JPH1154378A - Electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor which is formed by housing a capacitor element using a nonaqueous electrolyte solution in a sealing container and which permits maintenance of a withstand voltage to a high degree. SOLUTION: This capacitor is formed by housing a capacitor element 1, using a nonaqueous electrolyte solution in a sealing container 2a, 2b and has an adsorbent for adsorbing moisture mingled in the nonaqueous electrolyte solution. This adsorbent is non-reactive with the nonaqueous electrolyte solution. The adsorbent 4 may be mixed in the nunaqueous electrolyte solution or may be provided in the sealing container 2a, 2b. The adsorbent 4 uses aluminosilicate, having a weight ratio of silica to alumina equal to or less than 50, at a quantity within a range of 1 to 10 wt.% with respect to the nonaqueous electrolyte solution. The sealing container 2a, 2b is made of a synthetic resin, and a moisture-interrupting layer 5 made of a material having a moisture permeability which is lower than the synthetic resin is provided on the container wall.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor in which an electric double layer capacitor element using a non-aqueous electrolyte is housed in a closed container.

[0002]

2. Description of the Related Art When a solid surface contacts an electrolyte solution, selective adsorption of positive or negative ions occurs on the solid surface,
While the solid surface is charged positively or negatively, counter ions of opposite charges increase on the solution side, and an electric double layer in which positive and negative charges are arranged opposite to each other is formed at the interface between the solid surface and the electrolyte solution. It is known that the electric double layer can be used as a capacitor by using the solid surface as a solid electrode, and such a capacitor is called an electric double layer capacitor.

In the electric double layer capacitor, the capacitance when an electric field is applied to the solid electrode is proportional to the surface area of the solid electrode. Therefore, in general, a material having a large specific surface area such as activated carbon is used as the solid electrode. This is impregnated with an electrolytic solution, separated by a separator, and a current collecting member is attached to each of the solid electrodes on both sides of the separator.

[0004] The electric double layer capacitor has a farad-class large capacity and excellent charge / discharge cycle characteristics, and is therefore used for applications such as a backup power supply for electric equipment, and is further used as a vehicle battery. Are being considered.

An electric double layer capacitor used as a backup power supply for the electric equipment generally does not require a large capacity. Therefore, a capacitor element in which a solid electrode impregnated with the electrolytic solution is separated by a separator is made of a light metal such as aluminum. In a button-type container. According to the container, the container itself can be used as a current collecting member of the electric double layer capacitor and a connection terminal for an external circuit, and when a non-aqueous electrolytic solution is used as the electrolytic solution, moisture from outside may be used. This is advantageous because intrusion can be prevented.

On the other hand, when the electric double layer capacitor is used as a vehicle-mounted battery, it is necessary to increase the capacity of the capacitor element. There is a problem that the container itself becomes large and the weight increases. In addition, in the case of the metal container, when the container is enlarged with an increase in the capacity of the electric double layer capacitor, it is difficult to form the container in accordance with the storage space, the possibility of electric leakage increases, and assembly is difficult. There are also problems such as becoming.

In order to solve the above problem, it has been studied to form a container for housing the capacitor element with a synthetic resin. Such a container is disclosed, for example, in Japanese Patent Application Laid-Open No. 58-101416. 62-174910
And Japanese Patent Application Laid-Open No. 7-94374. According to the synthetic resin container described in each of the above publications, the resin is lightweight and easy to mold, the possibility of electric leakage is small because the synthetic resin itself has insulating properties, and it is easily fused by ultrasonic fusion, high frequency fusion, or the like. Because it can be worn, assembly is easy.

However, since the synthetic resin containers described in the above publications have a property of transmitting moisture, it is difficult to use an electric double layer capacitor using a non-aqueous electrolyte as the electrolyte in the containers for a long period of time. In addition, there is an inconvenience that the withstand voltage of the electric double layer capacitor is reduced due to moisture permeating into the container from outside via the synthetic resin.

In order to solve the above-mentioned inconvenience, Japanese Unexamined Patent Publication No.
Although it is conceivable to cover a synthetic resin container with an aluminum metal plate like a container of a lead storage battery described in JP-A-13549, it cannot be said that a sufficient effect is obtained.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances and has been made in view of the above circumstances. It is an object of the present invention to provide an electric double layer capacitor that can be used.

[0011]

To achieve the above object, an electric double layer capacitor according to the present invention comprises an electric double layer capacitor in which an electric double layer capacitor element using a non-aqueous electrolyte is housed in a closed container. , Characterized by comprising an adsorbent that is non-reactive with the non-aqueous electrolyte solution that adsorbs water mixed in the non-aqueous electrolyte solution.

According to the electric double layer capacitor of the present invention,
Since the moisture that invades into the closed container or is generated in the closed container is adsorbed by the adsorbent, it is possible to prevent water from being mixed into the non-aqueous electrolyte and to withstand the withstand voltage of the electric double layer capacitor. Can be maintained at a high level. Further, since the adsorbent has no reactivity with respect to the non-aqueous electrolyte, it is possible to avoid deterioration and deterioration of the non-aqueous electrolyte itself.

[0013] The adsorbent may be directly mixed with the non-aqueous electrolyte, or may be disposed in the closed container.

The adsorbent is preferably an aluminosilicate (zeolite) because it is non-reactive with the non-aqueous electrolyte. The present invention is characterized in that aluminosilicate having a weight ratio of silica to alumina of 50 or less is used in an amount of 1 to 10% by weight based on the nonaqueous electrolyte.

In the aluminosilicate, when the weight ratio of silica to alumina is 50 or less in the composition, excellent water adsorption capacity can be obtained, and the amount of water mixed in the non-aqueous electrolyte in the above-mentioned range can be reduced. It can be below the fixed amount.

Further, the present invention is characterized in that the closed container is made of a synthetic resin, and a water barrier layer made of a material having a lower water permeability than the synthetic resin is provided on a wall of the closed container. .

Since the closed container is made of a synthetic resin, it is lightweight and easy to mold, can reduce the possibility of electric leakage, and can be easily assembled by ultrasonic fusion, high frequency fusion or the like. it can. In such a synthetic resin container, the permeation of moisture from the outside may be a concern. However, as described above, by providing a moisture barrier layer made of a material having a lower water permeability than the synthetic resin on the vessel wall of the closed container. In addition, the penetration of the water can be prevented. Therefore, the withstand voltage of the electric double layer capacitor can be reliably maintained at a high level.

[0018]

Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory cross-sectional view showing the configuration of the electric double layer capacitor of the present embodiment. FIG. 2 shows the voltage maintenance ratio of the electric double layer capacitor using a non-aqueous electrolyte, the amount of water contained in the electrolyte, and the like. FIG. 3 is a graph showing the relationship between the water content of the non-aqueous electrolyte and the silica / aluminosilicate content.
FIG. 3 is a diagram showing a relationship with an alumina ratio. FIG. 4 is a diagram showing the change over time in the amount of water contained in the non-aqueous electrolyte solution and the withstand voltage in the electric double layer capacitor according to one embodiment of the present invention, and FIGS. FIG. 5 is a diagram showing a change over time in the amount of water contained in the nonaqueous electrolyte solution and the withstand voltage in the electric double layer capacitor of the comparative example.

As shown in FIG. 1 (a), the electric double layer capacitor of this embodiment has an element case body 2a made of synthetic resin for accommodating the capacitor element 1, and a top opening of the element case body 2a is closed. A moisture adsorbent 4 covered with a water-permeable separator 3 is provided at the bottom of the element case main body 2a. Also, the element case body 2a
The outer surface of the lid 2b is covered with a moisture blocking layer 5.

The capacitor element 1 is formed by mixing activated carbon powder with a conductive filler and a binder into a sheet shape, and laminating electrodes pressed on both sides of a current collector via a separator. The body is staggered into two sets so that they can be connected to an external circuit. A non-aqueous electrolyte is immersed in the electrodes. Further, the lid 2b
Has terminals (not shown) to which the two sets of current collectors are connected.

In the electric double layer capacitor having the above structure, the moisture adsorbent 4 is disposed at the bottom of the element case main body 2a, the capacitor element 1 is mounted thereon, and the electrolytic solution is injected. The main body 2a is closed by the lid 2b to be sealed. Element case body 2a and lid 2b
Are fused together by a method such as ultrasonic fusion or high frequency fusion.

As the resin forming the element case main body 2a and the lid 2b, a general-purpose resin such as polypropylene can be used. Element case body 2a and lid 2b
Any material can be used as the moisture blocking layer 5 covering the outer surface of the device, as long as the material has lower water permeability than the resin forming the element case main body 2a and the lid 2b.
For example, metal foil such as aluminum foil, polytetrafluoroethylene (PTFE), polyphenylene sulfide (PP
S), polyimide (PI), polyetheretherketone (PEEK) and other low-permeability resin films.

The element case body 2a and the lid 2
As a method of coating the outer surface of b with the moisture blocking layer 5, a material of the moisture blocking layer 5 such as the aluminum foil is previously formed on the outer shape of the element case main body 2a or the lid 2b, and is disposed in a mold.
A method of blow molding the element case main body 2a or the lid 2b in the mold can be used. The material of the moisture barrier layer 5 such as the aluminum foil may be subjected to a surface treatment such as a silanization treatment or an etching treatment in order to improve the adhesion to the element case main body 2a or the lid 2b. desirable.

Examples of the non-aqueous electrolyte include a solvent such as acetonitrile, propylene carbonate (propylene carbonate, PC), gamma butyrolactone (GBL), gamma valerolactone (GVL), and the like.
A) A solution in which a tetraalkylammonium salt such as a salt is dissolved is used. When the concentration of the electrolyte solution is, for example, PC as a solvent and the TEMA salt is dissolved,
The higher the concentration of MA salt, the higher the conductivity is expected.
In order to obtain stable solubility, the concentration is preferably about 1 mol / liter. The concentration of the electrolyte solution may be 1 mol / liter or less, and the concentration of the electrolyte solution does not limit the characteristics of the electric double layer capacitor of the present invention.

As the water adsorbent 4, those which are non-reactive with the electrolytic solution are used, and examples thereof include aluminosilicate (zeolite) and silica gel.
The aluminosilicate is classified into A-type, Y-type, X-type, ZSM-5 type and the like according to its composition, crystal structure and the like, and any of them can be used in the present embodiment. It is known that the higher the aluminum content in the composition of the aluminosilicate, the better the water adsorbing ability. The silica / alumina ratio (weight ratio of silica to alumina 1) in this embodiment is known. Is 50
It is preferred to use the following aluminosilicates.
Next, the reason will be described.

First, in the capacitor element 1 having the above structure, a 1 mol / liter-PC solution of a TEMA salt was used as an electrolytic solution, charged at 2.3 V and left for 72 hours, and the voltage retention ratio of the electrolytic solution was measured. Fig. 2 shows the relationship with the amount of water contained.
Shown in From FIG. 2, it can be seen that the non-aqueous electrolyte such as the PC solution of the TEMA salt contains more than 20 ppm of water.
It is clear that the voltage maintenance ratio drops sharply. For this reason, it is desired that the moisture adsorbent 4 has an ability to reduce the amount of water contained in the non-aqueous electrolyte to less than 20 ppm.

Next, the TE containing 80 ppm of water is used.
Various aluminosilicates having different silica / alumina ratios were added to the PC solution of the MA salt in an amount of 10% by weight based on the PC solution of the TEMA salt. FIG. 3 shows the amount of water contained. From FIG. 3, it is apparent that an aluminosilicate having a silica / alumina ratio of 50 or less is desirable in order to make the water content of the PC solution of the TEMA salt less than 20 ppm.

In this embodiment, an aluminosilicate having a silica / alumina ratio of more than 50 can be used. In this case, however, the ability to adsorb water is not sufficient, and the amount of water contained in the non-aqueous electrolyte is reduced. Since a large amount of aluminosilicate is required to make it less than 20 ppm, the volume to be used for the capacitor element 1 in the element case main body 2a is reduced.

In this embodiment, the aluminosilicate is used in an amount of 1 to 10% by weight based on the nonaqueous electrolyte. If the amount of aluminosilicate is less than 1% by weight with respect to the non-aqueous electrolyte, the effect of reducing the amount of water mixed into the non-aqueous electrolyte to a predetermined amount or less cannot be sufficiently obtained. The volume increases and the volume to be used for capacitor elements in the enclosure decreases.

In this embodiment, the moisture adsorbent 4 covered with the separator 3 is provided at the bottom of the element case main body 2a as shown in FIG. 1A. Is not limited to this, and FIG.
(B) As shown in FIG. 1 (c), a moisture adsorbent 4 formed in a pellet shape may be disposed at the bottom of the element case main body 2a via the separator 3 as shown in FIG. 1 (c).
The moisture adsorbent 4 formed in a plate shape may be arranged along the side wall of a. Further, the moisture adsorbent 4 may be mixed with the non-aqueous electrolyte.

Next, examples and comparative examples of the present invention will be described.

[0032]

Embodiment 1 First, 50 μm thick aluminum foil was previously
1 (a) by molding into a box having a size of 20 mm x 130 mm, placing the mold in a mold, and blow molding polypropylene resin using the mold.
a was molded. The element case main body 2a has a thickness of 2 mm, and is provided with a moisture blocking layer 5 made of the aluminum foil on the outer surface.

Next, 5 g of aluminosilicate as the moisture adsorbent 4 was covered with the separator 3 and disposed at the bottom of the element case main body 2a, and the capacitor element 1 was mounted thereon. In this embodiment, PTF is used as the separator 3.
An E microporous membrane, for example, Gore-Tex (trade name, manufactured by Gore-Tex Corporation) was used.

The capacitor element 1 has a specific surface area of 25.
A sheet made of a mixture of 83% by weight of activated carbon powder of 00m ² / g, 12% by weight of acetylene black as a conductive filler, and 5% by weight of tetrafluoroethylene powder as a binder is formed into a sheet, and is 48 mm × 100 mm and 50 mm thick.
An aluminum current collector was pressed on both sides to form electrodes, and the 38 current collectors were laminated via a Gore-Tex having a thickness of 25 μm as separators, and the current collectors of the respective electrodes were alternately combined into two sets. It is.

Next, the moisture adsorbent 4 and the capacitor element 1
After vacuum drying the element case body 2a in which
The electrolyte was injected. In this example, 109 ml of a 1 mol / l propylene carbonate solution of tetraethylammonium tetrafluoroborate was used as the electrolytic solution.

Then, the element case main body 2a was closed with a separately manufactured lid 2b made of polypropylene resin to manufacture an electric double layer capacitor. In addition, a moisture blocking layer 5 made of the aluminum foil is provided on the outer surface of the lid 2b, similarly to the element case body 2a.

Next, the electric double layer capacitor was stored at a humidity of 9%.
It was left in an atmosphere of 0% and 40 ° C., and the withstand voltage and the change over time in the water content in the electrolyte were measured. FIG. 4 shows the results.

From FIG. 4, according to the electric double layer capacitor of this embodiment, an increase in water content is recognized at the very beginning.
It is clear that the water content was suppressed to about 10 ppm until after 500 hours, and the withstand voltage maintained the initial value. The increase in the water content at the very beginning is considered to be due to the water oozing out from the activated carbon constituting the electrodes of the capacitor element 1.

[0039]

COMPARATIVE EXAMPLE 1 The same procedure as in Example 1 was carried out except that the size of the element case main body 2a shown in FIG. 1A was set to 50 mm × 20 mm × 125 mm and the moisture adsorbent 4 was not provided. A double layer capacitor was manufactured. Next, the electric double layer capacitor was left in an atmosphere at a humidity of 90% and 40 ° C., and the withstand voltage and the change with time of the water content in the electrolytic solution were measured. FIG. 5 shows the results.

It is apparent from FIG. 5 that the electric double layer capacitor of the present comparative example shows that the water content increased at the very beginning continues to increase gradually thereafter, and the withstand voltage tends to gradually decrease. It is considered that the gradual increase in the water content is due to the fact that the water oozing out from the activated carbon continues to increase without being removed inside the capacitor element.

[0041]

Comparative Example 2 The size of the element case main body 2a shown in FIG. 1A was set to 50 mm × 20 mm × 125 mm, the moisture adsorbent 4 was not provided, and the element case main body 2a and the lid 2b were provided.
Example 1 except that no moisture barrier layer 5 was provided on the outer surface of
An electric double layer capacitor was manufactured in exactly the same manner as described above. Next, the electric double layer capacitor was left in an atmosphere at a humidity of 90% and 40 ° C., and the withstand voltage and the change with time of the water content in the electrolytic solution were measured. FIG. 6 shows the results.

It is apparent from FIG. 6 that, with the electric double layer capacitor of this comparative example, the water content continues to increase with the lapse of time over 20 ppm, and the withstand voltage greatly decreases accordingly. . The increase in the water content is caused by the fact that, in addition to the water oozing out from the activated carbon, the water outside the electric double layer capacitor is passed through the element case main body 2a and the lid 2b where the water blocking layer 5 is not provided. It is thought that it penetrates inside.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view showing a configuration of an electric double layer capacitor according to an embodiment.

FIG. 2 is a diagram showing the relationship between the voltage maintenance ratio of an electric double layer capacitor using a non-aqueous electrolyte and the amount of water contained in the electrolyte.

FIG. 3 is a graph showing the relationship between the amount of water contained in a non-aqueous electrolyte and the silica / alumina ratio of aluminosilicate.

FIG. 4 is a diagram showing a change with time in the amount of water contained in the non-aqueous electrolyte and the withstand voltage in the electric double layer capacitor according to one embodiment of the present invention.

FIG. 5 is a diagram showing a change over time in the amount of water contained in the nonaqueous electrolyte and the withstand voltage in the electric double layer capacitor according to a comparative example of the present invention.

FIG. 6 is a diagram showing a change with time in the amount of water contained in the non-aqueous electrolyte and the withstand voltage in the electric double layer capacitor of another comparative example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electric double layer capacitor element, 2a, 2b ... Airtight container, 4 ... Adsorbent, 5 ... Water blocking layer.

Claims (5)

[Claims] 1. An electric double layer capacitor in which an electric double layer capacitor element using a non-aqueous electrolytic solution is housed in a closed container, wherein the non-aqueous electrolytic solution absorbs moisture mixed in the non-aqueous electrolytic solution. An electric double layer capacitor, comprising: 2. The electric double layer capacitor according to claim 1, wherein the adsorbent is mixed with the non-aqueous electrolyte. 3. The electric double layer capacitor according to claim 1, wherein the adsorbent is provided in the closed container. 4. The adsorbent according to claim 1, wherein aluminosilicate having a weight ratio of silica to alumina of 50 or less is used in an amount of 1 to 10% by weight based on the non-aqueous electrolyte. The electric double layer capacitor according to any one of claims 1 to 3. 5. The sealed container is made of a synthetic resin, and a water barrier layer made of a material having a lower water permeability than the synthetic resin is provided on a wall of the sealed container. The electric double layer capacitor according to claim 4.