WO2015146459A1

WO2015146459A1 - Activated carbon, method for producing activated carbon and method for treating activated carbon

Info

Publication number: WO2015146459A1
Application number: PCT/JP2015/055656
Authority: WO
Inventors: 慶三猪飼; 正利西田; 政喜藤井
Original assignee: Ｊｘ日鉱日石エネルギー株式会社
Priority date: 2014-03-27
Filing date: 2015-02-26
Publication date: 2015-10-01

Abstract

Provided are: an activated carbon that can sustain a high electrostatic capacity and show excellent output characteristics and high durability when used in an electric double-layer capacitor or a lithium ion capacitor; and a method for producing the activated carbon. The activated carbon has a specific surface area measured by the BET method of 1500-2500 m²/g and an average particle diameter (D₅₀) of 0.5-5 μm, shows a gentle peak assignable to d002 when measured using a wide-angle X-ray diffractometer, and carries not more than 0.5 meq/g of a surface functional group.

Description

Activated carbon, method for producing activated carbon, and method for treating activated carbon

The present invention relates to activated carbon, particularly activated carbon that is optimal for use in electric double layer capacitors and lithium ion capacitors.

Electric double layer capacitors (EDLCs) and lithium ion capacitors (LICs) have been studied as auxiliary power sources used for engine restarts after no-idling of automobiles, but their output and durability are improved. Thus, activated carbon for electrodes is required to improve performance.

The conventional activated carbon produced by using soft carbon as a raw material and activated using an alkali activator exhibits a high capacitance when used in an electric double layer capacitor or a lithium ion capacitor. However, this activated carbon is inferior to the output and durability of an electric double layer capacitor and a lithium ion capacitor compared to activated carbon obtained by using hard carbon such as coconut shell as a raw material and performing activation treatment using water vapor.

In Patent Document 1, activated carbon is manufactured, and an electric double layer capacitor is manufactured. In this manufacturing method, the surface of the carbonized material is nitrogenated and then activated. This method has a problem that nitride remains in the activated carbon after the activation treatment. In addition, there is a problem that the surface of the carbonized material becomes too hard due to nitriding, and the carbonized material is not sufficiently activated by the nitride.

In Patent Document 2, commercially available activated carbon is pulverized and used for an electric double layer capacitor. In this method, when the activated carbon is pulverized, the pores may be significantly damaged, or oxidation may occur due to friction during the pulverization and the surface functional groups may increase. As a result, a problem occurs in the durability performance of the activated carbon.

Patent Document 3 describes activated carbon having an average particle size of 5 μm or less. This activated carbon has extremely excellent electrical characteristics, but it is intended to directly obtain activated carbon having a small particle size, and a further excellent activated carbon has been demanded.

JP 2008-195559 A JP 2000-294461 A JP 2009-013012 A

An object of the present invention is to provide activated carbon excellent in power output and durability, activated carbon production method, and activated carbon treatment method while maintaining high capacitance when used in electric double layer capacitors and lithium ion capacitors. .

Investigating activated carbon that can provide the output and durability of these capacitors while maintaining the capacitance of electric double layer capacitors and lithium ion capacitors. As a result, if the activated carbon has a large specific surface area, a small particle diameter, a gentle peak derived from d002 measured using a wide-angle X-ray diffraction apparatus, and a small number of surface functional groups, the electric double layer capacitor It was found that the output and durability of these capacitors can be imparted while maintaining the capacitance of the lithium ion capacitors. And it discovered that the said activated carbon could be obtained by grind | pulverizing and heat-processing the activated carbon of the predetermined particle diameter obtained by activating treatment of soft carbon with an alkali activator.

That is, the activated carbon according to the present invention has a specific surface area by the BET method of 1500 m ² / g to 2500 m ² / g, an average particle diameter (D ₅₀ ) of 0.5 μm to 5 μm, and a wide-angle X-ray diffraction apparatus. It is activated carbon in which a gentle peak derived from d002 measured by use can be observed, and the surface functional group is 0.5 meq / g or less.
Another aspect of the present invention is a method for producing activated carbon, which includes a carbonization step for carbonizing soft carbon, and a soft carbon having an average particle diameter (D ₅₀ ) of 0.5 μm to 10 μm after the carbonization step. An activation treatment step of activating the carbide obtained by mixing the carbide with an alkali activator, a washing step of washing the activation product obtained by the activation treatment step, and a wet crushing step of wet crushing the activation product after the washing step; The activated product after the wet pulverization step is dry pulverized so that the average particle size (D ₅₀ ) of the activated product is 0.5 μm to 5 μm, and the activated product after the dry pulverization step is not treated. This is a method for producing activated carbon including at least a heat treatment step in which heat treatment is performed at a temperature of 400 ° C. to 700 ° C. under an atmosphere in which 10% by volume or less of hydrogen is added to an active gas or under reduced pressure.
In another aspect, the present invention is a method for treating activated carbon, wherein the treatment method has an average particle diameter (D ₅₀ ) of 5 μm to 10 μm, and a specific surface area by a nitrogen gas adsorption method of 1500 m ² / g to 2500 m ² / g. Activated carbon having an average pore diameter of 1.7 nm to 3.0 nm, a total pore volume of 0.5 ml / g to 2 ml / g, and an alkali metal content of 1000 mass ppm or less is dry-pulverized to obtain an average particle diameter At least a dry pulverization step (D ₅₀ ) of 0.5 μm to 5 μm and a heat treatment step of heat-treating the activated carbon after the dry pulverization step at a temperature of 400 ° C. to 700 ° C. in an inert atmosphere or under reduced pressure. It is the processing method of the activated carbon containing.

