Carbon material conductive paste, method of making and use thereof

Abstract

The application belongs to the field of carbon materials, and provides a carbon material conductive slurry, a preparation method and application thereof. The preparation method of the carbon material conductive slurry comprises the following steps: (1) performing pretreatment on carbon materials by using polyphenol in the presence of a first solvent to obtain a pretreated slurry; (2) mixing the pretreated slurry with a gas-producing agent and performing a modification reaction to obtain a mixed solution; (3) performing solid-liquid separation and drying on the mixed solution to obtain modified graphene / carbon nanotube composite powder; and (4) mixing the modified graphene / carbon nanotube composite powder with a dispersant and a second solvent to obtain the carbon material conductive slurry. The method can improve the interface compatibility of the graphene / carbon nanotube composite material, thereby improving the dispersion uniformity and storage stability thereof and improving the conductivity thereof in battery applications.

Description

Technical Field

[0001] This application belongs to the field of carbon materials, specifically, it provides a carbon material conductive paste, its preparation method, and its application. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) have advantages such as high energy density and long cycle life, making them the main electrochemical energy storage devices currently available. To improve the electron transport efficiency within the electrodes, conductive agents are often added to the positive and negative electrode materials to construct an effective conductive network. Novel carbon materials such as carbon nanotubes and graphene are widely used as conductive agents due to their excellent conductivity and prominent structural anisotropy. Typically, the conductive agent is added directly to the electrode slurry in dry powder form. However, this method has significant drawbacks: dry powder conductive agents have a large specific surface area and high surface energy, making them prone to agglomeration and difficult to disperse uniformly, resulting in locally high resistivity of the electrode; simultaneously, direct addition generates a large amount of dust, causing material waste and posing safety hazards; furthermore, dry powder addition makes it difficult to ensure sufficient contact between the conductive agent and active particles in the initial stage of slurry mixing, affecting electrode consistency and batch stability.

[0003] To address the aforementioned issues, relevant technologies employ a method of pre-preparing the conductive agent into a liquid conductive slurry. This involves uniformly dispersing the conductive agent in a solvent using a dispersant and mechanical force, and then adding the resulting conductive slurry to the main positive and negative electrode slurries. This pre-dispersion treatment improves the uniformity of the conductive agent's dispersion in the electrode slurry, reduces dust risk, and facilitates batch-to-batch stability control.

[0004] Currently, conventional conductive pastes mostly use a single carbon material as the conductive component. When graphene is used alone, its two-dimensional sheets are prone to recombination due to π-π interactions, resulting in a significant decrease in the effective conductive contact area. Furthermore, the contacts between the sheets are "surface-to-surface" or "point-to-surface," making it difficult to construct continuous long-range conductive pathways along the electrode thickness. When carbon nanotubes are used alone, although their one-dimensional linear structure can achieve "line-to-point" connections, they are extremely prone to entanglement, bundles, and agglomeration. Moreover, the contacts between carbon nanotubes are mainly "line-to-line" or "point-to-line," resulting in high contact resistance and limited conductive network efficiency. It is evident that a single conductive material cannot simultaneously meet the requirements for constructing efficient, uniform, and long-range stable conductive networks.

[0005] To overcome the limitations of single materials, it is necessary to combine graphene with carbon nanotubes. This combination can construct a multi-scale conductive network: graphene sheets provide a wide two-dimensional conductive substrate, while carbon nanotubes act as one-dimensional bridges, connecting adjacent graphene sheets and active particles, thereby improving the overall electronic conductivity of the electrode. It is precisely because of this synergistic effect that graphene / carbon nanotube composite conductive pastes are considered key conductive materials for high-performance secondary battery electrodes.

[0006] However, graphene and carbon nanotubes face poor dispersion stability during practical compounding. Their surface properties differ, resulting in weak interfacial bonding. In slurry systems, they compete for dispersant molecules, leading to uneven dispersant distribution and weakening the stabilizing effect. More seriously, the high aspect ratio of carbon nanotubes makes them prone to entanglement, and graphene sheets also tend to recombine. After interweaving and entanglement, the slurry is highly susceptible to gelation or rapid sedimentation and stratification. To suppress these instabilities, related technologies have had to use large amounts of dispersant to maintain temporary stability, but excessive dispersant significantly reduces the conductivity of the conductive network. Therefore, existing composite conductive slurries often struggle to simultaneously achieve high stability and high conductivity. How to effectively suppress the stacking, agglomeration, and sedimentation of graphene and carbon nanotubes while ensuring a low dispersant dosage, and achieve stable co-dispersion of the two, has become a pressing problem to be solved. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, the purpose of this application is to provide a carbon material conductive paste, its preparation method, and its application. The method of this application can improve the interfacial compatibility of graphene / carbon nanotube composite materials, thereby enhancing dispersion uniformity and storage stability, and improving their conductivity in battery applications.

