Preparation method of directly applicable dispersible graphene composite powder conductive agent

Abstract

The application belongs to the field of graphene materials, paint, lithium battery, and relates to a preparation method of directly applicable and easily dispersible graphene composite powder conductive agent, comprising: uniformly stirring expanded graphite powder, other carbon materials, dispersing agent and additive, intercalation swelling agent and deionized water, and fully wetting the expanded graphite in water; the intercalation swelling agent is ammonium inorganic matter which is easily decomposed into gas by heat; preparing aqueous slurry by peeling, and preparing graphene composite aqueous slurry by peeling, homogenizing and crushing the above mixture through peeling equipment; drying and swelling, drying the graphene composite aqueous slurry, and then heating and swelling to obtain graphene composite powder conductive agent. The conductive agent is easy to add and disperse in various systems, and has good conductivity and heat conductivity, etc., can solve the application difficulty of downstream customers graphene powder, solve the cost increase after preparing into slurry, and reduce the difficulty for the wide application of graphene powder.

Description

Technical Field

[0001] This invention belongs to the fields of graphene materials, coatings, and lithium batteries, and relates to a method for preparing an easily dispersible graphene composite powder conductive agent that can be directly applied. Background Technology

[0002] Graphene, with its lightweight, chemically stable properties, good lubrication and wear resistance, barrier properties, excellent electrical and thermal conductivity, and extremely high carrier mobility, has shown great potential applications in various industries. It has already begun to emerge in the fields of lithium batteries, rubber tires, heat dissipation films, and coatings, gaining a certain market share. With the further development and progress of technology, its market share and application scope will be further expanded.

[0003] However, graphene also presents several challenges, particularly in powder applications. Its high specific surface area makes the powder highly bubbly and prone to dispersion, hindering its feeding and making it difficult for users to disperse properly when added directly to the matrix. Graphene readily agglomerates, significantly reducing its effectiveness. While graphene offers advantages, its application remains challenging. In contrast, carbon black and conductive graphite offer simpler powder feeding and easier dispersion, but their poor electrical and thermal conductivity often necessitates large additions to meet customer requirements. Large additions reduce the matrix content in the product, leading to weakened matrix strength and reduced capacity in lithium batteries. Even powders with high conductivity, such as Ketjen black, are still relatively bubbly and dispersed compared to graphene, and their price is also high.

[0004] Currently, in some fields, such as the lithium battery industry, graphene is sold by preparing graphene NMP slurry, which solves the problem of fragmented applications by downstream customers. However, this also brings about increased costs (the cost of the solvent itself, the cost of preparing the graphene slurry, especially with the significant increase in NMP costs in early 2021, the cost of graphene NMP slurry has continued to rise, and NMP is only used as a carrier in the entire electrode preparation process and does not enter the final electrode or battery product), reduced product shelf life (such as increased moisture and sedimentation stability issues), and difficulties in transportation, etc. Moreover, the one-system slurry also limits its application range, making it impossible to use in more systems. It can only be used in slurries for specific systems, increasing the complexity and process steps of graphene use.

[0005] Although there are various methods for graphene preparation, such as oxidation-reduction, liquid-phase exfoliation, chemical vapor deposition (CVD), and micromechanical exfoliation, the main methods suitable for large-scale industrial production at present are oxidation-reduction and liquid-phase exfoliation. Oxidation-reduction produces thinner graphene sheets, but these have more defects, consume a lot of energy, are complex, and are difficult to scale up. The resulting waste acid and waste liquid cause serious environmental pollution, placing an additional burden on environmental protection. Liquid-phase exfoliation typically uses solvent systems with surface tension close to that of graphene, such as organic solvents like NMP and DMF. However, in recent years, national environmental policies have become increasingly stringent, and public awareness of environmental protection has generally increased. Furthermore, organic solvents such as NMP and DMF have high boiling points, making drying difficult. While ethanol is easy to dry, it is also flammable and explosive, and all of these methods are more expensive than water. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing easily dispersible graphene composite powder conductive agents that can be directly applied. First, a graphene aqueous slurry is prepared using a liquid-phase exfoliation method, and then further processed into powder. This powder is easy to add and disperse in various systems without agglomeration, while also possessing good electrical and thermal conductivity. This method solves the difficulties downstream customers face in applying graphene powder, addresses the increased cost after preparing the slurry, and resolves the issue of one solvent system being incompatible with other solvent systems, thus reducing the difficulty for the widespread application of graphene powder.

