Preparation Method and Application of Cathode Material for Lithium-Sulfur Battery

Abstract

The invention discloses a preparation method and application of a cathode material for a lithium-sulfur battery, belonging to the technical field of cathode materials for lithium-sulfur batteries. Ammonium tetrathiomolybdate is added to N,N-dimethylformamide to form a uniform mixed solution, and the reaction is carried out in a closed container. After the reaction is completed, filtration, washing, and drying are carried out to obtain molybdenum disulfide powder; bismuth salt and molybdenum salt are sequentially dissolved in a dilute solution of inorganic strong acid, an amine-based morphology regulator is added thereto for reaction, and then the obtained molybdenum disulfide powder and graphene oxide are sequentially added to obtain a mixed solution, and the reaction is carried out in a closed container. After the reaction is completed, freeze-drying is carried out to obtain a cathode material for a lithium-sulfur battery. By adding an amine-based morphology regulator, the morphology of the material can be changed, more active sites can be obtained, and the volume expansion problem is also solved by coating, which can improve the electrochemical performance of the lithium-sulfur battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials for lithium-sulfur batteries, and particularly relates to a preparation method and application of a cathode material for a lithium-sulfur battery. Background Art

[0002] Among numerous new energy storage methods, electrochemical energy storage has the advantages of convenience, long life, and low cost, and is widely used in daily life. In contrast, Li-S batteries with lithium metal as the anode and sulfur (sulfur-containing materials) as the cathode have attracted a great deal of attention. This is because Li-S batteries have extremely high theoretical discharge capacity (1672 mAh / g) and theoretical energy density (2600 Wh / kg), and are rich in resources, low in price, and environmentally friendly in the earth's crust.

[0003] However, the active substances sulfur and lithium sulfide in lithium-sulfur batteries have poor conductivity, and the reduction of the reaction kinetics rate causes the performance of the battery to decrease; the dissolution of polysulfides in the electrolyte will cause a shuttle effect, resulting in the dissolution of active substances and a decrease in the cycle retention rate; the volume change of the cathode material during charge and discharge is also an important reason for the shedding and structural collapse of the electrode material.

[0004] The Chinese patent document with the publication number CN106732667A discloses a preparation method for reducing and preparing a graphene-like molybdenum disulfide-bismuth molybdate composite material with a protein substance. First, an intercalated molybdenum disulfide powder is obtained through an intercalation reaction. Then, bismuth nitrate and sodium molybdate are dissolved in a solvent, and the intercalated molybdenum disulfide powder and protein are added to obtain a precursor material. Finally, the graphene-like molybdenum disulfide-bismuth molybdate composite material is obtained through calcination. In this method, the addition amounts and ratios of four solvents need to be controlled during the intercalation reaction, and the process is relatively cumbersome. From the SEM images, it can be seen that the morphology of the composite material is irregular and the number of exposed active sites is limited.

[0005] The Chinese patent document with the publication number CN106582720A discloses a method for reducing and preparing a graphene-like molybdenum disulfide-bismuth molybdate composite material with a saccharide organic carbon. First, an intercalated molybdenum disulfide powder is obtained through an intercalation reaction. Then, bismuth nitrate and sodium molybdate are dissolved in a solvent, and the intercalated molybdenum disulfide powder and saccharide organic carbon are added to obtain a precursor material. Finally, the graphene-like molybdenum disulfide-bismuth molybdate composite material is obtained through calcination. The composite material obtained by this method has an irregular structure and serious agglomeration, and the number of active sites is limited, resulting in a weak response to electrochemical performance.

[0006] The Chinese patent document with the publication number CN113206233A discloses a bismuth molybdate / sulfur composite material, its preparation method and a lithium-sulfur battery. A soluble bismuth salt and a molybdenum salt are dissolved in a solvent, and bismuth molybdate rich in oxygen vacancies is prepared through a solvothermal reaction. The bismuth molybdate is mixed with elemental sulfur and calcined to obtain the bismuth molybdate / sulfur composite material. The composite material synthesized by this method has enhanced adsorption capacity for polysulfide lithium, which can inhibit the shuttle effect of the material. However, due to volume expansion, the capacity retention rate of the material is only 63 - 75% (0.05C, 250 cycles), and the cycling stability is poor at low currents.

[0007] The Chinese patent document with the publication number CN115621435A discloses a cathode host material for a lithium-sulfur battery based on a manganese sulfide-molybdenum disulfide heterojunction, its preparation method and application. Using molybdenum disulfide nanosheets as the main body, manganese sulfide nanoparticles are anchored on the molybdenum disulfide nanosheets to form a composite material with a manganese sulfide-molybdenum disulfide heterostructure. The composite material has a two-dimensional nanosheet layer structure, which is beneficial to exposing more active sites and promoting the infiltration of the electrolyte. However, during the cycling process, the cycling performance will decline due to volume expansion (71%, 0.5C 300 cycles), and the stability is poor. Summary of the Invention

[0008] The object of the present invention is to provide a preparation method and application of a cathode material for a lithium-sulfur battery. By adding a morphology regulator, the morphology of the material can be changed to obtain more active sites, and the volume expansion problem is also solved by coating, which can improve the electrochemical performance of the lithium-sulfur battery.

[0009] In order to achieve the object of the present invention, a technical solution for a preparation method of a cathode material for a lithium-sulfur battery is provided, including the following steps:

[0010] (1) Ammonium tetrathiomolybdate is added to N,N-dimethylformamide to form a uniform mixed solution, and the reaction is carried out in a first sealed container. After the reaction is completed, filtration, washing, and drying are carried out to obtain molybdenum disulfide powder.

[0011] (2) A bismuth salt and a molybdenum salt are successively dissolved in a dilute solution of an inorganic strong acid, an amine-based morphology regulator is added thereto for reaction, and then the molybdenum disulfide powder and graphene oxide obtained in step (1) are successively added to obtain a mixed solution. The reaction is carried out in a second sealed container. After the reaction is completed, freeze-drying is carried out to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, that is, the cathode material for a lithium-sulfur battery.

[0012] Preferably, in step (1), the concentration of ammonium tetrathiomolybdate in N,N-dimethylformamide is 4 - 25 mM.

[0013] Preferably, in the step (1), the reaction temperature in the first sealed container is 160 - 200 °C, and the reaction time is 14 - 24 h; suction filtration is carried out three times with methanol, the drying temperature is 80 - 120 °C, and the drying time is 8 - 12 h.

[0014] Preferably, in the step (2), the molar ratio of bismuth salt to molybdenum salt is 1 - 2 : 1, the bismuth salt is any one of bismuth nitrate, bismuth chloride, or bismuth sulfate; the molybdenum salt is any one of sodium molybdate, ammonium molybdate, or potassium molybdate; the dilute solution of inorganic strong acid is any one of nitric acid, hydrochloric acid, or sulfuric acid solution, with a concentration of 0.5 - 1 M; the concentration of bismuth salt in the acidic solvent is 16 - 50 mM.

[0015] Preferably, in the step (2), the amine-based morphology regulator is any one of ethylenediamine, triethanolamine, dodecylamine, or aniline, the molar ratio of the morphology regulator to the molybdenum salt is 0.01 - 0.1:1; the molar ratio of molybdenum disulfide to the molybdenum salt is 0.15 - 0.875:1; the mass ratio of graphene oxide to the molybdenum salt is 0.04 - 0.5:1.

[0016] Preferably, in the step (2), the reaction temperature in the second sealed container is 120 - 180 °C, and the reaction time is 16 - 24 h; the freeze-drying temperature is -60~-40 °C, and the freeze-drying time is 24 - 48 h.

[0017] The present invention also provides an application of the prepared lithium-sulfur battery cathode material, which is applied to a lithium-sulfur battery.

