JP7203381B2 - Capacitor electrode, manufacturing method thereof, and capacitor - Google Patents

Description

The present invention relates to a capacitor electrode, a method for manufacturing the same, and a capacitor.

Graphene has a theoretical specific surface area of about 2600 m ² /g and is conductive, so it is promising as an electrode material for capacitors.

Patent Literature 1 proposes using an electrode in which nanoscale graphene platelets and a conductive binder are combined in a capacitor, and reports that a capacitance of 82 F/g can be obtained.

Patent Document 2 includes carbon nanotubes, graphene, an ionic liquid, and a three-dimensional network-like metal porous body that holds these in pores, and the ratio of the total amount of carbon nanotubes and graphene to the ionic liquid is 10 mass. % or more and 90% by mass or less, and the ratio of carbon nanotubes and graphene is in the range of 3:7 to 7:3 in mass ratio.

U.S. Pat. No. 7,623,340 JP 2014-225508 A

In order to effectively utilize the surface area of graphene, it is necessary to appropriately control the distance between graphene sheets and reduce the overlapping of graphene sheets. However, graphene having a flat shape tends to overlap each other during the manufacturing process of the electrode, making it difficult to control the distance between the graphene sheets, and a sufficiently high capacity cannot be obtained.

In addition, when graphene is charged and discharged, ions move in and out between graphene sheet layers, so that the deterioration of current collection paths due to expansion and contraction tends to increase. As in Patent Document 2, attempts have been made to reinforce the current collection path by using a metal porous body and carbon nanotubes (CNT), but the internal structure of the electrode tends to be heterogeneous, making stable production difficult.

One aspect of the present invention includes a metal porous body and first carbon filled in voids of the metal porous body, wherein the first carbon includes graphene, and the graphene has a three-dimensional structure. It relates to electrodes for capacitors.

Another aspect of the present invention relates to a capacitor including the capacitor electrode.

Still another aspect of the present invention includes a step of preparing an aqueous dispersion containing graphene oxide as a first carbon raw material, impregnating the aqueous dispersion into the metal porous body, and in the voids of the metal porous body, the and a step of reducing graphene oxide.

According to the present invention, a high-capacity capacitor electrode can be stably obtained using graphene.

1 is a partially cutaway perspective view of an electric double layer capacitor according to the present invention; FIG. 1 shows a scanning electron micrograph (SEM image) (a) and a transmission electron micrograph (TEM image) (b) of a composite of a metal porous body and xerogel obtained in Example 1. FIG. 1 is an X-ray diffraction profile of a composite of a metal porous body and xerogel obtained in Example 1. FIG. 3 is an electron micrograph of highly crystalline graphene used in Comparative Example 3. FIG. 4 is an X-ray diffraction profile of highly crystalline graphene used in Comparative Example 3. FIG.

A capacitor electrode according to this embodiment includes a metal porous body and first carbon filled in voids of the metal porous body, the first carbon includes graphene, and the graphene has a three-dimensional structure. In other words, the capacitor electrode has a metal porous body as a current collector, and graphene having a three-dimensional structure is supported on the metal porous body as an active material.

By filling the voids of the metal porous body with the first carbon having a three-dimensional structure, the current collecting property of the electrode is less likely to deteriorate, and the capacity deterioration is suppressed. The three-dimensional structure of graphene is a three-dimensional structure (that is, a fine structure) that is smaller than that of a metal porous body. The microscopic three-dimensional structure effectively reduces the overlap between graphene sheets. Furthermore, the fine structure of the first carbon is easily maintained by binding the first carbon having a three-dimensional structure to the skeleton of the metal porous body.

Here, graphene is a carbon material whose minimum unit is a graphene sheet having a thickness of one carbon atom, and usually constitutes a laminate in which a plurality of graphene sheets are laminated. A graphene sheet is an aggregate or molecule composed of sp2-bonded carbon having a thickness of one carbon atom, and has a honeycomb-like lattice structure that spreads out like a sheet. General graphene usually has a flat sheet-like form, but here, various forms of graphene sheet laminates with disordered layer structures (or disordered interlayer distances) are also included in the graphene category. . Graphene may partially include graphene analogs such as graphene oxide. Hereinafter, graphene is also referred to as a graphene sheet laminate.

