Eight-time hole forming preparation method of corrosion foil for aluminum electrolytic capacitor

Abstract

The invention discloses an eight-time hole forming preparation method of a corrosion foil for an aluminum electrolytic capacitor, and belongs to the field of aluminum electrolytic capacitor electrode material preparation. According to the method, after pretreatment, eight-time hole forming, nitric acid hole expanding and post-treatment of four groups of same-electrolyte different-parameter holes are sequentially carried out; through gradient regulation and control of parameters such as temperature and current density of each stage and cooperation with an exclusive electrolyte formula, accurate construction of a corrosion foil hole structure is realized. The 520V specific volume of the finished product reaches 0.880-0.950 [mu] F / cm < 2 >, the bending strength is greater than or equal to 72 turns, the aperture is 0.5-2.0 [mu] m, the aperture depth reaches 83.9-87.1% of the thickness of the aluminum foil, the aluminum foil with the purity of 99.95-99.99% is adapted, the base material cost and the process threshold are reduced, and the aluminum foil is suitable for severe scenes such as supercapacitors and lithium ion battery current collectors and has remarkable market competitiveness.

Description

Technical Field

[0001] This invention relates to the field of aluminum electrolytic capacitor electrode material preparation technology, specifically to an eight-stage perforation preparation method for etched foil for aluminum electrolytic capacitors. It is particularly suitable for the industrial production of high specific capacitance etched foil for high-voltage aluminum electrolytic capacitors, and can also be extended to applications such as supercapacitors and lithium-ion battery current collectors, where the performance requirements of electrode materials are stringent. Background Technology

[0002] Aluminum electrolytic capacitors, with their core advantages of low cost, large capacitance per unit volume, and fast charge / discharge response, have become key basic components in fields such as electronics, new energy, and rail transportation. They are widely used in core scenarios such as power supply circuit filtering, energy storage system energy buffering, and frequency converter voltage stabilization. As the core electrode material of aluminum electrolytic capacitors, the pore structure of the etched foil (including pore size and distribution, pore depth ratio, pore wall density, and branch pore density) directly determines the capacitor's specific capacitance, withstand voltage, service life, and mechanical adaptability, and is a core bottleneck restricting the performance upgrade of aluminum electrolytic capacitors.

[0003] With the surge in demand from downstream sectors for miniaturized, high-power, and long-life electronic components, the market demand for high-capacitance, high-mechanical-strength etched foils continues to rise. Currently, the mainstream etching foil perforation process in the industry mostly employs a 1-5 perforation cycle, supplemented by a single perforation and post-processing. While this can meet the basic requirements of conventional low- and medium-voltage capacitors, it faces numerous technical bottlenecks in the fabrication of high-performance products, as follows:

[0004] 1. Insufficient refinement of pore structure: Existing processes often employ a single electrolyte system or single-stage parameter control to achieve multi-stage pore formation. The corrosion characteristics of the electrolyte cannot adapt to the differentiated corrosion requirements of aluminum foil, which involve "surface nucleation - intermediate extension - deep branching." In the surface nucleation stage, the initial pore distribution is easily uneven due to excessively rapid corrosion rates. In the intermediate extension stage, the pores are prone to excessive lateral expansion and insufficient longitudinal extension. In the deep branching stage, the branched pores are easily scattered and have large differences in pore size, ultimately limiting the improvement of the effective specific surface area of ​​the etched foil. The specific capacitance of 520V grade etched foil is generally difficult to exceed 0.850μF / cm². 2 This cannot meet the application requirements of high-voltage miniaturized capacitors.

[0005] 2. Difficulty in balancing specific volume and mechanical strength: In borehole processes with up to 5 passes, the main borehole stage often sacrifices borehole wall density to increase borehole depth. When the specific volume of the etched foil reaches 0.850 μF / cm³... 2 When the above conditions are met, micro-cracks will appear on the hole wall due to excessive corrosion, and the bending strength will usually drop below 60 times. This makes it unsuitable for the winding, cutting and other processing steps in the capacitor production process, and it is prone to defects such as foil breakage and short circuits, which will significantly reduce the yield of finished capacitors.

[0006] 3. Stringent requirements for substrate purity: Existing perforation processes have low tolerance for the purity of aluminum foil substrates, typically requiring a purity of 99.99% or higher. Otherwise, impurities in low-purity aluminum foil can lead to defects such as blocked channels and localized absence of pores. Furthermore, the procurement cost of high-purity aluminum foil is 18-22% higher than that of 99.95% pure aluminum foil, significantly increasing the total production cost of the etched foil and weakening the company's market competitiveness.

[0007] 4. High difficulty in process compatibility and modification: Some new perforation processes use special electrolyte systems or special equipment to improve performance, which cannot be integrated with existing production lines. If enterprises want to upgrade the process, they need to invest a lot of money in equipment modification, and the modification cycle can be as long as 3 to 6 months. This not only affects the existing production capacity, but also poses a risk of technology compatibility.

[0008] 5. Insufficient adaptability to special scenarios: Scenarios such as supercapacitors and lithium-ion battery current collectors have extremely high requirements for the pore depth ratio and pore wall corrosion resistance of the etched foil. The pore depth of the etched foil prepared by the existing process can only reach 70~75% of the aluminum foil thickness, and the pore wall is prone to secondary corrosion in the electrolyte, which cannot meet the requirements of the harsh service environment.

[0009] In summary, existing etching foil perforation processes can no longer meet the demands of downstream industries for high performance, low cost, and wide applicability. There is an urgent need to develop a new perforation process that combines refined pore structure, synergistic performance, and controllable cost to break through the industry's technical bottleneck. Summary of the Invention

[0010] I. Purpose of the Invention

[0011] 1. A method for preparing etched foil with eight-stage differentiated porosity is provided, achieving a specific capacitance increase of 0.880–0.950 μF / cm for 520V grade etched foil. 2 At the same time, the bending strength is stabilized at over 72 cycles, solving the problem of balancing specific volume and mechanical strength.

[0012] 2. Precisely control the pore structure of the etched foil to keep the pore size between 0.5 and 2.0 μm and extend the pore depth to 83.9 to 87.1% of the aluminum foil thickness, thereby improving the effective specific surface area and utilization rate of the pores.

[0013] 3. Reduce the dependence of the process on the purity of the substrate, achieve stable compatibility with aluminum foil of 99.95~99.99% purity, and reduce the procurement cost of the substrate.

[0014] 4. Design process solutions that are compatible with existing production lines, eliminating the need for large-scale equipment modifications and shortening the process upgrade cycle.

[0015] 5. Improve the corrosion resistance and pore structure stability of the etched foil to meet the application requirements of harsh scenarios such as supercapacitors and lithium-ion battery current collectors.

[0016] II. Technical Solution

[0017] A method for preparing an eight-stage perforation process for etched foil used in aluminum electrolytic capacitors includes pretreatment, eight-stage perforation, nitric acid perforation, and post-treatment steps, as detailed below:

[0018] (1) Pretreatment: Place the aluminum foil in hydrochloric acid for 2-3 minutes, rinse with pure water for 15 seconds, and then set aside.

[0019] (2) Eight holes:

[0020] ① First group of pre-etched pits: Place the pretreated aluminum foil in a hydrochloric acid electrolyte system, first at 73~78℃, 1.6~2.0A / cm 2 Electrolysis for 10-25 seconds under the specified conditions, followed by electrolysis at 70-75℃ and 1.2-1.5 A / cm. 2 Electrolysis for 15-30 seconds under the specified conditions;

[0021] ② Second group of grain boundary corrosion porosity: Place the aluminum foil treated in step ① in a sulfuric acid electrolyte system, first at 70~80℃, 1.8~2.5A / cm 2 Electrolysis for 20-35 seconds under the specified conditions, followed by electrolysis at 68-75℃ and 1.6-2.0 A / cm. 2 Electrolysis for 20-35 seconds under the specified conditions;

[0022] ③ Third group of main boreholes: Place the aluminum foil treated in step ② in a sulfuric acid-hydrochloric acid-phosphoric acid mixed electrolyte system, first at 68~72℃, 1.8~2.2A / cm 2 Electrolysis for 20-40 seconds under the specified conditions, followed by electrolysis at 70-75℃ and 1.0-1.4 A / cm. 2 Electrolysis for 20-35 seconds under the specified conditions;

[0023] ④ Fourth group of branch holes: Place the aluminum foil treated in step ③ in a hydrochloric acid-acetic acid mixed electrolyte system, and supplement with ultrasound, first at 62~68℃, 1.5~2.0A / cm 2 Electrolysis for 30-45 seconds under the specified conditions, followed by electrolysis at 66-70℃ and 1.0-1.3 A / cm. 2 Electrolysis for 35-55 seconds under the specified conditions;

[0024] (3) Nitric acid pore enlargement: The aluminum foil after eight pore enlargements is placed in an electrolyte containing 8-12 wt% nitric acid, 0.02-0.05 wt% copper nitrate, and 0.5-0.8 wt% polyethylene glycol at 68-75°C and 1.2-1.6 A / cm. 2 Electrolysis for 6-10 minutes under the specified conditions;

[0025] (4) Post-treatment: Place the expanded aluminum foil in 5~9wt% nitric acid and etch it at 55~65℃ for 1~3min. After rinsing with pure water for 25s, dry it with hot air.

[0026] Furthermore, the aluminum foil in step (1) has a thickness of 120~150μm and a purity of 99.95~99.99%.

[0027] Further, the aluminum foil described in step (1) is placed in 5wt% hydrochloric acid, pickled at 70°C for 2-3 minutes, rinsed with pure water for 15 seconds, and then put into use.

[0028] Furthermore, in step (1), the purpose of pickling is to remove oil stains and loose oxide layer from the surface of aluminum foil, exposing fresh aluminum substrate to ensure uniformity of subsequent pore formation.

[0029] Further, the electrolyte composition of the hydrochloric acid system in step ① is: 8~12wt% hydrochloric acid, 0.5~1.2wt% citric acid, and 0.1~0.3wt% sodium dodecylbenzenesulfonate.

[0030] Furthermore, in step ①, citric acid is used to inhibit excessive local corrosion of the aluminum foil, and sodium dodecylbenzenesulfonate is used to improve the wettability of the electrolyte on the aluminum foil.

[0031] Further, the electrolyte composition of the sulfuric acid system in step ② is: 5-8 wt% sulfuric acid, 0.3-0.8 wt% sodium chloride, and 0.2-0.5 wt% disodium ethylenediaminetetraacetate.

[0032] Furthermore, in step ②, sodium chloride is used to selectively corrode the grain boundaries of the aluminum foil, and disodium ethylenediaminetetraacetate is used to chelate the metal ions generated during the corrosion process to prevent pore blockage.

[0033] Further, the electrolyte composition of the sulfuric acid-hydrochloric acid-phosphoric acid mixed system in step ③ is as follows: sulfuric acid 9~15wt%, hydrochloric acid 3~5wt%, phosphoric acid 1.5wt%, adipic acid 1.0~1.8wt%, and glycerol 2~4wt%.

[0034] Furthermore, in step ③, sulfuric acid provides a stable corrosive environment, hydrochloric acid enhances the longitudinal extension of the pores, phosphoric acid assists in the formation of deep pores, and glycerol is used to adapt the viscosity of the mixed acid to prevent pore collapse.

[0035] Further, the electrolyte composition of the hydrochloric acid-acetic acid mixed system in step ④ is: 3~5wt% hydrochloric acid, 2~4wt% acetic acid, 0.1~0.3wt% cerium nitrate, and 0.8~1.5wt% polyethylene glycol.

[0036] Furthermore, in step ④, cerium nitrate is used to induce branch pore formation, polyethylene glycol is used to inhibit excessive branch pore growth, and ultrasonic assistance is used to enhance the adequacy of contact between the electrolyte and the aluminum foil channels.

[0037] Furthermore, the ultrasound conditions in step ④ are 40kHz and 110~130W.

[0038] Furthermore, in step (3), copper nitrate is used to catalyze the uniform widening of the pores, and polyethylene glycol is used to inhibit excessive local corrosion of the pores.

[0039] Further, in step (4), the aluminum foil after the hole expansion is placed in 5~9wt% nitric acid, etched at 55~65℃ for 1~3min, rinsed with pure water for 25s, and then dried with hot air at 80℃ for 10min.

[0040] Furthermore, the etched foil prepared by the method is suitable for electrode material preparation scenarios of high-voltage aluminum electrolytic capacitors, supercapacitors, and lithium-ion battery current collectors.

[0041] III. Technical Advantages of the Invention Compared with Existing Technologies

[0042] 1. Synergistic advantages of process innovation and integrity

[0043] This invention is the first to construct a complete process system of "four groups of eight-stage same-liquid, different-parameter pore formation," breaking through the limitations of traditional 1-5 stage pore formation processes. It achieves a progressive pore formation process of "surface nucleation - grain boundary connectivity - main pore extension - branch refinement." Traditional processes involve independent segments in the pore formation stage, resulting in poor pore connectivity between stages. In contrast, this invention, through parameter gradient control within the same electrolyte system, ensures the continuity of pores from shallow to deep, improving pore utilization by 20-25% compared to traditional processes. Furthermore, the process requires no specialized equipment and can be directly integrated into existing production lines, reducing equipment modification costs by over 80% and shortening the modification cycle to 7-10 days, thus balancing technological innovation with industrial compatibility.

[0044] 2. Breakthrough advantages in both specific volume and mechanical strength

[0045] This invention achieves a synergistic improvement in specific volume and bending strength through the densification of the pore walls. In Examples 1-3 of this invention, the specific volume at 520V reaches 0.925μF / cm³. 2 0.946μF / cm 2 0.902μF / cm 2 The average value was 0.924 μF / cm. 2 Compared to the comparative example of 0.860 μF / cm 2The bending strength was improved by 7.44%; the bending strength was 74, 72, and 72 cycles respectively, with an average of 72.67 cycles, which is 25.29% higher than the comparative example of 58 cycles, completely solving the industry problem of "increased specific capacitance leading to decreased strength" in traditional processes. This advantage stems from the precise repair of the pore walls at each stage. For example, the secondary parameter adjustment of the second group of grain boundary pores improved the integrity of the pore walls to over 95%, and the glycerol viscosity control of the third group of main pores prevented pore collapse, ultimately achieving a performance balance. This advantage can increase the unit volume capacitance of downstream capacitors by 10-15%, while improving the winding yield to over 99%, significantly reducing the defective costs of capacitor production.

[0046] 3. Advantages in substrate compatibility and cost control

[0047] This invention achieves stable compatibility with aluminum foil of 99.95% to 99.99% purity, reducing substrate cost by 18% to 22% compared to traditional processes (requiring purity above 99.99%). Example 2 uses 99.95% low-purity aluminum foil and still achieves 0.946 μF / cm. 2 The high specific volume and 72-bending strength of the low-purity aluminum foil are comparable to those of products made from high-purity aluminum foil; while the comparative example, using 99.99% high-purity aluminum foil, still shows significantly lower performance. Furthermore, the market supply of low-purity aluminum foil is more abundant, avoiding the procurement cycle fluctuations associated with high-purity aluminum foil, ensuring supply chain stability, and providing companies with significant cost and supply advantages.

[0048] 4. Advantages of refined pore structure and high utilization rate

[0049] This invention achieves precise control over the pore structure through multi-stage parameter adjustment. The average ratio of pore depth to aluminum foil thickness is 85.73%, an increase of 3.16% compared to the comparative example's 83.1%, resulting in an effective specific surface area increase of over 25%. The refined pore structure significantly increases the contact area between the etched foil and the electrolyte, improving the capacitor's charge / discharge response speed by 12-18%. Furthermore, the dense pore walls ensure uniform electrolyte wetting, reducing leakage current by 15-20% and extending service life by over 25%. For example, a 520V high-voltage capacitor prepared using the etched foil of this invention achieves a service life of 5000 hours at 105℃, a 30% improvement over traditional products, meeting the long-life requirements of high-end power supply equipment.

[0050] 5. High adaptability to special scenarios

[0051] The etched foil prepared by this invention features a high pore depth ratio and strong pore wall corrosion resistance, making it suitable for demanding applications such as supercapacitors and lithium-ion battery current collectors. Supercapacitors have extremely high requirements for the pore depth and specific surface area of ​​electrode materials. The etched foil of this invention achieves a pore depth ratio of over 82% and a specific surface area that is more than 45% higher than traditional products, increasing the energy density of supercapacitors by more than 18%. Lithium-ion battery current collectors require electrode materials with excellent resistance to electrolyte corrosion. The pore walls of this invention form a dense oxide film after nitric acid post-treatment. After immersion in electrolyte for 1000 hours, the pore wall corrosion rate is less than 0.5%, far lower than the 3% of traditional products, ensuring the cycle stability of the battery. Furthermore, the high bending strength of the etched foil is suitable for the rolling processing of battery electrodes, preventing electrode breakage and improving the yield of finished batteries, providing a new solution for electrode materials in the new energy field. Detailed Implementation

[0052] In this invention, the method for preparing the etched foil for aluminum electrolytic capacitors using an eight-stage perforation process includes pretreatment, eight-stage perforation, nitric acid perforation, and post-treatment steps, as detailed below:

[0053] (1) Pretreatment: Place aluminum foil with a thickness of 120~150μm and a purity of 99.95~99.99% in 5wt% hydrochloric acid, pickle at 70℃ for 2~3min, rinse with pure water for 15s and set aside.

[0054] (2) Eight holes:

[0055] ① First group of pre-etched pits: Place the pretreated aluminum foil in a hydrochloric acid electrolyte system, first at 73~78℃, 1.6~2.0A / cm 2 Electrolysis for 10-25 seconds under the specified conditions, followed by electrolysis at 70-75℃ and 1.2-1.5 A / cm. 2 Electrolysis was performed for 15-30 seconds under the specified conditions. The electrolyte composition of the hydrochloric acid system was: 8-12 wt% hydrochloric acid, 0.5-1.2 wt% citric acid, and 0.1-0.3 wt% sodium dodecylbenzenesulfonate.

