An anode foil, a preparation method thereof, and an application thereof

Abstract

The present invention provides an anode foil and its preparation method and application. The pore-forming solution of the anode foil, by weight, comprises the following components: 3-4 parts of aluminum salt, 30-35 parts of sulfuric acid, 4-5 parts of hydrochloric acid, and 0.01-0.5 part of a metal surface treatment agent; the metal surface treatment agent is composed of one or more of polyoxyethylene ether, phosphate ester, and fluorosilicate. On the one hand, the metal surface treatment agent in the pore-forming solution of the anode foil can form more exposed aluminum bases on the crystal plane, reduce its pitting potential, obtain more uniform pore-forming points, and avoid the phenomenon that the pore-forming points gather at the grain boundary part while the pores are sparse in the crystal plane part; on the other hand, the metal surface treatment agent slows down the formation of the aluminum sulfate film to a certain extent, which is beneficial to the deepening and expansion of pores and reduces the proportion of fine and shallow ineffective pores. The number of pores on the surface of the anode foil prepared by the pore-forming solution provided by the present invention is ≥10<supgt;7< / supgt; / cm<supgt;2< / supgt>, and the pore diameter size is 1.15-1.19 μm. The pore uniformity on the surface of the anode foil prepared by the present invention is improved, and the electrostatic specific capacitance of the anode foil is significantly increased.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolytic capacitors, and more specifically, to an anode foil material, a preparation method thereof, and an application thereof. Background Art

[0002] As a common device on electronic circuits, a capacitor functions by charging and discharging. Its most basic function is to store electric charge, and based on this basic function, many functions and roles have been derived: passing alternating current, blocking direct current; passing high-frequency current, blocking low-frequency current; playing electrical roles such as energy storage, filtering, bypassing, coupling, decoupling, and phase shifting in a circuit. Aluminum electrolytic capacitors are the most special and crucial components among capacitors, having advantages such as large capacitance, low price, and small volume. Among them, the anode foil is the core raw material of aluminum electrolytic capacitors, and the performance of the anode foil largely determines many key technical indicators of aluminum electrolytic capacitors, such as capacitance, volume, leakage current, loss, and lifespan. Aluminum electrolytic capacitors are widely used in the whole machine markets such as industrial frequency conversion and consumer electronics. With the rapid development of electronic technologies in products such as smart homes, 5G, AI, wind and solar power generation, and new energy vehicles, as well as the further increase in the assembly density and integration level of electronic whole machines, the demand for the miniaturization of capacitors has become increasingly urgent, which puts higher requirements on the specific capacitance of the anode foil.

[0003] Currently, there are mainly two methods to increase the specific capacitance per unit area of aluminum electrolytic anode foil: One method is to increase the specific capacitance of the anode foil by increasing the thickness of the anode foil or maintaining a certain degree of corrosion remaining thickness during the preparation of the anode foil. However, this method will have problems such as increasing the winding volume during capacitor winding, affecting the selection of capacitor shell numbers, and also affecting the performance of aluminum electrolytic capacitors. Another method is to increase the surface area of the anode foil. The specific capacitance of the anode foil depends on the magnification of the surface area of the aluminum core layer covered by the oxide film of the anode foil, that is, the specific surface area. Generally, an electrochemical corrosion method is used to form tunnel holes with a certain depth perpendicular to the surface of the aluminum foil on the surface of the aluminum foil, increasing the specific surface area, thereby increasing the electrostatic capacitance of the anode foil.

[0004] The prior art uses electrochemical corrosion to prepare anode foil through processes such as pretreatment, pore formation, pore expansion, and post-treatment, so as to form tunnel holes with a certain depth perpendicular to the surface of the aluminum foil on the surface of the aluminum foil, increasing the specific surface area of the anode foil and increasing the specific capacitance of the aluminum electrolytic anode foil to a certain extent. However, since corrosion pores are more likely to germinate at grain boundaries during electrolytic pore formation, and it is difficult to form pores on crystal planes, it is easy to cause uneven pore formation on the surface of the anode foil, resulting in technical problems such as more pore formation and easy pore merging between grain boundaries, less pore formation on crystal planes, and more shallow pores. Moreover, with the increase in the pore formation current density, this problem of uneven pore formation becomes more prominent, affecting the electrostatic capacitance and mechanical properties of the aluminum electrolytic anode foil. Summary of the Invention

[0005] The present invention aims to overcome the technical problems in the prior art described above, namely, during the pore formation process of the anode foil, there are many pores formed between grain boundaries, which are prone to pore merging, fewer pores are formed on the crystal plane, and there are many shallow pores. The present invention provides a pore-forming solution for the anode foil, which can solve the problem of uneven pore formation during the pore formation process of the anode foil in the prior art.

