6) can react with water and oxygen to produce hydrofluoric acid (HF), a corrosive gas. This hydrofluoric acid can react with aluminum to cause a rapid exothermic reaction, and if it is adsorbed onto the aluminum surface as a secondary reaction and penetrates into the tissue, the brittleness of the tissue increases, causing cracks in the pouch film to occur even with micro-impacts. This leakage of the electrolyte can then cause lithium to react with the atmosphere, leading to ignition.

[0008] Due to these factors, packaging materials for cell pouches are required to possess various physical properties, such as mechanical flexibility and strength, high barrier properties, heat seal strength, chemical resistance to electrolytes (electrolytic resistance), electrical insulation, and thermal stability.

[0009] Currently, Japanese companies hold more than 70% of the global market for cell pouch films, and domestic secondary battery manufacturers also mostly use Japanese products. Given this high dependence on foreign sources for secondary battery materials, the localization of pouch materials is urgent; however, research is difficult due to the technical complexity of developing adhesives for the inner layer (heat seal layer) of the pouch film, particularly the adhesive between the inner layer (heat seal layer) and the barrier layer (aluminum layer). Furthermore, as high-capacity development is currently underway for batteries used in electric vehicles and Energy Storage Systems (ESS), standards for the physical properties of cell pouch materials—which serve as battery packaging—are being strengthened, and greater stability is required.

[0010] Korean Registered Patent No. 1629304 discloses an adhesive composition capable of forming a laminate that can maintain high adhesive strength even when immersed in an electrolyte solution, but it adds a separate epoxy curing agent to the adhesive composition and limits the evaluation of electrolytic resistance to immersion in an electrolyte solution at 85°C for a maximum of 4 weeks.

[0011] Accordingly, the present invention aims to provide a battery packaging material having excellent long-term electrolytic resistance by imparting excellent adhesive strength to an adhesive layer laminated between the barrier layer and the inner layer, in a laminated structure comprising an outer layer made of a heat-resistant resin film; a barrier layer made of a metal foil; and an inner layer made of a composition made of a thermoplastic polyolefin.

[0012] To solve the above problem, the present invention provides a packaging material for a battery comprising a laminated structure of an outer layer made of a heat-resistant resin film; a barrier layer made of a metal foil; and an inner layer made of a composition made of a thermoplastic polyolefin, wherein a first adhesive layer is further laminated between the barrier layer and the inner layer, and the first adhesive layer comprises 30 to 70 weight% polypropylene, 20 weight% or less polyethylene, 10 to 45 weight% propylene-based elastomer, and 1 to 10 weight% acid-modified polypropylene.

[0013] In addition, the present invention provides a packaging material for batteries characterized by the metal foil comprising one or more metals selected from the group consisting of aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), tin (Sn), zinc (Zn), indium (In), and tungsten (W).

[0014] In addition, the above acid-modified polypropylene provides a battery packaging material characterized by having a maleic anhydride graft content of 0.1 to 10 weight%.

[0015] In addition, the above-mentioned propylene-based elastomer provides a packaging material for batteries characterized by having a melting point of 140°C or lower.

[0016] In addition, the above-mentioned propylene-based elastomer is a propylene-α-olefin copolymer, and is characterized by comprising a first propylene-based elastomer having an ethylene comonomer content of 5 to 30 weight% and a second propylene-based elastomer having a 1-butene comonomer content of 10 to 50 weight%, thereby providing a packaging material for a battery.

[0017] In addition, the present invention provides a packaging material for a battery characterized in that the thickness of the outer layer is 10 to 40 μm; the thickness of the barrier layer is 25 to 50 μm; the thickness of the first adhesive layer is 25 to 50 μm; and the thickness of the inner layer is 25 to 50 μm.

[0018] In addition, the above packaging material provides a battery packaging material characterized by having an interfacial peel strength of 15 N / 15 mm or more between the aluminum foil and the first adhesive layer before loading, after loading with an electrolytic solvent, and after loading with an electrolyte, as measured according to the following method.

