JPH11274005A - Electric double layer capacitor - Google Patents

Abstract

[PROBLEMS] To provide an electric double layer capacitor having a low internal resistance, a large capacity per unit volume, and excellent voltage holding properties. In a non-aqueous electric double layer capacitor in which a separator is disposed between a positive electrode and a negative electrode made of a carbonaceous electrode, a sheet having a thickness of 10 to 80 μm and a porosity of 50 to 85% is used as the separator. And a spacer made of a net-like material having an opening ratio of 30 to 80% and an opening of 100 to 350 mesh.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electric double layer capacitor having a high output, a high energy density and an excellent voltage holding property.

[0002]

2. Description of the Related Art Conventionally, as a separator disposed between a positive electrode and a negative electrode of an electric double layer capacitor, a polyethylene nonwoven fabric, a polypropylene nonwoven fabric, a polyester nonwoven fabric,
Kraft paper, rayon fiber and sisal fiber mixed sheet, manila hemp sheet, glass fiber sheet and the like are known (JP-A-9-45586, JP-A-1-304719).
etc). The role of the separator is to electrically insulate between the positive electrode and the negative electrode, while facilitating the movement of ions in the electrolyte caused by charging and discharging.

In recent years, an electric double layer capacitor for charging and discharging a large current has been receiving attention. However, organic fiber-based separators such as polyethylene have low liquid absorption and retention properties of the electrolytic solution, and therefore have low ionic conductivity and high internal resistance of the electric double layer capacitor. Therefore, when an instantaneous large current discharge, which is one of the great characteristics of the electric double layer capacitor, is performed, the voltage drop is large and is not practical.

A conventional paper separator is excellent in heat resistance and tensile strength. Therefore, it is not suitable for an electric double layer capacitor used for a power supply which does not discharge a large current, such as a hybrid power supply with a solar cell. May be valid. However, when a conventional paper separator is used for an electric double layer capacitor in which the electrolyte for charging and discharging a large current is non-aqueous, the ion permeability is insufficient.

[0005]

In an electric double layer capacitor for charging / discharging a large current, it is desired to reduce the resistance and increase the capacity per unit volume (hereinafter referred to as capacity density). There is a need to. At the same time, the separator needs to have a high porosity from the viewpoint of the liquid absorbing property and liquid retaining property of the electrolytic solution. However, if the separator made of paper having a high porosity is made thin, the insulation between the positive electrode and the negative electrode becomes insufficient, resulting in micro-short-circuit, self-discharge, or a decrease in the production yield of the capacitor. There is.

Further, for example, when a plurality of electrodes are laminated with a separator interposed therebetween, or two electrodes are wound with a separator interposed therebetween, and an element in which the electrodes and the separator are closely stacked is impregnated with an electrolyte, for example, 100 μm In a separator made of paper having the following thickness, there is a limit in increasing the porosity, so that it takes time to inject the electrolytic solution, and there is a problem in productivity.

Accordingly, the present invention provides a separator having excellent heat resistance and ion permeability, excellent liquid absorbing properties and liquid retaining properties, and having a low strength and a high insulating property by using a separator which is thin but has high strength and excellent insulating properties. An object of the present invention is to provide an electric double layer capacitor having a high capacity density with high productivity.

[0008]

According to the present invention, there is provided an electric double layer formed by forming a device by disposing a separator between a positive electrode comprising a carbonaceous electrode and a negative electrode, and impregnating the device with a non-aqueous electrolyte. In the capacitor, the separator has a thickness of 10
Sheet having a thickness of 1 to 80 μm and a porosity of 50 to 85%
0-80 μm, aperture ratio 30-80%, and aperture 50-
Provided is an electric double-layer capacitor, wherein a spacer formed of a net-like material of 350 mesh is overlapped.

