Anode foil corrosion process, anode foil and application thereof

Abstract

The invention provides an anode foil corrosion process, an anode foil and application of the anode foil, and particularly relates to the technical field of corrosion of anode aluminum foils for aluminum electrolytic capacitors. The anode foil is an anode foil for an aluminum electrolytic capacitor; according to the corrosion process, an aluminum foil is subjected to pretreatment, first-stage corrosion, second-stage corrosion and aftertreatment in sequence to obtain an anode foil; wherein the first-stage corrosion process comprises the following steps: carrying out first-stage hole-forming corrosion on the pretreated aluminum foil by using sine wave alternating current, and then circularly carrying out the following process: carrying out second-stage hole-forming corrosion by using ultrasonic-assisted direct current and then carrying out chemical soaking. According to the corrosion process, the nucleation density and the distribution uniformity of tunnel holes are remarkably improved, the in-hole ion transmission efficiency is enhanced, the hole tip passivation phenomenon is reduced, the specific volume of the anode foil is increased to be larger than or equal to 10%, meanwhile, the current regulation and control mode is optimized, the first-stage corrosion period is shortened on the premise that the corrosion quality is guaranteed, the product performance and the production efficiency are considered, and the production cost is reduced. Good industrial application prospects are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of anode aluminum foil corrosion for aluminum electrolytic capacitor, in particular to an anode foil corrosion process, an anode foil and application thereof. BACKGROUND

[0002] In the production and manufacturing of medium and high voltage aluminum electrolytic capacitors, the performance core is highly dependent on the corrosion quality of the anode foil. The large number of tunnel holes formed on the surface of the anode foil through corrosion is the key structure for improving the capacity of the capacitor, and the number, uniformity and integrity of the tunnel holes directly determine the core performance indicators of the capacitor.

[0003] At present, the mainstream process for anode foil corrosion in the industry is the four-step electrochemical corrosion method. Although this process has become a general technology in the industry, it still has two major defects in actual application, and the problems mainly concentrate in the first-stage pore forming link. On the one hand, the traditional first-stage corrosion generally adopts a "one-stage single current" (mainly direct current) control mode. In order to ensure that the tunnel holes can grow fully and reach the expected pore diameter and depth, the corrosion reaction time needs to be prolonged, usually more than 60 seconds, which directly leads to low production efficiency of the anode foil, making it difficult to meet the demand for production capacity in large-scale production.

[0004] On the other hand, the control mode of single current parameter is difficult to simultaneously consider the pore distribution density and pore consistency of the tunnel holes. In the corrosion process, problems such as local pore blockage and uneven pore distribution may occur, which further leads to a decrease in the specific capacity of the anode foil; and if the parameters are adjusted to improve the pore quality, the reaction time will be further prolonged, forming a technical dilemma of "quality and efficiency cannot be considered simultaneously", which becomes a key bottleneck restricting the performance upgrading and production capacity improvement of medium and high voltage aluminum electrolytic capacitors.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The present application aims to provide an anode foil corrosion process, an anode foil and application thereof, and at least one of the above technical problems in the prior art is solved.

[0007] In order to achieve the above-mentioned purpose of the present application, the following technical solutions are adopted: The first aspect of the present application provides an anode foil corrosion process, wherein the anode foil is an anode foil for aluminum electrolytic capacitor; and the corrosion process is to obtain the anode foil by sequentially performing pretreatment, first-stage corrosion, second-stage corrosion and post-treatment on the aluminum foil. The process of the first-stage corrosion is to perform first-stage pore forming corrosion on the pretreated aluminum foil using sinusoidal alternating current, and then cyclically perform the following processes: second-stage pore forming corrosion using direct current with ultrasonic wave assistance, and then chemical soaking.

[0008] Furthermore, the frequency of the sinusoidal alternating current is 45~50Hz.

[0009] Preferably, the current density of the sinusoidal alternating current is 0.1~2.0 A / cm². 2 .

[0010] Preferably, the temperature for the first pitting corrosion is 25~50℃ and the time is 2~40s.

[0011] Furthermore, the DC current is applied in a decreasing manner.

[0012] Preferably, the direct current has an initial current density of 0.6~1.0 A / cm². 2 The current is applied for 0.5–3 seconds, and then decreases linearly from the initial current density to 0.01–0.1 A / cm² within 15–25 seconds. 2 Finally, maintain the endpoint current density for 2~6 seconds.

[0013] Furthermore, during the ultrasonic-assisted process, the frequency of the ultrasonic waves is 10~30KHz.

[0014] Preferably, the number of cycles is 2 to 6.

[0015] Furthermore, the purity of the aluminum foil is >99.99%.

[0016] Preferably, the thickness of the aluminum foil is 100~150μm.

[0017] Furthermore, the secondary corrosion involves immersing the aluminum foil, which has undergone primary corrosion, in a pore-expanding corrosion solution for further corrosion.

[0018] Preferably, the temperature of the secondary corrosion is 60~80℃ and the time is 10~20min.

[0019] Preferably, the pore-expanding corrosion solution comprises 0.3~0.8 mol / L nitric acid, 0.01~0.05 wt% organic slow-release agent, and the balance being water.

[0020] Preferably, the corrosive solution used for the first-stage corrosion includes 3-5 wt% hydrochloric acid, 25-30 wt% sulfuric acid, 0.5-1 wt% aluminum ions, and the balance is water.

[0021] Furthermore, the pretreatment is carried out in an acidic solution.

[0022] Preferably, the concentration of hydrochloric acid in the acid solution is 3-8 wt%, and the concentration of sulfuric acid is 25-35 wt%.

[0023] Preferably, the post-treatment is carried out in a nitric acid solution.

[0024] Preferably, the concentration of the nitric acid solution is 0.3~0.8 mol / L.

[0025] Furthermore, the anodic foil etching process also includes a process of boiling and drying in water after post-treatment, followed by formation.

[0026] Preferably, the voltage of the formation is 500~550V.

[0027] Preferably, the forming solution used in the forming process is a boric acid solution.

[0028] Preferably, the concentration of the boric acid solution is 90~110 g / L.

[0029] Preferably, the formation temperature is 85~95℃.

[0030] A second aspect of the present invention provides an anode foil, which is prepared using the anode foil etching process described in the first aspect.

[0031] A third aspect of the present invention provides the application of the aforementioned anode foil in medium- and high-voltage aluminum electrolytic capacitors.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects: The anolyte corrosion process provided by this invention significantly improves the nucleation density and uniformity of the tunnel holes through a three-in-one process of precise AC hole layout, DC linear current reduction segmented corrosion, and ultrasonic synergistic mass transfer. This enhances the ion transport efficiency within the holes, reduces the passivation phenomenon at the hole tips, and increases the specific volume of the anolyte foil by ≥10%. At the same time, the current control mode is optimized, shortening the first-stage corrosion cycle while ensuring corrosion quality. This process balances product performance and production efficiency, and has good prospects for industrial application.

[0033] The anode foil provided by this invention has a tunnel hole structure that achieves high density, uniform distribution, and deeper effective hole depth, which significantly improves the surface area and formation efficiency of the anode foil and enhances its energy storage capacity. The longitudinal growth and stability of the pores are good, reducing local blockage and passivation defects, resulting in denser and more consistent oxide film growth, thereby improving the voltage withstand performance and long-term reliability of the capacitor.

[0034] The application provided by this invention, given the advantages of the aforementioned anode foil, features higher specific capacitance and better electrochemical performance; the excellent pore structure also facilitates electrolyte wetting and ion conduction, reduces equivalent series resistance, and improves the high-frequency response characteristics and temperature stability of the capacitor. Overall, it provides key material support for achieving high capacity, long life, and high reliability operation of medium and high voltage aluminum electrolytic capacitors. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0036] Figure 1 The image shows a scanning electron microscope (SEM) image of the anode foil (without formation treatment) obtained in Example 1. Figure 2 This is a scanning electron microscope image of the anode foil (without formation treatment) obtained in Comparative Example 1. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0038] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0039] The first aspect of the present invention provides an anode foil etching process, wherein the anode foil is an anode foil for aluminum electrolytic capacitors; the etching process involves performing pretreatment, primary etching, secondary etching and posttreatment on the aluminum foil in a sequential manner to obtain the anode foil; The first-stage corrosion process is as follows: the pretreated aluminum foil is subjected to first-stage pitting corrosion using sinusoidal alternating current, followed by the following cyclic process: second-stage pitting corrosion using ultrasonic-assisted direct current, and then chemical immersion.

[0040] The anolyte corrosion process provided by this invention significantly improves the nucleation density and uniformity of the tunnel holes through a three-in-one process of precise AC hole layout, DC linear current reduction segmented corrosion, and ultrasonic synergistic mass transfer. This enhances the ion transport efficiency within the holes, reduces the passivation phenomenon at the hole tips, and increases the specific volume of the anolyte foil by ≥10%. At the same time, the current control mode is optimized, shortening the first-stage corrosion cycle while ensuring corrosion quality. This process balances product performance and production efficiency, and has good prospects for industrial application.

[0041] Introducing ultrasonic assistance during the second-stage pitting corrosion process using direct current, the micro-jet effect generated by ultrasonic cavitation effectively impacts the interior of the tunnel pores and the reaction interface, significantly accelerating the diffusion of corrosion products and the replenishment of fresh electrolyte within the pores, thus improving mass transfer conditions in the deep-pore region. This process alleviates localized polarization caused by ion concentration gradients and reduces the probability of passivation at the pore tip due to oxide accumulation or electrolyte depletion, thereby ensuring the corrosion reaction continues to deepen. Simultaneously, the favorable mass transfer environment helps maintain the openness and growth stability of the pores, promoting the formation of deeper and more uniformly structured tunnel pores, increasing the effective specific surface area of ​​the anode foil, and ultimately achieving a significant increase in specific volume.

[0042] Furthermore, the frequency of the sinusoidal alternating current is 45~50Hz.

[0043] Typical, but not limiting, frequencies of sinusoidal alternating current can be, for example, 45 Hz, 46 Hz, 47 Hz, 48 Hz, 49 Hz, or 50 Hz, or any value within the range of 45 to 50 Hz.

[0044] In the first-stage corrosion process, a 45-50Hz sinusoidal alternating current is introduced for initial pitting. The uniform distribution of the electric field increases the density and uniformity of pitting, thereby improving the specific volume.

[0045] Preferably, the current density of the sinusoidal alternating current is 0.1~2.0 A / cm². 2 .

[0046] A typical, but not limiting, current density of a sinusoidal alternating current can be, for example, 0.1 A / cm². 2 0.2 A / cm 2 0.5 A / cm 2 1.0 A / cm 2 1.5 A / cm 2 Or 2.0 A / cm 2 It can also be 0.1~2.0 A / cm 2 Any value within the range.

[0047] Preferably, the temperature for the first pitting corrosion is 25~50℃ and the time is 2~40s.

[0048] Typical, but not limiting, the temperature for the first pitting corrosion can be, for example, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃ or 50 ℃, or any value within the range of 25~50 ℃; the time for the first pitting corrosion can be, for example, 2 s, 5 s, 10 s, 15 s, 20 s, 25 s, 30 s, 35 s or 40 s, or any value within the range of 2~40 s.

[0049] Furthermore, the DC current is applied in a decreasing manner.

[0050] Preferably, the direct current has an initial current density of 0.6~1.0 A / cm². 2 The current is applied for 0.5–3 seconds, and then decreases linearly from the initial current density to 0.01–0.1 A / cm² within 15–25 seconds. 2 Finally, maintain the endpoint current density for 2~6 seconds.

[0051] This three-stage current control method for direct current employs a phased strategy of "high current for initial borehole formation → linear current reduction for increased depth and length → low current for stable borehole maintenance," precisely matching the inherent laws of tunnel borehole nucleation, longitudinal growth, and stabilization. The initial stage uses a current of 0.6~1.0 A / cm². 2 The high current density applied for a short period (0.5–3 s) significantly enhances the reaction intensity of active sites on the aluminum foil surface, promoting more uniform and dense pit nucleation and effectively increasing the porosity. Subsequently, the current density is linearly reduced to 0.01–0.1 A / cm² within 15–25 s. 2 This method achieves a smooth transition from lateral surface expansion to deep longitudinal pore growth in the corrosion reaction, avoiding bottlenecks or blockages caused by excessively rapid pore opening expansion, thus ensuring the continuity and depth of the pores. Finally, a constant current is maintained at the endpoint current density for 2–6 seconds to stabilize the electric field at the pore tip, suppressing localized over-corrosion and abnormal thickening of the passivation layer. This promotes the formation of a structurally complete, uniformly distributed tunnel pore network with optimized depth-to-diameter ratio. This current mode overcomes the limitations of traditional single or stepped decay currents, achieving synergistic control over the entire process of pore structure from density and depth to uniformity. It improves pore quality while increasing the specific capacitance of the anode foil, balancing corrosion efficiency and process stability.

[0052] Typical, but not limiting, starting current density can be, for example, 0.6 A / cm². 2 0.7 A / cm 2 0.8 A / cm 2 0.9 A / cm 2 Or 1.0 A / cm 2 The initial application time can be, for example, 0.5 s, 1 s, 2 s, or 3 s; the fall time can be, for example, 15 s, 18 s, 20 s, 22 s, or 25 s; and the final current density can be, for example, 0.01 A / cm³. 2 0.02 A / cm 2 0.05A / cm 2 Or 0.1 A / cm 2 The holding time can be, for example, 2 s, 3 s, 4 s, 5 s or 6 s; the above parameters can also take any value within their respective ranges.

[0053] Furthermore, during the ultrasonic-assisted process, the frequency of the ultrasonic waves is 10~30KHz.

[0054] Typically, but not limitingly, the frequency of ultrasound can be, for example, 10 kHz, 15 kHz, 20 kHz, 25 kHz or 30 kHz, or any value in the range of 10 to 30 kHz.

[0055] Preferably, the number of cycles is 2 to 6.

[0056] Typical, but not restrictive, the number of cycles can be, for example, 2, 3, 4, 5, or 6.

[0057] Furthermore, the purity of the aluminum foil is >99.99%.

[0058] Preferably, the thickness of the aluminum foil is 100~150μm.

