Aluminum foil and preparation method thereof

Abstract

The invention provides an aluminum foil and a preparation method thereof, the preparation method comprises the following steps: the aluminum foil is subjected to electrochemical corrosion in a mixed acid solution, the half cycle of alternating current adopted by the electrochemical corrosion comprises a plurality of wave crests, and the mixed acid solution comprises at least one of nitric acid and phosphoric acid; passivating the aluminum foil; washing the aluminum foil with water; and the steps of electrochemical corrosion, passivation treatment and water washing are repeated until the aluminum foil reaches the preset corrosion amount. The nitric acid can improve the overall corrosion amount, reduce the surface corrosion of the aluminum foil and promote the longitudinal development of corrosion. Phosphate radicals and aluminum ions can form a complex, so that the concentration of free Al < 3 + > in a hole etching area is reduced, corrosion reaction balance is pushed to move rightwards, and further corrosion is promoted.

Description

Technical Field

[0001] This disclosure relates to the field of capacitors, and in particular to aluminum foil and methods for its preparation. Background Technology

[0002] In recent years, with the rapid development of multilayer aluminum electrolytic capacitors, the capacitance requirements for low-voltage electrode foil have become increasingly stringent. Since silver paste accounts for approximately 20% of the total cost of multilayer aluminum electrolytic capacitors, the amount of silver paste used directly affects the product's price competitiveness. According to the manufacturing process of multilayer capacitors, the capacitance of the low-voltage electrode foil determines the number of layers, which indirectly determines the amount of silver paste used. Therefore, to improve the price competitiveness of multilayer aluminum electrolytic capacitors, it is necessary to significantly increase the capacitance of the low-voltage electrode foil. However, current aluminum foil manufacturing processes cannot yet meet the requirements for significantly increasing capacitance. Summary of the Invention

[0003] The embodiments of this disclosure provide a method for preparing aluminum foil, comprising: electrochemically etching the aluminum foil in a mixed acid solution, wherein the half-cycle of the alternating current used in the electrochemical etching includes multiple peaks, and the mixed acid solution includes at least one of nitric acid and phosphoric acid; passivating the aluminum foil; washing the aluminum foil with water; and repeating the steps of electrochemical etching, passivation, and washing with water until the aluminum foil reaches a predetermined amount of etching.

[0004] In some embodiments, aluminum foil is used for multilayer aluminum electrolytic capacitors, and the thickness of the aluminum foil is 150 μm or more.

[0005] In some embodiments, a half-cycle of alternating current comprises multiple half-waves, with the crest located on each half-wave, and each half-wave having the same amplitude.

[0006] In some embodiments, the waveform of the half-wave is a sine wave, and the current magnitude corresponding to the trough of the half-wave is N times the current magnitude corresponding to the crest, where 0 <N<1。

[0007] In some embodiments, the number of peaks in a half-cycle of alternating current is 4 to 5.

[0008] In some embodiments, the mixed acid solution further includes hydrochloric acid and sulfuric acid, wherein the mass concentration of hydrochloric acid in the mixed acid solution is 2% to 15%, and the mass concentration of sulfuric acid in the mixed acid solution is 0.1% to 1%; when the mixed acid solution includes nitric acid, the mass concentration of nitric acid in the mixed acid solution is 0.05% to 0.5%; and when the mixed acid solution includes phosphoric acid, the mass concentration of phosphoric acid in the mixed acid solution is 0.1% to 0.8%.

[0009] In some embodiments, during electrochemical corrosion, the reaction temperature is between 10°C and 60°C, the reaction time is between 2 min and 4 min, and the current density is 0.55 A / cm². 2 Up to 1A / cm2 The current frequency is 10Hz to 30Hz.

[0010] In some embodiments, the passivation treatment solution includes a phosphorus-containing solution or an ammonium-containing solution, the mass concentration of the phosphorus-containing solution or the ammonium-containing solution is 0.1% to 5%, the treatment temperature is 60°C to 90°C, and the treatment time is 30s to 120s.

[0011] In some embodiments, the preparation method further includes: immersing the aluminum foil in a phosphoric acid solution before electrochemical corrosion; chemically cleaning and washing the aluminum foil after the aluminum foil reaches a predetermined corrosion amount; and then heat-treating the aluminum foil.

[0012] In some embodiments, chemical cleaning uses a nitric acid solution with a mass concentration of 0.05% to 3%, a cleaning temperature of 30°C to 60°C, and a cleaning time of 1 min to 4 min; heat treatment is performed at a temperature of 400°C to 550°C for 1 min to 4 min.

[0013] Another embodiment of this disclosure provides an aluminum foil, which is an aluminum foil obtained according to any of the above preparation methods.

