Carbonaceous material, electrode material, electrode, power storage device, and method for producing carbonaceous material

Abstract

The present disclosure relates to a plant-derived carbonaceous material having a BET specific surface area of 1000 m2 / g or more and an oxygen desorption amount of 1.1 mass% or more according to thermal desorption spectroscopy from 1200°C to 2500°C.

Description

Carbonaceous material, electrode material, electrode, electricity storage device, and method for producing carbonaceous material

[0001] The present disclosure relates to a plant-derived carbonaceous material, an electrode material, an electrode, an electricity storage device, and a method for producing the carbonaceous material.

[0002] Carbonaceous materials are used in electrochemical devices such as nonaqueous electrolyte batteries (e.g., lithium-ion secondary batteries, sodium-ion secondary batteries), electric double-layer capacitors, and lithium-ion capacitors, and carbonaceous materials with properties suited to their applications are in demand. For example, electric double-layer capacitors, which are one type of electrochemical device, utilize a capacity (electric double-layer capacity) obtained solely from the physical adsorption and desorption of ions without involving a chemical reaction, and therefore have superior output and life characteristics compared to batteries. Due to their excellent properties, electric double-layer capacitors have been developed in a variety of applications, including backing up various memories, generating electricity from natural energy, and storing power sources such as UPS (Uninterruptible Power Supply). In recent years, electric double-layer capacitors have attracted attention as auxiliary power sources for electric vehicles (EVs) and hybrid vehicles (HVs), and for storing regenerative energy, due to their excellent properties and the fact that they are an urgent solution to environmental issues.

[0003] Such on-vehicle electric double layer capacitors are required to have high durability, and for example, as carbonaceous materials used in electric double layer capacitors, modified activated carbon (Patent Document 1) in which the BET specific surface area, hydrogen content / carbon content, amount of oxygen in the framework, etc. are adjusted to fall within specific ranges for the purpose of suppressing gas generation during charging and discharging, and carbonaceous materials (Patent Document 2) in which the silicon content, the total amount of surface functional groups, and the pore volume are adjusted to fall within predetermined ranges have been reported.

[0004] Furthermore, with the demand for electrochemical devices such as electric double layer capacitors, the use of plant waste such as vegetables and grains as raw materials has been considered. Patent Document 3 discloses a production method for obtaining activated carbon for electric double layer capacitors having a silicon content of 1% by weight or less by using plant-derived raw materials, carbonizing the raw materials at 800°C to 1400°C, and then treating the raw materials with an acid or alkali. Patent Document 4 discloses obtaining activated carbon for electric double layer capacitors with improved crystallinity by using plant-derived raw materials and increasing the intensity of the diffraction peak of the (002) plane obtained by powder X-ray diffraction.

[0005] International Publication No. 2018-207769 International Publication No. 2021-131907 Japanese Patent No. 5533912 Japanese Patent No. 6015823

[0006] Although various carbonaceous materials have been reported as electrode materials to date, the present inventors have examined conventionally known carbonaceous materials and found that further improvements are necessary in order to obtain electrodes for electricity storage devices that have sufficient capacitance at low current densities and are capable of exhibiting sufficient charge / discharge performance even at high current densities.

[0007] Therefore, an object of the present disclosure is to provide a carbonaceous material that has sufficient capacitance when the current density is low and that can be used to provide an electricity storage device or the like that has high rate characteristics and cycle characteristics, and a method for producing the same.

[0008] That is, the present disclosure includes the following preferred embodiments: [1] A BET specific surface area of ​​1000 m ２ [1] A carbonaceous material derived from a plant, having an oxygen desorption amount of 1.1 mass% or more at 1200°C to 2500°C in a temperature programmed desorption method. [2] The carbonaceous material according to [1], having an oxygen element content of 4 to 12 mass%. [3] The carbonaceous material according to [1] or [2], having a hydrogen element content of 1 mass% or less. [4] The carbonaceous material according to [1] or [2], having an R value of 1.15 to 1.40 in a Raman spectrum, and a half width of the G band of 70 cm －１ [5] The carbonaceous material according to any one of [1] to [3], wherein the BET specific surface area is 2500 m or more. ２ / g or less. [6] The carbonaceous material according to any of [1] to [5], wherein the amount of oxygen desorption at 1200°C to 2500°C in a temperature programmed desorption method is 10% by mass or less. [7] The carbonaceous material according to [1], which is a carbonaceous material derived from grain husks. [8] An electrode material comprising the carbonaceous material according to any of [1] to [7]. [9] An electrode comprising the electrode material according to [8].

[10] An electricity storage device comprising the electrode according to [9].

[11] A method for producing the carbonaceous material according to any of [1] to [7], comprising the steps of: carbonizing a plant-derived raw material at 320°C to 700°C in an inert gas atmosphere to obtain a char; subjecting the char to an alkali washing treatment to obtain a carbonaceous material precursor; and subjecting the carbonaceous material precursor to an activation treatment at 800°C or higher to obtain a carbonaceous material.

[12] The manufacturing method described in

[11] , wherein the plant-derived raw material is a raw material derived from grain husks.

[0009] According to the carbonaceous material of the present disclosure, it is possible to provide a carbonaceous material that can provide an electricity storage device or the like that has both high rate characteristics and cycle characteristics, and a method for producing the same.

[0010] FIG. 1 is a diagram illustrating the configuration of an electric double layer capacitor used to evaluate the carbonaceous materials of Examples and Comparative Examples.

[0011] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0012] The carbonaceous material of the present disclosure has a BET specific surface area of ​​1000 m ２ / g or more, and the amount of oxygen desorption at 1200°C to 2500°C as measured by temperature programmed desorption is 1.1 mass% or more.

