Aluminum powder sintering type electrolytic capacitor anode foil and preparation method thereof

Abstract

The invention relates to the technical field of aluminum electrolytic capacitors, and particularly discloses an aluminum powder sintering type electrolytic capacitor anode foil and a preparation method thereof.The magnesium element is introduced into spherical aluminum powder, a uniform fine grain structure is obtained during sintering, the porosity of the anode foil is improved, and the dielectric property of the anode foil is enhanced; the preparation method comprises the following steps: preparing spherical aluminum powder, then coating and modifying by using a silicon dioxide-titanium dioxide shell layer, keeping the sintering activity of aluminum, mixing the modified spherical aluminum powder with an additive to prepare modified aluminum powder slurry, coating the modified aluminum powder slurry on a high-purity aluminum foil, and sintering and forming to obtain the aluminum powder sintering type electrolytic capacitor anode foil with good dielectric property.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aluminum electrolytic capacitor, in particular to an aluminum powder sintering type electrolytic capacitor anode foil and a preparation method thereof. BACKGROUND

[0002] Electrolytic capacitors can be divided into aluminum electrolytic capacitors, tantalum electrolytic capacitors and niobium electrolytic capacitors according to the types of dielectric therein. Among them, aluminum electrolytic capacitors have the advantages of large capacity, small size, low cost and strong self-healing ability, and are widely used in the fields of electronic products, communication equipment and aerospace. The core of traditional aluminum electrolytic capacitors is high-purity aluminum foil, and a porous structure is formed on the surface of the aluminum foil through electrochemical corrosion, and then a dielectric oxide film is generated through anodic oxidation, that is, the dielectric layer of the capacitor, and the electrical properties thereof directly determine the capacitance and reliability of the capacitor. However, with the development of technology, the traditional corrosion method for preparing anode foil encounters a bottleneck in the improvement of the uniformity of the porous structure and the specific surface area, which restricts the further breakthrough of the performance of the capacitor.

[0003] Therefore, a new anode foil technology, aluminum powder sintering type anode foil technology, emerges as the times require. The aluminum powder sintering type anode foil technology discards the process of manufacturing a porous structure by the traditional corrosion method, and instead adopts the method of stacking and sintering high-purity aluminum powder on an aluminum foil base to form a three-dimensional conductive network, so as to more accurately and greatly improve the effective specific surface area of the anode foil, and then improve the capacitance and other properties of the aluminum electrolytic capacitor. Compared with the traditional corrosion method, the preparation process of the aluminum powder sintering method has fewer processes, high utilization rate of raw materials, no need for acid corrosion and waste acid and liquid discharge. However, there are still some technical problems to be solved, such as insufficient connection between aluminum powders during sintering, which leads to powder falling, so that part of the aluminum powder becomes an invalid dead zone, affecting the integrity of the conductive network; and excessive melting during sintering leads to a decrease in porosity, which is not conducive to the filling of the subsequent electrolyte. Therefore, it is particularly important to solve the problems of powder falling or excessively low porosity during sintering in order to promote the maturation of sintered aluminum electrolytic capacitors. SUMMARY

[0004] The present application aims to provide an aluminum powder sintering type electrolytic capacitor anode foil and a preparation method thereof, which solves the problem of performance degradation of the electrolytic capacitor caused by powder falling or excessively low porosity during sintering.

[0005] In order to solve the above technical problems, the present application provides the following technical solutions: A preparation method of an aluminum powder sintering type electrolytic capacitor anode foil, specifically comprising: Step 1: adding spherical aluminum powder into a magnesium nitrate ethanol solution to obtain Mg-Al powder; Step 2: adding the Mg-Al powder into a mixed sol obtained by hydrolysis of tetraethyl orthosilicate and tetrabutyl titanate to obtain Mg-Al powder@SiO2-TiO2; Step 3: Modify Mg-Al powder@SiO2-TiO2 with silane coupling agent KH-560 to obtain KH-560 modified Mg-Al powder@SiO2-TiO2; Step 4: KH-560 modified Mg-Al powder@SiO2-TiO2, pore-forming agent PMMA microspheres, binder polyvinyl butyral, plasticizer dibutyl phthalate and dispersant ammonium polyacrylate are added sequentially to a mixed solution composed of anhydrous ethanol and terpineol to form a modified aluminum powder slurry. Step 5: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, and after drying, sintering, cooling and cleaning, and formation treatment, the anode foil of aluminum powder sintered electrolytic capacitor is obtained.

[0006] As a limitation of the present invention, the preparation method of the Mg-Al powder is as follows: Magnesium nitrate hexahydrate was added to anhydrous ethanol and stirred at 200-300 rpm for 20-30 min. Spherical aluminum powder was added and ultrasonically dispersed for 20-30 min to form a suspension. The suspension was then dried by rotary evaporation at 90-100℃ for 1-2 h to obtain precursor powder. Under nitrogen protection, the precursor powder was placed in a vacuum furnace and kept at 450-470℃ for 1-2 h. After the holding time was completed, the powder was cooled to obtain Mg-Al powder. The mass ratio of magnesium nitrate hexahydrate to spherical aluminum powder is (1-2):(10-15).

