Surface modified carbon nanotube and preparation method thereof

Abstract

The invention relates to a surface-modified carbon nano tube and a preparation method thereof. The surface-modified carbon nano tube comprises a carbon nano tube and an oxygen-containing functional group bonded on the carbon nano tube, the molar content of the oxygen element in the surface-modified carbon nanotube is 2-8%, and in the Raman spectrum of the surface-modified carbon nanotube, the intensity ratio of a G peak to a D peak is 20-80. The surface-modified carbon nanotube provided by the invention is good in hydrophilicity, easy to disperse and excellent in structural integrity, and is beneficial to maintaining high conductivity and improving the cycle performance of a battery.

Description

Technical Field

[0001] This application relates to the field of carbon nanotube technology, and in particular to a surface-modified carbon nanotube and its preparation method. Background Technology

[0002] Carbon nanotubes are seamless, hollow, one-dimensional tubular structures formed by rolling up graphene, a six-membered ring network of carbon atoms. The binding energy between carbon nanotubes can reach up to 500 eV / μm, easily forming aggregates with diameters of 50 nm to 100 nm. Carbon nanotubes are widely used in lithium-ion batteries, primarily as electrode material additives, conductive agents, or independent electrode components. As a negative electrode material, carbon nanotubes possess unique advantages such as a hollow structure, high conductivity, and large specific surface area, resulting in high discharge capacity. As a negative electrode material additive, carbon nanotubes can be combined with other negative electrode materials such as graphite, lithium titanate, tin-based, and silicon-based materials. Their high conductivity can significantly improve the electron transport efficiency of the negative electrode material, alleviate the contact resistance problem of traditional conductive agents such as carbon black, and their three-dimensional network can also suppress the volume expansion of the negative electrode material during charging and discharging, extending battery cycle life.

[0003] Due to their high aspect ratio, carbon nanotubes tend to entangle and agglomerate together. In practical applications, carbon nanotubes need to be well dispersed to function. However, the dispersion of carbon nanotubes still faces the following two challenges: (1) Strong van der Waals forces and π-π stacking: The van der Waals forces between the tube bundles are extremely strong, easily forming bundles or tightly entangled aggregates, making it difficult to disperse uniformly in solvents or matrices; (2) Limited solvent selection: Only a few highly polar solvents such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF) or surfactants such as sodium dodecyl sulfate (SDS) and sodium dodecylbenzene sulfonate (SDBS) can effectively disperse them, but these may introduce impurities or affect performance. Although chemical modification can improve the dispersion effect of carbon nanotubes to some extent, it destroys the sp 2 The structure reduces the length of carbon nanotubes from 1 μm to 200 nm, resulting in a decrease in conductivity. Summary of the Invention

[0004] Therefore, it is necessary to provide a surface-modified carbon nanotube and its preparation method to address the above problems. The surface-modified carbon nanotubes described in this application not only have good hydrophilicity and are easy to disperse, but also have excellent structural integrity, which is beneficial for maintaining high conductivity and improving the cycle performance of the battery.

[0005] A surface-modified carbon nanotube includes a carbon nanotube and oxygen-containing functional groups bonded to the carbon nanotube.

[0006] The surface-modified carbon nanotubes have an oxygen molar content of 2% to 8%, and the intensity ratio of the G peak to the D peak in the Raman spectrum of the surface-modified carbon nanotubes is 20 to 80.

[0007] In one embodiment, the surface-modified carbon nanotubes have an oxygen molar content of 6% to 7% and an intensity ratio of G peak to D peak in the Raman spectrum of 60 to 70.

[0008] And / or, the surface-modified carbon nanotubes have an oxygen molar content of 7%~8% and an intensity ratio of G peak to D peak in the Raman spectrum of 50~60.

[0009] In one embodiment, the absorbance of the dispersion of the surface-modified carbon nanotubes is 0.55 to 1.55, and the mass concentration of the surface-modified carbon nanotubes in the dispersion is 0.1% to 1%.

[0010] In one embodiment, the surface-modified carbon nanotubes have an oxygen molar content of 6% to 7%, an intensity ratio of G peak to D peak in the Raman spectrum of 60 to 70, and an absorbance of 1.1 to 1.25.

[0011] And / or, the surface-modified carbon nanotubes have an oxygen molar content of 7%~8%, an intensity ratio of G peak to D peak in the Raman spectrum of 50~60, and an absorbance of 1.25~1.5.

[0012] In one embodiment, the oxygen-containing functional group includes at least one selected from carboxyl, phenolic hydroxyl, aldehyde, ketone carbonyl, ether, lactone, acid anhydride, and quinone groups.

[0013] And / or, the carbon nanotubes include at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes.

[0014] A method for preparing surface-modified carbon nanotubes as described above includes the following steps:

[0015] A modified gas is introduced and heated. The carbon nanotubes float under the action of external force and undergo a reaction. After the reaction is completed, surface-modified carbon nanotubes are obtained. The modified gas includes at least a gas containing oxygen.

[0016] In one embodiment, the oxygen-containing gas includes at least one of oxygen, ozone, chlorine dioxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide, and phosgene.

[0017] In one embodiment, the modified gas further includes at least one of nitrogen and argon;

[0018] When the modified gas is selected from a mixture of ozone and nitrogen, the volume fraction of ozone in the mixture is 10% to 20%.

[0019] Alternatively, when the modified gas is selected from a mixture of chlorine dioxide and nitrogen, the volume fraction of chlorine dioxide in the mixture is 20% to 30%.

[0020] In one embodiment, the flow rate of the modified gas is 1 L / min to 10 L / min;

[0021] And / or, the reaction temperature is 20℃~150℃, and the reaction time is 0.1h~10h.

[0022] In one embodiment, the preparation method includes the following steps:

[0023] Carbon nanotubes are contained in a quartz charging tube, which is then fixedly installed in an inner furnace. Modified gas is introduced from one end of the inner furnace and flows out from the other end. At the same time, a rotating component drives the quartz charging tube to rotate around its own axis. Lifting plates arranged axially on the inner wall of the quartz charging tube scoop up the carbon nanotubes, causing them to float. Under heating conditions, the carbon nanotubes react with the modified gas. After the reaction is completed, surface-modified carbon nanotubes are obtained.

[0024] The surface-modified carbon nanotubes described in this application contain a specific molar amount of oxygen and satisfy an intensity ratio of 20 to 80 for the G peak and D peak, indicating that the surface-modified carbon nanotubes have a uniform and appropriate distribution of oxygen-containing functional groups. This enhances the hydrophilicity of the modified carbon nanotubes, making them easier to disperse. This is beneficial for improving the bonding ability between carbon nanotubes and polymers, and for increasing the interfacial interaction between the modified carbon nanotubes and the negative electrode, binder, and current collector, thereby improving the peel strength and extending the cycle life of the battery. At the same time, it also better preserves the structural integrity of the carbon nanotubes, maintaining their high conductivity, and further optimizes the cycle performance of the battery through the synergistic effect with the structure. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of a carbon nanotube surface modification device according to an embodiment of this application;

[0027] Figure 2This is a schematic diagram showing the relative positions of the inner furnace and the heating element according to an embodiment of this application;

[0028] Figure 3 This is a three-dimensional cross-sectional view of a quartz loading tube according to an embodiment of this application;

[0029] Figure 4 This is a schematic diagram of an axial cross-section of a quartz loading tube according to an embodiment of this application.

[0030] Reference numerals: 10, quartz charging tube; 11, lifting plate; 20, rotating component; 30, inner furnace; 40, heating component; 50, sealing component; 51, screen; 52, heat insulation plug; 60, base. Detailed Implementation

[0031] To facilitate understanding of this application, it will be described in more detail below. However, it should be understood that this application can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0032] 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 this application pertains. The terminology used herein in the specification of this application is for the purpose of describing particular implementations or embodiments only and is not intended to limit the application. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items. In this application, when numerical ranges are involved, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, and every value between such minimum and maximum values. Further, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Furthermore, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges to which they are incorporated.

[0033] This application provides a surface-modified carbon nanotube, comprising a carbon nanotube and oxygen-containing functional groups bonded to the carbon nanotube.

[0034] The surface-modified carbon nanotubes have an oxygen molar content of 2% to 8%, and the intensity ratio of the G peak to the D peak in the Raman spectrum of the surface-modified carbon nanotubes is 20 to 80.

[0035] The surface-modified carbon nanotubes described in this application contain a specific molar amount of oxygen and satisfy an intensity ratio of 20 to 80 for the G peak and D peak, indicating that the surface-modified carbon nanotubes have a uniform and appropriate distribution of oxygen-containing functional groups. This enhances the hydrophilicity of the modified carbon nanotubes, making them easier to disperse. This is beneficial for improving the bonding ability between carbon nanotubes and polymers, and for increasing the interfacial interaction between the modified carbon nanotubes and the negative electrode, binder, and current collector, thereby improving the peel strength and extending the cycle life of the battery. At the same time, it also better preserves the structural integrity of the carbon nanotubes, maintaining their high conductivity, and further optimizes the cycle performance of the battery through the synergistic effect with the structure.

[0036] It should be noted that in the Raman spectrum of the surface-modified carbon nanotubes, both the G peak and the D peak are characteristic peaks of carbon atom crystals. Specifically, the G peak refers to the peak at 1560 cm⁻¹ in the Raman spectrum. -1 ~1600cm -1 The largest characteristic peak within the range, the D peak, refers to the peak at 1310 cm⁻¹ in the Raman spectrum. -1 ~1350cm -1 The maximum characteristic peak within the range. By comparing the intensity of the G peak and the D peak, the integrity of the surface-modified carbon nanotubes described in this application can be quantitatively characterized. If the molar content of oxygen in the surface-modified carbon nanotubes exceeds 8%, the tubular structure of the surface-modified carbon nanotubes will be excessively damaged, directly leading to a significant decrease in its conductivity, mechanical strength, and interfacial stability, thereby causing multiple problems such as increased battery internal resistance, shortened cycle life, and increased safety risks.

[0037] When traditional surface-modified carbon nanotubes only satisfy the requirement of an oxygen molar content of 2% to 8% but do not meet the requirement of a specific intensity ratio of the G peak to the D peak, the oxygen-containing functional groups distributed on the surface-modified carbon nanotubes disrupt the structure of the carbon nanotubes, thus affecting the electrical properties. When traditional surface-modified carbon nanotubes only satisfy the requirement of an intensity ratio of the G peak to the D peak of 20 to 80 but do not meet the requirement of a specific oxygen molar content, the high conductivity of the surface-modified carbon nanotubes is not fully utilized due to insufficient dispersion.

[0038] It is understood that the molar oxygen content of the surface-modified carbon nanotubes includes, but is not limited to, any value or any range between 2%, 3%, 4%, 5%, 6%, 7%, and 8%, and the intensity ratio of the G peak to the D peak in the Raman spectrum includes, but is not limited to, any value or any range between 20, 30, 40, 50, 60, 70, and 80, for example: the molar oxygen content of the surface-modified carbon nanotubes is 6%~7% and the intensity ratio of the G peak to the D peak in the Raman spectrum is 60~70; the molar oxygen content of the surface-modified carbon nanotubes is 7%~8% and the intensity ratio of the G peak to the D peak in the Raman spectrum is 50~60, etc.

[0039] In some embodiments of this application, the absorbance of the dispersion of the surface-modified carbon nanotubes is 0.55~1.55, and the mass concentration of the surface-modified carbon nanotubes in the dispersion is 0.1%~1%. The absorbance further indicates the dispersion performance of the surface-modified carbon nanotubes. In the beam path, when the surface-modified carbon nanotubes have excellent dispersibility, they can be uniformly and stably suspended in the solvent, effectively absorbing and scattering light, thereby achieving a high absorbance.

[0040] In some preferred embodiments of this application, the surface-modified carbon nanotubes contain 2% to 8% molar oxygen and satisfy the intensity ratio of the G peak to the D peak as 20 to 80, while the absorbance of the dispersion is 0.55 to 1.55. In this case, the surface-modified carbon nanotubes have both excellent dispersibility and high conductivity, and can significantly improve the peel strength of the electrode and the cycle performance of the battery when used in batteries.

[0041] It is understood that the absorbance of the surface-modified carbon nanotubes includes, but is not limited to, any value among 0.55, 0.75, 1.00, 1.25, and 1.55, or any range between two of them. For example, the surface-modified carbon nanotubes have a molar oxygen content of 6% to 7%, an intensity ratio of G peak to D peak in the Raman spectrum of 60 to 70, and an absorbance of 1.1 to 1.25; the surface-modified carbon nanotubes have a molar oxygen content of 7% to 8%, an intensity ratio of G peak to D peak in the Raman spectrum of 50 to 60, and an absorbance of 1.25 to 1.5, and so on.

[0042] It should be noted that this application does not limit the specific types of oxygen-containing functional groups, as long as they can bond with carbon nanotubes and the molar content of oxygen in the surface-modified carbon nanotubes reaches 2% to 8%.

[0043] In some embodiments of this application, the oxygen-containing functional group includes, but is not limited to, at least one of carboxyl, phenolic hydroxyl, aldehyde, ketone carbonyl, ether, lactone, acid anhydride, and quinone groups.

[0044] In some embodiments of this application, depending on the number of tube walls, the carbon nanotubes include, but are not limited to, at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes.

[0045] This application provides a method for preparing surface-modified carbon nanotubes as described above, comprising the following steps:

[0046] A modified gas is introduced and heated. The carbon nanotubes float under the action of external force and undergo a reaction. After the reaction is completed, surface-modified carbon nanotubes are obtained. The modified gas includes at least a gas containing oxygen.

[0047] This application optimizes the traditional process of gas-phase heating for carbon nanotube surface modification. Due to the low density and high specific surface area of ​​carbon nanotubes, they can float in the reaction chamber under external force, allowing them to adsorb the modifying gas and react fully. This results in the uniform and efficient growth of oxygen-containing functional groups on the carbon nanotube surface. The preparation method described in this application not only has a significant surface modification effect but also causes minimal structural damage to the carbon nanotubes, which helps maintain their structural integrity and thus improves dispersibility while maintaining high conductivity.

[0048] In some embodiments of this application, the oxygen-containing gas includes at least one of oxygen, ozone, chlorine dioxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide, and phosgene.

[0049] In some embodiments of this application, the modified gas further includes at least one of nitrogen and argon.

[0050] In some preferred embodiments of this application, the modified gas is selected from a mixture of ozone and nitrogen. More preferably, the volume fraction of ozone in the mixed gas is 10% to 20%, which is more conducive to controlling the molar content of oxygen on the surface-modified carbon nanotubes and achieving a balance between the intensity ratio of the G peak and the D peak.

[0051] In some preferred embodiments of this application, the modified gas is selected from a mixture of chlorine dioxide and nitrogen. More preferably, the volume fraction of chlorine dioxide in the mixed gas is 20% to 30%, which is more conducive to controlling the molar content of oxygen on the surface-modified carbon nanotubes and achieving a balance between the intensity ratio of the G peak and the D peak.

[0052] In some embodiments of this application, the flow rate of the modified gas is 1L / min to 10L / min, including but not limited to any one of 1L / min, 2L / min, 5L / min, 8L / min, 10L / min or any range between two.

[0053] In some embodiments of this application, after placing the carbon nanotubes before introducing the modified gas, a protective gas is first introduced to remove impurity gases from the reaction chamber and avoid introducing impurity functional groups. It is understood that the protective gas includes, but is not limited to, nitrogen, argon, etc.

[0054] In some embodiments of this application, the reaction temperature is 20℃~150℃, including but not limited to any one of 20℃, 50℃, 100℃, 120℃, 150℃ or any range between two; the reaction time is 0.1h~10h, including but not limited to any one of 0.1h, 1h, 5h, 8h, 10h or any range between two.

[0055] It should be noted that this application does not limit the specific method for achieving the floating state of carbon nanotubes under the action of external force. For example, a rotatable reactor can be used, in which the carbon nanotubes are lifted and float in the reaction chamber under the rotation of the reactor.

[0056] Please see Figures 1 to 4 This application provides a carbon nanotube surface modification device, which can be used to modify the surface of single-walled carbon nanotubes, oligowalled carbon nanotubes, carbon nanotube bundles, etc. Specifically, the carbon nanotube surface modification device includes a quartz loading tube 10 and a rotating component 20. The quartz loading tube 10 is used to contain carbon nanotubes, and a lifting plate 11 is provided on the inner wall of the quartz loading tube 10. The power output end of the rotating component 20 is driven and connected to the quartz loading tube 10.

[0057] The rotating component 20 drives the quartz loading tube 10 to rotate around its own axis, reducing the biased rotation effect of the quartz loading tube 10. Biased rotation causes the quartz loading tube 10 to vibrate violently during rotation, which places high demands on the structure and strength of both the rotating component 20 and the quartz loading tube 10, significantly shortening the lifespan of the device. Furthermore, the poor uniformity of carbon nanotube distribution within the quartz loading tube 10 affects the subsequent surface modification effect of the carbon nanotubes.

[0058] When the rotating component 20 drives the quartz loading tube 10 containing carbon nanotubes to rotate, the lifting plate 11 inside the quartz loading tube 10 scoops up the carbon nanotubes, reducing their agglomeration. Due to the low density and large specific surface area of ​​the carbon nanotubes, they can float in the internal space of the quartz loading tube 10 for a long time after being lifted. During this process, a modifying gas is introduced into the quartz loading tube 10, allowing the carbon nanotubes to adsorb oxygen-containing gases and undergo sufficient modification, enhancing the reaction depth and enabling the carbon nanotube surface to uniformly and efficiently produce functional groups, thereby improving the reaction yield.

[0059] The lifting plate 11 extends primarily along the axial direction of the quartz loading tube 10. Additionally, it extends radially from the inner wall of the quartz loading tube 10. That is, the lifting plate 11 has specific dimensions in both the radial and axial directions of the quartz loading tube 10 to ensure the reliability of its lifting function. Furthermore, multiple lifting plates 11 are provided, arranged in an array around the axis of the quartz loading tube 10. This improves the axial symmetry of the quartz loading tube 10, reduces the eccentricity of the quartz loading tube 10 during rotation, and decreases the torque pressure required to drive the rotation of the rotating component 20.

[0060] In some preferred embodiments of this application, four lifting plates 11 are provided, and the four lifting plates 11 are arranged in an array around the axis of the quartz loading tube 10. The number of lifting plates 11 can be determined according to actual production needs. For example, the number of lifting plates 11 can be two, three, five, six, etc. This application does not limit this.

[0061] The lifting plate 11 is fixed to the inner wall of the quartz loading tube 10 by welding, or the lifting plate 11 and the quartz loading tube 10 are integrally formed structures, and this application does not limit this.

[0062] The width of the lifting plate 11 in the radial direction along the quartz loading tube 10 has a dimensional relationship with the inner radius of the quartz loading tube 10 to ensure the lifting effect of the lifting plate 11. See Figure 3 and Figure 4 In some embodiments of this application, the inner radius of the quartz loading tube 10 is R, and the radial width of the lifting plate 11 along the quartz loading tube 10 is D, with the ratio of D to R being 0.2 to 0.5. More specifically, the ratio of D to R can be 0.2, 0.3, 0.4, 0.5, or other values ​​in the range of 0.2 to 0.5.

[0063] When the ratio of D to R is less than 0.2, the radial width of the lifting plate 11 relative to the inner radius of the quartz loading tube 10 is too short, making it unable to effectively scoop up and lift the carbon nanotubes. In this case, the carbon nanotubes mainly slide or slightly tumble relative to the bottom of the quartz loading tube 10, failing to form an effective scattering action, resulting in poor uniformity of the subsequent modification reaction of the carbon nanotubes.

[0064] When the ratio of D to R is greater than 0.5, the radial width of the lifting plate 11 in the quartz loading tube 10 is too long relative to the inner radius of the quartz loading tube 10. When the lifting plate 11 performs the scooping action, it will scoop up a large number of carbon nanotubes. The carbon nanotubes are still in an aggregated state and tumble as a whole, which cannot effectively solve the problem of reaction uniformity.

[0065] Furthermore, an excessively long lifting plate 11 presents other problems. For instance, during the modification reaction of carbon nanotubes, a modifying gas needs to be introduced, and an excessively long lifting plate 11 will disrupt the stability of the airflow. Additionally, during long-term use, an excessively long lifting plate 11 not only needs to bear the load of the carbon nanotubes and the thermal stress during the reaction, but its own weight is also significant, making it more prone to cracking or even breaking at the root of the lifting plate 11 where it connects to the quartz loading tube 10. In more severe cases, it may even cause the quartz loading tube 10 to rupture and become unusable. An excessively long lifting plate 11 not only increases its own weight and that of the quartz loading tube 10, but also places higher demands on the rotational power of the rotating component 20, requiring a greater rotational torque to drive the rotation of the quartz loading tube 10.

[0066] In this embodiment, the ratio of D to R is 0.2 to 0.5, which ensures the lifting and tumbling effect of the carbon nanotubes, reduces the load on the lifting plate 11 and the quartz loading tube 10 during rotation, and extends the service life of the quartz loading tube 10.

[0067] Furthermore, the circumferential thickness of the lifting plate 11 along the quartz loading tube 10 is 0.01 to 0.02 times the inner diameter of the quartz loading tube 10. In this way, during the process of introducing modified gas into the quartz loading tube 10 to modify the surface of carbon nanotubes, the lifting plate 11 can block the airflow without generating excessive airflow resistance, allowing the carbon nanotubes and modified gas to react fully.

[0068] In some embodiments of this application, the rotating component 20 drives the quartz loading tube 10 to rotate at a speed of 1 r / min to 5 r / min. The power source for the rotating component 20 can be an electric motor, which can be connected to the quartz loading tube 10 via gear transmission, belt transmission, etc., thereby driving the quartz loading tube 10 to rotate. Specifically, the rotating component 20 drives the quartz loading tube 10 to rotate at speeds of 1 r / min, 2 r / min, 3 r / min, 4 r / min, 5 r / min, or other values ​​within the range of 1 r / min to 5 r / min. In this case, to meet the stepless speed control of the rotating component 20 on the rotational speed of the quartz loading tube 10, the rotating component 20 can be driven by an electric motor and equipped with a friction wheel type or other gearbox capable of stepless speed regulation, or a combination of a variable frequency motor and gear transmission can be used to achieve stepless speed regulation. The type of rotating component 20 can be selected according to the speed requirement, and this application will not elaborate further.

[0069] See Figure 1 and Figure 2 In some embodiments of this application, the carbon nanotube surface modification device further includes an inner furnace 30 and a heating component 40. The quartz charging tube 10 is fixedly installed in the inner furnace 30, and the power output end of the rotating component 20 is driven and connected to the inner furnace 30.

[0070] It is understandable that uniform heating of carbon nanotubes is required in the vapor phase modification process. In this embodiment, the heating element 40 is located outside the inner furnace 30 and does not rotate with the inner furnace 30. The heating element 40 extends along the axial direction of the quartz charging tube 10, and the length of the heating element 40 along the axial direction of the quartz charging tube 10 is not less than the length of the quartz charging tube 10. The inner furnace 30 facilitates the installation of the quartz charging tube 10, and the rotating component 20 is connected to the inner furnace 30, eliminating the need for a structure on the quartz charging tube 10 to connect the power output end of the rotating component 20.

[0071] The heating element 40 is positioned outside the inner furnace 30 and does not rotate with it. Thus, the heating element 40 heats the inner furnace 30 from the outside, and the heat is transferred through the inner furnace 30 to the quartz loading tube 10, ultimately heating the carbon nanotubes inside the quartz loading tube 10. During heating, the inner furnace 30 and the quartz loading tube 10 rotate around the axis of the quartz loading tube 10 under the drive of the rotating component 20, while the heating element 40 remains stationary. Therefore, as the inner furnace 30 and the quartz loading tube 10 rotate, the quartz loading tube 10 is heated evenly around its perimeter. The heating element 40 only needs to be positioned on one side of the inner furnace 30, rather than surrounding it, thus significantly saving material usage and simplifying the structure, thereby reducing costs. Furthermore, the length of the heating element 40 along the axial direction of the quartz loading tube 10 is not less than the axial length of the quartz loading tube 10, thereby improving the uniformity of temperature distribution within the carbon nanotubes of the quartz loading tube 10.

[0072] In this embodiment, the heating element 40 is a resistance heating wire. Of course, in other embodiments, components that can achieve uniform heating, such as inductive heating and radiant heating, can also be used. The type of heating element 40 can be selected according to the heating requirements, and this application will not elaborate further.

[0073] In some embodiments of this application, the quartz charging tube 10 and the inner furnace 30 are connected along the axial direction of the quartz charging tube 10, and two breathable sealing members 50 are provided in the inner furnace 30. The two sealing members 50 are connected to the two ends of the axial direction of the quartz charging tube 10, and the sealing members 50 cover the opening of the quartz charging tube 10.

[0074] In the gas-phase modification process, carbon nanotubes also need to be placed in a stable modifying gas atmosphere. The through-type arrangement of the inner furnace 30 facilitates the assembly and disassembly of the quartz charging tube 10, and also facilitates the introduction of modifying gas into the inner furnace 30. The through-type arrangement of the quartz charging tube 10 facilitates the loading and unloading of carbon nanotubes, and also facilitates the introduction of modifying gas into the quartz charging tube 10.

[0075] The sealing element 50 is used to seal both ends of the quartz filling tube 10 during the gas-phase modification process, preventing carbon nanotubes from leaking out of the quartz filling tube 10 with the gas flow. The sealing element 50 is permeable, allowing the modified gas to pass through the sealing element 50 and enter and exit the quartz filling tube 10, thus meeting the requirements of the gas-phase modification process.

[0076] Specifically, the sealing component 50 includes a screen 51 and a hollow heat-insulating plug 52. The screen 51 is fixedly connected to the axial end of the quartz loading tube 10 and covers the opening of the quartz loading tube 10, thus effectively preventing carbon nanotubes from drifting out of the quartz loading tube 10. Further, the mesh size of the screen 51 is 80 to 200 mesh. The heat-insulating plug 52 abuts against the end of the screen 51 away from the quartz loading tube 10. Thus, the heat-insulating plug 52 can extend into the inner furnace 30 and abut against the screen 51, thereby allowing for the positioning and adjustment of the quartz loading tube 10 within the inner furnace 30. The heat-insulating plug 52 also improves the sealing performance of the inner furnace 30, reduces heat loss within the inner furnace 30, and improves the temperature stability within the quartz loading tube 10.

[0077] During installation, carbon nanotubes are first inserted into the quartz loading tube 10. Then, the screen 51 is fixed to both ends of the quartz loading tube 10 with Teflon fiberglass tape. Next, the quartz loading tube 10 is inserted into the inner furnace. Finally, the heat insulation plug 52 is inserted into the inner furnace 30 and pressed against the screen 51. The position of the quartz loading tube 10 in the inner furnace 30 is adjusted by pushing the heat insulation plug 52. After the position is adjusted, the inner furnace 30 is sealed with a silicone rubber sealing ring and closed with a stainless steel clamp.

[0078] When in use, modified gas is introduced into one end of the inner furnace 30. The modified gas enters the quartz charging tube 10 through the heat insulation plug 52 and the screen 51 and reacts with the carbon nanotubes. Then the modified gas flows out from the other end of the quartz charging tube 10 and flows through the heat insulation plug 52 and the screen 51, and finally flows out from the other end of the inner furnace 30. At this time, the exhaust gas after the reaction can be directed to the fume hood.

[0079] It is worth mentioning that during the process of introducing the modified gas into the quartz loading tube 10, the function of the lifting plate 11 is also to reduce the movement of carbon nanotubes along the axial direction of the quartz loading tube 10 by the airflow, thereby avoiding the situation where carbon nanotubes migrate and accumulate at one end of the axial direction of the quartz loading tube 10, and ensuring the surface modification effect of carbon nanotubes.

[0080] Specifically, the lifting plate 11 physically blocks the carbon nanotube material along the axial direction of the quartz loading tube 10 to a certain extent, thereby preventing the carbon nanotube from moving and migrating along the axial direction of the quartz loading tube 10.

[0081] In addition, the migration of carbon nanotubes along the axial direction of the quartz loading tube 10 is mainly caused by the drag of the airflow. The setting of the lifting plate 11 also generates turbulence on the modified gas, thereby reducing the migration of carbon nanotubes along the axial direction of the quartz loading tube 10 by reducing the local flow velocity of the airflow and reducing the drag force of the airflow on the carbon nanotubes.

[0082] After the carbon nanotubes are blocked by the lifting plate 11, their kinetic energy decreases as they move along the axial direction of the quartz loading tube 10 with the airflow. Under the guidance of the lifting plate 11, the carbon nanotubes can tumble and settle, and react fully with the modified gas in the quartz loading tube 10.

[0083] In some embodiments of this application, the carbon nanotube surface modification device further includes a base 60, with the inner furnace 30 and heating element 40 all mounted on the base 60, and the heating element 40 located below the inner furnace 30. The base 60 provides an installation platform for other components in the device, improving the stability of the device during operation. Furthermore, the heating element 40 can be directly mounted on the top of the base 60, and the inner furnace 30 can be mounted on the base 60 via a rotating bracket (not shown).

[0084] The following specific embodiments will further illustrate the surface-modified carbon nanotubes and their preparation method. However, those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified, specific conditions in the embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without a specified manufacturer are all commercially available conventional products. Specifically, the single-walled carbon nanotubes, gases, grinding balls, etc., used in the following embodiments and comparative examples are all commercially available products.

[0085] Example 1

[0086] 3g of single-walled carbon nanotubes were added to a rotary reactor, and argon gas was introduced for 2 hours, followed by switching to oxygen at a flow rate of 5L / min. The reactor was then turned on, heated to 80℃, and reacted for 10 hours. After the reaction was completed, the temperature was lowered to room temperature, and argon gas was introduced for 2 hours. Surface-modified carbon nanotubes were then discharged.

