Electrode foil and its preparation method and electrolytic capacitor

Abstract

This application provides an electrode foil, its preparation method, and an electrolytic capacitor, belonging to the field of electrode material technology. The preparation method of the electrode foil includes: performing a formation treatment, depolarization treatment, and post-treatment on an etched foil to obtain the electrode foil. In the post-treatment, the depolarized etched foil is immersed in an immersion solution; the immersion solution includes an organic polymer and polyphosphate or its salts; the main chain and / or side chains of the organic polymer are grafted with one or more functional groups selected from sulfonic acid groups, phosphate groups, phosphonic acid groups, carboxyl groups, and amide groups. The electrode foil prepared by this method has higher specific capacitance, better hydration resistance, flexural strength, and tensile strength, which is beneficial for improving the reliability and electrical performance of the electrolytic capacitor.

Description

Technical Field

[0001] This application belongs to the field of electrode material technology, and specifically relates to an electrode foil and its preparation method and electrolytic electrode. container. Background Technology

[0002] In the formation process of electrode foil for electrolytic capacitors, the mainstream traditional method usually involves immersing the aluminum foil in a solution containing phosphate (salt) for chemical treatment during the "intermediate treatment" or "depolarization process" stage. The core principle is that the phosphate (salt) reacts chemically with the surface of the alumina dielectric film formed after the aluminum foil is anodized to generate a hydration-resistant composite layer with aluminum phosphate as the main component, thereby inhibiting the occurrence of hydration reaction.

[0003] While existing phosphoric acid processing technology is mature and relatively low-cost, it still faces many insurmountable defects and technical bottlenecks in practical applications. For example, the resulting protective layer has poor density and stability, is thin and has weak mechanical strength, has limited ability to repair defects in the protective layer, has poor high-temperature hydration resistance, and has compatibility issues with subsequent processes. These issues have become bottlenecks restricting further improvement in the performance of aluminum electrolytic capacitors.

[0004] Therefore, there is an urgent need to develop electrode foils for electrolytic capacitors with higher specific capacitance, better hydration resistance, flexural strength, and tensile strength to meet the increasingly stringent requirements of the modern electronics industry for the performance of electrolytic capacitors. Summary of the Invention

[0005] This application provides an electrode foil, a method for preparing the same, and an electrolytic capacitor. The electrode foil has higher specific capacitance, better hydration resistance, flexural strength, and tensile strength, which is beneficial for improving the reliability and electrical performance of the electrolytic capacitor.

[0006] In a first aspect, embodiments of this application provide a method for preparing an electrode foil, the method comprising: Electrode foil is obtained by performing formation treatment, depolarization treatment, and post-treatment on the etched foil. In the post-processing, the depolarized etched foil is immersed in an immersion solution; the immersion solution includes an organic polymer and polyphosphate or its salt; the main chain and / or side chain of the organic polymer are grafted with one or more functional groups selected from sulfonic acid groups, phosphoric acid groups, phosphonic acid groups, carboxyl groups and amide groups.

[0007] In some embodiments, the polyphosphate or its salt comprises at least one selected from polyphosphate, ammonium polyphosphate, sodium pyrophosphate, sodium tripolyphosphate, potassium tetramethphosphate, sodium hexametaphosphate, potassium hexametaphosphate, sodium trimetaphosphate, and sodium tetramethphosphate.

[0008] In some embodiments, the organic polymer includes at least one of polystyrene sulfonic acid, polyvinylphosphonic acid, sodium alginate, sodium polyacrylate, polyacrylamide, and polyitacrylic acid.

[0009] In some embodiments, the immersion solution includes a first solution and a second solution, and the immersion treatment of the depolarized etched foil with the immersion solution includes: A first soaking treatment is performed using a first solution, the first solution comprising polyphosphate or a salt thereof; optionally, the solvent of the first solution comprises water. A second immersion treatment is performed using a second solution, the second solution comprising an organic polymer; optionally, the solvent of the second solution comprises water. In some embodiments, the post-processing involves first performing a first soaking treatment with a first solution, followed by a second soaking treatment with a second solution.

[0010] In some embodiments, the post-processing involves first performing a second soaking treatment using a second solution, followed by performing a first soaking treatment using a first solution.

[0011] In some embodiments, the mass percentage of the polyphosphate or its salt in the first solution is 0.5%-10% based on the total mass of the first solution.

[0012] In some embodiments, in the post-processing, a first solution is used to perform a first soaking treatment at a temperature of 40°C-75°C; optionally, the first soaking treatment time is 1 min-10 min.

[0013] In some embodiments, the organic polymer in the second solution is 0.1%-10% by mass, based on the total mass of the second solution.

[0014] In some embodiments, in the post-treatment, a second solution is used to perform a second soaking treatment at a temperature of 40°C-70°C; optionally, the time for the second soaking treatment is 0.5 min-8 min.

[0015] In some embodiments, the second solution further includes a chelating agent; the chelating agent contains two or more chelating groups, the chelating groups including one or more functional groups selected from phosphonic acid, carboxylic acid, hydroxyl, amino, and thiol groups.

[0016] In some embodiments, the chelating agent includes one or more of ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, and aminotrimethylene phosphonic acid.

[0017] In some embodiments, the mass ratio of the chelating agent and the organic polymer in the second solution is (1-5):10.

[0018] In some embodiments, the soaking solution further includes a third solution.

[0019] In some embodiments, the third solution comprises an organic polymer and polyphosphate or a salt thereof.

[0020] In some embodiments, the third solution includes the first solution and the second solution.

[0021] In some embodiments, the post-processing involves a third soaking treatment using a third solution.

[0022] In some embodiments, the content of each component in the third solution is the same as that in the first and second solutions.

[0023] In some embodiments, the post-treatment involves a third immersion treatment using a third solution at a temperature of 40°C-70°C; optionally, the third immersion treatment time is 0.5 min-8 min.

[0024] In some embodiments, the post-processing in the preparation method further includes: a supplementary formation process.

[0025] In some embodiments, the temperature of each of the re-forming processes is independently 60°C-90°C.

[0026] In some embodiments, the current density of each of the re-forming processes is independently 20 mA / cm²-200 mA / cm²; preferably 40 mA / cm²-120 mA / cm².

[0027] In some embodiments, the voltage for each of the reshaping processes is independently 1.02-1.2 times the rated voltage; optionally, it is a pulse voltage.

[0028] In some embodiments, the time for each of the replenishment processes is independently 0.5 min to 10 min.

[0029] In some embodiments, the solute in the replenishing solution used in each replenishing process independently includes one or more of ammonium dihydrogen phosphate, boric acid, and ammonium pentaborate.

[0030] In some embodiments, the solvent of the repair solution used in each repair process is water, independently.

[0031] In some embodiments, based on the total mass of the replenishing solution used in the replenishing treatment, the mass percentage of solute in the replenishing solution used in each replenishing treatment is independently 0.5%-10%.

[0032] In some embodiments, the post-processing in the preparation method further includes: heat treatment; optionally, the temperature of each heat treatment is independently 150℃-380℃, and more preferably 280℃-350℃; optionally, the time of each heat treatment is independently 2min-20min, and more preferably 2min-5min.

[0033] Secondly, embodiments of this application provide an electrode foil, which is prepared using the preparation method described in the first aspect.

[0034] Thirdly, embodiments of this application provide an electrolytic capacitor, which includes an electrode foil prepared by the preparation method described in the first aspect or the electrode foil described in the second aspect.

[0035] The preparation method of this application uses an immersion solution containing organic polymers and / or polyphosphoric acid or its salts to prepare electrode foil, which can synergistically solve the fundamental problems of poor density and stability of the composite protective layer in traditional phosphoric acid treatment and poor defect repair ability in phosphoric acid treatment. The preparation method of this application constructs a composite protective layer with high density, high stability, high mechanical strength and deep repair, comprehensively improving the hydration resistance and overall quality of the electrode foil.

[0036] Compared to the high phosphoric acid emissions of traditional phosphoric acid processes, the preparation method of this application uses polyphosphoric acid or its salts in combination with organic polymers to reduce phosphoric acid usage while achieving the same hydration resistance, and at the same time extends the service life of the bath solution, thereby reducing production costs.

[0037] The preparation method of this application uses polyphosphate or its salts and organic polymers, both of which have good water solubility and can be seamlessly integrated with existing chemical formation production lines without the need for large-scale modification of existing equipment, making it easy to promote and apply under existing production conditions. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0039] Figure 1 A schematic diagram showing the cross-section of the electrode foil according to an embodiment of this application is provided.

[0040] Description of the attached drawings: 100, electrode foil; 10, substrate; 20, composite protective layer; 21, product of organic polymer; 22, product of polyphosphate or its salt. Detailed Implementation

[0041] The electrode foil, its preparation method, and embodiments of the electrolytic capacitor of this application are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0042] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0043] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0044] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0045] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0046] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0047] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0048] Traditional electrode foils often employ a method where the raw electrode foil is immersed in a solution containing phosphate or its salts during the "intermediate treatment" stage of the formation process to improve its hydration resistance. Taking aluminum foil as an example, phosphate or its salts react chemically with the anode, and the Al2O3 on the surface further forms a denser, more hydration-resistant composite layer, mainly composed of AlPO4. This composite layer effectively prevents water molecules from penetrating the oxide film, thereby inhibiting the hydration reaction and preventing the oxide film from becoming porous and experiencing capacity decay. Although this process is relatively mature and low-cost, as mentioned in the background section, several problems remain to be solved: From the perspective of the physical properties of the composite layer, the formed aluminum phosphate composite layer is usually thin and lacks mechanical strength. During subsequent foil winding and cutting processes, it is prone to micro-cracks or damage due to physical stress. Furthermore, the composite layer contains numerous microscopic defects and pores. Regarding the repair capability of the composite layer, phosphate ions have difficulty effectively penetrating to the deepest parts of the corrosion pores, resulting in incomplete passivation inside the pores. Simultaneously, the inherent microstructural inhomogeneities (such as micropores and cracks) in the porous oxide film formed by anodizing cannot effectively repair or seal defects deep within the oxide film. Therefore, this severely restricts the improvement of the overall hydration resistance of the electrode aluminum foil. From the perspective of process window balance, blindly increasing the concentration or temperature of the treatment solution to improve the passivation effect may exacerbate the chemical dissolution of the alumina film, leading to irreversible loss of the aluminum foil's electrostatic capacity and posing a significant risk of performance degradation. To overcome at least some of the aforementioned defects, existing technologies have attempted to employ optimized processes such as power-on processing. While these processes can address the issues of permeability and capacity loss to some extent, they require additional specialized equipment, significantly increasing the complexity of the production process and manufacturing costs.

