A composite current collector and its preparation method

Abstract

This invention provides a composite current collector and its preparation method. The composite current collector includes: a PP base film; adhesive layers disposed on the upper and lower sides of the PP base film, the adhesive layers being obtained by treatment with a surfactant, an organic treatment agent, a first treatment agent, and a second treatment agent; metal layers disposed on the upper and lower sides of the adhesive layers; and protective layers disposed on the upper and lower sides of the metal layers. The solution of this invention can enhance the adhesion performance between the PP base film and the metal layers.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite current collector and its preparation method. Background Technology

[0002] Currently, composite current collectors based on polymer films are receiving widespread attention and application in the new energy industry. The preparation process typically involves depositing a metal (aluminum, copper, etc.) layer onto a polymer film (such as polypropylene, polyethylene, polyester, etc.) using physical vapor deposition (PVD). The resulting surface-metallized film with a certain conductivity is the composite current collector. Compared to traditional current collectors, polymer film-based composite current collectors offer advantages such as low cost, light weight, and good internal insulation. These characteristics enable composite current collectors to reduce battery costs and improve battery energy density and safety when used in batteries.

[0003] In existing current collector manufacturing processes, a layer of copper material, tens of nanometers thick, is typically sputtered onto a polymer film using magnetron sputtering to impart conductivity. This is then followed by electroplating to thicken the PP (polypropylene) base film by 1 μm on each side, creating a composite current collector. However, because PP (polypropylene) is a non-polar material with high surface bond energy, chemical bonds are difficult to break, resulting in poor adhesion to metals. The resulting composite copper current collector exhibits poor bonding strength, and the metal layer easily detaches from the PP base film, making it unsuitable for battery applications. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a composite current collector and a preparation method to solve the problem of poor bonding performance of PP composite current collector.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] A composite current collector, comprising:

[0007] PP base film;

[0008] The adhesive layers disposed on the upper and lower sides of the PP base film are obtained by treatment with surfactant, organic treatment agent, first treatment agent and second treatment agent;

[0009] Metal layers disposed on the upper and lower sides of the adhesive layer;

[0010] Protective layers are disposed on the upper and lower sides of the metal layer.

[0011] Optionally, the PP base film includes polypropylene and an antioxidant, wherein the mass percentage of polypropylene to antioxidant is (99%-99.5%):(0.5%-1%).

[0012] Optionally, the surfactant is one or more of the following: sodium dodecylbenzene sulfonate, sodium fatty alcohol polyoxyethylene ether sulfate, sodium α-alkenyl 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, etc.

[0013] The organic treatment agent is one or more of the following: toluene, xylene, cyclohexane, carbon tetrachloride, ethanol, propanol, isopropanol, n-butanol, ethylene glycol, propylene glycol, ethyl acetate, acetone, butanone, cyclohexanone, etc.

[0014] 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.

[0015] The second treatment agent is one or more of the following: chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate, etc. grafted PP, as well as blends or copolymers of polyethylene / polypropylene, block copolymers formed by copolymerizing isoborneol acrylate and acrylic acid, and ethylene-octene block copolymers.

[0016] Optionally, the material of the protective layer is one or more of benzotriazoles and their derivatives or silane coupling agents.

[0017] Optionally, the thickness of the PP base film is between 2um and 20um, and the thickness of the metal layer on each side is between 400 and 1500nm.

[0018] This invention also provides a method for preparing a composite current collector, comprising:

[0019] A PP-based film is prepared by mixing polypropylene with an antioxidant and then using a melt-biaxial stretching method.

[0020] The PP base film 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, ultrasonically immersed in a second treatment agent, and dried in an oven to obtain an adhesive PP base film.

[0021] The bonded PP base film is placed in the magnetron sputtering chamber, and a metal is used as the target material. A thin metal layer is formed on the bonded PP base film by magnetron sputtering. The two metal layers are deposited on the two surfaces of the base film by water-medium electroplating to obtain the metal layer.