[0007] Under nitrogen protection, magnesium nitrate adhering to spherical aluminum powder decomposes at high temperature to generate highly active magnesium oxide. Subsequently, magnesium diffuses into the aluminum lattice to form a Mg-Al solid solution. At the same time, some magnesium oxide reacts with aluminum oxide on the surface of aluminum powder to form a magnesium aluminum spinel phase, which destroys the dense oxide layer of aluminum powder and enhances sintering activity.

[0008] Magnesium has a low diffusion activation energy in aluminum, which facilitates grain boundary migration and atomic diffusion during sintering, thus lowering the sintering temperature. Simultaneously, magnesium tends to segregate at grain boundaries, inhibiting excessive growth of aluminum grains at high temperatures and resulting in a uniform, fine-grained structure. During sintering, the bonding between aluminum powders is enhanced, increasing the mechanical strength of the anode foil, improving pore connectivity, increasing specific surface area, reducing dead zones, and improving the capacitor's specific capacitance. During formation, a more uniform substrate structure helps form a dense dielectric oxide film, reducing oxide film defects, increasing the anode foil breakdown voltage, reducing losses and leakage current, and extending the capacitor's lifespan.

[0009] As a limitation of the present invention, the preparation method of the Mg-Al powder@SiO2-TiO2 is as follows: Tetrabutyl titanate was added to a mixed solution of anhydrous ethanol and deionized water and stirred at 200-300 rpm for 20-30 min to obtain a tetrabutyl titanate ethanol solution. Tetrabutyl titanate was added to the mixed solution of anhydrous ethanol and deionized water and stirred at 200-300 rpm for 20-30 min, then added to the tetrabutyl titanate ethanol solution and stirred until homogeneous. Mg-Al powder was added and ultrasonically dispersed for 20-30 min. The pH was adjusted to 3-4, and the reaction was carried out at 60-70℃ with stirring at 200-300 rpm for 3-4 h. After the reaction was completed, the product was separated by centrifugation, washed with anhydrous ethanol, vacuum dried at 70-80℃ for 3-4 h, and then calcined at 450-470℃ for 1-2 h under nitrogen protection. After calcination, the product was cooled to room temperature to obtain Mg-Al powder@SiO2-TiO2.

[0010] As a limitation of the present invention, the mass ratio of tetrabutyl orthosilicate, tetrabutyl titanate, and Mg-Al powder is (1-2):(0.5-1.5):(10-15).

[0011] Tetrabutyl orthosilicate and tetrabutyl titanate hydrolyze to generate corresponding silanol and titaniumol groups. The hydroxyl groups further condense to form a three-dimensional inorganic network that wraps around the surface of Mg-Al powder. After high-temperature heat treatment, a SiO2-TiO2 inorganic shell structure is formed.

[0012] The silica-titanium dioxide shell effectively isolates aluminum powder particles, preventing their agglomeration, refining the microstructure, preventing deep oxidation of aluminum powder particles before sintering, maintaining the sintering activity of aluminum, and inhibiting grain boundary migration through pinning effect during the sintering stage, which helps to improve porosity. During sintering, titanium dioxide reacts with aluminum to form Al3Ti compounds, which significantly improves the bonding strength between aluminum powder particles, while reducing the activation energy and sintering temperature. In addition, titanium dioxide itself has a high dielectric constant, which has a positive impact on the dielectric properties of the anode foil after being introduced into the system.

[0013] As a limitation of the present invention, the preparation method of the KH-560 modified Mg-Al powder@SiO2-TiO2 is as follows: Silane coupling agent KH-560 was added to a mixed solution of anhydrous ethanol and deionized water, stirred at 200-300 rpm for 20-30 min, and the pH was adjusted to 4-5. Mg-Al powder@SiO2-TiO2 was added, and the reaction was carried out at 70-80℃ and stirred at 300-400 rpm for 2-3 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filtrate was washed with anhydrous ethanol and dried under vacuum at 70-80℃ for 2-3 h to obtain KH-560 modified Mg-Al powder@SiO2-TiO2. The mass ratio of silane coupling agent KH-560 to Mg-Al powder@SiO2-TiO2 is (0.5-1.5):(10-15).

[0014] The silane coupling agent, through the silanol groups generated by its hydrolysis, undergoes a condensation reaction with the hydroxyl groups on the surface of the silica-titanium dioxide shell, forming stable Si-O-Si covalent bonds. This introduces epoxy groups onto the surface of the composite material, significantly enhancing the compatibility and dispersion stability of aluminum powder in the organic slurry system. It also optimizes the rheological properties of the modified aluminum powder slurry, facilitating the formation of a uniform and dense wet film during coating. In the subsequent sintering process, the good dispersibility avoids the problem of uneven density caused by aluminum powder agglomeration, promotes uniform release of thermal stress and the formation of pore structures in the anode foil, and improves the uniformity and consistency of oxide film growth during subsequent formation treatments.

[0015] As a limitation of this invention, the preparation method of the modified aluminum powder slurry is as follows: The binder polyvinyl butyral, the plasticizer dibutyl phthalate, and the dispersant ammonium polyacrylate were added to a mixed solution of anhydrous ethanol and terpineol. The mixture was stirred at 200-300 rpm for 20-30 minutes at 60-70°C. Then, KH-560 modified Mg-Al powder@SiO2-TiO2 and PMMA microspheres were added. The mixture was dispersed at 1500-2000 rpm for 50-60 minutes and then vacuum degassed at (-0.07)-(-0.09) MPa for 10-15 minutes to obtain the modified aluminum powder slurry. By weight, the modified aluminum powder slurry comprises 5-7 parts of binder polyvinyl butyral, 1.5-2 parts of plasticizer dibutyl phthalate, 0.5-1 parts of dispersant ammonium polyacrylate, 100-120 parts of KH-560 modified Mg-Al powder@SiO2-TiO2 and 10-20 parts of pore-forming agent PMMA microspheres.

[0016] The pore-forming agent PMMA microspheres completely decompose during the sintering process and escape in the form of gas, leaving uniformly distributed spherical pores in the sintering system, thereby improving the porosity of the anode foil.

[0017] As a limitation of the present invention, the preparation method of the anode foil of the aluminum powder sintered electrolytic capacitor is as follows: After surface activation treatment of high-purity aluminum foil, modified aluminum powder slurry is coated and vacuum dried. Then, it is transferred to a heating furnace and sintered under nitrogen protection. After sintering, it is cooled to room temperature with the furnace to obtain sintered aluminum foil. It is ultrasonically cleaned in phosphoric acid aqueous solution for 5-10 minutes, rinsed with deionized water, and transferred to ammonium borate solution for formation. Using sintered aluminum foil as anode and high-purity aluminum plate as cathode, aluminum powder sintered electrolytic capacitor anode foil is obtained.

[0018] As a limitation of this invention, the surface activation treatment of the high-purity aluminum foil specifically includes: High-purity aluminum foil was sequentially immersed in acetone and anhydrous ethanol, and ultrasonically cleaned for 5-10 minutes each. Then it was transferred to a plasma activation device, argon gas was introduced, and plasma activation treatment was carried out to obtain surface-activated high-purity aluminum foil. The process conditions for plasma activation treatment include: argon flow rate of 40-60 sccm, power supply of 120-150W, and activation time of 1-3 min.

[0019] As a limitation of the present invention, during coating, the wet film thickness is controlled to be 120-150 μm; during vacuum drying, the drying temperature is 80-90℃ and the drying time is 10-30 min; during sintering, the heating rate is 5-10℃ / min, the sintering temperature is 580-600℃, and the sintering time is 1-3 h; the phosphoric acid aqueous solution contains 5-10 wt% phosphoric acid; during formation, the ammonium borate solution contains 5-10 wt% ammonium borate, the solution temperature is 80-90℃, the electrode spacing is 5-10 cm, and the current density is 0.5-0.8 mA / cm². 2 The formation voltage is 180-220V, and the formation time is 20-30min.

[0020] During formation, under the influence of electric current, the aluminum on the surface of the sintered anode foil loses electrons and is oxidized, combining with oxygen ions in the solution to form a dense alumina film in situ. The ammonium borate solution is weakly acidic, which can inhibit the chemical dissolution of aluminum. The boric acid / borate system can buffer the pH, ensuring that the alumina film grows uniformly on the surface of the sintered anode foil. In addition, during formation, some borate ions are incorporated into the alumina lattice, and boron atoms replace aluminum in the lattice, increasing the disorder of the oxide film, inhibiting crystallization, and improving the long-term stability of the anode foil.

[0021] An anode foil for an aluminum powder sintered electrolytic capacitor is prepared using any of the preparation methods described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are: This invention introduces magnesium into spherical aluminum powder. Magnesium has a low diffusion activation energy in aluminum, which helps grain boundary migration and atomic diffusion during sintering, thus reducing the sintering temperature. At the same time, magnesium tends to agglomerate at grain boundaries, which can inhibit the excessive growth of aluminum grains at high temperatures, thereby obtaining a uniform fine-grained structure, improving the porosity of the anode foil, and enhancing the dielectric properties of the anode foil.

[0023] This invention coats spherical aluminum powder with a silica-titanium dioxide shell, effectively isolating aluminum powder particles, preventing their agglomeration, refining the microstructure, preventing deep oxidation of aluminum powder particles before sintering, maintaining the sintering activity of aluminum, and inhibiting grain boundary migration through pinning effect during the sintering stage, which helps to improve porosity. During sintering, titanium dioxide reacts with aluminum to form Al3Ti compound, which significantly improves the bonding strength between aluminum powder particles, while reducing the activation energy and sintering temperature. In addition, titanium dioxide itself has a high dielectric constant, which has a positive impact on the dielectric properties of the anode foil after being introduced into the system. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The terminology used in the embodiments is for describing specific implementation schemes, not for limiting the scope of protection of the present invention. The dosages in the embodiments are laboratory-scale tests and can be scaled up proportionally. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Spherical aluminum powder (sphericity: 0.9, particle size: 1.5μm, purity: 99.99%), high-purity aluminum foil (purity: 99.99%, thickness: 30μm, surface roughness: 0.5μm), PMMA microspheres (sphericity: 0.95, particle size: 1.0μm).

[0026] The specific steps of surface activation treatment for high-purity aluminum foil are as follows: High-purity aluminum foil was sequentially immersed in acetone and anhydrous ethanol for ultrasonic cleaning for 5 minutes, and then transferred to a plasma activation device. Argon gas was introduced for plasma activation treatment. The argon gas flow rate was set to 50 sccm, the power supply was set to 150W, and the activation time was set to 2 minutes to obtain surface-activated high-purity aluminum foil.

[0027] Example 1: A method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor, specifically as follows: Step 1: Add 10g of magnesium nitrate hexahydrate to 200mL of anhydrous ethanol, stir at 200rpm for 20min, add 100g of spherical aluminum powder, ultrasonically disperse for 20min to form a suspension, and rotary evaporate and dry at 100℃ for 2h to obtain precursor powder. Under nitrogen protection, place the precursor powder in a vacuum furnace and keep it at 450℃ for 2h. After the holding time is completed, cool to obtain Mg-Al powder. Step 2: Add 10g of tetraethyl orthosilicate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min to obtain a tetraethyl orthosilicate ethanol solution. Add 5g of tetrabutyl titanate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min, add to the tetraethyl orthosilicate ethanol solution, stir evenly, add 100g of Mg-Al powder, ultrasonically disperse for 20min, adjust the pH to 4, and react at 60℃ with stirring at 200rpm for 4h. After the reaction is complete, centrifuge to separate the product, wash with anhydrous ethanol, vacuum dry at 80℃ for 4h, calcine at 450℃ for 1h under nitrogen protection, and cool to room temperature after calcination to obtain Mg-Al powder@SiO2-TiO2. Step 3: Add 5g of silane coupling agent KH-560 to a mixed solution of 200mL anhydrous ethanol and 20mL deionized water, stir at 200rpm for 20min, adjust the pH to 5, add 100g of Mg-Al powder@SiO2-TiO2, and react at 70℃ and 400rpm for 2h. After the reaction is complete, cool to room temperature, filter, wash the filtrate with anhydrous ethanol, and vacuum dry at 80℃ for 2h to obtain KH-560 modified Mg-Al powder@SiO2-TiO2. Step 4: Add 5g of binder polyvinyl butyral, 1.5g of plasticizer dibutyl phthalate and 0.5g of dispersant ammonium polyacrylate to a mixed solution of 50mL anhydrous ethanol and 50mL terpineol. Stir at 60℃ and 200rpm for 20min. Add 100g of KH-560 modified Mg-Al powder@SiO2-TiO2 and 10g of pore-forming agent PMMA microspheres. Disperse at 2000rpm for 60min and degas under vacuum at -0.09MPa for 10min to obtain modified aluminum powder slurry. Step 5: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, controlling the wet film thickness to 120 μm. After coating, it is vacuum dried at 80℃ for 20 min, then transferred to a heating furnace. Under nitrogen protection, the temperature is increased to 580℃ at 5℃ / min and held for 2 h. After holding, it is cooled to room temperature with the furnace, ultrasonically cleaned in a 5wt% phosphoric acid aqueous solution for 5 min, rinsed with deionized water, and transferred to a 5wt% ammonium borate solution at 85℃ for formation. The sintered aluminum foil is used as the anode, and the high-purity aluminum plate is used as the cathode, with an electrode spacing of 5 cm and a current density of 0.5 mA / cm². 2 The anode foil of an aluminum powder sintered electrolytic capacitor was obtained by setting the voltage to 220V and the setting time to 30min.

[0028] Example 2: A method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor, specifically as follows: Step 1: Add 15g of magnesium nitrate hexahydrate to 200mL of anhydrous ethanol, stir at 200rpm for 20min, add 120g of spherical aluminum powder, ultrasonically disperse for 20min to form a suspension, and rotary evaporate and dry at 100℃ for 2h to obtain precursor powder. Under nitrogen protection, place the precursor powder in a vacuum furnace and keep it at 450℃ for 2h. After the holding time is completed, cool to obtain Mg-Al powder. Step 2: Add 15g of tetraethyl orthosilicate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min to obtain a tetraethyl orthosilicate ethanol solution. Add 10g of tetrabutyl titanate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min, add to the tetraethyl orthosilicate ethanol solution, stir evenly, add 120g of Mg-Al powder, ultrasonically disperse for 20min, adjust the pH to 4, and react at 60℃ with stirring at 200rpm for 4h. After the reaction is complete, centrifuge to separate the product, wash with anhydrous ethanol, vacuum dry at 80℃ for 4h, calcine at 450℃ for 1h under nitrogen protection, and cool to room temperature after calcination to obtain Mg-Al powder@SiO2-TiO2. Step 3: Add 10g of silane coupling agent KH-560 to a mixed solution of 200mL anhydrous ethanol and 20mL deionized water, stir at 200rpm for 20min, adjust the pH to 5, add 120g of Mg-Al powder@SiO2-TiO2, and react at 70℃ and 400rpm for 2h. After the reaction is complete, cool to room temperature, filter, wash the filtrate with anhydrous ethanol, and vacuum dry at 80℃ for 2h to obtain KH-560 modified Mg-Al powder@SiO2-TiO2. Step 4: Add 6g of binder polyvinyl butyral, 1.5g of plasticizer dibutyl phthalate and 1g of dispersant ammonium polyacrylate to a mixed solution of 50mL anhydrous ethanol and 50mL terpineol. Stir at 60℃ and 200rpm for 20min. Add 110g of KH-560 modified Mg-Al powder@SiO2-TiO2 and 15g of pore-forming agent PMMA microspheres. Disperse at 2000rpm for 60min and degas under vacuum at -0.09MPa for 10min to obtain modified aluminum powder slurry. Step 5: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, controlling the wet film thickness to 120 μm. After coating, it is vacuum dried at 80℃ for 20 min, then transferred to a heating furnace. Under nitrogen protection, the temperature is increased to 580℃ at 5℃ / min and held for 2 h. After holding, it is cooled to room temperature with the furnace, ultrasonically cleaned in a 5wt% phosphoric acid aqueous solution for 5 min, rinsed with deionized water, and transferred to a 5wt% ammonium borate solution at 85℃ for formation. The sintered aluminum foil is used as the anode, and the high-purity aluminum plate is used as the cathode, with an electrode spacing of 5 cm and a current density of 0.5 mA / cm². 2The anode foil of an aluminum powder sintered electrolytic capacitor was obtained by setting the voltage to 220V and the setting time to 30min.

[0029] Example 3: A method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor, specifically as follows: Step 1: Add 20g of magnesium nitrate hexahydrate to 200mL of anhydrous ethanol, stir at 200rpm for 20min, add 150g of spherical aluminum powder, ultrasonically disperse for 20min to form a suspension, and rotary evaporate and dry at 100℃ for 2h to obtain precursor powder. Under nitrogen protection, place the precursor powder in a vacuum furnace and keep it at 450℃ for 2h. After the holding time is completed, cool to obtain Mg-Al powder. Step 2: Add 20g of tetraethyl orthosilicate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min to obtain a tetraethyl orthosilicate ethanol solution. Add 15g of tetrabutyl titanate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min, add to the tetraethyl orthosilicate ethanol solution, stir evenly, add 150g of Mg-Al powder, ultrasonically disperse for 20min, adjust the pH to 4, and react at 60℃ with stirring at 200rpm for 4h. After the reaction is complete, centrifuge to separate the product, wash with anhydrous ethanol, vacuum dry at 80℃ for 4h, calcine at 450℃ for 1h under nitrogen protection, and cool to room temperature after calcination to obtain Mg-Al powder@SiO2-TiO2. Step 3: Add 15g of silane coupling agent KH-560 to a mixed solution of 200mL anhydrous ethanol and 20mL deionized water, stir at 200rpm for 20min, adjust the pH to 5, add 150g of Mg-Al powder@SiO2-TiO2, and react at 70℃ and 400rpm for 2h. After the reaction is complete, cool to room temperature, filter, wash the filtrate with anhydrous ethanol, and vacuum dry at 80℃ for 2h to obtain KH-560 modified Mg-Al powder@SiO2-TiO2. Step 4: Add 7g of binder polyvinyl butyral, 2g of plasticizer dibutyl phthalate and 1g of dispersant ammonium polyacrylate to a mixed solution of 50mL anhydrous ethanol and 50mL terpineol. Stir at 60℃ and 200rpm for 20min. Add 120g of KH-560 modified Mg-Al powder@SiO2-TiO2 and 20g of pore-forming agent PMMA microspheres. Disperse at 2000rpm for 60min. Degas under vacuum at -0.09MPa for 10min to obtain modified aluminum powder slurry. Step 5: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, controlling the wet film thickness to 120 μm. After coating, it is vacuum dried at 80℃ for 20 min, then transferred to a heating furnace. Under nitrogen protection, the temperature is increased to 580℃ at 5℃ / min and held for 2 h. After holding, it is cooled to room temperature with the furnace, ultrasonically cleaned in a 5wt% phosphoric acid aqueous solution for 5 min, rinsed with deionized water, and transferred to a 5wt% ammonium borate solution at 85℃ for formation. The sintered aluminum foil is used as the anode, and the high-purity aluminum plate is used as the cathode, with an electrode spacing of 5 cm and a current density of 0.5 mA / cm². 2 The anode foil of an aluminum powder sintered electrolytic capacitor was obtained by setting the voltage to 220V and the setting time to 30min.

