JP4973897B2 - Capacitors - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide an electric double layer capacitor having a large capacitance and excellent durability. <P>SOLUTION: This capacitor includes at least: a positive electrode wherein a porous metal body is filled with a positive electrode active material having activated carbon as a main component; a negative electrode wherein a negative electrode active material having, as a main component, a carbon material capable of absorbing and desorbing lithium ions is applied to a metal foil; and a nonaqueous electrolyte containing a lithium salt. Lithium ions are stored in the negative electrode by chemical or electrochemical methods. The porous metal body formed of a nonwoven fabric-like nickel chromium alloy having a porosity of 80 to 97%, which is produced by performing chromizing treatment on nonwoven fabric-like nickel having a nickel coating of 150 to 500 g/m<SP>2</SP>, which is obtained by coating a nonwoven fabric made of polyolefin-based fibers with nickel. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a capacitor, and more particularly to an electric double layer capacitor using an electric double layer.

  Electric double layer capacitors have recently attracted attention because of their large capacitance among various capacitors. For example, capacitors are widely used for memory backup of electrical equipment, and in recent years, the use of electric double layer capacitors has been promoted for this purpose as well. Further, it is expected to be used for vehicles such as hybrid vehicles and fuel vehicles.

  There are various types of electric double layer capacitors such as a button type, a cylindrical type, and a square type, and various types of capacitors are known (Patent Documents 1 to 5). The button type is, for example, a pair of polarizable electrodes with an activated carbon electrode layer provided on a current collector, and a separator is arranged between the electrodes to form an electric double layer capacitor element, which is stored in a metal case together with an electrolyte. It is manufactured by sealing with a sealing plate and a gasket that insulates both. For the cylindrical type, this pair of polarizable electrodes and separator are overlapped and wound to form an electric double layer capacitor element. The element is covered with an electrolytic solution and stored in an aluminum case, and sealed with a sealing material. It is manufactured by doing. The basic structure of the square type is the same as that of the button type or cylindrical type.

  The electric double layer capacitor used for the above-mentioned applications such as memory backup and automobile is required to have a higher capacity. That is, it is required to increase the capacity per unit volume and reduce the internal resistance. However, the conventional capacitor has a problem in that when the capacity is increased, the internal resistance increases and the capacity does not increase.

  In other words, when the current collector has a two-dimensional structure, if a thick electrode is produced to increase the capacity density, the distance between the current collector and the activated carbon becomes longer. Resistance increases, utilization of activated carbon decreases, and capacity density also decreases. As for internal resistance reduction, when a conductive additive is added for the purpose of improving electrical resistance, the amount of activated carbon is reduced, so that the capacity density is also reduced.

Moreover, since the capacity | capacitance of a positive electrode is small, there exists a problem that a capacity | capacitance does not increase even if it increases a negative electrode capacity | capacitance. That is, when an aluminum foil is used for the positive electrode current collector, if the activated carbon is applied thickly in order to increase the capacity, the capacity cannot be increased because the utilization factor drops or peels off. For this reason, the capacity | capacitance of a positive electrode is small compared with the carbon-type negative electrode which can take in and out Li, and the energy density of a cell cannot be made high.

In addition, since the potential of the activated carbon is 3 V (vs Li / Li ⁺ ), the cell voltage can only be increased to about 2.5 V due to the withstand voltage of the electrolyte. For this reason, there are problems such as low voltage, low energy density, and low output density.

Attempts have been made to make the current collector a porous body (three-dimensional structure) instead of a metal foil. However, even if a screen punch, punching metal, lath or the like is used as the porous body, the structure is substantially a two-dimensional structure, and a significant improvement in capacitance cannot be expected.
Currently, foamed nickel is a three-dimensional structure current collector that can be mass-produced, and is widely used as a current collector for an alkaline electrolyte secondary battery. However, in an electric double layer capacitor using a non-aqueous electrolyte for the purpose of increasing the voltage and capacity, nickel is easily oxidized by the non-aqueous electrolyte and dissolves in the electrolytic solution, so that charging is sufficient with long-term charging and discharging. Can not be.

  As metals other than nickel, there are aluminum and stainless steel having high corrosion resistance. However, these metals have a problem that a metal coating layer cannot be formed on a porous organic resin surface having high porosity. That is, since it is necessary to treat the aluminum plating in a very high temperature molten salt state, the organic resin cannot be used as an object to be plated, and it is difficult to plate the surface of the organic resin.

