Electrolyte for electrolytic copper foil, electrolytic copper foil and method of production thereof

Abstract

The application discloses an electrolyte for electrolytic copper foil, an electrolytic copper foil and a preparation method thereof. The electrolyte for electrolytic copper foil comprises a basic electrolyte and a composite additive. The basic electrolyte comprises copper sulfate, sulfuric acid and chloride ions. The composite additive is composed of an N-alkyl-substituted pyrrolidone derivative, polydiallyldimethylammonium chloride and a compound of sodium 3-hydroxypropane sulfonate and thiodiglycolic acid. The application adopts the optimized electrolyte, cooperates with a limited parameter electrodeposition process and a segmented annealing process, and prepares an ultrathin electrolytic copper foil, solves the problems that the traditional copper foil is difficult to have high strength and high elongation performance, has large residual internal stress and is easy to warp, and can meet the use requirements of high-energy-density power batteries, silicon-based negative electrode batteries and energy storage battery current collectors.

Description

Technical Field

[0001] This invention relates to the field of electrolytic copper foil technology, specifically to an electrolyte for electrolytic copper foil, the electrolytic copper foil itself, and a preparation method thereof. Background Technology

[0002] Electrolytic copper foil, as a core material for the negative electrode current collector in lithium-ion batteries, directly affects the battery's conductivity, electrode processing performance, and long-term stability. Technological iterations focus on achieving thicknesses below 6 μm while simultaneously improving tensile strength and elongation. Current technologies generally employ traditional additive systems such as gelatin and sodium polydisulfide dipropane sulfonate to regulate the electrodeposition process and prepare electrolytic copper foil. These additives primarily enhance the tensile strength of the copper foil by increasing cathode polarization and accelerating grain nucleation rates to achieve grain refinement. However, this approach has inherent drawbacks: the grain refinement process easily leads to the continuous accumulation of lattice distortion, resulting in a significant increase in residual internal stress within the copper foil. When the copper foil thickness drops below 4.5 μm, residual internal stress directly causes warping and reduced flatness of the copper foil surface; simultaneously, lattice distortion significantly reduces the copper foil elongation, leading to defects such as strip breakage and wrinkling during electrode coating, die-cutting, and high-speed winding processes, severely hindering the industrial application of ultra-thin copper foil. Meanwhile, high-end electrolytic copper foil for batteries requires a high (200) crystal plane preferred texture, which can further improve the mechanical strength and bending resistance of the copper foil. Existing conventional additive systems are difficult to induce copper grains to preferentially grow towards the (200) crystal plane, resulting in disordered crystal plane orientation and low texture of the finished copper foil, which cannot meet the requirements of high energy density power batteries.

[0003] In existing improvement technologies, some studies have attempted to use single leveling agents, grain refiners, novel additives (such as ethylene thiourea), rare earth ion doping, or grain twinning structure control to try to achieve synergistic optimization of low internal stress and high strength performance of electrolytic copper foil. However, single-function additives can only achieve single performance improvement and cannot simultaneously achieve high texture, high tensile strength, high elongation, and low residual internal stress. When different additives are simply compounded in binary form, the components cannot form a synergistic effect, and there are still problems of imbalance between strength and elongation and incomplete release of internal stress. Therefore, it is urgent to develop a composite electrolyte system that can synergistically control grain orientation and release internal stress, so as to prepare ultrathin electrolytic copper foil with high (200) crystal plane texture, low internal stress, and excellent strength and toughness for use in high energy density power batteries and silicon-based anode batteries. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems and provide an electrolyte for electrolytic copper foil, as well as the electrolytic copper foil and its preparation method, which can significantly improve the overall matching between the crystal texture and mechanical properties of electrolytic copper foil.

[0005] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0006] The first aspect of the present invention provides an electrolyte for electrolytic copper foil, the electrolyte comprising a base electrolyte and a composite additive; the concentration of the composite additive in the electrolyte of the electrolytic copper foil is 35-75 mg / L;

[0007] The basic electrolyte contains copper sulfate, sulfuric acid, and chloride ions;

[0008] The composite additive is composed of N-alkyl-substituted pyrrolidone derivatives, polydiallyl dimethyl ammonium chloride, and a compound of sodium 3-hydroxypropane sulfonate and thiodiacetic acid; the mass ratio of the N-alkyl-substituted pyrrolidone derivatives, polydiallyl dimethyl ammonium chloride, and the compound of sodium 3-hydroxypropane sulfonate and thiodiacetic acid is (5-12):(10-25):(20-45).

[0009] This invention optimizes the electrolyte formulation by using an N-alkyl-substituted pyrrolidone derivative, polydiallyl dimethyl ammonium chloride, and a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid to form a ternary composite additive. The three components can produce a significant synergistic effect within a specific ratio range. At the same time, the fixed ratio of sodium 3-hydroxypropanesulfonate and thiodiacetic acid is a necessary condition for achieving the low internal stress performance of copper foil.

[0010] Furthermore, in the electrolyte of the electrolytic copper foil, the concentration of copper sulfate is 72-86 g / L, the concentration of sulfuric acid (H2SO4) is 93-107 g / L, and the concentration of chloride ions (Cl) is [not specified]. - The concentration of ) is 12-18 mg / L.

[0011] Furthermore, the copper sulfate is preferably copper sulfate pentahydrate (CuSO4·5H2O); the chloride ions are added in the form of hydrochloric acid.

[0012] Furthermore, the N-alkyl-substituted pyrrolidone derivative is N-methylpyrrolidone or N-ethylpyrrolidone.

[0013] Preferably, the concentration of the composite additive in the electrolyte of the electrolytic copper foil is 40-60 mg / L.

[0014] Furthermore, in the compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid, the mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid is (1.5-2.5):1, preferably 2:1.

[0015] A second aspect of the present invention provides a method for preparing electrolytic copper foil based on the electrolyte of the electrolytic copper foil described in the first aspect, comprising the following steps:

[0016] (1) Dissolve copper sulfate, sulfuric acid, hydrochloric acid and composite additives in water to obtain the electrolyte for electrolytic copper foil;

[0017] (2) Electrodeposition is performed using the electrolyte of the electrolytic copper foil to obtain the original copper foil, and the original copper foil is post-processed to obtain the electrolytic copper foil.

[0018] Furthermore, in step (2), the electrodeposition uses a pretreated titanium plate as the cathode and a high-purity titanium plate as the anode.

[0019] Furthermore, in step (2), the electrodeposition temperature is 45-50 °C, and the cathode current density is 50-60 A / dm³. 2 The electrolyte circulation rate is 1.0-1.4 m / s.

[0020] Further, in step (2), the post-processing includes an annealing process; the annealing process is a segmented annealing, with the first annealing temperature at 180-220 ℃ and the holding time at 1-3 min; the second annealing temperature at 260-300 ℃ and the holding time at 2-4 min.

[0021] Furthermore, the annealing process includes steps of washing with water, passivation, and drying.

[0022] In a specific embodiment, the method for preparing electrolytic copper foil based on the electrolyte of electrolytic copper foil includes the following steps:

[0023] (1) Dissolve copper sulfate, sulfuric acid, hydrochloric acid and composite additives in deionized water at a preset concentration, stir evenly, and obtain the electrolyte for electrolytic copper foil;

[0024] (2) The pretreated titanium plate is used as the cathode, and the high-purity titanium plate is used as the anode. The electrolyte of the electrolytic copper foil is used at a temperature of 45-50 ℃ and a cathode current density of 50-60 A / dm. 2 Electrodeposition is performed under an electrolyte circulation flow rate of 1.0-1.4 m / s to obtain a copper foil substrate; the copper foil substrate is then subjected to water washing, passivation, drying, and annealing treatments to obtain the electrolytic copper foil.

