capacitor

Abstract

A capacitor according to the present disclosure comprises a first electrode, a second electrode, and an electrolyte. At least one of the first electrode and the second electrode includes, as an electrode active material, porous carbon particles at least partially coated with a nitrogen-containing carbon material. The nitrogen-containing carbon material includes a six-membered ring, and the six-membered ring includes one or more carbonyl carbons and / or two or more nitrogen atoms. The porous carbon particles at least partially coated with the nitrogen-containing carbon material have micropores with a pore diameter of 0.7-2 nm and first mesopores with a pore diameter greater than 2 nm and at most 5 nm, and the ratio (PV2 / PV1) of the first mesopore volume PV2 to the micropore volume PV1 is greater than 0.57.

Description

capacitor CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-041389, filed on March 15, 2024, in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a capacitor.

[0003] A capacitor such as an electric double layer capacitor includes, for example, a first electrode, a second electrode, and an electrolyte. In the capacitor, at least one of the first electrode and the second electrode includes an electrode active material, which is typically porous carbon particles such as activated carbon. For such capacitors, various modifications of the porous carbon particles such as activated carbon have been investigated.

[0004] Patent Document 1 below describes an electric double layer capacitor including a pair of polarizable electrodes including activated carbon and a coating layer made of silicon oxide or metal oxide formed on at least a portion of the surface of the activated carbon, a metal current collector, a separator disposed between the polarizable electrodes, and an electrolyte. Patent Document 1 also describes that by forming a coating layer made of silicon oxide or metal oxide on at least a portion of the surface of the activated carbon as described above, the voltage resistance of the electric double layer capacitor can be improved and the capacity can be maintained even after continuous treatment for 1000 hours at an applied voltage of 3.0 V to 3.5 V.

[0005] Patent Document 2 below describes an electrochemical capacitor using a polarizable electrode formed from a composition containing activated carbon and an organic electrolyte solution, in which the activated carbon satisfies the condition that (pore volume of 40 to 100 nm diameter) / (BJH total pore volume) is 0.1 or greater. It also describes that in order to obtain activated carbon with the above characteristics, the activated carbon is treated with low-temperature plasma containing carbon dioxide. Patent Document 2 below also describes that activated carbon that satisfies the above condition has a higher proportion of pores with diameters of 40 to 100 nm than commercially available activated carbon, thereby enhancing the reactivity between the electrolyte ions of the organic electrolyte solution and the polarizable electrode. Patent Document 2 below also describes that, due to the enhanced reactivity between the electrolyte ions and the polarizable electrode, activated carbon that satisfies the above condition has a capacitance that is approximately 1.5 times higher than commercially available activated carbon.

[0006] Patent Document 3 below describes an electric double layer capacitor composed of electrodes made of activated carbon sandwiched between separators and an electrolyte, in which the activated carbon is washed with water at or near the supercritical state at a temperature of 300°C or higher and a pressure of 23 to 30 MPa. Patent Document 3 also describes that such activated carbon effectively removes impurities and functional groups present in the pores while suppressing pore shrinkage. Patent Document 3 further describes that even after a voltage of 2.7 V is continuously applied for 1,000 hours to an electric double layer capacitor using such activated carbon, the capacitance can be maintained and an increase in resistivity can be suppressed.

[0007] Patent Document 4 below describes an activated carbon for electrode materials, which is composed of porous activated carbon having mesopores and macropores and is used as an electrode material for a power storage device, characterized in that at least a portion of the macropores are coated with a conductive polymer material. Patent Document 4 also describes a power storage device using the above activated carbon for electrode materials in the conductive material layer of at least one of the positive and negative electrodes. Patent Document 4 further describes that, as described above, activated carbon in which at least a portion of the macropores are coated with a conductive polymer material can chemically adsorb ions through an oxidation-reduction reaction (redox reaction) of the conductive polymer material, thereby effectively improving the adsorption of ions into the macropores and, as a result, increasing the initial discharge capacity of the power storage device. Patent Document 4 also describes that the presence of a conductive polymer improves the conductivity of the activated carbon surface, thereby further reducing its resistance, thereby reducing the initial internal resistance of the power storage device.

[0008] Japanese Patent Laid-Open No. 9-63905 Japanese Patent Laid-Open No. 2010-114356 Japanese Patent Laid-Open No. 2004-31713 Japanese Patent Laid-Open No. 2010-003940

[0009] In the above Patent Document 1, although the maintenance of the capacitance of the electric double layer capacitor over a long period of time (for example, 1000 hours) is considered, there is no consideration whatsoever of suppressing the increase in the internal resistance of the electric double layer capacitor over a long period of time.

[0010] Although Patent Document 2 discusses increasing the initial capacity of an electrochemical capacitor, it does not discuss at all how to maintain the capacity of an electrochemical capacitor over a long period of time or how to suppress an increase in internal resistance.

[0011] In the above Patent Document 3, studies have been conducted on maintaining the capacity of an electric double layer capacitor over a long period of time and suppressing an increase in resistivity, and although it can be said that the capacity has been maintained (about 80% of the initial capacity), it is difficult to say that the increase in resistivity has been sufficiently suppressed (about 150% of the initial resistivity).

[0012] In the above-mentioned Patent Document 4, although increasing the initial discharge capacity and decreasing the initial internal resistance of the energy storage device are considered, there is no consideration whatsoever of maintaining the capacity over a long period of time or suppressing an increase in the internal resistance.

[0013] As described above, it is difficult to say that sufficient research has been conducted yet on how to maintain the capacitance over a long period of time while suppressing an increase in the internal resistance of a capacitor.

[0014] Therefore, an object of the present disclosure is to provide a capacitor that can maintain capacity for a long period of time while suppressing an increase in internal resistance.

[0015] One aspect of the present invention relates to a capacitor including a first electrode, a second electrode, and an electrolyte solution, wherein at least one of the first electrode and the second electrode includes, as an electrode active material, porous carbon particles at least partially coated with a nitrogen-containing carbon material, the nitrogen-containing carbon material including a six-membered ring, and the six-membered ring includes at least one of one or more carbonyl carbons and two or more nitrogen atoms, the porous carbon particles at least partially coated with the nitrogen-containing carbon material have micropores with pore diameters of 0.7 nm or more and 2 nm or less and first mesopores with pore diameters of more than 2 nm and 5 nm or less, and a ratio of a first mesopore volume PV2 to a micropore volume PV1 (PV2 / PV1) of greater than 0.57.

[0016] According to the present disclosure, it is possible to provide a capacitor that can maintain capacity for a long period of time while suppressing an increase in internal resistance.

[0017] The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of structure and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0018] 1 is a partially cutaway perspective view of an organic electrolyte electric double layer capacitor according to an embodiment of the present disclosure. 2 is a diagram showing differential pore volume distributions of coated porous carbon particles according to Examples 1 and 2 and Comparative Examples 1 to 5.

[0019] Below, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that known components may be applied to components characteristic of the present disclosure. In this specification, when a "range from numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0020] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination, unless otherwise specified.

[0021] The present disclosure encompasses any combination of two or more features arbitrarily selected from the appended claims, i.e., any combination of two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0022] A capacitor according to an embodiment of the present disclosure includes a first electrode, a second electrode, and an electrolyte. The term "capacitor" may be read as "condenser." The term "capacitor" refers to an electricity storage device such as an electric double layer capacitor or a lithium ion capacitor.

