Anode foil, preparation method thereof and aluminum electrolytic capacitor

Abstract

The invention provides an anode foil and a preparation method thereof, and an aluminum electrolytic capacitor. The preparation method of the anode foil comprises the following steps: mixing aluminum powder, a binder and a solvent to form aluminum powder slurry; coating the surface of at least one side of the alloy base material foil with the aluminum powder slurry, and drying to obtain a dried foil; performing first crack treatment on the dried foil; sintering the dried foil subjected to the first crack treatment to obtain an unformed foil with an aluminum powder sintered layer on the surface of the alloy base material foil; sequentially carrying out pre-cleaning and first heat treatment on the unformed foil to remove residual substances in pores in the aluminum powder sintering layer; and sequentially carrying out second crack treatment and formation treatment on the non-formed foil subjected to heat treatment. The preparation method can obtain the anode foil with relatively high strength, relatively short hydration time and relatively low leakage current, and is beneficial to improving the strength and prolonging the service life of the anode foil.

Description

TECHNICAL FIELD

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

[0002] The anode foil for aluminum electrolytic capacitor is a key component of the aluminum electrolytic capacitor. The quality and performance of the anode foil directly affect the key indicators such as the capacity, loss, service life and reliability of the aluminum electrolytic capacitor. The sintered foil by hot extrusion is an anode foil prepared by a hot extrusion sintering process. The preparation process adopts aluminum powder and a base layer aluminum foil to form an anode foil by high-temperature sintering. The prepared anode foil has an aluminum powder sintering layer on the surface of the base layer foil.

[0003] With the rapid development of the integration of electronic products, the performance requirements of the aluminum electrolytic capacitor such as miniaturization, high capacity and long service life are becoming higher and higher. Therefore, as a key raw material of the aluminum electrolytic capacitor, higher requirements are put forward for the performance of the anode foil. How to develop an anode foil with longer service life and greater strength has become one of the important research directions in the field. SUMMARY

[0004] Based on this, the present application provides a preparation method of an anode foil capable of improving the strength of the anode foil, shortening the hydration time and reducing the leakage current, and correspondingly provides the anode foil and an aluminum electrolytic capacitor thereof.

[0005] The technical solution provided in the present application is as follows:

[0006] According to a first aspect of the present application, a preparation method of an anode foil is provided, comprising the following steps:

[0007] Mixing aluminum powder, a binder and a solvent to form an aluminum powder slurry;

[0008] Coating the aluminum powder slurry on at least one side surface of an alloy base material foil, drying to obtain a dried foil;

[0009] Performing a first crack treatment on the dried foil;

[0010] Performing a sintering treatment on the dried foil after the first crack treatment to obtain an unformed foil having an aluminum powder sintering layer on the surface of the alloy base material foil;

[0011] Sequentially performing a pre-cleaning and a first heat treatment on the unformed foil to remove residual substances in the pores in the aluminum powder sintering layer; and

[0012] Sequentially performing a second crack treatment and a formation treatment on the unformed foil after the heat treatment.

[0013] In any embodiment, the alloy substrate foil is a foil prepared by a compound casting process, the alloy substrate foil comprising a high-purity aluminum foil and an aluminum alloy layer disposed on a surface of the high-purity aluminum foil.

[0014] In any embodiment, the drying comprises the following steps: drying the alloy substrate foil coated with the aluminum powder slurry at 50℃, 100℃, 150℃, 200℃, 250℃, 300℃ in sequence for 2min in an air atmosphere.

[0015] In any embodiment, the first crack treatment is a rolling treatment of 1-10 times on the surface of the dried foil coated with the aluminum powder slurry by using a roller.

[0016] In any embodiment, the second crack treatment is a rolling treatment of 1-10 times on the aluminum powder sintered layer of the unformed foil after the heat treatment by using a roller.

[0017] In any embodiment, the sintering treatment comprises the following steps: heat preservation of the dried foil in vacuum or inert gas at 150℃-250℃ for 1h-4h, at 250℃-350℃ for 1h-4h, at 350℃-450℃ for 1h-4h, and at 560℃-650℃ for 2h-24h.

[0018] In any embodiment, the mass ratio of the solvent, the binder and the aluminum powder in the aluminum powder slurry is 28-60:2-10:30-70.

[0019] In any embodiment, the solvent comprises one or more of tributyl citrate, dimethyl adipate, diethylene glycol dimethyl ether, dibutyl phthalate, diethylene glycol butyl ether acetate, diethylene glycol butyl ether, diethylene glycol dibutyl ether and terpineol.

