Modified aluminum powder and its preparation method, electrode foil and electrolytic capacitor

Abstract

This application relates to the field of electrode foil technology, providing modified aluminum powder and its preparation method, electrode foil, and electrolytic capacitor. The modified aluminum powder comprises aluminum particles and a boehmite porous layer coating at least a portion of the surface of the aluminum particles. This application coats the surface of the aluminum particles with a boehmite porous layer, which not only transforms into γ-Al₂O₃ with a porous structure and large specific surface area during sintering, effectively mitigating the specific surface area loss caused by over-sintering; but also, the boehmite surface is rich in hydroxyl groups, exhibiting good dispersibility in the slurry, reducing the agglomeration of aluminum powder in the slurry, and synergistically improving the capacity of the electrode foil.

Description

Technical Field

[0001] This application relates to the field of electrode foil technology, and in particular to modified aluminum powder and its preparation method, electrode foil and electrolytic capacitor. Background Technology

[0002] Hot-pressed electrode foil avoids the traditional electrochemical etching method that uses strong acids to corrode aluminum foil. Instead, it involves coating an aluminum powder slurry layer onto the surface of an aluminum substrate and then sintering it to form a uniformly distributed electrode foil with a large specific surface area, thus avoiding the environmental pollution problems caused by acidic chemical reagents. However, during the sintering process, aluminum powder accumulation and over-burning can cause a loss of specific surface area in the hot-pressed electrode foil, resulting in a reduction in its capacity. Summary of the Invention

[0003] Therefore, it is necessary to provide modified aluminum powder that can improve the specific surface area of ​​electrode foil, its preparation method, electrode foil, and electrolytic capacitor.

[0004] In a first aspect, this application provides a modified aluminum powder, which includes aluminum particles and a boehmite porous layer coating at least a portion of the surface of the aluminum particles.

[0005] In some embodiments, the modified aluminum powder satisfies at least one of the following conditions:

[0006] (1) The volume average particle size Dv50 of the modified aluminum powder is 3μm~10μm;

[0007] (2) The thickness of the boehmite porous layer is 0.5 μm to 1.5 μm;

[0008] (3) The porosity of the boehmite porous layer is 20%~50%;

[0009] (4) The average pore size of the pores in the boehmite porous layer is 10 nm to 30 nm.

[0010] Secondly, this application provides a method for preparing modified aluminum powder as described in the first aspect, the method comprising:

[0011] Aluminum powder raw material, structure directing agent and water are mixed and heated to cause hydrolysis on the surface of aluminum powder raw material and form a boehmite porous layer on at least part of the surface of aluminum powder raw material under the guidance of structure directing agent.

[0012] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0013] (1) The volume average particle size Dv50 of aluminum powder raw material is 3μm~10μm;

[0014] (2) The mass ratio of aluminum powder raw material to structure guiding agent is (40~60):1;

[0015] (3) The ratio of the mass of aluminum powder raw material to the mass of water added is 1: (1~10).

[0016] In some embodiments, the structure-directing agent includes at least one of urea, cetyltrimethylammonium bromide, and Pluronic block copolymers.

[0017] In some implementations, the heating temperature is 70°C to 95°C, and the heating time is 2 hours to 6 hours.

[0018] In some embodiments, an acidic solution is used to pretreat the aluminum powder raw material to remove the aluminum oxide film on the surface of the aluminum powder raw material.

[0019] In some embodiments, the aluminum powder raw material is pretreated to meet at least one of the following conditions:

[0020] (1) The mass concentration of acidic substances in the acidic solution is 1%~5%;

[0021] (2) The acidic substances contained in the acidic solution include at least one of citric acid, oxalic acid, acetic acid, tartaric acid, hydrochloric acid, nitric acid, hydrofluoric acid and phosphoric acid;

[0022] (3) The temperature of the pretreatment is 10℃~30℃ and the time is 3h~8h.

[0023] Thirdly, this application also provides an electrode foil, the electrode foil including a substrate and an aluminum powder sintered layer disposed on at least one side surface of the substrate, the aluminum powder sintered layer being made of a slurry containing modified aluminum powder as described in the first aspect.

