Aluminum-plastic film, preparation method and application thereof, lithium ion battery and sodium ion battery

Abstract

The invention provides an aluminum-plastic film, a preparation method and application thereof, a lithium ion battery and a sodium ion battery. The aluminum-plastic film comprises an EVA-containing polyethylene layer, a flame-retardant layer, an aluminum foil layer and a protective layer which are sequentially stacked, and the EVA-containing polyethylene layer is prepared from EVA and polyethylene; during use, when the temperature of the battery reaches 100 DEG C, an EVA corresponding area of the polyethylene layer containing EVA can be automatically stripped, so that the flame-retardant layer is exposed to play a flame-retardant role, the temperature of the battery cell is prevented from further rising, and the thermal runaway of the battery cell is prevented; according to the aluminum-plastic film for preventing the thermal runaway of the battery, the mass ratio of the EVA to the polyethylene is (3-5): (5-7), and the inner layer of the aluminum-plastic film has good stripping force and tensile strength while an area corresponding to the EVA can be automatically stripped and the flame-retardant layer is exposed to play a flame-retardant role.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to an aluminum-plastic film, its preparation method and application, lithium-ion batteries, and sodium-ion batteries. Background Technology

[0002] In recent years, with economic development and social progress, lithium-ion and sodium-ion batteries have become increasingly widely used. However, the safety issues of lithium-ion and sodium-ion batteries have attracted increasing attention, especially thermal runaway. Thermal runaway refers to the phenomenon where, under abusive conditions (such as overcharging, short circuits, high temperatures, or mechanical damage), the internal chain reaction of a battery goes out of control, leading to a rapid increase in temperature and serious consequences such as fire and explosion. It is evident that thermal runaway poses a serious threat to people's lives and property.

[0003] Existing aluminum-plastic films used for battery encapsulation mostly have a "protective layer-aluminum foil layer-polyethylene layer" structure, which only provides basic encapsulation and barrier functions and lacks an early intervention mechanism against thermal runaway. When the battery temperature begins to rise, traditional aluminum-plastic films cannot actively trigger flame retardancy and can only passively withstand high temperatures, making it difficult to prevent the spread of thermal runaway. Therefore, developing an aluminum-plastic film that can play a flame-retardant role in the early stages of battery thermal runaway has become a key requirement for solving battery safety issues. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides an aluminum-plastic film, its preparation method and application, and a sodium-ion battery. The aluminum-plastic film of this invention includes a flame-retardant layer and a polyethylene layer containing EVA. When the battery temperature exceeds 100°C, the middle part of the polyethylene layer containing EVA will automatically peel off, allowing the flame-retardant layer inside the aluminum-plastic film to come into contact with the battery and begin to function, preventing the battery temperature from rising further.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an aluminum-plastic film, comprising: An aluminum foil layer with a protective layer on its surface; A flame-retardant layer is located on the surface of the aluminum foil layer away from the protective layer; A polyethylene layer containing EVA is located on the surface of the flame-retardant layer away from the aluminum foil layer.

[0006] Preferably, the material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, and the mass ratio of EVA to polyethylene is (3~5):(5~7); The material used in the polyethylene layer containing EVA, excluding the middle portion, is polyethylene.

[0007] Preferably, the central area of ​​the polyethylene layer containing EVA is 1 / 50 to 1 / 9 of the total area of ​​the polyethylene layer containing EVA.

[0008] Preferably, the flame-retardant layer contains a flame retardant, which includes phosphorus-based flame retardants and / or halogen-based flame retardants; The phosphorus-based flame retardant includes ethoxy(pentafluoro)cyclotriphosphazene; The halogenated flame retardant includes perfluoro2-methyl-3-pentanone.

[0009] Preferably, the thickness of the aluminum foil layer is 1~50μm, the thickness of the protective layer is 1~25μm, the thickness of the flame retardant layer is 5~20μm, and the thickness of the polyethylene layer containing EVA is 1~40μm; The protective layer is made of either nylon or PET.

[0010] Secondly, the present invention also provides a method for preparing the aluminum-plastic film, comprising the following steps: coating a first adhesive on the surface of an aluminum foil layer, then placing a protective layer on the first adhesive, and curing. A second adhesive is applied to the surface of the aluminum foil layer away from the protective layer. After the adhesive has cured, the flame retardant layer is placed on the second adhesive and pressed together. A polyethylene layer containing EVA was prepared using EVA and polyethylene as raw materials; A third adhesive is applied to the surface of the flame-retardant layer away from the protective layer. After the adhesive has cured, a polyethylene layer containing EVA is placed on the third adhesive and pressed together.

[0011] Preferably, the method for preparing the polyethylene layer containing EVA includes the following steps: A multi-channel co-extrusion die is provided, the die including a central channel and an outer channel located outside the central channel and coaxially arranged; The molten polyethylene and molten EVA are mixed and then injected into the middle channel; Molten polyethylene is injected into the outer flow channel; The material in the middle channel and the outer channel is simultaneously extruded onto the substrate through a multi-channel co-extrusion die, cooled, and peeled off to obtain a polyethylene layer containing EVA. In the step of mixing molten polyethylene and molten EVA and injecting them into the intermediate flow channel, the mass ratio of EVA to polyethylene is (3~5):(5~7); Polyethylene is heated to 105℃~135℃ to obtain molten polyethylene; EVA is heated to 75℃~100℃ to obtain molten EVA; In the step of placing the flame-retardant layer on the second adhesive and pressing, the pressing temperature is 180℃~200℃, the pressing pressure is 0.3Mpa~0.5Mpa, and the pressing time is 3~5s. The polyethylene layer containing EVA is placed on the third adhesive. In the pressing step, the pressing temperature is 60℃~70℃, the pressing pressure is 0.3Mpa~0.5Mpa, and the pressing time is 3~5s.

[0012] Preferably, the method for preparing the flame-retardant layer includes the following steps: Water, polyvinyl alcohol, ethoxy(pentafluoro)cyclotriphosphazene, perfluoro-2-methyl-3-pentanone, and methyl methacrylate were mixed, and ammonium persulfate was added. The mixture was stirred at 70~80℃ for 3~4 hours, coated onto a substrate, and vacuum baked to peel off the flame retardant layer. The vacuum baking process parameters were: vacuum degree -0.095~-0.098 MPa, baking temperature 80~100℃, and baking time 2~4 hours. The mass ratio of water, polyvinyl alcohol, ethoxy(pentafluoro)cyclotriphosphazene, perfluoro-2-methyl-3-pentanone, methyl methacrylate, and ammonium persulfate is (200~300):(2~3):(16~20):(4~5):(40~45):(0.2~0.3).

[0013] Thirdly, the present invention also provides the application of the aluminum-plastic film described above or the aluminum-plastic film prepared by the preparation method described above in the preparation of lithium-ion batteries or sodium-ion batteries.

[0014] Fourthly, the present invention also provides a lithium-ion battery or a sodium-ion battery, comprising the aluminum-plastic film described above or the aluminum-plastic film prepared by the preparation method described above.

[0015] The aluminum-plastic film, its preparation method, and its application of the present invention have the following advantages over the prior art: 1. The aluminum-plastic film for preventing battery thermal runaway of the present invention includes a polyethylene layer containing EVA, a flame retardant layer, an aluminum foil layer, and a protective layer stacked sequentially. The polyethylene layer containing EVA is made of EVA and polyethylene. In use, when the battery temperature exceeds 100°C, the corresponding area of ​​EVA in the polyethylene layer containing EVA will automatically peel off, exposing the flame retardant layer to begin to play a flame retardant role, preventing the cell temperature from rising further, thereby preventing cell thermal runaway. 2. The aluminum-plastic film for preventing battery thermal runaway of the present invention uses EVA and polyethylene in the middle of the polyethylene layer containing EVA, with the mass ratio of EVA to polyethylene being (3~5):(5~7). This ensures that the corresponding area of ​​EVA will automatically peel off, exposing the flame retardant layer to begin to play a flame retardant role, while also ensuring that the inner layer of the aluminum-plastic film has good peel force (peel force ≥33N / 15mm) and tensile strength (≥61N / 15mm). Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the aluminum-plastic film structure of the present invention; Figure 2 This is a schematic diagram of the structure of the polyethylene layer containing EVA according to the present invention; Figure 3 This is a schematic diagram of the structure of the multi-channel co-extrusion die of the present invention; Figure 4 This is a state diagram of the sodium-ion battery assembled with aluminum-plastic film in Example 1 at 200°C. Figure 5 The diagram shows the state of the sodium-ion battery assembled with aluminum-plastic film in Comparative Example 1 at 400°C. Figure 6 This is a state diagram of the sodium-ion battery assembled with aluminum-plastic film in Comparative Example 2 at 300°C. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] The following provides a detailed description of each example. It should be noted that the order of description of the embodiments below is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0020] This invention provides an aluminum-plastic film for preventing battery thermal runaway, such as... Figure 1 As shown, it includes: Aluminum foil layer 1, with a protective layer 2 on its surface; Flame retardant layer 3 is located on the surface of the aluminum foil layer away from the protective layer 2; A polyethylene layer 4 containing EVA is located on the surface of the flame-retardant layer 3 away from the aluminum foil layer 1.

[0021] The aluminum-plastic film for preventing battery thermal runaway of the present invention includes a polyethylene layer 4 containing EVA, a flame retardant layer 3, an aluminum foil layer 1, and a protective layer 2 stacked sequentially. The polyethylene layer 4 containing EVA is made of EVA (ethylene-vinyl acetate copolymer), a thermoplastic resin made by copolymerization of ethylene and vinyl acetate, and polyethylene. In use, when the battery temperature exceeds 100°C, the corresponding area of ​​EVA in the polyethylene layer 4 containing EVA will automatically peel off, exposing the flame retardant layer to begin to exert its flame retardant effect, preventing the cell temperature from rising further, thereby preventing thermal runaway of the cell.

[0022] Specifically, during battery thermal runaway, a large amount of gas is generated internally, causing the battery to bulge and the internal pressure (P) to rise rapidly. This pressure acts on the inner surface of the aluminum-plastic film. Since the interface containing the EVA layer 4, specifically the area containing EVA, is the weakest link (EVA has lower heat resistance than polyethylene and softens first when heated), the high-pressure gas will "pry open" this interface. The mechanical strength of the weak area (containing EVA) is insufficient to maintain the interfacial bond with the flame-retardant layer. Under slight pressure inside the battery (such as gas expansion due to temperature rise or slight deformation of the cell) or interlayer stress, "automatic peeling" naturally occurs, exposing the flame-retardant layer to begin its flame-retardant function.

[0023] In some embodiments, the material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, and the mass ratio of EVA to polyethylene is (3~5):(5~7); The material used in the polyethylene layer containing EVA, excluding the middle portion, is polyethylene.

[0024] In some embodiments, the central area of ​​the polyethylene layer containing EVA does not exceed 1 / 9 of the total area of ​​the polyethylene layer containing EVA. For example, the central area of ​​the polyethylene layer containing EVA is 1 / 50 to 1 / 9 of the total area of ​​the polyethylene layer containing EVA. Specifically, refer to... Figure 2 As shown, the material used in the central region 41 of the polyethylene layer containing EVA is EVA and polyethylene, while the material used in the outer region 42 outside the central region 41 is polyethylene. The geometric center of the central region 41 is the same as the geometric center of the entire polyethylene layer containing EVA. For example, if the surface of the entire polyethylene layer containing EVA is rectangular, the central region is also rectangular, and their geometric centers coincide. The area of ​​the central region 41 is 1 / 50 to 1 / 9 of the area of ​​the entire polyethylene layer containing EVA. By limiting the mass ratio of EVA to polyethylene, it is ensured that the corresponding area of ​​EVA will automatically peel off, exposing the flame retardant layer to begin to play its flame retardant role, while also ensuring that the aluminum-plastic film has good peel force and tensile strength.

[0025] In some embodiments, the material of the protective layer 2 is either nylon (a common name for polyamide (PA)) or PET.

[0026] In some embodiments, the flame-retardant layer contains a flame retardant, which includes phosphorus-based flame retardants and / or halogen-based flame retardants. Phosphorus-based flame retardants include ethoxy(pentafluoro)cyclotriphosphazene (CAS No. 33027-66-6, molecular formula C2H5F5N3OP3); Halogenated flame retardants include perfluoro(2-methyl-3-pentanone), also known as perfluorohexanone, CAS No.: 756-13-8, molecular formula: C6F. 12 O.

[0027] In some embodiments, the thickness of the aluminum foil layer is 1~50μm, the thickness of the protective layer is 1~25μm, the thickness of the flame retardant layer is 5~20μm, and the thickness of the polyethylene layer containing EVA is 1~40μm.

[0028] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned aluminum-plastic film, comprising the following steps: S1. Apply a first adhesive (coating thickness of 5~10μm) to the surface of the aluminum foil layer, then place the protective layer on the first adhesive and cure it; S2. Apply a second adhesive (coating thickness of 5~10μm) to the surface of the aluminum foil layer away from the protective layer. After curing (curing temperature of 30℃-50℃, curing time of 4-12h), place the flame retardant layer on the second adhesive and press it together. The pressing temperature is 180℃~200℃, the pressing pressure is 0.3Mpa~0.5Mpa, and the pressing time is 3~5s. S3. A polyethylene layer containing EVA is prepared using EVA and polyethylene as raw materials; S4. Apply a third adhesive (coating thickness of 5~10μm) to the surface of the flame-retardant layer away from the protective layer. After curing (curing temperature of 30℃-50℃, curing time of 4-12h), place the polyethylene layer containing EVA on the third adhesive and press it together. The pressing temperature is 60℃~70℃, the pressing pressure is 0.3Mpa~0.5Mpa, and the pressing time is 3~5s.

