Preparation method of carbon nano tube, carbon nano tube and conductive paste
By pre-oxidizing, shearing and compacting the carbon nanotubes, the solid content in the acid purifying and purification process is improved, and the problems of high acid consumption and high drying cost caused by low solid content are solved, and the preparation and production cost of high-purity carbon nanotubes are reduced.
Patent Information
- Application Number
- CN202311812514.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-26
- Publication Date
- 2025-06-27
AI Technical Summary
In the prior art, the solid content of carbon nanotubes is low during the acid cleaning and purification process, resulting in a high total acid consumption, high cost of acid wastewater treatment and high drying costs, thereby increasing the total cost of acid cleaning and purification.
By pre-oxidizing the initial powder of the carbon nanotube and mixing it with the solvent for shearing and compacting, the solid content of the carbon nanotube wet material is increased. Then, it was mixed with the acid solution and heated, filtered and washed and dried to obtain high-purity carbon nanotubes.
The solid content of carbon nanotubes during the acid cleaning and purification process is increased, the acid consumption and drying cost are reduced, the acid wastewater treatment cost is reduced, and the overall production cost is reduced, and the purity of carbon nanotubes is improved.
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Figure CN120208208A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of carbon nanomaterials, and particularly to a preparation method of carbon nanotubes, carbon nanotubes, and conductive pastes. Background Art
[0002] With the increasing penetration rate of new energy vehicles and the development of new energy storage industries, the advantages of lithium-ion batteries (commonly known as lithium batteries) have become more and more obvious. Among them, in lithium-ion batteries, conductive agents can build a conductive network with active substances, improving the battery's capacity, cycle stability, and high-rate charge and discharge performance. The conductive agents in lithium batteries are usually conductive carbon materials, such as carbon black, graphite, and carbon nanotubes. Among them, carbon nanotubes (CNTs), as one-dimensional linear nanomaterials, can build a three-dimensional "wire" - shaped conductive network, having significant advantages in reducing the internal resistance of the battery and improving the cycle and rate performance of lithium batteries, and gradually replacing traditional conductive and graphite - based conductive agent materials.
[0003] Currently, the carbon nanotubes produced on a large scale have low purity, containing a large amount of metal impurities and metal magnetic particles. Specifically, carbon nanotubes are mostly prepared by metal - based catalyst vapor growth, so the catalyst exists inside or between carbon nanotubes. Or due to the growth environment and equipment materials, for example, the contact between carbon nanotubes and metal - material tanks at high temperatures may cause metal contamination of carbon nanotubes. For application fields that are sensitive to the content of metal impurities, such as the application of carbon nanotubes in the lithium - battery system, during the high - potential charge and discharge process, metal impurities are easily oxidized and precipitated on the surface of the negative electrode, resulting in micro - short - circuit inside the battery, serious self - discharge, and even causing safety accidents. Therefore, it is necessary to further purify the metal impurities in carbon nanotubes.
[0004] Conventional purification methods include acid washing purification, high - temperature chlorination roasting method, and ultra - high - temperature purification method, etc. Among them, the high - temperature chlorination roasting method involves halogens, and its leakage risk coefficient is relatively high. Under the strict control of safety risks, this method has high requirements for production equipment, resulting in high investment and high risks. The ultra - high - temperature purification method is a purification method in which metal oxides are removed by sublimation in an ultra - high - temperature vacuum environment above 2000°C. The equipment used for this method has a high cost and high energy consumption. Acid washing purification requires pre - oxidation treatment of carbon nanotubes first, and then purification treatment with dilute acid solutions. This method has low safety risks and low requirements for equipment, and is widely used in industrial production.
[0005] However, because the BET specific surface area (total area per unit mass of carbon nanotubes) of carbon nanotubes is relatively high, when carbon nanotube powder is immersed in liquid (such as dilute acid solution), the surface of the carbon nanotube powder is converted from a gas-solid interface to a liquid-solid interface. Without the action of external forces, the carbon nanotube powder is not thoroughly wetted, resulting in a low solid content (solid content) of carbon nanotubes immersed in the dilute acid solution. Therefore, how to further increase the solid content of carbon nanotubes in the acid washing and purification process is still a technical challenge that the industry needs to solve urgently. Summary of the invention
[0006] In view of this, the embodiments of the present application provide a method for preparing carbon nanotubes, carbon nanotubes, and conductive paste to solve at least one problem existing in the background technology.
[0007] In a first aspect, an embodiment of the present application provides a method for preparing carbon nanotubes, the method for preparing carbon nanotubes comprising:
[0008] Performing a pre-oxidation treatment on the initial carbon nanotube powder to obtain pre-oxidized carbon nanotube powder;
[0009] Mixing the pre-oxidized carbon nanotube powder with a solvent to obtain a carbon nanotube wet material having a first solid content;
[0010] The carbon nanotube wet material having a first solid content is uniformly mixed with an acid solution having a first mass fraction, and subjected to a heating treatment to obtain a carbon nanotube mixed solution having a second mass fraction;
[0011] filtering the carbon nanotube mixed solution having the second mass fraction, and washing with water until it becomes neutral, to obtain a carbon nanotube wet material having a second solid content;
[0012] The carbon nanotube wet material with the second solid content is dried to obtain the carbon nanotube.
[0013] In conjunction with the first aspect of the present application, in an optional embodiment, after the pre-oxidized carbon nanotube powder is mixed with a solvent to obtain a carbon nanotube wet material having a first solid content, the method for preparing carbon nanotubes further comprises:
[0014] The carbon nanotube wet material with the first solid content is sheared to reduce the particle size of the carbon nanotube wet material with the first solid content.
[0015] In conjunction with the first aspect of the present application, in an optional implementation manner, after the wet carbon nanotube material having the first solid content is sheared, the method for preparing the carbon nanotubes further comprises:
[0016] Compacting the carbon nanotube wet material with the first solid content to make the carbon nanotube wet material with the first solid content have a higher powder packing density.
[0017] Combined with the first aspect of the present application, in an alternative embodiment, the solvent includes one or more of tap water, deionized water, pure water, and ultrapure water; and / or, the first solid content is 15%-60%.
[0018] Combined with the first aspect of the present application, in an alternative embodiment, the first solid content is 20%-50%.
[0019] Combined with the first aspect of the present application, in an alternative embodiment, the acid solution includes one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid, and citric acid; and / or, the first mass fraction is 1%-8%; and / or, the heating temperature for the heat treatment is the first preset temperature, the heating time is the preset time, the first preset temperature is 40°C-120°C, the preset time is 1h-48h; and / or, the second mass fraction is 8%-15%.
[0020] Combined with the first aspect of the present application, in an alternative embodiment, the first mass fraction is 2%-6%; and / or, the first preset temperature is 70°C-95°C, the preset time is 4h-24h.
[0021] Combined with the first aspect of the present application, in an alternative embodiment, the second solid content is 15%-30%; and / or, the drying temperature for the drying treatment is the second preset temperature, the second preset temperature is 50°C-450°C.
[0022] Combined with the first aspect of the present application, in an alternative embodiment, the powder packing density of the carbon nanotubes is 0.08 g / cm 3 -0.28 g / cm 3 ; and / or, the purity of the carbon nanotubes is higher than 99.6%.
[0023] In a second aspect, an embodiment of the present application provides a carbon nanotube, which is prepared by using the preparation method of the carbon nanotube in any one of the above embodiments.
[0024] In a third aspect, an embodiment of the present application provides a conductive paste, which includes carbon nanotubes prepared by using the preparation method of the carbon nanotube in any one of the above embodiments.
[0025] The present application provides a method for preparing carbon nanotubes, carbon nanotubes, and conductive paste. In the method for preparing carbon nanotubes, after pre-oxidizing carbon nanotube powder and mixing it with a solvent, the surface of the carbon nanotube powder is wetted in advance through an external force. This is beneficial for further wetting the surface of the carbon nanotube material by an acid solution when the wet carbon nanotube material is mixed with the acid solution later, reducing the difficulty of wetting, increasing the solid content of the carbon nanotubes in the pickling and purification process, and thus improving the problems of a relatively high total acid consumption and high acid wastewater treatment cost in pickling and purification, as well as a relatively high drying cost when removing solvents such as the acid solution, which leads to a relatively high pickling and purification cost. The embodiments of the present application can prepare a high-purity carbon nanotube.
[0026] Additional aspects and advantages of the present application will be given in part in the following description, will become apparent in part from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The schematic embodiments and descriptions thereof of the present application are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:
[0028] Figure 1 is a schematic flow chart of the method for preparing carbon nanotubes provided by the embodiments of the present application;
[0029] Figure 2 is a scanning electron microscope (SEM) image of the conductive paste prepared from the carbon nanotube powder obtained in Example 3. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0030] To make the technical solutions and beneficial effects of the present application more obvious and understandable, the following provides a detailed description by combining the drawings and listing specific embodiments. Although the drawings and the listing of specific embodiments show the exemplary embodiments of the present application, it should be understood that the present application can be implemented in various forms and should not be limited by the specific embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present application and to be able to fully convey the scope of the present application disclosed to those skilled in the art. These embodiments are only used to illustrate the present application and not to limit the scope of the present application.
[0031] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known to the public are not described; that is, not all features of the actual embodiments are described here, and the well-known functions and steps are not described in detail.
[0032] The purpose of the terms used herein is only to describe specific embodiments and is not a limitation of the present application. As used herein, the singular forms "a", "an" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms "comprising" and / or "including", when used in this specification, identify the presence of the described features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups. As used herein, the term "and / or" includes any and all combinations of the related listed items. As used herein, the terms "first\second\third\fourth" are only used to distinguish similar objects and do not represent a specific order for the objects. Understandably, "first\second\third\fourth" can be interchanged with a specific order or sequence or performed simultaneously under the condition of permission, so that the embodiments of the present application described herein can be implemented in an order other than those described herein.
[0033] To thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to explain the technical solutions of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may have other embodiments.
[0034] Unless otherwise defined, the technical and scientific terms used in the present application have the same meanings as those of the technical and scientific terms in the technical field to which the present application belongs.
[0035] For those not specified with specific techniques or conditions in the following embodiments, they are generally carried out according to the conventional techniques or conditions described in the literature in the art, or according to the conditions recommended in the product specifications and by the manufacturers. The numerical ranges in the following embodiments all include the end point values.
[0036] Unless otherwise specified, various starting materials, materials and reagents are commercially available or are synthesized according to known methods.
[0037] In the related art, when pickling and purifying carbon nanotubes, there is a problem that the solid content of carbon nanotubes in the dilute acid solution is low. Moreover, it will also lead to a high total acid consumption and high acid wastewater treatment cost in pickling and purification, and will also result in a high drying cost when removing solvents such as dilute acid solution, thus leading to a high pickling and purification cost.
[0038] Therefore, how to increase the solid content of carbon nanotubes in the dilute acid solution to reduce the acid consumption during the pickling and purification of carbon nanotubes, as well as reduce the solvent content before drying and improve the drying efficiency are the main technical difficulties.
[0039] Based on this, the embodiments of the present application provide a method for preparing carbon nanotubes. Figure 1Schematic flow chart of the method for preparing carbon nanotubes provided by the embodiments of the present application; as shown in the figure, the method includes:
[0040] Step S101: Perform pre-oxidation treatment on the initial carbon nanotube powder to obtain pre-oxidized carbon nanotube powder;
[0041] Step S102: Mix the pre-oxidized carbon nanotube powder with a solvent to obtain a carbon nanotube wet material with a first solid content;
[0042] Step S103: Mix the carbon nanotube wet material with a first solid content evenly with an acid solution with a first mass fraction, and perform heat treatment to obtain a carbon nanotube mixed solution with a second mass fraction;
[0043] Step S104: Filter the carbon nanotube mixed solution with a second mass fraction, and wash it with water until it is neutral to obtain a carbon nanotube wet material with a second solid content;
[0044] Step S105: Perform drying treatment on the carbon nanotube wet material with a second solid content to obtain carbon nanotubes.
[0045] It can be understood that in the embodiments of the present application, by mixing the pre-oxidized carbon nanotube powder with a solvent and pre-wetting the surface of the carbon nanotube powder through an external force, it is beneficial for the acid solution to further wet the surface of the carbon nanotube material when the carbon nanotube wet material is mixed with the acid solution later, reducing the wetting difficulty, increasing the solid content of the carbon nanotubes in the pickling purification process, and thus improving the problems of relatively high total acid consumption and relatively high acid wastewater treatment cost in pickling purification, and relatively high drying cost when removing solvents such as acid solution, which leads to relatively high pickling purification cost. The embodiments of the present application can prepare a high-purity carbon nanotube.
[0046] It should also be understood that although the steps in the above schematic flow chart are shown in sequence according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Moreover, at least some of the steps in the above schematic flow chart may include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time and are not necessarily carried out in sequence.
[0047] Next, the method for preparing carbon nanotubes provided by the embodiments of the present application and its beneficial effects will be further described in detail.
[0048] First, execute Step S101 to perform pre-oxidation treatment on the initial carbon nanotube powder to obtain pre-oxidized carbon nanotube powder.
[0049] In some embodiments, the initial carbon nanotube powder includes one or more of single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs).
[0050] In some embodiments, in an oxygen-containing atmosphere containing one or more of oxygen, air, carbon dioxide, water vapor, etc. and an inert gas (such as nitrogen), according to the properties of the initial carbon nanotube powder, a single process or a combined process can be performed to achieve pre-oxidation treatment of the initial carbon nanotube powder.
[0051] In some specific embodiments, the temperature range of the pre-oxidation treatment can be 200°C - 800°C. For example, the temperature range of the pre-oxidation treatment can be 250°C, 350°C, 450°C, 550°C, 650°C, or 750°C, etc., and no specific limitation is made here.
[0052] It can be understood that performing pre-oxidation treatment on the initial carbon nanotube powder can remove impurities such as amorphous carbon in the initial carbon nanotube powder and improve the purity of the initial carbon nanotube powder.
[0053] Then, step S102 is executed to mix the pre-oxidized carbon nanotube powder with a solvent to obtain a carbon nanotube wet material with a first solid content.
[0054] In some embodiments, the solvent can be water.
[0055] In some specific embodiments, the solvent can include one or more of tap water, deionized water, pure water, and ultrapure water. Alternatively, the solvent can also be used in combination with one or more of tap water, deionized water, pure water, and ultrapure water and other grades of water. In the embodiments of the present application, the solvent can be pure water.
[0056] In some embodiments, the first solid content can be 15% - 60%. For example, the first solid content can be 18%, 25%, 30%, 35%, 40%, 45%, or 55%, etc., and no specific limitation is made here. In the embodiments of the present application, the first solid content can be 20% - 50%.
[0057] It should be noted that the first solid content refers to the ratio of the mass of the pre-oxidized carbon nanotube powder to the mass of the carbon nanotube wet material. The mass of the carbon nanotube wet material is the sum of the mass of the pre-oxidized carbon nanotube powder and the mass of the solvent.
[0058] It can be understood that when the ratio of the pre-oxidized carbon nanotube powder to the solvent is too low, the surface of the pre-oxidized carbon nanotube powder (material) will be quickly wetted and become viscous, resulting in a low solid content of the mixed carbon nanotube wet material. When the ratio of the pre-oxidized carbon nanotube powder to the solvent is too high, the state of the carbon nanotube wet material is dry and thick, or in other words, the surface of the pre-oxidized carbon nanotube powder is not sufficiently wetted. Therefore, selecting the first solid content to be 15%-60% is beneficial to improving the wetting degree of the subsequent carbon nanotube powder in the acid solution.
[0059] In some embodiments, after mixing the pre-oxidized carbon nanotube powder with the solvent to obtain a carbon nanotube wet material with the first solid content, the method for preparing carbon nanotubes further includes:
[0060] Performing a shearing treatment on the carbon nanotube wet material with the first solid content to reduce the particle size of the carbon nanotube wet material with the first solid content.
[0061] It can be understood that under the shearing force, the aggregated or bundled carbon nanotube particles can be broken to reduce the particle size (microscopic particle size) of the carbon nanotubes, thereby improving the problem that the initial carbon nanotube powder is wound and knotted and agglomerated, resulting in poor dispersibility of the carbon nanotubes.
[0062] In some embodiments, after performing a shearing treatment on the carbon nanotube wet material with the first solid content, the method for preparing carbon nanotubes further includes:
[0063] Performing a compaction treatment on the carbon nanotube wet material with the first solid content to make the carbon nanotube wet material with the first solid content have a higher powder packing density.
[0064] It can be understood that performing a compaction treatment on the carbon nanotube wet material can increase the packing density and microscopic orientation degree of the carbon nanotubes, making the materials closer and having a certain orientation degree, and can reduce the viscosity threshold during the subsequent dispersion process of the carbon nanotubes.
[0065] In actual preparation, mixing the pre-oxidized carbon nanotube powder with the solvent can be carried out using a multi-functional mixer with a solvent spraying device and a powder feed inlet. For example, a high-speed mixer in which the material can rotate along the main axis and feed radially along the wall, a spiral conical mixer that can rotate both publicly and self-rotationally, or other multi-functional mixers with mixing functions and strong shearing and crushing, or a multi-roll grinder that can utilize the high shearing force generated between adjacent rollers with different rotational speeds and directions to process the material, or a screw extruder that can rotate in the same direction and generate a high shearing effect through mutual contact and between the barrel walls.
[0066] It should be noted that according to the situation of the initial carbon nanotube powder, single-type or multi-type equipment combinations can be used to perform a mixing treatment on the carbon nanotubes.
[0067] In a specific example, the oxidized carbon nanotube powder can be first mixed with a solvent to wet the surface of the oxidized carbon nanotube powder, and then the above-mentioned equipment is used to break the aggregated or bundled carbon nanotube particles under a shearing force to reduce the microscopic particle size of the carbon nanotubes, and further increase the packing density and microscopic orientation degree of the carbon nanotubes by means of roll pressing or extrusion molding, which is beneficial to the subsequent process treatment. Here, by pre-shearing and mixing and compacting the oxidized carbon nanotube powder, the aggregation or bundle diameter of the carbon nanotubes is reduced, and the carbon nanotube materials are made to be closer and have a certain degree of orientation, which can reduce the viscosity threshold during the continuous dispersion process of the carbon nanotubes.
[0068] It should be noted that as known to those skilled in the art, wetting is a process in which the gas on the solid surface is replaced by a liquid, and it can be divided into adhesion wetting, immersion wetting and spreading according to the degree of wetting. In some other embodiments, the pre-oxidized carbon nanotube powder is directly added to an acid solution. The wetting of the powder material by the acid solution is a transition from a gas-solid interface to a liquid-solid interface, which requires overcoming an energy barrier. Conventional stirring is relatively difficult, resulting in the surface of the powder material being difficult to be wetted, and further resulting in a low carbon nanotube content and a high viscosity during the pickling immersion.
[0069] In the embodiment of the present application, after the pre-oxidation treatment of the carbon nanotubes, a high-shear device can be pre-used to mix with a small amount of solvent, and the surface of the material can be pre-wetted by an external force. This is beneficial to further wetting the surface of the carbon nanotube material by the acid solution when the carbon nanotube wet material is subsequently added to the acid solution. The wetting difficulty is reduced, and the carbon nanotubes are more easily wetted in the acid solution, so that the carbon nanotube content is higher during the pickling immersion, so that less dilute acid solution can be used (or in other words, the solid content of the carbon nanotubes during the pickling immersion can be increased, and thus the usage amount of the acid solution can be reduced); moreover, the pickling effect can be improved, the metal impurities in the carbon nanotubes can be further reduced, and the purity of the carbon nanotubes can be improved.
[0070] Next, step S103 is executed, in which the carbon nanotube wet material with a first solid content is mixed uniformly with an acid solution with a first mass fraction, and a heat treatment is performed to obtain a carbon nanotube mixed solution with a second mass fraction.
[0071] In some embodiments, the acid solution can be a dilute acid solution.
[0072] In some specific embodiments, the acid solution can include one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid and citric acid.
[0073] In some embodiments, the first mass fraction may be 1% - 8%. For example, the first mass fraction may be 1.5%, 3%, 4.5%, 5%, 6.5%, 7% or 7.5%, etc., and no specific limitation is made here. In the embodiments of the present application, the first mass fraction may be 2% - 6%.
[0074] In the process of preparing carbon nanotubes, if the first mass fraction of the acid solution is too low, the pickling effect may be poor. Because when the concentration of the acid solution is low, pickling may be uneven, resulting in poor removal effect of metal impurities in the carbon nanotubes. If the first mass fraction of the acid solution is too high, the structure and properties of the carbon nanotubes may be damaged. Therefore, the first mass fraction of the acid solution is selected to be 1% - 8% to achieve the best removal effect. In this way, it is beneficial to improve the pickling and purification effect and further improve the purity of the prepared carbon nanotubes.
[0075] It should be noted that the first mass fraction here refers to the percentage of the mass of the solute to the mass of the solution in the acid solution. The first mass fraction can also be referred to as the "first mass content".
[0076] In some embodiments, the heating temperature for the heat treatment is the first preset temperature, and the heating time is the preset time. The first preset temperature may be 40°C - 120°C, and the preset time may be 1h - 48h. For example, the first preset temperature may be 50°C, 60°C, 70°C, 80°C, 90°C, 100°C or 110°C, etc., and the preset time may be 5h, 15h, 25h, 35h or 45h, etc., and no specific limitation is made here.
[0077] Here, if the heating temperature is too low and the heating time is too short, since the dissolution rate of the metal slows down at low temperature, the metal impurities may not be completely dissolved, affecting the purity of the carbon nanotubes. If the heating temperature is too high and the heating time is too long, it may damage the structure of the carbon nanotubes and have an adverse impact on the structure and properties of the carbon nanotubes. Therefore, selecting the first preset temperature to be 40°C - 120°C and the preset time to be 1h - 48h can achieve a better metal impurity removal effect while ensuring the stability of the structure and properties of the carbon nanotubes.
[0078] Furthermore, the first preset temperature may be 70°C - 95°C, and the preset time may be 4h - 24h.
[0079] It can be understood that after uniformly mixing the carbon nanotube wet material with the first solid content and the acid solution with the first mass fraction, the main function of the heat treatment is, on the one hand, to improve the pickling effect. Specifically, heating can promote the reaction rate between the acid and the metal surface, thereby improving the pickling effect; on the other hand, it can increase the solution activity. Specifically, heating can increase the activity of the acid solution, making it more effective in dissolving and removing impurities.
[0080] It should be noted that in some cases, appropriate heating can improve the pickling effect, but too high a temperature may damage the material. Therefore, during the pickling process, the appropriate heating method and temperature should be selected according to the specific situation.
[0081] In some embodiments, the second mass fraction can be 8% - 15%. For example, the second mass fraction can be 9%, 10%, 11%, 12%, 13% or 14%, etc., and no specific limitation is made here.