When the activated carbon having a predetermined particle diameter obtained by activating soft carbon with an alkali activator was pulverized and heat-treated, the specific surface area was hardly reduced. And it was possible to obtain activated carbon having a smaller particle diameter and fewer surface functional groups than activated carbon obtained by activating soft carbon with an alkali activator by a conventional method. The obtained activated carbon has a small particle size, a large surface area, and a small number of functional groups on the surface. Therefore, when used for an electric double layer capacitor or a lithium ion capacitor, the durability of these capacitors can be improved.

Wide-angle X-ray diffraction spectra of activated carbons of Example 1-2, Example 2-1, and Reference Example 1-1. It is a perspective view explaining the structure of a laminate cell.

Hereinafter, one aspect of the embodiment of the present invention will be described. However, the present invention is not limited to the embodiments described below.

First, the activated carbon of the present invention will be described. The activated carbon of the present invention has a specific surface area according to the BET method of 1500 m ² / g to 2500 m ² / g, an average particle diameter (D ₅₀ ) of 0.5 μm to 5 μm, and is measured using a wide-angle X-ray diffraction apparatus. A gentle peak derived from d002 can be observed, and the surface functional group is 0.5 meq / g or less.

Activated carbon having a specific surface area of less than 1500 m ² / g and activated carbon having a specific surface area of greater than 2500 m ² / g are inferior in nitrogen gas adsorption characteristics. Therefore, even if such activated carbon is used, the rate characteristics and float characteristics of the electric double layer capacitor electrode and the lithium ion capacitor electrode cannot be satisfied. When the specific surface area is 1500 m ² / g to 2500 m ² / g, the adsorption property of nitrogen gas is excellent. As a result, the rate characteristics and float characteristics of the electric double layer capacitor electrode and the lithium ion capacitor electrode can be satisfied.

When the average particle diameter (D ₅₀ ) of the activated carbon is 0.5 μm to 5 μm, the output and durability of the electric double layer capacitor electrode and the lithium ion capacitor electrode can be improved. When the average particle diameter is less than 0.5 μm or more than 5 μm, the output and durability of the capacitor electrode cannot be improved.

A gentle peak derived from d002 measured using a wide-angle X-ray diffraction apparatus is a characteristic indicating that it originates from soft carbon (graphitizable carbon). When the amorphous carbon starts to have a three-dimensional stacking regularity, a gentle peak can be observed in the early stage when the amorphous carbon starts to have crystallinity. This peak is a measure of the occurrence of microcrystals due to the beginning of three-dimensional stacking regularity.

When the surface functional group of the activated carbon is 0.5 meq / g or less, preferably 0.05 to 0.5 meq / g, more preferably 0.1 to 0.45 meq / g, an electric double layer capacitor electrode or lithium ion The output and durability of the capacitor electrode can be improved. When the surface functional group is larger than 0.5 meq / g, the output and durability of the capacitor electrode cannot be improved.

If activated carbon satisfying the above-mentioned specific surface area conditions is used for electric double layer capacitors and lithium ion capacitors, the output and durability of the power source can be improved while maintaining the high capacitance of these capacitors.

Next, a method for producing the activated carbon of the present invention will be described. The method for producing activated carbon includes at least a carbonization step, an activation treatment step, a cleaning step, a wet pulverization step, a dry pulverization step, and a heat treatment step.

The carbonization step in the method for producing activated carbon is a step of carbonizing soft carbon. Carbonization of soft carbon is due to a decrease in volatile matter. When the volatile matter is removed, the subsequent process of pulverization becomes easy. Moreover, it becomes easy to activate with an alkali activator. The carbonization condition of the soft carbon is such that the firing temperature is preferably 500 ° C. to 700 ° C., and the carbonization time is about 10 minutes to 2 hours as the holding time after reaching the target temperature. The firing temperature is more preferably 520 ° C. to 680 ° C. If it is this temperature range, activation by an alkali activator will become easy by carbonizing. However, when it exceeds around 700 ° C., it becomes difficult to activate. The cause is thought to be the start of the development of the graphite structure.

