Composite particle-free conductive ink as well as preparation method and application thereof

Abstract

The invention relates to composite particle-free conductive ink as well as a preparation method and application thereof. The composite particle-free conductive ink is characterized in that a conductive composition comprises a composite metal precursor, a complexing agent, a reducing agent, an organic additive and a solvent, the invention relates to a high-temperature-resistant metal complex which comprises the following components in percentage by mass: 5-50% of a metal precursor, 20-50% of a complexing agent, 0-10% of a reducing agent, 0-5% of an organic additive and the balance of a reducing agent. The composite particle-free conductive ink is prepared from a composite metal precursor, and the composite particle-free conductive ink is applied to an MLPC capacitor pole piece, so that silver elementary substances of a conductive coating are tightly combined, the compactness of a conductive film is enhanced, and the defects that holes appear in a silver layer on the surface of the pole piece and the surface of the silver layer is discontinuous are overcome; the resistivity between the pole pieces is effectively reduced, so that the conductive film has better conductivity, and the MLPC aluminum electrolytic capacitor with ultralow ESR is prepared.

Description

Technical Field

[0001] This invention relates to composite particle-free conductive ink, as well as its preparation method and application in MLPC capacitors, belonging to the field of capacitor technology, and particularly to a composite particle-free conductive ink, its preparation method and application. Background Technology

[0002] With the rapid development and upgrading of aluminum electrolytic capacitors, and the increasing demand for miniaturization and refinement in electronic products, the requirements for capacitors are also trending towards smaller size, higher capacitance, and lower resistance. However, as the number of electrode unit stacking layers in MLPC aluminum electrolytic capacitors increases, the vertical resistance increases, the stacking pressure increases, leakage current increases, and the risk of short circuits also increases dramatically. Currently, to address this issue, conductive silver paste containing resin or nanoparticle conductive ink is used to fill or connect the electrodes. This conductive silver paste can, to some extent, reduce the thickness of the stacked units, increase the effective conductive portion, and reduce the vertical resistance.

[0003] In addition, the nanoparticle conductive ink stabilizes the metal particles at the nanoscale, has a high metal content, and requires the addition of more dispersants to prevent the metal particles from agglomerating and settling. The resistivity also increases due to the dispersant, and the sintering temperature also increases with the boiling point of the dispersant.

[0004] Currently, the negative electrode of MLPC aluminum electrolytic capacitors consists of a conductive polymer layer, a conductive graphite layer, and a silver layer, distributed from the inside out. Adjacent negative electrodes are connected by conductive silver paste. However, because the binder phase of the conductive silver paste is resin, it shrinks during curing, creating pores on the electrode surface. This results in discontinuities in the silver layer surface. Furthermore, the molecular weight and proportion of hard segments of the resin, acting as an insulating layer, affect the insulation performance and also influence the vertical resistance between stacked cells. Improving the continuity of the silver layer and increasing the conductive pathways between stacked cells are among the key breakthrough directions for fabricating ultra-low ESR MLPCs. Summary of the Invention

[0005] To overcome the technical defects of existing technologies, this invention provides a composite particle-free conductive ink, its preparation method, and its application. The particle-free conductive ink is prepared by composite metal precursors. When applied to the electrodes of MLPC capacitors, the silver in the conductive coating is tightly bonded by staged heating, which enhances the density of the conductive film, improves the appearance of pores and discontinuities in the silver layer on the electrode surface, effectively reduces the resistivity between electrodes, and gives the conductive film better conductivity, thus realizing the preparation of ultra-low ESR MLPC aluminum electrolytic capacitors.

[0006] The technical problem solved by this invention is achieved through the following technical solution: A composite particle-free conductive ink, its preparation method, and its application are characterized in that: the conductive composition includes a composite metal precursor, a complexing agent, a reducing agent, an organic additive, and a solvent; the composition by mass percentage is 5-50% of the metal precursor, 20-50% of the complexing agent, 0-10% of the reducing agent, 0-5% of the organic additive, and the remainder is a reducing agent.

[0007] Preferably, the composite metal precursor is one or more of silver oxides, silver halides, and silver oxyacid salts.

[0008] Preferably, the silver halide is selected from one or more of silver fluoride, silver chloride, silver bromide, and silver iodide; the silver oxyacid salt is selected from one or more of silver nitrate, silver sulfate, silver acetate, silver phosphate, silver carbonate, silver chlorate, and silver citrate; and the silver oxide is selected from one or two of silver oxide and silver peroxide.

[0009] Preferably, the complexing agent is an amine complexing agent selected from one or more mixtures of ammonia, methylamine, ethylamine, propylamine, butylamine, hexylamine, isopropylamine, tetrahydroxypropylethylenediamine, isopropanolamine, monoethanolamine, diethanolamine, triethanolamine, 1,2-diaminopropane, ammonium tartrate, and polyaniline.

[0010] Preferably, the reducing agent is selected from one or more of formic acid, acetic acid, propionic acid, acetic acid, carbonic acid, benzoic acid, lactic acid, polyethylenediamine, glutamic acid, alanine, 4-methyldiamide, and citric acid.

[0011] Preferably, the organic additive includes at least one of thickener, surface additive, film-forming agent, dispersant, leveling agent, and defoamer.

[0012] Preferably, the solvent includes one or more of deionized water, ethanol, ethylene glycol, methanol, isopropanol, n-butanol, diethylene glycol, xylene, or γ-butyrolactone.

[0013] Preferably, the viscosity of the conductive composition is 5-50000 cP and the solid content is 10%-60%.

[0014] Preferably, the method for preparing the composite particle-free conductive ink includes the following steps: Step S1: Preparation of metal precursors: Different silver precursors are prepared by reacting silver oxyacid salts with salt solutions of different alkalinities as a substrate. Step S2: The prepared silver precursor is centrifuged, washed with water, and dried to obtain silver precursor powder; Step S3: Mix at least two silver precursors and add them to a mixed solution of amine complexing agent, solvent and reducing agent. Stir until completely dissolved and then filter. Next, add an appropriate amount of additive to adjust the viscosity and surface tension of the mixture. Stir until completely uniform to obtain conductive ink. Step S4: The conductive ink obtained in step S3 is coated onto the negative electrode of the stacked unit, and a conductive silver film is obtained after staged heating and curing.

[0015] Preferably, the composite particle-free conductive ink is used as a conductive material in MLPC aluminum electrolytic capacitors.

[0016] The composite particle-free conductive ink of the present invention is generated by reacting a silver precursor dissolved in a composite solution containing a complexing agent to form a silver complex. Since it does not contain metal particles, there is no agglomeration problem. After being coated on the stacked unit, the organic solvent can be evaporated by heat treatment, and the silver complex is reduced and decomposed into elemental silver, which adheres to the surface of the stacked unit, increasing conductivity and reducing vertical resistance.

[0017] The additives include at least one of thickeners, surfactants, film-forming agents, leveling agents, and defoamers.

[0018] The thickener can adjust the viscosity and help improve the adhesion of the composite particle-free conductive ink to the stacked unit. The thickener can be one or a mixture of several of polyvinylpyrrolidone, carboxymethyl cellulose, ethyl cellulose polymer, epoxy resin, polyurethane, polyester resin, phenolic resin, acrylic resin, and oxidized polyethylene wax.

[0019] The surfactant can reduce the surface tension of the composite particle-free conductive ink and increase the edge and corner coverage of the stacked unit. The surfactant can be one or a mixture of coupling agents, anionic surfactants, cationic surfactants, zwitterionic surfactants, and nonionic surfactants.

[0020] The leveling agent is used to spread the composite particle-free conductive ink evenly on the stacked unit, giving it good flowability and smoothness. The leveling agent is an organosilicon additive, polydimethylsiloxane, organically modified polysiloxane, polymethylalkylsiloxane, or at least one of esters, acrylates, polyethyl acrylates, and polyurethanes.

[0021] The defoamer is used to reduce existing foam and prevent foam formation. The defoamer is one or a mixture of mineral oil, vegetable oil, polyether-modified polysiloxane, fatty alcohol, glycerol, polyoxypropylene glycerol ether, fatty acid ester, and phosphate ester.

[0022] The solvent is deionized water or an organic solvent, and the organic solvent is one or a combination of several of methanol, ethanol, propanol, ethyl acetate, ethyl formate, ethyl butyrate, and xylene.

[0023] Among them, the composite particle-free conductive ink that can be used in MLPC aluminum electrolytic capacitors has a solid content of 10-60wt%, a viscosity of 0-200mPa.S, a conductive film coating thickness of 1-50μm, and a resistivity of 5-100 μΩ·cm on PET. This composite particle-free conductive ink can be stored in the dark at -20°C-5°C for several months without precipitation, thus improving its stability.

[0024] The composite particle-free conductive ink of the conductive composition has a viscosity of 5-50000 cP and a solid content of 10%-60%, preferably 30%-50%. When the solid content of composite particle-free conductive ink is 30-40%, the high-density packing paradox of particle-free systems is discussed. Conventional particle-free silver inks typically have a silver content of 10-25%, with 17% yielding 17 μΩ·cm, which is sintered at 130℃. A 60% solids content is close to the concentration of traditional granular silver paste, but granular paste requires resin adhesion, inevitably leaving organic residue after sintering.

[0025] Unexpected results: This invention's high-solids-content, particle-free conductive ink leaves almost zero resin residue after sintering. Furthermore, due to in-situ reduction of the precursor, the silver atom packing density is far higher than the random stacking of particulate slurries. Actual measurement data shows that the ESR increases significantly when the silver content is reduced from 60% to 10%. The parameters of this invention allow the silver content to be increased to 30%-50% without introducing impurities, making the resistivity of the silver layer approach the theoretical value of pure silver, effectively reducing resistivity and thus the ESR value.

[0026] Traditional high-solids slurries often require high-temperature sintering above 250°C, which can easily damage the aluminum foil oxide film, leading to increased leakage current and ESR rebound over time. The resistivity film can be formed with a solids content of 10-60% at temperatures below 150°C, as specified in this invention.

[0027] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a composite metal precursor to produce a particle-free conductive ink, solving the problem of metal particle agglomeration. The staged heating process allows the silver element in the conductive coating to bond tightly, enhancing the density of the conductive film, reducing the vertical resistivity of the electrode, and giving the conductive film better conductivity. At the same time, it improves corrosion resistance and stability. This invention can be applied to the electrode to prepare aluminum electrolytic capacitors with ultra-low ESR MLPC.

[0028] 2. This invention produces a particle-free conductive ink using a composite metal precursor. The phased heating process causes the silver in the conductive coating to bind together in an orderly and tight manner. Under a microscopic scale, the net content of silver between silver particles increases, reducing porosity and compensating for the shortcomings of current conductive inks.

[0029] 3. The particle-free conductive ink of the present invention, which can be applied to MLPC aluminum electrolytic capacitors, forms a good conductive film after being heated and sintered in stages. The resistivity of the metal conductive film formed on the PET substrate is 5-500 μΩ·cm, and the silver conductive coating formed on the stacked unit can effectively reduce the equivalent series resistance by 10-30%.

[0030] 4. By combining different silver precursors and controlling the metal content, it can be applied to multilayer units at different stages. When the content of the metallic silver precursor is 5-20%, it can be coated after the conductive silver layer as a reinforcing agent, reducing the equivalent series resistance by 10-30%. When the content of the metallic silver precursor is 20-50%, and the viscosity is adjusted to 100-200 mPa·s, it can replace the conductive silver layer and be directly coated after the conductive graphite layer. After staged heating, a silvery-white conductive film is formed on the surface. After repeating 1-5 times, the conductivity is greatly increased, and the equivalent series resistance is reduced by 10-50%.

[0031] 5. This conductive ink is particle-free and will not agglomerate when stored in the cold and away from light. Moreover, the preparation process is simple and can be mass-produced at low cost. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0033] Figure 1 This is the SEM image of Embodiment 1 of the present invention.

[0034] Figure 2 This is the SEM image of Embodiment 8 of the present invention.

[0035] Figure 3 This is the SEM image of Embodiment 10 of the present invention.

[0036] Figure 4 This is the SEM image of Comparative Example 1 of this invention. Detailed Implementation

[0037] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings: The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1 In this embodiment, composite particle-free conductive ink is prepared by weight percentage consisting of 5% metal precursor, 20% complexing agent, 1% reducing agent, 1% organic additive, and the remainder being reducing agent.

[0039] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Dissolve 1.5g of sodium carbonate and 3.4g of silver nitrate in 30mL of 10% sodium hydroxide solution to prepare the silver precursor.

[0040] Step S2: Stir the product from step S1 magnetically for 30 minutes, centrifuge the resulting suspension, wash with water, and dry to obtain silver precursor powder, denoted as powder A.

