Nitrogen-doped carbon nanotube / copper composite fiber, and preparation method and application thereof

Abstract

The application discloses nitrogen-doped carbon nanotube / copper composite fibers, a preparation method and application thereof. The nitrogen-doped carbon nanotube / copper composite fiber comprises a nitrogen-doped carbon nanotube fiber and a copper layer coated on the surface of the nitrogen-doped carbon nanotube fiber. The preparation method comprises the following steps: performing first annealing treatment on a carbon nanotube fiber to obtain a treated carbon nanotube fiber; applying a solution containing a nitrogen source to the surface of the treated carbon nanotube fiber, and then performing second annealing treatment to obtain a nitrogen-doped carbon nanotube fiber; and performing copper plating treatment on the surface of the nitrogen-doped carbon nanotube fiber to obtain the nitrogen-doped carbon nanotube / copper composite fiber. The preparation method provided by the application can effectively improve the copper / carbon nanotube composite interface strength through nitrogen doping, thereby improving the mechanical properties and conductive properties of the carbon nanotube / copper composite fiber.

Description

Technical Field

[0001] This invention belongs to the field of composite fiber technology, specifically relating to a nitrogen-doped carbon nanotube / copper composite fiber and its preparation method. Background Technology

[0002] With the rapid development of electronic technology and electrical equipment, traditional conductive materials such as copper have revealed some limitations in certain demanding applications. Copper's high density limits its use in applications requiring lightweight materials, such as aerospace, electric vehicles, and drones. Copper's relatively low mechanical strength and abrasion resistance make it susceptible to mechanical damage and deformation, affecting its application in high-intensity environments. Although copper possesses some corrosion resistance, its performance remains unsatisfactory in certain harsh environments (such as the ocean and chemical plants).

[0003] Carbon nanotubes possess extremely high strength and toughness, making them among the strongest materials known to date. Their density is significantly lower than copper, making them an ideal choice for lightweight materials. Carbon nanotubes exhibit extremely high electrical conductivity, enabling them to effectively conduct electric current. They also demonstrate excellent stability and corrosion resistance in harsh chemical environments. Carbon nanotube fibers (CNTFs) are macroscopic assemblies of carbon nanotubes, inheriting their excellent properties and possessing high strength, lightweight, and good electrical conductivity.

[0004] Therefore, researchers have developed a novel composite material—carbon nanotube / copper composite fiber—combining the conductivity of copper with the lightweight and high-strength properties of carbon nanotubes. For example, CN 116377712A further enhances the conductivity of carbon nanotube fibers by plating copper on them, compensating for the shortcomings of carbon nanotubes in large-scale current transmission. Similarly, CN112760974A shows that copper-plated carbon nanotube fibers combine the advantages of both copper and carbon nanotubes, exhibiting high strength and toughness, and capable of withstanding greater mechanical stress. In the fields of microelectronics and flexible electronics, materials like CN 117747311A are used to manufacture electrodes with high conductivity and high capacitance, improving device performance and lifespan. Copper-plated carbon nanotube fibers can also be used to manufacture lightweight, high-strength wires and structural components, reducing the weight of aircraft and spacecraft and improving fuel efficiency. Using this composite material in electric vehicles can reduce vehicle weight, improve battery efficiency, and extend driving range.

[0005] However, existing carbon nanotube / copper composite fibers have the following shortcomings: the adhesion between carbon nanotube fibers and the copper layer is weak, and the copper-carbon composite interface is not tightly bonded, which can easily lead to the copper layer falling off or peeling off, affecting the overall performance and service life of the material; in addition, due to the complex microstructure of the carbon nanotube fiber surface, the thickness and uniformity of the copper layer are difficult to control, which may lead to local thickness unevenness, affecting the conductivity and mechanical properties; and the copper plating process is complex, involving multiple steps, and has strict requirements for operating conditions, and the slightest carelessness may lead to plating quality problems. Summary of the Invention

[0006] The main objective of this invention is to provide a nitrogen-doped carbon nanotube / copper composite fiber, its preparation method, and its application, so as to overcome the shortcomings of the prior art.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0008] One aspect of the present invention provides a nitrogen-doped carbon nanotube / copper composite fiber, comprising nitrogen-doped carbon nanotube fibers and a copper layer coating the surface of the nitrogen-doped carbon nanotube fibers.