[0020] In any embodiment, the binder comprises one or more of ethyl cellulose, polypropylene carbonate and polyvinyl butyral resin.

[0021] In any embodiment, the mass fraction of aluminum in the aluminum powder is greater than 99.98%, and the D50 particle size of the aluminum powder is 2-4μm.

[0022] In any embodiment, the pre-cleaning is soaking treatment of the unformed foil in an alkaline solution with a mass fraction of 0.1%-0.5% for 1s-30s, and then soaking treatment in an acid solution with a mass fraction of 0.3%-0.8% for 1s-30s.

[0023] In any embodiment, the temperature of the first heat treatment is 280℃-320℃, and the time is 1min-5min.

[0024] In any embodiment, after the first heat treatment, the method further comprises a step of subjecting the unformed foil to a second heat treatment at 450℃ to 550℃ for 1min to 5min.

[0025] According to a second aspect of the present application, there is provided an anode foil prepared by the method for preparing an anode foil according to the first aspect of the present application.

[0026] In any embodiment, the thickness of the alloy base foil is 20μm to 50μm, and the thickness of the aluminum powder sintered layer on one side is 10μm to 60μm.

[0027] According to a third aspect of the present application, there is provided an aluminum electrolytic capacitor comprising the anode foil prepared by the method for preparing an anode foil according to the first aspect of the present application, or comprising the anode foil according to the second aspect of the present application.

[0028] Compared with the prior art, the present application has at least the following beneficial effects:

[0029] By using the alloy base foil, and subjecting the dried foil to a first crack treatment before sintering, and subjecting the unformed foil to a second crack treatment before formation, the tensile strength and bending times of the anode foil can be effectively improved, so that the prepared anode foil has high strength and good mechanical properties; by performing the pre-cleaning and heat treatment and other impurity removal processes after sintering and before formation, the residual substances in the coating pores can be effectively removed, the hydration time of the anode foil is shortened, the leakage current is reduced, and the service life of the anode foil and the aluminum electrolytic capacitor is prolonged. By combining the above processes, the anode foil has high strength and long service life at the same time, and can well meet the performance requirements of small size and long life of the aluminum electrolytic capacitor on the market. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the specific embodiments of the present application are described in detail. In the following description, a large number of specific details are set forth in order to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present application, therefore the present application is not limited to the specific embodiments disclosed below.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise expressly stated, it is in no way intended that any of the materials, protocols, reagents, devices, or equipments which are used, unless otherwise expressly stated, be limited to the specific examples that are described in this document.

[0032] Some embodiments of the present application provide a method for preparing an anode foil, comprising steps S100 to S600:

[0033] Step S100: mixing aluminum powder, a binder and a solvent to form an aluminum powder slurry.

[0034] In some embodiments, the mass ratio of the solvent, the binder and the aluminum powder in the aluminum powder slurry is 28-60:2-10:30-70.

[0035] In some embodiments, the solvent comprises one or more of tributyl citrate, dimethyl adipate, diethylene glycol dimethyl ether, dibutyl phthalate, diethylene glycol butyl ether acetate, diethylene glycol butyl ether, diethylene glycol dibutyl ether and terpineol. Optionally, the solvent is diethylene glycol butyl ether.

[0036] In some embodiments, the binder comprises one or more of ethyl cellulose, polypropylene carbonate and polyvinyl butyral resin. Optionally, the binder is ethyl cellulose.

[0037] In some embodiments, the aluminum powder uses high-purity aluminum powder particles, the mass fraction of aluminum in the aluminum powder is greater than 99.98%, and the D50 particle size of the aluminum powder is 2-4 μm.

[0038] Step S200: coating the aluminum powder slurry on at least one side surface of the alloy substrate foil, drying to obtain a dried foil.

[0039] In some embodiments, the aluminum powder slurry is coated on one side surface of the alloy substrate foil by transfer coating or extrusion coating; after drying, the aluminum powder slurry is coated on the other side surface of the alloy substrate foil by transfer coating or extrusion coating, and the dried foil is obtained after drying.

