JP2000208379A - Manufacturing method of electric double layer capacitor - Google Patents

Abstract

[PROBLEMS] To provide a large-capacity electric double-layer capacitor with less self-discharge and less decrease in the capacity after charging with time. A step of impregnating a non-aqueous electrolytic solution with an element in which a positive electrode and a negative electrode mainly composed of a carbon material having a specific surface area of 500 m ² / g or more are opposed via a separator, and a step of housing the element in a metal container; A method for manufacturing an electric double layer capacitor, comprising: a step of applying a voltage between a positive electrode and a negative electrode with a DC power supply;

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electric double layer capacitor, and more particularly to a method for manufacturing a low resistance and large capacity electric double layer capacitor.

[0002]

2. Description of the Related Art A conventional low-resistance large-capacity electric double layer capacitor is obtained by winding a pair of strip-shaped electrodes, each of which carries a thin-film polarizable electrode material mainly composed of activated carbon powder, on a current collector via a separator. An element was formed, the element was impregnated with an electrolytic solution, housed in a bottomed cylindrical metal container, and the opening was sealed with a sealing member. Japanese Patent Application Laid-Open No. 4-154106 discloses a rectangular container in which a plurality of rectangular positive electrodes and negative electrodes each having electrodes formed on both sides of a current collector are alternately stacked with a separator interposed therebetween. And an electric double-layer capacitor sealed with a sealing lid has been proposed.

In a conventional electric double layer capacitor using activated carbon, a normal withstand voltage per unit element is about 2.0 in an electric double layer capacitor of a non-aqueous electrolyte solution, depending on the selection of a solvent and a solute to be used. ~ 2.8V. Since the energy is proportional to the square of the voltage, the energy density is increased by improving the durability against high voltage application and the capacity density, and the internal resistance is lowered to reduce the output resistance so that more energy can be rapidly extracted. It is desired to increase. Also, from the viewpoint of energy conservation, it is desired to improve the voltage retention after charging.

Japanese Patent Application Laid-Open No. 7-22295 discloses a method of manufacturing a coin-type electric double layer capacitor using a non-aqueous electrolytic solution, by applying a voltage of 2 V in advance before sealing a container so that a 2 V voltage is applied during charging. It is described that even when a voltage of 5 μm is applied, the increase in the thickness of the cell over time and the increase in the internal resistance over time can be suppressed. However, this electric double layer capacitor has a high internal resistance, a small capacity, and insufficient voltage holding properties, and cannot be applied to power applications.

Japanese Patent Application Laid-Open No. 5-343263 discloses that a polarizable electrode is impregnated with a sulfuric acid electrolyte, a voltage of 1 V is preliminarily applied, an inert gas is sealed, and then sealing is performed. It is described that the resistance can be reduced and the capacity can be increased. However, since this electric double layer capacitor uses an aqueous electrolyte, the usable voltage of the unit element is at most 1 V, and the energy density is low and the voltage holding property is insufficient, so that application to power applications is difficult. .

To solve these problems, Japanese Patent Application Laid-Open No. 10-41
199 proposes a method of obtaining a large-capacity electric double-layer capacitor having excellent voltage holding properties and little decrease in capacity with time by preliminarily applying a voltage slightly higher than the rated voltage.

[0007]

As described above, it is desired to increase the rated voltage of the electric double layer capacitor in order to increase the energy density. However, when a high voltage is applied, the reaction of the surface functional groups of the activated carbon is increased. Gas is generated by decomposition of electrolyte solution or decomposition of impurities slightly contained in the capacitor cell, and when used for a long time, the internal pressure of the cell increases, the capacity decreases, and the resistance increases. .

According to the method described in Japanese Patent Application Laid-Open No. 10-41199, a voltage higher than the rated voltage is applied in the manufacturing process, and gas is generated and removed in advance.
The long-term reliability of electric double layer capacitors is increasing.
However, if the applied voltage is further increased to increase the energy, the capacity of the electric double layer capacitor is reduced and the resistance is increased also in this method.

