Carbonaceous material, manufacturing method thereof, electrode active material for electronic double-layer capacitor, electrode for electronic double-layer capacitor, and electronic double-layer capacitor

Abstract

To provide a carbonaceous material and a manufacturing method thereof, capable of suppressing gas generation on charging / discharging an electronic double-layer capacitor, and having excellent moldability and electrostatic capacitance.SOLUTION: A carbonaceous material has a content of silicon element of under 200 ppm, a powder electric conductivity of 10.0-22.0 S / cm, a total surface functional group amount of 0.22-0.36 meq / g, and a pore size of 4 nm or over and a pore volume of 0.10-0.20 cm3 / g measured in accordance with BJH method.SELECTED DRAWING: None

Description

Technical Field

[0001] This patent application claims priority under the Paris Convention with respect to Japanese Patent Application No. 2019-234855 (filing date: December 25, 2019), and the entire content thereof is incorporated herein by reference. The present invention relates to a carbonaceous material, a method for producing the same, an electrode active material for an electric double layer capacitor, an electrode for an electric double layer capacitor, and an electric double layer capacitor.

Background Art

[0002] An electric double layer capacitor, which is one type of electrochemical device, utilizes the capacitance (electric double layer capacitance) obtained only from physical ion adsorption and desorption without chemical reactions, and thus has excellent output characteristics and life characteristics compared to batteries. Due to these characteristics, it has been widely developed for various applications such as backup of various memories, power generation using natural energy, and power storage applications such as UPS (Uninterruptible Power Supply). In recent years, electric double layer capacitors have attracted attention as auxiliary power sources for electric vehicles (EVs) and hybrid vehicles (HVs), and for storage of regenerative energy, from the viewpoints of the above-mentioned excellent characteristics and urgent measures against environmental problems. Such in-vehicle electrochemical devices are required not only to have a higher energy density, but also to have higher durability and further improved capacitance under severe usage conditions (for example, under a severe temperature environment) compared to consumer applications.

[0003] In response to such requirements, various methods for improving the durability and capacitance of electrochemical devices have been studied. For example, Patent Document 1 discloses a modified activated carbon that can suppress gas generation during charge and discharge and is also useful for reducing resistance by limiting not only the surface functional groups in the activated carbon but also the amount of oxygen in the skeleton.

[0004] Patent Document 2 discloses an activated carbon for an electric double layer capacitor with a high capacitance and a reduced electrical resistance by subjecting an activator of a carbide to alkali washing and acid washing to reduce the silicon content to 200 to 3000 ppm.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the method for controlling the surface functional groups and the amount of oxygen in the skeleton described in Patent Document 1 above, the gas generation suppression effect was not sufficiently satisfactory. In Patent Document 2, focusing on the improvement of capacitance, the silicon element content in the activated carbon is specified within a specific range. Although there is a certain effect on the improvement of capacitance within the above range, the gas generation suppression effect may not necessarily be sufficiently satisfactory.

[0007] Therefore, an object of the present invention is to provide a carbonaceous material and a method for producing the same that suppress gas generation during charge and discharge of an electric double layer capacitor and are excellent in moldability and capacitance.

Means for Solving the Problems

[0008] As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention.

[0009] That is, the present invention includes the following preferred embodiments. 〔1〕The carbonaceous material has a silicon element content of less than 200 ppm, a powder conductivity of 10.0 to 22.0 S / cm, a total surface functional group amount of 0.22 to 0.36 meq / g, and a pore volume of 0.10 to 0.20 cm 3 / g for pores with a pore diameter of 4 nm or more measured by the BJH method. 〔2〕The carbonaceous material according to 〔1〕, having a BET specific surface area of 1400 to 2200 m 2 / g. 〔3〕The carbonaceous material according to 〔1〕 or 〔2〕, having an alkali metal content of less than 40 ppm. 〔4〕The carbonaceous material according to any one of 〔1〕 to 〔3〕, based on a plant-derived carbon precursor. 〔5〕The carbonaceous material according to any one of 〔1〕 to 〔4〕, wherein the plant-derived carbon precursor is a coconut shell. 〔6〕An electrode active material for an electric double layer capacitor, comprising the carbonaceous material according to any one of 〔1〕 to 〔5〕. 〔7〕An electrode for an electric double layer capacitor, comprising the electrode active material for an electric double layer capacitor according to 〔6〕. 〔8〕An electric double layer capacitor, comprising the electrode for an electric double layer capacitor according to 〔7〕. 〔9〕A step of washing the activated carbon obtained by carbonizing and activating a carbon precursor in an alkaline solution at 65 °C or higher, and a step of heat-treating and pulverizing the activated carbon after the alkali washing at 1000 to 1300 °C in an inert gas atmosphere after acid washing. A method for producing the carbonaceous material according to any one of 〔1〕 to 〔5〕, comprising the above steps.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a carbonaceous material and a method for producing the same, which suppress gas generation during charge and discharge of an electric double layer capacitor and are excellent in moldability and capacitance.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0013] <Carbonaceous material> The carbonaceous material of the present invention has a silicon element content of less than 200 ppm, a powder conductivity of 10.0 to 22.0 S / cm, a total surface functional group amount of 0.22 to 0.36 meq / g, and a pore volume of 0.10 to 0.20 cm with a pore diameter of 4 nm or more measured by the BJH method 3 / g.

[0014] The silicon element content of the carbonaceous material of the present invention is less than 200 ppm, preferably less than 100 ppm, more preferably less than 50 ppm, and even more preferably less than 20 ppm. When the silicon element content is 200 ppm or more, the amount of gas generated during charge and discharge tends to increase. Also, the lower limit of the silicon element content of the carbonaceous material of the present invention is not particularly limited, but is usually 1 ppm or more, and may be 5 ppm or more. The silicon element content of the carbonaceous material of the present invention can be adjusted by the concentration, temperature, etc. of the cleaning liquid in the alkali cleaning step in the manufacturing method of the carbonaceous material of the present invention described later. Also, the silicon element content of the carbonaceous material of the present invention can be measured by ICP (inductively coupled plasma) emission spectrometry, for example, as described in the examples below.

[0015] The powder conductivity of the carbonaceous material of the present invention is 10.0 S / cm or more, preferably 13.0 S / cm or more, more preferably 14.0 S / cm or more, even more preferably 14.5 S / cm or more, and particularly preferably 15.0 S / cm or more. Further, the powder conductivity of the carbonaceous material of the present invention is 22.0 S / cm or less, preferably 21.0 S / cm or less, and more preferably 20.0 S / cm or less. When the powder conductivity exceeds 22.0 S / cm, the carbon crystal structure of the carbonaceous material develops excessively, and accordingly, the pores of the carbonaceous material shrink, which may cause a decrease in the initial capacitance per unit weight. On the other hand, when the powder conductivity is less than 10.0 S / cm, the development of the carbon crystal structure of the carbonaceous material is not sufficient, and due to the low crystallinity, the electrical conductivity of carbon itself is not sufficient, and the resistance during charge and discharge increases, so the capacitance retention rate may decrease. The powder conductivity of the carbonaceous material of the present invention can be controlled within the above range by adjusting the heat treatment temperature and the like in the heat treatment step in the method for producing the carbonaceous material of the present invention described later. Further, the powder conductivity of the carbonaceous material of the present invention can be measured by the method described in the examples below.

