Carbonaceous material, method for producing same, electrode active material for electrochemical device, electrode for electrochemical device, and electrochemical device

Abstract

The present invention addresses the problem of providing: a carbonaceous material having high capacitance per volume and high durability; and a method for producing the carbonaceous material. Provided is a carbonaceous material having a BET specific surface area of 1500-1900 m2 / g, an average pore diameter of 1.84-2.05 nm at a nitrogen relative pressure P / P0 of 0.93 in a nitrogen adsorption isotherm as measured at a temperature of 77.4 K, and an average pore diameter of 1.54-2.05 nm at a nitrogen relative pressure P / P0 of 0.93 in a nitrogen adsorption isotherm as measured at a temperature of 77.4 K. The ratio of the pore volume of pores having a pore diameter of 3 nm or less as measured by the BJH method to the total pore volume as calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in a nitrogen adsorption isotherm is 65-90%; the ratio of the pore volume of pores having a pore diameter of 1-2 nm measured by the MP method to the total pore volume calculated by the amount of nitrogen gas adsorption at a relative pressure P / P0 = 0.93 in a nitrogen gas adsorption isotherm is 10-20%.

Description

This application is a divisional application of the PCT application with the filing date of July 17, 2019, application number 2019800482382, and invention title "Carbonaceous Material, Method for Producing the Same, Electrode Active Material for Electrochemical Device, Electrode for Electrochemical Device, and Electrochemical Device". Technical Field

[0001] The present invention relates to a carbonaceous material, a method for producing the same, an electrode active material for an electrochemical device, an electrode for an electrochemical device, and an electrochemical device. Background Art

[0002] Regarding an electric double layer capacitor which is one of electrochemical devices, since it utilizes the capacitance (electric double layer capacitance) obtained by the adsorption and desorption of ions by a physical method without accompanying chemical reactions, its output power characteristics and life characteristics are excellent compared to batteries. In addition, a lithium ion capacitor which is one of electrochemical devices is attracting attention as a hybrid capacitor capable of further increasing the energy density of an electric double layer capacitor. In recent years, in view of such excellent characteristics of these electrochemical devices and the urgent response to environmental problems, it has attracted attention in applications such as being mounted in automobiles for energy storage of renewable energy. However, the performance required for such in-vehicle electrochemical devices has become strict, and it is required to have high capacitance and high durability under more severe usage conditions (such as temperature environment) compared to consumer applications.

[0003] In response to such requirements, various electric double layer capacitors in which the pore distribution and specific surface area of activated carbon are controlled have been reported. For example, in Patent Document 1, an electric double layer capacitor using an electrode formed of activated carbon having a specific specific surface area, average pore diameter, total pore volume, and a high ratio of the volume of mesopores with a pore diameter of or more is disclosed.

[0004] In Patent Document 2, an electrode for an electric double layer capacitor using activated carbon having a specific BET specific surface area, pore volume, and average pore diameter and a relatively large average pore diameter is disclosed.

[0005] In Patent Document 3, an electric double layer capacitor using activated carbon having a specific BET specific surface area, powder packing density, and average particle diameter is disclosed.

[0006] Prior Art Documents Patent Documents Patent Document 1: Japanese Patent No. 3038676 Gazette Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-171538 Patent Document 3: Japanese Unexamined Patent Application Publication No. 2000-182904. Summary of the Invention

[0007] Problems to be Solved by the Invention The present inventors studied the activated carbons described in Patent Documents 1 to 3, and as a result, found that further improvement is required to obtain an electrode having a high electrostatic capacitance per unit volume and excellent durability. For example, in the case of an activated carbon having a high ratio of mesopore volume as described in Patent Document 1, it is known that due to an excessive number of mesopores, the bulk density of the electrode decreases and the electrostatic capacitance per unit volume decreases. In addition, in the case of an activated carbon having a relatively large pore diameter as described in Patent Document 2, it is known that due to the large pore diameter, the bulk density of the electrode decreases and the initial electrostatic capacitance per unit volume decreases. In the case of the activated carbon described in Patent Document 3, it is known that due to an excessively high ratio of micropore volume, there is a possibility of causing a decrease in durability and an increase in internal resistance.

[0008] Accordingly, an object of the present invention is to provide a carbonaceous material and a method for producing the same, which have a high electrostatic capacitance per unit volume and high durability.

[0009] Means for Solving the Problems The present inventors conducted a detailed study on a carbonaceous material and a method for producing the same in order to solve the above problems. As a result, it was found that the above problems can be solved by the following carbonaceous material, and thus the present invention was completed.

[0010] A carbonaceous material, wherein the BET specific surface area is 1500 to 1900 m 2 / g, the average pore diameter at a relative nitrogen pressure P / P0 = 0.93 in the nitrogen adsorption isotherm measured at a temperature of 77.4 K is 1.84 to 2.05 nm, the pore volume of pores having a pore diameter of 3 nm or less measured by the BJH method accounts for 65 to 90% of the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm, and the pore volume of pores having a pore diameter of 1 to 2 nm measured by the MP method accounts for 10 to 20% of the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm.

[0011] That is, the present invention includes the following preferred embodiments.

[0012] 〔1〕A carbonaceous material, wherein the BET specific surface area is 1500 to 1900 m 2 / g, The average pore diameter at a relative nitrogen pressure P / P0 = 0.93 in the nitrogen adsorption isotherm measured at a temperature of 77.4K is 1.84 to 2.05 nm. The proportion of the pore volume of pores with a pore diameter of less than 3 nm measured by the BJH method in the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 65 to 90%. Further, the proportion of the pore volume of pores with a pore diameter of 1 to 2 nm measured by the MP method in the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 10 to 20%.

[0013] 〔2〕The carbonaceous material according to the foregoing 〔1〕, wherein the proportion of the pore volume of pores with a pore diameter of 1 to 2 nm measured by the MP method in the total micropore volume measured by the MP method is 10 to 22%.

[0014] 〔3〕The carbonaceous material according to the foregoing 〔1〕 or 〔2〕, wherein the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 0.7 to 1.0 cm 3 / g.

[0015] 〔4〕The carbonaceous material according to any one of the foregoing 〔1〕 to 〔3〕, wherein the powder packing density when compressed at a pressure of 12 kN is 0.60 to 0.73 g / cm 3 .

[0016] 〔5〕The carbonaceous material according to any one of the foregoing 〔1〕 to 〔4〕, wherein the carbonaceous material is a material based on a carbon precursor derived from plants.

[0017] 〔6〕The carbonaceous material according to any one of the foregoing 〔1〕 to 〔5〕, wherein the carbon precursor derived from plants is derived from coconut shells.

[0018] 〔7〕An electrode active material for an electrochemical device, which is formed of the carbonaceous material according to any one of the foregoing 〔1〕 to 〔6〕.

[0019] 〔8〕A method for manufacturing the carbonaceous material according to any one of the foregoing 〔1〕 to 〔6〕, The method is a method for obtaining a carbonaceous material by carbonizing a carbon precursor, performing primary activation using an activating gas containing water vapor, performing washing, and performing secondary activation using an activating gas containing water vapor.

[0020] 〔9〕An electrode for an electrochemical device, which contains the electrode active material for an electrochemical device according to the foregoing 〔7〕.

[0021] 〔10〕An electrochemical device comprising the electrode for an electrochemical device described in the foregoing 〔9〕.

[0022] Effects of the Invention The carbonaceous material of the present invention has a micropore distribution suitable for reducing the internal resistance, and does not have an excessive mesopore distribution that causes a decrease in the electrostatic capacitance per unit volume. Therefore, when the carbonaceous material of the present invention is used as an electrode active material, an increase in resistance can be suppressed in an electrochemical device including an electrode containing the electrode active material, and the durability such as the electrostatic capacitance retention rate can be improved. In addition, the electrostatic capacitance per unit volume of the electrochemical device can be increased.

[0023] Generally, in the case of an electrochemical device, it is necessary to ensure the performance after a durability test. By using a material with a high capacitance retention rate and showing a high electrostatic capacitance per unit volume after a durability test, a capacitor element excellent in terms of cost and component performance can be designed. Therefore, an electrode containing the carbonaceous material of the present invention (the electrode active material for the electrochemical device of the present invention) can be suitably used as an electrode for electrochemical devices such as an electric double layer capacitor and a lithium ion capacitor that require high durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a view showing a sheet-like electrode composition.

[0025] Figure 2 is a view showing a current collector (etched aluminum foil) coated with a conductive adhesive.

[0026] Figure 3 is a view showing a polarized electrode obtained by bonding a sheet-like electrode composition to a current collector and welding an aluminum electrode tab by ultrasonic welding.

