Doped carbon nanotube fiber and preparation method thereof

Abstract

The invention discloses a doped carbon nanotube fiber and a preparation method thereof, and the preparation method comprises the following steps: firstly, carrying out nitrogen doping modification on a carbon nanotube fiber to obtain a nitrogen-doped carbon nanotube fiber; and then doping agent doping modification is performed on the nitrogen-doped carbon nanotube fiber by adopting a doping agent, so that the conductivity and doping stability of the carbon nanotube fiber are greatly improved. In addition, when the method is adopted to modify the carbon nanotube fibers, the influence on the strength of the carbon nanotube fibers is small in the process.

Description

Technical Field

[0001] The present invention belongs to the field of carbon nanotube fiber preparation, and in particular relates to a doped carbon nanotube fiber and a preparation method thereof. Background Art

[0002] Carbon nanotube fibers are micrometer-diameter, continuous macroscopic fibers constructed from nanometer-sized carbon nanotubes. These macroscopic materials possess the exceptional properties of carbon nanotubes, such as high strength, high conductivity, and low density. To maximize these exceptional properties, carbon nanotube fibers typically possess high density and high orientation. Wet spinning is the preferred method for producing these carbon nanotube fibers. However, the electrical conductivity of wet-spinning carbon nanotube fibers still lags behind that of metallic materials. This is primarily because wet-spinning carbon nanotube fibers are assembled from bundles of carbon nanotubes, with multiple fibers assembled into fiber bundles. This process inevitably creates voids and non-oriented regions, resulting in a decrease in electrical conductivity. Furthermore, the charge carrier concentration of carbon nanotubes is significantly lower than that of metallic materials. Therefore, optimizing the assembly structure and carrier concentration of carbon nanotube fibers is an effective approach to improving their electrical conductivity.

[0003] Significant progress has been made in introducing surface charge transfer dopants into carbon materials through doping. Doping improves the electrical conductivity of carbon nanotube fibers primarily by altering the Fermi level of the carbon nanotubes, increasing their carrier concentration and, consequently, enhancing their electrical conductivity. However, dopants are only physically adsorbed and intercalated into the carbon nanotubes within the fibers. This makes it difficult to maintain their conductive properties in extreme environments such as high humidity and high temperature, resulting in poor environmental stability. Summary of the Invention

[0004] To solve the above problems, the present invention provides a doped carbon nanotube fiber, comprising one or more carbon nanotube fibers, wherein the one or more carbon nanotube fibers are doped with at least two dopants, wherein at least one dopant is nitrogen doping and at least one dopant is a metal chloride or a halogen; the carbon nanotube fiber has an electrical conductivity of ≥14MS / m and a stability time in air of ≥24h.

[0005] The present invention also provides a method for preparing doped carbon nanotube fibers, which comprises firstly nitrogen-doping the carbon nanotube fibers to obtain nitrogen-doped carbon nanotube fibers; and then doping the nitrogen-doped carbon nanotube fibers with a dopant to obtain doped carbon nanotube fibers.

[0006] According to a specific embodiment of the present invention, the nitrogen doping is performed by a plasma method or a co-heating method, preferably a plasma method.

[0007] According to a specific embodiment of the present invention, nitrogen doping modification adopts a plasma method, which specifically includes the following steps: first, the carbon nanotube fibers are subjected to a first plasma treatment in an O2 / Ar mixed atmosphere; then, the carbon nanotube fibers are subjected to a second plasma treatment in an N2 / Ar mixed atmosphere to obtain nitrogen-doped carbon nanotube fibers.

[0008] According to a specific embodiment of the present invention, in the O2 / Ar mixed atmosphere, the volume ratio of O2 and Ar is 50:50 to 15:85; and / or, in the N2 / Ar mixed atmosphere, the volume ratio of N2 and Ar is 25:75 to 75:25.

[0009] According to a specific embodiment of the present invention, the radio frequency power of the first plasma treatment is 150W-250W; and / or, the radio frequency power of the second plasma treatment is 150W-250W.

[0010] According to a specific embodiment of the present invention, nitrogen doping modification adopts a co-mixing heating method, which specifically includes the following steps: mixing carbon nanotube fibers with nitrogen-containing organic matter, so that the nitrogen-containing organic matter is coated on the surface of the carbon nanotube fibers, and heating them under N2 or Ar atmosphere to obtain nitrogen-doped carbon nanotube fibers.

[0011] According to a specific embodiment of the present invention, the nitrogen-containing organic compound is selected from one or more of urea and acetonitrile.

[0012] According to a specific embodiment of the present invention, the mass ratio of carbon nanotube fibers to nitrogen-containing organic matter is 1:1 to 2:1.

[0013] According to a specific embodiment of the present invention, the dopant is a solid dopant, and the dopant doping adopts a dual-temperature zone gas phase transfer method, which specifically includes the following steps: placing the dopant and the carbon nanotube fiber in different areas of a dual-temperature zone system, and heating them separately under vacuum conditions; heating the area of ​​the dopant to above the boiling point of the dopant, and heating the area of ​​the carbon nanotube fiber to 20-30°C above the temperature of the dopant temperature zone, to achieve the deposition and intercalation of the dopant on the carbon nanotube fiber, and prepare the doped carbon nanotube fiber.

[0014] According to a specific embodiment of the present invention, the dopant is a solid dopant, preferably a metal chloride. The metal chloride is preferably one or more of CuCl2, FeCl3, and MoCl5.

[0015] According to a specific embodiment of the present invention, the dopant is a liquid dopant, and the dopant doping adopts a liquid phase doping intercalation method, which specifically includes the following steps: under vacuum conditions, the carbon nanotube fiber is suspended above the dopant, the temperature is raised to above the vaporization temperature of the dopant, and heating is performed to achieve full contact between the carbon nanotube fiber and the dopant gas, thereby achieving doping intercalation of the carbon nanotube fiber and preparing the doped carbon nanotube fiber.

[0016] According to a specific embodiment of the present invention, the dopant is a halogen element, preferably one or both of iodine and bromine.

[0017] According to a specific embodiment of the present invention, during the doping process of the dopant, the carbon nanotube fiber is kept in a tensioned state.

[0018] Beneficial effects:

[0019] The method of the present invention uses nitrogen doping and dopants to dope carbon nanotube fibers, which belong to two types of p-type doping and greatly improve the electrical conductivity of the carbon nanotube fibers. In addition, nitrogen doping is performed on the carbon nanotube fibers before they are modified by the dopant, so that some carbon atoms in the carbon nanotube fibers are replaced by nitrogen atoms. The nitrogen atoms serve as anchoring points, which can reduce the desorption effect of the dopant and improve its doping stability. Compared with doping with only a dopant, the stability of the electrical conductivity of the carbon nanotube fibers can be effectively improved. In addition, when the carbon nanotube fibers are doped using the method of the present invention, the strength of the carbon nanotube fibers decreases during the nitrogen doping process, and the strength of the carbon nanotube fibers after being treated with the dopant recovers to a certain extent, thereby improving the application performance of the carbon nanotube fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the process of preparing carbon nanotube fibers by wet spinning according to the present invention;

[0021] Figure 2 is a photograph of the carbon nanotube fiber prepared in Preparation Example 1;

[0022] Figure 3 Schematic diagram of the dual-temperature zone gas phase transfer method of the present invention;

[0023] Figure 4 is a scanning electron microscope photograph of the carbon nanotube fibers prepared in Example 1;

[0024] Figure 5 is a transmission electron microscope photograph of the carbon nanotube fibers prepared in Example 1;

[0025] Figure 6 1 and 2 are the current / voltage curves of the carbon nanotube fibers of Example 1 and Comparative Examples 1-3. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to specific embodiments.

[0027] The present invention provides a doped carbon nanotube fiber, comprising one or more carbon nanotube fibers, wherein the one or more carbon nanotube fibers are doped with at least two dopants, wherein at least one dopant is nitrogen doping and at least one dopant is a metal chloride or a halogen; the carbon nanotube fiber has an electrical conductivity of ≥14MS / m and a stability time in air of ≥24h.

[0028] The preparation method of the doped carbon nanotube fiber of the present invention comprises the following steps: firstly performing nitrogen doping modification on the carbon nanotube fiber to obtain nitrogen doped carbon nanotube fiber; and then performing dopant modification on the nitrogen doped carbon nanotube fiber with a dopant to obtain doped carbon nanotube fiber.

[0029] The carbon nanotube fibers of the present invention are prepared by wet spinning. Such fibers have the characteristics of high orientation and high density, and are easy to achieve batch production and high performance production.

[0030] Before modifying the carbon nanotube fibers with dopants, they are first nitrogen-doped. These nitrogen atoms serve as anchoring sites for subsequent dopants, providing a strong interaction force for the dopants within the carbon nanotube fibers and reducing the performance failure rate of the carbon nanotube fibers in extreme environments. Nitrogen doping can be achieved using a plasma method or a co-heating method, with the plasma method being preferred.

[0031] In an optional embodiment, the nitrogen doping is performed by a plasma method or a co-heating method, preferably a plasma method.

[0032] In an optional embodiment, nitrogen doping is performed by a plasma method, which specifically includes the following steps: first, the carbon nanotube fibers are subjected to a first plasma treatment in an O2 / Ar mixed atmosphere; then, the carbon nanotube fibers are subjected to a second plasma treatment in an N2 / Ar mixed atmosphere to obtain nitrogen-doped carbon nanotube fibers.

[0033] By controlling the atmosphere composition, plasma power intensity, and duration during the plasma treatment, the conductivity of the doped carbon nanotube fibers can be improved. The first plasma treatment uses a radio frequency power of 150W-250W for 3 minutes, while the second plasma treatment uses a radio frequency power of 150W-250W for 10 minutes.

[0034] In the O2 / Ar mixed atmosphere, the volume ratio of O2 to Ar is 50:50 to 15:85; and / or, in the N2 / Ar mixed atmosphere, the volume ratio of N2 to Ar is 25:75 to 75:25.

[0035] The purpose of the first plasma treatment, conducted in an O2 / Ar mixed atmosphere, is to pre-oxidize the carbon nanotube fibers. This process introduces defects such as oxygen vacancies into the carbon nanotube fibers without significantly damaging the carbon nanotube structure. The presence of an Ar atmosphere enhances the plasma's etching capability while ensuring a stable experimental environment without air interference during the treatment process.

[0036] The purpose of the second plasma treatment in a mixed atmosphere of N2 and Ar is to achieve nitrogen doping of the carbon nanotube fibers; the Ar atmosphere in the process is to ensure that there is no air interference during the treatment process and to provide a stable experimental environment.

[0037] In an optional embodiment, the nitrogen doping modification is performed using a co-heating method, specifically comprising the following steps: mixing the carbon nanotube fibers with a nitrogen-containing organic compound to coat the surface of the carbon nanotube fibers with the nitrogen-containing organic compound, and then heating the carbon nanotube fibers in an N2 or Ar atmosphere to obtain nitrogen-doped carbon nanotube fibers. The heating conditions are: a heating temperature of 180-220°C and a heating time of 12-24 hours.

[0038] The nitrogen-containing organic matter is selected from one or more of urea and acetonitrile. The mass ratio of the carbon nanotube fiber to the nitrogen-containing organic matter is 1:1 to 2:1.

[0039] In an optional embodiment, the dopant is a solid dopant, and the dopant is doped using a dual-temperature zone gas phase transfer method, specifically comprising the following steps: placing the dopant and the carbon nanotube fiber in different areas of a dual-temperature zone system and heating them separately under vacuum conditions; heating the dopant area to above the boiling point of the dopant, and heating the carbon nanotube fiber area to 20-30°C above the dopant temperature zone temperature, to achieve deposition and intercalation of the dopant on the carbon nanotube fiber, thereby preparing the doped carbon nanotube fiber. The solid dopant is a metal chloride, preferably one or more of CuCl2, FeCl3, and MoCl5. The dual-temperature zone system can be a double-ended flask. The heating time of the dual-temperature zone system is 1-72 hours.

[0040] The dopant temperature zone refers to the heating temperature of the dopant region.

[0041] Preferably, the temperature of the region of the carbon nanotube fiber is raised to 20-30° C. above the boiling point of the dopant.

[0042] Preferably, the mass ratio of the carbon nanotube fiber to the dopant is 1:0.5 to 1:5.

[0043] In an optional embodiment, the dopant is a liquid dopant, and the dopant modification is performed using a liquid-phase doping and intercalation method, specifically comprising the following steps: suspending the carbon nanotube fiber above the dopant under vacuum conditions, heating the carbon nanotube fiber to a temperature above the vaporization temperature of the dopant, and heating the carbon nanotube fiber to achieve full contact between the carbon nanotube fiber and the dopant gas, thereby achieving doping and intercalation of the carbon nanotube fiber, thereby producing the doped carbon nanotube fiber. The liquid dopant halogen element is preferably one or both of iodine and bromine.

[0044] By regulating the dopant / raw material ratio, doping temperature, doping time, etc. during the dopant modification process, the conductivity of the doped carbon nanotube fibers can be further improved.

[0045] In an optional embodiment, the carbon nanotube fibers are maintained in a tensioned state during the dopant modification process. Maintaining the carbon nanotube fibers in a tensioned state can further promote the nitrogen doping and doping effects of the carbon nanotube fibers, thereby helping to improve the electrical conductivity and stability of the prepared doped carbon nanotube fibers.

[0046] The conductivity of the doped carbon nanotube fiber prepared by the preparation method of the present invention is ≥14MS / m, and the stability time in air is ≥24h.

[0047] Preparation Example 1:

[0048] The carbon nanotube fibers prepared by wet spinning are shown in the following process diagram: Figure 1 shown.

[0049] The photo of the carbon nanotube fiber prepared in Preparation Example 1 is as follows Figure 2 shown by Figure 2 It can be seen that continuous spinning of carbon nanotube fibers can be achieved through wet spinning, providing a basis for batch processing of fibers.

[0050] Example 1

[0051] The carbon nanotube fibers obtained in Preparation Example 1 were first subjected to plasma pre-oxidation treatment for 3 minutes at 200W RF in a mixed atmosphere of O2 / Ar with a mixing ratio of 1:2; then the carbon nanotube fibers were nitrogen-doped for 10 minutes at 200W plasma in a mixed atmosphere of N2 / Ar with a mixing ratio of 1:2.

[0052] The carbon nanotube fibers that have undergone the above-mentioned nitrogen doping treatment and the dopant MoCl5 are placed at the two ends of a double-ended flask, the flask is evacuated, the temperature of the dopant end is raised to 270°C (the boiling point of MoCl5 is 268°C), and the temperature of the sample end is raised to 300°C to achieve the deposition and intercalation of the dopant on the carbon nanotube fibers. Among them, the mass ratio of carbon nanotube fibers to MoCl5 is 1:1.08; the heating treatment time is 24 hours. The schematic diagram of the dual-temperature zone blending heating is shown in Figure 2. Figure 3 shown.

[0053] The scanning electron microscope photo of the carbon nanotube fibers prepared in Example 1 is as follows: Figure 4 As shown by Figure 4 It can be seen that the doped carbon nanotube fibers maintain good orientation and dense structure, and no dopant particles appear on the fiber surface, proving the uniformity of doping; Figure 5 This is a transmission electron microscope photograph of the cross section of the carbon nanotube fiber prepared in Example 1. It can be seen that the doped carbon nanotube fiber still maintains good orientation and density. At the same time, it can be observed that the dopant is evenly distributed in the carbon nanotube fiber without obvious agglomeration.

[0054] Example 2

[0055] Other conditions and steps are the same as those in Example 1, except that MoCl5 is replaced by CuCl2.

[0056] Example 3

[0057] Other conditions and steps are the same as those in Example 1, except that MoCl5 is replaced by FeCl3.

[0058] Example 4

[0059] Other conditions are the same as those in Example 1, except that, the nitrogen doping treatment adopts the urea blending and heating method, and the specific steps are: mixing the carbon nanotube fibers and urea in a 1:1 ratio so that the urea is coated on the surface of the carbon nanotubes as much as possible, and heating the mixture to 200°C in an Ar atmosphere for 24 hours to achieve nitrogen doping of the carbon nanotube fibers.

[0060] Example 5

[0061] Other conditions are the same as those in Example 1, except that the dopant is liquid dopant iodine, and the doping method is a liquid phase doping intercalation method, which specifically includes: placing the carbon nanotube fiber and the liquid dopant iodine in a vacuum furnace, the carbon nanotube fiber is suspended in a tensioned state above the liquid dopant, and the high-temperature furnace is heated to 205°C (the vaporization temperature of iodine is 184°C) and maintained for 24 hours to ensure that the fiber is in full contact with the dopant, thereby achieving doping intercalation of the carbon nanotube fiber.

[0062] Comparative Example 1

[0063] Other conditions are the same as those in Example 1, except that nitrogen doping is eliminated and the sample obtained in Preparation Example 1 is directly doped with dopants.

[0064] Comparative Example 2

[0065] Other conditions were the same as those in Example 1, except that no dopant modification was performed after the nitrogen doping treatment, and the fibers were only treated at the same temperature.

[0066] Comparative Example 3

[0067] Other conditions were the same as those in Example 1, except that only the sample obtained in Preparation Example 1 was subjected to nitrogen doping treatment.

[0068] Comparative Example 4

[0069] Other conditions are the same as those in Example 5, except that nitrogen doping is eliminated and the sample obtained in Preparation Example 1 is directly doped with iodine as a liquid dopant.

[0070] The carbon nanotube fibers of Preparation Example 1, and the doped carbon nanotube fibers prepared in Examples 1-5 and Comparative Examples 1-4 were characterized and tested. The results are shown in Table 1. The specific testing methods are as follows:

[0071] (1) Linear density test method: Take 10 sections of fixed-length carbon nanotube fibers (>5m) and weigh the fibers using a high-precision balance. After calculating according to the linear density definition (the weight in grams of 1000-meter-long fiber or yarn at the standard regain), exclude the maximum and minimum values ​​and take the average value of the data as the linear density of the carbon nanotube fiber sample.

[0072] (2) Conductivity test method: Fix the carbon nanotube fiber on four pieces of copper tape with silver glue, with the distance between the two middle points of the silver glue being 8 cm. After the silver glue is fully dried, the resistance value of the carbon nanotube fiber is tested by the four-probe method.

[0073]

[0074] Where σ is the conductivity, the unit is Siemens per meter, S / m; L is the test length, 80mm; R is the test resistance value, the unit is ohm, Ω; S is the fiber cross-sectional area, the unit is square millimeter, mm 2 .

[0075] To ensure the stability of the test results, each group of samples was tested for at least 5 groups and the average value was taken.

[0076] (3) Tensile strength test method: Fix the carbon nanotube fiber on a universal tensile testing machine with a test length of 20 mm and a tensile speed of 1 mm / s. According to the formula

[0077]

[0078] Where τ is the tensile strength, in megapascals (MPa); F is the maximum load on the fiber, in Newtons (N); and S is the cross-sectional area of ​​the fiber, in square millimeters (mm). 2 .

[0079] To ensure the stability of the test results, each group of samples was tested for at least 5 groups and the average value was taken.

[0080] (4) Test method for stability time in air: Place the carbon nanotube fiber in a room temperature environment (temperature 25°C, humidity 30%), and characterize the electrical properties of the carbon nanotube fiber every 4 hours. When the performance attenuation rate is greater than 50% and has not recovered in the next test, the fiber doping effect is considered to have failed.

[0081] The cross-sectional areas of the carbon nanotube fibers mentioned above were obtained by cutting the fibers along the cross-section with a focused ion beam, characterizing the cross-sections with a scanning electron microscope, and processing the images with ImageJ software to obtain the fiber cross-sectional areas.

[0082] Table 1

[0083] Linear density (tex) Conductivity (MS / m) Tensile strength (GPa) Stability time in air (h) Preparation Example 1 0.19±0.13 8.54±0.06 2.60±0.17 72 Example 1 0.20±0.20 22.28±0.02 2.24±0.1 72 Example 2 0.19±0.16 16.32±0.03 2.03±0.1 64 Example 3 0.21±0.06 18.35±0.05 2.03±0.1 36 Example 4 0.18±0.12 15.32±0.03 1.92±0.3 24 Example 5 0.19±0.13 14.21±0.03 2.01±0.1 24 Comparative Example 1 0.21±0.14 13.42±0.07 2.35±0.14 16 Comparative Example 2 0.18±0.15 10.00±0.45 2.00±0.25 45 Comparative Example 3 0.18±0.15 9.10±0.45 1.83±0.25 36 Comparative Example 4 0.18±0.20 12.21±0.03 2.30±0.03 12

[0084] By analyzing Example 1 and Comparative Example 1, as well as Example 5 and Comparative Example 4, it can be seen that compared with directly subjecting carbon nanotube fibers to dopant treatment, the conductivity and stability of the doped carbon nanotube fibers prepared by first nitrogen doping them and then subjecting them to dopant modification treatment according to the present invention are significantly improved; the tensile strength is slightly reduced compared to that of only subjecting them to dopant treatment, but the reduction is very small.

[0085] Further analysis of Examples 1-3 and Comparative Example 2 reveals that, compared to plasma nitrogen doping of carbon nanotube fibers alone, nitrogen doping followed by dopant treatment of carbon nanotube fibers significantly improves the electrical conductivity of the nanotube fibers and also improves their tensile strength to a certain extent. Further analysis of Example 5 and Comparative Example 3 reveals that, compared to plasma nitrogen doping of carbon nanotube fibers alone, nitrogen doping followed by dopant treatment of carbon nanotube fibers significantly improves the electrical conductivity of the nanotube fibers and also improves their tensile strength to a certain extent.

[0086] Further analysis of Examples 1 and 4 reveals that nitrogen doping of carbon nanotube fibers can be achieved using both the plasma method and the co-heating method, but the conductivity and stability of the doped carbon nanotube fibers produced using the plasma method are superior. Examples 1 and 5 demonstrate that while both solid and liquid dopant doping methods can produce doped carbon nanotube fibers with excellent performance, the conductivity and stability of the doped carbon nanotube fibers produced using the solid dopant are superior.

[0087] A comprehensive analysis of the data in Table 1 shows that the technical solution of the present invention successively performs nitrogen doping modification and dopant modification, and the two work synergistically to improve the conductivity and stability of the nanotube fibers.

[0088] Unless otherwise specified, all terms used in the present invention have the meanings commonly understood by those skilled in the art. The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes, and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is defined solely by the claims.

Claims

1. A doped carbon nanotube fiber, characterized in that: The method comprises one or more carbon nanotube fibers, wherein the one or more carbon nanotube fibers are doped with at least two dopants, wherein at least one dopant is nitrogen doping and at least one dopant is a metal chloride or a halogen; the electrical conductivity of the doped carbon nanotube fibers is ≥14MS / m and the stability time in air is ≥24h.

2. A method for preparing doped carbon nanotube fibers according to claim 1, characterized in that: First, nitrogen-doped carbon nanotube fibers are subjected to nitrogen doping to obtain nitrogen-doped carbon nanotube fibers; and then a dopant is used to dope the nitrogen-doped carbon nanotube fibers to obtain the doped carbon nanotube fibers.

3. The preparation method according to claim 2, characterized in that The nitrogen doping is performed by a plasma method or a co-heating method, preferably a plasma method.

4. The preparation method according to claim 3, characterized in that The nitrogen doping adopts a plasma method, which specifically includes the following steps: first, the carbon nanotube fiber is subjected to a first plasma treatment in an O2 / Ar mixed atmosphere; then, the carbon nanotube fiber is subjected to a second plasma treatment in an N2 / Ar mixed atmosphere to obtain the nitrogen-doped carbon nanotube fiber.

5. The preparation method according to claim 4, characterized in that In the O2 / Ar mixed atmosphere, the volume ratio of O2 to Ar is 50:50 to 15:85; and / or, in the N2 / Ar mixed atmosphere, the volume ratio of N2 to Ar is 25:75 to 75:

25.

6. The preparation method according to claim 4, characterized in that The radio frequency power of the first plasma treatment is 150W-250W; and / or, the radio frequency power of the second plasma treatment is 150W-250W.

7. The preparation method according to claim 2, characterized in that The nitrogen doping adopts a blending heating method, which specifically includes the following steps: mixing carbon nanotube fibers with nitrogen-containing organic matter to coat the nitrogen-containing organic matter on the surface of the carbon nanotube fibers, and heating them under N2 or Ar atmosphere to obtain the nitrogen-doped carbon nanotube fibers.

8. The preparation method according to claim 7, characterized in that The nitrogen-containing organic matter is selected from one or more of urea and acetonitrile.

9. The preparation method according to claim 7, characterized in that The mass ratio of the carbon nanotube fibers to the nitrogen-containing organic matter is 1:1 to 2:

1.

10. The preparation method according to claim 2, characterized in that The dopant is a solid dopant, and the dopant doping adopts a dual-temperature zone gas phase transfer method, which specifically includes the following steps: placing the dopant and the carbon nanotube fiber in different areas of a dual-temperature zone system, and heating them separately under vacuum conditions; heating the dopant area to above the boiling point of the dopant, and heating the carbon nanotube fiber area to 20-30°C above the dopant temperature zone temperature, to achieve the deposition and intercalation of the dopant on the carbon nanotube fiber, and prepare the doped carbon nanotube fiber.

11. The preparation method according to claim 10, characterized in that: The solid dopant is a metal chloride, and the metal chloride is preferably one or more of CuCl2, FeCl3, and MoCl5.

12. The preparation method according to claim 2, characterized in that The dopant is a liquid dopant, and the dopant doping adopts a liquid phase doping intercalation method, which specifically includes the following steps: under vacuum conditions, the carbon nanotube fiber is suspended above the dopant, the temperature is raised to above the vaporization temperature of the dopant, and heating is performed to achieve full contact between the carbon nanotube fiber and the dopant gas, thereby achieving doping intercalation of the carbon nanotube fiber and preparing the doped carbon nanotube fiber.

13. The preparation method according to claim 12, characterized in that The liquid dopant is a halogen element, preferably one or both of iodine and bromine. 14 . The preparation method according to claim 2 , wherein during the doping process, the carbon nanotube fibers are kept in a tensioned state.

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