JP6371787B2 - Activated carbon, method for producing the same, and electric double layer capacitor using the activated carbon - Google Patents

Description

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

  Activated carbon is used for adsorption and the like because of its large specific surface area. In recent years, it is also used as an electrode material such as an electrode for an electric double layer capacitor. Since activated carbon has many micropores having a pore diameter of 2.0 nm or less, it has a feature that the specific surface area is larger than other porous materials. However, since micropores have a small pore size, if used as an adsorbent, the diffusion / migration speed of the adsorbed substance in the pores (hereinafter sometimes referred to as “migration speed”) is slow, and the electrode for an electric double layer capacitor When used in the above, the moving speed of the electrolyte ions (hereinafter sometimes referred to as “ion moving speed”) is slow. Therefore, even if the specific surface area was large, the adsorption sites in the pores could not be fully utilized.

  As a means for solving such a problem, it is conceivable to increase the moving speed of the adsorbed substance in the pores by increasing the pore diameter. However, simply increasing the pore diameter reduces the specific surface area per pore volume, and the amount of adsorption per activated carbon mass or the amount of adsorption per activated carbon volume (hereinafter sometimes referred to as “adsorption amount”). descend.

  Various techniques for improving the adsorption amount and the moving speed by adjusting the pore distribution and specific surface area of the activated carbon have been proposed for such problems.

For example, in Patent Document 1, the micropore volume is 10 to 60% of the total pore volume, the mesopore volume is 20 to 70% of the total pore volume, and the macropore volume is the total pore volume. A carbonaceous material that occupies 20% or less, has a total pore volume of 0.3 to 2.0 cm ³ / g, and a specific surface area of 1000 to 2500 m ² / g is disclosed.

In Patent Document 2, the BET specific surface area is 1000 m ² / g or more and 3000 m ² / g or less, and the area ratio in the BET specific surface area of pores having a pore diameter of 1.0 nm or more and 2.0 nm or less is 40% or more, And the activated carbon whose volume ratio in the total pore volume of the pore more than 2.0 nm and less than 50.0 nm is 40% or more is disclosed.

Further, Patent Document 3 discloses that the BET specific surface area is 2200 m ² / g or more and 2700 m ² / g or less, the average pore diameter is 2.2 nm or more and 2.8 nm or less, and the pores calculated by the Cranston inclay method An activated carbon for an electric double layer capacitor having a pore volume between 5.0 nm and 30.0 nm in diameter of 0.20 cm ³ / g or more and 0.60 cm ³ / g or less is disclosed.

JP 2001-89119 A JP 2011-20907 A JP 2011-176043 A

  Even if the pore distribution and specific surface area of the activated carbon are controlled as in Patent Documents 1 to 3, there is still room for study on the adsorption amount and the moving speed. In addition, for example, an electric double layer capacitor is required to have a large capacitance and a low internal resistance, but it has been difficult to satisfy both characteristics with conventional activated carbon.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an activated carbon that balances the adsorption amount and the moving speed in a well-balanced manner, a manufacturing method thereof, and an electric double layer capacitor using the activated carbon. To do.

The activated carbon according to the present invention that has solved the above-mentioned problems has a BET specific surface area (hereinafter sometimes referred to as “specific surface area”) of 1450 to 1950 m ² / g and a pore volume of 3 to 9 nm. It has a gist that it is 0.35 cm ³ / g and the average pore diameter is 2.05 to 2.60 nm.

  In the activated carbon of the present invention, the ratio of the pore volume having a pore diameter of 3 nm or more to the total pore volume is preferably 12 to 39%, and the average particle diameter is preferably 10 μm or less. It is.

  The activated carbon of the present invention may be granular or powdery.

  The present invention includes an electrode material for an electric double layer capacitor containing the activated carbon, an electrode for an electric double layer capacitor using the electrode material, and an electric double layer capacitor using the electrode.

  In the method for producing the activated carbon according to the present invention, the carbon raw material is carbonized, and then the carbon raw material derived material is sequentially processed by steam activation one or more times, and the carbon raw material derived material is subjected to the final steam activation. The gist is that at least one of a calcium compound and a potassium compound is attached, and the final water vapor activation is performed while the attached state is maintained.

  In the method for producing activated carbon of the present invention, (1) after adding at least one of the calcium compound and potassium compound to the carbon raw material and then carbonizing, or (2) carbonizing the carbon raw material and then the calcium After adhering at least one of a compound and a potassium compound, or (3) after carbonizing the carbon raw material, steam activation, and then adhering at least one of the calcium compound and the potassium compound, Steam activation is also a preferred embodiment.

  In the activated carbon of the present invention, the specific surface area, the pore volume of a specific pore diameter, and the average pore diameter are optimized, so that the adsorption amount and the moving speed are balanced in a balanced manner. Therefore, for example, if the activated carbon of the present invention is used for an electrode for an electric double layer capacitor as an electrode material for an electric double layer capacitor, the ion transfer rate in the pores of the activated carbon can be improved while increasing the capacitance. Therefore, an electric double layer capacitor having excellent capacitance and internal resistance can be obtained. Moreover, according to the manufacturing method of this invention, the said activated carbon of this invention can be manufactured easily.

