JPH10223487A - Electrode for electric double layer capacitor and electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a polarizable electrode layer from falling from a metal foil and to reduce the electric resistance of the polarizable electrode layer by a method wherein one face of the metal foil whose surface is etched and treated is coated with a polarizable electrode material so as to form the polarizable electrode layer and the polarizable electrode layer is rolled to a thickness at a specific % of its original thickness. SOLUTION: One face of an aluminum etched foil is coated with a polarizable electrode material so as to form a carbon layer. The carbon layer is dried, and it is then rolled to a thickness at 80 to 90% of its original thickness by using a rolling press. After its rolling operation, two coating electrodes 1, 2 which are cut off to be a rectangular shape are prepared, and derivation leads 3, 4 are caulked to them. Then, nonwoven fabrics by a Manilar fiber as separators 5, 6 are interposed between the two coating electrodes 1, 2, polarizable electrode layers are faced so as to be wound, and a capacitor element 7 is formed. The capacitor element 7 is impregnated with an electrolytic solution, it is then housed inside a metal case 8, an opening is sealed up with a rubber sealing body 9 having two through holes, and the drawing leads 3, 4 are drawn to the outside from the through holes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode for an electric double layer capacitor and an electric double layer capacitor.

[0002]

2. Description of the Related Art An electric double layer capacitor has a separator between two coated electrodes having a polarizable electrode layer (for example, a carbon layer) provided on both sides of a metal foil made of, for example, an aluminum foil.
An electrolytic solution is impregnated in a capacitor element which is wound with a capacitor interposed therebetween, placed in a metal case having a bottom, and an opening having a through hole for a lead lead connected to each of the electrodes. It has a structure in which it is sealed with a flexible sealing body and leads are drawn out of the sealing body through the through holes.

[0003] The surface of a metal foil is electrochemically etched, and a polarizable electrode material (for example, a carbon material containing activated carbon powder and carbon black) is formed on both surfaces of the metal foil.
A polarizable electrode layer (carbon layer) is formed by applying a carbon-based paint. The coated electrode having such a structure is pressed (rolled) as disclosed in JP-A-57-60828.

[0004]

However, a conventional coated electrode which has been formed by applying a polarizable electrode material to both surfaces of a metal foil to form a polarizable electrode layer and then pressing the metal foil is considered to have been used for a long time. The current collection efficiency inside the polar electrode layer decreases. In addition, a large distortion is likely to be generated in the polarizable electrode layer during winding, and the distortion tends to cause a problem that the internal resistance of the electric double layer capacitor is increased or the internal resistance is partially non-uniform. . Further, when the thickness of the polarizable electrode layer is increased in order to increase the capacitance, the polarizable electrode layer tends to fall off from the metal foil in a winding step and the like, and the electric resistance of the polarizable electrode layer also increases.

According to the present invention, a polarizable electrode layer formed by coating and rolling on an etched metal foil is less likely to fall off the metal foil, and no distortion of the polarizable electrode layer occurs during winding. It is an object of the present invention to provide an electrode for an electric double layer capacitor and an electric double layer capacitor in which the electric resistance of a polar electrode layer is low, and the current collection efficiency inside the polarizable electrode layer is maintained even after long-term use without reducing the current collection efficiency. The purpose is.

[0006]

The electrode for an electric double layer capacitor of the present invention is obtained by applying a polarizable electrode material to one side of a metal foil having a surface etched to form a polarizable electrode layer, Characterized by being rolled to a thickness of 80% to 90% of the thickness.

In the electric double layer capacitor according to the present invention, a polarizable electrode material is applied to one side of a metal foil having a surface etched to form a polarizable electrode layer.
Two coated electrodes rolled to a thickness of 0% to 90%
It is characterized in that the polarizable electrode layers are arranged so as to face each other, and then wound with a separator interposed between the coated electrodes, and sealed in a metal case together with the electrolytic solution.

As the metal foil, stainless steel, copper, nickel, tantalum, niobium, aluminum or the like can be used, with aluminum being preferred.

The thickness of the metal foil is preferably from 5 to 40 μm, and if it is less than 5 μm, the strength of the metal foil becomes insufficient and the production yield deteriorates. The thickness of the coated polarizable electrode layer after drying is preferably 5 to 150 μm,
If it is less than μm, the electrostatic capacity per unit area is small, and if it is 150 μm or more, the adhesion to the metal foil is reduced, and it is easy to fall off.

The etching is performed on one or both sides of the metal foil by an electrochemical, mechanical or chemical method.

The polarizable electrode material is activated carbon powder, carbon black, graphite, metal powder, semiconductor material, polymer substance mainly composed of carbon, conductive inorganic substance or conductive organic substance (polyacene, polyacetylene, polyaniline, etc.). It is preferable to select one or more of them from among the above, and disperse and dissolve a mixture containing a binder and the like in a solvent. In particular, a carbon-based coating material is preferred, and a coating material containing activated carbon powder, carbon black and a binder dispersed and dissolved in a solvent is preferred.

The average particle size of the activated carbon powder and carbon black is preferably 0.1 μm to 10 μm.
If it is less than 1 μm, it is difficult to obtain activated carbon powder and carbon black having a uniform size, and if it is 10 μm or more, it tends to fall off from the coated electrode, which is not preferable.

As the binder, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTF) is used.
E) and the like. As the solvent, N-methylpyrrolidone (NMP) or alcohol is preferably used.

The content ratio (weight) of the activated carbon powder, carbon black and binder is preferably 8: 1: 1.

The content ratio of the components in the polarizable electrode material to the solvent is preferably 5 to 50% by weight.

The coated electrode is preferably rolled to 80 to 90% of its original thickness. If it is less than 90%, the adhesive strength between the polarizable electrode layer and the metal foil is insufficient, and the electrode is easily dropped.
%, It is not preferable because the strength of the coated electrode is reduced. An ordinary rolling press is used for rolling.

[0017]

【Example】

<Examples 1 to 5> A polarizable electrode material having various thicknesses as shown in Table 1 was applied to one surface of an aluminum foil (aluminum etched foil) having various thicknesses as shown in Table 1 which was electrochemically etched. After coating, a polarizable electrode layer (carbon layer) is formed, dried, and then rolled to a thickness of 80% to 90% of the original thickness as shown in Table 1 using a rolling press. A coated electrode was obtained. The polarizable electrode material was activated carbon powder 80% by weight,
A coating component consisting of 15% by weight of carbon black and 5% by weight of polyvinylidene fluoride (PVDF) as a binder was added to N-methylpyrrolidone (NMP) as a solvent.
A solution obtained by dispersing and dissolving 0% by weight was used. After the rolling, two coated electrodes 1 and 2 (FIG. 1) cut into strips each having a width of 13 mm and a length of 120 mm were prepared, and lead wires 3 and 4 were crimped to each of them.

A non-woven fabric of 50 μm-thick manila fiber is interposed between the two coated electrodes 1 and 2 as separators 5 and 6, and the polarizable electrode layer is wound opposite to the capacitor element 7. After infiltrating the electrolytic solution into the capacitor element 7, the capacitor element 7 is housed in a bottomed aluminum metal case 8, the opening is drawn out, and a rubber seal having two through holes for leads is provided. The body was sealed with the body 9, and at this time, the lead leads 3, 4 connected to both electrodes were respectively drawn out from the through holes. The electrolyte used was 1 mol / liter of tetraethylammonium tetrafluoroborate (Et ₄ NBF).
₄ ) was dissolved in propylene carbonate (PC). Thus, a diameter of 8 mm and a height of 21 m
Thus, the electric double layer capacitors 10 of Examples 1 to 5 having a rated voltage of 2.5 V and 1F were obtained.

[0020]

[Table 1]

<Comparative Examples 1 to 5> In the same manner as in Examples 1 to 5, electric double layer capacitors (diameter 8 mm, height 21 mm, rated 2.5 V, 1F) of Comparative Examples 1 to 5 as shown in Table 2 were used. Obtained. In addition, the rolling was not performed in Comparative Example 2 and Comparative Example 3. In Comparative Example 5, polarizable electrode layers were formed on both surfaces of the aluminum etching foil.

[0022]

[Table 2]

In Examples 1 to 5 and Comparative Examples 1 to 5, the initial capacitance, the internal resistance, and the change rate of the capacitance after 70 hours at 70 ° C. with respect to the initial capacitance were measured. Table 3 shows the results.

[0024]

[Table 3]

From Table 3, it can be seen that the electric double-layer capacitors of Examples 1 to 5 have a lower internal resistance and a smaller rate of change in capacitance than the electric double-layer capacitors of Comparative Examples 1 to 5. Further, by visual inspection, a large amount of the polarizable electrode layer was dropped in Comparative Examples 2 and 3 in the comparative example, and a small amount of the polarizable electrode layer was dropped in Comparative Examples 1 and 5. However, in the coated electrodes of Examples 1 to 5, the polarizable electrode layer did not fall off. Further, in Comparative Example 5, distortion occurred in the polarizable electrode layer.

The electrode for an electric double layer capacitor and the electric double layer capacitor according to the present invention have not only a wound type electric double layer capacitor but also a coated electrode formed in a strip shape and laminated via a separator. Of course, it can also be used for multilayer electric double layer capacitors.

[0027]

According to the present invention, a coated electrode having a polarizable electrode layer formed only on one side of a metal foil has an original thickness of 80 to 9%.
By rolling to 0%, the polarizable electrode layer is densified, the internal resistance is reduced, and the risk of the polarizable electrode layer being more closely adhered to the metal foil and peeling off is reduced. A double layer capacitor is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electric double-layer capacitor of the present invention partially broken away and disassembled.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coating electrode 2 Coating electrode 3 Leader lead 4 Leader lead 5 Separator 6 Separator 7 Capacitor element 8 Metal case 9 Sealing body 10 Electric double layer capacitor

Claims (3)

[Claims] 1. A polarizable electrode material is applied to one side of a metal foil obtained by etching the surface to form a polarizable electrode layer.
An electrode for an electric double layer capacitor, which is rolled to a thickness of 80% to 90% of the original thickness. 2. After a polarizable electrode material is applied to one side of a metal foil obtained by etching the surface to form a polarizable electrode layer,
Two coated electrodes rolled to a thickness of 80% to 90% of the original thickness are arranged such that the polarizable electrode layers face each other,
An electric double layer capacitor characterized by being wound with a separator interposed between coated electrodes and sealed in a metal case together with an electrolytic solution. 3. A carbon-based paint is applied to one side of an aluminum etched foil having a thickness of 5 to 40 μm obtained by etching a surface of an aluminum foil to form a carbon layer having a thickness of 5 to 150 μm. Two coated electrodes rolled to a thickness of 80% to 90% of the original thickness are arranged so that the carbon layers face each other, and a separator is interposed between the coated electrodes. An electric double-layer capacitor characterized by being wound with a metal case together with an electrolytic solution.