Activated carbon

Abstract

The present invention relates to activated carbon which has a specific surface area of 1,150 m2 / g to 2,200 m2 / g as calculated by a BET method from the nitrogen adsorption / desorption isotherm, an adsorption amount of vitamin B12 of 10.2 mg / mL to 50 mg / mL after being in contact with 300 ppm of an aqueous solution of vitamin B12 for 24 hours, and a chlorine content of 2,500 ppm or less.

Description

activated carbon

[0001] The present invention relates to activated carbon for an electricity storage device.

[0002] In recent years, various types of electricity storage devices have been developed, including aqueous electrolyte batteries such as lead-carbon batteries, nonaqueous electrolyte batteries such as lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries, all-solid-state batteries, as well as electric double-layer capacitors and fuel cells, and there is a demand for carbonaceous materials that can improve performance depending on the application.

[0003] For example, lithium-sulfur batteries have been actively researched and developed because they offer a significantly larger discharge capacity than lithium-ion secondary batteries. Because sulfur does not have electronic conductivity, a method of combining sulfur with activated carbon or the like has been proposed. For example, Patent Document 1 describes porous carbon whose pores are filled with sulfur.

[0004] For example, an electric double layer capacitor, which is one type of energy storage device, utilizes a capacitance (electric double layer capacitance) obtained solely from the physical adsorption and desorption of ions without involving a chemical reaction, and therefore has superior output characteristics and lifespan characteristics compared to batteries. Further improvements in the capacitance, durability, and other properties of such electric double layer capacitors are required, and various methods have been proposed to improve these properties.

[0005] For example, Patent Document 2 discloses that when activated carbon derived from soft carbon having a specific surface area, particle size, and amount of surface functional groups within a specific range is used in an electric double layer capacitor, output and durability are imparted to the electric double layer capacitor while maintaining the capacitance of the electric double layer capacitor.

[0006] Furthermore, Patent Document 3 discloses that when activated carbon having a specific range for the ratio of the D peak height to the G peak height in the Raman spectrum and a specific surface area is used in an electric double layer capacitor, the electric capacitance per electrode can be increased.

[0007] JP 2013-118191 A International Publication No. 2015 / 146459 JP 2012-92013 A

[0008] In Patent Document 1, the pores of porous carbon are filled with sulfur to facilitate electron movement, thereby increasing capacity. However, increasing the sulfur filling rate to increase capacity can clog the pores, making it difficult for the electrolyte to diffuse, potentially increasing the resistance of the electricity storage device. In addition, Patent Documents 2 and 3 attempt to improve the capacitance of the electricity storage device by adjusting parameters such as the specific surface area. However, there is a limit to how much the capacitance of the electricity storage device can be improved by adjusting the parameters. In addition, Patent Documents 2 and 3 do not disclose anything about reducing the resistance of the electricity storage device by adjusting the parameters of the activated carbon.

[0009] Therefore, an object of the present invention is to provide activated carbon for an electricity storage device that is useful for improving the performance of an electricity storage device.

[0010] As a result of extensive research into solving the above problems, the inventors have found that the above problems can be solved by appropriately adjusting the pore volume, which is expressed in terms of the amount of vitamin B12 adsorbed, and have thus completed the present invention. That is, the present invention encompasses the following preferred embodiments.

[0011] [1] The specific surface area calculated by the BET method from the nitrogen adsorption / desorption isotherm is 1150 m ２ / g~2200m ２ [2] Activated carbon having a 1360 cm peak at 1360 cm in Raman spectroscopy analysis, an adsorption amount of vitamin B12 of 10.2 mg / mL to 50 mg / mL when contacted with a 300 ppm aqueous vitamin B12 solution for 24 hours, and a chlorine content of 2500 ppm or less. －１ The D band peak near 1580 cm －１The activated carbon according to [1], wherein the D / G value, which is the intensity ratio of the G band peak near the activated carbon, is 1.15 to 1.40. [3] The activated carbon according to [1] or [2], wherein the ratio of the amount of vitamin B12 adsorbed after contact with a 300 ppm aqueous solution for 2 hours to the amount of vitamin B12 adsorbed after contact with the aqueous solution for 24 hours is 58% or more. [4] The ratio of the amount of vitamin B12 adsorbed after contact with a 300 ppm aqueous solution for 24 hours to the specific surface area calculated by the BET method from the nitrogen adsorption / desorption isotherm is 0.00810 [(mg / mL) / (m ２ / g)] to 0.02470 [(mg / mL) / (m ２ / g)]. [5] An electrode material comprising the activated carbon according to any one of [1] to [4]. [6] An electrode comprising the electrode material according to [5]. [7] An electricity storage device comprising the electrode according to [6].

[0012] According to the present invention, it is possible to provide activated carbon for an electricity storage device that is useful for improving the performance of an electricity storage device.

[0013] FIG. 1 is a diagram showing a sheet-shaped electrode composition; FIG. 2 is a diagram showing a current collector (etched aluminum foil) to which a conductive adhesive has been applied; FIG. 3 is a diagram showing a polarizable electrode in which a sheet-shaped electrode composition and a current collector are bonded and an aluminum tab is ultrasonically welded; FIG. 4 is a diagram showing a bag-shaped exterior sheet; and FIG. 5 is a diagram showing an electric double layer capacitor.

[0014] Hereinafter, embodiments of the present invention will be described in detail. Note that the following description is for illustrating embodiments of the present invention, and is not intended to limit the present invention to the following embodiments.

[0015] <Activated carbon> The activated carbon of the present invention has a specific surface area of ​​1150 m2 calculated by the BET method from the nitrogen adsorption / desorption isotherm. ２ / g~2200m ２ / g, and when contacted with a 300 ppm aqueous vitamin B12 solution for 24 hours, the amount of vitamin B12 adsorbed is 10.2 mg / mL to 50 mg / mL, and the chlorine content is 2500 ppm or less.

[0016] The present inventors have investigated methods for improving the performance of electricity storage devices such as nonaqueous electrolyte batteries and electric double layer capacitors. They found that conventional technologies have focused only on micropores, through which adsorbates such as electrolytes are ultimately adsorbed, and mesopores, which correspond to the entrances through which the adsorbates are adsorbed into activated carbon. They aimed to improve the performance of electricity storage devices by appropriately adjusting the specific surface area, mesopore, and macropore volumes of carbonaceous materials such as activated carbon, but did not consider the pores through which the adsorbates migrate from mesopores to micropores. Specifically, the present inventors discovered that by appropriately adjusting the pore volume, which corresponds to the size of the pathways through which the adsorbate diffuses within the activated carbon before entering the mesopores and adsorbing into the micropores, the adsorbate can be smoothly transported, thereby achieving low resistance. Furthermore, the present inventors have discovered that the volume of the pores corresponding to the pathways through which the adsorbate enters the activated carbon can be expressed in terms of the amount of vitamin B12 adsorbed. Therefore, the present invention provides activated carbon that is particularly useful for reducing the resistance of electricity storage devices. Furthermore, when the activated carbon of the present invention is used in an electric double layer capacitor, the electrolyte is adsorbed into the micropores during diffusion without clogging the pathways, which results in an improvement in capacitance. Therefore, in this specification, when the power storage device is an electric double layer capacitor, its performance includes, for example, resistance and capacitance, and improving or increasing the performance of the electric double layer capacitor means, for example, a decrease in resistance and an increase in capacitance. Also, in this specification, when the power storage device is a non-aqueous electrolyte battery, its performance may include, for example, resistance and discharge capacity. Here, examples of electrolytes that can be used in power storage devices include, for example, LiPF in the case of a lithium-sulfur battery. ６ , LiBF ４ , LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiFSI (lithium bis(fluorosulfonyl)imide), etc., and in the case of an electric double layer capacitor, TEABF ４ (Tetraethylammonium tetrafluoroborate), TEAPF ６ tetraethylammonium salts such as tetraethylammonium hexafluorophosphate; TEMABF ４triethylmethylammonium salts such as (triethylmethylammonium tetrafluoroborate); TEPBF ４ tetraethylphosphonium salts such as (tetraethylphosphonium tetrafluoroborate); ionic liquids such as EMIBF ４ (1-ethyl-3-methylimidazolium tetrafluoroborate); tetramethylammonium salt; diethyldimethylammonium salt; ethyltrimethylammonium salt; tetrapropylammonium salt; tetrabutylammonium salt; tributylmethylammonium salt; tetramethylphosphonium salt; tetraethylphosphonium salt; tetrapropylphosphonium salt; tetrabutylphosphonium salt, and the like.

[0017] [Specific Surface Area] The activated carbon of the present invention has a specific surface area calculated by the BET method from the nitrogen adsorption / desorption isotherm (hereinafter also referred to as "BET specific surface area") of 1150 m ２ / g~2200m ２ / g. The BET specific surface area is 1150 m ２ / g~2200m ２ When the BET specific surface area is 1150 m / g, the capacitance or discharge capacity of the electricity storage device containing the activated carbon of the present invention tends to be high and the resistance tends to be low. ２ When the BET specific surface area is less than 2200 m / g, the average pore diameter becomes relatively small, making it difficult for the electrolyte to diffuse in the pores during charging and discharging, and the resistance tends to increase. Furthermore, the increased resistance tends to reduce the durability of the electricity storage device containing the activated carbon of the present invention. ２ If the BET specific surface area exceeds 1200 m / g, the bulk density of the activated carbon decreases, and the capacitance or discharge capacity per unit volume tends to decrease. ２ / g~2180m ２ / g, 1250m ２ / g~2160m ２ / g, 1300m ２ / g~2140m ２ / g, 1350m ２ / g~2120m ２ / g or 1400m ２ / g~2100m ２The BET specific surface area is also preferably 1400 m ２ / g~2200m ２ / g, more preferably 1500m ２ / g~2100m ２ / g, more preferably 1550m ２ / g to 2000m ２ / g, and even more preferably 1600m ２ / g~1950m ２ / g, particularly preferably 1650m ２ / g~1900m ２ / g, particularly preferably 1750m ２ / g~1900m ２ / g. When the BET specific surface area is equal to or greater than the lower limit and equal to or less than the upper limit, the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is likely to be increased, and the resistance is likely to be reduced. The BET specific surface area can be adjusted to within the above range by appropriately adjusting, for example, the type of raw material for the activated carbon; the temperature and / or atmosphere and / or time in the activation step during the production of the activated carbon; the number of activation steps; the temperature and / or atmosphere and / or time in the heat treatment step, etc. The BET specific surface area can be determined, for example, by the method described in the Examples below.

[0018] [Vitamin B12 Adsorption Amount] The activated carbon of the present invention exhibits an adsorption amount of vitamin B12 (hereinafter, sometimes simply referred to as "vitamin B12 adsorption amount") of 10.2 mg / mL to 50 mg / mL when contacted with a 300 ppm vitamin B12 aqueous solution for 24 hours. When the adsorption amount of vitamin B12 is 10.2 mg / mL or more, the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is likely to be high and the resistance is likely to be low. As described above, the adsorption amount of vitamin B12 represents the volume of pores, which corresponds to the size of the paths through which the electrolyte diffuses within the activated carbon. Therefore, when the adsorption amount of vitamin B12 is less than 10.2 mg / mL, the volume of pores that can serve as electrolyte diffusion paths is reduced, making it difficult for the electrolyte to diffuse within the pores during charge and discharge, which tends to increase resistance. Furthermore, the increased resistance tends to decrease the durability of electricity storage devices containing the activated carbon of the present invention. When the amount of vitamin B12 adsorbed exceeds 50 mg / mL, the pore volume increases, tending to decrease the capacitance or discharge capacity per unit volume. The amount of vitamin B12 adsorbed is preferably 10.5 mg / mL to 50 mg / mL, 10.8 mg / mL to 50 mg / mL, 11.0 mg / mL to 50 mg / mL, 11.5 mg / mL to 50 mg / mL, or 12.0 mg / mL to 50 mg / mL, more preferably 13 mg / mL to 50 mg / mL, even more preferably 15 mg / mL to 40 mg / mL, still more preferably 21 mg / mL to 30 mg / mL, and particularly preferably 24 mg / mL to 28 mg / mL. When the amount of vitamin B12 adsorbed is equal to or greater than the lower limit and equal to or less than the upper limit, the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is likely to be higher and the resistance is likely to be lower. The amount of vitamin B12 adsorption can be adjusted to fall within the above range by, for example, appropriately adjusting the temperature and / or atmosphere and / or time of the activation step during the production of activated carbon, the number of activation steps, the temperature and / or atmosphere and / or time of the heat treatment step, etc. The amount of vitamin B12 adsorption can be determined, for example, by the method described in the Examples below.

[0019] In the activated carbon of the present invention, the ratio of the amount adsorbed after 2 hours of contact with a 300 ppm aqueous vitamin B12 solution to the amount adsorbed after 24 hours of contact with the aqueous solution (amount adsorbed after 2 hours of contact with the aqueous vitamin B12 solution / amount adsorbed after 24 hours of contact with the aqueous vitamin B12 solution × 100) is preferably 58% or more, more preferably 60% or more, even more preferably 62% or more, even more preferably 65% ​​or more, particularly preferably 70% or more, and especially preferably 76% or more. When the ratio of the amount adsorbed after 2 hours of contact with vitamin B12 to the amount adsorbed after 24 hours of contact is equal to or greater than the lower limit mentioned above, the adsorption and desorption of the electrolyte within the pores during charging and discharging is rapid, and the electrolyte is more easily diffused, resulting in excellent rate characteristics and lower resistance. From the viewpoint of the balance between the adsorption rate and the desorption rate, the ratio is preferably 90% or less, more preferably 85% or less, and even more preferably 82% or less. In addition, 58% to 90% is preferable, 60 to 85% is more preferable, and 65 to 82%, 70 to 82%, and 76 to 82% are also suitable embodiments. The ratio can be adjusted within the above range by appropriately adjusting, for example, the temperature and / or atmosphere and / or time of the activation step during the production of activated carbon; the number of activation steps; the temperature and / or atmosphere and / or time of the heat treatment step, etc.

[0020] The activated carbon of the present invention preferably has a ratio of the amount of vitamin B12 adsorbed when contacted with a 300 ppm aqueous solution of vitamin B12 for 24 hours to the BET specific surface area [(amount of vitamin B12 adsorbed when contacted with a 300 ppm aqueous solution of vitamin B12 for 24 hours) / (BET specific surface area)] of 0.00810 (mg / mL) / (m ２ / g) to 0.02470 (mg / mL) / (m ２ / g), more preferably 0.00820 (mg / mL) / (m ２ / g) to 0.02440 (mg / mL) / (m ２ / g), more preferably 0.00830 (mg / mL) / (m ２ / g) to 0.02410 (mg / mL) / (m ２ / g), and more preferably 0.00840 (mg / mL) / (m ２ / g) to 0.02380 (mg / mL) / (m２ / g), and even more preferably 0.00850 (mg / mL) / (m ２ / g) to 0.02350 (mg / mL) / (m ２ / g), and particularly preferably 0.00860 (mg / mL) / (m ２ / g) to 0.02320 (mg / mL) / (m ２ When the ratio of the adsorption amount of vitamin B12 to the BET specific surface area is equal to or greater than the lower limit and equal to or less than the upper limit, the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is likely to be increased, and the resistance is likely to be reduced.

[0021] [Chlorine Content] The activated carbon of the present invention has a chlorine content of 2500 ppm or less. When the chlorine content is 2500 ppm or less, the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is likely to be high and the resistance is likely to be low. When the chlorine content exceeds 2500 ppm, chlorides are generated to form an SEI coating, which blocks pores, thereby reducing the capacitance or discharge capacity, increasing the resistance, and reducing durability. The chlorine content is preferably 1000 ppm or less, more preferably 400 ppm or less, even more preferably 100 ppm or less, still more preferably 50 ppm or less, particularly preferably 35 ppm or less, and extremely preferably 30 ppm or less. When the chlorine content is below the upper limit, the resistance is likely to be lower. Furthermore, the lower the content of chlorine as an impurity, the better. The lower limit of the chlorine content may be 0 ppm, and is preferably 1 ppm or more. Other suitable embodiments include 0 to 2500 ppm, 0 to 1000 ppm, 1 to 400 ppm, 1 to 100 ppm, 1 to 50 ppm, 1 to 35 ppm, 1 to 30 ppm, 1 to 10 ppm, and 1 to 5 ppm. The chlorine content can be adjusted within the above range by appropriately adjusting, for example, the type of raw material for the activated carbon; the type and / or concentration and / or time of the acid in the washing step during the production of the activated carbon; the temperature and / or atmosphere and / or time of the heat treatment step, etc. The chlorine content can be determined by fluorescent X-ray analysis, for example, by the method described in the Examples below.

[0022] In a preferred embodiment of the present invention, the activated carbon has a specific surface area of ​​1150 m2 or less as calculated by the BET method from a nitrogen adsorption / desorption isotherm. ２ / g~2200m ２ / g (preferably 1400m ２ / g~2200m ２ / g), the amount of vitamin B12 adsorbed when contacted with a 300 ppm aqueous vitamin B12 solution for 24 hours is 13 mg / mL to 50 mg / mL, and the chlorine content is 2500 ppm or less. In another preferred embodiment of the present invention, the activated carbon has a specific surface area of ​​1150 m or less as calculated by the BET method from the nitrogen adsorption / desorption isotherm. ２ / g~2200m ２ / g (preferably 1400m ２ / g~2200m ２ / g), the amount of vitamin B12 adsorbed when contacted with a 300 ppm aqueous solution of vitamin B12 for 24 hours was 10.2 mg / mL to 50 mg / mL, and the ratio of the amount of vitamin B12 adsorbed when contacted with a 300 ppm aqueous solution of vitamin B12 for 24 hours to the specific surface area calculated by the BET method from the nitrogen adsorption / desorption isotherm was 0.00810 [(mg / mL) / (m ２ / g)] to 0.02470 [(mg / mL) / (m ２ / g)] and the chlorine content is 2500 ppm or less. When an electricity storage device contains the activated carbon of one of these preferred embodiments, a higher electrostatic capacity or discharge capacity can be obtained, and also a lower resistance can be obtained.

[0023] [Ratio of D-band peak to G-band peak] The ratio of the D-band peak to the G-band peak in Raman spectroscopy of the activated carbon of the present invention was －１ The D band peak near 1580 cm －１ The D / G value, which is the intensity ratio of the G band peak near the D band, is preferably 1.15 to 1.40, more preferably 1.19 to 1.39, and even more preferably 1.21 to 1.35, or 1.21 to 1.32. Here, the D band peak is a peak caused by disorder and defects in the graphite structure, and the G band peak is a peak derived from the graphite structure. －１ The D band peak near 1300 cm －１~1375cm －１ , preferably 1330 cm －１ ~1370cm －１ It is observed in the range of 1580 cm －１ The G-band peak near 1560 cm －１ ~1615cm －１ , preferably 1565 cm －１ ~1610cm －１ The D / G ratio is observed in the range of . The value of D / G is related to the crystallinity of the activated carbon. When the value of D / G is equal to or greater than the lower limit, the crystallinity is not too low, so that the amorphous content is not too high, and the resistance of an electrical device containing the activated carbon of the present invention is likely to be low. When the value of D / G is equal to or less than the upper limit, the crystallinity of the activated carbon is not too high, so that the carbon edge is not likely to decrease due to the development of a graphite structure, and the electrolyte coordination sites are not likely to decrease. Therefore, the resistance of an electrical device containing the activated carbon of the present invention is likely to be low, especially at low temperatures. The value of D / G can be adjusted within the above range by, for example, appropriately adjusting the temperature and / or atmosphere and / or time of the activation step during the production of the activated carbon; the number of activation steps; the temperature and / or time and / or atmosphere of the heat treatment step, etc. The value of D / G can be determined, for example, by the method described in the Examples below.

[0024] In a preferred embodiment of the activated carbon of the present invention, the specific surface area is 1150 m ２ / g~2200m ２ / g, it is believed that the micropores through which the electrolyte is adsorbed are relatively developed, and when used in an electricity storage device, the capacitance or discharge capacity tends to be higher. In addition to the above, developed micropores also increase the adsorption rate, tending to result in activated carbon with excellent adsorption performance. This means that the activated carbon of a preferred embodiment of the present invention is not only suitable for electricity storage devices but can also be useful as an adsorbent. In such activated carbon, the chloroform adsorption amount is preferably 0.35 mg / g or more, more preferably 0.40 mg / g or more, more preferably 0.45 mg / g or more, and even more preferably 0.48 mg / g or more. Since a larger chloroform adsorption amount indicates better adsorption performance, the upper limit is not particularly limited, but is typically 5 mg / g or less. The chloroform adsorption amount can be adjusted within the above range by, for example, appropriately adjusting the temperature and / or atmosphere and / or time of the activation step during the production of the activated carbon; the number of activation steps; the temperature and / or time and / or atmosphere of the heat treatment step, etc. The amount of chloroform adsorbed can be determined, for example, by the method described in the Examples below.

[0025] <Method for Producing Activated Carbon> The activated carbon of the present invention can be produced, for example, by a method including carbonizing a plant-derived carbon precursor, activating, washing, and heat-treating the precursor to obtain activated carbon.

[0026] In one embodiment of the activated carbon manufacturing method of the present invention, a plant-derived carbon precursor is first carbonized. The plant from which the plant-derived carbon precursor is derived is not particularly limited, but examples include coconut shells, coffee beans, tea leaves, sugarcane, fruits (e.g., mandarin oranges or bananas), straw, broadleaf trees, coniferous trees, bamboo, and rice husks. These plants can be used alone or in combination, but coconut shells are preferred due to their large availability and commercial advantages. The coconuts from which the coconut shells are derived are not particularly limited, but examples include palm (oil palm), coconut, salak, and bay palm. In the present invention, these plants can be calcined to obtain char (e.g., coconut shell char). While char generally refers to a carbon-rich powdered solid produced when coal is heated without melting or softening, the term also refers to a carbon-rich powdered solid produced when organic matter is heated without melting or softening.

[0027] The method for producing char from plants is not particularly limited, but for example, char can be produced by burning (carbonizing) the plant raw material at a temperature of 300°C or higher, for example, about 400 to 800°C, in an atmosphere of an inert gas such as nitrogen, carbon dioxide, helium, argon, carbon monoxide, or fuel exhaust gas, a mixed gas of these inert gases, or a mixed gas containing these inert gases as a main component with other gases.

[0028] The carbon precursor is preferably 100 to 800 m ２ / g, more preferably 200 to 700 m ２ / g, more preferably 300 to 600m ２ When the BET specific surface area of ​​the carbon precursor is within the above range, it is easy to adjust the pore structure to the desired one.

[0029] After carbonization of the carbon precursor, primary activation is performed. The activation method is not particularly limited and can be selected depending on the desired contact ratio between the carbon precursor and the reaction gas, which will be described later. When the contact ratio between the carbon precursor and the reaction gas is to be high (e.g., about 70 to 100%), for example, a batch-type vertical fluidized bed activation furnace may be used. When the contact ratio between the carbon precursor and the reaction gas is to be low (e.g., about 10 to 50%), for example, a continuous horizontal rotary kiln may be used.

