A carbon nanotube material and preparation method and its application in batteries

Abstract

The present invention discloses a carbon nanotube material that can be curved or spiral in shape, contains metal nanoparticles at the ends of the carbon nanotube material, and has a hollow structure. The present invention utilizes a simple method to synthesize carbon nanotubes in situ, further enabling the adjustment of the morphology of the generated carbon nanotubes. The resulting spiral carbon nanotubes exhibit uniform pitch, small and relatively uniform diameter, strong conductivity, and high tensile strength. Even a small amount of these carbon nanotubes can enhance the electrical performance of batteries.

Description

Technical Field

[0001] The present invention relates to the field of material technology, and in particular to a carbon nanotube material that can be used in batteries and a preparation method thereof. Background Art

[0002] Conductive agents are relatively important in the field of electrochemistry. Conductive agents have excellent electron conduction properties, which can improve battery capacity, cycle performance, and reduce internal resistance.

[0003] Carbon nanotubes, a commonly used component of conductive agents, possess numerous excellent mechanical, electrical, and magnetic properties, finding widespread application in numerous fields. For example, carbon nanotubes exhibit excellent heat resistance, corrosion resistance, impact resistance, high-temperature resistance, excellent electrical and thermal conductivity, and biocompatibility. As early as 1992-1993, it was discovered that carbon nanotubes could be used as hydrogen storage materials, optical materials, and fuel cell electrode materials.

[0004] In the existing technology, carbon nanotubes are often added to improve the conductivity of battery active material particles. However, carbon nanotubes are difficult to disperse and the slurry process is time-consuming, which can easily lead to poor consistency in battery electrical performance. Therefore, in actual applications, the carbon nanotube content is generally small (about 0.5-2% of the mass of the active material). However, when the battery needs to be charged and discharged for a long time, or when the conductivity of the active material is low, a small amount of carbon nanotubes is difficult to maintain battery performance. Therefore, it is necessary to develop carbon nanotubes with as many active sites as possible. Even if a low content of carbon nanotubes is added, a fast electron transport network can be constructed to improve the battery's electrical performance. Summary of the Invention

[0005] The present invention addresses the problems in the prior art and discloses a carbon nanotube material with adjustable morphology. The carbon nanotube material of the present invention has a small diameter, a large specific surface area, a plurality of pore structures, and a plurality of active sites, and the tube diameter is uniformly dispersed. It can not only construct an electron transport network, but also improve the liquid absorption rate. When mixed with other materials, it can also inhibit the expansion of the material. In particular, the spiral carbon nanotubes form new anisotropic structural sites at the places where the spiral angle is formed, further improving the conductive activity. Moreover, the uniform and appropriate spiral angle and pitch can further prevent the aggregation of material particles when loaded with other materials, reduce internal resistance, and improve the stability of the carbon nanotubes after curling, preventing the nanotubes from breaking and reducing battery performance in the later stage. When the carbon nanotube material of the present invention is used in a battery, on the one hand, it can increase electron conduction and reduce the internal resistance of the battery. On the other hand, it can also improve the rate performance and cycle performance of the battery. Even in a high-voltage and high-energy-density battery system, the above effects can be stably exerted.

[0006] The present invention is achieved through the following technical solutions:

[0007] The present invention provides a carbon nanotube material. The carbon nanotube material can be adjusted to a curved shape or a spiral shape. Metal nanoparticles are present at the ends of the carbon nanotube material. The carbon nanotube material is a hollow structure.

