Method for improving processability of multi-walled carbon nanotubes

Abstract

The invention discloses a method for improving the processability of a multi-walled carbon nanotube, and belongs to the technical field of carbon nanotube materials. The method for improving the processability of the multi-walled carbon nanotube comprises the following steps: grinding and mixing the multi-walled carbon nanotube, a nitrogen source and a phosphorus source, then putting the mixture into a tubular furnace, introducing inert gas to remove air in the tubular furnace, raising the temperature of the tubular furnace to 500-600 DEG C, reacting for 30-60 minutes, and after the reaction is finished, cooling to room temperature under the inert gas condition to obtain the multi-walled carbon nanotube. The carbon nano tube doped with nitrogen and phosphorus elements is obtained. When the nitrogen and phosphorus doped carbon nanotube obtained by the method is used for preparing conductive slurry, the conductivity is better, the viscosity of the slurry is obviously reduced, and the coating and processing properties are good.

Description

Technical Field

[0001] This invention relates to a method for improving the processing performance of multi-walled carbon nanotubes, belonging to the field of carbon nanotube material technology. Background Technology

[0002] Carbon nanotubes are coaxial, hollow, seamless tubular structures mainly composed of single or multiple layers of graphite sheets rolled around a central point at a certain angle. Their walls are mostly composed of a hexagonal carbon atom mesh. As one-dimensional nanomaterials, they possess excellent mechanical, electrical, and chemical properties, thus showing broad development prospects in fields such as electronic devices, composite materials, and hydrogen storage materials.

[0003] In lithium-ion battery conductive materials, carbon nanotubes have become a key material due to their ability to significantly improve energy density and extend cycle life with relatively low addition amounts and usage costs. Currently, most carbon nanotubes used on a large scale are aggregated or tubular, with large specific surface area and aspect ratios, resulting in high viscosity of the carbon nanotube slurry. This severely affects dispersibility in solvents, hindering dispersion and long-term storage. While traditional single-element doping (such as nitrogen doping) can improve conductivity to some extent, it has limited ability to adjust the steric hindrance of carbon nanotubes in the slurry, making it difficult to simultaneously achieve a balance between low viscosity and high conductivity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for improving the processing performance of multi-walled carbon nanotubes. This method involves simultaneously doping the surface of carbon nanotubes with nitrogen and phosphorus elements. This affects the conductivity of the carbon nanotubes, thereby improving their dispersibility in slurries and the viscosity of conductive slurries, thus enhancing their processing performance and solving the problem of limited application of carbon nanotubes in conductive slurries.

[0005] To achieve the above objectives, the following technical solution is provided: This invention provides a method for improving the processing performance of multi-walled carbon nanotubes. The method involves grinding and mixing multi-walled carbon nanotubes with a nitrogen source and a phosphorus source, then placing the mixture into a tube furnace, introducing an inert gas to purge the air from the tube furnace, raising the temperature of the tube furnace to 500-600°C, reacting for 30-60 minutes, and after the reaction is completed, cooling to room temperature under inert gas conditions to obtain nitrogen and phosphorus-doped carbon nanotubes.

[0006] In one embodiment, the multi-walled carbon nanotubes have a specific surface area of ​​200-400 m² / g, a tube length of 20-30 μm, a tube diameter of 7-10 nm, and an aspect ratio of 2857-4286.

[0007] In one embodiment, the multi-walled carbon nanotubes are commercially available or homemade.

[0008] In one embodiment, the preparation of the multi-walled carbon nanotubes includes: (1) Cobalt nitrate hexahydrate, ferric nitrate nonahydrate, and aluminum nitrate nonahydrate were added to pure water to prepare a nitrate solution; washed vermiculite was added to the nitrate solution and soaked; the soaked vermiculite was calcined in a muffle furnace to obtain a catalyst; (2) Take the catalyst prepared in step (1) and add it into the tubular furnace reactor. Introduce a mixture of nitrogen and hydrogen gas, heat the reactor to 700~800℃, and introduce ethylene to react. After the reaction is completed, cool it to room temperature under nitrogen conditions to obtain a multi-walled carbon nanotube array. (3) The prepared multi-walled carbon nanotube array is acid-washed, water-washed, and dried to obtain multi-walled carbon nanotubes.

[0009] In one embodiment, the nitrogen source includes any one of urea, melamine, dicyandiamine, and thiourea.

[0010] In one embodiment, the phosphorus source is sodium hypophosphite.

[0011] In one embodiment, the mass ratio of the multi-walled carbon nanotubes to the nitrogen source and phosphorus source is 1:0.05~0.3:0.05~0.2.

[0012] In one embodiment, the inert gas is one or both of argon and nitrogen.

[0013] In one embodiment, the heating rate is 5~20°C / min.

[0014] The present invention also provides carbon nanotubes doped with nitrogen and phosphorus elements obtained by the method described above.

[0015] The present invention also provides the application of the above-described nitrogen and phosphorus-doped carbon nanotubes in the preparation of conductive pastes.

[0016] This invention also provides a method for preparing a conductive paste with good dispersibility and low viscosity, the method comprising: The dispersant and binder are dissolved in a solvent, and then the nitrogen- and phosphorus-doped carbon nanotubes mentioned above are added and ground and dispersed to obtain the final product.

[0017] In one embodiment, the dispersant includes one or more of sodium carboxymethyl cellulose, polyacrylic acid, and polyvinylpyrrolidone.

[0018] In one embodiment, the adhesive comprises one or more of epoxy resin, polyimide, polyvinylidene fluoride, polyurethane, and styrene-butadiene rubber.

[0019] In one embodiment, the solvent includes one or more of N-methylpyrrolidone, dimethylformamide, toluene, and xylene.

[0020] In one embodiment, the mass percentage of nitrogen- and phosphorus-doped carbon nanotubes in the conductive paste is 1-2%.

[0021] This invention also provides the application of the above-described conductive paste in the preparation of lithium-ion batteries and supercapacitors.

[0022] Beneficial effects: This invention discloses a method for improving the processing performance of multi-walled carbon nanotubes. The method involves mixing and grinding multi-walled carbon nanotubes with nitrogen and phosphorus sources, followed by a one-step dual-element doping process to obtain nitrogen- and phosphorus-doped carbon nanotubes. Sodium hypophosphite is used as the phosphorus source; its decomposition within a specific temperature range not only provides phosphorus but also its decomposition products (such as PH3) gently erode the surface of the carbon nanotubes, creating more defect sites. This allows for efficient co-doping with the nitrogen-containing groups generated by the decomposition of the nitrogen source. Other phosphorus sources, such as red phosphorus and PCl3, do not possess this gentle and controllable characteristic. The method is simple. The slurry prepared from the doped carbon nanotubes not only exhibits good conductivity but also significantly reduced viscosity, resulting in excellent coating and processing performance. Attached Figure Description

[0023] Figure 1 SEM image of the fabricated multi-walled carbon nanotube array; Figure 2 SEM images of nitrogen and phosphorus-doped carbon nanotubes prepared for implementation of column 2; Figure 3 (a) TEM image of carbon nanotubes; (b) TEM image of the prepared multi-walled carbon nanotube array; (c) TEM image of nitrogen and phosphorus doped carbon nanotubes prepared in Example 2. Figure 4 Raman diagrams of nitrogen- and phosphorus-doped carbon nanotubes for the fabrication of multi-walled carbon nanotube arrays and for embodiment 2. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The specific embodiments described below further illustrate the present invention.

[0025] The preparation of multi-walled carbon nanotubes involved in the embodiments and comparative examples of this invention: (1) Weigh 9.60 g of cobalt nitrate hexahydrate, 25.38 g of ferric nitrate nonahydrate and 24.76 g of aluminum nitrate nonahydrate, add them to 450 g of pure water to prepare a nitrate solution with a molar ratio of Co:Fe:Al of 1:1.9:2; add 100 g of washed vermiculite to the nitrate solution, soak at 95 °C for 8 hours, and calcine the impregnated vermiculite in a muffle furnace at 450 °C for 2 hours to obtain a catalyst; (2) 0.2 g of the prepared catalyst was added to a tubular furnace reactor, and a mixture of nitrogen and hydrogen gas was introduced. The reactor was heated to 700 °C, and then the catalyst was reacted in a mixture of ethylene, nitrogen, and hydrogen gas for 1 hour. The mixture was then cooled to room temperature under nitrogen conditions to obtain a multi-walled carbon nanotube array, as shown in the figure. Figure 1 As shown; the specific surface area of ​​the multi-walled carbon nanotube array is 200-400 m². 2 / g, tube length is 20-30μm, tube diameter is 7-10nm, and length-to-diameter ratio is 2857-4286; (3) The prepared multi-walled carbon nanotube array was acid-washed to remove metal impurities. After reacting at 80°C for 5 hours with a mass ratio of carbon nanotube: pure water: aqua regia of 1:50:5, it was washed with water until the pH was 6-7. Then, it was reacted at 95°C for 5 hours with a mass ratio of carbon nanotube: pure water: hydrofluoric acid (40%) of 1:50:7. After washing with water until the pH was 6-7, it was dried at 60°C to obtain multi-walled carbon nanotubes.

[0026] Example 1 A method for improving the processing performance of multi-walled carbon nanotubes includes the following: Weigh 1 gram of the multi-walled carbon nanotubes prepared above, and grind and mix them with 0.13 grams of dicyandiamine and 0.09 grams of sodium hypophosphite to obtain a carbon nanotube mixture. Then, place the mixture on a glass boat and transfer it to a tube furnace. After purging the air in the tube furnace with nitrogen, heat the downstream central heating zone of the tube furnace to 550°C at a rate of 10°C / min. React for 30 minutes. After the reaction is completed, cool to room temperature under nitrogen to obtain carbon nanotubes doped with nitrogen and phosphorus.

[0027] The method for preparing conductive paste from nitrogen- and phosphorus-doped carbon nanotubes as described above includes the following: 1.2 g of PVP (polyvinylpyrrolidone) was dissolved in 250 g of NMP (N-methylpyrrolidone), 0.4 g of PVDF (polyvinylidene fluoride) was added to the solution, and 4.8 g of the nitrogen- and phosphorus-doped carbon nanotubes prepared above were added to the solution. The mixture was ground and dispersed at 4000 RPM for 5 hours to obtain a multi-walled carbon nanotube conductive slurry.

[0028] Example 2 A method for preparing a multi-walled carbon nanotube conductive paste includes the following steps: Take 1 gram of the multi-walled carbon nanotubes prepared above, grind and mix them with 0.13 grams of melamine and 0.09 grams of sodium hypophosphite to obtain a carbon nanotube mixture. Then, place the mixture on a glass boat and transfer it to a tube furnace. After purging the air in the tube furnace with nitrogen, heat the central heating zone of the tube furnace to 550°C at a rate of 10°C / min and react for 30 min. After the reaction is completed, cool it to room temperature under nitrogen to obtain carbon nanotubes doped with nitrogen and phosphorus.

[0029] The method for preparing conductive paste from nitrogen- and phosphorus-doped carbon nanotubes as described above includes the following: 1.2 g of PVP (polyvinylpyrrolidone) was dissolved in 250 g of NMP (N-methylpyrrolidone), 0.4 g of PVDF (polyvinylidene fluoride) was added to the solution, and 4.8 g of the nitrogen- and phosphorus-doped carbon nanotubes prepared above were added to the solution. The mixture was ground and dispersed at 4000 RPM for 5 hours to obtain a multi-walled carbon nanotube conductive slurry.

[0030] Example 3 The only difference from Example 1 is that in step (1), dicyandiamine is replaced with urea, while the other parameters and conditions are the same as in Example 1.

[0031] Comparative Example 1 The only difference from Example 1 is that sodium hypophosphite is omitted in step (1), and only 0.22 g of dicyandiamine is added. All other parameters and conditions are the same as in Example 1.

[0032] Comparative Example 2 The only difference from Example 1 is that dicyandiamine is omitted in step (1), and only 0.22 g of sodium hypophosphite is added. All other parameters and conditions are the same as in Example 1.

[0033] Comparative Example 3 A method for preparing a multi-walled carbon nanotube conductive paste includes the following steps: (1) After grinding and mixing 1 gram of the multi-walled carbon nanotubes prepared above with 0.13 melamine, the mixture was transferred to a tube furnace and nitrogen gas was introduced to remove air. Then, the central heating zone of the tube furnace was heated to 550°C at a rate of 10°C / min and reacted for 30 min. After the reaction was completed, the mixture was cooled to room temperature under nitrogen gas to obtain nitrogen-doped carbon nanotubes. (2) Take 1 gram of nitrogen-doped carbon nanotubes obtained in step (1) and 0.09 grams of sodium hypophosphite and grind and mix them evenly to obtain a carbon nanotube mixture. Then transfer the mixture to a tube furnace, introduce nitrogen gas to remove the air in the tube furnace, and heat the central heating zone of the tube furnace to 550°C at a rate of 10°C / min. React for 30 min. After the reaction is completed, cool to room temperature under nitrogen gas to obtain nitrogen- and phosphorus-doped carbon nanotubes.

[0034] The method for preparing conductive paste from nitrogen- and phosphorus-doped carbon nanotubes as described above includes the following: 1.2 g of PVP (polyvinylpyrrolidone) was dissolved in 250 g of NMP (N-methylpyrrolidone), 0.4 g of PVDF (polyvinylidene fluoride) was added to the solution, and 4.8 g of the nitrogen- and phosphorus-doped carbon nanotubes prepared above were added to the solution. The mixture was ground and dispersed at 4000 RPM for 5 hours to obtain a multi-walled carbon nanotube conductive slurry.

[0035] Comparative Example 4 The only difference from Example 2 is that sodium hypophosphite in step (1) is replaced with red phosphorus, while the other parameters and conditions are the same as in Example 2.

[0036] Comparative Example 5 The only difference from Example 2 is that 0.5 g of melamine and 0.4 g of sodium hypophosphite were added and ground and mixed evenly with 1 g of multi-walled carbon nanotubes. All other parameters and conditions were the same as in Example 2.

[0037] Comparative Example 6 The only difference from Example 2 is that 0.03 g of melamine and 0.01 g of sodium hypophosphite were added and ground and mixed evenly with 1 g of multi-walled carbon nanotubes. All other parameters and conditions were the same as in Example 2.

[0038] Comparative Example 7 1.2 g of PVP (polyvinylpyrrolidone) was dissolved in 250 g of NMP (N-methylpyrrolidone), and 0.4 g of PVDF (polyvinylidene fluoride) was added to the solution. The multi-walled carbon nanotubes prepared above were added to the solution, and the mixture was ground and dispersed at 4000 RPM for 5 hours to obtain a conductive slurry of multi-walled carbon nanotubes.

[0039] Results Analysis Viscosity tests were performed on the conductive slurries prepared in the examples and comparative examples. The shear rate was 20 rpm when testing the viscosity. The resistivity of the slurry was tested using an RTS-8 four-probe tester. The test results are shown in Table 1. Table 1. Performance of conductive paste under different treatment conditions

[0040] As shown in Table 1, the conductive slurry prepared by the nitrogen and phosphorus-doped carbon nanotubes in Example 2 of the present invention has significantly reduced viscosity, better dispersion effect, and no significant increase in resistivity.

[0041] from Figures 1-3 As can be seen from the SEM and TEM images, the doped carbon nanotubes retain their original morphology and have not been significantly damaged. Figure 4 The images show the Raman plots of carbon nanotubes before and after doping. The ID / IG value of the carbon nanotubes did not change significantly after doping.

[0042] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for improving the processing performance of multi-walled carbon nanotubes, characterized in that, The method involves grinding and mixing multi-walled carbon nanotubes with nitrogen and phosphorus sources, then placing the mixture into a tube furnace, introducing inert gas to purge air from the furnace, raising the furnace temperature to 500-600°C, reacting for 30-60 minutes, and cooling to room temperature under inert gas conditions after the reaction to obtain nitrogen and phosphorus-doped carbon nanotubes.

2. The method according to claim 1, characterized in that, The multi-walled carbon nanotubes have a specific surface area of ​​200-400 m² / g, a tube length of 20-30 μm, a tube diameter of 7-10 nm, and an aspect ratio of 2857-4286.

3. The method according to claim 1, characterized in that, The multi-walled carbon nanotubes are either commercially available or self-made.

4. The method according to claim 1, characterized in that, The nitrogen source includes any one of urea, melamine, dicyandiamine, and thiourea.

5. The method according to claim 1, characterized in that, The phosphorus source is sodium hypophosphite.

6. The method according to claim 1, characterized in that, The mass ratio of the multi-walled carbon nanotubes to the nitrogen and phosphorus sources is 1:0.05~0.3:0.05~0.

2.

7. The nitrogen- and phosphorus-doped carbon nanotubes obtained by the method of any one of claims 1 to 6.

8. The application of the nitrogen- and phosphorus-doped carbon nanotubes of claim 7 in the preparation of conductive pastes.

9. A method for preparing a conductive paste with good dispersibility and low viscosity, characterized in that, The method includes: The dispersant and binder are dissolved in a solvent, and then the nitrogen- and phosphorus-doped carbon nanotubes as described in claim 7 are added and ground and dispersed to obtain the final product.

10. The application of the conductive paste according to claim 9 in the preparation of lithium-ion batteries and supercapacitors.

Images