Preparation method of copper foil, copper foil and foil generating system

Abstract

The invention belongs to the technical field of copper foils, and particularly relates to a preparation method of a copper foil, the copper foil and a raw foil system.The preparation method comprises the steps of raw foil electrolysis, roughening treatment and curing treatment.The raw foil electrolysis is that multi-step electro-deposition is conducted in an electrolyte to form the copper foil, the multi-step electrodeposition comprises at least two deposition stages adopting different current densities and different copper ion concentrations, and in the deposition stage process, a composite additive comprising at least two different molecular weight components is added into an electrolyte; the roughening treatment comprises at least two roughening stages, and the concentration of copper ions in the electrolyte in the later roughening stage is lower than the concentration of copper ions in the electrolyte in the previous roughening stage; the curing treatment comprises at least two curing stages, and the concentration of copper ions in the electrolyte in the later curing stage is lower than that of copper ions in the electrolyte in the previous curing stage. According to the method, the elongation of the super-thick electrolytic copper foil at high temperature can be improved, meanwhile, the low surface roughness of the super-thick electrolytic copper foil is maintained, and the high peel strength of the super-thick electrolytic copper foil is guaranteed.

Description

Technical Field

[0001] This application belongs to the field of copper foil technology, specifically relating to a method for preparing copper foil, copper foil, and a copper foil production system. Background Technology

[0002] Ultra-thick electrolytic copper foil (thickness ≥ 200 μm) is a core conductive material for high-end circuits such as servers and automotive electronics. It must simultaneously possess good high-temperature ductility, low surface roughness, and high peel strength to meet the requirements of high-temperature assembly, high-frequency signal transmission, and multi-layer structure reliability.

[0003] However, the relevant technical solutions struggle to balance the aforementioned key performance indicators. Improving one performance characteristic often leads to the degradation of others, resulting in a significant contradictory relationship between the various indicators. Summary of the Invention

[0004] The purpose of this application is to provide a method for preparing copper foil, copper foil and a green foil system, which can synergistically improve the elongation of ultra-thick electrolytic copper foil at high temperature, while maintaining its low surface roughness and ensuring its high peel strength.

[0005] The first aspect of this application provides a method for preparing copper foil, comprising: electrolysis of raw foil: performing multi-step electrodeposition in an electrolyte to form copper foil, the multi-step electrodeposition including at least two deposition stages using different current densities and different copper ion concentrations, wherein during the deposition stages, a composite additive comprising at least two different molecular weight components is added to the electrolyte; roughening treatment: subjecting the electrolyzed copper foil to roughening treatment, the roughening treatment including at least two roughening stages, wherein the copper ion concentration in the electrolyte of the later roughening stage is lower than the copper ion concentration in the electrolyte of the previous roughening stage; and curing treatment: subjecting the roughened copper foil to curing treatment, the curing treatment including at least two curing stages, wherein the copper ion concentration in the electrolyte of the later curing stage is lower than the copper ion concentration in the electrolyte of the previous curing stage.

[0006] In one exemplary embodiment of this application, the multi-step electrodeposition includes a first deposition stage, a second deposition stage, and a third deposition stage performed sequentially; the first deposition stage is performed at a first current density and a first copper ion concentration; the second deposition stage is performed at a second current density higher than the first current density and a second copper ion concentration lower than the first copper ion concentration, and the composite additive is added to the electrolyte; the third deposition stage is performed at a third current density lower than the first current density and a third copper ion concentration lower than the second copper ion concentration.

[0007] In one exemplary embodiment of this application, the composite additive includes a low molecular weight component and a medium molecular weight component.

[0008] In one exemplary embodiment of this application, the mass ratio of the low molecular weight component to the medium molecular weight component is 1.5-2.3:1.

[0009] In one exemplary embodiment of this application, the low molecular weight component is a polyethyleneimine derivative with a molecular weight of 800-2000 Da, and the medium molecular weight component is a hydroxyethyl cellulose with a molecular weight of 10000-30000 Da.

[0010] In one exemplary embodiment of this application, the third deposition stage is performed under ultrasound-assisted conditions.

[0011] In one exemplary embodiment of this application, the total amount of the composite additive is 10-50 ppm.

[0012] A second aspect of this application provides a copper foil prepared using any of the copper foil preparation methods described above, wherein the copper foil has a thickness of 200 to 220 μm and comprises at least two copper layers with different average grain sizes along its thickness direction.

[0013] In one exemplary embodiment of this application, at least two copper layers include a base layer, a transition layer, and a refinement layer. The transition layer is disposed between the base layer and the refinement layer, and the average grain size of the refinement layer is smaller than the average grain size of the base layer.

[0014] A third aspect of this application provides a green foil system for implementing any of the above-described preparation methods, comprising: at least two electrolytic cells arranged in series for sequentially performing different deposition stages of the multi-step electrodeposition; a guide roller group disposed between adjacent electrolytic cells for continuously conveying copper foil substrate between different electrolytic cells; and an additive dripping unit, including a metering pump and a controller signal-connected to the metering pump, the controller being used to control the dripping rate of the composite additive into the electrolyte in real time according to process parameters.

[0015] The copper foil preparation method, copper foil, and raw foil system of this application have the following beneficial effects:

[0016] By incorporating a composite additive comprising at least two different molecular weight components during the electrodeposition process, the synergistic effect between the components effectively regulates the crystallization behavior of the deposition interface, achieving grain refinement and suppressing dendrite growth. Furthermore, by employing gradient electrodeposition with at least two deposition stages of different current densities and copper ion concentrations, the electric field distribution and ion mass transfer during the deposition process are optimized, improving the stress state and structural compactness within the copper foil. Further, by employing multi-stage coarsening and curing treatments with progressively decreasing copper ion concentrations, a robust interface structure with a large bonding area and strong mechanical interlocking is gradually constructed. The combination of these technical features enables the final copper foil to simultaneously achieve increased high-temperature elongation, reduced surface roughness, and enhanced peel strength.

[0017] Other features and advantages of this application will become apparent from the following detailed description, or may be learned in part from practice of this application.

[0018] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0019] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0020] Figure 1 A schematic diagram of the structure of the copper foil provided in an embodiment of this application is shown.

[0021] Figure 2 A structural block diagram of the foil-making system provided in an embodiment of this application is shown.

[0022] Explanation of reference numerals in the attached figures: 100. Copper foil; 110. Substrate layer; 120. Transition layer; 130. Refining layer; 200. Green foil system; 210. Electrolytic cell; 211. First electrolytic cell; 212. Second electrolytic cell; 213. Third electrolytic cell; 220. Additive dripping unit; 230. Cathode roller; 240. Anode box; 250. Ultrasonic unit; 260. Plate heat exchanger; 270. Circulation unit. Detailed Implementation

[0023] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided to make this application more comprehensive and complete, and to fully convey the concept of the exemplary embodiments to those skilled in the art.

[0024] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0025] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this application. However, those skilled in the art will recognize that the technical solutions of this application can be practiced without one or more of the specific details, or other methods, components, apparatuses, steps, etc., can be employed. In other instances, well-known methods, apparatuses, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this application.

[0026] This application provides a method for preparing copper foil 100, which is mainly used for preparing ultra-thick copper foil 100 (e.g., 210μm thick copper foil 100). The method includes raw foil electrolysis, roughening treatment and curing treatment.

[0027] Among them, the green foil electrolysis is the process of forming the main body of copper foil 100 by electrodeposition in an electrolyte. The green foil electrolysis mainly adopts a multi-step gradient electrodeposition process, which includes at least two deposition stages, and different current densities and different copper ion concentrations are used in different deposition stages to control the deposition kinetics, crystal morphology and internal stress distribution.

[0028] In some embodiments, gradient electrodeposition may include a first deposition stage, a second deposition stage, and a third deposition stage performed sequentially.

[0029] The purpose of the first deposition stage is to form a dense, mechanically strong substrate layer 110, providing a stable support for subsequent deposition. The process parameters can be selected within the following ranges: copper ion concentration in the electrolyte is 100-110 g / L, sulfuric acid concentration is 120-140 g / L, electrolyte temperature is maintained at 50-54℃, and current density is controlled at 40-50 A / dm². Deposition continues under these conditions until a dense substrate layer 110 with a thickness of approximately 70 μm is formed.

[0030] The purpose of the second deposition stage is to construct a uniform transition structure (transition layer 120) to alleviate interlayer stress and reduce defect formation. During this stage, composite additives are added to the electrolyte. Simultaneously, process parameters are adjusted: the copper ion concentration in the electrolyte is reduced to 90-100 g / L, the sulfuric acid concentration is adjusted to 100-120 g / L, the electrolyte temperature is maintained at 50-54℃, but the current density is increased to 60-70 A / dm². A copper layer of approximately 80 μm can be deposited during this stage.

