JP4822555B2 - Non-woven nickel chrome current collector for capacitor, electrode and capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric double layer capacitor increased in capacitance, reduced in inner resistance with excellent durability. <P>SOLUTION: The collector for the capacitor is made of nonwoven fabric-like nickel-chromium obtained by chromizing nonwoven fabric-like nickel and having the chromium content of at least 25 wt.%. The collector is obtained by performing electro-conductive treatment on resin nonwoven fabric and electrically nickelizing the fabric to form a nickel-coated layer on the surface of the nonwoven fabric, removing the resin to form nonwoven fabric-like nickel and chromizing the nonwoven fabric-like nickel such that the chromium content is at least 25 wt.%. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a novel polarizable electrode for a capacitor and a method for producing the same.

  The electric double layer capacitor has recently attracted attention because of its 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. Furthermore, in recent years, 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. For example, the button type has a pair of polarizable electrodes with an activated carbon electrode layer on a current collector, and a separator is placed between the electrodes to lay the electric double layer capacitor element, and it is housed in a metal case together with the electrolyte. And it manufactures by sealing with a gasket which insulates a sealing plate and both. For the cylindrical type, this pair of polarizable electrodes and separators are stacked and rolled 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 square type is basically the same as the button type and cylindrical type.

The polarizable electrode used for this electric double layer capacitor is generally manufactured by applying activated carbon to a current collector that is an aluminum foil. For example, Patent Documents 1 to 3 disclose various current collectors that cross the polarizable electrodes for non-aqueous electrolyte electric double layer capacitors. Patent Document 1 discloses a metal current collector such as aluminum or stainless steel.
Patent Document 2 discloses a current collector obtained by electrically welding a stainless fiber mat to a stainless steel foil. Patent Document 3 discloses a porous current collector made of at least one metal selected from tantalum, aluminum, and titanium.

  Incidentally, electric double layer capacitors used for applications such as memory backup and driving vehicles are required to have a higher capacity. That is, improvement in capacitance and reduction in internal resistance are required. In order to achieve this, attempts have been made to add a conductive agent such as carbon black or carbon fiber to the activated carbon in the polarizable electrode, or to replace the current collector with a metal foil to make a porous body (three-dimensional structure). ing.

However, with regard to the conductive auxiliary agent, if a large amount of conductive auxiliary agent is added to lower the electrical resistance, the content of activated carbon in the polarizable electrode decreases, and conversely, the capacitance of the capacitor decreases. .
On the other hand, regarding current collectors, attempts have been made to use screens, punching metals, laths and the like as porous bodies, but 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, nickel cannot be used because it is oxidized or corroded by the non-aqueous electrolyte.
In addition, it is difficult to mass-produce current collectors having a three-dimensional structure with high porosity using stainless steel other than nickel.

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

  An object of the present invention is to provide a capacitor having a large capacitance, a small internal resistance, and excellent durability.

In view of the above problems, the present inventors have conducted extensive research and, as a result, non-woven nickel chrome having a chromium content of 25% by mass or more obtained by chromizing non-woven nickel as a current collector. The present invention has been found by using a current collector made of
That is, the present invention relates to a current collector made of non-woven nickel chrome for capacitors as described below, an electrode using this current collector, and a capacitor using this electrode.

( 1 ) A method for producing a current collector for a capacitor comprising non-woven fabric nickel-chromium, wherein the non-woven fabric nickel is subjected to chromizing treatment so that the chromium content is 25% by mass or more.
( 2 ) The non-woven fabric obtained by applying the conductive treatment and electrolytic nickel plating treatment to the non-woven fabric made of resin in this order to form a nickel coating layer on the surface of the non-woven fabric and then removing the resin. The method for producing a current collector for a capacitor according to ( 1 ), wherein the capacitor is nickel.
( 3 ) The nonwoven fabric-like nickel is subjected to conductive treatment and electrolytic nickel plating treatment in this order on the nonwoven fabric made of resin to form a nickel coating layer on the nonwoven fabric surface, and then the resin is incinerated and removed, followed by heat treatment in a reducing atmosphere. The method for producing a current collector according to ( 1 ), wherein the nickel is a non-woven nickel obtained by reducing nickel.
( 4 ) A method for producing a capacitor electrode, comprising filling a capacitor current collector obtained by the production method according to any one of ( 1 ) to ( 3 ) with an electrode material mainly composed of activated carbon.

  The current collector of the present invention is improved in corrosion resistance of nickel by chromizing non-woven nickel, and can be used favorably as a current collector without being oxidized even at a non-aqueous capacitor voltage. Because of the porous structure, a capacitor using a capacitor electrode in which the current collector is filled with activated carbon can obtain a high capacity density.

The current collector of the present invention can be produced as follows.
After forming the nickel coating layer on the surface of the resin nonwoven fabric, the base resin is removed, and if necessary, heat treatment is performed in a reducing atmosphere to reduce the nickel and to form a nonwoven nickel-plated porous structure ( Hereinafter, in the present specification, this is referred to as “nonwoven fabric-like nickel”, and this nonwoven fabric-like nickel is subjected to chromizing treatment, thereby producing a nonwoven-like nickel-chrome porous structure (hereinafter referred to as “nonwoven fabric”). Current collector made of “nickel-like chromium”. The chromizing treatment in the present invention refers to a treatment for diffusing and infiltrating chromium on the surface of nickel.

In order to form the nickel coating layer on the resin nonwoven fabric, a known nickel coating method can be employed. Examples of such a method include an electrolytic plating method, an electroless plating method, and a sputtering method. 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.

In order to form non-woven nickel chrome using the electroplating method, the resin non-woven fabric is sequentially subjected to conductive treatment and electrolytic nickel plating treatment, then the resin is removed, and then heated in a reducing atmosphere as necessary. The nickel is reduced by treatment to obtain non-woven nickel, and this is chromized to obtain a current collector made of non-woven nickel chromium.
The capacitor-like electrode of the present invention can be obtained by filling the above-described current collector of the present invention with an electrode material mainly composed of activated carbon.
Hereinafter, the present invention will be described in more detail.

[Nonwoven fabric]
The porous nonwoven fabric used in the present invention is not limited, and known or commercially available ones can be used. However, a thermoplastic resin is preferable, and for example, the porous nonwoven fabric is composed of an olefin homopolymer such as polyethylene, polypropylene, and polybutene. Examples thereof include fibers, woven fabric made of an olefin copolymer such as an ethylene-propylene copolymer, an ethylene-butene copolymer, and a propylene-butene copolymer, and a mixture of these fibers. 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 not limited and 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 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.

  The porosity of the nonwoven fabric is not limited and is usually 85 to 98% mild, 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.

The pore diameter of the nonwoven fabric is not limited, and is usually about 10 μm to 250 μm, preferably about 15 μm to 200 μm. The pore diameter of the present invention is measured by the bubble point method.
The average thickness of the non-woven fabric is not limited, and may be appropriately determined according to the use and purpose of the electric double layer capacitor to be manufactured. Usually, it is about 100 μm to 1000 μm, preferably about 150 μm to 800 μm.

  Prior to the plating described below, 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 this invention, it is preferable to use the nonwoven fabric obtained by the wet method from the saddle point which can manufacture the electrical power collector with a small areal weight and thickness variation, and uniform thickness.

[Current collector]
Hereinafter, a method for producing a current collector by sequentially conducting conductive treatment, electrolytic plating treatment, and chromizing treatment on a resin nonwoven fabric will be described.
(Conductive treatment)
The conductive treatment is not particularly limited as long as it is a treatment that can provide a conductive layer on the surface of the resin nonwoven fabric. 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 binder in this case, the same material as the active material paste described later can be used.

  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, before immersion in the plating bath, the foamed resin may be washed by immersing it in an activation liquid containing a small amount of palladium ions (manufactured by Kanigen Co., Ltd.).

The sputtering process using nickel (nickel sputtering process) is not limited as long as nickel is used as a target, and may be performed according to a conventional method. Specifically, after attaching a resin nonwoven fabric to the substrate holder, an inert gas (such as argon) is introduced and a DC voltage is applied between the holder and the target (nickel) to ionize the inert gas. Is caused to collide with nickel, and the nickel that is repelled is deposited on the surface of the nonwoven fabric. In the present invention, the sputtering process is preferably performed at a temperature at which the nonwoven fabric does not dissolve, and specifically, it may be performed at about 100 to 200 ° C, preferably about 120 to 180 ° C.
Basis weight of the conductive coating layer is not limited as long as capable of imparting conductivity to the nonwoven fabric, for ^{example, 5g / m 2 ~15g / m} 2 ^about, may be set to 7g / ^{m 2} ~10g / m 2 approximately.

(Electrolytic plating treatment)
Next, electrolytic nickel plating is applied to the resin nonwoven fabric on which the conductive coating layer is formed.
What is necessary is just to perform an electrolytic nickel plating process in accordance with a conventional method. 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.
By immersing the resin nonwoven fabric subjected to the above-mentioned conductive treatment in the above plating bath in the plating bath, connecting the resin nonwoven fabric to the cathode and the nickel counter electrode to the anode, and applying a direct current or pulse intermittent current on the conductive layer, Further, a nickel coating can be formed.

The basis weight (attachment amount) of the nickel coating layer is not limited, but the basis weight of the nickel coating layer with respect to the nonwoven fabric is 200 g / m ² or more and 500 g from the viewpoint of conductivity, porosity, strength, economy, corrosion resistance, and the like. / M ² or less (when a plurality of nickel coating layers are formed, the total amount is indicated). 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.

(Resin non-woven fabric removal treatment)
Next, the resin component in the conductive coating layer / nickel plating layer-formed nonwoven fabric 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 porous body which consists of a conductive coating layer and an electrolytic nickel plating layer is obtained. The obtained porous body is heat-treated in a reducing atmosphere to reduce the nickel, thereby obtaining a non-woven nickel.

(Chromizing treatment)
The current collector made of the non-woven nickel chrome of the present invention can be obtained by chromizing the nickel-plated non-woven fabric obtained above.
The chromizing treatment is a treatment for diffusing and infiltrating chromium into the nickel base material. Known methods can be used as the chromizing treatment method. For example, a powder pack method in which a non-woven nickel is mixed with a penetrating material in which chromium powder, halide, and alumina powder are mixed and heated in a reducing atmosphere. Can do. It is also possible to dispose the penetrating material and the non-woven nickel so that they are heated in a reducing atmosphere to form a gas for the penetrating material and to penetrate the non-woven nickel surface.
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. If the thickness of the fiber is thinner than 12 μm, the current collector becomes too fine and the filling capacity of the active material is deteriorated and the electrostatic capacity is reduced. The amount is reduced, the capacitance is reduced, and the current is also deteriorated due to the larger eyes.
Moreover, it is preferable that the porosity of nonwoven fabric-like nickel chromium is 80 to 98%. By setting it as 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 becomes possible to increase the output and capacity of the capacitor.

Since the current collector of the present invention has a structure composed of a coating layer obtained by chromizing nickel, the corrosion resistance of nickel is improved, and nickel can be used as a current collector without being oxidized even at a voltage of a nonaqueous capacitor. Furthermore, since the current collector of the present invention has a non-woven porous structure, it can be filled with more activated carbon, and the capacitance can be improved. In addition, since the activated carbon is encased 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 lowered. Can do. Further, since the current collector is excellent in oxidation resistance, the life of the capacitor can be extended.
The average thickness of the current collector is not limited, and is usually about 100 μm to 1000 μm, preferably about 150 μm to 800 μm.

[Capacitor electrode]
The capacitor electrode of the present invention can be obtained by using an electrode material containing activated carbon as a main component for the current collector. The electrode material mainly composed of activated carbon as used in the present invention refers to a material containing a conductive additive and / or a binder as necessary in addition to activated carbon, and refers to a material having a content of activated carbon of 60% by mass or more. Since the electrode of the present invention uses a current collector made of a non-woven nickel-chrome porous structure as a support, it has high strength and porosity and can be filled with more activated carbon. . Thereby, the capacity of the capacitor can be increased.

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 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 about 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.
Moreover, you may add various additives, such as a conductive support agent and a binder, as needed.

  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 content of a conductive support agent is not limited, about 0.1-10 mass parts is preferable with respect to 100 mass parts of activated carbon, More preferably, it is 0.2-5 mass parts. If it exceeds 10 parts by mass, the capacitance may decrease.

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, and carboxymethyl cellulose.
The binder content is not particularly limited, but is preferably 0.2 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the activated carbon. By setting it as this range, it is possible to improve the binding strength while preventing an increase in electrical resistance and a decrease in discharge capacity.

The filling amount (content) when the current collector is filled with activated carbon is not particularly limited, and may be appropriately determined according to the thickness of the current collector, the shape of the capacitor, and the like. It is about -40 mg / cm < ² >, Preferably it is about 16-32 mg / cm < ² >.
As a method for filling the current collector of the present invention with activated carbon or the like, for example, a known method such as press-fitting activated carbon paste may be used.
Examples of the press-fitting method include a method of immersing the current collector in activated carbon paste and reducing the pressure as necessary, and a method of filling the activated carbon paste while applying pressure from one side of the current collector with a pump or the like.

  The activated carbon paste should just contain activated carbon and a solvent, and the mixture ratio is not limited. The solvent is not limited, and examples thereof 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 butterfly. Good. Moreover, you may contain additives, such as the said conductive support agent and a binder, as needed.

The electrode of the present invention may be subjected to a drying treatment as necessary after the activated carbon paste is filled, thereby removing the solvent in the paste. Further, if necessary, after the activated carbon paste is filled, it may be compression-molded by pressurizing with a roller press or the like. The thickness before and after compression is not limited, but the thickness before 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. And it is sufficient.
The electrode may be provided with a lead terminal. The lead terminal may be attached by welding or applying an adhesive.

[Capacitor]
The capacitor of the present invention is obtained by pairing two electrodes of the present invention, placing a separator between these electrodes, and further impregnating the separator with an electrolytic solution.
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.

  As the electrolytic solution, a known or commercially available one can be used, and either an aqueous electrolytic solution or a nonaqueous electrolytic solution can be used. Examples of the aqueous electrolyte include alkaline aqueous solutions such as an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution. Non-aqueous electrolytes include, for example, propylene carbonate solution in which tetraalkylphosphonium tetrafluoroborate is dissolved, propylene carbonate solution or sulfolane solution in which tetraalkylammonium tetrafluoroborate is dissolved, and propylene carbonate in which triethylmethylammonium tetrafluoroborate is dissolved Examples include solutions. Among these, a nonaqueous electrolytic solution is preferable in the present invention. Thereby, an electrostatic capacitance can be improved.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The present invention is not limited to the following examples.

[Examples 1 and 2]
(Production of nonwoven fabric)
As a nonwoven fabric material, a core-sheath fiber having a polypropylene fiber as a core component and polyethylene as a sheath component (average fiber diameter is 17 μm, average fiber length is 50 mm, polypropylene component is 50% by mass, polyethylene component is 50% by mass) is used. It was. Using this core-sheath fiber, a porous nonwoven fabric was prepared by a wet method so that the basis weight was 40 g / m ² and the average thickness was 1.5 mm. The produced porous nonwoven fabric had a porosity of about 97% and a pore size of 15 μm to 200 μm.

(Preparation of current collector)
Obtained above nonwoven fabric (thickness 1.5 mm, porosity 97%) spackling apparatus (manufactured by ULVAC, Inc.) used, under argon, by performing the sputtering process at 0.99 ° C., the basis weight of 10 g / ^{m 2} A conductive coating layer (nickel layer) was formed to obtain a nonwoven fabric subjected to a conductive treatment.
Next, electrolytic nickel plating was applied to the obtained nonwoven fabric to form a nickel coating layer having a basis weight of 250 g / m ^{2 in} total with the conductive coating layer. This nonwoven fabric had a thickness of 1.7 mm and a porosity of 98%.
The electrolytic nickel plating bath was a Watt bath (nickel sulfate 330 g / 1, nickel chloride 50 g / 1, shelf acid 40 g / 1), and the electrodeposition conditions were a bath temperature of 60 ° C. and a current density of 30 A / dm ² . . A titanium basket containing nickel pieces was used as the counter electrode.

  The nickel-plated non-woven fabric obtained above is heated at 800 ° C. in the atmosphere to incinerate and remove the resin non-woven fabric, and then heated to 1000 ° C. in a hydrogen gas atmosphere to reduce nickel to obtain non-woven nickel. It was.

Next, the nonwoven nickel was subjected to chromizing treatment to produce a nonwoven nickel chromium.
Chromizing treatment, chromium powder, ammonium chloride, infiltrating material obtained by mixing alumina powder (chromium: 90 _mass%, NH 4 Cl: 1 _wt%, Al _{2 O} 3: 9 wt%) was filled into a nickel-plated non-woven fabric Then, heating was performed at 800 ° C. in a hydrogen gas atmosphere.
The chromium content in the non-woven nickel chrome was adjusted by the heating time of the chromizing treatment, and the chromium content was 25% by mass in Example 1 and 30% by mass in Example 2. The current collectors of Example 1 and Example 2 were designated as current collector a and current collector b, respectively. The thickness of the produced current collector was 1.2 mm.

(Production of electrodes)
100 parts by mass of activated carbon powder (specific surface area 2500 m ² / g, average particle size of about 5 μm), 2 parts by mass of ketjen black as a conductive additive, 4 parts by mass of polyvinylidene fluoride powder as a binder, and 15 parts of N-methylpyrrolidone as a solvent The activated carbon paste was prepared by adding a part 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 32 mg / cm ² in Example 1 and 31 mg / cm ² in Example 2. Next, after drying with a dryer at 100 ° C. for 1 hour to remove the solvent, pressure was applied with a roller press having a diameter of 500 mm (slit: 50 μm) to obtain electrode A and electrode B of Example 1. The thickness after pressing was 490 μm and 484 μm, respectively.

[Comparative Example 1]
An electrode C was produced in exactly the same manner as in Example 1, except that the heating time was adjusted so that the chromium content was 20% by mass. The filling amount of activated carbon was 30 mg / cm ² , and the thickness after pressurization was 486 μm.

[Comparative Example 2]
An aluminum foil (commercial product, thickness 20 μm) was used as a current collector. The activated carbon paste produced in Example 1 was applied by a doctor blade method so that the total on both sides was 8 mg / cm ² , but the activated carbon could not be sufficiently bonded to the aluminum foil because of insufficient adhesive strength.
Therefore, an activated carbon paste similar to that produced in Example 1 was produced except that the amount of polyvinylidene fluoride was changed to 8 parts by mass. This paste was applied to both surfaces of an aluminum foil by a doctor blade method, dried and pressed to produce an electrode D of Comparative Example 2. The amount of activated carbon applied was 8 mg / cm ² , and the electrode thickness was 174 μm.

[Comparative Example 3]
As the current collector, foamed nickel (commercial product, nickel basis weight 400 g / m ² , porosity 96%, average pore diameter 150 μm, thickness 550 μm) was used. This was filled with the activated carbon paste produced in Example 1 in the same manner as in Example 1, and then further pressurized and dried to produce Electrode E of Comparative Example 3. The filling amount of activated carbon was 31 mg / cm ² , and the thickness after pressurization was 480 μm.

[Production and testing of capacitors]
The electrodes A to E obtained above were punched into a diameter of 14 mm (2 sheets), a cellulose fiber separator (thickness 60 μm, density 450 mg / cm ³ , porosity 70%) was sandwiched between these electrodes. In this state, it was dried under reduced pressure at 180 ° C. for 5 hours. Thereafter, the electrode and the separator were impregnated with a propylene carbonate solution in which tetraethylammonium tetrafluoroborate was dissolved in a non-aqueous electrolyte so as to have a concentration of 1 mol / L using a stainless steel spacer. Further, the case lid was tightened and sealed through an insulating gasket made of propylene to produce coin-shaped test electric double layer capacitors AA to EE (corresponding to electrodes A to E, respectively). The rated voltage was 2.8V.

[Evaluation of capacitance]
Ten capacitors similar to those of Example 1 to Comparative Example 3 were respectively produced and subjected to aging by applying a voltage of 2.8 V at 65 ° C. for 6 hours, then 25 ° C. and 3.0 mA as a starting voltage of 1 mA. The initial electrostatic capacity and the internal resistance were examined. Table 1 shows the average value of capacitance per unit area, capacitance per unit deposition, and internal resistance. In the capacitors of Comparative Example 1 and Comparative Example 3, the aging voltage did not reach 2.8 V in all 10 cells, and the discharge could be performed for only a short time, so the capacitance and internal resistance could not be obtained. Since the voltage does not increase, current is used in addition to the battery reaction, and oxidation of the current collector is suspected.

As is apparent from Table 1, the capacitors of Examples 1 and 2 have a larger capacity per unit volume and a lower internal resistance than the capacitors using the Al foil of Comparative Example 2. In particular, in terms of capacitance, the capacitors of Examples 1 and 2 exhibit a capacitance that is three times or more that of the capacitor of Comparative Example 2. From this, in order to obtain a capacitance equivalent to that of the conventional capacitor shown in Comparative Example 2, the capacitor of the present invention (particularly the polarizable electrode portion) can be achieved with a length of 1/3 or less. I understand.
Further, it can be seen that the present invention can improve the energy density because the amount of the material (binder) that does not contribute to the capacitance can be reduced.
On the other hand, it can be seen from the results of Comparative Examples 1 and 3 that even if the current collector has a porous structure, if the chromium content is small, the oxidation resistance is insufficient and it is not suitable as a current collector.

[Durability evaluation]
Next, durability and charge / discharge cycle characteristics when the capacitor was held at a high voltage, which is important as capacitor characteristics, were examined. In addition, about the comparative example 1 and the comparative example 3, the subsequent test is not implemented.
(Durability test 1)
Durability when held at a high voltage is important in applications such as backup.
The capacitors of Examples 1 and 2 and Comparative Example 2 were held for 2000 hours while applying a voltage of 2.8 V at 65 ° C. Thereafter, the capacitance and internal resistance were measured at 25 ° C., and the rate of change in capacitance and internal resistance from the beginning was examined. The results are shown in Table 2.

  As is clear from Table 2, the change in capacitance and internal resistance of the example was small after 2000 hours as compared with the comparative example. 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 and internal resistance after 10,000 cycles were measured and compared with the initial characteristics. And evaluated. The results are shown in Table 3.

  From the above results, 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.

  Since the current collector of the present invention has oxidation resistance, electrolytic solution resistance, porosity, and high strength, the electrode obtained by filling it with activated carbon is excellent in durability and capacity density. It can be suitably used as a working electrode.

Claims (4)

  A method for producing a current collector for a capacitor comprising a non-woven fabric nickel-chromium, wherein the non-woven fabric nickel is subjected to chromizing treatment so that the chromium content is 25% by mass or more. The non-woven nickel is a non-woven nickel obtained by applying a conductive treatment and an electrolytic nickel plating treatment to a non-woven fabric made of resin in this order to form a nickel coating layer on the non-woven fabric surface and then performing a treatment for removing the resin. The method for producing a current collector for a capacitor according to claim 1 . After the non-woven nickel is subjected to conductive treatment and electrolytic nickel plating treatment in this order on the non-woven fabric made of resin to form a nickel coating layer on the non-woven fabric surface, the resin is incinerated and removed, and then heat treated in a reducing atmosphere to remove the nickel. The method for producing a current collector according to claim 1 , wherein the current collector is non-woven nickel obtained by reduction treatment. Method for manufacturing a capacitor electrode, which comprises filling an electrode material composed mainly of activated carbon collector capacitor obtained by the manufacturing method according to any one of claims 1 to 3.