[0082] Here, if the second mass fraction of the carbon nanotube mixture is too high, the removal effect of metal impurities in the carbon nanotubes will be poor, and the purity of the prepared carbon nanotubes will be low. If the second mass fraction of the carbon nanotube mixture is too low, there will be a problem that the acid solution is not maximally utilized for purification, resulting in a higher total acid consumption and higher acid wastewater treatment cost in pickling purification. Therefore, selecting the second mass fraction of the carbon nanotube mixture to be 8% - 15% can ensure the purification effect of the carbon nanotubes while providing the production capacity of pickling purification, reducing the usage amount of the acid solution, and reducing the production cost.
[0083] It should be noted that the second mass fraction here refers to the percentage of the mass of the carbon nanotube solute in the carbon nanotube mixture to the mass of the carbon nanotube mixture. The second mass fraction can also be called the "second mass content". Here, the second mass fraction is less than the first solid content.
[0084] In some embodiments, mixing the carbon nanotube wet material with the first solid content and the acid solution with the first mass fraction evenly and performing heat treatment can use a tank body made of acid-resistant corrosion material, with stirring and mixing, heating functions and a reflux device.
[0085] Next, perform step S104, filter the carbon nanotube mixture with the second mass fraction, and wash it with water until it is neutral to obtain a carbon nanotube wet material with the second solid content.
[0086] It should be noted that there will be residual acid in the carbon nanotube wet material after pickling purification. By washing with water, the residual acid in the carbon nanotube wet material can be washed away. Specifically, washing the carbon nanotube wet material until the filtrate after filtration is neutral (pH = 7) is called "washing to neutrality".
[0087] Here, the carbon nanotube wet material can be washed with one or more of tap water, pure water, deionized water, and ultrapure water.
[0088] In some embodiments, filtering the carbon nanotube mixture with the second mass fraction and washing it with water until it is neutral can use one or a combination of equipment such as a centrifuge, a filter press, and a filter.
[0089] In some embodiments, the second solid content may be 15%-30%. For example, the second solid content may be 17%, 20%, 23%, 25% or 27%, etc., and no specific limitation is made here.
[0090] It should be noted that the second solid content refers to the ratio of the mass of carbon nanotubes in the wet carbon nanotube material to the mass of the wet carbon nanotube material.
[0091] Finally, perform step S105 to dry the wet carbon nanotube material with the second solid content to obtain carbon nanotubes.
[0092] In some embodiments, the drying temperature for the drying process is the second preset temperature, and the second preset temperature T2 may be 50°C - 450°C. For example, the second preset temperature may be 80°C, 150°C, 180°C, 200°C, 250°C, 300°C, 350°C or 400°C, etc., and no specific limitation is made here.
[0093] Here, if the drying temperature is too low, it may cause the carbon nanotube powder to not be fully dried, resulting in moisture or other solvent residues in the carbon nanotube powder, affecting the stability and performance of the carbon nanotube powder. If the drying temperature is too high, the carbon nanotubes may undergo an oxidation reaction, resulting in changes in their structure and performance. Therefore, selecting a drying temperature of 50°C - 450°C can improve the drying efficiency and reduce the drying cost while ensuring the stability of the structure and performance of the carbon nanotubes.
[0094] In the embodiments of the present application, the second preset temperature may be 100°C - 350°C.
[0095] In some embodiments, the wet carbon nanotube material with the second solid content is dried until it reaches a constant weight. Equipment such as a vacuum electrothermal dryer, a microwave vacuum dryer, and a belt-type vacuum continuous dryer can be used, and the appropriate type can be selected or a combination can be used according to the operating pressure, operating method, heating method, drying medium, and movement type.
[0096] In some embodiments, the bulk density of the carbon nanotube powder is 0.08 g / cm 3 -0.28 g / cm 3 . The purity of the carbon nanotubes is higher than 99.6%.
[0097] Based on this, a specific example of the present application provides a purification method for pickling carbon nanotubes, including the following steps:
[0098] (1) Pre-oxidize the carbon nanotube powder (the initial carbon nanotube powder) to obtain the pre-oxidized carbon nanotube powder A1;
[0099] (2) Use device M1 to mix the pre-oxidized carbon nanotube powder A1 with a solvent to obtain a carbon nanotube wet material A2 with a first solid content P1 after mixing;
[0100] (3) Put the carbon nanotube wet material A2 with the first solid content P1 into device M2. Device M2 is filled with an acid solution with a first mass fraction C2 that has been pre-prepared. After stirring the carbon nanotube wet material A2 with the first solid content P1 and the acid solution with the first mass fraction C2 evenly and soaking for a preset time t at the first preset temperature T1, obtain a carbon nanotube mixture A3 with a second mass fraction C1 after acid treatment;
[0101] (4) Use device M3 to filter the carbon nanotube mixture A3 with the second mass fraction C1, and wash it with pure water until the filtrate after filtration is neutral to obtain a carbon nanotube wet material A4 with a second solid content P2;
[0102] (5) Place the carbon nanotube wet material A4 with the second solid content P2 in a drying device M4 and perform a drying treatment at the second preset temperature T2 to finally obtain purified carbon nanotubes A5.
[0103] It should be noted that the above step (2) can also be expressed as "Use device M1 to mix the pre-oxidized carbon nanotube powder A1 with a solvent at a first solid content P1 to obtain a carbon nanotube wet material A2 after mixing", and the above step (3) can also be expressed as "(3) Put the carbon nanotube wet material A2 into device M2 with an acid solution pre-configured to a first mass fraction C2 at a second mass fraction C1, stir evenly and soak for a preset time t at the first preset temperature T1 to obtain a carbon nanotube mixture A3 after acid treatment".
[0104] It can be understood that device M1 can refer to the multifunctional mixer with a solvent spraying device and a powder feed port in the above embodiment; device M2 can refer to the tank body with acid-resistant corrosion material, equipped with stirring and mixing, heating functions and a reflux device in the above embodiment; device M3 can refer to one or a combination of a centrifuge, a filter press, a filter, etc. in the above embodiment; the drying device M4 can refer to a vacuum electric heating dryer, a microwave vacuum dryer, a belt-type vacuum continuous dryer, etc. in the above embodiment.
[0105] The purification method of pickling carbon nanotubes provided by this application realizes the optimization of the carbon nanotube pickling purification process by performing a pre-oxidation treatment on the carbon nanotube powder, mixing it with a solvent, and then performing treatments such as shearing and compaction, and performing pickling treatment with a relatively high carbon nanotube content.
[0106] Specifically, in the first aspect, the content of carbon nanotubes in the pickling process is increased, the equipment investment is reduced, and the production efficiency is improved; in the second aspect, the amount of acid used and the output of acid waste liquid are relatively reduced, the cost is lowered; and the solid content of carbon nanotubes in the wet carbon nanotube material after pickling is increased, the drying cost is reduced, and the drying efficiency is provided; in the third aspect, the purity of carbon nanotubes after pickling is increased.
[0107] In summary, the purification method of pickled carbon nanotubes provided by this application solves the problems of low content of pickled carbon nanotubes and high acid waste water volume in the related art, further increases the solid content of the wet carbon nanotube material after pickling of carbon nanotubes, reduces the drying cost, and prepares carbon nanotubes that are relatively easy to disperse and have high purity.
[0108] The following further illustrates this application in conjunction with specific examples and comparative examples.
[0109] The carbon nanotubes in the specific examples and comparative examples listed in this application can be selected according to the above steps according to the difference in specific surface area (unit: m 2 / g) for experiments to obtain Examples 1-6 and Comparative Examples 1 and 2. Specifically, 90 m 2 / g (typical value) is selected in the range of 50 m 2 / g - 150 m 2 / g and recorded as CNT1; 340 m 2 / g (typical value) is selected in the range of 300 m 2 / g - 400 m 2 / g and recorded as CNT2; 800 m 2 / g is selected in the range of 700 m 2 / g - 900 m 2 / g and recorded as CNT3 (typical value).
[0110] Example 1
[0111] The CNT1 powder is pre-oxidized in a nitrogen atmosphere containing a small amount of air, and then high-shear mixed with pure water at a CNT1 content (the first solid content P1) of 45.0% and extruded using an extruder. The obtained wet carbon nanotube material is added to a dilute acid solution with a first mass fraction C2 of 6% according to a powder content (the second mass fraction C1) of 12% and stirred and mixed evenly. After soaking at a set temperature (the first preset temperature T1) of 85 °C for 12 h (the preset time t), it is filtered by a vacuum negative pressure filter and washed with pure water until the filtrate is neutral to obtain a wet carbon nanotube material with a powder content (the second solid content P2) of about 28.4%. Subsequently, a blast drying oven is used, and the temperature is set (the second preset temperature T2) at 120 °C and dried to a constant weight. The measured bulk density is 0.228 g / cm 3, the powder purity is 99.66%, and the residual metal content (main metal elements) is 233.74 ppm.
[0112] Example 2
[0113] The CNT1 powder is pre-oxidized in a nitrogen atmosphere containing a small amount of air, and then high-shear mixed with pure water at a CNT1 content (first solid content P1) of 40% and extruded using an extruder. The obtained carbon nanotube wet material is added to a dilute acid solution with a first mass fraction C2 of 4% according to a powder content (second mass fraction C1) of 10%, and stirred and mixed evenly. After soaking at a set temperature (first preset temperature T1) of 85 °C for 12 h (preset time t), vacuum negative pressure filtration is carried out, and washed with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of about 24.6%. Subsequently, a blast drying oven is used, and the temperature is set (second preset temperature T2) at 120 °C and dried to constant weight. The measured bulk density is 0.216 g / cm 3 , the powder purity is 99.64%, and the residual metal content (main metal elements) is 214.88 ppm.
[0114] Example 3
[0115] The CNT2 powder is pre-oxidized in a nitrogen atmosphere containing a small amount of air, and then high-shear mixed with pure water at a CNT2 content (first solid content P1) of 33.3% and extruded using an extruder. The obtained carbon nanotube wet material is added to a dilute acid solution with a first mass fraction C2 of 4% according to a powder content (second mass fraction C1) of 9%, and stirred and mixed evenly. After soaking at a set temperature (first preset temperature T1) of 90 °C for 8 h (preset time t), vacuum negative pressure filtration is carried out, and washed with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of about 22.4%. Subsequently, a blast drying oven is used, and the temperature is set (second preset temperature T2) at 240 °C and dried to constant weight. The measured bulk density is 0.212 g / cm 3 , the powder purity is 99.86%, and the residual metal content (main metal elements) is 183.06 ppm.
[0116] Example 4
[0117] The CNT2 powder is pre-oxidized in a nitrogen atmosphere containing a small amount of air, and then high-shear mixed with pure water at a CNT2 content (first solid content P1) of 33.3% and extruded using an extruder. The obtained carbon nanotube wet material is added to a dilute acid solution with a first mass fraction C2 of 2.5% according to a powder content (second mass fraction C1) of 10%, stirred and mixed evenly, soaked at a set temperature (first preset temperature T1) of 85°C for 8 h (preset time t), then filtered by a vacuum negative pressure filter, and washed with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of about 22.8%. Subsequently, a blast drying oven is used, and the temperature is set at (second preset temperature T2) 120°C and dried to a constant weight. The measured bulk density is 0.183 g / cm 3 , the powder purity is 99.85%, and the residual metal content (main metal elements) is 196.97 ppm.
[0118] Example 5
[0119] The CNT2 powder is pre-oxidized in a nitrogen atmosphere containing a small amount of air, and then high-shear mixed with pure water at a CNT2 content (first solid content P1) of 33.3% and extruded using an extruder. The obtained carbon nanotube wet material is added to a dilute acid solution with a first mass fraction C2 of 3% according to a powder content (second mass fraction C1) of 12%, stirred and mixed evenly, soaked at a set temperature (first preset temperature T1) of 85°C for 8 h (preset time t), then filtered by a vacuum negative pressure filter, and washed with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of about 23.2%. Subsequently, a blast drying oven is used, and the temperature is set at (second preset temperature T2) 120°C and dried to a constant weight. The measured bulk density is 0.202 g / cm 3 , the powder purity is 99.83%, and the residual metal content (main metal elements) is 212.02 ppm.
[0120] Example 6
[0121] Mix 95% CNT2 powder and 5% CNT3 powder, and then conduct pre-oxidation treatment in a nitrogen atmosphere containing a small amount of air and water vapor. Then, perform high-shear mixing with pure water at a first solid content P1 of 20.0% and extrude using an extruder. The obtained carbon nanotube wet material is added to a dilute acid solution with a first mass fraction C2 of 4% at a powder content (second mass fraction C1) of 8% and stirred and mixed evenly. Set the temperature (first preset temperature T1) at 90 °C and soak for 20 h (preset time t). Then, perform suction filtration using a vacuum negative pressure filter and wash with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of approximately 19.6%. Subsequently, use a blast drying oven and set the temperature (second preset temperature T2) at 240 °C to dry to a constant weight. The measured bulk density is 0.176 g / cm 3 , the powder purity is 99.75%, and the residual metal content (main metal elements) is 303.62 ppm.
[0122] Comparative Example 1
[0123] Conduct pre-oxidation treatment on CNT1 powder in a nitrogen atmosphere containing a small amount of air. Directly add it to a dilute acid solution with a first mass fraction C2 of 4% at a powder content (first solid content P1) of 4.3% and stir and mix evenly. Set the temperature at 85 °C (first preset temperature T1) and soak for 12 h (preset time t). Then, perform suction filtration using a vacuum negative pressure filter and wash with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of approximately 19.2%. Subsequently, use a blast drying oven and set the temperature (second preset temperature T2) at 120 °C to dry to a constant weight. The measured bulk density is 0.162 g / cm 3 , the powder purity is 99.62%, and the residual metal content (main metal elements) is 381.66 ppm.
[0124] Comparative Example 2
[0125] Conduct pre-oxidation treatment on CNT2 powder in a nitrogen atmosphere containing a small amount of air. Directly add it to a dilute acid solution with a first mass fraction C2 of 4% at a powder content (first solid content P1) of 3.5% and stir and mix evenly. Set the temperature at 90 °C (first preset temperature T1) and soak for 12 h (preset time t). Then, perform suction filtration using a vacuum negative pressure filter and wash with pure water until the filtrate is neutral to obtain a carbon nanotube wet material with a powder content (second solid content P2) of approximately 18.0%. Subsequently, use a blast drying oven and set the temperature (second preset temperature T2) at 240 °C to dry to a constant weight. The measured bulk density is 0.158 g / cm 3 , the powder purity is 99.80%, and the residual metal content (main metal elements) is 345.08 ppm.
[0126] The specific parameters in Examples 1-6 and Comparative Examples 1 and 2 are shown in Table 1.
[0127] Table 1
[0128]
[0129] It can be seen from Table 1 that by comparing Comparative Example 1 and the pickling processes of Examples 1-2, the carbon nanotube content (C1) increased from 4.3% to 10%-12%, while the dilute acid concentration remained unchanged or increased slightly, but the purity of the obtained carbon nanotube powder was comparable, and the metal content was significantly reduced. It can be concluded that when the pickling treatment is carried out in the examples and comparative examples, the pickling productivity of the method provided in the examples of the present application is more than twice as high, correspondingly reducing the acid waste liquid and the treatment cost. By comparing Comparative Example 2, the same conclusion can also be drawn for Examples 3-5, and the metal impurity content after pickling is further reduced, and the purity is slightly increased. It shows that the pre-oxidized carbon nanotube powder is pre-mixed with a solvent and then subjected to treatments such as shearing and compaction, and pickling treatment is carried out with a relatively high carbon nanotube content, which has a significant beneficial effect.
[0130] To further illustrate the easy dispersibility of the carbon nanotube powder obtained by the method provided in the examples of the present application. The carbon nanotube powders obtained from Example 1, Example 3, Comparative Example 1, and Comparative Example 2 were respectively selected, and polyvinylpyrrolidone was used as a dispersant, and a sand mill was used for dispersion treatment to prepare a conductive paste. The time required for the dispersion process of preparing 0.8 kg of the conductive paste and the viscosity of the paste were compared. The specific parameters are shown in Table 2.
[0131] Table 2
[0132] Number CNT content wt% Dispersant content wt% Dispersion time min Slurry viscosity cp Example 1 12 1.5 40 800 Example 3 3.2 0.8 25 844 Comparative Example 1 12 1.5 60 1004 Comparative Example 2 3.2 0.8 30 1232
[0133] It can be seen from Table 2 that by comparing Comparative Example 1 and Example 1, the time required for the dispersion of the carbon nanotube powder obtained in Example 1 for making a paste is only 2 / 3 of that of Comparative Example 1, and the viscosity of the paste is reduced by about 20%, and a similar dispersion degree can be achieved (using a particle size analyzer to test PSD (Particle Size Distribution), requiring D90 (90% of the particle size) < 3 μm). By comparing Comparative Example 2 and Example 3, the time required for the dispersion of the carbon nanotube powder obtained in Example 3 for making a paste is only 5 / 6 of that of Comparative Example 2, and the viscosity of the paste is reduced by about 30%.
[0134] Furthermore, the morphology of the carbon nanotube powder obtained in Example 3 was characterized. Figure 2SEM image of the conductive paste prepared with the carbon nanotube powder obtained in Example 3. This SEM image was obtained using a JEOL scanning electron microscope, with the secondary electron signal (SEI), under the scanning parameters of an acceleration voltage of 15.0 KV, a working distance (WD) of 8.1 mm, and a scanning magnification (X) of 25,000 times. The scale size of this SEM image is 1 μm.
[0135] Reference Figure 2 , it can be observed that there are no obvious large aggregates in the dispersed conductive paste, indicating that through the carbon nanotube preparation method of the present application, the carbon nanotubes are effectively dispersed. It can be seen that the carbon nanotubes obtained by the method provided in the embodiments of the present application have a certain local orientation, reducing the difficulty of dispersion, and a relatively stable conductive paste dispersion can be obtained.
[0136] Based on this, the embodiments of the present application also provide a kind of carbon nanotube, which is prepared by using the carbon nanotube preparation method of any one of the above embodiments.
[0137] Based on this, the embodiments of the present application also provide a kind of carbon nanotube.
[0138] In some embodiments, the carbon nanotube is an easily dispersible carbon nanotube, and its powder bulk density is 0.08 g / cm 3 - 0.28 g / cm 3 .
[0139] In some embodiments, the carbon nanotube is a high-purity carbon nanotube, and its purity is higher than 99.6%.
[0140] Based on this, the embodiments of the present application also provide a kind of conductive paste, which includes the carbon nanotubes prepared by using the carbon nanotube preparation method of any one of the above embodiments.
[0141] In some embodiments, the conductive paste may further include a dispersant and a matrix.
[0142] Specifically, the dispersant can be one or a mixture of several of polyvinylpyrrolidone and its modified copolymers, polyacrylic acid and its modified copolymers, polyacrylate dispersants, polyvinyl alcohol dispersants and their modified resin polymers, nitrile rubber, highly saturated nitrile rubber dispersants, cellulose ethers and their derivatives; the matrix can be one or a mixture of several of N-methylpyrrolidone, triethyl phosphate, ethanol, isopropanol, and water.
[0143] Based on this, the embodiments of the present application also provide the application of the conductive paste provided in any one of the above embodiments in a lithium-ion battery.
[0144] It should be noted that the carbon nanotube embodiments, conductive paste embodiments, and carbon nanotube preparation method embodiments provided in this application belong to the same concept; among the technical features in the technical solutions recorded in each embodiment, they can be arbitrarily combined without conflict.
[0145] It should be understood that the above embodiments are all exemplary and are not used to cover all possible implementation manners included in the claims. Without departing from the scope of the present disclosure, various deformations and changes can also be made on the basis of the above embodiments. Similarly, the technical features of the above embodiments can also be arbitrarily combined to form additional embodiments of the present application that may not be explicitly described. Therefore, the above embodiments only express several implementation manners of the present application and do not limit the protection scope of the patent of the present application.
Claims
1. A method for preparing carbon nanotubes, characterized in that, The preparation method of the carbon nanotubes includes: Performing pre-oxidation treatment on the initial carbon nanotube powder to obtain the pre-oxidized carbon nanotube powder; Mixing the pre-oxidized carbon nanotube powder with a solvent to obtain a carbon nanotube wet material with a first solid content; Mixing the carbon nanotube wet material with the first solid content uniformly with an acid solution with a first mass fraction, and performing heat treatment to obtain a carbon nanotube mixed solution with a second mass fraction; Filtering the carbon nanotube mixed solution with the second mass fraction and washing it with water until neutral to obtain a carbon nanotube wet material with a second solid content; Performing drying treatment on the carbon nanotube wet material with the second solid content to obtain the carbon nanotubes.
2. The method for preparing carbon nanotubes according to claim 1, characterized in that, After mixing the pre-oxidized carbon nanotube powder with the solvent to obtain a carbon nanotube wet material with a first solid content, the preparation method of the carbon nanotubes further includes: Performing shearing treatment on the carbon nanotube wet material with the first solid content to reduce the particle size of the carbon nanotube wet material with the first solid content.
3. The method for preparing carbon nanotubes according to claim 2, wherein, After performing shearing treatment on the carbon nanotube wet material with the first solid content, the preparation method of the carbon nanotubes further includes: Performing compaction treatment on the carbon nanotube wet material with the first solid content to make the carbon nanotube wet material with the first solid content have a higher powder packing density.
4. The preparation method of the carbon nanotubes according to any one of claims 1 to 3, characterized in that The solvent includes one or more of tap water, deionized water, pure water and ultrapure water; and / or, the first solid content is 15%-60%.
5. The preparation method of the carbon nanotubes according to claim 4, characterized in that The first solid content is 20%-50%.
6. The preparation method of the carbon nanotubes according to any one of claims 1 to 3, characterized in that The acid solution includes one or more of hydrochloric acid, sulfuric acid, hydrofluoric acid and citric acid; and / or, the first mass fraction is 1%-8%; and / or, the heating temperature for the heat treatment is a first preset temperature, the heating time is a preset time, the first preset temperature is 40°C-120°C, the preset time is 1h-48h; and / or, the second mass fraction is 8%-15%.
7. The preparation method of the carbon nanotubes according to claim 6, characterized in that The first mass fraction is 2%-6%; and / or, the first preset temperature is 70°C-95°C, the preset time is 4h-24h.
8. The preparation method of the carbon nanotubes according to any one of claims 1 to 3, characterized in that The second solid content is 15%-30%; and / or, the drying temperature for the drying treatment is a second preset temperature, the second preset temperature is 50°C-450°C.
9. The preparation method of the carbon nanotubes according to any one of claims 1 to 3, characterized in that The bulk density of the carbon nanotube powder is 0.08 g / cm 3 -0.28 g / cm 3 ; and / or, the purity of the carbon nanotube is higher than 99.6%.
10. A carbon nanotube, characterized in that, The carbon nanotubes are prepared by the preparation method of the carbon nanotubes according to any one of claims 1 to 9.
11. A conductive paste, characterized in that, The conductive paste includes carbon nanotubes prepared by the preparation method of the carbon nanotubes according to any one of claims 1 to 9.