JP2008195559A - Activated carbon for electric double-layer capacitor electrode and method for producing the activated carbon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide activated carbon for electric double-layer capacitor electrodes, which has high and excellent electrostatic capacity per unit volume and a long service life and to provide a method for producing the activated carbon for electric double-layer capacitor electrodes. <P>SOLUTION: The activated carbon for electric double-layer capacitor electrodes satisfies the following conditions (a) to (c). The condition (a) is that the nitrogen content is ≤1 wt.%. The condition (b) is that the pore volume of pores having ≤7 Å size is ≤15 cc/g when measured by a DFT method using carbon dioxide adsorption and the ratio of the pore volume of pores having ≤7 Å size to the total pore volume is ≥40%. The condition (c) is that the amount of surface functional groups is ≤0.5 meq/g. The method for producing the activated carbon for electric double-layer capacitor electrodes comprises the steps of: heat-treating pitch or easy-to-graphitize coke at 600-800°C to obtain a carbonized material; nitriding the carbonized material to obtain a nitrided material; and activating the nitrided material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to activated carbon for electric double layer capacitor electrodes and a method for producing the same.

  An electric double layer capacitor (hereinafter referred to as EDLC) is capable of charging / discharging a large current, has a long life and is excellent in high-temperature stability, and therefore has ideal characteristics as a power storage device such as a hybrid vehicle. However, the conventional EDLC has the only drawback that the energy density is insufficient.

  At present, activated carbon having a high specific surface area obtained by activating coconut straw, coke, phenol resin, etc. with water vapor or carbon dioxide is used as a polarizable electrode material of EDLC. However, when the activation degree is increased in order to obtain activated carbon with a high specific surface area having a high capacitance 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.

  Recently, a method has been proposed for obtaining activated carbon with a high capacitance from easily graphitizable carbon such as coke, mesocarbon microbeads, or mesophase pitch-based carbon fiber by activation using an alkali metal compound (hereinafter referred to as alkali activation). (For example, see Patent Documents 1 to 3).

  Further, it is disclosed that an excellent activated carbon for EDLC can be obtained by subjecting a specific raw material pitch to heat treatment and activation treatment (see, for example, Patent Documents 4 and 5), and selection of starting materials and treatment conditions for alkali activation. It is becoming clear that it is important to obtain activated carbon with high capacitance.

  Coke, which is often used as an alkali activation raw material, is an inexpensive raw material, but due to restrictions on the raw material or heat treatment conditions, there are many impurities such as metal and sulfur, and a high-performance material cannot be obtained. In addition, mesocarbon microbeads are also very expensive due to limitations of the production method and low yield. In the case of mesophase pitch-based carbon fiber, there is a restriction on the properties of the raw material pitch due to the spinning and infusibilization process, and the packing density does not increase compared to the granular shape when producing an electrode because it is fibrous. As described above, there is a problem that the electrostatic capacity per unit volume is lowered, and the activated carbon particle shape is very important for improving the capacity per unit volume.

  In addition, when calcining, pulverizing, and activating the bulk coke and needle coke obtained by liquid-phase carbonization of pitch, which is a graphitizable carbon raw material, the activated carbon has an anisotropic structure. Along the crack. This becomes a useless void that is not involved in the capacitance, and causes a decrease in the capacitance per unit volume. As such an example, an activated carbon raw material in which the pore volume of a crack corresponding to a pore diameter of 0.1 to 10 μm determined by a mercury intrusion method is 0.15 to 0.40 cc / g is disclosed (Patent Document 6). reference). In this case, the raw carbon already has such useless voids, and these voids are further expanded by applying alkali activation. As a result, sufficient electrode density is secured as an electrode for an electric double layer capacitor. Difficult to do.

  In order to obtain a high capacitance as an electrode for EDLC, a high capacitance per unit weight and a high electrode density are required. Usually, activated carbon having a large pore structure is required to obtain a high capacitance, but in this case, the electrode density is lowered. In addition, when trying to obtain a high electrode density, the firing temperature of the activated carbon raw material carbon is increased to improve the true density and to reduce the development of the pore structure due to activation. The capacitance of the will be low.

