Aluminum paste, electrode foil, and methods for preparing electrode foil

Abstract

This application relates to the field of electrode foil technology, and provides aluminum paste, electrode foil, and a method for preparing the electrode foil. The aluminum paste includes aluminum powder, a modified binder, a dispersant, and a solvent. The modified binder includes a binder material grafted with multiple modified groups, wherein the modified groups contain at least one of hydroxyl and carboxyl groups. This application employs a synergistic combination of modified binder and dispersant to reduce the introduction of organic materials into the aluminum paste, thereby improving the uniformity of aluminum powder dispersion and preventing aluminum powder agglomeration, thus improving the capacity and mechanical properties of the electrode foil.

Description

Technical Field

[0001] This application relates to the field of electrode foil technology, and in particular to aluminum paste, electrode foil, and methods for preparing electrode foil. Background Technology

[0002] Hot-pressed electrode foil is formed by coating an aluminum powder slurry onto the surface of an aluminum substrate and then sintering it to create an electrode foil with a uniform distribution and a large specific surface area. To ensure the stability of the aluminum powder slurry coating on the aluminum substrate, binders such as acrylates, cellulose compounds, polyurethanes, and epoxy resins are added to the aluminum slurry. These binders are usually used in conjunction with other additives (such as wetting agents, surfactants, and defoamers) to improve the uniformity of aluminum slurry dispersion and reduce aluminum powder agglomeration and sedimentation. However, the introduction of additional organic additives increases the burden of degreasing during the preparation process, which can easily leave impurity atoms in the sintered electrode foil and affect the surface structure of the electrode foil, thereby reducing its capacity and mechanical properties. Summary of the Invention

[0003] Therefore, it is necessary to provide aluminum paste, electrode foil, and a method for preparing the electrode foil that can improve the uniformity of aluminum paste dispersion and reduce agglomerated aluminum paste while reducing the amount of additives, thereby improving the capacity and mechanical properties of the electrode foil.

[0004] In a first aspect, this application provides an aluminum paste comprising aluminum powder, a modified binder, a dispersant, and a solvent. The modified binder comprises a binder grafted with multiple modified groups, wherein the modified groups contain at least one of hydroxyl and carboxyl groups.

[0005] In some embodiments, the adhesive material satisfies at least one of the following conditions:

[0006] (1) The bonding material includes at least one of cellulose adhesives, acrylic adhesives, polyurethane adhesives and epoxy resin adhesives;

[0007] (2) The weight-average molecular weight of the bonding material is 20,000 to 215,000.

[0008] In some embodiments, the modifying group satisfies at least one of the following conditions:

[0009] (1) The modified group also contains at least one of the following: chain alkyl groups, polyether groups, epoxy groups and amino groups of C8~29;

[0010] (2) The modified groups include at least one of polyethylene glycol groups, citric acid groups, polyacrylic acid groups and polymethacrylic acid groups.

[0011] In some embodiments, the binder material includes hydroxyethyl cellulose, the weight-average molecular weight of which is 90,000 to 150,000; and the modifying groups include citric acid groups.

[0012] In some embodiments, the mass ratio of the binder to the modified groups is 1:(1~8).

[0013] In some embodiments, the aluminum paste satisfies at least one of the following conditions:

[0014] (1) The solid content of the aluminum paste is 45%~70%;

[0015] (2) The mass percentage of modified binder in the aluminum paste is 2% to 10%;

[0016] (3) The mass percentage of dispersant in the aluminum paste is 0.2%~2%;

[0017] (4) The volume average particle size Dv50 of aluminum powder is 2μm~10μm;

[0018] (5) The dispersant includes at least one of polyethylene glycol, sodium hexametaphosphate, polyacrylates and styrene-maleic anhydride copolymers;

[0019] (6) The solvent includes at least one of water, propylene glycol methyl ether, diethylene glycol and ethylene glycol.

[0020] Secondly, this application also provides an electrode foil, the electrode foil including a substrate and a surface layer disposed on at least one side of the substrate, the surface layer being made of aluminum paste as in the first aspect.

[0021] Thirdly, this application also provides a method for preparing an electrode foil, the method comprising:

[0022] The aluminum paste of the first aspect is coated onto at least one side surface of the substrate and dried to obtain a dried foil;

[0023] Electrode foil is prepared by sequentially performing degreasing, sintering, and formation treatments on the dried foil to form a surface layer on the substrate.

