Method for preparing functional copper current collector, electroplating solution, functional copper current collector based on electroplating solution, and secondary battery

Abstract

The invention provides a method for preparing a functional copper current collector, the method comprises the operation of thickening a copper elementary substance layer through water electroplating treatment, and an electroplating solution adopted in the water electroplating treatment contains copper sulfate, sulfuric acid and a copper-cyanogen complex; in the electroplating solution, the mass concentration of copper sulfate is 58 g / L-70 g / L, and the mass concentration of copper sulfate to the mass concentration of sulfuric acid is 1: 2.5-4. In the method for preparing the functional copper current collector, the electroplating liquid is adopted on the basis of water electroplating treatment related to the functional copper current collector, so that a copper simple substance formed on the surface of a foil material through the water electroplating treatment can reach a finer grain size, the tensile strength and the elongation of the functional copper current collector are both improved, the resistivity is reduced, and the service life of the functional copper current collector is prolonged. Therefore, the surface smoothness of the prepared functional copper current collector is higher, the stability of the functional copper current collector when the functional copper current collector is used as a current collector of a secondary battery is improved, the service life of the secondary battery is prolonged, and the safety performance of the secondary battery is improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery material technology, specifically, it relates to a method for preparing a functional copper current collector, an electroplating solution, and a functional copper current collector and a secondary battery based thereon. Background Technology

[0002] With the rapid development of new energy and electronic technology, battery cycle life, safety performance, and energy density have become paramount. As a crucial component of a battery, the current collector gathers the current generated by the battery's active materials to form a larger output current; its performance directly impacts the battery's cycle life, energy density, and safety.

[0003] Currently, copper and aluminum foils are commonly used as current collectors in lithium-ion and sodium-ion batteries. These current collectors have high cost and weight, which is detrimental to battery cost control and energy density improvement. Based on the problems of traditional foil materials, composite foil current collectors offer significant advantages over traditional foil materials as a development and replacement. Composite foil current collectors typically have a "sandwich" structure, with an inner substrate layer mainly composed of polymers and metal conductive layers on both sides. Because the surface metal conductive layer of composite foil current collectors is thinner and the inner substrate layer is lighter, the overall weight of the current collector can be significantly reduced, thereby increasing the energy density of lithium-ion batteries. Simultaneously, the thinner surface metal conductive layer of composite foil current collectors is more easily broken than that of traditional foils during thermal runaway in lithium-ion batteries, thus isolating the active material from the current collector and preventing further thermal runaway.

[0004] However, while composite foil current collectors offer advantages such as low cost and light weight, the significant heat generated during secondary battery cycles causes volume changes, leading to excessive thermal shrinkage and substantial thermal deformation. Currently, most composite copper foil current collectors utilize electroplating to thicken the copper layer. Traditional acid-plated copper composite foil current collectors have limitations in tensile strength, elongation, and resistivity. Insufficient tensile strength and elongation make composite foil current collectors prone to irreversible structural damage after multiple battery cycles. This negatively impacts the cycle performance and safety of secondary batteries, hindering the effective improvement of energy density through the application of composite foil. Summary of the Invention

[0005] To improve the structural stability and reduce the resistivity of functional copper current collectors, this invention provides a method for preparing functional copper current collectors, an electroplating solution, and a functional copper current collector and a secondary battery based thereon.

[0006] According to a first aspect of the present invention, a method for preparing a functional copper current collector is provided, the method comprising the operation of thickening a copper elemental layer by aqueous electroplating, wherein the electroplating solution used in the aqueous electroplating process contains copper sulfate, sulfuric acid and a copper cyanide complex; wherein the mass concentration of copper sulfate in the electroplating solution is 58 g / L to 70 g / L, and the mass concentration of copper sulfate to the mass concentration of sulfuric acid is 1:2.5 to 4. Preferably, in the electroplating solution, the mass concentration of copper sulfate to the mass concentration of sulfuric acid is 1:2.7 to 3.5.

[0007] In existing electroplating solutions, the mass concentration of copper sulfate to sulfuric acid is approximately 1:1.2. However, in the method for preparing functional copper current collectors provided in this solution, the electroplating solution used in the water electroplating process has a relatively low copper sulfate content. Furthermore, the mass concentration ratio of copper sulfate to sulfuric acid is controlled between 1:2.5 and 4. Based on the composition of the electroplating solution, the electroplating rate of the water electroplating process can be controlled within a low range. In the method for preparing functional copper current collectors provided in this solution, the growth rate of copper grain nuclei during the water electroplating process is relatively low, resulting in a growth rate lower than the formation rate of copper grains, achieving the effect of finely crystallized copper grain nuclei in the copper elemental layer. Additionally, the electroplating solution used in the water electroplating process slows down the electroplating rate, which helps maintain the conductivity and ductility of the electroplating solution, resulting in a smooth coating surface. Furthermore, the electroplating solution also contains copper-cyanide complexes. Due to the low dissociation ability of these complexes, the reduction process of copper ions at the cathode becomes more difficult, thereby increasing the polarization of the cathode and facilitating further refinement of the copper grains constituting the copper elemental layer. In summary, in the above-mentioned method for preparing functional copper current collectors for thickening copper elemental layers, using an electroplating solution with high sulfuric acid content and containing copper-cyanide complexes as the electroplating solution for water electroplating slows down the rate of copper grain formation. Because the copper elemental layer formed on the foil surface through water electroplating achieves a finer grain size, the tensile strength and elongation of the functional copper current collector are improved, while the resistivity is reduced. This also helps to improve the smoothness of the copper surface, thereby enhancing the stability of the functional copper current collector when used as a current collector in secondary batteries, and improving the service life and safety performance of the secondary batteries.

[0008] Preferably, the mass concentration of sulfuric acid in the electroplating solution is 189 g / L to 210 g / L.

[0009] Preferably, the mass concentration of the copper cyanide complex in the electroplating solution is 0.002 g / L to 0.003 g / L. As mentioned above, the refining effect of the copper cyanide complex on copper grains is based on the fact that the copper cyanide complex enhances the cathode polarization. By controlling the mass concentration of the copper cyanide complex within the above range, the cathode polarization can be better controlled, thereby effectively refining the copper grains on the surface of the functional copper current collector while maintaining good structural stability of the functional copper current collector. If the concentration of the copper cyanide complex is lower than the above range, the cathode polarization is weaker, and the copper grains formed by water electroplating may still include coarse grains, making it difficult for the coating to achieve high surface quality and high gloss. It may also affect the corrosion resistance and wear resistance of the copper elemental layer. As the concentration of the copper cyanide complex increases, the cathode polarization is enhanced. If the mass concentration of the copper cyanide complex exceeds the above range, the coating crystals will become too fine and dense, which may cause the copper elemental layer to become brittle, reducing the toughness of the copper elemental layer and its bonding force with the polymer substrate.

[0010] Preferably, the raw materials for preparing the copper-cyanide complex include sodium cyanide and cuprous cyanide, with a mass ratio of sodium cyanide:cuprous cyanide = 6-8:20-30. At this ratio, the raw materials react fully, resulting in a copper-cyanide complex with high purity and good chemical stability. It is less prone to decomposition or other adverse changes during subsequent application in the preparation of functional copper current collectors, ensuring a stable composition in the electroplating solution containing the copper-cyanide complex during the preparation of functional copper current collectors. This results in copper grains with uniform grain size formed by water electroplating, leading to stable product quality of the functional copper current collector. If the ratio of sodium cyanide to cuprous cyanide used in preparing the copper-cyanide complex exceeds the above range, the stability of the resulting copper-cyanide complex may deteriorate. Furthermore, excessive raw material residue, entering the electroplating solution with the copper-cyanide complex, may cause side reactions with other materials, altering the performance of the electroplating solution and hindering the control of the grain size of copper grains formed by water electroplating. For example, excessive sodium cyanide can easily react with other materials in the electroplating solution, and excessive cuprous cyanide will remain in the electroplating solution, which is detrimental to the stability of the electroplating solution's quality and the maintenance of its application performance stability. Preferably, the preparation of the copper-cyanide complex includes the following operations: adding sodium cyanide and cuprous cyanide to water, stirring, and the sodium cyanide and cuprous cyanide undergo a complexation reaction in the solution to obtain the copper-cyanide complex. The product obtained after the complexation reaction is completed is the copper-cyanide complex solution. 6-8 g of sodium cyanide and 20-30 g of cuprous cyanide are required to prepare each liter of the above copper-cyanide complex solution.

[0011] Preferably, the preparation of the electroplating solution includes the following operations: S1. Preparing a high-acid, low-copper solution, wherein the mass concentration of copper sulfate is 58 g / L to 70 g / L, and the mass concentration of sulfuric acid is 190 g / L to 210 g / L; S2. Adding a copper-cyanide complex to the high-acid, low-copper solution to obtain the electroplating solution, wherein the amount of copper-cyanide complex added is sufficient, and the mass concentration of the copper-cyanide complex in the electroplating solution is 0.002 g / L to 0.003 g / L. Preferably, the above method for preparing a functional copper current collector includes the following operations: S1. Preparing a raw copper foil, the raw copper foil comprising a polymer substrate and a copper elemental layer to be thickened, the copper elemental layer being disposed on at least one surface of the polymer substrate; S2. Immersing the copper foil in a sulfuric acid solution to activate the raw copper foil, wherein the mass concentration of sulfuric acid in the sulfuric acid solution is 10 g / L to 20 g / L; S3. Performing an electroplating treatment on the raw copper foil to thicken the copper elemental layer. Regarding the selection of copper foil as a raw material applicable to this method, the cases of direct lamination of the copper elemental layer with the polymer substrate and the cases of having other interlayers between the copper elemental layer and the polymer substrate both fall under the category of "the copper elemental layer being disposed on at least one surface of the polymer substrate" as described in the above method.

[0012] In the above method, before electroplating the raw copper foil, the raw copper foil is activated by sulfuric acid solution. This removes the oxide layer on the surface of the raw copper foil, which helps to expose the copper elemental layer to be thickened. During the electroplating process, the copper grains formed by electroplating can be deposited more uniformly on the surface of the copper elemental layer, reducing the influence of impurities when generating copper grain nuclei, improving the generation efficiency of fine copper grains, improving the mechanical properties of the functional copper current collector, and reducing the resistivity of the functional copper current collector.

[0013] Preferably, step S1 of the above method further includes a water washing process on the raw copper foil. Water washing helps remove impurities from the surface of the raw copper foil, thereby improving the formation efficiency of fine copper grains and enhancing the performance of the functional copper current collector to some extent.

[0014] Preferably, in step S1 of the above method, the water washing process of the raw copper foil includes spraying water onto the raw copper foil during the water washing process. Spraying water washing provides a greater mechanical impact force to the raw copper foil, more effectively removing residual impurities (generally impurities generated during copper electroplating of the polymer substrate to form a copper elemental layer), electroplating solution, and other contaminants from the surface of the raw copper foil. In contrast, if the raw copper foil is immersed in water for water washing, the immersion mainly relies on the concentration difference and diffusion of impurity ions to remove impurities, resulting in a relatively weak cleaning effect. For example, some tiny particles may remain on the surface of the raw copper foil due to copper electroplating, adsorbed on the surface of the copper elemental layer. Spraying water washing can remove these particles using the impact force of the spray, while immersion water washing cannot completely remove these particles. In summary, the spray washing method helps to remove impurities from the surface of the raw copper foil more thoroughly, making the copper surface for subsequent electroplating more flat and smooth. This improves the quality and efficiency of copper grain nucleation during electroplating, effectively enhances the mechanical properties of functional copper current collectors, reduces their resistivity, and ultimately improves the performance of functional copper current collectors.

[0015] According to a second aspect of the present invention, an electroplating solution is provided, the electroplating solution containing copper sulfate, sulfuric acid and a copper cyanide complex; in the electroplating solution, the mass concentration of copper sulfate is 58 g / L to 70 g / L, and the mass concentration of copper sulfate to the mass concentration of sulfuric acid is 1:2.5 to 4.

[0016] Preferably, in the above electroplating solution, the mass concentration of the copper-cyanide complex is 0.002 g / L to 0.003 g / L.

[0017] According to a third aspect of the present invention, a functional copper current collector is provided, which is prepared by the method described above for preparing a functional copper current collector.

[0018] According to a fourth aspect of the invention, a secondary battery is provided, the secondary battery comprising an electrode sheet using the functional copper current collector as described above as the current collector. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0020] Example 1 1. Related equipment The equipment required for preparing the functional copper current collector in this embodiment includes a high-vacuum winding magnetron sputtering system and an electroplating production line. The high-vacuum winding magnetron sputtering system uses nickel-chromium alloy and copper as the target material. The electroplating production line includes a washing tank, an activation tank, and a copper plating tank. Before processing, it is ensured that all required equipment is functioning correctly.

[0021] The polymer base film used in this embodiment is a polypropylene film with a thickness of 4μm.

[0022] (1) Preparation of thin layers of copper grains The polymer substrate is placed in a high-vacuum winding magnetron sputtering equipment, and the sputtering program of the equipment is started to deposit a 20nm thick nickel-chromium alloy layer on the surface of the polymer base film, followed by a 60nm thick copper grain thin layer, thereby obtaining the raw material copper foil. (2) Electroplating thickened copper element The raw copper foil is transferred to the electroplating production line: S1. Water washing treatment: The raw copper foil is put into a water washing tank, and pure water is sprayed thoroughly on both sides of the raw copper foil in the water washing tank. S2. Activation treatment: After the raw copper foil has been washed, it is transferred to an activation tank containing sulfuric acid solution with a concentration of 15 g / L. The raw copper foil is then immersed in the sulfuric acid solution for 10 seconds. S3. Electroplating: After activation treatment, the raw copper foil is transferred to a copper bath containing electroplating solution. Electroplating is then performed on the raw copper foil to thicken the thin copper grain layer (i.e., the copper elemental layer) to a thickness of 1 μm, thereby obtaining the finished functional copper current collector. The average cathode current density in this step is 2 A / dm³. 2 The plating bath temperature was 20℃, and the electroplating time was 24s. The copper plating bath contained a copper-cyanide complex solution, a high-acid, low-copper solution, and hydrochloric acid, along with additives A and B (where additive A is a leveling agent, model JRM304-ZP, and additive B is a brightener, model JRM002-GL, manufactured by Suzhou Jereme Co., Ltd.). The hydrochloric acid concentration was 40 mg / L, the additives A and B concentration was 2.5 g / L, the copper sulfate concentration was 63.41 g / L, the sulfuric acid concentration was 195.12 g / L, and the copper-cyanide complex concentration was 0.0025 g / L. The copper-cyanide complex was prepared from sodium cyanide and cuprous cyanide at a mass ratio of sodium cyanide:cuprous cyanide = 7:25.

[0023] Example 2 This embodiment describes the preparation of a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this embodiment contains approximately 58.54 g / L copper sulfate and approximately 194.35 g / L sulfuric acid. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0024] Example 3 This embodiment describes the preparation of a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this embodiment contains copper sulfate at a mass concentration of 68.29 g / L and sulfuric acid at a mass concentration of 185.37 g / L. Apart from the above differences, all other raw materials and corresponding operating steps required for the preparation of the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0025] Example 4 This embodiment describes the preparation of a functional copper current collector according to Example 1. The difference from Example 1 is that the mass concentration of copper sulfate in the electroplating solution is approximately 63.41 g / L, and the mass concentration of sulfuric acid is approximately 180.49 g / L. Apart from the above differences, all other raw materials and corresponding operating steps required for the preparation of the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0026] Example 5 This embodiment describes the preparation of a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this embodiment contains approximately 63.41 g / L copper sulfate and approximately 210.52 g / L sulfuric acid. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0027] Example 6 This embodiment describes the preparation of a functional copper current collector according to Example 1. The difference from Example 1 is that in this embodiment, the electroplating solution contains approximately 61.90 g / L copper sulfate, approximately 190.48 g / L sulfuric acid, and approximately 0.005 g / L copper cyanide complex. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0028] Example 7 This embodiment refers to Example 1 for preparing a functional copper current collector. The difference from Example 1 is that in this embodiment, sodium cyanide and cuprous hydride are used in a mass ratio of 6:30 to sodium cyanide to cuprous cyanide during the preparation of the copper-cyanide complex. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0029] Example 8 This embodiment refers to Example 1 for preparing a functional copper current collector. The difference from Example 1 is that in this embodiment, sodium cyanide and cuprous hydride are used in a mass ratio of 8:20 to sodium cyanide to cuprous cyanide during the preparation of the copper-cyanide complex. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0030] Example 9 This embodiment refers to Example 1 for preparing a functional copper current collector. The difference from Example 1 is that in this embodiment, sodium cyanide and cuprous hydride are used in a mass ratio of sodium cyanide:cuprous cyanide = 5:30 during the preparation of the copper-cyanide complex. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0031] Example 10 This embodiment refers to Example 1 for preparing a functional copper current collector. The difference from Example 1 is that in this embodiment, sodium cyanide and cuprous hydride are used in a mass ratio of sodium cyanide:cuprous cyanide = 10:20 during the preparation of the copper-cyanide complex. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0032] Example 11 This embodiment prepares a functional copper current collector according to Example 1. The difference from Example 1 is that, during the electroplating process of the raw copper foil, the S2 activation treatment is replaced by thoroughly spraying a sulfuric acid solution (15 g / L) onto both sides of the raw copper foil. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0033] Example 12 This embodiment prepares a functional copper current collector according to Example 1. The difference from Example 1 is that, in the electroplating process of the raw copper foil, the sulfuric acid solution used in the S2 activation treatment is replaced with a sulfuric acid solution with a concentration of 40 g / L. Apart from the above difference, the other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0034] Example 13 This embodiment prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the activation treatment of the raw copper foil with sulfuric acid solution (S2) is omitted during the electroplating process of the raw copper foil. Apart from the above differences, the other raw materials and corresponding operation steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0035] Example 14 This embodiment prepares a functional copper current collector according to Example 1. The difference from Example 1 is that, in the electroplating process of the raw copper foil, the S1 water washing treatment is replaced by immersing the raw copper foil in pure water for 20 seconds. Apart from the above difference, the other raw materials and corresponding operating steps required for preparing the functional copper current collector in this embodiment are strictly consistent with those in Example 1.

[0036] Comparative Example 1 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this comparative example contains approximately 97.56 g / L copper sulfate and approximately 117.07 g / L sulfuric acid. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this comparative example are strictly consistent with those in Example 1.

[0037] Comparative Example 2 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this comparative example contains approximately 78.05 g / L copper sulfate and approximately 165.85 g / L sulfuric acid. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this comparative example are strictly consistent with those in Example 1.

[0038] Comparative Example 3 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this comparative example contains approximately 78.05 g / L copper sulfate and approximately 194.15 g / L sulfuric acid. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this comparative example are strictly consistent with those in Example 1.

[0039] Comparative Example 4 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the mass concentration of copper sulfate in this comparative example is approximately 63.41 g / L, and the mass concentration of sulfuric acid is approximately 134.63 g / L. Apart from the above differences, all other raw materials required for preparing the functional copper current collector in this comparative example and the corresponding operating steps are strictly consistent with those in Example 1.

[0040] Comparative Example 5 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the mass concentration of copper sulfate in this comparative example is approximately 195.12 g / L, and the mass concentration of sulfuric acid is approximately 58.54 g / L. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this comparative example are strictly consistent with those in Example 1.

[0041] Comparative Example 6 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that no copper cyanide complex is added during the preparation of the electroplating solution in this comparative example. Therefore, the electroplating solution in this comparative example has a copper sulfate concentration of approximately 63.41 g / L and a sulfuric acid concentration of approximately 195.12 g / L, and does not contain copper cyanide complex. Furthermore, 1-piperazine carboxamide and sodium N,N-dimethyldithiocarbonylpropane sulfonate are used instead of copper cyanide complex. The electroplating solution prepared in this comparative example has a concentration of 10 g / L for both 1-piperazine carboxamide and sodium N,N-dimethyldithiocarbonylpropane sulfonate. Apart from the above differences, all other raw materials and corresponding operating steps required for the preparation of the functional copper current collector in this comparative example are strictly consistent with those in Example 1.

[0042] Comparative Example 7 This comparative example prepares a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution in this comparative example contains approximately 63.4 g / L copper sulfate and approximately 195.1 g / L sulfuric acid, and does not contain copper-cyanide complex functional copper current collectors. Apart from the above differences, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this comparative example are strictly consistent with those in Example 1.

[0043] Comparative Example 8 This comparative example prepared a functional copper current collector according to Example 1. The difference from Example 1 is that the electroplating solution used in this comparative example consisted of 120 g / L copper sulfate, 100 g / L sulfuric acid, 40 mg / L hydrochloric acid, 16 ppm sodium polydithiopropane sulfonate, 2 ppm N,N-diethylthiourea, and 200 ppm polyoxyethylene ether. The electroplating solution prepared in this comparative example did not contain copper cyanide complexes; during the electroplating of activated raw copper foil using the above electroplating solution, the average cathode current density was 2 A / dm³. 2 The plating bath temperature was 30°C, and the electroplating time was 10 seconds. Apart from the differences mentioned above, all other raw materials and corresponding operating steps required for preparing the functional copper current collector in this comparative example were strictly consistent with those in Example 1.

[0044] Test case 1. Test Object The functional copper current collectors prepared in Examples 1-14 and Comparative Examples 1-8 were used as the test objects in this test example.

[0045] 2. Tensile strength and elongation test: The tensile strength and elongation at break of the prepared composite current collector were tested in accordance with GB / T 1040.3-2006.

[0046] 2. Resistivity test Cut a sample from the composite current collector, ensuring the sample surface is flat and free from obvious oxidation and contamination. Place the sample on the test platform of a four-probe resistivity meter and start the meter to measure the resistivity of the sample.

[0047] 3. Test Results In the preparation of functional copper current collectors, the embodiments and comparative examples all involve the application of an electroplating process to thicken the copper elemental layer of the functional copper current collector, with the difference being the electroplating solution used in the electroplating step. The test results show that, compared to the samples provided in Comparative Examples 1-8, the samples provided in Examples 1-14 all exhibit higher tensile strength, higher elongation, and lower resistivity. In the preparation of functional copper current collectors in Examples 1-14, the electroplating solution used in the electroplating process had a relatively low copper sulfate content. Furthermore, the mass concentration ratio of copper sulfate to sulfuric acid was controlled at 1:2.5-4. Based on the composition of the electroplating solution, the electroplating rate of the electroplating process could be controlled within a low range. In the preparation of functional copper current collectors in Examples 1-14, the growth rate of copper grain nuclei during the electroplating process was relatively low, resulting in a growth rate of copper grains lower than their formation rate, achieving the effect of finer crystallization of the copper elemental layer. Furthermore, the electroplating solution used in the electroplating process helps maintain the conductivity and ductility of the solution, resulting in a smooth coating surface. Additionally, the electroplating solution contains copper-cyanide complexes. Due to the low dissociation ability of these complexes, the reduction process of copper ions at the cathode becomes difficult, thereby increasing the polarization of the cathode and further refining the copper grains constituting the copper layer. In summary, in the methods for preparing functional copper current collectors in Examples 1-14, by using an electroplating solution with a high sulfuric acid content and containing copper-cyanide complexes as the electroplating solution for the electroplating process, the rate of copper grain formation through electroplating is slowed down. This allows for finer grain sizes of the copper formed on the foil surface through electroplating, thereby improving the tensile strength and elongation of the functional copper current collector, reducing resistivity, and also enhancing the smoothness of the copper surface.

[0048] In Examples 1-14 and Comparative Examples 1-8, only the electroplating solution used in Comparative Example 5 had a higher copper sulfate content than sulfuric acid content. This electroplating solution had the characteristics of "high copper and low acid". Using this electroplating solution to thicken the copper elemental layer of the functional copper current collector, the growth rate of copper grains was relatively fast. The copper grains obtained by water electroplating were relatively large, which made the tensile strength and elongation of the functional copper current collector prepared in Comparative Example 5 significantly lower than most of the test objects in this test example, and the resistivity was also at a significantly higher level.

[0049] Although the copper sulfate content in the electroplating solutions used in Comparative Examples 1-3 was lower than that in sulfuric acid, compared with the electroplating solutions used in Examples 1-14, the copper sulfate content in the electroplating solutions used in Comparative Examples 1-3 was higher and the sulfuric acid content was lower. This resulted in a higher mass concentration ratio of copper sulfate to sulfuric acid, which was not within the range of 1:2.5-4. Consequently, the surface of the copper elemental layer in the functional copper current collectors prepared in Comparative Examples 1-3 also contained large copper grains, making it difficult for these comparative examples to achieve good mechanical strength and electrical conductivity. The mass concentration ratios of copper sulfate to sulfuric acid in the electroplating solutions used in Comparative Examples 1, 2, and 3 were approximately 1:1.2, 1:2.125, and 1:2.487, respectively. As the mass concentration ratio of copper sulfate to sulfuric acid increased, the performance of the prepared functional copper current collectors improved somewhat, but there was still a significant difference compared with the performance of the functional copper current collectors prepared in Examples 1-14. The electroplating solution used in Comparative Example 4 has a similar mass concentration ratio of copper sulfate to sulfuric acid as that used in Comparative Example 2. However, since the copper sulfate content in Comparative Example 2 is significantly higher than that in Comparative Example 4, while the copper sulfate content in Comparative Example 4 is in the range of 58 g / L to 70 g / L, the performance of the functional copper current collector prepared in Comparative Example 4 is slightly better than that prepared in Comparative Example 2. However, the functional copper current collector prepared in Comparative Example 4 still has a significant gap in product performance compared with the functional copper current collectors prepared in Examples 1 to 14.

[0050] The electroplating solutions used in Comparative Examples 6-8 did not contain copper-cyanide complexes. The performance of the functional copper current collectors prepared by these comparative examples was significantly poor. In the functional copper current collectors prepared by Comparative Examples 7 and 8, large copper grains were clearly mixed in the copper elemental layer formed by water electroplating. In Comparative Example 6, although grain refiners (1-piperazine carboxamide and sodium N,N-dimethyl dithiocarbonyl propane sulfonate) were used to inhibit the growth of copper grains, the test results showed that this did not significantly improve the performance of the functional copper current collector. The functional copper current collector prepared by Comparative Example 6 still had low tensile strength, low elongation, and high resistivity.

[0051] In the electroplating solutions used in Examples 1-5, both the copper sulfate concentration (58 g / L to 70 g / L) and the copper sulfate to sulfuric acid ratio (1:2.5 to 4) were satisfied. However, based on the test results, the functional copper current collectors provided in Examples 1-3 showed better performance among the test objects provided in the above examples. Compared to the electroplating solutions used in the other examples, the sulfuric acid concentration in the electroplating solution used in Example 4 was relatively low, while the sulfuric acid concentration in the electroplating solution used in Example 5 was relatively high. In particular, comparing the electroplating solutions used in Example 5 and Example 2 to prepare the functional copper current collectors, the copper sulfate content in both solutions reached the range of 58 g / L to 70 g / L, and both had essentially the same copper sulfate to sulfuric acid mass concentration ratio. Because the sulfuric acid content in the electroplating solution used in Example 5 was higher than that in the electroplating solution used in Example 2, the functional copper current collector prepared in Example 5 was inferior to the functional copper current collector prepared in Example 2 in both mechanical and electrical properties. In summary, in this scheme, ensuring that the mass concentration of sulfuric acid in the electroplating solution used for water electroplating is within the range of 189 g / L to 210 g / L is beneficial to further improve the product performance of functional copper current collectors.

[0052] Compared to other embodiments, Example 6 used a higher concentration of copper-cyanide complex solution in the electroplating solution preparation process, resulting in a significantly higher copper-cyanide complex content in the electroplating solution compared to the solutions used in other embodiments. While the electroplating solution provided in Example 6 is similar to that provided in Example 1 in terms of copper sulfate content, sulfuric acid content, and their ratio, the performance of the functional copper current collector prepared in Example 6 is inferior to that prepared in Example 1. This is because the electroplating solution used in Example 6 contains a higher concentration of copper-cyanide complex, leading to an overly fine and dense copper elemental layer crystallization. This results in brittle copper elemental layer, reducing its toughness and adhesion to the polymer substrate.

[0053] In Examples 1 and 7-10, the total mass of sodium cyanide and cuprous cyanide used to prepare the copper-cyanide complex was the same; however, the ratio of sodium cyanide to cuprous cyanide was different. Therefore, the purity and stability of the copper-cyanide complex solutions obtained in these examples differed, leading to varying degrees of difference in the mechanical and electrical properties of the functional copper current collectors prepared in these examples. Based on the test results of the functional copper current collectors provided in the above examples in this test example, the functional copper current collectors prepared in Examples 1, 7, and 8 exhibited higher tensile strength, higher elongation, and lower resistivity. The raw material ratios used to prepare the copper-cyanide complex in these examples all satisfied the ratio of sodium cyanide to cuprous cyanide of 6-8:20-30 (mass ratio). Within the above-mentioned ratio range, the raw materials react fully, resulting in a copper-cyanide complex with high purity and good chemical stability. It is not easily decomposed or undergoes other adverse changes during subsequent application in the preparation of functional copper current collectors. This ensures that the electroplating solution containing the copper-cyanide complex maintains a stable composition during the preparation of functional copper current collectors, resulting in copper grains with uniform grain size formed by electroplating. Consequently, the functional copper current collectors produced have stable product quality. Compared to Examples 1, 7, and 8, Examples 9 and 10 show issues with the use of sodium cyanide in the preparation of the copper-cyanide complex, with one example having a lower sodium cyanide content and the other a higher sodium cyanide content. This leads to a decrease in the stability and purity of the resulting copper-cyanide complex, resulting in poorer process stability in the electroplating process for forming copper grains in Examples 9 and 10. Furthermore, this results in a small number of larger copper grains forming on the surface of the copper elemental layer of the functional copper current collectors produced in these two examples, consequently deteriorating the mechanical and electrical properties of the functional copper current collectors.

[0054] Compared to Example 1, Examples 11-13 differ in the implementation of the activation treatment methods involved in the preparation of the functional copper current collector. In Example 13, no activation treatment was performed on the raw copper foil during the preparation of the functional copper current collector. Therefore, the performance of the product obtained in Example 13 is inferior to that obtained in the other examples. In Examples 1, 11, and 12, the raw copper foil was activated with sulfuric acid solution before electroplating. This activated the raw copper foil, removing the oxide layer on its surface and exposing the copper elemental layer to be thickened. During electroplating, the copper grains formed by electroplating deposit more uniformly on the surface of the copper elemental layer, reducing the influence of impurities during the formation of copper grain nuclei, improving the formation efficiency of fine copper grains, enhancing the mechanical properties of the functional copper current collector, and reducing its resistivity.

[0055] Compared to Example 14, Example 1 uses a spray method to wash the raw copper foil, while Example 1 uses an immersion method. The performance of the functional copper current collectors obtained from both examples shows that the washing method has a certain impact on their performance. The spray method provides greater mechanical impact to the raw copper foil, which helps to remove impurities more thoroughly. This results in a smoother copper surface for subsequent electroplating, improving the quality and efficiency of copper grain nucleation and effectively enhancing the mechanical properties and reducing the resistivity of the functional copper current collector. In contrast, immersion in water removes impurities primarily through concentration differences and diffusion, resulting in a weaker cleaning effect. Consequently, the performance of the functional copper current collector obtained in Example 14 is inferior to that obtained in Example 1.

[0056] Table 1. Statistics of test results for Test Case 1 are shown in Table 1.

[0057] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for preparing a functional copper current collector, characterized in that: The method includes the operation of thickening a copper elemental layer by electroplating, wherein the electroplating solution used in the electroplating process contains copper sulfate, sulfuric acid and copper cyanide complex; in the electroplating solution, the mass concentration of copper sulfate is 58 g / L to 70 g / L, and the mass concentration of copper sulfate to the mass concentration of sulfuric acid is 1:2.5 to 4.

2. The method for preparing a functional copper current collector as described in claim 1, characterized in that: In the electroplating solution, the mass concentration of sulfuric acid is 189 g / L to 210 g / L.

3. The method for preparing a functional copper current collector as described in claim 1, characterized in that: In the electroplating solution, the mass concentration of the copper-cyanide complex is 0.002 g / L to 0.003 g / L.

4. The method for preparing a functional copper current collector as described in claim 1, characterized in that: The raw materials for preparing the copper-cyanide complex include sodium cyanide and cuprous cyanide, with a mass ratio of sodium cyanide:cuprous cyanide = 6-8:20-30.

5. The method for preparing a functional copper current collector according to any one of claims 1 to 4, characterized in that, Includes the following operations: S1. Prepare raw copper foil, the raw copper foil comprising a polymer substrate and a copper elemental layer to be thickened, the copper elemental layer being disposed on at least one surface of the polymer substrate; S2. The copper foil is immersed in a sulfuric acid solution to activate the raw copper foil. The sulfuric acid solution has a mass concentration of 10 g / L to 20 g / L. S3. Perform the electroplating treatment on the raw copper foil to thicken the copper elemental layer.

6. The method for preparing a functional copper current collector as described in claim 5, characterized in that: S1 also includes a water washing process for the raw copper foil: during the water washing process, water is sprayed onto the raw copper foil.

7. An electroplating solution, characterized in that: The electroplating solution contains copper sulfate, sulfuric acid, and a copper cyanide complex; in the electroplating solution, the mass concentration of copper sulfate is 58 g / L to 70 g / L, and the mass concentration of copper sulfate to the mass concentration of sulfuric acid is 1:2.5 to 4.

8. The electroplating solution as described in claim 7, characterized in that: In the electroplating solution, the mass concentration of the copper-cyanide complex is 0.002 g / L to 0.003 g / L.

9. A functional copper current collector, characterized in that: The functional copper current collector is prepared by the method described in any one of claims 1 to 6.

10. A secondary battery, characterized in that: The secondary battery includes an electrode sheet using the functional copper current collector as described in claim 9 as the current collector.

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