[0009] Another aspect of the present invention provides a method for preparing nitrogen-doped carbon nanotube / copper composite fibers, comprising:

[0010] The carbon nanotube fibers were subjected to a first annealing treatment to obtain the treated carbon nanotube fibers.

[0011] A solution containing a nitrogen source was applied to the surface of the treated carbon nanotube fibers, followed by a second annealing treatment to obtain nitrogen-doped carbon nanotube fibers.

[0012] The nitrogen-doped carbon nanotube fiber was subjected to copper plating to obtain nitrogen-doped carbon nanotube / copper composite fiber.

[0013] Another aspect of the present invention provides nitrogen-doped carbon nanotube / copper composite fibers prepared by the aforementioned preparation method, wherein the electrical conductivity of the nitrogen-doped carbon nanotube / copper composite fibers is 0.9 × 10⁻⁶. 7 -1.5×10 7 S / m, specific conductivity 4000-5000 S·m 2 / kg.

[0014] Another aspect of the present invention provides the application of the aforementioned nitrogen-doped carbon nanotube / copper composite fibers in the preparation of flexible composite wires.

[0015] Compared with the prior art, the technical solution of the present invention has at least the following advantages:

[0016] The preparation method provided by this invention involves nitrogen doping the surface of carbon nanotube fibers. This results in a more compact Cu / C composite interface compared to the original carbon nanotube / copper composite fibers. Furthermore, it improves the uniformity of copper layer deposition during copper plating, leading to a high-quality copper layer. The nitrogen-doped carbon nanotube / copper composite fibers provided by this invention exhibit high electrical conductivity and tensile strength, demonstrating excellent performance and making them suitable for fabricating flexible composite wires. Moreover, the preparation method provided by this invention is simple, highly controllable, and helps reduce costs. Attached Figure Description

[0017] 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, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the preparation process of nitrogen-doped carbon nanotube fibers in a typical embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of an electroplating mold and a DC copper plating device used in a typical embodiment of the present invention;

[0020] Figure 3 This is a scanning electron microscope image of the cross-section of the original carbon nanotube / copper composite fiber prepared in Comparative Example 1 of this invention.

[0021] Figure 4 This is a scanning electron microscope image of the cross-section of the nitrogen-doped carbon nanotube / copper composite fiber prepared in Example 1 of the present invention;

[0022] Figure 5 This is a scanning electron microscope image of the surface of the original carbon nanotube / copper composite fiber prepared in Comparative Example 1 of this invention.

[0023] Figure 6 This is a scanning electron microscope image of the surface of the nitrogen-doped carbon nanotube / copper composite fiber prepared in Example 1 of the present invention;

[0024] Figure 7 A comparison of the specific conductivity of the original carbon nanotube / copper composite fiber prepared in Comparative Example 1, the high-temperature annealed carbon nanotube / copper composite fiber prepared in Comparative Example 2, and the nitrogen-doped carbon nanotube / copper composite fiber prepared in Example 1.

[0025] Figure 8 This is a scanning electron microscope image of the surface of the nitrogen-doped carbon nanotube / copper composite fiber prepared in Example 1 of the present invention. Detailed Implementation

[0026] The invention will be more fully understood by reading the following detailed description. However, it should be understood that the detailed description disclosed below is merely exemplary of the invention, which can be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims and as a representative basis for teaching those skilled in the art to employ the invention in different ways in any suitable detailed embodiment.

[0027] As one aspect of the technical solution of the present invention, a nitrogen-doped carbon nanotube / copper composite fiber includes nitrogen-doped carbon nanotube fibers and a copper layer coating the surface of the nitrogen-doped carbon nanotube fibers.

[0028] In some implementations, the thickness of the copper layer is 1-5 μm.

[0029] As another aspect of the technical solution of the present invention, a method for preparing nitrogen-doped carbon nanotube / copper composite fibers includes:

[0030] The carbon nanotube fibers were subjected to a first annealing treatment to obtain the treated carbon nanotube fibers.

[0031] A solution containing a nitrogen source was applied to the surface of the treated carbon nanotube fibers, followed by a second annealing treatment to obtain nitrogen-doped carbon nanotube fibers.

[0032] The nitrogen-doped carbon nanotube fiber was subjected to copper plating to obtain nitrogen-doped carbon nanotube / copper composite fiber.

[0033] In some embodiments, the carbon nanotubes contained in the carbon nanotube fibers include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0034] In some embodiments, the carbon nanotube fibers include, but are not limited to, carbon nanotube fibers prepared by floating catalysis or carbon nanotube fibers prepared by electrospinning.

[0035] In some embodiments, the carbon nanotube fibers have a diameter of 30-100 μm.

[0036] In some embodiments, the preparation method includes: subjecting carbon nanotube fibers to the first annealing treatment under a protective atmosphere.

[0037] In some preferred embodiments, the protective atmosphere includes, but is not limited to, a nitrogen atmosphere or an argon atmosphere.

[0038] In some preferred embodiments, the temperature of the first annealing treatment is 500-800°C and the time is 1-3 hours.

[0039] In some embodiments, the concentration of the nitrogen source in the nitrogen-containing solution is 3-10 mg / mL.

[0040] In some embodiments, the nitrogen source includes, but is not limited to, any one or a combination of two or more of melamine, polyaniline, pyridine, and urea.

[0041] This invention uses nitrogen-containing macromolecules such as melamine as a nitrogen source. High-temperature annealing is used to modify the surface of carbon nanotube fibers with nitrogen-containing macromolecules, followed by copper plating to obtain nitrogen-doped carbon nanotube / copper composite fibers. Nitrogen doping on the surface of carbon nanotube fibers effectively improves the interfacial hydrophilicity, which is beneficial for improving the wettability of copper ions, promoting the uniform deposition of copper on the surface of carbon nanotube fibers and within some pores of the carbon nanotube fibers, and increasing the interfacial bonding strength of copper / carbon nanotubes, thereby improving the mechanical and electrical properties of the carbon nanotube / copper composite fibers.

[0042] In some implementations, the method of application includes, but is not limited to, soaking.

[0043] In some preferred embodiments, the soaking time is 10-60 minutes.

[0044] In some embodiments, the preparation method includes performing the second annealing treatment under a protective atmosphere.

[0045] In some preferred embodiments, the protective atmosphere includes, but is not limited to, any one or a combination of two or more of nitrogen, argon, and ammonia.

[0046] In some preferred embodiments, the second annealing treatment is performed at a temperature of 500-800°C for 1-3 hours.

[0047] In some implementations, the copper plating process employs methods including, but not limited to, electrodeposition.

[0048] In some preferred embodiments, the copper plating process is DC copper plating, specifically including: providing a copper sulfate electrodeposition solution, using a DC power supply as an external power source, employing a dual-electrode system for copper plating, using the nitrogen-doped carbon nanotube fiber as the negative electrode, and a copper plate as the positive electrode.

[0049] In some more preferred embodiments, the copper sulfate electrodeposition solution is obtained by mixing copper sulfate, concentrated sulfuric acid, concentrated hydrochloric acid and water in a mass-volume ratio of (100-300) g: (10-500) mL: (100-1000) μL: (1-3) L.

[0050] In some more preferred embodiments, the current of the DC power supply is 5-10mA.

[0051] In some more preferred embodiments, the copper plating process takes 10-60 seconds.

[0052] In some more specific embodiments, the preparation method of the nitrogen-doped carbon nanotube / copper composite fiber includes the following steps:

[0053] (1) Carbon nanotube fibers are annealed at high temperature (500-800℃, treatment time 1-3h) in an inert gas (e.g. nitrogen or argon) atmosphere;

[0054] (2) Subsequently, the high-temperature annealed carbon nanotube fibers are immersed in a nitrogen-containing solution, and after drying (80℃, 2-10h) and a second high-temperature annealing process, nitrogen-doped carbon nanotube fibers are obtained; the nitrogen-containing solution is mainly a nitrogen-containing macromolecule solution, including melamine, polyaniline, pyridine, urea, etc.; the concentration of the nitrogen-containing macromolecule solution is controlled at 3-10mg / mL, and the immersion time is 10-60min;

[0055] (3) Dissolve 180g CuSO4·5H2O, 33mL concentrated sulfuric acid and 100μL concentrated hydrochloric acid in 1L deionized water to prepare copper sulfate electrodeposition solution, and prepare nitrogen-doped carbon nanotube / copper composite fibers by electrodeposition method (e.g. DC copper plating); The DC copper plating method specifically includes the following steps: using a DC power supply as an external power supply, using a dual electrode system for copper plating, using nitrogen-doped carbon nanotube fibers as the negative electrode, and two symmetrically placed copper plates as the positive electrode for DC copper plating.

[0056] The nitrogen doping in the nitrogen-doped carbon nanotube fibers described in this invention can effectively promote the uniform deposition of copper on the surface of the carbon nanotube fibers and in some pores, enhance the interfacial composite of copper / carbon nanotubes, and form core-shell structured nitrogen-doped carbon nanotube / copper composite fibers.

[0057] In some more specific embodiments, the preparation process of the nitrogen-doped carbon nanotube fibers is as follows: Figure 1 As shown, carbon nanotube fibers (CNTF) are first annealed at high temperature in an argon atmosphere at 500°C. Then, the annealed carbon nanotube fibers (tCNTF) are immersed in a nitrogen-containing solution (such as melamine solution) to obtain immersed carbon nanotubes (tCNTF@N). After drying, they are annealed at high temperature again to obtain nitrogen-doped carbon nanotube fibers (CNTF@N).

[0058] In some more specific implementation plans, the following methods are adopted: Figure 2 The electroplating mold and DC copper plating device shown are used to perform copper plating on the surface of the nitrogen-doped carbon nanotube fiber (CNTF@N) by electrodeposition to obtain nitrogen-doped carbon nanotube / copper composite fiber.

[0059] As another aspect of the technical solution of the present invention, it also relates to nitrogen-doped carbon nanotube / copper composite fibers prepared by the aforementioned preparation method, wherein the electrical conductivity of the nitrogen-doped carbon nanotube / copper composite fibers is 0.9 × 10⁻⁶. 7 -1.5×10 7 S / m, specific conductivity 4000-5000 S·m 2 / kg.

[0060] As another aspect of the technical solution of the present invention, it also relates to the application of the aforementioned nitrogen-doped carbon nanotube / copper composite fiber in the preparation of flexible composite wires.

[0061] In summary, this invention first anneales carbon nanotube fibers at high temperature, then immerses the annealed carbon nanotube fibers in a nitrogen-containing solution for a second high-temperature annealing to obtain nitrogen-doped carbon nanotube fibers. Finally, nitrogen-doped carbon nanotube / copper composite fibers are prepared using an electrochemical deposition method. The preparation method of this invention is simple and controllable. Nitrogen-doped modified carbon nanotube fibers can effectively improve the interfacial strength of the copper / carbon nanotube composite, thereby improving the mechanical and electrical properties of the carbon nanotube / copper composite fibers, providing a new design approach for future lightweight and flexible composite wire fabrication.

[0062] The present invention is further illustrated below by way of examples, but the invention is not limited to the scope of the examples described. All reagents and raw materials used in the following examples are commercially available, and test methods not specifically specified are generally performed under conventional conditions or according to the conditions recommended by the respective manufacturers.

[0063] Example 1

[0064] This embodiment provides a nitrogen-doped carbon nanotube / copper composite fiber, the preparation method of which is as follows:

[0065] (1) Carbon nanotube fibers prepared by the floating catalytic method were subjected to high-temperature annealing under a nitrogen atmosphere. The carbon nanotube fibers had a diameter of 30 μm, the high-temperature annealing temperature was 500 °C, and the annealing time was 2 h.

[0066] (2) Prepare a 5 mg / mL melamine solution by dissolving melamine powder in a mixture of ethanol and water at a volume ratio of 3:7, and stirring at 60°C until the solution becomes clear and transparent. Immerse carbon nanotube fibers in the melamine solution for 10 minutes, then dry (at 80°C for 3 hours) and undergo a second high-temperature annealing to prepare nitrogen-doped carbon nanotube fibers. The second high-temperature annealing is performed at 500°C for 2 hours in a nitrogen atmosphere.

[0067] (3) Dissolve 180g CuSO4·5H2O, 33mL concentrated sulfuric acid and 100μL concentrated hydrochloric acid in 1L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual-electrode system for copper plating. Nitrogen-doped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 5mA and the copper plating time is set to 20s.

[0068] (4) After copper plating, the nitrogen-doped carbon nanotube / copper composite fibers were repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fibers were air-dried at room temperature to obtain the final nitrogen-doped carbon nanotube / copper composite fibers. A scanning electron microscope image of the surface is shown below. Figure 8 .

[0069] The electrical conductivity of the prepared nitrogen-doped carbon nanotube / copper composite fiber is 1.02 × 10⁻⁶. 7 S / m, specific conductivity 4196 S·m 2 / kg.

[0070] Example 2

[0071] This embodiment provides a nitrogen-doped carbon nanotube / copper composite fiber, the preparation method of which is as follows:

[0072] (1) Carbon nanotube fibers prepared by the floating catalytic method were subjected to high-temperature annealing under a nitrogen atmosphere. The carbon nanotube fibers had a diameter of 30 μm, the high-temperature annealing temperature was 500 °C, and the annealing time was 2 h.

[0073] (2) Prepare a 5 mg / mL melamine solution by dissolving melamine powder in a mixture of ethanol and water at a volume ratio of 3:7, and stirring at 60°C until the solution becomes clear and transparent. Immerse carbon nanotube fibers in the melamine solution for 20 minutes, then dry (at 80°C for 3 hours) and undergo a second high-temperature annealing to prepare nitrogen-doped carbon nanotube fibers. The second high-temperature annealing is performed at 500°C for 2 hours in a nitrogen atmosphere.

[0074] (3) Dissolve 180g CuSO4·5H2O, 33mL concentrated sulfuric acid and 100μL concentrated hydrochloric acid in 1L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual-electrode system for copper plating. Nitrogen-doped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 5mA and the copper plating time is set to 40s.

[0075] (4) After copper plating, the nitrogen-doped carbon nanotube / copper composite fiber is repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fiber is air-dried at room temperature to obtain the final nitrogen-doped carbon nanotube / copper composite fiber.

[0076] The electrical conductivity of the prepared nitrogen-doped carbon nanotube / copper composite fiber is 1.11 × 10⁻⁶. 7 S / m, specific conductivity 4387 S·m 2 / kg.

[0077] Example 3

[0078] This embodiment provides a nitrogen-doped carbon nanotube / copper composite fiber, the preparation method of which is as follows:

[0079] (1) Carbon nanotube fibers prepared by the floating catalytic method were subjected to high-temperature annealing under a nitrogen atmosphere. The carbon nanotube fibers had a diameter of 30 μm, the high-temperature annealing temperature was 500 °C, and the annealing time was 2 h.

[0080] (2) Prepare a 5 mg / mL melamine solution by dissolving melamine powder in a mixture of ethanol and water at a volume ratio of 3:7, and stirring at 60°C until the solution becomes clear and transparent. Immerse carbon nanotube fibers in the melamine solution for 60 minutes, then dry (at 80°C for 3 hours) and undergo a second high-temperature annealing to prepare nitrogen-doped carbon nanotube fibers. The second high-temperature annealing is performed at 600°C for 2 hours in a nitrogen atmosphere.

[0081] (3) Dissolve 180g CuSO4·5H2O, 33mL concentrated sulfuric acid and 100μL concentrated hydrochloric acid in 1L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual-electrode system for copper plating. Nitrogen-doped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 5mA and the copper plating time is set to 60s.

[0082] (4) After copper plating, the nitrogen-doped carbon nanotube / copper composite fiber is repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fiber is air-dried at room temperature to obtain the final nitrogen-doped carbon nanotube / copper composite fiber.

[0083] The electrical conductivity of the prepared nitrogen-doped carbon nanotube / copper composite fiber is 1.42 × 10⁻⁶. 7 S / m, specific conductivity 4807 S·m 2 / kg.

[0084] Example 4

[0085] This embodiment provides a nitrogen-doped carbon nanotube / copper composite fiber, the preparation method of which is as follows:

[0086] (1) Carbon nanotube fibers prepared by the floating catalytic method were subjected to high-temperature annealing under a nitrogen atmosphere. The carbon nanotube fibers had a diameter of 50 μm, the high-temperature annealing temperature was 650 °C, and the annealing time was 3 h.

[0087] (2) Prepare a 3 mg / mL melamine solution by dissolving melamine powder in a mixture of ethanol and water at a volume ratio of 3:7, and stirring at 60°C until the solution becomes clear and transparent. Immerse carbon nanotube fibers in the melamine solution for 20 minutes, then dry (at 80°C for 2 hours) and undergo a second high-temperature annealing to prepare nitrogen-doped carbon nanotube fibers. The second high-temperature annealing is performed at 500°C for 3 hours in a nitrogen atmosphere.

[0088] (3) Dissolve 100g CuSO4·5H2O, 10mL concentrated sulfuric acid and 500μL concentrated hydrochloric acid in 2L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual-electrode system for copper plating. Nitrogen-doped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 8mA and the copper plating time is set to 10s.

[0089] (4) After copper plating, the nitrogen-doped carbon nanotube / copper composite fiber is repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fiber is air-dried at room temperature to obtain the final nitrogen-doped carbon nanotube / copper composite fiber.

[0090] Example 5

[0091] This embodiment provides a nitrogen-doped carbon nanotube / copper composite fiber, the preparation method of which is as follows:

[0092] (1) Carbon nanotube fibers prepared by the floating catalytic method were subjected to high-temperature annealing under a nitrogen atmosphere. The diameter of the carbon nanotube fibers was 100 μm, the high-temperature annealing temperature was 800 °C, and the annealing time was 1 h;

[0093] (2) Prepare a 10 mg / mL melamine solution by dissolving melamine powder in a mixture of ethanol and water at a volume ratio of 3:7, and stirring at 60°C until the solution becomes clear and transparent. Immerse carbon nanotube fibers in the melamine solution for 20 minutes, then dry (at 80°C for 10 hours) and undergo a second high-temperature annealing to prepare nitrogen-doped carbon nanotube fibers. The second high-temperature annealing is performed at 800°C for 1 hour in a nitrogen atmosphere.

[0094] (3) Dissolve 300g CuSO4·5H2O, 500mL concentrated sulfuric acid and 1000μL concentrated hydrochloric acid in 3L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual-electrode system for copper plating. Nitrogen-doped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 10mA and the copper plating time is set to 60s.

[0095] (4) After copper plating, the nitrogen-doped carbon nanotube / copper composite fiber is repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fiber is air-dried at room temperature to obtain the final nitrogen-doped carbon nanotube / copper composite fiber.

[0096] Comparative Example 1

[0097] (1) The carbon nanotube fibers prepared by the floating catalytic method were not annealed. The diameter of the carbon nanotube fibers was 30 μm;

[0098] (2) Dissolve 180g CuSO4·5H2O, 33mL concentrated sulfuric acid and 100μL concentrated hydrochloric acid in 1L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual electrode system for copper plating. Undoped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 5mA and the copper plating time is set to 20s.

[0099] (3) After copper plating, the carbon nanotube / copper composite fiber is repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fiber is air-dried at room temperature to obtain the original carbon nanotube / copper composite fiber.

[0100] The electrical conductivity of the prepared carbon nanotube / copper composite fiber is 6.94 × 10⁻⁶. 6 S / m, specific conductivity 3004 S·m 2 / kg.

[0101] Comparative Example 2

[0102] (1) Carbon nanotube fibers prepared by the floating catalytic method were subjected to high-temperature annealing under a nitrogen atmosphere. The carbon nanotube fibers had a diameter of 30 μm, the high-temperature annealing temperature was 500 °C, and the annealing time was 1 h.

[0103] (2) Dissolve 180g CuSO4·5H2O, 33mL concentrated sulfuric acid and 100μL concentrated hydrochloric acid in 1L deionized water to prepare copper sulfate electrodeposition solution. Use a DC power supply as the external power source and adopt a dual electrode system for copper plating. Undoped carbon nanotube fibers are used as the negative electrode and symmetrically placed copper plates are used as the positive electrode. The copper plating current is set to 5mA and the copper plating time is set to 20s.

[0104] (3) After copper plating, the carbon nanotube / copper composite fiber is repeatedly washed with deionized water to remove residual electrolyte. Finally, the composite fiber is air-dried at room temperature to obtain high-temperature annealed carbon nanotube / copper composite fiber.

[0105] The electrical conductivity of the prepared carbon nanotube / copper composite fiber is 8.93 × 10⁻⁶. 6 S / m, specific conductivity 3968 S·m 2 / kg.

[0106] like Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, by comparing the scanning electron microscope (SEM) images of the cross-section and surface of the original carbon nanotube / copper composite fiber with those of the nitrogen-doped carbon nanotube / copper composite fiber, it can be seen that the copper-carbon interface is more tightly bonded after nitrogen doping, the copper layer has higher uniformity, and the copper layer surface is smoother; Figure 7 As shown, compared with the original carbon nanotube / copper composite fiber (CNTF) and the high-temperature annealed carbon nanotube / copper composite fiber (CNTF-500℃), the specific conductivity of nitrogen-doped carbon nanotube / copper composite fiber (CNTF@N) is significantly improved.

[0107] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0108] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A nitrogen-doped carbon nanotube / copper composite fiber, characterized in that, The nitrogen-doped carbon nanotube / copper composite fiber includes nitrogen-doped carbon nanotube fibers and a copper layer coated on the surface of the nitrogen-doped carbon nanotube fibers. The nitrogen-doped carbon nanotube / copper composite fiber is prepared by the following steps: carbon nanotube fibers are subjected to a first annealing treatment at 500-800℃ for 1-3 hours under a nitrogen or argon atmosphere; then immersed in a nitrogen source solution containing melamine, polyaniline, pyridine, or urea for 10-60 minutes; followed by a second annealing treatment at 500-800℃ for 1-3 hours under a nitrogen, argon, or ammonia atmosphere to obtain the nitrogen-doped carbon nanotube fiber; and the surface of the nitrogen-doped carbon nanotube fiber is subjected to DC copper plating to obtain the nitrogen-doped carbon nanotube / copper composite fiber, wherein the thickness of the copper layer is 1-5 μm.

2. A method for preparing nitrogen-doped carbon nanotube / copper composite fibers, characterized in that, include: Carbon nanotube fibers were subjected to a first annealing treatment at 500-800℃ for 1-3 h under a nitrogen or argon atmosphere to obtain the treated carbon nanotube fibers. The treated carbon nanotube fibers are immersed in a solution containing a nitrogen source for 10-60 min, and then subjected to a second annealing treatment at 500-800 °C for 1-3 h in a nitrogen, argon or ammonia atmosphere to obtain nitrogen-doped carbon nanotube fibers. The concentration of the nitrogen source in the nitrogen source solution is 3-10 mg / mL, and the nitrogen source is selected from any one or a combination of two or more of melamine, polyaniline, pyridine and urea. The nitrogen-doped carbon nanotube fiber was subjected to DC copper plating to obtain nitrogen-doped carbon nanotube / copper composite fiber.

3. The preparation method according to claim 2, characterized in that, The carbon nanotubes contained in the carbon nanotube fibers include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

4. The preparation method according to claim 2, characterized in that, The carbon nanotube fibers include carbon nanotube fibers prepared by the floating catalytic method or carbon nanotube fibers prepared by the electrospinning method.

5. The preparation method according to claim 2, characterized in that, The diameter of the carbon nanotube fibers is 30-100 μm.

6. The preparation method according to claim 2, characterized in that, The DC copper plating process specifically includes: providing a copper sulfate electrodeposition solution, using a DC power supply as an external power source, employing a dual-electrode system for copper plating, using the nitrogen-doped carbon nanotube fiber as the negative electrode, and a copper plate as the positive electrode.

7. The preparation method according to claim 6, characterized in that, The copper sulfate electrodeposition solution is obtained by mixing copper sulfate, concentrated sulfuric acid, concentrated hydrochloric acid and water in a mass-to-volume ratio of (100-300) g: (10-500) mL: (100-1000) μL: (1-3) L.

8. The preparation method according to claim 6, characterized in that, The DC power supply has a current of 5-10 mA.

9. The preparation method according to claim 6, characterized in that, The copper plating process takes 10-60 seconds.

10. The nitrogen-doped carbon nanotube / copper composite fiber prepared by the preparation method according to any one of claims 2-9, characterized in that, The electrical conductivity of the nitrogen-doped carbon nanotube / copper composite fiber is 0.9 × 10⁻⁶. 7 -1.5×10 7 S / m, specific conductivity 4000-5000 S·m 2 / kg.

11. The application of the nitrogen-doped carbon nanotube / copper composite fiber as described in claim 1 or 10 in the preparation of flexible composite wires.

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