Sulfur-doped graphene material as well as preparation method and application thereof

Abstract

The invention provides a sulfur-doped graphene material and a preparation method and application thereof, and belongs to the technical field of nano materials, the sulfur-doped graphene material comprises a two-dimensional layered matrix and a chalcogenide group doped on the two-dimensional layered matrix; the two-dimensional layered matrix is made of a graphene material; the chalcogenide group is or; wherein x is 1 or 2. The electronic structure, interlayer interaction and surface defects of graphene are regulated and controlled through sulfur doping, and the conductivity and lithium storage performance of the material are improved. A proper amount of sulfur is doped, so that more active sites are provided, and meanwhile, the structural stability is kept, so that the specific capacity and the cycle life are remarkably improved. The sulfur-doped graphene material disclosed by the invention has a wide application prospect, and is particularly suitable for the field of high-performance lithium storage negative electrode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a sulfur-doped graphene material, a preparation method thereof, and applications thereof. Background Art

[0002] As an emerging material, graphene is widely considered an ideal anode lithium storage material due to its high surface area, excellent conductivity, and exceptional chemical stability. The theoretical specific capacity of graphene can reach 580-650 mAh / g, thanks to the ability of lithium ions to anchor and embed on the sides and edges of its sheets. However, pure graphene has certain limitations in practical applications. First, lithium ions are difficult to stably embed and diffuse in defect-free graphene, limiting its high-rate performance. Furthermore, graphene sheets are prone to restacking due to van der Waals forces, resulting in a significant reduction in surface area and active sites, which in turn compromises its electrochemical performance. To overcome these issues, recent research has focused on enhancing the electrochemical performance of graphene through structural manipulation and surface engineering. For example, porous graphene, by introducing abundant defects and pore structures, not only provides more active sites but also significantly improves the kinetics of ion diffusion. Furthermore, heteroatom doping (such as nitrogen, sulfur, and phosphorus) has been shown to effectively enhance graphene's conductivity, electrode wettability, and surface reactivity.

[0003] Among the many heteroatoms, sulfur doping has attracted much attention due to its unique ability to regulate graphene's electronic structure and enhance local reactivity. By regulating the distribution of π electrons within the graphene carbon skeleton, sulfur atoms can effectively reduce the material's resistance and improve the charge transfer rate. Furthermore, the C-S bonds and lone electron pairs introduced by sulfur serve as important electrochemically active sites, significantly enhancing lithium-ion storage capacity. More importantly, sulfur doping can expand the graphene interlayer spacing and buffer the volume expansion during lithium-ion insertion / deinsertion, thereby significantly improving the material's cycling stability. However, traditional sulfur doping methods (such as chemical vapor deposition and thermal sulfurization) typically require the use of toxic or expensive sulfur source precursors and are complex to prepare, limiting the large-scale application of this technology. Therefore, developing a green, simple, and low-cost method for preparing sulfur-doped graphene has become a research priority in this field. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a sulfur-doped graphene material (S-SHSG). The sulfur-doped graphene material of the present invention has higher conductivity and a stable structure.

[0005] A further technical problem to be solved by the present invention is to provide a preparation method of a sulfur-doped graphene material and its application.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A sulfur-doped graphene material, comprising a two-dimensional layered matrix, and a chalcogen group doped on the two-dimensional layered matrix;

[0008] The two-dimensional layered matrix is a graphene material;

[0009] The chalcogen group is or ;

[0010] Wherein, x is 1 or 2.

[0011] Preferably, the two-dimensional layered matrix is a carbon material in which carbon atoms are arranged in a honeycomb two-dimensional lattice. More preferably, the two-dimensional layered matrix is a carbon material in which carbon atoms are arranged in a honeycomb two-dimensional lattice and is prepared by converting CO2 through a high-temperature self-propagating reaction.

[0012] Preferably, the sulfur-doped graphene material has a mesopore of 0.2-50 nm.

[0013] Preferably, the two-dimensional layered matrix has a flocculent lamellar structure.

[0014] The preparation method of the above-mentioned sulfur-doped graphene material, comprising the following steps:

[0015] The magnesium powder, magnesium oxide powder and magnesium sulfate powder are pre-mixed, and then subjected to dispersion treatment to obtain a uniform mixed powder A;

[0016] The uniform mixed powder A is placed in a sealed reaction tank, and pure CO2 gas is introduced, and after high-temperature self-propagating reaction, the precursor powder product B is obtained after cooling.

[0017] The precursor powder product B is sequentially subjected to acid washing, filtration and freeze-drying to obtain the sulfur-doped graphene material.

