Preparation method of high-stability graphene slurry

Abstract

The invention provides a preparation method of high-stability graphene slurry. The preparation method comprises the following steps: S1) preparing a graphene aqueous solution containing a surfactant; s2) carrying out homogenization treatment on the graphene aqueous solution; s3) concentrating the graphene aqueous solution obtained in the step S2) to obtain graphene aqueous slurry; and S4) stirring the graphene water-based slurry to enable the graphene water-based slurry to be colloidal, so as to obtain the graphene slurry. The preparation method provided by the invention solves the problems of easy agglomeration of graphene, high surfactant content, poor dispersion performance and the like in the prior art, so that the graphene slurry has relatively long storage stability, the surfactant in the slurry can be greatly reduced, the purity of graphene is improved, and the graphene slurry has good redispersion characteristic.

Description

Technical Field

[0001] The present invention relates to the technical field of graphene, and in particular to a method for preparing a high-stability graphene slurry. Background Art

[0002] Graphene, a typical two-dimensional material, consists of a single layer of carbon atoms tightly packed in a regular and orderly manner, forming a honeycomb lattice structure. Within this unique structure, the carbon atoms are firmly connected by strong covalent bonds. Graphene has attracted considerable attention for its excellent electrical and thermal conductivity, with its exceptional electrical conductivity promising broad application prospects in electronic devices and energy storage.

[0003] Graphene aqueous conductive paste, due to its excellent conductive properties and flexible sheet structure, can form a multi-dimensional conductive structure, which can effectively reduce the internal resistance of the battery and improve the charge and discharge efficiency and cycle stability. However, the preparation process of graphene aqueous paste still has some urgent problems to be solved. First, most graphene aqueous pastes on the market are conductive pastes compounded with carbon nanotubes, and there is no direct way to produce high-solid content graphene aqueous conductive pastes. Secondly, during storage, graphene conductive pastes with high solid content are prone to agglomeration due to the large specific surface area of graphene. Finally, to prevent the agglomeration of graphene conductive pastes, the content of surfactant components will be increased, which will lead to an increase in the internal resistance of the battery and affect the battery performance.

[0004] Therefore, it is of great significance to provide a method for preparing a graphene aqueous slurry with high stability. Summary of the Invention

[0005] The technical problem solved by the present invention is to provide a method for preparing a highly stable graphene slurry. The graphene slurry prepared in the present application has long storage stability and greatly reduces the surfactant in the slurry.

[0006] In view of this, the present application provides a method for preparing a high-stability graphene slurry, comprising the following steps:

[0007] S1) preparing a graphene aqueous solution containing a surfactant;

[0008] S2) homogenizing the graphene aqueous solution;

[0009] S3) concentrating the graphene aqueous solution obtained in step S2) to form a dilatant to obtain an aqueous graphene slurry;

[0010] S4) stirring the graphene aqueous slurry so that the graphene aqueous slurry is colloidal to obtain graphene slurry.

[0011] In some specific embodiments, in step S1), the graphene aqueous solution is prepared by:

[0012] mixing a graphene precursor, a surfactant and water to obtain a graphene aqueous solution;

[0013] The content of the graphene precursor is 0.1 to 10 parts by weight, the content of the surfactant is 0.1 to 1 part by weight, and the content of water is 90 to 99.8 parts by weight.

[0014] In some specific embodiments, the graphene precursor includes expanded graphite powder.

[0015] In some specific embodiments, the surfactant includes one or more of polymethylpyrrolidone, BYK420, lignin, and sodium dodecylbenzenesulfonate.

[0016] In some specific embodiments, the surfactant is selected from polymethylpyrrolidone, BYK420 and lignin in a mass ratio of (1-3): (0.5-1.5): 0.5, or the surfactant is selected from polymethylpyrrolidone, BYK420 and sodium dodecylbenzenesulfonate in a mass ratio of (1-3): (0.5-1.5): 0.5.

[0017] In some specific embodiments, in step S2), the homogenization pressure is 90-200 MPa, and the time is 3-10 h.

