A branched porous carbon nanotube material and its preparation method

Abstract

A porous carbon nanotube material with a branched structure. The average diameter of the porous carbon nanotubes is 60 nm, presenting a Y-shaped bifurcated structure. The interior of the carbon nanotubes has continuous bamboo-joint-like capsule-structured pores. The prepared porous carbon nanotube material with a bamboo-joint-like branched structure in the present invention has an outer diameter of about 60 nanometers and a bamboo-joint-like capsule structure inside. This unique structure can serve as a sodium ion storage space, and its branched structure is conducive to the rapid transport of ions and charges. When used as a positive electrode material for sodium ion batteries, at a current density of 100 mA g-1, the reversible capacity is 416 mAh g-1. At a current density of 2 A g-1, it has an excellent rate capacity of 257 mAh g-1, and has more than 4500 reversible charge-discharge cycles.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon nanotube material preparation, and particularly relates to a branched structure porous carbon nanotube material and a preparation method thereof. Background Art

[0002] Sodium-ion batteries (SIBs) have attracted extensive research interest due to their low cost, abundant reserves, and physical and chemical properties similar to those of lithium. However, the diameter of Na + is larger than that of Li + resulting in severe volume changes and slow diffusion kinetics, which directly damage the storage and transportation of Na + during the electrochemical process. In the past few decades, a large number of reports have shown that various carbon nanomaterials have been used as anodes for SIBs, such as carbon nanotubes, graphene, hard carbon, carbon nanospheres, carbon nanofibers, and porous carbon. It is reported that the minimum interlayer spacing for inserting Na + is at least 0.37 nm. However, the interlayer distance of traditional graphite-based anode materials is less than 0.37 nm, which cannot provide an ideal interlayer spacing to accommodate the insertion and extraction of Na + , resulting in poor Na + storage performance of graphite anode materials. And some other conversion materials, including metal oxides / sulfides and alloys, usually exhibit poor cycle stability and rate performance due to their inherent low conductivity and large volume expansion during cycling, which makes them far from the practical application of SIBs.

[0003] A large number of studies have been carried out in this field to explore new carbon anodes with expanded interlayer distances, edge-enriched nitrogen doping, and highly connected mesoporous structures. Among them, heteroatom doping is an effective means to expand the interlayer spacing of carbon-based materials, increase conductivity, and provide abundant defect / active sites to enhance ion storage. However, the preparation method is complex, and the obtained anodes cannot simultaneously meet the requirements of high capacity and fast charging performance. It is reported that a highly interconnected mesoporous structure can expose more active surface sites to the electrolyte and shorten the diffusion distance of ions. For example, in the article "Bamboo-Like Nitrogen-Doped Carbon Nanotube Forests as Durable Metal-Free Catalysts for Self-Powered Flexible Li–CO2 Batteries" published by Xuelian Li et al., bamboo-like carbon nanotubes were prepared. However, the disordered zigzag channels limit the effective adsorption of sodium ions, resulting in low capacity. Therefore, designing suitable anode materials for SIBs remains a huge challenge. Summary of the Invention

[0004] The object of the present invention is to provide a bamboo-jointed porous carbon nanotube material with a branched structure.

[0005] Another object of the present invention is to provide a preparation method of the above-mentioned bamboo-jointed porous carbon nanotube material with a branched structure. The prepared carbon nanotubes have a unique branched structure and a bamboo-jointed continuous pore distribution, making the material have excellent Na + storage performance.

[0006] The object of the present invention is achieved by the following technical solutions:

[0007] A porous carbon nanotube material with a branched structure, characterized in that: the average diameter of the porous carbon nanotubes is 60 nm, showing a Y-shaped bifurcation structure, and the carbon nanotubes have continuous bamboo-jointed capsule-like pore channels inside.

[0008] Furthermore, the above-mentioned porous carbon nanotube material with a branched structure is prepared by dissolving an imidazole aqueous solution, a urea aqueous solution, and a ferrocene aqueous solution in an acetonitrile aqueous solution to prepare a precursor solution, heating the silicon wafer as a substrate, converting the precursor solution into an evaporation gas by heating, and transporting the evaporation gas of the precursor solution to the surface of the heated silicon wafer for growth with a mixed gas of H2 and NH3, and then washing and drying after completion.

[0009] Furthermore, the concentration of the above-mentioned imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, and the concentration of the acetonitrile aqueous solution is 50 mol / L.

[0010] Furthermore, the volume ratio of the above-mentioned imidazole aqueous solution, urea aqueous solution, ferrocene aqueous solution, and acetonitrile aqueous solution is 1:0.5 - 0.8:0.1 - 0.15:10 - 20.

[0011] Furthermore, the heat treatment of the silicon wafer is to place the silicon wafer in a tube furnace, heat it to 550 - 650 °C at a rate of 10 °C / min, and then continue to heat it to 950 - 1050 °C at a rate of 5 °C / min, and then introduce a mixed gas of H2, NH3, and Ar until the temperature is stable.

[0012] Furthermore, the volume ratio of the above-mentioned H2, NH3, and Ar is 1:1:8.

[0013] Furthermore, after the temperature in the tube furnace is stable, the precursor is heated to be converted into an evaporation gas, and a mixed gas of H2 and NH3 with a volume ratio of 1:1 is used to transport the evaporation gas to the surface of the silicon wafer in the tube furnace for growth for 12 - 10 min.

[0014] Further, the product after the growth is washed successively with hydrochloric acid solution, acetone, deionized water and absolute ethanol, and then dried at 80 °C for 3 h.

[0015] A preparation method of a porous carbon nanotube material with a branched structure, characterized in that: an imidazole aqueous solution, a urea aqueous solution and a ferrocene aqueous solution are dissolved in an acetonitrile aqueous solution to prepare a precursor solution, a silicon wafer is used as a substrate for heat treatment, and the precursor solution is heated to be converted into an evaporation gas, and a mixed gas of H2 and NH3 is used to transport the precursor solution evaporation gas to the surface of the heated silicon wafer for growth, and after completion, it is washed and dried.

[0016] Further, the concentration of the above-mentioned imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, and the concentration of the acetonitrile aqueous solution is 50 mol / L.

[0017] Further, the volume ratio of the above-mentioned imidazole aqueous solution, urea aqueous solution, ferrocene aqueous solution and acetonitrile aqueous solution is 1:0.5 - 0.8:0.1 - 0.15:10 - 20.

[0018] In the present invention, imidazole and urea are used as composite carbon sources, and ferrocene is mainly used as a catalyst. A variety of carbon sources, nitrogen sources and the introduced mixed gas change the catalyst active sites during the reaction, thereby changing the growth direction of the carbon nanotubes to form a Y-shaped branched structure. At the same time, a continuous pore channel with a bamboo joint capsule structure is formed inside the carbon nanotubes, providing a large space for the storage of Na+, and the branched structure is conducive to the rapid transmission of ions and charges, so that the material has fast charging performance and excellent cycle stability when used as an anode material for sodium ion batteries.

[0019] Further, the heat treatment of the silicon wafer is to place the silicon wafer in a tube furnace, heat it up to 550 - 650 °C at a rate of 10 °C / min, and then continue to heat it up to 950 - 1050 °C at a rate of 5 °C / min. During this process, a mixed gas of H2, NH3 and Ar is continuously introduced until the temperature is stable.

[0020] Further, the volume ratio of the above-mentioned H2, NH3 and Ar is 1:1:8.

[0021] Further, after the temperature in the tube furnace is stable, the precursor is heated to be converted into an evaporation gas, and a mixed gas of H2 and NH3 with a volume ratio of 1:1 is used to transport the evaporation gas to the surface of the silicon wafer in the tube furnace for growth for 12 - 10 min.

[0022] Further, the product after the growth is washed successively with hydrochloric acid solution, acetone, deionized water and absolute ethanol, and then dried at 80 °C for 3 h.

[0023] Further, a preparation method of a porous carbon nanotube material with a branched structure is characterized by the following steps:

[0024] Step 1: Prepare the precursor solution

[0025] Add an imidazole aqueous solution, a urea aqueous solution, and a ferrocene aqueous solution to an acetonitrile aqueous solution, and stir at 100 - 200 rpm for 15 min to obtain a precursor solution; the concentration of the imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, the concentration of the acetonitrile aqueous solution is 50 mol / L, and the volume ratio of the imidazole aqueous solution, the urea aqueous solution, the ferrocene aqueous solution, and the acetonitrile aqueous solution is 1:0.5 - 0.8:0.1 - 0.15:10 - 20;

[0026] Step 2: Grow carbon nanotubes at high temperature

[0027] (1) Wash the silicon wafer with acetone and ethanol for 5 min respectively, and dry it at 80 °C for 30 min. Then fix the silicon wafer in a quartz boat and place the quartz boat in the central heating zone of a tube furnace;

[0028] (2) First, raise the temperature of the tube furnace to 550 - 650 °C at a rate of 10 °C / min, and then continue to heat it to 950 - 1050 °C at a rate of 5 °C / min. During this process, continuously introduce a mixed gas of H2, NH3, and Ar until the temperature stabilizes;

[0029] (3) Heat the precursor solution to convert it into evaporation gas, introduce the evaporation gas of the precursor mixed solution transported by a mixed gas of H2 and NH3 with a volume ratio of 1:1 into the tube furnace, and start the growth of the product on the surface of the silicon wafer in the tube furnace. The growth time is 12 - 20 min;

[0030] (4) Wash the obtained product with hydrochloric acid solution, isopropanol, acetone, deionized water, and absolute ethanol several times, and dry it at 80 °C for 3 hours and then collect it.

[0031] The present invention has the following technical effects:

[0032] The porous carbon nanotube material with a bamboo - joint - like branched structure prepared in the present invention has an outer diameter of about 60 nm and a bamboo - joint - like capsule structure inside. This unique structure can serve as a sodium - ion storage space, and its branched structure is conducive to the rapid transmission of ions and charges. When used as a cathode material for sodium - ion batteries, at a current density of 100 mA g -1 the reversible capacity is 416 mAh g -1 at a current density of 2 A g -1 it has an excellent rate capacity of 257 mAh g -1 , and has more than 4500 reversible charge - discharge cycles. Brief Description of the Drawings

[0033] Figure 1 : Schematic diagram of the structure of the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention.

[0034] Figure 2 : Scanning electron microscopy image of the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention.

[0035] Figure 3 : Transmission electron microscopy image of the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention and the porous carbon nanotube prepared in Comparative Example 1.

[0036] Figure 4 : Raman image of the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention.

[0037] Figure 5 : Pore size distribution diagram of the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention.

[0038] Figure 6 : Performance comparison diagram of the battery capacity - cycle number of the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention and the solid carbon nanofiber prepared in Comparative Example 1 at a current density of 1 A / g.

[0039] Figure 7 : Sodium ions when the porous carbon nanotube material with a bamboo joint-like branched structure prepared by the present invention is used as the positive electrode material of a sodium ion battery. Detailed Description of the Invention

[0040] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and should not be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0041] Example 1

[0042] A preparation method of a porous carbon nanotube material with a branched structure, characterized in that it is carried out according to the following steps:

[0043] Step 1: Prepare the precursor solution

[0044] An imidazole aqueous solution, a urea aqueous solution, and a ferrocene aqueous solution were added to an acetonitrile aqueous solution, and the mixture was stirred at 100 - 200 rpm for 15 min to obtain a precursor solution; the concentration of the imidazole aqueous solution was 0.35 mol / L, the concentration of the urea aqueous solution was 0.15 mol / L, the concentration of the ferrocene aqueous solution was 0.5 mol / L, the concentration of the acetonitrile aqueous solution was 50 mol / L, and the volume ratio of the imidazole aqueous solution, the urea aqueous solution, the ferrocene aqueous solution, and the acetonitrile aqueous solution was 1:0.68:0.12:15;

[0045] Step 2: High - temperature growth of carbon nanotubes

[0046] (1) The silicon wafer was washed with acetone and ethanol for 5 min respectively, dried at 80 °C for 30 min, then the silicon wafer was fixed in a quartz boat, and the quartz boat was placed in the central heating zone of a tube furnace;

[0047] (2) First, the temperature of the tube furnace was raised to 600 °C at a rate of 10 °C / min, and then continued to be heated to 1000 °C at a rate of 5 °C / min. During this process, a mixed gas of H2, NH3, and Ar was continuously introduced until the temperature was stable;

[0048] (3) The precursor solution was heated to be converted into evaporation gas, and a precursor mixed - solution evaporation gas transported by a mixed gas of H2 and NH3 with a volume ratio of 1:1 was introduced into the tube furnace, and the growth of the product started on the surface of the silicon wafer in the tube furnace, and the growth time was 15 min;

[0049] (4) The obtained product was washed several times with hydrochloric acid solution, isopropanol, acetone, deionized water, and absolute ethanol, and collected after drying at 80 °C for 3 hours.

[0050] When used as the cathode material of an ion battery, at a current density of 100 mA g -1 the reversible capacity is 416 mAh g -1 and at a current density of 2 A g -1 it has an excellent rate capacity of 257 mAh g -1 and has more than 4500 reversible charge - discharge cycles.

[0051] Figure 1 This is the schematic diagram of the morphology and structure of the carbon nanotubes prepared by the present invention. The scanning electron microscope image of the carbon nanotubes prepared by the present invention is as Figure 2 shown Figure 3 (a) is its transmission electron microscope image. It can be clearly seen that a Y - type branch structure is formed, and a uniform and continuous bamboo - joint capsule pore structure is formed inside the carbon nanotubes, which is consistent with Figure 1 the description.

[0052] Using the carbon nanotubes prepared in Example 1 as the anode material, at a current density of 100 mA g -1When the current density is 2 A g⁻¹, the rate capacity of the branched bamboo-shaped porous carbon nanotubes prepared in Example 1 is 416 mAh g⁻¹ -1 and it has excellent rate capacity of 257 mAh g⁻¹ -1 at a current density of 2 A g⁻¹, and has more than 4500 reversible charge-discharge cycles. -1

[0053] Comparative Example 1:

[0054] Compared with Example 1, there is no urea in the precursor solution in Comparative Example 1. When heating up and introducing the evaporated gas of the precursor solution, both H₂ and Ar are used as the mixed gas, and NH₃ is not adopted.

[0055] As Figure 3 (b) shows, although the bamboo-shaped continuous pore structure is also formed in the carbon nanotubes prepared in Comparative Example 1, the overall structure formed by the carbon nanotubes does not bifurcate, the overall diameter is larger, and the uniformity and continuity of the internal bamboo node pore structure are poor, and the pore size structure is not ideal. Using the carbon nanotubes prepared in Example 1 and Comparative Example 1 as anode materials, as Figure 6 shown, at a current density of 1 A / g, after 30 cycles, the rate capacities of the carbon nanotube anode materials corresponding to Example 1 and Comparative Example 1 are 368 mAh g⁻¹ -1 and 127 mAh g⁻¹ -1 .

[0056] Example 2

[0057] A preparation method of a porous carbon nanotube material with a branched structure, characterized in that it is carried out according to the following steps:

[0058] Step 1: Prepare the precursor solution

[0059] Add the imidazole aqueous solution, urea aqueous solution and ferrocene aqueous solution into the acetonitrile aqueous solution, stir at 150 rpm for 15 min to obtain the precursor solution; the concentration of the imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, the concentration of the acetonitrile aqueous solution is 50 mol / L, and the volume ratio of the imidazole aqueous solution, urea aqueous solution, ferrocene aqueous solution and acetonitrile aqueous solution is 1:0.5:0.1:10;

[0060] Step 2: Grow carbon nanotubes at high temperature

[0061] (1) Wash the silicon wafer with acetone and ethanol for 5 min respectively, dry it at 80 °C for 30 min, then fix the silicon wafer in the quartz boat, and place the quartz boat in the central heating zone of the tube furnace;

[0062] ​(2) First, raise the temperature of the tubular furnace to 550 °C at a rate of 10 °C / min, and then continue to heat it to 1050 °C at a rate of 5 °C / min. During this process, continuously introduce a mixed gas of H2, NH3, and Ar until the temperature stabilizes;

[0063] (3) Heat the precursor solution to convert it into vapor, introduce the evaporated gas of the precursor mixed solution transported by a mixed gas of H2 and NH3 with a volume ratio of 1:1 into the tubular furnace, and start the growth of the product on the surface of the silicon wafer in the tubular furnace. The growth time is 12 min;

[0064] (4) Wash the obtained product several times with hydrochloric acid solution, isopropyl alcohol, acetone, deionized water, and absolute ethanol, and collect it after drying at 80 °C for 3 hours.

[0065] The carbon nanotubes prepared by Example 2 are used as the anode material. At a current density of 100 mA g -1 when the rate capacity of the bamboo-jointed porous carbon nanotubes with a branched structure prepared in Example 2 is 419 mAh g -1 At a current density of 2 A g -1 it has an excellent rate capacity of 242 mAh g -1 and has more than 4500 reversible charge-discharge cycles.

[0066] Example 3

[0067] A preparation method of a porous carbon nanotube material with a branched structure is carried out according to the following steps:

[0068] Step 1: Prepare the precursor solution

[0069] Add an imidazole aqueous solution, a urea aqueous solution, and a ferrocene aqueous solution to an acetonitrile aqueous solution, and stir at 100 - 200 rpm for 15 min to obtain the precursor solution; the concentration of the imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, the concentration of the acetonitrile aqueous solution is 50 mol / L, and the volume ratio of the imidazole aqueous solution, the urea aqueous solution, the ferrocene aqueous solution, and the acetonitrile aqueous solution is 1:0.8:0.15:20;

[0070] Step 2: Grow carbon nanotubes at high temperature

[0071] (1) Wash the silicon wafer with acetone and ethanol for 5 min respectively, and dry it at 80 °C for 30 min. Then fix the silicon wafer in a quartz boat and place the quartz boat in the central heating zone of the tubular furnace;

[0072] (2) First, raise the temperature of the tube furnace to 650 °C at a rate of 10 °C / min, and then continue to raise the temperature to 950 °C at a rate of 5 °C / min. During this process, continuously introduce a mixed gas of H2, NH3, and Ar until the temperature stabilizes;

[0073] (3) Heat the precursor solution to convert it into evaporation gas, introduce the evaporation gas of the precursor mixed solution transported by a mixed gas of H2 and NH3 with a volume ratio of 1:1 into the tube furnace, and start the growth of the product on the surface of the silicon wafer in the tube furnace. The growth time is 20 min;

[0074] (4) Wash the obtained product several times with hydrochloric acid solution, isopropyl alcohol, acetone, deionized water, and absolute ethanol, and collect it after drying at 80 °C for 3 hours.

[0075] The carbon nanotubes prepared by Example 1 are used as the anode material. At a current density of 100 mA g -1 , the rate capacity of the bamboo-jointed porous carbon nanotubes with a branched structure prepared in Example 1 is 409 mAh g -1 . At a current density of 2 A g -1 , it has an excellent rate capacity of 253 mAh g -1 , and has more than 4500 reversible charge-discharge cycles.

Claims

1. A preparation method of a porous carbon nanotube material with a branched structure, characterized in that: An imidazole aqueous solution, a urea aqueous solution, and a ferrocene aqueous solution are dissolved in an acetonitrile aqueous solution to prepare a precursor solution. A silicon wafer is used as a substrate for heat treatment. After the temperature in the tube furnace is stabilized, the precursor solution is heated to be converted into evaporation gas. A mixed gas of H2 and NH3 with a volume ratio of 1:1 is used to transport the evaporation gas to the surface of the silicon wafer in the tube furnace for growth for 12 - 10 min. After completion, it is washed and dried. The prepared porous carbon nanotubes have an average diameter of 60 nm, a Y-shaped bifurcated structure, and continuous bamboo-joint-like capsule structure pores inside the carbon nanotubes.

2. The preparation method of the porous carbon nanotube material with a branched structure according to claim 1, characterized in that: The concentration of the imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, and the concentration of the acetonitrile aqueous solution is 50 mol / L.

3. The preparation method of the porous carbon nanotube material with a branched structure according to claim 1 or 2, characterized in that: The volume ratio of the imidazole aqueous solution, the urea aqueous solution, the ferrocene aqueous solution, and the acetonitrile aqueous solution is 1:0.5 - 0.8:0.1 - 0.15:10 - 20.

4. The preparation method of the porous carbon nanotube material with a branched structure as described in claim 1 or 2, characterized in that: The heat treatment of the silicon wafer is to place the silicon wafer in the tube furnace, heat it to 550 - 650 °C at a rate of 10 °C / min, and then continue to heat it to 950 - 1050 °C at a rate of 5 °C / min. During this process, a mixed gas of H2, NH3, and Ar is continuously introduced until the temperature is stabilized.

5. A preparation method of a porous carbon nanotube material with a branched structure, characterized in that, It is carried out according to the following steps: Step 1: Prepare the precursor solution Add the imidazole aqueous solution, the urea aqueous solution, and the ferrocene aqueous solution to the acetonitrile aqueous solution, and stir at 100 - 200 rpm for 15 min to obtain the precursor solution; the concentration of the imidazole aqueous solution is 0.35 mol / L, the concentration of the urea aqueous solution is 0.15 mol / L, the concentration of the ferrocene aqueous solution is 0.5 mol / L, the concentration of the acetonitrile aqueous solution is 50 mol / L, and the volume ratio of the imidazole aqueous solution, the urea aqueous solution, the ferrocene aqueous solution, and the acetonitrile aqueous solution is 1:0.5 - 0.8:0.1 - 0.15:10 - 20; Step 2: Grow carbon nanotubes at high temperature (1) Wash the silicon wafer with acetone and ethanol for 5 min respectively, and dry it at 80 °C for 30 min. Then fix the silicon wafer in a quartz boat and place the quartz boat in the central heating zone of the tube furnace; (2) First, raise the temperature of the tube furnace to 550 - 650 °C at a rate of 10 °C / min, and then continue to raise the temperature to 950 - 1050 °C at a rate of 5 °C / min. During this process, a mixed gas of H2, NH3, and Ar is continuously introduced until the temperature is stabilized; (3) Heat the precursor solution to be converted into evaporation gas, introduce the evaporation gas of the precursor mixed solution transported by a mixed gas of H2 and NH3 with a volume ratio of 1:1 into the tube furnace, and start the growth of the product on the surface of the silicon wafer in the tube furnace. The growth time is 12 - 20 min; (4) Wash the obtained product several times with hydrochloric acid solution, isopropanol, acetone, deionized water, and absolute ethanol, and collect it after drying at 80 °C for 3 hours.

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