JP2004149399A - Activated carbon, its manufacturing method and its use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide activated carbon which can increase electric capacity per one electrode without applying an excess voltage, and to provide a method for manufacturing the activated carbon and an electric double layer capacitor. <P>SOLUTION: The activated carbon has 10 to 1,500m<SP>2</SP>/g BET specific surface area obtained by a nitrogen adsorption method and contains no graphite microcrystal. The activated carbon is manufactured by the method including a process of heat treating coal pitch in two-stage temperature ranges of 400°C to 600°C and 600°C and 900°C, mixing the obtained carbonaceous source material with an alkaline metal compound to activate in a temperature range from 600°C to 900°C. The activated carbon is obtained by the above method. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to activated carbon useful as an electric double layer capacitor (also referred to as an electric double layer capacitor). More specifically, a method for producing activated carbon which can be suitably used as an electrode material for a capacitor having high electric capacity and high durability, an electrode for an electric double layer capacitor (polarizable electrode) using the activated carbon, and an electric double layer capacitor having the electrode About.
[0002]
[Prior art]
Electric double layer capacitors have characteristics that batteries do not have, such as rapid charging and discharging, strong resistance to overcharging and discharging, long life due to no chemical reaction, usable in a wide temperature range, and environmental friendliness because they do not contain heavy metals. And is conventionally used as a memory backup power supply. In recent years, large-capacity development has rapidly progressed, applications for high-performance energy devices have been promoted, and applications for power storage systems combined with solar cells and fuel cells, and engine assists for hybrid cars have been studied. I have.
[0003]
The electric double layer capacitor has a structure in which a pair of positive and negative polar electrodes made of activated carbon or the like are opposed to each other via a separator in a solution containing electrolyte ions. When a DC voltage is applied to the electrode, anions in the solution are attracted to the electrode polarized to the positive (+) side, and cations in the solution are attracted to the electrode polarized to the negative (−) side. The electric double layer formed at the interface with the substrate is used as electric energy.
[0004]
The conventional electric double layer capacitor is excellent in power density, but has a disadvantage in that the energy density is inferior. Therefore, when it is used for an energy device, further development of a larger capacity is required. In order to increase the capacity of an electric double layer capacitor, it is essential to develop an electrode material that forms a large number of electric double layers between solutions.
[0005]
Therefore, in order to form more electric double layers, the use of activated carbon having a large specific surface area has been studied. Such activated carbon has an excellent electric capacity per weight (F / g), but has a reduced electrode density. Therefore, there is a problem that the electric capacity per volume (F / ml) does not increase so much.
[0006]
In recent years, it has been proposed to produce activated carbon having microcrystals similar to graphite and use it as a raw material for a polarizable electrode (for example, see Patent Document 1). An electric double layer capacitor using the activated carbon as a raw material for a polarizable electrode can be said to be an excellent raw material in that it has a large electric capacity.
[0007]
However, this activated carbon also had problems and was not satisfactory. That is, since the activated carbon expands when a voltage is applied, a dimension limiting structure is required to suppress the expansion as described in the patent publication, and there is a major problem in the operation of assembling the capacitor. Also, unless a voltage of about 4 V is applied in advance, the electric capacity does not appear, which may cause decomposition of the electrolytic solution.
[0008]
[Patent Document 1]
JP-A-11-317333
[0009]
[Problems to be solved by the invention]
An object of the present invention is to provide an activated carbon that can increase the electric capacity per electrode without applying an excessive voltage.
[0010]
[Means for Solving the Problems]
The present invention has been made as a result of intensive studies to solve the above-mentioned problems, and the following constitutions of the present invention have been made to achieve the above objects.
1) The BET specific surface area determined by the nitrogen adsorption method is 10 m²/ G-1000m²/ G, activated carbon not containing graphite microcrystals.
2) The BET specific surface area determined by the nitrogen adsorption method is 10 m²/ G ~ 1500m²/ G, activated carbon not containing graphite microcrystals.
3) Raman spectrum G peak (1580 cm^-1D) peak height (1360 cm)^-1The activated carbon according to 1) or 2), wherein the ratio of the peak heights in ()) is 0.8 to 1.2.
4) The activated carbon has a BET specific surface area of 10 m determined by the nitrogen adsorption method.²/ G ~ 1500m²/ G, wherein the value of (electrode expansion coefficient) / (BET specific surface area) in the electrode containing the activated carbon is 0.12 or less.
5) The activated carbon has a BET specific surface area of 10 m determined by the nitrogen adsorption method.²/ G ~ 1500m²/ G, wherein the electrode containing the activated carbon has an electrode expansion coefficient of 50% or less and the density of the electrode is 0.70 g / ml or more.
6) The activated carbon according to any one of 1) to 5), which has a pore volume of 20 to 50 angstroms determined by a nitrogen adsorption method according to a BJH method of not less than 0.02 ml / g.
7) A polarizable electrode material containing the activated carbon according to any one of 1) to 6).
8) A polarizable electrode material comprising the activated carbon according to any one of 1) to 6) and a vapor grown carbon fiber.
9) The polarizable electrode material according to 8), wherein the vapor-grown carbon fiber has a hollow structure, an outer diameter of 2 to 500 nm, and an aspect ratio of 10 to 15000.
