JP3500493B2 - Porous electrode and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel porous electrode used as an electric double layer capacitor, an electrolytic capacitor, a carbon electrode for a lithium ion secondary battery and the like and a method for producing the same.

[0002]

2. Description of the Related Art Generally, carbon electrodes made of activated carbon are widely used as anodes / negative electrodes of electric double layer capacitors, cathodes of lithium ion secondary batteries, and the like. This carbon electrode uses a dispersion of polytetrafluoroethylene (PTFE) as a binder, and a mixture of activated carbon, carbon black or a conductive polymer is applied to a base material such as an aluminum foil and dried. Is manufactured by.

By the way, the electrostatic capacity of an electric double layer capacitor, a carbon electrode for a lithium ion secondary battery, etc. depends on the contact area (effective area) between the conductive fine particles and the electrolytic solution per unit projected area of the electrode foil. . That is, the capacitance is closely related to the specific surface area of the conductive fine particles themselves, the packing density of the conductive fine particles per unit projected area of the electrode foil, and the like.

However, there is a limit to increasing the specific surface area of the conductive fine particles, and it is almost impossible to expect a dramatic increase in capacitance due to the improvement of the specific surface area. Therefore, how to efficiently fill the electrode foil with the conductive fine particles is a major issue.

Since PTFE used as a binder in the carbon electrode is poor in adhesiveness, it is inferior in the filling property of the conductive fine particles and the adhesion between the conductive fine particles and the substrate.
Further, due to the low adhesiveness, the conductive fine particles are easily peeled off from the base material and have a drawback that they are susceptible to vibration and the like. These problems can be improved by adding a large amount of binder, but if added in a large amount, the resistance value increases, and in any case, it is impossible to obtain an electrode having sufficient practicality. Can not.

On the other hand, in order to improve the filling rate of the conductive fine particles, at least one of styrene-butadiene rubber and acrylonitrile-butadiene rubber is used as a binder other than PTFE, and activated carbon, carbon black, etc. are kneaded and mixed into a sheet. A method of forming a sheet has been proposed (Japanese Patent Laid-Open No. 8-250380).

[0007]

However, in the above technique, since the mixture obtained by evaporating the solvent is formed into a sheet, for example, as shown in FIG. Completely, or it also closes the fine pores of the conductive fine particles.
As a result, not only a sufficient contact state between the electrolytic solution and the conductive fine particles (electrode) cannot be ensured, but also the resistance value increases accordingly, so that a sufficiently satisfactory electrostatic capacitance cannot be obtained. .

Moreover, the binder used in the above technique exhibits swelling property (that is, low solvent resistance) with respect to the propylene carbonate-based organic solvent used as the solvent of the electrolytic solution. Therefore, the binder may be deteriorated with time, and there is a problem in stability and reliability.

As described above, in order to further increase the capacitance in the above technique, there is still room for improvement, particularly in terms of the state of contact between the electrolytic solution and the conductive fine particles.

Accordingly, the main object of the present invention is to provide an electrode material which can secure a good contact state between the electrolytic solution and the conductive fine particles and exhibit a more excellent capacitance. Another object of the present invention is to provide an electrode material having excellent adhesiveness, solvent resistance, vibration resistance and the like.

[0011]

The present inventor has conducted extensive studies in view of the problems of the prior art, and as a result, uses a material different from the conventional one as a binder and manufactures it by a specific method to obtain a unique structure. It was found that an electrode material having the above can be obtained, and finally the present invention was completed.

That is, the present invention relates to the following novel porous electrode and a method for producing the same.

1. A porous electrode in which conductive fine particles are dispersed in a porous rubber.

2. Pores characterized in that a mixture containing conductive fine particles and a rubber solution in which rubber is dissolved in a solvent is prepared, and then a coating film comprising the mixture is formed on a conductive substrate and dried. Of manufacturing a conductive electrode.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The porous electrode of the present invention is characterized in that conductive fine particles are dispersed in a porous rubber.
In this porous rubber, for example, as shown in FIG. 1B showing the electrode structure, a large number of gaps are formed (white portion). This gap is mainly a three-dimensional network as shown in FIG. 2, which shows the result of observation by a scanning electron microscope (100 times) of the electrode surface of the present invention (where rubber molecules are contracted by crosslinking to promote porosity). It is composed of continuous pores formed in. Its porosity (porosity) depends on the end product application,
It may be appropriately adjusted according to the type of rubber (binder) used.

The type of the porous rubber (also referred to as a binder) is not particularly limited as long as it can realize the above-described porosity, and any known rubber can be used. For example, various synthetic rubbers such as butyl rubber, ethylene propylene diene rubber, nitrile rubber, silicone rubber, and fluorosilicone rubber, as well as natural rubber can be used. These rubbers can be used alone or in combination of two or more.

However, the rubber may swell depending on the combination of the electrolytic solution and the rubber used, and in such a case, the swelling impairs the porosity of the rubber. Therefore, in the present invention, it is necessary to appropriately select a rubber that does not substantially swell with the electrolytic solution, depending on the type of electrolytic solution (solvent) used. That is, it is preferable to use rubber having solvent resistance to the electrolytic solution. In particular, when propylene carbonate is used as at least a part of the solvent of the electrolytic solution, it is preferable to select butyl rubber, ethylene propylene diene rubber or the like which has excellent solvent resistance to this solvent. Since these do not swell with propylene carbonate, excellent porosity can be stably maintained even when using the porous rubber, and as a result, a good contact state between the electrolytic solution and the conductive fine particles can be secured, and It is possible to provide an electrode material that exhibits excellent capacitance.

As the conductive fine particles, those similar to those used in known carbon electrodes and the like can be used. For example,
At least one kind of conductive fine powder selected from carbon-based powder, conductive polymer powder and metal powder can be used. Specifically, activated carbon, carbon-based powder such as carbon black (for example, acetylene black, Ketjen black), conductive polymer powder such as polyacetylene, polyparaphenylene, polyphenylene vinylene, polypyrrole, polyaniline, nickel, aluminum, tantalum, Metal powders such as titanium, ruthenium oxide, vanadium oxide and lithium permanganate can be used. These may also be used alone or in combination of two or more.

The average particle size of the conductive fine particles may be appropriately adjusted depending on the type and the like. For example, if the conductive fine particles are carbon-based powder, it is usually about 0.5 to 20 μm, preferably 1 to 15 μm, and if the conductive polymer powder is usually about 0.05 to 10 μm, preferably 0.1 to 3 μm. If it is a metal powder, it is usually about 0.01 to 10 μm, preferably 0.05 to 1 μm.

In addition to these two components (rubber and conductive fine particles), other components may be contained within a range not impairing the effects of the present invention. For example, various additives such as a rubber crosslinking agent, a rubber crosslinking accelerator, an adhesion enhancer, and a rubber deterioration inhibitor may be contained.

The porous electrode of the present invention is prepared by preparing a mixture containing a rubber solution in which rubber is dissolved in a solvent and conductive fine particles,
Then, a coating film made of the mixture is formed on a conductive substrate and dried to produce the film.

The same kind of rubber as described above can be used in the manufacturing method of the present invention. The solvent is not particularly limited as long as it can dissolve the rubber used, and may be appropriately selected from known solvents depending on the kind of rubber to be made porous and used. For example, in the case of butyl rubber, ethylene propylene diene rubber, etc., toluene, in the case of natural rubber, nitrile rubber, etc., cyclohexane, in the case of silicone rubber, fluorinated silicone rubber, etc., dimethylsiloxane can be used as a solvent.

