A molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube / sulfur composite material and a preparation method thereof, and a lithium-sulfur battery positive electrode and a lithium-sulfur battery

Abstract

The application discloses a molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube / sulfur composite material and a preparation method thereof, and a lithium-sulfur battery positive electrode and a lithium-sulfur battery. The preparation method comprises the following steps: mixing melamine and aluminum, reacting at a high temperature of 900-1500 DEG C for 0.5-4 h under the protection of an inert gas, immersing the obtained reaction product in an inorganic acid solution for 2-24 h to obtain a nitrogen-doped bamboo-shaped carbon fiber tube material, dispersing the nitrogen-doped bamboo-shaped carbon fiber tube material, thioacetamide, sodium molybdate and urea in a solvent, performing a solvothermal reaction, calcining the obtained reaction product in a reducing atmosphere, and finally smoking sulfur. The composite material has a hollow bamboo-shaped nitrogen-doped bamboo-shaped carbon fiber tube surface coated with sheet-shaped molybdenum disulfide nanosheets, and the sheet-shaped molybdenum disulfide nanosheets are loaded with sulfur. The lithium-sulfur battery positive electrode is prepared by taking the composite material as an active material, and then the lithium-sulfur battery is assembled. The lithium-sulfur battery has good cycle stability and rate performance.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterials technology for lithium-sulfur batteries, specifically relating to a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material, its preparation method, as well as a lithium-sulfur battery cathode and a lithium-sulfur battery. Background Technology

[0002] The tremendous progress in society and technology has brought about a crisis of non-renewable energy and irreversible environmental pollution, thus making abundant renewable energy sources a focus of continuous attention. Lithium-ion batteries are widely used in all aspects of our lives (such as smartphones, laptops, and electric vehicles), dramatically changing human lifestyles. However, with the further development of electrical products and the rapid growth of people's demands, the inherent shortcomings of lithium-ion batteries have begun to emerge, such as insufficient energy density and power density. In order to continuously promote the development of energy storage systems and meet people's requirements for high energy density and high power density energy storage devices, researchers have had to seek other solutions.

[0003] Lithium-sulfur batteries have a high theoretical capacity (1675 mA hg) due to the two-electron conversion reaction from S to Li2S. -1 ) and high energy density (2600Wh kg) -1 This has sparked widespread research interest and is considered one of the most promising next-generation energy storage systems. In addition, the abundance of natural sulfur reserves, its environmental friendliness, and low cost also make lithium-sulfur batteries more commercially advantageous in practical applications. Despite these significant advantages, the widespread application of lithium-sulfur batteries is still hindered by some factors. For example: (1) the low conductivity (conductivity ≈ 5 × 10⁻⁶) of elemental sulfur, the active material of the positive electrode, and the Li₂S / Li₂S₂ products generated during charging and discharging. -30 S cm -1 (1) It hinders the transport of electrons and ions during charging and discharging, and reduces the electrochemical reaction kinetics of the active substance sulfur; (2) The densities of S8 and Li2S are 2.07 and 1.66 g cm⁻¹, respectively. -3 The density difference causes the positive electrode to expand significantly in volume (~80%) during the cycle reaction; (3) The lithium polysulfide produced during the electrochemical reaction has high solubility in the electrolyte, resulting in a severe shuttle effect, which leads to a gradual decrease in battery capacity and a shortened battery life.

[0004] In lithium-sulfur batteries, adding transition metal compounds with adsorption effect on polysulfides and electrocatalytic effect on electrode reactions to the positive electrode material is a good method. Transition metal compounds with two-dimensional (2D) layered structure are of interest due to their large specific surface area, strong chemical adsorption on polysulfides, and weak van der Waals forces between each single molecule. In addition, transition metal sulfides can promote the conversion of polysulfides and become active sites for catalyzing polysulfide intermediates. This phenomenon is due to the strong electronegativity of sulfur atoms in metal sulfides, which enables them to capture electrons from transition metals.