FIG. 1 is a graph showing the relationship between the total pore volume and specific surface area of the activated carbon of the example. FIG. 2 is a graph showing the relationship between the pore volume of the activated carbon of the example having a pore diameter of 3 nm or more and the specific surface area. FIG. 3 is a graph showing the relationship between the volume ratio of pores having a pore diameter of 3 nm or more and the specific surface area of the activated carbon of the example. FIG. 4 is a graph showing the relationship between the average pore diameter and the specific surface area of the activated carbon of the example. FIG. 5 is a graph showing the relationship between the internal resistance at −30 ° C. of the activated carbon of the example and the capacitance per volume at room temperature. FIG. 6 is a graph showing the relationship between the capacitance per volume of the activated carbon of the example at room temperature and the pore volume with a pore diameter of 3 nm or more. FIG. 7 is a graph showing the relationship between the internal resistance at −30 ° C. of the activated carbon of the example and the pore volume having a pore diameter of 3 nm or more. FIG. 8 shows activated carbon No. of Example. It is a graph which shows the pore distribution of 1, 2, 6, 10. FIG. 9 is a schematic explanatory diagram of the electric double layer capacitor produced in the example.

  Although the technique which improves the characteristic of activated carbon by controlling the pore distribution and specific surface area of activated carbon like the said patent documents 1-3 was proposed, it was difficult to aim at the balance of adsorption amount and moving speed. For example, in electric double layer capacitor applications, electrostatic capacity and internal resistance are considered to have a trade-off relationship. That is, when the specific surface area of the activated carbon is increased, the proportion of fine pores such as micropores increases, but it is known that the ion migration rate decreases and the internal resistance increases in the fine pores. . On the other hand, when the pore diameter of the activated carbon is increased, the ion migration speed is improved and the internal resistance is decreased. However, since the total pore volume is increased and the bulk density of the activated carbon is decreased, the electrostatic capacity per unit volume of the capacitor cell is decreased. It is known that capacity decreases.

  The activated carbon of the present invention improves the movement speed by well-balanced adjustment of the specific surface area, the pore volume with a pore diameter of 3 nm or more, and the average pore diameter, and also sufficiently maintains the pores that contribute to the increase in adsorption amount. it can. Therefore, for example, when the activated carbon of the present invention is used, an electric double layer capacitor having a large capacitance and a small internal resistance can be obtained. In particular, the activated carbon of the present invention has not only a capacitance at normal temperature (25 ° C.) (including capacitance per volume and capacitance per mass, the same shall apply hereinafter) and internal resistance, but also a capacitance at −30 ° C. It also exhibits excellent characteristics in terms of capacitance (hereinafter also referred to as “low temperature capacitance”) and internal resistance at −30 ° C. (hereinafter also referred to as “low temperature internal resistance”).

  Hereinafter, the activated carbon of the present invention will be specifically described.

The specific surface area of the activated carbon of the present invention is 1450 to 1950 m ² / g. If the specific surface area is too small, the amount of adsorption decreases. Therefore, for example, a sufficient capacitance per mass as an electric double layer capacitor cannot be obtained. Moreover, when the specific surface area is too large, the bulk density decreases. Therefore, for example, a sufficient capacitance per volume as an electric double layer capacitor cannot be obtained. The specific surface area is preferably 1500 m ² / g or more, more preferably 1550 m ² / g or more, preferably 1900 m ² / g or less, and more preferably not more than 1880m ² / g.

Moreover, the activated carbon of the present invention has a pore volume of 0.09 to 0.35 cm ³ / g with a pore diameter of 3 nm or more. When the pore volume having a pore diameter of 3 nm or more is too small, the moving speed is lowered. Therefore, for example, when activated carbon is used for the electric double layer capacitor, the internal resistance increases. On the other hand, if the pore volume having a pore diameter of 3 nm or more is too large, the bulk density of the activated carbon decreases. More pore volume pore diameter 3nm preferably 0.10 cm ³ / g or more, more preferably 0.15 cm ³ / g or more, preferably 0.30 cm ³ / g hereinafter, more preferably 0.25 cm ³ / G or less. In the present invention, the pore volume having a pore diameter of 3 nm or more is a pore volume having a pore diameter of 3 nm or more and 30 nm or less.

  The activated carbon of the present invention has an average pore diameter of 2.05 to 2.60 nm. If the average pore diameter is too small, it becomes difficult for the adsorbent to enter and exit the activated carbon smoothly, and the moving speed decreases. On the other hand, if the average pore diameter is too large, the bulk density of the activated carbon decreases. The average pore diameter is preferably 2.10 nm or more, preferably 2.55 nm or less, more preferably 2.50 nm or less.

In the activated carbon of the present invention, the ratio of the pore volume having a pore diameter of 3 nm or more (hereinafter referred to as “pore volume having a pore diameter of 3 nm or more”) to the total pore volume is preferably 12 to 39%. When the ratio of the pore volume having a pore diameter of 3 nm or more is increased, the moving speed is improved, and therefore, it is more preferably 15% or more. On the other hand, if the ratio of the pore volume having a pore diameter of 3 nm or more becomes too high, the bulk density of the activated carbon decreases, and therefore it is more preferably 30% or less. In the present invention, the total pore volume is a pore volume having a pore diameter of 30 nm or less as measured by the method described in Examples.

  The average particle diameter of the activated carbon of the present invention is preferably 10 μm or less. The lower limit of the average particle diameter is not particularly limited, but is preferably 1.0 μm or more, more preferably 2.0 μm or more in consideration of handleability.

The total pore volume of the activated carbon of the present invention is preferably 0.70 cm ³ / g or more, more preferably 0.90cm ³ / g or more, even more preferably 0.94 cm ³ / g or more, preferably 3. 0 cm ³ / g or less, more preferably 2.0 cm ³ / g, more preferably not more than 1.10 cm ³ / g.

  The shape of the activated carbon may be various shapes depending on the application, and examples thereof include granular and powdery forms. For example, when using activated carbon as an electrode material for an electric double layer capacitor, granular activated carbon or powdered activated carbon may be used in consideration of handleability and bulk density.

  The method for producing the activated carbon of the present invention is not particularly limited as long as it can produce activated carbon having a specific surface area, a pore volume having a pore diameter of 3 nm or more, and an average pore diameter satisfying the predetermined range. Hereinafter, although the manufacturing method of the activated carbon of this invention is demonstrated concretely, the manufacturing method of this invention is not limited to the following manufacture example, It can change suitably.

  The activated carbon having the above-described features of the present invention is obtained by converting at least one of a calcium compound and a potassium compound (hereinafter referred to as “calcium compound etc.”) from a carbon raw material (a carbon raw material, a carbon raw material carbide, and a carbon raw material steam activated material described later). In the meaning including the same, the same applies hereinafter), and steam activation is performed while maintaining the attached state.

  Specifically, the carbon raw material is carbonized, and then the raw material derived from the carbon raw material is sequentially processed by steam activation one or more times, and when performing one water vapor activation, the water vapor activation or a plurality of water vapor activations are performed. When the activation is performed, a calcium compound or the like is attached to the carbon material-derived material until the last steam activation is performed, and the last steam activation may be performed while maintaining the attached state.

  The carbon raw material-derived material is not particularly limited as long as it is used as a raw material for ordinary activated carbon. For example, carbon raw materials such as coconut shell, phenol resin, coal, rayon; carbon raw material carbides obtained by carbonizing these carbon raw materials; and carbon raw material steam activated products obtained by steam activation of these carbon raw materials and carbon raw material carbides (hereinafter referred to as “steam activated charcoal”) And so on). Among these, coconut shell, coconut shell carbide, and coconut shell steam activated charcoal that can control the specific surface area and the pore volume of 3 nm or more in a well-balanced manner are preferable. In view of availability and cost, coconut shell steam activated charcoal that can be obtained at low cost in the market is more preferable.

  In the present invention, pores having a pore diameter of 3 nm or more can be developed while leaving micropores by activating water vapor in a state where a calcium compound or the like is attached to a carbon raw material-derived material. In addition, the timing which attaches a calcium compound etc. is not specifically limited, As long as the attachment state of a calcium compound etc. is maintained to a carbon raw material origin material at the time of steam activation, it can be added in arbitrary steps. In the present invention, a carbon material-derived material in which an adhering state of a calcium compound or the like is maintained before performing steam activation is referred to as an activation material, and the activation material includes the following adsorbed carbide and the adsorbed water vapor activation material.

  As described above, in the production method of the present invention, the calcium compound or the like may be attached to the carbon raw material-derived material before the final steam activation. Therefore, (1) after the carbon compound is carbonized after being added to the carbon raw material, the obtained carbonized carbide may be activated by steam, or (2) after the carbon raw material is carbonized, the calcium compound or the like is added. The obtained impregnated carbide may be steam activated. Alternatively, (3) after carbonizing the carbon raw material, steam activation may be performed, and then an impregnated steam activated product obtained by adhering a calcium compound or the like may be steam activated. Of course, the calcium compound or the like may be added at a plurality of locations in the manufacturing process, that is, at arbitrary different steps. For example, a calcium compound or the like may be added to a carbon raw material and then carbonized, and then the calcium compound or the like may be added again. Further, after carbonizing the carbon raw material, a calcium compound or the like may be attached and then steam activated, and the resulting carbon raw material steam activated product may be attached with a calcium compound or the like, and then steam activated.

  The shape of the carbon material-derived material is not particularly limited, and may be any shape such as a granular shape, a powdery shape, a granular shape, a spherical shape, a lump shape, a fibrous shape, and a plate shape.

  In the present invention, the carbon raw material is carbonized before or after the calcium compound is attached, but the carbonization treatment conditions are not particularly limited, and the carbon raw material is usually used in an inert gas atmosphere such as nitrogen, helium or argon. What is necessary is just to heat-process with the temperature and time which do not burn. The carbonization temperature is preferably 500 ° C. or higher, more preferably 550 ° C. or higher, preferably 1200 ° C. or lower, more preferably 1000 ° C. or lower. The holding time at the carbonization temperature is preferably 5 minutes to 3 hours.

  In the present invention, the carbon raw material carbide is steam activated one or more times. For example, the carbon raw material steam activated product obtained by performing steam activation on the carbon raw material carbide is adsorbed with a calcium compound or the like, and the steam is maintained while maintaining the attached state. You may activate. The water vapor activation conditions for producing the carbon raw material water vapor activated product are not particularly limited, and known water vapor activation conditions can be employed. By steam activation of the carbon raw material carbide, the specific surface area and total pore volume of the activated carbon can be increased, and the pore volume of the micropores effective for improving the adsorption amount can be increased. Therefore, when the obtained carbon raw material water vapor activation product is used as the activation raw material, the activated carbon of the present invention excellent in the adsorption amount and the moving speed can be obtained. Moreover, you may perform a well-known washing | cleaning process and heat processing as needed to a carbon raw material steam activation material.

  In the present invention, a calcium compound or the like is added to the carbon material-derived material. The method for attaching the calcium compound or the like is not particularly limited. For example, (i) a method of immersing a carbon material-derived material in a calcium compound-containing liquid, (ii) a method of spraying a calcium compound-containing liquid on the carbon material-derived material, and (iii) a calcium compound-containing powder on the carbon material-derived material. And the like. Then, you may dry as needed. In addition, the calcium compound and the like-containing liquid desirably has calcium and potassium dissolved in the liquid from the viewpoint of improving the attachment property at a simple and low cost. Examples of the calcium compound or potassium compound include calcium carbonate, potassium carbonate, and chloride. Examples include calcium and potassium chloride. Among these, it is preferable to use calcium chloride or potassium chloride which is excellent in water solubility and low cost. Further, in the above-mentioned attaching method, the attaching conditions can be appropriately selected according to the properties of the calcium compound, such as using an organic solvent or dry mixing.

  According to the said attachment method, water vapor activation can be performed, maintaining the attachment state of a calcium compound etc. to the carbon raw material origin. However, if the wet cleaning such as washing with water is performed after the addition of the calcium compound or the like, the calcium compound or the like is desorbed. Therefore, either the wet cleaning is not performed until the water vapor is activated after the addition, or after the wet cleaning, the calcium compound is again used. It is desirable to attach them.

  Activated carbon of the present invention obtained by the last steam activation to a carbon material-derived material while maintaining the adhering state of the calcium compound, etc., and a conventional product obtained by steam-activating the carbon material-derived material without attaching a calcium compound or the like Compared with activated carbon, the following can be seen. For example, as shown in FIG. 1, even when the specific surface area, total pore volume, etc. are the same, the use of the calcium compound or the like is performed only when the water vapor derived from the carbon raw material is finally activated while maintaining the attached state of the calcium compound or the like. As a result, the state of the activated carbon is more suitably controlled, and as a result, an activated carbon in which the amount of adsorption and the moving speed are balanced with each other can be obtained. As shown in FIG. 8, activated carbon No. obtained by the last steam activation while maintaining the adhering state of the calcium compound or the like. Nos. 1 and 2 are activated carbon No. 1 manufactured without adding calcium compounds or the like. Compared with 6, 10, the last water vapor activation while maintaining the adhering state of calcium compound, etc. allows the pore volume of the micropores to maintain a sufficient adsorption capacity while developing pores with a pore diameter of 3 nm or more. Thus, the pore distribution is effective for improving the moving speed. Therefore, the activated carbon obtained by the production method of the present invention not only has a sufficient capacitance as, for example, an electric double layer capacitor, but also has reduced internal resistance.

  The amount of at least one of calcium and potassium (hereinafter referred to as “calcium etc.”) is not particularly limited, and the desired specific surface area and pore diameter are determined depending on the activation conditions, the presence or absence of washing treatment or heat treatment after the activation treatment, and the like. What is necessary is just to adjust suitably so that the pore volume of 3 nm or more and an average pore diameter may be obtained. If the amount of calcium or the like is too small, pores having a pore diameter of 3 nm or more may not be sufficiently developed even when steam is activated. On the other hand, if the amount of calcium or the like is too large, the pore volume of the micropores may be remarkably reduced, or pores having a pore diameter of 3 nm or more may be developed too much to reduce the bulk density. Therefore, the amount of calcium or the like contained in the carbon raw material after the calcium or the like is added is preferably 2700 ppm or more, more preferably 3000 ppm or more, still more preferably 4000 ppm or more, preferably 20000 ppm or less, more preferably 15000 ppm. It is as follows.

  When a calcium compound or the like is added to a carbon raw material derived solution using a calcium compound or the like-containing liquid, it is desirable to remove the moisture by a drying treatment or the like as necessary, and then perform the next treatment.

  After a calcium compound or the like is attached to the carbon material-derived material, the final steam activation is performed while maintaining the attached state. In the steam activation, the heating furnace is heated to a predetermined temperature, and then activated by supplying steam.

  The water vapor activation conditions are not particularly limited as long as the activated carbon of the present invention having a specific surface area, a pore volume of 3 nm or more in pore diameter, and an average pore diameter in the predetermined range is obtained. For example, the steam activation atmosphere is preferably performed in an inert gas atmosphere such as nitrogen, argon, or helium. Moreover, the temperature at the time of performing steam activation (furnace temperature) is preferably 400 ° C. or higher, more preferably 450 ° C. or higher, preferably 1500 ° C. or lower, more preferably 1300 ° C. or lower. The heating time when performing steam activation is preferably 1 minute or more, more preferably 5 minutes or more, preferably 10 hours or less, more preferably 5 hours or less.

  The total amount of water vapor supplied during the activation process is not particularly limited. The supply mode of the water vapor is not particularly limited, and for example, either a mode in which the water vapor is supplied without dilution or a mode in which the water vapor is diluted with an inert gas and supplied as a mixed gas is possible. In order to advance the activation reaction efficiently, an embodiment in which the reaction is diluted with an inert gas and supplied is preferable. When supplying water vapor diluted with an inert gas, the water vapor partial pressure in the mixed gas (total pressure 101.3 kPa) is preferably 30 kPa or more, more preferably 40 kPa or more.

(Other processing)
The activated carbon obtained by performing the last steam activation while maintaining the adhering state of the calcium compound or the like may be further subjected to washing treatment, heat treatment, pulverization treatment and the like as necessary. The washing treatment is performed on the activated carbon after steam activation using a known solvent such as water (normal temperature water, including hot water of about 60 ° C.), an acid solution, or an alkaline solution. By washing the activated carbon, impurities such as metal impurities and ash can be removed.

  The heat treatment is desirably performed by further heating the activated carbon after steam activation or washing in an inert gas atmosphere. Residual chlorine contained in the activated carbon can be removed by heat treating the activated carbon. Although the heat treatment conditions are not particularly limited, for example, the heat treatment temperature is preferably 400 ° C. or higher and 1000 ° C. or lower, and the holding time is preferably 5 minutes or longer and 3 hours or shorter.

  In the pulverization treatment, the average particle diameter of the activated carbon may be appropriately adjusted according to the application using various known pulverizers.

  In the present invention, the activation treatment may be performed a plurality of times, but it is desirable not to carry out further activation after steam activation in a state where a calcium compound or the like is attached. If the activation is further performed after the activation of the water vapor, the desired specific surface area, the pore volume having a pore diameter of 3 nm or more, and the average pore diameter may not be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the electrode material for electric double layer capacitors containing the said activated carbon of this invention, the electrode for electric double layer capacitors using this electrode material, and the electric double layer capacitor using this electrode can be provided.

  The electrode material for an electric double layer capacitor is composed of the activated carbon of the present invention and a binder, preferably a conductivity imparting agent.

  As an electrode for an electric double layer capacitor, for example, a paste is prepared by further adding a solvent to an electrode material for an electric double layer capacitor obtained by kneading activated carbon, a conductivity-imparting agent, and a binder. After applying to current collector plates, such as foil, what removed the solvent by drying is mentioned.

  As the binder used for the electrode for the electric double layer capacitor, fluorine-based polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum pitch, phenol resin, and the like can be used. As the conductivity imparting agent, acetylene black, ketjen black, or the like can be used.

  An electric double layer capacitor generally has an electrode, an electrolytic solution, and a separator as main components, and has a structure in which a separator is disposed between a pair of electrodes. Configuration can be taken. Examples of the electrolytic solution include an electrolytic solution in which an amidine salt is dissolved in an organic solvent such as propylene carbonate, ethylene carbonate, and methyl ethyl carbonate; an electrolytic solution in which a quaternary ammonium salt of perchloric acid is dissolved; quaternary ammonium or lithium An electrolytic solution in which an alkali metal boron tetrafluoride salt or phosphorous hexafluoride salt is dissolved; an electrolytic solution in which a quaternary phosphonium salt is dissolved may be mentioned. Examples of the separator include cellulose, glass fiber, or a nonwoven fabric, cloth, or microporous film mainly composed of polyolefin such as polyethylene or polypropylene.

  The electric double layer capacitor of the present invention can be used for various portable device power supplies, home appliance standby power supplies, optical communication UPSs, and electric vehicle power supplies. In addition, since the activated carbon of the present invention is excellent in adsorption capacity and adsorption rate, it can be used as an adsorbent such as a gas adsorbent, an adsorbent for water purification, and an adsorbent for wastewater purification.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Activated carbon No. 1
Raw material: Immerse in 0.83% calcium chloride (CaCl ₂ ) aqueous solution holding coconut shell carbide at room temperature, stir for 1 hour, filter, dry the filtration residue at 110 ° C., and add calcium compound to coconut shell carbide Activated material (calcium added amount is 5034 ppm) was obtained. Next, the activation raw material was put into a rotary kiln furnace, heated to 900 ° C. (temperature increase rate: 10 ° C./min) under nitrogen flow (1 L / min), and then steam (water vapor partial pressure: 50 kPa) was supplied together with nitrogen. This was kept at 900 ° C. for 4.0 hours, and steam activation was carried out while maintaining the calcium compound adhering state. After steam activation, the metal was removed from the steam activated charcoal by pickling treatment (hydrochloric acid concentration 5.25%), and then washed with 0.25% ammonium hydrogen carbonate and 60 ° C. warm water. After that, it was put into a muffle furnace, heated to 760 ° C. under a nitrogen flow (2 L / min) (heating rate: 10 ° C./min), and then heat-treated at 760 ° C. for 2 hours. After the heat treatment, it was pulverized with a jet mill pulverizer, and activated carbon No. 1 was produced.

Activated carbon No. 2-4
Except for changing the raw material from coconut shell charcoal to coconut shell steam activated charcoal (manufactured by MCET, “Z10-30”), activated carbon No. In the same manner as in No. 1, an activation raw material in which a calcium compound was attached to coconut shell steam activated charcoal was obtained (the amount of attachment is described in Table 1). Except for changing the retention time during steam activation to 2.5 hours (activated carbon No. 2), 3.0 hours (activated carbon No. 3), and 4.0 hours (activated carbon No. 4), activated carbon No. In the same manner as in No. 1, activated carbon no. 2 to 4 were produced.

Activated carbon No. 5
Activated carbon No. After performing steam activation, washing, and heat treatment in the same manner as in No. 3, the particles are placed in a pulverization vessel (diameter 13 cm × 21 cm) together with zirconia balls (diameter 3 mm) and pure water, and the average particle size (D50) is 3. Activated carbon No. 1 pulverized to 0 μm. 5 was produced.

Activated carbon No. 6
Activated carbon No. 1 was changed except that the retention time during steam activation was changed to 2.0 hours. In the same manner as in No. 2, activated carbon no. 6 was produced.

Activated carbon No. 7
Raw material: Coconut shell steam activated charcoal (manufactured by MCET, “Z10-30”) was put into a rotary kiln furnace and heated to 900 ° C. under a nitrogen flow (1 L / min) (temperature increase rate: 10 ° C./min). Thereafter, steam (water vapor partial pressure: 50 kPa) was supplied together with nitrogen, and kept at 900 ° C. for 2.0 hours for steam activation. After steam activation, the metal was removed from the steam activated charcoal by pickling treatment (hydrochloric acid concentration 5.25%), and then washed with 0.25% ammonium hydrogen carbonate and 60 ° C. warm water. After that, it was put into a muffle furnace, heated to 760 ° C. under a nitrogen flow (2 L / min) (heating rate: 10 ° C./min), and then heat-treated at 760 ° C. for 2 hours. After the heat treatment, it was pulverized with a jet mill pulverizer, and activated carbon No. 7 was produced.

Activated carbon No. 8, 9
Except for changing the retention time during steam activation to 2.5 hours (activated carbon No. 8) and 3.0 hours (activated carbon No. 9), activated carbon No. In the same manner as in No. 7, activated carbon No. 8 and 9 were produced.

Activated carbon No. 10
Activated carbon imitating Production Example 2 of Patent Document 2 was produced. Specifically, raw material: 100 g of paper phenolic resin laminate carbon carbide (average particle size: 5 mm to 15 mm) is put into a rotary kiln furnace and heated to 900 ° C. under nitrogen flow (1 L / min) (temperature increase rate: 10). Then, steam (water vapor partial pressure: 71 kPa) was supplied together with nitrogen and kept at 900 ° C. for 3.0 hours for steam activation. After steam activation, the metal was removed from the steam activated charcoal by pickling treatment (hydrochloric acid concentration 5.25%), and then washed with hot water at 60 ° C. Then, it grind | pulverized with a jet mill grinder and activated carbon No.1. 10 was produced.

Activated carbon No. 11
Except for changing the retention time during steam activation to 3.5 hours, activated carbon No. In the same manner as in No. 10, activated carbon no. 11 was produced.

1. Calcium deposition amount About 5 g of activated carbon is put in a magnetic crucible, and after ashing by heating at 815 ° C. for 24 hours in the atmosphere, the amount of ash is measured and an X-ray fluorescence analyzer (manufactured by Rigaku, “ZSX100e”) Was used to calculate the calcium content in the ash, and the calcium content was listed in the “Ca content” column. In addition, activated carbon No. Since 7-11 do not impregnate calcium, the amount of calcium derived from the raw material.

2. Specific surface area and total pore volume After 0.2 g of activated carbon was heated under vacuum at 250 ° C., a nitrogen adsorption isotherm was determined using a nitrogen adsorption device (“ASAP-2400” manufactured by Micromeritic Co., Ltd.), and the BET method Was used to determine the specific surface area (m ² / g). Nitrogen from the nitrogen adsorption isotherm up to a pore diameter of 30 nm when the relative pressure P / P ₀ (P: gas pressure of the adsorbate in adsorption equilibrium, P ₀ : saturated vapor pressure of the adsorbate at the adsorption temperature) is 0.93. The total pore volume (cm ³ / g) was calculated from the adsorption amount.

3. The pore volume adsorption isotherm of each pore diameter was analyzed by the BJH method, and the pore volume having a pore diameter of 3 nm or more and the ratio of the pore volume having a pore diameter of 3 nm or more to the total pore volume were calculated.

Pore volume with a pore diameter of 3 nm or more (cm ³ / g) = total pore volume (cm ³ / g) −pore volume with a pore diameter of less than 3 nm (cm ³ / g) (1)
Ratio of pore volume (%) having a pore diameter of 3 nm or more = [pore volume of 3 nm or more (cm ³ / g) / total pore volume (cm ³ / g)] × 100
The total pore volume is a pore volume of 30 nm or less, and the pore volume of a pore diameter of 3 nm or more is a pore volume having a pore diameter of 3 to 30 nm.

4). Average pore diameter The pore diameter of the activated carbon was assumed to be cylindrical, and the average pore diameter was calculated based on the following formula.
Average pore diameter (nm) = (4 × total pore volume (cm ³ / g)) / specific surface area (m ² / g) × 1,000 (6)

5. Average particle size (50D)
Activated carbon was measured using a laser diffraction type particle size distribution measuring device (Salazu 2000, manufactured by Shimadzu Corporation), a volume-based cumulative frequency curve was obtained from the particle size distribution measurement results, and the particle size at a cumulative frequency of 50%. Was defined as the average particle size.

6). Electric double layer capacitor evaluation 6-1. Production of electric double layer capacitor 1 to 11 were used to manufacture electric double layer capacitors. Specifically, polytetrafluoroethylene (PTFE) powder and acetylene black are mixed with activated carbon so as to be activated carbon: PTFE: acetylene black = 8: 1: 1 (mass ratio), until a paste is obtained. Kneaded. Subsequently, it grind | pulverized with the mini blender and sieved with the stainless steel sieve of 500 micrometers, and the particle size was arrange | equalized. Next, using a metal mold with a diameter of 2.54 cm, the amount of charge was adjusted so that the thickness after pressing was 0.5 mm, and press molding was performed at a pressure of 50.4 MPa to prepare a capacitor electrode.

  The obtained capacitor electrode was dried under vacuum conditions at 200 ° C. for 1 hour, and then an electrolyte (1M tetraethylammonium tetrafluoroborate propylene carbonate solution) was used as an electrode in a glove box in which nitrogen gas was circulated. Vacuum impregnated. Using this electrode, an electric double layer capacitor was assembled as shown in FIG. The electric double layer capacitor shown in FIG. 9 has a separator (Celgard, “Celgard (registered trademark) # 3501”) 1 impregnated with the electrolytic solution sandwiched between the capacitor electrodes 2, and the electrodes are surrounded by an O-ring 3. Then, it was further sandwiched between aluminum plates 4 as current collector plates.

6-2. The charging / discharging terminal of the electrostatic capacity charging / discharging device (“ETAC (registered trademark) Ver. 4.4” manufactured by Enomoto Kasei Co., Ltd.) is connected to the current collecting plate of the electric double layer capacitor. The battery was charged with a constant current of 40 mA until it reached 5 V, and then charged with a constant voltage of 2.5 V for 30 minutes. After charging, the electric double layer capacitor was discharged with a constant current (discharge current 10 mA). At this time, the discharge times t1 and t2 required until the voltage between the current collector plates became V1 and V2 were measured, and the capacitance was obtained using the following formula (1). The mass-based capacitance (F / g) is calculated by dividing the obtained capacitance by the mass of activated carbon in the electrode material layer in the capacitor electrode, and divided by the total volume of the electrode material layer in the capacitor electrode. Thus, a volume-based capacitance (F / cm ³ ) was calculated. Moreover, internal resistance was calculated | required using following formula (2). The capacitance and internal resistance were measured at 25 ° C. and −30 ° C.

Where
I: 10 (mA)
t1: Discharge time required for the electric double layer capacitor voltage to reach V1 (sec)
t2: Discharge time (sec) required for the electric double layer capacitor voltage to reach V2
V0: discharge start voltage V1: 2.0 (V)
V2: 1.5 (V)

As shown in Table 1, activated carbon No. 1 satisfying the requirements of the present invention. The electric double layer capacitor using 1 to 5 has a capacitance at room temperature (25 ° C.) and a low temperature (−30 ° C.) and an internal resistance (sometimes referred to as “capacitor characteristics”). Excellent results were obtained compared to the case of no attachment. In particular, activated carbon No. Nos. 1 to 5 have a capacitance of 25 ° C. of 11.1 F / cm ³ or more and an internal resistance of −30 ° C. of 27Ω or less, and are suitable as electric double layer capacitors. On the other hand, activated carbon No. which did not satisfy the requirements of the present invention. The electric double layer capacitor using 6-11 was inferior in capacitor characteristics.

  In general, in the low temperature range of −30 ° C., the ion mobility decreases due to the increase in the viscosity and resistance of the electrolyte solution. Therefore, the low temperature capacitance tends to decrease and the low temperature internal resistance tends to increase. No. Nos. 1 to 5 had a good balance between the low-temperature capacitance and the low-temperature internal resistance.

  In particular, activated carbon No. 6 to 9 are activated carbon Nos. Compared with 1 to 5, the pore volume with a pore diameter of 3 nm or more is small as shown in FIG. 2, and the ratio of the pore volume with a pore diameter of 3 nm or more to the total pore volume is also low as shown in FIG. I understand that. As shown in FIG. 6-9 had a small average pore diameter. This is because the calcium compound was not attached at the time of steam activation (activated carbon No. 7 to 9), or even when the calcium compound was added, the heating time at the time of steam activation was short (activated carbon No. 6). Conceivable. No. 1 having a small pore volume with a pore diameter of 3 nm or more. 6 to 9 had a large capacitance per volume (FIG. 6), but also had a low temperature internal resistance (FIG. 7). Therefore, as shown in FIG. Nos. 6 to 9 had a large electrostatic capacity but also a large low-temperature internal resistance, and the balance of both characteristics was poor.

  On the other hand, activated carbon No. 10 and 11 are activated carbon Nos. Compared with 1 to 5, the pore volume with a pore diameter of 3 nm or more is large as shown in FIG. 2, and the ratio of the pore volume with a pore diameter of 3 nm or more to the total pore volume is also high as shown in FIG. I understand that. As shown in FIG. 10 and 11 also had a large average pore diameter. No. 1 having a pore volume of 3 nm or more and a large pore volume. 10 to 11 had a small capacitance (FIG. 6), but also had a low low temperature internal resistance (FIG. 7). Therefore, as shown in FIG. Nos. 10 and 11 had a small electrostatic capacity but also a low internal resistance at low temperature, and the balance between both characteristics was poor.

  Further, as shown in FIG. The pore volume of pore diameters of less than 3 nm for activated carbon No. Although smaller than 6, activated carbon no. It was bigger than 10. Activated carbon No. The pore volume of the pore diameters of 1 and 2 of 3 nm or more is activated carbon No. The activated carbon no. It was less than 10. That is, activated carbon No. 1, 2 and activated carbon No. From FIG. 6, it can be seen that pores with a pore diameter of 3 nm or more develop while suppressing a decrease in pore volume with a pore diameter of less than 3 nm by appropriately controlling the heat treatment time during steam activation. On the other hand, activated carbon No. 1, 2 and activated carbon No. From No. 10, it is possible to obtain a pore distribution exhibiting the above-mentioned predetermined effect by appropriately selecting the raw materials and controlling the Ca adhering amount to be within a predetermined range.

1: Separator 2: Electrode for capacitor 3: O-ring 4: Aluminum plate 5: Polytetrafluoroethylene plate 6: Stainless steel plate

Claims (10)

BET specific surface area of 1450-1950 m ² / g,
An activated carbon having a pore volume of 3 nm or more and a pore volume of 0.09 to 0.35 cm ³ / g and an average pore diameter of 2.05 to 2.60 nm.   The activated carbon according to claim 1, wherein the ratio of the pore volume having a pore diameter of 3 nm or more to the total pore volume is 12 to 39%.   The activated carbon according to claim 1 or 2, wherein the average particle size is 10 µm or less. The activated carbon granules, powdery, granular, spherical, agglomerated, and activated carbon according to any one of claims 1 to 3 are those selected from the group consisting of plate-shaped. The total pore volume of the activated carbon is 0.90 to 3.0 cm. ³ The activated carbon according to any one of claims 1 to 4, which is / g. An electrode material for an electric double layer capacitor comprising the activated carbon according to any one of claims 1 to 5 . An electrode for an electric double layer capacitor, wherein the electrode material according to claim 6 is used. An electric double layer capacitor comprising the electrode according to claim 7 . Carbonizing a carbon raw material selected from the group consisting of granular, powdery, granular, spherical, massive, and plate-like, and then sequentially treating the carbon raw material-derived material by steam activation one or more times,
Before the last steam activation, at least one of a calcium compound and a potassium compound is attached to the carbon material-derived material, and the last steam activation is performed while maintaining the attached state, and the activation after the attachment The method for producing activated carbon according to any one of claims 1 to 5, wherein the treatment is steam activation . After attaching at least one of the calcium compound and the potassium compound to the carbon raw material and then carbonizing, or after carbonizing the carbon raw material and then attaching at least one of the calcium compound and the potassium compound, Alternatively, after carbonizing the carbon raw material, steam activation, and then adhering at least one of the calcium compound and the potassium compound,
The method for producing activated carbon according to claim 9 , wherein the last steam activation is performed.