Anode foil, its pretreatment method and ai and aluminum electrolytic capacitor for energy storage device

Abstract

The present disclosure provides an anode foil and a pretreatment method and an AI and energy storage device aluminum electrolytic capacitor, the pretreatment method comprising: ultrasonic emulsification cleaning of the anode foil, wherein the emulsion cleaning solution comprises nanocellulose crystals (NCC), a chelating agent and a dispersing agent, the mass content of NCC in the emulsion cleaning solution is 0.1% to 1%; the anode foil is washed with water; the anode foil is activated with a weak acid solution, and the weak acid solution comprises an acid solution with a mass content of 0.1% to 1%. The pretreatment method of the present disclosure is green and environmentally friendly, and the process is stable. Through NCC emulsion deoiling and decontamination, combined with weak acid solution for oxide film removal and activation, complete deoiling and uniform activation can be achieved, and the active material will not be excessively corroded and peeled off, ultimately improving the electrode foil capacity and residual core uniformity, and inhibiting the power supply voltage fluctuation under the high algorithm load of the artificial intelligence server. It can also meet the requirements of high reliability and low maintenance cost of energy storage devices.

Description

Technical Field

[0001] This disclosure relates to the field of capacitors, and in particular to anode foil and its pretreatment methods, and aluminum electrolytic capacitors suitable for artificial intelligence and energy storage devices. Background Technology

[0002] Aluminum electrolytic capacitors have advantages such as large capacity, low cost, and small size, and are widely used in electronics, home appliances, and new energy fields. As the core component of aluminum electrolytic capacitors, the quality of the electrode foil directly determines key performance characteristics such as specific capacitance. The anode foil, as the substrate of the electrode foil, requires a pretreatment process that is crucial for improving its performance. This pretreatment mainly removes oil and impurities from the anode foil surface, removes the natural oxide film, and activates it, providing a clean, uniform, and highly active surface for subsequent etching (pore formation and enlargement).

[0003] Currently, pre-corrosion treatment often employs traditional acid and alkali washing processes, or cleaning processes using conventional surfactants as emulsifiers. These methods present several problems: First, in traditional processes, acid and alkali washing simultaneously remove oil and dirt, and activate the electrode. This can lead to uneven activation and excessive corrosion of the anode foil substrate, resulting in the stripping of active materials and affecting the electrode foil capacity and uniformity of residual cores. Second, conventional emulsifiers (such as sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether) have poor biodegradability and easily remain in wastewater after use, causing environmental pollution and failing to meet the current development requirements of green manufacturing. Third, conventional emulsifiers have limited improvement on the wettability of the anode foil surface, easily leading to localized oil residue and incomplete impurity removal. This results in uneven distribution and inconsistent pore sizes during subsequent corrosion, thus reducing the specific volume of the electrode foil. Fourth, conventional emulsifiers themselves are difficult to completely remove; small amounts of residue adhere to the anode foil surface, which cannot be completely removed even after rinsing. This affects the uniformity of pore formation in subsequent corrosion processes, leading to disordered pore distribution and uneven pore sizes, ultimately reducing the overall performance of the electrode foil. Summary of the Invention

[0004] The embodiments of this disclosure provide a pretreatment method for anode foil, comprising: cleaning the anode foil with an emulsion cleaning solution under ultrasonic conditions, wherein the emulsion cleaning solution includes nanocellulose crystals (NCC), a chelating agent and a dispersant, and the mass content of the nanocellulose crystals in the emulsion cleaning solution is 0.1% to 1%; washing the anode foil with water; and activating the anode foil with a weak acid solution, wherein the weak acid solution includes an acid solution with a mass content of 0.1% to 1%.

[0005] In some embodiments, when cleaning the anode foil with an emulsion cleaning solution under ultrasonic conditions, the ultrasonic power is 50W to 200W, the cleaning temperature is 20°C to 80°C, the cleaning time is 10s to 10min, and the pH of the emulsion cleaning solution is 6.5 to 7.5.

[0006] In some embodiments, the chelating agent includes at least one of disodium ethylenediaminetetraacetate, trisodium citrate, and sodium tripolyphosphate, and the chelating agent in the emulsified cleaning solution has a mass content of 0.05% to 2%.

[0007] In some embodiments, the dispersant includes at least one of polyethylene glycol, polyvinylpyrrolidone, and sodium dodecyl sulfate, and the mass content of the dispersant in the emulsified cleaning solution is 0.01% to 1%.

[0008] In some embodiments, when the anode foil is activated with a weak acid solution, the activation temperature is 30°C to 60°C, the activation time is 10s to 60s, the pH of the weak acid solution is 2 to 4, and the weak acid solution includes one or more of sulfuric acid, phosphoric acid, and citric acid.

[0009] In some embodiments, the particle size of the nanocellulose crystals is from 10 nm to 100 nm.

[0010] In some embodiments, the weak acid solution comprises 0.3% to 0.8% phosphoric acid by mass, and has a pH of 2.5 to 3.5.

[0011] In some embodiments, the particle size of the nanocellulose crystals is 20 nm to 50 nm, the chelating agent in the emulsion cleaning solution has a mass content of 0.1% to 1%, the dispersant in the emulsion cleaning solution has a mass content of 0.05% to 0.2%, the ultrasonic power is 80 W to 120 W, the cleaning temperature of the emulsion cleaning solution is 30 °C to 60 °C, the cleaning time in the emulsion cleaning solution is 2 min to 5 min; the water washing time is 30 s to 1 min; the mass content of the weak acid solution is 0.3% to 0.8%, the activation temperature is 35 °C to 50 °C, the activation time is 20 s to 40 s, and the pH of the weak acid solution is 2.5 to 3.5.

[0012] Another embodiment of this disclosure provides an anode foil, which is an anode foil obtained according to any of the above pretreatment methods.

[0013] Another embodiment of this disclosure provides an aluminum electrolytic capacitor suitable for artificial intelligence and energy storage devices, the aluminum electrolytic capacitor including the aforementioned anode foil.

[0014] The pretreatment method disclosed herein is green and environmentally friendly, and the process is stable. It uses NCC emulsification to remove oil and dirt, and then uses a weak acid solution to remove and activate the oxide film. This method can achieve thorough degreasing and uniform activation without excessive corrosion or stripping of active materials, ultimately improving the electrode foil capacity and the uniformity of residual cores. When applied to artificial intelligence devices, it can significantly suppress power voltage fluctuations under high computing loads of artificial intelligence servers. When applied to energy storage devices, it can meet the stringent requirements of high reliability and low maintenance costs for energy storage devices during long-term charge and discharge cycles. Attached Figure Description

[0015] Figure 1 A schematic flowchart of a pretreatment method for an anode foil according to an embodiment of the present disclosure is shown.

[0016] Figure 2 A scanning electron microscope (SEM) image of the residual core prepared from the anode foil of Embodiment 1 of this disclosure is shown.

[0017] Figure 3 SEM images of residual cores prepared from the anode foil of Embodiment 2 of this disclosure are shown.

[0018] Figure 4 SEM images of residual cores prepared from the anode foil of Embodiment 3 of this disclosure are shown.

[0019] Figure 5 SEM images of the residual core prepared from the anode foil of Comparative Example 1 of this disclosure are shown.

[0020] Figure 6 SEM images of residual cores prepared from the anode foil of Embodiment 4 of this disclosure are shown.

[0021] Figure 7 SEM images of the residual core prepared from the anode foil of Comparative Example 2 of this disclosure are shown.

[0022] Figure 8 SEM images of the residual core prepared from the anode foil of Comparative Example 3 of this disclosure are shown.

[0023] Figure 9 SEM images of the residual core prepared from the anode foil of Comparative Example 4 of this disclosure are shown.

[0024] Figure 10 SEM images of the residual core prepared from the anode foil of Comparative Example 5 of this disclosure are shown. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of this disclosure will be described in detail below with reference to the accompanying drawings.

[0026] Exemplary embodiments will be described more fully below with reference to the accompanying drawings; however, these exemplary embodiments may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will enable those skilled in the art to fully understand the scope of this disclosure.

[0027] Where there is no conflict, the various embodiments of this disclosure and the features thereof in the embodiments may be combined with each other.

[0028] As used herein, the term “and / or” includes any and all combinations of one or more related enumerated entries.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular forms “a” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It will also be understood that when the terms “comprising” and / or “made of” are used in this specification, the presence of the stated feature, integral, step, operation, element, and / or component is specified, but the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof is not excluded.

[0030] Unless otherwise specified, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art. It will also be understood that terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this disclosure, and will not be interpreted as having an idealized or overly formal meaning, unless expressly so defined herein.

[0031] Nanocellulose crystals (NCC), as a novel green nanomaterial, possess strong surface activity, biodegradability, and good dispersion stability. They can be used as a solid emulsifier to stabilize Pickering emulsions. Leveraging their nanoscale particle size and surface hydroxyl properties, they form a dense adsorption layer at the liquid-liquid interface, achieving long-term emulsion stability. Simultaneously, the abundant hydroxyl groups on the NCC surface allow for adsorption with the anode foil surface, exhibiting excellent emulsification and dispersion capabilities. This effectively improves the wettability of the cleaning solution on the anode foil surface, achieving efficient degreasing and decontamination. Ultrasonic treatment enhances the fluidity of the cleaning solution, accelerates the removal of impurities and oil, and promotes uniform dispersion of NCC in the system, further stabilizing the Pickering emulsion system. The synergistic effect of these two processes significantly improves the degreasing and decontamination effect. After NCC emulsification for degreasing and decontamination, a weak acid solution is used for oxide film removal and activation before entering the borehole tank. This avoids the defects of traditional processes, achieving uniform activation without excessive corrosion or stripping of active substances. Using NCC as a solid emulsifier to stabilize Pickering emulsion, combined with ultrasonic treatment for degreasing and decontamination, and then activated with a weak acid solution, this method can be applied to a corrosion pretreatment system, effectively solving the aforementioned problems of traditional pretreatment processes.

[0032] The pretreatment method provided in this disclosure is green and environmentally friendly, and the process is stable. It removes oil and dirt through NCC emulsification, and removes and activates the oxide film with a weak acid solution. This can achieve thorough oil removal and uniform activation without excessive corrosion or stripping of active materials, ultimately improving the electrode foil capacity and the uniformity of residual core.

[0033] like Figure 1As shown, embodiments of this disclosure provide a pretreatment method for anode foil, which can be used for corrosion pretreatment, including: S101, cleaning the anode foil with an emulsion cleaning solution under ultrasonic conditions. In some embodiments, the emulsion cleaning solution includes nanocellulose crystals (NCC), a chelating agent, and a dispersant. In some embodiments, the continuously conveyed anode foil is placed in the NCC emulsion cleaning solution, which is a Pickering emulsion system stabilized with NCC as a solid emulsifier, with deionized water as the continuous phase and oil as the dispersed phase. NCC adsorbs at the water-oil interface to form a dense adsorption layer, thereby achieving emulsion stabilization. In some embodiments, the synergistic effect of ultrasonic treatment and the NCC-stabilized Pickering emulsion can promote uniform dispersion of the Pickering emulsion, enhance the fluidity of the cleaning solution, accelerate the wetting, peeling, and dispersion of oil and impurities on the anode foil surface by NCC, and further stabilize the Pickering emulsion system, avoid stratification, improve degreasing and decontamination efficiency and cleanliness, and ensure that the anode foil surface is free of oil and impurities. In some embodiments, the chelating agent can form a stable chelate with metal impurity ions on the surface of the anode foil, preventing impurity residue from affecting subsequent weak acid activation and pore formation processes. In some embodiments, the dispersant can prevent NCC from agglomerating in the emulsion cleaning solution, ensuring the stability of the emulsion cleaning solution and improving the uniformity of degreasing and decontamination.

[0034] In some embodiments, the mass content of nanocellulose crystals in the emulsified cleaning solution is 0.1% to 1%. Within this range, a stable Pickering emulsion can be formed, resulting in excellent emulsification and cleaning effects, ensuring uniformity of subsequent activation, and thus improving the performance of the electrode foil. If the concentration is too low, the cleaning will be incomplete; if the concentration is too high, the dispersion will be uneven, the cost will increase, and the activation effect will be affected. In some embodiments, the mass content of nanocellulose crystals in the emulsified cleaning solution is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any suitable value between them.

[0035] like Figure 1 As shown, in some embodiments, the pretreatment method of this disclosure further includes: S102, washing the anode foil with water. After cleaning with the emulsion cleaning solution, washing with water can remove the residual emulsion cleaning solution from the surface, avoiding the residual emulsion cleaning solution from affecting the subsequent weak acid activation effect.

[0036] like Figure 1As shown, in some embodiments, the pretreatment method of this disclosure further includes: S103, using a weak acid solution to activate the anode foil with a weak acid solution to remove the oxide film and perform surface activation treatment. In some embodiments, the weak acid solution includes an acid solution with a mass content of 0.1% to 1%. This weak acid solution can remove the natural oxide film on the surface of the anode foil, while gently activating the surface of the anode foil without excessively corroding the anode foil substrate, avoiding the peeling off of active materials, ensuring uniform activation, and laying a good foundation for subsequent pore formation processes. In some embodiments, the mass content of the weak acid solution is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any suitable value between them. Too low a concentration affects the quality and efficiency of the natural oxide film and surface activation, while too high a concentration easily leads to excessive corrosion of the anode foil substrate, causing the active materials to peel off. In some embodiments, the weak acid solution includes one or more of sulfuric acid, phosphoric acid, and citric acid.

[0037] In some embodiments, the pretreatment method disclosed herein further includes a secondary water wash of the anode foil. The secondary water wash can remove residual weak acid solution from the surface, providing a clean, uniformly activated surface for subsequent pore-forming (etching) processes.

[0038] This disclosure uses NCC as an emulsifier. NCC is a biodegradable material, environmentally friendly, and produces no secondary pollution, meeting the requirements of green manufacturing and environmental protection policies, thus solving the problem of poor environmental performance of traditional emulsifiers. Simultaneously, NCC combined with ultrasonic treatment, through the stabilizing effect of Pickering emulsion, achieves efficient degreasing and decontamination, ensuring that the anode foil surface is free of oil and impurities. Furthermore, this disclosure adds a weak acid solution treatment step after NCC emulsification for degreasing and decontamination, but before entering the borehole tank. This step is specifically used to remove the natural oxide film on the anode foil surface and for activation. Compared to traditional alkaline degreasing and acidic activation processes, the weak acid treatment is gentler, achieving uniform activation without excessively corroding the anode foil substrate, preventing the stripping of active materials, and effectively solving the problems of uneven activation and excessive corrosion in traditional processes. This disclosure employs a combination of NCC emulsion cleaning solution and a weak acid activation system, ensuring a continuous and controllable process. The NCC emulsion cleaning solution thoroughly removes oil and impurities, providing a clean surface for weak acid activation. The weak acid activation precisely removes and activates the oxide film. The synergistic effect of these two processes results in a more uniform distribution of etched holes in the subsequent pore-forming (corrosion) process, improving electrode foil capacity and residual core uniformity. Furthermore, NCC, as a solid emulsifier, stabilizes the Pickering emulsion system, exhibiting good dispersion stability in a neutral cleaning system and exhibiting low foaming and stratification characteristics. This ensures the continuity and stability of the pretreatment process, reduces the probability of production failures, and improves production efficiency. Simultaneously, the stable properties of the Pickering emulsion allow oil to be evenly dispersed in the cleaning solution, preventing secondary adhesion of oil to the anode foil surface and further enhancing cleaning cleanliness, laying a solid foundation for subsequent weak acid activation. NCC, acting as a solid emulsifier to stabilize the Pickering emulsion, forms an extremely thin temporary adsorption layer on the anode foil surface. Combined with the peeling effect of ultrasonic treatment, this effectively assists in removing impurities and dispersed oil stains, and the residue easily detaches during subsequent rinsing, preventing any impact on the subsequent weak acid activation process. The controllable concentration of the weak acid solution and treatment conditions further ensure the surface quality of the anode foil after pretreatment, thereby improving the specific volume of the electrode foil and product consistency, and guaranteeing the stability of the subsequent aperture formation process. This pretreatment method is simple, easy to operate, requires no major modifications to existing production equipment, has controllable costs, and is easy to promote and apply industrially. Compared to traditional methods, it is easier to obtain a thoroughly degreased and uniformly activated anode foil surface, resulting in superior final product capacity and core uniformity.

