JP6360313B2 - Manufacturing method of polarizable electrode - Google Patents

Description

The present invention relates to a process for producing an electric double layer capacitor min polarity electrodes that are used to.

2. Description of the Related Art Conventionally, as a device for accumulating electric energy, an electric double layer capacitor is known that includes a pair of polarizable electrodes and an electrolytic solution and uses an interface electric double layer between the polarizable electrode and the electrolytic solution. The electric double layer capacitor performs charging / discharging by movement of electrolyte ions, and has a feature that it is suitable for applications in which rapid charging / discharging is repeated as compared with a chemical battery with chemical reaction.
In general, granular and fibrous activated carbon is mainly used for the polarizable electrode used in the electric double layer capacitor, and these are manufactured from synthetic resin such as phenol resin or natural material such as wood. Since these activated carbons have a high specific surface area, they are optimal as polarizable electrode materials. However, since the conductivity is low, it is necessary to add a conductive material such as furnace black or acetylene black. When producing a polarizable electrode from these mixed powders, it is necessary to use a binder for binding carbon particles. Thereafter, it is obtained by dispersing in methanol or water to form a slurry, applying it to a current collector, and drying.

  However, when a polarizable electrode is produced by this method, an increase in electrical resistance due to the non-conductivity of the binder is a problem. Therefore, in order to solve the above problems, the composition of the binder used for the polarizable electrode was reviewed, and a binder composed of a water-soluble polymer and a plasticizer was added to the activated carbon powder in an amount of 1 to 10% by weight. A technique using carbon black or ketjen black is disclosed (for example, see Patent Document 1).

JP 2004-111719 A

The technique described in Patent Document 1 uses a polarizable electrode composed of activated carbon powder, a binder made of a water-soluble polymer and a plasticizer, and a conductive material. It can be reduced more than the electrode, and has a certain effect on the reduction of electric resistance. Ideally, however, it is desirable not to use any binder with low conductivity for the production of polarizable electrodes. Furthermore, in order to improve the electrical conductivity of the polarizable electrode, it is necessary to improve the electrical conductivity of the activated carbon particles.
The present invention has been made in view of the above circumstances, and its object is to provide a method of manufacturing a conductivity capable improving a partial polar electrode without using a low conductivity binder.

In order to solve the above-described problem, a method for manufacturing a polarizable electrode according to the present invention includes a first carbon material particle having a capacitance and / or a pseudo capacitance, and a second carbon material particle having conductivity. Then, after further performing one or more mechanochemical treatments selected from mechanical milling, mechanofusion, and hybridization , they are integrated by discharge plasma sintering , and a binder for binding carbon particles to each other. It is produced without using a binder having low conductivity including a binder composed of a water-soluble polymer and a plasticizer . According to this configuration, it becomes possible to produce a polarizable electrode without using a binder having low conductivity, and a polarizable electrode exhibiting excellent conductivity can be obtained.

Main crab Carmi ring, mechanofusion, since one or more of mechanochemical treatment selected from the hybridization is carried out, easily adhere to the first carbon material and the second carbon, expected further improvement in electrical conductivity.

  In the above configuration, the first carbon material is activated carbon or the same material as the second carbon material, and the second carbon material is carbon black, graphite, glassy carbon, carbon nanowire, carbon nanotube, carbon whisker. Or it is preferable that it is a graphite whisker. According to this configuration, a polarizable electrode having good conductivity can be obtained using a widely spread material.

In the present invention, the conductivity can be improved without using a binder having low conductivity .

It is the figure which showed the SEM image of the polarizable electrode which concerns on the Example of this invention. It is the figure which showed the SEM image of the polarizable electrode which concerns on a comparative example.

The polarizable electrode of the present invention is manufactured by a discharge plasma sintering method after mixing particles of a first carbon material having a capacitor function and particles of a second carbon material having conductivity. This makes it possible to integrally form a polarizable electrode without using a binder having low conductivity and to obtain excellent conductivity, which is advantageous for improving the performance of the electric double layer capacitor.
Further, after mixing the particles of the first carbon material and the particles of the second carbon material, it is desirable to further apply one or more mechanochemical treatments selected from mechanical milling, mechanofusion, hybridization, and the like. Thereby, it becomes easy to adhere the particles of the first carbon material having a capacitor function and the particles of the second carbon material having conductivity, and further improvement in conductivity can be expected.

  When performing mechanical milling, the milling time (treatment time) is within a time range in which the second carbon particles are attached to the first carbon material particles and the carbon is prevented from being peeled off due to the destruction of one of the carbon materials. Is set. In this embodiment, milling time of 1 hour or more and 12 hours or less was desired. In less than 1 hour, the particles of the first carbon material and the second carbon particles do not adhere sufficiently, and in 12 hours or more, the first carbon material is broken and the adhered carbon materials are peeled off. End up.

Here, mechanical milling is also called mechanical alloying or ball milling, and it is finely mixed by repeatedly causing folding and rolling of powders using ball collision energy during ball milling in an inert atmosphere. I will do it.
On the other hand, in mechano-fusion, the powder raw material put in the rotating container is pressed and fixed inside by a centrifugal force, and receives a strong compression / shearing force between the inner pieces having different curvature radii. . In the hybridization, the surface of the fine particles is dry-modified and modified with fine particles using a force mainly composed of an impact force while dispersing the raw material in a high-speed air stream.
When mechanofusion and hybridization are performed, the number of rotations of the container into which the sample is put is increased, so that the processing time can be shorter than that in the case of performing mechanical milling.

In the case of mechanofusion, the treatment time is preferably about 15 to 90 minutes, depending on the number of rotations of the container. A device manufactured by Hosokawa Micron can be used.
In the case of hybridization, the treatment time can be shorter than that of mechanofusion, and the treatment time is preferably about 5 to 60 minutes. A device manufactured by Nara Machinery Co., Ltd. can be used.

In the present invention, a carbon material having a capacitance and / or pseudo capacitance is applied to the first carbon material. Specifically, activated carbon, carbon black, graphite and the like are recommended. The particle size of the first carbon material is preferably 3 μm to 30 μm.
As the second carbon material, a carbon material having excellent conductivity is applied. Specifically, carbon black (Ketjen black, acetylene black, furnace black, etc.), graphite, glassy carbon, carbon nanowire, carbon nanotube, which is highly conductive and easily adheres to the particle surface of the first carbon material, It is preferable to use at least one selected from the group of carbon whiskers and graphite whiskers.
Further, it is preferable to use a second carbon material having a particle size smaller than that of the first carbon material.
Examples of the present invention are shown below.

A polarizable electrode was manufactured by the following procedure. A predetermined amount of activated carbon (first carbon material) having an average particle diameter of 10 μm and a predetermined amount of furnace black (second carbon material) having an average particle diameter of 0.1 μm are rotated at a rotational speed of 122 rpm and a holding time of 6 hours in a ceramic pot. Mix under conditions. Thereafter, using a milling apparatus that uses balls as grinding media, 100 ceramic balls having a media diameter of 5 mm and 0.1 ml of methanol are added, and milling is performed under the condition of a rotational speed of 122 rpm. As the milling device, a table-top pot mill turntable (TYPE ANZ-50S) manufactured by Nippon Ceramics Co., Ltd. was used. By this milling, furnace black particles adhere to the activated carbon surface.
In this milling step, the blending ratio of activated carbon and furnace black and the milling time were variously changed as shown in Table 1. A milling time of 0 hr indicates that no milling is performed.

  Next, using a discharge plasma sintering apparatus (SPS-520S) manufactured by Fuji Electric Koki Co., Ltd., sintering of the mixed powder in which the mixing ratio and milling time of the activated carbon and furnace black listed in Table 1 were variously changed. The polarizable electrodes of Examples 1 to 18 having a thickness of 1 mm and a diameter of 20 mm were manufactured. The sintering was performed by filling 0.5 g of the mixed powder into a graphite mold, sintering temperature 1373 K, pressing force 70 MPa, and holding time 300 seconds.

  Next, the electrical conductivity (S · cm) of the polarizable electrodes of Examples 1 to 18 produced was measured. The measurement was performed by a four-probe method using a resistivity meter Loresta GP (MCP-T610) and a four-probe probe (RMH110) manufactured by Mitsubishi Chemical Corporation. Loresta is a registered trademark. Subsequently, a constant current charge / discharge test using a beaker cell was performed on each of the polarizable electrodes, and the capacitance (F / g) was measured. The capacitance was calculated by the following formula (1).

As the working electrode, a polarizable electrode was used, and the polarizable electrode and the separator were stacked on glassy carbon in this order and fixed by being sandwiched between acrylic plates. A platinum plate was used as the counter electrode, and a mercury / mercury sulfate electrode was used as the reference electrode. The electrolyte used was dilute sulfuric acid with a specific gravity of 1.285.
The constant current charge / discharge test was performed in a 25 ° C. water tank using a solartron 1286 type manufactured by Toyo Technica Corporation. The test conditions were 2 cycles in the range of -1.2 V to -0.6 V, and the current density was 50 mA / g.

(Comparative example)
After dry mixing 50 g of activated carbon (first carbon material) with an average particle size of 10 μm and 10 g of furnace black (second carbon material) with an average particle size of 0.1 μm, 15 g of polychloroprene as a binder and carboxy as a thickener Using 130 g of methyl cellulose (CMC) and 40 g of water as a dispersion medium, these were mixed with a mixer to produce a slurry. Then, this slurry was apply | coated on the acrylic board, it was made to dry for 12 hours at the drying temperature of 60 degreeC, and the polarizable electrode of the comparative example 19 of thickness 0.1mm was manufactured. The conductivity and capacitance were calculated by the same method as in the example.
The test results of Examples 1 to 18 and Comparative Example 19 are shown in Table 1.

As is apparent from Table 1, Examples 1 to 18 produced by a discharge plasma sintering apparatus without using a binder and a thickening material for Comparative Example 19 showed a significant improvement in conductivity.
Cross sections of these polarizable electrodes were observed with a scanning electron microscope (SEM). FIG. 1 shows an SEM photograph of Example 5 as an example, and FIG. 2 shows an SEM photograph of Comparative Example 19. As shown in FIG. 2, in the polarizable electrode of the comparative example, it was confirmed that the activated carbon and furnace black were adhered via a binder. However, there was a portion where the activated carbon particle surface was exposed. It can be seen that is not uniformly dispersed.

On the other hand, in the polarizable electrode of the example shown in FIG. 1, it was confirmed that furnace black adhered directly and uniformly to the surface of the activated carbon particles.
Moreover, the tendency for electrical conductivity to improve was seen as the processing time of mechanical milling became long. This is thought to be because furnace black (second carbon material) was dispersed by milling and adhered uniformly to the surface of the activated carbon (first carbon material), or the activated carbon was crushed due to an increase in milling time, and the density was further improved. It is done.

  However, the improvement in the conductivity due to the milling time reached a peak at 12 hours, and the conductivity decreased after 13 hours. This is thought to be because the activated carbon particles were destroyed by milling, and the adhered carbon particles were peeled off, resulting in insufficient formation of conductive paths. In addition, about the mixing ratio of activated carbon and furnace black, although electrical conductivity fell, so that the ratio of furnace black became small, it turned out that electrical conductivity can be improved by performing mechanical milling.

Moreover, even when the blending ratio of activated carbon and furnace black is changed to 1: 1, 5: 1, and 20: 1 as shown in Table 1, the polarizable electrodes of the examples all have high conductivity and Capacitance was obtained. In addition, as shown in Table 1, the higher the ratio of activated carbon having a capacitor function, the higher the capacitance, and the higher the ratio of furnace black with excellent conductivity, the higher the conductivity. there were. Therefore, it was possible to adjust the capacitance and conductivity obtained to some extent by adjusting the blending ratio.
As for the mixing ratio of activated carbon and furnace black, the conductivity decreases as the ratio of furnace black decreases, but it has been found that the conductivity can be improved by performing mechanical milling.

  In the above-described embodiment, an example in which mechanical milling was performed as a mechanochemical treatment after mixing the particles of the first carbon material and the particles of the second carbon material was shown. However, instead of mechanical milling, mechanofusion, high In the case of hybridization, the conductivity of the polarizable electrode was confirmed to be improved as in the case of mechanical milling.

  In the above embodiment, activated carbon is selected as the first carbon, furnace black is selected as the second carbon, and these are mixed. However, instead of the furnace black of the second carbon, other carbon black, graphite When glassy carbon, carbon nanowires, carbon nanotubes, or carbon whiskers were mixed, improvement in the conductivity of the polarizable electrode was confirmed as in the case of furnace black.

As described above, in the present embodiment, the first carbon material particles having a capacitor function and the second carbon material having conductivity equal to or higher than that of the first carbon material and finer than the first carbon material. Since the polarizable electrode was manufactured by mixing by the discharge plasma sintering method after mixing with the particles, it became possible to manufacture the polarizable electrode without using a low-conductivity binder. Can be obtained. As a result, it is possible to provide an electric double layer capacitor excellent in quick charge characteristics and large current discharge characteristics.
Further, since the second carbon material particles are made finer than the first carbon material particles, the second carbon material can be easily adhered to the surface of the first carbon material. Note that the second carbon material may not be finer than the first carbon material as long as adhesion is possible.

In addition, after the particles of the first carbon material and the particles of the second carbon material are mixed, one or more mechanochemical treatments selected from mechanical milling, mechanofusion, and hybridization are further performed. It becomes easy to adhere 2 carbon materials, and further improvement in electrical conductivity can be expected.
In addition, the processing time when performing the mechanochemical treatment is a time range in which the particles of the first carbon material and the particles of the second carbon are adhered and the separation of the carbon materials due to the destruction of one of the carbon materials is suppressed. Therefore, the first and second carbon materials can be attached and the destruction can be suppressed, which is advantageous for further improving the conductivity. In this case, it becomes easy to secure the capacitance by suppressing the destruction of the first carbon material.

  The first carbon material is the same as the activated carbon or the second carbon material, and the second carbon material is carbon black, graphite, glassy carbon, carbon nanowire, carbon nanotube, carbon whisker, or graphite whisker. Therefore, it is possible to obtain a polarizable electrode having a good conductivity by using a widely spread material.

The above-described embodiment is merely an aspect of the present invention, and can be arbitrarily modified and applied without departing from the gist of the present invention. For example, mechanical milling, mechanofusion, and hybridization performed as mechanochemical treatment are not limited to those described in the above examples. For example, conditions such as the rotational speed of mechanical milling may be changed, or alumina balls may be used instead of ceramic balls.
Further, the conditions for the discharge plasma sintering can be changed. For example, in the above-described embodiment, the sintering temperature of the discharge plasma sintering is 1373K, but the inventors have confirmed that excellent conductivity can be obtained even when the sintering temperature is 1873K.

Claims (2)

One selected from mechanical milling, mechanofusion, and hybridization after mixing particles of the first carbon material having electrostatic capacity and / or pseudo-capacitance and particles of the second carbon material having conductivity. After performing the above mechanochemical treatment, use a binder with low conductivity, including a binder for binding carbon particles and a binder composed of a water-soluble polymer and a plasticizer, integrated by discharge plasma sintering. A method for producing a polarizable electrode, comprising: The first carbon material is activated carbon or the same material as the second carbon material, and the second carbon material is carbon black, graphite, glassy carbon, carbon nanowire, carbon nanotube, carbon whisker or graphite whisker. The method for producing a polarizable electrode according to claim 1.