JP2013008811A - Collector for capacitor, electrode using the same, and capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor which has a large capacitance, a low internal resistance, and excellent durability, and to provide a collector for the capacitor and an electrode.SOLUTION: The collector for a capacitor is formed of a metal porous body having a three-dimensional network structure. The metal porous body is made of an alloy containing at least nickel and tin. Preferably, a tin content of the collector for a capacitor is 1 to 40 mass% inclusive.

Description

  The present invention relates to a current collector for a capacitor, an electrode using the current collector, and a capacitor using the electrode.

  Capacitors are widely used in electrical equipment and the like. Among various capacitors, electric double layer capacitors and hybrid capacitors have recently been attracting attention because of their large capacitance. For example, capacitors are widely used for memory backup, but capacitors are also being used for this purpose, and more recently, they are also expected to be used for vehicles such as hybrid vehicles and fuel vehicles.

  There are various types of capacitors such as a button type, a cylindrical type, and a square type. For example, in the button type, a polarizable electrode having an activated carbon electrode layer provided on a current collector is used as a pair, a separator is arranged between the electrodes to constitute a capacitor element, housed in a metal case together with an electrolyte, and a sealing plate And is sealed by a gasket that insulates the two. Cylindrical type is manufactured by stacking this pair of polarizable electrodes and separator, winding them to form a capacitor element, impregnating this element with electrolyte and storing it in an aluminum case, and sealing it with a sealing material Is done. The basic structure of the square type is almost the same as the button type or cylindrical type.

The polarizable electrode used for this capacitor is usually manufactured by applying a metal foil such as an aluminum foil to a current collector in the shape of a porous body such as a punching metal, a screen, and an extended metal, and applying activated carbon thereto. ing.
Various current collectors constituting electrodes for nonaqueous electrolyte capacitors have been proposed (see Patent Documents 1 to 3).

Patent Document 1 discloses a metal current collector made of aluminum, stainless steel, or the like in a net shape, a punching metal shape, or an expanded metal shape.
However, these current collector shape is two-dimensional structure, since the distance between the current collector and the active carbon when producing a thick electrode in order to increase the capacity density increases, away from the collector resistance Becomes higher, the utilization factor of the activated carbon becomes smaller, and the capacity density also becomes smaller. In addition, when a conductive additive is added to improve electric resistance, the amount of activated carbon is reduced, so that the capacity density is also reduced.
Patent Document 2 discloses a material in which a stainless steel fiber mat is electrically welded to a stainless steel foil. Patent Document 3 discloses a porous body made of at least one metal selected from tantalum, aluminum, and titanium.

  Incidentally, capacitors used for memory backup, automobiles and the like are required to have a higher capacity. That is, reduction of the capacity per unit volume and internal resistance is required. In order to achieve this, it is attempted to add a conductive agent such as carbon black or carbon fiber to the activated carbon in the polarizable electrode, or to change the current collector to a porous body (three-dimensional structure) instead of a metal foil. It has been.

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, for current collectors, attempts have been made to use screens, punching metals, laths, etc. as porous bodies, but the structure is essentially a two-dimensional structure, and a significant improvement in capacitance is expected. Can not.

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 a capacitor using a non-aqueous electrolyte, nickel cannot be used because it is oxidized or corroded by the non-aqueous electrolyte.
Metals other than nickel include aluminum and stainless steel, but it is necessary to treat aluminum in a very high temperature molten salt state, so organic resin cannot be used as an object to be plated. It is difficult to plate the surface.

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 organic resin surface. It is. As for stainless steel, a method has been proposed in which a porous body is obtained by applying powdered powder to an organic resin porous body and sintering, but stainless steel powder is very expensive. In addition, since the organic resin porous body to which the powder adheres is removed by incineration, there is a problem that the strength decreases and it cannot be used. From the above, a metal other than nickel has a three-dimensional structure with high porosity. It was difficult to mass-produce electric bodies.

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 low internal resistance, and excellent durability, a current collector for the capacitor, and an electrode.

In view of the above problems, the present inventors have conducted extensive research, and as a current collector, a current collector for a capacitor made of a metal porous body having a three-dimensional network structure, The present inventors have found that the above problems can be solved by using a current collector made of an alloy containing at least nickel and tin.
That is, the present invention relates to a foamed nickel tin current collector for capacitors as described below, an electrode using the current collector, and a capacitor capacitor using the electrode.

