An amorphous MoS2 / rGO active material, its preparation method, and its application in the preparation of cathode materials for sodium-ion batteries.

Abstract

This invention discloses an amorphous MoS2 / rGO active material, its preparation method, and its application in the preparation of cathode materials for sodium-ion batteries, belonging to the technical field of sodium-ion battery cathode materials and their preparation. This invention solves the problem that existing MoS2-based electrode materials have high crystallinity and are prone to large volume expansion during charge-discharge cycling, which disrupts the stability of the MoS2 structure and leads to significant capacity decay during cycling. This invention uses EG as a solvent to prepare an amorphous MoS2 / rGO active material using a one-pot solvothermal method, in which MoS2 is uniformly distributed on the three-dimensional carbon framework of rGO. The amorphous structure improves the cycle stability of sodium-ion batteries. Sodium-ion batteries prepared using this material as a cathode material exhibit a first-cycle discharge specific capacity of 142.1 mAh / g at a current density of 1 A / g, and a capacity decay rate of only 9% after 2000 cycles.

Description

Technical Field

[0001] This invention relates to an amorphous MoS2 / rGO active material, its preparation method, and its application in the preparation of cathode materials for sodium-ion batteries, belonging to the technical field of cathode materials and their preparation for sodium-ion batteries. Background Technology

[0002] With the development of green energy and electrochemical energy storage systems, the development of advanced energy storage devices is a necessary condition for sustainable development. Human demand for safer, more environmentally friendly, and longer-lasting batteries is also constantly increasing. Compared with lithium-ion batteries, sodium-ion batteries have the advantages of abundant raw materials and low prices, which makes sodium-ion batteries have obvious advantages in terms of economy, safety and temperature adaptability. They have gradually become a research hotspot for rechargeable batteries and are expected to become an ideal alternative to lithium-ion batteries.

[0003] However, due to the large mass and ionic radius of sodium ions, their higher reduction potential, and greater volume expansion, the insertion / extraction rate of sodium ions is slow, resulting in poor charge / discharge specific capacity and cycle stability of sodium-ion batteries. This has become a major factor affecting the rapid development of sodium-ion batteries. Currently, metal chalcogenides (such as molybdenum disulfide (MoS2)) with high theoretical specific capacity are one of the main negative electrode materials for sodium-ion batteries. However, because they store sodium through conversion reactions, this method of sodium storage inevitably leads to significant volume expansion and electrode structure damage, ultimately resulting in poor cycle stability during battery charge and discharge. Therefore, researching how to suppress capacity decay during sodium-ion battery cycling and improve its cycle stability is of great significance for improving the electrochemical performance of sodium-ion batteries.

[0004] Currently, the main approach to addressing the poor cycle stability of MoS2-based sodium-ion batteries is to combine them with framework materials (porous carbon, graphene, etc.) possessing high cycle stability to achieve a synergistic effect and thus improve cycle stability. However, the preparation of MoS2 / carbon composite materials is often complex, involving processes such as high-temperature pyrolysis and chemical vapor deposition. These methods result in high crystallinity, causing significant orientational volume expansion during sodium ion insertion, which undermines the stability of the molybdenum disulfide structure. Amorphizing MoS2, on the other hand, holds promise for resolving this volume expansion issue during cycling, thereby improving the structural stability of MoS2 during sodium ion insertion / extraction and enhancing the cycle stability of the MoS2 electrode. Therefore, providing an amorphous MoS2 active material and its application in the preparation of cathode materials for sodium-ion batteries is essential. Summary of the Invention

[0005] To address the problem that existing MoS2-based electrode materials have high crystallinity and are prone to large volume expansion during charge-discharge cycles, which disrupts the stability of the MoS2 structure and leads to significant capacity decay during cycling, this invention provides an amorphous MoS2 / rGO active material, its preparation method, and its application in the preparation of cathode materials for sodium-ion batteries.

[0006] The technical solution of the present invention:

[0007] One of the objectives of this invention is to provide an amorphous MoS2 / rGO active material, which is prepared by a one-pot solvothermal method using molybdenum source, sulfur source and pretreated graphene oxide as raw materials and ethylene glycol as solvent.