[0014] The electrochemical corrosion method disclosed herein employs an alternating current half-cycle comprising multiple peaks. This ensures sufficient corrosion to further enhance electrostatic capacitance while avoiding prolonged maintenance of peak current, significantly reducing the occurrence of co-corrosion during aluminum foil preparation. Furthermore, the mixed acid solution includes at least one of nitric acid and phosphoric acid. Nitric acid can increase the overall corrosion rate while reducing surface corrosion of the aluminum foil, promoting vertical corrosion progression. During the reaction, as the aluminum foil continues to react, a large amount of aluminum ions are released. The accumulation of aluminum ions in the pitting areas will affect the depth of the corrosion process. However, the addition of phosphoric acid allows phosphate ions to form complexes with aluminum ions (such as [Al(HPO4)]). + This reduces free Al in the pitting region. 3+ The concentration of this concentration shifts the corrosion reaction equilibrium to the right, promoting further corrosion. Attached Figure Description

[0015] Figure 1 A flowchart of a method for preparing aluminum foil according to an embodiment of this disclosure is shown.

[0016] Figure 2 A scanning electron microscope image of the treated aluminum foil of Comparative Example 1 is shown.

[0017] Figure 3 A schematic waveform diagram of the AC waveform of Comparative Example 1 is shown.

[0018] Figure 4 A schematic waveform diagram of the AC waveform of Example 5 is shown.

[0019] Figure 5 A schematic waveform diagram of the AC waveform of Example 6 is shown.

[0020] Figure 6 A schematic waveform diagram of the AC waveform of Example 7 is shown.

[0021] Figure 7 A schematic waveform diagram of the AC waveform of Example 8 is shown.

[0022] Figure 8 A schematic waveform diagram of the AC waveform of Example 9 is shown. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0024] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will enable those skilled in the art to fully understand the scope of this disclosure.

[0025] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0026] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0027] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0028] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0029] The embodiments of this disclosure provide a method for preparing aluminum foil, referring to... Figure 1 ,include:

[0030] S1. Electrochemical etching of aluminum foil in a mixed acid solution, wherein the half-cycle of the alternating current used in the electrochemical etching includes multiple peaks. The capacitance of an aluminum electrolytic capacitor is proportional to the surface area of ​​the electrode. By electrochemically etching the aluminum foil, the surface area of ​​the aluminum foil can be significantly increased, thereby improving the capacitance. Specifically, through electrochemical etching, a large number of tiny pores and pits (honeycomb or tunnel-like structures) are formed on the surface of the aluminum foil, increasing the actual surface area by tens or even hundreds of times compared to the geometric surface area. The half-cycle of the alternating current used in the electrochemical etching of this disclosure includes multiple peaks, ensuring that the amount of etching required to further increase the capacitance is met while avoiding prolonged maintenance of the peak current time, thus significantly reducing the occurrence of pinhole formation during aluminum foil preparation. In some embodiments, the waveform of the half-cycle of the alternating current consists of one or more of a sine wave, a triangular wave, a trapezoidal wave, and a square wave.

[0031] In some embodiments, the mixed acid solution includes at least one of nitric acid and phosphoric acid. Nitric acid can increase the overall corrosion rate while reducing surface corrosion of the aluminum foil, promoting vertical corrosion progression. Furthermore, during the reaction, as the aluminum foil continues to react, a large amount of aluminum ions are released. The accumulation of aluminum ions in the pitting area will affect the depth of the corrosion process. However, with the addition of phosphoric acid, phosphate ions can form complexes with aluminum ions (such as [Al(HPO4)]). + This reduces free Al in the pitting region. 3+ The concentration of [amount] shifts the corrosion reaction equilibrium to the right, promoting further corrosion and increasing the surface area of ​​the aluminum foil.

[0032] In some embodiments, refer to Figure 1 The preparation method further includes: S2, passivating the aluminum foil; S3, washing the aluminum foil with water; repeating the steps of electrochemical corrosion, passivation, and water washing until the aluminum foil reaches the predetermined corrosion amount. The electrochemically corroded aluminum foil has an extremely high specific surface area and a large number of active sites. The surface aluminum atoms are very active and easily react with moisture or oxygen in the air, leading to uneven surface oxidation or the generation of hydrogen gas. Passivation treatment can quickly generate a uniform and stable oxide film on the aluminum foil surface, preventing further uncontrolled oxidation or corrosion. After passivation treatment, washing the aluminum foil with water can remove residual chemicals on the aluminum foil surface, such as the passivation solution. In some embodiments, the predetermined corrosion amount is approximately 60% of the weight of the aluminum foil. This allows for a significant increase in the surface area of ​​the aluminum foil without excessively affecting its mechanical strength.

