JP2014078593A - Electric double layer capacitor, and porous electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel and improved electric double layer capacitor which makes possible to increase an electrostatic capacitance per unit volume, i.e. an energy density in comparison to those achieved in the past while keeping the advantage of an electric double layer capacitor.SOLUTION: To solve the above problem, an electric double layer capacitor is provided according to one aspect of the invention, which comprises: a porous electrode having a half-value width of a maximum peak of one degree or larger where the X-ray diffraction intensity reaches the maximum; and an electrolyte including electrolytic ions capable of being adsorbed and released by 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 having a maximum half-value width of 1 degree or more at which the X-ray diffraction intensity is maximum, and adsorption / desorption to the porous electrode are possible. An electric double layer capacitor is provided, comprising an electrolyte containing electrolyte ions.

  According to this aspect, the electric double layer capacitor has a porous electrode having a half-value width of the maximum peak of 1 degree or more. Accordingly, since the pores in the porous electrode are further subdivided, the mesopores are increased, and consequently the specific surface area per unit volume of the mesopores is increased. Thereby, the electric double layer capacitor can improve the electrostatic capacity per unit volume, that is, the energy density, as compared with the conventional case.

  Here, the porous electrode may contain at least one kind of metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt.

  According to this aspect, since the porous electrode contains at least one metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt, the specific surface area per mesopore unit volume is easily increased. be able to. Therefore, the energy density of the electric double layer capacitor is improved as compared with the conventional case.

  The porous electrode may include mesopores, and the diameter of the mesopores may be 2 nm or more and 30 nm or less.

  According to this viewpoint, since the diameter of the mesopores is 2 nm or more and 30 nm or less, the electrolyte ions are effectively adsorbed and desorbed inside the mesopores. Therefore, 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, since the electrolyte contains electrolyte ions having a diameter of 2 nm or less, the electrolyte ions are effectively adsorbed and desorbed inside the mesopores. Therefore, the energy density and output characteristics of the electric double layer capacitor are improved as compared with the conventional case.

  According to another aspect of the present invention, the porous structure for an electric double layer capacitor has an amorphous phase in which the half-value width of the maximum peak at which the X-ray diffraction intensity is maximum is 1 degree or more. An electrode is provided.

  According to this aspect, the porous electrode has an amorphous phase in which the half width of the maximum peak at which the X-ray diffraction intensity is maximum is 1 degree or more. Therefore, by applying the porous electrode to the electric double layer capacitor, the capacitance per unit volume of the electric double layer capacitor is increased, and consequently the energy density is improved.

  According to another aspect of the present invention, the X-ray diffraction intensity includes 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. For an electric double layer capacitor comprising: producing an alloy having a peak half-width of 0.9 degrees or more, and treating the alloy with an acid or an alkaline solution. An electrode manufacturing method is provided.

  According to this aspect, a porous electrode having a maximum peak half-value width of 1 degree or more is generated by treating an alloy having a maximum peak half-value width of 0.9 degrees or more with an acid or an alkaline solution. be able to. Therefore, by applying the porous electrode to the electric double layer capacitor, the capacitance per unit volume of the electric double layer capacitor is increased, and consequently the energy density is improved.

  Here, the first metal may include at least one metal selected from the group consisting of aluminum, lead, tin, and zinc.

  According to this aspect, since the first metal can be easily removed from the alloy, the porous electrode can be easily manufactured.

  Further, the second metal may include at least one metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt.

  According to this aspect, since the porous electrode contains at least one metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt, the specific surface area per mesopore unit volume is easily increased. be able to. Therefore, the energy density of the electric double layer capacitor is improved as compared with the conventional case.

  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. Specifically, the porous metal has a maximum peak half width of 1 degree or more. Accordingly, since the pores in the porous electrode are further subdivided, the mesopores are increased, and consequently the specific surface area per unit volume of the mesopores is increased. Thereby, the electric double layer capacitor can improve the electrostatic capacity per unit volume, that is, the energy density, 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.

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 material. 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 a graph which shows the relationship between X-ray diffraction angle 2 (theta) and diffraction intensity, such as an alloy after mechanical alloying. It is the graph which expanded and displayed the maximum peak part of FIG. It is a graph which shows the correspondence of a half value width and an electrostatic capacitance.

  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. Specifically, the electric double layer capacitor has a porous electrode having a half width of the maximum peak of X-ray diffraction intensity of 1 degree or more. Hereinafter, embodiments of the present invention will be described.

(Configuration of electric double layer capacitor)
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 (porous positive electrode) 11 made of a porous material 20 and an anode electrode (porous material) made of a porous material 20. Negative electrode) 12 and an electrolyte 13 disposed between these electrodes.

  As shown in FIG. 2, the porous material 20 is made of a porous metal having mesopores 22 formed therein. 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 electrolyte 13 includes electrolyte ions that can be adsorbed to and desorbed from the porous positive electrode 11 and the porous negative electrode 12. The type of electrolyte ion is not particularly limited, and any electrolyte ion may be used as long as it is applied to a known electric double layer capacitor. 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. In the present embodiment, the diameter of the electrolyte ion means the diameter of the solvated electrolyte ion.

  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. FIG. 3 shows the pore size distribution in the porous copper. 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 of FIG. 3 is obtained by immersing a Cu—Al alloy (50:50 mass%) having an average diameter (average particle diameter) of 10 μm in a 1N sodium hydroxide aqueous solution at 70 ° C. for 3 hours, thereby After removing aluminum, it was obtained by washing with water and vacuum drying. In addition, the porous material 20 of this embodiment forms the amorphous phase in such porous copper. Details will be described later.

  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, electrolyte ions can be easily adsorbed and desorbed on the porous copper of FIG. 3, but it is not easy to adsorb and desorb electrolyte ions on the activated carbon of FIG.

  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. In addition, the manufacturing method of the electric double layer capacitor using porous copper and activated carbon, and the measuring method of an electrostatic capacitance were the same as that of Example 1 mentioned later, and the same thing was used for the positive electrode and the negative electrode. 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. In other words, the specific surface area of the mesopores that easily adsorb electrolyte ions is not a simple specific surface area but is a factor that substantially controls the capacitance.

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. In the case of conventional activated carbon, the specific surface area per unit volume of mesopores does not exceed 450 m ² / cm ³ . This may be because the specific surface area of conventional activated carbon decreases when the mesopore ratio is increased.

On the other hand, the upper limit value of the specific surface area per unit volume of mesopores theoretically changes according to 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.

In formula (3-1), L _n is the diameter (m) of the electrolyte ion.

  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. That is, the preferable upper limit value of the specific surface area per unit volume of mesopores varies depending on the diameter of the electrolyte ions.

  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, when the diameter of the electrolyte ions is 2 nm, the capacitance should start to decrease at a specific surface area per mesopore unit volume of 1500 m ² / cm ³ . However, since the electrolyte ions are not actually spheres, when they are close to the same size as the mesopores, it becomes difficult to enter the pores due to steric hindrance, and as shown in the figure, it is reduced at 1200 m ² / cm ^3. Turn. 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. Thus, the upper limit value of the specific surface area per unit volume of mesopores varies depending on the diameter of the electrolyte ions.

However, the contents described above are theoretical. As will be described later, the present inventor has described that the amorphous phase in which the half-value width of the maximum peak at which the X-ray diffraction intensity (that is, the intensity with respect to the X-ray diffraction angle 2θ) is the maximum is 1 degree or more is It has been found that the specific surface area per unit volume of mesopores increases dramatically. And when this inventor examined the upper limit using this technique, if the specific surface area per mesopore unit volume is 1600 m < ² > / cm < ³ > or less and the diameter of electrolyte ion is 2 nm or less, The inventors have found that a good capacitance can be obtained regardless of the particle size of the electrolyte ions. Further, the inventor of the present invention has a larger capacitance as the specific surface area per unit volume of mesopore is larger if the specific surface area per unit volume of mesopore is 450 m ² / cm ³ or more and 1600 m ² / cm ³ or less. I also found out. The diameter of the electrolyte ion is more preferably 1.5 nm or less.

Therefore, the specific surface area per mesopore unit volume of the porous material 20 is preferably 450 m ² / cm ³ or more and 1600 m ² / cm ³ or less. 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, Ti, Cu, Co, and Fe, for example. In addition, as shown in the Example mentioned later, when the porous material 20 is comprised with Ni, an electrostatic capacitance becomes large especially. However, since Ni has a large specific gravity, when the porous material 20 is made of Ni, the electric double layer capacitor 10 becomes heavy. Therefore, a part of Ni may be replaced with lightweight Ti. Further, the above theory holds when the porous material 20 constitutes an electric double layer.

