Anode foil and method of making same and aluminum electrolytic capacitor

Abstract

This invention belongs to the field of electrode material technology, specifically relating to an anode foil, its preparation method, and an aluminum electrolytic capacitor. The preparation method of the anode foil includes performing a secondary porosimetry etching on the aluminum foil after primary porosimetry etching. The secondary porosimetry etching includes multiple stages of porosimetry etching, with a mid-treatment process between each adjacent stage. This preparation method involves multiple stages of porosimetry etching, and the mid-treatment process between each adjacent stage effectively increases the pore size of the etched foil, making it suitable for preparing ultra-high voltage anode foils with low loss and high specific capacitance.

Description

Technical Field

[0001] This invention belongs to the field of electrode material technology, specifically relating to an anode foil and its preparation method, and an aluminum electrolytic capacitor. Background Technology

[0002] Ultra-high voltage aluminum electrolytic capacitors possess advantages such as high voltage withstand capability and large specific capacitance, making them a crucial fundamental component in electronic engineering. Compared to medium- and high voltage capacitors, ultra-high voltage aluminum electrolytic capacitors are experiencing rapid development and are gaining increasing attention in the frequency converter field. The anode foil is a vital component of ultra-high voltage aluminum electrolytic capacitors, and its performance significantly impacts the capacitor's quality. With the development of electronic systems, capacitors face higher requirements such as miniaturization, low back pressure, low impedance, and long lifespan, which necessitates larger electrostatic capacitance and lower losses for the critical anode foil material.

[0003] Currently, the most mature manufacturing processes for anode aluminum foil used in aluminum electrolytic capacitors mainly include electrochemical etching, which aims to increase the effective area of ​​the aluminum foil, and formation processes, which aim to grow a high-quality aluminum oxide film. Among these, electrochemical etching is the foundation and key to the specific capacitance of the anode aluminum foil; the quality of the etching process determines whether high-capacitance, high-performance electrode foil can be obtained. The currently disclosed etching methods for ultra-high voltage anode foil for aluminum electrolytic capacitors employ a pretreatment-first-stage DC electrochemical etching-first-stage intermediate treatment-second-stage DC electrochemical etching-second-stage intermediate treatment-tertiary DC electrochemical etching-post-treatment approach. In actual production, the anode-etched foil prepared by the above process suffers from poor pore uniformity, small pore size, and numerous branch holes, which easily lead to pore blockage. Therefore, the existing etching processes for ultra-high voltage anode foil for aluminum electrolytic capacitors still need improvement. Summary of the Invention

[0004] The main objective of this invention is to propose an anode foil, its preparation method, and an aluminum electrolytic capacitor. The preparation method of this invention involves multi-stage pore-expanding corrosion, and a mid-treatment is provided between each two adjacent pore-expanding corrosion stages, which effectively increases the pore size of the etched foil and can be used to prepare ultra-high voltage anode foil with low loss and high specific capacitance.

[0005] To achieve the above objectives, the present invention provides the following technical solutions.

[0006] In a first aspect, the present invention provides a method for preparing an anode foil, the method comprising subjecting the aluminum foil after primary pitting corrosion to secondary pitting corrosion, the secondary pitting corrosion comprising multiple stages of pitting corrosion, and performing an intermediate treatment between each two adjacent stages of pitting corrosion.

[0007] In some embodiments of the present invention, each of the hole-enlarging corrosions is independently carried out using an acidic etching solution containing aluminum ions.

[0008] In some embodiments of the present invention, the concentration of aluminum ions in the acidic etching solution used for each stage of the hole-expanding corrosion is independently 0.1 mol / L to 0.4 mol / L.

[0009] In some embodiments of the present invention, the acidic etching solution used for each segment of the pore-expanding etching independently contains nitric acid and phosphoric acid.

[0010] In some embodiments of the present invention, the acidic etching solution used for each section of the pore-expanding etching independently contains nitric acid with a concentration of 0.2 mol / L to 0.8 mol / L and phosphoric acid with a mass percentage of 0.2% to 0.8%.

[0011] In some embodiments of the present invention, each segment of the pit-expanding corrosion is independently carried out using direct current electrochemical corrosion, with each segment having an independent current density of 0.1 A / cm. 2 ~0.4A / cm 2 .

[0012] In some embodiments of the present invention, the temperature of each segment of the pore-expanding corrosion is independently 50°C to 100°C.

[0013] In some embodiments of the present invention, the temperature of each segment of the pore-expanding corrosion is independently 60°C to 90°C.

[0014] In some embodiments of the present invention, the temperature of each segment of the pore-expanding corrosion is independently 68°C to 78°C.

[0015] In some embodiments of the present invention, the energizing time for each segment of the enlarged pore corrosion is independently 40s to 300s.

[0016] In some embodiments of the present invention, the energizing time for each segment of the enlarged pore corrosion is independently 50s to 200s.

[0017] In some embodiments of the present invention, the energizing time for each segment of the enlarged pore corrosion is independently 60s to 100s.

[0018] In some embodiments of the invention, each of the treatments is performed independently using a treatment solution containing a corrosion inhibitor.

[0019] In some embodiments of the present invention, the mass percentage of corrosion inhibitor in the treatment solution is independently 0.01% to 0.1%.

[0020] In some embodiments of the present invention, the corrosion inhibitors each independently include one or more of polyvinyl alcohol, thiourea, polyethylene glycol, polyacrylic acid, polyacrylamide, polystyrene sulfonic acid, sodium polystyrene sulfonate, and phosphate esters.

[0021] In some embodiments of the present invention, the processing solution in the process includes, independently, an acidic solution containing aluminum ions.

[0022] In some embodiments of the present invention, the treatment solutions in the process each contain oxalic acid independently.

[0023] In some embodiments of the present invention, the treatment solution in the process independently includes oxalic acid with a concentration of 0.5 mol / L to 1.6 mol / L and aluminum ions with a concentration of 0.1 mol / L to 0.3 mol / L.

[0024] In some embodiments of the present invention, the processing temperature of each process is independently 50°C to 100°C.

[0025] In some embodiments of the present invention, the processing temperature of each process is independently 50°C to 90°C.

[0026] In some embodiments of the present invention, the processing temperature of each process is independently 50°C to 80°C.

[0027] In some embodiments of the present invention, the processing time of each of the processes is independently 10s to 500s.

[0028] In some embodiments of the present invention, the processing time of each of the processes is independently 10s to 400s.

[0029] In some embodiments of the present invention, the processing time of each of the processes is independently 20s to 300s.

[0030] In some embodiments of the present invention, the intermediate treatment is performed after each segment of the enlarged etch.

