Insulating film for battery top cover, method for manufacturing the same, and battery

Abstract

This invention discloses an insulating film for battery top covers, its preparation method, and a battery, relating to the field of battery manufacturing technology. The insulating film for battery top covers comprises an insulating protective layer, a foamed flame-retardant layer, and an insulating adhesive layer stacked sequentially. The foamed flame-retardant layer includes a matrix resin and functional fillers dispersed in the matrix resin, with a mass ratio of matrix resin to functional fillers of 1:(1~1.5). The functional fillers, by weight, include: 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica. This invention addresses the problem in existing technologies where the insulating film's insulation performance deteriorates under high-temperature conditions and it cannot effectively cope with thermal runaway.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and more specifically, to an insulating film for a battery top cover, a method for preparing the same, and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in 3C electronics, electric vehicles, and other fields due to their advantages such as high power density, light weight, small size, and environmental friendliness. The battery top cover, located on top of the battery, is a crucial component of the battery encapsulation. It not only seals the battery to prevent external environmental influences but also integrates several important functional structures and components, including terminals, explosion-proof valves, sealing rings, electrolyte injection holes, gas vents, and insulating film layers. Currently, polycarbonate (PC) film is primarily used as the insulating film for the battery top cover. One side of the PC film is coated with acrylic pressure-sensitive adhesive for direct adhesion to the metal top cover surface. However, with increasingly stringent battery safety standards, PC insulating film has limitations in terms of thermal safety. The heat distortion temperature of PC film is 125℃~135℃, far below the operating temperature of the battery under thermal runaway conditions. When thermal runaway occurs, abnormal internal heating occurs, and the temperature exceeds 150℃. At this point, the PC film will rapidly melt, shrink, or even burn, leading to a significant decrease in its mechanical strength and insulation performance, failing to effectively protect the battery from the effects of high-temperature environments. Furthermore, in the event of battery thermal runaway, the explosion-proof valve will automatically open, causing high-temperature flammable gases and sparks inside the battery to escape. Existing PC insulation films cannot effectively prevent this phenomenon and may even become part of the fire source due to their own flammability, seriously threatening the overall safety of the battery. Summary of the Invention

[0003] The main objective of this invention is to provide an insulating film for battery top covers, a method for preparing the same, and a battery, in order to solve the problems in the prior art where the insulating film's insulation performance deteriorates under high-temperature conditions and it cannot effectively cope with thermal runaway.

[0004] To achieve the above objectives, according to one aspect of the present invention, an insulating film for a battery top cover is provided, the insulating film for a battery top cover comprising an insulating protective layer, a foamed flame-retardant layer and an insulating adhesive layer stacked sequentially.

[0005] The foamed flame retardant layer includes a matrix resin and functional fillers dispersed in the matrix resin, with a mass ratio of matrix resin to functional fillers of 1:(1~1.5).

[0006] The functional fillers, by weight, include: 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica.

[0007] Furthermore, the particle size of any single particle in the expandable graphite is 100 μm to 180 μm; and / or,

[0008] In the foamed flame-retardant layer, the areal density of expandable graphite is 30 g / m³. 2 ~60g / m 2 .

[0009] Furthermore, the preparation method of expandable graphite includes the following steps: mixing natural flake graphite, concentrated sulfuric acid solution, and glacial acetic acid at a first temperature to obtain a first mixture; mixing the first mixture with potassium permanganate to obtain a second mixture; subjecting the second mixture to a first reaction to obtain a first reaction product; and subjecting the first reaction product to sequential water washing and drying to obtain expandable graphite.

[0010] Furthermore, the mass ratio of natural flake graphite to concentrated sulfuric acid solution is 1:(2~4); and / or,

[0011] The mass ratio of natural flake graphite to glacial acetic acid is 1:(0.5~1.5); and / or,

[0012] The mass ratio of natural flake graphite to potassium permanganate is 1:(0.15~0.25); and / or,

[0013] The H2SO4 content in the concentrated sulfuric acid solution is 95%~98% by weight, and the solvent in the concentrated sulfuric acid solution is water.

[0014] Furthermore, the first temperature is 15℃~35℃, the temperature of the first reaction is 30℃~50℃, and the time of the first reaction is 30min~90min;

[0015] The drying temperature is 50℃~80℃, and the drying time is 4h~12h.

[0016] Furthermore, the insulating protective layer includes at least one of polyimide and polyethylene terephthalate; and / or,

[0017] The matrix resin includes at least one of acrylic resin and silicone resin; and / or,

[0018] The insulating adhesive layer includes acrylic resin.

[0019] Furthermore, the thickness of the insulating protective layer is 10 μm to 50 μm; and / or,

[0020] The thickness of the foamed flame-retardant layer is 50μm~100μm; and / or,

[0021] The thickness of the insulating adhesive layer is 15μm~25μm.

[0022] A second aspect of the present invention provides a method for preparing an insulating film for a battery top cover, comprising the following steps:

[0023] The matrix resin, functional filler and organic solvent are mixed to obtain a foamed flame retardant slurry;

[0024] The foamed flame-retardant slurry is applied to the insulating protective layer and then dried in three stages with increasing temperature to form a foamed flame-retardant layer on the surface of the insulating protective layer.

[0025] An insulating adhesive layer is attached to the surface of the foamed flame-retardant layer away from the insulating protective layer to obtain an insulating film for the battery top cover.

[0026] The mass ratio of the matrix resin to the functional filler is 1:(1~1.5); the functional filler, by weight content, includes: 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica.

[0027] Further, the step of mixing the matrix resin, functional filler, and organic solvent to obtain the foamed flame-retardant slurry includes:

[0028] The silane coupling agent KH-550 was mixed with ethanol to obtain a silane coupling agent solution;

[0029] A silane coupling agent solution is mixed with expandable graphite for surface treatment to obtain pretreated graphite.

[0030] The matrix resin, pretreated graphite, ammonium polyphosphate, melamine, pentaerythritol, titanate coupling agent, and fumed silica are mixed to obtain a foamed flame-retardant slurry.

[0031] The silane coupling agent solution contains 0.5% to 1.0% by weight of silane coupling agent KH-550; and / or,

[0032] The three-stage drying process includes sequentially performed first-stage drying, second-stage drying, and third-stage drying. The temperature for the first-stage drying is 70℃~90℃, the temperature for the second-stage drying is 100℃~130℃, and the temperature for the third-stage drying is 140℃~160℃. The drying time for each of the three stages is independently 1min~2min; and / or,

[0033] The organic solvent includes at least one of ethyl acetate, toluene, and alcohol solvents; the solid content of the foamed flame retardant slurry is 50% to 60%.

[0034] A third aspect of the present invention provides a battery comprising a battery cell, a housing, and a battery top cover. The housing is used to house the battery cell, and the battery top cover is used to encapsulate the housing. The battery top cover comprises a top cover body and an insulating film stacked together. The insulating film comprises an insulating film for a battery top cover according to the first aspect or an insulating film for a battery top cover prepared by the method for preparing an insulating film for a battery top cover according to the second aspect. The insulating adhesive layer of the insulating film for the battery top cover is bonded to the top cover body.

[0035] By applying the technical solution of this invention, by controlling the multi-layer structure of the insulating film for the battery top cover and the specific composition of the functional filler, it helps to ensure the electrical insulation performance of the insulating film for the battery top cover under normal conditions, and when the battery is threatened by high temperature, it can quickly activate the foaming flame retardant mechanism to form a physical barrier and a fireproof carbon layer, which greatly improves the active protection capability of the battery under thermal runaway conditions and helps to improve the safety performance of the battery under extreme conditions. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of the insulating film for the battery top cover in one embodiment of the present invention.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1-Insulating protective layer; 2-Foamed flame retardant layer; 3-Insulating adhesive layer. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0040] As described in the background section of this invention, existing technologies suffer from a significant decrease in the mechanical strength, insulation performance, and flame retardant properties of insulating films under high-temperature conditions, thus affecting battery thermal safety. To address this problem, in a typical embodiment of this invention, an insulating film for battery top covers is provided, such as... Figure 1 As shown, the insulating film for the battery top cover includes an insulating protective layer 1, a foamed flame-retardant layer 2, and an insulating adhesive layer 3 stacked sequentially; wherein, the foamed flame-retardant layer 2 includes a matrix resin and functional fillers dispersed in the matrix resin, and the mass ratio of the matrix resin to the functional fillers is 1:(1~1.5); the functional fillers include, by weight, 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica.

[0041] The insulating film for the battery top cover of this invention is mainly adhered to the surface of the battery top cover. The insulating film consists of an insulating protective layer 1, a foamed flame-retardant layer 2, and an insulating adhesive layer 3. The insulating protective layer 1, as the outermost layer, provides sufficient insulation to prevent electrical contact or short circuits between the battery terminals and the casing, effectively preventing internal short circuits in the battery. The insulating adhesive layer 3 is used to bond the insulating film to the battery top cover, ensuring that the insulating film will not detach. The foamed flame-retardant layer 2 is disposed between the insulating protective layer 1 and the insulating adhesive layer 3. The foamed flame-retardant layer 2 includes a matrix resin and functional fillers dispersed in the matrix resin.

[0042] When this insulating film for the battery top cover is applied to the battery, under normal operating conditions, the components of the insulating film remain stable and do not affect its electrical insulation performance. In the early stages of battery thermal runaway, or when the local temperature of the battery top cover reaches the initial expansion temperature of the expandable graphite, the expandable graphite expands due to heat. The graphite layer rapidly separates and expands, both along the surface of the battery top cover and in directions away from it, expanding in volume by tens to hundreds of times. This forms a physical barrier covering the entire surface of the battery top cover, helping to enhance the internal thermal insulation performance of the battery, effectively reducing heat conduction, preventing heat diffusion, and reducing accidents caused by battery thermal runaway. It also helps to isolate oxygen, effectively suppressing the emission of high-temperature gases, thereby effectively isolating the high-temperature area from direct contact with the outside environment and slowing down or preventing further deterioration of thermal runaway. Furthermore, the expanded graphite's resistivity increases due to changes in its graphite structure, further improving insulation performance and providing electrical safety protection even under extreme conditions. Meanwhile, ammonium polyphosphate (APP) acts as a synergistic flame retardant, melamine (MEL) as a foaming agent, and pentaerythritol (PER) as a char-forming agent. At high temperatures, APP, MEL, and PER undergo chemical reactions including esterification, foaming, and curing, working synergistically with the expansion process of expandable graphite to form a dense foamed carbon layer, effectively slowing the spread of thermal runaway. The foamed carbon layer also absorbs heat and releases water vapor, providing a cooling effect. Simultaneously, its dense structure isolates oxygen, inhibiting combustion reactions, thus significantly improving the safety and stability of the battery under high-temperature conditions. Titanate coupling agents and fumed silica enhance the dispersibility and stability of expandable graphite in the matrix resin, ensuring the foamed flame retardant layer maintains its performance during long-term storage and use. Therefore, by controlling the structure and components of the insulating film used in the battery top cover, this invention effectively solves the problems of decreased insulation performance and inability to effectively cope with thermal runaway in existing battery top covers under high-temperature conditions, contributing to improved battery safety performance under extreme conditions.

[0043] This invention helps ensure the electrical insulation performance of the insulating film for the battery top cover under normal conditions by controlling the multi-layer structure and specific composition of the functional filler. When the battery is threatened by high temperature, it can quickly activate the foaming flame retardant mechanism to form a physical barrier and a fireproof carbon layer, which greatly improves the active protection capability of the battery under thermal runaway conditions and helps improve the safety performance of the battery under extreme conditions.

[0044] In some embodiments, the particle size of any single particle in the expandable graphite is 100 μm to 180 μm. Controlling the particle size of the expandable graphite to meet the above requirements helps to further promote the uniform distribution of expandable graphite in the foamed flame-retardant layer, reduce agglomeration, and help to maximize the performance of the foamed flame-retardant layer. Specifically, the particle size of any single particle in the expandable graphite can be within the range of 100 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, or any combination thereof.

[0045] In some embodiments, the areal density of expandable graphite in the foamed flame-retardant layer 2 is 30 g / m³. 2 ~60g / m 2 Areal density refers to the mass of expandable graphite contained per unit area. By controlling the areal density of expandable graphite to meet the above requirements, a denser and more effective physical barrier can be formed during expansion, contributing to stronger thermal insulation and flame retardant properties. Specifically, in the foamed flame retardant layer 2, the areal density of expandable graphite can be 30 g / m³. 2 35g / m 2 40g / m 2 45g / m 2 50g / m 2 55g / m 2 60g / m 2 or a range consisting of any two of them.

[0046] In some embodiments, the method for preparing expandable graphite includes the following steps: mixing natural flake graphite, concentrated sulfuric acid solution, and glacial acetic acid at a first temperature to obtain a first mixture; mixing the first mixture with potassium permanganate to obtain a second mixture; subjecting the second mixture to a first reaction to obtain a first reaction product; and subjecting the first reaction product to sequential water washing and drying to obtain expandable graphite.

[0047] Natural flake graphite was mixed with concentrated sulfuric acid solution and glacial acetic acid at a first temperature. The concentrated sulfuric acid and glacial acetic acid acted together as intercalating agents. During mixing, the intercalating agents began to penetrate the graphite interlayers. Then, potassium permanganate was added. Potassium permanganate, as a strong oxidizing agent, reacted with the concentrated sulfuric acid-glacial acetic acid system in the intercalating agent, further promoting the oxidation and intercalation process between graphite layers and enhancing the graphite's expansion properties. Finally, unreacted intercalating agents and reaction byproducts, such as sulfates, were removed by washing with water to avoid introducing impurities in subsequent processing. Drying was then performed to remove moisture, ultimately yielding expandable graphite.

[0048] Specifically, concentrated sulfuric acid, during the preparation process, can intercalate into the graphite interlayers and oxidize the graphite edges and defects, making the graphite sheets easier to separate. Glacial acetic acid, acting as an auxiliary intercalating agent, works synergistically with concentrated sulfuric acid in the graphite interlayers to improve intercalation efficiency. It also regulates the pH and chemical activity of the entire intercalation system, helping to control the degree of graphite oxidation and ensuring controllable expansion properties. Potassium permanganate, as a strong oxidizing agent, enhances the oxidizing power of concentrated sulfuric acid, further promoting changes in the graphite interlayer structure and accelerating the intercalation process. Simultaneously, potassium permanganate promotes the formation of a more stable expanded graphite structure, improving the thermal stability of expandable graphite.

[0049] The expandable graphite prepared by the above method has good chemical stability and thermal responsiveness. It can rapidly form a physical barrier in the early stage of battery thermal runaway, effectively isolate oxygen, and inhibit the spread of thermal runaway. At the same time, the expanded graphite structure not only has high resistivity and effectively blocks current, but also provides a physical barrier for heat insulation and flame retardancy, which helps to improve the safety performance of the battery under high temperature conditions.

[0050] In some embodiments, the mass ratio of natural flake graphite to concentrated sulfuric acid solution is 1:(2~4). Controlling this mass ratio helps promote contact between the natural flake graphite and the concentrated sulfuric acid solution, thereby achieving more effective intercalation and oxidation, while reducing the risk of excessive graphite oxidation or structural damage due to excessive concentration. Specifically, the mass ratio of natural flake graphite to concentrated sulfuric acid solution can be within the range of 1:2, 1:2.5, 1:3, 1:3.5, 1:4, or any combination thereof.

[0051] In some embodiments, the mass ratio of natural flake graphite to glacial acetic acid is 1:(0.5~1.5). By controlling the mass ratio of natural flake graphite to glacial acetic acid, it is helpful to further promote the uniform reaction of natural flake graphite with concentrated sulfuric acid, reduce local overheating or over-oxidation, and further improve the thermal response performance and the consistency of the expansion effect of the prepared expandable graphite. Specifically, the mass ratio of natural flake graphite to glacial acetic acid can be within the range of 1:0.5, 1:0.8, 1:0.9, 1:1, 1:1.2, 1:1.5, or any combination thereof.

[0052] In some embodiments, the mass ratio of natural flake graphite to potassium permanganate is 1:(0.15~0.25). By controlling the mass ratio of natural flake graphite to potassium permanganate, it is helpful to promote the formation of a more stable expandable graphite structure and further improve the thermal stability of expandable graphite. Specifically, the mass ratio of natural flake graphite to potassium permanganate can be within the range of 1:0.15, 1:0.18, 1:0.2, 1:0.22, 1:0.25, or any combination thereof.

[0053] In some embodiments, the H2SO4 content in the concentrated sulfuric acid solution is 95%~98% by weight, and the solvent in the concentrated sulfuric acid solution is water. By controlling the H2SO4 content in the concentrated sulfuric acid solution, it is helpful to improve the reaction efficiency and depth, promote the deep change and high stability of the graphite interlayer structure, thereby forming a thicker and more heat-resistant foam carbon layer during expansion.

[0054] In some embodiments, the first temperature is 15°C to 35°C, the first reaction temperature is 30°C to 50°C, and the first reaction time is 30 min to 90 min; the drying temperature is 50°C to 80°C, and the drying time is 4 h to 12 h. By controlling the reaction conditions, it is helpful to promote the formation of expandable graphite.

[0055] This invention does not limit the specific types of the insulating protective layer, the base resin, and the insulating adhesive layer; they can be resins conventional in the art. For example, in some embodiments, the insulating protective layer 1 includes at least one of polyimide and polyethylene terephthalate; and / or, the base resin includes at least one of acrylic resin and silicone resin; and / or, the insulating adhesive layer 3 includes acrylic resin.

[0056] To further improve the overall performance of the insulating film used in battery top covers, the insulating protective layer 1 can be a modified or unmodified polyimide film, or a modified or unmodified polyethylene terephthalate film. When the insulating protective layer 1 is a modified polyethylene terephthalate film, the specific modification method can be copolymerization modification or copolymerization mixing. When using copolymerization modification, the modifier can be a phosphorus-containing monomer (such as a phosphate ester, phosphate ester, etc.); when using copolymerization mixing, the modifier can be ammonium polyphosphate (APP), triphenyl phosphate (TPP), melamine cyanurate (MCA), etc., or inorganic flame-retardant fillers, such as aluminum hydroxide (ATH), magnesium hydroxide (MH), etc. Copolymerization modification and blending of flame retardants help to further improve the flame-retardant performance of the insulating film used in battery top covers.

[0057] For similar reasons, the matrix resin can be a modified or unmodified acrylic resin, or a modified or unmodified silicone resin. When the matrix resin is a modified acrylic resin, rigid or heat-resistant monomers, such as methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN), can be introduced into the acrylic resin. Alternatively, multifunctional monomers (such as ethylene glycol dimethacrylate) can be introduced into the acrylic resin, or it can undergo cross-linking reactions with epoxy resins, amino resins, etc., to form a three-dimensional network structure. Heat-resistant additives, such as nano-silica sol, can also be added to the acrylic resin. When the matrix resin is a modified silicone resin, components such as phenylsiloxanes can be introduced into the silicone resin, or highly efficient catalysts (such as platinum catalytic systems) can be introduced. This invention does not impose further limitations on these aspects.

[0058] In some embodiments, the thickness of the insulating protective layer 1 is 10 μm to 50 μm, for example, a range of 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or any two of these. The thickness of the foamed flame-retardant layer 2 is 50 μm to 100 μm, for example, a range of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any two of these. The thickness of the insulating adhesive layer 3 is 15 μm to 25 μm, for example, a range of 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, or any two of these.

[0059] A second aspect of the present invention provides a method for preparing an insulating film for a battery top cover, comprising the following steps:

[0060] The matrix resin, functional filler and organic solvent are mixed to obtain a foamed flame retardant slurry;

[0061] The flame-retardant slurry is applied to the insulating protective layer 1, and after a three-stage drying process with increasing temperature, a foamed flame-retardant layer 2 is formed on the surface of the insulating protective layer 1.

[0062] The insulating adhesive layer 3 is attached to the surface of the foamed flame-retardant layer 2 away from the insulating protective layer 1 to obtain an insulating film for the battery top cover.

[0063] The mass ratio of the matrix resin to the functional filler is 1:(1~1.5); the functional filler, by weight content, includes: 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica.

[0064] The present invention provides a method for preparing an insulating film for battery top covers. Through steps such as mixing, coating, and three-stage drying, especially the need for the coated layer to undergo three-stage drying treatment with progressively increasing temperatures, it helps to gradually evaporate the solvent, reduce the formation of bubbles or wrinkles inside the film layer, and promote the dispersion and curing of functional fillers in the matrix resin to form a dense foamed flame-retardant layer. This helps to prepare an insulating film for battery top covers with excellent performance.

[0065] In some embodiments, coating can be performed using suitable coating methods such as gravure coating, anilox roller coating, or spraying to uniformly apply the foamed flame-retardant slurry onto the insulating protective layer to form a coating of a certain thickness.

[0066] In some embodiments, the step of mixing a matrix resin, functional filler, and organic solvent to obtain a foamed flame-retardant slurry includes:

[0067] The silane coupling agent KH-550 was mixed with ethanol to obtain a silane coupling agent solution;

[0068] A silane coupling agent solution is mixed with expandable graphite for surface treatment to obtain pretreated graphite.

[0069] The matrix resin, pretreated graphite, ammonium polyphosphate, melamine, pentaerythritol, titanate coupling agent, and fumed silica are mixed to obtain a foamed flame-retardant slurry; wherein the weight content of silane coupling agent in the silane coupling agent solution is 0.5%~1.0%.

[0070] In the above embodiments, surface modification of expandable graphite with silane coupling agent solution can significantly improve the compatibility and dispersibility of expandable graphite with matrix resin, thereby enhancing the overall stability and protective performance of the foamed flame retardant layer.

[0071] In some embodiments, the three-stage drying process includes a first stage of drying, a second stage of drying, and a third stage of drying performed sequentially. The temperature for the first stage of drying is 70°C to 90°C, the temperature for the second stage of drying is 100°C to 130°C, and the temperature for the third stage of drying is 140°C to 160°C. The drying time for each of the three stages of drying is 1 min to 2 min. By controlling the temperature and time of the three-stage drying process, it is helpful to promote the gradual and complete curing of the coating, reduce the performance degradation caused by overheating of the functional filler, and optimize energy consumption and efficiency during the drying process.

[0072] In some embodiments, the organic solvent includes at least one of ethyl acetate, toluene, and alcohol solvents; the solid content of the foamed flame retardant slurry is 50% to 60%. By controlling the specific type of organic solvent and the solid content of the slurry, it is helpful to promote uniform coating of the slurry, accelerate drying speed, reduce bubble generation, and thus help improve product quality.

[0073] In a third aspect, the present invention provides a battery comprising a battery cell, a housing containing the battery cell, and a battery top cover. The battery top cover is used to encapsulate the housing. The battery top cover comprises a top cover body and an insulating film stacked together. The insulating film comprises an insulating film for a battery top cover according to the first aspect or an insulating film for a battery top cover prepared by the method for preparing an insulating film for a battery top cover according to the second aspect. An insulating adhesive layer 3 of the insulating film for a battery top cover is bonded to the top cover body.

[0074] Because of the aforementioned high-performance insulating film for the battery top cover, the battery of the present invention exhibits excellent safety performance under extreme conditions.

[0075] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0076] It should be noted that the sources of the raw materials used in the following embodiments and comparative examples are as follows:

[0077] Natural flake graphite, sourced from Qingdao Chenyang Graphite Co., Ltd., model number LY-100 (fixed carbon content ≥99%, particle size 100 mesh).

[0078] The matrix resin is derived from Allnex's heat-resistant modified acrylic resin, model SETAPLEX 1260 (solid content approximately 60%); or from WACKER's silicone resin, model SILRES MPF 50E (solid content approximately 50%).

[0079] Ammonium polyphosphate, sourced from Hangzhou Jiersi Flame Retardant Chemical Co., Ltd., model APP-201 (degree of polymerization n>1000, low water solubility).

[0080] The melamine was sourced from Sichuan Jinxiang Sairui Chemical Co., Ltd., and was classified as industrial grade (purity ≥99.5%).

[0081] Pentaerythritol, sourced from Hubei Yihua Chemical Co., Ltd., is industrial grade (purity ≥98%).

[0082] The titanate coupling agent is sourced from Nanjing Nengde New Material Technology Co., Ltd., and its model number is NDZ-311.

[0083] Fumed silica, sourced from Evonik, model AEROSIL 200 (specific surface area 200±25m²). 2 / g).

[0084] The silane coupling agent KH-550 is sourced from Hubei Xinlantian New Material Co., Ltd., and is classified as industrial grade (γ-aminopropyltriethoxysilane, purity ≥98%).

[0085] The insulating protective layer is made of polyimide (PI) film, sourced from DuPont, USA, model Kapton HN (12.5μm or 25μm thick); or flame-retardant PET film, sourced from Zhuhai Huafeng New Materials Co., Ltd., model HF-PET-188 (25μm thick, UL94 V-0 rating).

[0086] The insulating adhesive layer is made of high-temperature resistant acrylic pressure-sensitive adhesive, which is derived from tesa double-sided tape, model tesa 69305 (adhesive layer thickness approximately 20μm); or from coating adhesive liquid, model LR-0893, derived from Mitsubishi Chemical.

[0087] Example 1

[0088] 100 parts by weight of natural flake graphite (80-100 mesh), 300 parts by weight of concentrated sulfuric acid (98% concentration), and 100 parts by weight of glacial acetic acid were mixed at 25°C to obtain a first mixture. The first mixture was then mixed with 20 parts by weight of potassium permanganate under stirring for 30 minutes to obtain a second mixture. The second mixture was subjected to a first reaction at 40°C for 60 minutes to obtain a first reaction product. The first reaction product was washed with deionized water until the filtrate was neutral, and then dried at 60°C for 8 hours to obtain expandable graphite.

[0089] I. The method for preparing the insulating film for the battery top cover in this embodiment includes the following steps:

[0090] A 25μm thick polyimide (PI) film (DuPont Kapton HN) is provided as the insulating protective layer 1, and a 20μm thick high-temperature resistant acrylic pressure-sensitive adhesive film (Tesa 69305) is provided as the insulating adhesive layer 3.

[0091] S1, 1.0 g of silane coupling agent KH-550 and 99 g of anhydrous ethanol were mixed and stirred at 25 °C (room temperature) for 30 minutes to obtain a silane coupling agent solution with a weight content of 1.0 wt%; the above silane coupling agent solution was mixed with 100 g of expandable graphite with a particle size of 100~180 mesh (about 100~180 μm) and surface treated at 60 °C for 60 minutes, then filtered and dried at 80 °C for 2 hours to obtain pretreated graphite;

[0092] S2, 100g of matrix resin (Zhanxin SETAPLEX 1260 heat-resistant modified acrylic resin, solid content 60%), 58g of pretreated graphite, 15g of ammonium polyphosphate, 8g of melamine, 7g of pentaerythritol, 1.5g of titanate coupling agent, and 2.5g of fumed silica were mixed and dispersed at high speed at 25℃ (room temperature) for 60 minutes to obtain a foamed flame-retardant slurry; wherein, the total weight of functional fillers was 92.0g, the weight content of expandable graphite was 63%, the weight content of ammonium polyphosphate was 16%, the weight content of melamine was 9%, the weight content of pentaerythritol was 8%, the weight content of titanate coupling agent was 1.6%, and the weight content of fumed silica was 2.7%;

[0093] S3. The foamed flame-retardant slurry is coated onto the insulating protective layer 1 using a microgravure coating method at a coating speed of 10 m / min. Then, a three-stage drying process is performed: first, drying at 80℃ for 2 minutes; then, drying at 120℃ for 2 minutes; and finally, drying at 150℃ for 2 minutes, forming a foamed flame-retardant layer 2 with a dry film thickness of approximately 80 μm on the surface of the insulating protective layer 1; wherein the areal density of expandable graphite is controlled to be 50 g / m³. 2 .

[0094] S4, the release film of the insulating adhesive layer 3 is removed and attached to the surface of the foamed flame retardant layer 2 away from the insulating protective layer 1. Rolling is performed to ensure no air bubbles, thus obtaining the insulating film for the battery top cover of this embodiment.

[0095] In this embodiment, the thickness of the insulating protective layer 1 (PI film) is 0.025 mm (25 μm), the dry film thickness of the foamed flame retardant layer 2 (functional coating) is 0.275 mm (275 μm), the thickness of the insulating adhesive layer 3 (pressure-sensitive adhesive) is 0.020 mm (20 μm), and the total thickness is 0.320 mm.

[0096] II. Battery Assembly

[0097] Based on the size of the battery top cover and the positions of the explosion-proof valve and terminals, the prepared battery top cover is cut into a specific shape using a die-cutting process with an insulating film top patch. The release film of the insulating adhesive layer 3 (pressure-sensitive adhesive layer) is peeled off, and the battery top cover is precisely attached to the outer surface (i.e., the side away from the battery cell) of the battery top cover (usually made of aluminum or steel). During the attachment process, it should be ensured that the insulating film is flat and free of air bubbles, and that key parts such as the explosion-proof valve and terminals are aligned with the corresponding areas of the insulating film, thus obtaining the battery of this embodiment.

[0098] Example 2

[0099] The difference from Example 1 is that in step S2, 100g of matrix resin is replaced with 92g of matrix resin, while the amounts of other components remain unchanged. In this case, the mass ratio of matrix resin to functional filler is 1:1.

[0100] Example 3

[0101] The difference from Example 1 is that in step S2, 100g of matrix resin is replaced with 61.3g of matrix resin, while the amounts of other components remain unchanged. In this case, the mass ratio of matrix resin to functional filler is 1:1.5.

[0102] Example 4

[0103] The difference from Example 1 is that in step S2, 100g of matrix resin (Zhanxin SETAPLEX 1260 heat-resistant modified acrylic resin, solid content 60%), 45g of pretreated graphite, 22g of ammonium polyphosphate, 12g of melamine, 11g of pentaerythritol, 2g of titanate coupling agent, and 3g of fumed silica are mixed and dispersed at high speed at 25°C (room temperature) for 60 minutes to obtain a foamed flame-retardant slurry. At this time, the mass content of expandable graphite is 45%.

[0104] Example 5

[0105] The difference from Example 1 is that in step S2, 100g of matrix resin (Zhanxin SETAPLEX 1260 heat-resistant modified acrylic resin, solid content 60%), 70g of pretreated graphite, 10g of ammonium polyphosphate, 6g of melamine, 6g of pentaerythritol, 1.5g of titanate coupling agent, and 2.5g of fumed silica are mixed and dispersed at high speed at 25°C (room temperature) for 60 minutes to obtain a foamed flame-retardant slurry. At this time, the mass content of expandable graphite is 70%.

[0106] Comparative Example 1

[0107] The preparation method of the insulating film for the top cover of this comparative battery includes the following steps:

[0108] An insulating film for the battery top cover of this comparative example was obtained by directly using a 0.175 mm thick polycarbonate (PC) film and coating one side with a common acrylic pressure-sensitive adhesive (approximately 0.145 μm thick).

[0109] Comparative Example 2

[0110] The preparation method of the insulating film for the top cover of this comparative battery includes the following steps:

[0111] An insulating protective layer (PI film, 25μm) was directly used, and an insulating adhesive layer (high temperature resistant acrylic pressure-sensitive adhesive, 20μm) was attached to one side of it to obtain the insulating film for the battery top cover of this comparative example.

[0112] Comparative Example 3

[0113] The difference from Example 1 is that in step S2, 100g of matrix resin (Zhanxin SETAPLEX 1260 heat-resistant modified acrylic resin, solid content 60%) and 70g of expandable graphite are mixed and dispersed at high speed at 25°C (room temperature) for 60 minutes to obtain foamed flame-retardant slurry. At this time, the mass content of expandable graphite is 70%.

[0114] Test methods

[0115] 1. Insulation performance test

[0116] The insulating film sample is cut to the specified size and laid flat between two metal electrode plates. A high-temperature insulating clamp is installed at the edge of the electrode plates to form a test fixture. The test fixture is then placed in a programmable temperature-controlled high-temperature chamber. The insulation resistance is measured using a high-resistance meter (such as KEITHLEY 6517B). Test procedure: Starting from room temperature, the temperature is increased to 600℃ at a rate of 10℃ / min, and the insulation resistance value is continuously recorded throughout the process. Special attention is paid to recording the data at four characteristic temperature points: 200℃, 300℃, 450℃, and 600℃.

[0117] 2. Expansion performance test

[0118] Thermomechanical analyzer or laser displacement sensor in conjunction with a high-temperature hot stage was used for testing. The sample (which could be individually peeled off to form a small disc with the foamed flame-retardant layer) was placed on the testing platform. Under air atmosphere, it was heated from room temperature to 600°C at a rate of 10°C / min, while continuously recording the dimensional changes in the thickness direction of the sample. The expansion height ratio = expanded thickness / original thickness.

[0119] 3. Flame retardant performance test

[0120] The insulating film sample (with the PI protective layer facing upwards) was fixed on a metal plate with a 3mm diameter hole, simulating an explosion-proof valve port. Using a butane torch, the flame (internal flame temperature approximately 800-1000°C) was aimed at the hole and continuously burned from the back of the sample for 60 seconds. Observe and record: a) burn-through time; b) whether the sample continued to burn after the flame was removed (self-extinguishing time); c) whether the flame burst out from the front of the sample; d) whether a complete carbon layer covered the hole on the front of the sample after the experiment.

[0121] 4. Battery thermal runaway performance test

[0122] The insulating film is fabricated into the final product's top patch structure and size, and then attached to the corresponding battery top cover surface. Thermal runaway is simulated by triggering localized overheating within the cavity through a heating element or short circuit. A high-speed camera records the moment the "explosion-proof valve" opens and the subsequent process, focusing on: whether the material ejected from the valve port is ignited and produces an open flame; the expansion and coverage behavior of the insulating film in the valve port area; and the duration of the open flame (if ignited).

[0123] The test results are shown in Table 1.

[0124] Table 1

[0125]

[0126] Compared to Comparative Examples 1-3, the insulating films for battery top covers in Examples 1-5 include an insulating protective layer 1, a foamed flame-retardant layer 2, and an insulating adhesive layer 3, stacked sequentially. The foamed flame-retardant layer 2 comprises a specific amount of expandable graphite, ammonium polyphosphate, melamine, pentaerythritol, titanate coupling agent, and fumed silica. Upon heating, it expands to form a stable high-temperature carbon layer, effectively providing physical coverage and insulation, and exhibiting excellent flame-retardant properties. The insulating films for battery top covers in Examples 1-5 possess excellent insulation and flame-retardant properties under high-temperature conditions, effectively addressing thermal runaway. The insulating film in Comparative Example 1 only contains a polycarbonate (PC) film and an acrylic pressure-sensitive adhesive layer. Traditional insulating films melt and fail at high temperatures, lacking active protection capabilities. Comparative Example 2 does not include a foamed flame-retardant layer; its insulating film only provides basic insulation during thermal runaway (and fails at high temperatures), failing to achieve active safety effects such as expansion, covering the explosion-proof valve, and isolating oxygen. Comparative Example 3 did not add flame-retardant synergistic components such as ammonium polyphosphate (APP), melamine (MEL), and pentaerythritol (PER). Although expandable graphite alone can expand, without the addition of an expandable flame-retardant system, the resulting char layer is loose, has poor strength, and is easily dispersed by airflow. Its long-lasting insulation and flame-retardant effects at 600°C are far inferior to those of Examples 1-5.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An insulating film for a battery top cover, characterized in that, The insulating film for the battery top cover includes an insulating protective layer (1), a foamed flame-retardant layer (2), and an insulating adhesive layer (3) stacked in sequence. The foamed flame retardant layer (2) includes a matrix resin and a functional filler dispersed in the matrix resin, wherein the mass ratio of the matrix resin to the functional filler is 1:(1~1.5). The functional filler comprises, by weight, 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica.

2. The insulating film for a battery top cover according to claim 1, characterized in that, The particle size of any single particle in the expandable graphite is 100μm~180μm; and / or, In the foamed flame-retardant layer (2), the areal density of the expandable graphite is 30 g / m³. 2 ~60g / m 2 .

3. The insulating film for a battery top cover according to claim 1 or 2, characterized in that, The method for preparing the expandable graphite includes the following steps: mixing natural flake graphite, concentrated sulfuric acid solution, and glacial acetic acid at a first temperature to obtain a first mixture; mixing the first mixture with potassium permanganate to obtain a second mixture; subjecting the second mixture to a first reaction to obtain a first reaction product; and subjecting the first reaction product to sequential water washing and drying to obtain the expandable graphite.

4. The insulating film for a battery top cover according to claim 3, characterized in that, The mass ratio of the natural flake graphite to the concentrated sulfuric acid solution is 1:(2~4); and / or, The mass ratio of the natural flake graphite to the glacial acetic acid is 1:(0.5~1.5); and / or, The mass ratio of the natural flake graphite to the potassium permanganate is 1:(0.15~0.25); and / or, The concentrated sulfuric acid solution contains 95% to 98% H2SO4 by weight, and the solvent in the concentrated sulfuric acid solution is water.

5. The insulating film for a battery top cover according to claim 3 or 4, characterized in that, The first temperature is 15℃~35℃, the temperature of the first reaction is 30℃~50℃, and the time of the first reaction is 30min~90min; The drying temperature is 50℃~80℃, and the drying time is 4h~12h.

6. The insulating film for a battery top cover according to any one of claims 1 to 5, characterized in that, The insulating protective layer (1) comprises at least one of polyimide and polyethylene terephthalate; and / or, The matrix resin includes at least one of acrylic resin and silicone resin; and / or, The insulating adhesive layer (3) comprises acrylic resin.

7. The insulating film for a battery top cover according to any one of claims 1 to 6, characterized in that, The thickness of the insulating protective layer (1) is 10 μm to 50 μm; and / or, The thickness of the foamed flame-retardant layer (2) is 50μm~100μm; and / or, The thickness of the insulating adhesive layer (3) is 15μm~25μm.

8. A method for preparing an insulating film for a battery top cover according to any one of claims 1 to 7, characterized in that, Includes the following steps: The matrix resin, functional filler and organic solvent are mixed to obtain a foamed flame retardant slurry; The foamed flame retardant slurry is applied to the insulating protective layer (1), and after a three-stage drying process with increasing temperature, a foamed flame retardant layer (2) is formed on the surface of the insulating protective layer (1). The insulating adhesive layer (3) is attached to the surface of the foamed flame retardant layer (2) away from the insulating protective layer (1) to obtain the insulating film for the battery top cover; The mass ratio of the matrix resin to the functional filler is 1:(1~1.5); the functional filler comprises, by weight, 45%~70% expandable graphite, 10%~20% ammonium polyphosphate, 5%~10% melamine, 5%~10% pentaerythritol, 1%~10% titanate coupling agent, and 2%~10% fumed silica.

9. The method for preparing the insulating film for the battery top cover according to claim 8, characterized in that, The steps for mixing the matrix resin, functional filler, and organic solvent to obtain the foamed flame-retardant slurry include: The silane coupling agent KH-550 was mixed with ethanol to obtain the silane coupling agent solution; The silane coupling agent solution is mixed with the expandable graphite for surface treatment to obtain pretreated graphite. The matrix resin, the pretreated graphite, the ammonium polyphosphate, the melamine, the pentaerythritol, the titanate coupling agent, and the fumed silica are mixed to obtain the foamed flame retardant slurry. Wherein, the weight content of silane coupling agent KH-550 in the silane coupling agent solution is 0.5%~1.0%; and / or, The three-stage drying process includes a first stage drying, a second stage drying, and a third stage drying performed sequentially. The temperature of the first stage drying is 70℃~90℃, the temperature of the second stage drying is 100℃~130℃, and the temperature of the third stage drying is 140℃~160℃. The drying time for each of the three stages is independently 1min~2min; and / or, The organic solvent includes at least one of ethyl acetate, toluene, and alcohol solvents; the solid content of the foamed flame retardant slurry is 50% to 60%.

10. A battery, characterized in that, The battery includes a cell, a casing, and a battery top cover. The casing is used to house the cell, and the battery top cover is used to encapsulate the casing. The battery top cover includes a top cover body and an insulating film stacked together. The insulating film includes the battery top cover insulating film according to any one of claims 1 to 7 or the battery top cover insulating film prepared by the method of preparing the battery top cover insulating film according to claim 8 or 9. The insulating adhesive layer (3) of the battery top cover insulating film is attached to the top cover body.

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