JP2011009609A - Nickel aluminum porous collector and electrode using the same, and capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor having high capacity and improved durability.SOLUTION: The capacitor includes a positive electrode where a positive active substance with active carbon as a body is filled into a metal porous body, a negative electrode where a metal foil is coated with a negative electrode active substance with a carbon material capable of occluding and detaching lithium ions as a body, and a nonaqueous electrolyte including a lithium salt. The metal porous body is a nickel aluminum alloy porous body manufactured by coating a porous body with nickel as a main constituent with aluminum and then performing heat treatment under an inert atmosphere or reducing atmosphere, and the lithium ions are occluded in the negative electrode by a chemical or electrochemical method.

Description

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

  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. For this reason, various types of current collectors constituting the electrodes have been proposed. For example, a metal current collector using aluminum, stainless steel or the like, a stainless steel fiber mat electrically welded to a stainless steel foil, or a porous material made of at least one metal selected from tantalum, aluminum and titanium It has been known.

  However, the conventional capacitor has a problem in that when the capacity is increased, the internal resistance increases and the capacity does not increase. In other words, when the current collector has a two-dimensional structure, if a thick electrode is produced to increase the capacity density, the distance between the current collector and the activated carbon becomes longer. Resistance increases, utilization of activated carbon decreases, and capacity density also decreases. As for internal resistance reduction, when a conductive additive is added for the purpose of improving electrical resistance, the amount of activated carbon is reduced, so that the capacity density is also reduced.

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

Further, 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. Thus, the current collector produced by plating nickel on the porous resin is inferior in corrosion resistance and cannot withstand the high charge / discharge voltage of a non-aqueous capacitor.

  Examples of the metal candidate for coating the porous resin include aluminum and stainless steel having high corrosion resistance other than nickel. However, these metals cannot form a metal coating layer on the 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

  In view of the above problems, an object of the present invention is to provide a capacitor having a high capacity and excellent durability.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors mainly have a positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body, and a carbon material that can occlude and desorb lithium ions in a metal foil. A negative electrode coated with a negative electrode active material, and a non-aqueous electrolyte containing a lithium salt. After the metal porous body is coated with aluminum on a porous body mainly composed of nickel, an inert atmosphere or reducing property It was a nickel aluminum alloy porous body produced by heat treatment in an atmosphere, and it was found that it was effective to occlude lithium ions in the negative electrode by a chemical or electrochemical technique, and the present invention was completed. That is, the capacitor according to the present invention has the following configuration.

(1) A positive electrode in which a metal porous body is filled with a positive electrode active material mainly composed of activated carbon, a negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil, and a lithium salt. A non-aqueous electrolyte, and the porous metal body is made of nickel-aluminum alloy porous material prepared by coating a porous body mainly composed of nickel with aluminum and then performing a heat treatment in an inert atmosphere or a reducing atmosphere. A capacitor in which lithium ions are occluded in the negative electrode by a chemical or electrochemical technique.
(2) The capacitor according to (1), wherein the aluminum content of the nickel aluminum alloy porous body is 5 wt% or more and less than 20 wt%.
(3) The nickel aluminum alloy porous body is a composite of at least nickel and Ni ₃ Al, and has a structure in which the periphery of nickel is covered with Ni ₃ Al. The capacitor as described in 2).
(4) The capacitor according to any one of (1) to (3) above, wherein the carbon material capable of occluding and desorbing lithium ions is a graphite-based material or a graphitizable carbon material.
(5) The capacitor according to any one of (1) to (4), wherein the metal foil is aluminum, copper, nickel, or stainless steel.
(6) The lithium salt is at least one selected from the group consisting of LiClO ₄ , LiBF ₄ , and LiPF ₆ , and the solvent of the non-aqueous electrolyte is ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, The capacitor as described in any one of (1) to (5) above, which is at least one selected from the group consisting of diethyl carbonate and ethyl methyl carbonate.
(7) The negative electrode capacity is larger than the positive electrode capacity, and the occlusion amount of lithium ions is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity. Capacitor.

Moreover, the manufacturing method of the electrical power collector which concerns on this invention, and the manufacturing method of the electrode for capacitors have the following structures.
(8) After covering a porous body mainly composed of nickel with aluminum, heat treatment is performed in an inert atmosphere or a reducing atmosphere to form a nickel-aluminum alloy porous body alloyed with aluminum into a positive electrode active mainly composed of activated carbon. A positive electrode obtained by filling a material, and a negative electrode obtained by applying a negative active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil and occluding lithium ions by a chemical or electrochemical method And a non-aqueous electrolyte containing a lithium salt to impregnate a capacitor to obtain a capacitor.

According to the present invention, a capacitor having a high capacity and excellent durability is provided.
In the capacitor according to the present invention, the capacity and voltage of the cell can be increased by using a metal porous body for the positive electrode and occluding lithium ions in the negative electrode. Further, the corrosion resistance of nickel is increased by alloying with aluminum, and nickel can be used as a current collector without being oxidized even at a voltage of a non-aqueous capacitor. Further, since nickel can have a porous structure, a porous current collector can be produced, and the capacity density increases.

The capacitor according to the present invention includes a positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body, a negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil, 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.
By using a metal porous body as a positive electrode current collector, the amount of active material that can be filled can be increased. Further, by storing lithium ions in the negative electrode, 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.

  Furthermore, the metal porous body is preferably a nickel-aluminum alloy porous body prepared by coating a porous body mainly composed of nickel with aluminum and then performing a heat treatment in an inert atmosphere or a reducing atmosphere. It is possible to increase the corrosion resistance of nickel by alloying with aluminum. Therefore, even when such a current collector is filled with an electrode material and used as a capacitor electrode, the current collector can be used satisfactorily without being oxidized in the non-aqueous electrolyte.

The capacitor according to the present invention is manufactured by making a positive electrode and a negative electrode face each other via a separator and impregnating a non-aqueous electrolyte containing a lithium salt.
Such a positive electrode is composed mainly of activated carbon in a nickel aluminum metal porous body in which nickel and aluminum are alloyed by performing heat treatment in an inert atmosphere or a reducing atmosphere after coating a porous body mainly composed of nickel with aluminum. It is obtained by filling the positive electrode active material. The negative electrode is obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil, and occluding lithium ions by a chemical or electrochemical method.

Below, each structure of the capacitor based on this invention and its manufacturing method are demonstrated in detail.
When manufacturing the capacitor according to the present invention, first, two pairs of positive and negative electrodes are made to face each other with a separator interposed therebetween. And it accommodates in a cell case using a required spacer, and impregnates electrolyte solution. Finally, the electric double layer capacitor can be manufactured by sealing the case with an insulating gasket. When a non-aqueous material is used, in order to reduce the moisture in the capacitor as much as possible, the capacitor is manufactured in an environment with little moisture, and the sealing is performed in an inert gas or a reduced pressure environment. The dew point of the capacitor production place is preferably −55 ° C. or lower.

-Separator-
A known or commercially available separator can be used. For example, an insulating film made of polyolefin, polyethylene terephthalate, polytetrafluoroethylene, polyamide, polyimide, cellulose, glass fiber or the like is preferable. The average pore diameter of the separator is usually about 0.01 μm to 5 μm, and the average thickness is usually about 10 μm to 100 μm. If the average pore diameter is too small, the ion movement path becomes long and the internal resistance becomes high, and if it is too large, the risk of short-circuiting increases. Therefore, the range of 0.05 μm to 3 μm is preferable. Moreover, since the danger of a short circuit will increase when the thickness of a separator is too small, and the movement path | route of an ion will become long and internal resistance will become high when too large, the range of 15 micrometers-70 micrometers is preferable.

-Positive electrode-
The positive electrode can be produced by filling a positive electrode current collector (metal porous body) with a positive electrode active material mainly composed of activated carbon.
[Positive electrode current collector]
The positive electrode current collector can be produced by coating aluminum with a porous body mainly composed of nickel and then heat-treating it in an inert atmosphere or a reducing atmosphere to alloy nickel and aluminum.

(Metal porous body)
As the nickel porous body, for example, a structure having continuous air holes such as foamed nickel and a nickel fiber nonwoven fabric can be preferably used. Since the active material is filled in the space of the porous body, the porosity should be high, at least 50% or more, preferably 70% or more, more preferably 90% or more.

  Foamed nickel is obtained by reducing nickel by subjecting a known urethane sheet to nickel plating, then incinerating and removing urethane, and heating in a reducing atmosphere. When nickel plating is applied to a urethane sheet, electrolytic nickel plating may be performed after the urethane sheet is subjected to conductive treatment. The conductive treatment may be performed by coating nickel by sputtering, or by electroless nickel plating or carbon coating.

  If the number of cells of the foamed nickel is too small, the pore diameter of the substrate becomes large, the active material holding performance is lowered, and the current collecting performance is also deteriorated. Therefore, 40 cells / inch or more is preferable. On the other hand, if the amount is too large, it is difficult to fill the active material or the skeleton becomes too thin and the strength of the base material is lowered. More preferably, it is 50 cells / inch or more and 80 cells / inch.

  Further, in order to obtain an electrode for a capacitor, it is necessary to adjust the thickness by a roller press. If the original thickness is thick, the current collecting property deteriorates due to the deformation by the roller press, so the thickness of the foamed nickel is 1.6 mm. The following is preferred. However, in order to sufficiently fill the active material, it is necessary to fill in a thicker state than the finished electrode, so 0.2 mm or more is preferable. More preferably, it is the range of 0.3 mm-1.4 mm.

Furthermore, the basis weight of nickel is greatly related to the electrical resistance and the strength of the substrate. If the amount is too small, both the current collecting performance and the strength of the base material are remarkably lowered and cannot be practically used. Therefore, 100 g / m ² or more is necessary. However, if the amount of nickel is excessively increased, the porosity of the base material is lowered and the capacity of the capacitor is reduced. Therefore, 500 g / m ² or less is preferable. More preferably, it is the range of 200-420 g / m < ² >.

(Alloying with aluminum)
A nickel-aluminum porous body can be obtained by coating a porous body mainly composed of nickel, such as the above-described foamed nickel, with aluminum and performing a heat treatment in an inert atmosphere or a reducing atmosphere.
The aluminum coating method is preferably sputtering, but can also be performed by vapor deposition, CVD, or calorizing treatment by powder pack.
The aluminum content needs to be less than 20 wt%. If the aluminum content is small, the corrosion resistance is inferior, so that it cannot be used as a current collector for a capacitor. For this reason, it is preferable that it exists in the range of 5 wt% or more and less than 20 wt%. More preferably, it is 7-16 wt%.

  The heat treatment may be in an inert atmosphere or a reducing atmosphere, and may be a hydrogen atmosphere or an argon atmosphere. Moreover, the heat processing temperature should just be the temperature which can be thermally diffused, without melting aluminum, and 640 degrees C or less is preferable. If the temperature is too low, thermal diffusion is slow and not industrial, so a temperature of 150 ° C. or higher is preferable. The heat treatment time may be appropriately changed depending on the heat treatment temperature.

The composition of the nickel-aluminum alloy must include at least nickel and Ni ₃ Al, and nickel should not be exposed on the surface of the substrate. If nickel is exposed, it will corrode from that part and cannot be used for capacitor electrodes. Moreover, since Ni ₃ Al is inferior in strength at normal temperature, if this ratio becomes too large, the strength of the substrate decreases. Ideally, Ni ₃ Al covers nickel without any gaps.

[Positive electrode active material]
The electrode material to be filled in the current collector is preferably mixed with a conductive additive, a binder or the like in addition to activated carbon and mixed with a solvent to form a paste. A surfactant may be added as necessary.
In order to increase the capacity of the capacitor, it is better that the amount of activated carbon as a main component is large, and it is preferable that the activated carbon is 90 wt% or more in the composition ratio after drying (after solvent removal). Moreover, although a conductive support agent and a binder are required, it is a factor of a capacity | capacitance fall, and since a binder also becomes a factor which increases internal resistance, it is better to have as few as possible. The conductive assistant is preferably 10 wt% or less, and the binder is preferably 10 wt% or less.

Activated carbon has a specific surface area of 2000 m ² / g or more because the larger the surface area, the larger the capacity of the capacitor. In addition, ketjen black, acetylene black, carbon fiber, or a composite material thereof can be used as the conductive auxiliary. As the binder, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, carboxymethylcellulose, xanthan gum and the like can be used. As the solvent, water or an organic solvent may be appropriately selected depending on the kind of the binder. In organic solvents, N-methylpyrrolidone is often used. Moreover, when using water for a solvent, you may use surfactant in order to improve a filling property.

  An activated carbon paste is obtained by mixing and stirring the electrode material mainly composed of the activated carbon. The activated carbon paste is filled in the current collector and dried, and the pressure is adjusted by a roller press or the like as necessary, whereby a capacitor electrode is obtained. In order to obtain a capacitor electrode, it is preferable that the thickness of the electrode is finally 300 to 1500 μm. For this reason, it is preferable that the thickness of the said current collector shall be 150 micrometers-700 micrometers.

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

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

[Negative electrode active material]
The negative electrode active material can be obtained by mixing a carbon material capable of occluding and desorbing lithium ions in a solvent and stirring with a mixer. If necessary, a conductive aid and a binder may be included.
(Carbon material)
The carbon material is not particularly limited as long as it can occlude and desorb lithium ions, and examples thereof include graphite materials and graphitizable carbon materials. Moreover, what has a theoretical capacity of 300 mAh / g or more is preferable.

(Conductive aid)
As the conductive auxiliary agent, a known or commercially available one can be used as in the case of the positive electrode active material. That is, for example, acetylene black, ketjen black, carbon fiber, natural graphite (scaly graphite, earthy graphite, etc.), artificial graphite, ruthenium oxide and the like can be mentioned.
(binder)
The binder is not particularly limited as in the case of the positive electrode active material, and a known or commercially available binder can be used. Examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl pyrrolidone, polyvinyl chloride, polyolefin, styrene butadiene rubber, polyvinyl alcohol, carboxymethyl cellulose and the like.

-Non-aqueous electrolyte-
Since the capacitor according to the present invention uses lithium, it is necessary to use a non-aqueous electrolyte as the electrolyte. As such a non-aqueous electrolyte, 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)
Examples of the solvent that dissolves the lithium salt include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. These may be used alone or in combination of any one or more.

  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.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these.
[Examples 1 and 2]
(Preparation of positive electrode current collector)
The foamed nickel was coated with aluminum by sputtering and then heat-treated to produce a current collector using a foamed nickel aluminum alloy substrate.
For foamed nickel, a urethane sheet (commercially available, 55 cells / inch, thickness 1.4 mm, porosity 96%) is subjected to conductive treatment, followed by a predetermined amount of nickel plating, and the urethane is incinerated at 800 ° C. in the atmosphere. After removal, it was heated to 1000 ° C. in a reducing atmosphere (hydrogen) to reduce nickel. For the conductive treatment, nickel of 10 g / m ² was coated by sputtering. The total amount of nickel plating was 400 g / m ² for the conductive treatment. The produced foamed nickel had a cell number of 55 cells / inch, a thickness of 1.4 mm, and a porosity of 95%.

  Foamed nickel was coated with aluminum by sputtering. Thereafter, heat treatment was performed at 550 ° C. for 3 hours in a furnace in a nitrogen atmosphere. The aluminum content was adjusted by the sputtering time, and nickel aluminum alloy base materials having aluminum contents of 5 wt% and 15 wt%, respectively, were prepared and used as positive electrode current collectors a and b, respectively. The thickness of the produced positive electrode current collector was 1.4 mm.

(Preparation of positive electrode)
The slit of the roller press was adjusted to 700 μm, and the positive electrode current collector obtained above was passed through to obtain a positive electrode current collector having a thickness of 0.72 mm.
To 21 wt% of activated carbon powder (specific surface area 2500 m ² / g, average particle size of about 5 μm), 1 wt% of ketjen black as a conductive additive, 2 wt% of polyvinylidene fluoride powder as a binder, and 75 wt% of N-methylpyrrolidone as a solvent are added. The activated carbon paste was prepared by stirring with a mixer. The composition ratio after drying and removing NMP was 92 wt% activated carbon powder, 3 wt% ketjen black, and 5 wt% polyvinylidene fluoride powder.
The activated carbon paste was filled in the positive electrode current collectors a and b so that the activated carbon content was 30 mg / cm ² . Actual filling amount was respectively ^{31mg / cm 2, 30mg / cm} 2. Next, after drying with a dryer at 200 ° C. for 1 hour to remove the solvent, the positive electrode A of Example 1 and the positive electrode B of Example 2 were pressed with a roller press having a diameter of 500 mm (slit: 300 μm). Got. The thickness after pressing was 470 μm and 473 μm, respectively.

(Preparation of negative electrode current collector)
A copper foil having a thickness of 20 μm was used.
(Preparation of negative electrode)
100 parts by weight of natural graphite powder capable of occluding and releasing lithium, 2 parts by weight of ketjen black (KB) as a conductive additive, 4 parts by weight of polyvinylidene fluoride powder as a binder, and 15 parts by weight of N-methylpyrrolidone (NMP) as a solvent Was added and stirred with a mixer to prepare a graphite-based negative electrode paste.
This graphite-based negative electrode paste was applied onto the copper foil (negative electrode current collector) 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 electrodes A ′ of Examples 1 and 2. The thickness after pressing was 220 μm.

(Manufacture of cells)
The positive electrode A and the negative electrode A ′ were transferred into a dry room (dew point −65 ° C.), and further dried at 180 ° C. for 12 hours in a reduced pressure environment. The obtained positive electrode A and negative electrode A ′ were punched out to a diameter of 14 mm, and then a lithium metal foil having a thickness of 15 μm was pressure bonded to the negative electrode A ′.
A single cell element is formed by sandwiching a polypropylene separator between the positive and negative lithium-bonded surfaces, and stored in an R2032-sized coin cell case using a stainless steel spacer, and 1 mol / L of LiPF ₆ is contained. A melted electrolytic solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 1 was injected to impregnate the electrode and the separator.
Further, the case lid was tightened and sealed through an insulating gasket made of propylene to produce a coin-shaped test capacitor 1. 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.
The same operation was performed for the positive electrode B and the negative electrode A ′ to produce the capacitor 2 of Example 2.

[Comparative Example 1]
Except that the sputtering time was adjusted so that the aluminum content was 20 wt%, the positive electrode C was manufactured in exactly the same manner as in Example 1, and an attempt was made to obtain the capacitor C. However, the current collector became very brittle. Thus, the current collector was cracked at the stage of thickness adjustment by the roller press, and the positive electrode could not be obtained and the capacitor 3 could not be produced.

[Comparative Example 2]
An aluminum foil (commercial product, thickness 20 μm) was used as the positive electrode current collector. The positive electrode active material paste prepared in Example 1 was applied by the doctor blade method so that the total on both sides was 8 mg / cm ² , but the adhesive strength was insufficient, so the positive electrode active material was sufficiently bonded to the aluminum foil. could not.
Therefore, a positive electrode active material paste similar to that prepared in Example 1 was prepared except that polyvinylidene fluoride was adjusted to 20 wt% after drying. The paste was applied to both surfaces of an aluminum foil by a doctor blade method, dried and pressed to produce a positive electrode D. The amount of activated carbon applied was 8 mg / cm ² , and the electrode thickness was 171 μm. The same operation as in the example was performed using the positive electrode D and the negative electrode A ′, and the capacitor 4 of Comparative Example 2 was produced.

[Comparative Example 3]
As the positive electrode current collector, foamed nickel (commercially available product, nickel basis weight 400 g / m ² , porosity 96 vol%, number of cells 55 cells / inch, thickness 720 μm) was used. This was filled with the positive electrode active material produced in Example 1 in the same manner as in Example 1, and then further pressurized and dried to produce positive electrode E. The filling amount of activated carbon was 31 mg / cm ² , and the thickness after pressing was 468 μm. The same operation as in the example was performed using the positive electrode E and the negative electrode A ′, and the capacitor 5 of Comparative Example 3 was produced.

[Comparative Example 4]
Using the same negative electrode as the positive electrode A used in Example 1 as the negative electrode, the same operation as in the example was performed to produce the capacitor 6 of Comparative Example 4. However, the electrolyte used was a propylene carbonate solution in which tetraethylammonium tetrafluoroborate was dissolved to 1 mol / L, and the separator used was a cellulose fiber separator (thickness 60 μm, density 450 mg / cm ³ , porosity 70%). It was.

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

  About the comparative example 1, since the electrode C was not able to be produced, it cannot measure. It has been found that the electrode becomes brittle when the aluminum content is too high. Further, in Comparative Example 3, the voltage could not be increased from the middle of the first charge, and charging could not be performed. It is thought that nickel cannot withstand the potential of the positive electrode and melts, and current is used for side reactions.

As can be seen from Table 1, the capacitor of the present invention has a larger capacity than the capacitor using the Al foil for the positive electrode current collector of Comparative Example 2, and the operating voltage range is an electric double layer capacitor having a normal configuration ( Greater than Comparative Example 4). The energy can be calculated by 1 / 2C (Emax ² -Emin ² ), where C (F) is the capacitance, Emax is the full charge voltage, and Emin is the voltage during discharge. Since it is proportional to the square, the energy density can be improved.

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

  As is clear from Table 2, the changes in 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, a charge / discharge cycle with a constant current of 1 mA was performed at an atmospheric temperature of 45 ° C. in Examples 1 and 2 and Comparative Example 2 between 2.5 and 4.2 V, and Comparative Example 4 between 0 and 2.5 V. Repeated 10,000 times, the discharge capacity after 10,000 cycles was measured and evaluated in comparison with the initial capacity. The results are shown in Table 3.

  As is clear from Table 3, the change in capacitance was as small as less than 5% even after 10,000 cycles, 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 electric double layer capacitor can be provided.

Claims (8)

A positive electrode filled with a positive electrode active material mainly composed of activated carbon in a metal porous body;
A negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil;
A non-aqueous electrolyte containing a lithium salt;
With
The metal porous body is a nickel aluminum alloy porous body prepared by coating aluminum with a porous body mainly composed of nickel and then performing a heat treatment in an inert atmosphere or a reducing atmosphere.
A capacitor in which lithium ions are occluded in the negative electrode by a chemical or electrochemical method.   The capacitor according to claim 1, wherein the aluminum content of the nickel aluminum alloy porous body is 5 wt% or more and less than 20 wt%. _3. The capacitor according to claim 1, wherein the nickel aluminum alloy porous body is a composite of at least nickel and Ni ₃ Al, and the nickel is covered with Ni ₃ Al. 4. .   The capacitor according to any one of claims 1 to 3, wherein the carbon material capable of inserting and extracting lithium ions is a graphite-based material or a graphitizable carbon material. The capacitor according to any one of claims 1 to 4, wherein the metal foil is aluminum, copper, nickel, or stainless steel. 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 capacitor according to claim 1, wherein the negative electrode capacity is larger than the positive electrode capacity, and the occlusion amount of lithium ions is 90% or less of the difference between the positive electrode capacity and the negative electrode capacity. After coating aluminum with a nickel-based porous body, heat treatment is performed in an inert atmosphere or a reducing atmosphere, and a nickel-aluminum porous body alloyed with aluminum is filled with a cathode active material mainly composed of activated carbon. A positive electrode obtained by
A negative electrode obtained by applying a negative electrode active material mainly composed of a carbon material capable of occluding and desorbing lithium ions to a metal foil, and occluding lithium ions by a chemical or electrochemical method,
A method for producing a current collector for a capacitor, wherein the capacitor is obtained by facing through a separator and impregnating a non-aqueous electrolyte containing a lithium salt.