JP2005251941A - Activated carbon for capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an activated carbon for capacitors which realize a high capacity, low resistance and long life time for electric double-layer capacitors. <P>SOLUTION: The activated carbon for the capacitor is made of coal containing ≥200 ppm transition metal. In the activated carbon, a mean diameter of 1 to 50 μm, BET ratio surface area is ≥2,000 m<SP>2</SP>/g and a pore volume is ≥1 mL/g, and the transition metal is contained by 200 to 10,000 ppm. The activated carbon has the effect of realizing the electric double-layer capacitor having superior characteristics. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to activated carbon for capacitors, and more particularly to activated carbon for capacitors used as an electrode material for electric double layer capacitors.

  In recent years, electric double layer capacitors have been attracting attention as a power source that has an ultra-large capacity instead of a conventional battery power source and is excellent in charge / discharge characteristics and quick chargeability.

  The electron conductor forms a very thin charge-separated layer of molecular level, commonly referred to as an electric double layer. This is due to the electron tunnel effect. The electric double layer capacitor is based on the principle that electric charges are accumulated in the electric double layer.

  Activated carbon is used as an electrode material for electric double layer capacitors because of its large surface area. For example, Patent Documents 1 to 4 disclose activated carbon that can be used for electrodes of electric double layer capacitors.

  Patent Document 1 discloses an electric double layer capacitor using activated carbon in which the amount of impurities such as Fe is limited. Furthermore, Patent Document 1 describes that the long-term reliability of a capacitor decreases when the amount of impurities in the activated carbon increases.

  Patent Documents 2 to 3 disclose activated carbon in which a metal compound such as Fe is intentionally supported later. Patent Document 4 discloses a production method in which a metal compound is supported on a raw material of activated carbon. The activated carbon disclosed in these patent documents increases the conductivity of the activated carbon itself by supporting a metal on the activated carbon.

In the electric double layer capacitor, when the capacity is increased, the ion concentration in the pores of the activated carbon is increased, and the ion migration resistance in the pores most contributing to the resistance performance is lowered. That is, in the electric double layer capacitor, it is difficult to simultaneously improve the capacitance, internal resistance, and durability.
Japanese Laid-Open Patent Publication No. 1-224111 JP 2002-43191 A JP 2002-367860 A JP 2001-210564 A

  This invention is made | formed in view of the said actual condition, and makes it a subject to provide the activated carbon for capacitors which can implement | achieve high capacity | capacitance, low resistance, and lifetime improvement for an electric double layer capacitor.

  In order to solve the above problems, the present inventors have repeatedly studied activated carbon for capacitors, and as a result, the activated carbon containing a transition metal component that has been removed as impurities in the past with a predetermined content is solved. I found out that I can do it.

That is, the activated carbon for a capacitor of the present invention is manufactured from coal containing 200 ppm or more of transition metal, has an average particle diameter of 1 to 50 μm, a BET specific surface area of 2000 m ² / g or more, and a pore volume of 1 mL / g or more. And containing a transition metal at 200 to 10000 ppm.

  The activated carbon for a capacitor of the present invention can realize high capacity, low resistance, and long life when an electric double layer capacitor is formed. That is, the electric double layer capacitor having excellent characteristics can be realized.

  The activated carbon for capacitors of the present invention is activated carbon containing a transition metal at 200 to 10,000 ppm. By containing a transition metal in the activated carbon, the conductivity of the activated carbon increases. As a result, in the electric double layer capacitor using the activated carbon for a capacitor of the present invention, the resistance is reduced by reducing the resistance of the electrode.

  Moreover, the transition metal contained in activated carbon exists in the state taken in in the structure of activated carbon. With this structure, when the activated carbon itself and the electric double layer capacitor are formed by the catalytic effect of the transition metal, the electrolytic solution is not decomposed. Specifically, since the transition metal is taken into the structure of the activated carbon, the transition metal does not elute into the electrolyte even when the electric double layer capacitor is formed. Thereby, it can suppress that a transition metal decomposes | disassembles electrolyte solution and shortens the lifetime of an electrical double layer capacitor.

  Furthermore, when the transition metal which is a transition metal is contained in the activated carbon, oxygen atoms can be removed by the reduction action of the transition metal, and gas generation can be suppressed in the capacitor cell. As a result, the electric double layer capacitor using the activated carbon for capacitors of the present invention has a long life.

