Graphene and preparation method and application thereof

Abstract

The application relates to the technical field of printing, in particular to graphene and a preparation method and application thereof. The graphene preparation method provided by the application comprises the following steps: S1, mixing graphite and polypropylene carbonate uniformly in the presence of a solvent, and performing solid-liquid separation to obtain a first graphene dispersion liquid with an upper dispersion liquid; the aliphatic thermoplastic plastic polypropylene carbonate which is copolymerized from propylene oxide and carbon dioxide is used as a dispersant; a C-H bond of the polypropylene carbonate and a pi bond of the graphite are used to form a van der Waals bond, the liquid phase exfoliation yield of the graphene is improved, the space repulsion force between the polypropylene carbonate molecules can enhance the dispersion stability of the graphene. Meanwhile, the decomposition temperature of the polypropylene carbonate is low, and the temperature for removing the dispersant polypropylene carbonate after the graphene prepared by mixing the polypropylene carbonate with the graphite is low.

Description

Technical Field

[0001] This invention relates to the field of printing technology, specifically to a graphene, its preparation method, and its applications. Background Technology

[0002] Graphene is a two-dimensional honeycomb lattice structure composed of carbon atoms. Its unique electronic and structural properties have led to its widespread application in numerous fields, including transistors, energy storage, sensors, displays, optoelectronics, and biomedicine. To achieve large-scale, low-cost manufacturing, graphene has been developed into solution-processable inks and is widely used in various printing technologies, such as screen printing, blade coating, aerosol jet printing, inkjet printing, and gravure printing. To achieve stable dispersion of graphene in solvents, N,N-dimethylformamide, whose surface tension matches the interfacial energy of graphene, is currently mostly used as a solvent. However, due to its toxicity, high price, and high boiling point, N,N-dimethylformamide poses safety risks and is difficult to remove when used in printing technologies.

[0003] Existing technology discloses a method for preparing graphene conductive films using printing or coating. Graphene is prepared by using polymer dispersants such as ethyl cellulose and polyvinyl alcohol, which fully utilizes the high conductivity of graphene. However, the yield of graphene prepared by this method is low, and when applied to printing technology, the processing temperature is too high when removing the polymer dispersant, which limits the use of the substrate and the device formed by the substrate and graphene, as well as other materials. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of low yield in the preparation of graphene by liquid phase exfoliation of graphite in the prior art, thereby providing a graphene and its preparation method and application, and improving the liquid phase exfoliation yield of graphene.

[0005] Another technical problem to be solved by the present invention is to overcome the defect in the printing process of inks made of graphene as raw material, where the temperature for removing the dispersant is too high, resulting in a limited range of applications for the substrate. The present invention provides graphene, its preparation method and application.

[0006] On one hand, the present invention provides a method for preparing graphene, characterized by comprising the following steps: S1, in the presence of a solvent, graphite and polypropylene carbonate are mixed and separated into solid and liquid phases to obtain an upper dispersion as a first graphene dispersion.

[0007] In one embodiment, step S2 is further included, in which the first graphene dispersion obtained in step S1 is separated into solid and liquid phases to obtain a filter residue of graphene powder.

[0008] In one embodiment, the method further includes step S3, dispersing the graphene powder obtained in step S2 in a solvent to obtain a second graphene dispersion, or dispersing the graphene powder obtained in step S2 and polypropylene carbonate in a solvent to obtain a second graphene dispersion, or mixing the graphene powder obtained in step S2 and a polypropylene carbonate solution to obtain a second graphene dispersion, wherein the polypropylene carbonate solution is a mixture of polypropylene carbonate and a solvent.

[0009] In one embodiment, the solvent in step S1 and / or step S3 is at least one of tetrahydrofuran, N-methyl-2-pyrrolidone, ethyl acetate, and diethylene glycol monomethyl ether, preferably at least one of tetrahydrofuran and ethyl acetate.

