JP2009218398A - Electrolyte and electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte which has superior cycle characteristic even in a long term and improves reliability of an electrochemical device, and to provide the electrochemical device. <P>SOLUTION: This electrolyte for electric double-layer capacitor contains a compound represented by a specific formula (1) (Y is an anion) and a compound represented by a specific formula (2) (X is an anion). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrolytic solution that reduces a decrease in capacitance and improves the reliability of an electrochemical device, and an electrochemical device using the same.

  An electrochemical device such as an electric double layer capacitor using a non-aqueous electrolyte has a characteristic that cycle characteristics are better than a lithium secondary battery. However, further improvement in characteristics is required for long-term use.

  As a means for solving such a problem, a non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution in which a lithium salt is dissolved in an organic solvent is used. As the non-aqueous electrolyte, a non-aqueous electrolyte secondary battery to which a salt having tropylium as a cation is added is disclosed (for example, Patent Document 1).

According to Patent Document 1, the coating on the surface of the negative electrode active material formed when a non-aqueous electrolyte containing a tropylium cation is used prevents the reaction between the charged negative electrode and the non-aqueous electrolyte. Presumed to have.
JP 2000-113905 A

  The subject of this invention is providing the electrolyte solution and electrochemical device which are excellent in cycling characteristics also in the long term, and improve the reliability of an electrochemical device.

  The present invention relates to the following inventions.

1. An electrolytic solution for an electric double layer capacitor comprising a compound represented by the formula (1) and a compound represented by the formula (2).

（Ｒ^１およびＲ^２は、互いに同一または異なってメチル基、エチル基、メトキシメチル基、エトキシメチル基を示し、Ｒ^１およびＲ^２で環構造を形成しても良い。Ｙは、アニオンである。）

(R ¹ and R ² may be the same or different and each represents a methyl group, an ethyl group, a methoxymethyl group or an ethoxymethyl group, and R ¹ and R ² may form a ring structure. Y is an anion. .)

〔Ｘは、アニオンである。〕

[X is an anion. ]

2. Further, an electrolytic solution containing an organic solvent.
3. An electrolytic solution in which the compound represented by the formula (2) is tropinium tetrafluoroborate or tropinium hexafluorophosphate.
4). An electrolytic solution in which the organic solvent is propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or γ-butyrolactone.
5. An electrochemical device using the above electrolytic solution.
6). Electric double layer capacitor using the above electrolyte.

  The electrolytic solution of the present invention can reduce a decrease in capacitance and improve the reliability of an electrochemical device. Surprisingly, the electrolytic solution of the present invention also has an effect that it does not express in advance an electrostatic capacity that easily deteriorates. As a result, the electrochemical device using the electrolytic solution of the present invention can improve reliability.

  The electrolytic solution for electric double layer capacitors of the present invention is an electrolytic solution for electric double layer capacitors containing a compound represented by formula (1) and a compound represented by formula (2).

（Ｒ^１およびＲ^２は、互いに同一または異なってメチル基、エチル基、メトキシメチル基、エトキシメチル基を示し、Ｒ^１およびＲ^２で環構造を形成しても良い。Ｙは、アニオンである。）

(R ¹ and R ² may be the same or different and each represents a methyl group, an ethyl group, a methoxymethyl group or an ethoxymethyl group, and R ¹ and R ² may form a ring structure. Y is an anion. .)

〔Ｘは、アニオンである。〕

[X is an anion. ]

Examples of R ¹ and R ² of the compound represented by the formula (1) include a methyl group, an ethyl group, a methoxymethyl group, and an ethoxymethyl group. Examples of the ring structure formed by R ¹ and R ² include a pyrrolidine ring.

Examples of the anion of Y of the compound represented by the formula (1) used in the present invention include BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ and N (CF ₃ SO ₂ ). ^{_{2 -, N (CF 3 CF}} 2 SO 2) 2 -, C (CF 3 SO 2) 3 -, N (CF 3 SO 2) (CF 3 CO) -, AlF 4 -, ClBF 3 -, (FSO 2 ) ₂ N ⁻ , C ₂ F ₅ BF ₃ ⁻ , CF ₃ BF ₃ ^{— and the} like.

