Preparation method of high-conductivity composite graphene, conductive ink and application thereof

Abstract

The invention provides a preparation method of high-conductivity composite graphene, conductive ink and application thereof, and the preparation method comprises the following steps: dispersing graphene into a solvent to obtain a graphene dispersion liquid; adding a silane coupling agent with an amino group into the graphene dispersion liquid, and reacting to obtain aminated graphene; and adding a first dispersing agent into the aminated graphene, adding silver powder after uniform dispersion, and grinding to form an Ag-N coordinate bond between the silver powder and the aminated graphene, thereby obtaining the high-conductivity composite graphene. In the preparation method of the high-conductivity composite graphene provided by the invention, a silane coupling agent with an amino group is added into a graphene dispersion liquid, amination modification is completed through a condensation reaction with a hydroxyl group on the surface of the graphene, silver powder and the amino group of the graphene form an Ag-N coordinate bond, so that silver particles are completely coated with the graphene, a continuous C-Ag-C conductive network is constructed, and the high-conductivity composite graphene is obtained. According to the network, path breakpoints are reduced, interface contact resistance is reduced, charge transmission efficiency is improved, conductivity reduction after graphene compounding is effectively inhibited, and high conductivity and high heat resistance are achieved.

Description

Technical Field

[0001] This invention relates to conductive materials, and more particularly to a method for preparing highly conductive composite graphene, conductive ink, and their applications. Background Technology

[0002] Graphene has broad development potential in conductive applications due to its theoretically high electrical conductivity. However, in practical applications, its electrical conductivity drops sharply when graphene is combined with other materials. This defect makes it difficult for graphene to meet the requirements of some high-conductivity applications with stringent conductivity requirements. Summary of the Invention

[0003] To address the problem that the conductivity of graphene decreases sharply when it is combined with other materials in existing technologies, this paper provides a method for preparing highly conductive composite graphene, conductive ink, and its applications.

[0004] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows: On one hand, the present invention provides a method for preparing highly conductive composite graphene, comprising the following operations: Graphene is dispersed in a solvent to obtain a graphene dispersion. An amino-containing silane coupling agent was added to a graphene dispersion, and after the reaction, amino-based graphene was obtained. A first dispersant is added to aminated graphene, and after it is evenly dispersed, silver powder is added. The mixture is then ground to form Ag-N coordination bonds between the silver powder and the aminated graphene, resulting in highly conductive composite graphene.

[0005] Optionally, the amino-containing silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane.

[0006] Optionally, based on the total mass of the highly conductive composite graphene as 100%, the amount of the amino-containing silane coupling agent added is 0.1% to 15%; The amount of the first dispersant added is 0.1% to 20%.

[0007] Optionally, the silver powder has a particle size of 0.5~5μm.

[0008] Optionally, in the highly conductive composite graphene, the mass ratio of the aminated graphene to the silver powder is 1:(1~5).

[0009] Optionally, the graphene is treated with a concentrated acid solution, which includes one or more of concentrated nitric acid and concentrated sulfuric acid.

[0010] Optionally, the graphene dispersion is heat-treated before adding an amino-containing silane coupling agent at a temperature of 60-70°C for 1-2 hours.

[0011] On the other hand, the present invention provides a conductive ink comprising highly conductive composite graphene prepared by the aforementioned preparation method.

[0012] Optionally, the conductive ink comprises the following components by mass: 1-20 parts of highly conductive composite graphene 1-50 parts of resin Second dispersant: 0.01~5 parts Leveling agent 0.01~5 parts.

[0013] Optionally, the conductive ink is applied to a heating device.