Soft carbon used as a starting material, that is, graphitizable carbon materials include carbonized petroleum coke and coal coke, etc., and mesophase pitch and mesophase pitch fiber spun from it, infusible and carbonized, etc. be able to. In the present invention, petroleum coke is preferred, and petroleum coke that is still taken out of the coker with this petroleum coke is particularly preferred. Petroleum raw coke preferably used as a starting material in the present invention is a laminated assembly of polycyclic aromatic compounds having an alkyl side chain, and is a heat-infusible solid.

Petroleum coke is a product mainly composed of solid carbon obtained by coking, which decomposes a heavy fraction of petroleum at a high temperature of about 500 ° C, and is clearly distinguished from ordinary coal-based coke. Called coke. There are two types of petroleum coke: the delayed coking method and the fluid coking method. Today, the majority is based on the delayed coking method.

The volatile content of raw coke produced by the delayed coking method is usually 6 to 13% by mass. On the other hand, the volatile content of raw coke produced by the fluid coking method is usually 4 to 7% by mass. In the present invention, raw coke produced by any method can be used. The use of the delayed coking method is particularly preferable because production of raw coke is easy and the quality is stable.

The heavy fraction of petroleum is not particularly limited, but heavy oil obtained as residual oil when petroleum is distilled under reduced pressure, heavy oil obtained by fluid catalytic cracking of petroleum, and petroleum Heavy oil obtained by hydrodesulfurization, and mixtures thereof.

The activation treatment step in the method for producing activated carbon is a step in which, after the carbonization step, the soft carbon carbide having an average particle size (D ₅₀ ) of 0.5 μm to 10 μm is mixed with an alkali activator and activated. After carbonizing soft carbon, activation treatment is performed using an alkali metal hydroxide.

The reaction conditions for the activation treatment in the activation treatment step are not particularly limited as long as the activation treatment reaction can sufficiently proceed. The activation reaction can be performed under the same reaction conditions as those of a known activation treatment performed in normal production of activated carbon.

The activation reaction in the activation treatment step can be carried out by mixing an alkali metal hydroxide, which is usually produced in activated carbon, with the soft carbon carbide and heating. The temperature condition during heating is preferably 400 ° C. or higher, more preferably 600 ° C. or higher, and still more preferably 700 ° C. or higher. This is because the activation process is sufficiently performed under such temperature conditions. In addition, the upper limit of the temperature at the time of a heating will not be specifically limited if it is the temperature which an activation reaction advances without trouble. Usually, it is preferably 900 ° C. or lower.

Examples of the alkali metal hydroxide used for the activation reaction in the activation treatment step include KOH, NaOH, LiOH, RbOH, and CsOH. Among these, KOH and NaOH are preferably used from the viewpoint of the activation effect. These alkali metal hydroxides can be used singly or in combination.

The alkali activation reaction is performed by mixing an activator such as an alkali metal hydroxide and a soft carbon carbide and heating the mixture. The mixing ratio of the carbide and the activator is not particularly limited. However, considering the cost and activation of the activator, the mass ratio of the carbide to the activator is preferably in the range of 1: 0.5 to 1: 5, and more preferably in the range of 1: 1 to 1: 3.

The soft carbon carbide used for the activation treatment has an average particle diameter (D ₅₀ ) of 0.5 μm to 10 μm. By using the carbide in such a range, the activation treatment is performed without any problem. When the average particle diameter of the carbide is less than 0.5 μm, it is not preferable because the particle diameter increases due to fusion of the carbide particles. Moreover, when the average particle diameter of the said carbide | carbonized_material is larger than 10 micrometers, since the particle diameter of activated carbon becomes larger than the target particle diameter, it is unpreferable. By setting the average particle diameter of the carbide to 1 μm to 8 μm, the two problems of “the fusion of the particles of the carbide” and “the particle diameter of the activated carbon becomes larger” can be more reliably eliminated. Is more preferable.

The soft carbon carbide may be one having an average particle diameter (D ₅₀ ) of 0.5 μm to 10 μm, and may include an adjusting step of preparing the carbide so as to have an average particle diameter in this range. The method for adjusting the average particle size is not particularly limited, but usually, a method of pulverizing with a pulverizing means such as a jet mill can be employed. The pulverization can be performed on the soft carbon carbide after the carbonization step, and may be performed on the soft carbon before the carbonization step.

The washing step in the method for producing activated carbon is a step of washing the activation product obtained by the activation treatment step. If the alkali metal remains in the activation material, there is a possibility of adverse effects when the electric double layer capacitor is formed. Therefore, the alkali metal is removed by a cleaning process. If the amount of alkali metal in the activated material is 1000 ppm by mass or less by this washing step, the performance of the electric double layer capacitor is not affected. For example, if the activation material is washed until the pH of the washing waste water reaches about 7 to 8, the alkali metal content can be sufficiently removed. As a method of cleaning the activated material, a method of washing the activated material with a cleaning liquid and performing solid-liquid separation can be employed. For example, the activator may be immersed in a cleaning solution, stirred and heated as necessary, mixed with the cleaning solution, and then removed.

It is preferable to use water and an acid aqueous solution as the cleaning liquid. For example, washing with water and washing with an acid aqueous solution can be appropriately combined, such as washing with water, followed by washing with an acid aqueous solution, and further washing with water.

As the acid aqueous solution, hydrohalic acid such as hydrochloric acid, hydroiodic acid and hydrobromic acid, and inorganic acid such as sulfuric acid and carbonic acid can be used. As the acid aqueous solution, for example, an acid aqueous solution having a concentration of 0.01 to 3N can be used. Cleaning with these cleaning liquids can be repeated a plurality of times as necessary.

The wet pulverization step in the method for producing activated carbon is a step of wet pulverizing the activated product after the washing step. The wet pulverization step is a step for adjusting the average particle diameter of the activated material to 5 μm to 10 μm in advance in order to facilitate the pulverization in the dry pulverization step.

Examples of the wet pulverization step include a step of slurrying the activated material and pulverizing it with a ball mill or the like. The slurry concentration when the activator is slurried is preferably in the range of 2% by mass to 40% by mass. In consideration of the treatment amount of the activated product during mass production and the average particle size of the activated product after wet pulverization, the slurry concentration is more preferably in the range of 5% by mass to 20% by mass. When the slurry concentration is less than 2% by mass, the efficiency of pulverization is deteriorated. On the other hand, if the slurry concentration exceeds 40% by mass, the fluidity of the slurry is impaired, so that the impact force by the ball or the like is reduced and the slurry becomes difficult to be crushed.

A pulverizer can be used for wet pulverization. The crusher is not particularly limited. Examples thereof include a ball mill, an attritor, a sand mill, and a bead mill. In wet grinding, it is preferable to use a ball mill.

An example of wet pulverization using a ball mill is shown below. Examples of the balls used for wet pulverization include alumina balls, zirconia balls, stainless steel balls, silicon nitride balls, tungsten carbide balls, and the like. In order to reduce the impact during pulverization, it is preferable to use at least two kinds of balls having different ball diameters. In this case, it is important to select a combination of balls in which the fusion particles are mainly crushed and the particles are pulverized relatively little.

The diameter of the large ball is preferably 1 mm to 30 mm, more preferably 5 mm to 20 mm. The diameter of the small ball is preferably in the range of 1/10 to 1/2 of the diameter of the large ball. Use a large ball and a small ball each having a uniform diameter. The ratio of the total weight of the large balls to the total weight of the small balls is preferably in the range of 1/10 to 10/1, more preferably in the range of 2/8 to 8/2.

If the ball milling time is too long or too short, activated carbon having the target particle size and specific surface area cannot be obtained. Therefore, the pulverization time is preferably 30 minutes to 5 hours, more preferably 60 minutes to 3 hours. The number of rotations is preferably 10 rpm to 100 rpm, more preferably 30 rpm to 60 rpm.

In the method for producing activated carbon, the wet pulverization step can be performed before or after the cleaning step. For example, before the washing step, activated material can be obtained by throwing the activated material into water to form an alkali slurry, washing the alkali slurry, wet pulverizing, and then carrying out the washing step. In addition, after the washing step, the activated carbon can be made into a water slurry and wet pulverized.

The dry pulverization step in the method for producing activated carbon is a step of dry pulverizing the activated product after the wet pulverization step so that the average particle diameter (D ₅₀ ) of the activated product is 0.5 μm to 5 μm. In the method for producing activated carbon, the first activated carbon is further dry-pulverized. By dividing the pulverization into wet pulverization and dry pulverization twice, in the wet pulverization step, the main purpose is to separate the fusion by alkali, and particle pulverization can be prevented as much as possible. And generation | occurrence | production of the functional group of a surface can be prevented as much as possible by a dry-type grinding | pulverization process.

In the dry pulverization step, the particles of the activated material can be pulverized by using, for example, a jet mill. In this case, the activated material can be pulverized in an atmosphere in which hydrogen gas is added to an inert gas such as nitrogen or argon at 10 volume% or less, preferably 0.5 to 8 volume%. By adding hydrogen gas, surface oxides can be reduced. Particularly in dry pulverization, the effect of reducing oxides is extremely large. In addition, the drying process which dries the said activation material can be provided between the said wet grinding process and the said dry grinding process. As the said drying process, what is necessary is just a process which can dry an activation thing, and it can be set as the process using well-known methods, such as hot air drying and natural drying.

In the heat treatment step in the method for producing activated carbon, the activated product after the dry pulverization step is heat-treated at a temperature of 400 ° C. to 700 ° C. in an atmosphere in which 10% by volume or less of hydrogen is added to an inert gas or under reduced pressure. It is a process to do. The activated product can be pulverized in the dry pulverization step so that the average particle diameter (D ₅₀ ) of the activated product during the heat treatment is 5 μm or less. A plurality of peaks may exist as the particle size distribution of the activation product. Moreover, a plurality of peaks may not exist, that is, a monomodal particle size distribution may be used.

In the heat treatment step, heating is performed in an atmosphere in which hydrogen gas is added to an inert gas such as nitrogen or argon at 10 volume% or less, preferably 0.5 to 8 volume%, or under reduced pressure. By heating, surface functional groups can be reduced. The heating temperature is 400 ° C to 700 ° C. If the temperature is lower than 400 ° C., there is no effect, and if it is 700 ° C. or higher, the pores of the activated carbon may be destroyed.

Next, a method for treating activated carbon will be described. The activated carbon treatment method includes at least a dry pulverization step and a heat treatment step. The dry pulverization step and the heat treatment step are as described in the method for producing activated carbon.

The activated carbon to be subjected to the dry pulverization step and the heat treatment step has an average particle size (D ₅₀ ) of 5 μm to 10 μm, a specific surface area by nitrogen gas adsorption method of 1500 m ² / g to 2500 m ² / g, and an average pore diameter of 1 Activated carbon having a thickness of 0.7 nm to 3.0 nm, a total pore volume of 0.5 ml / g to 2 ml / g, and an alkali metal content of 1000 mass ppm or less. The activated carbon can be obtained, for example, by performing the carbonization step, the activation treatment step, the washing step, and the wet pulverization step that have appeared in the method for producing activated carbon, followed by drying. Here, the average particle diameter can be adjusted by a wet grinding process. The amount of alkali metal can be adjusted in the cleaning process. The specific surface area, average pore diameter, and total pore volume can be adjusted by the carbonization temperature and the activation conditions such as the activation temperature and the alkali ratio.

The activated carbon described above can be used for electric double layer capacitors and lithium ion capacitors.

Next, the electric double layer capacitor will be described. The electric double layer capacitor includes an electrode including activated carbon. The electrode is configured by adding, for example, activated carbon and a binder, and more preferably a conductive agent. Moreover, the said electrode can be made into the electrode further integrated with the electrical power collector. As the activated carbon, the activated carbon of the present invention can be used.

As the binder used here, known ones can be used. For example, polyolefins such as polyethylene and polypropylene, fluorinated polymers such as polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin / vinyl ether copolymer cross-linked polymers, celluloses such as carboxymethyl cellulose, vinyl polymers such as polyvinyl pyrrolidone and polyvinyl alcohol And polyacrylic acid. The content of the binder in the electrode is not particularly limited. For example, when the activated carbon of the present invention is used, the binder can be contained in the range of usually about 0.1 to 30% by mass with respect to the total amount of the activated carbon and the binder.

As the conductive agent, powders of carbon black, powdered graphite, titanium oxide, ruthenium oxide and the like can be used. The blending amount of the conductive agent in the electrode can be appropriately selected according to the blending purpose. When the activated carbon of the present invention is used, it contains a conductive agent in the range of usually 1 to 50% by mass, preferably about 2 to 30% by mass, with respect to the total amount of the activated carbon, binder and conductive agent. Can do.

As a method of mixing the activated carbon, the binder, and the conductive agent, a known method can be used. For example, there is a method in which activated carbon, a binder, and a conductive agent are added to a solvent having a property of dissolving a binder to form a slurry, which is uniformly applied on a current collector. In addition, there is a method in which the activated carbon, the binder, and the conductive agent are kneaded without adding a solvent, and then pressure-molded at room temperature or under heating.

As the current collector, a current collector of a known material and shape can be used. For example, a current collector made of a metal such as aluminum, titanium, tantalum, or nickel, or an alloy such as stainless steel in a predetermined shape can be used.

A unit cell of an electric double layer capacitor can be generally formed by using a pair of the above electrodes as a positive electrode and a negative electrode, facing each other through a separator, and immersing in an electrolytic solution. As a separator, a polypropylene fiber nonwoven fabric, a glass fiber nonwoven fabric, a synthetic cellulose paper, etc. can be used.

As the electrolytic solution, a known aqueous electrolytic solution or organic electrolytic solution can be used. As the organic electrolyte, those used as solvents for electrochemical electrolytes can be used. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, sulfolane derivatives, 3-methylsulfolane, 1,2-dimethoxyethane, acetonitrile, glutaronitrile, valeronitrile, dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dimethoxy Ethane, methyl formate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used. In addition, these electrolyte solutions can be mixed and used.

The supporting electrolyte in the organic electrolytic solution is not particularly limited, and various electrolytes such as salts, acids, alkalis and the like that are usually used in the field of electrochemistry or the field of batteries can be used. Examples thereof include inorganic ion salts such as alkali metal salts and alkaline earth metal salts, quaternary ammonium salts, cyclic quaternary ammonium salts, and quaternary phosphonium salts. (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄ PBF ₄ , and (C ₂ H ₅ ) ₃ (CH ₃ ) PBF ₄ Etc. are mentioned as preferable.

The concentration of these salts in the electrolytic solution can be generally in the range of about 0.1 to 5 mol / l, preferably about 0.5 to 3 mol / l. A more specific configuration of the electric double layer capacitor is not particularly limited. For example, between a pair of electrodes consisting of a thin sheet or disk-like positive electrode and negative electrode having a thickness of 10 to 500 μm, a coin type accommodated in a metal case via a separator, and the pair of electrodes are interposed via a separator. Examples of the winding type include a rotating type, and a laminated type in which a large number of electrode groups are stacked via a separator.

Hereinafter, the present invention will be described more specifically based on examples and comparative examples, but the present invention is not limited to the following examples.

[Manufacture of activated carbon]
[Example 1-1]
Activated carbon was produced using petroleum raw coke as soft carbon. Petroleum raw coke was adjusted to a particle size of 3 mm or less so as to be easily pulverized, and carbonized for 1 hour at 550 ° C. in a nitrogen atmosphere using a rotary kiln (carbonization step). After carbonization, the carbonized product was pulverized with a jet mill so that the average particle size (D ₅₀ ) was 7.0 μm, and the average particle size was adjusted (adjustment step). After the adjusting step, 200 parts by mass of potassium hydroxide was added to 100 parts by mass of petroleum raw coke and mixed with a ball mill to obtain a mixture. The obtained mixture was placed in a ceramic electric tubular furnace, sealed, and the tubular furnace was placed in a nitrogen gas atmosphere, and then the temperature of the mixture rose from room temperature to 750 ° C. under a temperature rising condition of 20 ° C./min. The mixture was heated by a tubular furnace heater. When the temperature of the mixture reached 750 ° C., the temperature was maintained for 30 minutes, and activation treatment was performed (activation treatment step). After the activation treatment, mixing of water vapor and heating by the heater were stopped, and the mixture was naturally cooled to room temperature in a nitrogen gas atmosphere. After cooling to room temperature, the activated product subjected to the activation treatment was taken out from the tubular furnace, and the activated product was repeatedly washed with water and acid washed with hydrochloric acid to remove the remaining metallic potassium (cleaning step). After the washing step, the activated product was wet pulverized so that the average particle size (D ₅₀ ) was 7.0 μm (wet pulverization step). The specific surface area by the BET method of the activated carbon obtained through the above steps (hereinafter sometimes referred to as “first activated carbon”) was 2100 m ² / g. The first activated carbon was pulverized with a jet mill under a nitrogen atmosphere, and the average particle size (D ₅₀ ) was adjusted to 4.0 μm (dry pulverization step). After the dry pulverization, the first activated carbon was heat-treated at 600 ° C. for 2 hours in a nitrogen atmosphere (heat treatment step). The activated carbon of Example 1-1 was obtained through the above steps. The obtained first activated carbon had an average particle diameter of 7.0 μm, a specific surface area of 2100 m ² / g, an average pore diameter of 2.1 nm, a total pore volume of 1.1 ml / g, and an alkali metal amount of 120. The mass was ppm. Here, the average particle size was measured by a laser scattering particle size distribution measurement method. The specific surface area, average pore diameter and total pore volume were measured by a nitrogen gas adsorption method. The amount of alkali metal was measured by fluorescent X-ray analysis.

The activated carbon of Example 1-1 had a specific surface area according to the BET method of 2010 m ² / g, an average particle diameter (D ₅₀ ) of 4.0 μm, and a surface functional group of 0.38 meq / g. Further, when the obtained activated carbon was measured by X-ray diffraction, a gentle peak derived from d002 was observed around 2θ = 20 to 30 ° (FIG. 1).

[Example 2-1]
A first activated carbon was obtained by the same process as in Example 1-1. The first activated carbon was pulverized with a jet mill under a nitrogen atmosphere, and the average particle size (D ₅₀ ) was adjusted to 3.7 μm. Thereafter, the first activated carbon was heat-treated at 650 ° C. for 1 hour in a nitrogen atmosphere containing 5% by volume of hydrogen. Through the above steps, the activated carbon of Example 2-1 was obtained.
The average particle diameter (D ₅₀ ) of the obtained first activated carbon was 8.0 μm, the specific surface area by BET method was 2510 m ² / g, the average pore diameter was 2.2 nm, and the total pore volume was 1.4 ml / g, The amount of alkali metal was 80 mass ppm.

The activated carbon of Example 2-1 had a specific surface area by BET method of 2430 m ² / g, an average particle diameter (D ₅₀ ) of 3.7 μm, and a surface functional group of 0.35 meq / g. Further, when the obtained activated carbon was measured by X-ray diffraction, a gentle peak derived from d002 was observed around 2θ = 20 to 30 ° (FIG. 1).

[Example 3-1]
A first activated carbon was obtained by the same process as in Example 1-1 except that the ratio of the carbon material to potassium hydroxide was 1: 1.8. The first activated carbon was pulverized with a jet mill under a nitrogen atmosphere, and the average particle size (D ₅₀ ) was adjusted to 3.3 μm. Thereafter, the first activated carbon was heat-treated at 600 ° C. for 2 hours in a nitrogen atmosphere containing 3% by volume of hydrogen. The activated carbon of Example 3-1 was obtained through the above steps.
The obtained first activated carbon had an average particle size of 9.8 μm, a specific surface area of 1620 m ² / g, an average pore diameter of 1.9 nm, a total pore volume of 0.8 ml / g, and an alkali metal content of 150. The mass was ppm.

The activated carbon of Example 3-1 had a specific surface area by BET method of 1570 m ² / g, an average particle diameter (D ₅₀ ) of 3.3 μm, and a surface functional group of 0.36 meq / g. Further, when the obtained activated carbon was measured by X-ray diffraction, a gentle peak was observed in the vicinity of 2θ = 20 to 30 °.

[Comparative Example 1-1]
A first activated carbon was obtained by the same process as in Example 1-1. The first activated carbon was heat-treated at 600 ° C. for 1 hour in a nitrogen atmosphere without performing the dry pulverization step. Through the above steps, the activated carbon of Comparative Example 1-1 was obtained.
The obtained first activated carbon had an average particle diameter of 7.0 μm, a specific surface area of 2100 m ² / g, an average pore diameter of 2.1 nm, a total pore volume of 1.1 ml / g, and an alkali metal amount of 120. The mass was ppm.

The activated carbon of Comparative Example 1-1 had a specific surface area by BET method of 2070 m ² / g, an average particle diameter (D ₅₀ ) of 7.0 μm, and a surface functional group of 0.51 meq / g. Further, when the activated carbon obtained was measured by X-ray diffraction, a peak was observed in the vicinity of 2θ = 20 to 30 °.

[Comparative Example 2-1]
A first activated carbon was obtained by the same process as in Example 1-1 except that the activation temperature was set to 700 ° C. The first activated carbon was heat-treated at 600 ° C. for 1 hour in a nitrogen atmosphere without performing the dry pulverization step. Through the above steps, the activated carbon of Comparative Example 2-1 was obtained.
The obtained first activated carbon had an average particle size of 4.0 μm, a specific surface area of 1800 m ² / g, an average pore diameter of 1.9 nm, a total pore volume of 0.9 ml / g, and an alkali metal content of 100. The mass was ppm.

The activated carbon of Comparative Example 2-1 had a specific surface area by BET method of 1760 m ² / g, an average particle diameter (D ₅₀ ) of 4.0 μm, and a surface functional group of 0.62 meq / g. Further, when the activated carbon obtained was measured by X-ray diffraction, a peak was observed in the vicinity of 2θ = 20 to 30 °.

[Reference Example 1-1]
Activated carbon was produced using phenol charcoal as hard carbon (non-graphitizable carbon). Commercial activated carbon made from phenolic charcoal (specific surface area by BET method is 2200 m ² / g, average particle size (D ₅₀ ) is 8.2 μm) is pulverized with a jet mill in a nitrogen atmosphere to obtain an average particle size (D ₅₀ ) Was adjusted to 4.5 μm. Thereafter, heat treatment was performed at 600 ° C. for 2 hours in a nitrogen atmosphere. Through the above steps, the activated carbon of Reference Example 1-1 was obtained.

The activated carbon of Reference Example 1-1 had a specific surface area by BET method of 2200 m ² / g, an average particle diameter (D ₅₀ ) of 4.5 μm, and a surface functional group of 0.30 meq / g. Further, when the activated carbon obtained was measured by X-ray diffraction, no peak was observed in the vicinity of 2θ = 20 to 30 ° (FIG. 1).

[Reference Example 2-1]
Activated carbon was produced using petroleum coke as a starting material. Petroleum coke was pulverized with a jet mill so that the average particle size (D ₅₀ ) was 3.0 μm, and the average particle size was adjusted. After the adjustment process, the activation process was performed by the same process as the activation process described in Example 1-1. The activated carbon after the activation treatment had a specific surface area by BET method of 1603 m ² / g and an average particle size (D ₅₀ ) of 7.0 μm. However, the obtained activated carbon was fused to increase the particle size. As a result, when carbon coke is activated without being carbonized and activated after being finely divided, the particle size becomes large due to fusion, so even if it is used for an electric double layer capacitor or a lithium ion capacitor, the output of these capacitors or It is expected that it is difficult to improve durability.

[Production of laminate cell]
In order to evaluate the capacitor performance, a laminate cell was prepared using the activated carbon prepared in Examples 1-1 to 3-1, Comparative Examples 1-1, 2-1 and Reference Example 1-1. Carbon black (ECP600JD manufactured by Lion Co., Ltd.) 0.13 g as a conductive agent and 0.11 g of granular polytetrafluoroethylene (PTFE) as a binder are mixed with 1.5 g of activated carbon, and a roll press machine is used. The mixture was pressed into a sheet to prepare a carbon electrode sheet having a thickness of 150 to 200 μm. From this carbon electrode sheet, an electrode having a length of 1.4 cm and a width of 2.0 cm was cut out to obtain a positive electrode and a negative electrode. As shown in FIG. 2, the current collector 4 was attached to the positive electrode 2 and the negative electrode 3, the separator 5 was sandwiched between the positive electrode 2 and the negative electrode 3, and the outside was covered with the laminate film 6, thereby producing a laminate cell 1. . The positive electrode and the negative electrode are the same material and have the same shape.

