A carbon nanofiber of beaded carbon nanotubes and a preparation method thereof

Abstract

The invention relates to a carbon nanofiber of a beaded carbon nanotube and a preparation method thereof. Polyacrylonitrile, nickel acetate tetrahydrate and itaconic acid are added into N,N-dimethylformamide to dissolve to obtain a green transparent mixed solution; the mixed solution is made into a white fabric by electrostatic spinning; the white fabric is pre-oxidized in air to obtain a brown nanofiber material, and then the brown nanofiber material is carbonized in an argon environment in a tubular furnace using dicyandiamide as a carbon source to obtain a black carbon fiber material. The prepared carbon fiber material has the characteristics of good flexibility, high conductivity and strong lithium affinity.

Description

Technical Field

[0001] The invention belongs to the field of nano materials, and in particular relates to a method for preparing carbon nanofibers of vertically grown bead-chain carbon nanotubes. Background Art

[0002] The growing demand for high-capacity and high-power secondary batteries in transportation and grid-level energy storage systems continues to stimulate researchers to explore advanced electrode materials. Metallic lithium has a high theoretical specific capacity (3861mAh g -1 ), low electrochemical potential (-3.04 V compared to the standard hydrogen electrode), and low weight density (0.534 g cm -3 ), has always been an attractive option. Unfortunately, the practical application of Li metal anodes (LMAs) has not yet been realized due to the uncontrollable growth of Li dendrites during repeated electrochemical cycles, resulting in anode structural and interfacial instability.

[0003] In order to regulate the Li plating / stripping process of stable lithium metal anode, a lot of efforts have been made in recent years, including the development of compatible electrolytes, the design of rational three-dimensional Li regulation scaffolds, and the construction of artificial solid electrolyte interface (SEI). Among these methods, the three-dimensional substrate structure of LMAs exhibits excellent electrochemical performance due to the greatly reduced local charge density during the Li plating / stripping process and the ability to accommodate huge volume changes. + Due to the poor adsorption capacity, it is difficult for common three-dimensional substrates to + The concentration is tuned near the anode / electrolyte interface, resulting in limited cycle life and moderate rate capability.

[0004] Therefore, constructing host structures decorated with functional materials is widely used as an effective means to solve the lithium affinity. Li has different deposition characteristics on different substrates. Li metal can be selectively deposited on Ni, Ag, and Au nanoparticles because of their high solubility in Li, thereby achieving ultra-low or zero nucleation barrier for subsequent Li deposition. During the Li deposition process, nano-Ni first dissolves into Li to form a solid solution surface layer with a high lithium diffusion coefficient, which can serve as a buffer layer to eliminate the nucleation barrier of Li deposition under the layer. When Cu is used as the substrate, this solid solution feature does not exist. On the other hand, porous carbon fibers have been shown to be able to uniformly deposit Li and enhance the stability of the SEI layer due to their high specific surface area, good flexibility, and unique lithium affinity. The three-dimensional carbon matrix can effectively reduce the local current density, adapt to volume changes, and release compressive stress, thereby successfully inhibiting the growth of Li dendrites.

[0005] In addition, by using lithiophilic atom-doped carbon materials as lithium hosts, the lithium nucleation barrier on the lithiophilic atom-doped carbon sites is reduced, which can effectively regulate the uniform deposition of Li, thereby achieving Li dendrite-free deposition and extending the cycle time. Considering the above considerations, integrating these advantages into one structure and designing carbon fibers with functional sites is of great significance for high-performance LMAs. Summary of the invention

[0006] The purpose of the present invention is to provide a simple method for preparing carbon nanofibers with good flexibility, high conductivity and strong lithium affinity.

[0007] In order to solve the above technical problems, the present invention provides a method for preparing carbon nanofibers by electrospinning followed by chemical vapor deposition, comprising the following steps:

[0008] Step 1: Mix polyacrylonitrile, itaconic acid and nickel acetate tetrahydrate in N,N-dimethylformamide and stir to obtain a green transparent solution;

[0009] Step 2: electrospinning the green transparent solution into white fabric;

[0010] Step 3: pre-oxidizing the white fabric in air and heating it to obtain a brown nanofiber material;

[0011] Step 4: Place the brown nanofiber material at the downstream of a large silicon tube reactor in a horizontal tube furnace, and place the carbon source dicyandiamide at the upstream. First, heat up in an inert gas environment to decompose dicyandiamide into hydrocyanic acid, thereby covering the surface of the brown nanofiber material with a layer of C6N7(NH2)3. Then, continue to heat up to convert C6N7(NH2)3 into Ni-g-C3N4 through Ni single atom catalysis. Finally, continue to heat up to convert Ni-g-C3N4 into NiSA-N-CNT to obtain the vertically grown carbon nanofibers of bead-chain carbon nanotubes.

[0012] Furthermore, in step 1, the mass ratio of itaconic acid / nickel acetate tetrahydrate / polyacrylonitrile / N,N-dimethylformamide is 1:2:10:100.

[0013] Furthermore, in the step 2, the electrospinning voltage is 17 kV, the liquid supply speed is 1 ml / h, the roller speed is 3 r / min, and the slide stroke is 15 cm.

[0014] Furthermore, in step three, the white fabric is pre-oxidized in air at 300° C. for 2 h at a heating rate of 2° C. / min to obtain the brown nanofiber material.

[0015] Furthermore, in step 4, first, the temperature is raised to 400°C at a rate of 5°C / min in an argon environment and kept warm for 2 hours to decompose dicyandiamide into hydrocyanic acid, thereby covering a layer of C6N7(NH2)3 on the surface of the brown nanofiber material.

[0016] Further, in step four, the temperature is then continued to be raised to 650°C at a rate of 1°C / min and kept for 2 hours, and C6N7(NH2)3 is converted into Ni-g-C3N4 through Ni single atom catalysis.

[0017] Furthermore, in step four, finally, the temperature is raised to 800°C at 1°C / min and kept at this temperature for 1 hour to convert Ni-g-C3N4 into NiSA-N-CNT to obtain the carbon nanofibers of the vertically grown bead-chain carbon nanotubes.

[0018] Furthermore, in the step 4, the distance between the carbon source dicyandiamide and the brown nanofiber material is 10 cm.

[0019] The present invention also includes a carbon nanofiber of vertically grown bead-chain carbon nanotubes, which is prepared using any of the above-mentioned preparation methods.

[0020] Furthermore, the cross-sectional diameter of the carbon fiber is less than 100 nm, and the cross-sectional diameter of the carbon nanotube is 50 cm.

[0021] The present invention also includes the use of the prepared vertically grown carbon nanofibers of bead-chain carbon nanotubes as composite negative electrode precursors for lithium metal batteries.

[0022] The beneficial effects produced by the present invention are:

[0023] The 3D conductive network of carbon nanofibers prepared by the present invention effectively reduces the local charge density on the negative electrode surface. The beaded carbon nanotubes grown on the fiber surface can not only more efficiently transfer charges, but also increase the surface area for contacting more lithium ions. The carbon aerogel structure provides sufficient void space to withstand the volume expansion during lithium deposition / stripping.

[0024] The present invention adopts heteroatom-doped carbon material as the host material of lithium. Since the heterogeneous lithium nucleation barrier on the lithium-philic heteroatom-doped carbon site is reduced, Li deposition can be effectively regulated, thereby achieving dendrite-free Li deposition and extending the cycle time. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a scanning electron microscope image of the white fabric prepared in Example 1;

[0026] Figure 2 This is a scanning electron microscope image of the brown nanofibers prepared in Example 1;

[0027] Figure 3 This is a scanning electron microscope image of the carbon nanofibers prepared in Example 1;

[0028] Figure 4 is a scanning electron microscope image of a cross section of a composite negative electrode prepared using the carbon nanofibers prepared in Example 1 as a precursor after 1000 cycles of a half-cell;

[0029] Figure 5 This is a scanning electron microscope image of the surface of the composite negative electrode prepared using the carbon nanofibers prepared in Example 1 as a precursor after 200 cycles of the full battery;

[0030] Figure 6 This is an electrochemical test diagram of a composite negative electrode assembled half-cell prepared using the carbon nanofibers prepared in Example 1 as a precursor;

[0031] Figure 7 This is an electrochemical test diagram of a symmetrical battery assembled with a composite negative electrode prepared using the carbon nanofibers prepared in Example 1 as a precursor;

[0032] Figure 8 This is an electrochemical test diagram of a full battery assembled with a composite negative electrode prepared using the carbon nanofibers prepared in Example 1 as a precursor;

[0033] Fig. 9 This is an electrochemical test diagram of the full battery rate of the composite negative electrode assembled using the carbon nanofibers prepared in Example 1 as a precursor. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0035] Example

[0036] Polyacrylonitrile, itaconic acid, nickel acetate tetrahydrate and N,N-dimethylformamide in a mass ratio of 1:2:10:100 were mixed and stirred until the solution became green and transparent; the mixed solution was electrospun into white fabric, the electrospinning voltage was 17kv, the liquid supply speed was 1ml / h, the roller speed was 3r / min, and the slide stroke was 15cm. The white fabric obtained in the step was pre-oxidized in air at 300℃ for 2h, and the heating rate was 2℃ / min to obtain brown nanofiber material; the brown nanofiber material obtained in step 3 was placed downstream in the large silicon tube reactor of the horizontal tube furnace, and the carbon source dicyandiamide was placed upstream, the mass ratio of carbon material to carbon source dicyandiamide was 1:100, and the distance between carbon source dicyandiamide and brown nanofiber material was 10cm. The temperature was raised to 400℃ at a rate of 5℃ / min in an argon environment, and the temperature was kept at 400℃. 2h, dicyandiamide is decomposed into hydrocyanic acid, a layer of C6N7(NH2)3 is covered on the surface of the brown nanofiber material, and then the temperature is raised to 650℃ at a rate of 1℃ / min and kept for 2h. C6N7(NH2)3 is converted into Ni-g-C3N4 through Ni single atom catalysis. Finally, the temperature is raised to 800℃ at 1℃ / min and kept for 1h to convert Ni-g-C3N4 into NiSA-N-CNT, and the finished vertically grown carbon nanofibers of bead-chain carbon nanotubes are obtained.

[0037] The scanning electron microscope images of the white fabric, brown nanofibers and vertically grown bead-chain carbon nanotubes prepared in this example are as follows: Figure 1 , Figure 2 and Figure 3 As shown, the cross-sectional diameter of carbon fiber is less than 100nm, and the cross-sectional diameter of carbon nanotube is 50cm. Figure 4 and Figure 5 The scanning electron microscope images of the composite negative electrode surface after the carbon nanofibers prepared in this example were applied to the half-cell for 1000 cycles and the full-cell for 200 cycles are shown respectively. Figure 6-Figure 9 The electrochemical side view of the composite negative electrode prepared by using the carbon nanofibers prepared in this example as a precursor, shows that the 3D conductive network effectively reduces the local charge density on the negative electrode surface, and the beaded carbon nanotubes grown on the fiber surface can not only transfer charges more efficiently, but also increase the surface area for contacting more lithium ions. The carbon aerogel structure provides sufficient void space to withstand the volume expansion during lithium deposition / stripping. Figure 5 It can be seen that by adopting heteroatom-doped carbon materials as the host material for lithium, the Li deposition can be effectively regulated due to the reduction of the heterogeneous lithium nucleation barrier on the lithiophilic heteroatom-doped carbon sites, thereby achieving dendrite-free Li deposition and extending the cycle time.

[0038] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing carbon nanofibers of vertically grown beaded carbon nanotubes, characterized in that: The preparation method comprises the following steps: Step 1: Mix polyacrylonitrile, itaconic acid and nickel acetate tetrahydrate in N,N-dimethylformamide and stir to obtain a green transparent solution; Step 2: electrospinning the green transparent solution into white fabric; Step 3: pre-oxidizing the white fabric in air and heating it to obtain a brown nanofiber material; Step 4: Place the brown nanofiber material at the downstream of a large silicon tube reactor in a horizontal tube furnace, and place the carbon source dicyandiamide at the upstream. First, increase the temperature in an inert gas environment to decompose dicyandiamide into hydrocyanic acid, thereby covering the surface of the brown nanofiber material with a layer of C6N7(NH2)3. Then, continue to increase the temperature to convert C6N7(NH2)3 into Ni-g-C3N4 through Ni single atom catalysis. Finally, continue to increase the temperature to convert Ni-g-C3N4 into NiSA-N-CNT to obtain the vertically grown carbon nanofibers of bead-chain carbon nanotubes.

2. The preparation method according to claim 1, characterized in that: In step 1, the mass ratio of itaconic acid / nickel acetate tetrahydrate / polyacrylonitrile / N,N-dimethylformamide is 1:2:10:

100.

3. The preparation method according to claim 1, characterized in that: In the step 2, the electrospinning voltage is 17 kV, the liquid supply speed is 1 ml / h, the roller speed is 3 r / min, and the slide stroke is 15 cm.

4. The preparation method according to claim 1, characterized in that: In step three, the white fabric is pre-oxidized in air at 300° C. for 2 h at a heating rate of 2° C. / min to obtain the brown nanofiber material.

5. The preparation method according to claim 1, characterized in that: In step 4, first, the temperature is raised to 400°C at a rate of 5°C / min in an argon environment and kept at this temperature for 2 hours to decompose dicyandiamide into hydrocyanic acid, thereby covering the surface of the brown nanofiber material with a layer of C6N7(NH2)3.

6. The preparation method according to claim 1, characterized in that: In step 4, the temperature is then continued to be raised to 650°C at a rate of 1°C / min and kept at this temperature for 2h, and C6N7(NH2)3 is converted into Ni-g-C3N4 through Ni single atom catalysis.

7. The preparation method according to claim 1, characterized in that: In step 4, finally, the temperature is raised to 800° C. at 1° C. / min and kept at this temperature for 1 hour to convert Ni-g-C3N4 into NiSA-N-CNT to obtain the carbon nanofibers of the vertically grown bead-chain carbon nanotubes.

8. The preparation method according to claim 1, characterized in that: In the step 4, the distance between the carbon source dicyandiamide and the brown nanofiber material is 10 cm.

9. A carbon nanofiber, characterized in that: Carbon nanofibers prepared by the preparation method according to any one of claims 1-8.

10. An application of carbon nanofibers, characterized in that: The use of carbon nanofibers as claimed in claim 9 as a negative electrode composite precursor for a lithium metal battery negative electrode.

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