JPH1187191A - Electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electric double layer capacitor which can increase a rechargeable voltage sharply, by a method wherein the rest potential of a polarizing electrode body is set in the center, between the substantial decomposition starting voltage on the oxidation side or the high-potential side of an electrolytic solution, and the substantial decomposition starting voltage on the reduction side or the low-potential side of the electrolytic solution. SOLUTION: A rest potential of a polarizing electrode body is set near the center or lower, between the substantial decomposition starting voltage on the oxidation side or the high-potential side of a nonaqueous solvent electrolytic solution, and the substantial decomposition starting voltage on the reduction side or the low-potential side of the electrolytic solution. Concretely, when the rest potential of the polarizing electrode body is designated as E [V], the substantial decomposition starting voltage on the oxidation side or the high- potential side of the electrolytic solution is designated as (a) [V] and the substantial decomposition starting voltage on the reduction side or the low-potential side of the electrolytic solution is designated as (b) [V], (a+b)/2-1.0<=E<=(a+ b)/2+0.2 is established.

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 having excellent charge / discharge cycle durability and durability when a high voltage is applied, and having a large energy density.

[0002]

2. Description of the Related Art Electric double layer capacitors which can be charged and discharged with a large current are promising for applications such as electric vehicles and auxiliary power supplies. Therefore, it is desired to realize an electric double layer capacitor having a high energy density, capable of rapid charge / discharge, and having excellent durability when a high voltage is applied and charge / discharge cycle durability.

The energy stored in a capacitor cell is calculated by ・ · C · V ² , where C is the capacity per cell (F) and V is the voltage (V) that can be applied to the cell.
Since the square of the value of the applicable voltage V is reflected in the energy, it is effective to increase the voltage applied to the capacitor to improve the energy density. However, when the voltage is large, the decomposition of the electrolytic solution occurs.

[0004] For this reason, the withstand voltage per unit cell of a conventional electric double layer capacitor depends on the type of the solvent and the solute of the electrolytic solution used. 4 V (Japanese Unexamined Patent Publication No. 7-14)
However, when used at a high voltage of 2.5 V or more, there is a problem that an increase in internal series resistance or a decrease in capacitance occurs in a short time.

[0005] Therefore, it has been attempted to apply a voltage of 2.5 V to 2.8 V by examining in detail the electrodes on the positive and negative sides, the separator, the electrolytic solution, the container and the like. For example, phenolic resin, petroleum coke, etc. are activated by KOH activation. Electrodes using activated carbon are heat-treated in an inert atmosphere to improve durability. The durability has been improved by using a fired product such as acrylonitrile resin (Japanese Unexamined Patent Publication No.
162375), a method of improving durability by using porous aluminum as a current collector of a capacitor (Japanese Patent Laid-Open No.
No. 339941) and the like.

[0006]

However, none of these examples has been satisfactory to some extent. For example, the method of heat-treating an electrode using activated carbon obtained by activating a phenol resin, petroleum coke, or the like with KOH in an inert atmosphere has a problem that the initial capacitance is also reduced at the same time. Further, Japanese Unexamined Patent Publication No.
It can be said that the methods described in Japanese Patent Application Laid-Open No. 162375 and Japanese Patent Application Laid-Open No. 8-339994 cannot fundamentally improve the durability. For the above reasons, it is practically impossible to increase the applied voltage per unit cell to 3 V or more.
It was a major barrier to energy density.

As a method of increasing the applied voltage to 3 V or more,
Japanese Patent Application Laid-Open No. 8-107048 discloses a capacitor using an electrolyte containing graphite in which lithium foil is contacted and storing lithium as a negative electrode, activated carbon as a positive electrode, and lithium ions in a solute. Since it is a non-polarizable electrode and involves an oxidation-reduction reaction between the electrode and the electrolytic solution, there is a problem in durability. In addition, since the negative electrode contains lithium, the positive electrode (polarizable electrode) is already about 3 V in an uncharged state,
When a voltage is applied up to 4.3 V as in the described embodiment, the potential change due to charging is about 1.3 V. Therefore,
The energy density when used as a capacitor is smaller than that of a normal capacitor. For these reasons, there has been a demand for a high energy density electric double layer capacitor in which the charge potential of the positive electrode is equal to or lower than the decomposition voltage of the electrolytic solution and the potential difference due to charge and discharge is large, for example, 3 V or more.

