Composite membrane as well as preparation method and application thereof

Abstract

The invention provides a composite membrane as well as a preparation method and application thereof. The composite membrane comprises a base membrane and modified reinforcing layers loaded on two sides of the base membrane, the modified enhancement layer comprises a metal-organic framework material, a dispersing agent and a binding agent. The modified enhancement layer prepared from the metal-organic framework material is loaded on the surface of the base film, so that the thermal stability and mechanical strength of the film can be improved, the surface hydrophobicity of the film is improved, the surface adsorption capacity of the film is improved, and short circuit and thermal runaway caused by lithium dendrites can be effectively prevented when the film is applied to the composite current collector.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and relates to a composite film, a preparation method thereof and an application, and particularly relates to a composite film, a preparation method thereof, and a composite current collector. Background Art

[0002] Lithium batteries have been widely used due to many advantages such as high energy density, excellent cycle performance, and high discharge rate. The current collector is one of the indispensable components in lithium-ion batteries, which is beneficial to reducing the internal resistance of lithium-ion batteries, improving the Coulomb efficiency, cycle stability and rate performance of the batteries.

[0003] At present, composite current collectors based on polymer films have received extensive attention and applications in the new energy industry. The composite current collector includes a base film and metal layers on both surfaces of the base film.

[0004] During the preparation of the composite current collector, due to the low tensile strength of the base film, it is easy to cause film breakage, resulting in a low product yield. At the same time, in the subsequent application process, processes such as coating and product composite molding also put relatively high requirements on the tensile strength of the base film. In addition, during the use of the metallized polymer film, there is a problem of poor heat resistance, that is, when the temperature is too high, the polymer film substrate shrinks too much, resulting in the separation of the substrate from the metal layer. Therefore, in order to prepare a metallized polymer film with high performance and yield, it is necessary to improve the tensile strength and heat resistance of the base film.

[0005] In summary, among many composite current collectors based on the base film, the following problems exist: 1. The surface tension of the base film is relatively low, the adhesion of the metal layer on the surface of the base film is poor, the peel strength is low, it is easy to fall off and causes a relatively large internal resistance of the lithium battery. 2. Mechanical property indexes such as the elastic modulus and tensile strength of the base film are relatively low, which leads to easy film breakage and perforation during the preparation of the composite current collector, a reduction in the yield, and poor mechanical properties and adhesion of the prepared composite current collector. 3. During the use of the base film, there is a problem of poor heat resistance, that is, when the temperature is too high, the base film shrinks too much, resulting in the separation of the base film from the metal layer.

[0006] Therefore, in this field, it is desirable to develop a composite film that has a relatively high surface tension, excellent mechanical properties, excellent heat resistance, and excellent corrosion resistance. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a composite film, its preparation method and application, specifically to provide a composite film, its preparation method, and a composite current collector, aiming to solve the defects such as poor mechanical strength, poor heat resistance, easy perforation, and poor corrosion resistance of the base film in the preparation process of the existing composite current collector based on the base film, as well as the industry pain points such as easy shedding of the metal layer, poor structural stability, large internal resistance, and poor resistance to electrolyte corrosion of the composite current collector prepared from this base film.

[0008] To achieve this purpose, the present invention adopts the following technical solutions:

[0009] In the first aspect, the present invention provides a composite film, which includes a base film and modified reinforcement layers loaded on both sides of the base film;

[0010] The modified reinforcement layer includes metal-organic frameworks (MOFs), a dispersant, and a binder.

[0011] By loading a modified reinforcement layer prepared from metal-organic frameworks on the surface of the base film, the present invention can improve the thermal stability and mechanical strength of the composite film, improve the surface hydrophobicity of the composite film, and enhance its surface adsorption capacity. When used in a composite current collector, it can effectively prevent short circuits and thermal runaway caused by lithium dendrites.

[0012] Preferably, the ratio of the D50 particle size of the metal-organic framework material to the pore size of the base film is (0.7 - 1.3):1. For example, it can be 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, or 1.3:1, etc., but is not limited to the listed ratio values. Other unlisted ratio values within this range are also applicable. Within this range, the metal-organic framework material can better fill the micropores on the surface of the base film, forming a structure similar to "rivets" on the surface of the base film, enhancing the adhesion of the modified reinforcement layer.

[0013] Preferably, the metal-organic framework material includes any one or a combination of at least two of isoreticular metal-organic frameworks (IRMOFs), zeolitic imidazolate frameworks (ZIFs), MIL- type metal-organic frameworks (MILs), pore-type frameworks, and pore-channel frameworks (PCNs), and zeolitic imidazolate frameworks are preferred.

[0014] Preferably, the D50 particle size of the metal-organic framework material is 140 nm - 650 nm. For example, it can be 140 nm, 150 nm, 160 nm, 180 nm, 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm, 550 nm, 600 nm, 650 nm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The materials within this particle size range can better fill the micropores on the surface of the base film, forming a structure similar to "rivets" on the surface of the base film, improving the adhesion of the modified reinforcing layer.

[0015] Preferably, the pore size of the metal-organic framework material is 1 nm - 2 nm. For example, it can be 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The porosity is 50% - 60%. For example, it can be 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The metal-organic framework material has a large specific surface area and uniform pores, which is helpful for the deposition and attachment of metal nanoparticles during the subsequent preparation of the composite current collector.