[0008] According to the above design of the present invention, the hollow carbon nanotube material of the present invention can adjust its morphological characteristics, and can realize the further construction of the electron transport network of the carbon nanotube material under the premise of less addition amount. By adjusting the helicity of the carbon nanotubes, different active sites and specific surface areas are achieved, which is beneficial to improving the conductivity and electrolyte absorption rate of the carbon nanotube material; the carbon nanotube diameter distribution is uniform, which can avoid the agglomeration of the material and is conducive to dispersion, and ultimately only a small amount of addition is needed to improve the resistance, rate performance and cycle performance of the battery. The metal nanoparticles at the port of the carbon nanotube material are the nucleation sites formed by the carbon nanotube material of the present invention. During the in-situ synthesis process of the carbon nanotubes of the present invention, the morphology of the carbon nanotubes can be controlled to be straight, curved, or spiral to varying degrees by controlling the synthesis conditions, and the pitch of the spiral is relatively uniform, and the helical angle changes with the number of spiral turns to maintain the stability of the carbon nanotubes. When carbon nanotubes are used to improve the conductivity of silicon materials, since silicon materials have poor conductivity and high expansion compared to carbon materials, carbon nanotubes with a high degree of helicity are more conducive to improving the conductivity of silicon materials and inhibiting expansion; when carbon nanotubes are used in transition metal-containing positive electrode active materials, since the positive electrode expansion is relatively small and the conductivity requirement is less than that of silicon materials, the performance requirements can be met when the carbon nanotubes are straight, curved or low-degree helical; when carbon nanotubes are used in sulfur-containing positive electrodes, similar to the mechanism of silicon negative electrodes, the morphology of high-degree helicity has a greater advantage.

[0009] As a further solution, the diameter of the carbon nanotube material is 5nm-100nm, which is beneficial to improving the electrical properties of the carbon nanotube and also facilitates the bending of the carbon nanotube material.

[0010] As a further solution, the diameter of the carbon nanotube material is 20nm-40nm.

[0011] As a further solution, the pitch of the carbon nanotube material is 90nm-100nm. A suitable pitch not only facilitates stability of the carbon nanotubes after curling, but also prevents the conductive material from agglomerating and becoming difficult to disperse, which affects the battery's internal resistance. A pitch that is too large prevents further reduction in the spacing between active material particles after mixing with the active material, resulting in increased binder usage and increased battery internal resistance.

[0012] The pitch of the carbon nanotube material in the present invention refers to the straight-line distance between two points corresponding to the center of the plane of the spiral coil of two adjacent spirals.

[0013] As a further solution, the helix angle of the carbon nanotube material is 30°-120°.

[0014] The helical angle of the carbon nanotube material in the present invention refers to the bending angle formed when the nearly straight carbon nanotube deviates from the straight direction and begins to bend during its growth process, starting from the tube end. The spiral bending angles that appear successively can be expressed as θ1, θ2, and θ3, respectively.

[0015] As a further solution, the aspect ratio of the carbon nanotube material is 3 to 1000. If the aspect ratio is too small, the performance is similar to that of a spherical granular conductive agent, and the performance of the conductive battery is reduced; if the aspect ratio is too large, the nanotube structure is easily unstable.

[0016] As a further solution, the ratio of the diameter of the metal nanoparticles to the diameter of the carbon nanotube material is (1-1.5):(1-1.5). The similar diameters of the two allow the metal particles to be stably connected to the ends of the carbon nanotubes, promoting the formation of a longer spiral morphology through stable chemical bonding.

[0017] As a further solution, the carbon nanotube materials may share the same port, and the carbon nanotube materials connected to the same port may cross or entangle with each other.

[0018] As a further embodiment, the metal nanoparticles include one or more transition metals.

[0019] As a further embodiment, the metal nanoparticles include one or more of copper and iron.

[0020] The present invention also provides a method for preparing the carbon nanotubes, which comprises:

[0021] S1: uniformly mixing a carbon source, a nitrogen source, and a transition metal salt solution, optionally adding a phosphorus source and a fluorine source; and drying to obtain a solid precursor;

[0022] S2: grinding the solid precursor obtained in S1 and calcining it under inert gas to obtain a carbon nanotube material precursor;

[0023] S3: mixing the carbon nanotube material precursor obtained in S2 with the electrophilic reagent solution and the protonic acid solution for a certain period of time, and filtering to obtain the carbon nanotube material of the present invention.

[0024] In the method of the present invention, a carbon source, a nitrogen source, and a transition metal salt are calcined at high temperature to obtain non-helical and relatively short straight carbon nanotubes (CNTs), which are then treated under the combined action of an electrophilic reagent and a protonic acid to obtain the final carbon nanotube material product. During the high-temperature calcination, the carbon source reduces the transition metal salt to generate metal nanoparticles, and the nitrogen source generates nitrogen-containing polycyclic fragments (such as five-membered, six-membered, seven-membered, or even more-membered) or nitrogen-containing irregular fragments. The transition metal and nitrogen form a coordination bond, adsorbing more nitrogen-containing carbon fragments to migrate toward the metal nanoparticles and gradually grow. In this process, other irregularly structured fragments or particles are also formed. In step S3, after a mixed treatment of an electrophilic reagent and a protonic acid, the particles, chains, and irregular ring fragments that have not formed tubes are further broken and reorganized through chemical bonds, prompting the nanotubes to stably form a curved shape with a certain degree of helicity, and even to form a spiral shape that is stable to varying degrees. Furthermore, in step S3, defect sites within the tubes are filled with fragments, and the metal complexation effect forces previously separate tubes to join together, extending the tubes and creating a denser, more uniform morphology. Multiple bonds, through coordinated action, cross-link the carbon nanotubes to form a stable structure. Optionally, substances such as fluorine and phosphorus sources can be added to S1 to further promote the breaking and formation of chemical bonds through their polarity.

[0025] As a further solution, the carbon source in S1 includes one or more of biomass carbon source, carbon powder, graphene and activated carbon.

[0026] As a further embodiment, the nitrogen source in S1 includes one or more nitrogen-containing heterocycles and their derivatives, and guanidine salt derivatives;

[0027] As a further embodiment, the metal salt includes one or more of nitrates, chlorides, and acetates containing transition metals; the transition metal includes one or more of iron, cobalt, nickel, copper, and manganese;

[0028] As a further embodiment, the transition metal is one or more of iron and copper. Iron and copper are favorable for forming multi-coordinate bonds.

[0029] As a further embodiment, the transition metal is a mixture of iron and copper. The combination of iron and copper is more conducive to promoting the formation of the helical shape of the carbon nanotubes.

[0030] As a further embodiment, the molar ratio of carbon, nitrogen and metal elements in the carbon source, nitrogen source and transition metal salt in S1 is (5-20):(50-150):(1-5);

[0031] As a further approach, the molar ratio of carbon, nitrogen and metal elements in the carbon source, nitrogen source and transition metal salt in S1 is 10:100:1;

[0032] As a further embodiment, the electrophilic reagent solution in S3 includes at least one of aluminum chloride, boron trifluoride, sulfur trioxide, ferric bromide, titanium bromide, tin chloride, zinc chloride, ferric chloride, and molybdenum pentachloride; the protonic acid solution includes at least one of formic acid, trifluoroacetic acid, oxalic acid, hydrochloric acid, sulfuric acid, citric acid, camphorsulfonic acid, and benzoic acid;

[0033] As a further embodiment, the mass ratio of the carbon nanotube precursor, electrophilic reagent solution, and protic acid solution in S3 is 1:(5-10):(10-200). This not only promotes the formation of a stable helical structure of the carbon nanotubes, but also helps the carbon nanotubes to have an appropriate helicity. As a preferred embodiment of the present invention, the mass ratio of the carbon nanotube precursor, electrophilic reagent, and protic acid in S3 is specifically 1:10:100.

[0034] As a further solution, the treatment temperature in S3 is 10°C-100°C, and the reaction time is 1h-20h.

[0035] As a further solution, the treatment temperature in S3 is 40°C-80°C, and the reaction time is 4h-10h.

[0036] As a further embodiment, the calcination in S2 is performed under an inert atmosphere, wherein the inert atmosphere includes one or more of nitrogen, argon, and helium. The calcination temperature is 500°C-800°C, and the calcination time is 2 hours-10 hours. During the calcination process, when the calcination temperature is below 500°C, the product is more fragmented and less likely to form a tubular structure. When the temperature is above 800°C, some metal ions lose their coordination with the original ring structure, especially the metal-nitrogen bond is broken, and it is also difficult to form a long tubular structure.

