JP2013008813A - Capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor having a large capacitance and excellent durability at a low cost.SOLUTION: The capacitor comprises: a positive electrode produced by filling a metal porous body for positive electrode with a positive electrode active material composed mainly of active carbon; a negative electrode produced by holding a negative electrode active material capable of adsorbing and desorbing lithium ions in a collector for negative electrode; and a nonaqueous electrolyte. The metal porous body for positive electrode consists of an alloy containing at least nickel and tin, and lithium ions are adsorbed to the negative electrode by chemical or electrochemical method.

Description

  The present invention relates to a capacitor, and more particularly to a capacitor using Li ions.

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

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

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

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

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

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

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

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

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

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

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

  As a result of intensive studies to solve the above problems, the present inventors have occluded and desorbed lithium ions from a positive electrode filled with a positive electrode active material mainly composed of activated carbon in a positive electrode metal porous body and a negative electrode current collector. A negative electrode formed by holding a negative electrode active material, a non-aqueous electrolyte containing a lithium salt, the positive electrode metal porous body is made of an alloy containing at least nickel and tin, and the negative electrode is chemically treated with lithium ions The present invention has been completed by finding that it is effective to occlude by a mechanical or electrochemical method. That is, the capacitor according to the present invention has the following characteristics.

(1) At least
A positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body for a positive electrode;
A negative electrode obtained by holding a negative electrode active material capable of absorbing and desorbing lithium ions in a negative electrode current collector;
A non-aqueous electrolyte containing a lithium salt,
A capacitor characterized in that the positive electrode metal porous body is made of an alloy containing at least nickel and tin, and lithium ions are occluded in the negative electrode by a chemical or electrochemical method.
(2) The capacitor according to (1), wherein the content of tin in the positive electrode metal porous body is 1% by mass or more and 40% by mass or less.
(3) The capacitor according to (1) or (2) above, wherein the metal porous body for positive electrode further contains 10% by mass or less of phosphorus as a component.
(4) The capacitor according to any one of the above (1) to (3), wherein the metal porous body for positive electrode is subjected to electrolytic oxidation treatment in a liquid to improve corrosion resistance.
(5) The metal porous body for a positive electrode is
A foam-like nickel with a nickel basis weight of 200 g / m ² or more and 1000 g / m ² or less obtained by coating the foamed urethane with nickel and then burning off the urethane is coated with a metal containing at least tin, and then heat-treated. The capacitor as described in (4) above, which is a foamed nickel-tin alloy having a porosity of 80% or more and 97% or less, produced by diffusing tin into foamed nickel.
(6) The metal porous body for a positive electrode is
A non-woven fabric nickel having a nickel basis weight of 200 g / m ² or more and 1000 g / m ² or less obtained by coating a non-woven fabric made of polyolefin fiber with nickel is coated with a metal containing at least tin, and then heat-treated to form tin. The capacitor as described in (4) above, which is a non-woven nickel-tin alloy having a porosity of 80% or more and 97% or less produced by diffusing into foamed nickel.
(7) The negative electrode active material capable of absorbing and desorbing lithium ions is mainly composed of a carbon material, and the carbon material includes a graphite-based material or an easily graphitizable carbon material. The capacitor according to any one of 6).
(8) An alloy in which the negative electrode active material capable of occluding and desorbing lithium ions is mainly a metal, and the metal contains 20% by mass or more of one or more metals selected from the group consisting of aluminum, tin, and silicon. Or the capacitor according to any one of (1) to (6) above, which is a composite.
(9) The negative electrode current collector is a metal foil, and the metal foil is any one of aluminum, copper, nickel, or stainless steel. The capacitor as described.
(10) The negative electrode current collector is a metal porous body, and the porosity obtained by burning the urethane after the foamed urethane is coated with nickel is 80% or more and 97% or less, nickel The capacitor according to any one of (1) to (8) above, wherein the basis weight is foamed nickel having a weight per unit area of 200 g / m ² or more and 1000 g / m ² or less.
(11) The negative electrode current collector is a metal porous body, and the porosity obtained by coating the nonwoven fabric made of polyolefin fibers with nickel is 80% or more and 97% or less, and the nickel basis weight is The capacitor as described in any one of (1) to (8) above, which is a non-woven nickel of 200 g / m ² or more and 1000 g / m ² or less.
(12) The lithium salt is one or more selected from the group consisting of LiClO ₄ , LiBF ₄ , and LiPF ₆ ,
(1) to (1) above, wherein the solvent of the non-aqueous electrolyte is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The capacitor according to any one of 11).
(13) Any of (1) to (12) above, wherein the negative electrode capacity is larger than the positive electrode capacity, and the lithium ion storage capacity of the negative electrode is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity. Capacitor.

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

2 is a photograph showing an example of the surface appearance of a positive electrode current collector a produced in Example 1. FIG. 2 is an enlarged photograph of a positive electrode current collector a in FIG. 1. It is a graph which shows the data which confirmed that tin was spreading | diffusion uniformly in frame | skeleton of the electrical power collector a for positive electrodes.

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

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

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

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

After the positive electrode is filled with the activated carbon paste, the solvent in the paste may be removed by performing a drying treatment as necessary. Further, if necessary, after being filled with activated carbon paste, it may be compression-molded by pressurizing with a roller press or the like.
The thickness before and after compression is usually about 200 μm or more and 5000 μm or less, preferably about 300 μm or more and 3000 μm or less, more preferably about 400 μm or more and 2000 μm or less. 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.

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

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

(Conductive aid)
There is no restriction | limiting in particular in the kind of conductive support agent, A well-known or commercially available thing can be used. Examples thereof include acetylene black, ketjen black, carbon fiber, natural graphite (scaly graphite, earthy graphite, etc.), artificial graphite, ruthenium oxide and the like. Among these, acetylene black, ketjen black, carbon fiber and the like are preferable. Thereby, the electrical conductivity of the capacitor can be improved. Although the content of the conductive 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.

(Binder)
There is no restriction | limiting in particular in the kind of binder, A well-known or commercially available thing can be used. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, polyolefin, styrene butadiene rubber, polyvinyl alcohol, carboxymethyl cellulose and the like.
Although there is no restriction | limiting in particular also about content of a binder, Preferably it is about 0.5 mass part or more and about 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.

[Current collector for positive electrode]
The positive electrode current collector is a positive electrode metal porous body made of an alloy containing at least nickel and tin.
(Porous metal porous body)
The positive electrode metal porous body is made of an alloy containing at least nickel and tin. The positive electrode metal porous body is made of an alloy containing at least nickel and tin, whereby the positive electrode current collector is excellent in electrolytic resistance and corrosion resistance. Furthermore, an alloy containing nickel and tin has a low electrical resistance, and thus becomes a current collector with excellent 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 positive electrode current collector is made of an alloy containing nickel and tin, the compressive strength is relatively small compared to a conventional porous metal body. For this reason, through the compression process at the time of producing the positive electrode current collector and the positive electrode, the microprotrusions on the surface of the current collector and the electrode are crushed, and the short circuit can be suppressed. .

  Furthermore, the positive electrode 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 positive electrode metal porous body is 1% by mass or more, the effects of electrolysis resistance and corrosion resistance are sufficiently exhibited, but an intermetallic compound of nickel and tin in the metal porous body It is preferable that it is the range which does not produce | generate. Specifically, the tin content in the positive electrode metal porous 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%. % Mass or less, or 73 mass% or more and 99 mass% or less. 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 positive electrode metal porous body made of an alloy containing nickel and tin can be improved.