[0024] In some embodiments, the degreasing treatment includes: sequentially performing a first degreasing treatment and a second degreasing treatment on the dried foil; wherein, the temperature of the first degreasing treatment is 150℃~250℃, the holding time is 0.5h~1.5h, and the heating rate is 0.5℃ / min~1.5℃ / min; the temperature of the second degreasing treatment is 300℃~400℃, the holding time is 0.5h~1.5h, and the heating rate is 0.5℃ / min~1.5℃ / min.

[0025] In some embodiments, the preparation method satisfies at least one of the following conditions:

[0026] (1) The drying temperature is 40℃~80℃ and the time is 10min~15min;

[0027] (2) Before degreasing the dried foil, the preparation method also includes: cracking the dried slurry layer in the dried foil;

[0028] (3) The sintering temperature is 600℃~650℃, the holding time is 8h~12h, and the heating rate is 0.5℃ / min~1.5℃ / min.

[0029] Compared with traditional technologies, this application has at least the following beneficial effects:

[0030] This application incorporates a modified binder containing at least one hydrophilic dispersing group, either carboxyl or hydroxyl, into aluminum paste. This modified binder adsorbs onto the surface of aluminum powder, improving dispersion uniformity through electrostatic repulsion and forming a physical barrier layer to prevent agglomeration or sedimentation of aluminum powder particles during storage and use, thus enhancing storage stability. Simultaneously, the modified binder and dispersant work synergistically to maintain a uniform and stable dispersion of aluminum powder particles in the paste, creating favorable conditions for the subsequent preparation of a densely packed electrode foil with uniform pore size. This application also avoids the additional introduction of surfactants and other additives, thereby reducing the burden of degreasing treatment, effectively reducing residual impurities and surface structural defects, resulting in an electrode foil with superior capacity and mechanical properties. Attached Figure Description

[0031] Figure 1 This is a SEM image of the electrode foil prepared in Example 1 of this application;

[0032] Figure 2 This is a SEM image of the electrode foil prepared in Comparative Example 4 of this application. Detailed Implementation

[0033] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are only for illustrating the present application and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to make the disclosure of the present application more thorough and comprehensive. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. In addition, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0034] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0035] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0036] In traditional techniques, binders and surfactants are added to the aluminum paste. The surfactants adsorb onto the surface of the aluminum powder, forming hydrophobic or hydrophilic long chains, which improves the uniformity of aluminum powder dispersion and reduces agglomeration, thereby ensuring the surface stability of the foil after sintering and reducing aluminum powder shedding. However, the surfactants adsorbed on the aluminum powder are difficult to remove during the degreasing process, and can easily form residual impurities during sintering. At the same time, the surfactants adsorbed on the surface of the aluminum powder may hinder the contact of the aluminum powder during sintering, affecting the surface smoothness and density of the electrode foil.

[0037] Based on this, the first aspect of this application provides an aluminum paste, comprising aluminum powder, a modified binder, a dispersant, and a solvent. The modified binder comprises a binder grafted with multiple modified groups, wherein the modified groups contain at least one of hydroxyl and carboxyl groups.

[0038] In some embodiments, the bonding material includes at least one of cellulose-based adhesives, acrylate adhesives, polyurethane adhesives, and epoxy resin adhesives. It is understood that a suitable bonding material can be selected based on the bonding requirements of the adhesive and the properties of the aluminum paste.

[0039] Alternatively, the cellulose binder may be hydroxyethyl cellulose.

[0040] Optionally, the weight-average molecular weight of the binder is 20,000 to 215,000, for example, 20,000, 40,000, 60,000, 80,000, 100,000, 120,000, 140,000, 160,000, 180,000, 200,000, or 215,000; alternatively, it can be 90,000 to 150,000. The number-average molecular weight of the binder selected in this application results in high accessibility of grafting reaction sites, giving the modified binder good water solubility and moderate viscosity, thus preventing flocculation in the slurry and ensuring good flowability. If the molecular weight of the binder is relatively large, it may lead to poor grafting uniformity and high viscosity, resulting in difficulties in slurry coating. If the molecular weight of the binder is relatively small, the adhesion of the modified binder will decrease, making it easy for the slurry layer to delaminate during subsequent processing.

[0041] It should be noted that, in this application, the modified group containing at least one of hydroxyl and carboxyl groups means that the modified group can be a group containing hydroxyl, a group containing carboxyl, or a group containing both hydroxyl and carboxyl groups. The modified group can be at least one of hydroxyl and carboxyl groups, or it can be an organic group that substitutes for at least one of hydroxyl and carboxyl groups. For example, the organic group can be at least one of alkyl, alkenyl, cycloalkyl, epoxy, aryl, or amino groups.

