Activated carbon for highly reliable electric double layer capacitor with improved long-term reliability and method for producing the same

Abstract

To provide an activated carbon for a highly reliable electric double layer capacitor with improved long-term reliability and a method for producing the same.SOLUTION: The present invention includes a CO2-alkali complex activation step in which acid cleaning is allowed to proceed in a raw material step before activation treatment, and then a carbon material mixed with an alkaline-based activator is activated at a temperature of 700°C or higher under a CO2 atmosphere. According to the present invention, impurities are effectively removed by acid cleaning, and micro pores and meso pores are simultaneously developed by the CO2-alkali complex activation in which alkaline activation (chemical activation) and CO2 activation (physical activation) are allowed to simultaneously proceed, thereby improving the electrical characteristics of the electric double layer capacitor and improving the long-term reliability.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an activated carbon for a highly reliable electric double layer capacitor with improved long-term reliability and a method for producing the same. More specifically, the activated carbon is first treated with an acid to remove impurities from the raw material before activation, and then treated with an alkali (chemical activation) and CO. 2 The present invention relates to an activated carbon for a highly reliable electric double layer capacitor, which can improve the electrical characteristics and long-term reliability of the electric double layer capacitor by simultaneously performing activation (physical activation) and then performing high-temperature heat treatment to remove functional groups, thereby effectively removing impurities and functional groups and simultaneously developing micropores and mesopores, and a method for manufacturing the same. [Background technology]

[0002] Electric double layer capacitors (EDLCs) have a higher energy density and a larger capacity per unit volume than ordinary batteries, allowing for rapid charging and discharging. As a result, EDLCs are used not only as small power sources for memory backup in PCs, but also as power sources for electric and hybrid vehicles, and are in high demand in many fields.

[0003] In general, electric double layer capacitors (EDLCs) use activated carbon as the electrode active material. Activated carbon has a high specific surface area and is useful as an electrode material for electric double layer capacitors (EDLCs). The capacity of an electric double layer capacitor (EDLC) is determined by the amount of charge stored in the electric double layer, and the amount of charge increases as the specific surface area of ​​the electrode increases. As a result, activated carbon has a high specific surface area due to its porous structure, which can improve the capacity and energy density of an electric double layer capacitor (EDLC).

[0004] Activated carbon is produced by carbonizing raw materials (carbon precursors) such as plants or petroleum at high temperatures to obtain carbon materials, which are then activated to form a porous structure. In this case, activation is mainly performed by mixing an alkaline activator such as sodium hydroxide (NaOH) with the carbon material and then heating it in an inert gas atmosphere (chemical activation). During this activation process, alkali metals penetrate between the carbon crystal layers and react to form the pore structure of the activated carbon. For example, Japanese Patent Publication No. 2009-260177 and Japanese Patent Publication No. 2010-245482 disclose related technologies.

[0005] The pore structure of activated carbon, such as the pore size and pore distribution (volume fraction), functions as an important factor for the electrical properties of an electric double layer capacitor (EDLC). The specific surface area and density of the activated carbon change depending on the pore size and distribution, and the electrical properties of the electric double layer capacitor (EDLC), such as the capacity, resistance, energy density, and output characteristics, can change. However, conventional activated carbon and its manufacturing method have a high impurity content, limited control of the pore structure and functional groups, poor electrical properties, and difficulty in maintaining long-term reliability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-260177 [Patent Document 2] Japanese Patent Publication No. 2010-245482 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present invention aims to provide an activated carbon for an electric double layer capacitor, which can remove impurities and functional groups from the activated carbon, improve the pore structure (pore size, distribution, etc.), improve the electrical characteristics of the electric double layer capacitor (EDLC), and provide long-term reliability, and a method for producing the same.

[0008] Specifically, the present invention adds a primary acid washing process in which acid washing is performed at the raw material stage before activation treatment to more stably remove impurities, and then performs a combined activation of chemical and physical methods to improve activation efficiency. The specific surface area and pore structure are developed better overall than in existing processes, and finally, the heat treatment is performed at a very high temperature to minimize the content of functional groups and improve the electrical properties of electric double layer capacitors (EDLCs), thereby providing a highly reliable activated carbon for electric double layer capacitors and a manufacturing method thereof that can provide long-term reliability. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a carbonized carbon material that is acid washed before activation, and the carbon material mixed with an alkaline activator is then subjected to CO 2 The present invention provides activated carbon for electric double layer capacitors (EDLCs), which is activated under atmospheric conditions, has an impurity content of 400 ppm or less, and contains micropores and mesopores.