[0039] In some embodiments, when cleaning the anode foil with an emulsion cleaning solution under ultrasonic conditions, the ultrasonic power is 50W to 200W, the cleaning temperature is 20°C to 80°C, the cleaning time is 10s to 10min, and the pH of the emulsion cleaning solution is 6.5 to 7.5. In some embodiments, the ultrasonic power is 50W, 70W, 90W, 110W, 130W, 150W, 170W, 180W, 200W, or any suitable value between them. Too low an ultrasonic power results in insufficient energy, which is not conducive to removing stubborn oil stains and overcoming the aggregation tendency of NCC; too high an ultrasonic power may cause physical damage to the surface of the anode foil substrate (such as excessive cavitation corrosion), compromising surface smoothness. In some embodiments, the ultrasonic power is 80W to 120W. Ultrasonic treatment within this power range can synergistically work with NCC-stabilized Pickering emulsions, effectively removing oil and impurities from the anode foil surface without damaging the anode foil substrate. Simultaneously, it promotes uniform dispersion of NCC in the cleaning solution, further stabilizing the Pickering emulsion system, preventing NCC agglomeration and emulsion stratification, and further improving degreasing and cleaning effects and process stability. In some embodiments, too short a time may result in insufficient oil removal, while too long a time will reduce production efficiency. In some embodiments, the cleaning time in the emulsified cleaning solution is 2 to 5 minutes. In some embodiments, the cleaning temperature is 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, or any suitable value between them. Too low a temperature may reduce the emulsification efficiency of NCC, prolong the cleaning time, and decrease production efficiency; too high a temperature will increase energy consumption and cause excessively rapid water evaporation. In some embodiments, the cleaning temperature of the emulsified cleaning solution is 30°C to 60°C.

[0040] In some embodiments, the chelating agent includes at least one selected from disodium ethylenediaminetetraacetate (EDTA-2Na), trisodium citrate, and sodium tripolyphosphate, and the chelating agent in the emulsion cleaning solution has a mass content of 0.05% to 2%. In some embodiments, the mass content of the chelating agent in the emulsion cleaning solution is 0.05%, 0.1%, 0.5%, 0.8%, 1.1%, 1.4%, 1.7%, 2%, or any suitable value between them. If the mass content of the chelating agent is too low, its chelating ability for metal impurity ions will decrease; if the mass content of the chelating agent is too high, it may lead to an increase in the adsorption of the chelating agent itself on the anode foil surface, increasing the subsequent cleaning burden and cost. In some embodiments, the mass content of the chelating agent in the emulsion cleaning solution is 0.1% to 1%.

[0041] In some embodiments, the dispersant comprises at least one selected from polyethylene glycol, polyvinylpyrrolidone, and sodium dodecyl sulfate, and the mass content of the dispersant in the emulsion cleaning solution is 0.01% to 1%. In some embodiments, the mass content of the dispersant in the emulsion cleaning solution is 0.01%, 0.05%, 0.08%, 0.12%, 0.3%, 0.5%, 0.7%, 0.8%, 1%, or any suitable value between them. Too low a mass content of the dispersant is detrimental to the dispersion of NCC; too high a mass content of the dispersant increases the burden and cost of subsequent cleaning. In some embodiments, the mass content of the dispersant in the emulsion cleaning solution is 0.05% to 0.2%.

[0042] In some embodiments, when the anode foil is activated with a weak acid solution, the activation temperature is 30°C to 60°C, the activation time is 10s to 60s, and the pH of the weak acid solution is 2 to 4. In some embodiments, the activation temperature is 30°C, 40°C, 50°C, 60°C, or any suitable value between them. If the activation temperature is too low, the efficiency of removing the natural oxide film decreases; if the activation temperature is too high, excessive corrosion of the anode foil surface is likely. In some embodiments, the activation temperature is 35°C to 50°C. In some embodiments, the activation time is 10s, 20s, 30s, 40s, 50s, 60s, or any suitable value between them. If the activation time is too short, the removal of the natural oxide film may not be thorough; if the activation time is too long, excessive corrosion is likely. In some embodiments, the activation time is 20s to 40s. If the pH of the weak acid solution is too low, excessive corrosion is likely; if the pH of the weak acid solution is too high, the activation efficiency decreases. In some embodiments, the pH of the weak acid solution is 2.5 to 3.5.

