Method for producing ultrathin electrolytic copper foil with high tensile strength by using synthetic additive

Abstract

The invention provides a method for producing a high-tensile-strength ultrathin electrolytic copper foil by using a synthetic additive. The method comprises the following steps: providing a copper sulfate electrolyte; a composite additive is added into the copper sulfate electrolyte, the composite additive comprises a synthesized high-tensile additive C, the C is prepared by dissolving benzothiazole, polyethylene glycol methyl ether mercaptan, sodium hydroxide and 1, 3-propane sultone into ethyl alcohol to react, and the addition amount of the C is 10-50 mg / L; the addition amount of the collagen is 5 to 10 mg / L; hydroxyethyl cellulose, the addition amount of which is 40 to 50 mg / L; in the electrolytic bath, the temperature of the electrolyte is controlled to be 48-60 DEG C, the current density of a cathode surface is 3500-5000A / m < 2 >, and electrolytic deposition is carried out, so that copper ions are reduced on the surface of a cathode roller to form a copper foil; and carrying out heat treatment on the obtained copper foil at 60 DEG C for 30 hours to obtain the high-tensile-strength electrolytic copper foil with the thickness of 4.5 microns. According to the invention, the problems of insufficient tensile strength, high surface roughness and low elongation of the ultrathin electrolytic copper foil (less than or equal to 4.5 microns) in the prior art are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of electrolytic copper foil manufacturing, and specifically relates to a method for producing high-tensile-strength ultra-thin electrolytic copper foil by using a synthetic additive, which is particularly suitable for lithium battery negative electrode current collectors. Background Art

[0002] Tensile strength has long been a key physical property of copper foil, the negative electrode current collector for lithium batteries. Lithium battery anode materials primarily include graphite and silicon-based materials. Silicon-carbon anodes have a high theoretical capacity (4200 mAh / g), but their volume expands by 300% during charge and discharge, easily leading to deformation and fracture of the current collector. High-tensile-strength copper foil can mitigate this expansion through mechanical constraints, extending the battery's cycle life. Furthermore, rapid charging and discharging require battery materials to withstand high thermal loads and mechanical stresses. High-tensile-strength copper foil prevents electrode fracture and mitigates short-circuit risks. Commercially available 6µm copper foil products can achieve a tensile strength exceeding 500 MPa after heat treatment. However, with the demand for higher energy density in batteries, the thickness of copper foil is becoming increasingly thinner. Thinner copper foil reduces weight, resulting in higher overall battery energy density. However, maintaining high tensile strength while reducing copper foil thickness is difficult. Reduced thickness means a smaller cross-sectional area. When subjected to tension, the number of atomic bonds within the copper foil that support the force decreases, resulting in a decrease in overall load-bearing capacity.

[0003] In the existing technology, improving the tensile strength of copper foil through additives is a common method of copper foil manufacturing. The tensile strength is mainly improved through mechanisms such as grain refinement, surface flattening, and texture optimization. However, traditional additives are difficult to achieve high tensile strength (≥500MPa), low roughness (Rz<1.5um), and high elongation (≥3%) in ultra-thin copper foil (such as 4.5um). For example, although collagen and hydroxyethyl cellulose can improve the surface morphology, the improvement in tensile strength when used alone is limited; and the control range of process parameters such as chloride ion concentration and electrolyte temperature is relatively narrow, which can easily lead to surface defects or unstable performance of the copper foil. Therefore, a new additive formula and supporting process are urgently needed to solve the problem of balancing high tensile strength and comprehensive performance of ultra-thin copper foil. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a method for producing ultra-thin electrolytic copper foil with high tensile strength using synthetic additives. The present invention aims to solve the problems of insufficient tensile strength, high surface roughness and low elongation of ultra-thin electrolytic copper foil (≤4.5μm) in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is: The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive comprises the following steps: (1) providing a copper sulfate electrolyte, wherein the copper sulfate electrolyte comprises 80-100 g / L copper ions, 90-150 g / L sulfuric acid, and 20-30 ppm ammonia ions; (2) Adding a composite additive to the copper sulfate electrolyte, wherein the composite additive comprises: A high tensile strength additive C is synthesized, wherein the agent C is prepared by reacting benzothiazole, polyethylene glycol methyl ether mercaptan, sodium hydroxide and 1,3-propane sultone in ethanol, and the addition amount is 10-50 mg / L; Collagen, added at 5-10 mg / L; Hydroxyethyl cellulose, added at 40-50 mg / L; (3) In the electrolytic cell, control the electrolyte temperature to 48-60°C and the cathode surface current density to 3500-5000A / m 2 , electrolytic deposition is carried out to reduce copper ions on the surface of the cathode roller to form copper foil; (4) The obtained copper foil was heat-treated at 60°C for 30 hours to obtain a high tensile strength electrolytic copper foil with a thickness of 4.5 μm.

[0006] To further limit the above solution, the preparation method of the synthetic high tensile strength additive C is as follows: 0.97 mL of benzothiazole and 1.09 g of polyethylene glycol methyl ether thiol were dissolved in 20 mL of ethanol solution and stirred; 0.58 g of sodium hydroxide and 2.32 g of 1,3-propane sultone were added, and after sufficient reaction, the mixture was cooled to precipitate crystals, thereby obtaining the agent C.

[0007] To further limit the above solution, the collagen is a polypeptide collagen with a molecular weight of 3000.

[0008] To further limit the above scheme, the copper sulfate electrolyte has a copper ion content of 85 g / L, a sulfuric acid concentration of 100 g / L, and a chloride ion content of 27 ppm.

[0009] To further limit the above solution, the temperature of the electrolyte is 50±2°C; and the cathode current density is 4500A / m².

[0010] Further limitation of the above scheme: the thickness of the high tensile strength electrolytic copper foil prepared by this method is 4.5um, the tensile strength at room temperature after heat treatment is ≥500MPa, the elongation at room temperature after heat treatment is ≥3%, the M surface roughness Rz<1.5um, and the M surface brightness GU>200.

[0011] As a further limitation of the above solution, the high tensile strength electrolytic copper foil is used for the negative electrode current collector of lithium batteries.

[0012] The advantages of the present invention compared with the prior art are: 1. The electrolytic copper foil prepared by this scheme has high tensile strength: due to the grain refinement and leveling effect of the C agent, the tensile strength of the copper foil is ≥500MPa, which is significantly better than the control group without the addition of C agent (≤300MPa); 2. The electrolytic copper foil prepared by this scheme is ultra-thin and low-roughness: when the thickness is 4.5um, the M-surface roughness Rz is less than 1.5um, and the brightness GU is greater than 200, meeting the requirements of high-energy-density batteries for lightweight and interface contact; 3. The electrolytic copper foil prepared by this scheme has high elongation: the elongation after heat treatment is ≥3%, which is better than the traditional formula (≤2.5%) and can buffer the volume expansion of silicon-based negative electrodes; 4. Process stability of this solution: By strictly controlling the electrolyte parameters and additive concentration, performance consistency is achieved and defects such as surface mottling or burning are avoided. DETAILED DESCRIPTION

[0013] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0014] Example: A method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive, comprising the following steps: (1) continuously providing a copper sulfate electrolyte in an electrolytic cell, wherein the copper sulfate electrolyte contains 80-100 g / L copper ions, 90-150 g / L sulfuric acid, and 20-30 ppm ammonia ions; (2) directly adding the composite additive to the copper sulfate electrolyte, mixing it completely in the clean liquid tank, and then providing it to the raw foil electrolytic cell through a fine filter; The composite additives include: Synthetic high-tensile strength additive C: The additive C is prepared by reacting benzothiazole, polyethylene glycol methyl ether mercaptan, sodium hydroxide, and 1,3-propane sultone in ethanol, with an addition amount of 10-50 mg / L. The sulfur atoms and sulfur-nitrogen heterocyclic structures in the additive C can be adsorbed on the electrode surface, refining the grains and enhancing the leveling effect. Collagen: added in an amount of 5-10 mg / L; Hydroxyethyl cellulose: added in an amount of 40-50 mg / L; The above-mentioned composite additives, including Agent C (10-50 mg / L), collagen (5-10 mg / L, molecular weight 3000), and hydroxyethyl cellulose (40-50 mg / L), synergistically regulate copper deposition behavior, achieving both high tensile strength and low roughness of the copper foil through grain refinement, surface flattening, and texture optimization. (3) In the electrolytic cell, direct current is passed through the anode plate and the continuously rotating cathode roller, and the electrolyte temperature is controlled to be 48-60°C and the cathode surface current density is 3500-5000A / m 2 , electrolytic deposition is carried out to make copper ions continuously reduced and deposited on the surface of the cathode roller to form a dense copper foil; (4) The obtained copper foil was heat-treated at 60°C for 30 hours to obtain a high tensile strength electrolytic copper foil with a thickness of 4.5 μm.

[0015] The preparation method of the above-mentioned synthetic high tensile strength additive C is as follows: 0.97 mL of benzothiazole and 1.09 g of polyethylene glycol methyl ether mercaptan were dissolved in 20 mL of ethanol solution and stirred to mix. 0.58 g of sodium hydroxide and 2.32 g of 1,3-propane sultone were added, and the mixture was allowed to fully react before cooling to precipitate crystals, thereby obtaining the Agent C. The synthesized Agent C contains sulfur atoms and sulfur-nitrogen heterocyclic structures, which can be adsorbed on the electrode surface to increase cathode polarization and inhibit copper deposition. It has a leveling effect and easily obtains refined grains, thereby increasing the brightness and strength of the copper foil surface.

[0016] The collagen mentioned above is a polypeptide collagen with a molecular weight of 3000. It has an inhibitory effect in the electrolyte, improving the deposition shape of the peaks and valleys on the M-surface of electrolytic copper foil. Specifically, it promotes copper deposition in the surface "valleys" and inhibits copper deposition in the surface "peaks," resulting in a leveling effect. However, excessive content or molecular weight can increase the surface roughness of the copper foil and reduce its tensile strength and elongation.

[0017] The above-mentioned hydroxyethyl cellulose is a macromolecular polysaccharide composed of glucose, which can improve the wettability of the electroplating solution. Adding HEC can increase the viscosity of the electrolyte and improve the wettability of the plating solution. Appropriate addition can effectively improve the elongation while maintaining high tensile strength, but excessive addition will cause the surface to burn.

[0018] The chloride ion concentration in the copper sulfate electrolyte needs to be controlled within 30 ppm. Chloride ions have the effect of improving the density of the copper plating layer, but too high a concentration will cause cloud-like spots to form on the surface of the copper foil.

[0019] If the temperature of the copper sulfate electrolyte is lower than 48°C, the solution will crystallize, affecting normal production. If the temperature is too high, the cathode roller will oxidize, reducing the service life of the cathode roller.

[0020] When producing electrolytic copper foil, excessively high current density can lead to concentration polarization, resulting in a rough surface. The resulting high rotational speed can also prevent the foil from drying completely. When the current density is too low, the grain growth time is prolonged, resulting in a loose coating structure and increased porosity, which reduces conductivity and mechanical strength.

[0021] The electrolytic copper foil prepared by the above method needs to be heated in an oven at 60°C for 30 hours, because the heat treatment will accelerate the stabilization of the internal structure of the copper foil and alleviate the warping defects that are common in high-strength copper foil.

[0022] This proposal is a simple and stable production method for high-tensile strength ultra-thin electrolytic copper foil. The high-tensile strength electrolytic copper foil prepared by this method has a thickness of 4.5um. If the thickness is too low, it will cause breakage during the production process, which is not conducive to continuous production, thereby resulting in waste of labor and time costs. A high thickness will be very different from the goal of high energy density, so 4.5um thickness is the first choice for ultra-thin copper foil.

[0023] The electrolytic copper foil produced by using the electrolyte containing the composite additive has a room temperature tensile strength of ≥500MPa after heat treatment, a room temperature elongation of ≥3% after heat treatment, an M surface roughness Rz <1.5um, and an M surface brightness GU >200. No appearance defects occur.

[0024] The present invention strictly controls various parameters in the production process, from additive concentration, solution temperature and current density in the foil production process to temperature test of subsequent heat treatment, so as to obtain high-quality electrolytic copper foil with stable physical properties.

[0025] The following is further described by multiple examples and comparative examples: The copper sulfate electrolyte in Examples 1-6 and Comparative Examples 1-6 below has a copper ion content of 85 g / L, a H2SO4 concentration of 100 g / L, and a chloride ion content of 27 ppm. The electrolyte temperature is maintained at 50 ± 2°C, and the cathode surface current density is 4500 A / m 2 To verify the effect of Agent C on the basic physical properties of copper foil, the basic parameters and the amount of collagen and hydroxyethyl cellulose added in the experimental groups of Examples 1-6 and Comparative Examples 1-6 remained unchanged. The addition amount was gradually increased within the recommended range in the Examples, while the Comparative Examples used methods of no addition of Agent C, insufficient addition, and excessive addition for demonstration. The specific addition amounts are shown in Table 1: The copper foil with a thickness of 4.5 μm was prepared using the above method. The tensile strength, elongation, M-surface roughness and brightness after heat treatment were tested. The specific test results are shown in Table 2 below: Experimental data indicates that without Agent C, both tensile strength and elongation decrease, roughness increases, and brightness decreases significantly. When Agent C is insufficient or excessive, the tensile strength after heat treatment does not reach 500 MPa. In the examples, as the amount of Agent C increases, the tensile strength increases and then decreases. Using a tensile strength > 500 MPa after heat treatment as the standard, the optimal addition level of Agent C is 10-50 ppm.

[0026] In summary, the synthesized high tensile strength additive - Agent C can maintain the high tensile strength of the copper foil after heat treatment when producing 4.5um ultra-thin copper foil. Moreover, the elongation after heat treatment is ≥3%, the M surface roughness Rz is less than 1.5um, and the M surface brightness GU is greater than 200, with good and stable quality.

[0027] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0028] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for producing ultra-thin electrolytic copper foil with high tensile strength using synthetic additives, characterized in that: The following steps are involved: (1) providing a copper sulfate electrolyte, wherein the copper sulfate electrolyte comprises 80-100 g / L copper ions, 90-150 g / L sulfuric acid, and 20-30 ppm ammonia ions; (2) Adding a composite additive to the copper sulfate electrolyte, wherein the composite additive comprises: A high tensile strength additive C is synthesized, wherein the agent C is prepared by reacting benzothiazole, polyethylene glycol methyl ether mercaptan, sodium hydroxide and 1,3-propane sultone in ethanol, and the addition amount is 10-50 mg / L; Collagen, added at 5-10 mg / L; Hydroxyethyl cellulose, added at 40-50 mg / L; (3) In the electrolytic cell, control the electrolyte temperature to 48-60°C and the cathode surface current density to 3500-5000A / m 2 , electrolytic deposition is carried out to reduce copper ions on the surface of the cathode roller to form copper foil; (4) The obtained copper foil was heat-treated at 60°C for 30 hours to obtain a high tensile strength electrolytic copper foil with a thickness of 4.5 μm.

2. The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive according to claim 1, characterized in that: The preparation method of the synthetic high tensile strength additive C is as follows: 0.97 mL of benzothiazole and 1.09 g of polyethylene glycol methyl ether thiol were dissolved in 20 mL of ethanol solution and stirred; 0.58 g of sodium hydroxide and 2.32 g of 1,3-propane sultone were added, and after sufficient reaction, the mixture was cooled to precipitate crystals, thereby obtaining the agent C.

3. The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive according to claim 1, characterized in that: The collagen is a polypeptide collagen with a molecular weight of 3000.

4. The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive according to claim 1, characterized in that: The copper sulfate electrolyte has a copper ion content of 85 g / L, a sulfuric acid concentration of 100 g / L, and a chloride ion content of 27 ppm.

5. The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive according to claim 1, characterized in that: The temperature of the electrolyte is 50±2°C; the cathode current density is 4500A / m².

6. The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive according to claim 1, characterized in that: The high-tensile-strength electrolytic copper foil prepared by the method has a thickness of 4.5 μm, a room-temperature tensile strength of ≥500 MPa after heat treatment, a room-temperature elongation of ≥3% after heat treatment, an M-surface roughness Rz <1.5 μm, and an M-surface brightness GU >200.

7. The method for producing high tensile strength ultra-thin electrolytic copper foil using a synthetic additive according to claim 4, characterized in that: The high tensile strength electrolytic copper foil is used for a negative electrode current collector of a lithium battery.

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