[Capacitor performance evaluation]
A propylene carbonate (PC) solution of 1.5M triethylmethylammonium tetrafluoroborate (TEMA · BF ₄ ) was used as an electrolytic solution, and the capacitance retention was evaluated in order to evaluate the capacitor performance of the laminate cell. The electrode density was determined by measuring the sheet weight and the vertical and horizontal dimensions × thickness. The capacitance (C) was obtained by measuring the total amount of discharge energy (U) stored in the capacitor and calculating the value by the energy conversion method. The internal resistance (R) was calculated from the IR drop immediately after the start of discharge. Formulas (1) and (2) are shown below as calculation formulas for capacitance and internal resistance.

The capacitance retention rate is the ratio of the capacitance (B) when discharging at 50 mA to the capacitance (A) when discharging at 1 mA in a charge / discharge test at −30 ° C. (100 × B / A) was calculated as the capacitance retention. Also, the ratio of the capacitance (D) when 100 mA is discharged at 20 ° C. after applying 2.8 V at 60 ° C. for 1000 hours to the capacitance (C) when 100 mA is discharged at 20 ° C. (100 × D / C) was calculated as the capacitance retention. The results are shown in Table 1.

Generally, the capacitance decreases as the discharge current increases. When a charge / discharge test is performed at −30 ° C., the value of the capacitance retention rate when the capacitance retention rate at 50 mA discharge to the capacitance at 1 mA discharge is evaluated as the capacitance retention rate. The higher the value is, the larger current can flow. The fact that a large current can flow means that the output is high.
On the other hand, when a deterioration test is performed by continuously applying 2.8 V at 60 ° C. for 1000 hours, and the capacitance before and after the deterioration test is compared with the same discharge current of 100 mA discharge at 20 ° C., The higher the capacity retention rate, the better the durability.

When the charge / discharge test was performed at −30 ° C., the laminate cells of Example 1-2 to Example 3-2 were higher than those of Comparative Example 1-2, Comparative Example 2-2, and Reference Example 1-1. The capacitance retention was shown. That is, the laminate cell of the example was able to output higher than the laminate cell of the comparative example and the reference example.

In addition, when the deterioration test was carried out by continuously applying 2.8 V at 60 ° C. for 1000 hours, the laminated cells of Examples 1-2 to 3-2 were Comparative Example 1-2 and Comparative Example 2-2. In addition, the capacitance retention was higher than that of Reference Example 1-1. That is, the laminate cell of the example could exhibit higher durability than the laminate cell of the comparative example and the reference example.

From the above results, it was found that using the activated carbon of the present invention makes it possible to improve the output and durability of the electric double layer capacitor.

According to the present invention, since an electric double layer capacitor and a lithium ion capacitor excellent in output and durability can be provided while maintaining a high capacitance, it is industrially useful.

Claims

The specific surface area according to the BET method is 1500 m 2 / g to 2500 m 2 / g,
The average particle diameter (D 50 ) is 0.5 μm to 5 μm,
A gentle peak derived from d002 measured using a wide-angle X-ray diffraction apparatus can be observed,
Activated carbon having a surface functional group of 0.5 meq / g or less.
A carbonization process for carbonizing soft carbon;
After the carbonization step, an activation treatment step in which a soft carbon carbide having an average particle size (D 50 ) of 0.5 μm to 10 μm is mixed with an alkali activator and activated,
A washing step for washing the activation product obtained by the activation treatment step;
A wet pulverization step of wet pulverizing the activation product after the washing step;
A dry pulverization step in which the activated product after the wet pulverization step is dry pulverized to have an average particle size (D 50 ) of the activated product of 0.5 μm to 5 μm;
Production of activated carbon including at least a heat treatment step in which the activated product after the dry pulverization step is heat-treated at a temperature of 400 ° C. to 700 ° C. in an atmosphere in which 10% by volume or less of hydrogen is added to an inert gas or under reduced pressure. Method.
The average particle diameter (D 50 ) is 5 μm to 10 μm, the specific surface area by nitrogen gas adsorption method is 1500 m 2 / g to 2500 m 2 / g, the average pore diameter is 1.7 nm to 3.0 nm, and the total pore volume is 0.1. A dry pulverization step of dry pulverizing activated carbon having an alkali metal content of 1000 mass ppm or less to 5 ml / g to 2 ml / g, and an average particle size (D 50 ) of 0.5 μm to 5 μm;
A method of treating activated carbon comprising at least a heat treatment step of heat treating the activated carbon after the dry pulverization step at a temperature of 400 ° C. to 700 ° C. in an inert atmosphere or under reduced pressure.