Carbonaceous material, method for manufacturing the same, electrode active material for electric double layer capacitor, electrode for electric double layer capacitor, and electric double layer capacitor

Abstract

The present invention relates to a carbonaceous material which has an elemental silicon content of less than 200 ppm, while having a powder conductivity of from 10.0 to 22.0 S / cm, a total amount of surface functional groups of from 0.22 to 0.36 meq / g, and a pore volume of pores having a pore diameter of 4 nm or more of from 0.10 to 0.20 cm3 / g as determined by a BJH method.

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), which is incorporated herein by reference in its entirety. The present invention relates to carbonaceous materials, methods for producing the same, electrode active materials for electric double-layer capacitors, electrodes for electric double-layer capacitors, and electric double-layer capacitors. [Background technology]

[0002] Electric double-layer capacitors, a type of electrochemical device, utilize capacitance (electric double-layer capacitance) obtained solely from the physical adsorption and desorption of ions without chemical reactions, resulting in superior output and lifespan characteristics compared to batteries. Due to these characteristics, they have been widely developed for various applications such as memory backup, renewable energy power generation, and power storage in UPS (Uninterruptible Power Supply) systems. In recent years, electric double-layer capacitors have attracted attention for their superior characteristics and their role in addressing environmental issues, particularly as auxiliary power sources for electric vehicles (EVs) and hybrid vehicles (HVs) and for storing regenerative energy. Such automotive electrochemical devices require not only higher energy density but also greater durability and improved capacitance under more demanding operating conditions (e.g., extreme temperature environments) compared to consumer applications.

[0003] In response to these demands, various methods have been investigated to improve the durability and capacitance of electrochemical devices. For example, Patent Document 1 discloses a modified activated carbon that suppresses gas generation during charging and discharging by limiting not only the surface functional groups in the activated carbon but also the amount of oxygen within the framework, and is also useful for reducing resistance.

[0004] Patent Document 2 discloses activated carbon for electric double-layer capacitors, which has high capacitance and reduced electrical resistance, achieved by alkaline and acid washing of the activated carbide material to reduce the silicon content to 200-3000 ppm. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2018 / 207769 Brochure [Patent Document 2] Patent No. 5770550 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, the method for controlling surface functional groups and the amount of oxygen within the skeleton described in Patent Document 1 did not provide a sufficiently satisfactory gas generation suppression effect. Patent Document 2 focuses on improving capacitance and specifies the silicon element content in activated carbon within a certain range, but while this range has a certain effect on improving capacitance, the gas generation suppression effect may not necessarily be sufficiently satisfactory.

[0007] Therefore, the present invention aims to provide a carbonaceous material and a method for producing the same that suppresses gas generation during charging and discharging of electric double-layer capacitors and has excellent moldability and capacitance. [Means for solving the problem]

[0008] The inventors of this invention have conducted diligent studies to solve the above problems and have arrived at the present invention.

[0009] In other words, the present invention encompasses 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 / g 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 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 formability and capacitance.

Brief Description of the Drawings

[0011] [Figure 1] It is a diagram showing a sheet-like electrode composition. [Figure 2]This diagram shows a current collector (etched aluminum foil) with conductive adhesive applied to it. [Figure 3] This figure shows a polarized electrode formed by bonding a sheet-like electrode composition to a current collector and ultrasonically welding an aluminum tab to it. [Figure 4] This is a diagram showing a bag-shaped outer sheet. [Figure 5] This is a diagram of an electric double-layer capacitor. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described in detail below. However, the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without impairing the spirit of the invention.

[0013] <Carbonaceous materials> 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 content of 0.22 to 0.36 meq / g, and a pore volume of 4 nm or larger, as measured by the BJH method, of 0.10 to 0.20 cm³. 3 It is / 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. If the silicon element content is 200 ppm or more, the amount of gas generated during charging and discharging tends to increase. Furthermore, there is no particular lower limit to the silicon element content of the carbonaceous material of the present invention, but it 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 solution in the alkaline cleaning step in the method for producing the carbonaceous material of the present invention described later. Furthermore, the silicon element content of the carbonaceous material of the present invention can be measured by ICP (inductively coupled plasma) emission spectroscopy, for example, as described in the examples described later.

[0015] The powder conductivity of the carbonaceous material of the present invention is 10.0 S / cm or higher, preferably 13.0 S / cm or higher, more preferably 14.0 S / cm or higher, even more preferably 14.5 S / cm or higher, and particularly preferably 15.0 S / cm or higher. Furthermore, the powder conductivity of the carbonaceous material of the present invention is 22.0 S / cm or lower, preferably 21.0 S / cm or lower, and more preferably 20.0 S / cm or lower. If the powder conductivity exceeds 22.0 S / cm, the carbon crystal structure of the carbonaceous material develops excessively, and the pores of the carbonaceous material shrink as a result, which can lead to a decrease in the initial capacitance per unit weight. On the other hand, if the powder conductivity is less than 10.0 S / cm, the carbon crystal structure of the carbonaceous material does not develop sufficiently, and due to the low crystallinity, the electrical conductivity of the carbon itself is insufficient, the resistance during charging and discharging increases, which can lead to a decrease in the capacity retention rate. 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 other parameters in the heat treatment step of the carbonaceous material manufacturing method of the present invention described later. Furthermore, 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 electrolytic solution in the capacitor electrode increases, and by promoting the decomposition reaction of the electrolytic solution, the amount of gas generated 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 formability 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 the value is less than / g, it leads to an increase in the internal resistance of the electrode, and the amount of gas generated tends to increase. Here, the BJH method is a calculation method that is generally used for the analysis of mesopores (pores with a diameter of 2 nm to 50 nm), similar to the CI method and the DH method, and was proposed by Barrett, Joyner, and Halends. In the present invention, the pore volume of pores with a diameter of 4 nm or more can be calculated 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 the carbonaceous material of the present invention with a pore diameter of 4 nm or more can be controlled within the above range by appropriately selecting the type of carbon precursor used, or by appropriately adjusting the temperature and processing time of the activation step in the carbonaceous material manufacturing method of the present invention, which will be described later.

