Flame-retardant heat-dissipating aluminum-plastic film and preparation method thereof

Abstract

The application discloses a kind of flame-retardant heat dissipation type aluminum plastic film and preparation method thereof, it includes the following steps: (1) respectively to the surface of PP film, PA film and aluminum foil is carried out corona treatment;(2) the PP film, PA film and aluminum foil treated by corona are washed, static electricity is removed, after surface drying, obtain the PP film, PA film and aluminum foil after surface treatment;(3) polyethylene glycol, nano aluminum nitride and isofuroate diisocyanate adhesive are mixed, form the adhesive flame-retardant heat dissipation layer slurry;(4) the flame-retardant heat dissipation layer slurry is respectively evenly coated on the surface of the treated PP film and PA film side, respectively form first flame-retardant heat dissipation layer and second flame-retardant heat dissipation layer;(5) the aluminum foil both sides are respectively bonded with first and second flame-retardant heat dissipation layer, drying, obtain aluminum plastic film.The aluminum plastic film prepared by the application has excellent heat dissipation and flame retardancy, and can ensure stability during long-term use and is not prone to delamination separation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a flame-retardant heat-dissipating aluminum-plastic film and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries have been widely recognized as the future energy solution because they offer superior energy storage density and long life. Lithium ion batteries have been successful in many applications, such as mobile communication, mobile computing and electric vehicles. However, the performance, safety and life of the battery are largely dependent on the performance and quality of its constituent parts.

[0003] In soft-packaged lithium batteries, aluminum-plastic film plays a crucial role as the core material for cell packaging. Its main task is to provide necessary protection for the sensitive components inside the battery, shielding them from the external environment. For aluminum-plastic film, barrier property, cold stamping formability and puncture resistance are its three core performance indicators.

[0004] The conventional aluminum-plastic film structure consists of three layers: an outer protective layer, a middle aluminum foil layer and an inner heat-sealing layer. This three-layer structure has been proven effective in use, providing reliable packaging protection for lithium batteries. However, like most advanced materials, aluminum-plastic film also faces a series of challenges.

[0005] Firstly, lithium ion batteries generate heat during use, which causes the expansion of each layer in the aluminum-plastic film. Since the outer protective layer and the inner heat-sealing layer use high molecular materials, their expansion coefficients are much higher than that of the middle aluminum foil layer. This differential expansion behavior can increase the thermal stress inside the film material, causing the material to curl or deform.

[0006] Furthermore, the high molecular materials used in the inner heat-sealing layer, such as PP or CPP, although have good effects in packaging, their thermal conductivity performance is not satisfactory. When the battery is working, heat is likely to accumulate in these high molecular materials, thereby reducing their packaging performance, leading to delamination between the aluminum-plastic film and the aluminum foil, and corrosion of the aluminum foil by hydrofluoric acid in the electrolyte.

[0007] To overcome these challenges, researchers have tried various methods, such as modifying the outer protective layer, the inner heat-sealing layer, or introducing multiple functional layers. However, these attempts still have certain limitations. Although the added multiple functional layers can improve the thermal conductivity of the aluminum-plastic film and reduce the expansion of the high molecular materials, they may cause more serious delamination problems under the infiltration of the electrolyte, thereby affecting the charge-discharge performance and service life of the battery.

[0008] Therefore, developing an aluminum-plastic film with excellent heat dissipation and flame retardance, and capable of maintaining stability and preventing delamination during long-term use, has become an important research direction and urgent task. SUMMARY

[0009] The present application aims to provide a flame-retardant and heat-dissipation type aluminum-plastic film and a preparation method thereof.

[0010] To achieve the above-mentioned purpose, the present application provides the following technical solutions.

[0011] The present application provides a preparation method of a flame-retardant and heat-dissipation type aluminum-plastic film, comprising the following steps.

[0012] (1) The surfaces of the PP film, the PA film and the aluminum foil are respectively subjected to corona treatment, and after the corona treatment, the surfaces of the PP film, the PA film and the aluminum foil are all presented as concave-convex undulations with a concave depth of 50-70 nm;

[0013] (2) The PP film, the PA film and the aluminum foil subjected to the corona treatment are subjected to cleaning and electrostatic discharge treatment, and after the surfaces are dried, the PP film, the PA film and the aluminum foil subjected to the surface treatment are obtained;

[0014] (3) Polyethylene glycol with an average relative molecular mass of 1900-2200, nano-aluminum nitride and isophorone diisocyanate adhesive are mixed according to a weight ratio of (1-2):(2-4):(5-10), and deionized water is added to form a bonding flame-retardant and heat-dissipation layer slurry;

[0015] (4) The flame-retardant and heat-dissipation layer slurry is respectively and uniformly coated on one side surface of the treated PP film and the PA film to respectively form a first flame-retardant and heat-dissipation layer and a second flame-retardant and heat-dissipation layer; wherein the isophorone diisocyanate adhesive respectively protrudes from the surfaces of the first flame-retardant and heat-dissipation layer and the second flame-retardant and heat-dissipation layer;

[0016] (5) One side surface of the aluminum foil is bonded and compounded with the first flame-retardant and heat-dissipation layer, and the other side surface of the aluminum foil is bonded and compounded with the second flame-retardant and heat-dissipation layer, and then drying is performed to obtain the flame-retardant and heat-dissipation type aluminum-plastic film.

