Al4 cluster, macro preparation method thereof and application of Al4 cluster in aluminum electrolytic capacitor

Abstract

The invention discloses an Al4 cluster, a macro preparation method thereof and an application of the Al4 cluster in an aluminum electrolytic capacitor. The molecular formula of the Al4 cluster is [Al4 (mu2-A) 4 (mu3-A) 2]. (B) n, wherein A is selected from residues of a C1-C40 organic acid; mu2-A represents bridging coordination formed by two Al and two-coordinated O atoms on carboxyl of A and in phenolic hydroxyl; mu3-A represents bridging coordination formed by three Al and two-coordinated O atoms on carboxyl of A and in phenolic hydroxyl; b is selected from at least one of C1-C40 protonated organic amines; and n represents the number of B. The Al4 cluster is synthesized by adopting a solvothermal method and a one-step method, the preparation flow of the synthesis process is simple to operate, the product purity is relatively high, gram-level large-scale controllable rapid synthesis is realized, and meanwhile, the Al4 cluster has excellent temperature resistance and moisture resistance, can be used as an aluminum foil surface treatment material of an aluminum electrolytic capacitor, and can be applied to the field of aluminum electrolytic capacitors. Therefore, the electrical performance of the aluminum electrolytic capacitor is improved, and the reliability of the aluminum electrolytic capacitor is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum electrolytic capacitors, and specifically to an Al4 cluster, a method for its mass preparation, and its application in aluminum electrolytic capacitors. Background Art

[0002] Aluminum is the most abundant metallic element in the earth's crust. It is inexpensive and environmentally friendly, and has shown extensive applications in fields such as industrial catalysis, electro-optics, etc. For example, due to the compatibility and stability of alumina (AlOx) with device manufacturing processes, it is often used as a dielectric layer in modern electrical industries. Among capacitors using alumina as a dielectric material, polymer solid aluminum electrolytic capacitors are a new type of electronic component with characteristics such as high conductivity, low equivalent series resistance (ESR), good temperature-frequency characteristics, and high stability. With the development of emerging information technologies such as 5G and the Internet of Things driving the development of complete machines such as telecommunications equipment, communication terminals, and intelligent terminals towards high-speed communication, high-functional communication, and miniaturization, capacitors in circuits are required to have small external dimensions and large capacitances. In the power supply lines of the above-mentioned electronic devices, low working voltage and large capacitance aluminum electrolytic capacitors are mainly used for energy storage and filtering, and their capacitance is a key parameter directly affecting the working efficiency. However, limited by the dielectric constant of alumina, there are technical bottlenecks in the preparation of small-sized and large-capacity products. In addition, the dielectric layer structure of low-voltage formation foils is also prone to cause relatively large leakage currents in capacitors.

[0003] In recent years, aluminum oxide clusters (AlOCs) prepared using aluminum as a metal source have received extensive attention due to their advantages such as light weight, non-toxicity, and stability. Using such materials as dielectric materials can obtain internal molecular information through single crystal diffraction, and utilize the advantages of precise atoms to visually study the structure-activity relationship between structure and function. Aluminum oxide clusters have solution processability and precise atomic structures, allowing the adjustment of required properties through coordination chemistry, which cannot be achieved in traditional dielectric materials. Aluminum oxide clusters have a relatively high dielectric constant and low dielectric loss, and are ideal dielectric layer materials that can be applied to aluminum electrolytic capacitors. To improve the electrical performance level of polymer solid aluminum electrolytic capacitors, achieve the mass preparation of aluminum oxide clusters, and effectively combine them with alumina to improve the dielectric layer performance of aluminum electrolytic capacitors has become an urgent problem to be solved. Based on this, the present invention designs an Al4 cluster, a method for its mass preparation, and its application in aluminum electrolytic capacitors to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for the mass preparation of Al4 clusters and their application in aluminum electrolytic capacitors to solve the above technical problems.