[0008] The second objective of this invention is to provide a method for preparing the above-mentioned amorphous MoS2 / rGO active material, which includes the following steps:

[0009] (1) Pretreatment of graphene oxide;

[0010] (2) The pretreated graphene oxide was dispersed in ethylene glycol solvent to obtain a uniform and stable graphene oxide solution.

[0011] (3) Add the molybdenum source and sulfur source to the graphene oxide solution obtained in (2), heat and stir until the molybdenum source and sulfur source are completely dissolved to obtain the reaction solution;

[0012] (4) Transfer the reaction solution obtained in (3) to a high-pressure reactor and keep it at 160-200℃ for 20-24h. After the reaction is completed, cool to room temperature, filter, and soak the obtained precipitate in concentrated ammonia solution, ultrasonically clean it, and then wash it several times with anhydrous ethanol and deionized water and collect the precipitate.

[0013] (5) The product precipitate collected in (4) is frozen, dried and ground to obtain amorphous MoS2 / rGO material particles.

[0014] Further specifying, (1) the process of pretreating graphene oxide is as follows:

[0015] First, at 0–20°C, an ethylene glycol solution or a methanol solution of graphene oxide was placed in an ultrasonic machine with water as the conductive medium for ultrasonic treatment for 5–10 hours.

[0016] Then, the ultrasonically treated solution was centrifuged at 10,000–16,000 rpm for 5–10 min. After centrifugation, the supernatant was discarded, and the precipitate was washed repeatedly with deionized water until the washing liquid was clear, thus obtaining the pretreated graphene oxide.

[0017] Furthermore, the volume of the solution to be treated during the ultrasonic process shall not exceed 2 / 3 of the total volume of the container.

[0018] To further specify, the process of repeatedly washing the precipitate with deionized water until the washing liquid is clear is as follows: transfer the precipitate to a small beaker, add deionized water, and stir magnetically at room temperature. The solution volume should be 40-70% of the total container volume. Stir for 0.5-1 hour to disperse the graphene oxide precipitate in the deionized water and obtain a homogeneous solution. Centrifuge the homogeneous solution at 10,000-16,000 rpm for 5-10 minutes. After centrifugation, discard the supernatant. Repeat the above steps of adding deionized water, magnetic stirring, centrifugation, and discarding the supernatant 3-5 times until the supernatant becomes clear and transparent after centrifugation.

[0019] Further specifying, in (2) the mass-to-volume ratio of graphene oxide and ethylene glycol is 0.1-0.15 g: 50-75 mL.

[0020] Further specifying, in (3), the molybdenum source is ammonium molybdate or sodium molybdate, and the sulfur source is thiourea or sulfur.

[0021] Further specifying, in (3), the molar ratio of molybdenum source to sulfur source is (10-20):1.

[0022] Further specifying, the molar-volume ratio of molybdenum source, sulfur source and graphene oxide solution in (3) is 0.5-0.75 mmol: 10-15 mmol: 50-75 mL.

[0023] Further specified, (3) the heating and stirring temperature is 40-50℃, the speed is 400-500rpm, the stirring time is 1-2h, until the molybdenum source and sulfur source are completely dissolved and there are no obvious white particles.

[0024] Further specifying, in (4) the concentration of the concentrated ammonia solution is 90 vol.%.

[0025] Further specifying, in the ultrasonic cleaning process of (4), the relationship between the ultrasonic frequency of the ultrasonic machine, the ultrasonic time and the sample mass is that each 1-2g of product is ultrasonicated at 25-40W for 20-30s to remove the MoO3 generated in the hydrothermal reaction.

[0026] Further specifying, the process of washing repeatedly with anhydrous ethanol and deionized water in step (4) is as follows:

[0027] Add anhydrous ethanol to the precipitate after ultrasonic cleaning until the product is completely submerged. Let it stand for 5-7 hours and then discard the supernatant. Repeat the above steps of adding anhydrous ethanol, standing, and discarding the supernatant 3-5 times to remove residual ammonia.