[0016] The total surface functional group content of the carbonaceous material of the present invention is 0.22 meq / g or more, preferably 0.23 meq / g or more, and more preferably 0.24 meq / g or more. Further, the total surface functional group content of the carbonaceous material of the present invention is 0.36 meq / g or less, preferably 0.35 meq / g or less, and more preferably 0.34 meq / g or less. When the total surface functional group content exceeds 0.36 meq / g, the number of active sites reacting with the electrolyte in the capacitor electrode increases, and by promoting the decomposition reaction of the electrolyte, the gas generation amount during charge and discharge tends to increase. On the other hand, when the total surface functional group content is less than 0.22 meq / g, the hydrophobicity increases, and the affinity between activated carbon particles and between activated carbon particles and other materials changes, resulting in poor moldability of the carbonaceous material of the present invention, and it may become difficult to fabricate an electrode from the carbonaceous material. The total surface functional group content of the carbonaceous material of the present invention can be controlled within the above range by adjusting the heat treatment temperature and the like in the heat treatment step in the manufacturing method of the carbonaceous material of the present invention described later. The total surface functional group content of the carbonaceous material of the present invention can be measured by the method described in the examples below.

[0017] The pore volume of pores with a pore diameter of 4 nm or more measured by the BJH method of the carbonaceous material of the present invention is 0.10 cm 3 / g or more, preferably 0.11 cm 3 / g or more, and more preferably 0.13 cm 3 / g or more. Further, the pore volume of the carbonaceous material of the present invention is 0.20 cm 3 / g or less, preferably 0.18 cm 3 / g or less, and more preferably 0.17 cm 3 / g or less. When the pore volume of pores with a pore diameter of 4 nm or more exceeds 0.20 cm 3 / g, the bulk density of the electrode decreases, and the capacitance per unit volume tends to decrease. On the other hand, when the pore volume of pores with a pore diameter of 4 nm or more is 0.10 cm 3If it is less than / g, it will cause an increase in the internal resistance of the electrode and the gas generation amount is likely to increase. Here, the BJH method is a calculation method generally used for the analysis of mesopores (pores with a pore diameter of 2 nm or more and 50 nm or less), similar to the CI method and the DH method, and is a method proposed by Barrett, Joyner, Halends, etc. In the present invention, by applying the BJH method to the nitrogen adsorption isotherm measured by the nitrogen adsorption method as described in the examples, the pore volume of pores with a pore diameter of 4 nm or more can be calculated. The pore volume of pores with a pore diameter of 4 nm or more in the carbonaceous material of the present invention can be controlled within the above range by appropriately selecting the type of carbon precursor used or by appropriately adjusting the temperature, treatment time, etc. of the activation step in the method for producing the carbonaceous material of the present invention described later.

[0018] The pore volume of micropores (pores with a pore diameter of less than 2 nm) measured by the MP method of the carbonaceous material of the present invention is 0.60 cm 3 / g or more, preferably 0.63 cm 3 / g or more, more preferably 0.66 cm 3 / g or more. Further, the pore volume of the above micropores is preferably 1.20 cm 3 / g or less, more preferably 1.10 cm 3 / g or less, still more preferably 1.00 cm 3 / g or less. When the pore volume of the micropores is within the above range, the resistance presumably due to the diffusion resistance of non-aqueous electrolyte ions in the pores tends to decrease, and the bulk density of the electrode improves, and the capacitance per unit area tends to increase. Here, the MP method is a calculation method generally used for micropore analysis, similar to the HK method and the SF method. In the present invention, by applying the MP method to the nitrogen adsorption isotherm measured by the nitrogen adsorption method as described in the examples, the pore volume of the micropores can be calculated. The pore volume of the micropores of the carbonaceous material of the present invention can be controlled within the above range by appropriately selecting the type of carbon precursor used or by appropriately adjusting the temperature, treatment time, etc. of the activation step in the method for producing the carbonaceous material of the present invention described later.

[0019] The BET specific surface area of the carbonaceous material of the present invention is preferably 1400 m 2 / g or more, more preferably 1430 m 2 / g or more, still more preferably 1450 m 2 / g or more, even more preferably 1500 m 2 / g or more. Also, the BET specific surface area of the carbonaceous material of the present invention is preferably 2200 m 2 / g or less, more preferably 2150 m 2 / g or less, still more preferably 2100 m 2 / g or less, particularly preferably less than 2000 m 2 / g. When the BET specific surface area is within the above range, the resistance presumably due to the diffusion resistance of non-aqueous electrolyte ions in the pores tends to decrease, and also the bulk density of the electrode improves, and the capacitance per unit area tends to increase. The BET specific surface area of the carbonaceous material of the present invention can be controlled within the above range by appropriately adjusting the temperature, treatment time, etc. of the activation step in the method for producing the carbonaceous material of the present invention described later. The BET specific surface area of the carbonaceous material of the present invention can be measured, for example, by the method of measuring the nitrogen adsorption isotherm described in the examples below.

[0020] The alkali metal content of the carbonaceous material of the present invention is preferably less than 40 ppm, more preferably less than 20 ppm, and even more preferably less than 10 ppm. The lower limit of the alkali metal content of the carbonaceous material of the present invention is not particularly limited, and it may be 0 ppm, usually 1 ppm or more, and may be 3 ppm or more. Examples of alkali metal species that can be contained in the carbonaceous material include lithium, sodium, potassium, cesium, etc. Usually, sodium and / or potassium have a relatively high content, so it is important to control their contents. When the alkali metal content is within the above range, the possibility of the alkali metal element eluting into the electrolytic solution is reduced, and short circuits due to re-precipitation are less likely to occur. In addition, since the pores of the carbonaceous material are less likely to be blocked by alkali metals, the charge-discharge capacity tends to be high. The alkali metal content of the carbonaceous material of the present invention can be adjusted by alkali washing or acid washing in the method for producing the carbonaceous material of the present invention described below. The alkali metal content of the carbonaceous material of the present invention can be measured, for example, by the ICP emission spectrometry described in the examples below.

[0021] <Method for producing carbonaceous material> The carbonaceous material of the present invention is, for example a step of washing the activated carbon obtained by carbonizing and activating a carbon precursor in an alkaline solution at 65 °C or higher, and a step of heat-treating and pulverizing the activated carbon after the alkali washing at 1000 to 1300 °C in an inert gas atmosphere after acid washing. It can be produced by a method including

[0022] In the present invention, the carbon precursor serving as the raw material of the carbonaceous material is not particularly limited as long as it can form a carbonaceous material by activation, and can be widely selected from plant-derived carbon precursors, mineral-derived carbon precursors, natural material-derived carbon precursors, synthetic material-derived carbon precursors, etc. From the viewpoints of reducing harmful impurities, environmental protection, and commercial aspects, the carbonaceous material of the present invention is preferably based on a plant-derived carbon precursor. In other words, it is preferable that the carbon precursor serving as the carbonaceous material of the present invention is plant-derived.