[0005] To achieve the above purpose, the first technical solution provided by the present invention is:

[0006] A kind of Al4 cluster, the molecular formula of the Al4 cluster is: [Al4(μ2-A)4(μ3-A)2]·(B)n;

[0007] Among them, A in μ2-A and μ3-A is the same or different, and independently selected from residues of organic acids with C1-C40. The residue of the organic acid with C1-C40 refers to the group remaining after removing the hydrogen on the carboxyl group and phenolic hydroxyl group of the organic acid;

[0008] μ2-A represents that 2 Als form bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A;

[0009] μ3-A represents that 3 Als form bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A;

[0010] B is selected from at least one of protonated organic amines with C1-C40;

[0011] n represents the number of Bs, and is selected from integers or decimals between 1 and 30.

[0012] Preferably, A is selected from at least one of residues of 2,3-dihydroxybenzoic acid and residues of substituted 2,3-dihydroxybenzoic acid.

[0013] Preferably, part or all of B is in a free state, and B exists freely outside the Al4 cluster.

[0014] Preferably, the Al4 cluster is a pure-phase light brown massive crystalline substance, the cluster core size is 1.1±0.8nm, and it has a symmetric structure.

[0015] Preferably, the Al4 cluster is a 4-core cluster and is coordinated by μ2-A and μ3-A on the periphery.

[0016] The second technical solution provided by the present invention is:

[0017] A method for the bulk preparation of Al4 clusters, comprising the following steps:

[0018] Mix aluminum salt, organic acid, pyrazole, and N,N-dimethylformamide as reaction raw materials, and react under heating conditions to prepare the Al4 cluster;

[0019] Among them, the residue of the organic acid forms μ2-A and μ3-A in the molecular formula, and the dimethylamine protonated after the decomposition of N,N-dimethylformamide forms B in the molecular formula.

[0020] Preferably, the preparation method specifically comprises the following steps:

[0021] S1. Mix an aluminum salt, an organic acid, pyrazole, and N,N-dimethylformamide, and carry out a solvothermal reaction at a constant temperature of 50°C - 180°C for 24 - 240 hours to obtain a mixture, and the molar ratio of the aluminum salt to the organic acid is 1:(0.01 - 10);

[0022] S2. Separate the mixture obtained after the reaction in step S1, and the crystalline substance obtained is the Al4 cluster.

[0023] Preferably, the aluminum salt is selected from compounds formed by the aluminum ion and an alcohol after removing the hydrogen on the alcohol hydroxyl group, and the organic acid is selected from organic acids with 1 - 40 carbon atoms.

[0024] Preferably, the following steps are further included:

[0025] S3. Wash the separated crystalline substance with N,N-dimethylformamide or an alcohol, and then air-dry at room temperature.

[0026] The third technical solution provided by the present invention is:

[0027] An application of an Al4 cluster in an aluminum electrolytic capacitor, where the Al4 cluster is used as a surface treatment solution for the aluminum foil of the aluminum electrolytic capacitor.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. The Al4 cluster of the present invention is synthesized by a one-step method using the solvothermal method. The synthesis process has a simple operation flow, a relatively high product purity, and realizes gram-scale large-scale controllable rapid synthesis. At the same time, the Al4 cluster has excellent temperature and humidity resistance, can be used as a surface treatment material for the aluminum foil of aluminum electrolytic capacitors, is between the alumina film and the conductive polymer, improves the electrical performance of the aluminum electrolytic capacitor, and enhances the reliability of the aluminum electrolytic capacitor.

[0030] 2. The preparation method of the Al4 cluster of the present invention has simple and efficient process requirements, a short reaction time, and is convenient for large-scale production; and the post-treatment process of the preparation method of the present invention is simple, and only needs to be washed and separated, and then air-dried naturally to obtain a crystalline product. At the same time, the raw materials of the preparation method of the present invention are low-toxic, inexpensive, less polluting, and meet the requirements of green environmental protection.

