KR20120088214A - Method of preparing nano-sized iron oxide doped carbon nanotubes for supercapacitor electrodes and supercapacitor electrodes prepared using the same - Google Patents

Abstract

PURPOSE: A supercapacitor electrode of iron oxide nanoparticles doped carbon nanotube material and a manufacturing method thereof are provided to maintain high specific capacitance in a high speed charging/discharging process by doping iron oxide nanoparticles on the surface of the high conductivity carbon nanotube. CONSTITUTION: The surface of carbon nanotube is activated. Iron oxide nanoparticles are doped on the activated surface of the carbon nanotube. The particle size of the iron nanoparticle is 3nm to 30nm. A composite of the iron oxide and carbon nanotube, binder and conducting material are mixed. The mixture is coated on the surface of the carbon nanotube.

Description

Method of preparing an electrode for supercapacitors made of carbon nanotubes impregnated with iron oxide nanoparticles and a supercapacitor electrode manufactured by the above method {Method of preparing nano-sized iron oxide doped carbon nanotubes for supercapacitor electrodes and supercapacitor electrodes prepared using the same }

The present invention relates to a method for producing a supercapacitor electrode made of carbon nanotubes impregnated with iron oxide nanoparticles, and to a supercapacitor electrode manufactured by the above method, and more particularly to a carbon nano having a wide specific surface area and high electrical conductivity. The present invention relates to a method for producing a supercapacitor electrode prepared by depositing magnetite iron oxide nanoparticles capable of oxidation-reduction reaction to a tube.

Recently, due to global warming, depletion of fossil fuels and environmental pollution, the development of new energy conversion and storage devices is being activated. In particular, the use of supercapacitors as a storage device of electrical energy is emerging.

Supercapacitors are largely composed of an electric double layer capacitor (EDLC) using carbon (particles or fibers) having a high specific surface area depending on the electrode material, and a pseudo-capacitor made of a metal oxide or a conductive polymer. Can be classified.

Electric double layer capacitors use physical adsorption and desorption of ions and thus have very good life characteristics. However, since charges are accumulated only on the electrical double layer on the surface, there is a disadvantage in that the storage capacity is lower than that of the metal oxide-based or conductive polymer-based supercapacitor using the Faraday reaction.

Pseudocapacitors have a lot of capacity per unit weight (F / g) compared to electric double layer capacitors, and have excellent output characteristics, making them a new energy storage source. Among them, the metal oxide pseudocapacitor is a supercapacitor using a metal oxide having several valences capable of redox. In the electrode active material of the metal oxide supercapacitor, the ions and electrons required for the redox need to be rapidly moved in the electrolyte and the electrode at the time of charging and discharging. Therefore, the electrode interface has a high specific surface area, and the electrode active material has high electrical conductivity Is required.

It is no exaggeration to say that the electrode material of the pseudocapacitor has been limited to ruthenium oxide (RuO ₂ ) until now. Ruthenium oxide has been reported to have a high specific storage capacity of 720 F / g per unit weight using a sol-gel method. However, its precursors are expensive, and since the ions required for redox are limited to penetrate the inside thereof, they have a disadvantage in that they are difficult to use in large quantities.

Recent studies on metal oxide electrode materials include the development of new metal oxide electrode materials with higher capacity per unit weight, the study of increasing the specific surface area of metal oxide electrode materials to increase their capacity, and the reduction of electrode resistance closely related to the output characteristics. Emphasis is placed on technology development and low-cost production process development. Metal oxide electrode materials developed for these purposes include manganese dioxide (MnO ₂ ), vanadium oxide (V ₂ O ₅ ), nickel oxide (NiO), cobalt oxide (Co ₃ O ₄ ), molybdenum oxide (MoO ₃ ), and Ruthenium-based composite oxides; However, most of these materials are manufactured by an electrochemical process such as a sol-gel process or an electrochemical deposition, which is limited to a small amount of production and has difficulty in controlling the composition and impurity content of the component. Therefore, it is necessary to develop a low-cost metal oxide capable of exhibiting a high specific capacitance that can replace ruthenium oxide, and to mass-produce and control components by a simple process.

