JP7338993B2 - Porous carbon and method for producing porous carbon - Google Patents

Description

TECHNICAL FIELD The present invention relates to porous carbon having a large macropore volume and high electrical conductivity, and a method for producing the same.

The pores of porous carbon are classified into micropores with a pore size of less than 2 nm, mesopores with a pore size of 2 nm or more and less than 50 nm, and macropores with a pore size of 50 nm or more. Porous carbon with macropores has excellent adsorption properties for macromolecules, and in recent years, its use as a conductive material for lithium-sulfur batteries, which are expected to be next-generation high-capacity batteries, has been investigated. there is

Porous carbon having macropores is produced by (1) a method of calcining a polymer blend, (2) a method of using polymer fine particles with a controlled particle size as a template, and (3) a method of calcining an organic acid salt. be able to.

In method (1), porous carbon is produced by mixing a thermosetting resin and a thermoplastic resin, curing the thermosetting resin, then eluting and removing the thermoplastic resin with a solvent, and then baking the carbon. (for example, Patent Document 1).

In the method (2), porous carbon is produced by applying a solution containing a carbon source to colloidal crystals of fine polymer particles, then heat-treating to generate a polymer of the carbon source between the colloidal crystals, and sintering at a high temperature. (For example, Patent Document 2).

In the method (3), porous carbon is produced by baking an organic acid salt and removing the produced inorganic salt by acid washing (eg, Non-Patent Document 1, Non-Patent Document 2).

JP 2004-026954 A JP 2012-101355 A

J. MATER. CHEM. A (2013) 13738-13741 RSC ADVANCE (2015) 57576-57580

In the above methods (1) and (2), it is difficult to achieve both a large macropore volume and high electrical conductivity in porous carbon. In the above methods (1) and (2), it is difficult to control the specific surface area and porous structure of the porous carbon, and in addition, high-temperature firing is required to increase conductivity. This is because macropores are likely to be reduced when the treatment is carried out. In addition, the above methods (1) and (2) involve many steps and complicated operations, and are not suitable for industrial production. Compared with the methods (1) and (2), the method (3) is easier to control the specific surface area and the porous structure, and it is easier to obtain high conductivity even at relatively low temperatures. Therefore, the obtained porous carbon has macropores formed to some extent due to the organic acid salt, but the macropore volume is still small.

In view of the above, one aspect of the present invention is that the specific surface area by the BET method is 200 m ² /g or more and 650 m ² /g or less,
The macropore volume by the BJH method is 0.5 cm ³ /g or more,
It relates to porous carbon having a powder conductivity of 20 S/cm or more.

Another aspect of the invention is the step of:
(1) mixing an organic acid salt and a first organic acid to obtain a mixture;
(2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide;
(3) obtaining porous carbon from the carbide;
The step (3) relates to the method for producing porous carbon, including the step of acid-washing the carbide.

It is possible to provide porous carbon that can ensure high conductivity while having a large macropore volume.

BEST MODE FOR CARRYING OUT THE INVENTION 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 gist of the present invention.

The porous carbon according to one aspect of the present invention has a specific surface area of 200 m ² /g or more and 650 m ² /g or less by the BET method, and a macropore volume of 0.5 cm ³ /g or more by the BJH method, Powder conductivity is 20 S/cm or more.

Porous carbon can be prepared, for example, by the following steps:
(1) mixing an organic acid salt and an organic acid (first organic acid) to obtain a mixture;
(2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide;
(3) obtaining porous carbon from the carbide;
It can be produced by a method for producing porous carbon, in which step (3) includes a step of pickling the carbide. Other aspects of the invention include such manufacturing methods.

When a carbide is formed using an organic acid salt, a carbon skeleton grows with the organic acid salt as a nucleus. At this time, the coexistence of the first organic acid also causes carbon growth originating from the first organic acid around the core of the organic acid salt. As a result, the carbon skeleton derived from the first organic acid grows around the carbon skeleton derived from the organic acid salt. The first organic acid is more likely to generate gases such as water vapor and carbon dioxide than organic acid salts. Many large pores are formed. Therefore, the macropore volume of the resulting porous carbon can be increased. In addition, when the number of pores with large pore diameters increases, the electrical conductivity usually tends to decrease. A decrease can be suppressed, and high conductivity can be secured.

According to the above aspect of the present invention, the increased macropore volume can also increase the percentage of macropore volume. The ratio of the macropore volume to the total pore volume determined by the BJH method is, for example, 50% or more, and can be increased to 60% or more.

