Composite current collector and preparation method

Abstract

A composite current collector and a preparation method. The composite current collector comprises: a PP base film; bonding layers, which are arranged on the upper and lower sides of the PP base film and are obtained by a treatment of a surfactant, an organic treating agent, a first treating agent and a second treating agent; metal layers, which are arranged on the upper and lower sides of the bonding layers; and protective layers, which are arranged on the upper and lower sides of the metal layers. The bonding layers can enhance the bonding performance between the PP base film and the metal layers.

Description

Composite current collector and preparation method Technical Field

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

[0002] At present, composite current collectors based on polymer membranes have received widespread attention and application in the new energy industry. The preparation process of the composite current collector is usually: a layer of metal (aluminum, copper, etc.) material is deposited on a polymer film (such as polypropylene, polyethylene, polyester, etc.) by physical vapor deposition (PVD) method. The prepared surface metallized film with a certain conductivity is the composite current collector. Compared with traditional current collectors, composite current collectors based on polymer membranes have the characteristics of low cost, light weight, and good internal insulation. These characteristics enable the composite current collector to reduce the cost of the battery and improve the energy density and safety of the battery when used in the battery.

[0003] In existing current collector processes, a layer of metallic copper, several tens of nanometers thick, is typically deposited on a polymer film via magnetron sputtering to impart a certain degree of conductivity. This layer is then electroplated onto a PP (polypropylene) film (polypropylene film) to a thickness of 1 μm on each side to create a composite current collector. However, because PP (polypropylene) is a non-polar material with high surface bond energy, chemical bonds are difficult to break, and the resulting composite copper current collector exhibits poor adhesion, with the metal layer easily detaching from the polypropylene film (PP film), making it unsuitable for battery application.

[0004] Therefore, it is necessary to provide a composite current collector and a preparation method to solve the problem of poor bonding performance of polypropylene (PP) composite current collector.

[0005] Summary of the Invention

[0006] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0007] The present application provides a composite current collector and a preparation method thereof to solve the problem of poor bonding performance of a PP composite current collector.

[0008] The technical solution of this application is as follows:

[0009] A composite current collector, comprising:

[0010] PP base film;

[0011] Adhesive layers are provided on the upper and lower sides of the PP base film, wherein the adhesive layers are treated with a surfactant, an organic treatment agent, a first treatment agent, and a second treatment agent;

[0012] Metal layers disposed on the upper and lower sides of the bonding layer;

[0013] The protective layers are arranged on the upper and lower sides of the metal layer.

[0014] Optionally, the PP base film includes polypropylene and an antioxidant, and the mass percentage of the polypropylene to the antioxidant is (99%-99.5%):(0.5%-1%).

[0015] Optionally, the antioxidant is one or a combination of two or more of triphenyl phosphite, butylated hydroxyanisole, 2,6-di-tert-butyl-4-methylphenol, p-tert-butylcatechol, etc.

[0016] Optionally, the surfactant is one or a combination of two or more of sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium α-olefin sulfonate, sodium lauryl sulfate, sodium fatty acid methyl ester sulfonate, fatty alcohol polyoxyethylene ether, nonylphenol polyoxyethylene ether, sorbitan fatty acid ester, coconut oil fatty acid diethanolamine, polyether series, etc.;

[0017] The organic treatment agent is one or a combination of two or more of toluene, xylene, cyclohexane, carbon tetrachloride, ethanol, propanol, isopropanol, n-butanol, ethylene glycol, propylene glycol, ethyl acetate, acetone, butanone, cyclohexanone, etc.;

[0018] The first treating agent is one or a combination of two or more of ethanol, propanol, isopropanol, n-butanol, ethylene glycol, glycerol, ethyl acetate, acetone, butanone, ethyl acetate, ethylene glycol methyl ether, ethylene glycol ethyl ether, etc.;

[0019] In some embodiments, the second treatment agent comprises one or a combination of two or more of chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate, a polyethylene / polypropylene blend or copolymer, a block copolymer formed by copolymerization of isobornyl acrylate and acrylic acid, and an ethylene-octene block copolymer. Preferably, the second treatment agent is an organic solution comprising one or a combination of two or more of chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate, a polyethylene / polypropylene blend or copolymer, a block copolymer formed by copolymerization of isobornyl acrylate and acrylic acid, and an ethylene-octene block copolymer. Further preferably, the organic solution is an acetone solution.

[0020] The second treatment agent of the present application is one or a combination of two or more of chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate, polyethylene / polypropylene blends or copolymers, block copolymers formed by copolymerization of isobornyl acrylate and acrylic acid, and ethylene-octene block copolymers. Optionally, the material of the protective layer is one or a combination of two or more of benzotriazoles and their derivatives or silane coupling agents.

[0021] Optionally, the thickness of the PP base film is between 2 μm and 20 μm, and the thickness of the metal layer on each side is between 400 nm and 1500 nm.

[0022] The present application also provides a method for preparing a composite current collector, comprising:

[0023] preparing a PP base film, wherein the PP base film is obtained by mixing polypropylene with an antioxidant and then adopting a melt-biaxial stretching method;

[0024] The PP base film is immersed in a surfactant, washed and dried, and then immersed in an organic treatment agent, washed and dried, and then immersed in a first treatment agent, dried, and then immersed in a second treatment agent by ultrasonication, and dried in an oven to obtain a bonded PP base film;

[0025] The bonding PP base film is placed in a magnetron sputtering chamber, a metal target is used to form a metal thin layer on the bonding PP base film by magnetron sputtering, and the metal thin layer is deposited on the upper and lower surfaces of the base film by aqueous electroplating to obtain a metal layer;

[0026] The metal layer is treated with a benzotriazole antioxidant to form a stable oxide film on the surface of the metal layer, and the composite current collector is obtained after drying.

[0027] Optionally, the surfactant is a mixture of sodium lauryl sulfate, sodium fatty acid methyl ester sulfonate, and fatty alcohol polyoxyethylene ether; the organic treatment agent is a mixture of acetone and tetrachloroethylene; the first treatment agent is isopropyl alcohol, and the second treatment agent is chlorinated polypropylene.

[0028] Optionally, the mass ratio of sodium lauryl sulfate, sodium fatty acid methyl ester sulfonate, and fatty alcohol polyoxyethylene ether in the mixed solution of surfactants is 3:1:2.

[0029] Optionally, the mass ratio of acetone to tetrachloroethylene in the organic treatment agent is 6:4.

[0030] Optionally, the second treating agent is an acetone solution of chlorinated polypropylene.

[0031] Optionally, the mass concentration of chlorinated polypropylene is 5‰-10‰, the soaking time is 30s-300s, and the drying temperature in the oven is 80-120°C.

[0032] The second treating agent of the present application includes any conventional organic solution of the second treating agent, such as an acetone solution.

[0033] The above scheme of the present application includes at least the following beneficial effects: the solvent in the adhesive layer will swell and diffuse to the surface of the PP base film, thereby enhancing the mechanical interlocking force with the surface of the PP base film, thereby enhancing the bonding performance between the PP base film and the metal layer. The bonding force of the composite current collector prepared in this way is enhanced, the mechanical properties of the composite current collector are significantly improved, and the PP base film and the metal layer are not easy to fall off.

[0034] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0036] FIG1 is a schematic diagram of the composite current collector of the present application.

[0037] Description of Figure Numbers:

[0038] 1. PP base film; 2. Adhesive layer; 3. Metal layer; 4. Protective layer. DETAILED DESCRIPTION

[0039] The following describes exemplary embodiments of the present application in more detail with reference to the accompanying drawings. Although exemplary embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the present application and to fully convey the scope of the present application to those skilled in the art.

[0040] As shown in Figure 1, an embodiment of the present application proposes a composite current collector, including: a PP base film 1; an adhesive layer 2 arranged on the upper and lower sides of the PP base film 1, and the adhesive layer 2 is obtained by treating with a surfactant, an organic treatment agent, a first treatment agent and a second treatment agent; a metal layer 3 arranged on the upper and lower sides of the adhesive layer 2; and a protective layer 4 arranged on the upper and lower sides of the metal layer 3.

[0041] In some embodiments, the substance in the adhesive layer 2 diffuses to the surface of the PP base film 1 and mechanically interlocks with the area below the surface of the PP substrate to provide adhesion, thereby improving the bonding ability between the PP base film 1 and the metal layer 3.

