JP2014007220A - Electric double layer capacitor and porous electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel and improved electric double layer capacitor capable of improving electrostatic capacity per unit volume, more specifically energy density, than conventional ones, while maintaining the advantages of an electric double layer capacitor.SOLUTION: According to one aspect of the present invention, there is provided an electric double layer capacitor which includes: a porous electrode including porous metal having a mesopore formed therein, the mesopore having a specific surface area per unit volume of 450 m/cmor more; and an electrolyte containing electrolyte ions capable of being absorbed and desorbed to the porous electrode.

Description

  The present invention relates to an electric double layer capacitor and a porous electrode.

  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 the energy density (volume 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 7-320884 A JP 2009-153454 A JP 2009-13292 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 porous electrode including a porous metal having mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more, And an electrolyte containing electrolyte ions that can be adsorbed and desorbed on the electrode.

Since the electric double layer capacitor according to this aspect 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. Further, mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed in the porous metal. Therefore, the electric double layer capacitor can improve the energy density and the output characteristics as compared with the conventional one regardless of the particle diameter (diameter) of the electrolyte ions.

  Here, a porous positive electrode including a porous metal and a negative electrode including a material capable of occluding and releasing at least one lithium ion selected from the group consisting of graphite, lithium titanate, and hard carbon are provided. Also good.

  According to this aspect, the electric double layer capacitor can be manufactured by replacing the cathode electrode of the conventional lithium ion capacitor with the porous metal according to this aspect. That is, an electric double layer capacitor having a high output and a high energy density can be easily manufactured.

  Moreover, you may provide the porous positive electrode containing activated carbon, and the porous negative electrode containing a porous metal.

  According to this aspect, the electric double layer capacitor can be manufactured by replacing the anode electrode of the conventional lithium ion capacitor with the porous metal according to this aspect. That is, an electric double layer capacitor having a high output and a high energy density can be easily manufactured.

A porous positive electrode including a first porous metal having mesopores with a specific surface area per unit volume of 450 m ² / cm ³ or more, and a specific surface area per unit volume of 450 m ² / cm ³ or more. And a porous negative electrode including a second porous metal made of a metal different from the first porous metal.

  According to this viewpoint, both the porous positive electrode and the porous negative electrode are made of a porous metal. Here, the 1st porous metal which comprises a porous positive electrode differs in the 2nd porous metal which comprises a porous negative electrode, and the kind of metal. Therefore, the electric double layer capacitor according to this aspect can improve the energy density and the output characteristics as compared with the conventional case.

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

  According to this viewpoint, the electrolyte ions are effectively adsorbed and desorbed inside the mesopores, so that the energy density and output characteristics of the electric double layer capacitor are improved as compared with the conventional case.

  The electrolyte may contain electrolyte ions having a diameter of 2 nm or less.

  According to this viewpoint, the electrolyte ions are effectively adsorbed and desorbed inside the mesopores, so that the energy density and output characteristics of the electric double layer capacitor are improved as compared with the conventional case.

  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 electric double layer capacitor can improve the energy density and the output characteristics as compared with the conventional case.

According to another aspect of the present invention, there is provided a porous electrode for an electric double layer capacitor including a porous metal in which mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed. Is done.

The porous electrode according to this aspect includes a porous metal having a specific gravity larger than that of activated carbon. Therefore, by applying this porous electrode to an electric double layer capacitor, the capacitance per unit volume of the electric double layer capacitor can be made larger than before. That is, while maintaining the advantages of the electric double layer capacitor, the capacitance per unit volume, that is, the energy density can be improved as compared with the conventional case. Further, mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed in the porous metal. Therefore, the electric double layer capacitor can improve the energy density and the output characteristics as compared with the conventional one regardless of the particle diameter (diameter) of the electrolyte ions.

As described above, since the electric double layer capacitor according to the present invention 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. Further, mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed in the porous metal. Therefore, the electric double layer capacitor can improve the energy density and the output characteristics as compared with the conventional one regardless of the particle diameter (diameter) of the electrolyte ions.

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.

  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, with any of the techniques disclosed in any document, a satisfactory value for the energy density per unit volume of an electric double layer capacitor (hereinafter, also simply referred to as “energy density of an electric double layer capacitor” or “energy density”) is Not obtained. 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 is a so-called asymmetric electric double layer capacitor, and the positive electrode and the negative electrode are different. The inventor has come up with the electric double layer capacitors according to the following first to third embodiments as asymmetric electric double layer capacitors. Each embodiment will be described below.

<First Embodiment>
(Configuration of Electric Double Layer Capacitor According to First Embodiment)
Next, the configuration of the electric double layer capacitor 10 according to the first 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 (porous positive electrode) 11 composed of a porous material 20, an anode electrode 12 composed of a negative electrode material 21, and these And an electrolyte 13 disposed between the electrodes.

As shown in FIG. 2, the porous material 20 is composed of a porous metal in which mesopores 22 having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed. 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. The specific surface area per unit volume will be described later.

  As described above, the electrolyte ions are often adsorbed and desorbed on the porous material 20 in a solvated state. And the diameter of the solvated electrolyte ion is estimated to be 1-2 nm. Accordingly, 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 material 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 material 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. In addition, the porous copper of 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 sodium hydroxide aqueous 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 material 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 material 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. 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.

Moreover, the specific surface area per unit volume of the mesopores of the porous material 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 material 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 material 20, and a is a specific surface area (m ² / g) of the porous material 20. b is the volume of the pores 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 material 20. c is the abundance ratio of the mesopores 22.

  That is, in the present embodiment, the porous material 20 is designed based on the specific surface area per unit volume of 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 Examples described later, and the same positive electrode and negative electrode were used. For example, the capacitance of the porous copper was measured by setting the positive electrode and the negative electrode to porous copper. 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.

On the other hand, the upper limit value of the specific surface area per unit volume of mesopores varies depending on the diameter of the electrolyte ions. 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 material 20). Accordingly, when the specific surface area per mesopore unit volume is S1 (m ² / cm ³ ), the specific surface area of the porous material 20 of 1 cm ³ 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 attached per unit area (1 m ² ) of the surface of the porous material 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 material 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 material 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 disposed in the 1 cm ³ porous material 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.

For the above reason, the specific surface area per unit volume of the mesopores of the porous material 20 is 450 m ² / cm ³ or more. Further, the upper limit value of the specific surface area per unit volume of mesopores varies depending on the diameter of the electrolyte ions. Moreover, the porous material 20 is preferably composed of a transition metal (for example, an element existing between a Group 3 element and a Group 11 element in the periodic table). Specifically, the porous material 20 includes at least one metal selected from the group consisting of Ni, Cu, Co, and Fe, for example. The above theory holds when the porous material 20 forms an electric double layer.

  An inorganic compound layer may be formed on the surface of the porous material 20 (that is, the entire surface of the porous material 20 including the surface of the mesopores 22). That is, the surface of the mesopores 22 may be covered with an inorganic compound layer. 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 material 20 is prevented from coming into direct contact with the electrolyte (electrolytic solution). That is, when the porous material 20 is in direct contact with the electrolytic solution, the porous material 20 is easily eluted into the electrolytic solution when a voltage is applied to the porous material 20. And the higher the temperature, the higher the reaction activity of the porous material 20 and the greater the amount of elution. Therefore, the elution of the porous material 20 is prevented by covering the surface of the porous material 20, particularly the surface of the mesopores 22, with the inorganic compound layer, and consequently the cycle stability and thermal stability of the electric double layer capacitor 10. Will improve.

  The inorganic compound layer is composed of a compound of a metal and an anion constituting the porous material 20, that is, an inorganic compound. The anion constituting the inorganic compound layer includes, for example, 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 inorganic compound layer is preferably as thin as possible. This is because the thinner the inorganic compound layer is, the lower the electric resistance of the electric double layer capacitor 10 is, so that the rapid charge / discharge characteristics are prevented from deteriorating. The specific layer thickness is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 10 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 material 20 to the atmosphere). The layer thickness of the inorganic compound layer is measured by, for example, an X-ray photoelectron spectrometer AXIS-ULTRA-DLD manufactured by Kratos.

The negative electrode material 21 is a material capable of occluding and releasing lithium ions, and is composed of at least one material selected from the group consisting of graphite, lithium titanate, and hard carbon. Graphite is preferably a material that can insert and desorb lithium ions as much as possible, and is preferably used for lithium ion batteries or lithium ion capacitors. Specifically, the graphite is obtained by heat-treating, for example, artificial graphite or natural graphite. Li ₅ Ti ₄ O ₁₂ is preferred as the lithium titanate. That is, the negative electrode material 21 may be any material as long as it is a material used for the anode electrode of the lithium ion secondary battery.

  The anode electrode 12 is charged and discharged according to the principle of a lithium ion secondary battery (in other words, lithium ions are absorbed and desorbed between layers of the negative electrode material 21 capable of occluding and releasing lithium ions). Therefore, the negative electrode material 21 and the lithium ions capable of occluding and releasing lithium ions do not need to satisfy the requirements required for the porous metal and the electrolyte that forms the electric double layer with the porous metal. Thus, the electric double layer capacitor 10 according to the first embodiment constitutes a lithium ion capacitor, and the porous metal and the electrolyte ions form an electric double layer in the cathode electrode 11. Accordingly, the energy density and output are increased.

(Method for producing porous material (porous metal))
Next, a method for manufacturing the porous material 20 will be described. The porous material 20 is manufactured by forming an inorganic compound on the surface of the porous material 20 after manufacturing the porous material 20. 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 material 20. 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 the first 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 unit volume of the mesopores is 450 m ² / cm. ^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: Set to 1.

  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 material 20 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 on the surface of the porous material 20 is not particularly limited, and examples thereof include a method of exposing the porous material 20 to a gas atmosphere, a method of impregnating the porous material 20 with a solution, and the like. . Examples of other methods include chemical vapor deposition (CVD). Specifically, the method of exposing the porous material 20 to the gas atmosphere is a method of exposing the porous material 20 to a mixed gas of a reaction gas and an inert gas (for example, a rare gas).

  The reaction gas is a gas that can react with the porous material 20. 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 lower the concentration of the reaction gas, the thinner the inorganic compound layer. On the other hand, if the concentration of the reaction gas is too low, a missing portion where an inorganic compound layer is not formed on the surface of the mesopores 22 may occur. 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 reactive gas varies depending on the type of the reactive gas and the type of the porous material 20. 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.

Specifically, the method of impregnating the porous material 20 with the solution is as follows. The porous material 20 is made into a solution containing an anion capable of reacting with the porous material 20, such as a halogen ion, a nitrate ion, a sulfate ion, and an acetate ion. 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 2, FeCl 2, FeCl 2 , FeSO ₂ , 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 material 20 to a desired reached temperature at a temperature rising speed of 10 ° C./min or less and holding at the temperature after the temperature rising for 2 hours or more. Here, the ultimate temperature varies depending on the type of the porous material 20. For example, when the porous material 20 is Ni, Fe, or Co, the temperature is 400 to 500 ° C., and when the porous material 20 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.

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

  According to the method of forming an inorganic compound layer by a CVD method, a layer containing oxygen ions, halogen ions, nitrogen ions, hydroxide ions, carbonate ions, sulfur ions, and carbon ions can be formed as the inorganic compound layer. it can. 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 (the time for exposing the porous material 20 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.

<Second Embodiment>
The electric double layer capacitor 10 according to the second embodiment is different from the first embodiment in the configuration of the porous material 20 and the negative electrode material 21. In the second embodiment, the porous material 20 is made of activated carbon, and the negative electrode material 21 is made of the porous metal described above. Here, the activated carbon is not particularly limited, but is preferably used for an electric double layer capacitor or a lithium ion capacitor. In the electric double layer capacitor 10 according to the second embodiment, an electric double layer is formed in both the cathode electrode 11 and the anode electrode 12. In the anode electrode 12, the porous metal and the electrolyte ions constitute an electric double layer. Accordingly, the energy density and output are increased.

<Third Embodiment>
The electric double layer capacitor 10 according to the third embodiment differs from the first embodiment in the configuration of the porous material 20 and the negative electrode material 21. In the second embodiment, both the porous material 20 and the negative electrode material 21 are made of the porous metal described above. However, the porous metal constituting the porous material 20, that is, the first porous metal, and the porous metal constituting the negative electrode material 21, that is, the second porous metal, are different in metal type. For example, when the porous material 20 is porous nickel, the negative electrode material 21 is porous copper. In the electric double layer capacitor 10 according to the third embodiment, an electric double layer is formed in both the cathode electrode 11 and the anode electrode 12. That is, in both the cathode electrode 11 and the anode electrode 12, the porous metal and the electrolyte ions form an electric double layer. Accordingly, the energy density and output are increased.