[0024] Fourthly, this application provides an electrolytic capacitor, which includes electrode foil as described in the third aspect.

[0025] Compared with traditional technologies, this application has at least the following beneficial effects:

[0026] This application coats the surface of aluminum particles with a porous boehmite layer, which can not only be transformed into γ-Al2O3 with a porous structure and large specific surface area during sintering, effectively alleviating the specific surface area loss caused by over-burning; but also the boehmite surface is rich in hydroxyl groups, which has good dispersibility in the slurry, can reduce the agglomeration of aluminum powder in the slurry, and synergistically improve the capacity of the electrode foil. Detailed Implementation

[0027] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0029] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0030] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0031] It should be noted that in this application, boehmite refers to hydrated alumina (γ-AlOOH).

[0032] In traditional technology, aluminum powder is prone to forming an aluminum oxide film on its surface, which makes the aluminum powder poorly dispersed in the slurry and prone to agglomeration. Moreover, after sintering, due to particle accumulation and over-burning, the specific surface area of ​​the sintered aluminum powder layer becomes smaller, resulting in a reduction in the capacity of the electrode foil.

[0033] The first aspect of this application provides a modified aluminum powder, which includes aluminum particles and a boehmite porous layer coating at least a portion of the surface of the aluminum particles.

[0034] This application coats the surface of aluminum particles with a porous boehmite layer, which can not only be transformed into γ-Al2O3 with a porous structure and large specific surface area during sintering, effectively alleviating the specific surface area loss caused by over-burning; but also the boehmite surface is rich in hydroxyl groups, which has good dispersibility in the slurry, can reduce the agglomeration of aluminum powder in the slurry, and synergistically improve the capacity of the electrode foil.

[0035] In some embodiments, the volume average particle size Dv50 of the modified aluminum powder is 3μm to 10μm, for example, it can be 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm or 10.0μm.

[0036] In some embodiments, the thickness of the boehmite porous layer is 0.5 μm to 1.5 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm. The porosity of the boehmite porous layer is 20% to 50%, for example, it can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50%; optionally, it can be 30% to 50%. The average pore size of the pores contained in the boehmite porous layer is 10 nm to 30 nm, for example, it can be 10 nm, 12 nm, 14 nm, 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, or 30 nm.

[0037] This application controls the thickness and pore size of the boehmite porous layer as described above, so that the modified aluminum powder has a large specific surface area, which can effectively improve the problems of overburning and agglomeration of electrode foil, thereby increasing the capacity of electrode foil.

[0038] The second aspect of this application provides a method for preparing modified aluminum powder as described in the first aspect, the method comprising:

[0039] Aluminum powder raw material, structure directing agent and water are mixed and heated to cause hydrolysis on the surface of aluminum powder raw material and form a boehmite porous layer on at least part of the surface of aluminum powder raw material under the guidance of structure directing agent.

[0040] This application utilizes the spontaneous aggregation of structure-directing agents in the reaction system to form ordered template structures such as micelles and liquid crystal phases. This allows boehmite nanosheets to grow in situ after hydrolysis of the aluminum powder surface, thus forming a porous boehmite layer coating the aluminum powder surface. This porous boehmite layer not only transforms into γ-Al₂O₃ with a porous structure and large specific surface area during sintering, effectively mitigating the specific surface area loss caused by over-sintering and thus improving the electrode foil's capacity, but also, due to the rich hydroxyl content on the boehmite surface, exhibits good dispersibility in the slurry, reducing aluminum powder agglomeration and further enhancing the electrode foil's capacity.

[0041] It is understood that the structure-directing agent in this application refers to a material that spontaneously aggregates in the reaction system to form ordered template structures such as micelles and liquid crystal phases, and guides the product to grow into the monoclinic layered structure of boehmite by regulating the hydrolysis rate of aluminum ions and controlling the directional growth of crystal forms. It is adsorbed on specific crystal faces to guide the growth of boehmite into a porous plate-like structure, rather than directly reacting chemically with aluminum.

