Chemical conversion foil, method for producing the same, and electrolytic capacitor

Abstract

This application discloses a formed foil, its preparation method, and an electrolytic capacitor. The formed foil comprises: a formed foil substrate; a permeation layer disposed on at least one surface of the formed foil substrate; and an oxide film disposed on the surface of the permeation layer away from the formed foil substrate. The permeation layer contains non-metallic elements, and the content of the non-metallic elements decreases along the oxide film towards the formed foil substrate. By introducing plasma electrolytic permeation treatment before the foil formation process to form the permeation layer, the microstructure and chemical composition of the foil surface are optimized, reducing the defect density of the oxide film, improving the uniformity of the oxide film, reducing the probability of crack formation, reducing the risk of interface peeling, and reducing leakage current. This improves the specific capacitance, withstand voltage, and hydration resistance of the formed foil.

Description

Technical Field

[0001] This application relates to the field of formed foil. Specifically, this application relates to formed foil, methods for preparing the same, and electrolytic capacitors. Background Technology

[0002] As a core material for electrolytic capacitors, the performance of electrolytic foil directly determines the capacitor's capacitance, lifespan, and reliability. With the rapid development of emerging fields such as photovoltaics and electric vehicles, higher requirements are being placed on the performance of electrolytic foil. Under current process conditions, electrolytic foil suffers from problems such as high leakage current, low withstand voltage, low specific capacitance, and poor hydration resistance, which urgently need improvement. Summary of the Invention

[0003] This application aims to at least partially address the technical problems existing in the prior art. To this end, this application proposes a formed foil, its preparation method, and an electrolytic capacitor. By introducing plasma electrolysis treatment before the foil's formation process, the microstructure and chemical composition of the foil surface are optimized, reducing the oxide film defect density, improving oxide film uniformity, reducing the probability of crack formation, reducing the risk of interface peeling, and reducing leakage current. This improves the specific capacitance, withstand voltage, and hydration resistance of the formed foil.

[0004] In one aspect of this application, a formed foil is provided. According to an embodiment of this application, the formed foil includes: a formed foil substrate; a permeation layer disposed on at least one surface of the formed foil substrate; and an oxide film disposed on the surface of the permeation layer away from the formed foil substrate; wherein the permeation layer contains non-metallic elements, and the content of the non-metallic elements in the permeation layer decreases along the oxide film toward the formed foil substrate.

[0005] According to an embodiment of this application, a permeation layer is provided between the formed foil substrate and the oxide film obtained by the formation. On the one hand, the permeation layer effectively reduces the electron tunneling path by filling the defects on the substrate surface, thereby reducing leakage current; on the other hand, it alleviates the difference in thermal expansion coefficient between the oxide film and the substrate, reduces the probability of microcrack generation and the risk of interface peeling, and improves the density and uniformity of the oxide film, thereby synergistically improving specific capacity, pressure resistance and hydration resistance.

[0006] According to embodiments of this application, the non-metallic element includes at least one selected from carbon, boron, and nitrogen. This improves the voltage resistance, hydration resistance, and specific capacitance of the formed foil, while reducing leakage current.

[0007] According to an embodiment of this application, the permeation layer contains a metallization of the non-metallic element.

[0008] According to an embodiment of this application, the permeation layer further contains the same matrix metal element as the formed foil substrate; the non-metal element in the permeation layer exists in the form of a metallide; and the matrix metal element in the permeation layer exists in the form of an oxide.

[0009] According to an embodiment of this application, the oxide film contains the same matrix metal element as the formed foil substrate and exists in the form of an oxide.

[0010] According to embodiments of this application, the base metal element includes at least one selected from aluminum, titanium, copper, and nickel.

[0011] According to embodiments of this application, the thickness of the permeation layer is no more than 1 μm. In some embodiments, the thickness of the permeation layer is 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, or any value within the range of any two of the above values. This allows for better improvement of the chemical composition and microstructure of the foil surface, which is beneficial for enhancing the formation quality, stability, and electrochemical performance of the oxide film dielectric layer during the formation process, thereby improving the overall performance of the formed foil.

[0012] In another aspect of this application, a method for preparing the aforementioned formed foil is proposed. According to an embodiment of this application, the method includes: subjecting the foil to be treated to plasma electroporation treatment to obtain a pretreated foil; subjecting the pretreated foil to a formation treatment to obtain the formed foil; wherein the pretreated foil includes: the formed foil substrate and a pretreatment layer, the pretreatment layer being disposed on at least one surface of the formed foil substrate and containing the non-metallic element.

[0013] Plasma electroporation is a technique that uses liquid-phase plasma discharge to modify metal surfaces. By introducing it before formation treatment, it not only alters the chemical composition and microstructure of the foil surface but also improves the formation quality, stability, and electrochemical performance of the dielectric layer of the oxide film during subsequent formation processes. Specifically: 1. Accelerated film formation: A pretreatment layer (such as AlB2, Al4C3 or AlN) is formed on the oxide foil substrate through plasma electroporation treatment. These metal compounds can reduce the activation energy of oxides of the base metal elements (such as aluminum oxide, titanium oxide, copper oxide or nickel oxide). In addition, the vacancies and dislocations generated by high-energy plasma bombardment provide channels for oxygen ion diffusion, thereby increasing the oxide film growth rate. At the same time, it reduces local current concentration, reduces oxide film defect density, and improves oxide film uniformity.

