A method and application of high-quality polyethylene terephthalate as nitrogen-doped carbon nanotube material

Abstract

The present invention discloses a method and application of converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material, which belongs to the technical field of sodium ion battery materials. The method of converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material comprises the following steps: mixing a nickel-containing compound and polyethylene terephthalate, melting them, and obtaining a mixed precursor; cracking the mixed precursor under a protective atmosphere to obtain an intermediate; mixing the intermediate with a nitric acid solution, hydrothermally treating it to achieve nitrogen doping, and obtaining prefabricated nitrogen-doped nanotubes; calcining the prefabricated nanotubes under a protective atmosphere to obtain the nitrogen-doped carbon nanotubes. The preparation method of the present invention is simple, efficient, clean, environmentally friendly, and low-cost, has extremely high application value, and is suitable for further promotion.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery materials, and in particular to a method and application of converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material. Background Art

[0002] Polyethylene terephthalate (PET), composed of ethylene glycol and terephthalic acid, is one of the most common types of plastic and has been used in fields such as packaging materials and synthetic fibers. However, because they cannot be completely decomposed by nature, discarded polyethylene terephthalate poses a great threat to the environment. In order to deal with waste plastics, people have made a lot of efforts, including biodegradation landfill, incineration and recycling. Unfortunately, the biodegradation landfill technology of waste plastics is not efficient, and incineration will inevitably produce serious toxic gases. As an alternative method, recycling has attracted strong attention due to its huge environmental and economic benefits.

[0003] Generally speaking, there are two typical PET recycling methods, namely downcycling and upcycling. While the former can only produce low-quality recycled materials, the latter can economically convert waste plastics into high-value materials. A representative example is the upgrading of recycled PET (r-PET) into high-value carbonaceous materials, such as graphene and carbon nanotubes (CNTs). In order to further improve their performance, heteroatom doping (such as nitrogen) is very ideal because it can provide more reaction sites for carbonaceous materials and enhance the electronic properties of carbonaceous materials. However, it is worth noting that the current method for manufacturing nitrogen-doped graphene / carbon nanotubes still requires high-temperature calcination in an ammonia atmosphere, which not only has great environmental processing pressure, but also is complicated to operate and costly. Therefore, it is necessary to find a simple, environmentally friendly and low-cost nitrogen doping method to prepare high-performance r-PET derivatives. Summary of the Invention

[0004] The present invention aims to provide a method and application for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotubes. The preparation method of the present invention is simple, efficient, clean, environmentally friendly, low-cost, and has extremely high application value.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention is to provide a method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material, comprising the following steps:

[0007] (1) mixing a nickel-containing compound and polyethylene terephthalate, and melting them to obtain a mixed precursor;

[0008] (2) cracking the mixed precursor under a protective atmosphere to obtain an intermediate;

[0009] (3) mixing the intermediate with a nitric acid solution and subjecting it to hydrothermal treatment to obtain prefabricated nitrogen-doped nanotubes;

[0010] (4) calcining the prefabricated nitrogen-doped nanotubes under a protective atmosphere to obtain the nitrogen-doped carbon nanotubes.

[0011] Preferably, in step (1): the nickel-containing compound is one or more of nickel acetate, nickel nitrate and nickel sulfate; the polyethylene terephthalate is recycled solid waste polyethylene terephthalate; the melting temperature is 240-260°C; and the mass ratio of the nickel-containing compound to polyethylene terephthalate is 1:10-100.

[0012] The types and proportions of nickel-containing compounds defined in the present invention can make the carbon nanotubes prepared thereby more uniform in size and higher in yield, thereby improving their electrochemical stability.

[0013] Preferably, in step (2), the cracking is carried out at 600-900° C. for 1-5 hours; and the protective atmosphere is a mixture of 5% hydrogen and 95% argon, or a mixture of 5% hydrogen and 95% nitrogen, in terms of volume fraction.

[0014] Through the high-temperature cracking operation of the present invention, the nickel-containing compounds in the mixed precursor can be reduced to nickel element particles with excellent catalytic ability, and r-PET can be derived into light hydrocarbons and aromatic hydrocarbons, and then carbon nanotubes are generated under the catalytic action of the nickel element particles.