  In addition, the present inventor further examined a technique for increasing the specific surface area per unit volume of mesopores, and as a result of making the porous material 20 amorphous, the specific surface area per unit volume of mesopores. It was found that can be increased. More specifically, the present inventor has described that the amorphous phase in which the half-value width of the maximum peak at which the X-ray diffraction intensity (that is, the intensity with respect to the X-ray diffraction angle 2θ) is maximum is 1 degree or more is the porous material 20. It has been found that the specific surface area per unit volume of mesopores increases dramatically. Further, the present inventor has also found that the capacitance increases as the amorphous state of the porous material 20 progresses, that is, as the half width increases.

  In addition, the following reasons can be considered as a reason why the capacitance increases when the porous material 20 is amorphized. That is, as described above, since the abundance ratio of the mesopores 22 affects the capacitance of the electric double layer capacitor 10, it is preferable that the number of mesopores 22 is large. On the other hand, since the porous material 20 becomes amorphous, the crystal structure of the porous material 20 is disturbed. For example, the pores that are macropores during the crystallization of the porous material 20 It can be subdivided into mesopores 22 by amorphization. Therefore, the mesopores 22 are increased by making the porous material 20 amorphous, and the capacitance is increased.

  From such a viewpoint, the porous material 20 includes an amorphous phase in which the half width of the maximum peak at which the X-ray diffraction intensity is maximum is 1 degree or more. The half width is more preferably 1.2 degrees or more. On the other hand, since the half width increases as the amorphization of the porous material 20 progresses, it is assumed that the upper limit of the half width is not particularly limited. It reaches a peak. It is assumed that the half width when the amorphization reaches its peak is approximately 2.6 degrees. Therefore, the substantial upper limit of the half width is about 2.6 degrees. The method for making the porous material 20 amorphous is not particularly limited, and any method may be used as long as it can disturb the crystal structure of the metal. Examples of such a method include a mechanical alloying method, a rapid solidification method, and a thermal spraying method. Details of the method of making the porous material 20 amorphous will be described later. In the present embodiment, X-ray diffraction may be performed with an arbitrary apparatus. For example, X-ray diffraction is performed by RINT2200V / PCSV manufactured by Rigaku Corporation.

  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.

(Method for producing porous material (porous metal))
Next, a method for manufacturing the porous material 20 will be described. The porous material is manufactured, for example, by any one of the two manufacturing methods listed below.

(Method of treating alloy with acid or alkaline solution)
The first production method comprises amorphizing an alloy containing 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. (First step) and a step of treating the amorphized alloy with an acid or an alkaline solution (second step). The alloy itself is manufactured by an appropriate known method (for example, a melting method).

  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.

  In this embodiment, an amorphous phase is formed in the alloy by making the alloy amorphous. That is, in the alloy before the amorphousization, the first metal exists as a relatively large crystallite (for example, a crystallite having a size of about the macropore described above). There is a possibility that the number of mesopores 22 in the porous material 20 is not sufficient only by removing. Therefore, in the present embodiment, the first alloy is dispersed in the alloy by making the alloy amorphous. Thereby, the crystallite of the first metal can be as large as the mesopores 22.

  Therefore, the first manufacturing method controls the number of mesopores 22 by controlling the size of the first metal crystallites, and also controls the size, that is, the diameter of the mesopores 22. Can do. In the first manufacturing method, the desired mesopores 22 can be manufactured also by controlling the mass ratio of the first metal and the second metal.

  The method for making the alloy amorphous is not particularly limited, and any method that can disturb the crystal structure of the metal may be used. Examples of such a method include a mechanical alloying method, a rapid solidification method, and a thermal spraying method.

  The apparatus for performing the mechanical alloying method is not particularly limited, and may be a known mill apparatus such as a planetary ball mill, a vibration mill, an attritor ball mill, or the like. As a medium of the mechanical alloying method, for example, metal or ceramic balls of various sizes are used. The container and ball may be made of a ceramic such as zirconia if the alloy dislikes impurities, but it is preferable to use a ball having a large specific gravity in order to further increase the amorphization.

  The atmosphere in the container is preferably an inert gas atmosphere such as an argon atmosphere in order to suppress oxidation of the alloy. During mechanical alloying of the alloy, the alloy generates heat due to the energy applied to the alloy. Therefore, the mechanical alloying is performed while the container is cooled after the cooling jacket is attached to the container. In addition, it is preferable to add alcohol or the like to the container in order to promote adhesion suppression and miniaturization of the alloy charged in the container.

  In the mechanical alloying method, by controlling the material of the ball, the diameter of the ball, the amount of the ball, the operation time of the mill device (the stirring time of the alloy with the ball), and the rotation speed (rpm) of the container, the half width is reduced. Can be adjusted. Specifically, the full width at half maximum increases as the specific gravity of the ball increases, the diameter of the ball increases, the amount of balls increases, the operation time increases, and the rotation speed (rpm) increases. However, as described above, the full width at half maximum reaches a certain level, so these factors also have upper limit values. For example, the operation time may be about 1 to 10 hours, more specifically about 3 to 5 hours.

Examples of the rapid solidification method include an atomizing method, a roll rapid cooling method, a strip casting method, a spray roll method, a gas injection splat method, and a spray forming method. In the rapid solidification method, amorphization is advanced by quenching the molten alloy. Therefore, in the rapid solidification method, the half width can be adjusted by controlling the cooling rate of the molten metal. The full width at half maximum increases as the cooling rate of the molten metal increases. However, as described above, the full width at half maximum reaches a certain level, so these factors also have upper limit values. Specifically, the cooling rate is desirably in the range of 10 ³ to 10 ⁸ K / s. The rapid solidification method is performed in an inert gas atmosphere such as argon or helium in order to prevent oxidation of the alloy.

  Here, the lower limit of the half width of the alloy may be 0.9 degrees. That is, when the inventor has produced the porous material 20 by removing the first metal from the alloy (that is, developing the alloy), the half width of the porous material 20 is larger than the half width of the alloy. Also found that it would be bigger. And this inventor discovered that the half value width of the porous material 20 will be 1 degree | times or more, if the lower limit of the half value width of an alloy is 0.9 degree | times. Therefore, the lower limit of the half width of the alloy may be 0.9 degrees. The lower limit of the half width of the alloy is preferably 1.1 degrees or more. The upper limit of the half-value width of the alloy is presumed to be not particularly limited, but substantially reaches its peak when amorphization proceeds to some extent. It is presumed that the half width when the amorphization reaches its peak is about 2 degrees. Therefore, the upper limit value is substantially about 2 degrees.

  In the first production method, the amorphous metal is treated with an acid or an alkaline solution (for example, the alloy is immersed in an acid or an alkaline solution), thereby removing (eluting) the first metal from the alloy. ). As a result, the portion of the alloy occupied by the first metal becomes the mesopores 22.

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 mass 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).

  In addition, it is desired to remove the first metal as much as possible to make it porous. However, the first metal may not be completely removed after the treatment but may partially remain. The immersion time is preferably 3 hours or longer. On the other hand, the upper limit time of the immersion time depends on the concentration or 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.

(Method of reducing metal compound)
The second manufacturing method is a manufacturing method in which an anion in the metal compound is removed by making the metal compound amorphous and reducing the amorphous 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.

  Further, the degree of amorphization may be the same as in the first manufacturing method. For example, the half width of the metal compound may be 0.9 degrees or more.

(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.

Next, examples will be described. In each of the following examples, the maximum peak was observed when the X diffraction angle 2θ was 44.5 degrees or in the vicinity thereof. Examples 1 to 7 are examples for producing a porous electrode by a so-called mechanical alloying method, and Example 8 is an example for producing a porous electrode by a rapid solidification method. Example 9 is an example demonstrating that there is a correspondence between the capacitance per unit volume of the electric double layer capacitor and the half width of the porous electrode.
Example 1

  First, an amorphous alloy was produced by the first step. Specifically, 50 g of Ni—Al alloy (50:50 mass%) having an average particle diameter (diameter) of 10 μm, 5 ml of methanol, and 17.5 kg of stainless steel balls having a diameter of 8 mm were added to an Attritor ball mill (Model 1- 1) from Union Process. S). Next, the inside of the ball mill was replaced with argon gas, and then the ball mill was operated at 300 rpm for 10 hours. At that time, the alloy was cooled while flowing water at 15 ° C. using a water cooling jacket. As a result of measuring the half width of the obtained alloy with an X-ray diffractometer (RINT2200V / PCSV manufactured by Rigaku Corporation), the half width of the maximum peak (main peak) was 1.78 degrees.

  Next, porous nickel was produced by the second step. Specifically, the amorphous Ni—Al alloy produced in the first step was immersed in a 1N sodium hydroxide aqueous solution at 70 ° C. for 3 hours to remove aluminum. 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 obtained. Thereafter, the porous nickel was washed with water and vacuum-dried.

Subsequently, porous nickel was exposed to a stream of 4% by volume of oxygen gas diluted with argon (oxygen gas having 4% by volume of oxygen in the total volume of oxygen gas) at room temperature for 2 hours. This produced the porous electrode. 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 143 m ² / g, the pore volume was 0.097 cm ³ / g, the mesopores were 92%, and the micropores were The remaining 8%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the above equation (2), which was 1356 m ² / cm ³ . The pore size distribution was 2 to 12 nm, and the peak value of pores (the pore size (diameter) possessed by the most pores) was 2.6 nm.

  The average pore diameter (arithmetic mean value of pore diameters) was 2.6 nm. Moreover, as a result of measuring the half width of the porous electrode with an X-ray diffractometer, the half width of the maximum peak was 1.85 degrees.

  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.

Subsequently, 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. In addition, it was mixed in a mortar. Then, the mixture was shape | molded with the tablet press, and the pellet was obtained. A cell of an electric double layer capacitor using an aluminum mesh sandwiched between aluminum mesh as a working electrode and a counter electrode (porous positive electrode and negative electrode), a reference electrode using an Ag electrode, and an electrolyte using 1M-TEA-BF4 / PC Configured. The diameters of the electrolyte ions constituting the electrodes and the electric double layer, that is, TEA and BF ₄ (diameters of solvated ions) are 1.26 nm and 1.02 nm, respectively, by simulation.

  The cell was swept in the range of -1.25 to 1.25 V at a sweep rate of 100 to 1 mv / s at room temperature using a PARSTAT 2273 manufactured by Advanced Electrochemical System. Then, the capacitance per unit volume of the electric double layer capacitor was calculated using the capacitance obtained at 1 mv / s. The results are shown in Table 1.

(Example 2)
By performing the same treatment as in Example 1 except that a Ni—Fe—Al alloy (45: 5: 50 mass%) having an average particle size of 13 μm was used as the alloy in the first step, a porous electrode (porous A nickel-iron alloy with an oxygen film formed). As a result of measuring the half width of the alloy before the development treatment, that is, the Ni—Fe—Al alloy with an X-ray diffractometer, the half width of the main peak was 1.7 degrees. Moreover, as a result of measuring the half width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffractometer, the half width of the main peak was 1.8 degrees.

The specific surface area of the porous electrode was 132 m ² / g, the pore volume was 0.093 cm ³ / g, the mesopores were 94%, and the micropores were the remaining 6%. It was 1334 m < ² > / cm < ³ > when the specific surface area per mesopore unit volume was computed using these numerical values and said (2) Formula. The average pore diameter was 2.7 nm. The pore size distribution was 2 to 14 nm, and the peak value of pores (the pore size (diameter) of the most pores) was 2.8 nm. The thickness of the inorganic compound layer was measured to be 12 nm.

(Example 3)
By performing the same treatment as in Example 1 except that a Ni—Fe—Al alloy (37: 5: 58 mass%) having an average particle diameter of 11 μm was used as the alloy in the first step, a porous electrode (porous A nickel-iron alloy with an oxygen film formed). As a result of measuring the half width of the alloy before the development treatment, that is, the Ni—Fe—Al alloy with an X-ray diffractometer, the half width of the main peak was 1.78 degrees. Moreover, as a result of measuring the half width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffractometer, the half width of the main peak was 2.64 degrees.

The specific surface area of the porous electrode was 245 m ² / g, the pore volume was 0.137 cm ³ / g, the mesopores were 89%, and the remaining micropores were 11%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the above equation (2), and it was 1592 m ² / cm ³ . The average pore diameter was 3.3 nm. Further, the pore size distribution was 2.2 to 8 nm, and the peak value of pores (the pore size (diameter) possessed by the most pores) was 2.6 nm. Moreover, the thickness of the inorganic compound layer was measured to be 10 nm.

(Example 4)
First, an amorphous alloy was produced by the first step. Specifically, 2 g of Cu—Al alloy (50:50 mass%) having an average particle diameter of 18 μm, 5 ml of methanol, and 80 g of a chrome steel ball having a diameter of 10 mm were put into a planetary ball mill P-5 manufactured by Fritsch. Subsequently, after the inside of the ball mill was replaced with argon gas, the ball mill was operated for 15 minutes at a gravitational acceleration of 100 G and operated for 15 minutes as one set for a total of 8 hours. At that time, the alloy was cooled while flowing water at 15 ° C. using a water cooling jacket. Except for these treatments, the same treatment as in Example 1 was performed. This obtained the porous electrode (what formed the oxygen film in porous copper).

  As a result of measuring the half width of the alloy before the development treatment, that is, the Cu—Al alloy, using an X-ray diffractometer, the half width of the main peak was 1.35 degrees. Moreover, as a result of measuring the half-value width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffraction apparatus, the half-value width of the main peak was 1.55 degrees.

The specific surface area of the porous electrode was 55 m ² / g, the pore volume was 0.068 cm ³ / g, the mesopores were 98%, and the micropores were the remaining 2%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the formula (2), and it was 792 m ² / cm ³ . The average pore diameter was 3.9 nm. Further, the pore size distribution was 2.5 to 11 nm, and the peak value of pores (the pore size (diameter) possessed by the most pores) was 4.2 nm. The thickness of the inorganic compound layer was measured to be 15 nm.

(Example 5)
By performing the same treatment as in Example 1 except that a Ni—Co—Al alloy (37: 5: 58 mass%) with an average particle size of 10 μm was used as the alloy in the first step, a porous electrode (porous A nickel-cobalt alloy having an oxygen film formed thereon.

  As a result of measuring the half width of the alloy before the development treatment, that is, the Ni—Co—Al alloy with an X-ray diffractometer, the half width of the main peak was 1.68 degrees. Moreover, as a result of measuring the half-value width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffractometer, the half-value width of the main peak was 2.44 degrees.

The specific surface area of the porous electrode was 221 m ² / g, the pore volume was 0.199 cm ³ / g, the mesopores were 87%, and the micropores were the remaining 13%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the formula (2), and it was 966 m ² / cm ³ . The average pore diameter was 3.5 nm. Further, the pore size distribution was 2.2 to 7 nm, and the peak value of pores (the pore size (diameter) possessed by the most pores) was 3.1 nm. The thickness of the inorganic compound layer was measured to be 11 nm.

(Example 6)
By performing the same treatment as in Example 1 except that a Ni—Ti—Al alloy (30:20:50 mass%) having an average particle size of 10 μm was used as the alloy in the first step, a porous electrode (porous A nickel-titanium alloy having an oxygen film formed thereon.

  As a result of measuring the half width of the alloy before the development treatment, that is, the Ni—Ti—Al alloy with an X-ray diffractometer, the half width of the main peak was 1.6 degrees. Moreover, as a result of measuring the half width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffractometer, the half width of the main peak was 1.7 degrees.

The specific surface area of the porous electrode was 145 m ² / g, the pore volume was 0.097 cm ³ / g, the mesopores were 94%, and the micropores were the remaining 6%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the formula (2), and it was 1405 m ² / cm ³ . The average pore diameter was 2.7 nm. The pore size distribution was 2 to 11 nm, and the peak value of pores (the pore size (diameter) of the most pores) was 3.2 nm. The thickness of the inorganic compound layer was measured to be 13 nm.

(Example 7)
By performing the same treatment as in Example 1 except that the operation time of the attritor mill was 1 hour in the first step of Example 1, a porous electrode (a porous nickel having an oxygen film formed) was obtained. It was.

  As a result of measuring the half width of the alloy before the development treatment, that is, the Ni—Al alloy with an X-ray diffractometer, the half width of the main peak was 0.92 degrees. Moreover, as a result of measuring the half width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffractometer, the half width of the main peak was 1.03 degrees. Therefore, it was proved that if the half width of the maximum peak before the development process is 0.9 degrees or more, the half width of the maximum peak after the development process is 1.0 degrees or more.

The specific surface area of the porous electrode was 89 m ² / g, the pore volume was 0.085 cm ³ / g, the mesopores were 92%, and the micropores were the remaining 8%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the formula (2), and it was 963 m ² / cm ³ . The average pore diameter was 3.2 nm. The pore size distribution was 2 to 15 nm, and the peak value of pores (the pore size (diameter) of the most pores) was 4.2 nm. The thickness of the inorganic compound layer was measured to be 12 nm.

(Example 8)
First, an amorphous alloy was obtained by the first step. That is, nickel and aluminum were mixed at a mass ratio of 50:50, and the mixture was put into an arc melting apparatus (vacuum arc melting apparatus manufactured by Nisshin Giken). And Ni-Al alloy (50:50 mass%) was prepared using the arc melting apparatus in argon gas atmosphere. The operation time of the arc melting apparatus was 10 minutes, and the current value was 200A. Next, the Ni-Al alloy was made amorphous by using a single roll quenching device manufactured by Nisshin Giken. Specifically, the Ni—Al alloy was made amorphous by spraying a molten Ni—Al alloy onto a rotating copper roll in an argon gas atmosphere and quenching. Here, the cooling rate was 10 ⁵ K / s.

  Next, 2 g of the amorphized Ni—Al alloy, 5 ml of methanol, and 80 g of silicon nitride balls having a diameter of 5 mm were put into a planetary ball mill type P-5 manufactured by Fritsch. Next, the inside of the ball mill was replaced with argon gas, and then the ball mill was operated for 15 minutes at a gravitational acceleration of 100 G, and the operation with a 15-minute pause as one set was performed for a total of 2 hours. At that time, the alloy was cooled while flowing water at 15 ° C. using a water cooling jacket. Except for these treatments, the same treatment as in Example 1 was performed. This obtained the porous electrode (what formed the oxygen film in porous nickel). The average particle diameter of the porous electrode was 14 μm.

  As a result of measuring the half width of the alloy before the development treatment, that is, the amorphized Ni—Al alloy, using an X-ray diffractometer, the half width of the main peak was 1.12 degrees. Moreover, as a result of measuring the half-value width of the alloy after the development treatment, that is, the porous electrode with an X-ray diffractometer, the half-value width of the main peak was 1.25 degrees.

The specific surface area of the porous electrode was 97 m ² / g, the pore volume was 0.082 cm ³ / g, the mesopores were 93%, and the micropores were the remaining 7%. The specific surface area per unit volume of mesopores was calculated using these numerical values and the formula (2), and it was 1100 m ² / cm ³ . The average pore diameter was 3.5 nm. Moreover, the pore size distribution was 2 to 17 nm, and the peak value of pores (the pore size (diameter) possessed by the most pores) was 4.5 nm. The thickness of the inorganic compound layer was measured to be 15 nm.

Example 9
The first step of Example 1 was performed while changing the diameter of the stainless ball, the rotation speed of the attritor ball mill, and the operation time of the attritor ball mill. Thus, the correspondence between the half width of the porous electrode and the capacitance per unit volume of the electric double layer capacitor was investigated. In Example 9, the diameter of the stainless ball was selected from 3, 5, and 10 mm. Moreover, the rotational speed of the attritor ball mill was set within a range of 100 to 300 rpm. The operation time was set within a range of 1 to 10 hours.

(Comparative example)
The same treatment as in Example 1 was performed except that activated carbon MSP20 manufactured by Kansai Thermal Chemical Co., Ltd. was used as the porous electrode. That is, the electric double layer capacitor according to the comparative example is obtained by replacing the porous electrode of the electric double layer capacitor of Example 1 with activated carbon MSP20 manufactured by Kansai Thermochemical.

(Evaluation)
Table 1 shows values obtained by normalizing the volume capacitance (capacitance per unit volume of the electric double layer capacitor) of Examples 1 to 8 in a comparative example.

  Further, FIG. 7 shows an X-ray diffraction spectrum of the alloy after mechanical alloying obtained in Example 9. A curve L1 in FIG. 7 is an X-ray diffraction spectrum of the Ni—Al alloy not mechanically alloyed in Example 1. A curve L2 is an X-ray diffraction spectrum of an alloy (an alloy before the development treatment) obtained by performing mechanical alloying in Example 9 with the diameter of the stainless ball set to 5 mm. A curve L3 is an X-ray diffraction spectrum of an alloy (an alloy before unfolding treatment) obtained by mechanical alloying in Example 9 with the diameter of the stainless ball set to 10 mm. In addition, the rotational speed at the time of obtaining the porous electrode shown by the curves L2 and L3 was 300 rpm, and the operation time was 8 hours. FIG. 8 is an enlarged view of the maximum peak of FIG. According to FIG. 8, the half widths indicated by the curves L2 and L3 are both 0.9 degrees or more, specifically, 1.27 degrees and 1.48 degrees, respectively. Moreover, the half widths of the porous electrodes obtained by developing the alloys indicated by the curves L2 and L3 were 2.28 degrees and 2.51 degrees, respectively. According to FIG. 7, FIG. 8, and Example 9, the half-value width of the porous electrode can be made 0.9 degrees or more by mechanical alloying, and the half-value width is made 1.0 degree or more by the subsequent development process. It was confirmed that the full width at half maximum increases as the ball diameter increases.

  FIG. 9 shows the correspondence between the half width of the porous electrode and the capacitance per unit volume of the electric double layer capacitor. The horizontal axis of FIG. 9 indicates the half-value width of the maximum peak of the porous electrode, and the vertical axis indicates the volume capacitance of the electric double layer capacitor (normalized by the value of the comparative example). The point P1 shows the measured value obtained in Example 9, and the curve L4 is a curve obtained by connecting the points P1.

  According to Table 1 and FIGS. 7 to 9, the volume capacitance of the electric double layer capacitors produced using the porous electrodes of Examples 1 to 8 is the same as that of the electric carbon produced using the activated carbon of the comparative example. Compared to the multilayer capacitor, it was significantly improved by 2.1 to 3.4 times. Such an effect is obtained by reducing the crystallite size of aluminum by making the alloy crystalline amorphous, that is, by reducing the pore size generated when aluminum is removed with an alkaline solution. It is inferred that this is an effect.

More specifically, it is presumed that the specific surface area per unit volume of mesopores of the porous electrode is increased by the above treatment, and as a result, the capacitance is increased. Furthermore, the average pore diameter of the porous electrodes of Examples 1 to 8 is 2.6 to 3.9 nm. On the other hand, the diameter of BF ₄ ions (diameter of ions solvated with PC) used in the electrolyte is 1.02 nm and the diameter of TEA ions (diameter of solvated ions) is 1.26 nm by simulation. Therefore, the average pore diameter of the porous electrodes of Examples 1 to 8 approached the solvated electrolyte ion diameter. For this reason, it is presumed that the capacitance has increased.

Moreover, according to Examples 1-8, when the specific surface area per mesopore unit volume is 450 m ² / cm ³ or more and 1600 m ² / cm ³ or less, the capacitance per unit volume of the electric double layer capacitor Was confirmed to increase. It was also confirmed that the capacitance per unit volume of the electric double layer capacitor increased as the specific surface area per unit volume of mesopores increased.

  Further, according to FIGS. 7 to 9, the volume capacitance becomes larger than that of the comparative example from the vicinity where the half width exceeds 0.8, and the volume electrostatic capacity is increased when the half width becomes 1 degree or more. The capacity was clearly larger than the comparative example. In addition, when the half width was 1.2 degrees or more, the difference in volume capacitance from the comparative example was further increased. Further, according to FIG. 9, it was confirmed that the upper limit value is not particularly limited because the volume capacitance increases as the half width increases. However, as described above, it is presumed that the half-value width will reach its peak when it increases to a certain value (about 2.6 degrees).

  As described above, according to the present embodiment, the electric double layer capacitor 10 has the porous electrode whose half-value width of the maximum peak is 1 degree or more. Therefore, the electric double layer capacitor 10 can increase the specific surface area per unit volume of the mesopores, and by extension, the capacitance per unit volume, that is, the energy density can be improved as compared with the conventional case.

  Furthermore, since the porous electrode contains at least one metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt, the specific surface area per mesopore unit volume can be easily increased. Therefore, the energy density of the electric double layer capacitor is improved as compared with the conventional case.

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

  Further, since the electrolyte contains electrolyte ions having a diameter of 2 nm or less, the electrolyte ions are effectively adsorbed and desorbed inside the mesopores. Therefore, the energy density and output characteristics of the electric double layer capacitor are improved as compared with the conventional case.

  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 22 Mesopore

Claims (8)

A porous electrode having a maximum half-value width of 1 degree or more at which the X-ray diffraction intensity is maximum;
And an electrolyte containing electrolyte ions that can be adsorbed and desorbed on the porous electrode.   The electric double layer capacitor according to claim 1, wherein the porous electrode includes at least one metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt. The porous electrode includes mesopores;
The electric double layer capacitor according to claim 1, wherein the mesopore has a diameter of 2 nm to 30 nm.   The electric double layer capacitor according to claim 1, wherein the electrolyte contains electrolyte ions having a diameter of 2 nm or less.   A porous electrode for an electric double layer capacitor, characterized by having an amorphous phase with a half-value width of a maximum peak at which the X-ray diffraction intensity is maximized being 1 degree or more. A half value of a peak that includes 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 and has the maximum X-ray diffraction intensity. Producing an alloy having a width of 0.9 degrees or more;
Treating the alloy with the acid or alkaline solution; and a method for producing an electrode for an electric double layer capacitor.   The method for producing an electrode for an electric double layer capacitor according to claim 6, wherein the first metal includes at least one metal selected from the group consisting of aluminum, lead, tin, and zinc. . The electrode for an electric double layer capacitor according to claim 6 or 7, wherein the second metal includes at least one metal selected from the group consisting of nickel, titanium, copper, iron, and cobalt. Manufacturing method.

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