Preparation method of nitrogen-doped carbon loaded nitrogen-doped molybdenum disulfide nanocrystals / separator

Abstract

The application discloses a preparation method of nitrogen-doped carbon loaded nitrogen-doped molybdenum disulfide nanocrystal / separator. The nitrogen-doped carbon loaded nitrogen-doped molybdenum disulfide nanocrystal is prepared by one-step calcination, and is covered on a lithium-sulfur battery separator by vacuum filtration to form the nitrogen-doped carbon loaded nitrogen-doped molybdenum disulfide nanocrystal / separator. The nitrogen-doped carbon can improve the overall conductivity of the material, and physically blocks and chemically adsorbs polysulfides. In addition, the nitrogen-doped molybdenum disulfide nanocrystal has an ultra-small size, and the introduction of nitrogen doping can provide rich edge active sites, catalyze the conversion of polysulfides and induce the generation of final product lithium sulfide, thereby significantly optimizing the battery reaction kinetics process. The nitrogen-doped carbon loaded nitrogen-doped molybdenum disulfide nanometer crystal / separator prepared by the method has the advantages of simple preparation, high catalytic activity of the nitrogen-doped molybdenum disulfide nanocrystal, effective inhibition of the shuttle effect of polysulfides, and improvement of the cycle stability, coulombic efficiency and rate performance of the lithium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the field of chemical battery technology, specifically relating to a method for preparing nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / separators in lithium-sulfur batteries. Background Technology

[0002] In recent years, the depletion of fossil fuels and the aggravation of environmental pollution have become two major challenges restricting the sustainable development of society. To address these two crises, renewable and clean energy sources such as wind, solar, and tidal power have entered a phase of rapid development and will gradually replace fossil fuels as the dominant energy source in my country and the world in the near future. However, most clean energy sources are intermittent and are subject to external factors such as weather, climate, or geographical location, making continuous power generation impossible. Therefore, developing electrochemical energy storage devices with high energy density and cycle stability for storing electrical energy is crucial for achieving efficient energy utilization.

[0003] Since its commercialization in 1991, lithium-ion batteries have undergone extensive research over the past 30 years, continuously achieving breakthroughs in power density and energy density. They are now widely used in portable electronic devices, aerospace, and electric vehicles. After years of research, the energy density of lithium-ion batteries has approached its achievable limit (300~350 Wh / kg). -1 However, these current technologies fall short of meeting the demands of technological advancements for high-energy-density energy storage devices, thus necessitating the development of a new generation of battery systems with high specific capacity and energy density. Lithium-sulfur batteries utilize elemental sulfur as the positive electrode and metallic lithium as the negative electrode; the conversion between chemical and electrical energy originates from the redox reaction between elemental sulfur and lithium ions. Compared to lithium-ion batteries, lithium-sulfur batteries possess a higher theoretical specific capacity and energy density (1675 mAh g⁻¹). -1 2600 Wh kg -1 Sulfur is an abundant element on Earth (~2.9%) and is environmentally friendly, making it a promising candidate to replace lithium-ion batteries as the next generation of electrochemical energy storage devices. However, due to the unique solid-to-liquid (Li₂S₈) transition of lithium-sulfur batteries... x The reaction mechanism of Li2S (4≤x≤8) → solid involves soluble polysulfide intermediates generated during charging and discharging shuttling between the positive and negative electrodes. In addition to direct reactions with the metallic lithium at the negative electrode, long-chain and short-chain polysulfides also undergo side reactions with each other, leading to corrosion of the lithium negative electrode and loss of active materials, which reduces the battery's capacity and cycle stability.

[0004] Molybdenum disulfide (Mo2S) is a typical two-dimensional layered metal sulfide, consisting of two sulfur (S) atomic layers and one molybdenum (Mo) atomic layer, interconnected by van der Waals forces. Due to its unique electronic structure, tunable surface properties, abundant reserves, and low cost, Mo2S has been widely studied in energy storage devices and catalysis. However, Mo2S also has some drawbacks, such as poor intrinsic conductivity and layer stacking that masks numerous adsorption and catalytic active sites, severely limiting its further applications. Extensive research has been conducted to increase the number of active sites in Mo2S. Pan et al. prepared a layered structure of molybdenum disulfide-carbon-molybdenum disulfide nanotubes. The insertion of carbon layers not only improved the conductivity of molybdenum disulfide but also expanded the interlayer spacing, exposing more in-plane active sites, which enhanced the adsorption and catalytic activity for polysulfides (Pan Y, Gong L, Cheng X, et al. Layer Spacing Enlarged MoS2 Superstructural Nanotubes with Further Enhanced Catalysis and Immobilization for Li-S Batteries[J]. ACS Nano,2020, 14(5): 5917-5925.). Liu et al. prepared a cobalt-doped molybdenum disulfide using a one-step hydrothermal method. The introduction of cobalt atoms and sulfur-rich holes enhanced electron transfer and catalytic activity, thereby effectively improving the adsorption of polysulfides by molybdenum disulfide and the redox reaction kinetics of the battery (Liu W, Luo C, Zhang S, et al. Cobalt-Doping of Molybdenum Disulfide for Enhanced Catalytic Polysulfide Conversion in Lithium-Sulfur Batteries[J]. ACSNano, 2021, 15(4):7491-7499.). However, even so, there is still much room for improvement in the application of molybdenum disulfide in lithium-sulfur batteries. Summary of the Invention

[0005] In order to enrich the active sites of molybdenum disulfide and improve its adsorption and catalytic performance for polysulfides, thereby improving the electrochemical performance of lithium-sulfur batteries, this invention mainly provides a method for preparing nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / separators for lithium-sulfur batteries.

[0006] A method for preparing nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / separators includes the following steps: Step 1: Dissolve dicyandiamine and ammonium tetrathiomolybdate in N,N-dimethylformamide, stir until completely dissolved and mixed evenly, evaporate the solvent in a water bath at 70 ± 5 ℃, and grind the resulting solid product to obtain a dicyandiamine / ammonium tetrathiomolybdate mixture powder. Step 2: Under an inert atmosphere, the mixture powder of dicyandiamine / ammonium tetrathiomolybdate is calcined at high temperature to obtain nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals. Step 3: Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals are added to a water / ethanol mixture and sonicated to form a uniformly dispersed mixture. The mixture is then uniformly coated onto the lithium-sulfur battery separator using a vacuum filtration method. After drying, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / separator are obtained.

[0007] In step 1, the mass ratio of dicyandiamine to ammonium tetrathiomolybdate is 25:1. This ratio ensures that the molybdenum disulfide nanocrystals in the final product are uniformly loaded on nitrogen-doped carbon.

[0008] In step 2, the dicyandiamine / ammonium tetrathiomolybdate mixture powder is calcined at high temperature under an inert atmosphere. The calcination temperature is 700~800 ℃, the time is 2 h, and the heating rate is 2 ℃ min. -1 Under these conditions, it is possible to ensure that dicyandiamine and ammonium tetrathiomolybdate are completely decomposed into nitrogen-doped carbon and nitrogen-doped molybdenum disulfide nanocrystals.

[0009] In step 3, the volume ratio of water to ethanol in the water / ethanol mixed solution is 1:1~2. This is because of the hydrophobic properties of commercial lithium-sulfur battery separators. Adding ethanol can ensure that the separator is fully wetted, which is beneficial for vacuum filtration.

[0010] In step 3, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals are added to a water / ethanol mixed solution and sonicated to form a uniformly dispersed mixture with a concentration of 5 mg / mL. -1 At this concentration, nitrogen-doped carbon-loaded nitrogen-doped molybdenum disulfide nanocrystals can be uniformly dispersed and are not easily deposited.

[0011] In step 3, the areal loading of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals on the membrane is controlled to be 0.1–0.3 mg cm⁻¹ by controlling the volume of the mixing system required for a single vacuum filtration. -2 This loading capacity ensures that polysulfides are blocked between the cathode and the separator and are effectively catalyzed into the final product lithium sulfide without excessively reducing the energy density of the battery.

[0012] In step 3, the lithium-sulfur battery separator can be a commercially available PP separator.

[0013] Compared with the prior art, the present invention has the following advantages: This invention obtains nitrogen-doped molybdenum disulfide nanocrystals by dissolving and mixing dicyandiamine and ammonium tetrathiomolybdate, followed by high-temperature calcination. A nitrogen-doped molybdenum disulfide nanocrystal / separator for lithium-sulfur batteries is then prepared using a simple vacuum filtration method. On one hand, nitrogen doping enhances the material's conductivity while providing physical barrier and chemical adsorption for polysulfides. On the other hand, the ultra-small size (2-5 nm) of the nitrogen-doped molybdenum disulfide nanocrystals and the nitrogen-doped characteristics provide numerous active sites for the catalytic conversion of polysulfides, optimizing the redox kinetics of the battery system. Therefore, the shuttle effect is effectively suppressed in the presence of the nitrogen-doped molybdenum disulfide nanocrystal / separator, significantly improving the capacity, cycle stability, and rate performance of the lithium-sulfur battery. The preparation process of this invention is simple, the reaction is easily controlled, and the resulting product shows great promise for improving the performance of lithium-sulfur batteries. Attached Figure Description

[0014] Figure 1 This is a scanning electron microscope image of the nitrogen-doped molybdenum disulfide nanocrystals prepared in Example 1.

[0015] Figure 2 This is a transmission electron microscope (TEM) image of nitrogen-doped molybdenum disulfide nanocrystals prepared in Example 1.

[0016] Figure 3 This is a high-resolution transmission electron microscope image of nitrogen-doped molybdenum disulfide nanocrystals prepared in Example 1.

[0017] Figure 4 The image shows a scanning electron microscope (SEM) image of the surface of the nitrogen-doped molybdenum disulfide nanocrystal / membrane prepared in Example 1.

[0018] Figure 5 The image shows a scanning electron microscope (SEM) image of the cross-section of the nitrogen-doped molybdenum disulfide nanocrystals / membrane prepared in Example 1.

[0019] Figure 6 Scanning electron microscope image of molybdenum disulfide prepared for comparison.

[0020] Figure 7 Scanning electron microscope image of the surface of the molybdenum disulfide / diaphragm prepared for comparison.

[0021] Figure 8 Scanning electron microscope (SEM) image of the cross-section of the molybdenum disulfide / diaphragm prepared for comparison.

[0022] Figure 9 The graph shows the long-cycle charge-discharge performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 1 for lithium-sulfur batteries at a rate of 0.5 C.

[0023] Figure 10The rate performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 1 for lithium-sulfur batteries is shown in the figure.

[0024] Figure 11 The graph shows the long-cycle charge-discharge performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 2 for lithium-sulfur batteries at a rate of 0.5 C.

[0025] Figure 12 The rate performance diagram of the nitrogen-doped molybdenum disulfide nanocrystal / separator prepared in Example 2 for lithium-sulfur batteries is shown.

[0026] Figure 13 The graph shows the long-cycle charge-discharge performance of a molybdenum disulfide / separator prepared for comparison in a lithium-sulfur battery at a rate of 0.5 C.

[0027] Figure 14 The rate performance of the molybdenum disulfide / separator prepared for comparison in lithium-sulfur batteries is shown in the figure. Detailed Implementation

[0028] This invention first involves dissolving and precipitating dicyandiamine and ammonium tetrathiomolybdate to ensure thorough mixing, followed by high-temperature calcination. Dicyandiamine decomposes into nitrogen-doped carbon, and ammonium tetrathiomolybdate decomposes into nitrogen-doped molybdenum disulfide nanocrystals. Finally, a simple vacuum filtration method is used to uniformly coat the nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals onto the lithium-sulfur battery separator, resulting in a nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystal / separator.

[0029] I. The preparation process of the present invention will be described in detail below with reference to the embodiments.

[0030] Example 1 1) Preparation of dicyandiamine / ammonium tetrathiomolybdate mixture: Weigh 10 g of dicyandiamine and 400 mg of ammonium tetrathiomolybdate and dissolve them in 100 mL of N,N-dimethylformamide. Stir until completely dissolved and mixed evenly. Evaporate the solvent in a water bath at 70 ± 5 ℃. Grind the resulting solid product to obtain dicyandiamine / ammonium tetrathiomolybdate mixture powder.

[0031] 2) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals: Under an inert atmosphere, a mixture of dicyandiamine / ammonium tetrathiomolybdate powder was calcined at high temperature. The calcination temperature was set at 800 °C for 2 h, and the heating rate was 2 °C / min. -1 Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were obtained.

[0032] 3) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membrane: 25 mg of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were added to 50 mL of a 1:1 water / ethanol mixture. The mixture was sonicated to form a uniformly dispersed system. 5 mL of the mixture was transferred using a pipette and vacuum filtered to uniformly coat the lithium-sulfur battery membrane, with an areal loading of approximately 0.2 mg / cm³. -2 After drying at 60 °C for 12 h, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membranes were obtained.

[0033] Example 2 1) Preparation of dicyandiamine / ammonium tetrathiomolybdate mixture: Weigh 10 g of dicyandiamine and 400 mg of ammonium tetrathiomolybdate and dissolve them in 100 mL of N,N-dimethylformamide. Stir until completely dissolved and mixed evenly. Evaporate the solvent in a water bath at 70 ± 5 ℃. Grind the resulting solid product to obtain dicyandiamine / ammonium tetrathiomolybdate mixture powder.

[0034] 2) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals: Under an inert atmosphere, a mixture of dicyandiamine / ammonium tetrathiomolybdate powder was calcined at a high temperature of 700 °C for 2 h with a heating rate of 2 °C / min. -1 Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were obtained.

[0035] 3) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membrane: 25 mg of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were added to 50 mL of a 1:1 water / ethanol mixture. The mixture was sonicated to form a uniformly dispersed system. 5 mL of the mixture was transferred using a pipette and vacuum filtered to uniformly coat the lithium-sulfur battery membrane, with an areal loading of approximately 0.2 mg / cm³. -2 After drying at 60 °C for 12 h, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membranes were obtained.

[0036] Example 3 1) Preparation of dicyandiamine / ammonium tetrathiomolybdate mixture: Weigh 10 g of dicyandiamine and 400 mg of ammonium tetrathiomolybdate and dissolve them in 100 mL of N,N-dimethylformamide. Stir until completely dissolved and mixed evenly. Evaporate the solvent in a water bath at 70 ± 5 ℃. Grind the resulting solid product to obtain dicyandiamine / ammonium tetrathiomolybdate mixture powder.

[0037] 2) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals: Under an inert atmosphere, a mixture of dicyandiamine / ammonium tetrathiomolybdate powder was calcined at high temperature. The calcination temperature was set at 800 °C for 2 h, and the heating rate was 2 °C / min.-1 Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were obtained.

[0038] 3) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / separator: 25 mg of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were added to 50 mL of a water / ethanol (1:2) mixture. The mixture was sonicated to form a uniformly dispersed system. 5 mL of the mixture was transferred using a pipette and vacuum filtered to uniformly coat the lithium-sulfur battery separator, with an areal loading of approximately 0.2 mg / cm³. -2 After drying at 60 °C for 12 h, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membranes were obtained.

[0039] Example 4 1) Preparation of dicyandiamine / ammonium tetrathiomolybdate mixture: Weigh 10 g of dicyandiamine and 400 mg of ammonium tetrathiomolybdate and dissolve them in 100 mL of N,N-dimethylformamide. Stir until completely dissolved and mixed evenly. Evaporate the solvent in a water bath at 70 ± 5 ℃. Grind the resulting solid product to obtain dicyandiamine / ammonium tetrathiomolybdate mixture powder.

[0040] 2) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals: Under an inert atmosphere, a mixture of dicyandiamine / ammonium tetrathiomolybdate powder was calcined at high temperature. The calcination temperature was set at 800 °C for 2 h, and the heating rate was 2 °C / min. -1 Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were obtained.

[0041] 3) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membrane: 25 mg of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were added to 50 mL of a 1:1 water / ethanol mixture. The mixture was sonicated to form a uniformly dispersed system. 2.5 mL of the mixture was transferred using a pipette and vacuum filtered to uniformly coat the lithium-sulfur battery membrane, with an areal loading of approximately 0.1 mg / cm³. -2 After drying at 60 °C for 12 h, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membranes were obtained.

[0042] Example 5 1) Preparation of dicyandiamine / ammonium tetrathiomolybdate mixture: Weigh 10 g of dicyandiamine and 400 mg of ammonium tetrathiomolybdate and dissolve them in 100 mL of N,N-dimethylformamide. Stir until completely dissolved and mixed evenly. Evaporate the solvent in a water bath at 70 ± 5 ℃. Grind the resulting solid product to obtain dicyandiamine / ammonium tetrathiomolybdate mixture powder.

[0043] 2) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals: Under an inert atmosphere, a mixture of dicyandiamine / ammonium tetrathiomolybdate powder was calcined at high temperature. The calcination temperature was set at 800 °C for 2 h, and the heating rate was 2 °C / min. -1 Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were obtained.

[0044] 3) Preparation of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membrane: 25 mg of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals were added to 50 mL of a 1:1 water / ethanol mixture. The mixture was sonicated to form a uniformly dispersed system. 7.5 mL of the mixture was transferred using a pipette and vacuum filtered to uniformly coat the lithium-sulfur battery separator, with an areal loading of approximately 0.3 mg / cm³. -2 After drying at 60 °C for 12 h, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / membranes were obtained.

[0045] The nitrogen-doped molybdenum disulfide nanocrystals prepared in the above five examples exhibit consistent morphology, and their microstructure and the morphology of the fabricated separators are shown in the figure below. When the nitrogen-doped molybdenum disulfide nanocrystals / separator are used in a lithium-sulfur battery, the first-cycle discharge capacity at 0.5C rate can reach 10¹⁴ mAh g⁻¹. -1 Its rate performance is also excellent.

[0046] Figure 1 The image shows a scanning electron microscope (SEM) image of nitrogen-doped molybdenum disulfide nanocrystals prepared in Example 1. The nitrogen-doped carbon is clearly visible as a network structure, but it cannot be observed due to the small size of the nitrogen-doped molybdenum disulfide nanocrystals.

[0047] Figure 2 The image shows a transmission electron microscope (TEM) image of nitrogen-doped molybdenum disulfide nanocrystals prepared in Example 1. The image clearly shows that the nitrogen-doped carbon forms a network structure, while the nitrogen-doped molybdenum disulfide nanocrystals are not visible.

[0048] Figure 3 The image shows a high-resolution transmission electron microscope (TEM) image of nitrogen-doped molybdenum disulfide nanocrystals prepared in Example 1. The image shows that the nitrogen-doped molybdenum disulfide nanocrystals are uniformly loaded on nitrogen-doped carbon with a size of about 2-5 nm and a crystal plane spacing of 0.26 nm, corresponding to the (100) crystal plane of molybdenum disulfide.

[0049] Figure 4 The image shows a scanning electron microscope (SEM) image of the nitrogen-doped molybdenum disulfide nanocrystal / membrane prepared in Example 1. As can be seen from the image, the membrane surface has been uniformly covered and there are no obvious pore structures.

[0050] Figure 5The image shows a scanning electron microscope (SEM) image of the cross-section of the nitrogen-doped molybdenum disulfide nanocrystals / membrane prepared in Example 1. The thickness of the modified layer in the image is approximately 1.84 μm.

[0051] Figure 9 The graph shows the long-cycle charge-discharge performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 1 for lithium-sulfur batteries at a rate of 0.5 C. The first-cycle discharge specific capacity can reach 10¹⁴ mAh g⁻¹. -1 After 500 cycles, the specific capacity is still 645 mAh g. -1 The capacity retention rate is approximately 63.6%.

[0052] Figure 10 The graph shows the rate performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 1 for lithium-sulfur batteries. At current densities of 0.2 C, 0.5 C, 1 C, 2 C, and 3 C, the specific capacities reached were 1253, 1010, 853, 728, and 649 mAh g⁻¹, respectively. -1 This indicates that nitrogen-doped molybdenum disulfide nanocrystals / separator significantly improve the rate performance of lithium-sulfur batteries.

[0053] Figure 11 The graph shows the long-cycle charge-discharge performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 2 for lithium-sulfur batteries at a rate of 0.5 C. The first cycle releases 1018 mAh g⁻¹. -1 The specific capacity remains at 645 mAh g after 500 cycles. -1 The capacity retention rate was 63.3%.

[0054] Figure 12 The graph shows the rate performance of the nitrogen-doped molybdenum disulfide nanocrystals / separator prepared in Example 2 for lithium-sulfur batteries. The specific capacities at 0.2 C, 0.5 C, 1 C, 2 C, and 3 C are 1196, 991, 863, 734, and 635 mAh g⁻¹, respectively. -1 This also demonstrates that nitrogen-doped molybdenum disulfide nanocrystals / separators help improve the rate performance of lithium-sulfur batteries.

[0055] Comparative Example 1) Preparation of molybdenum disulfide: Ammonium tetrathiomolybdate powder was calcined at high temperature under an inert atmosphere. The calcination temperature was set at 800 °C for 2 h, and the heating rate was 2 °C / min. -1 Molybdenum disulfide was obtained.

[0056] 2) Preparation of molybdenum disulfide / membrane: 25 mg of molybdenum disulfide was added to 50 mL of a 1:1 water / ethanol mixture. The mixture was sonicated to form a uniformly dispersed system. 5 mL of this mixture was transferred using a pipette and vacuum filtered to uniformly coat the lithium-sulfur battery separator, with an areal loading of approximately 0.2 mg / cm³. -2 After drying at 60 °C for 12 h, molybdenum disulfide / diaphragm was obtained.

[0057] Figure 6 The image shows a scanning electron microscope (SEM) image of molybdenum disulfide prepared for comparison. It can be seen from the image that pure molybdenum disulfide is a relatively thick sheet-like structure with a diameter of 100 nm, indicating that there is severe stacking between the layers of molybdenum disulfide.

[0058] Figure 7 The image shows a scanning electron microscope (SEM) image of the molybdenum disulfide / diaphragm surface prepared for comparison. The image shows that the molybdenum disulfide is not uniformly distributed on the diaphragm surface.

[0059] Figure 8 The image shows a scanning electron microscope (SEM) image of the cross-section of the molybdenum disulfide / diaphragm prepared for comparison. The thickness of the molybdenum disulfide modified layer is approximately 1.46 μm.

[0060] Figure 13 The graph shows the long-cycle charge-discharge performance of the molybdenum disulfide / separator prepared for comparison in a lithium-sulfur battery at a 0.5 C rate. The first-cycle discharge capacity of the battery is 970 mAh g. -1 After 500 cycles, the capacity is still 645 mAh g. -1 The capacity retention rate was approximately 46%. In comparison, the lithium-sulfur battery assembled with nitrogen-doped molybdenum disulfide nanocrystals / separator exhibited higher specific capacity and better cycle stability.

[0061] Figure 14 The rate performance diagram of the molybdenum disulfide / separator prepared for comparison in lithium-sulfur batteries shows that it can achieve 1109, 718, 564, 505, and 475 mAh g⁻¹ at 0.2 C, 0.5 C, 1 C, 2 C, and 3 C, respectively. -1 The specific capacity of the nitrogen-doped molybdenum disulfide nanocrystal / separator demonstrates that it has superior rate performance when applied to lithium-sulfur batteries.

Claims

1. A method for preparing a nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystal / separator, characterized in that, Includes the following steps: Step 1: Dicyandiamine and ammonium tetrathiomolybdate are placed in N,N-dimethylformamide and stirred until completely dissolved. The solvent in the mixed solution is evaporated under water bath conditions of 70 ± 5 ℃. The resulting product is ground to obtain a mixture powder of dicyandiamine / ammonium tetrathiomolybdate. Step 2: Under an inert atmosphere, the mixture powder of dicyandiamine / ammonium tetrathiomolybdate is calcined at high temperature to obtain nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals. Step 3: Nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals are added to a water / ethanol mixture and sonicated to form a uniformly dispersed mixture. The mixture is then uniformly coated onto the lithium-sulfur battery separator using a vacuum filtration method. After drying, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals / separator are obtained. In step 1, the mass ratio of dicyandiamine to ammonium tetrathiomolybdate is 25:

1. In step 2, the dicyandiamine / ammonium tetrathiomolybdate mixture powder is calcined at high temperature under an inert atmosphere. The calcination temperature is 700~800 ℃, the time is 2 h, and the heating rate is 2 ℃ min. -1 .

2. The method as described in claim 1, characterized in that, In step 3, the volume ratio of water to ethanol in the water / ethanol mixed solution is 1:1~2.

3. The method as described in claim 1, characterized in that, In step 3, nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals are added to a water / ethanol mixed solution and sonicated to form a uniformly dispersed mixture with a concentration of 5 mg / mL. -1 .

4. The method as described in claim 1, characterized in that, In step 3, the areal loading of nitrogen-doped carbon-supported nitrogen-doped molybdenum disulfide nanocrystals on the membrane is controlled to be 0.1~0.3 mg / cm³ by controlling the volume of the mixing system required for a single vacuum filtration. -2 .

5. The method as described in claim 1, characterized in that, In step 3, the lithium-sulfur battery separator uses commercially available PP separator.

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