JP2004182508A - Method of producing carbon material for electric double layer capacitor electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing an electric double layer capacitor electrode material which has excellent durability and exhibits stably high capacitance by an industrially advantageous method. <P>SOLUTION: In the method of producing a carbon material for an electric double layer capacitor electrode, a pitch obtained by polymerizing condensed polycyclic hydrocarbon or a substance comprising the same in the presence of hydrogen fluoride-boron trifluoride is heat-treated, and is next subjected to activation treatment at 500 to 700°C using an activation agent comprising ≥70 wt.% sodium hydroxide. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a carbon material for an electrode of an electric double layer capacitor.
[0002]
[Prior art]
At present, as a polarizable electrode material of an electric double layer capacitor (EDLC), activated carbon having a high specific surface area obtained by activating coconut shell, coke, phenol resin or the like with steam, carbon dioxide or the like is used. However, when the activation rate is increased to obtain activated carbon having a high capacitance and a high specific surface area from these raw materials, there is a problem that the bulk density of the electrode material decreases and the energy density of the EDLC cannot be increased. .
[0003]
Recently, there has been disclosed a method for obtaining activated carbon having a high capacitance from an easily graphitizable carbon such as coke, mesocarbon microbeads, or mesophase pitch-based carbon fiber by using an alkali metal compound (hereinafter referred to as alkali activation). (For example, refer to Patent Documents 1 to 3.) In addition, the present inventors have disclosed that an excellent activated carbon for EDLC can be obtained by subjecting a specific pitch raw material to heat treatment and activation treatment, and the selection of starting materials to be subjected to alkali activation and the selection of processing conditions are high. It is clarified that it is important to obtain activated carbon having a capacitance (see Patent Document 4).
[0004]
Potassium hydroxide is mainly used for the above-mentioned alkali activation. However, since the activation reactivity is high, a void that does not contribute to the capacity is generated in carbon, which causes a problem that the capacitance per volume is reduced. In some cases, the reaction is performed at a high temperature of 750 ° C. or more, which causes an industrial problem of corrosion of the apparatus.
[0005]
Therefore, it is disclosed that a high-density and high-capacity capacitor material can be manufactured under relatively low-temperature activation conditions by using a mixture of potassium hydroxide and sodium hydroxide at a specific compounding ratio ( For example, Patent Documents 5 and 6) point out that when the amount of industrially advantageous sodium hydroxide is large, the capacitance does not increase and the electrode resistance increases.
[0006]
[Patent Document 1]
Japanese Patent No. 2548546 [Patent Document 2]
Japanese Patent No. 26334658 [Patent Document 3]
Japanese Patent No. 3149504 [Patent Document 4]
Japanese Patent Application Laid-Open No. 2002-93667 [Patent Document 5]
JP 2001-302226 A [Patent Document 6]
JP 2002-15958 A
[Problems to be solved by the invention]
As described above, in the conventional production method, when an activator containing sodium hydroxide as a main component, which is industrially advantageous, is used, the capacitance does not increase, and there is a problem that a practical material cannot be produced. Was. An object of the present invention is to provide a method for manufacturing an EDLC electrode material having excellent durability and stably exhibiting a high capacitance by an industrially advantageous method.
[0008]
[Means for Solving the Problems]
The present inventors have made intensive efforts to solve the above-mentioned problems, and as a result, heat-treated a specific pitch and then activated using an activator containing sodium hydroxide in a certain amount or more, so that the electrostatic capacity per volume was reduced. The inventors have found that an EDLC electrode material having a high capacity can be obtained, and have reached the present invention.
[0009]
That is, the present invention provides a method for heat treating a pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride, and then adding 70% by weight or more of sodium hydroxide. A method for producing a carbon material for an electric double layer capacitor electrode, comprising performing an activation treatment at 500 to 700 ° C. using an activator containing the same.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following description.
In the present invention, a synthetic pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride is used. This synthetic pitch is considered to be polymerized via cations generated by the addition of protons to the condensed polycyclic hydrocarbon.Since the generated pitch has a large amount of aliphatic hydrogen, it is softened. It is distinguished from conventional pitches by having features such as low points and high solubility in solvents. It is presumed that such a characteristic structure is related to good activation of the activator containing sodium hydroxide as a main component.
[0011]
The method for producing the synthetic pitch is not particularly limited. For example, the synthetic pitch can be obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing these in the presence of hydrogen fluoride and boron trifluoride. Examples of the condensed polycyclic hydrocarbon include, for example, naphthalene, monomethylnaphthalene, dimethylnaphthalene, anthracene, phenanthrene, acenaphthene, pyrene, and the like, as described in Japanese Patent No. 2931593, Japanese Patent No. 262253, or Japanese Patent No. 2526585. Condensed polycyclic hydrocarbons having these skeletons, mixtures thereof, or substances containing these can be used. Among them, condensed polycyclic hydrocarbons selected from naphthalene, monomethylnaphthalene, dimethylnaphthalene and anthracene, which are relatively inexpensive and easily available, and mixtures thereof are usually used.
[0012]
In the polymerization reaction, 0.1 to 20 mol of hydrogen fluoride and 0.05 to 1.0 mol of boron trifluoride are used as a polymerization catalyst per mol of the pitch raw material at a temperature of 100 to 400 ° C. for 5 to 5 mol. It is performed by reacting for 300 minutes. Next, by heating at a temperature of 250 to 400 ° C. under a nitrogen stream, light boilers may be removed.
[0013]
In the carbonization in the present invention, the above-mentioned pitch may be subjected to a carbonization treatment by a method of heat treatment with stirring or standing, and infusibilize a powdery or fibrous precursor obtained by pulverization or melt spinning. The carbonization treatment may be performed after oxygen is added by the treatment. Above all, a return medium treatment method described later, which enables continuous production of a granular or powdery pitch heat-treated product having a mosaic-shaped internal structure, is preferable because a high-capacity capacitor material can be produced at low cost.
[0014]
That is, a granular or powdered heat-treated product (referred to as a return medium) in which a pitch has been heat-treated is preliminarily charged into a reactor at 400 to 800 ° C., and the raw material pitch is supplied into the reactor under stirring to obtain a granular material. Alternatively, a heat-treated product having a powdery pitch can be manufactured.
[0015]
In this method, the added pitch first becomes a low-viscosity liquid by heating, and is dispersed on the surface of a previously prepared granular or powdered pitch heat-treated product (return medium). Thereafter, as the polymerization reaction by heat progresses, it finally changes into an infusible and insoluble heat-treated product. Since the return medium is always kept in a fluid state by stirring, the gas generated by the pitch reaction is quickly discharged out of the system, and the heat treatment can be efficiently performed in a small-volume reactor.
[0016]
The pitch is dispersed on the surface of the return medium, polymerization proceeds, and the pitch solidifies while being subjected to shear by the flow of the return medium. Therefore, the optical structure of the obtained heat-treated product has a mosaic structure. Further, it is presumed that a large number of fine defects are present inside the particles due to the heat treatment due to the rapid temperature rise. Such a unique property is also preferable in order to realize a good activator for the activator mainly containing sodium hydroxide thereafter.
[0017]
In the present invention, after performing the above-described heat treatment, an activation treatment is then performed using an activator containing sodium hydroxide as a main component. The mixing ratio of sodium hydroxide in the activator is 70% by weight or more, preferably 90% by weight or more. Components other than sodium hydroxide are not particularly limited, but alkali metal compounds such as lithium hydroxide, potassium hydroxide, potassium carbonate, and potassium chloride are preferred.
[0018]
The method and apparatus for activation are not particularly limited, but 1 to 4 parts by weight of an activator is uniformly mixed with 1 part by weight of the pitch heat-treated product, and the mixture is filled in a processing vessel. It is heated at 500 to 700 ° C., more preferably 550 to 650 ° C. in a lower heating furnace and is kept for 0.1 to 20 hours. When the temperature is lower than 500 ° C., the activation reaction hardly proceeds, and the degree of activation does not increase. Further, by setting the processing temperature to 700 ° C. or lower, the corrosion of the processing apparatus can be minimized. After activation, the mixture is cooled to room temperature to remove an alkaline component, and then poured into alcohol, filtered, and repeatedly washed with water until the filtrate becomes neutral. After that, it is dried to obtain activated carbon.
[0019]
When producing an electrode for EDLC, the activated carbon used is one whose particle size has been adjusted so as to have an average particle diameter of usually 1 to 50 μm, preferably 5 to 30 μm. The pulverizing treatment can be performed at any stage of the carbonized product and the activated product, and is not particularly limited. As the pulverizer, an optimal model is appropriately selected from an impact pulverizer, a jet mill, a micro atomizer, and the like. As for the classifier, an optimal model is appropriately selected from a mechanical classifier, a wind classifier and the like, and is not particularly limited.
[0020]
The carbon material thus obtained has a high capacitance per volume, and by using this as an electrode material, an EDLC with high energy density and high reliability can be obtained.
[0021]
【Example】
Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples.
[0022]
<Example 1>
In the presence of hydrogen fluoride and boron trifluoride, naphthalene was polymerized to synthesize a mesophase pitch (Mettler softening point: 230 ° C.). In order to heat-treat the obtained pitch, the temperature was increased to 530 ° C. at a rate of 5 ° C./min in a nitrogen atmosphere and maintained at this temperature for 1 hour. After cooling to room temperature, the resultant was coarsely pulverized to obtain a mesophase pitch heat-treated product for a return medium having an average particle size of about 0.5 mm.
Next, 200 g of this heat-treated product was previously charged as a return medium into a 170 mm diameter, 170 mm height tank-type reactor equipped with a stirrer, and the temperature was raised to 550 ° C. under a nitrogen stream while stirring. Here, the mesophase pitch was added to the reactor at a rate of 10 g per minute, and a total of 300 g was charged. After the charging was completed, the temperature was maintained at 550 ° C. for 10 minutes, and then the reactor was cooled and the content was taken out. As a result, 400 g of a granular heat-treated product was obtained. The same operation was repeated seven times to obtain a mesophase pitch heat-treated product having a substitution rate of about 99%. Further, the heat-treated product was heated to 750 ° C. in a tubular furnace at a rate of 5 ° C./min in a nitrogen atmosphere, and kept at this temperature for 2 hours to obtain a calcined product.
The calcined product was pulverized to an average particle size of 15 μm with an impact grinder, and 2 parts by weight of sodium hydroxide was uniformly mixed with 1 part by weight of the obtained calcined product powder. The temperature was raised to 600 ° C. in minutes and kept at this temperature for 2 hours. After cooling to room temperature, the mixture was poured into 2-propanol, and filtration and washing with water were repeated until the filtrate became neutral.
The obtained activated carbon was mixed at a weight ratio of activated carbon: conductive filler (Ketjen black): binder (Teflon (registered trademark)) of 90: 5: 5 to prepare an electrode. For electrode evaluation, a glass bipolar cell was used, and a glass fiber separator was sandwiched between a pair of electrodes and housed in the cell. As the electrolytic solution, propylene carbonate in which tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) was dissolved at 1 mol / liter was used.
In an Ar atmosphere, at room temperature, the battery was charged to a voltage of 2.7 V at a constant current of 10 mA / g, further charged at 2.7 V for 2 hours, and then discharged to 0 V at a constant current of 10 mA / g. This was repeated three times. Next, charging and discharging were performed in the same manner with the constant current of charging and discharging being 100 mA / g, and the capacitance was calculated from the amount of discharged electricity. The capacitance was calculated in accordance with the following equation based on the weight of carbon in both the positive and negative electrodes (activated carbon and Ketjen black). The capacitance per volume Cv (F / cc) was calculated by multiplying the capacitance per weight Cw (F / g) by the density of the electrode.
(Formula) Capacitance Cw (F / g) = discharged electricity (AH / g) × 3600 / 2.7
As a result, excellent values were obtained, with a capacitance per weight of 32.0 F / g, a capacitance per volume of 33.6 F / cc, and an electrode density of 1.05 g / cc. The resistance value calculated from the voltage drop immediately after the start of discharge when discharging at a current density of 5 mA / cm ² was 24 Ω · cm ² .
[0023]
<Example 2>
Activated carbon was obtained in the same manner as in Example 1, except that a mixture of 1.8 parts by weight of sodium hydroxide and 0.2 parts by weight of potassium hydroxide was used as an activator per 1 part by weight of the calcined product powder. . The capacitance of the obtained activated carbon was determined in the same manner as in Example 1. The capacitance per weight was 34.0 F / g, the capacitance per volume was 32.3 F / cc, and the electrode density was 0.95 g / cc. Value. The resistance was 20 Ω · cm ² .
[0024]
<Comparative example>
The petroleum-based needle coke was heated to 750 ° C. at a rate of 5 ° C./min in a nitrogen atmosphere and kept at this temperature for 2 hours. This was pulverized with an impact type pulverizer to an average particle size of 15 μm, 2 parts by weight of sodium hydroxide was uniformly mixed with 1 part by weight of the obtained carbon powder, and the mixture was heated to 600 ° C. at 5 ° C./min in a nitrogen atmosphere. The temperature was raised and kept at this temperature for 2 hours. After cooling to room temperature, the mixture was poured into 2-propanol, and filtration and washing with water were repeated until the filtrate became neutral.
The capacitance of the obtained activated carbon was determined in the same manner as in Example 1. As a result, the capacitance per weight was 22.0 F / g, the capacitance per volume was 22.0 F / cc, and the electrode density was 1.00 g / cc. The activation did not proceed so much and the capacitance was low. The resistance value was as high as 56 Ω · cm ² .
[0025]
【The invention's effect】
By heat-treating a specific pitch and then activating using an activator containing 70% by weight or more of sodium hydroxide, we can provide low-cost activated carbon suitable for EDLC electrodes that can stably exhibit high capacitance. can do.
By carrying out the present invention, an EDLC having a high energy density can be manufactured stably at a low cost, and is of great industrial significance.

Claims (3)

The pitch obtained by polymerizing a condensed polycyclic hydrocarbon or a substance containing the same in the presence of hydrogen fluoride / boron trifluoride is heat-treated, and then an activator containing 70% by weight or more of sodium hydroxide is used. A method for producing a carbon material for an electric double layer capacitor electrode, comprising activating at 500 to 700 ° C. The method for producing a carbon material for an electric double layer capacitor electrode according to claim 1, wherein the activator contains at least 90% by weight of sodium hydroxide. The pitch heat treatment method prepares granular or powdered heat-treated products in a reactor in advance, and supplies raw heavy oil or pitch to the reactor under stirring to produce granular or powdery pitch heat-treated products. The method for producing a carbon material for an electrode of an electric double layer capacitor according to claim 1, further comprising: