JP2002246269A - Electrochemical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrochemical element having a bag-like sealing member in which no gap appears at the opening (sealing) part of the sealing member even under a state clamping a lead terminal and a good adhesion state can be sustained stably while ensuring high reliability in electrical connection with a current collector. SOLUTION: At least a set of multilayered cell bodies 5 formed by laying sheet-like current collectors 4, each having a terminal part 4a at the end part thereof, in layers on the surface of a pair of sheet-like electrodes 2 and 2 laid in layers through a sheet-like separator 3 is contained in a bag-like sealing member 6. A lead terminal 7 is welded to the terminal part 4a of the current collector 4 such that the lead terminal 7 projects to the outside from the opening part of a sealing member 6 and seals the opening part of the sealing member 6. Traverse section at the sealing part of the lead terminal 7 is substantially rectangular in the central region and tapered at the end part thus manufacturing a electric double layer capacitor 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-type electrochemical device such as a battery and an electric double layer capacitor, and more particularly to an improvement in a lead terminal projecting outside a sealing member.

[0002]

2. Description of the Related Art In recent years, electrochemical devices such as lithium secondary batteries and electric double layer capacitors have been receiving attention. Among them, the electric double layer capacitor utilizes an electric double layer formed by the polarization of ions at the interface between the electrode and the electrolyte, and has both functions of a capacitor and a battery. It has been attracting attention as an auxiliary power supply for a large-capacity motor, such as a small-sized memory backup power supply or a driving source for a car, because it can charge a large capacity electrostatic capacity and can rapidly charge and discharge.

As an example of the configuration of such an electric double layer capacitor, a separator made of an insulating porous material is interposed between two polarizable electrodes containing activated carbon and an electrolytic solution, and the polarizer is located on the separator side of the polarizable electrode. A cell made of a laminate in which a current collector made of a metal foil or the like is disposed on each surface opposite to the surface, if desired, is sealed in a bag-like shape such as a laminated film made of a polymer film in which a plurality of layers are laminated. A configuration in which a lead terminal for electrically connecting the inside of an electric double-layer capacitor and an external circuit is protruded from an opening of the member, and the opening is sealed by heat fusion (heat sealing) or the like. Is known.

[0004]

However, in the above-mentioned conventional electric double-layer capacitor, the lead terminals are sandwiched between the bag and heat-fused, so that the close contact between the bag and the lead terminals is caused. Insufficiently, a gap is created, the electrolyte in the electric double layer capacitor leaks from this gap, and the moisture in the atmosphere enters from this gap,
As a result of the decomposition of the electrolytic solution by the action of moisture, there has been a problem that the capacitance of the electric double layer capacitor is reduced.

In order to enhance the sealing property of the sealing member, it is conceivable to make the cross section of the lead terminal circular or elliptical. In this case, however, the welding between the lead terminal and the terminal portion of the current collector is considered. There is a possibility that the resistance may decrease and the internal resistance of the electric double layer capacitor may increase.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide an electrochemical device having a bag-shaped sealing member. An object of the present invention is to provide an electrochemical device which can stably maintain a good adhesion state without generating a gap or the like in a sealing portion and has high reliability of electrical connection with a current collector.

[0007]

As a result of studying the above problem, the present inventors have found that the shape of the lead terminal is substantially rectangular at the center in the cross section at the opening (sealing) of the lead terminal. By having a tapered shape with an end portion, a good adhesion state can be stably maintained without a gap or the like even when the lead terminal is sandwiched, and the electrical contact with the current collector can be maintained. It has been found that the electrochemical device has high connection reliability.

That is, the electrochemical element of the present invention has a cell in which a sheet-like current collector having a terminal portion at an end is laminated on each surface of a pair of sheet-like electrodes laminated with a sheet-like separator interposed therebetween. At least one set of the laminates is accommodated in a bag-shaped sealing member, and a lead terminal is welded to a terminal portion of the current collector, and the lead terminal is projected outside from an opening of the sealing member. In this manner, the opening of the sealing member is sealed, and the shape of the lead terminal in the cross section at the opening is substantially rectangular in the central region, and the end portion is tapered. It is characterized by having.

Here, the width (w ₂ ) of the rectangular portion of the lead terminal relative to the entire width (w ₁ ) of the lead terminal
The ratio of (w ₂ / w ₁₎ is 0.4 to 0.9 that, it is desired surface roughness of the lead terminals (Ra) is 0.1 to 100 [mu] m.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The electrochemical device of the present invention is described below.
An example of the electric double layer capacitor will be described with reference to FIG. 1 which is a schematic sectional view and FIG. 2 which is a plan view. Figure 1,
According to 2, the electric double layer capacitor 1 has the separator 3 disposed and interposed between the polarizable electrodes 2 and 2 serving as a positive electrode and a negative electrode, and the opposite of the polarizable electrodes 2 and 2 from the separator bonding surface. On the surface, current collectors 4 forming a positive electrode and a negative electrode are laminated and bonded respectively.