[0017] Preferably, in step (1), the voltage of the corona treatment is 2.0-2.2 kV, the current is 8 A, the corona speed is 40-50 m / min, and the treatment time is 8-10 s.

[0018] Preferably, in step (2), the surface-treated PP film and the PA film satisfy the following relationship: A = 20Ra + 15μs + c, wherein 30 ≤ c ≤ 35, where A is the surface wetting tension (dyn), Ra is the surface roughness (μm), and μs is the friction coefficient.

[0019] Preferably, in step (3), the average particle size D1 of the isoflurone diisocyanate adhesive is greater than the average particle size D2 of the polyethylene glycol and the average particle size D3 of the nano-aluminum nitride, and D1 / D2 = (2-10):1 and D1 / D3 = (2-10):1.

[0020] Preferably, in step (3), the average particle size of the isoflurone diisocyanate adhesive is 0.5-10 μm, and the average particle size of the polyethylene glycol and the nano-aluminum nitride is 0.05-5 μm.

[0021] Preferably, in step (3), the polyethylene glycol is a solid-solid phase change material with a phase change temperature of 50-54°C.

[0022] Preferably, in step (3), 5% of the total mass of the flame-retardant heat dissipation layer slurry is added to the flame-retardant heat dissipation layer slurry.

[0023] Preferably, in step (3), 5% of the total mass of the flame-retardant heat dissipation layer slurry is added to the flame-retardant heat dissipation layer slurry, and the length-diameter ratio L / D of the nano-carbon fiber satisfies the relationship: 50 ≤ L / D ≤ 100, and the thermal conductivity of the nano-carbon fiber is 2000-3000 W / m·K.

[0024] Preferably, in step (3), the solid content of the flame-retardant heat dissipation layer slurry is 10-90 wt.%.

[0025] Preferably, in step (4), the method for coating is not particularly limited, and any method known in the art can be used as long as the flame-retardant heat dissipation layer slurry can be uniformly coated on the base film, for example, micro-gravure or blade coating can be used.

[0026] Preferably, in step (5), the drying temperature is 80-120°C.

[0027] Preferably, the thickness of the PA film is 20-40 μm, the thickness of the PP film is 30-80 μm, the thickness of the first and second flame-retardant heat dissipation layers is 2-10 μm, and the thickness of the aluminum foil is 30-60 μm.

[0028] The application also provides a flame-retardant heat-dissipation type aluminum-plastic film prepared by the above method.

[0029] The application further provides a lithium ion battery, which comprises an electric core formed by a positive electrode sheet, a negative electrode sheet and a diaphragm, an aluminum plastic film wrapping the electric core and an electrolyte, wherein the aluminum plastic film is the above-mentioned flame-retardant heat-dissipating aluminum plastic film.

[0030] Compared with the prior art, the application has at least the following beneficial effects:

[0031] (1) The application can make the surface of the material rough, and increase the surface tension by strongly impacting the PP film, PA film and aluminum foil under the action of the corona current, which is helpful to the adhesion and bonding of the adhesive. Under the observation of a high-power magnifying glass, it is found that the maximum depth of the surface of the PP film or PA film without corona treatment is not more than 28 nm, and the maximum depth can reach 70 nm after the corona treatment, and the surface presents obvious concave-convex undulation, and the micro true area is increased. The protruding isophorone diisocyanate adhesive in the flame-retardant heat-dissipating layer can avoid the influence of polyethylene glycol and nano-aluminum nitride particles, and form a good bonding effect with the aluminum foil, so that the aluminum plastic film is firmly bonded between the layers, and delamination is avoided.

[0032] (2) The application can produce a large amount of ozone under the action of a high-voltage electric field by corona treatment of the PP film and PA film. The ozone is a strong oxidizing agent, can oxidize the molecular oxygen in the high polymer material, and produce polar groups such as carbonyl and peroxide, thereby increasing the surface energy and the affinity of the adhesive, and improving the bonding strength between the base film and the coating. In addition, the generation of carbonyl groups will also produce new alpha-carbon atoms in the molecular chain, and active hydrogen will appear. The active hydrogen can chemically react with the active group isocyanate (-NCO) in the isophorone diisocyanate adhesive, so that a firm chemical bond is generated between the adherend and the adhesive, and the bonding strength is further increased, thereby avoiding the differential expansion and possible interlayer separation phenomenon, prolonging the service life of the flame-retardant heat-dissipating aluminum plastic film, and prolonging the safety performance and cycle service life of the lithium battery.

[0033] (3) The application sets the flame-retardant heat-dissipating layer, wherein the polyethylene glycol with an average relative molecular mass of 1900-2200 and the nano-aluminum nitride have sufficient latent heat and good thermal conductivity, respectively, can effectively absorb and transfer heat, avoid the phenomenon that heat is gathered to the PP film and PA film, improve the thermal conductivity of the aluminum plastic film and reduce the expansion of the high polymer material, thereby avoiding the interlayer peeling of the PP film, PA film and aluminum foil, and improving the packaging performance. In addition, the nano-aluminum nitride is also a good refractory material with high heat resistance, and can maintain good thermal conductivity, high strength and other properties when the battery is overheated due to charging and discharging, thereby avoiding the occurrence of potential safety hazards of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 Structure diagram of the aluminum-plastic film in an embodiment of the present application.

[0035] Wherein, 1-PP film, 2-first flame-retardant heat dissipation layer, 3-aluminum foil, 4-second flame-retardant heat dissipation layer, 5-PA film. DETAILED DESCRIPTION

[0036] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0037] According to a first aspect of the present application, the present application provides a preparation method of a flame-retardant heat dissipation type aluminum-plastic film, comprising the following steps:

[0038] (1) respectively performing corona treatment on the surfaces of the PP film, the PA film and the aluminum foil, after the corona treatment, the surfaces of the PP film, the PA film and the aluminum foil all present concave-convex undulations, and the depth of the concave pits is 50-70 nm;

[0039] (2) performing cleaning and destaticizing treatment on the PP film, the PA film and the aluminum foil after the corona treatment, and obtaining the PP film, the PA film and the aluminum foil after surface treatment after drying the surfaces;

[0040] (3) mixing polyethylene glycol with an average relative molecular mass of 1900-2200, nano-aluminum nitride and isophorone diisocyanate adhesive according to a weight ratio of (1-2):(2-4):(5-10), and adding deionized water to form a bonding flame-retardant heat dissipation layer slurry;

[0041] (4) respectively uniformly coating the flame-retardant heat dissipation layer slurry on one side surface of the treated PP film and the PA film to respectively form a first flame-retardant heat dissipation layer and a second flame-retardant heat dissipation layer; wherein the isophorone diisocyanate adhesive respectively protrudes from the surfaces of the first flame-retardant heat dissipation layer and the second flame-retardant heat dissipation layer;

[0042] (5) bonding and compounding one side surface of the aluminum foil with the first flame-retardant heat dissipation layer, bonding and compounding the other side surface of the aluminum foil with the second flame-retardant heat dissipation layer, and drying, to obtain the flame-retardant heat dissipation type aluminum-plastic film.

[0043] In an embodiment according to the present application, in step (1), the voltage of the corona treatment is 2.0-2.2 kV, the current is 8 A, the corona speed is 40-50 m / min, and the treatment time is 8-10 s.

[0044] The inventors found that the adhesion and firmness of the aluminum foil and the polymer material to the flame-retardant heat dissipation layer were obviously improved after the corona treatment, and when the corona current reached 8 A, the firmness of the flame-retardant heat dissipation layer to the surface of the aluminum foil and the polymer material was the highest, and when the corona current was greater than 8 A, the adhesion of the flame-retardant heat dissipation layer showed a sharp downward trend. It can be seen that the size of the corona current has a decisive effect on the adhesion of the material.

[0045] For the polymer material, as the corona current increases, the kinetic energy of the particles generated during the corona discharge increases, which is beneficial to opening the chemical bonds of the long molecular chains on the surface of the plastic, and the surface activity gradually increases, and the surface tension also increases accordingly. Therefore, the surface tension of the polymer material increases with the increase of the corona current, which is helpful for the adhesion and bonding of the adhesive. Further research found that the peak value of the surface tension of the polymer material appeared when the corona current was about 8 A, and when the current increased, the surface tension of the polymer material showed a downward trend. This is because the amount of air between the electrode and the corona roller has reached a relatively stable state, and the content of oxygen molecules in the air is certain. Even if the voltage and current value of the electrode are increased, more oxygen molecules cannot be activated, and more oxygen-containing functional groups remain on the surface of the polymer material. In addition, due to excessive corona, the surface structure of the polymer material is severely damaged, so when the corona current increases again, the surface tension of the polymer material will show a rapid downward trend. Compared with the polymer material without corona treatment, the firmness of the porous carbon coating layer on the surface of the polymer material after corona treatment is obviously improved. With the increase of the corona current intensity, the surface firmness of the polymer material and the adhesive is greatly improved, and the surface tension of the polymer material treated by 8 A current reaches the maximum.

[0046] In addition, when the corona speed is too fast or the corona treatment time is too short, the corona treatment will be insufficient, which will lead to a decrease in the adhesion of the flame-retardant heat dissipation layer. When the corona speed is too slow or the corona treatment time is too long, the phenomenon of corona breakdown of the material will easily occur, which will lead to the phenomenon of adhesive reverse adhesion. Therefore, the corona speed and the corona time also need to be controlled within a suitable range.

[0047] The inventors found that the maximum depth of the polymer material without corona treatment was not more than 28 nm, and the maximum depth after corona treatment could reach 70 nm, and the surface showed obvious concave and convex undulations, the color of the convex part was brighter, and the analysis showed that these brighter parts were granular substances, mainly composed of low molecular weight oxides. The change of surface micro-roughness and the increase of micro-real area truly reflect the influence of corona treatment on the structure and composition of the polymer material.

[0048] In an embodiment according to the present application, in step (2), the surface treated PP film and PA film satisfy the following relationship between the surface wetting tension A (dyn), the surface roughness Ra (μm) and the friction coefficient μs: A = 20Ra + 15μs + c, wherein 30 ≤ c ≤ 35. The relationship shows that there is a specific linear relationship between the surface wetting tension A of the PP film and PA film and the surface roughness Ra and the friction coefficient μs. When the friction coefficient μs or the surface roughness Ra increases, the surface wetting tension A also increases accordingly, which means that the greater the friction between the object and the slurry, the better the surface wetting effect. Through the relationship, the required surface wetting tension can be determined according to the control of the surface roughness and the friction coefficient in the actual preparation process, so as to better coat the functional coating slurry, thereby improving the high adhesion and performance stability.

[0049] In an embodiment according to the present application, the value range of A is 38-42 dyn, the value range of Ra is 0.08-0.16 μm, and the value range of μs is 0.4-0.7. Among them, with the increase of the surface roughness, the surface contact area increases, and the tension of the slurry also increases, but when the surface is too rough, the slurry is unevenly distributed, resulting in a smaller contact angle and a decrease in the surface wetting tension. Therefore, it is necessary to control the above parameters within a suitable range. Therefore, the above relationship and parameter range can be used to control the properties of the surface of the PP film and PA film in the actual preparation process, and by controlling the relationship between the surface wetting tension, the surface roughness and the friction coefficient of the surface treated PP film and PA film, the surface of the base film can be ensured to have good wetting and roughness, which is beneficial to the coating and adhesion of the flame-retardant heat dissipation layer and the base film.

[0050] In an embodiment according to the present application, in step (3), the average particle size D1 of the isophorone diisocyanate adhesive is greater than the average particle size D2 of the polyethylene glycol and the average particle size D3 of the nano-aluminum nitride, respectively; and it satisfies the following relationship, D1 / D2 = (2-10):1, D1 / D3 = (2-10):1. By controlling the average particle sizes of the isophorone diisocyanate adhesive and the polyethylene glycol, the isophorone diisocyanate adhesive protrudes from the surface of the flame-retardant heat dissipation layer, which improves the contact between the isophorone diisocyanate adhesive and the surface of the aluminum foil treated by corona, and increases the adhesion of the flame-retardant heat dissipation layer and the aluminum foil.

[0051] The isophorone diisocyanate adhesive also has good weather resistance and light stability, and the reaction speed of the isophorone diisocyanate adhesive with the hydroxyl group is 4-5 times faster than that of hexamethylene diisocyanate (HDI) with the hydroxyl group.

[0052] In an embodiment according to the present application, in step (3), the average particle size of the isorone diisocyanate adhesive is 0.5-10 μm; the average particle sizes of the polyethylene glycol and the nano-aluminum nitride are 0.05-5 μm, respectively.

[0053] In an embodiment according to the present application, in step (3), the polyethylene glycol is a solid-solid phase change material with a phase change temperature of 50-54℃. The polyethylene glycol is an organic solid-solid phase change material (solid ordered molecular connection structure changes into solid disordered molecular connection structure), and its phase change temperature increases with the increase of the polymerization degree, so the average relative molecular weight cannot be too high or too low. When it reaches its phase change temperature (50-54℃), solid-solid phase change occurs, heat is absorbed, and the heat dissipation effect of the flame-retardant heat dissipation layer is further improved. Although the conventional three-layer structure of the aluminum plastic film can be tightly compounded at room temperature, the high molecular materials on both sides show a large thermal shrinkage under high temperature conditions, while the metal material in the middle has good heat resistance, which leads to the peeling of the aluminum plastic film between the layers, the corrosion of the hydrogen fluoride in the electrolyte to the aluminum foil, and the battery leakage, etc. to cause safety hazards. The phase change material in the flame-retardant heat dissipation layer of the present application has good thermal conductivity, which quickly dissipates the heat generated inside the battery, avoids the phenomenon of heat aggregation on the aluminum plastic film inside the battery, prevents the battery from overheating or leaking, provides protection for the safety of the battery, and prolongs the service life of the battery.

[0054] In an embodiment according to the present application, in step (3), 5% of glass fiber based on the total mass of the slurry is added to the flame-retardant heat dissipation layer slurry. The glass fiber has the characteristics of high tensile strength, with a tensile strength of 6.3-6.9 g / d under standard conditions and 5.4-5.8 g / d under wet conditions. It has good heat resistance, and the strength is not affected when the temperature reaches 300℃. It has excellent electrical insulation, is a high-grade electrical insulation material, and is also used for thermal insulation materials and fireproof shielding materials. The addition of glass fiber to the flame-retardant heat dissipation layer can improve the tensile properties and puncture resistance of the aluminum plastic film, and also improve the flame-retardant properties of the aluminum plastic film with nano-aluminum nitride, prevent the aluminum plastic film from breaking and burning, and provide protection for the safety of the battery.

[0055] In an embodiment according to the present application, in step (3), 5% of the total mass of the flame-retardant heat dissipation layer slurry is added with nanocarbon fibers; wherein the aspect ratio L / D of the nanocarbon fibers satisfies the relationship: 50≤L / D≤100; and the thermal conductivity of the nanocarbon fibers is 2000-3000 W / m·K. By adding the above-mentioned nanocarbon fibers in the flame-retardant heat dissipation layer, the thermal conductivity and puncture resistance of the aluminum-plastic film can be effectively improved. When the aspect ratio is high, the carbon fibers can form a better network structure in the material, which helps to improve the thermal conductivity and strength of the material. However, too high aspect ratio (for example, greater than 100) will make the carbon fibers more prone to aggregation and entanglement during mixing and coating, which will affect the uniformity of the material and the final performance. The aspect ratio of the carbon fibers is within the above-mentioned range, which can avoid the problems of aggregation and breakage during processing while maintaining good strength and thermal conductivity.

[0056] In an embodiment according to the present application, in step (4), the method for coating is not particularly limited and any method known in the art can be used as long as it can uniformly coat the flame-retardant heat dissipation layer slurry on the PA film or PP film, for example, micro-gravure or blade coating can be used.

[0057] In an embodiment according to the present application, in step (5), the drying temperature is 80-120°C.

[0058] In an embodiment according to the present application, the thickness of the PP film is 30-80 μm; the thickness of the PA film is 20-40 μm; the thickness of the first and second flame-retardant heat dissipation layers is 2-10 μm; and the thickness of the aluminum foil is 30-60 μm. By controlling the thickness of each functional layer, the advantages of the multi-layer structure can be maximized at a reasonable cost, and the flame-retardant and heat dissipation effects of the aluminum-plastic film can be further optimized. Controlling the thickness can also maximize the adhesion of the flame-retardant heat dissipation layer, better match the thickness of each functional layer, enhance the composite adhesion strength between the flame-retardant heat dissipation layer and other functional layers, avoid delamination between the functional layers, and prolong the service life of the battery.

[0059] According to a second aspect of the present application, the present application also provides a flame-retardant heat dissipation type aluminum-plastic film prepared by the above-mentioned method for preparing a flame-retardant heat dissipation type aluminum-plastic film.

[0060] According to a third aspect of the present application, the present application also provides a secondary battery comprising an electrode core formed by a positive electrode sheet, a negative electrode sheet and a separator, an aluminum-plastic film wrapping the electrode core, and an electrolyte, wherein the aluminum-plastic film is the above-mentioned flame-retardant heat dissipation type aluminum-plastic film.

[0061] The method for preparing the lithium-ion battery of the present invention is well known to those skilled in the art. Generally, the method includes placing a battery cell into an aluminum-plastic film, adding an electrolyte, and then encapsulating it to obtain the battery. The encapsulation method, the composition of the battery cell and the electrolyte, and the amounts used are well known to those skilled in the art.

[0062] The present application will be further described below with reference to specific embodiments.

[0063] Example 1

[0064] like Figure 1 As shown, the flame-retardant heat-dissipating aluminum-plastic film provided in this embodiment includes the following functional layers, which are arranged from the inside out (from top to bottom): PP film 1, first flame-retardant heat-dissipating layer 2, aluminum foil 3, second flame-retardant heat-dissipating layer 4, and PA film 5.

[0065] Preparation of aluminum-plastic film:

[0066] This embodiment provides a method for preparing a flame-retardant and heat-dissipating aluminum-plastic film, including the following steps:

[0067] (1) The surfaces of PP film 1, PA film 5 and aluminum foil 3 are subjected to corona treatment respectively. After corona treatment, the surfaces of PP film 1, PA film 5 and aluminum foil 3 are all uneven, with a pit depth of 55-70nm; the thicknesses of PP film 1, PA film 5 and aluminum foil 3 are 45μm, 25μm and 55μm respectively.

[0068] (2) The corona-treated PP film, PA film and aluminum foil are cleaned, destaticated and dried to obtain surface-treated PP film, PA film and aluminum foil.

[0069] (3) Polyethylene glycol with an average relative molecular mass of 2000, nano-aluminum nitride, and isoflurane diisocyanate adhesive are mixed in a weight ratio of 2:2:10, and deionized water is added to form a bonding flame-retardant and heat-dissipating slurry; wherein, the average particle size of the isoflurane diisocyanate adhesive is D1 = 1.8 μm, which is greater than the average particle size of the polyethylene glycol D2 = 0.6 μm and the average particle size of the nano-aluminum nitride D3 = 0.6 μm, respectively; and they satisfy the following relationship: D1 / D2 = 3:1, D1 / D3 = 3:1;

[0070] (4) The flame-retardant heat dissipation slurry is uniformly coated on one side of the treated PP film and PA film to form a first flame-retardant heat dissipation layer and a second flame-retardant heat dissipation layer with a thickness of 5μm respectively; wherein, the isoflurone diisocyanate adhesive protrudes from the surface of the first flame-retardant heat dissipation layer and the second flame-retardant heat dissipation layer respectively.

[0071] (5) bonding and compounding one side surface of the aluminum foil with the first flame-retardant heat dissipation layer, bonding and compounding the other side surface of the aluminum foil with the second flame-retardant heat dissipation layer, and drying, to obtain the flame-retardant heat dissipation type aluminum plastic film.

