A composite carbon paste for improving leakage current of stacked solid capacitors and its preparation method

Abstract

This invention discloses a composite carbon paste for improving leakage current in stacked solid-state capacitors and its preparation method. The composite carbon paste comprises the following components by mass percentage: 10-20 wt% graphene, 20-30 wt% micronized graphite, and 0.5-5 wt% carbon nanotubes; the micronized graphite has a sheet-like structure with an aspect ratio of 10:1 to 50:1; the graphene has a particle size D50 of 0.5-50 μm, and the micronized graphite has a particle size D50 of 3-15 μm; the D50 of the micronized graphite is 0.5-3 times that of the graphene. This invention also discloses a method for preparing the composite carbon paste, including steps such as carbon nanotube pre-dispersion, graphene pre-dispersion, micronized graphite pre-dispersion, composite mixing, homogenization, and degassing. This invention utilizes sheet-like micro-powdered graphite and graphene to form a close-packed surface-to-surface structure, and optimizes the particle size distribution to construct a three-dimensional conductive network of surface-surface-line, forming a dense physical barrier layer and an efficient electron transport channel. This reduces the leakage current and equivalent series resistance (ESR) of the stacked solid capacitor, and the slurry exhibits good stability and the preparation method is simple.

Description

Technical Field

[0001] This invention relates to the field of capacitor technology, and more specifically, to a composite carbon paste for improving leakage current of stacked solid capacitors and its preparation method. Background Technology

[0002] Stacked solid-state capacitors (MLPCs) are widely used in 5G communications, AI servers, and new energy vehicles due to their excellent high-frequency characteristics, long lifespan, and high reliability. Equivalent series resistance (ESR) and leakage current are two key parameters for evaluating MLPC performance: ESR directly affects the capacitor's filtering efficiency and heat dissipation, while leakage current relates to the capacitor's long-term reliability and lifespan.

[0003] The cathode layer of MLPC is usually composed of carbon and silver conductive layers, in which the carbon conductive layer plays the role of collecting current and reducing contact resistance. Commonly used carbon materials include graphite emulsion (micronized graphite) and carbon black. However, the conductive network constructed by a single carbon material has the following shortcomings: (1) Single micronized graphite is a sheet-like particle, and the particles are mainly in surface-to-surface contact, but gaps are easily generated when stacked, resulting in discontinuous electron transport paths and high ESR; (2) The single carbon material layer is not dense enough and cannot effectively block electron migration, resulting in increased leakage current; (3) Although carbon nanotubes have one-dimensional high conductivity, they are very easy to agglomerate in aqueous systems and are difficult to disperse uniformly.

[0004] In the prior art, Chinese invention patent application CN110459410A discloses a supercapacitor slurry, its preparation method, and its application. This technical solution improves the dispersibility and solid content of the slurry by optimizing the feeding sequence and stirring process. However, this technical solution mainly targets supercapacitor electrode slurries, and its conductive network relies on conventional conductive carbon black or carbon nanotubes for construction. When applied to the cathode layer of stacked solid capacitors, the leakage current and ESR performance still need further improvement.

[0005] Therefore, there is an urgent need to develop a new type of graphite conductive paste specifically designed for stacked solid capacitors that can simultaneously improve leakage current and reduce ESR. Summary of the Invention

[0006] Therefore, in order to address the above-mentioned technical problems, this invention provides a composite carbon slurry for improving leakage current of stacked solid capacitors and its preparation method.

[0007] To address the aforementioned technical problems, the first aspect of this invention proposes a composite carbon paste for improving the leakage current of stacked solid capacitors, comprising the following components: graphene, micronized graphite, carbon nanotubes, dispersant, binder, anti-settling agent, surfactant, and solvent. The micronized graphite has a sheet-like structure with a diameter-to-thickness ratio of 10:1 to 50:1. The particle size D50 of the graphene is 0.5~50μm, and the particle size D50 of the micronized graphite is 3~15μm; The D50 of the micronized graphite is 0.5 to 3 times that of graphene.

[0008] Furthermore, based on the total mass of the composite carbon slurry as 100%, the mass percentage of each component is as follows: graphene 10~20wt%, micronized graphite 20~30wt%, carbon nanotubes 0.5~5wt%, dispersant 0.5~3wt%, binder 3~8wt%, anti-settling agent 1~3wt%, surfactant 0.3~1wt%, and the balance is solvent.