[0031] In some embodiments of the present invention, the secondary pore-expanding corrosion includes two to ten stages of pore-expanding corrosion.

[0032] In some embodiments of the present invention, the secondary pore-expanding corrosion includes three to eight pore-expanding corrosion stages.

[0033] In some embodiments of the present invention, the primary pitting corrosion employs an etching solution containing aluminum ions.

[0034] In some embodiments of the present invention, the concentration of aluminum ions in the etching solution for primary pitting corrosion is 0.1 mol / L to 0.3 mol / L.

[0035] In some embodiments of the present invention, the etching solution for primary pitting corrosion is an acidic solution containing aluminum ions.

[0036] In some embodiments of the present invention, the etching solution for primary pitting corrosion contains hydrochloric acid and sulfuric acid.

[0037] In some embodiments of the present invention, the etching solution for primary pitting corrosion contains hydrochloric acid with a concentration of 0.65 mol / L to 1.0 mol / L and sulfuric acid with a concentration of 3.0 mol / L to 4.5 mol / L.

[0038] In some embodiments of the present invention, the temperature of the primary pitting corrosion is 50°C to 100°C.

[0039] In some embodiments of the present invention, the temperature of the primary pitting corrosion is 60–90°C.

[0040] In some embodiments of the present invention, the temperature of the primary pitting corrosion is 68°C to 80°C.

[0041] In some embodiments of the present invention, the primary pitting corrosion is performed using direct current electrochemical corrosion with a current density of 0.35 A / cm. 2 ~0.70A / cm 2 .

[0042] In some embodiments of the present invention, the energizing time for the primary pitting corrosion is 20s to 200s.

[0043] In some embodiments of the present invention, the energizing time for the primary pitting corrosion is 20s to 100s.

[0044] In some embodiments of the present invention, the energizing time for the primary pitting corrosion is 40s to 80s.

[0045] In some embodiments of the present invention, the preparation method further includes a pretreatment performed before the primary porosimetry.

[0046] In some embodiments of the present invention, the pretreatment includes: placing the aluminum foil in an alkaline immersion solution and an acidic immersion solution in sequence.

[0047] In some embodiments of the present invention, the alkaline soaking solution contains at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and potassium bicarbonate.

[0048] In some embodiments of the present invention, the concentration of the alkaline soaking solution is 0.1 mol / L to 1 mol / L.

[0049] In some embodiments of the present invention, the temperature of the alkaline soaking solution is 40°C to 60°C.

[0050] In some embodiments of the present invention, the aluminum foil is immersed in the alkaline immersion solution for 20s to 90s.

[0051] In some embodiments of the present invention, the acidic soaking solution contains hydrochloric acid and sulfuric acid.

[0052] In some embodiments of the present invention, the acidic soaking solution contains hydrochloric acid with a concentration of 0.65 mol / L to 1.0 mol / L and sulfuric acid with a concentration of 3.0 mol / L to 4.0 mol / L.

[0053] In some embodiments of the present invention, the temperature of the acidic soaking solution is 50°C to 85°C.

[0054] In some embodiments of the present invention, the aluminum foil is immersed in the acidic immersion solution for 40s to 80s.

[0055] In some embodiments of the present invention, the preparation method further includes post-treatment and drying treatment.

[0056] In some embodiments of the present invention, the post-treatment uses a treatment solution containing nitric acid.

[0057] In some embodiments of the present invention, the mass percentage of nitric acid in the treatment solution is 3% to 10%.

[0058] In some embodiments of the present invention, the temperature of the post-processing is 60°C to 80°C, and the time of the post-processing is 2 min to 10 min.

[0059] In some embodiments of the present invention, the drying temperature is 60°C to 110°C, and the drying time is 2 min to 10 min.

[0060] In a second aspect, the present invention provides an anode foil, which is prepared by the preparation method described in the first aspect.

[0061] In a third aspect, the present invention provides an aluminum electrolytic capacitor comprising the anode foil described in the second aspect or an anode foil prepared by the preparation method described in the first aspect.

[0062] Compared with the prior art, the present invention achieves the following technical effects:

[0063] The preparation method provided by this invention involves multi-stage borehole enlargement corrosion, with a mid-treatment process between each pair of adjacent borehole enlargement corrosion stages. This mid-treatment process allows the large amount of aluminum ions accumulated within the tunnel borehole during the borehole enlargement process to be transported to the outside, enhancing ion mass transfer within the borehole. Simultaneously, it increases the acidity within the borehole, reduces reaction resistance, improves the local environment within the borehole, and facilitates the enlargement and homogenization of the tunnel borehole, thereby reducing the loss of the ultra-high pressure anode foil and increasing its specific volume.

[0064] The processing solution used in this invention contains a corrosion inhibitor, which can effectively inhibit excessive dissolution and thinning of the aluminum foil surface, thus avoiding unnecessary loss of specific volume.

[0065] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0066] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. In the drawings:

[0067] Figure 1 This is a process flow diagram of the preparation of ultra-high pressure anode foil in Embodiment 1 of the present invention;

[0068] Figure 2 This is a process flow diagram for preparing ultra-high pressure anode foil in Embodiment 2 of the present invention;

[0069] Figure 3 This is a process flow diagram of the preparation of ultra-high pressure anode foil in Comparative Example 2 of the present invention;

[0070] Figure 4 This is a surface SEM image of the ultra-high pressure anode foil prepared in Example 2 of the present invention;

[0071] Figure 5 This is a surface SEM image of the ultra-high pressure anode foil prepared in Comparative Example 2 of the present invention. Detailed Implementation

[0072] Exemplary embodiments of the present invention will now be described in more detail with reference to specific examples. It should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0073] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0074] In the description of the embodiments of the present invention, the technical terms "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0075] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0076] In the description of the embodiments of this invention, the term "and / or" is merely a description of the association relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists, A and B exist simultaneously, and B exists. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0077] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0078] The electrolytic corrosion process for ultra-high pressure anolyte foil typically involves: aluminum foil – pretreatment – ​​primary pitting corrosion – secondary pitting corrosion – post-treatment. The primary function of pretreatment is to remove surface oil and oxide films, adjust the surface condition of the aluminum foil, and promote the initial initiation of pitting. Primary pitting corrosion creates numerous tunnels with specific diameters and depths on the pretreated aluminum foil surface by applying direct current. Secondary pitting corrosion applies direct current to these tunnels, ensuring they reach the desired diameter to prevent clogging and reduced specific volume during subsequent formation processes. Therefore, secondary pitting corrosion plays a crucial role in adjusting the tunnel size, thereby affecting the specific volume and loss of the etched foil.

