JP2001076978A - Electric double-layer capacitor and electrode material for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high output electric double-layer capacitor and electrode materials for the capacitor. SOLUTION: This electric double-layer capacitor is provided with a positive electrode, a negative electrode, and nonaqueous electrolytic solution, and the positive electrode and/or the negative electrode are constituted of polarized electrodes with carbonaceous materials as main components. In this case, the carbonaceous materials are swept from +1.25 V to -1.25 V by a cyclic voltanmetry method in the nonaqueous electrolytic solution, and when the potential sweep rate is 100 mV/s, the differential capacity at +1 V is not less than 70% of the differential capacity at +1 V, when the potential sweeping speed is 10 mV/s.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor, and more particularly, to a high output capacitor used for various power supplies such as a backup power supply, a vehicle power supply, and an auxiliary power supply.

[0002]

2. Description of the Related Art The capacitance per unit area of an electrode of an electric double layer capacitor is large in the physical properties and shape of both a polarizable electrode as a solid and an electrolytic solution as a liquid due to its configuration and operating principle. to be influenced. As for the electrolyte,
Various solvents, electrolytes, and the like have been studied, and it can be said that they are almost optimized. On the other hand, physical properties that affect the capacitance on the solid side, such as specific surface area, resistance when applying or removing charge to the electrode, that is, resistance to movement of charge inside the material, diffusion and adsorption / desorption of electrolyte ions And the like against the movement of the like. In order to increase the specific surface area, a porous electrode mainly composed of a carbonaceous material such as activated carbon is mainly used as a polarizable electrode of a capacitor. However, the maximum specific surface area is currently about 3000 m ² / g. At present, the capacity per unit volume of the electric double layer capacitor using this has almost reached the limit.

In particular, in order to achieve a high capacity under a large current as well as a small current, it is important that the mobility of ions on the surface of a carbonaceous material used as a main material of a polarizable electrode of a capacitor is high. Becomes That is, in the charging / discharging process of the capacitor, the charging / discharging characteristics are controlled by the passing movement speed of the electrolyte ions in the pores of the carbonaceous material. When the specific surface area increases, the portion occupied by finer pores in the carbonaceous material increases, and in these fine pores, it is difficult for ions to move smoothly, and the number of conductive paths is reduced. There is a problem that resistance to the movement of ions increases. It is effective to measure the specific surface area of the carbonaceous material and the physical properties of the carbonaceous material itself to select the most suitable carbonaceous material for the capacitor. It is necessary that ions can move sufficiently quickly. If ions can move sufficiently quickly, charge accumulation (charge) and discharge (discharge) can be performed sufficiently quickly. In order to select such a carbonaceous material, it is necessary to understand the behavior of the carbonaceous material, which is the main material of the electrode, in the electrolytic solution, but no such attempt has been made.

[0004]

SUMMARY OF THE INVENTION The present inventors have proposed a simple method for comprehensively determining the electrochemical characteristics of a carbonaceous material such as activated carbon in an electrolytic solution. The present inventors have found that an optimum carbonaceous material can be selected as a main component of a polar electrode, and that a high-output capacitor can be obtained.

[0005]

That is, an electric double layer capacitor according to the present invention is an electric double layer capacitor having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode and / or the negative electrode have the following characteristics A and It is characterized by comprising a polarizable electrode whose main component is a carbonaceous material having at least one of the characteristics B. The characteristic A is a potential sweep rate of 100 mV / s in a measurement in which a potential is swept from a potential of +1.25 V to a potential of -1.25 V based on an immersion potential in the electrolytic solution by cyclic voltammetry.
It means that the differential capacity at a potential of +1 V based on the immersion potential at the time of is 70% or more of the differential capacity at a potential of +1 V based on the immersion potential at a potential sweep rate of 10 mV / s.