Accordingly, an object of the present invention is to provide a method of manufacturing an electric double layer capacitor having a high withstand voltage and stable performance even when used for a long time.

[0010]

According to the present invention, a positive electrode and a negative electrode each having an electrode made of a conductive material, a binder and a carbon material having a specific surface area of 500 m ² / g or more are formed on a metal current collector via a separator. A method for manufacturing an electric double layer capacitor, in which a nonaqueous electrolytic solution is impregnated in a facing element and accommodated in a metal container, and the metal container is sealed with a sealing member and hermetically sealed, wherein the element has a nonaqueous electrolytic solution. And the following step A and the following step B are performed after the impregnation. Step A: a step of applying a voltage between the positive electrode and the negative electrode of the electric double layer capacitor by a DC power supply, and a step B: a step of connecting the positive electrode and the negative electrode to the DC power supply in the opposite manner to the step A and applying a voltage.

In the present specification, the rated voltage is a voltage within a range in which the rate of change in capacitance can be suppressed within 30% when applied to the electric double layer capacitor at 60 ° C. for 1000 hours. Refers to a voltage determined as a voltage that can be applied when using. Further, in the present specification, the element refers to an element accommodated in one electric double layer capacitor container and having a positive electrode and a negative electrode opposed to each other with a separator interposed therebetween. When stacked and stored in a container, the entire stack is referred to as an element.

In the manufacturing method of the present invention, in the step A, the positive electrode of the electric double layer capacitor is connected to the positive terminal of the DC power supply, and the negative electrode is connected to the negative terminal of the DC power supply to apply a voltage to the electric double layer capacitor. In the electric double layer capacitor of the present invention, the positive electrode and the negative electrode may be made of the same constituent material or may be different. In the case of the same, the positive electrode and the negative electrode may be determined before connecting to a DC power supply.

In step B, the positive electrode of the electric double layer capacitor is connected to the negative terminal of the DC power supply, and the negative electrode is connected to the positive terminal of the DC power supply to apply a voltage to the electric double layer capacitor. Either step A or step B may be performed first.

Step A and step B may be repeated alternately. For example, as in step A-step B-step A, step A
The number of times of step and step B may not be the same. Step A and Step B
Is repeated, the time for applying the voltage in one step may be shortened.

In steps A and B, the voltage applied is preferably 1.00 to 1.15 times the rated voltage of the electric double layer capacitor, and the voltage applied in each step may be the same or different. . When a voltage lower than the rated voltage is applied, the effect of improving the voltage holding property is small, and when a voltage more than 1.15 times is applied, the initial capacity is reduced and the internal resistance is increased. In particular, 1.03 to 1.12 times is preferable.

The above voltage application is preferably performed at an ambient temperature of 15 to 85 ° C. in both the steps A and B. The atmosphere temperature in step A and the degree of atmosphere in step B may be the same or different. When voltage is applied while heating,
The effect of improving the voltage holding property is enhanced, and the voltage application time required to provide the desired voltage holding property can be reduced. Fifteen
If the temperature is lower than 85 ° C., the effect of heating is small, and if it exceeds 85 ° C., the initial capacity decreases and the internal resistance increases. Particularly, 20 to 70 ° C. is preferable.

In the steps A and B, the time for applying a voltage is preferably 2 hours or more for each step, and is usually preferably 5 to 50 hours. The voltage application time in step A and the voltage application time in step B may be the same or different. If the voltage application time in the process A and the process B is short, the voltage holding property does not increase, and the effect of improving the deterioration of the capacitor characteristics during long-term use is small. On the other hand, if the voltage application time is long, the productivity is deteriorated.

In the steps A and B, a voltage is applied to the element. Therefore, if the element is impregnated with the nonaqueous electrolytic solution, the element is sealed even if it is performed before the metal container is sealed. It may be done later. In addition, when a voltage is applied in steps A and B, a gas such as CO ₂ is generated. Therefore, if a voltage is applied before the metal container is sealed, an increase in the internal pressure of the capacitor during charging can be prevented, and as a result, the container swells. It is preferable because it can be suppressed. The voltage application before sealing the metal container may be performed after the element is housed in the metal container or before the element is housed in the metal container.

When Step A or Step B is performed after the metal container is sealed, the inside of the metal container may be depressurized to reduce the internal pressure after the voltage application is completed, and the swelling of the metal container may be restored. .

The electric double layer capacitor according to the present invention comprises:
A non-aqueous solvent is used as a solvent for the electrolytic solution to increase the withstand voltage. Specifically, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 1,2-dimethoxyethane, sulfolane, methylsulfolane, and at least one solvent selected from the group consisting of acetonitrile Is preferred in terms of chemical and electrochemical stability, electrical conductivity, and low-temperature characteristics. Among them, it is preferable to use mainly a carbonate-based solvent.

The solute of the electrolytic solution is represented by the general formula R ¹ R ²
A quaternary ammonium ion represented by R ³ R ⁴ N ⁺ or a quaternary phosphonium ion represented by the general formula R ¹ R ² R ³ R ⁴ P ⁺ (provided that R ¹ , R ² , R ³ , and R ⁴ has 1 to ⁴ carbon atoms
A quaternary onium cation such as
F ₄ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , C
lO ₄ ^- salt is a combination of an anion, and the like are preferable. Specifically, (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄
NBF ₄ and (C ₂ H ₅ ) ₃ (CH ₃ ) PBF ₄ are preferred.

When the above-mentioned electrolytic solution is used, the rated voltage can be 2.2 to 3.3 V because the withstand voltage of the electrolytic solution is high. It is preferable that the applied voltage applied in steps A and B to the element of the electric double layer capacitor having the rated voltage in this range is 2.2 to 3.5 V.

The positive and negative electrodes of the electric double layer capacitor according to the present invention are electrodes containing a carbon material having a specific surface area of 500 m ² / g or more. Specific examples of the carbon material include activated carbon, polyacene, and carbon black. In particular, it is preferable that the binder be made of activated carbon, a conductive material such as carbon black for imparting electron conductivity, and a binder, and be joined to the metal current collector. This electrode is, for example,
A small amount of solvent is added to the carbon material, carbon black and binder and mixed to form a slurry. The slurry is applied to a metal current collector or the metal current collector is immersed in the slurry, dried, and pressed if necessary. Thus, the electrode layer and the current collector can be integrally formed.

The carbon material has an average particle diameter of 30 μm.
When the specific surface area is equal to or less than 1200 to 3000 m ² / g, the capacity of the electric double layer capacitor can be increased and the internal resistance can be reduced, which is preferable.

Among the carbon materials, preferred activated carbons include coconut activated carbon, phenolic activated carbon, petroleum coke activated carbon, and the like, and phenolic activated carbon and petroleum coke activated carbon are preferred because of their large capacity. . As the activation treatment method of activated carbon, a steam activation treatment method,
There is a molten KOH activation treatment method and the like. The molten KOH activation treatment method is preferred in that a larger capacity can be obtained.

Examples of the binder contained in the electrode include polyvinylidene fluoride, a copolymer comprising a polymerized unit based on a fluoroolefin and a polymerized unit based on another monomer, carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid. , And polyimide are preferred, and a crosslinking agent or the like may be further added as necessary. Further, the solvent for the slurry is preferably one that dissolves a binder, and examples thereof include N-methylpyrrolidone, water, dimethylformamide, toluene, xylene, methyl ethyl ketone, ethyl acetate, methyl acetate, dimethyl phthalate, ethanol, methanol, and butanol. .

Further, a carbon material, a conductive material powder, and a fluororesin powder such as polytetrafluoroethylene as a binder are kneaded by adding a solvent, rolled to form a sheet, and a conductive adhesive is applied. A method in which an electrode is formed by electrically bonding to a metal current collector is also preferable. Use of an electrode obtained by this method is preferable because an electric double layer capacitor having a high capacitance density can be obtained.

In the present invention, in order to obtain an electric double layer capacitor having a large capacity of 10 F or more, a pair of band-shaped electrodes are wound facing each other with a separator interposed therebetween, and are accommodated in a cylindrical container or a plurality of positive electrodes. And a square shape in which an element formed by alternately stacking a and a negative electrode via a separator is housed in a square container,
It is preferable that the structure has a large electrode area.

The metal current collector used in the present invention only has to have resistance to an electrolytic solution, and for example, stainless steel, aluminum and the like can be preferably used. As the metal current collector, any of a foil, an expanded metal, a sheet-like fiber sintered body, and a plate-like metal foam can be used. Above all, thickness 20 ~
A current collector made of a 100 μm aluminum foil is preferable because the winding or lamination process is easy. When a metal foil is used for the current collector, if the surface is chemically, electrochemically or physically etched and roughened, the adhesion between the electrode layer made of a carbon material and the metal foil is improved, and the electric resistance is also increased. It is particularly preferable because it can be reduced.

In the present invention, as a separator interposed between the positive electrode and the negative electrode, glass fiber mat, manila hemp,
Cellulose paper, hydrophilized porous polytetrafluoroethylene film, polypropylene nonwoven fabric and the like can be mentioned. The metal container used in the present invention is preferably a container made of aluminum, an aluminum alloy, stainless steel, or iron.

In the present invention, the element is formed by heating and drying in advance and forming a positive electrode and a negative electrode with the sheet-like electrode joined to the metal current collector, and winding or laminating the positive electrode and the negative electrode with a separator interposed therebetween. After removing volatile components such as moisture of the element by vacuum drying at 250 ° C., it is preferable to impregnate with an electrolytic solution. It is preferable that the temperature of the atmosphere is raised to 40 to 80 ° C. during the impregnation because the viscosity of the electrolytic solution decreases and the electrolytic solution quickly impregnates the electrode. The impregnation with the electrolytic solution may be performed after the element is accommodated in the metal container or before the element is accommodated in the metal container.

[0032]

EXAMPLES The present invention will be specifically described below with reference to Examples (Examples 1 and 2) and Comparative Examples (Example 3), but the present invention is not limited thereto.

Example 1 Ethanol was added to a mixture comprising 80% by weight of activated carbon powder (specific surface area: 2000 m ² / g), Ketjen black EC 10% by weight, and polytetrafluoroethylene powder 10% by weight, in which a phenol resin was KOH-activated. Then, the mixture was kneaded, formed into a sheet, and dried to obtain a sheet having a thickness of 0.2 mm. This sheet is 50 μm thick
Was bonded to both surfaces of the aluminum foil through a conductive adhesive containing fine graphite powder, and then pressed and heat-treated.
From this sheet, an electrode sheet having an effective electrode surface of 60 mm × 65 mm and having a lead portion having a width of 16 mm and a length of 30 mm at the upper end was cut out and vacuum-dried.

This electrode sheet was used as a positive electrode and a negative electrode, and a glass fiber mat separator having a thickness of 150 μm was interposed therebetween.
Fifteen positive electrodes and fifteen negative electrodes were alternately laminated to produce a laminate. The laminate was wrapped with an insulating film except for the lead portion, fixed with an adhesive tape, and housed in a bottomed square aluminum container. The plurality of positive electrode lead portions and the plurality of negative electrode lead portions of the laminate were respectively combined so as not to cause a short circuit, and were ultrasonically bonded to the positive electrode terminal and the negative electrode terminal attached to the upper lid made of a rectangular aluminum plate.

Next, the upper lid is brought into close contact with the opening of the container,
Welded with AG laser. In addition, a positive electrode terminal and a negative electrode terminal made of aluminum fittings are attached to the upper lid via an insulating resin, and an injection port for injecting an electrolyte is present as an opening.

The laminate housed in this container is heated at 200 ° C.
Vacuum drying was performed for 24 hours to remove volatile impurities such as water.
Then, in a nitrogen atmosphere with a dew point of -45 ° C, the aluminum
After degassing the inside of the container, 2 mol / l
(C_TwoH_Five)_Three(CH_Three) NBF _FourContaining propylene carbonate
-Carbonate electrolyte is injected at normal pressure from the injection port, and
Impregnated. After that, seal the injection port with a polyethylene stopper.
I spoke.

Next, at room temperature, a positive terminal was connected to the positive output of the DC power supply, and a negative terminal was connected to the negative output, and a DC voltage of 2.6 V was applied between the positive electrode and the negative electrode for 24 hours (step A). Next, the positive terminal and the negative terminal are connected in reverse, that is, the positive output of the DC power supply is connected to the negative terminal, the negative output is connected to the positive terminal, and a DC voltage of 2.6 V is applied for 24 hours (step B). An electric double layer capacitor having a rated voltage of 2.5 V was obtained.

After charging the electric double layer capacitor at the rated voltage, the initial discharge characteristics were measured, and the capacitance value indicated at this time was used as the initial capacitance. The initial capacity was 750F. Next, the positive terminal of the DC power supply was connected to the positive electrode and the negative terminal was connected to the negative electrode, and a DC voltage of 2.0 V was applied to the electric double layer capacitor at 60 ° C. for 1000 hours. After applying
The battery was charged to 2.5 V and the discharge characteristics were measured to determine the capacity.
The ratio of this capacity to the initial capacity was defined as the capacity maintenance rate (%). The capacity retention was 97%.

[Example 2] An electric double layer capacitor was manufactured in the same manner as in Example 1 except that the order of Step A and Step B was reversed, that is, Step B was performed after the injection port was closed, and then Step A was performed. Was prepared. When the performance was measured in the same manner as in Example 1, the initial capacity was 750 F and the capacity retention was 96%.

[Example 3] Instead of applying a DC voltage between the positive terminal and the negative terminal for 24 hours and then connecting the positive terminal and the negative terminal in reverse and applying a DC voltage for 24 hours, the positive terminal and the negative terminal are connected. An electric double layer capacitor was obtained in the same manner as in Example 1, except that a DC voltage of 2.6 V was applied for 48 hours. When the performance was measured in the same manner as in Example 1 using this electric double layer capacitor, the initial capacity was 750 F and the capacity retention was 92%.

[0041]

According to the present invention, a large withstand voltage, a large capacity, a high energy density, a good voltage holding property, a very small decrease in the capacity after charging with time, and a high long-term reliability. An electric double layer capacitor having a capacity is obtained.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ken Ken Kawari 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Asahi Glass Co., Ltd.

Claims (4)

[Claims] 1. A conductive material, a binder and a specific surface area of 500 m ² /
g or more of a carbon material, an element in which a positive electrode and a negative electrode formed on a metal current collector are opposed to each other with a separator interposed therebetween is impregnated with a non-aqueous electrolyte solution and stored in a metal container. In a method for manufacturing an electric double layer capacitor in which a container is sealed and sealed with a sealing member, the following steps A and B are performed after the element is impregnated with a non-aqueous electrolyte. Manufacturing method of capacitor. Step A: a step of applying a voltage between the positive electrode and the negative electrode of the electric double-layer capacitor by a DC power supply, and a step B: a step of connecting the positive electrode and the negative electrode to the DC power supply in the opposite manner to the step A and applying a voltage. 2. The voltage applied in step A and step B is 1.0 V of the rated voltage of the electric double layer capacitor.
The method for manufacturing an electric double layer capacitor according to claim 1, wherein the ratio is 0 to 1.15 times. 3. The rated voltage of the electric double layer capacitor is 2.2.
3. The method for manufacturing an electric double layer capacitor according to claim 1, wherein the voltage applied in the step A and the step B is 2.2 to 3.5 V. 4. 4. The method according to claim 1, wherein in the steps A and B, the voltage is applied at an ambient temperature of 15 to 85 ° C.
Or the manufacturing method of the electric double layer capacitor of 3.