JPH1197309A - Manufacture of double layer capacitor and electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing an electric double layer capacitor and an electrode wherein an electrode volume capacity is increased and leak current is reduced with high reliability. SOLUTION: Relating to the manufacturing method, a PVDC(polyvinylidene chloride) resin carbide is sintered at 600-950 deg.C, an obtained sintered body is heated at 150-300 deg.C, then oxidized/reduced in electro chemical manner in an electrolytic solution, thus an electric double layer capacitor electrode 2 is obtained. The electrode 2 may be incorporated in an electric double layer capacitor for process.

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.

Attempts have been made to oxidize the surface of an activated carbon electrode with nitric acid or an oxidizing substance. However, the residue of the oxidizing agent or unnecessary surface functional groups introduced into the electric double layer capacitor are introduced. Efficiency is reduced and reliability is impaired.

A method of electrochemically redox-treating the surface is also known, but when used as an electric double layer capacitor, the anode and the cathode need to be treated separately, and the expected effect can be obtained. Not.

[0008]

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.

[0009]

According to the present invention, a PVDC resin carbide is sintered at a temperature of 600 to 950 ° C., and the obtained sintered body is heat-treated at a temperature of 150 to 300 ° C. This is a method for producing an electrode for an electric double layer capacitor which is electrochemically oxidized and reduced.

The present invention also relates to a method for manufacturing an electric double layer capacitor having an electrode made of a PVDC resin carbide, wherein charging is performed by incorporating the electrode heated at a temperature of 150 to 300 ° C. as an electric double layer capacitor. ,
Next, a method of manufacturing an electric double layer capacitor in which the charging and the reversing by changing the polarity of the electrodes is repeated to electrochemically perform a redox treatment.

[0011]

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. Next, the sintered body was immersed in 35 wt% sulfuric acid, boiled for 10 minutes, and then heated at 200 ° C. for 90 minutes in the air. Next, the electrode was immersed in 35% by weight sulfuric acid, and impregnated under reduced pressure for 24 hours. The electrode 2 was opposed to the electrode 2 with a 200-μm thick glass nonwoven fiber separator 1 interposed therebetween. 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 for electrochemical redox treatment in an electrolyte solution.
Charged to V and maintained for 1 hour, then changed the polarity of the electrode to 1.2 V, and maintained for 1 hour, then charged and discharged to 0.8 V at a current density of 20 mA / cm ² with respect to the projected area of the electrode. The capacity per electrode volume was measured repeatedly

Comparative Example 1 will be described. The electrodes were immersed in 35 wt% sulfuric acid, and impregnated under reduced pressure for 24 hours. The electrodes 2 were opposed to each other with a 200 μm-thick glass non-woven fiber separator 1 interposed therebetween. Further, a cell was produced by sandwiching and fixing the outer side of the cell with a fixing plate 4 made of Teflon (see FIG. 1). 35% by weight of this cell
0.8 V at a current density of 20 mA / cm ² immersed in sulfuric acid
Charge / discharge was repeated until the capacity per electrode volume was measured

A comparative example 2 will be described. The electrodes were immersed in 35 wt% sulfuric acid, and impregnated under reduced pressure for 24 hours. The electrodes 2 were opposed to each other with a 200 μm-thick glass non-woven fiber separator 1 interposed therebetween. Further, a cell was produced by sandwiching and fixing the outer side of the cell with a fixing plate 4 made of Teflon (see FIG. 1). 35% by weight of this cell
Immersion in sulfuric acid, current density 20m to the projected area of the electrode
The charge / discharge to 0.8 V at A / cm ² 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, after changing the polarity of the electrode and charging it to 1.2 V and holding it for 1 hour, charging and discharging up to 0.8 V at a current density of 20 mA / cm ² with respect to the projected area of the electrode was repeated to reduce the capacity per electrode volume. It was measured.

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

[Table 1]

As shown in Table 1, in the electrode subjected to the electrochemical oxidation-reduction treatment after the heat treatment in Example 1, the electrode volume capacity was improved and the leakage current was small. This is because the unnecessary surface functional groups of the electric double layer capacitor generated by the heat treatment are changed into inactive reducing or reversible reactive groups by performing the oxidation-reduction treatment electrochemically. , And stable performance can be obtained.

When only the heat treatment is performed as in Comparative Example 2, the electrode volume capacity increases, but the leakage current is large. As in Comparative Example 3, when only the oxidation-reduction treatment was performed electrochemically, the leakage current was small, but no remarkable increase in the electrode volume capacity was not recognized.

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.

[0020]

According to the present invention, it is possible to provide a method of manufacturing an electric double layer capacitor and an electrode which has increased electrode volume capacity, reduced leakage current, and obtained 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.
Producing an electrode for an electric double layer capacitor, characterized by subjecting the obtained sintered body to a heat treatment at a temperature of 150 to 300 ° C. and an electrochemical redox treatment in an electrolyte solution. Method. 2. A method for manufacturing an electric double layer capacitor having an electrode made of a PVDC resin carbide, comprising: charging an electrode heated at a temperature of 150 to 300 ° C. as an electric double layer capacitor; A method for manufacturing an electric double-layer capacitor, comprising repeating the charging while changing the polarity of the same to electrochemically perform an oxidation-reduction treatment.