JP7464388B2 - Sintered body of covalent organic framework, manufacturing method thereof, and electrode material using the sintered body - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act. Presented at the 46th Annual Meeting of the Carbon Society of Japan held at Okayama University on November 28, 2019.

The present invention relates to a sintered body of a covalent organic framework that can obtain a high specific surface area value, a manufacturing method thereof, and an electrode material using the sintered body.

Activated carbon is generally used as the polarizable electrode of an electric double layer capacitor because of its large surface area and excellent electrical conductivity (see Patent Documents 1 and 2).

However, because activated carbon has a complex and intricate pore structure, when it is used as a polarizable electrode, it becomes difficult for electrolyte ions to move in and out smoothly in the high-output range, resulting in a decrease in capacity in the high-output range.

As an alternative to activated carbon, a technology has been proposed for forming porous materials with large surface areas, using covalent organic frameworks obtained by heat-treating condensates of boron-containing compounds and alcohols or aldehydes (see Patent Document 3).

It has also been proposed that such covalent organic frameworks using boron-containing compounds can be fired and used as electrode materials. As such porous materials, for example, carbon nanotubes can be doped with boron to improve capacitance (see Non-Patent Document 1), and boron or nitrogen can be added during the formation of the porous material to improve the properties of the polarizable electrode (Non-Patent Document 2).

JP 2011-176043 A JP 2011-233845 A JP 2017-155120 A

Applied Physics A 82, 585-591 (2006) “Electric double layer capacitance of multi-walled carbon nanotubes and B-doping effect” Journal of Power Sources 186 (2009) 551-556 “Boron and nitrogen co-doped porous carbon and its enhanced properties as supercapacitor”

However, while boron contributes to improving properties, it was found that its presence also produces boron oxides during firing, which block the pores of the porous material and inhibit the improvement of the specific surface area.

Therefore, in the case of a sintered body of a covalent organic framework obtained by heat-treating the above-mentioned condensation product of a boron-containing compound and an alcohol or an aldehyde, the boron oxide produced in the sintered body inhibits the improvement of the specific surface area value, resulting in the inconvenience of being unable to fully utilize the effect of improving the characteristics by adding boron.

The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a sintered body of a covalent organic framework that can achieve a high specific surface area value in addition to the improved characteristics due to the addition of boron by removing boron oxide produced after sintering and adjusting the content of boron to a desired value close to the content of boron doped in the sintered body alone, a method for producing the same, and an electrode material using the sintered body.

The method for producing a sintered body of a covalent organic framework according to the present invention for solving the above problems includes a firing step of obtaining a sintered body by firing a covalent organic framework constituted by a substance containing at least boron, carbon, and oxygen, a washing step of washing the sintered body to remove boron oxide and impurities generated during the firing , and a crushing step of increasing the pores of the sintered body after the process treatment compared to before the process treatment, and in the washing step, washing is performed until the atomic weight ratio of boron contained in the total amount (excluding hydrogen) of the sintered body of the covalent organic framework after washing becomes ±5% of the predicted content by qualitative and quantitative analysis of boron in the sintered body after washing until diffraction data is formed in powder X-ray diffraction that does not have a peak at a diffraction angle derived from an oxide .

The method for producing the sintered body of the covalent organic framework includes a synthesis step of synthesizing a covalent organic framework by a synthesis reaction between 1,4-phenylenediboronic acid represented by the following formula (1) and 2,3,6,7,10,11-hexahydroxytriphenylene represented by the following formula (2), a firing step of firing the synthesized covalent organic framework to obtain a sintered body, a washing step of washing the sintered body to remove boron oxide generated during the firing , and a crushing step of increasing the pores of the sintered body after the process treatment compared to before the process treatment, and in the washing step, washing is performed until the atomic weight ratio of boron element contained in the total amount (excluding hydrogen) of the sintered body of the covalent organic framework after washing is 25 to 35%.

