JP2007189024A - Electrolytic solution for electric double layer capacitor and electric double layer capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic solution which is capable of giving excellent rate characteristics and long term reliability to an electric double layer capacitor, and to provide the electric double layer capacitor that is formed by using the same. <P>SOLUTION: In the electric double layer capacitor electrolytic solution, its aprotic solvent contains a spiro compound represented by formula (1) (wherein X and Y denote alkyl group or halogen in which the number of carbon atoms amounts 1 to 4, k and i denote 0 or a positive integer of 1 to 4, and n and m denote a number of 3 to 7.) within a range of 0.5 to 3.0 mol/L as an electrolyte, and has a viscosity coefficient of 40 mPa s or below at a temperature of -40°C; and the electrodes the electric double layer capacitor are impregnated with the above electrolytic solution at a temperature of 10°C or below. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electrolytic solution for an electric double layer capacitor and an electric double layer capacitor, and more particularly to an electrolytic solution for an electric double layer capacitor and an electric double layer capacitor excellent in rate characteristics at low temperature and long-term reliability. is there.

  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 in this electric double layer capacitor has a problem that the internal resistance of the capacitor increases when the viscosity of the electrolytic solution is high or the conductivity is low. Especially, it is charged at a high rate of 200 mA or higher at 25 ° C. or lower. When discharging, problems such as a decrease in the apparent capacitance occur, so that low viscosity, high conductivity and long-term durability are required over a wide temperature range.

  In particular, when the viscosity of the electrolyte is high and it is difficult for ions to move, the internal resistance of the capacitor increases during high-rate charge / discharge. Therefore, it is desirable that the viscosity of the electrolyte be as low as possible over a wide temperature range. ing.

  However, in order to reduce the viscosity, it is necessary to use a low dielectric constant solvent in which electrolyte ions are difficult to dissolve, or to greatly reduce the electrolyte ion concentration. In the former case, the electrolyte is deposited at a low temperature. However, in the latter case, the electrolyte ion concentration is insufficient, and there is a possibility that the capacitor cell characteristics are deteriorated.

Conventionally, as an electrolytic solution for an electric double layer capacitor, in consideration of long-term durability, tetraethylammonium tetrafluoroborate (hereinafter referred to as “PC”) in propylene carbonate (hereinafter abbreviated as “PC”). A solution in which a quaternary ammonium salt represented by triethylmethylammonium tetrafluoroborate (hereinafter abbreviated as “TEMA-BF ₄ ”) is dissolved in an electrolyte is abbreviated as “TEA-BF ₄ ”. Generally used (see, for example, Patent Document 1).

  However, when the electrolyte is used at a concentration range of about 0.7 to 1.5 mol / L which does not impair the reliability as an electrolytic solution, the electrolytic solution containing the electrolyte is viscous at an extremely low temperature such as −40 ° C. The rate increases, the charge / discharge characteristics at a high rate are remarkably lowered, and the apparent capacitance is greatly reduced.

  In addition, the electrolyte has a problem that it has almost no solubility in a low dielectric constant solvent.

Further, impregnation of the electrolytic solution into the electric double layer capacitor electrode is generally performed at a medium temperature or a high temperature such as normal temperature or 60 ° C. in consideration of the viscosity of the electrolytic solution. However, it has been pointed out that the system may further generate heat due to the interaction between the electrode and the electrolytic solution, and the deterioration of the electrolytic solution thereby affects the life characteristics of the produced electric double layer capacitor.
JP 2000-114105 A

  Therefore, the object of the present invention is to have a low viscosity at an electrolyte concentration that does not impair the reliability as an electrolytic solution, and excellent rate characteristics, in particular, there is little increase in the viscosity of the electrolytic solution even in a low temperature region, and it is high in a wide temperature range. An object of the present invention is to provide an electrolytic solution for an electric double layer capacitor that exhibits electrical conductivity and can be impregnated into an electrode at a low temperature and has excellent long-term reliability, and an electric double layer capacitor using the electrolytic solution.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that tetrafluoroborates represented by spiro- (1,1 ′)-spirobipyrrolidinium tetrafluoroborate in an aprotic solvent. Electrolytic solution in which acid quaternary spiro ammonium is dissolved has a low viscosity in a wide temperature range even at an electrolyte concentration that does not impair reliability as an electrolytic solution, and an apparent capacitance even at high rate charge / discharge in a low temperature region As a result, the present invention has been found to be excellent in long-term reliability.

（式中、Ｘ及びＹは、炭素数１〜４のアルキル基またはハロゲンを、ｋ及びｉは、０ま
たは１〜４の正整数を、ｎ及びｍは３〜７の数を示す）
で表されるスピロ化合物を電解質として０.５〜３.０ｍｏｌ／Ｌの範囲で含有し、その粘性率が、−４０℃において、４０ｍＰａ・ｓ以下であることを特徴とする電気二重層キャパシタ用電解液である。 That is, the present invention relates to the general formula [1] in an aprotic solvent.

(In the formula, X and Y are alkyl groups having 1 to 4 carbon atoms or halogen, k and i are 0 or a positive integer of 1 to 4, and n and m are 3 to 7)
For an electric double layer capacitor characterized in that it contains a spiro compound represented by the formula as an electrolyte in the range of 0.5 to 3.0 mol / L, and its viscosity is 40 mPa · s or less at −40 ° C. Electrolytic solution.

  In addition, the present invention is an electric double layer capacitor characterized by impregnating an electric double layer capacitor electrode with the above electrolytic solution at 10 ° C. or less, and a method for producing the same.

  The electrolytic solution for an electric double layer capacitor of the present invention is obtained by dissolving quaternary spiro ammonium tetrafluoroborate as an electrolyte in an aprotic solvent, and the electrolytic solution does not impair the reliability as the electrolytic solution. It exhibits low viscosity and excellent low-temperature characteristics at the electrolyte concentration, and also exhibits high conductivity over a wide temperature range.

  Therefore, the electric double layer capacitor produced using the electrolytic solution of the present invention has a low internal resistance over a wide temperature range, a low capacitance decrease rate and a high internal resistance increase rate even when operated at a high voltage, and a high Even if the rate charge / discharge is performed, the apparent capacitance does not decrease, the withstand voltage is high, and the long-term reliability is excellent.

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

（式中、Ｘ及びＹは、炭素数１〜４のアルキル基またはハロゲンを、ｋ及びｉは、０ま
たは１〜４の正整数を、ｎ及びｍは３〜７の数を示す）
で表されるテトラフルオロホウ酸第４級スピロアンモニウムを電解質として溶解させたものである。このテトラフルオロホウ酸第４級スピロアンモニウムは、非プロトン性溶媒への溶解度が高く、高濃度の電解液を調製することが可能であり、得られた電解液は、電解質濃度が高くても、広い温度範囲において、低粘性率、高電導度及び優れた低温特性を示す。 The electrolytic solution for an electric double layer capacitor of the present invention (hereinafter referred to as “the electrolytic solution of the present invention”) is mixed with the following general formula [1] in an aprotic solvent.

(In the formula, X and Y are alkyl groups having 1 to 4 carbon atoms or halogen, k and i are 0 or a positive integer of 1 to 4, and n and m are 3 to 7)
The quaternary spiro ammonium tetrafluoroborate represented by these is dissolved as an electrolyte. This quaternary spiroammonium tetrafluoroborate has high solubility in an aprotic solvent, and it is possible to prepare a high concentration electrolytic solution. Even if the obtained electrolytic solution has a high electrolyte concentration, It exhibits low viscosity, high conductivity and excellent low temperature characteristics over a wide temperature range.

Examples of the quaternary spiroammonium tetrafluoroborate represented by the general formula [1] used in the electrolytic solution of the present invention include, for example, azacyclobutane-1-spiro-1′-azacyclobutyl tetrafluoroborate, tetra Pyrrolidine-1-spiro-1′-azacyclobutyl fluoroborate, spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate, piperidine-1-spiro-1′-pyrrolidinium tetrafluoroborate, tetrafluoroboric acid Spiro- (1,1 ′)-bipiperidinium, 3-ethylpyrrolidinium tetrafluoroborate-1-spiro-1′-pyrrolidinium, 3-ethylpyrrolidinium tetrafluoroborate-1-spiro-1 ′-( 3'-ethyl) pyrrolidinium, 2,4-difluoropyrrolidinium tetrafluoroborate-1-s B-1'-pyrrolidinium tetrafluoroborate 2,4-difluoro pyrrolidinium-1-spiro-1 '- (2', 4'-difluorophenyl) include pyrrolidinium. Among these, in particular, spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate (hereinafter abbreviated as “SBP-BF ₄ ”) and piperidine-1-spiro-1′-pyrrolidinium tetrafluoroborate (hereinafter referred to as “SBP-BF ₄ ”) And abbreviated as “PSP-BF ₄ ”).

  The aprotic solvent used in the electrolytic solution of the present invention is not particularly limited as long as it is generally used in an electrolytic solution for an electric double layer capacitor. However, PC, dimethyl carbonate (hereinafter, “DMC”) ), Ethylene carbonate (hereinafter abbreviated as “EC”), sulfolane, fluorinated carbonate, and the like. Among these, considering the solubility, conductivity, temperature characteristics of the electrolyte, durability of the electrolyte, toxicity, etc., those selected from PC, EC or DMC are preferred, and two or more of them are used in combination. May be.

  The electrolytic solution of the present invention contains the quaternary spiroammonium tetrafluoroborate in the aprotic solvent in the range of 0.5 to 3.0 mol / L, preferably 0.5 to 2.5 mol / L. Manufactured by dissolving in a range of concentrations. If the concentration of quaternary spiroammonium tetrafluoroborate is 0.5 mol / L or less, the conductivity is insufficient and disadvantageous. If it exceeds 3.0 mol / L, the low-temperature characteristics are remarkably deteriorated and economically. It is inferior and inconvenient.

  The viscosity of the electrolytic solution of the present invention thus obtained is 40 mPa · s or less, preferably about 10 to 35 mPa · s at −40 ° C. In addition, the electrolytic solution of the present invention has the above-mentioned characteristics and has a low viscosity in a wide temperature range even at an electrolyte concentration that does not impair the reliability as an electrolytic solution. Therefore, it is 200 mA or more at −40 ° C. to 25 ° C., preferably It is suitable for high rate charge / discharge of about 200 mA to 1000 mA.

  The electrolyte solution of the present invention described above may be further mixed with additives other than the electrolyte as necessary. Examples of such additives include vinyl group-containing compounds such as vinylene carbonate and succinimide compounds such as benzyloxycarbonyloxysuccinimide.

  Although there is no limitation in particular in content of this additive, 0-3 mass% is preferable with respect to the whole electrolyte solution, Most preferably, it is 0.1-1 mass%.

  The production of the electric double layer capacitor using the electrolytic solution of the present invention can be carried out by a conventional method, but when impregnating the polarizable electrode with the electrolytic solution, it is preferably 10 ° C. or lower. When the electric double layer capacitor is produced, the impregnation temperature of the electrolyte solution of the present invention into the polarizable electrode is preferably as low as 10 ° C. or lower, but it is preferably performed at −20 to 10 ° C. in consideration of economy. . Specifically, an electric double layer capacitor is manufactured by impregnating two polarizable electrodes sandwiching a separator with the electrolytic solution of the present invention as a driving electrolytic solution at a pressure of about 100 mmHg and 10 ° C. or less, and then stainless steel or the like. It can carry out by accommodating in an exterior case.

  As the polarizable electrode used in the electric double layer capacitor, carbon materials such as activated carbon powder and activated carbon fibers, noble metal oxide materials, conductive polymer materials, and the like are used, and carbon materials are preferable because they are 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.

  The electric double layer capacitor of the present invention thus obtained is excellent in rate characteristics at low temperatures and long-term reliability. Specifically, when a coin type capacitor having a rated voltage of 2.7 V and a capacitance of 2.5 F is manufactured as the electric double layer capacitor of the present invention, it is 200 mA or more, preferably 200 mA or more at −40 to 25 ° C. Even at a high rate charge / discharge of 1000 mA, the apparent capacitance is 20% or more, preferably 30% or more at the start of charge / discharge. The coin-type electric double layer capacitor has a capacitance after 90 hours at 2.7 V 60 ° C. of 90% or more, preferably 95% or more of the initial capacitance.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples at all.

Example 1
Preparation of electrolyte for electric double layer capacitor (1):
An electrolytic solution for an electric double layer capacitor having an SBP-BF ₄ concentration of 1.5 mol / L is prepared by dissolving SBP-BF ₄ (spiro-tetrafluoroborate- (1,1 ′)-bipyrrolidinium tetrafluoroborate) as an electrolyte in PC. Prepared.

Example 2
Preparation of electrolyte for electric double layer capacitor (2):
An electrolytic solution for an electric double layer capacitor was prepared in the same manner as in Example 1, except that PSP-BF ₄ (piperidine-1-spiro-1′-pyrrolidinium tetrafluoroborate) was used as the electrolyte.

Comparative Example 1
Preparation of electrolyte for comparative electric double layer capacitor (1):
An electrolytic solution for an electric double layer capacitor was prepared in the same manner as in Example 1 except that TEMA-BF ₄ having a concentration of 1.5 mol / L was used as the electrolyte.

Comparative Example 2
Preparation of electrolyte for comparative electric double layer capacitor (2):
An electrolytic solution for an electric double layer capacitor was prepared in the same manner as in Example 1 except that TEA-BF ₄ having a concentration of 1.0 mol / L was used as the electrolyte.

Test example 1
Measurement of electrolyte viscosity:
The electrolytic solutions for electric double layer capacitors prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were −40 ° C., −30 ° C., −20 ° C., −10 ° C., 0 ° C., 10 ° C. and 25 ° C. The viscosity at each temperature was measured. The results are shown in FIG.

  As shown in FIG. 1, the electrolytes of the present invention (Examples 1 and 2) have a lower viscosity in a wide temperature range than the conventional general electrolytes (Comparative Examples 1 and 2). Showed the rate.

Test example 2
Life characteristics evaluation of electric double layer capacitors:
A sheet having a thickness of 0.4 mm was prepared by kneading and rolling 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 with a roll. This sheet was punched to a diameter of 13 mmφ to produce a disk-shaped polarizable electrode.

  Polypropylene separators are sandwiched between the two disk-like polarizable electrodes, and the electrolyte solutions of Examples 1, 2 and 1 and 2 are added to the electrodes at the temperatures shown in Table 1. The impregnation was performed under a vacuum degree of 100 mmHg. Table 1 shows the ratio to the theoretical filling amount calculated from the void volume of the electrode. Thereafter, this was housed in a stainless steel outer case to complete a coin-type electric double layer capacitor having a rated voltage of 2.7 V and a capacitance of 2.5 F. The obtained electric double layer capacitor was subjected to a life test of a cell impregnated with an electrolytic solution at each temperature at 2.7 V 60 ° C., and the capacitance after 1000 hours when compared with the initial capacitance was measured. The ratio was evaluated. The results are shown in Table 2. In addition, Table 3 shows the life test evaluation results (capacitance ratio after 1000 hours) of the electric double layer capacitor produced at the lowest temperature at which an impregnation rate of 98% was obtained.

  As shown in the table above, the polarizable electrode could be impregnated with the electrolyte solution of the example at a lower temperature than the electrolyte solution of the comparative example. In addition, the coin-type electric double layer capacitor of the example was superior in life characteristics to that of the comparative example.

Test example 3
Rate characteristics evaluation of electric double layer capacitor:
A sheet having a thickness of 0.4 mm was prepared by kneading and rolling 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 with a roll. This sheet was punched to a diameter of 13 mmφ to produce a disk-shaped polarizable electrode.

  A polypropylene separator is sandwiched between the two disk-like polarizable electrodes, and the electrolytes of Examples 1, 2 and 1 and 2 are evacuated at −20 ° C. and 100 mmHg. Impregnated at a degree. Thereafter, this was housed in a stainless steel outer case to complete a coin-type electric double layer capacitor having a rated voltage of 2.7 V and a capacitance of 2.5 F.

  The capacitance of this electric double layer capacitor was determined as follows. First, each electric double layer capacitor was charged at a constant voltage of 2.7 V for 10 minutes in a thermostatic chamber set at 25 ° C., and then allowed to stand for 2 hours to stabilize the temperature inside the capacitor. It was. Thereafter, a constant voltage charge of 2.7 V is performed again for 10 minutes, and then the voltage when discharging is performed to a predetermined voltage at a discharge rate of 2 mA, 5 mA, 10 mA, 20 mA, 30 mA, 50 mA, 100 mA, 300 mA, 500 mA, and 900 mA. From the gradient, the apparent capacitance was determined. The results are shown in FIG.

  As shown in FIG. 2, the electric double layer capacitor using the electrolytic solution of the present invention (Examples 1 and 2) is compared with the electric double layer capacitor using the general electrolytic solution (Comparative Examples 1 and 2). In addition, excellent capacitor characteristics were exhibited even when charging / discharging at a very high rate of 900 mA. In addition, according to this test example, it was found that a slight viscosity difference greatly affects the rate characteristics, with the viscosity of the electrolyte solution at −40 ° C. near 40 mPa · s as a threshold value.

  The electrolytic solution for an electric double layer capacitor exhibiting a viscosity of 40 mPa · s or less at −40 ° C. of the present invention and the electric double layer capacitor produced using the electrolytic solution have excellent capacitor characteristics over a wide temperature range. It can be used in a wide range of industrial fields from small electronic devices to large-sized automobiles.

FIG. 1 is a drawing showing the relationship between the temperature and viscosity of the electrolytic solution for an electric double layer capacitor prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2. FIG. 2 shows the discharge rate and the apparent capacitance of the electric double layer capacitor produced using the electrolytic solution for the electric double layer capacitor prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2. It is drawing which showed the relationship.

Claims (8)

In an aprotic solvent, the formula [1]

(Wherein X and Y are alkyl groups having 1 to 4 carbon atoms or halogen, k and i are 0 or a positive integer of 1 to 4, and n and m are 3 to 7)
For an electric double layer capacitor characterized in that it contains a spiro compound represented by the formula as an electrolyte in the range of 0.5 to 3.0 mol / L, and its viscosity is 40 mPa · s or less at −40 ° C. Electrolytic solution.   2. The electricity according to claim 1, wherein the spiro compound represented by the formula [1] is spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate or piperidine-1-spiro-1′-pyrrolidinium tetrafluoroborate. Electrolyte for double layer capacitors.   The electrolysis for electric double layer capacitor according to any one of claims 1 to 2, wherein the aprotic solvent is one or more aprotic solvents selected from propylene carbonate, ethylene carbonate or dimethyl carbonate. liquid.   The sprit- (1,1 ')-bipyrrolidinium tetrafluoroborate is contained in the aprotic solvent in the range of 0.5 to 3.0 mol / L. Electrolyte for electric double layer capacitors according to claim.   The aprotic solvent contains piperidine-1-spiro-1'-pyrrolidinium tetrafluoroborate in a range of 0.5 to 3.0 mol / L. Electrolyte for electric double layer capacitors according to claim.   The electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 5, which is for charging and discharging at a high rate of 200 mA or more.   An electric double layer capacitor, wherein a polarizable electrode is impregnated with the electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 6 at 10 ° C or lower. A method for producing an electric double layer capacitor, comprising impregnating a polarizable electrode with the electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 6 at 10 ° C or lower.

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