[0023] Examples of carbon precursors derived from minerals include petroleum-based and coal-based pitches, and coke. Examples of carbon precursors derived from natural materials include natural fibers such as cotton and hemp, regenerated fibers such as rayon and viscose rayon, and semi-synthetic fibers such as acetate and triacetate. Examples of carbon precursors derived from synthetic materials include polyamides such as nylon, polyvinyl alcohol-based materials such as vinylon, polyacrylonitrile-based materials such as acrylic, polyolefins such as polyethylene and polypropylene, polyurethanes, phenolic resins, and vinyl chloride-based resins.

[0024] In the present invention, the carbon precursors derived from plants are not particularly limited, and examples include fruits such as wood, charcoal, rice husks, coconut husks, palm husks, coffee beans, tea leaves, sugarcane, fruits (e.g., oranges, bananas), straw, rice hulls, broad-leaved trees, coniferous trees, and bamboo, but are not limited thereto. This exemplification includes waste after being used for its original purpose (e.g., used tea leaves), or a part of plant raw materials (e.g., peels of bananas or oranges). These plant raw materials may be used alone or in combination of two or more. Among these plant raw materials, coconut husks are preferred because they are easily available and can produce carbonaceous materials having various characteristics.

[0025] The coconut husks are not particularly limited, and examples include coconut husks of palm coconut (oil palm), coconut, salak, and giant palm. These coconut husks may be used alone or in combination of two or more. Coconut husks of coconut and palm coconut, which are biomass wastes generated in large quantities after using coconut for food, detergent raw materials, biodiesel oil raw materials, etc., are particularly preferred from the viewpoint of easy availability.

[0026] It is possible to obtain coconut shells by calcining them in the form of char (coconut shell char), and it is preferable to use this as a raw material. Here, char generally refers to a powdery solid rich in carbon produced without melting and softening when coal is heated, but here it also refers to a powdery solid rich in carbon produced by heating organic matter without melting and softening. The method for producing char from coconut shells is not particularly limited, and it can be produced using methods known in the art. For example, the raw coconut shells can be calcined (carbonized) at a temperature of 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 of these inert gases and other gases having these inert gases as the main component.

[0027] <Activation step> In the method for producing the carbonaceous material of the present invention, the activated carbon derived from coconut shells used can be obtained, for example, by subjecting the above carbon precursor (coconut shell char) to an activation treatment. The activation treatment is a treatment for forming pores on the surface of the carbon precursor and converting it into a porous carbonaceous substance, whereby activated carbon having a large specific surface area and pore volume can be obtained. If the carbon precursor is used as it is without performing the activation treatment, the specific surface area and pore volume of the obtained carbonaceous material are not sufficient, and it is difficult to ensure a sufficiently high initial capacity when used as an electrode material, and the carbonaceous material of the present invention cannot be obtained. The activation treatment can be performed by a general method in the art, and mainly two types of treatment methods, namely gas activation treatment and chemical activation treatment, can be mentioned.

[0028] As the gas activation treatment, for example, a method of heating a carbon precursor in the presence of water vapor, carbon dioxide, air, oxygen, combustion gas, or a mixed gas thereof is known. As the chemical activation treatment, for example, a method of mixing an activator such as zinc chloride, calcium chloride, phosphoric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide with a carbon precursor and heating it in an inert gas atmosphere is known. In the present invention, since chemical activation requires a step of removing the remaining chemical agent and the manufacturing method becomes complicated, it is preferable to use gas activation treatment.

[0029] When adopting steam activation as the gas activation treatment, from the viewpoint of efficiently promoting the activation, it is preferable to use a mixture of the same inert gas as that used in the carbonization treatment and steam, and the partial pressure of steam at that time is preferably in the range of 10 to 60%. When the partial pressure of steam is 10% or more, the activation can proceed sufficiently easily, and when it is 60% or less, the rapid activation reaction can be suppressed and the reaction can be easily controlled.

[0030] The total amount of the activation gas supplied in steam activation is preferably 50 to 10,000 parts by mass, more preferably 100 to 5,000 parts by mass, and still more preferably 200 to 3,000 parts by mass with respect to 100 parts by mass of the carbon precursor. When the total amount of the activation gas supplied is within the above range, the activation reaction can proceed more efficiently.

[0031] The specific surface area and pore volume of the activated carbon derived from coconut shells as raw materials can be controlled by changing the activation treatment method of the carbon precursor and its conditions. For example, when obtaining activated carbon by steam activation treatment, it can be controlled by the gas used, heating temperature, time, etc. In steam activation treatment, the specific surface area and pore diameter of the obtained activated carbon tend to be small when the heating temperature is low and large when the heating temperature is high. In the present invention, when obtaining activated carbon by steam activation treatment, the heating temperature (activation temperature) depends on the type of gas used, but is usually 700 to 1100 °C, preferably 800 to 1000 °C. Also, the heating time and heating rate are not particularly limited and may be appropriately determined according to the heating temperature, the specific surface area of the desired activated carbon, etc.

[0032] If necessary, the activation treatment may be carried out once or more than once. When the activation treatment is carried out more than once, for example, when the activated carbon after the first activation (hereinafter also referred to as primary activated carbon) is washed with an acid for the purpose of removing impurities such as alkali metals, it may include a step of washing with an acid. The acid washing step can be carried out by immersing the activated carbon after activation in a washing liquid containing an acid. After acid washing, in order to remove the remaining acid, it is sufficiently washed with water, preferably ion-exchanged water, and dried to obtain primary washed activated carbon. By activating this primary washed activated carbon again, secondary activated carbon is obtained. Hereinafter, the activated carbon subjected to the first or subsequent activation treatment is collectively referred to as activated carbon.

[0033] The conditions for acid washing after the activation are not particularly limited, and the type of acid used, concentration, washing temperature, washing time, etc. may be adjusted as appropriate. In a preferred embodiment, for example, the type of acid: hydrochloric acid, nitric acid, sulfuric acid, or a mixture thereof, preferably hydrochloric acid; concentration: 0.01 to 5 N, preferably 0.1 to 2 N; washing temperature: 40 to 120 °C, preferably 60 to 100 °C; washing time: 5 minutes to 6 hours, preferably 10 minutes to 3 hours, and acid washing may be carried out.

[0034] There are no restrictions on the activation conditions after the second time. Similar to the primary activation, the heating temperature, heating time, etc. may be appropriately determined according to the specific surface area of the activated carbon to be activated as desired.

[0035] <Alkali washing process> The method for producing the carbonaceous material of the present invention includes a step of washing the activated carbon after activation with an alkaline solution at 65°C or higher. The alkali washing step is a step for removing the silicon element contained in the activated carbon by washing the activated carbon with an alkaline washing solution at 65°C or higher. The alkali washing step can be carried out by immersing the activated carbon obtained after activation in a washing solution at 65°C or higher. Examples of the washing solution include an aqueous sodium hydroxide solution, potassium hydroxide, lithium hydroxide, etc. From the viewpoint of easy availability, an aqueous sodium hydroxide solution is preferably used.