[0006] On the other hand, the characteristic B is defined as a characteristic in which the potential is swept from a potential of +1.25 V to a potential of -1.25 V based on the immersion potential by cyclic voltammetry in the electrolytic solution at a potential sweep rate of 100 mV / s. The differential capacity at a potential of -1 V based on the immersion potential at this time is 70% or more of the differential capacity at a potential of -1 V based on the immersion potential at a potential sweep rate of 10 mV / s.

Here, the positive electrode and / or the negative electrode may be
It is preferable that the polarizable electrode be composed mainly of a carbonaceous material having both the characteristics A and B.

The present invention also provides an electrode material made of a carbonaceous material having the above characteristics A and / or characteristics B for the above electric double layer capacitor.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor measures the electrochemical behavior of a carbonaceous material alone in an electrolytic solution in order to examine the ease of movement of electrolyte ions within the pores of the carbonaceous material. It is important to know that such a measurement enables the selection of a carbonaceous material with high ion mobility even in a capacitor, and that a high-output capacitor can be obtained by using this material to produce a polarizable electrode. This has led to the present invention.

Japanese Patent Application Laid-Open No. 11-011921 discloses that activated carbon powder is mixed with a carbonizable resin such as phenol and polyvinyl butyral to prepare granules, which are molded, carbonized and heat-treated to obtain solid activated carbon. An attempt to measure the capacitance in the form of a sheet is disclosed. However, in this method, it is difficult to keep the process conditions uniform and the atmospheric conditions constant in the process of forming a solid or sheet, so that it is easily affected by disturbance, and the characteristics of the activated carbon can be sufficiently measured. However, the evaluation could be made only in a form that included the problem when forming the sheet. Furthermore, in order to assemble and test an actual electric double layer capacitor, it is necessary to thoroughly remove the water in the capacitor cell, especially when a non-aqueous electrolyte is used. It takes days to do.

On the other hand, the method of the present invention can measure the electrochemical behavior of a carbonaceous material with a very simple measurement and high accuracy, and furthermore, the electric property when a capacitor is assembled using the carbonaceous material. High correlation with characteristics. By using the measurement conditions of the present invention, it is possible to measure the characteristics of an arbitrarily selected carbonaceous material as a microelectrode (microelectrode) and to measure the nonaqueous electrolyte used in an actual capacitor. It is thought that it is possible. Another advantage is that the electrochemical properties of the carbonaceous material alone, which is not affected by other materials used for the polarizable electrode, can be evaluated.

Hereinafter, the present invention will be described in detail. The electric double layer capacitor of the present invention has a configuration including a positive electrode, a negative electrode, and a non-aqueous electrolyte. At least one of the positive electrode and the negative electrode is a polarizable electrode mainly composed of a highly responsive carbonaceous material. It is characterized by being.

Constituting the electric double layer capacitor of the present invention
Charcoal that forms the main component of at least one of the positive and negative electrodes
Materials with a large specific surface area should be used as material
From activated carbon, polyacene, carbon black, etc.
200m ^Two/ G ~ 3500m^Two/ G
The following powder can be preferably mentioned. Also the car
Fibers such as Bonfiber, carbon whisker, and graphite
The specific surface area of fiber or powder is 200m^Two/ G ~ 3500m^Two
/ G can be preferably used.

Activated carbon includes minerals such as petroleum, palms,
It can be obtained by carbonizing and activating a phenolic, rayon-based, acryl-based, pitch-based, etc. alone or composite material of the same or different system. Examples of the activation method include a method based on steam activation, a method based on chemical activation such as alkali activation, a method based on oxidizing atmosphere activation in which an activated carbon source is partially oxidized in an oxidizing atmosphere,
And single or multiple activation by a plurality of techniques. The particle size of the activated carbon is preferably 0.1 μm to 100 μm because the electrode can be easily made thinner and the capacitance density of the capacitor is easily increased.
More preferably, it is 1 μm to 20 μm.

The carbonaceous material used in the present invention has high responsiveness, and the carbonaceous material alone has at least one of the following properties A and B. The carbonaceous material used in the present invention has a differential capacity at a potential of +1 V based on an immersion potential at a potential sweep speed of 100 mV / s, and a potential of +1 V based on an immersion potential at a potential sweep speed of 10 mV / s. Is 70% or more of the differential capacity at (characteristic A), or the potential sweep rate is 100 mV /
The differential capacity at a potential of -1 V based on the immersion potential at s is 70% of the differential capacity at a potential of -1 V based on the immersion potential at a potential sweep rate of 10 mV / s.
(Characteristic B), and at least one of them is preferably 80% or more. If both are less than 70%, high capacity cannot be obtained in large current charging and discharging.

In the present invention, it is particularly preferable that the carbonaceous material has both the above characteristics A and B from the viewpoint of making the capacitor excellent in both the charge characteristics and the discharge characteristics.

In the present invention, the measurement conditions and the measurement method of the cyclic voltammetry method for confirming the characteristics of the carbonaceous material are as follows. Equipment used: HA-150, manufactured by Hokuto Denko Co., Ltd. Working electrode: Carbonaceous material Counter electrode: Pt plate Reference electrode: Ag / Ag ⁺ electrode Electrolyte composition: Same as that used for actual capacitor Applied voltage: Based on immersion potential From + 1.25V-
Sweep to 1.25V. Potential sweep speed: 10 mV / s and 100 mV / s Measurement method: A current value for a voltage at a sweep speed of 10 mV / s and 100 mV / s is measured, and a sweep speed of 10 mV / s is measured.
Differential capacity at +1 V and differential capacity at -1 V with reference to immersion potential at / m, sweep speed 100 mV
The differential capacity at +1 V and the differential capacity at -1 V were measured based on the immersion potential at / s, and the sweep speed was 1
Normalization is based on the differential capacity at the immersion potential at 0 mV / s.

Here, the immersion potential is a potential when a carbonaceous material is immersed in an electrolytic solution without passing an electric current. In the present invention, electrochemical measurement is performed based on this potential. The differential capacity before normalization (F) shown above is the capacity at the potential of interest, and the absolute value (A) of the current flowing in cyclic voltammetry is calculated as the absolute value of the sweep speed (F). (V / s). In the present invention, since it is difficult to define the volume and weight of one grain of the carbonaceous material to be measured, the measured differential capacity value is divided by the differential capacity at the immersion potential (based on the differential capacity at the immersion potential). ) Standardization is in progress.

In the present invention, the potential is swept from +1.25 V to -1.25 V on the basis of the immersion potential by a cyclic voltammetry method capable of arbitrarily changing the potential scanning speed, and the potential of the carbonaceous material is reduced. We are considering. As a measurement condition, sweeping from +1.25 V to -1.25 V based on the immersion potential is selected as a potential range as wide as possible without decomposing the non-aqueous electrolyte. In addition, the measurement potential is set to +1 V and -1 V with the immersion potential as a reference, and the measurement is performed by removing data variation based on a time delay when reversing the potential at ± 1.25 V. In addition, the potential sweep speed is set to 1
0 mV / s and the potential sweep speed of 100 mV / s
+1 V or -1 based on the immersion potential when s
The carbonaceous material is studied by measuring the differential capacity at V and determining the ratio. The reason for employing such a potential sweep speed is that the potential sweep speed is 10
If it is less than mV / s, the potential sweep speed is too slow and the measurement tends to take a long time. If it is more than 100 mV / s, the current flows too much and measurement errors tend to occur. It is easily predicted that the measured value itself changes by changing the potential sweep speed condition and the potential condition described above.

In the present invention, the diffusion rates of positive ions and negative ions of the electrolyte with respect to the carbonaceous material,
Due to the influence of the adsorption / desorption speed, at least one of the positive electrode and the negative electrode constituting the electric double layer capacitor is composed of a polarizable electrode mainly composed of a carbonaceous material satisfying at least one of the above characteristics A and B. The other electrode may be a polarizable electrode made of a material that does not satisfy the properties A and B, and may not be a polarizable electrode. For example, the negative electrode may be a carbonaceous material capable of inserting and extracting lithium ions used for the negative electrode of a lithium ion secondary battery.

In the present invention, at least one of the positive electrode and the negative electrode of the capacitor is a polarizable electrode, and is mainly composed of a carbonaceous material satisfying at least one of the above characteristics A and B. Material, more preferably a conductive material. This polarizable electrode, for example, after kneading a carbonaceous material powder and a binder such as polytetrafluoroethylene and preferably a conductive material in the presence of a solvent such as alcohol to form a sheet, and after drying, It is obtained by bonding to a current collector via a conductive adhesive or the like. Also, a powder of a carbonaceous material and a binder and preferably a conductive material are mixed with a solvent to form a slurry, coated on a current collector metal foil, and dried to obtain an electrode integrated with the current collector. You can also.

Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, a crosslinked polymer of a fluoroolefin / vinyl ether copolymer, carboxymethylcellulose, polyvinyl alcohol such as polyvinylpyrrolidone and polyvinylbutyral (PVB), or polyacrylic acid or phenol. , Coal tar and the like can be used. The content of the binder in the electrode is preferably about 0.5% to 20% by weight based on the total amount of the carbonaceous material and the binder. If the amount of the binder is less than 0.5% by weight, the strength of the electrode becomes insufficient, and if it exceeds 20% by weight, the electric resistance increases and the capacity decreases, which is not preferable. From the viewpoint of the strength and capacity balance of the electrode, the amount of the binder is more preferably 0.5% by weight to 10% by weight. As the crosslinking agent for the crosslinked polymer, amines, polyamines, polyisocyanates, bisphenols or peroxides are preferable.

As the conductive material, powders of carbon black, natural graphite, artificial graphite, titanium oxide, ruthenium oxide and the like are used. Among them, it is preferable to use Ketjen black or acetylene black, which is a kind of carbon black, since the effect of improving conductivity is large even in a small amount. The particle size of carbon black is
It is preferably from 0.001 μm to 1 μm, more preferably from 0.01 μm to 0.5 μm. The specific surface area thereof, 200m ² / g~1500m is preferably ² / g, more preferably 500 meters ² / g to 1
300 m ² / g. The amount of the conductive material such as carbon black in the electrode is preferably 5% by weight or more, more preferably 10% by weight or more based on the total amount with the carbonaceous material so as to improve the conductivity. If the compounding amount of the conductive material is too large, the compounding ratio of the carbonaceous material is reduced and the capacitance of the electrode is reduced. Therefore, the compounding amount of the conductive material in the electrode is set to 40% by weight or less, particularly 30% by weight or less. Is preferred.

As the solvent for forming the slurry, those capable of dissolving the above binder are preferable, and N-methylpyrrolidone, dimethylformamide, toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methyl acetate, ethyl acetate, dimethyl phthalate, methanol , Ethanol, isopropanol, butanol, water and the like are appropriately selected.

The current collector of the electrode may be any conductor that is electrochemically and chemically resistant. Stainless steel, aluminum, titanium, tantalum, nickel, or the like is used as a current collector for an electrode mainly composed of a carbonaceous material. Among them, stainless steel and aluminum are preferred current collectors in terms of both performance and cost. The shape of the current collector may be a foil, a nickel or aluminum foam metal having a three-dimensional structure, or a stainless steel net or wool.

Examples of the solvent of the non-aqueous electrolytic solution of the electric double layer capacitor of the present invention include, for example, electrochemically stable ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, sulfolane derivative, 3-methylsulfolane , 1,2-dimethoxyethane, acetonitrile, glutaronitrile, valeronitrile, dimethylformamide, dimethylsulfoxide, tetrahydrofuran, dimethoxyethane, methylformate, dimethyl carbonate, diethyl carbonate, and a solvent comprising at least one selected from ethyl methyl carbonate Is preferred. These can be used as a mixture.

