Highly conductive carbon nanotube composite fibers, methods of making, and systems for making

Abstract

This invention discloses a highly conductive carbon nanotube composite fiber, its preparation method, and a preparation system. The preparation method includes: providing a carbon nanotube precursor; subjecting it to densification treatment in an electrolyte to shrink and form a fiber precursor, and during the shrinkage process, using electrochemical deposition to deposit metal ions into the carbon nanotube precursor; simultaneously, continuously twisting the fiber precursor to obtain the highly conductive carbon nanotube composite fiber. The preparation method provided by this invention utilizes the loose network structure of the precursor, employs a metal ion electrolyte for densification treatment, and simultaneously achieves in-situ uniform composite of metal and carbon nanotube networks through electrochemical deposition; combined with continuous twisting, it enhances the radial penetration ability of metal nanoparticles, realizes the construction of a metal / carbon dual-network structure, has a uniform and rich interface, significantly improves the composite degree of carbon nanotubes and metals, and enhances the conductivity of the composite fiber.

Description

Technical Field

[0001] This invention relates to the field of composite material technology, and in particular to a highly conductive carbon nanotube composite fiber, its preparation method, and preparation system. Background Technology

[0002] Lightweight and highly conductive materials are currently one of the hot topics in the research of novel conductors. Carbon nanotube / copper composite conductors are considered to be the ideal structure for preparing novel high-performance conductors to date. Among them, the interface problem of carbon nanotubes / copper has always been the key factor affecting the improvement of the electrical performance of composite conductors.

[0003] In some existing technologies, a technical solution of carbon nanotube fiber and metal composite has been provided. For example, the literature Ninanobuffer layer provides light-weight CNT / Cu fibers with superior robustness, conductivity, and ampacity. Acs Applied Materials & Interfaces, Zou J, Liu D, Zhao J, Hou L, Liu T, Zhang X, et al. 2018, 10(9): 8197-8204. A technical solution of carbon nanotube fiber + nickel buffer layer + copper layer is provided. By constructing a nickel nanobuffer layer that can diffuse into the copper crystal and between the carbon nanotubes, the problem of copper / carbon interface performance mismatch in composite conductor is solved. However, nickel and carbon form a non-conductive solid solution and do not give full play to the advantages of carbon nanotubes. The electrical performance of composite conductor is not ideal.

[0004] Another existing technology: The importance of carbon nanotube wire density, structural uniformity, and purity for fabricating homogeneous carbon nanotube-copper wire composites by copper electrodeposition. Sundaram R, Yamada T, Hata K, Sekiguchi A, Jpn. J. Appl. Phys. 2018, 57, 04FP08. This technology provides a carbon nanotube fiber + copper acetate organic electrolyte + copper sulfate solution electrodeposition scheme. Organic plating is used to deposit metallic copper particles into the fiber interior, followed by aqueous solution electroplating to further promote copper particle growth. However, in this scheme, due to the relatively dense carbon nanotube fibers, it is difficult for the metal to penetrate the fiber interior and form a rich interface. Only a small portion of the copper enters the fiber interior, resulting in an unrich and uneven metal / carbon interface, and the composite conductor conductivity is only 6.1 × 10⁻⁶. 6 S / m.

[0005] Therefore, the carbon nanotube / metal composite solutions provided in the existing technology are all phase-separated composites, with the carbon nanotube phase and the metal phase existing independently. The problem of the interface composite between carbon nanotubes and metals has not been solved at the molecular level. Consequently, the composite fibers obtained have not achieved a very significant improvement in conductivity, and are still far from meeting the application requirements of lightweight and highly conductive fibers. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a highly conductive carbon nanotube composite fiber, its preparation method, and preparation system.

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

[0008] In a first aspect, the present invention provides a method for preparing highly conductive carbon nanotube composite fibers, comprising:

[0009] Provides aerogel-like carbon nanotube precursors;

[0010] The carbon nanotube precursor is introduced into an electrolyte for densification treatment, so that the carbon nanotube precursor shrinks to form a fiber precursor. During the shrinkage of the carbon nanotube precursor, metal ions in the electrolyte are deposited into the carbon nanotube precursor by electrochemical deposition.

[0011] Simultaneously, the fiber precursor is continuously twisted to obtain highly conductive carbon nanotube composite fibers.

[0012] Secondly, the present invention also provides a system for preparing highly conductive carbon nanotube composite fibers, comprising:

[0013] A carbon nanotube growth apparatus for providing aerogel-like carbon nanotube precursors;

[0014] An electrolytic densification device is used to introduce the carbon nanotube precursor into an electrolyte for densification treatment, so that the carbon nanotube precursor shrinks to form a fiber precursor, and during the shrinkage of the carbon nanotube precursor, metal ions in the electrolyte are deposited into the carbon nanotube precursor by electrochemical deposition.

[0015] A twisting and collecting device is used to continuously twist the fiber precursor simultaneously to obtain highly conductive carbon nanotube composite fibers.

[0016] Furthermore, the preparation system also includes a post-processing device for annealing the continuously twisted fiber precursor.

[0017] Thirdly, the present invention also provides highly conductive carbon nanotube composite fibers prepared by the above-described preparation method.

[0018] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0019] The preparation method provided by this invention utilizes the loose network structure of the precursor and uses a metal ion electrolyte for densification treatment. At the same time, it achieves in-situ uniform composite of metal and carbon nanotube network through electrochemical deposition. Combined with continuous twisting, it enhances the radial depth distribution capability of metal nanoparticles, realizes the construction of metal / carbon dual network structure, has a uniform and rich interface, significantly improves the composite degree of carbon nanotube and metal, and improves the conductivity of composite fiber.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the process for preparing highly conductive carbon nanotube composite fibers according to a typical embodiment of the present invention.

[0022] Figure 2 This is an electron microscope image of the axial cross-sectional morphology of carbon nanotube / copper composite fiber provided in a typical embodiment of the present invention;

[0023] Figure 3This is an electron microscope image of the axial cross-sectional morphology of carbon nanotube / nickel composite fiber provided in a typical embodiment of the present invention. Detailed Implementation

[0024] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0026] See Figures 1-3 This invention provides a method for preparing highly conductive carbon nanotube composite fibers, comprising the following steps:

[0027] Provides aerogel-like carbon nanotube precursors.

[0028] The carbon nanotube precursor is introduced into an electrolyte for densification treatment, which causes the carbon nanotube precursor to shrink and form a fiber precursor. During the shrinkage of the carbon nanotube precursor, metal ions in the electrolyte are deposited into the carbon nanotube precursor by electrochemical deposition.

[0029] Simultaneously, the fiber precursor is continuously twisted to obtain highly conductive carbon nanotube composite fibers.

[0030] In the above technical solution, a floating catalytic method is preferred for preparing carbon nanotube fibers. Before densification, the fiber precursor is in an aerogel state with a loose network structure. After being directly immersed in an electrolyte containing metal ions, the metal ions are fully and uniformly deposited in the fiber network structure under the action of current, achieving in-situ uniform composite. Furthermore, traditional carbon nanotube fiber collection often involves first collecting the fiber into rolls, and then performing post-processing such as twisting, stretching, or modification on the rolled fiber precursors. This method is preferred for ease of operation and reducing equipment complexity. However, in the technical solution provided in this embodiment of the invention, a method of simultaneous deposition and twisting is preferred. Precursor growth, densification, electrodeposition, and twisting are carried out continuously and simultaneously. The purpose of this setup is not only to obtain the formed fiber in a simple one-step process, but also to allow the twist to be transferred to the vicinity of the shrinkage portion generated during densification. Figure 1In the inverted conical region, abundant wrinkles and embedding phenomena are generated on the surface of the carbon nanotube precursor, which still has a certain degree of porosity. This allows the metal nanoparticles generated by electrochemical deposition to enter the fiber interior in large quantities and uniformly along with the wrinkles and embedding, fully composite and reduce porosity, thereby obtaining a carbon nanotube / metal composite phase with a very high degree of compositeness. In particular, this in-situ composite at the molecular level can also promote grain growth and bonding through subsequent annealing treatment, establish rich conductive pathways, and thus realize a carbon nanotube / metal dual network structure, which can significantly further improve the conductivity of the composite fiber.

