JP7305940B2 - 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 electric energy accumulated in an electric double layer formed at the interface between a polarizable electrode such as activated carbon and an electrolytic solution. Unlike conventional secondary batteries, it does not involve chemical reactions during charging and discharging, so it has a long life, high cycle characteristics, high output density, and a wide range of usable temperatures. It is also attracting attention as a power source for driving various devices including those for vehicles, and in particular, the development of electric double layer capacitors with high capacity and high output is underway.

In order to improve the energy density and obtain higher input characteristics and durability, it is desirable to optimize the pore structure of the activated carbon, which is the active material, the particle shape of the activated carbon, and even the electrode structure.

Since the capacitance of an electric double layer capacitor is proportional to the size of the electric double layer formed between the surface of the active material and the electrolyte, activated carbon with a large specific surface area is used. Further, a method is disclosed in which a pore structure that facilitates adsorption and desorption is defined in consideration of the size of electrolyte ions. For example, Patent Document 1 below discloses that the BET specific surface area is 1450 to 1950 m ² /g, the pore volume with a pore diameter of 3 nm or more is 0.09 to 0.35 cm ³ /g, and the average pore diameter is 2.05 to 2.05 An electric double layer capacitor has been proposed which has an electrode in which activated carbon with a thickness of 2.60 nm is used as an electrode active material. Further, for example, in Patent Document 2 below, a BET specific surface area of 2600 m ² /g or more and 4500 m ² /g or less and a mesopore volume V1 (cm ³ /g) of 0.8 < V1 ≤ 2.5 An electrode having a micropore volume V2 (cm ³ /g) of 0.92<V2≦3.0, an average particle size of 1 μm or more and 30 μm or less, and a sphericity of 0.80 or more An electric double-layer capacitor has been proposed that has electrodes made using an active material for the field.

JP 2017-171538 A JP 2015-198169 A

However, although various active materials suitable for electric double layer capacitors have been proposed as described above, there is a problem that the characteristics change greatly under continuous charging.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrode for an electric double layer capacitor whose characteristics change little under continuous charging, and an electric double layer capacitor comprising the electrode.

As a result of intensive studies, the present inventors have found an electrode for an electric double layer capacitor whose characteristics change is small under continuous charging by setting the pore diameter and the pore volume of the electrode itself within a predetermined range, and an electric device comprising the electrode. It has been found that a double layer capacitor can be obtained.
That is, according to the present invention, the following are provided.
[1] having a current collector and an electrode layer formed on the current collector,
The electrode layer contains a carbon material, a conductive aid, and a binder,
In the log differential pore volume distribution graph obtained by the mercury intrusion method in the electrode layer, the peak pore diameter A (unit: nm) and the log differential pore volume B at the peak pore diameter A (unit: cm ³ /g ) is 400 or more and 1500 or less.
[2] The peak pore diameter A is present in the range of 400 nm or more and 1000 nm or less,
The electrode for an electric double layer capacitor according to [1], wherein the Log differential pore volume B at the peak pore diameter A is 0.8 cm ³ /g or more and 2 cm ³ /g or less.
[3] The electrode layer is
Within the range of 65% by mass or more and 85% by mass or less of the carbon material,
Within the range of 10% by mass or more and 20% by mass or less,
The electrode for an electric double layer capacitor according to [1] or [2], containing the binder in the range of 5% by mass or more and 15% by mass or less.
[4] The electrode for an electric double layer capacitor according to any one of [1] to [3], wherein the carbon material has a specific surface area of 1000 m ² /g or more and 3000 m ² /g or less.
[5] The electrode for an electric double layer capacitor according to any one of [1] to [4];
and a non-aqueous electrolyte.
[6] having a positive electrode and a negative electrode,
Using a first electrode in which the positive electrode is the electrode for the electric double layer capacitor,
Using a second electrode in which the negative electrode is the electrode for the electric double layer capacitor,
The electric double layer capacitor according to [5], wherein the first electrode and the second electrode are the same.
[7] The electric double layer capacitor includes two or more single cells each having the positive electrode and the negative electrode,
The electric double layer capacitor according to [6], wherein the two or more single cells are connected in series.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an electrode for an electric double layer capacitor that exhibits a small change in characteristics under continuous charging, and an electric double layer capacitor including the electrode.

It is a cross-sectional schematic diagram of the electric double layer capacitor which concerns on this embodiment. The log differential pore volume distribution graph of the electrode layer according to the present embodiment.

Hereinafter, this embodiment will be described in detail with appropriate reference to the drawings. In the drawings used in the following description, there are cases where characteristic portions are enlarged for convenience in order to make it easier to understand the features of the present invention, and the dimensional ratios of each component may differ from the actual ones. be. The materials, dimensions, and the like exemplified in the following description are examples, and the present invention is not limited to them, and can be implemented with appropriate modifications without changing the gist of the invention.

(Electrode for electric double layer capacitor)
An electrode for an electric double layer capacitor according to this embodiment has a current collector and an electrode layer formed on the current collector.

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

[Electrode layer]
The electrode layer includes a carbon material that is an active material, a conductive aid, and a binder.

<Carbon material>
Carbon materials according to the present embodiment typically include "carbon materials" such as activated carbon, activated carbon fiber, non-porous activated carbon, and artificial graphite. Special carbon materials called "nanocarbon materials" are also included. Here, activated carbon, activated carbon fiber and non-porous activated carbon are examples of so-called "activated carbon".

There are no particular restrictions on the raw material for activated coal. Specific examples include plant-based wood, coconut shell, pulp effluent, fossil fuel-based coal, petroleum heavy oil, pyrolyzed coal, petroleum-based pitch, coke, synthetic resins such as phenol resin and furan resin. , polyvinyl chloride resins, polyvinylidene chloride resins, polyimide resins, polyamide resins, liquid crystal polymers, waste plastics, or waste tires containing phenolic resins.

Various methods such as gas activation and chemical activation can be applied to the activation method of the activated carbon. As the gas used for gas activation, steam, carbon dioxide, oxygen, chlorine, sulfur dioxide, sulfur vapor, etc. can be used. Examples of chemicals used for chemical activation include zinc chloride, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, calcium carbonate, phosphoric acid, sodium phosphate, calcium chloride, potassium sulfide, potassium sulfate, sodium sulfate, and the like. One type of these may be used alone, or two or more types may be mixed and used.

The form of the carbon material according to the present embodiment may be selected from crushed, granular, granular, fibrous, felt-like, woven, sheet-like, and other forms having a large specific surface area. , a granular or powdered electrode active material.

<BET specific surface area>
The BET specific surface area (also referred to as "BET specific surface area") of the carbon material according to the present embodiment is preferably 1000 m ² /g or more and 3000 m ² /g or less. It is more preferably 1500 m ² /g or more and 2500 m ² /g or less. If the specific surface area is less than 1000 m ² /g, the capacity will be low and it will be unsuitable as an electric double layer capacitor. If it exceeds 3000 m ² /g, the binder becomes insufficient, and the property change under continuous charge increases. As a method for measuring the BET specific surface area, for example, a nitrogen adsorption measuring device BELSORP-MAX manufactured by Microtrac Bell Co. is used to determine the specific surface area by the BET method of measuring the nitrogen adsorption isotherm of the sample.

<Average particle size>
When a granular electrode active material is used as the carbon material according to the present embodiment, the average particle size (D50) is preferably 1.5 to 10.0 μm. If the average particle diameter is less than 1.5 μm, the amount of fine powder increases, the viscosity of the paste increases during electrode production, and the electrode production efficiency decreases, which is not preferable. Moreover, when an electrode is manufactured using the obtained carbon material, one gap formed between the carbon materials becomes small, and movement of the electrolyte in the electrolytic solution may be suppressed. The average particle diameter of the carbon material is more preferably 2.0 μm or more, and still more preferably 4.0 μm or more. On the other hand, when the average particle size of the carbon material is 10 μm or less, the surface area of the particles is attributed to the capacity, so it is possible to obtain a high electrostatic capacity and to perform rapid charging and discharging. Furthermore, in electric double layer capacitors, it is important to increase the electrode area in order to improve the input/output characteristics. Therefore, it is necessary to reduce the thickness of the active material applied to the current collector plate when preparing the electrodes. In order to reduce the coating thickness, it is necessary to reduce the particle size of the active material. From such a viewpoint, it is more preferably 19 μm or less, still more preferably 8.0 μm or less, and still more preferably 7.5 μm or less. In addition, D50 is a particle size with a cumulative volume of 50%, and this value can be used as an average particle size. -3000S” and “Microtrac MT3000” manufactured by Nikkiso Co., Ltd.) can be used.

<Stack of electrode layers A×B>
The electrode for an electric double layer capacitor according to the present embodiment has a peak pore diameter A (unit: nm) and The product A×B with the log differential pore volume B (unit: cm ³ /g) is 400 or more and 1500 or less, preferably 1000 or more and 1500 or less. In addition, in this embodiment, a pore diameter means the diameter of a pore.

The "Log differential pore volume distribution graph" is a value (Log differential Pore volume) is obtained and plotted against the average pore diameter in the section between each measurement point.
FIG. 2 is a log differential pore volume distribution graph of the electrode layer according to this embodiment. As shown in FIG. 2, in the Log differential pore volume distribution graph, the horizontal axis is the pore diameter in units of nm, and the vertical axis is the Log differential pore volume (dV/d (log D)) in units of cm ³ /g.

"Peak pore diameter A" is the pore diameter at which the Log differential pore volume shows the maximum value in the Log differential pore volume distribution graph.

"Log differential pore volume B" is the log differential pore volume at the peak pore diameter A, and is the maximum value of the log differential pore volume.

Since the product A×B is set to 400 or more and 1500 or less, the electrolytic solution easily penetrates into the electrode layer, and the amount of the electrolytic solution retained increases, so that the characteristic change under continuous charging becomes small. Conceivable. If it is less than 400, the amount of electrolyte solution retained is small, so the change in characteristics increases during continuous charging. If it exceeds 1500, the amount of electrolyte retained becomes too large and the impedance increases, leading to an increase in characteristic changes under continuous charging. Further, when the product A×B is 1000 or more, the change in characteristics under continuous charging becomes smaller.

<Pore diameter of peak electrode layer A and Log differential pore volume B>
In the electric double layer capacitor electrode according to the present embodiment, the electrode layer preferably has a peak pore diameter A (unit: nm) obtained by mercury porosimetry of, for example, 250 or more and 1100 nm or less. It is more preferably 400 nm or more and 1000 nm or less.
In the electrode layer, the pore diameter of the peak electrode layer A obtained by mercury porosimetry is in the range of 400 nm or more and 1000 nm or less, and the Log differential pore volume B at the peak pore diameter A is 0.8 cm ³ / It is most preferably 2 cm ³ /g or more and 2 cm 3 /g or less.

When the peak pore diameter A is within this range, the change in properties under continuous charging becomes small. It is considered that this is because the electrolytic solution easily penetrates into the electrode layer. If the thickness is less than 400 nm, it is difficult for the electrolytic solution to penetrate, and the characteristic change increases under continuous charging. If the thickness exceeds 1000 nm, the amount of penetration of the electrolytic solution is too large, the impedance increases, and the characteristic change increases under continuous charging.
When the log differential pore volume B is within this range, the change in properties under continuous charging is small. It is considered that this is because the amount of the electrolytic solution held in the electrolytic layer increases. If it is less than 0.8 cm ³ /g, the amount of electrolyte solution retained is reduced, and the change in characteristics during continuous charging increases. If it exceeds 2 cm ³ /g, the amount of electrolyte retained is too large, and the increase in impedance increases the characteristic change under continuous charging.

<Composition of electrode layer>
In the electric double layer capacitor electrode according to the present embodiment, the electrode layer contains a carbon material in a range of 65% by mass or more and 85% by mass or less, a conductive agent in a range of 10% by mass or more and 20% by mass or less, a binder is preferably contained within the range of 5% by mass or more and 15% by mass or less. The electrode layer contains a carbon material in the range of 70% by mass to 80% by mass, a conductive agent in the range of 15% by mass to 20% by mass, and a binder in the range of 10% by mass to 15% by mass. It is more preferable to contain at
When the electrode composition is within these ranges, the balance between electrode strength and resistance is improved, and changes in characteristics under continuous charging are reduced.

<Conductivity aid>
The conductive aid is not particularly limited as long as it improves the conductivity of the electrode layer, and known conductive aids can be used. Examples thereof include carbon materials such as graphite and carbon black (acetylene black, ketjen black, other furnace blacks, channel blacks, thermal lamp blacks, etc.).

The content of the conductive aid in the electrode layer is not particularly limited, but is preferably 5% to 25% by mass, preferably 10% to 10% by mass, based on the sum of the masses of the active material, conductive aid, and binder. It is more preferably 20% by mass. By setting the content of the conductive additive within the above range, it is possible to suppress the tendency of the internal resistance to increase in the obtained electrode layer due to the amount of the conductive additive being too small. In addition, it is possible to suppress the tendency of difficulty in obtaining a sufficient volumetric energy density due to an increase in the amount of the conductive additive that does not contribute to the electric capacity.

<Binder>
The binder binds the active materials together and also binds the active material and the current collector. Any binder can be used as long as the above-mentioned bonding is possible. Examples include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene 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, binders such as vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFPTFE-based fluororubber), vinylidene fluoride-pentafluoropropylene fluororubber (VDF-PFP fluororubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubber (VDF-PFP-TFE fluororubber), vinylidene fluoride Vinylidene fluoride-based fluorine such as Ride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluororubber (VDF-PFMVE-TFE-based fluororubber), vinylidene fluoride-chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber) Rubber may be used.

In addition to the above, binders such as polyethylene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene/butadiene rubber, isoprene rubber, butadiene rubber, and ethylene/propylene rubber may be used. 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 be used. Further, syndiotactic 1,2-polybutadiene, ethylene/vinyl acetate copolymer, propylene/α-olefin (C2-C12) copolymer, and the like may be used.

Alternatively, an electronically conductive polymer or an ionically conductive polymer may be used as the binder. Examples of the electron-conducting conductive polymer include polyacetylene. In this case, since the binder also exhibits the function of the conductive additive particles, it is not necessary to add a conductive additive.

The content of the binder in the electrode layer is not particularly limited, but is preferably 3% to 30% by mass, preferably 5% to 15% by mass, based on the sum of the masses of the active material, conductive aid and binder. %, most preferably 10% to 15% by mass. By setting the content of the binder within the above range, it is possible to suppress the tendency that the amount of the binder is too small to form a strong active material layer in the obtained electrode layer. In addition, it is possible to suppress the tendency that the amount of the binder that does not contribute to the electric capacity increases, making it difficult to obtain a sufficient volumetric energy density.

[Method for producing electrode]
Electrodes can be produced by a commonly used method. For example, it can be produced by applying a paint containing a carbon material, a binder, a solvent, and a conductive aid on a current collector and removing the solvent in the paint applied on the current collector.

Examples of solvents that can be used include N-methyl-2-pyrrolidone and N,N-dimethylformamide.

The coating method is not particularly limited, and a method that is commonly employed in the production of electrodes can be used. For example, a slit die coating method and a doctor blade method can be used.

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

Then, the electrode on which the electrode layer is formed in this manner is then subjected to press processing 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 a roll press is used, the surface temperature of the heated press roll is set at room temperature or higher, and if it has a melting point, it is set at a temperature lower than the melting point. Choose from temperatures below °C. For example, when PVDF (polyvinylidene fluoride: melting point 150°C) is used as the binder, the temperature is preferably in the range of room temperature to 150°C, more preferably in the range of 25 to 80°C. When a styrene-butadiene copolymer is used as the binder, the temperature is preferably in the range of room temperature to 100°C, more preferably in the range of 25 to 80°C.

The pressurizing pressure and pressing speed during hot pressing are adjusted according to the pore size and pore distribution of the electrode layer to be obtained. The pressing pressure of the heating 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 pressing speed is preferably 15 m/min or less, more preferably 10 m/min or less, still more preferably 5 m/min or less. At the above pressing speed, an appropriate pore size and pore distribution can be obtained.

When manufacturing the electrodes (negative electrode and positive electrode) of the present embodiment, the product A×B of the peak pore diameter A of the electrode layer and the Log differential pore volume B at the peak pore diameter A is adjusted to be within the above range. It is necessary to. Examples of methods for adjusting the product A×B of the peak pore diameter A and the log differential pore volume B include the following methods. (1) A method of adjusting the material, particle size, and composition ratio of the carbon material, binder, and conductive material. (2) A method of adjusting the conditions for pressing the electrode layer. When the electrode layer is pressed using a roll press, the product A×B of the peak pore diameter A and the log differential pore volume B is adjusted by appropriately adjusting the line pressure, roll temperature, and feed rate. be able to.

As a method for adjusting the product A×B of the peak pore diameter A of the electrode layer and the Log differential pore volume B at the peak pore diameter A, for example, the average particle diameter (D50) of the carbon material is adjusted. It can be adjusted by enlarging it. A×B can be increased because the interparticle voids are increased by increasing the average particle size. On the other hand, by decreasing the average particle size, the inter-particle voids become smaller, so that A×B can be reduced.

As a method of adjusting the conditions for pressing the electrode layer, for example, by increasing the linear pressure of the roll press, the product A of the peak pore diameter A of the electrode layer and the Log differential pore volume B at the peak pore diameter A ×B can be increased. Also, A×B can be reduced by lowering the linear pressure.

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

(electric double layer capacitor)
FIG. 1 is a schematic cross-sectional view showing an electric double layer capacitor according to this embodiment. As shown in FIG. 1, the electric double layer capacitor 100 includes a positive electrode 20, a negative electrode 30 facing the positive electrode 20, and interposed between the positive electrode 20 and the negative electrode 30. It is an electric double layer capacitor comprising separators 10 in contact with each other and a non-aqueous electrolyte (not shown).

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

The power generating element 40 is composed of a pair of a positive electrode 20 and a negative electrode 30 arranged opposite to each other with a separator 10 interposed therebetween. The positive electrode 20 has a positive electrode active material layer 24 provided on a plate-like (film-like) positive electrode current collector 22 . The negative electrode 30 has 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 10 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. 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. For the positive electrode 20 and the negative electrode 30, it is preferable to use the electrodes for electric double layer capacitors 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. , the first electrode and the second electrode may be the same or different. More preferably, the first electrode and the second electrode are identical. Since the positive electrode and the negative electrode are the same electrodes for an electric double layer capacitor according to the above-described embodiment, the amount of electrolyte retained is balanced, and the change in characteristics during continuous charging is reduced. "The first electrode and the second electrode are the same" means, for example, that the first electrode and Cutting out the second electrode is included. That is, it means that the first electrode and the second electrode have the same electrode composition, shape, thickness, etc. within the allowable range of evaluation error.

[Non-aqueous electrolyte]
The non-aqueous electrolyte according to this embodiment is contained inside the positive electrode active material layer 24 , the negative electrode active material layer 34 , and the separator 10 . The solute of the non-aqueous electrolyte is a salt containing a cation and an anion. quaternary ammonium such as ammonium (DEME) or 1,3-dialkylimidazolium, 1,2,3-trialkylimidazolium, 1-ethyl-3-methylimidazolium (EMI) or 1,2-dimethyl-3- Imidazoliums such as propylimidazolium (DMPI), where the anion is BF ⁴⁻ , PF ⁶⁻ , ClO ⁴⁻ , AlCl ⁴⁻ or CF ₃ SO ³⁻ can be employed.

Solvents for the non-aqueous electrolyte of the electric double layer capacitor include propylene carbonate (abbreviation PC), ethylene carbonate (abbreviation EC), dimethyl carbonate (abbreviation DMC), diethyl carbonate (abbreviation DEC), acetonitrile (abbreviation AN), propio nitrile, γ-butyrolactone (abbreviation BL), dimethylformamide (abbreviation DMF), tetrahydrofuran (abbreviation THF), dimethoxyethane (abbreviation DME), dimethoxymethane (abbreviation DMM), sulfolane (abbreviation SL), dimethyl sulfoxide (abbreviation DMSO), Organic solvents such as ethylene glycol, propylene glycol, and methyl cellosolve are included. These may be used alone, or two or more of them may be mixed in an arbitrary ratio and used.

The solute concentration in these non-aqueous electrolytic solutions 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, so as to sufficiently bring out the characteristics of the electric double layer capacitor. A concentration of L or less is preferable because high electrical conductivity is obtained. In particular, when charging and discharging at a low temperature of −20° C. or less, a concentration of 2.2 mol/L or more is not preferable because the electric conductivity of the electrolytic solution is lowered. If it is 0.6 mol/L or less, the electrical conductivity is low both at room temperature and at low temperature, which is not preferable. For example, when an acetonitrile (AN) solution of triethylmethylammonium tetrafluoroborate is used as the electrolytic solution, the concentration of triethylmethylammonium tetrafluoroborate is preferably 0.9 to 1.9 mol/L.

[Separator]
As the separator 10, 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, it is excellent in suppressing self-discharge due to internal micro-shorts.

[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 leakage of the electrolytic solution to the outside and entry of moisture into the electric double layer capacitor 100 from the outside. For example, a metal laminate film in which a metal foil 52 is coated with polymer films 54 from both sides can be used as the exterior body 50 . As the metal foil 52, for example, an aluminum foil can be used, and as the polymer film 54, a film such as polypropylene can be used. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). etc. are preferred.

[Lead]
The leads 60 and 62 (electrode terminals: positive electrode terminal and negative electrode terminal) generally have a substantially rectangular 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. (for discharging) or electrically connected to a power supply (for charging). One end of the lead 60 (positive electrode terminal) is electrically connected to the positive electrode, and one end of the lead 62 (negative electrode terminal) is electrically connected to the negative electrode. Specifically, the lead 60 is electrically connected to the uncoated region of the positive electrode active material layer of the positive electrode current collector 22 , and the lead 62 is electrically connected to the uncoated region of the negative electrode active material layer of the negative electrode current collector 32 .
Leads 60 and 62 are formed from a conductive material. Preferably, the material is aluminum.
Preferably, a resin film (not shown) such as polypropylene is attached to the central portions of the leads 60 and 62, which serve as the sealing portions of the laminate film exterior body 50 described above. This prevents short circuits between the leads 60, 62 and the metal foils that make up the laminate film and improves sealing.
As a method for electrically connecting the current collectors (the positive electrode current collector 22 and the negative electrode current collector 32) and the leads 60 and 62, for example, ultrasonic welding is generally used, but resistance welding and laser welding are also possible. etc., and is not limited.

[Production 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 10 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. By inserting them into the package 50 together with the non-aqueous electrolyte and sealing the entrance of the package 50 in a sandwiched state, a single-cell electric double layer capacitor as shown in FIG. 1 can be fabricated. Also, two or more single-cell electric double layer capacitors can be connected in series to produce an electric double layer capacitor including two or more single cells. As a method of evaluating and calculating the electrical characteristics such as the capacity retention rate of a single cell electric double layer capacitor, for example, a method of calculating from the evaluation of an electric double layer capacitor including two or more single cells connected in series. mentioned.

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

(Examples 1 to 5 and Comparative Examples 1 to 4)
[Preparation of electrode]
Activated carbon having a specific surface area of about 1500 m ² /g by the BET method (particle size is shown in Table 1) was used as the carbon material as the active material, carbon black powder was used as the conductive aid, and polyfluoride was used as the binder. A slurry was prepared by using vinylidene chloride (PVDF) and blending the carbon material, the conductive aid, and the binder so that the mass ratio of the carbon material:conductive aid:binder=70:20:10. The resulting slurry was applied onto an aluminum foil having a thickness of 20 μm, dried at 140° C. for 30 minutes, and pressed with a roll press to obtain an electrode. A micrometer was used to measure the thickness. The roll press conditions were a line pressure of 450 kgf/cm, a heating roll temperature of room temperature, and a feed rate of 5 m/min. The linear pressure was calculated by the pressure applied to the pressure roll and the length of contact between the upper and lower rolls.

<Evaluation of Peak Pore Diameter A and Log Differential Pore Volume B>
The pore distribution of the electrode layer of the produced electrode was measured by the mercury intrusion method using a mercury porosimeter to obtain a log fine powder pore volume distribution graph as shown in FIG. From the obtained log fine powder pore volume distribution graph, the peak pore diameter A and the log differential pore volume B at the peak pore diameter A were read, and the product A×B was obtained. The results are shown in Table 1 together with the particle size of the carbon material used and the conditions of roll pressing.

[Non-aqueous electrolyte]
A non-aqueous electrolytic solution was prepared by dissolving tetraethylammonium tetrafluoroborate in acetonitrile (AN) so as to have a concentration of 1.0 mol/L.

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

[Production of electric double layer capacitor]
Each of the two electrodes obtained above was cut into pieces of 12.5 cm ² to form a positive electrode and a negative electrode. A positive electrode terminal and a negative electrode terminal are ultrasonically fused to each of the positive electrode and the negative electrode, and the separator is sandwiched between the positive electrode and the negative electrode. A single-cell electric double layer capacitor was fabricated by injecting a non-aqueous electrolyte and finally sealing the opening by fusion bonding. Two sets of these were produced and connected in series to produce electric double layer capacitors of Examples 1 to 5 and Comparative Examples 1 to 4. The produced electric double layer capacitors of Examples 1 to 5 and Comparative Examples 1 to 4 include two single cells connected in series, and the capacity retention rate was evaluated as one cell.

<Evaluation of Capacity Retention Rate>
For the electric double layer capacitors of Examples 1 to 5 and Comparative Examples 1 to 4, constant current charging was performed at 50 mA to 5.7 V, and after reaching 5.7 V, constant voltage charging was performed, and constant voltage charging was performed for 1 second. did Discharging was performed at a constant current of 50 mA and a final voltage of 0.1V. From the discharge curve (discharge voltage-discharge time) thus obtained, the time Δt [msec. ] and the following relational expression:
Capacity = {discharge current (50mA) x time Δt} / voltage (5.0-3.0V)
The initial capacity value (C ₀ ) was calculated by

After measuring the initial capacity value, a load was applied to the sample by applying a voltage of 5.0 V in a constant temperature bath set at 80°C. After 2000 hours at 80° C. and 5.0 V load, the capacity (C ₂₀₀₀ ) was calculated in the same manner as above. Then, the ratio of the capacity value (C ₂₀₀₀ ) to the initial capacity value (C ₀ ) (=C ₂₀₀₀ /C ₀ ×100) was calculated as the capacity retention rate (%). Table 1 shows the results. A case where the capacity retention rate was 70% or more was judged to be good, and a case where the capacity retention rate was 85% or more was judged to be excellent.

<Measurement of average particle size>
The average particle size (particle size distribution) of the carbon material was measured by a laser scattering method as follows. The sample was put into an aqueous solution containing 0.3% by mass of a surfactant (“Triton X100” manufactured by Wako Pure Chemical Industries, Ltd.), treated with an ultrasonic cleaner for 10 minutes or more, and dispersed in the aqueous solution. The particle size distribution was measured using this dispersion. The particle size distribution was measured using a particle size/particle size distribution analyzer ("Microtrac MT3000" manufactured by Nikkiso Co., Ltd.). D50 is the particle size at which the cumulative volume is 50%, and this value was used as the average particle size.

<BET specific surface area measurement>
The specific surface area was determined by the BET method for measuring the nitrogen adsorption isotherm of the active carbon material using a high-speed specific surface area/pore size distribution analyzer NOVA4200e manufactured by Quantachrome Instruments.

(Examples 6-11 and Comparative Examples 5-8)
As shown in Table 2, electric double layer capacitors were produced in the same manner as in Example 4, except that the linear pressure of the roll press was 100 to 1000 kgf/cm.
The electrode layer of the electric double layer capacitor and the electric double layer capacitor obtained in the same manner as in Example 4 were evaluated, and the results are shown in Table 2.

(Examples 12-18)
As shown in Table 3, the mass ratio of the carbon material, the conductive aid, and the binder was adjusted to carbon material: conductive aid: binder = 64: 20.5: 15.5 to 87: 9.0: 4.0. An electric double layer capacitor was produced in the same manner as in Example 4, except that
The electrode layer of the electrode for an electric double layer capacitor and the electric double layer capacitor obtained in the same manner as in Example 4 were evaluated, and the results are shown in Table 3.

(Example 19)
As shown in Table 4, the same electric double layer capacitor as in Example 4 was used except that the positive electrode used the electric double layer capacitor electrode of Example 4 and the negative electrode used the electric double layer capacitor electrode of Example 5. was made.
The electrode layer of the electric double layer capacitor and the electric double layer capacitor obtained in the same manner as in Example 4 were evaluated, and the results are shown in Table 4.

(Examples 20-27)
As shown in Table 5, an electric double layer capacitor was produced in the same manner as in Example 4 except that a carbon material having a specific surface area of 5 to 4000 m ² /g was used.
The electrode layer of the electric double layer capacitor and the electric double layer capacitor obtained in the same manner as in Example 4 were evaluated, and the results are shown in Table 5. Table 5 shows the initial capacity value as the capacity.

DESCRIPTION OF SYMBOLS 10... Separator, 20... Positive electrode (electric double layer capacitor electrode), 22... Positive electrode current collector (current collector), 24... Positive electrode active material layer (electrode layer), 30... Negative electrode (electric double layer capacitor electrode) , 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 film, 60, 62... Lead , 100 electric double layer capacitor

Claims (5)

having a current collector and an electrode layer formed on the current collector;
The electrode layer is
Within the range of 65% by mass or more and 85% by mass or less of the carbon material,
Within the range of 10% by mass or more and 20% by mass or less of the conductive aid,
Containing a binder in the range of 5% by mass or more and 15% by mass or less,
The total amount of the conductive aid and the binder is 20% by mass or more and 30% by mass or less,
The binder is polyvinylidene fluoride,
In the log differential pore volume distribution graph obtained by the mercury intrusion method in the electrode layer, the peak pore diameter A (unit: nm) and the log differential pore volume B at the peak pore diameter A (unit: cm ³ /g ) and the product A × B is 400 or more and 1500 or less,
The peak pore diameter A is present in the range of 630 nm or more and 1000 nm or less,
Log differential pore volume B at the peak pore diameter A is 0.8 cm ³ /g or more and 2 cm ³ /g or less
An electrode for an electric double layer capacitor characterized by: 2. The electrode for an electric double layer capacitor according to claim 1, wherein the carbon material has a specific surface area of 1000 m ^<2> /g or more and 3000 m ^<2> /g or less. The electric double layer capacitor electrode according to claim 1 or 2 ,
and a non-aqueous electrolyte. having a positive electrode and a negative electrode,
Using a first electrode in which the positive electrode is the electrode for the electric double layer capacitor,
Using a second electrode in which the negative electrode is the electrode for the electric double layer capacitor,
4. The electric double layer capacitor according to claim 3 , wherein said first electrode and said second electrode are the same. The electric double layer capacitor includes two or more single cells each having the positive electrode and the negative electrode,
5. The electric double layer capacitor according to claim 4 , wherein the two or more single cells are connected in series.

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