JP2007043015A - Electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor which ensures both large capacitance and low impedance. <P>SOLUTION: This electric double layer capacitor consists of a pair of electrodes and an electrolysis solution touching the above pair of electrodes. Each of the electrodes has a carbon material, a specific surface area of the carbon material is smaller than or equal to 500 m<SP>2</SP>/g, and the volume of a fine pores with a diameter of 1 nm or smaller in the carbon material is smaller than or equal to 0.1 cm<SP>3</SP>/g. The electrolysis solution contains an electrolyte and an organic menstruum, and the organic menstruum contains the compounds of the chemical formula (1) and chained carbonate. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an electric double layer capacitor.

  In recent years, electric double layer capacitors (EDLC) have attracted attention. This type of electric double layer capacitor includes a pair of electrodes and an electrolytic solution in contact with the pair of electrodes.

  As the electrolytic solution, a solution in which an electrolyte is dissolved in an organic solvent, generally called nonaqueous electrolytic solution, is used. A carbon material such as activated carbon is used for the electrode.

As a typical electrolytic solution, for example, an electrolytic solution in which tetraethylammonium tetrafluoroborate (TEA ⁺ BF ₄ ⁻ ) as an electrolyte is dissolved in propylene carbonate (PC) as an organic solvent, or triethylmonomethylammonium tetrafluoro in propylene carbonate. An electrolytic solution in which borate (TEMA ⁺ BF ₄ ⁻ ) is dissolved is known.

Moreover, the electrolyte solution containing a quaternary ammonium cation is also known (for example, refer patent document 1, 2).
JP 2003-243260 A JP 2004-87956 A

  In recent years, with respect to such an electric double layer capacitor, it is required to improve withstand voltage performance. However, with the conventional electric double layer capacitor, the withstand voltage characteristic was not sufficient.

  This invention is made | formed in view of the said subject, and it aims at providing the electric double layer capacitor which can further improve a withstand voltage characteristic.

  As a result of investigations by the present inventors, the inventors have found that an electric double layer capacitor containing a specific carbon material and a specific organic solvent can improve withstand voltage characteristics as compared with the conventional one, and have arrived at the present invention.

ここで、Ｒ^１及びＲ^２は、それぞれＨ、又は、Ｃ_ｎＨ_２ｎ＋１であり、ｎは１〜６のいずれかの整数である。Ｒ^１及びＲ^２は互いに同一でも異なっても良い。

ここで、Ｒ^３及びＲ^４は、それぞれＣ_ｎＨ_２ｎ＋１であり、ｎは１〜６のいずれかの整数である。Ｒ^３及びＲ^４は互いに同一でも異なっても良い。 The electric double layer capacitor according to the present invention includes a pair of electrodes and an electrolytic solution in contact with the pair of electrodes. The electrode has a carbon material, the specific surface area of this carbon material is 500 m ² / g or less, and the volume of pores having a pore diameter of 1 nm or less in this carbon material is 0.1 cm ³ / g or less. . Moreover, electrolyte solution has electrolyte and an organic solvent, and this organic solvent contains the compound of (1) Formula, and the chain carbonate of (2) Formula.

Here, R ¹ and R ² are each H or C _n H _{2n + 1} , and n is an integer of 1 to 6. R ¹ and R ² may be the same or different from each other.

Here, ^{R 3} and ^{R 4} are _C n _{H 2n + 1,} respectively, n represents an integer of 1-6. R ³ and R ⁴ may be the same as or different from each other.

Here, it is preferable that R ¹ and R ² are both H, or R ¹ is H and R ² is CH ₃ .

R ³ and R ⁴ are both CH ₃ , R ³ is CH ₃ and R ⁴ is C ₂ H ₅ , or R ³ and R ⁴ are both C ₂ H _5. Is preferred.

  The electrolyte is preferably an onium salt, particularly a quaternary ammonium salt.

  According to the present invention, an electric double layer capacitor having excellent withstand voltage characteristics is realized.

  An example of the electric double layer capacitor according to this embodiment will be described.

  FIG. 1 is a cross-sectional view showing an electric double layer capacitor 100 according to the present embodiment.

  The electric double layer capacitor 100 mainly includes a multilayer body 20, an exterior bag 50 that accommodates the multilayer body, and a pair of leads 60 and 62 connected to the multilayer body 20.

  The stacked body 20 is a structure in which a pair of electrodes 10 are arranged to face each other with a separator 18 interposed therebetween. Each of the electrodes 10 is a product in which an active material-containing layer 14 is provided on a current collector 12. Each active material-containing layer 14 is in contact with both sides of the separator 18. Leads 60 and 62 are connected to the ends of the current collectors 12 and 12, respectively, and the ends of the leads 60 and 62 extend to the outside of the outer bag 50.