[0023] In a capacitor according to an embodiment of the present disclosure, at least one of the first electrode and the second electrode contains porous carbon particles at least partially coated with a nitrogen-containing carbon material as an electrode active material. In a capacitor according to an embodiment of the present disclosure, the nitrogen-containing carbon material contains a six-membered ring and at least partially covers the porous carbon particles. In a capacitor according to an embodiment of the present disclosure, the porous carbon particles at least partially coated with the nitrogen-containing carbon material have micropores with a pore diameter of 0.7 nm or more and 2 nm or less and first mesopores with a pore diameter of more than 2 nm and 5 nm or less, and the ratio of the first mesopore volume PV2 to the micropore volume PV1 (PV2 / PV1) exceeds 0.57. Hereinafter, porous carbon particles at least partially coated with a nitrogen-containing carbon material will also be referred to as coated porous carbon particles. Hereinafter, an electrode containing coated porous carbon particles as an electrode active material will also be referred to as electrode (E). The coated porous carbon particles can be said to be particles containing porous particles and a nitrogen-containing carbon material coating at least a portion of the surface of the porous particles. That is, the coated porous carbon particles may be particles having a core-shell structure in which the porous carbon particles are the core and the nitrogen-containing carbon material is the shell. The boundary between the porous carbon particles and the nitrogen-containing carbon material does not need to be clear, and there may be a region having an intermediate structure and physical properties between the two.

[0024] When the capacitor according to the embodiment of the present disclosure is an electric double layer capacitor, ions are adsorbed onto the coated porous carbon particles in the electrolyte, thereby forming an electric double layer between the coated porous carbon particles and the electrolyte. This allows the electric double layer capacitor to exhibit capacitance. Furthermore, when ions are desorbed from the coated porous carbon particles, a non-Faradic current flows. That is, when the capacitor according to the embodiment of the present disclosure is an electric double layer capacitor, an electric double layer is formed during charging and disappears during discharging.

[0025] In the capacitor according to the embodiment of the present disclosure, it is important to use, as the electrode active material, coated porous carbon particles having a ratio of the first mesopore volume PV2 to the micropore volume PV1 (PV2 / PV1) of more than 0.57. The reason for this will be explained below.

[0026] Porous carbon particles such as activated carbon typically have hydrophilic acidic functional groups (e.g., carboxyl groups, hydroxyl groups, quinone groups, phenolic hydroxyl groups, etc.) on their surfaces (the inner wall surfaces of the pores). These hydrophilic acidic functional groups act as reactive sites for ions contained in the electrolyte solution. Therefore, for example, adsorption of ions contained in the electrolyte solution onto the hydrophilic acidic functional groups can reduce the ion concentration in the electrolyte solution, thereby increasing the internal resistance of the capacitor. Furthermore, chemical reactions between the acidic functional groups and the ions in the electrolyte solution can also increase the internal resistance of the capacitor. To mitigate this effect, for example, coating the hydrophilic acidic functional groups with a material capable of doping and dedoping ions can be considered. However, if the micropores (pore diameter 2 nm or less) and mesopores (pore diameter greater than 2 nm and less than 50 nm) present in the porous carbon particles are excessively small or crushed during the coating of the hydrophilic acidic functional groups, ion migration and diffusion within the porous carbon particles become difficult, resulting in an increase in the internal resistance of the capacitor. Furthermore, if the micropore volume and mesopore volume are not appropriately balanced after the hydrophilic acidic functional groups are coated, ion migration becomes difficult inside the porous carbon particles and, ultimately, inside the capacitor electrode, resulting in an increase in the internal resistance of the capacitor. Furthermore, if ion migration becomes difficult inside the electrode, it becomes difficult to maintain capacity over a long period of time (e.g., 1,000 hours). Therefore, an appropriate balance between the micropore volume and the mesopore volume is necessary so that hierarchical pores exist.

[0027] However, as described above, the capacitor according to the embodiment of the present disclosure uses coated porous carbon particles as the electrode active material, in which the ratio of the first mesopore volume PV2 to the micropore volume PV1 (PV2 / PV1) exceeds 0.57, i.e., coated porous carbon particles in which the micropore volume and the mesopore volume are present in an appropriate balance. This makes it possible to suppress the reduction of pores while coating the hydrophilic acidic functional groups, and to facilitate the migration of ions inside the porous carbon particles and inside the capacitor electrode. This allows the internal resistance of the capacitor to be sufficiently reduced. Furthermore, the capacity can be maintained for a long period of time.

[0028] PV2 / PV1 is preferably 0.58 or more, more preferably 0.60 or more, and even more preferably 0.62 or more. PV2 / PV1 is usually 5 or less. The micropore volume PV1 and the first mesopore volume PV2 can be calculated from the differential pore volume distribution of the coated porous carbon particles obtained as described below.

[0029] Here, in the coated porous carbon particles, the nitrogen-containing carbon material that covers at least a portion of the porous carbon particles is obtained by carbonizing a raw material of the nitrogen-containing carbon material at a high temperature, as described below. Such raw material is often a resin having a crosslinked structure, and is often carbonized in the form of a mixture mixed with the porous carbon particles. Furthermore, when obtaining such a mixture, the resin having a crosslinked structure is usually diluted with an organic solvent and then mixed with the porous carbon particles. Therefore, the PV2 / PV1 ratio can be adjusted, for example, by adjusting the concentration of the resin having a crosslinked structure in the organic solvent. Specifically, the PV2 / PV1 ratio can be reduced by increasing the concentration of the resin having a crosslinked structure in the organic solvent, and the PV2 / PV1 ratio can be increased by decreasing the concentration of the resin having a crosslinked structure in the organic solvent. The concentration of the resin having a crosslinked structure in the organic solvent is preferably less than 2% by mass, more preferably 1.5% by mass or less, and even more preferably 1.0% by mass or less. If the concentration of the resin having a cross-linked structure in the organic solvent is too high, the viscosity of the organic solvent containing the resin having a cross-linked structure will be too high, and the resin having a cross-linked structure will tend to be unevenly distributed in some parts of the porous particles. As a result, the micropores and mesopores in the coated porous carbon particles may become excessively small or may be crushed. Furthermore, a capacitor containing such coated porous carbon particles as an electrode active material may be unable to maintain capacity over a long period of time while suppressing an increase in internal resistance.

[0030] (Porous Carbon Particles) Porous carbon particles can be produced, for example, by heat-treating a carbonaceous raw material to obtain a carbide, and then activating the carbide to make it porous. Examples of porous carbon particles include, but are not limited to, activated carbon. The porous carbon particles may be coated porous carbon particles such that the ratio (PV2 / PV1) of the micropore volume PV1 having a pore diameter of 0.7 nm to 2 nm to the first mesopore volume PV2 having a pore diameter of more than 2 nm to 5 nm exceeds 0.57. Examples of carbonaceous raw materials include wood, coconut shells, pulp waste liquor, coal, coal-based pitch obtained by thermal decomposition of coal, heavy oil, petroleum-based pitch obtained by thermal decomposition of heavy oil, phenolic resin, petroleum coke, and coal coke. Examples of activation treatments include gas activation using a gas such as steam, and chemical activation using an alkali such as potassium hydroxide. The porous carbon particles may be pulverized. The porous carbon particles may also be pulverized and then classified. The pulverization treatment can be carried out using, for example, a ball mill, a jet mill, or the like.

[0031] The porous carbon particles can be obtained, for example, by pulverizing and sieving a carbonized product obtained by heat-treating coconut shells, and then activating the pulverized and sieved particles. The porous carbon particles can be obtained, for example, by adding a binder such as coal tar or pitch to finely pulverized coal and kneading them to obtain a kneaded mixture, compressing and molding the kneaded mixture to obtain a molded product, pulverizing and sieving the molded product, and then activating the particles obtained by pulverizing and sieving.

[0032] The pore distribution of the porous carbon particles can be adjusted by the type of carbonaceous raw material, the heat treatment temperature, the activation temperature, the degree of pulverization, etc. The porous carbon material may be used alone or in combination of two or more.

[0033] The porous carbon particles are usually in the form of particles. The average particle size of the porous carbon particles is, for example, 1 μm or more and 20 μm or less. The average particle size of the porous carbon particles may be 3 μm or more and 15 μm or less. The average particle size refers to the particle size (median diameter) at which the volume integrated value is 50% in the volume-based particle size distribution measured by a laser diffraction / scattering method.

[0034] The specific surface area A of the porous carbon particles is, for example, 1200 to 2500 m ２ / g. The specific surface area A is 1350 to 2300 m ２ / g. The specific surface area A may be 1200 m ２ / g or more, a high capacity can be easily achieved. ２ / g or less, the contact area with the electrolyte can be reduced, thereby suppressing decomposition of the electrolyte due to side reactions. The specific surface area A can be measured using, for example, BELSORP 28SA available from BEL Japan Co., Ltd. Specifically, it can be measured according to the following procedure.

[0035] <Procedure> (1) Take 0.20 g to 0.25 g of a sample of porous carbon particles and place it in a measurement cell consisting of a glass tube used for measuring specific surface area. Dry and degas the measurement cell. Drying and degassing is performed for at least one hour at a pressure of 6.67 Pa and a temperature of 250±5°C. (2) Measure the mass of the sample in the measurement cell to the nearest 0.1 mg. (3) Use the above measurement device to measure the amount of nitrogen adsorption of the sample at a temperature of -196°C. (4) From the results of the adsorption amount measurement, determine the specific surface area A using the BET multipoint method in a partial pressure (relative pressure) range of 0.001 to 0.2. Specifically, determine the specific surface area A within the range where a straight line can be drawn within the above partial pressure (relative pressure) range.

[0036] (Nitrogen-Containing Carbon Material) As described above, the nitrogen-containing carbon material contains a six-membered ring. The six-membered ring contains at least one of one or more carbonyl carbons and two or more nitrogen atoms. The six-membered ring may contain a carbon atom bonded to two nitrogen atoms. The six-membered ring may form a conjugated system involving all six atoms constituting the six-membered ring. The six-membered ring may contain both one or more carbonyl carbons and two or more nitrogen atoms. A six-membered ring containing both a carbonyl carbon and a nitrogen atom may be a six-membered ring containing two or three carbonyl carbons and two or three nitrogen atoms. The six-membered ring may have a 1,3,5-trione ring, a triazine ring, or both a 1,3,5-trione ring and a triazine ring structure (e.g., an isocyanuric ring). The six-membered ring may contain at least one ring selected from the group consisting of an isocyanuric ring, a triazine ring, and a 1,3,5-trione ring.

[0037] The six-membered ring is a structure derived from the raw material of the nitrogen-containing carbon material. On the other hand, nitrogen-containing carbon materials are produced by carbonizing raw materials at high temperatures. Therefore, the six-membered ring structure may not be clearly detected in the coated porous carbon particles. Even in such cases, the nitrogen-containing carbon material or its raw material can be determined by structural analysis combining FT-IR and XPS, or by the method described in JIS M8813:2004. The method described in JIS M8813:2004 can be performed using an oxygen, nitrogen, and hydrogen analyzer (for example, the "EGMA-830" manufactured by Horiba, Ltd.).

[0038] The six-membered ring has excellent structural stability. It is believed that this excellent structural stability contributes to improving the reliability of capacitors such as electric double layer capacitors. The nitrogen atom contained in the six-membered ring is believed to contribute to the development of excellent initial capacitance or reduced low-temperature resistance of the capacitor. It is presumed that this contribution is related to the presence of carbon atoms bonded to the two nitrogen atoms that make up the six-membered ring. Nitrogen-containing carbon materials are not only likely to develop pseudocapacitance associated with the Faraday reaction, but are also believed to have high reversibility of such pseudocapacitance.

[0039] The six-membered ring preferably contains, for example, an isocyanuric ring. The isocyanuric ring has excellent structural stability. The isocyanuric ring contains three carbonyl carbons bonded to two nitrogen atoms. The isocyanuric ring is particularly stable in an environment with little moisture or protic solvent.

[0040] The six-membered ring preferably includes, for example, a triazine ring. The triazine ring has excellent structural stability. The triazine ring includes three carbon atoms bonded to two nitrogen atoms. The triazine ring is particularly stable in an environment with little moisture or protic solvent.

[0041] The six-membered ring may have an aromatic ring bonded thereto as a substituent. The aromatic ring as a substituent may be bonded to the 1st, 3rd, and 5th positions of the six-membered ring. The aromatic ring as a substituent may be a phenyl group. The phenyl group may further have a substituent. The substituent bonded to the phenyl group may be a C1-C6 alkyl group such as a methyl group, an ethyl group, or a propyl group, or a C1-C6 alkenyl group.

[0042] The nitrogen-containing carbon material may further contain a 1,3,5-trione ring (hereinafter simply referred to as a trione ring). The double-bonded oxygen of the trione ring is thought to contribute to the development of excellent initial capacitance or reduced low-temperature resistance of the capacitor. The trione ring has excellent structural stability and is particularly stable in environments with little moisture or protic solvents.

[0043] An isocyanuric ring contains three carbon atoms bonded to two nitrogen atoms and is also a trione ring, so that a nitrogen-containing carbon material containing an isocyanuric ring is also useful as an electrode active material.

[0044] The nitrogen-containing carbon material can be prepared or produced, for example, using polyisocyanate as a raw material. The polyisocyanate preferably has an aromatic ring. Among them, toluene diisocyanate forms a crosslinked product having an isocyanuric ring by the trimerization reaction shown below. The isocyanuric ring of the crosslinked product of the aromatic ring-containing polyisocyanate has an aromatic ring bonded to a nitrogen atom as a substituent. Such a crosslinked product is suitable as a raw material for a nitrogen-containing carbon material having excellent structural stability.

[0045]

[0046] By adding a polyhydric alcohol to polyisocyanate or toluene diisocyanate, a crosslinked material with excellent thermal decomposition properties (easily carbonizable) can be produced. When the easily carbonizable crosslinked material is heated in an inert atmosphere, the desired nitrogen-containing carbon material can be obtained at low cost.

[0047] The polyhydric alcohol is preferably one having a structure that easily forms a space between the isocyanuric rings, such as glycerin, triglycerin, polyalkylene glycol, alkanediol (HO-(CH ２ ) ｎ Alkanediol (HO-(CH ２ ) ｎ The carbon number n of the —(CH OH) may be, for example, 2 to 10. The isocyanate group and the alcoholic hydroxyl group react to form a urethane bond. A flexible linking group can be formed inside the crosslinked product via the urethane bond. For example, when an alkanediol is used, the linking group can be a —(CH ２ ) ｎ - has the structure.

[0048] The amount of polyhydric alcohol added to polyisocyanate can be selected appropriately. The amount of polyhydric alcohol added is, for example, 100 parts by mass to 1,000 parts by mass, 200 parts by mass to 700 parts by mass, or 250 parts by mass to 500 parts by mass per 100 parts by mass of polyisocyanate. Since polyisocyanate is expensive, it is desirable from a cost perspective to increase the proportion of polyhydric alcohol.

[0049] The crosslinked body as described above is carbonized in an inert atmosphere in the state of a mixture mixed with a porous carbon material. By carbonizing the crosslinked body in this manner, an electrode active material in which at least a portion of the porous carbon particles is covered with a nitrogen-containing carbon material (i.e., coated porous carbon particles) can be obtained. The inert atmosphere may be any non-oxidizing atmosphere, and may be, for example, a reduced pressure atmosphere (e.g., 0.1 MPa or less (preferably 10 Pa or less)), a reducing atmosphere (e.g., a hydrogen atmosphere of 0.01 MPa or less), or an inert gas atmosphere (e.g., N ２ , Ar, Ne, He, etc.).

[0050] The heating temperature of the mixture is preferably 800° C. or less. The heating temperature may be 750° C. or less. If the heating temperature exceeds 800° C., the nitrogen content C Ｎ tends to be excessively low, or the number of six-membered rings containing at least one carbonyl carbon and two or more nitrogen atoms tends to be excessively reduced.

[0051] The heating time can be appropriately selected depending on the heating conditions, and can be, for example, about 0.5 to 5 hours.

[0052] (Coated porous carbon particles) The coated porous carbon particles function as an electrode active material that exhibits capacity by doping and dedoping ions. Doping the coated porous carbon particles is a concept that includes the adsorption of ions to the coated porous carbon particles, the occlusion of ions by the coated porous carbon particles, and chemical interactions between the coated porous carbon particles and ions. Dedoping of ions from the coated porous carbon particles is a concept that includes the desorption of ions from the coated porous carbon particles, the release of ions from the coated porous carbon particles, and the release of chemical interactions between the coated porous carbon particles and ions. In the coated porous carbon particles, both the porous carbon particles and the nitrogen-containing carbon material have the function of doping and dedoping ions. That is, in the coated porous carbon particles, capacity is exhibited by doping and dedoping ions in both the porous carbon particles and the nitrogen-containing carbon material.

[0053] Here, "doping ions into coated porous carbon particles" refers mainly to the adsorption of ions onto the coated porous carbon particles, and "undoping ions from coated porous carbon particles" refers mainly to the desorption of ions from the coated porous carbon particles. As explained above, when ions are adsorbed onto the coated porous carbon particles, an electric double layer is formed, thereby generating capacitance. That is, as will be described later, an active layer (electrode layer) formed from a slurry containing coated porous carbon particles functions as a polarizable electrode. However, the active layer (electrode layer) may also be one in which the Faraday reaction contributes to the capacitance.

[0054] The coated porous carbon particles preferably have a micropore volume PV1 of 0.42 mL / g or more and a first mesopore volume PV2 of 0.25 mL / g or more. The micropore volume PV1 is more preferably 0.43 mL / g or more, and more preferably 0.44 mL / g or more. The micropore volume PV1 is preferably 1.5 mL / g or less, and more preferably 1.2 mL / g or less. The first mesopore volume PV2 is more preferably 0.32 mL / g or more, and more preferably 0.35 mL / g or more. The first mesopore volume PV2 is preferably 2.0 mL / g or less, and more preferably 1.5 mL / g or less. When the micropore volume PV1 and the first mesopore volume PV2 are within the above-mentioned numerical ranges, when the coated porous carbon particles are used as an electrode active material for a capacitor, it becomes easier to maintain the capacity over a long period of time and suppress an increase in the internal resistance of the capacitor.

[0055] The coated porous carbon particles preferably have a ratio (PV3 / PVT) of the second mesopore volume PV3, which is the volume of pores greater than 2 nm and less than 50 nm, to the total pore volume PVT, of greater than 0.36. PV3 / PVT is more preferably 0.37 or greater, and even more preferably 0.38 or greater. PV3 / PVT is preferably 5 or less, and even more preferably 3 or less. When PV3 / PVT is within the above-mentioned range, when the coated porous carbon particles are used as an electrode active material for a capacitor, it becomes easier to maintain the capacity over a long period of time while suppressing an increase in internal resistance.

[0056] The differential pore volume distribution of the coated porous carbon particles can be determined, for example, by analyzing an adsorption isotherm measured by a gas adsorption method using nitrogen gas using the Barrett Joyner Hallenda (BJH) method or the Density Functional Theory (DFT) method. The total pore volume is the integrated value of the pore volume in the differential pore volume distribution obtained by analysis using the BJH method.

[0057] When the coated porous carbon particles are derived from at least one of the first electrode and the second electrode removed from a capacitor, the sample for measuring the differential pore volume distribution is preferably prepared by immersing the coated porous carbon particles in a highly volatile solvent (e.g., dimethyl carbonate), washing under a reduced pressure of less than 0.1 MPa, and then drying under a reduced pressure of less than 0.1 MPa for 2 hours or more. Drying can be carried out, for example, at room temperature (23±2°C).

[0058] The differential pore volume distribution of coated porous carbon particles can be measured, for example, using a BELSORP 28SA instrument available from BEL Japan Co., Ltd. The Dollimore Heal method (DH method), which is calculated based on the capillary condensation theory (Kelvin's equation), can be used as an analytical theory for mesopores. The differential pore volume distribution of micropores can also be analyzed using the MP method (R. SH. MICHAi et al., J. Coll. Inter. Sci., 26 (1968) 45). The MP method assumes that the pores have a slit shape, and the sum of the pore volumes having the slit width can be calculated as a function of the slit width. The pore volume distribution may also be calculated using the DFT method. The DFT method, also known as molecular dynamics simulation, is a method for analyzing adsorption phenomena from statistical and thermodynamic theory at the molecular level. As the apparatus, an autosorb-iQ apparatus manufactured by Anton Paar can be used.

[0059] The coated porous carbon particles are 1650 m ２ It is preferable that the specific surface area A1 is 1700 m / g or more. ２ / g or more, and 1800m ２ / g or more. The specific surface area A1 is 2600 m ２ / g or less is more preferable, and 2500m ２ / g or less. When the specific surface area A1 is within the above range, when the material is used as an electrode active material for a capacitor, it becomes easier to maintain the capacity over a long period of time and to suppress an increase in the internal resistance of the capacitor. The specific surface area A1 can be measured in the same manner as the specific surface area A.

