Preparation method of boric acid-assisted low-temperature sintered porous aluminum foil

Abstract

The invention belongs to the technical field of electrode material preparation, and particularly relates to a preparation method of boric acid-assisted low-temperature sintered porous aluminum foil. The preparation method comprises the following steps: dispersing aluminum powder, boric acid and binder raw materials in a solvent to form dispersed slurry; and coating a matrix with the dispersed slurry, drying, sintering at 450-600 DEG C under protective gas, reacting boric acid with aluminum oxide on the surface of the aluminum powder to form low-melting-point aluminoborate, reducing the sintering temperature, promoting aluminum atom diffusion, increasing sintering neck formation, and sintering to obtain the porous aluminum foil. Boron oxide generated by decomposition of boric acid is added to react with aluminum oxide to form low-melting-point aluminoborate, the sintering liquidus temperature is reduced, aluminum atom diffusion is promoted, and low-temperature sintering at 450-600 DEG C is achieved. The aluminum powder sintered foil is suitable for energy storage devices such as an aluminum electrolytic capacitor and a lithium ion battery, has the advantages of low-temperature energy conservation, high porosity and strong mechanical property, and solves the problems of aluminum oxide obstruction and high high-temperature energy consumption of the traditional aluminum powder sintered foil.

Description

Technical Field

[0001] This invention belongs to the field of electrode material preparation technology, specifically relating to a method for preparing boric acid-assisted low-temperature sintering porous aluminum foil. Background Technology

[0002] Aluminum powder sintering is a new technology for preparing porous aluminum foil that has emerged in recent years. Compared with the traditional electrochemical etching method, this method is simple, pollution-free, and can achieve a higher specific surface area, making it a promising alternative process.

[0003] The core of aluminum powder sintering lies in forming sintering necks through surface diffusion (Kingery model), grain boundary diffusion (Ashby model), and volume diffusion (Coble model) of aluminum atoms at high temperatures, thereby solidifying the aluminum powder and improving its mechanical strength. These classic models are based on the ideal assumption of "two spherical particles in contact." However, in reality, aluminum powder comes into contact with oxygen to varying degrees during preparation, transportation, and use, forming alumina (Al2O3, melting point ~2050℃) on the surface, which hinders direct contact between aluminum particles. To enhance aluminum diffusion and form sintering necks, traditional processes involve increasing the sintering temperature or extending the holding time. However, high temperatures and long holding times have the following core drawbacks: 1. High-temperature energy consumption and oxidation issues: high energy consumption and severe aluminum powder oxidation; 2. Risk of pore collapse: high temperatures easily cause pore collapse between aluminum powder particles, reducing the specific surface area; 3. Low production efficiency: long holding times lead to long production cycles and low efficiency. In other words, traditional processes have not solved the problem of alumina on the aluminum powder surface hindering the formation of sintering necks. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing porous aluminum foil using boric acid-assisted low-temperature sintering, thereby addressing the problems of alumina on the surface of aluminum powder hindering the formation of sintering necks and high energy consumption at high temperatures. Based on the fact that boric acid decomposes to generate boron oxide (B2O3) during heating, on one hand, boron oxide reacts with the alumina on the surface of aluminum powder to form a low-melting-point molten boroaluminate, lowering the liquidus temperature of the aluminum powder sintering process, allowing the sintering process to be carried out at a lower temperature, and also reducing the melting loss of the aluminum foil substrate. On the other hand, boron oxide has high chemical activity and can penetrate to the grain boundaries of aluminum powder particles, promoting the diffusion of aluminum atoms and accelerating the formation and growth of sintering necks, thus improving sintering efficiency and the mechanical strength of the aluminum foil. Achieving low-temperature sintering at 450℃~600℃, the prepared porous aluminum foil is suitable for energy storage devices such as aluminum electrolytic capacitors and lithium-ion batteries, offering advantages such as low-temperature energy saving, high porosity, and strong mechanical properties.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] The purpose of this invention is to provide a method for preparing boric acid-assisted low-temperature sintering porous aluminum foil, comprising the following steps: S1. Aluminum powder, boric acid and binder raw materials are dispersed in a solvent to form a dispersion slurry.

[0007] S2. The dispersion slurry is coated onto the substrate and dried. Then, it is sintered at 450℃~600℃ under a protective gas. Boric acid reacts with the alumina on the surface of the aluminum powder to form low-melting-point borosilicate, which lowers the sintering temperature and promotes the diffusion of aluminum atoms, increasing the formation of sintering necks. After sintering, porous aluminum foil is obtained.

[0008] Furthermore, the amount of boric acid used in the dispersion slurry is 0.2 wt.% to 3 wt.%.

[0009] Furthermore, in the dispersion slurry, the amount of aluminum powder is 45wt.% to 70wt.%, and the amount of binder is 1wt.% to 10wt.%.

[0010] Furthermore, during the sintering process, the temperature is increased to 200℃ at a rate of 1℃ / min to 2℃ / min, then increased to 450℃ at a rate of 0.5℃ / min to 1℃ / min, and then increased to the target temperature at a rate of 0.1℃ / min to 0.5℃ / min, and held for 1h to 100h.

[0011] Furthermore, the coating thickness is 50μm to 100μm.

[0012] Furthermore, the binder is methylcellulose, polyethylene glycol, polyvinyl alcohol, or polypyrrolidone, and the solvent is water, ethanol, or N-methylpyrrolidone.

[0013] Furthermore, the aluminum powder particles are spherical or flake-shaped with a particle size of 1μm to 10μm.

[0014] Furthermore, during the sintering process, the protective gas is nitrogen or an inert gas.

[0015] Furthermore, after sintering, the sample is annealed at 400℃~500℃ for 3h~10h.

[0016] Furthermore, during the dispersion process, the mixture is stirred at 300 r / min to 5000 r / min for 10 min to 60 min, and then vacuum degassed at -0.09 MPa for 10 min to 30 min to obtain the dispersion slurry.

[0017] Compared with the prior art, the present invention has the following advantages: The present invention provides a method for preparing boric acid-assisted low-temperature sintering porous aluminum foil. By adding boric acid as a sintering aid to a dispersion slurry, the boric acid decomposes during heating to generate boron oxide (B₂O₃). On one hand, the boron oxide reacts with the alumina on the surface of the aluminum powder to form a low-melting-point molten boroaluminate, lowering the liquidus temperature of the aluminum powder sintering, allowing the sintering process to be carried out at a lower temperature and reducing the melting loss of the aluminum foil substrate. On the other hand, boron oxide has high chemical activity and can penetrate to the grain boundaries of aluminum powder particles, promoting the diffusion of aluminum atoms and accelerating the formation and growth of sintering necks, thereby improving sintering efficiency and the mechanical strength of the aluminum foil. This invention achieves low-temperature sintering at 450℃ to 600℃, and the prepared porous aluminum foil is suitable for energy storage devices such as aluminum electrolytic capacitors and lithium-ion batteries, offering advantages such as low-temperature energy saving, high porosity, and strong mechanical properties.

[0018] The preparation of three-dimensional porous aluminum foil typically requires aluminum powder to be coated and then sintered to form an interconnected pore structure. The addition of boric acid in this invention does not destroy this porous structure; on the contrary, it preserves more pores by lowering the sintering temperature (high temperatures easily lead to pore closure). Furthermore, the low-melting-point eutectic of boric acid can fill the spaces between aluminum powder particles, enhancing the interparticle bonding force and improving the mechanical strength of the three-dimensional porous aluminum foil. Attached Figure Description

[0019] Figure 1 These are microstructure diagrams of the porous aluminum foils prepared in Example 2 and Comparative Example 1 of the present invention. Figure 1 In the text, a represents Example 2, and b represents Comparative Example 1. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0021] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0022] Traditional processes address this by increasing sintering temperature or extending holding time. However, high temperatures and prolonged holding times present the following key drawbacks: 1. High-temperature energy consumption and oxidation: High energy consumption and severe aluminum powder oxidation; 2. Risk of pore collapse: High temperatures easily cause pore collapse between aluminum powder particles, reducing specific surface area; 3. Low production efficiency: Prolonged holding times lead to long production cycles and low efficiency. In other words, traditional processes, addressing the core contradiction of "alumina on the aluminum powder surface hindering contact," cannot simultaneously achieve the synergistic optimization of low-temperature sintering, strong interfacial bonding, and high porosity by increasing sintering temperature or extending holding time.

[0023] Based on this, the present invention provides a method for preparing boric acid-assisted low-temperature sintering porous aluminum foil, comprising the following steps: S1. Aluminum powder, boric acid and binder raw materials are dispersed in a solvent to form a dispersion slurry.

[0024] In some embodiments, the dispersion slurry comprises, by weight percentage: 45 wt.%–70 wt.% aluminum powder, 0.2 wt.%–3 wt.% boric acid, 1 wt.%–10 wt.% binder, and 17 wt.%–53.8 wt.% solvent, totaling 100%. It should be noted that if the amount of boric acid is too small, a continuous and complete boroaluminate cannot be formed on the surface of all aluminum powder particles, resulting in reduced sintering activity, obstructed atomic diffusion channels, and difficulty in the formation and growth of sintering necks. If the amount of boric acid is too large, it remains in the pores, reducing the surface area and becoming structural defect points. The amount of aluminum powder used also affects the smoothness and uniformity of the coating on the substrate surface.

[0025] In some embodiments, the aluminum powder particles are spherical or flake-shaped with a particle size of 1 μm to 10 μm, wherein the purity of the aluminum powder is ≥99.99%; the binder is methylcellulose (MC), polyethylene glycol (PEG), polyvinyl alcohol (PVA), or polypyrrolidone (PVP), and the solvent is water, ethanol, or N-methylpyrrolidone (NMP); boric acid is analytical grade (≥99.5%). It should be noted that the molecular weight of polyethylene glycol is between 1,000 and 500,000, the molecular weight of polyvinyl alcohol is between 10,000 and 1,000,000, and the molecular weight of polypyrrolidone is between 10,000 and 360,000. In a specific embodiment, the molecular weight of polyethylene glycol is 2,000, the molecular weight of polyvinyl alcohol is 126,000, and the molecular weight of polypyrrolidone is 58,000. The binder, aluminum powder, and phosphorus-containing compound are uniformly dispersed in the solvent to form a stable slurry, and the binder decomposes and volatilizes during the sintering process. If too much binder is used, it is not easy to remove during the sintering process and remains in the porous foil, decomposing into carbon, which leads to a significant increase in leakage current. If too little binder is used, the aluminum powder cannot be well adhered to the substrate, resulting in powder shedding.

[0026] In some embodiments, during the dispersion process, the mixture is stirred at 300 r / min to 5000 r / min for 10 min to 60 min, and then vacuum degassed at -0.09 MPa for 10 min to 30 min to obtain a dispersed slurry. It should be noted that the present invention preferably employs planetary stirring, which breaks up agglomerates through high-speed stirring, achieving micro-dispersion and ensuring sufficient contact between aluminum powder, boric acid, binder, and water. This promotes wetting and stabilization, forming a slurry system with uniform composition and stable performance. However, high-speed stirring easily forms microbubbles within the slurry; therefore, vacuum degassing is necessary to remove these bubbles and prevent defects during subsequent coating processes.

[0027] S2. The dispersion slurry is coated onto the substrate and dried. Then, it is sintered at 450℃~600℃ under a protective gas. Boric acid reacts with the alumina on the surface of the aluminum powder to form low-melting-point borosilicate, which lowers the sintering temperature and promotes the diffusion of aluminum atoms, increasing the formation of sintering necks. After sintering, porous aluminum foil is obtained.

[0028] In some embodiments, the coating method can be a conventional method in the existing preparation of porous aluminum foil. When a substrate is required, the selection of the substrate is also a conventional method in the preparation of porous aluminum foil. Preferably, the substrate is an aluminum base material with a purity ≥99.99% and a thickness of 20μm to 50μm, the thickness of which can be selected according to the thickness of the porous aluminum foil. Coating methods can include microgravure, transfer, blade coating, or extrusion coating. The coating thickness is 50μm to 120μm. It should be noted that the coating is double-sided, with a single-sided coating thickness of 50μm to 120μm. The coating thickness has little impact on the pore shape, pore size, and distribution of the porous aluminum foil, but if the single-sided coating is too thick, it is prone to powder shedding; if the coating is too thin, the specific surface area is too small.

[0029] In some embodiments, drying is performed by forced air drying at 60°C to 120°C for 6 min to 15 min, so that the solvent residue is ≤4 wt.%.

[0030] In some embodiments, during the sintering process, the temperature is increased from room temperature to 200°C at a rate of 1°C / min to 2°C / min, then increased to 450°C at a rate of 0.5°C / min to 1°C / min, and then increased to the target temperature at a rate of 0.1°C / min to 0.5°C / min, and held for 1 hour to 100 hours. It should be noted that when the sintering temperature is greater than 450°C, the temperature is increased to the target temperature at a rate of 0.1°C / min to 0.5°C / min. This invention employs a programmed temperature rise method, wherein the protective gas is nitrogen or an inert gas with a flow rate of 5 L / min to 50 L / min. In this invention, during the programmed temperature rise process, when the temperature reaches 200°C or 450°C, a certain period of holding can be performed, or the heating rate can be directly changed without holding. Holding is beneficial to improving the performance of porous aluminum foil, but it increases the production cycle. Therefore, this invention preferably does not perform holding and directly changes the heating rate. Boric acid decomposes during heating to produce boron oxide (B₂O₃). B₂O₃ reacts with alumina (Al₂O₃, melting point ~2050℃) on the surface of aluminum powder to form low-melting-point boroaluminates (e.g., 9Al₂O₃·2B₂O₃, melting point approximately 1350℃). The presence of this low-melting-point eutectic lowers the liquidus temperature of the aluminum powder during sintering, allowing the sintering process to proceed at lower temperatures and reducing melt loss in the aluminum foil substrate. Furthermore, the B₂O₃ produced by boric acid decomposition has high chemical reactivity, allowing it to penetrate to the grain boundaries of aluminum powder particles, promoting aluminum atom diffusion, accelerating the formation and growth of sintering necks, thereby improving sintering efficiency and the mechanical strength of the aluminum foil. It should be noted that the preparation of three-dimensional porous aluminum foil typically requires aluminum powder to form an interconnected pore structure through sintering after coating. The addition of boric acid does not destroy this porous structure; on the contrary, it retains more pores due to the lower sintering temperature (high temperatures easily lead to pore closure). In addition, the low-melting-point eutectic of boric acid can fill the spaces between aluminum powder particles, enhancing the interparticle bonding force and improving the mechanical strength of the three-dimensional porous aluminum foil.

[0031] In some embodiments, after sintering, an annealing treatment is performed at 400℃~500℃ for 3h~10h. It should be noted that after sintering, an annealing treatment can also be performed to eliminate sintering stress and prevent the aluminum foil from warping.

[0032] The boric acid-assisted low-temperature sintering method for preparing porous aluminum foil in this invention reduces the sintering temperature to 450℃~600℃ (40℃~190℃ lower than the traditional method), reducing energy consumption by 25%~40%; it features low oxidation rate (aluminum powder oxidation rate ≤1%), improved conductivity by 15%~25%; and high porosity (porosity 35%~45% (connected porosity ≥90%), with a specific surface area ≥5m². 2 / g; Strong mechanical properties: interfacial bonding strength ≥10MPa, bending strength ≥15MPa, aluminum powder shedding rate ≤0.5%; High-efficiency production: heat preservation time is shortened to 1h~100h, and efficiency is increased by 30%~60%.

[0033] The following specific examples will provide further explanation.

[0034] Example 1 A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder, boric acid, and methylcellulose are dispersed in ethanol and stirred at 1000 rpm for 30 min using a planetary stirrer. Then, the mixture is degassed under vacuum at -0.09 MPa for 20 min to form a dispersion slurry. By mass percentage, the dispersion slurry comprises: 60 wt.% aluminum powder, 0.2 wt.% boric acid, 5 wt.% methylcellulose, and 34.8 wt.% ethanol, totaling 100%. The aluminum powder is 1 μm spherical aluminum powder.

[0035] S2. The dispersion slurry is coated onto the substrate using a micro-gravure coating method. The coating thickness on one side is 90 μm. The substrate is dried at 80 °C for 13 min to reduce the solvent residue to 3.1 wt.%. Under a nitrogen protective atmosphere, the temperature is increased from room temperature to 200 °C at a flow rate of 10 L / min and then increased to 450 °C at a rate of 0.8 °C / min. The temperature is held for 92 h and sintered to obtain a porous aluminum foil.

[0036] The porous aluminum foil prepared in Example 1 was subjected to performance tests. The interfacial bonding strength was 10.2 MPa (tensile method); tensile strength was 21.3 MPa; bending strength was 78 cycles (R=1.0 mm); porosity was 36.1% (mercury porosimetry); and specific surface area was 5.8 m². 2 / g (BET method); Oxidation rate: 0.9% (oxygen content analyzer).

[0037] Example 2 A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder, boric acid, and polyethylene glycol are dispersed in ethanol and stirred at 2000 rpm for 20 min using a planetary stirrer. Then, the mixture is degassed under vacuum at -0.09 MPa for 15 min to form a dispersion slurry. By mass percentage, the dispersion slurry comprises: 65 wt.% aluminum powder, 0.5 wt.% boric acid, 3 wt.% polyethylene glycol, and 31.5 wt.% ethanol, totaling 100%. The aluminum powder is 3 μm spherical aluminum powder.

[0038] S2. The dispersion slurry is coated onto the substrate by transfer coating, with a single-sided coating thickness of 70 μm. It is dried at 90℃ for 10 min to reduce the solvent residue to 2.5 wt.%. Under an argon protective atmosphere, the temperature is increased from room temperature to 200℃ at a flow rate of 20 L / min, then increased to 450℃ at a rate of 0.7℃ / min, and then increased to 520℃ at a rate of 0.3℃ / min. The temperature is held for 63 h, sintered, and then annealed at 450℃ for 6 h to obtain porous aluminum foil.

[0039] The porous aluminum foil prepared in Example 2 was subjected to performance tests. The interfacial bonding strength was 11.5 MPa (tensile method); tensile strength was 23.8 MPa; bending strength was 72 cycles (R=1.0 mm); porosity was 38.6% (mercury porosimetry); and specific surface area was 6.3 m². 2 / g (BET method); Oxidation rate: 0.5% (oxygen content analyzer).

[0040] Example 3 A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder, boric acid, and polyvinyl alcohol are dispersed in N-methylpyrrolidone using a planetary stirrer at 5000 rpm for 10 min, followed by vacuum degassing at -0.09 MPa for 10 min to form a dispersion slurry. The dispersion slurry comprises, by mass percentage: 70 wt.% aluminum powder, 1 wt.% boric acid, 10 wt.% polyvinyl alcohol, and 19 wt.% N-methylpyrrolidone, totaling 100%. The aluminum powder is 5 μm spherical aluminum powder.

[0041] S2. The dispersion slurry is coated onto the substrate using a doctor blade coating method, with a single-sided coating thickness of 120 μm. It is then dried at 120℃ for 10 min to reduce the solvent residue to 3.0 wt.%. Under a nitrogen protective atmosphere, the temperature is increased from room temperature to 200℃ at a flow rate of 30 L / min, then increased to 450℃ at a rate of 0.5℃ / min, and finally increased to 580℃ at a rate of 0.5℃ / min. The temperature is held for 14 h, and after sintering, a porous aluminum foil is obtained.

