KR101274989B1

KR101274989B1 - Electric double layer capacitor using doped carbon-based electrode

Info

Publication number: KR101274989B1
Application number: KR1020110098071A
Authority: KR
Inventors: 김용중; 이성영
Original assignee: 재단법인 포항산업과학연구원
Priority date: 2011-09-28
Filing date: 2011-09-28
Publication date: 2013-07-30
Also published as: KR20130034181A

Abstract

The present invention relates to an electric double layer capacitor, and more particularly, to a capacitor using a doped carbon-based electrode which has improved capacitance by doping a group 5 element and a group 3 element to the anode and cathode materials, respectively. Through this, a high capacity electric double layer capacitor can be provided even when using an aqueous electrolyte as well as an organic electrolyte.

Description

ELECTRIC DOUBLE LAYER CAPACITOR USING DOPED CARBON-BASED ELECTRODE}

The present invention relates to an electric double layer capacitor, and more particularly, to an electric double layer capacitor using a doped carbon-based electrode which has improved capacitance by doping the anode and cathode materials, respectively.

A capacitor is a device that can store electricity, and basically has a structure in which two electrode plates are opposed to each other, and is called a capacitor or a capacitor. An electric double layer capacitor is a reinforcement of the performance of the capacitor, in particular the capacity of the capacitor, and is a component used for the purpose of a battery, and a capacitor used in an electronic circuit has an electric rechargeable battery function.

The basic idea is to collect power and release it as needed, and it is one of the necessary parts to operate electronic circuits stably. It operates stably even after a long time in a repeated charging and discharging environment, and it is usually used for the purpose of supplying small power when the power is cut off while being charged from AC power. It is usually installed inside a device, and is used for safety devices that temporarily supply power to a setting memory or operate at a power failure.

An electric double layer capacitor is an energy storage device using a pair of charge layers (electric double layers) with different signs, which can be semi-permanently charged and discharged, and have good output characteristics compared to general storage batteries, resulting in short charge and discharge time, durability and Excellent stability and semi-permanent life. An electric double layer capacitor is generally composed of a cell constructed by placing two electrodes of a cathode and an anode facing each other with a separator interposed therebetween, and then impregnating the electrolyte.

However, the electric double layer capacitor has better output characteristics than the battery, but the energy storage density is lower than that of the general battery, as the voltage gradually decreases at the same time as the discharge and has a low operating voltage per cell.

Energy density (energy storage), which is one source of energy storage, is a good indicator for comparing the amount of energy in electric double layer capacitors as well as batteries. The energy density can be obtained by dividing the energy obtained by the following equation by the total volume of the electric double layer capacitor.

Energy (J) = 1 / 2CV ²

(C: capacitance F per cell, V; voltage applicable to the cell)

Energy is proportional to capacity C and voltage V ² . The capacitance is determined by the electrode material, and V is determined by the electrolyte solution used. Therefore, in order to increase the energy density of the electric double layer capacitor, it is necessary to develop an electrode material having a high capacitance and to develop an electrolyte having a large available voltage.

The capacitance of the electric double layer capacitor is determined by the amount of charge accumulated in the electric double layer. Therefore, the capacitance can be changed according to the characteristics of the dielectric as shown in the following equation.

C = ε ₀ * ε _r * S / δ

(C: capacitance, ε ₀ : vacuum dielectric constant, ε _r : relative dielectric constant, S: surface area of the electrode, δ: ion diameter.)

Since the storeable energy is proportional to the area forming the electrical double layer, a material having a high specific surface area such as activated carbon is suitable as an electrode. It is an activated carbon-based carbon electrode material that can satisfy these characteristics. In particular, a carbon electrode material having a very high carbon purity is required in order to lower electrical resistance. In addition, as the electrode material, metal oxides such as activated carbon, ruthenium oxide, and titanium oxide having a large specific surface area are used, but materials other than carbon electrodes are very expensive, and carbon is generally used the most.