(1) A capacitor current collector made of a porous metal body having a three-dimensional network structure,
A current collector for a capacitor, wherein the porous metal body is made of an alloy containing at least nickel and tin.
(2) The capacitor current collector as described in (1) above, wherein the tin content is 1% by mass or more and 40% by mass or less.
(3) The current collector for capacitors as described in (1) or (2) above, wherein the metal porous body further contains 10% by mass or less of phosphorus as a component.
(4) The current collector for a capacitor according to any one of (1) to (3) above, wherein the corrosion resistance is improved by subjecting the porous metal body to electrolytic oxidation treatment in a liquid.
(5) The capacitor current collector according to any one of (1) to (4) above, wherein an average pore diameter of the metal porous body is 20 μm or more and 900 μm or less.
(6) The current collector for capacitors according to any one of (1) to (5) above, wherein the porosity of the metal porous body is 80% or more and 97% or less.
(7) The current collector for capacitors according to any one of the above (1) to (6), wherein the metal basis weight of the metal porous body is 200 g / m ² or more and 1000 g / m ² or less.
(8) A capacitor electrode, wherein the capacitor current collector according to any one of (1) to (7) is filled with an electrode material mainly composed of activated carbon.
(9) The electrode material comprising the activated carbon as a main component contains 100 parts by mass of activated carbon and 0.1 to 10 parts by mass of a conductive additive, as described in (8) above Capacitor electrode.
(10) A step of coating a nickel porous body having a three-dimensional network structure with a metal containing at least tin;
Then, a step of performing a heat treatment to diffuse tin into the nickel porous body,
A method for producing a current collector for a capacitor comprising an alloy containing at least nickel and tin.
(11) The nickel porous body having the three-dimensional network structure is subjected to conductive treatment and electrolytic nickel plating treatment in this order on the foamed resin to form a nickel coating layer on the surface of the foamed resin. The method for producing a current collector for a capacitor as described in (10) above, which is a nickel porous body having a three-dimensional network structure obtained by performing the removal treatment.
(12) After the nickel porous body having the three-dimensional network structure is subjected to conductive treatment and electrolytic nickel plating treatment in this order on the foamed resin to form a nickel coating layer on the foamed resin surface, the foamed resin is Capacitor collection according to (10) above, characterized in that it is a nickel porous body having a three-dimensional network structure obtained by incineration removal and subsequent heat treatment in a reducing atmosphere to reduce nickel. A method of manufacturing an electric body.
(13) A method for producing a capacitor electrode, wherein the capacitor current collector obtained by the production method according to any one of (10) to (12) is filled with an electrode material mainly composed of activated carbon. .
(14) A capacitor using the capacitor electrode according to (8) or (9).
(15) The capacitor as described in (14) above, wherein a non-aqueous electrolyte is used as the electrolyte.

  In the current collector of the present invention, the metal porous body having a three-dimensional network structure is made of an alloy containing at least nickel and tin, so that the corrosion resistance of the metal porous body is improved, and the metal porous body can be formed even with a non-aqueous capacitor voltage. It can be used favorably as a current collector without being oxidized, and a high capacity density can be obtained because it is a porous structure having a three-dimensional network structure.

It is a photograph which shows an example of the surface external appearance of the electrical power collector for capacitors of this invention. It is an enlarged photograph of FIG. It is a graph which shows the data which confirmed that tin was spreading | diffusion uniformly in frame | skeleton of the electrical power collector for capacitors of this invention.

  The capacitor current collector according to the present invention is a capacitor current collector made of a porous metal body having a three-dimensional network structure, and the porous metal body is made of an alloy containing at least nickel and tin. Features. Since the metal porous body is an alloy containing at least nickel and tin, the current collector for a capacitor of the present invention is excellent in electrolytic resistance and corrosion resistance. Furthermore, since the alloy containing nickel and tin has a small electric resistance, it is possible to provide a current collector for a capacitor excellent in current collecting performance.

  In general, since the surface of the porous metal body has minute hard protrusions due to the cross section of the skeleton of the porous metal body, when used as a current collector or electrode, the minute protrusions are in close contact with the separator. When this occurs, there may be a problem that a short circuit occurs through the separator. However, since the current collector for a capacitor of the present invention is made of an alloy containing nickel and tin, the compressive strength is relatively small as compared with a conventional metal porous body. For this reason, by passing through the compression process when producing the capacitor current collector and the capacitor electrode, the microprotrusions on the surface of the current collector and the electrode are crushed and the short circuit can be suppressed. .

  Furthermore, the metal porous body made of an alloy containing at least nickel and tin can be produced by a plating method as described later. For this reason, manufacturing cost can be suppressed and it can provide at low cost.

  When the content of tin in the metal porous body is 1% by mass or more, the effects of electrolytic resistance and corrosion resistance are sufficiently exhibited, but an intermetallic compound of nickel and tin is generated in the metal porous body. It is preferable that the range is not. Specifically, the content of tin in the porous metal body is 1% by mass or more and 40% by mass or less, 43% by mass or more and 56% by mass or less, 61% by mass or more, and 72% by mass. Or less than or equal to 73 mass% and less than or equal to 99 mass%. The tin content is more preferably 15% by mass or more and 25% by mass or less. Thereby, the electrolysis resistance, corrosion resistance, heat resistance, and strength of the porous metal body made of an alloy containing nickel and tin can be improved.

  Moreover, it is preferable that said metal porous body further contains 10 mass% or less phosphorus as a component. Thereby, the electrolytic resistance and corrosion resistance of the metal porous body are further improved. However, since heat resistance will fall when phosphorus is included too much, it is preferable that the content rate of phosphorus in the said metal porous body is 10 mass% or less.

Moreover, it is preferable that the said metal porous body is what improved corrosion resistance by carrying out the electrolytic oxidation process in the liquid. As a result, it is possible to obtain a metal porous with further improved electrolytic resistance and corrosion resistance.
The electrolytic oxidation treatment can be performed by, for example, a linear sweep voltammetry method. That is, the sample can be processed by applying a potential once over a wide range to examine a potential having a high current value and then applying a potential having a high current until the current becomes sufficiently small.

The method for producing a current collector for a capacitor according to the present invention includes a step of coating a nickel porous body having a three-dimensional network structure with a metal containing at least tin, and then performing a heat treatment to put tin into the nickel porous body. And a step of diffusing up to.
For example, the capacitor current collector of the present invention can be produced as follows.
First, after forming a nickel coating layer on the surface of the foamed resin, the resin as the base material is removed, and then heat treatment is performed in a reducing atmosphere as necessary to reduce nickel to obtain foamed nickel. Next, the foamed nickel is coated with a metal containing at least tin, and then heat-treated to diffuse the tin into the foamed nickel, whereby a capacitor current collector made of an alloy containing at least nickel and tin is obtained. Obtainable.

In addition, after conducting the conductive treatment on the surface of the foam resin, a nickel coating layer is formed, followed by tin plating, and finally heat treatment to remove the foam resin and diffuse tin. Thus, the capacitor current collector of the present invention can be obtained.
Further, a method of conducting a conductive treatment on the foamed resin, plating with tin, subsequently plating with nickel, and then plating with tin again is possible. Thereafter, the capacitor current collector of the present invention can be obtained through a resin removal step, a tin diffusion step, and a reduction step.
In yet another method, a capacitor current collector of the present invention, foamed resin was electroconductive treatment, nickel porous body - can also be produced by the tin alloy plating.

In order to form the nickel coating layer on the surface of the foamed resin, 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.

  For example, when the electrolytic plating method is adopted as a method for forming the nickel coating layer, the conductive resin and electrolytic nickel plating treatment are sequentially performed on the foamed resin surface, and then the resin is removed, and then reduced if necessary. Foamed nickel can be obtained by reducing the nickel by heat treatment in a neutral atmosphere. Then, a current collector made of an alloy containing nickel and tin is formed by coating the foamed nickel with a metal containing at least tin and then performing heat treatment to diffuse the tin into the foamed nickel. Get.

The capacitor electrode of the present invention can be obtained by filling the current collector obtained above with an electrode material mainly composed of activated carbon.
Hereinafter, the present invention will be described in more detail.

[Foamed resin]
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 not limited and is usually about 80% to 97%, preferably about 90% to 96%.
The average pore diameter of the foamed resin is usually about 20 μm to 900 μm, preferably about 30 μm to 700 μm, more preferably about 100 μm to 500 μm. In addition, the average hole diameter in this invention is calculated | required by measuring by the bubble point method.
The thickness of the foamed resin is not limited and is appropriately determined according to the use of the capacitor, etc., but is usually about 200 μm or more and 5000 μm or less, preferably about 300 μm or more and 3000 μm or less, more preferably 400 μm or more, 2000 μm What is necessary is just below.

[Current collector]
Hereinafter, a method for producing the current collector of the present invention by sequentially conducting conductive treatment, electrolytic plating treatment, removal treatment of foamed resin, reduction treatment, tin plating treatment, and heat treatment on the foamed resin will be described in detail.

(Conductive treatment)
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.

(Electrolytic plating treatment)
If the thickness of the nickel plating film is increased by the above-described electroless plating treatment and / or sputtering treatment, there is no need for the electrolytic plating treatment. However, from the viewpoint of productivity and cost, the foamed resin is first conductive as described above. It is preferable to employ a method in which a nickel plating layer is formed by an electrolytic plating method and then by an electrolytic plating method.
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 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.

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.
Basis weight of the conductive coating layer is not limited, usually 5 g / m ² or more, 15 g / m ² degree or less, preferably 7 g / m ² or more, may be set to the degree 10 g / m ² or less.
The basis weight of the electrolytic nickel plating layer is not limited and is preferably about 200 g / m ² or more and 1000 g / m ² or less, more preferably about 250 g / m ² or more and 700 g / m ² or less.
The total weight of the conductive coating layer and the electrolytic nickel plating layer is preferably 200 g / m ² or more and 1000 g / m ² or less, more preferably 250 g / m ² or more and 700 g / m ² or less. . If the total amount is less than this range, the strength of the current collector may decline. 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.

(Foamed resin removal treatment, reduction treatment)
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 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.

(Tin plating process)
The step of coating the foamed nickel obtained above with an alloy containing at least tin can be performed, for example, as follows. That is, as a sulfuric acid bath, a plating bath having a composition of stannous sulfate 55 g / L, sulfuric acid 100 g / L, cresol sulfonic acid 100 g / L, gelatin 2 g / L, β naphthol 1 g / L is prepared, and the cathode current density is set. Tin plating can be performed at 2 A / dm ² , an anode current density of 1 A / dm ² or less, a temperature of 20 ° C., and stirring (cathode oscillation) of 2 m / min.

  The amount of tin plating is such that the final metal composition of the metal porous body has a nickel content of 60% by mass to 99% by mass and a tin content of 1% by mass to 40% by mass. It is preferable to adjust to. Moreover, it adjusts so that the content rate of tin may be 43 mass% or more and 56 mass% or less, or 61 mass% or more and 72% mass or less, or 73 mass% or more and 99 mass% or less. Is also preferable. Furthermore, it is most preferable to adjust so that the content rate of tin may be 15 mass% or more and 25 mass% or less. Thereby, the electrolysis resistance, corrosion resistance, heat resistance, and strength of the porous metal body made of an alloy containing nickel and tin can be improved.

Further, in order to improve the adhesion of tin plating, it is desirable to perform strike nickel plating immediately before, wash the metal porous body, and put it into the tin plating solution without getting dried. Thereby, the adhesiveness of a plating layer can be improved.
The conditions for strike nickel plating can be as follows, for example. That is, a wood strike nickel bath having a composition of nickel chloride 240 g / L, hydrochloric acid (having a specific gravity of about 1.18) 125 ml / L is prepared, the temperature is set to room temperature, and nickel or carbon is used for the anode. It can be carried out.

  Summarizing the above plating procedures, degreasing by an A-screen (cathodic electrolytic degreasing 5 ASD × 1 minute), hot water washing, water washing, acid activity (hydrochloric acid immersion 1 minute), wood strike nickel plating treatment (5-10 ASD × 1 minute), It is processed to tin plating without washing and drying, washing with water and drying.

(Plating solution circulation during plating)
In general, it is difficult to uniformly plate the inside of a porous substrate such as a foamed resin. It is preferable to circulate the plating solution in order to prevent non-attachment of the inside or to reduce the difference in the amount of plating adhesion between the inside and the outside. As a circulation method, there are methods such as using a pump and installing a fan inside the plating tank. Moreover, if a plating solution is sprayed on a base material using these methods, or a base material is made to adjoin a suction port, the plating solution can easily flow inside the base material, which is effective.

(Heat treatment)
After tin plating, nickel with low corrosion resistance may be exposed on the surface of the metal porous body as it is, so it is necessary to perform a heat treatment to diffuse the tin component. Tin can be diffused in an inert atmosphere (reduced pressure, nitrogen, argon, etc.) or in a reducing atmosphere (hydrogen).
In this heat treatment step, the tin component is sufficiently diffused in the nickel plating layer, and the concentration ratio between the front side and the inner side tin of the metal porous body skeleton is a range where the front side concentration / inner concentration is 2/1 or more and 1/2 or less. It is preferable that More preferably, it is 3/2 or more and 2/3 or less, still more preferably 4/3 or more and 3/4 or less, and most preferably, it is uniformly diffused.

  If the heat treatment temperature is too low, it takes time for diffusion, and if it is too high, the heat treatment temperature may soften and damage the porous structure by its own weight. However, when the tin concentration is 40% by mass or more, it is necessary to set the upper limit to 850 ° C. More preferably, it is 400 degreeC or more and 800 degrees C or less, More preferably, it is 500 degreeC or more and 700 degrees C or less.

(Nickel-tin alloy plating)
In the above description, the method of performing nickel plating on the porous substrate, then tin-plating, and alloying by heat treatment has been described, but after conducting the conductive treatment on the porous substrate, the nickel-tin alloy plating is performed. It is also possible to apply. The composition of the nickel-tin alloy plating solution in this case is such that the final metal composition of the metal porous body has a nickel content of 60% by mass or more and 99% by mass or less, and a tin content of 1% by mass or more, 40 It is preferable to adjust so that it may become mass% or less. Moreover, it adjusts so that the content rate of tin may be 43 mass% or more and 56 mass% or less, or 61 mass% or more and 72% mass or less, or 73 mass% or more and 99 mass% or less. Is also preferable. Furthermore, it is most preferable to adjust so that the content rate of tin may be 15 mass% or more and 25 mass% or less. Thereby, the electrolysis resistance, corrosion resistance, heat resistance, and strength of the porous metal body made of an alloy containing nickel and tin can be improved.
And after forming nickel-tin alloy plating, a porous metal base material is obtained by removing a porous body base material and then heat-processing in a reducing atmosphere and reducing a metal.

(Metal weight)
The total metal basis weight of the conductive coating layer, nickel, and tin in the final porous metal body is preferably 200 g / m ² or more and 1000 g / m ² or less. More preferably, they are 250 g / m < ² > or more and 700 g / m < ² > or less, More preferably, they are 300 g / m < ² > or more and 500 g / m < ² > or less. If the total amount is less than 200 g / m ² , the strength of the current collector may be reduced. On the other hand, if the total amount exceeds 1000 g / m ² , the filling amount of the polarizable material is reduced, and the cost is disadvantageous.

(Average pore diameter)
The capacitor current collector of the present invention has an average pore size of usually about 20 μm to 900 μm, preferably about 30 μm to about 700 μm, more preferably about 100 μm to about 500 μm.
(Porosity)
The capacitor current collector of the present invention preferably has a porosity of 80% or more and 97% or less, and more preferably 90% or more and 96% or less.

(Confirmation of metal porous body composition)
Quantitative measurement using inductively coupled plasma (ICP) can be performed to determine the mass% of the contained element.

(Diffusion confirmation of tin)
By conducting energy dispersive X-ray spectroscopy (EDX) measurement from a cross section of a porous metal body and comparing the spectrum of the skeleton front side and the skeleton inner side, the diffusion state of tin can be confirmed. .

[electrode]
The electrode of the present invention is obtained by filling the capacitor current collector of the present invention with an electrode material mainly composed of activated carbon. 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. As activated carbon, what is generally marketed for capacitors can be used.
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 m ² / g or more and 3000 m ² / g or less. By setting this range, the capacitance of the capacitor can be increased, and the internal resistance can be reduced.

Moreover, you may contain 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 the content of the conductive auxiliary agent 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.

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 mass part or more and 5 mass parts or less 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.

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. cm ² or more, 40 mg / cm ² degrees or less, preferably 16 mg / cm ² or more, may be set to the degree 32 mg / cm ² or less.
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 about 200 μm to 5000 μm, preferably about 300 μm to 3000 μm, more preferably about 400 μm to 2000 μm. The thickness after compression molding is usually about 100 μm to 3000 μm, preferably about 150 μm to 2000 μm, more preferably about 200 μm to 1000 μm.
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 comprises a pair of two capacitor electrodes of the present invention, a separator disposed between these electrodes, and a separator impregnated with an electrolyte 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 or more and 5 μm or less, and the thickness is usually about 10 μm or more and 100 μm or less.

As the electrolytic solution, a known or commercially available electrolytic solution can be used, and any of a calcareous aqueous solution and a nonaqueous electrolytic solution can be used. Examples of the alkaline electrolyte include alkaline aqueous solutions such as an aqueous potassium hydroxide solution and an aqueous sodium hydroxide solution. Examples of non-aqueous electrolytic shielding include propylene carbonate solution in which tetraalkylphosphonium tetrafluoroborate is dissolved, propylene carbonate solution or sulfolane solution in which tetraalkylammonium tetrafluoroborate is dissolved, and propylene carbonate solution in which triethylmethylammonium tetrafluoroborate is dissolved. Etc.
Among these, a nonaqueous electrolytic solution is preferable in the present invention. By using such a non-aqueous electrolyte, the capacitance can be improved.

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

[Example 1]
(Preparation of current collector)
As the foamed resin, a foamed urethane resin sheet (commercially available product, average pore diameter 90 μm, thickness 1.4 mm, porosity 96%) was used.
A sputtering treatment was performed on the foamed urethane resin sheet using nickel as a target, thereby forming a conductive coating layer (nickel layer) on the surface of the foamed urethane resin sheet. The basis weight of the conductive coating layer was 10 g / m ² .
Next, the obtained urethane foam resin sheet on which the conductive coating layer was formed was subjected to electrolytic plating. As an electrolytic nickel plating bath, a Watt bath (nickel sulfate 330 g / l, nickel chloride 50 g / l, boric acid 40 g / 1) was used. A titanium basket containing nickel pieces was used as the counter electrode. The electrodeposition conditions were a bath temperature of 60 ° C. and a current density of 30 A / dm ² .
The basis weight of the electrolytic nickel plating layer was set to 200 g / m ^{2 in} total for the conductive coating layer.

  The foamed structure after electrolytic plating was heat-treated at 800 ° C. in the atmosphere to incinerate and remove the urethane resin, and then heated to 1000 ° C. in a hydrogen gas atmosphere to reduce nickel to obtain a nickel porous body.

A nickel porous body having a basis weight of 200 g / m ² prepared in the above was subjected to tin plating of basis weight 2 g / m ^2, it is diffused tin by heat treatment, nickel 99 wt%, the capacitor current collector tin 1% by weight of the composition A was obtained.
FIG. 1 and FIG. 2 show external appearance photographs of the capacitor current collector. In addition, FIG. 2 is the photograph observed by magnifying 300 times with an electron microscope.

As a plating solution for tin plating, a composition of 55 g / L of stannous sulfate, 100 g / L of sulfuric acid, 100 g / L of cresolsulfonic acid, 2 g / L of gelatin, and 1 g / L of β-naphthol is used for 1000 g of water did. The bath temperature of the plating bath was 20 ° C., and the anode current density was 1 A / dm ² . The plating solution was agitated so as to be 2 m / min by the cathode oscillation.
In the heat treatment step, heat treatment was performed at 550 ° C. for 10 minutes in a reducing (hydrogen) atmosphere.
In the EDX spectrum comparison, there was no difference between the front side and the inside of the current collector, and it was confirmed that tin was evenly diffused.

[Example 2]
A current collector for a capacitor was produced in the same manner as in Example 1 except that the basis weight of tin plating on the nickel porous body was 59.7 g / m ² . As a result, a nickel-tin alloy capacitor current collector B having a Sn content of 23% by mass was obtained.
In the EDX spectrum comparison, as shown in FIG. 3, there was no difference between the front side and the inner side of the current collector, and it was confirmed that tin was evenly diffused.

[Example 3]
A current collector for a capacitor was produced in the same manner as in Example 1 except that the basis weight of tin plating on the nickel porous body was 133 g / m ² . As a result, a nickel tin alloy capacitor current collector C having a Sn content of 40% by mass was obtained.
In the EDX spectrum comparison, there was no difference between the front side and the inside of the current collector, and it was confirmed that tin was evenly diffused.

[Example 4]
A current collector for a capacitor was produced in the same manner as in Example 1 except that the basis weight of tin plating on the nickel porous body was 216.7 g / m ² . As a result, a nickel-tin alloy capacitor current collector D having a Sn content of 52 mass% was obtained.
In the EDX spectrum comparison, there was no difference between the front side and the inner side, and it was confirmed that tin was evenly diffused.

[Example 5]
In the same manner as in Example 2, a nickel-tin alloy current collector having a Sn content of 23% by mass was prepared with a tin plating basis weight of 59.7 g / m ² . Further, a capacitor current collector E was obtained by applying a potential of 0.2 V vs. SHE for 15 minutes in an aqueous sodium sulfate solution having a concentration of 1 mol / L.
In the EDX spectrum comparison, there was no difference between the front side and the inner side, and it was confirmed that tin was evenly diffused.

(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.
The activated carbon paste was filled into the capacitor current collectors A to E so that the activated carbon content was 30 mg / cm ² . The actual loading of the current collector A is 30 mg / cm ^2, current collectors B is is 31 mg / cm ^2, a collector C is 31 mg / cm ^2, the current collector D is 31 mg / cm ² And current collector E was 30 mg / cm ² .

Next, 100 ° C. in a dryer, after removal of the 1 hour dried the solvent, diameter 500 mm roller press: give (slit 50 [mu] m) and pressurized capacitor electrode A~E of Examples 1 to 5 It was.
The thickness after pressing was 483 μm for electrode A, 485 μm for electrode B, 485 μm for current collector C, 484 μm for electrode D, and 484 μm for electrode E.

[Comparative Example 1]
In the same manner as in Example 1, the urethane foam after the conductive treatment was subjected to nickel plating, and the urethane was removed by heat treatment to produce a current collector F for a capacitor made of a nickel porous body.
Then, in the same manner as in Example 1, 31 mg / cm ² of activated carbon paste was filled, and an electrode F was produced so that the thickness after pressurization was 482 μm.

[Comparative Example 2]
As the current collector G, an aluminum foil (commercial product, thickness 20 μm) was used.
The activated carbon paste produced in Example 1 was applied by the doctor blade method so that the total on both sides was 8 mg / cm ² , but because the adhesive strength was insufficient, the activated carbon paste could not be sufficiently adhered to the aluminum foil. .
Therefore, a positive electrode active material paste similar to that produced in the example was produced except that the amount of polyvinylidene fluoride was changed to 8 parts by mass. The paste G was applied to both surfaces of an aluminum foil by a doctor blade method, dried and pressed to produce an electrode G of Comparative Example 2. The amount of activated carbon applied was 8 mg / cm ² , and the electrode thickness was 176 μm.

[Comparative Example 3]
In the same manner as in Example 1, the electrofoamed urethane foam was subjected to nickel electroplating, the urethane was removed by heat treatment, and then tin plating was performed. Unlike Example 1, a current collector H for a capacitor was obtained without performing a heat treatment step after tin plating.
Then, in the same manner as in Example 1, 29 mg / cm ² of activated carbon paste was filled, and an electrode H was produced so that the thickness after pressurization was 479 μm.

[Production and testing of capacitors]
The obtained electrodes A to H were punched into two diameters of 14 mm (two 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 HH (corresponding to electrodes A to H, respectively). The rated voltage was 2.5V.

[Evaluation of capacitance]
Ten capacitors similar to those in Examples 1 to 5 and Comparative Examples 1 to 3 were respectively produced, and after aging by applying a voltage of 2.5 V at 65 ° C. for 6 hours, the temperature was set to 25 ° C. and 2.5 V was applied. Discharging was performed at a current of 1 mA as the starting voltage, and the initial capacitance and internal resistance were examined.
Table 1 shows the average value of capacitance per unit area, capacitance per unit deposition, and internal resistance. Capacitor of Comparative Example 1 and Comparative Example 3, the voltage of the aging at 10 cell total number does not reach up to 2.5V, because discharge also could only little time, could not ask for capacitance and internal resistance. Since the voltage does not increase, current is used in addition to the battery reaction, and nickel elution and oxidation of the current collector are suspected.

As is apparent from Table 1, the capacitors of Examples 1 to 5 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 to 5 exhibit a capacitance that is three times or more that of the capacitor of Comparative Example 2. Therefore, it can be seen that 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.
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, from the results of Comparative Example 1 and Comparative Example 3, even if the current collector has a porous structure, it does not contain tin or is not alloyed. It turns out that it is unsuitable.

[Durability evaluation]
Next, the durability and charge / discharge cycle characteristics when the capacitor characteristics were maintained at an important high voltage were investigated. 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 to 5 and Comparative Example 2 were held for 2000 hours while applying a voltage of 2.5 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 can be seen from Table 2, the capacitance of the capacitor of the example and the internal resistance were small after 2000 hours as compared with the capacitor of the comparative example. Therefore, it was found that the capacitor of the present invention has a high capacitance and is excellent in durability.

(Durability test 2)
Charging / discharging cycle characteristics are important indicators of cell life. As test conditions, charge and discharge cycles with a constant current of 1 mA at an ambient temperature of 45 ° C. between 0.5 and 2.5 V were repeated 10,000 times, and the discharge capacity and internal resistance after 10,000 cycles were measured. Evaluation was made in comparison. The results are shown in Table 3.

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 the present invention has been described based on the embodiments, the present invention is not limited to the above-described embodiments. Various modifications can be made to the above-described embodiments within the same and equivalent scope as the present invention.

  The current collector of the present invention has oxidation resistance, electrolytic solution resistance, and porosity, and an electrode obtained by filling activated carbon with the current collector is excellent in durability and capacity density. Can do.

Claims (15)

A current collector for a capacitor comprising a porous metal body having a three-dimensional network structure,
A current collector for a capacitor, wherein the porous metal body is made of an alloy containing at least nickel and tin.   The current collector for capacitors according to claim 1, wherein the tin content is 1% by mass or more and 40% by mass or less.   The current collector for capacitors according to claim 1 or 2, wherein the porous metal body further contains 10 mass% or less of phosphorus as a component.   The current collector for a capacitor according to claim 1, wherein the metal porous body is subjected to electrolytic oxidation treatment in a liquid to improve corrosion resistance.   5. The capacitor current collector according to claim 1, wherein an average pore diameter of the metal porous body is 20 μm or more and 900 μm or less.   The current collector for a capacitor according to any one of claims 1 to 5, wherein the porosity of the metal porous body is 80% or more and 97% or less. 7. The capacitor current collector according to claim 1, wherein the metal basis weight of the metal porous body is 200 g / m ² or more and 1000 g / m ² or less.   8. A capacitor electrode, wherein the capacitor current collector according to claim 1 is filled with an electrode material mainly composed of activated carbon.   9. The electrode for a capacitor according to claim 8, wherein the electrode material mainly composed of activated carbon contains 0.1 part by mass or more and 10 parts by mass or less of a conductive additive with 100 parts by mass of activated carbon. . Coating a nickel porous body having a three-dimensional network structure with a metal containing at least tin;
Then, a step of performing a heat treatment to diffuse tin into the nickel porous body,
A method for producing a current collector for a capacitor comprising an alloy containing at least nickel and tin.   The nickel porous body having the three-dimensional network structure is formed by subjecting the foamed resin to a conductive treatment and an electrolytic nickel plating treatment in this order to form a nickel coating layer on the foamed resin surface, and then removing the foamed resin. The method for producing a current collector for a capacitor according to claim 10, wherein the method is a nickel porous body having a three-dimensional network structure obtained by applying the step.   After the nickel porous body having the three-dimensional network structure is subjected to conductive treatment and electrolytic nickel plating treatment in this order on the foamed resin to form a nickel coating layer on the foamed resin surface, the foamed resin is incinerated and removed. The manufacturing method of a current collector for a capacitor according to claim 10, which is a nickel porous body having a three-dimensional network structure obtained by subsequently performing a heat treatment in a reducing atmosphere to reduce nickel. Method.   A method for producing a capacitor electrode, comprising filling a current collector for a capacitor obtained by the production method according to claim 10 with an electrode material mainly composed of activated carbon.   A capacitor using the capacitor electrode according to claim 8.   The capacitor according to claim 14, wherein a nonaqueous electrolytic solution is used as the electrolytic solution.