A molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material, its preparation method, and a lithium-ion energy storage device.

Abstract

This invention belongs to the field of electrochemical energy storage, and discloses a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material, its preparation method, and a lithium-ion energy storage device. The invention uses graphene oxide, sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea, and dicyandiamine as raw materials, and prepares the composite material using a simple hydrothermal method and heat treatment in an argon / hydrogen mixed atmosphere. The method is simple and low-cost. The prepared molybdenum / tin selenide (MoSe2-SnSe) nanoparticles loaded on sulfur-nitrogen co-doped graphene form a three-dimensional hierarchical composite structure, which can effectively improve the conductivity of the electrode material and alleviate the volume expansion effect of the electrode material during charge and discharge, thereby achieving the goal of improving the electrochemical performance of lithium-ion batteries and lithium-ion hybrid capacitors.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage, specifically relating to a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material, its preparation method, and a lithium-ion energy storage device. Background Technology

[0002] In recent years, with the construction of new energy systems, higher requirements have been placed on energy storage devices. In particular, the rapid development of electric vehicles and the widespread application of mobile digital electronic devices necessitate a safe, inexpensive energy storage component that combines high energy density and long cycle stability. Among numerous energy conversion and storage devices, lithium-ion batteries and supercapacitors have become research hotspots. While their compositions are similar, their different energy storage mechanisms lead to significant differences in various performance aspects. Lithium-ion batteries primarily rely on lithium intercalation, alloying reactions, or conversion reactions on the material surface and in the bulk phase for charge storage, thus exhibiting high specific capacity. Supercapacitors, on the other hand, rely on double-layer or pseudocapacitive conversion reactions to store charge, resulting in high power density and long cycle life. Therefore, developing an energy storage device that combines high energy density and high power density from the internal design is crucial, leading to the development of lithium-ion capacitors.

[0003] Lithium-ion capacitors, as a type of asymmetric capacitor, combine the negative electrode materials of lithium-ion batteries and the positive electrode materials of supercapacitors, thus possessing the electrochemical characteristics of both devices. During charging, lithium ions in the electrolyte intercalate into the negative electrode to form a lithium intercalation compound, while anions in the electrolyte adsorb onto the surface of the activated carbon in the positive electrode to form an electrical double layer. The discharging process is the reverse of the charging process; lithium ions are extracted from the lithium intercalation material, and anions desorb from the activated carbon surface and return to the electrolyte. This design significantly increases the energy density, reduces weight, and widens the voltage range of lithium-ion capacitors. Furthermore, the graphite + activated carbon design makes lithium-ion capacitors easier to recycle. In practice, some lithium-ion capacitors have already been commercialized. However, compared to lithium-ion batteries, the electrochemical performance of lithium-ion capacitors still has considerable room for improvement. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material, its preparation method, and a lithium-ion energy storage device. The composite material of the present invention has the characteristics of lower cost, high electrochemical performance, and structural stability.

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

[0006] A method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material includes the following steps:

[0007] Sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea, and dicyandiamine were mixed with a graphene oxide dispersion to obtain suspension A; wherein the mass ratio of sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea, and dicyandiamine was 1:(0.8~2):(0.8~1.8):(1~3), and the mass ratio of sodium molybdate tetrahydrate to graphene oxide was (1.5~3):1;

[0008] The suspension A was subjected to a hydrothermal reaction at 160–190 °C. After the reaction was completed, the product was cooled, centrifuged, washed, and freeze-dried to obtain the precursor material.

[0009] The precursor material and selenium powder were placed in a reducing atmosphere and calcined at 500–600 °C. After calcination, the molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material was obtained.

[0010] Preferably, the dispersant of the graphene oxide dispersion is a mixed solvent of water and ethanol, wherein the mixed solvent of water and ethanol is obtained by mixing water and ethanol in a volume ratio of (1-3):1;

[0011] In the graphene oxide dispersion, the solid-liquid ratio of graphene oxide to dispersant is (40~60):40, with units of mg / mL.

[0012] Preferably, the hydrothermal reaction of suspension A at 160–190 °C lasts for 18–22 hours.

[0013] Preferably, after the hydrothermal reaction of suspension A is completed, the product is cooled to room temperature and then centrifuged, washed, and freeze-dried.

[0014] Preferably, the reducing atmosphere during the calcination of the precursor material is a mixture of hydrogen and argon.

[0015] Preferably, in the hydrogen and argon mixture, the volume fraction of hydrogen is 5% to 10%; and during the calcination of the precursor material, the flow rate of the hydrogen and argon mixture is 30 to 70 SCCM.

[0016] Preferably, when calcining the precursor material, the heating rate is 3-5℃ / min and the calcination time is 2-3 hours.

[0017] The present invention also provides a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material prepared by the preparation method described above.

[0018] The present invention also provides a lithium-ion energy storage device, comprising a positive electrode and a negative electrode, wherein the negative electrode is made of the molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material as described above.

[0019] Preferably, the lithium-ion energy storage device is a lithium-ion battery and a lithium-ion hybrid capacitor.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The molybdenum / tin selenide / sulfur-nitrogen co-doped graphene (MoSe2-SnSe@SNG) composite material provided by this invention features a stable three-dimensional porous composite structure formed by in-situ growth of heterostructured MoSe2-SnSe composite nanoparticles on both sides of the sheet structure of a two-dimensional SNG. In the MoSe2-SnSe@SNG composite structure, the MoSe2-SnSe nanoparticles can suppress SNG stacking, while the SNG can effectively suppress particle agglomeration and volume expansion of the MoSe2-SnSe nanoparticles during charging and discharging. Furthermore, the SNG acts as a three-dimensional conductor, effectively improving the electronic conductivity of MoSe2-SnSe. The MoSe2-SnSe composite material, as a conversion-alloy type anode, exhibits high theoretical specific capacity. Simultaneously, the heterostructure interface between MoSe2 and SnSe provides more lithium storage active sites, and the synergistic effect of both effectively improves the electrochemical performance of lithium-ion batteries and lithium-ion capacitors. Therefore, the MoSe2-SnSe@SNG composite material disclosed in this invention is a relatively ideal lithium storage anode material. The preparation method of the MoSe2-SnSe@SNG composite material provided by this invention is simple, adjustable and controllable, requires low raw material costs, and has a relatively simple preparation process, resulting in higher purity of the product and making it more suitable for large-scale production. Attached Figure Description

[0022] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings, wherein:

[0023] Figure 1 This is the X-ray powder diffraction spectrum of the MoSe2-SnSe@SNG composite material prepared in Example 3 of this invention.

[0024] Figure 2 This is a SEM image of the MoSe2-SnSe@SNG composite material prepared in Example 3 of this invention.

[0025] Figure 3 This is a TEM image of the MoSe2-SnSe@SNG composite material prepared in Example 3 of this invention.

[0026] Figure 4 This is a SEM image of the MoSe2@SNG composite material prepared in Example 3 of this invention.

[0027] Figure 5 This is a SEM image of the SnSe@SNG composite material prepared in Example 3 of this invention.

[0028] Figure 6 This is a graph showing the lithium storage cycle performance of SnSe@SNG, MoSe2@SNG, MoSe2-SnSe@SNG and SNG composite materials prepared in Example 3 of this invention at 0.2 A / g.

[0029] Figure 7 This is a graph showing the lithium-ion rate performance of the lithium-ion hybrid capacitor assembled with MoSe2-SnSe@SNG and activated carbon AC prepared in Example 3 of this invention.

[0030] Figure 8 The rate performance diagram shows the MoSe2-SnSe@SNG||AC lithium-ion hybrid capacitor assembled in Example 3. Detailed Implementation

[0031] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely for illustration and explanation and are not intended to limit the present invention.

[0032] The preparation method of the molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material of the present invention includes the following steps:

[0033] (1) Sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea and dicyandiamine were added to the dispersion of graphene oxide and stirred at room temperature for 1 hour. After stirring evenly, suspension A was obtained. Suspension A was transferred to a high-pressure reactor for hydrothermal reaction. The hydrothermal reaction temperature was 160-190 °C and the reaction time was 18-22 hours. After the reaction was complete, the reaction product was cooled, centrifuged, washed and freeze-dried to obtain the precursor material. The mass ratio of sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea and dicyandiamine was 1:(0.8-2):(0.8-1.8):(1-3), and the mass ratio of sodium molybdate tetrahydrate to graphene oxide was (3-1.5):1. In the dispersion of graphene oxide, the solvent was a mixed solvent of water and ethanol in a volume ratio of (1-3):1.

[0034] (2) The above-mentioned precursor product and selenium powder were placed in a reducing atmosphere and calcined at 500-600 °C for 2-3 hours, with a heating rate of 3-5 °C / min and a protective gas flow rate of 30-70 SCCM, to obtain the MoSe2-SnSe@SNG composite material (i.e., MoSe2-SnSe nanoparticles loaded on sulfur-nitrogen co-doped graphene composite material). The reducing atmosphere used above was a mixture of argon and hydrogen, Ar / H2 (wherein, the volume ratio of Ar to H2 in Ar / H2 was 95% / 5% or 90% / 10%).

[0035] The MoSe2-SnSe@SNG composite material of this invention can be applied to lithium-ion energy storage devices (such as lithium-ion batteries and lithium-ion hybrid capacitors). The MoSe2-SnSe@SNG composite material of this invention can effectively improve the conductivity of electrode materials and alleviate the volume expansion effect of electrode materials during charging and discharging, thereby achieving the goal of improving the electrochemical performance of lithium-ion batteries and lithium-ion capacitors.

[0036] Example 1

[0037] The preparation method of the MoSe2-SnSe@SNG composite material in this embodiment includes the following steps:

[0038] 1. First, 40 mg of graphene oxide was dispersed in 40 mL of a distilled water / ethanol mixed solvent (water:ethanol volume ratio of 1:1) to obtain a graphene suspension. Then, 60 mg of sodium molybdate tetrahydrate, 48 mg of sodium stannate trihydrate, 48 mg of thiourea, and 60 mg of dicyandiamine were added to the above graphene suspension, and the mixture was stirred at room temperature for 1 hour until homogeneous to obtain suspension A. Suspension A was transferred to an autoclave for hydrothermal reaction at 160 °C for 22 hours. After the reaction was complete, the reaction product was cooled, centrifuged, washed, and freeze-dried to obtain the precursor material.

[0039] 2. The above-mentioned polymer precursor product and selenium powder were placed in a reducing atmosphere (Ar to H2 volume ratio of 90% / 10%), the gas flow rate was 30 SCCM, and the temperature was increased to 500 ℃ at 5℃ / min and maintained for 3 hours to obtain MoSe2-SnSe@SNG composite material.

[0040] Comparative Example 1

[0041] The steps are basically the same as in Example 1 above, except that sodium molybdate tetrahydrate or sodium stannate trihydrate is not added in step 1 to obtain SnSe@SNG or MoSe2@SNG composite materials.

[0042] Example 2

[0043] The preparation method of the MoSe2-SnSe@SNG composite material in this embodiment includes the following steps:

[0044] 1. First, 50 mg of graphene oxide was dispersed in 40 mL of a distilled water / ethanol mixed solvent (water:ethanol volume ratio of 2:1) to obtain a graphene suspension. Then, 100 mg of sodium molybdate tetrahydrate, 100 mg of sodium stannate trihydrate, 180 mg of thiourea, and 300 mg of dicyandiamine were added to the above graphene suspension, and the mixture was stirred at room temperature for 1 hour until homogeneous to obtain suspension A. Suspension A was transferred to an autoclave for hydrothermal reaction at 180 °C for 20 hours. After the reaction was complete, the reaction product was cooled, centrifuged, washed, and freeze-dried to obtain the precursor material.

[0045] 2. The above-mentioned polymer precursor product and selenium powder were placed in a reducing atmosphere (Ar to H2 volume ratio of 90% / 10%), the gas flow rate was 50 CCM, and the temperature was increased to 550 ℃ at 3 ℃ / min and maintained for 2 hours to obtain MoSe2-SnSe@SNG composite material.