[0030] From the viewpoint of easily increasing the capacitance or discharge capacity and easily reducing the resistance of an electricity storage device containing the activated carbon of the present invention, it is preferable to use a mixed gas of an inert gas and water vapor in the primary activation. In this case, the partial pressure of the water vapor is usually 10 to 60%, preferably 20 to 55%, and more preferably 30 to 50%. When the partial pressure of the water vapor is within the above range, activation easily proceeds sufficiently and a rapid activation reaction is easily suppressed.

[0031] In order to facilitate increasing the capacitance or discharge capacity and reducing the resistance of an electricity storage device containing the activated carbon of the present invention, the mixed gas is preferably supplied so that the amount of catalytic reaction gas per carbon precursor, calculated by the following formula, is 0.1 to 10.0 mL / min / kg. Furthermore, when the secondary activation or subsequent activation steps described below are not performed, it may be preferable to supply the catalytic reaction gas per carbon precursor so that it is 3.0 to 10.0 mL / min / kg. When the amount of contact reaction gas per carbon precursor is within the above range, pores of a size expressed by the amount of vitamin B12 adsorbed are likely to develop, and the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is likely to be high and the resistance is likely to be low.

[0032] Furthermore, from the viewpoint of appropriately developing pores having a size represented by the amount of vitamin B12 adsorbed, the contact ratio between the carbon precursor and the reaction gas is preferably 15% or more. In the case of a vertical furnace, the contact ratio between the carbon precursor and the reaction gas is 100% because the reaction gas flows uniformly from the hearth to the upper part, and in the case of a horizontal furnace, the contact ratio can be determined by the ratio of the volume of the carbon precursor to the volume of the furnace.

[0033] The activation temperature in the primary activation is usually 700 to 1100°C, preferably 800 to 1000°C. The activation time and the temperature rise rate are not particularly limited and can be adjusted appropriately depending on the type, shape, size, etc. of the plant-derived carbon precursor selected. The BET specific surface area of ​​the primary activated carbon obtained after the primary activation is 1000 to 2000 m ２ It is preferable to carry out the primary activation until the ion concentration reaches about 1 / g.

[0034] Next, the primary activated carbon is washed. Washing can be performed by immersing the primary activated carbon in a washing solution containing an acid. Examples of the washing solution include mineral acids and organic acids. Examples of mineral acids include hydrochloric acid and sulfuric acid. Examples of organic acids include saturated carboxylic acids such as formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid, and citric acid; and aromatic carboxylic acids such as benzoic acid and terephthalic acid. From the viewpoint of washability, the acid used in the washing solution is preferably a mineral acid, more preferably hydrochloric acid. After washing with the acid, it is preferable to further wash with water or the like to remove excess acid. This operation can reduce the load on the activation equipment during secondary activation and subsequent steps.

[0035] The cleaning solution can usually be prepared by mixing an acid with an aqueous solution. Examples of the aqueous solution include water and a mixture of water and a water-soluble organic solvent. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, propylene glycol, and ethylene glycol.

[0036] The concentration of the acid in the cleaning solution is not particularly limited, and may be adjusted appropriately depending on the type of acid used. The acid concentration of the cleaning solution is preferably 0.1 to 2.0 normal, more preferably 0.2 to 1.5 normal, and even more preferably 0.3 to 1.0 normal. When the acid concentration in the cleaning solution is within the above range, impurities contained in the primary activated carbon can be efficiently removed, which is preferable.

[0037] The pH of the cleaning solution is not particularly limited, and may be adjusted appropriately depending on the type of acid used, the substance to be removed, and the like.

[0038] The temperature of the cleaning solution when the primary activated carbon is immersed is not particularly limited, but is preferably 0 to 98° C., more preferably 10 to 95° C., and even more preferably 15 to 90° C. If the temperature of the cleaning solution when the primary activated carbon is immersed is within the above range, cleaning can be carried out for a practical time with reduced load on the equipment, which is preferable.

[0039] The method for washing the primary activated carbon is not particularly limited as long as it allows the primary activated carbon to be immersed in the washing solution, and may include a method in which the washing solution is continuously added, allowed to remain for a predetermined time, and then the immersion is continued while the solution is removed, or a method in which the primary activated carbon is immersed in the washing solution, allowed to remain for a predetermined time, drained, and then new washing solution is added and the immersion-drainage process is repeated. Furthermore, the method may involve replacing all or part of the washing solution. The time for which the primary activated activated carbon is immersed in the washing solution can be adjusted appropriately depending on the acid used, the acid concentration, the treatment temperature, etc.

[0040] The washing time is not particularly limited, but from the viewpoint of the economic efficiency of the reaction equipment and the structural integrity of the activated carbon, it is preferably 0.05 to 4 hours, more preferably 0.1 to 3 hours.

[0041] When the primary activated carbon is immersed in a cleaning solution, the mass ratio between the cleaning solution and the primary activated carbon may be adjusted as appropriate depending on the type, concentration, temperature, etc. of the cleaning solution used. The mass of the primary activated carbon to be immersed relative to the mass of the cleaning solution is usually 0.1 to 50 mass%, preferably 1 to 20 mass%, and more preferably 1.5 to 10 mass%. Within the above range, impurities dissolved in the cleaning solution are less likely to precipitate from the cleaning solution, and redeposition to the primary activated carbon is easily suppressed.

[0042] The atmosphere in which the cleaning is carried out is not particularly limited and may be appropriately selected depending on the method used for cleaning, but the cleaning is usually carried out in the air.

[0043] Washing may be carried out once or multiple times with one type of washing solution, or multiple times with a combination of two or more types of washing solutions.

[0044] Washing can remove impurities that may be present in the activated carbon, such as alkali metals such as lithium, sodium, and potassium, alkaline earth metals such as beryllium, magnesium, and calcium, and transition metals such as iron, copper, and nickel, which are present in the plant-derived carbon precursor.

[0045] After washing, the primary activated carbon may be dried. Drying is an operation for removing moisture and the like adsorbed on the primary activated carbon, and for example, the moisture and the like adsorbed on the primary activated carbon can be removed by heating the primary activated carbon. In addition to or instead of heating, drying can be performed by means of, for example, reduced pressure, heating under reduced pressure, or freezing to remove moisture and the like adsorbed on the primary activated carbon.

[0046] From the viewpoint of removing moisture adsorbed on the primary activated carbon, the drying temperature is preferably 100 to 330°C, more preferably 110 to 300°C, and even more preferably 120 to 250°C.

[0047] The drying time varies depending on the drying temperature, but is preferably 0.1 hour or more, more preferably 0.5 hour or more, and even more preferably 1 hour or more from the viewpoint of removing moisture adsorbed on the primary activated carbon, and is preferably 24 hours or less, more preferably 12 hours or less, and even more preferably 6 hours or less from the viewpoint of economy.

[0048] Drying can be carried out under normal pressure or reduced pressure. When drying is carried out under normal pressure, it is preferable to carry out the drying under an inert gas atmosphere such as nitrogen gas or argon gas, or under an air atmosphere with a dew point of −20° C. or lower.

[0049] Secondary activation may be carried out after the above-mentioned washing and drying. In the secondary activation, the amount of contact reaction gas per primary activated carbon is preferably supplied so as to be 5 to 30 mL / min / kg, from the viewpoint of easily increasing the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention and easily reducing the resistance. The activation temperature, contact ratio, water vapor partial pressure, and other conditions may be within the same range as those for the primary activation. The BET specific surface area of ​​the secondary activated carbon obtained after the secondary activation is preferably 1150 to 2200 m. ２ / g (preferably 1400 to 2200 m ２ / g, more preferably 1600 to 2200 m ２ It is preferable to carry out the secondary activation until the ion exchange capacity reaches 1 / g.