  The current collector 12 is formed of a metal foil such as an aluminum foil, for example.

The active material-containing layer 14 is formed of, for example, a mixture of a carbon material that becomes an active material and a binder. Here, a carbon material having a specific surface area of 500 m ² / g or less and a pore volume having a pore diameter of 1 nm or less of 0.1 cm ³ / g or less is used as the carbon material. The specific surface area can be easily obtained, for example, by the BET method or the like, and the volume of pores having a pore diameter of 1 nm or less can be easily obtained by the MP method or the like based on the adsorption isotherm. An example of the carbon material that satisfies the conditions regarding the specific surface area and the pore volume is acetylene black.

  As the binder, for example, a fluororesin such as polyvinylidene fluoride (PVDF) can be used.

  The separator 18 is made of an insulating porous body. Examples of the insulating porous material include cellulose nonwoven fabric.

  The laminate 20 is impregnated with an electrolytic solution for an electric double layer capacitor. The electrolytic solution for the electric double layer capacitor is mainly impregnated in the separator 18 and the active material containing layer 14 in the electrode 10.

  Here, the electrolytic solution for an electric double layer capacitor according to the present embodiment will be described in detail. The electrolytic solution for an electric double layer capacitor according to this embodiment includes an electrolyte and an organic solvent.

  The electrolyte is not particularly limited, and examples thereof include onium salts such as ammonium salts, sulfonium salts, and phosphonium. Particularly suitable electrolytes include quaternary ammonium salts such as tetraethylammonium tetrafluoroborate and triethylmonomethylammonium tetrafluoroborate.

ここで、Ｒ^１及びＲ^２は、それぞれＨ、又は、Ｃ_ｎＨ_２ｎ＋１であり、ｎは１〜６のいずれかの整数である。Ｒ^１及びＲ^２は互いに同一でも異なっても良い。

ここで、Ｒ^３及びＲ^４は、それぞれＣ_ｎＨ_２ｎ＋１であり、ｎは１〜６のいずれかの整数である。Ｒ^３及びＲ^４は互いに同一でも異なっても良い。 The organic solvent includes, in particular, a compound of the formula (1) and a chain carbonate of the formula (2).

Here, R ¹ and R ² are each H or C _n H _{2n + 1} , and n is an integer of 1 to 6. R ¹ and R ² may be the same or different from each other.

Here, ^{R 3} and ^{R 4} are _C n _{H 2n + 1,} respectively, n represents an integer of 1-6. R ³ and R ⁴ may be the same as or different from each other.

The compound of the formula (1) is so-called sulfolane or a derivative thereof. Preferable examples of the compound of formula (1) include those in which R ¹ is a methyl group or a hydrogen atom, and R ² is a hydrogen atom.

The compound of the formula (2) is a so-called chain carbonate, and preferred examples of the compound of the formula (2) are dimethyl carbonate in which R ³ and R ⁴ are methyl groups, and R ³ and R ⁴ are ethyl groups. Examples thereof include diethyl carbonate and ethyl methyl carbonate in which R ³ is a methyl group and R ⁴ is an ethyl group, and these can be used alone or in any ratio.

  The ratio of the compound of formula (1) to the compound of formula (2) is not particularly limited, but the weight of the compound of formula (1): The weight of the compound of formula (2) is 1:10 to 10: 1. It is preferable that

  The electrolyte concentration in the electrolytic solution is preferably in the range of 0.5 to 3 mol / L.

  Such an electrolytic solution may be in a gel form. For example, a gel electrolyte obtained by mixing the compounds of formulas (1) and (2), an electrolyte, a plasticizer, and a polymer matrix does not flow but becomes a film electrolyte having self-supporting properties.

  The exterior bag 50 seals the laminated body 20 and the electrolytic solution for the electric double layer capacitor therein. The outer bag 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution for the electric double layer capacitor to the outside and penetration of moisture into the electric double layer capacitor 100. For example, as the outer bag 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a synthetic resin film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil, and a film such as polypropylene can be used as the synthetic resin film.

  The leads 60 and 62 are made of a conductive material such as aluminum.

  Such an electric double layer capacitor 100 is excellent in withstand voltage characteristics as compared with the conventional one. For example, the rate of increase in impedance before and after the high-temperature high-voltage energization test is extremely small compared to the conventional case. The reason why such characteristics are obtained is not clear, but it is considered that the electrolyte solution effect due to the pore structure is reduced.

