Vacuum impregnation process for an aluminum electrolytic capacitor core package

Abstract

The application discloses a kind of aluminum electrolytic capacitor core package vacuum impregnation preparation processes, it is related to aluminum electrolytic capacitor manufacturing technical field.The process includes: to anode aluminum foil cleaning, vacuum wetting and forming interface modification layer;Anode aluminum foil, cathode aluminum foil and electrolytic paper are wound into capacitor element;Under vacuum environment, introduce PEDOT:PSS dispersion liquid, and using anode convergence, cylindrical network opposite electrode and cathode current-limiting ground electrode configuration to apply pulse direct current electric field, so that conductive polymer colloidal grain enters anode foil etching channel and deposits on interface modification layer;Subsequently, water / organic solvent gradient replacement, isopropanol / acetone transition replacement, supercritical CO2 drying and multiple concentration decreasing re-impregnation;Finally, liquid electrolyte secondary impregnation, assembly sealing and aging are carried out.The process can improve the impregnation sufficiency of conductive polymer in the deep channel of high-voltage anode foil, the interface anchoring stability and the skeleton retention ability after drying.

Description

Technical Field

[0001] This invention relates to the field of aluminum electrolytic capacitor manufacturing technology, specifically to a vacuum impregnation process for preparing aluminum electrolytic capacitor cores. Background Technology

[0002] Aluminum electrolytic capacitors are widely used in power supply filtering, inverter buses, industrial control, and automotive electronics due to their high capacitance per unit volume, moderate cost, and mature technology. As new energy vehicles, high-voltage energy storage converters, photovoltaic inverters, and high-power power modules develop towards higher voltage, higher ripple current, and longer lifespan, traditional liquid aluminum electrolytic capacitors are facing increasingly stringent requirements in terms of equivalent series resistance, leakage current stability, and high-temperature lifespan. To balance low impedance and self-healing capabilities, hybrid aluminum electrolytic capacitors, where conductive polymers and liquid electrolytes form the conductive path, have become an important development direction. Among these, PEDOT-type conductive polymers have attracted attention due to their good conductivity and high film-forming stability.

[0003] Existing solid-liquid hybrid aluminum electrolytic capacitors typically employ static vacuum impregnation, pressure impregnation, or multiple impregnation methods to introduce PEDOT:PSS dispersion into the wound element, followed by solvent removal through hot air drying or vacuum drying. However, after etching and anodizing, high-voltage anode aluminum foil forms numerous elongated channels with complex distributions of pore size, neck, and depth. When PEDOT:PSS particles in the dispersion enter deeper channels, they are easily affected by residual gas, capillary resistance, interfacial charge repulsion, and particle agglomeration. This causes the conductive polymer to remain at the pore opening or in shallow areas, making it difficult to form a continuous, stable, and depth-controllable deposition layer on the pore walls of the anodized film.

[0004] Meanwhile, maintaining the structure of aqueous PEDOT:PSS dispersions presents challenges during the drying process. Conventional hot air drying or rapid desolventizing methods can lead to capillary shrinkage caused by liquid evaporation within the pores, resulting in collapse, cracking, or localized desorption of the deposited conductive polymer framework. This negatively impacts the capacitor's equivalent series resistance, leakage current, and voltage withstand consistency. On the other hand, while adding wetting agents can reduce surface tension, it is generally difficult to alter the interfacial adsorption state between the anodic oxide film and PEDOT:PSS particles. Blindly increasing the applied electric field strength can cause water electrolysis, bubble blockage, oxidative degradation of the conductive polymer, or localized damage to the dielectric layer. Therefore, improving the penetration ability, interfacial anchoring ability, and post-drying structure retention of PEDOT within the deep pores of high-voltage anodic foil without compromising the integrity of the anodic oxide film remains a key challenge in the vacuum impregnation preparation of aluminum electrolytic capacitor cores. Summary of the Invention

[0005] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a vacuum impregnation process for aluminum electrolytic capacitor cores, which solves the problems of existing PEDOT:PSS static vacuum impregnation which is difficult to penetrate deep etching channels of high-voltage anode aluminum foil, insufficient anchoring of the interface between conductive polymer and oxide film pore walls, easy collapse of polymer skeleton due to conventional hot air or vacuum drying, and easy side reactions and dielectric layer damage caused by increasing electric field strength.