[0049] Research has shown that soaking the composite layer in a solution containing organic polymers and polyphosphates or their salts after the formation process can further fill the defects and pores inside the composite layer, while simultaneously generating a polymer layer in situ on the surface of the composite layer.

[0050] Based on this, embodiments of this application provide a method for preparing an electrode foil, which enables the electrode foil to have higher specific capacitance, better hydration resistance, flexural strength and tensile strength, which is beneficial to improving the reliability and electrical performance of electrolytic capacitors.

[0051] Method for preparing electrode foil This application provides a method for preparing an electrode foil, the method comprising: performing a formation treatment, a depolarization treatment, and a post-treatment on an etched foil to obtain the electrode foil. In the post-processing, the etched foil that has undergone the depolarization treatment is immersed in an immersion solution; the immersion solution includes an organic polymer and polyphosphate or its salt; the main chain or side chain of the organic polymer is grafted with one or more functional groups selected from sulfonic acid group, phosphoric acid group, phosphonic acid group, carboxyl group and amide group.

[0052] The etched foil itself includes a substrate and a composite protective layer disposed on at least one side of the substrate. The substrate is a metallic material containing the element M, such as aluminum (Al), tantalum (Ta), niobium (Nb), or any one or more valve-equalizing metallic elements.

[0053] Organic polymers can be homopolymers or copolymers.

[0054] Polyphosphoric acid is a mixture of chain or cyclic phosphoric oxygen-containing inorganic acid polymers formed by the dehydration condensation of two or more orthophosphoric acid units through the formation of POP covalent bonds by sharing oxygen atoms.

[0055] Polyphosphates are salts formed when the ionizable hydrogen in the above-mentioned acids is completely or partially replaced by metal cations, or condensed polyphosphates formed by phosphate units directly linked by shared oxygen atoms.

[0056] It is understood that the electrode foil itself includes a substrate and a composite protective layer disposed on at least one side of the substrate. The substrate is a metallic material containing element M, such as aluminum (Al), tantalum (Ta), niobium (Nb), or any one or more valve-equalizing metallic elements. The composite protective layer is prepared through the aforementioned formation treatment, depolarization treatment, and post-treatment. The composite protective layer includes components of polyphosphate ions and organic polymers. The composite protective layer also includes element M.

[0057] Taking aluminum corrosion foil as an example, polyphosphate or its salts, as long-chain inorganic polymers, react with the alumina surface through a mechanism different from that of small-molecule phosphoric acid. The polyphosphate anions in polyphosphate or its salts, with their chain structure, can form complexes with metal elements on the corrosion foil surface, such as aluminum, that have higher coordination numbers and stronger bond energies. This reaction is not limited to the surface but can also penetrate into the composite protective layer through the anchoring effect of chain segments, effectively penetrating to the deepest part of the corrosion pores. This leads to passivation of the pores, forming a layer with significantly increased thickness and a denser microstructure, such as aluminum polyphosphate. Compared to the amorphous aluminum phosphate layer formed by traditional small-molecule phosphoric acid, the polyphosphate or its salts in this composite protective layer have a more regular lattice arrangement, significantly reduced internal porosity and defect density, thus constructing a more robust physicochemical barrier. This inhibits the penetration and diffusion of water molecules under harsh environments, effectively preventing the hydration degradation of the internal alumina layer, ensuring the long-term stability of dielectric properties, and solving the problems of increased leakage current and shortened lifespan. Meanwhile, organic polymers, as macromolecular materials, possess excellent film-forming and adhesive properties, enabling them to fill and repair microcracks that may occur during the formation of polyphosphates or their salts, and to form a highly resilient organic layer in situ on the surface. These organic polymers contain sulfonic acid groups (-SO3H), phosphate groups (-OPO3H2), phosphonic acid groups (-PO3H2), carboxylic acid groups (-COOH), and amide groups (-CONH2), which facilitates their organic bonding with the corrosion foil surface layer. This results in the formation of a highly resilient composite protective layer containing organic matter in situ on the surface, improving the density, stability, and mechanical strength of the electrode foil surface, reducing leakage current during use, and enhancing voltage stability.

[0058] The "rigid-flexible" structure of polyphosphate or its salts and organic polymers significantly improves the overall mechanical strength and deformation resistance of the electrode foil, making it less susceptible to damage during subsequent winding, cutting and other processing, thereby ensuring product consistency and yield.

[0059] More importantly, solutions of organic polymers and polyphosphates or their salts have suitable rheological properties, enabling them to effectively penetrate into the deep and complex pores of the corrosion foil with their excellent wetting and spreading capabilities. This deep penetration allows the "voids" and "defects" on the inner wall of the pores to be further passivated and sealed, achieving comprehensive and deep repair of the inhomogeneity of the microstructure of the surface film.

[0060] In summary, the preparation of electrode foil using an immersion solution containing organic polymers and polyphosphoric acid or its salts can synergistically solve the fundamental problems of poor density and stability of the composite protective layer in traditional phosphoric acid treatment, as well as the poor defect repair capability in phosphoric acid treatment. The preparation method of this application constructs a composite protective layer with high density, high stability, high mechanical strength, and deep repair, comprehensively improving the hydration resistance and overall quality of the electrode foil.

[0061] In the embodiments of this application, the magnitude of leakage current is mainly related to the quality of the surface film of the electrode foil. By adopting the method of the embodiments of this application, defects such as pores in the surface film or composite protective layer can be reduced, the density of the surface film can be increased, and the overall dielectric properties of the film layer can be improved, thereby reducing leakage current and increasing the capacity of the electrode foil.

[0062] Compared to the high phosphorus emissions of traditional phosphoric acid processes, the preparation method of this application reduces phosphorus consumption and extends the service life of the bath while achieving the same hydration resistance through the synergistic effect of polyphosphoric acid or its salts and organic polymers, thereby reducing production costs.

[0063] The preparation method of this application uses polyphosphate or its salts and organic polymers, both of which have good water solubility. This allows for seamless integration with existing chemical formation production lines without requiring large-scale modifications to existing equipment, making it easy to promote and apply under existing production conditions.

[0064] In some embodiments, the polyphosphoric acid or its salt may include at least one selected from polyphosphoric acid, ammonium polyphosphoric acid, sodium pyrophosphate (dimer), sodium tripolyphosphate (trimer), potassium tetramethonium phosphate, sodium hexametaphosphate, potassium hexametaphosphate, sodium trimetaphosphate (cyclic trimer), and sodium tetramethonium phosphate (cyclic tetramer). The polyphosphoric acid is preferably tetrapolyphosphoric acid, with CAS number 8017-16-1 and a molecular weight of 337.93 Da.

[0065] In this application, polyphosphoric acid or its salts, through their unique long-chain molecular structure, can preferentially solve the problems of poor density and insufficient repair capacity of traditional phosphoric acid treatment layers. Unlike traditional small-molecule phosphoric acid, which can only form amorphous or microcrystalline loose layers, polyphosphoric acid or its salts have more coordination sites, enabling them to construct polyphosphoric acid-containing components with higher cross-linking degree and more stable structure with aluminum ions on the alumina surface. This allows for deep chemical cross-linking, greatly enhancing the density of the composite protective layer, effectively sealing the micropores of the oxide film, and cutting off the permeation channels of water molecules, thereby significantly improving hydration resistance. Moreover, polyphosphoric acid or its salts in solution with different chain lengths play a tiered repair role, with shorter-chain molecules able to penetrate deep into minute defects and pores for in-situ repair. This inside-out densification construction compensates for the defects of thin layers and insufficient mechanical strength in traditional processes, providing a robust inorganic framework support for the film layer on the electrode foil surface.

[0066] In some embodiments, the weight-average molecular weight of the organic polymer is ≥10000 g / mol, and may be 10000 g / mol to 100000 g / mol.

[0067] In this application, organic polymers utilize the steric hindrance effect of their long chains and the effects of specific functional groups to construct organic components with high adhesion and high toughness on an inorganic framework, solving the problems of poor stability and insufficient mechanical strength of the original protective layer. First, through electrostatic adsorption, the negatively charged groups such as sulfonate and carboxylate groups on the polymer chains generate a strong attraction with the weakly positively charged alumina surface, achieving initial anchoring of the polymer on the dielectric film surface and pore inlets. Second, hydrogen bonding can further tighten the interfacial bonding by combining the hydroxyl groups on the oxide film layer of the etched foil surface with the oxygen atoms in the polymer. More importantly, specific functional groups (such as phosphonic acid groups) can undergo exclusive adsorption with metal atoms (M atoms) to form stable internal complex salt chemical bonds. This chemical bonding ensures the long-term stability of the composite protective layer under harsh environments.

[0068] In some embodiments, the organic polymer containing sulfonic acid groups (-SO3H) can be polystyrene sulfonic acid, sulfonated polyether ether ketone, sulfonated polyimide, sulfonated lignin, acrylic acid-2-acrylamide-2-methylpropanesulfonic acid copolymer (containing sulfonic acid groups and carboxylic acid groups), maleic anhydride-acrylic acid-sulfonated styrene copolymer (containing sulfonic acid groups and carboxylic acid groups), etc.

[0069] In some embodiments, the organic polymer containing phosphonic acid groups (-OPO3H2) can be polyvinylphosphonic acid, phosphonopolycarboxylic acid (typically containing phosphonic acid groups and carboxylic acid groups), phosphonoacylcarboxylic acid copolymer (containing phosphonic acid groups and carboxylic acid groups), etc.