[0009] Furthermore, the particle size D50 of the graphene is 5~12μm, the particle size D50 of the micronized graphite is 5~15μm, and the D50 of the micronized graphite is 0.5~1 times that of the graphene.

[0010] Furthermore, the carbon nanotubes have a diameter of less than 15 nm and a length of 1~15 μm, and the carbon nanotubes are subjected to hydrophilic modification treatment, including carboxylation or hydroxylation.

[0011] Furthermore, the adhesive is selected from one or more of waterborne acrylic resin, polyvinylidene fluoride, waterborne polyurethane, and sodium carboxymethyl cellulose; the dispersant is selected from one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate, polyethylene glycol, aminosilane coupling agent, and 1-pyrene carboxylic acid; the anti-settling agent is selected from one or more of fumed silica, sodium carboxymethyl cellulose, sodium polyacrylate, and polyvinylpyrrolidone; and the solvent is selected from one or more of deionized water, ethanol, 1-butyl-3-methylimidazolium tetrafluoroborate, glycerol, N-methylpyrrolidone, dihydro-L-glucanone, and γ-valerolactone.

[0012] Furthermore, the surfactant is selected from one or more of nonionic surfactants, anionic surfactants, or cationic surfactants.

[0013] A second aspect of this invention provides a method for preparing the above-mentioned composite carbon slurry, comprising the following steps: S1. Carbon nanotube pre-dispersion: Mix carbon nanotubes with 1 / 3 to 1 / 2 of the total mass of dispersant, add solvent to adjust the solid content to 1 to 3 wt%, and then perform ultrasonic-assisted dispersion or low-speed ball milling dispersion to obtain carbon nanotube pre-dispersion liquid. S2. Graphene pre-dispersion: Mix graphene with the remaining dispersant, add solvent to adjust the solid content to 2~5wt%, and then ball mill at low speed to obtain graphene pre-dispersion liquid; S3. Pre-dispersion of micronized graphite: Micronized graphite is added to a solvent to adjust the solid content to 10~20wt%, and then ball-milled at low speed to obtain a pre-dispersion of micronized graphite. S4. Composite mixing: The three pre-dispersion liquids obtained in steps S1, S2 and S3 are added to the mixing container in sequence, surfactant is added, and the mixture is ball-milled or stirred at low speed until it is uniformly mixed. Then the binder is added and the mixing continues. S5. Homogenization and Degassing: The mixed slurry obtained in step S4 is subjected to high-pressure homogenization or ultrasonic treatment, and then vacuum degassing treatment to obtain composite carbon slurry.

[0014] Further, in step S1, the ultrasonic-assisted dispersion has a power of 200-500W, a frequency of 20-50kHz, and a time of 30-60min; the low-speed ball milling dispersion has a rotation speed of 100-300rpm and a time of 1-2h; the solid content of the carbon nanotube pre-dispersion liquid is 1-3wt%; in step S2, the low-speed ball milling has a rotation speed of 100-300rpm and a time of 1-2h, and the solid content of the graphene pre-dispersion liquid is 2-5wt%; in step S3, the low-speed ball milling has a rotation speed of 100-300rpm and a time of 1-2h, and the solid content of the micronized graphite pre-dispersion liquid is 10-20wt%.

[0015] Furthermore, in step S4, the rotation speed of the low-speed ball mill is 100~300 rpm, and the time is 2~4 h; the rotation speed of the low-speed stirring is 200~400 rpm, and the time is 1~2 h; the mixing time after adding the binder is 1~2 h.

[0016] Furthermore, in step S5, the vacuum degree of the vacuum degassing treatment is -0.095MPa to -0.098MPa, and the time is 10 to 30 minutes.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a composite carbon paste for improving leakage current in stacked solid-state capacitors and its preparation method. By using sheet-like micro-powdered graphite in the composite paste and controlling the particle size and ratio of graphene to micro-powdered graphite, a close-packed three-dimensional conductive network of "face-to-face-to-line" is formed. This structure, on the one hand, forms a dense physical barrier layer through the close face-to-face stacking of sheet-like micro-powdered graphite and graphene, effectively suppressing electron migration and local electric field concentration, thereby significantly reducing leakage current. On the other hand, by using large-particle-size graphene as a conductive framework, medium-particle-size micro-powdered graphite to fill the voids, and small-particle-size carbon nanotubes to bridge the microscopic gaps, a continuous, low-resistance electron transport channel is constructed, thereby effectively reducing the equivalent series resistance.