[0040] In some specific examples, after the aluminum powder slurry is coated on one side surface of the alloy base material foil, the alloy base material foil coated with the aluminum powder slurry is dried in an air atmosphere at 50°C, 100°C, 150°C, 200°C, 250°C and 300°C in sequence, and each temperature section is dried for 2 minutes; then the aluminum powder slurry is coated on the other side surface of the alloy base material foil, and the alloy base material foil coated with the aluminum powder slurry is dried in an air atmosphere at 50°C, 100°C, 150°C, 200°C, 250°C and 300°C in sequence, and each temperature section is dried for 2 minutes, thereby obtaining a dried foil. In this embodiment, the thickness of the single-sided film layer after drying is 10 μm to 60 μm.

[0041] In some embodiments, the alloy base material foil is a foil prepared by a composite cast rolling process. In this embodiment, the alloy base material foil includes a high-purity aluminum foil and an aluminum alloy layer, the aluminum alloy layer is arranged on the surface of the high-purity aluminum foil, forming an alloy base material foil with the high-purity aluminum foil as the core layer and the aluminum alloy as the surface layer, and the aluminum alloy layer can be an aluminum alloy layer with a purity of 3N.

[0042] Step S300: performing first crack treatment on the dried foil.

[0043] After the aluminum powder slurry is coated on the surface of the alloy base material foil and dried, the first crack treatment is performed on the dried foil to generate some fine cracks in the coating layer on the dried foil, which is beneficial to form a more uniform and reasonable pore distribution in the aluminum powder coating layer in the subsequent sintering process, and helps the electrolyte to better penetrate and store charges, thereby improving the capacitance of the aluminum electrolytic capacitor. In addition, the aluminum powder coating layer will be subjected to different degrees of stress during preparation and use. By manufacturing cracks in the coating layer in advance through the first crack treatment, part of the stress can be released, avoiding the situation that the coating layer is broken or peeled off due to large stress concentration in the subsequent process or use.

[0044] In some embodiments, the roller is rolled on the surface of the dried foil coated with the aluminum powder slurry for 1 to 10 times to perform the first crack treatment on the dried foil to generate some fine cracks in the coating layer on the dried foil. It can be understood that the number of rolling times of the roller in the first crack treatment step can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0045] Step S400: performing sintering treatment on the dried foil after the first crack treatment to obtain an unformed foil with an aluminum powder sintering layer on the surface of the alloy base material foil.

[0046] After the first crack treatment generates some fine cracks in the aluminum powder coating on the surface of the alloy base foil, the dried foil is further sintered to form a firm bond between the aluminum powder particles and between the aluminum powder and the alloy base foil, thereby enhancing the adhesion of the coating on the alloy base foil. This makes the coating less likely to fall off during subsequent use, which helps to improve the stability and reliability of the aluminum electrolytic capacitor. In addition, the sintering process can also promote the formation of a porous microstructure in the aluminum powder coating, which helps to increase the effective surface area of the anode foil and thus improve the capacitance of the aluminum electrolytic capacitor.

[0047] In some embodiments, the sintering process is a first holding at 150-250℃ for 1-4h, a second holding at 250-350℃ for 1-4h, a third holding at 350-450℃ for 1-4h, and a fourth holding at 560-650℃ for 2-24h, followed by natural cooling to room temperature.

[0048] The use of the above-mentioned programmed temperature rising steps for sintering the dried foil helps to accurately control the chemical reaction rate in the aluminum powder coating, making the reaction of each substance in the aluminum powder coating more complete and uniform. At the same time, the use of programmed temperature rising helps to avoid the thermal shock caused by sudden temperature rise on the aluminum powder coating and the alloy base foil.

[0049] In addition, the use of the above-mentioned programmed temperature rising sintering steps also helps to promote the gradual evolution and optimization of the microstructure in the coating, forming a uniform, dense and reasonable pore distribution coating structure; and helps to escape the gas and volatile impurities generated during the sintering process of the coating, improving the purity and quality of the coating.

[0050] It can be understood that the temperature of the first heat preservation can be 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, and any value within the range formed by any two of the above values; the time of the first heat preservation can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, and any value within the range formed by any two of the above values; the temperature of the second heat preservation can be 250℃, 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, and any value within the range formed by any two of the above values; the time of the second heat preservation can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, and any value within the range formed by any two of the above values; the temperature of the third heat preservation can be 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, and any value within the range formed by any two of the above values; the time of the third heat preservation can be 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, and any value within the range formed by any two of the above values; the temperature of the fourth heat preservation can be 560℃, 570℃, 580℃, 590℃, 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, and any value within the range formed by any two of the above values; the time of the fourth heat preservation can be 2h, 5h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, 24h, and any value within the range formed by any two of the above values.