[0029] Specifically, a first adhesive is coated on the surface of the aluminum foil layer, and then a protective layer is placed on the first adhesive and cured; wherein the curing temperature is 80~90℃ and the time is 1~2h.

[0030] In some embodiments, a method for preparing a polyethylene layer containing EVA includes the following steps: A multi-channel co-extrusion die head is provided, the die head including a central channel and an outer channel located outside the central channel and coaxially arranged; The molten polyethylene and molten EVA are mixed and then injected into the middle channel; Molten polyethylene is injected into the outer flow channel; The material in the middle flow channel and the outer flow channel is simultaneously extruded onto the substrate (e.g., polytetrafluoroethylene (PTFE) substrate, chrome-plated / nickel-plated metal plate, etc.) through a multi-channel co-extrusion die, cooled, and the coating is peeled off from the substrate to obtain a polyethylene layer containing EVA. In the step of mixing molten polyethylene and molten EVA and injecting it into the intermediate flow channel, the mass ratio of EVA to polyethylene is (3~5):(5~7). Polyethylene is heated to 105℃~135℃ to obtain molten polyethylene; EVA is heated to 75℃~100℃ to obtain molten EVA.

[0031] like Figure 3As shown, the die head 5 includes a middle flow channel 51 and an outer flow channel 52 located outside the middle flow channel 51 and coaxially arranged. When molten polyethylene and molten EVA are mixed and injected into the middle flow channel, and molten polyethylene is injected into the outer flow channel, after being extruded simultaneously through the multi-flow channel co-extrusion die, the mixture is cooled to obtain a polyethylene layer containing EVA. The middle flow channel 51 corresponds to the central region 41. After EVA and polyethylene are extruded through the middle flow channel 51, the central region (containing EVA and polyethylene, and the mass ratio of EVA to polyethylene is (3~5):(5~7)) is obtained. The outer flow channel 52 corresponds to the outer region 42. After polyethylene is extruded through the outer flow channel 52, the outer region 42 (containing only polyethylene) is obtained.

[0032] The melting temperature range of low-density polyethylene (LDPE) is 105~115℃, and the melting temperature range of high-density polyethylene (HDPE) is 130~135℃.

[0033] In some embodiments, the method for preparing the flame-retardant layer includes the following steps: Water, polyvinyl alcohol (PVP), ethoxy(pentafluoro)cyclotriphosphazene, perfluoro-2-methyl-3-pentanone, and methyl methacrylate (MMA, chemical formula C5H8O2, CAS number 80-62-6) are placed in a mixer and stirred at 10000~12000 rpm for 5~10 min. Then ammonium persulfate is added, and the mixture is stirred at 70~80℃ for 3~4 h. The mixture is then coated onto a substrate (the substrate can be polytetrafluoroethylene (PTFE) substrate, chrome-plated stainless steel plate, etc.), and vacuum baked to peel the coating off the substrate to the flame retardant layer. The vacuum baking process parameters are: vacuum degree: -0.095~-0.098 MPa, baking temperature: 80~100℃, baking time: 2~4 h. The mass ratio of water, polyvinyl alcohol, ethoxy(pentafluoro)cyclotriphosphazene, perfluoro-2-methyl-3-pentanone, methyl methacrylate, and ammonium persulfate is (200~300):(2~3):(16~20):(4~5):(40~45):(0.2~0.3).

[0034] In some embodiments, the first adhesive, the second adhesive, and the third adhesive are all polyurethane adhesives, such as polyurethane PU potting compound 363AB from Shenzhen Zhaoyuheng Technology Co., Ltd.

[0035] Based on the same inventive concept, the present invention also provides the application of the above-mentioned aluminum-plastic film or the aluminum-plastic film prepared by the above-mentioned preparation method in the preparation of lithium-ion batteries or sodium-ion batteries.

[0036] Based on the same inventive concept, this invention also provides a lithium-ion battery or a sodium-ion battery, comprising the aforementioned aluminum-plastic film or the aluminum-plastic film prepared by the aforementioned preparation method. Specifically, the dry cell and the aluminum-plastic film are packaged together, and then subjected to electrolyte injection, formation, and capacity testing to form a lithium-ion battery or a sodium-ion battery.

[0037] The following detailed embodiments further illustrate the aluminum-plastic film for preventing battery thermal runaway, its preparation method, and its application. This section further explains the invention in conjunction with specific embodiments, but should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in the art.

[0038] In the following examples and comparative examples, the polyethylene used is H790495 high-density polyethylene, purchased from Maclean's Reagents; EVA specifically refers to P815473 ethylene-vinyl acetate copolymer, purchased from Maclean's Reagents. The specific polyvinyl alcohol is 767382 polyvinyl alcohol, Mw9000-10000, purchased from Maclean's Reagents; The first adhesive, the second adhesive, and the third adhesive are all polyurethane adhesives, specifically polyurethane PU potting compound 363AB from Shenzhen Zhaoyuheng Technology Co., Ltd.

[0039] Example 1 This embodiment provides an aluminum-plastic film for preventing battery thermal runaway, comprising: An aluminum foil layer with a protective layer on its surface; The flame-retardant layer is located on the surface of the aluminum foil layer away from the protective layer; The polyethylene layer containing EVA is located on the surface of the flame-retardant layer away from the aluminum foil layer; The material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, with a mass ratio of EVA to polyethylene of 3:7; the material used in the position outside the middle of the polyethylene layer containing EVA is polyethylene. The central area of ​​the polyethylene layer containing EVA (in a cuboid shape) is 1 / 9 of the total area of ​​the polyethylene layer containing EVA (in a cuboid shape). The aluminum foil layer is 40 μm thick, the protective layer is made of nylon (commercially available conventional nylon, which has not been modified in this invention) and is 15 μm thick, the flame retardant layer is 20 μm thick, and the polyethylene layer containing EVA is 30 μm thick. This embodiment also provides a method for preparing the above-mentioned aluminum-plastic film, including the following steps: S1. Apply a first adhesive (coating thickness of 8μm) to the surface of the aluminum foil layer, then place the protective layer on the first adhesive and cure it; S2. Apply a second adhesive (coating thickness of 8 μm) to the surface of the aluminum foil layer away from the protective layer, and allow it to cure (curing temperature of 30°C, curing time of 6 h). Then, place the flame retardant layer on the second adhesive and press it together. The pressing temperature is 190°C, the pressing pressure is 0.4 MPa, and the pressing time is 5 s. S3. A polyethylene layer containing EVA is prepared using EVA and polyethylene as raw materials; S4. Apply a third adhesive (coating thickness of 8μm) to the surface of the flame-retardant layer away from the protective layer, and after it has cured (curing temperature of 30℃, curing time of 6h), place the polyethylene layer containing EVA on the third adhesive and press it together; wherein, the pressing temperature is 60℃, the pressing pressure is 0.3Mpa, and the pressing time is 5s. A first adhesive is applied to the surface of the aluminum foil layer, and then a protective layer is placed on the first adhesive and cured; wherein the curing temperature is 80℃ and the time is 1 hour. A method for preparing a polyethylene layer containing EVA includes the following steps: A multi-channel co-extrusion die head is provided, the die head including a central channel and an outer channel located outside the central channel and coaxially arranged; The molten polyethylene and molten EVA are mixed and then injected into the middle channel; Molten polyethylene is injected into the outer flow channel; The material in the middle flow channel and the outer flow channel is simultaneously extruded onto the substrate (polytetrafluoroethylene (PTFE) substrate) through a multi-channel co-extrusion die. After cooling, the coating is peeled off from the substrate to obtain a polyethylene layer containing EVA. In the step of mixing molten polyethylene and molten EVA and injecting it into the intermediate flow channel, the mass ratio of EVA to polyethylene is 3:7. Polyethylene is heated to 135°C to obtain molten polyethylene; EVA is heated to 95°C to obtain molten EVA; The method for preparing a flame-retardant layer includes the following steps: 200 parts by weight of water, 2 parts by weight of polyvinyl alcohol (PVP), 16 parts by weight of ethoxy(pentafluoro)cyclotriphosphazene, 4 parts by weight of perfluoro-2-methyl-3-pentanone, and 40 parts by weight of methyl methacrylate were placed in a mixer and stirred at 10,000 pm for 5 min. Then, 0.2 parts by weight of ammonium persulfate were added, and the mixture was stirred at 70°C for 4 h. The mixture was then coated onto a substrate (polytetrafluoroethylene (PTFE) substrate) and vacuum baked to peel off the coating from the substrate to the flame retardant layer. The vacuum baking process parameters were: vacuum degree -0.098 MPa, baking temperature 80°C, and baking time 2 h. Example 2 The aluminum-plastic film provided in this embodiment is the same as that in embodiment 1, except that the material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, and the mass ratio of EVA to polyethylene is 4:6. The rest is the same as in embodiment 1. The method for preparing the aluminum-plastic film provided in this embodiment is the same as that in Embodiment 1, except that in the step of mixing molten polyethylene and molten EVA and injecting it into the intermediate flow channel, the mass ratio of EVA to polyethylene is 4:6; the rest is the same as in Embodiment 1. Example 3 The aluminum-plastic film provided in this embodiment is the same as that in embodiment 1, except that the material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, and the mass ratio of EVA to polyethylene is 5:5. The rest is the same as in embodiment 1. The method for preparing the aluminum-plastic film provided in this embodiment is the same as that in Embodiment 1, except that in the step of mixing molten polyethylene and molten EVA and injecting them into the intermediate flow channel, the mass ratio of EVA to polyethylene is 5:5; the rest is the same as in Embodiment 1.

