JPH0239514A - Solid electric double-layer capacitor - Google Patents

Abstract

PURPOSE:To remove internal short circuit and to improve reliability by arranging a separator which bears macromolecular solid electrolyte. CONSTITUTION:A unit cell 1 is formed of a pair of dielectrics 2 and 3 arranged at the outside, a pair of polarizable electrodes 4 and 5 arranged inside the dielectrics 2 and 3, and a separator 6 arranged between the polarizable electrodes 4 and 5. The separator 6 bears alkaline metallic ion conductive solid electrolyte, which is obtained by making crosslinked polymer solidly dissolve alkaline metallic ions, in a nonconductive porous film. For solid electrolyte borne in this nonconductive porous film, polymer electrolyte the same as that used in preparation of the polarizable electrodes 4 and 5 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric double layer capacitor using a solid electrolyte.

[Prior art and its problems] In recent years, electric double layer capacitors using electrolyte have been widely used for memory backup power supplies.

Although this electric double layer capacitor has a risk of leakage, U.S. Pat. No. 4.638.407 and U.S. Pat. .542, etc. This solid electric double layer capacitor also has the advantage that a laminated structure can be easily formed. A solid electric double layer capacitor consists of a current collector layer/a polarizable electrode layer mainly made of carbon containing a solid electrolyte/a solid electrolyte layer/a polarizable electrode layer mainly made of carbon containing a solid electrolyte/a current collector layer. A layered structure consisting of solid electrolytes has been proposed, but solid electrolytes have the disadvantage that they are easily deformed when pressure is applied, and that layered bodies are easily short-circuited when pressurized.

On the other hand, the use of a polymer solid electrolyte as the solid electrolyte is disclosed in U.S. Pat.
．． No. 303.748 and U.S. Patent No. 40654.27
No. 9, etc., but in both cases the electric type conductivity is 1.
Since it is as low as 0-' to 10-"S.cam-', it has the disadvantage that the internal resistance of the capacitor is high.

[Object of the invention] The present invention provides an electric double layer capacitor that prevents internal short circuits, has improved voltage retention, and employs a high performance, high heat resistance, and highly reliable solid polymer electrolyte with low internal resistance. The purpose is to Specifically, internal short circuits are prevented by supporting a solid polymer electrolyte on a non-conductive porous thin film.

[Structure of the Invention] First, a schematic diagram of a unit cell of a solid electric double layer capacitor according to the present invention is shown in FIG. It consists of a pair of polarizable electrodes 4.5 arranged inside the electric body 2.3 and a separator 6 arranged between the polarizable electrodes 4 and 5.

The current collector 2.3 may be made of the same material that is electronically conductive and electrochemically resistant to corrosion, but the current collector 2 on the anode side in particular may be made of a material that does not dissolve even when anodic polarization. A hard metal plate, an electronically conductive polymer carbon sheet, etc. are used. Specific examples of the metal plate of the current collector 2.3 include valve metals such as stainless steel and aluminum, and high molybdenum steel. These metals are preferred because they are more difficult to dissolve than copper, zinc, iron, etc., especially 5US316.
L, high chromium/molybdenum containing steel, and aluminum are particularly preferred.As the high chromium/molybdenum containing steel, C
rO~30%, Mol~10%, and Fe, N
Particularly preferred is one consisting of i, the current collector 2゜3 is reticulated,
Either sheet form can be used.

For the current collector 2.3, a polymer organic-inorganic composite is used in addition to the above-mentioned metals. Polymers include polymer conductors,
An example of the organic-inorganic composite is an electronically conductive elastomer made of graphite particles and rubber.

The polarizable electrode 4.5 is formed from high specific surface area carbon, polymer and alkali metal salt. By forming a solid solution with the polymer, the alkali metal salt becomes an alkali metal ion conductive solid electrolyte. A polymer having a polyether molecular structure is used as the polymer, and a cross-linked polyfunctional polyether structure is particularly preferable because it can increase the electrical conductivity by making it amorphous. Another advantage is that the softening point can be raised to 130 to 170°C, and the operating temperature range of solid electric double layer capacitors can be higher than the upper limit of 70 to 85°C for electric double layer capacitors using electrolytes. be. A solid solution of an alkali metal salt and a polymer impregnates or mixes carbon to form a polarizable electrode, but if there is free halogen and/or moisture in the system, the current collector 2.3 will electrochemically corrode. If a voltage of 1.23 V or more is applied to the unit cell l, gas generation will occur due to water decomposition, so both are undesirable.The water content in the system should be 500 ppm or less, preferably lOOppm or less,'f1 separation. Halogen is 20
It is preferably 0 ppm or less, preferably 50 ppm+ or less.

When a polarizable electrode is formed by impregnating carbon with a solid polymer electrolyte or by cross-connecting it, pores may remain. In such cases, the density of the polarizable electrode can be increased by pressurizing the electrode or adding a small amount of alcohol as a plasticizer to cross-wire the polarizable electrode, lowering the resistance of the electrode and increasing the capacitance. There is also. In addition, a carbon-free polymer solid electrolyte layer of 1 to 50 μm is placed on the polarizable electrode.
If I is provided, the resistance of the electric double layer capacitor may be lowered.

In this polarizable electrode 4.5, in order to develop the capacity of an electric double layer capacitor, it is important that the solid electrolyte sufficiently covers the surface of the carbon and forms a wide solid-solid interface. Due to the viscosity of the polymer, the carbon must have a specific primary and secondary structure to fill the carbon micropores sufficiently, and the molecular weight of the polymer is also too high to fill the bores. The molecular weight of the polyether is 500, which is not preferred because it becomes difficult.
-10,000 is preferred, and 700-4,000 is particularly preferred.

As the polyfunctional polyether structure, polyethylene oxide, polypropylene oxide, or a copolymer of ethylene oxide and propylene oxide is used.

The crosslinked polymer includes the above-mentioned polyfunctional polymer, 4-methyl-1,3-phinynylene diisocyanate, and
It is synthesized by the action of hexamethylene diisocyanate or sebacyl chloride.

Alkali metal salts include LiClO4, NaClO4, LiB
Selected from F4°LiCFx5Os.

The electric type conductivity of conventional solid solutions of polyethylene oxide, polypropylene oxide, and polyfunctional polyether with lithium ions is 10-I' to 1O-10S cm-
', whereas the electrical type conductivity of a solid solution of crosslinked polyfunctional polyether and lithium ions is 10-3 to 1O
-5S-c+a-' and has high characteristics.

Next, the separator 6 according to the present invention is made of a non-conductive porous thin film supporting an alkali metal ion conductive solid electrolyte obtained by dissolving alkali metal ions in a crosslinked polymer.

Non-conductive porous thin film is polypropylene fiber non-woven fabric,
It is made of glass fiber nonwoven fabric, polypropylene-glass fiber mixed paper, porous polypropylene thin film, porous fluorine resin film, etc., and has a thickness of 10 to 200 μι. The porous thin film preferably has a porosity of 60 to 90%.

As the solid electrolyte supported on this non-conductive porous thin film, the same polymer electrolyte as that used to create the polarizable electrode 4.5 described above is used. Further, the amount of polymer solid electrolyte supported on the separator is 30 to 95%, preferably 60 to 90%.

The separator 6 of the present invention has, for example, 100 to 2 glass fibers.
It is obtained by immersing a mixed paper consisting of 0% polypropylene fibers and 0 to 80% polypropylene fibers in a solution consisting of a polyfunctional polymer, a crosslinking agent, an alkali metal salt, and an organic solvent, and crosslinking the mixture by heating. Furthermore, the separator 6 is made by dispersing short glass fibers, polypropylene short fibers, and fluororesin short fibers in a solution consisting of a polyfunctional polymer, a crosslinking agent, an alkali metal salt, and an organic solvent, and then dispersing the solvent after casting. It can also be obtained by removing and heating crosslinking.

Note that the resistance may sometimes be lowered by pressurizing a separator carrying a solid electrolyte or a polarizable electrode and a laminate of this separator.

The current collector 2.3 and the polarizable electrode 4.5 are bonded together by physical pressure bonding or by using a carbon-based adhesive such as AquaTac, Everyohm, Hitazol, or the like. In order to further ensure bonding, it is also effective to chemically or physically roughen the surfaces of current collector 2.3 and/or polarizable electrode 4.5. Furthermore, a metal such as aluminum may be plasma sprayed onto one side of the polarizable electrode 4.5, and this may be welded to the current collector 2.3 to integrate it.

If the desired withstand voltage cannot be obtained with the above-mentioned unit cell l of the electric double layer capacitor, a withstand voltage of 3 to IOV can be obtained by stacking the unit cells l and forming a housing. The shape of the housing is roughly divided into a button cell type shown in FIG. 2, a film cell type shown in FIG. 3, and a cylindrical cell type shown in FIG.

The button self is obtained by incorporating a plurality of stacked unit cells 1 and caulking an exterior metal case 8 and an exterior metal cap 9 via an insulating gasket IO. In this case, it is preferable that the metal case 8 and the metal cap 9 also serve as a current collector located on the outside as shown in the figure. Further, one of the current collectors 2 and 3 of adjacent unit cells 1 may be omitted as shown.

