JP2001052972A - Manufacture of alkali activated carbon for electrode of electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkali activated carbon for the electrode of an electric double-layered capacitor capable of enhancing electrode density. SOLUTION: At providing an alkali activated carbon, there are provided successively a process where a mesophase pitch lump is crushed to provide a pulverized powder, a process where the pulverized powder is processed for infusibility at 300-450 deg.C in an atmospheric current, a process where the pulverized powder is carbonized at 600-900 deg.C in an inert gas current to provide a carbide powder, a process where the carbide powder is alkali-activation processed at 500-1000 deg.C in an inert gas atmosphere then a post-process provides an alkali activated carbon, and a process where the alkali activated carbon is crushed.

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 alkali activated carbon for an electrode of an electric double layer capacitor.

[0002]

2. Description of the Related Art Conventionally, as this type of activated carbon for electrodes,
In order to increase the capacitance, alkali activated carbon using mesophase pitch as a raw material has been used.

[0003] This alkali activated carbon is produced by spinning using a mesophase pitch to produce a fibrous material, then subjecting the fibrous material to an infusibilization treatment and a subsequent carbonization treatment, and then to an alkali activation treatment It is manufactured by a method of performing a pulverization treatment or performing an alkali activation treatment after the pulverization treatment.

[0004]

However, since the alkali activated carbon according to the conventional method is obtained by pulverizing a fibrous material, even if the length is shortened by pulverization, it is broken in the longitudinal direction, that is, the fiber end face is broken. It is difficult to cause breakage such as fragmentation, and excessive pulverization may cause deterioration of performance. Therefore, alkali activated carbon contains many particles in columnar form.
When an electrode is constructed using such an alkali activated carbon,
The columnar particles are randomly dispersed and voids are easily formed between them, so that the electrode density (g / cc) is low and the capacitance density (F / cc) of the electric double layer capacitor is increased. The problem was that it was not possible.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing an alkaline activated carbon capable of increasing the electrode density by employing a specific means.

According to the present invention, in order to achieve the above object,
A step of subjecting the bulk mesophase pitch to a pulverization process to obtain a pulverized powder;
A step of performing infusibilizing treatment at a temperature of 450 ° C. or less, a step of subjecting the pulverized powder to a carbonizing treatment in an inert gas stream at a temperature of 600 ° C. to 900 ° C. to obtain a carbonized powder, In an inert gas atmosphere, at least 500 ° C, 100
Performing an alkali activation treatment under a condition of 0 ° C. or lower, and then performing a post-treatment to obtain an alkali activated carbon; and sequentially performing a pulverizing process on the alkali activated carbon, the alkali activation for an electrode of an electric double layer capacitor. A method for producing charcoal is provided.

[0007] The alkali activated carbon obtained by the above-mentioned method is composed of crushed powder of lumpy mesophase pitch as a starting material, and is therefore composed of lumpy particles. Therefore, it is possible to greatly increase the electrode density.

[0008] In the infusibilization treatment, the temperature is 30
If the temperature is lower than 0 ° C., the infusibilization is insufficient, so that the pulverized powder is melted in the next carbonization step. On the other hand, if the temperature exceeds 450 ° C., the oxidation excessively proceeds, which is not preferable. In the carbonization treatment, if the temperature is lower than 600 ° C., the density of the alkali activated carbon obtained in the next step is reduced.
When the temperature exceeds 00 ° C., activation of the carbonized powder becomes very difficult to proceed. Further, in the alkali activation treatment, the temperature is 50
If the temperature is lower than 0 ° C., the activation hardly proceeds. On the other hand, if the temperature is higher than 1000 ° C., excessive activation lowers the density of the alkali activated carbon and the yield thereof.

[0009]

1 and 2, a cylindrical electric double-layer capacitor 1 has an Al container 2, an electrode winding body 3 accommodated in the container 2, and an electrode wound body 3 injected into the container 2. Electrolyte solution. The container 2 comprises a bottomed cylindrical main body 4 and a terminal plate 5 for closing one end opening thereof.
Are provided with positive and negative terminals 6, 7 and a safety valve 8.

The wound electrode body 3 has a positive electrode laminated band 9 and a negative electrode laminated band 10. The positive electrode laminated band 9 is formed by attaching a band-shaped polarizable electrode e to both sides of a band-shaped current collector 11 made of aluminum foil using a conductive adhesive, and PTFE (polytetrafluoroethylene) is applied to one of the band-shaped polarizable electrodes e. The first separator 13 made of ethylene is superposed. A belt-like positive electrode 12 is constituted by the pair of polarizable electrodes e. Further, the first separator 13 is impregnated and held with the electrolytic solution. The negative electrode laminated strip 10 is a strip-shaped current collector 1 made of aluminum foil.
A band-shaped polarizable electrode e is adhered to both sides of each of the electrodes 4 using a conductive adhesive, and a second separator 16 made of PTFE is superposed on one band-shaped polarizable electrode e.
A strip-shaped negative electrode 15 is constituted by the pair of polarizable electrodes e. In addition, the second separator 16 is impregnated and held with the electrolytic solution.

In manufacturing the wound electrode body 3, the second separator 16 of the negative electrode lamination strip 10 is superimposed on the exposed polarizable electrode e of the positive electrode lamination strip 9, and the superposed product is
The first separator 13 of the positive electrode laminated strip 9 is spirally wound so as to be located on the outermost side.

As the electrolyte, borofluorinated fourth ammonium
Compounds, such as TEMA.BF _Four[(C_TwoH_Five)_Three
CH_ThreeN ・ BF_Four(Triethyl borofluoride ammonium
), Solute] PC (propylene carbonate,
Medium) solution is used.

As activated carbon for electrodes, alkali activated carbon using mesophase pitch as a raw material is used, and the alkali activated carbon is produced by the following method.

That is, a step of subjecting the bulk mesophase pitch to a pulverization process to obtain a pulverized powder;
A step of performing infusibilizing treatment at a temperature of 300 ° C. or more and 450 ° C. or less;
A step of obtaining a carbonized powder by performing a carbonization treatment at a temperature of 900 ° C. or less;
The step of performing an alkali activation treatment at a temperature of 1000 ° C. or lower and then performing a post-treatment to obtain an alkali activated carbon, and the step of pulverizing the alkali activated carbon are sequentially performed.

The treatment time is preferably 0.5 hours or more and 10 hours or less in each of the infusibilization treatment, the carbonization treatment, and the alkali activation treatment. In any of the processes, if the processing time is less than the lower limit value, the intended purpose cannot be achieved. On the other hand, if the processing time exceeds the upper limit value, the characteristics of the processed product may be impaired.

The alkali activated carbon obtained by the above-mentioned method is composed of fine lump particles because the pulverized powder of the lump mesophase pitch is used as a starting material. Since the structure is close to the close-packed structure, the electrode density can be greatly increased.

Hereinafter, a specific example will be described. [Example] First, alkali activated carbon using mesophase pitch as a raw material, and in this example, KOH activated carbon were produced by the following method.

(A) The pulverized mesophase pitch is pulverized at room temperature to produce a pulverized powder having an average particle size of 300 μm. Then, the pulverized powder is subjected to infusibilization treatment at 350 ° C. for 2 hours in an air stream. After that, the pulverized powder was mixed with nitrogen
Carbonization was performed at 00 ° C. for 1 hour to obtain carbonized powder.
(B) mixing carbonized powder with KOH twice as much as the carbon weight thereof, and then subjecting the mixture to a potassium activation treatment as an alkali activation treatment at 800 ° C. for 5 hours in a nitrogen atmosphere;
Thereafter, the mixture was subjected to post-treatments such as neutralization with hydrochloric acid, washing and drying to obtain KOH-activated carbon. (C) KO
The H activated carbon was subjected to a pulverization treatment by a jet mill to obtain a fine KOH activated carbon having a predetermined average particle size. Hereinafter, this fine KOH activated carbon is simply referred to as KOH activated carbon.

KOH activated carbon having a predetermined average particle size, graphite powder (conductive filler) and PTFE (binder)
The weight ratio was 5: 12.5: 2.5, the weighed material was kneaded, and then rolled using the kneaded material to produce an electrode sheet having a thickness of 175 μm. A plurality of band-shaped polarizable electrodes e having a width of 95 mm and a length of 1500 mm are cut out from the electrode sheet, and these two band-shaped polarizable electrodes e are
The positive electrode laminated band 9 was manufactured using a belt-shaped current collector 11 having a width of 105 mm, a length of 1500 mm, and a thickness of 40 μm, a conductive adhesive, and a 75 μm-thick first separator 13 made of PTFE. Further, the negative electrode laminated band 10 was manufactured using the same two band-shaped polarizable electrodes e, the band-shaped current collector 14 and the conductive adhesive, and using the second separator 16 having a thickness of 75 μm. .

Then, the second separator 1 of the negative electrode laminated band 10 is applied to the exposed band-shaped polarizable electrode e of the positive electrode laminated band 9.
6 and the superimposed product is placed on the first
Is wound in a spiral so that the separator 13 is located at the outermost position, thereby producing the electrode winding body 3.
And an electrolytic solution prepared by dissolving 1.5 mol of TEMA.BF ₄ in a PC solution are placed in a bottomed cylindrical main body 4 of a container 2 having an inner diameter of 50 mm and a length of 130 mm. And closed to obtain a cylindrical electric double layer capacitor 1. At the time of the closing, both the current collectors 1 of the positive electrode laminated band 9 and the negative electrode laminated band 10
1 is connected to the positive terminal 6 and the negative terminal 7 of the terminal plate 5, respectively. In the same manner, four more cylindrical electric double layer capacitors 1 were manufactured. These capacitors 1 are examples (1) to (5). [Comparative Example] A fibrous material having an average diameter of 10 µm was produced by spinning using a mesophase pitch, and then the fibrous material was subjected to infusibilization treatment, carbonization treatment, and alkali activation treatment under the same conditions as in the above-mentioned Example. Then, a pulverization treatment was sequentially performed to obtain a KOH-activated carbon having a predetermined average particle size.

Next, five cylindrical electric double layer capacitors 1 were manufactured in the same manner as in the above embodiment. These capacitors 1 are examples (6) to (10). [Performance of Electric Double Layer Capacitor] Table 1 shows the average particle size of the KOH-activated carbon for the examples (1) to (10) of the electric double layer capacitor 1, the positive and negative electrodes 12, 15 and therefore the electrodes of the polarizable electrode e. The density and the capacitance density (F / cc) are shown. The average particle size of the KOH activated carbon was measured using a particle size distribution analyzer, and charging was performed at 45 V in an atmosphere of 2.5 V.

[0022]

[Table 1]

FIG. 3 shows a microscopic structure of the surface of the polarizable electrode e in the embodiment. From FIG. 3, it can be seen that the fine massive particles have a structure close to the close-packed structure.

FIG. 4 shows the microstructure of the surface of the polarizable electrode e in the comparative example. From FIG. 4, it can be seen that the columnar particles are randomly dispersed and voids are generated between them.

FIGS. 5 and 6 show examples (1) to (4) based on Table 1.
9 is a graph showing the relationship between the average particle size and the electrode density for (5) and Examples (6) to (10).
As shown in FIG. 5, when the KOH activated carbon according to the embodiment is used, the electrode density is reduced to about 1 g / cc as in Examples (2) and (3).
However, in the case of the comparative example, the electrode density is only about 0.9 g / cc as in Examples (7) and (8).

As is clear from Table 1, FIGS. 5 and 6, Examples (1) to (5) using the KOH-activated carbon according to the examples are Examples (6) to (10) using the KOH-activated carbon according to the comparative example. ), The electrode density is higher, and the capacitance density is correspondingly higher. This is, as shown in FIGS.
This is due to the difference in the particle shape of the OH-activated carbon.

Next, a cycle test was performed on Example (2) having the highest electrode density in Examples (1) to (5) and Example (7) having the highest electrode density in Examples (6) to (10). Then, the capacitance deterioration rate and the internal resistance rise rate were examined, and the results shown in FIGS. In the cycle test, under a 45 ° C atmosphere, 20V at 2.5V, 30A
Charge for a minute, then discharge to zero farads,
This was defined as one cycle, and 200 cycles were repeated.

As is apparent from FIGS. 7 and 8, it is understood that both the capacitance deterioration rate and the internal resistance rise rate of Example (2) are lower than those of Example (7). This is because KOH-activated carbon made from mesophase pitch has the characteristic that it expands at the initial stage of repeated charging and discharging. Due to the expansion, the electrode density further increases in Example (2). The descent becomes extremely slow over time.
In this case, it is considered that the separation between the columnar particles due to the expansion and the accompanying expansion of the voids proceed rapidly with time.

[0029]

According to the present invention, by employing the above-described means, it is possible to obtain an alkali activated carbon composed of fine aggregated particles, thereby increasing the electrode density and improving the characteristics of the electric double layer capacitor. Can be done.

[Brief description of the drawings]

FIG. 1 is a cutaway perspective view of a main part of a cylindrical electric double layer capacitor.

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3 is a microscopic view of the surface of an example of a polarizable electrode.

FIG. 4 is a microscopic view of the surface of another example of the polarizable electrode.

FIG. 5 is a graph showing an example of the relationship between the average particle size of KOH-activated carbon and the electrode density.

FIG. 6 is a graph showing another example of the relationship between the average particle size of KOH-activated carbon and the electrode density.

FIG. 7 is a graph showing the relationship between the number of cycles and the capacitance deterioration rate.

FIG. 8 is a graph showing the relationship between the number of cycles and the rate of increase in internal resistance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical electric double layer capacitor 2 Container 3 Electrode winding body 11, 14 Strip current collector 12 Strip positive electrode 15 Strip negative electrode 13, 16 Separator

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[Procedure amendment]

[Submission date] October 18, 2000 (2000.10.
18)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

[0021] Then, to produce five the cylindrical electric double-layer capacitor 1 in the same manner as in the case of the embodiment. These capacitors 1 are examples (6) to (10). [Performance of Electric Double Layer Capacitor] Table 1 shows the average particle size of the KOH-activated carbon for the examples (1) to (10) of the electric double layer capacitor 1, the positive and negative electrodes 12, 15 and therefore the electrodes of the polarizable electrode e. The density and the capacitance density (F / cc) are shown. The average particle size of the KOH activated carbon was measured using a particle size distribution analyzer, and charging was performed at 45 V in an atmosphere of 2.5 V.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

FIG. 3 shows the microstructure of the surface of the polarizable electrode e in Example (2) . From FIG. 3, it can be seen that the fine massive particles have a structure close to the close-packed structure.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

FIG. 4 shows the microstructure of the surface of the polarizable electrode e in Example (7) . From FIG. 4, it can be seen that the columnar particles are randomly dispersed and voids are generated between them.

Claims (1)

[Claims] A step of subjecting the bulk mesophase pitch to a pulverization process to obtain a pulverized powder;
A step of performing infusibility treatment at a temperature of 300 ° C. or more and 450 ° C. or less, and a step of subjecting the pulverized powder to a carbonization treatment at 600 ° C. or more and 900 ° C. or less in an inert gas stream to obtain a carbonized powder. , 500 g of the carbonized powder in an inert gas atmosphere.
A step of performing an alkali activation treatment under the condition of not less than 1000 ° C. and not more than 1000 ° C. and then performing a post-treatment to obtain an alkali activated carbon; and a step of performing a pulverization treatment on the alkali activated carbon. A method for producing an alkali activated carbon for an electrode of a double-layer capacitor.