JPH0845792A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To provide an electric double layered capacitor with a high breakdown voltage and high energy density per unit volume of a cell. CONSTITUTION:The solvent of electrolyte of an electric double layered capacitor contains maleic anhydride and/or its derivative. Preferably, the solvent of the electrolyte is composed of mixed solvent of maleic anhydride and/or its derivative and chain carbonate and/or cyclic carbonate.

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 having high withstand voltage and high reliability.

[0002]

2. Description of the Related Art Conventionally, as electrolytes used in electric double layer capacitors, perchlorates, hexafluorophosphoric acid, tetrafluoroboric acid or tetraalkylammonium salts of trifluoromethanesulfonic acid, ammonium salts or alkali metals are used. It is known that an electrolyte such as a salt is dissolved in an organic solvent such as propylene carbonate, γ-butyrolactone, acetonitrile and dimethylformamide (JP-A-48-50255, JP-A-49-68254 and JP-A-49-68254). Sho 59-232409, etc.).

[0003]

The electrostatic energy stored in the capacitor is represented by (1/2) CV ² where C is the capacitance of the capacitor and V is the voltage. The higher the withstand voltage of, the greater the electric energy that can be stored per unit volume of the cell, that is, the energy density. However, in the conventional electric double layer capacitor using the electrolytic solution as described above, the withstand voltage of the unit cell is generally around 2.5 V, and the energy density per unit volume of the cell cannot be increased. That is, 2.7 is added to the conventional electric double layer capacitor.
When a voltage of 5 V or more is applied, the solvent of the electrolytic solution is decomposed to reduce the capacity of the capacitor, or gas is generated to expand the outer case, thereby increasing the internal resistance,
Further, the electrolytic solution may leak from the cell, and there is a problem that such a deterioration phenomenon appears remarkably when the electric double layer capacitor is used especially at a high temperature, and the energy density cannot be increased.

[0004]

The present invention has been made to solve the above-mentioned problems, and an electric double layer capacitor of the present invention comprises a polarizable electrode immersed in an electrolytic solution and an electrolytic solution. An electric double layer capacitor using an electric double layer formed at the interface is characterized in that the solvent of the electrolytic solution contains maleic anhydride and / or its derivative.

The inventors of the present invention have extensively studied various measures for suppressing the above-mentioned decomposition phenomenon of the solvent, and as a result, by adding maleic anhydride and / or its derivative to the solvent component of the electrolytic solution, the electrolytic solution It has been found that decomposition can be effectively suppressed. That is, in the present invention, by using the above-mentioned solvent, the withstand voltage of the electric double layer capacitor can be remarkably increased, and the electric double layer capacitor in which the energy density per unit volume of the cell is dramatically increased is provided. It is now available.

As the maleic anhydride derivative used in the present invention, an alkyl group such as a methyl group or an ethyl group, a methoxy group, an ethoxy group or a halogen atom at the carbons at the 2 and / or 3 positions of maleic anhydride is used. Examples include substituted maleic anhydride. Among these, methylmaleic acid having a methyl group or an ethyl group bonded to the carbon at the 2-position of the maleic acid skeleton, or ethylmaleic acid, which has a low melting point and is stable against oxidation and reduction, is particularly preferable. It is preferably used.

Further, it is preferable to use a mixed solvent of maleic anhydride and / or its derivative and a chain carbonate and / or a cyclic carbonate as the above-mentioned solvent. Examples of preferable chain carbonate include dimethyl carbonate and diethyl carbonate. Preferred cyclic carbonates include ethylene carbonate and propylene carbonate.

Of the solvent components of the electrolytic solution used in the present invention, the combined content of maleic anhydride and its derivative is preferably 5 to 90% by volume, more preferably 10 to 80% by volume. Is.

With such a solvent composition disclosed in the present invention, the usable withstand voltage can be dramatically increased and the energy density of the capacitor can be greatly increased.

As the electrolyte (solute) of the electrolytic solution used in the present invention, those which are usually used, for example, cations such as alkali metal ions, alkaline earth metal ions, tetraalkylammonium ions and tetraalkylphosphonium ions, A salt formed by combining an anion selected from tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroarsenate ion, perchlorate ion and trifluoromethanesulfonate ion is preferably used. Among these salts, tetraalkylammonium or tetraalkylphosphonium tetrafluoroborate salts, hexafluorophosphate salts, hexafluorophosphate salts, hexafluorophosphate salts Fluoroarsenate, perchlorate or trifluoromethanesulfonate are particularly suitable electrolytes.

These solutes are added to the above-mentioned solvent in an amount of 0.1-3.
0 mol / liter solvent, preferably 0.4-2.0 m
An electrolytic solution dissolved in a concentration of ol / liter solvent is preferably used.

The material of the polarizable electrode used in the present invention is not particularly limited, but it is preferable to use activated carbon powder or activated carbon fiber which is electrochemically inert to the electrolytic solution and has a large specific surface area. In particular, a binder such as polytetrafluoroethylene is added to the activated carbon powder, roll-formed into a sheet, and more preferably an electrode subjected to a uniaxial or biaxial stretching treatment has a capacity per unit volume,
It is preferably used because it has excellent strength and long-term reliability.

As the separator used in the present invention, a separator usually used in electric double layer capacitors, for example, a separator made of polypropylene fiber non-woven fabric or glass fiber mixed non-woven fabric is preferably used.

[0014]

EXAMPLES Examples and comparative examples of the present invention will now be specifically described with reference to the drawings, but the present invention is not limited to these examples.

As an example and a comparative example of the present invention, FIG.
A unit cell (diameter 20 mm, thickness 2.0 mm) of a coin type electric double layer capacitor as shown in (1) was prepared as follows.

First, activated carbon powder (specific surface area 2000 m ²
/ G) was added with 10% by weight of polytetrafluoroethylene, wet-kneaded, and roll-formed into a sheet.
The sheet thus obtained is punched into a disc shape to form a polarizable electrode 1 (diameter 15 mm, thickness 0.7 mm), and the polarizable electrode 1 and the polarizable electrode 2 having the same composition and shape as the polarizable electrode 1 are formed. It was housed in an outer container made of a stainless steel can 5 with a separator 3 made of polypropylene fiber non-woven fabric sandwiched therebetween. Next, the electrolytic solution having various compositions shown in Table 1 was injected into the unit cell to sufficiently impregnate the polarizable electrodes 1 and 2 and the separator 3 with the electrolytic solution, and then the stainless steel was inserted through the polypropylene packing 6. Steel cap 4
And the end of the can 5 was caulked and sealed to be integrated. In addition,
The electrolyte was used at a concentration of 1.0 mol / liter solvent.

[0017]

[Table 1]

Next, when a unit cell of the electric double layer capacitor prepared as described above is used and a voltage of 3.5 V is applied to each cell using various electrolytic solutions as shown in Table 1, The initial capacity (F ₀ ) and the initial internal resistance of the cell were measured, and then the capacity and the internal resistance were measured after the cell was stored at 70 ° C. for 1000 hours while applying 3.5 V to the cell. Regarding the capacity, the capacity deterioration rate (%) from the initial capacity (F ₀ ) was calculated. The internal resistance was measured at 25 ° C. by the AC two-terminal method (frequency 1 KHz). The measurement results of Examples 1 to 11 and Comparative Examples 1 and 2 are shown in Table 2.

[0019]

[Table 2]

According to Tables 1 and 2, Example 1 of the present invention containing maleic anhydride or a derivative thereof in an amount of 5 to 70% by volume.
In Nos. 11 to 11, an electric double layer capacitor having excellent characteristics with a small rate of change in capacity and a small internal resistance is obtained even at an applied voltage of 3.5 V, which is extremely high as an electric double layer capacitor. Particularly, in Examples 1 to 7 of the present invention containing maleic anhydride or its derivative in an amount of 30 to 70% by volume, the capacity change rate was extremely small,
In addition, the electric resistance of the electric double layer capacitor is extremely small and the electric double layer capacitor has excellent characteristics.

[0021]

According to the present invention, the breakdown voltage is high, and therefore,
An electric double layer capacitor having high energy density is provided. For example, assuming that the withstand voltage of a conventional electric double layer capacitor of the same volume is 2.5 V and the electric capacities when the same voltage is applied are equal, the electrostatic energy that can be stored per unit volume of the cell is (1 / 2) Since it is proportional to CV ² , the energy density of an electric double layer capacitor with a withstand voltage of 3.0V is 1.44 times that of a conventional electric double layer capacitor, and 1. 2 with an electric double layer capacitor of a withstand voltage of 3.5V.
It is 96 times.

When it is necessary to connect the unit cells of the electric double layer capacitor in series to maximize the withstand voltage, the number of connections can be reduced, and as a result, the reduction rate of the capacitance caused by the series connection is reduced. The effect that can be produced also occurs.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of a unit cell of an electric double layer capacitor used in Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 1, 2 ... Polarizable electrode 3 ... Separator 4 ... Cap 5 ... Can 6 ... Packing

Front page continued (72) Inventor Kazuya Hiratsuka 1150, Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Asahi Glass Co., Ltd. Central Research Laboratory (72) Inventor Manahara, 1150, Hazawa-machi, Kanagawa-ku, Yokohama, Japan Asahi Glass Co., Ltd. In the laboratory

Claims (7)

[Claims] 1. An electric double layer capacitor utilizing an electric double layer formed at an interface between a polarizable electrode immersed in an electrolytic solution and the electrolytic solution, wherein the solvent of the electrolytic solution is maleic anhydride and / or its solvent. An electric double layer capacitor containing a derivative. 2. The maleic anhydride derivative is maleic anhydride in which the carbons at the 2 and / or 3 positions of maleic anhydride are substituted with an alkyl group, a methoxy group, an ethoxy group or a halogen. Electric double layer capacitor. 3. The electric double layer capacitor according to claim 1, wherein the solvent of the electrolytic solution contains a mixed solvent of the maleic anhydride and / or its derivative and a chain carbonate and / or a cyclic carbonate. 4. The chain carbonate is dimethyl carbonate and / or diethyl carbonate.
The electric double layer capacitor described. 5. The electric double layer capacitor according to claim 3, wherein the cyclic carbonate is ethylene carbonate and / or propylene carbonate. 6. The electric double layer capacitor according to claim 1, wherein the combined content of the maleic anhydride and its derivative in the solvent of the electrolytic solution is 5 to 90% by volume. . 7. A solute of the electrolytic solution is a cation composed of a tetraalkylammonium ion or a tetraalkylphosphonium ion, and tetrafluoroborate ion, hexafluorophosphate ion, hexafluoroarsenate ion, perchlorate ion. And a anion selected from the group consisting of trifluoromethanesulfonate ion.
The electric double layer capacitor according to any one of items 1 to 6.