[0018] The present invention has the following beneficial effects compared with the prior art:

[0019] 1. The technical solution of the preparation method of the lithium-sulfur battery cathode material provided by the present invention promotes the formation of heterojunctions through the reaction in an acidic solvent in a sealed environment and the induction of a morphology regulator, and obtains a graphene oxide-supported molybdenum disulfide-bismuth molybdate composite material with a certain hierarchical structure. The heterojunctions can form more active sites during the charge and discharge process of the lithium-sulfur battery, improving the battery performance.

[0020] 2. The technical solution of the preparation method of the lithium-sulfur battery cathode material provided by the present invention changes the morphology of the bismuth molybdate matrix by adding a morphology regulator, and obtains a heterojunction material with different morphologies after being compounded with molybdenum disulfide. The exposed active sites further promote the adsorption and migration of carriers, enhancing the electrochemical performance of the lithium-sulfur battery.

[0021] 3. The technical solution of the preparation method of the lithium-sulfur battery cathode material provided by the present invention obtains a rod-shaped heterojunction material with nanosheet wrinkles through the addition of graphene oxide. The formation of the wrinkles enables ions in the electrolyte to adsorb and react with the material at different angles. The addition of graphene oxide wraps the heterojunction material, which can effectively control the collapse of the material structure caused by volume expansion and the decline of cycle performance.

[0022] 4. The application of the prepared lithium-sulfur battery cathode material provided by the present invention is tested for performance in a blue battery test system by assembling it into a lithium-sulfur battery. This material has excellent specific capacity and good cycle stability. At a current density of 0.2C, the capacity can reach 1125-1258 mAh / g. After cycling 300 times at a current density of 1C, the capacitance value is 77-84% of the initial value. Brief Description of the Drawings

[0023] Figure 1 SEM spectrum of the GO@MoS2-Bi2MoO6 material prepared in Example 1;

[0024] Figure 2 XRD spectra of the MoS2 and GO@MoS2-Bi2MoO6 materials prepared in Example 1;

[0025] Figure 3 Pore size distribution diagram of the GO@MoS2-Bi2MoO6 material prepared in Example 1;

[0026] Figure 4 Rate performance diagrams of the materials obtained in Example 1 and the comparative example;

[0027] Figure 5 Curve of capacity retention rate and Coulomb efficiency of the GO@MoS2-Bi2MoO6 material prepared in Example 1 cycled 300 times at a current density of 1C. Detailed Description of the Embodiments

[0028] The following further illustrates the specific implementation of the present invention in conjunction with the drawings and examples, but the implementation and protection of the present invention are not limited thereto. Example 1

[0029] (1) Add 0.6 mmol of ammonium tetrathiomolybdate to 30 mL of N,N-dimethylformamide to form a homogeneous mixed solution, transfer it to a first sealed container and react at 180 °C for 24 h. After the reaction, filter it three times with methanol to remove the excess N,N-dimethylformamide, and dry it at 100 °C for 12 h to obtain molybdenum disulfide powder;

[0030] (2) Dissolve 3 mmol of bismuth nitrate and 1.5 mmol of sodium molybdate successively in 80 mL of 0.5 M nitric acid solution. Add 6 mL of dodecylamine to it, and then add 0.2 g of molybdenum disulfide powder and 0.05 g of graphene oxide successively to obtain a mixed solution. Transfer it to a second sealed container and react at 180 °C for 20 h. After the reaction is completed, freeze-dry at -50 °C for 36 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, which is the cathode material for lithium-sulfur batteries. Example 2

[0031] (1) Add 0.4 mmol of ammonium tetrathiomolybdate to 25 mL of N,N-dimethylformamide to form a uniform mixed solution. Transfer it to a first sealed container and react at 200 °C for 22 h. After the reaction is completed, filter it three times with methanol to remove the excess N,N-dimethylformamide, and dry it at 120 °C for 8 h to obtain molybdenum disulfide powder;