10) The polarizable electrode material according to 8) or 9), wherein the vapor-grown carbon fiber has a branched structure.
11) The vapor grown carbon fiber has a pore volume of 0.01 ml / g to 0.4 ml / g, and has a BET specific surface area of 30 m determined by a nitrogen adsorption method.²/ G-1000m²/ G, the polarizable electrode material as described in any one of 8) to 10) above.
12) A laminate of a polarizable electrode sheet containing the polarizable electrode material according to any one of 7) to 11) and a current collector.
13) The laminate according to 12), wherein the current collector is selected from aluminum, carbon-coated aluminum, stainless steel, and titanium.
14) An electrode forming composition comprising the polarizable electrode material according to any one of 7) to 11).
15) A conductor formed from the composition according to 14).
16) An electric double layer capacitor including the polarizable electrode material according to any one of 7) to 11).
17) a step of heat-treating the coal-based pitch in two temperature ranges of 400 ° C. to 600 ° C. and 600 ° C. to 900 ° C., and then a step of mixing and heating the heat-treated coal-based pitch with an alkali metal compound to activate it. A method for producing activated carbon, characterized in that:
18) A step of heat-treating the coal-based pitch in a two-stage temperature range of 400 ° C. to 600 ° C. and 600 ° C. to 900 ° C. in the vapor of the alkali metal, and then mixing and heating the heat-treated coal-based pitch with the alkali metal compound. A method for producing activated carbon, comprising a step of activating the activated carbon.
19) The method for producing activated carbon according to 17) or 18), wherein the alkali metal compound is at least one alkali hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide and cesium hydroxide. .
20) The method for producing activated carbon according to 19), wherein the alkali metal is at least one selected from the group consisting of potassium, sodium and cesium.
21) The BET specific surface area obtained by the nitrogen adsorption method, which is obtained by any one of the production methods of 17) to 20), is 10 m.²/ G-1000m²/ G, activated carbon not containing graphite microcrystals.
22) The BET specific surface area obtained by the nitrogen adsorption method, obtained by any one of the production methods of 17) to 20), of 10 m²/ G ~ 1500m²/ G, activated carbon not containing graphite microcrystals.
23) Raman spectrum G peak (1580 cm) obtained by any one of the production methods of 17) to 20).^-1D) peak height (1360 cm)^-1) Is 0.8 to 1.2, and the BET specific surface area determined by the nitrogen adsorption method is 10 m.²/ G-1000m²/ G of activated carbon containing no graphite microcrystals.
24) G peak of Raman spectrum (1580 cm) obtained by any one of the production methods of 17) to 20).^-1D) peak height (1360 cm)^-1) Is 0.8 to 1.2, and the BET specific surface area determined by the nitrogen adsorption method is 10 m.²/ G ~ 1500m²/ G of activated carbon containing no graphite microcrystals.
25) The BET specific surface area obtained by the nitrogen adsorption method, which is obtained by any one of the production methods of 17) to 20), is 10 m.²/ G ~ 1500m²/ G, wherein the value of (electrode expansion coefficient) / (BET specific surface area) is 0.12 or less.
26) The BET specific surface area obtained by the nitrogen adsorption method, which is obtained by any one of the manufacturing methods of 17) to 20), is 10 m.²/ G ~ 1500m²/ G, wherein the electrode expansion coefficient is 50% or less, and the density of the polarizable electrode is 0.70 g / ml or more.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
The electrical properties of activated carbon greatly depend on the structural properties of the activated carbon, such as specific surface area, pore distribution, and crystal structure. The structural characteristics of such activated carbon are determined by the raw material structure, carbonization conditions, and activation conditions.
[0012]
Therefore, in order to obtain activated carbon useful as an electrode material, it is necessary to optimize the structure of the raw material, carbonization conditions, and activation conditions, but the present inventors optimally select coal-based pitch as the raw material. Was determined to be. Compared to petroleum-based carbon materials, coal-based pitch has fewer side chains, a higher proportion of aromatic compounds, and a mixture of polycyclic aromatic compounds with various molecular structures. This is because it is considered that these compounds form various complicated microcrystalline structures and the like and exhibit excellent electrical characteristics.
[0013]
The coal pitch to be selected is not particularly limited, but one having a softening point of 100 ° C. or lower, more preferably 60 ° C. to 90 ° C. is used.
[0014]
Then, this coal-based pitch is subjected to heat treatment including baking and carbonization in two stages at a temperature of 400 ° C to 600 ° C and 600 ° C to 900 ° C, preferably 450 ° C to 550 ° C and 650 ° C to 850 ° C.
[0015]
When the coal-based pitch is heated between 400 ° C. and 600 ° C., a thermal decomposition reaction occurs, gas and light fractions are eliminated, and the residue undergoes polycondensation and finally solidifies. In the first stage of the carbonization step, the state of micro-bonds between carbon atoms is almost determined, and the structure of the crystallite determined in this step determines the basis of the structure of the activated carbon as the final product.
[0016]
In the first stage carbonization step, the heating rate is 3 ° C./hr to 10 ° C./hr, more preferably 4 ° C./hr to 6 ° C./hr, and the holding time at the maximum temperature is 5 hours to 20 hours. It is more preferably performed for 8 hours to 12 hours.