[0042] In some embodiments, the modified group further contains at least one of C8-C29 chain alkyl groups, polyether groups, epoxy groups, and amino groups, with at least one of carboxyl groups and hydroxyl groups attached to the aforementioned groups. Optionally, the modified group further contains C15-C26 chain alkyl groups. By introducing the aforementioned groups into the modified group, this application can synergistically cooperate with carboxyl and hydroxyl groups to optimize the chemical structure of the modified group. The long-chain alkyl and polyether segments can form a steric hindrance layer of a certain thickness on the surface of the aluminum powder, thereby providing a strong steric hindrance effect that effectively blocks aluminum powder particles and further reduces the viscosity of the slurry; and epoxy and amino groups can improve the mechanical strength of the electrode foil.

[0043] Optionally, the modifying group includes at least one selected from polyethylene glycol groups, citric acid groups, polyacrylic acid groups, phosphate ester groups, and polymethacrylic acid groups. Optionally, the modifying group includes at least one selected from polyethylene glycol groups and citric acid groups. Citric acid groups have strong anchoring ability, while polyethylene glycol groups can enhance dimensional stability and rheological properties, effectively improving the dispersion uniformity of the aluminum paste.

[0044] In some embodiments, the binder in the modified binder includes hydroxyethyl cellulose. Optionally, the molecular weight of the hydroxyethyl cellulose is 90,000 to 150,000. Further optionally, the modifying groups include citric acid groups. The modified binder used in this application effectively improves the dispersion uniformity of the aluminum paste.

[0045] It is understood that the modified binder in this application can be a commercially available product or can be prepared by chemical synthesis.

[0046] For example, cellulose-modified binders can be prepared by oxidizing the hydroxyl groups on the cellulose chain with an oxidizing agent such as sodium periodate, and then grafting polyacrylic acid (PAA) or polymethyl methacrylate (PMAA) side chains onto the cellulose backbone through free radical polymerization to introduce modified groups containing carboxyl groups onto the cellulose chain. Exemplarily, a method for preparing the above-mentioned modified binder is provided, comprising: mixing hydroxyethyl cellulose, citric acid, and a catalyst (sodium hypophosphite) in distilled water, wherein the mass ratio of hydroxyethyl cellulose to citric acid is (1~10):1, the amount of catalyst added is 10%~20% of the mass of citric acid, and the mass ratio of distilled water to citric acid is (5~15):1; reacting at a temperature of 60℃~85℃ for 1h~4h to obtain citric acid-modified hydroxyethyl cellulose.

[0047] Acrylic ester modified adhesives can be obtained by copolymerizing polyethylene glycol macromonomers (such as PEG-MA, polyethylene glycol monomethacrylate) containing polymerizable end groups (such as methacrylate) with conventional monomers such as butyl acrylate and methyl methacrylate; or, during the polymerization process, a chain transfer agent with functional groups is used to introduce hydroxyl groups or other groups onto the polymer chain segments, and then a coupling reaction is carried out with isocyanate-terminated polyethylene glycol.

[0048] Polyurethane-modified adhesives can directly use hydrophilic polyethylene glycol as one of the soft segments to introduce hydroxyl groups into the polyurethane backbone. Furthermore, chain extenders containing carboxyl or sulfonic acid groups (such as dimethylolpropionic acid, DMPA) can be used to introduce ionic centers, achieving water dispersion through neutralization and salt formation. PEG-modified epoxy resin curing agents, or the synthesis of polyethylene glycol-epoxy resin block copolymers, can improve the compatibility and dispersibility of the modified adhesive with flexible substrates (such as aluminum substrates in electrode foils).

[0049] In some embodiments, the mass ratio of the binder to the modified groups is 1:(1~8), for example, it can be 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7 or 1:8, and 1:2 is optional. This application selects the content of binder and modified groups in the modified adhesive as described above, and utilizes the principle of polarity / interaction regulation to improve the interfacial adhesion performance and cohesive strength of the adhesive. Taking cellulose adhesive as an example, due to the insufficient number of active sites on the cellulose chain to form interactions, it cannot provide sufficient interfacial bonding force and intermolecular forces, thus lacking sufficient polar groups to form strong interactions such as hydrogen bonds with the substrate surface, which may lead to insufficient adhesive strength. If a relatively large number of modified groups are introduced, it may lead to excessively high system polarity, resulting in poor compatibility with low-polarity substrates; moreover, excessive side chains will hinder the movement and entanglement of polymer chain segments and increase the rigidity of molecular chains, leading to brittleness and decreased toughness of the adhesive layer, and even microcracks due to internal stress, which will reduce the overall adhesive strength.

[0050] In some embodiments, the solid content of the aluminum paste is 45% to 70%, for example, it can be 45%, 50%, 55%, 60%, 65% or 70%. The solid content of the aluminum paste is basically the same as the aluminum powder content in the aluminum paste.

[0051] The modified binder in the aluminum paste contains 2% to 10% by mass, for example, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The dispersant in the aluminum paste contains 0.2% to 2% by mass, for example, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, or 2.0%. By adding the modified binder and dispersant as described above, compared to traditional aluminum pastes which contain less binder and dispersant, this application effectively improves the dispersion uniformity of the aluminum paste. This not only enhances the stability and structural uniformity of the electrode foil but also reduces the residue of impurity elements during debinding and sintering.

[0052] If the amount of modified binder added is relatively small, aluminum powder agglomeration may occur, making it impossible to form a stable slurry and causing aluminum powder delamination after coating. If the amount of modified binder added is relatively large, the slurry viscosity may be high, resulting in poor flowability, difficulty in coating, and a reduction in the specific surface area of ​​the electrode foil, affecting the electrode foil capacity. If the amount of dispersant added is relatively large, strong cross-linking may occur, affecting the preparation of electrode foil cracks and reducing the mechanical properties of the electrode foil.

[0053] In some embodiments, the dispersant includes at least one selected from polyethylene glycol, sodium hexametaphosphate, polyacrylates, and styrene-maleic anhydride copolymers. Optionally, the number average molecular weight of polyethylene glycol may be 200 to 4000.

[0054] The solvent includes at least one of water, propylene glycol methyl ether, diethylene glycol, and ethylene glycol. Optionally, deionized water can be used as the solvent. The modified binder of this application can use deionized water as a solvent, thereby reducing the use of organic reagents. Moreover, water is more easily decomposed or volatilized in subsequent drying or sintering processes. Compared with some high-boiling-point organic solvents, it can effectively reduce carbonization residues on the electrode foil surface, and is environmentally friendly and reduces costs.

[0055] In some embodiments, the volume average particle size Dv50 of the aluminum powder is 2μm to 10μm, for example, it can be 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm or 10μm, and can be selected as 3μm to 5μm.

[0056] Optionally, the viscosity of the aluminum paste can be from 4000 mPa·s to 7000 mPa·s, for example, it can be 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, 5500 mPa·s, 6000 mPa·s, 6500 mPa·s or 7000 mPa·s.

[0057] A second aspect of this application also provides an electrode foil, the electrode foil comprising a substrate and a surface layer disposed on at least one side of the substrate, the surface layer being made of aluminum paste as in the first aspect.

[0058] In some embodiments, the substrate may be aluminum foil. Optionally, the thickness of the aluminum foil may be 30 μm to 35 μm.

[0059] It is understandable that the surface layer refers to the aluminum powder sintered from the aluminum paste, and the surface layer has good uniformity of distribution and a large specific surface area.

[0060] A third aspect of this application also provides a method for preparing an electrode foil, the method comprising:

[0061] The aluminum paste of the first aspect is coated onto at least one side surface of the substrate and dried to obtain a dried foil;

[0062] Electrode foil is prepared by sequentially performing degreasing, sintering, and formation treatments on the dried foil to form a surface layer on the substrate.

[0063] This application uses the aforementioned aluminum paste to prepare electrode foil. The aluminum paste has good dispersion uniformity, allowing aluminum powder to be evenly distributed on the substrate surface, and the aluminum powder particles are tightly bonded together. The surface layer formed after sintering is smooth, uniform, and dense. Moreover, the aluminum paste contains low content and few types of organic reagents, which can effectively reduce the residual impurity elements in the organic reagents and reduce their impact on the electrical properties of the electrode foil.

[0064] In some embodiments, the degreasing process includes sequentially performing a first degreasing process and a second degreasing process on the dried foil.

