JPH11307404A - Electric double layer capacitor and its manufacture, ana active carbon for positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double layer capacitor in which capacity deterio ration at a low current density side can be reduced, and the change of discharg ing characteristics can be reduced, by changing materials and an activation condition or the like as active carbon to be used for the both poles of the electric double layer capacitor, and constituting positive and negative poles by using active carbon having different electrode fine hole structure and electrode/electrolyte boundary structure. SOLUTION: As the active carbon for a positive pole of an electric double layer capacitor, a specific surface area by a BET method is made smaller than the specific surface area of active carbon for a negative pole, or surface acid base amounts by a titrating method is made smaller than the surface acid base amounts of active carbon for a negative pole, or natural potential is made smaller than the natural potential of the active carbon for a negative pole or less. Also, the positive pole is manufactured by using the vapor active carbon of PVDC (polyvinylidene choloride) resin oxide, or the negative pole is manufactured by using alkaline active carbon.

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, an activated carbon for a positive electrode, and a method for producing an electric double layer capacitor. The present invention relates to a method for manufacturing a multilayer capacitor, activated carbon for a positive electrode, and an electric double layer capacitor.

[0002]

2. Description of the Related Art An electric double layer capacitor is a capacitor which uses an electrostatic solution impregnated in activated carbon powder and uses the capacitance of an electric double layer formed at the interface between the activated carbon and the electrolytic solution. The withstand voltage and the maximum operating temperature depend on the decomposition voltage and temperature of the electrolytic solution, and the rated voltage is as low as several volts. However, since the capacitance in the farad order can be easily obtained, a semiconductor memory is used instead of a battery. It has been widely used for low current density applications such as backup of (D-RAM), and has recently been studied for use in applications having higher current densities, for example, in place of in-vehicle lead-acid batteries. ing.

[0003] Electric double layer capacitors using organic electrolytes are required to have higher energy densities, and are required to have improved withstand voltage and increased capacitance. In the current electric double layer capacitor, when a high voltage of 3V or more is applied, gas is generated from the inside of the capacitor or the capacity is reduced.
There is a problem that the internal resistance increases. The cause is considered to be decomposition of PC (propylene carbonate) in the pores of the positive electrode activated carbon, but the mechanism is not clear. Regarding the capacitance, a high capacity can be obtained with activated carbon having a large specific surface area, which can be obtained by alkali-activating pitch-based carbon with KOH or the like. The problem has not been solved.

The conventional electric double layer capacitor uses the same activated carbon material for both the positive electrode and the negative electrode, and is configured so that the electrode volume is the same. Hitherto, it has been proposed to increase the capacity and the voltage of electric double layer capacitors by changing the specific surface area of the positive electrode and the negative electrode (Japanese Patent Application Laid-Open No. 60-21).
No. 1821). However, they merely show a technical direction, and could not substantially increase the capacity and improve the withstand voltage.

[0005]

According to the present invention, as a result of investigating the stability of the electric double layer at the positive electrode and the negative electrode and the reactivity of the organic electrolytic solution, the deterioration of the organic electric double layer capacitor is included in the electrolytic solution. The electrochemical reaction of oxygen and moisture at the activated carbon anode causes a shift in the potential window during charging over time, and the electrochemically reduced product reacts with tetraethylamine at the cathode. Headings,
By this, the activated carbon used for both electrodes of the capacitor can be obtained by changing the raw material, the activation conditions, and the like, and by forming the positive electrode and the negative electrode using activated carbon having a different electrode pore structure and an electrode-electrolyte interface structure. An object of the present invention is to provide an electric double layer capacitor in which a decrease in capacity on the low current density side is small and a change in discharge characteristics is small.

[0006]

According to the present invention, there is provided an active carbon for a positive electrode of an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the specific surface area by the BET method is smaller than the specific surface area of the activated carbon for a negative electrode. Activated carbon for positive electrode of double layer capacitor.

In the present invention, the specific surface area is 1000 to 2
Activated carbon for a positive electrode of an electric double layer capacitor of 500 m ² / g.

Further, the present invention provides an active carbon for a positive electrode of an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the amount of surface acidic groups by titration is smaller than the amount of surface acidic groups of the activated carbon for the negative electrode. Activated carbon for positive electrode of double layer capacitor.

Further, the present invention relates to a method for producing a composition having a surface acidic group content of 0.02
Activated carbon for a positive electrode of an electric double layer capacitor having a meq / g or less.

[0010] The present invention also relates to an activated carbon for a positive electrode of an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the activated carbon for a positive electrode of the electric double layer capacitor has a natural potential lower than that of the activated carbon for the negative electrode. It is.

And a natural potential of -1.0 to -0.5 V
vs. This is activated carbon for a positive electrode of an electric double layer capacitor of Ag / Ag +.

Further, the present invention is activated carbon for a positive electrode of an electric double layer capacitor, which is steam activated carbon of PVDC resin carbide.

Further, the present invention relates to an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the activated carbon for the positive electrode is steam activated carbon of PVDC resin carbide, while the activated carbon for the negative electrode is alkali activated carbon. An electric double layer capacitor.

The present invention is the electric double layer capacitor, wherein the positive electrode has a volume larger than that of the negative electrode.

Further, the present invention is the electric double layer capacitor wherein the volume of the positive electrode is 1.2 to 2.2 times the volume of the negative electrode.

The present invention also relates to a method for manufacturing an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the positive electrode is manufactured using activated carbon obtained by steam-activating PVDC resin carbide, while the negative electrode is manufactured using This is a method for producing an electric double layer capacitor produced using alkali-activated activated carbon.

Further, the present invention is a method for producing an electric double layer capacitor in which the positive electrode is manufactured using activated carbon having a smaller specific surface area by the BET method than the negative electrode.

Further, the present invention is a method for producing an electric double layer capacitor in which the positive electrode is made using activated carbon having a smaller amount of surface acidic groups than the negative electrode.

The present invention is also a method for manufacturing an electric double layer capacitor in which the positive electrode is made of activated carbon having a natural potential equal to or lower than that of the negative electrode.

The present invention is a method for producing an electric double layer capacitor in which the positive electrode is manufactured using activated carbon activated by steam activated PVDC resin carbide, and the negative electrode is manufactured using activated carbon activated by alkali.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described. The present invention has been obtained by newly developing an activated carbon that is optimal for each of a positive electrode and a negative electrode as an organic electrolytic solution electric double layer capacitor. This means that an electric double layer capacitor having a high withstand voltage in which the decomposition reaction does not take place to a high potential can be formed by maximizing the electric double capacity of the electrode activated carbon.

An organic electrolytic solution electric double layer capacitor as an example of the present invention uses activated carbon obtained by steam-activating PVDC (polyvinylidene chloride) resin carbide as a positive electrode activated carbon, and alkali-activating PVDC resin carbide as an activated carbon of a negative electrode. It is a combination of activated carbon. Therefore, the specific surface areas of the positive electrode and the negative electrode, the electric double layer capacity per unit volume, and the natural potential (rest potentia)
Since 1) is different, when an electric double layer capacitor is formed using this example, it is necessary to change the electric double layer capacitance and the like of both electrodes in consideration of the material characteristics of the activated carbon.

An example of the optimum conditions for the electrode activated carbon for the organic electrolytic solution electric double layer capacitor of the present invention will be described. For the positive electrode, activated carbon obtained by steam-activating PVDC resin carbide is used as a raw material. Specific surface area by BET method is 1000-2
500 m ² / g, the amount of surface acidic groups by titration is 0.02
meq / g or less, natural potential is -1.0 to -0.5 Vv
s. Ag / Ag + is preferred. On the other hand, the negative electrode
Activated carbon obtained by activating petroleum pitch, coke, coconut shell, PVDC resin carbide, or the like with an alkali such as KOH or NaOH is used as a raw material. 2000 BET specific surface area
4,000 m ² / g, the amount of surface acidic groups determined by titration is 0.
05 meq / g or less, natural potential is -1.0 to -0.4 V
vs. Ag / Ag + is preferred. When these activated carbons are used for the electrodes of an electric double layer capacitor, it is necessary to change the electric double layer capacitance of the opposing electrodes to control the potential during charging. When the activated carbon electrodes having the same volume are combined, the electric double layer capacity on the positive electrode side is reduced, so that the potential reached during charging on the positive electrode side is increased. For this reason, the positive electrode side is 1.2 to
The volume ratio is preferably set to 2.2 times. Also, the negative electrode activated carbon is
Activated carbon having a large capacitance density (F / cm ³ ), for example, pitch or coke-based alkali activated carbon or PVDC resin steam activated carbon can be used.

An embodiment will be described. The case of an organic electric double layer capacitor will be described. The activated carbon for a positive electrode is obtained by activating steam of a PVDC resin carbonized at 600 ° C. at 900 ° C., and has a specific surface area of about 700 m ² by the BET method.
/ G increased from 1700 m ² / g. On the other hand, the activated carbon for the negative electrode is obtained by adding KOH to a PVDC resin carbide carbonized at 600 ° C. and activating it at 750 ° C. for 7 hours, and has a specific surface area of 2500 m ² / g after the activation treatment. Then, the size of the positive electrode is 25 × 25 ×
0.4 mm, the size of the negative electrode was 25 × 25 × 0.7 mm, carbon black was added to each activated carbon, and the carbon was bound using a Teflon binder to produce an electrode. An electric double layer capacitor was formed using a PC solution of TEABF4 (tetraethylammonium tetrafluoroborate) as an organic electrolytic solution and a microporous Teflon film as a separator. The electrode was dried at 180 ° C. in a vacuum oven. After the inside of the oven was replaced with high-purity nitrogen, the electrode was directly introduced into a glove having a dew point of −60 ° C. or less and an oxygen concentration of 1% or less, for measurement.

A comparative example will be described. Electrodes were produced in the same manner as in the example using the activated carbon for the negative electrode in the example as the activated carbon for the positive electrode and the activated carbon for the negative electrode, and an electric double layer capacitor was assembled using an organic electrolytic solution.

With respect to the electric double layer capacitors of Examples and Comparative Examples, discharge characteristics and ESR after applying a constant voltage of 3.3 V
(Equivalent series resistance, 1 kHz, 10 mA) was examined over time. The discharge capacity was calculated from the slope when discharging at a constant current after charging at a constant voltage of 10 min. ESR was measured with an impedance meter. FIG. 1 shows the measurement results of the embodiment.
(A) and (b) show the measurement results of the comparative example in FIGS. 2 (a) and (b), respectively.

According to this, in the electric double layer capacitor of the embodiment, even after the voltage is applied for 500 hours, the capacity decrease on the low current density side is as small as about 15% or less, and the change of the discharge characteristics is small. On the other hand, the electric double layer capacitor of the comparative example has a remarkable decrease in capacity particularly on the high current density side,
It can be seen that the ESR increases in proportion to the voltage application time.

[0028]

According to the present invention, as a result of investigating the stability of the electric double layer and the reactivity of the organic electrolyte at the positive electrode and the negative electrode,
The deterioration of the organic electric double layer capacitor is that oxygen and water contained in the electrolytic solution undergo an electrochemical reaction at the activated carbon anode, causing a potential window shift during charging with time,
And found that the product electrochemically reduced at the cathode reacts with tetraethylamine, and thereby, the activated carbon used for both electrodes of the capacitor changes the raw material, activation conditions, etc. A positive electrode using activated carbon having an electrode pore structure and an electrode-electrolyte interface structure,
By configuring the negative electrode, it is possible to obtain an electric double layer capacitor in which a decrease in capacity on the low current density side is small and a change in discharge characteristics is small.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of characteristics of an electrode for an electric double layer capacitor manufactured in an example.

FIG. 2 is an explanatory diagram of characteristics of an electrode for an electric double layer capacitor manufactured in a comparative example.

Claims (15)

[Claims] 1. An active carbon for a positive electrode of an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein a specific surface area by a BET method is smaller than a specific surface area of the active carbon for a negative electrode. Activated carbon for positive electrode. 2. The activated carbon for a positive electrode of an electric double layer capacitor according to claim 1, wherein a specific surface area is 1000 to 2500 m ² / g. 3. The activated carbon for a positive electrode of an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the amount of surface acidic groups by titration is smaller than the amount of surface acidic groups of the activated carbon for negative electrodes. Activated carbon for the positive electrode of electric double layer capacitors. 4. The activated carbon for a positive electrode of an electric double layer capacitor according to claim 3, wherein the amount of surface acidic groups is 0.02 meq / g or less. 5. The active carbon for a positive electrode of an electric double layer capacitor comprising a positive electrode, a negative electrode, and an organic electrolytic solution, wherein the natural potential is lower than the natural potential of the active carbon for a negative electrode. Activated carbon. 6. The activated carbon for a positive electrode of an electric double layer capacitor according to claim 5, wherein the natural potential is from -1.0 to -0.5 Vvs. Activated carbon for a positive electrode of an electric double layer capacitor, which is Ag / Ag +. 7. The activated carbon for an electric double layer capacitor according to claim 1, wherein the activated carbon is a steam activated carbon of PVDC resin carbide. . 8. An electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the activated carbon for the positive electrode is steam activated carbon of PVDC resin carbide, while the activated carbon for the negative electrode is alkali activated carbon. Electric double layer capacitor. 9. The electric double layer capacitor according to claim 8, wherein a volume of the positive electrode is larger than a volume of the negative electrode. 10. The electric double layer capacitor according to claim 9, wherein the volume of the positive electrode is 1.2 to 2.2 times the volume of the negative electrode. 11. A method for manufacturing an electric double layer capacitor comprising a positive electrode, a negative electrode and an organic electrolyte, wherein the positive electrode is produced using activated carbon obtained by steam-activating a PVDC resin carbide, while the negative electrode is produced by using activated carbon activated by an alkali. A method for manufacturing an electric double layer capacitor, characterized by being manufactured by using the method described above. 12. The method of manufacturing an electric double layer capacitor according to claim 11, wherein the positive electrode is manufactured using activated carbon having a smaller specific surface area by a BET method than the negative electrode. Manufacturing method. 13. The method for manufacturing an electric double layer capacitor according to claim 11, wherein the positive electrode is manufactured using activated carbon having a smaller amount of surface acidic groups than the negative electrode. Production method. 14. The method for manufacturing an electric double layer capacitor according to claim 11, wherein the positive electrode is manufactured using activated carbon having a natural potential equal to or lower than that of the negative electrode. A method for manufacturing an electric double layer capacitor. 15. The method of manufacturing an electric double layer capacitor according to claim 11, wherein the positive electrode is made of activated carbon obtained by steam-activating a PVDC resin carbide, while the negative electrode is made of an alkali. A method for producing an electric double layer capacitor, characterized by being produced using activated carbon activated.