A method for quantitatively controlling the grain size of copper foil electrodeposited by power ultrasound

Abstract

The present application belongs to the technical field of electrolytic copper foil, and particularly relates to a method for quantitatively controlling grain size of electrodeposited copper foil by using power ultrasound. In the method, an ultrasonic field with a series of ultrasonic amplitudes is applied to an electrolyte to perform electrodeposition, and copper foils under different ultrasonic amplitudes are deposited on a cathode. An average grain size is exponentially fitted with the ultrasonic amplitude to obtain formula I. The ultrasonic amplitude is controlled according to the formula I to perform electrodeposition, and a copper foil with a required average grain size is obtained. In the method, the quantitative relationship between the power ultrasound characteristics and the grain size is combined, the ultrasonic amplitude is adjusted to realize copper foil grain refinement, and a functional correlation between the ultrasonic amplitude and the target grain size is established, so that the copper foil grain structure can be accurately and controllably prepared, the uniformity of the grain size is improved, the consistency and stability of the copper foil product are improved, and the method is suitable for preparing self-supporting or carrier type electrolytic copper foils with controllable grain size.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrolytic copper foil and particularly relates to a method for quantitatively controlling the grain size of electrodeposited copper foil by using power ultrasound. BACKGROUND

[0002] Copper foil has a wide range of applications in electronics, communications, batteries and other fields due to its excellent electrical conductivity, thermal conductivity and good ductility. In particular, in lithium-ion batteries and high-frequency high-speed circuits, copper foil, as one of the key materials, has increasingly high requirements for its performance. The mechanical properties, electrical conductivity and corrosion resistance of copper foil are largely dependent on its microstructure, especially the size and distribution of the grains. Therefore, controlling the refinement degree of copper foil grains is of great significance to improving its overall performance.

[0003] With the development of technology, copper foils with smaller thickness (such as thickness < 5 µm) are needed. Currently, the mainstream industrial technology uses electrodeposition method for preparation. However, in the traditional electrodeposition process, the grain growth is easily affected by factors such as ion diffusion rate, uneven distribution of current density and hydrogen evolution, resulting in coarse and unevenly distributed grains, which in turn limits the further improvement of the performance of copper foil. In the process of preparing copper foil by electrodeposition method, the grain size directly determines the key properties such as electrical conductivity, mechanical properties, thermal stability and interface bonding of the copper foil. Excessive grain size can lead to a decrease in mechanical strength of the material, weakening of the grain boundary and poor reliability. On the other hand, too fine grain size can cause an increase in electron scattering at the grain boundary, resulting in a decrease in electrical conductivity, especially in high-frequency electronic applications. In addition, uneven grain size can also cause stress concentration and performance fluctuations in the copper foil, reducing the consistency and stability of the product. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a method for quantitatively controlling the grain size of electrodeposited copper foil by using power ultrasound. The present application establishes a functional relationship between the ultrasonic amplitude and the grain size of the copper foil, and inversely calculates the ultrasonic amplitude corresponding to the desired grain size of the copper foil, thereby achieving precise control of the grain size of the copper foil and improving the consistency and stability of the copper foil product.

[0005] In order to achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] The present application provides a method for quantitatively controlling the grain size of electrodeposited copper foil by using power ultrasound, comprising the following steps:

[0007] (1) applying an ultrasonic field with a series of ultrasonic amplitudes in the electrolyte for electrodeposition to deposit copper foils with different ultrasonic amplitudes on the cathode;

[0008] (2) obtaining the average grain size of the copper foil under different ultrasonic amplitudes in step (1), and performing exponential fitting on the average grain size of the copper foil under different ultrasonic amplitudes and the series of ultrasonic amplitudes to obtain a functional relationship between the average grain size and the ultrasonic amplitude, as shown in formula I:

[0009] Formula I, wherein d is the average grain size, in units of µm, A is the ultrasonic amplitude, in units of µm, d 0 , k and d min is a fitting parameter;

[0010] (3) setting the ultrasonic amplitude of the ultrasonic field in step (1) to the ultrasonic amplitude corresponding to the required average grain size of the copper foil determined according to the formula I, and continuing the electrodeposition of step (1) to obtain a copper foil with the required average grain size.

[0011] Preferably, the frequency of the ultrasonic field is 20-100 kHz; the series of ultrasonic amplitudes is any three or more point values in the range of 2-42 µm; and the ultrasonic field is a continuous ultrasonic field or an intermittent ultrasonic field.

[0012] Preferably, the current density of the electrodeposition is 0.5-100 A / dm 2 ; the current during the electrodeposition process is a constant current; the temperature of the electrolyte during the electrodeposition process is 20-60℃; and the time of the electrodeposition is 5-3600 s.

[0013] Preferably, the equipment used for the electrodeposition is an electrolytic cell; and the distance between the anode and the cathode in the electrolytic cell is 1-5 cm.

[0014] Preferably, the electrolyte comprises a soluble copper salt, a conductive medium, and a solvent; the soluble copper salt comprises one or more of copper sulfate, copper chloride, and copper pyrophosphate; and the conductive medium comprises sulfuric acid and / or sodium chloride.

[0015] Preferably, the mass concentration of the soluble copper salt in the electrolyte is 70-80 g / L, and the mass concentration of the conductive medium is 90-100 g / L.

[0016] Preferably, the generating device of the ultrasonic field is an ultrasonic emission system; and the ultrasonic emission system comprises an ultrasonic power supply, an ultrasonic transducer, and an amplitude changer.