[0079] To control the pore size, an intermediate treatment can be added to the two-stage pore-expanding corrosion process. Its main function is to transport the large amount of aluminum ions accumulated inside the tunnel pore during the pore-expanding process to the outside, enhancing ion mass transfer within the pore. Simultaneously, it increases the acidity within the pore, reduces reaction resistance, improves the local environment within the pore, and facilitates pore expansion and homogenization. For example, the existing technology for etching ultra-high voltage anode foil for aluminum electrolytic capacitors employs a pretreatment-first-stage DC electrochemical etching-first intermediate treatment-second-stage DC electrochemical etching-secondary intermediate treatment-tertiary DC electrochemical etching-post-treatment approach. However, in actual production, the anode-etched foil prepared by the above process exhibits poor pore uniformity, small pore size, and numerous branch pores, easily leading to pore blockage. Furthermore, in the above method, the second intermediate treatment uses a hydrochloric acid-based mixed solution for DC electrochemical etching, which easily introduces chloride ions into the next-stage pore-expanding corrosion solution, causing secondary porosity and affecting the performance of the etched foil. The additional DC electrochemical etching also increases the production cost of ultra-high voltage etched foil, resulting in decreased profits. Therefore, developing efficient ultra-high pressure corrosion methods is crucial for producing high-performance ultra-high pressure corrosion foils.

[0080] This invention provides a method for preparing anode foil, which includes performing secondary pitting corrosion on aluminum foil after primary pitting corrosion. The secondary pitting corrosion comprises multiple stages of pitting corrosion, with a mid-treatment process performed between each pair of adjacent pitting corrosion stages. In this invention, the mid-treatment process transports the large amount of aluminum ions accumulated within the tunnel pores generated during the pitting process to the outside, enhancing ion mass transfer within the pores. Simultaneously, it increases the acidity within the pores, reduces reaction resistance, improves the local environment within the pores, and facilitates the expansion and homogenization of the tunnel pores, thereby reducing the loss of ultra-high pressure anode foil and increasing its specific volume.

[0081] Preprocessing

[0082] In an embodiment of the present invention, the pretreatment includes immersing the aluminum foil in an alkaline immersion solution and an acidic immersion solution in sequence.

[0083] In some embodiments of the present invention, the concentration of the alkaline soaking solution is 0.1 mol / L to 1 mol / L. The concentration of the alkaline soaking solution provided by the present invention can be any value within the range formed by any two values ​​within the above-mentioned range, for example, it can be 0.1 mol / L to 0.6 mol / L, or 0.6 mol / L to 1 mol / L, and so on. The concentration of the alkaline soaking solution provided by the present invention can also be one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, and 1 mol / L, or any value satisfying the above-mentioned range.

[0084] In some embodiments of the present invention, the alkaline soaking solution contains at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and potassium bicarbonate.

[0085] In some embodiments of the present invention, the alkaline soaking solution may be, but is not limited to, an aqueous solution of sodium hydroxide, an aqueous solution of potassium hydroxide, an aqueous solution of sodium bicarbonate, or an aqueous solution of potassium bicarbonate.

[0086] In some embodiments of the present invention, the temperature of the alkaline soaking solution is 40°C to 60°C. Exemplarily, the temperature of the alkaline soaking solution can be one of 40°C, 45°C, 50°C, 55°C, and 60°C, or any value satisfying the above range.

[0087] In some embodiments of the present invention, the immersion time of the aluminum foil in the alkaline immersion solution is 20s to 90s. The immersion time provided by the present invention can be any value within the range formed by any two values ​​within the above-mentioned range, for example, it can be 20s to 50s, or 50s to 90s, and so on. The immersion time provided by the present invention can also be one of 20s, 30s, 40s, 50s, 60s, 70s, 80s, and 90s, or any value satisfying the above-mentioned range.

[0088] In some embodiments of the present invention, the acidic soaking solution contains hydrochloric acid and sulfuric acid.

[0089] In some embodiments of the present invention, the acidic soaking solution contains hydrochloric acid with a concentration of 0.65 mol / L to 1.0 mol / L and sulfuric acid with a concentration of 3.0 mol / L to 4.0 mol / L. Exemplarily, the concentration of hydrochloric acid can be one of 0.65 mol / L, 0.68 mol / L, 0.70 mol / L, 0.72 mol / L, 0.75 mol / L, 0.78 mol / L, 0.80 mol / L, 0.82 mol / L, 0.85 mol / L, 0.88 mol / L, 0.90 mol / L, 0.92 mol / L, 0.95 mol / L, 0.98 mol / L, or 1.0 mol / L, or any value satisfying the above range. The concentration of sulfuric acid can be one of 3.0 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L, or 4.0 mol / L, or any value satisfying the above range.

[0090] In some embodiments of the present invention, the temperature of the acidic soaking solution is 50°C to 85°C. The temperature of the acidic soaking solution provided by the present invention can be any value within the range formed by any two values ​​within the above-mentioned range, for example, it can be 50°C to 70°C, or 70°C to 85°C, and so on. The temperature of the acidic soaking solution provided by the present invention can also be one of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, and 85°C, or any value satisfying the above-mentioned range.

[0091] In some embodiments of the present invention, the immersion time of the aluminum foil in the acidic immersion solution is 40s to 80s. The immersion time provided by the present invention can be any value within the range formed by any two values ​​in the above range, such as 40s to 60s, 60s to 80s, and so on. The immersion time provided by the present invention can also be one of 40s, 50s, 60s, 70s, and 80s, or any value that satisfies the above range.

[0092] In some embodiments of the present invention, the aluminum foil is immersed in an alkaline immersion solution at 40°C to 60°C for 20 to 90 seconds, and then immersed in an acidic immersion solution at 50°C to 85°C for 40 to 80 seconds.

[0093] Primary pitting corrosion

[0094] In an embodiment of the present invention, the pretreated aluminum foil is placed in an etching solution containing aluminum ions for primary porosimetry.

[0095] In some embodiments of the present invention, the concentration of aluminum ions in the etching solution for primary pitting corrosion is 0.1 mol / L to 0.3 mol / L. Exemplarily, the concentration of aluminum ions in the etching solution can be one of 0.1 mol / L, 0.2 mol / L, or 0.3 mol / L, or any value satisfying the above range.

[0096] In some embodiments of the present invention, the etching solution for primary pitting corrosion is an acidic solution containing aluminum ions.

[0097] In some embodiments of the present invention, the etching solution for primary pitting corrosion contains hydrochloric acid and sulfuric acid.

