JPH01283811A - Electric double-layer capacitor - Google Patents

Abstract

PURPOSE:To seek to reduce equivalent serial resistance and leakage current by putting a separator which contains floss silk at a part between electrodes. CONSTITUTION:Floss silk mixed paper 40mum in thickness consisting of, e.g., floss silk 70wt.% and Manila hemp fiber 30wt%, floss silk mixed paper 100mum in thickness consisting of floss silk fiber 70wt.% and polypropylene resin fiber 30wt.%, or the like is used as a separator 5. For floss silk, since the size of the fiber is thin at 1/2-1/100 of Manila hemp and bending of the fiber is complicated and further the size is ununiform, holding amount of electrolyte is improved by cutting, beat unravelling, papering work, etc., and the electric resistance value can be decreased. Also, separator consisting of woven fabric containing floss silk or nonwoven fabric is thin yet strong and close, therefore leakage currents are small and voltage maintaining characteristics become excellent. Hereby, leakage currents and equivalent serial resistance can be reduced.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, and in particular an electric double layer capacitor that uses an electric double layer formed at the interface between a polarizable electrode and an electrolyte. This relates to multilayer capacitors.

[Prior art] Electric double layer capacitors utilize an electric double layer formed at the interface between a polarizable electrode made of graphite, carbon black, activated carbon, etc. and an electrolyte. Separators are used for insulation and isolation and to hold the electrolyte. As a separator,
Electrolytic paper, polyethylene nonwoven fabric, polypropylene nonwoven fabric,
It is known to use porous paper made by mixing polyester nonwoven fabric or a mixture thereof with glass fibers having a diameter smaller than that of these fibers.

[Problems to be Solved by the Invention] A separator is formed by punching out a sheet-like material, but especially in the case of a separator made of a large amount of glass fiber (20 to 60%), the sheet-like material naturally contains glass. Due to the presence of fibers, the punching die for the separator is subject to severe wear, resulting in increased costs due to die replacement.

It is also known to use vegetable fiber paper such as kraft paper or Manila hemp paper as a separator, but this has the disadvantage that the leakage current of the electric double layer capacitor is large. Increasing the thickness of the separator reduces leakage current, but increases equal series resistance, which is not desirable.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides an electric double layer capacitor having a separator containing cotton.

The raw material for cotton cotton is cocoon, and the thickness of the fibers is as thin as 1/2 to 1/100 of Manila hemp, and the fibers have complicated bends and are uneven in thickness, making it difficult to cut, beat, and make paper. As a result, even when cotton is used alone, the amount of electrolyte retained can be improved, and since it is dense, the electrical resistance value when soaked with electrolyte can be reduced. In addition, when making mixed paper by incorporating vegetable fibers such as manila hemp and kraft in order to strengthen the mechanical strength, the cotton fibers are tightly entangled in the gaps between the thick fibers of manila hemp and kraft, and the very thin gaps are , the withstand voltage of the separator, which is electrolytic paper, is improved.

The separator according to the present invention is made of pure cotton fiber,
It is made of a mixture of other vegetable fibers, synthetic resin fibers, glass fibers, or mixed fibers thereof.

The separator according to the present invention, which is made of a woven or nonwoven fabric containing cotton, has high strength and is dense even if it is thin. Therefore, an electric double layer capacitor using such a separator has a small leakage current and a high chargeability. The voltage holding characteristic, which indicates the degree of voltage maintenance after being left unloaded, becomes good.

Furthermore, since the separator has good electrolyte retention properties, the reliability of the electric double layer capacitor is improved.

Further, the separator according to the present invention can be applied to a disk-shaped or wound-type electric double layer capacitor, and can be used either as a single sheet or as a stack of a plurality of sheets.

There are the following three types of electric double layer capacitors using the separator according to the present invention. The first type of electric double layer capacitor has a polarizable electrode formed on a current collector made of expanded metal, a separator is interposed between the current collector on which the other polarizable electrode is formed, and this is wound. It is then rotated, impregnated with electrolyte, and assembled together with a sealing body in a cylindrical case. The second type of electric double layer capacitor has a separator between a polarizable electrode formed inside an exterior metal case that also serves as a current collector and another polarizable electrode formed inside an exterior metal cap that also serves as a current collector. is impregnated with a non-aqueous electrolyte, and the metal case and metal cap are integrally caulked with an insulating gasket interposed. The third type of electric double layer capacitor consists of a carbon paste electrode made of powdered activated carbon and an electrolyte formed inside a conductive current collector that is electronically conductive and ion-impermeable, and the other conductive current collector. A separator is interposed between the electric body and the carbon paste electrode formed inside the electric body, and the surrounding area is integrated with an insulating gasket.

Examples of the nonaqueous electrolyte used in the second type of electric double layer capacitor include perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid, bar alkylsulfonic acid, and trifluoromethanesulfonic acid. Solutes such as tetraalkyl ammonium salts, tetraalkylphosphonium salts, or amine salts are combined with propylene carbonate, γ-butyrolactone, acetonitrile, dimethylformamide, 1
．． Examples include those dissolved in polar solvents such as 2-dimethoxyethane, sulfolane, and nitromethone at a concentration of about 0.3 to 1.5 M/12.

The aqueous electrolyte used in the third type of electric double layer capacitor is an inorganic acid with high electrical conductivity,
Alternatively, those using an inorganic salt as a solute are preferable. As the solute (electrolyte) of such an electrolytic solution, for example, acids such as sulfuric acid, tetrafluoroboric acid, and nitric acid, and chlorides such as potassium chloride, sodium chloride, calcium chloride, and ammonium chloride are preferably used. Among these electrolytes, [acid, boric acid tetrafluoride] is particularly preferable because it provides high conductivity.The concentration of the aqueous electrolyte can be appropriately selected in the range of 10 to 90% by weight. In general, if the concentration is 90% by weight or more, problems such as precipitation of solutes will occur in cold weather, and if the concentration is less than 10% by weight, the conductivity will decrease and the internal resistance of the capacitor will increase, which is undesirable.

As the electrode used in the present invention, activated carbon powder with a large specific surface area, carbon black, activated carbon fiber, etc. can be used, for example, and it is also possible to use as an electrode a paste made by mixing activated carbon powder with an electrolyte. . An electrode with even better volume per unit volume and mechanical strength is polytetrafluoroethylene (hereinafter referred to as PT).
An example of this is an electrode made by forming a sheet of activated carbon powder using a binder with excellent chemical resistance such as FE (abbreviated as FE). For such a sheet-like electrode, first, preferably 1 to 50% by weight, more preferably 5 to 30% by weight of PTFE is mixed with activated carbon fine powder, and the resulting viscous mixture is compressed and extruded. Alternatively, a sheet formed by rolling or a combination of these methods can be suitably used. This sheet-like molded product is further subjected to stretching treatment in one or two axial directions, if necessary.

This stretching treatment is carried out at 20-380°C, preferably at 20-20°C.
At 0°C, the chain length is preferably 1.1 to 5.0 times, particularly preferably 1.2 to 2.0 times, by a known method (for example, JP-A-59-166541). It will be done. The stretched product thus obtained can be used as it is, but if necessary, it can be further rolled or compressed using a roll, press, etc., and then fired or semi-baked before use.

Among the current collectors used in the non-aqueous electrolyte in the present invention,
It is preferable to use an iron-based alloy containing 16 to 35% Cr and 1 to 0 wt% Mo, aluminum or an aluminum clad material. As the aluminum clad material, a clad material of aluminum and 5US304 is preferable in terms of cost. The aluminum surface is placed in contact with the electrolyte or electrode. This current collector may be bonded to the electrode using a conductive adhesive.

[Example J] Examples of the electric double layer capacitor according to the present invention will be described below together with comparative examples with reference to FIG. 1.

(Example 1) 80 wt% activated carbon with a specific surface area of 2000 m''/g
10wt% carbon black and 10% PTFE powder.
The mixture consisting of wt% was formed into a mixed wire roll and the thickness
．． A 6 mm sheet-like electrode was created.

A disk-shaped electrode 1.2 with a diameter of 13 mm is formed from this sheet-shaped electrode.
punched out.

After adhering the disc-shaped electrode 1.2 to each of the stainless steel cap 3 and the stainless steel case 4 via a conductive adhesive (not shown), a disc-shaped electrode 1.2 was dehydrated by vacuum heating and drying. The punched separator 5 is used as the electrode 1
．． A propylene carbonate solution of 1 M tetraethylammonium tetrafluorophosphonate was injected as an electrolytic solution between the electrodes 1.2 and the separator 5, and the electrodes 1.2 and the separator 5 were sufficiently impregnated. Thereafter, the cap 3 and the case 4 are integrated via an insulating gasket 6 made of polypropylene, and the cap 3 and the case 4 are caulked and sealed to form a coin-shaped rated 2.8.
v・2. OF electric double layer capacitor 7 (diameter 20mm
・Thickness: 2 mm)

In this Example 1, cotton fiber 7 is used as the separator 5.
Thickness 40 consisting of 0wt% and Manila hemp fiber 30wt%
A cotton-mixed paper of μm size was used.

(Example 2) 100wt of cotton fiber with a thickness of 40μm as the separator 5
% was used. The rest is the same as in Example 1.

(Example 3) As the separator 5, a 100 μm thick cotton mixed paper made of 70 wt% cotton fibers and 30 wt% polypropylene resin fibers was used. The rest is the same as in Example 1.

(Comparative Example 1) 70wt% polypropylene resin fiber as separator 5
A mixed paper having a thickness of 100 μm and containing 30 wt % of glass fiber and 30 wt % of glass fiber was used. The rest is the same as in Example 1.

(Comparative Example 2) As the separator 5, 00% by weight of polypropylene resin fiber I with a thickness of 1001L11 was used.

The rest is the same as in Example 1.

(Comparative Example 3) As the separator 5, 100 wt % of polypropylene resin fibers with a thickness of 200 μm were used.

The rest is the same as in Example 1.

(Example 4) An electrically conductive and ion-impermeable rubber sheet made of polyolefin containing electrically conductive carbon was placed on an insulating unvulcanized butyl rubber sheet 11 with a thickness of 0.28 mm and a through hole of 5.6 mm in diameter. A current collector sheet 12 with a thickness of 60 μm is bonded, and a paste electrode 13 made of activated carbon powder with an average particle size of 100 μm and a specific surface area of 1400 m”/g and a 30% sulfuric acid aqueous solution is placed inside the current collector sheet 12.
100 cotton fibers with a thickness of 100 μm
A pair of electrode-filled sheets were combined via a wt% separator 14, and a press pressure of 5 Kg/cIm was applied at 120°C.
Vulcanize the butyl rubber sheet by holding it for a period of time,
By punching this, a disk-shaped electric double layer capacitor 15 with a diameter of 10 mm was produced (see FIG. 2). Equivalent series resistance is 2.5Ω, leakage current is 0. It was O12mA.

Next, as electrical characteristics of Examples 1 to 3 and Comparative Examples 1 to 3, equivalent series resistance and leakage current were measured. The results are shown in Table 1. The equivalent series resistance was measured using an IKHz AC bridge.

Table 1 Electrical Characteristics [Effect of the Invention 1 As mentioned above, an electric double layer capacitor using a separator partially containing cotton can reduce the equivalent series resistance and leakage current. It is.

[Brief explanation of the drawing]

1 and 2 are partial cross-sectional views of an electric double layer capacitor according to the present invention. In the figure, 1.2...electrode, 3...-cap, 4...-
Case, 5... Separator, 6... Gasket, 7
... Electric double layer capacitor, 11.12 ... Sheet, 13 ... Paste electrode, 14 ... Separator, 1
5... Electric double layer capacitor. Patent applicant Elna Co., Ltd.

Claims (1)

[Claims] (1) An electric double layer capacitor characterized in that a separator containing at least a portion of cotton cotton is interposed between electrodes.