  Such an electric double layer capacitor 100 may be manufactured as follows. First, the laminate 20 to which the leads 60 and 62 are connected, the outer bag 50, and the electrolytic solution for the electric double layer capacitor are prepared. At this time, the laminated body 20 and the exterior bag 50 are each sufficiently dried. For example, after heating in air, the moisture can be sufficiently reduced by heating in vacuum.

  Subsequently, the multilayer body 20 is accommodated in the exterior bag 50, the electrolytic solution for the electric double layer capacitor is dropped into the multilayer body 20, and then the exterior bag 50 is sealed to complete the above-described electric double layer capacitor.

  In addition, the electric double layer capacitor 100 is not limited to the above-mentioned form, For example, what laminated | stacked many laminated bodies 20 etc. may be sufficient.

<Example 1>
The electric double layer capacitor of Example 1 was produced as follows.

<Production of electrode>
By using acetylene black as a carbon material as an active material and PVDF as a binder, these are mixed so that the active material: binder = 70: 30, and N-methylpyrrolidone is added to the resulting mixture and kneaded. A paint was prepared. The specific surface area of acetylene black was 60 m ² / g, and the volume of pores having a pore diameter of 1 nm or less in acetylene black was 0.08 cm ³ / g.

  This paint was applied on one side of an etching aluminum foil of 30 μm by the doctor blade method, then left in air at 150 ° C. for 30 minutes, and then heated at 175 ° C. for 12 hours under vacuum to dry the coating film. . Next, an aluminum foil was punched into a rectangular shape having a tab portion around the coating film formation region, and a pair of electrodes for an electric double layer capacitor was obtained.

<Creating a cell>
The cell was produced in an environment having a dew point of −40 ° C. or lower. Two punched electrodes were opposed to each other through a regenerated cellulose nonwoven fabric as a separator, and the center part was thermocompression bonded to obtain a laminate. Aluminum leads were welded to the tab portions of the laminate by ultrasonic welding. The laminate with the leads was put into a bag-like aluminum laminate film having two of the four sides opened, the lead was taken out from one opening, and the opening of the laminate film was thermocompression bonded with the lead sandwiched therebetween. After injecting the electrolyte for the electric double layer capacitor into the laminate from the last remaining opening of the aluminum laminate outer bag containing the laminate, sealing the remaining opening by vacuum thermocompression bonding and aging, The electric double layer capacitor of Example 1 having the form 1 was obtained. The electrolytic solution is obtained by dissolving tetraethylammonium tetrafluoroborate (TEA ⁺ BF ₄ ⁻ ) as an electrolyte in a mixed organic solvent in which the weight of sulfolane (SL): weight of diethyl carbonate (DEC) = 1: 1. The electrolyte concentration in the electrolytic solution was 0.6 mol / L.

<Example 2>
In Example 2, the carbon material was replaced with acetylene black having a specific surface area of 450 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.08 cm ³ / g, in the same manner as in Example 1. An electric double layer capacitor was obtained.

<Example 3>
In Example 3, an electric double layer capacitor was obtained in the same manner as in Example 1 except that the weight ratio of the organic solvent was SL: DMC (dimethyl carbonate) = 1: 1.

<Example 4>
In Example 4, the carbon material is replaced with acetylene black having a specific surface area of 450 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.08 cm ³ / g, in the same manner as in Example 3. An electric double layer capacitor was obtained.

<Example 5>
In Example 5, an electric double layer capacitor was obtained in the same manner as in Example 1 except that the weight ratio of the organic solvent was SL: EMC (ethyl methyl carbonate) = 1: 1.

<Example 6>
In Example 6, the carbon material was replaced with acetylene black having a specific surface area of 450 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.08 cm ³ / g, in the same manner as in Example 5. An electric double layer capacitor was obtained.

<Example 7>
In Example 7, an electric double layer capacitor was obtained in the same manner as in Example 2 except that the weight ratio of the organic solvent was SL: DEC: DMC = 1: 1: 1.

<Example 8>
In Example 8, an electric double layer capacitor was obtained in the same manner as in Example 2 except that the weight ratio of the organic solvent was SL: DEC: EMC = 1: 1: 1.

<Example 9>
In Example 9, an electric double layer capacitor was obtained in the same manner as in Example 2 except that the weight ratio of the organic solvent was SL: DEC: DMC: EMC = 1: 1: 1.

<Comparative Example 1>
In Comparative Example 1, an electric double layer capacitor was obtained in the same manner as in Example 1 except that only the organic solvent was PC (propylene carbonate).