  The configuration of each embodiment is summarized as shown in Table 1 below.

  As described above, in the first embodiment, the positive electrode of a known lithium ion capacitor is replaced with a porous metal, and in the second embodiment, the negative electrode of a known lithium ion capacitor is replaced with a porous metal. Is. Therefore, the electric double layer capacitor 10 of the first to second embodiments can be manufactured by replacing any electrode of a known lithium ion capacitor with a porous metal. That is, according to these embodiments, the electric double layer capacitor 10 having a high energy density and a high output can be easily manufactured.

Next, examples of the first to third embodiments 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 sodium hydroxide solution. The immersion time was 3 hours. The same applies to the following embodiments. In addition, the solubility with respect to the sodium hydroxide aqueous solution of nickel is smaller than the solubility with respect to the sodium hydroxide of aluminum. In other words, nickel is insoluble in aqueous sodium hydroxide solution, while aluminum is soluble in aqueous sodium hydroxide solution. Thereby, porous nickel was produced. 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 material sandwiched between aluminum meshes was used as the positive electrode. Artificial graphite was used for the negative electrode. A cell was constructed using an Ag electrode as the reference electrode and 1M-LiBF ₄ / EC / DEC (ethylene carbonate / dimethyl carbonate) (1: 1) as the electrolyte. Moreover, in order to pre-dope lithium ions in the negative electrode, a lithium foil was inserted in advance, and pre-doping was performed by short-circuiting this with the negative electrode. That is, Example 1 corresponds to the first embodiment. The diameter of the electrolyte ions constituting the positive electrode and the electric double layer, that is, BF ₄ (diameter of solvated ions) is 1.02 nm by simulation.

  The rate characteristics were evaluated by charging and discharging the cell in the range of 1 mA to 60 mA using a BioLogic VSP apparatus. The charge / discharge range at this time was 2.2 to 3.8V. The energy density was calculated based on the capacity when charging / discharging from 0 V to 2.5 V at 1 mA.

(Example 2)
The porous Ni of Example 1 was used as the negative electrode, activated carbon MSP20 manufactured by Kansai Thermal Chemical was used as the positive electrode, and 1M-TEA-BF ₄ / PC (tetraethylammonium-tetrafluoroborate / propylene carbonate) was used as the electrolyte. These electrode configurations are the same as those in the first embodiment. Further, the rate characteristics of Example 2 were evaluated in the same manner as Example 1 except that the charge / discharge range was changed from 1V to 2.5V. The energy density was evaluated in the same manner as in Example 1. Example 2 corresponds to the second embodiment. In addition, the electrolyte ion which comprises a negative electrode and an electrical double layer, ie, the diameter of TEA (diameter of the solvated ion), will be 1.26 nm by simulation.

(Example 3)
The same treatment as in Example 1 was performed except that the artificial graphite of Example 1 was changed to Li ₄ Ti ₅ O ₁₂ and lithium pre-doping was not performed. That is, Example 3 corresponds to the first embodiment.

Example 4
Aluminum was removed from the Cu-Al alloy by adding a Cu-Al alloy having an average diameter of 15 m (molar ratio: 50:50) to the 1N aqueous sodium hydroxide solution. In addition, the solubility with respect to the sodium hydroxide aqueous solution of copper is smaller than the solubility with respect to the sodium hydroxide of aluminum. In other words, copper is insoluble in aqueous sodium hydroxide, while aluminum is soluble in aqueous sodium hydroxide. Thereby, porous copper was produced | generated. The produced porous copper was washed with water and vacuum-dried.

Next, a copper oxide layer was formed as an inorganic compound layer on the surface of the porous copper by exposing the porous copper 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. 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 21.2 m ² / g, and the pore volume per unit mass of the porous electrode, that is, the pore volume was 0.044. (Cm ³ / g), the abundance ratio of mesopores was 94%, and the abundance ratio of micropores was 6%. Further, from these values and the formula (2), the specific surface area per unit volume of the mesopores of the porous electrode was 453 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 9 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 11 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 material sandwiched between aluminum meshes was used as a negative electrode. The positive electrode (porous nickel) of Example 1 was used as the positive electrode. A cell was constructed using an Ag electrode as the reference electrode and 1M-TEA-BF ₄ / PC as the electrolyte. That is, Example 4 corresponds to the third embodiment. The diameter of the electrolyte ions constituting the positive electrode and the electric double layer, that is, the BF ₄ ions (the diameter of the solvated ions) is 1.02 nm by simulation. In addition, the electrolyte ions constituting the negative electrode and the electric double layer, that is, the diameter of TEA (the diameter of solvated ions) is 1.26 nm as described above.

  The rate characteristics of Example 4 were evaluated in the same manner as Example 1 except that the charge / discharge range was changed from 1 V to 2.5 V. The energy density was evaluated in the same manner as in Example 1. In addition, lithium pre dope was not performed.

(Example 5)
Aluminum was removed from the Co—Al alloy by adding a Co—Al alloy having an average diameter of 10 μm (molar ratio 50:50) to the 1N aqueous sodium hydroxide solution. Note that the solubility of Co in aqueous sodium hydroxide is smaller than the solubility of aluminum in sodium hydroxide. In other words, Co is insoluble in aqueous sodium hydroxide solution, but aluminum is soluble in aqueous sodium hydroxide solution. Thereby, porous cobalt was produced. The produced porous cobalt was washed with water and vacuum-dried.

Next, the cobalt oxide layer was formed as an inorganic compound layer on the surface of the porous cobalt by exposing the porous cobalt to a mixed gas (4 volume% oxygen gas + 96 volume% argon gas) stream 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 25 m ² / g, and the volume of the pore per unit mass of the porous electrode, that is, the pore volume was 0.05 (cm ³ / g), the abundance ratio of mesopores was 94%, and the abundance ratio of micropores was 6%. Further, from these values and the formula (2), the specific surface area per unit volume of the mesopores of the porous electrode was 470 m ² / cm ³ . The pore size distribution was 3.5 to 24 nm, and the peak value of pores (the pore size (diameter) of the most pores) was 14 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 17 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 material sandwiched between aluminum meshes was used as a negative electrode. The activated carbon of Example 2 was used for the positive electrode. A cell was constructed using an Ag electrode as the reference electrode and 1M-TEA-BF ₄ / PC as the electrolyte. That is, Example 5 corresponds to the second embodiment. In addition, as described above, the diameter of the electrolyte ions constituting the negative electrode and the electric double layer, that is, the TEA ions (diameter of solvated ions) is 1.26 nm.

  The rate characteristics of Example 5 were evaluated in the same manner as in Example 1 except that the charge / discharge range was changed from 1 V to 2.5 V. The energy density was evaluated in the same manner as in Example 1. In addition, lithium pre dope was not performed.

(Comparative Example 1)
The same treatment as in Example 1 was performed except that in Example 1, activated carbon MSP20 manufactured by Kansai Thermal Chemical was used instead of porous nickel.

(Comparative Example 2)
The same treatment as in Example 1 was performed except that activated carbon MSP20 manufactured by Kansai Thermal Chemical Co., Ltd. was used in the negative electrode in Example 2.

(Comparative Example 3)
The same treatment as in Example 1 was performed except that activated carbon MSP20 manufactured by Kansai Thermal Chemical Co., Ltd. was used in Example 3.

(Evaluation)
Table 2 shows the electrodes and measurement results of each example. In Table 2, the measured values of Examples 1 to 5 are standardized in the comparative example.

  According to Table 2, the energy density (volume energy density) of Examples 1 to 5 was improved by 10 to 65% relative to the comparative example, and the output characteristics were also improved by 70 to 140%. In particular, by changing the activated carbon of the prior art to porous nickel, the capacitance per unit volume of the asymmetric electric double layer capacitor was improved, and consequently the energy density of the asymmetric electric double layer capacitor was improved. The output characteristics are particularly effective, and the output characteristics are greatly improved due to the effect of the metal conductivity higher than when activated carbon is used. Further, since porous copper is easily dissolved electrochemically at a high potential, it is preferably used in the negative electrode, and the output characteristics are greatly improved as shown in Example 4 in combination with porous nickel.

  As described above, since the electric double layer capacitor 10 according to the first to third embodiments includes the porous metal having a specific gravity larger than that of the 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.

More specifically, the electric double layer capacitor 10 according to the first to third embodiments includes a porous metal including a porous metal in which mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed. Quality electrode. Here, the porous electrode is the cathode electrode 11 in the first embodiment, the anode electrode 12 in the second embodiment, and the cathode electrode 11 and the anode electrode 12 in the third embodiment. Therefore, the electric double layer capacitor 10 can improve the energy density and the output characteristics as compared with the conventional case regardless of the particle diameter (diameter) of the electrolyte ions.

  In addition, the electric double layer capacitor 10 according to the first embodiment includes a cathode electrode 11 including a porous metal, and at least one negative electrode material 21 selected from the group consisting of graphite, lithium titanate, and hard carbon. Including an anode electrode 12. Here, the negative electrode material 21 is a material capable of occluding and releasing lithium ions. Therefore, according to the second embodiment, the electric double layer capacitor 10 can be manufactured by replacing the cathode electrode of the conventional lithium ion capacitor with the porous metal according to the first embodiment. That is, the electric double layer capacitor 10 with high output and high energy density can be easily manufactured.

  The electric double layer capacitor 10 according to the second embodiment includes a cathode electrode 11 including activated carbon and an anode electrode 12 including a porous metal. Therefore, according to the third embodiment, the electric double layer capacitor 10 can be manufactured by replacing the anode electrode of the conventional lithium ion capacitor with the porous metal according to the second embodiment. That is, the electric double layer capacitor 10 with high output and high energy density can be easily manufactured.

  In the electric double layer capacitor 10 according to the third embodiment, the cathode electrode 11 and the anode electrode 12 are both made of a porous metal. Here, the porous metal constituting the cathode electrode 11 differs from the porous metal constituting the anode electrode 12 in the type of metal. Therefore, the electric double layer capacitor 10 according to the third embodiment can improve the energy density and the output characteristics as compared with the related art.

  Furthermore, in the first to third embodiments, the diameter of the mesopores is 2 nm or more and 30 nm or less. Therefore, electrolyte ions are effectively adsorbed and desorbed inside the mesopores, so that the energy density and output characteristics of the electric double layer capacitor 10 are improved as compared with the conventional case.

  The electrolyte ion has a diameter of 2 nm or less. Therefore, electrolyte ions are effectively adsorbed and desorbed inside the mesopores, so that the energy density and output characteristics of the electric double layer capacitor 10 are improved as compared with the conventional case.

  The porous metal is composed of at least one metal selected from the group consisting of nickel, copper, iron, and cobalt. The electric double layer capacitor 10 can improve energy density and output characteristics as compared with the conventional one.

  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 material 21 Negative electrode material 22 Mesopore

Claims (8)

A porous electrode including a porous metal in which mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed;
And an electrolyte containing electrolyte ions that can be adsorbed and desorbed on the porous electrode. A porous positive electrode comprising the porous metal;
2. An electric double layer capacitor according to claim 1, comprising: a negative electrode including a material capable of occluding and releasing at least one lithium ion selected from the group consisting of graphite, lithium titanate, and hard carbon. . A porous positive electrode containing activated carbon;
The electric double layer capacitor according to claim 1, further comprising a porous negative electrode containing the porous metal. A porous positive electrode comprising a first porous metal in which mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed;
A porous negative electrode including a second porous metal having mesopores with a specific surface area per unit volume of 450 m ² / cm ³ or more and made of a metal different from the first porous metal; The electric double layer capacitor according to claim 1, further comprising:   5. The electric double layer capacitor according to claim 1, wherein a diameter of the mesopore is 2 nm or more and 30 nm or less.   The electric double layer capacitor according to claim 1, wherein the electrolyte contains electrolyte ions having a diameter of 2 nm or less.   The electric double layer according to any one of claims 1 to 6, wherein the porous metal is made of at least one metal selected from the group consisting of nickel, copper, iron, and cobalt. Capacitor. A porous electrode for an electric double layer capacitor composed of a porous metal in which mesopores having a specific surface area per unit volume of 450 m ² / cm ³ or more are formed.

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