[0008]

Means for Solving the Problems Accordingly, the present inventors have:
As a result of intensive studies to solve the above problems, as a radical solution completely different from the conventional method of making the electrolyte difficult to decompose or reducing the impurities of the electrode, the natural solution of the electrode was By adjusting the potential arbitrarily, the range in which decomposition due to oxidation or reduction of the electrolytic solution occurs can be used to its full extent, and as a result, the capacity of the capacitor has not changed, but its energy density has been increased. It has been found that the present invention can be achieved. Such a concept has never been performed in a capacitor that does not perform an oxidation-reduction reaction.

An object of the present invention is to provide an electric double layer capacitor having a high energy density capable of greatly increasing the chargeable / dischargeable voltage more than ever before. Another object of the present invention is to provide an electric double layer capacitor excellent in durability when a high voltage is applied.

That is, the gist of the present invention is to provide an electric double layer capacitor using a non-aqueous solvent electrolyte and a polarizable electrode for both electrodes, wherein the natural potential of the polarizable electrode is the natural potential of the electrolytic solution. A battery characterized by using a substance located at the center (near) of the substantial decomposition start voltage on the oxidation side or the high potential side and the substantial decomposition start voltage on the reduction side or the low potential side of the electrolytic solution. More preferably, the self-potential of the polarizable electrode body is E [V], the substantial decomposition initiation voltage on the oxidizing side or high potential side of the electrolytic solution is a [V], and the reduction of the electrolytic solution is performed. When the substantial decomposition start voltage on the side or the low potential side is b [V], (a + b) /2−1.0≦E≦ (a + b) /2+0.2. Exists in double layer capacitors.

According to another aspect, the gist of the present invention is to provide an electric double layer capacitor using a non-aqueous solvent electrolyte and a polarizable electrode for both electrodes, wherein the polarizable electrode body is at least one selected from metals and inorganic substances. A substance to which one or more substances are added is used, and the natural potential of the polarizable electrode body before addition is E1 [V], the natural potential after addition is E2 [V],
When the substantial decomposition start voltage on the oxidation side or high potential side of the electrolytic solution is a [V] and the substantial decomposition start voltage on the reduction side or low potential side of the electrolytic solution is b [V], E1 > (A + b) / 2, E2 is a + b−E1
<E2 <E1 When E1 <(a + b) / 2, E2 is a + b−E1
>E2> E1.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The greatest feature of the present invention is that, in a non-aqueous electrolytic solution-based electric double layer capacitor using a polarizable electrode body, a polarizable electrode body in which a spontaneous potential generated when an electrode is immersed in the non-aqueous electrolyte solution is used as a positive electrode. In addition, more preferably, by using the positive electrode and the negative electrode, the chargeable / dischargeable voltage can be greatly increased more than ever, and an electric double layer capacitor having a high energy density can be provided. In addition, since the potential at the time of charging does not exceed the decomposition voltage of the electrolytic solution, the charge / discharge cycle durability and the durability when a high voltage is applied are greatly improved.

First, the principle will be described. According to the study by the present inventors, the current electric double layer capacitor does not have improved durability and the chargeable voltage is limited to 2.8 V because of the change in the potential of the positive electrode and the negative electrode of the electric double layer capacitor. And the decomposition voltage of the electrolyte. The decomposition voltage of the electrolytic solution is different depending on the solvent, solute, etc. of the electrolytic solution, but as a representative of those which are hardly decomposed, for example, in the case of a propylene carbonate solution of a quaternary alkylammonium salt, an electrode substantially composed of a carbonaceous substance is used. It is said that the decomposition start voltage on the oxidation side when used is around 4.4 V (vs. Li / Li ⁺ ). On the other hand, since the natural potential of a normal carbonaceous electrode is around 3 V (vs. Li / Li ⁺ ), when the potential difference between the positive and negative electrodes due to polarization after charging is 2.8 V or more, the potential on the oxidation side is 4. 4 V (vs. Li / Li ⁺ ) or more,
It is believed that electrochemical decomposition of the electrolyte occurs. As a result, when a conventional carbonaceous electrode is used, the capacity is reduced due to gas or the like generated by decomposition of the electrode solution, and there is a problem in durability when used for a long time. That is, in principle, the voltage that can be applied to the electric double layer capacitor is
Since the maximum voltage is about 2.8 V, it is impossible to apply a voltage higher than that, and there is a limit in improving the energy density.