[0040] Comparative Example 1 This comparative example provides an aluminum-plastic film (excluding the flame-retardant layer), comprising: An aluminum foil layer with a protective layer on its surface; The polyethylene layer containing EVA is located on the surface of the aluminum foil layer away from the protective layer; The material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, with a mass ratio of EVA to polyethylene of 3:7; the material used in the polyethylene layer containing EVA outside the middle is polyethylene. The central area of ​​the polyethylene layer containing EVA (in a cuboid shape) is 1 / 9 of the total area of ​​the polyethylene layer containing EVA (in a cuboid shape). The aluminum foil layer is 40 μm thick, the protective layer is made of nylon (commercially available conventional nylon, which has not been modified in this invention) and is 15 μm thick, the flame retardant layer is 20 μm thick, and the polyethylene layer containing EVA is 30 μm thick. This comparative example also provides a method for preparing the above-mentioned aluminum-plastic film, including the following steps: S1. Apply a first adhesive (coating thickness of 8μm) to the surface of the aluminum foil layer, then place the protective layer on the first adhesive and cure it; S2. A polyethylene layer containing EVA is prepared using EVA and polyethylene as raw materials; S3. Apply a second adhesive (coating thickness of 8μm) to the surface of the aluminum foil layer away from the protective layer. After curing (curing temperature of 30℃, curing time of 6h), place the polyethylene layer containing EVA on the second adhesive and press it together. The pressing temperature is 60℃, the pressing pressure is 0.3Mpa, and the pressing time is 5s. A first adhesive is applied to the surface of the aluminum foil layer, and then a protective layer is placed on the first adhesive and cured; wherein the curing temperature is 80℃ and the time is 1 hour. The method for preparing the polyethylene layer containing EVA is the same as in Example 1.

[0041] Comparative Example 2 This embodiment provides an aluminum-plastic film (containing no EVA), comprising: An aluminum foil layer with a protective layer on its surface; The flame-retardant layer is located on the surface of the aluminum foil layer away from the protective layer; The polyethylene layer is located on the surface of the flame-retardant layer away from the aluminum foil layer; The aluminum foil layer is 40 μm thick, the protective layer is made of nylon (commercially available conventional nylon, which has not been modified in this invention) and is 15 μm thick, the flame retardant layer is 20 μm thick, and the polyethylene layer is 30 μm thick. This comparative example also provides a method for preparing the above-mentioned aluminum-plastic film, including the following steps: S1. Apply a first adhesive (coating thickness of 8μm) to the surface of the aluminum foil layer, then place the protective layer on the first adhesive and cure it; S2. Apply a second adhesive (coating thickness of 8 μm) to the surface of the aluminum foil layer away from the protective layer, and allow it to cure (curing temperature of 30°C, curing time of 6 h). Then, place the flame retardant layer on the second adhesive and press it together. The pressing temperature is 190°C, the pressing pressure is 0.4 MPa, and the pressing time is 5 s. S3. A polyethylene layer is prepared using polyethylene as a raw material; S4. Apply a third adhesive to the surface of the flame-retardant layer away from the protective layer, and press the polyethylene layer onto the third adhesive; wherein the pressing temperature is 60℃, the pressing pressure is 0.3Mpa, and the pressing time is 5s. A first adhesive is applied to the surface of the aluminum foil layer, and then a protective layer is placed on the first adhesive and cured; wherein the curing temperature is 80℃ and the time is 1 hour. The method for preparing the polyethylene layer includes the following steps: Provide a die head, which includes flow channels; Molten polyethylene is injected into the flow channel, extruded, and then cooled to obtain a polyethylene layer. Polyethylene is heated to 135°C to obtain molten polyethylene; The method for preparing the flame-retardant layer is the same as in Example 1.

