JPH09232190A - Electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double layer capacitor which has high working voltage, quick chargeability and dischargeability, resistance to charge and discharge cycle and high energy density. SOLUTION: A positive electrode 1 is made of a mixture of polarizing electrode material and collector of stainless steel fibers. A negative electrode 5 is made of a combination of carbon material in which lithium ions are absorbed and metallic collector. An element is made of the pair of electrodes sandwiching a separator 8 and is impregnated with non aqueous electrolytic solution 7.

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 a large energy density, capable of rapid charge / discharge, and excellent in charge / discharge cycle resistance.

[0002]

2. Description of the Related Art A conventional electric double layer capacitor is, for example, a pair of opposing polarizable electrodes each having a plate-like or foil-like metal current collector carrying a film-like polarizable electrode material mainly containing activated carbon powder. Between or a pair of opposing polarizable electrodes made of sheet-shaped activated carbon fibers to form an element, or wound with a separator sandwiched between a pair of sheet-like polarizable electrodes. It is configured to be turned into elements, and these elements are housed in a container in a state of being impregnated with an electrolytic solution, and the opening is sealed with a sealing member or the like so that the electrolytic solution does not evaporate from the opening of the container.

In US Pat. No. 5,096,663, US Pat. No. 5,080,963 and US Pat. No. 5,102,745, a mixture of stainless steel fibers, activated carbon fibers and cellulose fibers is placed on a stainless steel foil, and the stainless steel fibers are heated and sintered. At the very least, a composite polarizable electrode consisting of stainless steel fiber, activated carbon fiber and stainless steel foil,
An aqueous electrolyte solution or organic solvent system (non-aqueous system) is used for this polarizable electrode
An electric double layer capacitor impregnated with an electrolytic solution has been proposed. Activated carbon fibers have good conductivity to some extent, but they are not always sufficient, and there is a drawback that the capacity per unit volume cannot be increased because the density of the electrodes cannot be increased.

JP-A-60-161610 proposes a composite polarizable electrode in which a layer containing activated carbon powder is laminated on a mat of stainless steel fibers having finer pores than the particles of activated carbon powder. However, this composite polarizable electrode has the drawback that the bonding strength between the powder particles is weak and the internal resistance is large. Further, JP-A-61-36920 and JP-A-61-59716 propose composite polarizable electrodes composed of activated carbon fibers and short metal fibers. JP-A-2-16
No. 710 and Japanese Patent Application Laid-Open No. 2-16711 propose a composite polarizable electrode in which a felt of stainless steel fiber is arranged between a sheet-shaped activated carbon layer and a metal current collector plate.

Further, in Japanese Patent Laid-Open No. 4-154106,
An electric double layer capacitor in which an element in which a large number of sheet-shaped polarizable electrodes and separators are stacked is incorporated has been proposed for the purpose of increasing the capacity of large current. This element is composed of, for example, a plurality of sheet-shaped polarizable electrodes, which are formed in a rectangular shape, and separators are placed between the electrodes, and a large number of sheets are alternately stacked. The positive electrode lead member and the negative electrode lead member are caulked at the ends of the positive electrode and the negative electrode. The connected element is housed in a container, impregnated with an electrolytic solution, and sealed with a lid.

The electrodes of these electric double layer capacitors are
Both the positive electrode and the negative electrode are composed of polarizable electrodes mainly composed of activated carbon having a large specific surface area. Further, in order to reduce the internal resistance and obtain a large discharge current, JP-A-6-236829 proposes a collector using polar nickel as a collector of a polarizable electrode mainly composed of activated carbon powder. There is. Further, in order to increase the capacity of the electric double layer capacitor, activated carbon having a large specific surface area is used. However, the activated carbon powder having a large specific surface area usually has a maximum specific surface area of about 3000 m ² / g. Since it becomes large (bulky), the capacity per unit weight of the electric double layer capacitor obtained by using the activated carbon powder having a large specific surface area has almost reached the limit.

[0007]

An electric double layer capacitor having a large energy density capable of being charged and discharged with a large current of 10 A or more is promising for the power supply of electric vehicles and the storage of regenerative braking energy of vehicles. An object of the present invention is to provide an electric double layer capacitor which can be used for these purposes and which has a high working voltage and a large energy density, has a low internal resistance capable of rapid charge and discharge, and is excellent in charge and discharge cycle resistance. And

[0008]

The present invention has been made to achieve the above object, and a first electric double layer capacitor according to the present invention is a polarizable electrode containing activated carbon powder, conductive material powder and a binder. The material is combined with a stainless steel fiber current collector in a mixed state to form a positive electrode, and the polarizable electrode material containing activated carbon powder, conductive material powder and binder is combined with a metal current collector to form a negative electrode. A separator is disposed between the negative electrode and the negative electrode, and the positive electrode, the negative electrode, and the separator are impregnated with a non-aqueous electrolyte solution.

The activated carbon powder is a main constituent material of the polarizable electrode, and has a function of forming an electric double layer in an electrolytic solution in contact with a large surface of the activated carbon powder to store a large electric charge. Examples of the activated carbon include coconut husk activated carbon, phenol resin activated carbon, and petroleum coke activated carbon. Phenol resin-based activated carbon powder and petroleum coke-based activated carbon powder are preferably used because a large capacity can be obtained. Examples of the activated carbon activation treatment method include a steam activation treatment method and a molten KOH activation treatment. Activated carbon powder obtained by the molten KOH activation treatment method is preferable in that a larger capacity can be obtained. The activated carbon powder preferably has a large specific surface area, but if it is too large, it becomes bulky, and therefore it is preferable to select one having a specific surface area of 1000 to 2500 m ² / g. Further, if the particles of the activated carbon powder are too large, it is difficult for the particles to enter the narrow gaps of the stainless steel fiber, and it is difficult for the activated carbon powder to be evenly distributed in the polarizable electrode. However, it requires a certain cost and labor to make the activated carbon powder fine, and if it is too fine, the powder becomes difficult to handle. Therefore, the particle size of the activated carbon powder is preferably 1 to 30 μm.

