JPH11121295A - Electric double-layer capacitor, electrode, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor and an electrode having high capacity at a high current density and adequate strength for practical use. SOLUTION: An electrode 2 for an electric double-layer capacitor made of PVDC(polyvinylidene chloride) resin carbide is set to have a density of 0.65 to 0.75 g/cc, and a sheet resistance of 0.9 to 3.0 Ω/(square). The PVDC resin carbide is carbonized at a temperature range of 180 to 600 deg.C and is crushed into a powder having a means particle size of 8 to 12 μm. The carbide powder is sintered at a temperature range of 600 to 950 deg.C for its manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor, an electrode and a method for manufacturing the same.

[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 capacitance in the farad order can be easily obtained, a semiconductor memory is used instead of a 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.

Japanese Patent Application Laid-Open No. 63-3148 discloses a method in which a phenol resin is supported on activated carbon or carbon fiber and then activated repeatedly.
No. 21, the process is complicated,
It was costly. An electrode carbonized by adding a phenolic resin is described in JP-A-63-226019, but a phenolic resin carbide has a small number of pores and a small capacity that are optimal for an electrode for an electric double layer capacitor.

In order to solve these problems, PVDC
It has been proposed to use a carbide of (polyvinylidene chloride) resin (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 a dehydrochlorination reaction within its own molecular chain at 180 ° C to 250 ° C, and the second point is 450 ° C to 550 ° C.
In this case, an intermolecular bond is generated in the dehydrochlorination reaction between the molecular chains. 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.

[0006] However, 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, in order to manufacture an electrode using activated carbon powder, a slurry containing the powder is applied to a sheet by a doctor blade method or the like and press-formed by hot pressing or the like, or without using a slurry. In this case, a method of directly packing the powder together with a binder into a mold and compression molding by hot pressing has been used.

However, in any of the above-mentioned methods, since the molding is performed using pressure, the packing density of the electrodes is 0.9 to 1.2 g / c.
c, the density becomes too high, so that there are few gaps between particles required for the characteristics of the electric double layer capacitor, and there is a problem that the capacity at a high current density cannot be taken out.

Further, when a binder such as a phenol resin having a high residual carbon ratio is used as a binder, there is a problem that the capacity is reduced particularly when the amount of addition is large.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric double layer capacitor and an electrode having a high capacity even at a high current density and having a strength sufficient for practical use.

[0011]

SUMMARY OF THE INVENTION The present invention relates to an electrode for an electric double layer capacitor comprising a PVDC resin carbide.
It is an electrode for an electric double layer capacitor having a density of 0.65 to 0.75 g / cc and a sheet resistance of 0.9 to 3.0 Ω / □.

Further, the present invention relates to an electric double layer capacitor having an electrode made of a PVDC resin carbide, wherein the density of the electrode is 0.65 to 0.75 g / cc, and the sheet resistance of the electrode is 0.1 to 0.5 g / cc. It is an electric double layer capacitor having a resistance of 9 to 3.0Ω / □.

[0013] The present invention relates to a PVDC resin of 180
After carbonization at ℃ to 600 ℃, the average particle size is 8 to 12μm
This is a method for producing an electrode for an electric double layer capacitor in which the obtained carbide powder is sintered at 600 to 950 ° C.

Further, the present invention comprises a step of pouring a slurry in which a PVDC resin carbide is dispersed in a solvent comprising water or a mixture of water and an alcohol-based solvent into a mold, a step of removing volatile components of the slurry, This is a method for producing an electrode for an electric double layer capacitor having the following.

In the present invention, the slurry has a molecular weight of 2
Up to one million polyethylene glycol or derivatives thereof;
This is a method for producing an electrode for an electric double layer capacitor, comprising a resol type phenol resin and a powdery or fibrous resin having a residual carbon ratio of 30% or less.

[0016] The present invention relates to the present invention, wherein the addition amount of polyethylene glycol or a derivative thereof having a molecular weight of up to 2 million is as follows:
It is 5 to 18 wt% based on the PVDC resin carbide, and the resol type phenol resin is added in an amount of 5 to 8 w
The method for producing an electrode for an electric double layer capacitor, wherein the resin having a residual carbon ratio of 30% or less in the form of a powder or a fibrous material having a residual carbon ratio of 30% or less is 0.5% to 2.5% by weight.

Further, the present invention is a method for producing an electrode for an electric double layer capacitor, wherein the step of removing volatile components of the slurry is a step of drying at room temperature to 90 ° C.

Further, the present invention is a method for producing an electrode for an electric double layer capacitor, wherein molding is performed in a non-pressurized state.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described. The electric double layer capacitor, the electrode and the method for manufacturing the same according to the present invention will be described. One embodiment of the method for manufacturing an electrode for an electric double layer capacitor according to the present invention, in order, initial carbonization of PVDC resin, characteristics of PVDC resin carbide powder, production and molding of slurry, sintering process, characteristics of sintered electrode, comparison This will be explained by describing an example. First Embodiment A first embodiment will be described with reference to FIGS. FIG. 1 is an explanatory diagram of PVDC resin carbide powder particle size and electrode capacity, FIG. 2 is an explanatory diagram of polyethylene glycol addition amount and electrode capacity, FIG. 3 is an explanatory diagram of phenol resin and electrode capacity, and FIG. FIG. 5 is an explanatory diagram of a method for measuring characteristics of an electrode manufactured by the manufacturing method according to the embodiment.

(1) First, the initial carbonization of the PVDC resin will be described. 2 kg of PVDC resin is packed in a quartz tube, a thermocouple, an exhaust tube, and a gas injection tube are arranged, and sealed with a rubber stopper or the like. The quartz tube was set in a tubular furnace and heated at 180 to 600 ° C. Until the peak temperature, the hydrogen chloride gas discharged by the dehydrochlorination reaction is discharged from the exhaust pipe at its own pressure. During cooling, air flows at 0.2 to 0.5 L (liter) per minute from the gas injection pipe, and is 100 ° C. or less. Became PVDC
The resin carbide was taken out and pulverized to an average particle size of 8 to 12 μm to obtain a PVDC resin carbide powder. When an electrode is manufactured using an electrode having an average particle size exceeding 12 μm, the capacity at a high current density sharply decreases. Also, 8
If it is less than μm, it takes a long time to pulverize, and the particles are too fine, so that cracks are apt to be formed during molding or sintering of the electrode, and the capacity is not significantly improved even if the average particle size is less than 8 μm. Was. (See Fig. 1)

(2) Next, the characteristics of the PVDC resin carbide powder will be described. PVD obtained in the above carbonization step
The C resin carbide powder was put into ion-exchanged water, boiled for 60 minutes and cooled to room temperature. Then, the carbide was filtered off, and the hydrogen ion concentration of the filtrate was measured to be 0.012 to 0.25 mm.
ol / g. Also, when the amount of acidic groups remaining in the carbide without being extracted with water was measured, it was found to be 0.22-0.
33 mmol / g. From the above, it can be seen that in the initial carbonization step (1), a PVDC resin carbide having an acidic component extracted into water and an acidic group not extracted into water could be obtained.

(3) The preparation and molding of the slurry will be described. Water: alcohol = 7: 3 mixed solvent, polyethylene glycol (PE)
G) is added in an amount of 5 to 18% by weight, and a resol type phenol resin is added in an amount of 5 to 8% by weight.
After adding t%, the PVDC resin carbide was added and stirred for 2 hours. Due to the acidic substances contained in the PVDC resin carbide and the acidic groups on the surface, the pH gradually decreases, and
The pH became 2 to 4 in 6 hours, and the slurry was balanced in a good dispersion state. Pour the stirred slurry into a 120 cm square mold and press
For 4 to 24 hours. When the pH is more alkaline than the above conditions, the dispersion is not performed well, and the dispersion and adsorption of the phenol resin are particularly poor. Therefore, the molded body and the sintered body become powdery and have no strength. vice versa,
On the acidic side, polymerization of the phenol resin occurs too quickly, tends to be non-uniform, is hard, and cracks are generated, so that the molded body and the sintered body have too high densities. It should be noted that even if an attempt is made to adjust the pH with an acid, the molding cannot be performed because the balance cannot be obtained. This is due to the presence of surface acidic groups.
Is shifted. Resoles polymerize in the presence of an acid. Therefore, it is polymerized and adsorbed by the acidic group present on the carbide surface. In addition, the dispersion state is balanced by the acidic group, so that a good molded product can be obtained. Thus, the surface acidic groups contribute to the balance of dispersion and promote the adsorption of the phenolic resin. PEG
The addition of (polyethylene glycol) improves the dispersion of the polyester fiber and the dispersion of the phenol resin. PEG
If the molecular weight exceeds 2,000,000, the phenolic resin and other additives in the slurry will aggregate, making it difficult to obtain a good molded product. FIG. 2 shows the relationship between the amount of PEG added and the capacity at a high current density. That is, when the amount of PEG added exceeds 18 wt%, the capacity sharply decreases, and when it is less than 5 wt%, the dispersibility of the slurry deteriorates and the strength of the molded body decreases, which is not practical.
The polyester fiber reinforces the molded body, prevents cracks and cracks from occurring, and burns out at the sintering step to form uniform voids in the electrode. This void serves as a path for the electrolyte, thus reducing diffusion resistance and minimizing losses, especially at high current densities. This property has a strong correlation with the density, and the performance can be controlled by adjusting the density. The use of polyester fiber as an additive is 60
This is because the residual carbon ratio at 0 ° C. or higher is as low as about 0.3 to 15%. For comparison, when a cellulose fiber having a residual carbon ratio of 40 to 50% is added, the capacity decreases at a high current density. Was done. (Refer to Comparative Example 3) However, the residual coal rate is about 30%
When a plasticized phenol resin was added, a capacity equivalent to that of polyester fiber was obtained. That is, in order to form an optimal gap between particles, a resin having a residual carbon ratio of 30% or less may be used, and is not limited to polyester fiber. If the addition amount of these resins is 0.5 wt% or more, it contributes to the improvement in capacity at high current density.
If the content exceeds wt%, dispersion in the slurry becomes poor, and “unevenness” in the density tends to occur. The phenol resin acts as a binder and affects the strength and resistance of the electrode. Since the resistance value of the electrode also affects the loss on the high current density side, the performance can be controlled more narrowly by adjusting it in accordance with the electrode density. The addition amount of the phenol resin is preferably 5 to 8% by weight, and if it is less than 5% by weight, the electrode strength after molding and sintering is weak, and is not practical. Also, 8w
When the content exceeded t%, a decrease in capacity was observed. (See FIG. 3) Since this molding method is performed at a temperature equal to or lower than the boiling point of the solvent, a uniform electrode can be obtained without generating bubbles or the like. And
Since the operation is performed in a non-pressurized state, the density of the electrode does not increase too much, and furthermore, no residual stress or the like is generated in the electrode, so that an electrode having stable characteristics can be easily obtained.

(4) The sintering process will be described. The compact is sandwiched between carbon plates and sintered at 600 to 950 ° C. in a neutral or reducing atmosphere. If the slurry composition is constant, the sheet resistance of the electrode depends on the sintering temperature.
The higher the temperature, the lower the sheet resistance and the lower the loss. However, if the temperature exceeds 950 ° C., the sintering proceeds too much and there is no effective pore in the electrode for the electric double layer capacitor, so that the capacity decreases. If the temperature is lower than 600 ° C., the sintering of the grain boundaries is insufficient, and the sheet resistance becomes extremely high. As a result, the loss increases.

(5) The characteristics of the sintered electrode will be described.
The density of the electrode manufactured in the above steps is 0.65 to 0.7.
5 g / cc and the sheet resistance of the electrode is 0.9 to 0.9 g / cc.
It was 3.0Ω / □. When the cross section of the electrode was observed with an electron microscope, it was found that interparticle voids of 5 to 20 μm were distributed.

(6) A comparative example will be described. Comparative Example 1
Will be described. 200kg /
compacting in cm ^2, it was sintered at 850 ° C., density 0.
An electrode having 64 g / cc and a sheet resistance of 1.3Ω / □ was obtained.
Comparative Example 2 will be described. 2 slurry of PVDC resin carbonized powder
Pressure molding at 0 kg / cm ² , sintering at 850 ° C,
An electrode having a density of 0.82 g / cc and a sheet resistance of 0.6 Ω / □ was obtained. Comparative Example 3 will be described. The slurry was formed by adding 2% by weight of cellulose fiber to the slurry. Other steps were the same as in the example. The obtained electrode has a density of 0.61 g / c.
c, sheet resistance was 1.8Ω / □. Comparative Example 4 will be described. The same molded product as in the example was sintered at 960 ° C. An electrode having an electrode density of 0.68 g / cc and a sheet resistance of 0.55 Ω / □ was obtained. Comparative Example 5 will be described. The amount of polyethylene glycol (PEG) added to the slurry was 21% by weight. Other steps were the same as in the example. The resulting electrode is
The density was 0.76 g / cc and the sheet resistance was 0.6 Ω / □.

After the electrodes obtained in Example 1 and Comparative Examples 1 to 5 were polished to a thickness of 1 mm, the sheet resistance was measured by a four-terminal four-needle method. Next, after impregnating the electrode 2 with water or diluted sulfuric acid, the electrode 2 is heated in the air at a temperature of 200 ° C. for 90 minutes, immersed again in 35 wt% sulfuric acid, and impregnated under reduced pressure for 24 hours to form a 200 μm thick glass nonwoven. An electrode 2 is opposed to the separator 1 made of fiber, a Pt plate is disposed outside the collector 2 to form a current collector plate 3, and a cell is produced by sandwiching and fixing the outer side with a fixing plate 4 made of Teflon. (See FIG. 4).
This cell was immersed in 35 wt% sulfuric acid, and the electrode volume capacity at a current density of 0.5 A / cm ² with respect to the electrode projected area was measured. Table 1 shows the measurement results.

[Table 1]

As can be seen from the results in Table 1, Example 1
-1 to 5 electrodes (the density is 0.65 to 0.75 g / cc and the sheet resistance is 0.9 to 3.0 Ω / □)
The electrodes of Comparative Examples 1 to 5 (the density is less than 0.65
The electrode volume capacity is increased as compared with the case of exceeding 75 g / cc or the sheet resistance is less than 0.9 Ω / □. This is because the capacitance at a high current density of 0.5 A / cm ² is affected by the equivalent series resistance and the diffusion resistance of the cell, and the higher these resistances, the greater the resistance loss and the more the capacitance cannot be taken out. The density of the electrode has a high correlation with the diffusion resistance of the cell, and as the density decreases, the diffusion resistance tends to decrease.
When the ratio is less than / cc, the capacitance decreases because the total amount of electrodes decreases as in Comparative Examples 1 and 3. Conversely, as the density increases, the diffusion resistance tends to increase. When the density exceeds 0.75 g / cc as in the electrode of Comparative Example 2, the sheet resistance does not increase, but the capacity decreases. Further, the sheet resistance has a high correlation with the equivalent series resistance (ESR) of the cell, and is also a sign of the progress of sintering. When the sheet resistance decreases, the ESR also decreases.
In the electrode lowered to about 0.6Ω / □ as in the case of the above electrode, the sintering proceeds too much, and the electrode structure that can be effectively used as an electric double layer capacitor is reduced. Therefore, even if the density is low, the capacity is small. That is, it has been found that there is a region where the electrode density and the sheet resistance are optimally balanced, and it is difficult to obtain a high capacitance in other regions. The range is from 0.65 to the density of the electrode manufactured in the steps of this embodiment.
0.75 g / cc, and the sheet resistance of the electrode is 0.9 to 3.0 Ω / □. Electrodes having a density and sheet resistance in this range exhibit a high capacity of around 26 F / cc.

[0028]

According to the present invention, it is possible to obtain an electric double layer capacitor and an electrode having a high capacity even at a high current density and having a strength sufficient for practical use.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of PVDC resin carbide powder particle size and electrode capacity.

FIG. 2 is an explanatory diagram of the amount of polyethylene glycol added and the electrode capacity.

FIG. 3 is an explanatory diagram of a phenol resin and an electrode capacity.

FIG. 4 is an explanatory diagram of a method for measuring characteristics of an electrode manufactured by the manufacturing method according to the present embodiment.

[Explanation of symbols]

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

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Takashi Noji 8 Tsuchinana, Fujisawa-shi, Kanagawa Prefecture Isuzu Central Research Institute Co., Ltd. (72) Inventor Tsutomu Masuko 6850 Omachi, Omachi City, Nagano Prefecture Showa Denko Co., Ltd.

Claims (8)

[Claims] 1. An electrode for an electric double layer capacitor made of PVDC resin carbide, wherein the density is 0.65 to 0.75 g / cc and the sheet resistance is 0.9 to 3.0 Ω / □. Characteristic electrode for electric double layer capacitors. 2. An electric double layer capacitor comprising an electrode made of PVDC resin carbide, wherein the density of the electrode is 0.65 to 0.75 g / cc,
An electric double layer capacitor characterized in that the electrode has a sheet resistance of 0.9 to 3.0 Ω / □. 3. An electric machine characterized in that a PVDC resin is carbonized at 180 ° C. to 600 ° C., and then pulverized to an average particle size of 8 to 12 μm, and the obtained carbide powder is sintered at 600 ° C. to 950 ° C. A method for manufacturing an electrode for a multilayer capacitor. 4. A method for producing an electrode for an electric double layer capacitor according to claim 3, wherein a slurry in which a PVDC resin carbide is dispersed in water or a solvent composed of a mixture of water and an alcohol solvent is poured into a mold. And a step of removing volatile components of the slurry. 5. The method for manufacturing an electrode for an electric double layer capacitor according to claim 4, wherein the slurry comprises polyethylene glycol or a derivative thereof having a molecular weight of up to 2 million, a resole type phenol resin, a powdery or fibrous material. A resin with a residual carbon ratio of 30% or less,
A method for producing an electrode for an electric double layer capacitor, comprising: 6. The method for producing an electrode for an electric double layer capacitor according to claim 5, wherein the amount of polyethylene glycol or a derivative thereof having a molecular weight of up to 2 million is 5 to 5% with respect to the PVDC resin carbide.
18 wt%, the amount of resol type phenolic resin added is 5 to 8 wt%, and the powdery or fibrous resin having a residual carbon ratio of 30% or less is 0.5 to 2.5 wt%. A method for producing an electrode for an electric double layer capacitor, characterized by comprising: 7. The method for producing an electrode for an electric double layer capacitor according to claim 4, wherein the step of removing volatile components of the slurry is a step of drying at room temperature to 90 ° C. A method for producing an electrode for an electric double layer capacitor, characterized by comprising: 8. The method for producing an electrode for an electric double layer capacitor according to claim 4, wherein the molding is performed in a non-pressurized state. Production method.