JPH1197307A - Manufacture of electric double layer capacitor and electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase capacitance, reduce leakage current, and improve reliability, by chemically oxidizing a sintered member in which polyvinylidene chloride(PVDC) resin carbide is sintered in a specified temperature range, and electrochemically oxidizing and reducting the sintered member in electrolyte. SOLUTION: A sintered member in which PVDC resin carbide is sintered at 600-950 deg.C is chemically oxidized, and electrochemically reduced in electrolyte, and an electrode for electric double layer capacitor is manufactured. After charging is performed by incorporating the electrode for electric double layer capacitor as an electric double layer capacitor, charging is repeated by changing polarities of electrodes, oxidizing and reducing treatment is electrochemically performed, and an electric double layer capacitor is manufactured. Concretely, a sintered body polished to be 1 mm in thickness is dipped in nitric acid of 1N, boiled for 60 minutes, boiled and washed with ion exchange water, and repeatedly boiled and washed as far as conductivity of cleaning fluid becomes at most 2 μS/cm. Thus an electrode is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electric double layer capacitor and a method for manufacturing an electrode.

[0002]

2. Description of the Related Art An electric double layer capacitor is a capacitor utilizing an electrostatic solution of an activated carbon powder and an electrolytic solution impregnated in an activated carbon powder. The withstand voltage and the maximum operating temperature depend on the decomposition voltage and temperature of the electrolytic solution, and the rated voltage is as low as several volts. However, since the Farad order capacitance can be easily obtained, the semiconductor memory is used instead of the battery. It has been widely used for low current density applications such as backup of (D-RAM), and has recently been studied for use in applications having higher current densities, for example, in place of in-vehicle lead-acid batteries. ing.

Heretofore, as an electrode for an electric double layer capacitor, a material obtained by mixing a binder with activated carbon and sintering or a material subjected to an activation treatment (impurity removal treatment by oxidation) after sintering has been used. However, the use of these 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 electrodes for electric double layer capacitors. c) sintering at a relatively high temperature to promote sintering,
There are few effective pores acting as electrodes for electric double layer capacitors. 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.

[0004] To solve these problems, PVDC
It has been proposed to use (polyvinylidene chloride) resin carbide (see JP-A-7-249551).
The use of PVDC resin (or vinylidene chloride-based copolymer) carbide has advantages over other activated carbons because of 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. When heated in the temperature range of the first point, pores are formed by the dehydrochlorination reaction, and the pores are called micropores having a diameter of 36 ° or less. It works effectively as an interface with the liquid. For this reason, activation treatment as an electrode is unnecessary. Further, when the heating is performed at a temperature not lower than the temperature range of the second point, sintering can be advanced even at a relatively low temperature while maintaining effective micropores by the dehydrochlorination reaction. For this reason, generation of mesopores or macropores having a large diameter, which is unnecessary for the electrode for an electric double layer capacitor, can be suppressed. For this reason,
The PVDC resin carbide has a smaller specific surface area than activated carbon, but has a higher sintering density than activated carbon and a larger capacity per volume.

However, the PVDC resin carbide has the following problems. a) It is difficult to mold because it is binderless. b) Ohmic resistance is high because graphite does not advance during sintering at low temperature (850 ° C. or lower). 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.

Conventionally, there has been an attempt to oxidize the surface of an activated carbon electrode of an electric double layer capacitor with an oxidizing substance such as nitric acid. However, surface functional groups which are unnecessary as an electric double layer capacitor due to the remaining oxidizing agent. Has been introduced, and as a result, Coulomb efficiency and the like have deteriorated, and reliability has been impaired. Also, a method of electrochemically redox-treating the surface is known, but when used as an electric double-layer capacitor, the anode and the cathode need to be treated separately, which requires complicated work. Not as effective. Furthermore, these studies have not been conducted on activated carbon obtained by carbonizing a resin that has not been subjected to activation treatment, such as a PVDC resin, at a low temperature.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of manufacturing an electric double layer capacitor and an electrode having a high reliability by increasing a capacity and reducing a leakage current.

[0008]

According to the present invention, a sintered body obtained by sintering a PVDC resin carbide at 600 to 950 ° C. is chemically oxidized, and then electrochemically oxidized and reduced in an electrolytic solution. This is a method for producing an electrode for an electric double layer capacitor to be treated.

Further, the present invention relates to a method for manufacturing an electric double layer capacitor having an electrode made of PVDC resin carbide, in which a chemically oxidized electrode is incorporated as an electric double layer capacitor and charged. This is a method for manufacturing an electric double layer capacitor in which charging is repeated while changing the polarity of the electric double layer, and the oxidation and reduction are performed electrochemically.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described. The manufacturing method of the electric double layer capacitor and the electrode of the present invention will be described with reference to examples.

Embodiment 1 of a method for manufacturing an electrode for an electric double layer capacitor will be described. First, a sintered body is prepared. PVD
C resin was carbonized at 300 ° C., crushed by a vibration milling machine, packed in a 25 mm square carbon mold,
While being molded at a pressure of 0 kg / cm ² , current sintering was performed until the temperature reached 850 ° C., and polishing was performed to a thickness of 1 mm to produce a sintered body. The obtained sintered body was immersed in 1N nitric acid and boiled for 60 minutes. Next, boiling washing was performed using ion-exchanged water, and boiling washing was repeated until the conductivity of the washing liquid became 2 μS / cm or less, thereby obtaining an electrode. 35 wt% of the obtained electrode
% Sulfuric acid, vacuum impregnation for 24 hours, 200 μm
The electrodes 2 are opposed to each other with a thick glass non-woven fiber separator 1 interposed therebetween, and a Pt plate is disposed outside thereof to form a current collecting plate 3, which is further sandwiched and fixed by a fixing plate 4 made of Teflon. Thus, a cell was produced (see FIG. 1). This cell is 35w
The battery was immersed in t% sulfuric acid and charged to 1.2 V.
Then, the electrode was charged to 1.2 V by changing the polarity of the electrode, and the voltage was held for 1 hour to perform electrochemical oxidation-reduction treatment.
The charge / discharge was repeated up to 0.8 V at / cm ² to measure the capacity per electrode volume.

Comparative Example 1 will be described. First, a sintered body is manufactured in the same manner as in the first embodiment. The sintered body was immersed in nitric acid, boiled for 60 minutes, and chemically oxidized. The nitric acid concentration at this time was 1N and 6N. Next, boiling washing was performed using ion-exchanged water, and boiling washing was repeated until the conductivity of the washing liquid became 2 μS / cm or less, thereby obtaining an electrode. The obtained electrode was immersed in 35 wt% sulfuric acid, and impregnated under reduced pressure for 24 hours. The electrode 2 was opposed to the non-woven fiber separator 1 having a thickness of 200 μm, and a Pt plate was disposed outside the electrode 2 to collect a current collector plate. 3, and the cell was fabricated by sandwiching and fixing a Teflon fixing plate 4 from the outside (see FIG. 1).
This cell was immersed in 35 wt% sulfuric acid, and the current density was 2 mA.
The charge / discharge was repeated up to 0.8 V at / cm ² to measure the capacity per electrode volume.

A comparative example 2 will be described. The electrode was immersed in 35 wt% sulfuric acid without being subjected to chemical oxidation and electrochemical oxidation, and was impregnated under reduced pressure for 24 hours.
The electrodes 2 are opposed to each other with a glass non-woven fiber separator 1 having a thickness of 00 μm therebetween, a Pt plate is disposed outside the collector 2 to form a current collector plate 3, and a fixing plate 4 made of Teflon is further fixed from the outside thereof. Thus, a cell was produced (see FIG. 1). This cell was immersed in 35 wt% sulfuric acid, and the current density was ² mA / cm ^2.
The charge / discharge to 0.8 V was repeated, and the capacity per electrode volume was measured.

In Comparative Example 3, the electrodes were immersed in 35 wt% sulfuric acid, impregnated under reduced pressure for 24 hours, and the electrodes 2 were opposed to each other with a 200 μm-thick glass nonwoven fiber separator 1 interposed therebetween.
A Pt plate was disposed outside the collector plate 3 to form a current collector plate 3. From the outside, a cell was produced by sandwiching and fixing with a fixing plate 4 made of Teflon (see FIG. 1). This cell is immersed in 35 wt% sulfuric acid, charged to 1.2 V, and the voltage is maintained for one hour. Next, the polarity of the electrode was changed, and the battery was charged to 1.2 V, held for 1 hour, electrochemically oxidized and reduced, and then charged to 0.8 V at a current density of ² mA / cm ² with respect to the projected area of the electrode. The discharge was repeated, and the capacity per electrode volume was measured.

The leakage current of each electrode was measured at a constant current of 125 mA up to 0.8 V, and the leakage current after 30 minutes was measured. Table 1 shows the measurement results.

[Table 1]

As shown in Table 1, in the electrode of Example 1, which was electrochemically oxidized and then electrochemically oxidized and reduced, the electrode volume capacity was improved and the leakage current was small. This is because the surface functional groups unnecessary for the electric double-layer capacitor generated by the chemical oxidation treatment can be changed to the reducing or reversible reactive groups, and thus are more stable than the electrodes of Comparative Examples 1 to 3. You get performance. In the electrode of Comparative Example 1 only with the chemical oxidation treatment, the electrode volume capacity increases, but the leakage current increases. On the other hand, in the electrode of Comparative Example 3 with the electrochemical oxidation only treatment, the leakage current decreases. However, no significant increase in electrode volume capacity was observed.

Although the method of manufacturing the electrode has been described,
It is also possible to electrochemically perform the oxidation-reduction treatment by incorporating the electrode that has been subjected to the chemical oxidation treatment into the electric double layer capacitor, and to achieve the same effect.

[0018]

According to the present invention, the electrode volume capacity can be increased,
It is possible to provide a method of manufacturing an electric double-layer capacitor and an electrode with reduced leakage current and high reliability.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a method for measuring characteristics of an electrode manufactured by a manufacturing method according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Electrode 3 Current collector 4 Fixing plate

Claims (2)

[Claims] 1. A PVDC resin carbide at 600 to 950 ° C.
A method for producing an electrode for an electric double layer capacitor, characterized by chemically oxidizing a sintered body sintered in step (1), and then performing electrochemical oxidation and reduction in an electrolytic solution. 2. A method of manufacturing an electric double layer capacitor having an electrode made of a PVDC resin carbide, comprising charging a chemically oxidized electrode as an electric double layer capacitor, and then changing the polarity of the electrode. A method for producing an electric double layer capacitor, comprising repeating oxidation and reduction by electrochemical charging and charging.