The film cell 11 contains a plurality of unit cells 1 in a single tank 1, and this is assembled into a laminate material 14 consisting of two heat-weldable polymer films 12 and a current collector metal foil 13.
．． 15 and heat sealing the periphery.

The cylindrical cell 16 uses electronically conductive and gas-liquid impermeable carbon-containing rubber for the current collector 2.3 of the unit cell 1, and insulating rubber 17 is used around the side surface of the laminate of the unit cell 1. obtained by coating with This cylindrical cell 16 may be housed in a metal case (not shown), and a metal terminal may be taken out.

[Example] A porous separator with a thickness of 50μ consisting of 30% glass fiber and 70% polypropylene fiber was used as a trifunctional polyether with an ethylene oxide/propylene oxide ratio of 8/2 and a polyether with a molecular weight of 311,500;
It was immersed in a solution consisting of hexamethylene diisocyanate, lithium perchlorate, and dimethylformamide, then pulled out, dried in a nitrogen stream at 80° C., and crosslinked and cured.

On the other hand, the above-mentioned trifunctional polyether, hexamethylene diisocyanate, lithium perchlorate, and dimethylformamide were added to carbon powder with a specific surface of 950 m"/g, and the mixed paste was cast, dried, and thermally crosslinked. A polarizable sheet with a thickness of 200 um was obtained.The conductivity of the solid electrolyte without carbon is 10-'S.c.
5US316L foil with a thickness of 30 μm was used as the m-′ internal current collector. Furthermore, 5US316L with a thickness of 250 μI was used for the metal case and metal cap of the button cell.

Next, the separator sheet obtained as described above was
Punch out 3 sheets of 3+++n, punch out 6 sheets of polarizable electrode sheet with a diameter of 12fffl+, punch out 2 sheets of 5US316L foil with a diameter of 13 mm, and make polarizable electrodes/separators/
Polarizable electrode/current collector/polarizable electrode/separator/polarizable electrode/current collector/polarizable electrode/separator/polarizable electrode are laminated in this order, and this laminate is connected to a metal via an insulating gasket made of polypropylene. Built into the case and metal case,
I got the button cell by coloring. In addition, prior to caulking, the water content in the system was reduced to 50 ppIm or less by vacuum drying at 100° C. for 16 hours. Also,
Free halogen in the solid electrolyte was 5 ppm or less.

Using the button type electric double layer capacitor obtained in this way, a charge/discharge cycle of 5.5μ was repeated 100 times.
No changes were observed. In addition, 1 at room temperature and 5.0
After charging for an hour, I tracked the open circuit voltage and found that after 24 hours it was 4.
．． It was 2v.

A pressure of 10 kg/cs+'' was continuously applied from above and below to this button-type electric double layer capacitor at 80° C. for 5 hours, but no short circuit was observed.

[Effects] According to the present invention described above, since the separator supporting the solid polymer electrolyte is disposed between the polarizable electrodes, it is possible to provide a highly reliable solid electric double layer capacitor without internal short circuits. can.

[Brief explanation of the drawing]

Fig. 1 shows a unit cell of a solid electric double layer capacitor according to the present invention, Fig. 2 shows a button cell of the same, Fig. 3 shows a film cell of the same, and Fig. 4 shows a cylindrical shape of the same. It is a figure showing a cell. In the figure, 1...-unit cell, 2, 3... current collector, 4
．． 5... Polarizable electrode, 6... Separator, 7-...
Button cell, 11... Film cell, 16... Cylindrical cell Figure 1 Figure 3 Figure 4

Claims (7)

[Claims] (1) A solid electric double layer capacitor using a pair of polarizable electrodes made of carbon and a solid polymer electrolyte, characterized in that a separator supporting a solid polymer electrolyte is arranged. (2) The solid electric double layer capacitor according to claim (1), wherein the solid polymer electrolyte has a crosslinked, multifunctional polyether structure in which an alkali metal salt is dissolved. (3) Claim (1) or (2) characterized in that the solid polymer electrolyte is a cross-linked trifunctional ethylene oxide and propylene oxide copolymer and has lithium ions dissolved therein. A solid electric double layer capacitor described in . (4) Claim (1), (2) or (3) characterized in that the water content in the solid polymer electrolyte is 500 ppm or less.
) The solid electric double layer capacitor described in ). (5) Free halogen in the polymer solid electrolyte is 200pp
3. The solid electric double layer capacitor according to claim 1, wherein the solid electric double layer capacitor has a thickness of m or less. (6) The solid electric double layer capacitor according to claim (1), wherein the separator has a thickness of 10 to 200 μm. (7) The solid electric double layer capacitor according to claim (1), wherein the amount of solid polymer electrolyte supported on the separator is 30 to 95%.