[0065] Optionally, the temperature of the first degreasing treatment is 150℃~250℃, for example, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, or 250℃; the holding time is 0.5h~1.5h, for example, 0.5h, 0.7h, 0.9h, 1.1h, 1.3h, or 1.5h; the heating rate is 0.5℃ / min~1.5℃ / min, for example, 0.5℃ / min, 0.7℃ / min, 0.9℃ / min, 1.1℃ / min, 1.3℃ / min, or 1.5℃ / min. The atmosphere can be an inert atmosphere or a vacuum atmosphere. An inert atmosphere refers to a gas that does not react with the foil, such as nitrogen or argon.

[0066] The second degreasing treatment temperature is 300℃~400℃, for example, 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃, or 400℃; the holding time is 0.5h~1.5h, and the heating rate is 0.5℃ / min~1.5℃ / min. The atmosphere can be an inert atmosphere or a vacuum atmosphere. An inert atmosphere refers to a gas that does not react with the foil, such as nitrogen or argon.

[0067] This application employs a two-step degreasing process, which works in conjunction with vaporization to remove binders and additives from the foil surface. As the gas escapes from the foil surface, micropores are formed between the powder particles, thereby increasing the specific surface area of ​​the foil and creating a favorable foundation for particle migration and sintering during subsequent sintering. If only a one-step degreasing process is used, the removal of binders and additives may be insufficient, affecting the subsequent sintering process and the electrochemical performance of the finished electrode foil.

[0068] In some embodiments, the drying temperature is 40°C to 80°C, for example, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C; the drying time is 10 min to 15 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min, or 15 min. Optionally, the slurry layer coated on the substrate surface is dried using a step-by-step heating method, with a heating rate of 1°C / min to 5°C / min. The above-described drying method for the slurry layer ensures the structural integrity of the dried slurry layer and avoids problems such as cracking.

[0069] In some embodiments, before degreasing the dried foil, the preparation method further includes: cracking the dried slurry layer in the dried foil. It is understood that cracking refers to applying mechanical force or other methods to the dried slurry layer to form cracks with a certain direction on the slurry layer, thereby improving the bending resistance of the electrode foil. For example, cracks extending along the width direction of the substrate or along the length direction of the substrate can be formed on the dried slurry layer, or a first crack extending along the width direction of the substrate and a second crack extending along the length direction of the substrate can be formed on the dried slurry layer.

[0070] Cracks can be treated using existing crack-forming devices, depending on the direction of crack formation. Alternatively, staggered rollers can be used to apply force to the slurry layer to form cracks.

[0071] In some embodiments, the sintering temperature is 600℃~650℃, for example, 600℃, 610℃, 620℃, 630℃, 640℃, or 650℃; the holding time is 8h~12h, for example, 8h, 9h, 10h, 11h, or 12h; and the heating rate is 0.5℃ / min~1.5℃ / min. The atmosphere can be an inert atmosphere or a vacuum atmosphere. An inert atmosphere refers to a gas that does not react with the foil, such as nitrogen or argon. The sintering treatment described above enables the electrode foil to form a good surface structure, thereby improving its capacitance and mechanical properties.

[0072] Understandably, the formation process can be selected based on the performance requirements of the electrode foil, and existing formation methods can be used.

[0073] Exemplarily, a method for preparing the above-mentioned electrode foil is provided, comprising the following steps:

[0074] Aluminum powder with a Dv50 of 2μm to 10μm, a modified binder, a dispersant, and a solvent are mixed and defoamed to obtain an aluminum paste with a solid content of 45% to 70%. The modified binder accounts for 2% to 10% of the mass of the aluminum paste, and the dispersant accounts for 0.2% to 2% of the mass.

[0075] The aluminum paste is applied to at least one side of the substrate and dried to form a dried foil.

[0076] A roller is used to crack the dried slurry layer in the above-mentioned dried foil to form a crack structure on the dried slurry layer.

[0077] After the above crack treatment, the dried foil is first heated to 150℃~250℃ at a rate of 0.5℃ / min~1.5℃ / min for a first degreasing treatment of 0.5h~1.5h; then heated to 300℃~400℃ at a rate of 0.5℃ / min~1.5℃ / min for a second degreasing treatment of 0.5h~1.5h.

[0078] The dried foil after the second degreasing treatment is heated to 600℃~650℃ at a rate of 0.5℃ / min~1.5℃ / min and sintered for 8h~12h.

[0079] The sintered foil is subjected to chemical formation treatment to form a surface layer on the surface of the substrate.

[0080] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0081] PEG-200 refers to polyethylene glycol with a number average molecular weight of approximately 200, purchased from TCI (Shanghai) Chemical Industry Development Co., Ltd., under the brand name TCI.

