A method for forming high-voltage anode foil

Abstract

This invention discloses a formation method for high-voltage anode foil, belonging to the technical field of anode foil for electrolytic capacitors. This formation method uses five to six stages of formation. Boric acid (0.1–10 wt%), tertiary phosphoric acid treatment, and tertiary high-temperature treatment in the formation solution improve the leakage current, loss, lifespan, and high-temperature resistance of the aluminum anode foil. Carboxylic acid treatment and hypophosphite (0.01–0.5 wt%) in the formation solution improve the density and hydration resistance of the oxide film. Hypophosphite and citric acid and citrate (0.01–0.5 wt%) in the formation solution increase the capacity of the aluminum anode foil. At a voltage specification of 650–950 VF, the high-voltage anode foil for aluminum electrolytic capacitors produced using this method exhibits high capacity, high-temperature resistance, and long lifespan, making it suitable for the production of 5G anode foil. The production process is simple to operate, the product has good stability, and it is suitable for industrial mass production.

Description

Technical Field

[0001] This invention relates to the field of electrolytic capacitor anode foil technology, and more specifically to a method for forming high-voltage anode foil. Background Technology

[0002] Capacitors are currently an indispensable electronic component in my country's modern industrial production, with a large usage volume and wide application range. The most common capacitors in my country are mainly of three types: electrolytic, organic film, and ceramic. Among them, aluminum electrolytic capacitors account for 50% of the production volume, which shows that aluminum electrolytic capacitor technology is more popular than the other two types.

[0003] With the rapid development of modern technology, electronic technology is also constantly advancing, leading to further improvements in the assembly density and integration level of electron positive electrodes. This, in turn, places higher demands on aluminum electrolytic capacitors. The current development trend of aluminum electrolytic capacitors is towards larger capacitance, smaller size, lower cost, and high-frequency, low-impedance performance. In recent years, the technological development of aluminum electrolytic capacitors in my country has mainly focused on three aspects: surface-mount technology, high specific capacitance manufacturing technology, and solid-state electrolyte technology. Due to their simple manufacturing process, low price, superior performance, and reliable quality, aluminum electrolytic capacitors have been widely used in electronic products. Moreover, with the rapid development of the electrical and electronic industries, the production scale and market demand for aluminum electrolytic capacitors continue to grow. To adapt to the trend of miniaturization and high performance in electronic products, it is necessary to develop capacitors with high specific capacitance.

[0004] In recent years, with the rapid development of aluminum electrolytic capacitor production, the electrode foil manufacturing industry has also developed rapidly. It has evolved from small-scale, decentralized production to large-scale, specialized production; the output of electrolytic foil has increased, and its quality has improved significantly. The main preparation processes for aluminum electrode foil include heat treatment-anodization and hydrothermal treatment-anodization.

[0005] Heat treatment-anodic oxidation method: Aluminum foil is directly heated at high temperature and then anodized. After the hot aluminum oxide film is anodized in the electrolyte, the film contains many crystalline oxide films γ′-Al2O3. Compared with aluminum anode foil without heat treatment, the specific volume is greatly improved, while the oxide film formation time is shortened and the power consumption is reduced.

[0006] Hydrothermal treatment-anodic oxidation method: The aluminum surface is first reacted with boiling water to form a hydrated oxide film, and then anodized. Part of the hydrated oxide film is dehydrated and crystallized under the action of an electric field. After the aluminum anode foil undergoes an oxidation reaction in the electrolyte, the amorphous oxide film formed on the surface also crystallizes under the action of a high electric field, forming a crystalline composite oxide film. Compared with the amorphous oxide film, this method increases the specific volume of the aluminum anode foil and reduces the power consumption during formation.

[0007] After heat treatment and hydrothermal treatment, the aluminum foil surface exhibits a thermal oxide film and a hydrated oxide film. However, once the anodizing process is completed and the power is turned off, oxygen in the pores is easily expelled, while electrolyte solution is absorbed. This causes the film to hydrolyze and deteriorate, losing its original voltage-bearing capacity. Therefore, electrolytic capacitors made from aluminum electrode foil generally have high leakage current and are prone to generating large amounts of gas, thus reducing their lifespan.

[0008] Currently, there are two main formation methods:

[0009] The first approach employs a five-stage formation method, comprising pretreatment, first to third-stage formation, first liquid feeding, fourth to fifth-stage formation, first high-temperature treatment, fifth-stage first-stage remedial formation, first phosphoric acid treatment, fifth-stage second-stage remedial formation, second high-temperature treatment, fifth-stage third-stage remedial formation, and post-treatment. The first to fourth stages use adipic acid and its ammonium salt, citric acid and its ammonium salt, and sebacic acid and its ammonium salt as the formation solution; the fifth stage uses ammonium pentaborate and boric acid as the formation solution. This method produces a high-voltage anolyte oxide film with advantages such as good density, high capacity, and good water resistance. However, the anolyte has high leakage current, high loss, and short lifespan, making it unsuitable for long-life products.

[0010] The second approach involves a six-stage formation process, comprising pretreatment, first and second-stage formation, first liquid feeding, third and fourth-stage formation, second liquid feeding, fifth and sixth-stage formation, first high-temperature treatment, sixth-stage second-stage formation, first phosphoric acid treatment, second high-temperature treatment, sixth-stage third-stage formation, and post-treatment. Boric acid and ammonium pentaborate are used as the formation solutions for all stages from the first to the sixth. This method offers advantages such as short voltage ramp-up time and low leakage current, but the produced formed foil has lower capacity and poorer foil toughness, making it unsuitable for producing miniaturized products.

[0011] In summary, current anode foil formation processes still cannot achieve anode foils that simultaneously possess high specific capacity, high temperature resistance, and low loss. Based on these limitations, this invention proposes a high-pressure anode foil formation process that effectively solves the aforementioned problems. Summary of the Invention

[0012] The purpose of this invention is to provide a method for forming high-voltage anode foil, including a formation production line process and the composition of the formation bath. The high-voltage aluminum electrolytic capacitor anode foil produced by this method has the characteristics of short voltage rise time, high capacity, low leakage current, low loss, long life, and high temperature resistance, and is suitable for leaded, horn-shaped, and bolt-shaped aluminum electrolytic capacitors. At the same time, this method is simple to produce, the bath solution is easy to control, and the quality consistency and stability are high, making it suitable for mass production in enterprises.

[0013] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0014] A method for forming high-voltage anode foil involves electrochemically reacting the aluminum foil in a forming solution to form an oxide film on its surface, which serves as a dielectric. This forming method includes the following steps:

[0015] (1) Primary Formation: The aluminum foil after pretreatment and acid treatment is placed in the primary formation solution for the first-stage formation treatment (first-stage electrochemical treatment). The treatment temperature is 80-95℃, the current density is 30-60mA / cm2, the applied voltage is 30-35%×vf, and the formation time is 8-18 minutes. The primary formation solution consists of: boric acid 0.3-3wt%, ammonium carbonate or ammonium pentaborate 0.05-0.8wt%, citric acid and citrate 0.05-0.8wt%, hypophosphite 0.05-0.8wt%, and the remainder is water. The vf refers to the final voltage for forming the product, which is determined according to the actual needs of the product.

[0016] (2) Secondary Formation: The aluminum foil after primary formation is placed in a secondary formation solution for secondary formation treatment (secondary electrochemical treatment). The treatment temperature is 80-95℃ and the current density is 30-60 mA / cm². 2 The applied voltage is 60-70% × vf, and the formation time is 8-18 minutes; the secondary formation solution consists of: boric acid 0.3-3 wt%, ammonium carbonate or ammonium pentaborate 0.03-0.6 wt%, citric acid and citrate 0.03-0.6 wt%, hypophosphite 0.03-0.6 wt%, and the remainder is water;

[0017] (3) Tertiary Formation: The aluminum foil after secondary formation is placed in a tertiary formation solution for tertiary formation treatment (third-stage electrochemical treatment). The treatment temperature is 80-95℃ and the current density is 25-55 mA / cm². 2 The applied voltage is 85-95% × vf, and the formation time is 8-18 minutes; the three-stage formation solution consists of: boric acid 0.5-5 wt%, ammonium carbonate or ammonium pentaborate 0.02-0.5 wt%, citric acid and citrate 0.02-0.5 wt%, and the remainder is water;

[0018] (4) Liquid electrostatication: The aluminum foil after three-stage formation is placed in a liquid electrostatication formation solution and formed for 8 to 18 minutes under the conditions of temperature 15 to 45°C, voltage 15 to 35V and current 650 to 1550A; the liquid electrostatication formation solution is an aqueous solution of adipic acid or adipic acid salt solution with a concentration of 2 to 7 wt%, or a citric acid solution or a citrate solution with a concentration of 2 to 7 wt%, or a phosphoric acid solution or a phosphate solution with a concentration of 2 to 7 wt%.

[0019] (5) Fourth-stage formation: The aluminum foil after liquid electro-forming is placed in the fourth-stage formation solution for fourth-stage formation treatment (fourth-stage electro-forming treatment). The treatment temperature is 80-95℃ and the current density is 10-40 mA / cm². 2 The applied voltage is 95-110% × vf, and the formation time is 12-27 minutes; the composition of the four-stage formation solution is: boric acid 1-10 wt%, ammonium pentaborate 0.01-0.3 wt%, and the remainder is water;

[0020] (6) First Formation of the Fifth Stage: The aluminum foil after the fourth stage formation is placed in the first formation solution of the fifth stage for the first formation treatment of the fifth stage (first electrochemical treatment of the fifth stage). The treatment temperature is 80-95℃ and the current density is 15-40 mA / cm². 2 The applied voltage is 110–130% × vf, and the formation time is 25–35 minutes.

[0021] (7) Fifth-stage second formation: After the aluminum foil has undergone the fifth-stage first formation treatment, it is subjected to the first phosphoric acid treatment, the first high-temperature treatment, and the second phosphoric acid treatment in sequence. Then, the aluminum foil is placed in the fifth-stage second formation solution for the fifth-stage second formation treatment (fifth-stage second electrostatic treatment). The treatment temperature is 80-95℃ and the current density is 1-15mA / cm. 2 The applied voltage is 110–130% × Vf, and the formation time is 8–18 minutes.

[0022] (8) Fifth-stage third formation: After the aluminum foil has undergone the fifth-stage second formation treatment, it is subjected to a second high-temperature treatment and a third phosphoric acid treatment in sequence. Then, the aluminum foil is placed in the fifth-stage third formation solution for the fifth-stage third formation treatment (fifth-stage third electrochemical treatment). The treatment temperature is 80-95℃ and the current density is 1-15mA / cm. 2 The applied voltage is 110–130% × Vf, and the formation time is 8–18 minutes.

[0023] (9) Fifth-stage fourth formation: After the aluminum foil has undergone the fifth-stage third formation treatment, it is subjected to a third high-temperature treatment. Then, the aluminum foil is placed in the fifth-stage fourth formation solution for the fifth-stage fourth formation treatment (fifth-stage fourth electrochemical treatment). The treatment temperature is 50-80℃ and the current density is 1-15mA / cm. 2 The applied voltage is 110–130% × Vf, and the formation time is 0.5–3 minutes;

[0024] (10) Post-treatment: The aluminum foil after the fifth-stage fourth formation treatment is chemically treated in a phosphoric acid solution with a concentration of 0.1-1wt% and a temperature of 20-30℃ for 1-5 minutes, then taken out and dried to obtain the high-voltage anode foil.

[0025] In step (1) above, the pretreatment is as follows: the etched aluminum foil with a purity of 99.99% is treated in pure water at a temperature of 90-98℃ for 10-20 minutes.

[0026] In step (1) above, the acid treatment is as follows: the pretreated aluminum foil is subjected to acid treatment in an aqueous solution of monocarboxylic acid or polycarboxylic acid at a treatment temperature of 50-80°C for 1-8 minutes; the concentration of the aqueous solution of monocarboxylic acid or polycarboxylic acid is 0.1-1.0 wt%.

[0027] In step (7) above, the first phosphoric acid treatment is: the aluminum foil that has undergone the first formation treatment of the fifth stage is chemically treated in a phosphoric acid solution with a concentration of 1-5 wt% and a temperature of 30-50°C for 1-5 minutes.

[0028] In step (7) above, the first high-temperature treatment is to treat the aluminum foil after the first phosphoric acid treatment at 400-550°C for 1-3 minutes.

[0029] In step (7) above, the second phosphoric acid treatment is to chemically treat the aluminum foil after the first high-temperature treatment in a phosphoric acid solution with a concentration of 4-8 wt% and a temperature of 55-75°C for 2-8 minutes.

[0030] In step (8) above, the second high-temperature treatment is to treat the aluminum foil after the fifth-stage second formation at 400-550°C for 1-3 minutes.