Moreover, according to the aspect of the present invention, high conductivity of the porous carbon can be ensured. The conductivity of porous carbon can be evaluated by powder conductivity. The powder conductivity of the porous carbon is 20 S/cm or more, and a high value of 25 S/m or more can be secured.

On the other hand, when the organic acid salt is used and the first organic acid is not used, the macropore volume itself becomes small. Also, when the organic acid salt is not used and the first organic acid is used, the metal compound derived from the organic acid salt, which is the source of the macropores, is not formed, and thus macropores are hardly formed.

The specific surface area, pore volume, and powder conductivity are determined by the following procedure.
(Specific surface area)
The specific surface area of porous carbon by the BET method (hereinafter sometimes simply referred to as the BET specific surface area) is obtained by using the BET equation from the adsorption isotherm measured for porous carbon by a gas adsorption method using nitrogen gas. It is the required specific surface area. More specifically, the BET specific surface area is determined by the following procedure.

Using "Autosorb-iQ-MP" manufactured by Quantachrome Co., Ltd., the amount of nitrogen adsorbed to the porous carbon at liquid nitrogen temperature is measured as follows. A sample tube is filled with porous carbon, which is a measurement sample, and the sample tube is cooled to -196 ° C., the pressure is reduced once, and then nitrogen (purity 99.999%) is adsorbed on the measurement sample at a desired relative pressure. and measure the adsorption isotherm. The BET specific surface area is obtained from the obtained adsorption isotherm by a multipoint method (eg, 3 points) in the range of relative pressures of 0.05 to 0.1.

(pore volume)
The adsorption isotherm of porous carbon measured when determining the BET specific surface area is analyzed by the BJH (Barrett Joyner Hallenda) method, and the pore volume with a pore diameter of 50 nm or more and 200 nm or less is defined as a macropore volume, and 2 nm or more and less than 50 nm. The pore volume of is defined as the mesopore volume. The adsorption isotherm of porous carbon is analyzed by the DFT (Density Functional Theory) method, and the pore volume with a pore diameter of less than 2 nm is defined as the micropore volume. More specifically, the QS- DFT method (Slit Pore, Equilibrium Model) is adopted as the DFT method.
Further, the total pore volume of the BJH method is an integrated value of the pore volume obtained from the pore size distribution obtained by analyzing the adsorption isotherm of the porous carbon by the BJH method.

(powder conductivity)
The powder conductivity is the reciprocal of the volume resistivity of porous carbon measured using a commercially available powder resistance measuring device. The volume resistivity is measured by using a powder resistivity measurement unit "MCP-PD51" and a resistivity meter "Loresta GP MCP-T610" manufactured by Mitsubishi Chemical Analytech Co., Ltd., and pressurizes porous carbon, which is a measurement sample, to 63 MPa. Measured with

Hereinafter, porous carbon according to embodiments of the present invention and a method for producing the same will be described in more detail.

[Porous carbon]
The BJH macropore volume of the porous carbon is 0.5 cm ³ /g or more, and can be as large as 0.55 cm ³ /g or more or 0.6 cm ³ /g or more. When the macropore volume is in such a range, it is possible to ensure high adsorption properties due to the macropores. The macropore volume is, for example, 1.2 cm ³ /g or less, and may be 1 cm ³ /g or less. When the macropore volume is in such a range, it becomes easier to suppress the decrease in conductivity.

In the porous carbon according to the present embodiment, many large pores such as mesopores and macropores are formed, while micropores tend to be few. The micropore volume of the porous carbon measured by the DFT method is, for example, 0.25 cm ³ /g or less, and may be 0.2 cm ³ /g or less. When the micropore volume is within such a range, the volume ratio of the macropores is likely to be increased, and the effects of the macropores (for example, high adsorption and liquid permeability) are likely to be exhibited. Although the lower limit of the micropore volume is not particularly limited, it is, for example, 0.05 cm ³ /g or more, and may be 0.1 cm ³ /g or more. When the micropore volume is within such a range, it becomes easier to control the BET specific surface area of the porous carbon and to ensure high conductivity.

According to this embodiment, the volume of the macropores can be increased, so the ratio of the macropores can be increased. The ratio of the macropore volume to the total pore volume determined by the BJH method is, for example, 50% or more, and may be 55% or more. It is also possible to increase the percentage of macropore volume to 60% or more. When the ratio of the macropores is within such a range, the effects of the macropores are likely to be exhibited. Although the upper limit of the ratio of macropores is not particularly limited, it is preferably 80% or less, and may be 75% or less, from the viewpoint of easily ensuring high conductivity.

The BET specific surface area of the porous carbon is 200 m ² /g or more, and may be 250 m ² /g or more or 300 m ² /g or more. When the BET specific surface area is in such a range, higher conductivity is likely to be obtained. The BET specific surface area is 650 m ² /g or less, and may be 500 m ² /g or less. When the BET specific surface area is within such a range, the volume ratio of the macropores is likely to be increased, and the effects of the macropores are likely to be exhibited.

Porous carbon exhibits high conductivity, and its powder conductivity is 20 S/cm or more, and may be 25 S/cm or more, and a high value of 40 S/m or more or 50 S/m or more can be obtained. can also The higher the powder conductivity, the better the conductivity, and although the upper limit is not particularly limited, it may be, for example, 100 S/cm or less.

Since porous carbon has many macropores, the average interplanar spacing d002 of (002) planes obtained from the X-ray diffraction spectrum is larger than that of highly crystalline graphite or the like. The d002 of porous carbon is, for example, 0.36 nm or more. From the viewpoint of easily ensuring higher conductivity, d002 is preferably 0.38 nm or less.

d002 is obtained from the following Bragg formula by wide-angle X-ray diffraction using CuKα rays.
λ=2d×sin θ
λ: wavelength of CuKα rays (= 0.15418 nm)
d: average interplanar spacing d002 of (002) plane
θ: angle of 1/2 of 2θ of the peak position obtained by the centroid method Wide-angle X-ray diffraction is performed using Rigaku Co., Ltd. “MiniFlex II”, and the sample holder is filled with CuKα rays monochromatic by a Ni filter as a radiation source. It is performed on the powder of the porous carbon that has been made. In the obtained diffraction pattern, the peak position is obtained by the centroid method (a method of obtaining the centroid position of the diffraction line and obtaining the peak position with the corresponding 2θ value), and the diffraction of the (111) plane of the high-purity silicon powder for standard substance Correct using the peak.

[Method for producing porous carbon]
According to this embodiment, by using the organic acid salt and the first organic acid, porous carbon having a large macropore volume and high electrical conductivity can be produced by a simple method. In addition, the production method according to the present embodiment can use inexpensive raw materials, has a small number of steps, and does not include steps that are technically difficult, so it is advantageous in terms of cost and is excellent in terms of safety. and suitable for industrial production.
Each step will be described below.

(1) Mixing Step In this step, the organic acid salt and the first organic acid, which are raw materials of the porous carbon, are mixed. By using the organic acid salt, the carbon skeleton is easily formed by carbonization with the organic acid salt as a nucleus, and the structure of the carbon skeleton can be easily controlled. Moreover, by using the first organic acid, the growth of carbon derived from the first organic acid proceeds around the carbon skeleton derived from the organic acid salt, and many macropores can be formed. The combination of the organic acid salt and the first organic acid optimizes the structure of the carbon skeleton and the pore structure, and ensures high electrical conductivity.

(First organic acid)
The first organic acid is not particularly limited, but preferably has a melting point lower than the decomposition temperature of the organic acid salt. Such a first organic acid tends to generate water vapor and/or carbon dioxide gas when the carbon skeleton derived from the organic acid salt is formed in step (2). Therefore, by using such a first organic acid, the volume of macropores can be increased. Also, if the first organic acid is solid at room temperature (for example, 20° C. or higher and 35° C. or lower), dry mixing can be performed, which is convenient.

The first organic acid preferably has two or more functional groups selected from the group consisting of a carboxy group and a hydroxy group (provided it has at least one carboxy group). Examples of such first organic acids include polycarboxylic acids and hydroxycarboxylic acids. In the first organic acid, the total number of carboxy groups and hydroxy groups per molecule is, for example, 2 or more, preferably 3 or more. In the first organic acid, the total number of carboxy groups and hydroxy groups per molecule is, for example, 8 or less, and may be 6 or less or 4 or less. The first organic acid may have other functional groups such as alkyl groups (for example, monovalent functional groups other than carboxy groups and hydroxy groups), but carbonization is likely to proceed, and the structure of the carbon skeleton is In addition to being easy to control, those having no other functional groups are preferable from the viewpoint of easily ensuring higher conductivity of the porous carbon. For the same reason, aliphatic carboxylic acids (especially chain aliphatic carboxylic acids) are preferred.

The hydroxycarboxylic acid may have one carboxy group, but preferably has two or more (that is, it is a polyvalent carboxylic acid having a hydroxy group). Hydroxycarboxylic acids include, for example, malic acid, citric acid, gluconic acid and the like. Malonic acid, succinic acid, maleic acid, etc. are mentioned as polyhydric carboxylic acid which does not have a hydroxy group. Also, the polyvalent carboxylic acid may be a polyvalent ketocarboxylic acid. Examples of polyvalent ketocarboxylic acids include polyvalent β-ketocarboxylic acids (oxaloacetic acid, acetonedicarboxylic acid, etc.).

The number of carbon atoms in the first organic acid may be, for example, 8 or less or 7 or less. From the viewpoint of facilitating securing, it is preferably 6 or less. The number of carbon atoms in the first organic acid is preferably 3 or more, and may be 4 or more, from the viewpoint of facilitating control of the timing of gas generation by decomposition of the first organic acid during carbonization.

A 1st organic acid may be used individually by 1 type, and may be used in combination of 2 or more types.
At least citric acid is preferably used as the first organic acid. Citric acid is readily available, inexpensive, and highly safe. In addition, the use of citric acid facilitates control of the timing of gas generation, particularly when the organic acid salt is carbonized. Therefore, it becomes easy to increase the volume of the macropores.

The ratio of the first organic acid to the total amount (100% by mass) of the first organic acid and the organic acid salt is, for example, 10% by mass or more, preferably 15% by mass or more or 20% by mass or more. The ratio of the first organic acid is, for example, 60% by mass or less. When the ratio of the first organic acid is within such a range, the ratio of macropore volume in the porous carbon can be increased. The ratio of the first organic acid is preferably 55% by mass or less, more preferably 45% by mass or less or 30% by mass or less. When the ratio of the first organic acid is within such a range, the effect of suppressing a decrease in conductivity can be further enhanced.

(Organic acid salt)
The organic acid salt is preferably a salt of an organic acid (second organic acid) and a metal so that the organic acid salt easily becomes a nucleus during carbon growth of the first organic acid. As the second organic acid, those exemplified for the first organic acid (polyvalent carboxylic acid, hydroxycarboxylic acid, etc.) are preferable from the viewpoint of facilitating carbonization.

The metal constituting the organic acid salt may be a transition metal or the like, but is preferably an alkali metal or a Group 2 metal of the periodic table so as to be easily removed when pickling the carbide. Alkali metals include lithium, sodium, potassium and the like. Magnesium and alkaline earth metals (such as calcium) are preferred as the Group 2 metals of the periodic table. Alkali metals (sodium, potassium, etc.), magnesium, calcium, etc. are preferred, and alkali metals are particularly preferred, from the viewpoint of being inexpensive and easy to remove. The organic acid salt may contain one kind of metal, or two or more kinds thereof. Two or more organic acid salts having different metals and/or second organic acids may be used in combination.

Specific examples of organic acid salts include citrate (sodium citrate, potassium citrate, lithium citrate, etc.), gluconate (sodium gluconate, potassium gluconate, lithium gluconate, etc.), and maleate. (sodium maleate, potassium maleate, lithium maleate, etc.), malonates (sodium malonate, potassium malonate, lithium malonate, etc.), succinates (sodium succinate, potassium succinate, lithium succinate, etc.) , malate (sodium malate, potassium malate, lithium malate, etc.). Alkali metal salts of citric acid (especially sodium citrate) are preferred from the standpoint of easy availability and low cost.

(others)
The method for mixing the organic acid salt and the first organic acid is not particularly limited as long as both components can be mixed, and either dry mixing or wet mixing may be employed.

When using a first organic acid that is solid at room temperature, dry mixing can be used. In the dry mixing, from the viewpoint of mixing the first organic acid and the organic acid salt more uniformly, for example, it is preferable to mix these components by grinding them in a mortar or pulverizing them in a ball mill to form a powder. . It is not particularly limited to these cases, and a known dry mixer may be used.

Wet mixing is utilized when the first organic acid is liquid at room temperature. Alternatively, wet mixing may be performed using a solvent. For example, the organic acid salt and/or the first organic acid can be dissolved in a solvent and mixed together. One component of the organic acid salt and the first organic acid may be dissolved in a solvent and the other component may be added to the solution and mixed. may be mixed. After wet-mixing both components, the solvent may be removed by volatilization if necessary.

The solvent is not particularly limited, and examples thereof include water, organic solvents, mixtures thereof, and the like. Examples of organic solvents include alcohols (ethanol, methanol, isopropyl alcohol, ethylene glycol, etc.), ethers (tetrahydrofuran, 1,4-dioxane, dimethoxyethane, etc.), but are not limited to these. The solvent is selected according to the type of the first organic acid and/or organic acid salt. A solvent may be used individually by 1 type, and may combine 2 or more types. It is preferable to use water as a solvent because both the organic acid salt and the organic acid are easily dissolved and the equipment can be simplified, and a mixture of water and an organic solvent (preferably a water-soluble organic solvent) is may be used.

(2) Step of Obtaining Carbide In this step, a carbide is generated by heat-treating the mixture obtained in step (1) above. The heat treatment is performed under an inert gas atmosphere. Inert gases include, for example, nitrogen and/or argon.

The heat treatment is preferably performed at least at a temperature of 600° C. or higher and 800° C. or lower (first temperature). By heat-treating at such a temperature, it is possible to suppress an increase in the micropore volume and increase the ratio of the macropore volume, and it becomes easy to ensure high electrical conductivity of the porous carbon. In addition, the removal of the metal component derived from the organic acid salt is facilitated in the washing step. The first temperature is preferably 650° C. or higher and 780° C. or lower, and more preferably 650° C. or higher and 750° C. or lower.

The heat treatment may be performed in one step, in multiple steps, or while the temperature is being raised. Even when the heat treatment is performed in multiple stages or while the temperature is raised, it is preferable to perform the heat treatment at least at the first temperature. That is, the step (2) preferably includes at least a step of heat-treating at the first temperature (primary heat-treating step).

The primary heat treatment time is, for example, 30 minutes or more and 4 hours or less, or may be 30 minutes or more and 2 hours or less.

Step (2) may include a preliminary heat treatment step at a temperature below the first temperature prior to the primary heat treatment step. The temperature in the preliminary heat treatment step may be lower than the first temperature, and may be lower than 650°C, or may be lower than or equal to 600°C or lower than 600°C. The temperature in the preliminary heat treatment step is, for example, 400° C. or higher or 500° C. or higher. By performing such a preliminary heat treatment step, it is possible to obtain a carbide having more uniform physical properties. The preliminary heat treatment step is performed under an inert gas atmosphere as described above.

(3) Step of forming porous carbon Step (3) includes a step of washing the carbide obtained in step (2). Cleaning of the carbide is performed at least by acid cleaning. Acid washing removes residues of organic acid salts (such as metal components) in the carbide to obtain porous carbon. Charcoal is usually washed with water after acid washing. The acid washing and water washing are preferably repeated until the residue of the organic acid salt in the carbide is sufficiently removed.

The cleaning liquid used for acid cleaning is usually an aqueous acid solution. An inorganic acid is suitable as the acid used for washing. Inorganic acids include, for example, hydrochloric acid, nitric acid, and/or sulfuric acid. Hydrochloric acid is preferable from the viewpoint of easily dissolving the residue of the organic acid salt and easily suppressing oxidation of the carbide. The concentration of protons (or hydrochloric acid) in the cleaning solution is, for example, 0.01 mol/L or more and 1.0 mol/L or less, preferably 0.05 mol/L or more and 0.5 mol/L or less. By adjusting the concentration of protons (or acid) in the cleaning liquid, the number of times of acid cleaning can be reduced, and the amount of acid remaining in the carbide can be reduced.

Acid washing and water washing may be carried out at room temperature (for example, 20° C. or higher and 35° C. or lower), but from the viewpoint of efficient washing, it is preferable to carry out at a temperature of 40° C. or higher (especially 60° C. or higher). The temperature of acid washing and water washing is usually less than 100°C and may be 90°C or less.

The charcoal (porous carbon) obtained after acid washing and water washing may be dried. Drying may be performed, for example, under heating (for example, using a hot air dryer) or under reduced pressure. A known dryer can be used for drying. The drying temperature is, for example, 50° C. or higher and 150° C. or lower. By drying at such a temperature, the drying can be performed in a relatively short time while suppressing oxidation of the porous carbon.

Step (3) can optionally include a secondary heat treatment step of heat treating the porous carbon at a second temperature after the acid washing step. The secondary heat treatment step is preferably performed after acid cleaning and water cleaning. If necessary, the above drying may be performed before the secondary heat treatment. By performing drying before the secondary heat treatment, it is possible to suppress oxidation of the porous carbon due to adsorbed water in the secondary heat treatment.

The second temperature is, for example, 650° C. or higher, and may be 650° C. or higher and 1000° C. or lower. The second temperature may be lower than or equal to the first temperature, but is preferably higher than the first temperature from the viewpoint of obtaining higher conductivity. The second temperature is, for example, 750° C. or higher (or 780° C. or higher), preferably higher than 750° C. (or 780° C.), and may be 800° C. or higher. The second temperature is preferably 950° C. or lower, and may be 900° C. or lower, from the viewpoint of suppressing shrinkage of the carbon structure due to heating and suppressing reduction in macropores.

The secondary heat treatment is preferably performed in an inert gas atmosphere so that oxidation of the porous carbon does not proceed. Inert gases include nitrogen and/or argon.

The secondary heat treatment time is, for example, 30 minutes or more and 4 hours or less, or may be 30 minutes or more and 2 hours or less.

(others)
Porous carbon may be pulverized and used depending on the application. Pulverization is not particularly limited, and for example, a known pulverizer (eg, ball mill, centrifugal roll mill, ring roll mill, centrifugal ball mill, etc.) can be used. Pulverization is preferably carried out in an inert gas atmosphere in order to prevent the particle surfaces from being oxidized. The particle size distribution of the porous carbon may be controlled by classification, if necessary.

The average particle size of porous carbon is determined depending on the application. The average particle size of porous carbon may be, for example, 2 μm or more and 30 μm or less.
The average particle diameter of the porous carbon is the median diameter (D50) at which the cumulative volume is 50% in the volume-based particle size distribution determined by a laser diffraction/scattering type particle size distribution analyzer.

[Example]
EXAMPLES The present invention will be specifically described below based on examples and comparative examples, but the present invention is not limited to the following examples.

<<Examples 1 to 3 and Comparative Example 1>>
The raw materials shown in Table 1 were mixed at the ratio shown in Table 1 using a mortar. The resulting mixture was heated to the first temperature shown in Table 1 at a heating rate of 5° C./min in a nitrogen gas atmosphere. Then, a carbide was obtained by heat-treating at the first temperature for 60 minutes. The carbide was washed with a 0.1 mol/L hydrochloric acid aqueous solution at 80° C. for 30 minutes (acid washing) and washed with water. Acid washing and water washing were repeated three times in total. A porous carbon was obtained by drying with hot air at 80°C. Trisodium citrate dihydrate was used as the organic acid salt, and citric acid was used as the organic acid (first organic acid).

<<Examples 4-5>>
The porous carbon obtained in Example 1 was heated to the second temperature shown in Table 1 at a heating rate of 10° C./min in a nitrogen gas atmosphere. Next, a heat treatment (secondary heat treatment) was performed at a second temperature for 60 minutes under a nitrogen gas stream to obtain porous carbon.

<<Comparative Example 2>>
Porous carbon was produced in the same manner as in Example 1, except that glucose was used instead of the first organic acid.

[evaluation]
For the porous carbons obtained in Examples and Comparative Examples, the BET specific surface area, each pore volume, macropore volume ratio, powder electrical conductivity, and d002 were obtained by the procedure described above.
Table 2 shows the results. In Tables 1 and 2, A1-A5 are Examples 1-5, and B1-B2 are Comparative Examples 1-2.

As shown in Table 2, the porous carbon of Comparative Example 3, which was produced using glucose instead of the organic acid, formed a dense porous structure. Specifically, the macropore volume was as small as 0.20 cm ³ /g, the ratio was as low as 40%, and the powder electrical conductivity was as low as 14 S/cm. On the other hand, by combining the organic acid salt and the first organic acid, the porous carbon of the example secures a high powder conductivity of 20 S/m or more, while maintaining a high conductivity of 0.5 cm ³ /g or more. Macropore volume can be ensured. In addition, in Examples, a high macropore volume ratio of 50% or more (further 60% or more) can be secured.

Compared to Comparative Example 1 using only an organic acid salt, in Example 1, the mesopore volume and macropore volume are large, and the micropore volume is small, so that large pores are more likely to occur than small pores. It can be said that there are Since the mesopore volume and the macropore volume are large in the other examples as well, it can be said that the use of the first organic acid facilitates the formation of large pores, as in the case of the first example.

Heat treatment at a higher temperature tends to increase the crystallinity of the porous carbon, so that the electrical conductivity is improved, but the mesopores and macropores are reduced and the micropores are increased. However, in the examples, the combination of the organic acid salt and the first organic acid can optimize the structure of the carbon skeleton, and can suppress the decrease in the macropore volume (Examples 4 and 5). ).

According to the production method according to one aspect of the present invention, by using an organic acid salt and an organic acid in combination, porous carbon having a large macropore volume and high conductivity can be easily produced. Since porous carbon has high conductivity, it is suitable for use as a conductive material. In addition, since porous carbon has a relatively large BET specific surface area and a large macropore volume, it also has a high affinity for liquids such as electrolytic solutions. Therefore, it can be used as an electrode material for batteries, capacitors, and the like that use an electrolytic solution. Porous carbon has high adsorptivity and can adsorb large molecules (including macromolecules), so it is expected to be used not only as an adsorbent but also as a conductive material for lithium-sulfur batteries. be.

Claims (15)

A specific surface area by the BET method is 200 m ² /g or more and 650 m ² /g or less,
The macropore volume by the BJH method is 0.67 cm ³ /g or more,
The powder conductivity under pressure of 63 MPa is 20 S / cm or more,
Porous carbon that is not boron-doped, sulfur-doped, phosphorous-doped, or nitrogen-doped. A specific surface area by the BET method is 200 m ² /g or more and 650 m ² /g or less,
The macropore volume by the BJH method is 0.67 cm ³ /g or more,
Porous carbon having a powder conductivity of 51 S/cm or more under pressure of 63 MPa. 3. The porous carbon according to claim 1, wherein the macropore volume accounts for 60% or more of the total pore volume measured by the BJH method. The porous carbon according to any one of claims 1 to 3, wherein the macropore volume is 0.67 cm ³ /g or more and 1.2 cm ³ /g or less. The porous carbon according to any one of claims 1 to 4, wherein the specific surface area is 200 m ² /g or more and 500 m ² /g or less. The porous carbon according to any one of claims 1 to 5, having a micropore volume of 0.2 cm ³ /g or less by the DFT method. 2. The porous carbon according to claim 1 , wherein said powder conductivity is 25 S/cm or more. The following steps:
(1) mixing an organic acid salt and a first organic acid to obtain a mixture;
(2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide;
(3) obtaining porous carbon from the carbide;
The step (3) includes acid washing the carbide,
A method for producing porous carbon, wherein the mixture does not contain substances for boron doping, sulfur doping, phosphorus doping, and nitrogen doping. The step (2) includes a primary heat treatment step of heat-treating at a first temperature,
The method for producing porous carbon according to claim 8, wherein the first temperature is 600°C or higher and 800°C or lower. 10. The method for producing porous carbon according to claim 9, wherein said step (3) further includes a secondary heat treatment step of heat-treating at a second temperature higher than said first temperature after said acid washing step. The method for producing porous carbon according to claim 10, wherein the second temperature is 900°C or lower. The following steps:
(1) mixing an organic acid salt and a first organic acid to obtain a mixture;
(2) heat-treating the mixture in an inert gas atmosphere to obtain a carbide;
(3) obtaining porous carbon from the carbide;
The step (2) includes a primary heat treatment step of heat-treating at a first temperature,
the first temperature is 600° C. or higher and 800° C. or lower;
The step (3) includes a step of pickling the carbide, and a secondary heat treatment step of heat-treating at a second temperature higher than the first temperature after the pickling step. A method for producing porous carbon. . The first organic acid is at least one selected from the group consisting of polyvalent carboxylic acids and hydroxycarboxylic acids,
The method for producing porous carbon according to any one of claims 8 to 12, wherein the first organic acid has 6 or less carbon atoms. The porous material according to any one of claims 8 to 13, wherein the organic acid salt is a salt of a second organic acid and at least one selected from the group consisting of alkali metals and Group 2 metals of the periodic table. Carbon production method. The second organic acid is at least one selected from the group consisting of polyvalent carboxylic acids and hydroxycarboxylic acids,
The method for producing porous carbon according to claim 14, wherein the second organic acid has 6 or less carbon atoms.