A method for preparing and applying a three-dimensional self-supporting rGO-MoO2-S cathode material

Abstract

This invention discloses a method for preparing and applying a three-dimensional self-supporting rGO-MoO2-S cathode material. This material is composed of nitrogen-doped rGO, ultrafine MoO2 nanoparticles, and sulfur, exhibiting high specific surface area, porous structure, and excellent electrochemical performance. The preparation method involves dissolving MoCl5 in deionized water, adding ammonia and GO nanosheet dispersion, stirring until homogeneous, and then preparing GO-MoO2 hydrogel via a hydrothermal method. After freeze-drying and high-temperature calcination under a nitrogen atmosphere, a self-supporting rGO-MoO2 aerogel is obtained. Finally, it is composited with sulfur to prepare the rGO-MoO2-S cathode material. As a cathode material for sodium-sulfur batteries, this material can effectively suppress the shuttle effect of NaPSs from both physical encapsulation and chemical adsorption levels, improving battery cycle stability and rate performance. The self-supporting structure eliminates the need for additional binders and conductive additives, further enhancing the actual energy density of the battery. This provides a high-performance cathode material for the large-scale energy storage application of room-temperature sodium-sulfur batteries, which is of great significance.

Description

Technical Field

[0001] This invention relates to the fields of energy storage materials and electrochemical technology, specifically to a method for preparing and applying a three-dimensional self-supporting rGO-MoO2-S cathode material. Background Technology

[0002] With the transformation of the global energy structure and the advancement of sustainable development concepts, the demand for large-scale energy storage technologies is increasing, especially in the fields of smart grids and renewable energy storage. Room temperature sodium-sulfur batteries (RT Na-S batteries) are considered a highly promising next-generation energy storage technology due to their high theoretical energy density (1274 Wh / kg), low cost, and the abundance and environmental friendliness of sodium and sulfur resources. However, the use of sulfur as a cathode material presents numerous challenges, limiting its further development and practical application.

[0003] First, sulfur has extremely low electrical conductivity (approximately 5 × 10⁻⁶). -30 The slow reaction kinetics of sulfur (S / cm) make it difficult to meet the requirements of rapid charge and discharge. Secondly, sulfur expands significantly in volume (approximately 170%) during charge and discharge, which disrupts the structural integrity of the material and leads to decreased cycle stability. More importantly, during the reaction, sodium polysulfides (NaPSs) dissolve, triggering a "shuttle effect" between the positive and negative electrodes. This not only results in the loss of active material but also causes passivation of the sodium metal negative electrode, further reducing battery performance and lifespan. Therefore, developing high-performance sulfur cathode materials to address these issues has become a key research focus.

[0004] In recent years, researchers have focused on developing carbon-based materials with high specific surface area, high conductivity, and porous structures as sulfur hosts to improve their electrochemical performance. Among these, graphene aerogels have attracted considerable attention due to their excellent conductivity (2–3 S / cm), low density, good mechanical flexibility, and compatibility with other additives. However, graphene aerogels can only physically inhibit the dissolution of polysulfides. To improve the electrochemical performance of sodium-sulfur batteries, researchers have further introduced polar metal oxides (such as MoO2) to enhance the chemisorption and catalytic conversion capabilities of polysulfides. MoO2 has shown promising applications in lithium-sulfur batteries due to its low resistivity and high chemical stability, but research on it in room-temperature sodium-sulfur batteries remains limited. Current research largely focuses on the optimization of single materials, while the design and application of composite materials still face many challenges. For example, although MoO2 possesses good chemical stability, its insufficient specific surface area makes it difficult to use as a host material independently. Therefore, how to organically combine MoO2 with graphene aerogels to achieve a synergistic effect of physical confinement and chemisorption is a key research issue.

[0005] Based on the above background, this invention proposes a design and preparation method for a three-dimensional self-supporting rGO-MoO2-S cathode material. It aims to effectively solve the shuttle effect of polysulfides through the dual action of physical and chemical processes, improve the cycle stability and rate performance of the battery, and provide a feasible solution for the practical application of room temperature sodium-sulfur batteries. Summary of the Invention

[0006] The present invention aims to provide a three-dimensional self-supporting rGO-MoO2-S cathode material for room temperature sodium-sulfur batteries and its preparation method. The material has excellent electrochemical performance and can significantly improve the cycle stability and rate performance of sodium-sulfur batteries.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0008] A method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material includes the following steps:

[0009] (1) First, MoCl5 was dissolved in deionized water and stirred for the first time to form a transparent solution. Ammonia and GO nanosheet dispersion were added to it and stirred for the second time. The mixed solution was transferred to a reaction vessel for hydrothermal treatment and then washed with deionized water to obtain GO-MoO2 hydrogel.