  A characteristic of EDLC is that it has a longer life than a so-called secondary battery. In general, activated carbon obtained by alkali activation has more functional groups than activated gas by gas activation, and is said to be disadvantageous in terms of life. As a method for suppressing a decrease in capacitance in repeated use of alkali-activated activated carbon, a method of heat-treating activated carbon has been disclosed (see Patent Documents 7 and 8).

  Patent Document 7 describes a method of heat-treating activated carbon at 500 to 900 ° C. in a reducing gas atmosphere, and Patent Document 8 describes a method of heat-treating activated carbon at 200 to 850 ° C. in a reducing gas atmosphere in the presence of a transition metal catalyst. However, this method can suppress a decrease in capacitance, but has a problem that it does not lead to improvement in capacitance itself.

Patent Document 9 discloses a method for increasing the capacitance by activating coke after heat treatment at 550 to 1000 ° C. in an atmosphere containing ammonia gas.
Japanese Patent No. 2548546 Japanese Patent No. 2634658 Japanese Patent No. 3149504 Japanese Patent Laid-Open No. 2002-93667 JP 2001-180923 A JP 2003-51430 A JP 2002-25867 A JP 2002-362912 A JP 2006-12938 A

  An object of the present invention is to solve the above-described problems in the prior art, and to provide an activated carbon for an EDLC electrode having a high electrostatic capacity per unit volume and having a long life, and a method for producing the same.

As a result of detailed examination of starting materials, processing methods, conditions, and the like of activated carbon for EDLC electrodes, the present inventors have found that the EDLC electrode per unit volume by carbonized preparation conditions before activation treatment and heat treatment under specific conditions. The inventors have found that a high-performance activated carbon for EDLC electrodes having a high electrostatic capacity can be produced, and reached the present invention. That is, the present invention is as follows.
(1) Activated carbon for electric double layer capacitor electrodes that satisfies the following conditions (a) to (c).
(A) The nitrogen content is 1 wt% or less,
(B) The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption is 0.15 cc / g or less, and the ratio of the pore volume of 7 mm or less to the total pore volume is 40% or more,
(C) The amount of surface functional groups is 0.5 meq / g or less.
(2) Activated carbon activated carbon that is activated by nitriding a carbonized product obtained by heat-treating pitch or graphitizable coke at a temperature of 600 ° C. or higher and 800 ° C. or lower to form a nitrided product. Manufacturing method.
(3) The method for producing activated carbon for an electric double layer capacitor electrode according to the second item, wherein the difference in nitrogen content between the activated carbon and the nitride is 1.0 wt% or more.
(4) The method for producing activated carbon for an electric double layer capacitor electrode as described in the second item, wherein the H / C atomic ratio of the carbonized product is 0.40 or less or the true density of the carbonized product is 1.42 g / cc or more.
(5) The method for producing activated carbon for an electric double layer capacitor electrode as described in the second item, wherein the nitride has an H / C atomic ratio of 0.150 or more and an N / C atomic ratio of 0.016 or more.
(6) The activated carbon for an electric double layer capacitor electrode according to the second item, wherein the reactor for performing the nitriding treatment does not substantially contain a metal material in a portion in contact with the carbonized material and the nitrogenous gas at 500 ° C. or higher. Production method.
(7) The method for producing activated carbon for an electric double layer capacitor electrode according to Item 2, wherein the pitch is a pitch obtained by polymerizing a condensed polycyclic hydrocarbon in the presence of hydrogen fluoride / boron trifluoride.

  According to the present invention, it is possible to produce activated carbon for EDLC electrodes having a very high electrode density, a high capacitance per unit volume, and a small life of electrostatic capacitance. large. By using this material, an EDLC having a high energy density and a long life can be realized, which is very useful as a power source for hybrid vehicles, UPSs and the like.

