Preparation method of high-stability aqueous graphene slurry

Abstract

The application discloses a preparation method of high-stability water-based graphene slurry and belongs to the technical field of battery slurry, in particular to a preparation method of water-based graphene slurry, which comprises the following steps: carrying out swelling treatment on expandable graphite to obtain expanded graphite, carrying out oxidation treatment on the expanded graphite to obtain oxidized expanded graphite, mixing the oxidized expanded graphite and a dispersant in water to obtain a graphene mixture, and adding a thickening agent into the graphene mixture to obtain the water-based graphene slurry; the dispersant comprises lignin sulfonate and a glycol-based polymer; the mass ratio of the oxidized expanded graphite and the lignin sulfonate is 2-5:0.5-4, and the mass ratio of the oxidized expanded graphite and the glycol-based polymer is 2-5:0.5-4. The application provides a simple graphene slurry preparation process, improves the dispersion stability of the graphene slurry, and improves the long-term storage stability of the slurry.

Description

Technical Field

[0001] This invention belongs to the field of battery slurry technology, specifically relating to a method for preparing a highly stable aqueous graphene slurry. Background Technology

[0002] Graphene is a two-dimensional nanomaterial composed of a single layer of carbon atoms bonded together in a honeycomb lattice. Graphene possesses excellent electrical and thermal conductivity and strength, and is currently used as an additive in lithium-ion and sodium-ion batteries in the form of graphene slurries. The two-dimensional sheet-like structure of graphene can form a good conductive network between active materials, and the amount added is typically only 1 / 3 to 1 / 2 that of traditional carbon black. Currently, the main methods for improving the dispersion stability of graphene include chemical dispersion methods, which modify the surface of graphene by introducing dispersants and chemical doping, and physical dispersion methods, which utilize mechanical, ultrasonic, and microwave radiation techniques.

[0003] While graphene offers significant advantages in electronic conduction, its oleophobic and hydrophobic nature makes it prone to agglomeration due to interlayer van der Waals forces, hindering the production of graphene conductive slurries with good dispersion stability. This has become a key issue restricting the application of graphene in lead-acid batteries, lithium batteries, and sodium batteries. Furthermore, the prepared slurry must possess long-term storage stability to prevent sedimentation and re-agglomeration. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a highly stable aqueous graphene slurry with good stability, good dispersibility, and the ability to stand for a long time.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A method for preparing an aqueous graphene slurry includes: expanding expandable graphite to obtain expanded graphite; oxidizing the expanded graphite to obtain oxidized expanded graphite; mixing the oxidized expanded graphite with a dispersant in water to obtain a graphene mixture; and adding a thickener to the graphene mixture to obtain an aqueous graphene slurry. The dispersant includes lignin sulfonate and glycol-based polymer. The mass ratio of oxidized expanded graphite to lignin sulfonate is 2-5:0.5-4, and the mass ratio of oxidized expanded graphite to glycol-based polymer is also 2-5:0.5-4. This invention provides a simple graphene slurry preparation process, improving the dispersion stability and long-term storage stability of the slurry. The lignin sulfonate binds to graphene through hydrophobic interactions and π-π interactions. The negatively charged hydrophilic sulfonic acid groups extend into the water and prevent particle aggregation through electrostatic repulsion. The glycol-based polymer binds to the lignin sulfonate, and its long-chain structure further disperses the graphene and prevents slurry sedimentation through steric hindrance.

[0007] Preferably, the puffing process is carried out at 600-1000℃ for 5-120 seconds.

[0008] Preferably, the oxidant used in the oxidation process is a hydrogen peroxide solution.

[0009] Preferably, the oxidation treatment involves stirring at 50-70°C for 1-6 hours.

[0010] Preferably, the lignin sulfonate includes sodium lignin sulfonate and / or lignin derivatives, which are formed by reacting sodium lignin sulfonate, formaldehyde, and an amino compound. In this invention, the lignin derivative has an aliphatic chain structure, a benzene ring structure, and a structure including the amino compound 2-aminotoluene-5-sulfonic acid. The polyethylene glycol contains a long-chain structure of ethylene glycol. When the lignin derivative and polyethylene glycol are used as dispersants, the combined use of the lignin derivative and polyethylene glycol, after being uniformly mixed with a thickener, further disperses the graphene and prevents slurry sedimentation.