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

Moreover, it is preferable that the said metal porous body for positive electrodes is what improved corrosion resistance by carrying out the electrolytic oxidation process in a liquid. Thereby, the metal porous for positive electrodes which further improved the electrolysis resistance and the corrosion resistance can be obtained.
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 positive electrode metal porous body includes, for example, a step of covering foamed nickel or non-woven nickel with a metal containing at least tin, and a step of subsequently performing a heat treatment to diffuse tin into the foamed nickel. It can produce by the manufacturing method which has these. Thus, by using foamed nickel or non-woven fabric nickel as the base material, a porous metal body for a positive electrode having a large porosity is obtained, and the filling properties and retention of the active material are excellent. As such foamed nickel and non-woven nickel, those based on foamed urethane or non-woven fabric can be preferably used.
In addition, as a base material before plating with tin, a metal plate with a large number of small holes, a metal plate with unevenness and a pseudo three-dimensional structure, a sintered body Or a structure of continuous air holes is used.

In addition, after conducting a conductive treatment on the surface of a porous resin body (foamed resin, non-woven resin, etc.) having a three-dimensional network structure, a nickel coating layer is formed, followed by tin plating. The positive electrode metal porous body can also be obtained by performing a heat treatment to remove the resin porous body and diffuse tin.
Furthermore, a method of conducting a conductive treatment on a porous resin body having a three-dimensional network structure, plating with tin, subsequently plating with nickel, and then plating with tin again is possible. Thereafter, the positive electrode metal porous body can be obtained through a resin removal step, a tin diffusion step, and a reduction step.
In still another method, the positive electrode metal porous body can be produced by conducting a conductive resin porous body having a three-dimensional network structure and plating the resin porous body with a nickel-tin alloy. it can.

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

As the foamed resin, any known or commercially available one can be used as long as it is porous, and examples thereof include foamed urethane and foamed styrene. Among these, urethane foam is preferable from the viewpoint of particularly high porosity.
The porosity of the foamed resin is usually about 80% to 97%, preferably about 90% to 96%.
The average pore diameter 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 appropriately determined depending on the application of the capacitor, 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 about 400 μm or more and 2000 μm or less. That's fine.

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

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

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

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

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

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

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

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

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

The average fiber diameter of the resin fibers is usually about 9 μm to 70 μm, preferably about 10 μm to 50 μm. The average fiber length is not limited and is usually about 5 mm to 100 mm, preferably about 30 mm to 70 mm.
The porosity of the nonwoven fabric is usually about 80% to 97%, preferably about 90% 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 usually about 20 μm or more and 900 μm or less, preferably about 30 μm or more and about 700 μm or less, more preferably about 100 μm or more and about 500 μm or less. The pore diameter is measured by the bubble point method.
The average thickness of the nonwoven fabric may be appropriately determined according to the use and purpose of the capacitor to be produced, 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 about 400 μm or more and 2000 μm or less. And it is sufficient.

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

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

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

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

Similarly to the foamed resin, the electrolytic nickel plating treatment may be performed according to a conventional method. The weight per unit area of the electrolytic nickel plating layer is about 200 g / m ² or more and about 1000 g / m ² or less, preferably 250 g / m ² or more with respect to the nonwoven fabric, from the viewpoint of conductivity, porosity, strength, corrosion resistance, economy, and the like. 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. . When the total amount is below this range, the strength of the current collector may be reduced. On the other hand, if the total amount exceeds this range, the filling amount of the polarizable material is reduced or the cost is disadvantageous.

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

(Tin plating process)
The step of coating the foamed nickel or non-woven nickel 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.

  In the final metal composition of the positive electrode metal porous body, the amount of tin plating is such that the nickel content is 60% by mass or more and 99% by mass or less, and the tin content is 1% by mass or more and 40% by mass or less. It is preferable to adjust so that it becomes. 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.

Moreover, in order to improve the adhesion of tin plating, it is desirable to perform strike nickel plating immediately before, wash the foamed nickel and the non-woven nickel, and put them into the tin plating solution without being 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 a porous base material such as foamed resin, resin nonwoven fabric, foamed nickel or nonwoven fabric nickel. 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 having low corrosion resistance may be exposed on the surface of the positive electrode 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 into the nickel plating layer, and the concentration ratio of the front side and the inner side tin of the metal porous body skeleton for the positive electrode is such that the front side concentration / inside concentration is 2/1 or more and 1/2 or less. It is preferable to be in the range. 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 resin porous substrate and then tin-plating and alloying by heat treatment has been described. After conducting the conductive treatment on the resin porous substrate, nickel-tin Alloy plating can also be applied. In this case, the composition of the nickel-tin alloy plating solution is such that the final metal composition of the positive electrode 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. It is preferable to adjust so that it may be 40 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, the resin porous body base material is removed, and then a metal porous body for positive electrode is obtained by reducing the metal by heat treatment in a reducing atmosphere.

(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 positive electrode current collector usually has an average pore size of about 20 μm to 900 μm, preferably about 30 μm to about 700 μm, and more preferably about 100 μm to about 500 μm.
(Porosity)
The positive electrode current collector preferably has a porosity of 80% to 97%, more preferably 90% to 96%.

(Confirmation of composition of metal porous body for positive electrode)
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. .

Since the positive electrode current collector produced by the above method is made of an alloy containing at least nickel and tin, the corrosion resistance of nickel is improved, and nickel can be used as a current collector without being oxidized even at a non-aqueous capacitor voltage. it can. Furthermore, since the positive electrode current collector has a porous structure, it can be filled with more activated carbon, and the capacitance can be improved. Moreover, since the activated carbon is enclosed in the voids in the porous body, the content of the binder (insulator) for binding the activated carbon and the current collector can be reduced, and the internal resistance can be reduced. Can do.
The average thickness of the positive electrode current collector is usually about 200 μm or more and 5000 μm or less, preferably about 300 or 3000 μm or less, more preferably about 400 μm or more and 2000 μm or less.

-Negative electrode-
The negative electrode can be produced by applying a negative electrode active material capable of occluding and desorbing lithium ions to a negative electrode current collector made of a metal foil, a negative electrode metal porous body, or the like.
Examples of the method for holding the negative electrode active material in the negative electrode current collector include a method in which the negative electrode active material is made into a paste and the negative electrode active material paste is applied by a doctor blade method or the like. Moreover, you may press-mold with a roller press etc. after drying as needed, and you may fill.

As a negative electrode active material capable of occluding and desorbing lithium ions, a carbon material or metal based material capable of occluding and desorbing lithium ions as described later can be used.
In order to occlude lithium ions in the carbon material or metal, for example, a Li foil is pressure-bonded to a negative electrode produced through the following steps, and the manufactured cell (capacitor) is kept warm in a constant temperature layer at 60 ° C. for 24 hours. And the like. In addition, a carbon material or metal capable of occluding and desorbing lithium ions and a lithium material are mixed and mixed by a mechanical alloy method, or a Li metal is incorporated into a capacitor cell and a negative electrode and the Li metal are short-circuited. Is mentioned.

[Current collector for negative electrode]
As the negative electrode current collector, a metal foil or a negative electrode metal porous body can be preferably used.
(Metal foil)
As the current collector for the negative electrode, a metal foil can be preferably used. Such a metal foil is preferably, for example, aluminum, copper, nickel, or stainless steel.

(Metal porous material for negative electrode)
As the negative electrode current collector, a negative electrode metal porous body can also be preferably used. As described above, the capacitor according to the present invention uses a carbon material capable of occluding and releasing lithium ions or a negative electrode active material mainly composed of metal. Since the metal alloyed with lithium ions undergoes a large volume change upon reaction with lithium, when a copper foil or the like having a normal configuration is used, peeling occurs and the life characteristics are deteriorated. However, in the present invention, a negative electrode metal porous body is used for the negative electrode current collector, and the negative electrode active material is held in the skeleton of the negative electrode metal porous body, so that the metal peels even if the volume changes. Thus, a capacitor having excellent life characteristics can be obtained.