[0010] In one embodiment, in step S1, the mass ratio of graphite to polypropylene carbonate is 1:(1-8).

[0011] Preferably, the mixing method in step S1 includes ultrasonic treatment of graphite and polypropylene carbonate at 160W-360W for 2h-12h.

[0012] In one embodiment, the mixing method in step S1 can be achieved by shear mixing to exfoliate the graphene.

[0013] Preferably, in step S1, the solid-liquid separation method includes centrifuging the mixed graphite and polypropylene carbonate at a speed of 1000rpm-3000rpm for 20min-60min. In this embodiment of the invention, the ultrasonically dispersed liquid is centrifuged to remove unpeeled material. The resulting upper dispersion can also be separated to obtain graphene of different sizes by different centrifugation speeds.

[0014] Preferably, in step S1, the total mass ratio of graphite and polypropylene carbonate to the volume ratio of solvent is (2-9):200, in mg:mL; and / or,

[0015] Preferably, the solid-liquid separation method for the graphene dispersion in step S2 is filtration. After filtration and drying, granular graphene powder is obtained.

[0016] Preferably, in step S3, the mass ratio of graphene powder to polypropylene carbonate is (5-200):(0-200).

[0017] Preferably, the total mass ratio of graphene powder and polypropylene carbonate to the volume ratio of solvent is (5-400):1, in mg:mL.

[0018] On the other hand, the present invention provides graphene prepared by the above-described graphene preparation method.

[0019] On the other hand, the present invention provides an ink comprising at least one of the above-mentioned first graphene dispersion, graphene powder, and second graphene dispersion.

[0020] In one embodiment, the application of ink in printing technology includes the following steps: after printing with the ink, heating at 150-250°C for 30 min-3 h to obtain a graphene film.

[0021] Preferably, the concentration of the graphene and polypropylene carbonate mixture in the ink is 1 mg / mL-5000 mg / mL, and can be 5 mg / mL-400 mg / mL.

[0022] The printing and coating technologies include at least one of the following: screen printing, flexographic printing, aerosol jet printing, inkjet printing, gravure printing, offset printing, 3D printing, laser printing, doctor blade coating, spraying, dip coating, roller coating, spin coating, brush coating, and electrophoretic coating.

[0023] The technical solution of this invention has the following advantages:

[0024] 1. This invention provides a method for preparing graphene, comprising the following steps: S1, in the presence of a solvent, graphite and polypropylene carbonate are mixed, and solid-liquid separation is performed to obtain an upper dispersion as a first graphene dispersion. This invention uses polypropylene carbonate, an aliphatic thermoplastic copolymerized from propylene oxide and carbon dioxide, as a dispersant. The van der Waals bonds formed by the CH bonds of polypropylene carbonate and the π bonds of graphite improve the liquid-phase exfoliation yield of graphene. The steric hindrance between polypropylene carbonate molecules enhances the dispersion stability of graphene. Simultaneously, polypropylene carbonate has a low decomposition temperature, resulting in a low temperature at which the dispersant polypropylene carbonate is removed after mixing it with graphite to obtain graphene.

[0025] 2. The graphene preparation method provided by the present invention further includes step S2, which involves solid-liquid separation of the graphene dispersion obtained in step S1 to obtain graphene powder as filter residue. The present invention can separate graphene from the first graphene dispersion to obtain graphene powder through solid-liquid separation.

[0026] 3. The graphene preparation method provided by this invention further includes step S3, dispersing the graphene powder obtained in step S2 and polypropylene carbonate in a solvent to obtain a second graphene dispersion. This invention uses polypropylene carbonate to mix with exfoliated graphene, which can effectively increase the dispersibility of graphene, adjust the rheological properties of the obtained second graphene dispersion, and improve the stability of the second graphene dispersion.