[0082] Example 1

[0083] Aluminum powder with a Dv50 of 3 μm, a modified binder, PEG-200, and deionized water were mixed and vacuum degassed to obtain an aluminum paste with a solid content of 55%. The modified binder was citric acid-grafted hydroxyethyl cellulose. The mass ratio of the modified binder, PEG-200, and deionized water was 9:1:90, meaning the modified binder accounted for 4.05% of the aluminum paste by mass, and PEG-200 accounted for 0.45% by mass.

[0084] The preparation method of the modified binder includes: dissolving 33g of citric acid and 4g of sodium hypophosphite (SHP) in 500mL of distilled water; after complete dissolution, adding 67g of hydroxyethyl cellulose (weight average molecular weight approximately 120,000) powder; stirring at room temperature to allow HEC to fully swell and adsorb; and adding water until the system is moist and loose (non-flowing paste). The mixture is then dried at 60℃ for 5h to obtain a solid mixture. This solid mixture is pulverized and reacted at 140℃ for 1.5h to graft citric acid onto the hydroxyethyl cellulose. During this process, the mixture is turned over every 30min to prevent localized charring. The reaction product is cooled and washed four times with distilled water. Unreacted citric acid, catalyst, and byproducts are removed by filtration. The filter cake is vacuum dried at 50℃ for 24h, pulverized, and sieved (80 mesh) to obtain citric acid-grafted hydroxyethyl cellulose. The mass ratio of hydroxyethyl cellulose to citric acid groups is approximately 1:2.

[0085] The aluminum paste was applied to both sides of an aluminum foil substrate with a thickness of 30 μm to form a paste layer with a thickness of 130 μm. The aluminum foil substrate coated with the paste layer was placed in a program-controlled temperature and humidity chamber for drying. The initial drying temperature was set to 40°C and increased to 80°C at a rate of 2°C / min. The initial humidity was set to 60%RH. After complete drying, a dried foil sheet was obtained.

[0086] The dried foil is fed to three rollers arranged in an alternating pattern for cracking treatment. The axis of the rollers is perpendicular to the direction of the foil's movement. The winding and unwinding tension of the dried foil is 50N. The two sides of the foil are subjected to cracking treatment eight times to form cracks that extend along the length of the aluminum foil.

[0087] After the above crack treatment, the dried foil is first heated to 200°C at a rate of 1°C / min for a first degreasing treatment of 1 hour; then heated to 350°C at a rate of 1°C / min for a second degreasing treatment of 1 hour.

[0088] The dried foil after the second degreasing treatment was heated to 620°C at a rate of 0.5°C / min and sintered for 10 hours.

[0089] The sintered and dried foil was heated to 520V in a 100g / L boric acid solution for 20 minutes, then placed in air at 500℃ for 2 minutes, and finally heated in a 100g / L boric acid solution for 10 minutes to prepare the product as shown in the image. Figure 1 The electrode foil shown.

[0090] Example 2

[0091] Electrode foils were prepared according to the method of Example 1, except that the mass ratio of modified binder, PEG-200 and deionized water was 9:1:90, and the mass ratio of hydroxyethyl cellulose to citric acid groups in the modified binder was approximately 1:2; that is, the mass percentage of modified binder in aluminum paste was 4.5%, and the mass percentage of PEG-200 was 0.5%.

[0092] Example 3

[0093] Electrode foils were prepared according to the method of Example 1, except that the solid content of the aluminum paste was 50%, and the mass ratio of the modified binder, PEG-200 and deionized water was 15:1:84; that is, the mass percentage of the modified binder in the aluminum paste was 7.5%, and the mass percentage of PEG-200 was 0.5%.

[0094] Example 4

[0095] Electrode foils were prepared according to the method of Example 1, except that the solid content of the aluminum paste was 60%.

[0096] Example 5

[0097] Electrode foils were prepared according to the method of Example 1, except that the solid content of the aluminum paste was 40%.

[0098] Example 6

[0099] Electrode foils were prepared according to the method of Example 1, except that the dispersant was replaced with an equal mass of deionized water, and the mass percentage of the dispersant in the aluminum paste was 0.1%.

[0100] Example 7

[0101] Electrode foils were prepared according to the method of Example 1, except that some of the deionized water was replaced with an equal mass of dispersant, i.e., the mass percentage of the dispersant in the aluminum paste was 3%.

[0102] Example 8

[0103] Electrode foils were prepared according to the method of Example 1, except that the raw material ratio in the preparation of the modified binder was adjusted so that the mass ratio of hydroxyethyl cellulose to citric acid groups in the modified binder was approximately 1:0.5.

