JPH025007B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a small-sized, large-capacity wet electric double layer capacitor. Conventional Structure and Problems Conventionally, the basic structure of this type of electric double layer capacitor is as shown in FIG. It is constructed by laminating layers and injecting electrolyte. In addition, as shown in FIG. 2, the polarizable electrode 1 is made of activated carbon powder, graphite, carbon black, 4
Using a paste made by adding fluorinated ethylene, polyvinylpyrrolidone, etc., as the conductive electrode 2,
A thin metal plate, net or punched metal is used, and a polarizable electrode material is formed and pressed on the surface, or a rubber-like material is applied to a rolling roller.
A polarizable electrode body and a conductive electrode are formed. Then, a polarizable electrode body having a pair of conductive electrodes is wound up with a separator 3 interposed therebetween, and an electrolytic solution is injected therein. A specific example of the configuration shown in FIG. 1 is shown in FIG.
It has a structure in which an activated carbon fiber cloth is used as the polarizable electrode body 1, and a metal layer of aluminum, titanium, etc., or a conductive resin layer is formed as the conductive electrode 2. After injecting an electrolytic solution into these through a separator 3, the positive and negative electrodes are insulated with a gasket 4 and sealed with a coin-shaped case 5. Here, the metal conductive electrode 2 is formed by a plasma spraying method or an arc spraying method, and the conductive resin layer is formed by a screen printing method, a spray method, or a dip method. It is formed by When a conductive resin is used, the internal impedance becomes larger than when a metal layer is used, resulting in a capacitor that is not suitable for strong discharge applications. Next, we will discuss the withstand voltage of the capacitor, which is a problem with conventional construction methods. The withstand voltage largely depends on the conductive electrode and electrolyte used. Therefore,
We will discuss the withstand voltage when using (1) an aqueous electrolyte and (2) a non-aqueous electrolyte. (1) When using an aqueous electrolyte Aqueous electrolytes have two orders of magnitude higher conductivity than non-aqueous electrolytes and can provide capacitors suitable for strong discharge. However, in aqueous solutions of acids or bases, the decomposition voltage shows a nearly constant value of about 1.7V, regardless of the type of electrolyte (e.g., at 1N and 25℃).
_H2SO4 ; _1.67V , NaOH; 1.69V). That is,
At this voltage, oxygen begins to be generated at the anode and hydrogen begins to be generated at the cathode. However, the theoretical reversible potential difference between the oxygen and hydrogen electrodes for this reaction at 1 atm is about 1.23V, and the value of 1.7V is much more polarized than this. In reality, the residual current gradually increases as it approaches the decomposition voltage of around 1.7V, and unless the voltage applied to the capacitor is controlled below 1.23V, the leakage current will increase and the capacitor characteristics, including reliability, will deteriorate significantly. do. As long as an aqueous electrolyte is used in this way, it is impossible to obtain a highly reliable capacitor that has a withstand voltage of 1.23 V or more. (2) When using a non-aqueous electrolyte A solute such as lithium perchlorate or tetraethylammonium perchlorate is dissolved in a solvent such as propylene carbonate, γ-butyllactone, N-N-dimethylformamide, or acetonitrile. Although electrolytes have lower conductivity than aqueous electrolytes, it is widely known that they have higher withstand voltage. Here, the withstand voltage is regulated at the anode by the oxidative decomposition of the electrolyte and the dissolution of the anode electrode, while at the cathode it is regulated by the reductive decomposition of the electrolyte or the cathode electrode. When stainless steel or aluminum is used for the conductive electrode or case on the anode side, when the anode is polarized, it dissolves instead of becoming passivated, and a current begins to flow due to this dissolution. And this potential is
Since it is lower than the anodic oxidation potential of the activated carbon electrode in the electrolyte using the above organic solvent or the decomposition potential of the electrolyte, when stainless steel or aluminum is used as the current collector and case, the anode potential is limited by these dissolution potentials. , it is not possible to effectively use the electrochemically stable potential range determined by polarizable electrodes and electrolytes. Furthermore, when titanium is used as the cathode side conductive electrode, titanium oxide in titanium becomes titanium bronze through a reaction as shown in the following formula. TiO ₂ +H ⁺ +e→HTiO ₂ Due to this reaction, current begins to flow due to cathode polarization, becoming a leakage current in the capacitor. However, this reaction amount is very small. In this way, it can be seen that the withstand voltage of a capacitor is greatly influenced by the electrolyte used and the conductive electrode. Furthermore, electric double layer capacitors are currently used as backup power sources for memory devices, and many memories operate at 5.5V. Even if liquid is used, withstand voltage cannot be obtained unless three-layer single cells are connected in series. Therefore, when stacked in series, the combined capacity is reduced to 1/7 to 1/8 of a single cell in the case of an aqueous electrolyte, and 1/3 of a single cell in the case of a non-aqueous electrolyte. This shows how advantageous it is to obtain a capacitor with high withstand voltage. As described above, with the conventional conductive electrode configuration, it is difficult to increase the maximum usable breakdown voltage to 2.3 V or more per single cell. In addition to what has been described above, it is difficult to completely cover the inner surface of the case of the exterior seal with a conductive electrode such as titanium. Therefore, a capacitor with a high withstand voltage cannot be obtained unless titanium or the like having a high dissolution potential is used for the anode-side case for anode polarization. OBJECTS OF THE INVENTION The object of the present invention is to obtain a high-voltage electric double layer capacitor by improving the anode-side conductive electrode and case of such a conventional electric double layer capacitor. Structure of the Invention In order to achieve this object, the present invention provides a conductive electrode made of titanium on at least one end surface of the anode-side polarizable electrode, and a case made of titanium. Description of Examples Before describing specific examples, the withstand voltage of an electric double layer capacitor will be described. The withstand voltage of an ideal capacitor is such that when the capacitor is polarized anode or cathode, the decomposition potential of the case, polarizable electrode, and conductive electrode is greater than the oxidation or reduction potential of the electrolyte, and the decomposition current is caused by the decomposition of the electrolyte. It is regulated. Therefore, as shown in the iE curve shown in FIG. 4, it is sufficient that the decomposition potential 6 of the case, polarizable electrode, and conductive electrode is greater than the decomposition voltage 7 of the electrolyte. Note that the i-E curves obtained when the constituent materials of the capacitor of the present invention are subjected to anode polarization and cathode polarization, which will be described in the following specific examples, are obtained using the usual three-pole method, with silver on the opposing electrode and carbon on the reference electrode. It was determined through an experiment using Example 1 Polarizable electrode with specific surface area of 2000 m ² /g, 2-4 nm
The capacitor shown in FIG. 5 was fabricated using activated carbon fibers in which 80% or more of the pore diameter was present, and the anode and cathode conductive electrodes and case shown in Table 1. For the formation of conductive electrodes as current collectors,
In the case of a 200 μm thick layer of titanium or aluminum metal, a plasma spraying method or an arc spraying method was used, and a conductive paint containing carbon particles as conductive particles was formed by a coating method, a spray method, or the like.
Further, the electrolytic solution used was one based on the solutes and solvents shown in Table 1. Table 1 shows the rate of change in capacitance from the initial value after a reliability test of 5000 hours of 2V application.

