A multi-level porosity gradient sintered foil and a method of making the same
By using a multi-level pore gradient sintered foil structure and gradient sintering process, the problems of strength, specific capacitance, frequency characteristics, and oxide film quality of traditional sintered aluminum foil have been solved, and the overall performance of high-performance aluminum electrolytic capacitors has been improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SOUTHWEST JIAOTONG UNIV
- Filing Date
- 2026-03-19
- Publication Date
- 2026-06-19
AI Technical Summary
Traditional sintered aluminum foil suffers from decreased mechanical strength, deteriorated high-frequency performance, poor oxide film uniformity and density, and uneven ceramic phase distribution when its specific capacity is increased, resulting in damage to its overall performance.
A multi-level pore gradient sintered foil structure, including an aluminum foil substrate, a bonding layer, a transition layer, and a functional layer, is adopted. The core-shell structure of Al2O3@TiO2 composite powder is used to prepare the composite oxide film by sol-gel method and sintering it under programmed temperature gradient to form a uniform composite oxide film.
The mechanical strength and high-frequency characteristics of the sintered foil were improved, the leakage current was reduced, and high specific capacity and excellent overall performance were achieved.
Smart Images
Figure CN122245974A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aluminum electrolytic capacitor technology, specifically relating to a multi-level pore gradient sintered foil and its preparation method. Background Technology
[0002] Sintered aluminum foil, as a key material for high-performance aluminum electrolytic capacitors, provides a huge specific surface area through its three-dimensional porous structure, thereby achieving high specific capacitance. However, traditional sintered aluminum foil faces the following long-standing technical contradictions that have not been well resolved: 1) The contradiction between strength and specific capacitance: To improve specific capacitance, it is necessary to increase porosity or use finer aluminum powder, but this will lead to a decrease in the mechanical strength of the sintered layer, making it prone to cracking and powdering during subsequent winding processing; 2) The contradiction between high-frequency characteristics and capacitance: Sintered layers with high specific capacitance often have fine pores, which is not conducive to electrolyte wetting and ion migration, resulting in an increase in equivalent series resistance and a deterioration in high-frequency performance; 3) Oxide film quality: Traditional sintering processes (atmospheric pressure sintering) have high temperatures and long times, which easily lead to coarse aluminum grains, resulting in poor uniformity and density of the dielectric oxide film formed by subsequent energy generation, and higher leakage current.
[0003] Existing technologies have attempted to enhance strength by adding a single ceramic phase (such as Al2O3) or to improve the dielectric constant by using TiO2. However, simple mixing easily leads to uneven distribution of the ceramic phase and severe agglomeration of TiO2, which impairs the overall performance. Furthermore, neither approach can systematically solve all the aforementioned problems simultaneously. Therefore, it is crucial to develop a novel electrode foil that can synergistically improve strength, specific capacity, frequency characteristics, and reliability. Summary of the Invention
[0004] In view of the above-mentioned prior art, the present invention provides a multi-level pore gradient sintered foil and its preparation method, which solves the problem that sintered aluminum electrode foil in the prior art cannot simultaneously achieve high mechanical strength, high specific capacity, excellent high frequency characteristics (low ESR) and low leakage current.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a multi-level pore gradient sintered foil is provided, comprising an aluminum foil substrate and a bonding layer and a functional layer sequentially coated thereon from the inside out. The bonding layer is composed of aluminum powder, and the functional layer is composed of aluminum powder and Al2O3@TiO2 composite powder. The Al2O3@TiO2 composite powder has a core-shell structure, wherein the mass percentage of TiO2 is 10% to 50%.
[0006] Based on the above technical solution, the present invention can be further improved as follows.
[0007] Furthermore, a transition layer is provided between the bonding layer and the functional layer. The transition layer is composed of aluminum powder and Al2O3@TiO2 composite powder, and the mass percentage of TiO2 in the Al2O3@TiO2 composite powder is 5%~30%.