[0014] 2. Enhanced interfacial bonding: The pretreatment layer alleviates the difference in thermal expansion coefficients between the oxide film and the substrate of the formed foil, reduces the probability of microcracks, reduces the risk of interfacial delamination, and improves the specific volume, pressure resistance and hydration resistance of the formed foil.

[0015] 3. Suppress leakage current: The permeation layer can fill defects on the substrate surface, reduce electron tunneling paths, and effectively reduce leakage current.

[0016] According to embodiments of this application, the electrolyte used in the plasma electroporation treatment includes a compound of the non-metallic element. This allows for the introduction of non-metallic elements into the pretreatment layer, thereby improving the performance of the formed foil.

[0017] According to embodiments of this application, the electrolyte comprises at least one of the following groups (1) to (4): (1) The electrolyte comprises sodium tetraborate or its hydrate and a conductive agent. This allows for the introduction of element B into the pretreatment layer, thereby improving the performance of the formed foil. Sodium tetraborate (Na2B4O7) or its hydrate is chosen because of its good water solubility, weakly alkaline solution, strong pH buffering capacity, moderate active boron content, stable process, and excellent compatibility with the substrate and subsequent formation processes.

[0018] (2) The electrolyte comprises glycerol and ethanol. This allows for the introduction of carbon elements into the pretreatment layer, improving the performance of the electrolytic foil. Glycerol (C3H8O3) serves as the primary carbon source, generating active carbon atoms under plasma action to achieve carburization on the substrate surface; simultaneously, glycerol increases the electrolyte viscosity, stabilizes plasma discharge, and inhibits substrate corrosion. Ethanol (C2H6O), as an auxiliary carbon source and wetting agent, reduces the surface tension of the electrolyte, improves the wettability of the substrate surface, makes the discharge more uniform, and adjusts the electrolyte viscosity and process stability. The combination of these two components enables a mild, uniform, and controllable plasma electrolytic carburization process.

[0019] (3) The electrolyte comprises urea, a conductive agent, and inorganic nanoparticles. This allows for the introduction of C and N elements into the pretreatment layer, improving the performance of the formed foil. Urea (CH4N2O) provides both carbon and nitrogen sources, has good water solubility, near-neutral solution, mild decomposition, stable plasma discharge, and is free of metal impurity ions, making it highly compatible with the substrate and subsequent formation processes. Inorganic nanoparticles can stabilize plasma, optimize the diffusion layer structure, and improve the performance of subsequent film formation.

[0020] (4) Sodium tetraborate or its hydrate, glycerol, and sulfate. This allows for the introduction of C and B elements into the pretreatment layer, improving the performance of the formed foil. Sulfate can act as a conductive salt and stabilizer, enhancing the conductivity and stability of the system.

[0021] According to embodiments of this application, the conductive agent includes at least one of sodium hydroxide, potassium hydroxide, and ammonia water.

[0022] According to embodiments of this application, the inorganic nanoparticles include nano-silica.

[0023] According to embodiments of this application, the sulfate includes at least one of sodium sulfate, ammonium sulfate, and potassium sulfate.

[0024] According to an embodiment of this application, the solvent of the electrolyte is deionized water.

[0025] According to embodiments of this application, the plasma electroosmosis treatment satisfies at least one of the following groups (i) to (iv): (i) The electrolyte comprises: sodium tetraborate or its hydrate (e.g., 15 g / L, 20 g / L, 25 g / L, 30 g / L or any value within the range of any two of the above values) with a mass-volume concentration of 15 g / L to 30 g / L and NaOH (e.g., 0 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L, 10 g / L or any value within the range of any two of the above values) with a mass-volume concentration of 0 g / L to 10 g / L.

[0026] (ii) The electrolyte comprises: glycerol (e.g., 10 g / L, 15 g / L, 20 g / L or any value between any two of the above values) with a mass-volume concentration of 10 g / L to 20 g / L and ethanol (e.g., 5 g / L, 10 g / L, 15 g / L or any value between any two of the above values) with a mass-volume concentration of 5 g / L to 15 g / L.

[0027] (iii) The electrolyte comprises: urea (e.g., 10 g / L, 15 g / L, 20 g / L or any value between any two of the above values) with a mass-volume concentration of 10 g / L to 20 g / L, NH3·H2O (e.g., 0 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L, 10 g / L or any value between any two of the above values) with a mass-volume concentration of 0 g / L to 10 g / L, and nano-silica (0 g / L, 0.2 g / L, 0.4 g / L, 0.6 g / L, 0.8 g / L, 1 g / L or any value between any two of the above values) with a mass-volume concentration of 0 g / L to 1 g / L.

[0028] (iv) The electrolyte comprises: sodium tetraborate or its hydrate (e.g., 15 g / L, 20 g / L, 25 g / L, 30 g / L or any value between any two of the above values) with a mass-volume concentration of 15 g / L to 30 g / L; glycerol (e.g., 10 g / L, 15 g / L, 20 g / L or any value between any two of the above values) with a mass-volume concentration of 10 g / L to 20 g / L; and Na2SO4 (4 g / L, 6 g / L, 8 g / L, 10 g / L or any value between any two of the above values) with a mass-volume concentration of 4 g / L to 10 g / L.