[0087] Example 2

[0088] 3g of single-walled carbon nanotubes were added to a rotary reactor. Argon gas was introduced for 2 hours, then switched to ozone (oxygen source, concentration 100mg / L) at a flow rate of 5L / min. The tail gas was treated with a 10% sodium sulfite solution. The reactor was started, and the temperature was raised to 80℃, reacting for 10 hours. After the reaction, the temperature was lowered to room temperature, and argon gas was introduced for 2 hours. The surface-modified carbon nanotubes were then discharged.

[0089] Example 3

[0090] 3g of single-walled carbon nanotubes were added to a rotary reactor. After purging with argon gas for 2 hours, the mixture of ozone and nitrogen was switched (ozone to nitrogen flow rate ratio 1:19), with a total flow rate of 5L / min. The tail gas was treated with a 10% sodium sulfite solution. The reactor was started, and the temperature was raised to 80℃, and the reaction was allowed to proceed for 10 hours. After the reaction, the temperature was lowered to room temperature, and argon gas was purged for 2 hours. Surface-modified carbon nanotubes were then discharged.

[0091] Example 4

[0092] 3g of single-walled carbon nanotubes were added to a rotary reactor. After purging with argon gas for 2 hours, the mixture of ozone and nitrogen was switched (ozone to nitrogen flow rate ratio of 3:17), with a total flow rate of 5L / min. The tail gas was treated with a 10% sodium sulfite solution. The reactor was started, and the temperature was raised to 80℃, and the reaction was allowed to proceed for 10 hours. After the reaction, the temperature was lowered to room temperature, and argon gas was purged for 2 hours. Surface-modified carbon nanotubes were then discharged.

[0093] Example 5

[0094] 3g of single-walled carbon nanotubes were added to a rotary reactor. Argon gas was introduced for 2 hours, then chlorine dioxide was introduced at a flow rate of 3L / min. The exhaust gas was treated with a series of 30% sodium hydroxide solution and 10% sodium sulfite solution. The reactor was started, and the temperature was raised to 60℃, reacting for 6 hours. After the reaction, the temperature was lowered to room temperature, and argon gas was introduced for 2 hours. The surface-modified carbon nanotubes were then discharged.

[0095] Example 6

[0096] 3g of single-walled carbon nanotubes were added to a rotary reactor. After purging with argon gas for 2 hours, the mixture of chlorine dioxide and nitrogen gas (chlorine dioxide to nitrogen gas flow rate ratio of 1:19) was switched on, with a total flow rate of 3L / min. The tail gas was treated with a series of 30% sodium hydroxide solution and 10% sodium sulfite solution. The reactor was started, and the temperature was raised to 60℃, with the reaction proceeding for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and argon gas was purged for 2 hours. Surface-modified carbon nanotubes were then discharged.

[0097] Example 7

[0098] 3g of single-walled carbon nanotubes were added to a rotary reactor. After purging with argon gas for 2 hours, the mixture of chlorine dioxide and nitrogen gas (chlorine dioxide to nitrogen gas flow rate ratio of 1:3) was switched on, with a total flow rate of 3L / min. The tail gas was treated with a series of 30% sodium hydroxide solution and 10% sodium sulfite solution. The reactor was started, and the temperature was raised to 60℃, and the reaction was allowed to proceed for 6 hours. After the reaction was completed, the temperature was lowered to room temperature, and argon gas was purged for 2 hours. Surface-modified carbon nanotubes were then discharged.

[0099] Comparative Example 1

[0100] Single-walled carbon nanotubes were used directly without surface modification.

[0101] Comparative Example 2

[0102] Place 2g of single-walled carbon nanotubes into the reaction chamber of the U-shaped reaction tube, connect the outlet of the solvent bottle and the inlet of the reaction chamber with a connecting tube, and connect one end of the outlet of the reaction chamber to the exhaust gas treatment device.

[0103] Using a solvent bottle as the bubbling device, first open the solvent bottle and inject 60mL of water as the solvent into the solvent bottle, then tighten the stopper. Connect the air inlet pipe to the ozone output pipe of the ozone generator, turn on the ozone generator, and control the ozone generator to produce ozone with a volume percentage concentration of 3.6%. Pass the ozone and oxygen mixture through the water in the solvent bottle to allow the mixture to undergo a solvent bubbling reaction.

[0104] The mixed gas, after being bubbled by the solvent, is continuously passed through a reaction chamber containing single-walled carbon nanotubes to oxidize and modify the carbon nanotubes. The oxidation treatment time is 5 hours, and the flow rate of the mixed gas is 0.4 L / min. After the reaction is completed, the ozone generator or the reaction gas pipeline is turned off to stop the reaction and obtain surface-modified carbon nanotubes.

[0105] The surface-modified carbon nanotubes prepared in Examples 1-7 and Comparative Example 2, as well as the single-walled carbon nanotubes of Comparative Example 1, were characterized and tested:

[0106] (1) IG / ID: The IG / ID of the modified carbon nanotubes was calculated by Raman spectroscopy.

[0107] (2) Molar content of oxygen: X-ray photoelectron spectroscopy (XPS) was used to test the surface chemical composition and elemental valence states of carbon nanotubes; carbon nanotubes were pressed into sheets or evenly sprinkled on conductive tape, with a vacuum degree <1×10 -8 mbar, binding energy calibrated using C1s (284.8 eV), X-ray source monochromatic Al Kα (1486.6 eV), power 25 W~50 W, high-resolution narrow spectrum selected, pass energy 20 eV~55 eV, step size 0.1 eV.

[0108] (3) UV absorbance: Dissolve 0.5g sodium carboxymethyl cellulose in 80g deionized water, add 0.5g carbon nanotubes, and sonicate in a 600W ultrasonic oscillator for 0.5h to form a dispersion; take a small amount of the dispersion in a cuvette, dilute its concentration by 1000 times, and test its absorbance by UV-Vis absorption spectroscopy.

