JP2001223143A - Method for reactivating electric field of electrochemical capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for reactivating electric field of electrochemical capacitor by which the capacitance density of an electrochemical capacitor can be improved even when the same polarizable electrode is used by optimizing the first charging condition. SOLUTION: In this method, the electric field of the electrochemical capacitor is reactivated by expanding the volume of a polarizable electrode 26 composed mainly of a carbon material containing partially oxidized microcrystalline carbon resembling graphite by charging, and contracting the volume of the electrode 26 by discharging while the electrode 26 is dipped in an organic electrolytic solution. The constant-current charging which is performed in the first charging step is performed with a current smaller than an actually used current, and/or the first charging is performed in such a way that constant-current charging is performed until a relaxation current becomes sufficiently small after constant-current charging is performed until the voltage of the capacitor becomes a prescribed voltage higher than an actually used voltage and lower than a decomposition voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrochemical capacitor using a high-performance carbon material having a large capacitance for a polarizable electrode. The present invention relates to a method for activating an electric field of an electrochemical capacitor, which makes it possible to improve the capacitance density even when using an electric field.

[0002]

2. Description of the Related Art An electrochemical capacitor, which is one of the capacitors, has a farad-class large capacity and excellent charge / discharge cycle characteristics. In addition to being used as batteries, from the viewpoint of effective use of energy, use in applications such as storage of nighttime power is also being studied.

As shown in FIG. 1, a single electrode cell 10, which is one of the basic structures of such an electrochemical capacitor, is generally connected to current collectors 20 and 22 made of a metal material on the positive electrode side, respectively. Polarizing electrode 24 and negative polarizable electrode 2
6 are formed, and the polarizable electrodes 24 and 26 are
And a polarizable electrode 24
26 is impregnated with an electrolytic solution composed of a solvent and an electrolyte.

Further, the single capacitor cell 12 shown in FIG.
Means that the single electrode cell 10 shown in FIG.
Are electrically connected in parallel via the electrode lead-out portions 30 and 32 formed in the first portion. Such a single-capacitor cell 12 is suitably used as a relatively large-capacity electrochemical capacitor used for automobiles and the like. These single electrode cells 10 and single capacitor cells 12
Both are plate-type, and have characteristics that high filling and large area are easy.

In contrast to such a flat-type electrochemical capacitor, there is also a wound-type electrochemical capacitor 70 as shown in FIG. 3, which has a structure suitable for increasing the capacity, similarly to the single capacitor cell 12. . Wound electrochemical capacitor 70
In the above, a separator 28 is provided between a positive electrode sheet 72 in which the positive electrode-side polarizable electrode 24 is formed on the current collector 20 and a negative electrode sheet 74 in which the negative electrode-side polarizable electrode 26 is formed on the current collector 22. The wound body 76 produced by winding the cylindrical body in a state in which is interposed is used. For example, the wound body 76 is accommodated in a case 78 and filled with an electrolytic solution, and each of the electrode sheets 72. It is manufactured by sealing the open end surface of the case 78 with the sealing plate 82 on which the electrode terminals 80 are formed, while ensuring conduction between the electrode terminals 80 and the electrode terminals 80.

As such a polarizable electrode material for an electrochemical capacitor, a material mainly composed of activated carbon having a specific surface area of 1000 m ² / g or more has been conventionally used.
However, the capacitance density of an electrochemical capacitor using such activated carbon is limited to about 15 F / cc, and the withstand voltage is also about 3 V. In order to increase the capacity of the polarizable electrode material, a new high-capacity polarizable electrode material produced by heat-treating a carbon material together with an alkali compound has been reported (Japanese Patent Application Laid-Open No. 9-275042,
JP-A-9-320906).

[0007]

Here, the capacitance of the electrochemical capacitor can be confirmed by performing a charging / discharging process after the production. However, depending on the initial charging condition, the same polarizable electrode material is used. Even with the used electrochemical capacitor, it is expected that a difference will appear in the capacitance. That is, the inventor of the present invention aims to form as many fields as possible to exhibit capacitance in the polarizable electrode material and to allow the polarizable electrode material to stably exist, that is, the interaction between anions and cations in the electrolytic solution and the polarizable electrode material. By optimizing the initial charging conditions, it was considered possible to form a large number of action fields and make them exist stably.

[0008] The optimization of the first charging condition is as follows.
The present invention can be applied without depending on the type of the polarizable electrode material used. In particular, as in the case where a carbon material having partially oxidized graphite-like microcrystalline carbon is used as the polarizable electrode material, the relationship between the potential in the first charge and the charge time is the potential in the second and subsequent charges. And behavior different from the relationship between time and time, since the initial charging conditions are considered to be deeply involved in the development of capacitance,
Optimizing the initial charging conditions is considered very important.

Further, in a polarizable electrode material using a carbon material having partially oxidized graphite-like microcrystalline carbon, a volume change occurs due to charge and discharge. Therefore, it is necessary to maintain good reversibility of the volume change. It is expected that the first charging condition is a major factor for obtaining a structure that can achieve the above-mentioned structure and a large capacitance.

As described above, in the electrochemical capacitor, although the initial charging condition is very important from the viewpoint of increasing the capacitance, the condition has not yet been optimized. The present invention has been made in view of the above-mentioned problems, and has as its object to provide an electric electrode using a carbon material having partially oxidized graphite-like microcrystalline carbon as a polarizable electrode material. It is an object of the present invention to provide a method for activating an electric field of an electrochemical capacitor which can increase the capacitance by optimizing the initial charging condition of the chemical capacitor.

[0011]

That is, according to the present invention, as a first electric field activation method, a polarizable electrode mainly composed of a carbon material having partially oxidized graphite-like microcrystalline carbon is used. An electric field activation method for an electrochemical capacitor that is immersed in an organic electrolyte solution, and the polarizable electrode expands in volume by charging, and contracts in volume by discharging, wherein constant current charging in the first charging is used in actual use. After performing a constant current charge until a predetermined voltage not less than the actual use voltage and not more than the decomposition voltage of the electrolyte is performed, the relaxation current is sufficiently reduced at the predetermined voltage. A method for activating an electric field of an electrochemical capacitor, characterized in that constant voltage charging is performed until the voltage is reduced.

According to the present invention, as a second electric field activation method, a polarizable electrode mainly composed of a carbon material having partially oxidized graphite-like microcrystalline carbon is immersed in an organic electrolyte. An electric field activation method for an electrochemical capacitor in which the polarizable electrode expands in volume by charging, and contracts in volume by discharging, after performing the first charge and discharge, reversing the polarity of the polarizable electrode. A method of activating an electric field of an electrochemical capacitor, characterized by performing recharging.

In the first charge and / or recharge in the second electric field activation method, it is preferable to apply the conditions of the first electric field activation method. That is, in the first charging and / or recharging in the second electric field activation method, the constant current charging is performed with a low current that is lower than the current used during actual use, and / or the actual use voltage or higher and the decomposition voltage of the electrolytic solution or lower. It is preferable to apply a method of performing constant-current charging until the relaxation voltage becomes sufficiently small at the predetermined voltage after the constant-current charging until the predetermined voltage is reached.

In such an electric field activation method of the present invention, it is preferable that the charging current of the constant current charging in the first charging or recharging is set to half or less of the charging current in actual use. When an electrolytic solution using propylene carbonate as a solvent, which is generally used in an electrochemical capacitor, is used, the charging voltage of constant voltage charging, which is performed until the relaxation current becomes sufficiently small, exceeds 3 V per unit cell. It is preferable to set the range to less than 5V.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An electrochemical capacitor (hereinafter, referred to as “capacitor”) to which the electric field activation method of the present invention is suitably applied
That. ), A polarizable electrode mainly composed of a carbon material having partially oxidized graphite-like microcrystalline carbon (hereinafter referred to as “carbon material”) is immersed in an organic electrolytic solution, and the polarizable electrode is charged. It has the property of expanding its volume due to discharge and contracting its volume by discharging. Hereinafter, the carbon material will be described first.

In producing a carbon material, first, petroleum coke, coal coke, petroleum pitch (tar), coal pitch (tar), phenolic resin, mesophase carbon, polyvinyl chloride, polyvinylidene chloride, polyimide, coconut shell, sawdust, etc. Is heat-treated in an inert gas atmosphere in a temperature range of about 700 ° C. to 1000 ° C. to obtain a carbonized material. One of these organic materials may be used alone, or a mixture of two or more thereof may be used. As the inert gas, nitrogen gas, argon gas,
A rare gas such as helium gas is preferably used.

Next, the obtained carbonized material is preferably pulverized so as to have a predetermined particle size. Here, when the carbonized material is obtained in the form of a powder because the organic material is in the form of a powder or the like, the pulverizing treatment is not necessarily required. This pulverization makes it possible to make the partial oxidation reaction uniform in the next step and to shorten the heat treatment time.
The pulverization treatment here can be performed by various known methods regardless of a dry type or a wet type.

Next, by partially oxidizing the obtained powdered carbonized material, a carbon material having microcrystalline carbon similar to graphite can be obtained. Here, as a method of partial oxidation, heat treatment with an oxidizing gas such as air or oxygen,
In addition to a chemical oxidation method using hot nitric acid or the like, an oxidation method in which heat treatment is performed in an inert gas atmosphere together with at least one kind of an oxygen-containing alkali compound containing an alkali metal and an oxygen element (hereinafter, referred to as “alkali metal or the like”). Can be mentioned.

As the alkali metal element, potassium,
Sodium and lithium are preferably used. As the oxygen-containing compound of these alkali metals, hydroxides such as potassium hydroxide and sodium hydroxide and carbonates such as potassium carbonate and sodium carbonate are preferably used. These alkali metals and the like may be used in combination of two or more.

After the carbonized material is thus heat-treated with an alkali metal or the like, it is isolated by washing, filtering, and drying using an alcohol-based solvent such as methanol or ethanol, distilled water, or the like, and used for a polarizable electrode. It becomes a carbon material.

Next, “partially oxidized graphite-like microcrystalline carbon” will be described together with the structure of the carbon material. When various organic raw materials are carbonized at a temperature of 1000 ° C. or lower, incomplete 6 as shown in FIGS.
Turbulent structure carbon 90 or turbostratic structure carbon 91 having a member ring network surface is obtained. The term “microcrystalline carbon similar to graphite” refers to microcrystalline carbon 95 having a thickness of 0.1 nm to several tens of nm, which is regularly stacked in the turbostratic carbon 90/91.

It should be noted that the turbostratic carbon 90 shown in FIG.
Has a structure in which the layers between the microcrystalline carbons 95 are not oriented so that the planes of the layers are substantially parallel, but are completely parallel, and are stacked at an irregular angle. Such turbostratic carbon 90 is often found when an organic material that is apt to be graphitized in the carbonization process is used.

On the other hand, the structure of the turbostratic carbon 91 shown in FIG. 4B has a structure in which the microcrystalline carbon 95 is randomly arranged in a mesh pattern. In the case of using an organic material in which graphitization hardly occurs, it is often observed.

When these turbostratic carbon layers 90 and 91 are oxidized, for example, in the air, first, portions 97 having low regularity as crystals are oxidized and volatilized as carbon monoxide and carbon dioxide. When the oxidation proceeds further, microcrystalline carbon 95
The edge portion of itself and the incomplete portion of the six-membered ring structure are oxidized, and finally all the carbon is oxidized to a gas.

However, by controlling the oxidizing conditions, it is possible to stop oxidizing a part of the carbon material. The carbon material thus obtained is a “carbon material having partially oxidized graphite-like microcrystalline carbon”. is there. This carbon material
As shown in FIG. 12, the acidic functional group is mainly bonded to the edge or the imperfect structure of the six-membered ring retina of the microcrystal. FIG. 12 schematically shows one mode of the molecular structure of the carbon material, and it goes without saying that the carbon material according to the present invention is not limited to the carbon material having the structure of FIG. Nor.

Now, a polarizable electrode is manufactured using such a carbon material as a main material. This polarizable electrode is produced by adding a conductive additive such as an organic binder or carbon black to a carbon material, mixing, kneading, or the like, and processing it into various shapes such as a plate shape or a sheet shape.

Note that a carbon material can be used as a material for a polarizable electrode regardless of the structure of a capacitor.
For example, the single electrode cell 1 shown in FIG.
0 and the single capacitor cell 12 shown in FIG. 2, and furthermore, a structure like the wound body 76 shown in FIG. 3 is housed in a case and impregnated with an organic electrolytic solution to produce capacitors having various structures. Is done.

Although the structure of the capacitor is different,
There is no change in the organic electrolyte used. Solute of organic electrolyte,
That is, tetraethylammonium (TE
A⁺), Tetrabutylammonium (TBA⁺), Trie
Tylmethylammonium (TEMA⁺) And others
Quaternary ammonium tetrafluoroboric acid (BF_Four ^-) Salt or 6
Fluorinated phosphoric acid (PF₆ ^-) Salt or tetraethylphospho
(TEP⁺) Such as BF of quaternary phosphonium_FourSalt or
PF₆Salt or general formula

[0029]

Embedded image

(Wherein R ₁ and R ₂ are alkyl groups having 1 to 5 carbon atoms, and R ₁ and R ₂ may be the same or different groups). _Four
A salt or a PF ₆ salt, particularly a BF ₄ salt or a PF ₆ salt of 1-ethyl-3-methyliridazolium (EMI ⁺ ) is preferably used.

On the other hand, propylene carbonate (PC), γ-butyl lactone (GB
L), ethylene carbonate (EC), sulfolane (S
Those containing at least one of L) are preferably used.
A solvent containing at least one of PC, GBL, EC and SL is used as a main solvent, and dimethyl carbonate (DM
It is also possible to use a solvent containing at least one of C), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) as a sub-solvent.

Here, the main solvent refers to a solvent capable of obtaining sufficient performance as an electrolyte solvent even when the substance is used alone, and the auxiliary solvent refers to a solvent having a low performance as an electrolyte solvent when the substance alone is used. When used in combination with a main solvent, it refers to a solvent that can achieve performance higher than that of the main solvent alone or the auxiliary solvent alone. That is, the main solvent and the sub-solvent are not classified according to the addition ratio.
There are no restrictions, such as:

In the first charge and discharge of the capacitor thus manufactured, generally, first, constant current charging is performed until a predetermined voltage is reached, and then constant current charging is performed at a predetermined voltage after the constant current charging for a certain period of time. Charging is performed by performing voltage charging, and discharging is performed by performing constant current discharging at a predetermined current value from the charged state. In addition to the confirmation of the capacitance in this manner, the capacitance of the capacitor is substantially determined by the first charging. In a capacitor using the above-described carbon material, when the capacitor is charged, it is considered that a capacitance is generated in the capacitor by adsorption of ions to a product generated by an electrochemical reaction at the time of the first charge.

FIG. 10 shows the time change of the voltage in the first (first) charge / discharge and the second and subsequent charge / discharge of the capacitor having the thickness of the polarizable electrode of 0.5 mm manufactured using the above-described carbon material. It is a graph shown. This graph shows the charging / discharging characteristics of one single electrode cell. The constant current charging in charging was performed at 4 mA / cm ² until the voltage reached 4 V, and then the constant voltage charging was performed at 4 V for 20 minutes. Thereafter, the result of discharging at a constant current of ² mA / cm ² is shown.

A comparison between the first charge / discharge curve and the second charge / discharge curve shows that the voltage change in the constant current charging region immediately after the start of charging is remarkably different.
However, in the second and subsequent charging / discharging, almost no change appears in the charging / discharging curve. This indicates that the constant current charging in the initial charging and discharging, particularly at the charging stage, is closely related to the formation of the structure, structure and morphology related to the charging and discharging of the polarizable electrode, that is, the development of the capacitance. Guessed. Therefore, in the present invention, the first charging process, that is, the charging of the first polarizable electrode is considered to play a role of activation for developing capacitance, and this is referred to as “electric field activation”. Things.

The first method of the electric field activation is a process in a constant current charging stage in which the constant current charging in the first charging is performed at a current lower than the current used in actual use, and the first charging is performed in the actual use. After performing constant-current charging until a predetermined voltage equal to or higher than the voltage and equal to or lower than the decomposition voltage of the electrolytic solution, at least in the processing in the constant-voltage charging step of performing constant-voltage charging until the relaxation current becomes sufficiently small at the predetermined voltage One of the processes is performed.

First, the constant current charging stage in the first charging will be described. The constant current charging is performed until reaching a constant voltage charging voltage to be performed later. In the present invention, the constant current charging is performed with a current lower than the current used in actual use. As is well known, capacitors do not always have to be used with a constant charging current,
Charging with a large current may shorten the service life of the capacitor. Preferably, charging is performed through a charging circuit that controls a constant current and a constant voltage. The value of such constant current is the current used during actual use (charging current).
Is the value of

The constant voltage charging voltage is set to an appropriate value in consideration of withstand voltage and life, and the constant voltage at this time is an actual operating voltage. And the material of the polarizable electrode. Therefore, the current value of the constant current charging in the first charging of the present invention is appropriately determined to a value suitable for the intended use and the constituent materials.

In the capacitor using the above-described carbon material, the charging current at the time of constant current charging is set to １ ／ or less, preferably about ４ of the charging current at the time of actual use, as will be described in Examples described later. By doing so, it became clear that the capacitance can be increased.

One reason why the capacitance increases due to the constant current charging with the small current value described above is considered as follows. That is, as shown in FIG. 11, the capacitor of the present invention is considered to be represented by an equivalent circuit in which capacitor elements having capacitances C _{1 to} C _n are connected in multiple stages, and therefore, the capacitor elements in the subsequent stages are charged. Therefore, it is necessary to take a long time with a low current. Therefore, it is considered that by performing the first charging under mild conditions, the electric field was activated to the capacitor element in the subsequent stage, and the capacitance was considered to have increased. Note that R _{1 to} R _n in FIG. 11 represent resistance.

Next, the constant voltage charging stage in the first charging will be described. In the first charging, the previously performed constant current charging is preferably performed by the above-described first electric field activation method, but the constant current charging is performed at a predetermined voltage equal to or higher than the actual use voltage and equal to or lower than the decomposition voltage of the electrolytic solution. Do until. The actual voltage used depends on the application, the withstand voltage, etc., and the decomposition voltage of the electrolytic solution is determined by the solvent and solute used. In the capacitor using the carbon material described above,
This predetermined voltage is preferably set to a value exceeding 3 V and less than 4.5 V per single cell.

In this case, “per single cell” means that one capacitor is configured by connecting a plurality of single electrode cells 10 shown in FIG. 1 in parallel, that is, the single capacitor shown in FIG. In the case of the cell 12 or the like, this is synonymous with “per capacitor”. On the other hand, when one capacitor is formed by connecting a plurality of single electrode cells 10 in series, it means “per single electrode cell”, and a predetermined voltage is applied to each single electrode cell 10. As described above, the required voltage to be applied to one capacitor is the product of the number of serially connected single electrode cells 10 and a predetermined voltage applied to the single electrode cell.

When the constant voltage charging is started, the charging current value gradually decreases. In the present invention, the charging process is continued until the relaxation current during the constant voltage charging becomes sufficiently small. Thus, it is presumed that an increase in the capacitance appears due to the formation of the field of the development of the capacitance even in the details of the carbon material in the polarizable electrode.

After completion of the constant voltage charging at a predetermined voltage equal to or higher than the working voltage and equal to or lower than the decomposition voltage of the electrolyte, constant current charging is further performed to a higher voltage with the decomposition voltage of the electrolyte as an upper limit, and the charging is continued at the ultimate voltage Perform constant voltage charging and complete the first charging. In this case, the constant voltage charging at a higher voltage does not necessarily require the processing time to be performed until the relaxation current becomes sufficiently small.

Next, a second electric field activation method will be described. In the second electric field activation method, after the first charge and discharge are performed, the polarity of the polarizable electrode is reversed to perform recharge. Of course, discharging is performed after recharging. That is,
In the second electric field activation method, a single electric field activation process is completed by performing charging and discharging twice.

Here, it is also preferable to apply the above-described first electric field activation method to the first charging. The magnitude of the discharge current is not particularly limited, but is preferably equal to the current value in the constant current charge of the first charge. After this first discharge, the polarity of the power supply is reversed and recharging is performed. At this time, without changing the polarity of the power supply, the lead wires from the power supply may be connected and changed so that the positive and negative electrodes of the capacitor are reversed.

The above-described first electric field activation method can be applied to the charging method in the recharging. After the recharging is completed, discharging is performed, and for subsequent charging and discharging, either electrode may be used as the positive electrode. For example, the capacitor may be marked with a positive / negative mark or the like and put to practical use according to the mark.

One of the reasons why the capacitance is increased by the second electric field activation method is considered as follows. That is, in the electrode using the partially oxidized carbon material, oxidation occurs at the positive electrode and reduction occurs at the negative electrode during the first charge. As shown in FIG. 12, in the carbon material, many acidic functional groups formed by partial oxidation are present at the edges of the six-membered ring retina of microcrystalline carbon. It is removed by the reaction. Therefore, it is presumed that holes formed by partial oxidation at the edge portion are widened, a path for the movement of cations is formed, and a wider field for expressing capacitance is formed.

On the other hand, the oxidation of the acidic functional group of the functional group occurs in the positive electrode, but it is presumed that its structure does not basically change much. For this reason, when the polarity is reversed after the first charge / discharge and the recharge / discharge is performed, this time, the electrode which was the positive electrode becomes the negative electrode, reduction occurs, and the acidic functional group is removed. As a result, it is presumed that the pores formed at the edges due to partial oxidation at both electrodes are widened, thereby forming a path for the movement of cations and anions, thereby forming a wider field for expressing capacitance. .

[0050]

EXAMPLES Next, examples of the present invention will be described, but it goes without saying that the following examples do not limit the present invention. Using petroleum coke as an organic material,
100 g of petroleum coke in a nitrogen atmosphere at 800 ° C.
Heat treatment was performed for about an hour to perform carbonization treatment, and the mixture was cooled to room temperature. The heating rate at this time was 100 ° C./hour. Thereafter, the obtained carbonized material was pulverized to an average particle size of 35 μm. 50 g of this carbonized material powder and potassium hydroxide 1
00 g in an alumina crucible and placed in a nitrogen gas atmosphere at 80
Heat treatment was performed at 0 ° C. for 2 hours to partially oxidize. After cooling, unnecessary potassium compounds such as potassium hydroxide were removed by washing with water, and the powder was separated by filtration and dried to obtain a powdery carbon material.

To 1 g of the obtained carbon material, 0.1 g of carbon black as a conductive additive and PTFE (polytetrafluoroethylene) as a binder were added, mixed, kneaded, and rolled to a thickness of 0 g. It was formed into a 0.5 mm sheet. From the electrode sheet thus prepared, a punched one having a diameter of 19 mm was used as a positive and negative polarizable electrode, an aluminum foil was used as a current collector, a glass fiber nonwoven fabric was used as a separator, and PC was used as a solvent and tetraethylammonium. An electrolyte having a concentration of 1 mol / L was prepared using tetrafluoroborate (TEABF ₄ ) as a solute, and a plurality of capacitors having the same structure as the single electrode cell 10 shown in FIG. 1 were prepared. The production of the capacitor was performed in a glove box in an argon gas atmosphere having a dew point of 80 ° C. or less.

The first charge / discharge of the three manufactured capacitors was performed at a constant current of 2 mA (Example 1), 5 mA (Example 2), and 10 mA (Comparative Example) at a constant current of 4 mA, and then 4 V. And then discharging at a discharge current of 5 mA. After that, 2V, 2.5V, 3V, 3.5V, 4V
A current-carrying test was performed to charge and discharge at a voltage of. The charging current and the discharging current in the energization test were 10 mA and 5 mA, respectively.

FIG. 5 shows test results showing the relationship between the obtained capacitance density (the size of the capacitance per unit volume) and the voltage. As shown in FIG. 5, it was confirmed that in Examples 1 and 2 in which the value of the first charging current was reduced, the capacitance density was increased as compared with the comparative example.

Further, two capacitors manufactured as described above were used, and one of them was charged at 10 mA to 3.5 V, then was charged at 3.5 V for 24 hours, and thereafter, was supplied with current at 10 mA to 4 V. Then, the battery was charged at a constant voltage maintained at 4 V for 20 minutes, and discharged at 10 mA. The capacitor that has been charged for the first time is referred to as a third embodiment. The other capacitor is the same as the comparative example described above,
A constant current charge is performed up to 4 V with a constant current of mA, and then 4 V
And then discharged at 10 mA. FIG. 6 shows the results of conducting the above-described energization test on the capacitors of Example 3 and Comparative Example in which the electric field activation was performed in this manner. In Example 3, an increase in capacitance was confirmed as compared with the comparative example.

Further, two capacitors manufactured as described above were used, and both of them were charged at a constant current of 10 mA to a constant current of 4 V, and then charged at a constant voltage of 4 V for 20 minutes. Discharged at 10 mA. Thereafter, the polarity of the power supply was inverted for only one battery, and recharging was performed under the same charge / discharge conditions. The capacitor that has been recharged with the polarity inverted is referred to as a fourth embodiment. The capacitor that has not been recharged is equivalent to the comparative example described above. FIG. 7 shows the results of conducting the above-described energization test on these capacitors. In Example 4 in which the polarity was reversed and recharging was performed, it was confirmed that the capacitance density was increased as compared with the comparative example.

Furthermore, using the capacitor manufactured as described above, an energization test was performed under the same conditions as in Example 2 except that only the initial charging voltage was increased to 4.5 V (Example 5). Specifically, constant current charging was performed to 4.5 V at a constant current of 5 mA, and then constant voltage charging was performed at 4.5 V for 20 minutes, followed by discharging at a discharge current of 5 mA. Further, charging and discharging were performed at a voltage of 2, 2.5, 3, 3.5, and 4V. Here, the charging current was 10 mA, and the discharging current was 5 mA. 8 and 9 show the results of the current test.
The internal resistance shown in FIG. 9 was calculated by the following equation (1). Internal resistance (Ω · cm ² ) = resistance (Ω) × electrode area (cm ² ) (1)

In the fifth embodiment, the second embodiment (first charging voltage 4
Although the internal resistance was slightly higher than in the case of V), the effect of increasing the capacitance density was large, and a higher capacitance was obtained. This is presumably because the hole formed by the partial oxidation in the edge portion of the microcrystalline carbon was further expanded as a result of increasing the initial charging voltage. The method of increasing the initial charge voltage may increase the electrolyte resistance and increase the internal resistance.However, since the merit of increasing the capacitance density is greater, the method of load leveling of the electric power where the internal resistance is not a problem is considered. It can be suitably used in such applications.

[0058]

As described above, according to the present invention, by optimizing the initial charging conditions, the capacitance density can be improved even when the same polarizable electrode is used. Effects can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of the structure of a single electrode cell.

FIG. 2 is a perspective view showing an example of the structure of a single capacitor cell.

FIG. 3 is a perspective view showing an example of the structure of a wound capacitor.

FIG. 4 is an explanatory view schematically showing a microstructure of a carbon material suitably used in the present invention.

FIG. 5 is an explanatory diagram showing the relationship between the capacitance density and the voltage of an electrochemical capacitor in which the constant current charging conditions in the first charging are different.

FIG. 6 is an explanatory diagram showing a relationship between a capacitance density and a voltage of an electrochemical capacitor in which constant voltage charging conditions in the first charging are different.

FIG. 7 is an explanatory diagram comparing the relationship between the capacitance density and the voltage of the electrochemical capacitor by the presence or absence of charge / discharge with the polarity of the electrode inverted.

FIG. 8 is an explanatory diagram showing the relationship between the capacitance density and the voltage of an electrochemical capacitor in which the constant voltage charging conditions in the first charging are different.

FIG. 9 is an explanatory diagram showing the relationship between the internal resistance and the voltage of the electrochemical capacitor in which the constant voltage charging conditions in the first charging are different.

FIG. 10 is a graph (chart) showing charge / discharge characteristics of an electrochemical capacitor using the carbon material of the present invention.

FIG. 11 is an equivalent circuit diagram of the electrochemical capacitor of the present invention.

FIG. 12 is an explanatory view schematically showing a molecular structure of microcrystalline carbon in a carbon material suitably used for the electrochemical capacitor of the present invention.

[Explanation of symbols]

10 single electrode cell, 12 single capacitor cell, 22.2
4 ... current collector, 26 ... polarizable electrode, 28 ... separator, 3
0.32 ... electrode extraction part, 70 ... wound type capacitor,
72: positive electrode sheet, 74: negative electrode sheet, 76: wound body,
78 ... case, 80 ... electrode terminal, 82 ... sealing plate, 90
91: turbostratic carbon, 95: microcrystalline carbon, 97: low-order part.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02J 1/00 306 H01G 9/00 531 F term (Reference) 4G046 HA06 HB00 HC03 HC11 HC12 HC19 5E082 AB03 AB04 AB09 BB03 BC40 EE02 EE28 MM35 5G065 HA01 HA07 HA17 NA01

Claims (5)

[Claims] 1. A polarizable electrode mainly composed of a carbon material having partially oxidized graphite-like microcrystalline carbon, is immersed in an organic electrolyte, and the polarizable electrode expands in volume by charging, and An electric field activation method for an electrochemical capacitor that contracts in volume by discharging, wherein a constant current charge in the first charge is performed at a current lower than a current used in actual use, and / or the first charge is performed in an actual use voltage. A method for activating an electric field of an electrochemical capacitor, comprising: performing constant current charging until a predetermined voltage equal to or lower than the decomposition voltage of the electrolytic solution is reached, and then performing constant voltage charging until the relaxation current is sufficiently reduced at the predetermined voltage. . 2. A polarizable electrode mainly composed of a carbon material having microcrystalline carbon similar to graphite partially oxidized, is immersed in an organic electrolyte, and the polarizable electrode expands in volume by charging, and A method for activating an electric field of an electrochemical capacitor which contracts in volume by discharging, wherein after performing initial charging and discharging, the polarity of the polarizable electrode is reversed to perform recharging. Activation method. 3. The method according to claim 1, wherein the first charging and / or recharging is performed with a constant current charging at a low current lower than a current used in actual use, and / or a predetermined voltage not lower than the actual use voltage and lower than the decomposition voltage of the electrolyte. 3. The method according to claim 2, wherein the constant-current charging is performed until the relaxation current is sufficiently reduced at the predetermined voltage. 4. The method for activating an electric field of an electrochemical capacitor according to claim 1, wherein a charge current of the constant current charge in the first charge is equal to or less than a half of a charge current in actual use. . 5. The method according to claim 1, wherein a predetermined voltage equal to or higher than the actual use voltage and equal to or lower than the decomposition voltage of the electrolyte is in a range of more than 3 V and less than 4.5 V per cell. An electric field activation method for the electrochemical capacitor according to claim 1.