[0025] This invention utilizes an optimized electrolyte, combined with a controlled electrodeposition process and a segmented annealing process, to produce ultrathin electrolytic copper foil (4.0-6.0 μm thick). This electrolytic copper foil exhibits a (200) crystal plane texture ≥85%, tensile strength ≥450 MPa, and elongation at break ≥12%. This invention solves the problems of traditional copper foils, such as difficulty in achieving both high strength and high elongation, large residual internal stress, and easy warping of the plate surface. It can meet the application requirements of high-energy-density power batteries, silicon-based anode batteries, and energy storage battery current collectors.

[0026] The third aspect of the present invention provides an electrolytic copper foil prepared by the method described in the second aspect.

[0027] Furthermore, the thickness of the electrolytic copper foil is 4.0-6.0 μm.

[0028] The above-described technical solution of the present invention has the following beneficial effects:

[0029] 1. This invention effectively inhibits abnormal copper grain growth and achieves high-crystalline texture control of copper foil through the synergistic effect of N-alkyl-substituted pyrrolidone derivatives and polydiallyl dimethylammonium chloride. This induces copper crystals to form a preferred orientation structure dominated by the (200) crystal plane, significantly improving the tensile strength of electrolytic copper foil. This invention limits the two components to a specific mass ratio range and combines them with a fixed ratio of sodium 3-hydroxypropanesulfonate and thiodiacetic acid. The combined use of these three components produces a synergistic effect.

[0030] 2. This invention introduces a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid as a stress-relieving agent, which can be adsorbed at the crystal growth interface, weakening lattice distortion and effectively reducing the residual stress inside the electrolytic copper foil, thus solving the problem of easy warping of ultra-thin electrolytic copper foil.

[0031] 3. While ensuring the high tensile strength of electrolytic copper foil, this invention significantly improves the elongation at break of electrolytic copper foil, achieving simultaneous optimization of strength and elongation performance, and can be fully adapted to high-end processing procedures such as electrode die-cutting and winding. Detailed Implementation

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0033] The present invention will be further described below with reference to specific embodiments, so that those skilled in the art can better understand and implement the present invention, but the embodiments are not intended to limit the present invention.

[0034] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0035] The pretreatment method of the cathode titanium plate in the following examples and comparative examples is as follows: wet polishing is carried out step by step with 400# and 800# sandpaper to remove the surface oxide layer, and then it is cleaned with pure water; the purity of the high-purity titanium plate is ≥99.5%.

[0036] In the following examples and comparative examples, the copper foil was washed with pure water; passivation was performed by electroplating with a mixed solution of chromic anhydride (1 g / L) and glucose (3 g / L) to prevent oxidation; and the copper foil was air-dried at 50°C.

[0037] Example 1

[0038] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil includes the following steps:

[0039] (1) Dissolve CuSO4·5H2O, H2SO4, hydrochloric acid, and composite additives in deionized water and stir until homogeneous to obtain the electrolyte for electrolytic copper foil. The concentration of CuSO4·5H2O is 75 g / L, the concentration of H2SO4 is 95 g / L, and the concentration of Cl... - The concentration of the additive is 15 mg / L, and the concentration of the compound additive is 40 mg / L. The compound additive is composed of N-methylpyrrolidone, polydiallyl dimethylammonium chloride, and a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid, with a mass ratio of 8:15:20 and a mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid of 2:1.

[0040] (2) The pretreated titanium plate was used as the cathode and the high-purity titanium plate was used as the anode. The electrolyte for electrolytic copper foil was used at a temperature of 48 ℃ and a cathode current density of 55 A / dm. 2 Electrodeposition was performed under an electrolyte circulation flow rate of 1.2 m / s to obtain a copper foil substrate. The copper foil substrate was then subjected to water washing, passivation, drying, and segmented annealing treatment (180 ℃ / 2 min + 260 ℃ / 3 min) to obtain an electrolytic copper foil.