  Stainless steel is also widely used as a material for the positive electrode current collector, but for the same reason as stainless steel, it is difficult to obtain a highly porous current collector by plating the surface of the organic resin. . As for stainless steel, there is provided a method for obtaining a porous material by applying it to a powdered organic resin porous material and sintering it, but stainless steel powder is very expensive. In addition, after the powder adheres, the organic resin porous body, which is the base material, is removed by incineration.

Japanese Patent Laid-Open No. 11-274012 JP 09-232190 A Japanese Patent Laid-Open No. 11-150042 Japanese Patent No. 3252868 Japanese Patent No. 3689948

  An object of the present invention is to provide a capacitor having a large capacitance and excellent durability at a low cost.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors mainly have a positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body, and a carbon material that can occlude and desorb lithium ions in a metal foil. The present invention was completed by finding that a negative electrode coated with the negative electrode active material described above and a non-aqueous electrolyte containing a lithium salt were effective, and it was effective to occlude lithium ions in the negative electrode by chemical or electrochemical techniques. I let you. That is, the capacitor according to the present invention is as described below.

(1) At least a positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body, a negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil, and a lithium salt A capacitor in which lithium ions are occluded in a negative electrode by a chemical or electrochemical method, and the metal porous body is obtained by coating a nonwoven fabric made of polyolefin fibers with nickel A non-woven nickel-chromium alloy having a chromium content of 25% by mass or more and a porosity of 80-97%, produced by performing chromizing treatment on non-woven nickel having a nickel basis weight of 150-500 g / m ^2. Capacitor characterized by.
(2) The capacitor as described in (1) above, wherein the carbon material capable of inserting and extracting lithium ions is a graphite-based material or an easily graphitizable carbon material.
(3) The capacitor according to (1) or (2), wherein the metal foil of the negative electrode is any one of aluminum, copper, nickel, and stainless steel.
(4) The lithium salt is at least one selected from LiClO ₄ , LiBF ₄ and LiPF ₆ , and the solvent of the non-aqueous electrolyte is ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl The capacitor as described in any one of (1) to (3) above, which is at least one selected from methyl carbonate.
(5) The negative electrode capacity is larger than the positive electrode capacity, and the occlusion amount of lithium ions is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity, according to any one of (1) to (4) above Capacitor.

  According to the present invention, a capacitor having a large capacitance and excellent durability can be provided at low cost. In the capacitor according to the present invention, the capacity and voltage of the capacitor can be increased by increasing the filling amount of the positive electrode active material by using a metal porous body for the positive electrode current collector and inserting lithium ions in the negative electrode.

  The capacitor according to the present invention includes a positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body, a negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil, It is comprised by the non-aqueous electrolyte containing a lithium salt. And it is characterized in that lithium ions are occluded in the negative electrode by a chemical or electrochemical method. Thereby, the potential of the negative electrode is lowered, and the cell voltage can be increased. Furthermore, since the energy of the capacitor is proportional to the square of the voltage, the capacitor has high energy.

However, in the present invention, since lithium ions are used as a charge by a non-aqueous electrolyte containing a lithium salt, there is a risk of dendrite growth and short circuit due to lithium deposition. For this reason, the amount of occlusion of lithium ions in the negative electrode requires that the sum of the amount occluded in advance and the amount charged be equal to or less than the storable amount of the negative electrode.
Therefore, the capacitor according to the present invention is characterized in that the negative electrode capacity is larger than the positive electrode capacity, and lithium ions are occluded in the negative electrode up to 90% of the difference between the negative electrode capacity and the positive electrode capacity. By setting the amount of occlusion of lithium ions during discharging to 90% or less of the difference between the negative electrode capacity and the positive electrode capacity, it is possible to absorb the degree of variation in the amount of occlusion of lithium ions in the negative electrode surface during charging.

The capacitor according to the present invention can be manufactured by the following method.
The capacitor according to the present invention can be produced by forming a pair of two positive and negative electrodes, placing a separator between these electrodes, and impregnating the electrolyte. A known or commercially available separator can be used. For example, an insulating film made of polyolefin, polyethylene terephthalate, polyamide, polyimide, cellulose, glass fiber or the like is preferable. The average pore diameter of the separator is not particularly limited, and is usually about 0.01 μm to 5 μm, and the average thickness is usually about 10 μm to 100 μm.
Hereinafter, each configuration will be described in more detail.

-Positive electrode-
The positive electrode used for the capacitor according to the present invention can be produced by filling a positive electrode current collector (metal porous body) with a positive electrode active material mainly composed of activated carbon.
The filling amount (content) when the current collector is filled with the positive electrode active material is not particularly limited, and may be appropriately determined according to the thickness of the current collector, the shape of the capacitor, etc. 13~40mg / cm ² or so, it may be the preferred 16~32mg / cm ² approximately.
As a method for filling the positive electrode active material, for example, activated carbon or the like may be made into a paste, and a known method such as a press-fitting method may be used for the activated carbon positive electrode paste. Other methods include, for example, a method of immersing the current collector in an activated carbon positive electrode paste and reducing the pressure as necessary, and a method of filling the activated carbon positive electrode paste while applying pressure from one side of the current collector with a pump or the like. .

After the positive electrode is filled with the activated carbon paste, the solvent in the paste may be removed by performing a drying treatment as necessary. Further, if necessary, after being filled with activated carbon paste, it may be compression-molded by pressurizing with a roller press or the like. The thickness before and after compression is usually 300 μm to 1500 μm, preferably 400 μm to 1200 μm, and the thickness after compression molding is usually about 150 μm to 700 μm, preferably about 200 μm to 600 μm. do it.
The electrode may be provided with a lead terminal. The lead terminal may be attached by welding or applying an adhesive.

[Positive electrode active material]
The activated carbon positive electrode paste is obtained, for example, by stirring activated carbon powder in a solvent with a mixer. The activated carbon paste should just contain activated carbon and a solvent, and the mixture ratio is not limited. Examples of the solvent include N-methyl-2-pyrrolidone and water. In particular, when polyvinylidene fluoride is used as a binder, N-methyl-2-pyrrolidone may be used as a solvent. When polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose, or the like is used as a binder, water is used as a solvent. Good. Moreover, additives, such as a conductive support agent and a binder, may be included as needed.

(Activated carbon)
The activated carbon can use what is generally marketed for electric double layer capacitors. Examples of the raw material for the activated carbon include wood, coconut shell, pulp waste liquid, coal, heavy petroleum oil, coal / petroleum pitch obtained by pyrolyzing them, and resins such as phenol resins. The activation is generally performed after carbonization, and examples of the activation method include a gas activation method and a chemical activation method. The gas activation method is a method in which activated carbon is obtained by contact reaction with water vapor, carbon dioxide gas, oxygen or the like at a high temperature. The chemical activation method is a method in which activated carbon is obtained by impregnating the above-mentioned raw material with a known activation chemical and heating it in an inert gas atmosphere to cause dehydration and oxidation reaction of the activation chemical. Examples of the activation chemical include zinc chloride and sodium hydroxide.
The particle size of the activated carbon is not limited, but is preferably 20 μm or less. The specific surface area is not limited, and is preferably about 800 to 3000 m ² / g. By setting this range, the capacitance of the capacitor can be increased, and the internal resistance can be reduced.

(Conductive aid)
There is no restriction | limiting in particular in the kind of conductive support agent, A well-known or commercially available thing can be used. Examples thereof include acetylene black, ketjen black, carbon fiber, natural graphite (scaly graphite, earthy graphite, etc.), artificial graphite, ruthenium oxide and the like. Among these, acetylene black, ketjen black, carbon fiber and the like are preferable. Thereby, the electrical conductivity of the capacitor can be improved. Although the content of the conductive assistant is not limited, it is preferably about 0.1 to 10 parts by mass with respect to 100 parts by mass of the activated carbon. If it exceeds 10 parts by mass, the capacitance may decrease.

(Binder)
There is no restriction | limiting in particular in the kind of binder, A well-known or commercially available thing can be used. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, polyolefin, styrene butadiene rubber, polyvinyl alcohol, carboxymethyl cellulose and the like.
Although there is no restriction | limiting in particular also about content of a binder, Preferably it is 0.5-5 mass parts with respect to 100 mass parts of activated carbon. By setting this range, the binding strength can be improved while suppressing an increase in electrical resistance and a decrease in capacitance.

[Positive electrode current collector]
The positive electrode current collector can be obtained by subjecting a metal porous body to chromizing treatment.
(Metal porous body)
As the metal porous body, from the viewpoint of the filling property and porosity of the active material, a material based on foamed urethane or nonwoven fabric, such as foamed nickel and nonwoven fabric nickel, can be preferably used. In addition, a metal plate having a large number of small holes, a metal plate having a three-dimensional structure by receiving irregularities, a sintered body, a structure of continuous air holes, and the like are used.
In the present invention, non-woven nickel is used as the metal porous body. Hereinafter, both foamed nickel and non-woven nickel will be described.

<Foamed nickel>
Foamed nickel is obtained by forming a nickel coating layer on the surface of the foamed resin, removing the resin as the base material, and then heat-treating in a reducing atmosphere as necessary to reduce nickel. .

