KR101324279B1

KR101324279B1 - Complex of nickel oxide and activated graphite nanofiber and electrode for super capacitor including the complex

Info

Publication number: KR101324279B1
Application number: KR1020120022403A
Authority: KR
Inventors: 박수진; 유혜민
Original assignee: 인하대학교 산학협력단
Priority date: 2012-03-05
Filing date: 2012-03-05
Publication date: 2013-11-01
Also published as: KR20130101335A

Abstract

According to the present invention, an activated graphite nanofiber containing nickel oxide nanoparticles obtained by preparing an optimal activated graphite nanofiber having a high specific surface area by weight using an activator and then supporting nickel oxide by a chemical supporting method and The present invention relates to an electrode for a high capacity supercapacitor using the same, and the nickel oxide / active graphite nanofiber composite prepared according to the present invention exhibits a high energy capacity and thus may be usefully used as a high capacity supercapacitor electrode having an excellent energy density.

Description

Nickel oxide / active graphite nanofiber composites and electrodes for supercapacitors including the composites TECHNICAL FIELD

The present invention relates to a nickel oxide / active graphite nanofiber composite and a supercapacitor electrode including the composite, and more particularly, to prepare an optimal active graphite nanofiber having a high specific surface area by weight ratio using an activator. The present invention relates to an activated graphite nanofiber containing nickel oxide nanoparticles obtained by supporting nickel oxide using a chemical supporting method, and an electrode for a high capacity supercapacitor using the same.

In order to prevent global warming due to carbon dioxide generation, clean energy sources have become an important issue for humankind. Accordingly, the development of photovoltaic power generation, wind power generation and hybrid electric vehicles is being actively performed, and the development of stable and excellent energy accumulation system is required.

Supercapacitor or ultracapacitor refers to a capacitor having a very large capacity, and may be referred to as an energy storage device of a different category from conventional capacitors and batteries.

The difference can be divided by the energy density and the power density value. The supercapacitor has a higher energy density than the conventional capacitor, but has a smaller value than the battery. However, power density and cycle life are much higher than those of batteries.

Conventional supercapacitors mainly used transition metal oxides, conductive polymers, and the like, and ruthenium oxides, in particular, exhibit the best characteristics as electrodes.

However, in the case of the transition metal oxide, although the electrode material of the shooter capacitor shows a very good energy density and output density, the development of an optimal material that can replace it due to the expensive raw material is domestic patent registration No. 10-0649092, etc. In recent years, supercapacitor research has been steadily progressing.

In particular, development of transition metal oxides that can replace expensive ruthenium oxides is ongoing, but capacitors having transition metal oxides as electrodes have a problem in that cycle characteristics and stability are deteriorated. Difficulties have arisen in the application and practical use.

In addition, in order for the transition metal oxide to be used as an electrode material of a shooter capacitor, it is necessary to satisfy conditions such as generation of a continuous surface redox reaction in a wide specific surface area and an available potential region.

Therefore, the inventors of the present invention, while researching electrode materials having low cost, large specific surface area, excellent power density, and cycle stability, have low cost NiO, MnO ₂ , CoO _x, and V ₂ O that can replace the expensive ruthenium oxide. _A metal oxide such as ₅ was prepared in the form of a nanocomposite obtained by being supported and fixed on a graphite nanofiber, which is a carbon material, as a support to increase the capacitance value.

In addition, by activating the graphite nanofibers carbon material before supporting the metal oxide to prepare a support having an optimal specific surface area value of the material to complete the present invention.

As a result, the present invention has been made to solve the above problems and the necessity of the above, the main object of the present invention is nickel oxide / obtained by effectively complexing nickel oxide nanoparticles with activated graphite nanofibers having an optimum specific surface area value / An active graphite nanofiber composite and a supercapacitor electrode using the composite are provided.

In order to achieve the above object, the present invention provides a nickel oxide / activated graphite nanofiber composite and a manufacturing method thereof.

In addition, the present invention provides a supercapacitor electrode including the nickel oxide / active graphite nanofiber composite.

According to the present invention as described above, the electrode was manufactured by depositing a metal oxide layer electrochemically by a constant current method or a cyclic potential current method by spinning with an electrospinning method on the current collector, but the present invention The metal oxide is characterized in that it can be prepared by relatively simple and inexpensive support on the carbon support by a chemical reduction method.

In addition, the activated graphite nanofibers containing nickel oxide nanoparticles prepared according to the present invention, that is, the nickel oxide / active graphite nanofiber composites exhibit high energy capacity and thus are useful as high capacity supercapacitor electrodes having excellent energy density. Can be.

Figure 1 is a scanning electron micrograph of the active graphite nanofibers by weight ratio of the activator according to an embodiment of the present invention.
2 is an X-ray diffraction graph confirming the support of nickel oxide according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

The present invention provides a nickel oxide / active graphite nanofiber composite in which nanoparticles of nickel oxide are supported on activated graphite nanofibers having an optimum specific surface area.

In the present invention, the graphite nanofiber is one of the carbon support, 100 ~ 150 nm in diameter, 25 ~ 30 ㎛ in length is preferably straight (straight), to produce an active graphite nanofiber having an optimal specific surface area value In order to do this, pretreatment with an activator is preferred.

At this time, the pretreatment is preferably using any one of potassium hydroxide (KOH), sodium hydroxide (NaOH) or zinc chloride (ZnCl ₂ ) as the activator, the activator 1 to 1 by weight based on the graphite nanofibers. 5 times is better to use.

Further, in the present invention, the nickel oxide / active graphite nanofiber composite is characterized in that the nickel oxide is supported by 15 to 60% by weight relative to the active graphite nanofiber, finally containing 9 to 33% by weight of nickel oxide, The nickel oxide has a particle size of 5 to 50 nm.

In addition, the present invention provides a method for producing the nickel oxide / activated graphite nanofiber composite.

The method for producing a nickel oxide / active graphite nanofiber composite of the present invention comprises the steps of: (1) activating graphite nanofibers; (2) dispersing nickel nitrate in the activated graphite nanofibers in a neutral solution; And (3) chemically reducing the activated graphite nanofibers in which the nickel nitrate is dispersed using an alkaline solution.

In this case, in the step (1), the graphite nanofibers are preferably activated by pretreatment of the linear graphite nanofibers having a diameter of 100 to 150 nm and a length of 25 to 30 μm with an activator, and the activator is potassium hydroxide (KOH). ), Using either 1 to 5 times the weight ratio of sodium hydroxide (NaOH) or zinc chloride (ZnCl ₂ ), based on graphite nanofibers, to increase the specific surface area to have an optimal specific surface area. good.

In addition, the graphite nanofibers preferably include a step of carbonizing at 800 to 900 ℃ upon activation.

In addition, in step (2), ultrasonic waves may be used to evenly disperse nickel ions in the graphite nanofibers. Preferably, the nickel nitrate is added to 15 to 60% by weight with respect to the activated graphite nanofibers, it is good to disperse using ultrasonic waves for 20 to 30 minutes.

In addition, in the step (3), it is preferable to first change the solution to an alkaline atmosphere of pH 11-12, and then add a reducing agent. In this case, it is preferable to slowly add the alkaline solution to evenly disperse the crystals of nickel oxide in the graphite nanofibers.

In addition, formaldehyde (HCHO) may be used as the reducing agent, and the alkaline solution may be any compound which shows basicity in water solubility such as sodium hydroxide (NaOH), aqueous ammonia solution (NH ₄ OH) or potassium hydroxide (KOH). Can be.

Alternatively, in the step (3), it is possible to produce the nickel oxide / activated graphite nanofiber composite of the present invention by a reduction method of changing the solution to an alkaline atmosphere of pH 11-12, and heat treatment in an oxygen atmosphere.

The nickel oxide / active graphite nanofiber composite of the present invention prepared by the above method contains nickel oxide in an amount of 9 to 33% by weight, and the nickel oxide has a particle size of 5 to 50 nm.

