JPS60211821A - Electric couble layer capacitor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a small-sized, large-capacity wet type electric double layer capacitor.

Conventional Structure and Its Problems FIG. 1 shows an example of the structure of a conventional electric double layer capacitor.

It has a structure in which an activated carbon fiber cloth is used as the polarizable electrode body 1, and a metal layer such as aluminum or titanium, and a conductive resin layer are formed as the twisted conductive electrode 2. After stacking these with the separator 3 in between and press-fitting the electrolyte, the coin-shaped case 6 is placed with the positive and negative electrodes insulated with the gasket 4.
It was stored inside and sealed. Here, the metal conductive electrode 2 is formed by a plasma spraying method, an arc spraying method, or when a conductive resin is used, a conductive resin containing conductive particles mainly made of carbon is formed by a screen printing method, a spray method,
Polymers are formed in either of the dip methods.

When using conductive resin, it is more difficult to use than when using metal layer.
The internal impedance increases, making the capacitor unsuitable for strong discharge applications.

Conventionally, this type of capacitor includes (1) an aqueous electrolyte;
(2) Using a non-aqueous electrolyte The non-aqueous, ie, organic electrolyte of (2) has a lower electrical conductivity than an aqueous electrolyte, but has a higher withstand voltage. Propylene carbonate, γ-butyllactone, N-N-dimethylformamide, acetonitrile, etc. are used as the solvent, and tetraalkylammonium perchlorates such as tetraethylammonium perchlorate or tetraalkylammonium 67 compounds are used as solvents. Solutes such as phosphate or fluoroborate salts and perchlorates of lithium, sodium, and potassium are used.

In particular, the electric double layer capacitors currently in practical use are
Activated carbon is used as a polarizable electrode.

When activated carbon is used as a polarizable electrode, the capacitor characteristics are largely influenced by the following three items.

■Specific surface area ■Pore diameter @ Pore volume The capacity of an electric double layer capacitor is expressed by the formula 0.

The charge per unit area is d, the dielectric constant of the medium is δ, the average distance between the solid surface and the electrolyte ions is φ, and the double layer potential. Therefore, the amount of charge accumulated per single cell is Q, and the double layer formation If the area is S, then Q can be expressed by the formula (■).

Therefore, in an electric double layer capacitor, the larger the double layer formation area, the larger the amount of charge stored. Therefore, the condition (1): The larger the specific surface area, the better. However, in order to increase the specific surface area, it is necessary to advance the activation, which has the disadvantage that the mechanical strength is significantly reduced.

Generally, the larger the specific surface area, the larger the pore volume. However, no matter how large the specific surface area is, the second
As shown in the figure, if the pore diameter (2) is small, a double layer cannot be formed efficiently. In the figure, 6 is a polarizable electrode, 6a is a pore, and 6b is an electrolyte ion. According to the theory of capillary shrinkage, in order to form a double layer efficiently, the pore diameter 8 is required to be 704 times or more the electrolyte ion diameter, as shown in FIG. In particular, at low temperatures below O'C, the viscosity of organic solvents increases and aqueous electrolytes begin to freeze.
The mobility of electrolyte ions is greatly reduced, making it difficult to form a double layer, and once formed, the double layer cannot be easily discharged.

''For two reasons, conventional electric double layer capacitors that use activated carbon fibers as polarizable electrodes and organic electrolyte as the separated electrolyte have a specific surface area of 2000 td/2 for both the positive and negative electrodes.
Activated carbon fibers have been used which are extremely large (9 nm) and have pore diameters mostly in the range of 2 to 4 nm.

However, activated carbon fibers having such great characteristics have the disadvantage that the activation yield is very low at about 20%.

OBJECT OF THE INVENTION The object of the present invention is to obtain an electric double layer capacitor with improved electric double layer formation efficiency per unit volume.

Structure of the Invention In order to achieve this object, the present invention is such that the specific surface area of the polarizable electrode body on the positive electrode side is smaller than the specific surface area of the polarizable electrode body on the negative electrode side.

DESCRIPTION OF EMBODIMENTS Before describing specific examples, an electric double layer formed of activated carbon, carbon, or graphite and electrolyte ions used in the positive and negative electrodes of the present invention will be described.

The effects of the present invention are more pronounced when an organic electrolyte is used than an aqueous electrolyte, and when activated carbon fibers are used rather than activated carbon particles.

The reason for this is explained below.

When an electrolyte such as tetraethylammonyl perchlorate or lithium perchlorate is dissolved in an organic solvent such as propylene carbonate or γ-butyllactone, the perchlorate ion (C1O-) has an ionic radius of 2.36A. Although dilithium ion (Ll) has a small ionic radius of 0.6A, aprotic polar solvents generally solvate cations more strongly than anions, so ions including solvation Conversely, the diameter is larger for cations than for anions. FIG. 4 schematically shows the state. 9 is a solvated anion, 10 is a solvated cation, 11 is a positive electrode activated carbon fiber, 11' is a negative electrode activated carbon fiber, and 6a is a pore. When carbonization is activated from the same starting material, the products shown in Table 1 are produced. Therefore, in order to create a coin-shaped capacitor, such a capacitor is punched out with the same area, so to form a double layer with the positive electrode, that is, the anion, stage (2) in Table 1 is required.
When used, the activation yield is good, the resistance is low, and the strength is strong. However, on the negative electrode side, activated carbon fibers as shown in stage (3) have been sufficiently activated and have a large specific surface area and a pore diameter large enough to allow solvated cations to penetrate into the pores. Must be used.

The pores of the granular activated carbon 12 and the activated carbon fibers 11 are shown below.
Schematically shown in the figure. As can be seen from this figure, activated carbon particles have micropores 14 within macropores 13, so electrolyte can penetrate more easily than activated carbon fibers, which have micropores 14 directly. . Therefore, when activated carbon particles are used for both the positive and negative electrodes, it is considered that the effects of the present invention will not be noticeable.

As described above, the present invention is very effective with a polarizable electrode body such as an activated carbon fiber whose pore size can be easily controlled, and an organic electrolyte system that strongly solvates cations. That is, it is necessary to use a material that is capable of penetrating into pores even with strongly solvated cations in the negative polarizable electrode and forming a double layer. However, for the positive polarizable electrode, we use a material that has a higher carbonization activation yield, stronger strength, and lower electrical resistance than the negative electrode to which anions can penetrate, and when combined with the negative polarizable electrode body, A double layer can be formed most efficiently, raw materials can be used effectively, and productivity can be improved.

(Example 1) Phenol-based, acrylonitrile-based, and rayon-based fibers were carbonized and carbonized, respectively, to obtain carbon fibers and activated carbon fibers having the characteristics shown in ■ to @ in Table 2. The current collector was formed by forming an aluminum layer with a thickness of about 300 μm using a plasma spraying method. In the combination of Table 2 ■ ~ @ shown in Table 3, the 6th
As shown in the figure, positive.

Coin-shaped capacitors with different polarizable negative electrode bodies were fabricated, and their characteristics are also shown in the same table. In FIG. 6, 16 is a positive electrode case, 16 is a positive polarizable electrode having a current collector (aluminum) 16a, 17 is a negative electrode case, and 18 is a current collector (
negative polarizable electrode having aluminum) 18a, 19
is a separator, and 20 is a gasket. The electrolyte contains
Electrochemically stable tetraethylammonium perchlorate is mixed with propylene carbonate and γ-butyl lactone.
:1 An organic electrolyte solution in which 1 mole was dissolved in a mixed solvent was used. The electrodes are each punched into a circular shape with a diameter of 14. The electrode combinations shown in Table 3 of carbon fibers and activated carbon fibers having the characteristics shown in Table 2 are used. s.

4, 8.9.10.11.12.13.15.17.1
No. 8 shows good capacitor characteristics. In other words, it has a sufficiently large capacity without using highly activated positive and negative electrodes like σ7, and has good low-temperature characteristics.
You can get a low impedance capacitor.

In the fifth and sixth cases, solvated cations cannot easily enter the negative electrode side, resulting in extremely poor low-temperature characteristics.

(Example 2) As a negative polarizable electrode, the specific surface area is 14002? i/
2. For 100 parts of activated carbon particles with a pore diameter of 20 to 1 ooA and 80 or more particles, 1 part of Polyflon was added as a binder and pressed onto a titanium net, and the positive electrode was C9d in Table 2. A capacitor shown in FIG. 6 was constructed using activated carbon fibers. Table 4 shows the capacitor characteristics. From Table 4, it can be seen that this example also exhibits good characteristics.

(Example 3) Table 3 1! ; With the combination of 4, large capacitors shown in FIGS. 7 and 8 were manufactured. Height: 10cm, Width: 5c
The size is m. In the figure, 21 is a positive electrode lead, 22 is a positive electrode, 23 is a separator, 24 is a negative electrode lead, 25 is a negative electrode, 26 is a polyethylene laminate resin, and Figure 8 is a cross section of Figure 7 taken along line a-a'. It is a diagram. Table 6 shows the characteristics of this capacitor. In this example, the electrolytic solution used was one in which 1 mole of lithium perchlorate was dissolved in a 1:1 mixed solvent of propylene carbonate and γ-butyl lactone.

Table 6 Effects of the Invention As described above, the present invention uses electrodes that can efficiently form an electric double layer with anions and cations as the positive electrode and the negative polarizable electrode, respectively, so the present invention has a low impedance, small size and large capacity. An electric double layer capacitor can be obtained.

[Brief explanation of drawings]

Figure 1 is a cross-sectional front view of an example of a conventional electric double layer capacitor, Figures 2 to 6 are schematic diagrams showing the pores of a polarizable electrode and the state of electrolyte ions, and Figure 6 is a front view of a conventional electric double layer capacitor. FIG. 7 is a cross-sectional view showing an electric double layer capacitor according to an embodiment of the invention, FIG. 7 is a plan view showing an electric double layer capacitor according to another embodiment of the invention, and FIG. It is a cut sectional view. 16...Positive polarizable electrode, 18...Negative polarizable electrode, 22...Positive electrode, 26...Negative electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 5 Figure 7 α' Figure 8 6

Claims (4)

[Claims] (1) It has an electric double layer formed at the polarizable electrode body and the electrolyte interface, and is characterized in that the specific surface area of the polarizable electrode body on the positive electrode side is smaller than the specific surface area of the polarizable electrode body on the negative electrode side. Electric double layer capacitor. (2) The pore diameter of the polarizable electrode body on the positive electrode side is distributed over 10% to 3QA, and the pore diameter of the polarizable electrode body on the negative electrode side is distributed over 70% over 20 to 40A. An electric double layer capacitor according to claim 1. (3) The electric double layer capacitor according to claim 1, wherein activated carbon or carbon in the form of fibrous paper, felt, or porous is used as the polarizable electrode body. (4) The electric double layer capacitor according to claim 1, wherein an organic electrolyte is used as the electrolyte.