[0018] In some specific embodiments, in step S3), the concentration method includes membrane filtration, heating evaporation, reduced pressure distillation or filter press concentration, and / or the concentration pressure is 0.1-0.2 MPa.

[0019] In some specific embodiments, in step S4), the stirring speed is 1000-1200 rpm, and the stirring time is 2-5 hours.

[0020] In some specific embodiments, the graphene particle size D50 in the graphene slurry is 3-4 μm.

[0021] In some specific embodiments, the viscosity of the graphene slurry is 2100-2600 mPa·s;

[0022] And / or, the solid content of the graphene slurry is 4-8wt%.

[0023] The present application provides a method for preparing a highly stable graphene slurry, which comprises the following steps: firstly, preparing a graphene aqueous solution containing a surfactant, then homogenizing the graphene aqueous solution, and obtaining a graphene solution containing graphene microplatelets through liquid phase stripping, then concentrating the graphene solution to remove a large amount of surfactant and water in the solution, making it a dilatant fluid, and obtaining an aqueous graphene slurry, and finally stirring the aqueous graphene slurry to form a network structure inside the material, and obtaining a graphene slurry; the graphene in the graphene slurry prepared by the present application forms a network structure, thereby greatly improving the stability of the slurry, effectively improving the agglomeration and sedimentation problems of the graphene in the solution, and solving the problems of easy agglomeration of the graphene in the graphene slurry, high surfactant content, and poor dispersion performance, so that the graphene slurry has a long storage stability, can greatly reduce the surfactant in the slurry, improve the purity of the graphene, and has good dispersion characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a physical photo of the graphene slurry prepared in Example 1 of the present invention;

[0025] Figure 2 This is a SEM photo of the graphene slurry prepared in Example 1 of the present invention;

[0026] Figure 3 This is a particle size distribution diagram of the graphene slurry prepared in Example 1 of the present invention;

[0027] Figure 4 This is a photo of the graphene slurry prepared in Example 1 of the present invention after being left to stand for 6 months;

[0028] Figure 5 This is a physical picture of the graphene slurry prepared in Example 1 of the present invention and Comparative Example 3 after being left to stand for 6 months. DETAILED DESCRIPTION

[0029] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0030] In view of the problems of graphene slurry agglomeration and high surfactant content in the prior art, the present application provides a method for preparing a high-stability graphene slurry, which concentrates the initially peeled graphene aqueous solution to form a dilatant fluid mainly composed of graphene, which is ultimately conducive to obtaining a colloidal graphene slurry with a network structure after stirring, thereby improving the stability of the graphene slurry and solving the problems of easy agglomeration, high surfactant content, and poor dispersion performance of graphene slurry in the prior art. The graphene slurry prepared in the present application can uniformly form a stable dilatant fluid with the aqueous solution, so that the graphene slurry has a long storage stability, can significantly reduce the surfactant in the slurry, improve the purity of graphene, and have good dispersion characteristics. Specifically, the embodiment of the present invention discloses a method for preparing a high-stability graphene slurry, comprising the following steps:

[0031] S1) preparing a graphene aqueous solution containing a surfactant;

[0032] S2) homogenizing the graphene aqueous solution;

[0033] S3) concentrating the graphene aqueous solution obtained in step S2) to form a dilatant to obtain an aqueous graphene slurry;

[0034] S4) stirring the graphene aqueous slurry so that the graphene aqueous slurry is colloidal to obtain graphene slurry.