[0018] The method for preparing composite carbon slurry disclosed in this invention effectively solves the problem of easy agglomeration of carbon nanotubes in aqueous systems by pre-dispersing and then compounding them. At the same time, by adding an anti-settling agent, the resulting slurry shows no obvious sedimentation after standing for 30 days, has good process stability, and is suitable for industrial production. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0020] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below.

[0021] Example 1

[0022] This embodiment provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors.

[0023] 1. Material Composition The composite carbon slurry of the present invention is mainly composed of graphene, solvent, micronized graphite, carbon nanotubes, surfactant, binder, dispersant and anti-settling agent.

[0024] The surfactant, used to improve the hydrophilicity and dispersion uniformity of carbon nanotubes, can be selected from one or more of nonionic surfactants (such as Triton X-100, Span series, Tween series), anionic surfactants (such as sodium dodecyl sulfate, sodium dodecylbenzene sulfonate), or cationic surfactants (such as hexadecyltrimethylammonium bromide); the binder can be selected from one or more of waterborne acrylic resin, polyvinylidene fluoride (PVDF), waterborne polyurethane (WPU), and sodium carboxymethyl cellulose (CMC); the dispersant can be selected from one or more of polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyacrylate (such as BYK-110), polyethylene glycol (PEG-2000), KH-550 (aminosilane coupling agent), and 1-pyrene carboxylic acid; the anti-settling agent can be selected from fumed SiO2, sodium carboxymethyl cellulose (CMC), sodium polyacrylate (PAAS), and polyvinylpyrrolidone (PVP). One or more of K30; the solvent may be selected from one or more of deionized water, ethanol, 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), glycerol, N-methylpyrrolidone (NMP), Cyrene (dihydro-L-glucosidone), and γ-valerol (GVL).

[0025] Specifically, this embodiment uses the following composition (by weight percentage): Graphene (≤10 layers, D50=8μm): 15wt% Micronized graphite (flakes, D50=8μm, aspect ratio 30:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is waterborne polyurethane; Dispersant: 2 wt%, the dispersant is polyvinylpyrrolidone; Anti-settling agent: 2wt%, wherein the anti-settling agent is fumed silica; Solvent (deionized water): 48.5 wt%.

[0026] 2. Preparation method S1. Carbon nanotube pre-dispersion: Mix carbon nanotubes with 1 / 3 of the total mass of the dispersant, add deionized water to adjust the solid content to 2wt%, and then perform ultrasonic-assisted dispersion at a power of 300W, a frequency of 40kHz, and a time of 1H. Cool in an ice-water bath to obtain a carbon nanotube pre-dispersion solution.

[0027] S2. Graphene pre-dispersion: Mix graphene with the remaining dispersant, add deionized water to adjust the solid content to 4wt%, and then perform low-speed ball milling at 200 rpm for 1.5 hours to obtain graphene pre-dispersion.

[0028] S3. Pre-dispersion of micronized graphite: Add micronized graphite to deionized water to adjust the solid content to 15wt%, and then perform low-speed ball milling at 200rpm for 1.5H to obtain a pre-dispersion of micronized graphite.

[0029] S4. Composite mixing: The three pre-dispersion liquids obtained in steps S1, S2 and S3 are added to the mixing container in sequence, surfactant is added, and ball milling is performed at a low speed of 250 rpm for 3 hours until the mixture is uniform. Then, binder is added and ball milling at a low speed is continued for 1 hour.

[0030] S5. Homogenization and Degassing: The mixed slurry obtained in step S4 is subjected to high-pressure homogenization at a pressure of 50 MPa for 2 cycles. Then, it is subjected to vacuum degassing at a vacuum degree of -0.098 MPa for 20 min to obtain the finished composite conductive slurry.

[0031] Example 2

[0032] This embodiment provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference between this embodiment and Embodiment 1 is that the material composition ratio is different.

[0033] 1. Material Composition Graphene (≤10 layers, D50=8μm): 10wt% Micronized graphite (flakes, D50=4μm, aspect ratio 30:1): 20wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 0.5 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive (waterborne polyurethane): 3wt%; Dispersant (polyvinylpyrrolidone): 0.5 wt%; Anti-settling agent (fumed silica): 1 wt% Solvent (deionized water): 64.5 wt%.