[0109] (4) The determination of oxygen-containing functional groups was performed using the Boehm titration method, and the specific operation is as follows:

[0110] The modified carbon nanotube sample was placed in a vacuum drying oven and dried at 105℃ for 4 hours to remove surface adsorbed water. After cooling to room temperature, it was placed in a desiccator for later use. Three portions of the pretreated modified carbon nanotube sample (each approximately 0.1 g, accurate to 0.0001 g) were weighed and placed into three 250 mL stoppered conical flasks, numbered 1, 2, and 3 respectively: Flask 1: 25 mL of 0.05 mol / L NaHCO3 solution was added; Flask 2: 25.00 mL of 0.05 mol / L Na2CO3 solution was added; Flask 3: 25.00 mL of 0.05 mol / L NaOH solution was added.

[0111] Purge each conical flask with nitrogen for 5 minutes to isolate it from carbon dioxide in the air. Quickly seal the flasks and place them on a magnetic stirrer. Stir at a constant temperature of 25°C for 24 hours to ensure that the functional groups react fully with the base.

[0112] After the reaction was completed, the mixture in each conical flask was filtered with dry filter paper. 5 mL of the initial filtrate was discarded to avoid the influence of filter paper adsorption. 20.00 mL of the filtrate was then taken into three new stoppered conical flasks and labeled 1', 2', and 3'.

[0113] Add 2 drops of methyl orange indicator to 1' (NaHCO3 system), and titrate with 0.05 mol / L HCl standard solution until the solution changes from yellow to orange. Record the volume of HCl consumed, V1.

[0114] Add 2 drops of phenolphthalein indicator to 2' (Na2CO3 system) and 3' (NaOH system), respectively, and titrate with 0.05 mol / L HCl standard solution until the red color of the solution disappears. Record the volumes of HCl consumed, V2 and V3.

[0115] Simultaneously perform a blank experiment: take three 25.00 mL aliquots of the corresponding blank alkaline solution, titrate them using the same procedure, and record the volume V of HCl consumed in the blank. 01 V 02 V 03 .

[0116] Each experiment was conducted in triplicate, and the average value was taken as the final volume data. After data recording and processing, the content of acidic oxygen-containing functional groups was obtained.

[0117] The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120] The surface-modified carbon nanotubes obtained in Examples 1-7 and Comparative Example 2, as well as the single-walled carbon nanotubes of Comparative Example 1, were used to prepare electrode sheets and silicon-carbon negative electrode coin cells, respectively, and their performance was tested.

[0121] (1) Peel strength of electrode: The negative electrode slurry was prepared based on the above carbon nanotube dispersion. The ratio was: artificial graphite:PAA:SBR:SWCNTs:CMC=97:1.3:1.5:0.1:0.1. The slurry preparation method was as follows: the above substances were prepared into an aqueous dispersion with a solid content of 40%, and the negative electrode slurry was obtained by degassing in a vacuum degassing machine for 20 minutes. After the slurry was prepared, the electrode was prepared by coating, baking and rolling. The peel strength of the electrode was tested by a tensile tester. The test method was as follows: the electrode was cut into strips of 20cm×2.5cm. A steel plate with a thickness of 1mm was glued to the current collector side with double-sided tape. Transparent tape was pasted on the coating side. The electrode was peeled in the 180° direction at a speed of 100mm / min using a tensile testing machine, and the peel stress was measured.

[0122] (2) 30-cycle capacity retention of silicon-carbon negative electrode coin cells:

[0123] (i) Preparation of silicon carbide slurry: According to the mass ratio of SiC:CMC:PAA:SBR:carbon nanotube dispersion = 96.85:0.3:1.5:1.2:0.15, weigh the materials and stir and disperse them in a degassing machine (800 rpm, 30 s; 2000 rpm, 10 min).

[0124] (ii) Coating and baking: a) Wipe the copper foil with alcohol and lay it flat on the coating machine. Press the button to turn on the vacuum pump so that the copper foil is adsorbed on the coating machine; b) Place the iron rod of the coating machine on it, select a 200μm scraper and place it against one end of the iron rod. Place the slurry evenly in front of the scraper and press the coating machine button to coat; c) Transfer the coated electrode to an 80℃ forced-air oven to dry for 30 minutes.

[0125] (iii) Electrode punching, weighing and drying: a) Punch holes in the electrode on a flat and uniform part; b) Select electrode with intact surface and weigh it. Select 5 to 6 electrode sheets for each test and select those with similar weight as experimental electrode sheets; c) Lay the bag containing the electrode sheets neatly in a vacuum drying oven, press it down with a weight, adjust the temperature to 90℃, and maintain vacuum drying for more than 8 hours.

[0126] (iv) Button assembly: a) Separator cutting: Wrap the separator in clean paper and punch it with a 19mm punching machine. Put the cut separator in a bag and vacuum dry at 80℃ for about 3 days before use; b) Assemble the button in the following order: negative electrode shell, gasket, lithium sheet, electrolyte (1.0MLiPF6-EC / DMC / EMC-FEC / PS system), separator, electrolyte, electrode sheet, and positive electrode shell. After assembly, use tweezers to place the battery with the negative electrode facing up in the sealing machine mold and press the automatic sealing machine run button (the sealing machine is set to pressure 550kg, speed switching 5s, and holding time 2s) to seal; c) Wipe the battery casing with ethanol-soaked lint-free paper and mark the serial number.

[0127] (v) Button test: a) Wipe the test cabinet fixture with a lint-free paper dampened with ethanol and clamp the battery onto the fixture; b) Select the test program: silicon-carbon cycle / silicon-carbon full charge expansion - input standard specific capacity - electrode quality operation program.

[0128] The specific parameters for the cyclic test are set as follows: first, let it stand for 10 hours, then discharge at a constant current of 0.1C to 0.005V, 0.08C to 0.001V, 0.05C to 0.005V, and 0.02C to 0.005V. After standing for 10 minutes, charge at a constant current of 0.1C to 1.5V. After standing for 10 minutes, repeat the constant current discharge and constant current charge cycle for 30 cycles.

[0129] The test results are shown in Table 2.

[0130] Table 2

[0131]

[0132] According to Tables 1 and 2, comparing Example 1 and Comparative Example 1, it can be seen that the IG / ID value of the surface-modified carbon nanotubes prepared in Example 1 is almost unchanged, the carbon nanotubes retain their integrity and have fewer oxygen-containing functional groups grafted.