As the foamed resin, any known or commercially available one can be used as long as it is porous, and examples thereof include foamed urethane and foamed styrene. Among these, urethane foam is preferable from the viewpoint of particularly high porosity.
The porosity of the foamed resin is usually about 80 to 97%, preferably about 90 to 96%. The average pore diameter is usually about 20 μm to 200 μm, preferably about 30 μm to 100 μm. The thickness of the foamed resin is appropriately determined according to the use of the electric double layer capacitor, but is usually about 300 μm to 1600 μm, preferably about 400 μm to 1200 μm.

  In order to form the nickel coating layer on the surface of the foamed resin, a known nickel coating method can be employed. For example, an electrolytic plating method, an electroless plating method, a sputtering method, and the like can be given. These coating methods may be used alone, or a plurality of coating methods may be used in combination. From the viewpoint of productivity and cost, it is possible to first apply a conductive treatment to the foamed resin surface by an electroless plating method or a sputtering method, and then apply a nickel plating method to the desired basis weight by an electrolytic plating method. preferable.

  The conductive treatment is not limited as long as a conductive layer can be provided on the surface of the foamed resin. Examples of the material constituting the conductive layer (conductive coating layer) include graphite, in addition to metals such as nickel, titanium, and stainless steel. Among these, nickel is particularly preferable. As specific examples of the conductive treatment, for example, when nickel is used, electroless plating treatment, sputtering treatment, and the like are preferably exemplified. Moreover, when using materials, such as metals, such as titanium and stainless steel, and graphite, the process which coats the foamed resin with the mixture obtained by adding a binder to the fine powder of these materials is mentioned preferably.

  As the electroless plating treatment using nickel, for example, the foamed resin may be immersed in a known electroless nickel plating bath such as a nickel sulfate aqueous solution containing sodium hypophosphite as a reducing agent. If necessary, the foamed resin may be immersed in an activation liquid containing a trace amount of palladium ions (cleaning liquid manufactured by Kanigen Co., Ltd.) or the like before immersion in the plating bath. As a sputtering process using nickel, for example, after attaching a foamed resin to a substrate holder, ionization is performed by applying a DC voltage between the holder and the target (nickel) while introducing an inert gas. The nickel particles blown off may be deposited on the foamed resin surface by colliding the inert gas with nickel.

  If the thickness of the nickel plating film is increased by electroless plating and / or sputtering, there is no need for electrolytic plating, but from the viewpoint of productivity and cost, the foamed resin is first made conductive. Then, it is preferable to employ a method of forming a nickel plating layer by electrolytic plating.

  What is necessary is just to perform an electrolytic nickel plating process in accordance with a conventional method. By immersing the foamed resin having a conductive layer formed on the surface by electroless plating or sputtering in a plating bath, connecting the foamed resin to the cathode, and connecting the nickel counter electrode to the anode, and applying a direct current or pulsed intermittent current, A nickel coating can be further formed on the conductive layer. As the plating bath used for the electrolytic nickel plating treatment, a known or commercially available bath can be used, and examples thereof include a watt bath, a chloride bath, a sulfamic acid bath, and the like.

The basis weight (attachment amount) of the conductive coating layer and the electrolytic plating layer is not particularly limited. The conductive coating layer only needs to be formed continuously on the foamed resin surface, and the electrolytic nickel plating layer only needs to be formed on the conductive coating layer to the extent that the conductive coating layer is not exposed.
The basis weight of the conductive coating layer is not limited, and is usually about 5 to 15 g / m ² , preferably about 7 to 10 g / m ² . The basis weight of the electrolytic nickel plating layer is not limited and is usually about 150 to 500 g / m ² , preferably about 200 to 450 g / m ² .
The total amount of the basis weight of the conductive coating layer and the electrolytic nickel plating layer is preferably 200 g / m ² or more and 500 g / m ² or less. When the total amount is below this range, the strength of the current collector may be reduced. On the other hand, if the total amount exceeds this range, the filling amount of the polarizable material is reduced, which is disadvantageous in terms of cost.

  Next, the foamed resin component in the conductive coating layer / nickel plating layer-formed foamed resin obtained as described above is removed. Although the removal method is not limited, it is preferably removed by incineration. Specifically, the heating may be performed in an oxidizing atmosphere such as air of about 600 ° C. or higher. Moreover, you may heat at about 750 degreeC or more in reducing atmosphere, such as hydrogen. Thereby, the metal porous body which consists of a conductive coating layer and an electrolytic nickel plating layer is obtained. Foamed nickel is obtained by heat-treating the obtained porous body in a reducing atmosphere to reduce nickel.