In addition, since the nickel oxide / active graphite nanofiber composite of the present invention has a high charge capacity, it is useful as an electrode for high capacity supercapacitors of excellent energy density.

Accordingly, the present invention provides an electrode for a high capacity supercapacitor comprising the nickel oxide / active graphite nanofiber composite.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these examples are for illustrative purposes only and that the scope of the present invention is not construed as being limited by these examples.

Example 1.

1 g of graphite nanofibers and 1 g of KOH were added to 50 ml of distilled water, stirred for at least 6 hours, dried in an oven to remove distilled water, and then heated to 800 ° C. under a nitrogen atmosphere in a tubular furnace at a temperature rising rate of 5 ° C./min. Heat treatment for 1 hour.

To remove KOH residue, treatment with 0.5 N HCl for 6 hours or more, wash thoroughly with distilled water until the pH is neutral, and completely dry in vacuum oven over 100 ℃ for 12 hours to activate activated graphite nano Fibers were prepared.

Example 2.

Activated graphite nanofibers were prepared in the same manner as in Example 1, but 2 g of KOH was used.

Example 3.

An active graphite nanofiber was prepared in the same manner as in Example 1, but 4 g of KOH was used.

Example 4.

Activated graphite nanofibers were prepared in the same manner as in Example 1, but 5 g of KOH was used.

Example 5.

1 g of graphite nanofibers and 1 g of KOH were added to 50 ml of distilled water, stirred for at least 6 hours, dried in an oven to remove distilled water, and then heated up to 900 ° C. at a temperature rising rate of 5 ° C./min. Under a nitrogen atmosphere in a tubular furnace. Heat treatment for 1 hour, and to remove KOH residue, after treatment with 0.5 N HCl for 6 hours or more, washed thoroughly with distilled water until the pH is neutral, for 12 hours in a vacuum oven of 100 ℃ or more It was completely dried to prepare activated graphite nanofibers.

Table 1 shows, was clean the N _2/77 K the structure of an active graphite nanofibers prepared in Examples 1 to 5, 1 is observing the above-prepared active graphite nanofiber in the scanning microscope picture.

sample S _BET
(M < 2 > / g) V _Total
(Cm3 / g) V _Micro
(Cm3 / g) V _Meso
(Cm3 / g) D _P
(Nm) Comparative Example 1 133 0.219 0.010 0.209 6.5 Example 1 216 0.347 0.035 0.312 6.4 Example 2 658 0.650 0.158 0.492 3.9 Example 3 970 1.048 0.208 0.840 4.3 Example 4 166 0.235 0.042 0.193 5.4 Example 5 712 0.801 0.150 0.651 4.5

In the above _description , S _BET is a specific surface area calculated using the Brunauer-Emmett-Teller equation in a relative pressure range of 0.03 to 0.22, and V _Total is an estimated value of total pore volume at a relative pressure P / P0 = 0.990. In addition, V _Micro is a volume excluding mesopore volume from V _Total , V _Meso is a mesopore volume determined from Barret-Joyner-Halenda (BJH), and D _p is an average pore diameter.

Example 6.

1 g of activated graphite nanofibers prepared by treating KOH at 4 times (w / w) with respect to graphite nanofibers were placed in 200 ml of distilled water and dispersed by ultrasonic treatment for 20 to 30 minutes. 0.15 g (15% by weight) of nickel nitrate was added to 1 g of the active graphite nanofibers and dispersed again by ultrasonic and mechanical stirring.

In order to prevent oxidation of nickel nitrate in the air before loading, nitrogen gas was injected and carried out under a nitrogen atmosphere. 20 ml of a 2 M NaOH solution was formed to form nickel oxide in a mixture of sufficiently dispersed active graphite nanofibers and nickel ions. Was added slowly. At this time, the pH of the mixed solution was maintained from 11 to 12, and 3 ml of formaldehyde (HCHO) was slowly added as a reducing agent.

The mixed solution was mechanically stirred at 80 ° C. for 1 hour to prepare a nickel oxide / active graphite nanofiber composite through a chemical reduction method in which nickel oxide was supported on activated graphite nanofibers.

Example 7.

A nickel oxide / active graphite nanofiber composite was prepared in the same manner as in Example 6, but 0.30 g (30 wt%) of nickel nitrate was added to 1 g of the active graphite nanofiber.

Example 8.

A nickel oxide / active graphite nanofiber composite was prepared in the same manner as in Example 6, but 0.45 g (45 wt%) of nickel nitrate was added to 1 g of the active graphite nanofiber.

Example 9.

A nickel oxide / active graphite nanofiber composite was prepared in the same manner as in Example 6, but 0.60 g (60 wt%) of nickel nitrate was added to 1 g of the active graphite nanofiber.

Example 10.

1 g of activated graphite nanofibers prepared by treating KOH amount at 4 times (w / w) with respect to graphite nanofibers was placed in 200 ml of ethylene glycol and dispersed by ultrasonic treatment for 20 to 30 minutes. When dispersed, 0.45 g (45 wt%) of nickel nitrate was added to 1 g of the active graphite nanofibers, and dispersed again by ultrasonic and mechanical stirring.

In order to prevent oxidation of nickel nitrate in the air before loading, it was carried out under nitrogen atmosphere by injecting nitrogen gas, and 20 ml of 2 M NaOH to form nickel oxide in a mixture of sufficiently dispersed active graphite nanofibers and nickel ions. After the solution was slowly added, it was mechanically stirred at 120 ° C. for 1 hour.

Then, after heating up to 300 ° C. at an elevated temperature rate of 5 ° C./min. In an oxygen atmosphere in a muffle furnace, nickel oxide / active graphite is supported by converting nickel into nickel oxide through a heat treatment under a condition of maintaining for 2 hours. Nanofiber composites were prepared.

Table 2 below shows the nickel oxide content of the nickel oxide / active graphite nanofiber composites prepared in Examples 6 to 10.

sample Ni content (wt.%) Example 6 9 Example 7 21 Example 8 33 Example 9 26 Example 10 15

Comparative Example.

Graphite nanofibers not carrying nickel oxide were prepared as comparative examples.

Experimental Example 1. Electrode production and charge / discharge experiment

An electrode was prepared using the active graphite nanofibers and the nickel oxide / active graphite nanofiber composites prepared in the above examples as electrode materials.

Specifically, 0.8 g of electrode material powder, 0.1 g of polyvinyldifluoride (PVDF) and 0.1 g of carbon black (SUPER-P, SEMYUNG EVER ENERGY, KOREA) were used as 10 ml N-methylpyrrolidone (N- methyl pyrrolidon) was mixed as a solvent and stirred for 30 minutes using a mechanical stirrer to prepare a slurry.

The slurry was coated on a nickel (Ni) form using a doctor blade to a thickness of about 0.2 mm, dried at room temperature, dried once again under vacuum and 110 ° C, and then pressed. .

The prepared electrode material was used as a working electrode, Ag / AgCl was used as a reference electrode, and Pt electrode was used as a counter electrode, respectively, and measured at room temperature using 6 M KOH solution.

The voltage range was set from ?? 0.6 V to 0.4 V, and the specific capacitance value was calculated by experimenting with 0.5 Ag ^-1 as the current density.

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

Measurement Example 1. Measurement of Specific Surface Area of Carbon Support

The surface structure characteristics of the activated graphite nanofibers prepared according to the present invention were measured by adsorbing nitrogen gas under 77 K in a liquid nitrogen atmosphere. After the nitrogen adsorption isotherm experiment, BET (Brunauer- Emmett-Teller) specific surface area was calculated.

Measurement Example 2 Surface Observation of Carbon Support

Surfaces before and after modification of the activated graphite nanofibers prepared according to the present invention were observed through a scanning electron microscope (Scanning Electron Microscope, SEM; S-4200, Hitachi, Japan) (see Fig. 1).

