Aluminum-plastic composite film and battery

Abstract

The application belongs to the technical field of new materials, and specifically discloses an aluminum-plastic composite film and a battery. The aluminum-plastic composite film at least comprises a substrate layer, an adhesive layer and a metal layer; a material stress-strain curve (SS curve) of the substrate layer and an integral area of the horizontal coordinate of the metal strain specific region are A; 1000≤A≤1900; the proportional limit or yield point of the metal layer is the breaking point of the aluminum-plastic composite film, and represents a displacement-tension curve of the substrate layer stretched at a speed of 1-100 mm / min. The battery takes the aluminum-plastic composite film as a packaging material. The application improves the integral area of the SS curve of the substrate layer material in the metal strain specific region, thereby improving the forming limit of the aluminum-plastic composite film, so that the aluminum-plastic composite film is not prone to generating pinholes and cracks during forming, and provides an outer layer material with excellent forming property for the soft packaging of new energy batteries such as lithium batteries.

Description

Technical Field

[0001] This application relates to the field of new materials technology, and in particular to an aluminum-plastic composite film and battery. Background Technology

[0002] New energy batteries come in various packaging forms. Generally, lithium batteries can be mainly classified into three types: cylindrical batteries, prismatic batteries, and pouch batteries. Pouch batteries use aluminum-plastic film as their outer casing, making them lighter than prismatic and cylindrical batteries, which use aluminum casings.

[0003] Aluminum-plastic film for lithium batteries is generally a multi-layered composite film material consisting of aluminum foil or other metal foil as the middle barrier layer (also known as the metal layer), a high-temperature resistant and puncture-resistant film such as nylon or polyester on one side as the outer protective layer (also known as the substrate layer), and a plastic film such as polyolefin or polyamide on the other side as the inner heat-sealing layer (also known as the sealing layer). The layers are bonded together with adhesives. It provides barrier properties, resistance to electrolyte corrosion, and mechanical strength, and is used to encapsulate soft-pack lithium battery cells to protect the internal materials of the battery. However, the aluminum-plastic film used to package lithium battery cells is usually quite thin, making it prone to pinholes and cracks during encapsulation. This allows electrolyte to seep into the metal layer, forming metal deposits, which can potentially cause a short circuit. Therefore, the molding limits of the aluminum-plastic film are crucial for lithium batteries.

[0004] The mechanical properties of the substrate layer material have a significant impact on the forming performance of aluminum-plastic film. A certain tensile strength and elongation of the substrate layer are necessary conditions to ensure the forming performance of aluminum-plastic film. Maximizing the elongation at break while maintaining the strength of nylon (or polyester film) within a certain range has always been an important issue in the industry. Currently, the elongation at break of existing aluminum-plastic film substrate layer materials is much greater than the elongation of the aluminum-plastic film itself, and companies pursuing high-depth drawing aluminum-plastic film still consider maximizing the elongation of the material when selecting materials. However, the substrate layer material does not play any positive role after the corresponding aluminum-plastic film breaks. Therefore, it is possible to consider using a cheaper substrate layer material as a substitute, thereby meeting the drawing depth requirements while reducing the cost of aluminum-plastic film and thus increasing the product's profit margin. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this application is to provide an aluminum-plastic composite film and battery, which improves the deep drawing performance by increasing the effective integral of the substrate layer of the aluminum-plastic composite film, that is, improving its forming limit, making it less prone to pinholes or cracks during forming, thereby providing better packaging materials for batteries such as lithium batteries.

[0006] To achieve the above and other related objectives, this application provides an aluminum-plastic composite film, which includes at least a substrate layer, an adhesive layer and a metal layer;

[0007] The stress-strain curve of the substrate layer and the area of ​​its integral over a specific region of metal strain are denoted as A.

[0008] ;1000≤A≤1900;

[0009] This refers to the proportional limit or yield point of the metal layer. This is the break point of the aluminum-plastic composite film. This represents the displacement-tensile force curve of the substrate layer stretched at a speed of 1~100mm / min.

[0010] Furthermore, the stress-strain curve is obtained through a tensile test, and the tensile conditions used in the tensile test include: speed 5~100mm / min, clamp distance 50mm, and extensometer gauge length 30mm.

[0011] Furthermore, the substrate layer is a polyester film, a polyamide film, a polyester / polyamide co-extruded film, or a composite film comprising a polyester film and a polyamide film.

[0012] Furthermore, the thickness of the substrate layer is 1.5~90μm, preferably 40~60μm.

[0013] Furthermore, the substrate layer is a composite film composed of a polyester film with a thickness of 6~38μm and a polyamide film with a thickness of 15~30μm.

[0014] Furthermore, the adhesive used to form the adhesive layer is a polyurethane adhesive or an epoxy resin adhesive.

[0015] Furthermore, the metal layer is one or more of aluminum foil, stainless steel foil, coated iron foil, and copper foil, preferably aluminum foil.

[0016] Furthermore, the thickness of the metal layer is 20~150μm, preferably 60~100μm.

[0017] Furthermore, the aluminum-plastic composite film includes a substrate layer, an adhesive layer, a metal layer, an adhesive layer, and a sealing layer; or, the aluminum-plastic composite film includes a substrate layer, an adhesive layer, a metal layer, and a sealing layer.

[0018] Furthermore, the sealing layer is a polymer film with a melting point of 140~260℃.

[0019] Furthermore, the thickness of the sealing layer is 10~150μm, preferably 90~100μm.

[0020] This application also provides a battery, wherein the battery uses the aluminum-plastic composite film as the packaging material as described above.

[0021] As described above, the aluminum-plastic composite film and battery of this application have the following beneficial effects:

[0022] This application provides a multi-layer composite aluminum-plastic composite film. By selecting a material that increases the integral area of ​​the SS curve in a specific region of metal strain, the elongation of the substrate layer can be changed, so that the elongation of the corresponding aluminum-plastic composite film meets the preset requirements, thereby increasing the tensile strength of the substrate layer and improving the deep drawing performance of the aluminum-plastic composite film. That is, it improves the forming limit of the aluminum-plastic composite film, making it less prone to pinholes and cracks during forming. This provides an excellent formability selection scheme for the outer layer material of soft packaging for new energy batteries such as lithium batteries. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] In the attached diagram:

[0025] Figure 1 This is a comparison chart of the stretch curves of PET film, aluminum foil (AL), and aluminum-plastic composite film in Example 1 of this application.

[0026] Figure 2 This is the tensile curve of PET050 in Example 1 of this application. Detailed Implementation

[0027] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. This application can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0028] In this application, unless otherwise stated, the term "multiple" means two or more.

[0029] The character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0030] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0031] One embodiment of this application provides an aluminum-plastic composite film, comprising at least a substrate layer, an adhesive layer, and a metal layer; wherein the stress-strain curve (SS curve) of the substrate layer and the area of ​​its abscissa integrated over a specific region of metal strain are defined as A.

[0032] ;1000≤A≤1900;

[0033] This refers to the proportional limit or yield limit of the metal layer. This refers to the breakaway point of the aluminum-plastic composite film. This represents the displacement-tensile force curve of the substrate layer stretched at a speed of 1~100mm / min.

[0034] The SS curve is obtained through tensile testing, which is conducted according to national standards GB / T 1040.1-2018 "Determination of tensile properties of plastics - Part 1: General" and GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Room temperature test method". In one embodiment of this application, the tensile conditions used in the tensile test include: speed 5~100 mm / min, clamp distance 50 mm, and extensometer gauge length 30 mm. Here, speed refers to the beam displacement rate. For the metal layer material and aluminum-plastic composite film, tensile tests can be performed in the direction parallel to the rolling direction (MD) and the direction perpendicular to the rolling direction (TD); for the substrate layer material, tensile tests can be performed in the MD, TD, a direction obliquely 45° to the rolling direction (hereinafter referred to as oblique 45°), and a direction obliquely 135° to the rolling direction (hereinafter referred to as oblique 135°).

[0035] The proportional limit of a metallic layer is the maximum stress in which the stress and strain of a metallic material remain proportional during the elastic deformation stage; that is, the stress at which the SS curve begins to show nonlinearity. When the stress is below the proportional limit, the stress-strain relationship is linear, and the material is in the elastic stage.

[0036] The yield point of a metal layer is the critical stress value at which a metal material begins to undergo significant plastic deformation. It is usually judged by the inflection point of the SS curve that deviates from the linear relationship or by a deviation of 0.2% of the original gauge length.

[0037] The breakage point (also known as the fracture point) of an aluminum-plastic composite membrane occurs at the fracture stage on the SS curve. When the stress reaches the tensile strength (i.e., the fracture strength), the material has undergone significant plastic deformation and cannot recover its shape by increasing the stress. Ultimately, it fractures due to localized stress concentration or structural failure. Therefore, the breakage point of an aluminum-plastic composite membrane refers to the stress at which it cannot withstand further deformation and breaks.

[0038] The embodiments described above in this application allow the integral area of ​​the SS curve of the substrate layer material and its abscissa in a specific region of metal strain to be within the range of 1000 to 1900. This can change the elongation of the substrate layer, so that the elongation of the corresponding aluminum-plastic composite film meets the preset requirements, thereby increasing the tensile strength of the substrate layer. This, in turn, can improve the deep drawing performance of the aluminum-plastic composite film, that is, improve the forming limit of the aluminum-plastic composite film, making it less prone to pinholes and cracks during forming. This provides an outer layer material with excellent formability for soft packaging of new energy batteries such as lithium batteries.

[0039] When used as battery packaging material, the substrate layer of the aluminum-plastic composite film serves as an outer protective layer. Its main function is to protect the intermediate metal layer from physical damage (such as scratches and punctures), while also possessing insulation, heat resistance, and bending resistance. It can also effectively block oxygen permeation, maintaining a stable internal environment within the battery cell. In some embodiments of this application, the substrate layer is a polyester film, polyamide film, polyester / polyamide co-extruded film, or a composite film comprising polyester film and polyamide film, with a thickness of 1.5~90μm, preferably 40~60μm. Polyester film refers to a thin film material made of polyester resin, including but not limited to polyethylene terephthalate (PET), polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolyester, polycarbonate, etc. Polyamide film refers to a thin film material made of polyamide (PA, commonly known as "nylon") resin. Polyamide resin includes, but is not limited to, nylon 6, nylon 6,6, copolymers of nylon 6 and nylon 6,6, nylon 6,10, and poly(m-phenylene adipamide) (MXD nylon). Polyester / polyamide co-extruded film refers to a composite film made by extruding polyester resin and polyamide resin simultaneously. Specifically, two or more different plastics, including polyester resin and polyamide resin, are melted and plasticized separately using two or more extruders and then fed into a die, or the plastics supplied by the various extruders are combined through a distributor and fed into an inlet die to prepare the formed composite film. Composite films containing polyester film and polyamide film refer to multilayer composite films made by laminating polyester film and polyamide film, with lamination methods such as dry lamination or extrusion lamination. Dry lamination involves coating a film with a solvent-based adhesive using a coating device (typically a gravure screen roller coating), removing the solvent in a laminator, drying the film, and then laminating it with other film layers under hot pressing. Extrusion lamination involves melting polyester or polyamide resin in an extruder and extruding it into a flat die to form a sheet film. The film then immediately laminates with one or more other films using cooling rollers and laminating rollers.

[0040] In some embodiments of this application, in order to improve the formability and electrolyte resistance of the aluminum-plastic composite film, the substrate layer is selected as a composite film composed of a polyester film with a thickness of 6~38μm and a polyamide film with a thickness of 15~30μm.

[0041] In the preparation of aluminum-plastic composite films, the metal layer and the substrate layer are typically dry-laminated. An adhesive layer is provided to firmly bond the substrate layer and the metal layer; the adhesive layer is formed by curing an adhesive that bonds the substrate layer and the metal layer. In some embodiments of this application, the adhesive used to form the adhesive layer is a polyurethane adhesive or an epoxy resin adhesive, and its curing form can be solvent-evaporating, emulsion-type, chemically reactive, or hot-melt type, etc. Regarding the thickness of the adhesive layer, it can be, for example, 1~10 μm, preferably 2~5 μm.

[0042] When used as battery packaging material, the metal layer of the aluminum-plastic composite film acts as an intermediate barrier layer, preventing moisture and oxygen from penetrating the battery cell and preventing electrolyte leakage. Its mechanical strength also helps withstand external impacts, protecting the structural integrity of the battery cell. In some embodiments of this application, the metal layer is one or more combinations of aluminum foil, stainless steel foil, plated iron foil, and copper foil, preferably aluminum foil. The aluminum foil material can be pure aluminum or aluminum alloy, such as aluminum-iron alloy or aluminum-manganese alloy. The thickness of the metal layer is 20-150 μm, preferably 60-100 μm. Further, one or both surfaces of the metal layer undergo surface treatment to improve corrosion resistance, adhesion stability, etc. Exemplarily, the surface treatment of the metal layer is performed using chemical methods, such as passivation treatment or degreasing treatment, but is not limited to these. Passivation treatment refers to generating a stable passivation film on the surface of the metal layer using a passivation solution, enhancing corrosion resistance and surface roughness, etc. Passivation solutions include, for example, HNO3 or H2SO4. Degreasing treatment refers to the removal of grease and oxides from the surface of aluminum foil using an alkaline solution, such as KOH or K2CO3.

[0043] In some embodiments of this application, the aluminum-plastic composite film includes a substrate layer, an adhesive layer, a metal layer, and a sealing layer. During the preparation of this aluminum-plastic composite film, the metal layer and the sealing layer are dry-laminated. The adhesive layer is provided to firmly bond the sealing layer and the metal layer, and is formed by curing an adhesive that bonds the sealing layer and the metal layer. In some embodiments of this application, the adhesive used to form the adhesive layer is a polyurethane adhesive or an epoxy resin adhesive, and its curing form can be solvent-evaporating, emulsion-type, chemically reactive, or hot-melt type, etc. Regarding the thickness of the adhesive layer, it can be, for example, 1~10 μm, preferably 2~5 μm.

[0044] In some embodiments of this application, the aluminum-plastic composite film includes a substrate layer, an adhesive layer, a metal layer, and a sealing layer. During the preparation of this aluminum-plastic composite film, the metal layer and the sealing layer are thermally bonded. Thermal bonding involves melting and extruding the resin particles of the sealing layer, coating them onto the metal layer using a casting method, and then curing them at high temperature to form the sealing layer, ensuring a tight bond between the sealing layer and the metal layer.

[0045] When used as a battery packaging material, the aluminum-plastic composite film's sealing layer serves as an inner heat-sealing layer, directly contacting the internal environment of the battery cell. Therefore, it must possess chemical corrosion resistance, insulation, and heat-sealing properties. Combined with the metal layer, it ensures a tight seal and prevents electrolyte corrosion of the metal layer. The sealing layer is a polymer film with a melting point of 140-260°C and a thickness of 10-150 μm, preferably 40-80 μm. Exemplarily, the polymer film includes, but is not limited to, polyolefin films. Polyolefin films are thin film materials made of polyolefin resins, including, but not limited to, polyethylene, polypropylene, modified polyethylene, and modified polypropylene.

