An oil-based multi-walled carbon nanotube slurry, a preparation method and application thereof

Abstract

The application provides an oil-based multi-walled carbon nanotube slurry as well as a preparation method and application thereof. The oil-based multi-walled carbon nanotube slurry comprises 1-23% by mass fraction of multi-walled carbon nanotubes, 0.1-5% by mass fraction of sodium 4-styrenesulfonate, 0.5-35% by mass fraction of polyvinylidene fluoride and 57-98.4% by mass fraction of N-methylpyrrolidine. The multi-walled carbon nanotubes in the oil-based slurry are uniformly dispersed, and the multi-walled carbon nanotubes exist in a monodisperse form and are not prone to agglomeration. The oil-based multi-walled carbon nanotube slurry has stable physical and chemical properties, can be stored for a long time and is not prone to stratification. The oil-based slurry can be directly used in the homogenization process of the oil-based slurry, the multi-walled carbon nanotubes in the pole piece prepared after coating are uniformly distributed, the preparation process of the oil-based slurry is simple, the system temperature in the preparation process is constant and controllable, and the oil-based slurry can be prepared and applied on a large scale.

Description

Technical Field

[0001] This invention belongs to the field of carbon nanotube slurry preparation, and particularly relates to an oil-based multi-walled carbon nanotube slurry, its preparation method, and its application. Background Technology

[0002] Carbon nanotubes, as a novel carbon material, are widely used in material reinforcement and conductive material preparation due to their high tensile strength and good electrical conductivity. Especially with the development of the new energy industry, the demand for carbon nanotube conductive agents in the power supply sector continues to increase. However, currently mass-produced carbon nanotubes are multi-walled carbon nanotubes, which are microscopically aggregates. Directly using aggregated multi-walled carbon nanotubes results in minimal or even worse performance improvements. This is mainly because the aggregated multi-walled carbon nanotubes are not effectively dispersed, or the well-dispersed carbon nanotubes re-aggregate. Therefore, if the dispersion and slurry stability issues of multi-walled carbon nanotubes cannot be resolved, their commercial application will be severely limited. Furthermore, especially in non-aqueous solvents, the dispersion process of carbon nanotubes requires a large amount of energy, leading to an increase in the temperature of the dispersion system. Higher system temperatures easily cause the volatilization of non-aqueous solvents, resulting in an increase in the solid content of the system, making the dispersion of multi-walled carbon nanotubes even more difficult.

[0003] In summary, it is indeed necessary to provide an oil-based multi-walled carbon nanotube slurry with uniform dispersion and stable slurry performance. Summary of the Invention

[0004] To address the above problems, the inventors provide an oil-based multi-walled carbon nanotube slurry, its preparation method, and its applications. In this oil-based slurry, the multi-walled carbon nanotubes are uniformly dispersed and exist in a monodisperse form, making them less prone to aggregation. The slurry exhibits stable physicochemical properties, can be stored for extended periods, and is not prone to stratification. This slurry can be directly used in the homogenization process of oil-based slurries, resulting in uniformly distributed multi-walled carbon nanotubes in the coated electrode. The preparation process is simple, with a constant and controllable system temperature, enabling large-scale preparation and application.

[0005] Since multi-walled carbon nanotubes (MWCNTs) are aggregates, reducing the van der Waals forces between them is necessary to break their entangled structure. This allows for rapid uncoupling of the aggregates and effectively prevents re-aggregation. To reduce these van der Waals forces, polyvinylidene fluoride (PVDF) and sodium 4-styrene sulfonate are added to the carbon nanotube slurry of this invention. PVDF can be mechanically agitated and wrapped around the surface of the dispersed MWCNTs, increasing the affinity of MWCNTs for organic solvents and locking more organic solvent around the MWCNTs, thus stabilizing the slurry system. Sodium 4-styrene sulfonate, with its benzene rings, provides significant steric hindrance. When sodium 4-styrene sulfonate is distributed on the surface of the MWCNTs, it prevents contact and aggregation between the carbon nanotubes.

[0006] The ultrasonic dispersion equipment is used in the dispersion process of multi-walled carbon nanotubes. Its main purpose is to cut the carbon nanotubes short at the defects of the multi-walled carbon nanotubes by a large energy input, so as to obtain monodisperse carbon nanotubes with a small aspect ratio. Carbon nanotubes with a small aspect ratio are easier to disperse.

[0007] To achieve the above-mentioned objectives, one aspect of the present invention provides an oil-based multi-walled carbon nanotube slurry, characterized in that it comprises multi-walled carbon nanotubes in a mass fraction of 1% to 33%, sodium 4-styrene sulfonate in a mass fraction of 0.1% to 5%, polyvinylidene fluoride in a mass fraction of 0.5% to 15%, and N-methylpyrrolidone in a mass fraction of 47% to 98.4%.

[0008] In some embodiments, the diameter of the multi-walled carbon nanotubes ranges from 6 nm to 500 nm, and the length of the multi-walled carbon nanotubes ranges from 1 micrometer to 30 micrometers.

[0009] In some embodiments, the multi-walled carbon nanotubes undergo pretreatment or surface functionalization. Such pretreatment or surface functionalization includes acid washing, inert atmosphere ablation, ambient atmosphere ablation, nitriding, ammoniation, etc.

[0010] In some embodiments, the mass fraction of multi-walled carbon nanotubes is 1% to 10%, the mass fraction of sodium 4-styrene sulfonate is 0.1% to 3%, and the mass fraction of polyvinylidene fluoride is 0.5% to 10%.

[0011] Another aspect of the present invention provides a method for preparing the above-mentioned oil-based multi-walled carbon nanotube slurry, characterized by comprising the following steps:

[0012] Step 1: Add multi-walled carbon nanotubes and sodium 4-styrene sulfonate to N-methylpyrrolidone. Use a mechanical stirrer to physically mix the solution, and use an ultrasonic disperser to disperse the multi-walled carbon nanotubes. Use a water bath or oil bath to keep the system temperature below 50°C. After dispersion, you will get solution 1.

[0013] Step 2: Disperse polyvinylidene fluoride in N-methylpyrrolidone and mechanically stir to obtain solution 2;

[0014] Step 3: Mix solution 1 and solution 2 to obtain oil-based multi-walled carbon nanotube slurry.

[0015] In some embodiments, the multi-walled carbon nanotubes in step one are pretreated, and the pretreatment includes at least one of acid washing, inert atmosphere ablation, ambient atmosphere ablation, nitriding, and ammoniation.

[0016] In some embodiments, the mechanical stirring speed in step one is in the range of 300 rpm to 3000 rpm, the ultrasonic dispersion power is in the range of 10 kHz to 50 kHz, and the ultrasonic dispersion equipment operates for 5 hours to 24 hours.

[0017] In some embodiments, the dissolution time in step two is 4 to 48 hours.

[0018] In some implementations, the mixing time in step three is 1 to 12 hours, preferably 2 to 8 hours.

[0019] Another aspect of the present invention provides the application of the above-mentioned oil-based multi-walled carbon nanotube slurry in the preparation of positive electrode sheets for sodium-ion batteries, lithium-ion batteries, and supercapacitors.

[0020] This invention has at least the following advantages:

[0021] 1. The multi-walled carbon nanotubes in this oil-based slurry are uniformly dispersed and exist in a monodisperse form, making them less prone to aggregation.

[0022] 2. This oil-based multi-walled carbon nanotube slurry has stable physicochemical properties, can be stored for a long time, and is not prone to separation.

[0023] 3. This oil-based slurry can be directly used in the homogenization process of oil-based slurries, and the multi-walled carbon nanotubes are evenly distributed in the electrode sheet prepared after coating.

[0024] 4. The preparation process of this oil-based slurry is simple, and the system temperature is constant and controllable during the preparation process, which allows for large-scale preparation and application. Attached Figure Description

[0025] Figure 1 This is an optical microscope image (magnification 500x) of multi-walled carbon nanotubes dispersed in N-methylpyrrolidone before ultrasound.

[0026] Figure 2 An optical microscope image (magnification 500x) of the oil-based multi-walled carbon nanotube slurry prepared in Example 1.

[0027] Figure 3 An optical microscope image (magnification 500x) of the multi-walled carbon nanotube slurry prepared in Example 2.

[0028] Figure 4 An optical microscope image (magnification 500x) of the oil-based multi-walled carbon nanotube slurry prepared in Example 3.

[0029] Figure 5 An optical microscope image (magnification 500x) of the oil-based multi-walled carbon nanotube slurry prepared in Example 4. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Example 1

[0032] Multi-walled carbon nanotubes (purchased from Shandong Dazhan Nanomaterials Co., Ltd., model GTC-304) were placed in a mixture of nitric acid and sulfuric acid, stirred for 2 hours, filtered, washed 5 times with deionized water, and dried.

[0033] 10g of pretreated multi-walled carbon nanotubes and 2g of sodium 4-styrenesulfonate (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) were weighed and added to 500ml of N-methylpyrrolidone. The solution was physically mixed using a mechanical stirrer at a speed of 600rpm. At the same time, the multi-walled carbon nanotubes were dispersed using an ultrasonic disperser. The dispersion was carried out for 6 hours to obtain solution 1, and the temperature of solution 1 was maintained at 45℃.

[0034] Figure 1 This is an optical microscope image (magnification 500x) of multi-walled carbon nanotubes dispersed in an aqueous solution before ultrasound. The image shows that the multi-walled carbon nanotubes exist as spherical aggregates in the solvent, with smaller particles clustering together to form larger particles.

[0035] 1 g of polyvinylidene fluoride (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.) was uniformly dispersed in 50 ml of N-methylpyrrolidone. After dissolving for 4 hours using a mechanical stirrer at 300 rpm, solution 2 was obtained.

[0036] Solution 1 and solution 2 were mixed for 2 hours to obtain an oil-based multi-walled carbon nanotube slurry.

[0037] Figure 2An optical microscope image (magnification 500x) of the prepared oil-based multi-walled carbon nanotube slurry. The image shows very few particulate multi-walled carbon nanotube aggregates throughout the field of view, and the particle size is significantly reduced, indicating that the multi-walled carbon nanotubes were effectively dispersed.

[0038] Example 2

[0039] Other conditions are the same as in Example 1, except that the mixing time of solution 1 and solution 2 is changed to 1 hour. Figure 3 An optical microscope image (magnification 500x) of the prepared multi-walled carbon nanotube slurry. The image shows large, black, granular multi-walled carbon nanotubes, indicating that a short mixing time is insufficient to obtain a uniformly dispersed multi-walled carbon nanotube slurry.

[0040] Example 3

[0041] Other conditions are the same as in Example 1, except that the mass of the multi-walled carbon nanotubes is changed to 30g. Figure 4 This is an optical microscope image (500x magnification) of the prepared oil-based multi-walled carbon nanotube slurry. The image shows a field of view filled with particulate matter, with numerous pores between the particles. This indicates that the multi-walled carbon nanotubes and solvent were not sufficiently mixed. This is because the multi-walled carbon nanotubes have a high solids content, and with limited solvent, they cannot be effectively dispersed.

[0042] Example 4

[0043] Other conditions are the same as in Example 1, except that the ultrasonic dispersion time is changed to 2 hours. Figure 5 The image shows an optical microscope photograph (magnification 500x) of the prepared oil-based multi-walled carbon nanotube slurry. The image shows that the multi-walled carbon nanotubes are initially dispersed, changing from small spherical aggregates to sheet-like aggregates. This indicates that due to the short ultrasonic dispersion time, the entangled structure of the multi-walled carbon nanotube spheres was not completely broken up.

[0044] While specific embodiments of the present invention have been described in detail, they are not intended to limit the invention. Any modifications, substitutions, and improvements made to those details within the spirit and principles of the invention should be included within the scope of protection of the invention. The full scope of the invention is given by the appended claims and any equivalents.

Claims

1. A method for preparing oil-based multi-walled carbon nanotube slurry, characterized in that, Includes the following steps: Step 1: Add surface-functionalized multi-walled carbon nanotubes and sodium 4-styrene sulfonate to N-methylpyrrolidone. Use a mechanical stirrer to physically mix the solution, and use an ultrasonic disperser to disperse the multi-walled carbon nanotubes. The ultrasonic disperser operates for 5 to 24 hours. Use a water bath or oil bath to keep the system temperature below 50°C. After dispersion, solution 1 is obtained. Step 2: Disperse polyvinylidene fluoride in N-methylpyrrolidone and mechanically stir to obtain solution 2; Step 3: Mix solution 1 and solution 2 to obtain oil-based multi-walled carbon nanotube slurry. The mixing time is 1 to 12 hours.

2. The method according to claim 1, characterized in that, The surface-functionalized multi-walled carbon nanotubes in step one are obtained by treatment with a mixture of nitric acid and sulfuric acid.

3. The method according to claim 1, characterized in that, The mechanical stirring speed range in step one is 300 rpm to 3000 rpm, and the ultrasonic dispersion power range is 10 kHz to 50 kHz.

4. The method according to claim 1, characterized in that, The dissolution time in step two is 4 to 48 hours.

5. An oil-based multi-walled carbon nanotube slurry, characterized in that, The oil-based multi-walled carbon nanotube slurry is obtained by the method according to any one of claims 1 to 4, wherein the oil-based multi-walled carbon nanotube slurry comprises 1% to 23% by mass of multi-walled carbon nanotubes, 0.1% to 5% by mass of sodium 4-styrene sulfonate, 0.5% to 15% by mass of polyvinylidene fluoride, and 57% to 98.4% by mass of N-methylpyrrolidone.

6. The oil-based multi-walled carbon nanotube slurry according to claim 5, characterized in that, The multi-walled carbon nanotubes have a diameter ranging from 6 nm to 500 nm and a length ranging from 1 micrometer to 30 micrometers, and have undergone surface functionalization treatment.

7. The application of the oil-based multi-walled carbon nanotube slurry as described in claim 5 or 6 in the preparation of positive electrode sheets for sodium-ion batteries, lithium-ion batteries, and supercapacitors.

Images