Specific examples of the compound (1) include the following compounds.
N-ethyl-N-methylpyrrolidinium tetrafluoroborate, N, N-diethylpyrrolidinium tetrafluoroborate, N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, N-ethyl-N-methoxymethylpyrrole Dinium tetrafluoroborate, N-methyl-N-ethoxymethylpyrrolidinium tetrafluoroborate, N-ethyl-N-ethoxymethylpyrrolidinium tetrafluoroborate, spiro- (1,1 ′)-bipyrrolidinium tetra Examples thereof include fluoroborate.

Of these, compounds that are liquid at 25 ° C. are preferred, for example, N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, N-methyl-N-ethoxymethylpyrrolidinium tetrafluoroborate, N-ethyl-N— Mention may be made of ethoxymethylpyrrolidinium tetrafluoroborate.
Examples of the X anion of the compound represented by the formula (2) include BF ₄ ⁻ and PF ₆ ^— . Specific examples of compound (2) include tropinium tetrafluoroborate and tropinium hexafluorophosphate. These compounds are known compounds and can be synthesized by known methods.

The electrolytic solution of the present invention may use an organic solvent as necessary. Examples of the organic solvent include cyclic carbonate ester, chain carbonate ester, phosphate ester, cyclic ether, chain ether, lactone compound, chain ester, nitrile compound, amide compound, sulfone compound and the like.
Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, 4-fluoro-1,3-dioxolan-2-one, 4- (trifluoromethyl) -1,3-dioxolan-2-one, and the like. Of these, ethylene carbonate and propylene carbonate are preferable.

  As chain carbonate ester, dimethyl carbonate, ethyl methyl carbonate, methyl normal propyl carbonate, methyl isopropyl carbonate, normal butyl methyl carbonate, diethyl carbonate, ethyl normal propyl carbonate, ethyl isopropyl carbonate, normal butyl ethyl carbonate, dinormal propyl carbonate, Examples include diisopropyl carbonate, dinormal butyl carbonate, fluoroethyl methyl carbonate, difluoroethyl methyl carbonate, and trifluoroethyl methyl carbonate, and dimethyl carbonate and ethyl methyl carbonate are preferable.

Examples of the phosphate ester include trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, and the like.
Examples of the cyclic ether include tetrahydrofuran and 2-methyltetrahydrofuran.
Examples of the chain ether include dimethoxyethane.
Examples of the lactone compound include γ-valerolactone and γ-butyrolactone.
Examples of the chain ester include methyl propionate, methyl acetate, ethyl acetate, and methyl formate.
Examples of the nitrile compound include acetonitrile.
Examples of the amide compound include dimethylformamide.
Examples of the sulfone compound include, but are not limited to, sulfolane and methyl sulfolane.

A cyclic carbonate, a chain carbonate, a lactone compound, and a sulfone compound are preferable.
These solvents may be used alone or in combination of two or more.

In the electrolytic solution of the present invention, the content of the compound represented by the formula (1) is 0.005 to 90% by weight, preferably 0.01 to 50% by weight, more preferably 0.1 to 0.1% by weight in the electrolytic solution. 10% by weight is good.
In the electrolytic solution of the present invention, the content of the compound represented by the formula (2) is 0.005 to 90% by weight, preferably 0.01 to 50% by weight, more preferably 0.1 to 0.1% by weight in the electrolytic solution. 10% by weight is good.

  In the electrolytic solution of the present invention, when the organic solvent is used, the content of the organic solvent is 0.1 to 90% by weight, preferably 20 to 80% by weight, more preferably 30 to 70% by weight in the electrolytic solution. good.

The electrolytic solution containing the electrolytic solution additive represented by the formula (2) has characteristics that it has excellent cycle characteristics even in the long term and has a small capacity reduction rate as compared with the electrolytic solution not containing.
Hereinafter, a method for preparing the electrolytic solution for an electric double layer capacitor of the present invention will be described. The working environment is not particularly limited as long as the atmosphere adversely affects the performance of the electric double layer capacitor, so long as the atmosphere does not mix, but the preparation work is performed in a glove box with an inert atmosphere such as argon or nitrogen. It is preferable to do. The moisture in the working environment can be managed with a dew point meter, and is preferably −60 ° C. or lower. If the temperature exceeds minus 60 ° C., when the working time becomes long, the electrolyte solution absorbs moisture in the atmosphere, so that the amount of moisture in the electrolyte solution increases. The moisture in the electrolyte can be measured with a Karl Fischer moisture meter. The electrode drying temperature is preferably 130 ° C. or higher. More preferably, it is preferably 180 ° C. or higher.

  An electric double layer capacitor can be suitably produced using the electrolytic solution of the present invention obtained above. As an example of this electric double layer capacitor, for example, a laminate type can be cited. However, the shape of the electric double layer capacitor is not limited to the laminate type, but is a laminated type in which electrodes are stacked and accommodated in a can body, a wound type in which the electrodes are wound and stored, or an insulating type It may be a so-called coin type made of a metal can electrically insulated by a gasket. Hereinafter, as an example, the structure of a laminated electric double layer capacitor will be described.

  1 and 2 are views showing a laminated electric double layer capacitor. The electrode 3 and the aluminum tab 1 are bonded to each other, are arranged to face each other via the separator 4, and are stored in the laminate 2. The electrode is composed of a polarizable electrode portion made of a carbon material such as activated carbon and a current collector portion. The laminate container body 2 is sealed by thermocompression bonding so that moisture and air from the outside of the container do not enter.

The polarizable electrode material is preferably a material having a large specific surface area and high electrical conductivity, and needs to be electrochemically stable with respect to the electrolyte within the range of applied voltage to be used. Examples of such materials include carbon materials, metal oxide materials, conductive polymer materials, and the like. In view of cost, the polarizable electrode material is preferably a carbon material.
As the carbon material, an activated carbon material is preferable, and specific examples include sawdust activated carbon, coconut shell activated carbon, pitch coke activated carbon, phenol resin activated carbon, polyacrylonitrile activated carbon, and cellulose activated carbon.
Examples of the metal oxide material include ruthenium oxide, manganese oxide, and cobalt oxide. Examples of the conductive polymer material include a polyaniline film, a polypyrrole film, a polythiophene film, and a poly (3,4-ethylenedioxythiophene) film.

  For the electrode, the polarizable electrode material is kneaded with a binder such as PTFE, and the pressure-molded one is bound to a current collector such as an aluminum foil with a conductive adhesive, or the polarizable electrode material is It can be obtained by mixing a binder together with a thickener such as CMC or an organic solvent such as pyrrolidone together with a binder, applying the paste to a current collector such as an aluminum foil, and then drying.

  The separator preferably has high electronic insulation, excellent wettability of the electrolyte, and high ion permeability, and needs to be electrochemically stable within the applied voltage range. The material of the separator is not particularly limited, but papermaking made of rayon, Manila hemp or the like; polyolefin-based porous film; polyethylene nonwoven fabric; polypropylene nonwoven fabric or the like is preferably used.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, it is not limited to these at all. The propylene carbonate (PC) used in the examples is a lithium battery grade manufactured by Kishida Chemical Co., Ltd., and the water content of the electrolyte was measured with a Karl Fischer moisture meter (Hiranuma Sangyo Co., Ltd., Hiranuma trace moisture measuring device AQ-7). .

(Production of electrodes)
As a polarizable electrode, 80% by weight of activated carbon powder (pitch, coke activated carbon, water vapor activated, specific surface area 1400-1500 m ² / g), 10 parts by weight of acetylene black and 10 parts by weight of polytetrafluoroethylene powder in a roll Kneaded. Thereafter, the sheet was rolled to produce a sheet having a thickness of 0.1 mm, and bonded to 0.03 mm etched aluminum with a conductive paste such as carbon paste to obtain an electrode sheet. This sheet was punched with a mold and dried at 220 ° C. under high vacuum to produce a laminate-type electrode.

(Production of electric double layer capacitor)
A laminate type electric double layer capacitor having a rated voltage of 2.7 V and a capacitance of 24F to 18F was prepared using a laminate type electrode, a cellulose type separator, and an electrolyte.

