JP4017299B2 - Electric double layer capacitor and electrode material therefor - Google Patents

Description

【００３２】
【表２】

【００３３】
表２より、本発明によれば比較例に比べ、小電流時の静電容量に対する大電流時の静電容量低下が小さく、高出力電気二重層キャパシタが得られる。
【００３４】
【発明の効果】
本発明によれば、電気二重層キャパシタを組み立てずに電極材料用の炭素質材料を電気化学的に評価できる。そして、大電流の条件下において容量が大きいため、高出力電気二重層キャパシタを提供できる。[0001]
BACKGROUND 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 sources such as a backup power source, a vehicle power source, and an auxiliary power source.
[0002]
[Prior art]
The capacitance per unit electrode area of the electric double layer capacitor is greatly influenced by the physical properties and shape of both the polarizable electrode as a solid and the electrolyte as a liquid, from the configuration and operating principle. With regard to the electrolytic solution, various solvents, electrolytes, and the like have been studied and it can be said that the electrolyte is almost optimized. On the other hand, physical properties and shapes that affect the capacitance on the solid side, specific surface area, resistance when applying and removing charges to the electrode, that is, resistance to movement of charge inside the material, diffusion of electrolyte ions, adsorption and desorption For example, resistance to movement of the 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 the polarizable electrode of the capacitor, but the specific surface area is currently about 3000 m ² / g. The current situation is that the capacity per unit volume of the electric double layer capacitor using this has almost reached its limit.
[0003]
In particular, in order to obtain a high capacity not only under a minute current but also under a large current, it is important that the ion mobility on the surface of the carbonaceous material used as the main material of the polarizable electrode of the capacitor is high. That is, in the charging / discharging process of the capacitor, the charging characteristics / discharging characteristics are governed by the passing speed of the electrolyte ions in the pores of the carbonaceous material. As the specific surface area increases, the portion occupied by finer pores in the carbonaceous material increases, and in this fine pore, it is difficult for ions to move smoothly and the conductive path is reduced. There is a problem in that resistance to ion movement increases.
It is effective to select the most suitable carbonaceous material for the capacitor by measuring the specific surface area of the carbonaceous material and the physical characteristics such as internal connection resistance, but in order to obtain a capacitor with a high capacity even under a large current, the electrolyte It is necessary that ions can move sufficiently quickly. If ions can move sufficiently quickly, charge accumulation (charging) and discharging (discharging) can be performed sufficiently quickly. In order to select such a carbonaceous material, it is necessary to grasp 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]
[Problems to be solved by the invention]
If there is a simple method for comprehensively judging the electrochemical characteristics of a carbonaceous material such as activated carbon in an electrolytic solution, the present inventors have found that the most suitable carbon for the main component of the polarizable electrode used in the capacitor. The inventors have found that a high-quality capacitor can be obtained by selecting a quality material, and have reached the present invention.
[0005]
[Means for Solving the Problems]
That is, the electric double layer capacitor of the present invention is
In the electric double layer capacitor having a positive electrode, a negative electrode, and an electrolytic solution, the positive electrode and / or the negative electrode is composed of a polarizable electrode whose main component is a carbonaceous material having the following characteristic A. .
Characteristic A means that the current value measured 100 ms after the start of the step is the maximum current value immediately after the start of the step in the measurement in which the immersion potential is stepped by +50 mV from the immersion potential in the electrolyte solution by the chronoamperometry method. It means 10% or less.
Here, the electrolytic solution is preferably a non-aqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent.
[0006]
The present invention also provides an electrode material made of a carbonaceous material having the characteristic A for the electric double layer capacitor.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
In order to examine the ease of movement of electrolyte ions in the pores of the carbonaceous material, it is important for the inventor to measure the electrochemical behavior of the carbonaceous material alone in the electrolyte. Through such measurement, it was found that a carbonaceous material having high ion mobility can be selected for the capacitor, and that a polarizable electrode can be produced using this material, and a high output capacitor can be obtained.
[0008]
In JP-A-11-011921, the activated carbon powder and a carbonized resin such as phenol and polyvinyl butyral are mixed to prepare a granulated body, and after molding, carbonized heat treatment is performed to obtain solid activated carbon, which is formed into a sheet. Attempts to measure capacitance have been disclosed. However, in this method, it is difficult to make the process condition variation and the atmospheric condition constant in the solid or sheet process, so it is easy to be disturbed and the characteristics of activated carbon can be measured sufficiently. In addition, the evaluation was possible only in the form of incorporating the troubles in making the sheet. Furthermore, in order to assemble and test an actual electric double layer capacitor, it is necessary to thoroughly remove the moisture in the capacitor cell, particularly when a non-aqueous electrolyte solution is used. It takes days to do.
[0009]
On the other hand, the method of the present invention can measure the electrochemical behavior of a carbonaceous material with high accuracy by a very simple measurement, and the electrical characteristics when a capacitor is assembled using the carbonaceous material. Correlation is high. Using the measurement conditions of the present invention, it is possible to measure the characteristics of an arbitrarily selected carbonaceous material as microelectrodes (microelectrodes), and to measure the same electrolyte used in an actual capacitor. It is thought that it is because it is possible. In addition, there is an advantage that the electrochemical characteristics of the carbonaceous material alone that is not affected by other materials used for the polarizable electrode can be evaluated.
[0010]
The present invention is described in detail below.
The electric double layer capacitor of the present invention has a configuration including a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. At least one of the positive electrode and the negative electrode is a polarizable electrode mainly composed of a carbonaceous material having high response. It is characterized by being.
[0011]
Examples of the carbonaceous material constituting the main component of at least one of the positive electrode and the negative electrode constituting the electric double layer capacitor of the present invention include materials having a large specific surface area, and are composed of activated carbon, polyacene, carbon black, and the like. the specific surface area can be preferably exemplified a powder which is 200m ² / g~3500m ² / g. Further, it is possible to carbon fibers, carbon whiskers, fibers or powders also a specific surface area such as graphite is preferably used as long as 200m ² / g~3500m ² / g.
[0012]
Activated carbon can be obtained by carbonizing and activating mineral materials such as petroleum, palms, phenols, rayons, acrylics, pitches, etc., and the same or different composite materials. it can. As the activation method, a method by steam activation, for example, a method by chemical activation such as alkali activation, a method by oxidizing atmosphere activation in which an activated carbon source is partially oxidized in an oxidizing atmosphere, and a single method or a plurality of methods thereof Can be obtained by multiple activation.
The particle diameter of the activated carbon is preferably 0.1 μm to 100 μm, more preferably 1 μm to 20 μm, because the electrode can be easily thinned and the capacitance density of the capacitor is likely to be high.
[0013]
The carbonaceous material used in the present invention is highly responsive and has the characteristic A by itself.
In the carbonaceous material used in the present invention, the current value measured after 100 ms from the start of the step is the maximum current value immediately after the start of the step in the measurement of the immersion potential from the immersion potential to +50 mV step by chronoamperometry. (Characteristic A) and preferably 5% or less. When it is 10% or less, a high-capacity electric double layer capacitor can be obtained even in rapid charge / discharge with a large current.
[0014]
In the present invention, the measurement conditions and measurement method of the chronoamperometry (potential step) method for confirming the characteristics of the carbonaceous material are as follows.
Equipment used: HA-150, manufactured by Hokuto Denko
Working electrode: Carbonaceous material Counter electrode: Pt plate Reference electrode: Ag / Ag ⁺ electrode Electrolyte composition: Same as that used for the actual capacitor Applied voltage: Current value by stepping +50 mV from immersion potential to immersion potential Are measured continuously, and the maximum current during that time and the current value flowing 100 ms after the start of the step are measured.
[0015]
Here, the immersion potential is a potential when the carbonaceous material is immersed in the electrolyte without passing an electric current. In the present invention, electrochemical measurement is performed based on this potential.
Normally, when a carbonaceous material is measured in an electrolytic solution by a chronoamperometry method, the measured current value shows a decreasing curve determined by a time constant composed of a capacitance and a resistance component. Here, the resistance component is measured not only by the electrical electron resistance but also by the total resistance including ion diffusion and absorption / desorption resistance, so the curve according to the current value measured in the present invention is a simple decrease curve. It is not limited.
[0016]
In the present invention, the case where the change in potential is changed from the immersion potential to +50 mV stepwise with respect to the immersion potential is considered. If the step potential is too high, unintentional reaction currents due to reactive substances inside or outside the electrolyte, electrolyte, or carbonaceous material are likely to be involved in the measurement, and conversely if the step potential is too low, Since the influence of chemical measurement noise increases, 50 mV is selected as the step potential. If measured at different step potentials, it is easily expected that the ratio of the current value flowing after 100 ms to the maximum current will change.
Similarly, in the present invention, the ratio of the current value flowing 100 ms after changing the potential to the maximum current is examined, but it is easy to change the value itself by changing this measurement time. To be predicted.