[0018] The pore volume of micropores (pores with a diameter of less than 2 nm) measured by the MP method of the carbonaceous material of the present invention is 0.60 cm³. 3 It is preferable that it be 0.63 cm or more, 3 It is more preferable that it be 0.66 cm or more. 3 It is even more preferable that the amount is 1 / g or more. Furthermore, the pore volume of the above micropores is 1.20 cm³. 3 It is preferable that it be less than or equal to / g, and 1.10cm 3 It is more preferable that it be less than or equal to / g, and 1.00 cm 3 It is even more preferable that the value be less than or equal to / g. When the pore volume of the micropores is within the above range, the resistance, which is thought to be due to the diffusion resistance of non-aqueous electrolyte ions within the pores, tends to decrease, and the bulk density of the electrodes tends to improve, and the capacitance per unit area tends to increase. Here, the MP method is a calculation method that is generally used for micropore analysis, similar to the HK method and the SF method. In the present invention, the pore volume of the micropores can be calculated 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 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 and processing time of the activation step in the carbonaceous material manufacturing method of the present invention, which will be described later.

[0019] The BET specific surface area of ​​the carbonaceous material of the present invention is preferably 1400 m². 2 It is 1430m or more per gram, and more preferably 1430m 2 It is 1450m or more per gram, and more preferably 1450m 2 It is 1500m or more per gram, and more preferably 1500m 2 It is 1 / g or more. Furthermore, the BET specific surface area of ​​the carbonaceous material of the present invention is preferably 2200 m². 2 It is less than or equal to / g, and more preferably 2150m 2 It is less than or equal to / g, and more preferably 2100m 2 Less than or equal to / g, particularly preferably 2000m 2 It is less than / g. When the BET specific surface area is within the above range, the resistance, which is thought to be due to the diffusion resistance of non-aqueous electrolyte ions in the pores, tends to decrease, and the bulk density of the electrode tends to improve, 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 and processing time of the activation step in the method for producing the carbonaceous material of the present invention, which will be described later. The BET specific surface area of ​​the carbonaceous material of the present invention can be measured, for example, by the method for measuring nitrogen adsorption isotherms 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, but 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, and cesium. Since sodium and / or potassium are usually present in large quantities, it is important to control their content. When the alkali metal content is within the above range, the possibility of alkali metal elements dissolving into the electrolyte is reduced, and short circuits due to reprecipitation are less likely to occur. In addition, blockage of the pores of the carbonaceous material by alkali metals is less likely to occur, so the charge and discharge capacity tends to be higher. The alkali metal content of the carbonaceous material of the present invention can be adjusted by alkaline washing or acid washing in the method for producing the carbonaceous material of the present invention described later. The alkali metal content of the carbonaceous material of the present invention can be measured, for example, by ICP emission spectroscopy described in the examples described later.

[0021] <Method for manufacturing carbonaceous materials> The carbonaceous material of the present invention is, for example, A step of washing activated carbon obtained by carbonizing a carbon precursor in an alkaline solution at 65°C or higher, and The activated carbon, after alkaline washing, is then acid washed, heat-treated at 1000-1300°C under an inert gas atmosphere, and then pulverized. It can be manufactured by a method that includes [a specific component].

[0022] In the present invention, the carbon precursor that serves as the raw material for the carbonaceous material is not particularly limited as long as it forms a carbonaceous material upon activation, and can be broadly selected from plant-derived carbon precursors, mineral-derived carbon precursors, natural material-derived carbon precursors, and synthetic material-derived carbon precursors. From the viewpoint of reducing harmful impurities, protecting the environment, and commercial interests, it is preferable that the carbonaceous material of the present invention is based on a plant-derived carbon precursor; in other words, it is preferable that the carbon precursor that becomes the carbonaceous material of the present invention is plant-derived.

[0023] Examples of mineral-derived carbon precursors include petroleum-based and coal-based pitch and coke. Examples of natural material-derived carbon precursors 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 synthetic material-derived carbon precursors include polyamides such as nylon, polyvinyl alcohols such as vinylon, polyacrylonitriles such as acrylic, polyolefins such as polyethylene and polypropylene, polyurethane, phenolic resins, and vinyl chloride resins.

[0024] In the present invention, the plant-derived carbon precursor is not particularly limited, but examples include, but is not limited to, wood, charcoal, rice husks, coconut shells, fruit shells such as palm shells, coffee beans, tea leaves, sugarcane, fruits (e.g., oranges, bananas), straw, rice husks, broad-leaved trees, coniferous trees, and bamboo. These examples include waste materials after their original use (e.g., used tea leaves) or parts of plant raw materials (e.g., banana or orange peels). These plant raw materials may be used individually or in combination of two or more. Among these plant raw materials, coconut shells are preferred because they are readily available and can be used to produce carbonaceous materials with various properties.

[0025] The coconut shells used are not particularly limited, but examples include those of palm oil palm, coconut palm, salak palm, and giant palm. These coconut shells may be used individually or in combination of two or more types. Coconut palm and palm shells, which are biomass waste generated in large quantities after coconuts are used as food, detergent raw materials, biodiesel oil raw materials, etc., are particularly preferred from the viewpoint of availability.

[0026] It is possible to obtain char (coconut shell char) by calcining coconut shells, and it is preferable to use this as a raw material. Here, char generally refers to a carbon-rich powdery solid produced when coal is heated without melting or softening, but here it also refers to a carbon-rich powdery solid produced when organic matter is heated without melting or softening. The method for producing char from coconut shells is not particularly limited and can be produced using methods known in the field. For example, it can be produced by calcining (carbonizing) the coconut shells, which are the raw material, 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 mixture of these inert gases, or a mixture of these inert gases with other gases.

