JP7617531B2 - Capacitor electrode, method for producing same, and capacitor - Google Patents

Description

The present invention relates to a capacitor electrode, a manufacturing method thereof, and a capacitor.

Graphene has a theoretical specific surface area of about 2600 ^m2 /g and is electrically conductive, making it a promising electrode material for capacitors. However, unless the distance between graphene sheets is appropriately controlled, the flat graphene sheets overlap to a large extent, and the surface area of graphene cannot be fully utilized.

Patent Document 1 proposes the use of a graphene sheet assembly film in which multiple graphene sheet laminates, in which two or more graphene sheets are laminated via a first carbon nanotube, are electrically and mechanically connected to each other in a three-dimensional manner via a second carbon nanotube. It also proposes the use of single-walled carbon nanotubes with a length of 5 to 20 μm as the first and second carbon nanotubes.

International Publication No. 2012/073998

However, when using typical carbon nanotubes (CNTs), the basal planes of the CNTs interposed between the graphene sheets inhibit ion diffusion between the graphene sheets, which tends to increase resistance at low temperatures.

One aspect of the present invention relates to a capacitor electrode that includes a first carbon and a second carbon other than the first carbon, the first carbon includes graphene, the second carbon is short carbon fibers having an average length of 10 μm or less and/or carbon particles having an average diameter of 0.1 μm or less, and the graphenes are stacked together via the second carbon.

Another aspect of the present invention relates to a capacitor having the above-mentioned capacitor electrode.

Yet another aspect of the present invention relates to a method for producing an electrode for a capacitor, comprising the steps of preparing an aqueous dispersion containing graphene oxide, which is a first carbon raw material, and a second carbon, and reducing the graphene oxide in the aqueous dispersion, in which the second carbon is short carbon fibers having an average length of 10 μm or less and/or carbon particles having an average diameter of 0.1 μm or less.

According to the present invention, it is possible to obtain a capacitor electrode using graphene that has high capacity and low resistance even at low temperatures.

1 is a partially cutaway perspective view of an electric double layer capacitor according to the present invention. 1 is a transmission electron microscope (TEM) photograph of the xerogel obtained in Example 1. 2B is an enlarged TEM photograph of a portion of FIG. 2A. 1 is a scanning electron microscope (SEM) photograph of highly crystalline graphene used in Comparative Example 3.

The capacitor electrode according to this embodiment includes a first carbon and a second carbon other than the first carbon, the first carbon includes graphene, and the second carbon is short carbon fibers having an average length of 10 μm or less and/or carbon particles having an average diameter of 0.1 μm or less. The graphenes are stacked together via the second carbon. This significantly improves ion diffusion between the graphenes, resulting in a low-resistance capacitor electrode. Furthermore, the second carbon is interposed between the graphenes, which suppresses overlap between the graphene sheets, allowing the surface area of the graphene to be more effectively utilized. On the other hand, when the second carbon is short carbon fibers and/or carbon particles, ion diffusion between the graphenes is not hindered, as is the case when general CNTs are used.

Here, graphene is a carbon material whose smallest unit is a graphene sheet having a thickness of one carbon atom, and usually constitutes a laminate of multiple graphene sheets. Also, a graphene sheet is an aggregate or molecule composed of sp2 bonded carbon having a thickness of one carbon atom, and has a honeycomb lattice structure that spreads out in a sheet shape. Ordinary graphene usually has a flat sheet shape, but here, various graphene sheet laminates having a disordered layer structure (or a disordered interlayer distance) are also included in the category of graphene. Graphene may partially contain graphene analogs such as graphene oxide. Hereinafter, graphene is also referred to as a graphene sheet laminate.

The capacitor electrode has, for example, a metal collector and an electrode layer supported on the collector, and the first carbon and the second carbon are contained in the electrode layer as active materials that adsorb and desorb ions.

(a) The first carbon graphene may have a microscopic three-dimensional structure (i.e., a fine structure). By having a three-dimensional structure, overlapping of graphene sheets is significantly suppressed, and the surface area of the graphene can be more effectively utilized. A plurality of protrusions or a plurality of depressions are formed on the main surface of the graphene sheet laminate having a three-dimensional structure. Such a three-dimensional structure allows the distance between the graphene sheets to be appropriately controlled, and the overlapping of the graphene sheets to be effectively reduced.

The average number of layers of the graphene sheet laminate in graphene is, for example, 10 layers or less, and may be 5 layers or less. It is preferable that the graphene is closer to the minimum unit of graphene sheet (i.e., single layer sheet) having a thickness of one carbon atom. The average number of layers may be the number of layers estimated from the interplanar distance (d002) calculated from the diffraction peak attributed to the 002 plane of the X-ray diffraction profile (for example, Abstracts of the 2015 Autumn Meeting of the Physical Society of Japan, p. 1014). Alternatively, it may be an estimated value obtained from an electron microscope (SEM, etc.) photograph of graphene. For example, the number of layers of graphene sheets can be estimated from the scale of the SEM photograph of graphene and the interplanar distance of the 002 plane (hereinafter also referred to as the basal plane) of the graphene sheet. For example, 20 arbitrary graphene sheet laminates are selected, the number of layers of each is estimated, the maximum value and the minimum value are omitted, and the average value of the middle 10 values is taken as the average number of layers.

The interlayer distance between graphene sheets in graphene (i.e., the distance between basal planes) may vary randomly. Random variation in the interlayer distance means that the graphene has low crystallinity. The greater the disorder in the graphene stacking structure, the more significant the variation in the interlayer distance.

The graphene may have a three-dimensional structure, for example, a crimped structure or a folded structure. In this case, each graphene sheet laminate has a microporous structure. This improves the diffusion of ions near the surface of the graphene. The presence of the crimped structure or the folded structure can be confirmed by an electron microscope (SEM, TEM, etc.) photograph of the graphene.

The crimped structure may be, for example, a structure having multiple randomly formed fold-like raised portions and recessed portions. A folded structure is a structure having a folded portion in which a single graphene sheet laminate is partially folded multiple times, and is included in the category of crimped structures. The height of the raised portion or the depth of the recessed portion formed in the folded portion may be greater than the thickness of the carbon portion of the graphene sheet laminate having that structure, and may be more than twice the thickness of the carbon portion.

The X-ray diffraction profile of the first carbon typically has a diffraction peak P1 that is assigned to the 002 plane. The greater the overlap between the graphene sheets and the higher the crystallinity of the graphene, the sharper the diffraction peak P1 becomes.

On the other hand, when graphene has a three-dimensional structure, the diffraction peak P1 becomes broad and can be separated into multiple peaks. A halo pattern attributed to an amorphous phase may be observed on the higher angle side of the diffraction peak P1 in the X-ray diffraction profile of the first carbon.

The interplanar distance (d002) of the 002 plane of the first carbon calculated from the X-ray diffraction profile may be, for example, 0.338 nm (3.38 Å) or more. d002 is calculated by waveform separation of the diffraction peaks observed in the region around 2θ = 26.38°, calculating d002 for each component, and calculating the average. The distance (d002) of the 002 plane of the first carbon is preferably 0.340 nm (3.40 Å) or more, more preferably 0.360 nm (3.60 Å) or more, and even more preferably 0.370 nm (3.70 Å) or more.

(b) Second Carbon The second carbon may be short carbon fibers having an average length of 10 μm or less and/or carbon particles having an average diameter of 0.1 μm or less.

(i) Short Carbon Fiber The short carbon fiber may be, for example, a vapor-grown carbon fiber, a carbon nanotube, a carbon nanofiber, etc. The short carbon fiber may have a hollow space (hollow portion) therein.

The average length of the short carbon fibers may be 10 μm or less, but from the viewpoint of increasing ion diffusion between graphenes, 2 μm or less is preferable, and 0.1 μm or less is more preferable. The average length of the short carbon fibers can be analyzed from an electron microscope (SEM, TEM, etc.) photograph. For example, 20 short carbon fibers are arbitrarily selected, the length of each is measured, the maximum and minimum values are omitted, and the average of the middle 10 values is taken as the average length. Since the short carbon fibers are short, 10 μm or less, they can be approximated to be roughly linear. Therefore, the length of the short carbon fibers means the length of the straight line when both ends of the short carbon fibers are connected by a straight line.

The average diameter of the short carbon fibers is, for example, 200 nm or less, and may be 5 nm or more and 200 nm or less, or 10 nm or more and 170 nm or less. The diameter of the short carbon fibers is the maximum length in the direction perpendicular to the length direction of the short carbon fibers, and the average diameter can be analyzed from an electron microscope (SEM, TEM, etc.) photograph. For example, 20 short carbon fibers are arbitrarily selected, the diameters of each are measured, and the maximum and minimum values are omitted, and the average value of the middle 10 values is taken as the average diameter.

(ii) Carbon particles The average diameter of the carbon particles may be 0.1 μm or less, but from the viewpoint of increasing the ion diffusion between graphenes, it is preferable that it is 0.05 μm or less, and more preferable that it is 0.03 μm or less. The average diameter of the carbon particles can be analyzed from an electron microscope (SEM, TEM, etc.) photograph. For example, 20 arbitrary carbon particles are selected, the maximum diameter of each is measured, the maximum value and the minimum value are omitted, and the average value of the intermediate 10 values is taken as the average diameter. In addition, when the carbon particles can be separated, they can be measured by a laser diffraction type particle size distribution measuring device. In this case, the median diameter at 50% of the cumulative volume in the volume-based particle size distribution may be taken as the average diameter.

Specific examples of carbon particles include graphite, non-graphitizable carbon, easily graphitizable carbon, and carbon black. Among these, carbon black is preferred, and for example, acetylene black, ketjen black, thermal black, furnace black, channel black, and the like can be used. Note that multiple carbon particles (here, primary particles) may be linked to form a chain structure (secondary particles). In this case, the average diameter is the average diameter of the primary particles. The length of the chain structure is not particularly limited, but is preferably 2 μm or less, more preferably 0.5 μm or less, and more preferably 0.05 μm or less.

(iii) First Carbon/Second Carbon Ratio The ratio of the first carbon to the total of the first carbon and the second carbon may be 40 to 98% by mass, and may be 80 to 98% by mass. In order to obtain a capacitor electrode with a high capacity, it is desirable to have a large ratio of graphene having a large surface area. On the other hand, if the ratio of the first carbon is too large, the amount of the second carbon interposed between the graphene is reduced, and the effect of suppressing the overlapping of the graphene sheets is reduced. If the ratio of the first carbon is within the above range, the overlapping of the graphene sheets is significantly suppressed, and therefore the capacity of the capacitor electrode can be efficiently increased.

(c) Binder The capacitor electrode may contain a binder. The binder has a role of supporting the bonding between the first carbons, between the second carbons, or between the first carbon and the second carbon when the mixture of the first carbon and the second carbon is formed into a sheet-like or film-like electrode layer. The binder also has a role of supporting the bonding between the electrode layer and the current collector.

Examples of binders that can be used 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.

(d) Third Component The electrode layer may contain other active materials such as activated carbon in addition to the first carbon and the second carbon. In addition, the present invention does not exclude the case where the electrode layer contains CNTs having an average length of more than 10 μm, and the electrode layer may contain a small amount of CNTs.

(e) Current collector A metal foil, a metal porous body, etc. can be used as the current collector. The material of the current collector can be aluminum, copper, nickel, iron, stainless steel, platinum, etc. An alloy mainly composed of these metals can also be used. The metal foil can be a plain foil, but it can also be a foil roughened by etching or the like, or a foil subjected to plasma treatment. The metal porous body has, for example, a three-dimensional mesh structure.

The mass per unit area of the metal porous body may be, for example, 500 g/m ² or less, or 150 g/m ² or less. The porosity of the metal porous body may be, for example, 80 vol% to 98 vol%, or may be 90 vol% to 98 vol%.

The average pore size of the voids in the metal porous body may be, for example, 50 μm or more and 1000 μm or less, or may be 400 μm or more and 900 μm or less, or 450 μm or more and 850 μm or less.

Next, an example of a method for manufacturing a capacitor electrode will be described.
(i) Dispersion preparation step First, an aqueous dispersion containing a first carbon raw material and a second carbon is prepared. The first carbon raw material is a precursor of the first carbon, and graphene oxide is used here. The second carbon is short carbon fibers with an average length of 10 μm or less and/or carbon particles with an average diameter of 0.1 μm or less.

The aqueous dispersion may contain a dispersant such as carboxymethyl cellulose (CMC) in addition to the first carbon raw material, the second carbon, and water.

Graphene oxide is a graphene analogue that has oxygen-containing functional groups, and is a material that is exfoliated from graphite in a single layer or multiple layers via the oxidation of graphite. The oxygen-containing functional groups are hydrophilic groups such as hydroxyl groups, carbonyl groups, and carboxyl groups, and are water-dispersible.

Graphite can be oxidized, for example, using an oxidizing agent in water. Examples of the oxidizing agent that can be used include sulfuric acid, potassium permanganate, chromic acid, sodium dichromate, sodium nitrate, peroxide, persulfate, and organic peracid. A water-soluble solvent may be added to the water. Examples of the water-soluble solvent include alcohols, ketones such as acetone, and ethers such as dioxane and tetrahydrofuran. An aqueous dispersion of graphene oxide is produced by an oxidation reaction in water. By adding a second carbon to the aqueous dispersion of graphene oxide, an aqueous dispersion containing the first carbon raw material and the second carbon is obtained.

