JP2001135555A - Electrode in electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode in an electric double layer capacitor for reducing contact resistance with a collector. SOLUTION: An electrode(e) of an electric double layer capacitor includes an active substance 15 and a conductive material 16 and at the same time, joined to collectors 10 and 13. In this case, an electrode surface 18 of the electrode(e) joined with the collectors 10 and 13 has conductive-material density higher than that of an electrode inside 19.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for an electric double layer capacitor, and more particularly to an electrode containing an active material and a conductive material and joined to a current collector.

[0002]

2. Description of the Related Art A high contact resistance between a current collector and an electrode causes an increase in the internal resistance of an electric double layer capacitor.
Therefore, in order to reduce the contact resistance, conventionally, a current collector made of, for example, aluminum foil is subjected to an etching treatment to increase a contact area, or an electrode is adhered to the current collector with an adhesive containing a conductive filler. Then, burring or punching is performed on the current collector and the electrode to improve the adhesion between the current collector and the electrode.

[0003]

However, the above-mentioned conventional means cannot reduce the contact resistance as expected in spite of the high operating cost. Therefore, it is desired to further reduce the contact resistance. I have.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an electrode for an electric double layer capacitor capable of reducing a contact resistance with a current collector by improving an electrode structure. And

[0005] To achieve the above object, according to the present invention,
In an electrode for an electric double layer capacitor including an active material and a conductive material and bonded to a current collector, the conductive material concentration at the surface of the electrode bonded to the current collector is higher than the conductive material concentration inside the electrode. An electrode for an electric double layer capacitor is provided.

With the above-described configuration, the resistance of the electrode surface is reduced, and the contact resistance between the electrode surface and the current collector is reduced, thereby reducing the internal resistance of the electric double layer capacitor. It is possible to lower it.

[0007]

1 and 2, a rectangular electric double-layer capacitor 1 has an Al container 2, an electrode laminate 3 housed in the container 2, and a capacitor 2 injected into the container 2. And an electrolytic solution. The container 2 comprises a bottomed rectangular tube-shaped main body 4 and a terminal plate 5 for closing one end opening thereof.
Are provided with positive and negative terminals 6,7.

The electrode stack 3 has a plurality of positive electrode stacks 8 and a plurality of negative electrode stacks 9 arranged alternately. The positive electrode laminate 8 includes a positive electrode plate 11 in which a polarizable electrode e as an electrode is adhered to both surfaces of an aluminum foil current collector 10 using an adhesive containing a conductive filler, and one of the positive electrode plates 11. It comprises a PTFE (polytetrafluoroethylene) separator 12 superimposed on the polarizable electrode e. The negative electrode laminate 9 includes a negative electrode plate 14 in which a polarizable electrode e as an electrode is attached to both surfaces of an aluminum foil current collector 13 using an adhesive containing a conductive filler, and a positive electrode plate of the negative electrode plate 14. PTFE superimposed on the polarizable electrode e on the 13th side
And a separator 12. The separator 12 is
The positive electrode plate 11 faces the exposed polarizable electrode e.
A separator 12 is superimposed on the exposed polarizable electrode e of the negative electrode laminate 9 facing the inner surface of the container 2. The electrolytic solution is impregnated and held in each separator 12.

As shown in FIG. 3, the polarizable electrode e comprises a fibrous active material 15, a fine-particle conductive material 16, and a string-like binder 17 for connecting them. In the polarizable electrode e, the conductive material concentration at the electrode surface 18 joined to the current collectors 10 and 13 is higher than the conductive material concentration inside the electrode 19.

[0010] The electrode surface portion 18 having realized such a low resistance is applied to the current collectors 10 and 13 by the adhesive 2 containing a conductive filler.
0, the adhesive 20 becomes the current collectors 10, 1
3, the contact resistance between the current collectors 10, 13 and the electrode surface portion 18 can be reduced, whereby the internal resistance of the electric double layer capacitor 1 can be reduced. is there.

The polarizable electrode e having the above-mentioned structure is obtained from a sheet-shaped polarizable electrode formed by subjecting the electrode composition to rolling once or twice or more. The electrode composition is composed of the fibrous active material 15, the particulate conductive material 16, and the binder 17, as described above. The fibrous active material 15 was spun from mesophase pitch as a raw material.
Alternatively, fibrous mesophase activated carbon which has been subjected to a grinding treatment after spinning is used, has a diameter of 5 to 30 μm and a length of 1 μm.
It is not more than 00 μm. As the fine particle conductive material 16, for example, graphite powder or carbon black such as acetylene black or Ketjen black is used, and the particle size is 1 nm to 100 μm. Further, PTFE powder is used as the binder 17.

When such a composition is subjected to rolling, the fibrous mesophase activated carbon has a high degree of graphitization and a high hardness. The fine graphite powder is edible from between them and transferred to the electrode surface portion 18 side.
Therefore, the amount of graphite powder on the electrode surface 18 increases as the number of times of rolling increases, and the resistance of the electrode surface 18 gradually decreases. The electrode surface portions 18 are formed on both sides of the sheet-shaped polarizable electrode.

Hereinafter, a specific example will be described. [Example I] 87 wt% of fibrous mesophase activated carbon having a diameter of 5 to 30 µm and a length of 100 µm or less, and a particle size of 1 nm to 10
10 wt% of acetylene black having a thickness of 0 μm and 3 wt% of a binder made of PTFE powder are blended, and extrusion is performed using the blend to obtain a different thickness.
The extruded sheets were formed, and the extruded sheets were rolled once, three, five, and seven times, respectively, to form four sheet-shaped polarizable electrodes having the same thickness.

Table 1 shows the relationship between the thickness of each extruded sheet, the number of times of rolling, and the thickness of the sheet-shaped polarizable electrode.

[0015]

[Table 1]

Each of the sheet-shaped polarizable electrodes is adhered to both sides of the belt-shaped current collector using an adhesive containing a conductive filler, and is punched to form 20 positive plates 11 having a length of 70 mm and a width of 60 mm; Twenty negative electrode plates 14 having the same dimensions were manufactured. Using these, the rectangular electric double layer capacitor 1 shown in FIGS. 1 and 2 was manufactured, and charged and discharged at 30 A to measure the internal resistance.

[0017]

[Table 2]

From Table 2, it can be seen that as the number of rolling increases, the internal resistance of the electric double layer capacitor 1 decreases because the contact resistance between the current collectors 10, 13 and the polarizable electrode e decreases accordingly. In this case, considering the practicality and productivity of the electric double layer capacitor 1, its internal resistance is 2.
7 mΩ or less, and therefore the number of times of rolling is suitably 7 or more. [Example II] 82 wt% of fibrous mesophase activated carbon having a diameter of 5 to 30 µm and a length of 100 µm or less, and a particle size of 1 nm to 10
0μm acetylene black 10wt%, PVDF
8 wt% binder (polyvinylidene fluoride) powder
%, And a slurry was prepared using 40 wt% of the blend and 60 wt% of NMP (N-methyl-2-pyrrolidone). Using this slurry, coating films were formed on both sides of the belt-shaped current collector under the application of the doctor blade method, and this was repeated to produce four laminated sheets having different coating film thicknesses. Next, once, three times,
Five and seven rolling operations were performed to form four laminated sheets having sheet-shaped polarizable electrodes of the same thickness. The thickness of each coating film before rolling is the same as the thickness of each extruded sheet in Table 1, and the relationship between the number of times of rolling and the thickness of the sheet-shaped polarizable electrode is as follows. The relationship is the same as that of the thickness.

Each of the rolled laminated sheets was subjected to a punching process to produce 20 positive plates 11 of 70 mm long and 60 mm wide and 20 negative plates 14 of the same dimensions. Using these, the rectangular electric double layer capacitor 1 shown in FIGS.
Was manufactured and charged and discharged at 30 A to measure the internal resistance. The results shown in Table 3 were obtained.

[0020]

[Table 3]

From Table 3, it can be seen that as the number of rolling increases, the internal resistance of the electric double layer capacitor 1 decreases because the contact resistance between the current collectors 10 and 13 and the polarizable electrode e decreases accordingly. In this case, considering the practicality and productivity of the electric double-layer capacitor 1, its internal resistance is 3.
0 mΩ or less, and therefore the number of rolling times is suitably 7 or more.

[0022]

According to the present invention, an electrode for an electric double layer capacitor capable of reducing the contact resistance between the current collector and the current collector can be provided. , It is possible to reduce the internal resistance of the capacitor.

[Brief description of the drawings]

FIG. 1 is a perspective view of a rectangular electric double layer capacitor.

FIG. 2 is an exploded perspective view of the electrode stack.

FIG. 3 is an explanatory view showing a junction structure between a current collector and a polarizable electrode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electric double layer capacitor 10, 13 ... Current collector 15 ... Active material 16 ... Conductive material 18 ... Electrode surface part 19 ………… Inside the electrode e ……………… Polarizable electrode (electrode)

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[Procedure amendment]

[Submission date] October 18, 2000 (2000.10.
18)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

The electrode stack 3 has a plurality of positive electrode stacks 8 and a plurality of negative electrode stacks 9 arranged alternately. The positive electrode laminate 8 includes a positive electrode plate 11 in which a polarizable electrode e as an electrode is adhered to both surfaces of an aluminum foil current collector 10 using an adhesive containing a conductive filler, and one of the positive electrode plates 11. It comprises a PTFE (polytetrafluoroethylene) separator 12 superimposed on the polarizable electrode e. The negative electrode laminate 9 includes a negative electrode plate 14 in which a polarizable electrode e as an electrode is attached to both surfaces of an aluminum foil current collector 13 using an adhesive containing a conductive filler, and a positive electrode plate of the negative electrode plate 14.
PTFE superimposed on the polarizable electrode e on the eleventh side
And a separator 12. The separator 12 is
The positive electrode plate 11 faces the exposed polarizable electrode e.
A separator 12 is superimposed on the exposed polarizable electrode e of the negative electrode laminate 9 facing the inner surface of the container 2. The electrolytic solution is impregnated and held in each separator 12.

Claims (2)

[Claims] 1. An electric double layer capacitor electrode including an active material (15) and a conductive material (16) and joined to a current collector (10, 13).
An electrode for an electric double-layer capacitor, wherein the conductive material concentration of the electrode surface portion (18) to be joined to 3) is higher than the conductive material concentration of the inside of the electrode (19). 2. The electrode for an electric double layer capacitor according to claim 1, wherein the active material is fibrous mesophase activated carbon.