[0029] According to embodiments of this application, the plasma electroosmosis treatment satisfies at least one of the following conditions: the power supply for the plasma electroosmosis treatment is a pulsed power supply; the pulse voltage of the plasma electroosmosis treatment is 250V-300V (e.g., 250V, 260V, 270V, 280V, 290V, 300V or any value within the range of any two of the above values); the frequency of the plasma electroosmosis treatment is 5 kHz-12 kHz (e.g., 5 kHz, 6 kHz, 7 kHz, 8 kHz, 9 kHz, 10 kHz, 11 kHz, 12 kHz or any value within the range of any two of the above values); the duty cycle of the plasma electroosmosis treatment is 60%-90% (e.g., 60%, 70%, 80%, 90% or any value within the range of any two of the above values); the duration of the plasma electroosmosis treatment is 240s-360s (240s, 250s, 260s, 270s, 280s). The plasma electrolysis treatment temperature is 70℃-90℃ (70℃, 75℃, 80℃, 85℃, 90℃ or any value within the range of any two of the above values). This allows for the formation of a uniform, dense, and appropriately thick permeation layer on the substrate surface, ensuring sufficient penetration and distribution gradient of non-metallic elements while avoiding excessive damage to the substrate structure.

[0030] According to embodiments of this application, the formation process includes at least primary formation and secondary formation, preferably primary formation, secondary formation, tertiary formation and quaternary formation, wherein the formation solution and formation voltage used in each formation stage are independently the same or different.

[0031] According to embodiments of this application, the forming solution used in each stage of formation independently includes boric acid and citric acid.

[0032] According to embodiments of this application, the primary formation solution comprises an aqueous solution of boric acid, citric acid, and ammonium adipate.

[0033] According to an embodiment of this application, the primary formation solution comprises boric acid (e.g., 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any value within the range of any two of the above values) with a mass percentage concentration of 2wt%-10wt%, citric acid (e.g., 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, or any value within the range of any two of the above values) with a mass percentage concentration of 0.2wt%-2wt%, and ammonium adipic acid (0.5wt%, 1wt%, 1.5wt%, 2wt%, or any value within the range of any two of the above values) with a mass percentage concentration of 0.5wt%-2wt%.

[0034] According to embodiments of this application, the formation solutions for the secondary, tertiary, and quaternary formations are each independently an aqueous solution comprising boric acid and citric acid.

[0035] According to embodiments of this application, the formation solutions for the secondary, tertiary, and quaternary formations each independently include boric acid (e.g., 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any value within the range of any two of the above values) and citric acid (e.g., 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, or any value within the range of any two of the above values) with a mass percentage concentration of 2wt%-10wt%.

[0036] According to an embodiment of this application, the voltage of the first-stage formation is 70V-190V (e.g., 70V, 80V, 90V, 100V, 110V, 120V, 130V, 140V, 150V, 160V, 170V, 180V, 190V, or any value within the range of any two of the above values), the time of the first-stage formation is 240s-360s (e.g., 240s, 260s, 280s, 300s, 320s, 340s, 360s, or any value within the range of any two of the above values), and the temperature of the first-stage formation is 70℃-90℃ (e.g., 70℃, 75℃, 80℃, 85℃, 90℃, or any value within the range of any two of the above values).

[0037] According to an embodiment of this application, the voltage of the secondary formation is 350V-370V (e.g., 350V, 360V, 370V or any value within the range of any two of the above values), the time of the secondary formation is 400s-500s (e.g., 400s, 450s, 500s or any value within the range of any two of the above values), and the temperature of the secondary formation is 70℃-90℃ (e.g., 70℃, 75℃, 80℃, 85℃, 90℃ or any value within the range of any two of the above values).

[0038] According to an embodiment of this application, the voltage of the three-stage formation is 500V-520V (e.g., 500V, 510V, 520V or any value within the range of any two of the above values), the time of the three-stage formation is 550s-650s (e.g., 550s, 600s, 650s or any value within the range of any two of the above values), and the temperature of the three-stage formation is 70℃-90℃ (e.g., 70℃, 75℃, 80℃, 85℃, 90℃ or any value within the range of any two of the above values).

[0039] According to an embodiment of this application, the voltage of the four-stage formation is 570V-590V (e.g., 570V, 580V, 590V, or any value within the range of any two of the above values), the time of the four-stage formation is 900s-1200s (e.g., 900s, 950s, 1000s, 1050s, 1100s, 1150s, 1200s, or any value within the range of any two of the above values), and the temperature of the four-stage formation is 70℃-90℃ (e.g., 70℃, 75℃, 80℃, 85℃, 90℃, or any value within the range of any two of the above values).

[0040] According to an embodiment of this application, the formation process further includes a boiling process.

[0041] According to an embodiment of this application, the boiling treatment includes placing the foil after plasma electrolysis treatment in water at a temperature greater than 95°C (e.g., 95°C, 96°C, 97°C, 98°C, 99°C, 100°C or any value within the range of any two of the above values) for 8 min to 12 min (8 min, 9 min, 10 min, 11 min, 12 min or any value within the range of any two of the above values).

[0042] According to embodiments of this application, the formation process further includes one or more steps of heat treatment, formation supplementation treatment, depolarization treatment, and stabilization treatment.

[0043] According to an embodiment of this application, the heat treatment includes a first heat treatment and a second heat treatment; the temperatures of the first heat treatment and the second heat treatment are each independently between 520°C and 580°C (e.g., 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, or any value within the range of any two of the above values); the times of the first heat treatment and the second heat treatment are each independently between 100s and 200s (e.g., 100s, 120s, 140s, 160s, 180s, 200s, or any value within the range of any two of the above values).

[0044] According to an embodiment of this application, the repair formation process includes a first repair formation process, a second repair formation process, and a third repair formation process, each of which is carried out independently in an aqueous solution containing boric acid and ammonium pentaborate.

[0045] According to an embodiment of this application, the first, second, and third replenishment treatments are each carried out independently in an aqueous solution containing 2wt%-10wt% boric acid (e.g., 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or any value within the range of any two of the above values) and 0.5wt%-2wt% ammonium pentaborate (0.5wt%, 1.0wt%, 1.5wt%, 2.0wt%, or any value within the range of any two of the above values).

[0046] According to an embodiment of this application, the voltage of each of the first, second, and third re-forming processes is independently 570V-590V (e.g., 570V, 580V, 590V, or any value within the range of any two of the above values), the time of each of the first, second, and third re-forming processes is independently 400s-500s (e.g., 400s, 450s, 500s, or any value within the range of any two of the above values), and the temperature of each of the first, second, and third re-forming processes is independently 70℃-90℃ (e.g., 70℃, 75℃, 80℃, 85℃, 90℃, or any value within the range of any two of the above values).

[0047] According to an embodiment of this application, the depolarization treatment is carried out in a phosphoric acid aqueous solution (in which the mass percentage concentration of phosphoric acid is 6wt%-8wt%, for example 6 wt%, 7 wt%, 8 wt% or any value within the range of any two of the above values), the temperature of the depolarization treatment is 60℃-70℃ (for example 60℃, 65℃, 70℃ or any value within the range of any two of the above values), and the time of the depolarization treatment is 120s-600s (120s, 150s, 200s, 250s, 300s, 350s, 400s, 450s, 500s, 550s, 600s or any value within the range of any two of the above values).

[0048] According to an embodiment of this application, the stabilization treatment is carried out in an aqueous solution of ammonium dihydrogen phosphate (the mass percentage concentration of ammonium dihydrogen phosphate in the aqueous solution of ammonium dihydrogen phosphate is 0.5wt%-3wt%, for example 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, or any value within the range of any two of the above values), the stabilization treatment temperature is 50℃-60℃ (for example 50℃, 55℃, 60℃ or any value within the range of any two of the above values), and the stabilization treatment time is 60s-360s (60s, 100s, 150s, 200s, 250s, 300s, 360s or any value within the range of any two of the above values).

[0049] In another aspect, this application proposes an electrolytic capacitor. According to an embodiment of this application, the electrolytic capacitor comprises: the formed foil described above or formed foil obtained using the method described above for preparing formed foil. Therefore, the electrolytic capacitor of this application has high capacitance, high withstand voltage, resistance to hydration, low leakage current, and a long service life.

[0050] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application.

[0051] Beneficial effects This application introduces plasma electrolytic permeation treatment before the foil formation process to form a permeation layer, which optimizes the microstructure and chemical composition of the foil surface, reduces the defect density of the oxide film, improves the uniformity of the oxide film, reduces the probability of crack formation, reduces the risk of interface peeling, and reduces leakage current. This improves the specific capacitance, pressure resistance, and hydration resistance of the formed foil.

[0052] Terminology Explanation It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0053] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0054] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0055] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this application but do not exclude other contents.

[0056] The unit of mass-volume concentration, “g / L”, indicates how many grams of a specific component are contained in 1L of solution.

[0057] “wt%” indicates weight percentage. Detailed Implementation

[0058] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0059] This application proposes a method for preparing electroformed foil, comprising the following steps: 1. Sample preparation: Select high-pressure etched foil (99.99% Al) and cut it into 100mm×100mm foil sheets.

[0060] 2. Prepare the permeation electrolyte: Different electrolytes are selected based on the different permeating elements. Boronizing electrolyte: an aqueous solution of Na₂B₄O₇·10H₂O with a mass-volume concentration of 15 g / L-30 g / L and NaOH with a mass-volume concentration of 0 g / L-10 g / L.

[0061] Carburizing electrolyte: an aqueous solution of glycerol with a mass-volume concentration of 10 g / L-20 g / L and ethanol with a mass-volume concentration of 5 g / L-15 g / L.

[0062] Carbonitriding electrolyte: an aqueous solution of urea with a mass-volume concentration of 10 g / L-20 g / L, NH3·H2O with a mass-volume concentration of 0 g / L-10 g / L, and nano-silica with a mass-volume concentration of 0 g / L-1 g / L.

[0063] Boron-carbon co-permeation electrolyte: an aqueous solution of Na₂B₄O₇·10H₂O with a mass-volume concentration of 15 g / L-30 g / L, glycerol with a mass-volume concentration of 10 g / L-20 g / L, and Na₂SO₄ with a mass-volume concentration of 4 g / L-10 g / L.

