A flexible self-supporting lithium-sulfur battery positive electrode material containing boron, vanadium and tungsten composite and its preparation method

Abstract

The present invention discloses a flexible, self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite and a preparation method thereof. Using flexible carbon cloth (CC) as a substrate, a B-V-WS2 composite material doped with boron (B) and vanadium (V) anions and cations was designed. Among them, the three-dimensional sheet structure of the 1T phase WS2 exposes abundant active sites, further improving the conversion efficiency of polysulfides; the dual doping advantage of B and V significantly regulates the electronic structure and catalytic activity of WS2. The co-doping of B and V not only enhances the adsorption capacity of WS2 for polysulfides, but also accelerates the kinetics of sulfur redox reactions, thereby effectively suppressing the shuttle effect and improving sulfur utilization. In addition, B and V doping also stabilizes the 1T phase structure, suppressing its transformation to the thermodynamically stable 2H phase during the cycle process, thereby significantly improving the stability of the battery cycle process. Thanks to these advantages, after being applied to lithium-sulfur batteries, excellent cycle stability and rate performance are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur batteries, and in particular relates to a flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite and a preparation method thereof. Background Art

[0002] Electrochemical storage devices, especially those with high energy density, are becoming the focus of technology and market. Among them, lithium-sulfur batteries based on lithium negative electrodes and sulfur positive electrodes can provide high energy density. Although lithium-sulfur batteries are regarded as excellent alternatives to lithium-ion batteries due to their high theoretical capacity and high energy density, the energy density and cycle stability of actual lithium-sulfur batteries are usually restricted by many factors. Among them, slow sulfur redox kinetics and the shuttle effect of polysulfides are the main obstacles to the development of lithium-sulfur batteries. These factors will inevitably lead to a decrease in sulfur utilization and cycle stability. In order to alleviate the above problems, a series of modification strategies can be used to explore how to accelerate sulfur redox kinetics and thus optimize the electrochemical performance of lithium-sulfur batteries.

[0003] At present, layered transition metal chalcogenides (such as WS2) as typical two-dimensional (2D) nanomaterials can improve the performance of lithium-sulfur batteries to a certain extent due to their high specific surface area and layered structure that is conducive to ion transport. However, WS2 still has some disadvantages in practical applications: slow sulfur redox kinetics, severe polysulfide shuttle effect, poor cycle stability and rapid capacity decay, which limit its further application in lithium-sulfur batteries (Advanced Engineering Materials 2023, 25(20): 2300542; Advanced Functional Materials 2024, 34(3): 2309437). Therefore, effective modification methods are needed to achieve its performance optimization.

[0004] Limitations of existing modification methods: (1) Heterostructure construction: Although heterojunction can improve electron transport and catalytic activity, its preparation process is complicated, and its adsorption and conversion effect on polysulfides is limited, making it difficult to completely solve the shuttle effect problem; (2) Crystal phase regulation: By controlling the crystal phase of WS2 (such as 1T phase and 2H phase), the conductivity and catalytic activity can be improved, but the effect of single crystal phase regulation is limited, especially in the long cycle process, the 1T phase is easy to transform into the 2H phase, resulting in performance degradation; (3) Single element doping: Although single element doping (such as B or V doping) can partially improve the electronic structure and catalytic performance of WS2, its scope of action is limited, and the adsorption and conversion ability of polysulfides is not significantly improved, and the shuttle effect problem is still prominent, such as (Small 2023, 19 (11): 2206926; Materials Today Chemistry 2024, 42: 102351; Applied Surface Science 2022, 599 154022). Summary of the Invention

[0005] In response to the problems of severe polysulfide shuttle effect and slow polysulfide conversion rate in the reaction process of existing lithium-sulfur batteries, resulting in poor cycle stability and rapid capacity decay, the purpose of the present invention is to provide a flexible self-supporting lithium-sulfur battery positive electrode material containing boron, vanadium and tungsten composites and a preparation method thereof, which can effectively adsorb polysulfides and promote the conversion of polysulfides, and has excellent cycle stability and rate performance.

[0006] A flexible, self-supporting lithium-sulfur battery cathode material containing a boron-vanadium-tungsten composite, characterized in that the preparation materials of the lithium-sulfur battery cathode material include BV-WS2@CC and elemental sulfur, and the BV-WS2@CC is a composite material after reaction, including a conductive carbon material substrate carbon cloth and a BV-WS2 material grown on the surface of the conductive carbon material substrate;

[0007] Furthermore, in the BV-WS2@CC composite material, B accounts for 1% to 10% of WS2;

[0008] Furthermore, the V content of the BV-WS2@CC composite material accounts for 1% to 10% of WS2;

[0009] Furthermore, the elemental sulfur is dissolved in the CS2 solution and infiltrated into the BV-WS2@CC composite material.

[0010] Furthermore, the content of elemental sulfur is 10 wt% to 50 wt%.

[0011] The present invention also provides a method for preparing the above-mentioned battery positive electrode material, which is applied to the above-mentioned flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite, comprising the following steps:

[0012] (1) Cleaning the carbon cloth and acidifying the carbon cloth to obtain the final desired carbon cloth;

[0013] (2) adding a tungsten source, a sulfur source, a boron source, and a vanadium source into a solvent and vigorously stirring to obtain a mixed solution;

[0014] (3) The treated carbon cloth is tilted and poured into the mixed solution, and the reaction is post-treated to obtain an intermediate loaded with BV-WS2@CC;

[0015] (4) The intermediate is cut and immersed in a solution of sulfur powder dissolved in CS2 for treatment. Under a protective atmosphere, the material is heated and sulfurized to obtain the lithium-sulfur battery positive electrode material BV-WS2@CC / S.

[0016] Furthermore, in step (1), the carbon cloth size is 2 × 4~5 cm 2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40-48 mL; the post-acidification treatment is heating at 90-100°C for 6-8 hours, then ultrasonically cleaning with deionized water and 99% alcohol three times in a row, and vacuum drying for 12-15 hours.

[0017] Furthermore, in step (2), the tungsten source is sodium tungstate; the sulfur source is thioacetamide; the boron source is boric acid; the vanadium source is ammonium metavanadate, and the molar ratio of the tungsten source, the sulfur source, the boron source, and the vanadium source is 90:518:0.9~9:0.9~9; and the solvent is DMF.

[0018] Furthermore, in step (3), the reaction temperature is 200°C and the reaction time is 20 h; after the reaction, the carbon cloth with the material is taken out, and the treatment operation is to rinse the carbon cloth with deionized water and 99% alcohol, and vacuum dry it for 12 to 15 h to prepare the intermediate BV-WS2@CC composite material.

[0019] Furthermore, in step (4), the protective atmosphere is one of nitrogen, helium, and argon, the heating rate is 2 to 4°C / min, and the temperature is maintained at 155 to 180°C for 11 to 14 hours to obtain a BV-WS2@CC / S composite material.

[0020] The present invention also provides a lithium-sulfur battery, wherein the positive electrode of the lithium-sulfur battery is made of the above-mentioned lithium-sulfur battery positive electrode material.

[0021] The beneficial effects of the present invention are:

[0022] The present invention proposes a synergistic modification strategy of B and V co-doping combined with 1T phase WS2. A three-dimensional sheet-like structure of 1T phase WS2 is grown on a flexible carbon cloth by a hydrothermal method, and B and V anion-cation dual doping is introduced, which significantly improves the cycling performance of WS2 in lithium-sulfur batteries. The specific advantages are: (1) B and V anion-cation co-doping not only synergistically enhances the conductivity and catalytic activity of WS2, but also inhibits its transformation to the thermodynamically stable 2H phase during the cycle by stabilizing the 1T phase structure, thereby greatly improving the cycling stability and capacity retention rate; (2) The hydrothermal method, as the core preparation process, can efficiently synthesize three-dimensional sheet-like 1T phase WS2 under mild conditions. The process is simple and easy to scale up. At the same time, by precisely controlling the morphology and crystal phase, WS2 exposes more active sites to improve the catalytic performance; (3) This method, combined with a flexible carbon cloth substrate, not only provides excellent conductivity and mechanical support, but also provides sufficient space for high sulfur loading, effectively preventing electrode damage. Through the synergistic effect of B and V co-doping and 1T phase WS2, this material exhibits high sulfur utilization, significantly suppressed shuttle effect and excellent cycle stability in lithium-sulfur batteries, providing an innovative solution to the bottleneck problem of traditional lithium-sulfur batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 X-ray diffraction patterns of 1.5%-BV-WS2@CC prepared in Example 1, V-WS2@CC prepared in Comparative Example 2, B-WS2@CC prepared in Comparative Example 3, and WS2@CC prepared in Comparative Example 1, as well as the X-ray diffraction standard card of 2H-WS2.