[0015] Preferably, in step (3), the mass ratio of nitric acid in the nitric acid solution is 3-30%; and the hydrothermal treatment is carried out at 150-250° C. and 0.5-4 MPa for 0.5-24 h.

[0016] In the hydrothermal treatment of the present invention, on the one hand, the nickel element particles are dissolved by the reaction, leaving purified carbon nanotubes, and on the other hand, part of the nitric acid in the nitric acid solution is converted into ammonia, and then the generated ammonia triggers in situ nitrogen doping in the carbon nanotubes under the nitric acid-based hydrothermal process to obtain prefabricated nitrogen-doped nanotubes.

[0017] Preferably, in step (4): the calcination is carried out at 5°C·min -1 The temperature is raised to 500-900° C. at a rate of 0.1-3 hours, and the reaction is carried out for 0.1-3 hours; the protective atmosphere is one of nitrogen, carbon dioxide, and argon.

[0018] The calcination operation of the present invention can remove surface functional groups of the nanotubes, forming a rich microporous structure, which is beneficial to electrochemical energy storage.

[0019] The second technical solution of the present invention is to provide nitrogen-doped carbon nanotubes obtained by the method of converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material.

[0020] The third technical solution of the present invention is to provide an application of the nitrogen-doped carbon nanotubes in the preparation of battery electrode materials.

[0021] Preferably, the battery electrode material is a sodium ion battery negative electrode material.

[0022] The beneficial technical effects of the present invention are as follows:

[0023] After the melting and cracking operations of the present invention, r-PET can be imbued with significant intrinsic defects, and these defects enable induced nitrogen doping of the r-PET using only nitric acid-assisted hydrothermal treatment. In contrast, carbon nanotubes prepared using acetylene as a carbon source lack intrinsic defects and cannot be nitrogen-doped using this process, requiring calcination in an ammonia atmosphere. Compared to traditional methods that use acetylene as a carbon source and ammonia calcination for nitrogen doping, this new method avoids the use and emission of ammonia, reducing costs and minimizing the environmental impact of the entire production process.

[0024] The nitrogen-doped carbon nanotubes provided by the present invention have rich defect structures and nitrogen doping amounts, and can be used to prepare sodium ion battery negative electrode materials. The sodium ion batteries assembled with them have excellent electrochemical properties such as high reversible capacity, significant cycle stability, and excellent electron and sodium ion transmission rates, and have important application prospects in the field of high-performance sodium ion batteries.

[0025] The nitrogen-doped carbon nanotubes prepared by the present invention are nanotube-like structures with abundant micropores, and the pore volume is 0.05-0.1cm 3 ·g -1 , outer diameter is 25-35nm, specific surface area is 100-300m 2 ·g -1 , micropore size is 0.5-1.5nm; and the nitrogen doping amount brought about by the preparation process of the present invention is also very high, reaching 2.5-3.8at.%; through these properties, the structural stability and conductivity of carbon nanotubes can be effectively enhanced, thereby improving the cycle stability of sodium ion battery negative electrode materials.

[0026] Moreover, the preparation method of the present invention is simple, efficient, clean, environmentally friendly, low-cost, has extremely high application value, and is suitable for further promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM image of the nitrogen-doped carbon nanotubes obtained in Example 1.

[0028] Figure 2This is the X-ray diffraction pattern of the nitrogen-doped carbon nanotubes obtained in Example 1.

[0029] Figure 3 This is the pore size distribution diagram of the nitrogen-doped carbon nanotubes obtained in Example 1.

[0030] Figure 4 These are the TEM images and HRTEM images of the nitrogen-doped carbon nanotubes obtained in Example 1; wherein, (a) is the TEM image of the nitrogen-doped carbon nanotubes obtained in Example 1, (b) is the HRTEM image of the lattice structure of the nitrogen-doped carbon nanotubes obtained in Example 1, and (c) is the HRTEM image of the intrinsic defects of the nitrogen-doped carbon nanotubes obtained in Example 1.

[0031] Figure 5 These are the mapping diagrams of the nitrogen-doped carbon nanotubes obtained in Example 1; wherein, (a) is the C element mapping diagram of the nitrogen-doped carbon nanotubes obtained in Example 1, (b) is the O element mapping diagram of the nitrogen-doped carbon nanotubes obtained in Example 1, and (c) is the N element mapping diagram of the nitrogen-doped carbon nanotubes obtained in Example 1.

[0032] Figure 6 This is the SEM image of the carbon material obtained after carbonization in Comparative Example 1.

[0033] Figure 7 Graph showing the nitrogen atomic ratio content of nitrogen-doped carbon nanotubes obtained in Example 1, Comparative Example 1, and Comparative Example 2.

[0034] Figure 8 Graph showing the intensity ratio of the Raman D peak to the Raman G peak of the nitrogen-doped carbon nanotubes obtained in Example 1, Comparative Example 1, and Comparative Example 2.

[0035] Figure 9 1-3 and Comparative Example 1-2 are performance comparison charts of button batteries prepared using the products of Examples 1-3 and Comparative Example 1-2 as raw materials.

[0036] Figure 10 This is the process flow chart of Example 1. DETAILED DESCRIPTION

[0037] Various exemplary embodiments of the present invention are now described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terms used in the present invention are only for describing specific embodiments and are not intended to limit the present invention.

[0038] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or stated range, and any other stated value or intervening value in the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present invention.

[0040] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0041] The room temperature in the following examples and comparative examples of the present invention refers to 25±2°C.

[0042] The raw materials used in the following examples and comparative examples of the present invention are all commercially available products.

[0043] Example 1

[0044] Preparation of nitrogen-doped carbon nanotubes:

[0045] (1) Weigh 1.0 g of nickel acetate and 10 g of r-PET, and melt-mix them at 255° C. using a twin-screw extruder to obtain a mixed precursor;

[0046] (2) placing the mixed precursor in a tube furnace and performing cracking and carbonization at 700°C in a mixed atmosphere of 95% argon and 5% hydrogen for 3 h to obtain an intermediate;

[0047] (3) The intermediate was transferred to a hydrothermal reactor containing a 9% by mass nitric acid solution and reacted at 160°C and 0.6 MPa for 10 h. After the reactor was cooled, it was taken out and repeatedly washed with distilled water and anhydrous ethanol three times to obtain prefabricated nitrogen-doped nanotubes;

[0048] (4) The prefabricated nitrogen-doped nanotubes were placed in a tube furnace and heated at 5°C·min under a carbon dioxide atmosphere. -1 The temperature was raised to 500°C at a rate of 1000°C and calcined at this temperature for 1 hour. After cooling to room temperature in the furnace, the mixture was taken out to obtain nitrogen-doped carbon nanotubes.

[0049] Figure 1 This is a SEM image of the nitrogen-doped carbon nanotubes obtained in Example 1. As can be seen from the image, the carbon nanotubes are very densely arranged, indicating that the preparation method of the present invention can well utilize r-PET to prepare high-quality carbon nanotubes.

[0050] Figure 2 This is the X-ray diffraction pattern of the nitrogen-doped carbon nanotubes obtained in Example 1. As can be seen from the figure, typical carbon nanotubes were prepared in the present invention.

[0051] Figure 3 This is a pore size distribution diagram of the nitrogen-doped carbon nanotubes obtained in Example 1. It can be seen that the carbon nanotubes prepared in the present invention have a rich microporous structure.

[0052] Figure 4 The following are TEM and HRTEM images of the nitrogen-doped carbon nanotubes obtained in Example 1; (a) is a TEM image of the nitrogen-doped carbon nanotubes obtained in Example 1, (b) is an HRTEM image of the lattice structure of the nitrogen-doped carbon nanotubes obtained in Example 1, and (c) is an HRTEM image of the intrinsic defects of the nitrogen-doped carbon nanotubes obtained in Example 1. It is clearly seen from (a) that the product of the present invention is mostly tubular; from (b), it can be seen that the carbon nanotubes produced in the present invention have a typical carbon lattice stripe structure; and from (c), it can be seen that they contain a large number of intrinsic defects.

[0053] Figure 5 These are mapping diagrams of the nitrogen-doped carbon nanotubes obtained in Example 1; (a) is the C element mapping diagram of the nitrogen-doped carbon nanotubes obtained in Example 1, (b) is the O element mapping diagram of the nitrogen-doped carbon nanotubes obtained in Example 1, and (c) is the N element mapping diagram of the nitrogen-doped carbon nanotubes obtained in Example 1. The diagrams demonstrate that the carbon nanotubes produced by the present invention have a rich nitrogen doping content and are uniformly doped.

[0054] Example 2

[0055] Preparation of nitrogen-doped carbon nanotubes:

[0056] (1) Weighing 0.5 g of nickel nitrate and 10 g of r-PET, melt-mixing them at 260° C. using a twin-screw extruder to obtain a mixed precursor;

[0057] (2) placing the mixed precursor in a tube furnace and performing cracking and carbonization at 700°C in a mixed atmosphere of 95% argon and 5% hydrogen for 3 h to obtain an intermediate;

[0058] (3) The intermediate was transferred to a hydrothermal reactor containing a 12% mass fraction of nitric acid solution and reacted at 165°C and 0.7 MPa for 10 h. After the reactor was cooled, it was taken out and repeatedly washed with distilled water and anhydrous ethanol three times to obtain prefabricated nitrogen-doped nanotubes;

[0059] (4) The prefabricated nitrogen-doped nanotubes were placed in a tube furnace and heated at 5°C·min under a carbon dioxide atmosphere. -1The temperature was raised to 500°C at a rate of 1000°C and calcined at this temperature for 1 hour. After cooling to room temperature in the furnace, the mixture was taken out to obtain nitrogen-doped carbon nanotubes.

[0060] Example 3

[0061] Preparation of nitrogen-doped carbon nanotubes:

[0062] (1) Weighing 0.5 g of nickel sulfate and 10 g of r-PET, melt-mixing them at 250° C. using a twin-screw extruder to obtain a mixed precursor;

[0063] (2) placing the mixed precursor in a tube furnace and performing cracking and carbonization at 700°C in a mixed atmosphere of 95% argon and 5% hydrogen for 3 h to obtain an intermediate;

[0064] (3) The intermediate was transferred to a hydrothermal reactor containing a 15% mass fraction of nitric acid solution and reacted at 155°C and 0.6 MPa for 12 h. After the reactor was cooled, it was taken out and repeatedly washed with distilled water and anhydrous ethanol three times to obtain prefabricated nitrogen-doped nanotubes;

[0065] (4) The prefabricated nitrogen-doped nanotubes were placed in a tube furnace and heated at 5°C·min under a carbon dioxide atmosphere. -1 The temperature was raised to 500°C at a rate of 1000°C and calcined at this temperature for 1 hour. After cooling to room temperature in the furnace, the mixture was taken out to obtain nitrogen-doped carbon nanotubes.

[0066] Example 4

[0067] Preparation of nitrogen-doped carbon nanotubes:

[0068] (1) Weighing 0.1 g of nickel nitrate and 10 g of r-PET, melt-mixing them at 245° C. using a twin-screw extruder to obtain a mixed precursor;

[0069] (2) placing the mixed precursor in a tube furnace and performing cracking and carbonization at 900°C in a mixed atmosphere of 95% nitrogen and 5% hydrogen for 1 h to obtain an intermediate;

[0070] (3) The intermediate was transferred to a hydrothermal reactor containing a 15% mass fraction of nitric acid solution and reacted at 240°C and 3 MPa for 1 hour. After the reactor was cooled, it was taken out and repeatedly washed with distilled water and anhydrous ethanol three times to obtain prefabricated nitrogen-doped nanotubes;

[0071] (4) The prefabricated nitrogen-doped nanotubes were placed in a tube furnace and heated at 5°C·min under an argon atmosphere. -1 The temperature was raised to 900°C at a rate of 1000°C and calcined at this temperature for 1 hour. After cooling to room temperature in the furnace, the mixture was taken out to obtain nitrogen-doped carbon nanotubes.

[0072] Comparative Example 1

[0073] The only difference from Example 1 is that the addition of nickel acetate is omitted and an equal mass of r-PET is added.

[0074] Comparative Example 2

[0075] Preparation of acetylene-derived multi-walled carbon nanotubes:

[0076] (1) Acetylene-derived multi-walled carbon nanotubes purchased from Bayer MaterialScience were used as raw materials, with a carbon content of >99 wt.% and a bulk density of 140-230 kg·m -3 , with an outer diameter of 13 nm and an average inner diameter of 4 nm;

[0077] (2) transferring the multi-walled carbon nanotubes to a hydrothermal reactor containing a 9% by mass nitric acid solution and reacting at 160° C. for 10 h. After the reactor cooled, the reactor was taken out and washed three times with distilled water and anhydrous ethanol to obtain prefabricated nanotubes;

[0078] (3) Place the prefabricated nanotubes in a tube furnace and heat them at 5°C·min under an argon atmosphere. -1 The temperature was raised to 500°C at a rate of 100°C and calcined at this temperature for 1 hour. After cooling to room temperature in the furnace, the carbon nanotubes were obtained.

[0079] Comparative Example 3

[0080] Preparation of nitrogen-doped carbon nanotubes:

[0081] (1) Acetylene-derived multi-walled carbon nanotubes purchased from Bayer MaterialScience were used as raw materials, with a carbon content of >99 wt.% and a bulk density of 140-230 kg·m -3 , with an outer diameter of 13 nm and an average inner diameter of 4 nm;

[0082] (2) The multi-walled carbon nanotubes were placed in a tube furnace and heated at 5°C / min in a 50% ammonia:50% argon mixed atmosphere. -1 The temperature was raised to 500°C at a rate of 1000 ℃ and calcined at this temperature for 6 hours. After cooling to room temperature in the furnace, the mixture was taken out to obtain nitrogen-doped carbon nanotubes.

[0083] Figure 6 : is a SEM image of the carbon material obtained after carbonization in Comparative Example 1. As can be seen from the figure, the carbon material obtained after carbonization of pure PET in Comparative Example 1 is irregular carbon nanoparticles.

[0084] Figure 7 Figure 2 shows the nitrogen atomic ratios of the nitrogen-doped carbon nanotubes obtained in Example 1, Comparative Example 1, and Comparative Example 2. As can be seen from the figure, the nitrogen-doped carbon nanotubes prepared in Example 1 contain a relatively high nitrogen doping level. Comparative Example 1, despite omitting nickel acetate, also exhibits some nitrogen doping, while the carbon nanotubes prepared in Comparative Example 2 exhibit virtually no nitrogen doping.

[0085] Figure 8 Figure 1 shows the Raman D-to-G peak intensity ratios for the nitrogen-doped carbon nanotubes obtained in Example 1, Comparative Example 1, and Comparative Example 2. As can be seen, Comparative Example 1 still has a high degree of defects compared to Example 1, while the acetylene-derived carbon nanotubes in Comparative Example 2 have significantly lower defects than the r-PET-derived carbon nanotubes in Example 1. This demonstrates that nitrogen doping is more readily achieved with a higher degree of defects.

[0086] Effect verification

[0087] 1) To verify the microscopic morphology of the prepared nitrogen-doped carbon nanotubes, the present invention conducted pore volume, outer diameter, specific surface area, and nitrogen content tests on Examples 1-3 and Comparative Examples 1 and 3: pore volume was measured using a fully automatic surface / porosity analyzer based on a nitrogen physical adsorption isotherm at 77K; specific surface area was calculated using the Brunauer-Emmett-Teller (BET) equation; outer diameter was measured using the average outer diameter of the carbon nanotubes as measured by transmission electron microscopy; and nitrogen content was measured using the atomic ratio measured by X-ray photoelectron spectroscopy (N1s) spectrum. The test results are shown in Table 1.

[0088] Table 1 Micromorphology test of nitrogen-doped carbon nanotubes

[0089] <![CDATA[Pore volume (cm 3 ·g -1 )]]> Outer diameter (nm) <![CDATA[Specific surface area (m 2 ·g -1 )]]> Nitrogen content (at.%) Example 1 0.07 35 253 3.6 Example 2 0.05 28 215 2.6 Example 3 0.06 32 226 2.7 Comparative Example 1 0.02 / 20 2.5 Comparative Example 3 0.01 13 324 1.2

[0090] As can be seen from the data of Examples 1-3 in Table 1, the carbon nanotubes produced by the present invention have high specific surface areas and nitrogen doping levels, resulting in enhanced structural stability and conductivity, making them more suitable for use in battery electrodes. A comparison of Example 1 with Comparative Example 1 also demonstrates that the nickel-containing compound added by the present invention effectively catalyzes the formation of carbon nanotubes in subsequent reactions.

[0091] 2) Sodium ion batteries were prepared using the products of Examples 1-3 and Comparative Examples 1-2 as raw materials, respectively, in the following steps:

[0092] (1) Nitrogen-doped carbon nanotubes: conductive carbon black: binder CMC (mass concentration 10 mg mL -1 )=8:1:1 mass ratio to prepare negative electrode slurry, grind it evenly and coat it on copper foil, and let it stand in a vacuum drying oven at 70℃ for 10h. After drying, cut it into circular electrode pieces with a diameter of 6mm to obtain sodium ion battery negative electrode pieces.

[0093] (2) The above-mentioned negative electrode was used as the working electrode, the potassium plate was used as the counter electrode, Celgard 2500 was used as the separator, and 1.0 mol·L -1 NaPF6 solution (solvent is DIGLYME) was used as the electrolyte to prepare 2025 button batteries.

[0094] (1) The charge and discharge performance test was carried out at room temperature. The test conditions were as follows: the button cell was charged at a current density of 1 A·g -1 The test results are as follows: Figure 9 shown.

[0095] Figure 9 The performance comparison chart of button batteries made with the products of Examples 1-3 and Comparative Examples 1-2 as raw materials. As can be seen from the figure, the specific capacity of the button batteries of Examples 1-3 after testing is greater than 200 mAh g -1 The specific capacity of the button cell prepared in Comparative Example 1 is significantly lower than that of Examples 1-3. This is because no nickel acetate is added in Comparative Example 1, and there is no subsequent catalytic effect, so carbon nanotubes cannot be generated in a directional manner. Only irregular carbon particles are formed. Although nitrogen is also doped, its specific surface area is reduced and the adsorption sites are also reduced.

[0096] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material, characterized in that: The steps include: (1) mixing a nickel-containing compound and polyethylene terephthalate, and melting them to obtain a mixed precursor; (2) cracking the mixed precursor under a protective atmosphere to obtain an intermediate; (3) mixing the intermediate with a nitric acid solution and subjecting it to hydrothermal treatment to obtain prefabricated nitrogen-doped nanotubes; (4) calcining the prefabricated nitrogen-doped nanotubes under a protective atmosphere to obtain the nitrogen-doped carbon nanotubes.

2. The method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material according to claim 1, characterized in that: In step (1), the nickel-containing compound is one or more of nickel acetate, nickel nitrate and nickel sulfate; the polyethylene terephthalate is recycled solid waste polyethylene terephthalate; the melting temperature is 240-260° C.; and the mass ratio of the nickel-containing compound to the polyethylene terephthalate is 1:10-100.

3. The method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material according to claim 1, characterized in that: In step (2), the cracking is carried out at 600-900° C. for 1-5 hours; and the protective atmosphere is a mixture of 5% hydrogen and 95% argon, or a mixture of 5% hydrogen and 95% nitrogen, in terms of volume fraction.

4. The method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material according to claim 1, wherein: In step (3), the mass ratio of nitric acid in the nitric acid solution is 3-30%; and the hydrothermal treatment is carried out at 150-250° C. and 0.5-4 MPa for 0.5-24 h.

5. The method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material according to claim 1, wherein: In step (4): the calcination is carried out at 5°C·min -1 The temperature is raised to 500-900° C. at a rate of 0.1-3 hours, and the reaction is carried out; the protective atmosphere is one of nitrogen, carbon dioxide, and argon.

6. Nitrogen-doped carbon nanotubes obtained by the method for converting high-quality polyethylene terephthalate into nitrogen-doped carbon nanotube material according to any one of claims 1 to 5.

7. Use of the nitrogen-doped carbon nanotubes according to claim 6 in preparing battery electrode materials.

8. The use according to claim 7, characterized in that The battery electrode material is a sodium ion battery negative electrode material.

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