[0027] Figure 4 is a view showing a bag-shaped outer packaging sheet.

[0028] Figure 5 is a view showing an electric double layer capacitor.

[0029] Figure 6 is a view showing the relationship between the specific surface area of the carbonaceous material and the ratio of the pore volume of micropores having a pore width of 1 to 2 nm to the total pore volume.

[0030] Figure 7 is a view showing the relationship between the average pore diameter of the carbonaceous material and the electrostatic capacitance per unit volume of the carbonaceous material measured at -30 °C before the durability test.

[0031] Figure 8 is a view showing the relationship between the average pore diameter of the carbonaceous material and the capacitance retention rate measured at -30 °C after the durability test.​​​​​​​​

[0032] Figure 9 A graph showing the relationship between the proportion (Proportion B) of the pore volume of micropores with a pore diameter of 1 to 2 nm in a carbonaceous material in the total pore volume and the electrostatic capacitance per unit volume of the carbonaceous material in the measurement at -30°C before and after the durability test.

[0033] Figure 10 A graph showing the relationship between the proportion (Proportion B) of the pore volume of micropores with a pore diameter of 1 to 2 nm in a carbonaceous material in the total pore volume and the capacity retention rate of the carbonaceous material in the measurement at -30°C after the durability test. Detailed Embodiments

[0034] Hereinafter, the embodiments of the present invention will be described in detail. It should be noted that the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the gist of the present invention.

[0035] For the carbonaceous material of the present invention, the BET specific surface area is 1500 to 1900 m 2 / g, the average pore diameter at a nitrogen relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm measured at a temperature of 77.4 K is 1.84 to 2.05 nm, the proportion of the pore volume of pores with a pore diameter of 3 nm or less measured by the BJH method in the total pore volume calculated from the nitrogen adsorption amount at a nitrogen relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 65 to 90%, and the proportion of the pore volume of pores with a pore diameter of 1 to 2 nm measured by the MP method in the total pore volume calculated from the nitrogen adsorption amount at a nitrogen relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 10 to 20%.

[0036] The BET specific surface area of the carbonaceous material of the present invention is 1500 to 1900 m 2 / g. Generally, the electrostatic capacitance per unit area is fixed. Therefore, when the BET specific surface area is less than 1500 m 2 / g, the electrostatic capacitance per unit mass becomes excessively small. On the other hand, when the BET specific surface area is greater than 1900 m 2 / g, the bulk density of the electrode manufactured using such activated carbon decreases, and the electrostatic capacitance per unit volume becomes excessively small. From the viewpoints of easily increasing both the electrostatic capacitance per unit mass and the electrostatic capacitance per unit volume, the BET specific surface area is preferably 1550 to 1850 m 2 / g, and more preferably 1600 to 1800 m 2 ​​ / g. It should be noted that regarding durability, in addition to the specific surface area, the average pore diameter, pore distribution, and pore volume have a greater impact. Therefore, comprehensive consideration is required.

[0037] In the carbonaceous material of the present invention, the average pore diameter at a relative nitrogen pressure P / P0 = 0.93 in the nitrogen adsorption isotherm measured at a temperature of 77.4 K is 1.84 to 2.05 nm. When the average pore diameter is less than 1.84 nm, the migration resistance of ions in the pores increases, so the internal resistance increases and the durability decreases, which is not ideal. In addition, when the average pore diameter is greater than 2.05 nm, the electrode density decreases, which is not ideal. For the above average pore diameter, from the viewpoint of easily maintaining high durability and easily increasing the electrode density, it is preferably less than 2.05 nm, more preferably 2.00 nm or less. In addition, from the same viewpoint, it is preferably 1.85 nm or more.

[0038] It should be noted that the above BET specific surface area and average pore diameter can be calculated by the nitrogen adsorption method. For example, they can be measured by the method described in the examples.

[0039] In the carbonaceous material of the present invention, the proportion (hereinafter, also referred to as "proportion A") of the pore volume of pores with a pore diameter of 3 nm or less measured by the BJH method in the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 65 to 90%. Proportion A can be calculated by the following formula (a): [Mathematical formula 1]

[0040] When proportion A is greater than 90%, the internal resistance of the electrode increases and the durability performance decreases, which is not ideal. In addition, when proportion A is less than 65%, the bulk density decreases and the electrostatic capacitance per unit volume decreases, which is not ideal. From the viewpoint of easily maintaining high durability and easily increasing the electrostatic capacitance, proportion A is preferably 70 to 85%, more preferably 72 to 83%.

[0041] Here, the so-called BJH method, like the CI method and the DH method, is a calculation method commonly used for the analysis of mesopores, and is a method advocated by Barrett, Joyner, Halenda, etc. In the present invention, by applying the BJH method to the nitrogen adsorption / desorption isotherm measured by the nitrogen adsorption method, the pore volume can be calculated. It should be noted that in this specification, mesopores are pores having a pore diameter of 2 nm or more, and micropores represent pores having a pore diameter of 2 nm or less. In addition, the pore volume of pores having a pore diameter of 3 nm or less measured by the BJH method is calculated by removing the pore volume of pores having a pore diameter of 3 nm or more measured by the BJH method from the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm.

[0042] In the carbonaceous material of the present invention, the proportion (hereinafter also referred to as "proportion B") of the pore volume of micropores having a pore diameter of 1 to 2 nm measured by the MP method in the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 10 to 20%. Proportion B can be calculated using the following formula (b): [Mathematical formula 2]

[0043] When the ratio B is less than 10%, the internal resistance of the electrode increases and the durability decreases, which is not ideal. In addition, when the ratio B is greater than 20%, the bulk density decreases and the electrostatic capacitance per unit volume decreases, which is not ideal. From the viewpoint of easily improving durability, the ratio B is preferably 11% or more, more preferably 12% or more, and further preferably 12.3% or more. From the viewpoints of easily maintaining high durability and easily increasing the electrostatic capacitance, the ratio B is preferably 11 to 18%, more preferably 12 to 15%. The pores with a pore diameter of 1 to 2 nm are the pores with a relatively large pore diameter among the micropores. In the carbonaceous material having a specific average pore diameter of 1.84 to 2.05 nm as defined in the present invention, small micropores with a pore diameter of 1 nm or less are relatively easy to exist, but it is difficult to maintain the above average pore diameter and make a large number of larger micropores with a pore diameter of 1 to 2 nm exist. For example, when trying to make a large number of larger micropores with a pore diameter of 1 to 2 nm exist, mesopores with a pore diameter of 3 nm or more are also likely to increase, and as a result, the average pore diameter is likely to exceed the upper limit of the above range. Therefore, the feature that the carbonaceous material of the present invention has a specific average pore diameter and the ratio B is 10 to 20% means that compared with the general carbonaceous material having an average pore diameter in the same range as that of the carbonaceous material of the present invention, there are a large number of pores with a pore diameter of 1 to 2 nm. It is considered that in the carbonaceous material of the present invention, by having a specific average pore diameter and increasing the ratio of specific pores with a pore diameter of 1 to 2 nm, the effects of increasing the electrostatic capacitance per unit volume and improving the durability are achieved.

[0044] In the carbonaceous material of the present invention, the ratio (hereinafter also referred to as "ratio C") of the pore volume of the pores having a pore diameter of 1 to 2 nm measured by the MP method to the total micropore volume measured by the MP method is preferably 10 to 22%, more preferably 11 to 21%, and further preferably 11 to 20%. The ratio C can be calculated by the following formula (c): [Mathematical formula 3]

[0045] When the ratio C is above the above lower limit value, it is easy to reduce the internal resistance of the electrode and easy to improve the durability. In addition, when the ratio C is below the above upper limit value, it is easy to increase the bulk density and easy to increase the electrostatic capacitance per unit volume. It should be noted that the ratio C being in the above range means that there are a large number of larger micropores with a pore diameter of 1 to 2 nm in all the micropores. Here, in the present specification, the total micropore volume measured by the MP method is the pore volume of the micropores having a pore diameter of 2 nm or less measured by the MP method.

[0046] Here, the so-called MP method is a method that uses "t-plot" (B.C. Lippens, J.H. de Boer, J. Catalysis, 43 19 (1965)) to calculate the micropore volume, micropore area, and micropore distribution, and is a method devised by M. Mikhail, Brunauer, and Bodor. In the present invention, by applying the MP method to the nitrogen adsorption isotherm measured by the nitrogen adsorption method, the pore volume can be calculated.