[0031] In step (8) above, the third phosphoric acid treatment is: chemically treating the aluminum foil after the second high-temperature treatment in a phosphoric acid solution with a concentration of 4-8 wt% and a temperature of 55-75°C for 2-8 minutes.

[0032] In step (9) above, the third high-temperature treatment is to treat the aluminum foil after the fifth-stage third formation at 400-550°C for 1-3 minutes.

[0033] In steps (6)-(9) above, the composition of the fifth-stage first formation solution, the fifth-stage second formation solution, the fifth-stage third formation solution and the fifth-stage fourth formation solution is: boric acid 1-10 wt%, ammonium carbonate or ammonium pentaborate 0.01-0.3 wt%, and the remainder is water.

[0034] The advantages and beneficial effects of this invention are as follows:

[0035] 1. In order to make the aluminum electrolytic capacitor anode foil have low leakage current, low loss, long life and high temperature resistance, the present invention adds an acid treatment after the pretreatment. At the same time, hypophosphite (including sodium hypophosphite and ammonium hypophosphite), citric acid and citrate, boric acid, ammonium pentaborate and other substances are used in the formation bath. Multi-stage heat treatment and three-stage phosphoric acid treatment are used to improve capacity, reduce hydration, extend the life of anode foil and increase high temperature resistance.

[0036] 2. The high-voltage anode foil production method provided by this invention produces high-voltage aluminum electrolytic capacitor anode foil with characteristics such as short voltage rise time, high capacity, low leakage current, low loss, long life, and high temperature resistance. Anode foil with high voltage specifications of 650VF to 950VF prepared using this method can be widely used in long-life leaded, horn-shaped, and bolt-shaped aluminum electrolytic capacitors. Furthermore, this production method has a simple formation bath composition, simple solution preparation and production process operation, stable control, and good product consistency, making it suitable for industrial mass production.

[0037] 3. The high-voltage anode foil production method provided by the present invention uses a five- to six-stage formation process. Boric acid (0.1-10 wt%), tertiary phosphoric acid treatment, and tertiary high-temperature treatment in the formation solution are used to improve the electrical properties of the aluminum anode foil, such as leakage current, loss, lifespan, and high-temperature resistance. Carboxylic acid treatment and hypophosphite (0.01-0.5 wt%) in the formation solution are used to improve the density and hydration resistance of the oxide film. Hypophosphite and citric acid and citrate (0.01-0.5 wt%) in the formation solution are used to improve the capacity of the aluminum anode foil. Attached Figure Description

[0038] Figure 1 The pressure rise curve of the foil prepared according to the present invention.

[0039] Figure 2 The pressure boost curve of the foil prepared by conventional methods.

[0040] Figure 3 Long-term LC test (4h) of foil at 800vf; in the figure, x-time (s), y-LC (mA), orange-LC of the foil of this invention, blue-LC of conventional foil. Detailed Implementation

[0041] To further understand the present invention, the present invention is described below with reference to examples. However, the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0042] Example 1:

[0043] The specific operating steps are as follows:

[0044] (1) Pretreatment: The etched aluminum foil with a purity of 99.99% is treated in pure water at a temperature of 95-98℃ for 15 minutes;

[0045] (2) Acid treatment: The pretreated aluminum foil was acid treated in an aqueous solution containing 0.4 wt% acetic acid at a temperature of 70°C for 5 min.

[0046] (3) Primary formation: The acid-treated aluminum foil is subjected to a first-stage electrochemical treatment in an aqueous solution containing 0.8 wt% boric acid, 0.3 wt% ammonium carbonate, 0.3 wt% citric acid, triammonium citrate, and 0.3 wt% sodium hypophosphite at a temperature of 90°C and a current density of 50 mA / cm². 2 The applied voltage was 30% Vf, and the formation time was 9 minutes.

[0047] (4) Secondary formation: The aluminum foil after primary formation is subjected to a second-stage electrochemical treatment in an aqueous solution containing 1.5 wt% boric acid, 0.2 wt% ammonium carbonate, 0.2 wt% citric acid, triammonium citrate, and 0.2 wt% sodium hypophosphite. The temperature is 90℃ and the current density is 45 mA / cm². 2 The applied voltage was 65% Vf, and the formation time was 9 minutes.