Therefore, the inventors of the present invention have proposed that a polarizable electrode body has a spontaneous potential such that the potential at the time of charging reaches a potential at which a substantial decomposition start voltage of the electrolytic solution occurs on the high potential side (oxidation side). It is possible to increase the potential difference at the time of charging and discharging by using an electrode that has an electric double layer capacitor. I found it.

Theoretically, as a polarizable electrode, the natural potential of the non-aqueous solvent electrolyte is substantially equal to the decomposition starting voltage on the oxidizing side or high potential side, and the natural potential on the reducing side or low potential side of the electrolytic solution. By using a capacitor that is closer to the center of the substantial decomposition start voltage, it is possible to maximize the potential difference during charging and discharging even when the same electrolytic solution is used, and to provide a durable electric double layer capacitor. It is thought that it can be obtained. However, actually, when the potential at the time of charging is higher than the decomposition start voltage on the high potential side (oxidation side),
For example, a phenomenon that impairs the performance or durability of the electric double layer capacitor, such as generation of gas by decomposition of the electrolyte or the like, is likely to occur. On the other hand, when the potential becomes lower than the decomposition start voltage on the low potential side (reduction side), The formation of passivation around the electrodes tends to suppress decomposition. Therefore, the spontaneous potential of the polarizable electrode body is substantially the decomposition start voltage on the oxidizing side or high potential side of the non-aqueous solvent electrolyte,
It is preferable to be near the center of the substantial decomposition start voltage on the reduction side or the low potential side of the electrolytic solution or lower. Specifically, the natural potential of the polarizable electrode body is set to E [V],
When the substantial decomposition start voltage on the oxidation side or the high potential side of the electrolytic solution is a [V] and the substantial decomposition start voltage on the reduction side or the low potential side of the electrolytic solution is b [V], (a + b) /2−1.0≦E≦(a+b)/2+0.2.

As the polarizable electrode body of the present invention, any one may be used as long as its natural potential satisfies the above conditions, and an electrode composed of at least one substance usually selected from carbonaceous substances and inorganic substances is used. . Further, when the natural potential of the substance used as the polarizable electrode is out of the above conditions, the natural potential is adjusted by adding at least one substance selected from metals and inorganic substances to the polarizable electrode. Is also good.

When the spontaneous potential of the polarizable electrode is adjusted by adding a substance as described above, a polarizable electrode body to which at least one substance selected from metals and inorganic substances is added is used. The natural potential of the polarizable electrode body before the addition is E1 [V], the natural potential after the addition is E2 [V], and the substantial decomposition start voltage on the oxidation side or the high potential side of the electrolytic solution is a. When [V] and the substantial decomposition start voltage on the reduction side or low potential side of the electrolytic solution are b [V], when E1> (a + b) / 2, E2 is a + b−E1
<E2 <E1 When E1 <(a + b) / 2, E2 is a + b−E1
>E2> E1.

The decomposition starting voltage of the electrolytic solution is measured by a usual electrochemical technique such as cyclic voltammetry. In the present invention, a region where the oxidation-reduction current is extremely small (for example, a region where the redox current is 0.1% by cyclic voltammetry).
When it exceeds 1 mA / cm ² ), it is considered that the electrolytic solution substantially starts to decompose, and this voltage is defined as a substantial decomposition starting voltage of the electrolytic solution. Although it cannot be said unconditionally depending on measurement conditions such as temperature, in the case of a typical non-aqueous electrolyte described later, the substantial decomposition onset voltage from room temperature to 70 ° C. is 4.2 V to 4.5 V on the oxidation side ( relative to Li / Li ⁺⁾ or, is about 0.1V～0.2V (relative to Li / Li ⁺⁾ or a reducing side.