[0013] The carbonaceous material of the present disclosure has a BET specific surface area of ​​1000 m ２ The BET specific surface area of ​​the carbonaceous material is preferably 1200 m ２ / g or more, more preferably 1300m ２ The BET specific surface area is preferably 2500 m / g or more.２ / g or less, more preferably 2400m ２ / g or less, more preferably 2300m ２ / g or less. Generally, when the same raw material is treated in the same way, the capacitance per unit area is constant. ２ If the average pore diameter is less than 1 / g, it is difficult to sufficiently increase the capacitance per unit mass, particularly when the current density is low. Furthermore, since the average pore diameter is relatively small, resistance, which is thought to be due to the diffusion resistance of electrolyte ions in the pores, tends to increase during charging and discharging under a large current. On the other hand, from the viewpoint of capacitance per volume, in order to increase the bulk density of an electrode manufactured using the carbonaceous material and increase capacitance per volume, a BET specific surface area of ​​2500 m is preferred. ２ In one embodiment, the BET specific surface area of ​​the carbonaceous material is preferably 1000 m ２ / g~2500m ２ / g, more preferably 1200m ２ / g~2400m ２ / g, more preferably 1300m ２ / g~2300m ２ The BET specific surface area of ​​the carbonaceous material can be calculated by the nitrogen adsorption method described in the examples below.

[0014] The carbonaceous material of the present disclosure has an oxygen desorption amount of 1.1 mass% or more between 1200°C and 2500°C as measured by temperature-programmed desorption. If the oxygen desorption amount is less than 1.1 mass%, the material cannot exhibit sufficient charge / discharge performance and has poor rate characteristics, particularly at high current densities, for reasons that are unclear. Furthermore, in this case, the cycle characteristics cannot be sufficiently improved. Oxygen desorption occurs when the carbonaceous material is gradually heated from room temperature. The oxygen desorbed at temperatures below 1200°C is believed to be derived primarily from oxygen compounds, such as lactones, phenols, and quinones, present on the surface of the carbonaceous material. The oxygen desorbed at temperatures above 1200°C is believed to be derived from oxygen compounds contained within the carbon or oxygen compounds bonded to metals. By measuring the oxygen desorption amount between 1200°C and 2500°C, the total amount of oxygen contained as such oxygen compounds can be quantified. From the viewpoints of cycle characteristics and rate characteristics, the amount of oxygen desorption from 1200°C to 2500°C is preferably 1.1 mass% to 10 mass%, more preferably 1.2 mass% to 7 mass%, even more preferably 1.3 mass% to 5 mass%, and even more preferably 1.3 mass% to 4.5 mass%. From the same viewpoint, the amount of oxygen desorption may be preferably 1.1 mass% or more, more preferably 1.2 mass% or more, and even more preferably 1.3 mass% or more. From the same viewpoint, the amount of oxygen desorption may be preferably 10 mass% or less, more preferably 7 mass% or more, even more preferably 5 mass% or more, and even more preferably 4.5 mass% or less.

[0015] The oxygen element that desorbs between 1200°C and 2500°C is presumed to be contained in the carbon skeleton as an ether skeleton or other structure, since it desorbs at high temperatures. Because ether skeletons have a high affinity for electrolytes, the inclusion of such a skeleton in the carbon skeleton is thought to increase the permeability of the electrolyte and to enable a high capacitance to be maintained, especially when a large current is passed through. Furthermore, when the amount of oxygen desorption between 1200°C and 2500°C is 1.1% by mass or more, the affinity between the ether skeleton and the electrolyte prevents dryout, thereby suppressing a decrease in capacitance and improving cycle characteristics.

[0016] The amount of oxygen desorption from the carbonaceous material of the present disclosure at 1200°C to 2500°C can be controlled within the above range by selecting a raw material with a high oxygen element content and adjusting the production conditions for the carbonaceous material described below, particularly the temperature and time of the carbonization step.

[0017] From the viewpoint of cycle characteristics, the carbonaceous material of the present disclosure preferably has an oxygen desorption amount below 1200°C in a temperature programmed desorption method of 9 mass % or less, more preferably 8 mass % or less, and even more preferably 7.5 mass % or less.

[0018] The carbonaceous material of the present disclosure is a plant-derived carbonaceous material. The plant that serves as the carbon source is not particularly limited, but examples include coconut shells (e.g., palm, coconut, salak, and bay palm), coffee beans, tea leaves, sugarcane, fruits (e.g., mandarin oranges and bananas), straw, broadleaf trees, coniferous trees, bamboo, and grain husks (e.g., rice husks, buckwheat husks, and wheat husks). Among these, grain husks are preferred as raw materials. Rice husks, in particular, contain large amounts of oxides such as silicic acid, calcium, and magnesium. Therefore, using rice husks as a raw material to produce a carbonaceous material facilitates adjusting the oxygen desorption amount in a temperature-programmed desorption method between 1200°C and 2500°C to a desired range of 1.1 mass% or more, making them suitable for use. Rice husk-derived carbonaceous materials are characterized by a high content of silicic acid compared to carbonaceous materials derived from other plants.

[0019] From the viewpoint of cycle characteristics and rate characteristics, the oxygen element content of the carbonaceous material is preferably 4 to 12 mass%, more preferably 4.5 to 11.5 mass%, and even more preferably 5 to 11 mass%. The oxygen element content and the hydrogen element content described later in the carbonaceous material of the present disclosure are values ​​calculated by elemental analysis, specifically, by the method described in the examples.

[0020] From the viewpoint of reducing resistance, the hydrogen element content of the carbonaceous material is preferably 1% by mass or less, more preferably 0.5% by mass or less. The lower limit of the hydrogen element content is not particularly limited, but is usually 0.2% by mass or more, and may be 0.3% by mass or more. That is, suitable ranges include 0.2 to 1% by mass and 0.3 to 0.5% by mass. When the hydrogen content is 1% by mass or less, the crystallinity is increased, which is thought to improve the electrical conductivity of the carbonaceous material itself, and the resistance tends to be reduced.