[0046] Another embodiment of this application provides a battery that uses an aluminum-plastic composite film as the packaging material as described in the above embodiments / examples. The battery is preferably a pouch battery, including, but not limited to, secondary batteries used in portable electronic devices (such as smartphones and tablets), electric vehicle power batteries, and energy storage systems. Types of secondary batteries include, for example, lithium-ion batteries, lithium-ion polymer batteries, lead-acid batteries, nickel / hydrogen batteries, nickel / cadmium batteries, nickel / iron batteries, nickel / zinc batteries, silver oxide / zinc batteries, metal-air batteries, multivalent cation batteries, capacitors, and capacitors.

[0047] In one embodiment of this application, the battery is a pouch lithium-ion battery, comprising a battery element having at least a positive electrode, a negative electrode, and an electrolyte. The battery element is packaged within an aluminum-plastic composite film as described in the above embodiments / examples, with the sealing layer located on the inner side and the substrate layer on the outer side. Other structural and specific details of the battery are designed in a conventional manner and with existing technology, and will not be elaborated here.

[0048] The following specific examples illustrate this application in detail. It should also be understood that the following examples are only for illustrative purposes and should not be construed as limiting the scope of protection of this application. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of this application fall within the scope of protection of this application. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0049] Example 1

[0050] I. Preparation of Aluminum-Plastic Composite Film

[0051] Using 80μm thick aluminum foil as the base material, passivation treatment is performed on both sides of the aluminum foil with passivation liquid. Then, adhesive is applied to both sides of the passivated aluminum foil, and PET film and polypropylene film are respectively attached to both sides of the aluminum foil. The film is then hot-pressed together using a machine. Finally, it is placed in an oven at 80℃ for curing treatment to produce an aluminum-plastic composite film.

[0052] II. The Influence of Material Mechanical Properties on the Formability of Aluminum-Plastic Composite Films

[0053] Tensile test:

[0054] Using a JDC cutter, PET, aluminum foil, and aluminum-plastic composite film were cut into strips measuring 15mm x 200mm. Tensile tests were performed on PET, aluminum foil, and aluminum-plastic composite film according to national standards GB / T 1040.1-2018 "Determination of Tensile Properties of Plastics - Part 1: General Rules" and GB / T228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Test Method at Room Temperature". The tensile conditions were as follows: speed as shown in Table 1, clamp distance 50mm, and extensometer gauge length 30mm.

[0055] The tensile strength and elongation of PET single-layer film, aluminum foil single-layer film, and aluminum-plastic composite film are not simply additive. This indicates that there is a certain synergistic effect between PET single-layer film and aluminum foil single-layer film after lamination. Figure 1 As can be seen, the PET film did not play a synergistic reinforcing role during the elastic deformation of the aluminum foil film; instead, the aluminum foil primarily absorbed energy. After the aluminum-plastic composite film broke, the PET film also ceased to absorb energy. This demonstrates the interfacial synergistic reinforcing effect of the aluminum-plastic composite film. The tensile strength integral between the yield point of the aluminum foil and the breaking point of the aluminum-plastic composite film is termed the "effective energy" of PET. Aluminum-plastic composite films were prepared using PET1 films with thicknesses of 25 μm and 12 μm, and PET2 films with thicknesses of 25 μm, 30 μm, 12 μm, and 27 μm as substrate layers. Tensile tests were conducted to measure yield strength, tensile strength, and elongation. Figure 2 The effective energy was calculated using Origin 2024 Pro, and the results are shown in Table 1.

[0056] Table 1

[0057]

[0058] Note: PET1 and PET2 are two different types of PET film, both of which are commercially available products.

[0059] 1. Aluminum foil is stretched according to MD and TD respectively. After the yield strength results meet the Grubbs test, the average of the corresponding abscissas is taken as Yx, and Y is calculated. x The value is 9.0451mm, so we select the value based on 9mm.

[0060] 2. Different PET types will alter the breaking point of the aluminum-plastic composite film, but this will only amplify or reduce the difference in results, without affecting the size comparison of the structure. The aluminum-plastic composite film of sample 3 was selected and stretched according to MD and TD standards respectively. The stroke results corresponding to the breaking point satisfied the Grubbs test, and the average value was taken as B. x B was calculated x The value is 39.3389mm, so we select 39mm.