The method for producing the sintered body of the covalent organic framework may be such that, in the washing step, washing is performed until the atomic ratio of oxygen element contained in the total amount (excluding hydrogen) of the sintered body of the covalent organic framework after washing is 3.5% or less.

In the above-mentioned method for producing a sintered body of a covalent organic framework, the pulverization step may be a step of pulverizing the sintered body before the washing step, a step of wet-pulverizing the sintered body simultaneously with the washing step, or a step of pulverizing the sintered body after the washing step.

The sintered body of the covalent organic framework may be a sintered body obtained by the manufacturing method of a sintered body of a covalent organic framework described above, and may form diffraction data in powder X-ray diffraction that has no peaks at diffraction angles derived from oxides, the atomic weight ratio of boron element contained in the total amount (excluding hydrogen) of the sintered body is 25 to 35%, and the specific surface area is 400 m ² /g or more.

The sintered body of the covalent organic framework may be a sintered body obtained by the manufacturing method of a sintered body of a covalent organic framework described above, and may form diffraction data in powder X-ray diffraction that has no peaks at diffraction angles derived from oxides, and may have an atomic weight ratio of oxygen element contained in the total amount of the sintered body (excluding hydrogen) of 3.5% or less, and a specific surface area of ⁴⁰⁰ m2 /g or more.

The electrode material of the present invention, which aims to solve the above problems, includes a sintered body obtained by the above-described method for producing a sintered body of a covalent organic framework.

In the method for producing the fired body of the covalent organic framework, the solvent used in the synthesis step is not particularly limited, and one or more single or mixed solvents selected from mesitylene, 1,4-dioxane, N,N-dimethylacetone, dichlorobenzene, tetrahydrofuran, methanol, toluene, and acetic acid can be used. For example, 1,4-dioxane may be used alone as the solvent, or a mixture of mesitylene and 1,4-dioxane, N,N-dimethylacetone and dichlorobenzene, tetrahydrofuran and methanol, 1,4 dioxane and toluene, 1,4 dioxane and acetic acid, or a mixture of mesitylene, 1,4 dioxane, and acetic acid may be used.

In the above-mentioned method for producing a fired body of a covalent organic framework, the reaction conditions in the synthesis step are not particularly limited as long as an organic framework having a covalent bond can be formed by reacting an aromatic compound having a functional group, and operations such as heating, pressurization, decompression, stirring, and cooling are performed as necessary. These include a combination of multiple operations and a stepwise operation. The covalent organic framework is not particularly limited as long as it forms a shape in which regular ring structures such as lattice and hexagonal shapes are connected, and includes those that form a general shape of an organic porous body (COF: Covalent Organic Framework). For example, it is formed by reacting at a temperature of about 50 to 250°C for about 3 to 100 hours. The temperature may be increased and/or cooled in a stepwise manner. The pressure may be increased and/or reduced in a stepwise manner.

In the above-mentioned method for producing a fired body of a covalent organic framework, the firing conditions in the firing step are not particularly limited as long as they are conditions that can carbonize the covalent organic framework, and it is preferable to perform firing at a temperature equal to or higher than the decomposition temperature of the covalent organic framework for about 30 minutes to 5 hours. For example, firing can be performed under conditions of 600°C or higher, preferably 600°C to 1200°C, and for 30 minutes to 5 hours. In addition, firing may be performed, for example, in an inert gas atmosphere (nitrogen gas or argon gas atmosphere). In this case, the inert gas atmosphere may be replaced with a firing atmosphere at a gas flow rate of 0.1 to 1.0 liters/minute. In addition, firing may be performed by increasing the temperature from a predetermined temperature at a heating rate of about 5 to 10°C/minute.

In the above-mentioned method for producing a sintered body of a covalent organic framework, the conditions for washing the sintered body in the washing step to remove boron oxide from the sintered body are not particularly limited, and the carbide that has undergone the sintering step may be washed with a solvent, filtered, and then dried. In this case, the solvent used is not particularly limited as long as it can dissolve boron oxide without decomposing the synthesized covalent organic framework, and various solvents such as water and acidic aqueous solutions can be used. Among these, water is preferable because it is inexpensive and safe to use. However, as the solvent, it is desirable to select a solvent that dissolves only boron oxide so as not to dissolve and remove the boron doped in the carbon atom portion that constitutes the sintered body when dissolving and removing boron oxide by washing. In addition, when an acidic aqueous solution is used as the solvent, it is preferable to use a low-concentration acidic aqueous solution that is not subject to the "Law Concerning the Examination and Regulation of Manufacture, etc. of Chemical Substances (Chemical Substances Control Law)" and can be handled as an ordinary substance. This washing process is carried out until the atomic weight ratio of boron contained in the total amount of the fired covalent organic framework (excluding hydrogen) reaches 25-35%, since the remaining amount of boron approaches a predetermined value in proportion to the solvent used in the washing process, the washing time, and the number of washings. This can be achieved by removing the boron oxide described above.

In addition, in the washing step, washing is preferably performed so that not only the boron element described above but also the atomic weight ratio of the oxygen element contained in the total amount (excluding hydrogen) of the fired body of the covalent organic framework is 3.5% or less. The oxygen element can be removed simultaneously with the removal of the boron oxide using the same solvent as the above-mentioned solvent. However, the oxygen element may be removed specifically by washing using a solvent other than that used for removing the boron oxide. This washing removes the oxidized impurities contained in the fired body of the covalent organic framework, and a fired body with a higher specific surface area is obtained. In this case, the amount of oxygen element remaining decreases in proportion to the solvent used in the washing step, the washing time, and the number of washings, so washing is performed according to the desired remaining amount.

The cleaning process may involve cleaning the fired body of the covalent organic framework while heating it together with a solvent, or it may involve ultrasonic cleaning.

The fired body of the covalent organic framework according to the present invention is obtained by the above-mentioned manufacturing method.

The sintered body of the covalent organic framework is formed by sintering a covalent organic framework that is continuously formed with a molecular structure as shown in Fig. 1. When the sintered body shown in Fig. 1 is predicted only from the sintered body from which unreacted components, by-products, oxidized impurities, etc. have been removed, the predicted atomic weight ratios of boron, carbon, and oxygen among the other components excluding hydrogen atoms that cannot be detected by elemental analysis by EDS are 25% to 35% for boron, 68% to 72% for carbon, and 0.2% to 3.5% for oxygen in the total amount (excluding hydrogen atoms). As shown in Fig. 2, the sintered body of the covalent organic framework has voids 10 formed in the portion from which the boron oxide 20 has been removed by removing boron oxide 20 produced during sintering in a washing step, and as shown in Fig. 3, the sintered body 1 after washing has a larger specific surface area than the sintered body 2 before washing. In this state, the atomic weight ratio of boron element contained in the total amount (excluding hydrogen) of the fired body 1 of the covalent organic framework is 25 to 35%.

Whether or not the boron oxide 20 has been removed from the fired body 2 before cleaning and the atomic weight ratio of the boron element contained in the total amount (excluding hydrogen) of the fired body 1 after cleaning has reached a predetermined value of 25 to 35% can be indirectly confirmed by subjecting the powder of the fired body 1 after cleaning to X-ray diffraction and confirming that there is no peak at the diffraction angle derived from the boron oxide 20. Therefore, for example, as shown in FIG. 4, the fired body 1 of the covalent organic framework of the present invention can be confirmed as to whether or not the boron oxide 20 has been removed in the cleaning step by confirming that the X-ray diffraction forms diffraction data 11 that does not have a peak 20a at the diffraction angle derived from the boron oxide 20. That is, when boron oxide 20 is generated in the covalent organic framework, the peak 20a at the diffraction angle derived from the boron oxide 20 is prominently detected in the diffraction data 21 of the fired body 2 of the covalent organic framework, and therefore it can be clearly grasped. In addition, when the diffraction angle data 11 of the sintered body 1 of the covalent organic framework is measured after the washing step, the peak 20a derived from the boron oxide 20 that was detected prominently decreases, and in exchange, the pores are restored and the peaks on the low angle side (10° or less) increase. If this phenomenon is recognized, the prominent peak 20a can be identified as the peak 20a derived from the boron oxide 20. At the same time, it can be confirmed that the voids 10 are formed in the part from which the boron oxide 20 has been removed, the pores are restored, and the specific surface area has increased. In this state, the boron oxide is removed and the boron in the sintered body 1 becomes almost only the boron element incorporated in the sintered body, so that the atomic weight ratio of the boron element contained in the total amount (excluding hydrogen) of the sintered body 1 is 25 to 35%, and this confirmation can be confirmed by qualitative and quantitative analysis of each element in the sintered body 1 by elemental analysis of EDS using a transmission electron microscope. If the atomic weight ratio of boron element is outside the above range, boron oxide will not be sufficiently removed, and a large amount of impurities will remain in addition to the sintered body 1, which was the original purpose, and a sintered body with a high specific surface area will not be formed.

In addition, when the boron oxide is removed, excess oxygen elements are also removed, but impurities other than boron and oxygen elements present as oxides reacted with scale are also removed, so that the atomic weight ratio of oxygen elements contained in the total amount (excluding hydrogen) of the fired body 1 of the covalent organic framework becomes 3.5% or less. By washing so that the atomic weight ratio of the amount of this oxygen element becomes 3.5% or less, the fired body 1 after washing has a larger specific surface area than the fired body 2 before washing, and a fired body 1 with an even higher specific surface area can be obtained. However, depending on the oxide, it may be necessary to wash using a solvent different from the solvent used for boron oxide.

As shown in FIG. 5, even the sintered body 1 that has undergone the washing process has become secondary particles 1a due to agglomeration. Even if the washing process is carried out as these secondary particles 1a, the boron oxide, etc. on the surface of the secondary particles 1a is removed, and the specific surface area of the sintered body 1 after washing increases, but the boron oxide, etc. inside is not completely removed. Therefore, it is more preferable to carry out a washing process in which the sintered body 1 that has become secondary particles 1a due to agglomeration is pulverized to release the agglomerated state and wash it while it is being made into primary particles 1b.

As a result, boron oxide 20 and the like that have not been removed so far because they are embedded in the secondary particles 1a are removed, and as shown in Fig. 3, the specific surface area of the primary particles 1b after pulverization is further improved compared to the specific surface area of the secondary particles 1a before pulverization. In addition, since the primary particles 1b are in a deaggregated state, the pore size and pore volume of the pore distribution are larger than those of the secondary particles 1a, as shown in Fig. 6. Therefore, when used as an electrode material for an electric double layer capacitor, it is possible to form an electrode with high density by making the particles closer to each other, and as shown in Fig. 7, it can be confirmed that the capacitance of the electrode using the sintered body 1 of the pulverized primary particles 1b can be increased to a high capacity that can be discharged for a long time, compared to the capacitance of the electrode using the sintered body 1 of the secondary particles 1a before pulverization.

In addition, as shown in Figure 8, when looking at the relationship between the resistance component and capacitance component of the impedance of an electrode using sintered body 1 of secondary particles 1a before crushing and an electrode using sintered body 1 of primary particles 1b after crushing, the resistance (diameter of the arc portion) before crushing is large while the resistance after crushing is small. This confirms that the electrode using sintered body 1 of sintered primary particles 1b after crushing has denser particles and a lower resistance value than the electrode using sintered body 1 of primary particles 1b before crushing, and thus forms an electrode with no loss.

The pulverization process may be performed to the extent that it is possible to increase the specific surface area. As described above, the washing process and the pulverization process may be performed simultaneously using wet pulverization, or a normal dry pulverization process may be performed before the washing process and then a normal washing process may be performed. In addition, the washing and fixing process and the pulverization process may be performed simultaneously using wet pulverization, and then a normal removal machine process may be performed again, or a normal washing process may be performed, and then another washing process and a pulverization process may be performed simultaneously using wet pulverization.

The washing step may be repeated several times, not just once. In this case, the washing step may be performed by simultaneously carrying out a grinding step by wet grinding for each washing step, or may be performed by carrying out only a normal washing step, or may be a combination of these.

From the viewpoint of use as an electrode material, since the capacity as an electrode must be secured, the above-mentioned material prepared so that the specific surface area after washing is 400 m ² /g or more is preferable, but in the sense of simply forming a fired body 1 with a high specific surface area, it is not necessary to use a covalent organic framework that has undergone the synthesis process described above. That is, the firing process, washing process, and pulverization process may be performed using a covalent organic framework composed of a substance containing at least boron, carbon, and oxygen. Examples of this covalent organic framework include various types, such as one in which one or two hydroxyl groups of boric acid are substituted with alkyl groups, and one in which multiple boron groups having hydroxyl groups are bonded to alkyl groups.

As described above, according to the present invention, a sintered body of a covalent organic framework with a high specific surface area can be obtained by removing boron oxide through a washing process and adjusting the content of boron doped into the sintered body to a predetermined value. In addition, by carrying out a crushing process before or simultaneously with the washing process, agglomerated secondary particles can be converted into primary particles, and a sintered body of a covalent organic framework with a higher specific surface area can be obtained.

FIG. 2 is a schematic diagram showing the molecular structure of a covalent organic framework related to a fired body of the covalent organic framework according to the present invention. FIG. 2 is a schematic diagram illustrating the state of the fired body of the covalent organic framework according to the present invention before and after a washing process. 1 is a graph showing nitrogen adsorption isothermal curves of fired bodies of the covalent organic frameworks according to Example 1, Example 2, and Comparative Example 1. FIG. 1 is a graph showing powder X-ray diffraction data of the fired bodies of the covalent organic frameworks according to Example 1, Example 2, and Comparative Example 1. FIG. 2 is a schematic diagram showing the state of a fired body when a grinding step is performed and when a grinding step is not performed in the method for producing a fired body of a covalent organic framework according to the present invention, and an electron microscope photograph thereof. FIG. 1 is a graph showing the pore distribution of a sintered body when a grinding step is performed and when a grinding step is not performed in a manufacturing method of a sintered body of a covalent organic framework according to the present invention. FIG. 1 is a graph showing the capacitance over time of an electric double layer capacitor formed from a sintered body when a pulverization step is performed and when a pulverization step is not performed in a manufacturing method for a sintered body of a covalent organic framework according to the present invention. FIG. 1 is a graph showing the relationship between the resistance component of impedance and the capacitance component of impedance in electric double layer capacitors formed from sintered bodies when a pulverization step is performed and when a pulverization step is not performed in a manufacturing method for a sintered body of a covalent organic framework according to the present invention.

The following describes an embodiment of the present invention.

[Comparative Example 1]
(Powder (synthetic material))
Two types of powders were used: 1,4-phenylenediboronic acid (hereinafter referred to as BDBA) having a molecular structure represented by the following formula (1), and 2,3,6,7,10,11-hexahydroxytriphenylene (hereinafter referred to as HHTP) having a molecular structure represented by the following formula (2).

(catalyst)
Two solvents were used: mesitylene and 1,4-dioxane.

(Synthesis of Covalent Organic Frameworks)
The inside of a glove box with a circulation purification device (Glove box UN-800L/Gas circulation purification device CM-200: manufactured by UNICO Co., Ltd.) was set to an environment with an oxygen concentration of 0.001 ppm or less and a dew point of -80 ° C. or less, and in this glove box with a circulation purification device, BDBA: 0.055 g, HHTP: 0.071 g, mesitylene: 4 mL, and 1,4 dioxane: 16 mL were placed in a 50 mL hydrothermal synthesis vessel (HU-50: manufactured by San-Ai Science Co., Ltd.) to prepare six sets. Thereafter, the six sets of 50 mL hydrothermal synthesis vessels (hereinafter referred to as hydrothermal synthesis vessels) were heated at 90 ° C. for 72 hours to synthesize a covalent organic framework (synthesis by dehydration condensation). The molecular structure of the covalent organic framework thus synthesized is outlined in FIG. 1.

(Firing of the covalent organic framework)
The obtained covalent organic framework was heated in a nitrogen gas atmosphere at a gas flow rate of 0.3 L/min from room temperature 25° C. at a temperature increase rate of 10° C./min. After reaching 1000° C., it was fired at that temperature for 5 hours to obtain a fired body of the covalent organic framework.

(Nitrogen adsorption measurement (specific surface area/pore distribution measurement))
The powder of the fired body of the covalent organic framework obtained above was dried under reduced pressure at 200°C for 20 hours, and the moisture adsorbed on the fired body was desorbed in a room temperature atmosphere. Then, 0.02 g of the powder of the fired body was placed in a sample tube, and a nitrogen adsorption isotherm was measured in a liquid nitrogen atmosphere using a specific surface area/pore distribution measuring device (BELLSORP-miniII: manufactured by Microtrack Bell Co., Ltd.). The specific surface area was also calculated using the analysis program of the same device (Type I (ISO9277) BET automatic analysis). The results are shown in Figure 3.

(Powder X-ray Diffraction)
Approximately 0.02 g of the powder of the fired body of the covalent organic framework obtained above was placed on a sample holder, leveled, and subjected to diffraction. The measuring device and measuring conditions are as follows. The results are shown in FIG.
Measurement model: X-ray diffraction device RINT-Ultima+ (Rigaku Corporation)
Measurement conditions: Measurement angle range is 2θ = 2° to 40°
Scan speed 4°/min

(Qualitative and quantitative analysis)
The powder of the fired body of the covalent organic framework obtained above was subjected to qualitative and quantitative analysis using a transmission electron microscope. The results are shown in Table 1.
Measurement model: JEM-2100F (manufactured by JEOL Ltd.)
Measurement conditions: Acceleration voltage 200 kV

[Example 1]
The fired body of the covalent organic framework obtained in Comparative Example 1 was washed with pure water.
This washing was performed by placing the obtained sintered powder in a beaker containing 200 milliliters of pure water, heating and stirring at 50°C for 10 minutes, recovering the supernatant liquid with a pipette after the particles had settled, and heating and drying the powder remaining at the bottom of the beaker at 50°C for primary recovery, and then drying the recovered sample at 150°C for 12 hours under reduced pressure to obtain the final powder.

The results of the nitrogen adsorption isotherm of the fired body of the covalent organic framework thus obtained are shown in FIG. 3 together with the results of Comparative Example 1.

The results of powder X-ray diffraction of the fired body of the covalent organic framework obtained in this manner are shown in Figure 4 together with the results of Comparative Example 1.

Furthermore, in order to determine the composition and component amounts of the fired body of the covalent organic framework obtained in this manner, qualitative and quantitative analysis was performed using a scanning electron microscope. The results are shown in Table 2.

[Example 2]
A fired body prepared in the same manner as in Example 1 was wet-pulverized under the following conditions to prepare a fired body of Example 2.

(Wet grinding)
Using a planetary ball mill PULVERISETTE 6 (FRITSCH (Fritsch Japan Co., Ltd.)), 15 g each of zirconia balls with diameters of 1.0 mm and 0.5 mm, 0.1 g of the sintered body, and 25 ml of pure water were placed in a zirconia container and milled at a rotation speed of 400 rpm for 10 hours to obtain a milled product.
The fired body of the covalent organic framework of Example 2 thus obtained was subjected to electron microscopic photographs under the following conditions. The results are shown in FIG. 5. Nitrogen adsorption measurements were also performed using the same method as in Example 1 above to determine the specific surface area and pore distribution. Powder X-ray diffraction was also performed using the same method as in Example 1 above. The results of the nitrogen adsorption isotherm are shown in FIG. 3, and the results of the powder X-ray diffraction are shown in FIG. 4. Furthermore, the results of the pore distribution are shown in FIG. 6.

(Electron microscope photograph)
Measurement model: JSM-6010LA (manufactured by JEOL Ltd.)
Measurement conditions: accelerating voltage 15 kV, working distance 11 mm, spot size 30
Measurement magnification: 10,000 times

Furthermore, electrode test pieces were formed using the sintered bodies of the covalent organic frameworks of Examples 1 and 2 in the manner described below, and the discharge capacity and interparticle resistance due to differences in the sintered bodies of the covalent organic frameworks were evaluated using these electrodes in the manner described below.

(Preparation of electrode test pieces)
The fired bodies obtained in Examples 1 and 2 were used as active materials, and the active materials, conductive assistant (acetylene black), and binder (PVDF (polyvinylidene fluoride resin)) were kneaded in a weight ratio of 8:1:1. This kneaded mixture was made into a paste form and applied onto an aluminum foil having a thickness of 20 μm, dried, and pressed to a thickness of 50 μm, thereby preparing electrode test pieces for each fired body.

(Capacitance measurement of electrode test strip)
The discharge capacity (hereinafter, also referred to as capacity) of each electrode test piece prepared above was measured using an electrochemical meter (VSP300 manufactured by Biologic). The results are shown in Figure 7. In Figure 7, the vertical axis represents the amount of electricity [C] flowing during discharge divided by the weight (g) of the active material (sintered body) and the discharge voltage (V) [weight specific capacity F/g].

(Measurement conditions for AC impedance method)
For each of the electrode test pieces prepared above, measurements were performed by an AC impedance method using an electrochemical measuring device (VSP300 manufactured by Biologic Co., Ltd.) to determine the relationship between the resistance component and the capacitance component of the impedance. The results are shown in FIG.
Measurement conditions: Sweep frequency 1MHz to 10mHz
Applied voltage: 5 mV

[Comparative Example 2]
The specific surface area was measured by the same nitrogen adsorption measurement as in Comparative Example 1, and the specific surface area was found to be 1680 ^m2 /g. Using the activated carbon, an electrode test piece was prepared by the same method as in Examples 1 and 2, and the discharge capacity was measured by the same method. The results are shown in Figure 7.

From the above results, the diffraction data 11 (see FIG. 4(b)) of the sintered body 1 of the covalent organic framework according to the present invention does not produce the peak 20a derived from oxides, as in the diffraction data 21 (see FIG. 4(a)) of the sintered body 2 of the covalent organic framework according to Comparative Example 1. Therefore, it can be confirmed that the pores of the sintered body 1 are not blocked by the generation of oxides during or after sintering, and many pores are formed.

Furthermore, as shown in FIGS. 2 to 6 , even when the sintered body 1 of the covalent organic framework according to the present invention is in the state of secondary particles 1a, boron oxide 20 (see FIG. 2) is removed, thereby obtaining a sintered body 1 with a high specific surface area . However, by adding a further pulverization step and a washing step using wet pulverization, the agglomerations of the secondary particles 1a can be broken down into primary particles 1b, and therefore the boron oxide 20 (see FIG. 2) that has remained inside is also removed, thereby obtaining a sintered body 1 with an even higher specific surface area .

Furthermore, the sintered body 1 from which the primary particles 1b have been formed and the boron oxide 20 has been removed can be used as an even more excellent electrode material because the pore size and pore volume can be increased as can be seen from the pore distribution. Moreover, since the aggregated state has been broken down into primary particles 1b, the particles can be tightly attached to each other to form an electrode. Therefore, it is possible to increase the electrode capacity and form an electrode with reduced interparticle resistance (the arc portion in FIG. 9 has become smaller). In particular, when the sintered body 1b of the covalent organic framework according to Example 2 is evaluated as an electrode , it is possible to obtain a discharge capacity equivalent to that of an electrode made from the activated carbon 3 used in Comparative Example 2, and it was confirmed that the sintered body 1b has very high performance as an electrode material.

Furthermore, it was confirmed that by washing the sintered body of the covalent organic framework according to the present invention, the boron content was reduced to approximately 31%, which is close to the content of boron doped in the sintered body, and the oxygen content was significantly reduced to 0.2%.

The present invention can be embodied in various other forms without departing from its spirit or main features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as being limiting. The scope of the present invention is defined by the claims and is not limited in any way by the text of the specification. Furthermore, all modifications and changes that fall within the scope of the claims are within the scope of the present invention.

1 Sintered body 1a Secondary particles (sintered body)
1b Primary particles (sintered body)
11 Diffraction data of fired body 20 Boron oxide

Claims (7)

A synthesis step of synthesizing a covalent organic framework by a synthesis reaction between 1,4-phenylenediboronic acid represented by the following formula (1) and 2,3,6,7,10,11-hexahydroxytriphenylene represented by the following formula (2);
a firing step of firing the synthesized covalent organic framework to obtain a fired body;
a washing step of washing the fired body to remove boron oxide and impurities generated during firing;
A grinding step for increasing the pores of the fired body after the processing step compared to before the processing step,
A method for producing a sintered body of a covalent organic framework, characterized in that in the washing step, washing is performed until an atomic weight ratio of boron element contained in a total amount (excluding hydrogen) of the sintered body of the covalent organic framework after washing is 25 to 35% .

2. The method for producing a sintered body of a covalent organic framework according to claim 1, wherein in the washing step, washing is performed until an atomic ratio of oxygen element contained in a total amount (excluding hydrogen) of the sintered body of the covalent organic framework after washing becomes 3.5% or less . 3. The method for producing a sintered body of a covalent organic framework according to claim 1 or 2, wherein the pulverization step comprises pulverizing the sintered body before the cleaning step, wet-pulverizing the sintered body simultaneously with the cleaning step, or pulverizing the sintered body after the cleaning step . A sintered body obtained by the method for producing a sintered body of a covalent organic framework according to claim 1, wherein in powder X-ray diffraction, diffraction data is formed that has no peaks at diffraction angles derived from oxides, the atomic weight ratio of boron element contained in the total amount (excluding hydrogen) of the sintered body is 25 to 35%, and the specific surface area is 400 m ² /g or more. A sintered body of a covalent organic framework obtained by the manufacturing method of a sintered body of a covalent organic framework according to claim 2, which forms diffraction data in powder X-ray diffraction that has no peaks at diffraction angles derived from oxides, has an atomic weight ratio of oxygen element contained in the total amount of the sintered body (excluding hydrogen) of 3.5% or less , and has a specific surface area of 400 ^m2 /g or more. A sintered body obtained by the method for producing a sintered body of a covalent organic framework according to claim 1, wherein in powder X-ray diffraction, diffraction data is formed that has no peaks at diffraction angles derived from oxides, the atomic weight ratio of boron element contained in the total amount (excluding hydrogen) of the sintered body is 25 to 35%, and the specific surface area is 400 m ² /g or more. 3. An electrode material comprising a sintered body of a covalent organic framework obtained by the method for producing a sintered body of a covalent organic framework according to claim 2, which produces diffraction data in powder X-ray diffraction that has no peaks at diffraction angles derived from oxides, and which has an atomic weight ratio of oxygen element of 3.5% or less in the total amount of the sintered body (excluding hydrogen) and a specific surface area of 400 ^m2 /g or more.

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