(a) Metal porous body As the metal porous body, for example, a sponge metal, an etching foil, a metal particle sintered body, or the like can be used, but a metal porous body having a three-dimensional network structure is preferable. The three-dimensional network structure may be, for example, a structure in which fibrous or rod-shaped parts made of metal are connected three-dimensionally to form a network-like skeleton. The skeleton may be a hollow structure having a cavity inside. A metal porous body having a three-dimensional network structure can be produced, for example, by plating a resin porous body having continuous pores with a metal and then removing the resin porous body. In this case, the three-dimensional network structure has communicating voids (that is, communicating pores).

The mass per unit area of the porous metal 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% to 98% by volume, and may be 90% to 98% by volume. The average pore diameter of the pores of the metal porous body may be, for example, 50 μm or more and 1000 μm or less, may be 400 μm or more and 900 μm or less, or may be 450 μm or more and 850 μm or less.

Aluminum, copper, nickel, iron, stainless steel, platinum and the like can be used as the material of the metal porous body. Alloys containing these metals as main components may also be used.

(b) The first carbon graphene has a micro three-dimensional structure. Since the graphene sheet laminate has a three-dimensional structure, the overlapping of the graphene sheets is remarkably suppressed, and the graphene sheet laminate and the metal porous body are combined to maintain the microstructure of the graphene sheet laminate, and the graphene. It becomes possible to effectively utilize the surface area. Here, a plurality of raised portions or a plurality of depressed portions are formed on the main surface of the graphene sheet laminate having a three-dimensional structure. With such a three-dimensional structure, the distance between the graphene sheets is appropriately controlled, and the overlapping of the graphene sheets is effectively reduced.

The average number of stacked graphene sheet laminates in graphene is, for example, 10 layers or less, and may be 5 layers or less. Graphene is more desirable as it approaches the smallest unit graphene sheet (ie, monolayer 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, the Physical Society of Japan 2015 Autumn Meeting Summary Collection p1014). Alternatively, an estimated value obtained from an electron microscope (SEM or the like) photograph of graphene may be used. For example, the number of stacked graphene sheets can be estimated from the scale of the SEM photograph of graphene and the interplanar distance between the 002 planes (hereinafter also referred to as basal planes) of the graphene sheets. For example, arbitrarily select 20 graphene sheet laminates, estimate the number of laminates for each, omit the 5th maximum value and the 5th minimum value, and 10 intermediate graphene sheet stacks. The average value of the numerical values may be taken as the average lamination number.

The interlayer distance (that is, the distance between basal planes) between graphene sheets in graphene may vary randomly. Random variation of interlayer distance means that graphene has low crystallinity. The greater the disorder in the laminated structure of graphene, the more pronounced the change in the interlayer distance.

The graphene sheet laminate may have, for example, a crimped structure or a folded structure as a three-dimensional structure. At this time, each graphene sheet laminate itself has a microporous structure. Therefore, diffusion of ions in the vicinity of the surface of the graphene sheet laminate is improved. The presence of a crimped structure or a folded structure can be confirmed by an electron microscope (SEM, TEM, etc.) photograph of the graphene sheet laminate.

The crimped structure may be, for example, a structure having a plurality of randomly formed fold-like protuberances and depressions. A folded structure is a structure having a folded portion in which one graphene sheet laminate is partially folded multiple times, and is included in the category of a crimped structure. 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 the structure, and may be at least twice the thickness of the carbon portion. good.

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

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

The distance (d002) between the 002 planes 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 separating the diffraction peak observed in the region near 2θ=26.38°, calculating d002 for each component, and averaging them. The distance (d002) between the 002 planes of the first carbon is preferably 0.340 nm (3.40 Å) or more, and more preferably 0.360 nm (3.60 Å) or more from the viewpoint of maintaining a high surface area of graphene, 0.370 nm (3.70 Å) or more is more preferable.

(c) Second carbon The capacitor electrode may further contain a second carbon filled in the voids of the metal porous body. As the second carbon, it is desirable to use 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.

Since the second carbon is short carbon fibers and/or carbon particles, it easily fills the voids of the metal porous body, enabling stable production of the electrode. Therefore, the internal structure of the electrode is less likely to become heterogeneous. In addition, when common CNTs are interposed between graphene sheet laminates, ion diffusion is likely to be inhibited, and resistance at low temperatures tends to increase. An increase in resistance is also suppressed.

When the capacitor electrode contains the second carbon in addition to the first carbon, the graphenes are desirably laminated via the second carbon. This further suppresses the overlapping of the graphene sheets, making it possible to more effectively utilize the surface area of the graphene.

(i) Short carbon fiber The short carbon fiber may be, for example, vapor-grown carbon fiber, carbon nanotube, carbon nanofiber, or the like. The short carbon fiber may have a hollow space (hollow portion) inside.