[0017] Preferably, the lower end ultrasonic emission end portion of the amplitude horn is located near the cathode and directly inserted into the electrolyte; the diameter of the lower end ultrasonic emission end portion of the amplitude horn is > 5 mm; the distance between the lower end ultrasonic emission end portion of the amplitude horn and the cathode is < 10 cm.

[0018] Preferably, the thickness of the copper foil is 0.5-20 µm.

[0019] Preferably, the average grain size of the copper foil is 0.3-2 µm.

[0020] The present application provides a method for quantitatively controlling the grain size of electrodeposited copper foil using power ultrasound, comprising the following steps:

[0021] (1) applying an ultrasonic field with a series of ultrasonic amplitudes in the electrolyte for electrodeposition to deposit copper foils under different ultrasonic amplitudes on the cathode;

[0022] (2) obtaining the average grain size of the copper foils under different ultrasonic amplitudes in step (1), and performing exponential fitting of the average grain size of the copper foils under different ultrasonic amplitudes with the series of ultrasonic amplitudes to obtain a functional relationship between the average grain size and the ultrasonic amplitude, as shown in formula I:

[0023] Formula I, wherein d is the average grain size, unit µm, A is the ultrasonic amplitude, unit µm, d 0 , k and d min is a fitting parameter;

[0024] (3) setting the ultrasonic amplitude of the ultrasonic field in step (1) to the ultrasonic amplitude corresponding to the required average grain size of the copper foil determined according to the formula I, and continuing the electrodeposition of step (1) to obtain the copper foil with the required average grain size.

[0025] The present application combines the quantitative relationship between the power ultrasound characteristics and the grain size, realizes the grain refinement of the copper foil by adjusting the ultrasonic amplitude, and establishes the functional relationship between the ultrasonic amplitude and the target grain size, thereby realizing the precise and controllable preparation of the copper foil grain structure, improving the uniformity of the grain size, and improving the consistency and stability of the copper foil product. This method is suitable for preparing self-supporting or carrier type electrolytic copper foils with controllable grain size, and can be widely applied in the manufacturing of lithium battery current collectors, high-frequency circuits and precision electronic materials. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1Schematic diagram of the structure of the device used for the method of controlling the grain size of copper foil in the examples, wherein (a) is the side view, (b) is the top view, 1 is the amplitude horn, 2 is the electrolytic cell, 3 is the cathode, and 4 is the anode.

[0027] Figure 2 The grain size distribution diagram of the self-supporting copper foil under different ultrasonic amplitudes in Example 1.

[0028] Figure 3 The grain size distribution diagram of the copper foil with carrier under different ultrasonic amplitudes in Example 2. DETAILED DESCRIPTION

[0029] The present application provides a method for quantitatively controlling the grain size of electrodeposited copper foil by using power ultrasound, comprising the following steps:

[0030] (1) applying an ultrasonic field with a series of ultrasonic amplitudes in the electrolyte to carry out electrodeposition, and depositing copper foils under different ultrasonic amplitudes on the cathode;

[0031] (2) obtaining the average grain size of the copper foils under different ultrasonic amplitudes in step (1), and performing exponential fitting on the average grain size of the copper foils under different ultrasonic amplitudes and the series of ultrasonic amplitudes to obtain a functional relationship between the average grain size and the ultrasonic amplitude, as shown in formula I:

[0032] Formula I, wherein d is the average grain size, unit µm, A is the ultrasonic amplitude, unit µm, d 0 , k and d min is a fitting parameter;

[0033] (3) setting the ultrasonic amplitude of the ultrasonic field in step (1) to the ultrasonic amplitude corresponding to the required average grain size of the copper foil determined according to the formula I, and continuing the electrodeposition of step (1) to obtain the copper foil with the required average grain size.

[0034] Unless otherwise specified, the present application has no special requirements for the source of the raw materials used, and commercially available goods known to those skilled in the art can be used.

[0035] Step (1), the present application applies an ultrasonic field with a series of ultrasonic amplitudes in the electrolyte to carry out electrodeposition, and deposits copper foils under different ultrasonic amplitudes on the cathode.

[0036] As an embodiment, the equipment for the electrodeposition is an electrolytic cell; the material of the cathode is a substrate with electrical conductivity; the substrate with electrical conductivity includes a stainless steel plate, an industrial pure titanium plate, a nickel sheet, a copper foil or a substrate with electrical conductivity treatment, and in particular embodiments, an industrial pure titanium plate; the substrate in the substrate with electrical conductivity treatment includes a glass or a polymer film; the polymer film is a polyimide (PI) film or a PET carbon film; the glass is ITO glass; the electrical conductivity treatment includes metal sputtering or surface coating of an electrical conductivity coating, and in particular embodiments, metal sputtering of an electrical conductivity coating; the metal sputtering is vacuum sputtering of a copper layer; the surface coating of the electrical conductivity coating is in the form of chemical plating or electroplating, and in particular embodiments, chemical plating; the electrical conductivity coating includes an electrical conductivity polymer coating or a carbon-based coating, and in particular embodiments, an electrical conductivity polymer coating; the thickness of the cathode is 0.1-3 mm, and in particular embodiments, 3 mm; the titanium plate has good electrical conductivity, mechanical strength and electrolytic stability.

