Carbon nanotube dispersion liquid as well as preparation method and application thereof

Abstract

The invention provides a carbon nanotube dispersion liquid as well as a preparation method and application thereof. The preparation method comprises the following steps: S1, carrying out impurity removal treatment on crushed carbon nanotubes; s2, mixing the carbon nanotubes subjected to impurity removal treatment with a solution containing a first dispersing agent, and grinding and dispersing to obtain a first dispersion liquid; s3, performing primary homogeneous dispersion on the first dispersion liquid to obtain homogeneous dispersion liquid. The carbon nanotube prepared by the preparation method provided by the invention is controllable in tube length and tube diameter, large in length-diameter ratio and excellent in dispersion stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon materials, and in particular relates to a carbon nanotube dispersion liquid and a preparation method and application thereof. Background Art

[0002] Carbon nanotubes (CNTs) are among the most representative nanomaterials with excellent performance. Their extremely strong C-C covalent bonds endow CNTs with exceptional mechanical properties and structural stability, resulting in superior mechanical, electrical, thermal, and functional properties. However, CNTs have a large aspect ratio and specific surface area, which makes them prone to entanglement and agglomeration, tending to form large bundles or clusters. This makes it difficult to effectively disperse CNTs in the matrix, resulting in reduced performance and low utilization. These issues have seriously hindered the mechanical, electrical, and thermal applications of CNTs. Effective dispersion of CNTs is key to their industrial application.

[0003] Among the currently available dispersion technologies, ultrasound and ball milling can break carbon nanotubes and disperse carbon nanotube agglomerates, but they will also cause the carbon nanotubes to stick together more densely. Mechanical stirring and grinding can only mix carbon nanotube agglomerates with the matrix powder on a macro scale, but are powerless to disperse the carbon nanotube agglomerates themselves. The addition of surfactants and acid-base washing methods can break and disperse the flocculent carbon nanotubes on the surface of the agglomerates, but have no significant effect on tightly entangled carbon nanotubes.

[0004] At the same time, the currently commonly used polymer dispersants can coat carbon nanotubes, prevent carbon nanotube agglomeration, and maintain the stability of the slurry. However, the long chains of polymer substances are easily cut off under high pressure and strong mechanical forces to form small molecular substances. Although the dispersibility is good, the slurry stability is poor, the viscosity will decrease, and it is easy to cause gelation and carbon nanotube flocculation.

[0005] Therefore, it is necessary to provide a stably dispersed carbon nanotube dispersion. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a carbon nanotube dispersion and its preparation method and application. The carbon nanotubes obtained by the preparation method provided by the present invention have controllable tube length and diameter, large aspect ratio, and excellent dispersion stability.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a carbon nanotube dispersion, the method comprising:

[0009] S1. removing impurities from the carbon nanotube fragments;

[0010] S2. The carbon nanotubes after impurity removal treatment are mixed with a solution containing a first dispersant and ground and dispersed to obtain a first dispersion;

[0011] S3. The first dispersion liquid is homogeneously dispersed for the first time to obtain a homogeneous dispersion liquid.

[0012] In existing carbon nanotube dispersion methods, the carbon nanotubes are severely damaged during the dispersion process, resulting in carbon nanotube bundles in the dispersion having larger diameters and smaller lengths. Therefore, the present invention selects carbon nanotube scraps and, through impurity removal, removes metal impurities such as onion-shaped carbon nanotubes, amorphous carbon, and catalysts contained in the carbon nanotubes. A strong external dispersing force is then used to break up the entangled and bonded carbon nanotubes. Simultaneously, a first dispersant capable of occupying space is introduced to prevent secondary entanglement and agglomeration of the carbon nanotubes, thereby ensuring dispersion between the carbon nanotubes and reducing damage and truncation of the carbon nanotubes. This successfully produces a carbon nanotube dispersion with longer bundles and smaller diameters. Furthermore, the carbon nanotube bundles in the carbon nanotube dispersion obtained by the preparation method provided by the present invention have a more concentrated length and diameter distribution, resulting in uniform bundles and superior performance.

[0013] A carbon nanotube dispersion with longer tube bundles and smaller diameters can make the dispersion more conductive and increase the utilization rate of the carbon nanotubes. When used, only a very small amount of dispersion needs to be added to form a good conductive network.

[0014] Preferably, the carbon nanotube scraps are selected from single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0015] Preferably, the length of the carbon nanotube fragments is ≤2 mm, such as 1.5 mm, 1.2 mm, 1 mm, 0.8 mm, 0.5 mm, 0.4 mm, 0.2 mm, etc., preferably 300-500 μm, such as 300 μm, 320 μm, 350 μm, 380 μm, 400 μm, 420 μm, 450 μm, 480 μm, 500 μm, etc.

[0016] In the present invention, the length or diameter of carbon nanotube raw materials, carbon nanotube scraps or carbon nanotube bundles refers to the average length or average diameter.

[0017] Preferably, the total mass content of metal contained in the carbon nanotube scraps is ≤20,000 ppm, for example, 20,000 ppm, 18,000 ppm, 15,000 ppm, 10,000 ppm, 8,000 ppm, etc.

[0018] Preferably, the carbon nanotube crushed material is obtained by crushing the carbon nanotube raw material.

[0019] Preferably, the length of the carbon nanotube raw material is ≥30μm, such as 30μm, 40μm, 50μm, 60μm, etc., preferably ≥50μm, and the preferred diameter is 1-3nm, such as 1nm, 1.2nm, 1.5nm, 1.8nm, 2nm, 2.2nm, 2.4nm, 2.5nm, 2.6nm, 2.8nm, 3nm, etc.

[0020] The carbon nanotube raw material selected in the present invention, combined with a subsequent dispersion method, can produce a carbon nanotube dispersion with carbon nanotube bundles ranging in length from 5 to 15 μm and diameters from 1 to 20 nm. The carbon nanotube bundles in the carbon nanotube dispersion obtained in the present invention have a higher aspect ratio, resulting in improved conductivity and higher carbon nanotube utilization.

[0021] Preferably, the total metal content of the carbon nanotubes after the impurity removal treatment is ≤ 8000 ppm, for example, 8000 ppm, 6000 ppm, 5000 ppm, 4000 ppm, etc. The resulting carbon nanotubes have a low total metal content. When used in the preparation of secondary batteries, they can effectively reduce the initial efficiency of the secondary battery and prevent metal particles from piercing the separator, causing a short circuit, or even explosion or spontaneous combustion.

[0022] Preferably, the impurity removal treatment comprises calcining the carbon nanotube fragments, or performing an acid treatment, or first calcining and then performing an acid treatment.

[0023] Preferably, the calcination temperature is 300-500°C, for example 300°C, 350°C, 400°C, 450°C, 500°C, etc., preferably 330-400°C, and the calcination time is 3-12h, for example 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc., preferably 4-8h.

[0024] Preferably, the carbon nanotubes are acid-treated using a mixed acid solution.

[0025] Preferably, the mixed acid comprises a non-oxidizing acid and an oxidizing acid, and preferably the mass ratio of the non-oxidizing acid to the oxidizing acid is (2-5):(0.5-1.5), wherein the 2-5 may be 2, 3, 4, 5, and the 0.5-1.5 may be 0.5, 0.6, 0.8, 1, 1.2, 1.5, etc.

[0026] Preferably, the non-oxidizing acid is selected from hydrochloric acid.

[0027] Preferably, the oxidizing acid is selected from nitric acid.

[0028] Preferably, the mass concentration of the mixed acid solution is 5-15%, such as 5%, 6%, 8%, 10%, 12%, 14%, 15%, etc., preferably 7-12%.

[0029] Preferably, the solid-liquid ratio of the carbon nanotubes and the mixed acid solution is 1:(50-500), such as 1:50, 1:100, 1:150, 1:200, 1:300, 1:400, 1:500, etc., preferably 1:(80-300).

[0030] Preferably, the temperature of the acid treatment is 40-80°C, such as 40°C, 50°C, 60°C, 70°C, 80°C, etc., preferably 50-70°C.

[0031] Preferably, the acid treatment time is 4-24 h, such as 4 h, 5 h, 8 h, 10 h, 12 h, 15 h, 18 h, 20 h, 24 h, etc., preferably 6-18 h.

[0032] Preferably, the method further comprises washing after the acid treatment, preferably washing to neutrality.

[0033] Preferably, the diameter of the bundles formed by the carbon nanotubes in the first dispersion is 80-300 nm, for example, 80 nm, 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, etc.

[0034] Preferably, the first dispersant is selected from any one or a combination of at least two of sodium benzenesulfonate, sodium naphthalenesulfonate, sodium dodecylbenzenesulfonate, sodium dodecyl sulfate, sodium dodecylsulfonate, sodium polystyrenesulfonate (molecular weight ≤ 10000), sodium cholate, sodium deoxycholate, sodium lauroyl-N-methylaminoacetate, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, Tween-85, and Triton X-405, preferably any one or a combination of at least two of sodium benzenesulfonate, sodium naphthalenesulfonate, sodium polystyrenesulfonate and sodium dodecylbenzenesulfonate.

[0035] The first dispersant of the present invention adopts a compound with a relatively small molecular weight, which has a strong interaction with carbon nanotubes. The aromatic ring structure included therein can utilize the non-covalent interaction of charge effect and π-π conjugation. The non-covalent interaction is a dynamic equilibrium process between adsorption and desorption governed by thermodynamics, and will not destroy the π electron conjugated system of the carbon nanotubes. Therefore, the first dispersant introduced by the present invention can improve the dispersion ability of carbon nanotubes while ensuring that the properties of carbon nanotubes do not change; and the sulfonic acid group included therein can form an ion layer based on ionic action, making the carbon nanotubes easier to disperse; therefore, the present invention preferably uses a dispersant that includes both an aromatic ring and a sulfonic acid.

[0036] Preferably, the addition amount of the first dispersant is 0.2-20 times the mass of the carbon nanotubes after the impurity removal treatment, such as 0.2 times, 1 times, 2 times, 4 times, 5 times, 6 times, 8 times, 10 times, 12 times, 15 times, 18 times, 20 times, etc., preferably 0.3-10 times.

[0037] Preferably, the solid content of the mixed solution after mixing in step S2 is 0.5-3%, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, etc., preferably 1-2%.

[0038] Preferably, the mixing speed in step S2 is 800-2500 rpm, for example, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 1800 rpm, 2000 rpm, 2200 rpm, 2500 rpm, etc., and the mixing time is preferably 20-120 min, for example, 20 min, 30 min, 50 min, 60 min, 80 min, 100 min, 120 min, etc.

[0039] Preferably, the grinding and dispersing adopts at least one of a colloid mill, a three-roll mill or a disc mill.

[0040] Preferably, the linear speed of the grinding and dispersing is 15-70 m / s, for example, 15 m / s, 20 m / s, 30 m / s, 40 m / s, 50 m / s, 60 m / s, 70 m / s, etc.; the pore size is 0.15-2 mm, for example, 0.15 mm, 0.2 mm, 0.3 mm, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm, 1.5 mm, 1.6 mm, 1.8 mm, 2 mm, etc.; the power is 5-60 kw, for example, 5 kw, 10 kw, 20 kw, 30 kw, 40 kw, 50 kw, 60 kw, etc.; and the time is 10-120 min, for example, 10 min, 20 min, 40 min, 50 min, 60 min, 80 min, 100 min, 120 min, etc.

[0041] Preferably, the diameter of the bundles formed by the carbon nanotubes in the homogeneous dispersion is 30-150 nm, for example, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 120 nm, 130 nm, 150 nm, etc.; the length is 10-30 μm, for example, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, etc.

[0042] The preparation method provided by the present invention ensures that the diameter of the carbon nanotube bundles in the homogeneous dispersion is 30-150 nm and the length is 10-30 μm. The carbon nanotube bundles within this range are conducive to maintaining the length of the carbon nanotube bundles, and are conducive to further reducing the diameter of the carbon nanotube bundles and further increasing the aspect ratio during subsequent processing.

[0043] Preferably, in step S3, before performing the first homogeneous dispersion, the solid content of the first dispersion is adjusted to 0.8-1.2%, for example, 0.8%, 0.9%, 1%, 1.1%, 1.2%, etc.

[0044] Preferably, the parameters of the first homogeneous dispersion include: first dispersed at 20-40 MPa, such as 20 MPa, 25 MPa, 28 MPa, 30 MPa, 32 MPa, 35 MPa, 40 MPa, etc., preferably 25-35 MPa, for 10-40 times, for example 10 times, 15 times, 20 times, 25 times, 30 times, 35 times, 40 times, etc., preferably 15-30 times, and then dispersed at 40-80 MPa, such as 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, etc., preferably 50-70 MPa, for 10-50 times, for example 10 times, 20 times, 25 times, 30 times, 35 times, 40 times, 50 times, etc., preferably 20-40 times.

[0045] Preferably, the preparation method further comprises:

[0046] S4. The homogeneous dispersion liquid is mixed with a second dispersant and subjected to a second homogeneous dispersion to obtain the carbon nanotube dispersion liquid.

[0047] Preferably, the diameter of the bundles formed by the carbon nanotubes in the carbon nanotube dispersion is 1-20 nm, for example, 1 nm, 2 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 15 nm, 16 nm, 18 nm, 20 nm, etc., and the length is 5-15 μm, for example, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc.

[0048] Preferably, the second dispersant is selected from any one of acrylic acid copolymer (PAA), polyvinyl pyrrolidone (PVP) or carboxymethyl cellulose (CMC), or a combination of at least two thereof.

[0049] The second dispersant introduced in the present invention is a polymer dispersant, which can coat the carbon nanotubes to avoid entanglement of long-diameter carbon nanotubes, and at the same time can increase the dispersion stability of the dispersion, prevent flocculation, and prevent stratification and sedimentation.

[0050] Preferably, the amount of the second dispersant added is 0.2-20 times the mass of the carbon nanotubes after the impurity removal treatment, such as 0.2 times, 1 times, 2 times, 4 times, 5 times, 6 times, 8 times, 10 times, 12 times, 15 times, 18 times, 20 times, etc., preferably 0.5-10 times.

[0051] Preferably, the method further comprises adjusting the solid content of the solution after mixing the homogeneous dispersion and the second dispersant to 0.5-2%, such as 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2%, etc., preferably 0.8-1.5%.

[0052] Preferably, the parameters of the second homogeneous dispersion include: dispersing 30-80 times, for example, 30 times, 40 times, 50 times, 60 times, 70 times, 80 times, etc., preferably 40-60 times, under 80-120 MPa, for example, 80 MPa, 90 MPa, 100 MPa, 110 MPa, 120 MPa, etc., preferably 85-110 MPa.

[0053] After obtaining the homogeneous dispersion, the present invention introduces a polymer dispersant for coating in order to ensure the stability of the dispersion state of the carbon nanotube dispersion, thereby ensuring the stability of the slurry dispersion. At the same time, the present invention adopts a low-pressure homogenization method to avoid the polymer dispersant from being cut off, so that the finally obtained carbon nanotube dispersion has excellent dispersion stability.

[0054] The preparation method provided by the present invention can evenly disperse carbon nanotubes through the use of multi-stage forces and multi-stage dispersants. The formed tube bundles have a better aspect ratio, small tube diameter, concentrated length distribution, more uniform tube bundles and better performance.

[0055] The dispersion obtained by the preparation method provided by the present invention has good stability and will not settle and stratify; at the same time, it causes little damage to the carbon nanotubes, the tube bundles are long, the utilization rate of the carbon nanotubes is high, and the performance is better; the preparation method is simple in process, the preparation time is short, and an aqueous solvent is used in the preparation process, which is green and environmentally friendly, and has few additives and low cost.

[0056] In a second aspect, the present invention provides a carbon nanotube dispersion prepared by the preparation method described in the first aspect.

[0057] Preferably, the solid content of the carbon nanotube dispersion is 0.5-2%, such as 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2%, etc., preferably 0.8-1.5%.

[0058] Preferably, in the carbon nanotube dispersion, the diameter of the tube bundles formed by the carbon nanotubes is 1-20 nm, for example, 1 nm, 2 nm, 4 nm, 5 nm, 6 nm, 8 nm, 10 nm, 12 nm, 14 nm, 15 nm, 16 nm, 18 nm, 20 nm, etc., and the length is 5-15 μm, for example, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc.

[0059] The carbon nanotube bundles in the carbon nanotube dispersion prepared by the present invention are long, small in diameter and have a large aspect ratio. Therefore, the carbon nanotube dispersion has good conductivity and high utilization rate of the carbon nanotubes, and a good conductive network can be formed with a very small addition amount.

[0060] In a third aspect, the present invention provides an application of the carbon nanotube dispersion as described in the second aspect in mechanics, electricity, and thermodynamics, preferably in electricity, further preferably in electrochemical devices, and even more preferably in secondary batteries.

[0061] Compared with the prior art, the present invention has the following beneficial effects:

[0062] (1) The preparation method provided by the present invention causes little damage to carbon nanotubes. The carbon nanotube bundles in the prepared carbon nanotube dispersion are long and small in diameter. The length of the bundles is greater than 1 μm, and optimally can reach greater than 5 μm, and the diameter is less than 36 nm, and optimally can reach less than 20 nm.

[0063] (2) The carbon nanotube dispersion obtained by the preparation method provided by the present invention has good conductivity, can improve the utilization rate of carbon nanotubes, and can form a good conductive network with a very small addition amount;

[0064] (3) The preparation method provided by the present invention can obtain a dispersion liquid in which carbon nanotubes are uniformly dispersed, and has good dispersion stability without sedimentation and stratification;

[0065] (4) The preparation method provided by the present invention is simple in process, takes a short time, and uses aqueous solvents, which is green and environmentally friendly;

[0066] (5) The preparation method provided by the present invention requires few additives and has low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 This is a SEM image of the carbon nanotube dispersion obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0068] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0069] Example 1

[0070] This embodiment provides a method for preparing a carbon nanotube dispersion, as follows:

[0071] (1) Select Wei Carbon I1993 carbon nanotubes with a length of ≥50 μm, a diameter of 1.6-2.2 nm, and a metal Fe content of 2%;

[0072] (2) Using a blade crusher to crush the carbon tube raw material to a length of 300-500 μm;

[0073] (3) The crushed carbon nanotubes were calcined at 350 °C for 6 h to remove the onion carbon nanotubes and amorphous carbon;

[0074] (4) The calcined carbon nanotubes were mixed with a mixed acid solution of hydrochloric acid and nitric acid (mass ratio 3:1) at a solid-liquid ratio of 1:100, treated at 60°C for 8 hours, washed to neutrality, dried, and the metal content was detected to be ≤4000 ppm;

[0075] (5) The carbon nanotubes obtained in step (4) were mixed with a solution containing sodium dodecylbenzene sulfonate, with the mass of sodium dodecylbenzene sulfonate being 0.5 times the mass of the carbon nanotubes. The solid content of the mixed solution was 2%. The mixed solution was dispersed at 1800 rpm for 30 min, and then ground and dispersed using a colloid mill. The grinding and dispersion process was performed at a linear speed of 30 m / s, a pore size of 0.3 mm, a power of 7.5 kW, and a time of 20 min to obtain a first dispersion containing carbon nanotube bundles having a diameter of about 100 nm.

[0076] (6) adjusting the solid content of the first dispersion to 1%, and then performing homogeneous dispersion: first dispersing at 30 MPa for 20 times, and then dispersing at 60 MPa for 30 times, to obtain a homogeneous dispersion containing carbon nanotube bundles with a diameter of about 50 nm and a length of about 20 μm;

[0077] (7) According to the principle that the mass of PAA copolymer is 1 times the mass of carbon nanotubes, PAA copolymer (purchased from Zhejiang Yanyi) is added to the homogeneous dispersion, and the solid content is adjusted to 1%. The mixture is homogenized and dispersed 50 times at 100 MPa to obtain the carbon nanotube dispersion.

[0078] Figure 1 This is a SEM image of the carbon nanotube dispersion obtained in this example. As can be seen from the figure, the carbon nanotubes are uniformly dispersed in the dispersion. At the same time, the tube bundles are long and have extremely small diameters. That is, the carbon nanotube bundles in the dispersion obtained by the present invention have a high aspect ratio.

[0079] Example 2

[0080] This embodiment provides a method for preparing a carbon nanotube dispersion.

[0081] The difference from Example 1 is that in this example, PAA in step (7) is replaced by CMC (purchased from Ashland 7MF).

[0082] Example 3

[0083] This embodiment provides a method for preparing a carbon nanotube dispersion.

[0084] The difference from Example 1 is that, in this example, the sodium dodecylbenzenesulfonate in step (5) is replaced by sodium dodecylsulfonate.

[0085] Example 4

[0086] This embodiment provides a method for preparing a carbon nanotube dispersion.

[0087] The difference from Example 1 is that in this example, the mixed acid solution in step (4) is replaced by a 9% hydrochloric acid solution.

[0088] Example 5

[0089] This embodiment provides a method for preparing a carbon nanotube dispersion.

[0090] The difference from Example 1 is that, in this example, the homogeneous dispersion method in step (6) is: dispersion 100 times at 100 MPa.

[0091] Example 6

[0092] This embodiment provides a method for preparing a carbon nanotube dispersion, as follows:

[0093] (1) Select Wei Carbon I1993 carbon nanotubes with a length of ≥50 μm, a diameter of 1.6-2.2 nm, and a metal Fe content of ≤2%;

[0094] (2) Using a blade crusher to crush the carbon tube raw material to a length of 300-500 μm;

[0095] (3) The crushed carbon nanotubes were calcined at 500 °C for 12 h to remove the onion carbon nanotubes and amorphous carbon;

[0096] (4) The calcined carbon nanotubes were mixed with a mixed acid solution of hydrochloric acid and nitric acid (mass ratio 2:1.5) at a solid-liquid ratio of 1:150, treated at 80°C for 4 hours, washed to neutrality, dried, and the metal content was detected to be ≤2000 ppm;

[0097] (5) mixing the carbon nanotubes obtained in step (4) with a solution containing sodium dodecylbenzene sulfonate in a manner such that the mass of the sodium dodecylbenzene sulfonate is 0.2 times the mass of the carbon nanotubes, with the solid content of the mixed solution being 0.5%, dispersing the mixed solution at 2500 rpm for 20 min, and then grinding and dispersing the mixture using a colloid mill at a linear speed of 70 m / s, a pore size of 2 mm, a power of 60 kW, and a time of 10 min to obtain a first dispersion;

[0098] (6) adjusting the solid content of the first dispersion to 0.8%, and then performing homogeneous dispersion: first dispersing at 40 MPa 10 times, and then dispersing at 80 MPa 10 times to obtain a homogeneous dispersion;

[0099] (7) PAA (purchased from Yamen) was added to the homogeneous dispersion according to the mass of PAA being 0.2 times the mass of the carbon nanotubes, and the solid content was adjusted to 0.5%. The mixture was homogenized and dispersed 30 times at 120 MPa to obtain the carbon nanotube dispersion.

[0100] Example 7

[0101] This embodiment provides a method for preparing a carbon nanotube dispersion, as follows:

[0102] (1) Select Wei Carbon I1993 carbon nanotubes with a length of ≥50 μm, a diameter of 1.6-2.2 nm, and a metal Fe content of ≤2%;

[0103] (2) Using a blade crusher to crush the carbon tube raw material to a length of 300-500 μm;

[0104] (3) The crushed carbon nanotubes were calcined at 300 °C for 12 h to remove the onion carbon nanotubes and amorphous carbon;

[0105] (4) The calcined carbon nanotubes were mixed with a mixed acid solution of hydrochloric acid and nitric acid (mass ratio of 5:0.5) at a solid-liquid ratio of 1:50, treated at 40°C for 24 hours, washed to neutrality, dried, and the metal content was detected to be ≤6000 ppm;

[0106] (5) mixing the carbon nanotubes obtained in step (4) with a solution containing sodium naphthalenesulfonate so that the mass of the carbon nanotubes is 20 times the mass of the sodium naphthalenesulfonate; the solid content of the mixed solution is 3%; the mixed solution is dispersed at 800 rpm for 120 min; and then ground and dispersed using a colloid mill at a linear speed of 15 m / s, a pore size of 0.15 mm, a power of 5 kW, and a time of 120 min to obtain a first dispersion;

[0107] (6) adjusting the solid content of the first dispersion to 1.2%, and then performing homogeneous dispersion: first dispersing at 20 MPa for 40 times, and then dispersing at 40 MPa for 50 times to obtain a homogeneous dispersion;

[0108] (7) PVP (purchased from Ashland K30) was added to the homogeneous dispersion according to the mass of PVP being 20 times the mass of carbon nanotubes, and the solid content was adjusted to 2%. The mixture was homogenized and dispersed 80 times at 80 MPa to obtain the carbon nanotube dispersion.

[0109] Comparative Example 1

[0110] This comparative example provides a method for preparing a carbon nanotube dispersion.

[0111] The difference from Example 1 is that in this comparative example, the carbon nanotube raw material selected in step (1) is about 5 μm in length (purchased from OCSIAL).

[0112] Comparative Example 2

[0113] This comparative example provides a carbon nanotube dispersion, which is commercially available from OCSIAL.

[0114] Comparative Example 3

[0115] This comparative example provides a method for preparing a carbon nanotube dispersion.

[0116] The difference from Example 1 is that in this comparative example, step (3) of calcining and removing impurities is not performed.

[0117] Comparative Example 4

[0118] This comparative example provides a method for preparing a carbon nanotube dispersion.

[0119] The difference from Example 1 is that in this comparative example, step (5) of mixing with the solution containing sodium dodecylbenzenesulfonate is not performed.

[0120] Performance Testing

[0121] The carbon nanotube dispersions provided in Examples 1-7 and Comparative Examples 1-4 were tested for performance as follows:

[0122] (1) Tube bundle length and diameter:

[0123] 1) Sample preparation: Weigh a certain mass of the sample to be tested, accurately weigh its mass as M0, solid content as S%, add PDI with a mass of M1 to dilute, stir and ultrasonicate for 5 minutes, the calculation formula of M1 is: M1 = M0 * (S * 500 / 13 - 1);

[0124] 2) Sample preparation: Weigh a certain amount of diluent, accurately weigh its mass as M2, add anhydrous ethanol of mass M3 to dilute, stir and sonicate for 1 minute. The calculation formula of M3 is: M3 = 9 * M2;

[0125] 3) Use a 2 mL test tube to pipette a drop of the diluted solution onto a silicon wafer, dry it, and test it with SEM.

[0126] 4) Under a magnification of 1KX-5KX, find a uniformly dispersed area, photograph and measure the carbon nanotube length in multiple areas, and collect at least 50 carbon nanotube samples, and calculate the average value (the specific magnification is determined according to the dispersion situation, and it is sufficient to clearly observe the carbon nanotube length);

[0127] 5) Under a magnification of 50KX-100KX, find a suitable area, photograph and measure the long diameter of carbon nanotubes in multiple areas, and collect at least 50 carbon nanotube samples, and calculate the average value (the specific magnification depends on the actual situation, as long as the carbon nanotubes can be clearly observed).

[0128] (2)Abs:

[0129] 1) Turn on the instrument and preheat for 30 minutes, using deionized water as the blank;

[0130] 2) Sample preparation: Weigh a certain mass of the sample to be tested and dilute it with water to a concentration of 0.001%;

[0131] 3) Stir the diluted mixed solution evenly with a clean glass rod (3-5 minutes) until no colloidal particles are visible to the naked eye. (The mother liquor is easier to disperse by stirring. Be careful of any residue sticking to the wall and undispersed residue in the dropper).

[0132] 4) Use a pipette to draw up the dispersed mixture, rinse the cuvette three times, then inject 2 / 3 of the highly diluted solution, wipe the outside of the cuvette clean with a low-dust wipe, place it in the instrument, let it stand for 30 seconds, set the wavelength to 267nm, and read the absorbance value Abs after the value stabilizes;

[0133] 5) Repeat step 4) 2 times. The difference between the 3 results is ±0.09, and the average is taken.

[0134] (3) Viscosity:

[0135] 1) Fill the test container with the sample to be measured, ensuring that no bubbles are introduced;

[0136] 2) Place the container containing the prepared sample in a constant temperature bath and maintain the temperature at 25±0.2℃ for more than 1 hour before testing;

[0137] 3) Select the appropriate rotor and speed (depending on the viscosity to be tested, the 3#30 rpm range of 4000 is preferred, and if it exceeds 90%, change to the 3#12 rpm range of 10000), so that the reading falls between 20% and 90% of the range. Keep the rotor and sample at a constant temperature at the same time, and wipe it dry with dust-free paper before use;

[0138] 4) Start the motor, operate the instrument according to the instruction manual, and record the viscosity value for 1 minute;

[0139] 5) Stop the motor, wait until the rotor stops, then restart the motor and test again; test once every 1 minute, for 3 consecutive times, and report the lowest measured value;

[0140] 6) After the test is completed, remove the rotor and clean it with a suitable solvent.

[0141] (4) Stability:

[0142] 1) Weigh a certain amount of dispersion and dilute it with water until the carbon nanotube solid content reaches 0.001%;

[0143] 2) Disperse the diluted solution at high speed for 1 minute to ensure that the slurry is well dispersed in water;

[0144] 3) Transfer the dispersed slurry aqueous solution to a clean 100 mL centrifuge tube with the liquid level near the 80 mL mark. One centrifuge tube is sufficient for one sample (Note: The mass of the four centrifuge tubes should remain consistent after filling).

[0145] 4) The remaining dispersed solution was subjected to UV testing, and the peak value at a wavelength of 267 nm was read and recorded as the OD value of the sample before centrifugation;

[0146] 5) Place the centrifuge tube in a centrifuge and centrifuge at 9500 rpm for 30 min.

[0147] 6) After centrifugation, gently remove the centrifuge tube and place it on a centrifuge tube rack (Note: Do not shake the centrifuge tube vigorously);

[0148] 7) Gently open the centrifuge tube cap and use a pipette to aspirate the supernatant after centrifugation for UV testing (Note: When aspirating the supernatant, place the pipette tip in the middle of the liquid surface, submerge 2 mm below the liquid surface, and aspirate gently. Do not allow the liquid to flow back after aspirating).

[0149] 8) Read the peak value at a wavelength of 267 nm and record it as the OD value of the sample after centrifugation;

[0150] 9) Sample slurry stability = OD value of sample after centrifugation / OD value of sample before centrifugation.

[0151] The test results are shown in Table 1:

[0152] Table 1

[0153]

[0154]

[0155] Note: The bundle length and bundle diameter are average values.

[0156] From the examples and performance tests, it can be seen that the preparation method provided by the present invention can obtain a carbon nanotube dispersion with a high aspect ratio, wherein the tube bundle length is above 2.5 μm, and optimally can reach above 10 μm, and the diameter is relatively small, and optimally can reach below 20 nm.

[0157] From the comparison between Example 1 and Example 3, it can be seen that the use of a dispersant containing an aromatic ring is more conducive to the dispersion of carbon nanotubes, as the aromatic ring is more likely to form π-π conjugation with the carbon nanotubes, which is more conducive to peeling off the carbon nanotubes and the aggregation between the carbon nanotubes, and the dispersibility is stronger. Therefore, the use of a dispersant containing an aromatic ring is more conducive to the dispersion of carbon nanotubes, and it is easier to obtain carbon nanotube bundles with longer lengths.

[0158] From the comparison between Example 1 and Example 4, it can be seen that during the acid treatment, the carbon nanotubes are treated simultaneously with an oxidizing acid and a non-oxidizing acid. The oxidizing acid can modify the carbon nanotubes and increase the dispersibility of the carbon nanotubes, thereby ensuring that the carbon nanotube bundles in the obtained dispersion are longer.

[0159] A comparison between Example 1 and Example 5 shows that, during homogeneous dispersion, the use of multi-stage dispersion and the control of the dispersing force are more conducive to obtaining carbon nanotube bundles with a higher aspect ratio. In Example 5, the aspect ratio of the carbon nanotube bundles is reduced due to the one-step dispersion. However, due to the longer time and higher pressure, the dispersant segments are broken, the slurry viscosity is reduced, and the Abs is higher.

[0160] A comparison between Example 1 and Comparative Example 1 shows that the specific raw materials selected by the present invention can obtain a carbon nanotube dispersion with a higher aspect ratio; a comparison between Example 1 and Comparative Example 2 shows that the carbon nanotube bundles in the carbon nanotube dispersion obtained by the present invention have a higher aspect ratio, lower viscosity, and better stability.

[0161] From the comparison between Example 1 and Comparative Example 3, it can be seen that calcination in the preparation method to remove non-carbon tube carbon and coated amorphous carbon is beneficial to the removal of metal ions contained in carbon nanotubes, carbon nanotubes are easy to disperse, and the slurry has low viscosity, is not easy to gel, and has good stability.

[0162] From the comparison between Example 1 and Comparative Example 4, it can be seen that the present invention uses the first dispersant to disperse the carbon nanotubes before homogeneous dispersion, which can promote the dispersion of the carbon nanotubes, so that the diameter of the carbon nanotube bundles in the final dispersion is smaller and the aspect ratio is higher, and the stability of the carbon nanotube dispersion is greatly increased.

[0163] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a carbon nanotube dispersion, characterized in that: The preparation method comprises: S1. removing impurities from the carbon nanotube fragments; S2. The carbon nanotubes after impurity removal treatment are mixed with a solution containing a first dispersant and ground and dispersed to obtain a first dispersion; S3. The first dispersion liquid is homogeneously dispersed for the first time to obtain a homogeneous dispersion liquid.

2. The preparation method according to claim 1, characterized in that The carbon nanotube scraps are selected from single-walled carbon nanotubes and / or multi-walled carbon nanotubes; Preferably, the length of the carbon nanotube fragments is ≤2 mm, preferably 300-500 μm; Preferably, the total metal content of the carbon nanotube scrap is ≤20000 ppm; Preferably, the carbon nanotube crushed material is obtained by crushing the carbon nanotube raw material; Preferably, the length of the carbon nanotube raw material is ≥30 μm, preferably ≥50 μm, and the diameter is preferably 1-3 nm.

3. The preparation method according to claim 1 or 2, characterized in that The total metal content of the carbon nanotubes after the impurity removal treatment is ≤8000ppm; Preferably, the impurity removal treatment comprises calcining the carbon nanotube fragments, or performing an acid treatment, or first calcining and then performing an acid treatment; Preferably, the calcination temperature is 300-500°C, preferably 330-400°C, and the calcination time is 3-12h, preferably 4-8h; Preferably, the carbon nanotubes are acid-treated using a mixed acid solution; Preferably, the mixed acid comprises a non-oxidizing acid and an oxidizing acid, and preferably the mass ratio of the non-oxidizing acid to the oxidizing acid is (2-5):(0.5-1.5); Preferably, the non-oxidizing acid is selected from hydrochloric acid; Preferably, the oxidizing acid is selected from nitric acid; Preferably, the mass concentration of the mixed acid solution is 5-15%, preferably 7-12%; Preferably, the solid-liquid ratio of the carbon nanotubes to the mixed acid solution is 1:(50-500), preferably 1:(80-300); Preferably, the temperature of the acid treatment is 40-80°C, preferably 50-70°C; Preferably, the acid treatment time is 4-24h, preferably 6-18h; Preferably, the method further comprises washing after the acid treatment, preferably washing to neutrality.

4. The preparation method according to any one of claims 1 to 3, characterized in that The diameter of the bundles formed by the carbon nanotubes in the first dispersion is 80-300 nm; Preferably, the first dispersant is selected from any one or a combination of at least two of sodium benzenesulfonate, sodium naphthalenesulfonate, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium dodecylsulfonate, sodium polystyrenesulfonate, sodium cholate, sodium deoxycholate, sodium lauroyl-N-methylaminoacetate, dodecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, Tween-85, and Triton X-405, preferably any one or a combination of at least two of sodium benzenesulfonate, sodium naphthalenesulfonate, sodium polystyrenesulfonate, and sodium dodecylbenzenesulfonate; Preferably, the amount of the first dispersant added is 0.2-20 times, preferably 0.3-10 times, the mass of the carbon nanotubes after the impurity removal treatment; Preferably, the solid content of the mixed solution after mixing in step S2 is 0.5-3%, preferably 1-2%; Preferably, the mixing speed in step S2 is 800-2500 rpm, and the mixing time is preferably 20-120 min; Preferably, the grinding and dispersion adopts at least one of a colloid mill, a three-roll mill or a disc mill; Preferably, the linear speed of the grinding and dispersing is 15-70 m / s, the pore size is 0.15-2 mm, the power is 5-60 kW, and the time is 10-120 min.

5. The preparation method according to any one of claims 1 to 4, characterized in that The diameter of the bundles formed by the carbon nanotubes in the homogeneous dispersion is 30-150 nm and the length is 10-30 μm; Preferably, in step S3, before performing the first homogeneous dispersion, the solid content of the first dispersion is adjusted to 0.8-1.2%; Preferably, the parameters of the first homogeneous dispersion include: first dispersing at 20-40 MPa, preferably 25-35 MPa, for 10-40 times, preferably 15-30 times, and then dispersing at 40-80 MPa, preferably 50-70 MPa, for 10-50 times, preferably 20-40 times.

6. The preparation method according to any one of claims 1 to 5, characterized in that The preparation method further comprises: S4. The homogeneous dispersion liquid is mixed with a second dispersant and subjected to a second homogeneous dispersion to obtain the carbon nanotube dispersion liquid.

7. The preparation method according to claim 6, characterized in that The diameter of the tube bundles formed by the carbon nanotubes in the carbon nanotube dispersion is 1-20 nm, and the length is 5-15 μm.

8. The preparation method according to claim 6 or 7, characterized in that The second dispersant is selected from any one or a combination of at least two of acrylic acid copolymer, polyvinyl pyrrolidone or carboxymethyl cellulose; Preferably, the amount of the second dispersant added is 0.2-20 times, preferably 0.5-10 times, the mass of the carbon nanotubes after the impurity removal treatment; Preferably, the further comprising: adjusting the solid content of the solution to 0.5-2%, preferably 0.8-1.5%, after mixing the homogeneous dispersion and the second dispersant; Preferably, the parameters of the second homogeneous dispersion include: dispersing at 80-120 MPa, preferably 85-110 MPa, for 30-80 times, preferably 40-60 times.

9. A carbon nanotube dispersion prepared by the method according to any one of claims 1 to 8; Preferably, the solid content of the carbon nanotube dispersion is 0.5-2%, preferably 0.8-1.5%; Preferably, in the carbon nanotube dispersion, the diameter of the bundles formed by the carbon nanotubes is 1-20 nm and the length is 5-15 μm.

10. Use of the carbon nanotube dispersion according to claim 9 in mechanics, electricity, and thermodynamics, preferably in electricity, further preferably in electrochemical devices, and even more preferably in secondary batteries.

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