[0010] The present invention is also characterized in that, of the total pore volume of the activated carbon, micropores having a pore size of 2 nm or less account for 30 volume % or more, and mesopores having a pore size of more than 2 nm and 50 nm or less account for 10 volume % or more.

[0011] The present invention is also characterized in that a pretreatment is carried out in the raw material process, in which the raw materials are crushed to an appropriate particle size.

[0012] The present invention is also characterized in that the crushed raw materials are carbonized at an appropriate temperature to remove volatile materials.

[0013] In addition, the present invention is characterized in that impurities are primarily removed through primary acid washing, which is a process for washing the carbonized raw material with an acid.

[0014] The present invention also relates to a method for producing a nitrogen-containing CO2 The activation is carried out under atmospheric conditions.

[0015] In addition, the present invention is characterized in that impurities and alkali are secondarily removed through a secondary washing step of washing the activated carbon material with an acid.

[0016] The present invention is also characterized in that the oxygen functional groups are removed from the washed and dried activated product by a high-temperature heat treatment process. Effect of the Invention

[0017] According to the present invention, impurities can be removed more effectively through acid washing in the raw material process, and side reactions due to impurities during chemical activation are suppressed, resulting in higher activation efficiency. In addition, chemical activation and physical activation proceed simultaneously in a single process, resulting in a pore structure in which micropores and mesopores are well developed simultaneously with higher efficiency. Furthermore, oxygen functional groups as well as impurities are effectively removed by high-temperature heat treatment.

[0018] Therefore, the present invention has the effect of improving the electrical properties of electric double layer capacitors (EDLCs) such as well-developed micropores and mesopores, high distribution rate (volume %), high specific surface area, low resistance, suppression of side reactions, and appropriate electrode density, thereby improving long-term reliability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] As used herein, the term "and / or" is used to mean the inclusion of at least one of the preceding or following listed elements. As used herein, the term "one or more" means one or more than one.

[0020] The present invention relates to a method for treating a carbonized material by acid washing before activation, and the carbonized material mixed with an alkaline activator is then subjected to CO 2 The activated carbon for electric double layer capacitors according to the present invention is activated by chemical activation with an alkaline activator and CO 2This results in a pore structure in which micropores and mesopores are simultaneously developed, with physical activation by oxidation progressing simultaneously.

[0021] In the present invention, a micropore refers to a pore present in activated carbon whose size (diameter) is 2 nm (nanometers) or less (i.e., diameter (2 nm)), a mesopore refers to a pore present in activated carbon whose size (diameter) is more than 2 nm and less than 50 nm (i.e., 2 nm < diameter (50 nm)), and a macropore refers to a pore present in activated carbon whose size (diameter) is more than 50 nm (i.e., diameter > 50 nm).

[0022] The activated carbon for electric double layer capacitors according to the present invention is 2 -It contains micropores and mesopores simultaneously through alkali-based complex activation, but has an appropriate pore distribution diagram (pore volume fraction). The activated carbon for electric double layer capacitors according to the present invention may have micropores of 30 volume % or more and mesopores of 10 volume % or more of the total pore volume of the activated carbon. In a specific example, the micropores may be about 30 to 80 volume %, and the mesopores may be about 10 to 30 volume %. The remaining pore volume may be occupied by macropores. When the micropores and mesopores have a volume fraction in the appropriate range, the electrical characteristics of the electric double layer capacitor (EDLC) can be improved due to a high specific surface area, low resistance, and appropriate electrode density. Hereinafter, the electric double layer capacitor may be abbreviated as "EDLC" in some cases.

[0023] In the method for producing activated carbon for EDLC according to the present invention, the raw material is crushed to a size of 50 μm or less and carbonized at 500° C. or more to effectively remove volatile materials, and then the impurities are removed at the raw material stage by primary acid washing using hydrochloric acid or the like, thereby minimizing the impurity content that affects long-term reliability and improving activation efficiency due to side reactions of impurities. In the present invention, the raw material means a carbon material before activation. In the present invention, impurities are well known. Most of the impurities are ash. The activated carbon for EDLC according to the present invention has a low impurity content of 400 ppm or less, preferably 350 ppm or less or 300 ppm or less, at least by primary acid washing.

[0024] The method for producing activated carbon for EDLC according to the present invention is to mix a carbon material with an alkaline activator and CO 2 Activation process at temperatures of 700°C or higher in an atmosphere (CO 2 -Alkaline complex activation process. In addition, the method for producing activated carbon for EDLC according to the present invention includes a process for drastically reducing oxygen functional groups by performing heat treatment at a temperature of 1,000°C or higher to remove oxygen functional groups.

[0025] The method for producing activated carbon for EDLC according to the present invention includes, according to a specific embodiment, (1) a step of preparing a carbon material, (2) a washing step of washing the carbon material with an acid (primary acid washing step), (3) a step of washing the carbon material with CO 2 (4) a washing / drying process for washing and drying the activated carbon (secondary acid washing process), and (5) a heat treatment process for heat treating the washed / dried activated carbon. The heat treatment process may be carried out in a state where a reducing agent is mixed with the washed / dried activated carbon according to an embodiment of the present invention. Hereinafter, exemplary embodiments of each process will be described as follows.

[0026] (1) Carbon materials First, the raw material (carbon precursor) is carbonized. The raw material is not particularly limited, and can be selected from, for example, plants (such as coconut shells), petroleum, and / or coal. The raw material can be selected from, for example, coconut shells as a plant-based material.

[0027] Such raw material (such as coconut charcoal) is, for example, cut into particles and thoroughly dried, and then carbonized at a temperature of 400°C to 800°C. More specifically, it is carbonized at a temperature of 500°C to 700°C. The carbonization time is not limited. The carbonization time may vary depending on the carbonization temperature, and may be, for example, about 10 minutes to 24 hours. As a specific example, the carbonization may be performed for 30 minutes to 10 hours under a temperature condition of 500°C to 700°C. Through this carbonization process, the raw material (such as coconut shell) is carbonized while impurities such as volatile components present in the raw material are removed.

[0028] The carbonized carbon material can be pulverized. The carbon material is pulverized to a size of, for example, 50 μm (micrometers) or less. Preferably, the carbon material is pulverized to a fixed size of 0.1 to 20 μm, more preferably 5 to 15 μm. The pulverization method is not particularly limited, and can be performed by a normal method such as a ball mill, a rotary mill, or a vibration mill.

[0029] (2) Cleaning process (primary acid cleaning process) A primary acid washing step is carried out in which the carbonized carbon material, preferably the pulverized carbon material after carbonization, is acid washed. An acid aqueous solution containing at least one selected from hydrochloric acid, nitric acid, sulfuric acid, etc. can be used for the acid washing. The acid washing is carried out before activation. Such acid washing can remove volatile substances and metal impurities that may cause side reactions due to impurities during chemical activation to the maximum extent possible, thereby reducing the impurity content of the final product and maximizing the activation efficiency. An acid aqueous solution with a concentration of 0.5 to 10 wt % can be used for the acid washing. The acid washing can be carried out by impregnating the carbon material with an acid aqueous solution having a weight of about 15 to 25 times that of the carbon material.

[0030] (3) Activation process The acid-washed carbon material (e.g., carbonized coconut shell powder) is porous and activated, where the activation is carried out according to the present invention by CO 2 - The process proceeds through alkaline complex activation. Specifically, the carbon material mixed with the alkaline activator is treated with CO 2 It is activated by heat treatment at a temperature of 700°C or higher in an atmosphere.

[0031] More specifically, the acid-washed carbon material is mixed with an alkaline activator, and the carbon material mixed with the alkaline activator is subjected to CO 2 High temperature is applied in a closed container (chamber, etc.) in the presence of alkali activation (chemical activation) and CO 2 Activation (physical activation) is carried out in a single step. Here, the single step is alkaline activation (chemical activation) and CO 2 This means that activation (physical activation) does not proceed separately, but proceeds simultaneously in one closed container (e.g., chamber). In this activation process, fine pores are generated by alkaline activation (chemical activation), and CO 2 Mesopores are generated by activation (physical activation).

[0032] CO 2 -Alkaline complex activation proceeds at temperatures of 700°C or higher. If the temperature is too low, e.g., below 700°C, 2 Physical activation by CO may not be preferable. Activation can be carried out at a specific temperature of, for example, 700°C to 1,200°C. 2 The alkali complex activation can proceed within the above temperature range for 30 minutes to 3 hours.