[0048] (5) Tertiary formation: The aluminum foil after secondary formation is subjected to a third-stage electrochemical treatment in an aqueous solution containing 4 wt% boric acid, 0.2 wt% ammonium pentaborate, 0.1 wt% citric acid, and triammonium citrate. The temperature is 90℃ and the current density is 30 mA / cm². 2 Apply a voltage of 90% VF and process for 12 minutes;

[0049] (6) Liquid power supply: The aluminum foil after the three-stage formation is formed in a 5wt% ammonium adipate aqueous solution at a temperature of 25℃, a voltage of 15V and a current of 1500A for 10 minutes.

[0050] (7) Fourth-stage formation: The aluminum foil after liquid electro-forming is subjected to a fourth-stage electro-treatment in an aqueous solution containing 5 wt% boric acid and 0.1 wt% ammonium pentaborate at a temperature of 90°C and a current density of 25 mA / cm². 2 Apply a voltage of 105% Vf and process for 15 minutes;

[0051] (8) Fifth-stage first formation: The aluminum foil after the fourth-stage formation is subjected to the fifth-stage electrochemical treatment in an aqueous solution containing 6 wt% boric acid and 0.06 wt% ammonium pentaborate at a temperature of 90°C and a current density of 20 mA / cm². 2 Apply a voltage of 120% Vf and process for 28 minutes;

[0052] (9) First phosphoric acid treatment: The aluminum foil after the first five-stage formation is chemically treated in a 4wt% phosphoric acid solution at 30℃ for 3 minutes;

[0053] (10) First high-temperature treatment: The aluminum foil treated with phosphoric acid is treated at 520°C for 2 minutes;

[0054] (11) Second phosphoric acid treatment: The aluminum foil after the first high-temperature formation is chemically treated in a 6wt% phosphoric acid solution at 65℃ for 6 minutes;

[0055] (12) Fifth-stage second formation: The aluminum foil after the second phosphoric acid treatment is subjected to a fifth-stage second electrochemical treatment in an aqueous solution containing 6 wt% boric acid and 0.06 wt% ammonium pentaborate at a temperature of 90°C and a current density of 15 mA / cm². 2 Apply a voltage of 120% Vf and convert for 9 minutes;

[0056] (13) Second high-temperature treatment: The aluminum foil that has undergone the fifth-stage second formation is treated at 520°C for 2 minutes;

[0057] (14) Third phosphoric acid treatment: The aluminum foil after the second high-temperature formation is chemically treated in a 6wt% phosphoric acid solution at 65℃ for 6 minutes;

[0058] (15) Fifth-stage third formation: The aluminum foil after the second phosphoric acid treatment is subjected to a third electrochemical treatment in an aqueous solution containing 6 wt% boric acid and 0.06 wt% ammonium pentaborate, at a temperature of 80-90℃ and a current density of 10 mA / cm². 2 Apply a voltage of 120% Vf and convert for 9 minutes;

[0059] (16) Third high-temperature treatment: The aluminum foil that has undergone the fifth-stage third formation is treated at 520°C for 2 minutes;

[0060] (17) Fifth-stage fourth-stage electrochemical treatment: The aluminum foil after the third high-temperature treatment is subjected to a fifth-stage fourth-stage electrochemical treatment in an aqueous solution containing 6 wt% boric acid and 0.06 wt% ammonium pentaborate at a temperature of 75°C and a current density of 5 mA / cm². 2 The applied voltage is 120% Vf, and the formation time is 2 minutes;

[0061] (18) Post-treatment: The aluminum foil that has been repaired above is chemically treated in a 0.5wt% ammonium dihydrogen phosphate solution at 30℃ for 3 minutes, then removed, cleaned and dried.

[0062] The terminal voltage vf is 700V.

[0063] The main performance indicators of the aluminum foil after formation are shown in Table 1.

[0064] Table 1

[0065]

[0066] Aluminum foils of the same specifications were prepared using conventional methods, and the main performance indicators of the aluminum foils after formation are shown in Table 2.

[0067] Table 2

[0068]

[0069] In the table, Tr(s) represents the boost time;

[0070] Tr60(s): This refers to the pressure rise time after the aluminum foil has been boiled in water for 1 hour.

[0071] Vt(V): is the withstand voltage value;

[0072] Vt60(V): This is the water resistance and pressure resistance value; it refers to the pressure resistance value of aluminum foil after being boiled in boiling water for 1 hour.

[0073] Cap(uF / cm 2 ): refers to specific volume;

[0074] Loss: Loss as measured by routine testing.

[0075] Lifetime: The lifetime measured after the sample is fabricated into a capacitor.

[0076] Figure 1 The foil voltage boost curve prepared in this embodiment is shown below. Figure 2 The voltage boost curve of the foil prepared by conventional methods; Figure 3 Long-term LC testing (4 hours) of foil at 800 vf;

[0077] From Table 1-2 and Figure 1-3 It can be seen that after adopting the technical solution of the present invention, the voltage rise time of aluminum foil is significantly shortened, the capacitance is increased, and the performance of resistance to hydration, loss and life is significantly improved.

[0078] Example 2:

[0079] The specific operating steps are as follows:

[0080] (1) Pretreatment: The etched aluminum foil with a purity of 99.99% is treated in pure water at a temperature of 95-98℃ for 20 minutes;

[0081] (2) Acid treatment: The pretreated aluminum foil was acid treated in an aqueous solution containing 0.3wt% fumaric acid at a temperature of 70℃ for 6 minutes.

[0082] (3) Primary formation: The acid-treated aluminum foil is subjected to a first-stage electrochemical treatment in an aqueous solution containing 1 wt% boric acid, 0.25 wt% ammonium carbonate, 0.25 wt% citric acid, triammonium citrate, and 0.25 wt% sodium hypophosphite at a temperature of 90°C and a current density of 50 mA / cm². 2 The applied voltage is 30% Vf, and the formation time is 10 minutes;

[0083] (4) Secondary formation: The aluminum foil after primary formation is subjected to a second-stage electrochemical treatment in an aqueous solution containing 2 wt% boric acid, 0.15 wt% ammonium carbonate, 0.15 wt% citric acid and triammonium citrate, and 0.15 wt% sodium hypophosphite. The temperature is 90℃ and the current density is 45 mA / cm². 2 The applied voltage was 65% Vf, and the formation time was 10 minutes.

[0084] (5) Tertiary formation: The aluminum foil after secondary formation is subjected to a third-stage electrochemical treatment in an aqueous solution containing 5 wt% boric acid, 0.05 wt% ammonium carbonate, 0.08 wt% citric acid, and triammonium citrate. The temperature is 90℃ and the current density is 30 mA / cm². 2 Apply a voltage of 90% VF and process for 15 minutes;

[0085] (6) Liquid feeding: The aluminum foil after the three-stage formation is formed in 6wt% phosphoric acid, at a temperature of 25℃, a voltage of 15V and a current of 1400A for 15 minutes.

[0086] (7) Fourth-stage formation: The aluminum foil after liquid electro-forming is subjected to a fourth-stage electro-treatment in an aqueous solution containing 6 wt% boric acid and 0.03 wt% ammonium carbonate at a temperature of 85°C and a current density of 25 mA / cm². 2 Apply a voltage of 105% Vf and process for 18 minutes;

[0087] (8) Fifth-stage first formation: The aluminum foil after the fourth-stage formation is subjected to the fifth-stage electrochemical treatment in an aqueous solution containing 6.5 wt% boric acid and 0.02 wt% ammonium carbonate at a temperature of 85°C and a current density of 20 mA / cm². 2 Apply a voltage of 120% VF and process for 25 minutes;

[0088] (9) First phosphoric acid treatment: The aluminum foil after the first five-stage formation is chemically treated in a 5wt% phosphoric acid solution at 35℃ for 4 minutes;

[0089] (10) First high-temperature treatment: The aluminum foil treated with phosphoric acid is treated at 480°C for 2 minutes;

[0090] (11) Second phosphoric acid treatment: The aluminum foil after the first high-temperature formation is chemically treated in a 6wt% phosphoric acid solution at 65℃ for 7 minutes;

[0091] (12) Fifth-stage second formation: The aluminum foil after the second phosphoric acid treatment is subjected to a fifth-stage second electrochemical treatment in an aqueous solution containing 6.5 wt% boric acid and 0.02 wt% ammonium carbonate at a temperature of 85°C and a current density of 15 mA / cm². 2 Apply a voltage of 120% Vf and process for 10 minutes;

[0092] (13) Second high-temperature treatment: The aluminum foil after the fifth-stage second formation is treated at 480℃ for 2 minutes;

[0093] (14) Third phosphoric acid treatment: The aluminum foil after the second high-temperature formation is chemically treated in a 6wt% phosphoric acid solution at 60℃ for 7 minutes;

[0094] (15) Fifth-stage third formation: The aluminum foil after the second phosphoric acid treatment is subjected to a third electrochemical treatment in an aqueous solution containing 6.5 wt% boric acid and 0.02 wt% ammonium carbonate at a temperature of 85°C and a current density of 10 mA / cm². 2 Apply a voltage of 120% Vf and process for 10 minutes;

[0095] (16) Third high-temperature treatment: The aluminum foil that has undergone the fifth-stage third formation is treated at 480℃ for 2 minutes;

[0096] (17) Fifth-stage fourth-stage electrochemical treatment: The aluminum foil after the third high-temperature treatment is subjected to a fifth-stage fourth-stage electrochemical treatment in an aqueous solution containing 6.5 wt% boric acid and 0.02 wt% ammonium carbonate at a temperature of 70 ℃ and a current density of 5 mA / cm². 2 The applied voltage is 120% Vf, and the formation time is 3 minutes;

[0097] (18) Post-treatment: The aluminum foil that has been repaired above is chemically treated in a 0.5wt% ammonium dihydrogen phosphate solution at 30℃ for 5 minutes, then removed, cleaned and dried.

[0098] The terminal voltage is 800V.

[0099] The main performance indicators of the aluminum foil after formation are shown in Table 1.

[0100] Table 1

[0101]

[0102] Aluminum foils of the same specifications were prepared using conventional methods, and the main performance indicators of the aluminum foils after formation are shown in Table 2.

[0103] Table 2

[0104]

[0105] This invention discloses a formation method for the anode of a high-voltage aluminum electrolytic capacitor. Using this method, at voltage specifications of 650-950VF, due to the introduction of some inorganic and organic acids in the production process, the anode foil of the aluminum electrolytic capacitor exhibits lower loss and leakage current, higher capacitance, shorter voltage rise time, shorter hydration time, longer lifespan, and stronger ripple resistance. The formation process is simple to operate, produces highly consistent and stable products, and has low raw material costs, making it suitable for industrial mass production.

[0106] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for forming a high-voltage anode foil, characterized in that: An aluminum foil undergoes an electrochemical reaction in a forming solution to form an oxide film on its surface, which serves as a dielectric. This forming method includes the following steps: (1) Primary formation: The aluminum foil after pretreatment and acid treatment is placed in the primary formation solution for the first-stage formation treatment. The treatment temperature is 80-95℃ and the current density is 30-60mA / cm. 2 The applied voltage is 30-35% × vf, and the formation time is 8-18 minutes; wherein: the primary formation solution consists of: boric acid 0.3-3 wt%, ammonium carbonate or ammonium pentaborate 0.05-0.8 wt%, citric acid and citrate 0.05-0.8 wt%, hypophosphite 0.05-0.8 wt%, and the remainder is water; vf refers to the final voltage for forming the product, which is determined according to the actual product requirements; (2) Secondary formation: The aluminum foil after primary formation is placed in a secondary formation solution for secondary formation treatment. The treatment temperature is 80-95℃ and the current density is 30-60 mA / cm. 2 The applied voltage is 60-70% × vf, and the formation time is 8-18 minutes; the secondary formation solution consists of: boric acid 0.3-3 wt%, ammonium carbonate or ammonium pentaborate 0.03-0.6 wt%, citric acid and citrate 0.03-0.6 wt%, hypophosphite 0.03-0.6 wt%, and the remainder is water; (3) Tertiary formation: The aluminum foil after secondary formation is placed in a tertiary formation solution for tertiary formation treatment. The treatment temperature is 80-95℃ and the current density is 25-55mA / cm. 2 The applied voltage is 85-95% × vf, and the formation time is 8-18 minutes; the three-stage formation solution consists of: boric acid 0.5-5 wt%, ammonium carbonate or ammonium pentaborate 0.02-0.5 wt%, citric acid and citrate 0.02-0.5 wt%, and the remainder is water; (4) Liquid electrostatication: The aluminum foil after three-stage formation is placed in a liquid electrostatication formation solution and formed for 8 to 18 minutes under the conditions of temperature 15 to 45°C, voltage 15 to 35V and current 650 to 1550A; the liquid electrostatication formation solution is an aqueous solution of adipic acid or adipic acid salt with a concentration of 2 to 7 wt%, or a solution of citric acid or citrate with a concentration of 2 to 7 wt%, or a solution of phosphoric acid or phosphate with a concentration of 2 to 7 wt%. (5) Fourth-stage formation: The aluminum foil after liquid electro-forming is placed in the fourth-stage formation solution for fourth-stage formation treatment. The treatment temperature is 80-95℃ and the current density is 10-40 mA / cm. 2 The applied voltage is 95–110% × vf, and the formation time is 12–27 minutes; the composition of the four-stage formation solution is: boric acid 1–10 wt%, ammonium pentaborate 0.01–0.3 wt%, and the remainder is water; (6) Fifth-stage first formation: The aluminum foil after the fourth-stage formation is placed in the fifth-stage first formation solution for the fifth-stage first formation treatment. The treatment temperature is 80-95℃ and the current density is 15-40mA / cm. 2 The applied voltage is 110–130% × vf, and the formation time is 25–35 minutes. (7) Fifth-stage second formation: After the aluminum foil has undergone the fifth-stage first formation treatment, it is subjected to the first phosphoric acid treatment, the first high-temperature treatment and the second phosphoric acid treatment in sequence. Then, the aluminum foil is placed in the fifth-stage second formation solution for the fifth-stage second formation treatment. The treatment temperature is 80-95℃ and the current density is 1-15mA / cm. 2 The applied voltage is 110–130% × vf, and the formation time is 8–18 minutes. (8) Fifth-stage third formation: After the aluminum foil has undergone the fifth-stage second formation treatment, it is subjected to a second high-temperature treatment and a third phosphoric acid treatment in sequence. Then, the aluminum foil is placed in the fifth-stage third formation solution for the fifth-stage third formation treatment. The treatment temperature is 80-95℃ and the current density is 1-15mA / cm. 2 The applied voltage is 110–130% × vf, and the formation time is 8–18 minutes. (9) Fifth-stage fourth formation: After the aluminum foil has undergone the fifth-stage third formation treatment, it is subjected to a third high-temperature treatment. Then, the aluminum foil is placed in the fifth-stage fourth formation solution for the fifth-stage fourth formation treatment. The treatment temperature is 50-80℃ and the current density is 1-15mA / cm. 2 The applied voltage is 110–130% × Vf, and the formation time is 0.5–3 minutes; In steps (6)-(9), the composition of the fifth-stage first formation solution, the fifth-stage second formation solution, the fifth-stage third formation solution and the fifth-stage fourth formation solution is: boric acid 1-10 wt%, ammonium carbonate or ammonium pentaborate 0.01-0.3 wt%, and the remainder is water; (10) Post-treatment: The aluminum foil after the fifth-stage fourth formation treatment is chemically treated in a phosphoric acid solution with a concentration of 0.1-1 wt% and a temperature of 20-30°C for 1-5 minutes, then taken out and dried to obtain the high-voltage anode foil.

2. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (1), the pretreatment is to treat the etched aluminum foil with a purity of 99.99% in pure water at a temperature of 90-98℃ for 10-20 minutes.

3. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (1), the acid treatment is as follows: the pretreated aluminum foil is subjected to acid treatment in an aqueous solution of monocarboxylic acid or polycarboxylic acid at a treatment temperature of 50-80°C for 1-8 min; the concentration of the aqueous solution of monocarboxylic acid or polycarboxylic acid is 0.1-1.0 wt%.

4. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (7), the first phosphoric acid treatment is: the aluminum foil that has undergone the first formation treatment of five stages is chemically treated in a phosphoric acid solution with a concentration of 1-5 wt% and a temperature of 30-50°C for 1-5 minutes.

5. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (7), the first high-temperature treatment is to treat the aluminum foil after the first phosphoric acid treatment at 400-550°C for 1-3 minutes.

6. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (7), the second phosphoric acid treatment is to chemically treat the aluminum foil after the first high-temperature treatment in a phosphoric acid solution with a concentration of 4-8 wt% and a temperature of 55-75°C for 2-8 minutes.

7. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (8), the second high-temperature treatment is to treat the aluminum foil after the fifth-stage second formation at 400-550°C for 1-3 minutes.

8. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (8), the third phosphoric acid treatment is to chemically treat the aluminum foil after the second high-temperature treatment in a phosphoric acid solution with a concentration of 4-8 wt% and a temperature of 55-75°C for 2-8 minutes.

9. The formation method of high-voltage anode foil according to claim 1, characterized in that: In step (9), the third high-temperature treatment is to treat the aluminum foil after the fifth-stage third formation at 400-550°C for 1-3 minutes.

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