Patent Application
20220177308
The present disclosure relates to a technique for manufacturing a carbon material, and particularly to a method for manufacturing a carbon material, a method for manufacturing an electrode containing a carbon material, an electrode containing a carbon material, an electrochemical device including the electrode, and a carbon material.
A carbon material has excellent mechanical properties, electrical characteristics, and thermal properties, and is therefore widely used in various forms. Particularly, a carbon material doped with nitrogen or oxygen is expected to be applied to, for example, a capacitor electrode having a specific capacity increased by an electrochemical effect.
As a method for manufacturing a nitrogen-doped carbon material, for example, Patent Literature 1 discloses a method for heating a covalent organic framework (COF) in a nitrogen atmosphere to carbonize the COF.
The specific surface area of the azine-linked COF (ACOF1) described in Non Patent Literature 1 slightly increases due to carbonization, but the specific surface area of the COF1 decreases to about ⅓ due to carbonization. This is considered to be because pores of the COF were crushed in the carbonization process. When such a carbon material is used as a capacitor electrode, the magnitude of the specific surface area may affect characteristics such as specific capacity. Therefore, a technique for manufacturing a carbon material having a larger specific surface area is desired.
The present disclosure has been made in view of such a problem, and an object thereof is to provide a technique for improving characteristics of a carbon material.
In order to solve the above problem, a method for manufacturing a carbon material according to an aspect of the present invention includes: a step of adding a guest substance into pores of a covalent organic framework; and a step of heating and carbonizing the covalent organic framework containing the guest substance.
A method for manufacturing an electrode according to another aspect of the present invention includes a step of forming an electrode containing a carbon material manufactured by the above manufacturing method, in which at least a part of the carbon material is exposed from a surface of the electrode in the step.
An electrode according to still another aspect of the present disclosure contains a carbon material manufactured by the above manufacturing method.
An electrochemical device according to still another aspect of the present disclosure includes the above electrode and an electrolyte.
Still another aspect of the present disclosure is a carbon material. The carbon material is a carbon material containing a nitrogen atom, in which the content of the nitrogen atom is more than 0% and less than 10% in terms of weight percentage, and a Brunauer-Emmett-Teller (BET) surface area is more than 200 m2/g and less than 4000 m2/g.
According to the present disclosure, a technique for improving a carbon material can be provided.
A method for manufacturing a carbon material of the present disclosure includes a step of adding a guest substance into pores of a covalent organic framework (COF), and a step of heating and carbonizing the covalent organic framework containing the guest substance. The guest substance contained in the COF functions as a template material for preventing the pores of the COF from being crushed when the COF is carbonized, and also functions as an activator that contributes to expanding a carbon layer and generating pores.
The COF may be any host substance having pores capable of containing the guest substance. For example, the covalent organic framework may contain an anthraquinone moiety and a phloroglucinol moiety. The anthraquinone moiety may be derived from 2,6-diaminoanthraquinone, and the phloroglucinol moiety may be derived from 2,4,6-triformyl phloroglucinol. Specific examples of such a COF include a structure represented by the following chemical formula (AQ-COF).
The COF may contain an element with which a carbon material to be manufactured is doped. The COF may be designed according to the type and amount of an element with which a carbon material to be manufactured is doped. For example, when a carbon material doped with oxygen and nitrogen is manufactured, a COF formed of an organic molecule containing an oxygen atom and a nitrogen atom may be used. As a result, a carbon material to be manufactured can be efficiently doped with a desired element.
The guest substance may be any substance as long as it is contained in pores of the COF. As a result, at least in an initial stage of carbonization of the COF, it is possible to prevent pores of the COF from being crushed and to maintain the skeleton of the COF. Therefore, it is possible to increase the specific surface area of a carbon material to be manufactured.
The guest substance may be a salt or a base. For example, the guest substance may be a carbonate, a bicarbonate, a carboxylate, or a metal hydroxide, and specifically may be potassium carbonate (K2CO3), potassium bicarbonate (KHCO3), sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), ammonium carbonate ((NH4)2CO3), ammonium bicarbonate (NH4HCO3), potassium hydroxide (KOH), or sodium hydroxide (NaOH). As a result, by carbonizing the COF and then washing the carbonized COF with water or an acid, the guest substance can be easily removed to obtain a carbon material.