[0056] ② Second group of grain boundary corrosion porosity: Place the aluminum foil treated in step ① in a sulfuric acid electrolyte system, first at 70~80℃, 1.8~2.5A / cm 2 Electrolysis for 20-35 seconds under the specified conditions, followed by electrolysis at 68-75℃ and 1.6-2.0 A / cm. 2 Electrolysis was performed for 20-35 seconds under the specified conditions. The electrolyte composition of the sulfuric acid system was: 5-8 wt% sulfuric acid, 0.3-0.8 wt% sodium chloride, and 0.2-0.5 wt% disodium ethylenediaminetetraacetate.

[0057] ③ Third group of main boreholes: Place the aluminum foil treated in step ② in a sulfuric acid-hydrochloric acid-phosphoric acid mixed electrolyte system, first at 68~72℃, 1.8~2.2A / cm 2 Electrolysis for 20-40 seconds under the specified conditions, followed by electrolysis at 70-75℃ and 1.0-1.4 A / cm. 2 Electrolysis was performed for 20-35 seconds under the specified conditions. The electrolyte composition of the sulfuric acid-hydrochloric acid-phosphoric acid mixed system was as follows: sulfuric acid 9-15 wt%, hydrochloric acid 3-5 wt%, phosphoric acid 1.5 wt%, adipic acid 1.0-1.8 wt%, and glycerol 2-4 wt%.

[0058] ④ Fourth group of branch holes: Place the aluminum foil treated in step ③ in a hydrochloric acid-acetic acid mixed electrolyte system, and supplement with 40kHz, 110~130W ultrasound, first at 62~68℃, 1.5~2.0A / cm 2 Electrolysis for 30-45 seconds under the specified conditions, followed by electrolysis at 66-70℃ and 1.0-1.3 A / cm. 2 Electrolysis was performed for 35-55 seconds under the specified conditions. The electrolyte composition of the hydrochloric acid-acetic acid mixed system was as follows: 3-5 wt% hydrochloric acid, 2-4 wt% acetic acid, 0.1-0.3 wt% cerium nitrate, and 0.8-1.5 wt% polyethylene glycol.

[0059] (3) Nitric acid pore enlargement: The aluminum foil after eight pore enlargements is placed in an electrolyte containing 8-12 wt% nitric acid, 0.02-0.05 wt% copper nitrate, and 0.5-0.8 wt% polyethylene glycol at 68-75°C and 1.2-1.6 A / cm. 2 Electrolysis for 6-10 minutes under the specified conditions;

[0060] (4) Post-treatment: Place the expanded aluminum foil in 5~9wt% nitric acid and etch it at 55~65℃ for 1~3min. After rinsing with pure water for 25s, dry it with hot air at 80℃ for 10min.

[0061] Technical principle of the invention:

[0062] This invention is a combination of combined invention and selective invention. Its inventiveness lies in the fact that by combining the process of "four groups of eight times of the same liquid with different parameters to generate pores", and by accurately selecting the electrolyte formula and process parameters at each stage, a synergistic technical effect of 1+1>2 is achieved.

[0063] 1. Synergistic effect of each electrolyte component

[0064] The first group of hydrochloric acid system electrolytes: hydrochloric acid is the main corrosive agent, providing H+. +To achieve surface nucleation of aluminum foil; citric acid is used as a corrosion inhibitor to inhibit excessive local corrosion by complexing aluminum ions and ensure the uniformity of initial pores; sodium dodecylbenzene sulfonate is used as a surfactant to improve the wettability of the electrolyte on the aluminum foil and avoid uneven pore distribution caused by surface tension. The three work together to achieve "shallow pore uniform nucleation".

[0065] The second group of sulfuric acid electrolytes: sulfuric acid provides a stable, strongly acidic corrosive environment; sodium chloride contains Cl... - It can selectively corrode the grain boundaries of aluminum foil, guiding the channels to extend along the grain boundaries; disodium ethylenediaminetetraacetate can chelate the Al produced during corrosion. 3+ Metal ions are used to prevent ion deposition and blockage of pores, and the three work together to achieve "dense interconnection of grain boundary pores".

[0066] The third group of electrolytes uses a sulfuric acid-hydrochloric acid-phosphoric acid mixture: sulfuric acid ensures the stability of the corrosive environment, hydrochloric acid enhances the longitudinal extension of the pores, phosphoric acid can form a temporary protective film on the pore wall to control transverse corrosion, adipic acid improves the buffering capacity of the electrolyte, and glycerol adjusts the viscosity of the mixed acid to prevent pore collapse. The multi-component synergy achieves "stable extension of deep pores".

[0067] The fourth group of hydrochloric acid-acetic acid mixed electrolyte system: hydrochloric acid and acetic acid are combined to achieve mild and uniform corrosion, cerium nitrate can induce the formation of branch pores on the sidewall of the main channel, polyethylene glycol inhibits the excessive growth of branch pores, and ultrasonic vibration is used to enhance the mass transfer of electrolyte in the channel, so as to achieve "fine distribution of branch pores".

[0068] Nitric acid pore-expanding electrolyte: The strong oxidizing property of nitric acid enables uniform pore widening, copper nitrate acts as a catalyst to improve the uniformity of pore expansion, and polyethylene glycol inhibits local excessive corrosion. The three work together to complete the final shaping of the pores.

[0069] 2. Unexpected effects of process parameter selection

[0070] This invention sets a gradient of temperature and current density within the same electrolyte system. For example, in the first group of pre-etched pores, the first pore formation uses 73~78℃ and 1.6~2.0A / cm². 2 High-parameter rapid borehole formation, reducing the temperature by 3~8℃ and the A / cm² of the second borehole formation. 2 Current density is used to achieve uniformity and compactness of the pore core, avoiding the problem of "excessive corrosion on the surface and no pores in the deep layer" caused by a single parameter; in the fourth group of branch pores, the combination of ultrasonic assistance and gradient current improves the density of branch pores, and the specific surface area is increased by more than 45% compared with the traditional process, achieving technical effects far exceeding those of conventional processes.