[0031] The key technical means of this invention lies in enabling electrochemical deposition to occur on the surface of a loose precursor, and combining the densification and twisting processes to achieve a uniform and fine composite of deposited metals. The methods for growing the carbon nanotube precursor are commonly found in existing technologies. For example, carbon sources, organometallic sources, and sulfur sources can be used to carry out gas-phase growth in a hydrogen and argon atmosphere in a reactor tube, thereby forming the aerogel-like carbon nanotube precursor. The electrochemical deposition can be copper plating, nickel plating, or electroplating of other common metals, such as silver plating or gold plating. The electrolyte used can be a self-prepared electrolyte or various commercially available mature electroplating electrolytes. Any electrolyte capable of electroplating metals is acceptable.

[0032] In some embodiments, the electrochemical deposition is preferably performed using a constant voltage method. In conjunction with the above-mentioned composite mechanism, since abundant wrinkles and embedding phenomena are generated during the composite process, the actual effective electroplating area of ​​the shrinkage portion is not a stable constant value during the electrodeposition process. Therefore, choosing a constant voltage method can significantly avoid the negative impact of the above-mentioned changes, thereby obtaining composite fibers that are more uniform in the length direction.

[0033] In some embodiments, the voltage for electrochemical deposition can be 1.2-1.5V. Traditional copper or nickel electroplating typically requires around 5V or even higher voltages. However, in this invention, the voltage used for electrochemical deposition is significantly lower than that of traditional electroplating. This is because the inventors discovered that if the voltage value of traditional electroplating is directly applied, the resulting metal nanoparticles have a certain degree of continuity and adhesion, and the grain size is relatively large. This makes it difficult for them to uniformly penetrate the interior of the composite fiber through the morphological changes of the carbon nanotube aggregates during the densification and continuous twisting processes. Furthermore, some adhered or large metal nanoparticles can even damage the microstructure of the fiber, affecting the conductivity and mechanical properties of the composite fiber.

[0034] Furthermore, the inventors have discovered that if the voltage range or its vicinity taught by the prior art is used, when the voltage value is too high, a more intense reduction reaction occurs on the surface of the contraction section, resulting in the uncontrollable deposition of metal particles accompanied by the generation of a large amount of hydrogen gas. This severely damages the structure of the composite fiber, causing the already unstable contraction section, which is still in a partially aerogel state, and the fiber precursor to break. As a result, the processing is not continuous, and it is impossible to continuously collect composite fibers.

[0035] See also Figure 1 In some embodiments, the electrochemically deposited anode can be disposed in the electrolyte and positioned near the contraction portion of the carbon nanotube precursor, and the anode is electrically connected to the positive terminal of a DC power supply; the electrochemically deposited cathode can include the contraction portion, and the contraction portion is electrically connected to the negative terminal of the DC power supply through the fiber precursor. Specifically, the shape of the anode can be funnel-shaped, square, annular, etc., and there are no specific shape requirements for the anode. It only needs to have an area at least twice the area of ​​the contraction portion. The anode can be located on either side of the contraction portion or below the contraction portion, but the distance between the anode and the contraction portion should be controlled within 5-6 cm.

[0036] In some embodiments, the metal ions may include any one or a combination of two or more of copper ions, nickel ions, and silver ions.

[0037] In some embodiments, the metal ions may be provided by a metal salt, and the concentration of the metal salt in the electrolyte may be 20-180 g / L.

[0038] In some embodiments, the electrolyte may also include a pH adjuster and an electroplating additive.

[0039] In some specific examples, the concentration of the metal salt is 20-180 g / L; more specifically, for example, in copper plating, a 2 mL / L electrolyte starter (mainly composed of 0.5% concentrated sulfuric acid, 1.5% PEG, 3% polyether 002, and 2.5% polyether 003) needs to be added to improve the brightness and smoothness of the plating layer. Other additives may be omitted for the time being. However, it is clear that the composition of the electrolyte to which this invention applies is not limited to the specific composition shown in this example.

[0040] In some embodiments, the carbon nanotube precursor can be prepared using a floating gas-phase catalytic method.

[0041] In some embodiments, the diameter of the carbon nanotubes in the carbon nanotube precursor can be 1–10 nm.

[0042] In some embodiments, the travel rate of the fiber precursor can be 5-20 m / min.

[0043] In some implementations, the rotational speed of the continuous twisting can be 15-30 r / min.

[0044] In some embodiments, the preparation method may further include an annealing treatment of the continuously twisted fiber precursor.

[0045] In some embodiments, the annealing process can be performed in an atmosphere containing hydrogen.

[0046] In some embodiments, the annealing atmosphere may be a mixture of hydrogen and a protective gas.

[0047] In some implementations, the annealing treatment can be performed at a temperature of 300-500°C for 1-3 hours.

[0048] Based on the above exemplary technical solutions, as some specific application examples, the preparation of a highly conductive carbon nanotube composite fiber can be implemented using the following specific process:

[0049] 1. Preparation of carbon nanotube precursors:

[0050] With the assistance of a carrier gas, a mixed liquid carbon source of ethanol, ferrocene, and thiophene is injected into a high-temperature reactor tube. Under high temperature conditions, the liquid carbon source is vaporized. Ferrocene molecules first decompose at high temperature to obtain iron nanoparticles as a catalyst, and thiophene molecules decompose at high temperature to obtain sulfur atoms as a growth promoter. Ethanol molecules are cracked at high temperature and generate carbon atoms at the position of the iron catalyst particles, which further grow carbon nanotubes and form an aerogel-like carbon nanotube precursor.

[0051] 2. Preparation of carbon nanotube / copper composite fibers or carbon nanotube / nickel composite fibers:

[0052] The carbon nanotube precursor is drawn into an electrolyte containing copper ions (replacing the traditional pure water densification during carbon nanotube fiber collection), including any one of copper sulfate electrolyte, copper methanesulfonate electrolyte, and copper acetate electrolyte. The appropriate current density is obtained by adjusting the voltage of the electrochemical reaction, thereby controlling the copper grain size. The carbon nanotube / copper composite fiber is obtained by electrochemical deposition and twisting simultaneously.

[0053] Alternatively: the carbon nanotube precursor is introduced into an electrolyte containing nickel ions, including any one of nickel sulfate electrolyte, nickel acetate electrolyte, or nickel sulfamate electrolyte, and the nickel grain size is controlled by adjusting the current density, and carbon nanotube / nickel composite fibers are obtained by simultaneous plating and twisting.

[0054] 3. Post-processing of carbon nanotube / nickel composite fibers and carbon nanotube / copper composite fibers:

[0055] The carbon nanotube composite fibers were annealed at a hydrogen flow rate of 150 sccm, an argon flow rate of 300 sccm, an annealing temperature of 300-500℃, and for 1-3 hours to eliminate grain boundaries and promote grain growth.

[0056] In the mixed atmosphere, the volume fraction of hydrogen can be around 33% as mentioned above, or it can be higher than that. The role of annealing is to promote the connection and diffusion of metal nanoparticles and eliminate grain boundaries, thereby significantly improving the electrical conductivity of composite fibers. In some specific applications, the electrical conductivity of composite fibers can be doubled through annealing.

[0057] Although there are some existing technologies that use annealing to improve the electrical conductivity of carbon / metal composite fibers, these technologies do not form a "molecular-level" carbon nanotube / metal composite. Their annealing mainly changes the structure of the metal phase, but does not significantly alter the composite structure between the metal and carbon nanotube interfaces. Therefore, existing technologies cannot achieve the multiplier effect of improving electrical conductivity through simple annealing as this invention does.

[0058] More specifically, taking carbon nanotube / copper composite fibers as an example, 2 wt% ferrocene and 1% thiophene can be dissolved in 95% anhydrous ethanol. After ultrasonic mixing, the solution is filtered to remove impurities, preparing a reaction solution for the floating gas-phase catalytic method. The carbon source / catalyst reaction solution is loaded into the syringe of a fixed micro-injection pump. Using a corundum tube as the growth furnace tube, once the furnace temperature reaches the set temperature, the carrier gas argon / hydrogen mixture is turned on, and the carbon source / catalyst is injected into the reaction system at a certain rate. Generally, the growth temperature is 1250℃–1350℃, the argon flow rate is 300–400 sccm, the hydrogen flow rate is 300–380 sccm, and the carbon source injection rate is 5.5–7.0 mL / h. Subsequently, an aerogel-like carbon nanotube precursor is collected at the tail end of the furnace tube.

[0059] Based on this, the collection rate can reach 5-20 m / min. The electrolyte composition can be: copper sulfate pentahydrate 100-180 g / L, sulfuric acid 15-40 mL / L, and hydrochloric acid 50-100 μL / L. Constant voltage electroplating is used, with the voltage controlled at 1.2-1.5 V. The preferred collection rate is 6 m / min.

[0060] Then, anneal it using the method described above.

[0061] See also Figure 1 This invention also provides a system for preparing highly conductive carbon nanotube composite fibers, comprising:

[0062] A carbon nanotube growth apparatus for providing aerogel-like carbon nanotube precursors.

[0063] An electrolytic densification apparatus is used to introduce the carbon nanotube precursor into an electrolyte for densification treatment, so that the carbon nanotube precursor shrinks to form a fiber precursor, and during the shrinkage of the carbon nanotube precursor, metal ions in the electrolyte are deposited into the carbon nanotube precursor by electrochemical deposition.

[0064] A twisting and collecting device is used to continuously twist the fiber precursor simultaneously to obtain highly conductive carbon nanotube composite fibers.

[0065] In some embodiments, the preparation system further includes a post-processing device for annealing the continuously twisted fiber precursor.

[0066] See also Figure 2 and Figure 3 The present invention also provides highly conductive carbon nanotube composite fibers prepared by the preparation method provided in any of the above embodiments.

[0067] In some embodiments, the highly conductive carbon nanotube composite fiber includes a carbon nanotube fiber matrix and metal nanoparticles, wherein the metal nanoparticles are distributed at least among multiple carbon nanotubes inside the carbon nanotube fiber matrix.

[0068] In some embodiments, the particle size of the metal nanoparticles is 50-200 nm.

[0069] In some embodiments, the mass fraction of metal nanoparticles in the highly conductive carbon nanotube composite fiber is above 90%.

[0070] In some embodiments, the electrical conductivity of the highly conductive carbon nanotube composite fiber is 1.5 × 10⁻⁶. 7 S / m or higher, more preferably 3.0 × 10⁻⁶ 7 S / m or higher.

[0071] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0072] Example 1

[0073] This embodiment illustrates the preparation process of highly conductive carbon nanotube / copper composite fibers, as detailed below:

[0074] 1. Dissolve 2 wt% ferrocene and 1 vol% thiophene in 95% anhydrous ethanol, mix by ultrasonication, and then filter to remove impurities from the solution to prepare a reaction solution for floating gas-phase catalysis.

[0075] 2. The carbon source / catalyst reaction solution was loaded into the syringe of a fixed micro-injection pump. Once the furnace temperature reached the set temperature, the argon / hydrogen carrier gas mixture was turned on, and the carbon source / catalyst was injected into the reaction system at a controlled rate. The required growth temperature was 1300℃, the argon flow rate was 350 sccm, the hydrogen flow rate was 350 sccm, and the carbon source injection rate was 6 mL / h. Subsequently, carbon nanotube aerogel was collected at the tail end of the furnace tube.

[0076] 3. The carbon nanotube aerogel was drawn into an electroplating solution with the following components: 180 g / L copper sulfate pentahydrate, 33 mL / L sulfuric acid, and 100 μL / L hydrochloric acid. Constant voltage electroplating was used, with the voltage controlled at 1.2 V. The collection rate was 6 m / min. Simultaneously with electroplating, the collected composite fibers were continuously twisted at a twisting speed of 20 r / min. Finally, continuous carbon nanotube composite fibers were collected.

[0077] 4. The carbon nanotube composite fibers obtained in step 3 are annealed in an annealing furnace with a hydrogen flow rate of 150 sccm, an argon flow rate of 300 sccm, an annealing temperature of 300℃, and an annealing time of 3 hours.

[0078] The composite fiber prepared in this embodiment, after axial peeling, has the following internal morphology: Figure 2 As shown, multiple copper nanoparticles are uniformly and densely distributed within the fiber, and the copper nanoparticles achieve a fine molecular-level composite with the carbon nanotubes. Furthermore, the copper nanoparticles establish fine electrical connections at the carbon nanotube network overlaps, reducing internal contact resistance. Resistance testing using a resistance meter shows that the conductivity of the carbon nanotube / copper composite fiber prepared in step 3 is 1.5 × 10⁻⁶. 7 After annealing in step 4, the conductivity (S / m) increased to 3.0 × 10⁻⁶. 7 S / m. EDS testing showed that the internal wt% of the carbon nanotube / copper composite fiber reached 90%.

[0079] Example 2

[0080] The preparation process of the highly conductive carbon nanotube / nickel composite fiber in Example 1 is largely the same as that in Example 1, with the only difference being:

[0081] In step 2, the copper plating electrolyte is replaced with a nickel plating electrolyte, and the electrolyte ratio is nickel sulfate hexahydrate: 240 g / L; nickel chloride hexahydrate: 20 g / L; boric acid: 20 g / L.

[0082] The composite fiber prepared in this embodiment, after axial peeling, has the following internal morphology: Figure 3As shown, multiple nickel nanoparticles are uniformly and densely distributed within the fiber. These nickel nanoparticles achieve a fine molecular-level composite with the carbon nanotubes, and the nickel nanoparticles establish delicate electrical connections at the carbon nanotube network junctions, reducing internal contact resistance. Resistance testing using a resistance meter revealed that the conductivity of the unannealed carbon nanotube / nickel composite fiber prepared in this embodiment is 1.3 × 10⁻⁶. 6 After annealing, the conductivity (S / m) increased to 1.95 × 10⁻⁶. 6 S / m.

[0083] Example 3

[0084] The preparation process of the highly conductive carbon nanotube / silver composite fiber in Example 1 is largely the same as that in Example 1, with the only difference being:

[0085] In step 2, the copper plating electrolyte is replaced with a silver plating electrolyte. The electrolyte composition is as follows: Ecosilver Ag 23g / L, Ecosilver Cosalt 100g / L, Ecosilver 210 Additive 200g / L (reagents were purchased from Shanghai Zeshi Chemical Technology Co., Ltd.).

[0086] The composite fibers prepared in this embodiment were tested with a resistance meter, and the conductivity of the unannealed carbon nanotube / silver composite fibers was 3.5 × 10⁻⁶. 7 After annealing, the conductivity (S / m) increased to 5.2 × 10⁻⁶. 7 S / m.

[0087] Example 4

[0088] The preparation process of the highly conductive carbon nanotube / nickel composite fiber in Example 1 is largely the same as that in Example 1, with the only difference being:

[0089] The voltage for electrochemical deposition was 1.5V, the electrolyte contained 20g / L of copper sulfate pentahydrate, the fiber precursor travel rate was 20m / min, and the continuous twisting speed was 30r / min. The mixed atmosphere during annealing was 1:1 hydrogen and argon, and the annealing temperature was 500℃ for 1 hour.

[0090] The resulting composite fiber has the same electrical conductivity before and after annealing as in Example 1.

[0091] Example 5

[0092] The preparation process of the highly conductive carbon nanotube / nickel composite fiber in Example 1 is largely the same as that in Example 1, with the only difference being:

[0093] The voltage for electrochemical deposition was 1.3V, the electrolyte contained 100g / L of copper sulfate pentahydrate, the fiber precursor travel rate was 10m / min, and the continuous twisting speed was 15r / min. The mixed atmosphere during annealing was 2:1 hydrogen and argon, and the annealing temperature was 400℃ for 2 hours.

[0094] The resulting composite fiber has the same electrical conductivity before and after annealing as in Example 1.

[0095] Comparative Example 1

[0096] The preparation process of this comparative example, Example 1, of highly conductive carbon nanotube / copper composite fiber is largely the same as that of Example 1, with the only difference being:

[0097] In step 3, the fiber precursor is not continuously twisted simultaneously during electroplating. Instead, it is first collected into rolls and then twisted with the same twist degree independently.

[0098] Because the synchronous twisting process was missing in this comparative example, the sufficient encapsulation and embedding phenomenon during the precursor shrinkage process could not be formed. Therefore, the composite fiber obtained in this comparative example did not have a complete composite of metal nanoparticles and carbon nanotubes.

[0099] The conductivity test results show that although the mass fraction of the composite copper nanoparticles in this comparative example is the same as in Example 1, the copper nanoparticles in this comparative example tend to become sparser towards the center of the fiber, failing to achieve radial homogeneous composite formation. Therefore, the conductivity after annealing is 1.2 × 10⁻⁶. 7 S / m is significantly lower than that of Example 1.

[0100] Comparative Example 2

[0101] The preparation process of this comparative example, Example 1, of highly conductive carbon nanotube / copper composite fiber is largely the same as that of Example 1, with the only difference being:

[0102] In step 3, the electroplating voltage is adjusted to 5V.

[0103] Since the voltage in this comparative example is referenced from the numerical range of traditional electroplated copper, the copper nanoparticles formed under these conditions are relatively large and adhere to each other, which is not conducive to uniform distribution and in-situ molecular-level composite.

[0104] The conductivity test results show that, although the mass fraction of the composite copper nanoparticles in this comparative example is even higher than that in Example 1, the conductivity after annealing is 1.8 × 10⁻⁶. 7The S / m ratio is significantly lower than that of Example 1. This should be due to the size of the copper particles and their mutual adhesion caused by the inappropriate voltage, which prevents them from penetrating deep into the fiber to achieve molecular-level composite.

[0105] Furthermore, the mechanical strength of the composite fibers in Example 1 and this comparative example was tested. The tensile strength of the composite fiber in Example 1 was found to be 1100 MPa, while the tensile strength of the composite fiber provided in this comparative example was 750 MPa. This indicates that the relatively large metal nanoparticles bonded together under higher voltage also negatively impact the mechanical properties of the composite fibers. Simultaneously, at higher voltages, surface hydrogen evolution is severe, and the composite fiber structure is damaged, affecting mechanical properties. It is very easy for the fiber precursor or contraction section to be severely damaged, leading to interruptions in the collection process.

[0106] Comparative Example 3

[0107] The preparation process of this comparative example, Example 1, of highly conductive carbon nanotube / copper composite fiber is largely the same as that of Example 1, with the only difference being:

[0108] In step 3, the electroplating is switched to a constant current mode, with a fixed current of 0.05A. At this time, the current density estimated based on the area of ​​the contracted section is 2.5A / dm². 2 .

[0109] Using a constant current mode, as the actual effective electroplating area of ​​the shrinkage section changes continuously during densification, it is impossible to achieve the most stable current density, which will affect the uniformity of the composite fiber.

[0110] The conductivity of the composite fiber provided in this comparative example and Example 1 was tested at 1 meter intervals, with a total of 25 test points. Finally, the conductivity CV value of the composite fiber provided in Example 1 was 1.5%, while the conductivity CV value of the composite fiber provided in this comparative example was 3.8%.

[0111] Based on the above embodiments and comparative examples, it is clear that the preparation method provided by the present invention utilizes the loose network structure of the fiber before densification prepared by the floating method, uses a metal ion electrolyte instead of an aqueous solution for densification treatment, and achieves in-situ uniform composite of metal and carbon nanotube network through electrochemical deposition; and with continuous twisting, the radial depth distribution capability of metal nanoparticles is enhanced, realizing the construction of metal / carbon dual network structure with uniform and rich interface, which greatly improves the degree of composite between carbon nanotube and metal and improves the conductivity of composite fiber.

[0112] Furthermore, the preparation method provided by this invention is simple and can be carried out continuously, resulting in composite fibers with good continuity, making it very suitable for use in the preparation of lightweight, highly conductive wires.

[0113] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for producing a high-conductivity carbon nanotube composite fiber, characterized by, The application relates to a preparation method of high-conductivity carbon nanotube composite fibers. The method comprises the following steps: providing carbon nanotube precursors in aerogel state; making the carbon nanotube precursors enter electrolyte for densification treatment, so that the carbon nanotube precursors are shrunk to form fiber precursors, and in the process of shrinking of the carbon nanotube precursors, metal ions in the electrolyte are deposited in the carbon nanotube precursors by electrochemical deposition, the electrochemical deposition is carried out in a constant voltage mode, and the voltage of the electrochemical deposition is 1.2-1.5 V; meanwhile, the fiber precursors are continuously twisted, so that the twist is transferred to the vicinity of the reverse-cone-shaped shrinkage part generated in the densification process, and metal nanoparticles generated in the electrochemical deposition enter the fiber interior along the wrinkle and embedding phenomenon generated by the twist, thereby obtaining the high-conductivity carbon nanotube composite fibers. The anode of the electrochemical deposition is arranged in the electrolyte and is arranged close to the shrinkage part of the carbon nanotube precursors, the anode is electrically connected with the positive electrode of a direct-current power supply; The area of the anode is more than 2 times of the area of the shrinkage part, and the distance between the anode and the surface of the shrinkage part is 5-6 cm; 2. The production method according to claim 1, characterized by, And / or, the cathode of the electrochemical deposition comprises the shrinkage part, and the shrinkage part is electrically connected with the negative electrode of a direct-current power supply through the fiber precursors. The metal ions comprise any one or a combination of two or more of copper ions, nickel ions and silver ions; the metal ions are provided by metal salt, the concentration of the metal salt in the electrolyte is 20-180 g / L, and the electrolyte further comprises a pH regulator and an electroplating additive. The carbon nanotube precursors are prepared by a floating vapor phase catalysis method, and the diameter of the carbon nanotubes in the carbon nanotube precursors is 1-10 nm.

3. The preparation method according to claim 1, characterized in that, The running speed of the fiber precursors is 5-20 m / min; 4. The method of claim 1, wherein, And / or, the rotating speed of the continuous twisting is 15-30 r / min.

5. The preparation method according to claim 1, characterized in that, The application further relates to the following steps: The fiber precursors after the continuous twisting are subjected to annealing treatment, the atmosphere of the annealing treatment is a mixed atmosphere of hydrogen and a protective gas, the volume fraction of the hydrogen in the mixed atmosphere is greater than 33%, the temperature of the annealing treatment is 300-500 DEG C, and the time is 1-3 hours.

6. The method of claim 1, wherein, The application relates to a carbon nanotube growth device for providing carbon nanotube precursors in aerogel state; an electrolytic densification device for making the carbon nanotube precursors enter electrolyte for densification treatment, so that the carbon nanotube precursors are shrunk to form fiber precursors, and in the process of shrinking of the carbon nanotube precursors, metal ions in the electrolyte are deposited in the carbon nanotube precursors by electrochemical deposition; a twisting and collecting device for continuously twisting the fiber precursors at the same time, thereby obtaining high-conductivity carbon nanotube composite fibers; and a post-treatment device for annealing the fiber precursors after the continuous twisting.

8. The high-conductivity carbon nanotube composite fibers prepared by the preparation method in any one of claims 1-6.

7. A system for producing a high-conductivity carbon nanotube composite fiber for carrying out the production method according to any one of claims 1 to 6, characterized by The high-conductivity carbon nanotube composite fibers comprise a carbon nanotube fiber substrate and metal nanoparticles, and the metal nanoparticles are distributed between at least multiple carbon nanotubes in the interior of the carbon nanotube fiber substrate. ​ ​ ​ ​ ​ 9. The highly conductive carbon nanotube composite fiber according to claim 8, wherein, ​ The metal nanoparticles have a particle size of 50-200 nm, the mass fraction of the metal nanoparticles in the high-conductivity carbon nanotube composite fiber is above 90%, and the conductivity of the high-conductivity carbon nanotube composite fiber is above 1.5*10 7 S / m.

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