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

Abstract

This application relates to carbonaceous materials derived from plants, with a BET specific surface area of ​​1000 m². 2 / g or more, and the oxygen desorption amount at 1200℃~2500℃ in the temperature-raising desorption method is 1.1% by mass or more.

Description

Technical Field

[0001] This application relates to carbonaceous materials derived from plants, electrode materials, electrodes, energy storage devices, and methods for manufacturing carbonaceous materials. Background Technology

[0002] Carbonaceous materials are used in non-aqueous electrolyte batteries such as lithium-ion secondary batteries and sodium-ion secondary batteries, as well as electrochemical devices such as electric double-layer capacitors and lithium-ion capacitors, with a focus on finding carbonaceous materials with properties suitable for their applications. For example, electric double-layer capacitors, as one type of electrochemical device, utilize capacity (electric double-layer capacity) obtained solely through physical ion adsorption and desorption without chemical reactions. Therefore, compared to batteries, they exhibit superior output and lifespan characteristics. Due to their excellent properties, electric double-layer capacitors have been developed for various applications, including backup devices for various storage devices, power generation based on natural energy sources, and power storage applications such as UPS (Uninterruptible Power Supply). In recent years, considering these superior properties and the urgent need for solutions to environmental problems, electric double-layer capacitors have attracted considerable attention for their use as auxiliary power sources for electric vehicles (EVs) and hybrid vehicles (HVs), as well as for the storage of renewable energy.

[0003] For automotive-grade electric double-layer capacitors, high durability is required. For example, as a carbonaceous material used in electric double-layer capacitors, there are reports of modified activated carbon (Patent Document 1) with BET specific surface area, hydrogen content / carbon content, and amount of oxygen in the framework adjusted to a specific range for the purpose of suppressing gas generation during charging and discharging; and carbonaceous materials with silicon content, total surface functional group content, and pore volume adjusted to a specified range (Patent Document 2), etc.

[0004] Furthermore, with the increasing demand for electrochemical devices such as electric double-layer capacitors, research has been conducted on using plant-based waste materials such as vegetables and grains as raw materials. Patent Document 3 discloses a manufacturing method in which plant-derived raw materials are carbonized at 800°C to 1400°C and then treated with acid or alkali to obtain activated carbon for electric double-layer capacitors with a silicon content of less than 1% by weight. Patent Document 4 discloses a method in which plant-derived raw materials are used to increase the intensity of the diffraction peaks on the (002) plane obtained by powder X-ray diffraction, thereby obtaining activated carbon for electric double-layer capacitors with improved crystallinity.

[0005] Existing technical documents Patent documents Patent Document 1: International Publication No. 2018-207769 Patent Document 2: International Publication No. 2021-131907 Patent Document 3: Japanese Patent No. 5533912 Specification Patent Document 4: Specification of Japanese Patent No. 6015823. Summary of the Invention

[0006] The problem the invention aims to solve To date, various carbonaceous materials have been reported as electrode materials, but the inventors have learned during their research on existing known carbonaceous materials that further improvements are needed to obtain electrodes for energy storage devices that have sufficient electrostatic capacity at low current densities and can perform adequate charge and discharge performance at high current densities.

[0007] Therefore, the subject of this application is to provide a carbonaceous material and a method for manufacturing the same, wherein the carbonaceous material can provide energy storage devices with sufficient electrostatic capacity under low current density, as well as high speed characteristics and cycle characteristics.

[0008] Methods for solving problems That is, this application includes the following suitable methods.

[0009] [1] Carbonaceous materials derived from plants, with a BET specific surface area of ​​1000 m². 2 / g or more, and the oxygen desorption amount at 1200℃~2500℃ in the temperature-raising desorption method is 1.1% by mass or more.

[0010] [2] The carbonaceous material described in [1] has an oxygen content of 4 to 12 by mass.

[0011] [3] The carbonaceous material according to [1] or [2] has a hydrogen content of less than 1% by mass.

[0012] [4] The carbonaceous material according to any one of [1] to [3] has an R value of 1.15 or more and 1.40 or less based on Raman spectroscopy, and a half-width of 70 cm⁻¹ for the G band. -1 above.

[0013] [5] The carbonaceous material according to any one of [1] to [4] has a BET specific surface area of ​​2500 m². 2 / g or less.

[0014] [6] The carbonaceous material according to any one of [1] to [5], wherein the amount of oxygen desorbed at 1200°C to 2500°C in the temperature-induced desorption method is less than 10% by mass.

[0015] [7] The carbonaceous material according to [1] is a carbonaceous material derived from grain husks.

[0016] [8] Electrode material, comprising any one of [1] to [7] carbonaceous material.

[0017] [9] An electrode comprising the electrode material described in [8].

[0018]

[10] An energy storage device comprising the electrodes described in [9].

[0019] A method for manufacturing carbonaceous materials as described in any one of

[11] , [1] to [7], comprising: The process of carbonizing plant-derived raw materials at 320℃~700℃ in an inactive gas atmosphere to obtain carbides. The process of performing alkaline cleaning treatment on the aforementioned carbides to obtain a carbonaceous material precursor; and The process of activating the aforementioned carbonaceous material precursor at temperatures above 800°C to obtain the carbonaceous material.

[0020]

[12] According to the manufacturing method described in

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

[0021] Invention Effects According to the carbonaceous material of this application, a carbonaceous material and a method thereof can be provided that can provide energy storage devices and the like with both high-speed characteristics and cycle characteristics. Attached Figure Description

[0022] Figure 1 This is a diagram illustrating the configuration of the electric double-layer capacitor used in the evaluation of the carbonaceous materials in the embodiments and comparative examples. Detailed Implementation

[0023] The embodiments of the present invention will now 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 spirit of the invention.

