High tap density carbon nanotubes and methods for making the same

Abstract

The present application relates to the technical field of carbon nanotubes, in particular to a high tap density carbon nanotube and a preparation method thereof, the preparation method comprising: feeding the carbon nanotubes mixed with oily materials into a screw extruder to obtain the product. The present application mixes the carbon nanotubes with oily materials, shortens the distance between adjacent carbon nanotubes through the mutual attraction of the two, and prepares for improving the tap density of the carbon nanotubes, and then extrudes the carbon nanotubes through the screw extruder; a part of the oily materials will be pressed into the cavities of the carbon nanotubes during the extrusion, which promotes the further mixing of the carbon nanotubes and the oily materials, further shortens the distance between adjacent carbon nanotubes, removes the oily materials in the extrusion step, improves the tap density, and the tap density of the prepared product reaches 0.21 g / cm 3 , simplifies the subsequent purification operation, reduces the transportation cost of the carbon nanotubes, and is environmentally friendly and pollution-free.

Description

Technical Field

[0001] This invention relates to the field of carbon nanotube technology, specifically to a high tap density carbon nanotube and its preparation method. Background Technology

[0002] Carbon nanotubes (CNTs) are one-dimensional quantum materials with a unique structure. They are mainly composed of carbon atoms arranged in a hexagonal pattern, forming several to dozens of layers of coaxial cylindrical tubes.

[0003] Carbon nanotubes possess exceptional physical and chemical properties, including excellent mechanical properties, thermal stability, unique electrical properties, thermal conductivity, hydrogen storage, adsorption, and catalytic activity. Therefore, they have attracted considerable attention from researchers both domestically and internationally since their discovery. Carbon nanotubes show broad application prospects in numerous fields, including nanoelectronic devices, catalyst supports, electrochemical materials, and composite materials.

[0004] However, due to the hollow tubular structure and nanoscale nature of carbon nanotubes, their tap density is relatively low; before pulverization, the tap density of carbon nanotubes is typically 0.12 g / cm³. 3 After crushing, the compacted density drops to 0.03~0.08 g / cm³. 3 about.

[0005] Carbon nanotubes with lower tap density have the following main defects: (1) Increase the cost of the purification process. For the same weight of carbon nanotubes, carbon nanotubes with lower density will occupy a larger volume of the purification furnace, which will reduce the purification capacity accordingly. (2) Carbon nanotubes with lower tap density also increase the transportation cost of carbon nanotubes; (3) At a relatively low tap density, fine carbon nanotube particles can also cause environmental pollution, exposing workers to dust. Summary of the Invention

[0006] To address the technical problems of low tap density in existing carbon nanotube technologies, such as difficulty in purification, high transportation costs, and environmental pollution, this invention provides a high-tap-density carbon nanotube and its preparation method, which can improve the tap density of carbon nanotubes, with the highest tap density of the obtained product reaching 0.21 g / cm³. 3 This simplifies the subsequent purification process of carbon nanotubes, reduces the transportation cost of carbon nanotubes, and is environmentally friendly and pollution-free.

[0007] In a first aspect, the present invention provides a method for preparing high tap density carbon nanotubes, comprising: mixing carbon nanotubes with an oily material and then feeding the mixture into a screw extruder for extrusion.

[0008] Furthermore, carbon nanotubes are mixed with oily materials in the form of a carbon nanotube dispersion. The carbon nanotube dispersion is prepared by dispersing carbon nanotubes in a solvent and stirring until homogeneous. This ensures that the carbon nanotubes are uniformly dispersed, which is beneficial for subsequent mixing to form a homogeneous material. The solvent can be evaporated and removed during subsequent extrusion and heating.

[0009] Furthermore, the solvent includes one of N-methylpyrrolidone, acetone, methanol, or ethanol, and the stirring is carried out at a temperature of 55~80°C and under normal or pressurized conditions.

[0010] Furthermore, the oily materials include one of ethylene bis-stearamide and paraffin wax.

[0011] Furthermore, the weight ratio of carbon nanotubes to oily materials is 1:0.5~2.

[0012] Furthermore, the screw extruder is a twin-screw extruder, and the screw extruder extrusion process is such that the discharge port temperature of the screw extruder is set to 230~240℃.

[0013] Furthermore, the carbon nanotubes are purified carbon nanotubes with a purity of ≥98wt%; or, the carbon nanotubes are one or a combination of several of the following: wound carbon nanotubes, arrayed carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes.

[0014] Furthermore, the tap density of the obtained carbon nanotubes is 0.15-0.30 g / cm³. 3 The preferred value is 0.17-0.25 g / cm³. 3 More preferably, it is 0.20-0.22 g / cm³. 3 .

[0015] Secondly, the present invention provides a high tap density carbon nanotube prepared by the above preparation method.

[0016] The principle of this invention is as follows: This invention mixes carbon nanotubes with an oily material, using the oily material as a medium. Through the mutual attraction between the carbon nanotubes and the oily material, the distance between adjacent carbon nanotubes is shortened, preparing for increased tap density. Then, the mixture is extruded using a screw extruder. In the early stages of extrusion, the carbon nanotubes are compressed, further reducing the distance between adjacent carbon nanotubes. In the later stages of extrusion, by adjusting the extrusion temperature, the oily material is removed during the extrusion process. The resulting product is high-tap-density carbon nanotubes, without the need for a separate purification process.

[0017] The beneficial effects of this invention are as follows: This invention can improve the tap density of carbon nanotubes, with the highest tap density of the obtained product reaching 0.21 g / cm³. 3The tap density of carbon nanotubes can be increased by up to 4 times, which greatly reduces the transportation cost of carbon nanotubes and solves the problem of difficult material feeding caused by the low density of carbon nanotubes in downstream applications. It is also environmentally friendly and pollution-free.

[0018] During extrusion, due to the significant difference in boiling points between the oily material and carbon nanotubes, the oily material can be completely volatilized and separated from the carbon nanotubes by adjusting the extruder outlet temperature, without introducing new impurities. The oily material is then condensed and recycled by the recovery system for reuse, resulting in low loss of oily material throughout the process.

[0019] The preparation method provided by this invention is applicable to wound carbon nanotubes, arrayed carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a high-magnification SEM image of Comparative Example 1 before carbon nanotube treatment, which is a specific embodiment of the present invention.

[0022] Figure 2 This is a high-magnification SEM image of carbon nanotubes after treatment in Example 1 of the specific implementation of the present invention.

[0023] Figure 3 This is a low-magnification SEM image of Comparative Example 1 before carbon nanotube treatment, which is a specific embodiment of the present invention.

[0024] Figure 4 This is a low-magnification SEM image of carbon nanotubes after treatment in Example 1 of the specific implementation of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0026] Example 1 A method for preparing high tap density carbon nanotubes, comprising: (1) 100g of carbon nanotubes GTCO-301 with a purity of 99.5% (tap density 0.082g / cm³) were placed in the container. 3 The mixture consists of wound carbon nanotubes (10-20nm in diameter, multi-walled carbon nanotubes, manufactured by Shandong Dazhan Nanomaterials Co., Ltd.) and 100g of paraffin wax (manufacturer: Maoming Yuanmao Petrochemical Co., Ltd., No. 10 white oil). The mixture is prepared by mixing the two materials in a high-speed mixer at room temperature and 1500rpm for 5 minutes.

[0027] (2) The mixture obtained in step (1) is fed into a Coperion twin-screw extruder (type 35). The extrusion pressure is 20 MPa. The temperatures of each zone of the twin-screw extruder are 160-180℃, 210-220℃, 210-220℃, 210-220℃, 210-220℃, 200-210℃, 200-210℃, 200-210℃, 200-210℃, and 200-210℃, respectively. The twin-screw speed is 300-400 rpm. The discharge port temperature is set to 230℃. The mixture is extruded through the extruder. The mass of carbon nanotubes after treatment is 98g (paraffin wax volatilizes during the extrusion process).

[0028] The tap density of the carbon nanotubes prepared in Example 1 was measured to be 0.211 g / cm³. 3 After being processed by the preparation process provided by this invention, the tap density of carbon nanotubes GTCO-301 increased from 0.082 g / cm³. 3 Increased to 0.211 g / cm³ 3 This means that the tap density increases by 157%, which can significantly reduce the transportation cost of carbon nanotubes. Furthermore, the increased powder density makes it easier to feed the material during the slurry preparation process, effectively avoiding the problems of dust flying and clogging the feeding port during the feeding process.

[0029] Comparative Example 1 Comparative Example 1 is the carbon nanotube GTCO-301 before treatment in Example 1 (tap density 0.082 g / cm³). 3 Manufacturer: Shandong Dazhan Nanomaterials Co., Ltd.

[0030] Depend on Figure 1 and Figure 2 As shown in the scanning electron microscope (SEM) images, at high magnification (50,000x), the morphology and structure of the carbon nanotubes treated in Example 1 and the untreated carbon nanotubes GTCO-301 in Comparative Example 1 did not change significantly.

[0031] Depend on Figure 3 and Figure 4It can be seen that at a low magnification (2000 times), the carbon nanotubes GTCO-301 treated in Example 1 have a more uniform particle size and a higher particle agglomerate density. The particles are mainly concentrated in the 5-10 micrometer range, and the gaps between the particles are smaller. In contrast, the untreated carbon nanotubes GTCO-301 in Comparative Example 1 mainly exist in the form of loose agglomerates with a larger particle size.

[0032] Example 2 A method for preparing high tap density carbon nanotubes, comprising: (1) 100g of GTCO-290 carbon nanotubes with a purity of 99.5% (tap density 0.035g / cm³) 3 The mixture consists of arrayed carbon nanotubes (3-8 nm in diameter, single-walled carbon nanotubes, manufactured by Shandong Dazhan Nanomaterials Co., Ltd.) and 80 g of ethylene bis-stearamide (manufacturer: LG Korea). The mixture is stirred in a high-speed mixer at 2000 rpm for 10 min to obtain the final mixture.

[0033] (2) The mixture obtained in step (1) is fed into a Coperon twin-screw extruder (type 35). The extrusion pressure is 25 MPa. The temperatures of each zone of the twin-screw extruder are 160-180℃, 210-220℃, 210-220℃, 210-220℃, 210-220℃, 200-210℃, 200-210℃, 200-210℃, 200-210℃, 200-210℃, 200-210℃, and 200-210℃. The twin-screw speed is 300-400 rpm. The discharge port temperature is set to 240℃. The mixture is extruded through the extruder. The mass of carbon nanotubes after processing is 95g.

[0034] The tap density of the carbon nanotubes prepared in Example 2 was measured to be 0.174 g / cm³. 3 After being processed by the preparation process provided by this invention, the tap density of carbon nanotube powder GTCO-290 is reduced from 0.035 g / cm³. 3 Increased to 0.174 g / cm³ 3 That is, the tapped density increased by 397%, which is a significant increase in tapped density.

[0035] Comparative Example 2 Comparative Example 2 is carbon nanotubes GTCO-290 before treatment in Example 2 (tap density 0.035 g / cm³). 3 Manufacturer: Shandong Dazhan Nanomaterials Co., Ltd.

[0036] Test case (1) Carbon nanotubes from Example 1 and Comparative Example 1 were ground and dispersed according to the weight percentage ratio of 5% CNTs + 1% PVP (polyvinylpyrrolidone) + 0.2% piperazine + 93.8% NMP (N-methyl-2-pyrrolidone) to obtain two CNTs slurries. Each CNTs slurry was tested for electrode resistivity at different weights and was labeled as Example 11 group, Example 12 group, and Comparative Example 11 group and Comparative Example 12 group, respectively. The LFP slurry formulation and resistivity test data used in the electrode resistivity test are shown in Table 1.

[0037] Table 1 LFP paste formulation and resistivity test data

[0038] In Table 1, PVDF stands for polyvinylidene fluoride and LFP stands for lithium iron phosphate.

[0039] As shown in Table 1, when the treated carbon nanotubes are applied to lithium batteries, their electrode resistivity not only does not decrease, but also increases by more than 6%, indicating that after being processed by the process method provided by this invention, the carbon nanotubes still maintain their original dispersion properties and their conductivity is improved.

[0040] (2) Carbon nanotubes from Example 2 and Comparative Example 2 were ground and dispersed according to the weight percentage ratio of 2.33% CNTs + 0.87% HNBR (hydrogenated nitrile butadiene rubber) + 0.3% piperazine + 96.5% NMP to obtain two CNTs slurries. Each CNTs slurry was tested for electrode resistivity at different weights and was labeled as Example 21, Example 22, Comparative Example 21, and Comparative Example 22, respectively. The NCM slurry formulation and resistivity test data used in the electrode resistivity test are shown in Table 2.

[0041] Table 2 NCM paste formulation and resistivity test data

[0042] In Table 2, NCM is the cathode material for ternary lithium batteries.

[0043] As shown in Table 2, when the treated carbon nanotubes are applied to lithium batteries, their electrode resistivity not only does not decrease, but also increases by more than 6%, indicating that after being processed by the process method provided by this invention, the carbon nanotubes still maintain their original dispersion properties and have better conductivity.

[0044] Example 3 The difference between Example 3 and Example 1 is that in step (1), carbon nanotubes GTCO-301 are first dispersed in N-methylpyrrolidone organic solvent and stirred at room temperature at 65°C to obtain a carbon nanotube dispersion, which is then mixed with 200g of paraffin wax. The extrusion pressure of the extruder is 30MPa.

[0045] The tap density of the carbon nanotubes prepared in Example 3 was tested to be 0.292 g / cm³. 3 .

[0046] Example 4 The difference between Example 4 and Example 1 is that the carbon nanotubes in step (1) are GT-1001 with a purity of 98% (array carbon nanotubes with a diameter of 1-3 nm, single-walled carbon nanotubes). They are first dispersed in N-methylpyrrolidone organic solvent and stirred at room temperature at 65°C to obtain a carbon nanotube dispersion, which is then mixed with 200g of paraffin wax. The extrusion pressure of the extruder is 30MPa.

[0047] The tap density of the carbon nanotubes prepared in Example 4 was tested to be 0.258 g / cm³. 3 .

[0048] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for preparing high tap density carbon nanotubes, characterized in that, Carbon nanotubes are obtained by mixing them with an oily material and then feeding the mixture into a screw extruder for extrusion.

2. The preparation method according to claim 1, characterized in that, Carbon nanotubes are mixed with oily materials in the form of a carbon nanotube dispersion. The carbon nanotube dispersion is prepared by dispersing carbon nanotubes in a solvent and stirring until homogeneous.

3. The preparation method according to claim 2, characterized in that, The solvent includes one of N-methylpyrrolidone, acetone, methanol or ethanol, and stirring is carried out at a temperature of 55~80℃ and under normal or pressurized conditions.

4. The preparation method according to claim 1, characterized in that, Oily materials include one of ethylene bis-stearamide and paraffin wax.

5. The preparation method according to claim 1, characterized in that, The weight ratio of carbon nanotubes to oily materials is 1:0.5~2.

6. The preparation method according to claim 1, characterized in that, The screw extruder is a twin-screw extruder, and the extrusion process of the screw extruder is to set the discharge port temperature of the screw extruder to 230~240℃.

7. The preparation method according to claim 6, characterized in that, The extrusion pressure of the screw extruder is 20-30 MPa.

8. The preparation method according to claim 6, characterized in that, The carbon nanotubes are purified carbon nanotubes with a purity of ≥98 wt%; or The carbon nanotubes are one or a combination of several of the following: wound carbon nanotubes, arrayed carbon nanotubes, multi-walled carbon nanotubes, and oligo-walled carbon nanotubes.

9. The preparation method according to claim 1, characterized in that, The tap density of the obtained carbon nanotubes was 0.15-0.30 g / cm³. 3 The preferred value is 0.17-0.25 g / cm³. 3 More preferably, it is 0.20-0.22 g / cm³. 3 .

10. A high tap density carbon nanotube prepared by the preparation method according to any one of claims 1-9.

Images