[0060] In the differential pore volume distribution, the coated porous carbon particles preferably have a first peak in the range of more than 0 nm to less than 1 nm, a second peak in the range of 1 nm to 2 nm, and a third peak in the range of more than 2 nm to 5 nm. The presence of such small pores is advantageous for the movement of ions inside the coated porous carbon particles, and in turn, inside the electrode. In the fine powder pore volume distribution, the peak top P1 of the first peak is 1.5 cm. ３ / (g nm) or more, and the peak top P2 of the second peak is 1.0 cm ３ / (g nm) or more, and the peak top P3 of the third peak is 1.3 cm ３ When the coated porous carbon particles exhibit the above-described characteristics in the differential pore volume distribution, the pore volume distribution becomes hierarchical, and an environment favorable for ion migration is easily formed inside the coated porous carbon particles, and further inside the electrode.

[0061] Peak top P1 is 1.6 cm ３ / (g nm) or more, or 1.7 cm ３ The peak top P1 may be located in the range of 3.5 cm / (g nm) or more. ３ / (g nm) or less, or 3.2 cm ３ The peak top P2 may be located in the range of 1.1 cm / (g nm) or less. ３ The peak top P2 may be located in the range of 2.0 cm / (g nm) or more. ３ / (g nm) or less, or 1.8 cm３ The peak top P3 may be located in the range of 1.4 cm / (g nm) or less. ３ / (g nm) or more, or 1.5 cm ３ The peak top P3 may be located in the range of 2.5 cm / (g nm) or more. ３ / (g nm) or less, or 2.2 cm ３ / (g·nm) or less.

[0062] In the differential pore volume distribution of the coated porous carbon particles, when the height of peak top P1 is defined as HP1, the height of peak top P2 is defined as HP2, and the height of peak top P3 is defined as HP3, HP1, HP2, and HP3 preferably satisfy the relationship HP1 > HP3 > HP2. By satisfying such a relationship, an environment favorable for ion migration inside the electrode is easily formed.

[0063] The coated porous carbon particles may have at least one peak in the range of 50 nm or more in the differential pore volume distribution. That is, the coated porous carbon particles may have macropores. When the coated porous carbon particles have macropores, the pore volume distribution can be made more hierarchical. This makes it easier to create an environment more favorable for ion migration inside the electrode.

[0064] In the coated porous carbon particles, the nitrogen content C Ｎ is preferably less than 3 mass%. Ｎ The nitrogen content C may be 2 mass% or less. Ｎ The nitrogen content C may be 0.15 mass% or more, or 1 mass% or more. Ｎ By keeping the above numerical range, the content of six-membered rings containing two or more nitrogen atoms can be kept within an appropriate range. This further suppresses the reaction between the above-mentioned hydrophilic acidic functional groups and electrolyte ions on the surface of porous carbon particles such as activated carbon. As a result, an increase in internal resistance can be suppressed. In addition, ion migration and diffusion are facilitated, which also suppresses an increase in internal resistance.

[0065] In the coated porous carbon particles, the oxygen content C Ｏ is preferably less than 6 mass%. Ｏ The oxygen content C may be 5 mass% or less. Ｏ The oxygen content C may be 1 mass % or more, or 3 mass % or more. Ｏ By keeping the value within the above range, the content of trione rings can be kept within an appropriate range. This further suppresses the reaction between the hydrophilic acidic functional groups and electrolyte ions on the surface of porous carbon particles such as activated carbon. As a result, an increase in internal resistance can be suppressed. In addition, ion migration and diffusion are facilitated, which also suppresses an increase in internal resistance.

[0066] <Organic Electrolyte> The organic electrolyte contains a non-aqueous solvent and an organic salt that dissolves in the non-aqueous solvent. The non-aqueous solvent refers to a solvent other than water, and includes organic solvents. The organic salt is a salt in which at least one of the anion and cation contains an organic substance. The concentration of the organic salt in the organic electrolyte is, for example, 0.5 to 2.0 mol / L. Compared to aqueous electrolytes, organic electrolytes have a wider potential window (voltage resistance) and can withstand higher voltages, which greatly contributes to improving the energy density and power density of capacitors.

[0067] The non-aqueous solvent is preferably a high-boiling point solvent. Examples of high-boiling point solvents include lactones such as γ-butyrolactone; carbonates such as propylene carbonate; polyhydric alcohols such as ethylene glycol and propylene glycol; cyclic sulfones such as sulfolane; amides such as N-methylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone; esters such as methyl acetate; ethers such as 1,4-dioxane; ketones such as methyl ethyl ketone; and aldehydes such as formaldehyde. Among these, it is preferable to use an aprotic solvent from the viewpoint of enhancing the structural stability of the coated porous carbon particles. The non-aqueous solvent preferably contains an aprotic solvent in an amount of 80% by mass or more.

[0068] Examples of organic salts in which the cation contains an organic substance include onium salts such as quaternary ammonium salts. Examples of organic salts in which the anion (or both ions) contains an organic substance include salts of carboxylic acids and onium salts (carboxylate onium salts). Examples of carboxylate onium salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-ethylimidazolinium phthalate. Such organic salts are thought to increase the polarity of the organic electrolyte solution, contribute to improving the wettability of the coated porous carbon particles, and also increase pseudocapacity through a redox reaction derived from the nitrogen atoms contained in the organic salt. They may also increase the carrier concentration at the interface between the carbon material (NC) and the organic electrolyte solution, improving the space charge capacity, and induce charge imbalance within the hexagonal carbon plane.

[0069] The anion preferably contains a fluorine atom from the viewpoint of improving the withstand voltage characteristics. Examples of the anion include BF ４ － , and PF ６ － These fluorine atom-containing anions may be used alone or in combination of two or more. Preferred organic salts include tetraalkylammonium salts such as ethyltrimethylammonium tetrafluoroborate and triethylmethylammonium tetrafluoroborate.

[0070] The organic electrolyte solution may contain a small amount of water, but from the viewpoint of enhancing the structural stability of the coated porous carbon particles, the water content of the organic electrolyte solution is preferably 50 ppm by mass or less.

[0071] (Electrode (E)) The electrode (E) may include an active layer and a current collector supporting the active layer. The current collector is not particularly limited, and a known current collector used in electrodes of electrochemical devices can be used. As the current collector, a metal foil, a porous metal body, etc. can be used. As the material of the current collector, aluminum, copper, nickel, iron, stainless steel, platinum, etc. can be used. As the material of the current collector, an alloy containing the above metals as a main component can also be used. As the metal foil, a plain foil, a foil that has been roughened by etching or the like, a foil that has been plasma-treated, etc. can be used. The porous metal body has, for example, a three-dimensional mesh structure.

[0072] The electrode (E) may contain optional components such as a binder, a conductive additive, etc. The binder plays a role in assisting the bonding between the coated porous carbon particles and between the coated porous carbon particles and the current collector.

[0073] Examples of binders include fluororesins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), and water-soluble resins such as carboxymethyl cellulose (CMC), polyethylene oxide (PEO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylic acid (PAA), and polyvinyl acetate.

[0074] Examples of the conductive additive include carbon black and carbon fiber. The conductive additive preferably contains carbon black. Examples of carbon black include acetylene black and ketjen black.

[0075] The electrode (E) can be produced, for example, by dispersing the coated porous carbon particles together with optional components (such as a binder and a conductive additive) in a dispersion medium such as water to obtain a slurry, then applying the slurry to a current collector to obtain a coating film, and drying the obtained coating film to obtain an active layer (electrode layer). That is, the electrode (E) can be produced, for example, as one comprising a current collector and an active layer (electrode layer) disposed on the current collector. Note that the active layer (electrode layer) may be rolled to further enhance adhesion to the current collector.

[0076] (Capacitor) Next, an example of a capacitor including the electrode (E) will be described. Fig. 1 is a partially cutaway perspective view of an electric double layer capacitor (EDLC (NC)) including an organic electrolyte solution.

[0077] The illustrated EDLC (NC) 10 includes a wound type capacitor element 1. The capacitor element 1 is configured by winding a first electrode 2 and a second electrode 3, each of which is a sheet-like electrode (E), with a separator 4 interposed therebetween.

[0078] The first electrode 2 has a first current collector and a first active layer containing coated porous carbon particles supported on the surface of the first current collector, and exhibits capacitance by adsorbing and desorbing ions. The second electrode 3 has a second current collector and a second active layer containing coated porous carbon particles supported on the surface of the second current collector, and exhibits capacitance by adsorbing and desorbing ions. The first current collector and the second current collector may be made of, for example, aluminum foil. The surfaces of the first current collector and the second current collector may be roughened by etching or other techniques.

[0079] The separator 4 is made of, for example, a nonwoven fabric primarily composed of cellulose. Lead wires 5a and 5b are connected to the first electrode 2 and the second electrode 3, respectively, as lead members. The capacitor element 1 is housed in a cylindrical outer case 6 together with an organic electrolyte solution (not shown). The outer case 6 is made of, for example, a metal such as aluminum, stainless steel, copper, iron, or brass. The opening of the outer case 6 is sealed with a sealing member 7. The lead wires 5a and 5b are led out to the outside, passing through the sealing member 7. The sealing member 7 is made of, for example, a rubber material such as butyl rubber.

[0080] Although the above embodiment has been described with reference to a wound-type capacitor, the scope of application of the present invention is not limited to this and may also be extended to capacitors of other structures, such as stacked-type or coin-type capacitors.

[0081] (Additional Notes) The above description discloses the following technologies. (Technology 1) A capacitor comprising a first electrode, a second electrode, and an electrolyte solution, wherein at least one of the first electrode and the second electrode comprises porous carbon particles at least partially coated with a nitrogen-containing carbon material as an electrode active material, the nitrogen-containing carbon material comprising a six-membered ring, the six-membered ring comprising at least one of one or more carbonyl carbons and two or more nitrogen atoms, the porous carbon particles at least partially coated with the nitrogen-containing carbon material having micropores with pore diameters of 0.7 nm or more and 2 nm or less and first mesopores with pore diameters of more than 2 nm and 5 nm or less, and wherein the ratio of the first mesopore volume PV2 to the micropore volume PV1 (PV2 / PV1) exceeds 0.57. (Technology 2) The capacitor according to Technology 1, wherein the six-membered ring comprises at least one selected from the group consisting of an isocyanuric ring, a triazine ring, and a 1,3,5-trione ring. (Technology 3) The capacitor according to Technology 1 or 2, wherein the micropore volume PV1 is 0.42 mL / g or more and the first mesopore volume PV2 is 0.25 mL / g or more. (Technology 4) The capacitor according to any one of Technology 1 to 3, wherein the porous carbon particles at least partially coated with the nitrogen-containing carbon material have second mesopores having pore diameters of more than 2 nm and less than 50 nm, and a ratio of the second mesopore volume PV3 to the total pore volume PVT (PV3 / PVT) exceeds 0.36. (Technology 5) The porous carbon particles at least partially coated with the nitrogen-containing carbon material have, in a differential pore volume distribution, a first peak in the range of more than 0 nm and less than 1 nm, a second peak in the range of 1 nm or more and 2 nm or less, and a third peak in the range of more than 2 nm and 5 nm or less, and a peak top P1 of the first peak is 1.5 cm ３ / (g nm) or more, and the peak top P2 of the second peak is 1.0 cm ３ / (g nm) or more, and the peak top P3 of the third peak is 1.3 cm ３ / (g nm) or more. (Technology 6) The capacitor according to any one of Techniques 1 to 4, wherein when the height of the peak top P1 is HP1, the height of the peak top P2 is HP2, and the height of the peak top P3 is HP3, the HP1, the HP2, and the HP3 satisfy the relationship HP1 > HP3 > HP2. (Technology 7) In the porous carbon particles at least partially coated with the nitrogen-containing carbon material, the nitrogen content C Ｎ The capacitor according to any one of Techniques 1 to 6, wherein the oxygen content C in the porous carbon particles at least partially coated with the nitrogen-containing carbon material is less than 3 mass %. Ｏ The capacitor according to claim 7, wherein the content of the SiO 2 is less than 6% by mass.

[0082] While the present invention has been described in terms of presently preferred embodiments, such disclosure should not be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0083] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0084] Example 1 A wound-type electric double layer capacitor was produced with a rated voltage of 2.7 V. A specific method for producing the electric double layer capacitor will be described below.

[0085] (1) Preparation of Coated Porous Carbon Particles One part by mass of propanediol as an alkanediol was added to 15 parts by mass of 2,4-toluene diisocyanate, and the mixture was left to stand at room temperature for 24 hours to harden, thereby obtaining a crosslinked product. After mixing the general-purpose activated carbon and the crosslinked product to obtain a mixture, the mixture was heated at a temperature of 700°C for 0.5 hours under a nitrogen atmosphere, thereby obtaining coated porous carbon particles according to Example 1. The mixture contained 20 g of general-purpose activated carbon and 6 g of the crosslinked product diluted 200 times with butyl acetate. That is, the concentration C of the crosslinked product in the butyl acetate was 0.5% by mass. The general-purpose activated carbon was diluted with 2407 m ２ / g and a specific surface area SS of 1.23 cm ３ / g, and a total pore volume PVT of 0.60 cm ３ / g, and a micropore volume PV1 of 0.34 cm ３ / g, and a first mesopore volume PV2 of 0.44 cm ３ The coated porous carbon particles according to Example 1 had a second mesopore volume PV3 of 2143 m / g. As explained above, the micropore volume PV1 is the pore volume of micropores having a pore diameter of 0.7 nm or more and 2 nm or less, the first mesopore volume PV2 is the pore volume of first mesopores having a pore diameter of more than 2 nm and 5 nm or less, and the second mesopore volume PV3 is the pore volume of second mesopores having a pore diameter of more than 2 nm and less than 50 nm, as explained above. The specific surface area SS, total pore volume PVT, micropore volume PV1, first mesopore volume PV2, and second mesopore volume PV3 were measured according to the methods explained above in the embodiment section. Furthermore, the coated porous carbon particles according to Example 1 had a surface area of ​​2143 m / g. ２ / g and a specific surface area SS of 1.08 cm ３ / g, and a total pore volume PVT of 0.50 cm ３ / g, and a micropore volume PV1 of 0.33 cm ３ / g, and a first mesopore volume PV2 of 0.42 cm ３ The results are shown in Table 1 below. Table 1 also shows the ratio of the first mesopore volume PV2 to the micropore volume PV1 (PV2 / PV1) and the ratio of the second mesopore volume PV3 to the total pore volume PVT (PV3 / PVT).

[0086] The coated porous carbon particles according to Example 1 were subjected to a structural analysis using a combination of FT-IR and XPS, and the presence of C—O bonds, C═O bonds, C═N bonds, C—N bonds, etc. was confirmed, and the presence of an isocyanuric ring was inferred. In other words, it was inferred that the coated porous carbon particles according to Example 1 were at least partially coated with a nitrogen-containing carbon material.

[0087] The coated porous carbon particles according to Example 1 were measured for nitrogen content C by a method conforming to JIS M8813:2004. Ｎ , and oxygen content C Ｏ When the nitrogen content C Ｎ is 1.1 mass%, and the oxygen content C Ｏ The analysis was performed using an oxygen, nitrogen, and hydrogen analyzer (EGMA-830 model, manufactured by Horiba Ltd.).

[0088] The differential pore volume distribution of the coated porous carbon particles according to Example 1 was measured by a known method. The results are shown in Figure 2. From Figure 2, it was confirmed that the coated porous carbon particles according to Example 1 have a first peak in the range of more than 0 nm and less than 1 nm, a second peak in the range of 1 nm or more and 2 nm or less, and a third peak in the range of more than 2 nm and 5 nm or less. The peak top P1 of the first peak was 1.9 cm ３ / (g nm) or more, and the peak top P2 of the second peak is 1.1 cm ３ / (g nm) or more, and the peak top P3 of the third peak is 1.5 m ３ It was confirmed that the value was 1 / (g·nm) or more.

[0089] (2) Preparation of Electrode (E) 100 parts by mass of the coated porous carbon particles (electrode active material) according to Example 1, 10 parts by mass of CMC (binder), and 10 parts by mass of acetylene black (conductive additive) were dispersed in an appropriate amount of water to prepare a slurry. The resulting slurry was applied to a current collector made of Al foil with a thickness of 30 μm to form a coating film. Next, the coating film was vacuum dried at 110° C. and then rolled to form an active layer, thereby obtaining an electrode (E).

[0090] (3) Preparation of Organic Electrolyte Solution Triethylmethylammonium tetrafluoroborate (organic salt) was dissolved in propylene carbonate (nonaqueous solvent) to a concentration of 1.0 mol / L to prepare an organic electrolyte solution.

[0091] (4) Preparation of Electric Double Layer Capacitor A pair of electrodes (E) was prepared, and lead wires were connected to each of them to obtain a pair of electrodes (E) with lead wires. Next, the pair of electrodes (E) with lead wires was wound with a separator interposed therebetween to form a capacitor element, and then this capacitor element was housed in a predetermined exterior case together with an organic electrolyte solution and sealed with a sealing member to produce the capacitor according to Example 1. Thereafter, an aging treatment was performed at 60°C for 6 hours while applying a rated voltage of 2.5V.

[0092] [Example 2] A capacitor according to Example 2 was fabricated in the same manner as in Example 1, except that in the mixture, 6 g of the crosslinked body was diluted 100 times with butyl acetate, i.e., the concentration of the crosslinked body in butyl acetate was set to 1.0 mass %. Then, the capacitor according to Example 2 was also subjected to the same aging treatment as in Example 1.

[0093] The coated porous carbon particles according to Example 2 had a particle size of 1893 m ２ / g and a specific surface area SS of 0.96 cm ３ / g, and a total pore volume PVT of 0.44 cm ３ / g, and a micropore volume PV1 of 0.30 cm ３ / g, and a first mesopore volume PV2 of 0.37 cm ３ / g. These results are shown in Table 1 below. Table 1 also shows PV2 / PV1 and PV3 / PVT. Furthermore, FIG. 2 shows the results of measuring the differential pore distribution of the coated porous carbon particles according to Example 2.

[0094] Comparative Example 1 A capacitor according to Comparative Example 1 was fabricated in the same manner as in Example 1, except that general-purpose activated carbon was used instead of the coated porous carbon particles. The capacitor according to Comparative Example 1 was also subjected to the same aging treatment as in Example 1. The specific surface area SS, total pore volume PVT, micropore volume PV1, first mesopore volume PV2, and second mesopore volume PV3 of the general-purpose activated carbon were as described above. PV2 / PV1 and PV3 / PVT were as shown in Table 1 below. FIG. 2 shows the results of measuring the differential pore distribution of the coated porous carbon particles according to Comparative Example 1.

[0095] A capacitor according to Comparative Example 2 was fabricated in the same manner as in Example 1, except that in the mixture, 6 g of the crosslinked body was diluted 50 times with butyl acetate, i.e., the concentration of the crosslinked body in butyl acetate was set to 2.0 mass %. The capacitor according to Comparative Example 2 was also subjected to the same aging treatment as in Example 1.

[0096] The coated porous carbon particles according to Comparative Example 2 had a particle size of 1626 m ２ / g and a specific surface area SS of 0.83 cm ３ / g, and a total pore volume PVT of 0.41 cm ３ / g, and a micropore volume PV1 of 0.23 cm ３ / g, and a first mesopore volume PV2 of 0.29 cm ３ / g. These results are shown in Table 1 below. Table 1 also shows PV2 / PV1 and PV3 / PVT. Furthermore, FIG. 2 shows the results of measuring the differential pore distribution of the coated porous carbon particles according to Comparative Example 2.

[0097] A capacitor according to Comparative Example 3 was fabricated in the same manner as in Example 1, except that in the mixture, 6 g of the crosslinked body was diluted 33 times with butyl acetate, i.e., the concentration of the crosslinked body in butyl acetate was set to 3.0 mass %. The capacitor according to Comparative Example 3 was also subjected to the same aging treatment as in Example 1.

[0098] The coated porous carbon particles according to Comparative Example 3 had a particle size of 1354 m ２ / g and a specific surface area SS of 0.68 cm ３ / g, and a total pore volume PVT of 0.32 cm ３ / g, and a micropore volume PV1 of 0.18 cm ３ / g, and a first mesopore volume PV2 of 0.22 cm ３ / g. These results are shown in Table 1 below. Table 1 also shows PV2 / PV1 and PV3 / PVT. Furthermore, FIG. 2 shows the results of measuring the differential pore distribution of the coated porous carbon particles according to Comparative Example 3.

[0099] A capacitor according to Comparative Example 4 was fabricated in the same manner as in Example 1, except that in the mixture, 6 g of the crosslinked body was diluted 20 times with butyl acetate, i.e., the concentration of the crosslinked body in butyl acetate was set to 5.0 mass %. The capacitor according to Comparative Example 4 was also subjected to the same aging treatment as in Example 1.

[0100] The coated porous carbon particles according to Comparative Example 4 had a particle size of 1179 m ２ / g and a specific surface area SS of 0.60 cm ３ / g, and a total pore volume PVT of 0.28 cm ３ / g, and a micropore volume PV1 of 0.13 cm ３ / g, and a first mesopore volume PV2 of 0.17 cm ３ / g. These results are shown in Table 1 below. Table 1 also shows PV2 / PV1 and PV3 / PVT. Furthermore, FIG. 2 shows the results of measuring the differential pore distribution of the coated porous carbon particles according to Comparative Example 4.

[0101]

[0102] [Evaluation] <Initial Capacity> The capacitors according to each example (Examples 1 and 2 and Comparative Examples 1 to 5) were charged at a constant current of 100 mA / g in a room temperature (23±2°C) environment until the voltage reached 2.7 V, and then the state in which a voltage of 2.7 V was applied was maintained for 7 minutes. Thereafter, constant current discharge was performed at a current of 100 mA / g in a room temperature environment until the voltage reached 0 V.

[0103] During the discharge, the time t (sec) required for the voltage to drop from 2.16 V to 1.08 V was measured. Note that 2.16 V corresponds to 80% of 2.7 V (the voltage at full charge), and 1.08 V corresponds to 40% of 2.7 V. Using the measured time t, the initial capacity C1 (F) before the float charge test was calculated for each capacitor according to the following formula (A): Initial capacity C1 = Id × t / ΔV1 (A) In formula (A), Id is the current value calculated from 100 mA / g and the amount (g) of electrode active material, and ΔV1 is the value obtained by subtracting 1.12 V from 2.16 V.

[0104] <Initial Resistance> Using the discharge curve (vertical axis: discharge voltage, horizontal axis: discharge time) obtained from the above discharge, a linear approximation line was calculated for the range from 0.5 seconds to 2 seconds after the start of discharge on this discharge curve, and the voltage VS at the intercept of this approximation line was calculated. Then, the value (V0-VS) obtained by subtracting the voltage VS from the voltage VO at the start of discharge (0 seconds after the start of discharge) was calculated as ΔV2. Using ΔV2 (V) and the current value Id during discharge (current value calculated from 100 mA / g and the amount of electrode active material (g)), the internal resistance (DCR) R1 (Ω) before the float test for each capacitor according to the example was calculated using the following formula (B): Internal Resistance R1 = ΔV2 / Id (B)

[0105] <Float Charge Test> Four capacitors for each example (Examples 1 and 2 and Comparative Examples 1 to 5) were prepared. The four capacitors were then charged at a constant current of 100 mA / g in a 50°C environment until the voltage reached 2.7 V. The four capacitors were then held at a voltage of 2.7 V for a predetermined time (92 hours, 230 hours, 536 hours, and 1060 hours). In this manner, the four capacitors were stored for a predetermined time with a voltage of 2.7 V applied. The four capacitors that had been held for the predetermined time were then discharged at a constant current of 100 mA / g in a 50°C environment until the voltage reached 0 V.

[0106] Thereafter, in the same manner as in the measurement of capacity and internal resistance before the float test, four capacitors according to each example were charged and discharged at room temperature, and the capacity and resistance were determined after 92 hours, 230 hours, 536 hours, and 1060 hours. The measured capacity values ​​are shown in Table 2A below, and the measured resistance values ​​are shown in Table 2B below. Furthermore, the capacity retention rate and resistance increase rate relative to the initial value were calculated after 92 hours, 230 hours, 536 hours, and 1060 hours. The capacity retention rate is the relative value of the capacity at each time when the initial capacity is taken as 100%, and the resistance increase rate is the relative value of the resistance at each time when the initial resistance is taken as 100%. The capacity retention rate is shown in Table 2C below, and the resistance increase rate is shown in Table 2D below.

[0107]

[0108]

[0109]

[0110]

[0111] From Tables 2A to 2D, it can be seen that the capacitors according to each example (Examples 1 and 2) have a relatively high initial capacitance of 120 F / g or more, and that approximately 80% of the capacitance is maintained even after 1060 hours. Furthermore, the capacitors according to each example have a low initial resistivity of 0.80 Ω or less, and even after 1060 hours, they show a low value of less than 1 Ω. Furthermore, it can be seen that the resistance increase rate remains at approximately 20%. In contrast, the capacitor according to Comparative Example 1 has a relatively high initial capacitance of 133 F / g or more, and although approximately 80% of the capacitance is maintained even after 1060 hours, the initial resistance exceeds 0.9 Ω, and after 1060 hours, it exceeds 1 Ω. Furthermore, the capacitor according to Comparative Example 2 has a relatively high initial capacitance of approximately 120 F / g, and although approximately 80% of the capacitance is maintained even after 1060 hours, the initial resistance exceeds 1.0 Ω, and after 1060 hours, it exceeds 1.2 Ω. Furthermore, it can be seen that the capacitors according to Comparative Examples 3 to 5 had far worse results than the capacitors according to Examples 1 and 2 in terms of the initial capacitance, initial resistance, capacity retention rate, and resistance increase rate.

[0112] The capacitor according to the present disclosure can be used in applications where it is required to maintain capacitance for a long period of time while suppressing an increase in internal resistance.

[0113] 1: capacitor element, 2: first electrode, 3: second electrode, 4: separator, 5a, 5b: lead wire, 6: outer case, 7: sealing member, 10: capacitor

Claims

1. A capacitor comprising: a first electrode, a second electrode, and an electrolyte; at least one of the first electrode and the second electrode comprises porous carbon particles at least partially coated with a nitrogen-containing carbon material as an electrode active material; the nitrogen-containing carbon material comprises a six-membered ring; the six-membered ring comprises at least one carbonyl carbon and two or more nitrogen atoms; the porous carbon particles at least partially coated with the nitrogen-containing carbon material have micropores with pore diameters of 0.7 nm or more and 2 nm or less and first mesopores with pore diameters of more than 2 nm and 5 nm or less; and a ratio of first mesopore volume PV2 to micropore volume PV1 (PV2 / PV1) greater than 0.

57.

2. The capacitor according to claim 1, wherein the six-membered ring includes at least one selected from the group consisting of an isocyanuric ring, a triazine ring, and a 1,3,5-trione ring.

3. The capacitor according to claim 1 or 2, wherein the micropore volume PV1 is 0.42 mL / g or more, and the first mesopore volume PV2 is 0.25 mL / g or more.

4. The capacitor according to claim 1 or 2, wherein the porous carbon particles at least partially coated with the nitrogen-containing carbon material have second mesopores with pore diameters of more than 2 nm and less than 50 nm, and the ratio of the second mesopore volume PV3 to the total pore volume PVT (PV3 / PVT) exceeds 0.

36.

5. The porous carbon particles at least partially coated with the nitrogen-containing carbon material have, in a differential pore volume distribution, a first peak in the range of more than 0 nm to less than 1 nm, a second peak in the range of 1 nm to 2 nm, and a third peak in the range of more than 2 nm to 5 nm, and the peak top P1 of the first peak is 1.5 cm ３ / (g nm) or more, and the peak top P2 of the second peak is 1.0 cm ３ / (g nm) or more, and the peak top P3 of the third peak is 1.3 cm ３ The capacitor according to claim 1 or 2, wherein the capacitance is in the range of 1 / (g·nm) or more.

6. The capacitor according to claim 5, wherein when the height of the peak top P1 is HP1, the height of the peak top P2 is HP2, and the height of the peak top P3 is HP3, the heights HP1, HP2, and HP3 satisfy the relationship HP1>HP3>HP2.

7. In the porous carbon particles at least partially coated with the nitrogen-containing carbon material, the nitrogen content C Ｎ The capacitor according to claim 1 or 2, wherein the content of ZnO is less than 3 mass %.

8. In the porous carbon particles at least partially coated with the nitrogen-containing carbon material, the oxygen content C Ｏ The capacitor according to claim 7 , wherein the content of ZnO is less than 6% by mass.

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