Formation process of formed foil for aluminum electrolytic capacitor formed by high-gear etched foil

Abstract

The invention relates to a formation process of a formed foil for an aluminum electrolytic capacitor. Sequentially carrying out primary hydration treatment, primary heat treatment and secondary hydration treatment on the etched foil, and immersing the etched foil in a reaction matrix solution of an aluminum-based metal organic framework for pretreatment; performing four-stage medium-high voltage electroforming to densify the porous oxide film on the surface of the etched foil to form a compact crystalline oxide film; and carrying out secondary heat treatment, depolarization treatment and repair formation to finally prepare the medium-high voltage formed foil with excellent performance. Sintering heat treatment is added in pretreatment, so that internal defects of crystallized hydrated oxide expand under heating; an aluminum matrix metal organic framework is added for pretreatment before electric formation, and the MOFs material grows in situ in a crystalline oxide film on the surface of a medium-high voltage formed foil precursor, so that a positive effect on the total pore volume of the formed foil can be achieved, the electrostatic capacity is further improved, and meanwhile, the performance stability of the formed foil is improved.

Description

Technical Field

[0001] The invention relates to the technical field of medium and high voltage formed foils, and in particular to a forming process of formed foils for aluminum electrolytic capacitors formed by high-grade corrosion foil formation. Background Art

[0002] Aluminum electrolytic capacitors are the most widely used capacitor products in electronic complete systems. Their core material is anodized aluminum foil, which is a dielectric aluminum oxide produced through a series of chemical processes such as electrochemical anodization of high-purity aluminum foil after corrosion and expansion. The dielectric aluminum oxide is anodized in an inorganic or organic oxygen-containing acid that does not dissolve aluminum oxide to obtain a dense voltage-resistant film. The quality of the film is directly related to many performance indicators of aluminum electrolytic capacitors, such as capacity, leakage current, bending strength, and service life. With the development of society and the advancement of science and technology, the demand for miniaturization, portability, integration, and long life of electronic equipment products is becoming more and more urgent. In order to adapt to this development trend, the film formation process needs to be continuously optimized and improved to improve the quality of the oxide film to meet people's growing demand for electronic equipment.

[0003] Continuously improving the capacity of formed foil for aluminum electrolytic capacitors is always one of the main topics of the research and development of formed foil technology. While increasing the capacity, it is also necessary to ensure better water resistance and longer service life. The most direct way to increase the capacity of formed foil is to increase the capacity of the raw material - the corrosion foil, and directly use high-grade corrosion foil for formation. This method is the most direct way to increase the capacity of the formation, but due to the increase in the capacity of the corrosion foil, the film of the corrosion foil itself becomes thicker, the corrosion holes increase, and the specific surface area increases, which will cause problems during the formation, such as abnormal boost curve, unqualified water resistance, increased leakage current, poor bending, etc. Therefore, it is necessary to optimize the process flow of high-grade corrosion foil in the formation, so that the capacity of the formed foil after the high-grade corrosion foil is formed can be greatly improved, and other properties are also excellent. Summary of the invention

[0004] The present invention aims to provide a high-grade etching foil for aluminum electrolytic capacitors with a forming process, so as to improve the capacity and performance of the formed foil for aluminum electrolytic capacitors. In order to improve the capacity of the formed foil, the first and most direct approach is to start with the etching foil, and replace the existing low-grade capacity etching foil (125HD15) with a high-grade capacity etching foil (135HD21) for forming. After the raw materials are replaced, due to the increase in foil thickness, more problems will occur after forming, such as abnormal boost curve, unqualified water resistance, increased leakage current and increased energy consumption. Then, by improving the process, a high-temperature sintering is added in the pre-treatment of the process flow to change the crystal form of hydrated alumina, and a very thin barrier layer of crystal oxide film is generated on the surface to reduce energy consumption; after the water boiling, MOFs treatment is added, that is, after the water boiling treatment, it is immersed in a trimethylol MOFs solution for treatment. The porous nature and regular pore structure of the metal organic framework structure can be used to regulate the pore structure of the oxide film on the surface of the formed foil, improve the stability of the formed foil, and ensure good performance such as leakage current and water resistance while increasing the capacity, which is helpful to improve the cycle stability and service life of aluminum electrolytic capacitors; then, the composition of the electrolytic cell liquid is optimized to obtain a denser oxide film, thereby increasing the capacitance of the formed foil; finally, due to the significant increase in the capacity of the formed foil, it may cause abnormal boost curves and thus lead to low anode foil capacity or bulging of the capacitor, so the post-treatment is optimized, and diammonium phosphate is used for post-treatment at 45°C for 2 minutes to weaken the post-treatment, further ensuring that the boost curve is normal at high capacity, and other properties cannot deteriorate while ensuring the capacity increase.

[0005] The technical solution of the present invention is as follows: A high-grade corrosion-foil-formed aluminum electrolytic capacitor forming process, the process comprising the following steps: Step 1: placing the corroded foil in pure water for the first hydration treatment, so that a loose hydrated oxide film is formed on the surface of the corroded foil; Step 2: subjecting the corroded foil after the first hydration treatment in step 1 to a first heat treatment, so that the internal defects are opened under heating after the first heat treatment, and the hydrated oxide is heated to be transformed into a crystalline oxide; Step 3: performing a second hydration treatment on the corroded foil after the treatment in step 2, placing the foil in pure water above 90° C. for a second hydration treatment for 3-7 minutes, and obtaining a medium-high pressure chemically formed foil precursor; Step 4: Immerse the medium-high pressure chemical foil precursor obtained in step 3 in a reaction matrix solution of an aluminum-based metal organic framework, so that the MOFs material is in situ grown on the crystalline oxide film on the surface of the medium-high pressure chemical foil precursor, and a porous oxide film with uniform pore size and regular pore structure is obtained, thereby enhancing the corrosion resistance of the metal surface and the quality of the oxide film; Step 5: subjecting the pretreated corrosion foil in step 4 to at least four levels of medium and high voltage electrochemical formation to further adjust the electronic structure and surface properties of the material, so that the porous oxide film on the surface of the corrosion foil is densified to form a dense crystalline oxide film; Step 6: subjecting the dense oxide film corrosion foil obtained in step 5 to a second heat treatment to obtain a medium-high voltage chemical foil semi-finished product; Step 7: immersing the semi-finished foil obtained in step 6 into a phosphoric acid solution for depolarization treatment; Step 8: Place the depolarized medium- and high-voltage formed foil semi-finished product obtained in step 7 in an electrochemical forming solution for repairing and forming, and finally obtain a medium- and high-voltage formed foil with excellent performance.

[0006] Preferably, in step 1, the first hydration treatment is carried out in pure water above 90° C. for 2-5 minutes; Preferably, in step 2, the first heat treatment condition is: heat treatment at 450-570° C. for 0.5-3 min.

[0007] Preferably, in step 4, the pretreatment conditions are: the bath temperature is 50-80°C, and the treatment time is 2-5h; In step 4, the bath liquid is trimethylol MOFs with high porosity, and the trimethylol MOFs are dissolved in DMF solvent to prepare a solution with a concentration of 2-10 g / L; Preferably, in step 6, the second heat treatment condition is: 450-570° C., and the second heat treatment is performed for 1-3 min.

[0008] Preferably, in step 7, the depolarization treatment conditions are: phosphoric acid concentration 3-7 ml / L, temperature 45-80° C., and treatment for 3-5 min.

[0009] Preferably, the medium-high voltage electrification in step 5 is converted into a four-stage formation, comprising the following steps: Step 51: Place the pretreated corroded foil obtained in step 4 in a solution having a boric acid mass percentage of 5-8% and an ammonia pentaborate concentration of In a mixed solution of 5-50g / L and ammonium citrate concentration of 2-10g / L, the first-stage formation is carried out under the conditions of bath temperature of 75-90℃, current density of 20-30mA / cm2, voltage of 120-190V, and the formation time is 5-8min; Step 52: After washing the corroded foil after the primary chemical formation in step 51, place it in a mixed aqueous solution with a boric acid mass percentage of 5-8%, an ammonium ethylenediaminetetraacetate concentration of 1-4g / L, and a sodium metasilicate concentration of 0.1-1g / L, and perform secondary chemical formation under the conditions of a bath temperature of 75-90°C, a current density of 20-30mA / cm2, and a voltage of 200-390V, and the formation time is 7-10min; Step 53: After washing the corroded foil after the secondary formation in step 52, place it in a mixed solution with a boric acid mass percentage of 5-8%, an ammonia pentaborate concentration of 2-10g / L, and an ammonium citrate concentration of 1-4g / L, and perform a tertiary formation under the conditions of a bath temperature of 75-90°C, a current density of 20-30mA / cm2, and a voltage of 400-590V, and the formation time is 10-15min; Step 54: After washing the corroded foil after the three-stage chemical formation in step 53, place it in a mixed solution with a mass percentage of boric acid of 5-8% and a concentration of ammonium pentaborate of 1-5g / L at a bath temperature of 75-90°C, a current density of 20-30mA / cm2, and a voltage of 600-700V, and perform a four-stage chemical formation for 15-30min; Preferably, the repairing step in step 8 comprises the following steps: Step 81: After washing the depolarized medium-high voltage electrolytic foil semi-finished product obtained in step 7, the semi-finished product is placed in a mixed solution with a boric acid mass percentage of 5-8% and an ammonia pentaborate concentration of 0.5-3 g / L, and the bath temperature is 75-90° C., the current density is 20-30 mA / cm2, and the voltage is 600-700 V, and the second electrolytic formation of the four-stage electrolytic formation is performed for 5-10 min; Step 82: placing the foil obtained in step 81 at 450-570° C. for a third high temperature heat treatment for 1-3 min; Step 83: Place the foil obtained after high temperature in step 82 in a mixed solution with a boric acid mass percentage of 5-8% and an ammonia pentaborate concentration of 0.5-3 g / L at a bath temperature of 75-90° C., a current density of 20-30 mA / cm2, and a voltage of 600-700 V, and perform the third electrochemical formation of the four-stage formation for 5-10 minutes; Step 84: The foil obtained after the treatment in step 83 is subjected to phosphating treatment, with a concentration of 3-10 ml / L of diammonium phosphate, a temperature of 45-80° C., and a treatment time of 1-7 minutes; Step 85: Post-dry the foil obtained after the treatment in step 84 at 150-350° C. for 3-5 minutes.

[0010] Beneficial effects of the present invention: 1) The present invention creatively adds sintering heat treatment to the pre-treatment, so that the internal defects of the crystalline hydrated oxide are opened under heating, and the hydrated oxide is heated to be transformed into crystalline oxide, which is of great benefit to saving energy consumption and reducing costs; 2) The present invention creatively adds an aluminum-based metal organic framework for pretreatment before electrochemical formation. The porous nature of the MOFs material can regulate the pore structure of the oxide film on the surface of the electrochemical foil. At the same time, the metal organic framework is tightly combined with the crystalline oxide film on the surface of the electrochemical foil, thereby improving the stability of the electrochemical foil. While increasing the capacity, it also ensures good performance such as leakage current and water resistance, which helps to improve the cycle stability and service life of aluminum electrolytic capacitors. 3) The present invention creatively adds macromolecular organic matter into the electrochemical process, which has a significant effect on increasing capacity; 4) The present invention can enable high-capacity corrosion foil to be mass-produced in workshops, and obtain chemical foil with excellent performance such as normal boost curve, qualified water resistance, small leakage current, good bending, etc.; 5) The present invention starts with raw materials and selects high-grade etched foil for chemical formation, which has a significant effect on improving capacity, but at the same time increases the difficulty of chemical formation, so the chemical formation process is improved. DETAILED DESCRIPTION

[0011] The following will be combined with the specific embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. The embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0012] Example 1 Step 1: Place the corrosion foil with a corrosion capacity of 21 levels in pure water at 93°C for the first hydration treatment for 7 minutes, so that a loose hydrated oxide film is formed on the surface of the corrosion foil; Step 2: The corroded foil after hydration treatment in step 1 is subjected to a short-term heat treatment at 550° C. for 0.5 min, so that the internal defects are opened under heating and the hydrated oxide is heated to be transformed into a crystalline oxide; Step 3: The corroded foil treated in step 2 is subjected to a second hydration treatment, and placed in pure water at 93° C. for a second hydration treatment for 5 minutes to obtain a multi-layer oxide film in different states; Step 4: immerse the corrosion foil with multiple layers of different oxide films on the surface obtained in step 3 in a mixed solution of trimethylol MOFs, a reaction matrix of an aluminum-based metal organic framework, and DMF, with a bath solution concentration of 6 g / L, a temperature of 70° C., and a treatment time of 3 h; Step 5: The corrosion foil pretreated in step 4 is subjected to at least four levels of medium and high voltage electrochemical processing to densify the porous oxide film on the surface of the corrosion foil to form a dense crystalline oxide film.

[0013] The specific steps include: Step 51: placing the pretreated corroded foil obtained in step 4 in a mixed solution of 5% boric acid by mass, 30 g / L ammonia pentaborate, and 8 g / L ammonium citrate, and performing primary formation under the conditions of a bath temperature of 85° C., a current density of 30 mA / cm2, and a voltage of 170 V, for 7 min; Step 52: After washing the corroded foil after the primary chemical formation in step 51, place it in a mixed aqueous solution with a mass percentage of 5% boric acid, a concentration of 4g / L of ammonium ethylenediaminetetraacetate, and a concentration of 0.4g / L of sodium metasilicate, and perform secondary chemical formation under the conditions of a bath temperature of 85°C, a current density of 20mA / cm2, and a voltage of 390V, and the formation time is 8min; Step 53: After washing the corroded foil after the secondary formation in step 52, place it in a mixed solution with a boric acid mass percentage of 5%, an ammonia pentaborate concentration of 10g / L, and an ammonium citrate concentration of 2g / L, and perform a tertiary formation under the conditions of a bath temperature of 85°C, a current density of 20mA / cm2, and a voltage of 590V, and the formation time is 12min; Step 54: After washing the corroded foil after the three-stage chemical formation in step 53, place it in a mixed solution with a mass percentage of 5% boric acid and a concentration of 5g / L of ammonium pentaborate at a bath temperature of 85°C, a current density of 20mA / cm2, and a voltage of 650V, and perform a four-stage chemical formation for 25min; Step 6: placing the dense oxide film obtained in step 54 at 530° C. for a second heat treatment for 2 minutes to obtain a medium- and high-pressure chemically formed foil semi-finished product; Step 7: Immerse the semi-finished foil obtained in step 6 in a phosphoric acid solution for depolarization treatment, with a phosphoric acid concentration of 5 ml / L, a temperature of 60° C., and a treatment time of 5 min; Step 8: placing the depolarized medium- and high-voltage electrolytic foil semi-finished product obtained in step 7 in an electrolytic electrolytic solution for repair electrolytic ... Step 81: After washing the depolarized medium- and high-voltage electrolytic foil semi-finished product obtained in step 7, the semi-finished product is placed in a mixed solution with a boric acid mass percentage of 7% and an ammonia pentaborate concentration of 3 g / L, and the bath temperature is 90° C., the current density is 20 mA / cm2, and the voltage is 650 V, and the second electrolytic formation of the four-stage electrolytic formation is performed for 7 minutes; Step 82: placing the foil obtained in step 81 at 550° C. for a third high temperature heat treatment for 1.5 min; Step 83: Place the foil obtained after high temperature in step 82 in a mixed solution with a boric acid mass percentage of 7% and an ammonia pentaborate concentration of 3g / L at a bath temperature of 90°C, a current density of 20mA / cm2, and a voltage of 650V, and perform the third electrochemical formation of the four-stage formation for 7 minutes; Step 84: The foil obtained after the treatment in step 83 is subjected to phosphating treatment, with a concentration of 10 ml / L of diammonium phosphate, a temperature of 75° C., and a treatment time of 4 minutes; Step 85: Post-dry the foil obtained after the treatment in step 84 at 350° C. for 3 minutes.

[0014] At the same time, the present invention also provides Examples 2 to 12, which are different from Example 1 in that the process parameters of processing steps S1, S2, S3 and S4 are specifically shown in Table 1.

[0015] Table 1 Summary of some process parameters in Examples 1-12

[0016] Meanwhile, a comparative test is also conducted in the present invention to better illustrate the chemically formed foil and the preparation method thereof in the present invention.

[0017] Comparative Example 1 Based on Example 1, a low-grade etching foil (specifically, a 15-grade etching foil was used in the experiment) was used for chemical formation, and the rest was the same as Example 1.

[0018] Comparative Example 2 Based on Example 1, the first heat treatment (step 2) and the second hydration treatment (step 3) are omitted, and the rest are the same as Example 1.

[0019] Comparative Example 3 Based on Example 1, the first heat treatment (step 2) is omitted, and the rest is the same as Example 1.

[0020] Comparative Example 4 Based on Experimental Example 3, steps 1, 2-3, and 5-8 were performed without pretreatment (step 4); the rest was the same as in Example 1.

[0021] Comparative Example 5 Based on Experimental Example 3, steps 2-4 are omitted and steps 1 and 5-8 are performed; the rest is the same as in Example 1.

[0022] The performance of the formed foils obtained in specific examples 1-12 and comparative examples 1-5 was tested, and the results are shown in Table 2.

[0023] Table 2 Performance test results of specific examples 1-12 and comparative examples 1-5

[0024] It can be seen from the data in Table 2 that the capacity of Examples 1-12 is increased by more than 20% relative to the low-grade corrosion foil of Comparative Example 1, and the energy consumption is saved by 25.9% relative to Comparative Example 2. After the addition of MOFs treatment to Examples 1-12, the performance is significantly improved relative to Comparative Example 4. Therefore, after adding heat treatment, multiple hydration treatments, and MOFs pretreatment, the energy consumption, capacity, leakage current performance, and hydration resistance of the chemically formed foil manufactured by the present invention are all better than those of the anode foil that has not undergone the pretreatment process.

[0025] Example 2 Based on Example 1, the bath solution in step 52 is optimized, and the rest is the same as Example 1.

[0026] Table 3

[0027] As shown in Figure 3, further experiments on the electrolytic cell show that when boric acid is not added, the capacity is increased by 15.11% relative to that with boric acid, but the performance is not good (mainly manifested in the large leakage current). EDTA is mainly beneficial to the capacity improvement. Adding a small amount of EDTA to the boric acid electrolyte helps to promote the formation of crystalline oxides and obtain a barrier film with higher crystallinity, thereby reducing its thickness and increasing its field strength and specific capacitance. When adding EDTA, a small amount of sodium metasilicate needs to be added. Since sodium metasilicate has certain adhesion and film-forming properties, it can be used to form a protective film, otherwise corrosion is prone to occur. Example 3 Based on Example 1, the position and concentration of the reaction matrix solution of the aluminum-based metal organic framework in step 4 are optimized, specifically as follows: Example 3-2: Step 4 is placed after step 54, and the rest is the same as Example 1. Example 3-3: Step 4 is placed after step 6, and the rest is the same as Example 1. Example 3-4: Step 4 is placed after step 7, and the rest is the same as in Example 1. Table 4

[0028] As shown in Figure 4, relevant experiments were conducted on MOFs materials. The results showed that the concentration and action position had a significant impact on the capacity, energy consumption and electrical parameters of the foil. After hydration, MOFs were used for pretreatment to obtain a porous oxide film with uniform pore size and regular pore structure, which was more conducive to the subsequent formation. Finally, the formed foil had the best performance and energy consumption. The technical solution of the present invention is explained through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above specific embodiments to be implemented. Any improvements made by technicians in the relevant field based on the present invention, or equivalent replacement of the materials selected by the present invention, etc., fall within the scope of protection of the patent.

Claims

1. A high-grade corrosion-resistant foil forming process for aluminum electrolytic capacitors, characterized in that: The process comprises the following steps: Step 1: placing the corroded foil in pure water for the first hydration treatment, so that a loose hydrated oxide film is formed on the surface of the corroded foil; Step 2: subjecting the corroded foil after the first hydration treatment in step 1 to a first heat treatment, so that the internal defects are opened under heating after the first heat treatment, and the hydrated oxide is heated to be transformed into a crystalline oxide; Step 3: performing a second hydration treatment on the corroded foil treated in step 2 to obtain a medium-high pressure chemically formed foil precursor; Step 4: immersing the medium-high pressure chemically formed foil precursor obtained in step 3 into a reaction matrix solution of an aluminum-based metal organic framework for treatment; Step 5: subjecting the pretreated etched foil in step 4 to at least four levels of medium and high voltage electrochemical formation to form a dense crystalline oxide film; Step 6: subjecting the dense oxide film corrosion foil obtained in step 5 to a second heat treatment to obtain a medium-high voltage chemical foil semi-finished product; Step 7: immersing the semi-finished foil obtained in step 6 into a phosphoric acid solution for depolarization treatment; Step 8: Place the depolarized medium- and high-voltage formed foil semi-finished product obtained in step 7 in an electrochemical forming solution for repairing and forming, and finally obtain a medium- and high-voltage formed foil with excellent performance.

2. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade corrosion-resistant foil formation according to claim 1, characterized in that: In the step 1, the first hydration treatment is carried out in pure water above 90° C. for 4-10 minutes.

3. The process for forming the formed foil for aluminum electrolytic capacitors according to claim 1, characterized in that: In step 2, the first heat treatment condition is: heat treatment at 450-570° C. for 0.5-3 min; The second hydration treatment condition of step 3 is: placing in pure water above 90° C. for the second hydration treatment for 3-7 minutes.

4. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade corrosion-resistant foil formation according to claim 1, characterized in that: In step 4, the treatment conditions are: solution temperature is 50-80° C., and the treatment time is 2-5 hours.

5. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade corrosion-resistant foil formation according to claim 1, characterized in that: In step 4, the reaction matrix solution is trimethylol MOFs dissolved in DMF solvent to form a solution with a concentration of 2-10 g / L.

6. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade etching foil formation according to claim 1, characterized in that: In step 6, the second heat treatment condition is: 450-570° C., and the second heat treatment is performed for 1-3 minutes.

7. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade corrosion-resistant foil formation according to claim 1, characterized in that: In step 7, the depolarization treatment conditions are: phosphoric acid concentration 3-7 ml / L, temperature 45-80° C., and treatment for 3-5 min.

8. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade corrosion-resistant foil formation according to claim 1, characterized in that: The medium and high voltage electrification in step 5 is converted into a four-stage formation, comprising the following steps: Step 51: placing the pretreated corroded foil obtained in step 4 in a mixed solution with a boric acid mass percentage of 5-8%, an ammonia pentaborate concentration of 5-50 g / L, and an ammonium citrate concentration of 2-10 g / L, and performing primary formation under the conditions of a bath temperature of 75-90° C., a current density of 20-30 mA / cm2, and a voltage of 120-190 V, and the formation time is 5-8 min; Step 52: After washing the corroded foil after the primary chemical formation in step 51, place it in a mixed aqueous solution with a mass percentage of 5-8% boric acid, a concentration of 1-4g / L of ammonium ethylenediaminetetraacetate, and a concentration of 0.1-1g / L of sodium metasilicate, and perform secondary chemical formation under the conditions of a bath temperature of 75-90°C, a current density of 20-30mA / cm2, and a voltage of 200-390V. The chemical formation time is 7-10min to obtain a uniform and dense oxide film; Step 53: After washing the corroded foil after the secondary formation in step 52, place it in a mixed solution with a boric acid mass percentage of 5-8%, an ammonia pentaborate concentration of 2-10g / L, and an ammonium citrate concentration of 1-4g / L, and perform a tertiary formation under the conditions of a bath temperature of 75-90°C, a current density of 20-30mA / cm2, and a voltage of 400-590V, and the formation time is 10-15min; Step 54: After washing the corroded foil after the three-stage formation in step 53, place it in a mixed solution with a boric acid mass percentage of 5-8% and an ammonia pentaborate concentration of 1-5g / L at a bath temperature of 75-90°C, a current density of 20-30mA / cm2, and a voltage of 600-700V for four-stage formation for 15-30min.

9. The process for forming the formed foil for aluminum electrolytic capacitors by high-grade corrosion-resistant foil formation according to claim 1, characterized in that: The repairing step in step 8 comprises the following steps: Step 81: After washing the depolarized medium-high voltage electrolytic foil semi-finished product obtained in step 7, the semi-finished product is placed in a mixed solution with a boric acid mass percentage of 5-8% and an ammonia pentaborate concentration of 0.5-3 g / L, and the bath temperature is 75-90° C., the current density is 20-30 mA / cm2, and the voltage is 600-700 V, and the second electrolytic formation of the four-stage electrolytic formation is performed for 5-10 min; Step 82: placing the foil obtained in step 81 at 450-570° C. for a third high temperature heat treatment for 1-3 min; Step 83: Place the foil obtained after high temperature in step 82 in a mixed solution with a boric acid mass percentage of 5-8% and an ammonia pentaborate concentration of 0.5-3 g / L at a bath temperature of 75-90° C., a current density of 20-30 mA / cm2, and a voltage of 600-700 V, and perform the third electrochemical formation of the four-stage formation for 5-10 minutes; Step 84: The foil obtained after the treatment in step 83 is subjected to phosphating treatment, with a concentration of 3-10 ml / L of diammonium phosphate, a temperature of 45-80° C., and a treatment time of 1-7 minutes; Step 85: Post-dry the foil obtained after the treatment in step 84 at 150-350° C. for 3-5 minutes.

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