[0027] 4. The present invention provides an ink comprising at least one of the above-mentioned first graphene dispersion, graphene powder, or second graphene dispersion. This ink can be applied in printing technology. The application of the first graphene dispersion and / or the second graphene dispersion in the printing technology includes the following steps: after printing with the ink, heating at 150-250°C for 30 min-3 h to obtain a graphene film. Compared to traditional polymer dispersants, the present invention uses polypropylene carbonate, which can reduce the dispersant removal temperature, simplify the post-processing of printed graphene, expand the compatibility of substrates and materials, and also reduce process costs. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the molecular structures of graphite, polypropylene carbonate, and graphene / polypropylene carbonate in this invention.

[0030] Figure 2 This is a photograph of the graphene powder in Example 2 of the present invention;

[0031] Figure 3 This is a photograph of the second graphene dispersion in Example 2 of the present invention;

[0032] Figure 4 This is a physical image of the graphene electrode prepared in Application Example 1 of this invention;

[0033] Figure 5 This is a physical image of the graphene interdigitated electrode prepared in Application Example 1 of this invention;

[0034] Figure 6 This is a thermogravimetric analysis result of the second graphene / polypropylene carbonate composite material prepared in Example 2 of the present invention;

[0035] Figure 7 The graphene concentration detection result of the first graphene dispersion prepared in Example 7 of this invention;

[0036] Figure 8 This is the stability test result of the first graphene dispersion prepared in Example 7 of the present invention;

[0037] Figure 9 These are the redispersion rate test results of the second graphene dispersion prepared in Example 3 and Comparative Example 3 of this invention;

[0038] Figure 10 These are the stability test results of the second graphene dispersions prepared in Example 3 and Comparative Example 3 of this invention;

[0039] Figure 11 The Fourier transform infrared spectra of polypropylene carbonate, graphene, and graphene / polypropylene carbonate composite material in Example 2 of this invention are shown.

[0040] Figure 12 The graphene / polypropylene carbonate composite material in Example 2 of this invention has a thickness of 1420-1480 cm. -1 Fourier transform infrared spectrum of the region;

[0041] Figure 13 This is a SEM image of the graphene / polypropylene carbonate composite material in Example 2 of this invention;

[0042] Figure 14 This is a graph showing the viscosity test results of the second graphene dispersion in Example 2 of the present invention;

[0043] Figure 15 This is the cyclic voltammetry diagram of the miniature supercapacitor device prepared by Example 1 of the present invention at a scan rate of 5 mV / s;

[0044] Figure 16 This is a graph showing the capacitance retention rate of the miniature supercapacitor device prepared in Example 1 of this invention during charge-discharge cycles. Detailed Implementation

[0045] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0046] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0047] The polypropylene carbonate used in this embodiment of the invention has the structural formula shown in formula (Ⅰ), purchased from Sigma-Aldrich, with a molecular weight of 50kDa, which can be 500kDa, 150kDa, 40kDa, or 30kDa.

[0048]

[0049] See Figure 1As shown, polypropylene carbonate b can assist in the exfoliation of graphite a to form monolayer graphene / polypropylene carbonate c1, bilayer graphene / polypropylene carbonate c2, and multilayer graphene / polypropylene carbonate (not shown in the figure).

[0050] Example 1

[0051] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0052] Dissolve 4g of polypropylene carbonate in 200mL of tetrahydrofuran solvent, add 1g of graphite powder, sonicate the mixture at 200W for 2 hours, then centrifuge at 1000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0053] Example 2

[0054] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0055] (1) Dissolve 4g of polypropylene carbonate in 200mL of tetrahydrofuran solvent, add 1g of graphite powder, sonicate the mixture at 200W for 2 hours, then centrifuge at 1000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0056] (2) The graphene / polypropylene carbonate dispersion was filtered, dried, and ground to obtain a graphene / polypropylene carbonate composite material, which was graphene powder, such as... Figure 2 As shown;

[0057] (3) Dissolve 24 mg of polypropylene carbonate in 4 mL of solvent, then add 56 mg of graphene / polypropylene carbonate composite material to obtain a second graphene dispersion of 20 mg / mL. The solvent is a mixture of tetrahydrofuran and diethylene glycol ether with a volume ratio of 93:7. The second graphene dispersion is as follows: Figure 3 As shown, in this embodiment, diethylene glycol ether is added to adjust the boiling point of the dispersion and prevent the polypropylene carbonate in the dispersion from volatilizing.