[0017]
In the present invention, due to the influence of the diffusion rate and adsorption / desorption rate of the positive ions and negative ions of the electrolyte with respect to the carbonaceous material, at least one of the positive electrode and the negative electrode constituting the electric double layer capacitor has the characteristic A described above. The other electrode may be a polarizable electrode made of a material not satisfying the characteristic A, or may not be a polarizable electrode. Good. 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.
[0018]
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 the carbonaceous material having the characteristic A described above, and is not particularly limited, but a binder, more preferably a conductive material is added. Configured. This polarizable electrode is, for example, kneaded in the presence of a solvent such as alcohol, a carbonaceous material powder and a binder such as polytetrafluoroethylene, and preferably a conductive material, in the form of a sheet, dried, It is obtained by bonding to a current collector through a conductive adhesive or the like. Also, a carbonaceous material powder and a binder and preferably a conductive material are mixed with a solvent to form a slurry, which is coated on a current collector metal foil and dried to obtain an electrode integrated with the current collector. You can also
[0019]
Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin / vinyl ether copolymer crosslinked polymer, polyvinyl alcohol such as carboxymethyl cellulose, polyvinyl pyrrolidone, and polyvinyl butyral (PVB), or polyacrylic acid, phenol, and coal tar. Etc. can be used. The content of the binder in the electrode is preferably about 0.5 wt% to 20 wt% in 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 is insufficient, and if it exceeds 20% by weight, the electrical resistance increases and the capacity decreases, which is not preferable. From the strength and capacity balance of the electrode, the blending amount of the binder is more preferably 0.5 wt% to 10 wt%. In addition, as a crosslinking agent of a crosslinked polymer, amines, polyamines, polyisocyanates, bisphenols or peroxides are preferable.
[0020]
As the conductive material, powder of carbon black, natural graphite, artificial graphite, titanium oxide, ruthenium oxide or the like is used. Of these, ketjen black or acetylene black, which is a kind of carbon black, is preferably used since the effect of improving conductivity is large even in a small amount. Moreover, it is preferable that the particle size of carbon black is 0.001 micrometer-1 micrometer, More preferably, it is 0.01 micrometer-0.5 micrometer. The specific surface area thereof is preferably from 200m ² / g~1500m ² / g, it is more preferably 500m ² / g~1300m ² / g. The blending amount of the conductive material such as carbon black in the electrode is preferably 5% by weight or more, particularly 10% by weight or more in the total amount with the carbonaceous material so as to improve the conductivity. If the blending amount of the conductive material is too large, the blending ratio of the carbonaceous material decreases and the capacitance of the electrode decreases. Therefore, the blending amount of the conductive material in the electrode is 40% by weight or less, particularly 30% by weight or less. Is preferred.
[0021]
As the solvent for forming the slurry, those capable of dissolving the above binder are preferable, 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.
[0022]
The current collector of the electrode may be an electrochemically and chemically corrosion-resistant conductor. Stainless steel, aluminum, titanium, tantalum, nickel, etc. are used as the current collector of the electrode mainly composed of a carbonaceous material. Of these, 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, a stainless steel net, or wool.
[0023]
As an electrolytic solution of the electric double layer capacitor of the present invention, an aqueous electrolytic solution or a non-aqueous electrolytic solution can be used. From the viewpoint of having a high withstand voltage, a non-aqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent is used. It is preferable to use it.
[0024]
Examples of organic solvents include electrochemically stable ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, sulfolane derivatives, 3-methylsulfolane, 1,2-dimethoxyethane, acetonitrile, glutaronitrile, valeronitrile. , Dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dimethoxyethane, methyl formate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate are preferred. These can also be used as a mixture.
[0025]
As the electrolyte of the non-aqueous electrolyte solution, R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ² R ³ R ⁴ P ⁺ (R ¹ , R ² , R ³ , R ⁴ each independently has 1 to And a quaternary onium cation represented by BF ₄ ⁻ , PF ₄ ⁻ , ClO ₄ ⁻ , CF ₃ SO ₃ ^— or (SO ₂ R ⁵ ) (SO ₂ R ⁶ ) N ^- (R ^5, R ⁶ represents an alkyl group or an alkylene group having 1 to 4 carbon atoms each independently, R ⁵ and R ⁶ may form a ring.) the salts consisting of an anion selected from preferable.
Specifically, for example, (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ , (C ₂ H ₅ ) ₄ PBF ₄ and (C ₂ H ₅ ) ₃ (CH ₃ ) PBF _{4 and the} like are preferable. The concentration of these salts in the electrolytic solution is preferably about 0.1 mol / l to 2.5 mol / l, more preferably about 0.5 mol / l to 2 mol / l. When the propylene carbonate solution of (C ₂ H ₅ ) ₄ NBF ₄ and (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ is used as an electrolyte, the capacitance of the electric double layer capacitor can be increased and the charge / discharge cycle durability can be improved. It is particularly preferable because it is excellent.