[0014] The beneficial effects of this application are as follows: In the preparation method of the highly conductive composite graphene provided in this application, an amino-containing silane coupling agent is added to a graphene dispersion. After the amino-containing silane coupling agent is added, it undergoes a condensation reaction with the hydroxyl groups on the graphene surface, thereby modifying the graphene. The organic functional groups of the amino-containing silane coupling agent can bind to the active sites on the graphene surface, while the inorganic functional groups can form chemical bonds with silver powder. A first dispersant is added and the mixture is ground. The mechanical force generated by grinding promotes the formation of Ag-N coordination bonds between the silver particles and the amino groups on the graphene surface, significantly enhancing the bonding strength between the silver particles and graphene. This allows the graphene to completely coat the surface of the silver particles, forming a continuous C-Ag-C composite conductive network, reducing the number of breakpoints in the conductive pathway, significantly reducing the interfacial contact resistance, and improving the charge transport efficiency. This effectively suppresses the decreasing trend of conductivity after graphene compositing. At the same time, with the synergistic effect of graphene and silver, the prepared highly conductive composite graphene possesses both high conductivity and high heat resistance. Attached Figure Description

[0015] Figure 1 It is a heating device provided by existing technology; Figure 2 This is the heating device provided by the present invention.

[0016] The reference numerals in the accompanying drawings are as follows: 1. Electrode; 2. Substrate; 3. Conductive layer. Detailed Implementation

[0017] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0018] This invention provides a method for preparing highly conductive composite graphene, comprising the following steps: Graphene is dispersed in a solvent to obtain a graphene dispersion. An amino-containing silane coupling agent was added to a graphene dispersion, and after the reaction, amino-based graphene was obtained. A first dispersant is added to aminated graphene, and after it is evenly dispersed, silver powder is added. The mixture is then ground to form Ag-N coordination bonds between the silver powder and the aminated graphene, resulting in highly conductive composite graphene.

[0019] Specifically, the amino-containing silane coupling agent undergoes a condensation reaction with the hydroxyl groups on the graphene surface to achieve graphene amination modification, introducing amino active sites on the graphene surface to provide interaction sites for subsequent chemical bonding with silver powder. The addition of the first dispersant further improves the dispersibility of the system and avoids the agglomeration of silver powder. The mechanical force generated by grinding promotes the formation of Ag-N coordination bonds between silver powder and aminated graphene. This chemical bonding significantly enhances the bonding strength between silver powder and graphene, allowing graphene to completely coat the silver particles and construct a continuous C-Ag-C composite conductive network. This network structure can reduce the number of breakpoints in the conductive path, lower the interfacial contact resistance, and improve the charge transport efficiency, fundamentally suppressing the decreasing trend of conductivity after graphene composite. At the same time, with the synergistic effect of the high heat resistance of graphene and the high conductivity of silver, the product has both high conductivity and high heat resistance.

[0020] Furthermore, the preparation method of the highly conductive composite graphene specifically includes the following operations: Graphene was treated with 80% concentrated nitric acid for 30 minutes to introduce hydroxyl and nitro groups at the edges and surface of the graphene. The treated graphene is filtered and washed to remove excess nitric acid, resulting in pretreated graphene. Pretreated graphene was dispersed in ethanol, and the dispersion was heated in a water bath at 70°C to obtain a graphene dispersion. γ-aminopropyltriethoxysilane was slowly added dropwise and the reaction was continued for 6 hours. During this period, the ethoxy group of γ-aminopropyltriethoxysilane was hydrolyzed to generate silanol groups, which underwent a condensation reaction with the hydroxyl groups on the surface of graphene. At the same time, amino groups were grafted onto the surface of graphene, and after the reaction, aminated graphene was obtained. Aminated graphene and the first dispersant were added to deionized water and dispersed evenly. Then, the aminated graphene and silver powder were mixed at a ratio of 1:1~5 (silver powder 1μm) to obtain a mixed solution. The mixture was ball-milled at a rotation speed of 3000 r / min and a revolution speed of 500 r / min for 2 hours. After centrifugation, highly conductive composite graphene was obtained.

[0021] The first dispersant may be the same as the second dispersant.

[0022] In some embodiments, the amino-containing silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane.