[0043] In some embodiments, the particle size of the nanocellulose crystals is from 10 nm to 100 nm. In some embodiments, the particle size of the nanocellulose crystals is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or any suitable value between them. If the particle size of the nanocellulose crystals is too large, it can easily cause sedimentation; if the particle size is too small, the stability of the nanocellulose crystals will be reduced. In some embodiments, the particle size of the nanocellulose crystals is from 20 nm to 50 nm. NCC in this particle size range has superior emulsifying and dispersing properties, can better wet the anode foil surface, and improves the degreasing and cleaning effect.

[0044] In some embodiments, the weak acid solution comprises 0.3% to 0.8% phosphoric acid by mass, with a pH of 2.5 to 3.5. Under these conditions, the oxide film is removed more thoroughly, activation is more uniform, and the corrosiveness to the anode foil substrate is minimized, thus minimizing the stripping of active materials and further enhancing the surface activity of the anode foil after pretreatment. In some embodiments, the water rinsing time is 30 seconds to 1 minute, and the second water rinsing time is 50 seconds to 2 minutes.

[0045] The electrode foil prepared according to the method provided in the embodiments of this disclosure, when applied to artificial intelligence devices such as AI servers, can significantly suppress power voltage fluctuations under high computing loads of AI servers; when applied to energy storage devices, it can meet the stringent requirements of high reliability and low maintenance costs for energy storage devices during long-term charge-discharge cycles.

[0046] The following description, in conjunction with specific embodiments, will provide a better understanding of this disclosure.

[0047] Example 1 A method for pre-treatment of electrode foil for aluminum electrolytic capacitors, specifically for the pre-treatment of anode foil with a thickness of 130 μm, includes the following steps: (1) Neutral emulsion cleaning: Prepare a neutral NCC emulsion cleaning solution. This cleaning solution is a Pickering emulsion system stabilized by NCC as a solid emulsifier. Deionized water is used as the solvent (continuous phase). NCC (particle size 20nm, solid emulsifier), EDTA-2Na, and polyethylene glycol are added. The mass content of NCC is 0.1wt%, the mass content of EDTA-2Na is 0.1wt%, and the mass content of polyethylene glycol is 0.05wt%. The pH value is adjusted to 7.0. NCC adsorbs at the water-oil interface to form a dense adsorption layer, thereby stabilizing the Pickering emulsion. Place a 130μm thick optical foil in this cleaning solution and ultrasonically treat it (power 100W) for 2min at 40℃ to promote uniform dispersion of the Pickering emulsion and improve the degreasing and decontamination effect. (2) Cleaning: The anode foil is placed in a water washing tank and cleaned for 1 minute to remove the residual emulsified cleaning solution on the surface; (3) Weak acid activation: The rinsed anode foil is placed in a 0.5wt% dilute phosphoric acid solution (pH 3.0) and treated at 40℃ for 30s to remove the natural oxide film on the surface and activate it; (4) Secondary cleaning: The anode foil activated by weak acid is placed into a water washing tank and cleaned for 1.5 minutes to remove the residual dilute phosphoric acid solution on the surface.

[0048] Example 2 A method for pre-treating electrode foil for aluminum electrolytic capacitors, specifically for anode foil pre-treatment, comprises the following steps: (1) Neutral emulsion cleaning: Prepare a neutral NCC emulsion cleaning solution. This cleaning solution is a Pickering emulsion system stabilized by NCC as a solid emulsifier. Deionized water is used as the solvent (continuous phase). NCC (particle size 50nm, solid emulsifier), trisodium citrate, and polyvinylpyrrolidone are added. The mass content of NCC is 1wt%, the mass content of trisodium citrate is 0.5wt%, and the mass content of polyvinylpyrrolidone is 0.2wt%. The pH value is adjusted to 6.8. NCC adsorbs at the water-oil interface to form a dense adsorption layer, thereby stabilizing the Pickering emulsion. Place a 130μm thick optical foil in this cleaning solution and ultrasonically treat it (power 120W) for 5min at 60℃ to promote uniform dispersion of the Pickering emulsion and improve the degreasing and decontamination effect. (2) Cleaning: The anode foil is placed in a water washing tank and cleaned for 1 minute to remove the residual emulsified cleaning solution on the surface; (3) Weak acid activation: The rinsed anode foil is placed in a 0.8wt% dilute sulfuric acid solution (pH 2.5) and treated at 50℃ for 20s to remove the natural oxide film on the surface and activate it; (4) Secondary cleaning: The anode foil activated by weak acid is placed into the water washing tank and cleaned for 1.5 minutes to remove the residual dilute sulfuric acid solution on the surface.

[0049] Example 3 A method for pre-treating electrode foil for aluminum electrolytic capacitors, specifically for anode foil pre-treatment, comprises the following steps: (1) Neutral emulsion cleaning: Prepare a neutral NCC emulsion cleaning solution. This cleaning solution is a Pickering emulsion system stabilized by NCC as a solid emulsifier. Deionized water is used as the solvent (continuous phase). NCC (particle size 30nm, solid emulsifier), sodium tripolyphosphate, and sodium dodecyl sulfate are added. The mass content of NCC is 0.5wt%, the mass content of sodium tripolyphosphate is 1wt%, and the mass content of sodium dodecyl sulfate is 0.1wt%. The pH value is adjusted to 7.2. NCC is adsorbed at the water-oil interface to form a dense adsorption layer, thereby stabilizing the Pickering emulsion. A 130μm thick optical foil is placed in this cleaning solution and ultrasonically treated (power 80W) for 3min at 30℃ to promote uniform dispersion of the Pickering emulsion and improve the degreasing and decontamination effect. (2) Cleaning: The anode foil is placed in a water washing tank and cleaned for 1 minute to remove the residual emulsified cleaning solution on the surface; (3) Weak acid activation: The rinsed anode foil is placed in a 0.3wt% dilute citric acid solution (pH 3.5) and treated at 35℃ for 40s to remove the natural oxide film on the surface and activate it; (4) Secondary cleaning: The anode foil activated by weak acid is placed into the water washing tank and cleaned for 1.5 minutes to remove the residual dilute citric acid solution on the surface.

[0050] Example 4 and Comparative Examples 1-2 only changed the mass content of NCC, while the other conditions were completely the same as in Example 1, to explore the effect of different NCC concentrations on the pretreatment effect.

[0051] Comparative Example 1 A method for pretreatment of electrode foil for aluminum electrolytic capacitors, comprising the following steps: (1) Neutral emulsion cleaning: Prepare a neutral NCC emulsion cleaning solution, using deionized water as the solvent (continuous phase), add NCC (particle size 20nm), EDTA-2Na, and polyethylene glycol, wherein the mass content of NCC is 0.05wt%, the mass content of EDTA-2Na is 0.1wt%, and the mass content of polyethylene glycol is 0.05wt%, and adjust the pH value to 7.0; under 40℃ conditions, ultrasonic treatment (power 100W) for 2min; Steps (2)-(4) are exactly the same as in Example 1.

[0052] Example 4 A method for pretreatment of electrode foil for aluminum electrolytic capacitors, comprising the following steps: (1) Neutral emulsion cleaning: Prepare a neutral NCC emulsion cleaning solution, using deionized water as the solvent (continuous phase), add NCC (particle size 20nm), EDTA-2Na, and polyethylene glycol, wherein the mass content of NCC is 0.8wt%, the mass content of EDTA-2Na is 0.1wt%, and the mass content of polyethylene glycol is 0.05wt%, and adjust the pH value to 7.0; under 40℃ conditions, ultrasonic treatment (power 100W) for 2min; Steps (2)-(4) are exactly the same as in Example 1.

[0053] Comparative Example 2 A method for pretreatment of electrode foil for aluminum electrolytic capacitors, comprising the following steps: (1) Neutral emulsion cleaning: Prepare a neutral NCC emulsion cleaning solution, using deionized water as the solvent (continuous phase), and add NCC (particle size 20nm), EDTA-2Na, and polyethylene glycol, wherein the mass content of NCC is 1.5wt%, the mass content of EDTA-2Na is 0.1wt%, and the mass content of polyethylene glycol is 0.05wt%, and adjust the pH value to 7.0; under 40℃ conditions, ultrasonic treatment (power 100W) for 2min; Steps (2)-(4) are exactly the same as in Example 1.

[0054] Comparative Example 3 (no ultrasonic treatment, all other conditions are exactly the same as in Example 1) A method for pre-treating electrode foil for aluminum electrolytic capacitors, specifically for anode foil pre-treatment, comprises the following steps: (1) Neutral emulsification cleaning: Prepare a neutral NCC emulsification cleaning solution with the same formula and pH value as in Example 1 (NCC mass content 0.1wt%, particle size 20nm, EDTA-2Na 0.1wt%, polyethylene glycol 0.05wt%, pH=7.0); place a 130μm thick optical foil in the cleaning solution for 2min, and do not perform ultrasonic treatment at 40℃; Steps (2)-(4) are exactly the same as in Example 1.

[0055] Comparative Example 4 (Traditional neutral surfactant cleaning + conventional acid activation) A method for pre-treating electrode foil for aluminum electrolytic capacitors, specifically for anode foil pre-treatment, comprises the following steps: (1) Neutral cleaning: Prepare a neutral cleaning solution using deionized water as the solvent, and add sodium dodecylbenzenesulfonate (a conventional emulsifier), EDTA-2Na, and polyethylene glycol, wherein the mass content of sodium dodecylbenzenesulfonate is 0.1wt%, the mass content of EDTA-2Na is 0.1wt%, and the mass content of polyethylene glycol is 0.05wt%. Adjust the pH value to 7.0. Place a 100μm thick continuous conveying anode foil in the cleaning solution and ultrasonically treat it (power 100W) for 2min at 40℃. (2) Cleaning: Same as in Example 1; (3) Conventional acid activation: The rinsed anode foil was placed in a 5wt% dilute sulfuric acid solution (pH 1.0) and treated at 40℃ for 30s; (4) Second cleaning: Same as in Example 1.