As the metal porous body for the negative electrode, the porosity obtained by coating the foamed urethane with nickel and then burning out the urethane is 80% or more and 97% or less, and the nickel basis weight is 200 g / m ² or more and 1000 g / m ² or less. Foamed nickel can be preferably used. In addition, a non-woven nickel having a porosity of 80% or more and 97% or less and a nickel basis weight of 200 g / m ² or more and 1000 g / m ² or less obtained by coating a nonwoven fabric made of polyolefin fibers with nickel is also preferably used. Can do.
These metal porous bodies for negative electrodes can be produced by the same method as the foamed nickel and non-woven nickel used as the base material of the positive electrode current collector described above.

[Negative electrode active material]
The negative electrode active material is obtained by mixing a carbon material or metal powder capable of occluding and desorbing lithium ions in a solvent and stirring the mixture with a mixer. A conductive auxiliary agent and a binder may be included as needed.

(Carbon material that can absorb and desorb lithium ions)
The carbon material capable of occluding and desorbing lithium ions is not particularly limited as long as it can occlude and desorb lithium ions, and examples thereof include graphite materials and graphitizable carbon materials. Moreover, what has a theoretical capacity of 300 mAh / g or more is preferable.

(Metal that can absorb and desorb lithium ions)
The metal that can occlude and desorb lithium ions is not particularly limited as long as it can occlude and desorb lithium ions, and examples thereof include aluminum, tin, and silicon. Moreover, it is preferable that it is an alloy containing 20 mass% or more of any one or more metals among aluminum, tin, and silicon, or a composite. In particular, those having a theoretical capacity of 300 mAh / g or more are preferable. Preferred examples of the composite include an aluminum-nickel alloy, a copper tin alloy in which copper and tin are mixed (tin 10 mass% or more and 70 mass% or less), and a composite of silicon powder and silica powder.
In addition, when the metal to be alloyed with lithium is filled in the negative electrode, such a metal material has a larger capacity than a conventional graphite material, so that the amount of use can be reduced. Therefore, the thickness of the negative electrode can be reduced to reduce the volume of the cell, and the volume energy density of the capacitor can be improved.

(Conductive aid)
As the conductive auxiliary agent, a known or commercially available one can be used as in the case of the positive electrode active material. That is, for example, acetylene black, ketjen black, carbon fiber, natural graphite (scaly graphite, earthy graphite, etc.), artificial graphite, ruthenium oxide and the like can be mentioned. Among these, acetylene black, ketjen black, carbon fiber and the like are preferable. Furthermore, it is preferable to mix acetylene black or ketjen black and carbon fiber, and the mixing ratio is preferably 20% by weight or less of the total amount of carbon fiber. Thereby, the electrical conductivity of the capacitor can be improved.
(Binder)
The binder is not particularly limited as in the case of the positive electrode active material, and a known or commercially available binder can be used. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, polyolefin, styrene butadiene rubber, polyvinyl alcohol, carboxymethyl cellulose and the like. It may be selected according to the solvent to be used, but when N-methyl-2-pyrrolidone is used as the solvent, polyvinylidene fluoride is preferable, and when water is used, a mixture of polytetrafluoroethylene and carboxymethyl cellulose is preferable. In these combinations, the internal resistance of the capacitor can be kept low, and a large capacitance can be obtained.

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

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

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.
[Example 1]
(Preparation of current collector for positive electrode)
Tin was plated on the foamed nickel, followed by heat treatment to diffuse the tin, and a positive electrode current collector a having a composition of 99 mass% nickel and 1 mass% tin was produced.
1 and 2 show photographs of the appearance of the positive electrode current collector a. In addition, FIG. 2 is the photograph observed by magnifying 300 times with an electron microscope.