[0016] Preferably, the raw materials for preparing the metal-organic framework material include metal salts, organic ligands, and solvents.

[0017] Preferably, the metal salts include any one or a combination of at least two of zinc nitrate hexahydrate, cobalt nitrate hexahydrate, zinc acetate, zirconium chloride, and titanium isopropoxide.

[0018] Preferably, the organic ligands include any one or a combination of at least two of 2-methylimidazole, formic acid, trimesic acid, and 2-aminoterephthalic acid.

[0019] Preferably, the mass ratio of the metal salt to the organic ligand is 1:5 - 2:1. For example, it can be 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, etc., but is not limited to the listed ratios. Other unlisted ratios within this ratio range are equally applicable.

[0020] Preferably, the solvents include any one or a combination of at least two of deionized water, methanol, and N,N-dimethylformamide.

[0021] Preferably, the synthesis method of the metal-organic framework material includes any one or a combination of at least two of solvothermal synthesis, microwave synthesis, ultrasonic synthesis, electrochemical synthesis, and mechanical grinding methods, preferably at least one of solvothermal synthesis and mechanical grinding methods.

[0022] Preferably, in the solvothermal synthesis method, a metal salt and an organic ligand are first dissolved in a solvent, then stirred, and then added to a stainless steel reaction kettle with a polytetrafluoroethylene lining to react.

[0023] Preferably, in the mechanical grinding method, a metal salt and a solvent are mixed, and an organic ligand and a solvent are mixed separately, and then poured into a grinding machine. Inside the grinding machine, the force and heat generated by high-speed movement cause changes inside the material, trigger the breaking and reconnecting of molecular bonds, and then a new material is synthesized.

[0024] Preferably, by weight parts, the modified reinforcing layer includes: 4-12 parts of metal-organic framework material (for example, it can be 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts or 12 parts, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable), 0.5-1 part of dispersant (for example, it can be 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part or 1 part, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable), 0.5-6 parts of binder (for example, it can be 0.5 part, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts or 6 parts, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable).

[0025] Preferably, the unilateral thickness of the modified reinforcing layer is 50nm-500nm, for example, it can be 50nm, 100nm, 200nm, 300nm, 400nm or 500nm, etc., but not limited to the listed values, and other unlisted values within this value range are equally applicable, and preferably 100nm-200nm.

[0026] Preferably, the material of the base film includes any one or a combination of at least two of polyterephthalate, polyamide, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, biaxially oriented polyethylene terephthalate, polybutylene terephthalate, poly(p-phenyleneterephthalamide), polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl formal, polyvinyl butyral, polyurethane, polycarbamate, polyacrylonitrile, polyvinyl acetate, polyoxymethylene, phenolic resin, epoxy resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, polysulfone, polyethersulfone, polyphenylene ether. Preferably, it is any one or a combination of at least two of polyimide (PI), polyethylene (PE), polypropylene (PP), and biaxially oriented polyethylene terephthalate (BOPET).

[0027] Preferably, the surface of the base film has uniformly distributed micropores.

[0028] Preferably, the porosity of the base film is 20%-70%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%, etc., but is not limited to the listed values. Other unlisted values within this range are also applicable. The porosity reflects the number of through holes on the base film. The higher the porosity, the more through holes and the more ion transport channels, and the higher the energy density of the composite current collector prepared thereby. However, the mechanical strength of the base film is lower, and it is more likely to deform and perforate. The lower the porosity, the higher the mechanical strength of the base film, but the fewer through holes and the fewer ion transport channels, and the smaller the energy density of the composite current collector prepared thereby. Preferably, it is 30%-40%.

[0029] Preferably, the pore diameter of the base film is 50nm-1000nm, for example, it can be 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 850nm, 900nm, 950nm or 1000nm, etc., but is not limited to the listed values. Other unlisted values within this range are also applicable. The larger the pore diameter, the more beneficial it is to improve the conductivity of the composite current collector and reduce the internal resistance, but the mechanical properties will also decrease, and the adhesion of the metal layer becomes poor. If the pore diameter is too small, it is not conducive to reducing the internal resistance of the composite current collector. Preferably, it is 200nm-500nm. As a preferred technical solution of the present invention, by controlling the D50 particle size of the metal-organic framework material to be basically the same as the pore diameter of the micropores on the surface of the base film, controlled within 140nm-650nm, the metal-organic framework material can be better filled into the micropores on the surface of the base film, forming a structure similar to "rivets" on the surface of the base film, and improving the adhesion of the modified reinforcement layer.

[0030] Preferably, the thickness of the base film is 1 μm - 15 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable, and preferably it is 2 μm - 8 μm.

[0031] In a second aspect, the present invention provides a method for preparing a composite film as described in the first aspect. The preparation method includes the following steps:

[0032] (1) Mix a metal-organic framework material, a dispersant, a binder, and a solvent to obtain a metal-organic framework material slurry;

[0033] (2) Coat the metal-organic framework material slurry on both sides of the base film and dry it to obtain the composite film.