[0031] 3. The present invention establishes a class of Al4 clusters as surface treatment solutions for the aluminum foil of aluminum electrolytic capacitors, realizing the application of crystalline products of aluminum oxide clusters in aluminum electrolytic capacitors. Description of the Drawings

[0032] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0033] Figure 1 It is a schematic structural diagram of the Al4 cluster in Embodiment 1;

[0034] Figure 2 It is a crystal photograph of the Al4 cluster in Embodiment 1;

[0035] Figure 3 It is an X-ray powder diffraction pattern of the Al4 cluster in Embodiment 1;

[0036] Figure 4 It is an infrared spectrum diagram of the crystalline substance of the Al4 cluster in Embodiment 1. Detailed implementation manners

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] The first technical solution provided by the present invention is specifically as follows:

[0039] An Al4 cluster, the molecular formula of the Al4 cluster is: [Al4(μ2-A)4(μ3-A)2]·(B)n;

[0040] Wherein, A in μ2-A and μ3-A is the same or different, and independently selected from the residues of organic acids with C1-C40, and the residue of the organic acid with C1-C40 refers to the group remaining after removing the hydrogen on the carboxyl group and the phenolic hydroxyl group of the organic acid;

[0041] μ 2- A represents that 2 Als form a bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A;

[0042] μ3-A represents that 3 Als form a bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A;

[0043] B is selected from at least one of protonated organic amines with C1-C40;

[0044] n represents the number of Bs, and is selected from an integer or a decimal between 1 and 30.

[0045] According to an embodiment of the present invention, in the aluminum electrolytic capacitor material with the Al4 cluster as the dielectric layer, μ2-A, μ3-A, B, and Al form the aluminum electrolytic capacitor material with the Al4 cluster as the dielectric layer.

[0046] According to an embodiment of the present invention, A is selected from at least one of the residues of 2,3-dihydroxybenzoic acid and the residues of substituted 2,3-dihydroxybenzoic acid. Preferably, A is selected from the residues of 2,3-dihydroxybenzoic acid.

[0047] According to an embodiment of the present invention, the "substituent" is a conventional substituent in the art, for example, selected from a hydroxyl group, a C1-6 alkyl group, a C1-6 alkoxy group, an amino group, a nitro group, a carboxyl group, a phenyl group, or a halogen atom. Preferably, it is a hydroxyl group, a methyl group, an amino group, or a halogen atom, and more preferably a halogen atom.

[0048] Exemplarily, A is selected from at least one of the residues of 2,3-dihydroxybenzoic acid, the residues of 2,3,4-trihydroxybenzoic acid, the residues of 4-methyl-2,3-dihydroxybenzoic acid, the residues of 2,3-dihydroxy-4-methoxybenzoic acid, the residues of 4-amino-2,3-dihydroxybenzoic acid, the residues of 4-nitro-2,3-dihydroxybenzoic acid, the residues of 2,3-dihydroxy-1,4-benzenedicarboxylic acid, the residues of 4-phenyl-2,3-dihydroxybenzoic acid, and the residues of 4-chloro-2,3-dihydroxybenzoic acid. Preferably, it is the residue of 2,3-dihydroxybenzoic acid.

[0049] According to an embodiment of the present invention, in the aluminum electrolytic capacitor material with the Al4 cluster as the dielectric layer, part or all of B exists in a free state. Preferably, B exists freely outside the Al4 cluster.

[0050] According to an embodiment of the present invention, n is selected from integers from 1 to 30; more preferably selected from integers from 1 to 15; further preferably selected from integers from 1 to 5; and even more preferably selected from 1 or 4.

[0051] According to an embodiment of the present invention, the Al4 cluster is a pure-phase light brown massive crystalline substance.

[0052] According to an embodiment of the present invention, the Al4 cluster is an inorganic-organic hybrid compound.

[0053] According to an embodiment of the present invention, the cluster core size of the Al4 cluster is 1.1 ± 0.8 nm, for example, 1.5 nm or 1.0 nm.

[0054] According to an embodiment of the present invention, the Al4 cluster has a symmetric structure.

[0055] According to an embodiment of the present invention, the Al4 cluster is a 4-core cluster, and its periphery is coordinated by μ2-A and μ3-A.

[0056] The second technical solution provided by the present invention is specifically as follows:

[0057] A method for the macroscale preparation of an Al4 cluster, comprising the following steps:

[0058] Mix aluminum salt, organic acid, pyrazole, and N,N-dimethylformamide as reaction raw materials, and carry out a reaction under heating conditions to prepare the Al4 cluster;

[0059] Wherein, the residue of the organic acid forms μ2-A and μ3-A in the molecular formula, and the dimethylamine protonated after the decomposition of N,N-dimethylformamide forms B in the molecular formula.

[0060] According to an embodiment of the present invention, the macroscale preparation method specifically comprises the following steps:

[0061] 1) Mix the aluminum salt, organic acid, pyrazole, and N,N-dimethylformamide, and carry out a solvothermal reaction to obtain a mixture;

[0062] 2) Separate the mixture obtained after the reaction in step 1), and the crystalline substance obtained is the Al4 cluster.

[0063] According to an embodiment of the present invention, the aluminum salt is selected from compounds formed by the removal of hydrogen from the alcohol hydroxyl group of aluminum ions and alcohols.

[0064] According to an embodiment of the present invention, the aluminum salt is selected from at least one of aluminum ethoxide, aluminum n-propoxide, aluminum isopropoxide, aluminum tert-butoxide, aluminum sec-butoxide, and aluminum tert-butoxide, and preferably aluminum isopropoxide.

[0065] According to an embodiment of the present invention, the organic acid is selected from organic acids with C1-C40, and exemplarily, the organic acid is selected from at least one of 2,3-dihydroxybenzoic acid, 2,3,4-trihydroxybenzoic acid, 4-methyl-2,3-dihydroxybenzoic acid, 2,3-dihydroxy-4-methoxybenzoic acid, 4-amino-2,3-dihydroxybenzoic acid, 4-nitro-2,3-dihydroxybenzoic acid, 2,3-dihydroxy-1,4-phthalic acid, 4-phenyl-2,3-dihydroxybenzoic acid, and 4-chloro-2,3-dihydroxybenzoic acid, and preferably 2,3-dihydroxybenzoic acid.

[0066] According to an embodiment of the present invention, the molar ratio of the aluminum salt to the organic acid is 1:(0.01-10), for example 1:(0.1-5), and also 1:(0.2-3).

[0067] According to an embodiment of the present invention, the temperature of the heating reaction (solvothermal reaction) is 50 to 180 °C; preferably 120 to 180 °C, such as 120 to 160 °C, for example 160 °C. If the reaction temperature is too low, the reaction time will be longer and the crystal size will be smaller.

[0068] According to an embodiment of the present invention, the time of the heating reaction (solvothermal reaction) is 24 to 240 hours; preferably 36 to 180 hours, such as 72 hours, 96 hours.

[0069] Exemplarily, the heating reaction can be carried out at 80 °C for 120 hours or 144 hours, or at 100 °C for 72 hours or 96 hours.

[0070] Exemplarily, the heating reaction is carried out at 160 °C for 72 hours or 96 hours.

[0071] According to an embodiment of the present invention, step 1) specifically includes: mixing the aluminum salt, organic acid, pyrazole and N,N-dimethylformamide, stirring, reacting at a constant temperature, and then cooling to room temperature.

[0072] Preferably, the constant temperature reaction means standing reaction at a constant temperature. For example, the aluminum salt, organic acid, pyrazole and N,N-dimethylformamide are placed in an oven for heating reaction.

[0073] According to an embodiment of the present invention, in step 2), the separated solid is washed and dried.

[0074] Preferably, the separated crystalline substance is washed with N,N-dimethylformamide or alcohol and air-dried at room temperature. The alcohol can be methanol, ethanol, or n-butanol.

[0075] The third technical solution provided by the present invention is specifically as follows:

[0076] An application of an Al4 cluster in an aluminum electrolytic capacitor, wherein the Al4 cluster is used as a surface treatment solution for the aluminum foil of the aluminum electrolytic capacitor.

[0077] The present invention also provides a surface treatment solution for aluminum foil, and the surface treatment solution for aluminum foil includes the above-mentioned Al4 cluster as a surface treatment solution for the aluminum foil of the aluminum electrolytic capacitor.

[0078] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

[0079] The single crystal structure analysis of the present invention uses a Supernova single crystal diffractometer from Rigaku, Japan.

[0080] The radiation source for the X-ray powder diffraction pattern is Cu-Kα radiation.

[0081] Example 1:

[0082] The molecular formula of the Al cluster in this example is: [Al4(μ2-A)4(μ3-A)2]·(B)n;

[0083] where A is the residue of 2,3-dihydroxybenzoic acid; B is protonated dimethylamine, and n = 1 or 4;

[0084] It should be noted that in this example, there are two types of residues of A. μ2-A represents that 2 Als form bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A; μ3-A represents that 3 Als form bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A. The residue refers to the group remaining after removing all the hydrogens on the carboxyl group and phenolic hydroxyl group of the organic acid;

[0085] The molecular formula of the Al4 cluster in this example is [Al4(C7H3O4)4(C6H4O2)2]·(HC2H7N)4 (Al4C48N4O20H52). The crystal system of the Al4 cluster is monoclinic, the space group is P21 / n, and the unit cell parameters a are b is c is α is 90o, β is 106.12o, γ is 90o, V is And the relative molecular mass Mr of the Al4 cluster is 1112.87.

[0086] Refer to Figures 1-4 As shown, Example 2 is:

[0087] In Example 1, the basic preparation method of the Al4 cluster (Al4C 48 N4O 20 H 52 ) is as follows:

[0088] Put aluminum isopropoxide (1 mmol), 2,3-dihydroxybenzoic acid (2.5 mmol), pyrazole (30 mmol), and N,N-dimethylformamide (5 mL) into a 20 mL Teflon reactor, mix evenly at room temperature, keep it at a constant temperature of 160 °C in an oven for 3 days, take it out, naturally cool it to room temperature, separate the solid phase, rinse it with N,N-dimethylformamide, and dry it in an oven at 80 °C to obtain the light brown blocky crystalline target product Al4 cluster (Al4C 48 N4O 20 H 52 ), and the yield is about 75% (based on the mass of aluminum isopropoxide);

[0089] From Figure 1It can be seen that the crystal molecular formula of the Al4 cluster has 4 aluminum atoms, 4 2,3-dihydroxybenzoic acid ligands, and 2 catechols, and there are also 4 protonated dimethylamine ions on its periphery. Therefore, it can be expressed as [Al4(C7H3O4)4(C6H4O2)2]·(HC2H7N)4.

[0090] As can be seen from Figure 2 it, the Al4 cluster has a high purity and good crystallinity.

[0091] The Al4 cluster was taken for X-ray powder diffraction and infrared spectroscopy respectively:

[0092] As can be seen from Figure 3 it, the X-ray powder diffraction pattern of the Al4 cluster is consistent with the theoretical simulation ( Figure 3 in it, the "simulation diagram" is the X-ray powder diffraction pattern simulated according to the crystal structure; the "experimental diagram" is the X-ray powder diffraction pattern tested on the X-ray diffractometer;), the Al4 cluster has a high purity (95%) and is stable in air; its crystal form parameters are as follows: the crystal system of the Al4 cluster is monoclinic, the space group is P21 / n, and the unit cell parameter a is b is c is α is 90o, β is 106.12o, γ is 90o, and V is

[0093] As can be seen from Figure 4 it, the Al4 cluster has obvious vibration peaks of organic carboxylic acids.

[0094] Through single crystal X-ray analysis, the crystal parameters of the Al4 cluster are shown in Table 1:

[0095] Table 1

[0096]

[0097] Example 3, The macro-preparation method of the Al4 cluster (Al4C 48 N4O 20 H 52 ) is as follows:

[0098] On the premise of the synthesis method in Example 2, the products can be successfully obtained after expanding 10 times, 50 times, and 100 times.

[0099] Taking the 50-fold synthesis method as an example, aluminum isopropoxide (50 mmol), 2,3-dihydroxybenzoic acid (75 mmol), pyrazole (1500 mmol), and N,N-dimethylformamide (250 mmol) were placed in a 500 mL Teflon reaction kettle, mixed evenly at room temperature, kept at a constant temperature of 160 °C in an oven for 3 days, taken out, naturally cooled to room temperature, the solid phase was separated, rinsed with N,N-dimethylformamide, and dried in an oven at 80 °C to obtain the light brown blocky crystalline target product Al4 cluster (Al4C 48 N4O 20 H 52 ). The yield was about 70% (based on the mass of aluminum isopropoxide).

[0100] From Figure 3 it can be seen that the macroscale preparation of Al4 clusters has a high yield and purity.

[0101] It can be seen that the preparation method of the present invention can obtain Al4 clusters through macroscale preparation.

[0102] Example 4, the application of Al4 clusters in aluminum electrolytic capacitors is as follows:

[0103] (1) First, 1.2 g of Al4 was added to 100 mL of deionized water, magnetically stirred at room temperature for 15 min to obtain an Al4 solution. Then, the etched foil was vertically immersed in the Al4 solution, slowly vertically lifted after 5 min, taken out, and dried in a blast dryer at 135 °C for 5 min to obtain the Al4-treated etched foil;

[0104] (2) After cooling for 30 min, the etched foil was subjected to a primary chemical polymerization treatment and a secondary electrochemical polymerization treatment in sequence, and then coated with graphite, silver paste, laminated and bonded, epoxy resin encapsulated, and aged.

[0105] Example 5, the application of Al4 clusters in aluminum electrolytic capacitors is as follows:

[0106] (1) First, 1.2 g of Al4 was added to 100 mL of deionized water, magnetically stirred at room temperature for 15 min to obtain an Al4 solution. Then, the etched foil was vertically immersed in the Al4 solution, slowly vertically lifted after 5 min, taken out, and dried in a blast dryer at 160 °C for 5 min to obtain the Al4-treated etched foil;

[0107] (2) After cooling for 30 min, the etched foil was subjected to a primary chemical polymerization treatment and a secondary electrochemical polymerization treatment in sequence, and then coated with graphite, silver paste, laminated and bonded, epoxy resin encapsulated, and aged.

[0108] Example 6, the application of Al4 clusters in aluminum electrolytic capacitors is as follows:

[0109] (1) First, add 2.4 g of Al4 to 100 mL of deionized water, stir magnetically at room temperature for 15 min to obtain an Al4 solution. Then, vertically immerse the etched foil into the Al4 solution, slowly lift it vertically after 5 min, and after taking it out, dry it in a blast dryer at 135 °C for 5 min to obtain the Al4-treated etched foil;

[0110] (2) After cooling for 30 min, subject the etched foil to a primary chemical polymerization treatment and a secondary electrochemical polymerization treatment in sequence, and then perform graphite coating, silver paste coating, lamination bonding, epoxy resin encapsulation, and aging.

[0111] Example 7. The application of Al4 clusters in aluminum electrolytic capacitors is as follows:

[0112] (1) First, add 2.4 g of Al4 to 100 mL of deionized water, stir magnetically at room temperature for 15 min to obtain an Al4 solution. Then, vertically immerse the etched foil into the Al4 solution, slowly lift it vertically after 5 min, and after taking it out, dry it in a blast dryer at 160 °C for 5 min to obtain the Al4-treated etched foil;

[0113] (2) After cooling for 30 min, subject the etched foil to a primary chemical polymerization treatment and a secondary electrochemical polymerization treatment in sequence, and then perform graphite coating, silver paste coating, lamination bonding, epoxy resin encapsulation, and aging.

[0114] Comparative Example 1. The method for conventionally preparing an aluminum electrolytic capacitor is as follows:

[0115] Subject the etched foil to a primary chemical polymerization treatment and a secondary electrochemical polymerization treatment in sequence, and then perform graphite coating, silver paste coating, lamination bonding, epoxy resin encapsulation, and aging.

[0116] Test the capacitance (C), leakage current (IL), and tangent of loss angle (tanδ) of the capacitors prepared from four groups of examples (Examples 4 to 7) and one group of comparative examples under high humidity conditions in accordance with GB / T 6346.25-2018. The test conditions are an ambient temperature of 60 ± 2 °C, an ambient relative humidity of 92 ± 3% RH, and a duration of 498 h. The test results are shown in the following table, where the values in parentheses are the percentage changes in performance.

[0117]

[0118] From the test results of four groups of examples and one group of comparative examples, it can be seen that under the same test conditions, the capacitance of the capacitors prepared in the four groups of examples is greater than that of the capacitors prepared in the comparative example, and their dielectric losses and leakage currents are smaller than the corresponding capacitance and leakage current of the capacitors prepared in the comparative example. Moreover, the change rates of the capacitance, dielectric loss, and leakage current of the capacitors prepared in the four groups of examples are all smaller than those of the capacitance, dielectric loss, and leakage current of the capacitors prepared in the comparative example. This shows that by first sequentially performing chemical pretreatment with Al4 solution, primary chemical polymerization treatment, and secondary electrochemical polymerization treatment on the formed foil, and then performing graphite coating, silver paste coating, lamination bonding, epoxy resin encapsulation, and aging, a polymer chip multi-layer aluminum electrolytic capacitor with low dielectric loss, small leakage current, and stable capacitance can be obtained when used for a long time in a humid environment.