[0006] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A vacuum impregnation process for preparing aluminum electrolytic capacitor cores includes anode foil interface modification, winding into elements, electric field-assisted vacuum impregnation, solvent gradient replacement, isopropanol / acetone transition replacement, supercritical CO2 drying, multiple concentration-decreasing re-impregnation, secondary impregnation with liquid electrolyte, and assembly, sealing, and aging steps.

[0007] Preferably, the anode foil interface modification step includes cleaning the etched and anodized anode aluminum foil with deionized water and vacuum wetting it with an isopropanol / water mixture, and preferably forming an interface modification layer by polydopamine deposition, so that the pore walls of the anodized film have a more stable interfacial adsorption effect on PEDOT:PSS particles; without changing the aforementioned electric field-assisted impregnation and supercritical CO2 drying main process chain, aminopropylsilane grafting or cross-linked polyvinyl alcohol treatment can also be used as optional alternatives.

[0008] Preferably, in the electric field-assisted vacuum impregnation step, the anode lead of the capacitor element is connected to the positive electrode busbar, the cylindrical mesh counter electrode in the vacuum impregnation tank is connected to the negative electrode, and the cathode lead is grounded or connected to a reference potential through a current-limiting resistor. PEDOT:PSS dispersion is introduced under vacuum degassing and a pulsed DC electric field is applied, so that PEDOT:PSS particles enter the etching channels of the anode aluminum foil under the combined action of electric field driving and interface anchoring.

[0009] Preferably, the supercritical CO2 drying step is carried out after water / ethanol gradient replacement and isopropanol / acetone transition replacement. By extracting the organic solvent in the pores under supercritical conditions and controlling the rate of depressurization, the collapse damage to the PEDOT skeleton caused by capillary contraction at the liquid-gas interface is reduced.

[0010] Preferably, the multiple concentration-decreasing re-immersions employ at least three immersions with a PEDOT:PSS dispersion, and the solid content of the dispersion used in each subsequent immersion is lower than that used in the previous immersion, thereby forming a PEDOT deposition structure that decreases from the hole wall to the hole center within the anode aluminum foil channel, and reserving transport space for the secondary immersion of the liquid electrolyte.

[0011] (III) Beneficial Effects This invention provides a vacuum impregnation process for preparing aluminum electrolytic capacitor cores, which has the following advantages: The vacuum impregnation process for aluminum electrolytic capacitor cores improves the wetting and entry of PEDOT:PSS dispersion into etched channels by forming an interface modification layer on the pore wall of the anode aluminum foil oxide film, enhances the adsorption and deposition stability of conductive polymers at the pore wall, and reduces backflow, desorption, and shallow accumulation during the impregnation process.

[0012] The vacuum impregnation process for aluminum electrolytic capacitor cores employs pulsed DC electric field-assisted vacuum impregnation, enabling PEDOT:PSS particles to gain the driving force to directionally enter deep channels after vacuum degassing. By controlling the electric field strength, pulse mode, and current density, the risks of water electrolysis gas generation, local overheating, and dielectric layer damage are reduced.

[0013] The vacuum impregnation process for aluminum electrolytic capacitor cores employs solvent gradient replacement and supercritical CO2 drying to avoid the collapse and damage to the PEDOT skeleton caused by capillary shrinkage at the liquid-gas interface during conventional hot air drying, thus maintaining good three-dimensional connectivity of the conductive polymer within the pores.

[0014] The vacuum impregnation process for aluminum electrolytic capacitor cores improves the deposition sufficiency, pore distribution uniformity, and long-term structural stability of PEDOT through the synergistic combination of interface modification, electric field-assisted impregnation, supercritical CO2 drying, concentration-decreasing re-impregnation, and secondary impregnation with liquid electrolyte. This is beneficial for improving the core's withstand voltage, capacitance consistency, leakage current stability, low impedance performance, and high-temperature reliability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the vacuum impregnation process for preparing the aluminum electrolytic capacitor core of the present invention; Figure 2 This is a schematic diagram of the structure of the electric field-assisted vacuum impregnation device of the present invention; Figure 3 This is a schematic diagram of the interface modification layer and PEDOT gradient deposition structure within the pores of the anode aluminum foil of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: Preparation of 200 Φ16×25mm / 400V·68μF solid-liquid hybrid aluminum electrolytic capacitor core packages.