The measurement of the spontaneous potential of the polarizable electrode body is also performed using a usual electrochemical technique. In the measurement of potential in non-aqueous systems, the potential reference such as a standard hydrogen electrode in an aqueous solution is not strictly defined, but in practice, silver-silver chloride electrodes, platinum electrodes, lithium electrodes, and other electrodes are used. Generally done widely. In the present invention, it can be measured by a similar method. For example, if the substantial decomposition start voltage of the non-aqueous electrolyte is as described above, the natural potential of the polarizable electrode is 1.5 V
It is preferably at least 2.8 V (relative to Li / Li ⁺ ).
7 V or more and less than 2.7 V (vs. Li / Li ⁺ ) is more preferable. Specifically, in the case of an electric double layer capacitor using a quaternary alkylammonium salt propylene carbonate solution as an electrolytic solution and a carbonaceous electrode whose natural potential is adjusted to around 2.3 V as a polarizable electrode, about 4 V Even when a large voltage is applied, the decomposition start voltage becomes lower than the decomposition start voltage on the oxidizing side of the electrolyte, and even at a high voltage, the decomposition of the electrolyte does not occur. You. Further, since the applicable voltage is increased from 2.8V to about 4V, the maximum usable energy density of the electric double layer capacitor is greatly increased to about 2 to 6 times that of the related art. Therefore, its practical value is remarkable as an electric double layer capacitor which is required to have high energy density and durability used for a power supply of an electric vehicle or the like.

Before the addition of at least one substance selected from the group consisting of metals and inorganic substances, the polarizable electrode is preferably made of at least one substance selected from the group consisting of carbonaceous substances and inorganic substances.
Those composed of one or more substances are preferred. Examples of the carbon material include activated carbon, activated carbon plant-based wood, sawdust, coconut husk, pulp effluent, fossil fuel-based coal, petroleum heavy oil, or coal and petroleum-based tar and pitch obtained by thermally decomposing them. Coke, coal coke, tar pitch spun fiber, carbon fiber, natural graphite, artificial graphite, anthracite, fluid coke mesocarbon microbeads, carbon black, fine graphite fiber, carbon aerogel, synthetic polymer, phenolic resin, furan Resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, polyacrylonitrile, liquid crystal polymer, plastic waste, waste tire, fullerene, carbon nanotube, and the like can be used. As inorganic substances,
Ruthenium oxide, platinum oxide, osmium oxide, iridium oxide, tin oxide, manganese oxide, titanium oxide, vanadium oxide, chromium oxide, strontium oxide, tungsten oxide, cobalt oxide, nickel oxide Substances, zinc oxide, cadmium oxide, copper oxide, iron oxide, niobium oxide, molybdenum oxide, rhenium oxide, rhodium oxide, lithium oxide, rare earth oxide, ruthenium composite oxide, platinum composite oxide Material, osmium composite oxide, iridium composite oxide, tin composite oxide, manganese composite oxide, titanium composite oxide, vanadium composite oxide, chromium composite oxide, strontium composite oxide, tungsten composite oxide, cobalt composite oxide Material, nickel composite oxide, zinc composite oxide, cadmium composite oxide, copper composite oxide Oxides, iron composite oxide, niobium composite oxide, molybdenum composite oxide, rhenium complex oxide,
At least one metal oxide selected from a rhodium composite oxide, a lithium composite oxide, and a rare earth composite oxide, or a semiconductor oxide or a conductive oxide made of a metal composite oxide can be used. Among these, it is particularly preferable to use activated carbon which is relatively electrochemically and chemically stable and has a large solid-liquid interface for developing an electric double layer capacity.