[0031] The purpose of the third deposition stage is to refine the surface grain size to less than 5 μm and achieve a low roughness in the final working surface (refining layer 130). This stage further reduces the reaction intensity: a low-concentration electrolyte with a copper ion concentration of 80-90 g / L and a sulfuric acid concentration of 90-100 g / L is used, the liquid temperature is controlled at 48-52℃, and the current density is reduced to 30-40 A / dm². Finally, a final deposition of approximately 60 μm is completed, bringing the total thickness of the copper foil 100 to approximately 210 μm.

[0032] In other embodiments, ultrasonic assistance is employed in the third deposition stage, for example, by applying ultrasonic oscillations at a frequency of 40-100 kHz near the cathode roller 230, utilizing its cavitation effect to disrupt the boundary layer and promote grain refinement.

[0033] In some embodiments, the composite additive may include at least two components with different molecular weight ranges. For example, the composite additive includes a low molecular weight component and a medium molecular weight component.

[0034] The low molecular weight component is a polyethyleneimine (PEI) derivative with a molecular weight in the range of 800-2000 Da. Its main function is to rapidly diffuse and adsorb at the cathode deposition interface due to its small molecular size, acting as a primary grain refiner to effectively fill the micropores generated during the growth of copper foil 100 and reduce internal stress concentration points.

[0035] The medium molecular weight component is hydroxyethyl cellulose (HEC) with a molecular weight in the range of 10,000-30,000 Da. It mainly acts as a leveling agent, selectively inhibiting excessive dendrite growth during the deposition process, thereby significantly reducing the contour undulation of the 100mm rough surface of the copper foil and obtaining a smoother surface.

[0036] To achieve the best synergistic effect, the mass ratio of low molecular weight component to medium molecular weight component can be controlled within the range of 1.5-2.3:1. This ratio range can effectively balance the functions of rapid diffusion and micropore filling of low molecular weight component with the functions of dendrite suppression and surface leveling of medium molecular weight component, so that the two can work synergistically at the deposition interface to jointly optimize grain morphology and grain boundary structure.

[0037] Understandably, the total amount of composite additives added to the electrolyte should be precisely controlled, for example, to 10-50 ppm. This concentration range is sufficient to form an effective adsorption layer on the cathode surface to regulate the deposition process, while reducing the abnormal increase in electrolyte viscosity or side reactions caused by excessive addition, thus ensuring the stability of the deposition process and the reproducibility of the copper foil 100 performance.

[0038] The synergistic effect of low molecular weight polyethyleneimine (PEI) derivatives and medium molecular weight hydroxyethyl cellulose (HEC) refines the grains and optimizes the grain boundaries, thereby improving the compactness and grain boundary stability of copper foil 100 at high temperatures.

[0039] The copper foil 100 obtained by electrolysis of raw foil is roughened to construct a micro-rough structure on its surface, thereby enhancing the mechanical adhesion and bonding area with the insulating substrate (such as resin). The roughening process includes at least two stages, with the copper ion concentration in the electrolyte lower in each subsequent stage than in the previous stage. Controllable growth of the rough structure is achieved through a stepwise reduction in concentration and current.

[0040] In some alternative embodiments, the roughening process includes a three-stage roughening process.

[0041] In the first-stage roughening process, a high-concentration electrolyte is used, with a copper ion concentration of 18-22 g / L and a sulfuric acid concentration of 180-190 g / L. At a liquid temperature of 30-35°C, a high current density of 60-80 A / dm² is applied, with a short deposition time of approximately 5 seconds. Driven by the high concentration of copper ions and the high current, copper ions rapidly precipitate, forming relatively sparse but relatively large (approximately 1-2 μm) primary nodular crystals, which constitute the framework of the entire anchoring structure.

[0042] In the second-stage roughening process, the electrolyte concentration is adjusted to 14-16 g / L for copper ions and 160-180 g / L for sulfuric acid. The liquid temperature is maintained at 30-35°C, and the current density is reduced to 40-60 A / dm², with deposition lasting approximately 5 seconds. During this stage, the deposition rate slows down, allowing copper ions to deposit laterally and interstitially within the primary nodules, forming smaller, more densely distributed secondary nodules. This initially connects the isolated primary framework into a network.

[0043] In the third-stage roughening process, a lower concentration electrolyte is used, with copper ions at 10-12 g / L and sulfuric acid at 140-160 g / L. The liquid temperature is 30-35℃, and the current density is further reduced to 20-40 A / dm², with deposition lasting approximately 5 seconds. Under low concentration and low current conditions, the deposition tends to be uniform. This stage mainly fills the micropores formed in the first two stages and smooths the sharp protrusions, resulting in a three-dimensional network structure on a microscopic level and a smoother outline on a macroscopic level, providing an ideal substrate for subsequent curing treatment.

[0044] After roughening treatment, the copper foil 100 undergoes a curing process. This curing process aims to strengthen the bond between the roughened layer and the copper foil 100 substrate, welding them into a single unit, thereby significantly improving peel strength. The curing process in this method also includes at least two curing stages, with the copper ion concentration in the electrolyte lower in the later stage than in the earlier stage.

[0045] In some embodiments, the curing process includes a three-stage curing process.

[0046] In the first-stage curing process, an electrolyte with a high copper ion concentration (50-60 g / L) and a sulfuric acid concentration (95-105 g / L) is used. At a liquid temperature of 40-50°C, a high current density of 60-80 A / dm² is applied, and deposition lasts approximately 5 seconds. Utilizing the high copper concentration and strong current, blocky deposition rapidly occurs into the pores and valleys of the roughened layer, significantly increasing the actual contact and bonding area between the metals and enhancing the mechanical bonding force.

[0047] In the second-stage curing process, the electrolyte concentration is adjusted to a moderate level, with copper ions at 40-50 g / L and sulfuric acid at 80-90 g / L. The liquid temperature is maintained at 40-50℃, and the current density is reduced to 40-60 A / dm², with deposition lasting approximately 5 seconds. The reduced copper ion concentration and current in this stage result in a smoother deposition process. The formed copper layer effectively welds the blocky structure deposited in the first stage, making the entire cured layer a continuous and dense whole. This significantly improves its structural strength and adhesion to the substrate, thus significantly enhancing peel strength.

[0048] In the third-stage curing process, a low-concentration electrolyte is used, with copper ions at 30-40 g / L and sulfuric acid at 70-80 g / L. The electrolyte temperature is 40-50℃, and final deposition is carried out for approximately 5 seconds at a current density of 20-40 A / dm². This stage involves surface refinement to ensure a more uniform and smooth cured layer surface.

[0049] This application introduces composite additives in the second stage of multi-step gradient electrodeposition to synergistically regulate the deposition interface behavior, effectively improving the high-temperature elongation of copper foil 100 while significantly reducing its surface roughness. Furthermore, by utilizing a multi-step deposition process with gradient changes in current density and electrolyte concentration, the uniformity and density of the internal structure of copper foil 100 are optimized, thereby effectively reducing large-size copper nodule defects caused by concentration polarization while enhancing overall mechanical properties and further reducing roughness. In addition, by employing multi-stage roughening and curing treatment with decreasing concentration, a firmly bonded and uniformly structured interface layer is constructed on the surface of copper foil 100, ultimately achieving a significant improvement in peel strength.

[0050] See Figure 1As shown in the embodiments of this application, a high-performance ultra-thick electrolytic copper foil 100 prepared by the above method is also provided, with a thickness of 200 to 220 μm, for example, 200 μm, 210 μm, or 220 μm. This copper foil 100 is not an isotropic homogeneous material, but rather contains at least two copper layers with different average grain sizes along its thickness direction, which is a direct product of gradient electrodeposition.

[0051] Please continue to see Figure 1 As shown, the copper foil 100 can be a three-layer structure, which may include a base layer 110, a transition layer 120 and a refinement layer 130.

[0052] Among them, the base layer 110 corresponds to the layer formed in the first deposition stage mentioned above, and is the first layer deposited. This base layer 110 is formed under high concentration and high current, with a dense grain structure and high mechanical strength, which can provide basic support for the copper foil 100.

[0053] The transition layer 120 is located above the base layer 110 and is formed in the second deposition stage mentioned above. Under the action of composite additives and under the adjusted concentration and increased current, a uniform intermediate structure is formed. The transition layer 120 can coordinate the differences in physical properties between the base layer 110 and the refinement layer 130 and release internal stress.