[0008] In a first aspect, this application provides a method for preparing a conductive paste for carbon materials, comprising: (1) In the presence of a first solvent, polyphenols are used to pretreat carbon materials to obtain a pretreated slurry; wherein the first solvent is an aqueous solvent, the carbon materials include graphene and carbon nanotubes, and the mass ratio of polyphenols to carbon materials is (10~30):100. (2) The pretreated slurry is mixed with the gas-generating agent and modified to obtain a mixture; wherein the gas-generating agent can decompose to generate gas in the modification reaction, and the mass ratio of the gas-generating agent to the carbon material is (50~100):100. (3) The mixture is subjected to solid-liquid separation and drying to obtain modified graphene / carbon nanotube composite powder; (4) The modified graphene / carbon nanotube composite powder is mixed with a dispersant and a second solvent to obtain the carbon material conductive slurry.

[0009] In some embodiments of this application, the polyphenol is selected from at least one of tannic acid, catechin, gallic acid, caffeic acid, and anthocyanins.

[0010] In some embodiments of this application, based on the total amount of the carbon material, the mass percentage of graphene is 10% to 40%, and the mass percentage of carbon nanotubes is 60% to 90%.

[0011] In some embodiments of this application, the carbon nanotubes are multi-walled carbon nanotubes.

[0012] In some embodiments of this application, the graphene is at least one of physically exfoliated graphene, graphene oxide, and reduced graphene oxide, and the surface C / O atomic ratio of the graphene oxide is 6.0 to 6.5.

[0013] Furthermore, the graphene oxide is obtained by oxidizing physically exfoliated graphene with hydrogen peroxide; wherein the mass amount of hydrogen peroxide, calculated as H2O2, is 1% to 5% of the mass of the physically exfoliated graphene, the physically exfoliated graphene has 3 to 5 layers, and its surface C / O atomic ratio is not less than 20.

[0014] Furthermore, the oxidation treatment is carried out at a temperature of 20~40℃ for 1~2 hours.

[0015] In some embodiments of this application, the operating conditions for the pretreatment in step (1) include: a temperature of 20~40℃, a stirring speed of 200~500rpm, and a time of 1~3h.

[0016] In some embodiments of this application, the gas-generating agent is ammonium carbonate and / or ammonium bicarbonate. Further, the gas-generating agent is ammonium bicarbonate.

[0017] In some embodiments of this application, the operating conditions of the modification reaction in step (2) include: pH 4.5~6.0, temperature 20~40℃, stirring speed 200~500rpm, and time 1~3h.

[0018] Furthermore, the pH of the reaction system in step (2) is adjusted by adding phosphoric acid at a concentration of 0.5~1.0 mol / L.

[0019] In some embodiments of this application, in step (2), the gas-generating agent is added to the pretreated slurry in 3 to 5 portions, with an interval of 10 to 40 minutes between adjacent additions, and the amount added each time is 20% to 40% of the total mass of the gas-generating agent.

[0020] In some embodiments of this application, in step (4), the dispersant is selected from at least one of polyvinylpyrrolidone, nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, styrene-maleic anhydride copolymer, carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol and polyethyleneimine.

[0021] In some embodiments of this application, the second solvent is selected from at least one of water, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0022] In some embodiments of this application, based on a total amount of 100 parts by mass of the carbon material conductive paste, the amount of the dispersant is 0.5 to 3 parts by mass, the amount of the modified graphene / carbon nanotube composite powder is 5 to 10 parts by mass, and the amount of the second solvent is 88 to 93 parts by mass.

[0023] In some embodiments of this application, step (4) includes: dissolving the dispersant in the second solvent, then adding the modified graphene / carbon nanotube composite powder for grinding, followed by demagnetization and filtration to obtain a carbon material conductive slurry.

[0024] Secondly, this application provides a carbon material conductive paste prepared by the preparation method described in the first aspect of this application.

[0025] Thirdly, this application provides the application of the carbon material conductive paste described in the second aspect of this application in the preparation of secondary batteries.

[0026] In some embodiments of this application, the secondary battery is a lithium-ion battery.

[0027] This application has the following beneficial effects: The preparation method of this application employs a pretreatment system combining polyphenols and a gas-generating agent. Through the complementary effects of "physical expansion and depolymerization + chemical anchoring and stabilization," the agglomeration problem of nano-carbon materials is effectively improved. Specifically, a small amount (not exceeding the total amount of carbon material) of polyphenols is first used to pretreat carbon materials, including graphene and carbon nanotubes, allowing the polyphenols to initially adsorb onto the carbon material surface. Then, a small amount (not exceeding the total amount of carbon material) of a gas-generating agent is added. The gas-generating agent decomposes to produce gas, which exerts a physical expansion effect on the polyphenol-adsorbed carbon material, significantly weakening and breaking down the macroscopic agglomerates between the carbon materials. With the assistance of gas physical expansion, the polyphenols can more fully react chemically with the oxygen-containing groups on the carbon material surface, achieving chemical anchoring: the polyphenols act as a "molecular bridge," firmly anchoring at the graphene and carbon nanotube interface, strengthening the interfacial bonding between the two phases. Simultaneously, the steric hindrance effect of the polyphenols effectively inhibits microscopic re-agglomeration. Thus, a "bridging bridge" is constructed between the carbon material surface and the subsequently added dispersant, solving the problem of interface mismatch between graphene and carbon nanotubes. In this way, the modified composite material powder can be stably dispersed with only a small amount of dispersant when preparing conductive slurry, which greatly reduces the amount of dispersant used in conductive slurry, avoids the insulation effect caused by excessive dispersant, and enables conductive slurry to maintain high dispersibility while having excellent conductivity.

[0028] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Detailed Implementation

[0029] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0030] The "scope" disclosed in this application is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This type of scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0032] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0033] To improve the dispersibility of conductive pastes, polymeric dispersants, such as polyvinylpyrrolidone K30 (PVPK30, K value approximately 30), are typically added. However, for carbon nanotube and graphene composite systems, polymeric dispersants like PVP K30 have only one adsorption site for both materials, making it impossible to effectively anchor both carbon materials simultaneously. Furthermore, their steric hindrance makes it difficult to resist stacking and entanglement caused by van der Waals forces. In addition, the graphene-carbon nanotube interface is mismatched, lacking regulatory bridges and hindering synergistic dispersion. To address sedimentation issues, industrial processes often require increasing the amount of dispersant (e.g., a dispersant / carbon material mass ratio of 1 / 2 to 5) or compounding with polymeric binders such as PVDF, CMC, and SBR. However, this method significantly increases electrode resistivity, sacrificing conductivity; and composite pastes with simple physical mixing are still prone to agglomeration after the removal of mechanical forces. Therefore, existing technologies struggle to balance dispersion stability and high conductivity.

[0034] Therefore, this application provides a method for preparing a conductive paste for carbon materials. By synergistically treating carbon materials with a small amount of polyphenols and a gas-generating agent, a dual-mechanism system of "physical depolymerization + chemical anchoring" is constructed, reducing the amount of inert dispersant and solving the problem that conductivity and dispersion stability cannot be achieved simultaneously.

[0035] Specifically, the method for preparing the carbon material conductive paste provided in this application includes: (1) In the presence of a first solvent, polyphenols are used to pretreat carbon materials to obtain a pretreated slurry; wherein the carbon materials include graphene and carbon nanotubes. (2) The pretreated slurry is mixed with a gas-generating agent and subjected to a modification reaction to obtain a mixture; wherein the gas-generating agent can decompose to generate gas in the modification reaction; (3) The mixture is subjected to solid-liquid separation and drying to obtain modified graphene / carbon nanotube composite powder; (4) The modified graphene / carbon nanotube composite powder is mixed with a dispersant and a second solvent to obtain the carbon material conductive slurry.

[0036] In this application, the first solvent is an aqueous solvent, specifically water or a mixture of water and alcohol. When a mixture of water and alcohol is used, the volume ratio of water to alcohol is 1:(0.5~2). The alcohol is selected from one or more of ethanol, methanol, isopropanol, and ethylene glycol.

[0037] In some embodiments, the carbon material accounts for 7% to 15% of the total mass of the carbon material and the first solvent, for example, 7%, 8%, 10%, 12%, 15%, or any value between them. This ensures that the pretreated slurry has a suitable viscosity.

[0038] In this application, the mass ratio of polyphenol to carbon material is (10~30):100, for example, 10:100, 13:100, 15:100, 20:100, 25:100, 30:100, or any value between them. If the amount of polyphenol is too low, it will not be sufficient to chemically modify the surface of the carbon material; if the amount of polyphenol is too high, it may remain in the slurry, reducing conductivity, causing side reactions, or even deteriorating battery performance.

[0039] In this application, the polyphenol refers to a compound whose molecular structure contains two or more phenolic hydroxyl groups and typically contains catechol or pyrogallol units. As some embodiments, the polyphenol is selected from at least one of tannic acid, catechin, gallic acid, caffeic acid, and anthocyanins.

[0040] In some embodiments, the graphene is at least one of physically exfoliated graphene, graphene oxide, and reduced-redox graphene. As a preferred example, the graphene is graphene oxide.

[0041] In this invention, physically exfoliated graphene refers to graphene prepared by physically exfoliating graphite, including but not limited to mechanically exfoliated graphene and liquid-phase exfoliated graphene. Preferably, the physically exfoliated graphene is few-layer graphene, with 3 to 10 layers, more preferably 3 to 5 layers; the surface C / O atomic ratio is not less than 20, preferably 20 to 50, for example 20, 30, 37, 45, 49, 50 or any value between them.

[0042] In this invention, the graphene oxide is preferably edge-oxidized graphene oxide, that is, graphene whose edge sites are only partially oxidized, with a surface C / O atomic ratio of 6.0 to 6.5, for example 6.0, 6.2, 6.3, 6.5, or any value between them. This mild oxidation introduces only a small number of carboxyl or hydroxyl functional groups at the edges, providing reaction sites for subsequent chemical anchoring of polyphenols and steric hindrance of dispersants, which is beneficial for improving dispersibility; at the same time, it preserves the complete sp of the graphene basal surface. 2 The conjugated structure avoids conductivity loss due to complete oxidation. This edge-exfoliated graphene oxide can be prepared by lightly oxidizing physically exfoliated few-layer graphene with hydrogen peroxide. Compared to graphene oxide prepared using potassium permanganate in the Hummers method (whose surface C / O atomic ratio is typically 2-4), this edge-exfoliated graphene oxide has a higher surface C / O atomic ratio, no metal residue, and controllable oxidation degree, thus retaining better conductivity. As a preferred example, the graphene oxide is obtained by oxidizing physically exfoliated graphene with hydrogen peroxide, wherein the physically exfoliated graphene is few-layer graphene with 3-5 layers and a surface C / O atomic ratio of not less than 20, further 40-50; the amount of hydrogen peroxide used, calculated as H2O2, is 1%-5% of the mass of the physically exfoliated graphene. The oxidation treatment is carried out at a temperature of 20~40℃, such as 20℃, 30℃, 35℃, 40℃ or any value between them, for a time of 1~2h, such as 1h, 1.5h, 2h or any value between them; the oxidation treatment is carried out under stirring conditions, and the stirring speed can be 200~500rpm. After the above oxidation treatment, the surface C / O atomic ratio of graphene is reduced to 6.0~6.5, thus obtaining the edge-oxidized graphene.

[0043] In this application, the surface C / O atomic ratio can be measured by X-ray photoelectron spectroscopy (XPS).

[0044] In this application, the carbon nanotube can be at least one of single-walled carbon nanotubes, double-walled carbon nanotubes, and multi-walled carbon nanotubes. Preferably, the carbon nanotube is a multi-walled carbon nanotube, which has moderate conductivity, controllable dispersion, and lower cost. As an example, the diameter of the carbon nanotube can be 5~20 nm, and the length can be 10~30 μm.

[0045] In some embodiments, based on the total amount of carbon material, the graphene accounts for 10% to 40% by mass, for example, 10%, 15%, 20%, 24%, 30%, 35%, 40%, or any value between therewith, and the carbon nanotubes account for 60% to 90% by mass, for example, 60%, 65%, 70%, 76%, 80%, 90%, or any value between therewith. To further improve the conductivity and dispersion stability of the conductive paste, the graphene is preferably 15% to 35% of the total amount of carbon material.

[0046] In step (1), the pretreatment aims to pre-adsorb polyphenols onto the surface of the carbon material. According to some embodiments, the pretreatment is carried out under stirring conditions, with a stirring speed of 200–500 rpm, such as 200 rpm, 300 rpm, 350 rpm, 400 rpm, 500 rpm, or any value between therewith, and a stirring time of 1–3 h, such as 1 h, 1.5 h, 2 h, 3 h, or any value between therewith, and a pretreatment temperature of 20–40 °C, such as 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, or any value between therewith. As an example, the pretreatment is carried out at room temperature (25 ± 2 °C).

[0047] In some implementations, step (1) includes the following operations: (1-1) The graphene and the carbon nanotubes are added to the aqueous solvent and stirred at high speed to obtain a carbon material base liquid; wherein the stirring speed can be 1500~2000 rpm and the stirring time can be 15~30 min. (1-2) The polyphenols are mixed with the carbon material base liquid and stirred at 20-40°C for 1-3 hours to obtain the pretreated slurry.

[0048] In this application, the gas-generating agent refers to an auxiliary agent capable of generating gas through decomposition in the modification reaction, such as a carbonate or bicarbonate. As some embodiments, the gas-generating agent is ammonium carbonate and / or ammonium bicarbonate. Preferably, the gas-generating agent is ammonium bicarbonate.

[0049] In this application, the mass ratio of the gas-generating agent to the carbon material is (50~100):100, for example, 50:100, 55:100, 60:100, 80:100, 90:100, 100:100, or any value between them. Too little gas-generating agent will not produce enough gas to depolymerize the carbon material, while too much may interfere with the chemical anchoring effect of polyphenols on the carbon material surface.

[0050] In some embodiments, the operating conditions of the modification reaction include: pH 4.5–6.0, temperature 20–40°C (e.g., 20°C, 25°C, 30°C, 35°C, 40°C, or any value between them), stirring speed 200–500 rpm (e.g., 200 rpm, 300 rpm, 400 rpm, 500 rpm, or any value between them), and time 1–3 h (e.g., 1 h, 2 h, 3 h, or any value between them). Further, the pH of the reaction system is adjusted by using dilute phosphoric acid with a concentration of 0.5–1.0 mol / L. Maintaining the system pH at a weakly acidic condition of 4.5–6.0 is beneficial for maintaining the chemical reactivity of the polyphenols.

[0051] In some embodiments, in step (2), the gas-generating agent is added to the pretreated slurry in 3 to 5 batches (e.g., 3, 4, or 5 batches), with an interval of 10 to 40 minutes between each batch (e.g., 10, 20, 30, or 40 minutes, or any value between them). Each batch of addition accounts for 20% to 40% of the total mass of the gas-generating agent (e.g., 20%, 25%, 30%, 35%, or 40%, or any value between them). Batch addition of the gas-generating agent can prevent the gas from escaping too quickly and thus further improve the dispersion uniformity of the carbon material.

[0052] In this application, in step (3), the solid-liquid separation method is, for example, vacuum filtration. The washing is intended to remove byproducts such as salts generated in the reaction system and residual polyphenols. The washing can be done once or multiple times, for example, 2 to 5 times. The drying can be vacuum drying, and the vacuum drying temperature can be 50 to 70°C, for example, 50°C, 60°C, 70°C or any value between them.

[0053] In this application, a stable conductive paste can be obtained through step (4). This application does not specifically limit the dispersant used; it can be selected from existing conductive pastes. As an example, the dispersant can be at least one of polyvinylpyrrolidone (e.g., PVP K30, PVP K15, PVP K90), nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, styrene-maleic anhydride copolymer, carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol, and polyethyleneimine. In particular, the conductive paste of this application can maintain high stability with a very low dispersant content. The dispersant can be simultaneously adsorbed on the surface of carbon nanotubes and the surface of polyphenol-pretreated carbon materials, stabilizing the dispersion state of the paste through steric hindrance. Furthermore, a low dispersant content is beneficial for improving conductivity. Accordingly, based on a total amount of 100 parts by mass of the carbon material conductive paste, the mass of the dispersant is 0.5 to 3 parts, more preferably 0.5 to 2 parts, for example 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts, 1.5 parts, 2 parts or any value between them.

[0054] In this application, the second solvent can be selected based on the application of the conductive paste in the electrode material. When the conductive paste is used to prepare a positive electrode paste, the second solvent is typically an organic solvent; when the conductive paste is used to prepare a negative electrode paste, the second solvent is typically water. As some examples, the second solvent is selected from at least one of water, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

[0055] In some embodiments, based on a total amount of 100 parts by mass of the carbon material conductive paste, the mass of the second solvent can be 88 to 93 parts, for example, 88, 89, 90, 91, 92, 93 parts or any value between them.

[0056] In some embodiments, based on 100 parts by mass of the total amount of the carbon material conductive paste, the mass fraction of the modified graphene / carbon nanotube composite powder can be 5 to 10, for example, 5 parts, 7 parts, 8 parts, 8.5 parts, 9 parts, 10 parts or any value between them.

[0057] In some embodiments, step (4) includes: dissolving the dispersant in the second solvent, adding the modified graphene / carbon nanotube composite powder, grinding, demagnetizing, and filtering to obtain a conductive slurry. The grinding method can be ball milling or sand milling, preferably sand milling. Sand milling uses a smaller particle size grinding medium, which can effectively penetrate between the layers of carbon material while avoiding excessive shear force that could break the carbon nanotubes. As an example, zirconia beads with a diameter of 0.8 mm can be used as the grinding medium, and sand milling can be performed at a speed of 1500~2500 rpm for 1~2 hours to ensure that the graphene and carbon nanotubes are in full contact and form a good overlapping structure.

[0058] Secondly, this application provides a carbon material conductive paste prepared by the preparation method described in the first aspect of this application. As mentioned above, the carbon material conductive paste prepared by this application has high stability and can effectively improve conductivity when applied to positive and negative electrodes.

[0059] Thirdly, this application provides the application of the carbon material conductive paste described in the second aspect of this application in the preparation of secondary batteries. The secondary battery may include lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, etc. As a preferred example, the secondary battery is a lithium-ion battery.

[0060] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0061] In the following examples and comparative examples, the carbon nanotubes used are multi-walled carbon nanotubes with a diameter of 10-20 nm, a length of 10-30 μm, and a specific surface area >200 m². 2 / g, purity >98% (Zhongke Jinyan, model CNT304); unless otherwise stated, all fractions refer to parts by mass.

[0062] The graphene oxide used was edge-exfoliated graphene oxide with a surface C / O atomic ratio of 6.0, and was prepared as follows: 100 parts of physically exfoliated few-layer graphene (3-5 layers, C / O=49) was ultrasonically dispersed in 900 parts of water, and 16.7 parts of a 30% hydrogen peroxide solution (equivalent to 5 parts of H2O2) were added. The mixture was stirred at 200 rpm at 35°C for 2 hours to obtain a graphene oxide dispersion. After the reaction was completed, the product was centrifuged, washed with water until neutral, and vacuum dried to obtain graphene oxide.

[0063] Example 1 1) Preparation of modified graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. Two parts of tannic acid were added to this suspension, and the mixture was stirred continuously at 400 rpm for 2 h at room temperature to allow polyphenols to pre-adsorb onto the surface of the carbon materials, resulting in a pretreated slurry. Subsequently, an online pH monitor was connected, and a total of 10 parts of ammonium bicarbonate were added to the pretreated slurry in three batches under stirring at 400 rpm to continue the modification reaction. The three additions accounted for 35%, 35%, and 30% of the total amount, respectively. Throughout the addition and modification process, the pH of the system was controlled at 4.5–5.0 by adding 1 mol / L dilute phosphoric acid solution. The interval between two additions was 30 min. After the last batch of ammonium bicarbonate was added, the pH was maintained at 4.5–5.0, and the mixture was stirred for 30 min. After the reaction was completed, the resulting black mixture was filtered and separated. The filter cake was washed three times with deionized water (100 parts water each time) and finally dried under vacuum at 60℃ for 24 h to obtain modified graphene / carbon nanotube composite powder, denoted as G / C-1.

[0064] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube pre-dispersed powder (G / C-1) and stir evenly. Then put it into a sand mill and grind for 1 hour. The zirconium beads are 0.8mm and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, carbon material conductive slurry is obtained, which is denoted as A1.

[0065] Example 2 1) Preparation of modified graphene / carbon nanotube composite powder Modified graphene / carbon nanotube composite powder was prepared according to the method in Example 1, except that tannic acid was replaced with an equal mass of catechin. The prepared composite powder is designated as G / C-2.

[0066] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube composite powder (G / C-2) and stir evenly. Then put it into a sand mill and grind for 1 hour. The zirconium beads are 0.8mm and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as A2.

[0067] Example 3 1) Preparation of modified graphene / carbon nanotube composite powder Modified graphene / carbon nanotube composite powder was prepared according to the method in Example 1, except that ammonium bicarbonate was replaced with an equal mass of ammonium carbonate. The prepared composite powder is designated as G / C-3.

[0068] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube composite powder (G / C-3) and stir evenly. Then put it into a sand mill and grind for 1 hour. The zirconium beads are 0.8mm and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as A3.

[0069] Example 4 1) Preparation of modified graphene / carbon nanotube composite powder Modified graphene / carbon nanotube composite powder was prepared according to the method in Example 1, except that the amount of tannic acid was adjusted to 1.2 parts, and the prepared composite powder was designated as G / C-4.

[0070] 2) Preparation of conductive paste Take 20g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube composite powder (G / C-4) and stir evenly. Then put it into a sand mill and grind for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as A4.

[0071] Example 5 1) Preparation of modified graphene / carbon nanotube composite powder Modified graphene / carbon nanotube composite powder was prepared according to the method in Example 1, except that the amount of ammonium bicarbonate was adjusted to 5 parts, and the prepared composite powder was denoted as G / C-5.

[0072] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube composite powder (G / C-5) and stir evenly. Then put it into a sand mill and grind for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, carbon material conductive slurry is obtained, which is denoted as A5.

[0073] Example 6 1) Preparation of modified graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. Two and a half parts of tannic acid were added to this suspension, and the mixture was stirred continuously at 400 rpm for 2 h at room temperature to allow polyphenols to pre-adsorb onto the carbon material surface, resulting in a pretreated slurry. Subsequently, an online pH monitor was connected, and a total of eight parts of ammonium bicarbonate were added to the pretreated slurry in three batches under stirring at 400 rpm to continue the modification reaction. The three additions accounted for 40%, 40%, and 20% of the total amount, respectively. Throughout the addition and modification process, the pH of the system was controlled at 4.5–5.0 by adding 1 mol / L dilute phosphoric acid solution. The interval between two additions was 30 min. After the last batch of ammonium bicarbonate was added, the pH was maintained at 4.5–5.0, and the mixture was stirred for another 30 min. After the reaction was completed, the resulting black mixture was filtered and separated. The filter cake was washed three times with deionized water (100 parts water each time) and finally dried under vacuum at 60℃ for 24 hours to obtain modified graphene / carbon nanotube composite powder, denoted as G / C-6.

[0074] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube composite powder (G / C-6) and stir evenly. Then put it into a sand mill and grind for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as A6.

[0075] Example 7 1) Preparation of modified graphene / carbon nanotube composite powder Modified graphene / carbon nanotube composite powder was prepared according to the method in Example 1, except that graphene oxide was replaced with physically exfoliated few-layer graphene (3 to 5 layers, C / O=49, the same below) before hydrogen peroxide oxidation. The prepared composite powder was denoted as G / C-7.

[0076] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone. Add 90g of modified graphene / carbon nanotube composite powder (G / C-7), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size, and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained, which is denoted as A7.

[0077] Comparative Example 1 1) Preparation of graphene / carbon nanotube composite powder Three parts of physically exfoliated few-layer graphene and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 30 min to obtain a black suspension. The suspension was then filtered, and the filter cake was washed three times with deionized water (100 parts water each time). Finally, it was vacuum dried at 60℃ for 24 h to obtain graphene / carbon nanotube composite powder, denoted as G / C-d1.

[0078] 2) Preparation of conductive paste Take 30g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone solvent. Add 90g of composite powder (G / C-d1), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, carbon material conductive slurry is obtained, which is denoted as B1.

[0079] Comparative Example 2 1) Preparation of graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. The suspension was then filtered, and the filter cake was washed three times with deionized water (100 parts water each time). Finally, it was vacuum dried at 60℃ for 24 h to obtain graphene / carbon nanotube composite powder, denoted as G / C-d2.

[0080] 2) Preparation of conductive paste Take 30g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone solvent. Add 90g of composite powder (G / C-d2), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, carbon material conductive slurry is obtained, which is denoted as B2.

[0081] Comparative Example 3 1) Preparation of modified graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. Two parts of tannic acid were added to the suspension, and the mixture was stirred continuously at 400 rpm for 5 h at room temperature. The mixture was then filtered, and the filter cake was washed three times with deionized water (100 parts water each time). Finally, it was vacuum dried at 60 °C for 24 h to obtain the modified graphene / carbon nanotube composite powder, denoted as G / C-d3.

[0082] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone solvent. Add 90g of composite powder (G / C-d3), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as B3.

[0083] Comparative Example 4 1) Preparation of graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. Ten parts of ammonium bicarbonate were added to the suspension and stirred continuously at 400 rpm for 5 h at room temperature. The mixture was then filtered, and the filter cake was washed three times with deionized water (100 parts water each time). Finally, it was vacuum dried at 60 °C for 24 h to obtain graphene / carbon nanotube composite powder, denoted as G / C-d4.

[0084] 2) Preparation of conductive paste Take 30g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone solvent. Add 90g of composite powder (G / C-d4), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as B4.

[0085] Comparative Example 5 1) Preparation of modified graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. Ten parts of tannic acid were added to this suspension, and the mixture was continuously stirred at 400 rpm for 5 h at room temperature to modify the carbon material with polyphenols. The mixture was then filtered, and the filter cake was washed three times with deionized water (100 parts water each time). Finally, it was vacuum dried at 60℃ for 24 h to obtain the modified graphene / carbon nanotube composite powder, denoted as G / C-d5.

[0086] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone solvent. Add 90g of composite powder (G / C-d5), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, carbon material conductive slurry is obtained, which is denoted as B5.

[0087] Comparative Example 6 1) Preparation of modified graphene / carbon nanotube composite powder Three parts of graphene oxide and seven parts of carbon nanotubes were added to 90 parts of deionized water and pre-dispersed at 1500 rpm for 15 min to obtain a black suspension. Two parts of tannic acid were added to the suspension, and the mixture was stirred continuously at 400 rpm for 2 h at room temperature to allow polyphenols to be pre-adsorbed onto the surface of the carbon material, thus achieving pretreatment. Subsequently, 20 parts of ammonium bicarbonate were added, and the reaction was continued for 3 h. After the reaction was completed, the resulting black mixture was filtered and separated. The filter cake was washed three times with deionized water (100 parts water each time) and finally dried under vacuum at 60 °C for 24 h to obtain the modified graphene / carbon nanotube composite powder, denoted as G / C-d6.

[0088] 2) Preparation of conductive paste Take 10g of PVP K30 and dissolve it in 900g of N-methylpyrrolidone solvent. Add 90g of composite powder (G / C-d6), stir evenly, and then put it into a sand mill for 1 hour. The zirconium beads are 0.8mm in size and the sand milling speed is 2000rpm. After sand milling, after demagnetization and filtration, the carbon material conductive slurry is obtained and is denoted as B6.

[0089] Test case This test example is used to evaluate the performance of the conductive pastes A1~A7 and B1~B6 prepared in the above embodiments and comparative examples.

[0090] (1) Viscosity test The initial viscosity N0 of conductive pastes A1~A7 and B1~B6 was tested at 25℃. After each conductive paste was allowed to stand at 25℃ for one week, its viscosity N1 was tested again. Both tests used a No. 4 rotor at a speed of 60 rpm. The viscosity change rate was calculated according to Formula I: Viscosity change rate (%) = [(N1-N0) / N0] × 100% Equation I, (2) Settlement rate assessment The initial solid content S0 of conductive pastes A1~A7 and B1~B6 was tested respectively. After each conductive paste was allowed to stand at 25℃ for 1 week, the upper solid content S1 was tested again. The sedimentation rate was calculated using the following formula II: Settlement rate (%) = [(S0-S1) / S0] × 100% (Equation II) Solid content determination method: Take about 3g of sample, weigh it accurately with an analytical balance, dry it at 120℃ to constant weight, weigh the residual solid mass, and calculate the percentage of solid mass to total sample mass.

[0091] (3) Conductivity assessment Conductive slurries A1~A7 and B1~B6 were used as positive electrode additives for lithium-ion batteries to prepare battery slurries, and the resistivity of the electrode sheets was tested.

[0092] Battery slurry preparation: Weigh each component according to the mass ratio of NCM622:PVDF:carbon black:conductive slurry = 97.0:1.5:0.5:1.0, and add additional NMP to adjust the total slurry solid content to 75%. After slurry preparation, coat it onto a PET film, bake it at 120℃ for 2 hours, cut it into 6 5cm×5cm squares, and use a four-probe resistivity meter to test the resistivity of each group of 6 films, and take the average value.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095] Note: Dispersant content refers to its mass percentage in the conductive paste.

[0096] As shown in Table 1, the carbon-based conductive slurries of Examples 1-7 all exhibited good dispersion stability and conductivity under conditions of low dispersant dosage, and their overall performance was significantly better than that of the comparative examples. Comparing Example 1 with Comparative Examples 1-2, it can be seen that without polyphenols and gas-generating agents, even with a high dispersant dosage, the conductive slurry showed significant sedimentation (lower layer agglomeration and gelation), a significant increase in viscosity, and poor conductivity. In contrast, Example 1, with a low dispersant dosage, showed a smaller viscosity change rate, almost no sedimentation, and lower resistivity, indicating that the synergistic treatment of polyphenols and gas-generating agents can significantly improve the stability and conductivity of the slurry. Comparing Example 1 with Comparative Examples 3-4, it can be seen that neither polyphenols nor gas-generating agents alone could achieve the aforementioned synergistic effect; both are indispensable. Comparing Example 1 with Comparative Examples 5 and 6, it can be seen that excessive amounts of polyphenols or gas-generating agents would lead to decreased stability or deterioration of conductivity. Furthermore, Example 1, which uses edge-oxidized graphene, exhibits better overall performance than Example 7, which does not use edge-oxidized graphene, indicating that edge pre-oxidation of graphene contributes to polyphenol anchoring.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a carbon material conductive paste, characterized in that, include: (1) In the presence of a first solvent, polyphenols are used to pretreat carbon materials to obtain a pretreated slurry; wherein the first solvent is an aqueous solvent, the carbon materials include graphene and carbon nanotubes, and the mass ratio of polyphenols to carbon materials is (10~30):

100. (2) The pretreated slurry is mixed with the gas-generating agent and modified to obtain a mixture; wherein the gas-generating agent can decompose to generate gas in the modification reaction, and the mass ratio of the gas-generating agent to the carbon material is (50~100):

100. (3) The mixture is subjected to solid-liquid separation and drying to obtain modified graphene / carbon nanotube composite powder; (4) The modified graphene / carbon nanotube composite powder is mixed with a dispersant and a second solvent to obtain the carbon material conductive slurry.

2. The preparation method according to claim 1, characterized in that, The polyphenols are selected from at least one of tannic acid, catechin, gallic acid, caffeic acid, and anthocyanins.

3. The preparation method according to claim 1 or 2, characterized in that, Based on the total amount of carbon materials, the graphene accounts for 10% to 40% by mass, and the carbon nanotubes account for 60% to 90% by mass. Preferably, the carbon nanotubes are multi-walled carbon nanotubes.

4. The preparation method according to any one of claims 1-3, characterized in that, The graphene is at least one of physically exfoliated graphene, graphene oxide, and reduced graphene oxide, and the surface C / O atomic ratio of the graphene oxide is 6.0 to 6.

5. Preferably, the graphene oxide is obtained by oxidizing physically exfoliated graphene with hydrogen peroxide; wherein the mass amount of hydrogen peroxide (H2O2) is 1% to 5% of the mass of the physically exfoliated graphene, the physically exfoliated graphene has 3 to 5 layers, and its surface C / O atomic ratio is not less than 20. More preferably, the oxidation treatment is carried out at a temperature of 20-40°C for 1-2 hours.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (1), the pretreatment operating conditions include: temperature of 20~40℃, stirring speed of 200~500rpm, and time of 1~3h.

6. The preparation method according to any one of claims 1-5, characterized in that, The gas-generating agent is ammonium carbonate and / or ammonium bicarbonate, preferably ammonium bicarbonate; Preferably, in step (2), the operating conditions of the modification reaction include: pH 4.5~6.0, temperature 20~40℃, stirring speed 200~500rpm, and time 1~3h; More preferably, the pH of the reaction system in step (2) is adjusted by phosphoric acid at a concentration of 0.5 to 1.0 mol / L.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (2), the gas-generating agent is added to the pretreated slurry in 3 to 5 portions, with an interval of 10 to 40 minutes between two adjacent additions, and the amount added each time is 20% to 40% of the total mass of the gas-generating agent.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (4), the dispersant is selected from at least one of polyvinylpyrrolidone, nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, styrene-maleic anhydride copolymer, carboxymethyl cellulose, polyethylene glycol, polyvinyl alcohol and polyethyleneimine; Preferably, the second solvent is selected from at least one of water, N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; Preferably, based on 100 parts by mass of the total amount of the carbon material conductive paste, the amount of the dispersant is 0.5 to 3 parts by mass, the amount of the modified graphene / carbon nanotube composite powder is 5 to 10 parts by mass, and the amount of the second solvent is 88 to 93 parts by mass. Preferably, step (4) includes: dissolving the dispersant in the second solvent, then adding the modified graphene / carbon nanotube composite powder for grinding, followed by demagnetization and filtration to obtain a carbon material conductive slurry.

9. A carbon material conductive paste prepared by the preparation method according to any one of claims 1-8.

10. The application of the carbon material conductive paste according to claim 9 in the preparation of secondary batteries; Preferably, the secondary battery is a lithium-ion battery.

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