  If the amount of transition metal contained in the activated carbon is less than 200 ppm, the transition metal-containing effect cannot be obtained. If the amount of transition metal contained in the activated carbon exceeds 10,000 ppm, the activated carbon contains a large amount of impurities other than the transition metal, making it unsuitable as a capacitor activated carbon. A more preferable transition metal content is 200 to 5000 ppm.

  The transition metal contained in the activated carbon is not particularly limited as long as it is a transition metal. When there are a plurality of transition metals contained in the activated carbon, the total is preferably 200 to 10,000 ppm. The transition metal is preferably Fe.

The activated carbon for capacitors of the present invention is activated carbon having an average particle diameter of 1 to 50 μm, a BET specific surface area of 2000 m ² / g or more, and a pore volume of 1 mL / g or more.

  When the average particle diameter of the activated carbon is less than 1 μm, the electrode density is lowered and the capacitance of the capacitor is lowered. When the average particle diameter is more than 50 μm, the electrode density is similarly lowered and the capacitance of the capacitor is lowered.

The specific surface area of the activated carbon has a correlation with the capacity of the electric double layer capacitor. And a high capacity | capacitance electric double layer capacitor is obtained because a BET specific surface area becomes 2000 m < ² > / g or more. When the BET specific surface area is less than 2000 m ² / g, a high-capacity electric double layer capacitor cannot be obtained.

  The pore volume of activated carbon correlates with the specific surface area of activated carbon. That is, as the pore volume increases, the specific surface area increases. When the pore volume is less than 1 mL / g, activated carbon having a large specific surface area cannot be obtained, and a high-capacity electric double layer capacitor cannot be obtained.

  The activated carbon for capacitors of the present invention is manufactured from coal containing 200 ppm or more of transition metal. This coal contains a transition metal inside. By producing activated carbon from coal containing a transition metal inside in advance, activated carbon containing a transition metal inside can be produced. In the activated carbon for capacitors of the present invention, the transition metal contained in the raw material coal becomes the transition metal contained in the activated carbon described above. That is, the transition metal contained in the activated carbon is not particularly limited as long as it is a transition metal. The transition metal is preferably Fe.

  Coal contains transition metal at 200 ppm or more, so that activated carbon produced from this coal contains transition metal at 200 ppm or more. The transition metal contained in the coal is preferably 200 to 10,000 ppm, and more preferably 200 to 5000 ppm.

The activated carbon for capacitors of the present invention is preferably manufactured from coal having a volatile content of 20 wt% or less. The volatile matter of coal means that when coal is heated to a high temperature rapidly in an inert gas such as nitrogen or argon, the side chain part or bridge part of the polymer matrix of coal is cleaved by pyrolysis, resulting in low molecular weight carbonization. Low-boiling components such as hydrogen, CO, and H ₂ are generated and released in the form of gas to the outside of the particles. This is the so-called volatile matter of coal. That is, coal with a small volatile content has a high carbon density. Activated carbon produced from coal having a high carbon density also has a high carbon density, and a high capacitance can be obtained when used as an activated carbon for capacitors. If the volatile content exceeds 20 wt%, the carbon density of the coal is low, so the carbon density of the activated carbon produced from the coal is also low, and sufficient capacitance as the activated carbon for capacitors cannot be obtained. More preferable volatile matter of coal is 10 wt% or less. The volatile matter of coal can be measured by a method defined in JIS M8812.

  It is preferable that the ash is produced from coal of 5 wt% or less. The ash content of coal indicates the mass percentage of the amount of ash remaining when coal is heat ashed, and coal with a large distribution contains many impurities other than carbon. That is, activated carbon produced from coal with low ash content has high carbon purity. As a result, when used as an activated carbon for a capacitor, impurities are not eluted into the electrolytic solution, deterioration of the electrolytic solution is suppressed, and durability is improved. When the distribution exceeds 5 wt%, the electrolytic solution is deteriorated, which is not preferable as the activated carbon for capacitors. A more preferable coal ash content is 2 wt% or less. The ash content of coal can be measured by a method defined in JIS M8812.

  Examples of such coal include coal classified into anthracite, some subbituminous coal, lignite, and the like. As coal, it is more preferable to use anthracite.

  Production of activated carbon from coal containing 200 ppm or more of transition metal can be performed using a conventionally known method. That is, it can be manufactured by subjecting coal containing 200 ppm or more of transition metal to carbonization treatment, oxidation treatment, and activation treatment. In addition, these processes are suitably selected according to the state of coal containing 200 ppm or more of transition metal.

  For the carbonization treatment, for example, a method of steaming and burning raw material coal using a carbonization furnace or a method of heating in an inert gas atmosphere can be used.

  The activation treatment develops pores of carbonized coal and controls the pore diameter. As the activation treatment, advanced activation or chemical activation can be used. More preferably, it is an alkali activation treatment.

  The alkali activation treatment is a treatment method in which carbonized coal is mixed with an alkali compound and heat treatment is performed in an inert gas atmosphere. The amount of the alkali compound is preferably mixed in an amount of 0.5 to 5 times the equivalent of coal, more preferably 1.5 to 2.5 times the equivalent. Examples of the alkali compound include compounds such as KOH and NaOH. Moreover, 600-900 degreeC is preferable and the heating temperature at the time of an activation process has more preferably 750-850 degreeC. The heating time is preferably 0.5 to 10 hours, more preferably 3 to 5 hours.

  In order to make activated carbon containing 200 ppm or more of Fe, coal having no caking property as a raw material preferably contains 200 ppm or more of Fe. More preferably, it is 200-5000 ppm.

  Furthermore, it is preferable to perform a sizing treatment before the activation treatment when producing activated carbon from coal containing 200 ppm or more of transition metal. In the sizing treatment, the particle size of the carbonized coal is adjusted. By performing the sizing treatment, activation can be performed without causing unevenness when the activation treatment is performed. Specifically, the activated carbon is uniformly applied to each particle because the size of coal carbonized by the sizing treatment is uniform. As a result, unevenness does not occur in the pore size of the activated carbon to be produced, and the characteristics of the activated carbon are improved. It is preferable that the particle diameter of coal subjected to the activation treatment by this sizing treatment is 10 to 200 μm. More preferably, it is 20-100 micrometers.

  The sizing treatment is not particularly limited as long as it can treat the size of the carbonized coal. For example, the process which crushes carbonized coal and then sieving can be mentioned.

  The capacitor activated carbon of the present invention can produce an electric double layer capacitor having a high capacity, a low resistance and a long life when a capacitor electrode is formed. From the activated carbon for a capacitor according to the present invention, an electric double layer capacitor can be produced by using a conventionally known method, similarly to the electrode material of a conventional electric double layer capacitor.

  For example, the activated carbon for a capacitor of the present invention, a conductive material, and a binder are blended at a predetermined ratio and kneaded, and the kneaded product is rolled to produce an electrode plate. And it can manufacture by enclosing two electrode plates in a case in the state which interposed the separator with electrolyte solution.

  Hereinafter, the present invention will be described using examples.

  As an example of the present invention, activated carbon for capacitors was manufactured.

(Example)
First, coal containing Fe at 1000 to 2000 ppm was selected. Here, the Fe content in the coal was measured using a fluorescent X-ray analyzer (trade name: PW-1480, manufactured by PHILIPS).

  Moreover, the volatile matter and ash content of the selected coal were volatile matter: 10 wt% and ash content: 2 wt%. The volatile content and ash content were measured by the method defined in JIS M8812.

  The selected coal was fully carbonized. And the selected coal was sieved so that a particle size might be set to 100-300 micrometers.

  Thereafter, the selected coal was subjected to activation treatment with alkaline chemicals. As the activation treatment, it was mixed with KOH equivalent to twice the amount of coal, and subjected to a heat treatment (potassium activation treatment) at 800 ° C. for 4 hours in a nitrogen gas atmosphere.

  The activated carbon obtained by the activation treatment was washed with water until the amount of potassium (K) in the wastewater was 10000 ppm or less.

  The activated carbon for a capacitor of this example was manufactured by the above treatment.

The pore distribution, average particle diameter, BET specific surface area, pore volume and Fe content of the activated carbon for capacitors of this example were measured. The pore distribution, BET specific surface area, and pore volume were measured using a powder fluid measuring device (manufactured by Yuasa Ionics Co., Ltd., trade name: NOVA-3000), and the measurement results are shown in FIG. The measurement result of the average particle diameter was 10 μm. The pore volume was 1.16 mL / g. The measurement of the BET specific surface area was 2450 m ² / g. The Fe content of the activated carbon for a capacitor was 1800 ppm as measured in the same manner as the measurement of the Fe content of coal having no caking properties.

(Comparative Example 1)
Coal containing Fe at 15 ppm was treated in the same manner as in the example, to produce activated carbon for capacitors of this comparative example.

  Moreover, the volatile matter and ash content of the raw material coal were volatile content: 25 wt% and ash content: 5 wt%. The volatile content and ash content were measured by the method defined in JIS M8812.

The activated carbon for capacitors of this comparative example had an average particle size: 9 μm, a pore volume: 1.02 mL / g, a BET specific surface area: 2300 m ² / g, and an Fe content: 15 ppm. The measurement results of the pore distribution are also shown in FIG.

(Comparative Example 2)
3.65 g of iron acetylacetonate was blended with 30 g of petroleum mesophase pitch, and they were sufficiently pulverized and mixed using a mortar. The mixture was infusibilized at 480 ° C. for 90 minutes in an air stream. The mixture melted and formed a lump by cooling. The lump was pulverized to obtain a powder. This powder contains Fe at 1300 ppm.

  The volatile matter and ash content of this powder were volatile content: 30 wt% and ash content: 2 wt%. The volatile content and ash content were measured by the method defined in JIS M8812.

  The powder obtained by pulverization was carbonized at 700 ° C. for 1 hour in a nitrogen stream to obtain a carbide.

  The resulting carbide powder was mixed with KOH twice the weight thereof, and the mixture was subjected to an alkali activation treatment (potassium activation treatment) at 800 ° C. for 5 hours in a nitrogen stream to obtain activated carbon.

  The activated carbon was then pickled, washed with water, filtered and dried in sequence.

  The activated carbon for capacitors of this comparative example was obtained by the above procedure.

The activated carbon for capacitors of this comparative example had an average particle size: 9 μm, a pore volume: 1.10 mL / g, a BET specific surface area: 2400 m ² / g, and an Fe content: 1300 ppm.

(Comparative Example 3)
1 g of cobalt chloride (CoCl ₂ ) is dissolved in about 50 ml of distilled water, 3 g of activated carbon fine particles having a BET specific surface area of 3000 m ² / g are added to this solution, and the mixture is stirred with an ultrasonic cleaner for about 4 hours. The solution was well soaked inside. This activated carbon powder does not contain a transition metal. Moreover, this activated carbon powder was activated carbon powder manufactured from coal, and the volatile matter and ash content of the raw material coal were volatile content: 30 wt% and ash content: 1 wt%. The volatile content and ash content were measured by the method defined in JIS M8812.

  Thereafter, the activated carbon was filtered and added to a 1 mol / liter aqueous sodium hydroxide solution to precipitate a hydroxide and an oxide from which the hydroxide was dehydrated.

  The solution was filtered, further washed with water and air-dried, and then dried in air at about 150 ° C. for 12 hours using a dryer.

  The activated carbon for capacitors of this comparative example was obtained by the above procedure. In the activated carbon for capacitors of this comparative example, Co is supported on the surface of the activated carbon as a raw material.

The activated carbon of this comparative example had an average particle size: 9 μm, a pore volume: 1.07 mL / g, a BET specific surface area: 2350 m ² / g, and a Co content (supported amount): 1600 ppm.

(Evaluation)
First, the electric double layer capacitor was created using the activated carbon for a capacitor of an Example and a comparative example.

A compound in which activated carbon for capacitors, carbon black (conductive material), and PTFE (binder) were blended at a weight ratio of 80:10:10 was sufficiently kneaded. The resulting mixture was rolled to form a circle having a thickness of 0.1 mm and an area of 2 cm ² to produce an electrode.

The manufactured electrode was sealed in a coin-type cell together with a 1 mol / L TEA · BF ₄ PC (propylene carbonate) solution (electrolytic solution) to produce a button-type electric double layer capacitor.

  Subsequently, the capacitance, internal resistance, and durability performance of the created button type electric double layer capacitor were measured. The measurement results of capacitance, internal resistance, and durability performance are shown in Table 1 and FIGS. Here, the measurement of electrostatic capacity, internal resistance, and durability performance was performed using the charging / discharging apparatus (the Hokuto Denko company make, brand name: HJR1001SM8).

The capacitance is room temperature (20 ° C.), the voltage is 2.5 V, the current is ² mA / cm ² , and the CC-CV charge is performed for 5 minutes until the fully charged state is 2.5 V in 5 minutes. 100% discharge was performed. The slope of the discharge curve during this discharge was taken as the capacitance value.

  The internal resistance was calculated from an IR drop in which the voltage immediately after the start of discharge of the charge / discharge curve at the time of measuring the electrostatic capacitance decreased stepwise.

Durability performance is room temperature (20 ° C), voltage is 2.5V, current is 2mA / cm ² , CC-CV charge to 2.5V fully charged in 5 minutes and put in 70 ° C constant temperature bath. The capacitance after 100 hours was measured, and the rate of decrease from the 0-hour capacitance was calculated as the deterioration rate. At this time, the deterioration rate in a predetermined time between 0 and 100 hours was also measured. In addition, the measurement method of the said electrostatic capacitance was used for the measurement of the electrostatic capacitance at the time of measurement of a deterioration rate.

表１より、実施例のキャパシタ用活性炭から製造されたキャパシタ（以下、実施例のキャパシタとする）は、比較例１のキャパシタ用活性炭から製造されたキャパシタと比較しても、性能が向上していることがわかる。すなわち、実施例のキャパシタ用活性炭は比較例１のキャパシタ用活性炭と細孔分布、細孔容積およびＢＥＴ比表面積がほぼ同等であったが、これらのキャパシタ用活性炭から製造されたキャパシタにおいては性能の差が明らかである。具体的には、実施例のキャパシタは、１７．１Ｆ／ｍｌと高い静電容量、１．７１Ωと低い内部抵抗値および７．０％と低い劣化率が得られたことから、高容量化、低抵抗化および長寿命化が達成できた。

Table 1 shows that the capacitor manufactured from the activated carbon for capacitor of the example (hereinafter referred to as the capacitor of the example) has improved performance compared to the capacitor manufactured from the activated carbon for capacitor of Comparative Example 1. I understand that. That is, the capacitor activated carbon of the example had substantially the same pore distribution, pore volume, and BET specific surface area as the capacitor activated carbon of Comparative Example 1, but the capacitors manufactured from these capacitor activated carbons had the same performance. The difference is clear. Specifically, the capacitor of the example has a high capacitance of 17.1 F / ml, a low internal resistance value of 1.71 Ω, and a low deterioration rate of 7.0%. Low resistance and long life could be achieved.

  In addition, the activated carbon for capacitor of the example is the activated carbon for capacitor of Comparative Example 2 manufactured by supporting Fe as a raw material, the activated carbon for capacitor of Comparative Example 3 supported in the post-activation after activation, the Fe content, the pore volume. Although the BET specific surface areas were almost the same, the difference in performance was obvious in the capacitors manufactured from these activated carbons for capacitors. Specifically, the capacitor manufactured from the activated carbon for the capacitor of the example has a high capacitance of 17.1 F / ml and a low deterioration rate of 7.0%, and thus has a high capacity and a long life. It has been realized.

  As described above, the activated carbon for a capacitor according to the embodiment can realize high capacity, low resistance, and long life when an electric double layer capacitor is formed. That is, the electric double layer capacitor having excellent characteristics can be realized.

It is the diagram which showed the pore distribution of the activated carbon for capacitors of an Example and Comparative Examples 1-3. It is the graph which showed the electrostatic capacitance and internal resistance value of the electric double layer capacitor manufactured from the activated carbon for capacitors of an Example and a comparative example. It is the graph which showed the measurement result of the endurance performance of the electric double layer capacitor manufactured from the activated carbon for capacitors of an example and a comparative example.

Claims (4)

It is manufactured from coal containing 200 ppm or more of transition metal, has an average particle size of 1 to 50 μm, a BET specific surface area of 2000 m ² / g or more, a pore volume of 1 mL / g or more, and a transition metal of 200 to 10,000 ppm. Capacitor activated carbon characterized by containing. The activated carbon for capacitors according to claim 1, wherein the transition metal is iron (Fe). The activated carbon for a capacitor according to claim 1, which is produced from coal having a volatile content of 20 wt% or less. The activated carbon for a capacitor according to claim 1, wherein the activated carbon is produced from coal having an ash content of 5 wt% or less.

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