[0041] Example 2

[0042] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil includes the following steps:

[0043] (1) Dissolve CuSO4·5H2O, H2SO4, hydrochloric acid and composite additives in deionized water, stir evenly to obtain the electrolyte for electrolytic copper foil, wherein the concentration of CuSO4·5H2O is 80 g / L, the concentration of H2SO4 is 100 g / L, and the concentration of Cl is... - The concentration of the additive is 13 mg / L, and the concentration of the compound additive is 60 mg / L. The compound additive is composed of N-ethylpyrrolidone, polydiallyl dimethyl ammonium chloride, and a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid, with a mass ratio of 10:20:35 and a mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid of 2:1.

[0044] (2) The pretreated titanium plate was used as the cathode and the high-purity titanium plate was used as the anode. The electrolyte for electrolytic copper foil was used at a temperature of 50 °C and a cathode current density of 50 A / dm. 2 Electrodeposition was performed under an electrolyte circulation flow rate of 1.4 m / s to obtain a copper foil substrate. The copper foil substrate was then subjected to water washing, passivation, drying, and segmented annealing treatment (200 ℃ / 1 min + 280 ℃ / 2 min) to obtain an electrolytic copper foil.

[0045] Example 3

[0046] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil includes the following steps:

[0047] (1) Dissolve CuSO4·5H2O, H2SO4, hydrochloric acid and composite additives in deionized water and stir evenly to obtain the electrolyte for electrolytic copper foil, wherein the concentration of CuSO4·5H2O is 72 g / L, the concentration of H2SO4 is 105 g / L, and the concentration of Cl is 105 g / L. - The concentration of the additive is 18 mg / L, and the concentration of the compound additive is 55 mg / L. The compound additive is composed of N-ethylpyrrolidone, polydiallyl dimethyl ammonium chloride, and a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid, with a mass ratio of 6:12:40 and a mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid of 2:1.

[0048] (2) The pretreated titanium plate was used as the cathode and the high-purity titanium plate was used as the anode. The electrolyte for electrolytic copper foil was used at a temperature of 45 ℃ and a cathode current density of 60 A / dm. 2 Electrodeposition was performed under an electrolyte circulation flow rate of 1.0 m / s to obtain a copper foil substrate. The copper foil substrate was then subjected to water washing, passivation, drying, and segmented annealing treatment (220 ℃ / 3 min + 300 ℃ / 4 min) to obtain an electrolytic copper foil.

[0049] Comparative Example 1 (without compound additives)

[0050] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil is basically the same as in Example 1, except that in step (1), CuSO4·5H2O, H2SO4 and hydrochloric acid are dissolved in deionized water and stirred evenly to obtain an electrolyte for electrolytic copper foil, wherein the concentration of CuSO4·5H2O is 75 g / L, the concentration of H2SO4 is 95 g / L, and the concentration of Cl is 95 g / L. - The concentration was 15 mg / L.

[0051] Comparative Example 2 (additive only: N-methylpyrrolidone)

[0052] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil is basically the same as in Example 1, except that in step (1), CuSO4·5H2O, H2SO4, hydrochloric acid and the additive N-methylpyrrolidone are dissolved in deionized water and stirred evenly to obtain the electrolyte for electrolytic copper foil, wherein the concentration of CuSO4·5H2O is 75 g / L, the concentration of H2SO4 is 95 g / L, and the concentration of Cl... - The concentration of is 15 mg / L, and the concentration of N-methylpyrrolidone is 40 mg / L.

[0053] Comparative Example 3 (additive only: polydiallyldimethylammonium chloride)

[0054] A method for preparing electrolytic copper foil based on an electrolyte is basically the same as in Example 1, except that in step (1), CuSO4·5H2O, H2SO4, hydrochloric acid, and the additive polydiallyldimethylammonium chloride are dissolved in deionized water and stirred evenly to obtain the electrolyte for electrolytic copper foil. The concentration of CuSO4·5H2O is 75 g / L, the concentration of H2SO4 is 95 g / L, and the concentration of Cl... - The concentration of [unspecified substance] is 15 mg / L, and the concentration of polydiallyldimethylammonium chloride is 40 mg / L.

[0055] Comparative Example 4 (additives were N-methylpyrrolidone and polydiallyldimethylammonium chloride)

[0056] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil is basically the same as in Example 1, except that in step (1), CuSO4·5H2O, H2SO4, hydrochloric acid and additives are dissolved in deionized water and stirred evenly to obtain an electrolyte for electrolytic copper foil, wherein the concentration of CuSO4·5H2O is 75 g / L, the concentration of H2SO4 is 95 g / L, and the concentration of Cl... - The concentration of the active ingredient is 15 mg / L, and the concentration of the additive is 40 mg / L. The additive consists of N-methylpyrrolidone and polydiallyl dimethylammonium chloride in a mass ratio of 8:15.

[0057] Comparative Example 5 (The additive is a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid)

[0058] A method for preparing electrolytic copper foil based on an electrolyte for electrolytic copper foil is basically the same as in Example 1, except that in step (1), CuSO4·5H2O, H2SO4, hydrochloric acid and additives are dissolved in deionized water and stirred evenly to obtain an electrolyte for electrolytic copper foil, wherein the concentration of CuSO4·5H2O is 75 g / L, the concentration of H2SO4 is 95 g / L, and the concentration of Cl... -The concentration of the active ingredient is 15 mg / L, and the concentration of the additive is 40 mg / L. The additive is a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid, with a mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid of 2:1.

[0059] Comparative Example 6

[0060] A method for preparing electrolytic copper foil based on electrolyte is basically the same as that in Example 1, except that in step (1), the mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid is 1:1.

[0061] Comparative Example 7

[0062] A method for preparing electrolytic copper foil based on electrolyte is basically the same as that in Example 1, except that in step (1), the mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid is 3:1.

[0063] Comparative Example 8

[0064] A method for preparing electrolytic copper foil based on an electrolyte of electrolytic copper foil is basically the same as that in Example 1, except that: in step (1), the composite additive is composed of N-methylpyrrolidone, polydiallyl dimethylammonium chloride, and a compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid, with a mass ratio of 3:28:48 and a mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid of 2:1.

[0065] Test Example 1

[0066] The electrolytic copper foils prepared in Examples 1-3 and Comparative Examples 1-8 were tested for thickness, crystal texture, tensile strength, elongation at break, and internal stress. The test methods are as follows:

[0067] (1) Electrolytic copper foil thickness: The mechanical thickness was measured using a micrometer, and the test was conducted according to the IPC-4562A standard;

[0068] (2) Crystal plane texture: The texture of the (200) crystal plane was obtained by X-ray diffraction and calculation.

[0069] (3) Tensile strength and elongation at break: The tensile strength and elongation at break were tested using a universal testing machine in accordance with industry standards SJ / T11483-2014 5.6 and SJ / T11483-2014 5.7.

[0070] (4) Internal stress: using 100 cm 2 The sample is cut off by a disc sampler, and the warping height of the sample edge is measured with a steel ruler. The warping height is used to evaluate the stress release effect of the electrolytic copper foil. When the warping height is ≤5 mm, it is determined that the residual stress inside the electrolytic copper foil has been basically released.

[0071] The test results are shown in Table 1:

[0072] Table 1 Performance test results of various electrolytic copper foils

[0073]

[0074] As can be seen from the test results in Table 1, the electrolytic copper foils prepared in Examples 1-3 of this invention have high levels of (200) crystal texture, tensile strength and elongation at break, low residual internal stress, flat surface without warping, and excellent overall performance.

[0075] While N-alkyl-substituted pyrrolidone derivatives and polydiallyl dimethylammonium chloride are commonly used additives in the field, their use alone or in binary blends cannot simultaneously achieve the requirements of high crystal texture, high elongation, and low internal stress. This may lead to a significant decrease in elongation or high internal stress, making it difficult to meet practical application needs. Although similar sulfonates and thioorganic acids are used in the prior art for copper electrolyte modification, neither of these substances, used alone or with adjusted blending ratios, can achieve the stress control effect of this invention. Only when they are blended at a mass ratio of (1.5-2.5):1 can they stably exert a synergistic stress-relieving effect.

[0076] In addition, the components of the composite additive must be strictly controlled within the mass ratio range specified in this invention. Once the component dosage deviates from the specified range, the synergistic effect of the ternary composite system will fail, and key indicators such as the crystal texture, tensile strength, and elongation at break of the copper foil will all show a significant decline.

[0077] In summary, this invention breaks through the technical bottleneck of traditional electrolytic copper foil, which cannot simultaneously achieve high strength, high elongation, and low internal stress. The resulting electrolytic copper foil has excellent comprehensive performance and can be widely used in the current collector field of high energy density power batteries, energy storage batteries, and other products.

[0078] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An electrolyte for electrolytic copper foil, characterized in that, It includes a basic electrolyte and composite additives; the concentration of the composite additives in the electrolyte of the electrolytic copper foil is 35-75 mg / L; The basic electrolyte contains copper sulfate, sulfuric acid, and chloride ions; The composite additive is composed of N-alkyl-substituted pyrrolidone derivatives, polydiallyl dimethyl ammonium chloride, and a compound of sodium 3-hydroxypropane sulfonate and thiodiacetic acid; the mass ratio of the N-alkyl-substituted pyrrolidone derivatives, polydiallyl dimethyl ammonium chloride, and the compound of sodium 3-hydroxypropane sulfonate and thiodiacetic acid is (5-12):(10-25):(20-45).

2. The electrolyte for electrolytic copper foil according to claim 1, characterized in that, The electrolyte in the electrolytic copper foil contains copper sulfate at a concentration of 72-86 g / L, sulfuric acid at a concentration of 93-107 g / L, and chloride ions at a concentration of 12-18 mg / L.

3. The electrolyte for electrolytic copper foil according to claim 1, characterized in that, The N-alkyl-substituted pyrrolidone derivative is N-methylpyrrolidone or N-ethylpyrrolidone.

4. The electrolyte for electrolytic copper foil according to claim 1, characterized in that, The mass ratio of sodium 3-hydroxypropanesulfonate to thiodiacetic acid in the compound of sodium 3-hydroxypropanesulfonate and thiodiacetic acid is (1.5-2.5):

1.

5. A method for preparing electrolytic copper foil based on the electrolyte of any one of claims 1-4, characterized in that, Includes the following steps: (1) Dissolve copper sulfate, sulfuric acid, hydrochloric acid and composite additives in water to obtain the electrolyte for electrolytic copper foil; (2) Electrodeposition is performed using the electrolyte of the electrolytic copper foil to obtain the original copper foil, and the original copper foil is post-processed to obtain the electrolytic copper foil.

6. The method according to claim 5, characterized in that, In step (2), the electrodeposition temperature is 45-50℃, and the cathode current density is 50-60 A / dm³. 2 The electrolyte circulation rate is 1.0-1.4 m / s.

7. The method according to claim 5, characterized in that, In step (2), the post-processing includes an annealing process; the annealing process is a segmented annealing process, with the first annealing temperature at 180-220 ℃ and the holding time at 1-3 min; the second annealing temperature at 260-300 ℃ and the holding time at 2-4 min.

8. The method according to claim 7, characterized in that, The annealing process also includes steps of washing, passivation, and drying.

9. An electrolytic copper foil prepared by the method according to any one of claims 5-8.

10. The electrolytic copper foil according to claim 9, characterized in that, The thickness of the electrolytic copper foil is 4.0-6.0 μm.

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