[0051] Step S500: sequentially performing pre-cleaning and first heat treatment on the unformed foil to remove residual substances in the pores of the aluminum powder sintered layer.

[0052] After the sintering treatment, some residual substances (such as carbon residues) are usually left in the pores of the aluminum powder sintered layer. These residual substances in the pores occupy a certain pore space, so that the formation solution and the electrolyte solution cannot be well filled and infiltrated into the pores, affecting the capacity of the anode foil and the aluminum electrolytic capacitor. Moreover, these residual substances can prolong the hydration time of the anode foil and increase the leakage current, affecting the service life of the aluminum electrolytic capacitor.

[0053] By sequentially performing pre-cleaning and first heat treatment on the unformed foil formed after sintering, the residual substances in the pores of the aluminum powder sintered layer can be effectively removed, the anode foil has a higher capacity, and the hydration time of the anode foil is shortened, the leakage current is reduced, and the service life of the aluminum electrolytic capacitor is improved.

[0054] In some embodiments, the pre-cleaning is to immerse the unformed foil in an alkali solution with a mass fraction of 0.1% to 0.5% for 1s to 30s, and then immerse in an acid solution with a mass fraction of 0.3% to 0.8% for 1s to 30s.

[0055] By immersing the unformed foil in the alkali solution and then in the acid solution, the pre-cleaning process described above is beneficial to remove the residual substances in the pores of the sintered layer of aluminum powder. The alkali solution can be a conventional alkali solution, such as a sodium hydroxide solution; and the acid solution can be a conventional acid solution, such as a nitric acid solution.

[0056] It can be understood that the immersion time in the alkali solution can be 1s, 2s, 5s, 8s, 10s, 12s, 15s, 18s, 20s, 22s, 25s, 28s, 30s, or any value within the range formed by any two of the above values; and the immersion time in the acid solution can be 1s, 2s, 5s, 8s, 10s, 12s, 15s, 18s, 20s, 22s, 25s, 28s, 30s, or any value within the range formed by any two of the above values.

[0057] In some embodiments, the first heat treatment is at a temperature of 280°C to 320°C for 1min to 5min. By immersing the unformed foil in the alkali solution and then in the acid solution, and then performing the first heat treatment on the unformed foil, the combination of the alkali treatment, the acid treatment, and the first heat treatment is beneficial to further remove the residual substances in the pores of the sintered layer of aluminum powder.

[0058] It can be understood that the temperature of the first heat treatment can be 280°C, 285°C, 290°C, 295°C, 300°C, 305°C, 310°C, 315°C, 320°C, or any value within the range formed by any two of the above values; and the time of the first heat treatment can be 1min, 1.5min, 2min, 2.5min, 3min, 3.5min, 4min, 4.5min, 5min, or any value within the range formed by any two of the above values.

[0059] In some embodiments, after the first heat treatment and before the second crack treatment, a step of performing a second heat treatment on the unformed foil at 450-550°C for 1-5 minutes is further included. By performing the second heat treatment on the unformed foil under the above process conditions after the first heat treatment, the residual substances in the pores of the aluminum powder sintered layer can be further removed. In this way, by combining the alkali treatment, the acid treatment, the first heat treatment and the second heat treatment, the residual substances in the pores of the aluminum powder sintered layer can be fully removed. The first heat treatment is to place the unformed foil in a muffle furnace for heat treatment, and the second heat treatment is to place the unformed foil in an oven for heat treatment.

[0060] Step S600: sequentially performing a second crack treatment and a formation treatment on the unformed foil after the heat treatment.

[0061] After the second heat treatment, the unformed foil is subjected to a second crack treatment and then a formation treatment. By the second crack treatment step before the formation step, the bending frequency of the anode foil can be improved, and the anode foil has better mechanical properties. After the formation treatment, an anode foil with high strength, short hydration time, small leakage current and high specific capacity is finally obtained, and the use life of the aluminum electrolytic capacitor can be prolonged by using the anode foil. The thickness of the alloy base material foil in the anode foil is 20-50 μm, and the thickness of the aluminum powder sintered layer on one side is 10-60 μm. The formation treatment can use a conventional formation process.

[0062] In some embodiments, the second crack treatment is to roll the aluminum powder sintered layer of the unformed foil after the second heat treatment 1-10 times by using a roller. By the above-mentioned second crack treatment step, the bending performance of the anode foil can be effectively improved. In the second crack treatment step, the rolling frequency of the roller can be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 times.