[0024] Figure 2 These are the relaxation, folding, torsion, and rolling test diagrams of 1.5%-BV-WS2@CC / S in Example 1.

[0025] Figure 3 This is a rate performance diagram of 1.5%-BV-WS2@CC / S prepared in Example 1, WS2@CC / S prepared in Comparative Example 1, V-WS2@CC / S prepared in Comparative Example 2, and B-WS2@CC / S prepared in Comparative Example 3.

[0026] Figure 4 This is the cycle performance diagram of 1.5%-BV-WS2@CC / S prepared in Example 1 under high sulfur load.

[0027] Figure 5 These are the cycling performance diagrams of 1.5%-BV-WS2@CC / S prepared in Example 1, 3%-BV-WS2@CC / S prepared in Example 2, and 5%-BV-WS2@CC / S prepared in Example 3 at a current density of 1C.

[0028] Figure 6Raman images of 1.5%-BV-WS2@CC / S prepared in Example 1 and WS2@CC prepared in Comparative Example 1.

[0029] Figure 7 CV curves of symmetrical batteries of 1.5%-BV-WS2 prepared in Example 1, WS2 prepared in Comparative Example 1, V-WS2 prepared in Comparative Example 2, and B-WS2 prepared in Comparative Example 3. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below by way of examples so that those skilled in the art can better understand the present invention, but the present invention is not limited to the following examples.

[0031] Example 1

[0032] (1) Clean the carbon cloth (CC) and cut it into 2 x 4~5cm pieces. 2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40~48mL; the post-acidification treatment is heating at 90~100℃ for 6~8h, then ultrasonic cleaning is performed three times in succession with deionized water and 99% alcohol, and vacuum drying is performed for 12~15h.

[0033] (2) 0.48 g of sodium tungstate (Na2WO4·2H2O), 0.0015 g of boric acid (H3BO3), 0.003 g of ammonium metavanadate (NH4VO3), and 0.63 g of thioacetamide (TAA) were dissolved in 36 mL of DMF solution, stirred vigorously for 1 h, and then poured into a 60 mL polytetrafluoroethylene liner. The carbon cloth was placed tilted in the above mixed solution and heated at 200 °C for 20 h. After the reaction, the carbon cloth with the material was removed and rinsed with deionized water and 99% alcohol. The carbon cloth was vacuum dried for 12 h to prepare the 1.5%-BV-WS2@CC composite material.

[0034] (3) Dissolve 0.2 g of sulfur powder in 5 mL of CS2 solution. 2 The carbon cloth was cut into circular electrodes with a diameter of 10 mm. The electrodes were then immersed in a sulfur-containing CS2 solution for 10 minutes and dried at 45°C for 12 hours. The electrodes were heated at 155°C in a vacuum for 12 hours to obtain a sulfur loading of 2 mg cm -2 About 1.5%-BV-WS2@CC / S positive electrode material.

[0035] Example 2

[0036] (1) Clean the carbon cloth (CC) and cut it into pieces of 2 x 4~5 cm2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40~48 mL; the acidification post-treatment is heating at 90~100℃ for 6~8 hours, then ultrasonic cleaning is performed three times in succession with deionized water and 99% alcohol, and vacuum drying is performed for 12~15 hours.

[0037] (2) 0.48 g of sodium tungstate (Na2WO4·2H2O), 0.003 g of boric acid (H3BO3), 0.006 g of ammonium metavanadate (NH4VO3), and 0.63 g of thioacetamide (TAA) were dissolved in 36 mL of DMF solution, stirred vigorously for 1 h, and then poured into a 60 mL polytetrafluoroethylene liner. The carbon cloth was placed tilted in the above mixed solution and heated at 200 °C for 20 h. After the reaction, the carbon cloth with the material was removed, rinsed with deionized water and 99% alcohol, and vacuum dried for 12 h to prepare the 3%-B / V-WS2@CC composite material.

[0038] (3) Dissolve 0.2 g of sulfur powder in 5 mL of CS2 solution. 2 The carbon cloth was cut into circular electrodes with a diameter of 10 mm. The electrodes were then immersed in a sulfur-containing CS2 solution for 10 minutes and dried at 45°C for 12 hours. The electrodes were heated at 155°C in a vacuum for 12 hours to obtain a sulfur loading of 2 mg cm -2 About 3%-BV-WS2@CC / S positive electrode material.

[0039] Example 3

[0040] (1) Clean the carbon cloth (CC) and cut it into 2 x 4~5cm pieces. 2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40~48mL; the post-acidification treatment is heating at 90~100℃ for 6~8h, then ultrasonic cleaning is performed three times in succession with deionized water and 99% alcohol, and vacuum drying is performed for 12~15h.

[0041] (2) 0.48 g of sodium tungstate (Na2WO4·2H2O), 0.005 g of boric acid (H3BO3), 0.01 g of ammonium metavanadate (NH4VO3), and 0.63 g of thioacetamide (TAA) were dissolved in 36 mL of DMF solution, stirred vigorously for 1 h, and then poured into a 60 mL polytetrafluoroethylene liner. The carbon cloth was placed tilted in the above mixed solution and heated at 200 °C for 20 h. After the reaction, the carbon cloth with the material was removed, rinsed with deionized water and 99% alcohol, and vacuum dried for 12 h to prepare the 5%-B / V-WS2@CC composite material.

[0042] (3) Dissolve 0.2 g of sulfur powder in 5 mL of CS2 solution. 2 The carbon cloth was cut into circular electrodes with a diameter of 10 mm. The electrodes were then immersed in a sulfur-containing CS2 solution for 10 minutes and dried at 45°C for 12 hours. The electrodes were heated at 155°C in a vacuum for 12 hours to obtain a sulfur loading of 2 mg cm -2 About 5%-BV-WS2@CC / S positive electrode material.

[0043] Comparative Example 1

[0044] (1) Clean the carbon cloth (CC) and cut it into 2 x 4~5cm pieces. 2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40~48mL; the post-acidification treatment is heating at 90~100℃ for 6~8h, then ultrasonic cleaning is performed three times in succession with deionized water and 99% alcohol, and vacuum drying is performed for 12~15h.

[0045] (2) Dissolve 0.495 g of sodium tungstate (Na2WO4·2H2O) and 0.63 g of thioacetamide (TAA) in 36 mL of DMF solution, stir vigorously for 1 h, and pour into a 60 mL polytetrafluoroethylene-lined container. Tilt the treated CC into the mixed solution and heat at 200 °C for 20 h. After the reaction, remove the carbon cloth with the material, rinse it with deionized water and 99% alcohol, and vacuum dry it for 12 h to prepare the WS2@CC composite material.

[0046] (3) Dissolve 0.2 g of sulfur powder in 5 mL of CS2 solution. 2The carbon cloth was cut into circular electrodes with a diameter of 10 mm. The electrodes were then immersed in a sulfur-containing CS2 solution for 10 minutes and dried at 45°C for 12 hours. The electrodes were heated at 155°C in a vacuum for 12 hours to obtain a sulfur loading of 2 mg cm -2 WS2@CC / S positive electrode material.

[0047] Comparative Example 2

[0048] (1) Clean the carbon cloth (CC) and cut it into 2 x 4~5cm pieces. 2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40~48mL; the post-acidification treatment is heating at 90~100℃ for 6~8h, then ultrasonic cleaning is performed three times in succession with deionized water and 99% alcohol, and vacuum drying is performed for 12~15h.

[0049] (2) 0.48 g of sodium tungstate (Na2WO4·2H2O), 0.63 g of thioacetamide (TAA), and 0.003 g of ammonium metavanadate (NH4VO3) were dissolved in 36 mL of DMF solution, stirred vigorously for 1 h, and then poured into a 60 mL polytetrafluoroethylene liner. The treated CC was tilted and placed in the above mixed solution and heated at 200 °C for 20 h. After the reaction, the carbon cloth with the material was removed and rinsed with deionized water and 99% alcohol. The carbon cloth was vacuum dried for 12 h to prepare the V-WS2@CC composite material.

[0050] (3) Dissolve 0.2 g of sulfur powder in 5 mL of CS2 solution. 2 The carbon cloth was cut into circular electrodes with a diameter of 10 mm. The electrodes were then immersed in a sulfur-containing CS2 solution for 10 minutes and dried at 45°C for 12 hours. The electrodes were then heated at 155°C in a vacuum for 12 hours to obtain a sulfur loading of 2 mg cm -2 V-WS2@CC / S positive electrode material.

[0051] Comparative Example 3

[0052] (1) Clean the carbon cloth (CC) and cut it into 2 x 4~5cm pieces. 2 The acid used in the acidification treatment was 12 mol L -1 The amount of concentrated nitric acid used is 40~48mL; the post-acidification treatment is heating at 90~100℃ for 6~8h, then ultrasonic cleaning is performed three times in succession with deionized water and 99% alcohol, and vacuum drying is performed for 12~15h.

[0053] (2) Dissolve 0.48 g of sodium tungstate (Na2WO4·2H2O), 0.63 g of thioacetamide (TAA), and 0.0015 g of boric acid (H3BO3) in 36 mL of DMF solution, stir vigorously for 1 h, and pour into a 60 mL polytetrafluoroethylene liner. Place the treated CC tilted into the above mixed solution and heat at 200 °C for 20 h. After the reaction, remove the carbon cloth with the material, rinse the carbon cloth with deionized water and 99% alcohol, and vacuum dry it for 12 h to prepare the B-WS2@CC composite material.

[0054] (3) Dissolve 0.2 g of sulfur powder in 5 mL of CS2 solution. 2 The carbon cloth was cut into circular electrodes with a diameter of 10 mm. The electrodes were then immersed in a sulfur-containing CS2 solution for 10 minutes and dried at 45°C for 12 hours. The electrodes were then heated at 155°C in a vacuum for 12 hours to obtain a sulfur loading of 2 mg cm -2 B-WS2@CC / S positive electrode material on the left and right.

[0055] The positive electrode materials prepared in Examples 1, 2, 3 and Comparative Examples 1, 2, 3 were made into positive electrode sheets, and then lithium sheets were used as negative electrodes to assemble lithium-sulfur batteries.

[0056] The positive electrode materials prepared in Example 1 and Comparative Examples 1, 2, and 3 were made into pole pieces. The unsulfurized carbon cloth pole pieces were then placed in an oven and dried at 50° C. for 12 h. The carbon cloth pole pieces were directly used as working electrodes and counter electrodes to assemble into symmetrical batteries.

[0057] Figure 1 The shift of the (002) characteristic peak clearly indicates the formation of the 1T phase. On the WS2 matrix, the XRD peak shifted slightly and no other impurity peaks appeared, proving the successful incorporation of B and V.

[0058] Figure 2 It shows that when the material relaxes again, it still maintains good integrity and does not deform, indicating that the material grown on the carbon cloth has good mechanical stability.

[0059] Figure 3 The results show that the battery with 1.5%-BV-WS2@CC / S still has the highest discharge capacity (1081.62 mAh g) after 100 cycles. -1 ), the electrochemical cycling performance of this material is excellent.

[0060] Figure 4 The sulfur loading of 1.5%-BV-WS2@CC / S is 5.0 mg cm -2When the current density is 0.1 C, the initial surface capacity is as high as 6.01 mAh cm -2 After 100 cycles, the capacity is still 4.64 mAh cm -2 , indicating that 1.5%-BV-WS2@CC is a good high-sulfur-loaded cathode material for lithium-sulfur batteries.

[0061] Figure 5 It shows that 1.5%-BV-WS2@CC / S has better cycling performance among the materials prepared with different doping ratios.

[0062] Figure 6 Raman spectroscopy showed that the -1 Due to the in-plane E 1 2g and A 1 g The characteristic peak of WS2 in the vibration mode indicates the formation of 2H phase WS2. After co-doping with B and V, a low-frequency region J1 (131 cm -1 )、J2(188 cm -1 ), indicating the stable formation of the 1T phase WS2. Comparing the Raman spectra before and after doping reveals a significant increase in the J1 and J2 peaks, representing the 1T phase. This demonstrates that the addition of B and V promotes the stable formation of more 1T-WS2.

[0063] Figure 7 The reduction peak corresponds to the conversion of S8 to LiPSs, followed by further reduction to Li2S / Li2S2, while the oxidation peak represents the decomposition of Li2S into soluble LiPSs. The smaller spacing between the redox peaks in the symmetric cell indicates the rapid and reversible conversion of LiPSs. It can be seen that compared with Comparative Examples 1, 2, and 3, the 1.5%-BV-WS2 prepared in Example 1 has a higher peak current and a smaller redox peak potential, indicating its stronger catalytic ability for polysulfide conversion.

[0064] The above is only a preferred specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite, characterized in that: The preparation materials of the lithium-sulfur battery positive electrode material include BV-WS2@CC and elemental sulfur. The BV-WS2@CC is a composite material after the reaction, including a conductive carbon material base carbon cloth and a BV-WS2 material grown on the surface of the conductive carbon material base; In the BV-WS2@CC composites, B accounts for 1% to 10% of WS2; In the BV-WS2@CC composite material, V accounts for 1% to 10% of WS2; The elemental sulfur is dissolved in the CS2 solution and infiltrated into the BV-WS2@CC composite material.

2. The flexible self-supporting lithium-sulfur battery positive electrode material containing boron, vanadium and tungsten according to claim 1, characterized in that: The content of the elemental sulfur is 10 wt% to 50 wt%.

3. The method for preparing a flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite according to claim 1, characterized in that: The following steps are involved: (1) Clean the carbon cloth, cut it to a suitable size, and acidify the carbon cloth to obtain the final desired carbon cloth; (2) adding a tungsten source, a sulfur source, a boron source, and a vanadium source into a solvent and vigorously stirring to obtain a mixed solution; (3) The treated carbon cloth is tilted and poured into the mixed solution, and the intermediate loaded with BV-WS2@CC is obtained by post-reaction treatment; (4) The intermediate is cut, immersed in a solution of sulfur powder dissolved in CS2 and treated to obtain an initial electrode. Under a protective atmosphere, the electrode is heated and sulfurized to obtain the lithium-sulfur battery positive electrode material BV-WS2@CC / S.

4. The method for preparing a flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite according to claim 3, characterized in that: In step (1), cut the carbon cloth into 2 × 4~5 cm 2 The acid used for acidification treatment is 12 mol / L concentrated nitric acid, with a dosage of 40~48 ml; the post-acidification treatment is heating at 90~100℃ for 6~8 h, then ultrasonic cleaning three times with deionized water and 99% alcohol, and vacuum drying for 12~15 h.

5. The method for preparing a flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite according to claim 3, characterized in that: In step (2), the tungsten source is sodium tungstate; the sulfur source is thioacetamide; the boron source is boric acid; the vanadium source is ammonium metavanadate, and the molar ratio of the tungsten source, the sulfur source, the boron source, and the vanadium source is 90:518:0.9~9:0.9~9; and the solvent is DMF.

6. The method for preparing a flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite according to claim 3, characterized in that: In step (3), the reaction environment is 200° C. and the reaction time is 20 h. After the reaction, the carbon cloth with the material is taken out, and the treatment operation is to rinse the carbon cloth with deionized water and 99% alcohol, and vacuum dry it for 12 to 15 h to prepare the intermediate BV-WS2@CC composite material.

7. The method for preparing a flexible self-supporting lithium-sulfur battery positive electrode material containing a boron-vanadium-tungsten composite according to claim 3, characterized in that: In step (4), the protective atmosphere is one of nitrogen, helium, and argon atmospheres, the heating rate is 2 to 4°C / min, and the temperature is maintained at 155 to 180°C for 11 to 14 hours to obtain a BV-WS2@CC / S composite material.

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