The conductive material is blended for the purpose of increasing the conductivity of the polarizable electrode and lowering the internal resistance, and is a powder material exhibiting an order of magnitude higher (two digits or more) conductivity than activated carbon powder. Examples of the conductive material include powders of carbon black, natural graphite, artificial graphite, titanium oxide, ruthenium oxide and the like. Among these, it is preferable to use Ketjen black or acetylene black, which is one kind of carbon black, because the effect of improving conductivity is large even with a small amount. The content of the conductive material such as carbon black in the polarizable electrode is preferably 5% by weight or more, more preferably 10% by weight or more in the total amount with the activated carbon powder so that the conductivity can be improved. Since the capacity of the polarizable electrode decreases as the powder blending ratio decreases, the conductive material content in the polarizable electrode is 40%.
It is preferably not more than 30% by weight, particularly preferably not more than 30% by weight.

In the electric double layer capacitor of the present invention, in order to further reduce the internal resistance of the positive electrode which is the polarizable electrode,
Stainless steel fibers are mixed in the polarizable electrode.
Stainless steel fibers function as a stable current collector under the conditions of use on the positive electrode side, and even if the polarizable electrode on the positive electrode side is made thick to some extent, the internal resistance is small if stainless steel fibers are mixed inside the electrode. A polarizable electrode can be obtained, and if the polarizable electrode is thickened, a polarizable electrode having a large capacity can be obtained. Stainless steel fibers are electrochemical when assembled into electrodes,
Chemically resistant to corrosion.

Thin stainless steel fibers can reduce the internal resistance, but thin fibers having a fiber diameter of 1 μm or less are difficult to manufacture, and the gaps between the fibers are narrowed, so that it becomes difficult for the activated carbon powder to enter the gaps between the fibers. . The fiber diameter is 50
When it is at least μm, it becomes difficult to collect current evenly from the entire polarizable electrode. It is preferable to use a stainless steel fiber having a fiber diameter of 1 to 50 μm and a length of 1 mm or more so that an appropriately sized gap into which powder can enter can be formed and good current collecting performance can be obtained. As for the material of stainless steel fiber, commercially available products may be available.
4 or stainless steel 316L is particularly preferable. Further, the stainless steel fiber to be combined with the positive electrode is preferably stainless steel 316 because of its high corrosion resistance and stability,
It is preferable to combine cheaper stainless steel 304 fibers for the negative electrode. The use of stainless steel fibers pre-sintered to bond the fiber contacts further reduces the internal resistance of the polarizable electrode. This type of stainless steel fiber is available from, for example, Nippon Seisen Co., Ltd. (trade name: Naslon) and Charcoal Cross Co., USA. The fiber diameter of the stainless steel fiber is particularly preferably 1 to 15 μm.

The stainless steel fiber mat used as the current collector of the positive electrode is preferably joined to and electrically connected to the metal current collector plate. The mat or web of stainless steel fibers can be sintered, for example, by heating in an inert gas atmosphere at 1000 ° C. or higher, or in a reducing gas atmosphere. The strength of the current collector made of steel fiber is improved, and the electric resistance of the polarizable electrode can be reduced. When the electric resistance of the stainless steel fiber mat or the web itself is large, it is preferable to use a metal current collector plate together. The metal current collector may be anything that can be electrically joined to the stainless steel fiber,
Foil, expanded metal, punched foil, etc. can be used.

The current collector plate made of stainless steel fiber and metal may be subjected to electric welding, cold welding, ultrasonic welding, or a stainless steel fiber mat placed on the metal current collector plate in a reducing atmosphere up to the melting point of the metal. And the stainless steel fibers are joined to the current collector plate by heating at, or the mat of the stainless steel fibers is joined to the current collector plate with a conductive adhesive to be electrically connected. After the stainless steel fiber mat and the metal current collector plate are joined together, a polarizable electrode material mainly composed of activated carbon powder may be supported. It may be electrically joined to the current collector plate by electric welding or the like.

The binder is a binding component for keeping the activated carbon powder and the conductive material in the polarizable electrode together, and the binder is
For example, PTFE, polyvinylidene fluoride, fluoroolefin copolymer crosslinked polymer, fluoroolefin / vinyl ether copolymer crosslinked polymer, carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl alcohol and polyacrylic acid, polyimide and the like can be used.
When the content of the binder in the polarizable electrode is small, effective bond strength cannot be expressed, and the bond tends to loosen during charging / discharging to increase the internal resistance. When the content is too large, the internal resistance of the polarizable electrode becomes large. Therefore, the amount is preferably 1 to 20% by weight.

If the thickness of the polarizable electrode is too thin, the capacitance per unit area cannot be increased. If it is too thick, it is difficult to obtain a homogeneous and high-density electrode, and the internal resistance becomes high.
It is preferably 3 mm or less, particularly 0.2 to 2 mm. In addition, the porosity of the polarizable electrode is preferably 10% or more so that the electrolytic solution can penetrate into the polarizable electrode and the entire surface of the polarizable electrode inside can contribute to the accumulation of charges. However, if the porosity of the polarizable electrode is too large, the capacity of the polarizable electrode becomes small, so the porosity is preferably 60% or less. Also for the polarizable electrode of the negative electrode, it is preferable to combine the collector of the stainless steel fiber with the powder of the polarizable electrode material in a mixed state to have the same configuration as the positive electrode,
A negative electrode in which a collector of a porous metal such as porous nickel is combined in a mixed state with the powder of the polarizable electrode is also preferable.

