High-strength and high-compactness composite copper foil and preparation method thereof

Abstract

The invention discloses a high-strength and high-compactness composite copper foil and a preparation method thereof. A maleic anhydride modified adhesion layer is constructed on a high-molecular polymer base membrane to enhance interface bonding force; a compact seed layer is formed by high vacuum coating, and a protective layer is formed by high vacuum coating or chemical nickel plating to prevent acid etching; and finally, a copper-tin-phosphorus alloy thickening layer is deposited in a plating solution containing tin and phosphorus elements by adopting a pulse electroplating technology, and the strength of the plating layer is greatly improved by utilizing an alloying effect. Through triple technical paths of interface strengthening, structure densification and material alloying, the problems that the interface bonding force of the composite current collector is weak, the compactness of a plating layer is poor, the strength is low and the composite current collector is prone to acid etching are cooperatively solved, and the prepared composite copper foil has ultrahigh strength and high compactness; and the lithium battery is particularly suitable for a new generation of high-performance lithium batteries with extremely high requirements on safety and reliability.

Description

Technical Field

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

[0002] Composite copper foil, employing a "metal-polymer-metal" sandwich structure, is currently the optimal material to replace existing copper foil, exhibiting superior performance in improving energy density and safety. However, existing technologies face three core challenges: 1) weak adhesion between the polymer base film (PET, PP, PI, PE, etc.) and the metal coating, leading to easy peeling; 2) copper layers obtained through traditional chemical plating and water plating have coarse grains and numerous pores, resulting in poor coating density, uneven conductivity, and insufficient strength, while also posing a risk of breakage during rolling and cycling; 3) acidic electroplating solutions easily erode the interface between the initial coating and the base film, causing a "film dissolution" phenomenon and resulting in a loose structure. Currently, there is no mature solution that can systematically solve all of these problems. Therefore, developing a composite current collector that combines ultra-strong interface, extreme density, ultra-high strength, and excellent process stability has become an urgent industry need. Summary of the Invention

[0003] This invention provides a high-strength, high-density composite copper foil and its preparation method, which systematically solves the problems of weak interfacial bonding, poor coating density, insufficient mechanical strength, and susceptibility to acid etching in existing products.

[0004] To achieve the above objectives, the present invention provides the following technical solution: A first aspect of the present invention provides a high-strength, high-density composite copper foil, comprising a base film, a first adhesion layer, a first seed layer, a first protective layer, a first thickening layer, and a first anti-oxidation layer sequentially disposed on a first surface of the base film; and a second adhesion layer, a second seed layer, a second protective layer, a second thickening layer, and a second anti-oxidation layer sequentially disposed on a second surface of the base film.

[0005] The base film is made of PET, PP, PI or PE, with a thickness of 2µm to 6µm.

[0006] The first and second adhesion layers contain one or more surface modifiers, which are polyolefin derivatives with reactive functional groups.

[0007] The reactive functional group is selected from a combination of acid anhydrides, carboxylic acids, hydroxyl groups, epoxy groups, amino groups, isocyanate groups, or alkoxysilyl groups.

[0008] Preferably, the adhesion layer is selected from maleic anhydride-grafted polyolefin or a mixture of maleic anhydride-grafted polyolefin and silane coupling agent to obtain excellent organic and inorganic adhesive properties at the same time.

[0009] Specifically, organic functional group monomers / polymers form chemical bonds or strong interactions with the substrate layer or subsequent composite / coating materials by increasing the activity of functional groups. Non-reactive but highly polar / high surface energy polymers improve wettability and adhesion by physically increasing surface energy. Due to the poor surface polarity of the base film, the bonding force between it and the seed layer is weak. This invention provides an adhesion layer between the base film and the seed layer to improve the bonding strength at the interface between them, thereby reducing the risk of separation between the composite copper foil metal layer and the base film layer and extending its service life.

[0010] The first and second adhesion layers are formed by coating.

[0011] Preferably, the thickness of the first and second adhesion layers is 10 nm to 80 nm.

[0012] The first and second seed layers are made of copper.

[0013] The first seed layer and the second seed layer are formed by high vacuum coating.

[0014] Preferably, the thickness of the first seed layer and the second seed layer is 20nm~100nm.

[0015] The first and second protective layers are made of nickel, nickel-based alloys, palladium, or tin.

[0016] Specifically, nickel and nickel alloys have excellent acid resistance and good electrical conductivity. When attached to the seed layer as a protective layer, they can effectively prevent the seed layer from corroding rapidly after entering the water plating solution, thus affecting the density of the final product.

[0017] The first and second protective layers are formed by high vacuum coating or chemical plating.

[0018] Preferably, the thickness of the first protective layer and the second protective layer is 5nm~50nm.

[0019] The first thickened layer and the second thickened layer are formed by pulse electroplating.

[0020] The first thickened layer and the second thickened layer are copper, copper-tin, or copper-tin-phosphorus alloys.

[0021] Preferably, the first thickened layer and the second thickened layer are 700nm~2800nm.

[0022] The first and second antioxidant layers are formed by electroplating.

[0023] The first antioxidant layer and the second antioxidant layer are one or more metal alloys selected from nickel, zinc, titanium, or chromium. Preferably, the thickness of the first antioxidant layer and the second antioxidant layer is 10nm~50nm.

[0024] A second aspect of the present invention provides a method for preparing the high-strength, high-density composite copper foil described in the first aspect of the present invention.

[0025] Specifically, the method for preparing the high-strength, high-density composite copper foil includes the following steps: S1. A first adhesion layer and a second adhesion layer are formed on the first and second surfaces of the base film by coating. S2. A first seed layer and a second seed layer are formed on the surfaces of the first and second adhesion layers by high vacuum coating. S3. A first protective layer and a second protective layer are formed on the surfaces of the first seed layer and the second seed layer by high vacuum coating or chemical plating. S4. A first thickened layer and a second thickened layer are formed on the surfaces of the first protective layer and the second protective layer by pulse electroplating. S5. A first anti-oxidation layer and a second anti-oxidation layer are formed on the surfaces of the first thickened layer and the second thickened layer by electroplating.

[0026] The high-strength, high-density composite copper foil prepared on both sides of the base film using the above method effectively enhances the bonding force between the metal layer and the base film through the first and second adhesion layers. The first and second protective layers themselves have better corrosion resistance, making the "protective layer-seed layer" a whole, making the seed layer less susceptible to corrosion and effectively protecting its density, thus ensuring the density of the final product. The thickened layer is made by electroplating, which allows the metal to nucleate instantly, giving the thickened layer the advantages of small grains and low porosity. In addition, the addition of tin and phosphorus elements forms a copper-based alloy with copper, which has a good crystallization strengthening effect, thereby effectively improving the tensile strength of the final product.

[0027] Preferably, in S1, the coating method involves coating an adhesion layer on both sides of the base film: the coating speed is controlled at 3-20 m / min, the baking temperature is 60-80℃, and the baking time is 30-60 s.

[0028] Preferably, S2 specifically involves magnetron sputtering to deposit a seed layer on the surface of the adhesion layer: coating vacuum degree ≤ 8.5*E ~ -4pa, coating speed 3 ~ 20m / min, unwinding tension 50 ~ 200N, winding tension 60 ~ 220N, and argon gas 80 ~ 200sccm.

[0029] Preferably, S3 specifically involves chemically depositing a protective layer on the surface of the seed layer: bath temperature 40℃~45℃, bath pH value 4.3~4.7, mechanical stirring speed 300~400r / min, nitrogen flow rate 0.5-1.0m³ / h, and chemical plating speed 3~12m / min.

[0030] Preferably, S3 specifically involves magnetron sputtering to deposit a protective layer on the surface of the seed layer: coating vacuum degree ≤ 8.5*E ~ -4pa, coating speed 3 ~ 20m / min, unwinding tension 50 ~ 200N, winding tension 60 ~ 220N, and argon gas 80 ~ 200sccm.

[0031] Preferably, in S4, pulse electroplating deposits a thickened layer on the surface of the protective layer: electroplating speed 3~12m / min, unwinding tension 40~150N, winding tension 60~180N, peak current density 3-8A / dm², pulse frequency 50-500Hz, and duty cycle 20%-50%.

[0032] Preferably, in S5, an anti-oxidation layer is deposited on the surface of the thickened layer by electroplating: electroplating speed 3~12m / min, unwinding tension 40~150N, winding tension 60~180N, and current 1.5~4A.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention addresses the problems of weak interfacial bonding, poor coating density, low strength, and susceptibility to acid corrosion in composite current collectors through a three-pronged approach of interface strengthening, structural densification, and material alloying. The resulting composite copper foil exhibits ultra-high strength and high density, making it particularly suitable for next-generation high-performance lithium batteries with extremely high safety and reliability requirements.

[0034] 1. Super strong interface bonding: The adhesion layer greatly enhances the adhesion between the polymer base film and the metal layer through chemical bonding.

[0035] 2. Extremely dense structure: "Magnetron sputtering" ensures that the initial seed layer is pore-free and dense; "pulse electroplating" obtains a thickened layer with fine grains and low porosity through instantaneous nucleation and diffusion control.

[0036] 3. Excellent mechanical properties: The co-deposition of tin and phosphorus elements forms a copper-based alloy layer, which produces significant solid solution strengthening and grain refinement strengthening effects, thus doubling the tensile strength of the composite copper foil.

[0037] 4. Excellent process protection: The chemical nickel plating protective layer effectively blocks the subsequent acidic plating solution from corroding the underlying layer and base film, completely eliminating the risk of "film dissolution" and ensuring production yield and product reliability. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of a high-strength, high-density composite copper foil provided by the present invention.

[0040] Figure 2 This is a schematic diagram of a high-strength, high-density composite copper foil process provided by the present invention.

[0041] Figure 3 This is the AOI visual observation diagram of Example 1.

[0042] Figure 4 This is the AOI visual observation diagram of Example 2.

[0043] Figure 5 This is a visual observation diagram of AOI (Optical Area Intersection) as shown in Comparative Example 1. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] like Figure 1 The present invention provides a high-strength and high-density composite copper foil, comprising a base film 1, a first adhesion layer 2, a first seed layer 3, a first protective layer 4, a first thickening layer 5, and a first anti-oxidation layer 6 sequentially disposed on the first surface of the base film; and a second adhesion layer 7, a second seed layer 8, a second protective layer 9, a second thickening layer 10, and a second anti-oxidation layer 11 sequentially disposed on the second surface of the base film. Example

[0046] like Figure 2 A method for preparing composite copper foil includes the following steps: S1. Coating is performed on both sides of a 4.5µm thick PP base film. The coating solution is maleic anhydride-grafted polypropylene solution. The coating speed is controlled at 8m / min, the baking temperature is 80℃, the baking time is 40s, and the thickness of the adhesion layer is 30nm.

[0047] S2. A seed layer is deposited on the adhesion layer prepared in S1 by magnetron sputtering. Process parameters: coating vacuum degree ≤8.5*E~-4pa, coating speed 10m / min, unwinding tension 80N, winding tension 100N, argon gas 100sccm, seed layer thickness 50nm.

[0048] S3. A protective layer is deposited on the seed layer prepared in S2 by magnetron sputtering, with the same process parameters as in S2, and the thickness of the protective layer is 10 nm.

[0049] S4. A thickened layer is prepared on the protective layer prepared in S3 by pulse electroplating in a conventional acidic copper sulfate solution that does not contain tin or phosphorus. The process parameters are: electroplating speed 7m / min, unwinding tension 60N, winding tension 80N, peak current density 5A / dm², pulse frequency 100Hz, duty cycle 30%, and thickened layer thickness 800nm.

[0050] S5. An anti-oxidation layer is deposited on the thickened layer prepared in S4 by electroplating. Process parameters: electroplating speed 7m / min, unwinding tension 60N, winding tension 80N, current 2.5A, and anti-oxidation layer thickness 10nm. Example

[0051] S1, S2, S3, S5 use the same processes and parameters as in Example 1.

[0052] S4. A thickened layer is prepared on the protective layer prepared in S3 by pulse electroplating in an acidic copper sulfate plating solution containing 1.5 g / L stannous sulfate and 0.8 g / L sodium hypophosphite. The process parameters are: electroplating speed 7 m / min, unwinding tension 60 N, winding tension 80 N, peak current density 4 A / dm², pulse frequency 200 Hz, duty cycle 35%, and thickened layer thickness 800 nm. Example

[0054] S1, S2, S5 use the same processes and parameters as in Example 1.

[0055] The same process and parameters as in Example 2 and Example 4.

[0056] S3. A protective layer is deposited on the seed layer prepared in S2 by chemical plating. The process parameters are: bath temperature 42℃~43℃, bath pH value 4.5, mechanical stirring speed 350r / min, nitrogen flow rate 0.8m³ / h, plating speed 8m / min, and protective layer thickness 10nm.

[0057] Comparative Example 1: A 50nm seed layer was prepared on both sides of a 4.5µm thick PP base film by magnetron sputtering. Then, a thickened layer and an antioxidant layer were prepared on both sides of the seed layer by electroplating (DC power supply). The thickness of the thickened layer was 800nm ​​and the thickness of the antioxidant layer was 10nm.

[0058] Detection and analysis: The composite copper foils prepared in Examples 1, 2, and 3, and the composite copper foil prepared in Comparative Example 1, were subjected to appearance inspection and performance testing, respectively.

[0059] 1. AOI observation: The specific operation is as follows: Observe the pinhole condition of the sample in the AOI operation interface. The results are as follows. Figure 3-5 .

[0060] The observation results of pinholes in the examples and comparative examples show that the composite copper foil exhibits better density when a protective layer is present. This is because the seed layer is subject to backflow from the plating bath in the initial stage of entering the water plating solution, which in turn affects the density of the product. The protective layer effectively protects the seed layer from backflow during water plating, increases the density of the seed layer within the effective area, provides more deposited grains for the thickened layer, and improves the density of the product.

[0061] 2. Sheet resistance test: The specific operation is as follows: A four-probe resistivity meter (model: HPS2661) was used to perform sheet resistance testing according to the test methods in GB / T22638.6 standard. The specific test results are shown in Table 1 below: Table 1: Sheet resistance test results (unit: mΩ / □) The sheet resistance test results from the examples and comparative examples show that the composite copper foil exhibits lower sheet resistance and better conductivity when a protective layer is included. This is because the protective layer effectively protects the seed layer from backlash in the plating bath, improving the density of the product. When preparing metal layers of the same thickness, the denser the crystals, the greater the number of crystals within the same volume, resulting in lower sheet electron count and superior conductivity.

[0062] 3. Tensile strength and elongation test The specific operation was as follows: A Labthink tensile puncture machine (model: C610H) was used to conduct tensile strength and elongation tests according to the test methods in GB / T228.1-2021 standard. The specific test results for tensile strength are shown in Table 2 below. The specific test results for elongation are shown in Table 3 below. Table 2: Tensile strength test results (unit: MPa) Table 3: Elongation Test Results (Unit: %) The tensile strength and elongation test results from the examples and comparative examples show that when the thickened layer is prepared using pulse electroplating, the composite copper foil exhibits high tensile strength. Furthermore, the strength of the product is even higher when tin and phosphorus are added to the plating bath. This is because: 1) the protective layer improves the density of the product; 2) pulse electroplating, through instantaneous nucleation and diffusion control, achieves fine grains and low porosity; 3) the co-deposition of tin and phosphorus forms a copper-based alloy layer, producing significant solid solution strengthening and grain refinement effects, thus doubling the tensile strength of the composite copper foil.

[0063] 4. Peel force test The specific operation was as follows: A Labthink tensile puncture machine (model: C610H) was used to conduct tensile strength and elongation tests according to the test methods in GB / T2792-2014 standard. The specific test results are shown in Table 4 below. Table 4: Peel force test results (unit: MPa) The peel strength test results from the examples and comparative examples show that the adhesion between the metal layer and the polymer film is higher when a protective layer is present. This is because chemical bonding greatly enhances the adhesion between the polymer base film and the metal layer.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-strength, high-density composite copper foil, characterized in that, It includes a base film, and a first adhesion layer, a first seed layer, a first protective layer, a first thickening layer, and a first antioxidant layer sequentially disposed on the first surface of the base film; and a second adhesion layer, a second seed layer, a second protective layer, a second thickening layer, and a second antioxidant layer sequentially disposed on the second surface of the base film.

2. The high-strength, high-density composite copper foil according to claim 1, characterized in that, The base film is made of PET, PP, PI or PE, with a thickness of 2µm to 6µm.

3. The high-strength, high-density composite copper foil according to claim 1, characterized in that, The first and second adhesion layers contain one or more surface modifiers and have a thickness of 10 nm to 80 nm.

4. The high-strength, high-density composite copper foil according to claim 1, characterized in that, The first and second seed layers are made of copper, with a thickness of 20nm~100nm.

5. The high-strength, high-density composite copper foil according to claim 1, characterized in that, The first and second protective layers are made of nickel, nickel-based alloys, palladium or tin, with a thickness of 5nm to 50nm.

6. The high-strength, high-density composite copper foil according to claim 1, characterized in that, The first and second thickened layers are made of copper, copper-tin, or copper-tin-phosphorus alloys, with a thickness of 700 nm to 2800 nm.

7. The high-strength, high-density composite copper foil according to claim 1, characterized in that, The first and second antioxidant layers are made of one or more metal alloys selected from nickel, zinc, titanium, or chromium, with a thickness of 10 nm to 50 nm.

8. A method for preparing a high-strength, high-density composite copper foil as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. A first adhesion layer and a second adhesion layer are formed on the first and second surfaces of the base film by coating; S2. A first seed layer and a second seed layer are formed on the surfaces of the first and second adhesion layers by high vacuum coating. S3. A first protective layer and a second protective layer are formed on the surfaces of the first seed layer and the second seed layer by high vacuum coating or chemical plating. S4. A first thickened layer and a second thickened layer are formed on the surfaces of the first protective layer and the second protective layer by pulse electroplating; S5. A first anti-oxidation layer and a second anti-oxidation layer are formed on the surfaces of the first thickened layer and the second thickened layer by electroplating.

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