WO2006088004A1

WO2006088004A1 - Electrode material for electric double layer capacitor and method for producing same

Info

Publication number: WO2006088004A1
Application number: PCT/JP2006/302494
Authority: WO
Inventors: Tomoya Iwasaki; Hitoshi Hashizume; Makoto Shimizu
Original assignee: Shinano Kenshi Kabushiki Kaisha
Priority date: 2005-02-21
Filing date: 2006-02-14
Publication date: 2006-08-24
Also published as: CN1942985A; JPWO2006088004A1

Abstract

Disclosed is an electrode material for electric double layer capacitors wherein carbon nanofibers are uniformly dispersed. This electrode material enables to reduce the internal resistance, and is suitable for high-rate charge/discharge with a large current. Specifically disclosed is an electrode material for electric double layer capacitors which is composed of a composite carbon material obtained by dispersing carbon nanofibers in a solution wherein a polymer material having an atomic group including a heteroatom such as a nitrogen, oxygen or sulfur atom in a main chain or side chain is dissolved, drying the dispersion solution, and then firing the dried material at 500-3000˚C in a non-oxidizing atmosphere.

Description

Specification

Electric double layer capacitor electrode material and manufacturing method thereof

Technical field

TECHNICAL FIELD [0001] The present invention relates to an electric double layer capacitor electrode material, a manufacturing method thereof, and an electric double layer capacitor.

Background art

An electric double layer capacitor has been used as a small power storage device for a backup power source such as a portable device. However, in recent years, high power density capacitors are required for hybrid vehicles and fuel cell vehicles from the viewpoint of environmental issues. There is also a need for a capacitor that can extract a large current in a short time as a measure against momentary power interruption. Both of these are important to reduce internal resistance. For this reason, it is known that a conductive material such as carbon black is added to the activated carbon material as a polarizable electrode material to increase the conductivity and decrease the internal resistance. Furthermore, attempts have been made to reduce internal resistance by increasing the electrical conductivity by adding carbon nanofibers as a conductive material (Japanese Patent Laid-Open No. 2001-135554).

Patent Document 1: JP 2001-135554

Disclosure of the invention

[0003] However, even if carbon nanofibers are added as a conductive material, there is a problem that they cannot be uniformly dispersed and the contact resistance between the carbon nanofibers and the activated carbon material increases.

Accordingly, the present invention has been made to solve the above-described problems, and the object of the present invention is to provide an electric double layer suitable for high-current high-speed charge / discharge, which can uniformly disperse force-bonded nanofibers, reduce internal resistance, and It is in providing a capacitor electrode material and a manufacturing method thereof. The electrode material for an electric double layer capacitor according to the present invention is in a solution in which a polymer substance in which an atom group containing a helium atom such as nitrogen, oxygen or sulfur is present in the main chain or side chain is dissolved. Carbon nanofibers are dispersed, the dispersion solution is dried, and the dried product is also baked in a non-acidic atmosphere at 500 to 3,000 ° C. to obtain a composite carbon material force.

The composite carbon material is subjected to activation treatment, and a large number of pores are formed on the surface. It is characterized by.

In addition, the electrode material for the electric double layer capacitor is characterized by having a granularity of 1 μm to 1000 m.

The amount of carbon nanofibers relative to the polymer material is 1-30 wt%.

The polymer substance is characterized by comprising an amino acid, a protein having an amino acid strength, or a peptide.

In addition, the polymer material is also characterized by a silk material strength.

In addition, the composite carbon material includes a nitrogen element.

The carbon nanofiber is a single-layer, double-layer, or multi-layer carbon nanotube, a cap-stacked carbon nanotube, or a carbon nanohorn.

The electric double layer capacitor according to the present invention is a pair of electrode bodies made of a current collector and a polarizable electrode, a separator, and an electric double layer capacitor made of electrolytic solution. 9. An electrode material for an electric double layer capacitor as set forth in any one of 9 above.

In addition, the method for producing an electric double layer capacitor according to the present invention includes a polymer in which a polymer substance in which an atomic group containing a hetero atom such as nitrogen, oxygen, or sulfur is present in a main chain or a side chain is dissolved. The method includes a step of dispersing carbon nanofibers in a solution derived from a substance, a step of drying the dispersion solution, and a step of firing a dried product to form a composite carbon material.

The dried product is preferably pulverized and then calcined.

Alternatively, the composite carbon material formed by firing the dried product may be crushed into particles.

It is characterized in that carbon nanofibers are dispersed in an amount of 1 to 30 wt% with respect to the polymer substance.

It is characterized by using a silk material as a polymer material.

The invention's effect According to the present invention, the carbon nanofibers are uniformly dispersed and the carbide derived from the polymer material and the carbon nanofibers 1 are in close contact with each other, so that the internal resistance can be sufficiently reduced, and a high-current, high-speed Suitable for charging / discharging, high output electric double layer capacitor can be obtained.

Brief Description of Drawings

[0005] FIG. 1 is a Raman spectrum diagram of a fired product when coarse-grained silk is fired at a high temperature of 2000 ° C.

[Fig. 2] Raman spectrum of fired product when coarse silk is fired at a high temperature of 700 ° C.

[Fig. 3] Raman spectrum of the fired product when coarse silk is fired at a high temperature of 1000 ° C.

[Fig. 4] Raman spectrum of fired product when coarse silk is fired at a high temperature of 1400 ° C.

[Figure 5] SEM photograph of composite carbon material.

FIG. 6 is a graph showing measured values of powder resistance of a composite carbon material.

FIG. 7 is a graph showing capacitor characteristics (volume capacity) of Examples and Comparative Examples.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail.

The electric double layer capacitor is composed of a pair of electrode bodies composed of a current collector and a polarizable electrode, a separator, and an electrolyte (the structure itself can take various known structures and is not particularly shown).

This embodiment is characterized by the electrode material included in the polarizable electrode.

That is, in this electrode material, carbon nanofibers are dispersed in a solution in which a polymer substance in which atomic groups containing heteroatoms such as nitrogen, oxygen, and sulfur are present in the main chain or side chain is dissolved, The dispersion solution is dried, and the dried product is composed of a composite carbon material fired in a non-oxidizing atmosphere at 500 ° C. to 3000 ° C.

A silk material can be used for the polymer material.

The silk material is a general term for woven fabrics, knitted fabrics, powders, cotton, yarns, etc., which are rabbits or barbaric. These can be used alone or in combination.

These silk materials have a higher-order protein structure, and there are coordinating groups containing various amino acid residues on the surface (including the folded inner surface). As the polymer material, in addition to the silk material described above, a polymer material in which an atomic group containing donor atoms such as nitrogen, oxygen, and sulfur is present in the main chain or side chain can be used.

As such a polymer material, proteins such as keratin, milk protein, corn protein and collagen can also be used.

Specifically, carbon nanofibers are added to a solution in which the above polymer material is dissolved and dispersed well. To disperse the carbon nanofibers, apply ultrasonic vibration.

The amount of carbon nanofiber added to the polymer material is preferably about 1 to 30 wt%.

As the carbon nanofiber, single-walled, double-walled, or multi-walled carbon nanotubes, cap-stacked carbon nanotubes, or carbon nanohorns can be used. Next, the mixed solution is naturally dried or heated to about 80 ° C. to remove moisture and dried.

Next, this dried product is fired at a temperature of 500 ° C. to 3000 ° C. to obtain a composite carbon material. Next, an activation treatment is performed in which this composite carbon material is exposed to high-temperature steam at about 700 ° C. By this activation treatment, a large number of pores are formed on the surface of the carbide derived from the polymer material in the composite carbon material. As a result, the surface area is increased, which is suitable as an electrode material for the electric double layer capacitor. The pores are extremely small with a diameter of 1 Onm or less, and as a result, the composite carbon material has a surface area as large as 100 to 3000 m ² Zg.

Next, the activated composite carbon material is pulverized to a size of about 1 μπι to 1000 / ζ m, preferably about 5 m to 10 m. By pulverizing in this way, it is possible to obtain a polarizable electrode by binding with a binder such as PTFE (polytetrafluoroethylene). The dried product dried in the above drying step may be pulverized and fired. In addition, as the polarizable electrode, only the composite carbon material formed in the above-mentioned granular shape may be used, but other conductive materials such as activated carbon and carbon black may be used in combination.

The mixing ratio of the electrode material is not particularly limited. For example, the composite carbon material of the present embodiment: 15 to 90 wt%, conductive material such as carbon black 3 to 15 wt%, PTFE3 to 2 Owt%, CMC ( (Carboxymethylcellulose) 3 to 20 wt% is preferable.

The firing temperature is more preferable as the firing is performed at a higher temperature because the carbide derived from the polymer material becomes graphite and the conductivity is improved. Specifically, when it is fired at 1400 ° C or higher, it becomes a carbide with good conductivity.

On the other hand, when fired at a temperature lower than 1400 ° C, a large amount of nitrogen components remain in the polymer (especially silk material), and the presence of these functional groups causes electrons to accumulate, which immediately results in the capacitor. There is also an advantage that the capacity is improved. In terms of conductivity, carbon nanofibers make up for it. If necessary, adjust the conductivity by adding a conductive material such as carbon black.

In the present embodiment, as described above, since the carbon nanofibers are dispersed in the polymer solution, the dispersibility of the carbon nanofibers becomes uniform.

And since this polymer solution is dried and fired, the carbon nanofibers are bound by the carbide derived from the polymer, and the carbon nanofibers are also in contact with each other, so that the contact resistance is reduced and the high conductivity is obtained. It is obtained. Therefore, when an electric double layer capacitor is used, the internal resistance can be sufficiently reduced, and a high output electric double layer capacitor suitable for high-current high-speed charge / discharge can be obtained.

In order to confirm the conductivity of the silk material, the silk material was baked alone and the physical properties of the fired product were examined.

The firing temperature of the silk material is about 500 ° C to 3000 ° C.

The firing atmosphere is performed in an inert gas atmosphere such as nitrogen gas or argon gas or in a vacuum to prevent the silk material from burning and ashing.

As for the firing conditions, it is preferable that firing is performed in a plurality of stages while avoiding rapid firing. The firing conditions are the same when firing the composite material.

For example, in an inert gas atmosphere, up to the first firing temperature (for example, 500 ° C) The temperature is raised at a moderate temperature increase rate of 0 ° C. or less, preferably 50 ° C. or less per hour, and the primary calcination is carried out at this primary calcination temperature for several hours. Next, after cooling to room temperature, the temperature is increased to a secondary firing temperature (e.g., 700 ° C) at a moderate temperature increase rate of 100 ° C or less, preferably 50 ° C or less per hour. The secondary firing is performed for several hours at the secondary firing temperature. Then it is cooled. Similarly, a third firing (for example, 2000 ° C. of final firing) is performed to obtain a carbon material. The firing conditions are not limited to the above, and can be changed as appropriate depending on the type of silk material, the function of the desired carbon material, and the like.

As described above, firing is performed in multiple stages, and by heating at a moderate temperature rise rate and firing, dozens of amino acids are involved in an amorphous structure and a crystalline structure. However, rapid degradation of protein conformation is avoided.

Figure 1 shows the Raman spectrum of the fired product when coarse-grained silk is fired at a high temperature of 2000 ° C (final stage firing temperature). 2681cm ^_1 ,

It is understood that graphitized since the peak is observed at the 1335cm ^_1.

Figures 2, 3 and 4 show 700 coarse silks each. C, 1000. C, 1400. FIG. 5 is a Raman spectrum diagram of a fired product when fired with C. When the firing temperature is 1400 ° C, the peak value is low, but the peaks at the above three locations are observed.

When the firing temperature is less than 1000 ° C, the above-mentioned peak is not observed, so that graphitization hardly occurs and good conductivity cannot be expected.

Therefore, when used as a conductive material, it is preferable to fire at a high temperature of 1000-3000 ° C (final stage firing temperature).

As described above, the specific resistance of the carbon material obtained by firing the silk material (woven fabric) at 1400 ° C and 2000 ° C was measured (measured with a filament loosened from the single yarn). IX 10 is ^{_5 (Ω} · ^πι), but does not extend to the graphite (4~7 Χ 10-7 Ω -m), become a better resistivity carbon (4 X 10- ^5), good electrical conductivity It turns out that it has sex.

table 1

Silicon CNO Na Ms Al Si PS CI K Ca Fe wt% 66.1 27.4 2.1 0.1 0.3 0.1 0.3 0.1 0.1 0.1 0.1 3.2 0.2 Table 1 shows the results of elemental analysis (semi-quantitative analysis results) using an electron microanalyzer of the fired product obtained by firing a silk knitted silk fabric at 700 ° C in a nitrogen atmosphere.

Measurement conditions are acceleration voltage: 15 kV, irradiation current: 1 μΑ, and probe diameter: 100 m. The values in the table indicate the tendency of the detected elements and are not guaranteed values.

As is clear from Table 1, it can be seen that 27.4 wt% of nitrogen element remains. In addition, it can be seen that other elements derived from amino acids are multi-elements that remain. In this way, when the silk material is primarily fired at a relatively low temperature, many elements such as nitrogen element remain. This nitrogen element is derived from an amino acid residue.

As described above, when the silk material is fired, a large amount of elements such as nitrogen element remain, which is suitable as an electrode material for a capacitor. Example 1

In a 65 wt% aqueous solution 11 of calcium chloride dihydrate, 240 g of silk raw material was added, and the solution was heated and dissolved for 6 hours while maintaining the solution temperature at 95 ° C. After filtering the dissolved solution after the decomposition, the undissolved material was filtered off, and the filtrate was further desalted using a dialysis membrane with a molecular fraction of 300 to further dilute the sylk protein solution to 3 wt%. Silk protein aqueous solution was used. Carbon nanofibers were mixed with 3 ml of this 3 wt% silk protein aqueous solution, and the carbon nanofibers were dispersed by applying ultrasonic waves and dried at room temperature. After drying, it was pulverized and calcined at 700 ° C in a nitrogen atmosphere to obtain a composite carbon material powder. This material was steam activated at 700 ° C to obtain a high surface area composite carbon material. Figure 5 is an SEM photograph of the composite carbon material obtained in this way. It can be seen that the carbon nanofibers are bound by the carbide derived from the polymer material, and that the carbon nanofibers protrude in the shape of spines. When the electrode material is used, the protruding carbon nanofibers come into contact with each other, and high conductivity is obtained. FIG. 6 shows a powder of a composite carbon material formed using DWCNT and MWCNT as the carbon nanofiber and a composite carbon material (comparative example) formed using carbon black instead of the carbon nanofiber. This is a graph of measured resistance. Using this composite carbon material 75wt%, PTFE 15wt%, CMC 10wt%, a polarizable electrode material was formed. Example 2

Carbon nanofibers were mixed with 3 ml of a 3 wt% silk protein aqueous solution, and the carbon nanofibers were dispersed by applying ultrasonic waves and dried at 80 ° C. After drying, it was pulverized and calcined at 700 ° C in a nitrogen atmosphere to obtain a composite carbon material powder. This material was steam activated at 700 ° C to obtain a high surface area composite carbon material. Using this composite carbon material 75wt%, PTFE 15wt%, CMC 10wt%, a polarizable electrode material was formed. Example 3

Carbon nanofibers were mixed in 3 ml of a 3 wt% silk amino acid aqueous solution, and the carbon nanofibers were dispersed by applying ultrasonic waves and dried at 80 ° C. After drying, it was pulverized and calcined at 700 ° C in a nitrogen atmosphere to obtain a composite carbon material powder. This material was steam activated at 700 ° C to obtain a high surface area composite carbon material. Using this composite carbon material 75wt%, PTFE 15wt%, CMC 10wt%, a polarizable electrode material was formed. Example 4

Carbon nanofibers were mixed in 3 ml of a 3 wt% silk amino acid aqueous solution, and the carbon nanofibers were dispersed by applying ultrasonic waves and dried at 80 ° C. After drying, it was pulverized and calcined at 700 ° C in a nitrogen atmosphere to obtain a composite carbon material powder. This material was steam activated at 700 ° C to obtain a high surface area composite carbon material. Using this composite carbon material 75wt%, PTFE 15wt%, CMC 10wt%, a polarizable electrode material was formed. Example 5

Carbon nanofibers were mixed in 3 ml of a 3 wt% silk amino acid aqueous solution, and the carbon nanofibers were dispersed by applying ultrasonic waves and dried at room temperature. After drying, it was pulverized and fired at 700 ° C in a nitrogen atmosphere to obtain a composite carbon material powder. This material Furthermore, it was fired at 2000 ° C. in a nitrogen atmosphere to obtain a low resistance composite carbon material. Using this, a polarizable electrode material was obtained using 80 wt% activated carbon, 10 wt% low resistance composite carbon material, and 10 wt% PTFE.

As a comparative example, a commercially available carbon black was used in place of the low resistance composite carbon material, and a silk amino acid aqueous solution was dried and the dried product was crushed without adding carbon nanofibers or carbon black. A polarizable electrode material using a carbon material fired under the above conditions was obtained.

Using each of the above polarizable electrodes, it was built in a capacitor cell, charged to 2.5V with 5mA, held at 2.5V for 30 minutes, and then discharged with lmA, 4mA, and 10mA, respectively. Figure 7 shows the capacitor characteristics evaluation in this case. As shown in Fig. 7, both carbon nanofiber and carbon black are mixed. In the comparative example (without addition), discharge at 10 mA has a volume capacity higher than that at 1 mA and 4 mA. Decreasing force With carbon black and composite carbon materials, there was no reduction even when discharged at 10 mA. Compared with carbon black, the one with the above composite carbon material added had a higher volume capacity of 1F / CC.

In this way, capacitor characteristics equivalent to or better than those using composite carbon material and carbon black were obtained.

Claims

The scope of the claims

[I] Atomic groups containing heteroatoms such as nitrogen, oxygen, and sulfur are present in the main chain and side chain Carbon nanofibers are dispersed in a solution in which a polymer substance is dissolved, and the dispersed solution is dried. An electrode material for an electric double layer capacitor comprising the composite carbon material obtained by firing the dried product in a non-oxidizing atmosphere at 500 to 3000 ° C.

[2] The electrode material for an electric double layer capacitor according to [1], wherein the composite carbon material is subjected to an activation treatment, and a plurality of pores are formed on a surface thereof.

[3] The electrode material for an electric double layer capacitor according to claim 1 or 2, wherein the electrode material is granular.

[4] The electrode material for an electric double layer capacitor according to claim 3, wherein the electrode material has a granular shape of 1 μm to 1000 μm.

[5] The electrode material for an electric double layer capacitor according to any one of [1] to [4], wherein the amount of the carbon nanofibers relative to the polymer substance is 1 to 30 wt%.

6. The electrode material for an electric double layer capacitor according to any one of claims 1 to 5, wherein the polymer substance comprises an amino acid, a protein having an amino acid strength, or a peptide.

[7] The electrode material for an electric double layer capacitor as described in any one of [1] to [5], wherein the polymer substance has a silk material strength.

8. The electrode material for an electric double layer capacitor according to any one of claims 1 to 7, wherein the composite carbon material contains a nitrogen element.

[9] The electric double layer according to any one of claims 1 to 8, wherein the carbon nanofiber is a single-walled, double-walled, or multi-walled carbon nanotube, a cap-stacked carbon nanotube, or a carbon nanohorn. Electrode material for capacitors.

10. An electric double layer capacitor comprising a pair of electrode bodies comprising a current collector and a polarizable electrode, a separator, and an electrolytic solution. An electric double layer capacitor comprising an electrode material for a multilayer capacitor.

[II] Atomic groups containing heteroatoms such as nitrogen, oxygen, and sulfur are present in the main chain and side chain. Disperse carbon nanofibers in a solution derived from a polymer material in which the polymer material is dissolved. Process, Drying the dispersion solution;

A method of producing an electrode material for an electric double layer capacitor, comprising: baking a dried product to form a composite carbon material.

12. The method for producing an electrode material for an electric double layer capacitor according to claim 11, wherein the dried product is pulverized and then fired.

[13] The method for producing an electrode material for an electric double layer capacitor according to claim 11, wherein the composite carbon material formed by firing the dried product is pulverized into particles.

[14] The method for producing an electrode material for an electric double layer capacitor according to any one of [11] to [13], further comprising a step of applying an activation treatment to the composite carbon material.

[15] The method for producing an electrode material for an electric double layer capacitor according to any one of [11] to [14], wherein carbon nanofibers are dispersed in an amount of 1 to 30 wt% with respect to the polymer substance.

16. The method for producing an electrode material for an electric double layer capacitor according to any one of claims 11 to 15, wherein a silk material is used as the polymer substance.