[0042] The porous aluminum foil prepared in Example 3 was subjected to performance tests. The interfacial bonding strength was 13.8 MPa (tensile method); tensile strength was 28.2 MPa; flexural strength was 58 (R=1.0 mm); porosity was 34.1% (mercury porosimetry); and specific surface area was 5.6 m². 2 / g (BET method); Oxidation rate: 0.3% (oxygen content analyzer).

[0043] Example 4 A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder, boric acid, and polypyrrolidone are dispersed in water and stirred at 300 rpm for 60 min using a planetary stirrer. Then, the mixture is degassed under vacuum at -0.09 MPa for 30 min to form a dispersion slurry. The dispersion slurry comprises, by mass percentage: 45 wt.% aluminum powder, 2 wt.% boric acid, 1 wt.% polypyrrolidone, and 52 wt.% water, totaling 100%. The aluminum powder is 10 μm flake-shaped aluminum powder.

[0044] S2. The dispersion slurry is coated onto the substrate by extrusion coating, with a single-sided coating thickness of 60 μm. It is dried at 70℃ for 10 min to reduce the solvent residue to 2.2 wt.%. Under an argon protective atmosphere, the temperature is increased from room temperature to 200℃ at a flow rate of 5 L / min, then increased to 450℃ at a rate of 0.6℃ / min, and then increased to 600℃ at a rate of 0.3℃ / min. The temperature is held for 12 h, sintered, and then annealed at 500℃ for 3 h to obtain porous aluminum foil.

[0045] The porous aluminum foil prepared in Example 4 was subjected to performance tests. The interfacial bonding strength was 10.3 MPa (tensile method); tensile strength was 21.1 MPa; bending strength was 82 cycles (R=1.0 mm); porosity was 40.6% (mercury porosimetry); and specific surface area was 5.3 m². 2 / g (BET method); Oxidation rate: 0.4% (oxygen content analyzer).

[0046] Example 5 A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder, boric acid, and methylcellulose are dispersed in ethanol and stirred at 1500 rpm for 25 min using a planetary stirrer. Then, the mixture is degassed under vacuum at -0.09 MPa for 18 min to form a dispersion slurry. The dispersion slurry comprises, by mass percentage: 55 wt.% aluminum powder, 3 wt.% boric acid, 8 wt.% methylcellulose, and 34 wt.% ethanol, totaling 100%. The aluminum powder is 3 μm spherical aluminum powder.

[0047] S2. The dispersion slurry is coated onto the substrate using a micro-gravure coating method, with a single-sided coating thickness of 80 μm. It is dried at 80℃ for 7 min to reduce the solvent residue to 2.7 wt.%. Under a nitrogen protective atmosphere, the temperature is increased from room temperature to 200℃ at a flow rate of 15 L / min, then increased to 450℃ at a rate of 0.5℃ / min, and then increased to 550℃ at a rate of 0.2℃ / min. The temperature is held for 34 h, and after sintering, a porous aluminum foil is obtained.

[0048] The porous aluminum foil prepared in Example 5 was subjected to performance tests. The interfacial bonding strength was 12.5 MPa (tensile method); tensile strength was 25.6 MPa; bending strength was 73 cycles (R=1.0 mm); porosity was 36.9% (mercury porosimetry); and specific surface area was 6.2 m². 2 / g (BET method); Oxidation rate: 0.5% (oxygen content analyzer).

[0049] Example 6 A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder, boric acid, and polyethylene glycol are dispersed in water and stirred at 2500 rpm for 15 min using a planetary stirrer. Then, the mixture is degassed under vacuum at -0.09 MPa for 12 min to form a dispersion slurry. By mass percentage, the dispersion slurry comprises: 62 wt.% aluminum powder, 1 wt.% boric acid, 4 wt.% polyethylene glycol, and 33 wt.% water, totaling 100%. The aluminum powder is 5 μm spherical aluminum powder.

[0050] S2. The dispersion slurry was coated onto the substrate by transfer coating, with a single-sided coating thickness of 105 μm. It was dried at 105 °C for 6 min to reduce the solvent residue to 1.7 wt.%. Under an argon protective atmosphere, the temperature was increased from room temperature to 200 °C at a flow rate of 25 L / min, then increased to 450 °C at a rate of 0.5 °C / min, and then increased to 460 °C at a rate of 0.3 °C / min. The temperature was held for 72 h, sintered, and then annealed at 420 °C for 8 h to obtain porous aluminum foil.

[0051] The porous aluminum foil prepared in Example 6 was subjected to performance tests. The interfacial bonding strength was 11.8 MPa (tensile method); tensile strength was 27.4 MPa; bending strength was 91 cycles (R=1.0 mm); porosity was 39.0% (mercury porosimetry); and specific surface area was 6.1 m². 2 / g (BET method); Oxidation rate: 0.6% (oxygen content analyzer).

[0052] Comparative Example 1 A method for preparing sintered porous aluminum foil, differing from Example 2 in that boric acid is not added, includes the following steps: S1. Aluminum powder and polyethylene glycol raw materials are dispersed in ethanol and stirred at 2000 r / min for 20 min using a planetary stirrer. Then, the mixture is degassed under vacuum at -0.09 MPa for 15 min to form a dispersion slurry. The dispersion slurry comprises, by mass percentage: 65 wt.% aluminum powder, 3 wt.% polyethylene glycol, and 32 wt.% ethanol, totaling 100%. The aluminum powder is 3 μm spherical aluminum powder.

[0053] S2. The dispersion slurry is coated onto the substrate by transfer coating, with a single-sided coating thickness of 70 μm. It is dried at 90℃ for 10 min to reduce the solvent residue to 2.5 wt.%. Under an argon protective atmosphere, the temperature is increased from room temperature to 200℃ at a flow rate of 20 L / min, then increased to 450℃ at a rate of 0.7℃ / min, and then increased to 520℃ at a rate of 0.3℃ / min. The temperature is held for 63 h, sintered, and then annealed at 450℃ for 6 h to obtain porous aluminum foil.

[0054] The porous aluminum foil prepared in Comparative Example 1 was subjected to performance tests. The interfacial bonding strength was 5.8 MPa (tensile method); tensile strength was 14.6 MPa; bending strength was 117 cycles (R=1.0 mm); porosity was 27.7% (mercury porosimetry); and specific surface area was 4.1 m². 2 / g (BET method); Oxidation rate: 3.2% (oxygen content analyzer).

[0055] Comparative Example 2 A method for preparing sintered porous aluminum foil, differing from Example 3 in that boric acid is not added and the sintering temperature is raised to 650°C, includes the following steps: A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil includes the following steps: S1. Aluminum powder and polyvinyl alcohol are dispersed in N-methylpyrrolidone using a planetary stirrer at 5000 r / min for 10 min, followed by vacuum degassing at -0.09 MPa for 10 min to form a dispersion slurry. The dispersion slurry comprises, by mass percentage: 70 wt.% aluminum powder, 10 wt.% polyvinyl alcohol, and 20 wt.% N-methylpyrrolidone, totaling 100%, wherein the aluminum powder is 5 μm spherical aluminum powder.

[0056] S2. The dispersion slurry is coated onto the substrate using a doctor blade coating method, with a single-sided coating thickness of 120 μm. It is then dried at 120 °C for 10 min to reduce the solvent residue to 3.0 wt.%. Under a nitrogen protective atmosphere, the temperature is increased from room temperature to 200 °C at a flow rate of 30 L / min, then increased to 450 °C at a rate of 0.5 °C / min, and finally increased to 650 °C at a rate of 0.5 °C / min. The temperature is held for 14 h, and after sintering, a porous aluminum foil is obtained.

