JP2011258643A - Porous carbon material for electric double layer capacitor and method for producing the same, and electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous carbon material for an electric double layer capacitor, capable of improving long-term reliability when an electric double layer capacitor is charged and waited at a high temperature, a method for producing the porous carbon material, and an electric double layer capacitor manufactured using the porous carbon material.SOLUTION: The porous carbon material for an electric double layer capacitor contains 0.001 pt.mass or more and less than 0.1 pt.mass of a nonferrous metal oxide per 100 pts.mass of activated carbon, and a functional group amount of the porous carbon material is 0.1-0.5 mmol/g.

Description

  The present invention relates to a porous carbon material in which activated carbon contains a ceramic material such as zirconium oxide. By using this material as an active material, the long-term reliability of an electric double layer capacitor at a high temperature is improved. The present invention relates to a porous carbon material for electric double layer capacitors, a method for producing the same, and an electric double layer capacitor using the porous carbon material for electric double layer capacitors.

  An electric double layer capacitor is one of energy storage devices, and includes a pair of polarizable electrodes including a porous carbon material, a separator, an electrolyte solution, and the like.

  The capacitance of the electric double layer capacitor is said to be proportional to the surface area of the polarizable electrode. Therefore, it has been studied to obtain an electric double layer capacitor having a large capacitance by using a porous material having a large specific surface area for a polarizable electrode.

As such a porous material, a porous carbon material (hereinafter also referred to as “activated carbon”) that exhibits high conductivity, is electrochemically relatively stable carbonaceous material, and has a large specific surface area is used. Has been.
Examples of porous carbon materials used for polarizable electrodes include, as an example, carbonaceous raw materials such as coal, coal coke, coconut husk, wood powder, and resin, oxidizing gases such as water vapor, air, oxygen, and CO ₂ , Alternatively, a material in which pores are formed by a chemical such as zinc chloride or potassium hydroxide, that is, a material obtained by subjecting a carbonaceous raw material to a porous (hereinafter referred to as activation) treatment is exemplified.

As an electric double layer capacitor using such a porous carbon material, for example, Patent Document 1 discloses activated carbon, carbon black, and ceramic powder that is electrically inert to oxidation / reduction (aluminum oxide, oxidation). There is a polarizable electrode using a material formed by mixing zirconium and the like. In Patent Document 1, it is possible to accurately control the capacitance of the electric double layer capacitor by using this polar electrode.
In Patent Document 2, a porous carbon material (porous carbon particles), a conductive substance, and metal oxide particles (titanium oxide, aluminum oxide, silicon oxide, etc.) are kneaded with a binder such as butyl rubber. A polarizable electrode using the material is described. In Patent Document 2, by using this polarizable electrode, it is possible to obtain an electric double layer capacitor having a large capacitance and a small change with time.
Furthermore, Patent Document 3 describes that hydrophobic silica is added in addition to activated carbon as a material used for the polarizable electrode. In Patent Document 3, the life of the electric double layer capacitor is extended by using this polarizable electrode.

Japanese Unexamined Patent Publication No. Sho 63-316422 JP 2001-217162 A JP 2008-60199 A

As is well known, an electric double layer capacitor is discharged and charged by simple adsorption / desorption of positive and negative ions of an electrolyte to / from a polarizable electrode interface without a charge / discharge mechanism involving an electrochemical reaction. Therefore, it has a feature not found in secondary batteries that are general energy storage devices.
That is, the electric double layer capacitor has excellent instantaneous charge / discharge characteristics, stable charge / discharge characteristics over a wide temperature range, and low performance degradation due to repetition.

  Here, particularly in recent years, there is an increasing demand for long-term reliability at high temperatures for electric double layer capacitors that exhibit stable charge / discharge characteristics in such a wide temperature range.

The main factor that lowers the long-term reliability of electric double layer capacitors at high temperatures is thought to be the reaction of functional groups of porous carbon materials, metal impurities, and electrolytes that make up polarizable electrodes when waiting for charging at high temperatures. ing.
In addition, since the reaction of the electrolytic solution is promoted by the functional group of the porous carbon material, a measure to reduce this functional group is generally taken in order to increase the reliability of the electric double layer capacitor.

In order to reduce the functional group of the porous carbon material, a method of performing a heat treatment at a high temperature is generally used. Here, in order to obtain a sufficient functional group reduction effect, heat treatment at 800 ° C. or higher, which is an activation temperature when producing the porous carbon material, is necessary.
However, when heat treatment is performed at 800 ° C. or higher, the pore structure of the porous carbon material shrinks. As a result, when this porous carbon material is used for a polarizable electrode, there is a problem that the capacitance of the electric double layer capacitor is lowered.

  Therefore, there is a demand for a technique for improving the reliability of the electric double layer capacitor without forcibly reducing the functional group of the porous carbon material forming the polarizable electrode.

  An object of the present invention is to solve the above-mentioned problems of the prior art, and constitutes a polarizable electrode, which is a porous carbon material for an electric double layer capacitor and is a cause of deterioration of the electric double layer capacitor. The amount of activated carbon functional groups and the reaction of the electrolyte can be suppressed to prevent changes in the capacity and resistance of the electric double layer capacitor and gas expansion. An object of the present invention is to provide a porous carbon material for an electric double layer capacitor capable of enhancing the properties, a method for producing the porous carbon material, and an electric double layer capacitor using the porous carbon material.

The present inventors diligently studied to solve the problem of improving the reliability of the electric double layer capacitor at a high temperature.
As a result, it has been found that it is effective to use activated carbon as an active material in the porous carbon material constituting the polarizable electrode, and to add a non-ferrous metal oxide such as ceramic to the activated carbon. Furthermore, as a method for adding a non-ferrous metal oxide, it has been found that the effect is increased by applying a small nano-particle diameter oxide powder to the surface of activated carbon by applying a shearing force.
It has also been confirmed that this improves the reliability of the electric double layer capacitor by suppressing the change in capacity and resistance when the electric double layer capacitor is on standby for charging at a high temperature and gas expansion.

The phenomenon of lowering reliability that occurs when the electric double layer capacitor is on standby for charging at a high temperature can be generally considered as follows.
The functional group present on the surface of the activated carbon that constitutes the polarizable electrode has a molecular composition mainly composed of C, 0, and H, and loads the electric energy by charging as an active material of the electric double layer capacitor. If done, the decomposition proceeds especially at high temperatures. This decomposition reaction generates CO, H ₂ O, and the like, but the decomposition of propylene carbonate, which is a solvent of the electrolytic solution, is also promoted based on this H ₂ 0. In addition, since CO, H ₂ O, and the like are generated in the decomposition reaction of propylene carbonate and the like, these decomposition reactions proceed in a chain manner.

On the other hand, if a non-ferrous metal oxide (ceramic non-ferrous metal compound) is present in this reaction system, the non-ferrous metal oxide captures oxygen-containing compounds such as CO and H ₂ O. There is an effect to stop.
Therefore, a reduction in the reliability of the electric double layer capacitor can be suppressed by adding a small amount of such a non-ferrous metal oxide to the activated carbon constituting the polarizable electrode.

Examples of the non-ferrous metal oxide include silicon oxide, aluminum oxide, titanium oxide, and zirconium oxide.
In addition, as a method of adding the non-ferrous metal oxide to the activated carbon, a simple mixing method may be used. However, in order to enhance the effect of highly dispersing fine particles on the surface of the activated carbon, the particle diameter is nanometer. A method in which a minute size is adhered mechanochemically to the surface of activated carbon is more effective in solving the problem.

The present invention has been made by obtaining the above knowledge, and the porous carbon material for an electric double layer capacitor of the present invention comprises activated carbon 100 parts by mass and nonferrous metal oxide 0.001 parts by mass or more. Provided is a porous carbon material for an electric double layer capacitor, containing less than 1 part by mass and having a functional group content of the porous carbon material of 0.1 to 0.5 mmol / g.
In the porous material for an electric double layer capacitor of the present invention, the nonferrous metal oxide is preferably attached to the surface of the activated carbon, and the average primary particle size of the nonferrous metal oxide is Is preferably 1 to 100 nm, the oxide of the nonferrous metal is preferably one or more of zirconium oxide and aluminum oxide, and the activated carbon and the oxide of the nonferrous metal have a shearing force. It is preferable that the product is mixed by applying.

The electric double layer capacitor of the present invention provides an electric double layer capacitor using the porous material for an electric double layer capacitor of the present invention.

Furthermore, the method for producing a porous material for an electric double layer capacitor according to the present invention includes an activated carbon production step of obtaining activated carbon by heating an activated carbonaceous raw material at 300 to 1000 ° C. in a non-oxidizing atmosphere, 0.00100 parts by mass or more and less than 0.1 parts by mass of non-ferrous metal oxide is added to 100 parts by weight of activated carbon obtained in the activated carbon production process, and the activated carbon and non-ferrous metal oxide are mixed. And a mixing step. A method for producing a porous carbon material for an electric double layer capacitor is provided.
In such a method for producing a porous carbon material for an electric double layer capacitor of the present invention, it is preferable that the activated carbon and the non-ferrous metal oxide are mixed while applying a shearing force.

  According to the present invention having the above-described configuration, it is possible to suppress changes in capacity and resistance and gas expansion when the electric double layer capacitor is on standby for charging at high temperature, and to improve the reliability of the electric double layer capacitor. .

  Hereinafter, the porous carbon material for an electric double layer capacitor of the present invention, the method for producing the same, and the electric double layer capacitor will be described in detail.

  The porous carbon material for an electric double layer capacitor of the present invention comprises activated carbon and nonferrous metal oxide (ceramic nonferrous metal compound) of 0.001 part by mass or more and less than 0.1 part by mass with respect to 100 parts by mass of activated carbon. And a porous carbon material having a functional group amount of 0.1 to 0.5 mmol / g.

In the porous carbon material for electric double layer capacitor of the present invention (hereinafter referred to as porous carbon material), the activated carbon is not particularly limited, and the polarizable electrode of the electric double layer capacitor (the porous material forming the polarizable electrode) Various known activated carbons used for carbon materials can be used.
In addition, although there is no limitation in particular in the average particle diameter of activated carbon, 1-20 micrometers is preferable, More preferably, it is 3-10 micrometers.

The porous carbon material of the present invention contains such activated carbon and a non-ferrous metal oxide (ceramic non-ferrous metal compound).
Preferably, the porous carbon material of the present invention is obtained by attaching non-ferrous metal oxide nanometer-sized fine particles to the surface of activated carbon.

There are no particular limitations on the non-ferrous metal oxide, and various non-ferrous metal oxides can be used, but silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, and the like are preferably exemplified. Non-ferrous metal oxides may be used alone or in combination.
Among these, at least one of aluminum oxide and zirconium oxide is preferably used for the reason that there is little adverse effect on the durability of the electric double layer capacitor.

The content of the non-ferrous metal oxide (hereinafter also referred to as non-ferrous metal oxide) is 0.001 part by mass or more and less than 0.1 part by mass with respect to 100 parts by mass of the activated carbon.
When the content of the nonferrous metal oxide is less than 0.001 part by mass with respect to 100 parts by weight of the activated carbon, the effect of adding the nonferrous metal oxide cannot be sufficiently obtained.
On the contrary, when the content of the nonferrous metal oxide is 0.1 parts by mass or more with respect to 100 parts by weight of the activated carbon, there are too many nonferrous metal oxides, and the capacity of the electric double layer capacitor is reduced, the resistance is Inconvenience arises.

  The content of the non-ferrous metal oxide is preferably 0.002 parts by mass or more and 0.05 parts by mass or less with respect to 100 parts by weight of the activated carbon in that the above inconvenience can be more suitably prevented. Preferably, they are 0.01 mass part or more and 0.02 mass part or less.

In the porous carbon material of the present invention, the size of the non-ferrous metal oxide is not particularly limited, but is preferably nanometer-sized fine particles, and particularly preferably has an average primary particle size of 1 to 100 nm. In particular, the average primary particle size is preferably 5 to 50 nm.
By setting the average primary particle size of the non-ferrous metal compound to 1 nm or more, a suitable result can be obtained in that the non-ferrous metal compound can be attached to the surface of the activated carbon while suitably preventing scattering.
In addition, by setting the average primary particle size of the nonferrous metal compound to 100 nm or less, a suitable result can be obtained in that the nonferrous metal compound can be uniformly attached to the surface of the activated carbon.

In such a porous carbon material of the present invention, the amount of functional groups (mainly considered to be functional groups present on the surface of activated carbon or pores) is 0.1 to 0.5 mmol / g.
As described above, in the porous carbon material of the present invention including activated carbon, the existing functional group has a molecular composition mainly composed of C, 0, and H. For example, OH group, COOH group, and And a CHO group.

From the viewpoint of the reliability of the electric double layer capacitor, it is preferable that the amount of the functional group of the porous carbon material to be a polarizable electrode is small. However, when the amount of the functional group is 0.1 mmol / g or less, the functional group is reduced. Therefore, the pore structure of the activated carbon is contracted by the heat treatment for reducing the initial capacity of the electric double layer capacitor. Furthermore, the wettability of the binder solvent of the electric double layer capacitor to water is significantly reduced, and as a result, the binding force and adhesion of the porous carbon material are lowered, and the initial resistance is increased.
On the contrary, if the amount of the functional group exceeds 0.5 mmol / g, a large amount of reaction due to the functional group occurs during charging, and the high temperature stability of the electric double layer capacitor can be sufficiently obtained. Inconveniences such as a decrease in capacitance and an increase in resistance of the electric double layer capacitor occur.
The amount of the functional group is preferably 0.1 to 0.3 mmol / g in that the above disadvantage can be more suitably prevented.

  In addition, the quantity of the surface functional machine of this porous carbon material can be controlled by the heat treatment after activation treatment in the production of activated carbon described later, and by performing this heat treatment in the range of 300 to 1000 ° C. The amount of the surface functional machine of the porous carbon material can be preferably within the above range.

  Hereinafter, the present invention will be described in more detail by explaining the production method of the present invention for producing such a porous carbon material of the present invention.

Although there is no limitation in particular in the manufacturing method of activated carbon used for the porous carbon material of this invention, the following methods are illustrated as an example.
First, pitches such as coal-based tar or pitch and petroleum heavy oil are heated to about 350 ° C. or higher. The mesophase microspheres generated by this heating are collected by filtration or centrifugation, and then washed and dried using a solvent such as quinoline or tar oil to obtain powdery mesocarbon microspheres.

  Next, the obtained mesocarbon microspheres are carbonized to adjust the carbonization degree and crystallinity. The carbonization temperature at this time is selected from the range of 500 to 850 ° C, preferably 600 to 750 ° C.

  Next, the mesocarbon spherules adjusted for carbonization and crystallinity are made porous by activation treatment. The mesocarbon spherules may be made porous by a known method, for example, by a method similar to a normal alkali activation treatment.

First, the mesocarbon microspheres are heated at 700 to 900 ° C. in the presence of an alkali metal compound in an inert gas atmosphere such as nitrogen gas or argon gas.
Although the activation reaction proceeds even when the heating temperature is lower than 700 ° C., many oxygen-containing functional groups remain and the performance is deteriorated, and the resistance value is also increased, so that it is difficult to achieve the low resistance which is the object of the present invention. On the other hand, heating at a high temperature exceeding 900 ° C. is not preferable because the problem of device corrosion due to the alkali metal compound occurs and the activated pores shrink in the opposite direction. The heating temperature is preferably 750 to 850 ° C.

The holding time at this heating temperature is suitably from 0 to 5 hours.
The 0 hour can be realized by starting the temperature lowering at the same time as the heating temperature is reached. On the other hand, if the holding time exceeds 5 hours, the pores formed by activation become conversely contracted, which is not preferable.

Although the kind of alkali metal compound used in the heat treatment is not particularly limited, KOH, NaOH, CsOH, etc. are preferably used. Only one alkali metal compound may be used, or a plurality of alkali metal compounds may be combined.
Although the usage-amount of an alkali metal compound changes also with the specific surface areas to request, it should just be about 0.5 to 4 times by mass ratio with respect to a mesocarbon microsphere.

  After the alkali activation treatment, neutralization is usually performed with a hydrochloric acid solution or the like, followed by rinsing with ion exchange water or the like to obtain a base material of activated carbon.

Since this activated carbon substrate may contain many functional groups, it is functionalized by heat treatment at a temperature of 300 ° C. or higher, more preferably 450 ° C. or higher, in a non-oxidizing gas atmosphere such as nitrogen, argon, or hydrogen. The activated carbon used for the porous carbon material of the present invention is obtained by reducing the number of groups.
Here, as the functional group is reduced, the reliability of the electric double layer capacitor is improved. However, if the heat treatment temperature is excessively increased to reduce the functional group, the pore structure of the activated carbon contracts, and the electric double layer capacitor is reduced. The initial capacity is reduced. Therefore, the heat treatment temperature is set to 1,000 ° C. or lower, more preferably 800 ° C. or lower.

In addition, in the heat treatment of the activated carbon substrate, the holding time at the target heating temperature is also used. Although there is no limitation in particular, 5 hours or less are preferable and especially 1-3 hours are preferable.
In the heat treatment of the base material of activated carbon, it is sufficient to hold at the target heating temperature for 5 hours, and there is no effect even if the heat treatment holding time is further increased.

To 100 parts by mass of the activated carbon thus obtained, 0.001 part by mass or more and 0.1 part by mass or less of a nonferrous metal oxide (ceramic nonferrous metal compound) is added and mixed. The porous carbon material (for electric double layer capacitor) of the present invention is obtained.
Here, the addition amount of the non-ferrous metal oxide is preferably 0.002 parts by mass or more and 0.05 parts by mass or less, particularly 0.01 parts by mass or more and 0.02 parts by mass or less with respect to 100 parts by mass of the activated carbon. , As described above. Further, as described above, the non-ferrous metal oxide preferably has an average primary particle size of 1 to 100 nm, particularly 5 to 50 nm.
Further, as described above, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide and the like can be suitably used as the non-ferrous metal oxide.

There is no particular limitation on the mixing method of activated carbon and non-ferrous metal oxide (method of adding non-ferrous metal oxide to activated carbon).
Therefore, a simple mixing method may be used, but highly dispersing the nonferrous metal oxide on the surface of the activated carbon enhances the effect of adding the nonferrous metal oxide. Therefore, a method is preferred in which the activated carbon and the non-ferrous metal oxide are mixed by applying shear and the non-ferrous metal oxide is adhered to the surface of the activated carbon.

Examples of the heterogeneous method include a mixing method using mechanofusion, hybridization, a ball mill, a planetary ball mill, a bead mill, a thunder crusher, a grinder, and the like. Moreover, you may mix activated carbon and a nonferrous metal oxide combining these mixing methods (for example, performing several mixing methods sequentially).
When a ball mill or bead mill is used for mixing the activated carbon and the non-ferrous metal oxide, if a ceramic non-ferrous metal compound is used for the ball or bead of the grinding medium, the ball or bead is mixed with the ceramic system when colliding with the activated carbon. Nonferrous metal compounds are transferred. Therefore, as a result, a similar effect may be obtained when a nonferrous metal oxide is added to activated carbon and mixed by applying a shearing force.

The electric double layer capacitor of the present invention is a high performance electric double layer capacitor using such a porous carbon material (for electric double layer capacitor) of the present invention as a polarizable electrode.
The electric double layer capacitor of the present invention is basically a known electric double layer capacitor except that the porous carbon material of the present invention is used for a polarizable electrode or the like. Therefore, it can be produced according to the following general method.

  For example, a polarizable electrode that uses the porous carbon material of the present invention by adding an appropriate amount of a binder, a conductive agent or the like to the porous carbon material of the present invention as necessary, and forming it into a disk shape or a sheet shape. Active material layer).

When producing a disk-like or thick sheet-like polarizable electrode, polytetrafluoroethylene or the like is used as a binder, and a slurry is used to form a thin active material layer having a thickness of up to about 200 μm on the current collector. A method of applying the activated active material with a doctor blade or the like is preferably used.
For example, when polyvinylidene fluoride is used as a binder, it is dissolved in an organic solvent such as N-methyl-2-pyrrolidone, and a porous carbon material, and a conductive agent if necessary, are added to the slurry. The polarizable electrode can be produced by uniformly coating on the current collector and drying.
Further, for example, when styrene-butadiene rubber (SBR) is used as a binder, SBR is dispersed in water, and a porous carbon material, if necessary, a conductive agent and / or carboxymethyl cellulose (CMC) ) To form a slurry, which is uniformly coated on the current collector and dried, whereby a polarizable electrode can be produced.

  It is also possible to increase the density of the polarizable electrode by pressing at room temperature or under heating after drying.

The unit cell of an electric double layer capacitor generally uses a pair of polarizable electrodes obtained as described above, and through a liquid-permeable separator made of nonwoven fabric, paper, or other porous material as necessary. It is formed by facing and dipping in the electrolyte. The pair of polarizable electrodes may be the same or different from each other.
In using the electric double layer capacitor, the unit cell is used alone or a plurality of unit cells are connected in series and / or in parallel.

As the electrolytic solution of the electric double layer capacitor, either a non-aqueous solvent system or an aqueous system can be used.
The non-aqueous solvent electrolyte is obtained by dissolving an electrolyte in an organic solvent. Examples of the electrolyte include (C ₂ H ₅ ) ₄ PBF ₄ , (C ₃ H ₇ ) ₄ PBF ₄ , (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₃ CH ₃ NBF ₄ , (C ₃ H _{7) 4} NBF _4, etc. can be used _{(C 2 H 5) 4 PPF} 6, (C 2 H 5) 4 PCF 3 SO 3, LiBF 4, LiClO 4, LiCF 3 SO 3.
As the organic solvent, for example, ethylene carbonate, propylene carbonate, γ-butyllactone, dimethyl sulfoxide, dimethylformamide, acetonitrile, tetrahydrofuran, dimethoxyethane and the like can be used. A mixture of two or more of these can also be used.

  As described above, the porous carbon material for electric double layer capacitor of the present invention, the method for producing the porous carbon material for electric double layer capacitor, and the electric double layer capacitor have been described in detail. It goes without saying that various improvements and modifications may be made without departing from the scope of the present invention.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

[Example 1]
<Manufacture of porous carbon material>
To an activation raw material obtained by carbonizing mesocarbon spheres coarsely pulverized to an average particle size of 7 μm at 700 ° C., 3.0 times (mass ratio) of KOH is added and mixed uniformly. Heated for an hour (activation process).
In this heat treatment, holding at 450 ° C. for 1 hour was performed in the process of raising the temperature to 800 ° C.

After activation, the sample was washed with hydrochloric acid to neutralize it, then washed with ion-exchanged water until the washing solution showed neutrality, and then dried to obtain an activated carbon substrate.
Thereafter, the activated carbon substrate was subjected to a heat treatment at 700 ° C. for 3 hours in a nitrogen atmosphere to reduce functional groups, thereby obtaining activated carbon.

0.02 part by weight of zirconium oxide having an average primary particle size of 30 nm is added as a non-ferrous metal oxide to 100 parts by weight of the activated carbon obtained above, and a peripheral speed of 20 m is used using a Meso-Fusono (MF) manufactured by Hosokawa Micron. / S was performed for 30 minutes, nonferrous metal oxide was made to adhere to the surface of activated carbon, and the porous carbon material was obtained.
By this grinding treatment, the average particle size of the porous carbon material (activated carbon) was set to 7 μm.

The porous carbon material for the electric double layer capacitor thus obtained was measured for the BET specific surface area and the functional group amount. The measuring method is as follows.
<BET specific surface area>
Using a micromeritis ASAP2400, the specific surface area of the porous carbon material was calculated by the BET method based on the adsorption isotherm by N ₂ adsorption / desorption at 77K.
<Amount of functional group>
After dipping the porous carbon material in a 0.1N NaOH aqueous solution for 20 hours, the NaOH in the liquid excluding the porous carbon material was titrated with HCl, and the functional group amount of the porous carbon material was calculated from the amount of consumed NaOH. Was calculated.
The results are shown in Table 1 below.

<Preparation of polarizable electrode>
The prepared porous carbon material 85 mg, carbon black 10 mg, polytetrafluoroethylene 3 mg, and carboxymethylcellulose 2 mg were wet-mixed in ion-exchanged water to prepare a coating material. This paint was applied to a uniform thickness of 40 μm on a 20 μm aluminum foil current collector using a doctor blade.
This coating film was preliminarily dried with a thermostat at 80 ° C., and then pressed at a press pressure of 150 GPa to adhere the coating film to the aluminum foil. This was dried under reduced pressure (133.3 Pa) at 150 ° C. for 10 hours to obtain an electrode sheet.
Two pieces of this electrode sheet were cut into 5 cm × 5 cm squares to obtain polarizable electrodes for measuring capacitance of electric double layer capacitors. The density was calculated from the diameter, thickness and weight of the electrode, and this was used as the electrode density (unit: g / cm ³ ).

<Production of electric double layer capacitor>
Porous polyethylene (pore diameter 0.20 μm) was sandwiched between the pair of polarizable electrode plates prepared above in a glove box where the dew point was controlled at −80 ° C. or less and argon was circulating. This laminate was assembled in a bipolar cell packaged with an aluminum laminate sheet bag and filled with an electrolytic solution. Then, the opening part of the aluminum laminated sheet bag was heat-sealed, and the electrical double layer capacitor (laminate cell) was produced.
The electrolyte used was a solution in which tetraethylimidazole tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) was dissolved in propylene carbonate at a concentration of 1M.

About the produced electric double layer capacitor, the measurement of the initial stage electrostatic capacitance and resistance value, and the high temperature reliability test were done.
The high temperature reliability test was performed by measuring the capacitance retention rate and the amount of gas generated after charging and discharging at a high temperature.

<Capacitance>
Using a charge / discharge test apparatus (HJ1001SM8) manufactured by Hokuto Denko Co., Ltd., charge / discharge was performed for 3 cycles at a current density of 10 mA / cm ² and a charge / discharge voltage of 0 to 2.5V. Using the results of this charge / discharge test, the capacitance was calculated as follows.
First, a discharge curve (discharge voltage-discharge time) by the above charge / discharge test was drawn. Next, discharge energy (total discharge energy (W · s) when time integration of discharge voltage × current) is obtained from the discharge curve at the third cycle, and the capacitance is calculated from the value of this discharge energy by the following formula. did.
Capacitance (F) = 2 × discharge energy (W · s) / (discharge start voltage (V)) ²
The capacitance obtained above was divided by the mass of the porous carbon material constituting the polarizable electrode (positive electrode + negative electrode, unit: g) to obtain a capacitance per unit weight (F / g). Furthermore, the capacitance per unit weight is multiplied by the electrode density (g / cm ³ ) of the polarizable electrode calculated previously, and the obtained value is obtained as the capacitance per unit volume (F / cm ³ ). did.

<Resistance value>
The initial resistance value (Ω) of the electric double layer capacitor was determined by dividing the voltage drop (ΔV) from the start of discharge 0 to 0.2 seconds by the current value.

<High temperature reliability test>
The cell after the charge / discharge capacity measurement was put in a 700 ° C. thermostat, and 2.7 V constant voltage charging was continued for 3 days with a charge / discharge test apparatus (HJ1001SM8).
Thereafter, the cell is returned to room temperature of 25 ° C., and a charge / discharge test is performed in the same manner as described above to calculate the capacitance per unit volume (F / cm ³ ). The maintenance rate (%) of the electric capacity was calculated.
Moreover, the gas for a laminate cell expansion | swelling was extracted and the amount of generated gas (ml / g-AC) was measured.
The above results are also shown in Table 1.

[Example 2]
A device for depositing 0.02 part by weight of zirconium oxide on 100 parts by weight of activated carbon was replaced with a mechanofustry and a bead mill with a bead diameter of 2 mm was used for 30 minutes at a peripheral speed of 7.5 m / s. A porous carbon material was produced in the same manner as in Example 1, except that the average particle size of the activated carbon was pulverized to 5.0 μm. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 1.

[Example 3]
A porous carbon material was produced in the same manner as in Example 1 except that the amount of zirconium oxide added was 0.002 parts by weight. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 1.

[Example 4]
A porous carbon material was produced in the same manner as in Example 1 except that the amount of zirconium oxide added was 0.05 parts by weight. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 1.

[Example 5]
A porous carbon material was produced in the same manner as in Example 1 except that the heat treatment temperature of the activated carbon substrate was set to 900 ° C. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 1.

[Example 6]
A porous carbon material was produced in the same manner as in Example 1 except that the heat treatment temperature of the activated carbon substrate was 500 ° C. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 1.

[Example 7]
A porous carbon material was produced in the same manner as in Example 1 except that aluminum oxide having an average primary particle size of 30 nm was added as a non-ferrous metal oxide instead of zirconium oxide having an average primary particle size of 30 nm. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 1.

[Comparative Example 1]
A porous carbon material was produced in the same manner as in Example 1 except that zirconium oxide was not added and mechanofusion treatment was not performed. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 2.

[Comparative Example 2]
A porous carbon material was produced in the same manner as in Example 1 except that zirconium oxide was not added (mechanofusion treatment was performed). About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 2.

[Comparative Example 3]
A porous carbon material was produced in the same manner as in Example 1 except that the amount of zirconium oxide added was changed from 0.02 parts by weight to 0.1 parts by weight. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 2.

[Comparative Example 4]
A porous carbon material was produced in the same manner as in Example 1 except that the heat treatment temperature of the activated carbon substrate was 1300 ° C. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 2.

[Comparative Example 5]
A porous carbon material was produced in the same manner as in Example 1 except that the activated carbon substrate was not heat-treated. About the obtained porous carbon material, the specific surface area and the amount of functional groups were measured and measured in the same manner as in Example 1.
Thereafter, a polarizable electrode was produced in the same manner as in Example 1, and further, as in Example 1, the initial capacitance and resistance were measured, and a high temperature reliability test was performed.
The results are shown in Table 2.

In the above table, MF indicates mechanofusion processing, and BM indicates bead mill processing.

From the SEM images of the porous carbon materials of Examples 1 to 7 and EDX (energy dispersive X-ray analysis) of Zr or Al, it was confirmed that Zr and Al were attached to the surface of the activated carbon.
As shown in the above table, in Comparative Examples 1 and 2 in which the non-metal oxide is not added to the porous carbon material, the electrostatic capacity after charging / discharging at a high temperature is good although the initial capacitance is good. The capacity retention rate is low, that is, sufficient high temperature reliability is not obtained.
Moreover, although the nonmetallic oxide was added, the comparative example 3 with too much addition amount has a high initial resistance value.
Furthermore, in Comparative Example 4 where the heat treatment temperature of the activated carbon substrate is too high, the amount of the functional group of the porous carbon material is too small, and a sufficient electrostatic capacity cannot be obtained at the initial stage. Moreover, in the comparative example 5 which does not heat-process the base material of activated carbon, there are too many functional groups of a porous carbon material, As a result, gas generate | occur | produces in large quantities by charging / discharging at high temperature.

On the other hand, the electric double layer capacitor of the present invention having a polarizable electrode produced using the porous carbon material of the present invention has a capacitance maintenance rate at a high temperature as compared with the conventional electric double layer capacitor. It is an electric double layer capacitor that has high temperature and low gas generation and excellent high temperature reliability. Moreover, according to the manufacturing method of this invention, the porous carbon material which can obtain such an electrical double layer capacitor excellent in high temperature reliability can be manufactured suitably.
From the above results, the effect of the present invention is clear.

  It can be suitably used for the production of a high-performance electric double layer capacitor and various applications using the electric double layer capacitor.

Claims (8)

A porous carbon material used in an electric double layer capacitor,
100 parts by mass of activated carbon and 0.001 part by mass or more and less than 0.1 part by mass of a non-ferrous metal oxide, and the functional group amount of the porous carbon material is 0.1 to 0.5 mmol / g A porous carbon material for an electric double layer capacitor, comprising:   The porous carbon material for an electric double layer capacitor according to claim 1, wherein the oxide of the non-ferrous metal is attached to a surface of the activated carbon.   The porous carbon material for an electric double layer capacitor according to claim 1 or 2, wherein the non-ferrous metal oxide has an average primary particle size of 1 to 100 nm.   The porous carbon material for an electric double layer capacitor according to any one of claims 1 to 3, wherein the oxide of the nonferrous metal is at least one of zirconium oxide and aluminum oxide.   The porous carbon material for an electric double layer capacitor according to any one of claims 1 to 4, wherein the activated carbon and the non-ferrous metal oxide are mixed by applying a shearing force.   The electric double layer capacitor using the porous carbon material for electric double layer capacitors in any one of Claims 1-5. An activated carbon production process for obtaining activated carbon by heating the activated carbonaceous raw material at 300 to 1000 ° C. in a non-oxidizing atmosphere;
0.00100 parts by mass or more and less than 0.1 parts by mass of non-ferrous metal oxide is added to 100 parts by weight of activated carbon obtained in the activated carbon production process, and the activated carbon and non-ferrous metal oxide are mixed. And a mixing step. A method for producing a porous carbon material for electric double layer capacitors.   The method for producing a porous carbon material for an electric double layer capacitor according to claim 7, wherein mixing of the activated carbon and the non-ferrous metal oxide is performed while applying a shearing force.