JPH11251197A - Method for manufacturing carbon electrode for electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a carbon electrode for the electric double layer capacitor without deterioration in the electrode characteristic by uniformizing dispersion of carbon in a molded body and preventing carbon residue after sintering. SOLUTION: A carbide powder is made by slurry method in the method of manufacturing the carbon electrode for the electric double layer capacitor with the use of polyvinylidene chloride resin carbide powder. Resol-based phenol resin is used for the binder. Ion electrolyte is added to the slurry in the forming process. Ion concentration of the ion electrolyte in the slurry is set to be 200 ppm or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a carbon electrode for an electric double layer capacitor, and more particularly to a method for producing a carbon electrode for an electric double layer nindensa produced by a slurry method.

[0002]

2. Description of the Related Art An electric double-layer capacitor is a capacitor that uses an electrostatic double layer formed at the interface between activated carbon and an electrolytic solution by impregnating an activated carbon powder with an electrolytic solution. The withstand voltage and the maximum operating temperature depend on the electrolytic partial pressure and temperature of the electrolytic solution, and the rated voltage is as low as several volts. However, a farad-order capacitance can be easily obtained. It is widely used for low current density applications such as memory (D-RAM) backup,
Recently, studies have been made to use it for applications having higher current density, for example, in place of lead-acid batteries in vehicles.

Conventionally, as a carbon electrode for an electric double layer capacitor, a carbon material obtained by mixing a binder, for example, a phenol resin or a thermoplastic resin, with activated carbon and sintering it, or activating after sintering (impurity removal treatment by oxidation) is used. Was used.
However, the use of these carbon electrodes has caused the following problems. a) Activated carbon has a low density because it has many macropores and a high pore volume ratio. b) Although the specific surface area is large, the distribution of the pore diameter is wide, so that there are few effective pores acting as carbon electrodes for electric double layer capacitors. c) For sintering at a relatively high temperature for the purpose of promoting sintering,
There are few effective pores acting as carbon electrodes for electric double layer nindensa. d) When sintering at a low temperature (850 ° C. or lower), graphitization does not proceed, so there is no intergranular sintering strength and the resistance value is high. e) Since the phenol resin has a residual carbon ratio of about 60%,
After sintering, carbides that do not work effectively as electric double layer capacitors remain. Further, a thermoplastic resin that softens at a temperature of 200 ° C. or less cannot maintain voids between carbide particles during molding.

Further, the conventional electric double layer capacitor using activated carbon has a capacity of only about 30 F / cc because the shape of the pore diameter does not match the electrolytic solution. Further, although a monolithic sintered body is advantageous for reducing the internal resistance, it is difficult to form the activated carbon electrode, and only a compact one can be obtained by the compacting method.

In order to solve these problems, PVDC
It has been proposed to use (polyvinylidene chloride) resin carbide (see JP-A-7-249551).
The use of a PVDC resin (or a vinylidene chloride resin-based copolymer) carbide has advantages over other activated carbons, and is said to be due to the following. PVDC resins have two dehydrochlorination reaction temperatures. The first point is the dehydrochlorination reaction in the self-molecular chain at 180 ° C to 250 ° C, and the second point is the dehydrochlorination reaction between the molecular chains at 450 ° C to 550 ° C. I have. The pore formed by the dehydrochlorination reaction at the first point is
It is called a micropore of 36 ° or less, and when it is used as a carbon electrode for an electric double layer capacitor, it works effectively as an interface with an electrolytic solution. For this reason, activation treatment as a carbon electrode is unnecessary. In addition, sintering can proceed at a relatively low temperature while maintaining effective micropores by the dehydrochlorination reaction at the second point. For this reason, generation of mesopores or macropores having a large diameter, which is unnecessary for the carbon electrode for an electric double layer capacitor, can be suppressed.

[0006] For this reason, the PVDC resin carbide has a smaller specific surface area than activated carbon, but has a high sintering density and therefore a large capacity per volume. However, PVDC grit carbide has the following problems. a) It is difficult to mold because it is binderless. b) Since sintering at a low temperature (850 ° C. or lower) does not progress to graphitization, ohmic resistance is high. Therefore, at a high current density, the IR drop is large and the capacity cannot be taken out. c) The PVDC resin carbide can be sintered at a high density, but has a high diffusion resistance due to few voids and macropores between particles.

As a method for solving these problems, a molding method by a slurry method has been proposed, but carbon powder has poor dispersibility, and it has been difficult to obtain a uniform molded body. For this reason, means for adding a dispersant for uniform dispersion can be considered, but these are organic substances, and the dispersant residual carbon is similar to the problem e) in the case of using the conventional activated carbon, and the residual carbon of the electric double layer is the same. There is a need to sacrifice some capacity as an electric double layer capacitor because it is not suitable for a capacitor.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has an object to improve the electrode characteristics by making the dispersion of carbon in a molded body uniform and not remaining after sintering. It is an object of the present invention to provide a method for producing a carbon electrode for a capacitor for an electric double layer, which does not cause deterioration of the electrode.

[0009]

According to the present invention, there is provided a method of manufacturing a carbon electrode for an electric double layer capacitor using a polyvinylidene chloride resin carbide powder, wherein the carbide powder is formed by a slurry method. It is a manufacturing method of.

The present invention is also a method for producing a carbon electrode for an electric double layer capacitor, wherein the binder is a resol-based phenolic resin.

The present invention is a method for producing a carbon electrode for an electric double layer capacitor, wherein an ionic electrolyte is added to a slurry in a molding step.

Further, the present invention is a method for producing a carbon electrode for an electric double layer capacitor, wherein the ion concentration of the ionic electrolyte in the slurry is 200 ppm or more.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described. An embodiment of the method for producing a carbon electrode for an electric double layer capacitor according to the present invention will be described. Polyvinylidene chloride (PV
DC) baking the resin at 300 ° C. in a tube furnace;
A resin carbide having completed the first dechlorination reaction was obtained. This was ground in a nitrogen atmosphere using a vibration milling device. The average particle size at this time was 8 μm. 40 g of the obtained powder
Was dispersed in a solvent of water: ethanol = 3: 1 (volume ratio), and 7 wt% of Showanol BRL-120Z, a resole-based phenol resin, was added to prepare a slurry. In this embodiment, FeCl ₃ is added to the slurry in an amount of 0 to 1000 ppm as Fe ion concentration.
It was adjusted so as to be added. By adding FeCl ₃ , the dispersibility of carbon is improved, and camphor, which is a colloid of a phenol resin, undergoes salting out and precipitates, thereby preventing sedimentation of carbon and obtaining a uniform molded article. Subsequently, these slurries were poured into a mold and dried in an oven at 60 ° C. overnight to produce a molded body. Further, this was sintered at 870 ° C. in a muffle furnace to obtain a sintered body.

Next, a comparative example will be described. Instead of FeCl _{3 in} the examples, 20 wt% of polyethylene glycol (PEG) having a molecular weight of 200 was added as a dispersant,
Otherwise, a sintered body was produced in the same manner as in the example.

The sintered bodies obtained in the examples and comparative examples were subjected to a strength test, assembled into an electric double-layer capacitor, and the capacitance was measured. Here, the strength test was performed by applying a load from the front side and the back side during molding by a three-point bending method. The electric double layer capacity was determined by measuring the time from 60% to 50% of the voltage drop during discharge. The measurement results are shown in FIGS. FIG.
FIG. 4 is an explanatory diagram of the relationship between the concentration of Fe ions added to the slurry and the strength in the example. FIG. 2 is an explanatory diagram of the electric double layer capacitor capacitance at each current density in the example and the comparative example.

As shown in FIG. 1, the strength of the sintered body produced in the example is 200 ppm or more for Fe ions, and it can be seen that there is no difference in strength between the back side and the front side. As a result, it was found that when the Fe ion in the slurry was 200 ppm or more, the resin charcoal powder was uniformly dispersed. The strength of the sintered body produced in the comparative example was 14.2 on the front side.
Mpa and the back side were 14.9 Mpa. Therefore,
It was found that the sintered body produced in the example had a strength comparable to that produced in the comparative example.

FIG. 2 shows the measured data of the electric double layer capacity between the case where 500 ppm of Fe ion was added in the example and the comparative example. At any current density, the electrode manufactured in the example was manufactured in the comparative example. This indicates that the capacity is larger than that obtained.

In the embodiment, the Fe ion 500p
The Fe ion concentration after sintering at the time of adding pm and after sintering in the comparative example was determined by extracting each of the sintered bodies with water, and extracting the solution by ICP emission spectroscopy. As a result, the example was 27 ppm.
On the other hand, the comparative example showed almost the same value as 30 ppm.
This shows that Fe ions are almost lost during sintering.

In the examples, FeCl ₃ was used, but the reaction used in the present invention is salting out of colloid (precipitation by ions). It is clear that the same effect can be obtained even with any substance.

[0020]

According to the present invention, a carbon electrode for a capacitor for an electric double layer without deterioration of electrode characteristics can be obtained by making the dispersion of carbon in a molded body uniform and preventing it from remaining after sintering. Can be manufactured.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of the relationship between the concentration of Fe ions added to a slurry and the strength in an example.

FIG. 2 is an explanatory diagram of electric double layer capacitor capacity at each current density in an example and a comparative example.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroyuki Imai 8 Dosana, Fujisawa-shi, Kanagawa Prefecture Isuzu Central Research Institute Co., Ltd. (72) Inventor Eiji Okumura 8 Dosana, Fujisawa-shi, Kanagawa Prefecture Isuzu Central Research Inc. Inside

Claims (4)

[Claims] 1. A method for producing a carbon electrode for an electric double layer capacitor using a polyvinylidene chloride resin carbide powder, wherein the carbide powder is produced by a slurry method. . 2. The method for manufacturing a carbon electrode for an electric double layer capacitor according to claim 1, wherein the binder is a resol-based phenolic resin. 3. The method for producing a carbon electrode for an electric double layer capacitor according to claim 1, wherein an ionic electrolyte is added to the slurry during the forming step. . 4. The method for producing a carbon electrode for an electric double layer capacitor according to claim 3, wherein the ion concentration of the ionic electrolyte in the slurry is 200 pp.
m or more, and a method for producing a carbon electrode for an electric double layer capacitor.