[0010] (2) The GO-MoO2 hydrogel prepared in step (1) was freeze-dried and then calcined at high temperature in a nitrogen atmosphere to obtain a three-dimensional self-supporting rGO-MoO2 aerogel.

[0011] (3) Dissolve sulfur powder in CS2 and add it dropwise to the rGO-MoO2 aerogel prepared in step (2). After evaporating the solvent, seal it in a reaction vessel for annealing to obtain rGO-MoO2-S cathode material.

[0012] Based on the above technical solution, the present invention can be further improved as follows.

[0013] Preferably, in step (1), the amount of MoCl5 used is 25~30 mg, the amount of deionized water is 3~5 ml, the amount of ammonia water is 1~3 ml, and the concentration of GO is 5~10 mg / ml.

[0014] Preferably, in step (1), the first stirring time is 0.5~1 h, the second stirring time is 0.5~1.5 h, the hydrothermal temperature of the heat treatment is 150~180 ℃, the hydrothermal time is 10~16 h, and the number of washing cycles is 3~5.

[0015] Preferably, in step (2), the freeze-drying time is 24~72 h, the calcination temperature is 400~500℃, and the calcination time is 1~3 h.

[0016] Preferably, the amount of sulfur powder used in step (3) is 3~5 mg, and the amount of rGO-MoO2 aerogel used is 3~5 mg.

[0017] Preferably, the annealing temperature in step (3) is 150~180 ℃ and the annealing time is 10~14 h.

[0018] The present invention also provides a three-dimensional self-supporting rGO-MoO2-S cathode material, which is prepared by the above-described preparation method.

[0019] This invention also provides an application of a three-dimensional self-supporting rGO-MoO2-S cathode material in energy storage materials and electrochemistry.

[0020] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0021] 1. This invention utilizes the porous and fluffy structure of the three-dimensional self-supporting rGO-MoO2-S cathode material, which can effectively contact sulfur and shorten the diffusion distance of ions, thereby achieving rapid electron and ion transport. The polar MoO2 nanoparticles have a strong adsorption and catalytic effect on NaPSs, which can promote the catalytic conversion of NaPSs and further suppress its "shuttle effect". Combining the dual effects of physical encapsulation and chemical adsorption, as well as the rapid NaPSs conversion kinetics, the electrochemical performance of rGO-MoO2 aerogel is greatly improved. Experimental results show that the three-dimensional self-supporting rGO-MoO2-S has high specific capacity, good rate performance and long cycle stability, and is a cathode material with great practical application value for sodium-sulfur batteries.

[0022] 2. Based on the dual effects of physical confinement and chemical adsorption, this invention synthesizes a three-dimensional self-supporting rGO-MoO2-S cathode material through a hydrothermal-freeze-drying-annealing process. When the three-dimensional self-supporting rGO-MoO2-S prepared by this invention is used as a cathode material for sodium-sulfur batteries, it exhibits excellent specific capacity, rate performance, and cycle stability, making it a potential high-performance cathode material for sodium-sulfur batteries. Attached Figure Description

[0023] Figure 1 This is the XRD pattern of the three-dimensional self-supporting rGO-MoO2-S-1 of Example 1 of the present invention;

[0024] Figure 2 This is a transmission electron microscope image of the three-dimensional self-supporting rGO-MoO2-S-1 of Example 1 of the present invention;

[0025] Figure 3 This is an XPS diagram of the three-dimensional self-supporting rGO-MoO2-S-1 of Example 1 of the present invention;

[0026] Figure 4 This is an EDS elemental distribution diagram of the three-dimensional self-supporting rGO-MoO2-S-1 in Example 1 of the present invention;

[0027] Figure 5 This is a battery charge-discharge curve of the three-dimensional self-supporting rGO-MoO2-S-1 in Example 1 of the present invention at a current density of 0.1 A / g;

[0028] Figure 6 This is a rate performance diagram of the three-dimensional self-supporting rGO-MoO2-S-1 in Example 1 of the present invention;

[0029] Figure 7 This is a rate performance diagram of the three-dimensional self-supporting rGO-MoO2-S-2 in Example 2 of the present invention;

[0030] Figure 8 This is a rate performance diagram of the three-dimensional self-supporting rGO-MoO2-S-3 in Example 3 of the present invention;

[0031] Figure 9 This is a battery cycle performance diagram of the three-dimensional self-supporting rGO-MoO2-S-1 in Example 1 of the present invention at a current density of 0.5 A / g;

[0032] Figure 10 This is the coulombic efficiency diagram of the three-dimensional self-supporting rGO-MoO2-S-1 in Example 1 of the present invention at a current density of 0.5 A / g. Detailed Implementation

[0033] A method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material includes the following steps:

[0034] (1) First, MoCl5 was dissolved in deionized water and stirred for the first time to form a transparent solution. Ammonia water and graphene oxide (GO) nanosheet dispersion were added to it and stirred for the second time. The mixed solution was transferred to a reaction vessel for hydrothermal treatment and then washed with deionized water to obtain GO-MoO2 hydrogel.