[0058] Example 3

[0059] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0060] (1) Dissolve 4g of polypropylene carbonate in 200mL of tetrahydrofuran solvent, add 1g of graphite powder, sonicate the mixture at 200W for 2 hours, then centrifuge at 1000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0061] (2) The graphene dispersion was filtered and ground to obtain a graphene / polypropylene carbonate composite material, i.e., graphene powder.

[0062] (3) Dissolve 24 mg of polypropylene carbonate in 4 mL of solvent, and then add 56 mg of graphene / polypropylene carbonate composite material to it to obtain a second graphene dispersion of 20 mg / mL. The solvent is tetrahydrofuran.

[0063] Example 4

[0064] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0065] (1) Dissolve 1g of graphite powder and 8g of polypropylene carbonate in 200mL of tetrahydrofuran solvent. Sonicate the mixture at 360W for 5 hours, then centrifuge at 3000rpm for 20 minutes. Take out the upper layer of dispersion as the first graphene dispersion.

[0066] (2) The graphene dispersion was filtered and ground to obtain a graphene / polypropylene carbonate composite material, i.e., graphene powder.

[0067] (3) Dissolve 20 mg of polypropylene carbonate in 1 mL of solvent, and then add 380 mg of graphene / polypropylene carbonate composite material to it to obtain a second graphene dispersion of 400 mg / mL. The solvent is tetrahydrofuran.

[0068] Example 5

[0069] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0070] (1) Dissolve 4g of polypropylene carbonate in 200mL of tetrahydrofuran solvent, add 1g of graphite powder, sonicate the mixture at 160W for 12 hours, then centrifuge at 2500rpm for 40 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0071] (2) The graphene / polypropylene carbonate composite material obtained by filtering and grinding the first graphene dispersion is graphene powder.

[0072] (3) Dissolve 48.8 mg of polypropylene carbonate and 1.2 mg of graphene / polypropylene carbonate composite material in 10 mL of solvent to obtain a second graphene dispersion of 5 mg / mL. The solvent is tetrahydrofuran.

[0073] Example 6

[0074] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0075] (1) Dissolve 4g of polypropylene carbonate in 200mL of tetrahydrofuran solvent, add 1g of graphite powder, sonicate the mixture at 250W for 10 hours, then centrifuge at 1500rpm for 20 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0076] (2) The graphene dispersion was filtered and ground to obtain a graphene / polypropylene carbonate composite material, i.e., graphene powder.

[0077] (3) Dissolve 24 mg of polypropylene carbonate in 4 mL of solvent, and then add 56 mg of graphene / polypropylene carbonate composite material to it to obtain a second graphene dispersion of 20 mg / mL. The solvent is tetrahydrofuran.

[0078] Example 7

[0079] This embodiment provides a method for preparing graphene. The specific steps and methods are the same as those in Example 3. The difference is that in step (1), tetrahydrofuran is replaced with an equal volume of N-methyl-2-pyrrolidone, and in step (3), tetrahydrofuran is replaced with an equal volume of N-methyl-2-pyrrolidone.

[0080] Example 8

[0081] This embodiment provides a method for preparing graphene. The specific steps and methods are the same as those in Example 3. The difference is that tetrahydrofuran in step (1) is replaced with an equal volume of ethyl acetate, and tetrahydrofuran in step (3) is replaced with an equal volume of ethyl acetate.

