JPS59138327A - 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] Industrial applications The present invention relates to an electric double layer capacitor.

Conventional Structure and Problems Electric double layer capacitors basically consist of an activated carbon layer 1 and a collector electrode 2 of this layer 1 as unit polarizability electrodes, as shown in FIG. It consists of a separator 4 impregnated with an electrolytic solution between 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 1o as shown in FIG.
Expanded metal made from full minilam board,
Using a punching metal, a paste containing activated carbon powder as a main component and a fluororesin as a binder is supported as a polarizable electrode 11 on the surface of a current collector 10 using a molding press or a rolling roller, and a separator 12 is formed. A pair of current collectors and a polarizable electrode are wound through the coil, and an electrolyte is injected into the coil.

As shown in FIG. 3, the second electrode has a polarizable electrode 20 of cloth 9 made of activated carbon fibers or felt, and a sprayed metal layer 21 such as aluminum as a current collector. This type has a separator layer 22 impregnated with an electrolyte 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 greatly 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, the activated carbon that has been used as the polarizable electrode of electric double layer capacitors has a capacity of 300 to 3000 m2/
, 5', and the electric double layer capacity when using mercury as a polarizable electrode is 20 to 40 μF.
/ cA, theoretically activated carbon 1
You should get a large capacity of 80-1200F per 9r. However, in the conventional electric double layer capacitor, the capacity per unit weight of activated carbon is 1A, which is the above theoretical value.
Only o~a were taken out.

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, the temperature dependence of the capacitance is very large, as shown in Figure 4. It becomes a double layer capacitor. Note that the capacitance change rate ΔC on the vertical axis of the figure is at temperature 25
It is the rate of change with respect to the capacitance at C.

The poor utilization efficiency of the activated carbon surface area and the resulting poor temperature characteristics as described above are considered 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 1.8 times.

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 surface of the pores 32. However, as shown in the figure, in the pores 33 whose diameter is 2 o 8 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 2Q8 or less and is used as a polarizable electrode, the surface area utilization efficiency will be extremely low. Deteriorate.

In addition, considering temperature characteristics such as the ease with which the electrolyte can impregnate pores and the thickness of the electric double layer, the temperature dependence of the electric double layer capacity formed on the surface of activated carbon, which has many pores with a small inner diameter, is When compared with activated carbon, which has a high proportion of pores with large inner diameters, it is understandable that the pores are extremely large.

The above-mentioned influence of the pore diameter on the electric double layer capacitance characteristics is evident in electric double layer capacitors using repellent activated carbon as polarizable electrodes, which tend to be distributed in the region where the pore inner diameter is relatively small. From this point of view, there remains the possibility of significant improvement in capacitor characteristics.

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

Structure of the Invention The present invention is intended to achieve the above object, and is an electric double layer capacitor having the following structure.

Body) 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 more of the total pore inner surface area is used as a polarizable electrode.

(C) The polarizable electrode is made of a cloth or felt-like member made of activated carbon fibers having the above-mentioned characteristics, and one side of which is coated with a thermally sprayed current collecting layer of a metal such as aluminum.

When a cloth-like, paper-like or felt-like member made of activated carbon fibers having large inner diameter pores is used as a polarizable electrode as in the present invention, as described above, a considerable portion of the entire surface of the activated carbon is Since an electric double layer is formed, surface area utilization efficiency 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 temperature characteristics are the same as the conventional °"b+, t"rllK&$l't, 6°
Furthermore, considering the activation process, it is possible to obtain an electric double layer canopy with low internal resistance due to the low electrical resistance of activated carbon fibers and 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 phenol group (cured novolac fiber), rayon type, acrylic type, and pitch type 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 at a temperature within the range of 700 to 8 oQC in a mixed gas atmosphere consisting of water vapor and nitrogen. 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. Metal ions suitable for coexistence include lithium, sodium, potassium,
Calcium, magnesium, zinc, etc. υ, and the larger the ionic radius of a metal ion used as a catalyst, the larger the pores can be obtained. In reality, raw material fibers are activated by supporting salts of these metal ions (chlorides, phosphates, etc.).

Figure 7 shows the pore distribution of activated carbon after activation on the side of the catalyst used during activation. The distribution ratio of pores larger than 100 mm 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 10% or less, the surface area becomes large, but depending on the raw material fiber, It loses flexibility and cannot withstand mechanical shock during current collection processing.

Furthermore, in the past, the efficiency of surface area utilization was poor, so activation had to be continued 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 large 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 there is no longer a need for activation to proceed in the conventional manner in order to obtain unit capacity. The activated carbon cloth 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.

Furthermore, 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 becomes 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 -, 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, a specific example of the present invention will be described.

The surface area of the phenolic raw material fibers carbonized and activated by the above method is 300rrI2/9r, 500rr? /yr
An aluminum metal layer with a thickness of 50 μm is formed on the surface of a 1600 m 2 /9 r activated carbon fiber cloth (using Z n C12 as an activation catalyst) by plasma spraying. This was punched out into a circular shape with a diameter of 6 threads, and as shown in Figure 8, a polypropylene separator with a thickness of 0.1 mm was impregnated with 30 wt% propylene carbonate and 70 wt% γ-butyrolactone. The material 50 is sandwiched between the two circular polarizable electrodes 61 and sealed with a stainless steel case 62, 53 via a gasket 64.

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 that does not use an activation catalyst are also listed in the same table for comparison.

Also, in Figure 9, the specific surface area of both is 600m2/9.
Temperature characteristics of capacity between those using 1r activated carbon cloth,
-25C+250. Indicates a capacitance value of +7oC.

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.

In addition, the temperature characteristics of the capacitance and internal resistance 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 the drawing]

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 an embodiment of the electric double layer capacitor according to the present invention, and FIG. 9 is a diagram showing its temperature characteristics. 50...Separator, 61...Circular polarizable electrode, 52.53...Case, 54...
...gasket f. fig.

Claims (4)

[Claims] (1) Any of the cloth-like, paper-like, and felt-like members made of activated carbon fibers in which the inner surface area of pores with an inner diameter of 20 angstroms or more accounts for 1% or more of the total pore inner surface area. An electric double layer capacitor characterized in that it uses as a polarizable 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) Claim 1, characterized in that the activated carbon fiber is carbonized and activated using one or more of lithium, sodium, potassium, magnesium, calcium, zinc, and ion salts as a catalyst. The electric double layer capacitor described in Section 1. (4) The electric double layer capacitor according to claim 1, wherein the activated carbon fiber is a phenolic activated carbon fiber.