JPH07320987A - Electrode structure - Google Patents

Abstract

PURPOSE:To provide an electrode structure which can reduce the resistance by preventing the stripping off of an electrode material from a current collector. CONSTITUTION:In an electrode provided with a current collector 11 and electrode material 14 joined to the surface of the body 11, activated carbon fibers 13 are electrostatically flocked to the surface of the collector 11 and, at the same time, the material 14 is closely adhered and fixed to the surface of the collector 11. In addition, the activated carbon fibers 13 are directly flocked to the internal surface of a case for battery or cap. Moreover, the collector 11 can be constituted of a conductive resin sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure such as an electrode for an electric double layer capacitor or an electrode for a battery.

[0002]

2. Description of the Related Art As an electrode for an electric double layer capacitor, for example, an electrode having a spiral structure, a slurry as an electrode material is applied onto a metal sheet as a current collector,
After that, it is manufactured through a drying process, a rolling process, and a winding process.

For the electrode slurry, for example, a kneaded material of activated carbon powder, a binder (binder) and a thickener is used, and it is directly applied to the surface of the sheet by a doctor blade method or the like.

Further, as a battery electrode, for example, an electrode for a flat battery is manufactured as follows.

A net-shaped metal current collector is welded to the inner surface of a flat container-shaped metal case constituting the electrode current collector, and manganese dioxide as an active material, a conductive agent, etc., are welded onto the net-shaped current collector. A powdered electrode material consisting of a mixture of a binder and a binder is deposited, and the powdered electrode material is press-molded into a predetermined shape so that the electrode material is bitten into the net-shaped current collector, and the electrode material is placed on the inner bottom surface of the case. It is fixed to. After that, the fixed electrode material is impregnated by injecting an electrolytic solution.

[0006]

However, each electrode has the following problems (1) and (2).

(1) In the sheet electrode for the electric double layer capacitor, the electrode material may be partially peeled from the sheet in the drying and rolling steps, and the contact resistance between the sheet and the electrode material may increase. .

The cause of this problem is as follows.

The adhesive strength between the sheet and the electrode slurry mainly depends on the binder amount of the electrode slurry, and is not sufficient because the electrode slurry is only applied directly to the surface of the sheet.

In addition, the above-mentioned kneaded material may partially aggregate in the applied slurry.

In this case, when the slurry is dried and the viscosity thereof is lowered in the drying step, cracks may occur around the agglomerated portion and peel off from the sheet.

Also in the rolling step, if the rolling force acts on the agglomerated portion or the cracked portion of the slurry, the slurry is peeled off. Further, when the rolling force acts on the peeled portion generated in the drying step, the peeled portion further expands.

Also in the winding step, the compression force acts on the slurry in the circumferential direction as it is closer to the winding center, and the tensile force acts in the circumferential direction as it is farther from the winding center. Cracks or peeling may occur due to the tensile force.

Although it is possible to increase the adhesive strength by increasing the amount of the binder, the resistance of the electrode itself is increased, which has the opposite effect.

(2) In the battery electrode, when the electrode material is injected and impregnated with the electrolytic solution, the electrode swells and the electrode material peels from the inner bottom surface of the case, increasing the contact resistance between the electrode material and the case. I have something to do.

The cause of this problem is as follows.

The net-shaped current collector welded to the inner bottom surface of the case bites into the molded electrode material described above, but the net-shaped current collector only bites into the surface layer of the electrode material. Yes, it does not penetrate into the inside from its surface layer. Therefore, when the electrode material is impregnated with the electrolyte and swells, the diameter of the electrode material increases, so that the lower part of the electrode material partly separates from the net-shaped current collecting portion and rises to warp so as to separate from the bottom portion of the case. Is peeled off.

The present invention has been made to solve the above problems, and an object thereof is to provide an electrode structure capable of preventing the electrode material from peeling from the current collector and reducing the resistance. is there.

[0019]

To achieve the above object, the present invention provides an electrode comprising a current collector and an electrode material bonded to the surface of the current collector, wherein the surface of the current collector is The conductive carbon fibers are electrostatically flocked, and the electrode material is tightly locked to the surface of the current collector through the carbon fibers.