According to FIGS. 1 and 2, the cell laminate 5 of the current collector 4-the polarizable electrode 2-the separator 3-the polarizable electrode 2-the current collector 4 has a bag-like sealing member 6. The opening of the sealing member 6 is hermetically sealed and sealed by sealing the two layers of the sealing member 6 by heat sealing or the like. Furthermore, at a sealing (opening) portion 6a of the sealing member 6, a pair of lead terminals 7 (7a, 7b) for electrically connecting the inside and the outside of the sealing member 6 are sealed and sealed in a state of being sandwiched. Has been stopped.

Further, a strip-shaped terminal portion 4a is formed at one end of the current collector 4, and the terminal portion 4a is electrically connected to the lead terminal 7 by welding in the sealing member 6.

According to the present invention, it is a major feature that the lead terminal 7 has a substantially rectangular shape at the center in the cross section at the sealing portion 6a of the sealing member 6 and has a tapered end. Thereby, as shown in a schematic cross-sectional view of the sealing portion 6a of the sealing member 6 in FIG. 3, even when the lead terminal is sandwiched, no gap or the like is generated in the sealing portion 6a of the sealing member 6. A good contact state can be stably maintained, and the reliability of electrical connection by welding the current collector 4 to the terminal portion 4a can be maintained.

That is, if a tapered portion is not formed in the cross section of the lead terminal 7, a gap is formed between the sealing portion 6a of the sealing member 6 and the lead terminal 7 to be sandwiched, and the sealing of the electric double layer capacitor 1 is performed. As a result, the decomposition of the electrolytic solution proceeds, and the internal resistance of the electric double layer capacitor increases and its life is shortened. If the shape of the central region in the cross section of the lead terminal 7 is not a rectangle but a circle or an ellipse, the weldability between the lead terminal 7 and the terminal portion 4a of the current collector 4 is reduced, and the electric double layer capacitor 1 Internal resistance increases.

The shape of the portion of the lead terminal 7 other than the sealing portion 6a of the sealing member 6 does not necessarily have to be tapered at both ends, and the cross-sectional shape of this portion is generally rectangular as a whole. Is also good. Also, in FIG.
Current collector 4-Polarizable electrode 2-Separator 3-Polarizable electrode 2
-Although only one set of the cell stack 5 of the current collector 4 exists, the present invention is not limited to this, and a plurality of sets of the cell stack 5 may be provided.

Here, as shown in FIG. 4, the cross-sectional shape of the lead terminal 7 is such that (a) a taper is provided at a corner of a substantially rectangular shape, and (b) an R portion is provided at a corner of the substantially rectangular shape. (C) Both ends are shaved from both sides, and the cross section of the tapered portion has a pointed shape with an isosceles triangular shape. Those having a head shape are preferred.

In order to improve the weldability between the lead terminal 7 and the terminal portion 4a of the current collector 4 while improving the sealing property of the sealing member 6, for example, the lead terminal 7 shown in FIG. As shown in the cross section, the ratio (w ₂ / w ₁ ) of the width w ₂ of the rectangular portion of the lead terminal 7 to the entire width w ₁ of the lead terminal 7 is 0.
Desirably, it is 4 to 0.9.

Further, according to the present invention, the surface roughness (Ra) of the lead terminal 7 is increased in order to enhance the adhesion between the sealing member 6 and the lead terminal 7 and to enhance the sealing reliability between the two. 0.
1 to 100 μm, especially 0.1 to 50 μm, furthermore 1 to 1
Desirably, it is 0 μm.

(Structure of each member) On the other hand, the activated carbonaceous structure constituting the polarizable electrode 2 mainly comprises a mixture of activated carbon particles having a high specific surface area and a binder for binding the activated carbon particles. It is a component, which may be carbonized.

Further, maintaining the high capacitance of the capacitor,
In order to obtain the required strength as a structure, the activated carbon desirably has a specific surface area of 1,000 to 1,800 m ² / g.

The carbon component added as the binder is present between the activated carbon particles, but when the carbonization treatment is performed, the ratio of the carbon component to the activated carbonaceous structure is 5 to 5.
The content is preferably 50% by weight, whereby the sinterability and bonding between the activated carbon particles can be enhanced.

Further, the polarizable electrode 2 is preferably in the form of a plate.
JIS in terms of reliability of mechanical strength that can withstand impacts etc.
30k 3-point bending strength at room temperature according to R1601
It is preferably at least Pa, especially at least 60 kPa.
Further, the thickness of the polarizable electrode 2 is preferably 1.5 mm or less, particularly preferably 0.6 mm or less from the viewpoint of reducing the internal resistance.

The separator 3 is made of pulp, polyethylene, polypropylene, polyvinylidene fluoride (P
An organic film such as VdF) or a glass fiber nonwoven fabric and ceramics can be used, and are formed to insulate the polarizable electrodes 2 from each other. It is formed of a porous body through which ions can pass.

The current collector 4 is made of conductive metal foil, such as aluminum, titanium, tantalum, platinum, or gold, or stainless steel, and exchanges electric charge between the polarizable electrodes 2 and 2. In particular, it is desirable to use a metal foil mainly composed of aluminum from the viewpoint of corrosion resistance to a non-aqueous electrolyte having a high decomposition voltage. It is preferable to use various metals having electrolytic resistance. The thickness of the current collector 4 is preferably thin in order to reduce the internal resistance, but is 0.02 to 0.10 m in consideration of damage due to handling during assembly.
m is desirable.

On the other hand, the electrolytic solution impregnated in the polarizable electrode 2 and the separator 3 may be an aqueous solution such as sulfuric acid or nitric acid, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), γ-butyrolactone. (Γ-BL), N, N-dimethylformamide, sulfolane, 3-methylsulfolane and other nonaqueous solvents and quaternary ammonium salts, quaternary sulfonium salts, quaternary phosphonium salts and other nonaqueous electrolyte solutions are combined. Although it can be used, in the present invention, it is desirable to use a non-aqueous electrolyte having a high decomposition voltage. The amount of the electrolyte dissolved in the nonaqueous solvent was 0.5 to 2.0 mol / mol.
It is preferable to set it to 1 in order to obtain a stable and high capacitance.

The sealing member 6 has a bag shape and has a barrier function against the outside air and moisture. For example, at least a sealing resin is provided at the sealing portion,
In addition, a laminate film having a metal foil such as aluminum interposed therein can be used. Specifically, acid-modified polypropylene (PP) / polyethylene terephthalate (PE) laminated from the sealing portion side to the outer surface
T) / Al foil / PET laminate film, acid-modified polyethylene (PE) / nylon / Al foil / PET laminate film, ionomer / Ni foil / PE / PET laminate film, ethylene vinyl acetate (EVA)
A laminated film of / PE / Al foil / PET, an ionomer / PET / Al foil / PET laminated film, and the like can be used. Here, on the side of the sealing portion, acid-modified polyethylene (PE), acid-modified polypropylene (PP), ionomer, and ethylene vinyl acetate (EVA), which are one kind of polyolefin, have moisture resistance, gas permeability, and chemical resistance. Things.

The lead terminal 7 is made of a metal plate of aluminum, silver, platinum, gold or the like having a thickness of 0.1 to 1.0 mm from the viewpoints of strength, resistance value reduction, and sealing property of the sealing member. Further, in order to form the above-mentioned tapered portion on the lead terminal 7, both ends of the plate-like lead terminal are polished with a polishing plate, a lap plate, a file, or the like, or cut out using a canner, a knife, or the like. It can be easily manufactured.

Although the electric double layer capacitor has been described with reference to FIG. 1, the present invention is not limited to this. For example, a lithium battery, a nickel hydride battery and the like can be suitably used as described above. This is particularly effective for an electric double layer capacitor in which the characteristics of the capacitor greatly change due to the sealing property.

[0029]

EXAMPLE 100 parts by weight of polytetrafluoroethylene (PTFE) was added to 100 parts by weight of activated carbon, and the mixed powder obtained by mixing was roll-formed to prepare a 150-μm-thick sheet, which was formed into a sheet of 100 mm × 100 mm. A cut activated carbonaceous structure was produced. In addition, one made of pulp
02 mm × 102 mm × 50 μm thick sheet-like separator, and 100 mm × 100 mm × 30 μm thick
Then, a current collector made of aluminum foil having a band-shaped terminal portion having a width of 30 mm at one end thereof was prepared.

After drying these constituent members in a vacuum atmosphere, a cell 29 is formed under a non-oxidizing atmosphere by using a current collector-polarizable electrode-separator-polarizable electrode (current collector) as one unit cell. A cell laminate in which the layers were laminated was produced. In addition, the current collector is disposed on both end surfaces of the cell stack, and the cell stack has 30 current collectors, 58 polarizable electrodes,
The separator is composed of 29 separators, and the terminals of the current collector project from the same side surface of the cell stack, and the adjacent terminals are alternately arranged at opposite corners. did.

An aluminum plate having a thickness of 1.0 mm was cut into a width of 30 mm × 70 mm, and both ends in the width direction were polished with a polishing plate to produce two lead terminals having a cross section shown in Table 1. . A polypropylene coating was formed on the outer periphery of the lead terminal located at the sealing (opening) portion.

Next, the current collectors (having the same polarity) located at the same corner protruding from the outer peripheral surface of the cell laminate are connected to the lead terminals by ultrasonic welding, respectively. After that, the lead terminal was inserted into the outer bag of the laminated film.

Then, a non-aqueous electrolytic solution composed of a propylene carbonate (PC) solution of 1 mol / l of tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) is injected to impregnate the polarizable electrode and the separator with the electrolytic solution. After that, with the lead terminals protruding outside from the opening of the sealing member, the opening of the sealing member was sealed by thermocompression bonding.

With respect to the obtained 100 electric double layer capacitors, the number of leaks from the lead terminals was determined, and the yield (%) was calculated. In addition, 1 kHz, 50
The impedance was measured at A, and the internal resistance was calculated. Further, charging and discharging were performed at 70 ° C. and 2.5 V at a current of 50 A for 50 hours, and the charging and discharging were performed for 1000 hours.
The rate of change of the capacitance before and after the continuous time was measured. The results are shown in Table 1.

[0035]

[Table 1]

From Table 1, it is found that Sample No. having no tapered portion in the cross section of the lead terminal. In No. 1, the sealing property was poor, and liquid leakage occurred from the sealing (opening) portion of the sealing member, resulting in a low yield. In addition, the sample N which does not form a rectangular portion in the center portion
o. Sample No. 10 and Sample No. 10 having a circular cross-sectional shape. 12
In this case, the weldability between the lead terminal and the terminal portion of the current collector decreased, and the internal resistance of the electric double layer capacitor increased.

On the other hand, in accordance with the present invention, a sample No. having a lead terminal in which the central region in the cross section at the sealing (opening) portion is substantially rectangular and the end portion is tapered. . In the cases of 2 to 9 and 11, the yield is 85% or more, the internal resistance is 2.5 mΩ or less,
The rate of change (decrease) in capacitance after time was 10% or less, and had excellent characteristics. Among them, the ratio of the total width of the lead terminals rectangular section of a width of the lead terminal for _{(w 1) (w 2)} (w 2 / w 1) is 0.4 to 0.9, of the lead terminal Surface roughness (Ra) of 0.1 to 10
Sample No. 0 μm. For 2, 4 to 6, 8, and 11, the yield was 87% or more and the internal resistance was 2.3 mΩ or less.
It had excellent characteristics in which the rate of change (decrease) in capacitance after 00 hours was 10% or less.

[0038]

As described above in detail, in the electrochemical device of the present invention, the shape of the lead terminal is such that the center region in the cross section at the sealing (opening) portion of the lead terminal is substantially rectangular, and By making the portion tapered, it is possible to stably maintain a good adhesion state without any gap even when the lead terminal is sandwiched, and to improve the reliability of electrical connection with the current collector. It becomes a high electrochemical element.

The ratio (w ₂ / w ₁ ) of the width (w ₂ ) of the central region to the entire width (w ₁ ) of the lead terminal is set to 0.4 to 0.9, Surface roughness (R
By setting a) to 0.1 to 100 μm, the sealing property of the sealing member and the weldability between the lead terminal and the terminal portion of the current collector are further improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of an electric double-layer capacitor which is a preferred example of an electrochemical device of the present invention.

FIG. 2 is a plan view of the electric double layer capacitor of FIG.

3 is an enlarged view of a main part of a sealing (opening) portion of a sealing member of the electric double layer capacitor of FIG. 1;

FIG. 4 is a schematic diagram for explaining a cross-sectional shape of a lead terminal of the electrochemical device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electric double layer capacitor 2 ... Polarizable electrode 3 ... Separator 4 ... Current collector 4a ... Terminal part 5 ... Cell laminated body 6 ... Sealing member 6a ... Sealing (Opening) 7: Lead terminal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Shimazu 1-4-4 Yamashitacho, Kokubu-shi, Kagoshima F-term in Kyocera Research Institute 5H022 AA09 BB11 CC03 EE01 EE03 EE04

Claims (3)

[Claims] 1. A bag comprising at least one set of a cell laminate in which a sheet-like current collector having a terminal portion at an end is laminated on each surface of a pair of sheet-like electrodes laminated with a sheet-like separator interposed therebetween. While housed in a body-shaped sealing member,
A lead element is welded to a terminal part of the current collector, and the lead terminal is projected from the opening of the sealing member to the outside to seal the opening of the sealing member. An electrochemical device wherein a cross-sectional shape of the lead terminal at the opening is substantially rectangular in a central region and tapered at an end. _2. The ratio (w ₂ / w) of the width (w ₂ ) of the rectangular portion of the lead terminal to the entire width (w ₁ ) of the lead terminal.
_{2. The method according} to claim 1, wherein ₁ ) is 0.4 to 0.9.
An electrochemical device according to claim 1. 3. A lead terminal having a surface roughness (Ra) of 0.5.
The electrochemical device according to claim 1, wherein the thickness is 1 to 100 μm.