[0098] In some embodiments of the present invention, the etching solution for primary pitting corrosion contains hydrochloric acid with a concentration of 0.65 mol / L to 1.0 mol / L and sulfuric acid with a concentration of 3.0 mol / L to 4.5 mol / L. Exemplarily, the concentration of hydrochloric acid in the etching solution can be one of 0.65 mol / L, 0.70 mol / L, 0.75 mol / L, 0.80 mol / L, 0.85 mol / L, 0.90 mol / L, 0.95 mol / L, or 1.0 mol / L, or any value satisfying the above range. The concentration of sulfuric acid can be one of the following: 3.0 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.7 mol / L, 3.8 mol / L, 3.9 mol / L, 4.0 mol / L, 4.1 mol / L, 4.2 mol / L, 4.3 mol / L, 4.4 mol / L, 4.5 mol / L, or any value within the above range.

[0099] In some embodiments of the present invention, the temperature for primary pitting corrosion is 50°C to 100°C. This can be understood as the temperature of the etchant for primary pitting corrosion being 50°C to 68°C, specifically 68°C to 80°C, 80°C to 90°C, or 90°C to 100°C. Exemplarily, the temperature for primary pitting corrosion can be one of 50°C, 55°C, 60°C, 68°C, 70°C, 75°C, 78°C, 80°C, 85°C, 90°C, 95°C, or 100°C, or any value satisfying the above range.

[0100] In some embodiments of the present invention, primary pitting corrosion is performed using direct current electrochemical corrosion with a current density of 0.35 A / cm. 2 ~0.70A / cm 2 The current density for primary pitting corrosion provided by this invention can be any value within the range formed by any two values ​​mentioned above, for example, it can be 0.35 A / cm. 2 ~0.50A / cm 2 It can also be 0.50 A / cm 2 ~0.70A / cm 2 And so on. The current density for primary pitting corrosion provided by this invention can also be 0.35 A / cm. 2 0.38A / cm 2 0.40A / cm 2 0.42A / cm 2 0.45A / cm 2 0.48A / cm 2 0.50A / cm 2 0.52A / cm2 0.55A / cm 2 0.58A / cm 2 0.60A / cm 2 0.62A / cm 2 0.65A / cm 2 0.68A / cm 2 0.70A / cm 2 One of the above values ​​or any value that satisfies the above range.

[0101] In some embodiments of the present invention, the energizing time for primary pitting corrosion is 20s to 200s; for example, it can be 20s to 100s; or it can be 40s to 80s. Exemplarily, the energizing time for primary pitting corrosion can be one of 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, or 200s, or any value satisfying the above range.

[0102] In some embodiments of the present invention, the pretreated aluminum foil is placed in an acidic solution containing aluminum ions at 50°C to 100°C for primary pitting corrosion, and the current density for primary pitting corrosion is 0.35 A / cm. 2 ~0.70A / cm 2 The power-on time is 20s to 200s.

[0103] In some embodiments of the present invention, after the first-stage pitting corrosion is completed, the aluminum foil is washed with deionized water at room temperature. The washing time can be set according to actual needs, for example, 10 minutes.

[0104] Secondary pitting corrosion

[0105] In an embodiment of the present invention, the aluminum foil that has undergone primary pitting corrosion is subjected to secondary pitting corrosion.

[0106] It should be noted that the secondary hole-expanding corrosion in this embodiment of the invention includes multi-stage hole-expanding corrosion, for example, subjecting the aluminum foil after primary hole-expanding corrosion to 2 to 10 stages of hole-expanding corrosion; preferably, the secondary hole-expanding corrosion includes 3 to 8 stages of hole-expanding corrosion. The multi-stage hole-expanding corrosion provided by this invention can be 2 to 5 stages, 5 to 7 stages, or 7 to 10 stages, and so on. The multi-stage hole-expanding corrosion provided by this invention can also be one of 2, 3, 4, 5, 6, 7, 8, 9, or 10 stages, or any value satisfying the above range.

[0107] In some embodiments of the present invention, each section of the hole-expanding corrosion is independently carried out using an acidic etching solution containing aluminum ions.

[0108] In some embodiments of the present invention, the concentration of aluminum ions in the acidic etching solution used for each stage of pit enlargement etching is independently 0.1 mol / L to 0.4 mol / L. Exemplarily, the concentration of aluminum ions in the acidic etching solution used for each stage of pit enlargement etching can be one of 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or 0.4 mol / L, or any value satisfying the above range.

[0109] In some embodiments of the present invention, the acidic etching solution used for each stage of borehole enlargement etching independently contains nitric acid and phosphoric acid.

[0110] In some embodiments of the present invention, each stage of the borehole enlargement corrosion is carried out using an acidic etching solution containing nitric acid at a concentration of 0.2 mol / L to 0.8 mol / L and phosphoric acid at a mass percentage of 0.2% to 0.8%. Exemplarily, the concentration of nitric acid can be one of 0.2 mol / L, 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 satisfying the above range. The mass percentage of phosphoric acid can be one of 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, or 0.8%, or any value satisfying the above range.

[0111] In some embodiments of the present invention, the temperature of each stage of pit enlargement etching is independently 50°C to 100°C. This can be understood as the temperature of the acidic etching solution for each stage of pit enlargement etching being independently 50°C to 68°C; it can be 68°C to 78°C; it can also be 60°C to 90°C; or it can be 78°C to 100°C. Exemplarily, the temperature of each stage of pit enlargement etching can be one of 50°C, 55°C, 60°C, 65°C, 68°C, 70°C, 75°C, 78°C, 80°C, 85°C, 90°C, 95°C, and 100°C, or any value satisfying the above range.

[0112] In some embodiments of the present invention, each section of the pit-expanding corrosion is independently carried out using direct current electrochemical corrosion, with each section having an independent current density of 0.1 A / cm. 2 ~0.4A / cm 2 For example, the current density for each section of the borehole enlargement corrosion can be 0.1 A / cm². 2 0.2A / cm 2 0.3A / cm 2 0.4A / cm 2 One of the above values ​​or any value that satisfies the above range.

[0113] In some embodiments of the present invention, the energizing time for each stage of borehole enlargement corrosion is independently 40s to 300s. The energizing time for each stage of borehole enlargement corrosion provided by the present invention can be any value within the range formed by any two values ​​in the above range, such as 40s to 150s, 60s to 100s, 50s to 200s, or 150s to 300s. The energizing time for each stage of borehole enlargement corrosion provided by this invention can also be one of 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, 290s, and 300s, or any value satisfying the above range.

[0114] In some embodiments of the present invention, the aluminum foil after primary pitting etching is subjected to multi-stage pitting etching. Each stage of pitting etching independently uses an acidic etching solution containing aluminum ions at 50°C to 100°C, with a current density of 0.1 A / cm². 2 ~0.4A / cm 2 The power-on time is 40s to 300s.