The degree of oxidation (oxygen content) of graphene oxide may be, for example, 10 to 60% by mass, 20 to 50% by mass, or 30 to 50% by mass. The degree of oxidation of graphene oxide may be measured, for example, by X-ray photoelectron spectroscopy (XPS). The masses of carbon (C) and oxygen (O) contained in graphene oxide may be measured by XPS, and the mass ratio of oxygen to the total mass of carbon and oxygen may be calculated.

(ii) Reduction Step Next, the graphene oxide is reduced in an aqueous dispersion containing the graphene oxide (first carbon raw material) and the second carbon, i.e., in the presence of the second carbon. The reduction method is not particularly limited, but may be, for example, hydrothermal treatment. For example, the aqueous dispersion may be sealed in an autoclave and subjected to hydrothermal treatment to generate a gel-like product. The temperature of the hydrothermal treatment may be, for example, 150° C. or higher, preferably 170° C. or higher and 200° C. or lower.

The hydrothermal treatment can produce a cross-linked structure between the first carbon and the second carbon. For example, the first carbon and the second carbon are cross-linked via a functional group such as an ether bond (-O-). Such hydrothermal treatment produces a gel-like product that contains graphene that is composited with the second carbon and has a three-dimensional structure.

To further promote the reduction, the gel product may be contacted with a reducing agent. Examples of reducing agents include metal hydrides, borohydrides, boranes, hydrazines or hydrazides, ascorbic acids, thioglycolic acids, cysteines, sulfurous acids, thiosulfates, and dithionites. For example, the gel product may be immersed in an aqueous solution containing a water-soluble reducing agent such as sodium ascorbate. The temperature of the aqueous solution may be, for example, 20 to 110°C, 40 to 100°C, or 50 to 100°C. The amount of reducing agent used may be appropriately adjusted depending on the type of reducing agent, the oxidation degree of graphene oxide, the amount of gel product, and the like. The oxidation degree of graphene after reduction may be, for example, 40% by mass or less, or may be 20% by mass or less.

(iii) Freeze-drying process The gel product is then preferably freeze-dried. Freeze-drying makes it possible to obtain a dry gel (xerogel) in which the three-dimensional structure of graphene is highly maintained. Freeze-drying may be performed, for example, at −50° C. to 0° C., preferably −50° C. to −20° C., under reduced pressure of 100 Pa or less, and further 1 Pa or less.

Xerogel is a composite of graphene with a three-dimensional structure and a second carbon. The composite contains graphene with a three-dimensional structure stacked via the second carbon. The composite is used as an active material for capacitor electrodes that exhibit high capacitance.

(iv) Electrode Formation Step Next, the composite of the first carbon and the second carbon is dispersed in a dispersion medium such as water together with a binder to prepare a slurry. At this time, if the second carbon is interposed between the graphene, rearrangement of the graphene sheets is suppressed even in the slurry, and further overlapping of the graphene sheets is suppressed. In addition, in the composite obtained through the hydrothermal treatment, the first carbon and the second carbon are usually crosslinked via a functional group, and the degree of freedom of movement of the graphene is limited. Therefore, the three-dimensional structure is easily maintained even in the slurry.

The resulting slurry is applied to a current collector and the coating is dried to form an electrode layer supported on the current collector, thereby obtaining an electrode for a capacitor. The electrode layer may then be rolled.

Next, an example of a capacitor equipped with the above-mentioned capacitor electrode will be described. The above-mentioned capacitor electrode can be used as an electrode for, for example, an electric double layer capacitor, a lithium ion capacitor, etc.

FIG. 1 is a partially cutaway perspective view of an electric double layer capacitor 10. As shown in FIG.
The electric double layer capacitor 10 of the illustrated example 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 in the form of a sheet, with a separator 4 interposed therebetween. The first electrode 2 and the second electrode 3 each have a first current collector and a second current collector made of metal, and a first electrode layer and a second electrode layer carried on the surface thereof, respectively, and exhibit capacitance by adsorbing and desorbing ions. For example, aluminum foil is used for the first and second current collectors. The surface of the current collector may be roughened by a method such as etching. For example, a nonwoven fabric mainly composed of cellulose is used for the separator 4. 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 electrolyte (not shown). The material of the outer case 6 may be, for example, a metal such as aluminum, stainless steel, copper, iron, or brass. The opening of the exterior case 6 is sealed with a sealing member 7. The lead wires 5a, 5b are led out to the outside so as to pass through the sealing member 7. The sealing member 7 is made of a rubber material such as butyl rubber, for example.

The electrode layer contains an active material as an essential component, and may contain a binder, a conductive assistant, and the like as optional components. The active material contains a first carbon and a second carbon having the characteristics already described. The electrode layer is obtained, for example, by applying a slurry obtained by kneading the active material, a binder (e.g., carboxymethyl cellulose (CMC)), and the like together with water in a kneader to the surface of a current collector, drying the coating, and rolling it.

The electrolyte may be a mixture of a solvent and an ionic substance (e.g., an organic salt) dissolved in the solvent. The solvent may be a non-aqueous solvent or an ionic liquid. The concentration of the ionic substance in the electrolyte may be, for example, 0.5 to 2.0 mol/L.

As the non-aqueous solvent, a high boiling point solvent is preferable. For example, 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 formaldehyde can be used.

An organic salt is a salt in which at least one of the anion and cation contains an organic substance. Examples of organic salts in which the cation contains an organic substance include quaternary ammonium salts. Examples of organic salts in which the anion (or both ions) contains an organic substance include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono 1,2,3,4-tetramethylimidazolinium phthalate, and mono 1,3-dimethyl-2-ethylimidazolinium phthalate.

From the viewpoint of improving the withstand voltage characteristics, the anion preferably contains a fluorine atom, for example, BF ₄ ^- and/or PF ₆ ^- . Specific examples of preferred organic salts include tetraalkylammonium salts such as ethyltrimethylammonium tetrafluoroborate.

In the above embodiment, a wound type capacitor has been described, but the scope of application of the present invention is not limited to the above, and it may also be applied to capacitors of other structures, such as stacked or coin type capacitors.

The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

Example 1
In this example, a wound type electric double layer capacitor (Φ18 mm×L (length) 70 mm) was produced with a rated voltage of 2.8 V. A specific method for producing the electric double layer capacitor will be described below.

(i) Preparation of active material Carbon black (acetylene black (average primary particle diameter 35 nm) manufactured by Denka Corp.), which is the second carbon, was added to an aqueous dispersion containing 0.35 mass% of graphene oxide, which is the first carbon raw material, and mixed using a thin film swirling high-speed mixer (Filmix (registered trademark)) manufactured by Primix Corp. to prepare an aqueous dispersion with a total content of the first carbon raw material and the second carbon of 0.39 mass%.

Next, the aqueous dispersion was hydrothermally treated at 180°C for 1 hour to obtain a gelled product. The gelled product was then immersed in an aqueous solution of sodium ascorbate (sodium ascorbate concentration 1.0 mol/L) as a reducing agent, heated to 100°C and held for 2 hours to sufficiently reduce the graphene oxide. The gelled product was then freeze-dried at -20°C under reduced pressure of 100 Pa to obtain a xerogel.

Next, the xerogel (i.e., a composite of the first carbon and the second carbon) was dispersed in water together with CMC, which was a binder, to prepare a slurry. The amount of CMC used was 10 parts by mass per 100 parts by mass of the xerogel. The obtained slurry was applied to a current collector made of Al foil with a thickness of 30 μm, and the coating was vacuum dried at 110°C and rolled to form an electrode layer, thereby obtaining an electrode for a capacitor.

A pair of electrodes was prepared, each connected to a lead wire, and wound with a cellulose nonwoven separator to form a capacitor element, which was then housed in a specified exterior case together with an electrolyte and sealed with a sealing material to complete the electric double layer capacitor A1. The electrolyte used was a solution of ethyldimethylimidazolium tetrafluoroborate dissolved in propylene carbonate, a nonaqueous solvent, at a concentration of 1.0 mol/L. The capacitor was then aged for 16 hours at 60°C while applying the rated voltage.

[evaluation]
Fig. 2A shows a TEM image of the xerogel used in the preparation of the slurry in this example. Fig. 2B shows an enlarged TEM image of a portion of Fig. 2A. From these images, it can be seen that chain-like connections of primary particles of carbon black are present between multiple graphene sheet laminates.

The TEM image shows a curled or folded structure with multiple randomly formed pleat-like raised areas and depressions. The height of the raised areas or the depth of the depressions formed in the folded areas is sufficiently greater than the thickness of the carbon part, and is at least twice the thickness of the carbon part.

In addition, when the xerogel was subjected to X-ray diffraction measurement, a broad halo pattern attributable to the amorphous phase was observed at higher angles than the diffraction peak P1 attributable to the 002 plane, indicating the presence of a curled or folded structure. The obtained X-ray diffraction profile was analyzed to determine the d002 of graphene, which was confirmed to be approximately 0.34 nm or more.

Next, the capacitance of electric double layer capacitor A1 was determined at 25°C and -30°C. In addition, the ratio of -30°C capacitance to 25°C capacitance (C(-30/20)) was determined. Since ion diffusion is rate-limiting at low temperatures, it can be said that the larger the C(-30/20) ratio, the lower the resistance to ion diffusion.

Comparative Example 1
A xerogel was prepared in the same manner as in Example 1, except that acetylene black, which was the second carbon, was not used. An electric double layer capacitor B1 was produced using the xerogel, and was similarly evaluated.

Comparative Example 2
A xerogel was prepared in the same manner as in Example 1, except that the second carbon, acetylene black, was not used, and an electric double layer capacitor B2 was produced in the same manner as in Example 1, except that 10 parts by mass of acetylene black was added to the slurry per 100 parts by mass of the xerogel, and was evaluated in the same manner.

Comparative Example 3
Except for using highly crystalline graphene instead of xerogel, a slurry containing acetylene black was prepared in the same manner as in Comparative Example 2, and an electric double layer capacitor B3 was produced and evaluated in the same manner as in Example 1. Fig. 3 shows an electron microscope (SEM) photograph of the highly crystalline graphene according to this comparative example.

The evaluation results for the above examples and comparative examples are shown in Table 1.

Table 1 shows that the capacitance of capacitor A1 is significantly higher than those of capacitors B1 to B3, and that capacitor A1 is a low-resistance capacitor with excellent ion diffusion even at low temperatures. The capacitance of capacitors B1 and B2 is significantly lower than that of capacitor A1, and the capacitances are almost the same. From this, it can be said that even if xerogel and acetylene black are mixed when preparing the slurry, it is difficult to form a structure favorable for ion diffusion in which graphene is stacked with acetylene black, and it is also difficult to maintain the three-dimensional structure of graphene. On the other hand, in the xerogel obtained by reducing an aqueous dispersion of graphene oxide and second carbon (carbon black) and then freeze-drying it, it is considered that graphene is stacked with acetylene black and the three-dimensional structure of graphene is maintained. This is considered to be because the first carbon and the second carbon are cross-linked through a chemical bond such as an ether bond.

The present invention provides an electric double layer capacitor that has high capacity and low resistance even at low temperatures.

1: Capacitor element, 2: First electrode, 3: Second electrode, 4: Separator, 5a: First lead wire, 5b: Second lead wire, 6: Outer case, 7: Sealing material, 10: Capacitor

Claims (12)

A first carbon, which is graphene;
The second carbon is short carbon fibers or carbon particles,
The X-ray diffraction profile of the first carbon has a diffraction peak P1 assigned to a 002 plane, and has a halo pattern assigned to an amorphous phase on the higher angle side than the diffraction peak P1,
the interplanar distance of the 002 plane of the first carbon calculated from the X-ray diffraction profile is 0.360 nm or more;
The graphenes are stacked together via the second carbon .
Electrode for capacitor. 2. The capacitor electrode according to claim 1 , wherein the short carbon fibers are vapor-grown carbon fibers or carbon nanofibers. 2. The capacitor electrode according to claim 1 , wherein the carbon particles are selected from the group consisting of graphite, non-graphitizable carbon, graphitizable carbon and carbon black. The capacitor electrode according to claim 1 , wherein the chain-like linked carbon particles are interposed between layers of the graphene laminate. 5. The capacitor electrode according to claim 1, wherein a ratio of the first carbon to a total of the first carbon and the second carbon is 40 to 98 mass %. 6. The capacitor electrode according to claim 1, further comprising a bridge structure between the first carbon and the second carbon. The capacitor electrode according to claim 1 , wherein the graphene has an oxidation degree of 40 mass % or less. The capacitor electrode according to claim 1 , wherein the graphene has a three-dimensional structure. The capacitor electrode according to claim 1 , wherein an average number of stacked graphene sheets in the graphene is 10 or less. The capacitor electrode according to claim 1 , wherein an interlayer distance between graphene sheets in the graphene changes randomly. The capacitor electrode according to claim 1 , wherein the graphene has a curled structure or a folded structure. A capacitor comprising the capacitor electrode according to any one of claims 1 to 11 .

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