[0034] 2. Preparation method S1. Carbon nanotube pre-dispersion: Mix carbon nanotubes with half the total mass of dispersant, add deionized water to adjust the solid content to 1.5 wt%, and then disperse by low-speed ball milling at 150 rpm for 1.5 hours to obtain carbon nanotube pre-dispersion liquid.

[0035] S2. Graphene pre-dispersion: Mix graphene with the remaining dispersant, add deionized water to adjust the solid content to 3wt%, and then perform low-speed ball milling at 150 rpm for 2 hours to obtain graphene pre-dispersion.

[0036] S3. Pre-dispersion of micronized graphite: Add micronized graphite to deionized water to adjust the solid content to 12wt%, and then perform low-speed ball milling at 150rpm for 2 hours to obtain a pre-dispersion of micronized graphite.

[0037] S4. Composite mixing: The three pre-dispersion liquids obtained in steps S1, S2 and S3 are added to the mixing container in sequence, surfactant is added, and low-speed stirring is carried out at 300 rpm for 1.5 hours until the mixture is uniform. Then the binder is added and stirring is continued for 1 hour.

[0038] S5. Homogenization and Degassing: The mixed slurry obtained in step S4 is subjected to ultrasonic treatment with an ultrasonic power of 400W, a frequency of 45kHz, and a time of 30min. Then, it is subjected to vacuum degassing treatment with a vacuum degree of -0.095MPa and a time of 25min to obtain the finished composite conductive slurry.

[0039] Example 3

[0040] This embodiment provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference between this embodiment and Embodiment 1 is that the material composition ratio is different.

[0041] 1. Material Composition Graphene (≤10 layers, D50=12μm): 18wt% Micronized graphite (flakes, D50=10μm, aspect ratio 30:1): 28wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 4 wt% Surfactant (Triton X-100): 1 wt% Adhesive: 8 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 5 wt% and sodium carboxymethyl cellulose accounts for 3 wt%; Dispersant: 3 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 2 wt% and polyvinyl alcohol accounts for 1 wt%; Anti-settling agent: 3wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 2wt% and sodium carboxymethyl cellulose accounts for 1wt%; Solvent (deionized water): 35wt.

[0042] 2. Preparation method S1. Carbon nanotube pre-dispersion: Mix carbon nanotubes with half the total mass of dispersant, add deionized water to adjust the solid content to 2.5wt%, and then perform ultrasonic-assisted dispersion at a power of 200W, a frequency of 20kHz, and a time of 1.5H. Cool in an ice-water bath to obtain a carbon nanotube pre-dispersion.

[0043] S2. Graphene pre-dispersion: Mix graphene with the remaining dispersant, add deionized water to adjust the solid content to 5wt%, and then perform low-speed ball milling at 250rpm for 1H to obtain graphene pre-dispersion.

[0044] S3. Pre-dispersion of micronized graphite: Add deionized water to micronized graphite to adjust the solid content to 18wt%, and then perform low-speed ball milling at 250rpm for 1H to obtain a pre-dispersion of micronized graphite.

[0045] S4. Composite mixing: The three pre-dispersion liquids obtained in steps S1, S2 and S3 are added to the mixing container in sequence, surfactant is added, and ball milling is performed at a low speed of 200 rpm for 4 hours until the mixture is uniform. Then, binder is added and ball milling is continued for 1.5 hours.

[0046] S5. Homogenization and Degassing: The mixed slurry obtained in step S4 is subjected to high-pressure homogenization at a pressure of 60 MPa for 3 cycles, and then vacuum degassing is performed at a vacuum degree of -0.098 MPa for 15 min to obtain the finished composite conductive slurry.

[0047] Example 4

[0048] This embodiment provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference between this embodiment and Embodiment 1 is that the material composition ratio is different.

[0049] 1. Material Composition Graphene (≤10 layers, D50=6μm): 12wt% Micronized graphite (flakes, D50=15μm, aspect ratio 30:1): 22wt%; Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 1 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive (acrylic resin): 4wt% Dispersant (PEG-2000): 1 wt% Anti-settling agent (sodium polyacrylate): 1.5 wt%; Solvent (deionized water and glycerin in a volume ratio of 9:1): 58 wt.

[0050] 2. Preparation method The preparation method is the same as in Example 1.

[0051] Example 5

[0052] This embodiment provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference between this embodiment and Embodiment 1 is that the material composition ratio is different.

[0053] 1. Material Composition Graphene (≤10 layers, D50=5μm): 18wt% Micronized graphite (flakes, D50=15μm, aspect ratio 10:1): 28wt% Carbon nanotubes (hydroxylated multi-walled, 12 nm diameter, 8 μm length): 3 wt% Surfactant (hexadecyltrimethylammonium bromide): 0.5 wt%; Adhesive: 6 wt%, the adhesive is composed of waterborne polyurethane and polyvinylidene fluoride, wherein waterborne polyurethane accounts for 3 wt% and polyvinylidene fluoride accounts for 3 wt%; Dispersant: 2.5 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and 1-pyrene carboxylic acid, wherein polyvinylpyrrolidone accounts for 1.5 wt% and 1-pyrene carboxylic acid accounts for 1 wt%; Anti-settling agent: 2.5 wt%, wherein the anti-settling agent is composed of fumed silica and polyvinylpyrrolidone, wherein fumed silica accounts for 1.5 wt% and polyvinylpyrrolidone accounts for 1 wt%; Solvent (deionized water): 39.5 wt%.

[0054] 2. Preparation method The preparation method is the same as in Example 1.

[0055] Example 6

[0056] This embodiment provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference between this embodiment and Embodiment 1 is that the material composition ratio is different.

[0057] 1. Material Composition Graphene (≤10 layers, D50=30μm): 15wt% Micronized graphite (flakes, D50=15μm, aspect ratio 50:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 5 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 3 wt% and sodium carboxymethyl cellulose accounts for 2 wt%; Dispersant: 2 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 1.5 wt% and polyvinyl alcohol accounts for 0.5 wt%; Anti-settling agent: 2 wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 1.5 wt% and sodium carboxymethyl cellulose accounts for 0.5 wt%; Solvent (deionized water): 45.5 wt%.

[0058] 2. Preparation method The preparation method is the same as in Example 1.

[0059] Comparative Example 1 (Single Micronized Graphite) This comparative example provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference from Example 1 is that only micronized graphite is used, without adding graphene, carbon nanotubes, and surfactants.

[0060] In this comparative example, the material composition is as follows: Micronized graphite (flakes, D50=5μm, aspect ratio 30:1): 50wt% Adhesive (waterborne polyurethane): 5wt%; Dispersant (polyvinylpyrrolidone): 2wt% Anti-settling agent (fumed silica): 2wt%; Solvent (deionized water): 41 wt.

[0061] The preparation steps are the same as in Example 1, but only the micronized graphite is pre-dispersed (S3), and then directly mixed (S4, without adding surfactant), followed by homogenization and degassing steps.

[0062] Comparative Example 2 (without carbon nanotubes) This comparative example provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference from Example 1 is that no carbon nanotubes and surfactants are added.

[0063] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=8μm): 15wt% Micronized graphite (flakes, D50=5μm, aspect ratio 30:1): 30wt% Adhesive (waterborne polyurethane): 5wt%; Dispersant (polyvinylpyrrolidone): 2wt% Anti-settling agent (fumed silica): 2wt%; Solvent (deionized water): 46 wt.

[0064] The preparation steps are the same as in Example 1, but the carbon nanotube pre-dispersion step (S1) is omitted, and the remaining steps remain unchanged.

[0065] Comparative Example 3 (Conductive carbon black replacing micronized graphite) This comparative example provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference from Example 1 is that conductive carbon black (Super-P) is used instead of micronized graphite, and no surfactant is added.

[0066] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=8μm): 15wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Conductive carbon black (Super-P, D50=40nm): 25wt% Adhesive (waterborne polyurethane): 5wt%; Dispersant (polyvinylpyrrolidone): 2wt% Anti-settling agent (fumed silica): 2wt%; Solvent (deionized water): 49 wt%.

[0067] The preparation steps are the same as in Example 1, but the micronized graphite in S3 is replaced with conductive carbon black for pre-dispersion, and no surfactant is added during composite mixing, while the other steps remain unchanged.

[0068] Comparative Example 4 (Aspect Ratio Too Small) This comparative example provides a method for preparing a composite carbon paste to improve the leakage current of stacked solid capacitors. The difference from Example 1 is that the aspect ratio of the micro-powdered graphite is 3:1 (close to spherical).

[0069] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=8μm): 15wt% Micronized graphite (flakes, D50=5μm, aspect ratio 3:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 3 wt% and sodium carboxymethyl cellulose accounts for 2 wt%; Dispersant: 2 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 1.5 wt% and polyvinyl alcohol accounts for 0.5 wt%; Anti-settling agent: 2 wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 1.5 wt% and sodium carboxymethyl cellulose accounts for 0.5 wt%; Solvent (deionized water): 48.5 wt%.

[0070] The preparation steps are the same as in Example 1.

[0071] Comparative Example 5 (Absolute particle size out of range) This comparative example provides a composite carbon paste for improving leakage current of stacked solid capacitors and its preparation method. The difference between this example and Example 1 is that the particle size of graphene and the particle size of micronized graphite are different.

[0072] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=50μm): 15wt% Micronized graphite (flakes, D50=25μm, aspect ratio 30:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 3 wt% and sodium carboxymethyl cellulose accounts for 2 wt%; Dispersant: 2 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 1.5 wt% and polyvinyl alcohol accounts for 0.5 wt%; Anti-settling agent: 2 wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 1.5 wt% and sodium carboxymethyl cellulose accounts for 0.5 wt%; Solvent (deionized water): 48.5 wt%.

[0073] The preparation steps are the same as in Example 1.

[0074] Comparative Example 6 (Graphene particle size too small + particle size ratio exceeding the upper limit) This comparative example provides a method for preparing a composite carbon slurry. The difference between this method and Example 3 is that the D50 of graphene is 0.5 μm and the D50 of micronized graphite is 3 μm. At this point, the particle size of micronized graphite is 6 times that of graphene.

[0075] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=0.5μm): 15wt%; Micronized graphite (flakes, D50=3μm, aspect ratio 30:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 3 wt% and sodium carboxymethyl cellulose accounts for 2 wt%; Dispersant: 2 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 1.5 wt% and polyvinyl alcohol accounts for 0.5 wt%; Anti-settling agent: 2 wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 1.5 wt% and sodium carboxymethyl cellulose accounts for 0.5 wt%; Solvent (deionized water): 48.5 wt%.

[0076] The preparation steps are the same as in Example 3.

[0077] Comparative Example 7 (particle size ratio exceeds the upper limit of the core range) This comparative example provides a composite carbon paste for improving leakage current of stacked solid capacitors and its preparation method. The difference from Example 1 is that the particle size D50 of the micro-powdered graphite is 30 μm, the D50 of the graphene is 8 μm, and the particle size of the micro-powdered graphite is 3.75 times that of the graphene.

[0078] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=8μm): 15wt% Micronized graphite (flakes, D50=30μm, aspect ratio 30:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 3 wt% and sodium carboxymethyl cellulose accounts for 2 wt%; Dispersant: 2 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 1.5 wt% and polyvinyl alcohol accounts for 0.5 wt%; Anti-settling agent: 2 wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 1.5 wt% and sodium carboxymethyl cellulose accounts for 0.5 wt%; Solvent (deionized water): 48.5 wt%.

[0079] The preparation steps are the same as in Example 1.

[0080] Comparative Example 8 (particle size ratio exceeds the lower limit of the core range) This comparative example provides a composite carbon paste for improving leakage current of stacked solid capacitors and its preparation method. The difference from Example 1 is that the particle size D50 of the micro-powdered graphite is 2μm, the D50 of the graphene is 8μm, and the particle size of the micro-powdered graphite is 0.25 times that of the graphene.

[0081] In this comparative example, the material composition is as follows: Graphene (≤10 layers, D50=8μm): 15wt% Micronized graphite (flakes, D50=2μm, aspect ratio 30:1): 25wt% Carbon nanotubes (carboxylated multi-walled, 10 nm diameter, 10 μm length): 2 wt% Surfactant (Triton X-100): 0.5 wt% Adhesive: 5 wt%, the adhesive is composed of waterborne polyurethane and sodium carboxymethyl cellulose, wherein waterborne polyurethane accounts for 3 wt% and sodium carboxymethyl cellulose accounts for 2 wt%; Dispersant: 2 wt%, wherein the dispersant is composed of polyvinylpyrrolidone and polyvinyl alcohol, wherein polyvinylpyrrolidone accounts for 1.5 wt% and polyvinyl alcohol accounts for 0.5 wt%; Anti-settling agent: 2 wt%, wherein the anti-settling agent is composed of fumed silica and sodium carboxymethyl cellulose, wherein fumed silica accounts for 1.5 wt% and sodium carboxymethyl cellulose accounts for 0.5 wt%; Solvent (deionized water): 48.5 wt%.

[0082] The preparation steps are the same as in Example 1.

[0083] Table 1. Summary of particle size distribution for each embodiment and comparative example Verification Example The composite carbon slurries prepared in Examples 1-6 and Comparative Examples 1-8 were adjusted to a solid content of 3-10 wt% and a viscosity of 50-500 cP by adding deionized water. These slurries were then coated onto the cathode layer of a stacked solid-state capacitor (specification: 100 μF 6.3 V) using the same process, and then encapsulated and aged. Performance tests were performed on each group of capacitors, with 50 pieces tested for each group. All data in the table are average values.

[0084] 1. Testing Method At 25±3℃, the capacitance and loss tangent were tested at 120Hz using an LCR bridge tester, and the equivalent series resistance was tested at 100kHz. The leakage current was tested using a leakage current tester under the condition of applying a rated voltage of 6.3V for 120s, and the leakage current yield was calculated with a leakage current ≤3μA as the qualified product. The prepared slurry was left to stand at room temperature for 30 days to observe the stratification or sedimentation.

[0085] 2. The test results are shown in Table 2.

[0086] Table 2. Performance test results of each embodiment and comparative example. As shown in Table 2, the leakage current yield is as high as 96.0%~96.7%, while the leakage current of Comparative Example 1, which uses single micro-powdered graphite, is as high as 3.3 μA, the leakage current of Comparative Example 2 without carbon nanotubes is 2.3 μA, and the leakage current of Comparative Example 3, which uses conductive carbon black instead of micro-powdered graphite, is 2.0 μA. This is because the present invention uses sheet-like micro-powdered graphite instead of spherical / chain-like conductive carbon black. Sheet-like micro-powdered graphite and sheet-like graphene have similar two-dimensional morphologies, and the two can be tightly stacked face to face to form a dense physical barrier layer, which effectively suppresses electron migration and local electric field concentration, thereby significantly reducing leakage current.

[0087] Furthermore, the ESR of Examples 1-3 was as low as 11.2-11.8 mΩ, while the ESR of each comparative example was higher than 13.4 mΩ. This invention achieves the densest packing of carbon materials with different particle sizes by strictly controlling the particle size relationship between graphene and micronized graphite, with the D50 of micronized graphite being 0.5-3 times that of graphene. Large-particle-size graphene serves as a conductive framework, medium-particle-size micronized graphite fills the gaps between graphene sheets, and small-particle-size carbon nanotubes further bridge the microscopic gaps, forming a continuous, low-resistance three-dimensional conductive network, thereby effectively reducing ESR.

[0088] When the aspect ratio of the micronized graphite is too small (Comparative Example 4, aspect ratio 3:1), its ESR and leakage current are worse than those of the examples; when the particle size ratio exceeds the range of 0.5 to 3 times (Comparative Examples 5 to 8), its ESR and leakage current are also significantly worse than those of the examples. This indicates that the sheet-like structure of the micronized graphite (aspect ratio ≥ 10:1) is the key to achieving close packing between surfaces, while controlling the particle size ratio within the range of 0.5 to 3 times is a necessary condition for achieving the densest packing; both are indispensable. Furthermore, the ESR and leakage current of Comparative Example 3 are worse than those of the examples, proving that the technical solution of this invention, which uses sheet-like micronized graphite to replace spherical conductive carbon black, is superior to the prior art.

[0089] This invention effectively solves the problem of easy agglomeration of carbon nanotubes by pre-dispersing and then recombining them. The slurries in each embodiment show no stratification or only slight sedimentation after standing for 30 days, indicating good process stability and suitability for industrial production.

[0090] Obviously, the embodiments described above are merely some embodiments of this application, not all embodiments, and do not limit the patent scope of this application. This application can be implemented in many different forms; on the contrary, the purpose of providing these embodiments is to make the disclosure of this application more thorough and comprehensive. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing specific embodiments, or make equivalent substitutions for some of the technical features. Any equivalent structures made using the content of this application's specification, directly or indirectly applied to other related technical fields, are similarly within the patent protection scope of this application.

Claims

1. A composite carbon paste for improving leakage current in stacked solid-state capacitors, characterized in that, It includes the following components: graphene, micronized graphite, carbon nanotubes, dispersant, binder, antisettling agent, surfactant, and solvent; The micronized graphite has a sheet-like structure with a diameter-to-thickness ratio of 10:1 to 50:

1. The particle size D50 of the graphene is 0.5~50μm, and the particle size D50 of the micronized graphite is 3~15μm; The D50 of the micronized graphite is 0.5 to 3 times that of graphene.

2. The composite carbon slurry according to claim 1, characterized in that, Based on the total mass of the composite carbon slurry as 100%, the mass percentage of each component is as follows: graphene 10~20wt%, micronized graphite 20~30wt%, carbon nanotubes 0.5~5wt%, dispersant 0.5~3wt%, binder 3~8wt%, anti-settling agent 1~3wt%, surfactant 0.3~1wt%, and the balance is solvent.

3. The composite carbon slurry according to claim 2, characterized in that, The graphene has a particle size D50 of 5~12μm, the micronized graphite has a particle size D50 of 5~15μm, and the D50 of the micronized graphite is 0.5~1 times that of the graphene.

4. The composite carbon slurry according to claim 1, characterized in that, The carbon nanotubes have a diameter of less than 15 nm and a length of 1~15 μm, and the carbon nanotubes are hydrophilic modified, including carboxylation or hydroxylation.

5. The composite carbon slurry according to claim 1, characterized in that, The binder is selected from one or more of waterborne acrylic resin, polyvinylidene fluoride, waterborne polyurethane, and sodium carboxymethyl cellulose; the dispersant is selected from one or more of polyvinylpyrrolidone, polyvinyl alcohol, polyacrylate, polyethylene glycol, aminosilane coupling agent, and 1-pyrene carboxylic acid; the anti-settling agent is selected from one or more of fumed silica, sodium carboxymethyl cellulose, sodium polyacrylate, and polyvinylpyrrolidone; the solvent is selected from one or more of deionized water, ethanol, 1-butyl-3-methylimidazolium tetrafluoroborate, glycerol, N-methylpyrrolidone, dihydro-L-glucanone, and γ-valerolactone.

6. The composite carbon slurry according to claim 1, characterized in that, The surfactant is selected from one or more of nonionic surfactants, anionic surfactants, or cationic surfactants.

7. A method for preparing a composite carbon slurry according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1. Carbon nanotube pre-dispersion: Mix carbon nanotubes with 1 / 3 to 1 / 2 of the total mass of dispersant, add solvent to adjust the solid content to 1 to 3 wt%, and then perform ultrasonic-assisted dispersion or low-speed ball milling dispersion to obtain carbon nanotube pre-dispersion liquid. S2. Graphene pre-dispersion: Mix graphene with the remaining dispersant, add solvent to adjust the solid content to 2~5wt%, and then ball mill at low speed to obtain graphene pre-dispersion liquid; S3. Pre-dispersion of micronized graphite: Micronized graphite is added to a solvent to adjust the solid content to 10~20wt%, and then ball-milled at low speed to obtain a pre-dispersion of micronized graphite. S4. Composite mixing: The three pre-dispersion liquids obtained in steps S1, S2 and S3 are added to the mixing container in sequence, surfactant is added, and the mixture is ball-milled or stirred at low speed until it is uniformly mixed. Then the binder is added and the mixing continues. S5. Homogenization and Degassing: The mixed slurry obtained in step S4 is subjected to high-pressure homogenization or ultrasonic treatment, and then vacuum degassing treatment to obtain composite carbon slurry.

8. The preparation method according to claim 7, characterized in that, In step S1, the ultrasonic-assisted dispersion has a power of 200-500W, a frequency of 20-50kHz, and a time of 30-60min; the low-speed ball milling dispersion has a rotation speed of 100-300rpm and a time of 1-2h; the solid content of the carbon nanotube pre-dispersion liquid is 1-3wt%. In step S2, the low-speed ball milling has a rotation speed of 100-300rpm and a time of 1-2h; the solid content of the graphene pre-dispersion liquid is 2-5wt%. In step S3, the low-speed ball milling has a rotation speed of 100-300rpm and a time of 1-2h; the solid content of the micronized graphite pre-dispersion liquid is 10-20wt%.

9. The preparation method according to claim 7, characterized in that, In step S4, the low-speed ball milling speed is 100~300 rpm and the time is 2~4 h; the low-speed stirring speed is 200~400 rpm and the time is 1~2 h; the mixing time after adding the binder is 1~2 h.

10. The preparation method according to claim 7, characterized in that, In step S5, the vacuum degree of the vacuum degassing process is -0.095MPa to -0.098MPa, and the time is 10 to 30 minutes.

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