[0059] Typically, but not limitingly, the thickness of the aluminum foil can be, for example, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm or 150 μm, or any value in the range of 100 to 150 μm.

[0060] Furthermore, the secondary corrosion involves immersing the aluminum foil, which has undergone primary corrosion, in a pore-expanding corrosion solution for further corrosion.

[0061] Preferably, the temperature of the secondary corrosion is 60~80℃ and the time is 10~20min.

[0062] Typical, but not limiting, the temperature for secondary corrosion can be, for example, 60 ℃, 65 ℃, 70 ℃, 75 ℃ or 80 ℃, or any value within the range of 60~80 ℃; the time for secondary corrosion can be, for example, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min, or any value within the range of 10~20 min.

[0063] Preferably, the pore-expanding corrosion solution comprises 0.3~0.8 mol / L nitric acid, 0.01~0.05 wt% organic slow-release agent, and the balance being water.

[0064] Typical, but not limiting, nitric acid concentrations in the pore-expanding corrosion solution may be, for example, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, or 0.8 mol / L; the content of organic slow-release agents may be, for example, 0.01 wt%, 0.02 wt%, 0.03 wt%, 0.04 wt%, or 0.05 wt%; and the above components may also take any value within their respective ranges.

[0065] The role of secondary corrosion is to selectively expand the pores based on the dense tunneling formed by primary corrosion. This is achieved by immersing the primary-corroded aluminum foil in a pore-expanding corrosion solution containing nitric acid and an organic slow-release agent, reacting at 60-80°C for 10-20 minutes. This allows for moderate dissolution of the pore openings and walls, thereby enlarging the pore diameter and smoothing the pore structure. This process effectively reduces mass transfer resistance in narrow pore sections without disrupting the overall uniformity of the pore distribution, creating favorable conditions for uniform oxide film growth during subsequent formation. Simultaneously, the selective adsorption of the organic slow-release agent inhibits excessive corrosion of the pore walls, preventing pore connectivity or collapse, ensuring the integrity of the pore structure and optimizing the depth-to-diameter ratio. This further enhances the effective surface area and charge storage capacity of the anode foil, ultimately achieving a stable increase in specific capacity and improved electrochemical performance.

[0066] Preferably, the corrosive solution used for the first-stage corrosion includes 3-5 wt% hydrochloric acid, 25-30 wt% sulfuric acid, 0.5-1 wt% aluminum ions, and the balance is water.

[0067] Typical, but not limiting, the etchant used for primary corrosion may contain, for example, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, or 5 wt% hydrochloric acid; for example, 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, or 30 wt% sulfuric acid; for example, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, or 1 wt% aluminum ions; and each of the above components may take any value within its respective range.

[0068] Furthermore, the pretreatment is carried out in an acidic solution.

[0069] Preferably, the concentration of hydrochloric acid in the acid solution is 3-8 wt%, and the concentration of sulfuric acid is 25-35 wt%.

[0070] Typical, but not limiting, the concentration of hydrochloric acid in the acid solution may be, for example, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, or 8 wt%; the concentration of sulfuric acid in the acid solution may be, for example, 25 wt%, 27 wt%, 30 wt%, 32 wt%, 34 wt%, or 35 wt%; and the above components may also take any value within their respective ranges.

[0071] Preferably, the post-treatment is carried out in a nitric acid solution.

[0072] Preferably, the concentration of the nitric acid solution is 0.3~0.8 mol / L.

[0073] Typical, but not limiting, the concentration of the nitric acid solution can be, for example, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L or 0.8 mol / L, or any value in the range of 0.3 to 0.8 mol / L.

[0074] Furthermore, the anodic foil etching process also includes a process of boiling and drying in water after post-treatment, followed by formation.

[0075] Preferably, the voltage of the formation is 500~550V.

[0076] Typical, but not limiting, the voltage converted can be, for example, 500 V, 510 V, 520 V, 530 V, 540 V or 550 V, or any value in the range of 500 to 550 V.

[0077] Preferably, the forming solution used in the forming process is a boric acid solution.

[0078] Preferably, the concentration of the boric acid solution is 90~110 g / L.

[0079] Typical, but not limiting, concentrations of boric acid solutions can be, for example, 90 g / L, 95 g / L, 100 g / L, 105 g / L, or 110 g / L, or any value within the range of 90 to 110 g / L.

[0080] Preferably, the formation temperature is 85~95℃.

[0081] Typical, but not limiting, the temperature of the transformation can be, for example, 85°C, 87°C, 90°C, 92°C or 95°C, or any value in the range of 85°C to 95°C.

[0082] The boiling process can remove residual corrosion ions (such as Cl) from the surface of the aluminum foil. - SO4 2-The process involves thorough hydrolysis to form a uniform aluminum hydroxide transition layer, while simultaneously using thermal shrinkage to moderately seal minor defects and unstable shallow pore structures, thus improving surface stability. Subsequent drying ensures complete removal of moisture, preventing residual water vapor from affecting the quality of subsequent formation. Based on this, anodizing is performed in a boric acid solution at a high voltage of 500-550V to generate a dense, uniform, and highly dielectric amorphous aluminum oxide insulating film. This film serves as the dielectric of the capacitor, and its thickness directly corresponds to its withstand voltage. This process sequence not only improves the integrity and adhesion of the oxide film, reducing the risk of pinholes and breakdown, but also enhances the consistency and repeatability of film growth, thereby significantly improving the withstand voltage, leakage current characteristics, and long-term reliability of the anode foil. This provides a crucial guarantee for the high-performance and stable operation of medium- and high-voltage aluminum electrolytic capacitors.

[0083] The equipment used in the corrosion process of this invention (AC power supply, ultrasonic generator, corrosion tank) are all conventional equipment in the industry, and no special devices need to be added; the process parameters are all within the industrial controllable range, and it is easy to achieve large-scale mass production.

[0084] A second aspect of the present invention provides an anode foil, which is prepared using the anode foil etching process described in the first aspect.

[0085] The anode foil provided by this invention has a tunnel hole structure that achieves high density, uniform distribution, and deeper effective hole depth, which significantly improves the surface area and formation efficiency of the anode foil and enhances its energy storage capacity. The longitudinal growth and stability of the pores are good, reducing local blockage and passivation defects, resulting in denser and more consistent oxide film growth, thereby improving the voltage withstand performance and long-term reliability of the capacitor.

[0086] A third aspect of the present invention provides the application of the aforementioned anode foil in medium- and high-voltage aluminum electrolytic capacitors.

[0087] The application provided by this invention, given the advantages of the aforementioned anode foil, features higher specific capacitance and better electrochemical performance; the excellent pore structure also facilitates electrolyte wetting and ion conduction, reduces equivalent series resistance, and improves the high-frequency response characteristics and temperature stability of the capacitor. Overall, it provides key material support for achieving high capacity, long life, and high reliability operation of medium and high voltage aluminum electrolytic capacitors.

[0088] The present invention is further illustrated below with specific embodiments and comparative examples. However, it should be understood that these embodiments are merely for illustrative purposes and should not be construed as limiting the invention in any way. Unless otherwise specified, the raw materials used in the embodiments and comparative examples of the present invention were carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0089] Example 1 This embodiment provides an anode foil, and the specific etching process is as follows: (1) Pretreatment: Aluminum foil with a purity of 99.99% (iron 0.0001%, silicon 0.0001%, copper 0.0050%, thickness 127μm) was soaked in a solution containing 5wt% hydrochloric acid and 30wt% sulfuric acid at 80℃ for 2min.

[0090] (2) Primary corrosion: The aluminum foil was placed in a primary corrosion solution containing 3% hydrochloric acid, 30% sulfuric acid, and 1% aluminum ions. First, a 50Hz sinusoidal alternating current was used for spot corrosion at a temperature of 35℃ and a current density of 1.0A / cm. 2 The effect lasts for 5 seconds.

[0091] The following process was then repeated four times: etching was performed using direct current at a reaction temperature of 80℃, with 30kHz ultrasonic treatment assisted by pitting corrosion. The initial direct current density was 1.0A / cm². 2 After being energized for 1 second, the current density gradually decreased linearly to 0.1 A / cm². 2 The test took 20 seconds, and the current density eventually settled at the changed value of 0.1 A / cm². 2 Hold for 4 seconds, then chemically soak for 25 seconds.

[0092] (3) Secondary corrosion: Place the aluminum foil with the hole-forming process in a hole-expanding corrosion solution at a temperature of 80℃ and immerse it for 14 minutes.

[0093] (4) Post-treatment: After the secondary etching is completed, the aluminum foil is immersed in the post-treatment etching solution at 50°C for 6 minutes.

[0094] (5) The aluminum foil obtained is boiled and dried in water and then formed. The forming voltage is 520V and the forming solution is 90℃, 100g / L boric acid solution to obtain the anode foil.

[0095] Comparative Example 1 This comparative example provides an anode foil, and the specific etching process is as follows: (1) Pretreatment: Aluminum foil with a purity of 99.99% (0.0001% iron, 0.0001% silicon, 0.0050% copper, and a thickness of 127μm) was immersed in a mixed solution containing 3wt% hydrochloric acid and 35wt% sulfuric acid at a temperature of 80℃ for 120s.

[0096] (2) First-order pitting corrosion: The pretreated aluminum foil was placed in a mixed solution of 3wt% hydrochloric acid, 35wt% sulfuric acid and 3wt% aluminum ions at 75℃, and a decaying current was applied to perform fifth-order pitting corrosion. The initial current density was 1000mA / cm. 2The tail current density is 100 mA / cm². 2 The pore etching time is 25 seconds.

[0097] (3) Secondary pitting corrosion: The aluminum foil that has undergone primary pitting corrosion is placed in a mixed solution of 3wt% hydrochloric acid, 35wt% sulfuric acid and 3wt% aluminum ions at 75℃, and a decaying current is applied to perform fifth-stage pitting corrosion. The initial current density is 1000mA / cm. 2 The tail current density is 100 mA / cm². 2 The pore etching time is 25 seconds.

[0098] (4) Intermediate treatment: The aluminum foil that has undergone secondary pitting corrosion is immersed in a phosphoric acid solution with a temperature of 50℃ and a concentration of 5Wt% for 15s.

[0099] (5) Tertiary pitting corrosion: The intermediate-treated aluminum foil was placed in a mixed solution of 3wt% hydrochloric acid, 35wt% sulfuric acid and 3wt% aluminum ions at 75℃, and a decaying current was applied to perform tertiary pitting corrosion. The initial current density was 1000 mA / cm. 2 The tail current density is 100 mA / cm². 2 The pore etching time is 25 seconds.

[0100] (6) Quaternary pitting corrosion: The aluminum foil that has undergone tertiary pitting corrosion is placed in a mixed solution of 3wt% hydrochloric acid, 35wt% sulfuric acid and 3wt% aluminum ions at 75℃, and a decaying current is applied to perform quinary pitting corrosion with an initial current density of 1000mA / cm. 2 The tail current density is 100 mA / cm². 2 The pore etching time is 25 seconds.

[0101] (7) Treatment: Immerse the aluminum foil that has undergone secondary pitting corrosion in a phosphoric acid solution at 50°C and 5wt% concentration for 15 seconds.

[0102] (8) Fifth-order pitting corrosion: The aluminum foil that has undergone third-order pitting corrosion is placed in a mixed solution of 3wt% hydrochloric acid, 35wt% sulfuric acid and 3wt% aluminum ions at 75℃, and a decaying current is applied to perform fifth-order pitting corrosion. The initial current density is 1000mA / cm. 2 The tail current density is 100 mA / cm². 2 The pore etching time is 25 seconds.

[0103] (9) Pitting corrosion: The aluminum foil that has undergone pitting corrosion is placed in a pitting corrosion solution at a temperature of 70°C, and a current density of 100 mA / cm is applied. 2 The hole-expanding corrosion was performed using direct current for 720 seconds, and the corrosion solution was a solution containing 3 wt% nitric acid.

[0104] (10) Post-treatment: The etched foil after the hole expansion is immersed in a 5wt% nitric acid solution at 70℃ for 100s. The aluminum foil obtained is then dried by boiling in water and then formed. The forming voltage is 520V and the forming solution is a 90℃, 100g / L boric acid solution to obtain the anode foil.

[0105] Comparative Example 2 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the first-stage corrosion is carried out using a sinusoidal alternating current for 55 seconds. The rest of the preparation methods are the same as those in Embodiment 1, and will not be described again here.

[0106] Comparative Example 3 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the primary corrosion process uses a direct current of 1.0 A / cm throughout. 2 The process lasts 55 seconds. The rest of the preparation method is the same as in Example 1, and will not be repeated here.

[0107] Comparative Example 4 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that ultrasonic treatment is not performed during the DC corrosion process. The rest of the preparation methods are the same as those in Embodiment 1, and will not be described again here.

[0108] Test Example 1 The aluminum foils obtained in the examples and comparative examples were subjected to electrostatic capacitance and bending tests in accordance with the industry standard SJ / T 11140-2012, and the data obtained are recorded in Table 1.

[0109] Table 1

[0110] As can be seen from Table 1, the specific volume of Comparative Example 2 is only 0.75 μF / cm. 2 The specific volume decreased by 14.8% compared to Example 1; the specific volume of Comparative Example 3 was 0.72 μF / cm³. 2 The decrease was 18.2%. The reasons are: while alternating current can initially create holes, it cannot achieve deep longitudinal growth of the channels; a single constant direct current easily leads to uneven hole distribution and blunting of hole tips, ultimately failing to form the optimized structure of "high density + deep channels". Comparative Example 4: Specific capacitance 0.80 μF / cm³ 2 Compared to Example 1, the bending performance decreased by 9.1%, and the number of bends decreased from 66 to 63. This indicates that the "cavitation effect" of ultrasound can accelerate the discharge of corrosion products in the pores, replenish fresh electrolyte, and reduce pore blockage. It can both increase specific volume and improve the uniformity of pore structure (bending performance reflects structural integrity).

[0111] Example 2 This embodiment provides an anode foil. The specific corrosion process is different from that of Embodiment 1. The process in step (2) is repeated twice. The rest of the preparation methods are the same as those in Embodiment 1, and will not be described again here.

[0112] Example 3 This embodiment provides an anode foil. The specific corrosion process is different from that of Embodiment 1. The process in step (2) is repeated 6 times. The rest of the preparation methods are the same as those in Embodiment 1, and will not be described again here.

[0113] Example 4 This embodiment provides an anode foil. The specific corrosion process is different from that of Embodiment 1. The repeating process in step (2) only needs to be performed once. The rest of the preparation methods are the same as those in Embodiment 1, and will not be described again here.

[0114] Example 5 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the repeating process in step (2) is performed three times. The rest of the preparation methods are the same as those in Embodiment 1, and will not be repeated here.

[0115] Example 6 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the repeating process in step (2) is performed 5 times. The rest of the preparation methods are the same as those in Embodiment 1, and will not be repeated here.

[0116] Example 7 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the DC current density at the start of energization is 0.6 A / cm². 2 After being energized for 1 second, the current density gradually decreased linearly to 0.1 A / cm². 2 The test took 20 seconds, and the current density eventually settled at the changed value of 0.1 A / cm². 2 The solution is then kept at this temperature for 4 seconds, followed by a chemical soaking time of 25 seconds. The remaining preparation methods are the same as in Example 1 and will not be repeated here.

[0117] Example 8 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the DC current density is 1 A / cm² at the start of energization. 2 After energizing for 1 second, the current density gradually decreased linearly to 0.01 A / cm². 2 The test took 20 seconds, and the current density eventually settled at the changed value of 0.01 A / cm². 2 The solution is then kept at this temperature for 4 seconds, followed by a chemical soaking time of 25 seconds. The remaining preparation methods are the same as in Example 1 and will not be repeated here.

[0118] Example 9 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the DC current density at the start of energization is 0.1 A / cm². 2 After energizing for 1 second, the current density gradually increases linearly to 1 A / cm². 2 The process took 20 seconds, and the current density eventually settled at the changed value, which was 1 A / cm². 2 The solution is then kept at this temperature for 4 seconds, followed by a chemical soaking time of 25 seconds. The remaining preparation methods are the same as in Example 1 and will not be repeated here.

[0119] Test Example 2 The aluminum foils obtained in Examples 2-9 were tested using the same method as in Test Example 1, and the data obtained are recorded in Table 2.

[0120] Table 2

[0121] As shown in Table 2, as the number of repetitions of step 2 increases, the pore structure can be gradually optimized through multiple deep-hole drilling processes, thereby improving the specific volume; however, more repetitions are not necessarily better. From an industrial efficiency perspective, four repetitions are a more preferable option. Example 7: Specific volume 0.82 μF / cm³ 2 The initial current was slightly lower than that of Example 1, indicating that a slightly higher initiation current is more conducive to dense nucleation of initial pores; the specific capacitance of Example 8 was 0.89 μF / cm. 2 This is similar to Example 1, indicating that the endpoint current is between 0.01 and 0.1 A / cm. 2 The system can achieve stable hole performance within the specified range; Example 9 employs a "current rise mode" with a specific capacitance of only 0.60 μF / cm. 2 High current can easily lead to excessive corrosion of the orifice in the later stages, forming a "bottleneck blockage" that hinders the deep growth of the pore.

[0122] Example 10 This embodiment provides an anode foil. The specific corrosion process differs from that in Embodiment 1 in that the frequency of the ultrasonic wave is 10KHz. The rest of the preparation method is the same as in Embodiment 1, and will not be described again here.

[0123] Example 11 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the frequency of the ultrasonic wave is 30KHz. The rest of the preparation method is the same as that of Embodiment 1, and will not be described again here.

[0124] Example 12 This embodiment provides an anode foil. The specific corrosion process differs from that in Embodiment 1, except that the frequency of the ultrasonic wave is 5KHz. The rest of the preparation method is the same as in Embodiment 1, and will not be described again here.

[0125] Example 13 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that the frequency of the ultrasonic wave is 35KHz. The rest of the preparation method is the same as that of Embodiment 1, and will not be described again here.

[0126] Example 14 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that it uses a 50Hz sinusoidal alternating current for spot corrosion at a temperature of 35℃ and a current density of 2.0 A / cm². 2 The action time is 2 seconds. The rest of the preparation methods are the same as in Example 1, and will not be repeated here.

[0127] Example 15 This embodiment provides an anode foil. The specific corrosion process differs from that of Embodiment 1 in that it uses a 50Hz sinusoidal alternating current for spot corrosion at a temperature of 35℃ and a current density of 0.1A / cm². 2 The reaction time is 40 seconds. All other preparation methods are the same as in Example 1 and will not be repeated here.

[0128] Test Example 3 The aluminum foils obtained in Examples 10-15 were tested using the same method as in Test Example 1, and the data obtained are recorded in Table 3.

[0129] Table 3

[0130] As shown in Table 3, when the ultrasonic frequency is between 10-30 kHz, the specific volume is ≥0.84 μF / cm³. 2 The bending frequency should be at least 65 times. If the frequency is below 10 kHz, the cavitation effect is weak, resulting in insufficient mass transfer. If the frequency is above 30 kHz, excessive cavitation can easily damage the integrity of the pore walls. Example 14 uses 2.0 A / cm 2 Although the high current density can quickly form dense pits on the aluminum foil surface, the action time is only 2 seconds, resulting in a short current action period. Some initial pits are not fully formed, leading to a slightly lower specific capacitance. Example 15 uses 0.1 A / cm². 2 Although the low current density extended the action time to 40s, the low current did not provide sufficient "etching intensity" on the aluminum foil surface. The initial pit nucleation density was lower than that in Example 1, and some pits were shallower due to the weak current and slow reaction.

[0131] Characterization Example 1 The SEM images obtained by cross-sectional scanning electron microscopy of the anode foils (without formation treatment) obtained in Example 1 and Comparative Example 1 are shown below. Figure 1 and Figure 2 As shown.

[0132] from Figure 1It can be seen that there are a large number of uniformly distributed tunnel holes in the cross section of the aluminum foil, with small differences in hole spacing and no obvious local sparse or dense areas. The tunnel holes extend longitudinally and are continuous, without obvious blockage or "bottleneck" structures.

[0133] from Figure 2 It can be seen that this process results in poor uniformity of the aluminum foil holes, shallow tunnel depth, small hole diameter, and insufficient mass transfer within the holes, leading to premature termination of the corrosion reaction.

[0134] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An anodic foil etching process, characterized in that, The anode foil is an anode foil used in aluminum electrolytic capacitors; the corrosion process involves pre-treatment, primary corrosion, secondary corrosion, and post-treatment of the aluminum foil in sequence to obtain the anode foil. The first-stage corrosion process is as follows: the pretreated aluminum foil is subjected to first-stage pitting corrosion using sinusoidal alternating current, followed by the following cyclic process: second-stage pitting corrosion using ultrasonic-assisted direct current, and then chemical immersion.

2. The anodic foil etching process according to claim 1, characterized in that, The frequency of the sinusoidal alternating current is 45~50Hz; Preferably, the current density of the sinusoidal alternating current is 0.1~2.0 A / cm². 2 ; Preferably, the temperature for the first pitting corrosion is 25~50℃ and the time is 2~40s.

3. The anodic foil etching process according to claim 1, characterized in that, The direct current is applied in a decreasing manner; Preferably, the direct current has an initial current density of 0.6~1.0 A / cm². 2 The current is applied for 0.5–3 seconds, and then decreases linearly from the initial current density to 0.01–0.1 A / cm² within 15–25 seconds. 2 Finally, maintain the endpoint current density for 2~6 seconds.

4. The anodic foil etching process according to claim 1, characterized in that, During the ultrasonic-assisted process, the frequency of the ultrasonic waves is 10~30KHz. Preferably, the number of cycles is 2 to 6.

5. The anodic foil etching process according to any one of claims 1 to 4, characterized in that, The purity of the aluminum foil is >99.99%; Preferably, the thickness of the aluminum foil is 100~150μm.

6. The anodic foil etching process according to any one of claims 1 to 4, characterized in that, The secondary corrosion involves immersing the aluminum foil, which has undergone primary corrosion, in a pore-expanding corrosion solution for further corrosion. Preferably, the temperature for the secondary corrosion is 60~80℃ and the time is 10~20min; Preferably, the pore-expanding etching solution comprises 0.3~0.8 mol / L nitric acid, 0.01~0.05 wt% organic slow-release agent, and the balance being water; Preferably, the corrosive solution used for the first-stage corrosion includes 3-5 wt% hydrochloric acid, 25-30 wt% sulfuric acid, 0.5-1 wt% aluminum ions, and the balance is water.

7. The anodic foil etching process according to any one of claims 1 to 4, characterized in that, The pretreatment is carried out in an acid solution; Preferably, the concentration of hydrochloric acid in the acid solution is 3-8 wt%, and the concentration of sulfuric acid is 25-35 wt%. Preferably, the post-treatment is carried out in a nitric acid solution; Preferably, the concentration of the nitric acid solution is 0.3~0.8 mol / L.

8. The anodic foil etching process according to any one of claims 1 to 4, characterized in that, The anodic foil etching process also includes a post-treatment process of boiling and drying in water before forming. Preferably, the voltage of the formation is 500~550V; Preferably, the forming solution used in the formation is a boric acid solution; Preferably, the concentration of the boric acid solution is 90~110 g / L; Preferably, the formation temperature is 85~95℃.

9. An anode foil, characterized in that, It is prepared using the anodic foil etching process described in any one of claims 1 to 8.

10. The application of the anode foil according to claim 9 in medium and high voltage aluminum electrolytic capacitors.

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