JP2003229336A - Electric double-layer capacitor and electrode for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for an electric double-layer capacitor and the electric double-layer capacitor having superior durability with respect to a high-temperature atmosphere and fewer troubles in a handling process. <P>SOLUTION: The electric double-layer capacitor uses a separator made of a polyimide porous film having a nonlinear fine hole and an electrolyte solution and a pair of polarization electrodes as components. The separator for the electric double-layer capacitor has a polyimide porous film as a component. In the polyimide porous film, an average void diameter ranges from 0.01 to 10 μm, a void rate is 20 to 80%, a Gurley value is 50 to 1,000 second/100 ml, a film thickness ranges from 5 to 300 μm, and the non-linear fine hole is provided. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-capacity electric double layer capacitor suitable for a backup power supply for personal computers, a power supply for starting a cell motor, a power supply for automobiles and the like, and more particularly to an electrode for the capacitor. The present invention relates to an electric double layer capacitor having high voltage durability by using a polarized electrode having a pore structure that facilitates ion migration, and an electrode for the capacitor. In this specification, the term "non-linear fine continuous pores" refers to so-called open pores in which pores are continuous from any surface to other surfaces in a passage-like manner, and the surface on which the pores are bent is the opposite surface. Refers to those that are connected to (through holes).

[0002]

2. Description of the Related Art An electric double layer capacitor is a capacitor having a large capacitance of farad order utilizing an electric double layer formed at a boundary between a pair of polarized electrodes and an electrolyte. Since charge / discharge is a physical adsorption / desorption phenomenon of electrolyte ions on the electrode surface, the energy density is smaller than that of a secondary battery using a chemical reaction, but deterioration due to charge / discharge is extremely small. The electrode material in the electric double layer capacitor is required to have high electric conductivity, high corrosion resistance, electrochemical stability, capable of reversibly adsorbing and desorbing ionic species, and free of heavy metal.

Therefore, as the base material of the polarized electrode, generally, a powdered activated carbon is pressed or rolled together with a binder to form a polarized electrode, and a phenol type or a laser type is used. Fibers such as Yong-based, acrylic-based, and pitch-based fibers are subjected to flame resistance and carbonization activation treatment to form activated carbon or activated carbon cord fibers, which are used as polarized electrodes such as felt-like, fibrous, or paper-like. .

However, recently, it has been desired to realize an electric double layer capacitor which has a large withstand voltage and energy density, is excellent in rapid charge / discharge characteristics, and is excellent in charge / discharge cycle durability when a high voltage is applied. Various proposals have been made for the base material of the polarized electrode.

For example, Japanese Patent Application Laid-Open No. 11-297580 describes an activated carbon electrode containing no binder substance having a carbon-fluorine bond. In addition, JP-A-11-
No. 322322 discloses that the total content of elements consisting of alkali metals and alkaline earth metals is 100 ppm or more 20
It is less than 00 ppm and is Li / Li ⁺ in the non-aqueous electrolyte solution.
Potential is 1.5V or more and 2.85V
The following describes an electric double layer capacitor using an electrode containing a carbonaceous substance as a main material. In addition, Japanese Patent Laid-Open No.
In Japanese Patent Laid-Open No. 000-124084, a polarizable electrode containing a specific porous carbon material having a large specific surface area as a main component is used as a positive electrode and has a small specific surface area and a density of 1.8 to 2.2.
It describes an electric double layer capacitor having a high withstand voltage and energy density, which uses a non-polarized electrode having a lithium ion occluded in a carbon material at ³ g / cm ³ as a negative electrode, and has excellent rapid charge / discharge characteristics.

However, any of the electric double layer capacitors
The electrode material of the polarized electrode for use is also obtained by pressure molding of activated carbon powder and thermoplastic resin, and the electrostatic capacity of the polarized electrode is small. As a result of paying attention to the relationship between the specific surface area of the polarized electrode of the electric double layer capacitor and the electrostatic capacity of the electric double layer capacitor, the inventors have found that the larger the specific surface area, the higher the electrostatic capacity. Despite this principle, it was found that the specific surface area and the capacitance per unit volume are not in a proportional relationship in the prior art. This is because even if the electrode material has a high specific surface area, there are many pores that are not used when the ion transfer resistance is high.

[0007]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide an electric double layer capacitor having a large electrostatic capacity by using a polarized electrode which has a smooth ion movement during charge and discharge, and an electrode for the capacitor. Is to provide.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an electric double layer capacitor having a polarizing electrode composed of a porous carbonized film having non-linear fine continuous pores, a separator and an electrolyte solution as constituent elements. The present invention also relates to a polarized electrode composed of a porous carbonized film having non-linear fine continuous pores used in the electric double layer capacitor. further,
This invention has an average pore diameter of 0.01 to 10 μm and a porosity of 2
The present invention relates to a polarized electrode for an electric double layer capacitor, which is composed of a porous carbonized film having non-linear fine continuous pores having a thickness of 0 to 80% and a thickness of 5 to 300 μm.

