JPH0722295A - Production of electric double layer capacitor - Google Patents

Abstract

PURPOSE:To provide an electric double layer capacitor in which the inner pressure rise and swelling of case due to generation of gas after completion of product is prevented while preventing the capacitance from lowering due to increase of inner resistance by removing the moisture thoroughly from a polarizing electrode prior to sealing of the case. CONSTITUTION:Before an electric double layer capacitor cell is sealed, a positive pole can 1 and a negative pole can 4, each formed with a polarizing electrode 2 therein, are impregnated with an organic electrolyte, i.e., 1M(Et)4NBF4/PC, and opposed to each other through a separator 5. A voltage of 2.0V is then applied between the positive and negative cans 1, 4 from a constant voltage source 7 thus subjecting the residual moisture to electrolysis.

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 an electric double layer capacitor using an organic electrolyte.

[0002]

2. Description of the Related Art The procedure for manufacturing a coin type electric double layer capacitor, which is a typical example of an electric double layer capacitor, is roughly as follows. First, a powder mixture made of activated carbon powder, a binder, etc. is formed into flat disk-shaped pellets, and a metal forming a flat container-shaped metal case that constitutes one electrode terminal and a metal that constitutes the other electrode terminal The cover is placed inside the cover and impregnated with the organic electrolyte. Then, the metal cover is fitted into the metal case via a sealing gasket, the separator is sandwiched between the two pellets to face each other, and the metal case is caulked to the metal cover.

In the manufacturing process of such a coin-type electric double layer capacitor, each member except the organic electrolytic solution is heated in any process before the metal cover is caulked and sealed in the metal case. It is common practice to remove water by doing so. This is because if moisture remains in the sealed case, hydrogen gas and oxygen gas are generated when the voltage higher than the decomposition voltage of water is applied, and the case and cover expand. This is to prevent the problem that the contact state between the electrode mixture and the electrode mixture deteriorates, the internal resistance increases, and the electrostatic capacitance decreases.

[0004]

However, in such a method of removing water by heating, a porous substance having a large number of fine pores such as activated carbon powder is trapped in the fine pores. It is difficult to completely remove the water contained therein, and it has not been possible to completely prevent the problem of capacitance reduction due to water remaining in the case.

The present invention has been made to solve the above problems, and an object thereof is to completely remove water contained in a polarizable electrode in advance before sealing the case.
An object of the present invention is to provide a method for manufacturing an electric double layer capacitor which can prevent an increase in internal pressure due to gas generation after product completion, expansion of the case due to it, and a decrease in electrostatic capacitance due to increase in internal resistance.

[0006]

To achieve the above object, the present invention provides a positive electrode obtained by impregnating an electrode obtained by molding a powder mixture containing activated carbon powder into a predetermined shape with an organic electrolytic solution. In a method of manufacturing an electric double layer capacitor, which comprises a negative electrode and a negative electrode that face each other through a separator, and is housed in a flat container-shaped metal case and a metal cover, the metal case and the metal case after being impregnated with the organic electrolytic solution. Before sealing with the cover, a predetermined voltage is applied between the positive electrode and the negative electrode to electrolyze and remove water contained in the positive electrode and the negative electrode.

Here, it is preferable that the electrolysis is carried out after a predetermined time has elapsed since the electrodes were impregnated with the organic electrolytic solution.

Further, the impregnation with the organic electrolyte is 45 to
It is preferable to carry out at an ambient temperature of 70 ° C.

Furthermore, the voltage applied between the positive electrode and the negative electrode during the electrolysis is preferably set in the range of 1.8 to 2.3V.

[0010]

According to the present invention having the above-described structure, a predetermined voltage is applied between the positive electrode and the negative electrode of the electric double layer capacitor before sealing the electric double layer capacitor so that the moisture contained in the positive electrode and the negative electrode is increased. Since it is electrolyzed and removed, it is possible to remove even a small amount of water that could not be removed by high temperature drying by heating each member as in the related art.

If a voltage is applied after a predetermined time has passed since the electrode was impregnated with the organic electrolytic solution, the voltage is applied while the electrode is sufficiently impregnated with the electrolytic solution, so that the water content can be more completely removed. It can be carried out.

Further, if the impregnation of the organic electrolytic solution is carried out at an ambient temperature of 45 to 70 ° C., the viscosity of the organic electrolytic solution is lowered and the impregnation speed is improved, so that the working process time is shortened.

Further, when the voltage applied between the positive electrode and the negative electrode is in the range of 1.8 to 2.3 V, only the electrolysis of water can be performed without affecting the organic electrolytic solution.

[0014]

An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a coin type electric double layer capacitor in an assembled state. On the inner bottom surface of the positive electrode can 1 which is a flat container-shaped metal case and on the inner bottom surface of the corresponding negative electrode can 4 which is a metal cover, there are collectors 3 each formed of a metal net such as stainless steel. ,
It is fixed in advance by spot welding or the like. For the polarizable electrode 2, a powder mixture comprising 77 wt% of activated carbon, 20 wt% of acetylene black and 3 wt% of Teflon binder was placed in the positive electrode can 1 and the negative electrode can 4 and molded into a can. It was done. The positive electrode can 1 and the negative electrode can 4 on which the polarizable electrode 2 is formed are heated at 200 ° C. for 8 hours to remove most of water in advance, and then transferred to a dry box having a dew point of −50 ° C. or lower. The following preliminary electrolytic treatment was performed.

That is, the positive electrode can 1 and the negative electrode can 4 in which the polarizable electrode 2 was molded in the can were impregnated with 1M (Et) ₄ NBF ₄ / PC as an organic electrolyte, respectively, and as shown in FIG. A voltage of 2.0 V was applied between the positive and negative electrodes by a constant voltage power supply 7 with the separator 5 facing each other.

As described above, since the voltage applied between the positive electrode can 1 and the negative electrode can 4 is higher than the decomposition voltage of water, the polarizable electrodes 2 of the positive electrode can 1 and the negative electrode can 4 respectively have the following characteristics. Such a reaction proceeds.

Reaction in positive electrode can 1: 4OH ⁻ → 2H ₂ O + O ₂ ↑ + 4e ⁻ (1) Reaction in negative electrode can: 2H ⁺ + 2e ⁻ → H ₂ ↑ (2) Therefore, reaction formula (1) , (2), the whole reaction becomes 4H ⁺ + 4OH ⁻ → 2H ₂ O + 2H ₂ ↑ + O ₂ ↑, that is, 2H ₂ O → 2H ₂ ↑ + O ₂ ↑, and is contained in the activated carbon in the polarizable electrode 2. The water content is decomposed into hydrogen gas and oxygen gas and removed.

The ambient temperature when impregnating the organic electrolyte is preferably 45 ° C to 70 ° C. this is,
This is because it takes a long time until the polarizable electrode 2 is completely impregnated with the organic electrolyte under the condition that the ambient temperature does not reach 45 ° C. Further, when the ambient temperature exceeds 70 ° C. The problem is that the volatilization of the organic electrolyte causes a decrease in capacitance and the handling becomes complicated, and even if the ambient temperature is raised to about 60 ° C. or more, the impregnation speed is not improved so much. is there.

As described above, after the polarizable electrode 2 is impregnated with the organic electrolytic solution to remove water by electrolysis, the positive electrode can 1 is caulked to the negative electrode can 4, and then the coin type electric double layer capacitor of the present invention. Is completed.

Next, in the conventional coin-type electric double layer capacitor manufactured without performing the pre-electrolysis treatment of the present invention, and the manufacturing method of this embodiment, the ambient temperature at the time of impregnation and the pre-impregnation preliminary The performance was compared with the capacitor manufactured by changing the immersion time in the organic electrolytic solution until the electrolytic treatment was started. Table 1 shows the manufacturing specifications of each capacitor.
Shown in.

[0021]

[Table 1] First, for each coin type electric double layer capacitor, the rate of change in internal resistance and the rate of change in cell thickness when a voltage of 2 V was continuously applied were measured, and the results shown in FIGS. 3 and 4 were obtained. Obtained. As you can see from these figures,
In the conventional product in which the water content is not removed by the preliminary electrolytic treatment, the cell thickness rapidly increases immediately after the voltage is applied, and finally becomes about 8% thicker than before the voltage is applied. Along with that, the internal resistance also increased rapidly, becoming about 1.5 times the initial value. From this, it is presumed that gas generation due to residual moisture occurs inside the cell, causing an increase in internal pressure.