[0047] The total pore volume of the carbonaceous material of the present invention calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is preferably 0.7 to 1.0 cm 3 / g, more preferably 0.72 to 0.95 cm 3 / g, and even more preferably 0.75 to 0.90 cm 3 / g. When the total pore volume is within the above range, the balance between the capacitance and the resistance is good, and thus it is preferred. It should be noted that the above total pore volume can be calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm measured by the nitrogen adsorption method.

[0048] The powder packing density of the carbonaceous material of the present invention when compressed at a pressure of 12 kN is preferably 0.60 to 0.73 g / cm 3 and more preferably 0.62 to 0.72 g / cm 3 and even more preferably 0.63 to 0.71 g / cm 3 . When the powder packing density is above the lower limit value described above, the space volume becomes smaller. Therefore, it is easy to increase the electrode density and easy to increase the initial capacitance. In addition, when the powder packing density is below the upper limit value described above, due to the existence of a certain space volume, it is easy to reduce the internal resistance, easy to suppress the decrease in capacitance caused by the durability test, and easy to improve the durability.

[0049] The above powder packing density can be obtained by the following method: using the powder resistivity measurement unit MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd., filling the carbonaceous material into a container, and then compressing it at a pressure of 12 kN.

[0050] The average particle diameter of the carbonaceous material of the present invention is preferably 30 μm or less, more preferably 20 μm or less. In addition, the average particle diameter of the carbonaceous material of the present invention is preferably 2 μm or more, more preferably 4 μm or more. When the average particle diameter is above the above lower limit value, the amount of binder and the like required for electrode forming can be reduced, and thus, it is easy to suppress the decrease in the electrostatic capacitance per unit electrode weight. In addition, when the average particle diameter is below the above upper limit value, there is a tendency that the electrode layer is easily formed into a thin film, and thus, it is easy to reduce the resistance. It should be noted that the average particle diameter can be measured, for example, using a particle size and particle size distribution measuring device (for example, "Microtrac MT3000" manufactured by Nikkiso Co., Ltd.).

[0051] The potassium element content in the carbonaceous material of the present invention is preferably 500 ppm or less, more preferably 150 ppm or less, and still more preferably 120 ppm or less. When the content of the potassium element is below the above upper limit value, problems such as short circuit are less likely to occur in the electrochemical device containing the carbonaceous material. The potassium element content in the carbonaceous material is preferably as small as possible, and its lower limit value is 0 ppm or more, for example, 6 ppm or more. It should be noted that the content of the potassium element can be measured, for example, by fluorescence X-ray analysis.

[0052] The carbon precursor that becomes the raw material of the carbonaceous material of the present invention is not particularly limited as long as it is a carbon precursor that can form activated carbon by activation, and can be widely selected from carbon precursors from plants, carbon precursors from minerals, carbon precursors from natural raw materials, and carbon precursors from synthetic raw materials, etc. From the viewpoints of reducing harmful impurities, environmental protection, and commerce, the carbonaceous material of the present invention is preferably a material based on a carbon precursor from plants. In other words, the carbon precursor that becomes the raw material of the carbonaceous material of the present invention preferably comes from plants.

[0053] Examples of the carbon precursor from minerals include petroleum-based and coal-based pitches, and coke. Examples of the carbon precursor from natural raw materials include carbonized products of 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 the carbon precursor from synthetic raw materials include carbonized products of polyamide-based such as nylon, polyvinyl alcohol-based such as vinylon, polyacrylonitrile-based such as acrylic, polyolefin-based such as polyethylene and polypropylene, polyurethane, phenolic resin, and vinyl chloride-based resin.

[0054] As the carbon precursor derived from plants, there is no particular limitation, and examples thereof include coconut husks, coffee beans, tea leaves, sugarcane, fruits (e.g., oranges, bananas), straws, rice husks, broad-leaved trees, coniferous trees, and bamboo. The above examples include waste after the original use (e.g., used tea leaves), or a part of the plant raw material (e.g., the peels of bananas and oranges). These plant raw materials can be used alone, or two or more of these plant raw materials can be combined and used. Among these plant raw materials, coconut husks are preferred in terms of easy availability and the ability to produce carbonaceous materials with various properties. Therefore, the carbonaceous material of the present invention is preferably a material based on a carbon precursor derived from plants, and more preferably a material based on a carbon precursor derived from coconut husks.

[0055] As for the coconut husk, there is no particular limitation, and examples thereof include coconut husks of oil palm (oil coconut), coconut, salak, and sea coconut. These coconut husks can be used alone, or two or more of them can be combined and used. From the viewpoint of easy availability, coconut husks of coconut and oil palm, which are biomass wastes generated in large quantities after using coconut as a food, detergent raw material, biodiesel raw material, etc., are particularly preferred.

[0056] The carbonaceous material of the present invention, especially activated carbon, can be manufactured by a method including the following steps: carbonizing the above-mentioned carbon precursor, performing primary activation, performing washing, and further performing secondary activation to obtain a carbonaceous material. The present invention also provides a method for manufacturing a carbonaceous material, in which the carbon precursor is carbonized, primary activation is performed using an activation gas containing water vapor, washing is performed, and secondary activation is performed using an activation gas containing water vapor to obtain a carbonaceous material.

[0057] There is no particular limitation on the above carbonization and activation methods, and for example, known methods such as a fixed bed method, a moving bed method, a fluidized bed method, a multi-stage bed method, and a rotary kiln can be adopted.

[0058] In the method for manufacturing the carbonaceous material of the present invention, first, the carbon precursor is carbonized. As the carbonization method, there is no particular limitation, and examples thereof include: a method of firing the carbon precursor 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 as the main component and other gases.

[0059] After carbonizing the above carbon precursor, primary activation is performed. As the activation method, there are a gas activation method and a chemical activation method. In the present invention, from the viewpoint of less residue of impurities, the gas activation method is preferred. The gas activation method can be performed by reacting the carbonized carbon precursor with an activation gas (e.g., water vapor, carbon dioxide, etc.).

[0060] In the first activation, from the viewpoint of efficiently performing activation, a mixture of the same inert gas and water vapor as used during carbonization is preferred. At this time, the partial pressure of water vapor is preferably in the range of 10 to 60%. When the partial pressure of water vapor is 10% or more, it is easy to fully perform activation. When it is 60% or less, the rapid activation reaction is suppressed, and the reaction is easy to control.

[0061] Relative to 100 parts by mass of the carbon precursor, the total amount of the activation gas supplied during the first 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. When the total amount of the activation gas supplied is within the above range, the activation reaction can be carried out more efficiently.

[0062] The activation temperature during the first activation is usually 700 to 1100 °C, preferably 800 to 1000 °C. The activation time and the heating rate are not particularly limited and vary depending on the type, shape, size of the selected carbon precursor, and the desired pore diameter distribution, etc. It should be noted that when the activation temperature during the first activation is increased or the activation time is extended, the BET specific surface area of the obtained carbonaceous material tends to increase. Therefore, in order to obtain a carbonaceous material having a BET specific surface area within the desired range, the activation temperature and the activation time can be adjusted.

[0063] It is preferred to perform the first activation until the BET specific surface area of the carbonaceous material obtained after the first activation becomes about 1000 to 1400 m 2 / g. If it is 1000 m 2 or more, pores can be formed that can efficiently remove the contained impurities during subsequent washing. When it is 1400 m 2 or more, although it also depends on the BET specific surface area of the carbonaceous material obtained after the second activation, the change range accompanying activation becomes smaller, and it is difficult to form the desired pore diameter and pore distribution.

[0064] Next, the carbonaceous material obtained after the first activation is washed. The washing can be carried out by immersing the carbonaceous material obtained after the first activation in a washing liquid containing an acid. As the washing liquid, for example, inorganic acids or organic acids can be mentioned. As the inorganic acid, for example, hydrochloric acid, sulfuric acid, etc. can be mentioned. As the organic acid, for example, formic acid, acetic acid, propionic acid, oxalic acid, tartaric acid, citric acid and other saturated carboxylic acids, benzoic acid, terephthalic acid and other aromatic carboxylic acids, etc. can be mentioned. From the viewpoint of washability, the acid used in the washing liquid is preferably an inorganic acid, more preferably hydrochloric acid. It should be noted that it is preferred that after washing with an acid, further washing is carried out with water or the like to remove the excess acid. By this operation, the load on the activation equipment during the second activation can be reduced.

[0065] The washing liquid can usually be prepared by mixing an acid and an aqueous solution. Examples of the aqueous solution include water, a mixture of water and a water-soluble organic solvent, etc. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, propylene glycol, and ethylene glycol.

[0066] The concentration of the acid in the washing liquid is not particularly limited and can be appropriately adjusted according to the type of acid used. The acid concentration of the washing liquid is preferably 0.01 to 3.5% by mass, more preferably 0.02 to 2.2% by mass, and further preferably 0.03 to 1.6% by mass based on the total amount of the washing liquid. When the concentration of the acid in the washing liquid is within the above range, impurities contained in the carbonaceous material can be efficiently removed, which is therefore preferred.

[0067] The pH of the washing liquid is not particularly limited and can be appropriately adjusted according to the type of acid used, the object to be removed, etc.

[0068] The temperature of the washing liquid when impregnating the carbonaceous material is not particularly limited, preferably 0 to 98 °C, more preferably 10 to 95 °C, and further preferably 15 to 90 °C. When the temperature of the washing liquid when impregnating the carbonaceous material is within the above range, a practical time can be achieved and washing with reduced load on the device can be carried out, which is therefore preferred.

[0069] As a method for washing the carbonaceous material, there is no particular limitation as long as the carbonaceous material can be immersed in the washing liquid. It can be a method of continuously adding the washing liquid, allowing it to stay for a specified time, and carrying out impregnation while withdrawing, or a method of immersing the carbonaceous material in the washing liquid, allowing it to stay for a specified time, performing liquid separation, then re-adding the washing liquid, and repeatedly performing impregnation-liquid separation. Additionally, it can be a method of completely renewing the washing liquid or a method of partially renewing the washing liquid. The time for immersing the carbonaceous material in the washing liquid can be appropriately adjusted according to the acid used, the acid concentration, the treatment temperature, etc.

[0070] The washing time is not particularly limited. From the viewpoints of the economic efficiency of the reaction equipment and the structural retention of the carbonaceous material, it is preferably 0.05 to 4 hours, more preferably 0.1 to 3 hours.

[0071] The mass ratio of the washing liquid to the carbonaceous material when immersing the carbonaceous material in the washing liquid can be appropriately adjusted according to the type, concentration, and temperature of the washing liquid used. The mass of the impregnated carbonaceous material is usually 0.1 to 50% by mass, preferably 1 to 20% by mass, and more preferably 1.5 to 10% by mass relative to the mass of the washing liquid. When within the above range, impurities dissolved in the washing liquid are not likely to precipitate from the washing liquid, and reattachment to the carbonaceous material is easily inhibited. Additionally, the volumetric efficiency becomes appropriate, and thus it is preferred from the economic viewpoint.

[0072] The atmosphere for washing is not particularly limited and can be appropriately selected according to the washing method used. In the present invention, washing is usually carried out in an atmospheric atmosphere.

[0073] For washing, one kind of washing liquid can be used once or multiple times, or two or more kinds of washing liquids can be combined and used multiple times.

[0074] By washing, impurities contained in the carbonaceous material can be removed. Such impurities are impurities brought by the carbon precursor that is the raw material of the carbonaceous material, and examples include alkali metals such as lithium, sodium, and potassium; alkaline earth metals such as beryllium, magnesium, and calcium; and transition metals such as iron, copper, and nickel.

[0075] In the present invention, the potassium element content in the carbonaceous material after the above washing is preferably 500 ppm or less, more preferably 150 ppm or less, and still more preferably 120 ppm or less. In the present invention, in the case of using a carbonaceous material based on a carbon precursor derived from a plant, the potassium element can be the main component as an impurity. Therefore, in the above case, it is considered that the potassium element content in the carbonaceous material after washing decreases, and the contents of other impurities also decrease. It should be noted that the potassium element content in the carbonaceous material after the above washing is preferably as small as possible, and the lower limit value is 0 ppm or more, for example, 6 ppm or more.

[0076] If impurities such as alkali metals and alkaline earth metals contained in the carbonaceous material are present during activation, there is a tendency for larger pores with a pore diameter to further increase in number. In addition, if alkali metals, alkaline earth metals, etc. remain as impurities, it sometimes has an adverse effect on the performance of the capacitor. In the manufacturing method of the present invention, these impurities are removed first after the first activation, and then the second activation is further carried out. Thereby, it is possible to prevent an excessive increase in mesopores that tend to easily reduce the electrostatic capacitance per unit volume. In addition, by the manufacturing method of the present invention, it is possible to increase the proportion of pores having a pore diameter of 1 to 2 nm, which is a relatively large pore diameter, in micropores having a pore diameter of 2 nm or less. Therefore, it is possible to provide a carbonaceous material for an electrochemical device having a high electrostatic capacitance per unit volume and excellent durability.

[0077] In the present invention, the carbonaceous material obtained after washing is subjected to a second activation. The second activation can be carried out within the same condition range as the above first activation. It should be noted that the same applies to the second activation. When the activation temperature is increased or the activation time is extended, there is a tendency for the BET specific surface area of the obtained carbonaceous material to increase. Therefore, in order to obtain a carbonaceous material having a BET specific surface area within a desired range, it is only necessary to adjust the activation temperature and the activation time.

[0078] For the carbonaceous material obtained by secondary activation, it is preferably further washed to remove ash and metal impurities contained in the carbonaceous material after secondary activation. In addition, for the carbonaceous material obtained after secondary activation, heat treatment can be carried out at 500 to 1500 °C in an inert gas atmosphere or a vacuum atmosphere to remove the residues after washing by heating and to remove unnecessary surface functional groups, further improving the crystallization of carbon and increasing the conductivity.

[0079] In the present invention, the carbonaceous material obtained in the above manner is then pulverized. As the pulverization method, there is no particular limitation, and known pulverization methods such as a ball mill, a roll crusher, or a jet mill, or a combination thereof can be used. The average particle size of the pulverized carbonaceous material is not particularly limited, and from the viewpoints of improving the electrode density and reducing the internal resistance, it is preferably 30 μm or less, more preferably 20 μm or less, preferably 2 μm or more, and more preferably 4 μm or more.

[0080] In the present invention, the carbonaceous material obtained by pulverization can be classified. For example, by removing particles having a particle size of 1 μm or less, activated carbon particles having a narrow particle size distribution width can be obtained. By removing such fine particles, the amount of binder used in electrode formation can be reduced. The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. As the wet classifier, for example, a classifier utilizing the principles of gravity classification, inertial classification, hydraulic classification, centrifugal classification, etc. can be mentioned. As the dry classifier, a classifier utilizing the principles of sedimentation classification, mechanical classification, centrifugal classification, etc. can be mentioned. From the viewpoint of economy, it is preferable to use a dry classification device.

[0081] It is also possible to carry out pulverization and classification using one device. For example, a jet mill equipped with a dry classification function can be used to carry out pulverization and classification. In addition, devices for a pulverizer and a classifier independently can also be used. In this case, pulverization and classification can be carried out continuously or discontinuously.

[0082] In addition, for the obtained carbonaceous material, depending on the use, heat treatment can be carried out, and post-treatments such as chemical or physical modification of the surface can be carried out.

[0083] The obtained carbonaceous material can be dried. Drying is an operation for removing moisture and the like adsorbed on the carbonaceous material. For example, by heating the carbonaceous material, the moisture and the like adsorbed on the carbonaceous material can be removed. In addition to heating, or in addition to heating, drying can also be carried out by means such as reduced pressure, reduced pressure heating, and freezing to remove the moisture and the like adsorbed on the carbonaceous material.

[0084] From the viewpoint of removing moisture adsorbed on the carbonaceous material, the drying temperature is preferably 100 to 330 °C, more preferably 110 to 300 °C, and further preferably 120 to 250 °C.

[0085] Although the drying time also depends on the drying temperature employed, from the viewpoint of removing moisture adsorbed on the carbonaceous material, it is preferably 0.1 hour or more, more preferably 0.5 hour or more, and further preferably 1 hour or more. Additionally, from the viewpoint of economy, it is preferably 24 hours or less, more preferably 12 hours or less, and further preferably 6 hours or less.

[0086] Drying can be carried out under normal pressure or reduced pressure atmosphere. When drying is carried out under normal pressure, it is preferably carried out in an inert gas atmosphere such as nitrogen or argon, or in an air atmosphere with a dew point of -20 °C or lower.

[0087] The carbonaceous material of the present invention is suitable for use as an electrode active material for an electrochemical device. Therefore, the present invention also provides an electrode active material for an electrochemical device formed from the carbonaceous material of the present invention. It should be noted that in the following description, when the carbonaceous material of the present invention is used as an electrode active material for an electrochemical device, the "carbonaceous material of the present invention" may also be the "electrode active material for an electrochemical device formed from the carbonaceous material of the present invention". In addition, the present invention also provides an electrode for an electrochemical device containing the electrode active material for an electrochemical device of the present invention, and an electrochemical device equipped with the electrode for an electrochemical device. The electrode for an electrochemical device of the present invention can be manufactured by mixing the carbonaceous material of the present invention (the electrode active material for an electrochemical device formed from the carbonaceous material of the present invention) with a binder, other active materials as needed, and a conductive additive as needed, and molding the resulting mixture.