[0011] More preferably, the amino compound includes 2-aminotoluene-5-sulfonic acid.

[0012] More preferably, in the preparation of lignin derivatives, sodium lignin sulfonate and an alkaline reagent are added to deionized water, followed by the addition of an amino compound and an aqueous formaldehyde solution, and the mixture is refluxed for 2-8 hours.

[0013] Preferably, the thickener includes sodium carboxymethyl cellulose.

[0014] More preferably, sodium carboxymethyl cellulose has a degree of polymerization of 300-700.

[0015] This invention discloses an aqueous graphene slurry obtained by the above preparation method.

[0016] Preferably, in the preparation of lignin derivatives, sodium lignin sulfonate and an alkaline reagent are added to deionized water, followed by the addition of an amino compound. Formaldehyde aqueous solution is added at 80-90°C, and the mixture is refluxed for 2-8 hours. After the reaction is complete, the mixture is cooled to room temperature, and then an acidic reagent is added until a precipitate forms. The precipitate is then filtered, washed sequentially with isopropanol and petroleum ether, and dried to obtain the lignin derivative.

[0017] More preferably, in the preparation of lignin derivatives, the amount of sodium lignin sulfonate used is 20-40 wt% of deionized water.

[0018] More preferably, in the preparation of lignin derivatives, the alkaline reagent is sodium hydroxide, and the amount of sodium hydroxide used is 2-10 wt% of sodium lignin sulfonate.

[0019] More preferably, in the preparation of the lignin derivative, the amino compound is 2-aminotoluene-5-sulfonic acid, and the amount of 2-aminotoluene-5-sulfonic acid used is 10-30 wt% of sodium lignin sulfonate.

[0020] More preferably, in the preparation of the lignin derivative, the formaldehyde aqueous solution includes formaldehyde and water, wherein the formaldehyde and water are mixed in a volume ratio of 0.2-0.4:1, and the amount of formaldehyde aqueous solution used is 30-50 wt% of sodium lignin sulfonate.

[0021] More preferably, in the preparation of lignin derivatives, the acidic reagent is hydrochloric acid, and the amount of hydrochloric acid used is appropriate until no precipitation occurs.

[0022] More preferably, in the preparation of lignin derivatives, isopropanol and petroleum ether are used in appropriate amounts during washing.

[0023] The specific implementation steps for preparing the aqueous graphene slurry according to this invention are as follows:

[0024] S1. Expanding treatment is performed on expandable graphite;

[0025] S2. Take the expanded graphite and add it to the hydrogen peroxide solution. After stirring, filter, wash and dry to obtain the oxidized expanded graphite.

[0026] S3. Mix the oxidized expanded graphite, dispersant and water and sonicate them to form a homogeneous mixture;

[0027] S4. Add a thickener to the mixed solution, mix thoroughly, and then homogenize to obtain graphene slurry.

[0028] Preferably, the solid content of the obtained aqueous graphene slurry can be 3-10%.

[0029] Preferably, in the preparation of expanded graphite, expandable graphite is expanded at 600-1000℃ for 5-120s to obtain expanded graphite. The expansion of graphite weakens the interlayer forces, which is beneficial for the subsequent exfoliation of the graphene layer.

[0030] Preferably, in the preparation of oxidized expanded graphite, expanded graphite is added to a hydrogen peroxide solution and stirred at 50-70°C for 1-6 hours, followed by filtration, washing, and drying to obtain oxidized expanded graphite. Oxidation of expanded graphite with hydrogen peroxide further introduces oxygen-containing functional groups such as hydroxyl and carboxyl groups, promoting the separation of graphite layers from the expanded graphite to obtain graphene. The introduced functional groups also enhance the hydrophilicity of graphene, prevent agglomeration, and improve the dispersion stability of the slurry.