[0034] Preferably, the solvent in step (1) includes any one or a combination of at least two of deionized water, methanol, ethanol, isopropanol, phenethyl alcohol, propylene glycol, glycerol, ethyl acetate, trichloroethylene, tetralin, decalin, turpentine, carbon tetrachloride, butyl acetate, acetone, cyclohexanone, chloroform, toluene, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, dichloromethane, 1,2-dichloroethane, isophorone. Preferably, it is any one or a combination of at least two of N,N-dimethylformamide, methanol, and N-methylpyrrolidone.

[0035] Preferably, the dispersant includes any one or a combination of at least two of polyvinylpyrrolidone, sodium dodecyl sulfate, sodium dodecylbenzenesulfonate, polyethylene glycol, sodium carboxymethylcellulose, polyacrylic acid alkoxyamine, ethylene oxide, ethylene glycol, isopropanol, cetyltrimethylammonium bromide. Preferably, it is polyvinylpyrrolidone.

[0036] Preferably, the binder includes any one or a combination of at least two of starch, protein, aqueous acrylic resin, polyurethane resin, epoxy resin, vinyl acetate resin, modified epoxy resin, perfluorosulfonic acid resin, polyvinylidene fluoride, hydroxypropyl methylcellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol. Preferably, it is any one or a combination of at least two of aqueous acrylic resin, perfluorosulfonic acid resin, and polyvinylidene fluoride.

[0037] Preferably, the mass ratio of the solvent, metal-organic framework material, dispersant, and binder in step (1) is (28 - 600):(4 - 12):(0.5 - 1):(0.5 - 6). 28 - 600 can be, for example, 28, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, or 600, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. 4 - 12 can be, for example, 4, 5, 6, 7, 8, 9, 10, 11, or 12, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. 0.5 - 1 can be, for example, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. 0.5 - 6 can be, for example, 0.5, 1, 2, 3, 4, 5, or 6, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0038] Preferably, the coating process in step (2) includes any one or a combination of at least two of in-situ forming method, die coating method, knife coating method, Mayer rod coating method, roll coating method, dip coating method, and electrostatic spraying method.

[0039] In a third aspect, the present invention provides a composite current collector, which includes a composite film and conductive metal layers loaded on both sides of the composite film;

[0040] The composite film is the composite film described in the first aspect.

[0041] The composite film provided by the present invention enhances the surface tension, mechanical strength, corrosion resistance, and high-temperature resistance of the base film, and thus can improve the structural stability and service performance of the composite current collector.

[0042] Preferably, the material of the conductive metal layer includes any one of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, and silver, and preferably aluminum or copper.

[0043] Preferably, the single-sided thickness of the conductive metal layer is 1 - 2 μm. It can be, for example, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, etc., but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The greater the thickness of the conductive metal layer, the better the conductivity of the composite current collector, but its weight increases, which is not conducive to lightweight and improving the energy density of lithium batteries; the smaller the thickness of the conductive metal layer, the lighter the mass of the composite current collector, but its conductivity decreases, the internal resistance increases, and the risk of thermal runaway increases.

[0044] Preferably, for the conductive metal layers loaded on both sides of the composite film, the loading method can be selected from, but not limited to, any one or a combination of at least two of magnetron sputtering coating, vacuum evaporation coating, vacuum plasma coating, electroless plating, and electroplating. The loading method of the conductive metal layer provided by the present invention greatly improves the yield and production efficiency in the preparation process of the composite current collector, and can achieve cost reduction, efficiency increase, and large-scale mass production.

[0045] Preferably, when the conductive metal layer is an aluminum layer, the loading method of the conductive metal layer is preferably vacuum evaporation coating.

[0046] Preferably, when the conductive metal layer is a copper layer, the loading method of the conductive metal layer can be selected from the combination of magnetron sputtering coating and electroplating, or the combination of magnetron sputtering coating and vacuum evaporation coating, or the combination of magnetron sputtering coating, vacuum evaporation coating, and electroplating, or the combination of electroless plating and electroplating, and preferably the combination of magnetron sputtering coating and electroplating.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] (1) The present invention innovatively uses metal-organic framework materials (MOFs) to modify the surface of the base film, which can effectively improve the mechanical properties, thermal stability, and surface adsorption capacity of the base film;

[0049] (2) When the composite film provided by the present invention is used for the composite current collector, the hollow internal structure of the MOFs coating can provide sufficient space to buffer the mechanical stress generated by the volume change during the cycling process, thereby preventing the peeling of the composite current collector and its dissolution in the electrolyte, and improving the cycling performance;

[0050] (3) In the preparation method of the composite film provided by the present invention, coating modification can be carried out on the surface of the existing base film, and the involved treatment process is simple and easy to implement, with high production efficiency, low cost, high economic benefits, and easy for large-scale production;

[0051] (4) In the composite current collector prepared by the present invention, the composite film and the conductive metal layer are tightly combined, the conductive metal layer is uniformly and densely distributed, the internal stress between the conductive metal layers is small, and it has excellent uniformity, heat resistance, mechanical strength, and conductivity, and the comprehensive performance is excellent. Specific Embodiments

[0052] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0053] Unless otherwise specified, the information of some raw materials used in the following examples and comparative examples of the present invention is as follows:

[0054] Polypropylene film: from Shenzhen Xingyuan Materials Technology Co., Ltd.;

[0055] Polyvinylidene fluoride: Solvay, Solef 5130 - 1001, density 1.75 g / cm 3 , melting temperature 160 °C;

[0056] Polyvinylpyrrolidone: Aladdin, K30, average molecular weight 58000;

[0057] Biaxially oriented polyethylene terephthalate film: from Toray Group of South Korea.

[0058] Example 1

[0059] In this example, a composite film is provided, and its preparation process includes the following steps:

[0060] (1) Use a polypropylene film with a thickness of 4 μm, a porosity of 40%, and a pore diameter of 200 nm as the base film and set it aside;

[0061] (2) Synthesize zeolitic imidazolate framework material (ZIFs) by the following method: Weigh 6.57 g of 2 - methylimidazole and dissolve it in 100 mL of methanol, ultrasonic for 10 min to obtain solution A; weigh 2.97 g of zinc nitrate hexahydrate and dissolve it in 200 mL of methanol, ultrasonic for 10 min to obtain solution B; mix solution A and solution B, stir in a 60 °C reaction kettle for 2 h for full reaction, then filter under pressure to collect the precipitate product. After the product is washed with methanol and filtered under pressure 3 times, it is vacuum dried at 80 °C for 24 h to obtain a metal - organic framework material with a D50 particle size of 200 nm, a pore diameter of 2 nm, and a porosity of 55%;

[0062] (3) Prepare MOFs slurry: Weigh 5 g of the metal - organic framework material prepared in step (2), 0.5 g of polyvinylpyrrolidone as a dispersant, 1 g of polyvinylidene fluoride as a binder, and 500 mL of N - methylpyrrolidone as a solvent, mix and stir for 8 h to obtain MOFs slurry;

[0063] (4) Coat the two sides of the polypropylene film described in step (1) with MOFs slurry by transfer roll coating method to form a surface - modified enhanced layer. By controlling the distance between the coating rollers, the thickness of the modified enhanced layer is controlled to be 200 nm. After drying in an oven, a composite film is obtained.

[0064] In this example, a copper composite current collector is also provided, which specifically includes the following steps:

[0065] (1) Select the composite film provided above in this example as the carrier of metallic copper;

[0066] (2) Deposit a bottom copper layer with a thickness of 50 nm on both the upper and lower surfaces of the composite film by vacuum magnetron sputtering: the vacuum degree of the vacuum magnetron sputtering equipment cavity is 10 -3 Pa, the film winding tension is set to 80 N / m, the coating rate is set to 12 m / min, and a metallized polypropylene film with a surface sheet resistance of 1 Ω / sq is obtained;

[0067] (3) Thicken the bottom copper layer of the metallized polypropylene film by the process of roller horizontal plating. Use the metallized polypropylene film as the cathode and the copper plate as the anode. The current density of the electroplating bath increases from 0.5 ASD to 5 ASD in sequence. The copper ion concentration of the electroplating solution remains at 2 mol / L, and the coating rate remains at 10 m / min. Sequentially pass through the processes of alkaline ion replacement, water washing, acid ion replacement, anti-oxidation treatment and drying, and deposit an electroplated copper layer with a thickness of 1 μm on both bottom copper layers respectively.

[0068] Example 2

[0069] In this example, a composite film is provided, and its preparation process includes the following steps:

[0070] (1) Use a polypropylene film with a thickness of 4 μm, a porosity of 40%, and a pore diameter of 200 nm as the base film for standby;

[0071] (2) Synthesize zeolitic imidazolate framework material (ZIFs) by the following method: Weigh 3.28 g of 2-methylimidazole and dissolve it in 80 mL of methanol, and ultrasonicate for 10 min to obtain solution A; Weigh 2.92 g of cobalt(II) nitrate hexahydrate and dissolve it in 80 mL of methanol, and ultrasonicate for 10 min to obtain solution B; Mix solution A and solution B, stir strongly for 10 min, age at 25 °C for 24 h, then filter under pressure to collect the precipitate product. The product is washed with methanol and filtered under pressure 3 times, and then vacuum dried at 80 °C for 24 h to obtain a metal-organic framework material with a D50 particle size of 200 nm, a pore diameter of 2 nm, and a porosity of 50%;

[0072] (3) Prepare MOFs slurry: Weigh 5 g of the metal-organic framework material prepared in step (2), 0.5 g of polyvinylpyrrolidone as a dispersant, 1 g of polyvinylidene fluoride as a binder, and 500 mL of N-methylpyrrolidone as a solvent, mix and stir for 8 h to obtain MOFs slurry;

[0073] (4) Coat the MOFs slurry on both sides of the polypropylene film described in step (1) by the transfer roller coating method to form a surface modification enhancement layer. Control the thickness of the modification enhancement layer to be maintained at 200 nm by controlling the distance between the coating rollers. After drying in an oven, a composite film is obtained.

[0074] In this example, a copper composite current collector is also provided, and the specific implementation steps are the same as those in Example 1.

[0075] Example 3

[0076] In this example, a composite film is provided, and its preparation process includes the following steps:

[0077] (1) Use a polypropylene film with a thickness of 4 μm, a porosity of 40%, and a pore diameter of 400 nm as the base film and set it aside;

[0078] (2) Synthesize zeolitic imidazolate framework materials (ZIFs) by the following method: Weigh 2.46 g of 2-methylimidazole and 3.30 g of zinc acetate, mix and dissolve them in 300 mL of methanol, stir and react in a reaction kettle at 60 °C for 4 h, then filter under pressure to collect the precipitate product. After the product is washed with methanol and filtered under pressure 3 times, it is vacuum dried at 80 °C for 24 h to obtain a metal-organic framework material with a D50 particle size of 400 nm, a pore diameter of 1 nm, and a porosity of 60%;

[0079] (3) Prepare the MOFs slurry: Weigh 5 g of the metal-organic framework material prepared in step (2), 0.5 g of polyvinylpyrrolidone as a dispersant, 1 g of polyvinylidene fluoride as a binder, and 500 mL of N-methylpyrrolidone as a solvent, mix and stir for 8 h to obtain the MOFs slurry;

[0080] (4) Coat the MOFs slurry on both sides of the polypropylene film described in step (1) by the transfer roll coating method to form a surface modification enhancement layer. By controlling the distance between the coating rolls, the thickness of the modification enhancement layer is controlled to be maintained at 200 nm. After drying in an oven, a composite film is obtained.

[0081] In this example, a copper composite current collector is also provided, and the specific implementation steps are the same as those in Example 1.

[0082] Example 4

[0083] In this example, a composite film is provided, and its preparation process includes the following steps:

[0084] (1) Use a polypropylene film with a thickness of 4 μm, a porosity of 40%, and a pore diameter of 200 nm as the base film and set it aside;

[0085] (2) Synthesize zeolitic imidazolate framework materials (ZIFs) by the following method: Weigh 7.62 g of 2-methylimidazole and dissolve it in 300 mL of methanol, then ultrasonicate for 10 min to obtain solution A; weigh 2.35 g of zinc nitrate hexahydrate and dissolve it in 200 mL of methanol, then ultrasonicate for 10 min to obtain solution B; mix solution A and solution B, and stir in a reaction kettle at 60 °C for 4 h for full reaction. Then, filter under pressure to collect the precipitate product. After the product is washed with methanol and filtered under pressure three times, it is vacuum dried at 80 °C for 24 h to obtain a metal-organic framework material with a D50 particle size of 260 nm, a pore size of 1 nm, and a porosity of 60%;

[0086] (3) Prepare the MOFs slurry: Weigh 5 g of the metal-organic framework material prepared in step (2), 0.5 g of polyvinylpyrrolidone as a dispersant, 1 g of polyvinylidene fluoride as a binder, and 500 mL of N-methylpyrrolidone as a solvent, and mix and stir for 8 h to obtain the MOFs slurry;

[0087] (4) Coating the MOFs slurry on both sides of the polypropylene film described in step (1) by the transfer roll coating method to form a surface modification enhancement layer. By controlling the distance between the coating rolls, the thickness of the modification enhancement layer is controlled to be maintained at 200 nm. After drying in an oven, a composite film is obtained.

[0088] In this example, a copper composite current collector is also provided, and the specific implementation steps are the same as those in Example 1.

[0089] Example 5

[0090] In this example, a composite film is provided, and its preparation process includes the following steps:

[0091] (1) Use a polypropylene film with a thickness of 4 μm, a porosity of 40%, and a pore size of 200 nm as the base film and set it aside;

[0092] (2) Synthesize zeolitic imidazolate framework materials (ZIFs) by the following method: Weigh 3.85 g of 2-methylimidazole and dissolve it in 100 mL of methanol, then ultrasonicate for 10 min to obtain solution A; weigh 6.92 g of zinc nitrate hexahydrate and dissolve it in 400 mL of methanol, then ultrasonicate for 10 min to obtain solution B; mix solution A and solution B, and stir in a reaction kettle at 60 °C for 4 h for full reaction. Then, filter under pressure to collect the precipitate product. After the product is washed with methanol and filtered under pressure three times, it is vacuum dried at 80 °C for 24 h to obtain a metal-organic framework material with a D50 particle size of 140 nm, a pore size of 2 nm, and a porosity of 50%;

[0093] (3) Preparation of MOFs slurry: Weigh 5 g of the metal-organic framework material prepared in step (2), 0.5 g of polyvinylpyrrolidone as a dispersant, 1 g of polyvinylidene fluoride as a binder, and 500 mL of N-methylpyrrolidone as a solvent. Mix and stir for 8 h to obtain the MOFs slurry;

[0094] (4) Coat the MOFs slurry on both sides of the polypropylene membrane described in step (1) by the transfer roll coating method to form a surface modification enhanced layer. Control the thickness of the modification enhanced layer to be maintained at 200 nm by controlling the distance between the coating rolls. After drying in an oven, a composite membrane is obtained.

[0095] In this example, a copper composite current collector is also provided, and the specific implementation steps are the same as those in Example 1.