The average length of the short carbon fibers may be 10 μm or less, but is preferably 2 μm or less, more preferably 0.1 μm or less, from the viewpoint of increasing ion diffusivity between graphenes. The average length of short carbon fibers can be analyzed from electron microscope (SEM, TEM, etc.) photographs. For example, select 20 arbitrarily short carbon fibers, measure the length of each, omit the 5th maximum value and the 5th minimum value, and 10 intermediate values should be taken as the average length. In addition, since the short carbon fibers are as short as 10 μm or less, they can be approximated to be substantially linear. Therefore, the length of a short carbon fiber means the length of a straight line connecting both ends of the short carbon fiber.

The average diameter of the short carbon fibers is, for example, 200 nm or less, may be 5 nm or more and 200 nm or less, or may be 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 longitudinal direction of the short carbon fibers, and the average diameter can be analyzed from electron microscope (SEM, TEM, etc.) photographs. For example, select 20 arbitrarily short carbon fibers, measure the diameter of each, omit the 5th maximum value and the 5th minimum value, and 10 intermediate values The average value should be taken as the average diameter.

(ii) Carbon Particles The average diameter of the carbon particles may be 0.1 μm or less, but is preferably 0.05 μm or less, more preferably 0.03 μm or less, from the viewpoint of increasing the ion diffusibility between graphenes. The average diameter of carbon particles can be analyzed from electron microscope (SEM, TEM, etc.) photographs. For example, arbitrarily select 20 carbon particles, measure the maximum diameter of each, omit the 5th largest value and the 5th smallest value, and 10 values in between. The average value may be taken as the average diameter. In addition, when the carbon particles can be separated, the measurement can be performed with a laser diffraction particle size distribution analyzer. In this case, the median diameter of 50% 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, graphitizable carbon, and carbon black. Among them, carbon black is preferable, and for example, acetylene black, ketjen black, thermal black, furnace black, channel black and the like can be used. A plurality of carbon particles (here, primary particles) may be connected to form a chain structure (secondary particles). In this case, the mean diameter is the mean diameter of the primary particles. Although the length of the chain structure is not particularly limited, it is preferably 2 μm or less, more preferably 0.5 μm or less.

(iii) Ratio of first carbon/second carbon 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 high-capacity capacitor electrode, it is desirable that the proportion of graphene having a large surface area is large. On the other hand, if the ratio of the first carbon is too large, the amount of the second carbon interposed between the graphenes 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 can be significantly suppressed, and the capacitance of the capacitor electrode can be efficiently increased.

(d) Third Component The electrode layer may contain other active material such as activated carbon in addition to the first carbon and the second carbon. Also, the present invention does not exclude the case where the electrode layer contains CNTs having an average length of more than 2 μm, and the electrode layer may contain a small amount of CNTs.

Next, an example of a method for manufacturing capacitor electrodes will be described.
(i) Dispersion Preparation Step First, an aqueous dispersion containing graphene oxide, which is the first carbon raw material, is prepared. Graphene oxide is a precursor of the first carbon. In the case of manufacturing an electrode containing the second carbon in addition to the first carbon, the second carbon may be further mixed with the aqueous dispersion containing graphene oxide.

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

Graphene oxide is a graphene analogue having an oxygen-containing functional group, and is, for example, a material exfoliated from graphite in a single layer or multiple layers through oxidation of graphite. The oxygen-containing functional group is a hydrophilic group such as a hydroxyl group, a carbonyl group, a carboxyl group, etc., and has water dispersibility.

Oxidation of graphite can be performed, for example, in water using an oxidizing agent. Sulfuric acid, potassium permanganate, chromic acid, sodium dichromate, sodium nitrate, peroxides, persulfates, organic peracids and the like can be used as the oxidizing agent. A water-soluble solvent may be added to the water. Examples of water-soluble solvents include alcohols, ketones such as acetone, and ethers such as dioxane and tetrahydrofuran. An oxidation reaction in water produces an aqueous dispersion of graphene oxide. By adding the 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 can 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 metal porous body is impregnated with an aqueous dispersion containing graphene oxide, and then the graphene oxide is reduced in the pores of the metal porous body. The method for impregnating the porous metal body with the aqueous dispersion is not particularly limited, but examples thereof include a method of immersing the porous metal body in the aqueous dispersion and a method of coating the porous metal body with the aqueous dispersion.

In addition, although there is no particular limitation on the method for reducing graphene oxide, for example, hydrothermal treatment can be given. For example, a metal porous body impregnated with an aqueous dispersion may be sealed in an autoclave and hydrothermally treated to form a gel-like product in the pores of the metal porous body. The temperature of the hydrothermal treatment may be, for example, 150° C. or higher, and may be 170° C. or higher and 200° C. or lower.

In the hydrothermal treatment, a crosslinked structure between the metal porous body and the first carbon can be generated. For example, the metal porous body and the first carbon are crosslinked via a functional group such as an ether bond group (--O--). That is, hydrothermal treatment yields a gel-like product that is composited with a metal porous body and contains graphene having a three-dimensional structure.

When the aqueous dispersion contains the second carbon together with the graphene oxide, the graphene oxide is reduced in the presence of the second carbon. In this case, the hydrothermal treatment can also generate a crosslinked structure between the first carbon and the second carbon. For example, the first carbon and the second carbon are crosslinked via a functional group such as an ether linking group. That is, a gel-like product is obtained which is composited with the metal porous body and the second carbon and contains graphene having a three-dimensional structure.

The gelled product may be contacted with a reducing agent in order to further advance the reduction. Examples of reducing agents include metal hydrides, borohydrides, boranes, hydrazines or hydrazides, ascorbic acids, thioglycolic acids, cysteines, sulfites, thiosulfates, and dithionites. For example, the gelled product may be immersed together with the metal porous body 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, may be 40 to 100°C, or may be 50 to 100°C. The amount of the reducing agent to be used may be appropriately adjusted according to the type of reducing agent, the degree of oxidation of graphene oxide, the amount of gelled product, and the like. The degree of oxidation of graphene after reduction may be, for example, 40% by mass or less, or may be 20% by mass or less.

(iii) Freeze-drying step After that, the gel-like product is preferably lyophilized (freeze-dried). By freeze-drying, a dry gel (xerogel) in which the three-dimensional structure of graphene is highly maintained can be obtained. 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, preferably 1 Pa or less. Further, by freeze-drying the gel-like product in the pores of the metal porous body, the state of connection between the metal porous body and the first carbon (and the second carbon) is easily maintained. As a result, deterioration of the current collection path is suppressed even if expansion and contraction of graphene are repeated due to charging and discharging. A composite of a metal porous material and a xerogel obtained by freeze-drying can be used as it is as a capacitor electrode exhibiting high capacity.

Next, an example of a capacitor provided with the capacitor electrode will be described. The capacitor electrode can be applied as an electrode for, for example, an electric double layer capacitor, a lithium ion capacitor, or the like.

FIG. 1 is a partially cutaway perspective view of an electric double layer capacitor 10. FIG.
The illustrated electric double layer capacitor 10 includes a wound capacitor element 1 . The capacitor element 1 is configured by winding a sheet-like first electrode 2 and a sheet-like second electrode 3 with a separator 4 interposed therebetween. Each of the first electrode 2 and the second electrode 3 is a composite containing at least a first carbon (xerogel) and a metal porous body, and the first carbon develops capacity by adsorbing and desorbing ions. For the separator 4, for example, a nonwoven fabric containing cellulose as a main component is used. Lead wires 5a and 5b are connected to the first electrode 2 and the second electrode 3, respectively, as lead members. Capacitor element 1 is housed in a cylindrical exterior case 6 together with an electrolytic solution (not shown). The material of the exterior case 6 may be any metal such as aluminum, stainless steel, copper, iron, brass, or the like. The opening of the exterior case 6 is sealed with a sealing member 7 . The lead wires 5 a and 5 b are led out to the outside so as to pass through the sealing member 7 . A rubber material such as butyl rubber, for example, is used for the sealing member 7 .

The electrolytic solution may be a mixture of a solvent and an ionic substance (eg, 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 electrolytic solution may be, for example, 0.5 to 2.0 mol/L.

As the non-aqueous solvent, a high boiling point solvent is preferred. 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, N-methylacetamide, N,N-dimethylformamide, N- Amides such as 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 whose cations include organic substances include quaternary ammonium salts. Organic salts in which the anion (or both ions) contain an organic substance include, for example, trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, phthalate acid mono 1,3-dimethyl-2-ethylimidazolinium;

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

In the above embodiments, a wound capacitor has been described, but the scope of application of the present invention is not limited to the above, and it can also be applied to capacitors of other structures, such as laminated or coin-shaped capacitors.

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

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

An aqueous dispersion containing 0.35% by mass of graphene oxide, which is the first carbon raw material, was prepared. On the other hand, as a metal porous body having a three-dimensional network structure, an aluminum (Al) porous body having an average pore diameter of 510 μm and a thickness of 1 mm was prepared, and the metal porous body was immersed in an aqueous dispersion to fill the pores with the aqueous dispersion. filled.

Next, the Al porous body impregnated with the water dispersion was hydrothermally treated at 180° C. for 1 hour to obtain a composite of the Al porous body and the gel-like product. Subsequently, the composite is immersed in an aqueous solution of sodium ascorbate (sodium ascorbate concentration: 1.0 mol/L), which is a reducing agent, heated to 100° C. and held for 2 hours to sufficiently reduce graphene oxide and obtain a three-dimensional structure. was produced. After that, the gel-like product was lyophilized (freeze-dried) at −20° C. under a reduced pressure of 100 Pa to obtain a capacitor electrode, which is a composite of Al porous material and xerogel.

[evaluation]
(Structure of first carbon)
A scanning electron micrograph (SEM image) of the resulting composite of Al porous material and xerogel is shown in FIG. 2(a), and a transmission electron micrograph (TEM image) is shown in FIG. 2(b). Each image shows a crimped or folded structure with a plurality of randomly formed fold-like ridges and depressions. The height of the raised portion or the depth of the recessed portion formed in the folded portion is sufficiently larger than the thickness of the carbon portion, and is at least twice the thickness of the carbon portion.

(capacitance)
A pair of identical electrodes are prepared, lead wires are connected to each of them, and a capacitor element is formed by winding them with a cellulose non-woven fabric separator interposed therebetween. , completed the electric double layer capacitor A1. As the electrolytic solution, a solution obtained by dissolving ethyldimethylimidazolium tetrafluoroborate in propylene carbonate, which is a non-aqueous solvent, at a concentration of 1.0 mol/L was used. After that, aging treatment was performed at 60 for 16 hours while applying the rated voltage. The capacitance of the obtained electric double layer capacitor A1 was measured at 25°C.

(002 plane spacing (d002))
Next, the electric double layer capacitor was disassembled, and X-ray diffraction measurement of graphene contained in the electrodes was performed. By analyzing the obtained X-ray diffraction profile, d002 of the first carbon was determined to be 3.422 Å. FIG. 3 shows the X-ray diffraction profile of the composite of the metal porous material and the xerogel.

In FIG. 3, the diffraction peak P1 attributed to the 002 plane is relatively broad, and the waveform can be separated into a plurality of peaks. Also, a broad halo pattern attributed to the amorphous phase is observed on the higher angle side than the diffraction peak P1.

<<Comparative example 1>>
In the same manner as in Example 1, an aqueous dispersion containing 0.35% by mass of graphene oxide, which is the first carbon raw material, was prepared, and the aqueous dispersion was hydrothermally treated at 180° C. for 1 hour to obtain a gel-like product. Obtained. Subsequently, the gel-like product was reduced with an aqueous sodium ascorbate solution as a reducing agent in the same manner as in Example 1, and then the gel-like product was lyophilized (freeze-dried) at −20° C. under a reduced pressure of 100 Pa, A xerogel was obtained.

Next, the xerogel was dispersed in water together with CMC as a binder to prepare a slurry. The amount of CMC used was 10 parts by mass per 100 parts by mass of xerogel. The same porous metal body as in Example 1 was filled with the obtained slurry and dried by heating at 110° C. in a vacuum to obtain a capacitor electrode containing substantially the same amount of graphene as in Example 1. An electric double layer capacitor B1 was produced in the same manner as in Example 1, except that this electrode was used, and evaluated in the same manner.

<<Comparative Example 2>>
A slurry was prepared in the same manner as in Comparative Example 1 except that activated carbon (specific surface area: 2200 m ² /g) was used instead of xerogel, and an electric double layer capacitor B2 was produced and evaluated in the same manner as in Comparative Example 1.

<<Comparative Example 3>>
A slurry was prepared in the same manner as in Comparative Example 1 except that highly crystalline graphene was used instead of xerogel, and an electric double layer capacitor B3 was produced and evaluated in the same manner as in Comparative Example 1.

An electron micrograph of highly crystalline graphene is shown in FIG. The X-ray diffraction profile of highly crystalline graphene is shown in FIG.

In FIG. 4, the highly crystalline graphene is a flat sheet with no three-dimensional structures such as bumps or depressions. In FIG. 5, the peak P1 attributed to the 002 plane is extremely sharp, and no halo pattern on the high-angle side is seen. The d002 of highly crystalline graphene was determined to be 3.369 Å.

Table 1 summarizes the evaluation results of the above examples and comparative examples.

As described above, the capacitor A1 of Example 1 exhibits a significantly higher capacitance than the capacitor B3 using highly crystalline graphene, and has a higher capacitance than the capacitor B2 using activated carbon having a high surface area. Got. On the other hand, the capacity of the capacitor B1 in which the xerogel was slurried was lower than that of the capacitor B3. This is thought to be due to the collapse of the three-dimensional structure of graphene during the xerogel slurrying process.

According to the present invention, a high-capacity capacitor electrode can be stably obtained.

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

Claims (25)

a metal porous body;
graphene, which is the first carbon filled in the voids of the metal porous body;
and a short carbon fiber having an average length of less than 0.1 μm, which is a second carbon filled in the voids of the metal porous body . 2. The capacitor electrode according to claim 1, wherein said short carbon fibers are vapor-grown carbon fibers or carbon nanofibers. a metal porous body;
graphene, which is the first carbon filled in the voids of the metal porous body;
and carbon particles having an average diameter of 0.1 μm or less, which are the second carbon filled in the voids of the metal porous body. 4. The capacitor electrode according to claim 3, wherein said carbon particles are selected from the group consisting of graphite, non-graphitizable carbon, graphitizable carbon and carbon black. 5. The capacitor electrode according to claim 3, wherein said carbon particles are linked to form a chain structure. 6. The capacitor electrode according to claim 1, having a crosslinked structure between said porous metal body and said first carbon. 7. The capacitor electrode according to claim 1, having a crosslinked structure between said first carbon and said second carbon. The capacitor electrode according to any one of claims 1 to 7, wherein a ratio of said first carbon to a total of said first carbon and said second carbon is 40 to 98% by mass. 9. The capacitor electrode according to claim 1, wherein said graphene has a three-dimensional structure. 9. The capacitor electrode according to claim 1, wherein said graphene has a degree of oxidation of 40% by mass or less. The capacitor electrode according to any one of claims 1 to 10 , wherein said metal porous body has a three-dimensional network structure. The capacitor electrode according to any one of claims 1 to 11, wherein the graphene sheet laminate has an average number of laminated layers of 10 or less. The capacitor electrode according to any one of claims 1 to 12 , wherein the interlayer distance between graphene sheets in the graphene varies randomly. The capacitor electrode according to any one of claims 1 to 13 , wherein the graphene has a crimped structure or a folded structure. Claims 1 to 14 , wherein the X-ray diffraction profile of the first carbon has a diffraction peak P1 attributed to the 002 plane and a halo pattern attributed to an amorphous phase on a higher angle side than the diffraction peak P1. The capacitor electrode according to any one of . 16. The capacitor electrode according to claim 15 , wherein the interplanar distance between the 002 planes of the first carbon calculated from the X-ray diffraction profile is 0.338 nm or more. The capacitor electrode according to any one of claims 1 to 16 , wherein the graphenes are stacked with the second carbon interposed therebetween. A capacitor comprising the capacitor electrode according to any one of claims 1 to 17 . preparing an aqueous dispersion containing graphene oxide as the first carbon raw material;
and impregnating the aqueous dispersion into the metal porous body to reduce the graphene oxide in the voids of the metal porous body. 3. The method of claim 1, wherein the step of reducing the graphene oxide comprises hydrothermally treating the porous metal body impregnated with the aqueous dispersion to generate a gel-like product in the pores of the porous metal body. 20. The method for producing a capacitor electrode according to 19 above. 21. The method of manufacturing a capacitor electrode according to claim 20 , wherein the step of reducing the graphene oxide further comprises contacting the gelled product with a reducing agent. 22. The method of manufacturing a capacitor electrode according to claim 20 , further comprising the step of freeze-drying said gel-like product in said voids of said metal porous body. The aqueous dispersion further contains a second carbon,
The method for producing a capacitor electrode according to any one of claims 19 to 22 , wherein 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. a metal porous body;
and graphene, which is the first carbon filled in the voids of the metal porous body,
A capacitor electrode having a crosslinked structure between the metal porous body and the first carbon. a metal porous body;
and carbon filled in the voids of the metal porous body,
wherein the carbon consists only of graphene,
The electrode for a capacitor, wherein the graphene has a three-dimensional structure.

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