On the other hand, in the products 1 and 2 of the present invention of the group in which the organic electrolytic solution was impregnated at room temperature and the preliminary electrolysis treatment was performed, the cell thickness change rate and the internal resistance change rate were both compared with the conventional product. And is greatly suppressed. In particular, the product 2 of the present invention, which was left for 1 day after impregnation in the electrolytic solution and more fully impregnated with the electrolytic solution before starting the preliminary electrolysis treatment, has a higher performance improving effect than the product 1 of the present invention.

Furthermore, in the products 3 and 4 of the present invention of the group impregnated with the organic electrolytic solution at 60 ° C. and subjected to the pre-electrolytic treatment, almost no change was observed in both the cell thickness and the internal resistance. There wasn't. It is considered that this is because the viscosity of the organic electrolytic solution was lowered by increasing the temperature during the impregnation of the organic electrolytic solution, and the electrode mixture was easily impregnated.

[0024]

As described above in detail with reference to the embodiments, according to the method for manufacturing an electric double layer capacitor of the present invention, the positive electrode of the capacitor is formed after the impregnation of the organic electrolytic solution and before the sealing of the electric double layer capacitor. Since a predetermined voltage is applied between the negative electrode and the positive electrode and the negative electrode, the water contained in the negative electrode is electrolyzed and removed, so that it can be removed only by high temperature drying by heating each member as in the conventional case. It is possible to remove a small amount of water that has not been present, and it is possible to prevent expansion of the cell and increase in internal resistance due to expansion of the cell due to gas generation in the cell during use.

If a voltage is applied after a predetermined time has passed since the electrode was impregnated with the organic electrolytic solution, the voltage is applied while the electrode is sufficiently impregnated with the electrolytic solution. It can be done completely.

Further, the impregnation with the organic electrolytic solution is carried out at 45 to 70 ° C.
If the ambient temperature is used, the viscosity of the organic electrolytic solution is lowered and the impregnation rate is improved, so that the working process time is shortened.

Furthermore, if the voltage applied between the positive electrode and the negative electrode is in the range of 1.8 to 2.3 V, only the electrolysis of water can be carried out without affecting the organic electrolytic solution. It has various excellent effects.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a coin type electric double layer capacitor.

FIG. 2 is an explanatory view showing a preliminary electrolytic treatment step of the coin-type electric double layer capacitor according to the method of the present invention.

FIG. 3 is a graph showing the relationship between the voltage application time to the cell of the electric double layer capacitor and the cell thickness change rate.

FIG. 4 is a graph showing a relationship between a voltage application time to a cell of an electric double layer capacitor and an internal resistance change rate.

[Explanation of symbols]

 1 positive electrode can 2 polarizable electrode 3 current collector 4 negative electrode can 5 separator 6 sealing gasket 7 constant voltage power supply

Front page continuation (72) Inventor Mitsuhiro Nakamura 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Inventor Tatsuya Yamazaki 5-36-11 Shinbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. In the company

Claims (4)

[Claims] 1. A positive electrode and a negative electrode obtained by impregnating an electrode obtained by molding a powder mixture containing activated carbon powder into a predetermined shape with an organic electrolytic solution, and facing the positive electrode and the negative electrode with a separator interposed therebetween. Then, in a method for manufacturing an electric double layer capacitor which is housed in a flat container-shaped metal case and a metal cover, before the sealing of the metal case and the metal cover after the organic electrolyte impregnation, A method for producing an electric double layer capacitor, which comprises applying a predetermined voltage between a positive electrode and a negative electrode to electrolyze and remove water contained in the positive electrode and the negative electrode. 2. The method for producing an electric double layer capacitor according to claim 1, wherein the electrolysis is performed after a predetermined time has elapsed after the electrodes were impregnated with the organic electrolytic solution. 3. The method for manufacturing an electric double layer capacitor according to claim 1, wherein the impregnation with the organic electrolytic solution is performed at an ambient temperature of 45 to 70 ° C. 4. The manufacture of the electric double layer capacitor according to claim 1, wherein the voltage applied between the positive electrode and the negative electrode during the electrolysis is 1.8 to 2.3V. Method.