The non-aqueous electrolyte solution contains quaternary onium cations such as R ₄ N ⁺ and R ₄ P ⁺ (where R is an alkyl group) and BF ₄ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ and PF ₆ ^-, ClO ₄ ^- is preferable to use such non-aqueous electrolyte solution of low water combined with salt and anion dissolved in an organic solvent. In particular, 4
Asymmetric quaternary onium cations in which all of the alkyl groups are not the same, eg (C ₂ H ₅ ) ₃ (CH ₃ ) N ⁺ ,
A salt of (C ₂ H ₅ ) ₃ (CH ₃ ) P ⁺ is preferable because the solubility of the salt in a solvent is high and the electric conductivity of the electrolytic solution can be increased.

In the second electric double layer capacitor according to the present invention, a polarizable electrode material containing activated carbon powder, conductive material powder and a binder is combined with a collector of stainless steel fibers in a mixed state to form a positive electrode. A negative electrode is formed by combining a carbonaceous material capable of occluding and desorbing ions with a carbonaceous material in which lithium ions have been previously occluded by a chemical method and / or an electrochemical method and a collector of a porous metal or a fibrous metal. , A separator is arranged between the positive electrode and the negative electrode, the positive electrode,
It is characterized in that the negative electrode and the separator are impregnated with a non-aqueous electrolytic solution containing a lithium salt.

In this second electric double layer capacitor, the positive electrode is a polarizable electrode, whereas the negative electrode is a non-polarizable electrode, and this construction is characterized in that the working voltage can be increased. In this electric double layer capacitor, the electrolyte of the electrolytic solution is limited to a lithium salt whose cation is lithium ion. Examples of lithium salts that can be used include LiClO ₄ , L
iCF ₃ SO ₃ , LiBF ₄ , LiPF ₆ , LiAsF
₆ , LiSbF ₆ , LiCF ₃ CO ₂ and LiN (CF
₃ SO ₂ ) ₂ . Of these, LiClO ₄ , L
iN (CF ₃ SO ₂ ) ₂ , LiBF ₄ and LiPF ₆ are particularly preferable lithium salts in terms of stability and electric conductivity.

As the organic solvent of the non-aqueous electrolyte solution which can be used in the electric double layer capacitor of the present invention, propylene carbonate,
Ethylene carbonate, butylene carbonate, γ-butyrolactone, dimethyl sulfoxide, sulfolane, formamide, dimethylformamide, dioxolane, phosphoric acid triester, maleic anhydride, succinic anhydride, phthalic anhydride, 1,3-propane sultone, propylene carbonate derivative, Ethylene carbonate derivative, 4,
5-dihydropyran derivative, lactone derivative, sulfolane derivative, nitrobenzene, 1,3-dioxane, 1,
4-dioxane, 3-methyl-2-oxazolidinone,
An organic solvent composed of one or more selected from 1,2-dimethoxyethane, tetrahydrofuran, tetrahydrofuran derivative, sydnone compound, 2-methyltetrahydrofuran, dimethyl carbonate, diethyl carbonate, acetonitrile, nitromethane, alkoxyethane and dimethylacetamide can be preferably used.

Among these organic solvents, an organic solvent composed of one or more selected from propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, butylene carbonate, sulfolane, methylsulfolane, dimethyl carbonate and ethylmethyl carbonate is chemically selected. In addition, it is a particularly preferable organic solvent in terms of electrochemical stability, electric conductivity and low temperature characteristics.

The positive electrode of the second electric double layer capacitor of the present invention has the same structure as the positive electrode of the first electric double layer capacitor of the present invention. This type of polarizable electrode can be formed, for example, as follows. A solvent is mixed with activated carbon powder, carbon black and a binder to form a polarizable electrode material slurry, and the slurry is applied or impregnated on a stainless steel fiber mat or a joined body of a stainless steel fiber mat and a metal current collector. After drying, the composite electrode is consolidated if necessary, and the polarizable electrode material and the stainless steel fiber are mixed to form a composite electrode in which the current collector and the polarizable electrode material are integrated. The positive electrode of the polarizable electrode is electrically joined to the terminal or the metal container via a conductive adhesive or by electric welding or the like.

The porosity of the polarizable electrode can be adjusted by injecting a slurry in which a solvent is mixed with activated carbon powder, a conductive material and a binder into a mat or web of stainless steel fibers, drying and compressing the mixture to consolidate it. The performance of the electric double layer capacitor can be improved by consolidating and adjusting the porosity of the electrode to a preferable value. The porosity of the polarizable electrode is preferably 10 to 10.
80%. If the porosity is less than 10%, the electrolytic solution is difficult to penetrate into the electrode, and a part of the polarizable electrode material inside the electrode does not work effectively. When the porosity exceeds 80%, the polarizable electrode becomes bulky and the energy density becomes small. The porosity of the polarizable electrode is particularly preferably 15 to 60.
%. The thickness of the polarizable electrode is 0.1 to 3 mm,
In particular, it is preferably 0.2 to 2.0 mm.

As another method of mixing the polarizable electrode material in the joined body of the stainless steel fiber mat or web and the metal current collector plate, for example, a sheet is previously formed from activated carbon powder, conductive material powder and binder. Then, the composite electrode is obtained by adjusting the hardness with a solvent such as alcohol and pressing the sheet into a mat of stainless steel fibers by a roll press or the like.

The porous metal used for the current collector of the negative electrode of the second electric double layer capacitor may be any metal that is electrochemically and chemically resistant to corrosion. As the porous metal, porous nickel having a porosity of 80 to 99.5% can be preferably used. Further, it is preferable to use a sheet-shaped material having a thickness of 0.3 to 5 mm. Especially, the porosity is 8
5 to 99%, the average number of pores per 1 cm in length (means the average number of pores crossed by a 1 cm long straight line that penetrates a porous metal)
It is preferable to use porous nickel having a ratio of 5 or more.

A slurry in which a carbon material powder and a binder are mixed with a solvent is poured into a sheet of porous metal such as porous nickel, dried and pressed to be consolidated to adjust the porosity of the electrode. It is important to adjust the porosity of the electrode to an appropriate amount by this consolidation so as to improve the performance of the electric double layer capacitor. The porosity of this negative electrode is preferably 10-8.
It is set to 0%. When the porosity is less than 10%, the electrolytic solution is less likely to enter the electrode, and a part of the electrode material inside does not work effectively. Further, when the porosity is more than 80%, the electrode becomes bulky relative to the capacity, and the capacity per unit volume of the negative electrode becomes small. The porosity of the electrode is particularly preferably 1
It is set to 5 to 60%. The thickness of the negative electrode is preferably 0.1 to 3 mm, particularly 0.2 to 2.0 mm.

In order to make a coin type electric double layer capacitor, for example, a positive electrode which is a polarizable electrode in which current collectors of stainless steel fibers are combined in a mixed state is used by a conductive adhesive or welding to make stainless steel, aluminum or the like. It is electrically connected to the lid or case of the container. Next, a polarizable electrode, which is a combination of stainless steel fiber current collectors having the same structure as the positive electrode in a mixed state, is electrically connected to a case or lid of a container made of stainless steel, nickel or the like to form a negative electrode. Alternatively, a negative electrode material composed of a carbon material capable of inserting and extracting lithium and a binder is electrically connected to a case or a lid of a container made of stainless steel, nickel or the like to form a negative electrode. An electric double layer capacitor can be formed by disposing a separator between the positive electrode and the negative electrode thus obtained, and impregnating the positive electrode, the negative electrode and the separator with an electrolytic solution and housing them in a container.

The binder used when producing the polarizable electrode material or the negative electrode using the slurry of the polarizable electrode material or the negative electrode material is polyvinylidene fluoride, fluoroolefin copolymer crosslinked polymer, fluoroolefin / vinyl ether copolymer. Combined cross-linked polymer, carboxymethyl cellulose
Preference is given to using polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl alcohol, polyacrylic acid or polyimide.

The solvent of the slurry is preferably one which dissolves these binders, and N-methylpyrrolidone, water, dimethylformamide, toluene, xylene, methyl ethyl ketone, ethyl acetate, methyl acetate, dimethyl phthalate,
Ethanol, methanol, butanol or water are selected. Further, the cross-linking agent of the cross-linked polymer, amines,
Polyamines, polyisocyanates, bisphenols and peroxides can be preferably used.

Preferable activated carbon powder used in the electric double layer capacitor of the present invention includes coconut shell type activated carbon, phenol resin type activated carbon and petroleum coke type activated carbon powder. Among these activated carbon powders, it is particularly preferable to use a phenol resin-based activated carbon powder or a petroleum coke-based activated carbon powder because a large capacity can be obtained. Examples of the activation method of activated carbon include a steam activation method and a molten KOH activation method. Molten KOH in that a larger capacity can be obtained
The activation treatment method is particularly preferable. Further, the content of the conductive material powder such as carbon black in the polarizable electrode is preferably 5% by weight or more in the total amount with the activated carbon powder so that the effect of reducing the internal resistance can be obtained. 40% by weight because the product volume decreases when the compounding amount of
It is preferable to set the following. The compounding amount of the conductive material powder is 10
It is particularly preferable that the content be ˜30% by weight.

The activated carbon powder used for the polarizable electrode has an average particle size of 30 μm or less and a specific surface area of 1000 to 3000 m.
^{The use of 2} / g is preferable because the capacity of the electric double layer capacitor can be increased and the internal resistance can be lowered.

The carbon material capable of inserting and extracting lithium ions, which is the main material of the negative electrode, includes natural graphite, artificial graphite, graphitized mesocarbon microspheres, graphitizable carbon material,
Graphitized whiskers, vapor grown carbon fibers, fired products of phenol resin, furfuryl alcohol resin, or novolac resin can be used. Among these, it is preferable to use natural graphite, artificial graphite, graphitized mesocarbon small spheres or graphitizable carbon material (baked product of resin) because it has a large capacity for occluding and desorbing lithium ions.

As the natural graphite, it is preferable to use one having a developed crystal structure and few impurities. Here, the natural graphite having a developed crystal structure means that the interplanar spacing d ₀₀₂ measured by X-ray diffraction is less than 0.336 nm, and the crystallite size L _C is 150 nm or more. A carbon material having a developed crystal structure has a large capacity for absorbing and desorbing lithium ions, and if a carbon material with few impurities is used, excellent charge / discharge cycle resistance can be imparted.

In order to reduce impurities in natural graphite, washing with an acid such as nitric acid, sulfuric acid or hydrofluoric acid is usually carried out. However, since ash can be effectively removed, the purity of carbon finally treated with hydrofluoric acid. Is preferably 99% by weight or more of natural graphite.

As artificial graphite, a crystal structure has been developed,
It is preferable to use one having a small amount of impurities. Here, a crystal structure has been developed means that the above-mentioned d ₀₀₂ is 0.3365.
nm or less and the L _C is 50 nm or more. Since artificial graphite may have a high purity if starting materials are selected, it is preferable to use carbon having a carbon purity of 99.5% by weight or more.

As the graphitized mesocarbon microspheres, 25
It is preferable to use a graphite having a crystal structure developed with heat treatment at a high temperature of 00 ° C. or higher and having a small amount of impurities. Here, a crystal structure has been developed means that the d ₀₀₂ is 0.3.
It is 37 nm or less and the L _C is 20 nm or more.

As the graphitized whisker, it is preferable to use one having few impurities with a developed crystal structure. Here, the crystal structure has been developed means that the d ₀₀₂ is 0.33.
It is 65 nm or less and the L _C is 10 nm or more.

As the graphitized carbon fiber, it is preferable to use one in which the crystal structure of graphite, which is obtained by heat-treating acrylonitrile resin fiber or the like at a temperature of 2500 ° C. or more, has been developed and which has few impurities. Here, the one having a developed crystal structure means that the d ₀₀₂ is 0.3365 nm or less and the L _C is 1
It means that it is 0 nm or more.

As the furfuryl alcohol resin baked product, furfuryl alcohol resin is 1000 to 1500 ° C.
It is preferable to use the one which is heat-treated in step 1 with a small amount of impurities. Preferably, the heat treatment makes the d ₀₀₂ 0.3.
The thickness used is 75 to 0.39 nm.

As the novolac resin fired product, it is preferable to use a carbon material having an H / C atomic ratio of 0.25 to 0.28 obtained by heat-treating the novolac resin at a temperature of 700 ° C. or lower. This fired product preferably has d ₀₀₂ of 0.38 nm or more.

The carbon material powder used for the negative electrode is capable of occluding and desorbing lithium ions, because the capacity of the electric double layer capacitor can be increased and the internal resistance thereof can be decreased, so that the average particle size is 30 μm or less is used. Is preferred.
Regarding the amount of the binder contained in the electrode, if the binder is less than 1% by weight, the bonding strength of the electrode is small, and if it exceeds 20% by weight, the electric resistance of the electric double layer capacitor increases and the capacity decreases. Therefore, it is preferably 1 to 20% by weight in the total amount with the carbon material. Considering the balance between capacity and strength, a more preferable compounding amount of the binder is 1.5 to 10% by weight. The negative electrode may be in the form of a thick film containing a binder, a sheet, or a plate, and is preferably a composite in which a current collector and an electrode material are mixed.

Further, in the method of preliminarily occluding lithium ions in the carbon material capable of occluding and desorbing lithium ions, powdery lithium is previously mixed with powder of the carbon material capable of occluding and desorbing lithium ions, or Lithium ions are occluded and desorbed by immersing the foil-shaped lithium in a state in which foil-shaped lithium is electrically contacted with a molded body of a carbon material and a binder capable of occluding and desorbing lithium ions to ionize the lithium and absorb and desorb lithium ions. Chemical method of incorporating into a carbonaceous material, in a nonaqueous (organic) solvent electrolyte containing a lithium salt as an electrolyte, one side stores lithium ions,
An electrode formed by a detachable carbon material and a binder is placed, and a lithium metal electrode is placed on the other side to apply a current,
There is an electrochemical method of occluding lithium ions in a carbon material.

Among these methods, since the steps are simple, the carbon material capable of absorbing and desorbing lithium ions and the binder are also placed in the electrolytic solution in a state where the foil-shaped lithium is electrically contacted with the molded body. It is preferable to adopt a method in which lithium is ionized by immersion and incorporated in the carbon material.

Let the single pole capacity of the positive electrode be b (farad),
When the amount of lithium ions that can be desorbed from the negative electrode facing the positive electrode is d (milliampere) and the drop voltage is v (volt), the ratio bv / 3.6d is the value of the rapid charging of the electric double layer capacitor. Since this affects discharge characteristics and charge / discharge cycle durability, it is preferable to set this ratio within a predetermined range. Here, the unipolar capacity b of the positive electrode is obtained from a voltage decrease gradient when a pair of positive electrodes are opposed to each other with a separator in between and a direct current voltage is applied in the electrolytic solution followed by constant current discharge. .

In the present invention, the operating voltage of the electric double layer capacitor when a carbon material capable of inserting and extracting lithium ions is used for the negative electrode is, for example, 2.0 to 3.3 V, 2.
It can be set to 0-4.0V, 3.3V-4.5V.

The amount d of lithium ions that can be desorbed from the negative electrode is such that the negative electrode in which lithium ions are occluded by a chemical method or an electrochemical method is + at a potential based on the Li + / Li electrode standard.
It corresponds to an integrated amount of electricity (mAh) when discharged up to 1.0 V at a current density of 1 mA / cm ² , that is, when released.
Therefore, the ratio bv / 3.6d varies depending on the operating voltage range of the capacitor even if the electric double layer capacitor has the same configuration.

The ratio bv / 3.6d is preferably 0.0
The range is 5 to 0.90. If the ratio bv / 3.6d is less than 0.05, the energy density of the electric double layer capacitor decreases, which is not preferable. On the other hand, the ratio bv /
If 3.6d is more than 0.90, the initial energy density increases, but rapid charge / discharge becomes difficult, and charge / discharge cycle durability decreases. From the viewpoint of energy density, rapid charge / discharge characteristics, and charge / discharge cycle durability, the ratio bv / 3.6d is particularly preferably 0.1 to 0.8.

