An electrolyte solution for aluminum electrolytic capacitors and its application in high-capacitance solid aluminum electrolytic capacitors.

Abstract

This invention relates to an electrolyte solution for aluminum electrolytic capacitors and its application in high-capacity solid aluminum electrolytic capacitors. The electrolyte solution of this invention is prepared by compounding PEDOT:PSS dispersion, solvent, and three additives (i.e., perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral). The additives reduce water vapor permeability, inhibit the dissociation of acidic sulfonic acid groups, and enhance the adhesion of the film foil interface. They also inhibit the interface peeling and dielectric layer thickening caused by the moisture absorption expansion and reduction dedoping of PEDOT:PSS, thereby improving the temperature and moisture resistance of aluminum electrolytic capacitors and extending their service life.

Description

Technical Field

[0001] This invention relates to the technical field of solid aluminum electrolytic capacitors, and more specifically to an electrolyte solution for aluminum electrolytic capacitors and its application in high-capacitance solid aluminum electrolytic capacitors. Background Technology

[0002] Because solid aluminum electrolytic capacitors do not contain electrolyte, they do not pose the safety hazards of leakage or explosion associated with liquid aluminum electrolytic capacitors. Furthermore, their low internal resistance makes them widely used in low-voltage applications. Currently, PEDOT:PSS is commonly used as the conductive polymer in solid aluminum electrolytic capacitors, but PEDOT:PSS has relatively low conductivity. In addition, during the production of PEDOT:PSS dispersions, core packages, and core packages with PEDOT:PSS films, contact with airborne moisture is unavoidable. This residual moisture inside the solid aluminum electrolytic capacitor is electrolyzed during charging and discharging, producing H₂O. + In the presence of O2 and a localized strong acid environment, PEDOT:PSS is reduced to remove doping and corrodes the Al2O3 dielectric layer, accompanied by volume expansion, which ultimately leads to the peeling off of the conductive film and a decrease in capacitance. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide an electrolyte solution for aluminum electrolytic capacitors and its application in high-capacitance solid aluminum electrolytic capacitors.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides an electrolyte solution for aluminum electrolytic capacitors, characterized in that it comprises the following raw materials: PEDOT:PSS dispersion, solvent and additives; wherein the mass ratio of the PEDOT:PSS dispersion, solvent and additives is 1:(2-3):(0.03-0.1); the additives are perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin and polyvinyl butyral.

[0005] The specific functions of the additives in this invention are as follows: Perfluorohexylethylmethyldimethoxysilane is a fluorine-containing organosilicon compound containing fluorine atoms and silicon-oxygen bonds in its molecule. The fluorine atoms, with their high electronegativity, can form stable carbon-fluorine bonds, endowing the compound with excellent chemical stability and weather resistance, allowing it to remain stable at high temperatures and exhibiting good temperature resistance. The presence of silicon-oxygen bonds enables the compound to form a dense protective film on the material surface, significantly reducing water vapor permeability and improving the material's water resistance, thereby reducing acid production during water electrolysis and the reduction and dedoping of PEDOT:PSS. Furthermore, this protective film provides adhesion sites for subsequent polymers, synergistically enhancing film-foil interfacial adhesion.

[0006] Perfluorosulfonic acid resin is an ionomer copolymerized from perfluorovinyl ether monomers with sulfonic acid groups and tetrafluoroethylene. Its molecular structure contains a fluorocarbon backbone and perfluorosulfonic acid groups. In the resin, the hydrophobic perfluoro backbone preferentially binds to the hydrophobic PEDOT region. The perfluorosulfonic acid and PSS compete for complexation through an ionic dipole / hydrogen bond network, which weakens the PSS's encapsulation of PEDOT, forming a more continuous nanowire network, and inhibits -SO3H dissociation, reducing apparent acidity. Furthermore, the hydrophobic nature of the resin's fluorocarbon backbone slows down the penetration of water molecules and ions, delaying their corrosion of the aluminum foil, and further strengthening the hydrophobic network of the membrane, forming a synergistic water-blocking effect with the hydrophobic ends of the fluorosilane.