Measurement Example 3 Structure Analysis of Electrode Material

The electrode material for the supercapacitor prepared according to the present invention was confirmed by the X-ray diffraction analysis (X-ray Diffractometer, XRD; D / MAX 2200V / PC, Regaku) to confirm the structure of the nickel oxide / activated graphite nanofibers, The supported amount of nickel oxide supported using an inductively coupled plasma mass spectrometer (ICP-MS; ELAN6100, Perkin Elmer) was investigated.

Measurement example 4. Electrode material Charging and discharging characteristic

In order to confirm the electrical properties as an electrode material, specific capacitances of farads were calculated using 0.5-Ag- ¹ as the current density using an Electronic-Chemical Analyzer (IVIUMSTAT, HS Technology).

Reaction condition Specific surface area
(㎡g ^-1 ) Nickel oxide
Support amount (wt.%) Storage capacity
(Fg ^-1 ) Comparative Example 1 - 133 - 2.3 Example 1 KOH 1 g, 800 ℃ 216 - 55 Example 2 KOH 2 g, 800 ℃ 658 - 59 Example 3 KOH 4 g, 800 ℃ 970 - 63 Example 4 KOH 5 g, 800 ℃ 166 - 34 Example 5 KOH 4 g, 900 ° C 712 - 59 Example 6 15 wt.% NiO,
Chemical Reduction Method - 9 122 Example 7 30 wt.% NiO,
Chemical reduction - 21 208 Example 8 45 wt.% NiO,
Chemical reduction - 33 360 Example 9 60 wt.% NiO,
Chemical reduction - 26 301 Example 10 45 wt.% NiO,
Heat treatment reduction - 15 180

Having described specific portions of the present invention in detail, those skilled in the art will appreciate that these specific descriptions are only for the preferred embodiment and that the scope of the present invention is not limited thereby. It will be obvious. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims

delete

(1) mixing and stirring graphite nanofibers and an activator;
(2) removing the residue of the activator to produce activated graphite nanofibers;
(3) adding nickel nitrate to the activated graphite nanofibers under a nitrogen atmosphere to stir; And
(4) adjusting the pH to 11-12 and then adding a reducing agent; Method for producing a nickel oxide / activated graphite nanofiber composite comprising the step.

6. The method of claim 5,
The graphite nanofiber in the step (1) is a method of producing a nickel oxide / activated graphite nanofiber composite, characterized in that the straight (straight) having a diameter of 100 ~ 150 nm and a length of 25 ~ 30 ㎛.

6. The method of claim 5,
In step (1), the activator is potassium hydroxide (KOH), sodium hydroxide (NaOH) or zinc chloride (ZnCl₂) characterized in that the manufacturing method of the nickel oxide / activated graphite nanofiber composite.

6. The method of claim 5,
In step (1), the activator is a method for producing a nickel oxide / activated graphite nanofiber composite, characterized in that the mixture by adding 1 to 5 times by weight based on the graphite nanofibers.

6. The method of claim 5,
After mixing and stirring the graphite nanofibers and the activator in the step (1), the nickel oxide / activated graphite nanofiber composites further comprising the step of carbonizing by heat treatment at 800 to 900 ℃ under a nitrogen atmosphere Way.

6. The method of claim 5,
In the step (3), the nickel nitrate is prepared by adding 15 to 60 parts by weight based on 100 parts by weight of the active graphite nanofibers, and stirring.

6. The method of claim 5,
In the step (4), after adjusting the pH to 11 to 12 using aqueous sodium hydroxide solution (NaOH), aqueous ammonia solution (NH₄OH) or aqueous potassium hydroxide solution (KOH), formaldehyde (HCHO) is added as a reducing agent. A method for producing a nickel oxide / active graphite nanofiber composite.

6. The method of claim 5,
After the addition of the reducing agent in the step (4), the method of producing a nickel oxide / activated graphite nanofiber composite, characterized in that it further comprises the step of stirring for 1 hour at 80 ℃.

13. A supercapacitor electrode comprising a nickel oxide / active graphite nanofiber composite prepared by the method of any one of claims 5 to 12.