[0064] 3. Prepare the formation solution: The primary formation solution consists of an aqueous solution of boric acid (2wt%-10wt%), citric acid (0.2wt%-2wt%), and ammonium adipate (0.5wt%-2wt%).

[0065] The secondary formation solution consists of an aqueous solution of boric acid with a mass percentage concentration of 2wt%-10wt% and citric acid with a mass percentage concentration of 0.2wt%-2wt%.

[0066] The tertiary formation solution consists of an aqueous solution of boric acid with a mass percentage concentration of 2wt%-10wt% and citric acid with a mass percentage concentration of 0.2wt%-2wt%.

[0067] The quaternary formation solution consists of an aqueous solution of boric acid with a mass percentage concentration of 2wt%-10wt% and citric acid with a mass percentage concentration of 0.2wt%-2wt%.

[0068] The treatment solution for the first replenishment treatment is an aqueous solution of boric acid with a mass percentage concentration of 2wt%-10wt% and ammonium pentaborate with a mass percentage concentration of 0.5wt%-2wt%.

[0069] The treatment solution for the second replenishment process is an aqueous solution of boric acid with a mass percentage concentration of 2wt%-10wt% and ammonium pentaborate with a mass percentage concentration of 0.5wt%-2wt%.

[0070] The treatment solution for the third replenishment process is an aqueous solution of boric acid with a mass percentage concentration of 2wt%-10wt% and ammonium pentaborate with a mass percentage concentration of 0.5wt%-2wt%.

[0071] 4. Prepare the depolarization treatment solution: a phosphoric acid aqueous solution with a mass percentage concentration of 6wt%-8wt%.

[0072] 5. Prepare the stabilization treatment solution: an aqueous solution of ammonium dihydrogen phosphate with a mass percentage concentration of 0.5wt%-3wt%.

[0073] 6. Plasma electroosmosis treatment: The foil from step (1) is placed in the electrolyte from step (2) for plasma electroosmosis treatment. Different electrolytes are selected according to the different penetrating elements. The power supply for plasma electroosmosis treatment is a pulse power supply with a pulse voltage of 250V-300V, a frequency of 5 kHz-12kHz, a duty cycle of 60%-90%, a time of 240s-360s, and a temperature of 70℃-90℃.

[0074] 7. Boiling treatment: Place the foil from step (6) into water at >95℃ and boil for 8 min-12 min.

[0075] 8. Primary formation: Rinse the aluminum foil obtained in step (7) with water and place it in the primary formation solution prepared in step (3) for primary formation. The formation voltage of primary formation is 70V-190V, the constant pressure time is 240s-360s, and the temperature is 70℃-90℃.

[0076] 9. Secondary formation: Rinse the aluminum foil obtained in step (8) with water and place it in the secondary formation solution prepared in step (3) for secondary formation. The formation voltage of the secondary formation is 350V-370V, the constant pressure time is 400 s-500s, and the temperature is 70℃-90℃.

[0077] 10. Three-stage formation: Rinse the aluminum foil obtained in step (9) with water and place it in the three-stage formation solution prepared in step (3) for three-stage formation. The formation voltage of the three-stage formation is 500V-520V, the constant pressure time is 550s-650s, and the temperature is 70℃-90℃.

[0078] 11. Four-stage formation: Rinse the aluminum foil obtained in step (10) with water and place it in the four-stage formation solution prepared in step (3) for four-stage formation. The formation voltage of the four-stage formation is 570V-590V, the constant pressure time is 900s-1200s, and the temperature is 70℃-90℃.

[0079] 12. First heat treatment: Rinse the aluminum foil obtained in step (11) with water and heat it at a temperature of 520℃-580℃ for 100s-200s.

[0080] 13. First Formation Treatment: Rinse the aluminum foil obtained in step (12) with water and place it in the first formation treatment solution prepared in step (3) for the first formation treatment. The formation voltage of the first formation treatment is 570V-590V, the constant pressure time is 400s-500s, and the temperature is 70℃-90℃.

[0081] 14. Depolarization treatment: Rinse the aluminum foil obtained in step (13) with water and place it in the depolarization treatment solution prepared in step (3) for depolarization treatment. The temperature of the depolarization treatment is 60℃-70℃ and the time is 120s-600s.

[0082] 15. Second Forming Process: Rinse the aluminum foil obtained in step (14) with water and place it in the processing solution prepared in step (3) for the second forming process. The forming voltage of the second forming process is 570V-590V, the constant pressure time is 400s-500s, and the temperature is 70℃-90℃.

[0083] 16. Second heat treatment: Rinse the aluminum foil obtained in step (15) with water and heat it at a temperature of 520℃-580℃ for 100s-200s.

[0084] 17. Third Forming Process: Rinse the aluminum foil obtained in step (16) with water and place it in the processing solution prepared in step (3) for the third forming process. The forming voltage of the third forming process is 570V-590V, the constant pressure time is 400s-500s, and the temperature is 70℃-90℃.