[0026]
The electric double layer capacitor of the present invention includes a pair of sheet-like electrodes in which at least one electrode is the polarizable electrode described above in a case, a separator interposed between the pair of electrodes, a lead connected to the electrode, and a sheet Any configuration may be used as long as it contains at least the electrode electrode and the electrolyte impregnated in the separator. For example, an element in which a separator is sandwiched between a pair of electrodes is wound with a coin type sealed in a metal case with a gasket that insulates the metal case and the metal lid together with the electrolyte, and a pair of positive and negative electrodes are wound through the separator. Any configuration such as a winding type or a laminated type in which a large number of sheet-like electrodes are stacked via a separator can be employed.
[0027]
As the separator inserted between the positive electrode and the negative electrode in the present invention, for example, a polypropylene fiber nonwoven fabric, a glass fiber nonwoven fabric, a synthetic cellulose paper and the like can be suitably used.
[0028]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited to these.
Activated carbon is used as the carbonaceous material, and minerals such as petroleum, natural products such as palms, and synthetics such as phenolic resins can be used for existing activation methods such as steam activation, alkali activation and the like. These were selected from various activated carbons obtained by multiple activations.
The measurement of the electrochemical properties of the activated carbon alone is made by using a propylene carbonate solution containing (C ₂ H ₅ ) ₄ NBF ₄ having a concentration of 1 mol / l with respect to one activated carbon as an electrolyte, and as a measuring instrument, manufactured by Hokuto Denko Co., Ltd. Using HA-150, using a Pt plate as a counter electrode and an Ag / Ag ⁺ electrode as a reference electrode, the current waveform in the case of +50 mV step from immersion potential to immersion potential is measured by chronoamperometry, The value of the current flowing 100 ms after the start of the step is calculated as a percentage of the maximum current value immediately after the start of the step, and the result is shown in Table 1 as a current value ratio.
[0029]
Next, using each activated carbon, an actual electric double layer capacitor was produced by the following method. The electric double layer capacitor is a mixture containing 80% by weight of activated carbon powder having the characteristics selected above, 10% by weight of Ketjen Black EC, which is a kind of carbon black, and 10% by weight of polytetrafluoroethylene. The mixture was kneaded while adding ethanol, rolled and then dried at 200 ° C. for 2 hours to obtain an electrode sheet having a width of 10 cm, a length of 10 cm, and a thickness of 0.65 mm. Two disc-shaped electrodes having a diameter of 12 mm were punched from this sheet, and adhered to a stainless steel 316 case and an upper lid, respectively, with a graphite-based conductive adhesive. The upper lid and the case were vacuum-dried at 300 ° C. for 4 hours, and then the electrode was impregnated with a propylene carbonate solution containing (C ₂ H ₅ ) ₄ NBF ₄ having a concentration of 1 mol / l in a dry argon atmosphere. Next, both electrodes were opposed to each other through a polypropylene nonwoven fabric separator, and caulked and sealed using 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.
[0030]
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. Furthermore, the capacitance ratio obtained by dividing the capacitance when discharged at 0.5 A by the capacitance when discharged at 0.1 A was obtained and is shown in Table 2 together.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
From Table 2, according to the present invention, compared with the comparative example, the capacitance drop at the time of the large current with respect to the capacitance at the time of the small current is small, and the high output electric double layer capacitor is obtained.
[0034]
【The invention's effect】
According to the present invention, a carbonaceous material for electrode material can be electrochemically evaluated without assembling an electric double layer capacitor. And since a capacity | capacitance is large under the conditions of a large current, a high output electric double layer capacitor can be provided.

Claims (3)

An electric double layer capacitor having a positive electrode, a negative electrode, and an electrolytic solution, wherein the positive electrode and / or the negative electrode is composed of a polarizable electrode whose main component is a carbonaceous material having the following characteristic A Capacitor.
Characteristic A: In the measurement in which the immersion potential is stepped by +50 mV from the immersion potential to the immersion potential by the chronoamperometry method in the electrolyte, the current value measured 100 ms after the start of the step is 10% of the maximum current value immediately after the start of the step. It is as follows. The electric double layer capacitor according to claim 1, wherein the electrolytic solution is a non-aqueous electrolytic solution in which an electrolyte is dissolved in an organic solvent. 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 an electrolytic solution, comprising a carbonaceous material having the characteristic A in claim 1. An electrode material for an electric double layer capacitor.