Carbon nanotube-sulfur composite material embedded with quantum dot nitride and preparation method thereof

Abstract

The application discloses a carbon nanotube-sulfur composite material embedded with quantum dot nitride and a preparation method thereof. The carbon nanotube-sulfur composite material is prepared by hot melting and compounding of carbon nanotubes embedded with quantum dot nitride and sulfur. The quantum dot nitride is quantum dot tungsten nitride or a compound of quantum dot tungsten nitride and quantum dot molybdenum nitride. The carbon nanotube-sulfur composite material embedded with quantum dot nitride synthesized by the application can realize the functional synergistic effect of conductive material and catalytic material, improve the conductivity and catalytic capacity of the positive electrode material, inhibit the shuttle of polysulfide ions, and significantly improve the electrochemical performance of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to a carbon nanotube-sulfur composite material with embedded quantum dot nitrides and its preparation method, belonging to the field of functional materials. Background Technology

[0002] Lithium-sulfur batteries are a type of battery system with high energy density, boasting a theoretical energy density of up to 2600 Wh / kg, far exceeding that of existing lithium-ion battery systems. Because elemental sulfur possesses advantages such as high theoretical specific capacity (1675 mAh / g), low price, abundant reserves, and relatively environmental friendliness, lithium-sulfur batteries have become a hot topic in battery research. Typically, lithium-sulfur batteries use elemental sulfur or sulfur-based composite materials as the positive electrode and metallic lithium as the negative electrode.

[0003] Currently, lithium-sulfur batteries also have some inherent defects: 1) Elemental sulfur is an insulator of electrons and ions at room temperature, and this insulating property leads to low utilization of sulfur active materials and poor rate performance; 2) During charging and discharging, lithium polysulfides that are easily soluble in the electrolyte are generated inside the battery, forming the so-called "shuttle effect". The "shuttle effect" leads to irreversible loss of sulfur active materials, poor electrochemical reversibility, and rapid capacity decay, resulting in a short battery cycle life.

[0004] On the one hand, materials such as tungsten nitride and tungsten sulfide possess certain catalytic and chemisorption properties. However, ordinary material surfaces have only a limited number of polysulfide adsorption sites, while quantized materials not only avoid material stacking but also expose more active sites due to quantum size effects, effectively improving the chemisorption and catalytic conversion capabilities of polysulfides. On the other hand, carbon materials have a large specific surface area and excellent conductivity. To overcome the limitations of a single material composition, a strategy of using multiple material components to form composite materials can achieve synergistic effects, improve the conductivity and electrolyte wetting ability of the cathode material, suppress polysulfide ion shuttle, and significantly improve the electrochemical performance of lithium-sulfur batteries. Summary of the Invention

[0005] The purpose of this invention is to address some inherent defects in lithium-sulfur batteries. This invention proposes a carbon nanotube-sulfur composite material with embedded quantum dot nitrides. The technical solution for achieving this invention is as follows: A carbon nanotube-sulfur composite material with embedded quantum dot nitrides is formed by thermally melting carbon nanotubes with embedded quantum dot nitrides and sulfur.

[0006] Specifically, the quantum dot nitride is a quantum dot tungsten nitride or a compound of quantum dot tungsten nitride and quantum dot molybdenum nitride.

[0007] Specifically, the carbon nanotubes with embedded quantum dot nitrides are obtained by heat treatment of carbon nanotubes with embedded quantum dot oxides using ammonia.

[0008] Specifically, the carbon nanotubes with embedded quantum dot oxides are obtained by heat treatment in an inert gas with carbon nanotubes embedded with phosphotungstic acid or a mixture of phosphotungstic acid and phosphomolybdic acid.

[0009] Specifically, the carbon nanotubes with embedded quantum dot nitrides have a diameter of 1 to 2 nanometers and a length of 1 to 3 micrometers. The diameter of the quantum dot nitrides is greater than 0.8 nanometers and less than 1.4 nanometers.

[0010] A method for preparing a carbon nanotube-sulfur composite material with embedded quantum dot nitrides is characterized by: firstly, preparing a phosphotungstic acid solution of a certain concentration or a mixture of phosphotungstic acid and phosphomolybdic acid; then adding a certain mass of single-walled carbon nanotubes to the phosphotungstic acid solution or the mixture of phosphotungstic acid and phosphomolybdic acid, sonicating, and then allowing it to stand; then centrifuging, washing, filtering, and finally drying the single-walled carbon nanotubes to obtain carbon nanotubes embedded with phosphotungstic acid or a mixture of phosphotungstic acid and phosphomolybdic acid; heat-treating the carbon nanotubes embedded with phosphotungstic acid or the mixture of phosphotungstic acid and phosphomolybdic acid under inert gas conditions to obtain carbon nanotubes embedded with quantum dot oxides; heat-treating the carbon nanotubes embedded with quantum dot oxides under ammonia gas conditions to obtain carbon nanotubes embedded with quantum dot nitrides; and using a melting method to diffuse elemental sulfur into the carbon nanotubes embedded with quantum dot nitrides to form a carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride.

[0011] Specifically, the ultrasound session lasts 1 to 3 minutes, followed by a 24-hour rest period, and is repeated 3 times.

[0012] Specifically, the centrifugation, washing, and filtration of single-walled carbon nanotubes includes: centrifuging and washing the single-walled carbon nanotubes 5-10 times, and then washing and filtering them 3-5 times using a filter membrane.

[0013] Specifically, the heat treatment is carried out at a temperature of 600°C under inert gas conditions for 1-2 hours. Specifically, the heating treatment under ammonia gas conditions is carried out at a temperature of 600-800℃ for 2-4 hours.

[0014] The beneficial effects of this invention are that phosphotungstic acid, or a mixture of phosphotungstic acid and phosphomolybdic acid, is ultrasonically dispersed and filled into single-walled carbon nanotubes. Then, the phosphotungstic acid, or a mixture of phosphotungstic acid and phosphomolybdic acid, is washed away from the surface of the single-walled carbon nanotubes to obtain single-walled carbon nanotubes embedded with phosphotungstic acid, or a mixture of phosphotungstic acid and phosphomolybdic acid. Following oxidation and nitriding treatments, carbon nanotubes embedded with quantum dot nitrides are obtained. The carbon nanotube-sulfur composite material with embedded quantum dot nitrides synthesized in this invention possesses multiple advantages, including light weight, thin thickness, high efficiency in polysulfide interception, and good ion transport capabilities. By employing a strategy of using multiple material components to form a composite material, the carbon nanotube-sulfur composite material with embedded quantum dot nitrides synthesized in this invention can achieve synergistic effects, improve the conductivity and electrolyte wetting ability of the cathode material, suppress polysulfide ion shuttle, and significantly improve the electrochemical performance of lithium-sulfur batteries.

[0015] The carbon nanotube-sulfur composite material with embedded quantum dot nitrides for lithium-sulfur batteries described in this invention has a simple preparation process, safe reaction conditions, is easy to operate, and the reagents involved in the reaction have minimal environmental impact. It is suitable for large-scale production. Attached Figure Description

[0016] Figure 1 X-ray diffraction pattern of the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride prepared in Example 1; Figure 2 Transmission electron microscopy (TEM) image of the carbon nanotube composite material with embedded quantum dot tungsten nitride prepared in Example 1: Figure 3 The elemental distribution of C, W, and N in the carbon nanotube composite material with embedded quantum dot tungsten nitride prepared in Example 1 is shown in the diagram. Figure 4 The C, W, and N elemental energy spectrum of the carbon nanotube composite material with embedded quantum dot tungsten nitride prepared in Example 1 is shown below. Figure 5 The image shows a scanning electron microscope (SEM) image of the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride prepared in Example 1. Figure 6 The graph shows a comparison of the cycle life curves of the battery based on carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride prepared in Example 1 at a current density of 167.5 mAh / g. Figure 7 The results of stepped discharge tests of the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride and molybdenum nitride prepared in Example 2 at different current densities of 167.5 mA / g, 335 mA / g, 837.5 mA / g, 1675 mAh / g, and 3335 mA / g are shown. Figure 8The results of stepped discharge tests of the carbon nanotube-sulfur composite material battery with embedded quantum dot tungsten nitride and molybdenum nitride prepared in Example 3 at different current densities of 167.5 mA / g, 335 mA / g, 837.5 mA / g, 1675 mAh / g, and 3335 mA / g are presented. Detailed Implementation

[0017] Example 1 Preparation of carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride and electrode sheet: (1) First, prepare 10 mL of 30 mmol / L phosphotungstic acid solution, then add 50 mg of single-walled carbon nanotubes to the mixture, sonicate for 1 minute, let stand for 24 hours, and repeat 3 times. Centrifuge and wash the single-walled carbon nanotubes 10 times, then wash and filter them 3-5 times with a filter membrane, and dry them to obtain carbon nanotubes embedded with phosphotungstic acid.

[0018] (2) Carbon nanotubes with embedded phosphotungstic acid were treated at 600°C for 1 hour under inert gas conditions to obtain carbon nanotubes with embedded quantum dot tungsten oxide.

[0019] (3) Carbon nanotubes with embedded quantum dot tungsten oxide were treated at 700°C for 2 hours under ammonia gas conditions to obtain carbon nanotubes with embedded quantum dot tungsten nitride.

[0020] (4) Synthesis of carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride: 30 mg of carbon nanotubes with embedded quantum dot tungsten nitride were mixed with 70 mg of elemental sulfur, and the elemental sulfur was diffused onto the surface of the carbon nanotubes with embedded quantum dot tungsten nitride by melting method to form carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride.

[0021] In contrast, carbon nanotube-sulfur composite materials were also prepared following the same steps.

[0022] The carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride: Figure 1 This is an X-ray diffraction pattern. Figure 2 This is a transmission electron microscope (TEM) image of carbon nanotubes in quantum dot tungsten nitride. Figure 3 The image shows the elemental energy distribution of quantum dot tungsten nitride carbon nanotubes. Figure 4 This is the elemental energy spectrum of quantum dot tungsten nitride carbon nanotubes. (Example:) Figure 2 As shown, the carbon nanotubes have a diameter of 1-2 nanometers, while the diameter of the filler inside ranges from 0.8 nanometers to 1.4 nanometers. Figure 4 As shown, C, W, and N elements are uniformly distributed on the carbon paper. Figure 5 As shown, the elemental energy spectrum reveals the presence of C, W, and N.

[0023] (4) Preparation of sulfur electrode material: The carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride, acetylene black and PVDF prepared above are mixed in a weight ratio of 8:1:1, with N-methylpyrrolidone as a dispersant. The mixture is stirred thoroughly to make it uniform, rolled into sheets, and vacuum dried at 60°C for 10 hours for later use.

[0024] (5) Using the sulfur electrode material prepared above as the positive electrode, lithium metal as the negative electrode, and a carbon paper barrier layer supported on tungsten nitride, the electrolyte was prepared as anhydrous lithium nitrate with an additive of 0.1 mol / L, a mixed solution of 1,3-dioxane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and a 1.0 mol / L lithium di(trifluoromethanesulfonyl)imide solution. The lithium-sulfur battery was assembled in a glove box. The charge-discharge cycle life test results at a current density of 167.5 mA / g are as follows: Figure 6 As shown. For comparison, a lithium-sulfur battery using carbon nanotube-sulfur as the electrode material was assembled according to the above steps. The first-cycle discharge capacity using the carbon nanotube-sulfur composite material was 654.8 mAh / g. The highest discharge capacity of the lithium-sulfur battery using a carbon nanotube / sulfur composite material with embedded quantum dot tungsten nitride as the electrode material was 875.6 mAh / g. The highest discharge capacity of the lithium-sulfur battery using the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride as the electrode material was 1.34 times that of the lithium-sulfur battery using the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride as the electrode material. After 100 cycles, the highest discharge capacity of the lithium-sulfur battery was 491.9 mAh / g. The highest discharge capacity of the lithium-sulfur battery using the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride as the electrode material was 654.8 mAh / g. The highest discharge capacity of the lithium-sulfur battery using the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride as the electrode material was 1.32 times that of the lithium-sulfur battery using the carbon nanotube / sulfur composite material with embedded quantum dot tungsten nitride as the electrode material.

[0025] Example 2 Preparation of carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride and electrode sheet: (1) First, prepare 10 mL of 40 mmol / L phosphotungstic acid solution, then add 60 mg of single-walled carbon nanotubes to the mixture, sonicate for 1 minute, let stand for 24 hours, and repeat 3 times. Centrifuge and wash the single-walled carbon nanotubes 10 times, then wash and filter them 3-5 times with a filter membrane, and dry them to obtain carbon nanotubes embedded with phosphotungstic acid.

[0026] (2) Carbon nanotubes with embedded phosphotungstic acid were treated at 600°C for 2 hours under inert gas conditions to obtain carbon nanotubes with embedded quantum dot tungsten oxide.

[0027] (3) Carbon nanotubes with embedded quantum dot tungsten oxide were treated at 700°C for 4 hours under ammonia gas conditions to obtain carbon nanotubes with embedded quantum dot tungsten nitride.

[0028] (4) Synthesis of carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride: 60 mg of carbon nanotubes with embedded quantum dot tungsten nitride were mixed with 140 mg of elemental sulfur, and the elemental sulfur was diffused into the carbon nanotubes with embedded quantum dot tungsten nitride by melting method to form carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride.

[0029] In contrast, carbon nanotube-sulfur composite materials were also prepared following the same steps.

[0030] (4) Preparation of sulfur electrode material: The carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride, acetylene black and PVDF prepared above are mixed in a weight ratio of 8:1:1, with N-methylpyrrolidone as a dispersant. The mixture is stirred thoroughly to make it uniform, rolled into sheets, and vacuum dried at 60°C for 10 hours for later use.

[0031] (5) Using the sulfur electrode material prepared above as the positive electrode, lithium metal as the negative electrode, and a carbon paper barrier layer loaded with tungsten nitride, the electrolyte is anhydrous lithium nitrate with an additive of 0.1 mol / L, a mixed solution of 1,3-dioxane and ethylene glycol dimethyl ether prepared in a volume ratio of 1:1, and a 1.0 mol / L lithium di(trifluoromethanesulfonyl)imide solution. The mixture is then assembled into a lithium-sulfur battery in a glove box. As a comparison, a lithium-sulfur battery using carbon nanotube-sulfur composite material as the electrode material is assembled according to the above steps. The charge-discharge cycle life test results at different current densities of 167.5 mA / g, 335 mA / g, 837.5 mA / g, and 1675 mA / g are as follows: Figure 7 As shown, the lithium-sulfur battery using carbon nanotube-sulfur as the electrode material exhibits discharge capacities of 646.8 mAh / g, 650.5 mAh / g, 526 mAh / g, and 203.8 mAh / g at different current densities of 167.5 mA / g, 335 mA / g, 837.5 mA / g, and 1675 mA / g, respectively. The lithium-sulfur battery using a carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride as the electrode material exhibits discharge capacities of 894.2 mAh / g, 735.7 mAh / g, 611.7 mAh / g, and 513.8 mAh / g at the same current densities. The comparison shows that the lithium-sulfur battery using the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride as the electrode material shows a significant improvement in discharge capacity at different current densities.

[0032] Example 3 Preparation of carbon nanotube-sulfur composite materials with embedded quantum dot tungsten nitride and molybdenum nitride: (1) First, prepare 15 mL of a 30 mmol / L mixed solution of phosphotungstic acid and phosphomolybdic acid (the molar ratio of phosphotungstic acid to phosphomolybdic acid is 95:5). Then, add 60 mg of single-walled carbon nanotubes to the mixture, sonicate for 1 minute, let stand for 24 hours, and repeat 3 times. Centrifuge and wash the single-walled carbon nanotubes 10 times, then wash and filter them 3-5 times with a filter membrane, and dry them to obtain carbon nanotubes embedded with phosphotungstic acid and phosphomolybdic acid.

[0033] (2) Carbon nanotubes embedded with phosphotungstic acid and phosphomolybdic acid were treated at 600°C for 2 hours under inert gas conditions to obtain carbon nanotubes embedded with quantum dots tungsten oxide and molybdenum oxide.

[0034] (3) Carbon nanotubes with embedded quantum dot tungsten oxide and molybdenum oxide were treated at 700°C for 2 hours under ammonia gas conditions to obtain carbon nanotubes with embedded quantum dot tungsten nitride and molybdenum nitride.

[0035] (4) Synthesis of carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride and molybdenum nitride: 30 mg of carbon nanotubes with embedded quantum dot tungsten nitride and molybdenum nitride were mixed with 70 mg of elemental sulfur, and the elemental sulfur was diffused into the carbon nanotubes with embedded quantum dot tungsten nitride and molybdenum nitride by a melt method to form carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride and molybdenum nitride. As a comparison, carbon nanotube-sulfur composite material was also prepared according to the above steps.

[0036] (5) Using the carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride and molybdenum nitride as the positive electrode, lithium metal as the negative electrode, and a carbon paper barrier layer loaded with tungsten nitride as the electrolyte, anhydrous lithium nitrate with 0.1 mol / L additive, a mixed solution of 1,3-dioxane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and a 1.0 mol / L lithium di(trifluoromethanesulfonyl)imide solution, a lithium-sulfur battery was assembled in a glove box. The charge-discharge cycle life test results at different current densities of 167.5 mA / g, 335 mA / g, 837.5 mA / g, and 1675 mA / g are as follows: Figure 8 As shown, the discharge capacities of lithium-sulfur batteries prepared using carbon nanotube-sulfur composite materials with embedded quantum dot tungsten nitride and molybdenum nitride as electrode materials were 895.8 mAh / g, 759.8 mAh / g, 622.4 mAh / g, and 511.8 mAh / g, respectively. The comparison shows that the discharge capacity of lithium-sulfur batteries prepared using carbon nanotube-sulfur composite materials with embedded quantum dot tungsten nitride and molybdenum nitride as electrode materials is significantly improved under different current densities.

[0037] Finally, it should be noted that the described embodiments are only some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

Claims

1. A carbon nanotube-sulfur composite material with embedded quantum dot nitrides, characterized in that: The carbon nanotubes embedded with quantum dot nitrides are thermally melt-composite with sulfur. The quantum dot nitrides are tungsten nitride or a compound of tungsten nitride and molybdenum nitride. The process involves adding single-walled carbon nanotubes to a phosphotungstic acid solution or a mixture of phosphotungstic acid and phosphomolybdic acid, sonicating, and then allowing them to stand. The single-walled carbon nanotubes are then centrifuged, washed, filtered, and finally dried to obtain carbon nanotubes embedded with phosphotungstic acid or a mixture of phosphotungstic acid and phosphomolybdic acid. These carbon nanotubes are then heat-treated under an inert gas atmosphere to obtain carbon nanotubes embedded with quantum dot oxides. Finally, these carbon nanotubes embedded with quantum dot oxides are heat-treated under an ammonia-based gas atmosphere to obtain carbon nanotubes embedded with quantum dot nitrides.

2. The carbon nanotube-sulfur composite material with embedded quantum dot nitrides according to claim 1, characterized in that: The carbon nanotubes with embedded quantum dot nitrides have a diameter of 1 to 2 nanometers and a length of 1 to 3 micrometers.

3. The carbon nanotube-sulfur composite material with embedded quantum dot nitrides according to claim 1, characterized in that: The diameter of quantum dot nitrides is greater than 0.8 nanometers and less than 1.4 nanometers.

4. A method for preparing a carbon nanotube-sulfur composite material with embedded quantum dot nitrides, characterized in that: First, prepare a phosphotungstic acid solution or a mixture of phosphotungstic acid and phosphomolybdic acid of a certain concentration. Then, add a certain mass of single-walled carbon nanotubes to the phosphotungstic acid solution or the mixture of phosphotungstic acid and phosphomolybdic acid, sonicate, and then let stand. Next, centrifuge, wash, filter, and finally dry the single-walled carbon nanotubes to obtain carbon nanotubes embedded with phosphotungstic acid or a mixture of phosphotungstic acid and phosphomolybdic acid. Heat-treat the carbon nanotubes embedded with phosphotungstic acid or a mixture of phosphotungstic acid and phosphomolybdic acid under inert gas conditions to obtain carbon nanotubes embedded with quantum dot oxides. Heat-treat the carbon nanotubes embedded with quantum dot oxides under ammonia gas conditions to obtain carbon nanotubes embedded with quantum dot nitrides. Diffusion of elemental sulfur into the carbon nanotubes embedded with quantum dot nitrides is carried out using a melting method to form a carbon nanotube-sulfur composite material with embedded quantum dot tungsten nitride.

5. The method for preparing the carbon nanotube-sulfur composite material with embedded quantum dot nitrides according to claim 4, characterized in that: The ultrasound session lasts 1 to 3 minutes, followed by resting and repeated multiple times.

6. The method for preparing the carbon nanotube-sulfur composite material with embedded quantum dot nitrides according to claim 4, characterized in that: The process of centrifuging, washing, and filtering single-walled carbon nanotubes includes: centrifuging and washing the single-walled carbon nanotubes 5-10 times, and then washing and filtering them 3-5 times using a filter membrane.

7. The method for preparing the carbon nanotube-sulfur composite material with embedded quantum dot nitrides according to claim 4, characterized in that: The heat treatment temperature under inert gas conditions is 600℃.

8. The method for preparing the carbon nanotube-sulfur composite material with embedded quantum dot nitrides according to claim 4, characterized in that: The temperature for heating treatment under ammonia gas conditions is 600-800℃.

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