Method for preparing aluminum electrolytic capacitor

Abstract

The present invention relates to the technical field of capacitors. Disclosed is a method for preparing an aluminum electrolytic capacitor, at least comprising the following steps: winding an anode foil, a double-layer electrolyte paper, and a cathode foil to form a core assembly; performing impregnation treatment on the core assembly; and drying the impregnated core assembly and placing the core assembly into a case so as to form an aluminum electrolytic capacitor, wherein the double-layer electrolyte paper comprises a microporous layer and a substrate layer, the microporous layer is arranged close to the anode foil, conductive graphite is adsorbed onto the microporous layer, the raw material of the microporous layer is a bamboo pulp fiber, and the raw materials of the substrate layer are the bamboo pulp fiber and a wood pulp fiber. In the aluminum electrolytic capacitor prepared in the present application, the electrolytic paper comprises the microporous layer and the substrate layer, and the conductive graphite is adsorbed onto the microporous layer, thereby effectively improving the resistance to high-voltage alternating-current surge and cycle performance of the aluminum electrolytic capacitor.

Description

A method for preparing an aluminum electrolytic capacitor Technical Field

[0001] This invention relates to the field of capacitor technology, and more specifically to a method for preparing an aluminum electrolytic capacitor. Background Technology

[0002] The rapid development of the global electronics and information industries has brought new and enormous markets to aluminum electrolytic capacitors, while also posing new challenges. The requirements for miniaturization, stability, high performance, and low cost of aluminum electrolytic capacitors are becoming increasingly urgent, especially high capacitance and miniaturization, which significantly influence the miniaturization and integration of electronic circuits. Therefore, developing aluminum electrolytic capacitors that are small in size, have large capacitance, long service life, and are inexpensive has become a current research hotspot, while also generating huge business opportunities and a broad market. Technical issues

[0003] Electrolytic paper is a core material in the production of aluminum electrolytic capacitors. It acts as an insulator between the anode and cathode foils, preventing short circuits between them. It also absorbs the working electrolyte, serving as a cathode carrier. Furthermore, it possesses excellent high-temperature resistance, corrosion resistance, and mechanical strength. The performance and quality of the electrolytic paper significantly impact the performance of the aluminum electrolytic capacitor. Currently, aluminum electrolytic capacitors are developing towards lower losses, lower impedance, and miniaturization. Electrolytic paper plays a crucial role in increasing the operating voltage and extending the lifespan of aluminum electrolytic capacitors. Therefore, promoting the reduction of losses and lower impedance, and improving the electrical strength of electrolytic paper, has become an important direction for its research and development. Although the production of electrolytic paper for aluminum electrolytic capacitors is ongoing, the types of materials used are still limited. Therefore, discovering new materials or methods for preparing electrolytic paper to improve the performance of aluminum electrolytic capacitors is a pressing need. Technical solutions

[0004] The purpose of this invention is to provide a method for preparing an aluminum electrolytic capacitor, thereby solving the following technical problems:

[0005] Existing aluminum electrolytic capacitors have problems with their electrolytic paper, including poor impact resistance, high equivalent series resistance, and low reliability.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A method for manufacturing an aluminum electrolytic capacitor includes at least the following steps:

[0008] The anode foil, double-layer electrolytic paper, and cathode foil are wound into a core package;

[0009] The core package is impregnated;

[0010] The impregnated core package is dried and then placed into a shell to form an aluminum electrolytic capacitor;

[0011] The double-layer electrolytic paper includes a microporous layer and a substrate layer, with the microporous layer disposed close to the anode foil. Conductive graphite is adsorbed on the microporous layer. The raw material of the microporous layer is bamboo pulp fiber, and the raw material of the substrate layer is bamboo pulp fiber and wood pulp fiber.

[0012] As a further aspect of the present invention: the thickness of the microporous layer is 30-50 μm, and the density is 0.55-0.70 g / cm. 3 .

[0013] As a further aspect of the present invention: the thickness of the substrate layer is 40-60 μm, and the density is 0.65-0.80 g / cm. 3 .

[0014] As a further aspect of the present invention, the method for preparing the double-layer electrolytic paper includes the following steps:

[0015] After the bamboo pulp and wood pulp are thoroughly mixed, they are transferred to a refiner for refining, and then a paper machine is used to prepare the substrate layer.