[0033] In some embodiments, aluminum foil is used in multilayer aluminum electrolytic capacitors, and the thickness of the aluminum foil is 150 μm or more. Currently, the thickness of mainstream low-voltage electrode foil on the market is only up to 125 μm. Under the existing process conditions where the power supply waveform is a rectangular wave, further increasing the electrode foil thickness to 150 μm and simultaneously increasing the corrosion amount will result in multi-regional corrosion pitting and co-occurrence (e.g., Figure 2 The current waveform of a rectangular wave capacitor is insufficient to significantly increase capacitance. The rectangular wave current reaches its maximum instantaneous value, causing pores to form on the active sites of the high-purity aluminum foil surface. It also maintains the peak current for a relatively long time, concentrating the large current on the activated pits. However, when producing 150μm products, this prolonged reaction time further increases the corrosion, resulting in numerous co-occurrences on the aluminum foil surface. Therefore, this waveform is unsuitable for producing products with longer reaction times. This disclosure addresses this issue by adjusting the power supply waveform and the composition of the mixed acid solution to set the peak current level. This ensures sufficient corrosion for further capacitance increases while avoiding prolonged peak current maintenance, significantly reducing co-occurrences when producing 150μm products. By using aluminum foil with a thickness of 150μm or more, the number of layers can be reduced to achieve the same capacitance, thereby reducing the amount of silver paste used and lowering the cost of aluminum electrolytic capacitors.

[0034] In some embodiments, such as Figures 4 to 8 As shown, a half-cycle of alternating current includes multiple half-waves and multiple peaks. The peaks are located on the half-waves, and each half-wave has the same amplitude. The number of peaks in a half-cycle of alternating current is 2 to 6. In some embodiments, as the number of peaks in the positive half-cycle increases, each peak in the positive half-cycle is equivalent to a high current density pulse, forming micro-current hot spots on the aluminum surface (such as preferential dissolution at grain boundaries and defects). At the same time, the continuous action of multiple peaks leads to an increase in the density of corrosion pits, making it easier to form honeycomb or porous structures. The waveform of multiple peaks promotes the overlap of corrosion pits, forming interconnected channels and significantly increasing the surface area of ​​the aluminum foil. However, if the number of peaks in the positive half-cycle exceeds a certain amount, the continuous peaks keep the aluminum surface in a state of anodic dissolution, and there is not enough time to repair the local passivation film through cathodic reactions (such as H+ reduction) in the negative half-cycle. The aluminum foil surface changes from local pitting corrosion (high specific surface area) to overall uniform dissolution (low specific surface area). At the same time, when the number of peaks is too large, the H+ in the electrolyte... + And Al 3+ Diffusion cannot keep up with the reaction rate, leading to the formation of an ion-depleted layer at the interface, which hinders the further progress of the reaction. In some embodiments, the number of peaks in a half-cycle of alternating current is 4 to 5. This can significantly increase the surface area of ​​the aluminum foil.

[0035] In some embodiments, the plurality of half-waves constituting a half-cycle of alternating current include one or more waveforms selected from sine waves, triangular waves, trapezoidal waves, and square waves.

[0036] In some embodiments, the waveform of the half-wave is a sinusoidal waveform, and the current magnitude corresponding to the trough of the half-wave is N times the current magnitude corresponding to the crest, where 0 <N<1。

[0037] In some embodiments, the waveform of the half-wave is a sine wave, and the current magnitude corresponding to the trough of the half-wave is 0.7 times the current magnitude corresponding to the peak. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current can instantaneously change to 0.7, then change to the maximum current point 1 through a sine curve, and then gradually change to the low point 0.7 through a sine curve. By making the current magnitude corresponding to the trough of the half-wave 0.7 times the current magnitude corresponding to the peak, it is possible to avoid the alternating current remaining at a high current value for a long time, and also to avoid the problem of reduced electrochemical corrosion efficiency caused by the slowed corrosion rate due to low current.

[0038] In some embodiments, the mixed acid solution further includes hydrochloric acid and sulfuric acid, wherein the mass concentration of hydrochloric acid in the mixed acid solution is 2% to 15%, and the mass concentration of sulfuric acid in the mixed acid solution is 0.1% to 1%. Aluminum readily forms a dense natural oxide film (Al₂O₃) in air, which hinders electrochemical reactions. Hydrochloric acid is a strong acid with strong complexing properties, and the Cl₂ in it... - Ions have strong penetrating power and can damage or partially dissolve this oxide film, exposing the active aluminum matrix; Cl - It can also adsorb onto the aluminum surface, inducing the formation of localized pitting corrosion, thereby initiating the corrosion process. In some embodiments, the mass concentration of hydrochloric acid in the mixed acid solution is 2%, 5%, 8%, 10%, 12%, 15%, or any suitable value between them. If the hydrochloric acid concentration is too high, the high concentration of HCl provides a large amount of H+ and Cl-, causing the aluminum surface oxide film to be rapidly destroyed, the corrosion reaction to be violent, and over-corrosion to occur easily, resulting in pore merging, thinning of pore walls, or even perforation, and a decrease in structural stability. If the hydrochloric acid concentration is too low, the corrosion rate is too slow, and the efficiency is reduced. Sulfuric acid can stabilize the corrosion process and form a more regular pore structure. Sulfuric acid is also a strong acid, but its anion SO42- 2- The destructive power of sulfuric acid on oxide films is weaker than that of Cl-. Sulfuric acid has a milder dissolving effect on oxide films, resulting in a smoother corrosion process that is conducive to the formation of larger but more regular and stable pore structures. In some embodiments, the mass concentration of sulfuric acid in the mixed acid solution is 0.1%, 0.3%, 0.5%, 0.8%, 1%, or any suitable value between them. If the sulfuric acid concentration is too high, the corrosion rate is too fast, and over-corrosion is likely to occur. If the sulfuric acid concentration is too low, the corrosion rate is too slow, and efficiency is reduced.

[0039] In some embodiments, the mass concentration of nitric acid in the mixed acid solution is 0.05% to 0.5%. In some embodiments, the mass concentration of nitric acid in the mixed acid solution is 0.05%, 0.1%, 0.3%, 0.5%, or any suitable value between them. Nitric acid has strong oxidizing properties; if the concentration is too high, it will produce strong passivation, inhibiting electrochemical corrosion; if the concentration is too low, its effect of reducing surface corrosion of aluminum foil and promoting longitudinal corrosion is relatively limited. Controlling the nitric acid concentration within the above-mentioned range allows for effective protection of the aluminum foil surface condition while avoiding over-protection that could lead to a reduction in the number of pits and affect the corrosion effect.

[0040] In some embodiments, the mass concentration of phosphoric acid in the mixed acid solution is 0.1% to 0.8%. In some embodiments, the mass concentration of phosphoric acid in the mixed acid solution is 0.1%, 0.3%, 0.5%, 0.8%, or any suitable value between them. Phosphoric acid itself has a high viscosity, and excessively high concentrations will lead to poor liquid flowability; if the phosphoric acid concentration is too low, its effect on shifting the corrosion reaction equilibrium to the right is relatively limited.

[0041] In some embodiments, the reaction temperature in electrochemical corrosion is between 10°C and 60°C, and the reaction time is between 2 min and 4 min. In some embodiments, the reaction temperature can be 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, or any suitable value between them. If the reaction temperature is too low, the corrosion rate is slow and the efficiency is low; if the reaction temperature is too high, the corrosion rate is fast and the corrosion uniformity deteriorates. In some embodiments, the reaction time is 2 min, 3 min, 4 min, or any suitable value between them. If the reaction time is too short, the corrosion is insufficient and the surface area is small; if the reaction time is too long, over-corrosion is likely to occur, and the mechanical strength of the aluminum foil will decrease.

[0042] In some embodiments, the current density in electrochemical corrosion is 0.55 A / cm. 2 Up to 1A / cm 2 The current frequency is from 10 Hz to 30 Hz. In some embodiments, the current density is 0.55 A / cm². 2 0.6A / cm 2 0.7A / cm 2 0.8A / cm 2 0.9A / cm 2 1A / cm 2 Or any suitable value in between. If the current density is too low, the corrosion rate is slow and the efficiency is low; the corrosion-formed pores are shallow and small, the corrosion depth is insufficient, the specific surface area increase is limited, and the capacitance is low. Therefore, a current density below 0.55 A / cm² is not recommended. 2This slows down the corrosion rate, resulting in a more uniform dissolution of the aluminum surface, which tends to form a smoother but rougher surface. If the current density is too high, corrosion will be too rapid, potentially causing excessive dissolution of the aluminum foil and reducing its mechanical strength. Furthermore, when the current density is set to greater than 1 A / cm², corrosion will be too rapid, potentially causing excessive dissolution of the aluminum foil and reducing its mechanical strength. 2 When the aluminum foil reaction rate is too fast, the electrolyte mass transfer cannot replenish H+ or remove Al3+ in time, leading to local concentration polarization or thermal effects, unstable pit structure, and a tendency for co-occurrence. In some embodiments, the current frequency is 10Hz, 20Hz, 30Hz, or any suitable value between them. If the current frequency is too low, anodic dissolution dominates, resulting in a high corrosion rate but easily forming an inhomogeneous structure; if the current frequency is too high, the charge transfer rate cannot keep up with the frequency change, which is not conducive to further improving the corrosion effect, and the reaction exhibits segregation.

[0043] In some embodiments, the passivation treatment solution includes a phosphorus-containing solution or an ammonium-containing solution, such as ammonium sulfate, ammonium nitrate, ammonium phosphate, etc. In some embodiments, the mass concentration of the phosphorus-containing solution or ammonium-containing solution is 0.1% to 5%, the treatment temperature is 60°C to 90°C, and the treatment time is 30s to 120s. In some embodiments, the mass concentration of the phosphorus-containing solution or ammonium-containing solution is 0.1%, 1%, 2%, 3%, 4%, 5%, or any suitable value between them. If the concentration is too low, the passivation ability is relatively limited; if the concentration is too high, it easily leads to cleaning difficulties and residues. In some embodiments, the treatment temperature is 60°C, 70°C, 80°C, 90°C, or any suitable value between them. If the temperature is too low, the passivation reaction kinetics are insufficient, and the passivation film growth is slow; if the temperature is too high, it easily leads to localized over-oxidation or corrosion. In some embodiments, the treatment time is 30s, 60s, 80s, 100s, 120s, or any suitable value between them. If the processing time is too short, the passivation film will not form sufficiently; if the processing time is too long, the oxide film will be too thick, affecting efficiency.

[0044] In some embodiments, the preparation method further includes: immersing the aluminum foil in a phosphoric acid solution before electrochemical corrosion; after the aluminum foil reaches a predetermined corrosion amount, chemically cleaning and washing the aluminum foil, followed by heat treatment. In some embodiments, immersing the aluminum foil in a phosphoric acid solution can remove some oil or natural oxide film from the surface of the aluminum foil. In some embodiments, chemical cleaning can remove residual corrosion treatment solution and some metal ion impurities. Water washing then removes any residue of the chemical cleaning solution. Heat treatment can thoroughly remove moisture, prevent self-corrosion, stabilize the surface oxide film, improve storage stability, eliminate residual stress, improve mechanical properties, and promote pore structure stability, preventing collapse.

[0045] In some embodiments, chemical cleaning uses a nitric acid solution with a mass concentration of 0.05% to 3%, a cleaning temperature of 30°C to 60°C, and a cleaning time of 1 min to 4 min. In some embodiments, the concentration of the nitric acid solution used for chemical cleaning is 0.05%, 0.5%, 1%, 2%, 3%, or any suitable value between them. If the concentration of the nitric acid solution is too low, the oxidizing power is weak, making it difficult to effectively remove residual chlorides (such as AlCl3), sulfides, or metallic impurities, and failing to inhibit the self-corrosion reaction of aluminum; it also has poor solubility for metal ions such as Fe and Cu. If the concentration of the nitric acid solution is too high, the oxidizing properties lead to excessive passivation of the aluminum surface; it may trigger localized severe reactions, causing damage to the microporous structure or pitting corrosion; it generates toxic gases (NO, NO2), polluting the environment and harming health; the risk of nitrate (NO3-) residue increases, and it may decompose and produce gas at high temperatures. In some embodiments, the cleaning temperature is 30°C, 40°C, 50°C, 60°C, or any suitable value between them. If the temperature is too low, molecular activity is low, reaction kinetics are insufficient, and mass transfer within the micropores is slow; if the temperature is too high, nitric acid volatilization is accelerated, causing reagent loss and environmental pollution; it also accelerates aluminum dissolution, potentially leading to excessive corrosion or thinning of the pore walls. In some embodiments, the cleaning time is 1 min, 2 min, 3 min, 4 min, or any suitable value between them. If the cleaning time is too short, residues may not be sufficiently removed; if the cleaning time is too long, prolonged contact with nitric acid may lead to excessive surface oxidation, forming a non-ideal thick film; localized enlargement or edge corrosion may occur at the micropore openings.

[0046] In some embodiments, the heat treatment temperature is 400°C to 550°C, and the treatment time is 1 min to 4 min. In some embodiments, the heat treatment temperature is 400°C, 450°C, 500°C, 550°C, or any suitable value between them. If the treatment temperature is too low, bound water or water in the capillaries cannot be completely evaporated. If the treatment temperature is too high, recrystallization may occur, altering the crystal structure of the aluminum foil and affecting its mechanical strength and electrochemical behavior. In some embodiments, the treatment time is 1 min, 2 min, 3 min, 4 min, or any suitable value between them. If the treatment time is too short, moisture in the internal micropores will not be completely evaporated, especially for thick foils or porous structures. If the treatment time is too long, it may cause deformation or microcracks in the aluminum foil.

[0047] To better understand this disclosure, specific embodiments are described below.

[0048] Comparative Example 1

[0049] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0050] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, 0.08% nitric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 3 The AC waveform shown is subjected to electro-erosion; the current density is 0.55 A / cm². 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0051] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0052] The electrode foil after intermediate processing was cleaned with tap water.

[0053] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0054] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0055] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0056] Comparative Example 2

[0057] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0058] The treated electrode foil was placed in a mixed acid solution with a hydrochloric acid concentration of 10% and a sulfuric acid concentration of 0.5%, at a solution temperature of 26℃; Figure 4 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, the current instantaneously changes to 0.7 in the initial stage, then changes back to the maximum current point 1 via a sine curve, and then gradually changes back to the low point 0.7 via a sine curve, and so on. The positive half-cycle contains two peaks and one trough; the current density is 0.55 A / cm². 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0059] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0060] The electrode foil after intermediate processing was cleaned with tap water.

[0061] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0062] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0063] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0064] Example 1

[0065] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0066] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, and 0.08% nitric acid at a temperature of 26°C. Figure 4 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point 1 via a sine curve, and then gradually changes back to the low point 0.7 via a sine curve, and so on. The positive half-cycle contains two peaks and one trough; the current density is 0.55 A / cm. 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0067] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0068] The electrode foil after intermediate processing was cleaned with tap water.

[0069] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0070] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0071] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0072] Example 2

[0073] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0074] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 4 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point 1 via a sine curve, and then gradually changes back to the low point 0.7 via a sine curve, and so on. The positive half-cycle contains two peaks and one trough; the current density is 0.55 A / cm. 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0075] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0076] The electrode foil after intermediate processing was cleaned with tap water.

[0077] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0078] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0079] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0080] Example 3

[0081] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0082] The treated electrode foil was placed in a mixed acid solution with a concentration of 2% hydrochloric acid, 1% sulfuric acid, 0.05% nitric acid, and 0.8% phosphoric acid at a temperature of 11°C. Figure 4 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, initially, the current instantaneously changes to 0.7, then changes back to the maximum current point 1 via a sine curve, and then gradually changes back to the low point 0.7 via a sine curve, and so on. The positive half-cycle contains two peaks and one trough; the current density is 0.7 A / cm². 2 The current frequency was 10Hz, and the reaction time was 4min; after corrosion, the sample was washed with tap water.

[0083] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.1%, the treatment temperature was 90℃, and the treatment time was 2 min.

[0084] The electrode foil after intermediate processing was cleaned with tap water.

[0085] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0086] After electrochemical corrosion, the electrode foil was placed in a 0.05% nitric acid solution at a cleaning temperature of 60°C for 4 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0087] After the electrode foil was cleaned with pure water, it was heat-treated at 400℃ for 4 minutes.

[0088] Example 4

[0089] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0090] The treated electrode foil was placed in a mixed acid solution with a concentration of 15% hydrochloric acid, 0.1% sulfuric acid, 0.5% nitric acid, and 0.1% phosphoric acid, at a solution temperature of 56°C. Figure 4 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point of 1 via a sine curve, and then gradually changes back to the low point of 0.7 via a sine curve, and so on. The positive half-cycle contains two peaks and one trough; the current density is 1 A / cm. 2 The current frequency was 30Hz, and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0091] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.5%, the treatment temperature was 60℃, and the treatment time was 30s.

[0092] The electrode foil after intermediate processing was cleaned with tap water.

[0093] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0094] After electrochemical corrosion, the electrode foil was placed in a 3% nitric acid solution at a cleaning temperature of 30°C for 1 minute. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0095] After the electrode foil has been cleaned with pure water, it is heat-treated at 550℃ for 1 minute.

[0096] Example 5

[0097] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0098] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, 0.08% nitric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 4 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point 1 via a sine curve, and then gradually changes back to the low point 0.7 via a sine curve, and so on. The positive half-cycle contains two peaks and one trough; the current density is 0.55 A / cm. 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0099] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0100] The electrode foil after intermediate processing was cleaned with tap water.

[0101] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0102] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0103] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0104] Example 6

[0105] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0106] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, 0.08% nitric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 5The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point of 1 via a sine curve, and then gradually changes back to the low point of 0.7 via a sine curve, and so on. The positive half-cycle contains three peaks and two troughs; the current density is 0.55 A / cm. 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0107] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0108] The electrode foil after intermediate processing was cleaned with tap water.

[0109] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0110] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0111] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0112] Example 7

[0113] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0114] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, 0.08% nitric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 6 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point of 1 via a sine curve, and then gradually changes back to the low point of 0.7 via a sine curve. This process is repeated. The positive half-cycle contains four peaks and three troughs; the current density is 0.55 A / cm². 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0115] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0116] The electrode foil after intermediate processing was cleaned with tap water.

[0117] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0118] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0119] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0120] Example 8

[0121] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0122] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, 0.08% nitric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 7 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point of 1 via a sine curve, and then gradually changes back to the low point of 0.7 via a sine curve. This process is repeated. The positive half-cycle contains five peaks and four troughs; the current density is 0.55 A / cm². 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0123] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0124] The electrode foil after intermediate processing was cleaned with tap water.

[0125] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0126] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0127] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0128] Example 9

[0129] A 150μm thick sheet of 99.99% high-purity aluminum foil was immersed in a 0.5% phosphoric acid solution for 2 minutes.

[0130] The treated electrode foil was placed in a mixed acid solution with a concentration of 10% hydrochloric acid, 0.5% sulfuric acid, 0.08% nitric acid, and 0.5% phosphoric acid, at a solution temperature of 26°C. Figure 8 The AC waveform shown is subjected to electro-erosion. Taking the positive half-cycle as an example, assuming the maximum current is 1, in the initial stage, the current instantaneously changes to 0.7, then changes back to the maximum current point of 1 via a sine curve, and then gradually changes back to the low point of 0.7 via a sine curve. This process is repeated. The positive half-cycle contains six peaks and five troughs; the current density is 0.55 A / cm². 2 The current frequency was 15Hz and the reaction time was 2min; after corrosion, the sample was washed with tap water.

[0131] The electrochemically etched electrode foil was placed in an ammonium sulfate solution for intermediate treatment. The solution concentration was 0.4%, the treatment temperature was 80℃, and the treatment time was 1 min.

[0132] The electrode foil after intermediate processing was cleaned with tap water.

[0133] Repeat the steps of corrosion, intermediate treatment and water washing until the amount of corrosion reaches 60% of the original weight.

[0134] After electrochemical corrosion, the electrode foil was placed in a 0.2% nitric acid solution at a cleaning temperature of 45°C for 2 minutes. After chemical cleaning, the electrode foil was then cleaned with pure water.

[0135] After the electrode foil was cleaned with pure water, it was heat-treated at 530℃ for 2 minutes.

[0136] Figure 3 A schematic waveform diagram of the AC waveform in Comparative Example 1 is shown. Figures 4 to 8 Schematic waveform diagrams of the AC waveforms for Examples 5-9 are shown respectively. In addition, the withstand voltage and specific capacitance of the aluminum foil samples were tested: the withstand voltage was tested using the GB / T 2693 method, and the specific capacitance was tested using the GB / T 2693-2018 method. Table 1 shows the test results for Comparative Examples 1-2 and Examples 1-9.

[0137] Table 1

[0138] category Withstand pressure (V) <![CDATA[Specific capacitance (μF / cm 2 )]]> Comparative Example 1 11.3 258 Comparative Example 2 11.3 255 Example 1 11.4 267 Example 2 11.4 268 Example 3 11.3 269 Example 4 11.3 270 Example 5 11.4 272 Example 6 11.3 280 Example 7 11.3 286 Example 8 11.5 292 Example 9 11.3 277

[0139] As can be seen from the above, using the alternating current with the waveform of Comparative Example 1 easily leads to the co-occurrence of corrosion pits. By using the sinusoidal alternating current and mixed acid solution of this disclosure for electrochemical corrosion, the specific volume of the aluminum foil can be significantly improved.

[0140] Comparative examples 5-9 show that the specific capacitance of the aluminum foil gradually increases with the increase in the number of positive half-cycle peaks, reaching its highest value when there are 5 positive half-cycle peaks. Subsequently, the specific capacitance decreases significantly when the number of positive half-cycle peaks increases to 6. This is because with the increase in the number of positive half-cycle peaks, each positive half-cycle peak is equivalent to a high current density pulse, forming micro-current hot spots on the aluminum surface (such as preferential dissolution at grain boundaries and defects). At the same time, the continuous effect of multiple peaks leads to an increase in the density of corrosion pits, making it easier to form honeycomb or porous structures. In contrast, the single-peak structure of Comparative Example 1 is more likely to generate isolated corrosion pits. The multi-peak waveform promotes the overlap of corrosion pits, forming interconnected channels and significantly increasing the surface area. However, if the number of peaks in the positive half-cycle exceeds a certain amount, the continuous peaks keep the aluminum surface in a state of anodic dissolution, preventing the localized passivation film from being repaired during the negative half-cycle through cathodic reactions (such as H+ reduction). The aluminum foil surface changes from localized pitting corrosion (high specific surface area) to overall uniform dissolution (low specific surface area). Simultaneously, when the number of peaks is excessive, the H+ in the electrolyte... + And Al 3+ Diffusion cannot keep up with the reaction rate, resulting in the formation of an ion depletion layer at the interface, which affects the further advancement of the reaction.

[0141] The difference between Examples 10-16 and Example 8 lies in the concentration of nitric acid in the mixed acid solution; otherwise, they are the same as Example 8. Table 2 shows the pressure resistance and specific volume of Examples 8 and Examples 10-16.

[0142] Table 2

[0143]

[0144] As can be seen from the above, the specific volume of aluminum foil is improved when the concentration of nitric acid in the mixed acid solution is between 0.05% and 0.5%.

[0145] The difference between Examples 17-22 and Example 8 lies in the concentration of phosphoric acid in the mixed acid solution; otherwise, they are the same as Example 8. Table 3 shows the pressure resistance and specific volume of Examples 8 and Examples 17-22.

[0146] Table 3

[0147]

[0148] As can be seen from the above, the specific volume of aluminum foil is improved when the concentration of phosphoric acid in the mixed acid solution is between 0.1% and 0.8%.

[0149] The difference between Examples 23-28 and Example 8 is the current density; otherwise, they are the same as Example 8. Table 4 shows the withstand voltage and specific capacitance of Examples 8 and Examples 23-28.

[0150] Table 4

[0151] category <![CDATA[Current density (A / cm 2 )]]> Withstand pressure (V) <![CDATA[Specific capacitance (μF / cm 2 )]]> Example 8 0.55 11.5 292 Example 23 0.5 11.3 271 Example 24 0.6 11.5 291 Example 25 0.7 11.4 290 Example 26 0.8 11.4 289 Example 27 1 11.4 285 Example 28 1.1 11.3 266

[0152] As can be seen from the above, when the current is 0.55 A / cm 2 Up to 1A / cm 2 At this time, the improvement effect on the specific volume of aluminum foil is better.

[0153] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A method for preparing aluminum foil, characterized in that, include: Electrochemical etching of aluminum foil in a mixed acid solution, wherein the half-cycle of the alternating current used in the electrochemical etching process includes multiple peaks, and the mixed acid solution includes at least one of nitric acid and phosphoric acid; The aluminum foil is passivated. The aluminum foil is washed with water; Repeat the steps of electrochemical corrosion, passivation treatment, and water washing until the aluminum foil reaches the predetermined corrosion amount.

2. The preparation method according to claim 1, characterized in that, The aluminum foil is used in multilayer aluminum electrolytic capacitors, and the thickness of the aluminum foil is 150 μm or more.

3. The preparation method according to claim 1, characterized in that, The half-cycle of the alternating current comprises multiple half-waves, with the wave crest located on each half-wave, and each half-wave having the same amplitude.

4. The preparation method according to claim 3, characterized in that, The waveform of the half-wave is a sine wave, and the current magnitude corresponding to the trough of the half-wave is N times the current magnitude corresponding to the crest, where 0 <N<1。 5. The preparation method according to claim 4, characterized in that, The number of peaks in half a cycle of the alternating current is 4 to 5.

6. The preparation method according to any one of claims 1 to 5, characterized in that, The mixed acid solution also includes hydrochloric acid and sulfuric acid, wherein the mass concentration of hydrochloric acid in the mixed acid solution is 2% to 15%, and the mass concentration of sulfuric acid in the mixed acid solution is 0.1% to 1%. When the mixed acid solution includes nitric acid, the mass concentration of nitric acid in the mixed acid solution is 0.05% to 0.5%. When the mixed acid solution includes phosphoric acid, the mass concentration of phosphoric acid in the mixed acid solution is 0.1% to 0.8%.

7. The preparation method according to any one of claims 1 to 5, characterized in that, In the electrochemical corrosion, the reaction temperature is 10℃ to 60℃, the reaction time is 2 min to 4 min, and the current density is 0.55 A / cm. 2 Up to 1A / cm 2 The current frequency is 10Hz to 30Hz.

8. The preparation method according to any one of claims 1 to 5, characterized in that, The passivation treatment solution includes a phosphorus-containing solution or an ammonium-containing solution, wherein the mass concentration of the phosphorus-containing solution or the ammonium-containing solution is 0.1% to 5%, the treatment temperature is 60°C to 90°C, and the treatment time is 30s to 120s.

9. The preparation method according to any one of claims 1 to 5, characterized in that, Also includes: Prior to the electrochemical corrosion, the aluminum foil was immersed in a phosphoric acid solution. After the aluminum foil reaches a predetermined corrosion level, it is chemically cleaned and washed with water, and then heat-treated.

10. The preparation method according to claim 9, characterized in that, The chemical cleaning uses a nitric acid solution with a mass concentration of 0.05% to 3%, a cleaning temperature of 30°C to 60°C, and a cleaning time of 1 min to 4 min; The heat treatment temperature is 400℃ to 550℃, and the treatment time is 1 min to 4 min.

11. An aluminum foil, characterized in that, The aluminum foil is the aluminum foil obtained by the preparation method according to any one of claims 1 to 10.

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