Here, the carbon fibers are electrostatically flocked directly on the inner surface of the battery case or cap constituting the electrode.

Preferably, the current collector is a conductive resin sheet.

More preferably, the conductive carbon fiber is an activated carbon fiber.

[0023]

According to the electrode structure of the present invention, conductive carbon fibers are electrostatically planted on the surface of the current collector, and the electrode material is provided on the surface of the current collector through the carbon fibers. Since the electrode material does not peel off from the current collector, the electrode having low resistance can be obtained.

When the carbon fibers are electrostatically flocked directly on the inner surface of the battery case or cap forming the electrode, the electrode material is adhered to the inner surface of the case or the cap through the carbon fibers. And because it is locked,
The electrode material does not peel off from the case or the cap, and an electrode with low resistance is obtained.

When the current collector is a conductive resin sheet, the flocking strength of the carbon fibers can be improved and the electrode material and the current collector can be more firmly and firmly locked.

When the conductive carbon fiber is the activated carbon fiber, the surface area of the activated carbon fiber is large, so that the contact area with the electrode material is increased and the resistance can be further reduced.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to the drawings.

First, an embodiment in which a sheet electrode is used as a current collector is shown in FIGS. 1 and 2 (a). FIG. 1 shows a partially enlarged cross-sectional view of the electrode of this embodiment.
And a carbon fiber 13 electrostatically flocked on the surface thereof and an electrode material 14 arranged on the carbon fiber 13,
The carbon fiber 13 and the carbon fiber 13 are fixed to each other through the carbon fiber fixing layer 12, and the carbon fiber 13 rises to the surface of the current collector 11 and enters the inside of the electrode material 14.

The manufacturing method will be described with reference to FIG. 2A. Polyvinylidene fluoride mixed with conductive carbon as a conductive adhesive at a maximum of 40% on both surfaces of an aluminum sheet-shaped current collector 11 having a thickness of about 20 μm. (Hereafter, PVDF
And the fiber length of 0. is applied to each surface of the current collector 11.
Electrostatic flocking of 3 mm of activated carbon fiber 13 was carried out at a flocking density of about 50,000 fibers / cm 2. At this time, the activated carbon fibers 13 were pierced into the applied PVDF to collect the current collector 1.
The activated carbon fiber fixing layer 12 was formed on both surfaces of No. 1 of FIG.

The electrostatic flocking uses a power of 25,000 V and a current of 0.2 mA to generate a magnetic field in the downward direction in the vertical direction, and the current collector 1 in which the sheet surface is horizontal in the magnetic field.
1 is placed and a sieve containing activated carbon fibers 13 is placed above the current collector 11 with a certain distance kept in opposition to each other, and the sieve is subjected to horizontal microvibration to activate the activated carbon fibers 13. It is done by dropping. As a result, the activated carbon fibers 13 that are falling fall vertically downward with the longitudinal direction thereof standing upright along the direction of the magnetic field, and are pierced perpendicularly to the sheet surface.

After that, a slurry electrode material 14 is applied onto the activated carbon fiber fixing layer 12 and the activated carbon fiber 13 by a doctor blade method, dried and then rolled to a thickness of 0.22 mm by roll rolling. Width 40 mm length 250
A sheet-like electrode was produced by cutting into a size of mm.

Here, as the slurry electrode material 14, used was a mixture of activated carbon powder, acetylene black as a conductive agent, and PVDF as a binder in a weight ratio of 60:20:20, respectively.

In the above electrode, since the active carbon fiber having a large surface area is used as the fiber for electrostatic flocking, the contact area between the active carbon fiber 13 and the electrode material 14 is increased and the resistance can be reduced.

As the material of the sheet-shaped current collector, in addition to the aluminum metal foil, for example, a conductive resin sheet in which a conductive carbon material is dispersed in resin may be used. In this case, when electrostatic flocking is performed, Since the conductive adhesive used adheres to the sheet more firmly than the metal foil, the carbon fiber and the resin sheet can be adhered via this conductive layer, and the flock density and flock strength can be increased. Therefore, the electrode material and the current collector can be more firmly fixed.

Next, a separator is sandwiched between the two sheet-like electrodes and wound in a spiral shape so that the separator is sandwiched between them, thereby producing a polarizable electrode element, which is placed in a cylindrical case. A spiral-type electric double layer capacitor was manufactured by hermetically sealing with an electrolytic solution.

A comparison test of the internal resistance and the discharge capacity of the spiral electric double layer capacitor employing the electrode manufactured as in the above-mentioned example and the conventional electrode was conducted. In this test, for the internal resistance, the impedance when the frequency of the AC power supply was 1 kHz was used as the internal resistance using the AC method, and for the discharge capacity, constant current discharge of 1 A was performed after constant voltage charging of 2.3 V. The capacity was defined as the discharge capacity. At this time, the case where the normal carbon fiber which is not surface activated is used as the fiber for electrostatic flocking is shown in FIG.
The case where the above-mentioned activated carbon fiber shown in (a) is used is set as Example 2, and as in the conventional case, as shown in FIG. The above-mentioned test was conducted on 10 samples in each example, with the case where no hair was transplanted as Comparative Example 1. As a result, as shown in Table 1, the internal resistance of Examples 1 and 2 was about 0.5 times smaller than that of Comparative Example 1, and the discharge capacity of Examples 1 and 2 was smaller than that of Comparative Example 1. It is about 1.5 times as large. In addition, Example 1
As a result, Example 2 was slightly superior in internal resistance and discharge capacity. This is because the activated carbon fiber having a large surface area is used as the carbon fiber, and thus the contact area between the activated carbon fiber and the electrode material becomes larger.

[0037]

[Table 1] Next, an embodiment in which a flat container-shaped metal case is used as a current collector will be described with reference to FIG. In this embodiment, electrostatic flocking is applied to the inner bottom surface of this metal case.

In FIG. 3A, the activated carbon fiber 23 is directly attached to the inner surface of a flat container-shaped metal case 21 as a current collector.
Electrostatically flock. After that, the electrode material 24 is molded using, for example, a press molding die. This press-molding die is composed of a lower die, a die, a punch, and the like.
Is installed with its inner surface facing upward, and then the die is lowered to be installed on the inner bottom surface of the case 21. In this state, a required amount of the powder electrode agent is put into the cavity formed inside the die, and then the punch is lowered to mold the powder electrode agent.

The electrostatic flocking was performed under the same conditions as in the case of the above-mentioned sheet electrode.

At this time, due to the uprightness of the activated carbon fiber 23, the activated carbon fiber 23 is molded in a state of standing upright with respect to the inner surface of the case 21 and enters the inside of the electrode material 24.

According to this structure, since the electrode material 24 is tightly locked to the surface of the case 21 through the activated carbon fiber 23, the electrode material 24 is not peeled from the case 21 and the electrode having a small resistance is formed. Is obtained.

In the above electrode, since the activated carbon fiber having a large surface area is used as the fiber for electrostatic flocking, the contact area between the activated carbon fiber 23 and the electrode material 24 is increased and the resistance can be reduced.

Electrodes are formed by using electrode materials different from those described above on the caps that form the flat battery and fit into the case, and electrolytic solution is injected into each electrode to form an intermediate portion of the electrodes. A separator is placed in the case, a cap is fitted to the case through a sealing gasket, the opening of the case is crimped to seal the inside, and a flat battery is manufactured with one electrode as a positive electrode and the other electrode as a negative electrode. .

Separately from the battery, the powder electrode material is mixed and granulated with manganese dioxide, a conductive agent, and a binder as an electrode active material, and the cap is made of metallic lithium as a negative electrode. The lithium battery is completed.

Next, a drop test and a peel test of the electrode material were carried out in the case of the flat battery employing the electrode of this example and the conventional electrode. In this test, the case in which the electrode was placed was dropped from the height of 20 cm to the floor surface, and whether or not the electrode dropped out of the case, and peeling due to swelling when the electrolytic solution was injected into the electrode material. It was confirmed whether or not. At this time, the case of using normal carbon fiber which is not surface activated as the fiber for electrostatic flocking is set as Example 3, and the case of using the above-mentioned activated carbon fiber is set as Example 4 similarly. As a comparative example 2, a case in which an electric body was directly welded to the inner surface of the case and an electrode active material was directly pressure-bonded thereto was used, and 20 tests were conducted for each example. As a result, as shown in Table 2, in the comparative example, 18 pieces were dropped out, whereas in Examples 3 and 4, none were dropped out. Regarding the peeling by the liquid injection, as shown in FIG. 3 (b), 15 pieces occurred in the comparative example, while in contrast to Examples 3 and 4 shown in FIG. 3 (a).
There was nothing peeled off.

The internal resistance was measured when a flat battery was formed using a case that did not peel in the peel test. As a result, as shown in Table 2, the internal resistances of Examples 3 and 4 were about 2/3 times smaller than those of Comparative Example 2. In addition, the result of Example 4 was slightly superior to that of Example 3. This is because the activated carbon fiber having a large surface area is used as the carbon fiber, and thus the contact area between the activated carbon fiber and the electrode material becomes larger.

[0047]

[Table 2] Although only one of carbon fiber and activated carbon fiber is used as the electrostatic flocked fiber in this embodiment, for example, the ratio of carbon fiber is 50% and activated carbon fiber is 50%.
You may use it combining suitably.

Further, the thickness of the electrode material can be set by appropriately changing the length of the electrostatic flocked fiber. Therefore, the capacity can be set by changing the thickness of the electrode material, and for example, the capacity can be increased by increasing the fiber length.

[0049]

According to the electrode structure of the present invention, conductive carbon fibers are electrostatically planted on the surface of the current collector, and the electrode material serves as the collector of the current collector through the carbon fibers. Since the electrode material is adhered and locked to the surface, the electrode material does not peel off from the current collector, and an electrode having low resistance is obtained.

When the carbon fibers are electrostatically flocked directly on the inner surface of the battery case or the cap forming the electrode, the electrode material is adhered to the inner surface of the case or the cap through the carbon fibers. And because it is locked,
The electrode material does not peel off from the case or the cap, and an electrode with low resistance is obtained.

When the current collector is a conductive resin sheet, the flocking strength of carbon fibers can be improved, and the electrode material and the current collector can be more firmly and firmly locked.

When the conductive carbon fiber is activated carbon fiber, the contact area with the electrode material is increased and the resistance can be further reduced.

Further, by increasing the fiber length of the carbon fiber, the electrode material locked on the current collector can be made thicker and the capacity can be increased.

Further, since the adhesion strength between the electrode material and the current collector is improved, the durability against external shock due to dropping of the battery can be improved.

[Brief description of drawings]

FIG. 1 is a partially enlarged sectional view of a sheet electrode according to the present invention.

FIG. 2A is a sectional view of a sheet electrode according to the present invention, and FIG. 2B is a sectional view of a conventional sheet electrode.

3A is a sectional view of a flat electrode according to the present invention, and FIG. 3B is a sectional view of a conventional flat electrode.

[Explanation of symbols]

 11 Aluminum Sheet-shaped Current Collector 12 Activated Carbon Fiber Fixing Layer 13 Activated Carbon Fiber 14 Electrode Material 21 Metal Case 23 Activated Carbon Fiber 24 Electrode Material 25 Net Current Collector 26 Electrolyte

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01M 4/66 A 4/70 A (72) Inventor Masahiro Suga 11 Ichigaya Sanai-cho, Shinjuku-ku, Tokyo Address Miyoshi Shoko Co., Ltd.

Claims (4)

[Claims] 1. An electrode comprising a current collector and an electrode material bonded to the surface of the current collector, wherein conductive carbon fibers are electrostatically flocked onto the surface of the current collector and the carbon An electrode structure characterized in that the electrode material is tightly locked to the surface of the current collector through a fiber. 2. The electrode structure according to claim 1, wherein the carbon fibers are electrostatically flocked directly on an inner surface of a battery case or a cap constituting an electrode. 3. The electrode structure according to claim 1, wherein the current collector is a conductive resin sheet. 4. The electrode structure according to claim 1, wherein the conductive carbon fiber is an activated carbon fiber.