JP2000049052A - Manufacture of electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely remove water contained in an electrode and a separator without using a dry vessel of high breakdown strength by housing an element in a vessel, sealing the vessel, drying the entire vessel in an atmosphere of specific dew point, injecting a nonaqueous electrolyte through a liquid-injection port, and sealing the liquid-injection port. SOLUTION: With an electrode whose main component is carbon material as a positive electrode and a negative electrode, they are alternately laminated through a separator to form an element, which is housed in a case. Then a plurality of positive-electrode leads and a plurality of negative-electrode leads are welded, respectively, to a positive-electrode terminal and a negative-electrode terminal fitted to a lid, and the case is sealed with the lid. Then, the case housing the element is moved into an atmosphere whose dew point is -20 deg.C or below, and heated for drying at 100-300 deg.C. The inside of the case is vacuated for deairing, and a propylene carbonate solution comprising (C2H5)3 (CH3) NBF4 is injected through the liquid-injection port under the atmospheric pressure as an electrolyte, and then the liquid-injection port is closed.

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 a method for manufacturing a large capacity electric double layer capacitor.

[0002]

2. Description of the Related Art In recent years, demand for an electric double layer capacitor utilizing an electric double layer formed at the interface between a polarizable electrode and an electrolyte, especially a coin-shaped capacitor, has rapidly increased as a memory backup power supply. On the other hand, for applications requiring a large capacity, such as a power supply for an electric vehicle, it is desired to develop an electric double layer capacitor having a large capacity per unit volume, a low internal resistance, a high energy density and a high output density. It is rare.

[0003] Electrolyte for an electric double layer capacitor includes a non-aqueous electrolyte and an aqueous electrolyte. However, since the operating voltage is high and the energy density in a charged state can be increased, an electric double layer capacitor using a non-aqueous electrolyte is used. Is attracting attention. When a non-aqueous electrolytic solution is used, the presence of moisture inside the electric double layer capacitor cell deteriorates the performance due to the electrolysis of the moisture. Therefore, the polarizable electrode needs to be sufficiently dehydrated, and is usually heated under reduced pressure. A drying process is performed.

In an electric double layer capacitor having a non-aqueous electrolyte, activated carbon having a high specific surface area, fine particles of a carbon material such as carbon black, fibers and the like are mainly used for electrodes. Then, after forming into a sheet using a binder having high heat resistance, it is joined to a current collector to obtain an electrode body, or a carbon material is dispersed in a solution in which the binder is dissolved to form a coating solution, and the collector is formed. A positive electrode body and a negative electrode body are obtained by coating on the electric body to obtain an electrode body. In the case of a large-capacity electric double layer capacitor, a positive electrode body and a negative electrode body are formed into a band shape, wound around a separator and accommodated in a cylindrical container, or a plurality of rectangular positive electrode bodies and a plurality of rectangular positive electrode bodies are formed. They are stacked alternately and housed in a rectangular container.

In the case of mass-producing an electric double layer capacitor having the above structure, it is necessary to simultaneously vacuum dry a plurality of cells in which an electrode body and a separator are closely housed in a conventional method. There is a problem in that the system becomes large and costly, and that it takes a long time to make the inside of the system to be dried in vacuum.

On the other hand, there is a method in which parts such as an electrode body and a separator are first vacuum dried, and a cell is assembled in a dry atmosphere. However, in order to efficiently vacuum dry each component of a plurality of cells at once, a drying container having high pressure resistance is required, and the apparatus becomes large. Further, when all operations after drying are performed in a dry atmosphere, there is a problem that the line of the dry atmosphere becomes long.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention does not require a drying vessel having high pressure resistance, and reliably removes water contained in the electrodes and the separator without practical problems. It is an object of the present invention to provide a method for manufacturing a non-aqueous electrolyte-based electric double layer capacitor that can be removed to a certain extent.

[0008]

According to the present invention, a positive electrode and a negative electrode mainly composed of a carbon material are opposed to each other with a separator interposed therebetween to form an element. The container is sealed with a lid having a, and then the container is dried in an atmosphere having a dew point of −20 ° C. or less, and a non-aqueous electrolyte is injected from the liquid inlet to impregnate the element. Provided is a method for manufacturing an electric double layer capacitor, wherein the liquid port is sealed.

In the present invention, the carbon material of the electrodes (positive electrode and negative electrode) of the electric double layer capacitor has a specific surface area of 700.
~2500m ² / g, especially 1000~2000m ² /
The value of g is preferable because the capacity is large and the strength can be increased. Examples of the carbon material include activated carbon, carbon black, polyacene, etc., and it is particularly preferable to use activated carbon powder, and it is more preferable to add about 5 to 20% by weight of a highly conductive carbon black as a conductive material.

The electrode is preferably formed so as to contain about 5 to 20% by weight of a binder from the viewpoint of a balance between strength, conductivity and capacity. As a method of manufacturing an electrode, for example, a mixture of activated carbon powder, carbon black, a binder, and a liquid lubricant is kneaded and then rolled to form a sheet.
The obtained sheet-shaped electrode is bonded to the current collector via a conductive adhesive and dried by heating (hereinafter, the current collector and the electrode are bonded or the electrode is formed on the current collector. The one in which the current collector and the electrode are integrated is called an electrode body). As the binder, polytetrafluoroethylene is particularly preferable because it has heat resistance and chemical resistance, and imparts strength to the electrode even in a small amount by forming into a fiber, and does not easily inhibit the conductivity of the electrode. The electrodes may be joined to one side of the current collector, or may be joined to both sides.

The electrode body is formed by dispersing a carbon material in a solution in which a binder such as polyvinylidene fluoride is dissolved in a solvent to form a slurry. The slurry is applied to a current collector and dried to form an electrode layer. You may get it.

The current collector may be any material that has excellent conductivity and is electrochemically durable, such as valve metals such as aluminum, titanium and tantalum, stainless steel, precious metals such as gold and platinum, graphite and glassy. Carbon-based materials such as conductive rubber containing carbon and carbon black can be preferably used. Aluminum is particularly preferred because it is lightweight, has excellent conductivity, and is electrochemically stable.

The electrode bodies obtained as described above are used as a positive electrode body and a negative electrode body, and are housed in a container facing each other with a separator interposed therebetween. In order to obtain a particularly large capacity, a positive electrode body and a negative electrode body each having an electrode layer formed on both surfaces of a current collector are formed into a rectangle, and a plurality of the layers are alternately laminated with a separator therebetween to form an element. It is preferable to house it in a mold container. It is also preferable that the positive electrode body and the negative electrode body are formed in a belt shape, wound around a separator, and housed in a bottomed cylindrical container.

The positive electrode body and the negative electrode body each have a lead attached to the current collector, and the plurality of positive electrode leads and the plurality of negative electrode leads are collectively respectively attached to the positive electrode terminal and the negative electrode terminal previously attached to the lid and / or the container. Connected by a method such as sonic welding. At this time, the lead may be constituted by a part of the current collector.

Next, the opening of the container is sealed with a lid. In the present invention, the container is preferably excellent in corrosion resistance to the electrolytic solution and light, for example, aluminum is preferable. The same applies to the lid, and any of metal, resin, rubber and the like can be used. If the container is made of aluminum, it is preferable that the lid is made of aluminum and sealed by ultrasonic welding.
Further, the container may be sealed by caulking. In this case, the lid may be made of resin or rubber as well as aluminum. However, in the present invention, the container is not sealed at this stage because the lid has a liquid inlet for injecting the electrolytic solution.

According to the present invention, at this time, the container accommodating the elements is moved to an atmosphere having a dew point of -20 ° C. or lower, and dried by heating. The higher the drying temperature, the more easily the moisture can be removed in a short time, but the temperature is preferably set to 100 to 300 ° C. because it is set in consideration of the heat resistant temperature of the binder contained in the electrode.
If the binder is polytetrafluoroethylene, 18
0-300 ° C is preferred.

In the manufacturing method of the present invention, the heating and drying atmosphere is an atmosphere having a dew point of -20 ° C. or less, and the atmosphere can be maintained by flowing a gas containing no water into the heating and drying system. The gas can be either an inert gas such as air or nitrogen or an inert gas such as argon, but a gas containing oxygen may react on the activated carbon surface,
Nitrogen or an inert gas is preferred because the formation of surface functional groups can reduce capacity. It is more preferable that the heating and drying atmosphere has a dew point of −40 ° C. or less.

In the present invention, after the container is cooled, the electrolyte is injected from the injection port so that the element is impregnated with the electrolyte. After the inside of the container is evacuated so that the element is easily impregnated with the electrolyte,
Preferably, an electrolyte is injected. By evacuating the inside of the container, gas present between the electrode and the separator or in the gap between the electrode and the separator can be removed, so that the electrolyte can be easily impregnated into the element. Since the inside of the container is filled with the drying gas at the time of taking out from the drying atmosphere in the above-mentioned drying, the operation of injecting the electrolyte may be performed in the air. After the injection of the electrolytic solution, the injection port is immediately closed to seal the container.

The non-aqueous electrolyte used in the present invention is not particularly limited, and a solution containing an ion-dissociable salt in a known organic solvent can be used. For example, R ¹ R ² R ³ R ⁴ N ⁺ , R
Quaternary onium cations such as ¹ R ² R ³ R ⁴ P ⁺ (R ¹ , R ² , R ³ and R ⁴ are each independently an alkyl group having 1 to 6 carbon atoms); BF ₄ ⁻ , PF _{6 ^{-, ClO 4 -, CF 3}} S
O ₃ ^- anions consisting of salts such as, propylene carbonate, butylene carbonate, diethyl carbonate,
An organic electrolyte dissolved in γ-butyrolactone or the like can be preferably used.

[0020]

EXAMPLES Next, Examples (Examples 1 to 8) and Comparative Examples (Example 9)
The present invention will be described in detail with reference to -12), but the present invention is not limited to these.

Ethanol is added to a mixture of 80% by weight of activated carbon powder obtained by subjecting a phenolic resin to KOH activation treatment, 10% by weight of carbon black and 10% by weight of polytetrafluoroethylene powder, kneaded, formed into a sheet, and dried. Thus, an electrode sheet having a thickness of 0.2 mm was obtained. This electrode sheet was adhered to both sides of an aluminum foil having a thickness of 40 μm using a conductive adhesive containing graphite fine powder and rolled, and then heat-treated, the effective electrode area was 60 mm × 65 mm, and the electrode sheet was not joined. Current collector 16mm x 50
A plurality of electrode bodies each having mm as a lead were cut out and dried at 260 ° C. in a vacuum.

The above-mentioned electrode body was used as a positive electrode body and a negative electrode body. Fifteen sheets were alternately laminated via a glass mat separator to form an element, which was housed in an aluminum case. Next, a plurality of positive electrode leads and a plurality of negative electrode leads were collectively welded to the positive electrode terminal and the negative electrode terminal attached to the lid, respectively, and then the case was sealed with the lid. The lid has a small hole serving as a liquid inlet for the electrolyte.

Next, the case accommodating the above element was heated and dried under the conditions shown in Table 1. Then, the inside of this case was evacuated by vacuuming, and 1.5 mol
/ L of (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ propylene carbonate solution was injected as an electrolyte, and the injection port was plugged and sealed to produce an electric double layer capacitor.

After a DC voltage of 2.5 V was applied to the electric double layer capacitor for 72 hours, the battery was charged to 2.5 V and the discharge characteristics were measured to determine the initial discharge capacity. Then 60
A DC voltage of 2.0 V was applied for 1000 hours in the air at ℃, and the battery was charged again to 2.5 V to obtain a discharge capacity, and a capacity retention ratio with respect to the initial discharge capacity was calculated. Table 1 shows the results.

[0025]

[Table 1]

[0026]

According to the present invention, the moisture contained in the electrodes and the separator can be reliably removed to the same extent as when dried under vacuum without requiring a drying container having high pressure resistance. Therefore, a large-capacity non-aqueous electrolyte type electric double layer capacitor can be provided with high production efficiency.

Claims (4)

[Claims] 1. An element is formed by opposing a positive electrode and a negative electrode mainly composed of a carbon material via a separator, housed in a bottomed cylindrical container, and then sealed with a lid having a liquid inlet. Then, the container is dried in an atmosphere having a dew point of −20 ° C. or less, a non-aqueous electrolyte is injected from the liquid inlet to impregnate the element, and then the liquid inlet is sealed. Manufacturing method of an electric double layer capacitor. 2. The method for manufacturing an electric double layer capacitor according to claim 1, wherein the drying temperature in the atmosphere having a dew point of −20 ° C. or less is 100 to 300 ° C. 3. The method according to claim 1, wherein the gas in the atmosphere having a dew point of −20 ° C. or less is nitrogen. 4. A non-aqueous electrolyte is injected after the container is sealed with a lid and the container is evacuated.
A method for manufacturing the electric double layer capacitor according to the above.