[0007] To achieve the objectives of this invention, the following technical solution is adopted:

[0008] A method for preparing a conductive agent from easily dispersible graphene composite powder that can be directly applied includes the following steps:

[0009] (1) Pre-dispersion: A certain amount of expanded graphite powder, other carbon materials, dispersants and additives, and intercalators are added.

[0010] The intercalating agent and deionized water are stirred evenly to ensure that the components are fully mixed and the expanded graphite is fully wetted in the water. The intercalating agent is an ammonium inorganic substance that is easily decomposed into gas when heated.

[0011] (2) Preparation of water-based slurry by peeling: The above mixture is peeled, homogenized and crushed by peeling equipment to prepare graphene composite water-based slurry. In this process, the intercalating swelling agent can also be effectively inserted between the layers, providing conditions for subsequent drying and swelling, and thus effective dispersion.

[0012] (3) Drying and puffing: The graphene composite aqueous slurry is dried and then heated and puffed to obtain graphene composite conductive agent powder.

[0013] Furthermore, the expanded graphite in step (1) has an expansion ratio of 200-600 times and a mesh size of 20-400 mesh.

[0014] Furthermore, other carbon materials in step (1) include carbon black, Ketjen black, acetylene black, carbon nanotubes, etc.

[0015] And / or, in step (1), the dispersant is a block copolymer wetting and dispersing agent, which is a copolymer of various components such as polyol, polyacid, ethylene oxide, propylene oxide, ethylene oxide, styrene, etc., preferably an ethylene oxide and propylene oxide coblock copolymer.

[0016] And / or, the auxiliary agent in step (1) is a small molecule amine, such as ethylenediamine, ethanolamine, triethanolamine and ammonia, etc.

[0017] And / or, the intercalating swelling agent in step (1) is an ammonium inorganic substance that is easily decomposed into gas when heated, such as ammonium bicarbonate, ammonium carbonate, ammonium sulfate, or diammonium hydrogen phosphate.

[0018] Further, the components and contents in step (1) are as follows: expanded graphite powder 3.5-8 wt%, preferably 4-6 wt%; dispersant 0.05-4 wt% (if the amount is too small, the adsorption and wetting dispersion on the graphene surface and between layers will not be sufficient, making it difficult to completely wet the graphene and resulting in poor peeling effect; if the amount is too large, it will be wasteful, and the wetting and dispersing agent is a non-conductive substance after all. After meeting the adsorption amount of graphene, it is better to have less in the slurry); additives 0.02%-0.3%; intercalation expansion agent 0.5%-5%, preferably 1-3%; other carbon materials 0%-4%, preferably the mass ratio of other carbon materials to expanded graphite is 0-0.5:1.

[0019] Furthermore, in step (2), the stripping equipment includes sand mills, ultrasonic equipment, homogenizers, micro-jet systems, microchannels, etc. Different equipment controls different parameters. The rotation speed is the parameter of the sand mill, with a rotation speed range of 600-1000 rpm; the pressure is the parameter of the homogenizer, with a pressure range of 600-1100 bar; the number of passes is the parameter of the sand mill and the homogenizer. The number of passes for the sand mill is generally 20-40, and the number of passes for the homogenizer is generally 1-3.

[0020] Furthermore, the number of graphene layers in the slurry after step (2) ranges from 3 to 15; the particle size ranges from 1 to 20 μm (specifically, effective exfoliation is achieved by controlling parameters such as rotation speed, pressure, and number of passes).

[0021] Furthermore, in step (3), the drying method can be selected from freeze drying, spray drying, vacuum drying, critical drying, microwave drying, etc., with freeze drying and spray drying being preferred.

[0022] Furthermore, in step (3), the puffing is carried out in a muffle furnace with an air atmosphere and a puffing temperature of 100-600℃. The appropriate puffing temperature is selected according to different intercalating puffing agents. Since the selected intercalating puffing agents can decompose at relatively low temperatures, their puffing temperature is also not high.