[0088] The carbonaceous material of the present invention has a micropore distribution suitable for reducing the internal resistance and does not have an excessive mesopore distribution that causes a decrease in the electrostatic capacitance per unit volume. Therefore, when the carbonaceous material of the present invention is used as an active material in an electrode for an electrochemical device, not only the electrostatic capacitance per unit volume (in the case of using a carbonaceous material having a similar specific surface area) is maintained, but also an increase in resistance can be suppressed, and the durability such as the capacity retention rate is improved, and the withstand voltage property is improved. The carbonaceous material of the present invention is useful as an electrode active material for an electrochemical device such as an electric double layer capacitor or a lithium ion capacitor, and an electrode containing the carbonaceous material of the present invention (the electrode active material for an electrochemical device formed from the carbonaceous material of the present invention) can be suitably used as an electrode for an electrochemical device such as an electric double layer capacitor or a lithium ion capacitor that requires high durability. At this time, the electrode may contain, in addition to the carbonaceous material of the present invention, a substance that can become an electrode active material. Examples

[0089] Hereinafter, the present invention will be described by way of examples, but the present invention is not limited by any of these examples.

[0090] First, the measurement methods of various physical property values, the manufacturing methods of electrodes and electrode elements, and the durability test methods in the examples and comparative examples are shown below.

[0091] [BET specific surface area] Using BELSORP-mini manufactured by BEL Japan, Inc., the carbonaceous material was heated at 300 °C for 3 hours under a nitrogen gas flow (nitrogen gas flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the carbonaceous material at 77.4 K was measured. From the obtained nitrogen adsorption isotherm, analysis based on the multi-point method was performed by the BET equation, and the specific surface area was calculated from the straight line in the region of the relative pressure P / P0 = 0.01 to 0.1 of the obtained curve.

[0092] [Total pore volume · average pore diameter] Using BELSORP-mini manufactured by BEL Japan, Inc., the carbonaceous material was heated at 300 °C for 3 hours under a nitrogen gas flow (nitrogen gas flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the carbonaceous material at 77.4 K was measured. The total pore volume was determined from the nitrogen adsorption amount at the relative pressure P / P0 = 0.93 in the obtained adsorption isotherm. In addition, based on the following formula, the average pore diameter was calculated from the total pore volume obtained as described above and the BET specific surface area described above.

[0093] [Mathematical formula 4] Average pore diameter (nm) = total pore volume (cm 3 / g) / specific surface area (m 2 / g) × 4000.

[0094] [Mesopore volume based on the BJH method] Using BELSORP-mini manufactured by BEL Japan, Inc., the carbonaceous material was heated at 300 °C for 3 hours under a nitrogen gas flow (nitrogen gas flow rate: 50 mL / min), and then the nitrogen adsorption isotherm of the carbonaceous material at 77.4 K was measured. For the obtained nitrogen adsorption isotherm, the BJH method was applied to calculate the mesopore volume. It should be noted that when performing analysis based on the BJH method, the t-method analysis standard isotherm "NGCB-BEL.t" provided by BEL Japan, Inc. was used for analysis.

[0095] First, using the BJH method, the pore volume of pores with a pore diameter of 3 nm or more calculated within the range of relative pressure P / P0 = 0.93 is obtained. Next, the pore volume of pores with a pore diameter of less than 3 nm is calculated as follows: the total pore volume calculated as described above is subtracted by the pore volume of pores with a pore diameter of 3 nm or more calculated as described above.

[0096] [Micropore volume based on the MP method] Using BELSORP-mini manufactured by BEL Japan, Inc., the carbonaceous material is heated at 300 °C for 3 hours under a nitrogen gas flow (nitrogen gas flow rate: 50 mL / minute), and then the nitrogen adsorption isotherm of the carbonaceous material at 77.4 K is measured. For the obtained nitrogen adsorption isotherm, the MP method is applied to calculate the pore volume of micropores. It should be noted that when performing the analysis based on the MP method, the standard isotherm for t-method analysis "NGCB-BEL.t" provided by BEL Japan, Inc. is used for the analysis.

[0097] The pore volume of pores with a pore diameter of 1 - 2 nm is calculated as follows: the pore volume of pores with a pore diameter of less than 2 nm obtained by the MP method is subtracted by the pore volume of pores with a pore diameter of less than 1 nm. In addition, the pore volume of pores with a pore diameter of less than 2 nm is used as the total micropore volume.

[0098] [Powder packing density] The carbonaceous material is dried at 120 °C under a reduced pressure atmosphere (at a gauge pressure of -95 kPa or less) for 12 hours or more, and then about 0.9 g is filled into a measurement container (probe cylinder: internal volume φ20 mm × 50 mm) and compressed with a probe piston until it reaches 12 kN, and the thickness of the carbonaceous material is measured. From the weight of the carbonaceous material and the volume under 12 kN compression, the powder packing density is obtained based on the following formula.

[0099] [Mathematical formula 5] Powder packing density (g / cm 3 ) = weight of carbonaceous material (g) / volume after 12 kN compression (cm 3 ).

[0100] [Average particle size] In the presence of a surfactant, the carbonaceous material is dispersed in ion-exchanged water using ultrasonic waves, and then the particle size distribution is measured using "Microtrac MT3000" manufactured by Nikkiso Co., Ltd. to obtain the average particle size.

[0101] [Potassium element content] The content of potassium element is measured by the following method. First, a standard curve of the potassium element content is prepared from a standard solution of known concentration. Next, the pulverized test sample is dried at 115 °C for 3 hours. Then, 0.1 g is placed in a decomposition container, 10 ml of nitric acid is added, and they are mixed. Then, using a microwave sample pretreatment device ("MARS6" manufactured by CEM Corporation), the sample is dissolved. The dissolved solution is taken out, fixed volume to 25 ml to prepare a measurement solution, and then analyzed using an ICP emission spectroscopic analyzer ("ICPE-9820" manufactured by Shimadzu Corporation). The concentration of the potassium element is obtained from the value obtained and the standard curve prepared before, and the potassium element content (metal content) is obtained from the following formula.

[0102] [Mathematical formula 6]

[0103] [Fabrication of test electrode] The carbonaceous material (electrode active material for electrochemical device), conductive additive, and binder as electrode constituent members are previously dried under reduced pressure (0.1 kPa or less) at 120 °C for 16 hours or more before use.

[0104] Weigh the carbonaceous material, conductive additive, and binder so that the ratio of (mass of carbonaceous material) : (mass of conductive additive) : (mass of binder) is 81:9:10, and carry out kneading. As the above-mentioned conductive additive, conductive carbon black "Denka Black Granular" manufactured by Denka Co., Ltd. is used, and as the above-mentioned binder, polytetrafluoroethylene "6J" manufactured by Mitsui DuPont Fluorochemical Co., Ltd. is used. After kneading, in order to further achieve uniformity, it is cut into small pieces with a side length of 1 mm or less, and a pressure of 400 kg / cm 2 is applied using a button molding machine to obtain a button-shaped secondary molded product. Using a roll press, the obtained secondary molded product is formed into a sheet with a thickness of 160 μm ± 5% (8 μm), and then cut into a specified size (30 mm × 30 mm) to fabricate Figure 1 the electrode composition 1 as shown. Then, the obtained electrode composition 1 is dried at 120 °C under a reduced pressure atmosphere for 16 hours or more, and then the mass, sheet thickness, and size are measured for the following determination.

[0105] [Fabrication of measurement electrode element] As Figure 2 shown, the conductive adhesive 2 "HITASOL GA-703" manufactured by Hitachi Chemical Co., Ltd. is coated on the etched aluminum foil 3 manufactured by Takizawa Co., Ltd. so that the coating thickness becomes 100 μm. Then, as Figure 3As shown, the etched aluminum foil 3 coated with the conductive adhesive 2 is bonded to the pre-cut sheet-like electrode composition 1. Then, using an ultrasonic welder, the tab 4 made of aluminum with a sealing material 5 manufactured by Takizawa Co., Ltd. is welded to the etched aluminum foil 3. After welding, vacuum drying is performed at 120°C to obtain the polarizable electrode 6 having an aluminum current collector.

[0106] As Figure 4 shown, the aluminum laminated resin sheet manufactured by Takizawa Co., Ltd. is cut into a rectangle (200 mm in length × 60 mm in width), folded in half, and one side ( Figure 4 in (1)) is thermocompression bonded to prepare a bag-shaped outer packaging sheet 7 with the remaining two sides open. Through a cellulose separator “TF-40” (not shown) manufactured by Nippon Kodo Paper Industry Co., Ltd., a laminate formed by overlapping two pieces of the above-mentioned polarizable electrodes 6 is produced. The laminate is inserted into the outer packaging sheet 7, and one side ( Figure 5 in (2)) where the tab 4 contacts is thermocompression bonded to fix the polarizable electrode 6. Then, vacuum drying is performed at 120°C for 16 hours or more in a reduced-pressure atmosphere, and then an electrolyte is injected into a drying oven under 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. is used. In the outer packaging sheet 7, the electrolyte is infiltrated into the laminate, and then the remaining one side ( Figure 5 in (3)) of the outer packaging sheet 7 is thermocompression bonded to produce Figure 5 the double-layer capacitor 8 shown.

[0107] [Capacitance Measurement] For the obtained double-layer capacitor 8, using “CAPACITOR TESTER PFX2411” manufactured by Kikusui Electronics Industry Co., Ltd., constant current charging is performed at 25°C and -30°C with a current of 50 mA relative to the electrode surface area until a voltage of 3.0 V is reached, and then additional charging is performed at 3.0 V for 30 minutes under constant voltage. After the additional charging is completed, discharging is performed at 25 mA. The obtained discharge curve data is calculated by the energy conversion method as the capacitance (F). Specifically, discharging is performed until the post-charging voltage becomes 0, and at this time, the capacitance (F) is calculated from the discharge energy of the discharge. Then, the capacitance (F / cc) obtained by dividing by the electrode volume is obtained.

[0108] [Durability Test] The durability test is carried out as follows. After performing the electrostatic capacitance measurement described above, in a constant temperature bath at 60°C, while applying a voltage of 3.0 V, it is maintained for 400 hours, and then, in the same manner as above, at 25°C and -30°C, the electrostatic capacitance measurement is carried out. From the electrostatic capacitance before and after the durability test, according to the following formula, the capacitance retention rate at each temperature is obtained. In the constant temperature bath at 60°C, the application of a voltage of 3.0 V is started, and then it is maintained for 25 hours. After operation, it is taken as before the durability test, and after maintaining for 400 hours, it is taken as after the durability test.

[0109] [Mathematical formula 7]

[0110] [Example 1] Regarding the carbon (specific surface area: 370 m 2 / g) made from the coconut shell of Philippine coconuts, using propane combustion gas + water vapor (water vapor partial pressure: 25%), at 850°C, it is activated once until it reaches the following specific surface area, and a primary activated granular activated carbon with a specific surface area of 1185 m 2 / g and a potassium element content of 7949 ppm is obtained. Then, using hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water), pickling is carried out at a temperature of 85°C for 30 minutes. Then, in order to remove the remaining acid, it is thoroughly washed with ion-exchanged water and dried to obtain a primary washed granular activated carbon with a potassium element content of 150 ppm. Regarding this primary washed granular activated carbon, next, using propane combustion gas (water vapor partial pressure 15%), it is activated twice at 950°C until it reaches the following specific surface area, and a secondary activated granular activated carbon with a specific surface area of 1715 m 2 / g and an average pore diameter of 1.97 nm is obtained. Regarding the obtained secondary activated granular activated carbon, after performing acid water washing and drying in the same manner as the primary washing, heat treatment is carried out at 700°C to obtain a secondary washed granular activated carbon. This granular activated carbon is finely pulverized until the average particle diameter becomes 6 μm, and a carbonaceous material (1) with a specific surface area of 1729 m 2 / g, an average pore diameter of 1.98 nm, and a potassium element content of 8 ppm is obtained. In addition, using the carbonaceous material (1), according to the aforementioned method for manufacturing the electrode, an electrode composition (1) is obtained, and a polarizable electrode (1) is manufactured using it. Furthermore, a double-layer capacitor (1) is manufactured using the polarizable electrode (1).

[0111] [Example 2] Operating in the same manner as in Example 1, a specific surface area of 1206 m 2The primary activated granular activated carbon of 83 ppm potassium element content was obtained by subjecting granular activated carbon to acid water washing and drying in the same manner as the primary washing in Example 1. Then, the granular activated carbon was further activated with propane combustion gas (water vapor partial pressure 15%) at 930 °C until the following specific surface area was obtained, resulting in a secondary activated granular activated carbon with a specific surface area of 1682 m 2 / g and an average pore diameter of 1.85 nm. After subjecting the obtained secondary activated granular activated carbon to acid water washing and drying in the same manner as the secondary washing in Example 1, heat treatment was carried out at 700 °C to obtain a secondary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, resulting in a carbonaceous material (2) with a specific surface area of 1697 m 2 / g, an average pore diameter of 1.85 nm, and a potassium element content of 9 ppm. In addition, using the carbonaceous material (2), the electrode composition (2), the polarizable electrode (2), and the electric double layer capacitor (2) were produced in the same manner as in Example 1.

[0112] [Example 3] By operating in the same manner as in Example 1, a primary activated granular activated carbon with a specific surface area of 1163 m 2 / g was obtained. Then, acid water washing and drying were carried out in the same manner as the primary washing in Example 1 to obtain a primary washed granular activated carbon with a potassium element content of 70 ppm. For this granular activated carbon, propane combustion gas (water vapor partial pressure 15%) was further used for secondary activation at 950 °C until the following specific surface area was obtained, resulting in a secondary activated granular activated carbon with a specific surface area of 1530 m 2 / g and an average pore diameter of 1.84 nm. After subjecting the obtained secondary activated granular activated carbon to acid water washing and drying in the same manner as the secondary washing in Example 1, heat treatment was carried out at 700 °C to obtain a secondary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, resulting in a carbonaceous material (3) with a specific surface area of 1547 m 2 / g, an average pore diameter of 1.85 nm, and a potassium element content of 16 ppm. In addition, using the carbonaceous material (3), the electrode composition (3), the polarizable electrode (3), and the electric double layer capacitor (3) were produced in the same manner as in Example 1.

[0113] [Example 4] By operating in the same manner as in Example 1, a specific surface area of 1181 m was obtained 2The primary activated granular activated carbon of 16 ppm potassium element content was obtained by subjecting granular activated carbon to acid water washing and drying in the same manner as the primary washing in Example 1 after the primary activation with propane combustion gas (water vapor partial pressure: 15%) at 970 °C until the specific surface area reached the following value. The secondary activated granular activated carbon with a specific surface area of 1565 m 2 / g and an average pore diameter of 1.84 nm was obtained. After subjecting the obtained secondary activated granular activated carbon to acid water washing and drying in the same manner as the secondary washing in Example 1, heat treatment was carried out at 700 °C to obtain secondary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle diameter reached 6 μm, and a carbonaceous material (4) with a specific surface area of 1588 m 2 / g, an average pore diameter of 1.85 nm, and a potassium element content of 5 ppm was obtained. In addition, using the carbonaceous material (4), an electrode composition (4), a polarizable electrode (4), and an electric double layer capacitor (4) were produced in the same manner as in Example 1.

[0114] [Example 5] By operating in the same manner as in Example 1, primary activated granular activated carbon with a specific surface area of 1360 m 2 / g was obtained. Then, acid water washing and drying were carried out in the same manner as the primary washing in Example 1 to obtain primary washed granular activated carbon with a potassium element content of 22 ppm. For this granular activated carbon, propane combustion gas (water vapor partial pressure: 15%) was further used for secondary activation at 970 °C until the specific surface area reached the following value, and secondary activated granular activated carbon with a specific surface area of 1865 m 2 / g and an average pore diameter of 1.93 nm was obtained. After subjecting the obtained secondary activated granular activated carbon to acid water washing and drying in the same manner as the secondary washing in Example 1, heat treatment was carried out at 700 °C to obtain secondary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle diameter reached 6 μm, and a carbonaceous material (5) with a specific surface area of 1871 m 2 / g, an average pore diameter of 1.93 nm, and a potassium element content of 11 ppm was obtained. In addition, using the carbonaceous material (5), an electrode composition (5), a polarizable electrode (5), and an electric double layer capacitor (5) were produced in the same manner as in Example 1.