[0082] Example 9

[0083] This embodiment provides a method for preparing graphene, and the specific steps and methods are as follows:

[0084] (1) Dissolve 10g of polypropylene carbonate in 400mL of tetrahydrofuran solvent, add 4g of graphite powder, sonicate the mixture at 250W for 10 hours, then centrifuge at 2000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0085] (2) The graphene / polypropylene carbonate composite material obtained by filtering and grinding the first graphene dispersion is graphene powder.

[0086] (3) Weigh 100 mg of graphene and mix it with 1 mL of polypropylene carbonate solution to obtain a second graphene dispersion. The concentration of the polypropylene carbonate solution is 50 mg / mL and the solvent of the polypropylene carbonate solution is diethylene glycol monomethyl ether.

[0087] Comparative Example 1

[0088] This comparative example provides a method for preparing graphene, with the same specific steps and methods as in Example 1, except that polyvinylpyrrolidone of equal mass is used instead of polypropylene carbonate.

[0089] Comparative Example 2

[0090] This comparative example provides a method for preparing graphene, with the same specific steps and methods as in Example 1, except that an equal mass of ethyl cellulose is used instead of polypropylene carbonate.

[0091] Comparative Example 3

[0092] This comparative example provides a method for preparing graphene, the specific steps and methods are as follows:

[0093] (1) Put 5g of graphite powder into 200mL of tetrahydrofuran solvent, sonicate the mixture at 200W for 2 hours, then centrifuge at 1000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0094] (2) The first graphene dispersion was filtered to obtain a filter residue as a composite material;

[0095] (3) Add 20 mg of the composite material to 1 mL of tetrahydrofuran to obtain a second graphene dispersion of 20 mg / mL.

[0096] Comparative Example 4

[0097] This comparative example provides a method for preparing graphene, the specific steps and methods are as follows:

[0098] (1) Put 5g of graphite powder into 200mL of N-methyl-2-pyrrolidone solvent, sonicate the mixture at 200W for 2 hours, then centrifuge at 1000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0099] (2) The first graphene dispersion was filtered to obtain a filter residue as a composite material;

[0100] (3) Add 20 mg of the composite material to 1 mL of N-methyl-2-pyrrolidone solvent to obtain a second graphene dispersion of 20 mg / mL.

[0101] Comparative Example 5

[0102] This comparative example provides a method for preparing graphene, the specific steps and methods are as follows:

[0103] (1) Place 5g of graphite powder into 200mL of ethyl acetate, sonicate the mixture at 200W for 2 hours, then centrifuge at 1000rpm for 30 minutes, and take out the upper layer of dispersion as the first graphene dispersion.

[0104] (2) The first graphene dispersion was filtered to obtain the filter residue as a composite material;

[0105] (2) Add 20 mg of the composite material to 1 mL of ethyl acetate to obtain a second graphene dispersion of 20 mg / mL.

[0106] Application Example 1

[0107] Using the first graphene dispersion prepared in Example 2, graphene electrodes for a micro supercapacitor were printed on baking paper resistant to 250°C using aerosol jet printing technology. Figure 4 As shown, the dispersant polypropylene carbonate was then removed by heating at 220°C for 30 minutes, resulting in a graphene interdigitated electrode, as shown. Figure 5 As shown;

[0108] Micro-supercapacitors were obtained by printing ion gel electrolytes on graphene electrodes. The ion gel was an ink prepared with poly(styrene-b-methyl methacrylate-b-styrene) triblock copolymer (Polymer Source Inc.), ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and ethyl acetate. The mass ratio of poly(styrene-b-methyl methacrylate-b-styrene) triblock copolymer, ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and ethyl acetate was 1:9:90 (w / w / w).

[0109] The measured specific area capacitance of the miniature supercapacitor reached 324.33 μF / cm². 2 The good stability of the ink during charge-discharge cycles demonstrates the practical application potential of the ink prepared according to the embodiments of the present invention in energy storage.

[0110] Application Example 2

[0111] The graphene electrode of a micro supercapacitor was printed on baking paper that is heat-resistant to 250°C using the first graphene dispersion prepared in Example 1. Then, the dispersant polypropylene carbonate was removed by heating at 250°C for 30 minutes.

[0112] Application Example 3

[0113] The graphene electrode of a micro supercapacitor was printed on baking paper with a heat resistance of 250°C using the first graphene dispersion prepared in Example 2. Then, the dispersant polypropylene carbonate was removed by heating at 150°C for 3 hours.

[0114] Experimental Example 1

[0115] Thermogravimetric analysis (TGA) was performed on the second graphene / polypropylene carbonate composite material prepared in Example 2 using a thermogravimetric analyzer (TA instrument, TGA 55). The synthesis air flow rate was 40 mL / min, and the temperature was increased from room temperature to 500 °C at a rate of 2 °C / min. The results are shown in [Figure number missing]. Figure 6 It can be seen that the dispersant polypropylene carbonate begins to degrade at around 150°C.

[0116] Experimental Example 2

[0117] The upper dispersion in Example 1 was filtered to obtain a filter cake. The filter cake was heated at 220°C for 30 minutes to remove the dispersant polypropylene carbonate. The conductivity of the graphene filter cake was tested using a four-probe measurement technique.

[0118] The upper dispersion in Example 1 was filtered to obtain a filter cake. The filter cake was heated at 220°C for 30 minutes to remove the dispersant polypropylene carbonate. After the filter cake was compressed using a rolling mill, the conductivity of the graphene filter cake was tested using a four-probe measurement technique.

[0119] The upper dispersions of Comparative Examples 1 and 2 were filtered to obtain filter cakes. The filter cakes were then heated at 350°C for 30 minutes to remove the dispersant. The conductivity of the graphene filter cakes was measured using a four-probe measurement technique.

[0120] The upper dispersion of Comparative Example 1 was filtered to obtain a filter cake. The filter cake was heated at 350°C for 30 minutes to remove the dispersant. The filter cake obtained after filtering the upper dispersion of Comparative Example 1 was compressed using a rolling mill. The conductivity of the graphene filter cake was tested using a four-probe measurement technique. The test results are shown in Table 1.

[0121] Table 1. Conductivity of graphene / polypropylene carbonate dispersion

[0122]

[0123] It can be seen that the average conductivity of the graphene material obtained after filtering the graphene / polypropylene carbonate dispersion prepared in Example 1 of this invention, after removing the dispersant by heating at 220°C for 30 min, is 8 × 10⁻⁶. 3 S / m, after compression, the density of the graphene material increases, the connections between graphene sheets become tighter, and the conductivity increases to 6.687×10. 4 S / m. Compared to Comparative Examples 1-2 which used PVP or EC dispersants, the graphene material prepared in this embodiment of the invention reduces the temperature for removing the dispersant while ensuring good conductivity.

[0124] Experimental Example 3

[0125] The exfoliated graphene concentration in the first graphene dispersions prepared in Examples 3, 7, 8 and Comparative Examples 3-5 was measured, and the results are shown in [Figure 1]. Figure 7 .

[0126] The method for detecting the concentration of exfoliated graphene is as follows:

[0127] The yield of exfoliated graphene was determined using a muffle furnace (Thermo Fisher Scientific, BF51894C-1). Specifically, 3 × 10 mL of the first graphene dispersion prepared in each example and comparative example was taken, and 10 mL of each dispersion was placed in an aluminum dish. Three test cases were set up. The aluminum dishes of each test case were placed on a heating plate to remove the solvent from the first graphene dispersion. The aluminum dishes were then placed in the muffle furnace and heated at 250°C for 2 hours to remove polypropylene carbonate from the samples. After annealing, the concentration of the graphene dispersion was determined by the weight of graphene in the aluminum dish, and the graphene concentration was the average of the three test cases.

