JP2013214679A - Electric double-layer capacitor, porous electrode, and electric double-layer capacitor manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel and improved electric double-layer capacitor which retains advantages of an electric double-layer capacitor and can increase capacitance per unit volume, i.e., energy density, over the prior art.SOLUTION: According to an aspect of the present invention, an electric double-layer capacitor comprises: a plurality of porous electrodes which include a porous metal with mesopores formed and an inorganic compound layer covering surfaces of the mesopores; and an electrolyte disposed between the plurality of porous electrodes.

Description

  The present invention relates to an electric double layer capacitor, a porous electrode, and a method for manufacturing an electric double layer capacitor.

  As a technique for storing electric energy, an electric double layer capacitor and a secondary battery described in Patent Document 1 are known. The electric double layer capacitor has much longer life, safety, and output density than the secondary battery. However, the electric double layer capacitor has a problem that its energy density is lower than that of the secondary battery. By the way, the energy density of an electric double layer capacitor is shown by the following formula | equation (1).

ここで、Ｃは静電容量であり、Ｖは電気二重層キャパシタの印加電圧である。

Here, C is a capacitance, and V is an applied voltage of the electric double layer capacitor.

  Therefore, in order to improve the energy density of the electric double layer capacitor, a technique for improving the capacitance and applied voltage of the electric double layer capacitor has been proposed.

As a technique for improving the capacitance of the electric double layer capacitor, a technique for increasing the specific surface area of activated carbon constituting an electrode of the electric double layer capacitor is known. The activated carbon currently known has a specific surface area of 1000 to 2000 m ² / g.

  On the other hand, as a technique for improving the applied voltage of the electric double layer capacitor, a lithium ion capacitor using the principle of the electric double layer capacitor is known. The lithium ion capacitor is also referred to as a hybrid capacitor. In the lithium ion capacitor, one of the electrodes constituting the electric double layer capacitor is made of graphite which is a negative electrode material of a lithium ion battery, and lithium ions are inserted into the graphite. The applied voltage of the lithium ion capacitor is larger than that of a general electric double layer capacitor, that is, both electrodes are made of activated carbon.

JP 2011-046584 A JP 2009-158532 A JP 2004-221523 A JP-A-9-55342 JP 2011-9609 A JP 2010-170901 A

  However, the technology for improving the specific surface area of activated carbon has a problem that the bulk density of activated carbon decreases as the specific surface area of activated carbon increases. Since the specific gravity of the activated carbon was as small as about 2, the bulk density was significantly reduced. For this reason, this technique has a problem that even if the specific surface area of the activated carbon is increased, the surface area per unit volume, that is, the capacitance per unit volume does not become a satisfactory value. On the other hand, the lithium ion capacitor has a problem that the energy density is not yet satisfactory and the life and output density, which are the advantages of the electric double layer capacitor, are sacrificed.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to maintain the advantages of an electric double layer capacitor and to provide a capacitance per unit volume, that is, an energy density. It is an object of the present invention to provide a new and improved electric double layer capacitor or the like that can improve the conventional capacitor.

  In order to solve the above problems, according to one aspect of the present invention, a plurality of porous electrodes including a porous metal in which mesopores are formed, and an inorganic compound layer covering the surface of the mesopores, And an electrolyte disposed between the plurality of porous electrodes. An electric double layer capacitor is provided.

  Since the electric double layer capacitor includes a porous metal having a specific gravity larger than that of activated carbon, the capacitance per unit volume can be increased as compared with the conventional case. Therefore, the electric double layer capacitor can improve the capacitance per unit volume, that is, the energy density, as compared with the conventional one while maintaining the advantages of the electric double layer capacitor.

  Furthermore, the porous electrode includes an inorganic compound layer covering the surface of the mesopores. This inorganic compound layer can suppress the direct contact between the porous metal and the electrolyte, and the oxidation of the porous metal in the atmosphere. Therefore, the electric double layer capacitor can also improve cycle stability and thermal stability.

  Here, the anion constituting the inorganic compound layer is at least one kind of anion selected from the group consisting of oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, sulfur ions, and carbon ions. Also good.

  According to this viewpoint, the inorganic compound layer can more reliably prevent contact between the porous metal and the electrolyte.

Moreover, the specific surface area per mesopore unit volume of the porous electrode may be 450 m ² / cm ³ or more.

  According to this viewpoint, the energy density per unit volume becomes larger than that of the conventional one.

  The mesopore diameter may be 2 nm or more and 30 nm or less.

  According to this viewpoint, the energy density per unit volume becomes larger than that of the conventional one.

  Moreover, the diameter of the electrolyte ions contained in the electrolyte may be 2 nm or less.

  According to this viewpoint, the electrolyte ions can easily enter and exit the mesopores. Therefore, the energy density per unit volume becomes larger than before.

  The porous metal may be composed of at least one metal selected from the group consisting of nickel, copper, iron and cobalt.

  According to this viewpoint, the porous metal can react well with the anion to form an inorganic compound layer.

  According to another aspect of the present invention, there is provided an electrical double layer capacitor comprising: a porous metal having mesopores formed therein; and an inorganic compound layer covering the surface of the mesopores. A porous electrode is provided.

  Since the porous electrode which concerns on this viewpoint contains the porous metal whose specific gravity is larger than activated carbon, the electrostatic capacitance per unit volume of an electric double layer capacitor can be enlarged conventionally. Therefore, the porous electrode can improve the electrostatic capacity per unit volume of the electric double layer capacitor, that is, the energy density, while maintaining the advantages of the electric double layer capacitor.

  Furthermore, the porous electrode includes an inorganic compound layer covering the surface of the mesopores. This inorganic compound layer can suppress the direct contact between the porous metal and the electrolyte, and the oxidation of the porous metal in the atmosphere. Therefore, the porous electrode can also improve the cycle stability and thermal stability of the electric double layer capacitor.

  According to another aspect of the present invention, a step of manufacturing a plurality of porous electrodes including a porous metal having mesopores formed thereon and an inorganic compound layer covering the surface of the mesopores, Disposing an electrolyte between porous electrodes, and providing a method for manufacturing an electric double layer capacitor.

  According to this aspect, since the electric double layer capacitor is manufactured using a porous metal having a specific gravity greater than that of the activated carbon, the capacitance per unit volume of the electric double layer capacitor can be increased as compared with the conventional case.

  Furthermore, according to this aspect, since the inorganic compound layer covering the surface of the mesopores is formed, an electric double layer capacitor having improved cycle stability and thermal stability can be manufactured.

  Here, you may manufacture a porous electrode by exposing the porous metal in which the mesopore was formed in the reaction gas which can react with a porous metal.

  According to this viewpoint, the inorganic compound layer can be more reliably formed.

  The reactive gas may contain at least one gas selected from the group consisting of air, oxygen gas, halogen gas, nitrogen gas, water vapor, carbon dioxide gas, and hydrogen sulfide gas.