In addition, a number of documents have been proposed for the carbon-based electrode material, but the present invention relates to a hybrid capacitor in which the positive electrode and the negative electrode are used as the same material or one electrode is replaced with a dissimilar material. However, this technique is complicated by using different materials. Therefore, a method of using the same material and improving its properties by a simple process is required.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor, and in order to expand the capacitance, an electrode material used for the positive electrode is doped with an element including a positive charge, and an electrode material used for the negative electrode is doped with an element containing a negative charge to induce high capacitance. To provide a capacitor that can.

One aspect of the present invention is an electric double layer capacitor, and includes a carbon-based anode doped with a Group 5 element and a carbon-based cathode doped with a Group 3 element.

The carbon-based anode and the cathode is preferably made of activated carbon.

Preferably, the activated carbon is one of carbon black, carbon nanotube (CNT), carbon nanofiber (CNF), vapor grown carbon fiber (VGCF), and graphite (Graphite). Do.

It is preferable that the said Group 5 element is nitrogen (N).

The doping amount of the nitrogen is preferably 1-30 at.%.

The doping layer of the carbon-based anode is preferably 1-10nm.

It is preferable that the said group 3 element is boron (B).

The boron doping amount is preferably 1-30 at.%.

The doping layer of the carbon-based negative electrode is preferably 1-10nm.

The capacitance of the capacitor is preferably 65 F / cc or more.

According to the present invention, the capacitance of the capacitor can be increased by reducing the solvation size of the electrolyte by the doped anode and cathode.

In addition, even in the case of using an organic electrolyte as well as an aqueous electrolyte, a high capacity electric double layer capacitor may be provided.

1 is a schematic diagram of a capacitor including a doped electrode as an embodiment of the present invention.
FIG. 2 is a graph illustrating an impedance change before and after nitrogen doping plasma treatment.
3 is a graph illustrating a relationship between a capacity per volume and a discharge current density before and after nitrogen doping plasma treatment.
4 is a graph illustrating a relationship between a capacity per weight and a discharge current density before and after nitrogen doping plasma treatment.

Hereinafter, the present invention will be described in detail.

The present inventors have realized that by introducing heterogeneous elements into the electrode material of a capacitor, it is possible to reduce the solvation size of the electrolyte and thereby increase the capacitance.

First, an electric double layer capacitor using a doped carbon electrode, which is an aspect of the present invention, will be described in detail.

The electric double layer capacitor basically includes a positive electrode, a negative electrode and an electrolyte. In the case of the aqueous electrolyte, the electrolyte and the electrode have increased capacitance by the Faraday reaction, but in the case of the organic electrolyte, this effect is not easy. The electrode of the present invention can provide a capacitor having a high capacity in the case of an aqueous electrolyte as well as an organic electrolyte.

The present invention provides an electrode having a polarity by doping heterogeneous elements in the electrode material used for the positive electrode and the negative electrode. The positive electrode may be doped with a Group 5 element to introduce a positive charge, and the negative electrode may be doped with a Group 3 element to introduce a negative charge.

However, in the present invention, it is preferable to apply nitrogen among group 5 elements and boron among group 3 elements.

1 shows a schematic diagram of an electric double layer capacitor as an embodiment of the present invention. In the electric double layer capacitor, a positive electrode 1 and a negative electrode 2 are opposed to each other, and the positive electrode 1 and the negative electrode 2 are connected to the power 3 and are impregnated in the electrolyte solution 4. Ions present in the electrolyte may move toward the electrode to exchange charges.

As described above, the capacitance is inversely proportional to the ion diameter contained in the electrolyte. When the positive charge is charged to the positive electrode, the negative charge present in the electrolyte is opposite to the positive electrode. When nitrogen in the Group 5 element is doped, nitrogen may be doped in Pyridinic type, and positive charges may be sufficiently introduced into the positive electrode by the combination of such nitrogen. When the ions contained in the electrolyte are adsorbed to the anode by such a positive charge, the diameter of the electron cloud is reduced to reduce the ion radius. Ion radius has an inverse relationship with capacitance, which increases the capacitance. In addition, the surface potential of the entire carbon electrode material according to nitrogen is moved in the positive direction to improve the decomposition stability at high voltage.