<Comparative example 2>
In Comparative Example 2, the carbon material was replaced with acetylene black having a specific surface area of 250 m ² / g and a pore diameter of 1 nm or less having a pore diameter of 0.08 cm ³ / g, and the same as Comparative Example 1 An electric double layer capacitor was obtained.

<Comparative Example 3>
Comparative Example 3 was the same as Comparative Example 1 except that the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.08 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative example 4>
In Comparative Example 4, the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less having a pore diameter of 0.08 cm ³ / g, in the same manner as in Example 1. An electric double layer capacitor was obtained.

<Comparative Example 5>
Comparative Example 5 was the same as Comparative Example 4 except that the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative Example 6>
Comparative Example 6 was the same as Comparative Example 4 except that the carbon material was replaced with acetylene black having a specific surface area of 60 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative Example 7>
In Comparative Example 7, the carbon material was replaced with acetylene black having a specific surface area of 450 m ² / g and a pore diameter of 1 nm or less having a pore diameter of 0.3 cm ³ / g, in the same manner as in Comparative Example 4. An electric double layer capacitor was obtained.

<Comparative Example 8>
Comparative Example 8 was the same as Comparative Example 3 except that the carbon material was replaced with acetylene black having a specific surface area of 60 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative Example 9>
In Comparative Example 9, the carbon material was replaced with acetylene black having a specific surface area of 450 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g in the same manner as in Comparative Example 8. An electric double layer capacitor was obtained.

<Comparative Example 10>
Comparative Example 10 was the same as Comparative Example 8 except that the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.08 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative Example 11>
Comparative Example 11 was the same as Comparative Example 8 except that the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative Example 12>
In Comparative Example 12, the carbon material was replaced with acetylene black having a specific surface area of 60 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g in the same manner as in Example 5. An electric double layer capacitor was obtained.

<Comparative Example 13>
Comparative Example 13 was the same as Comparative Example 12 except that the carbon material was replaced with acetylene black having a specific surface area of 450 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.3 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative example 14>
Comparative Example 14 was the same as Comparative Example 12 except that the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less and a pore volume of 0.08 cm ³ / g. An electric double layer capacitor was obtained.

<Comparative Example 15>
In Comparative Example 15, the carbon material was replaced with acetylene black having a specific surface area of 800 m ² / g and a pore diameter of 1 nm or less having a pore diameter of 0.3 cm ³ / g, in the same manner as in Comparative Example 12. An electric double layer capacitor was obtained.

<Characteristic evaluation of electric double layer capacitor>
About the electric double layer capacitor of each Example and each comparative example, the energization test of 70 degreeC and 3.0V was continuously performed for 500 hours, and the increase rate of the impedance before and after an energization test was measured. The respective values are shown in FIG.

  In Examples 1-9, while the increase rate of the impedance was less than 130%, in Comparative Examples 1-15, the increase rate of the impedance was large.

FIG. 1 is a cross-sectional view showing an electric double layer capacitor according to an embodiment. FIG. 2 is a table showing capacitor conditions and impedance increase rates before and after the current test for Examples 1 to 9 and Comparative Examples 1 to 15.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Electrode, 18 ... Separator, 20 ... Laminated body, 50 ... Exterior bag, 80 ... Electrolyte, 100 ... Electric double layer capacitor

Claims (5)

A pair of electrodes, and an electrolyte solution in contact with the pair of electrodes,
The electrode has a carbon material, the specific surface area of the carbon material is 500 m ² / g or less, and the volume of pores having a pore diameter of 1 nm or less in the carbon material is 0.1 cm ³ / g or less. Yes,
The electrolytic solution has an electrolyte and an organic solvent,
The said organic solvent is an electric double layer capacitor containing the compound of (1) Formula, and the chain carbonate of (2) Formula.

Here, R ¹ and R ² are each H or C _n H _{2n + 1} , and n is an integer of 1 to 6. R ¹ and R ² may be the same or different from each other.

Here, ^{R 3} and ^{R 4} are _C n _{H 2n + 1,} respectively, n represents an integer of 1-6. R ³ and R ⁴ may be the same as or different from each other. ^2. The electric double layer capacitor according to claim 1, wherein R ¹ and R ² are both H, or R ¹ is H and R ² is CH ₃ . R ³ and R ⁴ are both CH ₃ , R ³ is CH ₃ and R ⁴ is C ₂ H ₅ , or R ³ and R ⁴ are both C ₂ H _5. The electric double layer capacitor according to claim 1 or 2.   The electric double layer capacitor according to claim 1, wherein the electrolyte is an onium salt.   The electric double layer capacitor according to claim 4, wherein the electrolyte is a quaternary ammonium salt.

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