[0046] Comparative Example 2

[0047] The steps are basically the same as in Example 2 above, except that sodium molybdate tetrahydrate or sodium stannate trihydrate is not added in step 1 to obtain SnSe@SNG or MoSe2@SNG composite materials.

[0048] Example 3

[0049] The preparation method of the MoSe2-SnSe@SNG composite material in this embodiment includes the following steps:

[0050] 1. First, 60 mg of graphene oxide was dispersed in 40 mL of a distilled water / ethanol mixed solvent (water:ethanol volume ratio of 2:1) to obtain a graphene suspension. Then, 180 mg of sodium molybdate tetrahydrate, 360 mg of sodium stannate trihydrate, 540 mg of thiourea, and 540 mg of dicyandiamine were added to the above graphene suspension, and the mixture was stirred at room temperature for 1 hour until homogeneous to obtain suspension A. Suspension A was transferred to an autoclave for hydrothermal reaction at 190℃ for 22 hours. After the reaction was complete, the reaction product was cooled, centrifuged, washed, and freeze-dried to obtain the precursor material.

[0051] 2. The above-mentioned polymer precursor product and selenium powder were placed in a reducing atmosphere (Ar to H2 volume ratio of 95% / 5%), the gas flow rate was 60 CCM, and the temperature was increased to 600 °C at 3 °C / min and maintained for 2 hours to obtain MoSe2-SnSe@SNG composite material.

[0052] Comparative Example 3

[0053] The steps are basically the same as in Example 3 above, except that sodium molybdate tetrahydrate or sodium stannate trihydrate is not added in step 1 to obtain SnSe@SNG or MoSe2@SNG composite materials.

[0054] The structure and morphology of the obtained samples were characterized using X-ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. The results are shown in the figure. Figure 1 , Figure 2 , Figure 3 .Depend on Figure 1 As can be seen, the XRD patterns of the MoSe2-SnSe@SNG, MoSe2@SNG, and SnSe@SNG composite samples all show XRD diffraction peaks corresponding to the standard cards for MoSe2 and SnSe, proving the successful preparation of the MoSe2-SnSe@SNG composite material. From SEM (… Figure 2 ) and TEM ( Figure 3 As shown in the figure, MoSe2-SnSe nanoparticles can be uniformly loaded onto the SNG substrate to form a three-dimensional hierarchical composite material, and the two-dimensional thin film material, i.e., the SNG substrate, can be clearly observed in the TEM image. In contrast, the two-dimensional MoSe2 nanosheets were not clearly observed in the SEM image of MoSe2@SNG. Figure 4 This is mainly attributed to the uniform dispersion of two-dimensional MoSe2 nanosheets within the SNG framework. SEM images of SnSe@SNG clearly show that SnSe nanosheets can be uniformly loaded onto the SNG substrate surface. Figure 5 ).

[0055] Example 4

[0056] The preparation method of the MoSe2-SnSe@SNG composite material in this embodiment includes the following steps:

[0057] 1. First, 60 mg of graphene oxide was dispersed in 40 mL of a distilled water / ethanol mixed solvent (water:ethanol volume ratio of 3:1) to obtain a graphene suspension. Then, 180 mg of sodium molybdate tetrahydrate, 180 mg of sodium stannate trihydrate, 180 mg of thiourea, and 540 mg of dicyandiamine were added to the above graphene suspension, and the mixture was stirred at room temperature for 1 hour. After stirring until homogeneous, suspension A was obtained. Suspension A was transferred to an autoclave for hydrothermal reaction at 190°C for 18 hours. After the reaction was complete, the reaction product was cooled, centrifuged, washed, and freeze-dried to obtain the precursor material.

[0058] 2. The above-mentioned polymer precursor product and selenium powder were placed in a reducing atmosphere (Ar to H2 volume ratio of 95% / 5%), the gas flow rate was 70 SCCM, and the temperature was increased to 600 ℃ at 3℃ / min and maintained for 2 hours to obtain MoSe2-SnSe@SNG composite material.

[0059] Comparative Example 4

[0060] The steps are basically the same as in Example 4 above, except that sodium molybdate tetrahydrate or sodium stannate trihydrate is not added in step 1 to obtain SnSe@SNG or MoSe2@SNG composite materials.

[0061] To demonstrate the beneficial effects of the present invention, the inventors sampled the composite materials from Examples 1 to 4 above, prepared working electrodes respectively, and then assembled them into lithium-ion batteries and lithium-ion hybrid capacitors respectively. The electrochemical performance of the batteries and hybrid capacitors was then tested. The specific experimental results are as follows:

[0062] (1) Preparation of working electrode

[0063] The powdered composite material prepared in the above examples was mixed evenly with acetylene black and polyvinylidene fluoride at a mass ratio of 7:2:1; then, an appropriate amount of N-methylpyrrolidone was added dropwise and the mixture was stirred evenly; the evenly mixed slurry was uniformly coated onto copper foil and dried in a vacuum drying oven at 80 °C; finally, it was punched into a disc with a diameter of 12 mm and weighed. Based on the feeding ratio, the mass of the active material in the electrode was 1.6 ± 0.1 mg cm⁻¹. -2 .

[0064] (2) Lithium-ion battery assembly

[0065] Using the electrode prepared in step (1) above as the working electrode, pure lithium metal as the counter electrode and reference electrode, polypropylene porous membrane Celgard 2400 as the separator, and the electrolyte is 1 mol / L LiPF6 / ethylene carbonate (EC)-dimethyl carbonate (DMC)-ethyl methyl carbonate (EMC), wherein the volume ratio of EC, DMC and EMC is 1:1:1.

[0066] (3) Assembly of lithium-ion hybrid capacitors

[0067] Using the electrode prepared in step (1) above as the negative electrode, activated carbon (AC) as the positive electrode, Celgard 2400 as the separator, and 1 mol / L LiPF6 / EC-DMC-EMC as the electrolyte, a MoSe2-SnSe@SNG||AC lithium-ion hybrid capacitor was assembled according to a negative electrode to positive electrode mass ratio of 3:1. Before assembling the lithium-ion hybrid capacitor, the electrode loaded with MoSe2-SnSe@SNG was tightly bonded to the Li sheet, and then placed in an electrolyte containing LiPF6 for 2 hours for activation.

[0068] The entire assembly process was completed in a glove box filled with Ar atmosphere, and the glove was sealed using a sealing machine.

[0069] (4) Electrochemical performance testing

[0070] The electrochemical performance of lithium-ion batteries and lithium-ion hybrid capacitors was tested using assembled CR2025 coin cells as test devices. Specific capacity, cycle stability, and rate performance were measured using a Wuhan Landian CT2001A battery tester. Test results are shown below. Figures 6-8 .

[0071] Figure 6 The lithium storage cycling performance of MoSe2-SnSe@SNG, MoSe2@SNG, and SnSe@SNG prepared in Example 3 is presented in a comparative manner at different current densities of 0.2 A / g. Figure 6 As observed, the specific capacities of the MoSe2-SnSe@SNG, MoSe2@SNG, and SnSe@SNG composite materials prepared in Example 3 after 100 cycles were 780, 594, and 464 mAh / g, respectively, with capacity retention rates of 85%, 69%, and 57%. This result indicates that the electrical performance of MoSe2-SnSe@SNG is optimal, and also proves the effectiveness of this synthesis method. The difference in cycling performance between Examples 1-4 ranged from 1% to 3%, with the MoSe2-SnSe@SNG composite material in Example 3 exhibiting the best cycling performance. Furthermore, the MoSe2-SnSe@SNG composite materials in Examples 1-4 all showed better cycling performance than the MoSe2@SNG and SnSe@SNG composite materials at the same current density.

[0072] Figure 7 The graph shows the charge-discharge curves of the MoSe2-SnSe@SNG||AC lithium-ion hybrid capacitor assembled in Example 3 under a current density of 0.05 A / g, with a voltage range of 0.01~4.0 V. It can be seen that the charge-discharge curve of the lithium-ion hybrid capacitor is not an ideal linear shape, indicating that the hybrid ion capacitor exhibits a "coupling effect" between two different forms of energy storage (battery and capacitor).

[0073] Figure 8The figure shows the rate performance of the MoSe2-SnSe@SNG||AC lithium-ion hybrid capacitor assembled in Example 3. The specific capacitances of this lithium-ion capacitor are 92 mAh / g, 83 mAh / g, 76 mAh / g, 66 mAh / g, 59 mAh / g, 50 mAh / g, and 44 mAh / g under current densities of 0.1 A / g, 0.2 A / g, 0.5 A / g, 1 A / g, 2 A / g, 4 A / g, and 5 A / g, respectively. When the current density returns to 0.1 A / g, the specific capacitance recovers to 82 mAh / g. The rate performance data of Examples 1-4 differ by 1%-4%, with the MoSe2-SnSe@SNG||AC of Example 3 exhibiting the best rate performance. As can be seen from the above, the composite material of the present invention has good conductivity, controllable composition and morphology, and a hierarchical composite structure, achieving a structure-property relationship where structure determines properties, and properties determine performance. The MoSe2-SnSe@SNG composite material provided by this invention can significantly improve capacity and cycle stability when used as a negative electrode material for lithium-ion batteries or capacitors.

[0074] As can be seen from the above scheme, the method of the present invention is simple and low in cost. The prepared molybdenum / tin selenide MoSe2-SnSe nanoparticles loaded on sulfur and nitrogen co-doped graphene have a three-dimensional hierarchical composite structure, which can effectively improve the conductivity of electrode materials and alleviate the volume expansion effect of electrode materials during charging and discharging, thereby achieving the goal of improving the electrochemical performance of lithium-ion batteries and lithium-ion capacitors.

[0075] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material, characterized in that, The molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material is a MoSe2-SnSe@SNG composite material, which includes the following process: Sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea, and dicyandiamine were mixed with a graphene oxide dispersion to obtain suspension A; wherein the mass ratio of sodium molybdate tetrahydrate, sodium stannate trihydrate, thiourea, and dicyandiamine was 1:(0.8~2):(0.8~1.8):(1~3), and the mass ratio of sodium molybdate tetrahydrate to graphene oxide was (1.5~3):1; The suspension A was subjected to a hydrothermal reaction at 160–190 °C. After the reaction was completed, the product was cooled, centrifuged, washed, and freeze-dried to obtain the precursor material. The precursor material and selenium powder were placed in a reducing atmosphere and calcined at 500–600 °C. After calcination, the molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material was obtained.

2. The method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material according to claim 1, characterized in that, The dispersant for the graphene oxide dispersion is a mixed solvent of water and ethanol, wherein the mixed solvent of water and ethanol is obtained by mixing water and ethanol in a volume ratio of (1-3):

1. In the graphene oxide dispersion, the solid-liquid ratio of graphene oxide to dispersant is (40~60):40, with units of mg / mL.

3. The method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material according to claim 1, characterized in that, Suspension A was subjected to a hydrothermal reaction at 160–190 °C for 18–22 hours.

4. The method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material according to claim 1, characterized in that, After the hydrothermal reaction of suspension A is completed, the product is cooled to room temperature and then centrifuged, washed, and freeze-dried.

5. The method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material according to claim 1, characterized in that, The reducing atmosphere during the calcination of the precursor material is a mixture of hydrogen and argon.

6. The method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material according to claim 1, characterized in that, In the hydrogen and argon mixture, the volume fraction of hydrogen is 5% to 10%; during the calcination of the precursor material, the flow rate of the hydrogen and argon mixture is 30 to 70 SCCM.

7. The method for preparing a molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material according to claim 1, characterized in that, When calcining the precursor material, the heating rate is 3-5℃ / min, and the calcination time is 2-3 hours.

8. A molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material prepared by the preparation method according to any one of claims 1-7.

9. A lithium-ion energy storage device, characterized in that, It includes a positive electrode and a negative electrode, wherein the negative electrode is made of the molybdenum / tin selenide / sulfur-nitrogen co-doped graphene composite material as described in claim 8.

10. A lithium-ion energy storage device according to claim 9, characterized in that, The energy storage device is a lithium-ion battery or a lithium-ion hybrid capacitor.

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