[0070] In some embodiments, the organic polymer containing phosphate groups (-PO3H2) can be polymethacryloyloxyethyl phosphate (polymer side chain with phosphate groups), phosphate-functionalized (meth)acrylic resin, cellulose phosphate, etc.

[0071] In some embodiments, the organic polymer containing a carboxylic acid group (-COOH) can be polyacrylic acid, polyitacrylic acid, polymaleic acid, sodium polyacrylate, or sodium alginate (a natural polycarboxylate).

[0072] In some embodiments, the organic polymer containing an amide group (-CONH2) can be polyacrylamide, protein (or polypeptide), etc.

[0073] In some embodiments, the organic polymer includes at least one of polystyrene sulfonic acid, polyvinylphosphonic acid, sodium alginate, sodium polyacrylate, polyacrylamide, and polyitacrylic acid.

[0074] In this application, polystyrene sulfonic acid (PSSA) is used as an example in the preparation of the electrode foil. The role of PSSA is as follows: The molecular structure of PSSA consists of a hydrophobic styrene backbone and hydrophilic sulfonic acid groups. In aqueous solution, the sulfonic acid groups of PSSA are completely ionized, generating a high density of negatively charged sulfonate ions and free H+ ions. + .

[0075] a) Adsorption and anchoring: The sulfonate groups on the PSSA chain are firmly anchored to the surface of the alumina film and the pore entrance through electrostatic adsorption and hydrogen bonding.

[0076] b) Film formation and steric hindrance effect: The long molecular chains of PSSA form an extremely thin but very dense organic polymer protective film (physical barrier) on the oxide film surface through mutual entanglement. With the help of steric hindrance effect, it plays the role of physical barrier, effectively blocking water molecules from contacting the internal alumina medium film, and inhibiting the occurrence of hydration reaction from the root.

[0077] c) Hydrogen bond competition mechanism: The sulfonic acid group in its molecule acts as a strong hydrogen bond acceptor, which can "steal" water molecules and combine with them to form hydrogen bonds, reducing the number of free water molecules that can be used to undergo hydration reaction with alumina, and further improving hydration resistance.

[0078] d) Changes in surface properties: The coating of polymer film can also change surface properties, reduce the surface energy of the oxide film, decrease its hydrophilicity and increase its hydrophobicity, making it less susceptible to water wetting.

[0079] e) Reduced defects and improved electrical performance: The excellent sealing properties of this protective film help reduce oxide film defects caused by hydration reactions, thereby reducing leakage current and improving electrical performance.

[0080] f) Synergistic enhancement: Polyphosphoric acid first forms a robust "inorganic framework", and then the organic polymer membrane of PSSA performs "flexible sealing". The combination of the two constructs a complete dual protection system.

[0081] In this application, taking polyvinylphosphonic acid (PVPA) as an example, the role of PVPA in the preparation process of the electrode foil is as follows: g) Extremely strong metal chelating ability: Phosphonic acid group (-PO3H2) has a strong affinity for Al. 3+ It has extremely strong coordination ability and can form very stable, hydrolysis-resistant complexes. The large number of phosphonic acid groups on the PVPA molecular chain will strongly chelate with aluminum ions on the alumina surface and in the rigid framework of "aluminum polyphosphate", forming a strong chemical bond, which enables it to be firmly attached to the alumina surface after polyphosphate treatment.

[0082] h) Good film-forming and adsorption properties: As a high molecular electrolyte, its molecular chains can spread on the oxide film to form a dense, continuous, network-like flexible organic component, which can effectively physically cover and block any micropores and cracks that may remain in the oxide film.

[0083] i) High hydrophilicity and ionic conductivity: Phosphonic acid groups are hydrophilic groups, but once they are chelated and crosslinked with metal ions, the resulting membrane can effectively block the penetration of water molecules.

[0084] j) Excellent hydrolytic stability: Due to the strong CP covalent bonds, PVPA is very stable in high temperature, acidic or alkaline aqueous solutions, and is not easily decomposed, providing long-term protection.

[0085] k) Synergistic enhancement: This forms a binary composite structure of "rigid aluminum polyphosphate skeleton + flexible PVPA chelate sealing layer". The rigid skeleton provides support, while the flexible sealing layer isolates corrosive media (especially water). The synergistic effect of the two can effectively improve the hydration resistance and corrosion protection.

[0086] In some embodiments, the immersion solution includes a first solution and a second solution, and the immersion treatment of the etched foil after the depolarization treatment with the immersion solution includes: A first soaking treatment is performed using a first solution, wherein the first solution comprises the polyphosphate or a salt thereof; A second immersion treatment is performed using a second solution, the second solution comprising an organic polymer.

[0087] In some embodiments, the depolarized etched foil can be first immersed in a first solution and then immersed in a second solution. Alternatively, the depolarized etched foil can be first immersed in a second solution and then immersed in the first solution. That is, the order of the two immersions is not limited.

[0088] In some embodiments, the solvent of the first solution includes water.

[0089] In some embodiments, the mass percentage of the polyphosphoric acid or its salt in the first solution is 0.5%-10% based on the total mass of the first solution. Optionally, the mass percentage of the polyphosphoric acid or its salt in the first solution can be any value from 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or a range of any two of the above values.

[0090] In some embodiments, when the target rated voltage of the electrode foil is ≤170V, the mass percentage of the polyphosphoric acid or its salt in the first solution is 3%-8%; optionally, the mass percentage of the polyphosphoric acid or its salt in the first solution can be any value from 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or a range of any two of the above values.

[0091] When the target rated voltage of the electrode foil is ≤170V, it is a low-voltage electrode foil.

[0092] In some embodiments, when the target rated voltage of the electrode foil is >170V, the mass percentage of the polyphosphoric acid or its salt in the first solution is 1%-5%; optionally, the mass percentage of the polyphosphoric acid or its salt in the first solution can be any value among 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range of any two of the above values.

[0093] When the target rated voltage of the electrode foil is >170V, it is a medium-high voltage electrode foil.

[0094] In some embodiments, the post-processing involves using a first solution to perform a first immersion treatment at a temperature of 40°C-75°C; for example, the first immersion treatment is performed at any value of 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, or 75°C, or a range consisting of any two of the above values.

[0095] In some embodiments, the first soaking time in the post-processing is 1 min to 10 min. Optionally, the first soaking time can be any value among 1 min, 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min, or a range of any two of the above values.

[0096] In some embodiments, when the target rated voltage of the electrode foil is ≤170V, the first immersion treatment time is 3min-10min; optionally, the first immersion treatment time can be any value among 3min, 3.5min, 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, 8min, 9min, and 10min, or a range of any two of the above values.

[0097] In some embodiments, when the target rated voltage of the electrode foil is >170V, the first immersion treatment time is 2min-10min; optionally, the first immersion treatment time can be any value among 2min, 2.5min, 3min, 3.5min, 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, 8min, 9min, and 10min, or a range of any two of the above values.

[0098] In some embodiments, the solvent of the second solution includes water.

[0099] In some embodiments, based on the total mass of the second solution, the mass percentage of the organic polymer in the second solution is 0.1%-10%; optionally, the mass percentage of the organic polymer in the second solution can be any value from 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10% or a range of any two of the above values.

[0100] In some embodiments, when the target rated voltage of the electrode foil is ≤170V, the mass percentage of the organic polymer in the second solution is 4%-8%; optionally, the mass percentage of the organic polymer in the second solution can be any value from 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or a range of any two of the above values.

[0101] In some embodiments, when the target rated voltage of the electrode foil is >170V, the mass percentage of the organic polymer in the second solution is 2%-6%; optionally, the mass percentage of the organic polymer in the second solution can be any value from 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6% or a range of any two of the above values.

[0102] In some embodiments, the post-processing involves using a second solution to perform a second immersion treatment at a temperature of 40°C-70°C; for example, the second solution may be used to perform the second immersion treatment at any value of 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, or 70°C, or a range consisting of any two of the above values.

[0103] In some embodiments, the second soaking time in the post-processing is 0.5 min to 8 min. Optionally, the second soaking time can be any value from 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, or a range of any two of the above values.

[0104] In some embodiments, when the target rated voltage of the electrode foil is ≤170V, the second immersion treatment time is 2min-8min; optionally, the second immersion treatment time can be any value among 2min, 2.5min, 3min, 3.5min, 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, 7.5min, and 8min, or a range of any two of the above values.

[0105] In some embodiments, when the target rated voltage of the electrode foil is >170V, the second immersion treatment time is 1min-8min; optionally, the second immersion treatment time can be any value among 1min, 1.5min, 2min, 2.5min, 3min, 4min, 4.5min, 5min, 5.5min, 6min, 6.5min, 7min, 7.5min, and 8min, or a range of any two of the above values.

[0106] In some embodiments, the second solution further includes a chelating agent. Thus, the chelating agent can be used synergistically with the organic polymer, utilizing its strong chelating ability to compensate for the polymer's shortcomings in this regard, thereby significantly enhancing the overall formulation system's blocking and stabilizing effect on metal ions such as aluminum ions.

[0107] In some embodiments, the chelating agent contains two or more coordinating atoms (such as oxygen, nitrogen, and phosphorus) that can provide lone pairs of electrons, thereby forming a stable chelate ring with the metal ion.

[0108] In some embodiments, the chelating agent contains two or more chelating groups, including one or more functional groups selected from phosphonic acid, carboxylic acid, hydroxyl, amino, and thiol groups.

[0109] In some embodiments, the chelating agent includes one or more of ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, and aminotrimethylene phosphonic acid.

[0110] In some embodiments, the mass ratio of the chelating agent to the organic polymer in the second solution is (1-5):10; optionally, the mass ratio of the chelating agent to the organic polymer in the second solution can be any one of 1:10, 2:10, 3:10, 4:10, 5:10 or a range of ratios between any two of the above ratios.

[0111] In some embodiments, the soaking solution further includes a third solution. The third solution may include an organic polymer and polyphosphate or a salt thereof.

[0112] In some embodiments, the third solution includes the first solution and the second solution.

[0113] In some embodiments, the content of each component in the third solution is the same as that in the first and second solutions.

[0114] In some embodiments, a third immersion treatment is performed using a third solution.

[0115] In this embodiment of the application, the depolarized etched foil may be first soaked in a first solution and then soaked in a second solution, or a third solution may be used for a third soaking treatment. This is beneficial for further filling or removing internal defects on the surface of the original etched foil, such as micropores and holes.

[0116] In some embodiments, the third immersion treatment is performed using a third solution at a temperature of 40°C-70°C. Optionally, the third immersion treatment is performed using a third solution at any value of 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, or 70°C, or a range consisting of any two of the above values. In some embodiments, the third soaking time is 0.5 min to 8 min. Optionally, the third soaking time is any value from 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, 4 min, 4.5 min, 5 min, 5.5 min, 6 min, 6.5 min, 7 min, 7.5 min, 8 min, or a range of any two of the above values.

[0117] In some embodiments, the post-processing in the preparation method further includes: a supplementary formation process.

[0118] In some embodiments, the temperature of each supplementary forming process is independently 60°C-90°C; alternatively, the temperature of each supplementary forming process can be any value among 60°C, 65°C, 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, and 90°C, or a range of any two of the above values.

[0119] In some embodiments, the current density of each of the reshaping processes is independently 20 mA / cm²-200 mA / cm²; optionally, it is 40 mA / cm²-120 mA / cm²; optionally, the current density of each of the reshaping processes can be any value among 20 mA / cm², 40 mA / cm², 50 mA / cm², 60 mA / cm², 80 mA / cm², 85 mA / cm², 90 mA / cm², 95 mA / cm², 100 mA / cm², 105 mA / cm², 110 mA / cm², 115 mA / cm², 120 mA / cm², 160 mA / cm², 180 mA / cm², and 200 mA / cm², or a range of any two of the above values.

[0120] In some embodiments, the voltage of each of the supplementary forming processes is independently 1.02-1.2 times the target rated voltage; optionally, it is a pulse voltage; optionally, the voltage of each of the supplementary forming processes can be any value among 1.02 times, 1.05 times, and 1.2 times the target rated voltage, or a range of any two of the above values.

[0121] In some embodiments, the time for each supplementary formation process is independently 0.5 min to 10 min. Optionally, the time for each supplementary formation process can be any value from 0.5 min, 1 min, 1.2 min, 1.4 min, 1.6 min, 1.8 min, 2 min, 2.2 min, 2.4 min, 2.6 min, 2.8 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, or a range of any two of the above values.

[0122] In some embodiments, the solute in the replenishing solution used in each replenishing process independently includes one or more of ammonium dihydrogen phosphate, boric acid, and ammonium pentaborate.

[0123] In some embodiments, the solvent of the repair solution used in each repair process is water, independently.

[0124] In some embodiments, based on the total mass of the supplementary formation solution used in the supplementary formation process, the mass percentage of solute in the supplementary formation solution used in each supplementary formation process is independently 0.5%-10%; optionally, the mass percentage of solute in the supplementary formation solution used in each supplementary formation process can be any value from 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range of any two of the above values.

[0125] In some embodiments, the post-processing in the preparation method further includes heat treatment.

[0126] In some embodiments, after the second immersion treatment with the second solution, no rinsing is required before the heat treatment, in order to increase the amount of polyphosphate or its salts and / or organic polymers adhering.

[0127] In some embodiments, the temperature of each heat treatment is independently between 150°C and 380°C, and further optionally between 280°C and 350°C; optionally, the temperature of each heat treatment can be any value or a range of any two of the above values ​​from 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, and 380°C.

[0128] In some embodiments, the duration of each heat treatment is independently 2 min to 20 min, and more preferably 3 min to 5 min. Optionally, the duration of each heat treatment can be any value from 2 min, 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, or a range of any two of the above values.

[0129] In some embodiments, the formation process includes at least primary formation and secondary formation; optionally, the formation process includes at least primary formation, secondary formation and tertiary formation; optionally, the formation process includes at least primary formation, secondary formation, tertiary formation and quaternary formation; optionally, the formation process includes at least primary formation, secondary formation, tertiary formation, quaternary formation and quinary formation; optionally, the formation process includes at least primary formation, secondary formation, tertiary formation, quaternary formation and quinary formation; optionally, the formation process includes at least primary formation, secondary formation, tertiary formation, quaternary formation and quinary formation.

[0130] In some embodiments, the formation solution for each of the formation processes independently comprises an aqueous solution of ammonium adipate with a mass percentage of 215wt%-15wt%.

[0131] In some embodiments, the temperature of each of the formation processes is independently between 50°C and 90°C.

[0132] In some embodiments, the time for each of the formation processes is independently 2 min to 10 min.

[0133] In some embodiments, the current density in each of the formation processes is independently 50 mA / cm²-200 mA / cm².

[0134] In some embodiments, the voltage of each stage of the formation process is greater than the voltage of the previous stage of the formation process, and the voltage of the last stage of the formation process is 85%-100% of the rated voltage.

[0135] In some embodiments, the depolarization process includes: heat treatment in depolarization, phosphoric acid treatment in depolarization, and regeneration treatment in depolarization.

[0136] In some embodiments, the temperature of each heat treatment in the depolarization is independently 400°C-550°C, the time of each heat treatment in the depolarization is independently 0.5 min-10 min, and the heat treatment in the depolarization is performed at least once.

[0137] In some embodiments, the temperature of each phosphoric acid treatment in the depolarization is independently 40°C-85°C, the time of each phosphoric acid treatment in the depolarization is independently 0.5 min-10 min, the phosphoric acid treatment in the depolarization is performed at least once, and the solution used in each phosphoric acid treatment in the depolarization is independently a phosphoric acid solution, optionally an aqueous solution of phosphoric acid.

[0138] In some embodiments, the temperature of each re-formation treatment in the depolarization process is independently between 60°C and 90°C, and the time of each re-formation treatment in the depolarization process is independently between 0.5 min and 10 min, and the re-formation treatment in the depolarization process is performed at least once. The re-formation treatment in the depolarization process is typically performed after heat treatment in the depolarization process and / or heat treatment with phosphoric acid in the depolarization process.

[0139] In some embodiments, the polyphosphoric acid or its salt may be added to the phosphoric acid treatment solution used in depolarization, wherein the mass percentage of the added polyphosphoric acid or its salt is 0.2wt%-2wt% based on the total mass of the phosphoric acid treatment solution used in depolarization.

[0140] In some embodiments, the polyphosphate or its salt is added to the solution used in the replenishment treatment during depolarization, and the mass percentage of the added polyphosphate or its salt is 0.2 wt% to 5 wt% based on the total mass of the solution used in the replenishment treatment during depolarization. This improves the efficiency of the replenishment treatment.

[0141] Electrode foil This application provides an electrode foil, which is prepared using the above-described preparation method.

[0142] In some embodiments, the substrate includes a composite protective layer disposed on at least one side of the substrate.

[0143] Figure 1 A schematic diagram showing the cross-section of the electrode foil according to an embodiment of this application is provided. Figure 1 As shown, the electrode foil 100 includes a substrate 10 and a composite protective layer 20, the composite protective layer 20 including an organic polymer product 21 and a polyphosphate or its salt product 22.

[0144] In some embodiments, the substrate material is the same as the etched foil. The composite protective layer is obtained through the above-described formation treatment, depolarization treatment, and post-treatment. Generally, when the substrate is aluminum, the composition of the composite protective layer may include AlPO4, alumina, etc. In the embodiments of this application, the composite protective layer includes the above-described organic polymer and polyphosphate or its salt.

[0145] According to the embodiments of this application, the formed composite protective layer can effectively isolate water molecules. The inorganic components of polyphosphate or its salts improve the robustness of the composite protective layer, and the organic components of the organic polymer further improve the density and sealing of the composite protective layer, thus constructing a dual waterproof mechanism. This can more effectively inhibit the penetration of water molecules and the occurrence of hydration reactions, and significantly improve the hydration resistance of the electrode foil.

[0146] According to the embodiments of this application, the polyphosphate group forming the "backbone" possesses excellent thermal stability, enabling it to withstand the high-temperature environment in subsequent processes and ensuring that the entire electrode foil maintains good performance under different temperature conditions. The composite protective layer has a higher glass transition temperature and thermal stability, maintaining structural integrity even at higher temperatures, thus providing excellent high-temperature hydration resistance and broadening the application temperature range of aluminum electrolytic capacitors.

[0147] The electrode foil provided in this application, while maintaining stable electrode foil capacity, has a more complete and defect-free composite protective layer on its surface, which is expected to significantly reduce the leakage current of the foil, thereby improving the electrical performance of the electrolytic capacitor and ensuring its stable and reliable operation.

[0148] Furthermore, taking aluminum corrosion foil as an example, the phosphate groups in polyphosphates and the sulfonate groups in polystyrene sulfonic acid (PSSA) can interact together with the alumina surface on the corrosion foil to form a protective film with a higher degree of cross-linking and a more complex network structure. Its comprehensive performance is superior to the effect achieved by any single reagent treatment.

[0149] There are no particular restrictions on the type of material used for the electrode foil substrate; the substrate material can be a metal with a valve function.

[0150] Valve-acting metals refer to a class of metals capable of forming a dense oxide film with unidirectional electrical conductivity. Based on the concept of composite protective layers formed by chemical transformations such as immersion treatment and re-forming treatment, any one or more metals such as aluminum (Al), tantalum (Ta), and niobium (Nb), or alloys containing any of these metals, can be used.

[0151] In some embodiments, the substrate of the electrode foil may be aluminum or the like. The thickness of the electrode foil is not particularly limited, for example, it may be 15 μm or more and 300 μm or less.

[0152] In some embodiments, the electrode foil may be a low-voltage electrode foil, such as an electrode foil with a target rated voltage ≤170V. For example, the target withstand voltage of the electrode foil may be 35V, 50V, 80V, 100V, 150V, 170V, etc.

[0153] In some embodiments, the electrode foil may be a medium- or high-voltage electrode foil, such as an electrode foil with a target rated voltage > 170V. For example, the target withstand voltage of the electrode foil may be 180V, 200V, 250V, 280V, 350V, 400V, 450V, 480V, 500V, 600V, etc.

[0154] Electrolytic capacitors This application provides an electrolytic capacitor, which includes an electrode foil prepared by the above-described preparation method or the electrode foil described above.

[0155] In some embodiments, the electrolytic capacitor may be an aluminum electrolytic capacitor or the like.

[0156] In some embodiments, the electrolytic capacitor includes a core and an electrolyte, the core being formed by winding an anode foil, a cathode foil, and electrolytic paper disposed between the anode foil and the cathode foil.

[0157] The anode foil can be the aforementioned electrode foil, thereby enabling the production of electrolytic capacitors with high capacity and high reliability.

[0158] In some embodiments, the electrolytic capacitor may further include a lead member connected to the anode foil. In this case, the anode foil and the lead member can be connected by a riveting joint. The cathode foil may be a metal foil containing valve-acting metals such as Al, Ta, and Nb.

[0159] As needed, the surface of the metal foil can be roughened by etching. That is, the cathode foil can be a metal foil with a porous portion and a core continuous with the porous portion. For example, an etched metal foil similar to that of the anode foil can be used (without formation or only low-pressure formation).

[0160] There are no particular restrictions on the electrolytic paper; for example, nonwoven fabrics containing fibers such as cellulose, polyethylene terephthalate, vinylon, and polyamides (e.g., aliphatic polyamides, aromatic polyamides, etc.) can be used. The electrolyte contains an electrolyte solution. The electrolyte solution is in direct contact with the composite protective layer or in contact with it through a conductive polymer.

[0161] In some embodiments, the electrolyte may contain an acidic component (anion) and a basic component (cation). A salt (solute) may be formed from the acidic and basic components.

[0162] The electrolyte contains a non-aqueous solvent and ionic substances dissolved therein, i.e., solutes, such as organic salts. The non-aqueous solvent can be an organic solvent or an ionic liquid. A high-boiling-point solvent is preferred. Examples include polyols such as ethylene glycol, sulfones such as sulfolane, lactones such as γ-butyrolactone, esters such as methyl acetate, carbonates such as propylene carbonate, ethers such as 1,4-dioxane, and ketones such as methyl ethyl ketone. An organic salt is a salt in which at least one of the anion and cation contains an organic compound. Examples of organic salts include trimethylamine maleate, triethylamine borosalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazoline phthalate, and mono-1,3-dimethyl-2-ethylimidazoline phthalate.

[0163] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0164] Example 1 This application provides a method for preparing an electrode foil, the method comprising: formation treatment, depolarization treatment, and post-treatment. The target rated voltage of the electrode foil is 115Vf, specifically: S01, Formation Treatment: A 120μm thick etched foil was placed in an ammonium adipate solution and subjected to primary, secondary, tertiary, quaternary, and quinary formation processes sequentially. Each formation process consisted independently of an ammonium adipate aqueous solution with a mass percentage of 12wt%. The temperature for each formation process was 70℃, and the time for each formation process was 6min. The current density for each formation process was 100mA / cm², and the voltage for each formation process was 20%, 40%, 60%, 80%, and 100% of its target rated voltage of 115Vf, respectively. That is, the primary formation voltage was 23V, the secondary formation voltage was 46V, the tertiary formation voltage was 69V, the quaternary formation voltage was 92V, and the quinary formation voltage was 115V.

[0165] S02, Depolarization treatment: Phosphoric acid treatment in depolarization 1: After cleaning the aluminum foil obtained by the above formation treatment steps, immerse it in a 3 wt% phosphoric acid aqueous solution at 55°C for 5 min.

[0166] The re-forming treatment in depolarization 1: After cleaning, the aluminum foil is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 85℃ for 2 min, a current density of 100 mA / cm², and a re-forming voltage of 118 V.

[0167] Heat treatment during depolarization: After cleaning, the aluminum foil is heat-treated at 520℃ for 2 minutes.

[0168] Phosphoric acid treatment 2 in depolarization: The heat-treated aluminum foil was immersed in a 1 wt% phosphoric acid aqueous solution at 65°C for 3 min.

[0169] Re-forming treatment 2 in depolarization: After cleaning, the aluminum foil is placed in a 2wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 85℃ for 2 minutes, a current density of 100mA / cm², and a re-forming voltage of 118V.

[0170] S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for first immersion treatment at a temperature of 65℃ for 4 minutes. The first solution is a 3wt% sodium tripolyphosphate solution with water as the solvent.

[0171] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 85℃ for 2 minutes, a current density of 100mA / cm², and a re-forming voltage of 118V.

[0172] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 55°C for 5 minutes. The second solution is a solution of 3 wt% polyvinylphosphonic acid and 0.6 wt% hydroxyethylidene diphosphonic acid, with water as the solvent.

[0173] Post-processing heat treatment: The aluminum foil is heat treated at a temperature of 280°C for 5 minutes to obtain the electrode foil.

[0174] Example 2 Compared with Example 1, the difference lies in the post-processing technology, specifically: S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 75°C for 3 minutes. The first solution is a solution of 2 wt% potassium hexametaphosphate and 4 wt% polyphosphoric acid, and the solvent is water.

[0175] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 65℃ for 5 min, a current density of 100 mA / cm², and a re-forming voltage of 118 V.

[0176] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 55°C for 5 minutes. The second solution is a polystyrene sulfonic acid solution with a mass percentage of 0.5 wt% and water as the solvent.

[0177] Post-processing heat treatment: The aluminum foil is heat treated at 380°C for 2 minutes to obtain the electrode foil.

[0178] Example 3 Compared with Example 1, the difference lies in the post-processing technology, specifically: S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for first immersion treatment at a temperature of 40℃ for 8 minutes. The first solution is a 4 wt% potassium tetramethod phosphate solution with water as the solvent.

[0179] Post-processing re-forming treatment: After cleaning, the aluminum foil was placed in an aqueous solution of 0.5 wt% sodium tripolyphosphate and 2 wt% ammonium dihydrogen phosphate for re-forming treatment at 85°C for 4 min, with a current density of 100 mA / cm² and a re-forming voltage of 118 V. Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 70°C for 5 minutes. The second solution is a solution of sodium alginate (4 wt%) and aminotrimethylenephosphonic acid (1 wt%), with water as the solvent.

[0180] Post-processing heat treatment: The aluminum foil is heat treated at a temperature of 280°C for 5 minutes to obtain the electrode foil.

[0181] Example 4 Compared with Example 1, the difference lies in the post-processing technology, specifically: S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for first immersion treatment at a temperature of 65℃ for 4 minutes. The first solution is a 3wt% sodium tripolyphosphate solution with water as the solvent.

[0182] Post-processing re-forming treatment: After cleaning, the aluminum foil was placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at 85℃ for 2 min, with a current density of 100 mA / cm² and a re-forming voltage of 118 V. Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 55°C for 5 minutes. The second solution is a 3 wt% polyvinylphosphonic acid solution with water as the solvent.

[0183] Post-processing heat treatment: The aluminum foil is heat treated at a temperature of 280°C for 5 minutes to obtain the electrode foil.

[0184] Example 5 Compared with Example 1, the difference lies in the post-processing technology, specifically: S03, Post-processing: Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 55°C for 5 minutes. The second solution is a polystyrene sulfonic acid solution with a mass percentage of 0.5 wt% and water as the solvent.

[0185] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 65℃ for 5 min, a current density of 100 mA / cm², and a re-forming voltage of 118 V.

[0186] First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 75°C for 3 minutes. The first solution is a solution of 2 wt% potassium hexametaphosphate and 4 wt% polyphosphoric acid, and the solvent is water.

[0187] Post-processing heat treatment: The aluminum foil is heat treated at 380°C for 2 minutes to obtain the electrode foil.

[0188] Example 6 Compared with Example 1, the difference lies in the post-processing technology, specifically: S03, Post-processing: The first immersion treatment and the second immersion treatment are combined: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 70°C for 5 minutes. The first solution is a solution of potassium hexametaphosphate (2 wt%), tetrapolyphosphoric acid (4 wt%), and polystyrene sulfonic acid (0.5 wt%), with water as the solvent.

[0189] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 65℃ for 5 min, a current density of 100 mA / cm², and a re-forming voltage of 118 V.

[0190] Post-processing heat treatment: The aluminum foil is heat treated at 380°C for 2 minutes to obtain the electrode foil.

[0191] Example 7 Compared with Example 1, the difference lies in the post-processing, which does not include a heat treatment step. The specific steps are as follows: S03, Post-processing: First immersion treatment: The cleaned aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 65°C for 4 minutes. The first solution is a 3 wt% sodium tripolyphosphate solution with water as the solvent.

[0192] Post-processing re-forming treatment: The cleaned aluminum foil was placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 85℃ for 2 minutes, a current density of 100 mA / cm², and a re-forming voltage of 118 V. Second immersion treatment: The cleaned aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 55°C for 5 minutes. The second solution is a solution of 3 wt% polyvinylphosphonic acid and 0.6 wt% hydroxyethylidene diphosphonic acid, and the solvent is water.

[0193] The aluminum foil is dried naturally to obtain the electrode foil.

[0194] Example 8 Compared with Example 1, the difference lies in the shortened preparation process of depolarization treatment and post-treatment, as follows: S01, Formation Treatment: A 120μm thick etched foil was placed in an ammonium adipate solution and subjected to primary, secondary, tertiary, quaternary, and quinary formation processes sequentially. Each formation process consisted independently of an ammonium adipate aqueous solution with a mass percentage of 12wt%. The temperature for each formation process was 70℃, the time for each formation process was 6min, the current density for each formation process was 100mA / cm², and the voltage for each formation process was 20%, 40%, 60%, 80%, and 100% of its target rated voltage of 115Vf, respectively. That is, the primary formation voltage was 23V, the secondary formation voltage was 46V, the tertiary formation voltage was 69V, the quaternary formation voltage was 92V, and the quinary formation voltage was 115V.

[0195] S02, depolarization treatment and post-processing: Phosphoric acid treatment 1: After cleaning, the aluminum foil is immersed in a mixture of 1 wt% sodium tripolyphosphate, 0.5 wt% ammonium polyphosphate and 3 wt% phosphoric acid. The solvent is water, the temperature is 55℃ and the time is 5 min.

[0196] Repair treatment 1: After cleaning, the aluminum foil is placed in an aqueous solution of 0.5 wt% tetrapolyphosphoric acid and 2 wt% ammonium dihydrogen phosphate for repair treatment at a temperature of 85℃ for 2 min, a current density of 100 mA / cm², and a repair voltage of 118 V.

[0197] Heat treatment: After cleaning, the aluminum foil is heat treated at 520℃ for 2 minutes.

[0198] Phosphoric acid treatment 2: The heat-treated aluminum foil was immersed in a solution of 1 wt% sodium tripolyphosphate, 0.5 wt% ammonium polyphosphate and 3 wt% phosphoric acid. The solvent was water, the temperature was 65℃ and the time was 3 min.

[0199] Repair treatment 2: After cleaning, the aluminum foil is placed in a mixed aqueous solution of 0.7 wt% polyvinylphosphonic acid and 2 wt% ammonium dihydrogen phosphate for repair treatment at a temperature of 85 ℃ for 2 min, a current density of 100 mA / cm², and a repair voltage of 118 V.

[0200] The aluminum foil is cleaned and dried to obtain the electrode foil.

[0201] Comparative Example 1 Compared with Example 1, there are only steps S01 and S02, but no step S03, that is, there is no post-processing, as detailed below: S01, Formation Treatment: A 120μm thick etched foil was placed in an ammonium adipate solution and subjected to primary, secondary, tertiary, quaternary, and quinary formation processes sequentially. Each formation process consisted independently of an aqueous solution of 12wt% ammonium adipate, a temperature of 70℃, and a time of 6 min. The current density was 100 mA / cm², and the voltage was 20%, 40%, 60%, 80%, and 100% of the target rated voltage of 115Vf, respectively. Specifically, the primary formation voltage was 23V, the secondary formation voltage was 46V, the tertiary formation voltage was 69V, the quaternary formation voltage was 92V, and the quinary formation voltage was 115V.

[0202] S02, Depolarization treatment: Phosphoric acid treatment in depolarization 1: After cleaning the aluminum foil obtained by the above formation treatment steps, immerse it in a 3 wt% phosphoric acid aqueous solution at 55°C for 5 min.

[0203] Re-forming treatment 1 in depolarization: After cleaning, the aluminum foil was placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at 85℃ for 2 min, with a current density of 100 mA / cm² and a re-forming voltage of 118 V. Heat treatment during depolarization: After cleaning, the aluminum foil is heat-treated at 520℃ for 2 minutes.

[0204] Phosphoric acid treatment 2 in depolarization: The heat-treated aluminum foil was immersed in a 1 wt% phosphoric acid aqueous solution at 65°C for 3 min.

[0205] The second step in depolarization is to clean the aluminum foil and place it in a 2 wt% ammonium dihydrogen phosphate aqueous solution for a replenishment treatment at a temperature of 85°C for 2 min, a current density of 100 mA / cm², and a replenishment voltage of 118 V. After cleaning and drying, the electrode foil is obtained.

[0206] Comparative Example 2 Compared with Example 1, only steps S01 and S02 are present, and the intensity of treatment with phosphoric acid and ammonium dihydrogen phosphate is enhanced. Step S03 is absent, as detailed below: S01, Formation Treatment: A 120μm thick etched foil was placed in an ammonium adipate solution and subjected to primary, secondary, tertiary, quaternary, and quinary formation processes sequentially. Each formation process consisted independently of an ammonium adipate aqueous solution with a mass percentage of 12wt%. The temperature for each formation process was 70℃, and the time for each formation process was 6min. The current density for each formation process was 100mA / cm², and the voltage for each formation process was 20%, 40%, 60%, 80%, and 100% of its target rated voltage of 115Vf, respectively. That is, the primary formation voltage was 23V, the secondary formation voltage was 46V, the tertiary formation voltage was 69V, the quaternary formation voltage was 92V, and the quinary formation voltage was 115V.

[0207] S02, Depolarization treatment: Phosphoric acid treatment in depolarization 1: After cleaning the aluminum foil obtained by the above formation treatment steps, immerse it in a 9 wt% phosphoric acid aqueous solution at a temperature of 65°C for 5 min.

[0208] Re-forming treatment 1 in depolarization: After cleaning, the aluminum foil is placed in a 5 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at 85℃ for 2 min, with a current density of 100 mA / cm² and a re-forming voltage of 118 V. Heat treatment during depolarization: After cleaning, the aluminum foil is heat-treated at 520℃ for 2 minutes.

[0209] Phosphoric acid treatment 2 in depolarization: The heat-treated aluminum foil was immersed in a 9 wt% phosphoric acid aqueous solution at 65°C for 3 min.

[0210] The second step in depolarization is to clean the aluminum foil and place it in a 5 wt% ammonium dihydrogen phosphate aqueous solution for a replenishment treatment at a temperature of 85°C for 2 min, a current density of 100 mA / cm², and a replenishment voltage of 118 V. After cleaning and drying, the electrode foil is obtained.

[0211] Comparative Example 3 Compared with Example 1, steps S01 and S02 are the same, but step S03 is modified by soaking only in polyphosphate, as follows: S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for first immersion treatment at a temperature of 65℃ for 4 minutes. The first solution is a 3wt% sodium tripolyphosphate solution with water as the solvent.

[0212] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 85℃ for 2 minutes, a current density of 100mA / cm², and a re-forming voltage of 118V.

[0213] Post-processing heat treatment: After cleaning, the aluminum foil is heat treated at 280℃ for 5 minutes to obtain the electrode foil.

[0214] Comparative Example 4 Compared with Example 1, steps S01 and S02 are the same, but step S03 is modified by soaking only with organic polymer and chelating agent, as follows: S03, Post-processing: Second immersion treatment: After cleaning, the aluminum foil is immersed in the second solution at a temperature of 55°C for 5 minutes. The second solution is a solution of polyvinylphosphonic acid (3 wt%) and hydroxyethylidene diphosphonic acid (0.6 wt%), with water as the solvent.

[0215] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 85℃ for 2 minutes, a current density of 100mA / cm², and a re-forming voltage of 118V.

[0216] Post-processing heat treatment: The aluminum foil is heat treated at 280℃ for 5 minutes to obtain the electrode foil.

[0217] Test Example 1: Performance Testing 1. Electrode foil performance testing The electrode foils prepared in the above embodiments and comparative examples were tested respectively, and the test data are detailed in Table 1.

[0218] (1) Testing of specific capacitance Cap, withstand voltage Vt, hydration resistance Tr60, flexural strength and tensile strength: The tests are conducted in accordance with the SJ / T11140-2022 standard "Electrode foil for aluminum electrolytic capacitors". Withstand voltage refers to the voltage value maintained after 180s from the start of the voltage rise time. If the flexural strength and tensile strength of the electrode foil are high, the material has a stronger ability to resist damage (such as cracking) under the same winding conditions, and therefore it is not easy for cracks to occur, which helps to improve the overall reliability of the capacitor. (2) Leakage current detection: The withstand voltage test was completed according to the SJ / T 11140-2022 standard "Electrode Foil for Aluminum Electrolytic Capacitors". Then, in the same test solution as the withstand voltage test, the test current was set (1mA for low voltage foil and 2mA for high voltage foil), and the test voltage was 90%Vf. After continuous voltage application for 10 minutes, the current value measured at this time is the leakage current value of the sample.

[0219] Table 1

[0220] As can be seen from the above test results, the first solution and the second solution used in this application for soaking include organic polymers and polyphosphate or its salts, which makes the electrode foil prepared in the example have a high specific capacity, and Tr60 is ≤18s, indicating excellent hydration resistance. Compared to Comparative Example 1, which did not use the first and second solutions (i.e., omitted the SO3 step), the prepared electrode foil had a Tr60 of 50s, indicating poor hydration resistance. Comparative Example 2 required a higher phosphorus content in the entire processing solution to achieve better hydration resistance, but the specific volume was only 8.412 μF·cm⁻¹. -2 The specific volume decays severely, and the high phosphorus content in the bath solution leads to a shortened service life of the bath solution, electrode plates, rollers, etc., increasing the cost of wastewater treatment.

[0221] Compared to Comparative Examples 3 and 4, none of them used solutions of organic polymer and polyphosphate or its salts for soaking. In Comparative Example 3, only polyphosphate was used for soaking, and no organic polymer was used. The Tr60 of the prepared electrode foil was 45s, indicating poor hydration resistance. In Comparative Example 4, only organic polymer and chelating agent were used for soaking, and no polyphosphate was used. The Tr60 of the prepared electrode foil was 33s, indicating relatively poor hydration resistance compared to the examples.

[0222] In summary, the electrode foil preparation method of this application can improve the overall quality of the electrode foil oxide film: increase specific capacitance, reduce leakage current, and enhance hydration resistance.

[0223] 2. Performance testing of capacitors containing electrode foil The electrode foils prepared in Example 1 and Comparative Examples 1-4 of this application were used to prepare capacitors of the same specifications: rated voltage 63V, dimensions Φ10mm x L20mm, and capacitance approximately 220μF. All prepared capacitors were subjected to the rated voltage at 105℃ for 2000h, and then measured after the capacitors returned to 20℃. The data are shown in Table 2.

[0224] Table 2

[0225] Note: Cs is capacitance; ESR is equivalent series resistance; I LC This represents the leakage current. Where ΔCs / Cs = [(initial capacity value - capacity measurement value after 2000 hours of load) / initial capacity] × 100%.

[0226] Table 2 shows that the initial values ​​of the capacitors fabricated from the electrode foils prepared in Example 1 and Comparative Examples 1 to 4 are relatively similar. However, after a load life test at 105°C for 2000 hours, the equivalent series resistance (ESR) and leakage current (IL) of the capacitors fabricated from the electrode foils prepared in Comparative Examples 1 to 4 significantly increased. LC The increase was significant, but the capacity decrease rate was higher than that of Example 1. The capacitor prepared by the electrode foil of Example 1 has better stability.

[0227] The electrode foil preparation method provided in this application can be used to prepare low-voltage electrode foil (target rated voltage ≤170V), as detailed in Examples 1-11.

[0228] Example 9 This application provides a method for preparing an electrode foil, the method comprising: formation treatment, depolarization treatment, and post-treatment. The target rated voltage of the electrode foil is 27Vf, specifically: S01, Formation Treatment: A 120 μm thick etched foil was placed in an ammonium adipate solution and subjected to primary, secondary, and tertiary formation treatments sequentially. Each formation treatment solution independently consisted of an ammonium adipate aqueous solution with a mass percentage of 15 wt%. The temperature for each formation treatment was independently 60 °C, the time for each formation treatment was independently 5 min, the current density for each formation treatment was independently 40 mA / cm², and the voltage for each formation treatment was independently 30%, 60%, and 100% of its target rated voltage of 27 Vf, respectively. That is, the primary formation voltage was 8.1 V, the secondary formation voltage was 16.2 V, and the tertiary formation voltage was 27 V.

[0229] S02, Depolarization treatment: Phosphoric acid treatment in depolarization: After cleaning the aluminum foil obtained by the above formation process, it is immersed in a 0.5 wt% phosphoric acid aqueous solution at 45°C for 4 min.

[0230] Re-forming treatment 1 in depolarization: After cleaning, the aluminum foil is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at 60℃ for 2 min and a current density of 40 mA / cm². 2 The voltage for the supplementary forming is 28V.

[0231] Heat treatment during depolarization: After cleaning, the aluminum foil is heat-treated at 430℃ for 10 minutes.

[0232] Re-forming treatment 2 in depolarization: The heat-treated aluminum foil was placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at 65°C for 2 min and a current density of 40 mA / cm². 2 The voltage for the supplementary forming is 28V.

[0233] S0, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 50°C for 7 minutes. The first solution is a solution of sodium trimetaphosphate (0.5 wt%) and polyphosphoric acid (2.5 wt%), with water as the solvent.

[0234] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 60°C for 1 minute. The second solution is a polystyrene sulfonic acid solution with a mass percentage of 0.5 wt% and water as the solvent.

[0235] The aluminum foil was heat-treated at 150°C for 20 minutes to obtain the electrode foil.

[0236] Example 10 This application provides a method for preparing an electrode foil, the method comprising: formation treatment, depolarization treatment, and post-treatment. The target rated voltage of the electrode foil is 73Vf, specifically: S01, Formation Treatment: A 120 μm thick etched foil was placed in an ammonium adipate solution and subjected to primary, secondary, tertiary, and quaternary formation processes sequentially. Each formation process consisted independently of an ammonium adipate aqueous solution with a mass percentage of 10 wt%. The temperature for each formation process was 85 °C, the time for each formation process was 7 min, the current density for each formation process was 50 mA / cm², and the voltage for each formation process was 20%, 50%, 80%, and 100% of its target rated voltage of 73 Vf, respectively. That is, the primary formation voltage was 14.6 V, the secondary formation voltage was 36.5 V, the tertiary formation voltage was 58.4 V, and the quaternary formation voltage was 73 V.

[0237] S02, Depolarization treatment: Phosphoric acid treatment 1 in depolarization: After cleaning the aluminum foil obtained by the above formation treatment steps, immerse it in a 1.6 wt% phosphoric acid aqueous solution at a temperature of 85°C for 0.5 min.

[0238] Heat treatment during depolarization: After cleaning, the aluminum foil is heat-treated at 480℃ for 5 minutes.

[0239] Phosphoric acid treatment 2 in depolarization: The heat-treated aluminum foil was immersed in a 1.6 wt% phosphoric acid aqueous solution at 65°C for 3 min.

[0240] Re-forming treatment in depolarization: After cleaning, the aluminum foil was placed in a 1 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at 70℃ for 5 min and a current density of 50 mA / cm². 2 The voltage for the supplementary forming is 75V.

[0241] S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 60°C for 4 minutes. The first solution is a 3 wt% sodium tripolyphosphate solution with water as the solvent.

[0242] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 65°C for 0.5 min. The second solution is a 5 wt% sodium polyacrylate solution with water as the solvent.

[0243] The aluminum foil is dried naturally to obtain the electrode foil.

[0244] Example 11 This application provides a method for preparing an electrode foil, the method comprising: formation treatment, depolarization treatment, and post-treatment. The target rated voltage of the electrode foil is 132Vf, specifically: S01, Formation Treatment: A 120μm thick etched foil was placed in an ammonium azelaate solution and subjected to sequential primary, secondary, tertiary, quaternary, and quinary formation processes. Each formation process consisted independently of an ammonium azelaate aqueous solution with a mass percentage of 10wt%. The temperature for each formation process was 70℃, the time for each formation process was 5 min, the current density for each formation process was 100 mA / cm², and the voltage for each formation process was 20%, 40%, 60%, 80%, and 100% of its target rated voltage of 132Vf, respectively. That is, the primary formation voltage was 26.4V, the secondary formation voltage was 52.8V, the tertiary formation voltage was 79.2V, the quaternary formation voltage was 105.6V, and the quinary formation voltage was 132V.

[0245] S02, Depolarization treatment: Phosphoric acid treatment in depolarization 1: After cleaning the aluminum foil obtained by the above formation treatment steps, immerse it in a 5 wt% phosphoric acid aqueous solution at 70°C for 2 min.

[0246] The re-forming treatment in depolarization 1: After cleaning, the aluminum foil is placed in a 2wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 75℃ for 2 minutes, a current density of 100mA / cm², and a re-forming voltage of 135V.

[0247] Heat treatment 1 in depolarization: After cleaning the aluminum foil, heat treatment is performed at a temperature of 520℃ for 2 minutes.

[0248] Phosphoric acid treatment 2 in depolarization: The heat-treated aluminum foil was immersed in a 5 wt% phosphoric acid aqueous solution at 65°C for 2 min.

[0249] Heat treatment 2 in depolarization: After cleaning the aluminum foil, heat treatment is performed at a temperature of 400℃ for 3 minutes.

[0250] Re-forming treatment 2 in depolarization: The heat-treated aluminum foil was placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 75°C for 2 min, a current density of 100 mA / cm², and a re-forming voltage of 135 V.

[0251] S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is immersed in the first solution at a temperature of 65°C for 3 minutes. The first solution is a 5 wt% sodium hexametaphosphate solution with water as the solvent.

[0252] Post-processing re-forming treatment: After cleaning, the aluminum foil is placed in a 2 wt% ammonium dihydrogen phosphate aqueous solution for re-forming treatment at a temperature of 75℃ for 2 min, a current density of 100 mA / cm², and a re-forming voltage of 135 V.

[0253] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 70°C for a time of 0.5 min. The second solution is a 3 wt% polyacrylamide solution with water as the solvent.

[0254] Post-processing heat treatment: The aluminum foil is heat treated at 350°C for 5 minutes to obtain the electrode foil.

[0255] The electrode foil preparation method provided in this application can also be used for the preparation of medium and high voltage electrode foils (target rated voltage > 170V), as detailed in Examples 12-13.

[0256] Example 12 This application provides a method for preparing an electrode foil, the method comprising: formation treatment, depolarization treatment, and post-treatment. The target rated voltage of the electrode foil is 500Vf, specifically: S01, Formation Treatment: A 120μm thick etched foil was boiled in water for 10 minutes and then placed in a mixture of boric acid and ammonium pentaborate for sequential primary, secondary, tertiary, quaternary, quinary, sixth, and seventh-stage formation treatments. Each formation treatment independently consisted of 10 wt% boric acid and 0.15 wt% ammonium pentaborate aqueous solution. The temperature and time for each formation treatment were independently set at 85℃ and 10 minutes, respectively. n, the current density in each formation process is 150mA / cm², and the voltage in each formation process is 5%, 10%, 20%, 40%, 60%, 80%, and 100% of the target rated voltage of 500Vf, respectively. That is, the formation voltage of the first stage is 25V, the formation voltage of the second stage is 50V, the formation voltage of the third stage is 100V, the formation voltage of the fourth stage is 200V, the formation voltage of the fifth stage is 300V, the formation voltage of the sixth stage is 400V, and the formation voltage of the seventh stage is 500V.

[0257] S02, Depolarization treatment: Phosphoric acid treatment in depolarization 1: After cleaning the aluminum foil obtained by the above formation treatment steps, immerse it in a 5 wt% phosphoric acid aqueous solution at 85°C for 1 min.

[0258] The re-forming treatment in depolarization 1: After cleaning, the aluminum foil is placed in a mixed aqueous solution of boric acid (10 wt%) and ammonium pentaborate (0.09 wt%) for re-forming treatment at a temperature of 80℃ for 10 min, a current density of 150 mA / cm², and a re-forming voltage of 510 V.

[0259] Phosphoric acid treatment 2 in depolarization: After cleaning, the aluminum foil is immersed in a 5 wt% phosphoric acid aqueous solution at 65°C for 3 min.

[0260] Heat treatment 1 in depolarization: After cleaning the aluminum foil, heat treatment is performed at a temperature of 550℃ for 2 minutes.

[0261] Phosphoric acid treatment in depolarization 3: The heat-treated aluminum foil was immersed in a 5 wt% phosphoric acid aqueous solution at 40°C for 5 min.

[0262] Heat treatment 2 in depolarization: After cleaning the aluminum foil, heat treatment is performed at a temperature of 530℃ for 2 minutes.

[0263] Re-forming treatment 2 in depolarization: The heat-treated aluminum foil was placed in a mixed aqueous solution of boric acid (10 wt%) and ammonium pentaborate (0.09 wt%) for re-forming treatment at a temperature of 80°C for 6 min, a current density of 150 mA / cm², and a re-forming voltage of 510 V.

[0264] S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 40°C for 5 minutes. The first solution is a 5 wt% potassium hexametaphosphate solution with water as the solvent. Potassium hexametaphosphate is a polyphosphate.

[0265] Post-processing repair treatment: After cleaning, the aluminum foil is placed in a mixed aqueous solution of 10 wt% boric acid and 0.09 wt% ammonium pentaborate for repair treatment at a temperature of 80℃ for 6 min, a current density of 150 mA / cm², and a repair voltage of 510 V.

[0266] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 45°C for 4 minutes. The second solution is a solution of 3 wt% polyitacic acid and 0.3 wt% diethylenetriaminepentimidephosphonic acid, with water as the solvent.

[0267] Post-processing heat treatment: The aluminum foil is heat treated at 200°C for 15 minutes to obtain the electrode foil.

[0268] Example 13 This application provides a method for preparing an electrode foil, the method comprising: formation treatment, depolarization treatment, and post-treatment. The target rated voltage of the electrode foil is 600Vf, specifically: S01, Formation Treatment: A 120 μm thick etched foil was boiled in water for 12 minutes and then subjected to sequential primary, secondary, tertiary, quaternary, quinary, and sixth-stage formation treatments in a mixture of boric acid and ammonium pentaborate. Each formation treatment solution independently consisted of 10 wt% boric acid and 0.15 wt% ammonium pentaborate aqueous solution. The temperature for each formation treatment was 85 °C, and the time for each formation treatment was independently 15 minutes. The current density in each formation process is independently 200mA / cm², and the voltage in each formation process is independently 10%, 20%, 40%, 60%, 80%, and 100% of its target rated voltage of 600Vf, respectively. That is, the formation voltage of the first stage is 60V, the formation voltage of the second stage is 120V, the formation voltage of the third stage is 240V, the formation voltage of the fourth stage is 360V, the formation voltage of the fifth stage is 480V, and the formation voltage of the sixth stage is 600V.

[0269] S02, Depolarization treatment: Phosphoric acid treatment in depolarization 1: After cleaning the aluminum foil obtained by the above formation treatment steps, it is immersed in an aqueous solution of 1% polyphosphoric acid and 5 wt% phosphoric acid at a temperature of 65°C for 7 min.

[0270] The re-forming treatment in depolarization 1: After cleaning, the aluminum foil is placed in a mixed aqueous solution of boric acid (10 wt%) and ammonium pentaborate (0.09 wt%) for re-forming treatment at a temperature of 85℃ for 6 min, a current density of 200 mA / cm², and a re-forming voltage of 620 V.

[0271] Phosphoric acid treatment 2 in depolarization: After cleaning, the aluminum foil was immersed in a 5 wt% phosphoric acid aqueous solution at 85°C for 0.5 min.

[0272] The second step in the depolarization process is to clean the aluminum foil and place it in a mixed aqueous solution of 10 wt% boric acid and 0.09 wt% ammonium pentaborate for a re-forming treatment at a temperature of 85°C for 6 min, a current density of 200 mA / cm², and a re-forming voltage of 620 V.

[0273] Heat treatment 1 in depolarization: After cleaning the aluminum foil, heat treatment is performed at a temperature of 450℃ for 3 minutes.

[0274] Re-forming treatment 3 in depolarization: The heat-treated aluminum foil was placed in a mixed aqueous solution of 10 wt% boric acid and 0.09 wt% ammonium pentaborate for re-forming treatment at 85°C for 6 min and a current density of 200 mA / cm². 2 The voltage for the supplementary voltage is 620V.

[0275] Heat treatment 2 in depolarization: After cleaning the aluminum foil, heat treatment is performed at a temperature of 550℃ for 2 minutes.

[0276] Re-forming treatment 4 in depolarization: The heat-treated aluminum foil was placed in a mixed aqueous solution of 10 wt% boric acid and 0.09 wt% ammonium pentaborate for re-forming treatment at 85°C for 6 min and a current density of 200 mA / cm². 2 The voltage for the supplementary voltage is 620V.

[0277] S03, Post-processing: First immersion treatment: After cleaning, the aluminum foil is placed in the first solution for the first immersion treatment at a temperature of 55°C for 3 minutes. The first solution is a 2 wt% ammonium pyrophosphate solution with water as the solvent.

[0278] Post-processing re-forming: After cleaning, the aluminum foil was placed in a mixed aqueous solution of 10 wt% boric acid and 0.09 wt% ammonium pentaborate for re-forming at 85°C for 6 min and a current density of 200 mA / cm². 2 The voltage for the supplementary voltage is 620V.

[0279] Second immersion treatment: After cleaning, the aluminum foil is placed in the second solution for a second immersion treatment at a temperature of 70°C for 3 minutes. The second solution is a solution of sodium alginate (3 wt%) and aminotrimethylenephosphonic acid (0.3 wt%), with water as the solvent.

[0280] Post-processing heat treatment: The aluminum foil is heat treated at 380°C for 2 minutes to obtain the electrode foil.

[0281] The electrode foils prepared in Examples 9-13 were tested according to the above method, and the results are shown in Table 3.

[0282] Table 3

[0283] As shown in Table 3, the electrode foil preparation method of this application is also applicable to the preparation of medium and high voltage electrode foils, and can further improve the hydration resistance of the electrode foil while increasing the specific volume of the electrode foil.

[0284] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for producing an electrode foil, characterized by, The preparation method includes: The electrode foil is prepared by performing formation treatment, depolarization treatment, and post-treatment on the etched foil. In the post-processing, the etched foil that has undergone the depolarization treatment is immersed in an immersion solution; the immersion solution includes an organic polymer and polyphosphate or its salt; the main chain and / or side chain of the organic polymer are grafted with one or more functional groups selected from sulfonic acid groups, phosphoric acid groups, phosphonic acid groups, carboxyl groups and amide groups.

2. The production method according to claim 1, characterized by, The polyphosphate or its salts include at least one of polyphosphate, ammonium polyphosphate, sodium pyrophosphate, sodium tripolyphosphate, potassium tetramethphosphate, sodium hexametaphosphate, sodium trimethphosphate, and sodium tetramethphosphate; and / or, the organic polymer includes at least one of polystyrene sulfonic acid, polyvinylphosphonic acid, sodium alginate, sodium polyacrylate, polyacrylamide, and polyitacrylic acid.

3. The production method according to claim 1 or 2, characterized by, The immersion solution includes a first solution and a second solution. Immersing the etched foil, which has undergone the depolarization treatment, in the immersion solution includes: The first soaking treatment is performed using the first solution, wherein the first solution includes the polyphosphate or a salt thereof; optionally, the solvent of the first solution includes water. The second immersion treatment is performed using the second solution, which includes the organic polymer; optionally, the solvent of the second solution includes water. Optionally, in the post-treatment, a first soaking treatment is performed using a first solution, followed by a second soaking treatment using a second solution; alternatively, in the post-treatment, a second soaking treatment is performed using a second solution, followed by a first soaking treatment using a first solution.

4. The preparation method according to claim 3, characterized in that, In the post-treatment, a first immersion treatment is performed using a first solution at a temperature of 40℃-75℃; optionally, the first immersion treatment time is 1min-10min; and / or, The second solution is used for a second soaking treatment at a temperature of 40℃-70℃; optionally, the soaking time is 0.5min-8min.

5. The preparation method according to claim 3, characterized in that, Based on the total mass of the first solution, the polyphosphate or its salt in the first solution comprises 0.5%-10% by mass; and / or, Based on the total mass of the second solution, the organic polymer in the second solution has a mass percentage of 0.1%-10%; optionally, the second solution further includes a chelating agent. Optionally, the chelating agent contains two or more chelating groups, the chelating groups including one or more functional groups selected from phosphonic acid group, carboxylic acid group, hydroxyl group, amino group, and mercapto group; optionally, the chelating agent includes one or more selected from ethylenediaminetetraacetic acid, hydroxyethylidene diphosphonic acid, diethylenetriaminepentamethylidene phosphonic acid, and aminotrimethylene phosphonic acid; optionally, the mass ratio of the chelating agent and the organic polymer in the second solution is (1-5):

10.

6. The preparation method according to claim 3, characterized in that, In the post-treatment, the soaking solution includes a third solution; the third solution includes an organic polymer and polyphosphate or a salt thereof; Optionally, the third solution includes the first solution and the second solution; optionally, the third solution is used for the third soaking treatment. Optionally, a third solution is used for a third immersion treatment at a temperature of 40℃-70℃; optionally, the time for the third immersion treatment is 0.5min-8min. Optionally, the content of each component in the third solution is the same as that in the first and second solutions.

7. The preparation method according to claim 1 or 2, characterized in that, The post-processing in the preparation method further includes: a remodeling process; Optionally, the temperature for each of the re-forming processes is independently 60°C-90°C; Optionally, the current density of each of the re-forming processes is independently 20 mA / cm²-200 mA / cm²; preferably 40 mA / cm²-120 mA / cm². Optionally, the voltage for each of the reshaping processes is independently 1.02-1.2 times the rated voltage; optionally, it is a pulse voltage. Optionally, the time for each of the replenishment processes is independently 0.5 min to 10 min; Optionally, the solute in the replenishing solution used in each replenishing treatment independently includes one or more of ammonium dihydrogen phosphate, boric acid, and ammonium pentaborate; Optionally, the solvent of the replenishing solution used in each replenishing process is water independently; Optionally, based on the total mass of the supplementary formation solution used in the supplementary formation process, the mass percentage of solute in the supplementary formation solution used in each supplementary formation process is independently 0.5%-10%.

8. The preparation method according to claim 1 or 2, characterized in that, The post-processing in the preparation method further includes: heat treatment; Optionally, the temperature of each heat treatment is independently 150°C-380°C, and more preferably 280°C-350°C; Optionally, the duration of each heat treatment is independently 2 min to 20 min, and more preferably 2 min to 5 min.

9. An electrode foil, characterized in that, The electrode foil is prepared by any one of claims 1-8.

10. An electrolytic capacitor, characterized in that, This includes the electrode foil prepared by any one of claims 1-8 or the electrode foil described in claim 9.

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