[0006] Another object of the present invention is to provide a pretreatment method for the anode foil.

[0007] Another object of the present invention is to provide a preparation method for the anode foil.

[0008] Another object of the present invention is to provide an anode foil.

[0009] Another object of the present invention is to provide an application of the anode foil in an aluminum electrolytic capacitor.

[0010] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0011] A pore-forming solution for the anode foil, in parts by weight, comprises the following components: 3 - 4 parts of aluminum salt, 30 - 35 parts of sulfuric acid, 4 - 5 parts of hydrochloric acid, and 0.01 - 0.5 part of a metal surface treatment agent; the metal surface treatment agent is composed of one or more of polyoxyethylene ether, phosphate ester, and fluorosilicate.

[0012] In the present invention, a pore-forming solution for the anode foil is provided. A metal surface treatment agent is added to the pore-forming solution, and the metal surface treatment agent is composed of one or more of polyoxyethylene ether, phosphate ester, and fluorosilicate. On the one hand, the metal surface treatment agent in the pore-forming solution for the anode foil can form more exposed aluminum bases on the crystal plane, reduce its pitting potential, obtain more uniform pore-forming points, and avoid the phenomenon that the pore-forming points gather in the grain boundary part and are sparse in the crystal plane part; on the other hand, the metal surface treatment agent slows down the formation of the aluminum sulfate film to a certain extent, which is beneficial to the deepening and expansion of pores and reduces the proportion of fine and shallow ineffective pores. The surface pore formation uniformity of the anode foil prepared by using the pore-forming solution for the anode foil provided by the present invention is significantly improved, and the electrostatic specific capacitance of the anode foil is significantly increased.

[0013] Preferably, the proportion of the metal surface treatment agent in the pore-forming solution for the anode foil of the present invention is 0.05 - 0.2 part.

[0014] The proportion of the metal surface treatment agent affects the amount of initial pore-forming points. In the processing and corrosion process of the aluminum anode foil, insufficient initial pore-forming quantity will lead to insufficient pore-forming points, resulting in easy pore aggregation at the grain boundary or dislocation, poor pore-forming uniformity, and low electrostatic capacitance; excessive initial pore-forming quantity will lead to insufficient energy distribution for a single pore, resulting in the inability of the pore to grow in the subsequent process, causing ineffective pore formation, and too many small pores on the anode foil are prone to pore merging, resulting in surface layer peeling, and ultimately reducing the number of effectively deepened pores on the anode foil.

[0015] Preferably, the metal surface treatment agent of the present invention is a phosphate ester surface treatment agent.

[0016] The main function of the phosphate ester and polyoxyethylene ether metal surface treatment agent of the present invention is to activate the surface of the aluminum foil, making it easier to obtain the opportunity of surface pore formation, achieving an increase in the number of surface pores and the uniformity of pore formation, thereby enhancing the electrostatic specific capacitance. However, if the treatment is too strong and the amount of pore formation is too large, it will also cause the pore diameter to not grow effectively, resulting in a decrease in the electrostatic capacitance instead.

[0017] The F-containing compounds in the fluorosilicate treatment agent will etch the metal surface. Its ability to activate the aluminum foil surface and create manufacturing defect points is stronger, which will significantly increase the number of pore formations and easily lead to a smaller pore diameter. The control requirements for this type of metal surface treatment agent are more stringent. When controlled well, its electrostatic specific capacitance is better than that of the phosphate ester type treatment agent, and its stability is slightly lower than that of the phosphate ester type metal surface treatment agent.

[0018] The polyoxyethylene ether in the metal surface treatment agent of the present invention is one or both of nonylphenol polyoxyethylene ether and lauryl alcohol polyoxyethylene ether.

[0019] The phosphate ester in the metal surface treatment agent of the present invention is one or more of nonylphenol polyoxyethylene ether phosphate, lauryl alcohol polyoxyethylene ether phosphate, and alkyl alcohol amide phosphate.

[0020] The fluorosilicate in the metal surface treatment agent of the present invention is one or more of sodium fluorosilicate, potassium fluorosilicate, magnesium fluorosilicate, and calcium fluorosilicate.

[0021] The present invention also protects a pretreatment method for an anode foil, which is to soak the anode foil after impurity removal in a pore-forming solution at 60 - 90 °C for 40 - 70 s, wherein the pore-forming solution is the anode foil pore-forming solution of claim 1.

[0022] The impurity removal method of the anode foil of the present invention is to soak the anode foil in a 5 - 20 wt% phosphoric acid solution at 60 - 90 °C for 40 - 70 s.

[0023] The present invention also protects a preparation method for an anode foil, which includes the following steps:

[0024] S1. Pretreatment: Perform pretreatment according to the above pretreatment method;

[0025] S2. Primary pore formation: Apply a variable current with an average current density of 0.4 - 0.8 A / cm 2 to the aluminum foil pretreated in S1 in a pore-forming solution at 70 - 75 °C, and repeatedly corrode to obtain a primary foil;

[0026] S3. Secondary reaming: The washed primary foil is placed in a reaming solution containing 1-2 wt% aluminum ions, ≤1 wt% phosphoric acid, and 5-8 wt% nitric acid, and direct current electrolysis is carried out at 60-75 °C and a current density of 0.15-0.2 A / cm 2 for 450-550 s of reaming corrosion to obtain the secondary foil;

[0027] S4. Post-treatment: The secondary foil is washed and dried to obtain the anodic foil material with uniform pore formation and high specific capacitance.

[0028] Preferably, the average current density applied in the primary pore formation in S2 is 0.5-0.6 A / cm 2 of variable current.

[0029] The variable current described in the present invention is that the applied current density conforms to the i = 0.7 t mode. Compared with the power supply modes of direct current or intermittent pulsed current, the initial current density ≥1.0 A / cm 2 , which increases the number of initial pore formation points on the surface of the anodic foil. Then, the current density decreases significantly, enabling the holes that can grow after pore formation to maintain the supply of current energy. In the later stage, a small current density is maintained to enable the holes to continue to deepen. If constant current or pulsed current is continuously applied, the holes on the surface of the anodic foil cannot become deeper longitudinally after pore formation, and the current will re-locate the pore formation points on the surface of the aluminum foil, which will instead damage the holes already formed on the foil surface and easily form too many shallow and fine holes, which is not conducive to the improvement of the electrostatic specific capacitance.

[0030] Preferably, the phosphoric acid content in the secondary reaming solution in S3 is 0.5-0.9 wt%.

[0031] The present invention uses phosphoric acid as the corrosion inhibitor in the secondary reaming solution. An appropriate phosphoric acid content can effectively protect the surface and shallow pores of the anodic foil, guide the current to deeply expand the inner layer pore diameter, expand the V-shaped pores formed on the surface of the anodic foil during the pore formation stage into U-shaped pores, effectively improve the uniformity of the depth of the pores on the surface of the anodic foil, and thus improve its electrostatic specific capacitance.

[0032] The cleaning method of the secondary foil in S4 of the present invention is to chemically clean the secondary foil in 5 wt% nitric acid at 60-70 °C for 60-120 s to remove the residual liquid and part of the aluminum phosphate film in the pores.

[0033] The drying temperature in S4 of the present invention is 120-200 °C.

[0034] The present invention also protects an anodic foil with uniform pore formation and high specific capacitance, and the anodic foil with uniform pore formation and high specific capacitance is prepared by the above preparation method.

[0035] The pore diameter size of the anodic foil with uniform pore formation and high specific capacitance described in the present invention is 0.8-1.3 μm.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] During the first-stage pore-forming process of the present invention, a metal surface treatment agent is added to the pore-forming solution to form more exposed aluminum bases on the crystal plane, reduce its pitting potential, obtain more uniform pore-forming points, and avoid the phenomenon that the pore-forming points gather at the grain boundary part and are sparse at the crystal plane part; and to a certain extent, it slows down the formation of the aluminum sulfate film, which is beneficial to the deepening and expansion of the pores, reduces the proportion of fine and shallow ineffective pores, and can significantly increase the pore-forming uniformity of the anode foil. The number of surface pores of the anode foil prepared with the anode foil pore-forming solution provided by the present invention is ≥ 10 7 / cm 2 , the pore size is 1.15 - 1.19 μm. The surface pore-forming uniformity of the anode foil prepared by the present invention is significantly improved, and the electrostatic specific capacitance of the anode foil is not less than 0.800 μF / cm 2 , and is significantly improved. Description of the Drawings

[0038] Figure 1 SEM image of the surface pore distribution of the anode foil prepared in Example 11.

[0039] Figure 2 SEM image of the surface pore distribution of the anode foil prepared in Example 13.

[0040] Figure 3 SEM image of the surface pore distribution of the anode foil prepared in Comparative Example 3.

[0041] Figure 4 SEM image of the surface pore distribution of the anode foil prepared in Comparative Example 4.

[0042] Figure 5 Graph of the surface pore size distribution of the anode foil prepared in Example 11.

[0043] Figure 6 Graph of the surface pore size distribution of the anode foil prepared in Example 13.

[0044] Figure 7 Graph of the surface pore size distribution of the anode foil prepared in Comparative Example 3.

[0045] Figure 8 Graph of the surface pore size distribution of the anode foil prepared in Comparative Example 4. Detailed Embodiments

[0046] The present invention will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Modifications, substitutions, and improvements made by those skilled in the art based on the understanding of the present invention still fall within the protection scope of the present invention. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are conventional raw material reagents purchased.

[0047] Source of raw materials: Sulfuric acid in the pore-forming solution was purchased from Shaoguan Xianghe Fine Chemicals; hydrochloric acid was purchased from Dongyangguang Electrochemical Factory, Ruyuan, Shaoguan; nonylphenol polyoxyethylene ether reagent was purchased from Jinan Huifengda Chemical Co., Ltd.; sodium fluorosilicate was purchased from Henan Mingzhixin Chemical Products Co., Ltd.; lauryl alcohol polyoxyethylene ether phosphate was purchased from Hai'an Petrochemical Factory, Jiangsu Province.

[0048] Examples 1 - 9

[0049] A pore-forming solution for anodic foil, the main components and their contents are shown in Table 1:

[0050] Table 1 Main components of the pore-forming solution for the anodic foil described in Examples 1 - 9

[0051]

[0052] Examples 10 - 18

[0053] A method for preparing a pore-forming uniform and high specific capacitance anodic foil material, characterized by comprising the following steps:

[0054] S1. Pretreatment: Immerse an aluminum foil with a purity greater than or equal to 99.985% and a thickness of 125 μm in a 10 wt% phosphoric acid solution at 65°C for 60 s; then immerse the aluminum foil in the pore-forming solution at 75°C for 60 s;

[0055] S2. Primary pore formation: Apply a variable current with an average current density of 0.5 A / cm² (the current change conforms to the i = 0.7 2 mode, t is the power-on time, and t takes 22 s) to the aluminum foil pretreated in S1 in the pore-forming solution at 73°C, and repeat the pore-forming cycle 5 times to obtain a primary pore-forming foil; t 2

[0056] S3. Secondary pore formation: After washing with water, place the primary foil in an expanding pore solution containing 2 wt% aluminum ions, 0.8 wt% phosphoric acid, and 7 wt% nitric acid, and perform multiple power-on expanding pore corrosion for a total of 520 s at 70°C and a current density of 0.15 A / cm² to obtain a secondary foil with effectively enlarged pore diameter; 2

[0057] S4. Post-treatment: After taking out the secondary foil from the expanding pore solution, wash it with deionized water, chemically clean it in a solution containing 1 wt% aluminum ions and 5 wt% nitric acid at 65°C for 80 s; then wash it in deionized water and dry it at 150°C to obtain the anodic foil material.

[0058] In the preparation of the anodic foil in S1 of Examples 10 - 18, the pore-forming solutions respectively correspond to the pore-forming solutions provided in Examples 1 - 9.

[0059] Example 19

[0060] The difference from Example 10 is that in S2. Primary pore formation: The aluminum foil pretreated in S1 is subjected to a variable current with an average current density of 0.8 A / cm² in the pore-forming solution at 70 °C 2 (the current change conforms to i = 0.7 t mode, t is the power-on time, and t is taken as 15 s), and the primary pore-forming cycle is repeated 5 times to obtain a primary pore-forming foil with a large number of pores.

[0061] Example 20

[0062] The difference from Example 10 is that in S2. Primary pore formation: The aluminum foil pretreated in S1 is subjected to a variable current with an average current density of 0.4 A / cm² in the pore-forming solution at 75 °C 2 (the current change conforms to i = 0.7 t mode, t is the power-on time, and t is taken as 25 s), and the primary pore-forming cycle is repeated 5 times to obtain a primary pore-forming foil with a large number of pores.

[0063] Example 21

[0064] The difference from Example 10 is that in S2. Primary pore formation: The aluminum foil pretreated in S1 is subjected to a variable current with an average current density of 0.6 A / cm² in the pore-forming solution at 75 °C 2 (the current change conforms to i = 0.7 t mode, t is the power-on time, and t is taken as 25 s), and the primary pore-forming cycle is repeated 5 times to obtain a primary pore-forming foil with a large number of pores.

[0065] Comparative Examples 1-2

[0066] An anodic foil pore-forming solution, the main components and contents of which are shown in Table 1:

[0067] Table 2 Main components of the anodic foil pore-forming solution described in Comparative Examples 1-2

[0068] Aluminum salt / part Sulfuric acid / part Hydrochloric acid / part Nonylphenol polyoxyethylene ether / part Comparative example 1 3.5 33 4.5 / Comparative example 2 3.5 33 4.5 0.8

[0069] Comparative Examples 3-4

[0070] The difference from Example 10 is that in the process of preparing the anodic foil in Comparative Examples 3-4, the pore-forming solutions in S1 correspond to the pore-forming solutions provided in Comparative Examples 1-2 in sequence.

[0071] Comparative Example 5

[0072] The difference from Example 10 is that in S2. Primary pore formation: The aluminum foil pretreated in S1 is subjected to a variable current with an average current density of 1.0 A / cm² in the pore-forming solution at 75 °C 2 (the current change conforms to i = 0.7 t mode, t is the power-on time, and t is taken as 15 s), and the primary pore-forming cycle is repeated 5 times to obtain a primary pore-forming foil with a large number of pores.

[0073] Comparative Example 6

[0074] It is different from Example 10 in that in S2. primary pore formation: the aluminum foil pretreated through S1 is subjected to a variable current with an average current density of 0.2 A / cm 2 in a pore-forming solution at 75 °C (the current change conforms to the i = 0.7 t mode, t is the power-on time, and t takes 25 s), and the primary pore-forming foil with a larger number of pores is obtained after 5 repeated pore-forming cycles.

[0075] Performance test

[0076] Number of pores and pore size on the surface of the anode foil

[0077] Electropolishing was carried out on Example 10, 13 and Comparative Examples 3 and 4, and pictures were taken at 1000 times magnification using a JEOL scanning electron microscope in Japan to obtain the SEM of the anode foil surface Figures 1 - 4 ; hole measurement and analysis were carried out through ipwin32 software, and the pore sizes and hole numbers of the corresponding samples are shown in Figures 5 - 8 and Table 3:

[0078] Table 3 Pore sizes and numbers on the surface of the anode foils obtained in Example 10, 13 and Comparative Examples 3 and 4

[0079] Sample Average pore diameter (μm) Pore number Example 10 1.19 <![CDATA[1.80×10 7 > Example 13 1.15 <![CDATA[1.97×10 7 > Comparative example 3 1.16 <![CDATA[1.60×10 7 > Comparative example 4 1.16 <![CDATA[1.61×10 7 >

[0080] Note: The number of pores described in Table 3 refers to the number of pores existing in 1 cm 2 of the anode foil

[0081] In the manufacturing process of the anode foil, the preferred pore formation position of the anode foil in the electrolytic cell is at the grain boundary with a higher dislocation density, and only then will it choose to find the opportunity for pore formation on the (100) texture plane with a lower elastic modulus in the crystal plane. In Example 10 and 13, a certain amount of metal surface treatment agent was added to the pore-forming solution in the process of preparing the anode foil. After the action of the metal surface treatment agent, the hole distribution on the surface of the obtained anode foil is shown in Figure 1 and Figure 2 , the number of defect points on the crystal plane increases, and the pitting potential decreases. Although pore formation will still preferentially occur at the grain boundary, the difference is reduced. Therefore, more and more uniform pores are formed, the probability of pore clusters is reduced, and as Figure 5 , 6 and Table 3 show that the average pore size on the surface of the anode foils obtained in Example 10 and 13 is not less than 1.15 μm, and the number of pores is not less than 1.80×10 7 , thus achieving the purpose of increasing its electrostatic capacitance. In Comparative Examples 3 and 4, a specific proportion of metal surface treatment agent was not added to the pore-forming solution in the process of preparing the anode foil, resulting in the formation of the surface of the obtained anode foil as shown in Figure 3 and Figure 4Such cases where there are aggregations of holes at the grain boundaries and hole clusters are formed by the holes, and as Figure 7 and Figure 8 shown, the pore diameters on the surface of the anode foil are relatively small, and the number of pores is also less than that of the anode foils obtained in Examples 10 and 13.

[0082] The anode foils of the above Examples 10 to 21 and Comparative Examples 3 to 6 were respectively tested. The test items included bending strength, tensile strength, electrostatic capacitance and product thickness. Among them, a MIT-DA bending machine of TOYOSEIKI in Japan was used to test the bending strength, a horizontal tensile tester was used to measure the tensile strength, a micrometer was used to measure the product thickness, and the electrostatic capacitance was measured by the EIAJ method. The test results are shown in Table 4.

[0083] Table 4 Performance test parameters of the anode foils prepared in Examples 10 to 21 and Comparative Examples 3 to 6

[0084]

[0085] It can be seen from Table 4 that the content of the metal surface treatment agent in the pore-forming solution of the process for preparing the anode foil should be controlled within a certain range. Compared with Example 1, the contents of the metal surface treatment agent in Example 18, Comparative Example 4 and Example 1 are 0.01 part, 0.8 and 0.05 part respectively. It can be seen that adding too much or too little of the metal surface treatment agent, resulting in too strong or insufficient surface treatment, will cause the electrostatic specific capacitance of the prepared anode foil to decrease.

[0086] There is a certain balance between the electrostatic capacitance and the bending strength of the anode foil. The bending strength of the anode foil with a high electrostatic capacitance will decrease. However, if the hole distribution and the depth uniformity are improved, the bending strength can be guaranteed while the electrostatic capacitance is increased. Compared with the examples, the surface treatment in Comparative Example 4 is too strong or the primary pore-forming charge in Comparative Example 5 is too large, which is likely to cause serious thickness reduction, and due to the fine pores, the tensile strength value increases; the primary pore-forming charge in Comparative Example 6 is too low and the pore-forming amount is insufficient, which will also result in an increase in the thickness of the etched foil product and an increase in the tensile strength.

[0087] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. Anodic foil pore-forming solution, characterized in that, Comprising the following components by weight parts: 3 - 4 parts of aluminum salt, 30 - 35 parts of sulfuric acid, 4 - 5 parts of hydrochloric acid and 0.01 - 0.5 part of metal surface treatment agent; the metal surface treatment agent is composed of one or more of polyoxyethylene ether, phosphate ester, fluorosilicate; The polyoxyethylene ether is one or two of nonylphenol polyoxyethylene ether and lauryl alcohol polyoxyethylene ether; The phosphate ester is one or more of nonylphenol polyoxyethylene ether phosphate, lauryl alcohol polyoxyethylene ether phosphate, alkyl alcohol amide phosphate; 2. The anodic foil pore-forming solution according to claim 1, wherein The metal surface treatment agent in the anodic foil pore - forming solution is 0.05 - 0.2 part.

3. The anodic foil pore-forming solution according to claim 1, characterized in that, The fluorosilicate is one or more of sodium fluorosilicate, potassium fluorosilicate, magnesium fluorosilicate, calcium fluorosilicate; 4. A pretreatment method for an anode foil, characterized in that, Soak the purified anodic foil in the pore - forming solution at 60 - 90 °C for 40 - 70 s, wherein the pore - forming solution is the anodic foil pore - forming solution of claim 1.

5. A method for preparing an anode foil, characterized in that, Including the following steps: S1. Pretreatment: Carry out pretreatment according to the pretreatment method of claim 4; S2. Primary pore formation: Apply a variable current with an average current density of 0.4 - 0.8 A / cm² to the aluminum foil pretreated in S1 in the pore-forming solution at 70 - 75 °C, and corrode repeatedly to obtain the primary foil; 2 ​ S3. Secondary reaming: The washed primary foil is placed in a reaming solution containing 1-2 wt% aluminum ions, ≤1 wt% phosphoric acid, and 5-8 wt% nitric acid, and direct current electrolysis is carried out at 60-75 °C and a current density of 0.15-0.2 A / cm 2 for 450-550 s of reaming corrosion to obtain the secondary foil; S4. Post - treatment: Wash and dry the secondary foil to obtain the anodic foil material with uniform pore formation and high specific capacitance.

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