[0024] The carbonaceous material used in this application has a BET specific surface area of ​​1000 m². 2 Carbonaceous materials derived from plants with an oxygen desorption rate of 1.1% by mass or more at 1200℃~2500℃ in the temperature-induced desorption method, and an oxygen desorption rate of 1.1% by mass or more.

[0025] The BET specific surface area of ​​the carbonaceous material in this application is 1000 m². 2 / g or more. The preferred BET specific surface area of ​​carbonaceous materials is 1200m². 2 / g or more, preferably 1300m 2 / g or more. Furthermore, the preferred specific surface area of ​​this BET is 2500 m². 2 / g or less, more preferably 2400m 2 / g or less, further preferably 2300m 2 / g or less. Generally, under the same processing conditions for the same raw material, the electrostatic capacitance per unit area is constant. Therefore, if the BET specific surface area is less than 1000m², 2 If the density is low ( / g), it is difficult to sufficiently increase the capacitance per unit mass, especially at low current densities. Furthermore, due to the relatively small average pore diameter, there is a tendency for increased resistance during high-current charging and discharging, which is attributed to the diffusion resistance of electrolyte ions within the pores. On the other hand, from the viewpoint of capacitance per unit volume, and from the viewpoint of increasing the volume density of electrodes manufactured using this carbonaceous material, thereby increasing the capacitance per unit volume, a BET specific surface area of ​​2500 m² is preferred. 2 / g and below the aforementioned upper limit. In one embodiment, the BET specific surface area of ​​the carbonaceous material is preferably 1000 m². 2 / g~2500m 2 / g, more preferably 1200m 2 / g~2400m 2 / g, further preferably 1300m 2 / g~2300m 2 / g. It should be noted that the BET specific surface area of ​​carbonaceous materials can be calculated using the nitrogen adsorption method described in the examples below.

[0026] In the temperature-induced desorption method for carbonaceous materials of this application, the oxygen desorption amount at 1200℃~2500℃ is 1.1% by mass or more. When this oxygen desorption amount is less than 1.1% by mass, although the reason is not yet clear, especially at high current densities, sufficient charge-discharge performance cannot be achieved, and the rate characteristics deteriorate. Furthermore, in this case, the cycle characteristics cannot be sufficiently improved. Here, oxygen desorption occurs when the carbonaceous material is slowly heated from room temperature. However, it can be assumed that the oxygen desorbed at temperatures below 1200℃ mainly originates from oxygen compounds such as lactones, phenols, and quinones present on the surface of the carbonaceous material. Furthermore, it can be assumed that the oxygen desorbed at temperatures above 1200℃ originates from oxygen compounds contained within the carbon and oxygen compounds bonded to the metal. By measuring the oxygen desorption amount at 1200℃~2500℃, the total amount of oxygen contained in the form of these oxygen compounds can be quantified. From the viewpoint of cycle characteristics and rate characteristics, the oxygen desorption amount at 1200℃ to 2500℃ is preferably 1.1% to 10% by mass, more preferably 1.2% to 7% by mass, further preferably 1.3% to 5% by mass, and even more preferably 1.3% to 4.5% by mass. From the same viewpoint, this oxygen desorption amount is preferably 1.1% by mass or more, more preferably 1.2% by mass or more, and even more preferably 1.3% by mass or more. Furthermore, from the same viewpoint, this oxygen desorption amount is preferably 10% by mass or less, more preferably 7% by mass or more, further preferably 5% by mass or more, and even more preferably 4.5% by mass or less.

[0027] Based on the viewpoint that desorption occurs at high temperatures, it can be inferred that the oxygen element desorbed at 1200℃~2500℃ is contained in the carbon skeleton in the form of structures such as ether skeletons. It can be considered that since the ether skeleton has a high affinity for the electrolyte, including this skeleton in the carbon skeleton improves the electrolyte permeability and, in particular, maintains a high capacitance even when a large current is applied. Furthermore, it can be considered that when the oxygen desorption amount is 1.1% by mass or more at 1200℃~2500℃, the affinity of the ether skeleton for the electrolyte prevents drying, thereby suppressing the decrease in capacitance and improving cycle characteristics.

[0028] The oxygen desorption rate of the carbonaceous material in this application at 1200℃~2500℃ can be controlled within the above range by selecting raw materials with high oxygen content and adjusting the temperature and time of the carbonization process under the manufacturing conditions of the carbonaceous material described later.

[0029] From the viewpoint of cycle characteristics, the amount of oxygen desorbed at below 1200°C in the temperature-raising desorption method of carbonaceous materials in this application is preferably 9% by mass or less, more preferably 8% by mass or less, and even more preferably 7.5% by mass or less.

[0030] The carbonaceous material used in this application is a carbonaceous material derived from plants. There are no particular limitations on the plants that can serve as carbon sources, but examples include coconut shells (e.g., oil palm, coconut, snake fruit, sea coconut), coffee beans, tea leaves, sugarcane, fruits (e.g., oranges, bananas), wheat straw, broad-leaved trees, coniferous trees, bamboo, and grain husks (e.g., rice husks, buckwheat husks, wheat husks).

[0031] Grain husks are preferred as a raw material, especially rice husks, which contain a large amount of oxides of silica, calcium, and magnesium. Therefore, by using rice husks as a raw material to manufacture carbonaceous materials, it is easy to adjust the oxygen desorption rate in the temperature-induced desorption method (1200℃~2500℃) to a desired range of 1.1% by mass or more, making it a preferred choice. Carbonaceous materials derived from rice husks are characterized by containing a large amount of silica compared to other plant-derived carbonaceous materials.

[0032] From the viewpoint of cycle characteristics and rate characteristics, the oxygen content of the carbonaceous material is preferably 4 to 12% by mass, more preferably 4.5 to 11.5% by mass, and even more preferably 5 to 11% by mass. The oxygen content and hydrogen content of the carbonaceous material in this application are values ​​calculated by elemental analysis, specifically calculated using the methods described in the embodiments.

[0033] From the perspective of reducing electrical resistance, the hydrogen content of carbonaceous materials is preferably 1% by mass or less, more preferably 0.5% by mass or less. There is no particular limitation on the lower limit of the hydrogen content, but it is typically 0.2% by mass or more, and can 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 increases, and therefore it can be considered that the conductivity of the carbonaceous material itself will increase, tending to result in lower electrical resistance.

[0034] The preferred R-value of the carbonaceous material in this application, based on Raman spectroscopy, is 1.15 to 1.40. The R-value is the value at 1360 cm⁻¹ of the Raman spectrum observed by laser Raman spectroscopy. -1 Nearby peak intensity (I) D ) and 1580cm -1 Nearby peak intensity (I) G The strength ratio (R value = I) D / I G ), here, 1360cm -1 The nearby peaks refer to the Raman peaks commonly known as the D-band, which are caused by disorder / defects in the graphite structure. Additionally, at 1580 cm⁻¹... -1 The nearby peak refers to the Raman peak commonly known as the G-band, which originates from the graphite structure. Here, at 1360cm... -1 The nearby peaks are typically around 1345 cm. -1~1375cm -1 Preferred height is 1350cm -1 ~1370cm -1 The range was observed. Additionally, 1580cm -1 The nearby peaks are typically around 1560 cm. -1 ~1615cm -1 Preferred height is 1565cm -1 ~1610cm -1 The range was observed.

[0035] The intensity ratio of these peaks, i.e., the R value, is related to the crystallinity of the carbonaceous material. If the crystallinity of the carbonaceous material is too high, the carbon edges are reduced due to the developed graphite structure, resulting in fewer coordination sites for the electrolyte. This leads to problems such as reduced performance at low temperatures and increased resistance. Conversely, if the crystallinity of the carbonaceous material is too low, there is more amorphous material, resulting in higher resistance. Consequently, the utilization efficiency of the electric double layer at the interface between the electrolyte and electrode materials decreases. From the above perspective, 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. If the R value is within the above range, the electric double-layer capacitor containing this carbonaceous material can maintain higher capacitance and energy density for a long time, even under high-voltage driving.

[0036] The half-width of the G band based on Raman spectroscopy for the carbonaceous material in this application is preferably 70 cm. -1 The above. The half-width at half-maximum (WHM) of the G-band is related to the amount of disorder / defects in the graphite structure contained in the carbonaceous material. Here, if the WHM is above or below the lower limit described below, the amount of disorder / defects in the graphite structure contained in the carbonaceous material becomes appropriate, and there are not too many carbon edges due to the development of the graphite structure, thereby increasing the sites for electrolyte coordination. Therefore, it has the effect of improving low-temperature properties and reducing diffusion resistance. Furthermore, if the WHM is below or below the upper limit described below, the amount of disorder / defects in the graphite structure contained in the carbonaceous material is appropriate, preventing excessive amorphous matter and reducing resistance. From these perspectives, 1580 cm⁻¹ -1 The half-width at half-maximum (WHM) of the nearby peaks (G-band half-maximum) is 70–100 cm. -1 The preferred size is 75~98cm. -1 More preferably 80~95cm -1 If the half-width of the G-band is within the above range, the electric double-layer capacitor containing the carbonaceous material can maintain a higher capacitance and energy density for a long time, even under high voltage driving.

[0037] It should be noted that the R value and the half-width of the G band based on Raman spectroscopy in this invention are calculated by the method described in the embodiments below.

[0038] The average particle size of the carbonaceous material in this application is not particularly limited and can be appropriately set according to the intended use of the carbonaceous material. For example, when the carbonaceous material is used in energy storage devices such as electric double-layer capacitors, 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 the median particle size (Dm) when the particle size distribution of the carbonaceous material is measured using a laser diffraction particle size distribution measuring device. 50 ).

[0039] The method for manufacturing carbonaceous materials in this application is not particularly limited as long as it can produce carbonaceous materials that meet the above characteristics. It can be manufactured by, for example, a method that includes at least the following steps: (1) carbonizing raw materials derived from plants at 320°C to 700°C in an inactive gas atmosphere to obtain a carbide (also called a carbonization step); (2) performing an alkaline cleaning treatment on the aforementioned carbide to obtain a carbonaceous material precursor (also called an alkaline cleaning step); and (3) performing an activation treatment on the aforementioned carbonaceous material precursor at 800°C or above to obtain a carbonaceous material (also called an activation treatment step). The present invention also provides a method for manufacturing carbonaceous materials including the above steps. The manufacturing method may also include other steps besides those mentioned above. For example, (a) a heat treatment step may be performed after the alkaline cleaning step and before the activation treatment step, and (b1) a pulverizing step and / or (b2) a grading step may be performed after the activation treatment step.

[0040] (1) Carbonization process The carbonization process (1) is a process of carbonizing plant-derived raw materials at 320°C to 700°C in an inert gas atmosphere to obtain carbonized materials. Plant-derived raw materials can be listed as those derived from the plants described above. Preferably, the plant-derived raw materials are derived from grain husks; from the viewpoint of easy availability, raw materials selected from rice husks, buckwheat husks, and wheat husks are more preferred; and even more preferred are raw materials derived from rice husks.

[0041] Carbides can be obtained by heating and carbonizing plant-derived raw materials at 320°C to 700°C in an inert gas atmosphere. The carbonization temperature is preferably 330°C to 700°C, more preferably 340°C to 700°C, and even more preferably 350°C to 700°C. When the carbonization temperature is below the upper limit mentioned above, the leaching solubility of silicon compounds contained in the carbides can be improved in the alkaline cleaning process described later. Furthermore, if the carbonization temperature is above the lower limit mentioned above, the generation of black liquor can be reduced in the alkaline cleaning process, making wastewater treatment easier. Additionally, when the carbonization temperature is below 320°C, it is difficult to achieve an oxygen desorption rate of 1.1% by mass or more at 1200°C to 2500°C for carbonaceous materials, and sometimes the rate characteristics and cycle characteristics of energy storage devices using electrodes manufactured using this carbon material are not obtained. When the carbonization temperature exceeds 700°C, crystallization occurs during carbonization, while amorphous (easily activated) portions separate and grow, generating larger void portions through subsequent activation, thus reducing the bulk density. Therefore, electrodes manufactured using this carbonaceous material tend to have lower bulk density and lower capacitance per unit volume. By performing carbonization within a specified temperature range, the rate characteristics and cycle characteristics (durability) of energy storage devices obtained using the carbonaceous material after cleaning, heat treatment, activation treatment, and pulverization (described later) can be improved. To ensure sufficient carbonization and maintain the solubility of silicon compounds in subsequent processes, the carbonization time from reaching the desired temperature is preferably 30 to 120 minutes. From the viewpoint of preventing excessively long carbonization times and suppressing equipment degradation, the heating rate is preferably 2°C / min to 20°C / min.

[0042] Carbonization can be carried out by firing (carbonizing) the carbon precursor that will become the raw material at a specific temperature in an atmosphere of inert gases such as nitrogen, carbon dioxide, helium, argon, carbon monoxide or fuel exhaust, a mixture of these inert gases, or a mixture of these inert gases as the main component with other gases.

[0043] For the furnace used in carbonization processing, various types of furnaces can be used, such as rotary furnaces, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving bed furnaces. Both continuous furnaces (for continuous raw material input and heat-treated product removal) and intermittent furnaces (for intermittent raw material input and heat-treated product removal) can be used. As for the heating method, any method capable of heating to the specified temperature is acceptable, including electric heating, gas combustion heating, high-frequency induction heating, and electrostatic heating. Furthermore, these heating methods can be used individually or in combination.

[0044] (2) Alkali cleaning process The alkaline cleaning process is a process of obtaining a carbonaceous material precursor by alkaline cleaning of the aforementioned carbides. By cleaning the carbides obtained in the carbonization process with an alkaline solution, silicon compounds and the like contained in the carbides can be removed. Alkaline cleaning can be performed by contacting the carbides obtained in the carbonization process with an alkaline solution (also called a cleaning liquid), or by immersing the carbides in the cleaning liquid, for example. Examples of the aforementioned cleaning liquid include aqueous solutions of sodium hydroxide, potassium hydroxide, and lithium hydroxide; from the perspective of availability, aqueous solutions of sodium hydroxide are preferred.

[0045] The temperature of the alkaline solution used for alkaline cleaning 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 concentration of silicon in the carbide can be reduced in a short time, and the process can be carried out safely; therefore, this is preferred.

[0046] The alkali concentration of the cleaning solution is not particularly limited and can be adjusted appropriately depending on the type of cleaning solution used. The alkali concentration of the cleaning solution is preferably 0.01N or higher, more preferably 0.03N or higher. The upper limit of the alkali concentration is preferably 10N or lower, more preferably 5N or lower. If the alkali concentration is too low, more cleaning cycles and cleaning time are required to remove silicon compounds; if it is too high, more residual alkali will remain. From a safety perspective, a concentration within the above-mentioned range is preferred.

[0047] There is no particular limitation on the pH of the cleaning solution. It can be adjusted appropriately according to the type of cleaning solution used. From the point of view of reducing the number of cleaning times or cleaning time, the pH is preferably 11 or higher.

[0048] The mass ratio of the cleaning solution to the carbide when immersing the carbide in the cleaning solution can be appropriately adjusted according to the type, concentration, temperature, and packing density of the cleaning solution used. The mass of the carbide to be immersed relative to the mass of the cleaning solution is preferably 2% by mass or more, more preferably 3% by mass or more. The upper limit of the mass ratio is preferably 50% by mass or less, more preferably 30% by mass or less. Within the above range, excessive energy is not required to heat the cleaning solution, and sufficient cleaning effect can be obtained, which is therefore preferable.

[0049] The atmosphere for alkaline cleaning is not particularly limited and can be appropriately selected depending on the method used in the cleaning process. In this invention, alkaline cleaning is typically carried out in an atmospheric atmosphere.

[0050] As for the method of alkaline cleaning of carbides, there are no particular limitations as long as the carbides can come into contact with the cleaning solution, preferably as long as the carbides can be immersed in the cleaning solution. It can be a method of continuously adding the cleaning solution and allowing it to remain for a predetermined time, removing it while immersing; or it can be a method of immersing the carbides in the cleaning solution and allowing it to remain for a predetermined time, then adding more cleaning solution after dehydration and repeating the immersion-dehydration process. Alternatively, it can be a method of completely replacing the cleaning solution or a method of partially replacing the cleaning solution. Furthermore, the cleaning solution can be stirred during immersion.

[0051] The immersion time of the carbide in the cleaning solution can be appropriately adjusted according to the cleaning solution used, the processing temperature, the immersion conditions, and the ash content of the carbide. When the ash content of the carbide is higher than 20%, from the viewpoint of sufficiently reducing silicon compounds in the carbide, it is preferable to stir in the cleaning solution for 20 minutes or more, 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, more preferably 5 hours or less, and even more preferably 3 hours or less. Stirring may or may not be performed during immersion.

[0052] After alkaline cleaning of the carbides, they can be washed with water to remove any residual cleaning solution. There is no specific pH requirement after the water wash.

[0053] (a) Heat treatment process Before the activation treatment step described later (3), a heat treatment step can be performed to heat-treat the carbonaceous material precursor after the aforementioned alkaline cleaning treatment in an inactive 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. If the heat treatment temperature is above the lower limit mentioned above, the carbon structure can be fully developed. In addition, if the heat treatment temperature is below the upper limit mentioned above, micropore shrinkage is less likely to occur, and the activation time described later will not be extended beyond what is necessary. From the viewpoint of developing the carbon structure and not causing excessive micropore shrinkage, the heat treatment time from reaching the desired temperature is preferably 10 minutes to 120 minutes. From the viewpoint of not making the heat treatment process too long and suppressing equipment deterioration, the heating rate is preferably 2°C / minute to 20°C / minute.

[0054] The heat treatment process is preferably carried out in an atmosphere of inert gas or in a gas atmosphere generated by activated carbon that is isolated from oxygen or air. Examples of inert gases used in heat treatment include nitrogen, argon, and helium. These gases can be used alone or in mixtures of two or more gases.

[0055] Furnaces used in heat treatment can be of various forms, including rotary furnaces, fluidized bed furnaces, fixed bed furnaces, moving bed furnaces, and moving plate furnaces. Both continuous furnaces (for continuous raw material input and heat-treated product removal) and intermittent furnaces (for intermittent raw material input and heat-treated product removal) are acceptable. As for the heating method, any method capable of heating to the specified temperature is acceptable, including electric heating, gas combustion heating, high-frequency induction heating, and electrostatic heating. Furthermore, these heating methods can be used individually or in combination.

[0056] (3) Activation treatment process The carbonaceous material of this application can be manufactured, for example, by heat-treating a carbonaceous material precursor after alkaline cleaning as needed, followed by an activation treatment. Activation treatment refers to the process of forming micropores on the carbon surface, transforming it into a porous carbonaceous material, thereby obtaining a carbonaceous material (activated carbon) with a large specific surface area and micropore volume. Without activation treatment, the resulting carbonaceous material has insufficient specific surface area and micropore volume, making it difficult to ensure a high initial capacity when used as an electrode material, thus failing to obtain the carbonaceous material of this application. Activation treatment can be carried out using methods commonly found in the art, primarily gas activation treatment and reagent activation treatment.

[0057] As a gaseous activation treatment, methods for heating carbon precursors in the presence of, for example, water vapor, carbon dioxide, air, oxygen, combustion gases, or mixtures thereof are known. Additionally, as a chemical activation treatment, methods for mixing activators such as zinc chloride, calcium chloride, phosphoric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, magnesium hydroxide, and calcium hydroxide with the carbon precursor and heating under an inert gas atmosphere are known. In the manufacturing method of this application, chemical activation requires a step of removing residual chemicals, which complicates the manufacturing process; therefore, gaseous activation treatment is preferred.

[0058] When using steam activation as the gas activation process, from the viewpoint of efficient activation, it is preferable to use a mixture of the same inactive gas and steam as the gas used in the carbonization process. In this case, the partial pressure of steam is preferably in the range of 10% to 60%. If the partial pressure of steam is above 10%, activation is easily and sufficiently carried out; if it is below 60%, rapid activation reactions are easily suppressed, and the reaction is easily controlled.

[0059] The total amount of activating gas supplied in the steam activation process is preferably 50 to 10,000 parts by mass relative to 100 parts by mass of the carbon precursor, more preferably 100 to 5,000 parts by mass, and even more preferably 200 to 3,000 parts by mass. If the total amount of activating gas supplied is within the above range, the activation reaction can be carried out more efficiently.

[0060] The specific surface area and pore volume of activated carbon can be controlled by changing the activation treatment method and conditions. For example, when activated carbon is obtained by steam activation treatment, these can be controlled by the heating temperature and time. In steam activation treatment, if the heating temperature is low, the specific surface area and pore diameter of the obtained activated carbon tend to be smaller; if the heating temperature is high, the specific surface area and pore diameter of the obtained activated carbon tend to be larger. In this invention, when activated carbon is obtained by steam activation, the heating temperature (activation temperature) also depends on the type of gas used, and is typically 700~1100°C, preferably 800~1000°C. Furthermore, the heating time and temperature rise time are not particularly limited, and can be appropriately determined based on the heating temperature and the desired specific surface area of ​​the activated carbon.

[0061] When carbon dioxide activation is used as the gaseous activation treatment, the processing temperature is preferably 800~1000℃, more preferably 800~900℃. In carbon dioxide activation, the same inactive gas or water vapor used in the carbonization treatment can be mixed in. Furthermore, the heating time and temperature rise time are not particularly limited, and can be appropriately determined based on the heating temperature and the desired specific surface area of ​​the activated carbon.

[0062] Depending on the needs, the activation treatment can be performed once or twice or more. There are no restrictions on the conditions for the second and subsequent activations. Similar to the first activation, the heating temperature, heating time, etc., can be appropriately determined based on the desired specific surface area of ​​the activated carbon.

[0063] (b1) Crushing process The method for manufacturing carbonaceous materials according to this application may, as needed, include (b1) a pulverizing step and / or (b2) a grading step described later after the (3) activation treatment step. The pulverizing step is a step used to control the shape and particle size of the final carbonaceous material to the desired granular shape and particle size. The average particle size of the carbonaceous material of the present invention is not particularly limited. For example, in the case of its use in electric double-layer capacitors, the average particle size of the carbonaceous material is preferably 1 to 15 μm, more preferably 2 to 10 μm. In this case, in the pulverizing step, it is preferable to pulverize in a manner that yields carbonaceous material with an average particle size within the above range.

[0064] There are no particular limitations on the crusher used in the crushing process. For example, well-known crushers such as cone crushers, double roll crushers, disc crushers, rotary crushers, ball mills, centrifugal roller mills, ring roller mills, centrifugal ball mills, and jet mills can be used alone or in combination.

[0065] (b2) Grading process The method for manufacturing carbonaceous materials according to the present invention may include a classification step (b2) after the activation treatment step (3). For example, by performing a classification step to remove particles with a particle size of 1 μm or less, carbonaceous material particles with a narrow particle size distribution can be obtained. By removing such particles, the amount of binder used in the electrode can be reduced. The classification method is not particularly limited, and examples include classification using sieves, wet classification, and dry classification. As a wet classifier, examples include classifiers that utilize the principles of gravity classification, inertial classification, hydraulic classification, and centrifugal classification. As a dry classifier, examples include classifiers that utilize the principles of sedimentation classification, mechanical classification, and centrifugal classification. From an economic point of view, a dry classifier is preferred.

[0066] (b1) The pulverizing process and (b2) the grading process can be performed as separate processes, or they can be performed simultaneously using a single device. For example, a jet mill with dry grading capabilities can be used to perform pulverizing and grading. When performed as separate processes, a separate device can be used for the pulverizer and the grader. In this case, pulverizing and grading can be performed continuously or discontinuously.

[0067] The carbonaceous material of this application can be suitable for use as an electrode active material in energy storage devices such as electric double-layer capacitors, lithium-ion capacitors, and lithium-ion secondary batteries. By using the carbonaceous material of this application, energy storage devices with excellent cycle characteristics (durability) and rate characteristics can be manufactured. Therefore, in one embodiment of this application, an electrode material comprising the carbonaceous material of this application, an electrode comprising the electrode material, and an energy storage device comprising the electrode can be provided. In one embodiment of this application, an electrode for an electric double-layer capacitor comprising the carbonaceous material of this application can be provided, and an electric double-layer capacitor having the electrode can also be provided.

[0068] The electrode material of this application includes the carbonaceous material of this application. This electrode material can be manufactured using manufacturing processes commonly found in the art, such as a process of mixing the carbonaceous material of this application (which will become the raw material) with components like a conductivity-improving agent, a binder, and a solvent; and a process of coating the resulting mixture onto a support and drying it. Furthermore, the aforementioned electrode (e.g., an electrode for an electric double-layer capacitor) can be manufactured using the aforementioned electrode material. An example manufacturing method includes the following steps: for example, a process of preparing a paste by adding a solvent to the aforementioned electrode material (which will become the raw material); a process of coating the aforementioned paste onto a current collector such as an aluminum foil or aluminum mesh, and then drying and removing the solvent; and a process of placing the aforementioned paste into a mold and pressing it into shape.

[0069] As conductive agents, acetylene black and Ketjen black can be used. As binders, fluorinated polymers such as polytetrafluoroethylene and polyvinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, petroleum asphalt, and phenolic resins can be used. Furthermore, as solvents, alcohols such as water, methanol, and ethanol; saturated hydrocarbons such as hexane and heptane; aromatic hydrocarbons such as toluene, xylene, and mesitylene; ketones such as acetone and methyl ethyl ketone; esters such as methyl acetate and ethyl acetate; amides such as N,N-dimethylformamide and N,N-diethylformamide; and cyclic amides such as N-methylpyrrolidone and N-ethylpyrrolidone can be used.

[0070] The energy storage device (e.g., an electric double-layer capacitor) of this application is characterized by having the aforementioned electrodes. Energy storage devices such as electric double-layer capacitors typically have a structure consisting mainly of electrodes, an electrolyte, and a separator, with a separator disposed between a pair of electrodes. Examples of electrolytes include electrolytes containing amidine salts dissolved in organic solvents such as propylene carbonate, ethylene carbonate, and methyl ethyl carbonate; electrolytes containing quaternary ammonium salts of perchloric acid dissolved in the aforementioned organic solvents; electrolytes containing boron tetrafluoride salts or phosphine hexafluoride salts of alkali metals such as quaternary ammonium and lithium dissolved in the aforementioned organic solvents; and electrolytes containing quaternary phosphonium salts. Examples of separators include nonwoven fabrics, cloths, and microporous membranes with cellulose, glass fiber, or polyolefins such as polyethylene and polypropylene as the main components. Energy storage devices such as electric double-layer capacitors can be manufactured by, for example, using methods commonly found in the art to configure these main components.

[0071] Energy storage devices such as double-layer capacitors manufactured using the carbonaceous materials of this application exhibit excellent cycle characteristics (durability) and rate characteristics by appropriately controlling the amount of oxygen desorption. Example

[0072] The present invention will be specifically described below through examples, but these examples do not limit the scope of the invention.

[0073] The physical property values ​​in the examples were determined according to the following method.

[0074] (Nitrogen adsorption isotherm, BET specific surface area) Analysis was performed using a gas adsorption capacity measuring device (Quantachrome, "Autosorb 3B"). Carbonaceous materials were used as the test sample, and a nitrogen adsorption isotherm showing the relationship between relative nitrogen pressure and nitrogen adsorption was obtained at 77 K. Based on this nitrogen adsorption isotherm, the BET specific surface area was calculated from the nitrogen adsorption volume at relative pressures of 0.05–0.10.

[0075] (Analysis of oxygen and hydrogen content) Elemental analysis was performed using an oxygen-nitrogen-hydrogen analyzer (EMGA-930, manufactured by Horiba Manufacturing Co., Ltd.) based on the inert gas melting method. The detection methods were: oxygen: inert gas melting-non-dispersive infrared absorption (NDIR), and hydrogen: inert gas melting-non-dispersive infrared absorption (NDIR). Calibration was performed using Sn capsules, with TiH2 (H standard sample), SS-3, and SS-10 (O standard sample) used. 5 mg of carbonaceous powder sample, pretreated by drying at 250°C for approximately 10 minutes, was placed into Sn capsules, degassed for 30 seconds within the analyzer, and then measured. Three samples were analyzed, and their average value was used as the analytical value for oxygen and hydrogen content. During oxygen content determination, the amount of oxygen desorption during the heating process (1200°C–2500°C) was simultaneously measured.

[0076] (Raman spectroscopy) Using a Raman spectrometer (NANOPHOTON's "Ramanforce Laser Raman Microscope"), the carbonaceous material being measured was placed on the observation stage base. The objective lens was set to 20x magnification, and the image was focused while being irradiated with an argon-ion laser. Details of the measurement conditions are shown below. Regarding the G band half-width, based on the spectrum obtained under the above measurement conditions, the G band (1590 cm⁻¹) was determined. -1 The peak half-width (nearby).

[0077] In addition, the R value is set as the intensity ratio I of each peak in the D-band and the G-band. D / I G (D peak intensity / G peak intensity).

[0078] Wavelength of argon ion laser: 532nm Laser power on the sample: 100-300 W / cm 2 Resolution: 5-7cm -1 Measurement range: 150-4000cm -1 Measurement mode: XY Averaging Exposure time: 20 seconds Total number of times: 2 Peak intensity determination: Baseline correction was performed automatically using Polynom-3. Peak search and fitting process using Gauss-Lorentz.

[0079] (Particle size distribution) The particle size distribution of carbonaceous materials was determined using a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, "SALD-200V"). The average particle size in this specification refers to the particle size at which the cumulative volume reaches 50% (D). 50 ).

[0080] (Example 1) The husks of Akita Komachi rice from Akita Prefecture, Japan, were heated at 350°C for 1 hour under a nitrogen atmosphere to obtain a carbide. 15g of the obtained carbide was then immersed in 300ml of a 1.0N sodium hydroxide aqueous solution at 80°C for 10 hours. The carbide was then removed, washed with distilled water, and dried. Subsequently, the carbide was heated at 900°C for 1 hour under a nitrogen atmosphere to remove volatile components. Next, the carbide was heated at 900°C in the presence of carbon dioxide to activate it until the activation yield reached 44%, thus obtaining a carbonaceous material.

[0081] The carbonaceous material was micronized with an average particle size of 7.5–9.0 μm to obtain a BET specific surface area of ​​1326 m². 2 / g of carbonaceous material (1). Various physical properties of the obtained carbonaceous material (1) were determined. The results are shown in Table 1.

[0082] (Example 2) The husks of Akita Komachi rice from Akita Prefecture, Japan, were heated at 500°C for 1 hour under a nitrogen atmosphere to obtain a carbide. The obtained carbide was then subjected to alkali treatment, washing with water, drying, and removal of volatile components using the same method as in Example 1. It was then activated by heating at 900°C in the presence of carbon dioxide until the activation yield reached 40%, thus obtaining a carbonaceous material.

[0083] The carbonaceous material was micronized with an average particle size of 7.5–9.0 μm to obtain a BET specific surface area of ​​1346 m². 2 / g of carbonaceous material (2). Various physical properties of the obtained carbonaceous material (2) were determined. The results are shown in Table 1.

[0084] (Example 3) The husks of Akita Komachi rice from Akita Prefecture, Japan, were heated at 700°C for 1 hour under a nitrogen atmosphere to obtain a carbide. The obtained carbide was then subjected to alkali treatment, washing with water, drying, and removal of volatile components using the same method as in Example 1. It was then activated by heating at 900°C in the presence of carbon dioxide until the activation yield reached 46%, thus obtaining a carbonaceous material.

[0085] The carbonaceous material was micronized with an average particle size of 7.5–9.0 μm to obtain a BET specific surface area of ​​1331 m². 2 / g of carbonaceous material (3). Various physical properties of the obtained carbonaceous material (3) were determined. The results are shown in Table 1.

[0086] (Example 4) The husks of Akita Komachi rice from Akita Prefecture, Japan, were heated at 600°C for 1 hour under a nitrogen atmosphere to obtain a carbide. The obtained carbide was then subjected to alkali treatment, washing, drying, and removal of volatile components using the same method as in Example 1. It was then activated by heating at 900°C in the presence of carbon dioxide until the activation yield reached 44%, thus obtaining a carbonaceous material.

[0087] The carbonaceous material was micronized with an average particle size of 7.5–9.0 μm to obtain a BET specific surface area of ​​1027 m². 2 / g of carbonaceous material (4). Various physical properties of the obtained carbonaceous material (4) were determined. The results are shown in Table 1.

[0088] (Comparative Example 1) The husks of Akita Komachi rice from Akita Prefecture, Japan, were heated at 300°C for 1 hour under a nitrogen atmosphere to obtain a carbide. The obtained carbide was then subjected to alkali treatment, washing with water, drying, and removal of volatile components using the same method as in Example 1. It was then activated by heating at 900°C in the presence of carbon dioxide until the activation yield reached 43%, thus obtaining a carbonaceous material.

[0089] The carbonaceous material was micronized to an average particle size of 7.5–9.0 μm, resulting in a BET specific surface area of ​​1256 m². 2 / g of carbonaceous material (5). Various physical properties of the obtained carbonaceous material (5) were determined. The results are shown in Table 1.

[0090] (Comparative Example 2) The husks of Akita Komachi rice from Akita Prefecture, Japan, were heated at 700°C for 1 hour under a nitrogen atmosphere to obtain a carbide. The obtained carbide was then subjected to alkali treatment, washing, drying, and removal of volatile components using the same method as in Example 1. It was then activated by heating at 900°C in the presence of carbon dioxide until the activation yield reached 80%, thus obtaining a carbonaceous material.

[0091] The carbonaceous material was micronized to an average particle size of 7.5–9.0 μm, resulting in a BET specific surface area of ​​850 m². 2 / g of carbonaceous material (6). Various physical properties of the obtained carbonaceous material (6) were determined. The results are shown in Table 1.

[0092] [Table 1] .

[0093] (Manufacturing of the experimental electrodes) Carbonaceous material, conductive additive, and binder were mixed at a mass ratio of 80:10:10 for 10 minutes. Acetylene black (DENKA BLACK, manufactured by DENKA Corporation) was used as the conductive additive, and polytetrafluoroethylene (POLYFLON D-210C, manufactured by DAIKIN INDUSTRIES) was used as the binder. After stirring, a small amount of alcohol was added while the carbonaceous material, conductive additive, and binder were kneaded. After kneading, a pressure of 10t was applied to the resulting mixture using a press to form a sheet with a thickness of approximately 0.3mm. Circular shapes with a diameter of 12mm were cut from the resulting sheet. A pressure of 1t was applied to press the circular shape onto a 15mm diameter aluminum mesh (manufactured by Taiyo Gold Mesh Co., Ltd., "4AL8-4 / 0w-457") to create an electrode.

[0094] (Assembly of the measuring electrode unit) like Figure 1 The measurement electrode unit was assembled as shown. Assembly of the measurement electrode unit was performed inside a glove box under an argon atmosphere. A bipolar aluminum pouch cell (manufactured by Hosen Co., Ltd., "HS FLAT CELL") was used as the positive electrode 4 and negative electrode 2. The electrodes, fabricated as described above, were overlapped with a 23mm diameter paper separator 3 (manufactured by Kōdō Paper Industry Co., Ltd., "TF4050"). After injecting the electrolyte 9, the unit was sealed. The electrolyte 9 was a 1.0 mol / L solution of tetraethylammonium tetrafluoroborate in propylene carbonate (manufactured by KISHIDA CHEMICAL Co., Ltd., "CPG-00005"). It should be noted that the assembly sequence of the unit, from bottom to top, is: unit (lower part) 1, electrode (negative electrode 2), separator 3, electrode (positive electrode 4), Teflon guide 5, electrode press 6, spring 7, unit (upper part) 8. Figure 1 The electric double-layer capacitor 10 is shown.

[0095] (Rate Test) For the double-layer capacitor 10, a charge-discharge test device (manufactured by Beidou Electric Co., Ltd., "HJ1005SD8") was used at 25℃ until a voltage of 2.5V was reached, with the charge-discharge current density ranging from 0.1 to 100 mA / cm². 2 Changes occur, and charging and discharging take place. Based on the obtained discharge curve data, the electrostatic capacitance C per unit mass of the carbonaceous material in the electrode is calculated using Equation 1. G[F / g]. Here, ΔV in Equation 1 is the maximum unit voltage (2.5V), m is the total mass of the carbonaceous materials of the positive and negative electrodes, and q is the discharge charge. The experimental conditions are shown in Table 2, and the experimental results are shown in Table 3.

[0096] [Mathematical Expression 1] .

[0097] (Cyclic test) For the double-layer capacitor 10, a charge-discharge test device (manufactured by Beidou Electric Co., Ltd., "HJ1005SD8") was used at 25°C until the voltage reached 2.5V, at a rate of 10mA / cm. 2 The charge and discharge current density was repeatedly applied for charging and discharging. Based on the obtained discharge curve data, the capacitance C per unit mass of the carbonaceous material in the electrode was calculated using Equation 1 above. G [F / g]. It should be noted that in Equation 1, ΔV is the maximum unit voltage (2.5V), m is the total mass of the carbonaceous materials in both the positive and negative electrodes, and q is the discharge charge. The capacity retention rate after 10,000 charge-discharge cycles is shown in Table 3.

[0098] [Table 2] .

[0099] [Table 3] .

[0100] It can be seen that the electric double-layer capacitor with electrodes made of carbonaceous material obtained in Examples 1-4 has high rate retention and cycle retention, and excellent rate characteristics and cycle characteristics (durability). In contrast, it can be seen that the electric double-layer capacitor with electrodes made of carbonaceous material obtained in Comparative Example 1 has low rate retention and cycle retention. It can be seen that the electric double-layer capacitor with electrodes made of carbonaceous material obtained in Comparative Example 2 has high rate retention, but low capacitance at low current densities.

[0101] Explanation of reference numerals in the attached figures Unit 1 (Lower Part) 2 Negative electrode 21 Molded body 22 Aluminum Mesh 3. Separators 4 Positive electrode 41 Molded body 42 Aluminum Mesh 5. Teflon guide element 6. Electrode pressing piece 7. Springs Unit 8 (Top) 9 Electrolyte 10. Electric double-layer capacitor.

Claims

1. Carbonaceous material derived from plants, with a BET specific surface area of ​​1000 m². 2 / g or more, and the oxygen desorption amount at 1200℃~2500℃ in the temperature-raising desorption method is 1.1% by mass or more.

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

3. The carbonaceous material according to claim 1 or 2, wherein the hydrogen content is less than 1% by mass.

4. The carbonaceous material according to any one of claims 1 to 3, wherein the R value based on the Raman spectrum is 1.15 or higher and 1.40 or lower, and the half-width of the G band is 70 cm. -1 above.

5. The carbonaceous material according to any one of claims 1 to 4, wherein its BET specific surface area is 2500 m². 2 / g or less.

6. The carbonaceous material according to any one of claims 1 to 5, wherein, In the temperature-induced desorption method, the oxygen desorption rate at 1200℃~2500℃ is less than 10% by mass.

7. The carbonaceous material according to claim 1, wherein it is a carbonaceous material 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 energy storage device comprising the electrode of claim 9.

11. A method for manufacturing the carbonaceous material according to any one of claims 1 to 7, comprising: The process of carbonizing plant-derived raw materials at 320℃~700℃ in an inactive gas atmosphere to obtain carbides. The process of performing alkaline cleaning treatment on the carbide to obtain a carbonaceous material precursor; as well as The process of activating the carbonaceous material precursor at a temperature above 800°C to obtain the carbonaceous material.

12. The manufacturing method according to claim 11, wherein, The plant-derived raw materials are derived from grain husks.

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