JPS61102023A - Electric double-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 Industrial Application The present invention relates to an electric double layer capacitor using activated carbon as a polarizable electrode.

Structures of conventional examples and their problems Electric double layer capacitors that use activated carbon as polarizable electrodes that have been devised to date are classified into the following two types.

The device K1 uses activated carbon powder as a polarizable electrode, and has a configuration as shown in FIGS. 1 and 2. That is, as shown in FIG. 1, an electrode material 1 obtained by mixing activated carbon powder, PTFE powder, and other organic binder is placed in a metal net such as aluminum or as a current collector 2 of foil.
The electrode 3 is supported on the electrode 3, and the electrode 3tl and the separator 4 are wound together to form an element, which is then impregnated with an electrolytic solution and then made into a housing. FIG. 2 shows an overall view of this capacitor, in which an element in which electrodes 3 and separators 4 are wound in an overlapping manner is housed in an exterior case 5.
It is sealed with a rubber sealing material 6. 7 and 8 are electrode leads.

The second one is shown in Fig. 3, for example,
This is described in Japanese Patent No. 5-99714. That is, it consists of an activated carbon fiber cloth 1o having a metal electrode 9 and a separator 11, and the activated carbon fiber cloth 1Q and the separator 11 are impregnated with an electrolytic solution. Cases 13 and 14 are connected via an insulating gasket ring 12.
These materials are housed and held in the capacitor, and a flat coin-shaped capacitor is constructed as a whole.

Capacitors using such powdered activated carbon or activated carbon fiber as polarizable electrodes are formed at the interface between activated carbon and an electrolyte (a nonaqueous mixed electrolyte of tetraethylammonium verchlorate and propylene carbonate, or an aqueous KOH solution, etc.). This is a high-capacity capacitor that utilizes the capacitance accumulated in the electric double layer. Electric double layer capacity is defined by the following formula.

Here, S is the surface area of activated carbon, ε is the dielectric constant of the electrolyte, and δ
is the thickness of the electric double layer. That is, assuming that ε and δ are constant, the larger the surface area of the activated carbon, the larger the capacity C, and in order to obtain a large capacity per nested volume, it is sufficient to use activated carbon with a large specific surface area. Figure 4 shows
20wt% in propylene carbonate as electrolyte
The vertical axis is the capacitance of a capacitor assembled into a circular shape with a diameter of 10ffff using a solution containing tetraethylammonium barchlorate dissolved in it, using activated carbon fiber cloth with a basis weight of 100.9/m as an electrode, and assembling it into a circular shape with a diameter of 10ffff. The relationship between the two is plotted with the specific surface area of the activated carbon fiber used on the horizontal axis. However, the capacitance value on the vertical axis is 5ooyd
The capacity of a capacitor using activated carbon with a specific surface area of /g is 1
The figure shows the capacity ratio in terms of unit activated carbon weight compared to this.

As can be seen from this figure, the electric double layer capacity increases as the surface area of activated carbon increases, and it follows the above formula. By the way, the solid line in the figure is the capacitance value at 25°C, and the broken line is the capacitance value at -25°C, both of which follow the above formula.
The capacity of C becomes extremely small. In other words, considering the formation of a double layer from low to high temperatures and its capacitance, factors other than the specific surface area of activated carbon must be considered, and in order to obtain a capacitor with stable capacitance over a wide temperature range, it is necessary to clarify this factor. It is necessary to

OBJECTS OF THE INVENTION The object of the present invention is to obtain an electric double layer capacitor that exhibits stable capacitance characteristics over a wide temperature range.

Structure of the Invention To achieve this object, the present invention uses activated carbon as a polarizable electrode in which the volume occupied by pores with a diameter of 21 m or more is 40% or more of the volume occupied by all pores. According to the present invention, since an electric double layer that is effective in a wide temperature range from low to high temperatures is formed on the surface of activated carbon, it is possible to obtain a small-sized, large-capacity capacitor with excellent temperature characteristics of capacitance.

DESCRIPTION OF EMBODIMENTS Before describing specific embodiments of the present invention, clarification of factors other than the specific surface area mentioned above will be described.

The present inventors focused on the pore volume distribution of activated carbon as this factor. (Details presented at the 1st Annual Meeting of the Carbon Materials Society, December 1982) Figure 5 shows the relationship between the pore diameter and pore volume of two types of activated carbon fibers that have approximately the same specific surface area. This shows that. The capacitor using B is (-2
Capacity at 6°C/(capacity at 25°C) were 1.0 and 0.5, respectively. In Figure 6, the diameter is 2
This shows the relationship between the ratio of the volume occupied by pores larger than nm to the total pore volume and the low-temperature capacity reduction ratio.
By using an activated carbon fiber electrode in which the pore volume of nm 2 or more accounts for 40% or more of the total pore volume, a capacitor with a small decrease in low temperature capacity can be obtained. These facts indicate that the thickness of the electric double layer due to solvated ions is ~1 nm, and considering the conductivity and viscosity of the electrolyte at low temperatures, the electrolyte can penetrate sufficiently even at low temperatures and form the electric double layer. It is supported that pores with a diameter of 2 nm or more are necessary for formation.

Next, specific examples of the present invention will be described.

(Example 1) A woven fabric (fabric weight: 100F/ηl) consisting of phenolic activated carbon fibers with a pore volume of 2 nm or more accounting for 080% of the total pore volume and a phenolic activated carbon fiber with a ratio of 020% of the total pore volume. One layer with a thickness of 30 μm is formed by plasma spraying.

This woven fabric is punched out into 10 diameter pieces to make separators.

A capacitor shown in FIG. 3 is constructed using a case and a gasket ring. As the electrolytic solution, a mixed solution of tetraethylammonium verchlorate and propylene carbonate was used.

(Example 2) The ratio of the pore volume of 2 nm or more to the total pore volume is ■
90%, ■20% activated carbon powder and PTFE are mixed and supported on an aluminum net.

The size of the net is 20M11X501tM. It is wound together with a separator to form a cylindrical capacitor as shown in FIG. The same electrolyte as in the example was used.

The following table lists the capacitance characteristics of the capacitors of Examples 1 and 2.

Effects of the Invention As described above, according to the present invention, it is possible to obtain a large capacitor with a high and stable capacitance over a wide temperature range, and a VTR using this.

Memory backup of devices such as computers is reliably achieved.In particular, when phenolic resin-based activated carbon fibers are used for electrodes, a significant reduction in size is achieved, and the effect from this point is also Thick 0

[Brief explanation of the drawing]

Figures 1 to 3 are perspective views, perspective views, and cross-sectional views showing typical configuration examples of conventional electric double layer capacitors, respectively. Figure 4 shows the specific surface area of activated carbon and the structure of a capacitor using this as an electrode. Figure 6 shows the pore size distribution of activated carbon. Figure 6 shows the ratio of the volume occupied by pores with a diameter of 2 nm or more to the total pore volume, and the relationship between the capacitor and the capacitor. It is a figure showing a low temperature capacity reduction rate. 3... Electrode, 10... Activated carbon fiber cloth. Name of agent: Patent attorney Toshio Nakao (1st person)
Fig. 2 Fig. 3 Fig. 4 A of self-representative and owner-owner: A-mediated investment (m73) → No. 5
In the figure ■hole flea tnrn+ - 6th rA

Claims (4)

[Claims] (1) An electric double layer capacitor using activated carbon as a polarizable electrode, in which the volume occupied by pores with a diameter of 2 nm or more is 40% or more of the volume occupied by all pores. (2) The electric double layer capacitor according to claim 1, wherein the activated carbon is any one of activated carbon fibers, activated carbon powder, and activated carbon particles. (3) The electric double layer capacitor according to claim 2, wherein the activated carbon is activated carbon fiber obtained by carbonizing and activating phenolic resin fiber. (4) The electric double layer capacitor according to claim 1, wherein the polarizable electrode is a woven fabric, nonwoven fabric, felt, paper, etc. made of activated carbon fibers.