Mixed arrangement carbon nano tube as well as preparation method and application thereof

Abstract

The invention belongs to the related technical field of nano material preparation, and discloses a mixed arrangement carbon nanotube and a preparation method and application thereof, and the preparation method comprises the following steps: S1, sequentially depositing an Al2O3 buffer layer and a Fe catalyst layer on a Si substrate or a SiO2 substrate, and then carrying out argon plasma etching; s2, the substrate is subjected to first-step annealing, and after cooling, the substrate is exposed in an oxygen-containing atmosphere to oxidize Fe; and S3, carrying out second-step annealing on the substrate, then introducing H2, Ar and C2H4 into the reaction chamber, and growing on the substrate through water-assisted chemical vapor deposition to obtain the mixed arrangement carbon nanotubes. According to the preparation method, the process of the preparation method is improved, the obtained product is the mixed arrangement carbon nanotubes, and compared with a horizontal or vertical orientation single orientation arrangement carbon nanotube array, the mixed arrangement carbon nanotubes have vertical orientation channels and a hierarchical pore structure and have better performance when being applied to an energy storage device.

Description

Technical Field

[0001] The present invention belongs to the technical field related to the preparation of nanomaterials, and more specifically, relates to a hybrid arrangement of carbon nanotubes and a preparation method and application thereof. Background Art

[0002] As a typical one-dimensional nanomaterial, carbon nanotubes exhibit important potential in the fields of energy storage (such as lithium-ion batteries, supercapacitors), catalytic carriers, gas adsorption and separation, etc. due to their high specific surface area, excellent electrical conductivity and mechanical properties. The traditional methods for preparing carbon nanotubes mainly include chemical vapor deposition, arc discharge method and laser ablation method. The carbon nanotubes prepared by chemical vapor deposition have a single structure, including horizontally or vertically oriented array structures. Among them, the horizontally arranged carbon nanotubes usually extend parallel to the substrate to form a dense conductive network, but the porosity is relatively low (<30%). The vertically arranged carbon nanotubes are usually arranged perpendicular to the substrate in an orderly manner to form nano-scale open channels, but the aggregation between the tube bundles is serious, reducing the connectivity between the pores. The arc discharge method uses a high current to evaporate a graphite electrode in an inert gas to generate multi-walled carbon nanotubes. The product usually shows a disordered entangled morphology, with a wide diameter distribution (10 nm to 100 nm), and is accompanied by a large amount of amorphous carbon impurities. The laser ablation method can prepare single-walled carbon nanotube bundles by bombarding a metal-doped graphite target with a pulsed laser, but their arrangement direction is random, and the specific surface area is limited by the bundle aggregation effect. In addition, the template method (such as anodic aluminum oxide template) can regulate the carbon tube diameter through confined growth, but the template removal process is prone to cause structural collapse and it is difficult to achieve orientation control.

[0003] The above traditional methods generally have the problem of structural singularity, or are limited by the single orientation arrangement, resulting in limited mass transfer efficiency, or are restricted by the disordered entanglement, reducing the connectivity of the conductive network. At the same time, they lack the ability to in-situ construct multi-level pores, seriously restricting the performance breakthrough of carbon nanotubes in the fields of energy storage, catalysis, etc. Especially in the development trend of miniaturization and extreme working conditions of new energy devices, single-structure carbon nanotubes can no longer meet the requirements of multi-functional integration. Summary of the Invention

[0004] In view of the above deficiencies or improvement requirements of the prior art, the purpose of the present invention is to provide a hybrid-aligned carbon nanotube and its preparation method and application. By improving the process of the preparation method, first, the Si substrate coated with Al2O3 and Fe is subjected to plasma etching, and the substrate is treated by a two-step annealing process. In this way, the carbon nanotubes generated by water-assisted chemical vapor deposition are hybrid-aligned carbon nanotubes. Compared with the carbon nanotube arrays with a single orientation arrangement of horizontal or vertical orientation, they have vertical oriented channels (as shown in the examples below, the diameter of the vertical oriented channels is 70 nm to 200 nm), and have a hierarchical pore structure (that is, they have micropores, mesopores and macropores at the same time), and have better performance. The hybrid-aligned carbon nanotubes obtained by the present invention, due to having both vertical oriented channels and a hierarchical pore structure, can ensure rapid ion transport and improve the charge storage density, and are particularly suitable for use as electrodes in low-temperature supercapacitors (the low temperature can especially be -100 °C to -30 °C).