[0008] Furthermore, the mass ratio of aluminum powder to Al2O3@TiO2 composite powder in the functional layer is 75~90:10~25, and the mass ratio of aluminum powder to Al2O3@TiO2 composite powder in the transition layer is 90~95:5~10.
[0009] The beneficial effects of the above-mentioned further technical solutions of this invention are as follows: The multi-level pore gradient sintered foil structure includes, from the aluminum foil substrate outwards, a bonding layer, a transition layer, and a functional layer. The bonding layer ensures a strong bond with the substrate. In the transition layer, Al2O3 provides reinforcement, and TiO2 prepares for the subsequent formation of a high-dielectric-constant composite oxide film. The functional layer has the maximum porosity and specific surface area, and is the main contributor to the capacity. The core-shell structure of the Al2O3@TiO2 composite powder ensures that the TiO2 nanoparticles are highly dispersed and firmly attached to the Al2O3 support, preventing them from agglomerating during sintering, thereby forming a more uniform and dense composite dielectric layer after energization.
[0010] Furthermore, the above-mentioned method for preparing multi-level pore gradient sintered foil includes the steps of preparing Al2O3@TiO2 composite powder using a sol-gel method or a liquid phase coating method, and the steps of sequentially coating an aluminum foil substrate with a slurry containing Al2O3@TiO2 composite powder and then performing programmed temperature-controlled gradient sintering.
[0011] The beneficial effects of the above-mentioned further technical solutions of the present invention are as follows: the preparation method of Al2O3@TiO2 composite powder is selected by sol-gel method or liquid phase coating method, which ensures that TiO2 nanoparticles are uniformly attached to Al2O3 core to form a stable core-shell structure, fundamentally solving the problem of TiO2 dispersion and enhancing the interfacial bonding strength between ceramic phase and metal matrix.
[0012] Furthermore, the method for preparing a multi-level pore gradient sintered foil includes the following steps: (1) Preparation of Al2O3@TiO2 composite powder: Nano Al2O3 is dispersed in ethanol, and then a titanium source is added. After hydrolysis, drying and calcination, the powder is obtained. (2) Preparation of slurry a: Aluminum powder is used as a solid component. The solid component is dispersed in a solution composed of organic binder, plasticizer and solvent, and ball-milled until uniform to obtain the slurry a. (3) Preparation of slurry b: Aluminum powder and Al2O3@TiO2 composite powder are used as solid components, and the rest of the preparation method is the same as that of slurry a; if the multi-level pore gradient sintered foil has no transition layer, this step is omitted; (4) Preparation of slurry c: Aluminum powder and Al2O3@TiO2 composite powder are used as solid components, and a pore-forming agent is added; the rest of the preparation method is the same as that of slurry a. (5) Layer-by-layer coating: Apply paste a, paste b and paste c to the aluminum foil substrate in sequence on both sides, corresponding to the bonding layer, transition layer and functional layer respectively; (6) Gradient sintering: The aluminum foil obtained in step (5) is sent into a vacuum sintering furnace filled with protective gas for gradient sintering; (7) Formation treatment: The aluminum foil after gradient sintering is subjected to formation treatment, that is, multi-level pore gradient sintered foil.
[0013] Furthermore, the average particle size of the nano-Al2O3 is 25~35 nm, the titanium source is tetrabutyl titanate, and the calcination temperature is 600℃ for 2 h.
[0014] Furthermore, the aluminum powder has an average particle size of 3~5 μm, the organic binder is polyvinylidene fluoride, and its addition amount is 3% of the solid component mass; the plasticizer is phenolic resin, and its addition amount is 1% of the solid component mass; the solvent is ethylene glycol; and the pore-forming agent is starch, and its addition amount is 5% of the solid component mass.
[0015] Furthermore, the solid content in slurry a, slurry b, and slurry c is 65 wt%.