[Table] From this table, the conductive electrode of the anode and the case are
It is known that those made of titanium are the most reliable.
Karu. This is due to the fact that titanium has anode polarization versus other gold.
This is because it is more stable than the genus. Also, the cathode
When using titanium conductive electrodes and cases, some
Titanium oxide forms titanium bronze, but it is not reliable
There are no phenomena that are particularly problematic in terms of gender, etc.
Nakatsuta. Furthermore, when using each electrolyte in the same table
However, this value also indicates that the anode current collection
Using titanium for the body and case provides good capacitance.
It is clear that data can be obtained. Furthermore, Figure 5
Inside, 8 is the anode side polarizable electrode, 9 is the anode side
conductive electrode, 10 is a cathode side polarizable electrode, 11
12 is a conductive electrode on the cathode side, and 12 is a conductive electrode on the anode side.
13 is a cathode side case. FIG. 6 shows the voltage-current characteristics of activated carbon. That
Currents 14, 15 flowing due to polarization of the electrode and cathode
This is thought to be caused by the decomposition of the electrolyte. During ~
The current 16 in the region between is the charging current to the electric double layer.
be. Figure 7 shows the voltage and current characteristics of titanium.
Figure 8 shows the voltage and current characteristics of aluminum. If we compare Figures 7 and 8, we can see how
It is clear that the
Ru. Also, in Figure 7, small peaks in cathode polarization
Arcs occur due to titanium bronze formation. Anode conductive electrode, anode shown in Table 1
The case using titanium is the conventional 2.3V.
It has a high withstand voltage of 2.9V compared to . Example 2 Polarizable electrode with specific surface area of 2100 m ² /g of binder
Separate activated carbon porous material with a porosity of 5% without using
Used as a polar electrode, with a large capacity as shown in Figure 9 a and b.
A quantitative capacitor was fabricated. Anode side polarizable electrode
A titanium plate 17 is used as the current collector (conductive electrode) of 8.
The conductive electrode 18 on the cathode side has a cathode
Aluminum on the side polarizable electrode 10
A titanium plate was provided as the plate. separator 3
Connect leads 19 and 20 made of the same material as the current collector through the
Then, add tetraethylammonium perchlorate to the
A solution dissolved in pyrene carbonate is used as an electrolyte.
After injection, heat-fusible felt sheet 21
It was laminated with. Table 2 shows the characteristics of this example.
show. The size of the polarizable electrode used here is 100
It is a rectangular parallelepiped with dimensions of mm x 50 mm x 2 mm thick. Figure 9b is the
A cross-sectional view of this embodiment taken along the line A-A' in Figure 9a.
It is. From Table 2, activated carbon porous material is used as a polarizable electrode.
Also, the anode current collector (conductive
If titanium is used for the case, the
A pressure-resistant and highly reliable capacitor can be obtained.
Ru. In addition, the reliability is the initial value after 5000 hours of 2V application.
It is expressed as the rate of change in capacitance and rate of change in leakage current.

[Table] Effects of the Invention As described above, according to the present invention, it is possible to obtain a small-sized, large-capacity electric double layer capacitor with higher withstand voltage and higher reliability than conventional capacitors.

[Brief explanation of drawings]

Figures 1 and 2 are a configuration diagram and a perspective view, respectively, of a conventional electric double layer capacitor, Figure 3 is a half-sectional front view of another conventional electric double layer capacitor, and Figure 4 is a diagram of an electric double layer capacitor. ideal i
-A characteristic diagram showing the E curve; FIG. 5 is a half-sectional front view of an electric double layer capacitor according to an embodiment of the present invention;
Figure 6 is a characteristic diagram showing the i-E curve of carbon, Figure 7 is a characteristic diagram showing the i-E curve of titanium, Figure 8 is a characteristic diagram showing the i-E curve of aluminum, and Figure 9 is a characteristic diagram showing the i-E curve of aluminum.
Figures a and b are a plan view and a sectional view showing an electric double layer capacitor according to another embodiment of the present invention. 1... Polarizable electrode body, 2... Conductive electrode, 3...
... Separator, 8 ... Anode side polarizable electrode, 9
... Anode side conductive electrode, 10 ... Cathode side polarizable electrode, 11 ... Cathode side conductive electrode, 1
2... Anode side case, 13... Cathode side case, 17... Titanium plate, 18... Titanium plate or aluminum plate.

Claims (1)

[Scope of Claims] 1. An electric double layer capacitor, characterized in that a conductive electrode made of titanium is provided on at least one end surface of a polarizable electrode on the anode side, and a case made of titanium is provided. 2. The electric double layer capacitor according to claim 1, wherein the conductive electrode formed on one end surface of the polarizable electrode is in contact with the case. 3. The conductive electrode is formed by one of thermal spraying methods such as plasma spraying and arc spraying, or vapor deposition methods.
The electric double layer capacitor according to claim 1, wherein the electric double layer capacitor is formed on a polarizable electrode. 4. The electric double layer capacitor according to claim 1, wherein activated carbon in the form of fiber cloth, paper, felt, or porous material is used for the polarizable electrode.