[0031] More preferably, in the preparation of oxidized expanded graphite, the concentration of hydrogen peroxide solution is 3-5 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution is 2-10:98-90.

[0032] Preferably, in the preparation of the graphene mixture, oxidized expanded graphite and a dispersant are added to water and ultrasonically treated at 20-40 kHz for 1-4 hours to obtain a uniform graphene mixture. Ultrasonic treatment exfoliates the oxidized expanded graphite into graphene.

[0033] More preferably, in the preparation of the graphene mixture, the dispersant is lignin sulfonate and polyethylene glycol, the mass ratio of oxidized expanded graphite to lignin sulfonate is 2-5:0.5-4, and the mass ratio of oxidized expanded graphite to polyethylene glycol is 2-5:0.5-4.

[0034] More preferably, in the preparation of the graphene mixture, the mass ratio of oxidized expanded graphite to water is 2-5:90-97.

[0035] More preferably, glycerol cocoate can be added during the preparation of the graphene mixture, with the mass ratio of oxidized expanded graphite to glycerol cocoate being 2-5:0.1-1. In this invention, after using lignin derivatives and polyethylene glycol, glycerol cocoate can be added. Under the combined effect of the lignin derivatives, glycerol cocoate, and polyethylene glycol, and after homogenization treatment with a thickener, graphene can be further dispersed and slurry sedimentation can be prevented.

[0036] Preferably, in the preparation of the aqueous graphene slurry, a thickener is added to the graphene mixture, and after uniform mixing, the mixture is homogenized at 80-160 MPa for 1-4 hours to obtain the aqueous graphene slurry. The homogenization process further exfoliates the graphene and ensures the solution is uniformly mixed. The long-chain structure of sodium carboxymethyl cellulose molecules can further disperse the graphene through steric hindrance, while simultaneously forming a robust network structure between molecules to enhance the long-term stability of the slurry.

[0037] More preferably, in the preparation of the aqueous graphene slurry, the thickener is sodium carboxymethyl cellulose, the degree of polymerization of sodium carboxymethyl cellulose is 300-700, the amount of graphene mixture used is based on the amount of oxidized expanded graphite used therein, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose is 2-5:0.5-1.

[0038] This invention prepares expanded graphite by expanding expanded graphite at high temperature, then oxidizes the expanded graphite in hydrogen peroxide solution to obtain oxidized expanded graphite, and then mixes the oxidized expanded graphite and a dispersant in water and ultrasonically treats the mixture to obtain a graphene mixture. The dispersant includes lignin sulfonate and glycol-based polymers. A thickener, sodium carboxymethyl cellulose, is added to the graphene mixture and homogenized to obtain an aqueous graphene slurry. Therefore, this invention has the following beneficial effects: the obtained aqueous graphene slurry has good stability, good dispersibility, and storage stability. Thus, this invention is a method for preparing a highly stable aqueous graphene slurry with good stability, good dispersibility, and the ability to stand for a long time. Attached Figure Description

[0039] Figure 1 This is a SEM image of graphene.

[0040] Figure 2 This is a graph showing the absorbance ratio results.

[0041] Figure 3 The graph shows the results of centrifugal sedimentation rate. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] The concepts involved in this application will first be described with reference to the accompanying drawings. It should be noted that the following descriptions of various concepts are only for the purpose of making the content of this application easier to understand and do not constitute a limitation on the scope of protection of this application; furthermore, the embodiments and features in the embodiments of this application can be combined with each other unless otherwise specified. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0044] Example 1: A method for preparing an aqueous graphene slurry

[0045] Preparation of expanded graphite: Expandable graphite was expanded at 800℃ for 30s to obtain expanded graphite.

[0046] Preparation of expanded oxidized graphite: Expanded graphite was added to a hydrogen peroxide solution and stirred at 60°C for 4 hours. The mixture was then filtered, washed, and dried to obtain expanded oxidized graphite. The concentration of the hydrogen peroxide solution was 3 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution was 5:95.

