JPS59172230A - 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.Constitution of a conventional example and its problems An electric double layer capacitor is basically as shown in FIG. , an activated carbon layer 1 and a current collecting electrode 2 of this layer 1 are used as unit polarizable electrodes, and a separator 4 impregnated with an electrolytic solution is provided between the polarizable electrodes 3.3.

Conventionally, there have been the following two types of configuration examples of this type of electric double layer capacitor.

That is, the first one is a current collector 10 as shown in FIG.
Expanded metal made from aluminum plate,
Using a punching metal, on the surface of the current collector 10, as a polarizable electrode 11, a paste containing activated carbon as a main component and a binder such as fluororesin is supported by a molding press or a rolling roller, A pair of current collectors and a polarizable electrode are wound together with a separator 12 in between, and an electrolyte is injected.

As shown in FIG. 3, the second electrode is a polarizable electrode 20 made of cloth or felt made of activated carbon fibers, and a sprayed metal layer such as aluminum is used as a current collector. 21, and is of a type in which a separator layer 22 impregnated with an electrolyte exists between two polarizable electrodes.

Especially for the latter type, an aluminum metal layer is thermally sprayed on one side of the activated carbon cloth, and this is punched out into a circular shape of the desired diameter.
It is possible to manufacture a flat plate by laminating it with a separator, and the manufacturing process is much improved compared to the former one, and by using a case 23 as shown in FIG.

A small, coin-shaped, large-capacity capacitor has been realized.

By the way, activated carbon that has been used as a polarizable electrode for electric double layer capacitors has a power of 300 to 3000 nf.
/El, and the electric double layer capacity when using mercury as a polarizable electrode is 20 to 40 μF.
/cA, theoretically 1g of activated carbon
A large capacity of 80-1200F per unit should be obtained. However, in conventional electric double layer capacitors, the capacity per unit weight of activated carbon is 1/30 of the above theoretical value.
~1/10L was taken out.

Furthermore, if we pay attention to the temperature characteristics of the storage capacity of electric double layer capacitors, we can see that in capacitors with particularly poor surface area utilization efficiency, the temperature dependence of the capacitance is very large, as shown in Figure 4. It becomes a multilayer capacitor. Note that the capacitance change rate ΔC on the vertical axis of the figure is at temperature 25
' is the rate of change with respect to the capacitance at C.

As described above, the poor utilization efficiency of the activated carbon surface area and the resulting poor temperature characteristics are thought to be due to the pore size distribution of the activated carbon used, as described below.

That is, FIG. 5 is a schematic diagram of an electric double layer formed on the surface of activated carbon. When an electric field is applied to the system of the activated carbon base 30 and the electrolyte 31 in contact with it, charges are accumulated on the surface of the activated carbon, and the thickness of the interfacial electric double layer at this time is about 10A.

Therefore, as shown in Figure 5, its diameter is 10 x 2-20
In the pores 32 that are larger than a human being, an electric double layer is formed up to the inside of the pores 32, and electric double layer capacity is accumulated up to the inner wall surface of the pores 32. However, as shown in the figure, in the pores 33 whose diameter is 20 A or less, an electric double layer is not formed between the inner wall and the electrolyte. In other words, no matter how large the specific surface area per unit weight of activated carbon is, if that large specific surface area originates from pores with a pore diameter of 20λ or less and is used as a polarizable electrode, the surface area utilization efficiency will be extremely low. Deteriorate.

However, considering temperature characteristics such as the ease with which the electrolyte impregnates the pores and the thickness of the electric double layer, the temperature dependence of the electric double layer capacity formed on the activated carbon surface, which has many small pores, is large. Compared to activated carbon, which has a high proportion of pores in its inner diameter, it is surprisingly large.

The effect of the pore diameter on the electric double layer capacitance characteristics described above is remarkable in electric double layer capacitors using fibrous activated carbon as polarizable electrodes, which tend to be distributed in areas where the pore inner diameter is relatively small. As described above, there remains the possibility of significant improvement in capacitor characteristics from the viewpoint of appearance.

Purpose of the Invention The present invention aims to solve the above-mentioned problem of inefficient use of activated carbon surface area and poor temperature characteristics when activated carbon having many pores with small inner diameter is used. The purpose of the present invention is to provide a small, large-capacity, high-performance electric double layer capacitor whose utilization efficiency approaches the theoretical efficiency.

Structure of the Invention The present invention is intended to achieve the object set forth in 1.
This is an electric double layer capacitor having the following configuration.

(a) Activated carbon fibers having pores with an inner diameter of 20 angstroms or more are used as polarizable electrodes.

(b) An activated carbon fiber having an inner diameter of 20 angstroms or more and an inner surface area of pores of 1% or less of the total pore inner surface area is used as a polarizable electrode.

(Ol) The above polarizable electrode is made of a cloth or felt-like member made of activated carbon fibers having the above-mentioned characteristics, and a metal sprayed current collection layer of aluminum or the like is applied on one side of the cloth.

When a cloth-like, paper-like or felt-like part made of activated carbon fibers having pores as large as the inner diameter is used as a polarizable electrode as in the present invention, as described above, a large portion of the entire surface of the activated carbon is Since the electric double layer is formed in the area, the efficiency of surface area utilization is high, and as a result, an electric double layer capacitor that is smaller and has a larger capacity than the conventional one can be obtained. Also, the altitude characteristics are greatly improved compared to conventional ones.

Furthermore, considering the activation process, an electric double layer capacitor with low internal resistance can be obtained because the activated carbon fiber itself can have a low electrical resistance and a large pore diameter.

Description of Examples First, a method for producing activated carbon fibers used in the present invention will be described.

FIG. 6 is a diagram of a typical manufacturing process for activated carbon fibers. In other words, raw material fibers such as phenolic (cured novolac fiber), rayon, acrylic, and pinch fibers are directly carbonized.
There are two methods: activating carbon fiber, and activating carbon fiber after it has been made into carbon fiber. Such activation of carbon fiber (A in Figure 6,
Step B) is generally carried out in a mixed gas atmosphere consisting of water vapor and nitrogen at a temperature within the range of 000 to 800'C. By the way, when metal ions are allowed to coexist in the raw material fiber during such activation, the pore diameter of the activated carbon fiber after activation can be controlled. That is, compared to the case of activation with water vapor alone, pores are formed that have an inner diameter proportional to the diameter of the metal ion used in the catalyst. Examples of metal ions that are suitable for coexistence include lithium, sodium, potassium, calcium, magnesium, and zinc, and the larger the ionic radius of a metal ion used as a catalyst, the larger the pores will be obtained. In fact, salts of these metal ions (chloride, nitrate, phosphate, etc.) are added to the raw #4 fiber.
It is activated by supporting or hydroxide.

Figure 7 shows the pore distribution of activated carbon after activation, depending on the catalyst used during activation. - The proportion of pore distribution increases.

Furthermore, the surface area of carbon fibers, electrical resistance and flexibility are inversely proportional, and as the surface area increases as the fibers are activated, the carbonization yield decreases and the electrical resistance and flexibility deteriorate. In order to use it as a polarizable electrode of an electric double layer capacitor, the carbonization yield is preferably 10% or more, although it varies depending on the type of raw material fiber.If the carbonization yield is less than 10%, the surface area will be small, but depending on the raw material fiber, It loses flexibility and cannot withstand mechanical shock during current collection processing.

Furthermore, in the past, the utilization efficiency of surface area was poor, so activation had to proceed until a large specific surface area was obtained.

For this reason, activated carbon cloths that have conventionally been able to obtain satisfactory capacitance values tend to have low electrical resistance and weak mechanical strength. However, when an activated catalyst like the one of the present invention is used, the surface area utilization efficiency is significantly improved, so it is no longer necessary to proceed with activation as in the past in order to obtain a unit capacity, and the activated carbon obtained in this way The fabric itself has low resistance and high strength. As a result, the electric double layer capacitor obtained using such activated carbon fibers has excellent characteristics of small size and large capacity.From a different perspective, when comparing the characteristics of electric double layer capacitors with the same desired capacity, , in the case of using the activated carbon fiber of the present invention, the activated carbon itself has a low electrical resistance;
A major feature of this material is that the internal resistance of the capacitor is extremely low due to its large pore diameter.

However, considering that the activated carbon cloth is used as a polarizable electrode by punching as described later, the increased mechanical strength of the activated carbon cloth means that the manufacturing process is easier, and the activated carbon cloth of the present invention It is also very advantageous in terms of manufacturing.

Furthermore, the ratio of pores larger than 20 angstroms to the total pores is that the pore internal surface area is 1% of the total pore internal surface area.
If it is less than 20%, the effects specific to the present invention cannot be expected much.

When the inner surface area of pores of 20 angstroms or more is 1% or more, the effect becomes significant.

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

Surface area of phenolic raw material fibers carbonized and activated by the above method: 3oo77//gr, soom/yr, 150077
//gr activated carbon fiber cloth (using ZnCl2 as an activation catalyst) was coated with a thickness of 50μ by plasma spraying.
Form an aluminum metal layer of m. This is punched out into a circular shape with a diameter of 5mm, and as shown in Figure 8, it is made of polypropylene and has a thickness of 0.1W! A Wl separator impregnated with sowt% propylene carbonate and 70wt% γ-butyrolactone 5o is sandwiched between the two circular polarizable electrodes 51, and then passed through a gasket 54 with a stainless steel case 52, 53. Seal the casing.

The table below shows the characteristics of this electric double layer capacitor. In addition, the characteristics of an electric double layer capacitor using a conventional activated carbon cloth without using an activation catalyst are also listed in the same table for comparison.

Figure 9 also shows the temperature characteristics of the capacity of the two using activated carbon cloth with a specific surface area of 6o0m/9r at -25°C.
Capacity values at +25°C and +70'C are shown.

3. Effects of the Invention As described above, according to the present invention, the utilization efficiency of the activated carbon surface area is significantly increased, and as a result, the capacitor can be made smaller and have a larger capacity, and the material cost can be significantly reduced.

However, the temperature characteristics and internal resistance of the capacitance are significantly improved, and a high-performance electric double layer capacitor can be obtained.

The increased strength of the activated carbon also facilitates the handling of the activated carbon cloth during manufacturing.

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of an electric double layer capacitor, Figure 2 is a partially cutaway perspective view showing an example of the configuration of a conventional electric double layer capacitor, and Figure 3 is a sectional view of a flat coin type electric double layer capacitor. , Fig. 4 is a diagram showing the temperature characteristics of the capacitance of a conventional electric double layer capacitor, Fig. 6 is a schematic diagram of the activated carbon-electrolyte interface showing the relationship between the pore diameter and the electric double layer, and Fig. 6 is a diagram showing the temperature characteristics of the capacitance of a conventional electric double layer capacitor. FIG. 7, which is a diagram showing the fiber manufacturing process, is a diagram showing the relationship between the activation method of activated carbon and the pore size distribution. FIG. 8 is a block diagram of a fourth embodiment of the electric double layer capacitor according to the present invention, and FIG. 9 is a diagram showing its temperature characteristics. 50...Separator, 51...Circular polarizable electrode, 52.53...Case, 54.Old.
·gasket. Name of agent: Patent attorney Toshio Nakao and 1 other person @2
Fig. 3 Fig. 4 Jii taka ('C) Fig. 5 ■ Fig. 6 Fig. 7

Claims (5)

[Claims] (1) The inner surface area of pores with an inner diameter of 20 angstroms or more is divided into cloth-like, paper-like, and felt-like members made of activated carbon fibers that account for 1% or more of the total pore inner surface area. An electric double layer capacitor characterized in that it is used as a polar electrode. (2) Claims characterized in that the polarizable electrode is one in which a metal electrode is formed on one side of a cloth-like, paper-like, or felt-like member made of activated carbon fibers. The electric double layer capacitor according to item 1. (3) The activated carbon fiber is carbonized and activated using any one or more of salts of lithium, sodium, potassium, magnesium, calcium, and zinc ions as a catalyst. The electric double layer capacitor according to item 1. (4) The electric double layer capacitor according to claim 3, wherein the ions are in the form of metal salts or hydroxides. (5) The electric double layer capacitor according to claim 1, wherein the activated carbon fiber is a phenolic activated carbon fiber.