[0023] Specifically, the amino-containing silane coupling agent contains both an amino group (-NH2) and a hydrolyzable alkoxy group (such as -OC2H5, -OCH3). The silanol groups generated after the alkoxy groups are hydrolyzed can undergo a condensation reaction with the hydroxyl groups on the graphene surface to achieve stable grafting of graphene. The amino group, as an active functional group, can form Ag-N coordination bonds with the metal sites on the surface of silver powder to ensure the chemical bonding effect between silver powder and graphene. In addition, any of the above-mentioned amino-containing silane coupling agents can achieve the corresponding effect.

[0024] In some embodiments, based on the total mass of the highly conductive composite graphene as 100%, the amount of the amino-containing silane coupling agent added is 0.1% to 15%; The amount of the first dispersant added is 0.1% to 20%.

[0025] Specifically, adding 0.1% to 15% of the amino-containing silane coupling agent can effectively cover the amino sites on the graphene surface, ensuring effective bonding with silver powder without introducing too much insulating component. If the amount of the amino-containing silane coupling agent added is less than 0.1% (lower limit), there are insufficient amino sites grafted on the graphene surface, which cannot fully form Ag-N coordination bonds with silver powder. The bonding force between silver powder and graphene is weak, and interface separation is prone to occur, resulting in discontinuous conductive network. If the amount of the amino-containing silane coupling agent added is higher than 15% (upper limit), the excess coupling agent will form an organic coating layer on the graphene surface. This organic layer is an insulating phase, which will increase the charge transport resistance and reduce the conductivity of the composite system. Further testing revealed that the amino-containing silane coupling agent exhibits better performance when its addition amount is set within the range of 0.5% to 1.5%. The addition of the first dispersant at a rate of 0.1% to 20% can achieve uniform dispersion of silver powder and aminated graphene, ensuring the full formation of Ag-N coordination bonds during the grinding process, while avoiding the introduction of additional conductive losses.

[0026] If the amount added is less than 0.1% (lower limit), the dispersion effect is insufficient, and the silver powder is prone to agglomerate into large particles, which will damage the continuity of the conductive network. If the amount added exceeds 20% (the upper limit), the excess dispersant will be adsorbed on the surface of silver powder and graphene, forming an insulating interface layer and increasing the contact resistance.

[0027] In some embodiments, the silver powder has a particle size of 0.5~5μm.

[0028] Specifically, the 0.5~5μm silver powder has a moderate particle size, which not only has sufficient specific surface area to form effective bonds with graphene, but also avoids excessive agglomeration, ensuring the density and continuity of the conductive network in the composite system, and further improving the conductivity of the highly conductive composite graphene.

[0029] If the silver powder particle size is less than 0.5μm, the specific surface area of ​​the silver powder is too large and the surface energy is high, making it very easy to agglomerate. Agglomerated silver powder particles will form conductive islands, blocking the charge transport path. At the same time, small-diameter silver powder is prone to lattice distortion during the grinding process, affecting its own conductivity.

[0030] If the silver powder particle size is greater than 5μm, the contact area between the silver powder and the aminated graphene is reduced, making it difficult to form a dense C-Ag-C conductive network. This reduces the continuity of the conductive pathway and increases the interfacial contact resistance.

[0031] Furthermore, the particle size of the silver powder includes, but is not limited to, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0032] In some embodiments, the mass ratio of the aminated graphene to the silver powder in the highly conductive composite graphene is 1:(1~5).

[0033] In the highly conductive composite graphene, the mass ratio of the aminated graphene to the silver powder is 1:(1~5) to achieve the optimal synergy between graphene and silver powder. Specifically, graphene serves as the conductive framework and silver powder serves as the conductive node. The C-Ag-C composite conductive network formed by the two has both the high structural stability of graphene and the high electron mobility of silver. While suppressing the decrease in conductivity, it also takes into account high conductivity and high heat resistance.

[0034] If the proportion of silver powder is less than 1:1 by mass (i.e., the mass of silver powder is less than that of graphene), the silver powder cannot fully fill the gaps between graphene sheets, making it difficult to form a continuous metal conductive path, and the effect of improving the conductivity of the composite system is limited. If the proportion of silver powder is higher than 1:5 by mass (i.e., the mass of silver powder is more than 5 times that of graphene), the excess silver powder will accumulate in the system, which will not only increase production costs, but also cause defects in the conductive network due to the agglomeration between silver powder particles, and reduce the heat resistance of the composite system (the melting point of silver is lower than the heat resistance temperature of graphene). In some embodiments, the graphene is treated with a concentrated acid solution, the concentrated acid solution including one or more of concentrated nitric acid and concentrated sulfuric acid.

[0035] Specifically, concentrated acid solutions have strong oxidizing and intercalating properties. On the one hand, they can introduce a large number of oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups onto the graphene surface through oxidation. These oxygen-containing functional groups provide abundant action sites for the subsequent condensation reaction of silane coupling agents, significantly improving the efficiency of graphene amination modification. On the other hand, the intercalation effect of concentrated acid can exfoliate graphene aggregates, allowing the graphene sheets to be fully dispersed and reducing the problem of blocked conductive pathways caused by agglomeration.

[0036] Untreated graphene has few active sites and exhibits severe agglomeration, making it difficult to effectively bind with silane coupling agents. Consequently, it cannot form stable Ag-N coordination bonds with silver powder, ultimately leading to a decrease in conductivity after composite formation. Therefore, this pretreatment step provides a prerequisite for subsequent modification and composite processes and is a key pretreatment operation for achieving high conductivity.

[0037] In some embodiments, the graphene dispersion is heat-treated at a temperature of 60-70°C for 1-12 hours before the addition of an amino-containing silane coupling agent.

[0038] This heat treatment process optimizes the state of the graphene dispersion, improves the uniformity and effectiveness of subsequent amination modification, and facilitates the formation of a composite conductive network.

[0039] Specifically, a temperature of 60-70℃ can accelerate the movement of solvent molecules in the graphene dispersion, promote the uniform dispersion of graphene sheets, and activate the hydroxyl activity on the graphene surface, providing suitable thermodynamic conditions for the condensation reaction of the silane coupling agent. If the temperature is below 60℃, the reaction kinetics are insufficient, the graphene dispersion is poor, and the reaction efficiency between the coupling agent and graphene is low. If the temperature is above 70℃, the solvent is prone to evaporate too quickly, and the graphene will undergo secondary agglomeration, affecting the subsequent modification effect.

[0040] A heat treatment time of 1 to 12 hours can ensure sufficient dispersion of graphene and activation of surface active sites. If the time is less than 1 hour, the graphene dispersion and site activation will be insufficient. If the time is longer than 12 hours, it will increase energy consumption and may lead to excessive oxidation of functional groups on the graphene surface, which will reduce the modification effect.

[0041] Another embodiment of the present invention provides a conductive ink comprising highly conductive composite graphene prepared by the aforementioned preparation method.

[0042] Specifically, the conductive ink includes the preparation method of conductive composite graphite provided in this application. The conductive ink continues the C-Ag-C continuous conductive network structure of highly conductive composite graphene. After printing into a film, it can form a dense conductive layer with low charge transmission resistance, making it suitable for application scenarios with stringent requirements for conductivity performance. Meanwhile, graphene's high heat resistance endows the ink with excellent high-temperature stability, enabling it to maintain stable conductivity in high-temperature environments and expanding the application range of conductive inks.

[0043] In some embodiments, the conductive ink comprises the following components by mass: 1-20 parts of highly conductive composite graphene 1-50 parts of resin Second dispersant: 0.01~5 parts Leveling agent 0.01~5 parts.

[0044] Specifically, the highly conductive composite graphene (1-20 parts) serves as the core conductive functional phase of the ink. This content range ensures the formation of a continuous conductive network after the ink film is formed. If the content is too low, the conductivity will be insufficient; if the content is too high, the film-forming properties of the ink will deteriorate, and cracking and peeling will easily occur.

[0045] Resin (1-50 parts) serves as the film-forming carrier for the ink. The resin can coat highly conductive composite graphene particles, giving the ink good adhesion and film strength. The resin content needs to be matched with the conductive filler. Too high a content will dilute the conductive components and reduce the conductivity, while too low a content will prevent the formation of a stable film.

[0046] The second dispersant (0.01~5 parts) is designed to meet the dispersion requirements of the ink system, further improving the dispersion uniformity of highly conductive composite graphene in the resin matrix, preventing filler agglomeration, and ensuring the consistency of the conductive properties of the printed film.

[0047] Leveling agent (0.01~5 parts): Improves the leveling and wetting properties of ink, enabling the ink to spread evenly during the printing process, reducing surface defects such as pinholes and craters, and improving the surface quality and electrical conductivity of printed materials.

[0048] This formulation achieves a balance between conductivity, film-forming properties, and printability, giving the conductive ink high conductivity, good adhesion, and excellent printability.

[0049] Reference Figures 1-2 In some embodiments, the conductive ink is applied to a heating device.

[0050] Specifically, Figure 1 The traditional long-side electrode structure, with electrode 1 arranged along both long sides of the conductive layer, is only suitable for small-sized, low-power heating devices. The core reason is that ordinary graphene ink has discontinuous conductive pathways, high interface resistance, and significant charge transport losses. This necessitates shortening the lateral current transport path to compensate for insufficient conductivity. Even so, a significant temperature gradient still occurs due to voltage drop, resulting in poor heating uniformity. Figure 2 The conductive ink uses the highly conductive composite graphene provided in this application, which has an electrode structure at both ends, with electrode 1 only placed at the end of the conductive layer 3. This allows current to be transmitted along the entire length of the conductive layer, making it suitable for large-size, high-power heating devices. Compared to... Figure 1 The settings, Figure 2 Based on the C-Ag-C continuous conductive network constructed from the highly conductive composite graphene of this application, the strong bond of Ag-N coordination bonds prevents the graphene from detaching from the silver powder, significantly reducing interfacial contact resistance and charge transport loss, so that there is no significant voltage drop during long-distance current transmission. The current density is uniform in each region of the conductive layer 3, ultimately achieving excellent heating temperature consistency. At the same time, with the synergistic effect of graphene and silver, the ink can still maintain stable performance under high-temperature heating conditions, completely solving the layout and application problems of traditional inks that are limited by insufficient conductivity.

[0051] This conductive ink is based on a C-Ag-C composite conductive network, which has high conductivity and can reduce the energy consumption of heating devices. At the same time, the high heat resistance of graphene and the oxidation resistance of silver enable the ink to maintain stable conductivity and structural integrity under long-term high-temperature heating environment, solving the problems of easy aging and rapid degradation of conductivity of traditional graphene-based heating inks.

[0052] Graphene exhibits the NTC effect, meaning its resistance decreases as temperature increases. This characteristic makes graphene heating elements difficult to control during use. Silver, on the other hand, exhibits the PTC effect, meaning its resistance increases as temperature rises. The conductive ink in this product uses a C-Ag-C composite conductive network, where the NTC effect of graphene cancels out the PTC effect of silver. The resulting heating element offers stable power output and is easier to control during use.

[0053] The present invention will be further illustrated by the following examples.

[0054] Example 1 This embodiment illustrates the preparation method of the highly conductive composite graphene, the conductive ink, and its application disclosed in this invention, and includes the following steps: Graphene was treated with 80% concentrated nitric acid for 30 minutes to introduce hydroxyl and nitro groups at the edges and surface of the graphene. The treated graphene is filtered and washed to remove excess nitric acid, resulting in pretreated graphene. Pretreated graphene was dispersed in ethanol, and the dispersion was heated in a water bath at 70°C to obtain a graphene dispersion. γ-aminopropyltriethoxysilane was slowly added dropwise and the reaction was continued for 6 hours to obtain amino-graphene. Aminated graphene and the first dispersant were added to deionized water and dispersed evenly. Then, the aminated graphene and silver powder were mixed at a ratio of 1:5 (silver powder particle size 1μm) to obtain a mixed solution. The mixture was ball-milled (the ratio of large balls: medium balls: small balls was 1:3:4, the diameter of the large balls was 10 mm, the diameter of the medium balls was 6 mm, and the diameter of the small balls was 3 mm). The ball milling speed was 3000 r / min for rotation and 500 r / min for revolution. The ball milling time was 2 h. After centrifugation, highly conductive composite graphene was obtained. Highly conductive composite graphene was added to the second dispersant (organosilicon) and dispersed at high speed at a speed of 800 r / min. Leveling agent and defoamer were added during the dispersion process, and the dispersion was continued for 30 min. After the dispersion was completed, conductive ink was prepared. The conductive ink contains 3 parts of highly conductive composite graphene, 10 parts of resin, 0.05 parts of second dispersant, and 0.03 parts of leveling agent.

[0055] Conductive ink is screen-printed to obtain the corresponding heating device.

[0056] Example 2 This embodiment illustrates the preparation method of the highly conductive composite graphene, the conductive ink, and its application disclosed in this invention, and includes the following steps: Graphene was dispersed in ethanol, and the dispersion was heated in a water bath at 70°C to obtain a graphene dispersion. γ-aminopropyltriethoxysilane was slowly added dropwise and the reaction was continued for 6 hours. After the reaction, aminographene was obtained. In the process of obtaining aminographene, the graphene was not treated with concentrated acid solution. Aminated graphene and the first dispersant were added to deionized water and dispersed evenly. Then, the aminated graphene and silver powder were mixed at a ratio of 1:5 (silver powder particle size 1μm) to obtain a mixed solution. The mixture was ball-milled (the ratio of large balls: medium balls: small balls was 1:3:4, the diameter of the large balls was 10 mm, the diameter of the medium balls was 6 mm, and the diameter of the small balls was 3 mm). The ball milling speed was 3000 r / min for rotation and 500 r / min for revolution. The ball milling time was 2 h. After centrifugation, highly conductive composite graphene was obtained. Highly conductive composite graphene was added to the second dispersant (organosilicon) and dispersed at high speed at a speed of 800 r / min. Leveling agent and defoamer were added during the dispersion process, and the dispersion was continued for 30 min. After the dispersion was completed, conductive ink was prepared. The conductive ink contains 3 parts of highly conductive composite graphene, 10 parts of resin, 0.05 parts of second dispersant, and 0.03 parts of leveling agent.

[0057] Conductive ink is screen-printed to obtain the corresponding heating device.

[0058] Comparative Example 1 This comparative example is used to illustrate the preparation method of the highly conductive composite graphene, the conductive ink, and its application disclosed in this invention, and includes the following steps: Silver powder (particle size 1 μm) was dispersed in deionized water at a speed of 300 rpm. During the dispersion process, γ-aminopropyltriethoxysilane was added to the deionized water to modify the silver powder. Graphene was treated with 80% concentrated nitric acid for 30 minutes to introduce hydroxyl and nitro groups at the edges and surface of the graphene. The treated graphene is filtered and washed to remove excess nitric acid, resulting in pretreated graphene. Pretreated graphene and modified silver powder were mixed in a 1:5 ratio and dispersed at 800 r / min for 30 min. After dispersion, the mixture was ball-milled (the ratio of large balls:medium balls:small balls was 1:3:4, the diameter of large balls was 10 mm, the diameter of medium balls was 6 mm, and the diameter of small balls was 3 mm; the ball milling speed was 3000 r / min for rotation and 500 r / min for revolution; the ball milling time was 2 h) to obtain the graphene composite. The graphene composite was added to the second dispersant (organosilicon) and dispersed at high speed at a speed of 800 r / min. During the dispersion process, leveling agent and defoamer were added and the dispersion was continued for 30 min. After the dispersion was completed, conductive ink was prepared. The conductive ink contains 3 parts of highly conductive composite graphene, 10 parts of resin, 0.05 parts of second dispersant, and 0.03 parts of leveling agent.

[0059] Conductive ink is screen-printed to obtain the corresponding heating device.

[0060] Comparative Example 2 This comparative example illustrates the preparation method of the highly conductive composite graphene, the conductive ink, and its applications disclosed in this invention, and includes the following steps: Graphene was treated with 80% concentrated nitric acid for 30 minutes to introduce hydroxyl and nitro groups at the edges and surface of the graphene. The treated graphene is filtered and washed to remove excess nitric acid, resulting in pretreated graphene. Pretreated graphene was dispersed in ethanol, and the dispersion was heated in a water bath at 70°C to obtain a graphene dispersion. Vinyltriethoxysilane was slowly added dropwise, and the reaction was continued for 6 hours. Modified graphene was obtained after the reaction. Modified graphene and the first dispersant were added to deionized water and dispersed evenly. Then, aminated graphene and silver powder were mixed at a ratio of 1:5 (silver powder particle size 1μm) to obtain a mixed solution. The mixture was ball-milled (the ratio of large balls: medium balls: small balls was 1:3:4, the diameter of the large balls was 10 mm, the diameter of the medium balls was 6 mm, and the diameter of the small balls was 3 mm). The ball milling speed was 3000 r / min for rotation and 500 r / min for revolution. The ball milling time was 2 h. After centrifugation, highly conductive composite graphene was obtained. Highly conductive composite graphene was added to the second dispersant (organosilicon) and dispersed at high speed at a speed of 800 r / min. Leveling agent and defoamer were added during the dispersion process, and the dispersion was continued for 30 min. After the dispersion was completed, conductive ink was prepared. The conductive ink contains 3 parts of highly conductive composite graphene, 10 parts of resin, 0.05 parts of second dispersant, and 0.03 parts of leveling agent.

[0061] Conductive ink is screen-printed to obtain the corresponding heating device.

[0062] Performance testing The following performance tests were performed on Examples 1-2 and Comparative Examples 1-2 prepared above: After the heating device is fabricated, the sheet resistance of the coating is tested using a four-probe tester. The emissivity of the coating was measured using a thermal imager; The resistance R1 of the heating element is measured using a multimeter. The heating device is then energized and heated. When the heating element reaches 400℃, the resistance R2 is calculated, and the rate of change of resistance is R2 / R1-1.

[0063] The test results are entered into Table 1.

[0064] Table 1 As shown in Table 1, Example 1 exhibits the best overall performance with a sheet resistance of only 0.5Ω, an emissivity of 0.98, and a resistance change rate of 0 from 25 to 400℃. This is because the graphene is pretreated with concentrated nitric acid to introduce abundant hydroxyl groups, which are then modified by γ-aminopropyltriethoxysilane to form active sites. Silver powder forms strong Ag-N coordination bonds with the amino groups, constructing a continuous C-Ag-C conductive network. This reduces the interfacial contact resistance and cancels out the NTC effect of graphene and the PTC effect of silver powder, while maintaining the high emissivity of graphene. In Example 2, because the graphene was not treated with concentrated acid, there were insufficient surface active sites, the silver powder and graphene were not tightly bonded, and the continuity of the conductive network was poor. Therefore, the sheet resistance increased to 5Ω, the emissivity decreased slightly to 0.9, and the resistance change rate was -14%, resulting in a certain NTC effect. However, the overall effect was still better than that of Comparative Examples 1 and 2. Comparative Example 1 uses silane coupling agent to directly modify silver powder. Graphene and silver powder are only physically mixed, which is easy to separate and cause the conductive network to break. The sheet resistance increases significantly to 23Ω, the emissivity drops to 0.75, the resistance change rate reaches -25%, and a significant NTC effect is observed. Comparative Example 2 uses amino-free vinyltriethoxysilane-modified graphene, which cannot form Ag-N coordination bonds with silver powder. The conductive network is difficult to construct, the sheet resistance soars to 210Ω, the emissivity remains at 0.75, the resistance change rate reaches -30%, and the NTC effect is most obvious. In summary, the above discussion fully demonstrates that in the preparation method of the highly conductive composite graphene provided by this invention, an amino-containing silane coupling agent is added to the graphene dispersion. After the addition of the amino-containing silane coupling agent, a condensation reaction occurs with the hydroxyl groups on the graphene surface, simultaneously modifying the graphene. The organic functional groups of the amino-containing silane coupling agent can bind to the active sites on the graphene surface, while the inorganic functional groups can form chemical bonds with silver powder. After adding a first dispersant and grinding, the mechanical force generated by grinding promotes the formation of Ag-N coordination bonds between silver particles and the amino groups on the graphene surface, significantly enhancing the bonding strength between silver particles and graphene. This allows graphene to completely coat the surface of silver particles, forming a continuous C-Ag-C composite conductive network, reducing the number of breakpoints in the conductive pathway, significantly reducing interfacial contact resistance, and improving charge transport efficiency. It effectively suppresses the decreasing trend of conductivity after graphene compositing. At the same time, with the synergistic effect of graphene and silver, the prepared highly conductive composite graphene possesses both high conductivity and high heat resistance.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing highly conductive composite graphene, characterized in that, Includes the following operations: Graphene is dispersed in a solvent to obtain a graphene dispersion. An amino-containing silane coupling agent was added to a graphene dispersion, and after the reaction, amino-based graphene was obtained. A first dispersant is added to aminated graphene, and after it is evenly dispersed, silver powder is added. The mixture is then ground to form Ag-N coordination bonds between the silver powder and the aminated graphene, resulting in highly conductive composite graphene.

2. The method for preparing highly conductive composite graphene according to claim 1, characterized in that, The amino-containing silane coupling agent includes one or more of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltriethoxysilane, and N-phenyl-γ-aminopropyltrimethoxysilane.

3. The method for preparing highly conductive composite graphene according to claim 1, characterized in that, Based on the total mass of the highly conductive composite graphene as 100%, the amount of the amino-containing silane coupling agent added is 0.1%~15%; The amount of the first dispersant added is 0.1% to 20%.

4. The method for preparing highly conductive composite graphene according to claim 1, characterized in that, The silver powder has a particle size of 0.5~5μm.

5. The method for preparing highly conductive composite graphene according to claim 1, characterized in that, In the highly conductive composite graphene, the mass ratio of the aminated graphene to the silver powder is 1:(1~5).

6. The method for preparing highly conductive composite graphene according to claim 1, characterized in that, The graphene is treated with a concentrated acid solution, which includes one or more of concentrated nitric acid and concentrated sulfuric acid.

7. The method for preparing highly conductive composite graphene according to claim 1, characterized in that, Before adding the amino-containing silane coupling agent, the graphene dispersion is subjected to heat treatment at a temperature of 60-70°C for 1-2 hours.

8. A conductive ink, characterized in that, The high-conductivity composite graphene prepared by the preparation method according to any one of claims 1 to 7.

9. The conductive ink according to claim 8, characterized in that, Includes the following mass components: 1-20 parts of highly conductive composite graphene 1-50 parts of resin Second dispersant: 0.01~5 parts Leveling agent 0.01~5 parts.

10. The conductive ink according to claim 8, applied to a heating device.

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