[0019] [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer Before Immersion]

[0020] For a sample cut to a length of 100 mm and a width of 15 mm after aging for one day under constant temperature and humidity conditions of 23±2℃ and 50±5% of a film laminated with PET (12 µm thickness), a second adhesive layer (3 µm thickness), nylon (15 µm thickness), a second adhesive layer (3 µm thickness), aluminum foil (40 µm thickness), the first adhesive layer (40 µm thickness), and a PP inner layer (40 µm thickness), the T-shaped peel strength at the interface between the aluminum foil and the first adhesive layer was measured using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min;

[0021] [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer After Electrolytic Solvent Immersion]

[0022] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a primary sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / EMC / DMC = 3 / 3 / 4 v / v part composition) at 85℃ for 1, 7, 28, and 56 days, and a secondary sample cut to a length of 100 mm and a width of 15 mm was measured for each sample using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min;

[0023] [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer After Electrolyte Immersion]

[0024] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a first sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / DEC / DMC=1 / 1 / 1 v / v part composition, containing LiPF61 M) at a temperature of 85℃ for 1, 7, 28, and 56 days, and a second sample cut to a length of 100 mm and a width of 15 mm was measured using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min for each sample, and the T-shaped peel strength of the interface between the aluminum foil and the first adhesive layer was measured.

[0025] According to the present invention, a battery packaging material comprising a laminated structure including an outer layer made of a heat-resistant resin film; a barrier layer made of a metal foil; and an inner layer made of a composition including a thermoplastic polyolefin, wherein the adhesive layer laminated between the barrier layer and the inner layer is composed of a polypropylene-based resin, and the polyethylene, propylene-based elastomer, and acid-modified polypropylene are composed of a specific composition, thereby stably securing the adhesive strength of the initial film and, in particular, providing a battery packaging material that achieves stable adhesive strength even in long-term electrolytic solvent and electrolyte loading evaluations in terms of long-term reliability.

[0026] The present invention will be described in detail below through preferred embodiments. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor may appropriately define the concepts of terms to best describe their invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention. Therefore, the configurations of the embodiments described in this specification are merely the most preferred embodiments of the present invention and do not represent all aspects of the technical spirit of the present invention; thus, it should be understood that various equivalents and modifications capable of replacing them may exist at the time of filing this application.

[0027]

[0028] The present invention discloses a packaging material for a lithium battery comprising a laminated structure including an outer layer made of a heat-resistant resin film; a barrier layer made of a metal foil; and an inner layer made of a composition including a thermoplastic polyolefin, wherein a first adhesive layer is further laminated between the barrier layer and the inner layer, and the first adhesive layer comprises 30 to 70 weight% polypropylene, 20 weight% or less polyethylene, 10 to 50 weight% propylene-based elastomer, and 1 to 10 weight% acid-modified polypropylene.

[0029] The outer layer is provided on a barrier layer containing a metal foil and is the outermost layer of a lithium battery packaging material that can be exposed to the outside. It is preferable that the outer layer be formed using a material having heat resistance, cold resistance, pinhole resistance, insulation, chemical resistance, moldability, etc., along with abrasion resistance, so as to protect the barrier layer containing the metal foil. The outer layer made of such a heat-resistant resin film may include a polyamide-based resin or a polyester-based resin. The polyamide-based resin may be nylon, which is advantageous for molding due to its high elongation, and the polyester-based resin may be polybutylene terephthalate (PBT) or polyethylene terephthalate (PET), which can achieve high chemical resistance, pinhole resistance, insulation, mechanical strength, etc.

[0030] The outer layer may have a thickness of approximately 10 to 40 μm, taking into account a sufficient degree of wear resistance, heat resistance, pinhole resistance, chemical resistance, moldability, insulation, etc. If the thickness of the outer layer is too thin, the moldability of the battery packaging material may be reduced due to insufficient strength of the outer layer. On the other hand, if it is too thick, the barrier layer including the inner layer and metal foil provided below the outer layer must be implemented with a relatively thin thickness, so problems such as reduced thermal adhesion strength and reduced peel strength between layers may occur in the battery packaging material. However, the thickness of the outer layer is not limited to the above range and may have an appropriate thickness depending on the application of the cell pouch to be implemented, for example, a thin-film cell pouch implemented with a total thickness of approximately 88 μm, a general-purpose cell pouch implemented with a total thickness of approximately 113 μm, or a medium-to-large cell pouch implemented with a total thickness of approximately 153 μm to 183 μm.

[0031] The barrier layer comprising the metal foil is intended to block the entry and exit of moisture or air from the outside and gas generated internally, and may come into contact with an inner layer and a first adhesive layer. The barrier layer comprising the metal foil may include a metal having gas barrier properties and moisture barrier properties, for example, one or more selected from the group consisting of aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), tin (Sn), zinc (Zn), indium (In), tungsten (W), etc. (a single metal or a mixture of single metals), or two or more alloys selected from these. As a preferred embodiment, the barrier layer comprising the metal foil may include aluminum (Al) or an aluminum alloy, taking into account moisture barrier properties, gas barrier properties, and formability. The barrier layer comprising the metal foil may have a thickness of about 25 to 80 μm to ensure a sufficient degree of gas barrier properties and moisture barrier properties. However, the thickness of the barrier layer including the metal foil is not limited to this, and may have an appropriate thickness depending on the intended use of the cell pouch to be implemented, that is, generally, a thin-film cell pouch implemented with a total thickness of about 88 μm, a standard-type cell pouch implemented with a total thickness of about 113 μm, or a medium-to-large-sized cell pouch implemented with a total thickness of about 153 μm to 183 μm.

[0032] It is desirable that the barrier layer containing the metal foil be chemically treated on at least one side, preferably on the inner side, and preferably on both sides, in order to stabilize adhesion and prevent dissolution or corrosion. Here, chemical treatment refers to a treatment that forms an acid-resistant film on the surface of the barrier layer containing the metal foil. Examples of chemical treatment include chromate treatment using chromate compounds such as chromium nitrate, chromium fluoride, chromium sulfate, chromium acetate, chromium oxalate, chromium diphosphate, acetylacetate chromate, chromium chloride, and potassium chromium sulfate; chromate treatment using phosphate compounds such as sodium phosphate, potassium phosphate, ammonium phosphate, and polyphosphate; and chromate treatment using an amino phenol polymer.

[0033] The above inner layer is a layer made of a composition including a thermoplastic polyolefin that contacts the electrolyte of the battery, corresponding to the innermost part of the battery packaging material, and thermal bonding is performed for the purpose of sealing the battery.

[0034] That is, in the case of the inner layer, since it must have heat-sealability as a layer that acts as a sealing agent when producing a multilayer film in the form of a pouch, it can be composed of polyolefins such as polyethylene (PE) and polypropylene (PP), or copolymers thereof.

[0035] The above inner layer may have a thickness of about 25 to 50 μm for sufficient thermal bonding characteristics, but is not limited thereto and may have an appropriate thickness depending on the intended use of the cell pouch to be implemented, for example, a thin-film cell pouch implemented with a total thickness of about 88 μm, a general-purpose cell pouch implemented with a total thickness of about 113 μm, or a medium-to-large cell pouch implemented with a total thickness of about 153 μm to 183 μm.

[0036] As a packaging material for secondary batteries, the pouch type uses a soft pouch as a container, so it may be damaged for various reasons during various processes. Therefore, the present invention aims to provide a battery packaging material with ensured stability by imparting excellent adhesive strength to a first adhesive layer laminated between a barrier layer and an inner layer. Specifically, the first adhesive layer is composed of a polypropylene-based resin, comprising polyethylene, a propylene-based elastomer, and acid-modified polypropylene in a specific composition.

[0037] The type of polypropylene that serves as the base resin in the first adhesive layer is not particularly limited, and for example, a propylene homopolymer, a propylene-based binary copolymer, a propylene-based terpolymer, a propylene block copolymer, etc., may be used. Preferably, a copolymer of propylene and one type of α-olefin other than ethylene or propylene may be used, and more preferably, a terpolymer of propylene, ethylene, and 1-butene may be used. In this case, when a preferred propylene-based terpolymer is applied, the ethylene and 1-butene content may be 2 to 4 weight% and 2.5 to 4.5 weight%, respectively.

[0038] Here, in order to maximize the long-term electrolytic resistance of the packaging material for batteries, the propylene homopolymer may be mixed with the propylene-based terpolymer as the polypropylene. At this time, the mixing ratio of the propylene-based terpolymer and the propylene homopolymer may be a weight ratio of 5:1 to 1:1, and preferably a weight ratio of 4:1 to 2:1.

[0039] In the first adhesive layer above, polypropylene is included in an amount of 30 to 70 weight%, preferably 35 to 65 weight%, and more preferably 40 to 60 weight%. If the polypropylene content is less than 30 weight%, it is difficult to mold during film manufacturing and the adhesion to the barrier layer including the metal foil is reduced, and if it exceeds 70 weight%, the adhesion to the barrier layer including the metal foil is reduced.

[0040] In addition, the polyethylene in the first adhesive layer plays a role in compensating for the neck-in phenomenon that occurs during extrusion molding.

[0041] Considering the compatibility and processability of the components constituting the first adhesive layer, the above polyethylene has a density of 0.900 to 0.940 g / cm³ 3 , preferably 0.910 to 0.930 g / cm³ 3 And, a melt index (190℃, 2.16 kg load) of 5 to 20 g / 10 min, preferably 10 to 15 g / 10 min can be used.

[0042] In the first adhesive layer above, polyethylene is included in an amount of 20 weight% or less, preferably 2 to 20 weight%, and more preferably 5 to 15 weight%. If the polyethylene content is too low, a necking phenomenon may occur during extrusion molding, and if it exceeds 20 weight%, the adhesion to the barrier layer containing the metal foil is reduced.

[0043] The acid-modified polypropylene in the first adhesive layer above is a resin added to increase the adhesion between the barrier layer containing the metal foil and the inner layer by imparting polar groups. This acid-modified polypropylene is a polymer in which an acid component, such as a carboxylic acid, is grafted onto polypropylene, and the acid component used for modification may be a carboxylic acid such as maleic acid, acrylic acid, itaconic acid, or crotonic acid, or an anhydride thereof.

[0044] In the present invention, the acid-modified polypropylene may preferably be a modified polypropylene grafted with a polar functional group, maleic anhydride, in an amount of 0.1 to 10 weight%, preferably 2 to 5 weight%. If the maleic anhydride graft content of the modified polypropylene is less than 0.1 weight%, the adhesion to the barrier layer including the metal foil may be reduced, and if it exceeds 10 weight%, fish eyes may occur due to the large amount of polar functional groups and low molecular weight may be generated, resulting in lower surface tension after corona surface treatment and reduced adhesion to the barrier layer.

[0045] In the first adhesive layer, acid-modified polypropylene is included in an amount of 1 to 10 weight%, preferably 2 to 8 weight%, and more preferably 3 to 7 weight%. If the acid-modified polypropylene content is less than 1 weight%, the improvement in adhesion to the barrier layer may not be satisfactory, and if it exceeds 10 weight%, the adhesion to the barrier layer may also decrease due to a large amount of polar functional groups.

[0046] In addition, the first adhesive layer includes a propylene-based elastomer to further improve the adhesive strength between the barrier layer containing a metal foil and the inner layer while reinforcing the soft properties of the multilayer film material pouch. Here, although the use of an ethylene-based elastomer could be considered as the elastomer, it was confirmed that the adhesive strength is significantly improved when a propylene-based elastomer is used in combination with other components constituting the first adhesive layer compared to when an ethylene-based elastomer is used.

[0047] At this time, when producing packaging materials through a lamination process of an outer layer, a barrier layer, and an inner layer, it is preferable to use a propylene-based elastomer with a melting point of 140°C or lower to increase productivity by enabling adhesive strength to be developed from a low temperature, and more preferably, one with a melting point of 60 to 140°C, and even more preferably 70 to 110°C.

[0048] In addition, the above-mentioned propylene-based elastomer may be used as a single type or a mixture of two or more types. In the present invention, it was confirmed that adhesive strength is maximized when a mixture is used of two types of propylene-α-olefin copolymers of a specific composition, wherein the first propylene-based elastomer has an ethylene comonomer content of 5 to 30 wt%, preferably 10 to 25 wt%, more preferably 13 to 20 wt%, and the second propylene-based elastomer has a 1-butene comonomer content of 10 to 50 wt%, preferably 15 to 45 wt%, more preferably 20 to 40 wt%. At this time, the density of the first propylene-based elastomer is 0.84 to 0.88 g / cm³. 3 It may be, and the density of the above 2-propylene-based elastomer is 0.88 to 0.92 g / cm³ 3 It may be. In addition, it is most preferable that the melting point of the first propylene-based elastomer is 100 to 110°C, and it is most preferable that the melting point of the second propylene-based elastomer is 70 to 80°C.

[0049] In the first adhesive layer, the propylene-based elastomer is included in an amount of 10 to 45 weight%, preferably 15 to 40 weight%, and more preferably 20 to 40 weight%. If the propylene-based elastomer content is less than 10 weight%, the effect of imparting soft properties to the packaging material and the degree of improvement in adhesion to the barrier layer are negligible, and if it exceeds 45 weight%, it is difficult to form during film manufacturing and the degree of improvement in adhesion to the barrier layer containing metal foil is negligible. In addition, when the first propylene-based elastomer and the second propylene-based elastomer are used in combination, it is preferable to use them in an amount of 5 to 20 weight% each, and more preferably 10 to 15 weight% each.

[0050] The first adhesive layer may have a thickness of about 25 to 50 μm to impart soft properties to the packaging material and improve sufficient adhesive strength, but is not limited thereto and may have an appropriate thickness depending on the intended use of the cell pouch to be implemented, for example, a thin-film cell pouch implemented with a total thickness of about 88 μm, a general-purpose cell pouch implemented with a total thickness of about 113 μm, or a medium-to-large cell pouch implemented with a total thickness of about 153 μm to 183 μm.

[0051] Meanwhile, in the present invention, a second adhesive layer may be further formed to bond the outer layer and the barrier layer including the metal foil. In this case, if the outer layer is composed of multiple layers, the second adhesive layer may be interposed between the outer layers.

[0052] The second adhesive layer is formed by an adhesive capable of bonding a barrier layer including an outer layer and a metal foil, and the adhesive used to form the second adhesive layer may be a two-component curing adhesive or a one-component curing adhesive. In addition, the adhesive mechanism of the adhesive used to form the second adhesive layer is not particularly limited and can be selected from any of the following: a chemical reaction type, a solvent volatilization type, a hot melt type, a hot pressing type, etc.

[0053] Examples of resin components of an adhesive that can be used to form the second adhesive layer include, for instance, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, polycarbonate, copolymer polyester; polyether adhesives; polyurethane adhesives; epoxy resins; phenolic resins; polyamide resins such as nylon 6, nylon 66, nylon 12, copolymer polyamide; polyolefin resins such as polyolefin, acid-modified polyolefin, metal-modified polyolefin; polyvinyl acetate resins; cellulose adhesives; (meth)acrylic resins; polyimide resins; amino resins such as urea resin and melamine resin; rubbers such as chloroprene rubber, nitrile rubber, and styrene-butadiene rubber; silicone resins; fluorinated ethylene propylene copolymers, etc. The adhesive components of these may be used as a single type or in combination of two or more types.

[0054] The thickness of the second adhesive layer may be, for example, 2 to 10 μm.

[0055] The method for manufacturing a packaging material for batteries according to the present invention is not particularly limited as long as a laminate can be obtained by laminating each layer of a predetermined composition, but the following method is exemplified.

[0056] First, a laminate (laminated A) is formed in which a barrier layer comprising an outer layer, a second adhesive layer, and a metal foil is laminated in sequence. Specifically, the formation of laminate A can be performed by a dry lamination method in which an adhesive used for forming the second adhesive layer is applied and dried by a coating method such as extrusion, gravure coating, or roll coating on a barrier layer comprising a metal foil with a surface treated with chemical treatment, and then the outer layer is laminated to cure the second adhesive layer.

[0057] Next, an inner layer is laminated onto a barrier layer containing a metal foil of laminate A. At this time, the first adhesive layer interposed between the barrier layer containing the metal foil and the inner layer may be laminated by, for example, a method (co-extrusion lamination method) in which the first adhesive layer and the inner layer are laminated onto a barrier layer containing a metal foil of laminate A.

[0058] The battery packaging material according to the present invention comprises a first adhesive layer laminated between a barrier layer and an inner layer, composed of a polypropylene-based resin, and composed of polyethylene, a propylene-based elastomer, and acid-modified polypropylene in a specific composition to improve adhesive strength and ensure stability. Specifically, the battery packaging material according to the present invention may have an interfacial peel strength of 15 N / 15 mm or more, measured according to the following method, before loading, after loading with an electrolytic solvent, and after loading with an electrolyte, between the aluminum foil and the first adhesive layer, and preferably 16 N / 15 mm or more.

[0059] [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer Before Immersion]

[0060] For a sample cut to a length of 100 mm and a width of 15 mm after aging for one day under constant temperature and humidity conditions of 23±2℃ and 50±5% of a film laminated with PET (12 µm thickness), a second adhesive layer (3 µm thickness), nylon (15 µm thickness), a second adhesive layer (3 µm thickness), aluminum foil (40 µm thickness), the first adhesive layer (40 µm thickness), and a PP inner layer (40 µm thickness), the T-shaped peel strength at the interface between the aluminum foil and the first adhesive layer was measured using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min;

[0061] [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer After Electrolytic Solvent Immersion]

[0062] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a primary sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / EMC / DMC = 3 / 3 / 4 v / v part composition) at 85℃ for 1, 7, 28, and 56 days, and a secondary sample cut to a length of 100 mm and a width of 15 mm was measured for each sample using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min;

[0063] [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer After Electrolyte Immersion]

[0064] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a first sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / DEC / DMC=1 / 1 / 1 v / v part composition, containing LiPF61 M) at a temperature of 85℃ for 1, 7, 28, and 56 days, and a second sample cut to a length of 100 mm and a width of 15 mm was measured using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min for each sample, and the T-shaped peel strength of the interface between the aluminum foil and the first adhesive layer was measured.

[0065] The present invention will be explained in more detail below through specific embodiments and comparative examples.

[0066]

[0067] Examples and Comparative Examples

[0068] Using the first adhesive layer resin of the composition in Table 1 below, specimens were prepared and physical properties were measured according to the following method, and the results are shown in Table 1 below.

[0069] (1) Method for measuring the interfacial peel strength between the aluminum foil and the first adhesive layer before loading

[0070] A film laminated with PET (12 μm thickness), a second adhesive layer (3 μm thickness), nylon (15 μm thickness), a second adhesive layer (3 μm thickness), aluminum foil (40 μm thickness), the first adhesive layer (40 μm thickness), and a PP inner layer (40 μm thickness) was aged for one day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity. Then, for a sample cut to a length of 100 mm and a width of 15 mm, the T-shaped peel strength of the interface between the aluminum foil and the first adhesive layer was measured at 23℃ at a test speed of 50 mm / min using a measuring device (universal testing machine, Instron).

[0071] (2) Method for measuring the interfacial peel strength between the aluminum foil and the first adhesive layer after immersion in an electrolytic solvent

[0072] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a first sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / EMC / DMC = 3 / 3 / 4 v / v part composition) at 85℃ for 1, 7, 28, and 56 days, and a second sample cut to a length of 100 mm and a width of 15 mm was tested using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min to measure the T-shaped peel strength at the interface between the aluminum foil and the first adhesive layer. Here, EC is ethylene carbonate, EMC is ethylmethyl carbonate, and DMC is dimethyl carbonate. The electrolytic solvent is a solvent that does not contain an electrolyte such as a lithium salt. Typically, electrolyte loading evaluations are conducted under relatively harsh conditions, but in this invention, the loading evaluation was performed under both conditions of the electrolytic solvent and the electrolyte.

[0073] (3) Method for measuring the interfacial peel strength between the aluminum foil and the first adhesive layer after immersion in the electrolyte

[0074] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a first sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (composition of EC / DEC / DMC = 1 / 1 / 1 v / v part, containing LiPF61 M) at a temperature of 85℃ for 1, 7, 28, and 56 days, and a second sample cut to a length of 100 mm and a width of 15 mm was tested using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min for each sample, and the T-shaped peel strength of the interface between the aluminum foil and the first adhesive layer was measured. Here, EC is ethylene carbonate, DEC is diethyl carbonate, and DMC is dimethyl carbonate.

[0075]

[0076]

[0077]

[0078] Referring to Table 1, it is confirmed that when the first adhesive layer laminated between the barrier layer and the inner layer according to the present invention is composed of a polypropylene-based resin, and polyethylene, a propylene-based elastomer, and acid-modified polypropylene are composed of a specific composition (Examples 1 to 11), the adhesive strength at the interface between the barrier layer and the first adhesive layer is significantly improved up to 56 days after immersion in an electrolytic solvent or electrolyte, thereby realizing excellent long-term electrolytic resistance. It can be confirmed that this effect is maximized when the propylene-based elastomer and polypropylene among the components constituting the first adhesive layer are composed of a specific mixed composition (Examples 8 to 11).

[0079] In this regard, it can be seen that when an ethylene-based elastomer is used (Comparative Example 1), when the propylene-based elastomer content does not reach a certain level (Comparative Example 2), or when the propylene-based elastomer content is excessive (Comparative Example 3), delamination occurs at the interface between the barrier layer and the first adhesive layer, or the interfacial adhesive strength is significantly lower than that of the above example, making it difficult to achieve long-term electrolytic resistance.

[0080]

[0081] Preferred embodiments of the present invention have been described in detail above. The description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without changing the technical concept or essential features of the present invention.

[0082] Accordingly, the scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning, scope, and equivalent concepts of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. A packaging material for a battery comprising a laminated structure comprising: an outer layer made of a heat-resistant resin film; a barrier layer including a metal foil; and an inner layer made of a composition including a thermoplastic polyolefin, wherein A first adhesive layer is further laminated between the above barrier layer and the inner layer, and A packaging material for a battery, characterized in that the first adhesive layer comprises 30 to 70 weight% polypropylene, 20 weight% or less polyethylene, 10 to 45 weight% propylene-based elastomer, and 1 to 10 weight% acid-modified polypropylene.

2. In Paragraph 1, A battery packaging material characterized in that the metal foil comprises one or more metals selected from the group consisting of aluminum (Al), iron (Fe), copper (Cu), nickel (Ni), tin (Sn), zinc (Zn), indium (In), and tungsten (W).

3. In Paragraph 1, The above acid-modified polypropylene is a battery packaging material characterized by having a maleic anhydride graft content of 0.1 to 10 weight%.

4. In Paragraph 1, A battery packaging material characterized by the above-mentioned propylene-based elastomer having a melting point of 140°C or lower.

5. In Paragraph 1, A battery packaging material characterized in that the above-mentioned propylene-based elastomer is a propylene-α-olefin copolymer comprising a first propylene-based elastomer having an ethylene comonomer content of 5 to 30 weight% and a second propylene-based elastomer having a 1-butene comonomer content of 10 to 50 weight%.

6. In Paragraph 1, A packaging material for a battery characterized in that the thickness of the outer layer is 10 to 40 μm; the thickness of the barrier layer is 25 to 50 μm; the thickness of the first adhesive layer is 25 to 50 μm; and the thickness of the inner layer is 25 to 50 μm.

7. In Paragraph 1, A battery packaging material characterized by the fact that the interfacial peel strength between the aluminum foil and the first adhesive layer, measured according to the following method before loading, after loading with an electrolytic solvent, and after loading with an electrolyte, is 15 N / 15 mm or higher: [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer Before Immersion] For a sample cut to a length of 100 mm and a width of 15 mm after aging for one day under constant temperature and humidity conditions of 23±2℃ and 50±5% of a film laminated with PET (12 µm thickness), a second adhesive layer (3 µm thickness), nylon (15 µm thickness), a second adhesive layer (3 µm thickness), aluminum foil (40 µm thickness), the first adhesive layer (40 µm thickness), and a PP inner layer (40 µm thickness), the T-shaped peel strength at the interface between the aluminum foil and the first adhesive layer was measured using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min; [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer After Electrolytic Solvent Immersion] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a primary sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / EMC / DMC = 3 / 3 / 4 v / v part composition) at 85℃ for 1, 7, 28, and 56 days, and a secondary sample cut to a length of 100 mm and a width of 15 mm was measured for each sample using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min; [Method for Measuring Interfacial Peel Strength Between Aluminum Foil and First Adhesive Layer After Electrolyte Immersion] After aging the laminated film for 1 day under constant temperature and humidity conditions of 23±2℃ and 50±5% humidity, a first sample cut to a length of 150 mm and a width of 17 mm was immersed in an electrolyte solution (EC / DEC / DMC=1 / 1 / 1 v / v part composition, containing LiPF61 M) at a temperature of 85℃ for 1, 7, 28, and 56 days, and a second sample cut to a length of 100 mm and a width of 15 mm was measured using a measuring device (universal testing machine, Instron) at 23℃ at a test speed of 50 mm / min for each sample, and the T-shaped peel strength of the interface between the aluminum foil and the first adhesive layer was measured.

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