The guest substance may generate gas at a temperature that is about the same as or lower than a temperature at which the COF is carbonized. As a result, in a process of carbonizing the COF, gas is generated to expand a carbon skeleton, and pores can be generated. Therefore, the specific surface area of a carbon material to be manufactured can be increased. For example, potassium carbonate generates carbon monoxide or carbon dioxide gas according to the following formula, and thus functions as a foaming agent.
K2CO3+2C→2K↑+3CO↑
The guest substance may be thermally decomposed at a temperature higher than a temperature at which the COF is carbonized. As a result, in a process of carbonizing the COF, gas can be generated without thermal decomposition of the guest substance. Therefore, a carbon skeleton can be more effectively expanded, and pores can be generated.
The guest substance may contain a hetero element such as boron (B), nitrogen (N), oxygen (O), sulfur (S), or phosphorus (P). As a result, a carbon material to be manufactured can be efficiently doped with a hetero element. The guest substance may contain carbon (C). As a result, the content or density of carbon in a carbon material to be manufactured can be increased.
The step of heating and carbonizing the COF may be performed in the presence of a substance containing a hetero element such as boron (B), nitrogen (N), oxygen (O), sulfur (S), or phosphorus (P). For example, the step may be performed in an atmosphere of nitrogen (N2), oxygen (O2), nitrogen monoxide (NO), carbon monoxide (CO), carbon dioxide (CO2), ammonia (NH3), or the like. As a result, a carbon material to be manufactured can be efficiently doped with a hetero element.
In the step of heating and carbonizing the COF, the COF is heated to a temperature at which the COF is thermally decomposed and carbonized. Heating temperature, heating rate, and heating time may be adjusted such that the COF is sufficiently carbonized and the specific surface area of a carbon material to be manufactured increases according to the types, amounts, and the like of the COF, the guest substance, and the atmospheric substance.
According to the manufacturing method of the present disclosure, a porous hetero element-doped carbon material having a large specific surface area and favorable characteristics can be manufactured by a simpler method. In addition, since the type and amount of a hetero element with which a carbon material is doped can be controlled by controlling the types, compositions, amounts, reaction conditions, and the like of the COF, the guest substance, and the atmospheric substance, a carbon material having desired characteristics can be easily manufactured. In addition, it is possible to improve electrical characteristics, capacity, and the like when a carbon material is used as an electrode of a capacitor or a catalyst.
A method for manufacturing an electrode according to the present disclosure includes a step of forming an electrode containing a carbon material manufactured by the above manufacturing method, in which at least a part of the carbon material is exposed from a surface of the electrode. As a result, an electrode having favorable characteristics can be easily manufactured. The same applies to a case of manufacturing a catalyst containing a carbon material.
An electrode according to the present disclosure contains a carbon material manufactured by the above manufacturing method. As a result, an electrode having favorable characteristics can be achieved.
An electrochemical device according to the present disclosure includes the above electrode and an electrolyte. The electrochemical device may be an electrode, a capacitor, a catalyst, or the like. The carbon material may be in contact with the electrolyte. The electrolyte may contain an ionic liquid or an organic solvent. The ionic liquid may be a salt that is in a liquid state at a temperature at which the electrochemical device is used, and any type of known ionic liquid may be used. The organic solvent may be an organic substance capable of dissolving a lithium salt (LiPF6, LiBF4, LiClO4, or the like) or the like, and may be any type of known organic solvent such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or ethyl methyl carbonate (EMC). As a result, a potential window of the electrochemical device can be widened, and power density can be improved.
A carbon material (ONC) doped with oxygen and nitrogen was manufactured according to the manufacturing method according to the present disclosure, and characteristics thereof were evaluated.
An AQ-COF was synthesized by a common solvothermal synthesis method. Into a 10 mL Pyrex (registered trademark) tube, 2,4,6-triformyl phloroglucinol (TFP) (40 mg, 0.2 mmol), 2,6-diaminoanthraquinone (DAAQ) (68 mg, 0.3 mmol), dimethylacetamide/mesitylene (2.4 mL, volume ratio 3/1), and 6 M acetic acid (0.1 mL) were filled. The resulting mixture was sonicated for one min at room temperature and freeze-degassed three times. The tube was sealed and heated to 120° C. for three days under vacuum. The reaction mixture was cooled to room temperature, and a dark red precipitate was collected by centrifugation and washed with DMF and acetone. The powder was thoroughly washed with THF in a Soxhlet extractor for 24 hours and vacuum-dried at 120° C. overnight. An AQ-COF was isolated as a red powder at a yield of 80%.
By dispersing a binder (9% by weight) of ONC (91% by weight) and polyvinylidene fluoride (PVDF) in NMP, an active material slurry was prepared, and the prepared slurry was applied to an upper surface of a glassy carbon (GC) electrode. The geometric surface area of the GC electrode is 0.196 cm2, and the filling amount of the active material is 0.1 mg/cm2. An electrochemical experiment was performed in a 1 M sulfuric acid aqueous solution by a standard three-electrode method using an SP-150 single potentiostat electrochemical analyzer manufactured by Biologics Inc. The GC electrode coated with the active material, a platinum wire, and an Ag/AgCl aqueous solution electrode are regarded as a working electrode, a counter electrode, and a reference electrode, respectively.
An AQ-COF was synthesized by condensation of 2,4,6-triformyl phloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ) under common solvent thermal synthesis conditions. The binding, crystallinity, and permanent porosity of the resulting AQ-COF were measured by FT-IR, PXRD, and nitrogen adsorption measurement, respectively. The AQ-COF was compatible with a crystalline porous polymer having a two-dimensional layer with a β-ketoneamine-crosslinked hexagonal network and a one-dimensional nanochannel. The Brunauer-Emmett-Teller (BET) surface area and pore volume were calculated to be 1226 m2/g and 0.78 cm3/g, respectively.
The AQ-COF, potassium carbonate (K2CO3), and distilled water were kneaded, and the mixture was dried under vacuum. In an initial stage of heat treatment, K2CO3 functions as a template material for protecting the AQ-COF from being crushed. When the temperature reaches around 700° C., CO and K gases are released to fill a carbon layer. Expansion of the carbon layer results in a large specific surface area of the ONC.
Nitrogen adsorption isotherm measurement was performed at 77 K in order to evaluate the porosities of the ONC and the AQ-COF.
The microstructures of O and N with which porous carbon was doped were examined by X-ray photoelectron spectroscopy (XPS).
One method for manufacturing the ONC is to carbonize a hetero element-rich organic compound in-situ. Another method for introducing a hetero element into a carbon matrix can be implemented by post-treating porous carbon at high temperature in the presence of chemical species such as ammonia, amine, and urea.
The electrode of the ONC of the present Example was tested in a 1 M sulfuric acid aqueous solution system in a potential window of 0.8 V. The power density was 400 W/kg, and the energy density was 76 Wh/kg.
40 mg of ONC-T1 was ground with a grinder for one hour, the ground ONC-T1 was mixed with 4 mg (10%) of PVDF, and 0.1 mL of NMP was added dropwise thereto to prepare a slush for an electrode. The slush was applied to a surface of foamed nickel cut into a square of 0.8 cm×0.8 cm and dried under vacuum at 50° C. for eight hours. Subsequently, the coated foamed nickel was pressed with a hydraulic press. The coated foamed nickel was dried to adjust 2 to 4 mg of a mixed electrode, and the mixed electrode was vacuum-dried again with a hydraulic pump for two hours.
Constant current charge/discharge (GCD) curves were measured at 1 A/g and 2 A/g with each of the electric double layer supercapacitor and the coin cell supercapacitor.
In Example, the electrode containing the ONC was formed by coating a surface of a flat glass carbon electrode as a current collector with the ONC. However, an electrode may be formed by coating a surface of an electrode of any material, shape, and size with the ONC, or an electrode may be made of a material obtained by mixing the ONC with an electrode material of any material. For example, an electrode may be formed by applying the ONC to a surface of a paper-shaped carbon fiber. In either case, the ONC is disposed in contact with an electrolyte. Since the ONC of the present disclosure has oxidation-reduction activity, thereby increasing the capacity, it is more effective to include the ONC in an electrode on a positive electrode side that is to be reduced. The ONC of the present disclosure can adsorb many protons and lithium ions in pores, and is therefore suitable for use as an electrode of a large-capacity electric double layer capacitor using an electrolyte. However, the ONC of the present disclosure also has high conductivity, and therefore can be used as an electrode of a capacitor with a dielectric interposed between the electrodes.
The BET surface area of each of ONC-T1, ONC-T2, and ONC-T3 of Example is significantly larger than that of ONC-T0 of Comparative Example, and is about 800 to 3000 m2/g. The BET surface area of the ONC of the present disclosure may be 200 m2/g or more, 300 m2/g or more, 400 m2/g or more, 500 m2/g or more, 600 m2/g or more, 700 m2/g or more, 800 m2/g or more, 900 m2/g or more, 1000 m2/g or more, 1100 m2/g or more, 1200 m2/g or more, 1300 m2/g or more, 1400 m2/g or more, 1500 m2/g or more, 1600 m2/g or more, 1700 m2/g or more, 1800 m2/g or more, 1900 m2/g or more, or 2000 m2/g or more. In addition, the BET surface area of the ONC of the present disclosure may be less than 4000 m2/g, less than 3900 m2/g, less than 3800 m2/g, less than 3700 m2/g, less than 3600 m2/g, less than 3500 m2/g, less than 3400 m2/g, less than 3300 m2/g, less than 3200 m2/g, less than 3100 m2/g, less than 3000 m2/g, less than 2900 m2/g, less than 2800 m2/g, less than 2700 m2/g, less than 2600 m2/g, less than 2500 m2/g, less than 2400 m2/g, less than 2300 m2/g, less than 2200 m2/g, or less than 2100 m2/g. The BET surface area of the ONC with particularly high specific capacity is 200 to 4000 m2/g, and more specifically 1000 to 3000 m2/g.
The nitrogen content of each of ONC-T1, ONC-T2, and ONC-T3 of Example is about 0.8 to 6.2% by weight. The nitrogen content of the ONC of the present disclosure may be 0.8% by weight or more, 1% by weight or more, 1.5% by weight or more, 2% by weight or more, 2.5% by weight or more, 3% by weight or more, 3.5% by weight or more, 4% by weight or more, 4.5% by weight or more, or 5% by weight or more. The nitrogen content of the ONC of the present disclosure may be less than 10% by weight, less than 9.5% by weight, less than 9% by weight, less than 8.5% by weight, less than 8% by weight, less than 7.5% by weight, less than 7% by weight, less than 6.5% by weight, less than 6% by weight, less than 5.5% by weight, less than 5% by weight, less than 4.5% by weight, less than 4% by weight, less than 3.5% by weight, less than 3% by weight, less than 2.5% by weight, less than 2% by weight, or less than 1.5% by weight. The nitrogen content of the ONC with a particularly high specific capacity is 4 to 6% by weight, and more specifically 4.5 to 6% by weight.
The pore volume of each of ONC-T1, ONC-T2, and ONC-T3 of Example is significantly larger than that of ONC-T0 of Comparative Example, and is about 0.4 to 1.2 cm3/g. The pore volume of the ONC of the present disclosure may be 0.06 cm3/g or more, 0.07 cm3/g or more, 0.08 cm3/g or more, 0.09 cm3/g or more, 0.1 cm3/g or more, 0.15 cm3/g or more, 0.2 cm3/g or more, 0.25 cm3/g or more, 0.3 cm3/g or more, 0.35 cm3/g or more, 0.4 cm3/g or more, 0.45 cm3/g or more, 0.5 cm3/g or more, 0.55 cm3/g or more, 0.6 cm3/g or more, 0.65 cm3/g or more, 0.7 cm3/g or more, 0.75 cm3/g or more, 0.8 cm3/g or more, or 0.85 cm3/g or more. The pore volume of the ONC of the present disclosure may be less than 1.5 cm3/g, less than 1.4 cm3/g, less than 1.3 cm3/g, less than 1.2 cm3/g, less than 1.1 cm3/g, less than 1.0 cm3/g, less than 0.95 cm3/g, less than 0.9 cm3/g, less than 0.85 cm3/g, less than 0.8 cm3/g, less than 0.75 cm3/g, less than 0.7 cm3/g, less than 0.65 cm3/g, less than 0.6 cm3/g, less than 0.55 cm3/g, less than 0.5 cm3/g, or less than 0.45 cm3/g.
The specific capacity of each of ONC-T1, ONC-T2, and ONC-T3 of Example is significantly larger than that of ONC-T0 of Comparative Example, and is about 700 F/g to 1800 F/g for 1 A/g and about 430 to 860 F/g for 500 A/g. The specific capacity of the ONC of the present disclosure for 1 A/g may be 300 F/g or more, 400 F/g or more, 500 F/g or more, 600 F/g or more, 700 F/g or more, 800 F/g or more, 900 F/g or more, 1000 F/g or more, 1100 F/g or more, 1200 F/g or more, 1300 F/g or more, 1400 F/g or more, or 1500 F/g or more, and may be less than 2000 F/g, less than 1900 F/g, less than 1800 F/g, less than 1700 F/g, less than 1600 F/g, less than 1500 F/g, less than 1400 F/g, less than 1300 F/g, less than 1200 F/g, less than 1100 F/g, or less than 1000 F/g. The specific capacity of the ONC of the present disclosure for 500 A/g may be 100 F/g or more, 150 F/g or more, 200 F/g or more, 250 F/g or more, 300 F/g or more, 350 F/g or more, 400 F/g or more, 450 F/g or more, 500 F/g or more, 550 F/g or more, 600 F/g or more, 650 F/g or more, 700 F/g or more, 750 F/g or more, 800 F/g or more, or 850 F/g or more, and may be less than 1000 F/g, less than 950 F/g, less than 900 F/g, less than 850 F/g, less than 800 F/g, less than 750 F/g, less than 700 F/g, less than 650 F/g, less than 800 F/g, less than 550 F/g, or less than 500 F/g.
The present disclosure has been described above based on Example. The Example is intended to be illustrative only, and it will be understood by those skilled in the art that various modifications to combinations of constituting elements and processes can be made and that such modifications are also within the scope of the present disclosure.
An outline of one aspect of the present disclosure is as follows. A method for manufacturing a carbon material according to an aspect of the present disclosure includes a step of adding a guest substance into pores of a covalent organic framework, and a step of heating and carbonizing the covalent organic framework containing the guest substance. According to this aspect, it is possible to suppress crushing of the pores of the COF in the process of carbonizing the COF. Therefore, it is possible to increase the specific surface area of a carbon material to be manufactured.
The guest substance may generate gas by being heated. According to this aspect, in the process of carbonizing the COF, gas is generated to expand a carbon skeleton, and pores can be generated. Therefore, the specific surface area of a carbon material to be manufactured can be increased.
The guest substance may be thermally decomposed at a temperature higher than a carbonization temperature of the covalent organic framework. According to this aspect, in the process of carbonizing the COF, gas can be generated without thermal decomposition of the guest substance. Therefore, a carbon skeleton can be more effectively expanded, and pores can be generated.
The guest substance may be a salt or a base. For example, the guest substance may be a carbonate, a bicarbonate, a carboxylate, or a metal hydroxide, and more specifically may be potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonium bicarbonate, potassium hydroxide, or sodium hydroxide. After the heating step, a step of washing the obtained carbon material with an acid, water, or both the acid and water may be further included. According to this aspect, the COF is carbonized, and then washed with an acid, water, or both the acid and water. As a result, the guest substance can be easily removed to obtain a carbon material.
The covalent organic framework or the guest substance may contain a boron atom, a nitrogen atom, an oxygen atom, a sulfur atom, or a phosphorus atom. The carbonizing step may be performed in the presence of a substance containing a boron atom, a nitrogen atom, an oxygen atom, a sulfur atom, or a phosphorus atom. According to this aspect, a carbon material to be manufactured can be efficiently doped with a hetero element to improve characteristics.
A method for manufacturing an electrode according to another aspect of the present disclosure includes a step of forming an electrode containing a carbon material manufactured by the above manufacturing method, in which at least a part of the carbon material is exposed from a surface of the electrode in the step. According to this aspect, an electrode having favorable characteristics can be manufactured.
An electrode according to still another aspect of the present disclosure contains a carbon material manufactured by the above manufacturing method. According to this aspect, the characteristics of the electrode can be improved.
An electrochemical device according to still another aspect of the present disclosure includes the above electrode and an electrolyte. According to this aspect, the characteristics of the electrochemical device can be improved.
The carbon material may be in contact with the electrolyte. According to this aspect, the characteristics of the electrochemical device can be improved.
The electrolyte may contain an ionic liquid or an organic solvent. According to this aspect, the power density of the electrochemical device can be improved.
A carbon material according to still another aspect of the present disclosure is a carbon material containing a nitrogen atom, in which the content of the nitrogen atom is more than 0% and less than 10% in terms of weight percentage, and a Brunauer-Emmett-Teller (BET) surface area is more than 200 m2/g and less than 4000 m2/g. According to this aspect, a carbon material having excellent characteristics can be provided.
The carbon material may contain nitrogen in an amount of more than 4% and less than 6% in terms of weight percentage. According to this aspect, a carbon material having a large specific capacity can be provided.
The BET surface area may be larger than 1000 m2/g and less than 3000 m2/g. According to this aspect, a carbon material having a large specific capacity can be provided.
The present invention is applicable to an electrode containing a carbon material and an electrochemical device including the electrode.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-035188 | Feb 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/008001 | 2/27/2020 | WO | 00 |
