JP2000068164A - Electric double layer capacitor and method of manufacturing the same - Google Patents

Abstract

(57) [Problem] To provide an electric double layer capacitor having a large capacitance. SOLUTION: The electrode has a polarizable electrode made of a carbonaceous material that expands in a voltage application direction when a voltage is applied, and has a second dimension restriction after being activated in a first dimension restriction structure that restricts expansion when a voltage is applied. Electric double layer capacitor held in the structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor, and more particularly to an electric double layer capacitor having a large capacitance density and a method for manufacturing the same.

[0002]

2. Description of the Related Art Electric double layer capacitors are prepared by adding a small amount of a conductive agent and a binder to activated carbon having a large specific surface area, which is a main material, and kneading or rolling the same, or dissolving a similar material in a slurry to form a collector. Apply polarizable electrodes obtained by a method such as coating, mixing activated carbon with a small amount of non-carbonized resin, and sintering them. An electrolyte impregnated with a neutral electrolyte solution or a non-aqueous solvent electrolyte solution is used.

[0003] Activated carbon having a large specific surface area is used because the capacitance of an electric double layer capacitor is considered to be substantially proportional to the surface area of a polarizable electrode. Activated carbon is 8
After carbonizing the carbonaceous material at a temperature of
It is manufactured by activating the mixture in an atmosphere of water vapor, carbon dioxide, or the like at a temperature of from 1000 ° C. to 1000 ° C., or by mixing zinc chloride, potassium hydroxide and the like in an inert atmosphere.
In the activation process, the carbon material is produced by a method of forming a large number of pores suitable for adsorption on the surface of the carbon material generated in the carbonization process.

In order to increase the capacity of the electric double layer capacitor as much as possible, an activated carbon having a large surface area is used as the activated carbon. For example,
Japanese Patent Application Laid-Open No. 63-78513 discloses that activated carbon for electric double layer capacitors, which is mentioned as a conventional example, has a specific surface area of up to about 1500 m ² / g, but the surface area per unit volume is not sufficient. Therefore, the specific surface area obtained by calcining a mixture of petroleum coke and potassium hydroxide with petroleum coke as a raw material was 2000 to 3
It has been proposed to use 500 m ² / g of activated carbon.

However, when activated carbon is strongly activated in order to increase the surface area of activated carbon, the specific surface area per activated carbon weight increases as the activation proceeds, but the porosity also increases at the same time, so that the surface area per volume is constant. Instead, it decreases at the activation level. In addition, activated carbon activated strongly
The capacitance per electric double layer area tends to decrease as the activation proceeds.

[0006] The present inventors have found that even if activation is carried out beyond a certain limit, a larger capacitance density cannot be obtained, and it can be obtained by using a polarizable electrode depending on the specific surface area of activated carbon. Japanese Patent Application No. 10-50862 proposes to improve the limit of the capacitance density and obtain an electric double layer capacitor having a large energy density.

In this method, a carbonaceous material that expands when a voltage is applied is used as an electrode, and the energy density per unit volume is reduced by holding a polarizable electrode in a dimensional restriction structure that limits expansion when a voltage is applied. A large electric double layer capacitor.

[0008]

In an electric double layer capacitor using a carbonaceous material that expands when a voltage is applied, the carbon electrode expands in the thickness direction, for example, about twice per 4 V with charging. However, even if the capacitance increases, if the volume expands, the energy density per volume will decrease.Therefore, it is necessary to secure the energy density by limiting the dimensions so that the capacitor container cannot be expanded by providing strength. Required. Although various methods can be considered as a method of limiting the size, since the assumed expansion pressure is about 10 kg / cm ² , a container or a dimensional structure that can withstand an expansion force of 1 ton even if the electrode size of the small capacitor is 10 cm in length and width A restricting body is required, compared to a conventional electrode of the same size using activated carbon, which assumes a compression pressure of about 200 kg.
There were design and manufacturing problems.

As described above, since the size-limiting structure or the container of the capacitor requires a large strength, it is difficult to easily form an assembly of lightweight capacitors, such as a power source for an electric vehicle. However, there is a problem that it is difficult to use in applications where weight and the like are limited. An object of the present invention is to provide a lightweight electric double layer capacitor using an expanding carbonaceous material.

[0010]

According to the present invention, there is provided an electric double layer capacitor having a polarizable electrode made of a carbonaceous material which expands when a voltage is applied, and a rated voltage in a state where the first dimension limiting structure is attached. An electric double-layer capacitor that is retained in a second size-limiting structure having a smaller withstand pressure than the first size-limiting structure after an initial charge at a higher voltage. The dimension limiting structure is the above-described electric double layer capacitor that limits the expansion of the electrode in the voltage application direction when a voltage is applied. The electric double layer capacitor as described above, wherein an expansion pressure of ² kg / cm ² or more is generated in the electrode in a state where dimensions are limited against expansion of the polarizable electrode when voltage is applied. While using a non-aqueous solvent electrolyte as the electrolyte,
The above electric double layer capacitor using a carbonaceous material whose polarizable electrode has an interlayer distance d ₀₀₂ measured by an X-ray diffraction method of 0.365 to 0.385 nm. The above electric double layer capacitor, wherein the carbonaceous material is obtained by preliminarily heating petroleum coke, mixing with potassium hydroxide, and heat treating in an inert atmosphere. The electric double layer capacitor according to the above, wherein the carbonaceous material is obtained by carbonizing coconut and then heat-treating in an inert atmosphere or an atmosphere containing water vapor.

In a method for manufacturing an electric double layer capacitor, a capacitor having a polarizable electrode made of a carbonaceous material which expands when a voltage is applied is initially mounted at a voltage higher than a rated voltage with a first dimension limiting structure attached. The method for manufacturing an electric double layer capacitor according to the above, wherein after charging, the electric double layer capacitor is held in a second size restriction structure having a smaller withstand pressure than the first size restriction structure.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, the reason why the carbonaceous material that expands when a voltage is applied expands greatly is that an electric field activation period in which a voltage is first applied to a carbonaceous material to which no voltage is applied to activate the carbonaceous material. This is achieved only by focusing on the fact that the other period is about half of the initial inflation pressure.

The carbonaceous material is heat-treated at 600 to 900 ° C. to promote carbonization more than the conventional activated carbon raw material, mixed with 1 to 5 times by weight of potassium hydroxide, and mixed with about 700 wt. When heated at about 900 ° C. for about 2 hours, if the carbonaceous material is not heat-treated, it becomes activated carbon. However, activation is not progressed due to the progress of carbonization due to the effect of heat treatment, and the specific surface area is 1000 m ² / g. Stay below.

However, this carbonaceous material is subjected to steps such as washing and pulverization by a usual method, and a binder such as polytetrafluoroethylene and a conductive material such as carbon black are added and kneaded to form a sheet. When an electric double layer capacitor is produced by sufficiently dehydrating and impregnating with an electrolytic solution, for example, a 1 mol propylene carbonate solution of tetraethylammonium tetrafluoroborate, an electric double layer capacitor having a large capacitance density exceeding 28 F / cc can be obtained. .

When a voltage is applied using such a carbonaceous material that has not been activated, the carbonaceous material expands with the application of the voltage, and the activation of the carbonaceous material proceeds. If the expansion of the carbonaceous material can be limited by applying pressure from the outside, an electric double layer capacitor having a large energy density per volume can be obtained.

FIG. 1 is a diagram for explaining an example of a change in pressure and a change in voltage during charging. FIG. 1 shows an electric double-layer capacitor using a positive electrode and a negative electrode having a diameter of 20 mm and a thickness of 0.5 mm and an electrolyte of 1 molar concentration and a full charge voltage of 4 V at a constant current of 5 mA.
7 shows an example of the waveform of the pressure generated on the electrode surface when the terminal voltage of the capacitor and the expansion of the capacitor during the first three cycles of the charge / discharge cycle are set as described above. The rate of increase in capacitance and the increase in pressure with respect to the pressure waveform and voltage applied by the capacitor vary depending on the method of forming the electrodes and the carbon material, but those with a large capacity multiplication factor tend to expand, that is, the pressure also increases. .

However, when the carbonaceous material is charged to a high voltage during the activation process, a large expansion pressure is generated. The voltage of 4 V required for electric field activation is only applied at that time, and in the subsequent use state of the capacitor,
There is no such high voltage.

FIG. 2 is a diagram for explaining another example of a change in pressure and a change in voltage during charging. The first 4 V charge / discharge cycle is the same as in FIG. 1, but only this cycle is necessary for activation, and thereafter the charge / discharge cycle is a low voltage cycle as shown in FIG. Therefore, FIG. 2 shows that the charge and discharge up to 3 V can be performed only in the second and subsequent cycles, and the degree of increase in pressure is also reduced.

FIG. 3 is a diagram for explaining a method of manufacturing the electric double layer capacitor of the present invention. As shown in FIG. 3A, a predetermined number of unit capacitors 1 housed in a rectangular container in which positive and negative electrodes made of a carbonaceous material that expands by application of a voltage are stacked via a separator, are arranged in series and parallel. A capacitor assembly which is conductively connected and provided with end plates 2 on both sides thereof and compressed by a tension belt 3 which is a second size-limiting structure which can be tensioned by an inflation pressure generated in a normal use state of the electric double layer capacitor. 4 is produced. Next, the first dimension limiting structure 5 is mounted on the capacitor assembly 4 and the charging / discharging device 6 is mounted.
The unit capacitor is activated by applying a voltage equal to or higher than the rated voltage from the expansion of the carbonaceous material.

As the first dimension-limiting structure, a box-shaped or frame-shaped one can be used as long as it can hold the pressure generated during activation. The use of a capacitor whose holding interval of the multilayer capacitor can be adjusted, a device whose holding part of the electric double layer capacitor can be easily attached and detached by hydraulic pressure, air pressure, etc. Preferably, it is used.

Next, after charging is completed, discharging is performed, and in a state where the inflation pressure is reduced below the pressure applied by the tension belt 3 during normal use, as shown in FIG. The body 5 is removed and held only by the second dimension limiting structure. Next, as shown in FIG. 3C, the capacitor assembly 4 is housed in a container 7 to form an electric double layer capacitor.

Further, as shown in FIG. 3D, if a container 7 having a large strength capable of holding an inflation pressure is used, the container 7 can be used as a second size-limiting structure. Therefore, the electric double layer capacitor may be attached to the first dimension limiting structure in a state where the electric double layer capacitor is housed in the container 7, and after the activation, the first dimension limiting structure may be removed and used as an electric double layer capacitor.

For example, in the case where a tension belt is used, for example, 2 kg / cm
^{When the} pressure is increased by ² and the internal resistance is lowered by making the contact between the electrode and the current collector good and the internal resistance is lowered, charging is started by mounting the dimension limiting structure 5 and charging to 4 V is activated. When the electrode expands and a pressure of about 9 kg / cm ² is applied to the dimension limiting structure, the pressure decreases when the charging current is discharged after the activation is completed, so that the dimension limiting structure can be removed after the pressure decreases. . In the subsequent charging up to 3 V, the expansion pressure remains at about 7 kg / cm ² . If the pressure applied by the tension belt is subtracted, the pressure that the container must withstand is about 5 kg / cm ² , so that the design strength of the container can be reduced to about half.

The rate of rise of the voltage of the electric double layer capacitor at the time of activation is not increased rapidly, but by gradually increasing the voltage, an electrode far from the power supply electrode is sufficiently activated. Is preferred.

FIG. 4 is a diagram for explaining another embodiment of the present invention. By providing a spring body 8 in place of at least one end plate in the capacitor assembly 4, the tension belt 3 can be made of a rigid body. The tension applied to the body may be adjusted.

In the electric double layer capacitor of the present invention, only the activation of the electrodes may be performed before assembling, but after a predetermined number of unit electric double layer capacitors are laminated, the pressure against the maximum expansion pressure at the time of activation is increased. After activating by pressing, the dimensional structure restriction body may be removed.

The carbonaceous material used in the present invention is formed into a plate shape, and an electric double layer capacitor in which collector electrodes are laminated on both sides of the plate surface is assembled. When a voltage is applied between both collector electrodes, The carbonaceous material has the property of expanding, and in particular has the property of expanding in the direction of voltage application by both collector electrodes. Although performance is increased, it is preferable that an expansion pressure of ² kg / cm ² or more is generated.

As the carbonaceous material suitable for the electric double layer capacitor of the present invention, a low-temperature calcined carbon material that has not been activated can be used, but wood, fruit husk, coal, pitch, petroleum used as a raw material for activated carbon can be used. It can be manufactured using various materials such as coke. For example, it can be manufactured by performing a heat treatment in an inert atmosphere before the activation so that the activation does not greatly proceed, or a process in which the activation operation is performed in a short time. What fired at relatively low temperature of about ° C is preferable.

[0030]

The electric double layer capacitor of the present invention can withstand the expansion pressure at the time of voltage application only by providing a relatively small size limiting structure in the use state of the electric double layer capacitor. Thus, the range of use of the electric double layer capacitor having the expandable electrode can be expanded.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a change in pressure and a change in voltage during charging.

FIG. 2 is a diagram illustrating another example of a change in pressure and a change in voltage during charging.

FIG. 3 is a diagram illustrating a method for manufacturing an electric double layer capacitor of the present invention.

FIG. 4 is a diagram illustrating another embodiment of the electric double layer capacitor of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Unit capacitor, 2 ... End plate, 3 ... Tension belt, 4 ...
Capacitor assembly, 5: Size limiting structure, 6: Charge / discharge device, 7: Capacitor container, 8: Spring body

Claims (7)

[Claims] 1. An electric double layer capacitor having a polarizable electrode made of a carbonaceous material that expands when a voltage is applied,
After the initial charging is performed at a voltage higher than the rated voltage with the first dimension-limiting structure attached, the battery is held in the second dimension-limiting structure having a smaller withstand pressure than the first dimension-limiting structure. An electric double-layer capacitor characterized by the following: 2. The electric double layer capacitor according to claim 1, wherein the dimension limiting structure limits the expansion of the electrode in the voltage application direction when a voltage is applied. 3. The electric device according to claim 1, wherein an expansion pressure of ² kg / cm ² or more is generated in the electrode in a state where the size is limited against expansion of the polarizable electrode when a voltage is applied. Multilayer capacitors. 4. A non-aqueous solvent electrolyte is used as an electrolytic solution, and a polarizable electrode is made of a carbonaceous material having an interlayer distance d ₀₀₂ of 0.365 to 0.385 nm measured by an X-ray diffraction method. The electric double layer capacitor according to any one of claims 1 to 3, wherein 5. The carbonaceous material according to claim 1, wherein the petroleum coke is heat-treated in advance, mixed with potassium hydroxide and heat-treated in an inert atmosphere. The electric double-layer capacitor as described. 6. A carbonaceous material obtained by subjecting a coconut to carbonization and then heat-treating the same in an inert atmosphere or an atmosphere containing water vapor.
The electric double layer capacitor according to any one of the above. 7. A method for manufacturing an electric double-layer capacitor, comprising: a capacitor having a polarizable electrode made of a carbonaceous material that expands when a voltage is applied; The method of manufacturing an electric double layer capacitor according to claim 1, wherein after the initial charging is performed, the capacitor is held in a second dimension limiting structure having a smaller withstand pressure than the first dimension limiting structure.