[0005] To achieve the above object, according to one aspect of the present invention, a method for preparing a hybrid-aligned carbon nanotube is provided, including the following steps: S1: Magnetron sputtering is used to sequentially deposit an Al2O3 buffer layer and an Fe catalyst layer on a Si substrate or a SiO2 substrate, and then argon plasma etching is carried out to roughen the Fe catalyst layer; S2: The substrate obtained by treating in step S1 is heated in a flowing mixed gas of H2 and Ar for the first annealing, and after cooling, it is exposed to an oxygen-containing atmosphere to oxidize Fe; S3: The substrate obtained by treating in step S2 is heated in a flowing mixed gas of H2 and Ar for the second annealing, and then H2, Ar and C2H4 are introduced into the reaction chamber, and hybrid-aligned carbon nanotubes can be grown on the substrate by water-assisted chemical vapor deposition.

[0006] As a further preference of the present invention, the annealing temperature used for the first annealing in step S2 is 750 °C to 780 °C, and the annealing time is 225 s to 350 s; in the flowing mixed gas of H2 and Ar, the gas flow ratio of H2 and Ar is 4:1; The annealing temperature used for the second annealing in step S3 is 750 °C to 780 °C, and the annealing time is 225 s to 350 s; in the flowing mixed gas of H2 and Ar, the gas flow ratio of H2 and Ar is 4:1.

[0007] As a further preference of the present invention, in step S1, the etching time of the argon plasma etching is 5 minutes to 30 minutes, and the etching power range is 5 W to 40 W.

[0008] As a further preference of the present invention, in step S2, the oxygen-containing atmosphere is air; The exposure to an oxygen-containing atmosphere specifically means placing in air for at least 30 minutes.

[0009] As a further preference of the present invention, in step S3, the flow rate ratio of H2, Ar, and C2H4 gases used in the moisture-assisted chemical vapor deposition is 2:7:4, the water vapor concentration is 75 ppm, and the growth time of the moisture-assisted chemical vapor deposition is 22 minutes to 35 minutes.

[0010] According to another aspect of the present invention, the present invention provides a mixed arrangement of carbon nanotubes prepared by the above preparation method.

[0011] As a further preference of the present invention, the mixed arrangement of carbon nanotubes has a vertically oriented channel, and the diameter of the vertically oriented channel is 100 nm to 200 nm.

[0012] According to yet another aspect of the present invention, the present invention provides the application of the above mixed arrangement of carbon nanotubes as an electrode material in an energy storage device.

[0013] As a further preference of the present invention, the application is at a temperature of -100°C to 20°C.

[0014] According to still another aspect of the present invention, the present invention provides the application of the above mixed arrangement of carbon nanotubes as an electrode material in promoting the capacity retention rate of an energy storage device under low-temperature conditions, and the low-temperature conditions are -100°C to -50°C.

[0015] Through the above technical solution conceived by the present invention, different from the carbon nanotubes generated by the one-step annealing process of a Si substrate coated with Al2O3 and Fe in the prior art through moisture-assisted chemical vapor deposition, the preparation method of the present invention needs to first perform plasma etching on the Si substrate coated with Al2O3 and Fe to change the roughness of the catalyst layer. Then, two-step annealing treatment is also required. An oxidation operation is required before the second annealing treatment (wherein, the first annealing can form uniformly distributed catalyst nanoparticles, the oxidation operation can oxidize the catalyst nanoparticles and anchor them on the buffer layer, and the second annealing can reactivate the catalyst nanoparticles and achieve a focused state of isolated distribution). Finally, moisture-assisted chemical vapor deposition is performed to generate a mixed arrangement of carbon nanotubes.

[0016] Correspondingly, different from the horizontally or vertically oriented single - oriented carbon nanotube array structures prepared in the prior art, the carbon nanotubes obtained by the method of the present invention are mixed - arranged carbon nanotubes. On the one hand, they have both vertically - grown nanotube bundles and randomly - oriented nanotube bundles at the same time. The randomly - oriented nanotube bundles serve as a lateral framework to support the vertically - grown nanotube bundles. On the other hand, the mixed - arranged carbon nanotubes also have vertically - oriented channels and a hierarchical pore structure with micropores, mesopores, and macropores simultaneously. As shown in the following examples, the diameter size of the vertically - oriented channels d in the mixed - arranged carbon nanotubes can be distributed in the range of 70 nm to 200 nm. It is precisely due to the differences in the structure of the carbon nanotube materials that the mixed - arranged carbon nanotubes in the present invention are more suitable as electrode materials in extremely low - temperature environments compared to the single - oriented carbon nanotube array structures in the prior art. The working temperature of the corresponding device can be as low as - 100 °C and can maintain a high capacity in extremely low - temperature environments (of course, it can also be used as an electrode material at room temperature of 20 °C; that is to say, the working temperature range can be - 100 °C to 20 °C).

[0017] Before growing carbon nanotubes by the method of the present invention, the Si substrate deposited with Al2O3 and Fe is etched first to increase the surface roughness, improve the migration potential energy of metal atoms, and inhibit the aggregation or coalescence between metal particles. After the first annealing, the Si substrate is taken out and exposed to air to oxidize the Fe catalyst nanoparticles and "anchor" them on the buffer layer. Then, the second annealing is carried out to re - activate the Fe catalyst nanoparticles and achieve a distribution of aggregated and isolated states. The carbon nanotubes grown from the aggregated Fe catalyst nanoparticles have strong van der Waals force interactions and show vertical growth. While the carbon nanotubes grown from the isolated Fe catalyst nanoparticles have weak van der Waals forces and show random - direction growth, thus obtaining mixed - arranged carbon nanotubes with a vertically - oriented channel structure and hierarchical pore distribution.

[0018] Specifically, the present invention can achieve the following beneficial effects.

[0019] 1. The mixed - arranged carbon nanotubes obtained by the present invention have vertically - oriented channels and a hierarchical pore structure, which can improve the electrochemical performance of energy - storage devices. Taking the following examples as an example, the specific capacitance of the supercapacitor assembled with the mixed - arranged carbon nanotubes is 31.6 F / g at 20 °C, which is 184% higher than that of the vertical carbon nanotube array. Even at - 100 °C, the specific capacitance of this supercapacitor is still 30.2 F / g, and the capacitance retention rate is as high as 95.6%.

[0020] 2. The present invention can especially obtain mixed - arranged carbon nanotubes, the diameter size of whose vertically - oriented channels is distributed in the range of 70 nm to 200 nm, and which have a hierarchical pore structure with micropores, mesopores, and macropores simultaneously.

[0021] 3. The ion transport efficiency is greatly improved by the hybrid-aligned carbon nanotubes prepared by the method of the present invention. Taking Example 1 hereinafter as an example, the tortuosity of the ion transport path of the hybrid-aligned carbon nanotubes is 1.20, which greatly reduces the tortuosity of the ion transport path and realizes fast ion transport (the tortuosity of the ion transport path of the vertically aligned carbon nanotube array obtained in Comparative Example 1 is 2.76).

[0022] 4. The hybrid-aligned carbon nanotubes prepared by the method of the present invention can provide more charge adsorption sites and significantly improve the capacity of the electrode material.

[0023] In summary, the present invention obtains a carbon nanotube material with a hybrid alignment of multiple structures synchronously, changes the practice of separately regulating the alignment direction and pore structure in the traditional process, realizes the synchronous design and precise control of both, and promotes the application of carbon-based materials in the fields of efficient energy storage and the like. Description of the Drawings

[0024] Figure 1 is a schematic flow chart of the preparation method of the hybrid-aligned carbon nanotubes in the present invention.

[0025] Figure 2 is the SEM image of the carbon nanotubes prepared in Example 1, Example 2 and Comparative Example 1, wherein Figure 2 the (a) in Figure 2 corresponds to the hybrid-aligned carbon nanotubes prepared in Example 1, Figure 2 the (b) in

[0026] Figure 3 corresponds to the hybrid-aligned carbon nanotubes prepared in Example 2, Figure 3 the (c) in Figure 3 corresponds to the vertically aligned carbon nanotube array prepared in Comparative Example 1. Figure 3 the (c) in

[0027] Figure 4 is the constant current charge-discharge curves of the electrodes prepared from the carbon nanotube materials prepared in Comparative Example 1, Example 1 and Example 2 at -100°C to 20°C; wherein, Figure 3 the (a) in Figure 3 corresponds to the vertically aligned carbon nanotube array prepared in Comparative Example 1, Figure 3 the (b) in

[0027] Figure 4 corresponds to the hybrid-aligned carbon nanotubes prepared in Example 2,

[0028] Figure 5 is the comparison chart of the tortuosity of the ion transport paths of the hybrid-aligned carbon nanotubes prepared in Example 1 and Example 2 and the vertically aligned carbon nanotube array prepared in Comparative Example 1. Detailed implementation manners

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] As Figure 1 shown, in the preparation method of the hybrid-aligned carbon nanotubes in the present invention, first, a Si substrate coated with Al2O3 and Fe is etched by reactive ion etching (Al2O3 is an intermediate buffer layer, located on the upper surface of the Si substrate and in direct contact with the Si substrate; Fe is located above the Al2O3 layer), and then the first annealing treatment is carried out. After the treatment, it is taken out and placed in the air (for example, placed for 30 minutes), and then the second annealing is carried out, and the subsequent water-assisted chemical vapor deposition growth is directly carried out after the end of the second annealing (the growth time can be 22 minutes).

[0031] The following are specific embodiments.

[0032] Example 1 It includes the following steps: (1) First deposit a 30-nm-thick Al2O3 buffer layer on a clean Si substrate by magnetron sputtering, and then deposit a 2-nm-thick Fe catalyst layer. Place it in the reaction chamber of a reactive ion etching instrument and etch it with argon plasma. During the etching process, the Ar flow rate is 30 sccm, the etching time is 5 minutes, and the etching power is 30 W, so that the Fe thin film of the catalyst layer becomes rough.

[0033] (2) Put the Si substrate processed in step (1) into a tube furnace, heat it to 750°C in H2 (800 sccm) and Ar gas (200 sccm), and carry out the first annealing. The annealing time is 300 s, which makes the Fe nanoparticles evenly distributed on the surface of the catalyst layer. After cooling, take out the annealed Si substrate from the tube furnace and expose it to the air for 30 minutes of oxidation treatment, so that the catalyst Fe nanoparticles are oxidized and "anchored" on the Al2O3 buffer layer. After oxidation, put the Si substrate into the tube furnace again and carry out the second annealing at 750°C in H2 (800 sccm) and Ar gas (200 sccm), and the annealing time is 300 s.

[0034] (3) After annealing treatment, without moving the sample and still keeping the sample in the tube furnace, then water-assisted chemical vapor deposition is carried out at 1 atm using Ar, H2 and C2H4 (where the Ar gas flow rate is 350 sccm, the H2 gas flow rate is 100 sccm, and the C2H4 gas flow rate is 200 sccm). The water vapor concentration is controlled to be 75 ppm (the water vapor is introduced in the form of water-carrying argon; the same below). Carbon nanotubes with a mixed arrangement are grown using C2H4 as the carbon source at 750 °C for a growth time of 22 minutes.

[0035] The SEM image of the prepared carbon nanotubes with a mixed arrangement is as Figure 2 shown in (a) of []. Randomly oriented nanotube bundles serve as a lateral framework to support vertically growing nanotube bundles, forming vertically oriented channels and a hierarchical pore structure. The diameter of the vertically oriented channels is 100 nm to 200 nm. Further detection shows that the thickness of the carbon nanotubes with a mixed arrangement is 500 μm, the porosity is 98.8%, and the specific surface area is 487 cm 2 / g. The pore sizes include micropores (<2 nm), mesopores (3 - 4 nm), and macropores (>50 nm). It is denoted as the "d: 100 - 200 nm" sample.

[0036] Example 2 It includes the following steps: (1) First, deposit a 30-nm-thick Al2O3 buffer layer and then a 2-nm-thick Fe catalyst layer on a clean Si substrate by magnetron sputtering. Place it in the reaction chamber of a reactive ion etching instrument and etch it through argon plasma. During the etching process, the Ar flow rate is 30 sccm, the etching time is 5 minutes, and the etching power is 20 W to make the Fe thin film of the catalyst layer rough.

[0037] (2) The same as step (2) of Example 1.

[0038] (3) The same as step (3) of Example 1.

[0039] The SEM image of the carbon nanotubes with a mixed arrangement prepared in this example is as Figure 2 shown in (b) of []. Randomly oriented nanotube bundles serve as a lateral framework to support vertically growing nanotube bundles, forming vertically oriented channels and a hierarchical pore structure. The diameter of the vertically oriented channels is 70 nm to 120 nm. Further detection shows that the thickness of the carbon nanotubes with a mixed arrangement is 501 μm, the porosity is 98.7%, and the specific surface area is 525 cm 2 / g. The pore sizes include micropores (<2 nm), mesopores (3 - 0 nm), and macropores (>50 nm). It is denoted as the "d: 70 - 120 nm" sample.

[0040] By comparing Example 1 and Example 2, it is not difficult to see that when preparing the hybrid-aligned carbon nanotubes of the present invention, the diameter size of the vertical alignment channels of the hybrid-aligned carbon nanotubes can be regulated by adjusting the reactive ion etching power.

[0041] Comparative Example 1 This comparative example is for preparing a vertical carbon nanotube array without using argon plasma etching or two-step annealing (only using one-step annealing), and includes the following steps: (1) First deposit a 30-nm-thick Al2O3 buffer layer on a clean Si substrate by magnetron sputtering, and then deposit a 2-nm-thick Fe catalyst layer.

[0042] (2) Place the above Si substrate into a tube furnace, introduce H2 and Ar (the total gas flow rate is 1000 sccm, where the Ar gas flow rate is 800 sccm and the H2 gas flow rate is 200 sccm), and heat the tube furnace to 750 °C within 800 s.

[0043] (3) After the tube furnace is heated to 750 °C, perform annealing in a gas atmosphere of H2 and Ar (the total gas flow rate is 1000 sccm, where the Ar gas flow rate is 200 sccm and the H2 gas flow rate is 800 sccm), and the annealing time is 300 s.

[0044] (4) Set the growth temperature to 750 °C and the water vapor concentration to 75 ppm, and perform water-assisted chemical vapor deposition at 1 atm using Ar, H2, and C2H4 (where the Ar gas flow rate is 350 sccm, the H2 gas flow rate is 100 sccm, and the C2H4 gas flow rate is 200 sccm) to grow a vertical carbon nanotube array, and the growth time is 22 minutes.

[0045] The SEM image of the product obtained in this comparative example is as shown in (c) of Figure 2 It can be seen that the product is a vertical carbon nanotube array, but the tube bundles are relatively dense and there are almost no macropores. Further detection shows that the thickness of the vertical carbon nanotube array obtained in this comparative example is 502 μm, the porosity is 98.7%, the specific surface area is 470 cm 2 / g, and the pore diameter is mainly concentrated in mesopores (34 nm), with basically no micropores and no macropores.

[0046] Performance detection: In addition, in order to characterize the electrochemical performance of energy storage devices in extremely low-temperature environments, the hybrid-aligned carbon nanotubes with different vertically oriented channel diameters prepared in Example 1 and Example 2 and the vertically aligned carbon nanotube array prepared in Comparative Example 1 were fabricated into electrodes for testing. The specific operations are as follows: The hybrid-aligned carbon nanotubes with different vertically oriented channel diameters and the vertically aligned carbon nanotube array were used as electrode materials respectively, and the electrolyte used was a mixed electrolyte (i.e., a mixed solution of 1 M MeEt3NBF4, DOL, and acetonitrile) to assemble supercapacitors (the supercapacitors only differed in electrode materials, and other components and detailed parameter conditions were all the same). The temperature range for testing was from 20 °C to -100 °C, and the constant current charge-discharge curves of the hybrid-aligned carbon nanotube electrodes with different vertically oriented channel diameters and the vertically aligned carbon nanotube array were tested at -100 °C to 20 °C. The potential was 2.7 V, and the current density was 1 A / g. The results are as Figure 3 shown. As can be seen from Figure 3 (a) therein, for the vertically aligned carbon nanotube array of Comparative Example 1, as the temperature decreased from 20 °C to -100 °C, its charge-discharge time significantly and gradually shortened. For the hybrid-aligned carbon nanotubes with a vertically oriented channel diameter d of 70 - 120 nm prepared in Example 2 (i.e., the "d: 70 - 120 nm" sample), as Figure 3 (b) therein shows, the trend of its charge-discharge time gradually shortening with the decrease in temperature was somewhat alleviated. For the hybrid-aligned carbon nanotubes with a vertically oriented channel diameter d of 100 - 200 nm prepared in Example 1 (i.e., the "d: 100 - 200 nm" sample), as Figure 3 (c) therein shows, with the decrease in temperature, the change in charge-discharge time was the smallest.

[0047] According to Figure 3 the constant current charge-discharge curves, the capacities of the devices assembled with the hybrid-aligned carbon nanotubes obtained in Example 1 and Example 2 and the vertically aligned carbon nanotube array obtained in Comparative Example 1 at different temperatures were calculated, as shown in Table 1 and Figure 4As shown, it is not difficult to see that compared with the product of Comparative Example 1, the products of Example 1 and Example 2 can promote the capacity retention rate of the energy storage device at -50°C to -100°C (among them, the effect of Example 1 is the best). At 20°C and -100°C, the capacities of the devices assembled with the vertical carbon nanotube arrays of Comparative Example 1 are 11.1 F / g and 2.6 F / g respectively (the capacity at -100°C decreased by 76.6% compared with that at 20°C). The capacities of the devices assembled with the hybrid-aligned carbon nanotubes of Example 2 are 19.8 F / g and 12.5 F / g respectively (the capacity at -100°C decreased by 36.9% compared with that at 20°C, and the decrease rate decreased significantly). The capacities of the devices assembled with the hybrid-aligned carbon nanotubes of Example 1 are 31.6 F / g and 30.2 F / g respectively (the capacity at -100°C decreased by only 4.4% compared with that at 20°C, and the decrease rate is almost negligible). It can be seen that the device assembled with the hybrid-aligned carbon nanotubes with d of 100 - 200 nm in Example 1 has the largest capacity in the temperature range from 20°C to -100°C, and the capacity retention rate is as high as 95.6%:

[0048] In addition, the tortuosity of the ion transport path of the vertical carbon nanotube array of Comparative Example 1 and the hybrid-aligned carbon nanotubes of Examples 1 and 2 at room temperature can be calculated by referring to the known methods in the prior art (for example, Pouraghajan, F.; Knight, H.; Wray, M.; Mazzeo, B.; Subbaraman, R.; Christensen, J.; Wheeler, D. Quantifying Tortuosity of Porous Li-Ion Battery Electrodes: Comparing Polarization-Interrupt and Blocking-Electrolyte Methods. J. Electrochem. Soc. 2018, 165, A2644. DOI: https: / / doi.org / 10.1149 / 2.0611811jes.). The results are as Figure 5 shown. The tortuosity of the ion transport path of the vertical carbon nanotube array of Comparative Example 1 is the largest, which is 2.76. The tortuosities of the ion transport paths of the hybrid-aligned carbon nanotubes of Examples 2 and 1 are 1.80 and 1.20 respectively. It can be seen that the "d: 100 - 200 nm" sample has a more suitable vertically oriented channel, which greatly reduces the tortuosity of the ion transport path and improves the capacity of the device.

[0049] The above embodiments are only examples. The thickness of the hybrid-aligned carbon nanotubes can be adjusted by the growth time. According to actual needs, the thickness of the hybrid-aligned carbon nanotubes can also take other values (for example, other thicknesses within the range of 200 μm to 1000 μm). The gas flow ratios of H2, Ar, and C2H4 and the water vapor concentration used in the water-assisted chemical vapor deposition to grow the hybrid-aligned carbon nanotubes can all be adjusted according to the actual situation. In addition to the Si substrate, a SiO2 substrate can also be used.

[0050] In addition, the micropores, mesopores, and macropores appearing in the present invention satisfy the conventional definitions. The pore diameter of the micropores is less than 2 nm, the pore diameter of the mesopores is between [2 nm, 50 nm], and the pore diameter of the macropores is > 50 nm.

[0051] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should all be included within the protection scope of the present invention.

Claims

1. A method for preparing mixed arranged carbon nanotubes, characterized in that: The following steps are involved: S1: Al2O3 buffer layer and Fe catalyst layer are sequentially deposited on Si substrate or SiO2 substrate by magnetron sputtering, and then argon plasma etching is performed to roughen the Fe catalyst layer; S2: heating the substrate obtained in step S1 in a flowing H2 and Ar mixed gas for a first step annealing, and exposing it to an oxygen-containing atmosphere after cooling to oxidize Fe; S3: The substrate obtained in step S2 is heated in a flowing H2 and Ar mixed gas for a second annealing step, and then H2, Ar and C2H4 are introduced into the reaction chamber to grow mixed arranged carbon nanotubes on the substrate by water-assisted chemical vapor deposition.

2. The preparation method according to claim 1, characterized in that: The first annealing in step S2 uses an annealing temperature of 750° C. to 780° C. and an annealing time of 225 s to 350 s. In the flowing H2 and Ar mixed gas, the ratio of the H2 to Ar gas flow is 4:

1. The annealing temperature used in the second annealing in step S3 is 750° C. to 780° C., and the annealing time is 225s to 350s; in the flowing mixed gas of H2 and Ar, the gas flow ratio of H2 to Ar is 4:

1.

3. The preparation method according to claim 1, characterized in that: In step S1 , the etching time of argon plasma etching is 5 minutes to 30 minutes, and the etching power ranges from 5W to 40W.

4. The preparation method according to claim 1, characterized in that: In step S2, the oxygen-containing atmosphere is air; The exposure to the oxygen-containing atmosphere is specifically placing the mixture under air for at least 30 minutes.

5. The preparation method according to claim 1, characterized in that: In step S3, the ratio of the H2, Ar and C2H4 gas flows used in the moisture-assisted chemical vapor deposition is 2:7:4, the water vapor concentration is 75 ppm, and the growth time of the moisture-assisted chemical vapor deposition is 22 minutes to 35 minutes.

6. Mixed arranged carbon nanotubes prepared by the preparation method according to any one of claims 1 to 5.

7. The mixed arrangement of carbon nanotubes as claimed in claim 6, characterized in that: The mixed arranged carbon nanotubes have vertically oriented channels, and the diameter of the vertically oriented channels is 100nm to 200nm.

8. Use of the mixed arranged carbon nanotubes as claimed in claim 6 or 7 as electrode material in energy storage devices.

9. The use according to claim 8, characterized in that The application is at a temperature of -100°C to 20°C.

10. Use of the mixed arranged carbon nanotubes as claimed in claim 6 or 7 as an electrode material in promoting the capacity retention rate of energy storage devices under low temperature conditions, characterized in that: The low temperature condition is -100°C to -50°C.

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