In addition, methods for forming a metal oxide complex with a carbon material have been attempted. Among them, the carbon material has a relatively large specific surface area and is therefore suitable as an electrode for supercapacitors. Activated carbon used in the electric double layer capacitor is 1,000 m ² / g or more and had but has a specific surface area of the low electrical conductivity, but has a carbon material excellent electrical conductivity such as carbon black The specific surface area of from about 10 m ² / g or less Is very low. Therefore, the supercapacitor electrode prepared by impregnating metal oxides on these carbon materials shows a tendency to greatly decrease the capacity during high-speed charging and discharging even though it exhibits a high specific capacitance during low-speed charging and discharging.

Therefore, in order to overcome the above problems, there is a need for a metal oxide / carbon composite electrode for supercapacitors capable of maintaining high specific capacitances of metal oxides even at high speeds.

Accordingly, the inventors of the present invention provide iron oxide nanos having high specific capacitance through oxidation and reduction reactions on the surface of carbon nanotubes having excellent conductivity in order to prepare the electrode active materials for supercapacitors having the high specific capacitance and excellent charge / discharge cycle stability. As a result of uniform introduction of the particles, the present inventors found that the above-described electrochemical properties were satisfactory and completed the present invention.

The present invention has been made in view of the above problems, in order to obtain a supercapacitor electrode having excellent electrochemical characteristics, the raw material is low in price, high conductivity and iron oxide nanoparticles capable of mass production and component control It is an object of the present invention to provide a method for manufacturing a supercapacitor electrode capable of maintaining a high specific capacitance even at high charge and discharge by affixing to a surface of a carbon nanotube, and a supercapacitor electrode manufactured by the above method.

In order to achieve the above object, the present invention provides a method for producing a supercapacitor electrode of carbon nanotubes to which iron oxide nanoparticles are attached, and a supercapacitor electrode manufactured by the above method.

The present invention (1) activating the carbon nanotube surface; (2) depositing iron oxide nanoparticles on the surface of the activated carbon nanotubes; And (3) mixing and coating the iron oxide / carbon nanotube composite, a binder, and a conducting agent, to provide a method of manufacturing an electrode for a supercapacitor.

According to the present invention as described above, there is an effect of providing an electrode for a supercapacitor having an improved electrochemical specific capacitance and stable cycle characteristics.

In addition, by attaching and fixing iron oxide nanoparticles that can be mass-produced and control the composition of materials on the surface of carbon nanotubes with high conductivity, they can maintain a high specific capacitance even at high charge and discharge due to mutual complementation between the two materials. There is an effect of providing an electrode for a supercapacitor.

In addition, the electrode material for the supercapacitor according to the above method can be expected to have excellent performance when used for the light weight of the small-weight electrochemical energy storage device, large output pulse power and peak power.

1 is an X-ray diffraction diagram showing the structural characteristics of the carbon nanotubes, iron oxide, iron oxide / carbon nanotube composites prepared in Examples 1 to 4 and Comparative Examples 1 and 2.
FIG. 2 is a view showing surface characteristics of carbon nanotubes (a) acid-treated by transmission electron microscope and carbon nanotubes (b) containing 50% iron oxide.
3 is a view showing charge and discharge characteristics of the carbon nanotubes, iron oxides, iron oxide / carbon nanotubes composite electrodes prepared in Examples 1 to 4 and Comparative Examples 1 and 2.
4 is a view showing a change in specific capacitance according to the charge and discharge cycle of the carbon nanotube, iron oxide, iron oxide / carbon nanotube composite electrode prepared in Examples 1 to 4 and Comparative Examples 1 and 2.

Hereinafter, the present invention will be described in detail.

The present invention provides a method for producing a supercapacitor electrode made of carbon nanotubes to which iron oxide nanoparticles are attached, and a supercapacitor electrode manufactured by the method.

Specifically, the manufacturing method of the electrode for the supercapacitor of the present invention comprises the steps of: (1) activating the surface of the carbon nanotubes; (2) depositing iron oxide nanoparticles on the surface of the activated carbon nanotubes; And (3) mixing and coating the iron oxide / carbon nanotube composite, a binder, and a conductive agent.

As a first step, the carbon nanotubes activate the surface of the carbon nanotubes in order to attach the iron oxide nanoparticles.

The activation method is sulfuric acid to the introduced amount control of the reaction by high-temperature acid-treated in a carbon nanotube in a strong acid solution of iron oxide nanoparticle (H ₂ SO _4), hydrochloric acid (HCl), nitric acid (H ₂ NO ₃₎ that of It is preferable to use one or two or more liquid mixtures, and it is preferable that reaction temperature is 60-120 ^degreeC .

As a second step, the iron oxide nanoparticles are attached to the surface of the activated carbon nanotubes in order to produce an electrode for a supercapacitor having further improved specific capacitance and charge / discharge characteristics.

Impregnation of the iron oxide was dispersed carbon nanotubes, the surface-activated in an aqueous alkali solution characterized in that it is prepared by co-precipitation with Fe ^{2 +} Fe ^{3 +} cations and cations.

At this time, the alkaline aqueous solution is to adjust the pH, and there are sodium hydroxide (NaOH), aqueous ammonia solution (NH ₄ OH), potassium hydroxide (KOH) and the like, any one of the compounds that are water-soluble base, such as iron oxide crystal To prevent excessive growth, it is recommended to slowly add alkaline solution to keep the pH of the mixture at 10-13.

In addition, the Fe ^{2 +} cation is ferrochloride (FeCl ₂ · 4H ₂ O), iron acetate (Fe (CH ₃ CO ₂ ) ₂ , iron (II) gluconate (Fe (C ₆ H ₁₁ O ₇ ) ₂ ) , iron (II) sulphate (FeSO _4), and the like, and thus not particularly limited in the form of compounds containing these metals can be used as long as it is soluble in water. Furthermore, the Fe ^{3 +} cations are iron (III ) hydroxide (Fe (OH) _3), iron (III) and the like, phosphate (FePO _4), ferric chloride _{(FeCl 3? 6H 2 O)} , this also is not particularly limited.

In addition, it is preferable to synthesize the iron oxide nanoparticles by coprecipitation of FeCl _{2 ~} 4H ₂ O and FeCl _{3 ~} 6H ₂ O, in addition to the hydrothermal method or an electrochemical deposition method may be used. At this time, the precursor is represented by a ligand containing Fe ^{2 +} and Fe ^{3 +} , wherein the ligand can be used by selecting one or more from the group consisting of chloride, acetic acid, gluconate, sulfate, hydroxide, phosphate However, in order to synthesize iron oxide having a desired nano-size diameter, the above-described FeCl _{2 ~} 4H ₂ O and FeCl _{3 ~} 6H ₂ O is most preferred.

In addition, it is preferable to use ultrasonic waves to evenly disperse the iron ions on the surface of the carbon nanotubes, and the excessive use of ultrasonic waves may cause an increase in the aqueous solution temperature.

In addition, it is possible to control the electrochemical properties of the iron oxide / carbon nanotube composite electrode by changing the content of the iron oxide, iron oxide is preferably mixed in an amount of 10 to 70 parts by weight based on 100 parts by weight of carbon nanotubes.

In addition, the iron oxide nanoparticles preferably have a particle size of 3 ~ 30nm.

In the third step, the iron oxide / carbon nanotube composite is prepared by mixing poly (vinylidene fluoride) as a binder and carbon black as a conductive agent in an N-methyl pyrrolidone solvent to prepare a slurry and coating the nickel foam current collector. It is preferable to manufacture an electrode for supercapacitors.

In addition, the content of the iron oxide / carbon nanotube composite, the binder and the conductive agent is preferably mixed by 80:10:10 to prepare an electrode.

In addition, a protic aqueous solution may be used as an electrolyte during coating, preferably sulfuric acid (H ₂ SO ₂ ), sodium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), sodium sulfite (Na ₂ SO It is preferable to use at least one aqueous solution selected from the group consisting of ₃ ), most preferably 1.0 M Na ₂ SO ₃ aqueous solution.

The prepared electrode is preferably dried at 60 ° C. for about 12 hours in a vacuum oven to remove residual solvent.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are provided to illustrate the present invention, but the scope of the present invention is not limited thereto.

In the present invention, each characteristic value was measured by the following method.

1. Morphology of Iron Oxide / Carbon Nanotube Composites

The morphology of the iron oxide nanoparticles and the iron oxide / carbon nanotube composite was observed through a transmission electron microscope (Hitachi S-4200, Hitachi, Japan).

2. Structural Analysis of Iron Oxide / Carbon Nanotube Composites

X-ray diffraction analysis (Rigaku D / MAX, Rigaku, Japan) confirmed the structure of iron oxide and carbon nanotubes.

3. Analysis of Supercapacitor Characteristics of Electrode

The charge and discharge characteristics or cycle stability of the prepared electrode measured the specific capacitance after repeated 1000 times of constant current charge and discharge experiments.

Example  One

A multilayer carbon nanotube (Nanosolution, average diameter: 10-20 nm, average length: 50 µm) was immersed in 100 ml of a sulfuric acid / nitric acid (3: 1) mixed solution, and reacted at 100 ° C. for 12 hours, followed by distilled water. Washed and dried in oven for 8 hours to prepare.

Through the acid treatment, 1g of carbon nanotubes activated with an oxygen functional group were dispersed in 200ml of secondary distilled water by ultrasonic waves. After thoroughly _{FeCl 2? 4H 2 O (0.035g} ) and FeCl _3? 6H ₂ O into the (0.075g) and stirred mechanically with ultrasonic treatment in a nitrogen gas atmosphere at 50 ° C (see Table 1).

Sufficiently, 10 ml of 8.0 M NH ₄ OH solution was slowly added to the dispersed carbon nanotube and iron ions to form iron oxide. At this time, the pH of the mixed solution was mechanically stirred for 1 hour at 50 ° C. while maintaining a 10-13.

The chemical reaction to form iron oxide follows the following (Equation 1).

[Formula 1]

^{2Fe 3 + + Fe 2 + +} 8OH - → Fe 3 O 4 + 4H 2 O

After stirring, the iron oxide / carbon nanotube composite was separated from the mixed solution using a magnet. After separation, the mixture was washed sufficiently with secondary distilled water until the pH was neutral, and washed three more times with ethanol. Thereafter, it was dried completely at 100 ^° C. for 12 hours in a vacuum oven.

The structural changes and surface properties of the iron oxide / carbon nanotube composites obtained by the above method were measured and the results are shown in FIGS. 1 and 2.

Example  2

1g of the carbon nanotubes activated by the oxygen functional group through acid treatment was added to 200ml of secondary distilled water and dispersed by ultrasonication, followed by FeCl ₂ ? 4H ₂ O (0.143g) and FeCl ₃ ? 6H ₂ O (0.285 g) was added and mechanically stirred with sonication under nitrogen gas atmosphere at 50 ° C. (see Table 1).

The structural changes and surface properties of the iron oxide / carbon nanotube composites obtained by the above method were measured and the results are shown in FIGS. 1 and 2.

Example  3

1g of the carbon nanotubes activated by the oxygen functional group through acid treatment was added to 200ml of secondary distilled water and dispersed by ultrasonication, followed by FeCl ₂ ? 4H ₂ O (0.165g) and FeCl ₃ ? 6H ₂ O (0.335 g) was added and mechanically stirred with ultrasonication at 50 ° C. under nitrogen gas atmosphere (see Table 1).

The structural changes and surface properties of the iron oxide / carbon nanotube composites obtained by the above method were measured and the results are shown in FIGS. 1 and 2.

Example  4

1g of the carbon nanotubes activated by the oxygen functional group through acid treatment was added to 200ml of secondary distilled water and dispersed by ultrasonication, followed by FeCl ₂ ? 4H ₂ O (0.78g) and FeCl ₃ ? 6H ₂ O (1.56 g) was added and mechanically stirred with sonication under nitrogen gas atmosphere at 50 ° C. (see Table 1).

The structural changes and surface properties of the iron oxide / carbon nanotube composites obtained by the above method were measured and the results are shown in FIGS. 1 and 2.

Comparative example  One.

Purified carbon nanotubes were used as the electrode active material for the supercapacitor, and the electrodes described above were prepared using the same (see Table 1).

The structural changes and surface properties of the iron oxide / carbon nanotube composites obtained by the above method were measured and the results are shown in FIGS. 1 and 2.

Comparative example  2.

Iron oxide nanoparticles were prepared under the condition that no carbon nanotubes were present and used as an electrode active material for a supercapacitor, and the electrodes described above were prepared using the electrode (see Table 1).

The structural changes and surface properties of the iron oxide / carbon nanotube composites obtained by the above method were measured and the results are shown in FIGS. 1 and 2.

Experimental Example  One.

Evaluation of the electrochemical characteristics of the supercapacitor according to the preferred embodiment of the present invention as described above was performed as follows.

The specimens prepared in Examples 1-4 and Comparative Examples 1 and 2 were used as the electrode active materials, poly (vinylidene fluoride) (PVDF) was used as the binder, and carbon black was used as the conductive material. And the conductive agent constituted the electrode at a weight ratio of 80:10:10. The components of the electrode were stirred with an N-methyl pyrrolidone (NMP) solvent to prepare a slurry, and then coated on a nickel foam current collector having a size of 1 × 1 cm to prepare an electrode.

Further, the electrolytic solution was used as the protic aqueous solution of 1.0 M Na ₂ SO ₃ solution.

In addition, a platinum wire was used as a counter electrode, and a silver / silver chloride (Ag / AgCl) electrode was used as a reference electrode.

Each electrode manufactured as described above was performed in a dry room where vacuum was maintained. The measurement was performed after immersion for 24 hours in the prepared electrolyte solution before the discharge test.

The capacity of the prepared electrode is defined as follows.

[Formula 2]

The capacitance of the supercapacitor electrode is the product of the voltage change and the capacitance of the electrode, and the unit is F (farad), but divided by the weight (g) of the active material to compare the capacitance per weight of the active material (F / g) As shown.

The capacitance change of the iron oxide / carbon nanotube electrodes prepared as in Examples 1 to 4 and Comparative Examples 1 and 2 is shown in Table 2.

As a result, the iron oxide / carbon nanotube electrode material has the effect that the electrochemical properties vary depending on the content of the iron oxide particles introduced, the most excellent when the electrode is composed of carbon nanotube powder containing 50% of iron oxide Chemical properties and high capacity per unit weight were obtained. The initial specific storage capacity of the iron oxide prepared in [Comparative Example 2] is 250 F / g, whereas the initial storage capacity is very high, whereas the stability of the charge / discharge cycle is poor. Indicated. However, when the iron oxide nanoparticles were deposited on the surface of the carbon nanotubes, the initial specific storage capacity was reduced to 165 F / g, but showed an excellent charge and discharge efficiency of 86.7%.

As described above, specific portions of the contents of the present invention have been described in detail, and for those skilled in the art, these specific techniques are merely preferred embodiments, and the scope of the present invention is not limited thereto. Will be obvious. Accordingly, the substantial scope of the present invention will be defined by the appended claims and their equivalents.

Claims (19)

(1) activating the carbon nanotube surface;
(2) depositing iron oxide nanoparticles on the surface of the activated carbon nanotubes; And
(3) mixing and coating the iron oxide / carbon nanotube composite, a binder, and a conductive agent; and a method of manufacturing an electrode for a supercapacitor of carbon nanotube material to which the iron oxide nanoparticles are attached.
The method of claim 1,
The activation of the step (1) is a method for producing a supercapacitor electrode, characterized in that the acid treatment of carbon nanotubes in a strong acid solution at a high temperature.
The method of claim 2,
The strong acid solution is a method of manufacturing an electrode for a supercapacitor, characterized in that using one or two or more of a mixture of sulfuric acid (H ₂ SO ₄ ), hydrochloric acid (HCl), nitric acid (H ₂ NO ₃ ).
The method of claim 2,
The high temperature is a manufacturing method of the electrode for a supercapacitor, characterized in that 60 ~ 120 ℃.
The method of claim 1,
The (2) Impregnation of the step iron oxide is carried out using that after dispersing the carbon nanotubes, the surface-activated in an aqueous alkaline solution at least one of Fe ^{2 +} cations and Fe ^{3 +} cations the coprecipitation method, a hydrothermal method and an electrochemical vapor deposition method The manufacturing method of the electrode for supercapacitors characterized by the above-mentioned.
6. The method of claim 5,
The alkaline aqueous solution is a method of manufacturing an electrode for a supercapacitor, characterized in that the pH 10-13 at least one selected from the group consisting of sodium hydroxide (NaOH), aqueous ammonia (NH ₄ OH) and potassium hydroxide (KOH) solution.
6. The method of claim 5,
The Fe ^{2 +} cations Faroe chloride (FeCl ₂ and 4H ₂ O), iron acetate _{(Fe (CH 3 CO 2)} 2, iron (II) gluconate _{(Fe (C 6 H 11 O} 7) 2) and iron (II) A method for producing an electrode for supercapacitors, characterized in that at least one member selected from the group consisting of sulfate (FeSO ₄ ).
6. The method of claim 5,
The Fe ^{3 +} cations are iron (III) hydroxide (Fe (OH) _3), iron (III) phosphate (FePO _4), and ferric chloride, at least one member selected from the group consisting of (FeCl _3? 6H ₂ O) Method for producing an electrode for supercapacitors, characterized in that.
6. The method of claim 5,
In the coprecipitation method, a hydrothermal method, and electrochemical deposition the precursor is at least one selected from the group consisting of ligands containing a Fe ^{2 +} and Fe ^{3 +} as chloride, acetate, inclusive nose carbonate, sulfate, hydroxide, phosphate A method of manufacturing an electrode for supercapacitors, characterized in that.
6. The method of claim 5,
The dispersion is a method of manufacturing an electrode for a supercapacitor, characterized in that the ultrasonic treatment for 10 to 50 minutes.
The method of claim 1,
The iron oxide nanoparticles of step (2) is a method for producing a supercapacitor electrode, characterized in that the mixture of 10 to 70 parts by weight based on 100 parts by weight of carbon nanotubes.
The method of claim 1,
The iron oxide nanoparticles of step (2) is a method for producing a supercapacitor electrode, characterized in that it has a particle size of 3 ~ 30nm.
The method of claim 1,
The binder of step (3) is a manufacturing method of the electrode for the supercapacitor, characterized in that the vinylidene fluoride (CH ₂ CF ₂ ).
The method of claim 1,
The conductive material of step (3) is a method of manufacturing an electrode for a supercapacitor, characterized in that the carbon black (carbon black).
The method of claim 1,
Mixing of the step (3) is a method of manufacturing an electrode for a supercapacitor, characterized in that the mixing in N-methyl pyrrolidone solvent.
The method of claim 1,
In step (3), the iron oxide / carbon nanotube composite, the content of the binder and the conductive agent is a method of manufacturing an electrode for a supercapacitor, characterized in that the mixing in 80:10:10.
The method of claim 1,
In the step (3), the electrolyte is coated with sulfuric acid (H ₂ SO ₂ ), sodium hydroxide (KOH), lithium hydroxide (LiOH), sodium hydroxide (NaOH), sodium sulfite (Na ₂ SO ₃ ) as a protic aqueous solution. Method for producing a supercapacitor electrode, characterized in that at least one selected from the group consisting of.
The method of claim 1,
The supercapacitor electrode is a manufacturing method of the electrode for a supercapacitor, characterized in that it further comprises a 60 ℃, 12 hours drying in a vacuum oven.
An electrode for a supercapacitor made of carbon nanotubes to which iron oxide nanoparticles prepared by the method of any one of claims 1 to 18 are impregnated.

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