[0027] <Activation Process> The activated carbon derived from coconut shells used in the method for producing carbonaceous materials of the present invention can be obtained, for example, by activating the carbon precursor (coconut shell char). Activation is a process that forms pores on the surface of the carbon precursor, transforming it into a porous carbonaceous material, thereby obtaining activated carbon with a large specific surface area and pore volume. If the carbon precursor is used as is without activation, the specific surface area and pore volume of the resulting carbonaceous material will not be sufficient, making it difficult to secure a sufficiently high initial volume when used as an electrode material, and thus the carbonaceous material of the present invention cannot be obtained. Activation can be carried out by methods common in this field, and mainly two types of treatment methods can be mentioned: gas activation and chemical activation.

[0028] As a gas activation treatment, a method is known in which the carbon precursor is heated in the presence of, for example, water vapor, carbon dioxide, air, oxygen, combustion gas, or a mixture thereof. As a chemical activation treatment, a method is known in which an activator such as zinc chloride, calcium chloride, phosphoric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, magnesium hydroxide, or calcium hydroxide is mixed with the carbon precursor and heated in an inert gas atmosphere. In the present invention, chemical activation requires a step to remove residual chemicals, which complicates the manufacturing method, so gas activation treatment is preferred.

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

[0030] The total amount of activating gas supplied in steam activation is preferably 50 to 10,000 parts by mass, more preferably 100 to 5,000 parts by mass, and even more preferably 200 to 3,000 parts by mass, per 100 parts by mass of carbon precursor. When the total amount of activating gas supplied is within the above range, the activation reaction can be carried out more efficiently.

[0031] The specific surface area and pore volume of activated carbon derived from coconut shells, which is used as the raw material, can be controlled by changing the activation method and conditions of the carbon precursor. For example, when activated carbon is obtained by steam activation, these can be controlled by the gas used, heating temperature, and time. In steam activation, the specific surface area and pore diameter of the obtained activated carbon tend to decrease at lower heating temperatures and increase at higher heating temperatures. In the present invention, when activated carbon is obtained by steam activation, the heating temperature (activation temperature) depends on the type of gas used, but is usually 700 to 1100°C, and preferably 800 to 1000°C. Furthermore, the heating time and heating rate are not particularly limited and can be appropriately determined according to the heating temperature, the desired specific surface area of ​​the activated carbon, etc.

[0032] If necessary, the activation treatment may be performed once or more times. If the activation treatment is performed more than once, for example, the step of washing the activated carbon after the first activation (hereinafter also referred to as primary activation) with acid for the purpose of removing impurities such as alkali metals may be included. The acid washing step can be performed by immersing the activated carbon in a washing solution containing acid. After acid washing, the activated carbon is thoroughly washed with water, preferably deionized water, to remove any remaining acid, and then dried to obtain primary washed activated carbon. By activating this primary washed activated carbon again, secondary activated activated carbon can be obtained. Hereinafter, activated carbon that has undergone the first or second or subsequent activation treatments will be collectively referred to as activated activated carbon.

[0033] The conditions for acid washing after activation are not particularly limited, and the type and concentration of the acid used, the washing temperature and washing time, etc., may be adjusted as appropriate. In one preferred embodiment, for example, the acid may be: 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.

[0034] There are no restrictions on the conditions for subsequent activations; just like with the initial activation, the heating temperature and heating time should be determined appropriately according to the specific surface area of ​​the activated carbon to be activated.

[0035] <Alkaline cleaning process> The present invention provides a method for producing a carbonaceous material, which includes a step of washing the activated activated carbon with an alkaline solution at 65°C or higher. The alkaline washing step is a step for removing silicon elements contained in the activated activated carbon by washing it with an alkaline washing solution at 65°C or higher. The alkaline washing step can be carried out by immersing the activated activated carbon obtained after activation in a washing solution at 65°C or higher. Examples of the washing solution include aqueous sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution, etc., but aqueous sodium hydroxide solution is preferred due to its availability.

[0036] The liquid temperature during alkaline cleaning is preferably 65°C or higher, more 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. A liquid temperature within the above range is preferable because it allows for a sufficient reduction in the silicon element concentration in the activated carbon and can be carried out safely.

[0037] The concentration of alkali in the cleaning solution is not particularly limited and may be adjusted as appropriate depending on the type of cleaning solution used. The alkali concentration of the cleaning solution is preferably 0.01 N or higher, and more preferably 0.03 N or higher. The upper limit of the alkali concentration is preferably 10 N or lower, and more preferably 5 N or lower. If the alkali concentration is too low, it will be necessary to increase the number of washing cycles to remove the silicon element, and conversely, if it is too high, a large amount of residual alkali components will remain. Therefore, by setting the concentration within the above range, the alkali cleaning process can be carried out efficiently, which is preferable from the standpoint of productivity.

[0038] The pH of the cleaning solution used in alkaline cleaning is not particularly limited and may be adjusted as appropriate depending on the type of cleaning solution used, but a pH of 12 or higher is preferable as it can reduce the cleaning time or the number of cleaning cycles.

[0039] When immersing activated carbon in a cleaning solution, the mass ratio of the cleaning solution to the activated carbon may be adjusted as appropriate depending on the type, concentration, and temperature 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. 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 in which alkaline cleaning is performed is not particularly limited and may be appropriately selected depending on the cleaning method used. In this invention, cleaning is usually carried out in an atmospheric environment.

[0041] The method for alkaline washing activated carbon is not particularly limited as long as the activated carbon can be immersed in the washing solution. It may be a method in which the washing solution is continuously added, left for a predetermined time, and then removed while immersing, or a method in which the activated carbon is immersed in the washing solution, left for a predetermined time, drained, and then new washing solution is added and the immersion-draining process is repeated. It may also be a method in which all of the washing solution is replaced, or a method in which only part of the washing solution is replaced. Furthermore, the washing solution may be stirred during immersion.

[0042] The immersion time of the activated carbon in the washing solution can be adjusted as appropriate depending on the washing solution used, the processing temperature, etc., but it is preferably 5 minutes or more in order to sufficiently reduce the silicon in the activated carbon, preferably 50 minutes or less, more preferably 40 minutes or less, even more preferably 35 minutes or less, and still more preferably 30 minutes or less from the viewpoint of productivity.

[0043] After alkaline washing the activated carbon, it may be washed with water to remove any remaining washing solution.

[0044] <Acid washing process> The present invention relates to a method for producing a carbonaceous material, which includes a step of washing activated carbon after alkaline washing with an acidic solution. The acid washing step after alkaline washing is a step for removing impurities such as metals by washing the activated carbon after alkaline washing with an acidic washing solution. The acid washing step after alkaline washing can be carried out by immersing the activated carbon obtained after alkaline washing in an acidic washing solution. Examples of washing solutions include hydrochloric acid, nitric acid, and sulfuric acid, but hydrochloric acid is preferred because it does not oxidize the carbon.

[0045] The concentration of acid in the acid cleaning solution after alkaline cleaning is not particularly limited, and the concentration may be adjusted as appropriate depending on the type of cleaning solution used. The acid concentration of the cleaning solution is preferably 0.01 N or higher, and more preferably 0.1 N or higher. The upper limit of the acid concentration is preferably 5 N or lower, and more preferably 2 N or lower. If the acid concentration is too low, it will be necessary to increase the number of cleaning cycles, and conversely, if it is too high, a large amount of residual acid will remain. Therefore, by setting the concentration within the above range, the acid cleaning process can be carried out efficiently, which is preferable from the standpoint of productivity.

[0046] The pH of the acid cleaning solution after alkaline cleaning is not particularly limited and may be adjusted as appropriate depending on the type of cleaning solution used, but it is preferable that the pH be 2 or lower in order to reduce the number of cleaning cycles.

[0047] The temperature of the acid cleaning solution after alkaline cleaning is not particularly limited and may be adjusted as appropriate depending on the type of cleaning solution used, but it is preferable to use a temperature of 40°C to 100°C for high metal removal efficiency.

[0048] When immersing activated carbon in an acid washing solution, the mass ratio of the washing solution to the activated carbon may be adjusted as appropriate depending on the type, concentration, and temperature of the washing solution used. The mass of the activated carbon to be immersed relative to the mass of the washing 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 lower limit, a lot of energy may be required to raise the temperature of the washing solution, and if it is above the upper limit, it may be difficult to obtain a sufficient washing effect.

[0049] The atmosphere in which acid cleaning is performed after alkaline cleaning is not particularly limited and may be appropriately selected depending on the cleaning method used. In this invention, cleaning is usually carried out in an atmospheric environment.

[0050] The method for washing the activated carbon is not particularly limited as long as the activated carbon can be immersed in the washing solution. This may involve continuously adding the washing solution, letting it remain for a predetermined time, and then removing it while immersing the carbon, or it may involve immersing the activated carbon in the washing solution, letting it remain for a predetermined time, removing the solution, and then adding new washing solution and repeating the immersion-removal process. The washing solution may also be completely replaced, or only a portion of the washing solution may be replaced. The immersion time for the activated carbon in the washing solution can be adjusted as appropriate depending on the washing solution used, the processing temperature, etc., but it is preferable to immerse it for 5 minutes or more, and more preferably 10 minutes or more, in order to sufficiently remove metals.

[0051] After acid washing, the activated carbon may be washed with water. Furthermore, the method for producing carbonaceous materials of the present invention may include a deoxidation step to remove the acid derived from the acid washing solution remaining on the activated carbon. In the present invention, the deoxidation step refers to a step to remove the acid remaining on the activated carbon after acid washing, and a method of heating for a short time under an oxidizing gas atmosphere is preferred.

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

[0053] While there are no particular limitations on the heating time or temperature under an oxidizing gas atmosphere, it is preferable to treat at 500°C to 1000°C for 5 to 60 minutes to avoid significantly altering the prepared pore structure.

[0054] <Heat treatment process> The present invention relates to a method for producing a carbonaceous material, which includes a heat treatment step. By heat-treating the activated carbon after the alkaline and acid washing steps (hereinafter also referred to as alkaline and acid-washed activated carbon), the carbon structure can be developed and the conductivity can be controlled to a desired range. In addition, the amount of surface functional groups may be reduced from the desired range in this step, but this can be controlled to the desired range by performing the pulverization step described later 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 over 1100°C, and even more preferably 1150°C or higher. The upper limit of the heat treatment temperature is preferably 1300°C or lower, and more preferably 1250°C or lower. If the heat treatment temperature is too low, the development of the carbon structure is insufficient and the conductivity does not easily reach the desired value. Also, if the heat treatment temperature is too high, pore shrinkage occurs, and it may be difficult to secure a sufficiently high initial capacitance when used in electrochemical devices. The heat treatment time after reaching the desired temperature is preferably 10 to 120 minutes, in order to sufficiently develop the carbon structure without causing excessive pore shrinkage. The heating rate is preferably 2°C / min to 20°C / min, in order to prevent the heat treatment process from becoming too long and to suppress equipment deterioration.

[0055] The heat treatment is preferably carried out under inert gas conditions, or in a gas atmosphere generated from activated carbon with oxygen or air blocked. Examples of inert gases used in the heat treatment include nitrogen gas, argon gas, and helium gas. These gases may be used individually or as a mixed gas of two or more types.

[0056] Various types of furnaces can be used for heat treatment, including rotary kilns, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving bed furnaces. Both continuous furnaces, where raw materials are continuously fed in and products are removed, and batch furnaces, where this is done intermittently, are applicable. Any heating method capable of reaching the desired temperature is acceptable, including electric heating, gas combustion heating, high-frequency induction heating, and electrostatic heating. These heating methods may be used individually or in combination.

[0057] <Grinding process> The present invention relates to a method for producing a carbonaceous material, which includes a grinding step after a heat treatment step. The grinding step is a step for controlling the shape and particle size of the carbonaceous material to a desired shape and particle size. By controlling the amount of surface functional groups within an appropriate range through the grinding step, 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 in 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 crushing machines used for crushing are not particularly limited, and known crushing machines such as cone crushers, double roll crushers, disc crushers, rotary crushers, ball mills, centrifugal roll mills, ring roll mills, centrifugal ball mills, and jet mills can be used individually or in combination.

[0059] <Classification process> In the present invention, the method for producing carbonaceous material may include a classification step. For example, by removing particles that are extremely small or large compared to the desired particle size, it is possible to obtain carbonaceous material particles with a narrow particle size distribution width. This makes it possible to reduce the amount of binder used when constructing electrodes. The classification method is not particularly limited, but examples include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include those that utilize the principles of gravity classification, inertial classification, hydraulic classification, and centrifugal classification. Examples of dry classifiers include those that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification. From an economic standpoint, it is preferable to use a dry classification device.

[0060] Grinding and classification can also be performed using a single device. For example, grinding and classification can be carried out using a jet mill equipped with a dry classification function. Furthermore, it is also possible to use a device in which the grinder and classifier are independent. In this case, grinding and classification can be performed continuously or discontinuously.

[0061] The carbonaceous material of the present invention can be suitably used as an electrode active material for electric double-layer capacitors, etc. By using the carbonaceous material of the present invention, an electric double-layer capacitor can be made with low gas generation during charging and discharging and excellent capacitance. Therefore, in one embodiment of the present invention, an electrode active material for electric double-layer capacitors containing the carbonaceous material of the present invention can be provided, an electrode for electric double-layer capacitors containing the active material can be provided, and an electric double-layer capacitor equipped with the electrode can be provided.

[0062] The electrode active material for electric double-layer capacitors of the present invention can be manufactured using the carbonaceous material of the present invention. For example, the manufacturing process for electrode materials may include conventional manufacturing processes common in this field, such as a step of kneading the carbonaceous material of the present invention, which is the raw material, with components such as a conductivity imparting agent, a binder, and a solvent, and a step of coating and drying the kneaded product. Furthermore, the electrode for electric double-layer capacitors can be manufactured using the electrode active material, and the manufacturing process may include, for example, a step of preparing a paste by adding a solvent to the electrode active material, which is the raw material, a step of applying the paste to a current collector plate such as aluminum foil and then drying and removing the solvent, and a step of placing the paste in a mold and press molding it.

[0063] Examples of conductive agents that can be used in this electrode include acetylene black and Ketjenblack. As binders, examples of fluorinated polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, as well as carboxymethylcellulose, styrene-butadiene rubber, petroleum pitch, and phenolic resins can be used. As solvents, examples of alcohols such as water, 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 can be used.

[0064] The electric double-layer capacitor of the present invention is characterized by comprising the electrodes. An electric double-layer capacitor generally has a structure in which electrodes, an electrolyte, and a separator are the main components, with the separator placed between a pair of electrodes. Examples of electrolytes include an electrolyte obtained by dissolving an amidine salt in an organic solvent such as propylene carbonate, ethylene carbonate, or methyl ethyl carbonate; an electrolyte obtained by dissolving a quaternary ammonium salt of perchloric acid; an electrolyte obtained by dissolving a boron tetrafluoride or phosphate hexafluoride salt of an alkali metal such as quaternary ammonium or lithium; and an electrolyte obtained by dissolving a quaternary phosphonium salt. Examples of separators include cellulose, glass fiber, or nonwoven fabrics, cloths, and microporous films mainly composed of polyolefins such as polyethylene and polypropylene. An electric double-layer capacitor can be manufactured, for example, by arranging these main components in a manner that is common in the field.

[0065] The carbonaceous material of the present invention exhibits excellent moldability, and an electric double-layer capacitor equipped with electrodes manufactured from this carbonaceous material has a high gas generation suppression effect during charging and discharging and possesses excellent capacitance. [Examples]

[0066] The present invention will be specifically described below with reference to examples, but these examples are not intended to limit the scope of the present invention.

[0067] The physical properties in the examples were measured according to the method described below.

[0068] <Content of silicon, sodium, and potassium elements> The content of silicon, sodium, and potassium elements was measured by the following method. First, calibration curves for silicon, sodium, and potassium content were created from standard solutions of known concentrations. Next, the pulverized 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 the sample was dissolved using a microwave sample preparation device (CEM "MARS6"). The dissolved solution was taken out, made up to 25 ml to prepare the measurement solution, and then analyzed using an ICP emission spectrometer (Shimadzu Corporation "ICPE-9820"). The concentrations were determined from the obtained values ​​and the calibration curve created earlier, and the content of each element was calculated using the following formula.

[0069]

number

[0070] <Powder conductivity> The conductivity of carbonaceous materials was measured using the MCP-PD51 powder resistivity measurement unit manufactured by Mitsubishi Chemical Analytech Co., Ltd. For the conductivity measurement, a sample quantity was used such that the thickness of the activated carbon pellets was 3.5-4.5 mm when a load of 12 kN was applied. The conductivity of the activated carbon pellets was measured under the 12 kN load.

[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, a 0.1N ethanol solution was prepared as the measurement solution using sodium ethoxide manufactured by Kojun Chemical Laboratory Co., Ltd. 0.5g of the carbonaceous material to be used as the sample was added to 25ml of this measurement solution and stirred at 25°C for 24 hours. After stirring, the measurement solution and carbonaceous material were separated by centrifugation, and 10ml of the measurement solution was taken and neutralized by titration with 0.1N hydrochloric acid using Metrohm 888Titrando (Switzerland), with the titration endpoint being the point at which the pH becomes 4.0, to determine the sample titration volume. Meanwhile, a blank test was performed with a solution without the sample, and the blank titration volume was also determined, 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 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 according to the BET equation, and the specific surface area was calculated from the straight line in the region of relative pressure P / P0 = 0.01 - 0.1 of the obtained curve.

[0076] <Particle size distribution> The particle size of the carbonaceous material was measured by laser diffraction. Specifically, the carbonaceous material to be measured was placed in ion-exchanged water with a surfactant, and ultrasonic vibration was applied using an EMERSON BRANSONIC M2800-J to prepare a homogeneous dispersion. The particle size was then measured by transmission using a Microtrac MT3200 manufactured by Microtrac-Bell. The concentration of the carbonaceous material in the homogeneous dispersion was adjusted to fall within the measurement range displayed by the instrument. The surfactant used for homogeneous dispersion was "Polyoxyethylene (10) Octylphenyl Ether (Triton X-100)" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. An appropriate amount of surfactant was added to enable homogeneous dispersion without generating bubbles or other factors that would affect the measurement. The analytical conditions are shown below. (Analysis conditions) Number of measurements: 1 Measurement time: 30 seconds Distribution display; volume Particle size classification; standard Calculation mode; MT3000 Solvent name; WATER Upper measurement limit: 1408μm, lower measurement limit: 0.243μm Remaining ratio: 0.00 Passage ratio: 0.00 Residual ratio setting; disabled particle permeability; permeation 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] In this embodiment, the average particle size of the carbonaceous material is shown as the particle size at a volume fraction of 50% in the volume integrated particle size distribution display.

[0078] <Example 1> Char (specific surface area: 370 m²) is made from coconut husks from the Philippines. 2For each g of material, primary activation was performed at 850°C using propane combustion gas + water vapor (water vapor partial pressure: 25%), resulting in a specific surface area of ​​1185 m². 2 Primary activated activated carbon with a potassium content of 150 ppm was obtained. Subsequently, it was washed with hydrochloric acid (concentration: 0.5 N, diluent: deionized water) at a temperature of 85°C for 30 minutes. After that, to remove the residual acid, it was thoroughly washed with deionized water and dried to obtain primary washed activated carbon with a potassium content of 150 ppm. This primary washed activated carbon was secondary activated at 950°C using propane combustion gas (water vapor partial pressure 15%) to obtain a specific surface area of ​​1670 m². 2 Secondary activated carbon was obtained at a concentration of / g. The obtained secondary activated carbon was alkaline washed with an aqueous sodium hydroxide solution (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, and then thoroughly washed with deionized water to remove any remaining base. Next, it was acid washed with hydrochloric acid (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, then thoroughly washed with deionized water, dried, and then heat treated at 700°C for 60 minutes under a nitrogen + water vapor (water vapor partial pressure 3%) airflow to remove any remaining acid, thereby obtaining alkaline and acid washed activated carbon. Furthermore, the obtained alkali and acid-washed activated carbon was heated under a nitrogen stream from room temperature to 1000°C (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, then cooled to room temperature and finely pulverized to an average particle size of 6 μm to obtain carbonaceous material for capacitor electrodes. The processing 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 under a nitrogen stream from room temperature to 1100°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min), and then heat-treated at 1100°C for 60 minutes. After that, it was finely ground to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing 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 under a nitrogen stream from room temperature to 1200°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min, 1100 to 1200°C; 2°C / min), and then heat-treated at 1200°C for 60 minutes. After that, it was finely ground to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing 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 under a nitrogen stream from room temperature to 1300°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min, 1100 to 1300°C; 2°C / min), and then heat-treated at 1300°C for 60 minutes. After that, it was finely ground to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0082] <Example 5> Alkaline and acid-washed activated carbon was obtained from the secondary activated activated carbon obtained in the same manner as in Example 1, except that the concentration of the sodium hydroxide aqueous solution was 0.05 N. Furthermore, the obtained alkaline and acid-washed activated carbon was heated under a nitrogen stream from room temperature to 1100°C (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), and after heat treatment at 1100°C for 60 minutes, it was finely pulverized to an average particle size of 6 μm to obtain carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0083] <Example 6> Alkaline and acid-washed activated carbon was obtained by the same procedure as in Example 1, except that the washing time with an aqueous sodium hydroxide solution was 10 minutes, using the same method as in Example 1. Furthermore, the obtained alkaline and acid-washed activated carbon was heated under a nitrogen stream from room temperature to 1100°C (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), and after heat treatment at 1100°C for 60 minutes, it was finely pulverized to an average particle size of 6 μm to obtain a carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0084] <Example 7> Secondary activated activated carbon obtained in the same manner as in Example 1 was subjected to alkaline and acid-washed activated carbon using the same procedure as in Example 1, except that the washing temperature with an aqueous sodium hydroxide solution was set to 70°C. Furthermore, the obtained alkaline and acid-washed activated carbon was heated under a nitrogen stream from room temperature to 1100°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min), and after heat treatment at 1100°C for 60 minutes, it was finely pulverized to an average particle size of 6 μm to obtain carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0085] <Example 8> Using the same char as in Example 1, propane combustion gas + water vapor (water vapor partial pressure: 25%) was used, and the specific surface area was 1696 m² at 850°C. 2 Primary activation was performed until the potassium content reached 1 / g, and primary activated activated carbon was obtained. Then, it was pickled with hydrochloric acid (concentration: 0.5N, diluent: deionized water) at a temperature of 85°C for 30 minutes. After that, to remove the remaining acid, it was thoroughly washed with deionized water and dried to obtain primary activated washing activated carbon with a potassium element content of 18 ppm. This primary activated washing activated carbon was then secondary activated at 950°C using propane combustion gas (water vapor partial pressure 15%), resulting in a specific surface area of ​​2210 m². 2Secondary activated activated carbon was obtained at a concentration of / g. The obtained secondary activated activated carbon was alkaline washed with an aqueous sodium hydroxide solution (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, and then thoroughly washed with deionized water to remove any remaining base. Next, it was acid washed with hydrochloric acid (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, then thoroughly washed with deionized water, dried, and then heat treated at 700°C for 60 minutes under a nitrogen + water vapor (water vapor partial pressure 3%) atmosphere to remove any remaining acid, thereby obtaining activated alkali and acid-washed activated carbon. Furthermore, the activated alkali and acid-washed activated carbon obtained was heated under a nitrogen stream from room temperature to 1200°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min, 1100 to 1200°C; 2°C / min), and after heat treatment at 1200°C for 60 minutes, it was finely pulverized to an average particle size of 6 μm to obtain carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0086] <Example 9> A char similar to that in Example 1 was activated at 900°C using propane combustion gas + water vapor (water vapor partial pressure: 15%), resulting in a specific surface area of ​​1905 m². 2 Primary activated carbon was obtained at a concentration of / g. The obtained primary activated carbon was washed with an aqueous sodium hydroxide solution (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, and then thoroughly washed with deionized water to remove any remaining base. Next, it was washed with hydrochloric acid (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, then thoroughly washed with deionized water, dried, and then heat-treated at 700°C for 60 minutes under a nitrogen gas + water vapor (water vapor partial pressure 3%) atmosphere to remove any remaining acid, thereby obtaining alkaline and acid-washed activated carbon. Furthermore, the obtained alkali and acid-washed activated carbon was heated under a nitrogen stream from room temperature to 1200°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min, 1100 to 1200°C; 2°C / min), and then heat-treated at 1200°C for 60 minutes. After that, it was finely ground to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0087] <Comparative Example 1> Secondary activated carbon obtained in the same manner as in Example 1 was acid-washed with hydrochloric acid (concentration: 1N, diluent: deionized water) at 100°C for 30 minutes, then thoroughly washed with deionized water and dried. After that, it was heat-treated at 700°C for 60 minutes under a nitrogen gas + water vapor (water vapor partial pressure 3%) atmosphere to remove residual acid and obtain acid-washed activated carbon. Then, it was finely ground to an average particle size of 6 μm to obtain carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0088] <Comparative Example 2> Acid-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 to 1000°C; 2.5°C / min), and then heat-treated at 1000°C for 60 minutes. After that, it was finely pulverized to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0089] <Comparative Example 3> Acid-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 to 1100°C; 2.5°C / min), and then heat-treated at 1100°C for 60 minutes. After that, it was finely pulverized to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0090] <Comparative Example 4> Acid-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 to 1100°C; 2.5°C / min, 1100 to 1200°C; 2°C / min), and then heat-treated at 1200°C for 60 minutes. After that, it was finely pulverized to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing 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 finely ground to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing 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 under a nitrogen stream from room temperature to 1400°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1100°C; 2.5°C / min, 1100 to 1400°C; 2°C / min), and then heat-treated at 1400°C for 60 minutes. After that, it was finely ground to obtain a carbonaceous material for capacitor electrodes with an average particle size of 6 μm. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0093] <Comparative Example 7> A carbonaceous material for capacitor electrodes was obtained using the same procedure as in Example 7, except that the washing temperature with an aqueous sodium hydroxide solution was set to 25°C. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0094] <Comparative Example 8> A carbonaceous material for capacitor electrodes was obtained using the same procedure as in Example 7, except that the washing temperature with an aqueous sodium hydroxide solution was set to 60°C. The processing 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 finely ground to an average particle size of 6 μm, and then heated under a nitrogen stream from room temperature to 1000°C (heating rate: room temperature to 600°C; 10°C / min, 600 to 900°C; 5°C / min, 900 to 1000°C; 2.5°C / min), and heat-treated at 1000°C for 60 minutes to obtain a carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0096] <Comparative Example 10> A char similar to that in Example 1 was activated at 900°C using propane combustion gas + water vapor (water vapor partial pressure: 25%), resulting in a specific surface area of ​​1630 m². 2 Primary activated carbon was obtained at a concentration of / g. The obtained primary activated carbon was acid-washed with hydrochloric acid (concentration: 1N, diluent: deionized water) at a temperature of 100°C for 30 minutes, then thoroughly washed with deionized water, dried, and then heat-treated at 700°C for 60 minutes under a nitrogen gas + water vapor (water vapor partial pressure 3%) atmosphere to remove residual acid and obtain acid-washed activated carbon. Then, it was finely ground to an average particle size of 6 μm to obtain carbonaceous material for capacitor electrodes. The processing conditions and the physical properties of the obtained carbonaceous material are shown in Table 1.

[0097] [Table 1]

[0098] <Preparation of test electrodes> The electrode components, including the carbonaceous material (electrode active material for electric double-layer capacitors), conductive additive, and binder, were pre-dried under reduced pressure (0.1 kPa or less) at 120°C for at least 16 hours before use.

[0099] Carbonaceous material, conductive additive, and binder were weighed in amounts of 0.81g, 0.09g, and 0.1g, respectively, and mixed. The conductive additive used was "Denka Black Granular Conductive Black" manufactured by Denka Co., Ltd., and the binder used was "6J" polytetrafluoroethylene manufactured by Mitsui DuPont Fluorochemicals Co., Ltd. After mixing, the mixture was cut into flakes smaller than 1mm square to further improve uniformity, and then molded in a coin molding machine at a rate of 400kg / cm². 2 A coin-shaped secondary molded product was obtained by applying pressure. The obtained secondary molded product was formed into a sheet with a thickness of 160 μm ± 5% (8 μm) using a roll press machine, and then cut to a predetermined size (30 mm × 30 mm) to prepare electrode composition 1 as shown in Figure 1. The obtained electrode composition 1 was then dried at 120°C under a reduced pressure atmosphere for 16 hours or more, and its mass, sheet thickness, and dimensions were measured and used for the following measurements.

[0100] <Preparation of measurement electrode cells> As shown in Figure 2, a conductive adhesive 2 "HITASOL GA-703" manufactured by Hitachi Chemical Co., Ltd. was applied to an etched aluminum foil 3 manufactured by Hosen Co., Ltd. to a thickness of 100 μm. Then, as shown in Figure 3, the etched aluminum foil 3 coated with the conductive adhesive 2 was bonded to the previously cut sheet-shaped electrode composition 1. Next, an aluminum sealant tab 4 manufactured by Hosen Co., Ltd. was welded to the etched aluminum foil 3 using an ultrasonic welding machine. After welding, it was vacuum dried at 120°C to obtain a polarizing electrode 6 equipped with an aluminum current collector.

[0101] As shown in Figure 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 a bag-shaped outer sheet 7 was prepared with one side ((1) in Figure 4) heat-sealed and the remaining two sides open. A laminate was fabricated by stacking two of the polarizing electrodes 6 described above via a cellulose separator "TF-40" (not shown) manufactured by Nippon Kodo Paper Industry Co., Ltd. This laminate was inserted into the outer sheet 7, and the polarizing electrode 6 was fixed by heat-sealing the side where the tab 4 was in contact ((2) in Figure 5). Then, after vacuum drying at 120°C under reduced pressure for more than 16 hours, the electrolyte was injected in a dry box under an argon atmosphere (dew point below -90°C). As the electrolyte, a 1.0 mol / L tetraethylammonium tetrafluoroborate acetonitrile solution manufactured by Kishida Scientific Co., Ltd. was used. After impregnating the laminate with electrolyte solution within the outer sheet 7, the remaining side of the outer sheet 7 ((3) in Figure 5) was heat-pressed to fabricate the electric double-layer capacitor 8 shown in Figure 5.

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

[0103] <Measurement of gas generation amount> After the capacitance measurement described above, the cells were kept in a constant temperature bath at 60°C for 600 hours while a voltage of 3.0V was applied. The dry weight and water weight of the measurement electrode cell were measured, and the cell volume was determined from the generated buoyancy and the density of the water. The gas volume, calculated from the change in cell volume before and after the durability test, was corrected for the temperature difference during measurement. In other words, the amount of gas generated was calculated according to the following formula. In the formula, cell weight A represents the cell weight in air (g), and cell weight W represents the cell weight 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 + temperature measured after durability test (°C)) / (273 + temperature measured before durability test (°C)) The above gas generation amount was further divided by the mass of activated carbon constituting the electrode composition to obtain the gas generation amount per unit mass of activated carbon (cc / g). The results are shown in Table 2.

[0104] <Moldability> In the preparation of test electrodes, the number of electrode compositions 1 obtained using 0.81 g, 0.09 g, and 0.1 g of carbonaceous material, conductive additive, and binder, respectively, was defined as the moldability. The results are shown in Table 2.

[0105] [Table 2]

[0106] The carbonaceous materials obtained in Examples 1 to 9 exhibit excellent moldability, and electric double-layer capacitors equipped with electrodes made from these carbonaceous materials have low gas generation and high initial capacity. On the other hand, the carbonaceous material obtained in Comparative Example 9 has poor moldability, and electric double-layer capacitors equipped with electrodes made from the carbonaceous material obtained in Comparative Example 6 have low initial capacity, while electric double-layer capacitors equipped with electrodes made from the carbonaceous materials obtained in the other comparative examples have high gas generation. [Explanation of Symbols]

[0107] 1 Electrode composition 2. Conductive adhesive 3 Etched aluminum foil 4 tabs 5. Sealant 6-part polarity electrode 7. Bag-shaped outer sheet 8. Electric double-layer capacitor (1) One side that has been heat-sealed (2) One side on which the tabs touch (3) The remaining side of the bag-shaped outer sheet

Claims

1. The silicon element content is less than 200 ppm, the powder conductivity is 10.0 to 22.0 S / cm, the total surface functional group content is 0.22 to 0.36 meq / g, and the pore volume of pores with a diameter of 4 nm or more, as measured by the BJH method, is 0.10 to 0.20 cm³. ３ A carbonaceous material that is / g.

2. BET specific surface area is 1400-2200 m² ２ The carbonaceous material according to claim 1, wherein the weight is / g.

3. The carbonaceous material according to claim 1 or 2, wherein the alkali metal content is less than 40 ppm.

4. A carbonaceous material according to any one of claims 1 to 3, based on a plant-derived carbon precursor.

5. The carbonaceous material according to claim 4, wherein the plant-derived carbon precursor is coconut shell.

6. An electrode active material for an electric double-layer capacitor, comprising the carbonaceous material described in any one of claims 1 to 5.

7. An electrode for an electric double layer capacitor, comprising the electrode active material for an electric double layer capacitor described in claim 6.

8. An electric double layer capacitor comprising electrodes for an electric double layer capacitor as described in claim 7.

9. A step of washing activated carbon obtained by carbonizing a carbon precursor in an alkaline solution at 65°C or higher, and The activated carbon after alkaline washing is then acid washed, heat-treated at 1000-1300°C under an inert gas atmosphere, and then pulverized. A method for producing a carbonaceous material according to any one of claims 1 to 5, including the method described above.

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