[0063] Some embodiments of the present application also provide an aluminum electrolytic capacitor using the anode foil prepared by the above-mentioned preparation method of the anode foil. The above-mentioned aluminum electrolytic capacitor has a long use life by using the anode foil of the present application.

[0064] Overall, the present application can effectively improve the tensile strength and bending times of the anode foil by adopting an alloy substrate foil and performing a first crack treatment on the dried foil before sintering and a second crack treatment on the unformed foil before formation. The prepared anode foil has high strength and good mechanical properties. By performing impurity removal processes such as pre-cleaning and heat treatment after sintering and before formation, residual substances in the coating pores can be effectively removed, the hydration time of the anode foil is shortened, the leakage current is reduced, and the service life of the anode foil and the aluminum electrolytic capacitor is prolonged. Through the combination of the above processes, the anode foil has high strength and long service life at the same time, which can well meet the market performance requirements of small size and long life of aluminum electrolytic capacitors.

[0065] The present application will be further described below in conjunction with specific examples and comparative examples, but should not be understood as limiting the scope of protection of the present application.

[0066] Example 1:

[0067] An aluminum powder with an average particle size D50 of 3 µm was used to prepare an aluminum powder slurry with a solid content of 50 wt%. The organic slurry was prepared with a weight ratio of terpineol: ethyl cellulose (binder): ethylene glycol of 88:10:2.

[0068] A stainless steel scraper was used to uniformly coat the above-mentioned aluminum powder slurry on the alloy substrate foil prepared by the composite cast rolling process, and the foil was dried at 50℃, 100℃, 150℃, 200℃, 250℃ and 300℃, respectively, with a drying time of 2 min for each step. Then the same process was used to coat the aluminum powder slurry on the other side of the alloy substrate foil and dry it, obtaining a dried foil sheet.

[0069] The dried foil sheet was rolled on a 8mm diameter roller for 5 times on both sides, thereby performing a first crack treatment on the dried foil sheet to form micro cracks in the aluminum powder coating.

[0070] The dried foil sheet was placed in a vacuum environment for sintering treatment. The sintering treatment was divided into four steps: the first step was to heat treat at 200℃ for 1h, the second step was to heat treat at 300℃ for 1h, the third step was to heat treat at 400℃ for 1h, and the fourth step was to heat treat at 640℃ for 12h, obtaining an unformed foil.

[0071] The above-mentioned unformed foil was first soaked in a 0.3wt% NaOH solution at room temperature for 30s, then soaked in a 0.5wt% HNO3 solution at room temperature for 30s, then heat treated in a muffle furnace at 300℃ for 2min, and then heat treated in an oven at 500℃ for 3min.

[0072] The unformed foil was boiled in pure water at 95°C or higher for 5 minutes, and the foil was rolled on a 8mm diameter roller for 2 times on each side, thereby performing a second crack treatment on the unformed foil.

[0073] The unformed foil was subjected to chemical conversion in a 100g / L boric acid solution to 520V, constant voltage for 20 minutes, air placement at 500°C for 2 minutes, and foil covering in the chemical conversion solution for 10 minutes, thereby obtaining a positive electrode foil for aluminum electrolytic capacitors.

[0074] Comparative Example 1

[0075] An aluminum powder having an average particle size D50 of 3 pm was used to prepare an aluminum powder slurry having a solid content of 60 wt% with an organic slurry. The organic slurry was prepared with a weight ratio of terpineol: ethyl cellulose: ethylene glycol of 88:10:2.

[0076] The above aluminum powder slurry was uniformly coated on a high-purity aluminum base foil using a stainless steel spatula, and was subjected to drying treatment at 50°C, 100°C, 150°C, 200°C, 250°C, and 300°C, respectively, for 2 minutes at each step. Then, the same procedure was performed to coat the aluminum powder slurry on the other side of the high-purity aluminum base foil and to dry it, thereby obtaining a dried foil.

[0077] The dried foil was subjected to sintering treatment in a vacuum environment. The sintering treatment was performed in two steps, i.e., a first step at 400°C for 1 hour and a second step at 640°C for 2 hours, thereby obtaining an unformed foil.

[0078] The above unformed foil was subjected to chemical conversion in a 100g / L boric acid solution to 520V, constant voltage for 20 minutes, air placement at 500°C for 2 minutes, and foil covering in the chemical conversion solution for 10 minutes, thereby obtaining a positive electrode foil for aluminum electrolytic capacitors.