[0056] Comparative Example 5 (Traditional neutral surfactant cleaning + weak acid activation) A method for pre-treating electrode foil for aluminum electrolytic capacitors, specifically for anode foil pre-treatment, comprises the following steps: (1) Neutral cleaning: Prepare a neutral cleaning solution using deionized water as the solvent, and add sodium dodecylbenzenesulfonate (a conventional emulsifier), EDTA-2Na, and polyethylene glycol, wherein the mass content of sodium dodecylbenzenesulfonate is 0.1wt%, the mass content of EDTA-2Na is 0.1wt%, and the mass content of polyethylene glycol is 0.05wt%. Adjust the pH value to 7.0. Place a 130μm thick optical foil in the cleaning solution and ultrasonically treat it at 40℃ (power 100W) for 2min. (2) Cleaning: Same as in Example 1 (washing in a water bath for 1 minute); (3) Weak acid activation: exactly the same as in Example 1 (0.5wt% dilute phosphoric acid, pH=3.0, 40℃ treatment for 30s); (4) Secondary cleaning: Same as in Example 1 (water washing tank cleaning for 1.5 min).

[0057] The pretreated anode foils from the examples and comparative examples were subjected to the same perforation process (temperature controlled at 70°C, hydrochloric acid / sulfuric acid mixed medium (1 mol / L hydrochloric acid, 5 mol / L sulfuric acid), a 5-stage perforation process, and a current density of 5 A / cm²). 2 Each hole-forming process lasts 5 minutes; the hole-expanding process is controlled at 70℃, using nitric acid as the medium (nitric acid concentration 1.5 mol / L), and a current density of 0.5 A / cm². 2 (The initial etched holes were further enlarged and deepened by 15 minutes of hole expansion) to prepare an etched foil. The key properties of the etched foil were tested using the following methods, and the test results are shown in Table 1 and... Figures 2 to 10 As shown.

[0058] Specific volume test The etched foil was placed in a specific boric acid electrolyte (90 g / L) for constant voltage energy formation to generate an alumina dielectric film on its surface. Then, the voltage was increased (to 525±3V). The foil, along with the auxiliary cathode, was immersed in a test solution (80 g / L ammonium pentaborate) as the anode. Its electrostatic capacitance was measured using a capacitance meter (accuracy greater than ±0.3%, test frequency 120Hz), with the unit being μF / cm².

[0059] Residual core thickness test The sample was embedded and cured with epoxy resin under vacuum to prevent the pores from collapsing. After grinding and argon ion polishing to remove the surface deformation layer, carbon was sprayed to conduct electricity. Then, the thickness of the residual core was observed and measured in electron microscopy using backscattered electron (BSE) mode (5-10kV) by taking advantage of the high contrast between the bright aluminum substrate and the dark resin inside the pores.

[0060] Table 1 The electrode foils prepared in Examples 1-4 of this disclosure have significantly higher specific capacities than the comparative examples, and their residual core thickness reaches over 11.5 μm with high uniformity, significantly superior to the comparative examples. This disclosure uses NCC as a solid emulsifier to stabilize the Pickering emulsion system, combined with ultrasonic treatment. The synergistic effect of these two methods achieves efficient degreasing and decontamination, ensuring that the anode foil surface is free of oil and impurities. Subsequently, a weak acid solution treatment is added before entering the pore-forming tank, which gently removes the natural oxide film and achieves uniform activation without excessively corroding the anode foil substrate or stripping the active material. This provides a clean, uniform, and highly active surface for the subsequent pore-forming process, thereby significantly improving the specific capacity and residual core uniformity of the electrode foil and ensuring product performance stability.

[0061] In contrast, Comparative Examples 4-5, which used traditional emulsifiers for cleaning, failed to form a stable Pickering emulsion, resulting in poor degreasing and decontamination effects. The use of conventional high-concentration acid activation easily led to uneven activation and excessive corrosion, resulting in poor uniformity of the residual core. In Comparative Example 3, without ultrasonic treatment, the Pickering emulsion could not be evenly dispersed, the NCC adsorption layer was unevenly distributed, and the emulsification degreasing and decontamination effects were significantly reduced. Ultimately, the specific volume of the electrode foil and the uniformity of the residual core were significantly worse than those of the embodiments disclosed in this disclosure, fully demonstrating the significant advantages of this disclosure compared to traditional methods.

[0062] Comparing Examples 1, 4, and Comparative Examples 1-2, it is evident that when the NCC concentration is too low (Comparative Example 1, 0.05 wt%), a dense adsorption layer cannot be formed at the water-oil interface, resulting in poor Pickering emulsion stability, insufficient emulsification and cleaning effect, and a small amount of oil residue remaining on the anode foil surface, leading to generally poor uniformity in subsequent activation. When the NCC concentration is too high (Comparative Example 2, 1.5 wt%), the Pickering emulsion becomes too viscous, resulting in poor dispersibility. Even after ultrasonic treatment, local agglomeration still occurs, leading to uneven cleaning of the anode foil surface, NCC residue in some areas, affecting the subsequent activation effect, and increasing reagent costs, resulting in low cost-effectiveness. The NCC content disclosed in this invention is 0.1 wt%-1 wt%. Within this range, a stable Pickering emulsion can be formed, with excellent emulsification and cleaning effect, ensuring uniformity in subsequent activation and thus improving electrode foil performance. Too low a concentration results in incomplete cleaning, while too high a concentration leads to uneven dispersion, increased costs, and negatively impacts the activation effect.