[0016] Furthermore, the thickness of the aluminum foil substrate is 30 μm, and the coating thickness of slurry a, slurry b, and slurry c is 80 μm.
[0017] Furthermore, the gradient sintering process is as follows: heat to 300 ℃ at a rate of 5 ℃ / min and hold for 120 min, then heat to 550 ℃ at a rate of 5 ℃ / min and hold for 720 min, then continue to heat to 600~650 ℃ at a rate of 5 ℃ / min and hold for 240 min, and finally cool with the furnace to below 100 ℃ before unloading.
[0018] The beneficial effects of the above-mentioned further technical solution of this invention are as follows: the coated aluminum foil is subjected to multi-stage programmed temperature-controlled gradient sintering under a specific sintering atmosphere. The sintering process is divided into: slowly heating to 300 ℃ to fully remove organic binders; heating to 550 ℃ to remove carbon impurities; and then heating to a sintering temperature slightly below the melting point of aluminum (600~650 ℃), and holding at this temperature for a period of time. Compared with conventional single-temperature profile atmospheric pressure sintering, the gradient sintering process of this invention achieves two core functions by precisely controlling the temperature and time of each stage: first, it promotes the directional diffusion of elements such as Al and Ti from high concentration areas to low concentration areas, ultimately forming the designed compositional gradient distribution and optimizing the interface bonding and electrical performance gradient; second, through staged debinding, carbon removal, and densification, while achieving good sintering, it better preserves the designed multi-level porous structure, especially the high porosity of the functional layer. During gradient sintering, the sintering kinetics differ due to the varying titanium-aluminum alloy content in different regions. The high-titanium-aluminum alloy regions preferentially form a robust skeletal structure and form a strong and tough metallurgical bond with the aluminum foil.
[0019] The beneficial effects of this invention are: 1) Synergistic reinforcement of composite powder and advantages of core-shell structure: Al2O3@TiO2 core-shell composite powder prepared by sol-gel method or liquid phase coating method, with nano Al2O3 as the reinforcing phase, greatly improves the mechanical strength and toughness of sintered layer by pinning grain boundaries; while TiO2, in subsequent energization, forms a composite oxide film with higher dielectric constant together with aluminum matrix, significantly improving specific capacity per unit area; the core-shell structure effectively prevents the agglomeration of TiO2, ensuring that its function is fully utilized, which cannot be achieved by simple physical mixing.
[0020] 2) Synergistic optimization of gradient structure and gradient sintering process: The gradient structure design (bonding layer - transition layer - functional layer) fundamentally solves the contradiction between "interfacial bonding strength" and "high surface specific volume". Combined with a unique gradient sintering process, it not only achieves ideal diffusion and distribution of elements, but also precisely controls the pore structure and sintering density of each layer. The large pores and interconnected channels of the functional layer facilitate rapid electrolyte wetting and ion migration, significantly reducing ESR and improving high-frequency performance; the bonding layer ensures a strong bond with the substrate and the integrity of the overall structure.
[0021] 3) Comprehensive improvement in overall performance and reliability: The resulting sintered foil has high strength and good oxide film quality, resulting in a longer lifespan and lower leakage current. It is particularly suitable for high-performance, high-reliability aluminum electrolytic capacitors. Attached Figure Description
[0022] Figure 1 This is a schematic diagram illustrating the preparation of Al2O3@TiO2 composite powder. Figure 2 The images are SEM microstructure images, where a is the sintered foil prepared in Comparative Example 2, and b is the multi-level pore gradient sintered foil prepared in Example 2. Figure 3 The images are of actual sintered foils, where a is the sintered foil prepared in Comparative Example 2 and b is the multi-level pore gradient sintered foil prepared in Example 1. Detailed Implementation
[0023] The specific embodiments of the present invention will be described in detail below with reference to examples.
[0024] Example 1 A multi-level pore gradient sintered foil, the preparation steps of which are as follows: (1) Preparation of Al2O3@TiO2 composite powder: 100 g of Al2O3 with an average particle size of 30 nm was dispersed in ethanol, and tetrabutyl titanate was slowly added (so that the content of TiO2 was 20 wt% of Al2O3@TiO2 composite powder). After hydrolysis, it was dried at 80 ℃ for 6 h and then calcined at 600 ℃ for 2 h to obtain the product. (2) Preparation of slurry a: Spherical aluminum powder with an average particle size of 3~5 μm is used as the solid component. The solid component is dispersed in a solution composed of an organic binder (polyvinylidene fluoride, which is added at 3% of the mass of the solid component), a plasticizer (phenolic resin, which is added at 1% of the mass of the solid component) and a solvent (ethylene glycol). The mixture is ball-milled until uniform. The content of solid component in the slurry is 65 wt%. (3) Preparation of slurry b: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder are used as solid components, and the mass ratio of the two is 95:5; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (4) Preparation of slurry c: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder are used as solid components, with a mass ratio of 90:10, and 5% of the solid component mass of pore-forming agent (starch) is added; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (5) Layer-by-layer coating: Slurry a, slurry b and slurry c are coated sequentially on a 30 μm thick aluminum foil substrate, corresponding to the bonding layer, transition layer and functional layer respectively. The wet film thickness of each layer is 80 μm. Double-sided coating is performed and dried at 80 ℃ for 6 h. After removing most of the solvent, the aluminum foil blank thickness is about 130 μm. (6) Gradient sintering: The dried aluminum foil is sent into a vacuum sintering furnace filled with high-purity argon for gradient sintering: the temperature is increased from room temperature to 300 ℃ at a rate of 5 ℃ / min and held for 120 min to fully remove the organic carrier; then, the temperature is increased to 550 ℃ at a rate of 5 ℃ / min and held for 720 min to completely remove carbon impurities and create a clean interface for subsequent densification; then, the temperature is increased to 650 ℃ at a rate of 5 ℃ / min and held for 240 min to complete the sintering densification and the interdiffusion of Al and Ti elements to form a gradient composition; finally, the foil is cooled to below 100 ℃ in the furnace and removed from the furnace. (7) Formation treatment: The aluminum foil after gradient sintering is subjected to conventional formation treatment, that is, multi-level pore gradient sintered foil.
[0025] Example 2 A multi-level pore gradient sintered foil differs from Example 1 in that step (1) Al2O3@TiO2 composite powder preparation: 100 g of Al2O3 with an average particle size of 30 nm is dispersed in ethanol, and tetrabutyl titanate is slowly added (so that the content of TiO2 is 50 wt% of Al2O3@TiO2 composite powder), hydrolyzed and dried, and calcined at 600 ℃ for 2 h to obtain the product; the remaining steps are the same as in Example 1.
[0026] Example 3 A multi-level pore gradient sintered foil differs from Example 1 in that, in step (3) slurry b preparation: spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder are used as solid components, with a mass ratio of 90:10; the remaining preparation method is the same as slurry a, and the content of solid components in the slurry is 65 wt%; in step (4) slurry c preparation: spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder are used as solid components, with a mass ratio of 80:20; the remaining preparation method is the same as slurry a, and the content of solid components in the slurry is 65 wt%; the remaining steps are the same as in Example 1.
[0027] Example 4 A multi-level pore gradient sintered foil, the preparation steps of which are as follows: (1) Preparation of Al2O3@TiO2 composite powder: 100 g of Al2O3 with an average particle size of 30 nm was dispersed in ethanol, and tetrabutyl titanate was slowly added (so that the content of TiO2 was 20 wt% of Al2O3@TiO2 composite powder). After hydrolysis, it was dried at 80 ℃ for 6 h and calcined at 600 ℃ for 2 h to obtain the product. (2) Preparation of slurry a: Spherical aluminum powder with an average particle size of 3~5 μm is used as the solid component. The solid component is dispersed in a solution composed of polyvinylidene fluoride (3% by weight of solid component), phenolic resin (1% by weight of solid component) and ethylene glycol. The mixture is ball-milled until uniform. The content of solid component in the slurry is 65 wt%. (3) Preparation of slurry c: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder are used as solid components, with a mass ratio of 90:10, and 5% starch by mass of solid components is added; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (4) Layer-by-layer coating: Slurry a and slurry c are sequentially coated on a 30 μm thick aluminum foil substrate, corresponding to the bonding layer and functional layer respectively. The thickness of each wet film is 80 μm. Double-sided coating is performed and dried at 80 ℃ for 6 h. After removing most of the solvent, the thickness of the aluminum foil blank is about 130 μm. (5) Gradient sintering: The dried aluminum foil is sent into a vacuum sintering furnace filled with high-purity argon for gradient sintering: the temperature is raised from room temperature to 300 ℃ at a rate of 5 ℃ / min and held for 120 min to fully remove the organic carrier; then, the temperature is raised to 550 ℃ at a rate of 5 ℃ / min and held for 720 min to completely remove carbon impurities and create a clean interface for subsequent densification; then, the temperature is raised to 600 ℃ at a rate of 5 ℃ / min and held for 240 min to complete the sintering densification and the interdiffusion of Al and Ti elements to form a gradient composition; finally, the foil is cooled to below 100 ℃ in the furnace and removed from the furnace. (7) Formation treatment: The aluminum foil after gradient sintering is subjected to conventional formation treatment to obtain the sintered foil product.
[0028] Example 5 A multi-level pore gradient sintered foil, the preparation steps of which are as follows: (1) Preparation of Al2O3@TiO2 composite powder: 100 g of Al2O3 with an average particle size of 30 nm was dispersed in ethanol, and tetrabutyl titanate was slowly added (so that the content of TiO2 was 5 wt% of Al2O3@TiO2 composite powder). After hydrolysis, it was dried at 80 ℃ for 6 h and calcined at 600 ℃ for 2 h to obtain Al2O3@TiO2 composite powder 1; 100 g of Al2O3 with an average particle size of 30 nm was dispersed in ethanol, and tetrabutyl titanate was slowly added (so that the content of TiO2 was 10 wt% of Al2O3@TiO2 composite powder). After hydrolysis, it was dried at 80 ℃ for 6 h and calcined at 600 ℃ for 2 h to obtain Al2O3@TiO2 composite powder 2. (2) Preparation of slurry a: Spherical aluminum powder with an average particle size of 3~5 μm is used as the solid component. The solid component is dispersed in a solution composed of polyvinylidene fluoride (added at 3% of the solid component mass), phenolic resin (added at 1% of the solid component mass), and ethylene glycol. The mixture is ball-milled until uniform. The content of solid component in the slurry is 65 wt%. (3) Preparation of slurry b: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder 1 are used as solid components, and the mass ratio of the two is 95:5; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (4) Preparation of slurry c: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder 2 are used as solid components, with a mass ratio of 90:10, and 5% starch by mass of solid components is added; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (5) Layer-by-layer coating: Slurry a, slurry b and slurry c are coated sequentially on a 30 μm thick aluminum foil substrate, corresponding to the bonding layer, transition layer and functional layer respectively. The wet film thickness of each layer is 80 μm. Double-sided coating is performed and dried at 80 ℃ for 6 h. After removing most of the solvent, the aluminum foil blank thickness is about 130 μm. (6) Gradient sintering: The dried aluminum foil is sent into a vacuum sintering furnace filled with high-purity argon for gradient sintering: the temperature is increased from room temperature to 300 ℃ at a rate of 5 ℃ / min and held for 120 min to fully remove the organic carrier; then, the temperature is increased to 550 ℃ at a rate of 5 ℃ / min and held for 720 min to completely remove carbon impurities and create a clean interface for subsequent densification; then, the temperature is increased to 650 ℃ at a rate of 5 ℃ / min and held for 240 min to complete the sintering densification and the interdiffusion of Al and Ti elements to form a gradient composition; finally, the foil is cooled to below 100 ℃ in the furnace and removed from the furnace. (7) Formation treatment: The aluminum foil after gradient sintering is subjected to conventional formation treatment, that is, multi-level pore gradient sintered foil.
[0029] Example 6 A multi-level pore gradient sintered foil, the preparation steps of which are as follows: (1) Preparation of Al2O3@TiO2 composite powder: 100 g of Al2O3 with an average particle size of 30 nm was dispersed in ethanol, and tetrabutyl titanate was slowly added (so that the content of TiO2 was 30 wt% of Al2O3@TiO2 composite powder). After hydrolysis, it was dried at 80 ℃ for 6 h and calcined at 600 ℃ for 2 h to obtain Al2O3@TiO2 composite powder 1; 100 g of Al2O3 with an average particle size of 30 nm was dispersed in ethanol, and tetrabutyl titanate was slowly added (so that the content of TiO2 was 50 wt% of Al2O3@TiO2 composite powder). After hydrolysis, it was dried at 80 ℃ for 6 h and calcined at 600 ℃ for 2 h to obtain Al2O3@TiO2 composite powder 2. (2) Preparation of slurry a: Spherical aluminum powder with an average particle size of 3~5 μm is used as the solid component. The solid component is dispersed in a solution composed of polyvinylidene fluoride (3% by weight of solid component), phenolic resin (1% by weight of solid component) and ethylene glycol. The mixture is ball-milled until uniform. The content of solid component in the slurry is 65 wt%. (3) Preparation of slurry b: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder 1 are used as solid components, and the mass ratio of the two is 90:10; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (4) Preparation of slurry c: Spherical aluminum powder with an average particle size of 3~5 μm and Al2O3@TiO2 composite powder 2 are used as solid components, with a mass ratio of 80:20, and 5% starch by mass of solid components is added; the rest of the preparation method is the same as that of slurry a, and the content of solid components in the slurry is 65 wt%; (5) Layer-by-layer coating: Slurry a, slurry b and slurry c are coated sequentially on a 30 μm thick aluminum foil substrate, corresponding to the bonding layer, transition layer and functional layer respectively. The wet film thickness of each layer is 80 μm. Double-sided coating is performed and dried at 80 ℃ for 6 h. After removing most of the solvent, the aluminum foil blank thickness is about 130 μm. (6) Gradient sintering: The dried aluminum foil is sent into a vacuum sintering furnace filled with high-purity argon for gradient sintering: the temperature is increased from room temperature to 300 ℃ at a rate of 5 ℃ / min and held for 120 min to fully remove the organic carrier; then, the temperature is increased to 550 ℃ at a rate of 5 ℃ / min and held for 720 min to completely remove carbon impurities and create a clean interface for subsequent densification; then, the temperature is increased to 650 ℃ at a rate of 5 ℃ / min and held for 240 min to complete the sintering densification and the interdiffusion of Al and Ti elements to form a gradient composition; finally, the foil is cooled to below 100 ℃ in the furnace and removed from the furnace. (7) Formation treatment: The aluminum foil after gradient sintering is subjected to conventional formation treatment, that is, multi-level pore gradient sintered foil.
[0030] Comparative Example 1 A sintered foil, the preparation steps of which are as follows: (1) Slurry preparation: Spherical aluminum powder with an average particle size of 3~5 μm is dispersed in a solution composed of polyvinylidene fluoride (3% of the solid component mass), phenolic resin (1% of the solid component mass) and ethylene glycol, and ball-milled until uniform. The solid component content in the slurry is 65 wt%, and the slurry is obtained. (2) Layer-by-layer coating: A slurry is coated on a 30 μm thick aluminum foil substrate, the wet film thickness is 80 μm, double-sided coating is applied, and the substrate is dried at 80 ℃ for 6 h to remove most of the solvent, resulting in an aluminum foil green blank with a thickness of about 60 μm. (3) Gradient sintering: The dried aluminum foil is sent into a vacuum sintering furnace filled with high-purity argon for gradient sintering: the temperature is raised from room temperature to 300 ℃ at a rate of 5 ℃ / min and held for 120 min to fully remove the organic carrier; then, the temperature is raised to 550 ℃ at a rate of 5 ℃ / min and held for 720 min to completely remove carbon impurities and create a clean interface for subsequent densification; then, the temperature is raised to 650 ℃ at a rate of 5 ℃ / min and held for 240 min to complete the sintering densification and the interdiffusion of Al and Ti elements to form a gradient composition; finally, the foil is cooled to below 100 ℃ in the furnace and removed from the furnace. (4) Formation treatment: The aluminum foil after gradient sintering is subjected to conventional formation treatment to obtain sintered foil.
[0031] Comparative Example 2 A sintered foil, which differs from Example 1 in that step (1) preparation of Al2O3@TiO2 composite powder: 100 g of Al2O3 with an average particle size of 30 nm is physically mixed with nano TiO2 by mechanical ball milling; the remaining steps are the same as in Example 1.
[0032] Experimental Example The sintered foils prepared in Comparative Example 2 and Example 2 were observed by SEM, and the results are as follows: Figure 2 As shown, Figure 2 a is comparative example 2, where the aluminum powder particles exhibit significant agglomeration and severe molten adhesion; Figure 2 Example b is Example 2, where the aluminum powder particles are evenly distributed and agglomeration is significantly improved. This indicates that the sintered foil in this invention can achieve ideal diffusion and distribution of each component element, and can also precisely control the pore structure and sintering density of each layer.
[0033] The sintered foil prepared in Comparative Example 2 and the multi-level pore gradient sintered foil prepared in Example 1 are as follows: Figure 3 As shown, the sintered foil prepared in Comparative Example 2 was not gradient sintered, the binder was not cleanly removed, and the powder shedding was severe; the multi-level pore gradient sintered foil prepared in Example 1 did not shed powder and had good macroscopic integrity.
[0034] The performance of the sintered foils prepared in Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in Table 1. The multi-level porosity gradient sintered foils prepared using Al2O3@TiO2 composite powder in Examples 1-3 comprehensively outperformed Comparative Example 2, which used a simple mixture, in specific volume, pressure resistance, and boiling water tests. This demonstrates the key role of the core-shell structure in preventing TiO2 agglomeration, improving dielectric layer quality, and enhancing interfacial bonding. Compared to Comparative Example 1 with its single-layer structure, all examples showed significantly improved overall performance, reflecting the effectiveness of gradient design in resolving the contradiction between strength and capacity.
[0035] Table 1 Performance Test Results
[0036] In summary, this invention achieves a comprehensive improvement in the overall performance and reliability of sintered electrode foil through a gradient-doped titanium-aluminum alloy structural design: the resulting sintered foil has high strength and good oxide film quality, resulting in a longer lifespan and lower leakage current, making it particularly suitable for high-performance, high-reliability aluminum electrolytic capacitors.
[0037] Although specific embodiments of the present invention have been described in detail with reference to examples, they should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims are still within the scope of protection of this patent.
Claims
1. A multi-level pore gradient sintered foil, characterized in that: It includes an aluminum foil substrate and a bonding layer and a functional layer that are sequentially coated thereon from the inside out. The bonding layer is composed of aluminum powder, and the functional layer is composed of aluminum powder and Al2O3@TiO2 composite powder. The Al2O3@TiO2 composite powder has a core-shell structure, wherein the mass percentage of TiO2 is 10% to 50%.