  The present invention relates to an activated carbon that has a high capacitance per unit volume and has little capacitance deterioration, and provides an activated carbon that simultaneously satisfies a high capacitance per unit weight and a high electrode density, and a method for producing the same. Is a thing

  As the carbonized material used in the present invention, an easily graphitizable carbon precursor is preferable, and in order to obtain a high-capacitance electrode by using petroleum-based pitch, coal-based pitch or synthetic pitch and coke using these as starting materials. preferable. Among these, more preferable examples include naphthalene, methylnaphthalene, anthracene, phenanthrene, acenaphthene, as disclosed in Japanese Patent No. 2931593, Japanese Patent No. 26212253, Japanese Patent No. 2526585, or Japanese Patent Application Laid-Open No. 2000-319664. Examples thereof include synthetic pitches obtained by polymerizing condensed polycyclic hydrocarbons such as acenaphthylene and pyrene in the presence of hydrogen fluoride / boron trifluoride as super strong acid catalysts. Unlike other pitches, these are particularly preferably used because they have high chemical purity and the properties can be freely controlled.

  The graphitizable carbon precursor here is easily determined by measuring the diffraction peak based on the graphite structure by XRD when the carbonized product obtained by carbonization is graphitized at a high temperature of 2800 ° C. it can. The holding time in graphitization in this case is not particularly limited, but is usually held at the graphitizing temperature for about 10 minutes. The graphitized material starting from the graphitizable carbon precursor has an Lc value of 100 nm or more obtained from the 002 diffraction peak when analyzed based on the Japan Society for the Promotion of Science (established by the Japan Society for the Promotion of Science Carbon Material 117 Committee). Indicates a large value. However, when the calculated value of Lc exceeds 100 nm, the reliability of the absolute value is lowered, and in such a case, it is expressed as Lc having a size of typically> 100 nm. When a non-graphitizable carbon precursor that starts from a non-graphitizable resin or the like is used, the electrode density is greatly reduced because it is easily activated.

  It is necessary to give an appropriate nitrogen content to the carbonized material in order to increase the capacitance. For this purpose, a high capacitance can be obtained by selecting the carbonized material used for the nitriding treatment. That is, the carbonized material used for nitriding is heat-treated at 600 ° C. to 800 ° C. in an inert atmosphere, preferably 600 ° C. to 750 ° C., more preferably 600 ° C. to 725 ° C. Further, the H / C atomic ratio by elemental analysis is preferably 0.40 or less or the true density is preferably 1.42 g / cc or more, more preferably the H / C atomic ratio is 0.38 or less or the true density is 1. .425 or more, more preferably H / C atomic ratio is 0.36 or less or true density is 1.43 or more. When H / C is higher than 0.40 and the true density is lower than 1.42 g / cc due to the low heat treatment temperature, the density of the EDLC electrode due to activated carbon after nitriding and activation is severe, and high static The electric capacity cannot be obtained.

  Nitrides can be obtained by nitriding the above-mentioned carbonides, but in order to obtain activated carbon having a high capacitance, it can be obtained by activating a specific nitride. As the nitride, the H / C atomic ratio is 0.150 or more and the N / C atomic ratio is 0.016 or more, preferably the H / C atomic ratio is 0.152 or more and the N / C atomic ratio is 0. .016 or more, more preferably, the H / C atomic ratio is 0.155 or more and the N / C atomic ratio is 0.017 or more. Any value correlates with the formation of pores due to activation, and when these values are too low, the formation of pore structures due to activation is hindered and the capacitance is not expressed.

  The nitriding treatment of the carbonized material is not particularly limited, but is a method in which heat treatment is performed in an atmosphere containing a nitrogen-containing gas (the nitrogen-containing gas here does not include nitrogen gas that is inert to carbon). And a method using nitrogen plasma, co-carbonization with a nitrogen-containing organic substance, and the like.

Regarding the heat treatment temperature of the carbonized product in a nitrogen-containing gas atmosphere, the amount of nitrogen introduced is reduced if the temperature is too high or too low, and the capacitance is not improved. If the heat treatment temperature is too high, the carbon network surface develops too much and the formation of the pore structure by activation is inhibited.

  The heat treatment temperature is preferably 600 to 1000 ° C, more preferably 600 to 950 ° C, and further preferably 600 to 850 ° C. The heat treatment time is preferably 0.1 to 10 hours, more preferably 0.1 to 8 hours, and further preferably 0.1 to 6 hours. Of the nitrogen-containing gases, ammonia is preferable because of its reactivity with carbon. The nitrogen-containing gas may be diluted with an inert gas such as nitrogen or argon, and its concentration is preferably 0.1 to 100 vol%, more preferably 0.5 to 100 vol%, and still more preferably 1 to 100 vol%. It is.

The shape of the carbonized product during the heat treatment with the nitrogen-containing gas is not limited, but in order to contact more nitrogen-containing gas and introduce more nitrogen, it must be fine particles desirable. The particle diameter is preferably 10 mm or less, more preferably 7 mm or less, and still more preferably 5 mm or less.

  Further, in the heat treatment with the nitrogen-containing gas, the container material into which the carbonized product is put is preferably a non-metallic container that does not cause decomposition of the nitrogen-containing gas. In particular, it is necessary that the metal material is not substantially contained in the portion that comes into contact with the nitrogen-containing gas and the carbonized material at 500 ° C. or higher.

The heat treatment furnace used for the heat treatment with the nitrogen-containing gas is not particularly limited, and there are a stationary furnace, a rotary kiln furnace, a pusher furnace, a roller hearth furnace, etc., but the nitrogen-containing gas and the carbonized product are contacted at 500 ° C. or higher. Any heat treatment furnace may be used as long as the portion does not substantially contain a metal material.

The nitride obtained by such heat treatment is activated after pulverization, but chemical activation is preferred to obtain higher capacitance, and alkali activation with an alkali metal hydroxide is more preferred. In the activation treatment, powdered nitrides are used, but there are ball mills, roller mills, high-speed rotation mills, medium stirring mills, jet mills, etc. as methods for pulverizing the nitrides. In order to obtain a desired particle size, a plurality of pulverizers and classifiers may be used in combination.

  Although there is no particular limitation on the particle size of the obtained nitride particles, the electrode for EDLC is usually 50 to 500 μm, and even when it is thick, it is 500 μm or less. From the viewpoint of handling, the lower limit of the particle size is preferably 100 nm or more. Therefore, the recommended particle size of the nitride particles as the activated carbon raw material for EDLC is 100 nm to 500 μm, preferably 200 nm to 200 μm, and more preferably 500 nm to 100 μm.

  As an activator used for alkali activation to obtain a high capacitance, alkali metal compounds such as lithium hydroxide, sodium hydroxide, potassium hydroxide, potassium carbonate, potassium chloride are used. Among them, sodium hydroxide, Potassium hydroxide or a combination thereof is preferred.

  Although the alkali activation method and apparatus are not particularly limited, 1 to 6 parts by weight of an alkali metal compound is added to 1 part by weight of a nitride, and these are uniformly mixed and filled into a container. The method of mixing is not limited as long as the nitride particles and the alkali metal compound are in uniform contact, but the method of mixing the alkali metal compound with a mixer after pulverizing the alkali metal compound, There is a method of adding to the nitride particles.

  The mixture of the nitride and the alkali metal compound is heated from room temperature to 400 to 1000 ° C. in a heating furnace under an inert gas atmosphere such as nitrogen gas or argon gas and held for 0.5 to 20 hours. When the reaction temperature is lower than 400 ° C., the reaction hardly proceeds and the activation degree does not increase. When the reaction temperature is higher than 1000 ° C., the problem of erosion of the reactor due to precipitation or scattering of alkali metal occurs severely. The activation treatment is performed at a temperature of ° C, more preferably at a temperature of 600 to 800 ° C for 1 to 5 hours. The activated carbon obtained by the activation treatment is neutralized with hydrochloric acid and then washed with water until neutral.

  In order to achieve a capacitance per unit weight and a high electrode density, it is important that there is a small proportion of relatively large pores that are involved in the development of the capacitance but that cause a decrease in the electrode density. is there.

In order to measure such pores, a measurement method by gas adsorption is often used. Gases used for gas adsorption measurement include nitrogen, argon, helium, carbon dioxide, etc. Among them, carbon dioxide adsorption measurement is suitable. Since the adsorption measurement of carbon dioxide is performed at a high temperature as the gas adsorption measurement of 273K, it has a feature that the diffusion of the adsorbed gas is fast, that is, the measurement can be performed in a short time. Carbon dioxide has a high saturated vapor pressure (26200 torr), and a very small relative pressure region (P / P ₀ ) can be measured in the gas adsorption measurement result. The measurement of the low relative pressure region in gas adsorption results in a very small pore diameter region, and the measurement of carbon dioxide at 273K can measure pores of 3.5 to 15 mm. When nitrogen gas is used as an adsorbed gas, an ultrahigh vacuum is required to measure a small relative pressure region, and for that purpose, equipment such as a turbo molecular pump is required.

  For analysis of the pores, a DFT method (density functional theory) can be used. There are classical and macroscopic theories such as DR and BJH methods, and semi-empirical methods such as the HK and SF methods, but there are not only micropores but also narrow mesopores. In many cases, however, the filling of the adsorbed gas is not practical, which underestimates the pore size. Compared to them, the DFT method is considered to be quite accurate for pore size analysis in narrow pores at the molecular level.

  In order to obtain an EDLC electrode having a high density and a high capacitance per unit volume, pores of 7 mm or less are greatly involved. If there are many pores of 7 mm or less, the capacitance per unit weight increases, but if it is simply too many, or if the ratio to the total pore volume is small, that is, if there are many pores of 7 mm or more, As a result, the electrode density decreases, and as a result, the capacitance per unit volume decreases. From this, the pore volume of 7 mm or less is preferably 0.15 cc / g or less, and the ratio of the pore volume of 7 mm or less to the total pore volume is preferably 40% or more, more preferably 7% or less. The pore volume is 0.14 cc / g or less, and the ratio of the pore volume of 7 mm or less to the total pore volume is 45% or more, more preferably, the pore volume of 7 mm or less is 0.13 cc / g or less. The ratio of the pore volume of 7 mm or less to the total pore volume is 50% or more.

  Moreover, since the activated carbon obtained by the present invention has a pore structure different from that of the conventional activated carbon, it has a feature that the amount of functional groups present on the pore surface is small. As a result, it is possible to obtain an activated carbon having a long life with less capacitance deterioration as compared with conventional activated carbon.

  The oxygen functional group is considered to be one of the factors that cause degradation in the long-term performance of EDLC by causing decomposition in a voltage region of 2 V or higher, which is usually used in EDLC using an organic electrolyte solution. It is more preferable that the activated carbon for EDLC has a small amount of surface functional groups. The surface functional groups mentioned here are a carboxyl group, a quinone group, a hydroxyl group, and a carboxyl group, and each can be determined by a titration method with hydrochloric acid based on the Boehm method. The total amount of the functional groups can be determined by using sodium ethoxide, but the surface functional group amount of the activated carbon having a long life is preferably 0.5 meq / g or less, more preferably 0.4 meq. / G or less, more preferably 0.3 meq / g or less.

  The unique pore structure of activated carbon that develops high capacitance is brought about by the changing nitrogen content until the activated carbon is prepared. That is, nitrogen in the activated carbon raw material is reduced by the activation treatment and forms a pore structure. Therefore, the nitrogen content in the obtained activated carbon is preferably 1 wt% or less, more preferably 0.7 wt% or less, and still more preferably 0.5 wt% or less.

Furthermore, when the difference in nitrogen content between the activated carbon and its nitride is larger than a certain value, a high capacitance per unit volume is given, and the value is preferably 1.0 wt% or more, more preferably 1.2 wt%, more preferably 1.5 wt% or more.

EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited at all by these Examples.
Various measurements in the examples were performed by the following methods.
(1) Elemental analysis of carbonized product and nitrogenated product About 800 μg of carbonized product or nitrogenated product to be measured was measured using a Yanako CHN coder manufactured by Yanagimoto Seisakusho, and the contents of C, H, and N were determined.
(2) True density 2 g of carbonized product was put into a 50 ml pycnometer, 25 ml of 1-butanol was added, and after degassing under reduced pressure with an aspirator for 30 minutes, 1-butanol was added, and after being kept in a thermostat at 30 ° C. for 30 minutes The true density was determined by weighing.
(3) Particle size The particle size was measured using a dry laser particle size distribution measuring device HEROS manufactured by SYMPATEC.
(4) Functional group measurement 1 g of activated carbon was placed in 25 ml of an ethanol solution of sodium ethoxide 0.1N and ultrasonically dispersed for 10 minutes, followed by stirring for 3 hours. Furthermore, after standing still for 20 hours, it stirred for 30 minutes and the liquid which filtered activated carbon was titrated with 0.1N hydrochloric acid, and the amount of surface functional groups was calculated | required. At this time, in order to remove the influence of carbon dioxide gas in the atmosphere, 25 ml of an ethanol solution of 0.1N sodium ethoxide containing no activated carbon was used as a blank.
(5) Carbon dioxide gas adsorption measurement A gas adsorption isotherm at 0 ° C was obtained for 0.2 g of activated carbon using QUADRASORB SI manufactured by Cantachrome. By analyzing the obtained adsorption isotherm using the DFT method, the pore volume was determined.
(6) Polarizing electrode production method and measurement method An electrode was prepared by mixing in a weight ratio of 80:10:10 of activated carbon: conductive filler (Denka black): binder (Teflon (registered trademark)). For electrode evaluation, an aluminum bipolar cell was used, and a paper separator was sandwiched between a pair of electrodes and accommodated in the cell. As the electrolyte, propylene carbonate in which 1.8 mol / L of triethylmethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₃ CH ₃ NBF ₄ ) was dissolved was used.
Charged to a voltage of 2.7 V at a constant current of 100 mA / g in an argon gas atmosphere at room temperature, further charged for 2 hours at 2.7 V, then discharged to 0 V at a constant current of 100 mA / g. The capacitance was calculated from the amount of electricity. The capacitance was calculated according to the following formula based on the weight of carbon in the positive and negative electrodes (activated carbon and acetylene black). The capacitance Cv (F / cc) per volume was calculated by multiplying the capacitance Cw (F / g) per weight by the electrode density.
(Formula) Capacitance Cw (F / g) = Discharge Electricity (AH / g) × 3600 / 2.7

Example 1
In the presence of hydrogen fluoride and boron trifluoride, naphthalene is polymerized to synthesize pitch (softening point by Mettler method: 283 ° C, optical anisotropy of carbonized product: 100%, Lc value of graphitized product:> 100 nm) did.
Next, 1000 g of the pitch is placed in a stainless steel square container having a height of 400 mm and a bottom surface of 400 mm × 400 mm, heated in a vertical furnace to 730 ° C. in a nitrogen atmosphere, and held at this temperature for 1 hour. To obtain a carbonized product. The carbonized product had an H / C of 0.309 and a true density of 1.49 g / cc.
The carbonized product was pulverized to 32 μm or less. 5 g of the carbonized powder was put in an alumina container, and nitriding was carried out by holding at 750 ° C. for 4 hours in an ammonia / nitrogen (30/70 vol%) mixed gas atmosphere. The nitrogen content of this nitride was 4.8 wt%. The H / C atomic ratio and N / C atomic ratio of this nitride were 0.169 and 0.0449, respectively.
1 part by weight of the nitride powder and 1.8 parts by weight of 95% potassium hydroxide were uniformly mixed, heated to 750 ° C. at 5 ° C./min under a nitrogen atmosphere, and maintained at this temperature for 3 hours. . After cooling to room temperature, the mixture was poured into a methanol-water mixture, and acid washing with 0.1 mol / L hydrochloric acid aqueous solution, filtration, and water washing were repeated until the filtrate became neutral. The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption was 0.12 cc / g, and the ratio of the pore volume of 7 mm or less to the total pore volume was 56%.
The surface functional group amount of the activated carbon measured by the functional group was 0.20 meq / g.
The activated carbon had a nitrogen content of 0.5 wt%, and the difference in nitrogen content with the nitride was 4.3 wt%.
The polarizable electrode obtained from the activated carbon exhibited excellent values of a capacitance per weight of 39.3 F / g, a capacitance per volume of 41.6 F / cc, and an electrode density of 1.06 g / cc.
Moreover, when the electrostatic capacitance maintenance factor in 70 degreeC and 2.7V was measured, the electrostatic capacitance maintenance factor after 100 hours was 92.2%. The results are summarized in Table 1.