[0023] Aqueous graphene slurry was prepared using a liquid-phase exfoliation method, and then dried and expanded into graphene powder. The resulting graphene composite powder contains a dispersant that is readily soluble in most solvents, such as deionized water, NMP, DMF, ethanol, and isopropanol. Therefore, when the graphene composite powder is used directly in slurry mixing or added to a matrix, it does not float, is easy to feed, and is easy to disperse. The graphene composite powder also contains some other carbon materials, which can effectively reduce the degree of graphene folding during drying, making it easier to disperse when mixed into slurry or added to a matrix.

[0024] To address the challenge of wetting graphene with water in liquid-phase exfoliation, a block wetting and dispersing agent is employed. By adjusting different proportions, a suitable wetting ratio of graphene to water is achieved, while minimizing or even eliminating air bubbles. Additives are added to adjust the slurry's pH and viscosity, and to improve the wettability of graphene in the aqueous system. For the exfoliation equipment, commonly used and advanced technologies such as sand milling, ultrasonication, homogenization, microfluidics, and microchannel exfoliation are employed. Appropriate rotation speed, pressure, and number of passes are adjusted to exfoliate the graphene while preserving its original layered structure as much as possible.

[0025] By combining strong wetting with strong exfoliation technology, this method simultaneously addresses both wettability and exfoliation force to achieve strong wetting and strong exfoliation of expanded graphite in an aqueous system. This results in high-quality graphene composite aqueous slurry products with thinner sheets, fewer defects, and low or no foaming. The prepared graphene sheets are thinner and have better wettability, resulting in lighter individual graphene sheets that are less prone to settling. The wetting agents adsorbed on their surface can bind well with water, and the presence of other carbon materials further prevents graphene agglomeration. The thin sheets and intact graphene lattice with fewer defects allow for optimal utilization of graphene's inherent properties.

[0026] To prevent graphene from easily folding back during the drying process and to prevent the dried powder from easily dispersing when added to the matrix, an intercalation swelling agent, other carbon materials, and a dispersant are added during the preparation of the graphene aqueous slurry using the liquid-phase exfoliation method. Utilizing the milling action, the intercalation swelling agent can effectively insert into the interlayer spaces, and the carbon materials and dispersant can also be fully dispersed. During expansion, the intercalation swelling agent, inserted into the graphene layers, decomposes into a gas upon heating, effectively breaking up some of the folding caused by powder drying and further exfoliating the graphene to reduce its layer count. Because the intercalation swelling agent easily decomposes into a gas upon heating, the expansion temperature is relatively low. Furthermore, when the intercalating swelling agent is introduced into the graphene interlayer at a relatively low temperature compared to other swelling temperatures, the decomposition of the intercalating swelling agent into gas does not cause the dispersant to decompose, thereby further exfoliating the graphene. This results in graphene without intercalating swelling agent but with dispersant attached. During the swelling process, other carbon materials and dispersants can be further dispersed, which is more conducive to the wetting of graphene powder in later applications and its dispersion in solvents or resins with lower sheet thickness, thus fully exerting its good electrical conductivity.

[0027] This allows other carbon materials and dispersants to adhere between the exfoliated graphene sheets, preventing graphene folding and agglomeration during drying and facilitating easier dispersion of the powder into the matrix during use. The intercalating swelling agent inserted between the graphene layers decomposes into a gas upon heating during expansion, effectively breaking up some of the folding caused by powder drying and further exfoliating the graphene to reduce its layer count.

[0028] After drying, graphene powder has dispersants, intercalation expanding agents, and other carbon materials adhering to its surface. The dispersants, intercalation expanding agents, and other carbon materials separating different graphene layers effectively prevent the graphene layers from folding back together during drying. The intercalation expanding agents inserted between the graphene layers decompose into gas upon heating during expansion, effectively breaking up some of the folding caused by powder drying and further exfoliating the graphene, reducing the number of layers. When graphene composite powder is added to a downstream matrix, the presence of the dispersant provides good wettability and dispersibility, making it easier to penetrate and disperse evenly in the matrix; simultaneously, the presence of other carbon materials prevents the folding between graphene layers, further promoting the dispersion of the composite powder in the matrix.