[0047] Preparation of graphene mixture: Oxidized expanded graphite and a dispersant were added to water and ultrasonically treated at 20 kHz for 2 h to obtain a homogeneous graphene mixture. The dispersant was lignin sulfonate and polyethylene glycol. The mass ratio of oxidized expanded graphite to lignin sulfonate was 4:1, the mass ratio of oxidized expanded graphite to polyethylene glycol was 4:0.5, and the mass ratio of oxidized expanded graphite to water was 4:94.

[0048] Preparation of aqueous graphene slurry: A thickener was added to the graphene mixture, and after thorough mixing, the mixture was homogenized at 100 MPa for 2 hours to obtain the aqueous graphene slurry. The thickener was sodium carboxymethyl cellulose with a degree of polymerization of 500. The amount of graphene mixture used was based on the amount of oxidized expanded graphite in it, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose was 4:0.5.

[0049] Example 2: A method for preparing an aqueous graphene slurry

[0050] Preparation of lignin derivatives: Sodium lignin sulfonate and an alkaline reagent were added to deionized water, followed by the addition of an amino compound. Formaldehyde aqueous solution was added at 85°C, and the mixture was refluxed for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and an acidic reagent was added until a precipitate formed. The precipitate was filtered, washed sequentially with isopropanol and petroleum ether, and dried to obtain the lignin derivative. The amount of sodium lignin sulfonate used was 30 wt% of deionized water; the alkaline reagent was sodium hydroxide, with an amount of sodium hydroxide of 5 wt% of sodium lignin sulfonate; the amino compound was 2-aminotoluene-5-sulfonic acid, with an amount of 20 wt% of sodium lignin sulfonate; the formaldehyde aqueous solution consisted of formaldehyde and water mixed in a volume ratio of 0.3:1, with an amount of formaldehyde aqueous solution of 40 wt% of sodium lignin sulfonate; and the acidic reagent was hydrochloric acid, added until no precipitate formed. Appropriate amounts of isopropanol and petroleum ether were used during washing.

[0051] Preparation of expanded graphite: Expandable graphite was expanded at 800℃ for 30s to obtain expanded graphite.

[0052] Preparation of expanded oxidized graphite: Expanded graphite was added to a hydrogen peroxide solution and stirred at 60°C for 4 hours. The mixture was then filtered, washed, and dried to obtain expanded oxidized graphite. The concentration of the hydrogen peroxide solution was 3 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution was 5:95.

[0053] Preparation of graphene mixture: Oxidized expanded graphite and a dispersant were added to water and ultrasonically treated at 20 kHz for 2 h to obtain a homogeneous graphene mixture. The dispersant consisted of lignin derivatives and polyethylene glycol. The mass ratio of oxidized expanded graphite to lignin derivatives was 4:3, the mass ratio of oxidized expanded graphite to polyethylene glycol was 4:0.5, and the mass ratio of oxidized expanded graphite to water was 4:94.

[0054] Preparation of aqueous graphene slurry: A thickener was added to the graphene mixture, and after thorough mixing, the mixture was homogenized at 100 MPa for 2 hours to obtain the aqueous graphene slurry. The thickener was sodium carboxymethyl cellulose with a degree of polymerization of 500. The amount of graphene mixture used was based on the amount of oxidized expanded graphite in it, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose was 4:0.5.

[0055] Example 3: A method for preparing an aqueous graphene slurry

[0056] Preparation of lignin derivatives: Sodium lignin sulfonate and an alkaline reagent were added to deionized water, followed by the addition of an amino compound. Formaldehyde aqueous solution was added at 85°C, and the mixture was refluxed for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and an acidic reagent was added until a precipitate formed. The precipitate was filtered, washed sequentially with isopropanol and petroleum ether, and dried to obtain the lignin derivative. The amount of sodium lignin sulfonate used was 30 wt% of deionized water; the alkaline reagent was sodium hydroxide, with an amount of sodium hydroxide of 5 wt% of sodium lignin sulfonate; the amino compound was 2-aminotoluene-5-sulfonic acid, with an amount of 20 wt% of sodium lignin sulfonate; the formaldehyde aqueous solution consisted of formaldehyde and water mixed in a volume ratio of 0.3:1, with an amount of formaldehyde aqueous solution of 40 wt% of sodium lignin sulfonate; and the acidic reagent was hydrochloric acid, added until no precipitate formed. Appropriate amounts of isopropanol and petroleum ether were used during washing.

[0057] Preparation of expanded graphite: Expandable graphite was expanded at 800℃ for 30s to obtain expanded graphite.

[0058] Preparation of expanded oxidized graphite: Expanded graphite was added to a hydrogen peroxide solution and stirred at 60°C for 4 hours. The mixture was then filtered, washed, and dried to obtain expanded oxidized graphite. The concentration of the hydrogen peroxide solution was 3 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution was 5:95.

[0059] Preparation of graphene mixture: Oxidized expanded graphite and a dispersant were added to water and ultrasonically treated at 20 kHz for 2 h to obtain a homogeneous graphene mixture. The dispersant consisted of lignin derivatives and polyethylene glycol. The mass ratio of oxidized expanded graphite to lignin derivatives was 4:1, the mass ratio of oxidized expanded graphite to polyethylene glycol was 4:0.5, and the mass ratio of oxidized expanded graphite to water was 4:94.

[0060] Preparation of aqueous graphene slurry: A thickener was added to the graphene mixture, and after thorough mixing, the mixture was homogenized at 100 MPa for 2 hours to obtain the aqueous graphene slurry. The thickener was sodium carboxymethyl cellulose with a degree of polymerization of 500. The amount of graphene mixture used was based on the amount of oxidized expanded graphite in it, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose was 4:0.5.

[0061] Example 4: A method for preparing an aqueous graphene slurry

[0062] Preparation of lignin derivatives: Sodium lignin sulfonate and an alkaline reagent were added to deionized water, followed by the addition of an amino compound. Formaldehyde aqueous solution was added at 85°C, and the mixture was refluxed for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and an acidic reagent was added until a precipitate formed. The precipitate was filtered, washed sequentially with isopropanol and petroleum ether, and dried to obtain the lignin derivative. The amount of sodium lignin sulfonate used was 30 wt% of deionized water; the alkaline reagent was sodium hydroxide, with an amount of sodium hydroxide of 5 wt% of sodium lignin sulfonate; the amino compound was 2-aminotoluene-5-sulfonic acid, with an amount of 20 wt% of sodium lignin sulfonate; the formaldehyde aqueous solution consisted of formaldehyde and water mixed in a volume ratio of 0.3:1, with an amount of formaldehyde aqueous solution of 40 wt% of sodium lignin sulfonate; and the acidic reagent was hydrochloric acid, added until no precipitate formed. Appropriate amounts of isopropanol and petroleum ether were used during washing.

[0063] Preparation of expanded graphite: Expandable graphite was expanded at 800℃ for 30s to obtain expanded graphite.

[0064] Preparation of expanded oxidized graphite: Expanded graphite was added to a hydrogen peroxide solution and stirred at 60°C for 4 hours. The mixture was then filtered, washed, and dried to obtain expanded oxidized graphite. The concentration of the hydrogen peroxide solution was 3 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution was 5:95.

[0065] Preparation of graphene mixture: Oxidized expanded graphite and a dispersant were added to water and ultrasonically treated at 20 kHz for 2 h to obtain a homogeneous graphene mixture. The dispersant consisted of lignin derivatives, glycerol cocoate, and polyethylene glycol. The mass ratio of oxidized expanded graphite to lignin derivatives was 4:1, the mass ratio of oxidized expanded graphite to glycerol cocoate was 4:0.8, the mass ratio of oxidized expanded graphite to polyethylene glycol was 4:0.5, and the mass ratio of oxidized expanded graphite to water was 4:94.

