Formed foil for aluminum electrolytic capacitor and production process thereof

Abstract

The invention discloses a formed foil for an aluminum electrolytic capacitor and a production process thereof, and relates to the technical field of formed foil production.The production process comprises the steps that a corroded aluminum foil is unreeled, a leading foil serves as an auxiliary electrode to be connected in, first-stage electrolytic oxidation is conducted after steam, boiling water and water washing are conducted, second-stage electrolytic oxidation is conducted after water washing, and the formed foil is obtained. Adding a phosphoric acid solution for reaction after washing, carrying out three-section electrolytic oxidation, adding an ammonium adipate solution into a feed tank after washing, adding pure water for washing after reaction, carrying out roasting and phosphoric acid solution treatment, carrying out four-section electrolytic oxidation, carrying out third roasting, washing and post-treatment after washing, and drying, rolling and warehousing the prepared formed foil. According to the invention, the formed foil is prepared by designing a four-section method, so that the function of gradient adjustment of electrolysis parameters is realized, the problems of oxide film structure defects, electrical property degradation and process stability reduction caused by fixed voltage or simple segmentation are solved, and the compactness and voltage resistance of the oxide film can be optimized.

Description

Technical Field

[0001] The present invention relates to the technical field of formation foil production, and specifically to a formation foil for aluminum electrolytic capacitors and its production process. Background Art

[0002] Aluminum electrolytic capacitors are widely used in fields such as consumer electronics, industrial automation, new energy, new energy vehicles, and 5G communication. The rapid development of emerging industries directly drives the formation of high-performance requirements for capacitors. As the core material of the anode of aluminum electrolytic capacitors, the performance of the formation foil directly determines key indicators such as the capacitance, leakage current, and lifespan of the capacitors;

[0003] In the prior art, using a fixed voltage or current density to prepare the formation foil results in uneven electric field distribution, with the oxide film being locally too thick or too thin, and cracks being prone to occur during bending. At the same time, too high single-stage electrolysis parameters will cause differences in the density of the film layer, reducing the anti-bending performance.

[0004] Patent CN114197004B discloses a formation method for medium-high voltage formation foils for aluminum electrolytic capacitors. The above patent achieves no boron element in the entire formation process, and both the medium-voltage formation foil and the high-voltage formation foil prepared by this formation method have high specific capacitance, high bendability, and high anti-hydration property.

[0005] The above patent can form a hydrated oxide film on the surface of the aluminum foil through hydration treatment, which provides a basis for the subsequent formation of a crystalline oxide film. Through primary formation treatment and secondary formation treatment, a basic oxide film can be formed on the surface of the aluminum foil. Using ammonium hydrogen phosphate, hypophosphite, and fumaric acid can generate water-insoluble substances, a phosphide film and a fumaric acid polymer film, which inhibit the reaction between aluminum and water and improve the anti-hydration property. Through tertiary formation treatment, quaternary formation treatment, quinary formation treatment, and senary formation treatment, a stable oxide film is formed on the surface of the aluminum foil to increase the specific capacitance, and there is room for optimization in the adjustment of electrolysis parameters.

[0006] Therefore, this application proposes a formation foil for aluminum electrolytic capacitors with gradient adjustment of electrolysis parameters and its production process. Summary of the Invention

[0007] The purpose of the present invention is to provide a formation foil for aluminum electrolytic capacitors and its production process to solve the technical problem of electrolysis parameter adjustment proposed in the above background art.

[0008] To achieve the above purpose, the present invention provides the following technical solution: A production process of a formation foil for aluminum electrolytic capacitors, the production process is:

[0009] S1: Unroll the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 100°C - 120°C for 5 min - 10 min and boiling water treatment at 95°C - 100°C for 20 min - 30 min, add pure water at 25°C - 30°C for washing for 15 min - 20 min;

[0010] S2: Conduct the first-stage electrolytic oxidation, and after completion, pass in pure water for washing for 1.5 min - 2 min;

[0011] S3: Conduct the second-stage electrolytic oxidation, and after completion, pass in pure water at a temperature of 40°C - 45°C for washing for 2 min - 2.5 min;

[0012] S4: Add a phosphoric acid solution with a concentration of 10wt% - 15wt% and stir and react at a speed of 50 rpm - 100 rpm for 5 min - 15 min, then conduct the third-stage electrolytic oxidation, and after completion, pass in pure water for washing for 3 min - 3.5 min;

[0013] S5: Add an ammonium adipate solution with a concentration of 0.2wt% - 0.3wt% to the feed trough, after reacting for 30 min - 40 min, add pure water at 40°C - 45°C for washing for 3 min - 3.5 min;

[0014] S6: Pass in a constant voltage current of 120V - 150V, heat up to 450°C - 500°C to roast the aluminum foil for 20 min - 30 min, then add a phosphoric acid solution with a concentration of 30wt% - 35wt%, adjust the pH to 2.5 - 3, and treat for 20 min - 30 min;

[0015] S7: Conduct the fourth-stage electrolytic oxidation, and after completion, pass in pure water at 25°C - 30°C with a spraying pressure of 0.15MPa - 0.2MPa for washing for 2.5 min - 3 min;

[0016] S8: After the third roasting, washing and post-treatment, dry and wind up the prepared formed foil and store it in the warehouse.

[0017] Preferably, the conditions for the first-stage electrolytic oxidation in S2 are to pass in a boric acid solution with a concentration of 3.8wt% - 4.2wt%, add ammonia water to adjust the pH to 5.8 - 6.2 when starting up the electrolytic cell, the voltage is 50V - 80V, and the current density is 0.8A / dm 2 ~1.2A / dm 2 of constant voltage current, and react in an environment at a temperature of 25°C - 30°C for 30 min - 40 min.

[0018] Preferably, the conditions for the secondary electrolytic oxidation in S3 are as follows: a boric acid solution with a concentration of 2.5 wt% - 3.5 wt% is introduced. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 6 - 6.3, the voltage is 80 V - 100 V, and the current density is 0.6 A / dm 2 ~1 A / dm 2 constant voltage current, and the reaction is carried out for 40 min - 50 min in an environment with a temperature of 25°C - 30°C.

[0019] Preferably, the conditions for the tertiary electrolytic oxidation in S4 are as follows: a boric acid solution with a concentration of 2 wt% - 3 wt% is introduced. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 6.2 - 6.5, the voltage is 100 V - 120 V, and the current density is 0.4 A / dm 2 ~0.8 A / dm 2 constant voltage current, and the reaction is carried out for 50 min - 60 min in an environment with a temperature of 30°C - 35°C.

[0020] Preferably, S7 is specifically as follows:

[0021] S71: Add a boric acid solution with a concentration of 1.5 wt% - 2.5%. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 5.8 - 6.8. Use a voltage of 120 V - 150 V and a current density of 0.3 A / dm 2 ~0.6 A / dm 2 constant voltage current, and carry out the first four-stage electrolytic oxidation for 60 min - 70 min in an environment with a temperature of 35°C - 40°C. After completion, add pure water for washing;

[0022] S72: Add a boric acid solution with a concentration of 1 wt% - 2 wt%. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 5.8 - 6.8. Use a voltage of 150 V - 180 V and a current density of 0.2 A / dm 2 ~0.4 A / dm 2 constant voltage current, and carry out the second four-stage electrolytic oxidation for 70 min - 80 min in an environment with a temperature of 40°C - 45°C. After completion, add pure water for washing;

[0023] S73: Electrify and carry out the second roasting at 600°C - 650°C for 8 h - 14 h. Add a boric acid solution with a concentration of 0.5 wt% - 1.5%. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 5.8 - 6.8. Use a voltage of 180 V - 200 V and a current density of 0.1 A / dm 2 ~0.3 A / dm 2 constant voltage current, and carry out the third four-stage electrolytic oxidation for 80 min - 90 min in an environment with a temperature of 45°C - 50°C. Add pure water for washing;

[0024] S74: Add boric acid solution with a concentration of 0.3 wt% - 1 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.8, and use a voltage of 200V - 220V with a current density of 0.05A / dm 2 ~0.2A / dm 2 of constant voltage current, and conduct the fourth four-stage electrolytic oxidation for 90 min - 100 min in an environment of 50°C - 55°C.

[0025] Preferably, in S8, the temperature of the third calcination is raised to 400°C at a rate of 200°C / h and then held for 2 h, and then raised to 650°C at a rate of 150°C / h and held for 6 h - 8 h.

[0026] Preferably, in S8, the temperature of the water washing is 45°C - 60°C and the time is 20 min - 30 min.

[0027] Preferably, in S8, the operation of the post-treatment is to add phosphoric acid solution with a concentration of 5 wt% - 10 wt%, and stir for 0.5 h - 1 h in an environment with a pH of 2 - 3.

[0028] Preferably, in S8, the drying temperature is 120°C - 150°C and the time is 2 h - 3 h.

[0029] Preferably, the formed foil is prepared by the production process.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. By designing a four-stage method for preparing the formed foil, the present invention realizes the function of gradient adjustment of electrolysis parameters, solves the problems of oxidation film structure defects, electrical property deterioration and process stability decline caused by fixed voltage or simple segmentation, can optimize the denseness and voltage resistance performance of the oxidation film, improves the capacity conversion rate, and reduces energy consumption;

[0032] 2. By designing to add phosphoric acid during the preparation process, the present invention realizes the function of improving the performance of the oxidation film in stages, solves the problems of high oxidation film defect rate, insufficient voltage resistance performance, short service life and poor environmental friendliness, can enhance the denseness of the oxidation film, reduce the diffusion rate of microcracks, and reduce the raw material cost and the difficulty of wastewater treatment;

[0033] 3. By designing to conduct three calcinations, the present invention realizes the function of jointly regulating and improving the performance of the oxide layer from the micro and macro aspects, solves the problems of impurity interference, high dielectric loss and poor interface stability, can avoid impurity interference with electrolytic oxidation, reduces the dielectric loss, and improves the dielectric performance and structural stability of the finished formed foil;

[0034] 4. The present invention realizes the function of precisely controlling electrolysis conditions by designing a composite acid system of boric acid and ammonia water, solves the problems of serious environmental pollution, high energy consumption, and insufficient performance of the oxide film, can reduce the treatment difficulty of harmful substances in electrolysis waste liquid, enhance the performance of the oxide film, reduce the risk of oxide film peeling, and extend the service life of the capacitor. Brief Description of the Drawings

[0035] Figure 1 It is a schematic diagram of the production process flow of the formation foil of the present invention;

[0036] Figure 2 It is a schematic diagram of the four-stage electrolytic oxidation process flow of the present invention. Detailed Embodiments

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of the present invention.

[0038] Example 1: Please refer to Figure 1 and Figure 2 , a production process of a formation foil for an aluminum electrolytic capacitor, and the production process is as follows:

[0039] S1: Unroll the etched aluminum foil, connect the lead foil as an auxiliary electrode, after being treated with 120 °C steam for 10 min and 100 °C boiling water for 30 min, add 25 °C pure water for washing for 20 min;

[0040] S2: Conduct one-stage electrolytic oxidation, and after completion, pass pure water for washing for 2 min;

[0041] S3: Conduct two-stage electrolytic oxidation, and after completion, pass pure water with a temperature of 40 °C for washing for 2 min;

[0042] S4: Add a phosphoric acid solution with a concentration of 10 wt% and stir and react at a speed of 100 rpm for 10 min, then conduct three-stage electrolytic oxidation, and after completion, pass pure water for washing for 3 min;

[0043] S5: Add an ammonium adipate solution with a concentration of 0.3 wt% to the feed trough, react for 30 min, and then add 40 °C pure water for washing for 3 min;

[0044] S6: Pass a constant voltage current of 120 V, heat up to 450 °C and roast the aluminum foil for 30 min, then add a phosphoric acid solution with a concentration of 30 wt%, adjust the pH to 3, and treat for 20 min;

[0045] S7: Conduct four-stage electrolytic oxidation. After completion, pure water at 30°C is introduced for water washing at a spraying pressure of 0.2 MPa for 3 minutes;

[0046] S8: After the third calcination, water washing and post-treatment, the prepared formed foil is dried, wound and stored in the warehouse;

[0047] The conditions for the first-stage electrolytic oxidation in S2 are as follows: A boric acid solution with a concentration of 3.8 wt% is introduced. Ammonia water is added during the start-up of the electrolytic cell to adjust the pH to 5.8. The voltage is 50 V and the current density is 0.8 A / dm 2 constant voltage current, and the reaction is carried out for 30 minutes in an environment with a temperature of 25°C;

[0048] The conditions for the second-stage electrolytic oxidation in S3 are as follows: A boric acid solution with a concentration of 2.5 wt% is introduced. Ammonia water is added during the start-up of the electrolytic cell to adjust the pH to 6. The voltage is 80 V and the current density is 0.6 A / dm 2 constant voltage current, and the reaction is carried out for 40 minutes in an environment with a temperature of 30°C;

[0049] The conditions for the third-stage electrolytic oxidation in S4 are as follows: A boric acid solution with a concentration of 2 wt% is introduced. Ammonia water is added during the start-up of the electrolytic cell to adjust the pH to 6.2. The voltage is 100 V and the current density is 0.4 A / dm 2 constant voltage current, and the reaction is carried out for 50 minutes in an environment with a temperature of 35°C;

[0050] Specifically, S7 is as follows:

[0051] S71: Add a boric acid solution with a concentration of 1.5 wt%. Ammonia water is added during the start-up of the electrolytic cell to adjust the pH to 5.8. The voltage used is 120 V and the current density is 0.3 A / dm 2 constant voltage current, and the first four-stage electrolytic oxidation is carried out for 60 minutes in an environment with a temperature of 35°C. After completion, pure water is added for water washing;

[0052] S72: Add a boric acid solution with a concentration of 1 wt%. Ammonia water is added during the start-up of the electrolytic cell to adjust the pH to 5.8. The voltage used is 150 V and the current density is 0.2 A / dm 2 constant voltage current, and the second four-stage electrolytic oxidation is carried out for 70 minutes in an environment at 40°C. After completion, pure water is added for water washing;

[0053] S73: Electrify and conduct the second calcination at 600°C for 10 h. Add a boric acid solution with a concentration of 0.5 wt%. Ammonia water is added during the start-up of the electrolytic cell to adjust the pH to 5.8. The voltage used is 180 V and the current density is 0.1 A / dm 2 constant voltage current, and the third four-stage electrolytic oxidation is carried out for 80 minutes in an environment with a temperature of 45°C. Pure water is added for water washing;

[0054] S74: Add boric acid solution with a concentration of 0.3 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8, and use a voltage of 200 V and a current density of 0.05 A / dm 2 constant voltage current, and conduct the fourth four-stage electrolytic oxidation for 90 min in an environment of 50 °C;

[0055] In the third roasting in S8, the temperature is raised to 400 °C at a rate of 200 °C / h and then held for 2 h, and then raised to 650 °C at a rate of 150 °C / h and held for 8 h;

[0056] In S8, the temperature of the water washing is 45 °C and the time is 30 min;

[0057] In S8, the operation of the post-treatment is to add phosphoric acid solution with a concentration of 8 wt%, and stir for 0.5 h in an environment with a pH of 2;

[0058] In S8, the temperature of the drying is 120 °C and the time is 3 h;

[0059] Further, unwind the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 120 °C for 10 min and boiling water treatment at 100 °C for 30 min, add pure water at 25 °C for water washing for 20 min, introduce boric acid solution with a concentration of 3.8 wt%, add ammonia water to adjust the pH to 5.8 when starting up the electrolytic cell, and the voltage is 50 V and the current density is 0.8 A / dm 2 constant voltage current, react for 30 min in an environment with a temperature of 25 °C, after completion, introduce pure water for water washing for 2 min, introduce boric acid solution with a concentration of 2.5 wt%, add ammonia water to adjust the pH to 6 when starting up the electrolytic cell, the voltage is 80 V, and the current density is 0.6 A / dm 2 constant voltage current, react for 40 min in an environment with a temperature of 30 °C, after completion, introduce pure water at 40 °C for water washing for 2 min, add phosphoric acid solution with a concentration of 10 wt% and stir and react at a speed of 100 rpm for 10 min, introduce boric acid solution with a concentration of 2 wt%, add ammonia water to adjust the pH to 6.2 when starting up the electrolytic cell, the voltage is 100 V, and the current density is 0.4 A / dm 2 constant voltage current, react for 50 min in an environment with a temperature of 35 °C, after completion, introduce pure water for water washing for 3 min, add ammonium adipate solution with a concentration of 0.3 wt% to the feeding tank, after reacting for 30 min, add pure water at 40 °C for water washing for 3 min, introduce a constant voltage current of 120 V, raise the temperature to 450 °C and roast the aluminum foil for 30 min, then add phosphoric acid solution with a concentration of 30 wt%, adjust the pH to 3, treat for 20 min, add boric acid solution with a concentration of 1.5 wt%, add ammonia water to adjust the pH to 5.8 when starting up the electrolytic cell, and use a voltage of 120 V and a current density of 0.3 A / dm 2Constant voltage current, perform the first four-stage electrolytic oxidation for 60 min in an environment with a temperature of 35°C. After completion, add pure water for washing. Add a boric acid solution with a concentration of 1 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8. The applied voltage is 150 V and the current density is 0.2 A / dm 2 Constant voltage current, perform the second four-stage electrolytic oxidation for 70 min in an environment with a temperature of 40°C. After completion, add pure water for washing. Electrolyze at 600°C for the second roasting for 10 h. Add a boric acid solution with a concentration of 0.5 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8. The applied voltage is 180 V and the current density is 0.1 A / dm 2 Constant voltage current, perform the third four-stage electrolytic oxidation for 80 min in an environment with a temperature of 45°C. Add pure water for washing. Add a boric acid solution with a concentration of 0.3 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8. The applied voltage is 200 V and the current density is 0.05 A / dm 2 Constant voltage current, perform the fourth four-stage electrolytic oxidation for 90 min in an environment with a temperature of 50°C. After completion, spray and wash with pure water at 30°C under a spraying pressure of 0.2 MPa for 3 min. Heat up to 400°C at a rate of 200°C / h and keep warm for 2 h, then heat up to 650°C at a rate of 150°C / h and keep warm for 8 h to complete the third roasting. Wash with pure water at 45°C for 30 min. Subsequently, add a phosphoric acid solution with a concentration of 8 wt%. Stir in an environment with a pH of 2 for 0.5 h. Dry at 120°C for 3 h. Wind up the prepared formed foil and store it in the warehouse;

[0060] Control group 1: Fix the voltage intensity and fix the current density, keep other conditions unchanged, and carry out the preparation of the formed foil;

[0061] Control group 2: Replace S7 with a constant voltage current with a voltage of 180 V - 220 V and a current density of 0.1 A / dm 2 ~0.3 A / dm 2 to perform one-stage electrolytic oxidation, keep other conditions unchanged, and carry out the preparation of the formed foil;

[0062] Control group 3: Remove the phosphoric acid added during the preparation process, keep other conditions unchanged, and carry out the preparation of the formed foil;

[0063] Control group 4: Replace the composite acid system composed of boric acid and ammonia water with only boric acid, keep other conditions unchanged, and carry out the preparation of the formed foil;

[0064] Control group 5: Cancel the first two roastings, only keep the last roasting, keep other conditions unchanged, and carry out the preparation of the formed foil.

[0065] Example 2: Please refer to Figure 1 and Figure 2, A production process for etched foils used in aluminum electrolytic capacitors, the production process being as follows:

[0066] S1: Unwind the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 120°C for 10 min and boiling water treatment at 100°C for 30 min, add pure water at 25°C and wash for 20 min;

[0067] S2: Conduct first-stage electrolytic oxidation, and after completion, pass in pure water and wash for 2 min;

[0068] S3: Conduct second-stage electrolytic oxidation, and after completion, pass in pure water at a temperature of 40°C and wash for 2 min;

[0069] S4: Add a phosphoric acid solution with a concentration of 10 wt% and stir and react at a rotation speed of 100 rpm for 10 min, then conduct third-stage electrolytic oxidation, and after completion, pass in pure water and wash for 3 min;

[0070] S5: Add an ammonium adipate solution with a concentration of 0.3 wt% to the feed tank, after reacting for 30 min, add pure water at 40°C and wash for 3 min;

[0071] S6: Pass in a constant voltage current of 120 V, raise the temperature to 450°C and roast the aluminum foil for 30 min, then add a phosphoric acid solution with a concentration of 30 wt%, adjust the pH to 3, and treat for 20 min;

[0072] S7: Conduct fourth-stage electrolytic oxidation, and after completion, pass in pure water at 30°C with a spray pressure of 0.2 MPa and wash for 3 min;

[0073] S8: After the third roasting, washing and post-treatment, dry the prepared etched foil and wind it up and store it in the warehouse;

[0074] Further, during the preparation of the etched foil, the electrolytic oxidation process is divided into four stages, the voltage gradually increases from 50 V to 220 V, and the current density gradually decreases from 0.8 A / dm 2 gradually decreases to 0.05 A / dm 2 , the decrease in the voltage gradient reduces the risk of electric field distortion, and the decrease in the current density gradient inhibits local peroxidation, avoiding film layer cracks and specific capacitance deviation caused by traditional single oxidation. In the first-stage electrolytic oxidation, by passing in a boric acid solution with a concentration of 3.8 wt%, adding ammonia water to adjust the pH to 5.8 when starting up the electrolytic cell, the voltage is 50 V and the current density is 0.8 A / dm 2The constant voltage current reacts for 30 minutes in an environment with a temperature of 25 °C, causing an initial barrier layer to start forming on the surface of the pretreated etched aluminum foil. Under the action of a low voltage, dense amorphous aluminum oxide is generated, providing a substrate for the subsequent growth of the porous layer. The second-stage electrolytic oxidation is carried out by introducing a boric acid solution with a concentration of 2.5 wt%. Ammonia is added when starting up the electrolytic cell to adjust the pH to 6, the voltage is 80 V, and the current density is 0.6 A / dm 2 The constant voltage current reacts for 40 minutes in an environment with a temperature of 30 °C. By increasing the voltage to induce the electric breakdown effect, a microporous structure is formed on the initial barrier layer. At the same time, the current density is reduced to make the generated pores arranged orderly, increasing the effective surface area and the specific capacitance. The third-stage electrolytic oxidation is carried out by introducing a boric acid solution with a concentration of 2 wt%. Ammonia is added when starting up the electrolytic cell to adjust the pH to 6.2, the voltage is 100 V, and the current density is 0.4 A / dm 2 The constant voltage current reacts for 50 minutes in an environment with a temperature of 35 °C. The voltage is further increased to promote the longitudinal extension and lateral expansion of the pores under a high-voltage environment. For the first four-stage electrolytic oxidation, the voltage is increased to 120 V, and field-induced crystallization is induced by an ultra-high voltage to form γ-aluminum oxide. At the same time, the increase in temperature accelerates the ion migration to generate a crystalline layer with a higher dielectric constant, and at the same time, the structural defects in the first three stages of electrolytic oxidation are repaired. For the second four-stage electrolytic oxidation, the voltage is further increased to 150 V to densify and reconstruct the oxide layer, and the current density is reduced to 0.2 A / dm 2 , inhibiting the Joule heat effect and avoiding the generation of microcracks. For the third four-stage electrolytic oxidation, surface passivation treatment is carried out at a voltage increased to near the breakdown voltage to eliminate the residual pores. At the same time, the reduction in the concentration of the boric acid solution reduces the impurities, and the increase in temperature promotes the formation of a hydroxylated surface. For the fourth four-stage electrolytic oxidation, field-induced anodic polarization is carried out at a limit voltage of 200 V to induce the formation of an aluminum-rich layer on the surface, 0.05 A / dm 2 The ultra-low current density ensures slow oxidation, obtaining a nanoscale surface flatness, realizing the function of gradient adjustment of electrolysis parameters, solving the problems of structural defects of the oxide film, deterioration of electrical properties, and decline in process stability caused by fixed voltage or simple segmentation, being able to optimize the denseness and voltage resistance performance of the oxide film, improving the capacity conversion rate, and reducing energy consumption.

[0075] Example 3: Please refer to Figure 1 and Figure 2 , a production process of a forming foil for an aluminum electrolytic capacitor, the production process is as follows:

[0076] S1: Unroll the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 120 °C for 10 minutes and boiling water treatment at 100 °C for 30 minutes, add pure water at 25 °C for washing for 20 minutes;

[0077] S2: Conduct a period of electrolytic oxidation. After completion, introduce pure water for washing for 2 minutes.

[0078] S3: Conduct a second stage of electrolytic oxidation. After completion, introduce pure water at a temperature of 40 °C for washing for 2 minutes.

[0079] S4: Add a phosphoric acid solution with a concentration of 10 wt% and stir and react at a rotation speed of 100 rpm for 10 minutes. Then conduct a third stage of electrolytic oxidation. After completion, introduce pure water for washing for 3 minutes.

[0080] S5: Add an ammonium adipate solution with a concentration of 0.3 wt% to the feed trough. After reacting for 30 minutes, add pure water at 40 °C for washing for 3 minutes.

[0081] S6: Pass a constant voltage current of 120 V, heat up to 450 °C and roast the aluminum foil for 30 minutes. Then add a phosphoric acid solution with a concentration of 30 wt% and adjust the pH to 3, and treat for 20 minutes.

[0082] S7: Conduct a fourth stage of electrolytic oxidation. After completion, introduce pure water at 30 °C and wash with a spraying pressure of 0.2 MPa for 3 minutes.

[0083] S8: After the third roasting, washing and post-treatment, dry the prepared formed foil and roll it up for storage in the warehouse.

[0084] Further, after the second-stage electrolytic oxidation and washing with water, a phosphoric acid solution with a concentration of 10 wt% is added, and it is stirred at a speed of 100 rpm for 10 min. Through acid etching, the micropore diameter on the surface of the aluminum foil is enlarged, and the surface area is increased. Hydrogen ions in the phosphoric acid react with aluminum to form trivalent aluminum ions, promoting non-uniform corrosion to form a porous substrate, providing a structural basis for the subsequent growth of the oxide layer. After the first roasting, the second addition of phosphoric acid is carried out. The pH is adjusted to 3 using a phosphoric acid solution with a concentration of 30 wt%, and the intermetallic compounds remaining on the surface are dissolved to eliminate the abnormal local conductivity caused by impurities. After the fourth-stage electrolytic oxidation, after roasting and washing with water, a phosphoric acid solution with a concentration of 8 wt% is added, the pH is adjusted to 2 and stirred for 0.5 h. Through the coordination of phosphate ions with aluminum oxide, aluminum phosphate complexes are formed in the pores of the oxide film. The aluminum phosphate complexes have a higher dielectric strength, further improving the withstand voltage performance of the capacitor. At the same time, the Al-O-P bond energy formed by phosphoric acid treatment is higher than the Al-OH bond, which can inhibit the alumina hydration reaction during subsequent washing with water and high-temperature treatment, avoiding the swelling and rupture of the dielectric layer. After the third roasting, phosphoric acid selectively corrodes the amorphous phase at the crystallization site of alumina, improving the density of γ-aluminum oxide grains and further reducing the dielectric loss, realizing the function of improving the performance of the oxide film in stages, solving the problems of high defect rate, insufficient withstand voltage performance, short life, and poor environmental protection of the oxide film, being able to improve the density of the oxide film, reduce the diffusion rate of microcracks, and reduce the raw material cost and the difficulty of wastewater treatment.

[0085] Example 4: Please refer to Figure 1 and Figure 2 , a production process of a forming foil for aluminum electrolytic capacitors, and the production process is as follows:

[0086] S1: Unwind the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 120 °C for 10 min and boiling water treatment at 100 °C for 30 min, add pure water at 25 °C and wash for 20 min;

[0087] S2: Perform the first-stage electrolytic oxidation, and after completion, pass pure water through for washing for 2 min;

[0088] S3: Perform the second-stage electrolytic oxidation, and after completion, pass pure water at 40 °C through for washing for 2 min;

[0089] S4: Add a phosphoric acid solution with a concentration of 10 wt% and stir and react at a speed of 100 rpm for 10 min, then perform the third-stage electrolytic oxidation, and after completion, pass pure water through for washing for 3 min;

[0090] S5: Add an ammonium adipate solution with a concentration of 0.3 wt% to the feed trough, after reacting for 30 min, add pure water at 40 °C and wash for 3 min;

[0091] S6: Introduce a constant voltage current of 120V, heat up to 450°C and calcine the aluminum foil for 30 min. Subsequently, add a phosphoric acid solution with a concentration of 30 wt%, adjust the pH to 3, and treat for 20 min;

[0092] S7: Conduct four-stage electrolytic oxidation. After completion, introduce pure water at 30°C and wash with a spray pressure of 0.2 MPa for 3 min;

[0093] S8: After the third calcination, washing and post-treatment, dry and wind up the prepared formed foil and store it in the warehouse;

[0094] Furthermore, after completing three-stage electrolytic oxidation, after washing, add an ammonium adipate solution with a concentration of 0.3 wt% to the feed trough. A buffer system is formed through dissociation reaction in the electrolyte to avoid excessive corrosion of the aluminum substrate by strong acids and alkalis. The ammonium ions generated by dissociation increase the conductivity of the electrolyte, reduce the polarization voltage during the formation of the oxide film, and improve the oxidation efficiency. The adipate ions have a complexing effect on metal impurities such as divalent iron ions and divalent manganese ions, preventing them from depositing on the surface of the oxide film and causing local breakdown. Subsequently, calcine in an environment of 450°C for 30 min. Evaporate the residual moisture and organic solvents after phosphoric acid treatment through high-temperature calcination, and eliminate the free phosphoric acid and boric acid complexes adsorbed on the surface to avoid impurity interference in subsequent electrolytic oxidation. Amorphous aluminum oxide undergoes a phase change at 400°C - 500°C. Therefore, during the first calcination, part of the aluminum oxide is converted into γ-aluminum oxide, forming a crystalline framework structure with better dielectric properties. After completing the second four-stage electrolytic oxidation, conduct the second calcination, control the temperature at 600°C, and extend the time to 10 h. High temperature promotes the sintering of the pore walls of aluminum oxide, eliminates microcracks and internal stress in the pores, optimizes the pore size distribution from 10 nm - 50 nm to 20 nm - 30 nm, makes the pores more uniform. At the same time, long-term heat preservation enables the partial transformation of γ-aluminum oxide with high dielectric constant to θ-aluminum oxide, and the grain size grows from 5 nm to 15 nm. The grain boundary impurities are oxidized and volatilized, increasing the dielectric constant. After completing the four-stage electrolytic oxidation, conduct the third calcination. The temperature of the third calcination rises to 400°C at a rate of 200°C / h and is kept warm for 2 h, then rises to 650°C at a rate of 150°C / h and is kept warm for 8 h. During the calcination process, a diffusion effect occurs at the interface between the metal aluminum substrate and the oxide layer, generating Al-O-P bonds to fill the lattice vacancies, reducing the leakage current density, realizing the function of jointly regulating and improving the performance of the oxide layer from the micro and macro aspects, solving the problems of impurity interference, high dielectric loss, and poor interface stability, and being able to avoid impurity interference in electrolytic oxidation, reduce the dielectric loss, and improve the dielectric properties and structural stability of the finished formed foil.

[0095] Example 5: Please refer to Figure 1 and Figure 2 , a production process of a formed foil for aluminum electrolytic capacitors, and the production process is as follows:

[0096] S1: Unroll the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 120°C for 10 min and boiling water treatment at 100°C for 30 min, add pure water at 25°C for washing for 20 min;

[0097] S2: Conduct the first-stage electrolytic oxidation, and after completion, pass in pure water for washing for 2 min;

[0098] S3: Conduct the second-stage electrolytic oxidation, and after completion, pass in pure water at 40°C for washing for 2 min;

[0099] S4: Add a phosphoric acid solution with a concentration of 10 wt% and stir and react at a speed of 100 rpm for 10 min, then conduct the third-stage electrolytic oxidation, and after completion, pass in pure water for washing for 3 min;

[0100] S5: Add an ammonium adipate solution with a concentration of 0.3 wt% to the feed tank, after reacting for 30 min, add pure water at 40°C for washing for 3 min;

[0101] S6: Pass in a constant voltage current of 120 V, heat up to 450°C and roast the aluminum foil for 30 min, then add a phosphoric acid solution with a concentration of 30 wt%, adjust the pH to 3, and treat for 20 min;

[0102] S7: Conduct the fourth-stage electrolytic oxidation, and after completion, pass in pure water at 30°C for washing for 3 min with a spraying pressure of 0.2 MPa;

[0103] S8: After the third roasting, washing and post-treatment, dry and wind up the prepared formed foil and store it in the warehouse;

[0104] Furthermore, during the electrolytic oxidation of etched aluminum foil, by adding a composite acid system composed of boric acid and ammonia water, ammonia water neutralizes the acidity of boric acid to form an ammonium borate buffer system, which can stabilize the pH of the electrolyte, ensure extremely small pH fluctuations during electrolysis, avoid the dissolution of the oxide film or uneven current density caused by excessive local acidity, thereby ensuring uniform growth of the oxide film. During electrolysis, boric acid ionizes to produce borate ions and hydrogen ions, which participate in the anodic aluminum oxidation reaction. Borate ions form complexes with trivalent aluminum ions, which can delay the growth rate of the oxide film, promote the densification of the oxide film, and improve the dielectric strength and voltage resistance of the film layer. The composite acid system of boric acid and ammonia water adjusts the concentration gradient and pH in different electrolytic oxidations, and cooperates with the gradually increasing voltage and gradually decreasing current density to achieve the layered growth of the oxide film. High-concentration boric acid combined with low voltage forms a dense oxide film substrate, reducing leakage current. Low-concentration boric acid combined with high voltage induces a microporous structure, increasing the specific surface area and enhancing the capacitor capacity. During subsequent calcination, ammonium borate decomposes to form boron trioxide, and similarly, aluminum borate oxide composite structures are formed with aluminum oxide, enhancing the thermal stability and mechanical strength of the oxide film, reducing the generation of lattice defects at high temperatures. The composite acid system and phosphoric acid solution can synergistically treat the loose layer on the surface of the soluble oxide film, realizing the function of precisely controlling electrolysis conditions, solving the problems of serious environmental pollution, high energy consumption, and insufficient oxide film performance, reducing the treatment difficulty of harmful substances in electrolytic waste liquid, enhancing the performance of the oxide film, reducing the risk of oxide film peeling, and extending the service life of the capacitor.

[0105] Performance Test

[0106] Test 1: Prepare 5 pieces of formed foils without residual oxide film and damage on the surface prepared in Example 1 and Control Groups 1-5, with a size of 5 cm * 10 cm. Dry them in an oven at a temperature of 55 °C and a humidity of 20% for 12 h, and then place them in an environment at a temperature of 25 °C and a humidity of 60% to equilibrate for 1 h. Use an LCR digital bridge to measure the actual capacitance value at a frequency of 1 kHz and a voltage of 1 V. After testing 10 times and excluding abnormal data, take the average value, calculate the specific capacitance and deviation rate. The test standard is IEC60384-1. The test results are shown in Table 1, the formed foil capacitance test results table as follows: Table 1 Formed Foil Capacitance Test Results Table

[0107] Test 2: Prepare 5 pieces of formed foils without residual oxide film and damage on the surface prepared in Example 1 and Control Groups 1-5, with a size of 5 cm * 10 cm. Simulate the bending process through an automated bending device, record the springback angle and deformation amount. The test results are shown in Table 2, the formed foil bending test results table as follows: Table 2 Formed Foil Bending Test Results Table

[0108] Test 3: Prepare 5 pieces each of the etched foils with no residual oxide film and no damage on the surface prepared in Example 1 and Control Groups 1 - 5, with a size of 5 cm * 10 cm. Place the samples in a damp heat chamber at a temperature of 85 °C and a humidity of 85% for 500 h, measure the capacitance values of the samples before and after being placed in the damp heat chamber, calculate the capacitance attenuation rate, and the test results are shown in the following Table 3, the test results table of the etched foil's water hydration resistance performance: Table 3 Test results table of the etched foil's water hydration resistance performance

[0109] Working principle: Unroll the etched aluminum foil, connect the lead foil as an auxiliary electrode. After steam treatment at 100 °C - 120 °C for 5 min - 10 min and boiling water treatment at 95 °C - 100 °C for 20 min - 30 min, add pure water at 25 °C - 30 °C for washing for 15 min - 20 min, introduce boric acid solution with a concentration of 3.8 wt% - 4.2 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.2, with a voltage of 50 V - 80 V and a current density of 0.8 A / dm 2 ~1.2 A / dm 2 constant voltage current, react in an environment at a temperature of 25 °C - 30 °C for 30 min - 40 min. After completion, introduce pure water for washing for 1.5 min - 2 min, introduce boric acid solution with a concentration of 2.5 wt% - 3.5 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 6 - 6.3, with a voltage of 80 V - 100 V and a current density of 0.6 A / dm 2 ~1 A / dm 2 constant voltage current, react in an environment at a temperature of 25 °C - 30 °C for 40 min - 50 min. After completion, introduce pure water at a temperature of 40 °C - 45 °C for washing for 2 min - 2.5 min, add phosphoric acid solution with a concentration of 10 wt% - 15 wt% and stir and react at a rotation speed of 50 rpm - 100 rpm for 5 min - 15 min, introduce boric acid solution with a concentration of 2 wt% - 3 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 6.2 - 6.5, with a voltage of 100 V - 120 V and a current density of 0.4 A / dm 2 ~0.8 A / dm 2 constant voltage current, react in an environment at a temperature of 30 °C - 35 °C for 50 min - 60 min. After completion, introduce pure water for washing for 3 min - 3.5 min;

[0110] Add ammonium adipate solution with a concentration of 0.2 wt% - 0.3 wt% to the feed trough. After reacting for 30 min - 40 min, add pure water at 40°C - 45°C for washing for 3 min - 3.5 min. Pass a constant voltage current of 120 V - 150 V, heat up to 450°C - 500°C and calcine the aluminum foil for 20 min - 30 min. Then add phosphoric acid solution with a concentration of 30 wt% - 35 wt%, adjust the pH to 2.5 - 3, and treat for 20 min - 30 min;

[0111] Add boric acid solution with a concentration of 1.5 wt% - 2.5%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.8. Use a voltage of 120 V - 150 V and a current density of 0.3 A / dm 2 ~0.6 A / dm 2 of constant voltage current. Conduct the first four-stage electrolytic oxidation for 60 min - 70 min in an environment with a temperature of 35°C - 40°C. After completion, add pure water for washing. Add boric acid solution with a concentration of 1 wt% - 2 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.8. Use a voltage of 150 V - 180 V and a current density of 0.2 A / dm 2 ~0.4 A / dm 2 of constant voltage current. Conduct the second four-stage electrolytic oxidation for 70 min - 80 min in an environment with a temperature of 40°C - 45°C. After completion, add pure water for washing. Pass an electric current and conduct the second calcination at 600°C - 650°C for 8 h - 14 h. Add boric acid solution with a concentration of 0.5 wt% - 1.5 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.8. Use a voltage of 180 V - 200 V and a current density of 0.1 A / dm 2 ~0.3 A / dm 2 of constant voltage current. Conduct the third four-stage electrolytic oxidation for 80 min - 90 min in an environment with a temperature of 45°C - 50°C. Add pure water for washing. Add boric acid solution with a concentration of 0.3 wt% - 1 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.8. Use a voltage of 200 V - 220 V and a current density of 0.05 A / dm 2 ~0.2 A / dm 2 of constant voltage current. Conduct the fourth four-stage electrolytic oxidation for 90 min - 100 min in an environment with a temperature of 50°C - 55°C. After completion, pass pure water at 25°C - 30°C and wash with a spraying pressure of 0.15 MPa - 0.2 MPa for 2.5 min - 3 min;

[0112] The temperature is raised to 400°C at a rate of 200°C / h and then held for 2 h. It is then raised to 650°C at a rate of 150°C / h and held for 6 - 8 h to complete the third roasting. It is washed with pure water at a temperature of 45°C - 60°C for 20 - 30 min, a phosphoric acid solution with a concentration of 5wt% - 10wt% is added, and it is stirred in an environment with a pH of 2 - 3 for 0.5 - 1 h. After drying in an environment with a temperature of 120°C - 150°C for 2 - 3 h, the prepared formed foil is wound up and stored in the warehouse.

[0113] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non - restrictive. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claimed rights.

Claims

1. A production process of forming foil for aluminum electrolytic capacitors, characterized in that: The production process is as follows: S1: Unroll the etched aluminum foil, connect the lead foil as an auxiliary electrode, after steam treatment at 100°C - 120°C for 5 min - 10 min and boiling water treatment at 95°C - 100°C for 20 min - 30 min, add pure water at 25°C - 30°C for washing for 15 min - 20 min; S2: Conduct the first-stage electrolytic oxidation, and after completion, pass in pure water for washing for 1.5 min - 2 min; S3: Conduct the second-stage electrolytic oxidation, and after completion, pass in pure water at a temperature of 40°C - 45°C for washing for 2 min - 2.5 min; S4: Add a phosphoric acid solution with a concentration of 10wt% - 15wt% and stir and react at a rotation speed of 50 rpm - 100 rpm for 5 min - 15 min, then conduct the third-stage electrolytic oxidation, and after completion, pass in pure water for washing for 3 min - 3.5 min; S5: Add an ammonium adipate solution with a concentration of 0.2wt% - 0.3wt% to the feed trough, after reacting for 30 min - 40 min, add pure water at 40°C - 45°C for washing for 3 min - 3.5 min; S6: Pass in a constant voltage current of 120V - 150V, heat up to 450°C - 500°C to calcine the aluminum foil for 20 min - 30 min, then add a phosphoric acid solution with a concentration of 30wt% - 35wt%, adjust the pH to 2.5 - 3, and treat for 20 min - 30 min; S7: Conduct the fourth-stage electrolytic oxidation, and after completion, pass in pure water at 25°C - 30°C for washing with a spraying pressure of 0.15MPa - 0.2MPa for 2.5 min - 3 min; S8: After the third calcination, washing and post-treatment, dry the prepared formed foil and roll it up for storage in the warehouse.

2. The production process of the formation foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The conditions for a period of electrolytic oxidation in S2 are as follows: boric acid solution with a concentration of 3.8 wt% to 4.2 wt% is introduced. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 5.8 to 6.2, the voltage is 50 V to 80 V, and the current density is 0.8 A / dm 2 ~1.2 A / dm 2 constant voltage current. The reaction is carried out for 30 min to 40 min in an environment with a temperature of 25°C to 30°C.

3. The production process of the forming foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The conditions for the secondary electrolytic oxidation in S3 are as follows: a boric acid solution with a concentration of 2.5 wt% to 3.5 wt% is introduced. Ammonia water is added to adjust the pH to 6 to 6.3 when starting up the electrolytic cell. The voltage is 80 V to 100 V, and the current density is 0.6 A / dm 2 ~1 A / dm 2 of constant voltage current, and the reaction is carried out for 40 min to 50 min in an environment with a temperature of 25 °C to 30 °C.

4. The production process of a forming foil for an aluminum electrolytic capacitor according to claim 1, characterized in that: The conditions for the three-stage electrolytic oxidation in S4 are as follows: a boric acid solution with a concentration of 2 wt% to 3 wt% is introduced. When starting up the electrolytic cell, ammonia water is added to adjust the pH to 6.2 to 6.5, the voltage is 100 V to 120 V, and the current density is 0.4 A / dm 2 ~0.8 A / dm 2 constant voltage current, and the reaction is carried out for 50 min to 60 min in an environment with a temperature of 30 °C to 35 °C.

5. The production process of the forming foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The specific content of S7 is as follows: S71: Add boric acid solution with a concentration of 1.5 wt% - 2.5%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.

8. The operating voltage is 120V - 150V and the current density is 0.3A / dm 2 ~0.6A / dm 2 constant voltage current. Conduct the first four-stage electrolytic oxidation for 60 min - 70 min in an environment with a temperature of 35°C - 40°C. After completion, add pure water for water washing; S72: Add boric acid solution with a concentration of 1 wt% - 2 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.

8. The operating voltage is 150 V - 180 V and the current density is 0.2 A / dm 2 ~0.4 A / dm 2 constant voltage current. Conduct the second four-stage electrolytic oxidation for 70 min - 80 min in an environment of 40°C - 45°C. After completion, add pure water for water washing; S73: The second roasting is carried out at 600 °C to 650 °C for 8 h to 14 h with the addition of boric acid solution with a concentration of 0.5 wt% to 1.5 wt%. Ammonia water is added to adjust the pH to 5.8 to 6.8 during the start-up of the electrolytic cell. The applied voltage is 180 V to 200 V and the current density is 0.1 A / dm 2 ~0.3 A / dm 2 constant voltage current. The third four-stage electrolytic oxidation is carried out in an environment of 45 °C to 50 °C for 80 min to 90 min, and pure water is added for water washing; S74: Add boric acid solution with a concentration of 0.3 wt% - 1 wt%. When starting up the electrolytic cell, add ammonia water to adjust the pH to 5.8 - 6.

8. The operating voltage is 200V - 220V and the current density is 0.05A / dm 2 ~0.2A / dm 2 constant voltage current, and conduct the fourth four-stage electrolytic oxidation for 90 min - 100 min in an environment of 50°C - 55°C.

6. The production process of a forming foil for aluminum electrolytic capacitors according to claim 1, characterized in that: In S8, the temperature of the third calcination rises to 400°C at a rate of 200°C / h and is kept warm for 2 h, then rises to 650°C at a rate of 150°C / h and is kept warm for 6 h - 8 h.

7. The production process of the formation foil for aluminum electrolytic capacitors according to claim 1, characterized in that: In S8, the temperature of the washing is 45°C - 60°C, and the time is 20 min - 30 min.

8. The production process of a forming foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The operation of the post-treatment in S8 is to add a phosphoric acid solution with a concentration of 5wt% - 10wt% and stir in an environment with a pH of 2 - 3 for 0.5 h - 1 h.

9. The production process of a forming foil for an aluminum electrolytic capacitor according to claim 5, characterized in that: In S8, the temperature of the drying is 120°C - 150°C, and the time is 2 h - 3 h.

10. A formation foil for aluminum electrolytic capacitors, applicable to the production process of a formation foil for aluminum electrolytic capacitors described in any one of claims 1-9, characterized in that: The formed foil is prepared by the above production process.

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