[0016] After the bamboo pulp is fully broken down, it is transferred to a pulper for pulping and then a microporous layer is prepared using a paper machine.

[0017] Conductive graphite is dispersed in a dispersant and then sprayed or soaked in the microporous layer.

[0018] The substrate layer and the microporous layer containing adsorbed conductive graphite are pressed together and then dried to obtain a double-layer electrolytic paper.

[0019] As a further aspect of the present invention: the beating degree of the microporous layer is 90-95°SR, and the beating degree of the substrate layer is 85-90°SR.

[0020] As a further aspect of the present invention: the weight concentration of the conductive graphite is 0.01-0.1 g / ml, and the dispersant is an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate).

[0021] As a further aspect of the present invention, the impregnation treatment includes at least the following steps:

[0022] The core pack is impregnated with a dispersion to obtain a core pack impregnated with the dispersion;

[0023] The core package containing the impregnating dispersion is impregnated with a forming liquid to obtain the formed core package;

[0024] The formed core package is impregnated with electrolyte to obtain an electrolyte-impregnated core package.

[0025] As a further aspect of the present invention: the electrolyte includes at least one of boric acid, phosphoric acid, and adipic acid; the dispersion is an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate); and the formation solution is an aqueous solution of adipic acid amine. Beneficial effects

[0026] The beneficial effects of this invention are:

[0027] This application utilizes a double-layer electrolytic paper structure made from bamboo pulp fiber and wood pulp fiber, with conductive graphite adsorbed on the microporous layer near the anode foil. The resulting aluminum electrolytic capacitor possesses advantages such as high resistance to high-voltage AC surges, low equivalent series resistance, and high reliability. It can significantly improve the electrical performance of aluminum electrolytic capacitors, extend their service life, and has wide applications in home appliances, computers, servers, communication equipment, mobile phones, fast chargers, optoelectronic products, new energy, high-speed railways, aerospace, automotive industry, military industry, and other fields.

[0028] This application utilizes bamboo pulp fiber to form a microporous layer and a substrate layer formed by bamboo pulp fiber and wood pulp fiber. Wood pulp fiber has advantages such as high density, voltage resistance, and resistance to aluminum foil burrs, while bamboo pulp fiber has advantages such as high water absorption, excellent electrical properties, excellent temperature characteristics, wide operating temperature range, and moderate price. Furthermore, during the preparation process, as the grinding speed increases, the fiber beating degree increases, and the corresponding density also gradually increases. By creating a density difference between the microporous layer and the substrate layer, the greater the density difference between the two layers, the higher the electrical strength of the diaphragm, the higher the liquid absorption height, and the lower the ESR value per unit thickness. The combined use of these two materials ensures sufficient electrolyte on the surfaces of the cathode and anode aluminum foils, meeting the lower ESR requirements. This results in an aluminum electrolytic capacitor with strong resistance to high-voltage AC impact, reduces production costs, and to some extent addresses the problem of wood shortage.

[0029] In this application, the substrate layer is formed by a mixture of bamboo pulp fiber and wood pulp fiber. During the preparation process, as the degree of beating increases, the fiber length and fiber width in the pulp continuously decrease, while the content of fine fibers continuously increases. The fine fiber content and crimp index in bamboo pulp are greater than those in wood pulp. The bamboo pulp fibers disperse in the electrolytic paper to form a rich, fine, and uniform porous structure. This type of electrolytic paper can absorb sufficient electrolyte in the capacitor, resulting in a capacitor with low impedance and low loss. The presence of fine fibers is similar to adding reinforcing material to the electrolytic paper. It not only increases the uniformity of the electrolytic paper, making the applied field on the surface more uniform, but also fills the numerous pores between the electrolytic paper particles, reducing the pore size. This reduces the migration speed of charge carriers inside the electrolytic paper in the electric field, increases the charge injection amount, makes it difficult for charge to accumulate inside the electrolytic paper, reduces the damage of electrons to the cellulose chains inside the electrolytic paper, increases the breakdown strength of the electrolytic paper, and improves the ability of the obtained aluminum electrolytic capacitor to withstand high-voltage AC impact.