  According to this viewpoint, an inorganic compound layer that can more reliably suppress contact between the porous metal and the electrolyte can be formed.

  Alternatively, a porous electrode may be produced by impregnating a porous metal having mesopores in a solution containing an anion capable of reacting with the porous metal, followed by heat treatment.

  According to this viewpoint, the inorganic compound layer can be more reliably formed.

Moreover, the specific surface area per mesopore unit volume of the porous electrode may be 450 m ² / cm ³ or more.

  According to this aspect, an electric double layer capacitor having an energy density per unit volume larger than that of the conventional one can be manufactured.

  The mesopore diameter may be 2 nm or more and 30 nm or less.

  According to this aspect, an electric double layer capacitor having an energy density per unit volume larger than that of the conventional one can be manufactured.

  Moreover, the diameter of the electrolyte ions contained in the electrolyte may be 2 nm or less.

  According to this viewpoint, the electrolyte ions can easily enter and exit the mesopores. Therefore, the method for producing an electric double layer capacitor according to this aspect can produce an electric double layer capacitor having an energy density per unit volume larger than that of the conventional one.

  The porous metal may be composed of at least one metal selected from the group consisting of nickel, copper, iron and cobalt.

  According to this viewpoint, the inorganic compound layer can be more reliably formed.

  As described above, since the electric double layer capacitor according to the present invention includes a porous metal having a specific gravity higher than that of activated carbon, the capacitance per unit volume of the electric double layer capacitor can be increased as compared with the conventional case. Therefore, the porous electrode can improve the electrostatic capacity per unit volume of the electric double layer capacitor, that is, the energy density, while maintaining the advantages of the electric double layer capacitor.

It is a side view which shows the electric double layer capacitor which concerns on embodiment of this invention. It is sectional drawing which shows the structure of a porous metal. It is a graph which shows an example of the pore size distribution of porous copper. It is a graph which shows an example of the pore size distribution of activated carbon. It is a graph which shows the correspondence of the specific surface area per unit volume of mesopores, and the electrostatic capacitance per unit volume of a porous electrode for every diameter of electrolyte ion. It is the schematic diagram which modeled and showed the mesopore in a porous electrode with a cylinder. It is sectional drawing which expands and shows a part (area | region A in FIG. 2) of a porous metal.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[Problems of conventional electric double layer capacitors]
As described above, in the technology for improving the specific surface area of activated carbon, the capacitance per unit volume of the electric double layer capacitor (hereinafter, also simply referred to as “the capacitance of the electric double layer capacitor” or “capacitance”). There was a problem that satisfactory values could not be obtained. The present inventor completed the present invention by examining this problem. Therefore, this problem will be described in detail.

  As described above, the bulk density of activated carbon decreases as the specific surface area increases. On the other hand, when the specific surface area of the activated carbon exceeds a certain size, the capacitance reaches its peak. For these reasons, in the technique for improving the specific surface area of activated carbon, even if the specific surface area is increased, the capacitance does not reach a satisfactory value.

  The following can be considered as the reason why the capacitance reaches its peak. That is, the formation of pores in the activated carbon is performed by an alkali activation treatment, but this treatment can only be controlled macroscopically by controlling the specific surface area, and the pore size can be controlled. There wasn't. In particular, the increase of the specific surface area by the alkali activation treatment is achieved by increasing the micropores.

  More specifically, the activated carbon contains micropores having a diameter of less than 2 nm, mesopores having a diameter of 2 nm to less than 50 nm, and macropores having a diameter of 50 nm or more. Among these pores, the micropores have a small diameter, so that some electrolyte ions may not enter the inside of the micropores. Further, the number of electrolyte ions that can be adsorbed to the macropores is smaller than the volume of the macropores. This is because, among the pores, the portion where the electrolyte ions can be adsorbed is only the surface thereof, and the electrolyte ions are not adsorbed in the hollow portion. Therefore, it is considered that the reason why the electrostatic capacity reaches its peak is that the micropores and the macropores do not function effectively for the expression of the electrostatic capacity. In addition, the size (diameter) of the solvated electrolyte ions is 1 to 2 nm, which is almost equal to or smaller than that of the micropores. Therefore, it is expected that the electrolyte ions cannot be efficiently adsorbed to the micropores. Is done. Therefore, according to the above consideration, mesopores seem to be most preferable as pores for adsorbing electrolyte ions.

  In this regard, Patent Documents 2 and 3 refer to mesopores. However, the energy density per unit volume of the electric double layer capacitor (hereinafter, also simply referred to as “energy density of the electric double layer capacitor” or “energy density”) is not obtained by the technique disclosed in any of the documents. . On the other hand, Patent Documents 4, 5, and 6 refer to porous metals. However, Patent Documents 4 and 5 use a porous metal as a current collector. In Patent Document 6, the pores of the porous metal are much larger than mesopores. Therefore, the techniques disclosed in these documents do not contribute to the solution of the above problems.

  Moreover, in the technique which improves the specific surface area of activated carbon, it was necessary to remove an alkali component from activated carbon after alkali activation treatment. However, since this process is complicated and expensive, activated carbon by alkali activation treatment is an industrially difficult material to use. From such problems, conventionally, pores have been formed in activated carbon by a steam activation treatment. This method is less expensive than the alkali activation treatment, but the activated carbon produced by this method has a problem that its electrostatic capacity is lower than that of the activated carbon obtained by the alkali activation treatment.

  On the other hand, the electric double layer capacitor according to the present embodiment can improve the energy density as compared with the conventional one while maintaining the advantages of the electric double layer capacitor. In addition, the electric double layer capacitor according to the present embodiment is manufactured by a simpler process than before. Furthermore, the electric double layer capacitor according to the present embodiment can also improve cycle stability and thermal stability. That is, since the porous metal has a characteristic that the surface of the pore is easily oxidized in the atmosphere, the cycle stability may not be sufficient when the porous metal is used as an electrode of the electric double layer capacitor as it is. . Therefore, the electric double layer capacitor according to the present embodiment aims to improve cycle stability by protecting the surface of the mesopores.

[Configuration of Electric Double Layer Capacitor According to this Embodiment]
Next, the configuration of the electric double layer capacitor 10 according to the present embodiment will be described with reference to FIG. As shown in FIG. 1, the electric double layer capacitor 10 according to the present embodiment includes a cathode electrode 11 composed of a porous electrode 20, an anode electrode 12 composed of the porous electrode 20, and these porous electrodes. And an electrolyte 13 disposed between the electrodes.

  As shown in FIGS. 2 and 7, the porous electrode 20 includes a porous metal 20 a in which a large number of pores including mesopores 22 are formed, and an inorganic compound layer 23 that covers at least the surface of the mesopores 22. Is provided. As described above, the diameter of the mesopores 22 is 2 nm or more and less than 50 nm, but preferably 2 nm or more and 30 nm or less. In the present embodiment, the diameter of the particle or pore is, for example, the diameter when the particle is regarded as a sphere, and is measured by a known method, for example, a gas adsorption method.

  As described above, the electrolyte ions are often adsorbed and desorbed on the porous electrode 20 in a solvated state. And the diameter of the solvated electrolyte ion is estimated to be 1-2 nm. Therefore, since the diameter of the mesopores 22 is equal to or larger than the diameter of the electrolyte ions, the electrolyte ions can be easily adsorbed and desorbed from the porous electrode 20.

  The diameter of the solvated electrolyte ion is calculated by, for example, computational chemistry, that is, simulation. The diameter of the electrolyte ions is calculated as follows, for example. First, the molecular structure of the solvated electrolyte ion is calculated by molecular dynamics simulation using software called “Car-Parrinello Molecular Dynamics (CPMD)” (ver. 3.13.2). Next, the solvated electrolyte ion is regarded as a sphere, and its diameter is calculated based on the calculated molecular structure.

  Even if the diameter of the mesopores 22 is larger than 30 nm, the electrolyte ions can be easily adsorbed / desorbed to / from the porous electrode 20, so that the effect of this embodiment can be obtained. However, the larger the diameter of the mesopores 22 is, the larger the hollow portion of the mesopores 22, that is, the portion where the electrolyte ions are not adsorbed. Therefore, the diameter of the mesopores 22 is preferably 30 nm or less. In FIG. 3, the pore size distribution in the porous copper manufactured by the manufacturing method mentioned later is shown. The abscissa represents the pore diameter (pore diameter), and the ordinate represents the pore volume per unit mass of the porous copper as the frequency of the pore diameter. The porous copper in FIG. 3 was washed with water after removing aluminum from the Cu—Al alloy by adding a Cu—Al alloy (molar ratio 50:50) having an average diameter of 10 μm to the 1N aqueous potassium hydroxide solution. Obtained by vacuum drying.

  According to this example, the diameter of the mesopores is distributed within a range of 3 to 20 nm. That is, the pore size distribution of the mesopores is 3 to 20 nm. The peak value of the pores (the diameter of the most widely distributed pores) is 8 nm. On the other hand, FIG. 4 shows the pore size distribution of a certain activated carbon. In this example, the diameter of the pores is 2.5 nm or less, that is, most of the pores are micropores. Therefore, it is not easy to adsorb and desorb electrolyte ions on this activated carbon.

  In addition, the distribution range of the diameter of the mesopores 22 is preferably as narrow as possible (sharp). When the distribution range of the mesopores 22 is narrow, a large number of mesopores 22 have the same diameter, and therefore, the same number of electrolyte ions are adsorbed by many mesopores 22. Therefore, by designing the diameter of the electrolyte ions so that the number of electrolyte ions adsorbed on a certain mesopore 22 increases, the number of electrolyte ions adsorbed on other mesopores 22 inevitably increases. Therefore, the number of electrolyte ions adsorbed on the porous electrode 20 can be increased by narrowing the distribution range of the mesopores 22. On the other hand, if the distribution range of the mesopores 22 is wide, the diameter of the mesopores 22 varies, and therefore the number of electrolyte ions adsorbed on the mesopores 22 varies for each mesopore 22. Therefore, even if the diameter of the electrolyte ions is designed so that the number of electrolyte ions adsorbed on a certain mesopore 22 increases, the number of electrolyte ions adsorbed on other mesopores 22 also varies. As a result, it is difficult to increase the number of electrolyte ions adsorbed on the porous electrode 20. From this viewpoint, the distribution range of the diameter of the mesopores 22 is preferably 2 to 30 nm, more preferably 5 to 20 nm, and more preferably 5 to 10 nm.

  Furthermore, the total volume of the mesopores 22 relative to the total volume of all the pores, that is, the abundance ratio of the mesopores 22 is 70% or more. The total volume of the mesopores 22 and the total volume of all the pores are measured by, for example, a specific surface area measuring device ASAP2020 manufactured by Shimadzu Corporation.

  That is, as a result of intensive studies on the mesopores 22, the present inventor has found that the abundance ratio of the mesopores 22 affects the capacitance of the electric double layer capacitor 10. The present inventor shows that when the abundance ratio of the mesopores 22 is 70% or more, the electrostatic capacity per unit volume of the electric double layer capacitor 10, that is, the energy density per unit volume is remarkably improved. I found. The reason for this is that, for example, in micropores of 2 nm or less, the amount of adsorption of electrolyte ions decreases as described above, but the material of the present invention has a large number of mesopores larger than the electrolyte ion diameter of 70% or more. It is thought that the capacitance could be increased. In the activated carbon of the prior art, it is conceivable that the capacitance is low because the mesopores are as small as 30% or less. That is, the adsorption of the electrolyte ions that are the source of the expression of capacitance suggests that mesopores larger than the electrolyte ion diameter are important for increasing the capacitance.

  Further, since the mesopores 22 are pores that contribute to adsorption / desorption with electrolyte ions, the capacitance per unit volume of the electric double layer capacitor 10 is improved as the abundance ratio thereof increases. Therefore, the larger the abundance ratio of the mesopores 22 is, the better. Specifically, the abundance ratio of the mesopores 22 is more preferably 85% or more. The reason may be that mesopores capable of adsorbing electrolyte ions more efficiently are important, and it is better to have as many mesopores as possible to improve the capacitance. More preferably, the abundance ratio of the mesopores 22 is as close to 100% as possible. In the techniques disclosed in Patent Documents 2 and 3 described above, the abundance ratio of mesopores is less than 70%. For this reason, it is assumed that a satisfactory energy density cannot be obtained with these techniques.

The specific surface area per unit volume of mesopores of the porous electrode 20 is preferably 450 m ² / cm ³ or more, and more preferably 600 m ² / cm ³ or more. Here, the specific surface area per unit volume of the mesopores of the porous electrode 20 is obtained by the following formula (2).

In the formula (2), S is a specific surface area (m ² / cm ³ ) per mesopore unit volume of the porous electrode 20, and a is a specific surface area (m ² / g) of the porous electrode 20. b is the pore volume per unit mass of the porous electrode (cm ³ / g), and is calculated by dividing the total volume of all the pores by the mass of the porous electrode 20. c is the abundance ratio of the mesopores 22.

  That is, in the present embodiment, the porous electrode 20 is designed based on the specific surface area per unit volume of the mesopores rather than a simple specific surface area. The reason is as follows. In order to improve the capacitance per unit volume of the electric double layer capacitor, it is required that the site where electrolyte ions can be adsorbed and desorbed is wide. In the field of electric double layer capacitors, the specific surface area of a porous electrode has been used as an index indicating the size of such a site. However, the present inventor has found that the specific surface area of the porous electrode and the capacitance do not have a linear relationship.

For example, the present inventor manufactured an electric double layer capacitor using porous copper having a specific surface area of 21 m ² / g as a porous electrode, and measured its capacitance, obtaining a value of 21 F / g. It was. On the other hand, when this inventor manufactured the electric double layer capacitor using the activated carbon with a specific surface area of 1500-2400 m < ² > / g as a porous electrode, and measured the electrostatic capacitance, it was a value of 65-140 F / g. Got. The measurement method was the same as in the examples described later. The specific surface area was measured by, for example, a specific surface area measuring device ASAP2020 manufactured by Shimadzu Corporation. According to these measurement results, it is clear that the specific surface area of the porous electrode and the capacitance do not have a linear relationship. In addition, it is guessed that the mechanism which expresses an electrostatic capacity does not change with electrode materials.

Therefore, as a result of intensive studies on the specific surface area by the present inventor, the parameter affecting the capacitance is not a simple specific surface area, but a specific surface area with respect to the volume of the mesopores 22, that is, a ratio per unit volume of mesopores. It has been found that the surface area affects the capacitance. Therefore, the specific surface area per unit volume of mesopores can serve as an index when designing the electric double layer capacitor 10. Thus, the present inventor succeeded in finding an index for designing the electric double layer capacitor 10. As a result of further investigations on the specific surface area per mesopore unit volume by the present inventors, the specific surface area per mesopore unit volume is preferably 450 m ² / cm ³ or more, and 600 m ² / cm ³ or more. It has also been found to be more preferable. The capacitance increases particularly when the specific surface area per unit volume of mesopores is in these ranges. The reason for this is, for example, not the simple specific surface area, but the importance of how much specific surface area the mesopores that are likely to adsorb electrolyte ions have, which is the factor that substantially controls the capacitance, In the case of conventional activated carbon, when the mesopore ratio is increased, the specific surface area is decreased, and it is considered that this 450 m ² / cm ³ or more cannot be substantially achieved.

A preferable upper limit value of the specific surface area per unit volume of mesopores varies depending on the diameter of the electrolyte ion. Hereinafter, the reason for this will be described with reference to FIGS. FIG. 5 is a graph showing the correspondence between the specific surface area per unit volume of the mesopores and the capacitance per unit volume of the electric double layer capacitor 10 for each diameter of the electrolyte ions. The capacitance on the vertical axis is a so-called theoretical value and is calculated as follows. That is, as shown in FIG. 6, the mesopores 22 are modeled by a cylinder. In this model, all the pores become mesopores 22. The mesopores 22 are cylinders having the same shape, and the height of each cylinder is 1 cm. The diameter of each cylinder varies depending on the specific surface area per unit volume of mesopores. In addition, the cylinders are arranged so that the axial directions thereof are parallel to each other and are adjacent to each other (that is, spread in the porous electrode 20). Therefore, when the specific surface area per unit volume of mesopores is S1 (m ² / cm ³ ), the specific surface area of the 1 cm ³ porous electrode 20 is S1 (m ² ). And the theoretical value of an electrostatic capacitance is computed by the following formula | equation (3).

In formula (3), C ₀ is a theoretical value of capacitance, and S is a specific surface area per unit volume of mesopores. n is the number of electrolyte ions deposited per unit area (1 m ² ) of the surface of the porous electrode 20 and is given by the following equation (3-1). V _max is the upper limit voltage, that is, the maximum voltage that can be applied to the porous electrode 20, and is 2.5 V in the example of FIG. V _min is the lower limit voltage, that is, the minimum voltage that can be applied to the porous electrode 20, and is 1.0 V in the example of FIG.

Wherein (3-1), _{L n} is the ion diameter (m).

  According to FIG. 5, the capacitance increases with an increase in specific surface area per unit volume of mesopores regardless of the diameter of the electrolyte ions. Note that the diameter of the mesopores 22 decreases as the specific surface area per unit volume of the mesopores increases. Then, at the point where the diameter of the electrolyte ion coincides with the diameter of the mesopores 22, the capacitance is rapidly decreased.

  The relationship between the specific surface area per unit volume of the mesopores and the diameter of the mesopores 22 is expressed by the following formula (4).

Here, x is the diameter (m) of the mesopores 22, and n is the number of cylinders arranged in the 1 cm ³ porous electrode 20, which is expressed by the following formula (5). S is a specific surface area per unit volume of mesopores.

According to the equations (4) and (5), for example, when the diameter of the mesopores 22 is 2 nm, the specific surface area per unit volume of the mesopores is 1500 m ² / cm ³ . Therefore, the capacitance should start to decrease at a specific surface area per unit volume of mesopores of 1500 m ² / cm ³ , but in fact, the electrolyte ions are not spheres and are therefore as large as mesopores. When it is close to this, it becomes difficult to enter the pores due to steric hindrance, and as shown in the figure, it starts to decrease at a point of 1200 m ² / cm ³ . Therefore, the preferable upper limit value of the specific surface area per unit volume of mesopores varies depending on the diameter of the electrolyte ions. For example, when the diameter of the electrolyte ion is 2 nm, the preferable upper limit value is 1200 m ² / cm ³ . In other words, the capacitance can be increased by reducing the diameter of the electrolyte ions as much as possible.

  The porous electrode 20 is composed of an inorganic material, preferably composed of a metal, and more preferably composed of a transition metal (for example, an element present between a Group 3 element and a Group 11 element in the periodic table). The Specifically, the porous electrode 20 includes at least one metal selected from the group consisting of Ni, Cu, Co, and Fe, for example. Of these metal materials, Ni and Cu are particularly preferable. This is because porous nickel and porous copper have good reactivity with anions, and the inorganic compound layer 23 can be easily formed.

  Further, as shown in FIG. 7, an inorganic compound layer 23 is formed on the surface of the porous metal 20a (that is, the entire surface of the porous metal 20a including the surface of the mesopores 22). That is, the surface of the mesopores 22 is covered with the inorganic compound layer 23. Thereby, the cycle stability and thermal stability of the electric double layer capacitor 10 are improved. The reason why the cycle stability and thermal stability of the electric double layer capacitor 10 are improved is, for example, that the porous metal 20a is prevented from coming into direct contact with the electrolyte (electrolytic solution). That is, when the porous metal 20a is in direct contact with the electrolytic solution, the porous metal 20a is easily eluted into the electrolytic solution when a voltage is applied to the porous electrode 20. And the higher the temperature, the higher the reaction activity of the porous metal 20a and the greater the elution amount. Therefore, the elution of the porous metal 20a is prevented by covering the surface of the porous metal 20a, particularly the surface of the mesopores 22 with the inorganic compound layer 23. As a result, the cycle stability and thermal stability of the electric double layer capacitor 10 are prevented. Improves.

  The inorganic compound layer 23 is composed of a compound of a metal and an anion constituting the porous metal 20a, that is, an inorganic compound. The anion constituting the inorganic compound layer 23 includes, for example, at least one kind of anion selected from the group consisting of oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, sulfur ions, and carbon ions.

  The inorganic compound layer 23 is preferably as thin as possible. This is because the thinner the inorganic compound layer 23, the lower the electric resistance of the electric double layer capacitor 10 and the rapid charge / discharge characteristics are prevented from being deteriorated. The specific layer thickness is preferably 30 nm or less, more preferably 20 nm or less, and further preferably 15 nm or less. This is because if the layer thickness exceeds 30 nm, the electric resistance of the electric double layer capacitor 10 is greatly reduced, and the rapid charge / discharge characteristics are also greatly reduced. Each of the above ranges is thinner than a natural oxide film (an oxide film formed by exposing the porous metal 20a to the atmosphere). The layer thickness of the inorganic compound layer 23 is measured by, for example, an X-ray photoelectron spectrometer AXIS-ULTRA-DLD manufactured by Kratos.

[Method for producing porous electrode]
Next, a method for manufacturing the porous electrode 20 will be described. The porous electrode 20 is manufactured by forming an inorganic compound on the surface of the porous metal 20a after manufacturing the porous metal 20a. For example, the porous metal is produced by any one of the following two production methods.

[Method of treating alloy with acid or alkaline solution]
In the first production method, an alloy containing a first metal that is soluble in an acid or alkaline solution and a second metal that is less soluble in the acid or alkaline solution than the first metal is used in an acid or alkaline solution. It is a manufacturing method of processing. Although it is desired to remove the first metal as much as possible to make it porous, the first metal may not be completely removed after the treatment but may partially remain. The immersion time is preferably 3 hours or longer. However, this upper limit time depends on the concentration and temperature of the acid or alkaline solution. The concentration of the acid or alkali in the solution is preferably 1 to 20% by mass with respect to the total mass of the solution. The temperature of the solution is preferably in the range of room temperature to 90 ° C. Since the pore size distribution and the specific surface area per unit volume of mesopores vary depending on the values of these parameters, these parameters may be appropriately determined according to the purpose.

  The first metal includes, for example, at least one metal selected from the group consisting of aluminum, lead, tin, and zinc. The second metal is a metal constituting the porous metal 20a. Transition metals are particularly preferred because they are almost insoluble in acid or alkaline solutions. According to this manufacturing method, since the first metal elutes in the acid or alkaline solution, the portion of the alloy occupied by the first metal becomes the mesopores 22. Specifically, the mesopores 22 are formed by combining the vacancies formed by removing the first metal. Therefore, according to this manufacturing method, the size, that is, the diameter of the mesopores 22 also changes depending on the size of the first metal crystallite. That is, according to this manufacturing method, the desired mesopores 22 are manufactured by controlling the size of the crystallites of the first metal and the molar ratio between the first metal and the second metal. Can do.

As described above, in this embodiment, the diameter of the mesopores 22 is 2 nm or more and 30 nm or less, the abundance ratio of the mesopores 22 is 70% or more, and the specific surface area per mesopore unit volume is 450 m ² / cm ³ or more. Therefore, in order to obtain these values, the molar ratio of the first metal to the second metal is preferably in the range of 1: 3 to 3: 1, more preferably 1: 1 to 3: 1. Is set.

  Here, the average diameter of the alloy composed of the first metal and the second metal is preferably 100 μm or less, more preferably 50 μm, and further preferably 20 μm. Here, the average diameter is, for example, a value obtained by arithmetically averaging the diameters when each metal particle is regarded as a sphere. The average diameter is measured, for example, with a Hitachi ultra-high resolution field emission scanning electron microscope S-4800 (manufactured by Hitachi High-Tech).

[Method of reducing metal compound]
The second production method is a production method in which an anion in the metal compound is removed by reducing the metal compound. The metal compound is a compound of a metal constituting the porous metal 20a and an anion. Examples of the anion include inorganic anions containing oxygen and nitrogen, and organic anions such as carboxylate ions and metroxide ions. The reduction is performed, for example, by treating a metal compound with a reducing gas such as hydrogen or carbon monoxide. Thereby, the part which the anion occupied among the metal compounds becomes the mesopores 22. Therefore, according to this manufacturing method, the size, that is, the diameter of the mesopores 22 also changes depending on the size of the anion. That is, according to this manufacturing method, desired mesopores 22 can be manufactured by controlling the size of the anion.

As described above, in this embodiment, the diameter of the mesopores 22 is 2 nm or more and 30 nm or less, the abundance ratio of the mesopores 22 is 70% or more, and the specific surface area per mesopore unit volume is 450 m ² / cm ³ or more. Therefore, in order to obtain these values, the size of the anion, for example, the diameter is preferably 20 mm or less, more preferably 10 mm or less. Each one of the anions is smaller than the mesopores 22, but the mesopores 22 are formed by bonding vacancies formed by removing the anions. Examples of such anions include oxygen ions, oleate ions, metroxide ions, and the like.

[Method of forming an inorganic compound layer on the surface of a porous metal]
The method of forming the inorganic compound layer 23 on the surface of the porous metal 20a is not particularly limited, and examples thereof include a method of exposing the porous metal 20a to a gas atmosphere, a method of impregnating the porous metal 20a with a solution, and the like. It is done. Examples of other methods include chemical vapor deposition (CVD). Specifically, the method of exposing the porous metal 20a to a gas atmosphere is a method of exposing the porous metal 20a to a mixed gas of a reaction gas and an inert gas (for example, a rare gas).

  The reactive gas is a gas that can react with the porous metal 20a. The reaction gas includes, for example, at least one gas selected from the group consisting of air, oxygen gas, halogen gas, nitrogen gas, water vapor, carbon dioxide gas, and hydrogen sulfide gas.

  The concentration of the reaction gas (the concentration of the reaction gas in the entire mixed gas) is preferably low. This is because the layer thickness of the inorganic compound layer 23 becomes thinner as the concentration of the reaction gas is lower. On the other hand, if the concentration of the reaction gas is too low, there may be a missing portion where the inorganic compound layer 23 is not formed on the surface of the mesopores 22. The missing portion is oxidized by being exposed to the atmosphere. Therefore, if there are many missing portions, an excessively thick (more than 30 nm) oxide film (that is, a natural oxide film) may be formed in these missing portions.

  The specific upper limit value of the reaction gas concentration is, for example, preferably 6% by volume or less, and more preferably 4% by volume or less. On the other hand, the preferable lower limit value of the concentration of the reaction gas varies depending on the type of the reaction gas. For example, when the reaction gas is oxygen, a preferable lower limit of the concentration of the reaction gas is 1.5% by volume. Thus, the preferable concentration range of the reaction gas varies depending on the type of the reaction gas and the type of the porous metal 20a. Therefore, the above range is merely an example. Moreover, the time which exposes a porous metal to mixed gas should just be 10 minutes or more, for example. According to this method, a layer containing oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, and sulfur ions can be formed as the inorganic compound layer 23.

Specifically, the method of impregnating the porous metal 20a with the solution is as follows. The porous metal 20a is made into a solution containing anions capable of reacting with the porous metal 20a, such as halogen ions, nitrate ions, sulfate ions, acetate ions, and the like. It is a method of impregnating and then heat-treating. Such _{solutions, NiF 2, NiBr 2, NiCl} 2, NiI 2, CuBr 2, CuCl, CuCl 2, CoBr 2, CoCl 2, CoI 2, CoF 2, FeBr 2, FeBr 3, FeCl 2, FeCl 3 , FeSO ₄ , Ni (NO ₃ ) ₂ , NiSO ₄ , Ni (C ₂ H ₃ O ₂ ) ₂ , Cu (NO ₃ ) ₂ , CuSO ₄ , Co (C ₂ H ₃ O ₂ ) ₂ , Co (NO ₃₎ ) ₂ , CoSO ₄ , or Fe (NO ₃ ) ₂ . The anion concentration in the solution is, for example, 1% by mass with respect to the total mass of the solution, and the impregnation time is, for example, 10 minutes or more. The heat treatment is performed by heating the porous metal 20a to a desired ultimate temperature at a temperature increase rate of 10 ° C./min or less and holding the temperature at the temperature after the temperature increase for 2 hours or more. Here, the ultimate temperature varies depending on the type of the porous metal 20a. For example, when the porous metal 20a is Ni, Fe, or Co, the temperature is 400 to 500 ° C, and when the porous metal 20a is copper, the temperature is 150 to 300 ° C. According to this method, a layer containing oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, and sulfur ions can be formed as the inorganic compound layer 23.

  The inorganic compound layer 23 can also be formed by introducing the porous metal 20a into water and bubbling the reaction gas.

  According to the method of forming the inorganic compound layer 23 by the CVD method, a layer containing oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, sulfur ions, and carbon ions is formed as the inorganic compound layer 23. be able to. In addition, as reaction gas used for CVD method, hydrocarbon gas, such as acetylene gas other than the reaction gas mentioned above, is mentioned. Further, in the CVD method, the concentration of the reaction gas is 3 to 15% by volume, the holding time (time for exposing the porous metal 20a to the reaction gas) is 1 to 5 hours, and the temperature rising rate of the reaction gas is 10 ° C./min or less. It is preferable to do.

Next, examples of the present embodiment will be described.
[Example 1]
Aluminum was removed from the Ni-Al alloy by adding a Ni-Al alloy having an average diameter of 10 m (molar ratio 50:50) to the 1N aqueous potassium hydroxide solution. The immersion time was 3 hours. The same applies to the following embodiments. In addition, the solubility with respect to the potassium hydroxide aqueous solution of nickel is smaller than the solubility with respect to potassium hydroxide of aluminum. In other words, nickel is insoluble in aqueous potassium hydroxide, while aluminum is soluble in aqueous potassium hydroxide. Thereby, porous nickel was produced as a porous electrode. The produced porous nickel was washed with water and vacuum dried.

Next, a nickel oxide layer was formed as an inorganic compound layer on the surface of the porous nickel by exposing the porous nickel to a mixed gas (4% by volume oxygen gas + 96% by volume argon gas) airflow at room temperature for 2 hours. . Thereby, the porous electrode was created. When each parameter of the porous electrode was measured with a specific surface area measuring device ASAP2020 manufactured by Shimadzu Corporation, the specific surface area was 80 m ² / g, and the pore volume per unit mass of the porous electrode, that is, the pore volume was 0.07 (cm ³ / g), the abundance ratio of mesopores was 78%, and the abundance ratio of micropores was 22%. Further, from these values and the formula (2), the specific surface area per unit volume of the mesopores of the porous electrode was 933 m ² / cm ³ . The pore size distribution was 3 to 20 nm, and the peak value of pores (the pore size (diameter) of the most pores) was 6 nm.

  Moreover, elemental analysis in the thickness direction of the porous electrode was performed by analyzing the surface of the porous electrode with an X-ray photoelectron spectrometer AXIS-ULTRA-DLD manufactured by Kratos while performing argon etching. Thereby, the thickness of the inorganic compound layer was measured. As a result, the thickness of the inorganic compound layer was measured to be 12 nm.

  Further, carbon black as a conductive material is added to the obtained porous electrode by 5% by mass with respect to the mass of the porous electrode, and further PTFE (polytetrafluoroethylene) is added by 5% by mass with respect to the mass of the porous electrode. And mixed in a mortar. Thereafter, the mixture was molded with a tablet press to obtain pellets. A cell sandwiched between aluminum meshes is used as a working electrode and a counter electrode, the reference electrode is an Ag electrode, and the electrolyte is 1M-TEA-BF4 / PC (tetraethylammonium-tetrafluoroborate / propylene carbonate). Configured. This cell was subjected to a cycle test by sweeping this cell with a PARSTAT 2273 manufactured by Advanced Electrochemical System at a sweep speed of 1 mv / s in a range of -1.25 to 1.25V. The cycle test was performed at room temperature and a temperature of 60 ° C. Thus, the capacitance per unit volume of the electric double layer capacitor, the lifetime at room temperature, and the lifetime at 60 ° C. were calculated. In this example, the number of cycles when the electrostatic capacity reached 60% of the initial capacity (capacitance at the first cycle) was defined as the life.

[Example 2]
The same treatment as in Example 1 was performed except that the mixed gas was changed to (2% by volume of carbon dioxide gas + 98% by volume of argon gas). In Example 2, the inorganic compound layer was a nickel carbonate layer. The specific surface area of the porous electrode is 78 m ² / g, the pore volume per unit mass of the porous electrode, that is, the pore volume is 0.07 (cm ³ / g), the abundance ratio of mesopores is 77%, micro The abundance ratio of the pores was 23%, and the specific surface area per unit volume of the mesopores of the porous electrode was 903 m ² / cm ³ . The pore size distribution was 3 to 22 nm, and the pore peak value was 6 nm. The thickness of the inorganic compound layer was measured to be 15 nm.

[Example 3]
The same treatment as in Example 1 was performed except that the mixed gas was changed to (1% by volume fluorine gas + 99% by volume argon gas). In Example 3, the inorganic compound layer was a nickel fluoride layer. The specific surface area of the porous electrode is 74 m ² / g, the pore volume per unit mass of the porous electrode, that is, the pore volume is 0.0067 (cm ³ / g), the abundance ratio of the mesopores is 75%, micro The abundance ratio of the pores was 25%, and the specific surface area per unit volume of the mesopores of the porous electrode was 870 m ² / cm ³ . The pore size distribution was 3 to 25 nm, and the pore peak value was 7 nm. The thickness of the inorganic compound layer was measured to be 13 nm.

[Example 4]
The same treatment as in Example 1 was performed except that the alloy was a Cu-Al alloy having an average diameter of 10 μm (molar ratio was 50:50) and the mixed gas was (1% by volume fluorine gas + 99% by volume argon gas). went. In addition, the solubility with respect to the potassium hydroxide aqueous solution of copper is smaller than the solubility with respect to potassium hydroxide of aluminum. In Example 4, the inorganic compound layer was a copper fluoride layer. The specific surface area of the porous electrode is 21.2 m ² / g, the pore volume per unit mass of the porous electrode, that is, the pore volume is 0.044 (cm ³ / g), and the mesopore abundance ratio is 94%. The abundance ratio of micropores was 6%, and the specific surface area per mesopore unit volume of the porous electrode was 453 m ² / cm ³ . The pore size distribution was 2 to 20 nm, and the pore peak value was 10 nm. The thickness of the inorganic compound layer was measured to be 14 nm.

[Example 5]
The same treatment as in Example 1 was performed except that the mixed gas was changed to (1.2% by volume of oxygen gas + 98.8% by volume of argon gas). The specific surface area of the porous electrode is 78 m ² / g, the pore volume per unit mass of the porous electrode, that is, the pore volume is 0.07 cm ³ / g, the abundance ratio of the mesopores is 75%, The abundance ratio was 25%, and the specific surface area per mesopore unit volume of the porous electrode was 836 m ² / cm ³ . The pore size distribution was 3 to 23 nm, and the pore peak value was 7 nm. The thickness of the inorganic compound layer was measured to be 22 nm. When Examples 1 and 5 were compared, the inorganic compound layer became thick even though the oxygen gas concentration of Example 5 was lower than that of Example 1. The reason for this is that in Example 5, the above-described missing portion was formed, and this missing portion was oxidized in the atmosphere. In addition, since the layer thickness of Example 5 was also 30 nm or less, the characteristic better than the comparative example mentioned later was acquired.

[Example 6]
Aluminum was removed from the Ni-Al alloy by adding a Ni-Al alloy having an average diameter of 10 m (molar ratio 50:50) to the 1N aqueous potassium hydroxide solution. Subsequently, the porous nickel was washed with water, and the solvent was replaced with tetrahydrofuran (THF). The THF was then filtered. Subsequently, porous nickel was impregnated with a THF solution in which furfuryl alcohol was dissolved at a concentration of 1 mol / l for 10 minutes. Next, the porous nickel was taken out from the THF solution and transferred to an electric furnace in an argon atmosphere. Next, the porous nickel was heated to 700 ° C. at a temperature rising speed of 10 ° C./min and held at this temperature for 2 hours. Thereby, the porous electrode was created. In Example 6, the inorganic compound layer was a nickel hydroxide layer. The porous electrode was then cooled to room temperature.

In Example 6, the specific surface area of the porous electrode was 71 m ² / g, the pore volume per unit mass of the porous electrode, that is, the pore volume was 0.063 cm ³ / g, and the abundance ratio of mesopores was 80%. The abundance ratio of micropores was 20%, and the specific surface area per mesopore unit volume of the porous electrode was 901 m ² / cm ³ . The pore size distribution was 3 to 27 nm, and the pore peak value was 8 nm. The thickness of the inorganic compound layer was measured to be 12 nm. Further, the initial capacity and the like were measured by subjecting this sample to the same treatment as in Example 1.

[Comparative Example 1]
The same treatment as in Example 1 was performed except that the treatment with oxygen gas was not performed. In Comparative Example 1, the thickness of the inorganic compound layer was 31 nm. That is, in Comparative Example 1, the inorganic compound layer was formed by the porous nickel participating in the atmosphere.

[Comparative Example 2]
The same treatment as in Example 4 was performed, except that the treatment with oxygen gas was not performed. In Comparative Example 2, the thickness of the inorganic compound layer was 65 nm. That is, in Comparative Example 2, a very thick inorganic compound layer was formed by oxidizing porous copper in the atmosphere.

[Evaluation]
Table 1 shows the measurement results. In Table 1, the measured values of Examples 1 to 6 are standardized in the comparative example.

  According to Table 1, each of Examples 1 to 6 has a larger capacitance per unit volume than the comparative example. Further, it can be seen that the room temperature life of Examples 1 to 6 is 1.4 to 1.8 times longer than that of the comparative example in which the atmospheric gas is not treated. Also, the high temperature life was 1.9 to 2.5 times longer than that of the comparative example. In Examples 1 to 6, since the inorganic compound layer formed by the reaction gas can suppress the direct contact between the porous metal and the electrolyte, it seems that the life characteristics are improved. In addition, this feature became prominent at 60 ° C., which was a higher temperature. At high temperatures, the reaction activity between the porous metal and the electrolyte is increased, so it is considered that the effect of suppressing the contact between the porous metal and the electrolyte by the inorganic compound layer is increased.

  As described above, since the electric double layer capacitor 10 according to the present embodiment includes a porous metal having a specific gravity larger than that of activated carbon, the capacitance per unit volume can be increased as compared with the conventional case. Therefore, the electric double layer capacitor 10 can improve the capacitance per unit volume, that is, the energy density, as compared with the conventional one while maintaining the advantages of the electric double layer capacitor.

  Furthermore, the porous electrode 20 of the electric double layer capacitor 10 includes an inorganic compound layer 23 that covers the surface of the mesopores 22. The inorganic compound layer 23 can suppress the direct contact between the porous metal 20a and the electrolyte and the oxidation of the porous metal 20a in the atmosphere. Therefore, the electric double layer capacitor 10 can also improve cycle stability and thermal stability.

  Further, the anion constituting the inorganic compound layer 23 is at least one kind of anion selected from the group consisting of oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, sulfur ions, and carbon ions. Therefore, the inorganic compound layer 23 can more reliably prevent contact between the porous metal and the electrolyte.

Furthermore, since the specific surface area per unit volume of the mesopores of the porous electrode 20 is 450 m ² / cm ³ or more, the energy density per unit volume is larger than that in the prior art.

  Furthermore, since the diameter of the mesopores 22 is not less than 2 nm and not more than 30 nm, the energy density per unit volume is larger than that in the conventional case.

  Furthermore, since the diameter of the electrolyte ions is 2 nm or less, the electrolyte ions can easily enter and exit the mesopores 22. Therefore, also in this respect, the energy density per unit volume becomes larger than the conventional one.

  Further, the porous metal 20a is composed of at least one metal selected from the group consisting of nickel, copper, iron and cobalt. Therefore, the porous metal 20a can react well with the anion to form the inorganic compound layer 23.

  Furthermore, in the method for manufacturing the electric double layer capacitor 10 according to the present embodiment, the electric double layer capacitor 10 is manufactured using a porous metal having a specific gravity greater than that of activated carbon. The per-capacitance can be increased.

  Furthermore, in the manufacturing method of the electric double layer capacitor 10, since the inorganic compound layer 23 covering the surface of the mesopores 22 is formed, the electric double layer capacitor 10 with improved cycle stability and thermal stability can be manufactured. .

  Furthermore, the manufacturing method of the electric double layer capacitor 10 manufactures the porous electrode 20 by exposing the porous metal 20a to the reaction gas. Therefore, the manufacturing method of the electric double layer capacitor 10 can form the inorganic compound layer 23 more reliably.

  Further, the reaction gas includes at least one gas selected from the group consisting of air, oxygen gas, halogen gas, nitrogen gas, water vapor, carbon dioxide gas, and hydrogen sulfide gas. Therefore, the manufacturing method of the electric double layer capacitor 10 can form the inorganic compound layer 23 that can more reliably suppress the contact between the porous metal 20a and the electrolyte.

  Furthermore, in the method for manufacturing the electric double layer capacitor 10, the porous electrode 20 is manufactured by impregnating the porous metal 20a with a solution containing an anion capable of reacting with the porous metal 20a and then performing a heat treatment. Therefore, the manufacturing method of the electric double layer capacitor 10 can form the inorganic compound layer 23 more reliably.

Furthermore, since the specific surface area per mesopore unit volume of the porous electrode 20 is 450 m ² / cm ³ or more, the manufacturing method of the electric double layer capacitor 10 has a larger energy density per unit volume than before. The electric double layer capacitor 10 can be manufactured.

  Furthermore, since the diameter of the mesopores 22 is 2 nm or more and 30 nm or less, the manufacturing method of the electric double layer capacitor 10 can manufacture the electric double layer capacitor 10 having an energy density per unit volume larger than that of the conventional one.

  Furthermore, since the diameter of the electrolyte ions is 2 nm or less, the electrolyte ions can easily enter and exit the mesopores 22. Therefore, the manufacturing method of the electric double layer capacitor 10 can manufacture the electric double layer capacitor 10 whose energy density per unit volume is larger than the conventional one.

  Furthermore, since the porous metal 20a is composed of at least one metal selected from the group consisting of nickel, copper, iron, and cobalt, the manufacturing method of the electric double layer capacitor 10 makes the inorganic compound layer 23 more reliable. Can be formed.

  Furthermore, in this embodiment, since the abundance ratio of the mesopores 22 is 70% or more, while maintaining the advantages that the life, safety, and output density are much better than the secondary battery, The electrostatic capacity, i.e., energy density, can be made larger than the conventional one.

  Furthermore, the manufacturing method of the electric double layer capacitor 10 manufactures the porous metal 20a in which the abundance ratio of the mesopores 22 is 70% or more. Therefore, the electric double layer capacitor 10 having an energy density per unit volume larger than the conventional one can be easily manufactured.

  Furthermore, the method for manufacturing the electric double layer capacitor 10 includes an alloy including a first metal that is soluble in an acid or alkaline solution and a second metal that is less soluble in an acid or alkaline solution than the first metal. The porous metal 20a is produced by processing with an acid or an alkaline solution. Therefore, since the complicated post-treatment required for the conventional alkali activation treatment is not required, the electric double layer capacitor 10 having an energy density per unit volume larger than that of the conventional one can be easily manufactured.

  Furthermore, since the first metal includes at least one metal selected from the group consisting of aluminum, lead, tin, and zinc, it is easily dissolved in an acid or alkaline solution. Therefore, the electric double layer capacitor 10 having an energy density per unit volume larger than the conventional one can be easily manufactured.

  Furthermore, the molar ratio of the first metal to the second metal is preferably in the range of 1: 3 to 3: 1, more preferably 1: 1 to 3: 1, so that the energy density per unit volume is Electric double layer capacitor 10 larger than the conventional one can be easily manufactured.

  Furthermore, since the manufacturing method of the electric double layer capacitor 10 includes the step of reducing the metal compound, the complicated post-processing necessary for the conventional alkali activation treatment is not required. Therefore, the electric double layer capacitor 10 having an energy density per unit volume larger than the conventional one can be easily manufactured.

  Furthermore, since the diameter of the anion constituting the metal compound is preferably 20 mm or less, more preferably 10 mm or less, the electric double layer capacitor 10 having an energy density per unit volume larger than the conventional one can be easily manufactured. be able to.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Electric double layer capacitor 11 Cathode electrode 12 Anode electrode 20 Porous electrode 20a Porous metal 22 Mesopore

Claims (15)

A plurality of porous electrodes comprising a porous metal in which mesopores are formed, and an inorganic compound layer covering the surface of the mesopores,
And an electrolyte disposed between the plurality of porous electrodes.   The anion constituting the inorganic compound layer is at least one anion selected from the group consisting of oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, sulfur ions, and carbon ions. The electric double layer capacitor according to claim 1. ^3. The electric double layer capacitor according to claim 1, wherein a specific surface area per unit volume of mesopores of the porous electrode is 450 m ² / cm ³ or more.   The electric double layer capacitor according to any one of claims 1 to 3, wherein a diameter of the mesopore is 2 nm or more and 30 nm or less.   The electric double layer capacitor according to claim 4, wherein a diameter of an electrolyte ion contained in the electrolyte is 2 nm or less.   The electric porous body according to any one of claims 1 to 5, wherein the porous metal is composed of at least one metal selected from the group consisting of nickel, copper, iron and cobalt. Multilayer capacitor.   A porous electrode for an electric double layer capacitor, comprising: a porous metal having mesopores formed therein; and an inorganic compound layer covering a surface of the mesopores. Producing a plurality of porous electrodes comprising a porous metal having mesopores formed thereon and an inorganic compound layer covering the surface of the mesopores;
Disposing an electrolyte between the plurality of porous electrodes, and a method for producing an electric double layer capacitor.   9. The electric double layer capacitor according to claim 8, wherein the porous electrode is manufactured by exposing a porous metal in which mesopores are formed to a reactive gas capable of reacting with the porous metal. Manufacturing method.   10. The reaction gas according to claim 9, wherein the reaction gas includes at least one gas selected from the group consisting of air, oxygen gas, halogen gas, nitrogen gas, water vapor, carbon dioxide gas, and hydrogen sulfide gas. Manufacturing method of electric double layer capacitor.   9. The porous electrode is manufactured by impregnating a porous metal having mesopores formed in a solution containing an anion capable of reacting with the porous metal, and then heat-treating the porous metal. The manufacturing method of the electrical double layer capacitor of description. The specific surface area per mesopore unit volume of the porous electrode, characterized in that it is 450 m 2 ^/ cm ³ or more, a manufacturing method of the electric double layer capacitor according to any one of claims 8-11.   The method for producing an electric double layer capacitor according to any one of claims 8 to 12, wherein a diameter of the mesopore is 2 nm or more and 30 nm or less.   The method of manufacturing an electric double layer capacitor according to claim 13, wherein the diameter of the electrolyte ions contained in the electrolyte is 2 nm or less. The electric porous body according to any one of claims 8 to 14, wherein the porous metal is composed of at least one metal selected from the group consisting of nickel, copper, iron and cobalt. Manufacturing method of multilayer capacitor.

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