[0085] 18. Stabilization treatment: Rinse the aluminum foil obtained in step (17) with water, place it in the stabilization treatment solution prepared in step (3) for stabilization treatment. The stabilization treatment temperature is 50℃-60℃ and the time is 60s~360s. After rinsing with water and drying, the stabilized foil is obtained.

[0086] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0087] Example 1 A type of electrolytic foil, the preparation method of which includes: cutting foil sheets → plasma electrolysis treatment → boiling treatment → primary electrolytic formation → secondary electrolytic formation → tertiary electrolytic formation → quaternary electrolytic formation → first heat treatment → first re-forming treatment → depolarization treatment → second re-forming treatment → second heat treatment → third re-forming treatment → stabilization treatment.

[0088] The specific preparation process is as follows: Foil cutting: Select high-pressure etched foil (99.99% Al) and cut it into 100mm×100mm foil sheets.

[0089] Plasma electroosmosis treatment: The cut foil is subjected to plasma electroosmosis treatment in a penetrating electrolyte. The penetrating electrolyte is a boronizing electrolyte: an aqueous solution of Na2B4O7·10H2O with a mass-volume concentration of 20 g / L and NaOH with a mass-volume concentration of 5 g / L. The power supply for plasma electroosmosis treatment is a pulse power supply with a pulse voltage of 280V, a frequency of 10kHz, and a duty cycle of 70%. The plasma electroosmosis treatment time is 300s and the temperature is 80℃.

[0090] Boiling treatment: Immerse the foil after plasma electrolysis treatment in water at 100°C for 10 minutes.

[0091] Primary formation: The foil after boiling in water is placed in the primary formation solution (the primary formation solution is an aqueous solution of boric acid with a mass percentage concentration of 6 wt%, citric acid with a mass percentage concentration of 0.8 wt%, and ammonium adipate with a mass percentage concentration of 1 wt%) for primary formation. The primary formation voltage is 180 V, the constant voltage time is 300 s, and the temperature is 85℃.

[0092] Secondary formation: The foil after primary formation is rinsed with water and placed in the secondary formation solution (the secondary formation solution is an aqueous solution of boric acid with a mass percentage concentration of 6 wt% and citric acid with a mass percentage concentration of 0.6 wt%) for secondary formation. The formation voltage of the secondary formation is 360 V, the constant voltage time is 450 s, and the temperature is 85℃.

[0093] Tertiary formation: The foil after secondary formation is rinsed with water and placed in the tertiary formation solution (tertiary formation solution: an aqueous solution of boric acid with a mass percentage concentration of 6 wt% and citric acid with a mass percentage concentration of 0.4 wt%) for tertiary formation. The formation voltage of tertiary formation is 510 V, the constant voltage time is 600 s, and the temperature is 85℃.

[0094] Fourth-stage formation: The foil after the third-stage formation is rinsed with water and placed in the fourth-stage formation solution (fourth-stage formation solution: an aqueous solution of boric acid with a mass percentage concentration of 6 wt% and citric acid with a mass percentage concentration of 0.2 wt%) for fourth-stage formation. The fourth-stage formation voltage is 580 V, the constant voltage time is 1000 s, and the temperature is 85℃.

[0095] First heat treatment: Rinse the foil after the fourth-stage formation with water and perform the first heat treatment at 550℃ for 120 s.

[0096] First re-forming treatment: After the first heat treatment, the foil is rinsed with water and placed in the first re-forming treatment solution (the first re-forming treatment solution is an aqueous solution of boric acid with a mass percentage concentration of 8 wt% and ammonium pentaborate with a mass percentage concentration of 1 wt%) for the first re-forming treatment. The re-forming voltage of the first re-forming treatment is 580 V, the constant voltage time is 450 s, and the temperature is 85℃.

[0097] Depolarization treatment: After the first re-forming treatment, the foil is rinsed with water and placed in a 7wt% phosphoric acid aqueous solution for depolarization treatment at a temperature of 65℃ for 400 s.

[0098] Second replenishment treatment: Rinse the depolarized foil with water and immerse it in the second replenishment treatment solution (the second replenishment treatment solution is an aqueous solution of boric acid with a mass percentage concentration of 8 wt% and ammonium pentaborate with a mass percentage concentration of 1 wt%) for the second replenishment treatment. The voltage of the second replenishment treatment is 580V, the constant voltage time is 450 s, and the temperature is 85℃.

[0099] Second heat treatment: Rinse the foil after the second reforming treatment with water and perform a second heat treatment at 550℃ for 120 s.

[0100] Third replenishment treatment: Rinse the foil after the second heat treatment with water and put it into the treatment solution for the third replenishment treatment (the treatment solution for the third replenishment treatment is an aqueous solution of boric acid with a mass percentage concentration of 8 wt% and ammonium pentaborate with a mass percentage concentration of 1 wt%) for the third replenishment treatment. The voltage for the third replenishment treatment is 580 V, the constant voltage time is 450 s, and the temperature is 85℃.

[0101] Stabilization treatment: The foil after the third re-forming treatment is rinsed with water and placed in an aqueous solution of ammonium dihydrogen phosphate with a mass percentage concentration of 2wt% for stabilization treatment at a temperature of 55°C for 120s. After rinsing with water and drying, the formed foil is obtained.

[0102] Example 2 The electrolytic foil was prepared according to the method of Example 1, except that the electrolyte was a carburizing electrolyte: an aqueous solution of glycerol with a mass-volume concentration of 15 g / L and ethanol with a mass-volume concentration of 10 g / L.

[0103] Example 3 The electrolytic foil was prepared according to the method of Example 1, except that the electrolyte was a carbonitriding electrolyte: an aqueous solution of urea with a mass-volume concentration of 15 g / L, NH3·H2O with a mass-volume concentration of 5 g / L, and nano-SiO2 with a mass-volume concentration of 0.2 g / L.

[0104] Example 4 The electrolytic foil was prepared according to the method of Example 1, except that the electrolyte was a boron-carbon co-permeation electrolyte: Na2B4O7·10H2O with a mass-volume concentration of 20 g / L, glycerol with a mass-volume concentration of 15 g / L, and Na2SO4 with a mass-volume concentration of 5 g / L.

[0105] Example 5 The electrolytic foil was prepared according to the method of Example 1, except that the mass-volume concentration of Na2B4O7·10H2O in the boronizing electrolyte was 15 g / L.

[0106] Example 6 The electrolytic foil was prepared according to the method of Example 1, except that the mass-volume concentration of Na2B4O7·10H2O in the boronizing electrolyte was 30 g / L.

[0107] Example 7 The electrolytic foil was prepared according to the method of Example 1, except that the electrolyte was a phosphorus-impregnated electrolyte: NH4H2PO4 with a mass-volume concentration of 40 g / L and C6H8O7·H2O (citric acid monohydrate) with a mass-volume concentration of 2 g / L.

[0108] Example 8 The electrolytic foil was prepared according to the method of Example 1, except that the electrolyte was a boronizing electrolyte: an aqueous solution of Na2B4O7·10H2O with a mass-volume concentration of 40 g / L and NaOH with a mass-volume concentration of 10 g / L. The pulse voltage of the plasma electrolysis treatment was 280 V, the frequency was 10 kHz, the duty cycle was 85%, the time was 600 s, and the temperature was 80 °C.

[0109] Example 9 The electrolytic foil was prepared according to the method of Example 1, except that the electrolyte was a boronizing electrolyte: an aqueous solution of Na2B4O7·10H2O with a mass-volume concentration of 10 g / L and NaOH with a mass-volume concentration of 10 g / L.

[0110] Comparative Example 1 The electroformed foil was prepared according to the method in Example 1, except that the preparation method was as follows: cutting foil → boiling treatment → primary electroformation → secondary electroformation → tertiary electroformation → quaternary electroformation → first heat treatment → first supplementary formation treatment → depolarization treatment → second supplementary formation treatment → second heat treatment → third supplementary formation treatment → stabilization treatment.

[0111] Comparative Example 2 The electroformed foil was prepared according to the method in Example 1, except that the preparation method was as follows: cutting foil → boiling treatment → primary electroformation → secondary electroformation → tertiary electroformation → quaternary electroformation → first heat treatment → first re-forming treatment → depolarization treatment → second re-forming treatment → second heat treatment → third re-forming treatment → stabilization treatment → plasma electrolysis treatment.

[0112] Test case The performance of the formed foils prepared in each embodiment and comparative example was tested, as follows: The performance of the formed foil was tested according to the electronic industry standard SJ / T 11140-2022 "Electrode Foil for Aluminum Electrolytic Capacitors". Withstand voltage refers to the voltage maintained for 180 seconds after the voltage rise time; a higher voltage value indicates better performance. Specific capacitance is the electrostatic capacitance per unit area of ​​the formed foil after the withstand voltage test; its value reflects the strength of the formed foil's charge storage capacity, and a higher specific capacitance is better (except for special specifications). A 5-hour leakage current test was conducted on the formed foil of different embodiments and comparative examples, simulating the use scenario of aluminum electrolytic capacitors. The quality of the oxide film was identified by detecting the magnitude of the leakage current. Hydration resistance (i.e., voltage rise time) refers to the time required to raise the voltage of the formed foil to 90% of its rated forming voltage (Vf) at a specified current; a shorter voltage rise time indicates better oxide film quality.

[0113] The results are shown in Table 1. Compared with Comparative Examples 1-2, Examples 1-9, after introducing plasma electrolysis treatment, can form a permeation layer with a thickness of no more than 1 μm. The withstand voltage and specific capacity of the formed foil are improved, the leakage current is significantly reduced, and the hydration resistance is significantly improved.

[0114] Comparative Example 1 is a sample that has not undergone plasma electrolysis treatment. It is inferior to the Example in terms of withstand voltage and specific volume, and is also worse in terms of leakage current and hydration resistance.

[0115] Comparative Example 2 involved a formation treatment followed by plasma electroporation. The performance of the formed foil sample was similar to that of Comparative Example 1, indicating that the formation followed by electroporation did not significantly improve the foil's performance. The main reason is that the oxide film on the aluminum foil surface is already relatively complete and dense after formation, which increases the difficulty of subsequent plasma electroporation and greatly reduces the effectiveness of the electroporation process.

[0116] The non-metallic element introduced into the permeation layer in Example 7 is phosphorus. The performance of the prepared chemical foil sample (withstand voltage, specific capacitance, leakage current and hydration resistance) is better than that of Comparative Examples 1 and 2, but the withstand voltage is lower than that of the chemical foil prepared in Examples 1-6. Moreover, phosphorus has problems such as pollution, which increases the cost of subsequent permeation electrolyte treatment.

[0117] In Examples 8 and 9, the concentration in the permeate electrolyte exceeded the range of 15 g / L-30 g / L. The performance (withstand voltage, specific capacitance, leakage current and hydration resistance) of the prepared chemical foil samples was better than that of Comparative Examples 1 and 2, but the withstand voltage was lower than that of the chemical layer foils prepared in Examples 1-6, and the hydration resistance was relatively low.

[0118] Table 1

[0119] Note: All rates of change are calculated based on the parameters of Comparative Example 1. Taking the pressure resistance value of Example 1 as an example, the rate of change of the pressure resistance value of Example 1 = (pressure resistance value) / ... 实施例1 -Resistant pressure value 对比例1 ) × 100% / withstand voltage value 对比例1 .

[0120] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A type of electrolytic foil, characterized in that, include: Transformed into a foil substrate; A permeation layer is disposed on at least one surface of the formed foil substrate; An oxide film is disposed on the surface of the permeation layer away from the formed foil substrate; The permeation layer contains non-metallic elements, and the content of non-metallic elements in the permeation layer decreases along the direction from the oxide film to the formed foil substrate.

2. The electroformed foil according to claim 1, characterized in that, The nonmetallic element includes at least one of carbon, boron, and nitrogen.

3. The electroformed foil according to claim 1, characterized in that, The permeation layer further contains the same base metal element as the formed foil substrate; Optionally, the non-metallic elements in the permeation layer exist in the form of metal compounds; Optionally, the matrix metal element in the permeation layer exists in the form of an oxide; Optionally, the oxide film contains the same matrix metal element as the formed foil substrate and exists in the form of an oxide.

4. The electroformed foil according to claim 1, characterized in that, The base metal element includes at least one of aluminum, titanium, copper, and nickel.

5. The electroformed foil according to claim 1, characterized in that, The thickness of the permeable layer is no more than 1 μm.

6. A method for preparing the electroplated foil according to any one of claims 1-5, characterized in that, include: The foil to be treated is subjected to plasma electrolytic permeation treatment to obtain pretreated foil; The pretreated foil is subjected to a chemical transformation process to obtain the chemically transformed foil; The pretreated foil material includes: the formed foil substrate and a pretreatment layer, wherein the pretreatment layer is disposed on at least one surface of the formed foil substrate and contains the non-metallic element.

7. The method according to claim 6, characterized in that, The electrolyte used in the plasma electrolysis treatment includes compounds of the non-metallic elements; Optionally, the electrolyte comprises at least one of the following groups (1) to (4): (1) The electrolyte comprises: sodium tetraborate or its hydrate and a conductive agent; (2) The electrolyte comprises: glycerol and ethanol; (3) The electrolyte comprises: urea, a conductive agent, and inorganic nanoparticles; (4) The electrolyte comprises: sodium tetraborate or its hydrate, glycerol, and sulfate; Optionally, the conductive agent includes at least one of sodium hydroxide, potassium hydroxide, and ammonia water; Optionally, the inorganic nanoparticles include nano-silica; Optionally, the sulfate includes at least one of sodium sulfate, ammonium sulfate, and potassium sulfate; Optionally, the solvent of the electrolyte is deionized water.

8. The method according to any one of claims 6-7, characterized in that, The plasma electrolysis treatment satisfies at least one of the following groups (i) to (iv): (i) The electrolyte comprises: sodium tetraborate or its hydrate with a mass-volume concentration of 15 g / L-30 g / L and NaOH with a mass-volume concentration of 0 g / L-10 g / L; (ii) The electrolyte comprises: glycerol with a mass-volume concentration of 10 g / L to 20 g / L and ethanol with a mass-volume concentration of 5 g / L to 15 g / L; (iii) The electrolyte comprises: urea with a mass-volume concentration of 10 g / L-20 g / L, NH3·H2O with a mass-volume concentration of 0 g / L-10 g / L, and nano-silica with a mass-volume concentration of 0 g / L-1 g / L; (iv) The electrolyte comprises: sodium tetraborate or its hydrate at a mass-volume concentration of 15 g / L to 30 g / L, glycerol at a mass-volume concentration of 10 g / L to 20 g / L, and Na2SO4 at a mass-volume concentration of 4 g / L to 10 g / L.

9. The method according to any one of claims 6-8, characterized in that, The plasma electrolysis treatment satisfies at least one of the following conditions: The power source for the plasma electrolysis treatment is a pulse power source; Optionally, the pulse voltage of the plasma electroosmosis treatment is 250 V-300 V; Optionally, the frequency of the plasma electroosmosis treatment is 5 kHz-12 kHz; Optionally, the duty cycle of the plasma electroosmosis treatment is 60%-90%; Optionally, the plasma electroosmosis treatment time is 240s-360s; Optionally, the temperature of the plasma electroosmosis treatment is 70℃-90℃.

10. An electrolytic capacitor, characterized in that, include: The electroformed foil according to any one of claims 1-5 or the electroformed foil obtained by the method for preparing electroformed foil according to any one of claims 6-9.

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