[0018] Preferably, the mass ratio of the magnesium sulfate powder to the magnesium powder is greater than 0 and less than or equal to 0.5.

[0019] More preferably, the mass ratio of the magnesium sulfate powder to the magnesium powder is 0.05.

[0020] The high-temperature self-propagating reaction is carried out in a pure CO2 atmosphere.

[0021] The high-temperature self-propagating reaction is achieved by electric current. The high-temperature self-propagating reaction of the present application is carried out in a sealed reaction tank. Specifically, the uniform mixed powder A is loaded into a graphite boat or other reactor vessel, and a conductive wire is embedded therein. The conductive wire is powered by an external program to heat the uniform mixed powder A and start the high-temperature self-propagating reaction.

[0022] The application of the sulfur-doped graphene material or the sulfur-doped graphene material prepared by the preparation method above in a lithium storage negative electrode.

[0023] The beneficial effects of the application are as follows:

[0024] (1) The application adjusts the electronic structure, interlayer interaction and surface defects of graphene by sulfur doping, thereby improving the conductivity and lithium storage performance of the material. Appropriate sulfur doping provides more active sites while maintaining structural stability, thereby significantly improving the specific capacity and cycle stability.

[0025] (2) Magnesium sulfate decomposes to form magnesium oxide at high temperatures, so when used as a sulfur source for sulfur doping in graphene, it will not introduce other impurity phases during the high-temperature self-propagating reaction of magnesium and CO2, which helps to improve the purity of the product.

[0026] (3) The sulfur-doped graphene material of the application has broad application prospects and is particularly suitable for use in the field of high-performance negative electrode lithium storage.

[0027] (4) The preparation method provided by the application has the advantages of simple process, direct scalability and universality, and the prepared sulfur-doped graphene material has good structural stability. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 X-ray diffraction patterns of the sulfur-doped graphene materials prepared in Example 1, Example 3 and Example 4 and the pure graphene material prepared in Example 2;

[0029] Figure 2 Raman spectra of the sulfur-doped graphene materials prepared in Example 1, Example 3 and Example 4 and the pure graphene material prepared in Example 2;

[0030] Figure 3 Nitrogen adsorption-desorption isotherms of the sulfur-doped graphene materials prepared in Example 1, Example 3 and Example 4 and the pure graphene material prepared in Example 2;

[0031] Figure 4 X-ray photoelectron spectrograms of the sulfur-doped graphene materials prepared in Example 1, Example 3 and Example 4 and the pure graphene material prepared in Example 2;

[0032] Figure 5 Scanning electron microscope images of the sulfur-doped graphene materials prepared in Example 1, Example 3 and Example 4 and the pure graphene material prepared in Example 2;

[0033] Figure 6 Transmission electron microscope image of the sulfur-doped graphene material prepared in Example 1;

[0034] Figure 7This is the element energy spectrum distribution diagram of the sulfur-doped graphene material prepared in Example 1;

[0035] Figure 8 This is a graph showing the lithium storage rate performance of the graphene materials prepared in Examples 1 to 6. DETAILED DESCRIPTION

[0036] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0037] The present invention provides a sulfur-doped graphene material (S-SHSG), comprising a two-dimensional layered matrix, and chalcogenide groups doped on the two-dimensional layered matrix;

[0038] The two-dimensional layered matrix is ​​a graphene material (SHSG);

[0039] The sulfide group is 、 ;

[0040] Here, x is usually 1 or 2.

[0041] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0042] In the present invention, the method for preparing the sulfur-doped graphene material preferably comprises the following steps:

[0043] Magnesium powder, magnesium oxide powder and magnesium sulfate powder were manually pre-mixed and then placed in an airflow mill. The high-speed airflow allowed the powders in the mixture to be fully dispersed under the shear and turbulence of the airflow to obtain a uniform mixed powder A.

[0044] In the present invention, the mass ratio of the magnesium powder, magnesium oxide powder and magnesium sulfate powder is preferably 1:8:0-0.5, more preferably 1:8:0.05.

[0045] The uniform mixed powder A is placed in a sealed 20 L reaction tank and introduced with pure CO2 gas. After conductive heating by nickel-chromium wire, a high-temperature self-propagating reaction is initiated. After a few seconds, the precursor powder product B is obtained by natural cooling for 10-20 minutes.

[0046] In the present invention, the high temperature self-propagating reaction is preferably carried out under pure CO2 atmosphere.

[0047] In the present invention, the natural cooling time is 10 to 20 minutes, more preferably 20 minutes.

[0048] The precursor powder product B is acid-washed, filtered, and spray-dried to obtain the sulfur-doped graphene material.

