JP4908236B2 - Electrolytic solution for electric double layer capacitor and electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for an electric double-layer capacitor that has high heat resistance and durability and is superior in withstand voltage, and does not coagulate in a wide temperature range at high electric conductivity, and to provide an electric double-layer capacitor. <P>SOLUTION: The electric double-layer capacitor is made by dissolving quaternary ammonium tetrafluoroborate represented by a general formula [1] in a mixed solvent of sulfolane and chain-like sulfone, and the electric double-layer capacitor is manufactured by using the electrolyte. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an electrolytic solution for an electric double layer capacitor and an electric double layer capacitor using the same.

  An electric double layer capacitor is a charge storage device using an electric double layer formed at the interface between a polarizable electrode and an electrolyte.

  The electrolytic solution used for the electric double layer capacitor is required to be electrochemically stable so as not to react with the activated carbon electrode during charging, and to be liquid in a wide temperature range.

Conventionally, an electrolytic solution for an electric double layer capacitor is made of a quaternary ammonium salt typified by tetraethylammonium tetrafluoroborate (hereinafter abbreviated as “TEA-BF ₄ ”), particularly considering electric conductivity. A solution in which an electrolyte is dissolved in propylene carbonate (hereinafter abbreviated as “PC”) is generally used (see, for example, Patent Document 1).

  However, since the PC solvent reacts with the activated carbon electrode at a temperature exceeding 70 ° C., for example, when charged at 2.7 V, the electric double layer capacitor produced using the electrolytic solution has a limit of about 60 to 70 ° C. in heat resistance. There were drawbacks.

  A solvent comprising a sulfone compound such as sulfolane (hereinafter abbreviated as “SL”) has high heat resistance, and an electrolytic solution in which an electrolyte is dissolved in the solvent has a temperature of about 80 ° C. when charged at 2.7 V. It has heat resistance and is expected to have a withstand voltage of 3.0 V or more at about 60 ° C. On the other hand, SL has a freezing point of 28 ° C., and methylsulfolane having a lower freezing point has a temperature of 6 ° C. Therefore, the electrolyte containing the solvent solidifies in a low temperature region, and the electric double layer capacitor cannot be used. (See Patent Documents 2 to 3).

  In order to enable the operation of a capacitor at a low temperature, it has been proposed to use a mixed solvent in which a chain carbonate having a low viscosity is mixed with SL. However, the chain carbonate has a lower withstand voltage than SL, and SL An electrolytic solution using a mixed solvent in which a chain carbonate is mixed with is insufficient in terms of high heat resistance and high voltage resistance of SL. (See Patent Document 4).

Further, triethylmethylammonium tetrafluoroborate (hereinafter abbreviated as “TEMA-BF ₄ ”) and TEA-BF _{4 that} are generally used as electrolytes for electrolytic solutions for electric double layer capacitors are used at high voltage. There is a drawback that Hoffman decomposition is caused during charging and the ethyl group is easily detached.

JP 2000-114105 A JP H06-275468 A Japanese Patent Laid-Open No. H03-32203 JP H08-306591 A

  An object of the present invention is to provide an electrolytic solution for an electric double layer capacitor that has high heat resistance and durability, is excellent in withstand voltage, exhibits high electrical conductivity, and does not cause solidification in a wide temperature range. Another object of the present invention is to provide a highly reliable electric double layer capacitor using the electrolytic solution.

As a result of intensive studies, the present inventors have abbreviated as tetrafluoroborate spiro- (1,1 ′)-bipyrrolidinium (hereinafter “SBP-BF ₄ ”) to a mixed solvent containing SL and chain sulfone. And / or tetrafluoroborate spiro quaternary ammonium typified by piperidine-1-spiro-1′-pyrrolidinium tetrafluoroborate (hereinafter abbreviated as “PSP-BF ₄ ”). It has been found that the electrolyte solution made has high heat resistance and durability and high withstand voltage due to containing SL, and does not cause solidification in a wide temperature range by containing chain sulfone. The present invention has been completed.