2. The multi-level pore gradient sintered foil according to claim 1, characterized in that: A transition layer is provided between the bonding layer and the functional layer. The transition layer is composed of aluminum powder and Al2O3@TiO2 composite powder, and the mass percentage of TiO2 in the Al2O3@TiO2 composite powder is 5%~30%.
3. The multi-level pore gradient sintered foil according to claim 2, characterized in that: The mass ratio of aluminum powder to Al2O3@TiO2 composite powder in the functional layer is 75~90:10~25, and the mass ratio of aluminum powder to Al2O3@TiO2 composite powder in the transition layer is 90~95:5~10.
4. The method for preparing the multi-level pore gradient sintered foil according to any one of claims 1 to 3, characterized in that, The process includes the steps of preparing the Al2O3@TiO2 composite powder using a sol-gel method or a liquid phase coating method, and the steps of sequentially coating an aluminum foil substrate with a slurry containing the Al2O3@TiO2 composite powder and then performing programmed temperature gradient sintering.
5. The method for preparing a multi-level pore gradient sintered foil according to claim 4, characterized in that, Includes the following steps: (1) Preparation of Al2O3@TiO2 composite powder: Nano Al2O3 is dispersed in ethanol, and then a titanium source is added. After hydrolysis, drying and calcination, the powder is obtained. (2) Preparation of slurry a: Aluminum powder is used as a solid component. The solid component is dispersed in a solution composed of organic binder, plasticizer and solvent, and ball-milled until uniform to obtain the slurry a. (3) Preparation of slurry b: Aluminum powder and Al2O3@TiO2 composite powder are used as solid components, and the rest of the preparation method is the same as that of slurry a; if the multi-level pore gradient sintered foil has no transition layer, this step is omitted; (4) Preparation of slurry c: Aluminum powder and Al2O3@TiO2 composite powder are used as solid components, and a pore-forming agent is added; the rest of the preparation method is the same as that of slurry a. (5) Layer-by-layer coating: Apply paste a, paste b and paste c to the aluminum foil substrate in sequence on both sides, corresponding to the bonding layer, transition layer and functional layer respectively; (6) Gradient sintering: The aluminum foil obtained in step (5) is sent into a vacuum sintering furnace filled with protective gas for gradient sintering; (7) Formation treatment: The aluminum foil after gradient sintering is subjected to formation treatment, that is, multi-level pore gradient sintered foil.
6. The method for preparing a multi-level pore gradient sintered foil according to claim 5, characterized in that: The average particle size of the nano-Al2O3 is 25~35 nm, the titanium source is tetrabutyl titanate, and the calcination temperature is 600 ℃ for 2 h.
7. The method for preparing a multi-level pore gradient sintered foil according to claim 5, characterized in that: The aluminum powder has an average particle size of 3-5 μm; the organic binder is polyvinylidene fluoride, and its addition amount is 3% of the solid component mass; the plasticizer is phenolic resin, and its addition amount is 1% of the solid component mass; the solvent is ethylene glycol; and the pore-forming agent is starch, and its addition amount is 5% of the solid component mass.
8. The method for preparing a multi-level porosity gradient sintered foil according to claim 5, characterized in that: The solid content of each of the slurries a, b, and c is 65 wt%.
9. The method for preparing a multi-level pore gradient sintered foil according to claim 5, characterized in that: The thickness of the aluminum foil substrate is 30 μm, and the coating thickness of the slurry a, slurry b and slurry c is 80 μm.
10. The method for preparing a multi-level pore gradient sintered foil according to claim 5, characterized in that: The gradient sintering process is as follows: the temperature is increased to 300℃ at a rate of 5℃ / min and held for 120 min, then increased to 550℃ at a rate of 5℃ / min and held for 720 min, then increased to 600~650℃ at a rate of 5℃ / min and held for 240 min, and finally cooled to below 100℃ in the furnace before being removed from the furnace.