[0050] After the secondary activation, a tertiary activation or a higher activation may be carried out. Furthermore, washing or drying may be carried out between each activation after the secondary activation. From the viewpoint of economy, it is preferable to carry out the secondary activation. The conditions for the tertiary activation and the higher activation may be appropriately adjusted depending on the desired properties of the activated carbon.

[0051] The activated carbon obtained after the secondary activation or higher activation is preferably washed in the same manner as after the primary activation to further remove ash and metal impurities contained in the activated carbon.

[0052] After the primary activation or further activation, a heat treatment is carried out. Heat treatment increases the crystallinity, which tends to lower the resistance and also tends to reduce the amount of impurities in the activated carbon.

[0053] The heat treatment method is not particularly limited, but can be carried out in the same manner as the primary activation described above, and can be selected depending on the desired contact ratio between the activated carbon and the reaction gas after activation, which will be described later.

[0054] From the viewpoint of easily increasing the capacitance or discharge capacity and easily reducing the resistance of an electricity storage device containing the activated carbon of the present invention, it is preferable to use a mixed gas of an inert gas and water vapor in the heat treatment. In this case, the partial pressure of the water vapor is preferably 15% or less. When the partial pressure of the water vapor is within the above range, the crystallinity is high, and therefore the resistance is likely to be low.

[0055] In order to facilitate increasing the capacitance or discharge capacity and reducing the resistance of an electricity storage device containing the activated carbon of the present invention, the mixed gas is preferably supplied so that the amount of catalytic reaction gas per unit of activated carbon after activation, calculated by the following formula, is 0.1 to 5 mL / min / kg. When the amount of contact reaction gas per activated carbon after activation is within the above range, pores of a size expressed by the amount of vitamin B12 adsorbed are more likely to develop, and the capacitance or discharge capacity of an electricity storage device containing the activated carbon of the present invention is more likely to be increased and the resistance is more likely to be reduced.

[0056] From the viewpoint of appropriately developing the pores, the contact ratio between the activated carbon and the reaction gas after activation is preferably 20% or more. In the case of a vertical furnace, the contact ratio between the activated carbon and the reaction gas after activation is 100% because the reaction gas flows uniformly from the hearth to the upper part, and in the case of a horizontal furnace, the contact ratio can be determined by the ratio of the volume of the activated carbon after activation to the volume of the furnace.

[0057] The heat treatment temperature is usually 600 to 1000° C., preferably 700 to 900° C. The heat treatment time and temperature increase rate are not particularly limited, but from the viewpoint of reducing the load on the reaction equipment and maintaining the structure of the activated carbon, the heat treatment time is preferably 0.5 to 24 hours, more preferably 1 to 12 hours, and the temperature increase rate is preferably 10 to 60° C. / min, more preferably 20 to 50° C. / min.

[0058] The activated carbon after the heat treatment may be pulverized. The pulverization method is not particularly limited, and known pulverization methods such as a bead mill, ball mill, hammer mill, roll mill, rod mill, or jet mill, or a combination thereof, can be used. The average particle size of the pulverized activated carbon is not particularly limited, but from the viewpoint of improving electrode density and reducing resistance, it is preferably 100 μm or less, more preferably 90 μm or less, and preferably 1 μm or more, more preferably 2 μm or more. The average particle size can be measured, for example, using a particle size / particle size distribution measuring device.

[0059] The activated carbon obtained by pulverization may be classified. For example, by removing particles with a particle diameter of 1 μm or less, activated carbon particles with a narrow particle size distribution can be obtained. The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertia classification, hydraulic classification, centrifugal classification, etc. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, centrifugal classification, etc. From the viewpoint of economy, it is preferable to use a dry classifier.

[0060] The activated carbon of the present invention can be suitably used as an electrode material for various electricity storage devices such as electric double layer capacitors, lithium ion batteries, and lithium-sulfur batteries. It is particularly suitable as an electrode material for electric double layer capacitors, and use of the activated carbon of the present invention can result in an electric double layer capacitor that can achieve both high capacitance and low resistance. Furthermore, use of the activated carbon of the present invention can result in an electricity storage device that exhibits excellent performance at low temperatures. Therefore, in one embodiment of the present invention, an electrode material containing the activated carbon of the present invention can be provided. Furthermore, an electrode containing the electrode material and an electricity storage device containing the electrode can be provided.

[0061] The electrode of the present invention is characterized by using the activated carbon of the present invention. The electrode of the present invention can be produced, for example, by using an electrode material obtained by kneading the activated carbon of the present invention as a raw material with components such as a conductivity imparting agent (also referred to as a conductivity aid), a binder, and a solvent, applying and drying the kneaded mixture, adding a solvent to the electrode material to prepare a paste, applying the paste to a current collector such as aluminum foil, drying and removing the solvent, and placing the paste in a mold for press molding.

[0062] Examples of the conductivity-imparting agent that can be used include carbon black, acetylene black, and Ketjen black. Examples of the binder that can be used include fluorine-based polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum pitch, and phenolic resin. Examples of the solvent that can be used include water; alcohols such as methanol and ethanol; saturated hydrocarbons such as hexane and heptane; aromatic hydrocarbons such as toluene, xylene, and mesitylene; ketones such as acetone and ethyl methyl ketone; esters such as methyl acetate and ethyl acetate; amides such as N,N-dimethylformamide and N,N-diethylformamide; and cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone.

[0063] The power storage device of the present invention, particularly an electric double layer capacitor, is characterized by using the above-described electrodes. An electric double layer capacitor generally has a structure in which electrodes, an electrolyte, and a separator are primarily configured, with the separator disposed between a pair of electrodes. Examples of the electrolyte include an electrolyte solution obtained by dissolving an amidine salt in an organic solvent such as propylene carbonate, ethylene carbonate, or methyl ethyl carbonate; an electrolyte solution obtained by dissolving a quaternary ammonium salt of perchloric acid; an electrolyte solution obtained by dissolving a tetrafluoroborate or hexafluorophosphate of an alkali metal such as quaternary ammonium or lithium; and an electrolyte solution obtained by dissolving a quaternary phosphonium salt. Examples of the separator include nonwoven fabrics, cloths, and microporous films primarily composed of cellulose, glass fiber, or polyolefins such as polyethylene and polypropylene. An electric double layer capacitor can be manufactured, for example, by arranging these primary components using methods commonly used in the art.

[0064] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Physical properties in the examples and comparative examples were measured by the following methods.

[0065] <BET specific surface area> Using a BELSORP-mini manufactured by Microtrac-Bell Corporation, the activated carbons obtained in the examples and comparative examples were heated at 300°C for 3 hours under a nitrogen stream (nitrogen flow rate: 50 mL / min), and then the nitrogen adsorption / desorption isotherm of the activated carbon was measured at 77 K. The obtained adsorption / desorption isotherm was analyzed by a multipoint method using the BET equation, and the relative pressure P / P of the obtained curve was calculated. ０ The specific surface area was calculated from the straight line in the region of ρ = 0.01 to 0.1.

[0066] <Amount of Vitamin B12 Adsorption> [Concentration of Vitamin B12] The activated carbon obtained in the Examples and Comparative Examples was pulverized, vacuum dried at 120°C for 3 hours or more, and then allowed to cool to room temperature in a desiccator. Vitamin B12 (C) adjusted to 300 ppm was added to approximately 50 mg of the obtained activated carbon. ６３ H ８８ CoN １４ O １４ 100 mL of an aqueous solution of vitamin B12 (P: molecular weight 1355.4) (hereinafter sometimes referred to as "VB12") was added, stirred at 24°C (±1°C) for 2 or 24 hours, and filtered, and the filtrate was recovered. The absorbance at 550 nm of the 300 ppm vitamin B12 aqueous solution before adsorption used in the adsorption test and the vitamin B12 filtrate after adsorption treatment were measured, and the concentrations of the vitamin B12 aqueous solution before adsorption and the vitamin B12 filtrate after adsorption treatment were calculated based on a calibration curve prepared in advance.