[0029] This invention utilizes a novel process to prepare a graphene composite powder conductive agent, which exhibits significantly improved conductivity compared to traditional powder conductive agents such as carbon black, acetylene black, and conductive graphite. Furthermore, the powder is less prone to dispersion, making it easy to add and disperse within a matrix. While its conductivity is comparable to high-end conductive agents like graphene and carbon nanotubes, it is easier to add and disperse. It can be directly added as a powder, eliminating the need to first prepare graphene or carbon nanotubes into a slurry before mixing them with other materials. This reduces the steps required for customer use, lowers transportation and usage costs, and avoids problems associated with slurries such as sedimentation, self-agglomeration, and moisture.

[0030] In summary, the graphene composite powder conductive agent prepared by this invention possesses the excellent conductivity of graphene and carbon nanotubes, while also exhibiting the characteristics of carbon black and conductive graphite powders such as non-floating, easy addition, and easy dispersion. Moreover, it has low cost, relatively simple preparation process, and less environmental pollution. Attached Figure Description

[0031] Figure 1 This is a SEM image of the expanded graphene composite powder obtained in Example 1.

[0032] Figure 2 This is a SEM image of the product in Example 8.

[0033] Figure 3 This is a SEM image of the product in Example 7. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the embodiments:

[0035] Raw material description:

[0036] Expanded graphite: Qingdao Tianshengda Graphite Co., Ltd.;

[0037] Dispersant L62: Jiangsu Haian Petrochemical Plant.

[0038] Additive AD (i.e., ethanolamine): Nanjing Chemical Reagent Co., Ltd.

[0039] Carbon Black SP-Li: Haiyi Enterprise Development Co., Ltd.

[0040] Oxidation-reduction method graphene: Changzhou Sixth Element Graphene Technology Co., Ltd.

[0041] Carbon nanotubes: Shandong Dazhan Nanomaterials Co., Ltd.

[0042] Test method:

[0043] Electrode resistivity: The following formula was used to prepare an electrode sheet (PET substrate): silicon-based negative electrode material: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber latex (SBR): conductive agent (SW) = 91.95:2.55:3.5:2. After mixing, the slurry was coated to prepare the electrode sheet. After drying in a vacuum oven, the electrode sheet was cut into samples of appropriate size (minimum sample size 4cm*4cm). The thickness of the electrode sheet was measured using a height gauge, and the resistivity of the electrode sheet was measured using a Suzhou Jinglü ST2258C four-probe resistivity tester.

[0044] Example 1

[0045] Step 1: Mix expanded graphite powder (4.5wt%, expansion ratio 400 times, mesh size 200), carbon black (0.5wt%), wetting and dispersing agent L62 (1wt%), intercalating expansion agent ammonium carbonate (2wt%), ethanolamine (0.1wt%), and deionized water (balance 91.9%, the total amount of expanded graphite powder, carbon black, wetting and dispersing agent, intercalating expansion agent ammonium carbonate and deionized water is 100wt%). Pre-disperse the above mixture to ensure that the components are fully mixed. The expanded graphite and carbon black are fully wetted and dispersed in water under the action of the wetting and dispersing agent.

[0046] Step 2: Grind and peel the above mixture using a sand mill, controlling the speed at 800 rpm. When the particle size D50 is ground to 14 μm, perform a high-pressure homogenization at a pressure of 800-850 bar. Control the discharge temperature to <50℃ using a cooling water device to prepare graphene composite water-based slurry.

[0047] Step 3: Dry the graphene composite slurry by freeze drying. The lowest freezing temperature is -40℃, then vacuum is applied and the temperature is slowly raised to the highest temperature of 30℃ to prepare the dried graphene composite powder.

[0048] Step 4: In an air atmosphere, heat the muffle furnace to 200°C, place the graphene composite powder into the muffle furnace and expand it for 2 minutes, then remove it to obtain the expanded graphene composite powder.

[0049] Example 2

[0050] Compared with Example 1, the ammonium carbonate content was changed to 0.5%, while other aspects remained unchanged.

[0051] Example 3

[0052] Compared to Example 1, the ammonium carbonate content was changed to 3%, while other contents remained unchanged.

[0053] Example 4

[0054] Compared to Example 1, the ammonium carbonate content was changed to 5%, while other aspects remained unchanged.

[0055] Example 5

[0056] Compared with Example 1, in step 2, the control speed of the sand mill is changed from 800 rpm to 600 rpm, while other parameters remain unchanged.