  That is, in the present invention, a tetrafluoroborate spiro quaternary ammonium represented by the following general formula [1] and / or [2] is dissolved as an electrolyte in a mixed solvent containing SL and chain sulfone. An electrolytic solution for an electric double layer capacitor.

  The present invention also provides the electrolytic solution for an electric double layer capacitor, wherein the capacity mixing ratio of the SL and the chain sulfone is 70:30 to 90:10.

  The type of chain sulfone is not particularly limited, but a chain sulfone represented by the following general formula [3] is preferable.

（式中、Ｒ_１及びＲ_２はそれぞれ同一であっても異なっていてもよい直鎖又は分岐鎖のアルキル基を示す。）

(In the formula, R ₁ and R ₂ each represent a linear or branched alkyl group which may be the same or different.)

In the above formula [3], R ₁ and R ₂ are each preferably a linear or branched alkyl group having 1 to 3 carbon atoms which may be the same or different. Specific examples of the chain sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, propyl methyl sulfone, isopropyl methyl sulfone, propyl ethyl sulfone, isopropyl ethyl sulfone, dipropyl sulfone, diisopropyl sulfone, and the like. The above mixture is mentioned. Among these, dimethyl sulfone, ethyl methyl sulfone, and isopropyl methyl sulfone are more preferable.

  Furthermore, the present invention is an electric double layer capacitor in which a polarizable electrode sandwiching a separator is impregnated with the electrolytic solution for electric double layer capacitor, and this is sealed in a container.

  The electrolytic solution for an electric double layer capacitor of the present invention is obtained by dissolving a spiro quaternary ammonium tetrafluoroborate as an electrolyte in a mixed solvent containing SL and a chain sulfone, and the electrolytic solution has high heat resistance. It exhibits high performance and durability, and does not cause solidification over a wide temperature range with high conductivity. In particular, an electrolytic solution for an electric double layer capacitor having an SL capacity mixing ratio of 70 to 90 and a chain sulfone capacity mixing ratio of 10 to 30 in the mixed solvent has a wider driving temperature and extremely excellent heat resistance.

  In addition, the electric double layer capacitor manufactured using the electrolytic solution of the present invention has high reliability, high withstand voltage, high conductivity, and is effectively driven in a wide temperature range.

  Hereinafter, the electrolytic solution for electric double layer capacitor of the present invention will be described in detail.

  The electrolytic solution for an electrolytic double layer capacitor of the present invention is a tetrafluoroboric acid spiro quaternary quaternary compound represented by the general formula [1] and / or [2] in a mixed solvent containing SL and chain sulfone. Ammonium is dissolved as an electrolyte.

  Tetrafluoroborate spiro-type quaternary ammonium has high stability, can be dissolved in a mixed solvent of SL and chain sulfone at a high concentration, and an electrolyte with an extremely high withstand voltage can be prepared. is there.

  The mixing ratio of the SL and the chain sulfone in the mixed solvent is preferably such that the volume mixing ratio of SL is 70 to 90, and the volume mixing ratio of the chain sulfone is 10 to 30, more preferably, the SL is 75 to 85, the chain. In the case where the shape of the sulfone is 15 to 25, when the SL is more than 90 and the chain sulfone is less than 10, the effect of improving the withstand voltage, which is the addition effect of the chain sulfone, is inferior. If it exceeds 30, chain sulfone precipitates in the electrolyte at a low temperature, and the electric double layer capacitor characteristics may be deteriorated.

  In addition to SL and chain sulfone, other solvents or additives can be added as long as the durability of the electrolytic solution and the electric double layer capacitor is not deteriorated.

  The concentration of the tetrafluoroborate spiro-type quaternary ammonium in the electrolytic solution is more than 0.5 mol / L and not more than 3.0 mol / L, preferably more than 0.7 mol / L and not more than 2.0 mol / L. . If it is 0.5 mol / L or less, the electric conductivity is insufficient, which is inconvenient, and if it exceeds 3.0 mol / L, the low-temperature characteristics are remarkably lowered and the economy is inferior.

  The electric double layer capacitor of the present invention is manufactured by impregnating a polarizable electrode sandwiching a separator with the electrolytic solution of the present invention as a driving electrolytic solution, and then housing it in an outer case made of stainless steel or the like.

  As the polarizable electrode, a carbon material such as activated carbon powder or activated carbon fiber, a noble metal oxide material, a conductive polymer material, or the like is used. A carbon material is preferable because it is inexpensive. Moreover, as a separator, the separator which consists of well-known raw materials, such as polyethylene and a polypropylene-type nonwoven fabric, can be used.

  The electric double layer capacitor of the present invention can be produced in a shape such as a film type, a coin type, a cylindrical type, and a box shape, and is not particularly limited.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited at all by the Example.

Example 1
SBP-BF ₄ that is an electrolyte is dissolved in a mixed solvent in which the volume mixing ratio of SL and dimethyl sulfone (hereinafter abbreviated as “DMS”) is 80 and 20, respectively, and an electric concentration of 1.0 mol / L is obtained. An electrolyte for a double layer capacitor was prepared.

Separately, as a polarizable electrode, 90% by mass of activated carbon powder (particle diameter 20 μm, specific surface area 2,000 m ² / g) and 10% by mass of polytetrafluoroethylene powder were kneaded and rolled to a thickness of 0.4 mm. A sheet was produced. This sheet was punched into a diameter of 13 mmφ to produce a disk-shaped electrode.

  A polypropylene separator is sandwiched between two disk-shaped electrodes, and the electrolyte prepared above is vacuum-impregnated, and then accommodated in a stainless steel outer case. A coin having a rated voltage of 3.2 V and a capacitance of 1.5 F Type electric double layer capacitor was completed.

  The completed capacitor was subjected to a long-term reliability test by applying a voltage of 3.5 V for 1,000 hours in a thermostat at a temperature of 70 ° C. Table 1 shows the initial capacitance value and the change rate (%) of the capacitance value and capacitance after 1000 hours, and the change rate (%) of the internal resistance value and the internal resistance value. The capacitance of the capacitor is obtained from a voltage gradient when charged at a voltage of 3.5 V for 1 hour and then discharged at 1 mA, and the values in the table are average values of measured values of 15 samples.

  A similar test was performed in a thermostat bath at temperatures of 25 ° C., 0 ° C., −10 ° C., −20 ° C., and −30 ° C., and the capacitance value and internal resistance value at each temperature are shown in Table 2.

Example 2
In Example 1, except that PSP-BF4 was used as the electrolyte, an electrolytic solution for an electric double layer capacitor was obtained in the same manner, and the results of long-term reliability tests and temperature characteristics are shown in Tables 1 and 2, respectively.

Example 3
Table 1 shows the results obtained by conducting the long-term reliability test in the same manner as in Example 1 except that the SL and DMS capacity mixing ratios were set to 75 and 25, respectively.

Example 4
In Example 3, the electrolytic double layer capacitor electrolyte solution was obtained in the same manner except that PSP-BF4 was used as the electrolyte, and the results of long-term reliability tests are shown in Table 1.

Example 5
Table 1 shows the results of long-term reliability tests performed in the same manner as in Example 3 except that the capacity mixing ratios of SL and DMS were set to 85 and 15, respectively.

Example 6
In Example 5, the electrolytic double layer capacitor electrolyte solution was obtained in the same manner except that PSP-BF4 was used as the electrolyte, and the results of long-term reliability tests are shown in Table 1.

Example 7
In Example 1, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that isopropylmethylsulfone (hereinafter abbreviated as “IMS”) was used as the chain sulfone. The characteristics are shown in Table 1 and Table 2, respectively.

Example 8
In Example 2, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that isopropylmethylsulfone (hereinafter abbreviated as “IMS”) was used as the chain sulfone. The characteristics are shown in Table 1 and Table 2, respectively.

Example 9
In Example 1, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that ethyl methyl sulfone (hereinafter abbreviated as “EMS”) was used as the chain sulfone. The characteristics are shown in Table 1 and Table 2, respectively.

Example 10
In Example 2, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that ethyl methyl sulfone (hereinafter abbreviated as “EMS”) was used as the chain sulfone. The characteristics are shown in Table 1 and Table 2, respectively.

Comparative Example 1
In Example 1, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that TEA-BF4 was used as the electrolyte, and results of long-term reliability tests are shown in Table 1.

Comparative Example 2
In Example 1, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that TEMA-BF4 was used as the electrolyte, and results of long-term reliability tests are shown in Table 1.

Comparative Example 3
In Example 1, an electrolytic solution for an electric double layer capacitor was obtained in the same manner except that a pure SL solution of SBP-BF4 (hereinafter, abbreviated as “SBP-BF4 / SL”) was used as the electrolytic solution. Table 1 and Table 2 show the test results and temperature characteristics, respectively.

Comparative Example 4
In Example 1, an electrolytic solution for an electric double layer capacitor was similarly obtained except that a PC solution of SBP-BF4 (hereinafter, abbreviated as “SBP-BF4 / PC”) was used as the electrolytic solution, and a long-term reliability test was performed. Table 1 and Table 2 show the results of the measurement and temperature characteristics, respectively.

Comparative Example 5
In Example 1, an electric double layer capacitor was similarly used except that SBP-BF4 PC and an ethyl methyl carbonate solution (hereinafter abbreviated as “SBP-BF4 / PC + EMC”) as a chain carbonate were used as the electrolyte. Tables 1 and 2 show the results and temperature characteristics of the electrolytic solutions obtained and the long-term reliability tests.

  2. From Table 1, only the electrolyte prepared by dissolving the spiro-type quaternary ammonium tetrafluoroborate represented by the general formula [1] and / or [2] in a mixed solvent of SL and chain sulfone. It is apparent that the conventional electrolytic solution for electric double layer capacitors of 5 V shows high durability even in a reliability test under a remarkably high voltage application condition.

  Also, from Table 2, an electrolyte prepared by dissolving a spiro quaternary ammonium tetrafluoroborate represented by the general formula [1] and / or [2] in a mixed solvent of SL and a chain sulfone is widely used. Capacitor characteristics could be developed without solidification in a wide temperature range.

  Therefore, only the electrolytes obtained by dissolving the tetrafluoroborate spiro quaternary ammonium of Examples 1 to 10 in a mixed solvent of SL and chain sulfone have a high withstand voltage, extremely high durability, and a wide range. It is clear that it can be used in a wide temperature range. In addition, it can be confirmed that electric double layer capacitors fabricated using these electrolytes have high reliability, high voltage resistance, and improved operating characteristics in a wide temperature range, and all of these have excellent characteristics. It was.

  By using an electrolytic solution in which the tetrafluoroborate spiro-type quaternary ammonium of the present invention is dissolved in a mixed solvent of SL and a chain sulfone, the electric double layer capacitor is improved in withstand voltage and in a wide temperature range. An electric double layer capacitor that can be used and manufactured using the electrolytic solution can be used in a wide range of industrial fields from small electronic devices to large automobiles.

Claims (2)

The following general formula 1,

And / or the following general formula 2,

In the quaternary ammonium tetrafluoroborate represented is Ri Na is dissolved in a mixed solvent containing sulfolane and chain sulfone volume mixing ratio 70:30 to 90:10, the chain sulfone is dimethyl sulfone and / or electrolytic solution for an electric double layer capacitor, wherein ethylmethyl sulfone der Rukoto.   An electric double layer capacitor obtained by impregnating a polarizable electrode sandwiching a separator with the electrolytic solution for an electric double layer capacitor according to claim 1 and sealing the same in a container.