[0048]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

Example 1 Phenolic resin-based molten KOH activated activated carbon powder (specific surface area 2000 m ² / g,
Average particle size 5 μm) 76% by weight, Ketjen Black EC
(Mitsubishi Chemical Corporation product) 14% by weight and polyvinylidene fluoride 10% by weight were mixed with N-methylpyrrolidone to obtain a slurry of a polarizable electrode material. 4 cm of stainless 316L fiber mat with a thickness of about 2 mm (weight per unit area 500 g / m ² , average fiber diameter about 12 μm, average fiber length 10 mm or more)
Cut to 4 cm, and this mat is 50 μm thick and width 4
cm, 7 cm long stainless steel 316L foil 1 cm ²
A current collector was obtained by electrowelding at 20 locations, and the current collector was impregnated with the slurry and dried at 200 ° C. for 30 minutes to remove the solvent. Then, the dried sheet was compacted by a roll press to a thickness of 0.87 mm to obtain a polarizable electrode in which a polarizable electrode material and a current collector of stainless 316L fiber were combined in a mixed state. This polarizable electrode has an expanded size of 4.3 cm × 4.3 cm and a porosity of 35 cm.
%Met. A glass fiber separator is sandwiched between a pair of polarizable electrodes to face each other, and the effective electrode area is 4.3 cm ×
A device having a size of 4.3 cm was obtained.

This device was dried under reduced pressure at 200 ° C. for 3 hours, placed in a polypropylene container, and added with 1.4 mo.
A non-aqueous electrolyte solution containing 1 / l of (C ₂ H ₅ ) ₃ (CH ₃ ) NBF ₄ dissolved in propylene carbonate having a water content of 10 ppm as a solvent was impregnated. This electric double layer capacitor was charged at 2.8 V and discharged at a constant current of 10 mA to obtain the initial capacity and internal resistance of the electric double layer capacitor. The initial capacity of the obtained electric double layer capacitor is 27.
5F, internal resistance was 1.1Ω.

[Example 2] Stainless steel 316 used in Example 1
A mat of L fibers was punched into a circle, impregnated with the slurry of the polarizable electrode material used in Example 1, dried, and then consolidated by pressing to have a diameter of 12.5 mmφ, a thickness of 0.65 mm and a porosity of 35%. A polar electrode was obtained. This polarizable electrode was adhered to the inside of a case made of stainless steel 304 of a coin-shaped container in which aluminum was clad with a graphite-based conductive adhesive material. Next, thickness 2 mm, porosity 97%, straight line 1
A sheet of porous nickel having an average number of pores per cm of 25 was used as a current collector, the current collector was impregnated with the slurry of the polarizable electrode material used in Example 1, dried and then compacted by pressing to have a diameter of 12.5 mm. A polarizable electrode having a thickness of 0.65 mm and a porosity of 30% was obtained as a negative electrode.

This polarizable electrode was electrically welded to the inside of a stainless steel 304 lid of a coin type container, a polypropylene separator was sandwiched between both electrodes, and 1.5 m was placed in the container.
A coin-type electric double layer capacitor was assembled by injecting an electrolytic solution obtained by dissolving ol / l of (C ₂ H ₅ ) ₃ (CH ₃ ) PBF ₄ in propylene carbonate. When the initial capacity and internal resistance of the electric double layer capacitor were measured by charging at 2.8 V and discharging at a constant current of 10 mA, the initial capacity was 2.2.
F, the internal resistance was 3.3Ω. Also, this coin type electric double layer capacitor was placed in a high temperature bath at 70 ° C. for 2.8
The capacity after applying the voltage of V for 1000 hours is 1.8F,
The internal resistance was 9Ω. FIG. 1 is a vertical cross-sectional view of this coin type electric double layer capacitor. In the figure, 1 is a positive electrode, 2 is a conductive adhesive, 3 is a lid of a coin type container, 4 is a case of the coin type container, and 5 is a case. A negative electrode, 7 is an electrolytic solution, 8 is a separator, and 9 is an insulating gasket.

[Example 3] In Example 2, 1 mol was added to the electrolytic solution.
/ L of (C ₂ H ₅ ) ₃ (CH ₃ ) PBF ₄ in a mixed solvent of sulfolane and methyl ethyl carbonate (volume ratio 4:
A coin type electric double layer capacitor was assembled in the same manner as in Example 2 except that the one dissolved in 1) was used. The operating voltage of this electric double layer capacitor is 3.3V, the initial capacity is 2.2F, and the internal resistance is 4.1Ω when discharged at a constant current of 2 mA.
Met. This coin type electric double layer capacitor is 70 ℃
After being placed in a constant temperature bath of No. 3, and after a voltage of 3.3 V for 1000 hours, the capacity was 1.9 F and the internal resistance was 10Ω.

Example 4 4.3 cm × in the same manner as in Example 1 except that the impregnation condition and the compaction condition of the slurry of the polarizable electrode material were changed to change the porosity of the polarizable electrode to 5%.
A 4.3 cm device was assembled and impregnated with the same electrolyte as in Example 1 in a polypropylene container. This electric double layer capacitor is charged at 2.8 V, 10 mA / cm
The initial capacity when discharged at ² was 25.5 F and the internal resistance was 1.8 Ω.

Example 5 Fiber diameter of about 8 μm, average length of 10 m
316L fiber of stainless steel of m or more (Basis weight is 500g / m
The web ( ² ) (fibers are shrunk and entangled with each other) was sintered to obtain two plate-shaped sintered bodies having a thickness of 1 mm, a width of 4 cm and a length of 6 cm. 2 cm of one end of this sintered body was compressed to form a lead terminal, and the remaining 4 cm × 4 cm portion was impregnated with the slurry of the polarizable electrode material used in Example 1, dried at 180 ° C. and then consolidated by a roll press. A polarizable electrode having a thickness of 0.54 mm and a porosity of 25% was obtained. A glass fiber separator is sandwiched between a pair of polarizable electrodes to face each other, and the temperature is 200 ° C.
A device was obtained by drying under reduced pressure for 3 hours. This device was placed in a polypropylene container and 1.4 mol / l (C ₂
An electric double layer capacitor was assembled by injecting an electrolyte solution using propylene carbonate in which H ₅ ) ₃ (CH ₃ ) NBF ₄ was dissolved as a solvent. The electric double layer capacitor had a working voltage of 2.8 V, an initial capacity of 21.4 F and an internal resistance of 1.0 Ω.

Example 6 A polarizable electrode having the same structure as in Example 5 was used as the positive electrode, and the negative electrode was prepared as follows. Natural graphite powder (purity 99.3%, d ₀₀₂ = 0.3355n)
m, said L _C = 200 nm or more, average particle size 10 μm) 9
N-methylpyrrolidone was added to 0% by weight and 10% by weight of polyvinylidene fluoride in a weight ratio of 3 times, and the mixture was stirred while applying ultrasonic waves to obtain a slurry of a negative electrode material in which polyvinylidene fluoride was dissolved in N-methylpyrrolidone. It was

This negative electrode material slurry was measured to have a size of 4 cm ×
4 cm, thickness 2.0 mm, porosity 97%, basis weight 55
0 g / m ² , impregnated with porous nickel having an average pore number of 25 per 1 cm of a straight line, dried under reduced pressure at 200 ° C. for 30 minutes and then consolidated by a roll press, thickness 0.5 mm, porosity 35%, A negative electrode having a supported amount of natural graphite of 36 mg / cm ² was obtained. A nickel foil having a thickness of 20 μm, a width of 4 cm and a length of 3 cm was electrically welded to the end of the negative electrode to form a terminal.

This electrode, which had been dried under reduced pressure at 190 ° C. for 1 hour, was separated by a polypropylene separator to give a dimension 4.
1 mol / l of LiN (CF ₃ SO ₂ ) _{2 is} made to face a metal lithium plate having a size of 5 cm × 4.5 cm and a thickness of 0.5 mm.
Is immersed in an electrolytic solution dissolved in a 4: 1 mixed solvent of ethylene carbonate and ethyl methyl carbonate, and a voltage of 0.01 V is applied to the metal lithium electrode for 10 hours to electrochemically occlude lithium ions in the carbon material of the negative electrode. It was The amount of desorbable lithium ions in the stored lithium ions was 160 mAh.

Then, the metallic lithium plate was removed, and a polypropylene separator having a thickness of 180 μm was sandwiched between the positive electrode of the polarizable electrode and the negative electrode which occluded lithium ions, and the two were used for occluding lithium ions. An electric double layer capacitor was assembled in a polypropylene container containing an electrolytic solution of the same composition. The single pole capacity b of this positive electrode is 43
F. The ratio bv / 3.6d was 0.15, and the volume of the device, that is, the total volume of the positive electrode, the separator and the negative electrode was 1.952 cm ³ . This electric double layer capacitor is charged at 4V, and 10mA causes 4V to 2V
After constant current discharge, the capacity and internal resistance were obtained. The initial capacitance of the obtained electric double layer capacitor was 38 F, the internal resistance was 1.7 Ω, and the energy density was calculated to be 32 Wh / liter.

Example 7 The carbon material used for the negative electrode of Example 6 was prepared by adding the above-mentioned interplanar spacing d ₀₀₂ of 0.37 nm and L _C of 100 n.
m, an average particle size of 7 μm, a powder of a fired product of a furfuryl alcohol resin, and an effective element area in the same manner as in Example 6 except that an electrolyte solution obtained by dissolving 1 mol / l of LiBF ₄ in a solvent of propylene carbonate was used. A 4 cm x 4 cm electric double layer capacitor was assembled in a polypropylene container. The positive electrode capacity b of this positive electrode is 43 F, and the ratio bv / 3.6.
d was 0.13. The volume of this element is 1.952c
m ³ and 4V after charging the electric double layer capacitor with 4V
Was calculated to have an initial capacity of 39.5 F, an internal resistance of 1.7Ω and an energy density of 33.7 Wh / liter.

Example 8 (Comparative Example) In Example 1, instead of the stainless steel fiber mat, the thickness is 50 μm and the dimension is 4.
Using a stainless steel 316L foil of 3 cm × 4.3 cm as a current collector, the slurry of the polarizable electrode material used in Example 1 was applied onto the stainless steel foil, dried at 180 ° C. and pressed to obtain two polarizable electrodes. Got The thickness of the coating film after pressing is 70μ
m, and the porosity was 29%. When this coating film had a thickness of 70 μm or more, it tended to fall off from the stainless steel foil. An electric double layer capacitor was assembled in a polypropylene container in the same manner as in Example 1 by sandwiching a separator made of a mixture of glass fiber and polypropylene fiber between the obtained two polarizable electrodes so as to face each other. The obtained electric double layer capacitor was charged at 2.8 V and discharged at a constant current of 10 mA, the initial capacity was 3.1 F and the internal resistance was 1.0 Ω.
Met.

Example 9 (Comparative Example) In Example 6, a stainless steel 316L foil having a thickness of 50 μm was used as a current collector instead of the stainless steel fiber mat, and the polarizable electrode slurry used in Example 1 was used as stainless steel 316L. Coated on the foil. 18
The thickness of the coating film pressed after drying at 0 ° C. was 70 μm, and the porosity was 29%. Using this polarizable electrode as a positive electrode, a nickel foil having a thickness of 50 μm was used instead of the porous nickel used in the negative electrode in Example 6, and the slurry of the negative electrode material used in Example 6 was coated on the nickel foil. 180 coating film
When the film was dried and then pressed, the film thickness was about 70 μm and the porosity was 29%. When this film thickness was made thicker than 70 μm, the coating film tended to separate from the nickel foil.

Then, in the same manner as in Example 6, this electrode was opposed to the metal lithium plate with the polypropylene separator interposed therebetween, and the negative electrode was allowed to electrochemically occlude lithium ions. An element consisting of a negative electrode in which lithium ions were occluded in natural graphite, a positive electrode of a polarizable electrode and a separator was placed in a polypropylene container, and the electrolytic solution used in Example 6 was injected to assemble an electric double layer capacitor. The single electrode capacity b of this positive electrode was 5.40F. When this electric double layer capacitor is charged at 4V and discharged at a constant current of 10mA from 4V to 2V, the capacity is 4.7F and the internal resistance is 1.3Ω.
Met. The ratio bv / 3.6d was 0.17, the volume of the device was 0.672 cc, and the energy density was calculated to be 7.4 Wh / liter.

By comparing Examples 1, 2, 3 and 4 with Example 8 and comparing Examples 6 and 7 with Example 9, the initial capacity and durability under voltage application, internal resistance and energy density were confirmed. It can be seen that the electric double layer capacitor of the invention is remarkably excellent.

[0074]

The electric double layer capacitor having the structure of the present invention has a high operating voltage, a large capacity, and a low internal resistance. Therefore, it is possible to provide an electric double layer capacitor which has a large energy density and can be rapidly charged and discharged. The electric double layer capacitor of the present invention is effective for a relatively small size such as a coin type, but has an electrostatic capacity of 100 to 10,000 farads or a charging / discharging current of 5 to 1000 amperes.
It is particularly suitable for an electric double layer capacitor for ultra large capacity and large current. Therefore, by using the electric double layer capacitor of the present invention, in addition to memory backup, the power performance of engine / electric double layer capacitor hybrid vehicles and electric vehicles, which are promising in the future, can be significantly improved.
Since the regenerative braking energy of a hybrid vehicle or an electric vehicle can be effectively used, its industrial utility value is great.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a coin-type electric double layer capacitor according to the present invention.

[Explanation of symbols]

 1: Positive electrode 2: Conductive adhesive (graphite type) 3: Coin type container lid 4: Coin type container case 5: Negative electrode 7: Electrolyte solution 8: Separator 9: Insulation gasket

Claims (8)

[Claims] 1. A polarizable electrode material containing activated carbon powder, conductive material powder and a binder and a current collector of stainless steel fibers mixed together to form a positive electrode, which contains activated carbon powder, conductive powder and a binder. An electric current characterized by combining a polarizable electrode material with a metal current collector to form a negative electrode, arranging a separator between the positive electrode and the negative electrode, and impregnating the positive electrode, the negative electrode and the separator with a non-aqueous electrolyte solution. Double layer capacitor. 2. The solute of the non-aqueous electrolyte is R ₄ N ⁺ or R ₄
Quaternary onium cation represented by P ⁺ (where R is an alkyl group), BF ₄ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , PF
₆ ^- and ClO ₄ ^- 1 or more of the electric double layer capacitor according to claim 1, wherein the anion of the salt selected from. 3. A polarizable electrode material containing an activated carbon powder, a conductive material powder and a binder and a current collector of stainless steel fibers mixed together in a mixed state to form a positive electrode, which absorbs lithium ions,
A carbonaceous material in which a desorbable carbon material has been occluded with lithium ions in advance by a chemical method and / or an electrochemical method is combined with a collector of a porous metal or a fibrous metal to form a negative electrode, and a positive electrode and a negative electrode. An electric double layer capacitor, characterized in that a separator is disposed between the separators, and the positive electrode, the negative electrode and the separator are impregnated with a non-aqueous electrolytic solution containing a lithium salt. 4. The solute of the non-aqueous electrolyte solution is lithium ion, BF ₄ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , PF ₆ ⁻ and ClO.
₄ ^- claim 3 is one or more anions of salts selected from
The electric double layer capacitor described. 5. A stainless steel plate is combined with a stainless steel fiber as a current collector of the positive electrode.
5. The electric double layer capacitor according to any one of 1. 6. A stainless steel fiber current collector made of fibers having a diameter of 1 to 50 μm and a length of 1 mm or more in a state where the fibers are bonded to each other by sintering, and the polarizable electrode has a thickness of 0.1.
The electric double layer capacitor according to any one of claims 1 to 5, which has a porosity of 10 to 60% at -3 mm. 7. The electric double layer capacitor according to claim 1, wherein the stainless steel fiber combined with the positive electrode is made of stainless steel 316L. 8. A positive electrode is arranged on the case side or lid side of a button type container made of a stainless steel plate or a laminated plate of aluminum and stainless steel, and a negative electrode is arranged on the lid side or case side of a button type container made of stainless steel. The electric double layer capacitor according to any one of claims 1 to 7, wherein the positive electrode and the negative electrode are respectively joined to the lid side or the case side by a conductive adhesive or welding.