[0042] In some embodiments, the structure-directing agent includes at least one selected from urea, hexadecyltrimethylammonium bromide, and Pluronic block copolymers. Pluronic block copolymers are a class of high-molecular-weight nonionic surfactants with the molecular formula HO-(C2H4O). m -(C3H6O) n -H represents a polyoxyethylene-polyoxypropylene ether block copolymer. Optionally, the Pluronic series block copolymers include at least one of P123 (CAS registration number 106392-12-5) and F127 (CAS registration number 9003-11-6). This application employs the above-mentioned structure-directing agent to control the particle morphology and dispersion of modified aluminum powder, effectively preventing the agglomeration of aluminum powder particles.

[0043] In some embodiments, the volume average particle size Dv50 of the aluminum powder raw material is 3μm to 10μm, for example, it can be 3.0μm, 3.5μm, 4.0μm, 4.5μm, 5.0μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm or 10.0μm.

[0044] In some embodiments, the mass ratio of aluminum powder raw material to structure-directing agent is (40~60):1, for example, it can be 40:1, 42:1, 44:1, 46:1, 48:1, 50:1, 52:1, 54:1, 56:1, 58:1 or 60:1. The mass ratio of aluminum powder raw material to water added is 1:(1~10), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9 or 1:10; optionally, it can be 1:(4~6). The above-mentioned selection of the mass of structure-directing agent in this application aims to form a dense boehmite porous layer with relatively uniform pore size and thickness on the surface of the aluminum powder raw material, effectively increasing the specific surface area of ​​the aluminum powder and reducing the problem of aluminum powder agglomeration.

[0045] In some embodiments, the heating temperature is 70°C to 95°C, for example, it can be 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, 82°C, 84°C, 86°C, 88°C, 90°C, 92°C, 94°C, or 95°C. The heating time is 2 hours to 6 hours, for example, it can be 2.0 hours, 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, or 6.0 hours.

[0046] The heating temperature selected in this application is conducive to the stable growth of boehmite nanosheets on the surface of aluminum powder, and the formation of a well-crystallized, regularly structured, and porous boehmite layer, which effectively improves the problem of aluminum powder overheating.

[0047] It is understood that if the aluminum powder particles do not have an alumina film on their surface, pretreatment of the aluminum powder particles is unnecessary. In some embodiments, an acidic solution is used to pretreat the aluminum powder raw material to remove the alumina film on its surface. Further, the pretreated aluminum powder raw material is washed with deionized water to prevent impurities such as acidic substances from remaining on its surface. This application uses an acidic solution to pretreat the aluminum powder raw material, which can remove the oxide film on the aluminum powder surface. Moreover, because the naturally formed oxide film has an uneven thickness, it can form an uneven pit structure on the aluminum powder surface, further increasing the specific surface area of ​​the modified aluminum powder.

[0048] In some embodiments, the mass concentration of the acidic substance in the acidic solution is 1% to 5%, for example, it can be 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%. This application uses a low-concentration acidic solution to effectively remove the surface oxide film while avoiding excessive etching of the aluminum powder particles.

[0049] It is understood that the acidic substance may be at least one of organic and inorganic acids. In some embodiments, the acidic solution contains at least one of citric acid, oxalic acid, acetic acid, tartaric acid, hydrochloric acid, nitric acid, hydrofluoric acid, and phosphoric acid.

[0050] In some embodiments, the pretreatment temperature can be room temperature, for example, the temperature can be 10℃~30℃. The pretreatment time is 3h~8h, for example, it can be 3h, 4h, 5h, 6h, 7h or 8h.

[0051] In some embodiments, before pretreating the aluminum powder raw material, the preparation method further includes: degreasing the aluminum powder raw material to remove organic matter from the particle surface. Optionally, the degreasing treatment includes: ultrasonically treating the aluminum powder raw material with an organic solvent. The organic solvent can be at least one of anhydrous ethanol and propanol. It is understood that cleaning with an organic solvent can be performed after the degreasing treatment.

