WO2010067772A1

WO2010067772A1 - Electrical double layer capacitor

Info

Publication number: WO2010067772A1
Application number: PCT/JP2009/070463
Authority: WO
Inventors: 謙三高橋; 明天高; 舞小山
Original assignee: ダイキン工業株式会社
Priority date: 2008-12-08
Filing date: 2009-12-07
Publication date: 2010-06-17
Also published as: JPWO2010067772A1

Abstract

Disclosed is an electrical double layer capacitor having high electrostatic capacity, low internal resistance, and high withstand voltage. This electrical double layer capacitor is characterized by being equipped with an electrode that contains activated carbon and a binding material, and a nonaqueous electrolytic solution, and in that (I) the electrode density of the electrode is 0.45 g/cm³ or less and (II) the nonaqueous electrolytic solution is a nonaqueous electrolytic solution with a withstand voltage of 2.5 V or more.

Description

Electric double layer capacitor

The present invention relates to an electric double layer capacitor.

The electric double layer capacitor is expected to be used as a power source for electric vehicles and instantaneous power outages, and various studies have been made. Such an electric double layer capacitor is desired to have a high capacitance and a low internal resistance, and as a solvent for dissolving the electrolyte, a non-fluorine-based non-aqueous solvent (Patent Document 1) or a fluorine-based non-aqueous solvent (Patent Document 2). Is used.

Patent Document 1 also proposes a configuration of electrodes. By setting the electrode bulk density (electrode density) to a high density of 0.6 g / cm ³ or more, high capacitance and low internal resistance can be realized. It is stated.

JP 2001-143973 A International Publication No. 2008/084846

The electric double layer capacitor is required to have the above-mentioned high capacitance and low internal resistance, and also needs a high withstand voltage corresponding thereto.

An object of the present invention is to provide an electric double layer capacitor having a high capacitance, a low internal resistance, and a high withstand voltage.

That is, the present invention is an electric double layer capacitor comprising an electrode containing activated carbon and a binder and a non-aqueous electrolyte solution,
(I) The electrode density of the electrode is 0.45 g / cm ³ or less,
(II) The present invention relates to an electric double layer capacitor wherein the non-aqueous electrolyte is a non-aqueous electrolyte having a withstand voltage of 2.5 V or more.

As the non-aqueous electrolyte, a fluorine-based electrolyte is preferable.

According to the electric double layer capacitor of the present invention, an electric double layer capacitor having a high electrostatic capacity, a low internal resistance, and a high withstand voltage can be provided.

The electric double layer capacitor of the present invention includes an electrode (I) containing a specific component and a fluorine-based electrolyte (II). Each configuration will be described below.

(I) Electrode The electrode (I) used by this invention contains activated carbon (IA) and binder (IB).

(IA) Activated carbon Activated carbon (IA) has a role of increasing the capacitance of the electric double layer capacitor, and is not particularly limited as long as it plays the role, but an electric double layer capacitor having a large capacity and low internal resistance can be obtained. It is preferable to use activated carbon having an average particle size of 20 μm or less and a specific surface area of 1500 to 3000 m ² / g. Specific examples of the activated carbon include phenol resin-based activated carbon, coconut-based activated carbon, and petroleum coke-based activated carbon. Among these, it is preferable to use petroleum coke activated carbon or phenol resin activated carbon in that a large capacity can be obtained. Activated carbon activation treatment methods include a steam activation treatment method, a molten KOH activation treatment method, and the like, and it is preferable to use activated carbon obtained by a molten KOH activation treatment method in terms of obtaining a larger capacity.

More specifically, as described in Patent Document 2, activated carbon particles having a potassium content of 0 to 200 ppm measured by an extraction method, and an average particle diameter as described in Patent Document 1 are from 1 to Examples thereof include activated carbon particles having a pore volume of 10 cm and a pore volume of 1.5 cm ³ / g or less.

Further, natural graphite, artificial graphite, graphitized mesocarbon spherules, graphitized whiskers, gas-phase-grown carbon fibers, a furfuryl alcohol resin fired product, or a novolak resin fired product can be exemplified.

(IB) Binder The binder (IB) binds the particles when it is formed into an electrode using activated carbon (IA) and other electrode components such as a conductive material added as necessary. Used for.

Accordingly, there is no particular limitation as long as the object can be achieved, but usually, fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF); non-fluorine such as butadiene rubber and styrene-butadiene rubber System rubber is used.

Among these, a fluorine-based resin, particularly PTFE is preferable from the viewpoint of good pressure resistance and durability, and non-fluorine rubber is preferable from the viewpoint of good pressure resistance and good adhesion to the current collector.

(IC) Other electrode components In addition to the activated carbon (IA) and the binder (IB) described above, additives that are usually blended in electrodes for electric double layer capacitors may be blended. Examples of other additives include conductive materials and thickeners.

(IC-1) Conductive Material The conductive material is a non-activated carbon having a large specific surface area and has a role of imparting electron conductivity, and for example, carbonaceous materials such as carbon black, ketjen black, acetylene black, natural graphite, and artificial graphite An inorganic material such as a metal fiber, conductive titanium oxide or ruthenium oxide.

(IC-2) Thickener When preparing an electrode, activated carbon (IA), binder (IB), and other additives added as necessary are dispersed in a solvent, for example, water to form a slurry, and metal It is applied to a foil or current collector and molded. At that time, a thickener is added to uniformly disperse the particles in the slurry and adjust the fluidity to an appropriate fluidity.

Examples of the thickener include conventionally known carboxymethyl cellulose (CMC) and polyacrylic acid. Of these, polyacrylic acid is preferred from the viewpoint of good pressure resistance.

These electrode components are preferably blended in an amount of 2 to 6 parts by mass of binder (IB) with respect to 100 parts by mass of activated carbon (IA). In order to obtain higher capacitance, lower internal resistance, and higher withstand voltage, it is more preferable to add 3 to 5 parts by mass of the binder (IB) to 100 parts by mass of the activated carbon (IA).

For example, when the conductive material (IC-1) is blended, the capacitance of the capacitor is decreased if the amount is too large so as to obtain good conductivity (low internal resistance). It is preferable to set it as 20 mass%.

In addition, when the thickener (IC-2) is blended, it is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, with respect to 100 parts by mass of activated carbon (IA) from the viewpoint of homogenizing the electrode density. The lower limit is an amount that achieves the purpose of blending.

The electrode can be formed by various methods. For example, activated carbon (IA) and, if necessary, conductive material (IC-1) are dry mixed. In the mixing process, thickener (IC-2) and water are added as appropriate to disperse the particles. Next, a binder (IB) and water are added as appropriate, followed by wet mixing to prepare a homogeneous electrode forming slurry. This slurry is applied on a metal foil such as a current collector, pressed as appropriate, and dried to produce an electrode.

The electrode may be an electric double layer capacitor using the above electrodes for both electrodes, but a configuration using a non-polarizable electrode on one side, for example, a positive electrode mainly composed of a battery active material such as a metal oxide, and activated carbon mainly A configuration in which the negative electrode of the electrode of the present invention is combined is also possible.

The current collector may be any material that is chemically and electrochemically resistant to corrosion. As the current collector of the polarizable electrode mainly composed of activated carbon, stainless steel, aluminum, titanium or tantalum can be preferably used. Of these, stainless steel or aluminum is a particularly preferable material in terms of both characteristics and cost of the electric double layer capacitor to be obtained.

In the present invention, it is important to adjust the bulk density (electrode density) of the produced electrode to 0.45 g / cm ³ or less.

As described in Patent Document 1, it is known to increase the electrode density (0.6 g / cm ³ or more) from the viewpoint of improvement in capacitance and reduction in internal resistance. There is no example in which the electrode density is examined from the viewpoint of voltage, and the point that the withstand voltage is improved in the direction of lowering the density is a matter found for the first time in the present invention.

Electrode density is preferably 0.45 g / cm ³ or less from the viewpoint withstand voltage is good, more is 0.40 g / cm ³ or less. On the other hand, the lower limit is 0.30 g / cm ³ from the viewpoint of maintaining mechanical strength, in particular 0.35 g / cm ³ preferred.

The method for adjusting the electrode density is not particularly limited, and for example, the following method can be adopted.

(1) Method of adjusting solid content concentration of electrode slurry For example, it is preferable to adjust the solid content concentration to 15 to 25% by mass, preferably 18 to 22% by mass.

(2) Method of adjusting the pressure when pressing the electrode slurry coating after coating The pressing pressure may be appropriately selected according to the target electrode thickness and the like.

These methods may be performed alone or in combination.

(II) Non-aqueous electrolyte solution The non-aqueous electrolyte solution (II) used in the present invention is a non-aqueous electrolyte solution having a withstand voltage of 2.5 V or more, preferably a fluorine-based electrolyte solution. The nonaqueous electrolytic solution having a withstand voltage of 2.5 V or more includes a nonaqueous solvent (IIA) and an electrolyte salt (IIB).

(IIA) Non-aqueous solvent As the non-aqueous solvent (IIA), any fluorine-based solvent (IIA-1) or non-fluorinated solvent (IIA) can be used as long as the withstand voltage of the electrolytic solution can be 2.5 V or higher. -2).

(IIA-1) Fluorinated solvent As the fluorinated solvent (IIA-1), for example, a fluorinated solvent containing a fluorinated cyclic carbonate described in Patent Document 2 is excellent in high electric resistance and wide electrolyte solubility. This is preferable.
As the fluorine-containing cyclic carbonate, the formula (1):

(Wherein X ¹ to X ⁴ are the same or different and all are —H, —F, —CF ₃ , —CHF ₂ , —CH ₂ F, —C ₂ F ₅ or —CH ₂ CF ₃ ; At least one of X ¹ to X ⁴ is —F, —CF ₃ , —C ₂ F ₅ or —CH ₂ CF ₃ ). This is preferable from the viewpoint of high withstand voltage.

The fluorine-containing cyclic carbonate contained in the fluorine-based solvent (IIA-1) has particularly excellent properties such as a high dielectric constant and a high withstand voltage, and also has good solubility of electrolyte salt and reduction of internal resistance. From the point that the characteristics as an electric double layer capacitor in the present invention are improved,

At least one selected from the group consisting of is preferred.

The fluorine content of the fluorine-containing cyclic carbonate is preferably 15 to 55% by mass, more preferably 17 to 44% by mass from the viewpoint of dielectric constant and oxidation resistance.

In addition, as the fluorine-containing cyclic carbonate,

Etc. can also be used.

The content of the fluorinated cyclic carbonate in the fluorinated solvent (IIA-1) is preferably 100 to 20% by volume, more preferably 90 to 20% by volume in terms of good dielectric constant and viscosity.

As the fluorine-based solvent (IIA-1), the fluorine-containing cyclic carbonate represented by the formula (1) may be used alone, or other fluorine-containing electrolyte salt dissolving solvent or non-fluorinated electrolyte salt dissolving solvent. It may be used as a mixture. Moreover, since a fluorine-containing cyclic carbonate generally has a high melting point, it may cause an obstacle to operation at a low temperature by itself. In such a case, it is preferable to use it as a mixture of the fluorine-containing cyclic carbonate represented by the formula (1) and another fluorine-containing electrolyte salt dissolving solvent from the viewpoint of improving oxidation resistance, viscosity, and low temperature characteristics.

Solvents for dissolving the fluorine-containing electrolyte salt used as a co-solvent for the fluorine-containing cyclic carbonate represented by the formula (1) include fluorine-containing chain carbonates, fluorine-containing chain esters, fluorine-containing chain ethers, fluorine-containing lactones, And fluorine sulfolane derivatives.

As the fluorine-containing chain carbonate, from the viewpoint of good viscosity and oxidation resistance, the formula (2):

(Wherein Rf ^a1 and Rf ^a2 are the same or different and are an alkyl group having 1 to 4 carbon atoms or a fluorine-containing alkyl group having 1 to 4 carbon atoms, provided that at least one of them is a fluorine-containing group having 1 to 4 carbon atoms. Those represented by (which are alkyl groups) are preferred.

Among the fluorine-containing chain carbonates, the electrical properties in the present invention are particularly excellent in that they have excellent characteristics such as a high dielectric constant and a high withstand voltage, as well as the solubility of the electrolyte salt, the reduction in internal resistance, and the low-temperature characteristics. From the point that the characteristics as a multilayer capacitor are improved,

Etc. are preferable.

In addition, as fluorine-containing chain carbonate,

Etc. can also be used. Further, for example, compounds described in JP-A-06-21992, JP-A-2000-327634, JP-A-2001-256983 and the like can be mentioned.

Above all, from the point that oxidation resistance and solubility of electrolyte salt are good,

Is preferred.

Examples of the fluorine-containing chain ether include, for example, JP-A-08-037024, JP-A-09-097627, JP-A-11-026015, JP-A-2000-294281, JP-A-2001-052737, Examples thereof include compounds described in JP-A-11-307123.

Among these, from the viewpoint of good compatibility with other solvents and an appropriate boiling point, the formula (3):
Rf ^c1 -O-Rf ^c2 (3)
(Wherein, ^Rfc1 and ^Rfc2 are the same or different and both are fluorine-containing alkyl groups having 2 to 4 carbon atoms).

In particular, Rf ^c1 includes, for example, —CH ₂ CF ₂ CHF ₂ , —CH ₂ C ₂ F ₄ CHF ₂ , —CH ₂ CF ₃ , —CH ₂ C ₃ F ₆ CHF ₂ , —CH ₂ C ₂ F ₅ , —CH ₂ CF ₂ CHFCF ₃ , —CH ₂ CF (CF ₃ ) CF ₂ CHF ₂ , —C ₂ H ₄ C ₂ F ₅ , —C ₂ H ₄ CF _{3 and the} like, and Rf ^c2 For example, —CF ₂ CHFCF ₃ , —C ₂ F ₄ CHF ₂ , —C ₂ H ₄ CF ₃ , —CH ₂ CHFCF ₃ , and —C ₂ H ₄ C ₂ F ₅ are preferable.

As the fluorine-containing chain ester, since the flame retardancy is high and the compatibility with other solvents and the oxidation resistance are good, the formula (4):

(Wherein Rf ^b1 and Rf ^b2 are the same or different and both are fluorine-containing alkyl groups having 1 to 4 carbon atoms).

Examples of the fluorine-containing chain ester include CF ₃ C (═O) OC ₂ F ₅ , CF ₃ C (═O) OCH ₂ CF ₃ , CF ₃ C (═O) OCH ₂ CH ₂ CF ₃ , and CF _3. _{C (= O) OCH 2 C} 2 F 5, CF 3 C (= O) OCH 2 CF 2 CF 2 H, CF 3 C (= O) OCH (CF 3) 2, CF 3 C (= O) OCH ( CF ₃ ) _{2 and the} like. Among these, CF ₃ C (═O) OC ₂ F ₅ , CF ₃ C (═O) are preferred because they have good compatibility with other solvents, viscosity, and oxidation resistance. OCH ₂ C ₂ F ₅ , CF ₃ C (═O) OCH ₂ CF ₂ CF ₂ H, CF ₃ C (═O) OCH ₂ CF ₃ , CF ₃ C (═O) OCH (CF ₃ ) ₂ are particularly preferred. .

As the fluorine-containing lactone, for example, formula (5):

(Wherein X ⁵ to X ¹⁰ are the same or different and all are —H, —F, —Cl, —CH ₃ or a fluorine-containing methyl group; provided that at least one of X ⁵ to X ¹⁰ is fluorine-containing methyl A fluorine-containing lactone represented by the following formula:

Examples of the fluorine-containing lactone include those represented by the formula (6):

(In the formula, either one of A and B is CX ¹⁶ X ¹⁷ (X ¹⁶ and X ¹⁷ are the same or different, and all are —H, —F, —Cl, —CF ₃ , —CH ₃ or a hydrogen atom) may be substituted with a halogen atom include a hetero atom in the chain is also an alkyl group), the other is an oxygen atom; Rf ^e is a fluorine-containing ether group, a fluorine-containing alkoxy group or having two or more carbon atoms containing Fluoroalkyl group; X ¹¹ and X ¹² are the same or different, all are —H, —F, —Cl, —CF ₃ or —CH ₃ ; X ¹³ to X ¹⁵ are the same or different and both are —H, Examples thereof include -F, -Cl or an alkyl group in which a hydrogen atom may be substituted with a halogen atom and a hetero atom may be included in the chain; a fluorine-containing lactone represented by n = 0 or 1).

Among these, the point that the excellent characteristics such as high dielectric constant and high withstand voltage can be exhibited especially, and the characteristics as the electrolytic solution in the present invention are improved in that the solubility of the electrolyte salt and the reduction of internal resistance are good. From

Is preferred.

In addition, as fluorine-containing lactone,

Etc. can also be used.

Examples of the fluorine-containing sulfolane derivative include fluorine-containing sulfolane derivatives described in JP-A-2003-132994, and among them,

Is preferred.

As the fluorinated solvent (IIA-1), the fluorinated cyclic carbonate represented by the formula (1) can be used alone, or another non-fluorinated solvent or fluorinated solvent can be used as a cosolvent. As a solvent for dissolving an electrolyte salt as a co-solvent, a solvent for dissolving a fluorine-containing electrolyte salt is preferable from the viewpoint of good oxidation resistance and viscosity, and a fluorine-containing chain carbonate, a fluorine-containing chain ester, and a fluorine-containing chain ether. Is more preferable. In particular, the fluorine-based solvent (IIA-1) when operated at a high voltage of 3.5 V or more includes a fluorine-containing cyclic carbonate represented by the formula (1), a fluorine-containing chain carbonate, a fluorine-containing chain ester, and Those consisting of at least one selected from the group consisting of fluorine-containing chain ethers are preferred. Of these, fluorine-containing chain ethers are preferred from the viewpoint of good oxidation resistance.

As a particularly preferred combination of the fluorine-containing cyclic carbonate and the fluorine-containing chain ether, particularly from the viewpoint of good oxidation resistance and solubility of the electrolyte salt,

Fluorine-containing cyclic carbonates, CF ₃ CF ₂ CH ₂ —O—CF ₂ CFHCF ₃ , HCF ₂ CF ₂ CH ₂ —O—CF ₂ CFHCF ₃ , CF ₃ CF ₂ CH ₂ —O—CF ₂ CF ₂ H and It is a mixture with at least one fluorine-containing chain ether selected from the group consisting of HCF ₂ CF ₂ CH ₂ —O—CF ₂ CF ₂ H.

(IIA-2) Non-fluorinated solvent As the non-fluorinated solvent (IIA-2), non-fluorinated cyclic carbonate, non-fluorinated chain carbonate, non-fluorinated chain ester, non-fluorinated chain ether, non-fluorine Lactones, non-fluorine sulfolane derivatives, other solvents for dissolving non-fluorine electrolyte salts, and the like.

Examples of non-fluorinated cyclic carbonates include:

Etc.

As the non-fluorine chain carbonate, for example, the formula (7):

(Wherein, R ^a1 and R ^a2 are the same or different and both are alkyl groups having 1 to 4 carbon atoms).

Among the non-fluorine chain carbonates, the electric double layer capacitor according to the present invention is particularly advantageous in that it has excellent characteristics such as a high dielectric constant and a high withstand voltage, and also has good solubility in electrolyte salts and a reduction in internal resistance. From the point that the characteristics as

Etc. are preferable.

In addition, as non-fluorine chain carbonate,

Etc. can also be used.

(IIB) Electrolyte Salt The electrolyte salt (IIB) includes conventionally known ammonium salts and metal salts, liquid salts (ionic liquids), inorganic polymer type salts, organic polymer type salts, and the like. .

As the ammonium salt, conventionally known ones can be used, and examples include spiro-ring bipyridinium salts, imidazolium salts, tetraalkyl quaternary ammonium salts, N-alkylpyridinium salts, N, N-dialkylpyrrolidinium salts and the like.

Examples of the spiro ring bipyridinium salt include those represented by the formula (10-1):

(Wherein R ^f1 and R ^f2 are the same or different and both are alkyl groups having 1 to 4 carbon atoms; X ⁻ is an anion; n1 is an integer of 0 to 5; n2 is an integer of 0 to 5) Spirocyclic bipyridinium salt, formula (10-2):
(Wherein R ^f3 and R ^f4 are the same or different and both are alkyl groups having 1 to 4 carbon atoms; X ⁻ is an anion; n3 is an integer of 0 to 5; n4 is an integer of 0 to 5) Spiro ring bipyridinium salt or formula (10-3):

(Wherein R ^f5 and R ^f6 are the same or different and both are alkyl groups having 1 to 4 carbon atoms; X ⁻ is an anion; n5 is an integer of 0 to 5; n6 is an integer of 0 to 5) Spiro ring bipyridinium salts are preferred. In addition, the spiro-ring bipyridinium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorine-containing alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

The anion X ⁻ may be an inorganic anion or an organic anion. Examples of the inorganic anion include AlCl ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , TaF ₆ ⁻ , I ⁻ and SbF ₆ ⁻ . Examples of the organic anion include CH ₃ COO ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ^{− and the} like. Of these, BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ or (C ₂ F ₅ SO ₂ ) ₂ N ⁻ are highly dissociable and have low internal resistance under high voltage. In particular, PF ₆ ^- is more preferable.

Preferable specific examples of the spirocyclic bipyridinium salt include, for example,

Etc.

This spiro-ring bipyridinium salt is excellent in terms of solubility in a solvent, oxidation resistance, and ion conductivity.

As an imidazolium salt, for example, formula (11):

An imidazolium salt represented by the formula (wherein R ^g1 and R ^g2 are the same or different and both are alkyl groups having 1 to 6 carbon atoms; X ⁻ is an anion) is preferred. In addition, the imidazolium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorine-containing alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

Preferred examples of the anion X ⁻ are the same as those of the spiro ring bipyridinium salt.

Preferable specific examples of imidazolium salts include, for example, formula (12):

And ethylmethylimidazolium salt represented by the formula:

This imidazolium salt has low viscosity and is excellent in solubility in a solvent.

Examples of the tetraalkyl quaternary ammonium salt include the formula (13):

(Wherein R ^h1 , R ^h2 , R ^h3 and R ^h4 are the same or different, and all are alkyl groups which may contain an ether bond having 1 to 6 carbon atoms; X ⁻ is an anion) Preferred is a quaternary ammonium salt. In addition, the tetraalkyl quaternary ammonium salt in which part or all of the hydrogen atoms are substituted with fluorine atoms and / or fluorine-containing alkyl groups having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance. .

As a specific example,
Formula (13-1):

(Wherein R ^h1 , R ^h2 and X ⁻ are the same as in formula (13); x and y are the same or different, an integer of 0 to 4 and x + y = 4) Ammonium salt,
Formula (13-2):

Wherein R ^h5 is an alkyl group having 1 to 6 carbon atoms; R ^h6 is a divalent hydrocarbon group having 1 to 6 carbon atoms; R ^h7 is an alkyl group having 1 to 4 carbon atoms; z is 1 or 2; An alkyl ether group-containing trialkylammonium salt represented by X ⁻ is an anion). By introducing an alkyl ether group, the viscosity can be lowered.

Preferable specific examples of the tetraalkyl quaternary ammonium salt include, for example, Et ₄ NBF ₄ , Et ₄ NClO ₄ , Et ₄ NPF ₆ , Et ₄ NAsF ₆ , Et ₄ NSbF ₆ , Et ₄ NCF ₃ SO ₃ , Et ₄ N (CF ₃ SO ₂ ) ₂ N, Et ₄ NC ₄ F ₉ SO ₃ , Et ₃ MeBF ₄ , Et ₃ MeClO ₄ , Et ₃ MePF ₆ , Et ₃ MeAsF ₆ , Et ₃ MeSbF ₆ , Et ₃ MeCF ₃ SO ₃ Et ₃ Me (CF ₃ SO ₂ ) ₂ N, Et ₃ MeC ₄ F ₉ SO _{3 and the} like, and Et ₄ NBF ₄ , Et ₄ NPF ₆ , Et ₄ NSbF ₆ , Et ₄ NAsF _{6 and the} like are particularly preferable. .

N-alkylpyridinium salts include, for example, formula (14):

N-alkylpyridinium salts represented by the formula (wherein R ⁱ¹ is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; X ⁻ is an anion) are preferred. In addition, the N-alkylpyridinium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorine-containing alkyl group having 1 to 4 carbon atoms is preferable from the viewpoint of improving oxidation resistance.

As a preferable specific example, for example,

Etc.

This N-alkylpyridinium salt has low viscosity and is excellent in solubility in a solvent.

N, N-dialkylpyrrolidinium salts include, for example, formula (15):

Preferred examples include N, N-dialkylpyrrolidinium salts represented by the formula (wherein R ^j1 and R ^j2 are the same or different and both are alkyl groups having 1 to 6 carbon atoms; X ⁻ is an anion). Further, the oxidation resistance of the N, N-dialkylpyrrolidinium salt in which part or all of the hydrogen atoms are substituted with a fluorine atom and / or a fluorine-containing alkyl group having 1 to 4 carbon atoms is improved. It is preferable from the point.

As a preferable specific example, for example,

Etc.

This N, N-dialkylpyrrolidinium salt has low viscosity and is excellent in solubility in a solvent.

Of these ammonium salts, spiro-ring bipyridinium salts and imidazolium salts are preferred in terms of solubility in solvents, oxidation resistance, and ionic conductivity.

(In the formula, X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ or (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , particularly BF ₄ ⁻ or PF ₆ ⁻ . ),

(In the formula, X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ or (C ₂ F ₅ SO ₂ ) ₂ N ⁻ , particularly BF ₄ ⁻ or PF ₆ ⁻ ).
Is preferred.

Moreover, you may use together lithium salt as electrolyte salt. The lithium salt, for _{_{example, LiPF 6, LiBF 4, LiAsF}} 6, LiSbF 6, LiN (SO 2 C 2 H 5) 2 is preferred.

Furthermore, a magnesium salt may be used to improve the capacitance. As the magnesium salt, for example, Mg (ClO ₄ ) ₂ , Mg (OOC ₂ H ₅ ) _{2 and the} like are preferable.

The amount of electrolyte salt (IIB) blended varies depending on the required current density, application, type of electrolyte salt, etc., but 0.1 mol / liter or more and 2.5 mol / liter or less with respect to the non-aqueous solvent (IIA). Further, it is preferably 0.8 mol / liter or more and 1.8 mol / liter or less, more preferably 1.0 mol / liter or more and 1.6 mol / liter or less.

The electrolytic solution used in the present invention is prepared by dissolving an electrolyte salt (IIB) in a non-aqueous solvent (IIA).

In the present invention, the electrolytic solution may be a gel (plasticized) gel electrolytic solution in combination with a polymer material that dissolves or swells in the solvent used in the electrolytic solution of the present invention.

Examples of such polymer materials include conventionally known polyethylene oxide and polypropylene oxide, modified products thereof (JP-A-8-222270 and JP-A-2002-1000040); polyacrylate polymers, polyacrylonitrile, and polyvinylidene fluoride. Fluorine resins such as vinylidene fluoride-hexafluoropropylene copolymer (JP-A-4-506726, JP-A-8-507407, JP-A-10-294131); Examples thereof include composites with resins (Japanese Patent Laid-Open Nos. 11-35765 and 11-86630). In particular, it is desirable to use polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer as the polymer material for the gel electrolyte.

In addition, ion conductive compounds described in Japanese Patent Application No. 2004-301934 can also be used.

The electrolyte used in the present invention may contain other additives as necessary. Examples of other additives include metal oxides and glass.

Such an electrolyte solution can simultaneously improve flame retardancy, low temperature characteristics, solubility of electrolyte salts and compatibility with hydrocarbon solvents, and stable characteristics can be obtained at a withstand voltage of 3.5 V or more. It is excellent as an electrolyte for electric double layer capacitors. The upper limit of the withstand voltage is preferably as high as possible, and is appropriately set depending on the type and application of the non-aqueous electrolyte to be used.

In the electric double layer capacitor of the present invention, for example, a wound type electric double layer capacitor, the electrode (I) is usually wound through a separator or a current collector to constitute a wound element. Conventional separators and current collectors can be used as they are. The electric double layer capacitor is assembled by placing the non-aqueous electrolyte (II) and the winding element in a case made of aluminum or the like, and sealing and sealing with a rubber sealing body.

Also, a laminate type electric double layer capacitor or a coin type electric double layer capacitor can be obtained by a known method.

Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to such examples.

The measurement method and evaluation method employed in the examples are as follows.

(1) Stability of electrode slurry The electrode slurry prepared in Examples and Comparative Examples is placed in a polyethylene container and allowed to stand for 3 hours. Evaluation is based on the following criteria.
○: No precipitation occurred.
X: Precipitation occurred.

(2) Coating film bending test In accordance with JIS K5400, measurement is performed under the condition of φ2 using a bending tester (a coating film bending tester manufactured by Yasuda Seiki Seisakusho Co., Ltd.). Evaluation is based on the following criteria.
○: No cracks were observed visually.
X: The crack was confirmed visually.

(3) Electrode density (unit: g / cm ³ )
The external dimensions and mass are measured, and the bulk density (g / cm ³ ) is calculated from these values.

(4) Withstand voltage of electrolyte (unit: V)
Electrolytic solution was applied to a three-electrode voltage measuring cell (working electrode, counter electrode: platinum (where the area ratio of the counter electrode and working electrode is 5: 1), reference electrode: Ag, HS cell manufactured by Hosen Co., Ltd.) Then, the potential is pulled at 3 mV / sec with a potentiostat, and the decomposition current is measured. The maximum potential at which the decomposition current no longer increases is defined as the withstand voltage of the electrolyte.

(5) Capacitance, internal resistance, and withstand voltage of the capacitor Increase the charging voltage to the applied voltage (2.5V) while charging the laminate cell with a constant current with an electronic power supply. After maintaining the constant voltage state for 5 minutes and confirming that the charging current is sufficiently lowered and saturated, constant current discharge is performed and the cell voltage difference (ΔV) and the current value (I) are measured.

∙ The constant current value for charging and discharging is 10 mA / F, and 35 mA. The cell voltage and current are measured by 0.5 second sampling.

The current value (I) flowing through the cell is calculated by connecting a 1Ω fixed resistor in series to the cell and measuring the voltage across this end. This current value is used when measuring the internal resistance of the cell.

Using the measured values obtained, the capacitance of the capacitor (unit: F) and the internal resistance (unit: Ω) of the capacitor are calculated as follows.

(Capacitance of the capacitor)
After recording the time change of the cell voltage, the cell fully charged with each voltage is discharged at a constant current. Times T1 (seconds) and T2 (seconds) from when the voltage V1 (V) at the straight line of the cell voltage drop is reduced to V2 (V) are measured, and the capacitance is calculated from the following equation. Note that the value of the current flowing to the cell (the current value (I) calculated in (5) is used (see Japan Electronic Machinery Manufacturers Association Standard EIAJ RC-2377).
Capacitance = I × (T2-T1) / (V2-V1)

(Internal resistance of capacitor)
In the record, the cell voltage before the start of discharge and the cell voltage immediately after the discharge (the intersection of the auxiliary line and the time axis at the start of discharge) Using the voltage difference (ΔV) and the current value (I) flowing to the cell, the internal resistance R is calculated by the following equation (see Japan Electronic Machinery Manufacturers Association Standard EIAJ RC-2377).
R = ΔV / I

(Capacitor withstand voltage)
In addition to 2.5V, each of the cells in the same manner with 8 types of specified applied voltages (3.0V, 3.3V, 3.5V, 3.7V, 3.9V, 4.1V, 4.3V) Calculate the internal resistance value. Since the internal resistance value of the cell is constant regardless of the applied voltage unless the cell deteriorates, the maximum applied voltage value at which no increase in the internal resistance value of the cell is observed with the increase in the applied voltage is Of withstand voltage.

Example 1
(Production of electrodes)
Activated carbon particles (specific surface area 2100 m ² / g. Average particle size 11 μm. CEP21 manufactured by Nippon Oil Corporation. Activated carbon 1) and 100 parts by mass of ketjen black (EC600JD manufactured by Lion Corporation) as a conductive material, 3 parts by mass of acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) was dry mixed with a stirrer. It was transferred to a kneader and 2 parts by mass of polyacrylic acid (Aron A-10H manufactured by Toagosei Co., Ltd.) and 50 parts by mass of water were added.

Then, 4 parts by mass of particulate or particulate thermoplastic elastomer binder (AZ9001 manufactured by Nippon Zeon Co., Ltd., binder 1) and 80 parts by mass of water were added as a binder, and kneaded for a predetermined time.

Thereafter, the mixture was transferred to a stirrer, 130 parts by mass of water was added and wet-mixed for a predetermined time, then transferred to a homogenizer, 30 parts by mass of water was added, and the mixture was crushed for a predetermined time. Finally, after the slurry was filtered, 60 parts by mass of water was added to prepare a slurry for the electrode. When the stability of the obtained electrode slurry was examined, no precipitation occurred (evaluation: ◯).

In addition, 15 mass parts of water was added with respect to 100 weight part of slurry as viscosity adjustment just before application | coating.

Next, this slurry was applied onto an etched aluminum current collector (thickness 20 μm) previously coated with a conductive paste (T602 manufactured by Nippon Graphite Co., Ltd.) with a film thickness of 20 μm, and dried at 110 ° C. Later, press treatment was performed to produce a roll electrode having an activated carbon layer thickness of 80 μm (electrode density 0.40 g / cm ³ ).

When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

(Preparation of electrolyte)
Electrolyte using spirobipyrrolidinium tetra phosphate as an electrolyte salt (manufactured by Hoechst (Ltd.)), CF ₃ as an electrolyte solvent - ethylene carbonate (CF ₃ -EC) and fluorine-containing ether (HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H. A fluorine-based electrolytic solution having an electrolyte salt concentration of 1 mol / liter was prepared by mixing 1: 1 fluorine-containing ether 1). It was 5.0V when the withstand voltage of this fluorine-type electrolyte solution was measured.

(Production of laminated cell electric double layer capacitor)
The electrode is cut to a predetermined size (20 × 72 mm), and an electrode lead is bonded to the aluminum surface of the current collector by welding, and then a laminate container (product number: D-EL40H, manufacturer: Dai Nippon Printing Co., Ltd.) ) And sandwiched the separator. Subsequently, the electrolytic solution was injected and impregnated in a dry chamber, and then sealed to prepare an electric double layer capacitor (laminated type) of the present invention. As the separator, Celgard No. 2400 (a polyethylene porous film manufactured by Celgard Co., Ltd., film thickness: 25 μm, density: 0.56 g / cm ³ , maximum pore diameter: 0.125 × 0.05 μm) was used.

With respect to this laminated electric double layer capacitor, the withstand voltage (V), the electrostatic capacity (F) at 2.5 V, and the internal resistance (Ω) at each voltage were measured. The results are shown in Table 1.

Example 2
A slurry for the same electrode as in Example 1 was prepared, and 17.5 parts by mass of water was added to 100 parts by weight of the slurry as a viscosity adjustment immediately before application (the stability of this slurry evaluated separately was ○). ) Using this slurry, an electrode having a thickness of 80 μm was immediately prepared in the same manner as in Example 1. The electrode density of this electrode was 0.38 g / cm ³ . When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

A laminate type electric double layer capacitor was produced using a fluorine-based electrolyte prepared in the same manner as in Example 1 except that this electrode was used, and withstand voltage (V), capacitance at 2.5 V (F) , And the internal resistance (Ω) at each voltage was measured. The results are shown in Table 1.

Example 3
A slurry for the same electrode as in Example 1 was prepared, and 20 parts by mass of water was added to 100 parts by weight of the slurry as a viscosity adjustment immediately before application (the stability of this slurry evaluated separately was good). . Using this slurry, an electrode having a thickness of 80 μm was immediately prepared in the same manner as in Example 1. The electrode density of this electrode was 0.36 g / cm ³ . When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

Example 4
A slurry for the electrode as in Example 1 was prepared, and as a viscosity adjustment just before coating, 11.3 parts by mass of water was added to 100 parts by weight of the slurry (the stability of this slurry evaluated separately was ○). ) Using this slurry, an electrode having a thickness of 80 μm was immediately prepared in the same manner as in Example 1. The electrode density of this electrode was 0.43 g / cm ³ . When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

Comparative Example 1
The same slurry for electrodes as in Example 1 was prepared, and the solid content concentration was further set to 30% by mass (the stability of this slurry was good). A comparative electrode having a thickness of 80 μm was produced using this slurry. The electrode density of this electrode was 0.53 g / cm ³ . When this comparative electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

A laminate type electric double layer capacitor was produced using a fluorine-based electrolytic solution prepared in the same manner as in Example 1 except that this comparative electrode was used, and withstand voltage (V), capacitance at 2.5V. (F) and internal resistance (Ω) at each voltage were measured. The results are shown in Table 1.

Comparative Example 2
A slurry for the electrode as in Example 1 was prepared, and 7.5 parts by mass of water was added to 100 parts by weight of the slurry as a viscosity adjustment immediately before application (the stability of this slurry evaluated separately was ○). ) Using this slurry, an electrode having a thickness of 80 μm was immediately prepared in the same manner as in Example 1. The electrode density of this electrode was 0.46 g / cm ³ . When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

From the results shown in Table 1, when the electrode density is 0.45 g / cm ³ or less, while maintaining high electrostatic capacity and low internal resistance, and further utilizing the withstand voltage of the electrolyte, the electric double layer capacitor can further withstand the resistance. It can be seen that the voltage is improved.

Example 5
PTFE binder (D210C manufactured by Daikin Industries, Ltd .; binder 2) 10 parts by weight and 80 parts by weight of water were added as a binder, and the mixture was used for a predetermined time. An electrode having a thickness of 80 μm was immediately prepared in the same manner as in Example 1 using this slurry. The electrode density of this electrode was 0.40 g / cm ³ . When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

A laminate type electric double layer capacitor was produced using a fluorine-based electrolyte prepared in the same manner as in Example 1 except that this electrode was used, and withstand voltage (V), capacitance at 2.5 V (F) Was measured. The results are shown in Table 2.

Example 6
A slurry for the electrode was prepared in the same manner as in Example 1 except that YP50F (non-graphitizable carbon manufactured by Kuraray Chemical Co., Ltd., activated carbon 2) was used as the activated carbon, and this slurry was immediately used as in Example 1. Thus, an electrode having a thickness of 80 μm was produced. The electrode density of this electrode was 0.40 g / cm ³ . When this electrode was subjected to a bending resistance test and examined for mechanical durability, the electrode was not cracked (evaluation: ◯).

The electrolyte used was triethylmethylammonium BF ₄ as the electrolyte salt, and a 1: 1 mixture of PC (propylene carbonate) and fluorine-containing ether (HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H) as the electrolyte solvent. A fluorine-based electrolytic solution having an electrolyte salt concentration of 1 mol / liter was used. It was 5.0V when the withstand voltage of this fluorine-type electrolyte solution was measured.

A laminate type electric double layer capacitor was produced using a fluorine-based electrolyte prepared in the same manner as in Example 1 except that this electrode and the electrolyte were used, and withstand voltage (V), capacitance at 2.5V. (F) was measured. The results are shown in Table 2.

Comparative Example 3
A laminated electric double layer capacitor was produced in the same manner as in Example 6 except that the electrode of Comparative Example 1 was used as the electrode, and the withstand voltage (V) and the electrostatic capacity (F) at 2.5 V were measured. The results are shown in Table 2.

From Table 2, it can be seen that the withstand voltage of the capacitor decreases when the density exceeds 0.45.

Example 7
Using the same electrode as in Example 1, the electrolyte used was spirobipyrrolidinium tetraphosphate (SBP-BF ₆ ) (manufactured by Nippon Carlit Co., Ltd.) as the electrolyte salt, and CF ₃ -ethylene carbonate as the electrolyte solvent. A mixture of fluorine-containing ether (HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ .Fluorine-containing ether 2) in a ratio of 1: 1 was used, and a fluorine-based electrolytic solution having an electrolyte salt concentration of 1 mol / liter was used. It was 5.0V when the withstand voltage of this fluorine-type electrolyte solution was measured.

A laminate type electric double layer capacitor was produced in the same manner as in Example 1 except that this electrode and the electrolytic solution were used, and the withstand voltage (V) and the electrostatic capacity (F) at 2.5 V were measured. The results are shown in Table 3.

Example 8
Using the same electrode as in Example 1, the electrolyte used was triethylmethylammonium BF ₄ as the electrolyte salt, and PC (propylene carbonate) and fluorine-containing ether (HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H) were used as the electrolyte solvent. A mixture of 1: 1 was used, and a fluorine-based electrolytic solution having an electrolyte salt concentration of 1 mol / liter was used. It was 5.0V when the withstand voltage of this fluorine-type electrolyte solution was measured.

Comparative Example 4
A laminated electric double layer capacitor was produced in the same manner as in Example 1 except that the same electrode as in Comparative Example 1 was used and the same fluorine-based electrolytic solution as in Example 8 was used as the electrolytic solution. The capacitance (F) at 0.5 V was measured. The results are shown in Table 3.

Example 9
Using the same electrode as in Example 1, the electrolyte used was tetraethylammonium BF ₄ as the electrolyte salt, and PC (propylene carbonate) and fluorine-containing carbonate (CF ₃ CH ₂ OCOOCH ₂ CF ₃ ) were used as the electrolyte solvent at a ratio of 1: 1. A mixed electrolyte was used, and a fluorine electrolyte solution having an electrolyte salt concentration of 1 mol / liter was used. It was 5.0V when the withstand voltage of this fluorine-type electrolyte solution was measured.

Comparative Example 5
A laminated electric double layer capacitor was produced in the same manner as in Example 1 except that the same electrode as in Comparative Example 1 was used and the same fluorine-based electrolytic solution as in Example 9 was used as the electrolytic solution. The capacitance (F) at 0.5 V was measured. The results are shown in Table 3.

From Table 3, it can be seen that the withstand voltage of the capacitor decreases when the density exceeds 0.45.

Claims

An electric double layer capacitor comprising an electrode containing activated carbon and a binder and a non-aqueous electrolyte,
(I) The electrode density of the electrode is 0.45 g / cm 3 or less,
(II) An electric double layer capacitor, wherein the non-aqueous electrolyte is a non-aqueous electrolyte having a withstand voltage of 2.5 V or more.
The electric double layer capacitor according to claim 1, wherein the non-aqueous electrolyte is a fluorine-based electrolyte.