[0128] according to Figure 7 It can be seen that, in different solvents, the graphene dispersions prepared by using polypropylene carbonate as a dispersant in Examples 3, 7, and 8, compared with those prepared by Comparative Examples 3-5 without a dispersant, showed higher exfoliated graphene concentrations in Examples 3, 7, and 8, which used polypropylene carbonate as a dispersant. This proves that using polypropylene carbonate can improve the exfoliation effect of graphene and increase the yield of graphene.

[0129] Experiment Example 4

[0130] The stability of the first graphene dispersion prepared in Example 3 was tested, and the results are shown in [Figure 3]. Figure 8 .

[0131] The detection method is as follows:

[0132] The sedimentation behavior was measured using a UV-Vis spectrophotometer (Agilent, Cary 4000). Specifically, the first graphene dispersion prepared in Example 7 was diluted with 20 mg / mL polypropylene carbonate solutions A, B, and C (solvent in polypropylene carbonate solution A was N-methyl-2-pyrrolidone, solvent in polypropylene carbonate solution B was tetrahydrofuran, and solvent in polypropylene carbonate solution C was ethyl acetate) at a dilution ratio of 49:1 to obtain a diluted solution.

[0133] The first graphene dispersion prepared in Example 7 was diluted with solvents N-methyl-2-pyrrolidone, tetrahydrofuran, and ethyl acetate to obtain a diluted solution with a dilution ratio of 49:1.

[0134] All diluents were sonicated at 250W for 20 minutes to homogenize them.

[0135] The absorbance of each homogenized diluent was measured at 660 nm using a UV-Vis spectrophotometer to obtain the stability curves of graphene in different solvents. The absorbance was measured once a day for 160 hours.

[0136] according to Figure 8 It can be seen that the data obtained by diluting the first graphene dispersion with polypropylene carbonate compared with that without diluting the first graphene dispersion proves that polypropylene carbonate can improve the stability of the dispersion when diluting it. Therefore, it can be concluded that adding polypropylene carbonate can improve the stability of the second graphene dispersion when preparing it.

[0137] Experimental Example 5

[0138] The redispersion rate of the second graphene dispersions prepared in Example 3 and Comparative Example 3 was detected using a method that tracks the absorbance of the dispersion. The results are shown in [Figure number missing]. Figure 9 .

[0139] The detection method involves using a UV-Vis spectrophotometer to track absorbance at 660 nm. The upper dispersion from Example 1 was filtered to obtain a filter cake, which was then ground to obtain a filter residue. 5 mg of the filter residue was placed in 100 ml of solvent and dispersed to obtain a second graphene dispersion. The absorbance of the second graphene dispersion at 660 nm was measured. Then, the second graphene dispersion was centrifuged at 1000 rpm to obtain the centrifuged second graphene dispersion. The absorbance of the centrifuged second graphene dispersion at 660 nm was measured. The redispersion rate is the ratio of the absorbance value of the centrifuged second graphene dispersion to the absorbance value of the uncentrifuged second graphene dispersion.

[0140] according to Figure 9 It can be seen that the second graphene dispersion prepared using polypropylene carbonate as a dispersant has a high redispersibility.

[0141] Experimental Example 6

[0142] The stability of the second graphene dispersions prepared in Example 3 and Comparative Example 3 was tested using a method that tracks the absorbance of the dispersion. Specifically, a UV-Vis spectrophotometer was used to track the absorbance at 660 nm to obtain the absorbance values ​​of the second graphene dispersions prepared in Example 3 and Comparative Example 3. The absorbance was measured daily for 156 hours, and absorbance spectra were plotted. The results are shown below. Figure 10 ,according to Figure 10 It can be seen that inks made using polypropylene carbonate as a dispersant have high stability.