Example 2
As a carbonized material used for nitriding treatment with ammonia, the synthetic pitch used in Example 1 was continuously supplied to a rotary kiln (internal volume 0.15 m ³ ) containing 81 kg of zirconia balls, and held at 685 ° C. for 1 hour. A heat-treated product was used. The carbonized product had an H / C of 0.295 and a true density of 1.50 g / cc.
Activated carbon was obtained in the same manner as in Example 1 except that the nitriding treatment was followed by grinding to 32 μm or less. The surface functional group amount of the activated carbon was 0.20 meq / g. The nitrogen content of the nitride was 2.8 wt%, and the nitrogen content of the activated carbon was 0.4 wt%. The H / C atomic ratio and N / C atomic ratio of the nitride were 0.164 and 0.0252, respectively. The nitrogen content of the activated carbon was 0.4 wt%, and the nitrogen content difference between the nitride and the activated carbon was 2.4 wt%.
The pore volume of 7 cm or less by the DFT method using carbon dioxide adsorption was 0.10 cc / g, and the ratio of the pore volume of 7 cm or less to the total pore volume was 62%.
The capacitance per weight was 37.3 F / g, the capacitance per volume was 37.3 F / cc, and the electrode density was 1.00 g / cc. The capacitance maintenance ratio after 70 ° C., 2.7 V, and 100 hours was 91.5%. The results are summarized in Table 1.

Example 3
Activated carbon was obtained in the same manner as in Example 2 except that the heat treatment temperature in the rotary kiln was changed to 625 ° C. The surface functional group amount of the activated carbon was 0.30 meq / g.
The H / C atomic ratio of the carbonized product was 0.360, and the true density was 1.43 g / cc. The H / C atomic ratio and N / C atomic ratio of the nitride were 0.169 and 0.0173, respectively. The nitrogen content of the activated carbon was 0.5 wt%, and the difference between the nitrogen content of the nitride and the activated carbon was 1.5 wt%.
The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption was 0.09 cc / g, and the ratio of the pore volume of 7 mm or less to the total pore volume was 69%.
The capacitance per weight was 36.8 F / g, the capacitance per volume was 36.8 F / cc, and the electrode density was 1.00 g / cc. The results are summarized in Table 1.

Example 4
Activated carbon was obtained in the same manner as in Example 2 except that the heat treatment temperature in the rotary kiln was changed to 705 ° C. The surface functional group amount of the activated carbon was 0.25 meq / g.
The H / C atomic ratio of the carbonized product was 0.259, and the true density was 1.55 g / cc. The H / C atomic ratio and N / C atomic ratio of the nitride were 0.159 and 0.0270, respectively. The nitrogen content of the activated carbon was 0.4 wt%, and the difference between the nitrogen content of the nitride and the activated carbon was 2.6 wt%.
The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption was 0.09 cc / g, and the ratio of the pore volume of 7 mm or less to the total pore volume was 58%.
The capacitance per weight was 36.4 F / g, the capacitance per volume was 35.4 F / cc, and the electrode density was 0.97 g / cc. The results are summarized in Table 1.

Example 5
Activated carbon was obtained in the same manner as in Example 2 except that the heat treatment temperature in the rotary kiln was changed to 725 ° C. The surface functional group amount of the activated carbon was 0.22 meq / g.
The H / C atomic ratio of the carbonized product was 0.239, and the true density was 1.57 g / cc. The H / C atomic ratio and N / C atomic ratio of the nitride were 0.171 and 0.0304, respectively. The nitrogen content of the activated carbon was 0.5 wt%, and the difference between the nitrogen content of the nitride and the activated carbon was 2.6 wt%.
The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption was 0.10 cc / g, and the ratio of the pore volume of 7 mm or less to the total pore volume was 59%.
The capacitance per weight was 37.9 F / g, the capacitance per volume was 36.2 F / cc, and the electrode density was 0.96 g / cc. The results are summarized in Table 1.

Example 6
Activated carbon was obtained in the same manner as in Example 2 except that the carbonized material was pulverized before nitriding. The surface functional group amount of the activated carbon was 0.33 meq / g. The H / C atomic ratio and N / C atomic ratio of the nitride were 0.158 and 0.0486, respectively. The activated carbon had a nitrogen content of 0.5 wt%, and the difference in nitrogen content between the nitride and the activated carbon was 4.7 wt%.
The pore volume of 7 cm or less by the DFT method using carbon dioxide adsorption was 0.11 cc / g, and the ratio of the pore volume of 7 cm or less to the total pore volume was 63%.
The capacitance per weight was 39.5 F / g, the capacitance per volume was 36.1 F / cc, and the electrode density was 0.92 g / cc. The results are summarized in Table 1.

Example 7
1 kg of the same carbonized product as used in Example 2 was placed in a carbon container and subjected to nitriding treatment by holding at 820 ° C. for 4 hours in an atmosphere of 100 vol% ammonia. Thereafter, activated carbon was obtained in the same manner as in Example 1. The surface functional group amount of the activated carbon was 0.10 meq / g. The nitrogen content after nitriding was 4.7 wt%, and the activated carbon after activation was 0.3 wt%. The H / C atomic ratio and N / C atomic ratio of this nitride were 0.164 and 0.0252, respectively. The difference in nitrogen content between the nitride and the activated carbon was 4.4 wt%.
The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption was 0.095 cc / g, and the ratio of the pore volume of 7 mm or less to the total pore volume was 55%.
The capacitance per weight was 38.6 F / g, the capacitance per volume was 36.7 F / cc, and the electrode density was 0.95 g / cc. The results are summarized in Table 1. The capacitance retention rate after 70 ° C., 2.7 V, and 100 hours was 94.0%. The results are summarized in Table 1.

Claims (7)

An activated carbon for an electric double layer capacitor electrode that satisfies the following conditions (a) to (c).
(A) The nitrogen content is 1 wt% or less,
(B) The pore volume of 7 mm or less by the DFT method using carbon dioxide adsorption is 0.15 cc / g or less, and the ratio of the pore volume of 7 mm or less to the total pore volume is 40% or more,
(C) The amount of surface functional groups is 0.5 meq / g or less.   A method for producing activated carbon for an electric double layer capacitor electrode, in which a carbonized product obtained by heat-treating pitch or graphitizable coke at a temperature of 600 ° C. or higher and 800 ° C. or lower is subjected to nitriding treatment to form a nitride, and then activation treatment is performed. .   The method for producing activated carbon for an electric double layer capacitor electrode according to claim 2, wherein the difference in nitrogen content between the activated carbon and the nitride is 1.0 wt% or more.   The method for producing an activated carbon for an electric double layer capacitor electrode according to claim 2, wherein the H / C atomic ratio of the carbonized product is 0.40 or less or the true density of the carbonized product is 1.42 g / cc or more.   The method for producing an activated carbon for an electric double layer capacitor electrode according to claim 2, wherein the H / C atomic ratio of the nitride is 0.150 or more and the N / C atomic ratio is 0.016 or more.   The method for producing activated carbon for an electric double layer capacitor electrode according to claim 2, wherein the reactor for performing the nitriding treatment does not substantially contain a metal material in a portion in contact with the carbonized material and the nitrogen-containing gas at 500 ° C or higher. .   The method for producing activated carbon for an electric double layer capacitor electrode according to claim 2, wherein the pitch is a pitch obtained by polymerizing a condensed polycyclic hydrocarbon in the presence of hydrogen fluoride / boron trifluoride.