[0032] (2) Dissolve 3 mmol of bismuth chloride and 1.5 mmol of ammonium molybdate successively in 60 mL of 0.5 M hydrochloric acid solution. Add 8 mL of ethylenediamine to it, and then add 0.25 g of molybdenum disulfide powder and 0.03 g of graphene oxide successively to obtain a mixed solution. Transfer it to a second sealed container and react at 160 °C for 22 h. After the reaction is completed, freeze-dry at -60 °C for 24 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, which is the cathode material for lithium-sulfur batteries. Example 3

[0033] (1) Add 0.8 mmol of ammonium tetrathiomolybdate to 35 mL of N,N-dimethylformamide to form a uniform mixed solution. Transfer it to a first sealed container and react at 160 °C for 24 h. After the reaction is completed, filter it three times with methanol to remove the excess N,N-dimethylformamide, and dry it at 80 °C for 12 h to obtain molybdenum disulfide powder;

[0034] (2) Dissolve 1.5 mmol of bismuth sulfate and 1.5 mmol of potassium molybdate successively in 40 mL of 0.5 M sulfuric acid solution. Add 2 mL of aniline to it, and then add 0.1 g of molybdenum disulfide powder and 0.07 g of graphene oxide successively to obtain a mixed solution. Transfer it to a second sealed container and react at 140 °C for 24 h. After the reaction is completed, freeze-dry at -40 °C for 48 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, which is the cathode material for lithium-sulfur batteries. Example 4

[0035] (1) 0.1 mmol of ammonium tetrathiomolybdate was added to 25 mL of N,N-dimethylformamide to form a homogeneous mixed solution, which was transferred to a first sealed container and reacted at 180 °C for 20 h. After the reaction, it was filtered three times with methanol to remove the excess N,N-dimethylformamide, and dried at 100 °C for 8 h to obtain molybdenum disulfide powder;

[0036] (2) 2 mmol of bismuth chloride and 1 mmol of sodium molybdate were successively dissolved in 60 mL of 0.75 M hydrochloric acid solution. 4 mL of triethanol was added thereto, and then 0.15 g of molybdenum disulfide powder and 0.01 g of graphene oxide were successively added to obtain a mixed solution, which was transferred to a second sealed container and reacted at 120 °C for 24 h. After the reaction, it was freeze-dried at -45 °C for 42 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, namely the cathode material of the lithium-sulfur battery. Example 5

[0037] (1) 0.2 mmol of ammonium tetrathiomolybdate was added to 30 mL of N,N-dimethylformamide to form a homogeneous mixed solution, which was transferred to a first sealed container and reacted at 200 °C for 14 h. After the reaction, it was filtered three times with methanol to remove the excess N,N-dimethylformamide, and dried at 100 °C for 10 h to obtain molybdenum disulfide powder;

[0038] (2) 2 mmol of bismuth sulfate and 1 mmol of sodium molybdate were successively dissolved in 80 mL of 0.75 M sulfuric acid solution. 6 mL of dodecylamine was added thereto, and then 0.065 g of molybdenum disulfide powder and 0.09 g of graphene oxide were successively added to obtain a mixed solution, which was transferred to a second sealed container and reacted at 160 °C for 18 h. After the reaction, it was freeze-dried at -55 °C for 30 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material. Example 6

[0039] (1) 0.9 mmol of ammonium tetrathiomolybdate was added to 35 mL of N,N-dimethylformamide to form a homogeneous mixed solution, which was transferred to a first sealed container and reacted at 160 °C for 16 h. After the reaction, it was filtered three times with methanol to remove the excess N,N-dimethylformamide, and dried at 120 °C for 12 h to obtain molybdenum disulfide powder;

[0040] (2) Dissolve 2 mmol of bismuth nitrate and 1 mmol of ammonium molybdate in 40 mL of 1 M nitric acid solution in sequence. Add 8 mL of ethylenediamine thereto, and then add 0.3 g of molybdenum disulfide powder and 0.1 g of graphene oxide in sequence to obtain a mixed solution. Transfer it to a second sealed container and react at 180 °C for 16 h. After the reaction is completed, freeze-dry at -50 °C for 36 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, which is the cathode material for lithium-sulfur batteries. Example 7

[0041] (1) Add 1 mmol of ammonium tetrathiomolybdate to 40 mL of N,N-dimethylformamide to form a homogeneous mixed solution. Transfer it to a first sealed container and react at 200 °C for 18 h. After the reaction is completed, filter it with methanol three times to remove the excess N,N-dimethylformamide, and dry it at 80 °C for 10 h to obtain molybdenum disulfide powder;

[0042] (2) Dissolve 1 mmol of bismuth nitrate and 1 mmol of potassium molybdate in 60 mL of 1 M nitric acid solution in sequence. Add 10 mL of aniline thereto, and then add 0.35 g of molybdenum disulfide powder and 0.05 g of graphene oxide in sequence to obtain a mixed solution. Transfer it to a second sealed container and react at 140 °C for 20 h. After the reaction is completed, freeze-dry at -60 °C for 24 h to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, which is the cathode material for lithium-sulfur batteries. Comparative Example 1

[0043] In this comparative example, no morphology regulator and graphene oxide are added, and the others are the same as the process of Example 1. Comparative Example 2

[0044] In this comparative example, no morphology regulator is added, and the others are the same as the process of Example 1. Comparative Example 3

[0045] In this comparative example, no graphene oxide is added, and the others are the same as the process of Example 1. Comparative Example 4

[0046] In this comparative example, no molybdenum disulfide is added, that is: the operation of step (1) is not carried out, and no molybdenum disulfide is added in step (2), and the others are the same as the process of Example 1. Comparative Example 5

[0047] In this comparative example, the operation of step (2) is not carried out, that is: the material is molybdenum disulfide synthesized in step (1), and the others are the same as the process of Example 1. Comparative Example 6

[0048] In this comparative example, commercially purchased molybdenum disulfide powder was used, and the operation in step (1) was not carried out, that is: the operation in step (1) was not carried out, and commercially purchased molybdenum disulfide was added in step (2), and the others were the same as those in Example 1.

[0049] The prepared lithium-sulfur battery cathode material was assembled into a battery for testing:

[0050] The graphene oxide supported molybdenum disulfide-bismuth molybdate heterojunction composite material and sulfur powder were weighed at a mass ratio of 3:7, and high-energy vibration ball milling was carried out at a vibration frequency of 2000 r / min for 30 min, and heat preservation was carried out at 155 °C for 8 h in an argon atmosphere. After cooling, the sulfur-loaded composite material, that is, the active material, was obtained.

[0051] The electrode was prepared by doctor blade coating. The active material, acetylene black and PVDF were weighed at a mass ratio of 8:1:1, added with NMP and stirred into a viscous slurry, which was doctor blade coated on aluminum foil. After drying, it was cut by a slicing machine to obtain a φ12 electrode sheet. A lithium-sulfur battery was assembled in a glove box and left to stand for 2-4 h before electrochemical testing.

[0052] In this application, the above electrode sheet was used as the positive electrode, the negative electrode was metallic lithium, the separator was a Celgard separator, and the electrolyte was 1 mol / L lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), with ethylene glycol dimethyl ether DME and 1,3-dioxolane DOL (volume ratio 1:1) as solvents, and a CR2032 type lithium-sulfur battery was assembled for electrochemical testing. The test conditions for the galvanostatic charge-discharge curve (GCD): voltage window 1.8 - 3.0 V, current density 0.2 C, 0.5 C, 1 C, 2 C, 4 C. The capacity retention rate was tested by cycling 300 times at a current density of 1 C.

[0053] The performance of the electrode materials obtained from the examples and comparative examples is summarized in Table 1 below.

[0054]

[0055] Figure 1 It is the SEM spectrum of the GO@MoS2-Bi2MoO6 material in Example 1. After adding the dodecylamine morphology regulator, a rod-shaped material with MoS2 nanosheet clusters epitaxially grown on the rod-shaped matrix Bi2MoO6 can be obtained. Different composite materials with different structures will be obtained according to different morphology regulators. Due to its large aspect ratio, the rod-shaped matrix can load more MoS2 nanosheets and adsorb more electrolyte ions; after being coated with graphene oxide, the structure collapse caused by volume expansion during cycling can be reduced.

[0056] Figure 2XRD patterns of the MoS2 and GO@MoS2-Bi2MoO6 materials prepared in Example 1. For the MoS2 material, strong diffraction peaks appear at 2θ = 14.13°, 32.91°, and 35.97°. The characteristic peaks and the diffraction peaks at other angles correspond to the results of the MoS2 standard card, demonstrating the successful synthesis of the MoS2 material. From the XRD pattern of the GO@MoS2-Bi2MoO6 material, the diffraction peaks of Bi2MoO6, MoS2, and GO can well correspond to the standard card, indicating the successful preparation of the GO@MoS2-Bi2MoO6 composite material.

[0057] Figure 3 Pore size distribution diagram of the GO@MoS2-Bi2MoO6 material prepared in Example 1. The pore size distribution of the material is mainly concentrated in the micropore and mesopore regions, with a small part in the macropore region. The composite material has a hierarchical porous structure. The existence of micropores can adsorb and store more ions; the mesopores are concentrated in the range of 10 - 30 nm. Combining the existence of some macropores can increase the contact with more electrolytes, improve the diffusion ability of the electrolyte, and promote the rapid transport of electrons and ions, which can effectively improve the charge-discharge performance of the battery.

[0058] Figure 4 and Figure 5 are the rate performance diagram and the curves of capacity retention and Coulomb efficiency of the GO@MoS2-Bi2MoO6 material in Example 1 at a current density of 1C for 300 cycles. Through Figure 4 and Table 1, it can be found that the specific capacity of the material in Example 1 is 1481 mAh / g at a current density of 0.2C. As the current density increases, the specific capacity shows a gradually decreasing trend. The specific capacity is 1053 mAh / g at a current density of 4C, and the rate performance is 71.12%. Through Figure 4 and Table 1, it can be found that the specific capacities of the materials in the examples and comparative examples all show a gradually decreasing trend as the current density increases. This is because as the current density increases, the ions in the electrolyte do not have enough time to respond on the surface of the electrode material, that is, the polarization effect becomes larger, resulting in a gradual decrease in the specific capacity. Figure 5 is the test of Example 1 at a current density of 1C for 300 cycles. The specific capacity is 84.65% of the initial capacity, showing excellent cycle stability.

[0059] From the data in Table 1, it can be found that compared with the composite materials without adding morphology regulators or / and graphene oxide in Comparative Examples 1-3, the specific capacity of the GO@MoS2-Bi2MoO6 material in the Examples has been improved, and the capacity retention rate is also maintained at 77-84%. Compared with the materials without forming heterojunctions in Comparative Examples 4 and 5, the formation of heterojunctions in the Examples will form photo-generated electron-hole pairs, reduce the ion transition energy during the electrochemical reaction process, and improve the electrochemical activity, thus showing an improvement in electrochemical performance. In Comparative Example 6, an externally purchased molybdenum disulfide was used as a raw material to synthesize a heterojunction composite material, and both the specific capacity and the cycle performance were not ideal. With the addition of the morphology regulator, the different ductility of the molybdenum disulfide nanosheets grown on the matrix can increase the adsorption sites and diffusion channels of the material and electrolyte ions, thereby improving the electrochemical performance of the lithium-sulfur battery; coupled with the coating of graphene oxide on the outermost layer, the obtained GO@MoS2-Bi2MoO6 material can avoid the shedding of the electrode material and the collapse of the structure caused by volume expansion during charge and discharge. The addition of dodecylamine can obtain a rod-shaped material with MoS2 nanosheet clusters epitaxially grown on the rod-shaped matrix Bi2MoO6. Due to the large aspect ratio of the rod-shaped structure, more nanosheets can be loaded, increasing the specific surface area of the composite material. As can be seen from Table 1, when the addition amount of dodecylamine is 6 mL and the addition amount of graphene oxide is 0.05 g, the material exhibits the most excellent performance. The above results show that the GO@MoS2-Bi2MoO6 material has excellent electrochemical performance and cycle stability in lithium-sulfur batteries.

[0060] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification. The description of the above embodiments can be used to help understand the principle and method of the present invention. However, the above embodiments are not unique and should not be construed as a limitation of the present invention. At the same time, for those of ordinary skill in the art, according to the principle and method of the present invention, flexible changes can be made in the specific implementation manner and application scope.

Claims

1. A preparation method of a lithium-sulfur battery cathode material, characterized in that, It includes the following steps: (1) Add ammonium tetrathiomolybdate to N,N-dimethylformamide to form a uniform mixed solution, conduct the reaction in a first sealed container, and after the reaction is completed, perform suction filtration, washing, and drying to obtain molybdenum disulfide powder; (2) Dissolve bismuth salt and molybdenum salt in a dilute solution of inorganic strong acid in sequence, add an amine morphology regulator to react therein, then add the molybdenum disulfide powder and graphene oxide obtained in step (1) in sequence to obtain a mixed solution, conduct the reaction in a second sealed container, and after the reaction is completed, perform freeze-drying to obtain a graphene oxide-supported molybdenum disulfide-bismuth molybdate heterojunction composite material, which is the cathode material of the lithium-sulfur battery; In step (2), the amine morphology regulator is any one of ethylenediamine, triethanolamine, dodecylamine, or aniline, and the molar ratio of the morphology regulator to the molybdenum salt is 0.01-0.1:1; the molar ratio of molybdenum disulfide to the molybdenum salt is 0.15-0.875:1; the mass ratio of graphene oxide to the molybdenum salt is 0.04-0.5:

1.

2. The preparation method of the lithium-sulfur battery cathode material according to claim 1, characterized in that, In step (1), the concentration of ammonium tetrathiomolybdate in N,N-dimethylformamide is 4-25 mM.

3. The preparation method of the lithium-sulfur battery cathode material according to claim 1, characterized in that, In step (1), the reaction temperature in the first sealed container is 160-200 °C, and the reaction time is 14-24 h; perform suction filtration three times with methanol, the drying temperature is 80-120 °C, and the drying time is 8-12 h.

4. The preparation method of the lithium-sulfur battery cathode material according to claim 1, wherein, In step (2), the molar ratio of bismuth salt to molybdenum salt is 1-2:1, the bismuth salt is any one of bismuth nitrate, bismuth chloride, or bismuth sulfate; the molybdenum salt is any one of sodium molybdate, ammonium molybdate, or potassium molybdate; the dilute solution of inorganic strong acid is any one of nitric acid, hydrochloric acid, or sulfuric acid solution, and the concentration is 0.5-1 M; the concentration of bismuth salt in the acidic solvent is 16-50 mM.

5. The preparation method of the lithium-sulfur battery cathode material according to claim 1, characterized in that, In step (2), the reaction temperature in the second sealed container is 120-180 °C, and the reaction time is 16-24 h; the freeze-drying temperature is -60~-40 °C, and the freeze-drying time is 24-48 h.

6. Use of a lithium-sulfur battery cathode material prepared by the preparation method according to any one of claims 1-5, characterized in that, Apply the cathode material of the lithium-sulfur battery to the lithium-sulfur battery.

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