[0143] Experimental Example 7

[0144] The structure of polypropylene carbonate, graphene, and graphene / polypropylene carbonate composite materials in Example 2 was analyzed using infrared spectroscopy. The results are shown in [Figure 1]. Figures 11-12 It can be seen that the preparation method of Example 1 can achieve the composite of graphene and polypropylene carbonate, with a wavenumber of 1455 cm⁻¹ in polypropylene carbonate. -1 The CH bond at the point is split into three peaks in the graphene-polypropylene carbonate composite material.

[0145] Experimental Example 8

[0146] The graphene / polypropylene carbonate composite material prepared in Example 2 was scanned using a scanning electron microscope (SEM). The SEM images are shown below. Figure 13 .

[0147] Experimental Example 9

[0148] The viscosity of the second graphene dispersion prepared in Example 2 (the concentration of the graphene and polypropylene carbonate mixture in the second graphene dispersion was 20 mg / mL) was measured using a rheometer. The rheometer rotor had a diameter of 40 mm and an angle of 1°. The test results are shown in [Figure 1]. Figure 14 It can be seen that the viscosity range of the second graphene dispersion is 3.6 mPa·s-122.7 mPa·s.

[0149] Experimental Example 10

[0150] The cyclic voltammogram of the micro supercapacitor fabricated in Example 1 at a constant electrical displacement (VSP, BioLogic) scan rate of 5 mV / s is shown below. Figure 15 It can be seen that the electrode reaction of the micro supercapacitor formed by the second graphene dispersion prepared in the embodiments of the present invention is reversible.

[0151] The miniature supercapacitor fabricated in Example 1 operates at 100 μA / cm in the 0-1V range. 2 The current density was subjected to multiple charge-discharge cycles, and the capacitance retention rate was measured in each cycle to obtain... Figure 16 ,according to Figure 16 It can be seen that the micro supercapacitor formed by the second graphene dispersion prepared in the embodiments of the present invention exhibits good capacitance retention.

[0152] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing graphene, characterized in that, Includes the following steps: S1, in the presence of a solvent, graphite and polypropylene carbonate are mixed, and then separated into solid and liquid phases to obtain the upper dispersion, which is the first graphene dispersion. The mixing method includes ultrasonic treatment of graphite and polypropylene carbonate at 160W-360W for 2h-12h; and / or, The solid-liquid separation method includes centrifuging the mixed graphite and polypropylene carbonate at a speed of 1000 rpm to 3000 rpm for 20 min to 60 min.

2. The method for preparing graphene according to claim 1, characterized in that, It also includes step S2, which separates the first graphene dispersion obtained in step S1 into solid and liquid phases, and obtains the filter residue as graphene powder.

3. The method for preparing graphene according to claim 2, characterized in that, It also includes step S3, which involves dispersing the graphene powder obtained in step S2 in a solvent to obtain a second graphene dispersion, or... The graphene powder and polypropylene carbonate obtained in step S2 are dispersed in a solvent to obtain a second graphene dispersion.

4. The method for preparing graphene according to claim 3, characterized in that, The solvent in step S1 and / or step S3 is at least one selected from tetrahydrofuran, N-methyl-2-pyrrolidone, ethyl acetate, and diethylene glycol monomethyl ether; and / or, In step S1, the mass ratio of graphite to polypropylene carbonate is 1:(1-8).

5. The method for preparing graphene according to claim 4, characterized in that, In step S1, the total mass ratio of graphite and polypropylene carbonate to the volume ratio of solvent is (2-9):200, in mg:mL; and / or, The solvent in step S1 and / or step S3 is at least one of tetrahydrofuran and ethyl acetate.

6. The method for preparing graphene according to claim 5, characterized in that, The solid-liquid separation method for the graphene dispersion in step S2 is filtration.

7. The method for preparing graphene according to claim 6, characterized in that, The total mass ratio of graphene powder and polypropylene carbonate to the volume ratio of solvent is (5-400):1, in mg:mL.

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