[0028] Then, replace the anhydrous ethanol with deionized water, and repeat the process of adding deionized water, letting it stand, and discarding the supernatant 3 to 5 times, with a standing time of 1 to 2 hours, to remove any residual anhydrous ethanol.

[0029] Further specifying, in (5), the freezing process is quick-freezing or slow-freezing.

[0030] Furthermore, the slow-freezing conditions are specified as follows: maintaining the temperature at -20 to -30°C for 3 to 5 days.

[0031] Furthermore, the quick-freezing conditions are specified as follows: maintaining the temperature at -196℃ for 0.5 to 1 hour.

[0032] Further specifying, the drying process in (5) is carried out using a freeze dryer.

[0033] Further specifying, the grinding process in (5) is as follows: the dried sample is added into the mortar in (6), and the sample is rotated or rubbed with a mortar rod for 10 to 20 minutes until the sample particle size is observed to be 200 nm to 1 μm under an electron microscope.

[0034] The third objective of this invention is to provide an application of the above-mentioned amorphous MoS2 / rGO active material, specifically for the preparation of cathode materials for sodium-ion batteries.

[0035] The third objective of this invention is to provide a method for preparing a sodium-ion battery cathode material using the above-mentioned amorphous MoS2 / rGO active material. The method is as follows: the conductive agent Super P and the amorphous MoS2 / rGO active material are mixed evenly and then added to a mixed solution of NMP and PVDF. The mixture is stirred to obtain a viscous slurry. The viscous slurry is then coated onto an electrode substrate and subsequently dried to obtain the sodium-ion battery cathode material.

[0036] Further specifying, the mass ratio of conductive agent Super P to amorphous MoS2 / rGO active material is 0.02–0.04 g : 0.14–0.16 g.

[0037] Further specifying the preparation method of the NMP and PVDF mixed solution: mix NMP and PVDF in a wide-mouth bottle, stir magnetically for 0.5-1 hour until there is no white substance in the wide-mouth bottle, and seal with sealing glue to prevent NMP from absorbing water or deteriorating.

[0038] Further, the concentration of the NMP and PVDF mixed solution is specified to be 0.02–0.03 g / mL.

[0039] Further specified, the viscous slurry is coated onto the electrode substrate using mechanical coating or spin coating methods, with a coating thickness of 50–150 μm.

[0040] Further specifying the drying process, the process is as follows: place the slurry in a forced-air drying oven at 60-80℃ for 5-10 hours, and then place it in a vacuum drying oven at 60-80℃ for 10-20 hours to fully remove NMP solvent residue from the slurry.

[0041] Furthermore, the electrode substrate is a cleaned aluminum foil.

[0042] Beneficial effects:

[0043] This invention utilizes ethylene glycol (EG) as a solvent to prepare amorphous MoS2 / rGO active materials via a one-pot solvothermal method. Leveraging the self-assembly properties of rGO, a three-dimensional carbon framework is fabricated, allowing MoS2 to be uniformly distributed on the rGO surface, thus fixing the MoS2 structure. This not only prevents MoS2 aggregation but also solves the problem of excessively concentrated volume expansion during cycling. Furthermore, this material is used to prepare a cathode material for sodium-ion batteries. Its amorphous structure improves the cycle stability of sodium-ion batteries. At a current density of 1 A / g, the amorphous MoS2 / rGO composite electrode exhibits a first-cycle discharge specific capacity of 142.1 mAh / g, and the capacity decay rate after 2000 cycles is only 9%. This provides a new approach to solving the inherent problems of graphite-like structural materials in energy applications, and the method is simple, low-cost, and suitable for large-scale production. Attached Figure Description

[0044] Figure 1 Macroscopic morphology photograph of MoS2 / rGO-DI prepared for Comparative Example 1;

[0045] Figure 2 Macroscopic morphology photographs of MoS2 / rGO-EG prepared in Example 1;

[0046] Figure 3 SEM image of MoS2 / rGO-DI prepared for Comparative Example 1;

[0047] Figure 4 SEM images of MoS2 / rGO-EG prepared in Example 1;

[0048] Figure 5 EDS image of MoS2 / rGO-EG prepared in Example 1;

[0049] Figure 6 XRD spectra of MoS2 / rGO-EG and MoS2 / rGO-DI under different conditions;

[0050] Figure 7 TEM images and selected area diffraction patterns of MoS2 / rGO-EG prepared in Example 1;

[0051] Figure 8The elemental mapping test results of MoS2 / rGO-EG prepared in Example 1 are shown in the figure.

[0052] Figure 9 Charge-discharge cycle curves of Na||MoS2 / rGO-EG coin cells prepared in Example 1 and Comparative Example 1;

[0053] Figure 10 AC impedance diagrams of Na||MoS2 / rGO coin cells prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0054] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0055] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0056] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0057] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0058] Example 1:

[0059] Step 1: Raw material pretreatment

[0060] (1) Ultrasound: Add an appropriate amount of water to the ultrasonic machine as a conductive medium. Place a container containing 50 mL of ethylene glycol solution with 0.1 g of graphene oxide into the ultrasonic machine, turn on the ultrasonic generator, and disperse the graphene oxide evenly to reduce the size of the graphene sheets. The solution volume should not exceed 2 / 3 of the total volume of the container. Maintain the ultrasonic ambient temperature at 0-20℃, the ultrasonic time at 5 h, and the ultrasonic frequency at 40 kHz.

[0061] (2) Centrifugation: Take 25 mL of the sonicated graphene oxide solution and put it into the centrifuge in the correct position. Close the centrifuge door, set the speed to 16000 rpm, the centrifugation time to 10 min, turn on the centrifuge button, and discard the ethylene glycol supernatant after centrifugation.

[0062] (3) Magnetic stirring: Transfer the precipitate to a small beaker, add deionized water, the volume of deionized water should be 70% of the volume of the small beaker, and stir magnetically for 1 hour at room temperature to disperse the graphene oxide precipitate in the deionized water to obtain a homogeneous solution.

[0063] (4) Repeat step (2) centrifugation and step (3) magnetic stirring operation 3 times until the supernatant after centrifugation is transparent. It is considered that the ethylene glycol solvent in the original graphene oxide ethylene glycol solution has been completely removed, and the pretreated graphene oxide is obtained.

[0064] Step 2: Solvent heat treatment

[0065] (1) 50 mL of ethylene glycol solvent and 0.1 g of pretreated graphene oxide precipitate were magnetically stirred for 8 h to obtain a stable and homogeneous graphene oxide solution. Then, 0.5 mmol of ammonium molybdate was added and stirred at 600 rpm and 50 °C for 2 h to ensure that the ammonium molybdate was fully dissolved in the solution, thereby reducing the generation of MoO3. Subsequently, 10 mmol of thiourea was added and stirred until completely dissolved. Finally, the solution was transferred to a 100 mL hydrothermal reactor and placed in a forced-air drying oven at 160 °C for 24 h to complete the solvothermal treatment.

[0066] Step 3: Product Post-processing

[0067] (1) After the solvent heat treatment is completed, wait for the hydrothermal reactor to cool naturally to 20-30℃, and take out the black product precipitate into a clean small beaker.

[0068] (2) Pour in a concentrated ammonia solution with a volume concentration of 90% until the black product is submerged, and perform ultrasonic cleaning for 12 hours to remove the MoO3 generated in the hydrothermal reaction. The relationship between the ultrasonic frequency, ultrasonic time and sample mass is as follows: 40W ultrasonic for 30 seconds per 2g of product.

[0069] (3) Wash the product precipitate repeatedly with anhydrous ethanol and deionized water in sequence and collect the precipitate. First, add anhydrous ethanol until the product is completely submerged, let it stand for 5 hours, and then discard the supernatant. Repeat the process of adding anhydrous ethanol, letting it stand, and discarding the supernatant three times to remove any residual ammonia. The purpose of standing is to ensure complete precipitation of the product. Then, replace the anhydrous ethanol with deionized water and repeat the process of adding deionized water, letting it stand, and discarding the supernatant three times. The standing time is 2 hours to completely remove any residual anhydrous ethanol. Collect the precipitate.

[0070] (4) The product precipitate collected in (3) was freeze-dried at -60℃ for 48h.

[0071] (5) Place 0.3g of the freeze-dried sample in a mortar and grind it by rotation or friction with a mortar rod for 20 minutes until the particle size of the sample is observed to be 200nm~1μm under an electron microscope. Name it MoS2 / rGO-EG.

[0072] Step 4: Battery Assembly

[0073] (1) Mix NMP and PVDF in a wide-mouth bottle to prepare a solution with a concentration of 0.02 g / mL. Stir magnetically for 2 hours until there is no white substance in the wide-mouth bottle. Seal the bottle with sealant to prevent NMP from absorbing water or deteriorating.

[0074] (2) Weigh 0.04g of conductive agent Super P and 0.14g of MoS2 / rGO-EG and grind them in a mortar for 0.5h to make Super P and amorphous MoS2 / rGO active material evenly mixed.

[0075] (3) Add the well-mixed Super P and MoS2 / rGO-EG to the NMP / PVDF solution and stir for 12 hours to ensure thorough mixing and obtain a viscous slurry. The mass ratio of MoS2 / rGO-EG, conductive agent Super P, and PVDF in the viscous slurry is 7:2:1.

[0076] (4) The viscous slurry was mechanically coated onto the cleaned aluminum foil with a coating thickness of 150 μm. Then it was placed in a forced-air drying oven at 60°C for 10 h and then placed in a vacuum drying oven at 60°C for 10 h to fully remove the NMP solvent residue in the slurry, thus obtaining the positive electrode plate coated with MoS2 / rGO-EG.

[0077] (5) A sodium sheet was used as the counter electrode, an aluminum foil coated with MoS2 / rGO-EG was used as the working electrode, GF / A glass fiber was used as the separator, and 1.0M NaCIO4 in EC:DEC=1:1(Vol%)+5%FEC was used as the electrolyte. The battery assembly operation was carried out in a glove box filled with argon gas. The water and oxygen content in the glove box was <0.1ppm. The 2025 type coin cell was assembled, completely sealed and taken out from the glove box. It was left to stand for 12h to obtain the Na||MoS2 / rGO-EG coin cell, and then the electrochemical performance was tested.

[0078] Comparative Example 1:

[0079] The difference between this comparative example and Example 1 is that in step two, deionized water of the same volume was used instead of ethylene glycol as the solvent in the solvothermal treatment. The remaining process steps and parameter settings are the same as in Example 1. The amorphous MoS2 / rGO active material obtained is named MoS2 / rGO-DI, and the coin cell obtained is named Na||MoS2 / rGO-DI.

[0080] Example of results:

[0081] (1) The macroscopic morphology of MoS2 / rGO-EG and MoS2 / rGO-DI obtained in Example 1 and Comparative Example 1 was observed, such as Figure 1 and Figure 2 As shown, both MoS2 / rGO-DI and MoS2 / rGO-EG materials form columnar structures, demonstrating the successful preparation of the carbon framework. However, the MoS2 / rGO-DI column has a smaller volume; its diameter and height are approximately 2 / 3 times that of the MoS2 / rGO-EG material. Under the same mass conditions, MoS2 / rGO-EG has a larger volume and is more porous. Calculations show that the porosity of MoS2 / rGO-EG is approximately 3.37 times that of MoS2 / rGO-DI. For sodium-ion batteries, a larger porosity facilitates electrolyte penetration, promotes sodium ion transport within the electrode, and enhances the active sites for electrochemical reactions, thereby improving the battery's energy density and power density.

[0082] (2) The microstructures of MoS2 / rGO-EG and MoS2 / rGO-DI obtained in Example 1 and Comparative Example 1 were analyzed. Figure 3 and Figure 4 SEM images of MoS2 / rGO-EG and MoS2 / rGO-DI, respectively. Figure 5 EDS plot of MoS2 / rGO-EG, by Figure 3 and Figure 4 It can be seen that MoS2 / rGO-DI water exhibits a nano-flower-like structure and severe aggregation, while MoS2 / rGO-EG presents a lamellar structure without the formation of nano-flower-like MoS2 and shows no obvious aggregation. This is mainly because EG has a high surface tension, which plays a certain role in dispersing MoS2 and rGO. Further based on... Figure 5 The EDS plot shown indicates that the distribution of Mo, S, and C elements is uniform, which suggests that there is no significant aggregation of MoS2 in MoS2 / rGO-EG.

[0083] (3) X-ray diffraction analysis was performed on the MoS2 / rGO-EG and MoS2 / rGO-DI obtained in Example 1 and Comparative Example 1, such as... Figure 6The curves of MoS2 / rGO-EG and MoS2 / rGO-DI are shown. It can be seen that the MoS2 / rGO-EG curve is smooth, without sharp diffraction peaks, exhibiting an amorphous phase. Further annealing of the amorphous MoS2 / rGO-EG at 500℃ for 20 h (heating rate 5℃ / min) and X-ray diffraction analysis of the treated product are shown below. Figure 6 As shown in the "500℃ annealing" curve, the diffraction peaks at 14.2°, 32.9°, 39.5°, and 58.7° correspond to the characteristic peaks (002), (100), (110), and (103) of MoS2 in the 2H phase MoS2 standard card, and their diffraction peaks are similar to those of MoS2 / rGO-DI. This further illustrates that MoS2 / rGO-DI is crystalline, while MoS2 / rGO-EG obtained by solvothermal treatment with ethylene glycol is amorphous.

[0084] (4) TEM analysis was performed on the MoS2 / rGO-EG obtained in Example 1, and the results are as follows: Figure 7 As shown, no obvious aggregation of MoS2 nanosheets was observed. Further elemental mapping tests were performed, and the results are as follows... Figure 8 As shown, the test results indicate that C, Mo, and S elements are uniformly distributed, demonstrating that MoS2 is uniformly dispersed on the graphene sheet. This result corresponds to the SEM results, fully demonstrating the importance of EG for the uniform dispersion of MoS2. In addition, diffuse scattering halos can be observed from the selected area diffraction pattern, exhibiting typical amorphous diffraction rings, proving that MoS2 / rGO-EG is amorphous.

[0085] (5) Charge-discharge tests were conducted on the Na||MoS2 / rGO-EG coin cells and Na||MoS2 / rGO-DI coin cells assembled in Example 1 and Comparative Example 1. The results are as follows: Figure 9 As shown in the figure, at a current density of 1 A / g, the initial discharge capacity of MoS2 / rGO-EG is 142.94 mAh / g, and after 900 cycles, the discharge specific capacity is 130.94 mAh / g, with a capacity retention rate as high as 91.60%. The initial discharge specific capacity of MoS2 / rGO-DI is 92.84 mAh / g, and after 900 cycles, the discharge specific capacity is 65.39 mAh / g, with a capacity retention rate of 70.43%, both significantly lower than that of the coin cell assembled with MoS2 / rGO-EG. This is because, compared to crystalline MoS2, amorphous MoS2 exhibits no significant orientation during sodium ion intercalation, reducing the degree of local structural distortion and thus improving the discharge specific capacity and cycle stability of the half-cell.

[0086] (6) The AC impedance of the Na||MoS2 / rGO-EG coin cells and Na||MoS2 / rGO-DI coin cells assembled in Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 10 As shown, the EIS curve consists of three parts, representing the battery's internal resistance, charge transfer impedance (R), and other parameters. ct ) and Warburg impedance (Z w As shown in the figure, the MoS2 / rGO-EG composite electrode has a lower charge transfer resistance than the MoS2 / rGO-DI composite electrode, indicating that the MoS2 / rGO-EG composite electrode has better rate capacity and faster charge conduction kinetics. In addition, the slope of the MoS2 / rGO-EG composite electrode is larger in the low frequency region, indicating that its Weber impedance is smaller and it has stronger electron transport capability.

[0087] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. An amorphous MoS2 / rGO active material, characterized in that, The active material was prepared by a one-pot solvothermal method using molybdenum source, sulfur source and pretreated graphene oxide as raw materials and ethylene glycol as solvent. The preparation method includes the following steps: (1) Pretreatment of graphene oxide; (2) The pretreated graphene oxide was dispersed in ethylene glycol solvent to obtain a uniform and stable graphene oxide solution. (3) Add the molybdenum source and sulfur source to the graphene oxide solution obtained in (2), heat and stir until the molybdenum source and sulfur source are completely dissolved to obtain the reaction solution; (4) Transfer the reaction solution obtained in (3) to a high pressure vessel and keep it at 160-200℃ for 20-24h. After the reaction is completed, cool it to room temperature, filter it, and soak the obtained precipitate in concentrated ammonia solution, ultrasonically clean it, and then wash it several times with anhydrous ethanol and deionized water and collect the obtained product precipitate. (5) The product precipitate collected in (4) is frozen, dried and ground to obtain amorphous MoS2 / rGO material particles; The mass-to-volume ratio of graphene oxide to ethylene glycol in (2) is 0.1~0.15g:50~75mL; The molar ratio of molybdenum source to sulfur source in (3) is (10~20):

1.

2. A method for preparing the amorphous MoS2 / rGO active material according to claim 1, characterized in that, The preparation method includes the following steps: (1) Pretreatment of graphene oxide; (2) The pretreated graphene oxide was dispersed in ethylene glycol solvent to obtain a uniform and stable graphene oxide solution. (3) Add the molybdenum source and sulfur source to the graphene oxide solution obtained in (2), heat and stir until the molybdenum source and sulfur source are completely dissolved to obtain the reaction solution; (4) Transfer the reaction solution obtained in (3) to a high pressure vessel and keep it at 160-200℃ for 20-24h. After the reaction is completed, cool it to room temperature, filter it, and soak the obtained precipitate in concentrated ammonia solution, ultrasonically clean it, and then wash it several times with anhydrous ethanol and deionized water and collect the obtained product precipitate. (5) The product precipitate collected in (4) is frozen, dried and ground to obtain amorphous MoS2 / rGO material particles.

3. The preparation method according to claim 2, characterized in that, (1) The process of pretreating graphene oxide is as follows: First, at 0~20℃, an ethylene glycol solution or a methanol solution of graphene oxide was placed in an ultrasonic machine with water as the conductive medium for ultrasonic treatment. Then, the ultrasonically treated solution was centrifuged at 10,000 to 16,000 rpm for 5 to 10 minutes. After centrifugation, the supernatant was discarded, and the precipitate was washed repeatedly with deionized water until the washing liquid was clear, thus obtaining the pretreated graphene oxide.

4. The preparation method according to claim 2, characterized in that, (3) The molybdenum source is ammonium molybdate or sodium molybdate, and the sulfur source is thiourea or sulfur; the molar-volume ratio of the molybdenum source, sulfur source and graphene oxide solution is 0.5~0.75mmol:10~15mmol:50~75mL.

5. The preparation method according to claim 2, characterized in that, (4) The concentration of the concentrated ammonia solution is 90 vol.%.

6. The preparation method according to claim 2, characterized in that, (5) The freezing treatment is quick-freezing or slow-freezing. The slow-freezing conditions are: keep at -20 ~ -30℃ for 3 ~ 5 days; the quick-freezing conditions are: keep at -196℃ for 0.5 ~ 1 h.

7. An application of the amorphous MoS2 / rGO active material according to claim 1, characterized in that, Used to prepare cathode materials for sodium-ion batteries.

8. A method for preparing a sodium-ion battery cathode material, characterized in that, The conductive agent Super P and the amorphous MoS2 / rGO active material according to claim 1 are mixed evenly and then added to a mixed solution of NMP and PVDF. The mixture is stirred to obtain a viscous slurry. The viscous slurry is then coated onto the electrode substrate and dried to obtain the sodium-ion battery cathode material.

9. The preparation method according to claim 8, characterized in that, The mass ratio of amorphous MoS2 / rGO active material, conductive agent Super P and PVDF is 0.07~0.14:0.02~0.04:0.01~0.02.

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