[0119] It should be noted that in the present invention, a "cluster" is a relatively stable microscopic or submicroscopic aggregate composed of several to thousands of atoms, molecules, or ions through physical or chemical bonding forces, and its physical and chemical properties vary with the number of atoms contained therein. If the cluster is electrically neutral, it is a cluster molecule. If the cluster carries a positive charge or a negative charge, it is a cluster ion.

[0120] The above describes the exemplary embodiments of the present invention. However, the protection scope of this application is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An Al4 cluster, characterized in that: The molecular formula of the Al4 cluster is: [Al4(μ2-A)4(μ3-A)2]·(B)n; wherein A in μ2-A and μ3-A is the same or different and is independently selected from residues of organic acids having 1 to 40 carbon atoms, and the residue of the organic acid having 1 to 40 carbon atoms refers to the group remaining after removing the hydrogen atoms on the carboxyl group and phenolic hydroxyl group of the organic acid; μ2-A represents that two Al atoms form a bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A; μ3-A represents that three Al atoms form a bridging coordination with the bidentate O atoms on the carboxyl group and phenolic hydroxyl group of A; B is selected from at least one of protonated organic amines having 1 to 40 carbon atoms; n represents the number of B and is selected from an integer or decimal between 1 and 30.

2. The Al4 cluster according to claim 1, characterized in that: A is selected from at least one of the residues of 2,3-dihydroxybenzoic acid and the residues of substituted 2,3-dihydroxybenzoic acid.

3. The Al4 cluster according to claim 1, characterized in that: Part or all of B is in a free state, and B exists freely outside the Al4 cluster.

4. The Al4 cluster according to claim 1, characterized in that: The Al4 cluster is a pure-phase light brown massive crystalline substance, the cluster core size is 1.1±0.8 nm, and it has a symmetric structure.

5. The Al4 cluster according to claim 1, characterized in that: The Al4 cluster is a 4-core cluster and is coordinated by μ2 - A and μ3 - A on the periphery.

6. A method for the large-scale preparation of the Al4 cluster according to any one of claims 1-5, characterized in that: It includes the following steps: Mixing an aluminum salt, an organic acid, pyrazole, and N,N-dimethylformamide as reaction raw materials, and reacting under heating conditions to prepare the Al4 cluster; wherein the residues of the organic acid form μ2-A and μ3-A in the molecular formula, and the dimethylamine formed by the decomposition of N,N-dimethylformamide is protonated to form B in the molecular formula.

7. The method for the bulk preparation of Al4 clusters according to claim 6, wherein: The preparation method specifically includes the following steps: S1. Mix an aluminum salt, an organic acid, pyrazole, and N,N-dimethylformamide, and carry out a solvothermal reaction at a constant temperature of 50°C - 180°C for 24 - 240 hours to obtain a mixture, and the molar ratio of the aluminum salt to the organic acid is 1:(0.01 - 10); S2. Separating the mixture obtained after the reaction in step S1, and the obtained crystalline substance is the Al4 cluster.

8. The method for bulk preparation of Al4 clusters according to claim 6 or 7, characterized in that: The aluminum salt is selected from compounds formed by an aluminum ion and an alcohol after removing the hydrogen atom on the alcohol hydroxyl group, and the organic acid is selected from organic acids having 1 to 40 carbon atoms.

9. The method for bulk preparation of Al4 clusters according to claim 7, wherein: It further includes the following steps: S3. Cleaning the separated crystalline substance with N,N-dimethylformamide or alcohol, and then drying it at room temperature.

10. Use of the Al4 cluster according to any one of claims 1-5 in an aluminum electrolytic capacitor, characterized in that: The Al4 cluster is used as a surface treatment solution for the aluminum foil of an aluminum electrolytic capacitor.

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