[0079] Comparative Example 2

[0080] An aluminum powder having an average particle size D50 of 3 pm was used to prepare an aluminum powder slurry having a solid content of 70 wt% with an organic slurry. The organic slurry was prepared with a weight ratio of terpineol: ethyl cellulose: ethylene glycol of 88:10:2.

[0081] The above aluminum powder slurry was uniformly coated on a high-purity aluminum base foil using a stainless steel spatula, and was subjected to drying treatment at 50°C, 100°C, 150°C, 200°C, 250°C, and 300°C, respectively, for 2 minutes at each step. Then, the same procedure was performed to coat the aluminum powder slurry on the other side of the high-purity aluminum base foil and to dry it, thereby obtaining a dried foil.

[0082] The dried foil is placed in a vacuum environment for sintering treatment. The sintering treatment is divided into two steps, the first step is heat treatment at 400°C for 1h, and the second step is heat treatment at 640°C for 2h, to obtain an unformed foil.

[0083] The above unformed foil is immersed in a 100g / L boric acid solution for 20min, and then placed in air at 500°C for 2min, and covered with the foil in the immersion solution for 10min, to obtain an anode foil for aluminum electrolytic capacitors.

[0084] Comparative Example 3:

[0085] An aluminum powder with an average particle size D50 of 3pm is used to prepare an aluminum powder slurry with a solid content of 50wt% with an organic slurry. The organic slurry is prepared with a weight ratio of terpineol: ethyl cellulose: ethylene glycol of 88:10:2.

[0086] A stainless steel scraper is used to uniformly coat the above aluminum powder slurry on the substrate foil prepared by the composite cast rolling process, and then dried at 50°C, 100°C, 150°C, 200°C, 250°C and 300°C, respectively, with a drying time of 2min for each step. Then the same process is used to coat the aluminum powder slurry on the other side of the high-purity aluminum substrate foil and dry it, to obtain a dried foil.

[0087] The dried foil is placed in a vacuum environment for sintering treatment. The sintering treatment is divided into four steps, the first step is heat treatment at 200°C for 1h, the second step is heat treatment at 300°C for 1h, the third step is heat treatment at 400°C for 1h, and the fourth step is heat treatment at 640°C for 12h, to obtain an unformed foil.

[0088] The above unformed foil is boiled in pure water at 95°C for 5min, and then immersed in a 100g / L boric acid solution for 20min, and then placed in air at 500°C for 2min, and covered with the foil in the immersion solution for 10min, to obtain an anode foil for aluminum electrolytic capacitors.

[0089] Comparative Example 4:

[0090] An aluminum powder with an average particle size D50 of 3pm is used to prepare an aluminum powder slurry with a solid content of 50wt% with an organic slurry. The organic slurry is prepared with a weight ratio of terpineol: ethyl cellulose: ethylene glycol of 88:10:2.

[0091] A stainless steel scraper is used to uniformly coat the aluminum powder slurry on a high-purity aluminum substrate foil, and then dried at 50°C, 100°C, 150°C, 200°C, 250°C and 300°C, respectively, with a drying time of 2min for each step. Then the same process is used to coat the aluminum powder slurry on the other side of the high-purity aluminum substrate foil and dry it, to obtain a dried foil.

[0092] The above drying foil was rolled on a roller with a diameter of 8 mm for 5 times on each side to perform a first crack treatment on the drying foil, thereby forming micro cracks in the aluminum powder coating.

[0093] The drying foil was placed in a vacuum environment for sintering treatment. The sintering treatment was divided into four steps, the first step was heat treatment at 200°C for 1h, the second step was heat treatment at 300°C for 1h, the third step was heat treatment at 400°C for 1h, and the fourth step was heat treatment at 640°C for 12h, thereby obtaining an unformed foil.

[0094] The above unformed foil was first soaked in a 0.3wt% NaOH solution at room temperature for 30s, then soaked in a 0.5wt% HNO3 solution at room temperature for 30s, and then heat treated in a muffle furnace at 300°C for 2min.

[0095] The foil was boiled in pure water at 95°C for 5min, and then rolled on a roller with a diameter of 8 mm for 2 times on each side, thereby performing a second crack treatment on the unformed foil, thereby forming micro cracks in the aluminum powder sintering layer.

[0096] The unformed foil after the second crack treatment was converted in a 100g / L boric acid solution to 520V, constant voltage for 20min, and then placed in air at 500°C for 2min, and then covered in the conversion solution for 10min, thereby obtaining a positive foil for aluminum electrolytic capacitor.

[0097] Comparative Example 5:

[0098] An aluminum powder with an average particle size D50 of 3µm was used to prepare an aluminum powder slurry with a solid content of 50wt% by using an organic slurry. The organic slurry was prepared with a weight ratio of terpineol: ethyl cellulose: ethylene glycol of 88:10:2.

[0099] The above aluminum powder slurry was uniformly coated on the substrate foil prepared by the composite cast-rolling process using a stainless steel scraper, and then dried at 50°C, 100°C, 150°C, 200°C, 250°C and 300°C, respectively, with a drying time of 2min for each step. Then the same process was used to coat the aluminum powder slurry on the other side of the high-purity aluminum substrate foil and dry it, thereby obtaining a drying foil.

[0100] The drying foil was placed in a vacuum environment for sintering treatment. The sintering treatment was divided into four steps, the first step was heat treatment at 200°C for 1h, the second step was heat treatment at 300°C for 1h, the third step was heat treatment at 400°C for 1h, and the fourth step was heat treatment at 640°C for 12h, thereby obtaining an unformed foil.

[0101] The unformed foil was first soaked in 0.3wt% NaOH solution at room temperature for 30s, then soaked in 0.5wt% HNO3 solution at room temperature for 30s, and then heat treated in a muffle furnace at 300°C for 2min.

[0102] The foil was boiled in pure water at 95°C or above for 5min, and then formed in 100g / L boric acid solution to 520V, constant voltage for 20min, air placed at 500°C for 2min, and covered in the forming solution for 10min to obtain the positive-grade foil for aluminum electrolytic capacitor.

[0103] Comparative Example 6:

[0104] An aluminum powder with an average particle size D50 of 3pm was used to prepare an aluminum powder slurry with a solid content of 50wt%. The organic slurry was prepared with a weight ratio of terpineol: ethyl cellulose: ethylene glycol of 88:10:2.

[0105] A stainless steel scraper was used to evenly coat the above-mentioned aluminum powder slurry on the substrate foil prepared by the composite cast rolling process, and then dried at 50°C, 100°C, 150°C, 200°C, 250°C and 300°C, respectively, for 2min at each step. Then the same process was used to coat the aluminum powder slurry on the other side of the high-purity aluminum substrate foil and dry it to obtain the dried foil.

[0106] The foil was rolled on a 8mm diameter roller for 5 times on both sides to perform the first crack treatment on the dried foil, forming micro cracks in the aluminum powder coating.

[0107] The dried foil was placed in a vacuum environment for sintering treatment. The sintering treatment was divided into four steps: the first step was heat treatment at 200°C for 1h, the second step was heat treatment at 300°C for 1h, the third step was heat treatment at 400°C for 1h, and the fourth step was heat treatment at 640°C for 12h to obtain the unformed foil.

[0108] The foil was boiled in pure water at 95°C or above for 5min, and then the foil was rolled on a 8mm diameter roller for 2 times on both sides to perform the second crack treatment on the unformed foil, forming micro cracks in the aluminum powder sintering layer.

[0109] The foil was formed in 100g / L boric acid solution to 520V, constant voltage for 20min, air placed at 500°C for 2min, and covered in the forming solution for 10min to obtain the positive-grade foil for aluminum electrolytic capacitor.

[0110] The performance parameters of the anode foil prepared in the above examples and comparative examples are shown in Table 1.

[0111] Table 1

[0112]

[0113] In Table 1, Vt represents the withstand voltage, indicating the voltage that the anode foil can withstand; CAP represents the specific capacitance, indicating the capacitance of the anode foil; Tr60 represents the water resistance, indicating the voltage rise time measured after boiling the anode foil in water for one hour; a shorter time indicates better oxide film performance of the anode foil; Vt60 represents the withstand voltage after hydration, indicating the withstand voltage measured after boiling the anode foil in water for one hour. The test methods for the above performance parameters refer to the industry standard SJ / T11140-2012 for electrode foils for aluminum electrolytic capacitors.

[0114] The strength of the anode foil is evaluated using two dimensions: tensile strength and the number of bends. Higher tensile strength and a greater number of bends indicate higher anode foil strength. The lifespan of the anode foil is primarily evaluated by its Tr60 time and leakage current. A shorter Tr60 time and a smaller leakage current indicate a longer anode foil lifespan.