[0049] In the present invention, the acid washing aqueous solution is dilute sulfuric acid, and the concentration of the acid washing aqueous solution is preferably 2 mol / L.

[0050] In the present invention, the initial temperature of the high-temperature self-propagating reaction is preferably 25°C. This initial temperature is the temperature before power is applied, i.e., before the nickel-chromium wire becomes conductive. After power is applied, the reaction releases a large amount of heat energy within a few seconds, and the temperature instantly rises to 800-1000°C.

[0051] In the present invention, the washing reagent is preferably water. The present invention does not specifically limit the amount and frequency of use of the washing reagent, and washing can be performed until the pH value of the washing solution is greater than 7.

[0052] In the present invention, the drying method is preferably freeze-drying.

[0053] The present invention uses a high-temperature self-propagating reaction to allow metallic magnesium powder to reduce CO2 to produce free carbon atoms. The free carbon atoms are adsorbed on the surface of the magnesium oxide particles and gradually generate graphene sheets. At the same time, the large amount of heat generated by the reduction of CO2 by the metallic magnesium powder triggers the thermal decomposition and reduction of the magnesium sulfate powder. The generated sulfur atoms are also adsorbed on the surface of the magnesium oxide particles. During the growth of graphene, they replace the carbon atoms therein to form sulfur-doped graphene. The doping of sulfur atoms introduces heteroatom defects and chemical heterogeneity, which causes uneven charge distribution in graphene, thereby forming more active sites to enhance the adsorption, embedding and desorption capabilities of lithium ions; in addition, sulfur atom doping will regulate the electronic structure of graphene, optimize the conduction band and valence band, improve the conductivity of the material and accelerate charge transfer, which is conducive to the rapid diffusion of lithium ions in the electrode; the bonding form introduced by sulfur doping (such as key, bonds, etc.) can not only enhance the chemical stability of graphene, but also alleviate the volume expansion caused by lithium ion insertion, thereby significantly improving the cycle stability and mechanical stability; at the same time, the high electronegativity and oxidation state groups of sulfur (such as ) can further improve the contact between the electrode and the electrolyte, reduce impedance and improve Coulombic efficiency; under high-rate charge and discharge conditions, the high conductivity and rapid ion diffusion ability of sulfur-doped graphene enable it to maintain excellent specific capacity and stability.

[0054] The present invention also provides the use of the sulfur-doped graphene material described in the above technical solution or the sulfur-doped graphene material prepared by the preparation method described in the above technical solution in a lithium storage negative electrode.

[0055] The present invention does not specifically limit the application method of the sulfur-doped graphene material, and the application method well known to those skilled in the art can be adopted.

[0056] The sulfur-doped graphene material provided by the present invention, its preparation method and application are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] (1) Weigh 8 g of magnesium powder, 64 g of magnesium oxide powder, and 0.4 g of magnesium sulfate powder into a 500 mL beaker and stir with a glass rod to complete the first premixing. Seal the beaker with sealing film and shake the beaker to complete the second premixing. Then, transfer the sample to a jet mill. The high-speed airflow allows the powder in the mixture to be fully dispersed under the shear and turbulence of the airflow to obtain a uniform mixed powder A.

[0059] (2) Fill the evenly dispersed mixed powder A into a graphite boat and bury a nickel-chromium wire in it for subsequent heating by passing an electric current. Transfer the graphite boat to a 20 L sealed reaction tank. Vacuum to , then pass pure The gas is heated to 0.2 MPa, and after three cycles, the sealed reaction tank is filled with 0.4 MPa gas. The gas is used to participate in the reaction. A 5 A current is applied to the nickel-chromium wire via an external program. After 3 seconds, the tank pressure monitoring system shows a significant increase. After a reaction time of approximately 3-5 seconds, the tank pressure stops rising and the current switch is immediately turned off. The increase in tank pressure is approximately 1 MPa. After cooling naturally for 20 minutes, the precursor powder product B is removed.

[0060] (3) Transfer the precursor powder B to a beaker, add an appropriate amount of deionized water, and place it on a magnetic stirrer for uniform stirring at 1000 rpm to form a slurry. Use 1.5 L of 2 mol / L dilute sulfuric acid as an acid pickling agent and slowly add it to the slurry. Then, maintain the speed of 1000 rpm for 1 hour, let it stand for 12 hours, and pour off the supernatant. Separate the filtrate and the filter cake by negative pressure filtration, and maintain the pH value of the filter cake above 7. Finally, freeze-dry the filter cake to prepare the sulfur-doped graphene material (0.05 S-SHSG).

[0061] Example 2

[0062] Pure graphene material (SHSG) was prepared according to the method of Example 1. The difference from Example 1 is that magnesium sulfate powder is no longer added in step (1), and finally the graphene material (SHSG) was prepared.

[0063] Example 3

[0064] 0.1 S-SHSG was prepared according to the method of Example 1. The difference from Example 1 was that the amount of magnesium sulfate powder added in step (1) was adjusted to 0.8 g, and the mass ratio of magnesium powder, magnesium oxide powder and magnesium sulfate powder was approximately 1:8:0.1, and finally sulfur-doped graphene material (0.1 S-SHSG) was prepared.

[0065] Example 4

[0066] 0.5S-SHSG was prepared according to the method of Example 1. The difference from Example 1 was that the amount of magnesium sulfate powder added in step (1) was adjusted to 4 g, and the mass ratio of magnesium powder, magnesium oxide powder and magnesium sulfate powder was approximately 1:8:0.5, and finally sulfur-doped graphene material (0.5S-SHSG) was prepared.

[0067] Example 5

[0068] 0.5 S-SHSG was prepared according to the method of Example 1. The difference from Example 1 was that the amount of magnesium sulfate powder added in step (1) was adjusted to 0.08 g, and the mass ratio of magnesium powder, magnesium oxide powder and magnesium sulfate powder was approximately 1:8:0.01, and finally sulfur-doped graphene material (0.01 S-SHSG) was prepared.

[0069] Example 6

[0070] 0.5 S-SHSG was prepared according to the method of Example 1. The difference from Example 1 was that the amount of magnesium sulfate powder added in step (1) was adjusted to 0.2 g, and the mass ratio of magnesium powder, magnesium oxide powder and magnesium sulfate powder was approximately 1:8:0.025, and finally sulfur-doped graphene material (0.025 S-SHSG) was prepared.

[0071] The X-ray diffraction spectra of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 1 As shown. The characteristic peaks of MgO are almost absent in the samples synthesized in this example, indicating that the sulfur-doped graphene material successfully avoids the impurity problem in this material synthesis strategy. In addition, all samples exhibit a broad peak at approximately 30°, corresponding to the diffraction of the graphite (002) crystal plane, but with a slight shift toward lower angles. According to the Bragg formula (2dsinθ=nλ), the interlayer spacing of the samples has increased, suggesting that the incorporation of sulfur atoms increases the interlayer distance of the material.

[0072] The Raman spectra of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 2As shown in Figure 2, it can be seen that the Raman spectra of SHSG, 0.05 S-SHSG, 0.1 S-SHSG and 0.5 S-SHSG all have D peaks and G peaks at shifts of 1336 and 1578, respectively, where the D peak represents the hybridization of carbon atoms (i.e. type disordered carbon) and G peak stands for graphitized carbon. The strength ratios are 0.801, 0.893, 0.952 and 1.121, respectively, indicating that the degree of disorder of the composite material increases with the proportion of magnesium sulfate in the raw materials.

[0073] The nitrogen adsorption-desorption isotherms of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 3 As shown in the figure, according to BET theory, the specific surface areas of SHSG, 0.05 S-SHSG, 0.1 S-SHSG and 0.5 S-SHSG are , , and , and at this time due to the thermal decomposition of magnesium sulfate Sulfur doping on SHSG etches the carbon layer and increases surface defects. Furthermore, according to the IUPAC classification, the sample exhibits a typical type IV isotherm, with a large H4-type hysteresis loop around 0.4-1.0 P / P0, demonstrating the presence of a large number of mesopores (0.2-50 mm) in S-SHSG.

[0074] The high-resolution X-ray photoelectron spectra of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 4 As shown, from Figure 4 It can be seen that only C, O and S elements exist in the S-SHSG material. In the high-resolution XPS spectrum of C1s, the peaks at 284.23 eV and 283.9 eV correspond to the main and , along with 285.2 eV , 286.33 eV , 288.03 eV and 290.38 eV In addition, according to XPS test results, the element contents of SHSG, 0.05 S-SHSG, 0.1 S-SHSG, and 0.5 S-SHSG are shown in Table 1. It can be seen that as the proportion of magnesium sulfate increases, the sulfur atom doping gradually increases. This trend verifies the effectiveness of magnesium sulfate as a sulfur source in high-temperature self-propagating reactions.

[0075] surface The proportion of each element in S-SHSG (at.%)

[0076]

[0077] The scanning electron microscope images of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 5 As shown, the micromorphology of S-SHSG materials prepared via a high-temperature self-propagating reaction changes significantly with increasing magnesium sulfate content in the raw material, exhibiting a transition from flocculent lamellar structures to agglomerated layers. At low magnesium sulfate content, the material primarily exhibits a flocculent lamellar structure, demonstrating good dispersion and lamellar properties. However, as the magnesium sulfate content increases, the lamellar structures gradually stack, ultimately forming a dense, agglomerated layer structure. This morphological change is closely related to sulfur doping and its influence on the growth behavior of graphene sheets.

[0078] The transmission electron microscopy images of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 6 As shown, 0.05 S-SHSG exhibits a distinct multilayered structure, with 2-4 graphene layers clearly visible. The surface of the graphene sheets is rich in wrinkles, which are not only the result of spontaneous curling of the graphene sheets at the nanoscale but are also likely closely related to the intense gas release and stress induced by the dynamic environment during the reaction. These wrinkles increase the material's specific surface area, providing more active sites for lithium-ion storage and charge transport. They also help alleviate inter-sheet stacking, improving the material's conductivity and lithium storage performance.

[0079] The element energy spectrum distribution diagrams of the sulfur-doped graphene materials prepared in Examples 1 to 4 of the present invention are as follows: Figure 7 As shown, from Figure 7 It can be seen that C, O, and S elements are all distributed on the same material, proving the successful preparation of sulfur-doped graphene.

[0080] The electrochemical test method is to test the material performance by assembling a lithium half-cell. Sulfur-doped graphene material with different mass ratios is mixed with conductive carbon black and PVDF, and then stirred in N-methylpyrrolidone with a mass ratio of 7:2:1. The mixture is coated on copper foil and vacuum dried to obtain electrode plates. Figure 8 The lithium storage rate performance of the sulfur-doped graphene materials prepared in Examples 1 to 6 is as follows: Figure 8It can be seen that 0.05 S-SHSG has a specific capacity of 1045.34, 846.17, 657.71, 459.31, and 301.99 mAh / g at current densities of 0.05, 0.1, 0.2, 0.5, and 1 A / g, respectively. When the current density is restored to 0.05 A / g, it still has a capacity of 885.35 mAh / g. These results demonstrate that 0.05 S-SHSG has good kinetic performance and high specific capacity for lithium storage applications.

[0081] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0082] Any portions not described in detail in this specification are known in the art. The above embodiments are provided for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. Various equivalent substitutions and modifications that do not depart from the spirit and principles of the present invention are intended to be encompassed within the scope of the present invention.

Claims

1. A sulfur-doped graphene material, characterized in that: It includes a two-dimensional layered matrix, and a chalcogen group doped on the two-dimensional layered matrix; The two-dimensional layered matrix is ​​a graphene material; The sulfide group is or ; Where x is 1 or 2.

2. The sulfur-doped graphene material according to claim 1, characterized in that The two-dimensional layered matrix is ​​a carbon material in which carbon atoms are arranged in a honeycomb two-dimensional lattice.

3. The sulfur-doped graphene material according to claim 1, characterized in that There are mesopores of 0.2 to 50 nm in the sulfur-doped graphene material.

4. The sulfur-doped graphene material according to claim 1, characterized in that The two-dimensional layered matrix is ​​a flocculent lamellar structure.

5. The method for preparing the sulfur-doped graphene material according to any one of claims 1 to 4, characterized in that: The following steps are involved: After premixing magnesium powder, magnesium oxide powder and magnesium sulfate powder, the mixture is dispersed to obtain a uniform mixed powder A. Place the uniform mixed powder A in a closed reaction tank and introduce pure The gas undergoes a high-temperature self-propagating reaction and is then cooled to obtain a precursor powder product B; The precursor powder product B is sequentially acid-washed, filtered, and freeze-dried to obtain the sulfur-doped graphene material.

6. The method for preparing the sulfur-doped graphene material according to claim 5, wherein The mass ratio of the magnesium sulfate powder to the magnesium powder is greater than 0 and less than or equal to 0.

5.

7. The method for preparing the sulfur-doped graphene material according to claim 5, wherein: The mass ratio of the magnesium sulfate powder to the magnesium powder is 0.

05.

8. The method for preparing the sulfur-doped graphene material according to claim 5, wherein: The high temperature self-propagating reaction Carry out under atmosphere conditions.

9. The method for preparing the sulfur-doped graphene material according to claim 5, wherein: The high-temperature self-propagating reaction is achieved by electric current.

10. Use of the sulfur-doped graphene material according to any one of claims 1 to 4 or the sulfur-doped graphene material prepared by the preparation method according to any one of claims 5 to 9 in a lithium storage negative electrode.

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