[0017]
Next, a second-stage heat treatment is performed at a temperature of 600 ° C to 900 ° C. Also in this second stage carbonization step, the heating rate is 3 ° C./hr to 10 ° C./hr, more preferably 4 ° C./hr to 6 ° C./hr, and the holding time at the highest temperature is 5 hours to 20 hours. It is more preferably performed for 8 hours to 12 hours.
[0018]
It is also effective to carry out these heat treatment (carbonization) steps in the vapor of an alkali metal. The alkali metal acts as a catalyst in the carbonization process. That is, cross-linking between aromatics in the pitch is promoted, and the carbonization reaction proceeds. Examples of the alkali metal include compounds such as sodium, potassium, and cesium.
[0019]
As a method of performing the heat treatment in the vapor of the alkali metal, for example, the heat treatment can be performed by introducing an alkali metal vapor volatilized from an alkali activation reaction system described later into the carbonization step system. In addition, a raw material pitch is set around the reaction vessel of the alkali activation reaction, and the heat treatment (carbonization) step and the alkali activation step are performed in parallel by exposing the raw material pitch to an alkali metal vapor volatilized from the alkali activation reaction system and heating simultaneously. Can do it. As a result, the processing time as a whole can be shortened, and the cost for energy for heating can be reduced.
[0020]
Next, the carbon material (the heat-treated carbonaceous raw material) is pulverized to a particle size of about 1 μm to 100 μm, mixed with an alkali metal compound and heated to form fine pores in the carbon material to obtain activated carbon.
[0021]
The alkali activator is not particularly limited as long as it is a compound containing an alkali metal, but the present invention is effective for a substance that melts during activation. Potassium, sodium and calcium hydroxides, carbonates, sulfides and sulfates are preferred. For example, potassium hydroxide, sodium hydroxide, cesium hydroxide, potassium carbonate, sodium carbonate, potassium sulfide, sodium sulfide, potassium thiocyanate, potassium sulfate, and sodium sulfate can be used. Preferred are potassium hydroxide and sodium hydroxide, and more preferred is potassium hydroxide. These may be used alone or in combination of two or more.
[0022]
The mixing amount of the alkali metal compound with respect to the carbonaceous raw material can be determined according to the crystallinity of the carbonaceous raw material, the amount of surface functional groups, and the use of the obtained carbon material. When the crystallinity of the carbonaceous raw material is high and the number of surface functional groups is small, the required amount of the alkali metal compound tends to increase. For example, when potassium hydroxide is used, the mass ratio of potassium hydroxide to carbonaceous raw material 1 is about 0.5 to 7, more preferably about 1 to 5, and still more preferably about 2 to 4. When the mass ratio of potassium hydroxide is less than 0.5, the development of the pores is poor, and when the mass ratio is 7 or more, the pores (micropores) decrease due to overactivation and progress of the destruction of the pore walls, and the specific surface area tends to decrease. is there.
[0023]
The activation treatment temperature varies depending on the type and shape of the raw material and the activation reaction rate (activation reaction rate), but is performed at 250 ° C to 1000 ° C, more preferably 500 ° C to 900 ° C, and still more preferably 600 ° C to 800 ° C. Performed at ° C. When the activation temperature is 400 ° C. or lower, the progress of activation is insufficient, the pores in the activated carbon are small, and the electric capacity is reduced when used as a polarizable electrode material of an electric double layer capacitor. If the temperature is higher than 1000 ° C., problems such as shrinkage of the pores of the activated carbon, remarkable deterioration in charging characteristics at a high current density, and severe corrosion of the activation device occur.
[0024]
The activated carbon thus obtained has a feature that it exhibits a high electric capacity from the first cycle without applying an excessive voltage, and has a high retention rate of the electric capacity.
[0025]
When the activated carbon was observed with a transmission microscope, it was confirmed that the activated carbon had only a turbostratic structure without fine crystals similar to graphite as shown in FIG.
G peak of Raman spectrum (1580 cm^-1) D peak (1360 cm) with respect to height (height from the baseline to the peak point in the measured curve)^-1) Height ratio was 0.8-1.2.
[0026]
Here, the intensity ratio of the D peak to the G peak in the Raman spectrum is used as an index indicating the degree of graphitization of the carbon material. However, when this intensity ratio is indicated as the peak height ratio, the degree of graphitization is high. The smaller the value. In the case of activated carbon having microcrystals, the value was approximately 0.6, but in the case of the activated carbon having no microcrystal, the value was 0.8 to 1.2.
[0027]
Further, activated carbon used as an electrode for a capacitor needs to have a certain amount or more of pores of 20 to 50 angstroms which are considered to contribute to capacity development and diffusion of an electrolyte.
[0028]
The activated carbon of the present invention has a BET specific surface area of 10 m²/ G ~ 1500m²/ G, preferably 10 m²/ G-1000m²/ G, which is smaller than the BET specific surface area of the activated carbon obtained by the conventional method (typically 2000 m²/ G ~ 3000m²/ G). Further, the activated carbon of the present invention has a pore volume of 20 to 50 angstroms (Angstrom) by a BJH (Barrett, Joyner and Hallenda) method of 0.02 ml / g or more.
[0029]
Due to the above crystal structure and pore structure, the activated carbon exhibits a high electric capacity from the first cycle without the step of inserting an ion between graphite layers by applying an excessive voltage. it can. Further, it is considered that, since a sufficient carbonization step has been performed, the amount of functional groups on the carbon surface is reduced, and deterioration of electric capacity is suppressed.
[0030]
The activated carbon thus activated was measured for tap density with a tap density meter (manufactured by Kuramochi Kagaku Seisakusho), and found to be 0.35 to 0.70 g / ml when the number of taps was 50, and the powder resistance was 1 It was 0.4 Ωcm or less at 0.0 MPa.
[0031]
To 80 parts by mass of this activated carbon, 10 parts by mass of PTFE (polytetrafluoroethylene) and 10 parts by mass of carbon black were added, and an electrode formed by kneading and rolling was used as a polarizable electrode. Is as shown in equation (1).
[0032]
Electrode expansion coefficient / BET specific surface area ≦ 0.12 (1)
Here, the electrode expansion coefficient (%) = (electrode thickness at the time of charging 2.5 V−electrode thickness before charging) / (electrode thickness before charging) × 100, and the unit of the BET specific surface area is m²/ G.
[0033]
By making the activated carbon satisfying the expression (1), a high electric capacity can be exhibited from the first cycle without giving an excessive voltage. When (electrode expansion coefficient / BET specific surface area) exceeds 0.12, the electrode expansion coefficient tends to be high for the BET specific surface area, but such activated carbon develops capacity unless an excessive voltage is applied. It tends to disappear, which is not preferable in designing a capacitor. In addition, when there is substantially no electrode expansion, the electrode expansion coefficient becomes zero, so that the ratio of (electrode expansion coefficient / BET specific surface area) becomes zero. When the ratio is 0.12 or less, preferably 0 or more and 0.12 or less, and more preferably 0 or more and 0.1 or less, it is considered that there is no problem in capacitor design. This is more preferable in terms of capacitor design.
[0034]
Further, when the electrode density of the polarizable electrode at this time was measured, it was 0.70 g / ml or more and 1.05 g / ml or less, more preferably 0.72 g / ml or more and 1.03 g / ml or less, and further more preferably It is 0.74 g / ml or more and 1.00 g / ml or less. When the electrode density is less than 0.70 g / ml, the activated carbon has a small electric capacity per volume (F / ml). Conversely, if the electrode density is higher than 1.05 g / ml, it becomes difficult to penetrate the electrolyte solution, which leads to an increase in internal resistance, which is not preferable.
[0035]
In this case, the electrode expansion coefficient is 0% or more and 50% or less, more preferably 0% or more and 30% or less, and still more preferably 0% or more and 20% or less. Although the electrode density is high, the electrode expansion due to charge and discharge is small. Activated carbon.
[0036]
By adding the vapor grown carbon fiber to the activated carbon, the characteristics can be further improved. The vapor grown carbon fiber is produced by, for example, spraying benzene and metal catalyst particles in a hydrogen stream at about 1000 ° C., has a hollow structure inside, an outer diameter of 2 nm to 500 nm, and an aspect ratio of 10 nm. Characteristically, it is １５15,000.
[0037]
By mixing the vapor grown carbon fiber with the activated carbon, the contact resistance between particles is reduced, the electrode strength is improved, and the durability as a polarizable electrode is improved.
In this case, if the vapor-grown carbon fiber having many branches is mixed, the role as a cushion material inside the electrode is further enhanced, so that the activated carbon particles contract during charge and discharge, and the electrode strength is reduced or the particles are reduced. It is more effective to prevent the contact resistance between them from increasing.
[0038]
As the vapor-grown carbon fiber, a manufactured one baked at 1000 ° C. to 1500 ° C. or a further graphitized one can be used.
[0039]
It is also possible to use a gas-activated or chemical-activated gas-phase grown carbon fiber. In this case, the volume of micropores (pores of 20 angstrom or less) is 0.01 ml / g to 0.4 ml. / G, BET specific surface area 30m²/ G-1000m²/ G of which the surface structure is controlled to be better. Mixing carbon fibers with many micropores increases the ion diffusion resistance inside the electrode.
[0040]
In this case, the mixing amount of the vapor grown carbon fiber is preferably from 0.02% by mass to 50% by mass, and more preferably from 0.05% by mass to 30% by mass. If the content is less than 0.02% by mass, a sufficient effect cannot be obtained because the effect of increasing the number of contact points with the activated carbon particles is small. If it is 50% by mass or more, the content of activated carbon in the polarizable electrode decreases, and the electric capacity decreases.
[0041]
From the activated carbon of the present invention, a polarizable electrode and an electric double layer capacitor can be produced according to a known method. That is, the polarizable electrode is a method in which a conductive agent and a binder are added to activated carbon and kneading and rolling is performed, a conductive agent, a binder, and a solvent are added to the activated carbon to prepare a slurry-like paint, and a predetermined thickness is formed on the conductive base material. And a method in which the solvent is evaporated at room temperature or by heating, or a method in which uncarbonized resin is mixed with activated carbon and sintered.
[0042]
In this case, as the conductive base material, a foil, a plate-like material, a wire net-like expanded material of aluminum, carbon-coated aluminum, stainless steel, titanium or the like having a thickness of about 10 μm to 0.5 mm is used. In addition, conductive rubber, corrosion-resistant metal, graphite and the like are also used.
[0043]
For example, if necessary, carbon black or the like is added as a conductive agent to activated carbon powder or a mixture of activated carbon powder and vapor-grown carbon fiber, and after kneading a binder such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride, rolling is performed. By doing so, a sheet having a thickness of about 0.1 mm to 0.5 mm is formed. A metal plate (aluminum foil, aluminum plate, wire mesh aluminum expand, or the like) serving as a current collector is laminated on the electrode sheet, and immersed in an electrolytic solution via a separator to form an electric double layer capacitor.
[0044]
Further, a resin-based binder (such as polyvinylidene fluoride) or a water-soluble binder such as hydroxymethylcellulose, hydroxyethylcellulose, carboxycellulose, or hydroxypropylcellulose is mixed with the activated carbon powder or a mixture of the activated carbon powder and the vapor-grown carbon fiber. A paint for forming a polar electrode material layer is prepared, and the paint is applied on a current collector (for example, an aluminum foil or an aluminum plate) using a method such as a doctor blade, and then dipped in an electrolytic solution through a separator to remove the electric power. It can be a multilayer capacitor.
[0045]
In this case, any of a known non-aqueous solvent electrolyte solution and a water-soluble electrolyte solution can be used as the electrolyte for the electric double layer capacitor.
[0046]
Examples of the aqueous type (aqueous electrolyte solution) include a sulfuric acid aqueous solution, a sodium sulfate aqueous solution, a sodium hydroxide aqueous solution, a potassium hydroxide aqueous solution, an ammonium hydroxide aqueous solution, a potassium chloride aqueous solution, and a potassium carbonate aqueous solution.
[0047]
Non-aqueous (non-aqueous electrolyte solution) includes R¹R²R³R⁴N⁺Or R¹R²R³R⁴P⁺The cation represented by the formula (R¹, R², R³, R⁴Is each independently an alkyl group having 1 to 10 carbon atoms or an allyl group. ) And BF₄ ⁻, PF₆ ⁻, ClO₄ ⁻As an electrolyte, a quaternary ammonium salt or a quaternary phosphonium salt comprising an anion such as diethyl ether, dibutyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, Ethers such as diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, and ethylene glycol phenyl ether; formamide, N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethylformamide, N-methylacetamide, N, N- Dimethylacetamide, N-ethylacetamide, N, N-diethylacetamide, Amides such as N, N-dimethylpropionamide and hexamethylphosphorylamide; sulfur-containing compounds such as dimethyl sulfoxide and sulfolane; dialkyl ketones such as methyl ethyl ketone and methyl isobutyl ketone; ethylene oxide, propylene oxide, tetrahydrofuran, 2-methoxytetrahydrofuran, 1,2 Preferred are solutions of cyclic ethers such as -dimethoxyethane and 1,3-dioxolane; carbonates such as ethylene carbonate and propylene carbonate; γ-butyrolactone; N-methylpyrrolidone; organic solvents such as acetonitrile and nitromethane. Further, a carbonate-based nonaqueous solvent such as ethylene carbonate and propylene carbonate can be preferably used. Two or more electrolytes or solvents can be used respectively.
[0048]
The separator to be interposed between the electrodes as necessary may be a porous separator that transmits ions, and may be a microporous polyethylene film, a microporous polypropylene film, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a glass fiber mixed nonwoven fabric, a glass mat. Filters and the like can be preferably used.
[0049]
【Example】
Hereinafter, the present invention will be described more specifically by showing typical examples. These are merely examples for explanation, and the present invention is not limited to these. The measuring method of each characteristic in the following example is as follows.
[0050]
(1) BET specific surface area and pore volume
Using a NOVA1200 manufactured by Quantachrome Co., it was calculated from the nitrogen adsorption isotherm at the liquid nitrogen temperature using the BET method and the BJH method. The nitrogen adsorption amount was measured at a relative pressure (P / P0) of 0.01 to 1.0.
[0051]
(2) Raman spectrum
Using an Ar laser at 514.5 nm as excitation light and a CCD (Charge Coupled Device) as a detector, the Raman spectrum of a carbon material as a raw material of activated carbon was measured at a slit of 500 μm and an exposure of 60 seconds.
[0052]
(3) Electric capacity
10 parts by mass of PTFE (polytetrafluoroethylene) and 10 parts by mass of carbon black were added to 80 parts by mass of activated carbon having an average particle size of 30 μm, kneaded in an agate mortar, and rolled into a sheet having a thickness of 0.5 mm with a rolling roller. The sheet was punched into a disk having a diameter of 20 mm, and dried in a vacuum at 200 ° C. overnight to use as a polarizable electrode.
[0053]
The above-mentioned electrode was assembled and used in an evaluation cell as shown in FIG. 1 in a glove box in which high-purity argon was circulated. In FIG. 1, 1 is an aluminum upper cover, 2 is a fluoro rubber O-ring, 3 is a current collector made of aluminum, 4 is an insulating material made of Teflon (registered trademark), 5 is an aluminum container, and 6 is aluminum. A spring, 7 is a polarizable electrode, and 8 is a 1 mm thick separator made of glass fiber. PC (propylene carbonate) is used as a solvent for the electrolyte, and (C₂H₅)₄NBF₄LIPASTE-P / EAFIN (1 mol / l) manufactured by Toyama Pharmaceutical Co., Ltd. was used as an electrolyte.
[0054]
When measuring the change in the coefficient of electrode expansion during charge and discharge, a cell for evaluation as shown in FIG. 4 is used, and the displacement in the electrode thickness direction is measured using an indicator. Note that the electrode-retaining coil spring (6) shown in FIG. 4 may require a load of about 0.1 to 1.0 kgf to compress it by 1 cm. Those requiring a load of 0.3 kgf were used. The measurement temperature was room temperature (20 ° C to 30 ° C).
[0055]
The charge / discharge measurement was performed using a charge / discharge tester HJ-101SM6 manufactured by Hokuto Denko Co., Ltd., and the charge / discharge current was 5 mA (1.6 mA / cm).²), 50 mA (16 mA / cm²), 150 mA (48 mA / cm²) At 0 to 2.5 V or 0 to 3.0 V, and from the discharge curve obtained by the second constant current discharge, the electric capacity per mass of the bipolar activated carbon of the electric double layer capacitor (F / g) and the electric capacity per volume (F / ml) were calculated.
[0056]
The durability was evaluated as a ratio of the electric capacity after the 20th charge / discharge cycle test to the electric capacity after the second charge / discharge.
[0057]
(Example 1)
A coal pitch manufactured by Kawasaki Steel Co., Ltd. having a softening point of 86 ° C. was heat-treated at 500 ° C. (first stage) and 700 ° C. (second stage). The obtained carbonaceous material was mixed with 2.5 times the amount of KOH by mass ratio and filled in a crucible. This was heated to 750 ° C. at a rate of 3 ° C./hr, and then activated at 750 ° C. for 60 minutes. The activated carbon material was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum-dried at 200 ° C. to obtain activated carbon.
[0058]
The specific surface area of this activated carbon is 930m²/ G. The pore volume at 20 to 50 angstroms according to the BJH method was 0.0416 ml / g, the Raman spectrum was as shown in FIG. 2, and the ratio of the D peak height to the G peak height was 0.92.
[0059]
The electric capacity is 5 mA (1.6 mA / cm).²), 36.5 F / g and 31.0 F / ml during 2.5 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 98.4%. Charge / discharge current 5 mA (1.6 mA / cm²3) F / g and 32.0 F / ml during 3.0 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 96.9%. The electrode density of the activated carbon electrode was 0.85 g / ml, and the value of (electrode expansion coefficient / BET specific surface area) was 0.0108.
[0060]
(Example 2)
5% by mass of vapor grown carbon fiber was mixed with the activated carbon obtained by the method of Example 1 to obtain a polarizable electrode material. Charge / discharge current 5 mA (1.6 mA / cm²), The electric capacity during charge and discharge at 2.5 V was 36.4 F / g and 32.4 F / ml, and the capacity retention after charge and discharge for 20 cycles was 98.9%. Charge / discharge current 5 mA (1.6 mA / cm²) The electric capacity at the time of charging / discharging at 3.0 V was 39.5 F / g and 35.2 F / ml, and the 20-cycle capacity retention was 97.7%. The electrode density was 0.89 g / ml, and the value of (electrode expansion coefficient / BET specific surface area) was 0.008.
[0061]
(Example 3)
Activated carbon was produced in the same manner as in Example 1 except that a coal pitch manufactured by Kawasaki Steel Co., Ltd. having a softening point of 86 ° C. was heat-treated at 500 ° C. and 800 ° C., and used as a polarizable electrode material.
[0062]
The specific surface area of this activated carbon is 173m²/ G, and the pore volume of 20 to 50 Å according to the BJH method was 0.0271 ml / g. The ratio of the D peak height to the G peak height in the Raman spectrum was 0.93.
[0063]
In addition, the obtained activated carbon was determined by TEM (transmission electron microscope) (FIG. 3) to be an activated carbon having only a disordered layer structure, in which the carbon layer contained in the surface layer hardly contains a graphite structure with crystals. Was confirmed.
[0064]
Charge / discharge current 5 mA (1.6 mA / cm²), The electric capacity during charge and discharge at 2.5 V was 32.6 F / g and 31.9 F / ml, and the capacity retention after charge and discharge for 20 cycles was 98.7%. Charge / discharge current 5 mA (1.6 mA / cm²) The electric capacity at the time of 3.0 V charge / discharge was 35.5 F / g and 34.8 F / ml, and the 20-cycle capacity retention was 97.2%. The electrode density of the activated carbon electrode was 0.98 g / ml.
The value of (electrode expansion coefficient / BET specific surface area) was 0.0116.
[0065]
(Example 4)
The activated carbon obtained by the method of Example 3 was obtained by alkali-activating vapor grown carbon fiber (micropore volume: 0.3 ml, BET specific surface area: 530 m)²/ G) 5 mass% was mixed to obtain a polarizable electrode material. Charge / discharge current 5 mA (1.6 mA / cm²), The electric capacity during 2.5 V charge / discharge was 33.5 F / g and 33.5 F / ml, and the capacity retention after 20 cycles of charge / discharge was 99.0%. Charge / discharge current 5 mA (1.6 mA / cm²) The electric capacity at the time of charging / discharging at 3.0 V was 34.5 F / g and 34.5 F / ml, and the 20-cycle capacity retention was 98.0%. The electrode density of the activated carbon electrode was 1.0 g / ml, and the value of (electrode expansion coefficient / BET specific surface area) was 0.0082.
[0066]
(Example 5)
A coal pitch manufactured by Kawasaki Steel Co., Ltd. having a softening point of 86 ° C. was heat-treated at 500 ° C. (first stage) and 750 ° C. (second stage). The obtained carbonaceous material was mixed with 2.5 times the amount of KOH by mass ratio and filled in a crucible. This was heated to 750 ° C. at a rate of 3 ° C./hr, and then activated at 750 ° C. for 60 minutes. The activated carbon material was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum-dried at 200 ° C. to obtain activated carbon. The specific surface area of this activated carbon is 444m²/ G.
[0067]
The electric capacity is 5 mA (1.6 mA / cm).²), 35.5 F / g and 33.0 F / ml during 2.5 V charge / discharge, and the capacity retention after 20 cycles of charge / discharge was 97.8%. The electrode density of the activated carbon electrode was 0.93 g / ml, and the value of (electrode expansion coefficient / BET specific surface area) was 0.11.
(Comparative Example 1)
Using petroleum coke as a carbon material, 2.5 times the amount of KOH in a mass ratio was mixed and filled in a crucible. This was kept at 750 ° C. for 60 minutes for activation. The activated carbon material was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum-dried at 200 ° C. to obtain activated carbon. The specific surface area of this activated carbon is 1905m²/ G, and the ratio of the D peak height to the G peak height in the Raman spectrum was 0.98.
[0068]
Charge / discharge current 5 mA (1.6 mA / cm²), The electric capacity during charge and discharge at 2.5 V was 44.5 F / g and 24.0 F / ml, and the capacity retention after charge and discharge for 20 cycles was 96.3%. Charge / discharge current 5 mA (1.6 mA / cm²) 3.0 V charge / discharge electric capacity was 45.0 F / g and 24.3 F / ml, and the 20-cycle capacity retention was 94.0%. The electrode density of the polarizable electrode was 0.54 g / ml. The value of (electrode expansion coefficient / BET specific surface area) was 0.0005.
[0069]
(Comparative Example 2)
MCMB (mesocarbon microbeads manufactured by Osaka Gas Co., Ltd.) was used as a carbon material, and a 5-fold amount of KOH was mixed at a mass ratio and filled in a crucible. This was kept at 750 ° C. for 60 minutes for activation. The activated carbon material was washed with 1N hydrochloric acid and then with distilled water to remove residual KOH and metal impurities. This was vacuum-dried at 200 ° C. to obtain activated carbon. The specific surface area of this activated carbon is 127 m²/ G, the pore volume at 20 to 50 Å was 0.013 ml / g, and the ratio of the D peak height to the G peak height in the Raman spectrum was 0.92.
[0070]
Charge / discharge current 5 mA (1.6 mA / cm²), The electric capacity during charging and discharging at 2.5 V was 10.2 F / g and 9.4 F / ml, and the capacity retention after charging and discharging for 20 cycles was 99.1%. Charge / discharge current 5 mA (1.6 mA / cm²) The electric capacity at the time of 3.0 V charge / discharge was 11.5 F / g, 10.6 F / ml, and the 20-cycle capacity retention was 98.5%. The electrode density of the polarizable electrode was 0.92 g / ml. The value of (electrode expansion coefficient / BET specific surface area) was 0.394.
[0071]
【The invention's effect】
According to the present invention including the step of heat-treating coal-based pitch in a two-stage temperature range and activating alkali, it is possible to obtain activated carbon having a high electric capacity (F / ml) and good durability without applying an excessive voltage. did it.
[0072]
In particular, the electrode containing the activated carbon of the present invention, even when an excessive voltage of about 4 V is not applied, a sufficient capacity is developed from the first cycle by applying a commonly used voltage of about 2 to 3 V, and the electric power per weight is increased. Both the capacity (F / g) and the electric capacity per volume (F / ml) were high.
[0073]
The activated carbon of the present invention has a BET specific surface area of 10 to 1500 m.²/ G, the value of (electrode expansion coefficient) / (BET specific surface area) was 0.12 or less, which was unlikely to cause a problem in capacitor design.
[0074]
Furthermore, by mixing the vapor-grown carbon fiber with the activated carbon of the present invention, it was possible to obtain a polarizable electrode and an electric double layer capacitor exhibiting characteristics excellent in electrode strength and durability.
[Brief description of the drawings]
FIG. 1 is a sectional view of a cell for evaluating an electric double layer capacitor.
FIG. 2 is a Raman spectrum curve of the activated carbon produced in Example 1 of the present invention. 2, the vertical axis represents the spectrum intensity (Int.), And the horizontal axis represents the Raman shift (measurement wavelength; cm).^-1).
FIG. 3 is a transmission electron microscope (TEM) photograph (magnification: 2 million times) of the activated carbon produced in Example 3 of the present invention.
FIG. 4 is a schematic diagram of an electrode expansion measurement cell.
[Explanation of symbols]
1 Top lid
2 O-ring
3 current collector
4 Insulator
5 containers
6 Spring
7 electrodes
8 Separator

Claims (26)

BET specific surface area determined by a nitrogen adsorption method is ^{10m 2} / ^g~1000m 2 / g, the activated carbon containing no graphite crystallites. BET specific surface area determined by a nitrogen adsorption method is ^{10m 2} / ^g~1500m 2 / g, the activated carbon containing no graphite crystallites. Activated carbon according to claim 1 or 2 ratio of the peak height of D peak to peak height of G peak of the Raman spectrum (1580cm ^-1) (1360cm ^-1) is 0.8 to 1.2. Activated carbon, the BET specific surface area determined by the nitrogen adsorption method has a range of ^{10m 2} / ^g~1500m 2 / g, the electrode containing the activated carbon value of (electrode expansion rate) / (BET specific surface area) 0. Activated carbon that is 12 or less. Activated carbon, the BET specific surface area determined by the nitrogen adsorption method has a range of ^{10m 2} / ^g~1500m 2 / g, the electrode expansion rate of the electrode containing the activated carbon 50% or less, the density of the electrode 0.70g / Ml activated carbon. The activated carbon according to any one of claims 1 to 5, wherein a pore volume of 20 to 50 angstroms determined by a nitrogen adsorption method by a BJH method is 0.02 ml / g or more. A polarizable electrode material comprising the activated carbon according to claim 1. A polarizable electrode material comprising the activated carbon according to any one of claims 1 to 6 and a vapor grown carbon fiber. The polarizable electrode material according to claim 8, wherein the vapor-grown carbon fiber has a hollow structure, an outer diameter of 2 to 500 nm, and an aspect ratio of 10 to 15000. The polarizable electrode material according to claim 8 or 9, wherein the vapor grown carbon fiber has a branched structure. Wherein the vapor grown carbon fiber has a pore volume of 0.01ml / g~0.4ml / g, a BET specific surface area as determined by nitrogen adsorption method is ^{30m 2} / ^g~1000m 2 / g The polarizable electrode material according to any one of claims 8 to 10, wherein A laminate of a polarizable electrode sheet containing the polarizable electrode material according to any one of claims 7 to 11 and a current collector. The laminate according to claim 12, wherein the current collector is selected from aluminum, carbon-coated aluminum, stainless steel, and titanium. An electrode forming composition comprising the polarizable electrode material according to claim 7. A conductor formed from the composition according to claim 14. An electric double layer capacitor comprising the polarizable electrode material according to claim 7. A step of heat-treating the coal-based pitch in a two-stage temperature range of 400 ° C. to 600 ° C. and 600 ° C. to 900 ° C .; Characteristic activated carbon production method. A step of heat-treating the coal-based pitch in a two-stage temperature range of 400 ° C. to 600 ° C. and 600 ° C. to 900 ° C. in the vapor of the alkali metal; A method for producing activated carbon, comprising a step of activating. The method for producing activated carbon according to claim 17, wherein the alkali metal compound is at least one alkali hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, and cesium hydroxide. The method for producing activated carbon according to claim 19, wherein the alkali metal is at least one selected from the group consisting of potassium, sodium, and cesium. Obtained in any one of the manufacturing method according to claim 17 to 20, BET specific surface area as determined by nitrogen adsorption method is ^{10m 2} / ^g~1000m 2 / g, the activated carbon containing no graphite crystallites. Obtained in any one of the manufacturing method according to claim 17 to 20, BET specific surface area as determined by nitrogen adsorption method is ^{10m 2} / ^g~1500m 2 / g, the activated carbon containing no graphite crystallites. The ratio of the peak height of the D peak (1360 cm ^-1 ) to the peak height of the G peak (1580 cm ^-1 ) of the Raman spectrum obtained by the manufacturing method according to any one of claims 17 to 20 is 0.8 to ^1. .2 a and, activated carbon BET specific surface area determined by a nitrogen adsorption method does not contain graphite crystallites is ^{10m 2} / ^g~1000m 2 / g. The ratio of the peak height of the D peak (1360 cm ^-1 ) to the peak height of the G peak (1580 cm ^-1 ) of the Raman spectrum obtained by the manufacturing method according to any one of claims 17 to 20 is 0.8 to ^1. .2 a and, activated carbon BET specific surface area determined by a nitrogen adsorption method does not contain graphite crystallites is ^{10m 2} / ^g~1500m 2 / g. Obtained in any one of the manufacturing method according to claim 17 to 20, BET specific surface area as determined by nitrogen adsorption method is ^{10m 2} / ^g~1500m 2 / g, the (electrode expansion rate) / (BET specific surface area) Activated carbon having a value of 0.12 or less. Obtained in any one of the manufacturing method according to claim 17 to 20, BET specific surface area as determined by nitrogen adsorption method is ^{10m 2} / ^g~1500m 2 / g, the electrode expansion ratio of 50% or less, of the polarizable electrodes Activated carbon with a density of 0.70 g / ml or more.

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