[0052] In some embodiments, the modified aluminum powder obtained after heating is cleaned to reduce impurities remaining on the surface of the modified aluminum powder. The cleaning solvent can be deionized water or anhydrous ethanol.

[0053] Exemplary, a method for preparing the above-mentioned modified aluminum powder is provided, comprising the following steps:

[0054] Aluminum powder raw materials with Dv50 of 3μm~10μm are degreased and then pretreated with an acidic solution of 1%~5% by mass for 3h~8h at room temperature to remove the aluminum oxide film on the surface of the aluminum powder raw materials.

[0055] The pretreated aluminum powder, structure-directing agent, and water are mixed and heated to hydrolyze the aluminum on the surface of the aluminum powder and allow it to pass through the structure-directing agent. The mass ratio of aluminum powder to structure-directing agent is (40~60):1, and the mass ratio of aluminum powder to water is 1:(1~10). The mixture is heated at 70℃~95℃ for 2h~6h to obtain modified aluminum powder.

[0056] A third aspect of this application also provides an electrode foil, the electrode foil comprising a substrate and an aluminum powder sintered layer disposed on at least one surface of the substrate, the aluminum powder sintered layer being made of a slurry containing modified aluminum powder as described in the first aspect.

[0057] In some embodiments, the substrate may be aluminum foil.

[0058] In some embodiments, the method for preparing the electrode foil includes:

[0059] Modified aluminum powder, binder, additives, and solvent are mixed to form a slurry. The slurry is then coated onto the surface of a substrate and dried to form an aluminum powder layer. The substrate with the aluminum powder layer is then sintered and chemically formed to prepare the electrode foil.

[0060] The binder, additives, and solvents can be selected and their amounts controlled according to the coating requirements of the slurry. For example, the solid content of the slurry can be 50% to 60%. The binder can be ethyl cellulose; the additive can be ethylene glycol dispersant; and the solvent can be terpineol.

[0061] Optionally, before sintering the substrate with the aluminum powder layer, it can be subjected to a cracking process to form cracks in the aluminum powder layer on at least one surface of the substrate layer. For example, a roller can be used to surface-tension the substrate with the aluminum powder layer to form cracks.

[0062] A fourth aspect of this application also provides an electrolytic capacitor, which includes electrode foil as described in the third aspect.

[0063] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0064] Example 1

[0065] Aluminum powder with a Dv50 of 3.5 μm was ultrasonically treated with anhydrous ethanol to remove organic matter from its surface, and then cleaned with anhydrous ethanol. Next, the aluminum powder was cleaned with a 1% phosphoric acid solution at 25°C for 4 hours to remove the alumina film on its surface, and then cleaned with anhydrous ethanol, ensuring the cleaning solution was neutral in pH.

[0066] The treated aluminum powder, hexadecyltrimethylammonium bromide (CTAB), and deionized water were mixed and heated to hydrolyze the surface of the aluminum powder and form a boehmite porous layer in situ on the surface of the aluminum powder under the guidance of CTAB. The mass ratio of aluminum powder to CTAB was 50:1, and the mass ratio of aluminum powder to deionized water was 1:5. The heating temperature was 70℃, and the time was 6 hours. After the reaction, the mixture was washed with deionized water and anhydrous ethanol to obtain modified aluminum powder with a Dv50 of approximately 3.5 μm, a boehmite porous layer thickness of approximately 0.8 μm, a porosity of approximately 20%, and an average pore diameter of approximately 15 nm.

[0067] Example 2

[0068] The modified aluminum powder was prepared according to the method of Example 1, except that the mass concentration of the phosphoric acid solution was 3%, the Dv50 of the modified aluminum powder was about 3.5 μm, the thickness of the boehmite porous layer was about 1 μm, the porosity was about 25%, and the average diameter of the pores was about 14 nm.

[0069] Example 3

[0070] Modified aluminum powder was prepared according to the method in Example 1, except that the mass concentration of the phosphoric acid solution was 3%, the heating temperature for forming the boehmite porous layer was 80°C, and the heating time was 5 hours. The modified aluminum powder obtained had a Dv50 of 3.5 μm, a boehmite porous layer thickness of about 0.5 μm, a porosity of about 30%, and an average pore diameter of about 16 nm.

[0071] Example 4

[0072] Modified aluminum powder was prepared according to the method in Example 1, except that the mass concentration of the phosphoric acid solution was 3%, the mass ratio of aluminum powder to CTAB was 45:1, the heating temperature for forming the boehmite porous layer was 90°C, and the heating time was 4 hours. The modified aluminum powder obtained had a Dv50 of 3.5 μm, a thickness of approximately 1.2 μm in the boehmite porous layer, a porosity of approximately 40%, and an average pore diameter of approximately 18 nm.

[0073] Example 5

[0074] The modified aluminum powder was prepared according to the method of Example 4, except that the mass concentration of the phosphoric acid solution was 5%, the heating temperature when forming the boehmite porous layer was 80°C, the Dv50 of the modified aluminum powder was 3 μm, the thickness of the boehmite porous layer was about 0.5 μm, the porosity was about 10%, and the average diameter of the pores was about 30 nm.

[0075] Example 6

[0076] The modified aluminum powder was prepared according to the method of Example 4, except that the heating temperature was 60°C, the Dv50 of the modified aluminum powder was 3.5 μm, the thickness of the boehmite porous layer was about 0.5 μm, the porosity was about 25%, and the average diameter of the pores was about 12 nm.

[0077] Example 7

[0078] The modified aluminum powder was prepared according to the method of Example 4, except that the heating temperature was 100°C, the Dv50 of the modified aluminum powder was 3.5 μm, the thickness of the boehmite porous layer was about 1.5 μm, the porosity was about 20%, and the average diameter of the pores was about 21 nm.

[0079] Example 8

[0080] The modified aluminum powder was prepared according to the method of Example 4, except that the mass ratio of aluminum powder to CTAB was 30:1, the Dv50 of the modified aluminum powder was 3.5 μm, the thickness of the boehmite porous layer was about 0.8 μm, the porosity was about 15%, and the average diameter of the pores was about 11 nm.

[0081] Example 9

[0082] The modified aluminum powder was prepared according to the method of Example 4, except that the mass ratio of aluminum powder to CTAB was 70:1, the Dv50 of the modified aluminum powder was 3.5 μm, the thickness of the boehmite porous layer was about 1.5 μm, the porosity was about 21%, and the average diameter of the pores was about 8 nm.

[0083] Example 10

[0084] Modified aluminum powder was prepared according to the method of Example 4, except that the mass ratio of aluminum powder to water was 1:3, the Dv50 of the modified aluminum powder was 3.5 μm, the thickness of the boehmite porous layer was about 1.0 μm, the porosity was about 25%, and the average diameter of the pores was about 20 nm.

[0085] Example 11

[0086] Modified aluminum powder was prepared according to the method of Example 4, except that the mass ratio of aluminum powder to water was 1:7, the Dv50 of the modified aluminum powder was 3.5 μm, the thickness of the boehmite porous layer was about 0.6 μm, the porosity was about 24%, and the average diameter of the pores was about 12 nm.

[0087] Comparative Example 1

[0088] Modified aluminum powder was prepared according to the method of Example 1, except that no structure directing agent was added, and the Dv50 of the modified aluminum powder was 3.5 μm, and no boehmite porous layer was formed.

[0089] Comparative Example 2

[0090] The untreated aluminum powder from Example 1 was used directly as the modified aluminum powder.

[0091] The thickness, porosity, and average pore diameter of the boehmite porous layer in the aluminum powder prepared in the above embodiments and comparative examples were tested. The testing methods included:

[0092] Thickness: Cross-sectional observation using scanning electron microscopy (SEM) was employed. Aluminum powder coated with a boehmite layer was embedded in resin, cured, and then polished or cut with focused ion beam (FIB) to obtain a flat cross-section of the powder particles. High-resolution SEM was used to image the cross-section, allowing direct observation and measurement of the thickness of the boehmite layer on the aluminum powder surface.

[0093] Pore ​​size and porosity: These were obtained using the nitrogen adsorption method (BET / BJH), and the results are shown in Table 1.

[0094] Table 1

[0095]

[0096] Electrode foils prepared using aluminum powder obtained from the above embodiments and comparative examples include:

[0097] Aluminum powder and terpineol, ethyl cellulose and ethylene glycol in a mass ratio of 88:10:2 were mixed to obtain a slurry with a solid content of 55%.

[0098] The above slurry was coated on both sides of an aluminum foil with a thickness of 30 μm, and dried at 120°C to form a coated sample with a total thickness of 130 μm. The thickness of the aluminum powder slurry layer on both sides of the aluminum foil after drying in the coated sample was 50 μm.

[0099] It was placed in a sintering furnace and degreased at 400℃ for 1 hour in a vacuum environment, and then sintered at 640℃ for 2 hours.

[0100] The sintered foil was formed in a 100 g / L boric acid solution at 520 V for 20 min, and then placed in air at 500 °C for 2 min. Finally, it was formed in the solution for 10 min to obtain the electrode foil.

[0101] The electrode foil prepared above was tested using an LCR digital bridge, with ammonium pentaborate at a concentration of 85 g / L as the electrolyte. The test results are shown in Table 2, where Tr is the boost time in seconds, referring to the time taken at a specified current density (tested at a current density of 0.4 mA / cm²). 2 Under the given conditions, the time taken for the voltage to rise to 90% of the rated voltage (Vf) of an electrolytic capacitor from the initial voltage application. Vt is the oxide film withstand voltage, in volts (V), referring to the voltage reached 180 ± 10 seconds after the voltage rise point (Tr). tg is the loss tangent, referring to the loss factor or dielectric loss. CAP is the specific capacitance, in μF / cm². 2 , refers to the capacitance that the anode foil forming foil of an electrolytic capacitor can exhibit per unit area (usually taken as 1 cm²). Bending refers to bending strength / bending endurance, measured in cycles; it is the maximum number of bends that the anode foil forming foil of an electrolytic capacitor can withstand before breaking.

[0102] Table 2

[0103]

[0104] As can be seen from the table above:

[0105] Compared with Comparative Examples 1-2, Examples 1-11 show that the aluminum powder in the slurry prepared using the modified aluminum powder of this application has good uniformity of dispersion and basically does not agglomerate; furthermore, after sintering, an electrode foil with a large specific surface area is formed, and the capacity performance is significantly improved.

[0106] Specifically, compared with Examples 6-7, Example 4 shows that controlling the temperature for forming the boehmite porous layer in this application can improve the pore-forming function of the CTAB template, promote the growth of the target morphology of the boehmite porous layer, and form a 3D porous network structure, increasing the specific surface area and thus improving the capacity. However, excessively high temperatures may cause overgrowth or collapse of the boehmite porous layer.

[0107] Compared with Examples 8-9, Examples 1 and 4 show that, as a cationic structure directing agent, the appropriate addition of CTAB can reduce the interfacial tension between the aluminum surface and the solution, improve the contact area, enhance the etching effect, and thus increase the specific surface area and capacity. However, a relatively large addition of CTAB may lead to surface charge reversal due to multilayer adsorption, causing aluminum powder agglomeration in the system, resulting in pore blockage or excessive erosion of the aluminum matrix, leading to structural damage and a decrease in the specific surface area and performance of the aluminum powder.

[0108] Compared with Examples 10-11, Examples 1 and 4 show that controlling the amount of water added in this application is beneficial for forming a uniform and dense 3D porous layer, which helps to increase the specific surface area. If the amount of water added is too low, it may lead to insufficient hydrolysis of aluminum powder, and the high concentration of CTAB may cause a local high-viscosity environment, resulting in discontinuous and uneven thickness of the porous layer. If the amount of water added is too high, the boehmite lamellae will grow longitudinally, the lamellae will thicken, the pores will widen, and the specific surface area will decrease.

[0109] In Comparative Example 1, no structure-directing agent was added, resulting in aluminum powder that could not form an ideal three-dimensional porous structure, limiting the improvement in specific surface area. Furthermore, it was prone to agglomeration during slurry preparation, leading to a decrease in the capacity performance of the electrode foil. Compared to the traditional aluminum powder in Comparative Example 2, the modified aluminum powder in this application exhibits a capacity performance improvement of over 44.5%, and its bending properties are also significantly improved.

[0110] In summary, this application utilizes a structure-directing agent to enable the in-situ formation of boehmite nanosheets after hydrolysis of the aluminum powder surface, thereby forming a porous boehmite layer with a porous structure coating the aluminum powder surface. This porous boehmite layer not only transforms into γ-Al₂O₃ with a porous structure and large specific surface area during sintering, effectively mitigating the specific surface area loss caused by over-firing and thus improving the capacity of the electrode foil; furthermore, because the boehmite surface is rich in hydroxyl groups, it has good dispersibility in the slurry, reducing the agglomeration of aluminum powder in the slurry and further improving the capacity of the electrode foil.

[0111] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0112] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A modified aluminum powder, characterized in that, The modified aluminum powder includes aluminum particles and a boehmite porous layer covering at least a portion of the surface of the aluminum particles.

2. The modified aluminum powder as described in claim 1, characterized in that, The modified aluminum powder satisfies at least one of the following conditions: (1) The volume average particle size Dv50 of the modified aluminum powder is 3μm~10μm; (2) The thickness of the boehmite porous layer is 0.5 μm to 1.5 μm; (3) The porosity of the boehmite porous layer is 20%~50%; (4) The average pore size of the pores in the boehmite porous layer is 10 nm to 30 nm.

3. A method for preparing the modified aluminum powder according to claim 1 or 2, characterized in that, The method for preparing the modified aluminum powder includes: Aluminum powder raw material, structure guiding agent and water are mixed and heated to cause hydrolysis on the surface of the aluminum powder raw material and to form a boehmite porous layer on at least a portion of the surface of the aluminum powder raw material under the guidance of the structure guiding agent.

4. The method for preparing modified aluminum powder as described in claim 3, characterized in that, The preparation method satisfies at least one of the following conditions: (1) The volume average particle size Dv50 of the aluminum powder raw material is 3μm~10μm; (2) The mass ratio of the aluminum powder raw material to the structure guiding agent is (40~60):1; (3) The ratio of the mass of the aluminum powder raw material to the mass of water added is 1: (1~10).

5. The method for preparing modified aluminum powder as described in claim 3, characterized in that, The structure-directing agent includes at least one of urea, hexadecyltrimethylammonium bromide, and Pluronic block copolymers.

6. The method for preparing modified aluminum powder as described in claim 3, characterized in that, The heating temperature is 70℃~95℃, and the time is 2h~6h.

7. The method for preparing modified aluminum powder according to any one of claims 3-6, characterized in that, The aluminum powder raw material is pretreated with an acidic solution to remove the aluminum oxide film on the surface of the aluminum powder raw material.

8. The method for preparing modified aluminum powder as described in claim 7, characterized in that, The pretreatment of the aluminum powder raw material satisfies at least one of the following conditions: (1) The mass concentration of the acidic substance in the acidic solution is 1% to 5%; (2) The acidic substances contained in the acidic solution include at least one of citric acid, oxalic acid, acetic acid, tartaric acid, hydrochloric acid, nitric acid, hydrofluoric acid and phosphoric acid; (3) The temperature of the pretreatment is 10℃~30℃ and the time is 3h~8h.

9. An electrode foil, characterized in that, The electrode foil includes a substrate and an aluminum powder sintered layer disposed on at least one side of the substrate, wherein the aluminum powder sintered layer is made of a slurry containing the modified aluminum powder as described in claim 1 or 2.

10. An electrolytic capacitor, characterized in that, The electrolytic capacitor includes the electrode foil as described in claim 9.

Images