[0061] 3. This represents the displacement-tension curve of PET stretched at a speed (as shown in Table 1), with a clamping distance of 50 mm and an extensometer gauge length of 30 mm.

[0062] 4. Effective Energy Calculation Formula

[0063] Results Analysis: At the same speed (5 mm / mm), the MD, TD, 45° oblique angle, and 135° oblique angle of six PET samples (samples 1-6) were tested. Since the forming of aluminum-plastic composite film is actually an extension in different directions, the minimum values ​​in the four directions are the weak points of the material. The minimum effective energy is 27 μm PET2 > 25 μm PET1 > 25 μm PET2 > 30 μm PET2 > 12 μm PET1 > 12 μm PET2, which is consistent with the trend of formability.

[0064] The change in integral area corresponding to different velocities is due to the different times in which material molecules untangle and break, rather than to differences in the materials themselves. Therefore, when using this method to solve the problem of material selection, the integral areas of different materials should be compared using the same velocity and the same gauge length.

[0065] This demonstrates that aluminum-plastic composite films made from PET films with higher effective energy exhibit a higher forming limit. Therefore, improving the effective energy of the substrate layer material can enhance the formability of aluminum-plastic composite films.

[0066] Based on the above experimental results, the SS curve of the substrate layer material and the integral area of ​​its abscissa in a specific region of metal strain are controlled within the range of 1000~1900. This enables the substrate layer material to have higher effective energy, which can improve the deep drawing performance of the aluminum-plastic composite film, that is, effectively improve the forming limit of the aluminum-plastic composite film, making it less prone to pinholes and cracks during forming. This provides an outer layer material with excellent formability for soft packaging of new energy batteries such as lithium batteries.

[0067] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. An aluminum-plastic composite film, characterized in that, include: It includes at least a substrate layer, an adhesive layer, and a metal layer; The stress-strain curve of the substrate layer and the area of ​​its integral over a specific region of metal strain are denoted as A. ;1000≤A≤1900; This refers to the proportional limit or yield point of the metal layer. This is the break point of the aluminum-plastic composite film. This represents the displacement-tensile force curve of the substrate layer stretched at a speed of 1~100mm / min.

2. The aluminum-plastic composite film according to claim 1, characterized in that: The stress-strain curve is obtained through a tensile test. The tensile test conditions include: speed 5~100mm / min, clamp distance 50mm, and extensometer gauge length 30mm.

3. The aluminum-plastic composite film according to claim 1, characterized in that: The substrate layer is a polyester film, a polyamide film, a polyester / polyamide co-extruded film, or a composite film containing a polyester film and a polyamide film.

4. The aluminum-plastic composite film according to claim 1, characterized in that: The thickness of the substrate layer is 1.5~90μm.

5. The aluminum-plastic composite film according to any one of claims 1 to 3, characterized in that: The substrate layer is a composite film composed of a polyester film with a thickness of 6~38μm and a polyamide film with a thickness of 15~30μm.

6. The aluminum-plastic composite film according to claim 1, characterized in that: The adhesive used to form the adhesive layer is a polyurethane adhesive or an epoxy resin adhesive.

7. The aluminum-plastic composite film according to claim 1, characterized in that: The metal layer is one or more of aluminum foil, stainless steel foil, coated iron foil, and copper foil; And / or, the thickness of the metal layer is 20~150μm.

8. The aluminum-plastic composite film according to claim 1, characterized in that: The aluminum-plastic composite film includes a substrate layer, an adhesive layer, a metal layer, and a sealing layer; or, the aluminum-plastic composite film includes a substrate layer, an adhesive layer, a metal layer, and a sealing layer.

9. The aluminum-plastic composite film according to claim 8, characterized in that: The sealing layer is a polymer film with a melting point of 140~260℃; And / or, the thickness of the sealing layer is 10~150μm.

10. A battery, characterized in that: The battery uses the aluminum-plastic composite film as described in any one of claims 1 to 9 as the packaging material.

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