[0037] As a further solution, the calcination temperature in S2 is maintained at 550°C for 2 hours, and then the temperature is further increased to 750°C and maintained for 2 hours. Calcination at staged temperatures can enable the nucleation reaction and tube growth reaction to proceed more fully.

[0038] The present invention also provides a pole piece, a battery or an electrochemical device having the carbon nanotube material.

[0039] The characteristics and beneficial effects of the present invention are:

[0040] (1) The present invention synthesizes carbon nanotubes in situ by a simple method, and can further adjust the morphology of the generated carbon nanotubes, successfully synthesizing linear, curved, and spiral carbon nanotubes to varying degrees. The spiral carbon nanotubes obtained have uniform pitch, small and relatively uniform diameter, strong conductivity, and are not easy to break. Moreover, a small amount of application in batteries can improve the electrical performance of the batteries.

[0041] (2) The carbon nanotube material of the present invention can be directly used as a conductive agent or additive or composited with other materials, applied to negative electrode sheets or positive electrode sheets, coated on the surface of diaphragms / current collectors, etc., which can improve conductivity and liquid absorption rate, reduce internal resistance, enhance battery rate and cyclability; and when coated with materials, it can inhibit material expansion, increase stress, prevent material damage, reduce side reactions between materials and electrolytes, and inhibit battery gas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 Transmission electron microscopy (TEM) images of carbon nanotube materials (500 nm, 100 nm) corresponding to Example 1 and high-magnification (2 nm) transmission electron microscopy (HTEM) images corresponding to the carbon nanotube ports of Example 1;

[0044] Figure 2 a is a transmission electron microscopy (TEM) image of the carbon nanotube material corresponding to Example 4; Figure 2 b is the transmission electron microscopy (TEM) image of the carbon nanotube material corresponding to Example 6;

[0045] Figure 3 This is the scanning electron microscope (SEM) image of the carbon nanotube material corresponding to Comparative Example 1.

[0046] Figure 4 This is the transmission electron microscope (TEM) image of the carbon nanotube material corresponding to Comparative Example 2. DETAILED DESCRIPTION

[0047] To facilitate understanding of the carbon nanotube material of the present invention, the carbon nanotube material of the present invention will be described in more detail below, with examples of the present invention provided. However, the scope of the present invention is not limited thereby.

[0048] Example 1:

[0049] According to the molar ratio of carbon, nitrogen and metal elements of 10:100:1, a certain amount of sucrose, dicyandiamide and ferric nitrate nonahydrate were weighed and dissolved in 40 mL of anhydrous ethanol, and then dried by blast drying at 70°C to obtain a solid powder. The solid powder was then transferred to a tube furnace and calcined at 550°C for 2 hours under a nitrogen atmosphere. The temperature was continued to rise and maintained at 750°C for 2 hours. Aluminum chloride solution and trifluoroacetic acid solution (mass ratio 1:10:200) were added to the carbon nanotube precursor obtained after cooling to room temperature, mixed evenly, heated at 45°C for 20 hours, and filtered and dried to obtain the final product.

[0050] Example 2:

[0051] The iron salt in Example 1 was replaced with a copper salt of the same type, and the other conditions were the same.

[0052] Example 3:

[0053] The iron salt in Example 1 was replaced by a mixture of copper salt and iron salt with equal molar amounts of the same type of metal, and the other conditions were the same.

[0054] Example 4:

[0055] The carbon nanotube precursor, aluminum chloride and trifluoroacetic acid in Example 1 were mixed at a mass ratio of 1:5:200, with the rest being the same.

[0056] Example 5:

[0057] The trifluoroacetic acid solution in Example 1 was replaced with an equal amount of dilute hydrochloric acid solution, and the other procedures were the same.

[0058] Example 6:

[0059] The heating at 45°C for 10 h was replaced with the heating at 45°C for 20 h in Example 1, with the other conditions being the same.

[0060] Comparative Example 1:

[0061] The ferric nitrate in Example 1 was removed, and the other procedures were the same.

[0062] Comparative Example 2:

[0063] The aluminum chloride in Example 1 was removed, and the other procedures were the same.

[0064] Comparative Example 3:

[0065] Commercially available carbon nanotube materials (Shenyang Huijing Nanotechnology Co., Ltd.) were used.

[0066] Comparative Example 4:

[0067] The temperature of 750°C in Example 1 was changed to 900°C, and the other conditions were the same.

[0068] Comparative Example 5:

[0069] The dicyandiamide in Example 1 was removed, and the other procedures were the same.

[0070] We also used the obtained carbon nanotube materials in batteries and tested the batteries. The following takes the application in silicon negative electrode as an example:

[0071] Preparation of the battery:

[0072] Positive electrode: lithium cobalt oxide (LiCoO2) + carbon black (SP) + polyvinylidene fluoride (HSV900) (mass ratio 90:5:5) is prepared into a positive electrode slurry and coated on aluminum foil to make a positive electrode sheet;

[0073] Negative electrode: A negative electrode slurry was prepared in the mass ratio of silicon oxide negative electrode material: carbon nanotube material: SBR (styrene butadiene rubber): PAA (polyacrylic acid) = 96%: 1%: 0.5%: 2.5%, and coated on copper foil and dried to form a negative electrode sheet.

[0074] Battery assembly: A 16μm-thick PP separator was used as the separator. The electrolyte consisted of 1M LiPF6 (lithium hexafluorophosphate), EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate) (mass ratio of 1:1:1). Coin-shaped cells were assembled. Constant current charge and discharge testing was performed at 2.75-4.5V. The 0.3C / 0.3C cycle represented a 0.3C charge and 0.3C discharge cycle. The 3C / 0.3C discharge capacity retention rate represents the retention rate of the discharge capacity after an initial 3C charge followed by a 0.3C discharge cycle relative to the initial 0.3C / 0.3C discharge capacity. This was used to measure the battery's rate performance at 3C. The discharge capacity retention rate for the Nth cycle was calculated, taking the initial 0.3C discharge capacity retention rate as 100%.

[0075] The test process of the negative electrode full charge expansion rate is as follows: the thickness of the negative electrode sheet before battery assembly is L1; the battery is charged with constant current to 4.5V and the constant voltage is maintained to a current of 0.05C. The battery cell is disassembled and the negative electrode sheet is tested to determine the thickness L2 of the negative electrode sheet at the same full charge state. The negative electrode full charge expansion rate (%) = (L2-L1) / L1×100%.

[0076] Verification result analysis:

[0077] Table 1 Test results of the embodiments of the present invention and the comparative examples

[0078]

[0079] The carbon nanotube material obtained by the present invention was used in batteries and a series of tests were conducted. The test results are shown in Table 1. The electrical performance of the carbon nanotubes obtained in Examples 1 to 6 of the present invention in the batteries was significantly better than that of the batteries obtained in Comparative Examples 1 to 5. The main reason is that the carbon nanotubes in the present invention have a curled, curved or spiral morphology, such as Figure 1-Figure 2 As shown. New active sites can be formed at each curved corner, so that the carbon nanotube material can achieve the construction of a better electron transport network with a smaller addition amount. When the degree of spirality increases, the active sites increase and the negative electrode expansion is more strongly suppressed, reducing the capacity reduction caused by material fragmentation during charging and discharging. Under various material combinations and appropriate conditions, better battery performance is formed comprehensively. Therefore, Examples 1 to 6 of the present invention have better electrical performance. In addition, the morphological characteristics of the carbon nanotubes of the present invention also increase the active sites and specific surface area of the carbon nanotubes, which is beneficial to improve the electrolyte absorption rate of the carbon nanotube material, thereby improving the wettability of the negative electrode, and then improving the rate performance and cycle performance of the battery, inhibiting the side reactions of the negative electrode material and the electrolyte, reducing gas production, and improving the safety performance of the battery. In the present invention, the metal nanoparticles are the nucleation sites of the carbon nanotube material in the present invention, located at the end of the carbon nanotube, we can through Figure 3 It was found that in Comparative Example 1, due to the lack of metal salt, nucleation sites could not form at the ports. Consequently, a tubular material could not be formed, and the expansion of the negative electrode could not be suppressed. The conductivity of the sheet structure was also significantly reduced compared to the tubular structure. A comparison of Examples 1 to 3 revealed that the difference in bonding ability between the metal particles in Examples 1 and 2 affected the nucleation rate and the anisotropic growth rate of the carbon nanotubes. The appropriate choice of metal further promoted the helical shape of the carbon nanotubes, and the effect was more pronounced in bimetallic compared to monometallic.

[0080] In the method of the present invention, we further added an electrophilic reagent solution and a protonic acid solution. We found that the mixed treatment of the electrophilic reagent solution and the protonic acid can, on the one hand, cause the fragments such as particles, chains, five-membered or seven-membered rings that have not fully formed into tubes to further break and reorganize chemical bonds to promote the formation of stable bends in the carbon nanotubes, thereby forming structures of varying degrees of helicity; on the other hand, it can also fill the defect sites in the carbon nanotubes with fragments, and even promote the combination of originally separated tubes, making the entire morphology more dense, uniform, and stable. Figure 2As shown. By comparing Example 1 with Example 4, it was found that reducing the electrophilic reagent solution will lead to poor performance. The electrophilic reagent acts as an inducer to promote the grafting of nanotubes and the integrity of longer structures. Reducing the electrophilic reagent weakens the recombination effect, reduces the tubular helicity, and deteriorates the electrical properties. Further comparing Example 1 with Example 5, the electrical performance of Example 1 is better than that of Example 5. We believe that this is because the fluorine polarity of trifluoroacetic acid is strong, which is conducive to promoting the recombination of covalent bonds and facilitating the formation of multiple helices. Further comparing Example 1 with Example 6, the electrical performance of Example 1 is better than that of Example 6. Considering that it may be because the reaction time is shortened, which is not conducive to the further recombination of nanotubes, Figure 2 b We can see that some nano-scale fragments have not yet formed into helical tubes, indicating that the reaction time also affects the degree of helical formation. The formation of stable helical carbon nanotubes and the inability to separate the electrophilic reagent and the proton acid can also be verified by comparative example 2. Figure 4 Medium reaction.

[0081] We also added a nitrogen source during the preparation process. Although nitrogen is not a necessary condition for tubular formation, nitrogen doping can increase active sites and promote the formation of denser tubular structures. We verified this by comparing Examples 1-6 with Comparative Example 5. The rate performance and cycle performance of the batteries in Examples 1-6 were superior to those in Comparative Example 5, especially during long cycles. Without the addition of nitrogen, the nanotubes would become unstable as charge and discharge continued, and the breakage of the negative electrode material would not be effectively suppressed.

[0082] Finally, the formation of carbon nanotubes is inseparable from the sintering process. By comparing Examples 1-6 with Comparative Example 4, we found that the electrical performance of the batteries in Examples 1-6 was superior to that in Comparative Example 4. This is because when the temperature exceeds 800°C, some metal ions lose their coordination with the original nanotube structure, the metal-nitrogen bonds are broken, and more fragments are formed, which is not conducive to the formation of a tubular structure.

[0083] In summary, the use of the bent or highly helical carbon nanotubes with a certain helicity in the present invention in batteries can not only improve the electrical performance of the battery, but also reduce the expansion rate of the battery's negative electrode.

[0084] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanotube material, characterized in that: The preparation method comprises: S1: mixing the carbon source, nitrogen source and transition metal salt solution uniformly and drying to obtain a solid precursor; S2: grinding the solid precursor obtained in S1 and calcining it under inert gas to obtain a carbon nanotube material precursor; S3: mixing the carbon nanotube material precursor obtained in S2 with an electrophilic reagent and a protonic acid solution, and drying the mixture to obtain the carbon nanotube material of the present invention; The electrophilic reagent solution in S3 includes at least one of aluminum chloride, aluminum sulfate, boron trifluoride, sulfur trioxide, ferric bromide, titanium bromide, tin chloride, zinc chloride, ferric chloride, and molybdenum pentachloride; the protonic acid solution includes at least one of formic acid, trifluoroacetic acid, oxalic acid, hydrochloric acid, sulfuric acid, citric acid, camphorsulfonic acid, and benzoic acid; The temperature of the treatment in S3 is 10°C-100°C; The carbon nanotube material has a curved or spiral shape, metal nanoparticles are present at the ends of the carbon nanotube material, and the carbon nanotube material has a hollow structure.

2. The preparation method according to claim 1, characterized in that The metal nanoparticles include one or more of iron, cobalt, nickel, copper, and manganese.

3. The preparation method according to claim 1, characterized in that The metal nanoparticles include one or more of iron and copper.

4. The preparation method according to claim 1, characterized in that The metal nanoparticles are iron and copper.

5. The preparation method according to claim 1, characterized in that The carbon source in S1 includes a biomass carbon source; The nitrogen source in S1 includes one or more nitrogen-containing heterocycles and their derivatives, and guanidine derivatives; The transition metal salt includes one or more of nitrates, chlorides, and acetates containing transition metals; the transition metal includes one or more of iron, cobalt, nickel, copper, and manganese.

6. The preparation method according to claim 1, characterized in that The carbon source in S1 includes carbon powder; The nitrogen source in S1 includes one or more nitrogen-containing heterocycles and their derivatives, and guanidine derivatives; The transition metal salt includes one or more of nitrates, chlorides, and acetates containing transition metals; the transition metal includes one or more of iron, cobalt, nickel, copper, and manganese.

7. The preparation method according to claim 1, characterized in that The carbon source in S1 includes graphene; The nitrogen source in S1 includes one or more nitrogen-containing heterocycles and their derivatives, and guanidine derivatives; The transition metal salt includes one or more of nitrates, chlorides, and acetates containing transition metals; the transition metal includes one or more of iron, cobalt, nickel, copper, and manganese.

8. The preparation method according to claim 1, characterized in that The carbon source in S1 includes activated carbon; The nitrogen source in S1 includes one or more nitrogen-containing heterocycles and their derivatives, and guanidine derivatives; The transition metal salt includes one or more of nitrates, chlorides, and acetates containing transition metals; the transition metal includes one or more of iron, cobalt, nickel, copper, and manganese.

9. The preparation method according to claim 1, characterized in that The molar ratio of carbon, nitrogen and metal elements in the carbon source, nitrogen source and transition metal salt in S1 is (5-20):(50-150):(1-5); The mass ratio of the carbon nanotube material precursor, the electrophilic reagent solution and the protonic acid solution in S3 is 1:(5-10):(10-200).

10. The preparation method according to claim 1, characterized in that The reaction time of the treatment in S3 is 1h-20h; The calcination temperature in S2 is 500-800°C, and the calcination time is 2h-10h; The calcination condition in S2 is under an inert atmosphere.

11. The preparation method according to claim 1, characterized in that In the S2, the calcination temperature is maintained at 550° C. for 2 hours, and then the temperature is further increased to 750° C. and maintained for 2 hours.

12. The carbon nanotube material obtained by the preparation method according to any one of claims 1 to 11, characterized in that: The diameter of the carbon nanotube material is 5nm-100nm.

13. The carbon nanotube material according to claim 12, characterized in that: The diameter of the carbon nanotube material is 20nm-40nm.

14. The carbon nanotube material according to claim 12, characterized in that: The pitch of the carbon nanotube material is 90nm-100nm.

15. The carbon nanotube material according to claim 12, characterized in that: The helical angle of the carbon nanotube material is 30°-120°.

16. The carbon nanotube material according to claim 12, characterized in that The aspect ratio of the carbon nanotube material is not less than 3.

17. The carbon nanotube material according to claim 12, characterized in that: The ratio of the particle size of the metal nanoparticles to the diameter of the carbon nanotube material is (1-1.5):(1-1.5).

18. A pole piece or battery comprising the carbon nanotube material according to any one of claims 12 to 17 or the carbon nanotube material obtained by the preparation method according to any one of claims 1 to 11.

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