[0133] Compared with Example 2 and Comparative Example 2 (modified carbon nanotubes prepared according to the published invention patent CN104891469A), Comparative Example 2 has more oxygen-containing functional groups grown on the surface of carbon nanotubes, but the modification method causes greater damage to the carbon nanotube structure, its G / D ratio decreases significantly, the integrity of the carbon nanotubes is destroyed, and the conductivity deteriorates, which corresponds to the deterioration of the capacity retention rate after 30 cycles.

[0134] Comparing Examples 2, 3, and 4, it can be seen that ozone modification alone causes some damage to carbon nanotubes. The increased number of oxygen-containing functional groups grown on the surface can disrupt the carbon nanotube structure, leading to a decrease in the IG / ID value. However, when a mixed gas of ozone and nitrogen is introduced for modification, the modification effect of 15% ozone is better than that of 5% ozone. The IG / ID value decreases slightly, while a large number of oxygen-containing functional groups grow uniformly on the surface. This enhances the interfacial interaction between the modified carbon nanotube and the negative electrode, binder, and current collector, improves peel strength, and optimizes the 30-cycle performance of the coin cell due to the combined effect of improved dispersion and structural synergy.

[0135] Comparing Examples 5, 6, and 7, it can be seen that when carbon nanotubes are modified by introducing chlorine dioxide alone, the carbon nanotubes break down due to the excessive oxidizing power of the pure gas, resulting in a downward trend in the G / DIG / ID values. However, when modified by introducing a mixed gas of chlorine dioxide and nitrogen, the modification effect of 25% chlorine dioxide is better than that of 5% chlorine dioxide, the carbon nanotubes retain greater integrity, and the mechanical and electrical properties are significantly improved.

[0136] As shown in Tables 1 and 2, when using a suitable ratio of mixed gases for surface modification, damage to carbon nanotubes caused by excessive oxidizing power of pure gases can be effectively avoided, while simultaneously promoting the uniform growth of appropriate amounts of oxygen-containing functional groups on the surface. These oxygen-containing functional groups not only enhance the interfacial interactions between the modified carbon nanotubes and the anode, binder, and current collector, improving peel strength, but also improve their dispersibility. Through the synergistic effect of the structure, the cycling performance of the coin cell is significantly optimized, especially the 30-cycle performance is significantly improved. Furthermore, under suitable modification conditions, carbon nanotubes can better retain their integrity, and their mechanical and electrical properties are also greatly improved.

[0137] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0138] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A surface-modified carbon nanotube, characterized in that, The surface-modified carbon nanotubes include carbon nanotubes and oxygen-containing functional groups bonded to the carbon nanotubes. The surface-modified carbon nanotubes have an oxygen molar content of 2% to 8%, and the intensity ratio of the G peak to the D peak in the Raman spectrum of the surface-modified carbon nanotubes is 20 to 80.

2. The surface-modified carbon nanotubes according to claim 1, characterized in that, The surface-modified carbon nanotubes have an oxygen molar content of 6%~7% and an intensity ratio of G peak to D peak in the Raman spectrum of 60~70. And / or, the surface-modified carbon nanotubes have an oxygen molar content of 7%~8% and an intensity ratio of G peak to D peak in the Raman spectrum of 50~60.

3. The surface-modified carbon nanotubes according to claim 1, characterized in that, The absorbance of the dispersion of the surface-modified carbon nanotubes is 0.55~1.55, and the mass concentration of the surface-modified carbon nanotubes in the dispersion is 0.1%~1%.

4. The surface-modified carbon nanotubes according to any one of claims 1 to 3, characterized in that, The surface-modified carbon nanotubes have an oxygen molar content of 6%~7%, an intensity ratio of G peak to D peak in the Raman spectrum of 60~70, and an absorbance of 1.1~1.

25. And / or, the surface-modified carbon nanotubes have an oxygen molar content of 7%~8%, an intensity ratio of G peak to D peak in the Raman spectrum of 50~60, and an absorbance of 1.25~1.

5.

5. The surface-modified carbon nanotubes according to claim 1, characterized in that, The oxygen-containing functional group includes at least one of carboxyl, phenolic hydroxyl, aldehyde, ketone carbonyl, ether, lactone, acid anhydride, and quinone groups; And / or, the carbon nanotubes include at least one of single-walled carbon nanotubes and oligo-walled carbon nanotubes.

6. A method for preparing surface-modified carbon nanotubes as described in any one of claims 1 to 5, characterized in that, Includes the following steps: A modified gas is introduced and heated. The carbon nanotubes float under the action of external force and undergo a reaction. After the reaction is completed, surface-modified carbon nanotubes are obtained. The modified gas includes at least a gas containing oxygen.

7. The method for preparing surface-modified carbon nanotubes according to claim 6, characterized in that, The oxygen-containing gas includes at least one of oxygen, ozone, chlorine dioxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide, and phosgene.

8. The method for preparing surface-modified carbon nanotubes according to claim 7, characterized in that, The modified gas also includes at least one of nitrogen and argon; When the modified gas is selected from a mixture of ozone and nitrogen, the volume fraction of ozone in the mixture is 10% to 20%. Alternatively, when the modified gas is selected from a mixture of chlorine dioxide and nitrogen, the volume fraction of chlorine dioxide in the mixture is 20% to 30%.

9. The method for preparing surface-modified carbon nanotubes according to claim 6, characterized in that, The flow rate of the modified gas is 1 L / min to 10 L / min; And / or, the reaction temperature is 20℃~150℃, and the reaction time is 0.1h~10h.

10. The method for preparing surface-modified carbon nanotubes according to claim 6, characterized in that, The preparation method includes the following steps: Carbon nanotubes are contained in a quartz charging tube, which is then fixedly installed in an inner furnace. Modified gas is introduced from one end of the inner furnace and flows out from the other end. At the same time, a rotating component drives the quartz charging tube to rotate around its own axis. Lifting plates arranged axially on the inner wall of the quartz charging tube scoop up the carbon nanotubes, causing them to float. Under heating conditions, the carbon nanotubes react with the modified gas. After the reaction is completed, surface-modified carbon nanotubes are obtained.

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