JPH11222732A - Mesophase pitch-based activated carbon fiber and electric double layer capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double layer capacitor capable of expressing a high service capacity when used as an electrode material by crushing and treating to activate with an alkali mesophase pitch-based carbon fibers produced by carbonizing mesophase pitch-based and infusibilized fibers at a specific temperature. SOLUTION: This mesophase pitch-based activated carbon fibers are produced by crushing mesophase pitch-based carbon fibers produced by carbonizing mesophase pitch-based infusibilized fibers or after the infusibilization at 350-1000 deg.C, preferably 350-800 deg.C into 5-50 μm, preferably 10-30 μm average particle size, successively treating to activate the product with an alkali. The electric double layer capacitor is obtained by using the activated carbon fibers. Preferably, both of pores A having 0.4-1.5 μm pore radius measured by the MP method using nitrogen absorption and pores B having 3.5-6 nm pore radius measured by a mercury porosimeter are present in the activated carbon fibers, and a ratio Bv/Av as the pore volume Bv of the pores B to the pore volume Av of the pores A, is 0.01-0.25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an activated carbon fiber obtained by activating a mesophase pitch-based carbon fiber with an alkali metal compound, and an electric double layer capacitor having a high capacity using the activated carbon fiber. Things.

[0002]

2. Description of the Related Art In recent years, new electronic devices such as portable telephones and notebook personal computers have appeared one after another.
C memories and microcomputers are also becoming smaller and more sophisticated.
However, such an element such as an IC memory or a microcomputer may malfunction due to an instantaneous power interruption, such as erasing the memory or stopping the function of the electronic device. In fact, even if the voltage drops slightly by 10% to 20% if proper measures are not taken, computer equipment will stop or lose memory in just 0.003 to 0.02 seconds, Is paralyzed.

As a countermeasure, Ni-Cd batteries and aluminum electrolytic capacitors have been used as backup power supplies.
However, these power supplies have not been sufficient in terms of the operating temperature range, the number of charge / discharge cycles, the capacity, rapid charge / discharge performance, cost, and the like. An electric double layer capacitor has been developed in response to this market need. At first, activated carbon was used as an electrode material, but recently, an electric double layer capacitor using activated carbon fibers having a higher specific surface area has attracted attention.

[0004] Furthermore, applications from the conventional low-power field to a large-capacity field such as an auxiliary power supply for an electric vehicle battery have been considered. Passenger cars equipped with capacitors for the purpose of assisting the output of the engine have come to the stage of reference exhibition. The history of electric double layer research can be traced back to 1879, Helmholtz. Generally, when two different layers come into contact, positive and negative charges are arranged at the interface at a short distance. The charge distribution formed at this interface is called an electric double layer.

[0005] The electric double layer capacitor stores electric charge by applying a voltage to the electric double layer. However, it took a long time to put it into practical use, and at the beginning of the 1980's, we saw the appearance of large capacitors in Farad units using this principle. An electric double layer capacitor is a large-capacity capacitor using an electric double layer formed between an electrode material surface and an electrolytic solution. The electric double layer capacitor does not involve a chemical reaction in charging and discharging as in a normal secondary battery. For this reason, the internal resistance is much lower than that of the secondary battery, and a large current discharge is possible. Further, it has a feature that there is no limitation on the number of times of charging and discharging.

However, the biggest problem of the electric double layer capacitor is that the energy density is lower than that of the secondary battery, and various studies have been made to improve this point. For electric double layer capacitors, lithium perchlorate or 4 polar organic solvents such as propylene carbonate are used.
There are two main types, those using an organic solvent-based electrolyte in which an electrolyte such as a quaternary ammonium salt is dissolved, and those using an aqueous solution such as a sulfuric acid aqueous solution or a potassium hydroxide aqueous solution.

When an aqueous electrolytic solution is used, the capacity of the capacitor is about 1.10 compared to when an organic solvent electrolytic solution is used.
It can be increased from 3 times to 2 times, and the internal resistance is reduced by 1
It can be reduced from / 5 to 1/10. The reason that the internal resistance can be reduced when the aqueous electrolyte is used is that the electric resistance of the aqueous electrolyte is low.However, when the aqueous electrolyte is used, the voltage is reduced. 1
There is also a disadvantage that the amount of stored energy per volume is small because it can be increased only to V or more.

On the other hand, when an organic solvent-based electrolytic solution is used, the voltage of the electric double layer capacitor can be increased to a maximum of 3 V or more, and the amount of stored energy per capacitor volume (the amount of stored energy = 1) / ² CV ² , where C: capacitor capacity, V: voltage), so that the organic solvent system is more advantageous from the viewpoint of increasing the density of energy per volume. Activated carbon or activated carbon fiber having a large specific surface area is considered to be optimal as an electrode material of these electric double layer capacitors, and research on optimization of carbon materials is being actively conducted in various fields.

The electrode material of the electric double layer capacitor is usually
It is manufactured using a non-graphitic carbon material (so-called hard carbon) such as coconut shell, coal and phenolic resin as a raw material, and usually using activated carbon having a high specific surface area obtained by gas activation with water vapor or carbon dioxide. That is, the pores formed by the decarbonization phenomenon caused by the reaction between the carbon material and water vapor or carbon dioxide are utilized. However, in order to obtain an electrode material for an electric double layer capacitor having a large discharge capacity,
In the BET method, activated carbon having a specific surface area of 2000 m ² / g or more is required. In this case, an activation treatment is required to lower the activation yield to 20 wt% or less, and only the production cost of the obtained activated carbon is increased. However, there is also a problem that the bulk density of activated carbon itself is low and the bulk density as an electrode material cannot be increased.

According to the measurement by the present inventors, the discharge capacity of an electrode material using activated carbon having a specific surface area of 2000 m ² / g by the BET method manufactured from these raw materials in an organic solvent system is 30 F / g. Degree, and considering the specific surface area,
It is judged that there is still room for improvement. this is,
As described later, it is considered that all of the specific surface areas indicated by the BET method are not used for forming the electric double layer.

In the production of activated carbon, activation using an alkali metal compound (hereinafter referred to as "alkali activation" in the present invention) has been studied in order to increase the activation yield. For example, Japanese Unexamined Patent Publication (Kokai) No. 1-139865 discloses that a carbon fiber is alkali-activated. A high specific surface area in which this technology is applied to a carbon fiber having a mesophase of 50% or more (which falls into the category of graphitic carbon materials). The production of activated carbon fibers is disclosed in JP-A-5-247331. However, there is no suggestion to use a mesophase pitch-based activated carbon fiber, which is an easily graphite-based carbon material, as an electrode material for an electric double layer capacitor.

[0012]

In general, it has been said that the capacity per unit weight of activated carbon used for an electric double layer capacitor is proportional to the specific surface area of activated carbon. However, it has been found that this relationship is not always determined uniquely. Although various factors can be considered as this factor, it is considered that the microstructure and the distribution state of the pores of the activated carbon, which are influenced by the production method such as activation, and the like, are greatly related. For this reason,
In order to improve the capacity of the electric double layer capacitor, it is important not only to increase the specific surface area, but also to select a starting material and a manufacturing condition thereof.

[0013]

Means for Solving the Problems As a result of diligent studies on the above-mentioned problems, the present inventor has found that a mesophase pitch-based carbon fiber or an infusible fiber is used as a raw material, and after pulverization (milling), alkali activation is performed to reduce the pore distribution. The present inventors have found that an activated carbon fiber obtained by adjusting a specific range can provide a high capacity as an electrode material for an electric double layer capacitor, and completed the present invention.
That is, the present invention provides: a mesophase pitch-based infusible fiber or a mesophase pitch-based carbon fiber carbonized at a temperature of 350 ° C. or more and 1000 ° C. or less after infusibilization, with an average particle size of 5 μm or more and 50 μm or less.
Activated carbon fiber obtained by subjecting a product crushed to m or less to an alkali activation treatment. Further, there is provided an electric double layer capacitor using the activated carbon fiber described above as an electrode material. The activated carbon fiber has pores (A) having a pore radius of 0.4 to 1.5 nm measured by an MP method using nitrogen adsorption and pores having a pore radius of 3.5 to 6 nm measured by a mercury porosimeter.
And both pores (B) and the pore volume of the pores (A)
It is characterized in that activated carbon fibers having a ratio [(Bv) / (Av)] of (Av) to the pore volume (Bv) of the pores (B) of 0.01 to 0.25 are used for the electrode. It is also characterized in that activated carbon fibers made from a pitch consisting of a 100% optically anisotropic phase as a raw material are used as electrodes.

Hereinafter, the present invention will be described in detail. [I] Production of pitch-based activated carbon fiber: 1) Raw material pitch The raw material pitch of the pitch-based carbon fiber used in the present invention can be made from various raw materials such as petroleum and coal. The raw material pitch used here is not particularly limited as long as spinning is possible, but a pitch containing an optically anisotropic phase (mesophase) is preferable from the viewpoint of high conductivity. Further, as a result of the inventor's intensive study of the relationship between the properties of the pitch and the capacitance of the capacitor, the present inventors have found that an optically anisotropic phase (mesophase) 100 containing no optically isotropic component measured by observation with a polarizing microscope. % Pitch has been found to be particularly preferred. That is, in the case of a pitch in which optically isotropic components are mixed, the pitch structure becomes non-uniform, the activation reaction becomes non-uniform, the control of the pore structure becomes difficult, and the spinnability and infusibility tend to deteriorate. Can be seen.

2) Spinning The spinning method is not limited to conventional melt spinning, centrifugal spinning, vortex spinning, etc., but melt blow spinning is particularly preferred. In the mesophase pitch-based carbon fiber, the orientation of the graphite layer surface inside the fiber is important, and the degree of this orientation is substantially controlled by pitch viscosity during spinning, spinning speed, cooling speed, nozzle structure, and the like.

In the alkali activation, it is considered that it is important that the alkali metal compound spreads between the graphite layers and enters the graphite layer. To promote the activation more smoothly, the graphite layer into which the alkali metal compound easily enters is considered. A structure in which the end face exists on the fiber surface is preferable. Further, it is presumed that the orientation structure of the graphite layer surface also affects the activation yield. In addition to these, the melt blow spinning method can be said to be preferable in consideration of manufacturing costs such as construction costs and operation costs of the spinning apparatus and quality aspects such as yarn diameter control. Further, the melt blow spinning method is particularly suitable for producing a mat or felt-like carbon fiber aggregate.

3) Infusibilization Mesophase pitch is a thermoplastic organic compound. In order to perform heat (carbonization) treatment while maintaining the fiber form, infusibility treatment is required after spinning. The infusibilization can be continuously performed in a liquid phase or a gaseous phase by a conventional method, but is usually performed in an oxidizing atmosphere such as air, oxygen, and NO ₂ . For example, in the case of infusibilization in air, the average temperature rise rate is 1 to 15 ° C./min, preferably 3 to 12 ° C./min, and the treatment temperature range is 100 to 350 ° C., preferably 15 to 150 ° C.
This is performed at about 0 to 300 ° C. The infusibilizing step is an essential step in the present invention. When the infusibilizing step is not performed, that is, when the pitch fiber as-spun is uniformly mixed with the alkali metal compound and heat-treated, the pitch fiber is re-melted in the heating step, so that the orientation of the graphite layer surface formed in the spinning step is changed. In addition to disturbing, an extreme case is not preferable because the fiber shape is lost.

4) Carbonization The infusibilized fiber obtained as described above can be used as it is in the next activation treatment step.
It is desirable to perform carbonization in advance. Since the infusibilized fiber contains a large amount of low volatile components, not only the activation yield in the activation step is low, but also tar-like substances volatilized in the activation reaction may contaminate the reaction system. It is desirable to remove volatiles in advance by carbonization. The carbonization is performed in an inert gas such as nitrogen, and the treatment temperature range is 1000 ° C. or less, preferably 350 ° C. or more and 800 ° C.
It is as follows. When the upper limit of the treatment temperature exceeds 1000 ° C., the graphite structure of the carbon fiber develops, and the activation rate becomes extremely slow, which not only requires a long time for the reaction, but also increases the carbonization cost, which is not preferable. Therefore, except for special applications requiring high conductivity, mild carbonization of 1000 ° C. or lower, more preferably 800 ° C. or lower is preferable. The lower limit temperature is not particularly limited as long as carbonization is carried out smoothly, but is preferably 350 ° C. or higher because the infusion treatment is performed continuously from the viewpoint of activation yield and cost.

5) Milling The infusibilized fiber or carbonized fiber thus obtained can be activated as an electrode material even in a mat or felt state. In order to improve the uniformity of the specific surface by the uniform mixing and activation reaction and the bulk density of the electrode material, it is preferable to grind (mill) before activation. In this case, the particle diameter is preferably 5 μm or more and 50 μm or less, more preferably 10 μm, if expressed as an average particle diameter by a laser diffraction method.
Not less than 30 μm. If the average particle size exceeds 50 μm, the bulk density of the electrode material does not increase, and if the particle size is unnecessarily small, uniform activation becomes difficult. Therefore, the average particle size is preferably 5 μm or more.

As a milling method, it is effective to use a victory mill, a jet mill, a high-speed rotating mill, or the like. Milling can also be performed using a Henschel mixer, ball mill, crusher, or the like.However, according to these methods, the pressing force acts in the diameter direction of the fiber, and the occurrence of longitudinal cracks in the fiber axis direction increases, resulting in activation. It is not preferable because efficiency and uniformity are reduced. In addition, milling requires a long time and is not an appropriate milling method. For efficient milling, a suitable method is to cut the fibers by, for example, rotating a rotor attached with a blade at high speed. The fiber length can be controlled by adjusting the number of rotations of the rotor, the angle of the blade, and the like.

6) Alkali Activation As the alkali metal compound used for the alkali activation, potassium hydroxide, potassium carbonate, potassium nitrite, potassium sulfate, potassium chloride and the like are preferable, and among them, potassium hydroxide is most preferable. As described above, in order to activate the infusibilized fiber or the carbonized carbon fiber, the weight ratio of the infusibilized fiber or the carbonized fiber is 0.5 to 5 times.
After uniformly mixing the alkali metal compound by a factor of 1, preferably from 1 to 4 times, it is necessary to perform an activation treatment at a temperature of from 500 to 900 ° C., preferably from 600 to 800 ° C.

If the ratio of the alkali metal compound is less than 0.5 times, the efficiency of pore formation is poor. On the other hand, even if it is added more than 5 times, the increase in specific surface area of the carbon material obtained is small and inefficient. is there. If the activation temperature is lower than 500 ° C., the reaction hardly proceeds. If the activation temperature is higher than 900 ° C., it is not preferable from the viewpoint of deposition of metal potassium and corrosion of the apparatus. Further, the activation needs to be performed in an inert gas such as nitrogen.

7) Specific surface area of activated carbon fiber After activation, the reaction product is cooled to room temperature, and then unreacted alkali metal compounds can be removed by washing with water or the like. The BET specific surface area is 300 m ² / g or more, preferably 500-2800m
² / g, more preferably a mesophase pitch-based activated carbon fiber having a specific surface area of 600 to 2500 m ² / g,
It shows excellent characteristics as an electrode material for capacitors. The BET specific surface area is not unique, as can be seen from the examples of the present invention, but has a correlation with the specific surface area. If the BET specific surface area is less than 300 m ² / g, a sufficient discharge capacity cannot be obtained. The upper limit is not particularly limited, but even if the specific surface area is unnecessarily increased, the capacitance of the capacitor does not increase in proportion to the specific surface area.
It is not preferable because the activation yield is lowered.
² / g or less. The specific surface area as referred to herein refers to a value measured by the BET method using nitrogen adsorption, rounded off to the nearest tenth, and displayed from the tens digit in consideration of measurement accuracy.

8) Pore Distribution of Activated Carbon Fiber The pores of activated carbon are usually macropores (pore diameter of 50 nm or more), mesopores (pore diameter of 2 to 50 nm), micropores (pore diameter of 0.8). ~ 2nm), sub-micropore (pore diameter 0.8nm)
Below). The present inventor has proposed various B
As a result of comparative study of the mesophase pitch-based activated carbon fiber of the present invention having an ET specific surface area and the activated carbon fiber by gas activation of the non-mesophase pitch-based carbon fiber, the capacity of the capacitor is not only the BET specific surface area, but also the activated carbon. It has been found that it is greatly related to the distribution of pores inside. Furthermore, the present inventor studied the relationship between the pore distribution and the capacitor discharge capacity, and as a result, found that the pore radius was 0.4 to 1..
Existence of pore (A) in the region of 5 nm and pore radius of 3.5
The presence of pores (B) in the region of about 6 nm is strongly related to the discharge capacity of the capacitor.
It has been found that the activated carbon fibers in which both (A) and (B) are present and in an appropriate ratio tend to have a large discharge capacity per unit specific surface area.

That is, both the pore (A) having a pore radius of 0.4 to 1.5 nm and the pore (B) having a radius of 3.5 to 6 nm are present, and the pore (A) Activated carbon fibers having a ratio of volume (Av) to pore volume (Bv) of pores (Bv) [(Bv) / (Av)] of 0.01 to 0.25 are the capacitors having the highest capacitance per unit specific surface area. It turned out that capacity was obtained. The reason for this has not been elucidated yet, but the pores forming the electric double layer and contributing to the actual capacitor capacity are pores (A) having a radius of 0.4 to 1.5 nm, and the abundance ratio is high. However, this pore radius has a disadvantage that the electrolyte does not easily penetrate into the inside of the activated carbon fiber.
It is considered that the presence of the nano-pores (B) solves the problem and the capacity is greatly improved.

However, the pore volume (Bv) of the pore (B) is smaller than that of the pore (A).
If the pore volume exceeds 0.25 with respect to the pore volume (Av), the penetration of the electrolytic solution into the interior becomes advantageous, but the ratio of the pores (A) that contribute to the capacitor capacity per specific surface area decreases. This is undesirable. Although the presence of large pores having a radius of 6 nm or more is more advantageous in the permeation of the electrolytic solution, it is not preferable because the activation yield of activated carbon fibers at the same specific surface area decreases. In the present invention, the pore distribution and the pore volume were measured at a radius of 3.5 nm.
The above relatively large pores were analyzed by a mercury porosimeter, and the pores with a radius of 2 nm or less were analyzed by the MP method for the results of BET measurement by nitrogen adsorption.

<Mercury porosimeter> Radius about 3.5 nm
According to the measurement method generally used as the above macropore measurement method, mercury is injected into a cell in which a sample is placed under vacuum, and pressure is applied to the cell to inject mercury into the sample pores. Measure the volume of mercury injected into the pores at various pressures (pore volume) and calculate the relation between the pore radius and the pressure assuming a cylindrical pore.
The pore distribution is calculated from (1) and the relational expression (2) between the pore volume fraction and the total pore volume in the micropore radius section. r = −2σ cos θ / P × 10 ⁻⁶ ... (1) r: pore radius (nm) σ: surface tension of mercury (dyn / cm) θ: contact angle of mercury with the sample (°) P: mercury Injection pressure (N / m ² ) φ = (dV / V) × 100 (2) φ: pore volume fraction (%) V: cumulative pore volume (ml / g) in all sections dV: fine Pore volume in pore radius section dr (ml / g) <MP method> This is a method mainly used for analyzing micropores. The result of BET measurement by nitrogen adsorption is t-plotted and calculated by curvature analysis near the bend. .

[II] Production of Electric Double Layer Capacitor Electrode: 1) A method for producing an electrode in the present invention is not particularly limited. A conventionally known electrode manufacturing method can be used as it is. That is, a binder such as polyethylene, polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVDF) is added to mesophase pitch-based activated carbon fibers, and pressure roll molding is performed to form a sheet or plate to form an electrode material. It is possible. At this time,
It is also effective to add graphite powder or acetylene black as the conductive material. In addition, a conductive material such as aluminum may be deposited on a mat or felt-like material to improve current collecting properties and used as an electrode. Further, it is also possible to form an electrode after forming into paper. The electrode manufactured in this manner is cut into a desired size and shape, a separator is interposed between the two electrodes, the electrolyte is injected into the container, and the electrolyte is injected. It can be a polar cell.

2) As the electrolytic solution used in the present invention, any of an organic solvent type and an aqueous type can be used, but an organic solvent type is particularly preferable. Examples of the organic solvent include propylene carbonate, γ-butyrolactone, dimethyl sulfoxide, dimethylformamide, acetonitrile, ethylene carbonate, tetrahydrofuran, dimethoxyethane, and the like. These organic solvents can be used as one kind or as a mixed solvent of two or more kinds. Further, these solvents have a high affinity for water and a high solubility for water, and can be generally used by mixing with water at an arbitrary ratio.

Further, examples of the electrolyte used in these solvents include salts of cations and anions such as metal cations, quaternary ammonium cations, and carbonium cations. The anions used here are ClO ₄ ⁻ , BF ₄ ⁻ , PF ₄ ⁻ , PF ₆ ⁻ , A
sF _6- ^{and the} like. Specific examples of the electrolyte include LiClO ₄ , BuN · ClO ₄ , and NaBF ₄ .

In the case of an organic non-aqueous polar solvent, the concentration of the electrolyte is preferably 0.5 M / L to 3 M / L. Particularly preferably, it is in the range of 1 M / L to 2 M / L. The aqueous electrolyte used in the present invention is one using water as a solvent,
For example, NaCl, NaOH, KOH, HCl, H ₂ SO
_Although an aqueous solution such as ₄ can be mentioned, use of an aqueous solution of sulfuric acid is particularly desirable from the viewpoint of availability and the capacity of the capacitor. [III] Structure of Electric Double Layer Capacitor FIG. 1 shows a typical structure of the electric double layer capacitor of the present invention.

[0032]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto. <Measurement of Discharge Capacity> The discharge capacity of the electric double layer capacitor was determined by a constant current discharge method. That is, the battery was discharged at a constant current, the discharge curve at that time was regarded as a substantially straight line, and the DC capacitance was calculated from the temporal change rate of the capacitor voltage. Also, discharge capacity per unit weight of activated carbon fiber (F / g)
Was determined from the total weight of the active carbon fibers of the positive and negative electrodes.

EXAMPLE 1 A mesophase pitch having a Mettler softening point of 285 ° C. obtained by heat-treating petroleum cracking residual oil is a spinneret having 1,000 spinning holes of 0.2 mm in diameter in a slit of 2 mm in width. To produce pitch fibers. The spun pitch fibers were collected on the belt by sucking from the back surface of the belt whose collecting portion was formed of a stainless steel mesh having a mesh of 35 mesh. The obtained pitch fiber mat-like material is heated in air at an average heating rate of 4 ° C.
/ Minute to perform infusibilization treatment to obtain infusible fibers. The infusibilized fiber was carbonized at 700 ° C. in a nitrogen gas, and then pulverized (milled) to a mean particle size of 25 μm by a high-speed rotating mill.

To the carbon fiber mill, 2 to 4 times by weight of potassium hydroxide was added, and mixed uniformly.
Activating treatment under a nitrogen atmosphere for a period of time, then, after cooling to room temperature, pouring the reaction product into isopropyl alcohol, washing with water until neutral, and having a BET specific surface area of 1020
^{m 2 / g, 2070m 2 /} g, and three manufacturing activated carbon fibers having a specific surface area of 2490m ² / g. Although the yields of the obtained activated carbon fibers tend to decrease in inverse proportion to the specific surface area, they are 88 wt%, 77 wt%, and 7 wt%, respectively.
It was as high as 4 wt%. Table 1 summarizes these. Table 1 shows the distribution state of the pores of each activated carbon fiber together with the results calculated based on the analysis results by the mercury porosimeter and the MP method.

Further, acetylene black was added to the activated carbon fiber as a conductive additive at 10 wt%, PTFE as a binder was added at 7 wt%, and the resultant was roll-molded and pressed on a nickel mesh to form an electrode, as shown in FIG. Positive
Table 1 also shows the results of trial production of an electric double layer capacitor using filter paper as a separator between the electrodes of the negative electrode and propylene carbonate containing 1 M lithium perchlorate as an electrolyte as an electrolyte, and measuring the capacity. The obtained discharge capacities showed relatively large values of 30 F / g, 42 F / g, and 45 F / g.

COMPARATIVE EXAMPLE 1 An optically isotropic pitch having a Mettler softening point of 270 ° C. obtained by heat-treating petroleum cracking residual oil was spun with a spinning hole having a diameter of 0.2 mm in a slit of 2 mm width. Pitch fibers were produced by melt blow spinning using a die having 2,000 pieces. The spun pitch fibers were collected on the belt by sucking from the back surface of the belt whose collecting portion was formed of a stainless steel mesh having a mesh of 35 mesh. The obtained pitch fiber mat-like material is heated in air at an average heating rate of 4 ° C.
After performing the infusibilization treatment at / min, carbonization treatment was performed at 950 ° C. in nitrogen gas to obtain a carbon fiber mat. Using the carbon fiber mat under an atmosphere of 40% carbon dioxide, the temperature was 950 ° C., and the treatment time was changed to 2 hours, 6 hours, and 8 hours.
BET specific surface area is 1010, 2050, 2500 m ²
/ G of three types of activated carbon fibers were produced.

Each activation yield is 52 wt%, 24 w
t% and 19 wt%, and the yield was extremely lowered with an increase in the specific surface area. These activated carbon fibers were used in Example 1
Table 2 shows the results of analysis using the mercury porosimeter and the MP method in the same manner as in Example 1. Further, an electric double layer capacitor was trial-produced in the same manner as in Example 1 by using the activated carbon fiber ground to an average particle size of 25 μm, and the capacitance was measured. The discharge capacity increased with an increase in the specific surface area, but was 15 F / g, 24 F / g, and 32 F / g, which were inferior to those of the examples.

[0038]

[Table 1]

Example 2 The infusibilized fiber obtained in Example 1 was carbonized at 950 ° C. in nitrogen gas, and then pulverized (milled) with a high-speed rotating mill so as to have an average particle size of 25 μm. ) Was done. To the carbon fiber mill, 4 times by weight of potassium hydroxide was added, mixed uniformly, and activated at 800 ° C. for 4 hours under a nitrogen atmosphere. After cooling to room temperature, the reaction product was added to isopropyl alcohol. After charging, wash with water until neutral, BET specific surface area is 890m
² / g of activated carbon fiber was produced. The yield of the obtained activated carbon fiber was 90 wt%. Table 2 shows the results of calculating the distribution state of the pores based on the results of analysis by the mercury porosimeter and the MP method in the same manner as in Example 1. Table 2 also shows the results of trial production of an electric double layer capacitor and measurement of the capacitance in the same manner as in Example 1.

Example 3 The infusible fiber obtained in Example 1 was pulverized by a high-speed rotating mill so that the average particle size became 25 μm. To the infusibilized fiber mill, 4 times by weight of potassium hydroxide was added, mixed uniformly, and heated at 700 ° C for 2 hours.
After performing an activation treatment under a nitrogen atmosphere, then, after cooling to room temperature, the reactants are put into isopropyl alcohol,
Wash until neutral, BET specific surface area 2150m ²
/ G of activated carbon fiber was produced. The yield of the obtained activated carbon fiber was 70% by weight. Table 2 shows the results of calculating the distribution state of the pores based on the results of analysis by the mercury porosimeter and the MP method in the same manner as in Example 1. Also,
Table 2 also shows the results of trial production of an electric double layer capacitor and measurement of the capacitance in the same manner as in Example 1.

(Comparative Example 2) 700 ° C. obtained in Example 1
Without crushing the carbonized fiber carbonized in the above, the activation treatment is performed under the same activation conditions as in Example 1, then, after cooling to room temperature, the reactant is put into isopropyl alcohol,
Rinse with water until neutral, BET specific surface area is 1610 m ²
/ G of activated carbon fiber was produced. The yield of the obtained activated carbon fiber was 88 wt%. The activated carbon fiber was pulverized by a high-speed rotating mill so as to have an average particle diameter of 25 μm, and the distribution of pores was calculated based on the results of analysis by the mercury porosimeter and the MP method as in Example 1. Are shown in Table 2. Presence of pores having a relatively large radius of 3.5 to 6 nm was not detected, possibly due to the influence of the pulverization. Table 2 also shows the results of trial production of an electric double layer capacitor and measurement of the capacitance in the same manner as in Example 1.

(Reference Example 1) The infusibilized fiber obtained in Example 1 was carbonized at 600 ° C. in nitrogen gas, and then pulverized (milled) to a mean particle size of 25 μm by a high-speed rotating mill. ) Was done. To the carbon fiber mill, 4 times by weight of potassium hydroxide is added, uniformly mixed, activated at 500 ° C. for 10 hours under a nitrogen atmosphere, and then cooled to room temperature, and the reaction product is placed in isopropyl alcohol. After charging, the mixture was washed with water until neutral, and had a BET specific surface area of 1520.
m ² / g activated carbon fiber was produced. The yield of the obtained activated carbon fiber was 88 wt%. Table 2 shows the results of calculating the distribution of the pores of the activated carbon fibers based on the results of analysis by the mercury porosimeter and the MP method in the same manner as in Example 1.
Shown in Table 2 also shows the results of trial production of an electric double layer capacitor and measurement of the capacitance in the same manner as in Example 1.

[0043] After the infusibilized fibers obtained in Reference Example 2 Example 1 was subjected to charcoal treatment at 1100 ° C. in nitrogen gas,
Pulverization (milling) was performed with a high-speed rotating mill so that the average particle diameter became 25 μm. To the carbon fiber mill, 4 times by weight of potassium hydroxide was added, mixed uniformly, and activated at 800 ° C. for 4 hours under a nitrogen atmosphere. After cooling to room temperature, the reaction product was added to isopropyl alcohol. After the introduction, the BET specific surface area of the activated carbon fiber washed with water until it became neutral was measured and found to be as low as 360 m ² / g. The yield of the obtained activated carbon fiber was 95% by weight. Table 2 shows the results of calculating the distribution of the pores of the activated carbon fibers in the same manner as in Example 1 based on the results of analysis using a mercury porosimeter and the MP method. Table 2 also shows the results of trial production of an electric double layer capacitor and measurement of the capacitance in the same manner as in Example 1.

[0044]

[Table 2]

[0045]

According to the present invention, a mesophase pitch-based activated carbon fiber can be obtained in a high yield, and an electric double layer capacitor using the activated carbon fiber as an electrode material exhibits a high discharge capacity.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a typical structure of an electric double layer capacitor according to the present invention.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tomimori Hoshibibo 4 Kazu-gun, Kashima-gun, Toshima, Kashima Ishi Oil Co., Ltd.

Claims (4)

[Claims] 1. An infusible mesophase pitch fiber or a mesophase pitch carbon fiber carbonized at a temperature of 350 ° C. or more and 1000 ° C. or less after infusibilization, with an average particle size of 5 μm.
Activated carbon fibers obtained by pulverizing to at least 50 μm or less and subjecting them to an alkali activation treatment. 2. An electric double layer capacitor using the activated carbon fiber according to claim 1 as an electrode material. 3. The method according to claim 1, wherein the activated carbon fiber is an MP using nitrogen adsorption.
2. A pore (A) having a pore radius of 0.4 to 1.5 nm measured by a method and a pore radius measured by a mercury porosimeter.
5-6 nm pores (B) and both pores (A)
The ratio of the pore volume (Av) to the pore volume (Bv) of the pores (B) [(Bv)
The electric double layer capacitor according to claim 2, wherein activated carbon fibers having a ratio of (/ (Av)] of 0.01 to 0.25 are used for the electrodes. 4. The electric double layer capacitor according to claim 2, wherein a pitch comprising a 100% optically anisotropic phase is used as a raw material.