The substance to be added is not particularly limited as long as the spontaneous potential of the polarizable electrode body is changed by the addition. As a substance to be added, at least one selected from metals and inorganic substances may be used. For inorganic substances, ruthenium oxide, platinum oxide, osmium oxide, iridium oxide, tin oxide, manganese oxide, titanium oxide, vanadium oxide, chromium oxide, strontium oxide,
Tungsten oxide, cobalt oxide, nickel oxide, zinc oxide, cadmium oxide, copper oxide, iron oxide, niobium oxide, molybdenum oxide, rhenium oxide, rhodium oxide, lithium oxide, rare earth oxide Stuff,
Ruthenium composite oxide, platinum composite oxide, osmium composite oxide, iridium composite oxide, tin composite oxide, manganese composite oxide, titanium composite oxide, vanadium composite oxide, chromium composite oxide, strontium composite oxide, Tungsten composite oxide, cobalt composite oxide, nickel composite oxide, zinc composite oxide, cadmium composite oxide, copper composite oxide, iron composite oxide, niobium composite oxide, molybdenum composite oxide, rhenium composite oxide, Rhodium composite oxide, lithium composite oxide, rare earth composite oxide, it is also possible to use a semiconductor oxide or a conductive oxide composed of at least one or more metal oxides or composite oxides selected from, It is convenient and more effective to use a metal. The state of the metal and the inorganic substance is not particularly limited as long as the spontaneous potential of the electrode body changes, whether or not it is ionized. To lower the natural potential, a noble metal may be added, and to increase the natural potential, a noble metal may be added. For example, it is more effective to lower the natural potential with the current electrolytic solution. In this case, the additives include alkali metals such as lithium, sodium, potassium, rubidium and cesium, alkaline earth metals such as calcium and magnesium, and yttrium. , A rare earth metal such as neodymium or a substance containing these metals can be used. Among them, a substance containing an alkali metal element is preferable, and a substance containing a lithium element showing a very low potential is more preferable.

In the case where the polarizable electrode is substantially a carbonaceous substance, when lowering the natural potential, a metal having a low or high potential such as lithium or potassium which is easily absorbed into carbon is preferably used. Although not particularly limited, these metals can be added to the electrode body by an electrochemical method, a chemical method, a physical method, or the like. For example, as one of the simple methods, there is a lithium-containing electrode made of lithium metal or a substance containing lithium having a very low potential on the positive electrode side, and a carbon electrode, a separator and a non-aqueous electrolyte on the negative electrode side. By shortening the chemical cell, lithium can be added to the carbon electrode.

Further, hetero atoms such as boron, nitrogen and oxygen are introduced into the carbon skeleton, and surface functional groups such as amino group, carboxyl group, phenol group, carbonyl group and sulfone group are introduced into carbon. It is conceivable to adjust the natural potential by performing the above, but it is more effective to adjust the natural potential by adding a metal as described above.

It is preferable to use activated carbon having a large specific surface area for the electrode of the carbonaceous substance before adding a metal or the like in order to increase the capacity of the electric double layer capacitor. Since the specific surface area of the activated carbon is decreased is too large the bulk density energy density decreases, 200~3000m ² / g are preferred, more preferably 300~2300m ² / g. Raw materials for activated carbon include plant-based wood, sawdust,
Coconut shell, pulp waste liquor, fossil fuel-based coal, petroleum heavy oil,
Or coal and petroleum pitches obtained by pyrolyzing them,
Tar pitch spun fiber, synthetic polymer, phenolic resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, liquid crystal polymer, plastic waste, waste tire, etc. These carbonized materials are activated after carbonization. Activation methods are roughly classified into gas activation and chemical activation. In the gas activation method, chemical activation is chemical activation, whereas physical activation is also called physical activation, and the carbonized raw material is contact-reacted with steam, carbon dioxide, oxygen, and other oxidizing gases at high temperatures. Then, activated carbon is obtained. The chemical activation method is a method in which a raw material is uniformly impregnated with an activation chemical, heated in an inert gas atmosphere, and activated carbon is obtained by a dehydration and oxidation reaction of the chemical. The chemicals used include zinc chloride, phosphoric acid, sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, calcium carbonate and the like. Various methods for producing activated carbon have been described above, but are not particularly limited. The activated carbon has various shapes such as crushing, granulation, granule, fiber, felt, woven fabric and sheet shape, and any of them can be used in the present invention. Among these activated carbons, activated carbon obtained by chemical activation using KOH is particularly preferable because it tends to have a larger capacity than a steam activated product.

The activated carbon after the activation treatment is replaced with nitrogen, argon,
500 to 2 under an inert atmosphere such as helium or xenon
Heat treatment at 500C, preferably 700-1500C,
The electron conductivity may be increased by removing unnecessary surface functional groups or by developing the crystallinity of carbon. Further, by heating the activated carbon in a gas containing ammonia, hydrogen, water vapor, carbon dioxide, oxygen and air, hetero atoms such as hydrogen, oxygen and nitrogen are introduced into the carbon skeleton, and surface functional groups are introduced. Thus, the natural potential may be controlled.

The activated carbon powder has an average particle diameter of 3 to
It is preferably about 40 μm. When the average particle size exceeds 40 μm, the amount of the binder can be reduced, but the internal resistance of the electric double layer capacitor increases due to factors such as a decrease in the impregnation of the activated carbon particles with the electrolytic solution. Average particle size is 3
If it is less than μm, it is necessary to add about 70% by weight or more of a binder in order to obtain sufficient strength of the molded body, and the capacity of the electric double layer capacitor is reduced. In the case of granular activated carbon, the average particle diameter is preferably 30 μm or less from the viewpoint of improving the bulk density of the electrode and reducing the internal resistance.

The polarizable electrode mainly composed of activated carbon is composed of activated carbon, a conductive agent and a binder. The polarizable electrode can be formed by a conventionally known method. For example, it is obtained by adding and mixing polytetrafluoroethylene to a mixture of activated carbon and acetylene black, followed by press molding. Also, it is possible to form a polarizable electrode by sintering only activated carbon without using a conductive agent and a binder. The electrode may be any of a thin coating film, a sheet-like or plate-like molded body, and a plate-like molded body made of a composite.

The conductive agent used for the polarizable electrode is a group consisting of carbon black such as acetylene black and Ketjen black, natural graphite, thermally expanded graphite, carbon fiber, and metal fiber such as ruthenium oxide, titanium oxide, aluminum and nickel. At least one kind of conductive agent selected from the above is preferable. In terms of improving conductivity effectively with a small amount,
Acetylene black and Ketjen black are particularly preferred, and the amount of the activated carbon varies depending on the bulk density of the activated carbon. However, if the amount is too large, the proportion of the activated carbon is reduced and the capacity is reduced. About 30% is preferable.

As the binder, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethylcellulose, fluoroolefin copolymer crosslinked polymer,
Polyvinyl alcohol, polyacrylic acid, polyimide,
It is preferable to use at least one or more of petroleum pitch, coal pitch, and phenol resin. The current collector is not particularly limited as long as it has electrochemical and chemical corrosion resistance.Examples include, but are not limited to, stainless steel, aluminum, titanium, and tantalum for the positive electrode, and stainless steel for the negative electrode.
Nickel, copper and the like are preferably used.

The electrolyte is a non-aqueous electrolyte in order to obtain a capacitor having a large voltage that can be applied and a large energy density. Although the solute of the non-aqueous electrolyte is not particularly limited, R ₄ N ⁺ , R ₄ P ⁺ (where R is C _n H _{2n + 1)}
A quaternary onium cation such as triethylmethylammonium ion and an alkali metal cation such as lithium ion and potassium ion, and BF ₄ ⁻ , PF ₆ ⁻ , ClO ₄ ⁻ , or CF ₃ S
O ₃ ^- comprising preferably used in combination with the salt of an anion. The concentration of these salts in the non-aqueous electrolyte is adjusted so that the characteristics of the electric double layer capacitor can be sufficiently obtained.
1 to 2.5 mol / liter, particularly preferably 0.3 to 2.0 mol / liter. Further, the solvent of the non-aqueous electrolyte is not particularly limited, but propylene carbonate,
Ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone, N-methyl oxazolidinone, dimethyl sulfoxide, and at least one organic material selected from trimethyl sulfoxide Solvents are preferred. At least one selected from propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, sulfolane, methyl sulfolane, and γ-butyrolactone from the viewpoint of excellent electrochemical and chemical stability and electric conductivity. Is especially preferred.
In order to obtain a high withstand voltage, the water content in the non-aqueous electrolyte is preferably 200 ppm or less, more preferably 50 ppm or less. Incidentally, polyethylene oxide, polyvinylidene fluoride, polyvinylidene chloride, polyvinyl chloride, polyvinylpyrrolidone, polyvinylpyrrolidone-polyvinyl acetate copolymer, polyvinylidene fluoride-hexafluoropropylene, poly-1,5-diaminoanthoquinone, polyaniline, An electric double layer capacitor containing a polymer electrolyte obtained by mixing a polymer such as polypyrrole and polythiophene with the above-mentioned non-aqueous electrolyte is also included in the present invention.

[0031]

EXAMPLES Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to the following examples. (Example 1) Coal-based activated carbon powder obtained by KOH activation treatment (specific surface area 2270 m ² / g, average particle diameter 10 µm)
m) After kneading a mixture consisting of 80% by weight, 10% by weight of acetylene black, and 10% by weight of polytetrafluoroethylene, using a tablet press made by JASCO to make a diameter of 10 mm and a thickness of 0.5 mm by a hydraulic press. Was molded under pressure at a pressure of 50 kgf / cm ² to obtain a disk-shaped molded body.
The molded body was dried at 300 ° C. for 3 hours in a vacuum of 0.1 torr or less to obtain an electrode body. A coin cell as shown in FIG. 1 was assembled in an argon atmosphere using the obtained electrode body mainly composed of activated carbon. The activated carbon electrode body as the positive electrode 2 was sufficiently impregnated with a 1 mol / liter propylene carbonate solution of LiBF ₄ at a concentration of 1 mol / liter, and then adhered to the inner bottom of the stainless steel case 1. Further, after the above-mentioned propylene carbonate solution of LiBF ₄ was poured into the case 1, a polyethylene separator 3, a polypropylene gasket 4 and a negative electrode 5 each having a diameter of 10 mm and a thickness of 0. After 5 mm of metallic lithium was further placed on the stainless steel upper lid 6, the coin-shaped container cell was crimped and sealed.

In order to lower the natural potential of the activated carbon electrode, lithium was doped into the activated carbon electrode by short-circuiting. Specifically, the case 1 (positive electrode side) of the obtained coin-type cell and the upper lid 6
A lead wire was brought into contact with each (negative electrode side) for about 10 seconds to short-circuit the coin cell. When the potential difference between the positive electrode and the negative electrode after the short circuit was measured with a voltmeter, 2.47 V (vs. Li / L)
i ⁺ ), which was taken as the natural potential of the activated carbon electrode after lithium doping on the positive electrode side (vs. Li / Li ⁺ ). Next, a charging / discharging device “HJ-201” manufactured by Hokuto Denko was added to this coin-shaped cell.
The potential after charging with a constant current of 1.16 mA for 50 minutes using “B” was 4.06 V.

(Comparative Example 1) Example 1 was repeated except that the short-circuit treatment between the lithium electrode and the activated carbon electrode was not performed.
The natural potential of the coin cell assembled in the same manner as in 2.
99 V (vs. Li / Li ⁺ ) and 1.16 mA
The potential after charging for 50 minutes with a constant current of 4.56 V was obtained. The potential after this charge exceeded the decomposition voltage (about 4.4 V) on the positive electrode side of the electrolytic solution. From Example 1 and Comparative Example 1, it is found that the energy density of the capacitor of the present invention can be increased as compared with the conventional product.

Example 2 A coin cell having a reduced natural potential by short-circuiting was produced in the same manner as in Example 1 and then disassembled in argon to take out only the activated carbon molded body on the positive electrode side. Repeat the above operation and the natural potential is about 2.5V
Two activated carbon molded bodies (body Li / Li ⁺ ) were obtained. next,
A concentration of 1 mol / liter (C ₂ H) was applied to the two molded bodies.
₅ ) The positive electrode 2 and the negative electrode 5 each fully impregnated with a propylene carbonate solution of ₄ NBF ₄ were used as the positive electrode 2 and the negative electrode 5, and a separator was arranged between both electrodes to assemble a coin-type cell in the same manner as described above. A double layer capacitor was obtained.
After applying a voltage of 2.8 V for 1 hour at room temperature to the obtained electric double layer capacitor, the initial capacitance obtained by discharging at a constant current of 1.16 mA was 1.24F. In order to rapidly evaluate the long-term operation reliability of the capacitor under voltage application conditions, place the capacitor in a 70 ° C. constant temperature bath, apply a voltage of 2.8 V, and measure the capacitance after 500 hours. As a result, it was 1.22F, and there was almost no deterioration in capacity.

Comparative Example 2 In Example 2, Comparative Example 1
An electric double layer capacitor was assembled in the same manner as in Example 2 except that the activated carbon electrode not subjected to the short-circuit treatment was used.
The initial capacitance of the obtained electric double layer capacitor was 1.2.
It was 3F. The capacitance after the acceleration evaluation was 1.00 F, and the capacitance was significantly deteriorated.

Example 3 A voltage of 4.0 V was applied to an electric double layer capacitor manufactured in the same manner as in Example 2 at room temperature for 1 hour, and then a constant current discharge at 1.16 mA was performed. The capacitance was 1.28F. Further, the capacitance after repeating charge and discharge 50 times under the same conditions is 1.2.
7F, a capacity deterioration was hardly observed even when a high voltage was repeatedly applied, an electric double layer capacitor having a large energy density and excellent cycle repetition characteristics was obtained.

Comparative Example 3 In Example 3, Comparative Example 2
Evaluation was performed in the same manner as in Example 3 except that the electric double layer capacitor produced in the same manner as in Example 3 was used. The initial capacitance after applying the 4.0 V voltage is 1.26 F,
The capacitance after repeating this time was 0.90F.

[0038]

According to the present invention, it is possible to provide a capacitor having a larger maximum capacity and less deterioration than conventional ones.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a coin cell used for lithium doping of an electrode in Example 1 of the present invention.

FIG. 2 is a schematic diagram of a capacitor used in an example of the present invention.

[Explanation of symbols]

 11 Case of Stainless Steel Container 12 Activated Carbon Molded Body (Positive Electrode) 13 Gasket 14 Separator 15 Lithium Metal (Negative Electrode) 16 Stainless Steel Container Top Lid 21 Stainless Steel Container Case 22 Activated Carbon Molded Body 23 Gasket 24 Separator 25 Activated Carbon Molded Body 26 Stainless Steel Container top lid

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kazushi Matsuura 1000 Kamoshita-cho, Aoba-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Yokohama Research Laboratory

Claims (9)

[Claims] 1. An electric double layer capacitor using a non-aqueous solvent electrolyte and a polarizable electrode for both electrodes, wherein the polarizable electrode body has a natural potential on the oxidation side of the electrolytic solution or a high potential. An electric double layer capacitor, which is located near the center between the substantial decomposition initiation voltage on the side of the electrolyte and the substantial decomposition initiation voltage on the reduction side or the low potential side of the electrolytic solution. 2. The natural potential of the polarizable electrode body is E [V], the substantial decomposition onset voltage on the oxidizing side or high potential side of the electrolytic solution is a [V], and the reducing potential or low potential side on the electrolytic solution is 2. The electric double layer capacitor according to claim 1, wherein, when a substantial decomposition start voltage is b [V], (a + b) /2−1.0≦E≦ (a + b) /2+0.2. 3. An electric double layer capacitor using a non-aqueous solvent electrolyte and polarizable electrodes for both electrodes, wherein a polarizable electrode body to which at least one or more substances selected from metals and inorganic substances are added is used. And the natural potential of the polarizable electrode body before addition is E1 [V], the natural potential after addition is E2 [V], and the substantial decomposition start voltage on the oxidizing side or high potential side of the electrolytic solution is When a [V] and the substantial decomposition start voltage on the reduction side or the low potential side of the electrolytic solution are b [V], when E1> (a + b) / 2, E2 is a + b−E1
<E2 <E1 When E1 <(a + b) / 2, E2 is a + b−E1
>E2> E1. An electric double layer capacitor characterized by satisfying the following conditional expression: 4. The natural potential of the polarizable electrode body is Li / Li
The electric double layer capacitor according to claim 1, wherein when ⁺ is a counter electrode, the voltage is 1.5 V or more and less than 2.8 V. 5. The polarizable electrode body before addition of at least one or more substances selected from metals and inorganic substances is substantially composed of at least one substance selected from carbonaceous substances and inorganic substances. The electric double layer capacitor according to claim 3, wherein 6. The electric double layer capacitor according to claim 1, wherein the polarizable electrode is an activated carbon electrode. 7. The electric double layer capacitor according to claim 6, wherein the activated carbon has a specific surface area of 200 m ² / g or more and 3000 m ² / g or less. 8. The electric double layer capacitor according to claim 3, wherein the substance added to the polarizable electrode body contains at least one or more elements selected from alkali metals, alkaline earth metals and rare earth metals. 9. The electric double layer capacitor according to claim 8, wherein the substance added to the polarizable electrode body contains a lithium element.