[0007] Polyvinyl butyral is a product of the condensation of polyvinyl alcohol and butyraldehyde under acid catalysis. It possesses good flexibility, tensile strength, and impact strength. Its molecular structure contains long branched chains and hydroxyl groups. These hydroxyl groups can form hydrogen bonds with the sulfonic acid groups of PEDOT:PSS, enhancing the intermolecular forces of PEDOT:PSS, reducing its acidity, and simultaneously forming a dense cross-linked network. This reduces the free volume within the membrane, inhibits water vapor diffusion, improves the water resistance of the electrolyte layer, and reduces the impact of moisture on PEDOT:PSS, thereby improving the capacity and stability of the electrolyzer. Simultaneously, polyvinyl butyral exhibits excellent light resistance, heat resistance, and cold resistance, which can improve the temperature resistance of the electrolyte layer to a certain extent.

[0008] Preferably, the mass ratio of the perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin and polyvinyl butyral is 1:(0.5-1.5):(2-4).

[0009] Preferably, the solvent is at least one selected from methanol, ethylene glycol, dimethyl sulfoxide, and N-methylpyrrolidone.

[0010] More preferably, the solvent is dimethyl sulfoxide and N-methylpyrrolidone in a mass ratio of 1:(0.8-2).

[0011] Preferably, the solid content of the PEDOT:PSS dispersion is 1-3%, and the solvent is water.

[0012] In a second aspect, the present invention provides the application of the electrolyte solution for aluminum electrolytic capacitors in the first aspect in the preparation of solid electrolyte layers for aluminum electrolytic capacitors.

[0013] Thirdly, the present invention provides a high-capacitance solid aluminum electrolytic capacitor, comprising a housing and a core, wherein the core is sealed inside the housing by a rubber stopper, and the core comprises an anode foil, an electrolytic paper and a cathode foil, and the core has a solid electrolyte layer for aluminum electrolytic capacitors as described in the second aspect.

[0014] Fourthly, the present invention provides a method for preparing the high-capacitance solid aluminum electrolytic capacitor described in the third aspect, comprising the following steps: S1. Disperse the additive evenly in the solvent, add PEDOT:PSS dispersion and mix evenly to obtain the electrolyte solution for aluminum electrolytic capacitors in the first aspect. S2. The anode foil, electrolytic paper and cathode foil are wound into a core package, and the core package is immersed in an electrolyte solution of 3-4 times its weight of aluminum electrolytic capacitor for impregnation treatment. S3. Dry the impregnated core package to form a solid electrolyte layer inside the core package; S4. The dried core package is sealed inside the outer shell with a rubber stopper to obtain the high-capacitance solid aluminum electrolytic capacitor.

[0015] Preferably, in step S2, the impregnation is cyclic vacuum pressurized impregnation, specifically: first, maintain a vacuum of -0.08 to -0.09 MPa for 30-60 s, then maintain a vacuum of 0.15-0.30 MPa for 60-120 s, and repeat the above impregnation steps 1-2 times, with the temperature maintained at 25-35℃ during the impregnation process.

[0016] Preferably, in step S3, the drying step is as follows: first pre-drying at 60-80℃ for 20-30 min, then curing at 100-120℃ for 30-60 min, with a vacuum degree of -0.08~-0.09MPa during the drying process.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The electrolyte solution for aluminum electrolytic capacitors of the present invention is formulated by compounding PEDOT:PSS dispersion, solvent and three additives (i.e., perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin and polyvinyl butyral). The additives reduce water vapor permeability, inhibit the dissociation of acidic sulfonic acid groups and enhance the adhesion of the film foil interface, inhibit the interface peeling and dielectric layer thickening caused by the moisture absorption expansion and reduction dedoping of PEDOT:PSS, thereby improving the temperature and moisture resistance of aluminum electrolytic capacitors and extending the service life of aluminum electrolytic capacitors. Detailed Implementation

[0018] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0019] The source information of the raw materials used in the following examples and comparative examples is as follows: PEDOT:PSS dispersion: manufactured by Yancheng Bohong Electronic Chemical Co., Ltd., trade name PEDOT / PSS aqueous dispersion, solid content 1.7%; Perfluorohexylethylmethyldimethoxysilane: manufactured by Sichuan Shangfu Technology Co., Ltd. Perfluorosulfonic acid resin: Manufacturer: Chemours, Model: Nafion ® D2021; Polyvinyl butyral: Manufacturer is Guangdong Wengjiang Chemical Reagent Co., Ltd., model number is PA853412; Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0020] Example 1 An electrolyte solution for aluminum electrolytic capacitors comprises the following raw materials: PEDOT:PSS dispersion, solvent, and additives; wherein the mass ratio of the PEDOT:PSS dispersion, solvent, and additives is 1:2.2:0.07; the additives are perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral in a mass ratio of 1:0.6:3; and the solvent is dimethyl sulfoxide and N-methylpyrrolidone in a mass ratio of 1:1.

[0021] Example 2 An electrolyte solution for aluminum electrolytic capacitors, characterized in that it comprises the following raw materials: PEDOT:PSS dispersion, solvent, and additives; wherein the mass ratio of the PEDOT:PSS dispersion, solvent, and additives is 1:2:0.03; the additives are perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral in a mass ratio of 1:0.5:2; and the solvent is dimethyl sulfoxide and N-methylpyrrolidone in a mass ratio of 1:0.8.

[0022] Example 3 An electrolyte solution for aluminum electrolytic capacitors, characterized in that it comprises the following raw materials: PEDOT:PSS dispersion, solvent, and additives; wherein the mass ratio of the PEDOT:PSS dispersion, solvent, and additives is 1:3:0.1; the additives are perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral in a mass ratio of 1:1.5:4; and the solvent is dimethyl sulfoxide and N-methylpyrrolidone in a mass ratio of 1:2.

[0023] Example 4 The only difference between Example 4 and Example 1 is that the total mass of the additives remains the same, and the mass ratio of perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin and polyvinyl butyral is 1:3:0.6.

[0024] Example 5 The only difference between Example 5 and Example 1 is that the total mass of the additives remains the same, and the mass ratio of perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin and polyvinyl butyral is 3:0.6:1.

[0025] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the total mass of the additives remains the same, perfluorohexylethylmethyldimethoxysilane is not added, and perfluorosulfonic acid resin and polyvinyl butyral in a mass ratio of 0.6:3 are used to make up for the missing amount.

[0026] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that the total mass of the additives remains the same, perfluorosulfonic acid resin is not added, and perfluorohexylethylmethyldimethoxysilane and polyvinyl butyral in a mass ratio of 1:3 are used to make up for the missing amount.

[0027] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that the total mass of the additives remains the same, polyvinyl butyral is not added, and perfluorohexylethylmethyldimethoxysilane and perfluorosulfonic acid resin with a mass ratio of 1:0.6 are used to make up for the missing amount.

[0028] Comparative Example 4 The only difference between Comparative Example 4 and Example 1 is that no additives were added, and the missing amount was made up using a PEDOT:PSS dispersion and solvent with a mass ratio of 1:2.2.

[0029] Application Example 1-5 and Comparative Application Example 1-4 Application Examples 1-5 and Comparative Application Examples 1-4 solid aluminum electrolytic capacitors include a housing and a core package. The core package is sealed inside the housing by a rubber stopper. The core package includes an anode foil, an electrolytic paper, and a cathode foil. The core package has a solid electrolyte layer for aluminum electrolytic capacitors prepared from the electrolyte solution for aluminum electrolytic capacitors in Examples 1-5 or Comparative Examples 1-4. The method for preparing a high-capacitance solid aluminum electrolytic capacitor includes the following steps: S1. Disperse the additives evenly in the solvent, add PEDOT:PSS dispersion and mix evenly to obtain the electrolyte solution for aluminum electrolytic capacitors of Examples 1-5 or Comparative Examples 1-4. S2. The anode foil, electrolytic paper, and cathode foil are wound into a core package. The core package is then immersed in an electrolyte solution containing 3-4 times its mass of aluminum electrolytic capacitors for impregnation treatment. The impregnation is a cyclic vacuum pressurized impregnation, specifically: first, the impregnation is maintained at a vacuum of -0.085 MPa for 45 s, then at 0.20 MPa for 90 s, and the above impregnation steps are repeated twice. The temperature is maintained at 30°C during the impregnation process. S3. Dry the impregnated core package to form a solid electrolyte layer inside the core package; wherein the drying step is as follows: first pre-dry at 70°C for 25 min, then solidify at 110°C for 45 min, and the vacuum degree during the drying process is -0.085MPa. S4. The dried core package is sealed inside the outer shell with a rubber stopper to obtain the high-capacitance solid aluminum electrolytic capacitor.

[0030] Performance testing Solid aluminum electrolytic capacitors with a rated capacity of 450μF, used in Application Examples 1-5 and Comparative Examples 1-4, were selected. The initial capacitance CAP0, initial equivalent series resistance ESR0, and average capacitance retention after 20,000 cycles were tested according to GB / T6346.26-2018 "Fixed Capacitors for Electronic Equipment - Part 26: Standardized Conductive Polymer Solid Electrolyte Aluminum Fixed Capacitors". Then, the solid aluminum electrolytic capacitors in each group were aged at 200℃ and 70%RH for 1 hour. After aging, the capacitance CAP1 and equivalent series resistance ESR1 were measured again, and the capacitance decay rate and ESR increase rate were calculated using the following formulas: Average capacitance retention (%) = (C2 / C1) × 100%; where C2 is the capacitance value after 20,000 cycles, in F; and C1 is the initial capacitance value, in F. Capacity degradation rate (%) = (Cap0 - Cap1) / Cap0 × 100%; Equivalent series resistance ESR increase rate (%) = (ESR1-ESR0) / ESR0×100%; data for each group are shown in Table 1.

[0031] Table 1 Performance test results of solid aluminum electrolytic capacitors in each group Application Example 1 479.1 1.3 17.3 7.5 95.0 Application Example 2 474.7 1.7 18.5 8.3 94.6 Application Example 3 478.2 1.5 17.5 7.9 94.7 Application Example 4 463.2 2.7 20.1 11.0 90.9 Application Example 5 465.4 2.3 19.4 9.8 91.3 Comparative Application Example 1 455.8 7.0 22.0 28.4 77.1 Comparative Application Example 2 460.9 6.6 21.4 26.9 82.4 Comparative Application Example 3 454.6 7.3 23.6 29.7 74.6 Comparative Application Example 4 449.1 8.9 26.3 33.4 70.2

[0032] Combining the data from Application Example 1 and Application Examples 4-5 in Table 1, it can be seen that the performance of Application Examples 4-5 is lower than that of Example 1. This may be because the proportion of perfluorosulfonic acid resin in the electrolyte solution of Application Example 4 is relatively high. Although the conductivity is significantly improved, the proportion of polyvinyl butyral is too low, resulting in insufficient film density, many local pores, insufficient hydrophobicity and peel resistance, and more obvious capacity decay due to oxidation. The initial capacitance, initial equivalent series resistance, and retention rate of the solid aluminum electrolytic capacitor are all significantly reduced, the capacitance CAP decay rate is lower, and the equivalent series resistance ESR increase rate is higher, indicating that the high temperature and high humidity resistance is significantly reduced. In contrast, the proportion of perfluorosulfonic acid resin in the electrolyte solution of Application Example 5 is extremely low, and polyvinyl butyral is only 1 part. The structure of the solid electrolyte layer is loose, the conductivity improvement is insufficient, and the density is low. Therefore, when the mass of perfluorosulfonic acid resin and polyvinyl butyral in the electrolyte solution is not within the preferred range of 1:(0.5-1.5):(2-4), the initial performance, temperature resistance, and water resistance of the capacitor are all at a better level.

[0033] Combining the data from Application Example 1 and Comparative Application Examples 1-4 in Table 1, it can be seen that Comparative Application Example 4, without any additives, has the lowest capacitor performance among all sample groups, indicating that the addition of additives is a crucial parameter affecting capacitor performance. Comparative Application Examples 1-3, lacking one of the additives, have lower initial performance, temperature resistance, and water resistance than Application Example 1. This may be because: Comparative Application Example 1's electrolyte solution lacks perfluorohexylethylmethyldimethoxysilane, resulting in decreased film density and reduced water resistance, leading to increased moisture penetration. Furthermore, the PEDOT:PSS layer undergoes hygroscopic expansion and reduction dedoping, causing interfacial peeling and thickening of the dielectric layer, significantly reducing the average capacitance retention. Comparative Application Example 2, lacking perfluorosulfonic acid resin, failed to form a more continuous nanowire network. Excessive free acidic sulfonic acid groups within the PEDOT:PSS film etch the aluminum foil, while continuous reduction dedoping of PEDOT decreases carrier concentration, exacerbates hygroscopic expansion, increases microcracks within the film, and reduces the effective conductive area. Compared to Application Example 3, which did not contain polyvinyl butyral, the film structure was loose, the carrier transport paths were disordered, and the film had poor mechanical strength, making it prone to peeling during cycling and resulting in a significant decrease in average charge retention. The perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral in the electrolyte solution have a synergistic effect. By reducing water vapor permeability, inhibiting the dissociation of acidic sulfonic acid groups, and enhancing the interfacial adhesion of the film foil, they suppress interfacial peeling and dielectric layer thickening caused by moisture absorption expansion and reduction dedoping of PEDOT:PSS, thereby improving the temperature and moisture resistance of the aluminum electrolytic capacitor and extending its service life.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte solution for aluminum electrolytic capacitors, characterized in that, The product comprises the following raw materials: PEDOT:PSS dispersion, solvent, and additives; wherein the mass ratio of the PEDOT:PSS dispersion, solvent, and additives is 1:(2-3):(0.03-0.1); the additives are perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral; the mass ratio of the perfluorohexylethylmethyldimethoxysilane, perfluorosulfonic acid resin, and polyvinyl butyral is 1:(0.5-1.5):(2-4); and the solvent is dimethyl sulfoxide and N-methylpyrrolidone in a mass ratio of 1:(0.8-2).

2. The electrolyte solution for aluminum electrolytic capacitors as described in claim 1, characterized in that, The solid content of the PEDOT:PSS dispersion is 1-3%, and the solvent is water.

3. The application of the electrolyte solution for aluminum electrolytic capacitors as described in claim 1 or 2 in the preparation of solid electrolyte layers for aluminum electrolytic capacitors.

4. A high-capacitance solid aluminum electrolytic capacitor, comprising a casing and a core, wherein the core is sealed within the casing by a rubber stopper, and the core comprises an anode foil, electrolytic paper, and a cathode foil, characterized in that, The core package contains a solid electrolyte layer for an aluminum electrolytic capacitor as described in claim 3.

5. The method for preparing the high-capacitance solid aluminum electrolytic capacitor according to claim 4, characterized in that, Includes the following steps: S1. Disperse the additive evenly in the solvent, add PEDOT:PSS dispersion and mix evenly to obtain the electrolyte solution for aluminum electrolytic capacitors. S2. The anode foil, electrolytic paper and cathode foil are wound into a core package, and the core package is immersed in an electrolyte solution of 3-4 times its weight of aluminum electrolytic capacitor for impregnation treatment. S3. Dry the impregnated core package to form a solid electrolyte layer inside the core package; S4. The dried core package is sealed inside the outer shell with a rubber stopper to obtain the high-capacitance solid aluminum electrolytic capacitor.

6. The method for preparing a solid aluminum electrolytic capacitor as described in claim 5, characterized in that, In step S2, the impregnation is a cyclic vacuum pressurized impregnation, specifically operated as follows: first, maintain a vacuum of -0.08 to -0.09 MPa for 30-60 s, then maintain a vacuum of 0.15-0.30 MPa for 60-120 s, and repeat the above impregnation steps 1-2 times. During the impregnation process, the temperature is maintained at 25-35℃.

7. The method for preparing a solid aluminum electrolytic capacitor as described in claim 5, characterized in that, In step S3, the drying process is as follows: first, pre-dry at 60-80℃ for 20-30 min, then cure at 100-120℃ for 30-60 min, with a vacuum degree of -0.08~-0.09MPa during the drying process.