JPH0883736A - Active carbon electrode of electronic double-layer capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE: To stably obtain an active carbon electrode which is high in electrostatic capacitance and quality by a method wherein a carbide is subjected to a primary activation treatment to serve as a carbon material, binder is added to the carbon material, the binder-loaded carbon material is molded, and the molded body is subjected to a carbonization treatment and then to a secondary activation treatment. CONSTITUTION: Novolak phenolic resin is cured and then ground into particles prescribed in size, the resin particles are carbonized by a thermal treatment carried out in a nitrogen atmosphere. In succession, the carbonized particles are thermally treated into granular activated carbon material in a carbon dioxide gas atmosphere through a primary activation treatment. The granular activated carbon material is ground into powder, and phenolic resin, ethanol, and creosote are mixed as binder into the activated carbon powder, which is kneaded well and molded into a plate-like piece. The molded plate-like piece is subjected to a carbonization treatment in a nitrogen atmosphere, and thermally treated into a plate-like activated carbon in a carbon dioxide gas atmosphere through a secondary activation treatment. By this setup, an active carbon electrode high in electrostatic capacitance and quality can be stably obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an activated carbon electrode suitably used as an electric double layer capacitor and an activated carbon electrode obtained thereby.

[0002]

2. Description of the Related Art Electric double layer capacitors have been put to practical use as backup power sources for electronic devices such as personal computers, and have also been developed as auxiliary power sources for supplying instantaneous large current such as auxiliary batteries for automobiles. The electrode of this electric double layer capacitor is called a polarizable electrode and is required to have a large capacitance. Therefore, a conductive carbon material having a large specific surface area is used as the material of the polarizable electrode, and activated carbon which is already activated is particularly preferable. The activated carbon base material that has been activated includes powdery and fibrous materials.

In the production of activated carbon, various pyrolyzable carbon compounds such as carbonaceous materials such as coke, coal and coconut husk charcoal to thermosetting resins such as phenol resin are used as raw materials. FIG. 6a is an outline of the activated carbon manufacturing process using a phenol resin as a raw material. As shown in this figure, first, the phenol resin is hardened and then activated by a carbonization process in which components other than carbon are volatilized by dry distillation, and activated if necessary.
The powder is sized to obtain a powdery or granular activated carbon base material. There is also known a method in which acrylic fiber or the like is used as a carbon compound raw material and a fibrous activated carbon base material is similarly obtained through a process such as carbonization while maintaining the fiber shape.

Conventionally, the powdery or granular activated carbon base material is mixed with a sulfuric acid solution and used as a paste for a polarizable electrode of an electric double layer capacitor, but the contact resistance between activated carbon particles is large and large. I couldn't pass the current.
Similarly, when a fibrous activated carbon cloth was used, the contact resistance between fibers and the activated carbon density per unit volume were small, and a large current could not be obtained.

Therefore, as shown in FIG. 6b, a method is conceivable in which a binder is further added to the activated carbon base material to form a plate, and the added binder is similarly carbonized and sintered to form a plate-like formed body. For the binder, a thermally decomposable carbon compound that becomes carbonaceous after carbonization is selected, but in this case,
The same phenolic resin as the raw material is preferable. Even when fibrous activated carbon is used as the base material, if a space between the fibers is filled with a binder, and carbonized and similarly sintered, it becomes a plate-like material having a high density and can be expected to be used as a polarizable electrode.

[0006]

However, an activated carbon polarizable electrode for an electric double layer capacitor obtained by adding a binder to the conventional activated carbon base material and carbonizing / sintering it as described above has a static per unit weight. There is the disadvantage that the capacitance is often lower than that of the substrate. For the cause,
In the above-mentioned conventional method, not only the carbonaceous component generated by carbonization of the added binder is not activated,
It is speculated that this carbonaceous component may inhibit the activity of the base material for some reason. Therefore, as shown in FIG. 6c, the activated carbon base material was not activated before it was obtained, and an attempt was made to add the binder to the unactivated activated carbon powder, followed by molding, and finally performing activation treatment. It was not possible to obtain a strong product, and cracks were generated during the activation treatment, and molding was difficult. Furthermore, the electrostatic capacity did not improve as expected. As described above, the activated carbon electrode manufactured by the above-mentioned conventional method has a weak mechanical strength, and thus a large plate-like electrode suitable for large-current discharge is not obtained.

The present invention has been made in view of the above circumstances, and provides an activated carbon electrode suitable for an electric double layer capacitor having mechanical strength capable of being formed into a large plate shape and capable of discharging a large current. Is intended.

[0008]

The method for producing an activated carbon electrode for an electric double layer capacitor according to the present invention comprises a carbon base material obtained by subjecting a carbide obtained by carbonizing a carbon compound to a primary activation treatment. It is characterized in that a binder is added to a carbon substrate to form a molded body, and the molded body is carbonized and then subjected to a secondary activation treatment.

As the carbon compound, coconut husk, wood, coal, pitch, natural polymer, synthetic polymer and the like can be used, but a phenol resin is preferable. As the binder, phenolic resin powder is used as an alcohol or an organic solvent such as ketones such as acetone or cyclohexanone and creosote oil, coal tar, anthracene oil, kerosene, liquid paraffin, ethylene glycol, lipophilicity such as glycerin. Those dissolved in a liquid can be used.

Here, the activation treatment is to heat-treat the material in a carbon dioxide gas or steam atmosphere, and in the present invention, in the secondary activation treatment, the following formula (i) activation yield = (activation treatment (Weight after treatment / weight before activation treatment) × 100 ... (i) The temperature and time of the heat treatment are selected so that the activation yield of the secondary activation treatment obtained is 75% or more. Furthermore, the total activation yield obtained by the following formula (ii): total activation yield = activation yield of primary activation treatment x activation yield of secondary activation treatment ÷ 100 ... (ii) is 70 to 95%. Is characterized by.

The activated carbon electrode for an electric double layer capacitor of the present invention is characterized in that the activated carbon electrode produced by the above method has a specific surface area of 600 to 1500 m ² / g.

[0012]

The activated carbon molded body according to the conventional method (FIG. 6b) in which the activated activated carbon base material is molded into a plate-like electrode shape using a binder such as phenol resin and then the binder or the like is carbonized is based on the activity. It may be lower than that of wood. On the other hand, as shown in FIG. 6c, if it is not activated in the manufacturing process of the activated carbon of the base material and is activated once after sintering, the formability into a plate-shaped compact is poor.

Therefore, an activated carbon electrode for an electric double layer capacitor cannot be obtained by only activating once, and as shown in FIG. 1, a previously activated (primarily activated) activated carbon base material is formed into a plate shape by using a binder. It has been clarified that it is essential to carbonize the binder and the like after forming the electrode shape, and then activate again (secondary activation) in order to obtain an activated carbon electrode for an electric double layer capacitor. Furthermore, as a result of repeated trial and error on activation conditions and various studies, it was found that the activation yield is an extremely important requirement not only for moldability but also for electrostatic capacity.

First, in the secondary activation treatment, the activation treatment yield represented by the above formula (i) has a great influence on the formability, and unless the value is 75% or more, the electrode can be formed into a good electrode shape. Can not. Further, by selecting the temperature and time of the heat treatment so that the total activation yield, which is the product of the primary and secondary activation yields, falls within the range of 70 to 95%, the electrostatic capacity is high and stable. The value of capacitance is obtained. Furthermore, when the specific surface area is in the range of 600 to 1500 m ² / g, an activated carbon electrode having a stable and high capacitance can be obtained.

Therefore, by controlling the activation yield and the specific surface area in the process of manufacturing the activated carbon electrode, it is possible to stably obtain a high quality activated carbon electrode having excellent moldability and high electrostatic capacity.

[0016]

EXAMPLES The present invention will be described in more detail by way of examples. According to the manufacturing process shown in FIG. 1, an active carbon electrode was manufactured using phenol resin as a raw material. Example 1 below
In Example 2, in Example 1, the effect of activation treatment in a carbon dioxide gas atmosphere was investigated, and in Example 2, the effect of activation treatment in a steam atmosphere was examined. Experiments (1) to (11) in Example 1 were conducted by changing the temperature and time of the primary and secondary activation treatments and examining the influence thereof. Further, in Experiments (12) to (14), the results of not performing the secondary activation treatment, and in Experiment (15), the results of not performing the primary activation treatment are compared.

Example 1: Activation experiment in carbon dioxide atmosphere (1) After curing a novolac type phenol resin at 160 ° C.,
It was crushed to about 2 mm square. 900 ℃ in nitrogen gas
And heat treated for 30 minutes to carbonize. Next, in carbon dioxide,
Heat treatment at 900 ℃ for 1 hour to activate the primary surface area 65
A granular activated carbon base material of 0 m ² / g was obtained. Primary activation yield (=
The weight after activation / weight before activation) was 92%.

This granular activated carbon base material was pulverized to obtain a powder having an average particle size of 8 μm, and 15 parts by weight of a phenol resin as a binder, 8 parts by weight of ethanol, and 20 parts by weight of creosote were added to 100 parts by weight of the powder. And knead, press at a pressure of 500 kg / cm ² , 50 × 50
It was a plate-shaped molded product of × 1 (mm).

The molded body thus obtained was heated in a nitrogen gas at a heating rate of 100 ° C./h to 900 ° C. and held for 30 minutes to carry out a carbonization treatment, followed by heat treatment in a carbon dioxide gas at 800 ° C. for 10 hours. And then activated secondarily. The activation yield (= weight after activation / weight before activation) at that time was 93%. Therefore, the total activation yield is 0.92 × 0.93 × 100 = 86%.
The BET specific surface area of the obtained molded product was measured and found to be 74
It was 0 m ² / g.

Since the secondary activation treatment did not cause warping or cracks in the molded body, it is now expected that 14 mmφ
Cut out 2 (thickness 1mm) discs, 30w in vacuum
A t% sulfuric acid solution was impregnated into the measurement cell shown in FIG. 2 to determine the capacitance. In FIG. 2, reference numeral 1 is an activated carbon electrode,
2 is a gasket, 3 is a collecting electrode, and 4 is a separator.
Capacitance C is generally calculated by the following formula (ii) after charging, discharging at constant current I, and measuring time Δt during which voltage V1 drops to V2.
i) can be obtained. C = I × Δt / (V 2 −V 1) ... (iii) Here, after charging at 900 mV for 24 hours, 4 mA / cm ²
Discharged at 400 mA / cm ² after charging for 2 hours
Discharged. And in each case, V1 = 540 mV, V2 =
61 F when 360 mV and 4 mA / cm ² each
/ Cm ³ and 400 mA / cm ² , 26 F / cm ³ was obtained.

Experiments (2) to (11) The temperature and time of the primary and secondary activation treatments in Experiment (1) were changed to examine their influence on the moldability and the electrostatic capacity. The results of the experiment (1) are also summarized in Table 1.

Experiment (12) The molded body obtained in the experiment (1) was carbonized under the same conditions as in the experiment (1), and was subjected to the secondary activation treatment without being subjected to the secondary activation treatment.
Experiment by cutting two φ (1mm thick) discs
The capacitance was measured in the same manner as in. The results are listed in Table 1.

Experiment (13) The capacitance was measured in the same manner as in Experiment (12) except that the time for primary activation was set to 2 hours. The results are listed in Table 1.

Experiment (14) The electrostatic capacity was measured in the same manner as in Experiment (12) except that the primary activation time was 3 hours. The results are listed in Table 1.

Experiment (15) An activated carbon electrode was obtained and the capacitance was measured in the same manner as in Experiment (1) except that the primary activation was not performed. The results are listed in Table 1.

[0026]

[Table 1]

In Table 1 above, experiments (1) to (11)
Are the essential requirements in the method of the present invention
The following activation was carried out, and those conditions were changed. First, regarding the secondary activation, it was observed that when the activation yield was lowered, the formability into a plate-like shape was deteriorated. In experiments (4) and (5), the secondary activation yield was 76, respectively.
%, 75%, and an extremely slight warp that was not problematic in practical use was recognized. In the experiment (6), the secondary activation yield was 73%, warpage and cracking occurred, and a plate-shaped compact could not be obtained. From the above, the secondary activation yield was 7
It can be seen that if it is less than 5%, it can be molded into a plate-like electrode shape, but if it is 75% or more, sufficient moldability cannot be obtained. further,
In the experiment (15), the primary activation was not performed, and cracks were generated and brittle and could not be formed into a plate shape.

The capacitance of the plate shaped electrode is shown in FIG. 3 as a function of overall yield. In this figure, the points connected by a solid line are those obtained by primary and secondary activation, and the total yield is high in the range of 70 to 95% for both the current of 4 mA / cm ² and 400 mA / cm ^2. Although the electric capacity is shown, the electrostatic capacity is reduced at less than 70% and 95% or more. On the other hand, the points connected by the broken lines are those for which secondary activation is not performed (Experiments (12) to (14)), and the capacitance is low.

Example 2 Activation in Steam Atmosphere In Example 2, the primary and secondary activation treatments were performed in a steam atmosphere according to the manufacturing process shown in FIG. Experiment (1
6) to (22) are the results of investigating the effects of changing the temperature and time of the primary and secondary activation treatments. On the other hand, in Experiments (23) to (24), the results without the secondary activation treatment are compared.

Experiment (16) The novolak type phenol resin was cured and carbonized in the same manner as in Experiment (1). Continuously, in a steam atmosphere, 800
Heat treatment at ℃ for 3.5 hours for primary activation, specific surface area 620
to obtain a granular activated carbon substrate m ² / g. Primary activation yield is 94
%Met.

The above granular activated carbon base material was pulverized to an average particle size of 8 μm, and a binder was added in the same manner as in Experiment 1 to form a good molded product, which was then carbonized. Subsequently, heat treatment was performed at 800 ° C. for 9 hours in a steam atmosphere for activation. The activation yield was 85%. Therefore, the total activation yield is 0.94 × 0.85 × 100 = 80%. The BET surface area was measured and found to be 970 m ² / g. Also,
As a result of measuring the electrostatic capacity in the same manner as in the experiment (1), 4 m
When ^{A / cm 2 58F / cm 3} , it was 22F / cm ³ when 400 mA / cm ^2.

Experiments (17) to (22) In Experiment (16), the temperature and time of the primary and secondary activation treatments were changed to examine their influence on the moldability and the electrostatic capacity. The results are shown in Table 2 together with the result of the experiment (16).

Experiments (23) to (24) The conditions for the primary activation in the steam atmosphere were changed, the secondary activation was not performed, and the other conditions were the same as in the experiment (16). Since the plate formability was good, the capacitance was measured and the results are shown in Table 2.

[0034]

[Table 2]

In Table 2 above, experiments (16) to (2
In 2), primary and secondary activation, which are indispensable requirements in the method of the present invention, are carried out, and the conditions are changed. First, regarding the secondary activation, it was observed that when the activation yield was lowered, the formability into a plate-like shape was deteriorated. In experiments (21) and (22) in which the secondary activation yield did not reach 74%, 72% and 75%, warping and cracking occurred and a plate-shaped molded body was not obtained. It can be seen that moldability cannot be obtained.

Next, the capacitance of a plate-shaped electrode is shown in FIG. 4 as a function of the total activation yield. The points connected by solid lines in this figure indicate the primary and secondary activations. The current was 4 mA / cm ² and 400 mA /
cm ² together, but overall yield indicates a high capacitance in a range of 70% to 95%, is less than 70% and less than 95%, the capacitance is decreased. On the other hand, the points connected by broken lines are those for which secondary activation has not been performed (Experiments (23) to (2
4)), and it can be seen that the capacitance is lower than the previous one.

Further, as shown in FIG. 5, the BET specific surface area has a relation that it decreases as the total yield increases. Whether the activation treatment atmosphere is carbon dioxide gas or water vapor, there is no difference and the overall yield is 70 to 95, which shows good characteristics.
The BET specific surface area corresponding to the range of% is 600 to 16
It was 00 m ² / g.

[0038]

As described above, in the activated carbon electrode according to the present invention, the carbide obtained by curing and carbonizing a carbon compound is first activated to obtain an activated carbon base material, and a binder is added thereto. It is molded and subsequently subjected to secondary activation to manufacture.
In the present invention, by selecting the temperature and time so that the activation yields of the primary and secondary activations have specific values, it is possible to form a good plate shape suitable for an electrode and to obtain a specific specific surface area of the specific surface area. An activated carbon electrode can be obtained, and an excellent electrode for an electric double layer capacitor having a large capacitance can be obtained.

[Brief description of drawings]

FIG. 1 is a process drawing showing an example of a method for manufacturing an activated carbon electrode of the present invention.

FIG. 2 is a sectional view of an activated carbon electrode produced in an example of the present invention.

FIG. 3 is a graph showing the results of Examples of the present invention and is a graph showing the relationship between the electrostatic capacity and the activation yield of an activated carbon electrode produced by carbon dioxide gas activation.

FIG. 4 is a graph showing the results of the examples of the present invention and is a graph showing the relationship between the capacitance and the activation yield of the activated carbon electrode produced by steam activation.

FIG. 5 is a graph showing the results of the examples of the present invention and is a graph showing the relationship between the electrostatic capacity and the BET specific surface area of manufactured activated carbon electrodes.

[FIG. 6] FIG. 6 is a diagram illustrating a conventional manufacturing process of activated carbon and an activated carbon electrode.

[Explanation of symbols]

1 ... Activated carbon electrode, 2 ... Gasket, 3 ... Collection electrode,
4 ... Separator.

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[Procedure amendment]

[Submission date] September 20, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

Since the secondary activation treatment did not cause warping or cracks in the molded body, it is now expected that 14 mmφ
Cut out 2 (thickness 1mm) discs, 30w in vacuum
A t% sulfuric acid solution was impregnated into the measurement cell shown in FIG. 2 to determine the capacitance. In FIG. 2, reference numeral 1 is an activated carbon electrode,
2 is a gasket, 3 is a collecting electrode, and 4 is a separator.
Capacitance C is generally calculated by the following formula (ii) after charging, discharging at constant current I, and measuring time Δt during which voltage V1 drops to V2.
i) can be obtained. C = I × Δt / ( V1-V2 ) (iii) Here, after charging at 900 mV for 24 hours, 4 mA / cm ²
Discharged at 400 mA / cm ² after charging for 2 hours
Discharged. And in each case, V1 = 540 mV, V2 =
61F at 360 mV and 4 mV / cm ² each
/ Cm ³ and 400 mA / cm ² , 26 F / cm ³ was obtained.

Front Page Continuation (72) Inventor Akihiro Nakamura 3054-3 Shimokurosawa Shimokurosawa, Takane-cho, Kitakoma-gun, Yamanashi Prefecture Yamanashi Research Institute (72) Inventor Shinichi Marumo 3054-3 Shimokurosawa, Takane-cho, Kitakoma-gun Yamanashi Nihon Oxygen Yamanashi Laboratory Co., Ltd. (72) Inventor Toshiya Miyagawa 3054-3 Shimokurosawa Shimokurosawa, Takane-cho, Kitakoma-gun, Yamanashi Nihon Oxygen Co., Ltd. Yamanashi Laboratory

Claims (6)

[Claims] 1. A carbonized material obtained by carbonizing a carbon compound is subjected to a primary activation treatment to form a carbon base material, a binder is added to the carbon base material to form a molded body, and the molded body is carbonized. A method for producing an activated carbon electrode for an electric double layer capacitor, which is characterized by performing a secondary activation treatment later. 2. The method for producing an activated carbon electrode for an electric double layer capacitor according to claim 1, wherein the carbon compound is a phenol resin. 3. The method for producing an activated carbon electrode for an electric double layer capacitor according to claim 1, wherein the binder is a composition comprising a phenol resin powder, an organic solvent and a lipophilic liquid. 4. The primary activation treatment and the secondary activation treatment are heat treatments in a carbon dioxide gas atmosphere or a steam atmosphere.
And, the activation yield in the secondary activation treatment obtained by the following formula (i): activation yield = (weight after activation treatment / weight before activation treatment) × 100 (i) is 75%
It is above, The manufacturing method of the activated carbon electrode for electric double layer capacitors in any one of Claim 1 to 3 characterized by the above-mentioned. 5. The primary activation treatment and the secondary activation treatment are heat treatments in a carbon dioxide gas atmosphere or a steam atmosphere,
And the total activation yield obtained by the following formula (ii): total activation yield = activation yield of primary activation treatment x activation yield of secondary activation treatment ÷ 100 ... (ii) is 70 to 95%. A method for producing an activated carbon electrode for an electric double layer capacitor according to any one of claims 1 to 3. 6. An activated carbon electrode for an electric double layer capacitor, which is produced by the method for producing an activated carbon electrode for an electric double layer capacitor according to claim 1 and has a specific surface area of 600 to 1500 m ² / g.