[0030] This application also utilizes a dispersant containing conductive graphite to first spray or soak the microporous layer. Wood pulp fibers have good water absorption and form a richer, more uniform pore structure, allowing the microporous layer to fully adsorb conductive graphite particles. After forming a poly(3,4-ethylenedioxythiophene) film within the core, the poly(3,4-ethylenedioxythiophene) coats or covers the conductive graphite powder. During charge-discharge cycles, the conductive graphite powder supports the expansion and contraction of the poly(3,4-ethylenedioxythiophene) film, making it less likely for the poly(3,4-ethylenedioxythiophene) to detach from the anode foil surface. Furthermore, the more uniformly the conductive graphite is dispersed within the core, the better the supporting effect of the conductive graphite powder on the poly(3,4-ethylenedioxythiophene). The poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) dispersion used ensures uniform dispersion of the poly(3,4-ethylenedioxythiophene). Conductive graphite powder not only provides support for poly(3,4-ethylenedioxythiophene), but also does not affect the structure and conductivity of poly(3,4-ethylenedioxythiophene). Furthermore, the addition of conductive graphite powder reduces the internal resistance of aluminum electrolytic capacitors and improves their cycle performance. Embodiments of the present invention

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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. Example 1

[0032] The preparation method of double-layer electrolytic paper includes the following steps:

[0033] Weigh 25 g of wood pulp fiber (octane dry weight) and 15 g of bamboo pulp fiber (octane dry weight), add pure water and soak for 24 h. After thorough fiber disintegration using a fiber disintegrator, prepare the pulp to a 10% concentration and transfer it to a refiner for refining. Set the refiner pressure to 3.33 N / mm and measure the freeness at 85°SR. Collect the refined pulp, balance the moisture content, and then disintegrate it using a fiber disintegrator for 8000 rpm. Prepare several sheets with a basis weight of 10 g / m² using a Kaiser automatic paper machine. 2 The substrate layer of the electrolytic paper was stored in a constant temperature and humidity room for 24 hours for later use.

[0034] Weigh 30 g of bamboo pulp (octane-dry weight) fiber, add pure water and soak for 24 h. After thorough fiber disintegration using a fiber disintegrator, prepare the pulp to a 10% concentration and transfer it to a refiner for refining. Set the refining pressure to 3.33 N / mm and measure the freeness to 90°SR. Collect the refined pulp, balance the moisture content, and then disintegrate it using a fiber disintegrator for 8000 rpm. Prepare several sheets with a basis weight of 10 g / m² using a Kaiser automatic paper machine. 2 The microporous layer of the electrolytic paper for a single aluminum electrolytic capacitor is dried at 50°C for 1 hour for later use.

[0035] Conductive graphite powder was dispersed in an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), and ultrasonically vibrated for more than 5 hours. The weight concentration of conductive graphite in the dispersant was 0.05 g / ml. The microporous layer was soaked for 1 hour and stored in a constant temperature and humidity room for 24 hours for later use.

[0036] The microporous layer of the above-mentioned adsorbed conductive graphite and the above-mentioned substrate layer are stacked, pressed and compounded by a flat press, and then dried by a rotary dryer to obtain double-layer electrolytic paper.

[0037] The preparation method of aluminum electrolytic capacitors includes the following steps:

[0038] The anode foil, the aforementioned double-layer electrolytic paper, and the cathode foil are cut, and the anode foil, cathode foil, and double-layer electrolytic paper are wound into a core package using a core package winding machine. The electrolytic paper is located between the anode aluminum foil and the cathode aluminum foil, the microporous layer is set close to the anode foil, and the length of the electrolytic paper is longer than the length of the overlapping part of the anode and cathode aluminum foil, thus obtaining the core package.

[0039] The core package was placed in a sealed container and impregnated under pressure with a dispersion solution, which was an aqueous dispersion of the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate). The pressure of the impregnation was 8 kg and the impregnation time was 10 min. The core package was then dried at 180°C for 90 min to obtain the core package impregnated with the dispersion solution.

[0040] The core package containing the above-mentioned impregnation dispersion was immersed in an adipic acid amine formation solution with a mass concentration of 5%, and voltage was applied to the positive and negative electrodes of the core package simultaneously for formation repair treatment for 20 min. The voltage used was 12-16V and the current density was 0.01-0.03mA / pcs. After the formation repair treatment, the core package was dried at a temperature of 125℃ for 40 min to obtain the formed core package.

[0041] The core package after the above formation is immersed in an electrolyte containing triethylamine, phthalic acid and adipic acid, and voltage is applied to the positive and negative electrodes of the core package at the same time. Vacuum pressure impregnation treatment is performed for 15 minutes, and then the core package is dried at 125°C for 50 minutes to obtain the core package impregnated with electrolyte.

[0042] The electrolyte-impregnated core is assembled with an aluminum shell and a stopper to obtain a semi-finished capacitor. The semi-finished capacitor is then charged and aged by applying voltages of 0.5, 1, and 1.2 times the rated voltage in stages. The aging temperature is 125°C and the aging time is 120 minutes to obtain an aluminum electrolytic capacitor. Example 2

[0043] In the preparation steps of double-layer electrolytic paper, 20 g of wood pulp and 20 g of bamboo pulp (ocean dry weight) fiber are weighed to prepare the substrate layer;

[0044] The remaining components and preparation methods are completely consistent with those in Example 1. Example 3

[0045] In the preparation steps of double-layer electrolytic paper, 30 g of wood pulp and 10 g of bamboo pulp (ocean dry weight) fiber are weighed to prepare the substrate layer;

[0046] The remaining components and preparation methods are completely consistent with those in Example 1. Example 4

[0047] In the preparation steps of double-layer electrolytic paper, the freeness of the pulp used to prepare the substrate layer is 90°SR, and the freeness of the pulp used to prepare the microporous layer is 95°SR.

[0048] The remaining components and preparation methods are completely consistent with those in Example 1. Example 5

[0049] In the preparation steps of double-layer electrolytic paper, the freeness of the pulp used to prepare the substrate layer is 85°SR, and the freeness of the pulp used to prepare the microporous layer is 95°SR.

[0050] The remaining components and preparation methods are completely consistent with those in Example 1.

[0051] Comparative Example 1

[0052] The preparation method of electrolytic paper includes the following steps:

[0053] Weigh 70g of wood pulp (octane-dry weight) fibers, soak in pure water for 24 hours, and thoroughly decompose using a fiber decomposer. Prepare the pulp to a 10% concentration and transfer it to a refiner. Set the refiner pressure to 3.33 N / mm and measure the freeness at 85°SR. Collect the refined pulp, balance the moisture content, and decompose it using a fiber decomposer for 8000 rpm. Prepare several sheets with a basis weight of 10 g / m² using a Kaiser automatic paper machine. 2 The substrate layer of electrolytic paper is pressed and laminated by a flat press and then dried by a rotary dryer to obtain electrolytic paper.

[0054] The preparation steps of the aluminum electrolytic capacitor are exactly the same as those in Example 1.

[0055] Comparative Example 2

[0056] The preparation method of electrolytic paper includes the following steps:

[0057] Weigh 70g of bamboo pulp (octane-dry weight) fiber, add pure water and soak for 24 hours. After thorough fiber disintegration using a fiber disintegrator, prepare the pulp to a 10% concentration and transfer it to a refiner for refining. Set the refining pressure to 3.33 N / mm and measure the freeness to 85°SR. Collect the refined pulp, balance the moisture content, and then disintegrate it using a fiber disintegrator for 8000 rpm. Use a Kaiser automatic paper machine to prepare several sheets with a basis weight of 10 g / m². 2 The substrate layer of electrolytic paper is pressed and laminated by a flat press and then dried by a rotary dryer to obtain electrolytic paper.

[0058] The preparation steps of the aluminum electrolytic capacitor are exactly the same as those in Example 1.

[0059] Comparative Example 3

[0060] In the preparation steps of double-layer electrolytic paper, the pulp used to prepare the substrate layer is 40 g of wood pulp (ocean dry weight) fiber;

[0061] The remaining components and preparation methods are completely consistent with those in Example 1.

[0062] Comparative Example 4

[0063] In the preparation steps of double-layer electrolytic paper, the step of adsorbing conductive graphite powder is omitted;

[0064] The remaining components and preparation methods are completely consistent with those in Example 1.

[0065] Performance testing

[0066] (1) Performance testing of double-layer electrolytic paper

[0067] Liquid absorption height was tested according to national standard GB / T461.1-2002, electrical breakdown strength was tested according to national standard GB / T20628.2-2006, tensile strength was tested according to GB / T12914-2008, and breakdown voltage was tested according to national standard GB / T12656-1990. The test results are shown in Table 1.