[0104] Example 9

[0105] Electrode foils were prepared according to the method of Example 1, except that the raw material ratio in the preparation of the modified binder was adjusted so that the mass ratio of hydroxyethyl cellulose to citric acid groups in the modified binder was approximately 1:9.

[0106] Example 10

[0107] Electrode foils were prepared according to the method of Example 1, except that the weight-average molecular weight of hydroxyethyl cellulose in the modified binder was 60,000.

[0108] Example 11

[0109] Electrode foils were prepared according to the method of Example 1, except that the weight-average molecular weight of hydroxyethyl cellulose in the modified binder was 160,000.

[0110] Example 12

[0111] Electrode foils were prepared according to the method of Example 1, except that only the dried foil was subjected to a first degreasing treatment.

[0112] Example 13

[0113] Electrode foils were prepared according to the method of Example 1, except that only the dried foils underwent a second degreasing treatment.

[0114] Comparative Example 1

[0115] Electrode foils were prepared according to the method of Example 1, except that the solid content of the aluminum paste was 60%, the modified binder was replaced with hydroxyethyl cellulose without citric acid groups, and the mass ratio of hydroxyethyl cellulose, PEG-200 and deionized water was 6:1:93.

[0116] Comparative Example 2

[0117] Electrode foils were prepared according to the method of Example 1, except that the solid content of the aluminum paste was 60%, the modified binder was replaced with hydroxyethyl cellulose without citrate groups, PEG-200 was not added, and the mass ratio of hydroxyethyl cellulose to deionized water was 6:1:93.

[0118] Comparative Example 3

[0119] Electrode foils were prepared according to the method of Example 1, except that the modified binder in the aluminum paste was replaced with an equal mass of hydroxyethyl cellulose without citric acid groups.

[0120] Comparative Example 4

[0121] Electrode foils were prepared according to the method in Example 1, except that the modified binder was replaced with hydroxyethyl cellulose without citrate groups, and the PEG-200 in the aluminum paste was replaced with an equal mass of deionized water, resulting in the preparation of the electrode foil as shown in Example 1. Figure 2 The electrode foil shown.

[0122] The electrode foils prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods included:

[0123] The electrode foil prepared above was tested using an LCR digital bridge, with ammonium pentaborate at a concentration of 85 g / L as the electrolyte. The test results are shown in Table 1, where Tr is the boost time in seconds, referring to the time taken at a specified current density (tested at a current density of 0.4 mA / cm²). 2 Under the given conditions, the time taken for the voltage to rise to 90% of the rated voltage (Vf) of an electrolytic capacitor from the initial voltage application. Vt is the oxide film withstand voltage, in volts (V), referring to the voltage reached 180 ± 10 seconds after the voltage rise point (Tr). tg is the loss tangent, referring to the loss factor or dielectric loss. CAP is the specific capacitance, in μF / cm². 2 , refers to the capacitance that the anode foil forming foil of an electrolytic capacitor can exhibit per unit area (usually taken as 1 cm²). Bending refers to bending strength / bending endurance, measured in cycles; it is the maximum number of bends that the anode foil forming foil of an electrolytic capacitor can withstand before breaking.

[0124] Table 1

[0125]

[0126]

[0127] As can be seen from the table above:

[0128] (1) Compared with Examples 4-5, Example 1 controls the solid content of aluminum paste to ensure good uniformity of paste dispersion, further increasing the specific surface area of ​​foil, which can improve the capacity and bending resistance of electrode foil.

[0129] (2) Compared with Examples 6-7, Example 6 has a relatively low dispersant content, some aluminum powder particles agglomerate, and the slurry dispersion is poor; Example 7 has a relatively high dispersant content, which makes the slurry more flexible after drying and difficult to form crack structure, thereby reducing the mechanical properties of the electrode foil. Moreover, the dispersant is difficult to remove during the degreasing process, which also reduces the capacity performance of the electrode foil.

[0130] (3) Compared with Examples 8-9, Example 1 controls the amount of grafting of modified groups in the modified binder. Through the principle of polarity / interaction regulation, the interfacial adhesion performance and cohesive strength of the binder are improved, the mechanical strength is increased, and the appropriate amount of grafting is conducive to uniform slurry, forming a larger specific surface area and increasing the capacity of the electrode foil.