[0030] Based on Example 1, the following comparative experiments were conducted, specifically Comparative Example 1, Comparative Example 2, and Comparative Example 3, as described below: Comparative Example 1: This comparative example relates to a method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor. The difference from Example 1 is that the spherical aluminum powder was not modified with magnesium nitrate. Specifically: Step 1: Add 10g of tetraethyl orthosilicate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min to obtain a tetraethyl orthosilicate ethanol solution. Add 5g of tetrabutyl titanate to a mixed solution of 50mL anhydrous ethanol and 10mL deionized water, stir at 200rpm for 20min, add to the tetraethyl orthosilicate ethanol solution, stir evenly, add 100g of spherical aluminum powder, ultrasonically disperse for 20min, adjust the pH to 4, and react at 60℃ with stirring at 200rpm for 4h. After the reaction is complete, centrifuge to separate the product, wash with anhydrous ethanol, vacuum dry at 80℃ for 4h, calcine at 450℃ for 1h under nitrogen protection, and cool to room temperature after calcination to obtain Al powder@SiO2-TiO2. Step 2: Add 5g of silane coupling agent KH-560 to a mixed solution of 200mL anhydrous ethanol and 20mL deionized water, stir at 200rpm for 20min, adjust the pH to 5, add 100g of Al powder@SiO2-TiO2, and react at 70℃ and 400rpm for 2h. After the reaction is complete, cool to room temperature, filter, wash the filtrate with anhydrous ethanol, and vacuum dry at 80℃ for 2h to obtain KH-560 modified Al powder@SiO2-TiO2. Step 3: Add 5g of binder polyvinyl butyral, 1.5g of plasticizer dibutyl phthalate and 0.5g of dispersant ammonium polyacrylate to a mixed solution of 50mL anhydrous ethanol and 50mL terpineol. Stir at 60℃ and 200rpm for 20min. Add 100g of KH-560 modified Mg-Al powder@SiO2-TiO2 and 10g of pore-forming agent PMMA microspheres. Disperse at 2000rpm for 60min and degas under vacuum at -0.09MPa for 10min to obtain modified aluminum powder slurry. Step 4: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, controlling the wet film thickness to 120 μm. After coating, it is vacuum dried at 80℃ for 20 min, then transferred to a heating furnace. Under nitrogen protection, the temperature is increased to 580℃ at 5℃ / min and held for 2 h. After holding, it is cooled to room temperature with the furnace, ultrasonically cleaned in a 5wt% phosphoric acid aqueous solution for 5 min, rinsed with deionized water, and transferred to a 5wt% ammonium borate solution at 85℃ for formation. The sintered aluminum foil is used as the anode, and the high-purity aluminum plate is used as the cathode, with an electrode spacing of 5 cm and a current density of 0.5 mA / cm². 2 The anode foil of an aluminum powder sintered electrolytic capacitor was obtained by setting the voltage to 220V and the setting time to 30min.

[0031] Comparative Example 2: This comparative example relates to a method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor. The difference from Example 1 is that a SiO2-TiO2 layer is not formed on the surface of the Mg-Al powder. Specifically: Step 1: Add 10g of magnesium nitrate hexahydrate to 200mL of anhydrous ethanol, stir at 200rpm for 20min, add 100g of spherical aluminum powder, ultrasonically disperse for 20min to form a suspension, and rotary evaporate and dry at 100℃ for 2h to obtain precursor powder. Under nitrogen protection, place the precursor powder in a vacuum furnace and keep it at 450℃ for 2h. After the holding time is completed, cool to obtain Mg-Al powder. Step 2: Add 5g of silane coupling agent KH-560 to a mixed solution of 200mL anhydrous ethanol and 20mL deionized water, stir at 200rpm for 20min, adjust the pH to 5, add 100g of Mg-Al powder, and react at 70℃ and 400rpm for 2h. After the reaction is complete, cool to room temperature, filter, wash the filtrate with anhydrous ethanol, and vacuum dry at 80℃ for 2h to obtain KH-560 modified Mg-Al powder. Step 3: Add 5g of binder polyvinyl butyral, 1.5g of plasticizer dibutyl phthalate and 0.5g of dispersant ammonium polyacrylate to a mixed solution of 50mL anhydrous ethanol and 50mL terpineol. Stir at 60℃ and 200rpm for 20min. Add 100g of KH-560 modified Mg-Al powder@SiO2-TiO2 and 10g of pore-forming agent PMMA microspheres. Disperse at 2000rpm for 60min and degas under vacuum at -0.09MPa for 10min to obtain modified aluminum powder slurry. Step 4: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, controlling the wet film thickness to 120 μm. After coating, it is vacuum dried at 80℃ for 20 min, then transferred to a heating furnace. Under nitrogen protection, the temperature is increased to 580℃ at 5℃ / min and held for 2 h. After holding, it is cooled to room temperature with the furnace, ultrasonically cleaned in a 5wt% phosphoric acid aqueous solution for 5 min, rinsed with deionized water, and transferred to a 5wt% ammonium borate solution at 85℃ for formation. The sintered aluminum foil is used as the anode, and the high-purity aluminum plate is used as the cathode, with an electrode spacing of 5 cm and a current density of 0.5 mA / cm². 2 The anode foil of an aluminum powder sintered electrolytic capacitor was obtained by setting the voltage to 220V and the setting time to 30min.

