Formation foil for aluminum electrolytic capacitor and method for manufacturing the same

Abstract

The application belongs to the technical field of chemical foils, and particularly relates to a preparation method of a chemical foil for an aluminum electrolytic capacitor, comprising the following steps: S1, pretreatment: placing an etched aluminum foil in a hydrazine hydrate solution, and performing a pretreatment reaction under the action of ultrasonic waves to obtain a pretreated aluminum foil; and S2, performing multi-stage anodic oxidation and chemical formation and post-treatment on the pretreated etched aluminum foil to obtain a chemical foil. The preparation method can reduce the chemical formation energy consumption while improving the electrical performance of the chemical foil.

Description

Technical Field

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

[0002] Aluminum electrolytic capacitors are fundamental components of the electronics industry. With their advantages of high specific capacitance, high withstand voltage and low cost, they play an important role in power supply filtering, energy storage and other fields. They are also basic passive components that support the development of consumer electronics, industrial equipment, new energy and electric vehicles.

[0003] Anodized foil, a key material for the performance of aluminum electrolytic capacitors, has a decisive impact on the voltage rating, capacitance stability, and service life of the product, and is a technological bottleneck restricting the development of medium- and high-voltage high-performance products. Currently, the production of medium- and high-voltage anodized foil faces significant energy consumption pressure, with electricity costs accounting for over 40% of production costs. This high energy cost hinders the industry's green upgrading.

[0004] Therefore, there is still an urgent need for a method for preparing chemically formed foil that is low in energy consumption and also takes into account electrical performance. Summary of the Invention

[0005] In view of the above problems, this application provides anodized foil for aluminum electrolytic capacitors and its preparation method, which solves the problems of high energy consumption and difficulty in improving electrical performance in the preparation of existing anodized foil.

[0006] On one hand, the present invention provides a method for preparing formed foil for aluminum electrolytic capacitors, comprising the following steps: S1. Pretreatment: The etched aluminum foil is placed in a hydrazine hydrate solution and subjected to a pretreatment reaction under ultrasonic action to obtain the pretreated aluminum foil. S2. The pretreated aluminum foil is subjected to multi-stage anodizing and post-treatment to obtain anodized foil.

[0007] Specifically, in S1, the volume fraction of hydrazine hydrate (N2H4·H2O) in the hydrazine hydrate solution is 40%-60%.

[0008] Furthermore, the solvent of the hydrazine hydrate solution is water.

[0009] It should be noted that in S1, the frequency of the ultrasound is 80 kHz-120 kHz.

[0010] Preferably, in S1, the temperature of the pretreatment reaction is 20℃-40℃.

[0011] Preferably, in S1, the pretreatment reaction time is 12 min-32 min.

[0012] Furthermore, in S2, the multi-stage anodic oxidation formation includes primary formation, secondary formation, tertiary formation, and quaternary formation.

[0013] Furthermore, the formation solutions used in the primary and secondary formation processes each independently include boric acid and / or ammonium pentaborate.

[0014] Furthermore, the solvent for the primary and secondary formation solutions is water.

[0015] Furthermore, in the primary formation solution, the mass fraction of boric acid is 3wt%-8wt%, and the mass fraction of ammonium pentaborate is 0.1wt%-0.8wt%.

[0016] Furthermore, in the secondary formation solution, the mass fraction of boric acid is 3wt%-8wt%, and the mass fraction of ammonium pentaborate is 0.1wt%-0.6wt%.

[0017] Furthermore, the forming solutions used in the third-stage and fourth-stage formations each independently include boric acid and / or citric acid.

[0018] Furthermore, the solvent for the formation solutions in the third-stage and fourth-stage formations is water.

[0019] Furthermore, in the tertiary formation solution, the mass fraction of boric acid is 2wt%-10wt%, and the mass fraction of citric acid is 0.2wt%-2wt%.

[0020] Furthermore, in the formation solution of the fourth-stage formation, the mass fraction of boric acid is 2wt%-10wt%, and the mass fraction of citric acid is 0.2wt%-2wt%.

[0021] Furthermore, the formation voltage of the first-stage formation is 150V-180V.

[0022] Furthermore, the time for the primary formation is 250s-350s.

[0023] Furthermore, the current density of the first-stage formation is 5 mA / cm². 2 -15mA / cm 2 .

[0024] Furthermore, the formation voltage of the secondary formation is 240V-380V.

[0025] Furthermore, the time for the secondary formation is 400s-500s.

[0026] Furthermore, the current density of the secondary formation is 10 mA / cm². 2 -25mA / cm2 .

[0027] Furthermore, the formation voltage of the three-stage formation is 420V-500V.

[0028] Furthermore, the time for the three-stage formation is 550s-650s.

[0029] Furthermore, the current density of the three-stage formation is 15 mA / cm². 2 -25mA / cm 2 .

[0030] Furthermore, the formation voltage of the four-stage formation is 520V-600V.

[0031] Furthermore, the time for the fourth-level formation is 900s-1200s.

[0032] Furthermore, the current density of the four-stage formation is 15 mA / cm². 2 -25mA / cm 2 .

[0033] Furthermore, the temperatures for the primary, secondary, tertiary, and quaternary formations are each independently between 70°C and 90°C.

[0034] Furthermore, in S2, the post-processing includes: depolarization treatment, heat treatment, reshaping treatment, stabilization treatment, and drying treatment.

[0035] Furthermore, the depolarization process includes a first depolarization process and a second depolarization process.

[0036] Furthermore, the heat treatment includes a first heat treatment and a second heat treatment.

[0037] Furthermore, the repair process includes a first repair process, a second repair process, and a third repair process.

[0038] Further, after any of the treatments, the aluminum foil is washed with water. Each of the treatments includes: pretreatment, primary formation, secondary formation, tertiary formation, quaternary formation, first depolarization treatment, first heat treatment, first re-forming treatment, second depolarization treatment, second re-forming treatment, second heat treatment, third re-forming treatment, and stabilization treatment.

[0039] Furthermore, the depolarization solution used in the first depolarization treatment includes phosphoric acid.

[0040] Furthermore, the solvent of the depolarization treatment solution used in the first depolarization treatment is water.

[0041] Furthermore, in the depolarization solution used in the first depolarization treatment, the mass fraction of phosphoric acid is 4wt%-6wt%.

[0042] Furthermore, the temperature of the first depolarization treatment is 40℃-60℃.

[0043] Furthermore, the duration of the first depolarization process is 120s-240s.

[0044] Furthermore, the depolarization solution used in the second depolarization treatment includes phosphoric acid.

[0045] Furthermore, the solvent of the depolarization solution used in the second depolarization treatment is water.

[0046] Furthermore, in the depolarization solution used in the second depolarization treatment, the mass fraction of phosphoric acid is 6wt%-8wt%.

[0047] Furthermore, the temperature of the second depolarization treatment is 60℃-70℃.

[0048] Furthermore, the second depolarization process takes 120s-600s.

[0049] Furthermore, the temperatures of the first heat treatment and the second heat treatment are each independently 500℃-600℃.

[0050] Furthermore, the duration of the first heat treatment and the second heat treatment is independently 100s-240s.

[0051] Furthermore, the treatment solutions for the first, second, and third re-formation treatments each independently include boric acid.

[0052] Furthermore, the solvent for the treatment solutions in the first, second, and third replenishment treatments is water, each independently.

[0053] Furthermore, in the treatment solutions of the first, second, and third re-formation treatments, the mass fraction of boric acid is independently 2wt%-10wt%.

[0054] Furthermore, the voltages for the first, second, and third reshaping processes are each independently 570V-590V.

[0055] Furthermore, the time for the first, second, and third re-forming processes is independently 400s-500s.

[0056] Furthermore, the temperatures of the first, second, and third re-forming processes are each independently 70°C-90°C.

[0057] Furthermore, the current density of each of the first, second, and third re-forming processes is independently 15 mA / cm². 2 -25 mA / cm 2 .

[0058] Furthermore, the stabilization treatment solution includes ammonium dihydrogen phosphate.

[0059] Furthermore, the solvent of the stabilization treatment solution is water.

[0060] Furthermore, in the stabilization treatment solution, the mass fraction of ammonium dihydrogen phosphate is 0.5wt%-3wt%.

[0061] Furthermore, the stabilization treatment temperature is 50℃-70℃.

[0062] Furthermore, the stabilization treatment time is 60s-240s.

[0063] Furthermore, the drying temperature is 220℃-280℃.

[0064] Furthermore, the drying process takes 150s-240s.

[0065] On the other hand, the present invention also provides a formed foil for an aluminum electrolytic capacitor prepared by the above method.

[0066] Specifically, the specific capacitance of the formed foil at a withstand voltage of 580 V-610 V is 0.682 μF / cm. 2 -0.700μF / cm 2 .

[0067] On the other hand, the present invention also provides an aluminum electrolytic capacitor, comprising the above-described formed foil or formed foil prepared by the above method.

[0068] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention pretreats corroded aluminum foil before formation by ultrasonic treatment of hydrazine hydrate solution. The directional induction effect of hydrazine hydrate molecules promotes hydroxylation on the aluminum foil surface, generating a hydrated film precursor mainly composed of γ-AlOOH nanocrystals. At the same time, the ultrasonic cavitation effect forms uniformly distributed crystal nucleation sites in the hydrated film, reducing the activation energy of γ-Al2O3 crystal growth during subsequent anodizing, improving anodizing efficiency, reducing formation energy consumption, and enhancing the dielectric properties of the formed foil. Moreover, the process is simple and low in cost.

[0069] 2. This invention is based on a high-crystallinity hydrated film precursor provided by pretreatment, and adopts a multi-stage formation process (the formation voltage is gradually increased to a final voltage of 520V-600V), with the formation temperature of each stage independently controlled at 70℃-90℃; by utilizing the reduced film resistance of the pretreatment, the formation voltage is gradually increased to match the oxidation reaction rate with the film growth kinetics, reducing the risk of local breakdown or uneven growth of the oxide film, and achieving uniform increase in oxide film thickness and stable dielectric properties while reducing total energy consumption.

[0070] 3. This invention removes weak points in the oxide film through multi-stage depolarization treatment, stabilizes the Al2O3 crystal phase structure through heat treatment, repairs the film thickness and densifies the surface through multi-stage repair formation, and reduces the density of interface defects through stabilization treatment. The above post-treatment system works in conjunction with the preceding pre-treatment-formation process to eliminate residual stress in the oxide film, so that the formed foil meets the electrical performance requirements of medium and high voltage aluminum electrolytic capacitors.

[0071] 4. The alumina dielectric film formed into foil according to the present invention has a γ-Al2O3 crystal structure and a specific capacitance of 0.68 μF / cm at a withstand voltage of 580V-610V. 2 -0.70μF / cm 2 . Detailed Implementation

[0072] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

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

[0074] “wt%” indicates a percentage by mass.

[0075] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0076] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0077] On one hand, embodiments of the present invention provide a method for preparing electrolytic foil for aluminum electrolytic capacitors, comprising the following steps: S1. Pretreatment: The etched aluminum foil is placed in a hydrazine hydrate solution and subjected to a pretreatment reaction under ultrasonic treatment. S2. The pretreated aluminum foil is subjected to multi-stage anodizing and post-treatment to obtain medium- and high-voltage formed foil.

[0078] This invention places etched aluminum foil in a hydrazine hydrate solution and performs a pretreatment reaction under ultrasonic action. The directional induction effect of hydrazine hydrate molecules promotes hydroxylation on the aluminum foil surface, generating a hydrated film precursor mainly composed of γ-AlOOH nanocrystals. At the same time, the ultrasonic cavitation effect is used to form uniformly distributed crystal nucleation sites in the hydrated film, reducing the activation energy of γ-Al2O3 crystal growth during subsequent anodizing, thereby improving anodizing efficiency, reducing formation energy consumption, and enhancing the dielectric properties of the formed foil. Moreover, the process is simple and low in cost.

[0079] Specifically, in S1, the volume fraction of N2H4·H2O in the hydrazine hydrate solution is 40%-60%.

[0080] Furthermore, the solvent of the hydrazine hydrate solution is water.

[0081] In this invention, the volume fraction of hydrazine hydrate in the pretreatment solution is 40%-60%. Within this range, based on the balance between reaction safety and product crystal phase controllability: If the volume fraction of hydrazine hydrate is too high (>60%), the system's risk factor increases significantly (it becomes highly corrosive and the reaction is violent and difficult to control), while the increased solution viscosity hinders mass transfer; if the volume fraction of hydrazine hydrate is too low (<40%), the reaction kinetics are slow, and thermodynamically, it tends to generate amorphous Al(OH)3 rather than the target product γ-AlOOH. Within this range, a hydrated film precursor mainly composed of γ-AlOOH nanocrystals can be generated, reducing the formation of impurity phases.

[0082] It should be noted that in S1, the frequency of the ultrasound is 80 kHz-120 kHz.

[0083] In this invention, the ultrasonic frequency is 80 kHz-120 kHz, which balances the intensity of the cavitation effect with the integrity of the aluminum foil substrate. At frequencies too low (<80 kHz), the cavitation bubbles are large, easily damaging the microporous structure of the etched aluminum foil surface; at frequencies too high (>120 kHz), the cavitation effect weakens, making it difficult to generate effective micro-perturbations. Within the above frequency range, a gentle and uniform acoustic flow and micro-region perturbations can be generated, promoting the directional contact and adsorption of N2H4·H2O molecules on the aluminum surface, inducing the preferred orientation of γ-AlOOH, and simultaneously forming uniformly distributed crystal nucleation points in the hydrated film through the cavitation effect, reducing the activation energy of subsequent anodic oxidation.

[0084] Preferably, in S1, the temperature of the pretreatment reaction is 20℃-40℃.

[0085] Preferably, in S1, the pretreatment reaction time is 12 min-32 min.

[0086] In this invention, the pretreatment temperature is 20℃-40℃ and the time is 12 min-32 min, which achieves a balance between reaction rate and reagent stability. Too low a temperature (<20℃) leads to insufficient activation energy and slow kinetics; too high a temperature (>40℃) significantly increases the decomposition rate of N2H4·H2O, reduces the effective concentration, and generates bubbles that interfere with reaction uniformity. Simultaneously, the reduction reaction of hydrazine hydrate with aluminum is a strongly exothermic process; high temperatures intensify the reaction and cause heat accumulation, significantly increasing operational risks. Therefore, the pretreatment reaction requires strict temperature control. Too short a time (<12 min) results in incomplete hydration film growth and insufficient coverage; too long a time (>32 min) leads to an excessively thick film that is prone to cracking or excessive consumption of the aluminum substrate. These conditions facilitate the formation of a γ-AlOOH nanocrystalline layer with moderate thickness, high crystallinity, and strong bonding with the substrate, provided the reagents are stable, thus providing an ideal precursor with low defect density for subsequent formation.

[0087] In some embodiments, the volume fraction of N2H4·H2O in the hydrazine hydrate solution may be, for example, 40%, 45%, 50%, 55%, 60%, or a range of any two of these values, or other values ​​selected from the above range.

[0088] In some embodiments, the frequency of the preprocessing ultrasound may be, for example, 80 kHz, 90 kHz, 100 kHz, 110 kHz, 120 kHz, or a range of any two of these values, or other values ​​selected from the above range.

[0089] In some embodiments, the temperature of the pretreatment reaction may be, for example, 20°C, 25°C, 30°C, 35°C, 40°C, or a range of any two of these values, or other values ​​selected from the above range.

[0090] In some embodiments, the pretreatment reaction time may be, for example, 12 min, 15 min, 18 min, 21 min, 24 min, 27 min, 30 min, 32 min, or a range of any two of these values, or other values ​​selected from the above range.

[0091] Furthermore, the multi-stage anodic oxidation formation includes primary formation, secondary formation, tertiary formation, and quaternary formation.

[0092] Furthermore, the formation solutions used in the primary and secondary formation processes each independently include boric acid and / or ammonium pentaborate.

[0093] Furthermore, the solvent for the primary and secondary formation solutions is water.

[0094] Further, in the primary formation solution, the boric acid has a mass fraction of 3wt%-8wt%, and the ammonium pentaborate has a mass fraction of 0.1wt%-0.8wt%. Specifically, in the primary formation solution, the mass fraction of boric acid can be, for example, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, or any two of these values, or other values ​​selected from the above range; the mass fraction of ammonium pentaborate can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, or any two of these values, or other values ​​selected from the above range.

[0095] Further, in the secondary formation solution, the mass fraction of boric acid is 3wt%-8wt%, and the mass fraction of ammonium pentaborate is 0.1wt%-0.6wt%. Specifically, in the secondary formation solution, the mass fraction of boric acid can be, for example, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, or any two of these values, or other values ​​selected from the above range; the mass fraction of ammonium pentaborate can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, or any two of these values, or other values ​​selected from the above range.

[0096] Furthermore, the forming solutions used in the third-stage and fourth-stage formations each independently include boric acid and / or citric acid.

[0097] Furthermore, the solvent for the formation solutions in the third-stage and fourth-stage formations is water.

[0098] Further, in the tertiary formation solution, the mass fraction of boric acid is 2wt%-10wt%, and the mass fraction of citric acid is 0.2wt%-2wt%. Specifically, in the tertiary formation solution, the mass fraction of boric acid can be, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any two of these values, or other values ​​selected from the above range; the mass fraction of citric acid can be 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, or any two of these values, or other values ​​selected from the above range.

[0099] Further, in the formation solution of the fourth-stage formation, the mass fraction of boric acid is 2wt%-10wt%, and the mass fraction of citric acid is 0.2wt%-2wt%. Specifically, in the formation solution of the fourth-stage formation, the mass fraction of boric acid can be, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any two of these values, or other values ​​selected from the above range; the mass fraction of citric acid can be 0.2wt%, 0.4wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, or any two of these values, or other values ​​selected from the above range.

[0100] Furthermore, the formation voltage of the first-stage formation is 150V-180V. Specifically, the formation voltage of the first-stage formation can be, for example, 150V, 160V, 170V, 180V, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0101] Furthermore, the first-level transformation time is 250s-350s. Specifically, the first-level transformation time can be, for example, 250s, 270s, 290s, 310s, 330s, 350s, or a range of any two values ​​therein, or other values ​​selected from the above range.

[0102] Furthermore, the current density of the first-stage formation is 5 mA / cm². 2 -15mA / cm 2Specifically, the current density of the first-stage formation can be, for example, 5 mA / cm². 2 7 mA / cm 2 9 mA / cm 2 11 mA / cm 2 13 mA / cm 2 15 mA / cm 2 , or a range of any two of the values, or other values ​​selected from the range mentioned above.

[0103] Furthermore, the formation voltage of the secondary formation is 240V-380V. Specifically, the formation voltage of the secondary formation can be, for example, 240V, 260V, 280V, 300V, 320V, 340V, 360V, 380V, or any range of two values ​​therein, or other values ​​selected from the above range.

[0104] Furthermore, the time for the secondary formation is 400s-500s. Specifically, the time for the secondary formation can be, for example, 400s, 410s, 420s, 430s, 440s, 450s, 460s, 470s, 480s, 490s, 500s, or a range of any two values ​​thereof, or other values ​​selected from the above range.

[0105] Furthermore, the current density of the secondary formation is 10 mA / cm². 2 -25mA / cm 2 Specifically, the current density of the secondary formation can be, for example, 10 mA / cm². 2 15 mA / cm 2 20 mA / cm 2 25 mA / cm 2 , or a range of any two of the values, or other values ​​selected from the range mentioned above.

[0106] Furthermore, the formation voltage of the three-stage formation is 420V-500V. Specifically, the formation voltage of the three-stage formation can be, for example, 420V, 430V, 440V, 450V, 460V, 470V, 480V, 490V, 500V, or any range of two values ​​thereof, or other values ​​selected from the above range.

[0107] Furthermore, the time for the three-stage transformation is 550s-650s. Specifically, the time for the three-stage transformation can be, for example, 550s, 560s, 570s, 580s, 590s, 600s, 610s, 620s, 630s, 640s, 650s, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0108] Furthermore, the current density of the three-stage formation is 15 mA / cm². 2 -25mA / cm 2 Specifically, the current density of the three-stage formation can be, for example, 15 mA / cm². 2 20 mA / cm 2 25 mA / cm 2 , or a range of any two of the values, or other values ​​selected from the range mentioned above.

[0109] Furthermore, the formation voltage of the four-stage formation is 520V-600V. Specifically, the formation voltage of the four-stage formation can be, for example, 520V, 530V, 540V, 550V, 560V, 570V, 580V, 590V, 600V, or any range of two values ​​thereof, or other values ​​selected from the above range.

[0110] Furthermore, the time for the fourth-level transformation is 900s-1200s. Specifically, the time for the fourth-level transformation can be, for example, 900s, 950s, 1000s, 1050s, 1100s, 1150s, 1200s, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0111] Furthermore, the current density of the four-stage formation is 15 mA / cm². 2 -25mA / cm 2 Specifically, the current density of the fourth-stage formation can be, for example, 15 mA / cm². 2 20 mA / cm 2 25 mA / cm 2 , or a range of any two of the values, or other values ​​selected from the range mentioned above.

[0112] Furthermore, the temperatures for the primary, secondary, tertiary, and quaternary formations are each independently between 70°C and 90°C. Specifically, the temperatures for the primary, secondary, tertiary, and quaternary formations can each be, for example, 70°C, 75°C, 80°C, 85°C, 90°C, or a range consisting of any two of these values, or other values ​​selected from the aforementioned ranges.

[0113] In some embodiments, the multi-stage anodizing formation process is as follows: S2-1, Primary Formation: After cleaning the aluminum foil pretreated in S1 with water, it is placed in a mixed aqueous solution of boric acid (3wt%-8wt%) and ammonium pentaborate (0.1wt%-0.8wt%) for primary formation. The formation voltage for primary formation is 150V-180V, the temperature is 70℃-90℃, the time is 250s-350s, and the current density is 5 mA / cm². 2 -15mA / cm 2 This yields an electrode foil that has undergone primary formation; S2-2, Secondary Formation: After the electrode foil has undergone primary formation, it is cleaned with water and then placed in a mixed aqueous solution of boric acid (3wt%-8wt%) and ammonium pentaborate (0.1wt%-0.6wt%) for secondary formation. The formation voltage for secondary formation is 240V-380V, the temperature is 70℃-90℃, the time is 400s-500s, and the current density is 10 mA / cm². 2 -25 mA / cm 2 ; S2-3, Tertiary Formation: After the electrode foil has undergone secondary formation, it is cleaned with water and then placed in a mixed aqueous solution of boric acid (2wt%-10wt%) and citric acid (0.2wt%-2wt%) for tertiary formation. The formation voltage for tertiary formation is 420V-500V, the temperature is 70℃-90℃, the time is 550s-650s, and the current density is 15 mA / cm². 2 -25 mA / cm 2 ; S2-4, Quaternary Formation: After the electrode foil has undergone tertiary formation, it is cleaned with water and then placed in a mixed aqueous solution of boric acid (2wt%-10wt%) and citric acid (0.2wt%-2wt%) for quaternary formation. The formation voltage for quaternary formation is 520V-600V, the temperature is 70℃-90℃, the time is 900s-1200s, and the current density is 15 mA / cm². 2 -25 mA / cm 2 .

[0114] Some embodiments of this invention employ a multi-stage formation process (first-stage formation, second-stage formation, third-stage formation, and fourth-stage formation), with the formation voltage progressively increasing to a final voltage of 520V-600V, and the formation temperature for each stage independently controlled between 70℃ and 90℃; based on the high-crystallinity, low-resistance hydrated film precursor provided by pretreatment, a graded current density regime is implemented, with the first stage using 5 mA / cm². 2 -15 mA / cm 2To avoid breakdown of the initial thin dielectric, the current density is initially low. As the oxide film thickens and the withstand voltage increases, the current density of subsequent stages increases to 15 mA / cm². 2 -25 mA / cm 2 Furthermore, the final stage is allowed to remain stable, matching the anodic oxidation reaction rate with the film growth kinetics. The first two stages of formation use a boric acid-ammonium pentaborate system to provide a buffer environment and establish the initial oxide layer, while the latter two stages use a boric acid-citric acid system to optimize the microstructure of the oxide film, improving its crystallinity and hydration resistance. The above processes, combined with pretreatment, can reduce film resistance, reduce the risk of electrical breakdown caused by local current concentration, and simultaneously achieve uniform oxide film thickness.

[0115] Furthermore, in S2, the post-processing includes: depolarization treatment, heat treatment, reshaping treatment, stabilization treatment, and drying treatment.

[0116] Furthermore, the depolarization process includes a first depolarization process and a second depolarization process.

[0117] Furthermore, the heat treatment includes a first heat treatment and a second heat treatment.

[0118] Furthermore, the repair process includes a first repair process, a second repair process, and a third repair process.

[0119] Further, after any of the treatments, the etched aluminum foil is washed with water. Each of the treatments includes: pretreatment, primary formation, secondary formation, tertiary formation, quaternary formation, first depolarization treatment, first heat treatment, first re-forming treatment, second depolarization treatment, second re-forming treatment, second heat treatment, third re-forming treatment, and stabilization treatment.

[0120] Furthermore, the depolarization solution used in the first depolarization treatment includes phosphoric acid.

[0121] Furthermore, the solvent of the depolarization treatment solution used in the first depolarization treatment is water.

[0122] Furthermore, in the depolarization solution used for the first depolarization treatment, the mass fraction of phosphoric acid is 4wt%-6wt%. Specifically, in the depolarization solution used for the first depolarization treatment, the mass fraction of phosphoric acid can be, for example, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, or any two of these values, or other values ​​selected from the above range.

[0123] Furthermore, the temperature of the first depolarization treatment is 40℃-60℃. Specifically, the temperature of the first depolarization treatment can be, for example, 40℃, 45℃, 50℃, 55℃, 60℃, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0124] Furthermore, the duration of the first depolarization process is 120s-240s. Specifically, the duration of the first depolarization process can be, for example, 120s, 130s, 140s, 150s, 160s, 170s, 180s, 190s, 200s, 210s, 220s, 230s, 240s, or a range of any two values ​​thereof, or other values ​​selected from the above range.

[0125] Furthermore, the depolarization solution used in the second depolarization treatment includes phosphoric acid.

[0126] Furthermore, the solvent of the depolarization solution used in the second depolarization treatment is water.

[0127] Furthermore, in the depolarization solution used in the second depolarization treatment, the mass fraction of phosphoric acid is 6wt%-8wt%. Specifically, in the depolarization solution used in the second depolarization treatment, the mass fraction of phosphoric acid can be, for example, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, or any two of these values, or other values ​​selected from the above range.

[0128] Furthermore, the temperature of the second depolarization treatment is 60℃-70℃. Specifically, the temperature of the second depolarization treatment can be, for example, 60℃, 65℃, 70℃, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0129] Furthermore, the duration of the second depolarization process is 120s-600s. Specifically, the duration of the second depolarization process can be, for example, 120s, 150s, 200s, 250s, 300s, 350s, 400s, 450s, 500s, 550s, 600s, or a range of any two values ​​thereof, or other values ​​selected from the above range.

[0130] Furthermore, the temperatures of the first heat treatment and the second heat treatment are each independently between 500℃ and 600℃. Specifically, the temperatures of the first heat treatment and the second heat treatment can each be, for example, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0131] Furthermore, the duration of the first heat treatment and the second heat treatment are each independently between 100s and 240s. Specifically, the duration of the first heat treatment and the second heat treatment can be, for example, 100s, 120s, 140s, 160s, 180s, 200s, 220s, 240s, or a range of any two values ​​therein, or other values ​​selected from the above ranges.

[0132] Furthermore, the treatment solutions for the first, second, and third re-formation treatments each independently include boric acid.

[0133] Furthermore, the solvent for the treatment solutions in the first, second, and third replenishment treatments is water, each independently.

[0134] Furthermore, in the treatment solutions of the first, second, and third replenishment treatments, the mass fraction of boric acid is independently 2wt%-10wt%. Specifically, in the treatment solutions of the first, second, and third replenishment treatments, the mass fraction of boric acid can be, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or a range of any two of these values, or other values ​​selected from the above ranges.

[0135] Furthermore, the voltages for the first, second, and third reshaping processes are each independently between 570V and 590V. Specifically, the voltages for the first, second, and third reshaping processes can each be, for example, 570V, 580V, 590V, or a range consisting of any two of these values, or other values ​​selected from the aforementioned range.

[0136] Furthermore, the time for each of the first, second, and third supplementary forming processes is independently 400s-500s. Specifically, the time for each of the first, second, and third supplementary forming processes can be, for example, 400s, 450s, 500s, or a range consisting of any two of these values, or other values ​​selected from the aforementioned range.

[0137] Furthermore, the temperatures of the first, second, and third re-forming processes are each independently between 70°C and 90°C. Specifically, the temperatures of the first, second, and third re-forming processes can each be, for example, 70°C, 75°C, 80°C, 85°C, 90°C, or a range consisting of any two of these values, or other values ​​selected from the above range.

[0138] Furthermore, the current density of each of the first, second, and third re-forming processes is independently 15 mA / cm². 2 -25 mA / cm 2 Specifically, the current density of each of the first, second, and third re-forming processes can independently be, for example, 15 mA / cm². 2 20 mA / cm 2 25 mA / cm 2 , or a range of any two of the values, or other values ​​selected from the range mentioned above.

[0139] Furthermore, the stabilization treatment solution includes ammonium dihydrogen phosphate.

[0140] Furthermore, the solvent of the stabilization treatment solution is water.

[0141] Further, in the stabilization treatment solution, the mass fraction of ammonium dihydrogen phosphate is 0.5wt%-3wt%. Specifically, in the stabilization treatment solution, the mass fraction of ammonium dihydrogen phosphate can be, for example, 0.5wt%, 1wt%, 1.05wt%, 2wt%, 2.5wt%, 3wt%, or any two of these values, or other values ​​selected from the above range.

[0142] Furthermore, the stabilization treatment temperature is 50℃-70℃. Specifically, the stabilization treatment temperature can be, for example, 50℃, 55℃, 60℃, 65℃, 70℃, or a range of any two of these values, or other values ​​selected from the above range.

[0143] Furthermore, the stabilization treatment time is 60s-240s. Specifically, the stabilization treatment time can be, for example, 60s, 120s, 180s, 240s, or any two of these values, or other values ​​selected from the above range.

[0144] Furthermore, the drying temperature is 220℃-280℃. Specifically, the drying temperature can be, for example, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, or a range of any two of these values, or other values ​​selected from the above range.

[0145] Furthermore, the drying time is 150s-240s. Specifically, the drying time can be, for example, 150s, 160s, 170s, 180s, 190s, 200s, 210s, 220s, 230s, 240s, or a range of any two values ​​therein, or other values ​​selected from the above range.

[0146] In some embodiments, in S2, the post-processing procedure is as follows: S2-5, First depolarization treatment: After the electrode foil has undergone four-stage formation, it is cleaned with water and placed in a 4 wt-6 wt% phosphoric acid aqueous solution and treated at 40℃-60℃ for 120s-240s. S2-6, First heat treatment: After the electrode foil has undergone the first depolarization treatment, it is cleaned with water and then heat-treated at 500℃-600℃ for 100s-240s. S2-7. First Re-forming Treatment: After the first heat treatment, the electrode foil is cleaned with water and then placed in a 2 wt%-10 wt% boric acid aqueous solution for the first re-forming treatment. The voltage for the first re-forming treatment is 570V-590V, the time is 400s-500s, the temperature is 70℃-90℃, and the current density is 15 mA / cm². 2 -25 mA / cm 2 ; S2-8, Second depolarization treatment: After the electrode foil has undergone the first re-forming treatment, it is cleaned with water and placed in a 6wt%-8wt% phosphoric acid aqueous solution and treated at 60℃-70℃ for 120s-600s. S2-9. Second Formation Treatment: After the electrode foil has undergone the second depolarization treatment, it is cleaned with water and then placed in a 2 wt%-10 wt% boric acid aqueous solution for a second formation treatment. The voltage for the second formation treatment is 570V-590V, the time is 400s-500s, the temperature is 70℃-90℃, and the current density is 15 mA / cm². 2 -25mA / cm 2 ; S2-10, Second heat treatment: After the electrode foil has undergone the second reshaping treatment, it is cleaned with water and then heat-treated at 500℃-600℃ for 100s-240s. S2-11. Third Formation Treatment: After the second heat treatment, the electrode foil is cleaned with water and then placed in a 2 wt%-10 wt% boric acid aqueous solution for a third formation treatment. The voltage for the third formation treatment is 570V-590V, the time is 400s-500s, the temperature is 70℃-90℃, and the current density is 15 mA / cm². 2 -25 mA / cm 2 ; S2-12, Stabilization treatment: The electrode foil after the third re-forming treatment is placed in an aqueous solution of ammonium dihydrogen phosphate with a mass fraction of 0.5wt%-3wt% and treated at 50℃-70℃ for 60s-240s; S2-13. Drying treatment: After the electrode foil has been stabilized, it is cleaned with water and then dried at 220℃-280℃ for 150s-240s to obtain the stabilized foil.

[0147] Some embodiments of this invention employ a repair system involving alternating multi-stage depolarization treatment, multi-stage heat treatment, and multi-stage re-forming treatment. The first depolarization treatment uses a 4wt%-6wt% phosphoric acid aqueous solution at 40℃-60℃ to gently dissolve weak points in the oxide film and remove the surface aluminum hydroxide layer. Following the first depolarization treatment, a first heat treatment at 500℃-600℃ promotes the transformation of amorphous alumina to the γ-Al₂O₃ crystalline phase and eliminates residual stress. Subsequently, a first re-forming treatment at 570V-590V repairs the microcracks generated during the first heat treatment. The second depolarization treatment increases the phosphoric acid concentration to 6wt%-8wt% and raises the temperature to 60℃-70℃ for deep defect removal. After the second re-forming treatment and the second heat treatment, a third re-forming treatment further repairs the micro-defects in the film. Finally, a 0.5wt%-3wt% phosphoric acid solution is applied at 50℃-70℃. A wt% ammonium dihydrogen phosphate aqueous solution is used for stabilization treatment to seal surface micropores and improve the hydration resistance of the film. The above post-treatment system eliminates residual stress in the oxide film and reduces the defect density of the film through gradual repair and stabilization, so that the electrical performance of the electrolytic foil meets the requirements of medium and high voltage aluminum electrolytic capacitors.

[0148] On the other hand, the present invention also provides a formed foil for an aluminum electrolytic capacitor prepared by the above method.

[0149] Specifically, the specific capacitance of the formed foil at a withstand voltage of 580V-610V is 0.68μF / cm. 2 -0.7μF / cm2 .

[0150] On the other hand, embodiments of the present invention also provide an aluminum electrolytic capacitor, comprising the above-described formed foil or formed foil prepared by the above method.

[0151] The following detailed description, with reference to specific embodiments, illustrates the formation foil for aluminum electrolytic capacitors of the present invention and its preparation method.

[0152] Example 1 S1. Pretreatment: The etched aluminum foil (11cm×11cm) was placed in a 50% hydrazine hydrate aqueous solution at a constant temperature of 30℃ and ultrasonically treated for 18 min at a frequency of 120 kHz. S2-1, Primary Formation: After cleaning the pretreated etched aluminum foil with water, it is placed in a mixed aqueous solution of 5 wt% boric acid and 0.6 wt% ammonium pentaborate for primary formation. The formation voltage is 160 V, the temperature is 85 ℃, the time is 300 s, and the current density is 10 mA / cm². 2 This yields an electrode foil that has undergone primary formation; S2-2, Secondary Formation: After the electrode foil has undergone primary formation, it is cleaned with water and then placed in a mixed aqueous solution of 5 wt% boric acid and 0.4 wt% ammonium pentaborate for secondary formation. The formation voltage for secondary formation is 320 V, the temperature is 85 ℃, the time is 450 s, and the current density is 15 mA / cm². 2 ; S2-3, Tertiary Formation: After the electrode foil has undergone secondary formation, it is cleaned with water and then placed in a mixed aqueous solution of 6 wt% boric acid and 0.2 wt% citric acid for tertiary formation. The formation voltage for tertiary formation is 460 V, the temperature is 85 ℃, the time is 600 s, and the current density is 20 mA / cm². 2 ; S2-4, Quaternary Formation: After the electrode foil has undergone tertiary formation, it is cleaned with water and then placed in a mixed aqueous solution of 6 wt% boric acid and 0.2 wt% citric acid for quaternary formation. The formation voltage for quaternary formation is 580 V, the temperature is 85 ℃, the time is 1000 s, and the current density is 20 mA / cm². 2 ; S2-5, First depolarization treatment: After the electrode foil has undergone four-stage formation, it is cleaned with water and placed in a 5 wt% phosphoric acid aqueous solution and treated at 45 ℃ for 180 s. S2-6, First heat treatment: After the electrode foil has undergone the first depolarization treatment, it is cleaned with water and then heat-treated at 550℃ for 120s. S2-7. First Re-forming Treatment: After the electrode foil has undergone the first heat treatment, it is cleaned with water and then placed in an 8 wt% boric acid aqueous solution for the first re-forming treatment. The voltage for the first re-forming treatment is 580V, the time is 450s, the temperature is 85℃, and the current density is 20 mA / cm². 2 ; S2-8, Second depolarization treatment: After the first re-forming treatment, the electrode foil is cleaned with water and placed in a 7 wt% phosphoric acid aqueous solution and treated at 65 ℃ for 360 s. S2-9. Second Formation Treatment: After the electrode foil has undergone the second depolarization treatment, it is cleaned with water and then placed in an 8 wt% boric acid aqueous solution for a second formation treatment. The voltage for the second formation treatment is 580 V, the time is 450 s, the temperature is 85℃, and the current density is 20 mA / cm². 2 ; S2-10, Second heat treatment: After the electrode foil has undergone the second reshaping treatment, it is cleaned with water and then heat-treated at 550℃ for 120 s; S2-11. Third Formation Treatment: After the electrode foil has undergone the second heat treatment, it is cleaned with water and then placed in an 8 wt% boric acid aqueous solution for a third formation treatment. The voltage for the third formation treatment is 580V, the time is 450s, the temperature is 85℃, and the current density is 20 mA / cm². 2 ; S2-12, Stabilization treatment: The electrode foil after the third re-forming treatment is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution and treated at 60 ℃ for 120 s; S2-13. Drying treatment: After the electrode foil has been stabilized, it is cleaned with water and then dried at 250 ℃ for 180 s to obtain the stabilized foil.

[0153] Example 2 The difference from Example 1 is that in S1, the ultrasonic frequency is 80 kHz. The remaining steps and parameters are the same as in Example 1.

[0154] Example 3 The difference from Example 1 is that in S1, the pretreatment reaction time is 12 min. All other steps and parameters are the same as in Example 1.

[0155] Example 4 The difference from Example 1 is that in S1, the volume fraction of N2H4·H2O in the hydrazine hydrate aqueous solution is 40%. The remaining steps and parameters are the same as in Example 1.

[0156] Example 5 The difference from Example 1 is that in S1, the volume fraction of N2H4·H2O in the hydrazine hydrate aqueous solution is 60%. The remaining steps and parameters are the same as in Example 1.

[0157] Comparative Example 1: Step S1 without ultrasonic treatment The difference from Example 1 is that in S1, the etched aluminum foil is immersed in a 50% (v / v) hydrazine hydrate aqueous solution at a constant temperature of 30°C for 18 minutes, without ultrasonic treatment. The remaining steps and parameters are the same as in Example 1.

[0158] Comparative Example 2: Investigation of the pretreatment solution in step S1 The difference from Example 1 is that in S1, the etched aluminum foil is ultrasonically treated in pure water at a constant temperature of 30°C for 18 minutes at an ultrasonic frequency of 120 kHz. The remaining steps and parameters are the same as in Example 1.

[0159] Comparative Example 3: Investigation of the concentration of hydrazine hydrate aqueous solution in step S1 The difference from Example 1 is that in S1, the volume fraction of N2H4·H2O in the hydrazine hydrate aqueous solution is 30%. The remaining steps and parameters are the same as in Example 1.

[0160] Comparative Example 4: Investigation of the concentration of hydrazine hydrate aqueous solution in step S1 The difference from Example 1 is that in S1, the volume fraction of N2H4·H2O in the hydrazine hydrate aqueous solution is 70%. The remaining steps and parameters are the same as in Example 1.

[0161] Comparative Example 5: Investigation of the types of solutes in the pretreatment solution of step S1 The difference from Example 1 is that in S1, the etched aluminum foil was placed in a mixed aqueous solution of ammonium hypophosphite (0.45 wt%) and ammonium dihydrogen phosphate (0.1 wt%) at a constant temperature of 30°C and ultrasonically treated for 18 min at an ultrasonic frequency of 120 kHz. The remaining steps and parameters were the same as in Example 1.

[0162] Comparative Example 6: Investigation of the types of solutes in the pretreatment solution of step S1 The difference from Example 1 is that in S1, the etched aluminum foil was placed in a 0.5 wt% maleic acid aqueous solution at a constant temperature of 30°C and ultrasonically treated for 18 min at an ultrasonic frequency of 120 kHz. The remaining steps and parameters were the same as in Example 1.

[0163] Comparative Example 7: Traditional High-Temperature Boiling Method The difference from Example 1 is that in S1, the etched aluminum foil is boiled in water at 95°C or higher for 12 minutes. The remaining steps and parameters are the same as in Example 1.

[0164] [Performance Testing] The electrode foils prepared in Examples 1-5 and Comparative Examples 1-7 were subjected to electrical performance tests. The test methods were based on the industry standard SJ / T 11140-2022 "Electrode Foil for Aluminum Electrolytic Capacitors"; the test parameters are listed in Table 1, wherein: Vt (Vf): Converted to withstand voltage value, unit V; Cap: Specific volume, unit μF / cm³ 2 ; W: Normalized energy consumption, in kWh·m³ -2 (Energy consumption per unit area has been converted to a withstand voltage of 600 V).

[0165] Testing instruments: Vt was measured using a TV analyzer; Cap was measured using an LCR digital bridge; the amount of charge generated during the formation process was recorded using a TS680 small-sample formation process analyzer.

[0166] Table 1

[0167] Note: (1) The specific volume comparison (%) is calculated based on the specific volume value of Comparative Example 7, and the calculation formula is: Specific volume comparison (%) = [(specific volume value of the example or comparative example ÷ specific volume value of comparative example 7) - 1] × 100%; (2) Energy consumption comparison (%) is calculated based on the energy consumption value of Comparative Example 7. The calculation formula is as follows: Energy consumption comparison (%) = [(Energy consumption of the example or comparative example ÷ Energy consumption of comparative example 7) - 1] × 100%.

[0168] As can be seen from the data in Table 1, the preparation methods of Examples 1-5 of the present invention have all achieved synergistic optimization of energy consumption reduction and specific volume improvement.

[0169] Comparative Example 1 was soaked in hydrazine hydrate aqueous solution but without ultrasonic treatment. The specific volume was lower than that of Example 1, and the energy consumption was significantly higher than that of Example 1. This indicates that the lack of ultrasonic cavitation effect leads to insufficient crystal nucleation points and poor compactness in the hydrated film. Subsequent formation requires more energy to repair defects, and the specific volume of the product decreased significantly. This proves that ultrasonic treatment plays an important role in improving the quality of the film.

[0170] Comparative Example 2 used pure water for ultrasound, with a lower specific volume and higher energy consumption than Example 1. This indicates that pure water ultrasound cannot generate the γ-AlOOH hydrated film precursor. The lack of ordered structure guidance on the aluminum foil surface leads to a decrease in formation efficiency, proving that the chemical induction effect of hydrazine hydrate is the key to achieving low-energy formation.

[0171] Comparative Example 3 used a low-concentration hydrazine hydrate aqueous solution with a volume fraction of 30%. The specific volume was significantly lower than that of Example 4 (40%) and Example 1 (50%), while the energy consumption was higher than that of Example 1. This indicates that the low concentration leads to slow reaction kinetics and an increase in Al(OH)3 impurity phase. The γ-AlOOH content is insufficient, which cannot effectively reduce the formation activation energy.

[0172] Comparative Example 4 used a high-concentration hydrazine hydrate aqueous solution with a volume fraction of 70%. Although the energy consumption was similar to that of Example 1, the specific volume was lower than that of Example 1 (50%) and Example 5 (60%). This indicates that the specific volume improvement effect of hydrazine hydrate aqueous solution decreases after the volume fraction of hydrazine hydrate exceeds 60%, and high concentration brings operational risks.

[0173] Comparative Example 5 used ammonium hypophosphite instead of hydrazine hydrate, resulting in a significantly lower specific volume than Example 1 and a significant increase in energy consumption compared to Example 1. This system could not induce the directional growth of γ-AlOOH, resulting in poor quality of the generated amorphous hydrated film, which significantly increased the energy consumption of subsequent formation and reduced product performance.

[0174] Comparative Example 6 uses maleic acid instead of hydrazine hydrate, and the specific volume is significantly lower than that of Example 1. The energy consumption is increased compared with Example 1. The organic acid system has a different reaction mechanism than the aluminum surface and cannot generate the target γ-AlOOH nanocrystal precursor. The formation efficiency is significantly reduced, which proves that hydrazine hydrate plays a key role in inducing the formation of specific crystal phases.

[0175] Comparative Example 7 uses the traditional high-temperature boiling method, with specific volume and energy consumption as existing technical benchmarks. Compared with the examples, the hydrated film generated by the traditional method has low crystallinity and random orientation, and the subsequent formation energy consumption is high. The specific volume and consistency of the product are not as good as the method of the present invention, further demonstrating the technical advantages of hydrazine hydrate solution and ultrasonic synergistic pretreatment.

[0176] Based on the data in Table 1, this invention, through a specific processing technique—ultrasonic pretreatment with hydrazine hydrate solution—achieves a higher energy consumption and increased specific volume compared to the traditional boiling method, within a hydrazine hydrate volume fraction of 40%-60%, an ultrasonic frequency of 80 kHz-120 kHz, and a time range of 12 min-32 min. Comparative examples demonstrate the synergistic effect of hydrazine hydrate and ultrasound, the chemical induction specificity of hydrazine hydrate, and the necessity of the concentration window.

[0177] In summary, this invention pretreats corroded aluminum foil before formation by ultrasonic treatment with hydrazine hydrate solution. The directional induction effect of hydrazine hydrate molecules promotes hydroxylation on the aluminum foil surface, generating a hydrated film precursor mainly composed of γ-AlOOH nanocrystals. Simultaneously, the ultrasonic cavitation effect forms uniformly distributed crystal nucleation sites in the hydrated film, reducing the activation energy of γ-Al2O3 crystal growth during subsequent anodizing, thereby improving anodizing efficiency, reducing formation energy consumption, and enhancing the dielectric properties of the formed foil. Moreover, the process is simple and low-cost.

[0178] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing formed foil for aluminum electrolytic capacitors, characterized in that, Includes the following steps: S1. Pretreatment: The etched aluminum foil is placed in a hydrazine hydrate solution and subjected to a pretreatment reaction under ultrasonic treatment to obtain the pretreated aluminum foil. S2. The pretreated aluminum foil is subjected to multi-stage anodizing and post-treatment to obtain anodized foil.

2. The method according to claim 1, characterized in that, In S1, the volume fraction of hydrazine hydrate in the hydrazine hydrate solution is 40%-60%; And / or, the solvent of the hydrazine hydrate solution is water.

3. The method according to claim 1 or 2, characterized in that, In S1, the frequency of the ultrasound is 80 kHz-120 kHz; And / or, the temperature of the pretreatment reaction is 20℃-40℃; And / or, the pretreatment reaction time is 12 min-32 min.

4. The method according to any one of claims 1-3, characterized in that, In S2, the multi-stage anodic oxidation formation includes primary formation, secondary formation, tertiary formation and quaternary formation; And / or, the primary and secondary formation solutions each independently include boric acid and / or ammonium pentaborate; And / or, the solvent of the primary and secondary formation solutions is water; And / or, in the primary formation solution, the mass fraction of boric acid is 3wt%-8wt%, and the mass fraction of ammonium pentaborate is 0.1wt%-0.8wt%. And / or, in the secondary formation solution, the mass fraction of boric acid is 3wt%-8wt%, and the mass fraction of ammonium pentaborate is 0.1wt%-0.6wt%; And / or, the forming solutions used in the third-stage and fourth-stage formations each independently include boric acid and / or citric acid; And / or, the solvent of the formation solution in the third-stage and fourth-stage formation is water; And / or, in the formation solution of the three-stage formation, the mass fraction of boric acid is 2wt%-10wt%, and the mass fraction of citric acid is 0.2wt%-2wt%; And / or, in the formation solution of the fourth-stage formation, the mass fraction of boric acid is 2wt%-10wt%, and the mass fraction of citric acid is 0.2wt%-2wt%.

5. The method according to any one of claims 1-4, characterized in that, In S2, the formation voltage of the first-stage formation is 150V-180V; And / or, the time for the first-stage formation is 250s-350s; And / or, the current density of the first-stage formation is 5 mA / cm². 2 -15mA / cm 2 ; And / or, the formation voltage of the secondary formation is 240V-380V; And / or, the time for the secondary formation is 400s-500s; And / or, the current density of the secondary formation is 10 mA / cm². 2 -25mA / cm 2 ; And / or, the formation voltage of the three-stage formation is 420V-500V; And / or, the time for the third-level formation is 550s-650s; And / or, the current density of the three-stage formation is 15 mA / cm². 2 -25mA / cm 2 ; And / or, the formation voltage of the four-stage formation is 520V-600V; And / or, the time for the fourth-level formation is 900s-1200s; And / or, the current density of the fourth-stage formation is 15 mA / cm². 2 -25mA / cm 2 ; And / or, the temperatures for the primary, secondary, tertiary, and quaternary formations are each independently 70°C-90°C.

6. The method according to any one of claims 1-5, characterized in that, In S2, the post-processing includes: depolarization treatment, heat treatment, re-forming treatment, stabilization treatment, and drying treatment.

7. The method according to any one of claims 1-6, characterized in that, In S2, the depolarization process includes a first depolarization process and a second depolarization process; And / or, the heat treatment includes a first heat treatment and a second heat treatment; And / or, the repair forming process includes a first repair forming process, a second repair forming process, and a third repair forming process; And / or, after the depolarization treatment, heat treatment, reshaping treatment and stabilization treatment, the aluminum foil is rinsed with water respectively; And / or, the depolarization solution used in the first depolarization treatment includes phosphoric acid; And / or, the solvent of the depolarization treatment solution used in the first depolarization treatment is water; And / or, in the depolarization solution of the first depolarization treatment, the mass fraction of phosphoric acid is 4wt%-6wt%; And / or, the temperature of the first depolarization treatment is 40℃-60℃; And / or, the duration of the first depolarization process is 120s-240s; And / or, the depolarization solution used in the second depolarization treatment includes phosphoric acid; And / or, the solvent of the depolarization solution used in the second depolarization treatment is water; And / or, in the depolarization solution used for the second depolarization treatment, the mass fraction of phosphoric acid is 6wt%-8wt%; And / or, the temperature of the second depolarization treatment is 60℃-70℃; And / or, the duration of the second depolarization process is 120s-600s; And / or, the temperatures of the first heat treatment and the second heat treatment are each independently 500℃-600℃; And / or, the duration of the first heat treatment and the second heat treatment is independently 100s-240s; And / or, the treatment solutions for the first, second, and third replenishment treatments each independently include boric acid; And / or, the solvent of the treatment solution for the first, second and third replenishment treatments is water, each independently; And / or, in the treatment solutions of the first, second, and third re-formation treatments, the mass fraction of boric acid is independently 2wt%-10wt%; And / or, the voltages of the first, second, and third re-forming processes are each independently 570V-590V; And / or, the time for the first, second, and third supplementary formation processes is independently 400s-500s; And / or, the temperatures of the first, second, and third supplementary formation processes are each independently 70°C-90°C; And / or, the current density of the first, second, and third re-forming processes is each independently 15 mA / cm². 2 -25 mA / cm 2 ; And / or, the stabilization treatment solution includes ammonium dihydrogen phosphate; And / or, the solvent of the stabilization treatment solution is water; And / or, in the stabilization treatment solution, the mass fraction of ammonium dihydrogen phosphate is 0.5wt%-3wt%; And / or, the stabilization treatment temperature is 50℃-70℃; And / or, the stabilization treatment time is 60s-240s; And / or, the drying temperature is 220℃-280℃; And / or, the drying process takes 150s-240s.

8. A type of foil for aluminum electrolytic capacitors, characterized in that, Prepared using the method described in any one of claims 1-7.

9. The electroformed foil according to claim 8, characterized in that, The specific capacitance of the formed foil at a withstand voltage of 580 V-610 V is 0.682 μF / cm. 2 -0.700μF / cm 2 .

10. An aluminum electrolytic capacitor, characterized in that, Includes the chemically formed foil as described in claim 8 or 9, or the chemically formed foil prepared by the method described in any one of claims 1-7.

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