[0021] The carbonaceous material of the present disclosure preferably has an R value of 1.15 to 1.40 in a Raman spectrum. The R value is the value at 1360 cm in a Raman spectrum observed by laser Raman spectroscopy. －１ The peak intensity (I Ｄ ) and 1580 cm －１ The peak intensity (I Ｇ ) intensity ratio (R value = I Ｄ / I Ｇ ) where 1360 cm －１ The peak around 1580 cm is a Raman peak generally known as the D band, which is a peak caused by disorder and defects in the graphite structure. －１ The peak around 1360 cm is a Raman peak generally called the G band, which is a peak derived from the graphite structure. －１ The peak around 1345 cm －１ ~1375cm －１ , preferably 1350 cm －１ ~1370cm －１ It is observed in the range of 1580 cm －１ The peak around 1560 cm －１ ~1615cm －１ , preferably 1565 cm －１ ~1610cm －１ It is observed in the range of

[0022] The R value, which is the intensity ratio of these peaks, is related to the crystallinity of the carbonaceous material. If the crystallinity of the carbonaceous material is too high, the carbon edges will decrease due to the development of a graphite structure, resulting in fewer coordination sites for the electrolyte. This can lead to problems such as reduced characteristics at low temperatures and increased resistance. Furthermore, if the crystallinity of the carbonaceous material is too low, the amorphous content will increase, resulting in higher electrical resistance. This reduces the utilization efficiency of the electric double layer at the interface between the electrolyte and the electrode material. From the above perspectives, the R value is preferably 1.15 to 1.4, more preferably 1.20 to 1.35, and even more preferably 1.2 to 1.3. When the R value is within the above range, an electric double layer capacitor containing the carbonaceous material can maintain even higher capacitance and energy density over a long period of time, even when driven at a high voltage.

[0023] The carbonaceous material of the present disclosure preferably has a half-width of the G band in a Raman spectrum of 70 cm －１ The full width at half maximum of the G band is related to the amount of disorder and defects in the graphite structure contained in the carbonaceous material. When the full width at half maximum is equal to or greater than the lower limit shown below, the amount of disorder and defects in the graphite structure contained in the carbonaceous material becomes appropriate, and the carbon edges due to the development of the graphite structure do not become too numerous, thereby making it possible to increase the number of sites for electrolyte coordination. As a result, effects such as improved characteristics at low temperatures and reduced diffusion resistance are achieved. Furthermore, when the full width at half maximum is equal to or less than the upper limit shown below, the amount of disorder and defects in the graphite structure contained in the carbonaceous material becomes appropriate, preventing an excessive amount of amorphous matter, and making it possible to lower the electrical resistance. From these viewpoints, it is preferable to set the full width at half maximum to 1580 cm －１ The half-width of the peak (G band half-width) is 70 to 100 cm －１ and preferably 75 to 98 cm －１ , more preferably 80 to 95 cm －１ When the G-band half width is within the above range, an electric double layer capacitor containing the carbonaceous material can maintain a higher capacitance and energy density for a long period of time even when driven at a high voltage. The R value and the G-band half width in the Raman spectrum in the present invention are values ​​calculated by the method described in the Examples below.

[0024] The average particle size of the carbonaceous material of the present disclosure is not particularly limited and may be set appropriately depending on the application of the carbonaceous material. For example, when the carbonaceous material is used for an electric storage device such as an electric double layer capacitor, the average particle size of the carbonaceous material is preferably 1 to 15 μm, more preferably 2 to 10 μm. The average particle size is determined by measuring the particle size distribution of the carbonaceous material using a laser diffraction particle size distribution analyzer. ５０ )

[0025] The method for producing a carbonaceous material according to the present disclosure is not particularly limited as long as it can produce a carbonaceous material that satisfies the above characteristics. For example, the carbonaceous material can be produced by a production method including at least the following steps: (1) carbonizing a plant-derived raw material at 320°C to 700°C under an inert gas atmosphere to obtain a carbonized product (also referred to as the carbonization step); (2) subjecting the carbonized product to an alkali washing treatment to obtain a carbonaceous material precursor (also referred to as the alkali washing step); and (3) activating the carbonaceous material precursor at 800°C or higher to obtain a carbonaceous material (also referred to as the activation treatment step). The present invention also provides a method for producing a carbonaceous material that includes the above steps. The production method may further include steps other than those described above. For example, after the alkali washing step, a (a) heat treatment step may be performed before the activation treatment step, or after the activation treatment step, a (b1) crushing step and / or a (b2) classification step may be performed.

[0026] (1) Carbonization Step The carbonization step (1) is a step of carbonizing a plant-derived raw material at 320°C to 700°C under an inert gas atmosphere to obtain a carbonized product. Examples of the plant-derived raw material include the plant-derived raw materials described above. The plant-derived raw material is preferably a raw material derived from grain husks, and from the viewpoint of easy availability, more preferably a raw material selected from the group consisting of rice husks, buckwheat husks, and wheat husks, and even more preferably a raw material derived from rice husks.

[0027] A charcoal can be obtained by carbonizing a plant-derived raw material by heating it at 320°C to 700°C under an inert gas atmosphere. The carbonization temperature is preferably 330 to 700°C, more preferably 340 to 700°C, and even more preferably 350 to 700°C. When the carbonization temperature is below the above upper limit, the leaching of silicon compounds contained in the charcoal can be improved in the alkaline washing step described below. Furthermore, when the carbonization temperature is above the above lower limit, the generation of black liquor in the alkaline washing step can be reduced, facilitating wastewater treatment. Furthermore, when the carbonization temperature is lower than 320°C, it becomes difficult to achieve an oxygen desorption amount of 1.1% by mass or more from the carbonaceous material between 1200°C and 2500°C, and the rate characteristics and cycle characteristics of an electricity storage device using an electrode manufactured using the carbon material may not be obtained. If the carbonization temperature is higher than 700°C, crystallization proceeds during carbonization, while amorphous (easily activated) portions separate and grow. Subsequent activation generates relatively large voids, resulting in a low bulk density. Therefore, the bulk density of electrodes manufactured using the carbonaceous material tends to be low, resulting in a low capacitance per volume. Carbonization within a predetermined temperature range can improve the rate characteristics and cycle characteristics (durability) of an electricity storage device obtained using the carbonaceous material after cleaning, heat treatment, activation treatment, and pulverization, as described below. The carbonization time after reaching the desired temperature is preferably 30 to 120 minutes to ensure sufficient carbonization and maintain the leaching properties of the silicon compound in subsequent processes. The heating rate is preferably 2°C / min to 20°C / min to prevent the carbonization process from becoming too long and to suppress equipment deterioration.

[0028] The carbonization treatment can be carried out by calcining (carbonizing) the raw material carbon precursor at a specific temperature in an atmosphere of, for example, an inert gas such as nitrogen, carbon dioxide, helium, argon, carbon monoxide, or fuel exhaust gas, a mixed gas of these inert gases, or a mixed gas containing these inert gases as a main component and other gases.

[0029] As the furnace used for the carbonization treatment, various types of furnaces can be used, such as a rotary kiln, a fluidized bed furnace, a fixed bed furnace, a moving bed furnace, and a moving bed furnace, and both a continuous furnace in which raw materials are continuously charged and heat-treated products are removed, and a batch furnace in which this is done intermittently can be used. Any means capable of heating to a predetermined temperature can be used as the heating means, and electric heating, gas combustion heating, high-frequency induction heating, electrical heating, etc. can be used. Furthermore, these heating means can be used alone or in combination.

[0030] (2) Alkali Washing Step The alkali washing step is a step of subjecting the carbide to an alkali washing treatment to obtain a carbonaceous material precursor, and by washing the carbide obtained in the carbonization step with an alkaline solution, it is possible to remove silicon compounds and the like contained in the carbide. The alkali washing can be performed by bringing the carbide obtained in the carbonization step into contact with an alkaline solution (also referred to as a washing liquid), and can be performed, for example, by immersing the carbide in the washing liquid. Examples of the washing liquid include an aqueous sodium hydroxide solution, an aqueous potassium hydroxide solution, and an aqueous lithium hydroxide solution, and sodium hydroxide solution is preferred because of its ease of availability.

[0031] The temperature of the alkaline solution when alkaline washing is performed is not particularly limited, but is preferably 65° C. to 110° C., more preferably 70° C. to 105° C., and even more preferably 80° C. to 100° C. If the temperature of the alkaline solution is within the above range, the silicon element concentration in the carbide can be reduced in a short period of time and can be performed safely, which is preferable.

[0032] The alkali concentration of the cleaning solution is not particularly limited and may be adjusted appropriately depending on the type of cleaning solution used. The alkali concentration of the cleaning solution is preferably 0.01N or more, more preferably 0.03N or more. The upper limit of the alkali concentration is preferably 10N or less, more preferably 5N or less. If the alkali concentration is too low, it will be necessary to increase the number of washings or the washing time to remove the silicon compound, and if it is too high, the amount of residual alkali components will increase, and from the viewpoint of safety, it is preferable to set the concentration within the above range.

[0033] The pH of the cleaning solution is not particularly limited and may be adjusted appropriately depending on the type of cleaning solution used, but a pH of 11 or higher is preferred from the viewpoint of reducing the number of cleanings or cleaning time.

[0034] When immersing the carbide in the cleaning solution, the mass ratio between the cleaning solution and the carbide may be adjusted appropriately depending on the type, concentration, temperature, packing density, and other physical properties of the cleaning solution used. The mass of the carbide to be immersed relative to the mass of the cleaning solution is preferably 2 mass% or more, more preferably 3 mass% or more. The upper limit of the mass ratio is preferably 50 mass% or less, more preferably 30 mass% or less. Within the above range, excessive energy is not required to heat the cleaning solution, and a sufficient cleaning effect can be obtained, which is preferable.

[0035] The atmosphere in which the alkaline cleaning treatment is carried out is not particularly limited and may be appropriately selected depending on the cleaning method used. In the present invention, the alkaline cleaning treatment is usually carried out in the air.

[0036] The method for subjecting the carbide to alkaline washing treatment is not particularly limited as long as it allows the carbide to come into contact with the washing liquid, preferably as long as it allows the carbide to be immersed in the washing liquid. It may be a method in which washing liquid is continuously added, allowed to remain for a predetermined time, and immersed while removing the liquid, or a method in which the carbide is immersed in the washing liquid, allowed to remain for a predetermined time, drained, and then new washing liquid is added, and the immersion-draining process is repeated. Furthermore, it may be a method in which all or part of the washing liquid is renewed. Furthermore, the washing liquid may be stirred during immersion.

[0037] The time for immersing the carbide in the cleaning solution can be adjusted appropriately depending on the cleaning solution used, the treatment temperature, the immersion conditions, the ash content of the carbide, etc. When the ash content of the carbide is higher than 20%, from the viewpoint of sufficiently reducing the silicon compounds in the carbide, it is preferable to stir the carbide in the cleaning solution for 20 minutes or more, and more preferably 30 minutes or more. From the viewpoint of productivity, the immersion time is preferably 15 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less. Stirring may or may not be performed during immersion.

[0038] After washing the carbonized material with an alkali, the carbonized material may be washed with water to remove any remaining washing liquid. The pH of the water after washing is not particularly limited.