[0009]

Preferred embodiments of the present invention will be listed below. 1) The electric double layer capacitor as described above, wherein the electrolyte solution is a non-aqueous electrolyte solution. 2) The porous carbonized film has an average pore diameter of 0.01 to 10 μm,
The electric double layer capacitor having a porosity of 20 to 80% and a thickness of 5 to 300 μm. 3) The electric double layer capacitor as described above, wherein the porous carbonized film is a carbonized or graphitized porous heat resistant polymer film having non-linear fine continuous pores. 4) The electric double layer capacitor as described above, wherein the porous carbonized film is obtained by carbonizing or graphitizing a porous heat-resistant polyimide film having non-linear fine continuous pores.

In the electric double layer capacitor of the present invention, it is necessary to use a polarized electrode composed of a porous carbonized film having non-linear fine continuous pores, and the porous carbonized carbon having linear through holes is provided. The film has a small specific surface area and cannot increase the capacitance of the electric double layer capacitor.

The porous carbonized film having the non-linear fine continuous pores is preferably a porous film made of a high heat resistant resin having the non-linear fine continuous pores in an anaerobic atmosphere 800-1800.
At a temperature in the range of 1800 ° C., preferably in the range of 1800-3000 ° C. (and optionally in the range of 3000-3500 ° C.), if necessary under tension or while applying pressure perpendicular to the surface of the porous membrane. It can be obtained by carbonizing. The anaerobic atmosphere in the carbonization, it is necessary that there is no oxidizing gas such as oxygen,
Argon, helium, nitrogen and the like are suitable for the anaerobic gas, and it is particularly necessary to have an atmosphere of argon and helium for the heat treatment in the temperature range of 2000 ° C. or higher.

Examples of the above high heat resistant resin include a resin which becomes a high heat resistant polymer having a high molecular weight by condensation polymerization of an acid component and a diamine component, and preferably an aromatic polyimide. Porous film made of high heat resistant resin, for example, a solution of a polyimide precursor is cast into a film, and the polyimide precursor is deposited by contacting with a coagulating solvent through a solvent displacement rate adjusting material, and a fine It can be obtained by obtaining a polyimide precursor porous film having various continuous pores and then subjecting the polyimide precursor porous film to thermal imidization treatment or chemical imidization treatment.

The above-mentioned polyimide porous membrane having non-linear fine continuous pores preferably has an intrinsic viscosity that gives a polyimide having a glass transition temperature of 250 ° C. or higher (or does not show a glass transition temperature at a temperature of 250 ° C. or lower). It can be obtained by depositing a polymer component of an organic solvent solution of a polyimide having a number of 2.2 or more or a polyimide precursor that gives the polyimide by viscoelastic phase separation induced by solvent substitution and making it porous. The organic solvent solution of the polyimide or the polyimide precursor has a concentration of the polyimide or the polyimide precursor of 12% by weight or less and a solution viscosity of 400.
It is preferably poise or more. Further, it is preferable that the solvent substitution induction is performed by using a solvent substitution rate adjusting material while avoiding direct contact between the coagulation solvent and the polyimide or the organic solvent solution of the polyimide precursor.

As the solvent displacement rate adjusting material, when the multilayer film is brought into contact with a coagulating solvent to precipitate the polyimide precursor, the solvent of the polyimide precursor and the coagulating solvent can permeate at an appropriate rate. Those having a degree of transparency are preferable. As the solvent displacement rate adjusting material, specifically, a polyolefin such as polyethylene or polypropylene, a non-woven fabric or a porous film made of a material such as cellulose, or the like is used, and particularly when a microporous film made of polyolefin is used. It is preferable because the surface of the manufactured polyimide porous film is excellent in smoothness.

The polyimide precursor is cast and brought into contact with the coagulation solvent through the solvent displacement rate adjusting material to precipitate and porous the polyimide precursor. The coagulation solvent for the polyimide precursor includes alcohols such as ethanol and methanol, non-solvents of the polyimide precursor such as acetone and water, or 99.9 to 40% by weight of these non-solvents and the polyimide precursor. It is possible to use a mixed solvent of 0.1 to 60% by weight of the above solvent. The combination of the non-solvent and the solvent is not particularly limited, but a mixed solvent of the non-solvent and the solvent is used as the coagulation solvent because the polyimide precursor deposited has a uniform porous structure, which is preferable. In particular, it is preferable to use a mixed solvent composed of 0.1 to 50% by weight of the solvent of the polyimide precursor and 99.9 to 50% by weight of the non-solvent as the coagulation solvent.

The porous polyimide precursor film is then subjected to thermal imidization treatment or chemical imidization treatment. Thermal imidization of the polyimide precursor film, the polyimide precursor porous film from which the solvent displacement rate adjusting material has been removed is fixed using a pin, a chuck or a pin chill roller so that thermal contraction does not occur, and the film is exposed to the atmosphere. 280-5
It is carried out at 00 ° C. for 5 to 60 minutes.

The polyimide porous membrane having non-linear fine continuous pores produced in this manner has an average pore diameter of 0.01 to 10 although it varies somewhat depending on the selection of the production conditions.
μm (preferably 0.01 to 2 μm), porosity 20 to 80
% (Preferably 25 to 65%), thickness 5 to 300 μm
(Preferably 10 to 150 μm).

The above-mentioned polyimide porous membrane having non-linear fine continuous pores was heated in an anaerobic atmosphere at a temperature of 800-1800.
By heating at ℃, it is possible to obtain a porous carbonized film having non-linear fine continuous pores. By firing at a temperature within the above range, it is possible to obtain a carbide close to an amorphous form or having a crystallinity of about 20% or less. In addition, the porous polyimide film is heated to a temperature of 8 in an anaerobic atmosphere as described above.
By heating and carbonizing at 00-1800 ° C., a porous carbonized film having non-linear fine continuous pores can be obtained.

Further, after heating in an anaerobic atmosphere at a temperature of 800 to 1800 ° C. and then in an anaerobic atmosphere at a temperature of 1800 to 3500 ° C., non-linear fine continuous holes are formed. It is possible to obtain a porous graphite film made of a carbide having a high degree of crystallinity.

By any of the above methods, the average pore diameter is 0.01 to 10 μm, the porosity is 20 to 80%, and the thickness is 5 to 5.
300 μm, preferably with a density of 1.7-2.2 g / cm ^3.
It is possible to obtain a porous carbonized film having non-linear fine continuous pores.

The electrolytic solution used in the present invention may be either an aqueous solution type electrolytic solution or a non-aqueous electrolytic solution (organic solvent type electrolytic solution), but the non-aqueous electrolytic solution is preferable. As a specific example, an aprotic polar solvent having a high dielectric constant or a low viscosity, an organic solvent which is electrochemically stable and well dissolves the electrolyte salt shown below, and a mixture thereof are selected. Specific examples of these include propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate (EMC) and the like. Carbonates, lactones such as γ-butyrolactone (BL), dimethylformamide (DMF), dimethylacetamide (DMAC)
And other amide solvents, sulfolane, acetonitrile, dimethyl sulfoxide (DMSO), tetrahydrofuran, dimethoxyethane and the like.

As a specific example of the electrolyte salt, a quaternized alkylammonium salt is preferable as an electrolyte in a non-aqueous solvent, and a specific example is one having a structure of (R ₄ N) ⁺ (M) ^−. To be The alkyl group represented by R are exemplified by methyl, ethyl, or butyl group, as M is an anion component, tetrafluoro boron (BF _4), Pa - Kurore - DOO (ClO ₄₎ group and the like.

The separator of the present invention is, for example,
High density condenser paper called condenser paper, low density condenser paper called electrolytic paper, polyethylene and polypropylene film with micropores, polyethylene fiber or polypropylene fiber Examples of the nonwoven fabric used include sulfonated products of these polyolefin-based nonwoven fabrics.

In the electric double layer capacitor of the present invention, the above-mentioned porous carbonized film is used as a polarized electrode, and this polarized electrode and a current collector such as stainless steel, platinum or a graphite plate are bonded by a conductive adhesive. A positive electrode and a negative electrode were prepared, and a separator made of polyfluoroethylene resin was used with the separator interposed therebetween.
It can be obtained by placing it in a container such as a rubber container, providing a gasket such as neoprene rubber if necessary, injecting the electrolytic solution into the container preferably under reduced pressure, and sufficiently impregnating the electrolytic solution with a separator. it can.

[0025]

EXAMPLES The present invention will now be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In each of the following examples, the average pore diameter,
The porosity is obtained by the following.

Average pore size From the scanning electron micrograph of the surface of the porous film, the pore area was measured at arbitrary 50 or more open pores, and the pore shape was a perfect circle according to the following formula from the average value of the pore areas. The average diameter when it was assumed was calculated. Sa in the following equation means the average value of the pore area. Average pore diameter = 2 × (Sa / π) 1/2

Porosity The thickness and weight of the porous film cut into a predetermined size were measured, and the porosity was calculated from the weight per unit area by the following formula. In the following formula, S means the area of the porous film, d means the film thickness, w means the measured weight, D means the film density, the density of the polyimide is 1.34 g / cm ^3, and the true density of the carbide is 1. 7x
[1-Crystallinity (%) + 2.2 x crystallinity (%)] g /
It was set to cm ³ . Porosity = S × d × D / w × 100

Example 1 A non-linear fine porous polyimide film having a film thickness of 37 μm, an average pore diameter of 0.02 μm and a porosity of 45% was used as a positive electrode for a positive electrode.
Porous carbonization having an average pore diameter of 0.18 μm, a porosity of 43%, a crystallinity of 27%, a bending strength of 0.5 GPa and a thickness of 30 μm, obtained by carbonizing by heating at 00 ° C. in an inert atmosphere. A porous polyimide film was prepared for the negative electrode using a membrane (the result of the scanning electron micrograph of the cross section and confirmed that the porous carbonized film has fine continuous pores because of the passage of methanol). The average pore diameter was 0.14 μm, the porosity was 40%, and the crystallinity was 9 which was obtained by carbonization and graphitization by heating in an inert atmosphere at 2600 ° C.
4%, flexural strength 0.9 GPa, thickness 27 μm porous carbonized film (the result of a scanning electron micrograph of the cross section and the presence of fine continuous pores due to the passage of methanol through this porous carbonized film 30) in a nitrogen atmosphere
After heat treatment at 0 ° C. for 3 hours, it was transferred to a glove box in an argon atmosphere.

A polyethylene separator was sandwiched between two electrodes made of a porous carbonized film, and the whole was sandwiched by two platinum sheets as a current collector on the outside thereof. After that, the current collector, the electrode, and the separator were sandwiched with bolts from the outside through a polyfluorinated ethylene resin plate so that they were in good contact with each other. The obtained open cell type capacitor was pressure-bonded to a metal lithium foil, and the lithium electrode was immersed in a 1M LiBF ₄ / propylene carbonate electrolyte solution. Next, the lithium electrode and the porous carbonized film were connected by a lead wire and short-circuited for about 1 hour. After short-circuiting, the self-potential measured by connecting a voltmeter between the porous carbonized film and the lithium electrode was 2.1V for both sheets. Then, the electrode part was disassembled, and two porous carbon film electrode bodies were taken out.

On these two porous carbonized membranes, 1.3M triethylammonium tetrafluoroborate / propylene carbonate + ethylene carbonate (50/50,
A coin-type cell was assembled by fully impregnating an electrolyte solution of a capacity ratio) as a positive electrode and a negative electrode, and placing a polyethylene separator between both electrodes. The obtained electric double layer capacitor had an internal resistance of 1.85Ω, and after applying a voltage of 3.8 V at room temperature for 1 hour, it was 1 at 18 mA.
The initial capacitance obtained by constant current discharge to V is 3.4 F /
g, initial energy-density was 5.02J. In order to evaluate the long-term operation reliability of the capacitor under voltage application conditions, the rate of change in energy density after applying a voltage of 3.8 V for 800 hours at room temperature was -8%.

[0031]

According to the present invention, by using a polarized electrode having a pore structure that facilitates ion transfer,
An electric double layer capacitor having high voltage durability and an electrode for the capacitor can be obtained.

Claims (7)

[Claims] 1. An electric double layer capacitor comprising a polarized electrode composed of a porous carbonized film having non-linear fine continuous pores, a separator and an electrolyte solution as constituent elements. 2. The electrolytic solution is a non-aqueous electrolytic solution.
The electric double layer capacitor described in 1 .. 3. A porous carbonized film having an average pore diameter of 0.01 to 1
The electric double layer capacitor according to claim 1, wherein the electric double layer capacitor has a thickness of 0 μm, a porosity of 20 to 80%, and a thickness of 5 to 300 μm. 4. The electric double layer capacitor according to claim 1, wherein the porous carbonized film is a carbonized or graphitized porous heat resistant polymer film having non-linear fine continuous pores. 5. The electric double layer capacitor according to claim 1, wherein the porous carbonized film is obtained by carbonizing or graphitizing a porous heat-resistant polyimide film having non-linear fine continuous pores. 6. A polarized electrode composed of a porous carbonized film having non-linear fine continuous pores used in the electric double layer capacitor according to claim 1. Description: 7. An average pore diameter of 0.01 to 10 μm and a porosity of 2
An electrode for an electric double layer capacitor, which is composed of a porous carbonized film having non-linear fine continuous pores having a thickness of 0 to 80% and a thickness of 5 to 300 μm.