[0131] (4) Compared with Examples 10-11, the molecular weight of the bonding material in Example 10 is relatively small, resulting in decreased bonding performance and easy delamination of aluminum powder; the molecular weight of the bonding material in Example 11 is relatively large, resulting in higher slurry viscosity and poorer fluidity, which reduces the specific surface area of ​​the electrode foil and reduces capacity.

[0132] (5) Compared with Examples 12-13, Example 1 adopts a two-step degreasing method to effectively remove binders and additives, thereby avoiding carbon residue during sintering, effectively increasing the specific surface area of ​​the electrode foil, and achieving the effect of increasing capacity.

[0133] (6) Compared with Comparative Examples 1-4, Example 1 shows that the modified binder and dispersant in this application work synergistically to improve the uniformity of the slurry and enhance the specific surface area of ​​the electrode foil. Combined with Figure 1 and Figure 2 It can be seen that the aluminum powder particles in the electrode foil prepared in Example 1 of this application are evenly distributed, while the aluminum powder particles in Comparative Example 4 are obviously agglomerated. Combined with the electrode foil performance results, it can be seen that the electrode foil has better capacity and mechanical properties.

[0134] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0135] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. An aluminum paste, characterized by, The aluminum paste comprises aluminum powder, modified binder, dispersant and solvent; the modified binder comprises a binding material grafted with a plurality of modified groups containing at least one of hydroxyl and carboxyl.

2. The aluminum paste of claim 1, wherein The binding material satisfies at least one of the following conditions: (1) the binding material comprises at least one of cellulose binder, acrylate adhesive, polyurethane binder and epoxy resin binder; (2) the weight average molecular weight of the binding material is 20,000-215,000.

3. The aluminum paste of claim 1, wherein The modified group satisfies at least one of the following conditions: (1) the modified group further contains at least one of C8-C29 chain alkyl, polyether group, epoxy group and amino group; (2) the modified group comprises at least one of polyethylene glycol group, citric acid group, polyacrylic acid group and polymethacrylic acid group.

4. The aluminum paste of claim 1, wherein The binding material comprises hydroxyethyl cellulose, the weight average molecular weight of the hydroxyethyl cellulose is 90,000-150,000; and the modified group comprises citric acid group.

5. The aluminum paste of claim 1, wherein The mass ratio of the binding material to the modified group is 1:(1-8).

6. The aluminum paste of any one of claims 1-5, wherein, The aluminum paste satisfies at least one of the following conditions: (1) the solid content of the aluminum paste is 45%-70%; (2) the aluminum paste contains the modified binder with a mass ratio of 2%-10%; (3) the aluminum paste contains the dispersant with a mass ratio of 0.2%-2%; (4) the volume average particle size Dv50 of the aluminum powder is 2-10 μm; (5) the dispersant comprises at least one of polyethylene glycol, sodium hexametaphosphate, polyacrylate and styrene-maleic anhydride copolymer; (6) the solvent comprises at least one of water, propylene glycol methyl ether, diethylene glycol and ethylene glycol.

7. An electrode foil, characterized by The electrode foil comprises a base material and a surface layer arranged on at least one side surface of the base material, and the surface layer is prepared by the aluminum paste according to any one of claims 1-6.

8. A method for producing an electrode foil, characterized by, The preparation method of the electrode foil comprises: coating the aluminum paste according to any one of claims 1-6 to at least one side surface of a base material, drying to obtain a dried foil; forming a surface layer on the surface of the base material by sequentially performing degreasing treatment, sintering treatment and formation treatment on the dried foil, to prepare the electrode foil.

9. The method of producing an electrode foil according to claim 8, wherein The degreasing treatment comprises: sequentially performing first degreasing treatment and second degreasing treatment on the dried foil; wherein the temperature of the first degreasing treatment is 150-250 ℃, the holding time is 0.5-1.5 h, and the heating rate is 0.5-1.5 ℃ / min; the temperature of the second degreasing treatment is 300-400 ℃, the holding time is 0.5-1.5 h, and the heating rate is 0.5-1.5 ℃ / min.

10. The method for producing an electrode foil according to claim 8 or 9, characterized by, The preparation method satisfies at least one of the following conditions: (1) the temperature of the drying is 40-80 ℃, and the time is 10-15 min; (2) before the degreasing treatment on the dried foil, the preparation method further comprises: performing crack treatment on the dried slurry layer of the dried foil; (3) the temperature of the sintering treatment is 600-650 DEG C, the holding time is 8-12 hours, and the heating rate is 0.5-1.5 DEG C / min.

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