[0033] The alkaline activator may be, for example, potassium hydroxide (KOH), sodium hydroxide (NaOH) and / or calcium hydroxide (Ca(OH) 2) can be used. The mixing ratio of the carbon material and the alkaline activator is not particularly limited, but for example, they can be mixed and activated at a weight ratio of 1:0.1 to 10 (i.e., the weight ratio of the pulverized carbon material:activator=1:0.1 to 10). More specifically, they can be mixed and activated at a weight ratio of 1:0.2 to 5.

[0034] The above CO 2 -Alkaline complex activation develops micropores and mesopores at the same time, and the micropores can be 30% or more by volume and the mesopores can be 10% or more by volume of the total pore volume of the activated carbon. Such volume fractions can be determined by the activation temperature, time, the mixture ratio with the alkali activator and / or the CO 2 The injection flow rate and the like can be appropriately controlled and adjusted.

[0035] In the activation step, CO 2 CO is continuously injected into a container (e.g., a chamber) at a flow rate of 2 to 16 L / min. 2 CO should be injected at a flow rate of 6 to 12 L / min. 2 When CO is injected at a flow rate of 6 to 12 L / min, the specific surface area and capacitance can be improved. 2 can be injected mixed with an inert gas (such as nitrogen).

[0036] (4) Washing / drying process CO 2 - The activated carbon obtained by alkali complex activation is washed and dried. Washing is carried out to remove impurities present in the activated carbon. The washing can be selected from, for example, alkali washing and acid washing, or both in parallel. It is preferable to wash the activated carbon by alkali washing and acid washing in parallel.

[0037] In addition, when a metal compound such as KOH is used as an alkaline activator in the activation step, the washing preferably includes at least an acid washing (secondary acid washing) so as to remove impurities present in the raw material and the alkali metal compound (KOH, etc.), etc. As the acid washing (secondary acid washing), for example, an aqueous solution of an acid such as hydrochloric acid or sulfuric acid can be used.

[0038] After washing as described above, moisture present in the activated carbon is removed by drying. The drying method is not particularly limited, and can be carried out, for example, by hot air drying or natural drying.

[0039] (5) Heat treatment process Next, the washed and dried activated carbon is heat-treated, that is, a heat treatment process is performed in which the washed and dried activated carbon is heat-treated under specific conditions.

[0040] According to an embodiment of the present invention, in producing activated carbon, the carbon material is treated with CO 2 - When heat treatment is performed after alkali complex activation, side reactions (gas generation, etc.) can be minimized by controlling the surface functional groups, and excellent conductivity can be obtained.

[0041] Specifically, after the activated carbon is washed and dried, it is heat-treated at 600 to 1,200°C for 10 to 60 minutes. It is preferable to proceed at a high temperature of 1,000°C or higher, and specifically, it is preferable to heat-treat for 30 to 60 minutes at 1,000 to 1,200°C. Such heat treatment can be carried out, for example, in N2 gas containing 4% or less hydrogen gas. 2 The heat treatment step can be carried out in an inert gas atmosphere such as Ar. The heat treatment step is preferably carried out by mixing the activated carbon with a reducing agent. When the activated carbon is mixed with a reducing agent and then heat-treated, the functional groups of the activated carbon can be dramatically reduced.

[0042] According to the present invention, as described above, 2When heat-treated at a specific temperature range together with alkali complex activation, activated carbon having a high specific surface area, particularly excellent electrical conductivity, and high reliability can be produced. The activated carbon produced as described above has excellent resistance characteristics, and when producing an activated carbon composition (slurry) for EDLC electrodes, the content of the conductive material can be reduced, and the content of the activated carbon can be increased accordingly, resulting in a higher capacitance. As a result, when used as an EDLC electrode, it can have high output and / or long-term reliability. In addition, when heat-treated in a state where a reducing agent is further mixed, oxygen functional groups are minimized, improving electrical properties.

[0043] After the heat treatment, a classification process may be further carried out according to an exemplary embodiment of the present invention. The classification process is for classifying the heat-treated activated carbon to select activated carbon having a size of 60 μm or less, which may be carried out by, for example, passing the heat-treated activated carbon through a sieve to remove particles exceeding 60 μm.

[0044] More specifically, activated carbon with a size of 0.1 to 60 μm can be selectively obtained. Through such a classification process, activated carbon with a size of preferably 20 μm or less, more preferably 10 μm or less can be obtained as a final product. According to a specific embodiment, activated carbon with a uniform size of 0.5 μm to 10 μm can be obtained as a final product through the classification process. Such activated carbon is used as an electrode material (positive and negative electrode active materials) for EDLC.

[0045] Hereinafter, examples and comparative examples of the present invention will be illustrated. The following examples are provided to aid in understanding the present invention, and are not intended to limit the technical scope of the present invention. Note that the following comparative examples do not represent prior art, and are provided simply for comparison with the examples.

[0046] [Comparative Examples 1 to 3] A coconut shell was used as a raw material, and the coconut shell carbon material was prepared by carbonizing and crushing it. The carbon material and alkali (KOH) were mixed in a weight ratio of 1:2.1 (Comparative Example 1), 1:2.5 (Comparative Example 2), and 1:3.0 (Comparative Example 3). The mixture was then placed in a chamber, and CO 2 / N 2 Chemical activation and physical activation were simultaneously carried out at a temperature of 800°C in an atmosphere. The activated carbon obtained by the activation was then subjected to acid washing and water washing, and dried. The dried activated carbon was then heat-treated at a temperature of 840°C to produce activated carbon samples according to each comparative example.

[0047] [Examples 1 to 4] The coconut shell carbon material, which was made by carbonizing and crushing coconut shells as a raw material, was primarily acid-washed using hydrochloric acid. The primary acid washing was performed by impregnating the carbon material with a 3 wt% diluted hydrochloric acid solution that was 20 times the raw material ratio. Thereafter, the activation, acid washing (secondary) and drying processes were carried out in the same manner as in Comparative Example 3. The dried activated carbon was then heat-treated at temperatures of 840°C (Example 1), 1,000°C (Example 2), 1,100°C (Example 3) and 1,150°C (Example 4) to produce activated carbon samples according to each Example.

[0048] The specific surface area (m 2 / g), total porosity (cm 3 / g), mesopores (cm 3 The content of functional groups (meq / g), meq / g and ash content were evaluated, and the results are shown in Table 1 below. [Table 1]

[0049] As shown in Table 1, it can be seen that the impurity (Ash) content of the final product varies by more than two times depending on whether or not the raw material before activation is subjected to primary acid washing. It can also be seen that there is a large difference in the specific surface area and pore characteristics of the activation depending on whether or not the primary acid washing is performed. This can be seen as the content of impurities causing other side reactions during the activation process and inhibiting the activation of carbon, and it can be seen that the activation efficiency is increased by the acid washing. It can be seen that this increase in activation efficiency allows for heat treatment at a higher temperature and can significantly reduce the functional group. It can be seen that the increase in efficiency due to the primary acid washing can improve the specific surface area and pore characteristics and reduce the content of oxygen functional groups compared to when the primary acid washing is not performed. It can also be seen that heat treatment at a high temperature can significantly reduce the content of oxygen functional groups.

[0050] Therefore, according to the present invention, it is possible to obtain highly reliable activated carbon in which impurities and functional groups are controlled. Also, according to the present invention, it is possible to provide activated carbon which has high efficiency in removing impurities and functional groups and excellent electrical properties, which is of great industrial and technological value.

Claims

1. The carbonized carbon material is washed with acid before activation, and the carbon material mixed with an alkaline activator is then heated to CO 2 1. An activated carbon for an electric double layer capacitor, which is activated under an atmosphere, has an impurity content of 400 ppm or less, and contains micropores and mesopores.

2. In claim 1, The activated carbon for electric double layer capacitors is characterized in that, of the total pore volume of the activated carbon, micropores having a pore size of 2 nm or less account for 30 volume% or more, and mesopores having a pore size of more than 2 nm and 50 nm or less account for 10 volume% or more.

3. A cleaning process in which the carbonized carbon material is pickled; The acid-washed carbon material is mixed with an alkaline activator, and the carbon material mixed with the alkaline activator is subjected to CO 2 CO activated at temperatures above 700°C in an atmosphere 2 -Alkaline complex activation process, The CO 2 - a washing / drying process for washing and drying the alkali complex activated carbon; A method for producing activated carbon for an electric double layer capacitor, comprising a heat treatment step of heat treating the washed / dried activated carbon.

4. In claim 3, The heat treatment step comprises mixing the washed and dried activated carbon with a reducing agent and then heat treating the mixture.

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