As the electrolyte of the non-aqueous electrolyte, R¹R^Two
R^ThreeR^FourN⁺Or R¹R^TwoR^ThreeR^FourP⁺(R¹, R
^Two, R^Three, R^FourAre each independently an alkyl having 1 to 6 carbon atoms
Represents a hydroxyl group. A quaternary onium cation represented by
BF_Four ^-, PF_Four ^-, ClO _Four ^-, CF_ThreeSO_Three ^-Or
(SO_TwoR^Five) (SO_TwoR⁶) N^-(R^Five, R⁶Is it
Each independently an alkyl or alkylene group having 1 to 4 carbon atoms
And R^FiveAnd R⁶May form a ring. From)
Salts comprising the selected anion are preferred. Specifically
Is, for example, (C_TwoH_Five)_FourNBF_Four, (C_TwoH_Five)_Three
(CH_Three) NBF_Four, (C_TwoH_Five)_FourPBF_FourAnd (C
_TwoH_Five)_Three(CH_Three) PBF_FourEtc. are preferred
No. The concentration of these salts in the electrolyte is 0.1 mol
1 / l to 2.5 mol / l, further 0.5 mol / l
It is preferably about 2 mol / l. (C_TwoH_Five)
_FourNBF_Four, (C_TwoH_Five)_Three(CH_Three) NBF_FourProfessional
When the pyrene carbonate solution is used as the electrolyte, the electric double layer
Capacitor capacitance can be increased and charge / discharge cycle resistance
It is particularly preferable because of its excellent durability.

The electric double layer capacitor according to the present invention comprises a pair of sheet electrodes in a case, a separator interposed between the pair of electrodes, a lead connected to the electrodes, and a non-aqueous electrolyte impregnated in the sheet electrodes and the separator. Any configuration may be used as long as it contains at least the electrolyte. For example, an element in which a separator is interposed between a pair of electrodes, a coin type sealed in a metal case by a gasket that insulates both a metal case and a metal lid together with a non-aqueous electrolyte, a pair of positive and negative electrodes via a separator Any configuration such as a wound type formed by winding and a laminated type in which a large number of sheet electrodes are stacked via a separator can be adopted.

In the present invention, as the separator inserted between the positive electrode and the negative electrode, for example, a nonwoven fabric of polypropylene fiber, a nonwoven fabric of glass fiber, synthetic cellulose paper, or the like can be suitably used.

[0030]

The present invention will now be described by way of examples and comparative examples.
Although described in detail, the present invention is not limited to these. Charcoal
Activated carbon is used as the raw material, and minerals such as petroleum,
Natural products such as shigara, and synthetic products such as phenolic resin
The system can be activated by existing activation methods such as steam activation, alkali
Activation and their multiple activations
Activated carbon was selected and used. Activated carbon alone electrochemical
The property was determined by measuring the concentration of 1 mol / l (C
_TwoH_Five)_FourNBF_FourPropylene carbonate containing
The solution was used as an electrolyte, and Hokuto Denko's H
Using A-150, Pt plate as counter electrode, Ag / Ag⁺Electrodes
Cyclic voltammetry using as reference electrode
Is based on the immersion potential from +1.25 V based on the immersion potential.
Up to -1.25 V, sweep speed 10 mV / s and
The test was performed at 100 mV / s. Sweep speed 10mV / s
Capacity at +1 V with reference to immersion potential at
C^Ten, And the differential capacitance C at -1V²⁰, Sweep speed 10
Fine voltage at +1 V based on immersion potential at 0 mV / s
Volume C³⁰, And the differential capacitance C at -1V⁴⁰Measure
Was. Subsequently, the differential capacity C^Ten, C²⁰, C³⁰And C⁴⁰,
Differential capacity C at immersion potential at a drawing speed of 10 mV / s ⁰⁰
And the dimensionless differential capacity C¹, C^Two, C^ThreeAnd C
^FourAnd the results are shown in Table 1. Next, the differential capacity C
^ThreeIs the differential capacity C¹% And the differential capacity C^FourBut
Differential capacity C^TwoIs calculated, and the result is differentiated.
The capacity ratio is shown in Table 1.

Next, an actual electric double layer capacitor was manufactured using each activated carbon by the following method. The electric double layer capacitor is made by adding activated carbon powder having the characteristics selected above to 80.
A mixture containing 10% by weight of Ketjen Black EC and 10% by weight of polytetrafluoroethylene was kneaded while adding ethanol, roll-rolled, and then dried at 200 ° C. for 2 hours to have a width of 10 cm. , Length 10
cm and an electrode sheet having a thickness of 0.65 mm. Two disc-shaped electrodes having a diameter of 12 mm were punched out of this sheet, and bonded to a stainless steel 316 case and a top lid, respectively, with a graphite-based conductive adhesive. The upper lid and the case are vacuum-dried at 300 ° C. for 4 hours and then dried in a dry argon atmosphere for 1 mol.
the concentration of l / l of (C ₂ H _{5) 4} propylene carbonate solution containing NBF ₄ was impregnated to the electrodes. Then
The two electrodes were opposed to each other with a polypropylene nonwoven fabric separator interposed therebetween, and sealed with a polypropylene insulating gasket. The coin-type electric double layer capacitor had a diameter of 18.3 mm and a thickness of 2.0 mm.

The capacitance was calculated from the potential gradient when the coin-type electric double layer capacitor was discharged at a constant current of 0.1 A and 0.5 A, respectively, and the results are shown in Table 2. Further, a capacitance ratio obtained by dividing the capacitance at the time of discharging at 0.5 A by the capacitance at the time of discharging at 0.1 A was obtained, and also shown in Table 2.

[0033]

[Table 1]

[0034]

[Table 2]

From Table 2, according to the present invention, compared to the comparative example,
A decrease in the capacitance at a large current with respect to the capacitance at a small current is small, and a high-output electric double layer capacitor can be obtained.

[0036]

According to the present invention, a carbonaceous material for an electrode material can be electrochemically evaluated without assembling an electric double layer capacitor. Since the capacitance is large under the condition of a large current, a high-output electric double layer capacitor can be provided.

Continued on the front page (72) Inventor Kazuya Hiratsuka 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Asahi Glass Co., Ltd. 4G046 HA01 HA03 HA04 HA07 HB00 HB02 HC03 HC09 HC11

Claims (4)

[Claims] 1. An electric double layer capacitor having a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein said positive electrode and / or said negative electrode comprises a polarizable electrode mainly composed of a carbonaceous material having the following characteristic A. An electric double layer capacitor characterized by the above-mentioned. Characteristic A: In the measurement of sweeping from a potential of +1.25 V to a potential of -1.25 V based on the immersion potential by cyclic voltammetry in the non-aqueous electrolyte,
The differential capacity at a potential of +1 V based on the immersion potential at a potential sweep speed of 100 mV / s is a potential sweep speed of 1
It is 70% or more of the differential capacity at a potential of +1 V with reference to the immersion potential at 0 mV / s. 2. An electric double layer capacitor having a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein said positive electrode and / or said negative electrode comprises a polarizable electrode mainly composed of a carbonaceous material having the following characteristic B. An electric double layer capacitor characterized by the above-mentioned. Characteristic B: In the measurement of sweeping from a potential of +1.25 V to a potential of -1.25 V based on the immersion potential by cyclic voltammetry in the non-aqueous electrolyte,
The differential capacity at a potential of -1 V with respect to the immersion potential at a potential sweep speed of 100 mV / s is a potential sweep speed of 1
It is 70% or more of the differential capacity at a potential of -1 V with respect to the immersion potential at 0 mV / s. 3. The electric double layer capacitor according to claim 1, wherein the carbonaceous material further has the characteristic B according to claim 2. 4. An electrode material for an electric double layer capacitor used as a main component of at least one electrode of an electric double layer capacitor having a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the characteristics A and / or 3. An electrode material for an electric double layer capacitor, comprising a carbonaceous material having the characteristic B according to claim 2.