Foamed nickel is reduced after the urethane sheet (commercially available product, average pore diameter 90 μm, thickness 1.4 mm, porosity 96%) is subjected to conductive treatment, then plated with a predetermined amount of nickel, and urethane is removed by incineration at 800 ° C. in the atmosphere. It was made by heating to 1000 ° C. in a neutral atmosphere (hydrogen) and reducing nickel. For the conductive treatment, 10 g / m ² of nickel was applied by sputtering. The amount of nickel plating was set to 200 g / m ² in total for the conductive treatment. The produced foamed nickel had an average pore diameter of 80 μm, a thickness of 1.2 mm, and a porosity of 95%.

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.
The thickness of the produced positive electrode current collector a was 1.4 mm.

(Preparation of positive electrode)
100 parts by weight of activated carbon powder (specific surface area 2500 m ² / g, average particle size of about 5 μm), 2 parts by weight of ketjen black (KB) as a conductive additive, 4 parts by weight of polyvinylidene fluoride powder as a binder, N-methyl as a solvent Activated carbon positive electrode paste was prepared by adding 15 parts by mass of pyrrolidone (NMP) and stirring with a mixer.
This activated carbon paste was filled in the positive electrode current collector a so that the activated carbon content was 30 mg / cm ² . The actual filling amount was 31 mg / cm 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: 300 μm) to obtain positive electrode A of Example 1. The thickness of the positive electrode A after pressurization was 480 μm.

(Current collector for negative electrode)
A copper foil having a thickness of 20 μm was used as the negative electrode current collector a ′.
(Preparation of negative electrode)
100 parts by weight of natural graphite powder capable of occluding and releasing lithium, 2 parts by weight of ketjen black (KB) as a conductive additive, 4 parts by weight of polyvinylidene fluoride powder as a binder, and 15 parts by weight of N-methylpyrrolidone (NMP) as a solvent Was added and stirred with a mixer to prepare a graphite-based negative electrode paste.
This graphite-based negative electrode paste was applied onto the above copper foil using a doctor blade (gap 400 μm). The actual coating amount was 10 mg / cm ² . Next, after drying 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: 200 μm) to obtain negative electrode A ′ of Example 1. The thickness of the negative electrode A ′ after pressurization was 220 μm.

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

[Example 2]
A current collector for a positive electrode was produced in the same manner as in Example 1 except that the basis weight of tin plating on the foamed nickel was 59.7 g / m ² . As a result, a nickel-tin alloy positive electrode 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.
A coin-type capacitor B was produced in the same manner as in Example 1 except that this positive electrode current collector b was used.

[Example 3]
A current collector for a positive electrode was produced in the same manner as in Example 1 except that the basis weight of tin plating on the foamed nickel was 133 g / m ² . As a result, a nickel-tin alloy positive electrode 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.
A coin-type capacitor C was produced in the same manner as in Example 1 except that this positive electrode current collector c was used.

[Example 4]
A current collector for a positive electrode was produced in the same manner as in Example 1 except that the basis weight of tin plating on the foamed nickel was 216.7 g / m ² . As a result, a nickel-tin alloy positive electrode 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.
A coin-type capacitor D was produced in the same manner as in Example 1 except that this positive electrode current collector d was used.

[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 positive electrode current collector e was obtained by electrolytic oxidation 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.
A coin-type capacitor E was produced in the same manner as in Example 1 except that this positive electrode current collector e was used.

[Example 6]
A coin-type capacitor F was produced in the same manner as in Example 1 except that the negative electrode B ′ produced as follows was used as the negative electrode.
(Negative electrode current collector)
Foamed nickel produced by a method similar to the method for producing the positive electrode current collector a was used (nickel weight per unit area 400 g / m ² , average pore diameter 80 μm, thickness 1.2 mm, porosity 95%). This is designated as a negative electrode current collector b ′.
(Preparation of negative electrode)
21.5 parts by weight of silicon powder (average particle size of about 10 μm), 0.7 part by weight of ketjen black (KB) as a conductive additive, 2.5 parts by weight of polyvinylidene fluoride powder as a binder, and N-methylpyrrolidone as a solvent A silicon negative electrode paste was prepared by adding 75.3 parts by weight of (NMP) and stirring with a mixer.
This silicon paste was filled in a negative electrode current collector b ′ whose thickness was adjusted in advance by a roller press with a gap of 550 μm so that the silicon content was 13 mg / cm ² . The actual filling amount was 12.2 mg / cm 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 (gap: 150 μm) to obtain negative electrode B ′ of Example 6. The thickness after pressing was 185 μm.

[Example 7]
A coin-type capacitor in the same manner as in Example 1 except that the positive electrode B produced in the same manner as the positive electrode produced in Example 2 and the negative electrode B ′ produced in the same manner as the negative electrode produced in Example 6 were used. G was produced.

[Example 8]
A coin-type capacitor in the same manner as in Example 1 except that the positive electrode C produced in the same manner as the positive electrode produced in Example 3 and the negative electrode B ′ produced in the same manner as the negative electrode produced in Example 6 were used. H was produced.

[Example 9]
A coin-type capacitor in the same manner as in Example 1 except that the positive electrode D produced in the same manner as the positive electrode produced in Example 4 and the negative electrode B ′ produced in the same manner as the negative electrode produced in Example 6 were used. I was produced.

[Example 10]
A coin-type capacitor in the same manner as in Example 1 except that the positive electrode E produced in the same manner as the positive electrode produced in Example 5 and the negative electrode B ′ produced in the same manner as the negative electrode produced in Example 6 were used. J was produced.

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

[Comparative Example 2]
A capacitor L was manufactured using the same negative electrode as that used in Example 1 as the negative electrode. As the electrolytic solution, a propylene carbonate solution in which tetraethylammonium tetrafluoroborate was dissolved to 1 mol / L was used, and a separator made of cellulose fiber (thickness 60 μm, density 450 mg / cm ³ , porosity 70%) was used.

[Comparative Example 3]
A positive electrode G was produced in the same manner as in Example 1, except that the foamed nickel used in Example 1 (before tin plating) was used as the positive electrode current collector c.
Subsequent operations were exactly the same as in Example 1, and a coin-type capacitor M was produced.

[Comparative Example 4]
Unlike Example 1, the positive electrode current collector d was prepared in the same manner as in Example 1, except that the positive electrode current collector d produced without performing the heat treatment step after tin plating was used. did.
Subsequent operations were the same as those in Example 1, and a coin-type capacitor N was produced.

<Evaluation of capacitance>
Ten capacitors similar to those of Examples 1 to 10 and Comparative Examples 1 to 4 were respectively produced, charged at 2 mA / cm ² for 2 hours, and discharged at 1 mA / cm ² , and the initial capacitance and charging voltage were examined. It was. Their average values are shown in Table 1.

  As is apparent from Table 1, the capacitor of the present invention has a larger capacitance and a larger operating voltage range than the capacitor using the Al foil of Comparative Example 1 (Comparative Example 2). Therefore, the energy density can be improved. Further, in Comparative Examples 3 and 4, nickel is exposed because Sn is not included or diffusion is insufficient, and when elution is performed at 4.2 V, nickel is eluted and oxidized to charge. The voltage did not increase and could not be charged.

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

  As is clear from Table 2, the changes in capacitance and internal resistance were small after 2000 hours in the example, as in the comparative example having the conventional configuration. Therefore, it was found that the 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 / discharge cycles with a constant current of 1 mA between 2.5 and 4.2 V at an atmospheric temperature of 45 ° C. were repeated 10,000 times, and the discharge capacity after 10,000 cycles was measured and evaluated in comparison with the initial capacity. (Because Comparative Example 2 is an electric double layer capacitor, the voltage range was 0.5 to 2.5 V). The results are shown in Table 3.

As is apparent from Table 3, the change in capacitance was small even after 10,000 cycles had passed in the example as in the comparative example having the conventional configuration. Therefore, it was found that the capacitor of the present invention has a high capacitance and an excellent lifetime.
From the above, it has been found that when the current collector of the present invention is used as an electrode for a capacitor, a capacitor superior in capacity and durability compared to a conventional capacitor can be provided.
Although 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.

  Since the capacitor of the present invention has a large capacitance and excellent durability, it can be suitably used as a capacitor for automobiles such as hybrid vehicles and fuel vehicles.

Claims (13)

at least,
A positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body for a positive electrode;
A negative electrode obtained by holding a negative electrode active material capable of absorbing and desorbing lithium ions in a negative electrode current collector;
A non-aqueous electrolyte containing a lithium salt,
A capacitor characterized in that the positive electrode metal porous body is made of an alloy containing at least nickel and tin, and lithium ions are occluded in the negative electrode by a chemical or electrochemical method.   2. The capacitor according to claim 1, wherein the positive electrode metal porous body has a tin content of 1% by mass or more and 40% by mass or less.   The capacitor according to claim 1 or 2, wherein the metal porous body for a positive electrode further contains 10 mass% or less of phosphorus as a component.   4. The capacitor according to claim 1, wherein the metal porous body for positive electrode is subjected to electrolytic oxidation treatment in a liquid to improve corrosion resistance. The metal porous body for positive electrode,
A foam-like nickel with a nickel basis weight of 200 g / m ² or more and 1000 g / m ² or less obtained by coating the foamed urethane with nickel and then burning off the urethane is coated with a metal containing at least tin, and then heat-treated. 5. The capacitor according to claim 1, wherein the capacitor is a foamed nickel-tin alloy having a porosity of 80% or more and 97% or less, which is produced by diffusing tin into foamed nickel. . The metal porous body for positive electrode,
A non-woven fabric nickel having a nickel basis weight of 200 g / m ² or more and 1000 g / m ² or less obtained by coating a non-woven fabric made of polyolefin fiber with nickel is coated with a metal containing at least tin, and then heat-treated to form tin. The capacitor according to any one of claims 1 to 4, which is a non-woven nickel-tin alloy having a porosity of 80% or more and 97% or less, which is produced by diffusing into foamed nickel.   The negative electrode active material capable of occluding and desorbing lithium ions is mainly composed of a carbon material, and the carbon material includes a graphite-based material or a graphitizable carbon material. The capacitor described.   The negative electrode active material capable of occluding and desorbing lithium ions is mainly composed of a metal, and the metal is an alloy or composite containing at least 20% by mass of one or more metals selected from the group consisting of aluminum, tin, and silicon The capacitor according to claim 1, wherein the capacitor is a body.   The capacitor according to claim 1, wherein the negative electrode current collector is a metal foil, and the metal foil is one of aluminum, copper, nickel, or stainless steel. The negative electrode current collector is a metal porous body. The metal porous body has a porosity of 80% or more and 97% or less, and a nickel basis weight of 200 g, obtained by coating urethane on nickel on foamed urethane. The capacitor according to claim 1, wherein the capacitor is foamed nickel of not less than / m ^{2 and not} more than 1000 g / m ² . The negative electrode current collector is a metal porous body. The metal porous body has a porosity of 80% or more and 97% or less, and a nickel basis weight of 200 g / m obtained by coating a nonwoven fabric made of polyolefin fibers with nickel. The capacitor according to any one of claims 1 to 8, wherein the capacitor is non-woven nickel of ² or more and 1000 g / m ² or less. The lithium salt is at least one selected from the group consisting of LiClO ₄ , LiBF ₄ , and LiPF ₆ ;
The solvent of the non-aqueous electrolyte is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. The capacitor according to any one of the above.   The negative electrode capacity is larger than the positive electrode capacity, and the occlusion amount of lithium ions in the negative electrode is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity.