Packaging materials for secondary batteries

Abstract

The present invention provides a packaging material for secondary batteries having a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, which can be heat-sewn under low heat-sewn temperature conditions and exhibits improved heat resistance and shape stability in a high-temperature environment.The present invention provides a packaging material for secondary batteries having a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, which is characterized in that the composition constituting the inner layer has at least three endothermic peaks in a temperature-calorie curve when measured by a thermal fractionation analysis method (Successive Self-nucleation and Annealing (SSA) using a Differential Scanning Calorimetry (DSC)), and the endothermic peaks appear in the range of 90 to 180°C.

Description

[Technical field]

[0001] The present invention relates to a packaging material for secondary batteries, and more particularly to a packaging material for secondary batteries having a laminated structure of an outer layer, a metal foil gas barrier layer, and an inner layer.

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0151769, filed on November 5, 2021, the entire text of which is incorporated herein by reference. [Background technology]

[0003] Secondary batteries generally refer to lithium secondary batteries, which are used in portable terminal devices such as laptops, smartphones, tablet PCs, and video cameras, electric vehicles including hybrid vehicles, and smart grids for energy storage. Research is ongoing to make them smaller, lighter, and thinner, while also overcoming various environmental factors such as harsh thermal environments and mechanical shocks.

[0004] As a packaging material for such lithium batteries, unlike conventional can-type packaging materials, a pouch for secondary batteries is used as an exterior material having a multi-layer structure (e.g., an inner resin layer, an aluminum layer, and an outer resin layer) because it has the advantage of being able to freely change the shape of the battery. A commonly used pouch film for secondary batteries has a multi-layer structure in which an inner resin layer is made of an adhesive layer of polyolefin such as polyethylene (PE), cast polypropylene (cPP), polypropylene (PP), etc., or a copolymer thereof, which has thermal adhesiveness and acts as a sealant, an aluminum layer which is a metal foil that acts as a base material for maintaining mechanical strength and a barrier layer against moisture and oxygen, and an outer resin layer is made of a functional polymer film such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), nylon, or liquid crystal polymer (LCP) to protect the battery cell from external impact.

[0005] Conventionally, packaging materials have mainly been used that are made by pressing metal, especially aluminum, into a cylindrical or parallelepiped shape, etc. However, such metal can packaging materials have limitations in that the outer wall of the container is hard and the shape of the battery itself is determined by the shape of the metal can packaging material.

[0006] In an attempt to overcome such limitations, technologies for packaging materials made of multilayer plastic films have been developed. For example, Patent Document 1 discloses a cell pouch made of a base layer, an adhesive layer, a barrier layer, a dry lamination layer, and a sealant layer, with the sealant layer being made of a low-fluidity polypropylene layer and a high-fluidity polypropylene layer, and Patent Document 2 discloses a cell pouch in which biaxially oriented nylon, polyethylene terephthalate (PET), and polyolefin resin are laminated in the base film and surface protection layer, and a technology for coating the base film with a fluorine-based, silicone-based, or acrylic resin as a secondary processing step.

[0007] Pouch-type secondary batteries have the advantage of being flexible in shape and being able to realize a secondary battery with the same capacity with a smaller volume and mass. However, unlike can-type batteries, pouch-type batteries use a soft pouch as a container, and therefore may be damaged for various reasons during various processes. For example, in the process of storing an electrode assembly inside a pouch, protruding parts such as electrode tabs and electrode leads may cause damage such as cracks in the PP and cPP layers inside the pouch. If the aluminum layer is exposed due to such damage, a side reaction may occur due to its reactivity with the electrolyte. The aluminum layer exposed to the electrolyte may corrode due to a chemical reaction with the electrolyte that has permeated or diffused inside the battery and oxygen or moisture, which generates corrosive gas and causes a swelling phenomenon that expands the inside of the battery. For more information, see Lithium Hexafluorophosphate (LIPF) 6 ) reacts with water and oxygen to produce hydrofluoric acid (HF), a corrosive gas. This hydrofluoric acid can react with aluminum to produce a rapid exothermic reaction, and when it is absorbed by the aluminum surface in a secondary reaction and penetrates into the tissue, it increases the brittleness of the tissue, and even a small impact can cause cracks in the pouch film, and electrolyte leakage can cause a reaction between lithium and the air, resulting in fire.

[0008] Patent Document 3 describes a polymer film for cell packaging material that contains 1 to 30% by weight of low-density polyethylene (LDPE), 50 to 98% by weight of polypropylene (PP), and 1 to 20% by weight of cross-linked resin, in which LDPE is used to reduce the permeation rate of the electrolyte, PP is used to complement heat resistance, and the cross-linked resin is used to increase the compatibility of LDPE and PP, but does not mention in detail the changes in physical properties due to molecular weight, density, melting point, crystallinity, comonomer content, etc.

[0009] Patent Document 4 discloses a battery packaging material that is composed of a laminate in which a base layer, a metal layer, and a sealant layer are laminated in sequence, and in which multiple types of fatty acid amide-based lubricants are present in the sealant layer, at least one of which is a saturated fatty acid amide. However, when an extrusion lamination process is used, the fatty acid amide may volatilize, resulting in a loss of sleep properties.

[0010] Patent Document 5 discloses a resin composition for a sealant layer of a battery packaging material in which a first sealant layer is formed from an acid-modified polyolefin and a second sealant layer contains a polyolefin resin having an isotactic fraction (mm) of 99% or less. However, because commercially available or synthetic polyolefin resins cannot have an isotactic fraction exceeding 99%, it is difficult to specifically identify the category of polyolefin resins with an isotactic fraction (mm) of 99% or less. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 2003-0029141 [Patent Document 2] Korean Patent Publication No. 2002-0030737 [Patent Document 3] Korean Patent No. 1499740 [Patent Document 4] Japanese Patent No. 6808966 [Patent Document 5] Japanese Patent No. 5761278 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention provides a packaging material for secondary batteries that includes a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, and that can be heat-sewn under low heat-sewn temperature conditions and that exhibits improved heat resistance and dimensional stability in high-temperature environments. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides a packaging material for secondary batteries, which comprises a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, wherein the composition constituting the inner layer has at least three endothermic peaks in a temperature-calorie curve when measured by a thermal fractionation analysis method (Successive Self-nucleation and Annealing (SSA)) using a Differential Scanning Calorimetry (DSC), and the endothermic peaks appear in the range of 90 to 180°C.

[0014] In addition, the composition constituting the inner layer has, when analyzed by the thermal fractionation analysis method, an area including an endothermic peak below 100°C based on the total area of ​​all peaks does not exceed 10%, and an area including an endothermic peak above 150°C is more than 20% and less than 90%.

[0015] The present invention also provides a packaging material for a secondary battery, wherein the composition forming the inner layer contains at least one type of acid-modified polypropylene.

[0016] The present invention also provides a packaging material for a secondary battery, wherein the acid-modified polypropylene is a modified polypropylene grafted with maleic anhydride in an amount of 1 to 10% by weight.

[0017] The present invention also provides a packaging material for a secondary battery, wherein the heat-resistant resin is a polyamide-based resin or a polyester-based resin.

[0018] The present invention also provides a packaging material for secondary batteries, characterized in that the metal foil contains 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).

[0019] The present invention also provides a packaging material for secondary batteries, characterized in that the outer layer has a thickness of 15 to 30 μm, the metal foil gas barrier layer has a thickness of 25 to 45 μm, and the inner layer has a thickness of 25 to 120 μm. Effect of the Invention

[0020] According to the present invention, in a packaging material for a secondary battery having a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, the composition constituting the inner layer exhibits specific thermal characteristics when measured by a thermal fractionation analysis method using a differential scanning calorimeter, thereby making it possible to provide a packaging material for a secondary battery that can be heat-sewn under low heat-sewn temperature conditions and that exhibits improved heat resistance and dimensional stability in a high-temperature environment. [Brief description of the drawings]

[0021] [Figure 1] 1 is a graph showing an example of a case in which the measurement results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) do not show triple or more melting behavior. [Diagram 2] 1 is a graph showing an example of a heat treatment process in thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC). [Diagram 3]1 is a graph showing an example of a case in which triple or more melting behavior is observed as a result of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC). [Figure 4] 2 is a graph showing the measurement results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) for the inner layer in Example 1. [Diagram 5] 1 is a graph showing the results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) for the inner layer in Example 2. [Figure 6] 1 is a graph showing the results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) for the inner layer in Example 3. [Figure 7] 1 is a graph showing the results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) for the inner layer in Example 4. [Figure 8] 1 is a graph showing the measurement results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) for the inner layer in Comparative Example 1. [Figure 9] 1 is a graph showing the measurement results of thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC) for the inner layer in Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention will be described in detail below through preferred embodiments. Prior to this, the terms and words used in this specification and claims should not be interpreted in their ordinary or dictionary sense, but should be interpreted in their meaning and concept consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to best describe his / her invention. Therefore, the configuration of the embodiment described in this specification is merely one of the most preferred embodiments of the present invention, and does not fully represent the technical idea of ​​the present invention, so it should be understood that there may be various equivalents and modifications that can replace them at the time of this application.

[0023] The present invention discloses a packaging material for lithium secondary batteries, which has a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, and is characterized in that the composition constituting the inner layer has at least three endothermic peaks in a temperature-calorie curve measured by thermal fractionation analysis (SSA) using nucleation / annealing with a differential scanning calorimeter (DSC), and the endothermic peaks appear in the range of 90 to 180°C.

[0024] The inner layer is the innermost layer of the packaging material for the secondary battery, which is made of a composition containing a thermoplastic polyolefin and comes into contact with the electrolyte of the battery, and is thermally bonded for the purpose of sealing the lithium secondary battery.

[0025] The composition containing thermoplastic polyolefin, which is the inner layer of the packaging material for lithium secondary batteries according to the present invention, is characterized by having at least three endothermic peaks in a temperature-calorie curve when measured by thermal fractionation analysis (SSA) using a differential scanning calorimeter (DSC). That is, in the packaging material for lithium secondary batteries according to the present invention, the composition containing thermoplastic polyolefin of the inner layer shows melting behavior in three or more points, which can be observed with a DSC device.

[0026] In this case, it is preferable that the composition constituting the inner layer has an area including an endothermic peak of less than 100°C that does not exceed 10% based on the total area of ​​all peaks, and an area including an endothermic peak of more than 150°C that is more than 20% but less than 90%.

[0027] For example, the SSA measurement results shown in FIG. 1 do not show three or more types of melting behavior, and the region including an endothermic peak exceeding 150°C shows a temperature-calorie curve that accounts for 90% or more of the total peak area. However, if an inner layer made of a composition showing such SSA measurement results is used, it is difficult to realize a packaging material for a secondary battery having improved heat seamability, heat resistance, and dimensional stability, which is the problem solved by the present invention.

[0028] Here, the temperature-calorie curve by the thermal fractionation analysis using a differential scanning calorimeter is the result of repeatedly heating and cooling the thermoplastic resin to be analyzed from room temperature to a sufficiently high temperature, for example, about 200°C, at a rate of 10°C per minute using DSC, and holding at specific temperatures, for example, 180, 170, and 160°C, at 10°C intervals for a certain period of time to give self-nucleation and annealing (see Figures 2 and 3). That is, when the thermoplastic resin is heated and completely melted, and then cooled to a specific temperature (T) and gradually annealed, the lamellae that are not stable at the temperature (T) are still melted and only the stable lamellae crystallize, and at this time, the stability at the temperature (T) depends on the thickness of the lamellae, and the thickness of the lamellae depends on the chain structure. Therefore, by performing such heat treatment in stages, the thickness of the lamellae and its distribution according to the polymer chain structure can be quantitatively measured, and the distribution of each melting peak area can be measured accordingly.

[0029] In the present invention, in a packaging material for a secondary battery including a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, the inner layer is separately separated and a thermal fractionation analysis is performed using DSC. Since the inner layer is a result of including a crystal structure due to the chemical composition of the composition containing a thermoplastic polyolefin itself as well as a crystal structure due to the phenomenon of molding and heat treating the resin, in order to remove the history of molding and heat treating the resin, a thermal annealing heat treatment is performed at a sufficiently high temperature above the melting point at room temperature. The thermoplastic resin is maintained at a high temperature below the melting point for a sufficient time, for example, about 3 to 60 minutes. After such thermal annealing, the thermoplastic resin is cooled to room temperature at the same rate as the heating rate and heat treatment is performed, and the temperature of the maintenance section is lowered at a specific temperature interval until it reaches room temperature to provide self-nucleation and annealing.

[0030] Through such heat treatment, the composition constituting the inner layer changes from a melting point behavior that shows an endothermic peak only at the melting point to a thermoplastic resin with multiple melting behavior that shows endothermic phase transitions at phase transition temperatures lower than the melting point (see FIG. 3).

[0031] This indicates that the composition forming the inner layer of the present invention has an endothermic phase transition peak that occurs at a temperature lower than the inherent resin melting point, making it possible to perform thermal bonding below the melting point. It also indicates that it has multiple endothermic phase transitions in the range of 90 to 180°C, making it possible to perform bonding under a wide range of bonding temperature conditions. In addition, the region including endothermic peaks above 150°C is more than 20% but less than 90%, giving it mechanical rigidity and heat resistance, and thus exhibiting excellent thermal bonding strength after thermal bonding of the inner layer.

[0032] On the other hand, the composition containing the thermoplastic polyolefin constituting the inner layer in the present invention is constituted of multiple layers, preferably two or three layers.

[0033] In the present invention, the composition forming the inner layer includes at least one acid-modified polypropylene, and may include modified polypropylene grafted with maleic anhydride as the functional group of the acid-modified group at a content of 1 to 10 wt%, preferably 3 to 5 wt%. If the content of maleic anhydride is less than 1 wt%, adhesion to the metal foil gas barrier layer may decrease, and if it exceeds 10 wt%, fish eyes (F / E) and low molecules may occur due to a large amount of polar functional groups, and the surface tension after corona surface treatment may decrease, resulting in a decrease in adhesion to the metal foil gas barrier layer. Preferably, it may be configured as a layer that abuts against the metal foil gas barrier layer in a layer structure of two or three layers.

[0034] The inner layer may have a thickness of about 25 to 120 μm for sufficient thermal bonding properties, but is not limited thereto, and may have an appropriate thickness depending on the use of the cell pouch to be realized, for example, a thin cell pouch realized with a total thickness of about 88 μm, a general cell pouch realized with a total thickness of about 113 μm, or a medium to large cell pouch realized with a total thickness of about 153 μm.

[0035] The outer layer is the outermost layer of the packaging material for lithium secondary batteries that may be provided on the metal foil gas barrier layer and exposed to the outside, and is preferably formed using a material having heat resistance, cold resistance, pinhole resistance, insulating properties, chemical resistance, formability, etc., as well as abrasion resistance, so as to protect the metal foil gas barrier layer. 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 has a high elongation rate and is advantageous for forming, and the polyester-based resin may be polybutylene terephthalate (PBT) or polyethylene terephthalate (PET), which may realize high chemical resistance, pinhole resistance, insulating properties, mechanical strength, etc.

[0036] The outer layer may have a thickness of about 15 to 30 μm, taking into consideration sufficient abrasion resistance, heat resistance, pinhole resistance, chemical resistance, moldability, insulation, etc. If the thickness of the outer layer is too thin, the strength of the outer layer may be unpredictable, and the moldability of the secondary battery packaging material may be reduced. On the other hand, if the thickness of the outer layer is too thick, the inner layer and the metal foil gas barrier layer provided under the outer layer must be implemented with a relatively thin thickness, and problems such as a decrease in thermal adhesion strength and a decrease in peel strength between layers may occur in the secondary 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 about 88 μm, a general-type cell pouch implemented with a total thickness of about 113 μm, or a medium-sized or large-sized cell pouch implemented with a total thickness of about 153 μm.

[0037] In the present invention, a first adhesive resin layer may be further formed to bond the outer layer and the metal foil gas barrier layer.

[0038] The first adhesive resin layer is formed from an adhesive capable of bonding the outer layer and the metal foil gas barrier layer, and the adhesive used to form the first adhesive resin layer may be a two-component curing adhesive or a one-component curing adhesive. The adhesive bonding tool used to form the first adhesive resin layer is also not particularly limited, and may be selected from chemical reaction type, solvent volatilization type, heat melting type, heat pressure type, and the like.

[0039] Examples of the resin components of the adhesive that can be used to form the first adhesive resin layer include polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, polycarbonate, and copolymerized polyester, polyether-based adhesives, polyurethane-based adhesives, epoxy-based resins, phenol-based resins, polyamide-based resins such as nylon 6, nylon 66, nylon 12, and copolymerized polyamide, polyolefin-based resins such as polyolefin, acid-modified polyolefin, and metal-modified polyolefin, polyvinyl acetate-based resins, cellulose-based adhesives, (meth)acrylate-based resins, polyimide-based resins, amino resins such as urea resins and melamine resins, rubbers such as chloroprene rubber, nitrile rubber, and styrene-butadiene rubber, silicone-based resins, and fluorinated ethylene propylene copolymers. One of these adhesive components may be used alone, or two or more may be used in combination. The modified pattern of the two or more adhesive components is not particularly limited, and examples of the adhesive components include a mixed resin of amide and acid-modified polyolefin, a mixed resin of polyamide and metal-modified polyolefin, a mixed resin of polyamide and polyester, a mixed resin of polyester and acid-modified polyolefin, a mixed resin of polyester and metal-modified polyolefin, etc. Among these, from the viewpoint of excellent stretchability, durability and flexural suppression effect under high humidity conditions, and heat deterioration suppression effect during heat sewing, and of suppressing a decrease in lamination strength between the outer layer and the metal foil gas barrier layer and effectively suppressing the occurrence of delamination, preferred are polyurethane-based two-component curing adhesives, polyamide, polyester, or mixed resins of these and modified polyolefins.

[0040] Meanwhile, the thickness of the first adhesive resin layer may be, for example, 2 to 10 μm.

[0041] The metal foil gas barrier layer is for blocking the ingress and egress of moisture and air from the outside and gas generated from the inside, and may be in contact with the inner layer. The metal foil gas barrier layer includes a metal having gas barrier properties and moisture barrier properties, and may include, 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. (single metal or mixture of single metals), or an alloy of two or more selected from the group. In a preferred embodiment, the metal foil gas barrier layer may include aluminum (Al) or an aluminum alloy, taking into consideration all of moisture barrier properties, gas barrier properties, and formability. The metal foil gas barrier layer may have a thickness of about 25 to 45 μm in order to have sufficient gas barrier properties and moisture barrier properties. However, the thickness of the metal foil gas barrier layer is not limited thereto, and may have an appropriate thickness depending on the use of the cell pouch to be realized, i.e., generally, a thin-film cell pouch realized with a total thickness of about 88 μm, a general-type cell pouch realized with a total thickness of about 113 μm, or a medium- to large-sized cell pouch realized with a total thickness of about 153 μm.

[0042] It is preferable that at least one surface of the metal foil gas barrier layer, preferably at least the surface on the inner layer side, more preferably both surfaces, are chemically treated in order to stabilize adhesion and prevent dissolution and corrosion. Here, the chemical conversion treatment is a treatment for forming an acid-resistant coating on the surface of the metal foil gas barrier layer. Examples of the chemical conversion treatment include chromate treatment using chromium compounds such as chromium nitrate, chromium fluoride, chromium sulfate, chromium acetate, chromium oxalate, chromium biphosphate, chromate acetylacetate, chromium chloride, and calcium chromium sulfate, phosphoric acid chromate treatment using phosphoric acid-capable substances such as sodium phosphate, potassium phosphate, ammonium phosphate, and polyphosphoric acid, and chromate treatment using aminated phenol polymers.

[0043] As a chemical conversion treatment method for imparting corrosion resistance to the metal foil gas barrier layer, a method of forming a corrosion-resistant layer on the surface of the metal foil gas barrier layer by coating a dispersion of fine particles of metal oxides such as aluminum oxide, titanium oxide, cerium oxide, and tin oxide, or barium sulfate in phosphoric acid and baking at 150°C or higher can be mentioned. In addition, a resin layer in which a cationic polymer is crosslinked with a crosslinking agent can be formed on the corrosion-resistant layer. Here, examples of the cationic polymer include polyethyleneimine, an ionic polymer complex consisting of a polymer having polyethyleneimine and carboxyl acid, a primary amine-grafted acrylic resin in which a primary amine is grafted to the main skeleton of acrylic, polyallylamine or its derivative, and aminophenol. These cationic polymers may be used alone or in combination of two or more. Examples of the crosslinking agent include a compound having at least one functional group selected from the group consisting of an isocyanate group, a glycidyl group, a carboxyl group, and an oxazoline group, a silane coupling agent, and the like. These crosslinking agents may be used alone or in combination of two or more.

[0044] The chemical conversion treatment may be performed using one type of chemical conversion treatment alone, or may be performed using two or more types of chemical conversion treatment in combination. The chemical conversion treatment may be performed using one type of compound alone, or may be performed using two or more types of compounds in combination. Among these, a chromate treatment with chromic acid is preferred, and a chromate treatment using a combination of a chromic acid compound, a phosphoric acid compound, and an aminated phenol polymer is more preferred.

[0045] The chemical conversion treatment is carried out by applying a solution containing the compound used to form the acid-resistant coating to the surface of the metal foil gas barrier layer by a method such as bar coating, roll coating, bravia coating, or immersion, and then heating the metal foil so that its temperature is around 70 to 200°C.

[0046] In the present invention, a second adhesive resin layer may be further formed to bond the metal foil gas barrier layer and the inner layer.

[0047] The second adhesive resin layer may be formed by an adhesive capable of bonding the inner layer and the metal foil gas barrier layer. The adhesive used to form the second adhesive resin layer may be a two-component curing adhesive or a one-component curing adhesive. The adhesive bonding tool used to form the second adhesive resin layer is not particularly limited, and may be any of a chemical reaction type, a solvent volatilization type, a thermal melting type, a thermal pressure type, and the like.

[0048] Examples of the resin components of the adhesive that can be used to form the second adhesive resin layer include polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, polycarbonate, and copolymerized polyester, polyether-based adhesives, polyurethane-based adhesives, epoxy-based resins, phenol-based resins, polyamide-based resins such as nylon 6, nylon 66, nylon 12, and copolymerized polyamide, polyolefin-based resins such as polyolefin, acid-modified polyolefin, and metal-modified polyolefin, polyvinyl acetate-based resins, cellulose-based adhesives, (meth)acrylic resins, polyimide-based resins, amino resins such as urea resins and melamine resins, rubbers such as chloroprene rubber, nitrile rubber, and styrene-butadiene, silicone-based resins, and fluorinated ethylene propylene copolymers. These adhesive components may be used alone or in combination of two or more. The deformation pattern of two or more adhesive components is not particularly limited, and examples of the adhesive components include a mixed resin of polyamide and acid-modified polyolefin, a mixed resin of polyamide and metal-modified polyolefin, a mixed resin of polyamide and polyester, a mixed resin of polyester and acid-modified polyolefin, a mixed resin of polyester and metal-modified polyolefin, etc. Among these, from the viewpoint of excellent stretchability, durability and flexural suppression effect under high humidity conditions, and heat deterioration suppression effect during heat sewing, and of suppressing a decrease in lamination strength between the inner layer and the metal foil gas barrier layer to effectively suppress the occurrence of delamination, preferred are a polyurethane-based two-component curing adhesive, a polyolefin-based resin, or a mixed resin of these and a modified polyolefin.

[0049] On the other hand, the thickness of the second adhesive resin layer may be, for example, 2 to 60 μm.

[0050] The method for producing the packaging material for secondary batteries according to the present invention is not particularly limited as long as it can produce a laminate in which layers of predetermined composition are laminated together. The following method is exemplified.

[0051] First, a laminate (laminate A) is formed in which an outer layer, a first adhesive resin layer, and a metal foil gas barrier layer are laminated in this order. More specifically, the laminate A can be formed by a dry lamination method in which an adhesive used to form the first adhesive resin layer is applied to the barrier layer, the surface of which has been chemically treated, by a coating method such as extrusion, gravure coating, or roll coating, and then dried, and the outer layer is laminated and the first adhesive resin layer is cured.

[0052] Next, an inner layer is laminated on the metal foil gas barrier layer of the laminate A. When a second adhesive resin layer is provided between the metal foil gas barrier layer and the inner layer, for example, the following method may be used: (1) a method in which an adhesive for forming a second adhesive resin layer is solution-coated on the metal foil of the laminate A, and then the adhesive is laminated by a drying method at high temperature, and an inner layer previously formed into a two- or three-layer sheet is laminated on the second adhesive resin layer by a thermal lamination method (dry lamination method); (2) a method in which an inner layer consisting of two or three layers is laminated by co-extruding on the metal foil gas barrier layer of the laminate A (co-extrusion lamination method); or (3) a method in which a molten second adhesive resin layer is poured between the metal foil of the laminate A and a sealant layer previously formed into a two- or three-layer sheet, while bonding the laminate A and the inner layer via the second adhesive resin layer (sandwich lamination method). EXAMPLES

[0053] The present invention will now be described in more detail with reference to specific examples and comparative examples.

[0054] [Example 1] An outer layer was made of a stretched polyamide film (25 μm thick) and an aluminum thin film (30 μm thick) with a chromate phosphate coating on both sides as a metal foil gas barrier layer was bonded by dry lamination using an adhesive (polyurethane-based two-component curing adhesive, 3 μm thick). The inner layer was formed by the T-die casting method. The outer layer, the metal foil gas barrier layer bonded film, and an inner layer (40 μm thick) made of a composition containing thermoplastic polyolefin were bonded by dry lamination to obtain a packaging material for lithium secondary batteries.

[0055] The inner layer, which is made of a composition containing thermoplastic polyolefin, is composed of maleic anhydride (4 wt%), modified polypropylene 1 wt%, homopolypropylene 54 wt%, ethylene-propylene copolymer 25 wt%, and amorphous propylene rubber 20 wt%. When thermal fractionation analysis (SSA) was measured using a differential scanning calorimeter (DSC), the temperature-calorie curve had 12 endothermic peaks in the range of 90 to 180°C, and the region including endothermic peaks below 100°C was 0.12% based on the total peak area, and the region including endothermic peaks above 150°C was 77.5% (see Figure 4).

[0056] [Example 2] The outer layer is a stretched polyamide film (25 μm thick) and the metal foil gas barrier layer is a thin aluminum film (30 μm thick) with a chromate phosphate coating on both sides. The thin aluminum film is bonded by dry lamination using an adhesive (polyurethane-based two-component curing adhesive, 3 μm thick). The inner layer (40 μm thick) is made up of three layers and bonded to the film using the T-die casting method to obtain a packaging material for lithium secondary batteries.

[0057] The inner layer, which is made of a composition containing thermoplastic polyolefin, is composed of maleic anhydride (4 wt%), modified polypropylene 5 wt%, homopolypropylene 5 wt%, ethylene-containing propylene copolymer 35 wt%, ethylene and butene-containing propylene terpolymer 25 wt%, low-density polyethylene 12 wt%, and amorphous propylene rubber 18 wt%. When thermal fraction analysis (SSA) was measured using a differential scanning calorimeter (DSC), the temperature-calorie curve had 13 endothermic peaks in the range of 90 to 180°C, and the region including endothermic peaks below 100°C was 0.59% based on the total peak area, and the region including endothermic peaks above 150°C was 33% (see FIG. 5).

[0058] [Example 3] The outer layer is a stretched polyamide film (25 μm thick) and the metal foil gas barrier layer is a thin aluminum film (30 μm thick) with a chromate phosphate coating on both sides. The thin aluminum film is bonded by dry lamination using an adhesive (polyurethane-based two-component curing adhesive, 3 μm thick). The inner layer is made up of three layers and is formed by the T-die casting method. The outer layer, the metal foil gas barrier layer bonded film, and the inner layer (40 μm thick) made of a composition containing thermoplastic polyolefin are bonded by dry lamination to obtain a packaging material for lithium secondary batteries.

[0059] The inner layer, which is made of a composition containing thermoplastic polyolefin, is composed of maleic anhydride (4 wt%), modified polypropylene 1 wt%, homopolypropylene 44 wt%, linear low density polyethylene 20 wt%, and amorphous propylene rubber 35 wt%. When thermal fractionation analysis (SSA) was measured using a differential scanning calorimeter (DSC), the temperature-calorie curve had 18 endothermic peaks in the range of 90 to 180°C, and the region including endothermic peaks below 100°C was 1.21% based on the total peak area, and the region including endothermic peaks above 150°C was 87% (see FIG. 6).

[0060] [Example 4] The outer layer is a stretched polyamide film (25 μm thick) and the metal foil gas barrier layer is a thin aluminum film (30 μm thick) with a chromate phosphate coating on both sides. The thin aluminum film is bonded by dry lamination using an adhesive (polyurethane-based two-component curing adhesive, 3 μm thick). The inner layer is made up of three layers and is formed by the T-die casting method. The outer layer, the metal foil gas barrier layer bonded film, and the inner layer (40 μm thick) made of a composition containing thermoplastic polyolefin are bonded by dry lamination to obtain a packaging material for lithium secondary batteries.

[0061] The inner layer, which is made of a composition containing thermoplastic polyolefin, is composed of maleic anhydride (4 wt%), modified polypropylene 1 wt%, homopolypropylene 29 wt%, ethylene-propylene copolymer 35 wt%, low-density polyethylene 20 wt%, and amorphous propylene rubber 15 wt%. When thermal fractionation analysis (SSA) was measured using a differential scanning calorimeter (DSC), the temperature-calorie curve had 12 endothermic peaks in the range of 90 to 180°C, and the region including endothermic peaks below 100°C was 0.83% based on the total peak area, and the region including endothermic peaks above 150°C was 22.3% (see FIG. 7).

[0062] [Comparative Example 1] The outer layer is a stretched polyamide film (25 μm thick) and the metal foil gas barrier layer is a thin aluminum film (30 μm thick) with a chromate phosphate coating on both sides. The thin aluminum film is bonded by dry lamination using an adhesive (polyurethane-based two-component curing adhesive, 3 μm thick). The inner layer (40 μm thick) is made up of three layers and bonded to the film using the T-die casting method to obtain a packaging material for lithium secondary batteries.

[0063] The inner layer, which is made of a composition containing thermoplastic polyolefin, does not contain maleic anhydride modified polypropylene and is composed of 85% by weight of homopolypropylene and 15% by weight of amorphous propylene rubber. When thermal fractionation analysis (SSA) was measured using a differential scanning calorimeter (DSC), it had one endothermic peak in the temperature-calorie curve, and based on the total peak area, the area including the endothermic peak below 100°C was 0% and the area including the endothermic peak above 150°C was 91.2% (see FIG. 8).

[0064] [Comparative Example 2] The outer layer is a stretched polyamide film (25 μm thick) and the metal foil gas barrier layer is a thin aluminum film (30 μm thick) with a chromate phosphate coating on both sides. The thin aluminum film is bonded by dry lamination using an adhesive (polyurethane-based two-component curing adhesive, 3 μm thick). The inner layer (40 μm thick) is made up of three layers and bonded to the film using the T-die casting method to obtain a packaging material for lithium secondary batteries.

[0065] The inner layer, which is made of a composition containing thermoplastic polyolefin, does not contain maleic anhydride modified polypropylene, and is composed of 90% by weight of ethylene and butene-containing propylene terpolymer and 10% by weight of amorphous propylene rubber. When thermal fractionation analysis (SSA) was measured using a differential scanning calorimeter (DSC), it was found that the temperature-calorie curve had six endothermic peaks, and the region including endothermic peaks below 100°C was 0% based on the total peak area, and the region including endothermic peaks above 150°C was 0% (see FIG. 9).

[0066] [Test example] Using the prepared packaging material, a test specimen was prepared, and the physical properties were measured and evaluated according to the following methods. The results are shown in Table 1 below.

[0067] [Measurement and evaluation methods of physical properties] (1) Aluminum peel strength The prepared material was cured at 50° C. for 14 days, then cut into a piece with a width of 15 mm, and the peel strength was measured at 23° C., a peel speed of 50 mm / min, and a peel angle of 180°. (2) Thermal adhesive strength The above-prepared material was placed in contact with the inner layer film, heat-bonded at 200°C, 2kgf and 1s, and then cut to a length of 15mm. The peel strength was measured at 23°C, a peel speed of 100mm / min and peel angles of 180° and 160°. (3) Electrolyte resistance The specimens used in the measurement of the thermal adhesive strength were immersed in an electrolyte at 85° C. for 75 hours, and then the peel strength was measured in the same manner as in the measurement of the thermal adhesive strength. If the peel strength after immersion in the electrolyte was maintained at 90% or more of the peel strength before immersion in the electrolyte, it was marked with "◎", if it was 70% or more but less than 90%, it was marked with "△", and if it was less than 70%, it was marked with "×". The composition of the electrolyte was [EC / DEC / DMC=1 / 1 / 1(v / v%)+LiPF6(1 mol / L)+H 2 O300 ppm], where EC is ethylene carbonate, DEC is diethyl carbonate, and DMC is dimethyl carbonate. (4) Forming performance The packaging material thus produced was placed on a frame-shaped metal mold (10 cm x 10 cm) with the outer layer touching the edge of the mold, and a square pyramid was used to pressurize the inner layer film surface, and drawing was performed 5 times to a minimum depth of 6 mm. If there was no tearing at the corners of the packaging material, it was marked with "◎", if there was one to three tearing, it was marked with "△", and if there was four or more tearing, it was marked with "X".

[0068] [Table 1]

[0069] Referring to Table 1, if the inner layer of the packaging material for lithium secondary batteries according to the present invention, which is made of a composition containing thermoplastic polyolefin, contains at least one acid-modified polypropylene, and has at least three endothermic peaks in the range of 90 to 180°C when measured by thermal fractionation analysis, and satisfies that the region including endothermic peaks below 100°C does not exceed 10% based on the total peak area, and the region including endothermic peaks exceeding 150°C is more than 20% and less than 90%, it can be confirmed that it exhibits excellent thermal adhesion performance and excellent peel strength between the materials of each layer (aluminum peel strength, electrolyte resistance). In addition, it has multiple endothermic phase transitions in the range of 90 to 180°C and can be bonded under a wide range of bonding temperature conditions. In addition, it can be confirmed that the region including endothermic peaks above 150°C is more than 20% and less than 90%, and mechanical rigidity and heat resistance are imparted, resulting in excellent thermal bonding strength after the inner layer is thermally bonded.

[0070] In contrast, Comparative Example 1 has a high endothermic phase transition at a relatively high temperature compared to the Examples. This indicates that the thermal annealing region of the thermoplastic polyolefin constituting the inner layer is reduced at a relatively low thermal stitching temperature, and that thermal adhesion is not sufficient. It can also be confirmed that the peel strength and electrolyte resistance of aluminum are reduced because maleic anhydride-modified polypropylene is not included and adhesion to metal is insufficient. In addition, it can be confirmed that the region showing the endothermic phase transition at high temperatures has a high degree of crystallinity of the thermoplastic polyolefin, and although the mechanical rigidity is good due to the high degree of crystallinity, the forming performance is reduced.

[0071] In the case of Comparative Example 2, the region of 100 to 140°C shows 100% endothermic phase transition, and it can be bonded in a relatively low temperature range. However, the region showing endothermic phase transition is a low temperature range compared to the examples, and the crystallinity of the thermoplastic polyolefin that forms it is relatively low, and there is no endothermic peak in the region exceeding 150°C, so the mechanical rigidity is insufficient, which also affects the low peel strength after thermal bonding. In addition, as in Comparative Example 1, it can be confirmed that the peel strength and electrolyte resistance of aluminum are reduced because the adhesion with metal is insufficient due to the absence of maleic anhydride modified polypropylene. However, it can be confirmed that the forming performance due to the amorphous region is improved compared to Comparative Example 1 due to the relatively low crystallinity.

[0072] The 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 the present invention can be easily modified into other specific forms without changing the technical concept or essential features of the present invention.

[0073] Therefore, the scope of the present invention is defined by the claims set forth below rather than the above detailed description, and all modifications and variations that fall within the meaning, scope and equivalent concept of the claims should be interpreted as being included within the scope of the present invention.

Claims

1. A packaging material for a secondary battery, comprising a laminated structure of an outer layer made of a heat-resistant resin film, a metal foil gas barrier layer, and an inner layer made of a composition containing a thermoplastic polyolefin, The composition constituting the inner layer has at least three endothermic peaks in a temperature-calorie curve when measured by a successive self-nucleation and annealing (SSA) method using a differential scanning calorimetry (DSC), and the endothermic peaks appear in a range of 90 to 180° C.

2. 2. The packaging material for a secondary battery according to claim 1, wherein the composition constituting the inner layer has an area including an endothermic peak of less than 100° C. that does not exceed 10% based on the total area of ​​all peaks when analyzed by the thermal fractionation analysis method, and an area including an endothermic peak of more than 150° C. that is more than 20% and less than 90%.

3. 2. The packaging material for a secondary battery according to claim 1, wherein the composition forming the inner layer contains at least one acid-modified polypropylene.

4. 4. The packaging material for a secondary battery according to claim 3, wherein the acid-modified polypropylene is modified polypropylene grafted with maleic anhydride in an amount of 1 to 10 wt %.

5. 2. The packaging material for secondary batteries according to claim 1, wherein the heat-resistant resin is a polyamide-based resin or a polyester-based resin.

6. 2. The packaging material for secondary batteries according to claim 1, characterized in that the metal foil contains 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).

7. 2. The packaging material for a secondary battery according to claim 1, wherein the outer layer has a thickness of 15 to 30 μm, the metal foil gas barrier layer has a thickness of 25 to 45 μm, and the inner layer has a thickness of 25 to 120 μm.

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