[0115] [Example 6] By operating in the same manner as in Example 1, primary activated granular activated carbon with a specific surface area of 1058 m 2The primary activated granular activated carbon of 32 ppm potassium element content was obtained by subjecting granular activated carbon to acid water washing and drying in the same manner as the primary washing in Example 1. Then, the granular activated carbon was further reactivated at 950 °C using propane combustion gas (water vapor partial pressure: 15%) until the following specific surface area was obtained, and the secondary reactivated granular activated carbon with a specific surface area of 1530 m 2 / g and an average pore diameter of 1.84 nm was obtained. After subjecting the obtained secondary reactivated granular activated carbon to acid water washing and drying in the same manner as the secondary washing in Example 1, heat treatment was carried out at 700 °C to obtain the secondary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, and a carbonaceous material (6) with a specific surface area of 1538 m 2 / g, an average pore diameter of 1.84 nm, and a potassium element content of 13 ppm was obtained. In addition, using the carbonaceous material (6), an electrode composition (6), a polarizable electrode (6), and an electric double layer capacitor (6) were produced in the same manner as in Example 1.

[0116] [Comparative Example 1] By operating in the same manner as in Example 1, the primary activated granular activated carbon with a specific surface area of 1165 m 2 / g was obtained. Then, acid water washing and drying were carried out in the same manner as the primary washing in Example 1 to obtain the primary washed granular activated carbon with a potassium element content of 25 ppm. For this granular activated carbon, propane combustion gas (water vapor partial pressure: 15%) was further used for secondary reactivation at 930 °C until the following specific surface area was obtained, and the secondary reactivated granular activated carbon with a specific surface area of 1470 m 2 / g and an average pore diameter of 1.81 nm was obtained. After subjecting the obtained secondary reactivated granular activated carbon to acid water washing and drying in the same manner as the secondary washing in Example 1, heat treatment was carried out at 700 °C to obtain the secondary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, and a carbonaceous material (7) with a specific surface area of 1480 m 2 / g and an average pore diameter of 1.81 nm was obtained. In addition, using the carbonaceous material (7), an electrode composition (7), a polarizable electrode (7), and an electric double layer capacitor (7) were produced in the same manner as in Example 1.

[0117] [Comparative Example 2] By operating in the same manner as in Example 1, the primary activated granular activated carbon with a specific surface area of 1243 m 2Granular activated carbon activated once at 970 °C. Then, acid water washing and drying were carried out in the same manner as the first washing in Example 1 to obtain granular activated carbon after the first washing with a potassium element content of 61 ppm. For this granular activated carbon, propane combustion gas (water vapor partial pressure 15%) was further used for secondary activation at 970 °C until the following specific surface area was reached, obtaining granular activated carbon after secondary activation with a specific surface area of 2180 m 2 / g and an average pore diameter of 2.17 nm. For the obtained granular activated carbon after secondary activation, acid water washing and drying were carried out in the same manner as the second washing in Example 1, and then heat treatment was carried out at 700 °C to obtain granular activated carbon after the second washing. This granular activated carbon was finely pulverized until the average particle diameter became 6 μm, obtaining a carbonaceous material (8) with a specific surface area of 2184 m 2 / g, an average pore diameter of 2.17 nm, and a potassium element content of 8 ppm. In addition, using the carbonaceous material (8), the electrode composition (8), the polarizable electrode (8), and the electric double layer capacitor (8) were produced in the same manner as in Example 1.

[0118] [Comparative Example 3] The same operation as in Example 1 was carried out to obtain granular activated carbon activated once with a specific surface area of 1350 m 2 / g. Then, acid water washing and drying were carried out in the same manner as the first washing in Example 1 to obtain granular activated carbon after the first washing with a potassium element content of 23 ppm. For this granular activated carbon, propane combustion gas (water vapor partial pressure 15%) was further used for secondary activation at 970 °C until the following specific surface area was reached, obtaining granular activated carbon after secondary activation with a specific surface area of 2020 m 2 / g and an average pore diameter of 2.04 nm. For the obtained granular activated carbon after secondary activation, acid water washing and drying were carried out in the same manner as the second washing in Example 1, and then heat treatment was carried out at 700 °C to obtain granular activated carbon after the second washing. This granular activated carbon was finely pulverized until the average particle diameter became 6 μm, obtaining a carbonaceous material (9) with a specific surface area of 2027 m 2 / g, an average pore diameter of 2.06 nm, and a potassium element content of 18 ppm. In addition, using the carbonaceous material (9), the electrode composition (9), the polarizable electrode (9), and the electric double layer capacitor (9) were produced in the same manner as in Example 1.

[0119] [Comparative Example 4] For charcoal made from coconut shells of coconuts produced in the Philippines (specific surface area: 370 m 2 / g), propane combustion gas + water vapor (water vapor partial pressure: 25%) was used for primary activation at 850 °C until the following specific surface area was reached, obtaining a specific surface area of 1135 m 2 / g, a primary activated granular activated carbon with an average pore diameter of 1.72 nm and a potassium element content of 7636 ppm. Then, hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water) was used for pickling at a temperature of 85 °C for 30 minutes. Then, in order to remove the remaining acid, it was thoroughly washed with ion-exchanged water, dried, and heat-treated at 700 °C to obtain a primary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, and a carbonaceous material with a specific surface area of 1143 m 2 / g, a carbonaceous material (10) with an average pore diameter of 1.72 nm and a potassium element content of 29 ppm. In addition, using the carbonaceous material (10), the electrode composition (10), the polarizable electrode (10), and the electric double layer capacitor (10) were produced in the same manner as in Example 1.

[0120] [Comparative Example 5] Operating in the same manner as in Comparative Example 4, a primary activated granular activated carbon with a specific surface area of 1428 m 2 / g, an average pore diameter of 1.76 nm, and a potassium element content of 9821 ppm. Then, hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water) was used for pickling at a temperature of 85 °C for 30 minutes. Then, in order to remove the remaining acid, it was thoroughly washed with ion-exchanged water, dried, and heat-treated at 700 °C to obtain a primary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, and a carbonaceous material with a specific surface area of 1434 m 2 / g, a carbonaceous material (11) with an average pore diameter of 1.76 nm and a potassium element content of 15 ppm. In addition, using the carbonaceous material (11), the electrode composition (11), the polarizable electrode (11), and the electric double layer capacitor (11) were produced in the same manner as in Example 1.

[0121] [Comparative Example 6] Operating in the same manner as in Comparative Example 4, a specific surface area of 1663 m was obtained 2 / g, a primary activated granular activated carbon with an average pore diameter of 1.80 nm and a potassium element content of 11590 ppm. Then, hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water) was used for pickling at a temperature of 85 °C for 30 minutes. Then, in order to remove the remaining acid, it was thoroughly washed with ion-exchanged water, dried, and heat-treated at 700 °C to obtain a primary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, and a carbonaceous material with a specific surface area of 1685 m 2A carbonaceous material (12) with a specific surface area of 1.80 nm, an average pore diameter of 1.80 nm, and a potassium element content of 25 ppm. Various physical properties of the carbonaceous material (12) were measured. In addition, using the carbonaceous material (12), the same operations as in Example 1 were performed to prepare an electrode composition (12), a polarizable electrode (12), and an electric double layer capacitor (12).

[0122] [Comparative Example 7] The same operation as in Comparative Example 4 was performed to obtain a primary activated granular activated carbon with a specific surface area of 1901 m 2 / g, an average pore diameter of 1.83 nm, and a potassium element content of 13289 ppm. Then, using hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water), pickling was performed at a temperature of 85 °C for 30 minutes. Then, in order to remove the remaining acid, it was thoroughly washed with ion-exchanged water, dried, and heat-treated at 700 °C to obtain a primary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle diameter became 6 μm to obtain a carbonaceous material (13) with a specific surface area of 1921 m 2 / g, an average pore diameter of 1.83 nm, and a potassium element content of 12 ppm. In addition, using the carbonaceous material (13), the same operations as in Example 1 were performed to prepare an electrode composition (13), a polarizable electrode (13), and an electric double layer capacitor (13).

[0123] [Comparative Example 8] The same operation as in Comparative Example 4 was performed to obtain a primary activated granular activated carbon with a specific surface area of 2098 m 2 / g, an average pore diameter of 1.96 nm, and a potassium element content of 14107 ppm. Then, using hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water), pickling was performed at a temperature of 85 °C for 30 minutes. Then, in order to remove the remaining acid, it was thoroughly washed with ion-exchanged water, dried, and heat-treated at 700 °C to obtain a primary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle diameter became 6 μm to obtain a carbonaceous material (14) with a specific surface area of 2107 m 2 / g, an average pore diameter of 1.96 nm, and a potassium element content of 6 ppm. In addition, using the carbonaceous material (14), the same operations as in Example 1 were performed to prepare an electrode composition (14), a polarizable electrode (14), and an electric double layer capacitor (14).