The present invention also provides an electric double layer capacitor comprising a separator formed between a positive electrode comprising a carbonaceous electrode and a negative electrode, forming an element, and impregnating the element with a non-aqueous electrolyte. The separator has a thickness of 10 to 80 μm
And a sheet having a porosity of 50 to 85% and a particle size of 0.1 to 20.
10-80 μm in thickness composed of μm particles and a porosity of 50
Provided is an electric double layer capacitor characterized by stacking a spacer consisting of 〜80% of layers.

In the present invention, the thickness of the sheet is from 10 to 80.
μm. If the thickness is less than 10 μm, the strength is weak and handling is difficult. If the thickness exceeds 80 μm, when the separator is formed by overlapping the spacer, the ratio of the volume occupied by the separator in the electric double layer capacitor element becomes high, and the capacity density of the electric double layer capacitor cannot be sufficiently increased.
Preferably, the thickness of the sheet is between 20 and 60 μm.

In the present invention, the porosity of the sheet is 50 to 8
5%. If it is less than 50%, the liquid absorbing property and the liquid retaining property of the electrolytic solution are insufficient, and the ion permeability is insufficient. 8
If it exceeds 5%, the strength of the sheet is weak and handling is difficult. In particular, 60 to 80% is preferable. Further, it is preferable that the sheet in the present invention is not substantially opened. If the sheet has pinholes, micro-shorts may occur, so it is preferable that the sheets have as few pinholes as possible.

The sheet in the present invention is preferably made of a nonwoven fabric or a porous film made of polypropylene, polyethylene or polytetrafluoroethylene, or a cellulose paper. Particularly, cellulose paper is preferable because a sheet having high strength can be obtained even if the thickness is small and the porosity is high.

When using cellulose paper, it is preferable that the density is 0.30 to 0.55 g / cm ³ because the electrolyte absorbs and retains the electrolyte. Especially 0.35-
The range is preferably 0.50 g / cm ³ .

[0014] Porosity 5 with sufficient liquid absorption and liquid retention of electrolyte
The high porosity sheet of 0 to 85% has a thickness of, for example, 100 μm.
If it is less than m, the capacity density of the electric double layer capacitor can be increased, but it is easy to have pinholes. Therefore, when one sheet is used as the separator of the electric double layer capacitor, a short circuit may occur due to the pinhole, and self-discharge is likely to occur.

On the other hand, in the present invention, since the separator is formed by laminating the sheet and the spacer, the electrolytic solution is held on both the sheet and the spacer. Even if a sheet having a high density is used, the liquid can be sufficiently retained. The higher the density, the lower the probability that the sheet will have pinholes. Also, even if the sheet has pinholes, the presence of the spacer allows the distance between the opposing electrodes to be increased through the separator, so that self-discharge hardly occurs and the production yield of the electric double layer capacitor is increased. Can be

Further, since the spacer in the present invention is composed of a layer of net-like material or particles having a high porosity with a high aperture ratio and a large opening compared to a sheet, it is necessary to manufacture a high-capacity electric double layer capacitor. For example, when a plurality of electrodes are stacked via a separator or two electrodes are wound via a separator, and the electrode and the separator are closely stacked to impregnate the element with the electrolyte, the electrolyte is injected. In a short time, and the productivity of the electric double layer capacitor can be increased. That is, in the case of a separator having the same thickness, the separator including the sheet and the spacer is less likely to self-discharge than the sheet including the single sheet,
In addition, it is excellent in liquid absorption and liquid retention, and can increase the productivity of a high capacity electric double layer capacitor. Here, the aperture ratio indicates a ratio of a penetrating void.

Although the above sheet may be used alone,
A separator may be formed by stacking a plurality of the above sheets on a spacer. In this case, the thickness of the separator is increased, which is disadvantageous in terms of the capacity density of the electric double layer capacitor, but the retention of the electrolyte is enhanced, and sufficient insulation can be achieved even if the sheet or spacer is thin. Further, the sheet and the spacer may be used by being joined via an adhesive.

In the present invention, when cellulose paper is used as the sheet, papermaking made of rayon fiber,
Any mixed paper of cellulose and glass fiber can be used. In particular, fibers obtained by beating regenerated cellulose fibers are 50
It is preferable that the paper is a paper made by containing at least 10% by weight. Here, the regenerated cellulose fiber used as a raw material is a regenerated cellulose fiber such as a regenerated cellulose fiber having a high degree of polymerization or a solvent-spun rayon, which can be beaten by a beater installed in a usual papermaking process.

[0019] The regenerated cellulose fibers that can be beaten are uniformly fibrillated by beating treatment, and the flexibility is increased. Therefore, paper made by containing this fiber in an amount of 50% by weight or more has excellent tensile strength. In addition, since the fibers that have been beaten and fibrillated are extremely dense and the cross section of the fibrils is almost a perfect circle, if a paper made containing 50% by weight or more of these fibers is used as a separator, ion-permeability will increase. Excellent resistance and low resistance. The fiber obtained by beating the regenerated cellulose fiber is more preferably at least 65% by weight, even more preferably at least 80% by weight. The degree of beating is from Canadian standard freeness (hereinafter referred to as CSF value) specified in JIS-P8121 from 0 to 6.
It is preferred to beat until the volume reaches 00 ml.

Other materials to be added to the beaten regenerated cellulose fiber are not particularly limited, and fibers such as manila hemp, sisal hemp, kraft pulp and the like can be used. Further, it is preferable that these materials are beaten in accordance with the degree of beating of the regenerated cellulose fiber.

The net-like material in the present invention has a thickness of 10
６０60 μm, opening ratio 30-85%, and opening 50
３５０350 mesh. It is preferable that the aperture ratio is high in order to increase the liquid absorption of the electrolyte solution of the separator without inhibiting the ion conductivity, and it is preferable that the aperture ratio is low and the aperture is small in order to sufficiently insulate between the electrodes. The above range is selected. The net-like object more preferably has an opening ratio of 40 to 70%, and further preferably has an opening of 120 to 300 mesh. Here, the aperture means the number of meshes per inch.

When the thickness of the net-like object exceeds 60 μm, the capacitance density of the electric double layer capacitor decreases,
If it is less than 10 μm, the distance between the electrodes will be insufficient and micro short-circuiting will occur, or the strength of the net-like material will be weakened, making it difficult to handle the electric double layer capacitor during manufacture. In particular, 20 to 50 μm is preferable.

The net-like material in the present invention is preferably a net composed of fibers. For example, a punched film may be used instead of a net. In this case, the number of holes per inch generated by punching corresponds to the aperture in the present invention.

The fiber constituting the net is not particularly limited as long as it has a high tensile strength and a high stability to an electrolytic solution. In an electric double layer capacitor using a non-aqueous electrolyte, it is preferable to perform a drying treatment at a high temperature in order to sufficiently remove moisture in the capacitor element. Therefore, the net is preferably made of a material having high heat resistance. In order to efficiently remove water by heating and drying, a material having a heat resistance temperature of 150 ° C. or higher, particularly 200 ° C. or higher is preferable. Examples of such heat-resistant fibers include fluorinated polyolefins such as polyester, polyimide, and polytetrafluoroethylene, and polyparaphenylene sulfide.

The fibers constituting the net may be monofilaments or multifilaments, but monofilaments are preferred for reducing the thickness of the separator. The net is usually formed by weaving the fibers in a plain weave, but in order to reduce the thickness of the spacer, the smaller the fiber diameter of the fiber is, the more preferable it is in consideration of the strength of the spacer.
0 to 60 μm is preferred.

In the present invention, instead of the net-like material, a spacer composed of a layer having a thickness of 10 to 80 μm and having a porosity of 50 to 80% can be used instead of the net-like material. . In this case, the spacer may be a sheet-like spacer in which the particles are formed, or may be a coating film formed by dispersing the particles in a solvent, applying the particles to the sheet, and drying.

The particles are not particularly limited as long as they have high stability to an electrolytic solution, but preferably have heat resistance like a net-like material.
Examples include inorganic particles such as alumina and organic particles such as polytetrafluoroethylene.

Since the electric double layer capacitor of the present invention has a non-aqueous electrolyte, it is necessary to remove as much moisture in the electric double layer capacitor element as possible in order to reduce the leakage current and ensure a high withstand voltage. is there. The water content in the separator is preferably 1% by weight or less. For example, in the case of cellulose paper, the water content is usually 3 to 10% by weight.

In order to efficiently remove water, before the separator is placed between the positive electrode and the negative electrode, 90
It is preferred to heat at a temperature of at least ° C. Particularly, in order to obtain a large-capacity electric double layer capacitor, a cylindrical type in which a pair of long electrodes are wound through a separator and impregnated with an electrolytic solution in an electrolytic solution and housed in a bottomed cylindrical container, Alternatively, in the case where a device formed by alternately laminating a plurality of positive electrodes and negative electrodes with a separator interposed therebetween is impregnated with an electrolytic solution and formed into a rectangular container or the like and housed in a rectangular container, the element is formed by the electrodes and the separator. After that, it takes a long time to remove water.

If the heat treatment temperature is lower than 90 ° C., the removal of water from the separator becomes insufficient, and the effect of reducing leakage current and the like is reduced. If the temperature is too high, the sheets or spacers constituting the separator are thermally decomposed, and the heat treatment temperature is determined in consideration of their heat resistant temperature. For example, when a cellulose paper is used as a sheet, if the heat treatment temperature exceeds 250 ° C., thermal decomposition of the cellulose paper itself starts to decrease the strength or generate moisture. The heat treatment time is appropriately selected depending on the relationship with the heat treatment temperature, but is usually 3 seconds or more.

As a method of the heat treatment, a method such as contact with a heated heater, infrared irradiation, and heated air is appropriately selected. For example, the sheet or net-like material used in the present invention is usually obtained in a wound state, but in the wound state, it is difficult to effectively dehydrate in a short time by heating. Heating in a state where the layers are not closely stacked is preferable because dehydration can be effectively performed. Specifically, for example, a sheet roll and a net roll are heated in a dry atmosphere while being spread, and the sheet and the net roll are successively stacked and rewound to obtain 1 sheet.
Making two separator rolls, or cutting multiple sheets and net-like materials from sheet rolls and net-like rolls in advance, such as heat-resistant so that the sheets do not overlap tightly Dehydration may be performed by heating through a conductive spacer network.

In the electric double layer capacitor of the present invention, both the positive electrode and the negative electrode are carbonaceous electrodes mainly composed of a carbon material, and charge is stored in the electric double layer formed at the interface between the electrode and the electrolyte. The principle is to do. In order to increase the capacity of the electric double layer capacitor, the carbon material preferably has a large specific surface area, and the carbonaceous electrode has a specific surface area of 700.
It is preferable that the carbon material comprises up to 2500 m ² / g and an organic binder.

Activated carbon, carbon black, polyacene and the like can be used as the carbon material. A conductive material may be added to the carbonaceous electrode as needed to increase conductivity,
An organic binder is added to form a sheet on a metal current collector to form an electrode unit integrated with the current collector. As the organic binder used here, polyvinylidene fluoride,
Polytetrafluoroethylene, a polyimide resin, a polyamideimide resin and the like are preferable. Further, as the metal current collector, a foil, a net, or the like of aluminum, stainless steel, or the like can be used. Aluminum is particularly preferred because it is lightweight and has low resistance.

The electrolytic solution used for the electric double layer capacitor includes an aqueous electrolytic solution and a non-aqueous electrolytic solution. The withstand voltage is about 0.8 V in an aqueous system and about 2.5 V in a non-aqueous system. Since the electrostatic energy of the electric double layer capacitor is proportional to the square of the withstand voltage, it is preferable to use a non-aqueous electrolyte because the use of a non-aqueous electrolyte can increase the energy by about 9 times from the viewpoint of energy density.

As the solute of the non-aqueous electrolyte of the electric double layer capacitor of the present invention, R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ²
A quaternary onium cation represented by R ³ R ⁴ P ⁺ (wherein R ¹ , R ² , R ³ and R ⁴ are each independently an alkyl group having 1 to 6 carbon atoms), BF ₄ ⁻ , PF ₆ ^- , CF ₃ SO
_{^{3 -, AsF 6 -, N}} (SO 2 CF 3) 2 -, ClO 4 - are preferable mixed one kind or two or more of the salt comprising an anion such as.

Examples of the organic solvent used for the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, chain carbonates such as dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate, sulfolane and sulfolane derivatives. Are preferred. In particular, at least one selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, sulfolane and methyl sulfolane is preferable.

As the shape of the electric double layer capacitor of the present invention, a pair of long electrode bodies are wound through a long separator and impregnated with a non-aqueous electrolytic solution to form a bottomed cylindrical case. A plurality of cylindrical and rectangular electrode bodies housed therein are alternately stacked as a positive electrode body and a negative electrode body via a separator, impregnated with a non-aqueous electrolyte, and housed in a bottomed square case. Is preferable since a large capacity can be obtained.

[0038]

EXAMPLES Example 1 Solvent-spun rayon having a CSF value of 20
The mixture was beaten to a volume of 0.4 ml, and a cellulose paper having a thickness of 40 μm and a density of 0.40 g / cm ³ was formed using this. The breaking strength was 0.70 kg / cm width and the porosity was 72%.

An aperture of 250 mesh made of polyester monofilament having a fiber diameter of 30 μm, a thickness of 47 μm,
A polyester net having an opening ratio of 50% was overlaid on the above-mentioned cellulose paper, and this was punched into a rectangular shape having a width of 6.6 cm and a length of 13.6 cm to obtain a separator.

80% by weight of high-purity activated carbon powder having a specific surface area of 1800 m ² / g, 10% by weight of carbon black as a conductive material, and 10% by weight of polytetrafluoroethylene as a binder
The mixture consisting of 100% by weight was kneaded while dropping ethanol, and roll-rolled to prepare a sheet electrode having a thickness of 140 μm. This was dried at 200 ° C. for 30 minutes to remove ethanol, and then bonded to both sides of a 6-cm-wide and 13-cm-long portion of a 40-μm-thick aluminum foil current collector having a lead-out portion using a conductive adhesive. Then, the resultant was roll-pressed to produce an electrode integrated with the current collector having a thickness of 330 μm, thereby obtaining a positive electrode and a negative electrode.

The eighteen positive electrodes and the eighteen negative electrodes were alternately laminated with the separator interposed therebetween to obtain a laminated element. This element is housed in a bottomed rectangular aluminum case having a height of 15 cm, a width of 7 cm, and a thickness of 2.2 cm, and is provided with a positive electrode terminal and a negative electrode terminal which are attached in an insulating and airtight manner to an aluminum top lid having a liquid injection hole. After the leads were combined and ultrasonically welded, the upper lid was fitted into the square case opening, and the periphery was sealed by laser welding.

Next, with the injection hole in the upper lid opened, 200
After vacuum drying at 24 ° C. for 24 hours, a solution obtained by dissolving 1.5 mol / l of triethylmonomethylammonium tetrafluoroborate in propylene carbonate was used as an electrolyte, and the element was vacuum-impregnated through the injection hole and then injected. The hole was filled with a safety valve and hermetically sealed to obtain an electric double layer capacitor cell.

Using the above electric double layer capacitor cell,
After charging at a constant voltage of 2.5 V for 30 minutes, the battery was discharged at a constant current of 300 mA to 1.0 V, and the capacity was determined from the slope of a discharge curve from 2.5 V to 1.0 V. The internal resistance was calculated from the voltage drop at the beginning of discharge. 2.5V
After charging for 12 hours with a constant voltage at
The holding voltage after time was measured.

Further, the time from the completion of vacuum impregnation of the electrolytic solution into the element to the time when the electric double layer capacitor cell becomes the above-mentioned capacity and becomes constant was measured, and this was defined as the electrolytic solution impregnation time. Table 1 shows the results.

Example 2 (Comparative Example) An electric double layer was formed in the same manner as in Example 1 except that the separator was composed of one piece of the cellulose paper used in Example 1 and the number of electrode bodies was 23 for both the positive electrode and the negative electrode. A capacitor cell was manufactured. Using this cell,
Evaluation was performed in the same manner as in Example 1. Table 1 shows the results.

Example 3 (Comparative Example) An electric double layer capacitor cell was produced in the same manner as in Example 1 except that the separator was composed of the two cellulose papers used in Example 1. This cell was evaluated in the same manner as in Example 1. Table 1 shows the results.

[0047]

[Table 1]

[0048]

According to the present invention, an electric double layer capacitor having low internal resistance, low self-discharge, excellent voltage holding properties, and high capacitance density can be obtained. Further, even if the electric double layer capacitor of the present invention has a structure in which electrodes and separators are stacked and arranged at high density, it is excellent in liquid absorbing property of an electrolytic solution at the time of manufacturing, so that productivity is high. .

Further, since the separator of the present invention has high strength, it has sufficient strength for winding.
A wound electric double layer capacitor can also be easily manufactured. The electric double layer capacitor according to the present invention particularly has a discharge capacity of 5
It is suitable for wound type and laminated electric double layer capacitors for large capacity and large current of 0 to 20000F or discharge current of 1 to 1000A.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Narimaki Tomita 1150 Hazawacho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture Inside Asahi Glass Co., Ltd. (72) Inventor Naoki Yoshida 1150 Hazawacho, Kanagawa-ku, Yokohama-shi, Kanagawa Asahi Glass Co., Ltd (72) Inventor Yoshiaki Higuchi Asahi Glass Co., Ltd., 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa

Claims (5)

[Claims] 1. An electric double-layer capacitor in which a separator is disposed between a positive electrode and a negative electrode comprising a carbonaceous electrode to form an element, and the element is impregnated with a non-aqueous electrolytic solution. 10-80 μm and porosity 50-
85% sheet, 10-80 μm thickness and 30 aperture ratio
An electric double layer capacitor characterized by stacking a spacer made of a net-like material having a mesh size of about 80% and a mesh size of 50 to 350 mesh. 2. An electric double layer capacitor in which a separator is arranged between a positive electrode and a negative electrode comprising a carbonaceous electrode to form an element, and the element is impregnated with a non-aqueous electrolytic solution. 10-80 μm and porosity 50-
An electric double layer capacitor comprising an 85% sheet and a spacer formed of a layer having a particle size of 0.1 to 20 μm and a thickness of 10 to 80 μm and a porosity of 50 to 80%. 3. The electric double layer capacitor according to claim 1, wherein said sheet is made of cellulose paper. 4. The electric double layer capacitor according to claim 3, wherein said cellulose paper is a paper made by containing at least 50% by weight of fibers obtained by beating regenerated cellulose fibers. 5. The carbonaceous electrode has a specific surface area of 700 to 2500 m.
² / g of a carbon material and an organic binder, and the solute of the electrolytic solution is R ¹ R ² R ³ R ⁴ N ⁺ or R ¹ R ² R ³ R ⁴ P ⁺
(Wherein R ¹ , R ² , R ³ , and R ⁴ are each independently an alkyl group having 1 to 6 carbon atoms), and BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ^-, As
A salt comprising an anion of F ₆ ⁻ , N (SO ₂ CF ₃ ) ₂ ^— or ClO ₄ ⁻ , wherein the solvent of the electrolyte is propylene carbonate, ethylene carbonate, dimethyl carbonate,
5. The electric double layer capacitor according to claim 1, wherein the electric double layer capacitor is at least one selected from the group consisting of diethyl carbonate, methyl ethyl carbonate, sulfolane and methyl sulfolane.