[0022] The metal layer is treated with benzotriazole antioxidant to form a stable oxide film, which is then dried to obtain a composite current collector.

[0023] Optionally, the surfactant is a mixture of sodium dodecyl 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 isopropanol, and the second treatment agent is chlorinated polypropylene.

[0024] Optionally, the mass ratio of sodium dodecyl sulfate, sodium fatty acid methyl ester sulfonate, and fatty alcohol polyoxyethylene ether in the surfactant mixture is 3:1:2.

[0025] Optionally, the mass ratio of acetone to tetrachloroethylene in the organic treatment agent is 6:4.

[0026] Optionally, the concentration of chlorinated polypropylene is 5‰-10‰, the soaking time is 30s-300s, and the drying temperature in the oven is 80-120℃.

[0027] The above-mentioned solution of the present invention includes at least the following beneficial effects: the solvent in the adhesive layer expands and diffuses to the surface of the PP base film, enhancing the mechanical interlocking force with the surface of the PP base film, thereby enhancing the adhesion performance between the PP base film and the metal layer. The composite current collector prepared in this way has stronger adhesion, significantly improved mechanical properties, and the PP base film and metal layer are not easy to fall off. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the composite current collector of the present invention.

[0029] Explanation of icon numbers:

[0030] 1. PP base film; 2. Adhesive layer; 3. Metal layer; 4. Protective layer. Detailed Implementation

[0031] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0032] like Figure 1 As shown, an embodiment of the present invention proposes a composite current collector, comprising: a PP base film 1; an adhesive layer 2 disposed on the upper and lower sides of the PP base film 1, the adhesive layer 2 being obtained by treatment with a surfactant, an organic treatment agent, a first treatment agent and a second treatment agent; a metal layer 3 disposed on the upper and lower sides of the adhesive layer 2; and a protective layer 4 disposed on the upper and lower sides of the metal layer 3.

[0033] In this embodiment, the substance in the adhesive layer 2 diffuses to the surface of the PP base film 1 and provides adhesion by mechanically interlocking with the area below the surface of the PP substrate, thereby improving the bonding ability between the PP base film 1 and the metal layer 3.

[0034] In this embodiment, the adhesive layer 2 is obtained by treatment with a surfactant, an organic treatment agent, a first treatment agent, and a second treatment agent. The surfactant treatment is a pretreatment method, mainly to remove oxide scale, rust products, dust, various salts, water, powdering and decomposition products after surface oxidation and ultraviolet aging, etc. After the PP base film 1 is treated with a solvent, the solvent dissolves the non-crystalline surface, which increases the roughness. This increases the microscopic surface area and the anchoring points of the metal layer 3 on the PP substrate, thus facilitating the adhesion of the metal layer 3.

[0035] In this embodiment, the metal layer 3 is made of one or more of the following materials: copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, and silver. The metal layer 3 is prepared by one or more methods, including physical vapor deposition (but not limited to electron beam heating vacuum evaporation, laser heating vacuum evaporation, magnetron sputtering, etc.), electroplating, and chemical plating. The thickness of the metal layer 3 is between 400 and 1500 nanometers.

[0036] In one optional embodiment, the PP base film 1 comprises polypropylene and an antioxidant, wherein the mass percentage of the polypropylene to the antioxidant is (99%-99.5%):(0.5%-1%).

[0037] In this embodiment, the preferred mass percentage of polypropylene to antioxidant is 99.5% : 0.5%.

[0038] In this embodiment, the melt index of the polypropylene is 3.0-3.9 g / 10 min (230℃ / 2.16 kg). If the melt index is too low, the molecular weight is too high, resulting in poor film formation during the film stretching process; if the melt index is too high, the molecular weight is too low, leading to poor mechanical properties of the prepared PP film. Considering both process difficulty and production cost, the preferred thickness of the composite polypropylene film is between 2 micrometers and 20 micrometers.

[0039] In this embodiment, the antioxidant is one or more of the following: triphenyl phosphite, butylated hydroxyanisole, 2,6-di-tert-butyl-4-methylphenol, and p-tert-butylcatechol.

[0040] In one optional embodiment, the surfactant is one or more of the following: sodium dodecylbenzene sulfonate (LAS), sodium fatty alcohol polyoxyethylene ether sulfate (AES), sodium α-alkenyl 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, and polyether series; the organic treatment agent is toluene, xylene, cyclohexane, carbon tetrachloride, ethanol, propanol, isopropanol, n-butanol, or ethylene glycol. The first treatment agent is one or more of propylene glycol, ethyl acetate, acetone, butanone, cyclohexanone, etc.; the second treatment agent is one or more of chlorinated polypropylene, itaconic acid, dipentene copolymer, methyl methacrylate, butyl acrylate, glycidyl acrylate, etc. grafted onto PP and blends or copolymers of polyethylene / polypropylene, isoborneol acrylate and acrylic acid to form block copolymers, ethylene-octene block copolymers, etc.

[0041] In this embodiment, 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 wetting performance of the metal layer 3 on the PP substrate, enhancing the polarity of the plastic substrate surface, and consequently increasing the surface tension of the PP film.

[0042] In this embodiment, the effects of the second treatment agent on the PP base film 1 are as follows: (1) 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 1, causing the molecules in it to swell and diffuse and entangle with each other to generate good adhesion; (2) The adhesion caused by the dispersion force between the non-polar main chain of the second treatment agent and the non-polar polyolefin substrate; (3) When the crystal structure and size of the second treatment agent and the PP base film 1 are similar, a polymer crystal can be epitaxially grown on the other polymer crystal to form good adhesion.

[0043] In a preferred embodiment of the present invention, the second treatment agent used is chlorinated polypropylene. In this embodiment, the concentration of chlorinated polypropylene is 10‰, the soaking time is 60s, and the drying temperature is 90min.

[0044] In one optional embodiment, the material of the protective layer 4 is one or more of benzotriazoles and their derivatives or silane coupling agents.

[0045] In this embodiment, the reagents of the protective layer 4 include 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 conductive 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 resulting compound adheres to the copper surface, thereby preventing copper and sulfur from reacting further; or the silane coupling agent hydrolyzes to generate silanol (X-Si(OH)n), and the 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 reacting further with air.

[0046] In one optional embodiment, the thickness of the PP base film 1 is between 2um and 20um, and the thickness of the metal layer 3 on each side is between 400 and 1500nm.

[0047] The present invention also provides a method for preparing a composite current collector, comprising: preparing a PP-based film 1, wherein the PP-based film 1 is obtained by mixing polypropylene with an antioxidant and then using a melt-biaxial stretching method;

[0048] 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, ultrasonically immersed in a second treatment agent, and dried in an oven to obtain the bonded PP base film 1.

[0049] The bonded PP base film 1 is placed in the magnetron sputtering chamber, and a metal is used as the target material. A thin metal layer is formed on the bonded PP base film 1 by magnetron sputtering. The two metal layers 3 are deposited on the two surfaces of the PP base film 1 by water-medium electroplating to obtain the metal layer 3.

[0050] The metal layer 3 is coated with a benzotriazole antioxidant to form a stable oxide film, which is then dried to obtain a composite current collector.

[0051] In a preferred embodiment of the present invention, 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. In this embodiment, the metal layer 3 is formed by magnetron sputtering, which utilizes the interaction of magnetic and electric fields to make 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 the target material.

[0052] In one optional embodiment, 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 isopropanol, and the second treatment agent is chlorinated polypropylene.

[0053] In one optional embodiment, the mass ratio of sodium dodecyl sulfate (SDS), sodium fatty acid methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in the surfactant mixture is 3:1:2.

[0054] In one optional embodiment, the mass ratio of acetone to tetrachloroethylene in the organic treatment agent is 6:4.

[0055] In one optional embodiment, the concentration of chlorinated polypropylene is 5‰-10‰, the soaking time is 30s-300s, and the drying temperature in the oven is 80-120℃.

[0056] The following are specific embodiments of the above method:

[0057] Example 1:

[0058] 1. Preparation of PP base film

[0059] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, including the following steps: material mixing, melt extrusion, casting, longitudinal stretching, transverse stretching, and heat setting. The resulting film had a thickness of 4.5 micrometers.

[0060] 2. Preparation of the adhesive layer

[0061] Pretreatment: The PP base film is placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium fatty acid methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, rinsed with pure water, and then dried.

[0062] Organic treatment agent treatment: The pretreated PP base film is immersed in a mixed solution of acetone and tetrachloroethylene at a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0063] First treatment: The PP base film, after being treated and dried with the organic treatment agent, is immersed in isopropanol for 3 minutes, then removed and air-dried naturally.

[0064] Second treatment: The PP base film is ultrasonically immersed in 5‰ chlorinated polypropylene for 30 seconds, then removed, the residual liquid on the surface of the PP base film is wiped dry, and then dried in an oven at 80℃ for 10 minutes.

[0065] 3. Preparation of composite current collectors

[0066] The prepared enhanced PP base film was placed in a magnetron sputtering chamber to form a thick metal layer. After the metal layer was formed by magnetron sputtering, the two metal layers were deposited on the two surfaces of the PP base film by aqueous electroplating to form a composite current collector with a thickness of approximately 1 μm on each side. Next, the protective layer was prepared: the prepared composite current collector was treated with benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0067] Example 2:

[0068] It is basically the same as Example 1, except that the content of chlorinated polypropylene used is 10‰.

[0069] Example 3:

[0070] It is basically the same as Example 1, except that the content of chlorinated polypropylene used is 15‰.

[0071] Example 4:

[0072] It is basically the same as Example 1, except that the content of chlorinated polypropylene used is 20‰.

[0073] Example 5:

[0074] Example 2 is basically the same, except that the soaking time in chlorinated polypropylene is 60 seconds.

[0075] Example 6:

[0076] It is basically the same as Example 2, except that the soaking time in chlorinated polypropylene is 120s.

[0077] Example 7:

[0078] It is basically the same as Example 2, except that the soaking time in chlorinated polypropylene is 300s.

[0079] Example 8:

[0080] It is basically the same as Example 5, except that the baking temperature is 90°C.

[0081] Example 9:

[0082] It is basically the same as Example 5, except that the baking temperature is 100°C.

[0083] Comparative Example 1:

[0084] It is basically the same as Example 1, except that: no adhesive layer is set on the prepared PP base film, that is, it is not treated with surfactant, organic treatment agent, first treatment agent and second treatment agent.

[0085] 1. Preparation of PP base film

[0086] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, including the following steps: material mixing, melt extrusion, casting, longitudinal stretching, transverse stretching, and heat setting. The resulting film had a thickness of 4.5 micrometers.

[0087] 2. Preparation of composite current collectors

[0088] The prepared PP base film was placed in a magnetron sputtering chamber to form a thick metal layer. After the metal layer was formed by magnetron sputtering, the two metal layers were deposited on the two surfaces of the PP base film by aqueous electroplating to form a composite current collector with a thickness of approximately 1 μm on each side. Next, the protective layer was prepared: the prepared composite current collector was treated with benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0089] Comparative Example 2

[0090] It is basically the same as Example 4, except that the soaking time in chlorinated polypropylene is 300s and the baking temperature is 100℃.

[0091] 1. Preparation of PP base film

[0092] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, including the following steps: material mixing, melt extrusion, casting, longitudinal stretching, transverse stretching, and heat setting. The resulting film had a thickness of 4.5 micrometers.

[0093] 2. Preparation of the adhesive layer

[0094] Pretreatment: The PP base film is placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium fatty acid methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, rinsed with pure water, and then dried.

[0095] Organic treatment agent treatment: The pretreated PP base film is immersed in a mixed solution of acetone and tetrachloroethylene at a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0096] First treatment: The PP base film, after being treated and dried with the organic treatment agent, is immersed in isopropanol for 3 minutes, then removed and air-dried naturally.

[0097] Second treatment: The PP base film is ultrasonically immersed in 20‰ chlorinated polypropylene for 300 seconds, then removed, the residual liquid on the surface of the PP base film is wiped dry, and then dried in an oven at 100℃ for 10 minutes.

[0098] 3. Preparation of composite current collectors

[0099] The prepared enhanced PP base film was placed in a magnetron sputtering chamber to form a thick metal layer. After the metal layer was formed by magnetron sputtering, the two metal layers were deposited on the two surfaces of the PP base film by aqueous electroplating to form a composite current collector with a thickness of approximately 1 μm on each side. Next, the protective layer was prepared: the prepared composite current collector was treated with benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0100] Comparative Example 3

[0101] 1. Preparation of PP base film

[0102] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, including the following steps: material mixing, melt extrusion, casting, longitudinal stretching, transverse stretching, and heat setting. The resulting film had a thickness of 4.5 micrometers.

[0103] 2. Preparation of the adhesive layer

[0104] Pretreatment: The PP base film is placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium fatty acid methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, rinsed with pure water, and then dried.

[0105] Organic treatment agent treatment: The pretreated PP base film is immersed in a mixed solution of acetone and tetrachloroethylene at a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0106] First treatment: The PP base film, after being treated and dried with the organic treatment agent, is immersed in isopropanol for 3 minutes, then removed and air-dried naturally.

[0107] Second treatment: The PP base film is ultrasonically immersed in 22‰ chlorinated polypropylene for 350 seconds, then removed, the residual liquid on the surface of the PP base film is wiped dry, and then dried in an oven at 110℃ for 10 minutes.

[0108] 3. Preparation of composite current collectors

[0109] The prepared enhanced PP base film was placed in a magnetron sputtering chamber to form a thick metal layer. After the metal layer was formed by magnetron sputtering, the two metal layers were deposited on the two surfaces of the PP base film by aqueous electroplating to form a composite current collector with a thickness of approximately 1 μm on each side. Next, the protective layer was prepared: the prepared composite current collector was treated with benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0110] Comparative Example 4:

[0111] It is basically the same as Example 1, except that it is not treated with a second treatment agent.

[0112] 1. Preparation of PP base film

[0113] A film was prepared by mixing 99.5% polypropylene and 0.5% triphenyl phosphite using a melt-biaxial stretching method, including the following steps: material mixing, melt extrusion, casting, longitudinal stretching, transverse stretching, and heat setting. The resulting film had a thickness of 4.5 micrometers.

[0114] 2. Preparation of the adhesive layer

[0115] Pretreatment: The PP base film is placed in a mixed solution of sodium dodecyl sulfate (SDS), sodium fatty acid methyl ester sulfonate (MES), and fatty alcohol polyoxyethylene ether (AEO) in a mass ratio of 3:1:2, rinsed with pure water, and then dried.

[0116] Organic treatment agent treatment: The pretreated PP base film is immersed in a mixed solution of acetone and tetrachloroethylene at a mass ratio of 6:4 for 3 minutes, then rinsed with pure water and dried.

[0117] First treatment: The PP base film, after being treated and dried with the organic treatment agent, is immersed in isopropanol for 3 minutes, then removed and air-dried naturally.

[0118] 3. Preparation of composite current collectors

[0119] The prepared enhanced PP base film was placed in a magnetron sputtering chamber to form a thick metal layer. After the metal layer was formed by magnetron sputtering, the two metal layers were deposited on the two surfaces of the PP base film by aqueous electroplating to form a composite current collector with a thickness of approximately 1 μm on each side. Next, the protective layer was prepared: the prepared composite current collector was treated with benzotriazole antioxidant to form a stable oxide film, and finally dried at 100°C.

[0120] Test Evaluation:

[0121] As mentioned earlier, the purpose of treating the PP base film is to improve its surface adhesion and mechanical properties, thereby enhancing the performance of the composite current collector prepared using this PP base film as the substrate. Here, factors affecting the surface adhesion of the PP base film, such as surface tension, and the adhesion force between the PP base film and the surface metal layer in the composite current collector, were tested and characterized. Furthermore, the tensile strength of the prepared PP base film was also tested. The specific test methods are as follows:

[0122] ① Surface tension: The surface tension of the PP base film prepared above was tested according to GB / T 14216-2008.

[0123] ② Adhesion between the PP base film and the metal layer in the composite current collector: A layer of Permacel P-94 double-sided adhesive was bonded to a 1mm thick aluminum foil. A composite current collector was then bonded on top of the double-sided adhesive, and a layer of ethylene-acrylic acid copolymer film (DuPont Nurcel 0903, 50μm thick) was placed on top of the composite current collector. The film was then hot-pressed at 1.3×10⁵ N / m² and 120℃ for 10s, cooled to room temperature, and cut into 150mm×15mm strips. Finally, the ethylene-acrylic acid copolymer film of the sample strips was fixed to the upper clamp of a tensile testing machine, while the remaining parts were fixed to the lower clamp. After fixing, the two parts were peeled at an angle of 180° and a speed of 100mm / min. The peel force, i.e., the adhesion between the PP base film and the metal layer, was tested.

[0124] Table: Surface tension of polypropylene film and adhesion of composite current collector in each embodiment and comparative example.

[0125]

[0126]

[0127] Note: The elastic modulus, tensile strength and elongation at break of the polypropylene film and composite current collectors measured above are all indices in the MD direction (i.e., the machine direction, the direction of the film roll after unfolding).

[0128] In the table above, it can be seen from Examples 1-4 that within the concentration range of chlorinated polypropylene (i.e., 5‰-10‰), increasing the concentration of chlorinated polypropylene improves the adhesion performance of the polypropylene film and the composite current collector; when the concentration exceeds the range of chlorinated polypropylene by 10‰, the adhesion performance of the polypropylene film and the composite current collector decreases significantly.

[0129] As can be seen from Examples 2 and 5-7, the polypropylene film and composite current collector exhibit good adhesion performance within a processing time of 60s-300s.

[0130] As can be seen from Examples 5 and 8-9, within the baking temperature range of 80-120°C, increasing the baking temperature first improves the adhesion performance of the polypropylene film and the composite current collector, and then slightly decreases it.

[0131] Comparative Examples 2 and 3 show that when the chlorinated polypropylene content exceeds 5‰-10‰ and the soaking time exceeds 60s-300s, the surface tension of the polypropylene film and the adhesion of the composite current collector decrease, which is not conducive to improving the mechanical properties of the composite current collector. That is, when the chlorinated polypropylene content is 5‰-10‰ and the soaking time is 60s-300s, the adhesion of the composite current collector is strengthened, 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.

[0132] Comparative Example 1 was obtained without an adhesive layer, i.e., without treatment with surfactant, organic treatment agent, first treatment agent, and second treatment agent. Comparative Example 4 was treated with surfactant, organic treatment agent, and first treatment agent, but not with the second treatment agent. Compared with Comparative Example 1, the surface tension and adhesion of the polypropylene film in Comparative Example 4 were greater than those in Comparative Example 1. However, the improvement effect of surfactant, organic treatment agent, and first treatment agent was small. The surface tension of the polypropylene film only increased from 22 mN / m to 23 mN / m, and the adhesion of the composite current collector only increased from 1.3 N / cm to 1.5 N / cm, showing only a small improvement. Compared with Example 1, Comparative Example 4, treated with the second treatment agent, showed that the surface tension of the polypropylene film increased from 23 mN / m in the comparative example to 26 mN / m in Example 1, and the adhesion of the composite current collector increased from 1.5 N / cm to 1.8 N / cm. That is, the second treatment agent significantly improved the surface tension of the polypropylene film, significantly strengthened the adhesion of the composite current collector, and significantly improved the mechanical properties of the composite current collector.

[0133] In summary, the adhesive layers on both sides of the PP base film can greatly improve the surface tension of the polypropylene film and the adhesion of the composite current collector. The solvent in the adhesive layer expands and diffuses to the surface of the PP base film, enhancing the mechanical interlocking force with the PP base film surface, thereby enhancing the adhesion performance between the PP base film and the metal layer. The composite current collector prepared in this way has stronger adhesion and significantly improved mechanical properties, making it less likely for the PP base film and the metal layer to detach. 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, causing the molecules to swell and diffuse and entangle with each other to generate good adhesion. The adhesion is also due to the dispersion force between the non-polar main chain of the second treatment agent and the non-polar polyolefin substrate. When the crystal structure and size of the second treatment agent and the PP base film are comparable, one polymer crystal can be epitaxially grown on the other polymer crystal to form good adhesion.

[0134] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite current collector, characterized in that, include: PP base film; The adhesive layer disposed on the upper and lower sides of the PP base film is obtained by treating it with a surfactant, an organic treatment agent, a first treatment agent and a second treatment agent; specifically, the PP base film is immersed in the surfactant, washed and dried, then immersed in the organic treatment agent, washed and dried, then immersed in the first treatment agent, dried, ultrasonically immersed in the second treatment agent, and dried in an oven to obtain the bonded PP base film. Metal layers disposed on the upper and lower sides of the adhesive layer; Protective layers disposed on the upper and lower sides of the metal layer; The surfactant is a mixture of sodium dodecyl 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 isopropanol, and the second treatment agent is chlorinated polypropylene.

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

3. The composite current collector according to claim 1, characterized in that, The material of the protective layer is one or more of benzotriazoles and their derivatives or silane coupling agents.

4. The composite current collector according to claim 1, characterized in that, The thickness of the PP base film is between 2um and 20um, and the thickness of the metal layer on each side is between 400 and 1500nm.

5. A method for preparing a composite current collector, characterized in that, include: A PP-based film is prepared by mixing polypropylene with an antioxidant and then using a melt-biaxial stretching method. The PP base film 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, ultrasonically immersed in a second treatment agent, and dried in an oven to obtain an adhesive PP base film. The bonded PP base film is placed in the magnetron sputtering chamber, and a metal is used as the target material. A thin metal layer is formed on the bonded PP base film by magnetron sputtering. The two metal layers are deposited on the two surfaces of the PP base film by water-medium electroplating to obtain the metal layer. The metal layer is treated with benzotriazole antioxidant to form a stable oxide film, and after drying, a composite current collector is obtained. The surfactant is a mixture of sodium dodecyl 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 isopropanol, and the second treatment agent is chlorinated polypropylene.

6. The method for preparing the composite current collector according to claim 5, characterized in that, The mass ratio of sodium dodecyl sulfate, sodium fatty acid methyl ester sulfonate, and fatty alcohol polyoxyethylene ether in the surfactant mixture is 3:1:

2.

7. The method for preparing the composite current collector according to claim 6, characterized in that, The mass ratio of acetone to tetrachloroethylene in the organic treatment agent is 6:

4.

8. The method for preparing the composite current collector according to claim 7, characterized in that, The concentration of chlorinated polypropylene is 5‰-10‰, the soaking time is 30s-300s, and the drying temperature in the oven is 80-120℃.

Images