On the contrary, the negative electrode faces the positive charge included in the electrolyte, and in the case of the negative electrode doped with the Group 3 element, the negative electrode may further contain negative charges. Boron-containing carbon electrode material increases electron mobility according to the local potential change in the carbon grid and introduces opposite charges in the phase equilibrium of zero potential, thereby improving the overall polarization characteristics and adsorbing more ions. You have the ability.

According to the present invention, a carbon material may be used as a material of an electrode material for a capacitor, and as the carbon material, carbon black, carbon nanotube (CNT), carbon nanofiber (CNF), and vapor growth carbon fiber ( VGCF; Vapor Grown Cabon Fiber), graphite, and the like may be used, but are not necessarily limited thereto, and include all carbon materials capable of producing activated carbon including pores (pores) intended for the present invention during manufacture. can do.

The doping amount of the carbon-based positive electrode doped with the Group 5 element is preferably 1-30 at.%. In addition, the doping layer of the carbon-based anode is preferably 1-10nm. The doping amount represents at.% Of the Group 5 element present in the doping layer, and when the doping amount is 1-30 at.%, It is possible to secure the capacitance intended by the present invention.

In addition, the doping amount of the carbon-based positive electrode doped with the Group 3 element is preferably 1-30 at.%. In addition, the doping layer of the carbon-based negative electrode is preferably 1-10nm. The doping amount represents at.% Of the Group 3 element present in the doping layer, and when the doping amount is 1-30 at.%, It is possible to secure the capacitance intended by the present invention.

The doping described above in the present invention may be doped through plasma post-treatment. However, it is not necessarily limited to using the method of doping through the plasma post-treatment, and may include any method of doping an element.

The capacitance of the electric double layer capacitor including the cathode and the anode is preferably 30 ~ 40F / ㎠ per area. In addition, the capacitance per volume is preferably 65 F / cc or more.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

(Example)

The coke was pretreated at 600 ° C. and activated at 800 ° C., and KOH and NaOH were mixed 1: 1 to be used as the activator. The specific surface area of the activated carbon was 1100 m 2 / g. Electrodes were prepared, and the impedance spectra were measured and shown in FIG. 2, and the discharge current density and the capacity per volume are shown in FIGS. 3 and 4, respectively.

As shown in FIG. 2, when looking at the impedance result after the nitrogen plasma treatment, one semi-circle and a warburg impedance region appeared. It can be seen that the interface impedance between the electrode and the electrolyte is significantly reduced by nitrogen doping.

As shown in FIG. 3, the current density showed a discharge capacity in the range of 10 milliamps to 400 milliamps per gram, and as the current density increases, the difference in the discharge capacity before and after the plasma increases.

As shown in FIG. 4, in the case of the capacity per volume, the current density was 53 F / cc before the plasma treatment at 100 mA / g, but increased to 65 F / cc after the plasma treatment.

1. anode,
2. cathode,
3. power,
4. Electrolyte.

Claims

A carbon-based anode doped with a Group 5 element; And
An electric double layer capacitor comprising a carbon-based negative electrode doped with a group 3 element, the capacitance of which is at least 65F / cc.

The method according to claim 1,
The carbon-based anode and cathode is an electric double layer capacitor, characterized in that made of activated carbon.

The method according to claim 2,
The activated carbon is one of carbon black, carbon nanotube (CNT), carbon nanofiber (CNF), vapor grown carbon fiber (VGCF), and graphite (Graphite). Electric double layer capacitor.

The method according to claim 1,
The Group 5 element is an electric double layer capacitor, characterized in that nitrogen (N).

The method of claim 4,
Doping amount of the nitrogen is an electric double layer capacitor, characterized in that 1-30at.%.

The method according to claim 1,
The doped layer of the carbon-based anode is an electric double layer capacitor, characterized in that 1-10nm.

The method according to claim 1,
The group III element is an electric double layer capacitor, characterized in that boron (B).

The method of claim 7,
Doped amount of boron is an electric double layer capacitor, characterized in that 1-30at.%.

The method according to claim 1,
The doped layer of the carbon-based cathode is an electric double layer capacitor, characterized in that 1-10nm.

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