[0066] Preparation of aqueous graphene slurry: A thickener was added to the graphene mixture, and after thorough mixing, the mixture was homogenized at 100 MPa for 2 hours to obtain the aqueous graphene slurry. The thickener was sodium carboxymethyl cellulose with a degree of polymerization of 500. The amount of graphene mixture used was based on the amount of oxidized expanded graphite in it, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose was 4:0.5.

[0067] Example 5: A method for preparing an aqueous graphene slurry

[0068] Preparation of lignin derivatives: Sodium lignin sulfonate and an alkaline reagent were added to deionized water, followed by the addition of an amino compound. Formaldehyde aqueous solution was added at 85°C, and the mixture was refluxed for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and an acidic reagent was added until a precipitate formed. The precipitate was filtered, washed sequentially with isopropanol and petroleum ether, and dried to obtain the lignin derivative. The amount of sodium lignin sulfonate used was 30 wt% of deionized water; the alkaline reagent was sodium hydroxide, with an amount of sodium hydroxide of 5 wt% of sodium lignin sulfonate; the amino compound was 2-aminotoluene-5-sulfonic acid, with an amount of 20 wt% of sodium lignin sulfonate; the formaldehyde aqueous solution consisted of formaldehyde and water mixed in a volume ratio of 0.3:1, with an amount of formaldehyde aqueous solution of 40 wt% of sodium lignin sulfonate; and the acidic reagent was hydrochloric acid, added until no precipitate formed. Appropriate amounts of isopropanol and petroleum ether were used during washing.

[0069] Preparation of expanded graphite: Expandable graphite was expanded at 800℃ for 30s to obtain expanded graphite.

[0070] Preparation of expanded oxidized graphite: Expanded graphite was added to a hydrogen peroxide solution and stirred at 60°C for 4 hours. The mixture was then filtered, washed, and dried to obtain expanded oxidized graphite. The concentration of the hydrogen peroxide solution was 3 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution was 5:95.

[0071] Preparation of graphene mixture: Oxidized expanded graphite and a dispersant were added to water and ultrasonically treated at 20 kHz for 2 h to obtain a homogeneous graphene mixture. The dispersant consisted of lignin derivative, glycerol cocoate, and polyethylene glycol. The mass ratio of oxidized expanded graphite to lignin derivative was 4:1, the mass ratio of oxidized expanded graphite to glycerol cocoate was 4:0.2, the mass ratio of oxidized expanded graphite to polyethylene glycol was 4:0.5, and the mass ratio of oxidized expanded graphite to water was 4:94.

[0072] Preparation of aqueous graphene slurry: A thickener was added to the graphene mixture, and after thorough mixing, the mixture was homogenized at 100 MPa for 2 hours to obtain the aqueous graphene slurry. The thickener was sodium carboxymethyl cellulose with a degree of polymerization of 500. The amount of graphene mixture used was based on the amount of oxidized expanded graphite in it, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose was 4:0.5.

[0073] Comparative Example 1: A method for preparing an aqueous graphene slurry

[0074] Preparation of lignin derivatives: Sodium lignin sulfonate and an alkaline reagent were added to deionized water, followed by the addition of an amino compound. Formaldehyde aqueous solution was added at 85°C, and the mixture was refluxed for 4 hours. After the reaction was complete, the mixture was cooled to room temperature, and an acidic reagent was added until a precipitate formed. The precipitate was filtered, washed sequentially with isopropanol and petroleum ether, and dried to obtain the lignin derivative. The amount of sodium lignin sulfonate used was 30 wt% of deionized water; the alkaline reagent was sodium hydroxide, with an amount of sodium hydroxide of 5 wt% of sodium lignin sulfonate; the amino compound was 2-aminotoluene-5-sulfonic acid, with an amount of 20 wt% of sodium lignin sulfonate; the formaldehyde aqueous solution consisted of formaldehyde and water mixed in a volume ratio of 0.3:1, with an amount of formaldehyde aqueous solution of 40 wt% of sodium lignin sulfonate; and the acidic reagent was hydrochloric acid, added until no precipitate formed. Appropriate amounts of isopropanol and petroleum ether were used during washing.