[0039] (a) Heat Treatment Step Before the activation treatment step (3) described below, a heat treatment step may be performed in which the carbonaceous material precursor after the alkali cleaning treatment is heat-treated under an inert gas atmosphere. By performing the heat treatment step, volatile components contained in the carbonaceous material precursor can be removed and the carbon structure can be developed. The heat treatment temperature is preferably 800°C to 1200°C, more preferably 900°C to 1100°C. When the heat treatment temperature is equal to or higher than the lower limit, the carbon structure can be sufficiently developed. Furthermore, when the heat treatment temperature is equal to or lower than the upper limit, pore shrinkage is unlikely to occur, and the activation time described below does not become longer than necessary. The heat treatment time after reaching the desired temperature is preferably 10 minutes to 120 minutes from the viewpoint of developing the carbon structure and preventing excessive pore shrinkage. The temperature rise rate is preferably 2°C / min to 20°C / min from the viewpoint of preventing the heat treatment step from becoming too long and suppressing equipment deterioration.

[0040] The heat treatment step is preferably carried out in an inert gas atmosphere, or in an atmosphere of a gas generated from activated carbon while blocking oxygen or air. Examples of inert gases used in the heat treatment include nitrogen gas, argon gas, and helium gas. These gases may be used alone or as a mixed gas of two or more.

[0041] The furnace used for heat treatment can be any of various types, such as a rotary kiln, fluidized bed furnace, fixed bed furnace, moving bed furnace, or moving bed furnace. Both continuous furnaces, which continuously charge raw materials and remove heat-treated products, and batch furnaces, which do so intermittently, can be used. Any heating means capable of heating to a predetermined temperature can be used, including electric heating, gas combustion heating, high-frequency induction heating, and electric current heating. These heating means can be used alone or in combination.

[0042] (3) Activation Treatment Step The carbonaceous material of the present disclosure can be produced, for example, by subjecting a carbonaceous material precursor that has been subjected to an alkali washing treatment to an activation treatment, optionally followed by a heat treatment. Activation treatment is a process that forms pores on the carbon surface to convert the carbonaceous material into a porous carbonaceous material, thereby producing a carbonaceous material (activated carbon) with a large specific surface area and pore volume. If activation treatment is not performed, the resulting carbonaceous material will have an insufficient specific surface area or pore volume, making it difficult to ensure a sufficiently high initial capacity when used as an electrode material, and the carbonaceous material of the present disclosure cannot be obtained. Activation treatment can be performed by a method commonly used in the field, and two main types of treatment methods can be mentioned: gas activation treatment and chemical activation treatment.

[0043] Known examples of gas activation treatments include heating a carbon precursor in the presence of water vapor, carbon dioxide, air, oxygen, combustion gas, or a mixture of these. Also known examples of chemical activation treatments include mixing an activator, such as zinc chloride, calcium chloride, phosphoric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, magnesium hydroxide, or calcium hydroxide, with a carbon precursor and heating the mixture in an inert gas atmosphere. In the manufacturing method of the present disclosure, gas activation treatment is preferred because chemical activation requires a step of removing the remaining chemical, which makes the manufacturing method complicated.

[0044] When steam activation is employed 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 progressing the activation, and the partial pressure of the steam in this case is preferably in the range of 10 to 60%. When the partial pressure of steam is 10% or more, the activation tends to proceed sufficiently, and when it is 60% or less, a rapid activation reaction is suppressed and the reaction is easily controlled.

[0045] The total amount of activation gas supplied in steam activation is preferably 50 to 10,000 parts by mass, more preferably 100 to 5,000 parts by mass, and even more preferably 200 to 3,000 parts by mass, relative to 100 parts by mass of the carbon precursor. When the total amount of activation gas supplied is within the above range, the activation reaction can proceed more efficiently.

[0046] The specific surface area and pore volume of activated carbon can be controlled by changing the activation method and conditions. For example, when activated carbon is obtained by steam activation, they can be controlled by the heating temperature and time. In steam activation, the specific surface area and pore size of the resulting activated carbon tend to be smaller when the heating temperature is low and tend to be larger when the heating temperature is high. 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, preferably 800 to 1000°C. In addition, the heating time and temperature-rise time are not particularly limited and may be appropriately determined depending on the heating temperature, the desired specific surface area of ​​the activated carbon, and the like.

[0047] When carbon dioxide activation is employed as the gas activation treatment, the treatment temperature is preferably 800 to 1000°C, more preferably 800 to 900°C. In carbon dioxide activation, the same inert gas as that used in the carbonization treatment, water vapor, etc. may be mixed. In addition, the heating time and temperature rise time are not particularly limited and may be appropriately determined depending on the heating temperature, the specific surface area of ​​the desired activated carbon, etc.

[0048] The activation treatment may be carried out once or twice or more times as required. The conditions for the second or subsequent activation treatments are not limited, and similarly to the primary activation treatment, the heating temperature, heating time, etc. may be appropriately determined depending on the specific surface area of ​​the desired activated carbon.

[0049] (b1) Pulverization Step The method for producing a carbonaceous material according to the present disclosure may, as necessary, include a (b1) pulverization step and / or a (b2) classification step, described below, after the (3) activation treatment step. The pulverization step is a step for controlling the shape and particle size of the finally obtained carbonaceous material to a desired granular shape and particle size. The average particle size of the carbonaceous material of the present invention is not particularly limited, but when used, for example, in an electric double layer capacitor, the average particle size of the carbonaceous material is preferably 1 to 15 μm, more preferably 2 to 10 μm. In this case, it is preferable to perform pulverization in the pulverization step so as to obtain a carbonaceous material having an average particle size within the above range.

[0050] The crusher used for crushing is not particularly limited, and for example, known crushers such as a cone crusher, a double roll crusher, a disc crusher, a rotary crusher, a ball mill, a centrifugal roll mill, a ring roll mill, a centrifugal ball mill, and a jet mill can be used alone or in combination.

[0051] (b2) Classification Step The method for producing a carbonaceous material of the present invention may optionally include a classification step (b2) after the activation treatment step (3). For example, by performing a classification step that removes particles with a particle diameter of 1 μm or less, it is possible to obtain carbonaceous material particles with a narrow particle size distribution. Removal of such fine particles makes it possible to reduce the amount of binder used in constructing an electrode. The classification method is not particularly limited, and examples thereof include classification using a sieve, wet classification, and dry classification. Examples of wet classifiers include classifiers that utilize the principles of gravity classification, inertia classification, hydraulic classification, centrifugal classification, etc. Examples of dry classifiers include classifiers that utilize the principles of sedimentation classification, mechanical classification, centrifugal classification, etc. From the standpoint of economy, it is preferable to use a dry classifier.

[0052] The (b1) pulverization step and the (b2) classification step may be performed as separate steps, or may be performed at the same time using a single device. For example, pulverization and classification can be performed using a jet mill equipped with a dry classification function. When performed as separate steps, a device having a pulverizer and a classifier independent from each other can be used. In this case, pulverization and classification can be performed continuously, or pulverization and classification can be performed discontinuously.

[0053] The carbonaceous material of the present disclosure can be suitably used as an electrode active material in electricity storage devices such as electric double layer capacitors, lithium ion capacitors, and lithium ion secondary batteries. Use of the carbonaceous material of the present disclosure can result in an electricity storage device with excellent cycle characteristics (durability) and rate characteristics. Accordingly, in one embodiment of the present disclosure, it is possible to provide an electrode material containing the carbonaceous material of the present disclosure, an electrode containing the electrode material, and an electricity storage device containing the electrode. In one embodiment of the present disclosure, it is possible to provide an electrode for an electric double layer capacitor containing the carbonaceous material of the present disclosure, and it is also possible to provide an electric double layer capacitor including the electrode.

[0054] The electrode material of the present disclosure includes the carbonaceous material of the present disclosure. The electrode material can be produced by a manufacturing process common in the art for producing electrode materials, such as a process of kneading the carbonaceous material of the present disclosure as a raw material with components such as a conductivity imparting agent, a binder, and a solvent, and a process of applying the resulting kneaded mixture to a support and drying it. Furthermore, the electrode (e.g., an electrode for an electric double layer capacitor) can be produced using the electrode material. An example of the manufacturing process includes a process of adding a solvent to the electrode material as a raw material to prepare a paste, applying the paste to a current collector such as aluminum foil or aluminum mesh, and then drying and removing the solvent, and placing the paste in a mold for press molding.

[0055] Examples of the conductivity-imparting agent that can be used include acetylene black and Ketjen black. Examples of the binder that can be used include fluorine-based polymer compounds such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum pitch, and phenolic resin. Examples of the solvent that can be used include water, alcohols such as methanol and ethanol, saturated hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene, xylene, and mesitylene, ketones such as acetone and ethyl methyl ketone, esters such as methyl acetate and ethyl acetate, amides such as N,N-dimethylformamide and N,N-diethylformamide, and cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone.

[0056] The present disclosure also provides an electric storage device (e.g., an electric double layer capacitor) that includes the electrodes. Electric storage devices, such as electric double layer capacitors, generally comprise electrodes, an electrolyte, and a separator, with the separator disposed between a pair of electrodes. Examples of the electrolyte include an electrolytic solution obtained by dissolving an amidine salt in an organic solvent such as propylene carbonate, ethylene carbonate, or methyl ethyl carbonate; an electrolytic solution obtained by dissolving a quaternary ammonium salt of perchloric acid; an electrolytic solution obtained by dissolving a tetrafluoroborate or hexafluorophosphate salt of an alkali metal such as quaternary ammonium or lithium; and an electrolytic solution obtained by dissolving a quaternary phosphonium salt. Examples of the separator include a nonwoven fabric, cloth, or microporous film primarily composed of cellulose, glass fiber, or a polyolefin such as polyethylene or polypropylene. Electric storage devices, such as electric double layer capacitors, can be manufactured by arranging these main components using methods commonly used in the art.

[0057] An electric storage device such as an electric double layer capacitor manufactured using the carbonaceous material of the present disclosure has excellent cycle characteristics (durability) and rate characteristics by appropriately controlling the amount of oxygen desorption.

[0058] 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.

[0059] The physical properties in the examples were measured according to the methods described below.

[0060] (Nitrogen adsorption isotherm, BET specific surface area) Analysis was performed using a gas adsorption measurement device ("Autosorb3B" manufactured by Quantachrome). A carbonaceous material was used as a measurement sample, and a nitrogen adsorption isotherm showing the relationship between the relative pressure of nitrogen gas and the amount of nitrogen gas adsorbed at 77 K was obtained. From this nitrogen adsorption isotherm, the BET specific surface area was calculated from the nitrogen adsorption volume at a relative pressure of 0.05 to 0.10.

[0061] (Analysis of oxygen element content and hydrogen element content) Elemental analysis was carried out based on the inert gas fusion method using an oxygen, nitrogen and hydrogen analyzer ("EMGA-930" manufactured by Horiba Ltd.). The detection method of this device was oxygen: inert gas fusion-non-dispersive infrared absorption (NDIR), hydrogen: inert gas fusion-non-dispersive infrared absorption (NDIR), and calibration was performed using a Sn capsule and TiH ２ (H standard sample), SS-3 and SS-10 (O standard sample). As a pretreatment, 5 mg of a carbonaceous powder sample dried at 250°C for approximately 10 minutes was placed in a Sn capsule and measured after degassing for 30 seconds in an elemental analyzer. Three specimens were analyzed in the test, and the average values ​​were used as the analytical values ​​for the oxygen element content and hydrogen element content. When measuring the oxygen element content, the amount of oxygen desorption during heating from 1200°C to 2500°C was simultaneously measured.

[0062] (Raman Spectrum) Using a Raman spectrometer ("Laser Raman Microscope Ramanforce" manufactured by Nanophoton Inc.), the measurement target particles, which are carbonaceous materials, were set on the observation stage, the magnification of the objective lens was set to 20 times, the particles were focused, and measurements were taken while irradiating with argon ion laser light. The details of the measurement conditions are as follows. The G-band half width was determined from the spectrum obtained under the above measurement conditions by determining the G-band (1590 cm －１ The R value is the intensity ratio I of each peak between the D band and the G band. Ｄ / I Ｇ(D band peak intensity / G band peak intensity) Wavelength of argon ion laser light: 532 nm Laser power on sample: 100-300 W / cm ２ Resolution: 5-7cm －１ Measurement range: 150-4000 cm －１ Measurement mode: XY Averaging Exposure time: 20 seconds Number of integrations: 2 Peak intensity measurement: Baseline correction Polynom-3rd order automatic correction Peak search & fitting processing Gauss Lorentz

[0063] (Particle size distribution) The particle size distribution of the carbonaceous material was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, "SALD-200V"). The average particle size in this specification is the particle size (D ５０ ) is shown.

[0064] Example 1: A charcoal was obtained by heating the husks of Akita Komachi rice grown in Akita Prefecture at 350°C for 1 hour under a nitrogen atmosphere. 15 g of the obtained charcoal was immersed in 300 ml of a sodium hydroxide aqueous solution (concentration: 1.0 N) at a temperature of 80°C for 10 hours, after which the charcoal was removed, washed with distilled water, and dried. The charcoal was then heated at 900°C for 1 hour under a nitrogen atmosphere to remove volatiles. The charcoal was then activated in the presence of carbon dioxide at 900°C until an activation yield of 44% was achieved, thereby obtaining a carbonaceous material. The carbonaceous material was pulverized to an average particle size of 7.5 to 9.0 μm, and a BET specific surface area of ​​1326 m was obtained. ２ / g of carbonaceous material (1) was obtained. Various physical properties of the obtained carbonaceous material (1) were measured. The results are shown in Table 1.

[0065] (Example 2) A charcoal was obtained by heating the husks of Akita Komachi rice grown in Akita Prefecture at 500°C for 1 hour in a nitrogen atmosphere. The charcoal was then alkali-treated, washed with water, dried, and devolatilized in the same manner as in Example 1, and then heated at 900°C in the presence of carbon dioxide to activate the charcoal until the activation yield reached 40%, thereby obtaining a carbonaceous material. The carbonaceous material was then pulverized to an average particle size of 7.5 to 9.0 μm, and the BET specific surface area was 1346 m. ２ / g of carbonaceous material (2) was obtained. Various physical properties of the obtained carbonaceous material (2) were measured. The results are shown in Table 1.

[0066] (Example 3) A charcoal was obtained by heating the husks of Akita Komachi rice grown in Akita Prefecture at 700°C for 1 hour in a nitrogen atmosphere. The charcoal was then alkali-treated, washed with water, dried, and devolatilized in the same manner as in Example 1, and then heated at 900°C in the presence of carbon dioxide to activate the charcoal until the activation yield reached 46%, thereby obtaining a carbonaceous material. The carbonaceous material was then pulverized to an average particle size of 7.5 to 9.0 μm, and the BET specific surface area was 1,331 m. ２ / g of carbonaceous material (3) was obtained. Various physical properties of the obtained carbonaceous material (3) were measured. The results are shown in Table 1.

[0067] Example 4 A charcoal was obtained by heating the husks of Akita Komachi rice grown in Akita Prefecture at 600°C for 1 hour in a nitrogen atmosphere. The charcoal was then alkali-treated, washed with water, dried, and devolatilized in the same manner as in Example 1, and then heated at 900°C in the presence of carbon dioxide to activate the charcoal until the activation yield reached 44%, thereby obtaining a carbonaceous material. The carbonaceous material was then pulverized to an average particle size of 7.5 to 9.0 μm, and the BET specific surface area was 1027 m. ２ / g of carbonaceous material (4) was obtained. Various physical properties of the obtained carbonaceous material (4) were measured. The results are shown in Table 1.

[0068] Comparative Example 1: A charcoal was obtained by heating the husks of Akita Komachi rice grown in Akita Prefecture at 300°C for 1 hour in a nitrogen atmosphere. The charcoal was then alkali-treated, washed with water, dried, and volatiles removed in the same manner as in Example 1, and then activated by heating at 900°C in the presence of carbon dioxide until the activation yield reached 43%, thereby obtaining a carbonaceous material. The carbonaceous material was then pulverized to an average particle size of 7.5 to 9.0 μm, and the BET specific surface area was 1256 m. ２ / g of carbonaceous material (5) was obtained. Various physical properties of the obtained carbonaceous material (5) were measured. The results are shown in Table 1.

[0069] Comparative Example 2: A charcoal was obtained by heating the husks of Akita Komachi rice grown in Akita Prefecture at 700°C for 1 hour in a nitrogen atmosphere. The charcoal was then alkali-treated, washed with water, dried, and volatiles removed in the same manner as in Example 1, and then heated at 900°C in the presence of carbon dioxide to activate the charcoal until the activation yield reached 80%, thereby obtaining a carbonaceous material. The carbonaceous material was then pulverized to an average particle size of 7.5 to 9.0 μm, and the BET specific surface area was 850 m. ２ / g of carbonaceous material (6) was obtained. Various physical properties of the obtained carbonaceous material (6) were measured. The results are shown in Table 1.

[0070]

[0071] (Production of Test Electrode) A carbonaceous material, a conductive additive, and a binder were mixed and stirred for 10 minutes in a mass ratio of 80:10:10, respectively. Acetylene black (Denka Black, manufactured by Denka Co., Ltd.) was used as the conductive additive, and polytetrafluoroethylene (Polyflon D-210C, manufactured by Daikin Industries, Ltd.) was used as the binder. After stirring, the carbonaceous material, the conductive additive, and the binder were kneaded while adding a small amount of alcohol. The mixture obtained after kneading was molded into a sheet with a thickness of approximately 0.3 mm using a press under a pressure of 10 t. A circular molded body with a diameter of 12 mm was cut from the obtained sheet. The molded body was then pressure-bonded to a 15 mm diameter aluminum mesh (manufactured by Taiyo Wire Cloth Co., Ltd., "4AL8-4 / 0w-457") under a pressure of 1 t to prepare an electrode.

[0072] (Assembly of Measurement Electrode Cell) A measurement electrode cell was assembled as shown in FIG. 1. The assembly of the measurement electrode cell was carried out in a glove box under an argon atmosphere. Using a two-electrode aluminum flat cell (manufactured by Hosen Co., Ltd., "HS Flat Cell"), the electrodes prepared as described above were used as the positive electrode 4 and the negative electrode 2, and they were stacked via a 23 mm diameter paper separator 3 (manufactured by Nippon Advanced Paper Industries Co., Ltd., "TF4050") interposed therebetween. Then, after injecting the electrolyte 9, the cell was sealed. As the electrolyte 9, a 1.0 mol / L propylene carbonate solution of tetraethylammonium tetrafluoroborate (manufactured by Kishida Chemical Co., Ltd., "CPG-00005") was used. The cell was assembled in the following order from the bottom: cell (lower part) 1, electrode (negative electrode 2), separator 3, electrode (positive electrode 4), Teflon guide 5, electrode presser 6, spring 7, and cell (upper part) 8, to produce the electric double layer capacitor 10 shown in FIG. 1 .

[0073] (Rate Test) The electric double layer capacitor 10 was subjected to a charge / discharge test at 25° C. using a charge / discharge tester (HJ1005SD8 manufactured by Hokuto Denko Corporation) with a charge / discharge current density of 0.1 to 100 mA / cm 2 up to a final voltage of 2.5 V. ２ From the obtained discharge curve data, the capacitance C per unit mass of the carbonaceous material in the electrode was calculated. Ｇ [F / g] was calculated using Equation 1. Here, ΔV in Equation 1 is the maximum cell voltage (2.5 V), m is the total mass of the carbonaceous materials in the positive and negative electrodes, and q is the discharged quantity of electricity. The test conditions are shown in Table 2, and the test results are shown in Table 3.

[0074] (Cycle Test) The electric double layer capacitor 10 was subjected to a charge / discharge test at 25° C. using a charge / discharge tester (HJ1005SD8 manufactured by Hokuto Denko Corporation) up to a final voltage of 2.5 V, with a charge / discharge current density of 10 mA / cm ２ From the obtained discharge curve data, the capacitance C per unit mass of the carbonaceous material in the electrode was calculated. Ｇ[F / g] was calculated using the above formula 1. In formula 1, ΔV is the maximum cell voltage (2.5 V), m is the total mass of the carbonaceous materials in the positive and negative electrodes, and q is the discharged quantity of electricity. Table 3 shows the capacity retention rate after 10,000 charge-discharge cycles.

[0075]

[0076]

[0077] It was found that the electric double layer capacitors equipped with the electric double layer capacitor electrodes made from the carbonaceous materials obtained in Examples 1 to 4 had high rate retention and cycle retention, and were excellent in rate characteristics and cycle characteristics (durability). In contrast, it was found that the electric double layer capacitor equipped with the electric double layer capacitor electrodes made from the carbonaceous material obtained in Comparative Example 1 had low rate retention and cycle retention. It was found that the electric double layer capacitor equipped with the electric double layer capacitor electrodes made from the carbonaceous material obtained in Comparative Example 2 had a high rate retention, but low capacitance when the current density was low.

[0078] REFERENCE SIGNS LIST 1 Cell (lower part) 2 Negative electrode 21 Molded body 22 Aluminum mesh 3 Separator 4 Positive electrode 41 Molded body 42 Aluminum mesh 5 Teflon guide 6 Electrode presser 7 Spring 8 Cell (upper part) 9 Electrolyte 10 Electric double layer capacitor

Claims

1. BET specific surface area is 1000m ２ / g or more, and the amount of oxygen desorption at 1200°C to 2500°C as measured by a temperature programmed desorption method is 1.1 mass% or more.

2. The carbonaceous material according to claim 1, wherein the oxygen element content is 4 to 12 mass %.

3. The carbonaceous material according to claim 1 or 2, having a hydrogen element content of 1 mass % or less.

4. The R value of the Raman spectrum is 1.15 or more and 1.40 or less, and the half width of the G band is 70 cm －１ The carbonaceous material according to any one of claims 1 to 3.

5. BET specific surface area is 2500m ２ The carbonaceous material according to any one of claims 1 to 4, wherein the carbonaceous material has a molecular weight of 1 / g or less.

6. The carbonaceous material according to any one of claims 1 to 5, wherein the amount of oxygen desorption at 1200°C to 2500°C measured by temperature programmed desorption is 10 mass% or less.

7. The carbonaceous material according to claim 1, which is derived from grain husks.

8. An electrode material comprising the carbonaceous material according to any one of claims 1 to 7.

9. An electrode comprising the electrode material of claim 8.

10. An electricity storage device comprising the electrode according to claim 9.

11. A method for producing a carbonaceous material according to any one of claims 1 to 7, comprising the steps of: carbonizing a plant-derived raw material at 320°C to 700°C in an inert gas atmosphere to obtain a carbonized product; subjecting the carbonized product to an alkali washing treatment to obtain a carbonaceous material precursor; and activating the carbonaceous material precursor at 800°C or higher to obtain a carbonaceous material.

12. The method of claim 11, wherein the plant-derived raw material is a raw material derived from cereal husks.

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