[0115] The lifespan of aluminum electrolytic capacitors is primarily affected by water molecules in the air. Water molecules react with the oxide film of the anode foil, causing hydration and compromising its density, thus reducing the anode foil's lifespan. A shorter Tr60 time indicates better oxide film density and resistance to hydration reactions, resulting in a longer anode foil lifespan. Leakage current is directly related to the insulation performance of the anode foil. A lower leakage current indicates better insulation performance, effectively reducing energy loss and heat generation, minimizing damage to the oxide film, and thus contributing to a longer lifespan for both the anode foil and the capacitor.

[0116] As can be seen from the data in Table 1, the anode foil of this application has a large tensile strength, a large number of bending cycles, a small leakage current and a short hydration time, indicating that the anode foil has high strength and a long service life, which can correspondingly extend the life of aluminum electrolytic capacitors using the anode foil.

[0117] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0118] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing an anode foil, characterized in that, Includes the following steps: Aluminum powder, binder and solvent are mixed to form aluminum powder slurry; The aluminum powder slurry is coated onto at least one side of the alloy substrate foil and then dried to obtain a dried foil; The dried foil is subjected to a first crack treatment; The dried foil after the first crack treatment is sintered to obtain an unformed foil with an aluminum powder sintered layer on the surface of the alloy substrate foil. The unformed foil is subjected to pre-cleaning and a first heat treatment in sequence to remove residual substances in the pores of the aluminum powder sintered layer; and The unformed foil after heat treatment is then subjected to a second crack treatment and a formation treatment in sequence.

2. The method for preparing the anode foil according to claim 1, characterized in that, The alloy substrate foil is a foil sheet prepared by a composite casting and rolling process, and the alloy substrate foil includes a high-purity aluminum foil and an aluminum alloy layer disposed on the surface of the high-purity aluminum foil.

3. The method for preparing the anode foil according to claim 1, characterized in that, The drying process includes the following steps: The alloy substrate foil coated with the aluminum powder paste was dried in air at temperatures of 50°C, 100°C, 150°C, 200°C, 250°C, and 300°C for 2 minutes in sequence.

4. The method for preparing the anode foil according to claim 1, characterized in that, The first crack treatment involves rolling a roller on the surface of the dried foil coated with the aluminum powder paste 1 to 10 times. And / or, the second crack treatment involves rolling the aluminum powder sintered layer without foil after heat treatment 1 to 10 times.

5. The method for preparing the anode foil according to any one of claims 1 to 4, characterized in that, The sintering process includes the following steps: The dried foil is sequentially kept at 150℃~250℃ for 1h~4h, at 250℃~350℃ for 1h~4h, at 350℃~450℃ for 1h~4h, and at 560℃~650℃ for 2h~24h in a vacuum or inert gas environment.

6. The method for preparing the anode foil according to any one of claims 1 to 4, characterized in that, The mass ratio of the solvent, the binder, and the aluminum powder in the aluminum powder slurry is 28~60:2~10:30~70; And / or, the solvent includes one or more of the following: tributyl citrate, dimethyl adipate, diethylene glycol dimethyl ether, dibutyl phthalate, diethylene glycol butyl ether acetate, diethylene glycol butyl ether, diethylene glycol dibutyl ether, and terpineol. And / or, the adhesive comprises one or more of ethyl cellulose, polypropylene carbonate, and polyvinyl butyral resin; And / or, the aluminum powder contains an aluminum mass fraction greater than 99.98%, and the D50 particle size of the aluminum powder is 2μm~4μm.

7. The method for preparing the anode foil according to any one of claims 1 to 4, characterized in that, The pre-cleaning process involves immersing the unformed foil in an alkaline solution with a mass fraction of 0.1% to 0.5% for 1 to 30 seconds, followed by immersion in an acidic solution with a mass fraction of 0.3% to 0.8% for 1 to 30 seconds. And / or, the temperature of the first heat treatment is 280℃~320℃, and the time is 1min~5min; And / or, after the first heat treatment and before the second crack treatment, the process further includes a step of subjecting the unformed foil to a second heat treatment at 450°C to 550°C for 1 min to 5 min.

8. An anode foil, characterized in that, The anode foil is prepared by the anode foil preparation method according to any one of claims 1 to 7.

9. The anode foil according to claim 8, characterized in that, The thickness of the alloy substrate foil is 20μm~50μm, and the thickness of the aluminum powder sintered layer on one side is 10μm~60μm.

10. An aluminum electrolytic capacitor, characterized in that, The anode foil includes the anode foil prepared by the method described in any one of claims 1 to 7, or the anode foil described in claim 8 or 9.

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