[0075] Preparation of expanded graphite: Expandable graphite was expanded at 800℃ for 30s to obtain expanded graphite.

[0076] Preparation of expanded oxidized graphite: Expanded graphite was added to a hydrogen peroxide solution and stirred at 60°C for 4 hours. The mixture was then filtered, washed, and dried to obtain expanded oxidized graphite. The concentration of the hydrogen peroxide solution was 3 wt%, and the mass ratio of expanded graphite to hydrogen peroxide solution was 5:95.

[0077] Preparation of graphene mixture: Oxidized expanded graphite and a dispersant were added to water and ultrasonically treated at 20 kHz for 2 h to obtain a homogeneous graphene mixture. The dispersant consisted of lignin derivatives and polyethylene glycol. The mass ratio of oxidized expanded graphite to lignin derivatives was 4:0.1, the mass ratio of oxidized expanded graphite to polyethylene glycol was 4:0.5, and the mass ratio of oxidized expanded graphite to water was 4:94.

[0078] Preparation of aqueous graphene slurry: A thickener was added to the graphene mixture, and after thorough mixing, the mixture was homogenized at 100 MPa for 2 hours to obtain the aqueous graphene slurry. The thickener was sodium carboxymethyl cellulose with a degree of polymerization of 500. The amount of graphene mixture used was based on the amount of oxidized expanded graphite in it, and the mass ratio of oxidized expanded graphite to sodium carboxymethyl cellulose was 4:0.5.

[0079] Experimental example:

[0080] The graphene in the graphene mixture prepared in Example 1 was characterized by scanning electron microscopy, and the results are as follows: Figure 1 As shown.

[0081] This invention tests the stability of the aqueous graphene slurry in Examples 1-5 and Comparative Example 1. The aqueous graphene slurry was allowed to stand for 30 days. Then, 150 μL of the aqueous graphene slurry was diluted with 10 mL of deionized water. After stirring evenly, the absorbance of the diluted slurry was measured at 600 nm and compared with the absorbance of the diluted slurry after standing for 0 days. The ratio of the absorbance after 7 days to the absorbance at 0 days was used as a characterization of stability. The results are as follows: Figure 2As shown, S1 is Example 1, S2 is Example 2, S3 is Example 3, S4 is Example 4, S5 is Example 5, and D1 is Comparative Example 1. In this invention, expandable graphite is prepared by expanding graphite at high temperature. Then, the expanded graphite is oxidized in hydrogen peroxide solution to prepare oxidized expanded graphite. Next, the oxidized expanded graphite and a dispersant are mixed in water and ultrasonically treated to prepare a graphene mixture. The dispersant is lignin sulfonate and polyethylene glycol. A thickener is added to the graphene mixture and homogenized to obtain an aqueous graphene slurry. The thickener is sodium carboxymethyl cellulose. The aqueous graphene slurry prepared in this invention still has good stability after standing. In this invention, wood... Lignosulfonate is replaced with a lignin derivative, which is prepared by reacting sodium lignin sulfonate, formaldehyde, and 2-aminotoluene-5-sulfonic acid. This lignin derivative and polyethylene glycol are used as dispersants in the preparation of graphene mixtures. With other components remaining unchanged, the stability of the aqueous graphene slurry can be improved. However, the amount of lignin derivative used needs to meet certain limits. If the amount of lignin derivative used is too small, the stability of the resulting aqueous graphene slurry will deteriorate. In this invention, glycerol cocoate can also be added when preparing the graphene mixture. The use of glycerol cocoate with lignin derivative and polyethylene glycol can further improve the stability of the aqueous graphene slurry.

[0082] The stability of the aqueous graphene slurry in Examples 1-5 and Comparative Example 1 was further tested. The aqueous graphene slurry was centrifuged at 15000 r / min for 10 min, the solution was discarded, the precipitate was dried and weighed, and the uncentrifuged aqueous graphene slurry was dried and weighed. The centrifugation precipitation rate was calculated using the uncentrifuged dry weight as a reference. The results are as follows. Figure 3As shown, S1 is Example 1, S2 is Example 2, S3 is Example 3, S4 is Example 4, S5 is Example 5, and D1 is Comparative Example 1. In this invention, expandable graphite is prepared by expanding graphite at high temperature. Then, the expanded graphite is oxidized in hydrogen peroxide solution to prepare oxidized expanded graphite. Next, the oxidized expanded graphite and a dispersant are mixed in water and ultrasonically treated to prepare a graphene mixture. The dispersant is lignin sulfonate and polyethylene glycol. A thickener is added to the graphene mixture and homogenized to obtain an aqueous graphene slurry. The thickener is sodium carboxymethyl cellulose. The aqueous graphene slurry prepared in this invention has good centrifugal stability and low centrifugal sedimentation rate. In this invention, lignin sulfonate can also be replaced with lignin derivatives. The lignin derivative is prepared by reacting sodium lignin sulfonate, formaldehyde, and 2-aminotoluene-5-sulfonic acid. When this lignin derivative and polyethylene glycol are used as a dispersant in the preparation of graphene mixtures, the centrifugal stability of the aqueous graphene slurry is improved and the centrifugal sedimentation rate is reduced, while other components remain unchanged. However, the amount of lignin derivative used needs to be within a certain range; if the amount of lignin derivative used is too small, the centrifugal stability of the resulting aqueous graphene slurry will deteriorate, and the centrifugal sedimentation rate will increase. In this invention, glycerol cocoate can also be added during the preparation of the graphene mixture. The use of glycerol cocoate with the lignin derivative and polyethylene glycol can further improve the centrifugal stability of the aqueous graphene slurry and reduce the centrifugal sedimentation rate.

[0083] The embodiments and / or implementation methods described above are merely preferred embodiments and / or implementation methods for implementing the technology of the present invention, and are not intended to limit the implementation methods of the technology of the present invention in any way. Any person skilled in the art can make some modifications or alterations to other equivalent embodiments without departing from the scope of the technical means disclosed in the content of the present invention, but they should still be regarded as the technology or embodiments that are substantially the same as the present invention.

[0084] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. The above descriptions are only preferred embodiments of this application. It should be noted that due to the limitations of written expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of this application, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of this application.

Claims

1. A method for preparing an aqueous graphene slurry, comprising: Expanded graphite is obtained by expanding graphite through expansion treatment, and expanded graphite is obtained by oxidizing graphite through oxidation treatment. Oxidized expanded graphite is mixed with a dispersant in water to obtain a graphene mixture. A thickener is added to the graphene mixture to obtain an aqueous graphene slurry. The dispersant includes lignin sulfonate and glycol-based polymer. The mass ratio of oxidized expanded graphite to lignin sulfonate is 2-5:0.5-4, and the mass ratio of oxidized expanded graphite to glycol-based polymer is 2-5:0.5-4. The lignin sulfonate is a lignin derivative, which is formed by reacting sodium lignin sulfonate, formaldehyde, and an amino compound; the amino compound includes 2-aminotoluene-5-sulfonic acid.

2. The preparation method according to claim 1, characterized in that, In the puffing process, the puffing is carried out at 600-1000℃ for 5-120 seconds.

3. The preparation method according to claim 1, characterized in that, In the oxidation process, the oxidant used is hydrogen peroxide solution.

4. The preparation method according to claim 1, characterized in that, In the oxidation treatment, the mixture is stirred at 50-70°C for 1-6 hours.

5. The preparation method according to claim 1, characterized in that, In the preparation of the lignin derivative, sodium lignin sulfonate and an alkaline reagent are added to deionized water, followed by the addition of an amino compound and an aqueous formaldehyde solution, and the mixture is refluxed for 2-8 hours.

6. The preparation method according to claim 1, characterized in that, The thickener includes sodium carboxymethyl cellulose.

7. The preparation method according to claim 6, characterized in that, The degree of polymerization of the sodium carboxymethyl cellulose is 300-700.

8. The aqueous graphene slurry obtained by any of the preparation methods described in claims 1-7.

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