[0115] Mid-processing

[0116] In some embodiments of the present invention, an intermediate treatment is performed between each two adjacent sections of borehole enlargement corrosion. This can transport the large amount of aluminum ions accumulated in the tunnel borehole during the borehole enlargement process to the outside of the borehole, enhance the mass transfer of ions in the borehole, increase the acidity in the borehole, reduce reaction resistance, improve the local environment in the borehole, and facilitate the enlargement and homogenization of the tunnel borehole. This reduces the loss of the ultra-high pressure anode foil and increases the specific volume of the ultra-high pressure anode foil, resulting in an ultra-high pressure anode foil with low loss and high specific volume.

[0117] In some embodiments of the present invention, a mid-treatment is performed after each stage of borehole enlargement corrosion to further reduce the loss of the ultra-high pressure anode foil and increase the specific volume of the ultra-high pressure anode foil.

[0118] In some embodiments of the present invention, the intermediate treatment employs a treatment solution containing a corrosion inhibitor.

[0119] In some embodiments of the present invention, the mass percentage of the corrosion inhibitor in the treatment solution is independently 0.01% to 0.1%. Exemplarily, the mass percentage of the corrosion inhibitor in the treatment solution may be independently one of 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, or 0.1%, or any value satisfying the above range.

[0120] In some embodiments of the present invention, the corrosion inhibitors may be one or more of polyvinyl alcohol, thiourea, polyethylene glycol, polyacrylic acid, polyacrylamide, polystyrene sulfonic acid, sodium polystyrene sulfonate, and phosphate esters.

[0121] In some embodiments of the present invention, the processing solution in the intermediate treatment includes, independently, an acidic solution containing aluminum ions.

[0122] In some embodiments of the present invention, the treatment solutions in the intermediate treatment each contain oxalic acid independently.

[0123] In some embodiments of the present invention, the treatment solution in the intermediate treatment independently includes oxalic acid with a concentration of 0.5 mol / L to 1.6 mol / L and aluminum ions with a concentration of 0.1 mol / L to 0.3 mol / L. Exemplarily, the concentration of oxalic acid can be independently one of 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, and 1.6 mol / L, or any value satisfying the above range. The concentration of aluminum ions can be independently one of 0.1 mol / L, 0.2 mol / L, and 0.3 mol / L, or any value satisfying the above range.

[0124] In some embodiments of the present invention, the processing temperature of each intermediate treatment is independently 50°C to 100°C. This can be understood as the processing liquid temperature of each intermediate treatment being independently 50°C to 80°C, or 50°C to 90°C, or 80°C to 100°C. For example, the processing liquid temperature can be one of 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, and 100°C, or any value satisfying the above range.

[0125] In some embodiments of the present invention, the processing time of each intermediate processing step is independently between 10s and 500s. The processing time of the intermediate processing step provided by the present invention can be any value within the range formed by any two values ​​in the above range, for example, it can be independently between 10s and 20s, between 20s and 150s, between 10s and 400s, between 20s and 300s, between 150s and 300s, or between 300s and 500s. The processing time provided by this invention can also be independently one of 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, 200s, 210s, 220s, 230s, 240s, 250s, 260s, 270s, 280s, 290s, 300s, 350s, 400s, 450s, and 500s, or any value satisfying the above range.

[0126] In some embodiments of the present invention, the aluminum foil that has undergone pore-expanding corrosion is placed in a treatment solution containing a corrosion inhibitor at 50°C to 100°C for intermediate treatment for 10s to 500s.

[0127] Post-processing

[0128] In an embodiment of the present invention, the aluminum foil after the final intermediate treatment undergoes post-treatment. Of course, in some embodiments of the present invention, the aluminum foil after the final stage of hole-expanding etching may also undergo post-treatment depending on different process requirements.

[0129] In some embodiments of the present invention, the post-treatment uses a treatment solution containing nitric acid.

[0130] In some embodiments of the present invention, the mass percentage of nitric acid in the post-treatment solution is 3% to 10%. Exemplarily, the mass percentage of nitric acid can be one of 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value satisfying the above range.

[0131] In some embodiments of the present invention, the post-treatment temperature is 60°C to 80°C, which can be understood as the post-treatment liquid temperature being 60°C to 80°C. For example, the liquid temperature can be one of 60°C, 65°C, 70°C, 75°C, and 80°C, or any value satisfying the above range.

[0132] In some embodiments of the present invention, the post-processing time is 2 min to 10 min. Exemplarily, the post-processing time can be one of 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min, or any value that satisfies the above range.

[0133] In an embodiment of the present invention, the aluminum foil after the final intermediate treatment is placed in a treatment solution at 60°C to 80°C for post-treatment, and the treatment time is 2 min to 10 min.

[0134] In some embodiments of the present invention, after the post-treatment is completed, the aluminum foil is washed with deionized water at room temperature. The washing time can be set according to actual needs, for example, 20 minutes.

[0135] Drying process

[0136] In an embodiment of the present invention, the post-treated aluminum foil is dried.

[0137] In some embodiments of the present invention, the drying temperature is 60°C to 110°C. Exemplarily, the drying temperature can be one of 60°C, 70°C, 80°C, 90°C, 100°C, and 110°C, or any value satisfying the above range.

[0138] In some embodiments of the present invention, the drying time is 2 min to 10 min. Exemplarily, the drying time can be one of 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min, or any value that satisfies the above range.

[0139] In some embodiments of the present invention, the drying process can be carried out in an oven.

[0140] The present invention also provides an anode foil, which is prepared by the above-described preparation method.

[0141] The anode foil prepared by the method of the present invention can be an ultra-high voltage anode foil, with a voltage range applicable to 720V to 1000V, not limited to 850V. For example, the voltage of the anode foil can be one of 720V, 750V, 780V, 800V, 820V, 850V, 880V, 900V, 920V, 950V, 980V, and 1000V, or any value that meets the above range.

[0142] The present invention also provides an aluminum electrolytic capacitor comprising the above-described anode foil or an anode foil prepared by the above-described preparation method.

[0143] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0144] Example 1

[0145] A method for preparing an 850V anode foil, see [link to relevant documentation]. Figure 1 As shown, the preparation method is as follows:

[0146] 1) Pretreatment: First, immerse the aluminum foil (120μm) in a 0.25mol / L sodium hydroxide aqueous solution at 50℃ for 60s, and then immerse the aluminum foil in a mixed solution containing 1mol / L hydrochloric acid and 3.5mol / L sulfuric acid at 60℃ for 50s.