[0035] In the preparation method of high-stability graphene slurry, the present application first prepares a graphene aqueous solution containing a surfactant, and the preparation method of the graphene aqueous solution is a method well known to those skilled in the art; in the present application, the precursor of the graphene aqueous solution is expanded graphite powder. The graphene aqueous solution is obtained by mixing expanded graphite, a surfactant and water, wherein the content of expanded graphite is 0.1 to 10 parts by weight, the content of the surfactant is 0.1 to 1 part by weight, and the content of water is 90 to 99.8 parts by weight; specifically, the content of expanded graphite is 2 to 8 parts by weight, the content of the surfactant is 0.3 to 0.8 parts by weight, and the content of water is 91 to 96 parts by weight; more specifically, the content of expanded graphite is 3 to 6 parts by weight, the content of the surfactant is 0.4 to 0.6 parts by weight, and the content of water is 92 to 95 parts by weight; for example, the content of expanded graphite in the present application is 0.2 parts by weight, 0.5 parts by weight, 0.8 parts by weight, 1 part ... .2 weight parts, 1.5 weight parts, 2.1 weight parts, 2.6 weight parts, 2.8 weight parts, 3.2 weight parts, 3.6 weight parts, 3.9 weight parts, 4.0 weight parts, 4.2 weight parts, 4.5 weight parts, 4.8 weight parts, 5 weight parts, 5.3 weight parts, 6 weight parts, 6.8 weight parts, 7 weight parts, 7.9 weight parts, 8.3 weight parts, 8.9 weight parts, 9.1 weight parts, 9.7 weight parts; the content of surfactant is 0.4 weight part, 0.5 weight part, 0.6 weight part, 0.7 weight part, 0.8 weight part; the content of water is 92 weight parts, 93 weight parts, 94 weight parts, 95 weight parts, 96 weight parts, 97 weight parts, 98 weight parts, 99 weight parts.In the present application, the surfactant includes one or more of polymethyl pyrrolidone, BYK420, lignin and sodium dodecylbenzene sulfonate; specifically, the surfactant is selected from polymethyl pyrrolidone, BYK420 and lignin, or, the surfactant is selected from polymethyl pyrrolidone, BYK420 and sodium dodecylbenzene sulfonate (SDBS); more specifically, the surfactant is selected from polymethyl pyrrolidone, BYK420 and lignin in a mass ratio of (1-3): (0.5-1.5): 0.5, more specifically, the surfactant is selected from polymethyl pyrrolidone, BYK420 and lignin in a mass ratio of (1.5-2.5): (0.8-1.2): 0.5 Pyrrolidone, BYK420 and lignin; in some specific embodiments, the mass ratio of polymethylpyrrolidone, BYK420 and lignin is 1:0.5:0.5; or, more specifically, the surfactant is selected from polymethylpyrrolidone, BYK420 and SDBS in a mass ratio of (1-3): (0.5-1.5):0.5, more specifically, the surfactant is selected from polymethylpyrrolidone, BYK420 and SDBS in a mass ratio of (1.5-2.5): (0.8-1.2):0.5; in some specific embodiments, the mass ratio of polymethylpyrrolidone, BYK420 and SDBS is 1:0.5:0.5.

[0036] The present application then homogenizes the above-mentioned graphene aqueous solution to preliminarily peel off the surfactant and graphene in the graphene aqueous solution, so that the graphene is in the form of micro-flakes, and a graphene suspension is obtained. The homogenization treatment is to apply forces such as extrusion, strong impact and pressure expansion to the graphene aqueous solution, so that the surfactant and graphene are preliminarily peeled off to form graphene micro-flakes. The technical means of the homogenization treatment are technical means well known to those skilled in the art, and the present application does not impose any special restrictions on this; in the present application, the homogenization treatment is carried out in a high-pressure homogenizer, the pressure of the homogenization treatment is 90 to 200 MPa, and the time is 3 to 10 hours. Specifically, the pressure of the homogenization treatment is 100 to 180 MPa, and the time is 4 to 7 hours. More specifically, the pressure of the homogenization treatment is 120 to 160 MPa, and the time is 5 to 6 hours.

[0037] According to the present invention, after obtaining the graphene aqueous solution, it is concentrated to remove the surfactant and water in the graphene aqueous solution, so that the obtained graphene aqueous solution becomes a dilatant fluid, and a graphene aqueous slurry is obtained; the concentration method can be heating evaporation, vacuum distillation and membrane filtration or filter press concentration. In a specific embodiment, the concentration method is membrane filtration. The membrane filtration concentration method is more conducive to ensuring the uniform dispersion of the slurry, and the filtered waste liquid of the membrane is an aqueous dispersion containing a low concentration of surfactant, which can be reused. The concentration pressure is 0.1 to 0.2 MPa, specifically, the concentration pressure is 0.1 MPa or 0.2 MPa. The concentration pressure will affect the speed of the concentration process. The higher the concentration pressure, the faster the speed, a large amount of graphene will settle, and the viscosity will gradually increase, which is not conducive to the smooth discharge of the slurry.