[0035] (2) The GO-MoO2 hydrogel prepared in step (1) was freeze-dried and then calcined at high temperature in a nitrogen atmosphere to obtain a three-dimensional self-supporting rGO-MoO2 aerogel.

[0036] (3) Dissolve sulfur powder in CS2 and add it dropwise to the rGO-MoO2 aerogel prepared in step (2). After evaporating the solvent, seal it in a reaction vessel for annealing to obtain rGO-MoO2-S cathode material.

[0037] In step (1), the amount of MoCl5 used is 25~30 mg, the amount of deionized water is 3~5 ml, the amount of ammonia water is 1~3 ml, and the concentration of GO is 5~10 mg / ml.

[0038] In step (1), the first stirring time is 0.5~1 h, the second stirring time is 0.5~1.5 h, the hydrothermal temperature of the heat treatment is 150~180 ℃, the hydrothermal time is 10~16 h, and the number of washing cycles is 3~5.

[0039] In step (2), the freeze-drying time is 24~72 h, the calcination temperature is 400~500 ℃, and the calcination time is 1~3 h.

[0040] The amount of sulfur powder used in step (3) is 3~5 mg, and the amount of rGO-MoO2 aerogel used is 3~5 mg.

[0041] In step (3), the annealing temperature is 150~180 ℃ and the annealing time is 10~14 h.

[0042] The three-dimensional self-supporting rGO-MoO2-S cathode material prepared in step (3) has the following properties: at a current density of 0.1 A / g, the reversible capacity of the three-dimensional self-supporting rGO-MoO2-S can reach 1000~1250 mAh / g. Even at a high current density of 2 A / g, the capacity can still reach 40~250 mAh / g. At a current density of 0.5 A / g, after more than 300 cycles, the capacity is still as high as 483 mAh / g, with a capacity retention rate of 60.5%.

[0043] The present invention also provides a three-dimensional self-supporting rGO-MoO2-S cathode material, which is prepared by the above-described preparation method.

[0044] This invention also provides an application of a three-dimensional self-supporting rGO-MoO2-S cathode material in energy storage materials and electrochemistry.

[0045] To better understand the present invention, the following embodiments further illustrate its content, but the content of the present invention is not limited to the embodiments described below. Experimental results show that the amount of deionized water affects the dispersion uniformity of the reactants, while the amount of ammonia promotes the nucleation and growth of MoO2 nanoparticles, affecting their particle size and distribution, thereby resulting in different electrochemical properties of the three-dimensional self-supporting rGO-MoO2-S cathode material. Therefore, the main difference between the different embodiments lies in the amount of deionized water and ammonia used in the experiment, and they are numbered rGO-MoO2-S-1, rGO-MoO2-S-2, and rGO-MoO2-S-3 according to the different amounts used.

[0046] Table 1 Comparison of the amount of deionized water and ammonia used in different embodiments

[0047]

[0048] Table 1 is a summary of Examples 1-3.

[0049] Example 1 rGO-MoO2-S-1 (4 ml deionized water, 2 ml ammonia):

[0050] A method for preparing three-dimensional self-supporting rGO-MoO2-S cathode material includes the following steps:

[0051] (1) Preparation of GO-MoO2 hydrogel

[0052] First, 25-30 mg of MoCl5 was dissolved in 4 ml of deionized water and stirred for 0.5-1 h to form a transparent solution. Then, 2 ml of ammonia water and a dispersion of graphene oxide (GO) nanosheets with a concentration of 5-10 mg / ml were added and the mixture was stirred for another 0.5-1.5 h. The mixture was then transferred to a reaction vessel and hydrothermally treated at 150-180 °C for 10-16 h. After washing with deionized water 3-5 times, GO-MoO2 hydrogel was obtained.

[0053] (2) Preparation of rGO-MoO2 aerogel

[0054] The GO-MoO2 hydrogel prepared in step (1) was freeze-dried for 24-72 h, and then calcined at 400-500℃ for 1-3 h in a nitrogen atmosphere to obtain three-dimensional self-supporting rGO-MoO2.

[0055] (3) Preparation of rGO-MoO2-S cathode material

[0056] Dissolve 3-5 mg of sulfur powder in CS2 and add it dropwise to the rGO-MoO2 aerogel prepared in step (2). The amount of aerogel is 3-5 mg. After evaporating the solvent, seal the aerogel in a reactor and anneal it at a temperature of 150-180 °C for 11-14 h to obtain the rGO-MoO2-S cathode material.

[0057] Taking the three-dimensional self-supporting rGO-MoO2-S-1 product of this example as an example, its structure was determined by X-ray diffraction (XRD) patterns. Figure 1 The XRD pattern shows that the broad peak near 25° corresponds to the (002) structure of amorphous carbon. For example... Figure 2 The transmission electron microscope (TEM) image shows the morphology and nanostructure of the sample, in which MoO2 nanoparticles are loaded on the graphene layer.

[0058] like Figure 5As shown, XPS analysis identified the surface chemical composition of rGO-MoO2-S-1 synthesized when rGO-MoO2-S-1 was used as the cathode material for sodium-sulfur batteries. Figure 4 The EDS elemental mapping proved that Mo, O, C, N and S are distributed in rGO-MoO2-S, indicating that the synthesis process of the material is relatively uniform.

[0059] Taking the three-dimensional self-supporting rGO-MoO2-S-1 prepared above as an example as the positive electrode material of a sodium-sulfur battery, its electrochemical performance was tested. Figure 5 As shown, at a current density of 0.1 A / g, rGO-MoO2-S-1 exhibits a relatively long discharge curve, especially below 1.13 V, compared with Na... + Compared to Na, this is related to the conversion of soluble Na₂S₄ to insoluble Na₂S₂ / Na₂S, indicating that MoO₂ has a good catalytic effect on the conversion of polysulfides. For example... Figure 6 As shown, its reversible capacity is 1246.9 mAh / g at a current density of 0.1 A / g, and even at a high current density of 2 A / g, the capacity can still reach 220.1 mAh / g, and it has excellent cycle stability. Figure 9 and Figure 10 The cycling stability and coulombic efficiency of rGO-MoO2-S-1 were demonstrated. It can be seen that at a current density of 0.5 A / g, the capacity remains as high as 483 mAh / g after more than 300 cycles, with a capacity retention of 60.5%. These performance characteristics indicate that the three-dimensional self-supporting rGO-MoO2-S-1 possesses excellent high-rate performance and long cycle life, making it a potential high-performance cathode material for sodium-sulfur batteries.

[0060] Example 2 rGO-MoO2-S-2 (3.5 ml deionized water, 2.5 ml ammonia):

[0061] A method for preparing three-dimensional self-supporting rGO-MoO2-S cathode material includes the following steps:

[0062] (1) Preparation of GO-MoO2 hydrogel

[0063] First, 25-30 mg of MoCl5 was dissolved in 3.5 ml of deionized water and stirred for 0.5-1 h to form a transparent solution. Then, 2.5 ml of ammonia water and a graphene oxide (GO) nanosheet dispersion with a concentration of 5-10 mg / ml were added and the mixture was stirred for another 0.5-1.5 h. The mixture was then transferred to a reaction vessel and hydrothermally treated at 150-180 °C for 10-16 h. After washing with deionized water 3-5 times, GO-MoO2 hydrogel was obtained.

[0064] (2) Preparation of rGO-MoO2 aerogel

[0065] The GO-MoO2 hydrogel prepared in step (1) was freeze-dried for 24-72 h, and then calcined at 400-500℃ for 1-3 h in a nitrogen atmosphere to obtain three-dimensional self-supporting rGO-MoO2.

[0066] (3) Preparation of rGO-MoO2-S cathode material

[0067] Dissolve 3-5 mg of sulfur powder in CS2 and add it dropwise to the rGO-MoO2 aerogel prepared in step (2). The amount of aerogel is 3-5 mg. After evaporating the solvent, seal the aerogel in a reactor and anneal it at a temperature of 150-180 °C for 11-14 h to obtain the rGO-MoO2-S cathode material.

[0068] When the three-dimensional self-supporting rGO-MoO2-S-2 product of this example is used as the cathode material of a sodium-sulfur battery, its electrochemical performance is tested. Figure 7 As shown, its reversible capacity is 1130 mAh / g at a current density of 0.1 A / g, and even at a high current density of 2 A / g, the capacity can still reach 35.8 mAh / g, and it has excellent cycle stability.

[0069] Example 3 rGO-MoO2-S-3 (4.5 ml deionized water, 1.5 ml ammonia):

[0070] A method for preparing three-dimensional self-supporting rGO-MoO2-S cathode material includes the following steps:

[0071] (1) Preparation of GO-MoO2 hydrogel

[0072] First, 25-30 mg of MoCl5 was dissolved in 4.5 ml of deionized water and stirred for 0.5-1 h to form a transparent solution. Then, 1.5 ml of ammonia and a 5-10 mg / ml dispersion of graphene oxide (GO) nanosheets were added and the mixture was stirred for another 0.5-1.5 h. The mixture was then transferred to a reactor and hydrothermally treated at 150-180 °C for 10-16 h. After washing with deionized water 3-5 times, GO-MoO2 hydrogel was obtained.

[0073] (2) Preparation of rGO-MoO2 aerogel

[0074] The GO-MoO2 hydrogel prepared in step (1) was freeze-dried for 24-72 h, and then calcined at 400-500℃ for 1-3 h in a nitrogen atmosphere to obtain three-dimensional self-supporting rGO-MoO2.

[0075] (3) Preparation of rGO-MoO2-S cathode material

[0076] Dissolve 3-5 mg of sulfur powder in CS2 and add it dropwise to the rGO-MoO2 aerogel prepared in step (2). The amount of aerogel is 3-5 mg. After evaporating the solvent, seal the aerogel in a reactor and anneal it at a temperature of 150-180 °C for 11-14 h to obtain the rGO-MoO2-S cathode material.

[0077] When the three-dimensional self-supporting rGO-MoO2-S-3 product of this example is used as the cathode material of a sodium-sulfur battery, its electrochemical performance is tested. Figure 8 As shown, its reversible capacity is 1024 mAh / g at a current density of 0.1 A / g, and even at a high current density of 2 A / g, the capacity can still reach 45 mAh / g, and it has excellent cycle stability.

[0078] Comparing the above Examples 1-3, the rate performance of the three-dimensional self-supporting rGO-MoO2-S cathode material is compared. Table 2 lists the rate performance of Examples 1-3.

[0079] Table 2 Rate performance of Examples 1-3

[0080]

[0081] The comparison of the above embodiments shows that experimental conditions such as the amount of deionized water and ammonia have a certain impact on the electrochemical performance of three-dimensional self-supporting rGO-MoO2-S. By optimizing these conditions, this invention has prepared a high-performance three-dimensional self-supporting rGO-MoO2-S cathode material, providing a new approach and method for the development of room-temperature sodium-sulfur batteries.

[0082] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material, characterized in that, Includes the following steps: (1) First, MoCl5 was dissolved in deionized water and stirred for the first time to form a transparent solution. Ammonia and GO nanosheet dispersion were added to it and stirred for the second time. The mixed solution was transferred to a reaction vessel for hydrothermal treatment and then washed with deionized water to obtain GO-MoO2 hydrogel. (2) The GO-MoO2 hydrogel prepared in step (1) was freeze-dried and then calcined at high temperature in a nitrogen atmosphere to obtain a three-dimensional self-supporting rGO-MoO2 aerogel. (3) Dissolve sulfur powder in CS2 and add it dropwise to the rGO-MoO2 aerogel prepared in step (2). After evaporating the solvent, seal it in a reaction vessel for annealing to obtain rGO-MoO2-S cathode material. The volume ratio of deionized water to ammonia water is 2:

1.

2. The method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material according to claim 1, characterized in that: In step (1), the amount of MoCl5 used is 25-30 mg, the amount of deionized water is 3-5 ml, the amount of ammonia water is 1-3 ml, and the concentration of GO is 5-10 mg / ml.

3. The method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material according to claim 1, characterized in that: In step (1), the first stirring time is 0.5~1 h, the second stirring time is 0.5~1.5 h, the hydrothermal temperature of the heat treatment is 150~180 ℃, the hydrothermal time is 10~16 h, and the number of washing cycles is 3~5.

4. The method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material according to claim 1, characterized in that: In step (2), the freeze-drying time is 24~72 h, the calcination temperature is 400~500 ℃, and the calcination time is 1~3 h.

5. The method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material according to claim 1, characterized in that: The amount of sulfur powder used in step (3) is 3~5 mg, and the amount of rGO-MoO2 aerogel used is 3~5 mg.

6. The method for preparing a three-dimensional self-supporting rGO-MoO2-S cathode material according to claim 1, characterized in that: In step (3), the annealing temperature is 150~180 ℃ and the annealing time is 10~14 h.

7. A three-dimensional self-supporting rGO-MoO2-S cathode material, characterized in that: It is prepared by any one of the preparation methods described in claims 1-6.

8. The application of the three-dimensional self-supporting rGO-MoO2-S cathode material as described in claim 7 in energy storage materials and electrochemistry.

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