[0071] To make the present invention more fully disclosed, more specific embodiments are described below.

[0072] The following examples use aluminum foils of different purities and thicknesses for verification; the etched foils obtained in the examples and comparative examples were subjected to formation treatment according to the JCC testing standards of Japan Electric Machinery Co., Ltd., and then the withstand voltage and specific volume were tested; the bending strength was measured by the number of tests performed on the etched foil using an aluminum foil bending tester with a curvature radius of 1.0 mm; the aperture and hole depth were obtained by taking pictures with a scanning electron microscope at 500-1000x magnification and importing them into image analysis software for analysis and statistics.

[0073] Example 1

[0074] A method for preparing an eight-stage perforation process for etched foil used in aluminum electrolytic capacitors includes the following steps:

[0075] 1. Substrate selection: 99.97% pure aluminum foil, 135μm thick, surface flatness ≤5μm, no obvious scratches or oxide spots.

[0076] 2. Pretreatment: Place the aluminum foil in a 5wt% hydrochloric acid bath and pickle at a constant temperature of 70℃ for 2 minutes. During the pickling process, use a bubbling device to stir to ensure that the acid solution is evenly in contact with the aluminum foil. After pickling, rinse with pure water for 15 seconds. The rinsing pressure is controlled at 0.2MPa to ensure that there is no acid residue on the surface.

[0077] 3. First group of pre-corroded boreholes:

[0078] Electrolyte preparation: 10wt% hydrochloric acid, 0.8wt% citric acid, 0.2wt% sodium dodecylbenzenesulfonate, and pure water to 100%. Stir until completely dissolved, and control the electrolyte temperature at 73℃.

[0079] First aperture formation: Aluminum foil is connected to the positive electrode of the electrolytic cell, a titanium plate is used as the cathode, and the current density is 1.8 A / cm². 2 Electrolysis time is 15s, forming initial shallow pores of 0.2~0.4μm;

[0080] Second pore formation: Keeping the electrolyte composition unchanged, the temperature is lowered to 70℃, and the current density is reduced to 1.3A / cm². 2 Electrolysis time 20s, pore core homogenization to 0.3~0.6μm, pore density to 1.6×10 7 pcs / cm 2 .

[0081] 4. Second group of grain boundary corrosion porosity:

[0082] Electrolyte preparation: 6wt% sulfuric acid, 0.5wt% sodium chloride, 0.3wt% disodium ethylenediaminetetraacetate, and pure water to bring the total to 100%. Stir well and heat to 70℃.

[0083] First hole drilling: Current density 2.0 A / cm² 2Electrolysis time 25s, the channels extend along the grain boundaries to 28% of the aluminum foil thickness;

[0084] Second drilling: Temperature reduced to 68℃, current density decreased to 1.8A / cm² 2 The electrolysis time is 30 seconds, the channel extends to 42% of the aluminum foil thickness, and the pore wall integrity reaches 96%.

[0085] 5. Third group of main hair holes:

[0086] Electrolyte preparation: 12wt% sulfuric acid, 4wt% hydrochloric acid, 1.5wt% phosphoric acid, 1.5wt% adipic acid, 3wt% glycerol, and pure water to bring the total to 100%. Stir well and control the temperature at 68℃.

[0087] First hole drilling: Current density 2.0 A / cm² 2 Electrolysis time 30s, main pores widened to 0.9~1.2μm, pore depth reached 52% of aluminum foil thickness;

[0088] Second drilling: Temperature increased to 70℃, current density reduced to 1.2 A / cm² 2 The electrolysis time is 25s, the main pore extends to 78% of the aluminum foil thickness, and the pore size is optimized to 1.1~1.5μm.

[0089] 6. Fourth group of branch holes:

[0090] Electrolyte preparation: 4wt% hydrochloric acid, 3wt% acetic acid, 0.2wt% cerium nitrate, 1.2wt% polyethylene glycol, and pure water to 100%. After stirring evenly, cool to 62℃ and turn on the 40kHz, 120W ultrasonic device.

[0091] First hole formation: Current density 1.8 A / cm² 2 Electrolysis time 35s, primary branch pores of 0.3~0.5μm are generated on the sidewall of the main pore;

[0092] Second hole formation: Temperature increased to 66℃, current density reduced to 1.2A / cm² 2 With an electrolysis time of 40s, the branch pores are densified to 0.4~0.7μm, increasing the specific surface area by 50%.

[0093] 7. Pore enlargement with nitric acid: The electrolyte is prepared with 10wt% nitric acid, 0.03wt% copper nitrate, and 0.6wt% polyethylene glycol. The temperature is raised to 70℃, and the current density is 1.4A / cm². 2 Electrolysis time 8 min, main pore diameter widened to 1.5~2.0 μm.

[0094] 8. Post-treatment: The aluminum foil is etched with 8wt% nitric acid solution at 60℃ for 1 min, rinsed with pure water for 25 s, and then dried with hot air at 80℃ for 10 min. Laminar flow air is used during the drying process to avoid surface oxidation.

[0095] Test results: 520V specific capacitance 0.925μF / cm 2 It has a bending strength of 74 times, a pore size of 0.6~1.9μm, and a pore depth of up to 118μm (accounting for 86.2% of the aluminum foil thickness).

[0096] Example 2

[0097] A method for preparing an eight-stage perforation process for etched foil used in aluminum electrolytic capacitors includes the following steps:

[0098] 1. Substrate selection: 99.95% pure aluminum foil, 140μm thick, surface flatness ≤4.8μm, no obvious scratches or oxide spots.

[0099] 2. Pretreatment: Place the aluminum foil in a 5wt% hydrochloric acid bath and pickle at a constant temperature of 70℃ for 3 minutes. During the pickling process, use a bubbling device to stir to ensure that the acid solution is evenly in contact with the aluminum foil. After pickling, rinse with pure water for 15 seconds. The rinsing pressure is controlled at 0.2MPa to ensure that there is no acid residue on the surface.

[0100] 3. First group of pre-corroded boreholes:

[0101] Electrolyte preparation: 12wt% hydrochloric acid, 1.2wt% citric acid, 0.3wt% sodium dodecylbenzenesulfonate, and pure water to 100%. Stir until completely dissolved, and control the electrolyte temperature at 77℃.

[0102] First aperture formation: Aluminum foil is connected to the positive electrode of the electrolytic cell, a titanium plate is used as the cathode, and the current density is 1.8 A / cm². 2 Electrolysis time is 15s, forming initial shallow pores;

[0103] Second pore formation: Keeping the electrolyte composition unchanged, the temperature is lowered to 74℃, and the current density is reduced to 1.5A / cm². 2 Electrolysis time 20s, pore core homogenization to 0.4~0.6μm, pore density to 1.8×10 7 pcs / cm 2 .

[0104] 4. Second group of grain boundary corrosion porosity:

[0105] Electrolyte preparation: 8 wt% sulfuric acid, 0.8 wt% sodium chloride, 0.5 wt% disodium ethylenediaminetetraacetate, and pure water to bring the volume to 100%. Stir well and heat to 78°C.

[0106] First hole formation: Current density 2.2 A / cm² 2 Electrolysis time 30s, the pores extended along the grain boundaries to 28.2% of the aluminum foil thickness;

[0107] Second drilling: Temperature reduced to 72℃, current density reduced to 2.0 A / cm² 2 The electrolysis time is 35 seconds, and the pores extend to 45% of the aluminum foil thickness.

[0108] 5. Third group of main hair holes:

[0109] Electrolyte preparation: 15wt% sulfuric acid, 5wt% hydrochloric acid, 1.5wt% phosphoric acid, 1.8wt% adipic acid, 4wt% glycerol, and pure water to bring the total to 100%. Stir well and control the temperature at 71℃.

[0110] First hole formation: Current density 2.2 A / cm² 2 Electrolysis time 30s, main pores widened to 1~1.2μm, pore depth reached 52.3% of aluminum foil thickness;

[0111] Second drilling: Temperature increased to 73℃, current density decreased to 1.4 A / cm² 2 The electrolysis time is 35s, the main pore extends to 80% of the aluminum foil thickness, and the pore size is optimized to 1.2~1.5μm.

[0112] 6. Fourth group of branch holes:

[0113] Electrolyte preparation: 5wt% hydrochloric acid, 4wt% acetic acid, 0.3wt% cerium nitrate, 1.5wt% polyethylene glycol, and pure water to 100%. After stirring evenly, cool to 68℃ and turn on the 40kHz, 130W ultrasonic device.

[0114] First hole formation: Current density 1.8 A / cm² 2 Electrolysis time 40s, primary branch pores of 0.3~0.4μm are generated on the sidewall of the main pore;

[0115] Second drilling: Temperature increased to 70℃, current density reduced to 1.3A / cm² 2 With an electrolysis time of 50s, the branch pores are densified to 0.5~0.7μm, and the specific surface area is increased by 55%.

[0116] 7. Pore enlargement with nitric acid: The electrolyte is prepared with 12wt% nitric acid, 0.05wt% copper nitrate, and 0.8wt% polyethylene glycol. The temperature is raised to 73℃, and the current density is 1.6A / cm². 2 Electrolysis time: 10 min.

[0117] 8. Post-treatment: The aluminum foil is etched with 8.5wt% nitric acid solution at 65℃ for 1 min, rinsed with pure water for 25 s, and then dried with hot air at 80℃ for 10 min. Laminar flow air is used during the drying process to avoid surface oxidation.

[0118] Test results: 520V specific capacitance 0.946μF / cm 2It has a bending strength of 72 times, a pore size of 0.7~2.0μm, and a pore depth of up to 122μm (accounting for 87.1% of the aluminum foil thickness).

[0119] Example 3

[0120] A method for preparing an eight-stage perforation process for etched foil used in aluminum electrolytic capacitors includes the following steps:

[0121] 1. Substrate selection: 99.96% pure aluminum foil, 130μm thick, surface flatness ≤4.9μm, no obvious scratches or oxide spots.

[0122] 2. Pretreatment: Place the aluminum foil in a 5wt% hydrochloric acid bath and pickle at a constant temperature of 70℃ for 3 minutes. During the pickling process, use a bubbling device to stir to ensure that the acid solution is evenly in contact with the aluminum foil. After pickling, rinse with pure water for 15 seconds. The rinsing pressure is controlled at 0.2MPa to ensure that there is no acid residue on the surface.

[0123] 3. First group of pre-corroded boreholes:

[0124] Electrolyte preparation: 9wt% hydrochloric acid, 0.6wt% citric acid, 0.15wt% sodium dodecylbenzenesulfonate, and pure water to 100%. Stir until completely dissolved, and control the electrolyte temperature at 75℃.

[0125] First aperture formation: Aluminum foil is connected to the positive electrode of the electrolytic cell, a titanium plate is used as the cathode, and the current density is 1.7 A / cm². 2 Electrolysis time 20s, forming initial shallow pores;

[0126] Second pore formation: Keeping the electrolyte composition unchanged, the temperature is lowered to 72℃, and the current density is reduced to 1.4A / cm². 2 Electrolysis time 25s, the pore cores were homogenized to 0.4~0.6μm, and the pore density reached 1.7×10⁻⁶. 7 pcs / cm 2 .

[0127] 4. Second group of grain boundary corrosion porosity:

[0128] Electrolyte preparation: 7wt% sulfuric acid, 0.6wt% sodium chloride, 0.4wt% disodium ethylenediaminetetraacetate, and pure water to bring the total to 100%. Stir well and heat to 74℃.

[0129] First hole formation: Current density 2.2 A / cm² 2 Electrolysis time 25s, the pores extend along the grain boundaries to 28.4% of the aluminum foil thickness;

[0130] Second drilling: Temperature reduced to 72℃, current density decreased to 1.9 A / cm² 2 The electrolysis time is 30 seconds, and the pores extend to 43% of the aluminum foil thickness.

[0131] 5. Third group of main hair holes:

[0132] Electrolyte preparation: 10.5wt% sulfuric acid, 3.5wt% hydrochloric acid, 1.5wt% phosphoric acid, 1.2wt% adipic acid, 2.5wt% glycerol, and pure water to bring the total to 100%. Stir well and control the temperature at 70℃.

[0133] First hole drilling: Current density 2.1 A / cm² 2 Electrolysis time 30s, main pores widened to 0.9~1.1μm, pore depth reached 51.5% of aluminum foil thickness;

[0134] Second firing: Temperature increased to 73℃, current density decreased to 1.1 A / cm² 2 Electrolysis time 35s, main hole extended to 76% of aluminum foil thickness.

[0135] 6. Fourth group of branch holes:

[0136] Electrolyte preparation: 3.5wt% hydrochloric acid, 2.5wt% acetic acid, 0.15wt% cerium nitrate, 1.0wt% polyethylene glycol, and pure water to 100%. After stirring evenly, cool to 65℃ and turn on the 40kHz, 125W ultrasonic device.

[0137] First hole formation: Current density 1.8 A / cm² 2 Electrolysis time: 40s;

[0138] Second firing: Temperature increased to 68℃, current density reduced to 1.1 A / cm² 2 With an electrolysis time of 50 seconds, the specific surface area increased by 48%.

[0139] 7. Pore enlargement with nitric acid: The electrolyte is prepared with 9 wt% nitric acid, 0.04 wt% copper nitrate, and 0.7 wt% polyethylene glycol. The temperature is raised to 70°C, and the current density is 1.3 A / cm². 2 Electrolysis time: 8 minutes.

[0140] 8. Post-treatment: The aluminum foil is etched with 8wt% nitric acid solution at 62℃ for 1 min, rinsed with pure water for 25 s, and then dried with hot air at 80℃ for 10 min. Laminar flow air is used during the drying process to avoid surface oxidation.

[0141] Test results: 520V specific capacitance 0.902μF / cm 2 It has a bending strength of 72 times, a pore size of 0.5~1.8μm, and a pore depth of up to 113μm (accounting for 83.9% of the aluminum foil thickness).

[0142] Comparative example (traditional 5-stage porosimetry + nitric acid porosimetry + post-treatment)

[0143] 1. Substrate selection: 99.99% pure aluminum foil, 130μm thick;

[0144] 2. Step 1 (Pretreatment): Place the aluminum foil in a 5wt% hydrochloric acid bath and pickle at a constant temperature of 70℃ for 2 minutes. During the pickling process, use a bubbling device to stir to ensure that the acid solution is evenly in contact with the aluminum foil. After pickling, rinse with pure water for 15 seconds. The rinsing pressure is controlled at 0.2MPa to ensure that there is no acid residue on the surface.

[0145] 3. Step 2 (Pre-corrosion and porosity formation): Electrolyte preparation: 5wt% hydrochloric acid, 3wt% sulfuric acid, and pure water to 100%. Stir until completely dissolved. Control the electrolyte temperature at 73℃. Connect the aluminum foil to the positive electrode of the electrolytic cell. Use a titanium plate as the cathode. Current density: 1.8A / cm². 2 Electrolysis time: 15s;

[0146] 4. Step 3 (Grain boundary porosity): Electrolyte preparation: 6wt% sulfuric acid, 0.5wt% sodium chloride, and pure water to 100%. After stirring evenly, heat to 70℃ and apply at a current density of 1.5A / cm². 2 Electrolysis time: 30s;

[0147] 5. Step 4 (Main Borehole): Electrolyte preparation: 10.5wt% sulfuric acid, 3.5wt% hydrochloric acid, 1.5wt% phosphoric acid, pure water to 100%, stir well, control the temperature at 72℃, and apply a current density of 2.0 A / cm². 2 Electrolysis time: 50s;

[0148] 6. Step 5 (Branching): Electrolyte preparation: 4wt% hydrochloric acid, add pure water to 100%, stir well and cool to 75℃, at a current density of 1.8A / cm². 2 Electrolysis time: 40s;

[0149] 7. Step 6 (Trimming the hairline): Electrolyte preparation: 3.5wt% nitric acid, pure water to 100%, stir well and cool to 68℃, at a current density of 1.6A / cm². 2 Electrolysis time: 20s;

[0150] 8. Step 7: Prepare the electrolyte solution with 10wt% nitric acid, 0.03wt% copper nitrate, and 0.6wt% polyethylene glycol. Heat to 70℃ and set the current density to 1.4A / cm². 2 Electrolysis time: 8 minutes;

[0151] 9. Step 8: The aluminum foil is etched with 7.5wt% nitric acid solution at 65℃ for 1 min, rinsed with pure water for 25 s, and then dried with hot air at 80℃ for 10 min;

[0152] Test results: 520V specific capacitance 0.860μF / cm 2It has a bending strength of 58 times, a hole diameter of 1.0~2.2μm, and a hole depth of 108μm (accounting for 83.1% of the aluminum foil thickness).

[0153]

[0154] As shown in Table 1:

[0155] 1. Specific capacitance increase: The average specific capacitance at 520V for Examples 1-3 is 0.924 μF / cm. 2 The comparative example is 0.860 μF / cm. 2 The improvement is approximately 7.44% (0.924-0.860) / 0.860×100%. This improvement stems from the optimization of the channel utilization rate. The branch holes of this invention significantly increase the effective specific surface area, while the branch holes of the traditional process are scattered and have a low effective area ratio.

[0156] 2. Increase in bending strength: The average bending strength of the example was 72.67 cycles, and that of the comparative example was 58 cycles, with an increase of (72.67-58) / 58×100%≈25.29%. This increase is attributed to the densification treatment of the pore walls, the secondary repair of the second group of grain boundary pores, and the viscosity control of the third group of glycerol, which prevented the generation of microcracks in the pore walls.

[0157] 3. Increase in Pore Depth Ratio: The average pore depth ratio in the examples was (86.2% + 87.1% + 83.9%) / 3 ≈ 85.73%, while the comparative example was 83.1%, representing an increase of (85.73 - 83.1) / 83.1 × 100% ≈ 3.16%. The increase in pore depth stemmed from the longitudinal extension control during the main porosimetry stage. The addition of hydrochloric acid enhanced the longitudinal corrosion resistance of the pores, allowing the pore depth to exceed 80%.

[0158] 4. Pore size uniformity analysis: The pore size distribution range of the example is 0.5~2.0μm, with a range width of 1.5μm; the pore size of the comparative example is 1.0~2.2μm, with a range width of 1.2μm. However, the average pore size of the example is 1.25μm, while the average pore size of the comparative example is 1.6μm. The pore size uniformity of the example is improved, which is more conducive to the uniform wetting of the electrolyte.

[0159] In summary, the synergistic effect of the process parameters and electrolyte formulation of this invention achieves a comprehensive improvement in the performance of the etched foil. Comparison of examples and comparative examples shows that the pore structure of the traditional five-stage perforation process is relatively weak, resulting in significantly inferior key indicators such as specific capacitance and bending strength compared to this invention (eight-stage differentiated perforation). The gradient parameter design of this invention demonstrates significant advantages in process synergy, is adaptable to low-purity aluminum foil, offers outstanding cost advantages, and is suitable for demanding applications such as supercapacitors and lithium-ion battery current collectors, thus possessing industrial application value.

Claims

1. A method for preparing an eight-stage perforation process for etched foil used in aluminum electrolytic capacitors, characterized in that, The process includes pretreatment, eight-stage porosimetry, nitric acid porosimetry, and post-treatment steps, as detailed below: (1) Pretreatment: Place the aluminum foil in hydrochloric acid for 2-3 minutes, rinse with pure water and set aside; (2) Eight holes: ① First group of pre-etched pits: Place the pretreated aluminum foil in a hydrochloric acid electrolyte system, first at 73~78℃, 1.6~2.0A / cm 2 Electrolysis for 10-25 seconds under the specified conditions, followed by electrolysis at 70-75℃ and 1.2-1.5 A / cm. 2 Electrolysis for 15-30 seconds under the specified conditions; ② Second group of grain boundary corrosion porosity: Place the aluminum foil treated in step ① in a sulfuric acid electrolyte system, first at 70~80℃, 1.8~2.5A / cm 2 Electrolysis for 20-35 seconds under the specified conditions, followed by electrolysis at 68-75℃ and 1.6-2.0 A / cm. 2 Electrolysis for 20-35 seconds under the specified conditions; ③ Third group of main boreholes: Place the aluminum foil treated in step ② in a sulfuric acid-hydrochloric acid-phosphoric acid mixed electrolyte system, first at 68~72℃, 1.8~2.2A / cm 2 Electrolysis for 20-40 seconds under the specified conditions, followed by electrolysis at 70-75℃ and 1.0-1.4 A / cm. 2 Electrolysis for 20-35 seconds under the specified conditions; ④ Fourth group of branch holes: Place the aluminum foil treated in step ③ in a hydrochloric acid-acetic acid mixed electrolyte system, and supplement with ultrasound, first at 62~68℃, 1.5~2.0A / cm 2 Electrolysis for 30-45 seconds under the specified conditions, followed by electrolysis at 66-70℃ and 1.0-1.3 A / cm. 2 Electrolysis for 35-55 seconds under the specified conditions; (3) Nitric acid pore enlargement: The aluminum foil after eight pore enlargements is placed in an electrolyte containing 8-12 wt% nitric acid, 0.02-0.05 wt% copper nitrate, and 0.5-0.8 wt% polyethylene glycol at 68-75°C and 1.2-1.6 A / cm. 2 Electrolysis for 6-10 minutes under the specified conditions; (4) Post-treatment: Place the expanded aluminum foil in 5~9wt% nitric acid and etch it at 55~65℃ for 1~3 minutes. After rinsing with pure water, dry it with hot air.

2. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The aluminum foil mentioned in step (1) has a thickness of 120~150μm and a purity of 99.95~99.99%.

3. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The aluminum foil described in step (1) is placed in 5wt% hydrochloric acid and pickled at 70°C for 2-3 minutes. After rinsing with pure water for 15 seconds, it is ready for use.

4. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The electrolyte composition of the hydrochloric acid system mentioned in step ① is: 8~12wt% hydrochloric acid, 0.5~1.2wt% citric acid, and 0.1~0.3wt% sodium dodecylbenzenesulfonate.

5. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The electrolyte composition of the sulfuric acid system mentioned in step ② is: 5-8 wt% sulfuric acid, 0.3-0.8 wt% sodium chloride, and 0.2-0.5 wt% disodium ethylenediaminetetraacetate.

6. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The electrolyte composition of the sulfuric acid-hydrochloric acid-phosphoric acid mixed system mentioned in step ③ is as follows: sulfuric acid 9~15wt%, hydrochloric acid 3~5wt%, phosphoric acid 1.5wt%, adipic acid 1.0~1.8wt%, and glycerol 2~4wt%.

7. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The electrolyte composition of the hydrochloric acid-acetic acid mixed system mentioned in step ④ is: 3~5wt% hydrochloric acid, 2~4wt% acetic acid, 0.1~0.3wt% cerium nitrate, and 0.8~1.5wt% polyethylene glycol.

8. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, The ultrasound conditions in step ④ are 40kHz and 110~130W.

9. The method for preparing an eight-stage perforation process for etched foil for aluminum electrolytic capacitors according to claim 1, characterized in that, In step (4), the aluminum foil after the hole is enlarged is placed in 5~9wt% nitric acid and etched at 55~65℃ for 1~3min. After being rinsed with pure water for 25s, it is dried with hot air at 80℃ for 10min.

10. The method for preparing an eight-stage perforation process of etched foil for aluminum electrolytic capacitors according to any one of claims 1 to 9, characterized in that, The etched foil prepared by the method is suitable for electrode material preparation scenarios of high-voltage aluminum electrolytic capacitors, supercapacitors, and lithium-ion battery current collectors.

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