[0018] (1) Pretreatment of the anode foil interface. A 400V high-capacitance anode aluminum foil with a thickness of 110μm and a specific capacitance of 0.65μF / cm² was taken after etching and anodizing. The anode aluminum foil was ultrasonically cleaned in deionized water with a resistivity of 18.2MΩ·cm at a temperature of 40.0℃, an ultrasonic frequency of 40kHz, a power density of 0.70W / cm², and a treatment time of 6.5min. After ultrasonic cleaning, the anode aluminum foil was transferred to an isopropanol / water mixture for vacuum impregnation. The volume ratio of isopropanol / water was 1:1, the temperature of the mixture was 70.0℃, the vacuum degree was 5.0kPa, and the impregnation time was 15.0min.

[0019] Subsequently, polydopamine interfacial layer deposition was performed. A Tris-HCl buffer solution was prepared with a concentration of 10.0 mmol / L and a pH of 8.50 ± 0.05; dopamine hydrochloride was added to this buffer solution to achieve a concentration of 2.00 g / L. The vacuum-wetted anode aluminum foil was immersed in this reaction solution and reacted at 25.0 ± 0.5 °C for 6.0 h, with dissolved oxygen concentration maintained at 7.5 ± 0.5 mg / L by aeration. After the reaction, the anode aluminum foil was transferred to 60.0 °C deionized water and rinsed three times for 5.0 min each time. The anode aluminum foil was then dried in a vacuum oven at a vacuum of 2.0 kPa and a temperature of 80.0 °C for 2.0 h. Sampling tests showed that the average thickness of the interface layer on the surface of the anode aluminum foil was 3.02 nm. The Zeta potential test was conducted in a KNO3 aqueous solution at 25℃, pH 2.5 and KNO3 concentration of 1 mmol / L. The test object was a sample of the anode aluminum foil surface after interface modification. The Zeta potential of the anode aluminum foil surface was measured to be +20.5 mV.

[0020] (2) Cutting and winding. The interface-modified anode aluminum foil was cut into foil strips with a width of 14.5 mm, and the burrs on the cutting edges were controlled to be less than 3 μm. The anode foil strip, together with a cathode aluminum foil with a thickness of 50 μm and a width of 15.0 mm, and Manila hemp / wood pulp mixed electrolytic paper, were wound together to form cylindrical elements. The electrolytic paper had a basis weight of 32 g / m² and a thickness of 65 μm. The winding tension was controlled at 7.0 ± 0.2 N, and the resulting element had a diameter of 16.0 mm and a height of 25.0 mm. In this embodiment, 200 elements were prepared.

[0021] (3) Preparation of PEDOT:PSS dispersion. A PEDOT:PSS dispersion was prepared to a final solid content of 1.50 wt%; dimethyl sulfoxide was added to a final volume of 5.0 vol%, and ethylene glycol was added to a final volume of 5.0 vol%. The pH was adjusted to 2.50 ± 0.05 using 0.1 mol / L hydrochloric acid. The dispersion was filtered sequentially through a 0.45 μm filter membrane and a 0.22 μm filter membrane. After filtration, the median particle size d of the PEDOT:PSS colloidal particles was determined by dynamic light scattering. 50 The wavelength is 56.3 nm, the polydispersity index is 0.18, and the zeta potential is -41.8 mV. Before use, the dispersion should be stirred at 50 rpm for 30.0 min in a water bath at 35.0 °C.

[0022] (4) Electric field-assisted vacuum impregnation. 200 elements were suspended on a stainless steel hanger inside a 50L vacuum impregnation tank. The elements were arranged in a 10×20 array with a spacing of 12mm between adjacent elements. The anode leads were uniformly connected to the top copper busbar. A stainless steel cylindrical mesh was installed inside the impregnation tank as a counter electrode, with a distance of 1.5cm between the counter electrode and the element surface. The counter electrode was connected to the negative terminal of a pulsed DC power supply, and the element anode leads were connected to the positive terminal of the pulsed DC power supply. The cathode leads were grounded through a 100kΩ current-limiting resistor or connected to a reference potential. After closing the impregnation tank, the tank was evacuated to 1000Pa, and the temperature inside the tank was raised to 50.0℃ through a jacketed hot water circulation system. This vacuum level and temperature were maintained for 15.0min to remove residual gas inside the elements.

[0023] The PEDOT:PSS dispersion was pressurized with nitrogen and transported from the storage tank to the bottom of the impregnation tank at a pressure of 0.05 MPa. The dispersion temperature was maintained at 50.0°C, and the dispersion level was 50 mm above the top of the elements. A pulsed DC electric field was applied to the elements with a voltage of 30.0 V, corresponding to an electric field strength of 20.0 V / cm; the pulse frequency was 5.0 Hz, and the duty cycle was 50%. The electric field was applied for 30.0 min, maintaining a vacuum of 1000 Pa, a temperature of 50.0°C, and a current density of 0.21 mA / cm². In this embodiment, the current density was calculated based on the total projected area of ​​the end faces of 200 elements. The projected area of ​​the end face of a single element is approximately 2.01 cm², and the total projected area is approximately 402 cm², corresponding to a steady-state total current of approximately 84.4 mA. After the electric field effect ends, the power supply is cut off, and the mixture is allowed to stand for 10.0 min at a vacuum of 1000 Pa and a temperature of 50.0 °C. Then, pure nitrogen gas is introduced at a rate of 0.10 MPa / min to restore the impregnation tank to atmospheric pressure. The element is allowed to stand below the liquid surface for another 5.0 min before the dispersion is discharged and the element is removed.

[0024] (5) Water / ethanol gradient replacement, isopropanol / acetone transition replacement, and first supercritical CO2 drying. The wet spores after the first PEDOT:PSS impregnation were immediately transferred to a water / anhydrous ethanol gradient replacement system. The replacement sequence was water / anhydrous ethanol volume ratios of 75:25, 50:50, 25:75, and 0:100, with each replacement stage lasting 15.0 min at a temperature of 35.0 °C, all under nitrogen protection. After anhydrous ethanol replacement, the spores were transferred to a mixed solvent of isopropanol / acetone at a volume ratio of 80:20 for transition replacement at 35.0 °C for 15.0 min. After replacement, a sample was taken and the residual moisture content of the spores was found to be 165 ppm.

[0025] Two hundred elements, after transition replacement, were placed in a 50L supercritical CO2 reactor, with the elements suspended and dispersed within the reactor, spaced 15mm apart. The reactor was purged with nitrogen three times and then sealed. A liquid CO2 high-pressure pump was started, increasing the reactor pressure to 12.0MPa at a rate of 0.50MPa / min, while simultaneously raising the reactor temperature to 50.0℃. Isothermal and isobaric supercritical extraction was performed at 50.0℃ and 12.0MPa, with a continuous single-pass CO2 flow rate of 250g / min and an extraction time of 85.0min. Extraction was terminated when the organic solvent concentration dropped to less than 50ppm, as monitored online at the exhaust end. After extraction, the reactor temperature was maintained at 50.0℃, and the pressure was uniformly reduced to atmospheric pressure at a rate of 1.50±0.10MPa / h. After depressurization, dry nitrogen was purged at a flow rate of 0.5L / min for 30.0min, and the elements were then removed. The initial PEDOT deposition was measured at 14.5 mg per animal.

[0026] (6) Second and Third Impregnation. The anode foils that have completed the first impregnation and drying are returned to the vacuum impregnation tank, and the above-mentioned electric field-assisted vacuum impregnation, water / ethanol gradient replacement, isopropanol / acetone transition replacement, and supercritical CO2 drying steps are repeated. In the second impregnation, the PEDOT:PSS dispersion liquid solid content is adjusted to 1.00wt%, while the other process parameters remain unchanged, and the PEDOT deposition amount in the second impregnation is 9.8mg / anode. After the second drying, the above impregnation and drying steps are repeated again. In the third impregnation, the PEDOT:PSS dispersion liquid solid content is adjusted to 0.50wt%, while the other process parameters remain unchanged, and the PEDOT deposition amount in the third impregnation is 4.7mg / anode. After three impregnations and drying, the cumulative PEDOT deposition amount is 29.0mg / anode. ToF-SIMS depth profiling of the anode foil shows that the sulfur intensity ratio from the pore wall to the pore center in PEDOT is 3.1:1.0.

[0027] (7) Secondary impregnation with liquid electrolyte. The PEDOT deposited elements were transferred to a second vacuum impregnation tank and immersed in a γ-butyrolactone-based liquid electrolyte. The electrolyte consisted of 65.0 wt% γ-butyrolactone, 25.0 wt% ethylene glycol, 9.5 wt% dimethylimidazoline azelaic acid salt, and 0.5 wt% water, with a conductivity of 4.0 mS / cm at 25°C. The secondary impregnation with liquid electrolyte employed a vacuum-pressure composite impregnation process, with a vacuum degree of 5.0 kPa, a pressure of 0.30 MPa, an impregnation temperature of 80.0°C, and an impregnation time of 30.0 min. After impregnation, the element weight increased by 0.085 g / element.

[0028] (8) Assembly, sealing, and aging. All impregnated capacitors are installed into an SS316 aluminized shell with dimensions of Φ16.5mm × H32mm. A phenolic / butyl rubber plug is placed on the end face, with a sealing pressure of 0.80MPa. Mechanical edge sealing is then performed, followed by the installation of a PVC sleeve. The assembled capacitor is placed in an aging oven at 105.0℃, with a DC voltage of 480V applied and a current limit of 5mA per unit, for 4.0 hours.

[0029] (9) Finished Product Testing. Capacity and loss tests were conducted on 200 finished products at 120Hz, ESR tests at 100kHz, and leakage current tests at 400V rated voltage. The test results were as follows: average capacity 66.8μF, standard deviation 0.92μF; average ESR at 100kHz 24.5mΩ, standard deviation 1.8mΩ; average leakage current at 400V 1.85μA, maximum leakage current 3.1μA; average flashover voltage 512V, minimum 488V, maximum 535V; average tanδ at 120Hz 0.038, standard deviation 0.005.

[0030] Example 2: Alternative Solution for APTES Interface Layer. The difference between this example and Example 1 is that the interface layer on the anode aluminum foil surface is treated with APTES silanization; the remaining steps are the same as in Example 1. Specifically, the anode aluminum foil, after ultrasonic cleaning and isopropanol / water vacuum impregnation, is immersed in a 1.00 vol% γ-aminopropyltriethoxysilane anhydrous ethanol solution, and 0.05 vol% glacial acetic acid is added to catalyze hydrolysis; the reaction temperature is 60.0℃, and the reaction time is 1.5 h. After the reaction, it is dried at 105℃ for 30.0 min to allow the silane layer and the alumina dielectric layer to condense and fix. Subsequently, the steps of Example 1 are followed: cutting, winding, electric field-assisted vacuum impregnation, supercritical CO2 drying, secondary impregnation with liquid electrolyte, assembly sealing, and aging.

[0031] Example 3: PVA Interface Layer Alternative. This example differs from Example 1 in that the interface layer on the anode aluminum foil surface is treated with PVA hydroxylation; the remaining steps are the same as in Example 1. Specifically, the anode aluminum foil, after ultrasonic cleaning and vacuum wetting with isopropanol / water, is immersed in a 1.5 wt% polyvinyl alcohol aqueous solution with a polyvinyl alcohol degree of 99 mol%, a treatment temperature of 80.0℃, and a treatment time of 2.0 h; subsequently, it is cross-linked and cured using 0.05 wt% glutaraldehyde. After cross-linking, the anode aluminum foil is washed and dried, and then a solid-liquid hybrid aluminum electrolytic capacitor is prepared according to the subsequent steps of Example 1.

[0032] Other implementation methods. In different specifications or capacity designs, the thickness of the anode aluminum foil interface layer can be from 1.5 nm to 12 nm, preferably from 2 nm to 6 nm; the zeta potential of the modified anode aluminum foil in a KNO3 aqueous solution at 25°C, pH 2.5, and KNO3 concentration of 1 mmol / L to 10 mmol / L can be from +5 mV to +30 mV, preferably from +15 mV to +25 mV. The solid content of the PEDOT:PSS dispersion can be from 0.5 wt% to 3.5 wt%, the median particle size d50 can be from 20 nm to 150 nm, and the polydispersity index can be less than 0.5. During the electric field-assisted vacuum impregnation process, the vacuum degree of the impregnation tank can be from 100 Pa to 5000 Pa, and the temperature can be from 40 °C to 60 °C; the electric field strength can be from 2 V / cm to 100 V / cm, preferably from 10 V / cm to 35 V / cm; the current density is calculated based on the sum of the projected end faces of all capacitor elements in the same batch, and is controlled to be less than 2 mA / cm², preferably less than 0.5 mA / cm². Water / organic solvent gradient replacement can include multi-stage water / ethanol replacement and isopropanol / acetone transition replacement. During the supercritical CO2 drying process, the reaction temperature can be from 32 °C to 80 °C, and the pressure can be from 8 MPa to 25 MPa; the extraction endpoint is defined as an organic solvent content at the exhaust end being less than 50 ppm or an extraction time of 70 min to 100 min; the depressurization rate can be from 0.3 MPa / h to 3 MPa / h. The liquid electrolyte can be γ-butyrolactone-based electrolyte, ethylene glycol-based electrolyte, or a mixture thereof; the secondary impregnation of the liquid electrolyte can be vacuum impregnation, pressure impregnation, or a vacuum-pressure composite impregnation.

[0033] Experimental Example: Preparation and Comparative Testing of High-Voltage PEDOT Solid-Liquid Hybrid Aluminum Electrolytic Capacitors This experimental example illustrates the effect of the preparation process of this invention on the performance of aluminum electrolytic capacitors. Unless otherwise stated, the examples and comparative examples all used capacitors with nominal specifications of Φ16×25mm, 400V·68μF, and 200 samples were prepared for each group; the anode foil, cathode foil, electrolytic paper, shell, seal, liquid electrolyte and aging conditions were kept consistent, and only process variables such as interface modification, electric field-assisted impregnation, supercritical CO2 drying and re-impregnation gradient were changed; the leakage current DCL was read after applying the rated voltage of each group for 5 minutes as listed in Table 2.

[0034]

[0035]

[0036]

[0037]

[0038] The test results and microscopic sampling inspections show that a continuous PDA interface layer of approximately 3.02 nm can be observed in Example 1, the N / Al ratio on the XPS surface is significantly higher than that of the unmodified sample, and the PDA characteristic peaks of FTIR-ATR are clear. In Comparative Example 5, local pitting corrosion can be observed after the electric field exceeds the limit. Example 1 shows better performance than Comparative Example 1 in terms of flashover voltage, rated voltage pass rate, ESR, leakage current, PEDOT deposition amount, impregnation rate, BET specific surface area, and long-term capacity retention. Compared with Comparative Example 1, which removed interface modification, electric field assistance, supercritical CO2 drying, and re-impregnation gradient, the PEDOT deposition amount in Example 1 increased from 8.5±1.7 mg / unit to 28.96±0.84 mg / unit, and the BET specific surface area increased from 7.4±1.1 m² / g to 31.4±1.6 m² / g, indicating that the complete process can improve the sufficient deposition of PEDOT in the etched channels and the retention of the skeleton after drying.

[0039] In Comparative Example 2, after removing the PDA interface modification layer, the Zeta potential did not undergo positive regulation, the steady-state current density and bubble density increased during the electric field impregnation process, and the PEDOT deposition amount, sulfur gradient ratio, and electrical properties were all lower than in Example 1. These results indicate that the interface modification layer not only improves the wetting state but also affects the adsorption stability between PEDOT:PSS particles and the Al2O3 pore walls.

[0040] In Comparative Example 3, without the PDA interface modification layer, electric field-assisted impregnation was eliminated. PEDOT mainly entered the pores through diffusion and capillary action, and the cumulative deposition amount and sulfur gradient ratio were significantly lower than in Example 1. This result indicates that electric field-assisted impregnation can improve the ability of PEDOT:PSS particles to enter deep pores and deposit along the pore walls.

[0041] In Comparative Example 4, replacing the PDA interface modification layer with PEG-400 wetting agent reduced the contact angle, but the Zeta potential was not positively regulated, and PEG-400 residue was detected in the finished product. Although its short-term electrical performance was better than some comparative examples, its long-term capacity retention and accelerated lifetime were still lower than those of Example 1. These results indicate that simply reducing surface tension is not equivalent to forming a stable interface modification layer.

[0042] Comparative Example 5, under an electric field strength of 120 V / cm, showed a significant increase in current density, an increase in bubbles, insufficient PEDOT deposition, and localized pitting of the dielectric layer. This resulted in a drop in flashover voltage to 268.0 ± 42.3 V, an increase in the average DCL value to 62.5 μA, and a batch defect rate to 41.0%. These results indicate that the electric field strength needs to be controlled within an appropriate range, in conjunction with upper limits on current density and grounding of the cathode limiting current, to avoid adverse effects of side reactions on conductive polymer deposition and dielectric layer integrity.

[0043] In summary, under the same sample specifications and testing conditions, interface modification, electric field-assisted vacuum impregnation, supercritical CO2 drying, and three concentration-decreasing re-impregnations collectively improved the pore entry, interface anchoring, drying and shaping, and density gradient formation effects of PEDOT, thereby enhancing the electrical performance and long-term reliability of aluminum electrolytic capacitors.

[0044] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A vacuum impregnation process for preparing aluminum electrolytic capacitor cores, characterized in that, Includes the following steps: The anodic aluminum foil that has been etched and anodized is subjected to surface cleaning and vacuum wetting treatment, and an interface modification layer is formed on the pore wall of the oxide film of the anodic aluminum foil. The zeta potential of the anodic aluminum foil after the interface modification layer is formed is +5mV to +30mV when tested in a KNO3 aqueous solution at 25°C, pH 2.5 and KNO3 concentration of 1mmol / L to 10mmol / L. The anode aluminum foil after the interface modification layer is formed is wound together with the cathode aluminum foil and electrolytic paper to form a capacitor element; Prepare a PEDOT:PSS dispersion, place the capacitor element in a vacuum impregnation tank for pre-degassing, and then introduce the PEDOT:PSS dispersion to immerse the capacitor element in the PEDOT:PSS dispersion. With the capacitor elements immersed in the PEDOT:PSS dispersion, the anode lead of the capacitor element is connected to the positive busbar, the cylindrical mesh counter electrode in the vacuum impregnation tank is connected to the negative electrode, and the cathode lead of the capacitor element is grounded or connected to a reference potential through a current-limiting resistor. Subsequently, a pulsed DC electric field is applied to the anode aluminum foil through the anode lead, causing the PEDOT:PSS particles to enter the etched channels of the anode aluminum foil in a vacuum environment and deposit on the interface modification layer. The electric field strength of the pulsed DC electric field is 2V / cm to 100V / cm, and the current density is calculated based on the sum of the end-face projected areas of all capacitor elements in the same batch and is less than 2mA / cm². The wet spores impregnated with PEDOT:PSS were subjected to a water / organic solvent gradient displacement, and a transition displacement was performed with a mixed solvent of isopropanol / acetone before supercritical CO2 drying. Then, supercritical CO2 drying was carried out at a temperature of 32℃ to 80℃ and a pressure of 8MPa to 25MPa, and the pressure was depressurized at a rate of 0.3MPa / h to 3MPa / h. Following the decreasing solid content of the PEDOT:PSS dispersion, the dried element is subjected to at least two more processes of PEDOT:PSS dispersion impregnation, gradient replacement, isopropanol / acetone transition replacement, and supercritical CO2 drying, so that PEDOT forms a deposition structure in the etched channels of the anode aluminum foil that decreases from the hole wall to the hole center. The PEDOT deposited elements are subjected to secondary impregnation with liquid electrolyte to obtain aluminum electrolytic capacitor cores.

2. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 1, characterized in that: The thickness of the interface modification layer is 1.5 nm to 12 nm, and the interface modification layer is a polydopamine interface layer.

3. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 3, characterized in that: Before forming the interface modification layer, the anode aluminum foil is ultrasonically cleaned in deionized water and then vacuum-wetted in an isopropanol / water mixture. When the interface modification layer is a polydopamine interface layer, the vacuum-wetted anode aluminum foil is reacted in a reaction solution containing dopamine hydrochloride and Tris-HCl buffer. The pH of the reaction solution is 8.0 to 9.0, the reaction temperature is 20°C to 40°C, and the reaction time is 2h to 24h. After the reaction, the polydopamine interface layer is obtained by washing with water and vacuum drying.

4. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 3, characterized in that: The PEDOT:PSS dispersion has a solid content of 0.5wt% to 3.5wt%, a median particle size of 20nm to 150nm, a polydispersity index of less than 0.5, a pH of 1.8 to 3.5, and contains at least one co-solvent selected from dimethyl sulfoxide and ethylene glycol.

5. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 4, characterized in that: During the electric field-assisted impregnation process, the vacuum degree inside the vacuum impregnation tank is 100Pa to 5000Pa, and the temperature is 40℃ to 60℃; the cylindrical mesh electrode is a stainless steel cylindrical mesh, the distance between the cylindrical mesh electrode and the surface of the capacitor element is 1cm to 2cm, and the current-limiting resistor is 10kΩ to 1MΩ.

6. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 5, characterized in that: The electric field strength of the pulsed DC electric field is 10V / cm to 35V / cm, the pulse frequency is 1Hz to 20Hz, the duty cycle is 20% to 80%, the electric field application time is 10min to 60min, and after the electric field is applied, the vacuum impregnation tank is left to stand under vacuum, and then inert gas is introduced to restore the vacuum impregnation tank to normal pressure.

7. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 6, characterized in that: The water / organic solvent gradient replacement includes multiple stages of replacement with water / anhydrous ethanol volume ratios of 75:25, 50:50, 25:75, and 0:100, with each stage lasting 5 to 30 minutes. After the anhydrous ethanol replacement and before supercritical CO2 drying, a transitional replacement is performed using an isopropanol / acetone mixed solvent, wherein the volume ratio of isopropanol to acetone in the isopropanol / acetone mixed solvent is 60:40 to 90:

10.

8. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 7, characterized in that: The supercritical CO2 drying process includes: loading the elements after gradient displacement and isopropanol / acetone transition displacement into a supercritical CO2 reactor, increasing the pressure to supercritical pressure at a rate of 0.1 MPa / min to 1.0 MPa / min, and heating to supercritical temperature; extracting by introducing CO2 under isothermal and isobaric conditions for 70 min to 100 min, or extracting until the organic solvent content at the exhaust end is lower than 50 ppm; maintaining the reactor temperature constant and depressurizing at a controlled rate to atmospheric pressure after extraction.

9. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 8, characterized in that: The PEDOT:PSS dispersion impregnation, gradient displacement, and supercritical CO2 drying were performed three times. The solid content of the PEDOT:PSS dispersion used in the first impregnation was 1.0wt% to 2.0wt%. The solid content of the PEDOT:PSS dispersion used in the second impregnation was lower than that used in the first impregnation. The solid content of the PEDOT:PSS dispersion used in the third impregnation was lower than that used in the second impregnation.

10. The vacuum impregnation process for preparing aluminum electrolytic capacitor cores according to claim 9, characterized in that: The liquid electrolyte is a γ-butyrolactone-based electrolyte, an ethylene glycol-based electrolyte, or a mixture thereof. The secondary impregnation of the liquid electrolyte is performed by vacuum impregnation, pressure impregnation, or a vacuum-pressure composite impregnation, so that the liquid electrolyte fills the pores and electrolytic paper retained in the PEDOT deposition structure.

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