KR20170135564A - Method for manufacturing partially unzipped porous carbon nanotubes - Google Patents

Abstract

Disclosed is a method of producing a carbon nanotube in which a surface with an increased pore and specific surface area (SSA) is partially opened. According to an embodiment of the present invention, the carbon nanotubes in which a surface is partially opened include: a) treating a carbon nanotube with an acid so as to form an oxidized carbon nanotube in which a surface of the carbon nanotube is partially oxidized; and b) dispersing the carbon nanotube in a basic solution so as to partially open the surface of the carbon nanotube.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a carbon nanotube having a partially open surface,

The present invention relates to a method for manufacturing porous carbon nanotubes of a new type by partially opening multiple walls of carbon nanotubes. More particularly, the present invention relates to a method for producing porous carbon nanotubes in which a wall of a carbon nanotube is partially opened in a state in which graphene nanoribbons and carbon nanotubes coexist by utilizing a combination of an acid treatment method and a base activating reaction will be.

Nanocarbon materials based on carbon nanotubes including carbon nanotubes are emerging as next-generation high-functional materials that can be utilized as electronic materials, high-strength structural materials, and heat-radiating materials because of their excellent electrical, thermal and mechanical properties.

However, in spite of these superior properties, it has a lower specific surface area than other nano-carbon materials such as graphene to be utilized as an energy storage material including batteries, supercapacitors, and hydrogen storage materials, There is a limit due to the low pore volume due to the closed pores being located. Particularly, in the lithium-sulfur battery, which is currently in the spotlight, there is a serious problem that the active material is eluted into the electrolyte due to the polysulfide that necessarily occurs at the time of discharging, and the energy storage capacity due to the side reactions is decreased according to the cycle. To solve this problem, attempts have been made to introduce various porous materials such as tanonanotube and graphene. Suitable porous materials should have sufficient porosity, be capable of interacting with polysulfides, and be electrically conductive.

Japanese Patent Application Laid-Open No. 10-2015-0122928

In order to solve the above-mentioned problem, a porous material was developed based on a carbon nanotube. In order to effectively serve as an energy storage material material, in particular, in order to function as a suitable cathode material in a lithium-sulfur battery, it is necessary to secure pores inside the wall of the carbon nanotube so that sulfur can be sufficiently supported in the pores, And the specific surface area should also be improved in such a way that mass synthesis is possible. In addition, if it can interact with polysulfides around the pores, it can be an optimum material candidate for supporting sulfur, which is an active material of the lithium-sulfur battery.

For this purpose, a method of forming micropores in the walls of carbon nanotubes using cobalt oxide or high-temperature water molecules has been introduced, but there are limitations in the effectiveness.

Therefore, in order to manufacture the porous carbon nanotubes of the energy storage degree in a manner that can realize both the electrical and morphological characteristics of the porous carbon nanotubes and can be commercialized, it is necessary to use an inexpensive agent to mass- The electrical conductivity must meet the minimum level at which the electrical conductivity can be utilized for energy storage purposes.

Accordingly, a problem to be solved by the present invention is to expand the pore and specific surface area of an open wall surface of a carbon nanotube whose surface is partially opened, and at the same time to secure the movement of electrons in unexpanded portions, And to provide a method for synthesizing carbon nanotubes having a unique porous structure.

Another object of the present invention is to provide a method for synthesizing porous carbon nanotubes for use in energy storage, which can reduce costs in consideration of mass production processes and commercialization .

According to an aspect of the present invention, there is provided a method of manufacturing a carbon nanotube having a partially open surface according to an embodiment of the present invention, comprising the steps of: a) treating the carbon nanotube with an acid to partially oxidize the surface of the carbon nanotube Forming carbon nanotubes; and b) dispersing the carbon nanotubes in a basic solution to partially open the surface of the carbon nanotubes.

The acid treatment, but carried out by immersing the carbon nanotube in an acidic solution, the acidic solution is nitric acid (HNO _3), hydrochloric acid (HCl), sulfuric acid (H ₂ SO _4), phosphoric acid (H ₃ PO ₄₎ and their Or a mixture thereof.

The acid solution is sulfuric acid (H ₂ SO ₄₎ and the volume ratio of nitric acid when comprise a mixture of (HNO _3), the sulfuric acid (H ₂ SO ₄₎ and nitric acid (HNO ₃₎ is from 1: 1 to 4: 1.

The acid treatment may be carried out in a temperature atmosphere of 60 ° C to 120 ° C.

The acid treatment may be performed for 1 to 6 hours.

The basic solution includes a basic material, and the basic material is any one of sodium hydroxide (NaOH), potassium hydroxide (KOH), barium hydroxide (Ba (OH) ₂ ), and mixtures thereof.

The step b) may be performed in a temperature atmosphere of 800 ° C to 1000 ° C.

The step b) may be carried out for from 1 hour to 6 hours.

When the surface of the carbon nanotube is partially opened, graphene nanoribbons can be formed and bonded around the open surface.

The carbon nanotubes are multi-walled or single-walled structures.

According to the embodiments of the present invention, the acid-treated carbon nanotubes function as a starting point where the carbon nanotube walls are activated by the base activation reaction in the base activation reaction, . Thereby, the porous carbon nanotube having the walls of the carbon nanotubes partially opened with the shape of the graphene nanoribbles and the shape of the carbon nanotubes coexisting is provided. Accordingly, the carbon nanotubes according to the present invention have significantly increased specific surface area and pores than conventional carbon nanotubes.

In addition, oxygen functional groups may be introduced into the carbon nanotubes produced according to the present invention. Accordingly, the carbon nanotubes produced according to the present invention can have electric conduction characteristics that can be utilized as an energy storage material. Accordingly, the carbon nanotube manufactured according to the present invention can be utilized as an energy storage material.

In addition, such an acid treatment and a base activating reaction are advantageous in terms of manufacturing cost in comparison with a method using other materials since they enable a simple and large-scale process.

In addition, as a result of carrying out a positive electrode test of a battery carrying the positive active material sulfur of the lithium-sulfur battery using the carbon nanotube material having the partially opened surface, the performance of the lithium-sulfur battery was dramatically improved I could.

In addition, it has been confirmed that the above materials are more likely to be used for other energy storage materials such as hydrogen storage and supercapacitors.

The effects of the present invention are not limited to the effects mentioned above, and the effects of the other inventions can be clearly understood from the description of the claims.

1 is a flowchart illustrating a method of manufacturing a carbon nanotube having a partially open surface according to an embodiment of the present invention.
Fig. 2 is a TEM image of (a) low magnification and (b) high magnification, which were confirmed by different magnifications of partially open carbon nanotubes whose surfaces were made according to the manufacturing method of Fig.
FIG. 3 is a graph showing the results of deconvolution of an XPS C 1 _S peak of a partially open carbon nanotube surface produced by the manufacturing method of FIG.
FIG. 4 shows the BET isotherm of the partially open carbon nanotubes prepared according to the manufacturing method of FIG. 1 and the measured volume specific surface area and pore volume.
FIG. 5 is a graph showing the performance of the battery when the carbon nanotube whose surface is partially opened by the manufacturing method of FIG. 1 is used as a sulfur bearing member which is a cathode material of a lithium-sulfur battery.
FIG. 6 is a graph showing the hydrogen storage capacity when the surface of the carbon nanotube having a partially open surface prepared by the method of FIG. 1 is used as a hydrogen storage material.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. &Quot; and / or "include each and every combination of one or more of the mentioned items. ≪ RTI ID = 0.0 >

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. The terms " comprises "and / or" comprising "used in the specification do not exclude the presence or addition of one or more other elements in addition to the stated element.

Unless defined otherwise, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. Also, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

Hereinafter, a method of manufacturing a carbon nanotube whose surface is partially opened according to an embodiment of the present invention will be described.

Referring to FIG. 1, a method of fabricating a carbon nanotube having a partially open surface according to an embodiment of the present invention includes: treating the carbon nanotube with an acid to form a partially oxidized carbon nanotube B) dispersing the carbon nanotubes in a basic solution to partially open the surface of the carbon nanotubes (S20); c) forming the carbon nanotubes having a partially open surface And washing the nanotubes (S30).

First, carbon nanotubes are provided. Carbon nanotubes are double-walled, multi-walled or single-walled carbon nanotubes. Carbon nanotubes are carbon allotropes of large one-dimensional structure has an aspect ratio that is wound graphene sheets composed of sp ² carbon in a cylindrical cell structure having a diameter in the nanoscale. Carbon nanotubes are lighter than aluminum (1.0 g / m ³ ) due to their structural characteristics, have similar electrical conductivity (1 × 10 ⁹ A / cm ² ) and have the same thermal conductivity as natural diamond 6000W / m · K) and the strength is 100 times better than that of steel (1TPa).

Subsequently, the carbon nanotubes are immersed in an acidic solution to acid-treat the carbon nanotubes. Through the acid treatment, the carbon nanotubes are oxidized. That is, carbon nanotubes are formed. At this time, it is necessary to partially oxidize the outer wall surface of the carbon nanotube rather than to oxidize the entire surface. When the outer wall surface of the carbon nanotube is completely oxidized, it may be formed only of the graphene nanoribbons, and it may be difficult to manufacture the carbon nanotubes having the partially opened surfaces intended by the present invention. For example, oxygen functional groups may be bonded to the outer wall surface of the carbon nanotube.

The acidic solution may comprise any one of nitric acid (HNO ₃ ), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ) and mixtures thereof. The acidic solution can be prepared by dissolving the acidic substance in any one of methanol, ethanol, propanol, and deionized water, which are low molecular weight alcohols.

On the other hand, when the acid solution contains a mixed substance of sulfuric acid and nitric acid, the volume ratio of sulfuric acid and nitric acid may be 1: 1 to 4: 1.

The acid treatment can be carried out by immersing the carbon nanotubes in the above-mentioned acidic solution in a temperature atmosphere of 60 ° C to 120 ° C. If the acid treatment temperature is less than 60 占 폚, acidification on the surface of the carbon nanotube may not be performed smoothly. If the acid treatment temperature is higher than 120 ° C, acidification rapidly occurs on the surface of the carbon nanotubes, and the surface oxidation may occur on the surface. Thereby, it may happen that the purpose of partial oxidation can not be achieved, and ultimately, the surface of the carbon nanotube can not be partially opened.

On the other hand, the acid treatment time can be performed for 1 to 6 hours. If the acid treatment time is less than 1 hour, the surface of the carbon nanotube may not be sufficiently oxidized. On the other hand, if the acid treatment time exceeds 6 hours, there is a possibility that the surface of the carbon nanotube is entirely oxidized rather than partially oxidized.

Subsequently, an acid-treated carbon oxide nanotube is obtained, and then a base activating reaction is carried out. The base activated carbon nanotubes are subjected to a base activation reaction to open the surface of the carbon nanotubes.

The base activation reaction of the carbon oxide nanotubes is carried out by immersing the carbon oxide nanotubes in a basic solution.

Basic solutions include basic materials, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), barium hydroxide (Ba (OH) ₂ ), ZnCl ₂ , NaCl, CaCl ₂ , MgCl ₂ -6H ₂ O, Na ₂ CO ₃ , K ₂ CO ₃ , KCl, and mixtures thereof. A basic solution can be prepared by dissolving the basic substance in a solvent. The solvent may be any one of methanol, ethanol, propanol, and deionized water, which are low molecular weight alcohols. For example, when a basic aqueous solution is formed by dissolving potassium hydroxide (KOH) powder in a solvent, the mass ratio of potassium hydroxide (KOH) to solvent can be 8: 1, 4: 1, 2: 1, 1: .

The base activation reaction can be carried out in a temperature atmosphere of 800 ° C to 1000 ° C. If the reaction temperature is less than 800 ° C, base activation on the surface of the oxidized carbon nanotube can not be performed smoothly, and the surface of the carbon nanotube may not be opened well. If the reaction temperature exceeds 1000 ° C, the base activation reaction is smoothly performed, but the mechanical and structural stability of the carbon nanotubes may be deteriorated due to the increase of the reaction temperature.

On the other hand, the base activation reaction time can be performed for 1 hour to 6 hours. If the base activation reaction time is less than 1 hour, the surface of the carbon nanotube may not be sufficiently opened. On the other hand, if the acid treatment time exceeds 6 hours, the surface of the carbon nanotubes may be peeled off, and the peeled portion may be separated from the carbon nanotubes and formed of graphene nanoribbons or the like. Accordingly, a new type of carbon nanotubes formed by combining the carbon nanotubes and the graphene nanoribbons of the present invention may not be formed.

On the other hand, when the surface of the carbon nanotubes is opened by the base activation reaction, a graphene nanoribbon shape in which functional groups are bonded can be formed around the open surface. More specifically, a part of the carbon nanotubes maintains the shape of the carbon nanotubes, and the remaining part of the carbon nanotubes is opened to show the shape of the graphene nanoribbons. That is, the carbon nanotubes produced by the present invention may have the following shapes. Some have the original shape of the carbon nanotube, and the remaining part has the shape of graphene nanoribbles while the surface is opened.

This is because the base and the oxygen functional groups react with each other on the surface of the partially oxidized carbon nanotube and the surface of the carbon nanotube is opened. At this time, a portion of the carbon nanotubes adjacent to the open portion is formed in a graphen nano ribbon shape. That is, in the open portion of the surface of the carbon nanotube, the open portion and the graphene nanoribbon coexist. As a result, the surface of the carbon nanotubes subjected to the base activation reaction may include graphene nanoribbons formed around the openings and openings. Accordingly, the carbon nanotubes produced by the present invention have openings on the surface and coexist with graphene nanoribbons, which can dramatically increase pores and specific surface area compared to conventional carbon nanotubes . In addition, oxygen functional groups are introduced into the carbon nanotubes by an acid treatment and a base activating reaction. By this. The carbon nanotubes produced by the present invention may have electric conduction characteristics that can be utilized as energy storage materials. Accordingly, the carbon nanotube manufactured according to the present invention can be utilized as an energy storage material.

Subsequently, the carbon nanotubes whose surfaces formed through the base activation are partially opened are washed. This is to remove the impurities remaining in the carbon nanotubes during the manufacturing process and increase the purity of the carbon nanotubes.

Washing can be carried out using distilled or weakly acidic substances, ethanol, methanol, and the like. Preferably, washing can be performed several times with distilled water between 40 ° C and 80 ° C.

Subsequently, in order to remove the substances and the like used for cleaning, a drying process may be further performed. That is, drying of carbon nanotubes having partially open surfaces can be performed in a vacuum oven at a temperature atmosphere of, for example, 60 DEG C for 24 hours. At this time, temperature, pressure, and drying time can be controlled so that the surface characteristics of the carbon nanotubes are not damaged. The carbon nanotubes having a partially open surface according to the present invention can be prepared through washing and drying.

The carbon nanotube having a surface partially opened according to the present invention and having graphene nanoribbons bonded thereto can be used as an active material support of a secondary battery. For example, the lithium-sulfur battery can be used as a support for supporting sulfur, which is a positive electrode active material.

In addition, the carbon nanotube having a surface partially opened according to the present invention and having graphene nanoribbons bonded thereto can also be used as a hydrogen storage material capable of storing hydrogen.

In addition, the carbon nanotube having a surface partially opened and a graphene nanoribbons bonded according to the present invention can be utilized as a super capacitor.

Advantages and features of the present invention will be clearly described with reference to the following experimental examples. However, the present embodiments are presented so that those skilled in the art can fully understand the scope of the present invention. It is only defined by category.

Example  One

The present embodiment shows a process for manufacturing a carbon nanotube having a partially open surface according to the present invention.

According to step S10, acid-treated carbon nanotubes were prepared by treating the mixture of nitric acid (75 mL) and sulfuric acid (225 mL) in a volume ratio of 1: 4 at 60 ° C for 3 hours. Distilled water . Acid-treated carbon nanotubes dispersed in water were then obtained by vacuum filtration and dried in a 60 DEG C vacuum oven for 24 hours.

According to step S20, the acid-treated carbon nanotubes were dispersed by sonication in a KOH aqueous solution in which KOH powder was dissolved in distilled water at a mass ratio of 4: 1, and then water was evaporated on a hot plate at 100 ° C. Then, the mixture of the KOH and the acid-treated carbon nanotubes was treated in a tube-shaped electric furnace at a heating rate of 2 캜 / min at 1000 캜 for 2 hours in a nitrogen atmosphere.

Following the step S30, the sample was washed several times with distilled water at about 60 DEG C, and the distilled water in which impurities were dissolved was sent down through a vacuum filter. The drying of the partially opened carbon nanotubes washed through the above process was carried out in a vacuum oven at 60 ° C for 24 hours.

Example  2

In order to utilize the carbon nanotube whose surface is partially opened according to the present invention as a sulfur bearing material which is a cathode active material of a lithium-sulfur battery, the surface of the carbon nanotube having a partially opened surface prepared in Example 1, And then heat-treated at 155 ° C for 12 hours at a heating rate of 2 ° C / min in an autoclave filled with gas such as nitrogen or argon. Then, the possibility of utilizing the material as a sulfur bearing material through a method of producing an electrode material slurry generally used.

Example  3

In order to utilize a carbon nanotube having a partially open surface according to an embodiment of the present invention as a storage body for hydrogen storage, the hydrogen storage capacity of the carbon nanotube whose surface is partially opened according to the embodiment 1 of the present invention 77K and 1 bar.

Experimental Example  1 - Transmission electron microscope ( TEM ) analysis

2 is a (a) low magnification and (b) high magnification surface photograph of a partially open carbon nanotube surface prepared according to Example 1 of the present experiment. 2, it can be seen that the outer wall of the carbon nanotube is partly unfolded according to the embodiment of the present invention.

Experimental Example  2 - XPS  (X-ray photoelectron spectroscopy) analysis

FIG. 3 shows the results of analysis of C1s XPS of a carbon nanotube whose surface was partially opened according to Example 1 of the present invention. It was confirmed that many oxygen functional groups introduced by acid treatment and base (KOH) activation reaction were present.

Experimental Example  3 - BET isotherm analysis through nitrogen adsorption

4 is a result obtained by analyzing BET isotherm through nitrogen adsorption in order to confirm an increase in the specific surface area and pore volume of the carbon nanotube whose surface was partially opened according to Example 1 of the present invention. When the specific surface area and pore volume of the acid-treated carbon nanotubes not subjected to the base (KOH) activation reaction were compared, it was found that the surface of the carbon nanotubes partially activated by the base activation reaction for 2 hours and the surface area of the pores It can be seen that the volume has increased greatly. (Table 1).

Specific surface area
(m ² / g) Volume of pore
(cm < ³ > / g) Acid-treated carbon nanotubes 51.0 0.20 Carbon nanotubes with partially open surfaces 473.2 1.15

Experimental Example  4 - Cathode active material  sulfur As a carrier  Electrochemical experiment

FIG. 5 is an electrochemical test result for evaluating the availability of sulfur as a cathode active material of the lithium-sulfur battery mentioned in Experimental Example 2. FIG. The capacity was maintained up to 570 mAh / g up to 200 cycles even at the current density corresponding to 5C which is a rapid charge / discharge condition, that is, 8360 mA / g. That is, it can be seen that the carbon nanotube whose surface is partially opened according to the present invention is likely to be used as a carrier.

Experimental Example  5 - Hydrogen storage capacity  Measure

FIG. 6 shows the result of measurement of the hydrogen storage capacity using the carbon nanotubes partially opened on the surface of the carbon nanotube according to the third embodiment. As can be seen from FIG. 6, the carbon nanotube having the partially open surface according to the present invention can be utilized as a hydrogen storage material.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (13)

a) treating the carbon nanotubes with an acid to form carbon nanotubes in which the surface of the carbon nanotubes is partially oxidized; And
b) dispersing the carbon nanotubes in a basic solution to partially open the surface of the carbon nanotubes, the surface of the carbon nanotubes being partially opened. The method according to claim 1,
The acid treatment is performed by immersing the carbon nanotubes in an acidic solution,
The acidic solution is a solution of carbon nanotubes having a partially open surface containing any one of nitric acid (HNO ₃ ), hydrochloric acid (HCl), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ) Gt; 3. The method of claim 2,
When the acidic solution comprises a mixture of sulfuric acid (H ₂ SO ₄ ) and nitric acid (HNO ₃ )
Wherein a surface of the sulfuric acid (H ₂ SO ₄ ) and nitric acid (HNO ₃ ) is partially opened in a volume ratio of 1: 1 to 4: 1. 3. The method of claim 2,
Wherein the acid treatment is carried out in a temperature atmosphere of 60 占 폚 to 120 占 폚, the surface of the carbon nanotube being partially open. 3. The method of claim 2,
Wherein the acid treatment is performed for 1 to 6 hours, the surface of the carbon nanotube is partially opened. The method according to claim 1,
The basic solution includes a basic substance,
Wherein the basic substance is sodium (NaOH), potassium hydroxide (KOH), barium hydroxide (Ba (OH) _{2) hydroxide, ZnCl 2, NaCl, CaCl 2} , MgCl 2 -6H 2 O, Na 2 CO 3, K 2 CO 3 , KCl, and mixtures thereof. The method according to claim 6,
Wherein the step (b) is performed in a temperature atmosphere of 800 ° C to 1000 ° C. The method according to claim 6,
Wherein the step (b) is performed for 1 to 6 hours while the surface of the carbon nanotube is partially opened. The method according to claim 1,
When the surface of the carbon nanotube is partially opened,
Wherein the surface on which the graphene nanoribbon shape is located is partially opened around the opened surface of the carbon nanotube. The method according to claim 1,
Wherein the surface of the carbon nanotubes having a multiwall or single wall structure is partially opened. A carbon nanotube having a surface partially open according to any one of claims 1 to 10. The active material carrier of a secondary battery according to any one of claims 1 to 10, wherein the surface of the carbon nanotube is partially open. A storage container for hydrogen storage comprising a carbon nanotube having a surface partially open according to any one of claims 1 to 10.

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