[0068] Table 1: Statistical Table of Electrolytic Paper Performance Test Data from Examples 1-5 and Comparative Examples 1-4

[0069]

[0070] As shown in Table 1, the bilayer electrolytic paper with adsorbed conductive graphite prepared in this application has excellent water absorption, tensile strength, and electrical breakdown strength, and the breakdown voltage is above 440V. In contrast, the electrolytic paper prepared by using single wood pulp or bamboo pulp in Comparative Examples 1 and 2 has better liquid absorption height, but poorer electrical breakdown strength, tensile strength, and breakdown voltage. In Comparative Example 3, only wood pulp is used to prepare the substrate layer, and the resulting electrolytic paper has poor liquid absorption height and tensile strength. In Comparative Example 4, no conductive graphite powder is adsorbed into the microporous layer, and the resulting electrolytic paper has poor electrical breakdown strength and breakdown voltage.

[0071] (2) Performance testing of aluminum electrolytic capacitors

[0072] The capacitance (CAP) was measured at a frequency of 120Hz. The internal resistance and the capacitance after 5000 surge tests were measured at a rated voltage of 6.3V. The test results are shown in Table 2.

[0073] Table 2: Statistical Table of Performance Test Data of Aluminum Electrolytic Capacitors in Examples 1-5 and Comparative Examples 1-4

[0074]

[0075] As shown in Table 2, the aluminum electrolytic capacitors prepared in this application have good cycle performance and low internal resistance, with capacitance retention exceeding 96% after 5000 cycles. Comparative Examples 1 and 2, which use single-layer electrolytic paper without adsorbing conductive graphite, result in aluminum electrolytic capacitors with high internal resistance and poor cycle performance. In Comparative Examples 3 and 4, which use only wood pulp fiber to prepare the substrate layer and have a microporous layer that does not adsorb conductive graphite powder, the cycle performance and internal resistance of the resulting aluminum electrolytic capacitors are inferior to those obtained in the examples.

[0076] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for preparing an aluminum electrolytic capacitor, characterized in that, At least the following steps are included: The anode foil, double-layer electrolytic paper, and cathode foil are wound into a core package; The core package is impregnated; The impregnated core package is dried and then placed into a shell to form an aluminum electrolytic capacitor; The double-layer electrolytic paper includes a microporous layer and a substrate layer, with the microporous layer disposed close to the anode foil. Conductive graphite is adsorbed on the microporous layer. The raw material of the microporous layer is bamboo pulp fiber, and the raw material of the substrate layer is bamboo pulp fiber and wood pulp fiber. The preparation method of the double-layer electrolytic paper includes the following steps: After the bamboo pulp and wood pulp are thoroughly mixed, they are transferred to a refiner for refining, and then a paper machine is used to prepare the substrate layer. After the bamboo pulp is fully broken down, it is transferred to a pulper for pulping and then a microporous layer is prepared using a paper machine. Conductive graphite is dispersed in a dispersant and then sprayed or soaked in the microporous layer. The substrate layer and the microporous layer containing adsorbed conductive graphite are pressed together and then dried to obtain a double-layer electrolytic paper.

2. The method for preparing an aluminum electrolytic capacitor according to claim 1, characterized in that, The microporous layer has a thickness of 30-50 μm and a density of 0.55-0.70 g / cm³. 3 .

3. The method for preparing an aluminum electrolytic capacitor according to claim 1, characterized in that, The substrate layer has a thickness of 40-60 μm and a density of 0.65-0.80 g / cm. 3 .

4. The method for preparing an aluminum electrolytic capacitor according to claim 1, characterized in that, The beating degree of the microporous layer is 90-95°SR, and the beating degree of the substrate layer is 85-90°SR.

5. The method for preparing an aluminum electrolytic capacitor according to claim 1, characterized in that, The conductive graphite has a weight concentration of 0.01-0.1 g / ml, and the dispersant is an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate).

6. The method for preparing an aluminum electrolytic capacitor according to claim 1, characterized in that, The impregnation treatment includes at least the following steps: The core pack is impregnated with a dispersion to obtain a core pack impregnated with the dispersion; The core package containing the impregnating dispersion is impregnated with a forming liquid to obtain the formed core package; The formed core package is impregnated with electrolyte to obtain an electrolyte-impregnated core package.

7. The method for preparing an aluminum electrolytic capacitor according to claim 6, characterized in that, The electrolyte includes at least one of boric acid, phosphoric acid, and adipic acid; the dispersion is an aqueous dispersion of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate); and the formation solution is an aqueous solution of adipic acid amine.

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