The rubber concentration (solid content) in the rubber solution is
The amount of rubber in the mixture is not particularly limited as long as it is a predetermined amount described below, and may be appropriately set depending on the type of rubber used, the type of solvent, and the like. Usually, it may be about 5 to 30% by weight.

Next, the rubber solution and the conductive fine particles are mixed to prepare a mixture containing both components. The conductive fine particles used here may be the same as those described above. The proportion (solid content) of the binder can be appropriately set according to the use of the final product, the type of binder, etc., but is usually 2 to 100 parts by weight of the conductive fine particles.
The amount may be about 50 parts by weight, preferably 5 to 20 parts by weight. If the amount is less than 2 parts by weight, the binder cannot sufficiently hold the conductive fine particles. Also, 50
When the amount is more than the amount by weight, the binder begins to cover around the conductive fine particles which are the electrodes, so that sufficient electrostatic capacity cannot be obtained.

The rubber solution may further contain, if necessary,
You may mix | blend various additives, such as an adhesion enhancer, a rubber deterioration inhibitor, a rubber crosslinking agent, and a rubber crosslinking accelerator. Known materials can be used as these. For example, stearic acid, polyacrylic acid, vinyl acetate, polyvinyl alcohol or the like is used as an adhesion enhancer, t-butyl hexachloride (BHT) or the like is used as a rubber deterioration preventing agent, and a resin crosslinking agent, an S crosslinking agent or the like is used as a rubber crosslinking agent. be able to.

In particular, in the present invention, by adding a cross-linking agent to cross-link the rubber, it is possible to shrink the rubber molecules and promote the porosity of the rubber. At the same time, the stability of the propylene carbonate-based solvent can be further increased by adding the crosslinking agent. The addition amount of the cross-linking agent varies depending on the kind of the cross-linking agent and the like, but is usually 1 with respect to the rubber amount.
It should be about 10% by weight. Even if the amount added exceeds 10% by weight, it is economically unfavorable because the properties corresponding to it cannot be obtained, but it may exceed 10% by weight in some cases.

Any mixing method may be used as long as each component can be uniformly mixed. For example, a known stirrer such as a kneader, a mixer or a homogenizer may be uniformly mixed to form a slurry.

Then, using the obtained mixture, the coating film is formed on the conductive substrate and dried. As the conductive base material, the same material as that used as a collector for a known carbon electrode or the like can be used. For example, it is possible to use an etched foil or net in which the surface of a conductive metal such as copper, aluminum, titanium, tantalum, or nickel is corroded. In the present invention, the surface of the conductive metal may be treated with a silane coupling agent, a titanium coupling agent, or the like in advance to further improve the adhesion to the coating film.

The method for forming the coating is not particularly limited, and methods such as coating (brush coating, spraying, roller, etc.), doctor blade method, dipping (immersion) and the like can be appropriately adopted. The thickness of the film to be formed may be appropriately set depending on the use of the final product, the type of the conductive base material, etc., but is usually about 25 to 1000 μm, preferably 100.
˜500 μm.

In the present invention, if necessary, the coating formed on the conductive base material may be further contacted with a solvent capable of precipitating a rubber component prior to drying after the coating is formed, whereby the rubber component in the coating is deposited. You can also let it.

Basically, in order to make the rubber porous in the present invention, the rubber may be once dissolved in a solvent to prepare a rubber solution, and finally the coating film may be dried. On the other hand, by substituting with a solvent having a solubility (parameter) different from that of the solvent used in the rubber solution, it is possible to further promote the porosity of the rubber. In this case, it is preferable that the coating formed on the conductive substrate is brought into contact with the solvent before it is completely dried.

The solvent used in the above is not particularly limited as long as it has a solubility different from the solvent used in the rubber solution and can precipitate the rubber component, and it is known depending on the type of solvent in the rubber solution and the like. The solvent may be appropriately selected from the above solvents.
For example, when a rubber solution obtained by dissolving butyl rubber in toluene is used, it is possible to promote porosity by contacting a solvent such as methanol after forming the film. The method of contact is not particularly limited, and for example, dipping, spray coating or the like can be performed.

Further, in the present invention, after forming a coating film of a mixture on a conductive substrate, it is added to the coating film as needed unless the contact between the conductive fine particles and the electrolytic solution is extremely impaired. Pressure treatment may be applied. For example, it can be pressed by a press roller, a hydraulic press or the like. By pressurizing the coating, the filling property of the conductive fine particles and the like can be improved.

Finally, the formed film is dried. That is, the solvent is evaporated to make the rubber porous. The drying method may be any known method such as natural drying, heat drying, hot air drying, etc., but it is preferable to dry as quickly as possible in order to achieve porosity.

When a cross-linking agent is added to the mixture for cross-linking, it may be dried by heating or once dried and then heat-treated. The heat treatment temperature for cross-linking may be usually about 125 to 145 ° C. The heating time may be appropriately determined according to the heating temperature and the like.

Further, in the present invention, a foaming agent may be added in advance to a mixture containing a rubber solution and conductive fine particles, and self-foaming may be carried out by the above-mentioned heat treatment during drying or crosslinking. As a result, it is possible to achieve further porosity. As the foaming agent, those blended with known resins can be used, and examples thereof include benzenesulfonyl hydrazide and paratoluenesulfonyl hydrazide. The amount of the foaming agent added may be in the range of usually not exceeding 3% by weight (preferably 0.1 to 3% by weight). When it exceeds 3% by weight, it becomes difficult to control the thickness and the like, which is not preferable.

[0037]

In the porous electrode of the present invention, since the binder itself has a porous structure, the electrolytic solution can sufficiently contact the conductive fine particles without the binder covering the conductive fine particles as the electrode. Excellent capacitance and low resistance can be achieved. Furthermore, it has excellent adhesiveness, vibration resistance, solvent resistance, and the like, and can exhibit flexibility not obtained by conventional techniques.

As in the prior art, when rubber is mixed with activated carbon and carbon black and the mixture obtained by evaporating the solvent is molded into a sheet shape, the electrode material is changed as shown in FIG. 1 (a). Since the conductive fine particles are covered with rubber, a sufficient capacitance cannot be achieved.

On the other hand, as in the present invention, the rubber is once dissolved in a solvent, the conductive fine particles are mixed, and then the mixture is used as it is to form a film, and the rubber can be further deposited on the film as necessary. By drying the film after contact with the solvent, it is possible to effectively promote the porosity as shown in FIG. 1 (b) or FIG. Furthermore, if the rubber molecules are contracted by cross-linking the rubber, the region (contact area with the conductive fine particles) where the electrolytic solution permeates can be further expanded.

As described above, in the present invention, the binder portion of the electrode material has a porous structure having continuous pores formed in a three-dimensional network, so that the electrolytic solution and the conductive fine particles which are the electrodes are well satisfactorily formed. As a result of being able to realize the contact state, excellent capacitance and low resistance can be achieved all at once. In addition, since such a porous rubber is also excellent in adhesiveness, etc., it is difficult to improve the electrostatic capacity and the filling property of conductive fine particles, solvent resistance, vibration resistance, etc. And can be achieved at the same time.

[0041]

The porous electrode of the present invention has a peculiar structure in which the conductive fine particles are dispersed in the porous rubber, so that a good contact state between the electrolytic solution and the conductive fine particles can be achieved. it can.

Moreover, since this porous rubber is excellent in adhesiveness, it is also excellent in filling property of conductive fine particles to be electrodes and vibration resistance. Also, by crosslinking the rubber,
A wide range of solvents (especially solvents used in electrolytes) can be used to promote porosity and at the same time improve solvent resistance.
It is possible to obtain excellent stability.

Further, by selecting a rubber having solvent resistance in combination with the electrolytic solution, a further excellent effect can be obtained. In particular, in an electrolytic solution containing propylene carbonate as a solvent, if butyl rubber, which exhibits excellent solvent resistance to the solvent, or ethylene propylene diene rubber is used, the porosity can be stably maintained, Moreover, the above contact state can be secured, and an electrode having excellent stability and reliability can be obtained.

Further, in the present invention, unlike the case where PTFE is used, various additives such as an adhesion enhancer, a rubber stabilizer, a stabilizer for an electrolytic solution, and a surfactant can be easily used. As it is possible to improve the dispersibility of the binder,
It is possible to impart various properties such as prolonging the pot life after blending the mixture.

The porous electrode of the present invention as described above can be widely used in various applications such as an electric double layer capacitor, an aluminum electrolytic capacitor, a tantalum electrolytic capacitor, a titanium electrolytic capacitor, and an electrode for a lithium ion secondary battery. .

[0046]

EXAMPLES Examples and comparative examples will be shown below to further clarify the characteristics of the porous electrode according to the present invention.

Example 1 Butyl rubber was dissolved in toluene to prepare a rubber solution (solid content concentration: about 10% by weight). Then, activated carbon (BE
T specific surface area of 2000 m ² / g, average particle size of 10 μm) and acetylene black (average particle size of 0.8 μm) were mixed at a ratio (solid content) shown in Table 1 to prepare a slurry. After dipping a reticulated aluminum substrate into this slurry,
It was dried quickly to obtain an electrode foil.

Example 2 In the same manner as in Example 1, activated carbon, acetylene black and BHT were mixed in the proportions shown in Table 1 to prepare a slurry, which was dipped with a reticulated aluminum base material and then quickly dried. An electrode foil was obtained.

Example 3 In the same manner as in Example 1, activated carbon, acetylene black,
Aluminum powder and BHT were mixed in the proportions shown in Table 1 to prepare a slurry, and a drip-like aluminum base material was dipped in the slurry and then quickly dried to obtain an electrode foil.

Example 4 A conductive aluminum fine particle slurry of Example 3 was dipped on a reticulated aluminum base material and then baked at 140 ° C. for 10 minutes,
An electrode foil was obtained.

Example 5 A reticulated aluminum base material was dipped in the conductive fine particle slurry of Example 3 and then rapidly dipped in methanol to promote porosity. After drying methanol, 1 at 140 ℃
Heat treatment was performed for 0 minutes to obtain an electrode foil. Example 6 An electrode foil was obtained in the same manner as in Example 5 except that ethylene propylene diene rubber was used as a raw material instead of butyl rubber.

Comparative Example 1 Activated carbon fine particles, acetylene black and polytetrafluoroethylene dispersion were mixed in the proportions shown in Table 1, mixed with a mixer and made into a slurry. This was applied onto an aluminum foil and dried with a heater at 105 ° C. for 60 minutes.

[0053]

[Table 1] Test Example 1 An adhesive tape was attached to the electrode foils obtained in each of the Examples and Comparative Examples and slowly peeled vertically. The mechanical strength was evaluated based on the peeling state at that time. The results are shown in Table 2.
Also, as shown in FIG. 3, these electrode foils are 2 cm × 5 c
Cut out to m, sandwich paper with a propylene carbonate solution of tetraethylammonium perchlorate impregnated with 0.8 mol / l, and sandwich it with glass plates from both sides to fix it. did. Apply a DC current of 2.8 V to this cell for 5 minutes to charge it for 10 minutes.
It was discharged through a 0Ω resistance, and the capacity was calculated from the flowing current value and time. The results are shown in Table 2.

For comparison, a similar test was conducted using a rubber having no solvent resistance to the propylene carbonate used as the solvent of the electrolytic solution as described above. An electrode foil (Comparative Example 2) prepared in the same manner as in Example 5 except that SBR was used as a raw material instead of butyl rubber, and N was used instead of butyl rubber.
Table 2 also shows the results of the electrode foil (Comparative Example 3) produced in the same manner as in Example 5 except that BR was used as the raw material.

On the other hand, the electric double layer capacitor cell was put in a polypropylene bag, and the capacitance was measured after it was kept in hot water at 100 ° C. for 1 hour to evaluate the solvent resistance. Furthermore, an electric double layer capacitor cell was attached to a household electric stove and the electrostatic capacity after 3 hours of vibration was measured to evaluate the vibration resistance. The results are also shown in Table 2.

[0056]

[Table 2] As is clear from the results shown in Table 2, the porous electrode of the present invention has a high capacitance of 4 F / cm ² or more, a low DC discharge resistance of 40 mΩ or less, mechanical strength, solvent resistance, and
It can be seen that it has excellent vibration resistance.

[Brief description of drawings]

FIG. 1 is a schematic view of each structure of an electrode (a) in the related art and an electrode (b) of the present invention.

FIG. 2 is a diagram showing a fine pattern formed on a base material in the electrode of the present invention in which rubber molecules are contracted by crosslinking to further promote porosity.

FIG. 3 is a view showing an assembled state of the electric double layer capacitor cell produced in Test Example 1.

[Explanation of symbols]

1 Activated carbon particles 2 Carbon black or metal powder 3 binders 4 base material 5 electrodes 6 glass plates 7 paper

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01G 9/058 H01B 1/24 H01M 4/02 H01M 4/04

Claims (7)

(57) [Claims] 1. A porous electrode in which conductive fine particles containing activated carbon are dispersed in a porous rubber , wherein (1) part or all of the porous rubber is butyl rubber and
(2) the weight ratio of the conductive fine particles to the porous rubber is at least one of the conductive fine particles.
2 to 50 parts by weight of porous rubber to 100 parts by weight of particles
Yes, and (3) combining an electrolytic solution containing propylene carbonate as a solvent
Characterized by being used for electric double layer capacitors used together
And a porous electrode . 2. The porous electrode according to claim 1, wherein the conductive fine particles contain activated carbon and at least one of carbon-based powder, conductive polymer powder and metal powder. 3. The conductive fine particles contain activated carbon , and activated carbon, carbon black, polyacetylene, polyparaphenylene, polyphenylene vinylene, polypyrrole, polyaniline, aluminum, tantalum, titanium, nickel, vanadium oxide, ruthenium oxide, titanium nitride. The porous electrode according to claim 1, comprising at least one of lithium and permanganate powder. 4. Production of a porous electrode in which a mixture containing conductive fine particles and a rubber solution in which rubber is dissolved in a solvent is prepared, and then a coating film comprising the mixture is formed on a conductive substrate and dried. A method on a conductive substrate prior to drying.
The coating consisting of the mixture applied to the
A product characterized by contacting with a solvent capable of precipitating components
Build method . 5. Production of a porous electrode in which a mixture containing conductive fine particles and a rubber solution in which rubber is dissolved in a solvent is prepared, and then a coating film comprising the mixture is formed on a conductive substrate and dried. A method on a conductive substrate prior to drying.
A coating consisting of the mixture applied to was used in the rubber solution.
Rubber that has different solubility (parameter) from solvent and
A product characterized by contacting with a solvent capable of precipitating components
Build method . 6. further adding a crosslinking agent in the mixture, A process according to claim 4 or 5 to form a coating of the mixture on a conductive substrate, followed by heat treatment after heat-dried or dried. 7. The manufacturing method according to claim 4.
A is, (1) a conductive fine particles of activated carbon, (2) a portion of the rubber or all, butyl rubber and ethylene
At least one kind of propylene diene rubber, and (3) the weight ratio (solid content) of the conductive fine particles and the rubber is
2 to 50 parts by weight of rubber based on 100 parts by weight of the functional fine particles.
The method for producing a porous electrode according to claim 1, wherein