[0036] The liquid temperature during alkali washing is 65°C or higher, preferably 70°C or higher, and more preferably 80°C or higher. The upper limit of the liquid temperature is preferably 110°C or lower, more preferably 105°C or lower, and particularly preferably 100°C or lower. When the liquid temperature is within the above range, the concentration of the silicon element in the activated carbon can be sufficiently reduced and it can be carried out safely, which is preferable.

[0037] The concentration of the alkali in the washing solution is not particularly limited and may be appropriately adjusted according to the type of the washing solution used. The alkali concentration of the washing solution is preferably 0.01N or higher, and more preferably 0.03N or higher. The upper limit value of the alkali concentration is preferably 10N or lower, and more preferably 5N or lower. If the alkali concentration is too low, it is necessary to increase the number of washing times to remove the silicon element. On the contrary, if it is too high, the remaining alkali components will increase. Therefore, by setting the concentration within the above range, the alkali washing step can be carried out efficiently, which is preferable from the viewpoint of productivity.

[0038] The pH of the cleaning solution for alkaline cleaning is not particularly limited and may be appropriately adjusted according to the type of cleaning solution used, etc., but a pH of 12 or more is preferable in that it can reduce the cleaning time or the number of cleaning times.

[0039] When the activated carbon is immersed in the cleaning solution, the mass ratio of the cleaning solution to the activated carbon may be appropriately adjusted according to the type, concentration, temperature, etc. of the cleaning solution used. The mass of the activated carbon to be immersed relative to the mass of the cleaning solution is preferably 2% by mass or more, and more preferably 5% by mass or more. The upper limit of the mass ratio is preferably 50% by mass or less, and more preferably 30% by mass or less. Being within the above range is preferable because it does not require excessive energy to raise the temperature of the cleaning solution and a sufficient cleaning effect can be obtained.

[0040] The atmosphere for performing alkaline cleaning is not particularly limited and may be appropriately selected according to the method used for cleaning. In the present invention, cleaning is usually carried out in an air atmosphere.

[0041] As a method for alkaline cleaning the activated carbon, as long as the activated carbon can be immersed in the cleaning solution, it is not particularly limited. A method of continuously adding the cleaning solution, allowing it to stay for a predetermined time, and performing immersion while extracting, or a method of immersing the activated carbon in the cleaning solution, allowing it to stay for a predetermined time, draining the liquid, and then newly adding the cleaning solution and repeating immersion - draining may be used. Also, a method of completely renewing the cleaning solution or a method of partially renewing the cleaning solution may be used. Also, the cleaning solution may be stirred during immersion.

[0042] The time for immersing the activated carbon in the cleaning solution can be appropriately adjusted according to the cleaning solution used, the treatment temperature, etc., but 5 minutes or more is preferable because silicon in the activated carbon can be sufficiently reduced, and 50 minutes or less is preferable from the viewpoint of productivity, more preferably 40 minutes or less, even more preferably 35 minutes or less, and still more preferably 30 minutes or less.

[0043] After alkaline cleaning the activated carbon, in order to remove the remaining cleaning solution, the activated carbon may be washed with water.

[0044] <Pickling cleaning process> The method for producing a carbonaceous material of the present invention includes a step of cleaning the activated carbon after alkali cleaning with an acidic solution. The pickling cleaning step after alkali cleaning is a step for removing impurities such as metals by cleaning the activated carbon after alkali cleaning with an acidic cleaning solution. The pickling cleaning step after alkali cleaning can be performed by immersing the activated carbon obtained after alkali cleaning in an acidic cleaning solution or the like. Examples of the cleaning solution include hydrochloric acid, nitric acid, sulfuric acid, etc., but hydrochloric acid is preferable in that it does not oxidize carbon.

[0045] The concentration of the acid in the pickling cleaning solution after alkali cleaning is not particularly limited, and may be appropriately adjusted according to the type of cleaning solution used. The acid concentration of the cleaning solution is preferably 0.01 N or more, and more preferably 0.1 N or more. The upper limit of the acid concentration is preferably 5 N or less, and more preferably 2 N or less. If the acid concentration is too low, it is necessary to increase the number of cleaning times. On the contrary, if it is too high, the remaining acid components will increase. Therefore, by setting the concentration within the above range, the pickling cleaning step can be efficiently performed, which is preferable from the viewpoint of productivity.

[0046] The pH of the pickling cleaning solution after alkali cleaning is not particularly limited and may be appropriately adjusted according to the type of cleaning solution used, etc., but it is preferably pH 2 or less in terms of reducing the number of cleaning times.

[0047] The liquid temperature of the pickling cleaning solution after alkali cleaning is not particularly limited and may be appropriately adjusted according to the type of cleaning solution used, etc., but it is preferably 40°C to 100°C in terms of high metal removal ability.

[0048] When the activated carbon is immersed in the acid cleaning solution, the mass ratio of the cleaning solution to the activated carbon can be appropriately adjusted according to the type, concentration, temperature, etc. of the cleaning solution used. The mass of the activated carbon to be immersed relative to the mass of the cleaning solution is preferably 2% by mass or more, and more preferably 5% by mass or more. The upper limit of the mass ratio is preferably 50% by mass or less, and more preferably 30% by mass or less. If it is below the above lower limit, a large amount of energy may be required to raise the temperature of the cleaning solution, and if it is above the above upper limit, it is difficult to obtain a sufficient cleaning effect.

[0049] The atmosphere for performing acid cleaning after alkali cleaning is not particularly limited and may be appropriately selected according to the method used for cleaning. In the present invention, the cleaning is usually carried out in the air atmosphere.

[0050] As a method for cleaning the activated carbon, as long as the activated carbon can be immersed in the cleaning solution, it is not particularly limited. A method of continuously adding the cleaning solution, allowing it to stay for a predetermined time, and performing immersion while extracting, or a method of immersing the activated carbon in the cleaning solution, allowing it to stay for a predetermined time, draining the liquid, and then newly adding the cleaning solution and repeating immersion-draining may also be used. Further, a method of updating all of the cleaning solution or a method of updating a part of the cleaning solution may be used. The time for immersing the activated carbon in the cleaning solution can be appropriately adjusted according to the cleaning solution used, the treatment temperature, etc., but it is preferably 5 minutes or more, and more preferably 10 minutes or more in order to sufficiently remove the metal.

[0051] After acid cleaning, the activated carbon may be washed with water. Further, the method for producing the carbonaceous material of the present invention may include a deacidification step in order to remove the acid derived from the acid cleaning solution remaining in the activated carbon. In the present invention, the deacidification step refers to a step of removing the acid remaining in the activated carbon after acid cleaning, and a method of heating for a short time in an oxidizing gas atmosphere is preferable.

[0052] Examples of the oxidizing gas include oxygen, water vapor, carbon dioxide, and combustion gases obtained by burning kerosene or propane. These gases may be used alone or as a mixed gas of two or more types.

[0053] The heating time and temperature in an oxidizing gas atmosphere are not particularly limited, but it is preferably treated at 500°C to 1000°C for 5 minutes to 60 minutes so as not to significantly change the prepared pore structure.

[0054] <Heat treatment step> The method for producing the carbonaceous material of the present invention includes a heat treatment step. By heat-treating the activated carbon (hereinafter also referred to as alkali- and acid-washed activated carbon) after the alkali washing and acid washing steps, the carbon structure can be developed and the conductivity can be controlled within a desired range. Also, although the amount of surface functional groups may be reduced below the desired range in this step, it can be controlled within the desired range by performing the subsequent pulverization step after this heat treatment step. The lower limit of the heat treatment temperature is preferably 1000°C or higher, more preferably 1100°C or higher, even more preferably exceeding 1100°C, and still more preferably 1150°C or higher. The upper limit of the heat treatment temperature is preferably 1300°C or lower, more preferably 1250°C or lower. If the heat treatment temperature is too low, the development of the carbon structure is insufficient and it is difficult for the conductivity to reach the desired value. Also, if the heat treatment temperature is too high, pore shrinkage occurs, and it may be difficult to ensure a sufficiently high initial capacitance when used in an electrochemical device. The heat treatment time after reaching the desired temperature is preferably 10 minutes to 120 minutes from the viewpoint of sufficiently developing the carbon structure and not causing excessive pore shrinkage. The heating rate is preferably 2°C / min to 20°C / min from the viewpoint of not making the time of the heat treatment step too long and suppressing the deterioration of the equipment.

[0055] The heat treatment is preferably performed under an inert gas condition or in an atmosphere of gas generated from the activated carbon with oxygen or air blocked. Examples of the inert gas used for the heat treatment include nitrogen gas, argon gas, helium gas, etc. These gases may be used alone or as a mixed gas of two or more types.

[0056] As the furnace used for heat treatment, various types of furnaces such as rotary kilns, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and traveling grate furnaces can be used, and both continuous furnaces that continuously perform raw material input and product extraction and batch furnaces that perform them intermittently can be applied. As the heating means, there is no problem as long as it can heat to a predetermined temperature, and electric heating, gas combustion type heating, high-frequency induction heating, electric conduction heating, etc. can be applied. Further, these heating means may be used alone or in combination.

[0057] <Grinding process> The method for producing the carbonaceous material of the present invention includes a grinding process after the heat treatment process. The grinding process is a process for controlling the shape and particle size of the finally obtained carbonaceous material to a desired shape and particle size. By the grinding process, the amount of surface functional groups can be controlled within an appropriate range, so that the moldability of the carbonaceous material can be improved. The particle size of the carbonaceous material of the present invention is not particularly limited, but when used for electric double layer capacitor applications, it is preferable to grind the carbonaceous material so that the average particle size is preferably 1 to 15 μm, more preferably 2 to 10 μm.

[0058] The grinder used for grinding is not particularly limited, and for example, known grinders such as cone crushers, double roll crushers, disk crushers, rotary crushers, ball mills, centrifugal roll mills, ring roll mills, centrifugal ball mills, and jet mills can be used alone or in combination.

[0059] <Classification process> In the present invention, the method for producing the carbonaceous material may include a classification step. For example, by removing particles that are extremely smaller or larger than the desired particle size, it becomes possible to obtain carbonaceous material particles having a narrow particle size distribution width. Thereby, it becomes possible to reduce the amount of binder during electrode formation. The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. Examples of the wet classifier include classifiers utilizing principles such as gravitational classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of the dry classifier include classifiers utilizing principles such as sedimentation classification, mechanical classification, and centrifugal classification. From the viewpoint of economy, it is preferable to use a dry classification device.

[0060] It is also possible to perform pulverization and classification using one device. For example, pulverization and classification can be performed using a jet mill equipped with a dry classification function. Furthermore, it is also possible to use independent devices for the pulverizer and the classifier. In this case, pulverization and classification can be performed continuously, but they can also be performed discontinuously.

[0061] The carbonaceous material of the present invention can be suitably used as an electrode active material for an electric double layer capacitor or the like. By using the carbonaceous material of the present invention, it is possible to obtain an electric double layer capacitor with a small amount of gas generation during charge and discharge and excellent capacitance. Therefore, in one embodiment of the present invention, it is possible to provide an electrode active material for an electric double layer capacitor containing the carbonaceous material of the present invention, an electrode for an electric double layer capacitor containing the active material, and an electric double layer capacitor including the electrode.

[0062] The electrode active material for the electric double layer capacitor of the present invention can be manufactured by using the carbonaceous material of the present invention. For example, it can include the manufacturing processes common in the art in the field, such as the process of kneading components such as the carbonaceous material of the present invention as a raw material, a conductivity-imparting agent, a binder, and a solvent, and the process of coating and drying the kneaded product as the manufacturing process of the electrode material. Further, the electrode for the electric double layer capacitor can be manufactured by using the electrode active material, and the manufacturing process can include, for example, the process of adding a solvent to the electrode active material as a raw material to prepare a paste, the process of drying and removing the solvent after coating the paste on a current collector such as an aluminum foil, and the process of putting the paste into a mold and press-molding it.

[0063] As the conductivity-imparting agent used for this electrode, for example, acetylene black, ketjen black, etc. can be used. As the binder, for example, fluorine-based polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum pitch, phenol resin, etc. can be used. Further, as the solvent, for example, 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, cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone, etc. can be used.

[0064] The electric double layer capacitor of the present invention is characterized by including the above electrodes. An electric double layer capacitor generally has a structure in which an electrode, an electrolytic solution, and a separator are main components, and a separator is disposed between a pair of electrodes. 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, or methyl ethyl carbonate; an electrolytic solution in which a quaternary ammonium salt of perchloric acid is dissolved; an electrolytic solution in which a boron tetrafluoride salt or a phosphorus hexafluoride salt of an alkali metal such as quaternary ammonium or lithium is dissolved; and an electrolytic solution in which a quaternary phosphonium salt is dissolved. Examples of the separator include cellulose, glass fiber, or a non-woven fabric, a cloth, or a microporous film mainly composed of a polyolefin such as polyethylene or polypropylene. The electric double layer capacitor can be manufactured, for example, by arranging these main components by a method generally used in the related art in the past.

[0065] The carbonaceous material of the present invention is excellent in moldability, and an electric double layer capacitor including an electrode made from the carbonaceous material has a high gas generation suppression effect during charge and discharge and has excellent capacitance.

Examples

[0066] Hereinafter, the present invention will be specifically described by way of examples, but these do not limit the scope of the present invention.

[0067] The measurement of physical property values in the examples was performed according to the methods described below.

[0068] <Content of silicon element, sodium element, and potassium element> The contents of silicon element, sodium element, and potassium element were measured by the following method. First, a calibration curve for the contents of silicon element, sodium element, and potassium element was created from standard solutions of known concentrations. Next, the pulverized measurement sample was dried at 115 °C for 3 hours, then 0.1 g was placed in a decomposition container, 10 ml of nitric acid was added and mixed, and then the sample was dissolved using a microwave sample pretreatment device ("MARS6" manufactured by CEM). The resulting dissolved solution was taken out, made up to 25 ml to prepare a measurement solution, and then analyzed using an ICP emission spectroscopic analyzer ("ICPE-9820" manufactured by Shimadzu Corporation). The concentrations were determined from the obtained values and the previously created calibration curve, and the contents of each element were determined using the following formula.

