JPH1079329A - Laminate electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a folding-type laminate electric double layer capacitor with large capacitance by reducing contact resistance in a conventional folding- type electric double layer capacitor and also reducing relaxation potential. SOLUTION: By fixing an active material layer to a positive electrode collector 44 and a negative electrode collector 46, respectively, an electrode 48 for a positive electrode and an electrode 50 for a negative electrode are respectively constituted. A plurality of the electrodes 48, 50 are alternately laminated via a separator with an acute-angled fold line A and an obtuse-angled fold line B aligned. The active material layer is provided only on an opposite face to an internal layer on an outermost layer electrode of the laminate. The respective electrodes and respective separators laminated here are folded along the acute- angled fold line A and the obtuse-angled fold line B and impregnated in electrolytic solution to provide a laminate electric double layer capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated electric double layer capacitor in which an electrode having an active material layer fixed to a surface of a current collector is laminated.

[0002]

2. Description of the Related Art In order to increase the charge capacity and the discharge capacity of an electric double layer, a multilayer electric double layer capacitor is usually constituted by laminating a plurality of electrode layers. The positive electrode and the negative electrode, each having an active material layer fixed to both surfaces of the current collector, are alternately laminated with a separator interposed therebetween, and this is impregnated with an electrolyte.

In recent years, in order to reduce the size of the multilayer electric double layer capacitor and to simplify the manufacturing thereof, Japanese Patent Application Laid-Open No. 4-240
No. 708 discloses an electric double layer in which electrodes are stacked by folding. Specifically, as shown in FIG. 4, current collectors 14 and active material layers 16 are alternately fixed on both sides of the long separator sheet 12 with the fold 13 as a boundary. The current collector 14 and the active material layer 16 that are adjacent to each other are in close contact with each other by folding in a mountain fold and a valley along the fold 13, thereby forming an electrode.

When an external voltage is applied through the current collector 14 in the electric double layer configured as described above, the current collector 1
The electric charge is accumulated and charged in the active material layer 16 which is in close contact with the substrate 4, and the electric charge accumulated in the active material layer 16 is taken out via the current collector 14 during discharging.

[0005]

However, in the above-mentioned foldable electric double layer, the current collector and the active material layer come into close contact with each other by folding, but actually, the current collector and the active material layer There is a slight gap between
This void causes contact resistance and causes a reduction in capacity.

Further, in the above-mentioned conventional foldable electric double layer capacitor, since the active material layer adheres to only one surface of the current collector, the ratio of the current collector per unit volume becomes large. The capacity per unit volume will be reduced.

[0007] In addition to the above-mentioned problems, another cause of the decrease in the capacity of the electric double layer is known as a relaxation voltage. As shown in FIG. It is a phenomenon that decreases. The cause of this phenomenon is expected to be as shown in FIG. That is, the outer electrode 5 having the active material layers 52 on both surfaces
In the case of No. 3, it is considered that the charge moves to the back surface 53a at the time of power storage, and the moved charge cannot be taken out at the time of discharging.

The present invention has been made in view of the above problems, and has as its object to reduce the contact resistance in a conventional folding electric double layer and reduce the relaxation voltage to increase the capacity. An object of the present invention is to provide a foldable multilayer electric double layer capacitor.

[0009]

In order to achieve the above object, the present invention relates to a current collector, in which active material layers are fixed on both surfaces of a current collector, and at least one or more inner layer elongates laminated with a separator interposed therebetween. An electrode, an active material layer is fixed to the inner surface of the current collector, and an outer layer electrode laminated with an outer layer separator interposed between the laminated inner layer long electrodes, and each electrode is alternately a positive electrode and a negative electrode. The multilayer electric double layer capacitor is characterized in that it is folded in a mountain direction and a valley sequence in the longitudinal direction.

[0010] According to the above-described structure, in order to increase the number of laminations by laminating the inner long electrode and the outer long electrode, and to fold this into a mountain valley and a valley, a conventional laminated electric double layer is laminated one by one. Can be simplified. Further, in the above structure, since the active material layer is already fixed to the current collector, the contact when the current collector and the active material layer are brought into close contact with each other by folding as in a conventional folding electric double layer. Resistance can also be prevented.

Further, in the above configuration, since the outer layer long electrode is provided with the active material layer only on the inner side surface, a decrease in the potential stored during charging can be prevented, and the charge / discharge efficiency can be improved. .

[0012] In the above structure, it is desirable that a region having no active material layer is provided at a mountain fold position and a valley fold position of each electrode.

As described above, by providing the region without the active material layer at the mountain fold position and the valley fold position, the active material layer does not peel off when the mountain fold and valley fold occurs, and a short circuit due to this peeling is prevented. be able to.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the multilayer electric double layer capacitor according to the present invention will be described below with reference to the drawings.

FIG. 1 shows that in manufacturing a multilayer electric double layer capacitor, an inner long electrode 34 and an outer long electrode 32 each composed of a current collector 36 and an active material layer 38 are separated by a separator 40.
This shows a state in which the layers are stacked with interposing.

As shown in FIG. 1, an active material layer 38 is fixed to the inner layer long electrode 34 on both surfaces of a current collector 36. On the other hand, an active material layer 38 is fixed to one surface of a current collector 36 on the outer layer long electrode 32 provided on both sides of the inner layer long electrode 34 with a separator interposed therebetween. Here, the outer layer long electrode 32 also has a current collector 36 similar to the inner layer long electrode 34.
It is also possible to provide an active material layer 38 on both surfaces of the outer electrode, but as described later in detail, in order to reduce the relaxation voltage, the outer layer long electrode 32 is provided only on the surface facing the inner layer.
Is preferably provided.

The current collector 36 is formed of a long thin film made of a conductive material such as aluminum. As shown in FIG. 2, the current collector 36 has a plurality of terminal portions 4 at its upper end in order to eliminate internal resistance that may occur in a long current collector.
2 are formed so as to protrude, and the potential in the long current collector 36 can be made substantially uniform.

The terminal portion 42 is, for example, a mountain fold line A shown by a broken line or a valley fold line B shown by a dashed line in FIG.
Can be provided above. In the present embodiment, as shown in FIG. 2, the terminal portions 42 of the positive electrode current collector 44 are provided on each mountain fold line A, and the terminal portions 42 of the negative electrode current collector 46 It is provided above. Thus, the terminal 4
By providing 2 on the mountain fold line A or the valley fold line B, when folded, the respective terminal portions 42 are respectively arranged at substantially the same position and stacked, so that an external voltage is applied later. It becomes easy when connecting lead wires and the like.

The active material layer 38 is made of, for example, a conductive material such as carbon black as activated carbon, and a polytetrafluoroethylene (PTFE) or the like for binding the activated carbon and the conductive material. It is configured by adding a binder.

When the active material layer 38 is formed on the current collector 36, the above-described activated carbon, conductive material and PTF
E is stirred and mixed in water or an organic solvent to form a paste, the paste-like active material is applied to the surface of the current collector 36, and after firing, the active material layer 38 is formed.

The active material layer 38 may be formed on the entire surface of the current collector 36, but preferably, the mountain fold line A
And a region without an active material layer is provided on the valley fold line B. When the active material layers are provided on the mountain fold line A and the valley fold line B, when the electrodes are stacked and folded along each fold line as described later, stress is applied to the active material layer 38 on the fold line, and The material layer 38 may be partially peeled off, which may cause a short circuit. Therefore, it is desirable to provide a region without an active material layer on the mountain fold line A and the valley fold line B.

The active material layer 38 may be made of the same material as the electrodes for the positive electrode and the negative electrode, or the active material for the positive electrode and the active material for the negative electrode may be different depending on the purpose. It can also be composed of materials. By fixing such an active material layer 38 to the positive electrode current collector 44 and the negative electrode current collector 46, the positive electrode 48 and the negative electrode 5
0 are respectively configured.

In the case of laminating the electrodes configured as described above, the positive electrode 48 and the negative electrode 50 are stacked with the separator 40 interposed alternately along the mountain fold line A and the valley fold line B. Can be

The total number of electrode layers to be stacked is preferably at least three, that is, at least one inner layer long electrode 34 and two outer layer long electrodes 32. If the total number of electrode layers is two, that is, only the outer layer long electrode 32 is used, the active material layer 38 is formed on only one surface of the current collector 36 as in the related art. Therefore, the ratio of the current collector 36 per unit volume increases, and the capacity cannot be improved. Therefore, it is desirable that the total number of electrode layers be at least three or more, and more preferably that the number of the inner layer long electrodes 34 be increased to reduce the ratio of the current collector 36 per unit volume. By reducing the ratio of the current collector 36 in this manner, the capacity per unit volume can be increased.

As described above, in the present embodiment,
The inner layer long electrode 34 has an active material layer 3 on both sides of a current collector 36.
8 is provided, but in the case of the outer layer long electrode 32,
As described below, in order to reduce the relaxation voltage of unknown cause (a phenomenon in which the potential drops during storage after charging), it is desirable to provide the active material layer 38 only on the surface of the current collector 36 facing the inner layer. . Experimental results supporting this effect will be described with reference to FIG.

FIG. 3 shows outer electrodes of two different stacked electric double layer capacitors used in the experiment. That is,
The (A) capacitor has active material layers 52 on both sides of the current collector 51 of the outer electrode 53, while the (B) capacitor has one surface of the current collector 51 of the outer electrode 54 (the inner layer and the inner layer). The active material layer 52 is provided only on the opposite surface of the active material layer 52.

Table 1 shows the results of comparing the relaxation voltage amount and the charging / discharging efficiency of the multilayer electric double layer capacitor of FIG. 3A or 3B one minute after the completion of charging.

As shown in Table 1, in the capacitor (A) having the active material layers 52 on both surfaces of the outer electrode 53, the relaxation voltage after one minute from the completion of charging is 0.13V, In the case of the capacitor (B) provided with the active material layer 52 only on one side of the outer electrode 54, the voltage was 0.06V. As described above, a reduction in the relaxation voltage was observed in the capacitor (B) including the active material layer 52 on only one surface of the outer layer electrode 54.
The charging and discharging efficiency of the capacitor (A) is 99.0%, whereas the charging and discharging efficiency of the capacitor (B) is 99.0%.
9.5%, and the active material layer 52 is formed only on one side of the outer layer electrode 54.
It was shown that the capacitor (B) provided with a high charge / discharge efficiency. This is presumably because charge / discharge efficiency was improved by reducing the relaxation voltage.

This is because, as shown in FIG. 3A, in the case of the outer layer electrode 53 having the active material layers 52 on both surfaces, the electric charge moves to the back surface 53a at the time of charging, and the moved electric charge here. It can be considered that a phenomenon has occurred in which it cannot be taken out during discharge.

From the above results, in order to reduce the relaxation voltage and improve the charging / discharging efficiency, it is preferable that the outer electrode has the active material layer only on the surface facing the inner layer.

[0031]

[Table 1] FIG. 2 shows a method of folding the outer long electrode 32 and the inner long electrode 34 stacked with the separator 40 interposed therebetween in FIG.

In the case of folding, it is folded along a mountain fold line A shown by a broken line and a valley fold line B shown by a dashed line in FIG. Due to this folding, each terminal 42 of the positive electrode protrudes upward at one folded end, and each terminal 42 of the negative electrode extends at the other folded end.
2 will project upward.

The electrodes 32, 34 folded as described above
Is impregnated with a predetermined electrolyte to form a multilayer electric double layer capacitor.

When charging the multilayer electric double layer capacitor configured as described above, an external voltage is applied from the terminal portion 42 to thereby allow the active material layer on the positive electrode 48 via the current collector 36 to be charged. Negative charges are accumulated in 38, and positive charges are accumulated in the active material layer 38 on the negative electrode 50. On the other hand, at the time of discharging, the charge accumulated in the active material layer by charging is supplied to the outside from the current collector.

As described above, the multilayer electric double layer capacitor of the present embodiment has at least one inner layer long electrode 3
After laminating four and two outer layer long electrodes 32, a large number of laminations can be obtained by folding. for that reason,
Like an electric double layer in which multiple conventional plate-shaped electrodes are stacked,
There is no need to stack the electrodes one by one, and the manufacturing becomes easy.

Further, unlike the conventional foldable electric double layer, the present multilayer electric double layer capacitor has the active material layer and the current collector fixed to each other, so that the cause of the contact resistance such as a void is eliminated. Thus, more efficient charging and discharging can be performed.

Further, in the present embodiment, the inner layer long electrode 34 is provided with the active material layers 38 on both surfaces of the current collector 36, so that the inner layer long electrode 34 is different from the conventional foldable multilayer electric double layer capacitor. As a result, the ratio of the current collector per volume can be reduced. As a result, it is possible to obtain the same amount of charge in a smaller volume.

For example, when the current collector 36 is an aluminum foil having a thickness of 20 μm and an active material layer having a thickness of 50 μm is formed on the aluminum foil, the present embodiment and the conventional foldable multilayer electric double layer capacitor are used. And compare the overall thickness.

More specifically, in the present embodiment, when the number of current collectors is 6, and the number of laminations per current collector is 20 by folding, the total thickness is 15.5 cm. On the other hand, in the case of the conventional capacitor, when the number of stacked active material layers is the same as described above, it is 17.5 cm. Therefore, in the present embodiment, it is possible to reduce the thickness by 13%, that is, to reduce the size under the above conditions.

[0040]

As described above, according to the present invention, the stacked electrodes and the separator are folded, so that the electrodes can be continuously stacked, so that the manufacturing is easy. In addition, the size can be reduced by this folding. Furthermore, since the current collector and the active material layer in the present invention are fixed, contact resistance in a conventional folding electric double layer can also be prevented.

According to the present invention, the outermost electrode is provided with the active material layer only on the surface facing the inner layer, so that the relaxation voltage in the conventional laminated electric double layer can be reduced, Charge and discharge efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a stacking stage in a manufacturing process of a multilayer electric double layer capacitor according to an embodiment.

FIG. 2 is a view showing a folding stage in a manufacturing process of the multilayer electric double layer capacitor of the present embodiment.

FIG. 3 is a diagram showing a cause of a relaxation voltage and a principle for reducing the relaxation voltage.

FIG. 4 is a view showing a conventional foldable multilayer electric double layer capacitor.

FIG. 5 is a diagram showing a decrease in potential due to an internal resistance and a relaxation voltage.

[Explanation of symbols]

32 outer layer long electrode, 34 inner layer long electrode, 36 current collector, 38 active material layer, 40 separator, 42 terminal section, 44 positive electrode current collector, 46 negative electrode current collector, 48
Positive electrode, 50 Negative electrode.

Claims (2)

[Claims] An active material layer is fixed on both surfaces of a current collector, a plurality of inner layer long electrodes each laminated with a separator interposed therebetween, and an active material layer is fixed on an inner surface of the current collector. An outer electrode laminated on the laminated inner layer long electrode with an outer layer separator interposed therebetween, and the laminated electric double layer capacitor in which each electrode is alternately used as a positive electrode and a negative electrode. A multilayer electric double-layer capacitor folded in a valley. 2. The multilayer electric double-layer capacitor according to claim 1, wherein a region without an active material layer is provided at a mountain fold position and a valley fold position of each electrode.