[0038] Finally, the present application stirs the graphene aqueous slurry so that the graphene aqueous slurry is colloidal to obtain a graphene slurry; the stirring causes the graphene aqueous slurry to exhibit shear thickening under the action of shear force, and the graphene particles aggregate during the stirring process, and form particle clusters between each other to form a network structure, which increases the viscosity and becomes a colloidal graphene slurry. In the present application, the stirring method is a stirring method well known to those skilled in the art, which can be mechanical stirring, magnetic stirring or ultrasonic stirring, and this application is not particularly limited to this; specifically, the stirring speed is 1000-1200rpm, and the time is 2-5h, more specifically, the stirring speed is 1050-1150rpm, and the time is 3-4h, more specifically, the stirring speed is 1100-1120rpm; if the stirring speed is too low, a high-viscosity graphene slurry cannot be formed, and the dispersibility is extremely poor. After stirring, the present application obtains a graphene slurry with high stability, wherein the graphene particle size D50 is 3 to 4 μm, the viscosity is 2100 to 2600 mPa·s, and the solid content is 4 to 8 wt%.

[0039] The present application provides a method for preparing a highly stable graphene slurry, which firstly forms a suspension containing graphene by liquid phase exfoliation in the presence of a surfactant, then utilizes a concentration and optimization membrane filtration technology to remove the surfactant and water in the suspension to form a dilatant mainly composed of graphene, and finally forms a network structure in the solution by stirring, thereby greatly improving the stability of the slurry and effectively improving the agglomeration and sedimentation problems of the graphene slurry in the solution. The graphene slurry prepared in the present application has a storage stability of up to 6 months; furthermore, the preparation method of the graphene slurry of the present invention is simple, green and safe, and can be used for large-scale preparation of graphene slurry with a solid content of 4-8%, and can form a graphene slurry with stable dispersion and extremely low surfactant content, which greatly reduces the influence of the surfactant on battery performance, and has broad development prospects in fields requiring high surfactant content.

[0040] In order to further understand the present invention, the preparation method of the high-stability graphene slurry provided by the present invention is described in detail below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0041] Example 1

[0042] (A) 1 part of a surfactant and 95 parts of deionized water were stirred to prepare solution A, and then 2 parts of expanded graphite powder were added to solution A, wherein the surfactant was polymethylpyrrolidone, BYK420, and lignin in a mass ratio of 1:0.5:0.5, and the solution was further dispersed at a rotation speed of 30 rpm to obtain a graphene aqueous solution;

[0043] (B) transferring the graphene aqueous solution to a high-pressure homogenizer at a pressure of 100 MPa for 3 h to obtain a uniformly dispersed graphene aqueous solution;

[0044] (C) subjecting the graphene aqueous solution obtained in step (B) to membrane filtration and concentration at a pressure of 0.1 MPa to remove a large amount of surfactant and water to obtain an aqueous graphene slurry;

[0045] (D) The aqueous graphene slurry was transferred to a stirring tank and stirred at a speed of 1000 rpm for 2 hours. The aqueous graphene slurry became a colloidal graphene slurry with a solid content of 4 wt% and a surfactant content of 10 wt% of the graphene content in the graphene slurry. A small amount of the slurry was taken and its viscosity was tested by a viscometer. The viscosity of the slurry was 2443 mPa.s.

[0046] Figure 1 This is a photo of the graphene slurry prepared in this example. As can be seen from the figure, the graphene slurry is evenly dispersed; Figure 2 This is the SEM photo of the graphene slurry prepared in this embodiment. Figure 2 It can be seen that the graphene slurry prepared in this embodiment has a clear graphene sheet structure and no agglomeration phenomenon occurs.

[0047] Figure 3 : is the particle size distribution diagram of the graphene slurry prepared in this embodiment. It can be seen from the figure that the graphene particle size D50 of the graphene slurry prepared in this embodiment is mainly concentrated in 3-4 μm.

[0048] Figure 4 This is a physical picture of the graphene slurry prepared in this embodiment after standing for 6 months. As can be seen from the figure, the graphene slurry prepared in this embodiment is still evenly dispersed after standing for 6 months, and there is no sedimentation, agglomeration and the like, and has excellent storage stability.

[0049] Example 2

[0050] (A) 1 part of a surfactant and 95 parts of deionized water were stirred to prepare solution A, and then 2 parts of expanded graphite powder were added to solution A, wherein the surfactant was polymethylpyrrolidone, BYK420, and sodium dodecylbenzenesulfonate (SDBS) in a mass ratio of 1:0.5:0.5. The solution was stirred at a speed of 30 rpm to uniformly disperse the solution to obtain a graphene aqueous solution;

[0051] (B) transferring the graphene aqueous solution to a high-pressure homogenizer at a pressure of 100 MPa for 3 h to obtain a uniformly dispersed graphene aqueous solution;

[0052] (C) subjecting the graphene aqueous solution obtained in step (B) to membrane filtration and concentration at a pressure of 0.1 MPa to remove a large amount of surfactant and water to obtain an aqueous graphene slurry;

[0053] (D) The aqueous graphene slurry was transferred to a stirring tank and stirred at a speed of 1000 rpm for 2 hours. The aqueous graphene slurry became a colloidal graphene slurry with a solid content of 4 wt% and a surfactant content of 10 wt% of the graphene content in the graphene slurry. Some agglomeration occurred in the slurry. A small amount of the slurry was taken and its viscosity was tested by a viscometer. The viscosity of the slurry was 2108 mPa.s.

[0054] Comparative Example 1

[0055] The difference between this example and Example 1 lies in the content of the surfactant in step A. The other steps are the same as those in Example 1. The purpose of this example is to illustrate the effect of the surfactant content on the dispersion effect of graphene powder, specifically:

[0056] (A) 2 parts of a surfactant and 95 parts of deionized water were stirred to prepare solution A, and then 2 parts of expanded graphite powder were added to solution A, wherein the surfactant was polymethylpyrrolidone, BYK420, and lignin in a mass ratio of 3:1.5:0.5, and stirring was continued at a speed of 30 rpm to uniformly disperse the solution; thereby obtaining a graphene aqueous solution;

[0057] (B) transferring the graphene aqueous solution to a high-pressure homogenizer at a pressure of 90-180 MPa for 3 h to obtain a uniformly dispersed graphene aqueous solution;

[0058] (C) transferring the graphene aqueous solution obtained in step (B) to a rotating ceramic membrane at a pressure of 0.2 MPa to remove a large amount of surfactant and water to obtain an aqueous graphene slurry;

[0059] (D) The graphene aqueous slurry is transferred to a stirring tank and stirred at a speed of 1000 rpm for 2 h until the graphene aqueous slurry becomes gel-like.

[0060] After the graphene slurry prepared in this comparative example was left to stand for 3 months, the graphene slurry showed stratification, while the graphene slurry prepared in Example 1 showed no obvious stratification.

[0061] Comparative Example 2

[0062] The difference between this comparative example and Example 1 is that the working pressure of the rotating ceramic membrane in step (C) is adjusted to 0.3 MPa, and the other steps are the same as those in Example 1, specifically:

[0063] (A) 1 part of a surfactant and 95 parts of deionized water were stirred to prepare solution A, and then 2 parts of expanded graphite powder were added to solution A, wherein the surfactant was polymethylpyrrolidone, BYK420, and lignin in a mass ratio of 1:0.5:0.5, and stirring was continued at a speed of 30 rpm to uniformly disperse the solution to obtain a graphene aqueous solution;

[0064] (B) transferring the graphene aqueous solution to a high-pressure homogenizer at a pressure of 100 MPa for 3 h to obtain a uniformly dispersed graphene aqueous solution;

[0065] (C) transferring the graphene aqueous solution obtained in step (B) to a rotating ceramic membrane at a pressure of 0.3 MPa to remove a large amount of surfactant and water to obtain an aqueous graphene slurry;

[0066] (D) The graphene aqueous slurry is transferred to a stirring tank and stirred at a speed of 1000 rpm for 2 h until the graphene aqueous slurry becomes gel-like.

[0067] Compared with the graphene slurry obtained in Example 1, the solid content of the graphene slurry prepared in this comparative example is smaller, and there is a certain degree of agglomeration in the slurry.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that the rotation speed of the stirring tank in step (D) is adjusted to 500 rpm, specifically:

[0070] (A) 1 part of a surfactant and 95 parts of deionized water were stirred to prepare solution A, and then 2 parts of expanded graphite powder were added to solution A, wherein the surfactant was polymethylpyrrolidone, BYK420, and lignin in a mass ratio of 1:0.5:0.5, and the solution was further dispersed at a rotation speed of 30 rpm to obtain a graphene aqueous solution;

[0071] (B) transferring the graphene aqueous solution to a high-pressure homogenizer at a pressure of 100 MPa for 3 h to obtain a uniformly dispersed graphene aqueous solution;

[0072] (C) transferring the graphene aqueous solution obtained in step (B) to a rotating ceramic membrane at a pressure of 0.1 MPa to remove a large amount of surfactant and water to obtain an aqueous graphene slurry;

[0073] (D) The graphene aqueous slurry was transferred to a stirring tank and stirred at a speed of 500 rpm for 2 h to obtain a graphene slurry.

[0074] Compared with the graphene slurry prepared in Example 1, the graphene slurry prepared in this comparative example still has fluidity. Figure 5 As shown in the figure, the graphene slurry prepared in this comparative example seriously precipitated after standing for 3 months, while the graphene slurry prepared in Example 1 precipitated without stratification and had better stability.

[0075] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0076] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a high-stability graphene slurry, comprising the following steps: S1) preparing a graphene aqueous solution containing a surfactant; S2) homogenizing the graphene aqueous solution; S3) concentrating the graphene aqueous solution obtained in step S2) to form a dilatant to obtain an aqueous graphene slurry; S4) stirring the graphene aqueous slurry so that the graphene aqueous slurry is colloidal to obtain graphene slurry.

2. The preparation method according to claim 1, characterized in that In step S1), the preparation of the graphene aqueous solution is specifically as follows: mixing a graphene precursor, a surfactant and water to obtain a graphene aqueous solution; The content of the graphene precursor is 0.1 to 10 parts by weight, the content of the surfactant is 0.1 to 1 part by weight, and the content of water is 90 to 99.8 parts by weight.

3. The preparation method according to claim 2, characterized in that The graphene precursor includes expanded graphite powder.

4. The preparation method according to claim 2, characterized in that The surfactant includes one or more of polymethylpyrrolidone, BYK420, lignin and sodium dodecylbenzene sulfonate.

5. The preparation method according to claim 2 or 4, characterized in that The surfactant is selected from polymethylpyrrolidone, BYK420 and lignin in a mass ratio of (1-3): (0.5-1.5): 0.5, or the surfactant is selected from polymethylpyrrolidone, BYK420 and sodium dodecylbenzenesulfonate in a mass ratio of (1-3): (0.5-1.5): 0.

5.

6. The preparation method according to claim 5, characterized in that In step S2), the homogenization pressure is 90-200 MPa and the time is 3-10 hours.

7. The preparation method according to claim 5, characterized in that In step S3), the concentration means include membrane filtration, heating evaporation, reduced pressure distillation or filter press concentration, and / or the concentration pressure is 0.1 to 0.2 MPa.

8. The preparation method according to claim 5, characterized in that In step S4), the stirring speed is 1000-1200 rpm and the stirring time is 2-5 hours.

9. The preparation method according to claim 5, characterized in that The graphene particle size D50 in the graphene slurry is 3 to 4 μm.

10. The preparation method according to claim 5, characterized in that The viscosity of the graphene slurry is 2100-2600 mPa·s; And / or, the solid content of the graphene slurry is 4-8wt%.

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