[0147] 2) Primary pitting corrosion: The pretreated aluminum foil was placed in a mixed solution containing 1.0 mol / L hydrochloric acid, 3.5 mol / L sulfuric acid, and 0.2 mol / L aluminum ions at 70℃ for primary DC pitting corrosion, with a current density of 0.5 A / cm². 2 The power-on time is 60 seconds, and then the aluminum foil is washed with deionized water at room temperature for 10 minutes.

[0148] 3) Secondary Pitting Corrosion 1: The aluminum foil after step 2) is placed in a mixed aqueous solution containing 0.5 mol / L nitric acid, 0.3 mol / L aluminum ions, and 0.3% phosphoric acid at 73°C for secondary DC pitting corrosion. The current density is 0.25 A / cm². 2 The power-on time is 90 seconds.

[0149] 4) Secondary treatment 1: The aluminum foil after step 3) is placed in a mixed aqueous solution containing 0.8 mol / L oxalic acid, 0.2 mol / L aluminum ions and 0.03% polyvinyl alcohol at 60°C for chemical etching treatment for 90 seconds.

[0150] 5) Repeat steps 3) and 4) above 4 times, and record them as secondary pitting corrosion 2, intermediate treatment 2, secondary pitting corrosion 3, intermediate treatment 3, secondary pitting corrosion 4, intermediate treatment 4, secondary pitting corrosion 5, and intermediate treatment 5 respectively.

[0151] 6) Post-treatment: Immerse the aluminum foil from step 5) in a 5% nitric acid aqueous solution at 75°C for 3 minutes, and then wash the aluminum foil with deionized water at room temperature for 20 minutes.

[0152] 7) Drying treatment: Place the post-treated aluminum foil in an oven at 85℃ and dry for 5 minutes.

[0153] Example 2

[0154] A method for preparing an 850V anode foil, see [link to relevant documentation]. Figure 2 As shown, the preparation method is as follows:

[0155] 1) Pretreatment: First, immerse the aluminum foil (120μm) in a 0.35mol / L sodium hydroxide aqueous solution at 40℃ for 60s, and then immerse the aluminum foil in a mixed solution containing 1mol / L hydrochloric acid and 3.5mol / L sulfuric acid at 60℃ for 50s.

[0156] 2) Primary pitting corrosion: The pretreated aluminum foil was placed in a mixed solution containing 1.0 mol / L hydrochloric acid, 3.5 mol / L sulfuric acid, and 0.2 mol / L aluminum ions at 70℃ for primary DC pitting corrosion, with a current density of 0.5 A / cm². 2 The power-on time is 60 seconds, and then the aluminum foil is washed with deionized water at room temperature for 10 minutes.

[0157] 3) Secondary Pitting Corrosion 1: The aluminum foil after step 2) is placed in a mixed aqueous solution containing 0.5 mol / L nitric acid, 0.3 mol / L aluminum ions, and 0.3% phosphoric acid at 73°C for secondary DC pitting corrosion. The current density is 0.25 A / cm². 2 The power-on time is 65 seconds.

[0158] 4) Secondary treatment 1: The aluminum foil after step 3) is placed in a mixed aqueous solution containing 0.8 mol / L oxalic acid, 0.2 mol / L aluminum ions and 0.04% polystyrene sulfonic acid at 65°C for chemical etching treatment for 50 seconds.

[0159] 5) Repeat steps 3) and 4) above 6 times, and record them as secondary pitting corrosion 2, intermediate treatment 2, secondary pitting corrosion 3, intermediate treatment 3, secondary pitting corrosion 4, intermediate treatment 4, secondary pitting corrosion 5, intermediate treatment 5, secondary pitting corrosion 6, intermediate treatment 6, secondary pitting corrosion 7, and intermediate treatment 7 respectively.

[0160] 6) Post-treatment: Immerse the aluminum foil from step 5) in a 5% nitric acid aqueous solution at 75°C for 3 minutes, and then wash the aluminum foil with deionized water at room temperature for 20 minutes.

[0161] 7) Drying treatment: Place the post-treated aluminum foil in an oven at 85℃ and dry for 5 minutes.

[0162] Example 3

[0163] The remaining operations are the same as in Example 2, except that:

[0164] The process involves 7 steps of initial treatment, followed by 7 steps of secondary hole enlargement and etching, and then direct post-treatment.

[0165] Example 4

[0166] The remaining operations are the same as in Example 1, except that:

[0167] 4) Secondary treatment 1: The aluminum foil after step 3) is placed in a mixed aqueous solution containing 1.6 mol / L oxalic acid, 0.3 mol / L aluminum ions and 0.03% polyvinyl alcohol at 80°C for chemical etching treatment for 20 seconds.

[0168] Example 5

[0169] The remaining operations are the same as in Example 1, except that:

[0170] 4) Processing 1: The aluminum foil after step 3) is placed in a mixed aqueous solution containing 0.5 mol / L oxalic acid, 0.1 mol / L aluminum ions and 0.03% polyvinyl alcohol at 80°C for chemical etching treatment for 300 seconds.

[0171] Comparative Example 1

[0172] A method for preparing an 850V anode foil, the method is as follows:

[0173] 1) Pretreatment: First, immerse the aluminum foil (120μm) in a 0.35mol / L sodium hydroxide aqueous solution at 40℃ for 60s, and then immerse the aluminum foil in a mixed solution containing 1mol / L hydrochloric acid and 3.5mol / L sulfuric acid at 60℃ for 50s.

[0174] 2) Primary pitting corrosion: The pretreated aluminum foil was placed in a mixed solution containing 1.0 mol / L hydrochloric acid, 3.5 mol / L sulfuric acid, and 0.2 mol / L aluminum ions at 70℃ for primary DC pitting corrosion, with a current density of 0.5 A / cm². 2 The power-on time is 60 seconds, and then the aluminum foil is washed with deionized water at room temperature for 10 minutes.

[0175] 3) Secondary pitting corrosion 1: The aluminum foil after step 2) is placed in a mixed aqueous solution containing 0.5 mol / L nitric acid, 0.3 mol / L aluminum ions, and 0.3% phosphoric acid at 73℃ for secondary DC pitting corrosion, with a current density of 0.25 A / cm². 2 The power-on time is 65 seconds.

[0176] 4) Processing 1: The aluminum foil that has undergone step 3) is placed in a mixed aqueous solution containing 0.8 mol / L oxalic acid and 0.2 mol / L aluminum ions at 65°C for chemical etching treatment for 50 seconds.

[0177] 5) Repeat steps 3) and 4) above 7 times.

[0178] 6) Post-treatment: Immerse the aluminum foil from step 5) in a 5% nitric acid aqueous solution at 75°C for 3 minutes, and then wash the aluminum foil with deionized water at room temperature for 20 minutes.

[0179] 7) Drying treatment: Place the post-treated aluminum foil in an oven at 85℃ and dry for 5 minutes.