[0124] [Comparative Example 9] The same operation as in Comparative Example 4 was performed to obtain a specific surface area of 2200 m 2 / g, a primary activated granular activated carbon with an average pore diameter of 2.07 nm and a potassium element content of 15664 ppm. Then, hydrochloric acid (concentration: 0.5 equivalent, diluent: ion-exchanged water) was used for pickling at a temperature of 85 °C for 30 minutes. Then, in order to remove the remaining acid, it was thoroughly washed with ion-exchanged water, dried, and heat-treated at 700 °C to obtain a primary washed granular activated carbon. The granular activated carbon was finely pulverized until the average particle size became 6 μm, and a specific surface area of 2220 m 2 / g, a carbonaceous material (15) with an average pore diameter of 2.07 nm and a potassium element content of 13 ppm. In addition, using the carbonaceous material (15), the electrode composition (15), the polarizable electrode (15), and the electric double layer capacitor (15) were produced in the same manner as in Example 1.

[0125] The various physical properties of the carbonaceous materials (1) to (15) obtained by the above-described operations were measured according to the above method. In addition, ratios A to C were calculated. The results are shown in Tables 1 and 2. In addition, various measurements were also performed on the electric double layer capacitors (1) to (15) obtained by the above-described operations. The results are shown in Table 3. [Table 1] [Table 2] [Table 3]

[0126] <Evaluation of the Initial Performance and Performance after the Durability Test of the Electric Double Layer Capacitor> As an evaluation of the performance of the electric double layer capacitor, in the case of conducting a durability test, generally, the capacity and resistance are evaluated at room temperature (25 °C) before and after the accelerated test, and the changes are measured. However, in the evaluation at room temperature, in order to confirm the deterioration phenomenon, a long-term test is required. Therefore, by evaluating the capacity and resistance at low temperature, the deterioration phenomenon can be compared and confirmed earlier compared to the case of evaluating at room temperature.

[0127] In particular, it is considered that when comparing the measurements at low temperature, since it is at low temperature, the viscosity of the electrolyte increases, and the deterioration of the electrode material, the electrode interface, and / or the electrolyte can be significantly reflected by the evaluation of the capacity, resistance, etc. From this point of view, in the present invention, in order to clearly compare and study the deterioration phenomenon, a durability test (performed for a specified time at a load of 60 °C and 3 V) is carried out, and the subsequent deterioration state is compared with the evaluation at -30 °C as the center.

[0128] As shown in Table 3, among Examples 1 to 6, the electric double layer capacitors (1) to (6) respectively fabricated using the polarizable electrodes (1) to (6) of the carbonaceous material of the present invention have higher electrostatic capacitance per unit volume after the durability test at 25°C and -30°C than the electric double layer capacitors (7) to (15) fabricated using the carbonaceous materials (7) to (15) of Comparative Examples 1 to 9, and the capacitance retention rates also show good values.

[0129] Hereinafter, the results obtained in the examples and comparative examples will be described with reference to the drawings.

[0130] Figure 6 To represent the relationship between the specific surface area of the carbonaceous material and the ratio of the pore volume of micropores having a pore diameter of 1 to 2 nm to the total pore volume. In the case of gas-activated activated carbon, with the progress of activation, an increase in specific surface area and an expansion of pore diameter are achieved. However, as Figure 6 shown, in Examples 1 to 6 where secondary activation and secondary washing were performed after the first washing, compared with Comparative Examples 4 to 9 fabricated by a general manufacturing method (ordinary activation) with only one activation, the ratio of the pore volume of 1 to 2 nm in the total pore volume was increased with a lower specific surface area.

[0131] Figure 7 To represent the relationship between the average pore diameter of the carbonaceous material and the electrostatic capacitance per unit volume of the carbonaceous material in the measurement at -30°C before and after the durability test. In addition, Figure 8 To represent the relationship between the average pore diameter of the carbonaceous material and the capacitance retention rate in the measurement at -30°C after the durability test.

[0132] As Figure 7 and Figure 8 shown, in Examples 1 to 6 where the average pore diameter is included in the range of 1.84 to 2.05 nm, the initial electrostatic capacitance per unit volume (electrostatic capacitance before the durability test) is approximately the same, but the electrostatic capacitance retention rate after the durability test is high, and a high electrostatic capacitance per unit volume is also shown after the durability test. On the other hand, as in Comparative Example 1, when the average pore diameter is less than 1.85 nm, although the initial electrostatic capacitance is high, the electrostatic capacitance after the durability test is low and the capacitance retention rate decreases. In addition, as can be seen from Comparative Examples 2 and 3, when the average pore diameter is greater than 2.05 nm, although the capacitance retention rate is high, the initial electrostatic capacitance is low, and thus the electrostatic capacitance per unit volume after the durability test also becomes a low value.

[0133] Figure 9The relationship between the proportion (proportion B) of the pore volume of micropores with a pore diameter of 1 to 2 nm, measured by the MP method, in the total pore volume of a carbonaceous material, and the electrostatic capacitance per unit volume of the carbonaceous material in the measurement at -30°C before and after the durability test. In addition, Figure 10 The relationship between the proportion (proportion B) of the pore volume of micropores with a pore diameter of 1 to 2 nm, measured by the MP method, in the total pore volume of a carbonaceous material, and the capacitance retention rate in the measurement at -30°C after the durability test.

[0134] As Figure 9 and Figure 10 shown, in Examples 1 to 6 where proportion B is in the range of 10 to 20%, the initial electrostatic capacitance (electrostatic capacitance before the durability test) is high. In addition, the decrease in electrostatic capacitance during the durability test is small, so the capacitance retention rate is high. On the other hand, as can be seen from Comparative Example 1, when proportion A is less than 10%, the capacity decrease after the durability test is significant and the capacitance retention rate deteriorates. Also, as in Comparative Examples 2 and 3, when proportion A is higher than 20%, the capacitance retention rate is high, but the initial electrostatic capacitance is low.

[0135] As described above, for the electric double-layer capacitor which is a preferred embodiment of the electrochemical device of the present invention, the decrease in the initial capacity accompanied by pore expansion is suppressed, and sufficient electrostatic capacitance can be maintained even after the durability test. Even in the low-temperature region, sufficient electrostatic capacitance can be maintained. Therefore, even in a case where deterioration is promoted such as in a cold region, sufficient performance can be exhibited.

[0136] In summary, if the carbonaceous material of the present invention is used as an electrode active material for an electrochemical device in an electrode, an electrochemical device with a high electrostatic capacitance per unit volume and excellent durability can be obtained.

[0137] Explanation of reference numerals 1 Electrode composition 2 Conductive binder 3 Etched aluminum foil 4 Tab 5 Sealing material 6 Polarizable electrode 7 Outer packaging sheet 8 Electric double-layer capacitor.

Claims

1. Carbonaceous material, wherein, The BET specific surface area is 1500 to 1900 m 2 / g, The average pore diameter at a relative nitrogen pressure P / P0 = 0.93 in the nitrogen adsorption isotherm measured at a temperature of 77.4K is 1.84 to 2.05 nm. The proportion of the pore volume of pores with a pore diameter of less than 3 nm measured by the BJH method in the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 65 to 90%, and the proportion of the pore volume of pores with a pore diameter of 1 to 2 nm measured by the MP method in the total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 10 to 20%.

2. The carbonaceous material according to claim 1, wherein, The proportion of the pore volume of pores with a pore diameter of 1 to 2 nm measured by the MP method in the total micropore volume measured by the MP method is 10 to 22%.

3. The carbonaceous material according to claim 1, wherein, The total pore volume calculated from the nitrogen adsorption amount at a relative pressure P / P0 = 0.93 in the nitrogen adsorption isotherm is 0.7 to 1.0 cm 3 / g.

4. The carbonaceous material according to claim 1, wherein, The powder packing density when compressed under a pressure of 12 kN is 0.60 to 0.73 g / cm 3 .

5. The carbonaceous material according to claim 1, wherein, The carbonaceous material is a material based on a carbon precursor derived from plants.

6. The carbonaceous material according to claim 5, wherein, The carbon precursor derived from plants is derived from coconut shells.

7. The carbonaceous material according to claim 1, wherein, The average particle size is 2 μm or more and 30 μm or less.

8. The carbonaceous material according to claim 1, wherein, The potassium element content is 0 ppm or more and 500 ppm or less.

9. An electrode active material for an electrochemical device, which is formed of the carbonaceous material according to any one of claims 1 to 8.

10. A method for producing the carbonaceous material according to any one of claims 1 to 8. The method is a method for obtaining a carbonaceous material by carbonizing a carbon precursor, performing primary activation using an activating gas containing water vapor, performing washing, and performing secondary activation using an activating gas containing water vapor.

11. An electrode for an electrochemical device, which contains the electrode active material for an electrochemical device according to claim 9.

12. An electrochemical device, which includes the electrode for an electrochemical device according to claim 11.

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