<Nonwoven fabric nickel>
The non-woven nickel is obtained by forming a nickel coating layer on the surface of the non-woven resin, removing the resin as the base material, and then reducing the nickel by heat treatment in a reducing atmosphere as necessary.
The porous nonwoven fabric used in the present invention may be a known or commercially available one, but is preferably a thermoplastic resin. For example, fibers made of olefin homopolymers such as polyethylene, polypropylene, polybutene, woven fabric made of olefin copolymers such as ethylene-propylene copolymer, ethylene-butene copolymer, propylene-butene copolymer, and these fibers Of the mixture. The molecular weight and density of the polyolefin resin constituting the polyolefin resin fiber are not particularly limited, and may be appropriately determined according to the type of the polyolefin resin. Moreover, you may use the core-sheath-type fiber which consists of two types of components from which melting | fusing point differs.

  Specific examples of the core-sheath type composite fiber include a core-sheath type fiber having polypropylene as a core component and polyethylene as a sheath component. In this case, the blending ratio (mass ratio) of polypropylene resin: polyethylene resin is usually about 20:80 to 80:20, preferably about 40:60 to 70:30.

The average fiber diameter of the resin fibers is usually about 9 μm to 70 μm, preferably about 10 μm to 50 μm. The average fiber length is not limited and is usually about 5 mm to 100 mm, preferably about 30 mm to 70 mm. The porosity of the nonwoven fabric is usually about 80 to 97%, preferably about 86 to 96%. By setting this range, it is possible to fill the nonwoven fabric current collector with a large amount of activated carbon while maintaining the strength as a polarizable electrode, and it is possible to increase the output and capacity of the capacitor.
Moreover, the hole diameter of a nonwoven fabric is about 10 micrometers-about 250 micrometers normally, Preferably it is about 15 micrometers-200 micrometers. The pore diameter is measured by the bubble point method. The average thickness of the nonwoven fabric may be appropriately determined according to the use, purpose, etc. of the electric double layer capacitor to be produced, but is usually about 100 μm to 1000 μm, preferably about 150 μm to 800 μm.

  Prior to the plating treatment, the nonwoven fabric may be subjected to a pretreatment such as a confounding treatment such as a needle punch method or a hydroentanglement method, or a heat treatment near the softening temperature of the resin fiber. By this pretreatment, the bonds between the fibers are strengthened, and the strength of the nonwoven fabric can be improved. As a result, the three-dimensional structure necessary for filling the nonwoven fabric with activated carbon can be sufficiently retained.

  The nonwoven fabric is usually produced by any one of the known dry method and wet method, but may be produced by any method in the present invention. Examples of the dry method include a cart method, an air lay method, a melt blow method, and a spun bond method. Examples of the wet method include a method of dispersing single fibers in water and placing them on a net-like net. In the present invention, it is preferable to use a nonwoven fabric obtained by a wet method from the viewpoint of producing a current collector with a small basis weight and a small variation in thickness and a uniform thickness.

In order to form the nickel coating layer on the surface of the resin nonwoven fabric, a known nickel coating method can be employed as in the case of the foamed resin.
That is, an electroplating method, an electroless plating method, a sputtering method, and the like can be mentioned. These may be used alone or a plurality of coating methods may be combined. It is preferable to employ a method in which the surface of the resin nonwoven fabric is subjected to conductive treatment in the same manner as in the case of the foamed resin, and then nickel plating is applied to the desired basis weight by electrolytic plating.

For the conductive treatment, the same method as in the case of the foamed resin can be adopted. In addition, when performing a sputtering process as an electroconductive process, it is preferable to carry out at the temperature which a resin nonwoven fabric does not melt | dissolve. Specifically, it may be performed at about 100 to 200 ° C, preferably about 120 to 180 ° C.
The basis weight of the conductive coating layer is sufficient if it can impart conductivity to the nonwoven fabric. For ^{example, 5g / m 2 ~15g / m} 2 , preferably about may be set to 7g / m ² ~10g / m ² approximately.

Similarly to the foamed resin, the electrolytic nickel plating treatment may be performed according to a conventional method. Basis weight of the electroless nickel plating layer, conductivity, porosity, strength, corrosion resistance, from the viewpoint of economic efficiency, 150~500g / ^{m 2} about relative nonwoven, if preferably the 200~450g / ^{m 2} about Good. When the total amount is below this range, the strength of the current collector may be reduced. On the other hand, if the total amount exceeds this range, the filling amount of the polarizable material is reduced or the cost is disadvantageous.

  The removal treatment of the resin nonwoven fabric can be performed in the same manner as the foamed resin. That is, it may be incinerated by heating. Foamed nickel is obtained by heat-treating the obtained non-woven porous body under a reducing atmosphere to reduce nickel.

(Chromizing treatment)
The chromizing process is a process of diffusing and infiltrating chromium into the nickel film, and a known method can be adopted. For example, a powder pack method in which the metal porous body (foamed nickel, non-woven nickel, etc.) is filled with a penetrant mixed with chromium powder, halide, and alumina powder and heated in a reducing atmosphere can be employed. Alternatively, the infiltrating material and the porous metal body can be spaced apart and heated in a reducing atmosphere to form a gas for the infiltrating material to infiltrate the infiltrating material into nickel on the surface of the porous metal body.
Since nickel chrome has an established manufacturing method, it can be manufactured at a lower cost than aluminum or stainless steel porous bodies.

  The content of chromium in nickel chromium can be adjusted by the heating time of the chromization treatment. In the present invention, the chromium content must be 25% by mass or more by chromizing treatment. The chromium content is 25-50% by mass, preferably 30-40% by mass. If it is less than 25% by mass, the oxidation resistance is insufficient, and if it exceeds 50% by mass, the electrical resistance increases and the current collecting performance decreases.

The thickness of the fibers constituting the non-woven nickel chrome is preferably 12 to 90 μm. When the thickness of the fiber is thinner than 12 μm, the current collector becomes too fine and the filling property of the active material is deteriorated, and the electrostatic capacity is reduced. On the other hand, when the thickness is larger than 90 μm, the retention of the active material paste is deteriorated, the filling amount is reduced, and the capacitance is reduced. Furthermore, current collection is also worsened by the large eyes.
The porosity of foamed nickel chrome and non-woven nickel chrome is preferably 80 to 97%. By setting it as this range, it is possible to fill the current collector with a large amount of activated carbon while maintaining the strength as a polarizable electrode, and it becomes possible to increase the output and capacity of the capacitor.

The positive electrode current collector produced by the above method has a structure composed of a coating layer obtained by chromizing nickel, so that the corrosion resistance of nickel is improved, and the nickel is not oxidized even by the voltage of a non-aqueous capacitor. Can be used. Furthermore, since the positive electrode current collector has a porous structure, it can be filled with more activated carbon, and the capacitance can be improved. Moreover, since the activated carbon is enclosed in the voids in the porous body, the content of the binder (insulator) for binding the activated carbon and the current collector can be reduced, and the internal resistance can be reduced. Can do.
The average thickness of the current collector is usually about 100 μm to 1000 μm, preferably about 150 to 800 μm.

-Negative electrode-
The negative electrode can be produced by applying a negative electrode active material mainly composed of a carbon material capable of inserting and extracting lithium ions to a negative electrode current collector made of metal foil or the like. Examples of the method for applying the negative electrode active material include a method in which a carbon material is made into a paste and the negative electrode active material paste is applied by a doctor blade method or the like. Moreover, you may press-mold with a roller press etc. after drying as needed.
In order to occlude lithium ions in the carbon material, for example, a Li foil is pressure-bonded to the negative electrode produced through the following steps, and the manufactured cell (capacitor) is kept in a constant temperature layer at 60 ° C. for 24 hours. A method is mentioned. In addition, there are a method in which a carbon material and a lithium material are mixed and mixed by a mechanical alloy method, and a method in which Li metal is incorporated in a capacitor cell and the negative electrode and the Li metal are short-circuited.

[Negative electrode current collector]
A metal foil can be preferably used as the negative electrode current collector. Such metal is preferably, for example, aluminum, copper, nickel, or stainless steel.

[Negative electrode active material]
The negative electrode active material can be obtained by mixing a carbon material capable of occluding and desorbing lithium ions in a solvent and stirring with a mixer. A conductive auxiliary agent and a binder may be included as needed. (Carbon material)
The carbon material is not particularly limited as long as it can occlude and desorb lithium ions, and examples thereof include graphite materials and graphitizable carbon materials. Moreover, what has a theoretical capacity of 300 mAh / g or more is preferable.
(Conductive aid)
As the conductive auxiliary agent, a known or commercially available one can be used as in the case of the positive electrode active material. That is, for example, acetylene black, ketjen black, carbon fiber, natural graphite (scaly graphite, earthy graphite, etc.), artificial graphite, ruthenium oxide and the like can be mentioned.
(Binder)
The binder is not particularly limited as in the case of the positive electrode active material, and a known or commercially available binder can be used. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, polyolefin, styrene butadiene rubber, polyvinyl alcohol, carboxymethyl cellulose and the like.

-Non-aqueous electrolyte-
Since the capacitor according to the present invention contains lithium, it is necessary to use a nonaqueous electrolytic solution as the electrolytic solution. As such a nonaqueous electrolytic solution, for example, a solution obtained by dissolving a lithium salt necessary for charging and discharging in an organic solvent can be used.
(Lithium salt)
As the lithium salt, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ or the like can be used. These may be used alone or in combination of any one or more.
(solvent)
As the solvent for dissolving the lithium salt, for example, one or more selected from ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be preferably used.

  The capacitor according to the present invention manufactured by the above method preferably has a negative electrode capacity larger than the positive electrode capacity, and a lithium ion occlusion amount is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity. By regulating the capacity with the positive electrode in this way, a short circuit due to lithium dendrite growth can be prevented.

[Test Example 1]
(Preparation of positive electrode current collector)
The foamed nickel was chromized to produce a foamed nickel-chromium alloy substrate. Foamed nickel is reduced after the urethane sheet (commercially available product, average pore diameter 90 μm, thickness 1.4 mm, porosity 96%) is subjected to conductive treatment, then plated with a predetermined amount of nickel, and urethane is removed by incineration at 800 ° C. in the atmosphere. It was made by heating to 1000 ° C. in a neutral atmosphere (hydrogen) and reducing nickel. For the conductive treatment, 10 g / m ² of nickel was applied by sputtering. The total amount of nickel plating was 400 g / m ² for the conductive treatment. The produced foamed nickel had an average pore diameter of 80 μm, a thickness of 1.2 mm, and a porosity of 95%.

The chromizing treatment was performed using a powder pack method in which a base material was filled with a penetrating material mixed with chromium powder, a halide, and alumina and heated in a reducing atmosphere. The produced foamed nickel was filled with a penetrating material (chrome: 90%, NH ₄ Cl: 1%, Al ₂ O ₃ : 9%) and heated to 800 ° C. in a hydrogen gas atmosphere.
The content of the foamed nickel-chromium alloy substrate chromium thus obtained was adjusted by the heating time of the chromization treatment, and a substrate having a chromium content of 30 wt% was prepared, and the current collector a was obtained. . The thickness of the produced current collector was 1.4 mm.

(Preparation of positive electrode)
100 parts by weight of activated carbon powder (specific surface area 2500 m ² / g, average particle size of about 5 μm), ² parts by weight of ketjen black (KB) as a conductive additive, 4 parts by weight of polyvinylidene fluoride powder as a binder, N-methyl as a solvent Activated carbon positive electrode paste was prepared by adding 15 parts by weight of pyrrolidone (NMP) and stirring with a mixer.
This activated carbon paste was filled in the current collector so that the activated carbon content was 30 mg / cm ² . The actual filling amount was 31 mg / cm ² . Next, after drying by 100 degreeC with a dryer for 1 hour and removing a solvent, it pressurized with the roller press machine (slit: 500 micrometers) of diameter 500mm, and the positive electrode A of Test Example 1 was obtained. The thickness after pressing was 680 μm.

(Negative electrode current collector)
A copper foil having a thickness of 20 μm was used.
(Preparation of negative electrode)
100 parts by weight of natural graphite powder capable of occluding and releasing lithium, 2 parts by weight of ketjen black (KB) as a conductive additive, 4 parts by weight of polyvinylidene fluoride powder as a binder, and 15 parts by weight of N-methylpyrrolidone (NMP) as a solvent Was added and stirred with a mixer to prepare a graphite-based negative electrode paste.
This graphite-based negative electrode paste was applied onto the above copper foil using a doctor blade (gap 400 μm). The actual coating amount was 10 mg / cm ² . Next, after drying by 100 degreeC with a dryer for 1 hour and removing a solvent, it pressurized by the roller press machine (slit: 200 micrometers) of diameter 500mm, and negative electrode A 'of Test Example 1 was obtained. The thickness after pressing was 220 μm.

(Production of cell)
The positive electrode A and the negative electrode A ′ were further dried at 200 ° C. for 8 hours in a reduced pressure environment. These were transferred into a dry room (dew point −65 ° C.), and the obtained positive electrode A and negative electrode A ′ were punched out to a diameter of 14 mm, and then a 50 μm thick lithium metal foil was pressure bonded to the negative electrode A ′. Between the electrodes are opposed across a polypropylene separator and in single cell device, using a stainless steel spacer accommodated in R2032 size coin cell casing was dissolved LiPF ₆ of 1 mol / L, ethylene carbonate (EC ) And diethyl carbonate (DEC) mixed at a volume ratio of 1: 1 were injected to impregnate the electrodes and separator. Further, the case lid was tightened and sealed through an insulating gasket made of propylene to produce a coin-shaped test electric double layer capacitor A.
Then, it was left to stand in a 60 degreeC thermostat for 24 hours. By this operation, lithium pressure-bonded to the negative electrode is ionized and occluded in the negative electrode graphite.

[Test Example 2]
An aluminum foil (commercial product, thickness 20 μm) was used as the positive electrode current collector. The positive electrode active material paste produced in Test Example 1 was applied by a doctor blade method so that the total of both surfaces was 10 mg / cm ² and rolled, and positive electrode B of Test Example 2 was produced. The actual coating amount was 11 mg / cm ² , and the electrode thickness was 222 μm.
The subsequent operation was exactly the same as in Test Example 1 to produce a coin-type electric double layer capacitor B.

[Test Example 3]
An electric double layer capacitor C was produced using the same negative electrode as that used in Test Example 1 as the negative electrode. As the electrolytic solution, a propylene carbonate solution in which tetraethylammonium tetrafluoroborate was dissolved to 1 mol / L was used, and a separator made of cellulose fiber (thickness 60 μm, density 450 mg / cm ³ , porosity 70%) was used.

<Evaluation of capacitance>
Ten capacitors similar to those of Test Examples 1 to 3 were respectively prepared, charged at 2 mA / cm ² for 2 hours, and discharged at 1 mA / cm ² , and the initial capacitance and the charging voltage / operating voltage range were examined. Their average values are shown in Table 1.

  As is apparent from Table 1, the capacitor of the present invention has an electric capacitance larger than that of the capacitor using the Al foil of Test Example 2 and the electric voltage range of the normal configuration (Test Example 3). ), The energy density can be improved.

<Durability test 1>
Next, durability important as capacitor characteristics was examined. Durability when held at a high voltage is important in applications such as backup. While applying the charging voltage of each cell shown in Table 1 at 65 ° C., it was held for 2000 hours. Thereafter, the capacitance was measured at 25 ° C., and the rate of change in capacitance from the initial stage was examined. The results are shown in Table 2.

  As is clear from Table 2, the changes in the capacitance and the internal resistance of Test Example 1 were small even after 2000 hours, as in Test Examples 2 and 3 having the conventional configuration. Therefore, it was found that the electric double layer capacitor of the present invention has a high capacitance and is excellent in durability.

<Durability test 2>
The charge / discharge cycle characteristics were examined as another durability evaluation method. Cycle characteristics are an important indicator of cell life. As conditions, charge and discharge cycles with a constant current of 1 mA at an ambient temperature of 45 ° C. between 0.5 and 3.0 V were repeated 10,000 times, and the discharge capacity after 10,000 cycles was measured and evaluated in comparison with the initial capacity. Went. The results are shown in Table 3.

As is clear from Table 3, the change in the capacitance of Test Example 1 was small even after 10,000 cycles had passed, as was the case with Test Examples 2 and 3 of the conventional configuration. Therefore, it was found that the electric double layer capacitor of the present invention has a high capacitance and an excellent lifetime.
From the above, it has been found that when the current collector of the present invention is used as an electrode for a capacitor, a capacitor superior in capacity and durability compared to a conventional capacitor can be provided.
Although Test Example 1 described above is for a foamed nickel-chromium alloy, the same effect is obtained for a capacitor using a non-woven nickel-chromium alloy, which is a porous metal body using a nickel-chromium alloy obtained by chromizing treatment. It is clear that it is played.

Claims (5)

at least,
A positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body;
A negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil;
A capacitor comprising a non-aqueous electrolyte containing a lithium salt and having lithium ions occluded in a negative electrode by a chemical or electrochemical method
The metal porous body is made of a non-woven fabric nickel having a nickel basis weight of 150 to 500 g / m ² obtained by coating a non-woven fabric made of polyolefin fibers with nickel, and has a chromium content of 25 mass. % Or more and a non-woven nickel-chromium alloy having a porosity of 80 to 97%.   2. The capacitor according to claim 1, wherein the carbon material capable of occluding and desorbing lithium ions is a graphite-based material or a graphitizable carbon material.   The capacitor according to claim 1 or 2, wherein the metal foil of the negative electrode is any one of aluminum, copper, nickel, and stainless steel. The lithium salt is at least one selected from LiClO ₄ , LiBF ₄ , and LiPF ₆ , and the solvent of the non-aqueous electrolyte is ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate. The capacitor according to claim 1, wherein the capacitor is one or more selected.   5. The capacitor according to claim 1, wherein the negative electrode capacity is larger than the positive electrode capacity, and the occlusion amount of lithium ions is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity.