JP7425983B2 - Electrodes for electric double layer capacitors and electric double layer capacitors - Google Patents

Description

The present invention relates to an electrode for an electric double layer capacitor and an electric double layer capacitor.

An electric double layer capacitor is a capacitor that utilizes electrical energy stored in an electric double layer formed at the interface between a polarizable electrode such as activated carbon and an electrolyte. Unlike conventional secondary batteries, which do not involve chemical reactions during charging and discharging, they have a long life, have rapid charging characteristics and high cycle characteristics, and can be used over a wide range of temperatures. It is attracting attention as a power source for driving various devices. For example, biometric authentication cards with built-in electric double layer capacitors are being considered for the purpose of ensuring the security and convenience of credit cards.

When used as a storage power source for a built-in biometric authentication card, the characteristics required of an electric double layer capacitor are that it be capable of rapid charging, have low internal impedance, and have little IR drop (initial voltage drop). However, in a capacitor, impedance includes DC resistance and reactance, and reactance is proportional to the reciprocal of capacitance, so in order to achieve both low capacitance and low impedance, it is necessary to further reduce the internal resistance. It was difficult.

For example, Patent Document 1 discloses a technology using graphene or carbon nanotubes with high electrical conductivity as an active material instead of conventional activated carbon for the purpose of lowering impedance and increasing capacity.

JP2015-230906A

However, Patent Document 1 states that at a ratio of carbon nanotubes: conductive aid: binder = 8:1:1, the ratio of carbon nanotubes is too large, resulting in a capacitance higher than necessary, and the impedance at the desired capacitance is significantly increased. There was an issue of an increase in the number of people.

The object of the present invention has been made in view of the above circumstances, and uses graphene with high electrical conductivity as an active material, and sets the weight ratio of the active material and the conductive additive to 1:99 to 50:50 (conductive additive). An electric double layer capacitor with a desired capacitance and low internal resistance can be provided by making the capacitor rich in liquid.

That is, according to the present invention, the following are provided.
[1] It has a current collector and an electrode layer formed on the current collector, and the electrode layer includes an active material (A), a conductive aid (B), and a binder (C),
The active material (A) is graphene or graphene oxide,
The weight ratio (A:B) of the active material (A) and the conductive additive (B) is 1:99 to 50:50,
The total weight ratio ((A+B):C) of the active material (A) and the conductive additive (B) to the binder (C) is 90:10 to 65:35. Characteristic electrodes for electric double layer capacitors.
[2] An electric double layer capacitor using the electrode according to [1].
[3] The electric double layer capacitor according to [2], wherein the product of internal resistance R and capacitance C is CR≦250Ω·mF.

According to the present invention, an electric double layer capacitor having a desired capacitance and low internal resistance can be provided. Further, according to an embodiment of the present invention, it is possible to provide an electric double layer capacitor that has an internal resistance of about 1/10 or less of activated carbon when compared with the same capacitance.

1 is a schematic cross-sectional view showing a preferred embodiment of an electrode for an electric double layer capacitor of the present invention. 1 is a schematic cross-sectional view showing a preferred embodiment of an electric double layer capacitor of the present invention.

Hereinafter, this embodiment will be described in detail with reference to the drawings as appropriate. In the drawings used in the following explanation, characteristic parts of the present invention may be shown enlarged for convenience in order to make it easier to understand, and the dimensional ratio of each component may differ from the actual one. be. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be implemented with appropriate changes within the scope of the invention.

(Electrode for electric double layer capacitor)
Hereinafter, the electric double layer capacitor electrode 10 according to this embodiment will be described in detail. FIG. 1 is a schematic cross-sectional view showing an electrode 10 for an electric double layer capacitor according to this embodiment. As shown in FIG. 1, the electric double layer capacitor electrode 10 includes a current collector 12 and an electrode layer 14 formed on the current collector 12.

[Current collector]
The current collector 12 may be any conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

[Electrode layer]
The electrode layer 14 includes an active material (A), a conductive aid (B), and a binder (C). The active material (A) is graphene or graphene oxide. The weight ratio (A:B) of the active material (A) and the conductive agent (B) is 1:99 to 50:50, and the active material (A) and the conductive agent (B) (A+B), and the weight ratio ((A+B):C) of the binder (C) is 90:10 to 65:35.

<Active material (A)>
The active material (A) is graphene or graphene oxide.
Graphene used in the electrode layer of the electric double layer capacitor according to this embodiment is a two-dimensional sheet-like material in which carbon atoms are arranged in a hexagonal system.
Graphene may have a single layer or two or more layers. In the present invention, two or more layers of graphene are sometimes referred to as graphene sheets or graphene particles (aggregates) to distinguish them from single-layer graphene. The number of stacked graphene sheets is preferably 2 or more and 10 or less.
As the graphene, for example, one commonly used as an electrode material can be used.

Graphene can be prepared by mechanically exfoliating graphite or by chemically treating it.
Specifically, a method is known in which graphite is mechanically peeled off using adhesive tape. Furthermore, graphene can be prepared by subjecting graphite to an oxidation treatment to obtain graphene oxide, and then subjecting it to a reduction treatment.

The graphene oxide used in the electrode layer of the electric double layer capacitor according to this embodiment is a nanosheet exfoliated from graphite by subjecting the graphite to an oxidation treatment. For example, graphene containing carbonyl groups and the like can be mentioned. As graphene oxide that can be suitably used, reduced graphene oxide (product name: Exfoliated GO) manufactured by Nishina Materials Co., Ltd. can be mentioned.
The graphene oxide according to the present invention includes reduced graphene oxide (sometimes referred to as RGO) obtained by reducing the graphene oxide described above. In the present invention, graphene oxide that has not been subjected to reduction treatment may be referred to as primary graphene oxide to distinguish it from RGO.
Reduced graphene oxide (RGO) can be obtained, for example, by removing some or all of the carbonyl groups of graphene oxide, which is a nanosheet exfoliated as a single layer from graphite.
Primary graphene oxide has a carbonyl group, a hydroxyl group, etc., and thus has an affinity for polar solvents and the like, and is advantageous from the viewpoint of forming an electrode layer.
Since reduced graphene oxide has some or all carbonyl groups removed, it has high conductivity and is suitable as an electrode material. On the other hand, since reduced graphene oxide has a hydroxyl group, it has an affinity for polar solvents and the like, and is advantageous for constructing power storage devices.

Here, as the reduced graphene oxide that can be suitably used, "Graphelite RGO" manufactured by MICC TEC Co., Ltd. can be mentioned. This "grapherite RGO" has a particle size of 4 to 80 μm, a thickness of 2 to 40 nm, and has a linearly connected shape.

Primary graphene oxide can be obtained by oxidizing graphene obtained by mechanically peeling off graphite with an adhesive tape. Additionally, primary graphene oxide can be obtained by oxidizing graphite. Reduced graphene oxide can be obtained by reducing primary graphene oxide.

An example of obtaining primary graphene oxide by oxidizing graphite is shown below. In other words, when graphite is exposed to a strong oxidizing agent such as potassium permanganate or sulfuric acid in water, the carbon on the surface of each layer of graphite is oxidized, and substituents containing oxygen (carboxyl groups, hydroxyl groups, epoxides, etc.) are formed on the surface. ) is obtained. Graphite oxide exhibits hydrophilicity due to the presence of these substituents, and when dispersed in water, it exfoliates, yielding a monolayer or multilayer aqueous dispersion of primary graphene oxide.

The primary graphene oxide obtained as described above is obtained by, for example, performing a gentle reduction, and unlike primary graphene oxide, the primary graphene oxide has a structure that retains functional groups such as hydroxyl groups and carboxyl groups. A reduced graphene oxide having the following properties is obtained.

As the graphene oxide used in the electrode layer of the electric double layer capacitor according to the present embodiment, either primary graphene oxide or reduced graphene oxide may be used alone, or a mixture thereof may be used.
When used as an electrode layer of an electric double layer capacitor, it is desirable that the electric conductivity is high. The degree of oxidation and electrical conductivity of primary graphene oxide and reduced graphene oxide are in a proportional relationship, and the degree of oxidation is preferably 30% or less, more preferably 10% or less.

Graphene or graphene oxide (also referred to as "graphene-based material of the present invention") used for the electrode layer of the electric double layer capacitor of the present invention has a layer number of 1 to 100, excluding exceptions such as agglomerated parts, It is preferably 2 to 10. The weight ratio of graphene having 2 to 10 layers is 60 to 100%, preferably 70% to 100%, and more preferably 80 to 100%, based on the graphene contained in the electrode layer. .
The graphene-based material of the present invention has a sheet shape with a particle size of 0.1 to 50 μm and a thickness of 0.5 to 200 nm. From the viewpoint of operability when coating the electrode layer, the particle size is preferably 1 to 10 μm.

<Conductivity aid (B)>
The conductive aid (B) is not particularly limited as long as it improves the conductivity of the electrode layer, and any known conductive aid can be used. Examples include carbon materials such as graphite, carbon black (acetylene black, Ketjen black, other furnace blacks, channel blacks, thermal lamp blacks, etc.), carbon nanotubes, and carbon nanofibers. Carbon black, carbon nanotubes or carbon nanofibers are preferred.

For example, in the case of carbon black, the conductive aid (B) preferably has an average particle size of 20 to 100 nm, more preferably 25 to 90 nm. The BET specific surface area is preferably 25 to 200 m ² /g, more preferably 30 to 180 m ² /g.

<Binder (C)>
The binder (C) binds the active materials together and also binds the active materials and the current collector. The binder may be any binder as long as it is capable of the above-mentioned bonding, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF) ) and other fluororesins.

In addition to the above, as a binder, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFPTFE-based fluororubber), (fluororubber), vinylidene fluoride-pentafluoropropylene-based fluororubber (VDF-PFP-based fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-PFP-TFE-based fluororubber), vinylidene fluoride Vinylidene fluoride fluorine rubber such as Ride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene fluorine rubber (VDF-CTFE fluorine rubber), etc. Rubber may also be used.

Furthermore, in addition to the above, as a binder, for example, polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene/butadiene rubber, isoprene rubber, butadiene rubber, ethylene/propylene rubber, etc. may be used. In addition, thermoplastic elastomeric polymers such as styrene/butadiene/styrene block copolymers, hydrogenated products thereof, styrene/ethylene/butadiene/styrene copolymers, styrene/isoprene/styrene block copolymers, and hydrogenated products thereof may also be used. Furthermore, syndiotactic 1,2-polybutadiene, ethylene/vinyl acetate copolymer, propylene/α-olefin (carbon number 2 to 12) copolymer, etc. may be used.

Furthermore, an electronically conductive conductive polymer or an ionically conductive conductive polymer may be used as the binder. Examples of the electronically conductive polymer include polyacetylene. In this case, since the binder also performs the function of the conductive aid particles, it is not necessary to add the conductive aid.

<Composition ratio of each component contained in the electrode layer>
In the electrode layer, the active material (A) is graphene or graphene oxide. The weight ratio (A:B) of the active material (A) and the conductive aid (B) is preferably 1:99 to 50:50, more preferably 5:95 to 40:60. , more preferably from 10:90 to 30:70. When the weight ratio (A:B) is 1:99 to 50:50, the graphene or graphene oxide contained in the electrode layer can be well dispersed to form a conductive path in the electrode layer. As a result, the impedance of an electric double layer capacitor using such an electrode layer is reduced. Moreover, at the same time, the capacity can be reduced within a desired range.

The total weight ratio ((A+B):C) of the active material (A) and the conductive additive (B) to the binder (C) is 90:10 to 65:35. The ratio is preferably 90:10 to 70:30, even more preferably 90:10 to 80:20. When the weight ratio ((A+B):C) is within the range of 90:10 to 65:35, there is no peeling of the coating between the electrode layer and the seed electric body, and the balance between electrode strength and impedance is maintained. Good range is obtained.

[Method for manufacturing electrodes]
The electric double layer capacitor electrode 10 according to this embodiment can be manufactured by a commonly used method. For example, a slurry containing the active material (A) (graphene or graphene oxide) for an electric double layer capacitor of the present embodiment, a conductive agent (B), a binder (C), and a solvent (D) is placed on the current collector 12. It can be manufactured by coating the current collector 12 and removing the solvent in the slurry coated on the current collector 12.

As the solvent, for example, N-methyl-2-pyrrolidone, N,N-dimethylformamide, etc. can be used.

There are no particular limitations on the coating method, and any method commonly used for producing electrodes can be used. Examples include the slit die coating method and the doctor blade method.

The method for removing the solvent in the slurry applied onto the current collector is not particularly limited, and the current collector coated with the slurry may be dried in an atmosphere of 80° C. to 150° C., for example.

Then, the electrode on which the electrode layer has been formed in this manner is then subjected to a press treatment using a press device or the like to adjust the thickness of the electrode layer. A roll press can be used as the press device.

When using a roll press, the surface temperature of the heated press roll is set to a temperature above room temperature and below the melting point, preferably between 25°C and above and below the melting point, more preferably between 25°C and above and below 80°C. select. For example, when PVDF (polyvinylidene fluoride: melting point 150°C) is used as the binder, it is preferable to heat it in the range of room temperature to 150°C, and more preferably in the range of 25 to 80°C. When a styrene-butadiene copolymer (melting point 100°C) is used as the binder, it is preferably heated to a temperature in the range of room temperature to 100°C, more preferably in a range of 25 to 80°C.

The press pressure of the heated press roll is preferably 100 kgf/cm or more and 1000 kgf/cm or less, more preferably 300 kgf/cm or more and 900 kgf/cm or less, and more preferably 300 kgf/cm or more and 600 kgf/cm or less. The press speed is preferably 15 m/min or less, more preferably 10 m/min or less, even more preferably 5 m/min or less. Appropriate pore diameter and pore distribution can be obtained at the above press speed.

As a method for adjusting the composition ratio of the active material (A), the conductive agent (B), and the binder (C), for example, the weight ratio (A) of the active material (A) and the conductive agent (B) can be adjusted. :B) is within the range of 1:99 to 50:50, and the weight ratio (( An example of this is to prepare a slurry containing the active material (A), the conductive agent (B), and the binder (C) so that A+B):C) is within the range of 90:10 to 65:35.

Since the active material (A) is graphene or graphene oxide, the active material (A) can be well dispersed in a solvent, and then the conductive agent (B) or the binder (C) can be added. Alternatively, the binder (C) can be added after the active material (A) and the conductive additive (B) are well dispersed in the solvent.

Through the above steps, the electric double layer capacitor electrode of this embodiment can be manufactured.

(Electric double layer capacitor)
FIG. 2 is a schematic cross-sectional view showing the electric double layer capacitor according to this embodiment. As shown in FIG. 2, the electric double layer capacitor 100 includes a positive electrode 20, a negative electrode 30 facing the positive electrode 20, and a main surface of the positive electrode 20 and a main surface of the negative electrode 30. This is an electric double layer capacitor including a separator 18 and a non-aqueous electrolyte (not shown) that are in contact with each other. In the electric double layer capacitor according to this embodiment, the product of internal resistance R and capacitance C is preferably CR≦250Ω·mF, more preferably CR≦200Ω·mF, and CR≦100Ω. -mF is more preferable.

The electric double layer capacitor 100 mainly includes a power generation element 40, an exterior body 50 that hermetically houses the power generation element 40, and a pair of leads 60 and 62 (electrode terminals) connected to the power generation element 40.

The power generation element 40 includes a pair of positive electrode 20 and negative electrode 30, which are arranged to face each other with a separator 18 in between. The positive electrode 20 includes a positive electrode active material layer 24 provided on a plate-like (film-like) positive electrode current collector 22 . The negative electrode 30 includes a negative electrode active material layer 34 provided on a plate-like (film-like) negative electrode current collector 32 . The main surface of the positive electrode active material layer 24 and the main surface of the negative electrode active material layer 34 are in contact with the main surface of the separator 18, respectively. A lead 60 (positive electrode terminal) and a lead 62 (negative electrode terminal) are connected to the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the ends of the leads 60 and 62 are connected to the outside of the exterior body 50. It extends to.

[Positive electrode and negative electrode]
In the electric double layer capacitor 100 of this embodiment, the positive electrode 20 or the negative electrode 30 uses the electric double layer capacitor electrode of this embodiment described above. As the positive electrode 20 and the negative electrode 30, it is preferable to use the electric double layer capacitor electrodes of the present embodiment described above. For example, when the positive electrode 20 uses the first electrode made of the electric double layer capacitor electrode of the present embodiment described above, and the negative electrode 30 uses the second electrode made of the electric double layer capacitor electrode of the present embodiment described above. , this first electrode and this second electrode may be the same or different. More preferably, the first electrode and the second electrode are the same. Since the positive electrode and the negative electrode are the same in the electric double layer capacitor electrode of this embodiment described above, the amount of electrolyte retained can be balanced, and changes in characteristics under continuous charging can be reduced. "The first electrode and the second electrode are the same" means, for example, that the first electrode used for the positive electrode and the negative electrode are One example is cutting out the second electrode. That is, within the allowable range of evaluation error, the first electrode and the second electrode have the same electrode composition, shape, thickness, etc.

[Electrolyte]
The electrolytic solution according to this embodiment is contained inside the positive electrode active material layer 24, the negative electrode active material layer 34, and the separator 18. It may be an aqueous electrolyte or a non-aqueous electrolyte. A non-aqueous electrolyte is preferred. The solute of the non-aqueous electrolyte is a salt containing a cation and an anion, for example, the cation is tetraethylammonium, triethylmethylammonium, spiro-(1,1')-bipyrrolidinium or diethylmethyl-2-methoxyethyl. Quaternary ammonium such as ammonium (DEME) or 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, 1-ethyl-3-methylimidazolium (EMI) or 1,2-dimethyl-3- An imidazolium such as propylimidazolium (DMPI) in which the anion is BF ^4- , PF ^6- , ClO ^4- , AlCl ^4- or CF ₃ SO ^3- can be used.

Examples of solvents for the non-aqueous electrolyte of electric double layer capacitors include propylene carbonate (abbreviated as PC), ethylene carbonate (abbreviated as EC), dimethyl carbonate (abbreviated as DMC), diethyl carbonate (abbreviated as DEC), acetonitrile (abbreviated as AN), and propylene carbonate (abbreviated as DMC). Nitrile, γ-butyrolactone (abbreviation BL), dimethylformamide (abbreviation DMF), tetrahydrofuran (abbreviation THF), dimethoxyethane (abbreviation DME), dimethoxymethane (abbreviation DMM), sulfolane (abbreviation SL), dimethyl sulfoxide (abbreviation DMSO), Examples include organic solvents such as ethylene glycol, propylene glycol, and methylcellosolve. These may be used alone or in combination of two or more in any proportion.

The solute concentration in these non-aqueous electrolytes is preferably 0.6 mol/L or more and 2.2 mol/L or less, particularly 0.8 mol/L or more and 2.0 mol/L or less, so that the characteristics of the electric double layer capacitor can be fully brought out. A concentration of L or less is preferable because high electrical conductivity can be obtained. In particular, when charging and discharging at a low temperature of −20° C. or lower, a concentration of 2.2 mol/L or higher is undesirable because the electrical conductivity of the electrolytic solution decreases. If it is less than 0.6 mol/L, the electrical conductivity is low both at room temperature and at low temperature, which is not preferable. For example, when a solution of triethylmethylammonium tetrafluoroborate in acetonitrile (AN) is used as the electrolytic solution, the concentration of triethylmethylammonium tetrafluoroborate is preferably 0.9 to 1.9 mol/L.

[Separator]
As the separator 18, any one of a cellulose nonwoven fabric, a polyolefin porous film, an aramid fiber nonwoven fabric, or a mixture thereof can be used.
The thickness of the separator is preferably 10 μm or more and 50 μm or less. If the thickness is 10 μm or more, self-discharge due to internal micro-shorts can be suppressed effectively, while if the thickness is 50 μm or less, the electric double layer capacitor has excellent energy density and output characteristics.

[Exterior body]
The exterior body 50 seals the power generation element 40 and the electrolyte solution therein. The exterior body 50 is not particularly limited as long as it can prevent the leakage of the electrolyte to the outside and the intrusion of moisture and the like into the electric double layer capacitor 100 from the outside. For example, as the exterior body 50, a metal laminate film in which metal foil 52 is coated on both sides with polymer films 54 can be used. For example, aluminum foil can be used as the metal foil 52, and a polypropylene film can be used as the polymer film 54. For example, the material of the outer polymer membrane 54 is preferably a polymer with a high melting point, such as polyethylene terephthalate (PET), polyamide, etc., and the material of the inner polymer membrane 54 is preferably polyethylene (PE) or polypropylene (PP). etc. are preferred.

[Lead]
The leads 60 and 62 (electrode terminals: positive and negative terminals) are generally rectangular in shape, one end of which is electrically connected to the current collector of the electrode, and the other end of which is connected to an external load during use. (in the case of discharging) or electrically connected to the power source (in the case of charging). One end of lead 60 (positive electrode terminal) is electrically connected to the positive electrode, and one end of lead 62 (negative electrode terminal) is electrically connected to the negative electrode. Specifically, the lead 60 is electrically connected to the uncoated area of the positive electrode active material layer of the positive electrode current collector 22, and the lead 62 is electrically connected to the uncoated area of the negative electrode active material layer of the negative electrode current collector 32.
Leads 60, 62 are made of a conductive material. Preferably, the material is aluminum.
It is preferable that a resin film (not shown) such as polypropylene is attached to the center portions of the leads 60 and 62, which serve as the sealing portion of the laminate film exterior body 50. This prevents a short circuit between the leads 60, 62 and the metal foil constituting the laminate film, and improves sealing performance.
The electrical connection method for the above-mentioned current collectors (positive electrode current collector 22 and negative electrode current collector 32) and leads 60, 62 is, for example, generally ultrasonic welding, but resistance welding, laser welding, etc. etc., and is not limited.

[Fabrication of electric double layer capacitor]
By a known method, the leads 60 and 62 are welded to the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the separator 18 is placed between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode active material layer 34 of the negative electrode 30. A single-cell electric double layer capacitor as shown in FIG. 2 can be manufactured by inserting the capacitor in a sandwiched state into the exterior body 50 together with a non-aqueous electrolyte and sealing the entrance of the exterior body 50. Furthermore, an electric double layer capacitor including two or more single cells can be manufactured by connecting two or more single cell electric double layer capacitors in series. As a method for evaluating and calculating the electrical characteristics such as the capacity retention rate of a single cell electric double layer capacitor, for example, there is a method of calculating from the evaluation of an electric double layer capacitor including two or more single cells connected in series. Can be mentioned.

EXAMPLES Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Example 1)
[Preparation of electrode]
As the active material (A) of the present invention, reduced graphene oxide (product name: Exfoliated GO) manufactured by Nishina Materials Co., Ltd. is used, and as the conductive agent (B), carbon black powder (manufacturer: TIMCAL, product name: SUPER C-45, BET specific surface area: 45 m ² /g) was used, polyvinylidene fluoride (PVDF, manufacturer: ARKEMA, product name: KYNAR) was used as the binder (C), and the active material (A) and conductive The weight ratio (A:B) with the auxiliary agent (B) is set to A:B=1:99, and the total of the active material (A) and the conductive auxiliary agent (B) (A+B). A slurry was prepared by blending the binder (C) in a weight ratio ((A+B):C) of (A+B):C=70:30.

The obtained slurry was coated on a release sheet made by TDK, dried at a temperature of 110° C. for 30 minutes, and then pressed using a roll press to obtain an electrode material sheet with a coating thickness of 10 μm. A micrometer was used to measure the thickness. The conditions for the roll press were a linear pressure of 450 kgf/cm, a heated roll temperature of room temperature, and a feed speed of 5 m/min. Linear pressure was calculated based on the pressure applied to the pressure roll and the length of contact between the upper and lower rolls.

[Nonaqueous electrolyte]
A non-aqueous electrolyte solution was prepared in which tetraethylammonium tetrafluoroborate was dissolved in acetonitrile (AN) at a concentration of 1.0 mol/L.

[Separator]
A microporous polyethylene membrane with a thickness of 20 μm was prepared.

[Fabrication of electric double layer capacitor]
The two electrodes obtained above were each cut into pieces of 1.8 cm ² to form a positive electrode and a negative electrode. The positive and negative electrodes are ultrasonically fused to each of the positive and negative electrodes and laminated with the separator sandwiched between the positive and negative electrodes, then covered with an aluminum laminate material as an exterior body, and covered with the non-aqueous A single cell electric double layer capacitor was produced by injecting an electrolyte and finally sealing the opening by fusion.

<Evaluation of capacitance>
The electric double layer capacitor of Example 1 was charged at a constant current of 10 mA to 2.5 V, and after reaching 2.5 V, the charge was shifted to constant voltage charging, and constant voltage charging was performed for 1 second. Discharge was performed at a constant current of 10 mA, and the final voltage was 0V. From the discharge curve (discharge voltage - discharge time) obtained as a result, the time taken from 2.0V to 1.0V Δt [msec. ], and use the following relational expression:
Capacity = {discharge current (10mA) x time Δt}/voltage (2.0V-1.0V)
The initial capacity value (C ₀ ) was calculated. The initial capacitance value (C ₀ ) was defined as the capacitance C of the electric double layer capacitor. The results are shown in Table 1.

<IR drop evaluation>
When evaluating the capacitance, the value of the voltage drop (sometimes referred to as "IR drop" or "IR-drop") that occurs when charging and discharging is switched after full charge was determined. Discharge current: 10mA; Full charge voltage: 2.5V.
If the discharge curve curves slowly to diffuse and forms a constant straight line, measure the ΔV ₂ at the intersection of the initial discharge including this diffusion curve and the extended discharge straight line, and calculate the IR drop (JIS standard: IR drop = ΔV ₂ ). The results are shown in Table 1.

measuring equipment:
Power supply KIKUSUI PMC18-3A
Load KIKUSUI PLZ164W
Oscilloscope YOKOGAWA DL708E

<Evaluation of internal resistance>
Using the above IR drop (JIS standard: IR drop = ΔV ₂ ), the internal resistance R was calculated using the following formula. The results are shown in Table 1.
Internal resistance R (DC resistance) = ΔV ₂ /I

<Evaluation of paint film peeling>
Regarding the electrodes produced in each Example, Reference Example, and Comparative Example, the appearance of the coating film of the electrode layer was visually observed to evaluate the presence or absence of coating peeling. Incidentally, those in which peeling of the paint film was not observed were rated as "no". The peeling of the paint film was limited to the electrode surface and was rated as "almost no" if it was minor. If peeling of the coating occurred on the entire surface of the electrode and chipping of the coating was observed, it was classified as "severe peeling". The results are shown in Table 1.

(Examples 2 to 11, Comparative Examples 1 to 4)
An electrode for an electric double layer capacitor was produced in the same manner as in Example 1, except that a slurry adjusted to the blending ratio of active material (A), conductive aid (B), and binder (C) shown in Table 1 was used. .

Using the obtained electrode, an electric double layer capacitor was produced in the same manner as in Example 1. In the same manner as in Example 1, capacitance, IR-drop, internal resistance, CR product, coating peeling, etc. were evaluated. The results are shown in Table 1.

(Comparative Examples 5 to 7)
Using activated carbon (manufacturer: Kuraray, product name: Kuraray Coal (registered trademark), average particle size: 2 nm, BET non-surface area: 1600 m ² /g, etc.) as the active material (A), the active materials shown in Table 1 ( An electrode for an electric double layer capacitor was produced in the same manner as in Example 1, except that a slurry whose mixing ratio of A), conductive aid (B), and binder (C) was adjusted was used.

Using the obtained electrode, an electric double layer capacitor was produced in the same manner as in Example 1. In the same manner as in Example 1, capacitance, IR-drop, internal resistance, CR product, coating peeling, etc. were evaluated. The results are shown in Table 1.

From the results of Examples 1 to 7 in Table 1, when the weight ratio (A:B) of the active material (A) and the conductive aid (B) is 1:99 to 50:50, the internal resistance is 5Ω or less. , CR product values of 75Ω·mF or less were obtained. Furthermore, from the results of Examples 8 to 11, the weight ratio of the total (A+B) of the active material (A) and the conductive additive (B) to the binder (C) ((A+B):C) is 90:10 to When the ratio was 65:35, an internal resistance of 1.8Ω or less and a CR product of 18Ω·mF or less were obtained.
On the other hand, in the case of Comparative Examples 1 and 2, the internal resistance was 10Ω or more, and the CR product was more than 300Ω·mF. Moreover, in the case of Comparative Examples 3 and 4, the internal resistance was 50Ω or more, and the CR product was a value exceeding 500Ω·mF.
In Comparative Examples 5 to 7 in which activated carbon was used as the active material, the internal resistance was 30Ω or more, and the CR product was more than 600Ω·mF.

Generally, it is considered that the larger the proportion by weight of graphene, which has higher electrical conductivity than the conductive additive, reduces the internal resistance. However, in reality, when the graphene ratio exceeded 50 parts by weight, it was thought that graphene reagglomeration occurred during electrode layer formation, and the internal resistance increased unexpectedly (Comparative Examples 1 and 2).
Furthermore, in the case of using activated carbon (Comparative Examples 5 to 7), the internal resistance became extremely large with a binder having a weight ratio ((A+B):C) of 65:35. However, in the case of graphene, even when the weight ratio ((A+B):C) was 65:35, an internal resistance that was about one digit lower was obtained. The reason for this is presumed to be that the formation of conductive paths in the electrode layer was different due to the difference in the powder shapes of activated carbon and graphene (activated carbon is roughly spherical, graphene is two-dimensional sheet-like).

Note that the increases in resistance and IR-drop in Examples 1 and 2 and the increases in resistance and IR-drop in Comparative Examples 1 and 2 are unique to graphene. The reason for this is that if the graphene ratio is decreased, the effect of lowering the resistance will be reduced, and conversely, if the graphene ratio is increased to more than 50%, dispersion will not be successful and the electrical conductivity of the element will not be fully utilized.

10...Electrode for electric double layer capacitor,
12... Current collector (current collector),
14...electrode layer,
18...Separator,
20... Positive electrode (electrode for electric double layer capacitor),
22... Positive electrode current collector (current collector),
24... Positive electrode active material layer (electrode layer),
30... Negative electrode (electrode for electric double layer capacitor),
32... Negative electrode current collector (current collector),
34...Negative electrode active material layer (electrode layer),
40...Power generation element,
50...Exterior body,
52...Metal foil,
54...Polymer membrane,
60, 62...Reed,
100...Electric double layer capacitor.

Claims (3)

comprising a current collector and an electrode layer formed on the current collector, the electrode layer containing an active material (A), a conductive aid (B), and a binder (C),
The active material (A) is graphene or graphene oxide,
The weight ratio (A:B) of the active material (A) and the conductive additive (B) is 1:99 to 10:90 ,
The total weight ratio ((A+B):C) of the active material (A) and the conductive additive (B) to the binder (C) is 90:10 to 65:35. Characteristic electrodes for electric double layer capacitors. An electric double layer capacitor using the electrode according to claim 1. The electric double layer capacitor according to claim 2, wherein the product of internal resistance R and capacitance C is CR≦250Ω·mF.

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