JPH11317332A - Electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor with a large energy density and superior charging/discharging cycle durability. SOLUTION: This electric double-layer capacitor is provided with an electrode body constituted by forming a porous layer, including carbonaceous power and a fluorine polymer on the both faces or one face of an aluminum foil collector, separator, and nonaqueous electrolyte. The thickness of the porous layer is set at 80-200 μm, the thickness of the collector is set at 20-80 μm, and the thickness of the separator is set 30-170 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor suitable for high-power applications.

[0002]

2. Description of the Related Art An electric double layer capacitor is based on the principle that electric charges are accumulated in an electric double layer formed at an interface between a polarizable electrode and an electrolytic solution. Application to the field has been actively studied in recent years. For example, Japanese Patent Application Laid-Open No. 8-45793 proposes a large-capacity and high-output capacitor. As a specific application, application to an electric vehicle or a hybrid vehicle has attracted attention. These applications will meet the US Department of Energy's target of 500 W / kg in the near future and ultimately 15 W / kg.
There is a need to develop a power supply that operates at a high power density of 00 W / kg (AFBurke et. Al., Material Characteri
stics and the Performance of Electrochemical Capac
itors for Electric / hybrid Vehicle Applications, Ma
terials Research Society Spring Meeting, San Franc
isco, CA, 1995.4.17-21).

The specific gravity of the electric double layer capacitor cell depends on the structure and the housing, but when the unnecessary space is removed and the housing or the like is reduced in weight, it is about 1.4 to 1.8 g / cm.
Because it is ^3, in terms of the output per volume the power density 500 W / kg to about 800 W / L, 1000W /
kg is about 1600 W / L, 1500 W / kg is about 240
It corresponds to 0 W / L. There have been many reports on the initial performance of electric double layer capacitors that can be used at such a high power density. However, in applications such as electric vehicles, charge / discharge cycle reliability is required, for example, which requires durability for 50,000 or more charge / discharge cycles with a large current. No multilayer capacitor has been obtained.

[0004] Electrolyte for an electric double layer capacitor includes an organic electrolytic solution and an aqueous electrolytic solution. However, since an operating voltage is high and the energy density in a charged state can be increased, an electric double layer capacitor using an organic electrolytic solution is used. Is attracting attention. When an organic electrolytic solution is used, a carbon material such as activated carbon is used to improve the capacity per unit volume of the electric double layer capacitor (hereinafter, referred to as capacity density). In addition, when water is present inside the electric double layer capacitor cell, the performance is deteriorated due to the electrolysis of the water. Therefore, usually, the electrode is subjected to a heat treatment under reduced pressure to be sufficiently dehydrated.

[0005] As a method of manufacturing an electrode, for example, a carbon fine powder is dispersed in a solution in which a binder such as carboxymethyl cellulose is dissolved in a solvent to form a slurry, which is coated on a current collector, dried and dried. There is a method of forming an electrode layer. However, in this method, the bonding strength between the electrode and the current collector is weak. In addition, since the heat resistance of the binder is not sufficient, the electrode cannot be heat-treated at such a high temperature that impurities such as moisture in the electrode can be sufficiently removed. Further, in this method, for example, when the electrode is formed into a thick film having a thickness of 60 μm or more, it is difficult to uniformly dry and remove the solvent of the slurry. It is difficult to form on top with good productivity.

A kneaded product comprising a carbonaceous material such as activated carbon, a binder such as polytetrafluoroethylene (hereinafter referred to as PTFE), and a liquid lubricant is preformed and then stretched or rolled to form a sheet. A method for obtaining an electrode has been proposed (JP-A-63-107011, JP-A-2-107).
235320). According to this method, since PTFE is fibrous, ion conduction is hardly hindered, and the carbonaceous material is filled at a high density. By joining the electrode and the current collector via the conductive adhesive layer, the joining strength can be increased and the electrical contact resistance can be reduced. Also, PTFE
Is thermally and electrochemically stable, so that an electric double layer capacitor having high reliability, high capacity and low resistance can be formed.

However, in applications where charging and discharging with a large current is required, it is necessary to further reduce the resistance of the electrode. For this purpose, it is effective to reduce the thickness of the electrode. However, since the above-mentioned electrode is randomly fiberized by kneading PTFE, and a fibrous portion and a non-fibrous portion are generated, when the electrode is formed into a sheet having a thickness of, for example, 200 μm or less, irregularities are generated on the surface. There is a problem that is easy to make holes. Therefore, the capacity density of the electric double layer capacitor cannot be increased, and the internal resistance cannot be sufficiently reduced.

In view of the above problems, the present inventors screw extruded a mixture comprising a carbonaceous material, PTFE, and a processing aid, and then rolled the mixture to obtain a high-strength and 200 μm thick material.
A method for obtaining the following porous electrode sheet has been proposed (Japanese Patent Application No. 10-19758). According to this method, an electrode sheet can be obtained continuously and industrially with high productivity.

[0009]

SUMMARY OF THE INVENTION The present inventors have made it possible to easily control the thickness of a high-strength electrode sheet by the above-described electrode manufacturing method. An object of the present invention is to provide an electric double layer capacitor for power use, particularly an electric double layer capacitor having a high output density and a high energy density and excellent in charge / discharge cycle durability by utilizing this technology.

[0010]

According to the present invention, an electrode body formed by forming a porous layer containing carbonaceous powder and a fluoropolymer on at least one surface of an aluminum foil current collector is used as a positive electrode body and a negative electrode body. An electric double layer capacitor in which a porous layer of the positive electrode body and a porous layer of the negative electrode body are opposed to each other via a separator to form an element, and the element is impregnated with a non-aqueous electrolyte and accommodated in a closed container. Wherein the thickness of the porous layer is 80
To 200 μm, the thickness of the aluminum foil current collector is 20 to 80 μm, the thickness of the separator is 30 to 170 μm, and the density of the porous layer is 0.50 to 0.80 g. / Cm ³ , provided in the electric double layer capacitor.

In the present specification, a porous layer containing a carbonaceous powder and a fluoropolymer is formed as an electrode layer on one or both sides of an aluminum foil current collector and integrated with the current collector. That. When this electrode body is used on the positive electrode side, it is called a positive electrode body, and when it is used on the negative electrode side, it is called a negative electrode body.

The porous layer in the present invention preferably has a specific surface area of carbonaceous powder of 700 to 2500 m ² / g, and preferably contains activated carbon powder as a main component. When the specific surface area of the carbonaceous powder is less than 700 m ² / g, the capacitance of the electric double layer capacitor decreases. 2500 m ² / g
If the ratio exceeds the above range, it becomes difficult to form the electrodes with high density, and the capacitance per unit volume of the electrodes decreases. Especially preferably, it is 1000-1800 m < ² > / g. In addition to the activated carbon powder, a material having a large specific surface area such as carbon black and polyacene can be preferably used. In particular, it is preferable to use a mixture of activated carbon powder having a high specific surface area and highly conductive carbon black as a conductive material. In this case, it is preferable that carbon black is contained in the electrode layer in an amount of 5 to 20% by weight.

The current collector for electrically connecting the above-mentioned porous layers may be made of a material having excellent conductivity and being electrochemically durable, such as a valve metal such as aluminum, titanium and tantalum. Stainless steel or the like can be used, and among them, aluminum is preferred because it has a low specific gravity, has excellent conductivity, and is electrochemically stable.

The current collector is preferably in the form of a foil, which is inexpensive and inexpensive. However, if it is necessary to enhance the bonding property with the porous layer, a punching metal, an expanded metal or the like can be used as appropriate. Further, the collector foil may be subjected to a treatment such as etching to roughen the surface before use.

In the present invention, the thickness of the porous layer bonded to one side of the aluminum foil current collector is 80 to 200 μm. When it is less than 80 μm, the content of the carbonaceous powder per unit volume of the electric double layer capacitor element is small,
The capacity density decreases. On the other hand, when the thickness exceeds 200 μm, the resistance of the porous layer increases, the loss in high-power charge / discharge increases, and the energy density decreases. The thickness of the porous layer is particularly preferably from 100 to 180 μm.

In the present invention, the thickness of the aluminum foil current collector is 20 to 80 μm. If the thickness is less than 20 μm, the strength of the current collector is low, so that the strength of the electrode body is low, the yield in manufacturing the electric double layer capacitor is reduced, and a failure due to stress such as external vibration easily occurs when the electric double layer capacitor is used. When the thickness of the aluminum foil current collector exceeds 80 μm, the content of the aluminum foil current collector per unit volume of the electric double layer capacitor element increases, and the content of the carbonaceous powder relatively decreases, so that the capacity density decreases. However, the output density or the energy density decreases. The thickness of the aluminum foil current collector is preferably 30 to 60 μm.

In the present invention, the thickness of the separator is 30
１７０170 μm. If the thickness is less than 30 μm, pinholes are likely to be present in the separator, so that microscopic short-circuiting is likely to occur between the electrodes, the leakage current increases, and the voltage holding property decreases. When the thickness of the separator exceeds 170 μm, the voltage holding property is relatively easy to secure, but the separator content per unit volume of the electric double layer capacitor element increases, and the content of the carbonaceous powder relatively decreases, so that the capacity is reduced. Density decreases, power density and energy density decrease. Therefore, it is preferable that the material and thickness of the separator be further selected according to the demand for the voltage holding property according to the use in addition to the demand for the output density and the energy density for the use of the capacitor.

For example, when the electric double layer capacitor of the present invention is charged and discharged daily so as to be used as a combined power supply with a solar cell, the separator is preferably a sheet of 30 to 80 μm, and the material thereof is porous. It is preferably made of synthetic resin such as polypropylene or cellulose. Above all, a sheet made of cellulose is preferable because it has high strength and is inexpensive. Particularly, rayon paper is preferable because of its low resistance and high strength. Further, it is preferable to use two or more sheets of 20 to 40 μm as a separator, for example, of 40 to 80 μm in order to effectively reduce leakage current.

For applications requiring long-term energy storage of several days or more, especially one month or more, the separator must have a high voltage holding property.
It is preferable that the sheet is made of glass fiber, cellulose or porous polypropylene. Among them, glass fiber mats have heat resistance, oxidation resistance,
Since the solvent resistance is excellent, the voltage holding property is particularly high, and the durability of a large current charge / discharge cycle can be increased.

The above glass fiber mat has a maximum fiber diameter of 10
It is preferable to use fibers having a size of not more than μm because the strength is increased.
However, the glass fiber mat still has insufficient strength, for example, it is difficult to form a thin film having a thickness of less than 140 μm, so that a fluororesin such as polyvinylidene fluoride, which has heat resistance and is electrochemically stable, is used for the glass fiber. 0.
You may contain 2-5 weight%. As in the case of daily charge and discharge, it is preferable to stack two or more sheets having a thickness of 20 to 80 μm and adjust the thickness to a thickness of 60 to 170 μm to use the separator as a separator because the leakage current can be effectively reduced.

In the present invention, the density of the porous layer is 0.5
It is preferably from 0 to 0.80 g / cm ³ . If the density is less than 0.50 g / cm ³ , the capacitance of the electrode will be low, and if it exceeds 0.80 g / cm ³ , it will be difficult to impregnate the porous layer with the electrolyte or the resistance will increase, which is not preferable . Particularly, it is preferably 0.60 to 0.70 g / cm ³ .

In the present invention, the proportion of the fluoropolymer in the porous layer is preferably from 5 to 20% by weight. By containing the fluoropolymer in an amount of 5% by weight or more, practical electrode sheet strength can be obtained. However, if the content is too large, the resistance of the porous layer increases, so that the content is preferably 20% by weight or less. More preferably, it is 7 to 15% by weight.

In the present invention, the fluorine-containing polymer is P
TFE is preferred. PTFE can form a porous layer having low resistance and high strength and having continuously fine pores by fiberization. And it is preferable that the carbonaceous material is carried on the fluoropolymer to form the porous layer.
However, PTFE in the present invention includes not only a homopolymer of tetrafluoroethylene but also a copolymer obtained by adding 0.5 mol% or less of another monomer to tetrafluoroethylene and copolymerizing the same. Shall be considered. If the polymerization unit based on another monomer is 0.5 mol% or less, PTF
No melt fluidity is imparted to E, and it is possible to produce a high-strength and low-resistance electrode sheet by fibrillating similarly to tetrafluoroethylene homopolymer.

Examples of the other monomer include hexafluoropropylene, chlorotrifluoroethylene, perfluoro (alkyl vinyl ether), trifluoroethylene, and (perfluoroalkyl) ethylene.

The porous layer in the present invention is preferably obtained by extruding a mixture comprising a carbonaceous powder, PTFE, and a processing aid such as an organic solvent by screw extrusion, followed by roll rolling to form a sheet. . In particular, it is preferable to perform the roll rolling in the same direction as the screw extrusion, since the PTFE fiberizes vertically and horizontally to form a three-dimensional network structure. Since the electrode sheet obtained by the above method is sufficiently fibrous with PTFE and has high strength, even a sheet composed of a thin porous layer having a thickness of, for example, about 70 μm can be industrially continuously manufactured at a high speed. Further, the obtained sheet can be continuously bonded to an aluminum foil current collector.

In the porous layer of the present invention, it is preferable that the fluorine-containing polymer is fiberized to form a three-dimensional network structure, and the carbonaceous powder is supported by the network structure and bonded to each other. Fibers made of a fluorinated polymer are generated when external stress is applied to the fluorinated polymer such as kneading the fluorinated polymer and the carbonaceous powder together with a processing aid or extruding with a processing aid. The fibers are three-dimensionally spread by connecting nodes made of a fluoropolymer.

The diameter of the fiber, the length of the fiber connecting the two nodes, the density, and the like depend on the molding conditions. In the present invention, when observed with a scanning electron microscope (hereinafter, referred to as SEM) at a magnification of 10,000 times, it is preferable that the fiber is substantially a fiber having a diameter of 0.1 μm or less and a length of 2 μm or more. Further, the fiber having a diameter of 0.01 to 0.05 μm and a length of 3 to 20 μm preferably accounts for 50% or more, particularly preferably 80% or more of the volume of the entire fiber. Further, the density of the fibers is preferably 2 to 20 per 10 μm width in the direction perpendicular to the direction in which the fibers extend.

A higher fiber density is preferable in that the strength of the porous layer is improved, but a sufficient amount of carbonaceous powder is contained in the porous layer so that the capacity of the electric double layer capacitor can be sufficiently increased. In such a case, molding to increase the fiber density tends to be difficult. Similarly, when the porous layer contains a sufficient amount of carbonaceous powder, the diameter is more than 0.1 μm or the length is 2 μm.
m is less likely to be produced. In addition, if fibers having too small a diameter or too long occupy most of the fibers contained in the porous layer, the strength may be reduced.

FIGS. 2 and 3 show examples of SEM photographs of the cross section of the above-mentioned porous layer. FIG. 2 is a photograph observed at 3,000 times magnification, and FIG. 3 is a photograph observed at 10,000 times magnification.

In the present invention, the electrode sheet made of a porous layer is preferably bonded to an aluminum current collector via a conductive adhesive. As the conductive adhesive, an adhesive made of a conductive material made of carbon black or fine graphite and a thermosetting resin binder is preferable because of its high bonding strength and high thermal stability. As the thermosetting resin binder, a polyamide imide resin is preferable because it has particularly excellent heat resistance and bonding strength.

The electrode body obtained by using the above-mentioned conductive adhesive hardly undergoes deterioration, peeling, swelling and the like under severe conditions electrochemically and thermally. Therefore, the electric double layer capacitor having the electrode body is excellent in long-term voltage application durability, charge / discharge cycle reliability, and cold / heat cycle reliability.

In the present invention, the porosity of the separator is from 60 to
Preferably it is 95%. If the porosity is less than 60%, the liquid absorbing property and liquid retaining property of the electrolytic solution become insufficient, and the resistance of the separator increases. If the porosity exceeds 95%, the mechanical strength of the separator is insufficient, and the separator is liable to be damaged during the production of the electric double layer capacitor cell or to be easily short-circuited internally. Particularly for power applications, the porosity of the separator is preferably 70 to 90%.

[0033] In the present invention, in a state impregnated with the electrolytic solution, it is preferable that a unit area resistance of the electrode body is 3~9Ω · cm ^2, unit area resistance of the separator is 2 [Omega · cm
It is preferably ² or less. If the unit area resistance of the electrode body exceeds 9 Ω · cm ² , the resistance of the electric double layer capacitor element increases, and it is difficult to obtain a capacitor having a high output density. In order to make the unit area resistance of the electrode body less than 3 Ω · cm ² , it is necessary to make the thickness of the porous layer extremely thin or to increase the amount of the conductive material in the porous layer. Therefore, the amount of the carbonaceous powder contained in the electric double layer capacitor element per unit volume is reduced, the capacitance of the electric double layer capacitor element is reduced, and the energy density is reduced. In particular, the unit area resistance of the electrode body is preferably from 3.5 to 6 Ω · cm ² .

The unit area resistance of the separator is 2 Ω · cm ²
Is also not preferable because the resistance of the electric double layer capacitor element becomes high and an electric double layer capacitor with a high output density cannot be obtained. In order to achieve such a unit area resistance, it is important to select the best combination of the material and structure of the separator, the composition and structure of the electrode, the composition of the electrolytic solution, and the like.

The method for measuring the unit area resistance of the electrode body and the separator in the present invention is as follows. A positive electrode body and a negative electrode body made of the same electrode body are opposed to each other with a separator interposed therebetween, and are impregnated with an electrolytic solution to form a device 1, and its discharge resistance is measured. Next, an element 2 is formed in the same manner as in the element 1 except that a separator is formed by stacking two sheets constituting the separator in the element 1, and the discharge resistance is measured. From (1) and (2), the resistance of the electrode body and the resistance of the separator are calculated, and the resistance value per unit area is calculated.

Although two types of elements are used in the above, an element is formed by further stacking three or more sheets constituting the separator, and the resistances of the electrode body and the separator are calculated from the resistances of the three or more types of elements. Is also good.

The non-aqueous electrolyte used for the electric double layer capacitor of the present invention is not particularly limited, and any known organic solvent containing an ion-dissociable salt can be used. Among them, R ¹ R ² R ³ R ⁴ N ⁺ , R ¹ R ² R ³ R ⁴ P ⁺ (where R ¹ ,
R ² , R ³ and R ⁴ are alkyl groups having 1 to 6 carbon atoms, which may be the same or different), and BF ₄ ⁻ , PF ₆ ⁻ , and ClO ₄ ⁻ , CF ₃ S
O ₃ ^- is preferable to use salts of organic electrolyte dissolved in an organic solvent consisting of an anion such as.

Examples of the organic solvent include carbonates such as propylene carbonate, butylene carbonate, diethyl carbonate, and ethyl methyl carbonate;
-Lactones such as butyrolactone, sulfolane, acetonitrile and the like can be preferably used alone or as a mixed solvent of two or more. In power applications, propylene carbonate is used as the main solvent and 1.0 to 2.0 mol / L of (C ₂ H ₅ ) ₃ (CH ₃ ) NPF ₆ or 1.0-2.0mo
A solution in which 1 / L of (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ is dissolved is particularly preferred.

The structure of the electric double layer capacitor of the present invention is not particularly limited. However, in order to increase the capacity, a pair of strip-shaped electrode bodies each having an electrode layer formed on both sides of a current collector are wound with a separator interposed therebetween. A cylindrical electrode body impregnated with an electrolytic solution and closed and accommodated in a closed-bottomed cylindrical container, and a rectangular electrode body having an electrode layer formed on both surfaces of a current collector as a positive electrode body and a negative electrode body,
A laminated type in which a plurality of layers are alternately laminated via a separator, impregnated with an electrolytic solution, housed in a bottomed rectangular container, and hermetically sealed is particularly preferable.

[0040]

EXAMPLES Example 1 (Example) Specific surface area of 1500 m ² /
g, high-purity activated carbon powder 80% by weight having an average particle size of 10 μm,
10% by weight of carbon black and 10% by weight of PTFE (in this example, tetrafluoroethylene homopolymer) powder
Was mixed with propylene glycol. This mixture was extruded by a screw with a single screw extruder, roll-rolled, dried with hot air to remove propylene glycol, and had a thickness of 120 μm and a density of 0.64 g / cm.
The electrode sheet of No. ³ was produced.

When the surface of this electrode sheet was observed with a SEM at a magnification of 10,000 times, the volume of the PTFE fiber was 80%.
% Or more of the PTFE fibers had a length of 5 to 15 µm and a fiber diameter of 0.03 to 0.05 µm, and about 10 fibers existed per 10 µm in width. Area 4c from this electrode sheet
An mx 6 cm electrode was cut out.

4 cm wide and 6 c long with lead terminals
m, on one side of a rectangular pure aluminum foil with a thickness of 50 μm,
The electrodes were joined via a conductive adhesive having a polyamideimide resin as a binder, and heated to cure the adhesive by heat to form an electrode body. Two electrode bodies were prepared, and the electrode surfaces of the two electrode bodies were opposed to each other, and a cellulose fiber separator (density: 0.40 g / cm ³ , porosity: 74%, thickness: 40)
μm) was sandwiched between two glass sandwiching plates having a thickness of 2 mm to form an element. The total thickness of the two electrode bodies and the separator was 0.39 mm.

As an electrolytic solution, a solution obtained by dissolving 1.5 mol / l of (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ in propylene carbonate was used. The above element was vacuum-heated at 200 ° C. for 3 hours to remove impurities from the element, vacuum impregnated with an electrolytic solution, housed in a rectangular bottomed cylindrical container made of polypropylene, and sealed to form an electric double layer capacitor. Produced.

After measuring the volume of the device, the current density was 20 m
The DC resistance and capacitance of the device were measured at A / cm ² , and the capacitance density and unit area resistance were calculated. Table 1 shows the results. Since the unit area resistance is the sum of the resistance of the two electrode bodies and the resistance of the separator part, the relationship between the DC resistance of the capacitor element having five separators and the DC resistance of one capacitor element is given. From the sum of the resistances of the two electrode bodies and the resistance of one separator. Table 1 shows the sum of the resistances of the two electrode bodies.

Further, when the discharge start voltage is 2.5 V and the discharge end voltage is 1.25 V, the output density is 1600 W /
The energy density at L was determined and is shown in Table 1. However, the output density per volume and the energy density per volume were determined based on the volume of the capacitor element, and did not consider the volume required for the terminals and the housing.

In Table 1, the units of the electrode thickness, element volume, element capacitance, element resistance, element area resistance, electrode body area resistance, capacitance density, and energy density are μm, c, respectively.
c, F, Ω, Ω · cm ² , Ω · cm ² , F / cc, Wh /
L.

[Examples 2 to 6 (Example) and Examples 7 to 10]
(Comparative Example) An electric double layer capacitor was manufactured in the same manner as in Example 1 except that the forming conditions of the electrode sheet were changed and the thickness of the electrode sheet was as shown in Table 1, and the same evaluation as in Example 1 was performed. went. The results are shown in Table 1 together with Example 1.

Further, the thickness and energy density of the electrode sheet (output density: 1600 W / L) obtained from Examples 1 to 10
1 is shown in FIG.

Example 11 (Example) A high-purity activated carbon powder having a specific surface area of 1800 m ² / g and an average particle size of 10 μm was used in the same manner as in Example 1 except that the thickness was 130 μm and the density was 0.67 g / cm. The electrode sheet of No. ³ was produced. This is bonded to both sides of a 40-μm-thick aluminum foil current collector using a conductive adhesive with polyamideimide resin as a binder, and the conductive adhesive is thermally cured to integrate the electrode sheet and the current collector. After obtaining the sheet thus obtained, 34 electrode bodies having an effective electrode area of 6.3 cm × 12.3 cm were obtained from this sheet. Of these, 17 sheets were used as a positive electrode body and the remaining 17 sheets were used as a negative electrode body.
The device was formed by alternately laminating glass fibers of 0 μm or less through a thickness of 160 μm and a porosity of 92%.

The above laminated body element is 15 cm in height and 7 c in width.
m, 2.2 cm thick in a bottomed square aluminum case, sealed by laser welding using an aluminum top lid equipped with a positive electrode terminal and a negative electrode terminal,
Vacuum drying was performed at 0 ° C. for 5 hours to remove impurities.

Then, 1.5 mol / l of (C ₂ H ₅ ) ₃
After the element was vacuum impregnated with a propylene carbonate solution of (CH ₃ ) NPF ₆ as an electrolytic solution, a safety valve was arranged at an injection port, and a square electric having a width of 7 cm, a height of 15 cm, a thickness of 2.2 cm, and a weight of 380 g was provided. This was a double layer capacitor.

The initial electric discharge capacity of the obtained electric double layer capacitor was 1400 F, and the internal resistance was 2.8 mΩ.
The leakage current after charging at 2.5 V for 100 hours was 1 mA. After the battery was charged at 2.5 V for 100 hours, the circuit was opened at 25 ° C., and the capacitor was left to stand for 7 days. With a discharge start voltage of 2.5 V and a discharge end voltage of 1.25 V, the output energy density in constant output discharge at 500 W / kg was 1.7 Wh / kg. The average current at the time of discharging was 112A.

Then, in a 45 ° C. constant temperature bath, 0-2.5 V
Repeat 50,000 charge / discharge cycles with a constant current of 50A between 50,000 times, measure the discharge capacity and internal resistance after 50,000 cycles, and accelerate the long-term operation reliability of the electric double layer capacitor compared to the initial characteristics Was evaluated. The capacity after the cycle test was 1370 F, the internal resistance was 2.9 mΩ, and the charge / discharge reliability under a large current was high.

Also, two electrode bodies having an effective electrode area of 4 cm × 6 cm were cut out from the sheet prepared as described above except that the above-mentioned electrode sheet was bonded only to one side of the above-mentioned current collector.
An element was produced in the same manner as in Example 1 with the separator (glass fiber mat) interposed therebetween, and an electric double layer capacitor was produced in the same manner as in Example 1 except that the above electrolytic solution was used as the electrolytic solution. When the DC resistance was measured in the same manner as in Example 1, the resistance of the separator portion of this electric double layer capacitor was 1.2 Ω · cm ² , and the resistance of the two electrode bodies was:
It was 4.3 Ω · cm ² .

[0055]

[Table 1]

[0056]

As shown in FIG. 1, the energy density varies depending on the thickness of the electrode sheet which is a porous layer. This is because the energy density is determined by the capacitance density of the element and the resistance of the element. According to the present invention, an electric double layer capacitor having high energy density, low self-discharge, and excellent charge / discharge cycle durability can be obtained.

Since the electric double layer capacitor of the present invention has a low resistance and a high capacity density, in particular, a plurality of positive and negative electrode bodies are alternately laminated with a separator interposed therebetween, or a strip-shaped positive and negative electrode bodies are formed. By using a structure such as winding around a separator, the capacitor can be effectively used as a power capacitor of 100F or more, and more preferably 1000F or more.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the thickness of a porous layer and the energy density in Examples and Comparative Examples of the present invention.

FIG. 2 is a view showing the S of the porous layer cross section of the present invention at a magnification of 3,000 times.
EM photograph.

FIG. 3 is a cross-sectional view of a porous layer having a magnification of 10,000 times in the present invention.
EM photograph.

Claims (7)

[Claims] An electrode body comprising a porous layer containing a carbonaceous powder and a fluoropolymer formed on at least one surface of an aluminum foil current collector is used as a positive electrode body and a negative electrode body. And a porous layer of the negative electrode body are opposed to each other with a separator therebetween to form an element. In an electric double layer capacitor in which the element is impregnated with a non-aqueous electrolyte and housed in a closed container, An electric double layer capacitor, wherein the thickness is 80 to 200 μm, the thickness of the aluminum foil current collector is 20 to 80 μm, and the thickness of the separator is 30 to 170 μm. 2. The porous layer has a density of 0.50 to 0.80.
g / cm ³ an electric double layer capacitor according to claim 1. 3. The electric double layer capacitor according to claim 1, wherein the porosity of the separator is 60 to 95%. 4. An electrode body having a unit area resistance of 3 to 9 Ω · cm ^2.
4. The electric double layer capacitor according to claim 1, wherein the unit area resistance of the separator is 2 Ω · cm ² or less. 5. The porous layer has a carbonaceous powder supported on a network formed by fibers of a fluoropolymer having a diameter of 0.1 μm or less and a length of 2 μm or more. 5. The electric double layer capacitor according to 2, 3 or 4. 6. The sheet according to claim 1, wherein said porous layer is formed by screw-extruding a mixture of a carbonaceous powder, a fluoropolymer and a processing aid, followed by roll rolling.
The electric double layer capacitor according to 2, 3, 4 or 5. 7. The carbonaceous powder has a specific surface area of 700 to 2500.
m ² / g, and the fluoropolymer is composed of polytetrafluoroethylene and is 5 to 20% by weight in the porous layer.
The electric double layer capacitor according to claim 1, 2, 3, 4, 5, or 6, which is included.