[0067] [Packing Density] The packing density of the pulverized activated carbon was measured based on the measurement method described in JIS K1474:2014.

[0068] [Amount of adsorption after 24 hours of contact with an aqueous vitamin B12 solution] From the obtained vitamin B12 concentration and packing density, the amount of adsorption per mL of activated carbon after 24 hours of contact with an aqueous vitamin B12 solution was calculated using the following formula.

[0069] [Ratio of the amount adsorbed after 2 hours of contact with an aqueous vitamin B12 solution to the amount adsorbed after 24 hours of contact] The ratio of the amount adsorbed after 2 hours of contact with an aqueous vitamin B12 solution to the amount adsorbed after 24 hours of contact was determined using the following formula: The amount adsorbed after 2 hours of contact with the aqueous vitamin B12 solution was calculated in the same manner as above from the vitamin B12 concentration (ppm) after 2 hours of contact.

[0070] <Chlorine Content> The activated carbon obtained in each of the Examples and Comparative Examples was crushed, vacuum dried at 120°C for 3 hours or more, and then allowed to cool to room temperature in a desiccator. The obtained activated carbon was placed in a polyethylene container with a volume of 15 cm ３ The above was placed inside the sample, the back was held down with a plankton net, the measurement surface was covered with a polypropylene film, and the sample was placed in a top-irradiation sample holder. Measurements were performed using a Primus II (Rigaku Corporation) under a helium gas atmosphere with an output of 3 kW, a scan rate of 8 deg / min, and an X-ray source of 30 kV and 100 mA. The chlorine content was calculated from the detected elements and their X-ray intensities using SQX (Scan Quant X) analysis: a standardless fundamental parameter analysis (Rigaku Corporation).

[0071] <Ratio of D-band peak to G-band peak in Raman spectroscopy> The activated carbons obtained in the examples and comparative examples were pulverized, vacuum dried at 120°C for 3 hours or more, and then allowed to cool to room temperature in a desiccator. Raman spectra were measured using an "XploRA PLUS" manufactured by Horiba Ltd., using a light source with a laser wavelength of 532 nm. The test was performed on randomly sampled particles from each sample. The measurement conditions were a wavelength range of 500 to 2000 cm. －１ The exposure time was 10 seconds, the number of measurements was 50, and the average value of five points was calculated as the measurement value. The D / G value was 1360 cm －１ Nearby D band and 1580 cm －１ The intensity ratio of each nearby G band peak, ID / IG (D band peak intensity / G band peak intensity), was determined.

[0072] <Chloroform adsorption amount> An arbitrary amount of pulverized activated carbon was added to 100 mL of chloroform solution adjusted to an initial concentration of about 0.100 mg / L, and then the solution was shaken at 160 rpm for 2 hours at about 25° C. After leaving the solution to stand in a thermostatic chamber at 25° C. for 1 hour, the equilibrium adsorption amount of chloroform was calculated.

[0073] Specifically, the adsorption amount A (mg / g) was calculated using the following formula: where Co (mg / L) is the chloroform concentration in a blank sample containing no activated carbon, C (mg / L) is the chloroform concentration in a test sample containing activated carbon, and W (mg) is the mass of activated carbon added. The chloroform concentration was determined by the headspace method using ECD gas chromatography: A = (Co - C) x 1000 x 0.1 / W. Furthermore, a power approximation formula was calculated from the resulting adsorption amounts A for three different test sample concentrations, and the adsorption amount at a test sample concentration of 0.01 mg / L was calculated, which was taken as the equilibrium adsorption amount.

[0074] Example 1: Char made from coconut shells from the Philippines (specific surface area: approximately 400 m ２ 1 kg of char (100%) was charged into a fluidized bed activation furnace heated to 900°C, and propane combustion gas and steam (steam partial pressure: 35%) were introduced at a rate of 0.75 mL / min (temperature-corrected reaction gas rate: 3.22 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 3.22 mL / min / kg). ２ / g. Thereafter, the primary activated and washed carbon was pickled using hydrochloric acid (concentration: 0.5 N, diluent: ion-exchanged water) at a temperature of 70°C for 30 minutes, and then thoroughly washed with ion-exchanged water and dried. This primary activated and washed carbon was charged into a heat treatment furnace, and propane combustion gas + water vapor (water vapor partial pressure: 10%) was introduced at a rate of 0.70 mL / min (temperature-corrected reaction gas amount: 2.62 mL / min, contact ratio between the primary activated carbon and the reaction gas: 100%, contact reaction gas amount per primary activated carbon: 2.62 mL / min / kg). The carbon was heated to 750°C and then treated to obtain a specific surface area of ​​1641 m. ２ / g, and activated carbon was obtained.

[0075] The temperature-corrected reaction gas amount, the catalytic reaction gas amount per char, and the catalytic reaction gas amount per activated carbon were calculated according to the following formulas.

[0076] Example 2 Propane combustion gas + steam was introduced at a rate of 1.05 mL / min (temperature-corrected reaction gas rate: 4.51 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 4.51 mL / min / kg). ２ The primary activation was performed until the specific surface area reached 1737 m / g, and the propane combustion gas + steam flow rate was 0.55 mL / min (temperature-corrected reaction gas flow rate was 2.06 mL / min, the contact ratio between activated carbon and reaction gas was 100%, and the contact reaction gas flow rate per activated carbon was 2.06 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Example 1, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0077] Example 3 Propane combustion gas + steam was introduced at a rate of 1.00 mL / min (temperature-corrected reaction gas rate of 4.30 mL / min, contact ratio of char and reaction gas of 100%, contact reaction gas rate per char of 4.30 mL / min / kg). ２ The primary activation was performed until the specific surface area reached 1858 m / g, and the propane combustion gas + steam flow rate was 0.60 mL / min (temperature-corrected reaction gas flow rate was 2.25 mL / min, the contact ratio between activated carbon and reaction gas was 100%, and the contact reaction gas flow rate per activated carbon was 2.25 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Example 1, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0078] Example 4 Propane combustion gas + steam was introduced at a rate of 0.95 mL / min (temperature-corrected reaction gas rate: 4.08 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 4.08 mL / min / kg). ２The primary activation was performed until the specific surface area reached 1940 m / g, and the propane combustion gas + steam flow rate was 0.55 mL / min (temperature-corrected reaction gas flow rate was 2.06 mL / min, the contact ratio between activated carbon and reaction gas was 100%, and the contact reaction gas flow rate per activated carbon was 2.06 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Example 1, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0079] Example 5: Char made from coconut shells from the Philippines (specific surface area: approximately 400 m ２ 1 kg of char (1676 m² / g) was charged into a rotary kiln heated to 900°C, and propane combustion gas + steam (steam partial pressure: 35%) was introduced at a rate of 0.50 mL / min (temperature-corrected reaction gas rate: 2.15 mL / min, contact ratio of char to reaction gas: 15%, contact reaction gas rate per char: 0.32 mL / min / kg). ２ Primary activation was carried out until the char volume reached 1.50 / g. The contact ratio with the reaction gas was calculated from the ratio of the volume of the char to the volume of the furnace. The char was then pickled using hydrochloric acid (concentration: 0.5 N, diluent: ion-exchanged water) at a temperature of 70°C for 30 minutes, thoroughly washed with ion-exchanged water, and dried. This primarily activated and washed char was placed in a fluidized bed activation furnace heated to 950°C, and propane combustion gas + steam (steam partial pressure: 30%) was introduced at a rate of 2.50 mL / min (temperature-corrected reaction gas volume: 11.20 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas volume per char: 11.20 mL / min / kg). ２ / g. Thereafter, the carbon was pickled using hydrochloric acid (concentration: 0.5 N, diluted with ion-exchanged water) at a temperature of 70°C for 30 minutes, and then thoroughly washed with ion-exchanged water and dried. This secondarily activated and washed carbon was placed in a heat treatment furnace, and propane combustion gas + steam (steam partial pressure: 15%) was introduced at a rate of 0.75 mL / min (temperature-corrected reaction gas amount: 2.81 mL / min, contact ratio between activated carbon and reaction gas: 100%, contact reaction gas amount per activated carbon: 2.81 mL / min / kg). The carbon was then heated at 750°C until the specific surface area reached 2,108 m ２ / g, thereby obtaining activated carbon.

[0080] Example 6 Propane combustion gas + steam was introduced at a rate of 0.95 mL / min (temperature-corrected reaction gas rate: 4.08 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 4.08 mL / min / kg). ２ The primary activation was performed until the specific surface area reached 1482 m / g, and the amount of propane combustion gas and steam was 0.55 mL / min (temperature-corrected reaction gas amount was 2.06 mL / min, the contact ratio between activated carbon and reaction gas was 100%, and the contact reaction gas amount per activated carbon was 2.06 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Example 1, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0081] Example 7 Propane combustion gas + steam was introduced at a rate of 1.00 mL / min (temperature-corrected reaction gas rate: 4.30 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 4.30 mL / min / kg). ２ The primary activation was carried out until the specific surface area reached 1,320 m / g, and the propane combustion gas + steam flow rate was 0.60 mL / min (temperature-corrected reaction gas flow rate was 2.25 mL / min, the contact ratio between activated carbon and reaction gas was 100%, and the contact reaction gas flow rate per activated carbon was 2.25 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Example 1, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0082] Example 8 Propane combustion gas + steam was introduced at a rate of 0.95 mL / min (temperature-corrected reaction gas rate: 4.08 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 4.08 mL / min / kg). ２ The primary activation was performed until the specific surface area reached 1283 m / g, and the amount of propane combustion gas and steam was 0.55 mL / min (temperature-corrected reaction gas amount was 2.06 mL / min, the contact ratio between activated carbon and reaction gas was 100%, and the contact reaction gas amount per activated carbon was 2.06 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Example 1, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0083] Comparative Example 1 100 g of pine sawdust (moisture content 48% by mass) was mixed with 97.8 g of an 85% by mass aqueous phosphoric acid solution (mass of dry solids of phosphoric acid / mass of dry solids of sawdust = 1.6). This mixture was heated with stirring in a circulation dryer heated to a temperature of 175°C. The resulting mixture was placed in a rotary kiln heated to 300°C and oxidized by being held in air for 3 hours. This oxidized product was oxidized under nitrogen at 500°C until it had a specific surface area of ​​1097 m. ２ The primary activation was carried out until the specific surface area reached 1,146 m / g. Thereafter, the primary activated and washed carbon was thoroughly washed with ion-exchanged water and dried. This primary activated and washed carbon was placed in a heat treatment furnace, and propane combustion gas + steam (steam partial pressure: 10%) was introduced at a rate of 0.35 mL / min (temperature-corrected reaction gas amount: 1.31 mL / min, contact ratio between activated carbon and reaction gas: 100%, contact reaction gas amount per activated carbon: 1.31 mL / min / kg). ２ / g, and activated carbon was obtained.

[0084] Comparative Example 2: Char made from coconut shells from the Philippines (specific surface area: approximately 400 m ２ 1 kg of char (1621 m² / g) was charged into a fluidized bed activation furnace heated to 900°C, and propane combustion gas and steam (steam partial pressure: 35%) were introduced at a rate of 0.65 mL / min (temperature-corrected reaction gas rate: 2.79 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 2.79 mL / min / kg). ２ Thereafter, the activated carbon was pickled with hydrochloric acid (concentration: 0.5 N, diluted with ion-exchanged water) at a temperature of 70° C. for 30 minutes, thoroughly washed with ion-exchanged water, and dried to obtain activated carbon.

[0085] Comparative Example 3: Char made from coconut shells from the Philippines (specific surface area: approximately 400 m ２1 kg of char (1889 m² / g) was charged into a fluidized bed activation furnace heated to 900°C, and propane combustion gas + steam (steam partial pressure: 15%) was introduced at a rate of 0.25 mL / min (temperature-corrected reaction gas rate: 1.07 mL / min, contact ratio of char to reaction gas: 15%, contact reaction gas rate per char: 0.16 mL / min / kg). ２ Thereafter, the activated carbon was pickled with hydrochloric acid (concentration: 0.5 N, diluted with ion-exchanged water) at a temperature of 70° C. for 30 minutes, thoroughly washed with ion-exchanged water, and dried to obtain activated carbon.

[0086] Comparative Example 4: Char made from coconut shells from the Philippines (specific surface area: approximately 400 m ２ 1 kg of char (1865 m² / g) was charged into a rotary kiln heated to 900°C, and propane combustion gas + steam (steam partial pressure: 25%) was introduced at a rate of 0.50 mL / min (temperature-corrected reaction gas rate: 2.15 mL / min, contact ratio of char to reaction gas: 15%, contact reaction gas rate per char: 0.32 mL / min / kg). ２ Primary activation was carried out until the char volume reached 1.85 mL / g. The contact ratio with the reaction gas was calculated from the ratio of the volume of the char to the volume of the furnace. The char was then pickled using hydrochloric acid (concentration: 0.5 N, diluent: ion-exchanged water) at a temperature of 70°C for 30 minutes, thoroughly washed with ion-exchanged water, and dried. This primary activated and washed char was placed in a fluidized bed activation furnace heated to 950°C, and propane combustion gas + steam (steam partial pressure: 15%) was introduced at a rate of 1.85 mL / min (temperature-corrected reaction gas volume: 8.29 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas volume per char: 8.29 mL / min / kg). ２ / g. Thereafter, the carbon was pickled using hydrochloric acid (concentration: 0.5 N, diluted with ion-exchanged water) at a temperature of 70°C for 30 minutes, and then thoroughly washed with ion-exchanged water and dried. This secondarily activated and washed carbon was placed in a heat treatment furnace, and propane combustion gas + steam (steam partial pressure: 10%) was introduced at a rate of 0.45 mL / min (temperature-corrected reaction gas amount: 1.69 mL / min, contact ratio between activated carbon and reaction gas: 100%, contact reaction gas amount per activated carbon: 1.69 mL / min / kg). The carbon was then heated at 750°C until the specific surface area reached 2221 m ２ / g, thereby obtaining activated carbon.

[0087] Comparative Example 5: The oxidation-treated product was heated at 500°C under nitrogen to a specific surface area of ​​1548 m ２ The primary activation was performed until the specific surface area reached 1601 m / g, and the amount of propane combustion gas + steam (steam partial pressure: 10%) was introduced at 0.5 mL / min (temperature-corrected reaction gas amount: 1.87 mL / min, contact ratio between activated carbon and reaction gas: 100%, contact reaction gas amount per activated carbon: 1.87 mL / min / kg). ２ Activated carbon was obtained in the same manner as in Comparative Example 2, except that the heat treatment was carried out so that the saturation of the activated carbon was 1 / g.

[0088] Comparative Example 6: Char made from coconut shells from the Philippines (specific surface area: approximately 400 m ２ 1 kg of char (100%) was charged into a fluidized bed activation furnace heated to 900°C, and propane combustion gas and steam (steam partial pressure: 25%) were introduced at a rate of 0.60 mL / min (temperature-corrected reaction gas rate: 2.58 mL / min, contact ratio between char and reaction gas: 100%, contact reaction gas rate per char: 2.58 mL / min / kg). ２ / g. Thereafter, the primary activated and washed carbon was pickled using hydrochloric acid (concentration: 0.5 N, diluent: ion-exchanged water) at a temperature of 70°C for 30 minutes, and then thoroughly washed with ion-exchanged water and dried. This primary activated and washed carbon was charged into a heat treatment furnace, and propane combustion gas + water vapor (water vapor partial pressure: 10%) was introduced at a rate of 0.30 mL / min (temperature-corrected reaction gas amount: 1.12 mL / min, contact ratio between activated carbon and reaction gas: 100%, contact reaction gas amount per activated carbon: 1.12 mL / min / kg). The carbon was heated to 750°C and treated to obtain a specific surface area of ​​1,353 m２ / g, and activated carbon was obtained.

[0089] The physical properties of the activated carbons obtained in the Examples and Comparative Examples are shown in Table 1.

[0090] <Preparation of Test Electrodes> The activated carbon obtained in the Examples and Comparative Examples was pulverized to an average particle size of 6 μm. The pulverized activated carbon, conductive additive, and binder were previously dried under reduced pressure (0.1 kPa or less) at 120°C for at least 16 hours. The activated carbon, conductive additive, and binder were weighed and kneaded in a ratio of (mass of activated carbon):(mass of conductive additive):(mass of binder) of 81:9:10. The conductive additive was Denka Black Granular, a conductive carbon black manufactured by Denka Co., Ltd., and the binder was polytetrafluoroethylene 6J manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd. After kneading, the mixture was cut into flakes of 1 mm or less to achieve further uniformity, and then pressed at 400 kg / cm using a coin-forming machine. ２ A pressure of 1000 kJ / cm was applied to obtain a coin-shaped secondary molded product. The obtained secondary molded product was formed into a sheet having a thickness of 160 μm±5% using a roll press, and then cut into a predetermined size (30 mm×30 mm) to produce electrode composition 1 as shown in FIG. 1. The obtained electrode composition 1 was then dried at 120° C. in a reduced pressure atmosphere for 16 hours or more, and the mass, sheet thickness, and dimensions were measured and used in the following measurements.

[0091] <Preparation of Measurement Electrode Cell> As shown in FIG. 2, a conductive adhesive 2 "HITASOL GA-715" manufactured by Hitachi Chemical Co., Ltd. was applied to an etched aluminum foil 3 manufactured by Hosen Co., Ltd. to a coating thickness of 100 μm. Then, as shown in FIG. 3, the etched aluminum foil 3 coated with the conductive adhesive 2 was bonded to a sheet-like electrode composition 1 that had been cut previously. Then, a tab 4 with an aluminum sealant 5 manufactured by Hosen Co., Ltd. was welded to the etched aluminum foil 3 using an ultrasonic welding machine. After welding, the resultant was vacuum dried at 120°C to obtain a polarizable electrode 6 equipped with an aluminum current collector.

[0092] As shown in FIG. 4 , an aluminum laminated resin sheet manufactured by Hosen Co., Ltd. was cut into a rectangle (200 mm long x 60 mm wide), folded in half, and thermocompressed along one side ((1) in FIG. 4 ) with the remaining two sides open to prepare a bag-shaped exterior sheet 7. A laminate was prepared by stacking two of the polarizable electrodes 6 via a cellulose separator "TF-40" (not shown) manufactured by Nippon Kodoshi Kogyo Co., Ltd. This laminate was inserted into the exterior sheet 7, and one side ((2) in FIG. 5 ) where the tab 4 contacted was thermocompressed to fix the polarizable electrode 6. The laminate was then vacuum-dried at 120°C under reduced pressure for 16 hours or more, after which an electrolyte solution was injected into a dry box in an argon atmosphere (dew point of −90°C or less). A 1.0 mol / L acetonitrile solution of tetraethylammonium tetrafluoroborate manufactured by Kishida Chemical Co., Ltd. was used as the electrolyte. After the laminate was impregnated with the electrolyte in the exterior sheet 7, the remaining side of the exterior sheet 7 ((3) in FIG. 5) was thermocompression bonded to prepare the electric double layer capacitor 8 shown in FIG.

[0093] <Capacitance Measurement> The obtained electric double layer capacitor 8 was charged at a constant current of 50 mA per electrode surface area at −30° C. using a "CAPACITOR TESTER PFX2411" manufactured by Kikusui Electronics Co., Ltd., up to a final voltage of 3.0 V. It was then supplemented at a constant voltage of 3.0 V for 30 minutes, and discharged at 25 mA after the supplemental charge was completed. The obtained discharge curve data was calculated using an energy conversion method to obtain the capacitance (F). Specifically, after charging, the capacitor was discharged until the voltage reached zero, and the capacitance (F) was calculated from the discharge energy discharged at this time. The capacitance was then divided by the electrode volume to obtain the capacitance (F / cc).

[0094] <Resistance Measurement> Resistance measurements were performed at -30°C using an electrochemical measurement apparatus (VMP3 manufactured by BioLogic) by a constant voltage AC impedance measurement method, applying an amplitude width of 20 mV centered around 0 V, and at frequencies from 4 mHz to 1 MHz. A Cole-Cole plot was obtained showing the relationship between complex impedance, with the real part on the horizontal axis and the imaginary part on the vertical axis. From this plot, the resistance of the cable, etc. was excluded, and the electrode interface resistance (the point of contact between the semicircle and the real axis, the diameter of the arc) and the electrode diffusion resistance (the resistance value obtained by excluding the interface resistance from the point of contact between the tangent to the low-frequency side curve and the real axis) were determined.

[0095] The evaluation results are shown in Table 2.

[0096] It was confirmed that the electric double layer capacitors equipped with electrodes containing activated carbon obtained in Examples 1 to 8 had low resistance and high capacitance. In contrast, the electric double layer capacitors equipped with electrodes containing activated carbon obtained in Comparative Examples 1 to 6 were insufficient in at least one of resistance and capacitance. Therefore, it was found that the activated carbon of the present invention is useful for improving the performance of electricity storage devices.

[0097] REFERENCE SIGNS LIST 1 Electrode composition 2 Conductive adhesive 3 Etched aluminum foil 4 Tab 5 Sealant 6 Polarizable electrode 7 Bag-shaped exterior sheet 8 Electric double layer capacitor (1) One side bonded by thermocompression (2) One side where the tab is in contact (3) Remaining side of the bag-shaped exterior sheet

Claims

1. The specific surface area calculated from the nitrogen adsorption / desorption isotherm using the BET method is 1150 m ２ / g~2200m ２ / g, the amount of vitamin B12 adsorbed when contacted with an aqueous solution of 300 ppm of vitamin B12 for 24 hours is 10.2 mg / mL to 50 mg / mL, and the chlorine content is 2500 ppm or less.

2. 1360 cm in Raman spectroscopy －１ Nearby D band peak and 1580 cm －１ 2. The activated carbon according to claim 1, wherein the value of D / G, which is the intensity ratio of adjacent G band peaks, is 1.15 to 1.

40.

3. The activated carbon according to claim 1 or 2, in which the ratio of the amount of adsorption when contacted with a 300 ppm aqueous solution of vitamin B12 for 2 hours to the amount of adsorption when contacted with the aqueous solution for 24 hours is 58% or more.

4. The ratio of the amount of vitamin B12 adsorbed when in contact with a 300 ppm vitamin B12 aqueous solution for 24 hours and the specific surface area calculated by the BET method from the nitrogen adsorption / desorption isotherm was 0.00810 [(mg / mL) / (m ２ / g)] to 0.02470 [(mg / mL) / (m ２ 3. The activated carbon according to claim 1 or 2, wherein the molecular weight of the activated carbon is 1000 or more.

5. An electrode material comprising the activated carbon according to claim 1 or 2.

6. An electrode comprising the electrode material according to claim 5.

7. An electricity storage device comprising the electrode according to claim 6.

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