[0042] In some embodiments, the adhesive layer is treated with a surfactant, an organic treatment agent, a first treatment agent, and a second treatment agent. The surfactant treatment is a pretreatment method, primarily removing scale, rust products, dust, various salts, water, surface oxidation decomposition, and powdering and decomposition products from UV aging. The organic treatment agent treatment of the PP base film 1 increases the surface roughness of the amorphous portion of the solvent-dissolved portion. This increases the microscopic surface area and the number of anchor points for the metal layer 3 on the PP substrate, thereby facilitating the adhesion of the metal layer 3. Optionally, after the organic treatment, the PP base film 1 surface is rinsed with pure water and dried to remove as much solvent as possible and increase the surface roughness.

[0043] In some embodiments, the surface structure of the PP base film 1 changes after treatment with the first treatment agent. This is primarily due to the introduction of polar groups such as C=O, -OH, and -COOH, forming a thin film on the substrate surface. This improves the surface wettability of the metal layer 3 on the PP substrate, enhances the polarity of the plastic substrate surface, and subsequently increases the surface tension of the PP film. Optionally, the surface of the PP base film 1 is not rinsed with pure water after treatment with the first treatment agent, but is allowed to air dry directly to maximize the preservation of the surface polarity after treatment with the first treatment agent.

[0044] In some embodiments, the material of the metal layer 3 is one or more of copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, silver, etc., and the metal layer 3 is prepared by one or more of physical vapor deposition (including but not limited to electron beam vacuum evaporation, laser vacuum evaporation, magnetron sputtering, etc.), electroplating, chemical plating, etc. The thickness of the metal layer 3 is between 400 and 1500 nanometers.

[0045] In some embodiments, the PP base film 1 includes polypropylene and an antioxidant, and the mass percentage of the polypropylene to the antioxidant is (99%-99.5%):(0.5%-1%).

[0046] In some embodiments, the mass percentage of polypropylene to antioxidant may be: 99.5%:0.5%.

[0047] In some embodiments, the polypropylene has a melt index of 3.0-3.9 g / 10 min (230°C / 2.16 kg). A melt index that is too low and a molecular weight that is too high result in poor film-forming properties during film drawing. A melt index that is too high and a molecular weight that is too low result in poor mechanical properties of the resulting PP film. Considering both process difficulty and production cost, the thickness of the PP base film can be between 2 and 20 microns.

[0048] In some embodiments, the antioxidant is one or more of triphenyl phosphite, butylated hydroxyanisole, 2,6-di-tert-butyl-4-methylphenol, p-tert-butylcatechol, and the like.

[0049] In some embodiments, the surfactant is one or more of sodium dodecylbenzene sulfonate (LAS), sodium fatty alcohol polyoxyethylene ether sulfate (AES), sodium α-olefin sulfonate (AOS), sodium dodecyl sulfate (SDS), sodium fatty acid methyl ester sulfonate (MES), fatty alcohol polyoxyethylene ether (AEO), nonylphenol polyoxyethylene ether (OP series), sorbitan fatty acid ester (Span series), coconut oil fatty acid diethanolamine, polyether series, etc.; the organic treatment agent is toluene, xylene, cyclohexane, carbon tetrachloride, ethanol, propanol, isopropanol, n-butanol, ethylene glycol, One or more of propylene glycol, ethyl acetate, acetone, butanone, cyclohexanone, etc.; the first treatment agent is one or more of ethanol, propanol, isopropanol, n-butanol, ethylene glycol, glycerol, ethyl acetate, acetone, butanone, ethyl acetate, ethylene glycol methyl ether, ethylene glycol ethyl ether, etc.; the second treatment agent is one or more of chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate grafted PP and polyethylene / polypropylene blends or copolymers, block copolymers formed by copolymerization of isobornyl acrylate and acrylic acid, and ethylene-octene block copolymers.

[0050] In some embodiments, the purpose of treating the PP base film 1 with the first treatment agent is to change the surface structure of the substrate, introduce polar groups such as C=O, -OH, and -COOH, and form a thin film on the substrate surface, thereby improving the surface wettability of the metal layer 3 on the PP substrate, enhancing the polarity of the plastic substrate surface, and subsequently increasing the surface tension of the PP film. Therefore, optionally, after treatment with the first treatment agent, the surface of the PP base film 1 is not rinsed with pure water, but is directly air-dried to maximize the preservation of the surface polarity after treatment with the first treatment agent.

[0051] In some embodiments, the second treating agent treats the PP base film 1 to have the following effects: (1) during the synthesis of the second treating agent, organic solvents such as toluene and xylene are introduced, which diffuse into the PP base film 1, swell the molecules therein, and diffuse and entangle with each other to produce good adhesion; (2) adhesion is caused by the dispersion force between the non-polar main chain of the second treating agent and the non-polar polyolefin substrate; (3) when the crystal structure and size of the second treating agent are comparable to those of the PP base film 1, one polymer crystal can epitaxially grow on another polymer crystal to form good adhesion.

[0052] In some embodiments, the second treating agent is chlorinated polypropylene, which can be an acetone solution of chlorinated polypropylene, with a mass concentration of chlorinated polypropylene of 10‰, a soaking time of 60s, and a drying temperature of 90min.

[0053] In some embodiments, the material of the protective layer 4 is one or more of benzotriazoles and their derivatives or silane coupling agents.

[0054] In some embodiments, the reagent of the protective layer 4 includes one or more of benzotriazoles and their derivatives (such as BTA, TTA, Irgamet 39) or silane coupling agents. The function of the protective layer 4 is to prevent the metal layer from being chemically corroded or physically damaged. The working principle of the protective layer 4 is that the passivating agent in the protective layer 4 first reacts with copper, and the generated compound adheres to the copper surface, thereby preventing further reaction between copper and sulfur; or the silane coupling agent is hydrolyzed to generate silanol (X-Si(OH) n ), silanol combines with the metal surface and cross-links itself to form a dense protective film on the metal surface, thereby preventing the metal layer 3 from further reacting with the air.

[0055] In some embodiments, the thickness of the PP base film 1 is between 2 μm and 20 μm, and the thickness of the metal layer 3 on each side is between 400 nm and 1500 nm.

[0056] The present application also provides a method for preparing a composite current collector, comprising: preparing a PP base film 1, wherein the PP base film is obtained by mixing polypropylene with an antioxidant and then adopting a melt-biaxial stretching method;

[0057] The PP base film 1 is immersed in a surfactant, washed and dried, then immersed in an organic treatment agent, washed and dried, then immersed in a first treatment agent, dried without washing, then immersed in a second treatment agent by ultrasonication, and dried in an oven to obtain a bonded PP base film 1;

[0058] The adhesive PP base film 1 is placed in a magnetron sputtering chamber, and a metal thin layer is formed on the adhesive PP base film 1 by magnetron sputtering using a metal target. Then, metal layers 3 on both sides are deposited on the upper and lower surfaces of the PP base film 1 by aqueous electroplating to obtain metal layers 3.

[0059] The metal layer 3 is treated with a benzotriazole antioxidant to form a stable oxide film on the surface of the metal layer 3 , and then dried to obtain a composite current collector.

[0060] In some embodiments, the thickness of the PP base film 1 is 4.5 μm, and the thickness of the metal layer 3 on each side is 1000 nm. The metal layer 3 is formed by magnetron sputtering, that is, the interaction between the magnetic field and the electric field is used to make the electrons run in a spiral shape near the target surface, thereby increasing the probability of electrons colliding with argon gas to generate ions. The generated ions collide with the target surface under the action of the electric field, thereby sputtering out the target material.

[0061] In some embodiments, the surfactant is a mixture of sodium dodecyl sulfate (SDS), sodium methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO); the organic treatment agent is a mixture of acetone and tetrachloroethylene; the first treatment agent is isopropyl alcohol, and the second treatment agent is chlorinated polypropylene.

[0062] In some embodiments, the mass ratio of sodium dodecyl sulfate (SDS), sodium methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in the surfactant mixture is 3:1:2.

[0063] In some embodiments, the mass ratio of acetone to tetrachloroethylene in the organic treatment agent is 6:4.

[0064] In some embodiments, the mass concentration of the second treating agent chlorinated polypropylene is 5‰-10‰, the ultrasonic immersion time is 30s-300s, and the drying temperature in the oven is 80-120°C.

[0065] The following is a specific embodiment of the above method:

[0066] Example 1:

[0067] 1. Preparation of PP base film

[0068] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, which includes the following steps: material mixing - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - and heat setting. The resulting film had a thickness of 4.5 microns.

[0069] 2. Preparation of the Adhesive Layer

[0070] Pretreatment: The PP base film was placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, then rinsed with pure water and dried.

[0071] Organic treatment agent treatment: the pre-treated PP base film was immersed in a mixed solution of acetone and tetrachloroethylene with a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0072] First treatment agent treatment: the PP base film treated with the organic treatment agent and dried was immersed in isopropyl alcohol for 3 minutes, then taken out and naturally dried.

[0073] Second treatment agent treatment: The PP base film was placed in a 5‰ chlorinated polypropylene acetone solution and ultrasonically immersed for 30 seconds, then taken out, the residual liquid on the surface of the PP base film was wiped dry, and then dried in an oven at 80°C for 10 minutes.

[0074] 3. Composite Current Collector Preparation

[0075] The enhanced PP base film is placed in a magnetron sputtering chamber and sputtered to form a thick metal layer. After the magnetron sputtering metal layer is formed, the two metal layers are deposited on both surfaces of the PP base film by aqueous electroplating, forming a composite current collector with a thickness of approximately 1μm. Next, a protective layer is prepared: the prepared composite current collector is treated with a benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0076] Example 2:

[0077] The method is basically the same as Example 1, except that the content of chlorinated polypropylene used is 10‰.

[0078] Example 3:

[0079] The method is basically the same as Example 1, except that the content of chlorinated polypropylene used is 15‰.

[0080] Example 4:

[0081] The method is basically the same as Example 1, except that the content of chlorinated polypropylene used is 20‰.

[0082] Example 5:

[0083] Example 2 is basically the same, except that the immersion time in chlorinated polypropylene is 60 seconds.

[0084] Example 6:

[0085] The method is basically the same as Example 2, except that the immersion time in chlorinated polypropylene is 120 seconds.

[0086] Example 7:

[0087] The method is basically the same as Example 2, except that the immersion time in chlorinated polypropylene is 300 seconds.

[0088] Example 8:

[0089] The process is basically the same as Example 5, except that the baking temperature is 90°C.

[0090] Example 9:

[0091] The process is basically the same as Example 5, except that the baking temperature is 100°C.

[0092] Example 10:

[0093] The process is basically the same as Example 1, except that chlorinated polypropylene is replaced by methyl methacrylate.

[0094] Example 11:

[0095] The process is basically the same as Example 1, except that butyl acrylate is used instead of chlorinated polypropylene.

[0096] Comparative Example 1:

[0097] The method is basically the same as Example 1, except that no adhesive layer is provided on the PP base film, that is, no surfactant, organic treatment agent, first treatment agent, and second treatment agent are treated.

[0098] 1. Preparation of PP base film

[0099] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, which includes the following steps: material mixing - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - and heat setting. The resulting film had a thickness of 4.5 microns.

[0100] 2. Composite Current Collector Preparation

[0101] The prepared PP base film is placed in a magnetron sputtering chamber and sputtered to form a thick metal layer. After the metal layer is formed by magnetron sputtering, the two metal layers are deposited on both surfaces of the PP base film by aqueous electroplating, forming a composite current collector with a thickness of approximately 1μm. Secondly, the protective layer is prepared: the prepared composite current collector is treated with a benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0102] Comparative Example 2

[0103] The process is basically the same as Example 4, except that the immersion time in chlorinated polypropylene is 300 s and the baking temperature is 100°C.

[0104] 1. Preparation of PP base film

[0105] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, which includes the following steps: material mixing - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - heat setting. The resulting film had a thickness of 4.5 microns.

[0106] 2. Preparation of the Adhesive Layer

[0107] Pretreatment: The PP base film was placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, then rinsed with pure water and dried.

[0108] Organic treatment agent treatment: the pre-treated PP base film was immersed in a mixed solution of acetone and tetrachloroethylene with a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0109] First treatment agent treatment: the PP base film treated with the organic treatment agent and dried was immersed in isopropyl alcohol for 3 minutes, then taken out and naturally dried.

[0110] Second treatment agent treatment: The PP base film was placed in a 20‰ chlorinated polypropylene acetone solution and ultrasonically immersed for 300s, then taken out, the residual liquid on the surface of the PP base film was wiped dry, and then dried in an oven at 100°C for 10 minutes.

[0111] 3. Composite Current Collector Preparation

[0112] The enhanced PP base film is placed in a magnetron sputtering chamber and sputtered to form a thick metal layer. After the magnetron sputtering metal layer is formed, the two metal layers are deposited on both surfaces of the PP base film by aqueous electroplating, forming a composite current collector with a thickness of approximately 1μm. Next, a protective layer is prepared: the prepared composite current collector is treated with a benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0113] Comparative Example 3

[0114] 1. Preparation of PP base film

[0115] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, which includes the following steps: material mixing - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - and heat setting. The resulting film had a thickness of 4.5 microns.

[0116] 2. Preparation of the Adhesive Layer

[0117] Pretreatment: The PP base film was placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, then rinsed with pure water and dried.

[0118] Organic treatment agent treatment: the pre-treated PP base film was immersed in a mixed solution of acetone and tetrachloroethylene with a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0119] First treatment agent treatment: the PP base film treated with the organic treatment agent and dried was immersed in isopropyl alcohol for 3 minutes, then taken out and naturally dried.

[0120] Second treatment agent treatment: The PP base film was placed in a 22‰ chlorinated polypropylene acetone solution and ultrasonically immersed for 350s, then taken out, the residual liquid on the surface of the PP base film was wiped dry, and then dried in an oven at 110°C for 10 minutes.

[0121] 3. Composite Current Collector Preparation

[0122] The enhanced PP base film is placed in a magnetron sputtering chamber and sputtered to form a thick metal layer. After the magnetron sputtering metal layer is formed, the two metal layers are deposited on both surfaces of the PP base film by aqueous electroplating, forming a composite current collector with a thickness of approximately 1μm. Next, a protective layer is prepared: the prepared composite current collector is treated with a benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0123] Comparative Example 4:

[0124] The method is basically the same as Example 1, except that it is not treated with the second treating agent.

[0125] Comparative Example 5:

[0126] The method is basically the same as Example 1, except that the method is not treated with the first treating agent.

[0127] 1. Preparation of PP base film

[0128] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, which includes the following steps: material mixing - melt extrusion - sheet casting - longitudinal stretching - transverse stretching - heat setting. The resulting film had a thickness of 4.5 microns.

[0129] 2. Preparation of the Adhesive Layer

[0130] Pretreatment: The PP base film was placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, then rinsed with pure water and dried.

[0131] Organic treatment agent treatment: the pre-treated PP base film was immersed in a mixed solution of acetone and tetrachloroethylene with a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0132] First treatment agent treatment: the PP base film treated with the organic treatment agent and dried was immersed in isopropyl alcohol for 3 minutes, then taken out and naturally dried.

[0133] 3. Composite Current Collector Preparation

[0134] The enhanced PP base film is placed in a magnetron sputtering chamber and sputtered to form a thick metal layer. After the magnetron sputtering metal layer is formed, the two metal layers are deposited on both surfaces of the PP base film by aqueous electroplating, forming a composite current collector with a thickness of approximately 1μm. Next, a protective layer is prepared: the prepared composite current collector is treated with a benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0135] Test evaluation:

[0136] As mentioned above, the purpose of treating the PP base film is to improve the surface adhesion and mechanical properties of the film, and thus improve the performance of the composite current collector prepared with this PP base film as the substrate. Here, factors affecting the surface adhesion performance of the PP base film, namely the surface tension, the adhesion between the PP base film and the surface metal layer in the composite current collector, and other indicators were tested and characterized. In addition, the tensile strength of the prepared PP base film was also tested. The specific test methods are as follows:

[0137] ① Surface tension: The surface tension of the PP base films prepared in the above examples and comparative examples was tested in accordance with GB / T 14216-2008.

[0138] ② The adhesion between the PP base film and the metal layer in the composite current collector: a layer of Permacel P-94 double-sided tape was adhered to a 1 mm thick aluminum foil, the composite current collector was adhered on the double-sided tape, and a layer of ethylene acrylic acid copolymer film (DuPont Nurcel0903, thickness of 50 μm) was covered on the composite current collector. Then, a 1.3×10 5 N / m 2 The film was hot-pressed at 120°C for 10 seconds, cooled to room temperature, and cut into 150mm x 15mm strips. Finally, the ethylene acrylic acid copolymer film strip was fixed to the upper fixture of the tensile testing machine, and the remaining film strip was fixed to the lower fixture. After the two were fixed, they were peeled off at an angle of 180° and a speed of 100mm / min to test the peel force, i.e., the adhesion between the PP base film and the metal layer.

[0139] Table: Surface tension of polypropylene film and adhesive force of composite current collector in each embodiment and comparative example

[0140] Note: The elastic modulus, tensile strength and elongation at break of the polypropylene film and composite current collector measured above are all indicators in the MD direction (i.e., the direction of the film roll after it is unrolled).

[0141] In the above table, from Examples 1-4, it can be seen that: within the mass concentration of chlorinated polypropylene (i.e., 5‰-10‰), increasing the concentration of chlorinated polypropylene improves the bonding performance of the polypropylene film and the composite current collector; when the mass concentration range of chlorinated polypropylene is exceeded by 10‰, the bonding performance of the polypropylene film and the composite current collector is significantly reduced.

[0142] From Example 2 and Examples 5-7, it can be seen that within the processing time of 60s-300s, the bonding performance between the polypropylene film and the composite current collector is good.

[0143] From Example 5 and Examples 8-9, it can be seen that within the baking temperature range of 80-120° C., as the baking temperature increases, the bonding performance between the polypropylene film and the composite current collector first increases and then slightly decreases.

[0144] It can be seen from Comparative Examples 2 and 3 that when the mass content of chlorinated polypropylene exceeds 5‰-10‰ and the immersion time exceeds the range of 60s-300s, the surface tension of the polypropylene film and the adhesion of the composite current collector become smaller, which is not conducive to the improvement of the mechanical properties of the composite current collector. That is, when the mass content of chlorinated polypropylene is 5‰-10‰ and the immersion time is in the range of 60s-300s, the adhesion of the composite current collector is enhanced, the mechanical properties of the composite current collector are significantly improved, and the PP base film and the metal layer are not easy to fall off.

[0145] Comparative Example 1 was not provided with an adhesive layer, that is, it was not treated with a surfactant, an organic treatment agent, a first treatment agent, and a second treatment agent. Comparative Example 4 was treated with a surfactant, an organic treatment agent, and a first treatment agent, but not with a second treatment agent. Compared with Comparative Example 1, the surface tension of the polypropylene film and the adhesive force of the composite current collector in Comparative Example 4 were both greater than those in Comparative Example 1, but the surfactant, organic treatment agent, and first treatment agent had little effect on their improvement. The surface tension of the polypropylene film only increased from 22mN / m to 23mN / m, and the adhesive force of the composite current collector only increased from 1.3N / cm to 1.5N / cm, which was only a small improvement. Compared with Example 1, Example 1 was treated with the second treatment agent. The surface tension of the polypropylene film increased from 23mN / m in Comparative Example 4 to 26mN / m in Example 1, and the adhesive force of the composite current collector increased from 1.5N / cm to 1.8N / cm. That is, the second treatment agent significantly increased the surface tension of the polypropylene film, significantly strengthened the adhesive force of the composite current collector, and significantly improved the mechanical properties of the composite current collector.

[0146] In summary, the adhesive layers provided on the upper and lower sides of the PP base film can greatly increase the surface tension of the polypropylene film and the adhesion of the composite current collector. The solvent in the adhesive layer will expand and diffuse onto the surface of the PP base film, enhancing the mechanical interlocking force with the PP base film surface, thereby enhancing the adhesion between the PP base film and the metal layer. The composite current collector prepared in this way has enhanced adhesion, significantly improved mechanical properties, and is less likely to fall off the PP base film and the metal layer. The second treatment agent plays a more decisive role in improving the bonding ability between the PP base film and the metal layer. During the synthesis of the second treatment agent, organic solvents such as toluene and xylene are introduced. These solvents diffuse into the PP base film, swelling the molecules therein, and diffuse and entangle with each other to produce good adhesion. The dispersion force between the non-polar main chain of the second treatment agent and the non-polar polyolefin substrate leads to the generated adhesion. When the crystal structure and size of the second treatment agent and the PP base film 1 are comparable, one polymer crystal can epitaxially grow on the other polymer crystal, forming good adhesion.

[0147] The above is a preferred embodiment of the present application. It should be noted that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles described in the present application. These improvements and modifications should also be considered as the scope of protection of the present application.

Claims

1. A composite current collector comprising: PP base film; An adhesive layer is provided on the upper and lower sides of the PP base film, wherein the adhesive layer is treated with a surfactant, an organic treatment agent, a first treatment agent and a second treatment agent; A metal layer disposed on the upper and lower sides of the bonding layer; A protective layer is arranged on the upper and lower sides of the metal layer.

2. The composite current collector according to claim 1, wherein: The PP base film comprises polypropylene and an antioxidant, and the mass percentage of the polypropylene and the antioxidant is (99%-99.5%):(0.5%-1%).

3. The composite current collector according to claim 1 or 2, wherein: The surfactant is one or a combination of two or more selected from the group consisting of sodium dodecylbenzene sulfonate, sodium polyoxyethylene fatty alcohol ether sulfate, sodium α-olefin sulfonate, sodium dodecyl sulfate, sodium fatty acid methyl ester sulfonate, fatty alcohol polyoxyethylene ether, nonylphenol polyoxyethylene ether, sorbitan fatty acid ester, coconut oil fatty acid diethanolamine, polyether series, and the like.

4. The composite current collector according to any one of claims 1 to 3, wherein: The organic treatment agent is one or a combination of two or more of toluene, xylene, cyclohexane, carbon tetrachloride, ethanol, propanol, isopropanol, n-butanol, ethylene glycol, propylene glycol, ethyl acetate, acetone, butanone, cyclohexanone, etc.

5. The composite current collector according to any one of claims 1 to 4, wherein: The first treating agent is one or a combination of two or more of ethanol, propanol, isopropanol, n-butanol, ethylene glycol, glycerol, ethyl acetate, acetone, butanone, ethyl acetate, ethylene glycol methyl ether, ethylene glycol ethyl ether, etc.

6. The composite current collector according to any one of claims 1 to 5, wherein: The second treating agent is one or a combination of two or more of chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate, polyethylene / polypropylene blend or copolymer, block copolymer formed by copolymerization of isobornyl acrylate and acrylic acid, and ethylene-octene block copolymer.

7. The composite current collector according to any one of claims 1 to 6, wherein: The material of the protective layer is one or a combination of two or more of benzotriazoles and their derivatives or silane coupling agents.

8. The composite current collector according to any one of claims 1 to 7, wherein: The thickness of the PP base film is between 2 μm and 20 μm, and the thickness of the metal layer on each side is between 400 and 1500 nm.

9. A method for preparing a composite current collector, comprising: Preparing a PP base film, wherein the PP base film is obtained by mixing polypropylene and an antioxidant and then adopting a melt-biaxial stretching method; The PP base film is immersed in a surfactant, washed and dried, immersed in an organic treatment agent, washed and dried, immersed in a first treatment agent, dried, immersed in a second treatment agent by ultrasonic, and dried in an oven to obtain a bonded PP base film; The bonding PP base film is placed in a magnetron sputtering chamber, a metal is used as a target material, a metal thin layer is formed on the bonding PP base film by a magnetron sputtering method, and the metal thin layer is deposited on the upper and lower surfaces of the PP base film by a water medium electroplating method to obtain a metal layer; The metal layer is treated with a benzotriazole antioxidant to form a stable oxide film protective layer on the surface of the metal layer, and the composite current collector is obtained after drying.

10. The method for preparing a composite current collector according to claim 9, wherein: The surfactant is a mixed solution of sodium dodecyl sulfate, sodium fatty acid methyl ester sulfonate and fatty alcohol polyoxyethylene ether; the organic treatment agent is a mixed solution of acetone and tetrachloroethylene; the first treatment agent is isopropanol and the second treatment agent is chlorinated polypropylene.

11. The method for preparing a composite current collector according to claim 10, wherein: The mass ratio of sodium dodecyl sulfate, sodium fatty acid methyl ester sulfonate and fatty alcohol polyoxyethylene ether in the mixed solution of the surfactant is 3:1:

2.

12. The method for preparing a composite current collector according to claim 10, wherein: The mass ratio of acetone to tetrachloroethylene in the organic treatment agent is 6:

4.

13. The method for preparing a composite current collector according to any one of claims 9 to 12, wherein: The mass concentration of the second treatment agent is 5‰-10‰, the ultrasonic immersion time is 30s-300s, and the drying temperature in the oven is 80-120°C.

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