[0057] Example 6

[0058] Compared to Example 1, freeze drying was replaced with spray drying, and step 3 was changed to: the graphene composite slurry was dried by spray drying. The slurry first passed through an 80-mesh sieve into a tank for spray drying. The inlet air temperature was adjusted to 250°C and the outlet air temperature to 120°C to prepare graphene composite powder. Everything else remained the same.

[0059] Example 7

[0060] Compared with Example 1, in step 1, the addition amount of expanded graphite powder was changed from 4.5 wt% to 5.0 wt%, and the addition amount of carbon black was changed from 0.5 wt% to 0 wt%, while the others remained unchanged.

[0061] Example 8

[0062] Compared with Example 1, in step 1, the addition amount of expanded graphite powder was changed from 4.5 wt% to 4.0 wt%, and the addition amount of carbon black was changed from 0.5 wt% to 1.0 wt%, while the others remained unchanged.

[0063] Example 9

[0064] Compared with Example 1, in step 1, the addition amount of expanded graphite powder was changed from 4.5 wt% to 3.5 wt%, and the addition amount of carbon black was changed from 0.5 wt% to 1.5 wt%, while the others remained unchanged.

[0065] Example 10

[0066] Compared with Example 1, the muffle furnace expansion temperature in step 4 was changed from 200°C to 150°C, while other conditions remained unchanged.

[0067] Example 11

[0068] Compared with Example 1, ammonium carbonate in step 1 is replaced with ammonium sulfate, and the muffle furnace expansion temperature in step 4 is changed from 200°C to 300°C.

[0069] Comparative Example 1

[0070] Compared with Example 1, no ammonium carbonate was added, and muffle furnace expansion was not performed, i.e., step 4 was not performed, and the freeze-dried graphene composite powder was obtained directly from step 3.

[0071] Comparative Example 2

[0072] Compared with Example 1, the muffle furnace expansion temperature was set to 500°C, while other parameters remained unchanged.

[0073] Comparative Example 3

[0074] Compared with Example 8, muffle furnace expansion was not performed, that is, step 4 was not performed, and the spray-dried graphene composite powder was obtained directly from step 3.

[0075] Comparative Example 4

[0076] Compared with Example 1, in step 1, the addition amount of expanded graphite powder was changed from 4.5 wt% to 2.5 wt%, and the addition amount of carbon black was changed from 0.5 wt% to 2.5 wt%, while the others remained unchanged.

[0077] Comparative Example 5

[0078] Domestically produced graphene powder produced by oxidation-reduction method, with approximately 3-5 layers and a specific surface area greater than 500 m² / g, is provided by Changzhou Sixth Element Graphene Technology Co., Ltd.

[0079] Comparative Example 6

[0080] Multi-walled carbon nanotube powder, with a diameter of 6-15 nm and a specific surface area of ​​200-300 m² / g, is provided by Shandong Dazhan Nanomaterials Co., Ltd.

[0081] Comparative Example 7

[0082] Carbon black SP-Li, with a specific surface area of ​​62 m² / g, was provided by Haiyi Enterprise Development Co., Ltd.

[0083] Comparative Example 8

[0084] Using the redox graphene powder of Comparative Example 5, in step 1, the redox graphene powder (3.0 wt%), wetting and dispersing agent L62 (0.75 wt%), ethanolamine (0.1 wt%), and deionized water (the balance being 96.15%, and the total amount of expanded graphene powder, carbon black, wetting and dispersing agent, intercalating expansion agent ammonium carbonate, and deionized water being 100 wt%) was mixed. The above mixture was pre-dispersed to ensure that the components were fully mixed, and the redox graphene was fully wetted and dispersed in water under the action of the wetting and dispersing agent.

[0085] Step 2: Grind and peel the above mixture using a sand mill, controlling the speed at 800 rpm. When the particle size D50 is ground to 3 μm, perform a high-pressure homogenization at a pressure of 800-850 bar. Control the discharge temperature to <50℃ using a cooling water device to prepare an aqueous graphene slurry prepared by the oxidation-reduction method.

[0086] Comparative Example 9

[0087] Using the carbon nanotube powder of Comparative Example 6, in step 1, carbon nanotube powder (4.0 wt%), PVP (1.0 wt%), and deionized water (remaining) were mixed, and the above mixture was pre-dispersed to ensure that the components were fully mixed and that the carbon nanotubes were fully dispersed in water under the action of the dispersant.

[0088] Step 2: Grind the above mixture using a sand mill, controlling the rotation speed at 800 rpm. When the particle size D50 is ground to 1-2 μm, control the discharge temperature to <50℃ using a cooling water device to prepare an aqueous carbon nanotube slurry.

[0089] Electrode resistivity in the examples and comparative examples: A slurry was prepared according to the formula: silicon-based anode material SiOx: sodium carboxymethyl cellulose (CMC): styrene-butadiene rubber emulsion (SBR): conductive agent (SW) = 91.95:2.55:3.5:2. The slurry was then coated to prepare electrode sheets (PET substrate). After vacuum drying, the electrode sheets were cut into samples of appropriate sizes (minimum sample size 4cm*4cm). The electrode thickness was measured using a height gauge, and the electrode resistivity was measured using a Suzhou Jinglü ST2258C four-probe resistivity meter. Detailed results are shown in Table 1.

[0090] Table 1

[0091]

[0092] Using SiOx, which has poor conductivity, as the test substrate allows for a more obvious comparison of conductivity differences.

[0093] As can be seen from Comparative Examples 5, 6, 8, and 9, there is a significant difference between the direct application of redox graphene powder and carbon nanotube powder and their use after being well dispersed and prepared into an aqueous slurry. Direct application of the powder results in poor wetting and dispersion due to its large specific surface area and highly volatile nature (easily dispersed in the air), leading to severe agglomeration and noticeable particle size on the coated electrode. However, when prepared into an aqueous slurry, it is uniformly dispersed, easily combines with the matrix, and its conductivity is fully realized, resulting in excellent conductivity and a smooth, particle-free electrode. In contrast, the carbon black in Comparative Example 8 can be used directly, exhibiting good dispersibility and ease of feeding, and is easily dispersed in the matrix, but its conductivity is relatively poor.

[0094] As can be seen from Example 1 and Comparative Example 1, the powder expanded by the intercalating expander ammonium carbonate has significantly better conductivity than the powder not expanded by the intercalating expander.

[0095] As can be seen from Examples 1, 2, 3 and 4, as the amount of ammonium carbonate added as the intercalating expander increases, the conductivity of the dried and expanded graphene composite powder is better. It can also be observed during expansion that as the amount of ammonium carbonate added as the intercalating expander increases, the powder in the muffle furnace changes from almost motionless to slightly floating, and then to obvious floating and even severe powder dispersion during heating and expansion.

[0096] As shown in Example 1 and Comparative Example 2, the expansion temperature of 200℃ or 500℃ has little effect on the conductivity of the powder. However, through wettability testing, it was found that the surface of the slurry in Example 1 was smooth and without obvious particles, while in Comparative Example 2, particles appeared in the powder after expansion at 500℃. The wettability of the two was slightly worse than that of Example 1. This is because the dispersant basically did not decompose at 200℃, while it had basically decomposed at 500℃. The presence of the dispersant is more conducive to the powder wetting the matrix.

[0097] As can be seen from Examples 1 and 5, the intercalating expansion agent in the slurry intervenes in the interlayer with the help of the grinding force. If the grinding speed is reduced, the force is smaller, the degree of peeling and intervention is reduced, which will lead to the subsequent preparation of powder being worse and the conductivity being reduced.

[0098] As can be seen from Examples 1 and 6, different drying methods can cause great differences in the prepared powder. In terms of conductivity, the freeze-drying method in Example 1 is superior to the spray-drying method.

[0099] As can be seen from Example 6 and Comparative Example 3, the conductivity of powders prepared by spray drying, but prepared by expansion and not by expansion, is extremely different. The conductivity of the expanded powder in Example 6 is an order of magnitude lower than that of the unexpanded powder in Comparative Example 3. Based on this, it can be proved that freeze drying on the basis of intercalation with an expansion agent and expansion is more conducive to the formation of thin-layer graphene, and the two have a synergistic effect.

[0100] As shown in Examples 1, 7-9, and Comparative Example 4, different amounts of carbon black have an impact on the conductivity of the powder. Initially, when the amount of carbon black added is low, the conductivity tends to decrease, but the change is small. However, as the amount of carbon black continues to increase, the conductivity deteriorates significantly. Every effect has its advantages and disadvantages. With increasing carbon black content, the wettability of the composite powder improves because the carbon black adheres to the graphene layers or surface, allowing for better opening and dispersion during mixing with the matrix.

[0101] As can be seen from Examples 1 and 10, changes in the expansion temperature will also affect the conductivity of the powder, but it is acceptable as long as the temperature at which the intercalating expansion agent is completely decomposed is reached.

[0102] As can be seen from Examples 1 and 11, the same effect can be achieved by replacing the intercalating bulking agent with ammonium sulfate, but the temperature needs to reach the temperature at which the intercalating bulking agent is completely decomposed.

[0103] Figure 1 The image shows the SEM image of the expanded graphene composite powder prepared in Example 1. It can be seen that after freeze-drying and re-expanding, carbon black can be well inserted between graphene layers and adhered to the surface, reducing the overlap between graphene layers and facilitating the subsequent redispersion of graphene.

[0104] Figure 2 The image shows a SEM image of the product from Example 8. The graphene was spray-dried and the graphene clumps together in both spherical and sheet-like shapes. Carbon black was also present between the graphene layers and on the surface, making it denser than that produced by freeze-drying.

[0105] Figure 3 The image shown is an SEM image of the product in Example 7. Compared to Example 1, the graphene powder without added carbon black after drying and puffing has no interlayer surface separators, making it easier to stack back. However, when redispersed, the degree of dispersion is slightly weaker than that of the powder in Example 1.

[0106] This invention also tested the resistivity and cost of graphene electrode preparations using different methods, as detailed in Tables 2 and 3:

[0107]

[0108]

[0109] As shown in Table 2, in Examples 1 and 6, the conductivity is equivalent to that of Example 8 with a 2% addition amount when the addition amount is 3%. As shown in Table 3, the estimated unit cost of the powder shows that the cost of achieving the same conductivity is much lower for graphene produced by liquid phase exfoliation than that produced by oxygen reduction, giving it a cost advantage.

[0110] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and concept of the present invention, should be covered within the scope of protection of the present invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

Claims

1. A method for preparing a directly applicable, easily dispersible graphene composite powder conductive agent, characterized in that: Includes the following steps: (1) Pre-dispersion: The specified amount of expanded graphite powder, other carbon materials, dispersant, additives, intercalating swelling agent and deionized water are stirred and mixed thoroughly, and the expanded graphite is fully wetted in water to obtain a mixture; wherein, the intercalating swelling agent is ammonium carbonate, ammonium bicarbonate, ammonium dihydrogen phosphate or ammonium sulfate, and the dispersant is a copolymer of any of the following: polyol, polyacid, ethylene oxide, propylene oxide, butane oxide and styrene; (2) Preparation of water-based slurry by peeling: The above mixture is peeled, homogenized and crushed by peeling equipment to prepare graphene composite water-based slurry. The number of graphene layers in the treated slurry ranges from 3 to 15. (3) Drying and puffing: The graphene composite aqueous slurry is dried and then heated and puffed to obtain graphene composite powder conductive agent. The components and their contents in step (1) are as follows: expanded graphite powder 3.5~5wt%, dispersant 0.5~4wt%, additives 0.02%-0.3%, intercalating expansion agent 2%-5%, and other carbon materials 0%-1.5%; In step (2), the stripping equipment is a sand mill with a rotation speed range of 800-1000 rpm; In step (3), puffing is performed in a muffle furnace with an air atmosphere, and the puffing temperature is 100-300℃; The other carbon materials in step (1) are any one or more of carbon black, Ketjen black, acetylene black, and carbon nanotubes; the additives are any one or more of ethylenediamine, ethanolamine, triethanolamine, and ammonia.

2. The method for preparing the easily dispersible graphene composite powder conductive agent according to claim 1, characterized in that: In step (1), the expansion ratio of the expanded graphite powder is 200-600 times, and the mesh size is 20-400 mesh.

3. The method for preparing the easily dispersible graphene composite powder conductive agent according to claim 1, characterized in that: The graphene particle size range in the slurry after step (2) is 1-20 μm.

4. The method for preparing the easily dispersible graphene composite powder conductive agent according to claim 1, characterized in that: In step (3), the drying method can be any one of freeze drying, spray drying, vacuum drying, supercritical drying, or microwave drying.

Images