[0057] The porous aluminum foil prepared in Comparative Example 2 was subjected to performance tests. The interfacial bonding strength was 12.5 MPa (tensile method); tensile strength was 24.9 MPa; bending strength was 83 cycles (R=1.0 mm); porosity was 31.6% (mercury porosimetry); and specific surface area was 5.1 m². 2 / g (BET method); Oxidation rate: 5.5% (oxygen content analyzer).

[0058] Figure 1 These are microstructure diagrams of the porous aluminum foils prepared in Example 2 and Comparative Example 1 of the present invention. Figure 1 In the diagram, a represents Example 2, and b represents Comparative Example 1. Figure 1 As shown, after adding boric acid sintering aid, the sintering neck between aluminum powder particles is significantly larger than that of the sample without boric acid. A three-dimensional interpenetrating porous material is formed between the aluminum powder particles, and its mechanical strength is also greatly improved.

[0059] In summary, the boric acid-assisted low-temperature sintering porous aluminum foil preparation method disclosed in this invention utilizes the addition of boric acid. During sintering, boron oxide (B₂O₃) is generated through decomposition. The boron oxide reacts with the alumina on the surface of the aluminum powder to form low-melting-point boroaluminate, lowering the sintering liquidus temperature and promoting aluminum atom diffusion, thus achieving low-temperature sintering at 450℃~600℃. The preparation process includes: aluminum powder slurry preparation (containing boric acid), coating and drying, low-temperature sintering, and optional annealing. The resulting porous aluminum foil exhibits an interfacial bonding strength ≥10MPa, a porosity of 35%~45%, and a specific surface area ≥5m². 2 / g, with an oxidation rate of ≤1%, it is suitable for energy storage devices such as aluminum electrolytic capacitors and lithium-ion batteries. It has the advantages of low-temperature energy saving, high porosity, and strong mechanical properties, and solves the problems of alumina obstruction and high energy consumption at high temperatures in traditional aluminum powder sintered foil.

[0060] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0061] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing boric acid-assisted low-temperature sintering porous aluminum foil, characterized in that, Includes the following steps: Aluminum powder, boric acid, and binder raw materials are dispersed in a solvent to form a dispersion slurry; The dispersion slurry is coated onto the substrate and dried. Then, it is sintered at 450℃~600℃ under a protective gas. Boric acid reacts with the alumina on the surface of the aluminum powder to form low-melting-point borosilicate, which lowers the sintering temperature and promotes the diffusion of aluminum atoms, increasing the formation of sintering necks. After sintering, porous aluminum foil is obtained.

2. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, In the dispersion slurry, the amount of boric acid used is 0.2 wt.% to 3 wt.%.

3. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, In the dispersion slurry, the amount of aluminum powder is 45wt.% to 70wt.% and the amount of binder is 1wt.% to 10wt.%.

4. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, During the sintering process, the temperature is increased to 200℃ at a rate of 1℃ / min to 2℃ / min, then increased to 450℃ at a rate of 0.5℃ / min to 1℃ / min, and then increased to the target temperature at a rate of 0.1℃ / min to 0.5℃ / min, and held for 1h to 100h.

5. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, The coating thickness is 50μm to 100μm.

6. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, The binder is methylcellulose, polyethylene glycol, polyvinyl alcohol or polypyrrolidone, and the solvent is water, ethanol or N-methylpyrrolidone.

7. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, The aluminum powder particles are spherical or flake-shaped, with a particle size of 1μm to 10μm.

8. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, During the sintering process, the protective gas is nitrogen or an inert gas.

9. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, After sintering, the material is annealed at 400℃~500℃ for 3h~10h.

10. The method for preparing boric acid-assisted low-temperature sintering porous aluminum foil according to claim 1, characterized in that, During the dispersion process, the mixture is stirred at 300 r / min to 5000 r / min for 10 min to 60 min, and then degassed under vacuum at -0.09 MPa for 10 min to 30 min to obtain the dispersion slurry.

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