[0005] Lin et al. synthesized c-MoS2 nanosheets with sulfur vacancies and high specific surface area, which provided additional redox reaction sites for polysulfides during the operation of lithium-sulfur batteries (J. Mater. Chem. A, 11, 2023, 8265-8276). However, the cycle stability of these sulfur carriers still needs to be improved in practical applications of lithium-sulfur batteries. SUMMARY

[0006] To solve the above technical problems, the present application provides a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material and a preparation method thereof. The nitrogen-doped bamboo-like carbon fiber tube not only has the functions of conductivity and connection, but also can provide a certain physical adsorption effect for polysulfides. In addition, nitrogen atoms can effectively capture soluble polysulfides through chemical action, thereby synergizing with the hollow porous structure. At the same time, the ultra-thin molybdenum disulfide nanosheet containing 1T metal phase exposes more active sites while improving the conductivity, which greatly enhances its contribution to the redox kinetics of sulfur species and fully suppresses the shuttle effect, thereby improving the performance of lithium-sulfur batteries.

[0007] The present application also provides a lithium-sulfur battery positive electrode and a lithium-sulfur battery. The molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material described in the present application is used as an active material to prepare a lithium-sulfur battery positive electrode, and then assembled into a lithium-sulfur battery. The lithium-sulfur battery has good cycle stability and rate performance.

[0008] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0009] The present application provides a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material. The composition and morphology of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material are as follows: the surface of the hollow bamboo-like nitrogen-doped bamboo-like carbon fiber tube is coated with sheet-shaped molybdenum disulfide nanosheets, and the sheet-shaped molybdenum disulfide nanosheets are loaded with sulfur.

[0010] The present application also provides a preparation method of a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material. The preparation method comprises the following steps:

[0011] (1) Melamine and aluminum are mixed and reacted at a high temperature of 900-1500℃ for 0.5-4h under the protection of inert gas. The resulting reactants are soaked in an inorganic acid solution for 2-24h, washed and dried to obtain nitrogen-doped bamboo-shaped carbon fiber tube material, which has a hollow bamboo-shaped structure.

[0012] (2) Nitrogen-doped bamboo-shaped carbon fiber tube material, thioacetamide, sodium molybdate and urea are dispersed in a solvent and subjected to a solvothermal reaction. The resulting reactants are calcined in a reducing atmosphere to obtain molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tube material.

[0013] (3) Sulfur disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tubes were fumigated with sulfur to obtain molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tubes / sulfur composite materials.

[0014] In step (1), the ratio of melamine to aluminum is 20.0g:(0.1~0.5)g.

[0015] In step (1), the concentration of the inorganic acid solution is 1–8 mol / L. -1 Preferably 3-4 mol L -1 The inorganic acid solution is one or more of sulfuric acid, nitric acid, hydrochloric acid, and phosphoric acid; the soaking reaction temperature is 5–80°C, preferably 25–50°C; and the soaking time is preferably 12–18 hours.

[0016] In step (1), the preferred conditions for the high-temperature reaction are 1100-1200℃ for 2-3 hours.

[0017] In step (1), the inert atmosphere is nitrogen or argon.

[0018] In step (2), the ratio of nitrogen-doped bamboo-shaped carbon fiber tube material to thioacetamide, sodium molybdate, and urea is 0.05g:(0.05~0.35)g:(0.08~0.5)g:(0.01~0.1)g.

[0019] In step (2), the solvent is a mixture of water and any one or more of isopropanol, ethylene glycol, N,N-dimethylformamide or dimethyl sulfoxide, wherein the volume percentage of water in the mixed solvent is 3% to 45%, preferably 10% to 15%.

[0020] In step (2), the solvothermal reaction conditions are 160-240℃ for 6-36 hours, preferably 180-200℃ for 20-30 hours; the calcination conditions are heating and holding at 500-900℃ for 1-5 hours; the reducing atmosphere is a mixture of hydrogen and argon, wherein the volume percentage of hydrogen is 3-10%, preferably 5%.

[0021] In step (3), the heating and sulfur fumigation conditions are 125-185℃ for 6-48 hours, preferably 150-170℃ for 12-36 hours;

[0022] In step (3), the mass ratio of molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tubes to sulfur powder is 1:1.5 to 3.5.

[0023] In step (3), the inert atmosphere is nitrogen or argon.

[0024] The present invention also provides a lithium-sulfur battery cathode, which is prepared using the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material described in the present invention as the active material.

[0025] This invention also provides a lithium-sulfur battery, using the positive electrode of the lithium-sulfur battery described in this invention. It exhibits good stability at 1.0 Ag. -1 After 500 cycles at the current density, the specific capacity of the positive electrode is still as high as 403 mAh g. -1 above.

[0026] The method for preparing molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tubes / sulfur composite materials provided by this invention firstly uses melamine as a carbon source and aluminum as a catalyst to prepare hollow, bamboo-shaped nitrogen-doped carbon fiber tubes with a multi-layered structure through a high-temperature catalytic reaction followed by acid treatment. Then, the nitrogen-doped bamboo-shaped carbon fiber tubes are mixed with thioacetamide, sodium molybdate, and urea for a solvothermal reaction, followed by high-temperature calcination to obtain nitrogen-doped bamboo-shaped carbon fiber tubes coated with molybdenum disulfide nanosheets. Finally, sulfur is loaded onto the surface of the molybdenum disulfide nanosheets using a sulfur melt diffusion strategy to prepare the molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tubes / sulfur composite material.

[0027] The chemical reaction equations involved in the above reaction process are shown below:

[0028] C3H6N6→3C+3N2↑+3H2↑

[0029] CO(NH2)2+3H2O→NH4HCO3+NH3·H2O

[0030] 7CH3CSNH2+3Na2MoO4+2NH3·H2O+3H2O→6CH3COONa+3MoS2

[0031] + CH3COONH4 + 6NH3 + (NH4)2SO3

[0032] The synthesis method of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material provided by the application is simple, the hollow bamboo-like tubular structure provides abundant voids to buffer volume change, realizes effective electron transfer, is conducive to improving the sulfur loading capacity, and provides a buffer space for the volume expansion of sulfur; in addition, the nanosheet-shaped molybdenum disulfide has more exposed active sites, is conducive to the physical restriction and chemical adsorption of polysulfides, and accelerates the electrochemical reaction kinetics. With the material as a positive electrode of a lithium-sulfur battery, the cycle stability and rate performance of the lithium-sulfur battery are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 SEM image of the nitrogen-doped bamboo-like carbon fiber tube prepared for Example 1;

[0034] Figure 2 TEM image of the nitrogen-doped bamboo-like carbon fiber tube prepared for Example 1;

[0035] Figure 3 XRD image of the nitrogen-doped bamboo-like carbon fiber tube prepared for Example 1;

[0036] Figure 4 SEM image of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube composite material prepared for Example 1;

[0037] Figure 5 SEM image of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material prepared for Example 1;

[0038] Figure 6 SEM image of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material prepared for Example 2;

[0039] Figure 7 SEM image of the nitrogen-doped bamboo-like carbon fiber tube material prepared for Example 3;

[0040] Figure 8 SEM image of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube composite material prepared for Example 3;

[0041] Figure 9 TEM image of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube composite material prepared for Example 3;

[0042] Figure 10 XRD image of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube composite material prepared for Example 3;

[0043] Figure 11 SEM image of the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 3;

[0044] Figure 12 TEM image of the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 3;

[0045] Figure 13 The XRD pattern of the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 3;

[0046] Figure 14 SEM image of the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 4;

[0047] Figure 15 SEM image of the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 4;

[0048] Figure 16 The carbon nanotube material prepared using iron sheet as a catalyst in Comparative Example 1;

[0049] Figure 17 The carbon nanotube material prepared using cobalt sheet as catalyst in Comparative Example 1;

[0050] Figure 18 The carbon nanotube material prepared using nickel sheet as a catalyst in Comparative Example 1;

[0051] Figure 19 A lithium-sulfur battery was fabricated using the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 3 as the cathode material. The battery was tested at 0.2 Ag. -1 Results of 100 cycles at current density;

[0052] Figure 20 A lithium-sulfur battery was fabricated using the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material prepared in Example 3 as the cathode material, at 1.0 Ag... -1 Results of 500 cycles at current density. Detailed Implementation

[0053] The present invention will now be described in detail with reference to the embodiments.

[0054] Example 1

[0055] A method for preparing a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material includes the following steps:

[0056] (1) Place 20.0g of melamine and 0.1g of aluminum sheet in a high-temperature tube furnace and react at 1500℃ for 0.5h under a nitrogen atmosphere. Then soak it in 60mL of 1.0mol L... -1 The reaction was carried out in sulfuric acid solution at 5°C for 24 hours, followed by washing with deionized water and drying to obtain nitrogen-doped bamboo-like carbon fiber tubes. SEM images of the prepared nitrogen-doped bamboo-like carbon fiber tubes are shown below. Figure 1 As shown, Figure 2 This is a TEM image, and its XRD pattern is as follows: Figure 3 As shown;

[0057] (2) 0.05 g of nitrogen-doped bamboo-shaped carbon fiber tube material, 0.05 g of thioacetamide, 0.08 g of sodium molybdate, and 0.01 g of urea were dispersed in a mixed solvent of water and isopropanol with a water volume content of 3%. The mixture was reacted at 160 °C for 36 h. After washing with deionized water and drying, the mixture was reacted at 500 °C for 5 h in a hydrogen-argon mixture with a hydrogen volume percentage of 5% to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube composite material. The SEM image of the product is shown below. Figure 4 As shown in the figure, molybdenum disulfide nanosheets are uniformly distributed on the surface of nitrogen-doped bamboo-shaped carbon fiber tubes.

[0058] (3) 0.1 g of molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tubes were mixed evenly with 0.15 g of sulfur powder and transferred to a polytetrafluoroethylene vial filled with argon gas. The mixture was reacted at 125 °C for 48 h under an argon atmosphere to obtain a molybdenum disulfide nanosheets / nitrogen-doped bamboo-shaped carbon fiber tube / sulfur composite material. Its SEM image is shown below. Figure 5 As shown in the figure, sulfur is uniformly loaded on the nanotubes.

[0059] Example 2

[0060] A method for preparing a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material includes the following steps:

[0061] (1) Place 20.0g of melamine and 0.2g of aluminum sheet in a high-temperature tube furnace and react at 1300℃ for 1h under a nitrogen atmosphere. Then soak it in 60mL of 3.0mol / L... -1 The reaction was carried out in nitric acid solution at 20°C for 18 hours, followed by washing with deionized water and drying to obtain nitrogen-doped bamboo-shaped carbon fiber tube material.

[0062] (2) 0.05 g nitrogen-doped bamboo-like carbon nanotube material, 0.1 g thioacetamide, 0.15 g sodium molybdate and 0.03 g urea were dispersed in a water and ethylene glycol mixed solvent with a water volume content of 10%, and reacted at 180°C for 30 h. After washing with deionized water and drying, the product was reacted in a hydrogen and argon mixed gas with a hydrogen volume percentage of 5% at 600°C for 4 h to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube composite material;

[0063] (3) 0.1 g of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube material was uniformly mixed with 0.2 g of sulfur powder, and transferred to a polytetrafluoroethylene vial filled with argon. The reaction was carried out at 140°C for 40 h under an argon atmosphere to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube material / sulfur composite material. The SEM image of the product is shown in Figure 6 , from which it can be seen that sulfur is uniformly loaded on the nanotubes.

[0064] Example 3

[0065] A method for preparing a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube / sulfur composite material, comprising the following steps:

[0066] (1) 20.0 g of melamine and 0.3 g of aluminum foil were placed in a high-temperature tube furnace and reacted at 1200°C for 2 h under a nitrogen atmosphere. Then it was immersed in 60 mL of 4.0 mol / L hydrochloric acid solution at 50°C for 12 h, washed with deionized water and dried to obtain a nitrogen-doped bamboo-like carbon nanotube material. The SEM image of the prepared nitrogen-doped bamboo-like carbon nanotube is shown in -1 ; Figure 7

[0067] (2) 0.05 g of the nitrogen-doped bamboo-like carbon nanotube material, 0.15 g of thioacetamide, 0.25 g of sodium molybdate and 0.04 g of urea were dispersed in a water and N,N-dimethylformamide mixed solvent with a water volume content of 15%, and reacted at 200°C for 20 h. After washing with deionized water and drying, the product was reacted in a hydrogen and argon mixed gas with a hydrogen volume percentage of 5% at 700°C for 3 h to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube composite material. The SEM image of the product is shown in Figure 8 , and the TEM image is shown in Figure 9 , from which it can be seen that the molybdenum disulfide nanosheets are uniformly distributed on the surface of the nitrogen-doped bamboo-like carbon nanotube and have a hollow bamboo-like structure; and the XRD image of the product is shown in Figure 10 , from which the characteristic diffraction peaks of molybdenum disulfide can be seen;

[0068] ​(3) 0.1 g of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube material was mixed with 0.25 g of sulfur powder, and then transferred into a polytetrafluoroethylene vial filled with argon. The mixture was reacted at 150°C for 36 h under an argon atmosphere to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube material / sulfur composite. The SEM image thereof is shown in FIG. 6, the TEM image thereof is shown in FIG. 7, and the XRD image thereof is shown in FIG. 8. As can be seen from the images, the sulfur was uniformly loaded on the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube, and the molybdenum disulfide nanosheets were uniformly distributed on the outer layer of the nitrogen-doped bamboo-like carbon nanotube. As can be seen from the XRD image, the characteristic diffraction peaks of molybdenum disulfide and sulfur were observed. Figure 11 Figure 12 Figure 13

[0069] Example 4

[0070] A method for preparing a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube / sulfur composite, comprising the following steps:

[0071] (1) 20.0 g of melamine and 0.4 g of aluminum foil were placed in a high-temperature tube furnace and reacted at 1100°C for 3 h under a nitrogen atmosphere. Then, the product was immersed in a 60 mL 6.0 mol / L phosphoric acid solution at 65°C for 6 h, washed with deionized water, and dried to obtain a nitrogen-doped bamboo-like carbon nanotube material. -1

[0072] (2) 0.05 g of the nitrogen-doped bamboo-like carbon nanotube material, 0.25 g of thioacetamide, 0.35 g of sodium molybdate, and 0.08 g of urea were dispersed in a water and ethylene glycol mixed solvent with a water volume content of 30%, and reacted at 220°C for 12 h. After washing with deionized water and drying, the product was reacted at 800°C for 2 h in a hydrogen atmosphere with a hydrogen volume percentage of 5% to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube composite.

[0073] (3) 0.1 g of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube material was mixed with 0.3 g of sulfur powder, and then transferred into a polytetrafluoroethylene vial filled with argon. The mixture was reacted at 170°C for 12 h under an argon atmosphere to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube material / sulfur composite. The SEM image thereof is shown in FIG. 10, and as can be seen from the image, the sulfur was uniformly loaded on the nanotube. Figure 14

[0074] Example 5

[0075] A method for preparing a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon nanotube / sulfur composite, comprising the following steps:

[0076] ​​​​​(1) 20.0 g of melamine and 0.5 g of aluminum foil were placed in a high-temperature tube furnace and reacted at 900°C for 4 h under a nitrogen atmosphere. Then, it was immersed in 60 mL of 8.0 mol / L sulfuric acid solution and reacted at 80°C for 2 h, washed with deionized water and dried to obtain a nitrogen-doped bamboo-like carbon fiber tube material; -1

[0077] (2) 0.05 g of the nitrogen-doped bamboo-like carbon fiber tube material, 0.35 g of thioacetamide, 0.5 g of sodium molybdate and 0.1 g of urea were dispersed in a water and dimethyl sulfoxide mixed solvent with a water volume content of 45%, and reacted at 240°C for 6 h. After washing with deionized water and drying, it was reacted at 900°C for 1 h in a hydrogen atmosphere with a hydrogen volume percentage of 5% to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube composite material;

[0078] (3) 0.1 g of the molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube material was uniformly mixed with 0.35 g of sulfur powder, transferred to an argon-filled polytetrafluoroethylene vial, and reacted at 185°C for 6 h under an argon atmosphere to obtain a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube material / sulfur composite material. The SEM image thereof is shown in Figure 15 From the figure, it can be seen that the sulfur is uniformly loaded on the nanotube.

[0079] Comparative Example 1

[0080] 20.0 g of melamine and 0.5 g of iron foil, nickel foil or cobalt foil were placed in a high-temperature tube furnace and reacted at 1100°C for 4 h under a nitrogen atmosphere. Then, it was immersed in 60 mL of 5.0 mol / L sulfuric acid solution and reacted at 80°C for 2 h, washed with deionized water and dried to obtain a nitrogen-doped carbon nanotube material. The SEM image thereof is shown in -1 Figures 16-18 From the figure, it can be seen that the diameter of the nanotube is small, not bamboo-shaped, and uneven in thickness.

[0081] Application Example 1

[0082] Application of a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material in a lithium-sulfur battery

[0083] ​​The final product obtained in Example 3, molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / sulfur composite material, was used as the positive electrode active material for lithium-sulfur batteries. It was mixed with acetylene black and polyvinylidene fluoride (PVDF) in a weight ratio of 7.5:1.5:1, and prepared into a uniform slurry using N-methylpyrrolidone (NMP) as a solvent. The slurry was coated onto aluminum foil, and the resulting coating was transferred to an oven and dried at 60°C for 6 hours. Then, the sample was transferred to a vacuum drying oven and dried at 60°C for 12 hours. It was then crushed and cut into pieces using a tablet press. The lithium sheet was used as the counter electrode, and the electrolyte was a 1M mixed organic solvent containing lithium bis(trifluoromethanesulfonyl)imide (LITFSI). The mixed organic solvent was a mixture of 1,3-dioxolane (DOL) and dimethyl ether (DME) in a volume ratio of 1:1. 2% LiNO3 was added as an electrolyte additive. A polypropylene membrane (Celgard 240) was used as the battery separator. The lithium-sulfur battery was assembled under an argon atmosphere.

[0084] The charge-discharge performance of the obtained lithium-sulfur battery cathode material was tested using a battery tester at 0.2Ag. -1 The results of the cyclic stability test at current density are attached. Figure 19 As shown, at 1.0Ag -1 The results of the cyclic stability test at current density are attached. Figure 20 As shown in the figure, the molybdenum disulfide nanosheets / nitrogen-doped bamboo-like carbon fiber tubes / lithium-sulfur battery exhibits good cycle stability at 0.2 Ag. -1 After 100 cycles at current density, the specific capacity of the positive electrode reaches 655 mAh g. -1 In 1.0Ag -1 After 500 cycles at the current density, the specific capacity of the positive electrode is still as high as 403 mAh g. -1 .

[0085] The above detailed description of a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material, its preparation method, lithium-sulfur battery cathode, and lithium-sulfur battery, as well as the lithium-sulfur battery itself, is illustrative rather than limiting. Several embodiments can be listed within the defined scope. Therefore, variations and modifications that do not depart from the overall concept of the present invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a molybdenum disulfide nanosheet / nitrogen-doped bamboo-like carbon fiber tube / sulfur composite material, characterized in that, The preparation method comprises the following steps: (1) mixing melamine and aluminum, reacting at 900-1500℃ for 0.5-4h under the protection of inert gas, immersing the obtained reaction product in inorganic acid solution for 2-24h, washing and drying to obtain nitrogen-doped bamboo-shaped carbon fiber tube material; (2) dispersing the nitrogen-doped bamboo-shaped carbon fiber tube material, thioacetamide, sodium molybdate and urea in a solvent, carrying out solvothermal reaction, calcining the obtained reaction product in a reducing atmosphere to obtain molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube material; (3) fumigating the molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube material with sulfur to obtain molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube / sulfur composite material.

2. The production method according to claim 1, characterized by, In step (1), the amount ratio of melamine to aluminum is 20g:(0.1-0.5)g.

3. The preparation method according to claim 1, characterized in that, In step (1), the inorganic acid is at least one of sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and the concentration of the solution thereof is 1 to 8 mol / L -1 .

4. The method of claim 1, wherein, In step (2), the amount ratio of the nitrogen-doped bamboo-shaped carbon fiber tube material to thioacetamide, sodium molybdate and urea is 0.05g:(0.05-0.35)g:(0.08-0.5)g:(0.01-0.1)g. In step (2), the solvent is a mixed solvent of water and any one or more of isopropyl alcohol, ethylene glycol, N,N-dimethylformamide or dimethyl sulfoxide, wherein the volume percentage of water in the mixed solvent is 3%-45%.

5. The preparation method according to claim 1, characterized in that, In step (2), the solvothermal reaction is carried out at 160-240℃ for 6-36h, the calcination is carried out at 500-900℃ for 1-5h, and the reducing atmosphere is a mixed gas of hydrogen and argon, wherein the volume percentage of hydrogen is 3-10%.

6. The method of claim 1, wherein, In step (3), the heating and fumigation with sulfur are carried out at 125-185℃ for 6-48h, and the mass ratio of molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube to sulfur powder is 1:1.5-3.

5.

7. The preparation method according to claim 1, characterized in that, 8. The molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube / sulfur composite material prepared by the preparation method of any one of claims 1-7. The molybdenum disulfide nanosheet / nitrogen-doped bamboo-shaped carbon fiber tube / sulfur composite material of claim 8 is used as an active material.

9. A lithium-sulfur battery positive electrode, characterized by, The lithium-sulfur battery uses the lithium-sulfur battery positive electrode of claim 9 as the positive electrode.

10. A lithium-sulfur battery, characterized by, ​

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