[0096] Example 6

[0097] In this example, a composite membrane is provided, and its preparation process includes the following steps:

[0098] (1) Use a polypropylene membrane with a thickness of 8.0 μm, a porosity of 40%, and a pore diameter of 500 nm as the base membrane and set it aside;

[0099] (2) Synthesize zeolitic imidazolate framework materials (ZIFs) by the following method: Weigh 9.56 g of 2-methylimidazole and dissolve it in 400 mL of methanol, and ultrasonicate for 10 min to obtain solution A; weigh 2.11 g of zinc nitrate hexahydrate and dissolve it in 100 mL of methanol, and ultrasonicate for 10 min to obtain solution B; mix solution A and solution B, and stir in a reaction kettle at 60 °C for 4 h for sufficient reaction. Then, filter under pressure to collect the precipitate product. The product is washed with methanol and filtered under pressure 3 times, and then vacuum dried at 80 °C for 24 h to obtain the metal-organic framework material, with a D50 particle size of 500 nm, a pore diameter of 1 nm, and a porosity of 60%;

[0100] (3) Preparation of MOFs slurry: Weigh 5 g of the metal-organic framework material prepared in step (2), 0.5 g of polyvinylpyrrolidone as a dispersant, 1 g of polyvinylidene fluoride as a binder, and 500 mL of N-methylpyrrolidone as a solvent. Mix and stir for 8 h to obtain the MOFs slurry;

[0101] (4) Coat the MOFs slurry on both sides of the polypropylene membrane described in step (1) by the transfer roll coating method to form a surface modification enhanced layer. Control the thickness of the modification enhanced layer to be maintained at 200 nm by controlling the distance between the coating rolls. After drying in an oven, a composite membrane is obtained.

[0102] In this example, a copper composite current collector is also provided, and the specific implementation steps are the same as those in Example 1.

[0103] Example 7

[0104] This example is basically the same as Example 1, except that when preparing the composite film, BOPET with a thickness of 4 μm, a porosity of 30%, and a pore diameter of 200 nm is used as the base film.

[0105] Example 8

[0106] This example is basically the same as Example 6, except that the composite current collector prepared in this example is an aluminum composite current collector, and the specific implementation steps are as follows:

[0107] Select the composite film provided in this example as the carrier of metallic aluminum, and enter the vacuum evaporation chamber at a rate of 15 m / min for the deposition of metallic aluminum. The winding tension of the composite film is 80 N / m, and the vacuum degree of the vacuum evaporation chamber is 10 -5 Pa, the purity of the aluminum wire is 99.9%, the resistance heating evaporation temperature is 1100 °C, and the concentration of aluminum vapor in the chamber is maintained at 80 mol / L to obtain an aluminum composite current collector with a double-sided aluminum layer thickness of 1 μm.

[0108] Example 9

[0109] This example is basically the same as Example 8, except that when preparing the composite film, BOPET with a thickness of 6.5 μm, a porosity of 40%, and a pore diameter of 200 nm is used as the base film.

[0110] Example 10

[0111] This example is basically the same as Example 1, except that when preparing the composite film, the metal-organic framework material used is the zeolitic imidazolate framework material ZIF-8, which is directly purchased from Jiangsu Xianfeng Nano Materials Technology Co., Ltd., with a D50 particle size of 100 nm, a pore diameter of 0.8 nm, and a porosity of 60%.

[0112] Example 11

[0113] This example is basically the same as Example 1, except that when preparing the composite film, the metal-organic framework material used is the zeolitic imidazolate framework material ZIF-8, which is directly purchased from Guangdong Carbon Language New Materials Co., Ltd., with a D50 particle size of 750 nm, a pore diameter of 0.5 nm, and a porosity of 60%.

[0114] Comparative Example 1

[0115] This comparative example is basically the same as Example 1, except that in this comparative example, metallic copper is directly loaded on the upper and lower surfaces of a polypropylene film with a thickness of 4 μm, a porosity of 40%, and a pore diameter of 200 nm, and a 6-μm copper composite current collector (i.e., the thickness of the copper layers on both sides is 1 μm) is prepared by vacuum magnetron sputtering for priming and electroplating for thickening.

[0116] Comparative Example 2

[0117] This comparative example is basically the same as Example 9, except that in this comparative example, metallic aluminum is directly loaded on the upper and lower surfaces of BOPET with a thickness of 6.5 μm, a porosity of 40%, and a pore diameter of 200 nm, and an aluminum composite current collector with a thickness of 8.5 μm (i.e., the thickness of the aluminum layers on both sides is 1 μm) is prepared through a vacuum evaporation process.

[0118] Perform performance tests on the composite films (or base films) and composite current collectors provided in the examples and comparative examples of the present invention. The test methods are as follows:

[0119] (1) Surface tension: Perform surface tension tests on the composite films provided in the examples and the unmodified base films provided in the comparative examples in accordance with GB / T 14216-2008.

[0120] (2) Surface sheet resistance: Detect at a total of 5 positions around the perimeter and in the center of the composite current collector using a four-probe resistance tester, and take the average value.

[0121] (3) Thermal shrinkage rate test: Perform thermal shrinkage rate tests in accordance with the method of GB / T 13519-2008. The test conditions for samples containing BOPET are 150 °C / 1 h, and the test conditions for samples containing PP are 120 °C / 1 h.

[0122] (4) Peel strength: Conduct on a universal tensile testing machine and perform detection and analysis in accordance with the national standard GB / T 2792-2014.

[0123] (5) Puncture resistance: Use a puncture testing machine (model: CMT8102) from MTS Industrial Systems (China) Co., Ltd. The opening diameter of the specimen clamp is about 12 mm, the tip curvature radius is 0.5 mm, the temperature is 22 - 24 °C, and the puncture speed is 5 mm / sec.

[0124] (6) Tensile strength & elongation at break: Detect on a tensile testing machine (model: EM6.202) from MTS Industrial Systems (China) Co., Ltd. in accordance with the national standard GB / T 16492-2008. The larger the elongation at break, the less likely the composite current collector is to be broken, indicating better extensibility.

[0125] (7) High-temperature resistance test: Maintain in an oven at 150 ± 5 °C for 24 h, and observe the deformation degree of the composite current collector and the peeling of the metal layer. If the deformation degree ≤ 10% and there is no peeling of any metal layer, it is considered to pass the high-temperature resistance test; otherwise, it is considered to fail.

[0126] (8) Corrosion resistance test: At normal temperature and pressure, the composite current collector sample was completely immersed in 1 mol / L PF6EC / DMC / DEC electrolyte for 72 h, and the deformation, corrosion, peeling, etc. of the sample were observed. If there is no deformation, no obvious corrosion, and no peeling of any metal layer, it is regarded as passing the corrosion resistance test; otherwise, it is regarded as failing.

[0127] The test results of the composite film provided by the embodiment of the present invention and the unmodified base film provided by the comparative example are shown in Table 1.

[0128] Table 1

[0129]

[0130]

[0131] As can be seen from Table 1, in the present invention, by coating metal-organic framework material (MOFs) material reinforcing layers with D50 particle size similar to the micropore size of the base film on both surfaces of the base film, the surface tension, mechanical strength, heat resistance and puncture resistance of the base film are greatly improved. This is because as a crystalline porous material, MOFs material has both the rigidity of inorganic materials and the flexibility of organic materials, and has advantages such as large specific surface area, high porosity, and strong structural designability, and also has excellent chemical and thermal stability. When the ratio of the D50 particle size of the MOFs material to the pore diameter of the base film is in the range of (0.7 - 1.3):1, the MOFs particles can better embed into the micropores of the base film to form an inlaid structure similar to "rivets", which is beneficial to giving full play to the excellent performance of the MOFs material. It can not only effectively improve the mechanical strength, thermal stability and surface adsorption capacity of the base film, but also the hollow internal structure of the MOFs coating can provide enough space to buffer the mechanical stress applied to the surface. The mechanical strength of Example 10 is significantly lower than that of Example 1 because when the D50 particle size of the MOFs material is much smaller than the micropore size of the base film, the MOFs particles are prone to agglomeration and stacking on the surface of the base film, and their excellent performance cannot be reflected, and the enhancement effect on the mechanical strength of the base film is not obvious. The mechanical strength of Example 11 is also significantly lower than that of Example 1 because when the D50 particle size of the MOFs material is much larger than the micropore size of the base film, the MOFs particles cannot embed into the micropores of the base film and only weakly adhere to the surface of the base film through the action of the binder, which can improve the thermal stability and surface tension of the base film to a certain extent, but cannot improve its mechanical strength.

[0132] The test results of the composite current collectors prepared in the embodiments and comparative examples of the present invention are shown in Table 2.

[0133] Table 2

[0134]

[0135]

[0136] As can be seen from Table 2, the better the mechanical properties of the composite film, the better the mechanical properties of the prepared composite current collector. In addition, the composite current collector has good high-temperature resistance and corrosion resistance. The surface sheet resistance of the composite copper foils obtained in Examples 1-7 is lower than that of Comparative Example 1, and the surface sheet resistance of the composite aluminum foils obtained in Examples 8-9 is lower than that of Comparative Example 2, indicating that after the MOFs material is loaded on the surface of the base film, the surface adhesion is enhanced, which is more conducive to the deposition and adhesion of metal particles, the metal layer is denser, and the contact resistance is small. According to the test results of Examples 1-7 and Comparative Example 1, it is not difficult to find that the peel strength, tensile strength & elongation at break, and puncture strength of Examples 1-7 are higher than those of Comparative Example 1, while the thermal shrinkage rate of Examples 1-7 is significantly lower than that of Comparative Example 1, because the MOFs material layer on the surface of the base film endows it with more excellent mechanical properties and heat resistance. Similarly, the peel strength, tensile strength & elongation at break, and puncture strength of Examples 8 and 9 are also higher than those of Comparative Example 2, and the thermal shrinkage rates of Examples 8 and 9 are also significantly lower than those of Comparative Example 2, all because the MOFs enhanced layer improves the mechanical properties and heat resistance of the base film. The peel strength of Examples 10 and 11 is lower because when the D50 particle size of the MOFs material is too small or too large, the ratio of the D50 particle size of the metal-organic framework material to the pore size of the base film is outside the range of (0.7-1.3):1. At this time, the MOFs particles cannot be firmly embedded in the micropores of the base film, and the adhesion of the MOFs coating on the surface of the base film is very weak. The surface sheet resistance of Examples 10 and 11 is higher than that of Example 1. On the one hand, it is because the adhesion of the MOFs coating on the surface of the base film is poor. On the other hand, it is because the pore size of the MOFs particles is too small, resulting in non-uniform deposition of metal nanoparticles, and the metal layer is not dense enough, increasing the contact resistance.

[0137] The applicant declares that the present invention uses the above embodiments to illustrate the composite film and its preparation method and application of the present invention, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the raw materials selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite film, characterized in that The composite membrane comprises a base membrane and a modified reinforcement layer loaded on both sides of the base membrane; The modified reinforcement layer comprises a metal-organic framework material, a dispersant and a binder.

2. The composite membrane according to claim 1, characterized in that The ratio of the D50 particle size of the metal-organic framework material to the pore size of the base membrane is (0.7-1.3):

1.

3. The composite membrane according to claim 1 or 2, characterized in that The metal-organic framework material includes any one of a mesh metal-organic framework material, a zeolite imidazole framework material, a Levasir framework material, a porous framework material, and a channel framework material, or a combination of at least two of them, preferably a zeolite imidazole framework material; Preferably, the D50 particle size of the metal-organic framework material is 140nm-650nm; Preferably, the pore size of the metal-organic framework material is 1 nm-2 nm, and the porosity is 50%-60%.

4. The composite membrane according to any one of claims 1 to 3, characterized in that The raw materials for preparing the metal-organic framework material include metal salt, organic ligand and solvent; Preferably, the metal salt includes any one or a combination of at least two of zinc nitrate hexahydrate, cobalt nitrate hexahydrate, zinc acetate, zirconium chloride, and titanium isopropoxide; Preferably, the organic ligand includes any one of 2-methylimidazole, formic acid, trimesic acid, and 2-aminoterephthalic acid, or a combination of at least two thereof; Preferably, the mass ratio of the metal salt to the organic ligand is 1:5 to 2:1; Preferably, the solvent includes any one of deionized water, methanol, and N,N-dimethylformamide, or a combination of at least two thereof.

5. The composite membrane according to any one of claims 1 to 4, characterized in that The modified reinforcement layer comprises, by weight, 4-12 parts of metal-organic framework material, 0.5-1 parts of dispersant, and 0.5-6 parts of binder.

6. The composite membrane according to any one of claims 1 to 5, characterized in that The single-side thickness of the modified reinforcement layer is 50nm-500nm.

7. The composite membrane according to any one of claims 1 to 6, characterized in that The material of the base film includes any one or a combination of at least two of polyethylene terephthalate, polyamide, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, biaxially oriented polyethylene terephthalate, polybutylene terephthalate, poly(p-phenylene terephthalamide), polypropylene, acrylonitrile-butadiene-styrene copolymer, polyvinyl formal, polyvinyl butyral, polyurethane, polyurethane, polyacrylonitrile, polyvinyl acetate, polyoxymethylene, phenolic resin, epoxy resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, polysulfone, polyethersulfone, and polyphenylene ether, preferably any one or a combination of at least two of polyimide, polyethylene, polypropylene, and biaxially oriented polyethylene terephthalate; Preferably, the porosity of the base film is 20%-70%, preferably 30%-40%; Preferably, the pore size of the base film is 50nm-1000nm, preferably 200nm-500nm; Preferably, the base film has a thickness of 1 μm-15 μm, preferably 2 μm-8 μm.

8. A method for preparing a composite membrane according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) mixing a metal-organic framework material, a dispersant, a binder and a solvent to obtain a metal-organic framework material slurry; (2) coating the metal-organic framework material slurry on both sides of the base film and drying the slurry to obtain the composite film.

9. The preparation method according to claim 8, characterized in that: The solvent in step (1) comprises any one or a combination of at least two of deionized water, methanol, ethanol, isopropanol, phenylethyl alcohol, propylene glycol, glycerol, ethyl acetate, trichloroethylene, tetralin, decalin, turpentine, carbon tetrachloride, butyl acetate, acetone, cyclohexanone, chloroform, toluene, N,N-dimethylformamide, N-methylpyrrolidone, tetrahydrofuran, dichloromethane, 1,2-dichloroethane, and isophorone, preferably any one or a combination of at least two of N,N-dimethylformamide, methanol, and N-methylpyrrolidone; Preferably, the dispersant includes any one or a combination of at least two of polyvinyl pyrrolidone, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, polyethylene glycol, sodium carboxymethyl cellulose, polyacrylic acid alkylhydroxylamine, ethylene oxide, ethylene glycol, isopropanol, and hexadecyltrimethylammonium bromide, preferably polyvinyl pyrrolidone; Preferably, the binder comprises any one or a combination of at least two of starch, protein, water-based acrylic resin, polyurethane resin, epoxy resin, vinyl acetate resin, modified epoxy resin, perfluorosulfonic acid resin, polyvinylidene fluoride, hydroxypropyl methylcellulose, ethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol, preferably any one or a combination of at least two of water-based acrylic resin, perfluorosulfonic acid resin, and polyvinylidene fluoride; Preferably, the mass ratio of the solvent, metal-organic framework material, dispersant and binder in step (1) is (28-600):(4-12):(0.5-1):(0.5-6); Preferably, the coating process in step (2) includes any one of in-situ forming, die coating, blade coating, Meyer rod coating, roller coating, dip coating, and electrostatic spraying, or a combination of at least two thereof.

10. A composite current collector, characterized in that: The composite current collector comprises a composite film and a conductive metal layer supported on both sides of the composite film; The composite membrane is a composite membrane according to any one of claims 1 to 7; Preferably, the conductive metal layer is made of any one of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium and silver, preferably aluminum or copper; Preferably, the single-side thickness of the conductive metal layer is 1-2 μm.

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