[0063] In Comparative Example 3, without ultrasonic treatment, the Pickering emulsion could not be uniformly dispersed, the NCC adsorption layer was unevenly distributed, the emulsification and degreasing effects were significantly reduced, and there was a lot of residual oil and impurities on the anode foil surface; subsequent weak acid activation could not fully remove the natural oxide film on the surface, the activation was uneven, and the surface smoothness and activity of the electrode foil were insufficient. Compared with Example 1 (with ultrasonic treatment), the electrode foil capacity decreased by 3.5%.

[0064] In Comparative Example 4, the use of traditional surfactant cleaning and high-concentration strong acid activation not only resulted in poor degreasing effect, but also caused excessive corrosion of the anode foil surface by the strong acid, leading to uneven surface roughness, over-activation, reduced mechanical properties of the electrode foil, and a 2.1% decrease in capacity.

[0065] In Comparative Example 5, a conventional surfactant (sodium dodecylbenzenesulfonate) was used instead of the NCC solid emulsifier. Even under the same weak acid activation conditions as in Example 1, the cleaning effect was significantly worse than that in Example 1. The conventional surfactant has poor emulsification stability and insufficient degreasing and decontamination capabilities. Trace amounts of oil residue remained on the anode foil surface, preventing the weak acid activation from being fully effective. After activation, the surface activity was lower than in Example 1, and the electrode foil capacity decreased by 4.1%. This indicates that the Pickering emulsion system formed by the NCC solid emulsifier plays a crucial role in improving the pretreatment effect.

[0066] Example embodiments have been disclosed herein, and while specific terminology has been used, it is for illustrative purposes only and should be construed as such, and is not intended to be limiting. In some instances, it will be apparent to those skilled in the art that features, characteristics, and / or elements described in connection with particular embodiments may be used alone, or in combination with features, characteristics, and / or elements described in connection with other embodiments, unless otherwise expressly indicated. Therefore, those skilled in the art will understand that various changes in form and detail may be made without departing from the scope of this disclosure as set forth by the appended claims.

Claims

1. A pretreatment method for anode foil, characterized in that, include: An anode foil is cleaned using an emulsion cleaning solution under ultrasonic conditions. The emulsion cleaning solution includes nanocellulose crystals (NCC), chelating agents, and dispersants. The mass content of the nanocellulose crystals in the emulsion cleaning solution is 0.1% to 1%, and the particle size of the nanocellulose crystals is 10 nm to 100 nm. The anode foil is washed with water; The anode foil is activated by a weak acid solution, wherein the weak acid solution comprises an acid solution with a mass content of 0.1% to 1%. When cleaning the anode foil with an emulsion cleaning solution under ultrasonic conditions, the ultrasonic power is 50W to 200W, the cleaning temperature is 20℃ to 80℃, the cleaning time is 10s to 10min, and the pH of the emulsion cleaning solution is 6.5 to 7.

5.

2. The pretreatment method according to claim 1, characterized in that, The chelating agent includes at least one of disodium ethylenediaminetetraacetate, trisodium citrate, and sodium tripolyphosphate, and the mass content of the chelating agent in the emulsified cleaning solution is 0.05% to 2%.

3. The pretreatment method according to claim 1, characterized in that, The dispersant includes at least one of polyethylene glycol, polyvinylpyrrolidone, and sodium dodecyl sulfate, and the mass content of the dispersant in the emulsified cleaning solution is from 0.01% to 1%.

4. The pretreatment method according to claim 1, characterized in that, When the anode foil is activated with a weak acid solution, the activation temperature is 30°C to 60°C, the activation time is 10s to 60s, the pH of the weak acid solution is 2 to 4, and the weak acid solution includes one or more of sulfuric acid, phosphoric acid, and citric acid.

5. The pretreatment method according to claim 1, characterized in that, The weak acid solution comprises 0.3% to 0.8% phosphoric acid by mass and has a pH of 2.5 to 3.

5.

6. The pretreatment method according to any one of claims 1 to 5, characterized in that, The nanocellulose crystals have a particle size of 20 nm to 50 nm, the chelating agent in the emulsion cleaning solution has a mass content of 0.1% to 1%, the dispersant in the emulsion cleaning solution has a mass content of 0.05% to 0.2%, the ultrasonic power is 80 W to 120 W, the cleaning temperature of the emulsion cleaning solution is 30 °C to 60 °C, and the cleaning time in the emulsion cleaning solution is 2 min to 5 min. The water washing time is 30 seconds to 1 minute; The weak acid solution has a mass content of 0.3% to 0.8%, an activation temperature of 35°C to 50°C, an activation time of 20s to 40s, and a pH of 2.5 to 3.

5.

7. An anode foil, characterized in that, The anode foil is an anode foil obtained by the pretreatment method according to any one of claims 1 to 6.

8. An aluminum electrolytic capacitor, characterized in that, Suitable for artificial intelligence and energy storage devices, the aluminum electrolytic capacitor includes the anode foil as described in claim 7.

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