[0054] The refinement layer 130 is located on the outermost side, which is the working surface in contact with the outside. The refinement layer 130 is formed in the third deposition stage mentioned above. This layer is deposited under low concentration, low current and ultrasonic assistance, and the grains are significantly refined.

[0055] It is understood that the average grain size of the refinement layer 130 is smaller than the average grain size of the substrate layer 110, for example, it can be refined to below 5 μm, thereby obtaining extremely low surface roughness.

[0056] The 210μm copper foil 100 prepared by the above-mentioned copper foil 100 preparation method can improve the high temperature elongation (180℃) to more than 16.4% (Example 1 below), reduce the surface roughness (MRz) to about 10.5μm, and maintain the peel strength above 2.2 N / mm. See Table 1 below. The synergistic optimization of the three key indicators of high temperature elongation, low roughness and high peel strength has been successfully achieved.

[0057] See Figure 2 As shown, this application embodiment also provides a foil production system 200 for effectively implementing the above-described preparation method. This system is a multi-stage continuous production apparatus, and the foil production system 200 may include at least two electrolytic cells 210, a guide roller assembly, and an additive dispensing unit 220.

[0058] The green foil system 200 may include three independent electrolytic cells 210 connected in series. The main body of the cell is welded from 20mm thick PPH (polypropylene) plates, which have excellent corrosion resistance and thermal stability. The effective volume of a single cell is approximately 5000 liters, and the external dimensions are approximately 3000mm in length, 1800mm in width, and 1500mm in height.

[0059] Among them, see Figure 2 As shown, the three independent electrolytic cells 210 are the first electrolytic cell 211, the second electrolytic cell 212, and the third electrolytic cell 213.

[0060] The first electrolytic cell 211 corresponds to the first deposition stage in the foil electrolysis process, and is equipped with an electrolyte with high copper ion concentration and high acid concentration to form a high-strength dense substrate layer 110.

[0061] The second electrolytic cell 212 corresponds to the second deposition stage. The electrolyte concentration and current density are moderate, and the composite additives are added in this second electrolytic cell 212 to form a uniform intermediate transition layer 120.

[0062] The third electrolytic cell 213 corresponds to the third deposition stage. It is equipped with a low-concentration electrolyte and a low current density, and can integrate an ultrasonic unit 250 to generate a fine-textured layer 130 with a delicate surface and low roughness.

[0063] Understandably, a set of inter-cell guide rollers (not shown) is installed at the inlet and outlet of each electrolytic cell 210. This roller set consists of passive guide rollers coated with polyurethane, with a roller diameter of up to 150 mm. It ensures the smooth and continuous transfer of the copper foil 100 substrate between different electrolytic cells 210 and precisely maintains the wrap angle of the copper foil 100 on the cathode roller 230 between 85° and 95°, thereby guaranteeing the continuity of the deposition process and the uniformity of the deposition area.

[0064] It is worth mentioning that, see Figure 2 As shown, the electrolytic cell 210 employs a large-diameter titanium cathode roller 230, with a diameter of 2.5m and a working surface width of 1400mm. The roller body is made of TA2 grade industrial pure titanium, with a roller wall thickness of 25mm to ensure sufficient mechanical strength and excellent conductivity. The drive system is driven by a 15kW servo frequency converter motor through a precision planetary reducer, enabling stepless speed regulation within the range of 0.1 to 5.0 rpm. When producing 210μm ultra-thick copper foil 100, the operating speed is approximately 0.8 rpm. To ensure the high uniformity of the copper foil 100 thickness, the radial runout of the cathode roller 230 is precisely controlled to ≤0.1mm.

[0065] See Figure 2As shown, each electrolytic cell 210 is equipped with an independent titanium anode box 240, with dimensions of 1500mm (length) × 1200mm (width) × 100mm (thickness). The surface of the anode box 240 is a 3mm thick titanium mesh, which is coated with a rare metal oxide coating such as IrTa (iridium-tantalum) to form an insoluble anode (DSA anode) with high catalytic activity and long lifespan. The effective electrode spacing between the anode mesh and the working surface of the cathode roller 230 can be set to 55mm. This distance has been optimized to achieve the best balance between ensuring uniform current density distribution and smooth electrolyte flow.