[0032] Comparative Example 3: This comparative example relates to a method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor. The difference from Example 1 is that the surface of the spherical aluminum powder is not modified. Specifically: Step 1: Add 5g of binder polyvinyl butyral, 1.5g of plasticizer dibutyl phthalate and 0.5g of dispersant ammonium polyacrylate to a mixed solution of 50mL anhydrous ethanol and 50mL terpineol. Stir at 60℃ and 200rpm for 20min. Add 100g of spherical aluminum powder and 10g of pore-forming agent PMMA microspheres. Disperse at 2000rpm for 60min. Degas under vacuum at -0.09MPa for 10min to obtain modified aluminum powder slurry. Step 2: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, controlling the wet film thickness to 120 μm. After coating, it is vacuum dried at 80℃ for 20 min, then transferred to a heating furnace. Under nitrogen protection, the temperature is increased to 580℃ at 5℃ / min and held for 2 h. After holding, it is cooled to room temperature with the furnace, ultrasonically cleaned in a 5wt% phosphoric acid aqueous solution for 5 min, rinsed with deionized water, and transferred to a 5wt% ammonium borate solution at 85℃ for formation. The sintered aluminum foil is used as the anode, and the high-purity aluminum plate is used as the cathode, with an electrode spacing of 5 cm and a current density of 0.5 mA / cm. 2 The anode foil of an aluminum powder sintered electrolytic capacitor was obtained by setting the voltage to 220V and the setting time to 30min.

[0033] Testing experiment: Aluminum powder sintered electrolytic capacitor anode foils were prepared as samples according to each embodiment and comparative example, and porosity, dead zone width, specific capacitance and dielectric loss were tested.

[0034] Porosity Testing: The porosity of sintered aluminum powder electrolytic capacitors was tested according to the standard GB / T21650.1-2008, "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Porosimetry and Gas Adsorption Methods - Part 1: Mercury Porosimetry". A fully automated mercury porosimetry instrument was used to test 10 samples. -3 After vacuum degassing for 30 minutes, mercury was introduced, and the dilatometer reading was recorded. Then, the pressure was adjusted (0.5-30 psia) to allow mercury to enter the pores of the sample, and the open porosity of the sample was tested.

[0035] Dead zone width test: The dead zone width of the sample was tested by electrochemical impedance spectroscopy. The sample area was 10 mm × 10 mm, the electrolyte system was 4.3 mol / L ethylene glycol-ammonium borate aqueous solution, the test frequency range was 100 kHz-10 m Hz, the AC amplitude was 10 m V, and the dead zone ratio of the sample was tested.

[0036] Specific capacitance and dielectric loss test: Use a precision LCR meter to test the specific capacitance and dielectric loss of the sample. Set the test frequency to 120Hz and the test signal voltage to 1.0Vrms, and read the specific capacitance and loss factor of the sample.

[0037]

[0038] Conclusion: The test data shows that the anode foil of the aluminum powder sintered electrolytic capacitor prepared in the examples has higher open porosity and specific capacitance than the comparative examples, while the dead zone ratio and loss factor are lower than the comparative examples. In Comparative Example 3, the spherical aluminum powder was not treated with magnesium and was not coated with SiO2-TiO2. Compared with Comparative Example 1 and Comparative Example 2, its open porosity and specific capacitance test results were reduced more, while the dead zone ratio and loss factor were increased more. The anode foil of the aluminum powder sintered electrolytic capacitor provided by the present invention has good porosity and dielectric properties.

[0039] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor, characterized in that: Specifically: Step 1: Add spherical aluminum powder to magnesium nitrate ethanol solution to obtain Mg-Al powder; Step 2: Add Mg-Al powder to the mixed sol after hydrolysis of tetrabutyl orthosilicate and tetrabutyl titanate to obtain Mg-Al powder@SiO2-TiO2; Step 3: Modify Mg-Al powder@SiO2-TiO2 with silane coupling agent KH-560 to obtain KH-560 modified Mg-Al powder@SiO2-TiO2; Step 4: KH-560 modified Mg-Al powder@SiO2-TiO2, pore-forming agent PMMA microspheres, binder polyvinyl butyral, plasticizer dibutyl phthalate and dispersant ammonium polyacrylate are added sequentially to a mixed solution composed of anhydrous ethanol and terpineol to form a modified aluminum powder slurry. Step 5: After surface activation treatment of high-purity aluminum foil, a modified aluminum powder slurry is coated, and after drying, sintering, cooling and cleaning, and formation treatment, the anode foil of aluminum powder sintered electrolytic capacitor is obtained.

2. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 1, characterized in that: The preparation method of Mg-Al powder is as follows: Magnesium nitrate hexahydrate was added to anhydrous ethanol and stirred at 200-300 rpm for 20-30 min. Spherical aluminum powder was added and ultrasonically dispersed for 20-30 min to form a suspension. The suspension was then dried by rotary evaporation at 90-100℃ for 1-2 h to obtain precursor powder. Under nitrogen protection, the precursor powder was placed in a vacuum furnace and kept at 450-470℃ for 1-2 h. After the holding time was completed, the powder was cooled to obtain Mg-Al powder. The mass ratio of magnesium nitrate hexahydrate to spherical aluminum powder is (1-2):(10-15).

3. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 1, characterized in that: The preparation method of Mg-Al powder@SiO2-TiO2 is as follows: Tetrabutyl titanate was added to a mixed solution of anhydrous ethanol and deionized water and stirred at 200-300 rpm for 20-30 min to obtain a tetrabutyl titanate ethanol solution. Tetrabutyl titanate was added to the mixed solution of anhydrous ethanol and deionized water and stirred at 200-300 rpm for 20-30 min, then added to the tetrabutyl titanate ethanol solution and stirred until homogeneous. Mg-Al powder was added and ultrasonically dispersed for 20-30 min. The pH was adjusted to 3-4, and the reaction was carried out at 60-70℃ with stirring at 200-300 rpm for 3-4 h. After the reaction was completed, the product was separated by centrifugation, washed with anhydrous ethanol, vacuum dried at 70-80℃ for 3-4 h, and then calcined at 450-470℃ for 1-2 h under nitrogen protection. After calcination, the product was cooled to room temperature to obtain Mg-Al powder@SiO2-TiO2.

4. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 3, characterized in that: The mass ratio of tetrabutyl orthosilicate, tetrabutyl titanate, and Mg-Al powder is (1-2):(0.5-1.5):(10-15).

5. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 1, characterized in that: The preparation method of KH-560 modified Mg-Al powder@SiO2-TiO2 is as follows: Silane coupling agent KH-560 was added to a mixed solution of anhydrous ethanol and deionized water, stirred at 200-300 rpm for 20-30 min, and the pH was adjusted to 4-5. Mg-Al powder@SiO2-TiO2 was added, and the reaction was carried out at 70-80℃ and stirred at 300-400 rpm for 2-3 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filtrate was washed with anhydrous ethanol and dried under vacuum at 70-80℃ for 2-3 h to obtain KH-560 modified Mg-Al powder@SiO2-TiO2. The mass ratio of silane coupling agent KH-560 to Mg-Al powder@SiO2-TiO2 is (0.5-1.5):(10-15).

6. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 5, characterized in that: The preparation method of modified aluminum powder slurry is as follows: The binder polyvinyl butyral, the plasticizer dibutyl phthalate, and the dispersant ammonium polyacrylate were added to a mixed solution of anhydrous ethanol and terpineol. The mixture was stirred at 200-300 rpm for 20-30 minutes at 60-70°C. Then, KH-560 modified Mg-Al powder@SiO2-TiO2 and PMMA microspheres were added. The mixture was dispersed at 1500-2000 rpm for 50-60 minutes and then vacuum degassed at (-0.07)-(-0.09) MPa for 10-15 minutes to obtain the modified aluminum powder slurry. By weight, the modified aluminum powder slurry comprises 5-7 parts of binder polyvinyl butyral, 1.5-2 parts of plasticizer dibutyl phthalate, 0.5-1 parts of dispersant ammonium polyacrylate, 100-120 parts of KH-560 modified Mg-Al powder@SiO2-TiO2 and 10-20 parts of pore-forming agent PMMA microspheres.

7. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 1, characterized in that: The preparation method of the anode foil for aluminum powder sintered electrolytic capacitors is as follows: After surface activation treatment of high-purity aluminum foil, modified aluminum powder slurry is coated and vacuum dried. Then, it is transferred to a heating furnace and sintered under nitrogen protection. After sintering, it is cooled to room temperature with the furnace to obtain sintered aluminum foil. It is ultrasonically cleaned in phosphoric acid aqueous solution for 5-10 minutes, rinsed with deionized water, and transferred to ammonium borate solution for formation. Using sintered aluminum foil as anode and high-purity aluminum plate as cathode, aluminum powder sintered electrolytic capacitor anode foil is obtained.

8. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 7, characterized in that: The specific steps of surface activation treatment for high-purity aluminum foil are as follows: High-purity aluminum foil was sequentially immersed in acetone and anhydrous ethanol, and ultrasonically cleaned for 5-10 minutes each. Then it was transferred to a plasma activation device, argon gas was introduced, and plasma activation treatment was carried out to obtain surface-activated high-purity aluminum foil. The process conditions for plasma activation treatment include: argon flow rate of 40-60 sccm, power supply of 120-150W, and activation time of 1-3 min.

9. The method for preparing the anode foil of an aluminum powder sintered electrolytic capacitor according to claim 7, characterized in that: During coating, the wet film thickness is controlled at 120-150 μm; during vacuum drying, the drying temperature is 80-90℃ and the drying time is 10-30 min; during sintering, the heating rate is 5-10℃ / min, the sintering temperature is 580-600℃, and the sintering time is 1-3 h; the phosphoric acid aqueous solution contains 5-10 wt% phosphoric acid; during formation, the ammonium borate solution contains 5-10 wt% ammonium borate, the solution temperature is 80-90℃, the electrode spacing is 5-10 cm, and the current density is 0.5-0.8 mA / cm². 2 The formation voltage is 180-220V, and the formation time is 20-30min.

10. An anode foil for an aluminum powder sintered electrolytic capacitor, characterized in that: It is prepared by any one of the preparation methods according to claims 1-9.

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