[0180] Comparative Example 2

[0181] A method for preparing an 850V anode foil, see [link to relevant documentation]. Figure 3 As shown, the preparation method is as follows:

[0182] 1) Pretreatment: First, immerse the aluminum foil (120μm) in a 0.35mol / L sodium hydroxide aqueous solution at 40℃ for 60s, and then immerse the aluminum foil in a mixed solution containing 1mol / L hydrochloric acid and 3.5mol / L sulfuric acid at 60℃ for 50s.

[0183] 2) Primary pitting corrosion: The pretreated aluminum foil was placed in a mixed solution containing 1.0 mol / L hydrochloric acid, 3.5 mol / L sulfuric acid, and 0.2 mol / L aluminum ions at 70℃ for primary DC pitting corrosion, with a current density of 0.5 A / cm². 2 The power-on time is 60 seconds, and then the aluminum foil is washed with deionized water at room temperature for 10 minutes.

[0184] 3) Secondary pitting corrosion: The aluminum foil processed in step 2) is immersed in a mixed aqueous solution containing 0.5 mol / L nitric acid, 0.3 mol / L aluminum ions, and 0.3% phosphoric acid at 73°C for secondary DC pitting corrosion. The current density is 0.25 A / cm². 2 The power-on time is 510s.

[0185] 4) Post-treatment: Immerse the aluminum foil from step 3) in a 5% nitric acid aqueous solution at 75°C for 3 minutes, and then wash the aluminum foil with deionized water at room temperature for 20 minutes.

[0186] 5) Drying treatment: Place the post-treated aluminum foil in an oven at 85℃ and dry for 5 minutes.

[0187] Comparative Example 3

[0188] The remaining operations are the same as in Example 1, except that:

[0189] 4) Secondary treatment 1: The aluminum foil after step 3) is placed in a mixed aqueous solution containing 0.8 mol / L hydrochloric acid, 0.2 mol / L aluminum ions and 0.03% polyvinyl alcohol at 60°C for chemical etching treatment for 90 seconds.

[0190] Comparative Example 4

[0191] The remaining operations are the same as in Example 1, except that:

[0192] 4) Processing 1: The aluminum foil that has undergone step 3) is placed in a mixed aqueous solution containing 0.2 mol / L aluminum ions and 0.03% polyvinyl alcohol at 60°C for chemical etching treatment for 90 seconds.

[0193] Performance testing

[0194] Specific capacity and loss tangent tgδ: The anode foils prepared in the examples and comparative examples were subjected to formation treatment at 520V in a 10% boric acid solution at 90℃. Then, the capacitance and loss tangent tgδ were tested using a ZX8516B model electrostatic capacitance tester from Changzhou Zhixin Precision Electronics Co., Ltd. The measurement accuracy was ±2%, the test frequency was 120±5HZ, the measurement voltage was below 0.5Vrms, and the bath composition was: 1000mL pure water, 80g ammonium pentaborate, and the test temperature was 30±2℃.

[0195] Table 1. Performance of the ultra-high pressure anode foils prepared in the examples and comparative examples.

[0196] Test Project <![CDATA[Specific capacitance (μF / cm 2 )]]> tgδ Anode foil thickness (μm) Example 1 0.351 2.72 117 Example 2 0.358 2.58 116 Example 3 0.355 2.56 115 Example 4 0.346 2.94 117 Example 5 0.348 2.86 116 Comparative Example 1 0.331 2.65 114 Comparative Example 2 0.322 3.51 117 Comparative Example 3 0.330 3.24 116 Comparative Example 4 3.326 3.48 117

[0197] Combined with appendix Figure 4-5 As can be seen from Table 1, adding intermediate treatment after each stage of pit enlargement corrosion is beneficial for increasing the pit diameter (e.g., Figure 4 and Figure 5 As shown in the figure, this effectively improves the specific capacity of the ultra-high pressure anode foil and reduces losses. Moreover, by adding corrosion inhibitors to the treatment solution during the intermediate treatment, excessive dissolution and thinning of the aluminum foil surface can be inhibited, avoiding unnecessary loss of specific capacity. This also shows that corrosion inhibitors are crucial for improving the specific capacity of ultra-high pressure anode foil.

[0198] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included 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. A method for preparing an anode foil, characterized in that, The anode foil is an ultra-high voltage anode foil with a voltage of 720 V to 1000 V. The preparation method includes performing a secondary pitting corrosion on the aluminum foil after primary pitting corrosion. The secondary pitting corrosion includes multiple pitting corrosion stages, and an intermediate treatment is performed between each two adjacent pitting corrosion stages. Each intermediate treatment independently uses a treatment solution containing a corrosion inhibitor, and each intermediate treatment solution independently includes an acidic solution containing aluminum ions and oxalic acid. Each of the pore-expanding corrosion processes independently employs an acidic etching solution containing aluminum ions, and each of the acidic etching solutions used in the pore-expanding corrosion process independently contains nitric acid and phosphoric acid.

2. The method for preparing the anode foil as described in claim 1, characterized in that, The concentration of aluminum ions in the acidic etching solution used for each of the aforementioned pitting corrosion processes is independently 0.1 mol / L to 0.4 mol / L.

3. The method for preparing the anode foil as described in claim 1, characterized in that, Each of the sections described in the enlargement corrosion process uses an acidic etching solution containing nitric acid at a concentration of 0.2 mol / L to 0.8 mol / L and phosphoric acid at a mass percentage of 0.2% to 0.8%.

4. The method for preparing the anode foil as described in claim 1, characterized in that, Each section of the pitting corrosion process employs independent direct current electrochemical corrosion, with a current density of 0.1 A / cm². 2 ~0.4 A / cm 2 .

5. The method for preparing the anode foil as described in claim 1, characterized in that, The temperature for each segment of the pore-expanding corrosion is independently 50℃~100℃.

6. The method for preparing the anode foil as described in claim 5, characterized in that, The temperature for each segment of the pore-expanding corrosion is independently 60℃~90℃.

7. The method for preparing the anode foil as described in claim 5, characterized in that, The temperature for each segment of the pitting corrosion is independently 68℃~78℃.

8. The method for preparing the anode foil as described in claim 1, characterized in that, The energizing time for each segment of the pitting corrosion is independent, ranging from 40 s to 300 s.

9. The method for preparing the anode foil as described in claim 8, characterized in that, The energizing time for each segment of the pitting corrosion is independent, ranging from 50 s to 200 s.

10. The method for preparing the anode foil as described in claim 8, characterized in that, The energizing time for each segment of the pitting corrosion is independently 60 s to 100 s.

11. The method for preparing the anode foil as described in claim 1, characterized in that, The mass percentage of corrosion inhibitors in the treatment solution of the intermediate treatment is 0.01% to 0.1% for each individual.

12. The method for preparing the anode foil as described in claim 1, characterized in that, The corrosion inhibitors each independently include one or more of the following: polyvinyl alcohol, thiourea, polyethylene glycol, polyacrylic acid, polyacrylamide, polystyrene sulfonic acid, sodium polystyrene sulfonate, and phosphate esters.

13. The method for preparing the anode foil as described in claim 1, characterized in that, The treatment solution in the process independently includes oxalic acid with a concentration of 0.5 mol / L to 1.6 mol / L and aluminum ions with a concentration of 0.1 mol / L to 0.3 mol / L.

14. The method for preparing the anode foil as described in claim 1, characterized in that, The processing temperatures for each process are independently 50℃~100℃.

15. The method for preparing the anode foil as described in claim 14, characterized in that, The processing temperatures for each of the aforementioned processes are independently 50℃~90℃.

16. The method for preparing the anode foil as described in claim 14, characterized in that, The processing temperatures for each of the aforementioned processes are independently 50℃~80℃.

17. The method for preparing the anode foil as described in claim 1, characterized in that, The processing time for each of the aforementioned processes is independent, ranging from 10 s to 500 s.

18. The method for preparing the anode foil as described in claim 17, characterized in that, The processing time for each of the aforementioned processes is independent, ranging from 10 s to 400 s.

19. The method for preparing the anode foil as described in claim 17, characterized in that, The processing time for each of the aforementioned processes is independent, ranging from 20 s to 300 s.

20. The method for preparing the anode foil as described in claim 1, characterized in that, The intermediate treatment is performed after each segment of the enlarged etch.

21. The method for preparing the anode foil as described in claim 1, characterized in that, The secondary pore-expanding corrosion includes two to ten stages of pore-expanding corrosion.

22. The method for preparing the anode foil as described in claim 21, characterized in that, The secondary pore-expanding corrosion includes three to eight pore-expanding corrosion stages.

23. The method for preparing the anode foil as described in claim 1, characterized in that, The primary pitting corrosion uses an etching solution containing aluminum ions.

24. The method for preparing the anode foil as described in claim 23, characterized in that, The concentration of aluminum ions in the etching solution for primary pitting corrosion is 0.1 mol / L to 0.3 mol / L.

25. The method for preparing the anode foil as described in claim 23, characterized in that, The etching solution used for primary pitting corrosion is an acidic solution containing aluminum ions.

26. The method for preparing the anode foil as described in claim 23, characterized in that, The corrosive solution used in the primary pitting corrosion contains hydrochloric acid and sulfuric acid.

27. The method for preparing the anode foil as described in claim 26, characterized in that, The corrosive solution for primary pitting corrosion contains hydrochloric acid with a concentration of 0.65 mol / L to 1.0 mol / L and sulfuric acid with a concentration of 3.0 mol / L to 4.5 mol / L.

28. The method for preparing the anode foil as described in claim 1, characterized in that, The temperature for primary pitting corrosion is 50℃~100℃.

29. The method for preparing the anode foil as described in claim 28, characterized in that, The temperature for primary pitting corrosion is 60℃~90℃.

30. The method for preparing the anode foil as described in claim 28, characterized in that, The temperature for primary pitting corrosion is 68℃~80℃.

31. The method for preparing the anode foil as described in claim 1, characterized in that, The primary pitting corrosion was performed using direct current electrochemical corrosion with a current density of 0.35 A / cm². 2 ~0.70 A / cm 2 .

32. The method for preparing the anode foil as described in claim 1, characterized in that, The energizing time for the first-order pitting corrosion is 20 s to 200 s.

33. The method for preparing the anode foil as described in claim 32, characterized in that, The energizing time for the first-order pitting corrosion is 20 s to 100 s.

34. The method for preparing the anode foil as described in claim 32, characterized in that, The energizing time for the first-order pitting corrosion is 40 s to 80 s.

35. The method for preparing the anode foil as described in claim 1, characterized in that, The preparation method also includes a pretreatment performed before the primary pitting corrosion.

36. The method for preparing the anode foil as described in claim 35, characterized in that, The pretreatment includes placing the aluminum foil in an alkaline immersion solution and an acidic immersion solution in sequence.

37. The method for preparing the anode foil as described in claim 36, characterized in that, The alkaline soaking solution contains at least one of sodium hydroxide, potassium hydroxide, sodium bicarbonate, and potassium bicarbonate.

38. The method for preparing the anode foil as described in claim 36, characterized in that, The concentration of the alkaline soaking solution is 0.1 mol / L to 1 mol / L.

39. The method for preparing the anode foil as described in claim 36, characterized in that, The temperature of the alkaline soaking solution is 40℃~60℃.

40. The method for preparing the anode foil as described in claim 36, characterized in that, The aluminum foil is immersed in the alkaline immersion solution for 20 s to 90 s.

41. The method for preparing the anode foil as described in claim 36, characterized in that, The acidic soaking solution contains hydrochloric acid and sulfuric acid.

42. The method for preparing the anode foil as described in claim 41, characterized in that, The acidic soaking solution contains hydrochloric acid with a concentration of 0.65 mol / L to 1.0 mol / L and sulfuric acid with a concentration of 3.0 mol / L to 4.0 mol / L.

43. The method for preparing the anode foil as described in claim 36, characterized in that, The temperature of the acidic soaking solution is 50℃~85℃.

44. The method for preparing the anode foil as described in claim 36, characterized in that, The aluminum foil is immersed in the acidic immersion solution for 40 s to 80 s.

45. The method for preparing the anode foil as described in claim 1, characterized in that, The preparation method also includes post-processing and drying.

46. ​​The method for preparing the anode foil as described in claim 45, characterized in that, The post-treatment uses a treatment solution containing nitric acid.

47. The method for preparing the anode foil as described in claim 46, characterized in that, The mass percentage of nitric acid in the treatment solution is 3% to 10%.

48. The method for preparing the anode foil as described in claim 45, characterized in that, The post-processing temperature is 60℃~80℃, and the post-processing time is 2 min~10 min.

49. The method for preparing the anode foil as described in claim 45, characterized in that, The drying temperature is 60℃~110℃, and the drying time is 2 min~10 min.

50. An anode foil, characterized in that, The anode foil is prepared by any one of claims 1-49, and the anode foil is an ultra-high voltage anode foil with a voltage of 720 V to 1000 V.

51. An aluminum electrolytic capacitor, characterized in that, The aluminum electrolytic capacitor comprises the anode foil as described in claim 50 or the anode foil prepared by any one of claims 1-49.

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