[0066] In addition, see Figure 2 As shown, the ultrasonic unit 250 can be integrated into the third electrolytic cell 213. Specifically, four independently controllable piezoelectric ceramic ultrasonic transducers are installed parallel to the surface of the cathode roller 230, 300 mm below the roller. Their operating frequency range is 40-100 kHz. This ultrasonic unit 250 effectively disrupts the ion concentration polarization of the diffusion boundary layer on the cathode surface through ultrasonic cavitation, promoting grain nucleation and refinement, and preventing hydrogen bubbles from adhering to the surface of the copper foil 100 and forming pits. The total power of the ultrasonic unit 250 is 5 kW, and its power density, calculated based on the effective liquid volume in the cell, is approximately 50 W / L. It also supports pulse mode operation to optimize energy efficiency and performance.

[0067] In some embodiments, see Figure 2 As shown, each electrolytic cell 210 is equipped with an independent plate heat exchanger 260, with a single heat exchange area of ​​approximately 15 m2. It is precisely controlled by a PID (proportional-integral-derivative) temperature control module to ensure that the temperature fluctuation of the electrolyte in each cell is strictly controlled within ±0.5°C.

[0068] In some embodiments, see Figure 2 As shown, the foil production system 200 also includes a circulation unit 270, which can employ a magnetically driven pump (flow rate of 50 L / min) to continuously circulate the electrolyte within the tank and external circulation pipes, maintaining uniformity in composition and temperature. A bag filter with a filtration accuracy of 1 μm is installed on the circulation pipeline to continuously remove any solid particles that may be present in the electrolyte, ensuring the cleanliness of the deposition surface.

[0069] See Figure 2As shown, the additive dosing unit 220 is a unit for achieving precise and uniform dosing of composite additives. It may include a three-channel metering pump and a central controller (such as a PLC). The three channels are used to deliver low molecular weight polyethyleneimine (PEI) derivatives, medium molecular weight hydroxyethyl cellulose (HEC), and a backup additive, respectively. Its control logic is as follows: the central controller calculates and dynamically adjusts the dosing speed of each channel metering pump in real time based on the real-time rotational speed and theoretical current (ampere-hours) of the cathode roller 230. This additive dosing unit 220 has extremely high control precision; the additive dosing rate can be controlled with an accuracy of ±0.1 mL / min, thereby ensuring a stable additive concentration and consistent effect throughout the entire ultra-thick deposition process.

[0070] The workflow of the foil production system 200 is briefly described as follows: The copper foil 100 substrate is first drawn out from the cathode roller 230 of the first electrolytic cell 211, passes through the cathode rollers 230 of the second electrolytic cell 212 and the third electrolytic cell 213 and the inter-cell guide rollers in sequence, and is finally connected to the winding device to complete the threading.

[0071] After system startup, copper foil 100 moves at a constant speed, initiating continuous production. First, the green foil electrolysis begins. In the first electrolytic cell 211, copper foil 100 is deposited at a high current density, forming a dense base layer 110 approximately 70 μm thick. Next, it enters the second electrolytic cell 212, where it continues deposition at an even higher current density in an electrolyte solution containing composite additives, depositing approximately 80 μm to construct a uniform transition layer 120. Finally, in the third electrolytic cell 213, under the combined action of low current density and integrated ultrasonic assistance, a final surface refinement deposition of approximately 60 μm is completed, resulting in a green foil with a total thickness of approximately 210 μm. After deposition, the ultra-thick copper foil 100 is drawn from the third electrolytic cell 213 and undergoes a series of independent surface treatment processes, including roughening, curing, and anti-oxidation, before finally being dried and wound up. The entire process, through multi-cell series connection and a precise control system, achieves integrated and continuous production of ultra-thick copper foil 100 from green foil to pretreatment.

[0072] Comparative Example 1 A relatively conventional ultra-thick copper foil preparation process was adopted: although the foil production process is divided into three deposition steps, no specific functional additives are used; the subsequent surface treatment only involves one roughening and one curing process.

[0073] Comparative Example 2 In the foil production process, a single additive (high molecular weight gelatin) was used, and three roughening and three curing treatments were carried out. However, the process conditions (such as electrolyte concentration and current density) for each roughening and curing were kept the same, and gradient treatment could not be achieved.

[0074] Example 1 Embodiment 1 of this application adopts the technical solution protected by this application: in the foil production stage, a composite additive with a specific ratio is used, and a three-stage deposition process with a gradient change in current density and copper ion concentration is adopted; in the subsequent processing, a three-stage roughening and three-stage curing process with decreasing concentration is adopted.

[0075] Example 2 Based on Example 1, the process details were further optimized, and the ultrasonic-assisted frequency in the third deposition stage was increased to 80kHz.

[0076] The performance comparison of the copper foils prepared by the above methods is shown in the table below:

[0077] Table 1 The data comparison in the table above clearly shows that the ultra-thick copper foil prepared using the method of this application (Examples 1 and 2) achieves a more than 100% improvement in high-temperature elongation compared to Comparative Examples 1 and 2, while significantly reducing surface roughness (MRz) and effectively suppressing the formation of large copper nodules, while maintaining excellent peel strength. This fully demonstrates that the technical solution of this application, which combines a composite additive system with segmented molecular weight control, multi-step gradient electrodeposition, and multi-level concentration-decreasing post-treatment, can successfully synergistically reduce the problem of simultaneously achieving multiple performance characteristics of ultra-thick copper foil.

[0078] In the description of this specification, references to terms such as "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application. Therefore, any changes or modifications made in accordance with the claims and description of this application should fall within the scope of this patent application.

Claims

1. A method for preparing copper foil, characterized in that, include: Electrolysis of raw foil: A multi-step electrodeposition is performed in an electrolyte to form a copper foil, the multi-step electrodeposition including at least two deposition stages with different current densities and different copper ion concentrations, during the deposition stages, a composite additive including at least two different molecular weight components is added to the electrolyte; Roughening treatment: The electrolyzed copper foil is subjected to roughening treatment, which includes at least two roughening stages, and the copper ion concentration in the electrolyte in the later roughening stage is lower than the copper ion concentration in the electrolyte in the previous roughening stage. Curing treatment: The roughened copper foil is cured, and the curing treatment includes at least two curing stages, wherein the copper ion concentration in the electrolyte in the later curing stage is lower than the copper ion concentration in the electrolyte in the previous curing stage.

2. The preparation method according to claim 1, characterized in that, The multi-step electrodeposition includes a first deposition stage, a second deposition stage, and a third deposition stage performed sequentially. The first deposition stage is carried out at a first current density and a first copper ion concentration; the second deposition stage is carried out at a second current density higher than the first current density and a second copper ion concentration lower than the first copper ion concentration, and the composite additive is added to the electrolyte; the third deposition stage is carried out at a third current density lower than the first current density and a third copper ion concentration lower than the second copper ion concentration.

3. The preparation method according to claim 2, characterized in that, The composite additive includes low molecular weight components and medium molecular weight components.

4. The preparation method according to claim 3, characterized in that, The mass ratio of the low molecular weight component to the medium molecular weight component is 1.5-2.3:

1.

5. The preparation method according to claim 3 or 4, characterized in that, The low molecular weight component is a polyethyleneimine derivative with a molecular weight of 800-2000 Da, and the medium molecular weight component is a hydroxyethyl cellulose with a molecular weight of 10000-30000 Da.

6. The preparation method according to claim 2, characterized in that, The third deposition stage is performed under ultrasonic-assisted conditions.

7. The preparation method according to claim 1, characterized in that, The total amount of the compound additive is 10-50 ppm.

8. A copper foil prepared using the copper foil preparation method according to any one of claims 1 to 7, characterized in that, The copper foil has a thickness of 200 to 220 μm and includes at least two copper layers with different average grain sizes along its thickness direction.

9. The copper foil according to claim 8, characterized in that, The at least two copper layers include a base layer, a transition layer, and a refinement layer. The transition layer is disposed between the base layer and the refinement layer, and the average grain size of the refinement layer is smaller than the average grain size of the base layer.

10. A green foil system for implementing the preparation method according to any one of claims 1-7, characterized in that, include: At least two electrolytic cells connected in series are used to sequentially perform different deposition stages of the multi-step electrodeposition. The guide roller assembly, located between adjacent electrolytic cells, is used to continuously transfer copper foil substrate between different electrolytic cells. The additive dripping unit includes a metering pump and a controller connected to the metering pump via a signal. The controller is used to control the dripping rate of the composite additive into the electrolyte in real time according to process parameters.

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