[0072] Preparation of the lithium battery:

[0073] The negative electrode sheet, the separator, and the positive electrode sheet are wound into an electric core; the electric core, the electrolyte, and the aluminum plastic film are made into a lithium ion battery according to a conventional process; the separator used is a PP film; the active material used in the negative electrode sheet is artificial graphite, the active material used in the positive electrode sheet is lithium nickel cobalt manganese oxide, and the lithium salt of the electrolyte is 1M LiPF6, and the solvent is EC:DEC:DMC 3:4:3.

[0074] Example 2

[0075] Different from example 1, the thickness of the PP film 1 in this embodiment is 50μm, the thickness of the first flame-retardant heat dissipation layer 2 and the second flame-retardant heat dissipation layer 4 is 8μm, the thickness of the aluminum foil 3 is 40μm, and the thickness of the PA film 5 is 20μm.

[0076] The rest is the same as example 1, which will not be repeated here.

[0077] Example 3

[0078] Different from example 1, in the preparation step (3) of the aluminum plastic film, the polyethylene glycol, the nano-aluminum nitride, and the isophorone diisocyanate adhesive are mixed in a weight ratio of 3:4:8.

[0079] The rest is the same as example 1, which will not be repeated here.

[0080] Example 4

[0081] Different from example 1, in the preparation step (1) of the aluminum plastic film, the surface wetting tension A of the PP film 1 after surface treatment is 45dyn, the surface roughness Ra is 0.2μm, and the friction coefficient μs is 0.5; wherein the above satisfies the relationship: A=20Ra+15μs+c, and 30≤c≤35.

[0082] The rest is the same as example 1, which will not be repeated here.

[0083] Example 5

[0084] Different from example 1, the average particle size D1 of the isophorone diisocyanate adhesive in this embodiment is 5μm, which is greater than the average particle size D2 of the polyethylene glycol 1μm and the average particle size D3 of the nano-aluminum nitride 1μm; and it satisfies the following relationship, D1 / D2=5:1, D1 / D3=5:1.

[0085] The rest is the same as example 1, which will not be repeated here.

[0086] Example 6

[0087] Different from Example 1, in the preparation step (3) of the aluminum-plastic film, 5% of glass fibers in total mass of the flame-retardant heat dissipation layer slurry were added.

[0088] The rest is the same as Example 1, which will not be repeated here.

[0089] Example 7

[0090] Different from Example 1, in the preparation step (3) of the aluminum-plastic film, 5% of nano-carbon fibers in total mass of the flame-retardant heat dissipation layer slurry were added; wherein, the length-diameter ratio L / D of the nano-carbon fibers satisfies the relationship formula: L / D = 90; the thermal conductivity of the nano-carbon fibers is 3000 W / m·K.

[0091] The rest is the same as Example 1, which will not be repeated here.

[0092] Comparative Example 1

[0093] Different from Example 1, the preparation method of the aluminum-plastic film in the present comparative example is as follows: taking the PP film 1 with a thickness of 45 μm, the PA film 5 with a thickness of 25 μm and the aluminum foil 3 with a thickness of 55 μm, without performing the corona treatment, directly coating the flame-retardant heat dissipation layer slurry on the PP film 1 and the PA film 5.

[0094] The rest is the same as Example 1, which will not be repeated here.

[0095] Comparative Example 2

[0096] Different from Example 1, the preparation method of the aluminum-plastic film in the present comparative example is as follows: in the step (1), the surfaces of the PP film 1 and the PA film 5 are respectively subjected to the corona treatment, wherein the corona treatment voltage is 2.0 kV, the current is 10 A, the corona speed is 40 m / min, and the treatment time is 8 s.

[0097] The rest is the same as Example 1, which will not be repeated here.

[0098] Comparative Example 3

[0099] Different from Example 1, the preparation method of the aluminum-plastic film in the present comparative example is as follows: in the step (1), the surfaces of the PP film 1 and the PA film 5 are respectively subjected to the corona treatment, wherein the corona treatment voltage is 2.0 kV, the current is 6 A, the corona speed is 40 m / min, and the treatment time is 8 s.

[0100] The rest is the same as Example 1, which will not be repeated here.

[0101] Comparative Example 4

[0102] Different from example 1, the preparation method of the aluminum-plastic film of the present comparative example is as follows: in step (3), the polyethylene glycol, nano-aluminum nitride and polyacrylate adhesive are mixed according to a weight ratio of 2:2:10.

[0103] Other than example 1, which will not be repeated here.

[0104] Comparative example 5

[0105] Different from example 1, the preparation method of the aluminum-plastic film of the present comparative example is as follows: in step (3), the average particle size D1 of isophorone diisocyanate adhesive, the average particle size D2 of polyethylene glycol and the average particle size D3 of nano-aluminum nitride; satisfy the following relationship, D1=D2=D3.

[0106] Other than example 1, which will not be repeated here.

[0107] Comparative example 6

[0108] Different from example 1, the preparation method of the aluminum-plastic film of the present comparative example is as follows: in step (3), the nano-aluminum nitride and isophorone diisocyanate adhesive are mixed according to a weight ratio of 2:10, and deionized water is added to form a bonded composite layer slurry.

[0109] Other than example 1, which will not be repeated here.

[0110] Comparative example 7

[0111] Different from example 7, in the preparation step (3) of the aluminum-plastic film of the present comparative example, 5% of nano-carbon fibers in the total mass of the slurry are added to the flame-retardant heat dissipation layer slurry; wherein the aspect ratio L / D of the nano-carbon fibers satisfies the relationship: L / D=120; the thermal conductivity of the nano-carbon fibers is 1500 W / m·K.

[0112] Other than example 7, which will not be repeated here.

[0113] The aluminum-plastic films and lithium ion batteries prepared in examples 1-7 and comparative examples 1-7 are respectively tested for performance according to the national standard, and the test results are shown in Table 1:

[0114] Table 1

[0115]

[0116]

[0117] From the test results of example 1 and comparative example 1, it can be seen that the interlayer adhesion of the aluminum-plastic film of example 1 is better, which shows that by carrying out corona treatment on the surfaces of the PP film, the PA film and the aluminum foil, the interlayer adhesion of the aluminum-plastic film can be effectively increased.

[0118] From the test results of Example 1 and Comparative Example 2, it can be seen that the interlayer adhesion of the aluminum-plastic film of Example 1 is significantly better than that of Comparative Example 2, further illustrating that the optimal current for the corona treatment in step (1) is 8 A, and when the corona current is greater than 8 A, the surface tension of the PP film 1 and the PA film 5 decreases, resulting in a sharp decrease in the adhesion of the functional coating. It can be seen that the size of the corona current has a decisive effect on the adhesion of the PP film 1 and the PA film 5.

[0119] From the test results of Example 1 and Comparative Example 3, it can be seen that the interlayer adhesion of the aluminum-plastic film of Example 1 is significantly better than that of Comparative Example 3, further illustrating that the optimal current for the corona treatment in step (1) is 8 A, and as the corona current increases, the kinetic energy of the particles generated during the corona discharge increases, which is beneficial to opening the chemical bonds of the long molecular chains on the surface of the PP film 1 and the PA film 5, gradually increasing the surface activity and the surface tension.

[0120] From the test results of Example 1 and Comparative Example 4, it can be seen that the interlayer adhesion of the aluminum-plastic film of Example 1 is significantly better than that of Comparative Example 4, further proving that the adhesion of Example 1 is due to the chemical reaction between the active group isocyanate (-NCO) in the isophorone diisocyanate adhesive and the active hydrogen generated during the corona treatment of the PP film 1 and the PA film 5, generating a firm chemical bond and increasing the adhesion of the PP film 1 and the PA film 5 and the flame-retardant heat dissipation layer, thereby effectively avoiding the interlayer separation phenomenon. Under the action of a high-voltage electric field, the plastic molecules produce polar groups such as carbonyl groups, which produce new α-carbon atoms in the molecular chain and active hydrogen.

[0121] From the test results of Example 1 and Comparative Example 5, it can be seen that the interlayer adhesion of the aluminum-plastic film of Example 1 is significantly better than that of Comparative Example 5, further proving that by controlling the average particle size of the isophorone diisocyanate adhesive and the polyethylene glycol, the isophorone diisocyanate adhesive protrudes from the surface of the flame-retardant heat dissipation layer, which can improve the contact between the isophorone diisocyanate adhesive and the surface of the aluminum foil after the corona treatment, and increase the adhesion between the flame-retardant heat dissipation layer and the aluminum foil layer.

[0122] From the test results of Example 1 and Comparative Example 6, it can be seen that the high-temperature cycle performance of the battery of Example 1 is significantly better than that of Comparative Example 6, further proving that the addition of polyethylene glycol to the flame-retardant heat dissipation layer can improve the heat dissipation effect of the flame-retardant heat dissipation layer. This is because polyethylene glycol is an organic solid phase change material (solid ordered molecular connection structure changes to solid disordered molecular connection structure), which will undergo solid-solid phase change when it reaches its phase change temperature (50-54°C), absorbing heat and improving the heat dissipation effect of the battery.

[0123] From the test results of Example 1 and Example 4, it can be seen that the adhesion of the aluminum-plastic film of Example 4 is obviously improved, which indicates that when the surface wetting tension A, the surface roughness Ra and the friction coefficient μs satisfy a certain relationship, the interlayer adhesion of the aluminum-plastic film is improved.

[0124] From the test results of Example 1 and Example 6, it can be seen that the puncture resistance of the aluminum-plastic film of Example 6 is better, which indicates that the addition of 5% glass fiber in the flame-retardant heat dissipation layer can improve the tensile property and puncture resistance of the aluminum-plastic film, and also improve the flame-retardant property of the aluminum-plastic film together with the nano-aluminum nitride, preventing the aluminum-plastic film from breaking and burning, and providing a guarantee for the safety of the battery. The glass fiber has the characteristics of high tensile strength, which is 6.3-6.9 g / d in the standard state and 5.4-5.8 g / d in the wet state. It has good heat resistance, and the strength is not affected when the temperature reaches 300℃. It has excellent electrical insulation and is a high-grade electrical insulation material, and is also used as thermal insulation and fire shielding materials.

[0125] From the test results of Example 1 and Example 7, it can be seen that the puncture resistance and high-temperature cycle performance of the aluminum-plastic film of Example 7 are better, which indicates that the addition of 5% nano-carbon fiber in the total mass of the slurry in the flame-retardant heat dissipation layer, and the use of nano-carbon fiber with a specific aspect ratio and thermal conductivity can further improve the thermal conductivity and puncture resistance of the aluminum-plastic film.

[0126] From the test results of Example 7 and Comparative Example 7, it can be seen that the puncture resistance and high-temperature cycle performance of the aluminum-plastic film of Example 7 are better, which indicates that when the aspect ratio of the nano-carbon fiber is too large and the thermal conductivity is too low, the puncture resistance and thermal conductivity of the aluminum-plastic film will be reduced. Therefore, the nano-carbon fiber needs to have a suitable aspect ratio and thermal conductivity, which is more helpful to improve the puncture resistance and thermal conductivity of the aluminum-plastic film.

[0127] Based on the disclosure and teachings of the above specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present application is not limited to the above specific embodiments, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. A method for preparing a flame-retardant heat-dissipating aluminum-plastic film, characterized in that, The method comprises the following steps: (1) respectively performing corona treatment on the surfaces of the PP film, the PA film and the aluminum foil, after the corona treatment, the surfaces of the PP film, the PA film and the aluminum foil are all presented as concave-convex undulating shape, and the pit depth is 50-70 nm; (2) performing cleaning and electrostatic treatment on the PP film, the PA film and the aluminum foil after the corona treatment, and obtaining the PP film, the PA film and the aluminum foil after surface treatment after the surfaces are dried; (3) mixing polyethylene glycol with an average relative molecular mass of 1900-2200, nano-aluminum nitride and isoflurone diisocyanate adhesive according to the weight ratio of (1-2):(2-4):(5-10), and adding deionized water to form a bonding flame-retardant heat dissipation layer slurry; (4) respectively uniformly coating the flame-retardant heat dissipation layer slurry on one side surface of the treated PP film and PA film to respectively form a first flame-retardant heat dissipation layer and a second flame-retardant heat dissipation layer; wherein the isoflurone diisocyanate adhesive respectively protrudes from the surfaces of the first flame-retardant heat dissipation layer and the second flame-retardant heat dissipation layer; (5) bonding and combining one side surface of the aluminum foil with the first flame-retardant heat dissipation layer, bonding and combining the other side surface of the aluminum foil with the second flame-retardant heat dissipation layer, and drying to obtain the flame-retardant heat dissipation type aluminum plastic film; In step (1), the voltage of the corona treatment is 2.0-2.2 kV, the current is 8 A, the corona speed is 40-50 m / min, and the treatment time is 8-10 s; In step (3), the average particle size D1 of the isoflurone diisocyanate adhesive is greater than the average particle size D2 of the polyethylene glycol and the average particle size D3 of the nano-aluminum nitride; and it satisfies the following relationship, D1 / D2=(2-10):1, and D1 / D3=(2-10):

1.

2. The preparation method of the flame-retardant heat dissipation LAM according to claim 1, characterized in that, In step (2), the surface wetting tension A (dyn), the surface roughness Ra (μm) and the friction coefficient μs of the PP film and the PA film after surface treatment satisfy the relationship: A=20Ra+15μs+c, wherein 30≤c≤35.

3. The preparation method of the flame-retardant heat dissipation LAM according to claim 1, characterized in that, In step (3), the average particle size of the isoflurone diisocyanate adhesive is 0.5-10 μm; and the average particle sizes of the polyethylene glycol and the nano-aluminum nitride are respectively 0.05-5 μm.

4. The method for preparing the flame-retardant and heat-dissipating aluminum-plastic film according to claim 1, characterized in that, In step (3), the polyethylene glycol is a solid-solid phase change material with a phase change temperature of 50-54 ℃.

5. The preparation method of the flame-retardant heat dissipation LAM according to claim 1, characterized in that, In step (3), 5% of glass fibers in the total mass of the slurry are added to the flame-retardant heat dissipation layer slurry.

6. The preparation method of the flame-retardant heat dissipation LAM according to claim 1, characterized in that, In step (3), 5% of nano-carbon fibers in the total mass of the slurry are added to the flame-retardant heat dissipation layer slurry; wherein the length-diameter ratio L / D of the nano-carbon fibers satisfies the relationship: 50≤L / D≤100; and the thermal conductivity of the nano-carbon fibers is 2000-3000 W / m•K.

7. The method for preparing the flame-retardant and heat-dissipating aluminum-plastic film according to any one of claims 1 to 6, characterized in that, The thickness of the PA film is 20-40 µm; the thickness of the PP film is 30-80 µm; the thicknesses of the first flame-retardant heat dissipation layer and the second flame-retardant heat dissipation layer are both 2-10 µm; and the thickness of the aluminum foil is 30-60 µm.

8. A flame-retardant heat dissipating laminate film, characterized by: The flame-retardant heat dissipation type aluminum plastic film is prepared by the method according to any one of claims 1-7.

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