[0041] Step S3: Dissolve 0.1g of formic acid in 2mL of deionized water, then add 3.75mL of tetrahydroxypropylethylenediamine, 1g of silver nitrate, and 1g of powder A. Stir magnetically for 1-2 hours, and sonicate to ensure complete mixing. Filter the resulting solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.2g of polyvinylpyrrolidone as a thickener, 0.1g of organic modified polysiloxane as a leveling agent, and 0.2g of polyether modified polysiloxane as a defoamer. Stir until homogeneous to obtain a particle-free conductive ink with a composite silver precursor. Its viscosity is 2000-4000 cP, and its solid content is 20%-30%.

[0042] Step S4: Immerse the negative electrode of the stacked unit of the conductive graphite layer in the particle-free conductive ink for 1 minute to ensure thorough immersion; first, air dry at room temperature for 20 minutes, then heat to 100°C at a rate of 20°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the stacked unit was measured to have decreased by 16.4%. Example 2

[0043] In this embodiment, a composite particle-free conductive ink is prepared by weight percentage consisting of 10% metal precursor, 25% complexing agent, 2% reducing agent, 2% organic additive, and the remainder being a reducing agent.

[0044] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Dissolve 1.5g of ammonium citrate and 3.6g of silver nitrate in 30mL of 10% sodium hydroxide solution to prepare the silver precursor.

[0045] Step S2: Stir the product from step S1 magnetically for 40 minutes, centrifuge the resulting suspension, wash with water, and dry to obtain silver precursor powder, denoted as powder B.

[0046] Step S3: Dissolve 0.1g of formic acid in 2mL of deionized water, then add 3.75mL of triethanolamine, 1.2g of silver nitrate, and 1g of B powder. Stir magnetically for 1-2 hours, then sonicate to ensure complete mixing. Filter the resulting solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.2g of carboxymethyl cellulose as a thickener, 0.1g of organic polymethyl alkyl siloxane as a leveling agent, and 0.2g of fatty alcohol as a defoamer. Stir until homogeneous to obtain a composite silver precursor composite particle-free conductive ink. Its viscosity is 2000-3000 cP, and its solid content is 10%-30%.

[0047] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 1 minute to ensure thorough immersion; first, air dry at room temperature for 25 minutes, then heat to 100°C at a rate of 20°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 10.9%. Example 3

[0048] In this embodiment, a composite particle-free conductive ink is prepared by weight percentage consisting of 10% metal precursor, 30% complexing agent, 5% reducing agent, 5% organic additive, and the remainder being a reducing agent.

[0049] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Dissolve 1.5g of sodium oxalate and 3.6g of silver sulfate in 30mL of deionized water to prepare the silver precursor.

[0050] Step S2: Stir the product from step S1 magnetically for 60 minutes, centrifuge the resulting suspension, wash with water, and dry to obtain silver precursor powder, denoted as C powder.

[0051] Step S3: Dissolve 0.1g of acetic acid in 2mL of deionized water and 1mL of methanol, then add 3mL of monoethanolamine, 2.75mL of triethanolamine, 1.3g of silver nitrate, and 1.2g of C powder. Stir magnetically for 1-2 hours, then sonicate to ensure complete mixing. Filter the resulting solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.2g of ethyl cellulose polymer as a thickener, 0.1g of organic acrylate as a leveling agent, and 0.3g of polyoxypropylene glycerol ether as a defoamer. Stir for 60 minutes to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 3000-4000 cP, and its solid content is 15%-30%.

[0052] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 9.6%. Example 4

[0053] In this embodiment, composite particle-free conductive ink is prepared by weight percentage consisting of 20% metal precursor, 10% complexing agent, 5% reducing agent, 5% organic additive, and the remainder being reducing agent.

[0054] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Dissolve 2g of sodium acetate and 4.6g of silver acetate in 35mL of deionized water to prepare the silver precursor.

[0055] Step S2: Stir the product from step S1 magnetically for 60 minutes, centrifuge the resulting suspension, wash with water, and dry to obtain silver precursor powder, denoted as powder D.

[0056] Step S3: Dissolve 0.1g of benzoic acid in 3mL of deionized water and 1mL of propanol. Then add 3mL of ammonia, 1.75mL of triethanolamine, 1.3g of silver nitrate, and 1.2g of D powder. Stir magnetically for 120 min and sonicate to ensure complete mixing. Filter the resulting solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.3g of polyvinylpyrrolidone as a thickener, 0.1g of organic acrylate as a leveling agent, and 0.2g of ether-modified polysiloxane as a defoamer. Stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 4000 cP, and its solid content is 30%-50%.

[0057] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 12.9%. Example 5

[0058] In this embodiment, composite particle-free conductive ink is prepared by weight percentage consisting of 30% metal precursor, 30% complexing agent, 6% reducing agent, 5% organic additive, and the remainder being reducing agent.

[0059] A method for preparing a composite particle-free conductive ink includes the following steps: A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Dissolve 2.2 g of formic acid and 4.8 g of silver phosphate in 30 mL of deionized water and 30 mL of 10% sodium hydroxide solution to prepare the silver precursor.

[0060] Step S2: Stir the product from step S1 magnetically for 60 minutes, centrifuge the resulting suspension, wash with water, and dry to obtain silver precursor powder, denoted as E powder.

[0061] Step S3: Dissolve 0.2g of alanine in 30mL of deionized water and 1mL of diethylene glycol monobutyl ether. Then add 3.75mL of tetrahydroxypropyl ethylenediamine, 1.5g of silver nitrate, and 1.2g of E powder. Stir magnetically for 120 min and sonicate to ensure complete mixing. Filter the resulting solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.3g of epoxy resin as a thickener, 0.1g of polyethyl acrylate as a leveling agent, and 0.2g of polyoxypropylene glycerol ether as a defoamer. Stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 5000 cP, and its solid content is 30%-50%.

[0062] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 13.8%. Example 6

[0063] In this embodiment, the composite particle-free conductive ink is prepared by weight percentage consisting of 35% metal precursor, 40% complexing agent, 6% reducing agent, 8% organic additive, and the remainder being reducing agent.

[0064] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Mix 2g of propionic acid and 30mL of deionized water to obtain a mixture.

[0065] Step S2: Stir the mixture from step S1 magnetically for 60 minutes.

[0066] Step S3: Dissolve 0.5g of polyethylene diamine in 3mL of deionized water and 1mL of propanol, then add 3mL of 70% ammonia water, 1.75mL of diethanolamine, 1.5g of silver nitrate, and 1.5g of D powder (D powder obtained in Example 4). Stir magnetically for 120 min, and sonicate to ensure complete mixing. Filter the obtained solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.5g of polyurethane as a thickener, 0.1g of organic polyethyl acrylate as a leveling agent, and 0.3g of fatty acid ester as a defoamer. Stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 3000-5000 cP, and its solid content is 30%-60%.

[0067] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 15.3%. Example 7

[0068] In this embodiment, the composite particle-free conductive ink is prepared by weight percentage consisting of 40% metal precursor, 45% complexing agent, 6% reducing agent, 8% organic additive, and the remainder being reducing agent.

[0069] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Mix 3g of formic acid and 30mL of deionized water to obtain a mixture.

[0070] Step S2: Stir the mixture from step S1 magnetically for 60 minutes.

[0071] Step S3: Dissolve 0.8g of glutamic acid in 3mL of deionized water and 1mL of ethanol, then add 3mL of 70% ammonia water, 1.75mL of propylenediamine, 1.5g of silver nitrate, and 1.6g of D powder (D powder obtained in Example 4). Stir magnetically for 120 min, and sonicate to ensure complete mixing. Filter the obtained solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.5g of phenolic resin as a thickener, 0.2g of organic polydimethylsiloxane as a leveling agent, and 0.4g of ether-modified polysiloxane as a defoamer. Stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 1000-2000 cP, and its solid content is 30%-50%.

[0072] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 15.6%. Example 8

[0073] In this embodiment, the composite particle-free conductive ink is prepared by weight percentage consisting of 45% metal precursor, 50% complexing agent, 7% reducing agent, 8% organic additive, and the remainder being reducing agent.

[0074] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Mix 3g of formic acid and 30mL of deionized water to obtain a mixture.

[0075] Step S2: Stir the mixture from step S1 magnetically for 60 minutes.

[0076] Step S3: Dissolve 0.8g of 4-methyldiamide and 0.2g of citric acid in 3mL of deionized water and 1mL of ethanol. Then add 7mL of 70% ammonia, 1.7g of silver nitrate, and 1.7g of D powder (D powder obtained in Example 4). Stir magnetically for 120 min and sonicate to ensure complete mixing. Filter the obtained solution through a 0.22μm syringe filter to remove unreacted impurities. Add 1.7g of epoxy resin and stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 1000-2000 cP, and its solid content is 40%-60%.

[0077] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 18%. Example 9

[0078] In this embodiment, the composite particle-free conductive ink is prepared by weight percentage consisting of 50% metal precursor, 45% complexing agent, 10% reducing agent, 8% organic additive, and the remainder being reducing agent.

[0079] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Mix 4g of formic acid and 30mL of deionized water to obtain a mixture.

[0080] Step S2: Stir the mixture from step S1 magnetically for 60 minutes.

[0081] Step S3: Dissolve 1.2g of 4-methyldiamide in 3mL of deionized water and 1mL of ethanol, then add 8mL of 70% ammonia, 2g of silver nitrate, and 2g of powder B (the powder B obtained in Example 2). Stir magnetically for 120 min, and sonicate to ensure complete mixing. Filter the obtained solution through a 0.22μm syringe filter to remove unreacted impurities. Add 0.2g of polyvinylpyrrolidone and stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 1500-2000 cP, and its solid content is 30%-40%.

[0082] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 20%. Example 10

[0083] In this embodiment, the composite particle-free conductive ink is prepared by weight percentage consisting of 50% metal precursor, 45% complexing agent, 8% reducing agent, 10% organic additive, and the remainder being reducing agent.

[0084] A method for preparing a composite particle-free conductive ink includes the following steps: Step S1: Mix 5g of formic acid and 30mL of deionized water to obtain a mixture.

[0085] Step S2: Stir the mixture from step S1 magnetically for 60 minutes.

[0086] Step S3: Dissolve 1.2g of carbonic acid in 3mL of deionized water and 1mL of ethanol, then add 10mL of 70% ammonia, 3g of silver nitrate, and 3g of powder A (the powder A obtained in Example 1). Stir magnetically for 120 min, and sonicate to ensure complete mixing. Filter the obtained solution through a 0.22μm syringe filter to remove unreacted impurities. Add 1.2g of cellulose polymer and stir for 60 min to obtain a composite silver precursor particle-free conductive ink. Its viscosity is 2500-3000 cP, and its solid content is 20%-30%.

[0087] Step S4: Immerse the negative electrode of the multilayer unit with the conductive graphite layer in the particle-free conductive ink for 2 minutes to ensure thorough immersion; first, air dry at room temperature for 30 minutes, then heat to 100°C at a rate of 25°C / min and hold for 20 minutes, then heat to 150°C at the same rate and hold for 40 minutes. After staged heating and curing, a dense silver conductive coating is obtained. The resistance of the multilayer unit was measured to have decreased by 24%.

[0088] Comparative Example 1 Same as Example 1, except that the mass percentage of the metal precursor is 3% and the amount of formic acid added is 0.3g.

[0089] The conductive ink prepared in this comparative example was a turbid brownish-yellow solution that tended to settle after prolonged storage and was difficult to preserve. The resistance of the multilayer unit was measured to have decreased by 5.2%. Comparative Example 2

[0090] Same as Example 4, except that in step S1, 1.3g of silver nitrate is removed and the amount of D powder (silver acetate) added is changed to 1g.

[0091] The conductive ink prepared in this comparative example has a single silver precursor. After baking, the resistance of the stacked unit was measured to have decreased by 5.6%. Comparative Example 3

[0092] Same as Example 4, except that the reducing agent is oleic acid.

[0093] The conductive ink prepared in this comparative example still had undried oleic acid on its surface after curing at 150°C, making it impossible to measure its electrical properties and resistivity. Comparative Example 4

[0094] Same as Example 8, except that in step S1, epoxy resin is removed, while other conditions are the same as in Example 8.

[0095] The conductive ink prepared in this comparative example has a viscosity of 5 mPa·s, which is low. The amount coated on the stacked units of the conductive graphite layer is small, and the resistance of the stacked units decreased by 5.3% after baking. Comparative Example 5

[0096] Similar to Example 9, except that in step S4, the curing time is changed from heating at a rate of 20°C / min to 50°C and holding for 20 minutes, to directly heating to 100°C and holding for 20 minutes.

[0097] The conductive ink prepared in this comparative example exhibits uneven morphology on the stacked units of the conductive graphite layer. The rapid increase in temperature during ink decomposition leads to larger gaps between silver particles, slowing down electron transfer and resulting in higher resistance values. Comparative Example 6

[0098] Same as Example 10, except that step S4 is repeated twice.

[0099] The conductive ink prepared in this comparative example has a thicker silver layer, increasing the thickness of the electrode. The resistance of the multilayer unit was measured to be 5.2% lower.

[0100] The conductive coating of the present invention is obtained by impregnating or coating the above-mentioned composite particle-free conductive ink onto a laminated unit and then sintering it at a staged temperature.

[0101] The coating undergoes a phased heating process to form a dense conductive metallic layer on the laminated units. This heating process is divided into two to three stages, with the sintering temperature determined based on the type and content of the silver precursor and the boiling point of the solvent. The temperature range is 20-250°C, and the heat treatment time is 10-250 minutes. The density and continuity of the conductive coating are related to the number of heating stages; the more heating stages, the tighter the silver elemental bonds formed by the decomposition of the composite particle-free conductive ink, resulting in more conductive pathways. Furthermore, the higher the reducing agent content in the composite particle-free conductive ink, the lower the decomposition temperature, and even silver elemental precipitation at room temperature. Therefore, the reducing agent content must not exceed 5%, and the ink must be stored away from light to avoid its temperature influence. Preferably, after coating the multilayer unit with composite particle-free conductive ink, it is placed at room temperature for 1-50 min, then heated to 50-100°C and held for 10-100 min, and then heated to 150-250°C and held for 10-100 min. The heating rate is preferably 0-20°C / min.

[0102] The method of coating the composite particle-free conductive ink used in MLPC aluminum electrolytic capacitors onto the multilayer unit is any one of impregnation, drop coating, printing, imprinting or spraying.

[0103] In addition to polymer resin substrates used in flexible electronics, the substrate can also be used in the multilayer cells of MLPC aluminum electrolytic capacitors. Depending on the content of the metal precursor, it is applied to multilayer cells at different stages. When the metallic silver precursor content is 5-20%, it can be used to coat the conductive silver layer on the negative electrode of the multilayer cell, compensating for the pores caused by resin shrinkage during curing and enhancing the conductive pathway. When the metallic silver precursor content is 20-50%, with the viscosity adjusted to 100-200 mPa·s, it can replace the conductive silver layer and be directly coated onto the conductive graphite layer. After staged heating, a silvery-white conductive film forms on the surface. Repeating this process 1-5 times significantly increases conductivity, effectively reducing the ESR value of the MLPC aluminum electrolytic capacitor core after stacking.

[0104] Tests showed that the resistivity of the metal conductive layer formed on the PET substrate was 5-500 μΩ·cm, and the silver conductive coating formed on the stacked unit could effectively reduce the equivalent series resistance by 10-50%.

[0105] The combination of composite silver particle-free conductive ink and a staged heating process enhances the reduction of resistance and ESR in multilayer aluminum electrolytic capacitors. Conductive ink is coated onto the negative electrode of the multilayer unit and cured in stages with increasing temperature, achieving a staged "low-temperature welding" effect, simultaneously densifying the silver layer and protecting the oxide film. Meanwhile, the silver-free ink contains no organic resin and can achieve densification through the welding of nano-silver at temperatures far below the melting point of aluminum, approximately 200-250°C.

[0106] By employing staged heating, a low-resistance path can be formed before the oxide film decomposition temperature. Unexpectedly, this process doesn't "tolerate" the presence of the oxide film, but rather actively protects the integrity of the dielectric oxide film. This directly reduces the dielectric loss component in leakage current and equivalent series resistance, achieving dual optimization of conductivity and withstand voltage. It effectively reduces the ESR value.

[0107] The phased heating provides a precise kinetic window for the diffusion of silver atoms into the aluminum matrix. The initial low temperature allows the solvent to evaporate slowly, avoiding voids in the silver layer; the intermediate temperature plateau allows the nano-silver to begin surface diffusion; and the final temperature plateau triggers solid-state diffusion between silver and aluminum atoms.

[0108] An unexpected result was that the diffusion layer was not pure silver, but rather formed a transition layer that combined high conductivity with a certain degree of flexibility. This solved the core problems of traditional carbon and silver pastes, which suffer from high interfacial resistance, high ESR, and high heat generation under high current due to physical adsorption.

[0109] In MLPC aluminum electrolytic capacitors, the stacked cells are subjected to stress during multilayer packaging and thermal cycling. Traditional thick-film conductive layers are hard and brittle, and prone to microcracks.

[0110] The porous continuous network formed by high-temperature treatment of composite particulate inks exhibits a certain degree of flexibility. By controlling the heating rate through staged heating, a balance can be found between the sintered nano-silver network and the micropores left by solvent evaporation.

[0111] An unexpected effect is that this structure, while lacking rigidity, is also highly flexible, absorbing stress like a buffer layer. During long-term use, its contact resistance not only does not increase, but actually decreases due to tighter interface adhesion, which is significant for reducing ESR throughout the product's lifespan.

[0112] It should be emphasized that the embodiments described in this invention are illustrative rather than limiting. Therefore, this invention is not limited to the embodiments described in the specific implementation. Any other implementation methods derived by those skilled in the art based on the technical solutions of this invention also fall within the scope of protection of this invention.

Claims

1. A composite particle-free conductive ink, characterized in that: The conductive composition comprises a composite metal precursor, a complexing agent, a reducing agent, an organic additive, and a solvent; by mass percentage, the metal precursor is 5-50%, the complexing agent is 20-50%, the reducing agent is 0-10%, the organic additive is 0-5%, and the remainder is a reducing agent.

2. The composite particle-free conductive ink according to claim 1, characterized in that: The composite metal precursor is one or more of silver oxides, silver halides, and silver oxyacid salts.

3. The composite particle conductive ink according to claim 2, characterized in that: The silver halide is selected from one or more of silver fluoride, silver chloride, silver bromide, and silver iodide; the silver oxyacid salt is selected from one or more of silver nitrate, silver sulfate, silver acetate, silver phosphate, silver carbonate, silver chlorate, and silver citrate; the silver oxide is selected from one or two of silver oxide and silver peroxide.

4. The composite particle-free conductive ink according to claim 1, characterized in that: The complexing agent is an amine complexing agent selected from one or more mixtures of ammonia, methylamine, ethylamine, propylamine, butylamine, hexylamine, isopropylamine, tetrahydroxypropylethylenediamine, isopropanolamine, monoethanolamine, diethanolamine, triethanolamine, 1,2-diaminopropane, ammonium tartrate, and polyaniline.

5. The composite particle-free conductive ink according to claim 1, characterized in that: The reducing agent is selected from one or more of formic acid, acetic acid, propionic acid, acetic acid, carbonic acid, benzoic acid, lactic acid, polyvinyldiamine, glutamic acid, alanine, 4-methyldiamide, and citric acid.

6. The composite particle-free conductive ink according to claim 1, characterized in that: The organic additives include at least one of thickeners, surface additives, film-forming agents, dispersants, leveling agents, and defoamers.

7. The composite particle-free conductive ink according to claim 1, characterized in that: The solvent includes one or more of deionized water, ethanol, ethylene glycol, methanol, isopropanol, n-butanol, diethylene glycol, xylene, or γ-butyrolactone.

8. The composite particle-free conductive ink according to claim 1, characterized in that: The conductive composition has a viscosity of 5-50000 cP and a solid content of 10%-60%.

9. A method for preparing a composite particle-free conductive ink according to any one of claims 1-8, characterized in that: Includes the following steps: Step S1: Preparation of metal precursors: Different silver precursors are prepared by reacting silver oxyacid salts with salt solutions of different alkalinities as a substrate. Step S2: The prepared silver precursor is centrifuged, washed with water, and dried to obtain silver precursor powder; Step S3: Mix at least two silver precursors and add them to a mixed solution of amine complexing agent, solvent and reducing agent. Stir until completely dissolved and then filter. Next, add an appropriate amount of additive to adjust the viscosity and surface tension of the mixture. Stir until completely uniform to obtain conductive ink. Step S4: The conductive ink obtained in step S3 is coated onto the negative electrode of the stacked unit, and a conductive silver film is obtained after staged heating and curing.

10. The application of a composite particle-free conductive ink according to any one of claims 1-8, characterized in that: It is used as a conductive material in MLPC aluminum electrolytic capacitors.

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