[0042] Performance testing Sodium iron pyrophosphate was used as the positive electrode material, hard carbon was used as the negative electrode material, polyethylene membrane was used as the separator, and 1 mol / L NaPF6-EC / DMC (i.e., a mixed solvent of EC (ethylene carbonate) and DMC (dimethyl carbonate) with a volume ratio of 1:1 and a NaPF6 concentration of 1 mol / L) was used to form a dry cell by winding. The aluminum-plastic film and dry cell aluminum from Examples 1-3 and Comparative Examples 1-2 were packaged together, and after electrolyte injection and formation, sodium-ion batteries were obtained. The flame retardant performance of the sodium-ion batteries was tested, and the results are shown in Table 1 below. The test method was as follows: sodium-ion batteries assembled with different aluminum-plastic films were placed in a temperature chamber, and the temperature chamber was heated to 200°C at a rate of 5°C / min. The state changes of the batteries were observed inside the 200°C chamber for 30 minutes, and the duration of the battery in the three stages of expansion, smoke, and fire was recorded. The results are shown in Table 1 below.

[0043] Table 1 - Flame retardant properties of sodium-ion batteries assembled with different aluminum-plastic films

[0044] As can be seen from Table 1 above, the highest temperature of the sodium-ion batteries assembled with aluminum-plastic film in Examples 1-3 is much lower than that in Comparative Examples 1-2. Furthermore, the expansion time and smoke time of the sodium-ion batteries assembled with aluminum-plastic film in Examples 1-3 are higher than those in Comparative Examples 1-2 under the condition that no fire has occurred. The longer the expansion time and smoke time, the better the warning effect and the better the flame retardant performance.

[0045] Figure 4 This is a state diagram of the sodium-ion battery assembled with aluminum-plastic film in Example 1 at 200°C. Figure 4 As can be seen, it bulges, but does not catch fire or explode; Figure 5 The diagram shows the state of the sodium-ion battery assembled with aluminum-plastic film in Comparative Example 1 at 400°C. Figure 5 As can be seen, it bulged, then caught fire and exploded; Figure 6 The diagram shows the state of the sodium-ion battery assembled with aluminum-plastic film in Comparative Example 2 at 300°C. Figure 6 It can be seen that it bulges, does not catch fire, but explodes.

[0046] The aluminum-plastic films from Examples 1-3 and Comparative Examples 1-2 were placed in an electrolyte (1 mol / L NaPF6-EC / DMC, i.e., a mixed solvent of EC (ethylene carbonate) and DMC (dimethyl carbonate) with a volume ratio of 1:1, and the concentration of NaPF6 was 1 mol / L) and left to stand at 60°C for 24 h. After removal, they were cleaned with DMC and tested using a universal tensile testing machine for inner layer peel force (which refers to the adhesive strength between the polyethylene layer containing EVA and the flame retardant layer) and tensile strength (which refers to the aluminum-plastic film being subjected to tensile force at both ends of the aluminum-plastic film until the aluminum-plastic film breaks). The results are shown in Table 2 below.

[0047] Table 2 - Inner layer peel strength and tensile strength of aluminum-plastic films in Examples 1-3 and Comparative Examples 1-2

[0048] As can be seen from Table 2, the inner layer peel strength and tensile strength of the aluminum-plastic film in Examples 1-3 are better than those in Comparative Examples 1-2. Furthermore, Tables 1-2 show that a higher mass ratio of EVA to polyethylene is not always better. In Example 2, when the mass ratio of EVA to polyethylene is approximately 4:6, the aluminum-plastic film exhibits the best flame retardant performance and tensile strength. Compared to Comparative Example 1, Examples 1-3 contain an aluminum-plastic film that better prevents battery thermal runaway, preventing the battery from catching fire or exploding. Compared to Comparative Example 2, Examples 1-3 contain an aluminum-plastic film that better controls battery temperature and expansion time in the early stages of battery thermal runaway.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An aluminum-plastic film, characterized in that, include: An aluminum foil layer with a protective layer on its surface; A flame-retardant layer is located on the surface of the aluminum foil layer away from the protective layer; A polyethylene layer containing EVA is located on the surface of the flame-retardant layer away from the aluminum foil layer.

2. The aluminum-plastic film as described in claim 1, characterized in that, The material used in the middle of the polyethylene layer containing EVA includes EVA and polyethylene, and the mass ratio of EVA to polyethylene is (3~5):(5~7); The material used in the polyethylene layer containing EVA, excluding the middle portion, is polyethylene.

3. The aluminum-plastic film as described in claim 2, characterized in that, The central area of ​​the polyethylene layer containing EVA is 1 / 50 to 1 / 9 of the total area of ​​the polyethylene layer containing EVA.

4. The aluminum-plastic film as described in claim 1, characterized in that, The flame-retardant layer contains a flame retardant, which includes phosphorus-based flame retardants and / or halogen-based flame retardants. The phosphorus-based flame retardant includes ethoxy(pentafluoro)cyclotriphosphazene; The halogenated flame retardant includes perfluoro2-methyl-3-pentanone.

5. The aluminum-plastic film as described in claim 1, characterized in that, The thickness of the aluminum foil layer is 1~50μm, the thickness of the protective layer is 1~25μm, the thickness of the flame retardant layer is 5~20μm, and the thickness of the polyethylene layer containing EVA is 1~40μm. The protective layer is made of either nylon or PET.

6. A method for preparing an aluminum-plastic film as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A first adhesive is applied to the surface of the aluminum foil layer, and then a protective layer is placed on the first adhesive and cured. A second adhesive is applied to the surface of the aluminum foil layer away from the protective layer. After the adhesive has cured, the flame retardant layer is placed on the second adhesive and pressed together. A polyethylene layer containing EVA was prepared using EVA and polyethylene as raw materials; A third adhesive is applied to the surface of the flame-retardant layer away from the protective layer. After the adhesive has cured, a polyethylene layer containing EVA is placed on the third adhesive and pressed together.

7. The method for preparing the aluminum-plastic film as described in claim 6, characterized in that, The method for preparing the polyethylene layer containing EVA includes the following steps: A multi-channel co-extrusion die is provided, the die including a central channel and an outer channel located outside the central channel and coaxially arranged; The molten polyethylene and molten EVA are mixed and then injected into the middle channel; Molten polyethylene is injected into the outer flow channel; The material in the middle channel and the outer channel is simultaneously extruded onto the substrate through a multi-channel co-extrusion die, cooled, and peeled off to obtain a polyethylene layer containing EVA. In the step of mixing molten polyethylene and molten EVA and injecting them into the intermediate flow channel, the mass ratio of EVA to polyethylene is (3~5):(5~7); Polyethylene is heated to 105℃~135℃ to obtain molten polyethylene; EVA is heated to 75℃~100℃ to obtain molten EVA; In the step of placing the flame-retardant layer on the second adhesive and pressing, the pressing temperature is 180℃~200℃, the pressing pressure is 0.3Mpa~0.5Mpa, and the pressing time is 3~5s. The polyethylene layer containing EVA is placed on the third adhesive. In the pressing step, the pressing temperature is 60℃~70℃, the pressing pressure is 0.3Mpa~0.5Mpa, and the pressing time is 3~5s.

8. The method for preparing the aluminum-plastic film as described in claim 6, characterized in that, The method for preparing the flame-retardant layer includes the following steps: Water, polyvinyl alcohol, ethoxy(pentafluoro)cyclotriphosphazene, perfluoro-2-methyl-3-pentanone, and methyl methacrylate were mixed, and ammonium persulfate was added. The mixture was stirred at 70~80℃ for 3~4 hours, coated onto a substrate, and vacuum baked to peel off the flame retardant layer. The vacuum baking process parameters were: vacuum degree -0.095~-0.098 MPa, baking temperature 80~100℃, and baking time 2~4 hours. The mass ratio of water, polyvinyl alcohol, ethoxy(pentafluoro)cyclotriphosphazene, perfluoro-2-methyl-3-pentanone, methyl methacrylate, and ammonium persulfate is (200~300):(2~3):(16~20):(4~5):(40~45):(0.2~0.3).

9. The application of an aluminum-plastic film as described in any one of claims 1 to 5 or an aluminum-plastic film prepared by any one of claims 6 to 8 in the preparation of lithium-ion batteries or sodium-ion batteries.

10. A lithium-ion battery or sodium-ion battery, characterized in that, This includes aluminum-plastic film as described in any one of claims 1 to 5 or aluminum-plastic film prepared by any one of claims 6 to 8.

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