[0069] [Number]

[0070] [Powder conductivity] Using the powder resistivity measurement unit "MCP-PD51" manufactured by Mitsubishi Chemical Analytech Co., Ltd., the conductivity of the carbonaceous material was measured. For the measurement of conductivity, a sample in an amount such that the thickness of the activated carbon pellet was 3.5 to 4.5 mm when a load of 12 kN was applied was used, and the conductivity of the activated carbon pellet in a state where a load of 12 kN was applied was measured.

[0071] [Amount of surface functional groups] The amount of surface functional groups was measured by the hydrochloric acid titration method known from H.P. Boehm, Advan. Catal., 1966, 16, 179, etc. Specifically, using sodium ethoxide manufactured by High Purity Chemical Research Institute Co., Ltd., a 0.1 N ethanol solution was prepared as a measurement solution. To 25 ml of this measurement solution, 0.5 g of the carbonaceous material as a sample was added and stirred at 25 °C for 24 hours. After stirring, the measurement solution and the carbonaceous material were separated by centrifugation, 10 ml of the measurement solution was collected, and neutralization titration was performed using "888 Titrando" manufactured by Metrohm, Switzerland, with 0.1 N hydrochloric acid until the pH reached 4.0 as the titration endpoint to determine the sample titration amount. On the other hand, a blank test was performed with a solution not containing the sample to determine the blank test titration amount, and the amount of surface functional groups was calculated using the following formula. Amount of surface functional groups (meq / g) = {Titration volume of blank test (mL) - Titration volume of sample (mL)} × 0.1 × f (hydrochloric acid factor) / Weight of carbonaceous material used (g) × 25 (mL) / 10 (mL)

[0072] <Nitrogen adsorption isotherm> Using BELSORP-mini manufactured by Microtrac BEL Co., Ltd., the carbonaceous material used as a sample was heated at 300 °C for 3 hours under a nitrogen stream (nitrogen flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the carbonaceous material at 77 K was measured.

[0073] <Pore volume of pores with a diameter of 4 nm or more> For the obtained nitrogen adsorption isotherm, the pore volume of pores having a pore diameter of 4 nm or more calculated in the range of relative pressure P / P0 = 0.99 or less using the BJH method was determined. In the analysis by the BJH method, the reference t curve "NGCB-BEL.t" provided by Microtrac BEL Co., Ltd. was used for the analysis.

[0074] <Pore volume of micropores> For the obtained nitrogen adsorption isotherm, the pore volume of micropores was determined using the MP method. In the analysis by the MP method, the reference t curve "NGCB-BEL.t" provided by Microtrac BEL Co., Ltd. was used for the analysis.

[0075] <BET specific surface area> From the obtained nitrogen adsorption isotherm, analysis by the multi-point method was performed using the BET equation, and the specific surface area was calculated from the straight line in the region of relative pressure P / P0 = 0.01 to 0.1 of the obtained curve.

[0076] <Particle size distribution> The particle size of the carbonaceous material was measured by the laser diffraction measurement method. That is, the carbonaceous material to be measured was put into ion-exchanged water together with a surfactant, ultrasonic vibration was applied using BRANSONIC M2800-J manufactured by EMERSON to prepare a uniform dispersion liquid, and measurement was performed by the transmission method using Microtrac MT3200 manufactured by Microtrac Bell Co., Ltd. The concentration of the carbonaceous material in the uniform dispersion liquid was adjusted so as to fall within the measurement concentration range displayed by the same apparatus. In addition, as the surfactant used for the purpose of uniform dispersion, "Polyoxyethylene (10) octylphenyl ether (Triton X-100)" manufactured by Fujifilm Wako Pure Chemical Corporation was used. The surfactant was added in an appropriate amount that could achieve uniform dispersion and would not generate bubbles or the like that would affect the measurement. The analysis conditions are shown below. (Analysis conditions) Number of measurements; 1 time Measurement time; 30 seconds Distribution display; Volume Particle size classification; Standard Calculation mode; MT3000 Solvent name; WATER Measurement upper limit; 1408 μm, Measurement lower limit; 0.243 μm Residual ratio; 0.00 Passing ratio; 0.00 Residual ratio setting; Invalid Particle permeability; Transmission Particle refractive index; 1.81 Particle shape; Non-spherical Solvent refractive index; 1.333 DV value; 0.0150 - 0.0500 Transmittance (TR); 0.750 - 0.920 Flow rate; 50%

[0077] Hereinafter, in this example, the average particle size of the carbonaceous material indicates the value of the particle size at a volume ratio of 50% in the volume-integrated particle size distribution display.

[0078] <Example 1> Char made from coconut husks produced in the Philippines (specific surface area: 370 m 2For (g), primary activation was carried out at 850 °C using propane combustion gas + steam (steam partial pressure: 25%), and primary activated carbon with a specific surface area of 1185 m 2 / g was obtained. Then, it was washed with hydrochloric acid (concentration: 0.5 N, diluent: ion-exchanged water) at 85 °C for 30 minutes, and then thoroughly washed with ion-exchanged water and dried to remove the remaining acid, obtaining primary washed activated carbon with a potassium element content of 150 ppm. This primary washed activated carbon was secondarily activated at 950 °C using propane combustion gas (steam partial pressure 15%), and secondary activated carbon with a specific surface area of 1670 m 2 / g was obtained. For the obtained secondary activated carbon, it was alkali-washed at 100 °C for 30 minutes using an aqueous sodium hydroxide solution (concentration: 1 N, diluent: ion-exchanged water), and then thoroughly washed with ion-exchanged water to remove the remaining base. Next, it was acid-washed at 100 °C for 30 minutes using hydrochloric acid (concentration: 1 N, diluent: ion-exchanged water), and then thoroughly washed with ion-exchanged water and dried. Then, heat treatment was carried out at 700 °C for 60 minutes under a nitrogen + steam (steam partial pressure 3%) gas flow to remove the remaining acid, obtaining alkali and acid-washed activated carbon. Further, the obtained alkali and acid-washed activated carbon was heated from room temperature to 1000 °C under a nitrogen gas flow (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1000 °C; 2.5 °C / min), heat-treated at 1000 °C for 60 minutes, and then cooled to room temperature and pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0079] <Example 2> The alkali and acid-washed activated carbon obtained in the same manner as in Example 1 was heated from room temperature to 1100 °C under a nitrogen gas flow (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min), heat-treated at 1100 °C for 60 minutes, and then pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0080] <Example 3> The alkali- and acid-washed activated carbon obtained in the same manner as in Example 1 was heated from room temperature to 1200 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min, 1100 to 1200 °C; 2 °C / min), heat-treated at 1200 °C for 60 minutes, and then pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0081] <Example 4> The alkali- and acid-washed activated carbon obtained in the same manner as in Example 1 was heated from room temperature to 1300 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min, 1100 to 1300 °C; 2 °C / min), heat-treated at 1300 °C for 60 minutes, and then pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0082] <Example 5> For the secondary-activated activated carbon obtained in the same manner as in Example 1, alkali- and acid-washed activated carbon was obtained by the same operation as in Example 1 except that the concentration of the sodium hydroxide aqueous solution was 0.05 N. Further, the obtained alkali- and acid-washed activated carbon was heated from room temperature to 1100 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min), heat-treated at 1100 °C for 60 minutes, and then pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0083] <Example 6> For the secondary activated carbon obtained in the same manner as in Example 1, alkaline and acid-washed activated carbon was obtained by the same operation as in Example 1 except that the washing time with an aqueous sodium hydroxide solution was 10 minutes. Further, the obtained alkaline and acid-washed activated carbon was heated from room temperature to 1100 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min), heat-treated at 1100 °C for 60 minutes, and then pulverized to an average particle diameter of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0084] <Example 7> For the secondary activated carbon obtained in the same manner as in Example 1, alkaline and acid-washed activated carbon was obtained by the same operation as in Example 1 except that the washing temperature with an aqueous sodium hydroxide solution was 70 °C. Further, the obtained alkaline and acid-washed activated carbon was heated from room temperature to 1100 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min), heat-treated at 1100 °C for 60 minutes, and then pulverized to an average particle diameter of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0085] <Example 8> For the same char as in Example 1, primary activation was carried out at 850 °C using propane combustion gas + steam (steam partial pressure: 25%) until the specific surface area reached 1696 m 2 / g to obtain primary activated carbon. Then, it was acid-washed at 85 °C for 30 minutes using hydrochloric acid (concentration: 0.5 N, diluent: ion-exchanged water), and then thoroughly washed with ion-exchanged water and dried to remove the remaining acid, obtaining primary activated and washed activated carbon with a potassium element content of 18 ppm. This primary activated and washed activated carbon was then secondary-activated at 950 °C using propane combustion gas (steam partial pressure 15%) to a specific surface area of 2210 m 2Activated carbon with a secondary activation of / g was obtained. For the obtained activated carbon with secondary activation, an aqueous sodium hydroxide solution (concentration: 1N, diluent: ion-exchanged water) was used for alkali washing at 100 °C for 30 minutes, and then, in order to remove the remaining base, it was thoroughly washed with ion-exchanged water. Subsequently, hydrochloric acid (concentration: 1N, diluent: ion-exchanged water) was used for acid washing at a temperature of 100 °C for 30 minutes, and then it was thoroughly washed with ion-exchanged water and dried. After that, heat treatment was carried out at 700 °C for 60 minutes in a nitrogen + steam (steam partial pressure 3%) atmosphere to remove the remaining acid, and activated alkali and acid-washed activated carbon were obtained. Furthermore, the obtained activated alkali and acid-washed activated carbon were heated from room temperature to 1200 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min, 1100 to 1200 °C; 2 °C / min), heat-treated at 1200 °C for 60 minutes, and then pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0086] <Example 9> For the same char as in Example 1, activation was carried out at 900 °C using propane combustion gas + steam (steam partial pressure: 15%), and activated carbon with a specific surface area of 1905 m 2 / g of primary activated carbon was obtained. For the obtained primary activated carbon, an aqueous sodium hydroxide solution (concentration: 1N, diluent: ion-exchanged water) was used for washing at 100 °C for 30 minutes, and then, in order to remove the remaining base, it was thoroughly washed with ion-exchanged water. Subsequently, hydrochloric acid (concentration: 1N, diluent: ion-exchanged water) was used for washing at a temperature of 100 °C for 30 minutes, and then it was thoroughly washed with ion-exchanged water and dried. After that, heat treatment was carried out at 700 °C for 60 minutes in a nitrogen gas + steam (steam partial pressure 3%) atmosphere to remove the remaining acid, and alkali and acid-washed activated carbon were obtained. Furthermore, the obtained alkali and acid-washed activated carbon were heated from room temperature to 1200 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min, 1100 to 1200 °C; 2 °C / min), heat-treated at 1200 °C for 60 minutes, and then pulverized to an average particle size of 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0087] <Comparative Example 1> The secondary activated carbon obtained in the same manner as in Example 1 was pickled with hydrochloric acid (concentration: 1 N, diluent: ion-exchanged water) at a temperature of 100°C for 30 minutes, then thoroughly washed with ion-exchanged water and dried. After that, heat treatment was carried out at 700°C for 60 minutes in an atmosphere of nitrogen gas + steam (steam partial pressure 3%) to remove the remaining acid, and pickled and washed activated carbon was obtained. Then, it was finely pulverized so that the average particle size became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0088] <Comparative Example 2> The pickled and washed activated carbon obtained in the same manner as in Comparative Example 1 was heated from room temperature to 1000°C under a nitrogen stream (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900°C to 1000°C; 2.5°C / min), heat-treated at 1000°C for 60 minutes, and then finely pulverized so that the average particle size became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0089] <Comparative Example 3> The pickled and washed activated carbon obtained in the same manner as in Comparative Example 1 was heated from room temperature to 1100°C under a nitrogen stream (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900°C to 1100°C; 2.5°C / min), heat-treated at 1100°C for 60 minutes, and then finely pulverized so that the average particle size became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0090] <Comparative Example 4> The pickled and washed activated carbon obtained in the same manner as in Comparative Example 1 was heated from room temperature to 1200°C under a nitrogen stream (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900°C to 1100°C; 2.5°C / min, 1100 to 1200°C; 2°C / min), heat-treated at 1200°C for 60 minutes, and then finely pulverized so that the average particle size became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0091] <Comparative Example 5> The alkali and acid-washed activated carbon obtained in the same manner as in Example 1 was pulverized into fine powder so that the average particle diameter became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0092] <Comparative Example 6> The alkali and acid-washed activated carbon obtained in the same manner as in Example 1 was heated from room temperature to 1400 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1100 °C; 2.5 °C / min, 1100 to 1400 °C; 2 °C / min), heat-treated at 1400 °C for 60 minutes, and then pulverized into fine powder so that the average particle diameter became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0093] <Comparative Example 7> For Example 7, a carbonaceous material for a capacitor electrode was obtained by the same operation except that the washing temperature with an aqueous sodium hydroxide solution was 25 °C. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0094] <Comparative Example 8> For Example 7, a carbonaceous material for a capacitor electrode was obtained by the same operation except that the washing temperature with an aqueous sodium hydroxide solution was 60 °C. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0095] <Comparative Example 9> The alkali and acid-washed activated carbon obtained in the same manner as in Example 1 was pulverized into fine powder so that the average particle diameter became 6 μm, and then heated from room temperature to 1000 °C under a nitrogen stream (heating rate: room temperature to 600 °C; 10 °C / min, 600 to 900 °C; 5 °C / min, 900 °C to 1000 °C; 2.5 °C / min), and heat-treated at 1000 °C for 60 minutes to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0096] <Comparative Example 10> For the same char as in Example 1, activation was carried out at 900 °C using propane combustion gas + steam (steam partial pressure: 25%) to obtain primary activated carbon with a specific surface area of 1630 m 2 / g. The obtained primary activated carbon was pickled with hydrochloric acid (concentration: 1N, diluent: ion-exchanged water) at a temperature of 100 °C for 30 minutes, then thoroughly washed with ion-exchanged water and dried. After that, heat treatment was carried out at 700 °C for 60 minutes in an atmosphere of nitrogen gas + steam (steam partial pressure 3%) to remove the remaining acid, and pickled and washed activated carbon was obtained. Then, it was finely pulverized so that the average particle diameter became 6 μm to obtain a carbonaceous material for a capacitor electrode. The treatment conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0097]

Table 1

[0098] <Fabrication of Test Electrodes> The carbonaceous material (electrode active material for an electric double layer capacitor), conductive auxiliary material, and binder, which are electrode constituent members, were previously dried under reduced pressure (0.1 kPa or less) in an atmosphere of 120 °C for 16 hours or more and then used.

[0099] 0.81 g, 0.09 g, and 0.1 g of the carbonaceous material, conductive auxiliary material, and binder were weighed respectively and kneaded. As the above conductive auxiliary material, conductive carbon black "Denka Black Granular" manufactured by Denka Co., Ltd. was used, and as the above binder, polytetrafluoroethylene "6J" manufactured by Mitsui DuPont Fluorochemical Co., Ltd. was used. After kneading, in order to further homogenize, it was cut into flakes with a size of 1 mm square or less, and a pressure of 400 kg / cm 2 was applied with a coin molding machine to obtain a coin-shaped secondary molded product. The obtained secondary molded product was formed into a sheet with a thickness of 160 μm ± 5% (8 μm) by a roll press machine, then cut into a predetermined size (30 mm × 30 mm), and electrode composition 1 as shown in Fig. 1 was fabricated. Then, the obtained electrode composition 1 was dried at 120 °C in a reduced pressure atmosphere for 16 hours or more, and then the mass, sheet thickness, and dimensions were measured and used for the following measurements.

[0100] <Fabrication of Measurement Electrode Cell> As shown in Fig. 2, a conductive adhesive 2 "HITASOL GA-703" manufactured by Hitachi Chemical Co., Ltd. was applied to the etched aluminum foil 3 manufactured by Takizawa Co., Ltd. so that the coating thickness became 100 μm. Then, as shown in Fig. 3, the etched aluminum foil 3 coated with the conductive adhesive 2 was adhered to the sheet-shaped electrode composition 1 that had been cut in advance. Then, a tab 4 with an aluminum sealant 5 manufactured by Takizawa Co., Ltd. was welded to the etched aluminum foil 3 using an ultrasonic welder. After welding, it was dried in vacuum at 120 °C to obtain a polarizable electrode 6 including an aluminum current collector.

[0101] As shown in Fig. 4, an aluminum laminated resin sheet manufactured by Takizawa Co., Ltd. was cut into a rectangle (200 mm in length × 60 mm in width), folded in half, and one side ((1) in Fig. 4) was thermocompression bonded to prepare a bag-shaped outer package sheet 7 with the remaining two sides open. A laminate was prepared by stacking two of the above-mentioned polarizable electrodes 6 via a cellulose separator "TF-40" (not shown) manufactured by Nippon Kodo Paper Co., Ltd. This laminate was inserted into the outer package sheet 7, and one side ((2) in Fig. 5) where the tab 4 was in contact was thermocompression bonded to fix the polarizable electrode 6. Then, after vacuum drying at 120 °C under a reduced pressure atmosphere for 16 hours or more, an electrolyte was injected into a dry box with an argon atmosphere (dew point of -90 °C or lower). As the electrolyte, a 1.0 mol / L acetonitrile solution of tetraethylammonium tetrafluoroborate manufactured by Kishida Chemical Co., Ltd. was used. After impregnating the laminate with the electrolyte in the outer package sheet 7, the remaining one side ((3) in Fig. 5) of the outer package sheet 7 was thermocompression bonded to fabricate the electric double layer capacitor 8 shown in Fig. 5.

[0102] <Capacitance Measurement> The obtained electric double layer capacitor 8 was charged at a constant current of 50 mA per electrode surface area up to a charging voltage of 3.0 V at 25°C and -30°C using a "CAPACITOR TESTER PFX2411" manufactured by Kikusui Electronics Industry Co., Ltd. Further, it was charged under a constant voltage of 3.0 V for 30 minutes, and after the completion of the supplementary charging, it was discharged at 25 mA. The obtained discharge curve data was calculated by the energy conversion method and taken as the capacitance (F). Specifically, it was discharged until the voltage became zero after charging, and the capacitance (F) was calculated from the discharge energy discharged at this time. Then, the capacitance per electrode volume (F / cc) was obtained. The results are shown in Table 2.

[0103] <Measurement of gas generation amount> After the capacitance measurement described above, it was held for 600 hours while applying a voltage of 3.0 V in a constant temperature bath at 60°C. The dry weight and the weight in water of the measurement electrode cell were measured, the cell volume was obtained from the generated buoyancy and the density of water, and the gas volume amount calculated from the change in the cell volume before and after the durability test was corrected by the temperature difference at the time of measurement and obtained. That is, the gas generation amount was obtained according to the following formula. In the formula, cell weight A represents the weight of the cell in air (g), and cell weight W represents the weight of the cell in water (g). Gas generation amount (cc) = {(Cell weight A after durability test - Cell weight W after durability test) -(Cell weight A before durability test - Cell weight W before durability test)} / (273 + Measurement temperature after durability test (°C)) / (273 + Measurement temperature before durability test (°C)) The value obtained by dividing the above gas generation amount by the mass of the activated carbon constituting the electrode composition was taken as the gas generation amount per mass of activated carbon (cc / g). The results are shown in Table 2.

[0104] <Formability> In the production of the test electrode, the number of sheets of electrode composition 1 obtained by using 0.81 g, 0.09 g, and 0.1 g of the carbonaceous material, the conductive auxiliary material, and the binder, respectively, was taken as the formability. The results are shown in Table 2.

[0105]

Table 2

[0106] The carbonaceous materials obtained in Examples 1 to 9 have excellent moldability, and it can be seen that an electric double layer capacitor provided with an electrode made from the carbonaceous material has a small gas generation amount and a high initial capacitance. On the other hand, the carbonaceous material obtained in Comparative Example 9 is inferior in moldability, and an electric double layer capacitor provided with an electrode made from the carbonaceous material obtained in Comparative Example 6 has a low initial capacitance, and it can also be seen that an electric double layer capacitor provided with an electrode made from the carbonaceous materials obtained in other comparative examples has a large gas generation amount.

Explanation of symbols

[0107] 1 Electrode composition 2 Conductive adhesive 3 Etched aluminum foil 4 Tab 5 Sealant 6 Polarized electrode 7 Bag-shaped exterior sheet 8 Electric double layer capacitor (1) One side thermocompression bonded (2) One side where the tab contacts (3) The remaining side of the bag-shaped exterior sheet

Claims

【Claim 1】 The carbonaceous material has a silicon element content of less than 200 ppm, a powder conductivity of 10.0 to 22.0 S / cm, a total surface functional group amount of 0.22 to 0.36 meq / g, and a pore volume of 0.10 to 0.20 cm ３ / g with a pore diameter of 4 nm or more measured by the BJH method.

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