JP2003217987A - Laminated electric double-layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve so as to extend a voltage applying lifetime of an in-line laminated unit. <P>SOLUTION: Between two collection electrode plates 2, having one surfaces adhering active carbon electrodes, polarization electrodes 5 having both surfaces adhering the active carbon electrode and gel electrolytic films 4 functioning as a separator are alternately overlapped and pinched, and in outer peripheral parts thereof, packings 3 having a seal function are pinched and laminated. Further, these are clamped from both sides by an end plate 1, to form an in-line laminated capacitor unit of an airtight structure, and further a plurality of separators 4 are made to overlap for use. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a laminated electric double layer capacitor. More specifically, it is improved so that the voltage application life can be extended.

[0002]

2. Description of the Related Art As shown in FIG. 1, a conventional laminated electric double layer capacitor (hereinafter referred to as a capacitor) has an aluminum foil base material between two collector electrode plates 2 to which activated carbon electrodes are adhered. Polarized electrode (intermediate electrode) with activated carbon electrodes bonded on both sides
5 and the gel electrolyte membrane 4 having the function of a separator are alternately stacked and sandwiched to form a capacitor unit having a bipolar structure in which a plurality of cells are stacked. A rubber packing 3 having a sealing function so that the electrolytic solution and the electrolyte salt inside do not leak to the outer periphery of the activated carbon electrode and the collecting electrode.
Are sandwiched between. At the same time, the packing 3 also has an insulating function to prevent the intermediate electrodes 5 from touching each other.

When assembling the capacitor unit,
The cells for the required withstand voltage (1 cell withstand voltage of about 2.5V) are stacked, and as shown in FIG.
It is sandwiched from both sides with and is tightened with bolts 7 via the insulating spacer 6 to keep a sealed structure and apply a pressure to the inside of the cell. If a lead wire is attached to the collector electrode on the end face of the metal electrode, the multilayer capacitor unit will be connected in series within the unit and will have a withstand voltage of (1 cell withstand voltage) × (number of cell stacks).

This multilayer capacitor unit does not require a cable or the like as compared with a capacitor of the same capacity using a general winding method, and can be designed compact and have a high withstand voltage, so that the installation volume can be reduced. it can.

[0005]

As described above, the series laminated type electric double layer capacitor unit is connected in series in the unit by stacking a plurality of cells, and each cell shares the voltage, resulting in the withstand voltage of the unit. Can be higher
However, in practice, a plurality of stacked cells do not always share the voltage evenly. This is because variations in the shared voltage of each cell occur due to repeated charging / discharging operations and application of voltage to the unit for a long time.

Since the sum of the shared voltage of each cell is the voltage applied to the unit, if a cell with a low shared voltage occurs, naturally a cell with a high voltage also occurs. When the cell voltage rises, the deterioration is accelerated, the internal resistance increases, the capacitance decreases, and the unit characteristics deteriorate. In addition, a difference in performance gradually occurs between cells with high voltage and cells with low voltage, which becomes a factor to further disperse the shared voltage, and the deterioration of the unit is accelerated.

As described above, in the laminated electric double layer capacitor unit, variations in the shared voltage of each cell shorten the life of the unit. One of the factors that causes the shared voltage to vary is the difference in the self-discharge characteristics of each cell. Figure 3
The self-discharge characteristic according to the conventional example is shown in FIG. A cell with a small self-discharge has a good voltage retention and the shared voltage gradually increases, and a cell with a large self-discharge has a poor voltage retention and the shared voltage gradually decreases.

This mainly occurs when a voltage is applied to the unit for a long time, and once the variation occurs, it is difficult to restore it. The cause of the difference in the self-discharge characteristics is due to the difference in the electric shielding ability of the separator 4 that shields the electrodes. In the conventional example using the cellulose-based separator 4 having a thickness of 50nm, but tiny pinholes at a rate of about several to several m ^2,
There may be scratches. This tiny hole is difficult to detect with the naked eye and virtually uninspectable.

The second factor that causes the divided voltage to vary is the difference in the capacitance of each cell. If the electrostatic capacity is large, the voltage increase during charging will be small, and if the electrostatic capacity is small, the voltage increase will be large. As a result, the voltage at the completion of charging will vary from cell to cell. The cell with the higher voltage is
Deterioration progresses rapidly and the capacitance is further reduced to increase the voltage rise. In the conventional example, the electrode is used after being cut into a fixed size, but the electrodes have different densities, and even if they are cut into the same size, the weight is different. This weight difference becomes the capacitance difference.

The third factor is the physical contact of the aluminum foil current collector substrate. In the conventional example, A1085H aluminum foil having a thickness of 400 μm is used. The distance between the electrodes of the laminated unit is about 0.5 mm, and the aluminum foil is bent when tightened using packing.

When this bending comes into contact with the aluminum foils of the adjacent cells, a short circuit occurs and the voltage is hardly shared. When the sharing of the voltage of one cell is not performed, the voltage corresponding to that is dispersed and applied to other cells, and the sharing voltage of the whole is raised.

[0012]

A laminated electric double layer capacitor according to claim 1 of the present invention which solves the above problems has an activated carbon electrode on both sides between two collector electrode plates having an activated carbon electrode bonded on one side. Glued polarized electrodes and gel electrolyte membranes that function as separators are alternately stacked and sandwiched, and packing with a sealing function is sandwiched between them and laminated, and these are tightened from both sides with end plates to form a series laminated structure with a closed structure. Type capacitor unit, and further, a plurality of the separators are stacked and used.

A laminated electric double layer capacitor according to a second aspect of the present invention which solves the above-mentioned problems is that the weight of the activated carbon electrodes is equalized in the serial laminated type capacitor unit according to the first aspect. Characterize.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] In this embodiment, in order to equalize the voltage sharing among cells in a unit, variations in self-discharge characteristics of each cell are suppressed.
As shown in FIG. 1, the basic structure of the capacitor cell is composed of opposing activated carbon electrodes and a cellulose-based separator sandwiched between them, and is composed of an intermediate electrode which is an aluminum foil current collecting substrate with the activated carbon electrodes. . By sealing the collector electrode base material with packing, the polarization function and the separation function between the cells are fulfilled. Finally, the cell is impregnated with the electrolytic solution to complete the cell.

In order to equalize the self-discharge characteristics, in order to remove the influence of moisture, the activated carbon electrode and the aluminum foil current collecting base material are vacuum dried for 24 hours or longer in an environment of 150 ° C. and 10 ⁻⁵ Torr or lower. . The separator is 100 ° C, 10
-Vacuum drying is performed for 24 hours or more at ^-5 Torr or less. It is necessary to use an electrolyte solution having a water content of 10 ppm or less. In the conventional example, the separator is made of cellulose and has a thickness of 5
Although the thickness of 0 μm is used, if a separator has a pinhole, electron transfer occurs and self-discharge occurs as it is. Therefore, a thickness of 35 μm is used as two layers.

The thinner the separator, the higher the probability of pinholes existing, but the probability that two pinholes overlap at the same position is close to zero. It is also possible to increase the thickness of the separator to reduce the probability of pinholes, but it is difficult to approach 0 and if it is too thick, the internal resistance of the cell will increase. FIG. 4 shows the effect of suppressing the variation in self-approach according to this embodiment. As shown in FIG. 4, in this embodiment, by using two separators each having a thickness of 35 μm from the conventional 50 μm thick product, variations in the self-discharge characteristics of each cell of the unit are suppressed, and a voltage is applied to the unit for a long time. When applied, the sharing voltage can be equalized,
It has been possible to extend the voltage application life of the series-stacked unit to 5 times or more that of the conventional case.

[Embodiment 2] In this embodiment, in order to equalize the voltage sharing of each cell in the unit, the variation in the electrostatic capacitance of each cell is suppressed. Currently, the electrodes of capacitors have a fixed size (for example, 200 mm × 20
0mm) is cut and used as it is. In this embodiment, the electrode is cut to be slightly larger than the reference size (for example, 200 mm × 205 mm), and the reference electrode weight is determined (for example, 3.2 g). The weight of the cut electrode is measured and the ratio from the standard weight is obtained.

For example, since 3.4 g is 5% heavier, the electrodes are cut from 205 mm to 12 mm according to the area ratio, and the electrode weight is made uniform to 200 mm × 193 mm. It is necessary to preliminarily cut into a large size so as to prevent the weight less than the standard weight from coming out due to variations in electrode density. By carrying out such electrode weight measurement, calculation, and cutting steps at the time of assembling the capacitor to assemble the unit, it is possible to obtain a unit with extremely small variation in capacitance. Specifically, the variation in capacitance could be suppressed within ± 3%.

As described above, in this embodiment, by equalizing the weights of the activated carbon electrodes, it is possible to equalize the electrostatic capacities of each unit cell, and it is possible to suppress the shared voltage that fluctuates during charging / discharging. The cycle charge / discharge life of the laminated unit can be extended to more than twice that of the conventional one.

[Embodiment 3] This embodiment relates to manufacturing conditions of Embodiments 1 and 2. That is, a hard aluminum foil which is not subjected to the annealing treatment of the A1085H aluminum foil is used so that the aluminum foil does not bend when tightened with packing. However,
Since the hard aluminum foil is not heat-treated, oil and impurities are deposited on the surface thereof, which contributes to the performance deterioration of the capacitor. Therefore, in order to remove these impurities, when the aluminum foil is rolled, the aluminum foil is immersed in a sodium carbonate solution at about 70 ° C. for about 50 seconds and then rinsed with water.

By using the aluminum foil thus obtained as a collector electrode substrate, it is possible to obtain a capacitor unit which does not cause a short circuit between cells. As described above, in the present embodiment, by using the hard aluminum foil for the collector electrode base material, it was possible to prevent the occurrence of a short circuit between cells and prevent an increase in the shared voltage of each unit cell. .

[0022]

As described above in detail with reference to the embodiments, in the present invention, by using a plurality of separators in a stacked manner, it is possible to suppress variations in the self-discharge characteristics of each cell of the unit and to keep the unit for a long time. When a voltage is applied, the shared voltage can be equalized, and the voltage application life of the series laminated unit can be significantly extended compared to the conventional case. In addition, by equalizing the weight of the activated carbon electrodes, the capacitance of each unit cell can be equalized, and the shared voltage that fluctuates during charging and discharging can be suppressed, making the cycle charge and discharge life of the series stacked unit significantly larger than before. It can be postponed. Moreover, by using a hard aluminum foil for the collector electrode base material, it is possible to prevent a short circuit between cells and prevent an increase in the shared voltage of each unit cell.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram of a conventional laminated electric double layer capacitor unit.

FIG. 2 is a cross-sectional view of a conventional laminated electric double layer capacitor.

FIG. 3 is a graph showing a self-discharge characteristic according to a conventional example.

FIG. 4 is a graph showing self-discharge characteristics according to an example.

[Explanation of symbols]

1 End plate 2 collector electrode plate 3 rubber packing 4 Gel electrolyte membrane (separator) 5 Polarized electrode (intermediate electrode) 6 Insulation spacer 7 Tightening bolt

Claims (2)

[Claims] 1. A polarizing electrode having an activated carbon electrode adhered on both sides and a gel electrolyte membrane functioning as a separator are alternately sandwiched between two collector electrode plates having an activated carbon electrode adhered on one side, and a seal is provided on the outer peripheral portion thereof. Laminated packings having a function are sandwiched, and these are further tightened from both sides by end plates to form a series laminated capacitor unit having a hermetic structure. Further, a plurality of the separators are stacked and used. Multilayer capacitor. 2. The laminated electric double layer capacitor according to claim 1, wherein the activated carbon electrodes of the series laminated capacitor unit have the same weight.