(Evaluation methods)
The produced electric double layer capacitor was subjected to aging treatment by performing constant voltage charging at 2.7 V for 24 hours and discharging to 0.0 V in a thermostat set at 25 ° C. The initial capacitance is a constant voltage of 2.7 V for 30 minutes in a thermostatic chamber set at 25 ° C. and discharged to a predetermined voltage at 2.0 mA / cm ² . Asked. In the long-term reliability test, a floating test was performed by applying a voltage of 2.7 V until a predetermined time in a thermostat set to 60 ° C. Thereafter, the capacitance was measured by the same method as the initial capacitance measurement, and the capacity reduction rate was obtained.

Example 1
N-methoxymethyl-N-methylpyrrolidinium tetrafluoroborate (MMMP · BF ₄ ) (manufactured by Otsuka Chemical) 26 parts by weight, propylene carbonate (PC) 73.5 parts by weight, tropylium tetrafluoroborate (manufactured by Kanto Chemical) It mix | blended in the ratio of 0.5 weight part, and obtained the electrolyte solution.
Mixing was performed in a nitrogen atmosphere dry box with a dew point of −60 ° C. or lower, and it was confirmed that the water content of the solution was 30 ppm or lower. The characteristics of various electrolytic solutions in an electric double layer capacitor were evaluated. The results are listed in Table 1.

Example 2
N-methoxymethyl-N-methylpyrrolidinium tetrafluoroborate (MMMP · BF ₄ ) (manufactured by Otsuka Chemical) 26 parts by weight, propylene carbonate (PC) 73.4 parts by weight, hexamethylsiloxane (manufactured by ACROS) 0. 1 part by weight and 0.5 part by weight of tropylium tetrafluoroborate (manufactured by Kanto Chemical Co., Inc.) were blended in the same manner as in Example 1 to obtain an electrolytic solution. The performance of various electrolytes was measured. The results are listed in Table 1.

Example 3
N-methoxymethyl-N-methylpyrrolidinium tetrafluoroborate (MMMP • BF ₄ ) (manufactured by Otsuka Chemical) 26 parts by weight, propylene carbonate (PC) 73.65 parts by weight, hexamethylsiloxane (manufactured by ACROS) 1 part by weight and 0.25 parts by weight of tropylium tetrafluoroborate (manufactured by Kanto Chemical Co., Inc.) were blended in the same manner as in Example 1 to obtain an electrolytic solution.
The performance of various electrolytes was measured. The results are listed in Table 1.

Example 4
Spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate (SBP · BF ₄ ) (manufactured by Otsuka Chemical) 26 parts by weight, propylene carbonate (PC) 73.65 parts by weight, hexamethylsiloxane (manufactured by ACROS) An electrolyte solution was obtained in the same manner as in Example 1, except that 0.1 part by weight and 0.25 parts by weight of tropylium tetrafluoroborate (manufactured by Kanto Chemical) were blended.
The performance of various electrolytes was measured. The results are listed in Table 1.

Comparative Example 1
N-methoxymethyl-N-methylpyrrolidinium tetrafluoroborate (MMMP · BF ₄ ) (manufactured by Otsuka Chemical Co., Ltd.) was mixed at a ratio of 26 parts by weight and propylene carbonate (PC) at 74 parts by weight. An electrolytic solution was obtained.
The performance of various electrolytes was measured. The results are listed in Table 1.

It is a front view of the laminate type electric double layer capacitor of the present invention. It is an internal block diagram of the laminate type electric double layer capacitor of this invention.

Explanation of symbols

1 Aluminum tab 2 Laminate 3 Electrode 4 Separator

Claims (6)

An electrolytic solution for an electric double layer capacitor comprising a compound represented by the formula (1) and a compound represented by the formula (2).

(R ¹ and R ² may be the same or different and each represents a methyl group, an ethyl group, a methoxymethyl group or an ethoxymethyl group, and R ¹ and R ² may form a ring structure. Y is an anion. .)

[X is an anion. ] Furthermore, the electrolyte solution of Claim 1 containing an organic solvent. The electrolytic solution according to claim 1, wherein the compound represented by the formula (2) is tropinium tetrafluoroborate or tropinium hexafluorophosphate. The electrolytic solution according to claim 2, wherein the organic solvent is propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or γ-butyrolactone. The electrochemical device using the electrolyte solution in any one of Claims 2-4. The electric double layer capacitor using the electrolyte solution in any one of Claims 2-4.

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