[0037] As an embodiment, the preparation method of the cathode includes cutting the material of the cathode to a size suitable for the size of the electrolytic cell, and sequentially polishing, first cleaning, activation treatment and second cleaning; the polishing is mechanical polishing with sandpaper or polishing paste; the model of the sandpaper is 1000-3000, and in particular embodiments, 2000; the polishing paste is microparticle alumina; the particle size of the microparticle alumina is 0.5-2.5 µm, and in particular embodiments, 1-2 µm; the first cleaning is ultrasonic cleaning after water rinsing; the water is deionized water; the ultrasonic power of the ultrasonic cleaning is 100-1000 W, and in particular embodiments, 500-800 W, the temperature is 20-30 °C, and in particular embodiments, 25 °C, the time is 10-15 min, and in particular embodiments, 10 min; the activation treatment is immersing the material of the cathode after the first cleaning in a sulfuric acid solution; the concentration of the sulfuric acid solution is 5-10 wt%, and in particular embodiments, 10 wt%; the time of the activation treatment is 1-5 min, and in particular embodiments, 3 min; the second cleaning is rinsing with deionized water until the pH value of the effluent is 6.5-7.5, and in particular embodiments, 7.0. The polishing can remove the surface oxide layer and mechanical stress layer of the cathode material. The first cleaning can remove the residual particles and organic contaminants on the surface of the cathode material. The activation treatment helps to remove the natural oxide film on the surface of the cathode material, enhances the surface roughness and activity, and thus improves the initial nucleation density of copper and the adhesion of the deposited layer.

[0038] As an embodiment, the material of the anode in the electrolytic cell is an insoluble inert anode or a soluble copper anode, and in a specific embodiment, the material of the anode is an insoluble inert anode; the insoluble inert anode is an iridium tantalum titanium electrode; and the iridium tantalum titanium electrode is an iridium tantalum titanium coated titanium plate. The material of the anode is selected according to the stability of the electrodeposition system and the requirement of the metal source, and the anode used in the application has good electrochemical stability, corrosion resistance and electrical conductivity.

[0039] As an embodiment, the surface area of the anode is greater than that of the cathode; before the electrodeposition, the anode is sequentially subjected to water washing and acid washing; the water washing is deionized water flushing; the acid used in the acid washing is a sulfuric acid solution; the concentration of the sulfuric acid solution is 5-10wt%, and in a specific embodiment, the concentration is 5wt%; the temperature of the acid washing is 40-60℃, and in a specific embodiment, the temperature is 50℃; the time of the acid washing is 1-5min, and in a specific embodiment, the time is 3min; and after the water washing, the acid washing is replaced by acetone cleaning.

[0040] In the application, the specifications of the anode and the cathode are matched, and the surface area of the anode is greater than that of the cathode, so as to ensure uniform distribution of the electric field. Before use, the anode should be flushed with deionized water, and the surface of the anode can be acid washed according to the specific situation, so as to remove the oxidation pollutants in the transportation and storage process.

[0041] As an embodiment, the distance between the anode and the cathode is 1-5cm, and in a specific embodiment, the distance is 2-3cm. The above distance can be used to obtain a relatively uniform electric field strength distribution, so as to ensure uniform deposition of copper ions on the surface of the cathode.

[0042] As an embodiment, the electrolyte is a water-soluble electrolyte containing copper ions, and another embodiment includes a soluble copper salt, a conductive medium and a solvent; the soluble copper salt includes one or more of copper sulfate (CuSO4), copper chloride (CuCl2) and copper pyrophosphate (K2CuP2O7), and in a specific embodiment, the soluble copper salt is copper sulfate; the conductive medium includes sulfuric acid (H2SO4) and / or sodium chloride (NaCl), and in a specific embodiment, the conductive medium is sulfuric acid; the solvent includes water or a mixture of water and ethanol, and in a specific embodiment, the solvent is water; the mass concentration of the soluble copper salt in the electrolyte is 70-80g / L, and in a specific embodiment, the mass concentration is 80g / L; and the mass concentration of the conductive medium is 90-100g / L, and in a specific embodiment, the mass concentration is 100g / L.

[0043] When copper sulfate is used, the release rate of copper ions is stable, and a dense fine-grained structure can be obtained; in copper chloride, Cl -The presence of the additive can promote the selective adsorption of crystal faces, which is conducive to the refinement of the crystal grains and the formation of specific texture; the copper pyrophosphate system is suitable for neutral to weak alkaline environment. Sulfuric acid can provide a strong acidic environment, which is helpful for the formation of dense crystals and the improvement of the conductivity of the electrolyte; the chloride ion (Cl - ) in sodium chloride can participate in the regulation of the crystal grains and promote the refinement of the crystal grains.

[0044] As an embodiment, the electrolyte further comprises an additive; the additive comprises one or more of brightener, accelerator, inhibitor, adsorption type additive, complexing agent and synergist, and in particular embodiments, the brightener and the synergist; the brightener comprises one or more of polyethylene glycol (PEG), polypropylene glycol (PPG) and polyglycerol, and in particular embodiments, the polyethylene glycol; the number average molecular weight of the polyethylene glycol (PEG) is 200-1000, and in particular embodiments, 300-500; the addition amount of the brightener in the electrolyte is 50-500 mg / L, and in particular embodiments, 100-300 mg / L; the accelerator comprises sodium dimercaptopropane sulfonate (SPS) and / or 3-mercapto-1-propane sulfonic acid (MPS), and in particular embodiments, the sodium dimercaptopropane sulfonate; the addition amount of the accelerator in the electrolyte is 5-20 mg / L, and in particular embodiments, 10-15 mg / L; the inhibitor comprises carboxymethyl cellulose (CMC) and / or polyacrylamide (PAM), and in particular embodiments, the carboxymethyl cellulose; the addition amount of the inhibitor in the electrolyte is 10-200 mg / L, and in particular embodiments, 20-100 mg / L; the synergist is a substance containing chloride ion (Cl - ); the substance containing chloride ion (Cl - ) comprises NaCl and / or KCl, and in particular embodiments, the NaCl; the addition amount of the synergist in the electrolyte is 10-100 mg / L, and in particular embodiments, 20-50 mg / L; the adsorption type additive comprises imidazole substance and / or collagen, and in particular embodiments, the collagen; the imidazole substance comprises one or more of 2-methyl imidazole, 2-mercapto imidazole, 1,2-dimethyl imidazole, benzyl imidazole and ethyl imidazole, and in particular embodiments, the 2-methyl imidazole; the addition amount of the adsorption type additive in the electrolyte is 1-20 mg / L, and in particular embodiments, 5-10 mg / L; the complexing agent is pyrophosphoric acid and / or amine complexing agent; the amine complexing agent comprises one or more of ethylenediamine, triethanolamine and diethylenetriamine, and in particular embodiments, the triethanolamine; the addition amount of the complexing agent in the electrolyte is 50-2000 mg / L, and in particular embodiments, 200-1000 mg / L.

[0045] The present application adds additives to the electrolyte to adjust the morphology and performance of the deposited copper layer. The additives can improve the grain structure, surface flatness and physical properties of the deposited copper foil. Brighteners are used to suppress tip deposition, smooth the copper foil surface, and refine the grains. Accelerators are used to increase the electrodeposition rate, speed up the formation of crystal nuclei, and control the grain size. Inhibitors are used to control the ion migration speed and deposition speed, and prevent the formation of coarse grains. Synergists often work synergistically with other additives to improve flatness and grain refinement. In the present application, multiple additives work together to inhibit abnormal grain growth, improve the smoothness and density of the copper layer.

[0046] When the soluble copper salt is copper sulfate, the additives in the electrolyte include brighteners, synergists and accelerators; the brightener is polyethylene glycol (PEG); the synergist is a substance containing chloride ions (Cl - ); the accelerator is 3-mercapto-1-propanesulfonic acid (MPS); this electrolyte system is suitable for the deposition of high-brightness copper foil. When the soluble copper salt is copper chloride, the additives in the electrolyte include adsorption-type additives, and this electrolyte system is used to control the growth preference. When the soluble copper salt is copper pyrophosphate, the additive in the electrolyte is a complexing agent, and this electrolyte system is suitable for neutral to weakly basic environments and is suitable for low-stress deposition requirements of microelectronic devices.

[0047] As an embodiment, the preparation method of the electrolyte is: mixing the soluble copper salt, the conductive medium and the solvent, performing magnetic stirring, then standing, filtering; the temperature of the magnetic stirring is room temperature ~ 60℃, in specific embodiments it is 30 ~ 50℃, the rate is 200 ~ 600rpm, in specific embodiments it is 400rpm, the time is 10 ~ 60min, in specific embodiments it is 30 ~ 50min; the standing time is 10 ~ 30min, in specific embodiments it is 20min; the pore size of the filter membrane used for filtering is 0.22 ~ 1µm, in specific embodiments it is 0.5µm. The present application completely dissolves the soluble copper salt and the conductive medium by magnetic stirring, and removes impurities or suspended particles by standing and filtering to ensure that the electrolyte system is clean and stable.

[0048] As an embodiment, the ultrasonic field generating device is an ultrasonic emission system; the ultrasonic emission system comprises an ultrasonic power supply, an ultrasonic transducer and a horn; the ultrasonic transducer is installed on the top of the electrolytic cell, and the ultrasonic transducer is connected with the horn through a mechanical connection to form a complete energy transmission path; the lower end ultrasonic emission end part of the horn is located near the cathode and is directly inserted into the electrolyte; the diameter of the lower end ultrasonic emission end part of the horn is > 5 mm, and in a specific embodiment, it is ≥ 15 mm; the material of the horn is titanium alloy, stainless steel or quartz, and in a specific embodiment, it is titanium alloy; the material of the horn is a material with excellent acoustic performance and corrosion resistance, and the material of the horn cannot chemically react with the electrolyte.

[0049] As an embodiment, the distance between the lower end ultrasonic emission end part of the horn and the cathode is < 10 cm, and in a specific embodiment, it is 0.5-2 cm. The lower end ultrasonic emission end part of the horn is inserted into the electrolyte and is close to the deposition area (cathode), and the distance d between the emission end and the cathode has a significant effect on the sound pressure field distribution and cavitation effect. The present application uses the distance between the emission end and the cathode in the above range to obtain the maximum local disturbance and the most effective grain refinement effect. Too close may cause local cavitation to destroy the deposition morphology, and too far may attenuate the ultrasonic energy and weaken the effect.

[0050] As an embodiment, when the material of the horn can react with the electrolyte, a protective coating is provided on the outer surface of the horn; the material of the protective coating comprises one or more of silicon dioxide, aluminum oxide, polytetrafluoroethylene and polyvinylidene fluoride, and in a specific embodiment, it is silicon dioxide or aluminum oxide; the thickness of the protective coating is 5-50 µm, and in a specific embodiment, it is 10-20 µm; the protective coating does not react with the electrolyte, the adhesion level between the protective coating and the horn reaches HF1 level, and the peel strength is > 20 N / cm. σ The calculation formula of the peel strength is: σ = 2π σ · ρ ·(2π h ) f 2 · A 0, wherein: ρ ρ is the density of the material used for the protective coating (kg / m³); h h is the thickness of the protective coating (m); f f is the ultrasonic vibration frequency of the ultrasonic field (Hz); A A0 is the ultrasonic amplitude (µm).

[0051] ​The protective coating in the present application is arranged to prevent the amplitude rod from being corroded in the strong acidic electrolyte, so as to ensure the structural integrity and energy transmission efficiency of the amplitude rod in long-term operation, and ensure the efficient transmission of ultrasonic energy. The protective coating used in the present application is chemically stable with the electrolyte, and the adhesion strength with the body of the amplitude rod is greater than the amplitude and frequency requirement. By arranging the protective coating with high adhesion strength on the surface of the amplitude rod, not only the direct corrosion of the electrolyte to the substrate of the amplitude rod is effectively avoided, but also the structural integrity and adhesion stability are maintained under the condition of high-frequency ultrasonic vibration, so that the long-term stable use of the amplitude rod in the strong corrosion environment is realized, the durability and service life are significantly improved, and the equipment maintenance frequency and cost are reduced.

[0052] Figure 1 The structural schematic diagram of the device used for the method for controlling the grain size of the copper foil in the embodiment is shown in Figure 1, in which (a) is a side view and (b) is a top view. Figure 1 As can be seen from Figure 2, the amplitude rod is inserted into the electrolyte of the electrolytic cell and located between the cathode and the anode.

[0053] As an embodiment, the frequency of the ultrasonic field is 20-100 kHz, and in a specific embodiment, the frequency is 20-50 kHz; the amplitude of the series of ultrasonic waves is any value of more than 3 points in the range of 2-42 µm, and in a specific embodiment, the amplitude is 18 µm, 30 µm and 42 µm; the ultrasonic field is a continuous ultrasonic field or an intermittent ultrasonic field, and in a specific embodiment, the ultrasonic field is a continuous ultrasonic field. In the present application, the ultrasonic field is a continuous ultrasonic field to maintain a stable acoustic field environment. The frequency of the ultrasonic field has an influence on the cavitation threshold and the bubble size distribution, and a lower frequency (20-40 kHz) is conducive to the enhancement of cavitation intensity and the refinement of grains; a higher frequency is suitable for more fine and stable control.

[0054] As an embodiment, the specific process of the electrodeposition is as follows: the cathode and the anode are placed in the electrolytic cell, the electrode distance of the cathode and the anode is adjusted, the liquid level of the electrolyte is kept 2-3 cm higher than the top of the electrode, the electrolytic cell is placed in a constant-temperature water bath, the temperature of the electrolyte is controlled to be stable, power is turned on, the ultrasonic emission system is started to work synchronously, and electrodeposition is carried out; the current density of the electrodeposition is 0.5-100 A / dm 2 , and in a specific embodiment, the current density is 5-80 A / dm 2 ; the current in the electrodeposition process is a constant current; the temperature of the electrolyte in the electrodeposition process is 20-60 ℃, and in a specific embodiment, the temperature is 25-40 ℃; the time of the electrodeposition is 5-3600 s, and in a specific embodiment, the time is 30-600 s. The time t of the electrodeposition refers to the continuous deposition time experienced from the connection to the disconnection of the power supply, which depends on the target thickness of the expected copper foil and the deposition rate.

[0055] During the electrodeposition process, the current and ultrasound are applied to the electrolytic cell system at the same time to form a sound and electric coupling deposition environment, which helps to inhibit hydrogen evolution, enhance the migration rate of copper ions, and significantly affect the nucleation and growth behavior of copper.

[0056] When the electrolyte uses high-concentration copper salt or strong complex additive system, the current density can be appropriately reduced and the temperature of the electrolyte can be increased to prevent dendrite growth or surface roughness; when the additive concentration is high, the electrodeposition time should be appropriately prolonged and the current density should be reduced to avoid defects caused by too fast deposition.

[0057] When the electrolytic cell is a small experimental platform, and the distance between the cathode and the anode is less than 2 cm, a low current density (<20 A / dm 2 ) is suitable; when the electrolytic cell system is assisted by high-efficiency stirring or ultrasound, it can withstand higher current density and shorter deposition time.

[0058] When the target is sub-micron grain copper foil, a higher current density (such as 8-12 A / dm 2 ) is selected to promote rapid nucleation; when the target is copper foil with good structural uniformity and dense surface, a medium electrolyte temperature (30-40°C) and a moderate deposition rate are selected to regulate the grain growth rate.

[0059] The use of the above range of current density can not only improve the supersaturation of copper ions and enhance the nucleation rate, but also help to obtain smaller and more uniform grains, and avoid hydrogen evolution or dendrite growth caused by excessive current, which can damage the structural integrity. The use of the above range of electrolyte temperature can not only improve the diffusion rate of copper ions, but also help the growth and expansion of copper foil grains, tend to form larger grains, and can also delay grain growth, which is beneficial to grain refinement, and can also avoid defects and reduce deposition efficiency caused by low temperature. The deposition time directly determines the thickness of the copper foil; the grain structure is more easily affected by the initial conditions in the early deposition stage, and prolonging the deposition time will promote grain growth, even secondary recrystallization, leading to an increase in grain size. Therefore, if the target is fine-grained copper foil, the deposition should be terminated within the time interval when the grain size has not yet significantly increased.

[0060] Step (2), the average grain size of the copper foil obtained in step (1) under different ultrasonic amplitudes is obtained, and the average grain size of the copper foil under different ultrasonic amplitudes is exponentially fitted with the series of ultrasonic amplitudes to obtain a functional relationship between the average grain size and the ultrasonic amplitude, as shown in formula I:

[0061] Formula I, wherein d is the average grain size, unit µm, A is the ultrasonic amplitude, unit µm, d 0 ,k and d min fitting parameters.

[0062] As an embodiment, the process of obtaining the average grain size of the copper foil is as follows: immediately after the electro-deposition is completed, the power supply of the electrolytic cell and the generating device of the ultrasonic field are turned off, the cathode is taken out of the electrolytic cell, and then cleaning, dehydration treatment and drying are sequentially performed, and then the copper foil is peeled off from the cathode to obtain a free copper foil; the free copper foil is subjected to scanning electron microscope detection to obtain the average grain size of the copper foil; the cleaning is rinsing with deionized water; the solvent used for the dehydration treatment is ethanol; the temperature of the drying is 50-80°C, and in specific embodiments, it is 60°C, and the time is 0.5-5 min, and in specific embodiments, it is 1-3 min; the drying device is an oven; the present application does not have special limitations on the peeling method, and blades or other mechanical means can be used.

[0063] As an embodiment, the ultrasonic amplitude is detected by an instrument capable of measuring 20-100 kHz periodic displacement, and in specific embodiments, it is a laser vibration measuring instrument; the specific measurement process of the ultrasonic amplitude is as follows: an instrument capable of measuring 20-100 kHz periodic displacement is used to measure the ultrasonic amplitude under different power output driving voltages of the ultrasonic field generating device.

[0064] As an embodiment, the functional relationship between the average grain size and the ultrasonic amplitude is .

[0065] The effects of the thickness of the copper foil on the grain size are mainly as follows: the thickness of the copper foil indirectly regulates the grain size by affecting the grain growth time and space: 1. Grain growth space effect: in thin copper foils (<5 µm), the lateral and vertical growth space of the grains is limited, and the grain size is more dependent on the initial nucleation stage conditions, and the structure is usually fine and uniform. 2. Deposition time and recrystallization: when the thickness of the copper foil is larger (>10 µm), the extension of the deposition time may lead to the growth and preferred orientation evolution of the grains along the thickness direction, and even the increase of local coarsening or twin structure.

[0066] After a period of time t of electro-deposition, a copper foil with a target thickness h is formed, and the grain structure is refined; t and h are flexibly set according to product design, the copper foil can be a self-supporting structure or a carrier structure, and is suitable for various high-performance electronic application scenarios.

[0067] There is a predictable functional relationship between the average grain size of the copper foil and the amplitude of the applied ultrasonic waves in the present application. By conducting a series of exploratory deposition experiments in advance, the functional relationship can be obtained and used to guide the actual process parameter adjustment, thereby achieving the reverse deduction of the target grain size and the selection of the amplitude parameter. This strategy improves the repeatability and control efficiency of the grain structure control, and has obvious advantages. The ultrasonic amplitude selection method includes: ① measuring the ultrasonic amplitude response under different ultrasonic driving voltages with a laser vibration meter or the like; ② combining the pre-experiment to obtain the fitting function relationship between the ultrasonic amplitude and the grain size; ③ inputting the target grain size d to reverse the required ultrasonic amplitude A through the fitting relationship; and ④ applying the amplitude in the actual deposition process to achieve accurate control of the grain structure.

[0068] Step (3), the ultrasonic amplitude of the ultrasonic field in step (1) is set to the ultrasonic amplitude corresponding to the required average grain size of the copper foil determined according to the formula I, and the electro-deposition of step (1) is continued to obtain the copper foil with the required average grain size.

[0069] As an embodiment, the ultrasonic amplitude corresponding to the required average grain size of the copper foil determined according to the formula I is any value in the range of >0 and ≤42 μm, and in a specific embodiment, it is 2-42 μm.

[0070] As an embodiment, the thickness of the copper foil is 0.5-20 μm, and in another embodiment, it is 1-10 μm, and in a specific embodiment, it is 5 μm. The thickness h of the copper foil refers to the vertical thickness of the copper layer obtained by electro-deposition, which can be adjusted according to the requirements of different application scenarios: for copper foils for electronic devices such as high-frequency flexible circuits, the thickness of the copper foil is 2-5 μm; for battery current collectors or support type copper foils, the thickness of the copper foil is 5-20 μm; for ultra-thin self-supporting copper foils, such as applications of <2 μm, short-time high-current density electro-deposition can also be used to achieve.

[0071] As an embodiment, the average grain size of the copper foil is 0.3-2 μm, and in a specific embodiment, it is 0.4-1 μm.

[0072] In step (3), the electrolyte, electrolytic cell and ultrasonic field in the electro-deposition process are consistent with step (1), which will not be repeated here.

[0073] The ultrasonic amplitude of the present application A According to the target grain size d is preset, and is selected by reverse deduction according to the function relationship established by the pre-experiment.

[0074] The application prepares copper foil through ultrasonic-assisted electrodeposition, the grain structure of the copper foil is uniform and dense, the copper foil has strong mechanical properties and bonding strength, and is suitable for manufacturing high-end electronic functional components such as lithium batteries and integrated circuits. The application realizes fine control of the microstructure of the copper foil by constructing a functional relationship between ultrasonic regulation and grain size, avoids relying on experience for parameter adjustment, improves the repeatability and engineering adaptability of the preparation process, simplifies the process, reduces the cost and enhances the stability without changing the conventional electrolyte system, and has good industrial popularization value.

[0075] The technical solutions in the application will be clearly and completely described below in combination with the embodiments in the application, but they should not be understood as limitations on the protection scope of the application.

[0076] Example 1

[0077] (1) Electrolyte preparation

[0078] The electrolyte required for copper electrodeposition is prepared by using copper sulfate (CuSO4·5H2O) and sulfuric acid (H2SO4) as main components, and water as solvent, wherein the mass concentration of copper sulfate is 80 g / L, and the mass concentration of sulfuric acid is 100 g / L. In addition, additives, polyethylene glycol (PEG, the number average molecular weight is 400, and the addition amount in the electrolyte is 200 mg / L) and sodium chloride (the addition amount in the electrolyte is 20 mg / L) are added to the electrolyte. After the electrolyte is prepared, it is completely dissolved by magnetic stirring (stirring at 400 rpm for 30 min) at 30°C, and after standing for 20 min, it is filtered with a 0.5 µm filter membrane to remove impurities or suspended particles, so as to ensure that the system is clean and stable;

[0079] (2) Electrolytic cell configuration

[0080] An industrial pure titanium plate with a thickness of 3 mm is selected as a cathode substrate for electrodeposition, the titanium plate is cut to a size suitable for the size of the electrolytic cell, and after mechanical polishing with 2000 grit sandpaper, it is thoroughly washed with deionized water and ultrasonically cleaned at a power of 800 W for 10 min; after cleaning, the titanium plate is immersed in a 10 wt% dilute sulfuric acid solution for activation treatment for 3 min, and immediately after activation, it is thoroughly washed with deionized water until the pH value of the effluent is 7.0;

[0081] An iridium tantalum titanium coated titanium plate is used as an insoluble anode, the anode plate is matched with the cathode (titanium substrate) in size, and the surface area thereof should be equivalent to or slightly larger than the cathode area. The anode is washed with deionized water before use, and the surface is pickled with a 5 wt% dilute sulfuric acid solution at 50°C for 3 min;

[0082] The distance between the anode and the cathode is set to 3 cm;

[0083] (3) Ultrasonic emission system setting

[0084] An ultrasonic emission system is arranged, with its emission tip located near the deposition area and inserted into the electrolyte, 2 cm away from the cathode. The ultrasonic emission system is composed of an ultrasonic power supply, an ultrasonic transducer, and a horn. The ultrasonic transducer is installed on the top of the electrolytic cell and connected to the horn through a mechanical connection to form a complete energy transmission path. The lower end of the horn, the ultrasonic emission end part (15 mm in diameter), is directly inserted into the electrolyte, and its material is titanium alloy.

[0085] The working frequency of the ultrasonic generator is 20 kHz, and the amplitude of the ultrasonic emission end ranges from 12 to 42 µm. The ultrasonic system works continuously to maintain a stable acoustic field environment.

[0086] (4) Electrodeposition process

[0087] The treated cathode and anode are placed in the electrolytic cell, and the electrode distance is adjusted to the set value. The liquid level of the electrolyte is kept 2-3 cm higher than the top of the electrode. The electrolytic cell is placed in a 40°C constant temperature water bath to control the solution temperature stably.

[0088] After power-on, a constant current density of 8.0 A / dm² is applied, and the ultrasonic system is started to work synchronously. The deposition time is 150 s. During the electrodeposition process, the current and ultrasonic are applied to the system simultaneously to form an acoustic and electric coupling deposition environment, and a copper foil with a thickness of 5 µm is obtained. The laser vibration meter is used to measure the series of ultrasonic amplitudes under different ultrasonic driving voltages, which are 0, 18, 30, and 42 µm.

[0089] (5) Copper foil collection and detection

[0090] After deposition, the power and ultrasonic system are turned off, the titanium substrate is taken out of the electrolytic cell, the deposited copper layer is thoroughly rinsed with deionized water to remove residual electrolyte, and then dehydrated with ethanol. After drying in a 60°C oven for 1 min, the copper foil is peeled off from the titanium plate using a blade to obtain a free copper foil.

[0091] The scanning electron microscope (EBSD) observation shows that the average grain size is reduced from 2 µm without ultrasonic to about 0.6 µm, and the grain distribution is more uniform, indicating that the grain is significantly refined.

[0092] The ultrasonic amplitude and grain size data are shown in Table 1.

[0093] Table 1 Average grain size of copper foil under different ultrasonic amplitudes

[0094]

[0095] According to the above experimental results, the average grain size d is obtained under the ultrasonic amplitude AThe relationship between the grain size and the ultrasonic amplitude is approximately exponential. Using exponential fitting, we get:

[0096]

[0097] where, d The average grain size (µm), A The ultrasonic amplitude (µm), d 0 , k , d min The fitting parameters are as follows:

[0098]

[0099] The present application can inversely deduce the optimal amplitude setting according to the required grain size and the function between the obtained ultrasonic amplitude and the copper foil grain size, thereby realizing structure-controllable copper foil deposition.

[0100] Figure 2 The grain size distribution of the self-supporting copper foil under different ultrasonic amplitudes in Example 1. From Figure 2 It can be seen that under the condition of no ultrasonic wave (Static), the deposited copper layer presents a typical columnar crystal structure, the grain is coarse and the orientation is concentrated, showing a gradual nucleation dominated growth characteristic.

[0101] When the amplitude is 18 µm, the grain morphology starts to show a refinement trend, and some areas have shown equiaxed crystal embryos, indicating that low-intensity ultrasound has a certain excitation effect on the nucleation process.

[0102] When the amplitude is further increased to 30 µm, the grain is obviously refined, and the structure tends to be uniform and dense, indicating that the strong cavitation and micro-flow effect significantly promotes the occurrence of instantaneous nucleation and breaks the grain growth advantage direction under local disturbance.

[0103] Under the condition of an amplitude of 42 µm, the deposited copper layer presents a highly refined equiaxed crystal structure, the grain size is significantly reduced, the orientation is diversified, and the overall structure is the most dense.

[0104] In summary, the present application realizes the organization control of electrodeposited copper foil by adjusting the ultrasonic amplitude, especially under high amplitude conditions, effectively obtaining nanoscale equiaxed crystal copper foil, which is suitable for preparing high-strength and high-density metal materials.

[0105] Example 2

[0106] The difference from Example 1 is that a 35 µm commercial copper foil is selected as the substrate, and a layer of nickel is pre-deposited on its surface as the initial deposition layer, and the electroplating solution only contains the basic plating solution of copper sulfate, sulfuric acid and sodium chloride.

[0107] After the deposition, scanning electron microscopy (EBSD) observation shows that the average grain size is reduced from 2 μm without ultrasound to about 0.5 μm, and the grain distribution is more uniform, indicating that the grain is significantly refined.

[0108] Figure 3 The grain distribution diagram of the carrier copper foil under different ultrasonic amplitudes in Example 2 is shown in Figure 2. From Figure 2, it can be seen that the overall trend is the same as that of Example 1, indicating that the method of the present application has good universality and is suitable for different substrate materials and electrolyte systems, and can effectively realize grain refinement and uniform distribution. Figure 3

[0109] Comparative Example 1

[0110] The difference from Example 1 is that no ultrasonic field is applied during electrodeposition.

[0111] Comparative Example 2

[0112] The difference from Example 1 is that traditional mechanical stirring is used instead of ultrasonic assistance during electrodeposition. Although it has a certain effect on promoting the convection of the electrolyte, the degree of grain refinement is limited, the average grain size is about 1.5 μm, and the grain morphology is not uniform, there are obvious columnar crystals, the mechanical properties are limitedly improved, and the uniform fine grain effect under ultrasonic assistance cannot be achieved.

[0113] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application but not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which all belong to the protection scope of the present application.​

Claims

1. A method for quantitatively controlling the grain size of electrodeposited copper foil using power ultrasound, characterized by, The method comprises the following steps: (1) applying an ultrasonic field with a series of ultrasonic amplitudes in an electrolyte to carry out electrodeposition, and depositing copper foils under different ultrasonic amplitudes on a cathode; (2) obtaining the average grain size of the copper foils under different ultrasonic amplitudes in step (1), and performing exponential fitting on the average grain size of the copper foils under different ultrasonic amplitudes and the series of ultrasonic amplitudes to obtain a functional relationship between the average grain size and the ultrasonic amplitude, as shown in formula I: Formula I, wherein d is the average grain size in µm, A is the amplitude of the ultrasound waves in µm, d 0 , k and d min is a fitting parameter; (3) setting the ultrasonic amplitude of the ultrasonic field in step (1) to the ultrasonic amplitude corresponding to the required average grain size of the copper foil determined according to the formula I, and continuing the electrodeposition in step (1) to obtain the copper foil with the required average grain size. The frequency of the ultrasonic field is 20-100 kHz; the series of ultrasonic amplitudes are more than 3 point values selected from 2-42 µm; the ultrasonic field is a continuous ultrasonic field or an intermittent ultrasonic field. The current density of the electrodeposition is 0.5-100 A / dm 2 ; the current during the electrodeposition is constant current; the temperature of the electrolyte during the electrodeposition is 20-60 DEG C; and the time of the electrodeposition is 5-3600 s.

2. The method of claim 1, wherein, The equipment used for the electrodeposition is an electrolytic cell; the distance between the anode and the cathode in the electrolytic cell is 1-5 cm.

3. The method of claim 1, wherein, The electrolyte comprises a soluble copper salt, a conductive medium and a solvent; the soluble copper salt comprises one or more of copper sulfate, copper chloride and copper pyrophosphate; the conductive medium comprises sulfuric acid and / or sodium chloride.

4. The method of claim 3, wherein, The mass concentration of the soluble copper salt in the electrolyte is 70-80 g / L, and the mass concentration of the conductive medium is 90-100 g / L.

5. The method of claim 1, wherein, The generating device of the ultrasonic field is an ultrasonic emission system; the ultrasonic emission system comprises an ultrasonic power supply, an ultrasonic transducer and an amplitude changer.

6. The method of claim 5, wherein, The lower end ultrasonic emission end part of the amplitude changer is located near the cathode and is directly inserted into the electrolyte; the diameter of the lower end ultrasonic emission end part of the amplitude changer is > 5 mm; the distance between the lower end ultrasonic emission end part of the amplitude changer and the cathode is < 10 cm.

7. The method of claim 1, wherein, The thickness of the copper foil is 0.5-20 µm.

8. The method according to claim 1 or 7, characterized in that, The average grain size of the copper foil is 0.3-2 µm.

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