JPH06290785A - Electrode and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a lightweight electrode with high porosity and large specific surface area by constituting an electrode by use of a porous structure having fine pores in its skeleton. CONSTITUTION:An electrode is characterized in that it is constituted by use of a porous structure comprising a skeleton 1 having fine pores 2, e.g. a three- dimensional netting structure or a cloth structure. Portions of skeleton surface forming fine pores in a porous structure as the base are made nonconductive and then electroplated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode using a porous structure having a skeleton with fine pores and a method for manufacturing the electrode. The electrode of the present invention has a particularly high porosity, a large specific surface area, and is lightweight, and is an electrode for various batteries, for example, a positive electrode or a negative electrode for an alkaline secondary battery and its substrate, an electrode for a lead storage battery, a zinc electrode for a battery. In addition to the above, a wide range of applications such as electrodes for various electrochemical reactions and electrodes for various measurements are possible.

[0002]

2. Description of the Related Art Conventionally, porous metal has been used as various electrodes because it has a very large porosity, is lightweight, and has a large surface area per weight. As a conventional method for producing a porous metal body, a conductive metal is applied to the entire surface of the skeleton of a synthetic resin foam having a three-dimensional network structure as a base, and then a metal film and an electrodeposition of a metal film are formed on the skeleton surface. There is known a method of producing a three-dimensional mesh-like porous body made of only metal by removing the resin portion by heating or other methods after the deposition (Japanese Patent Publication No. 47-1).
No. 0524, etc.). There is also known a method of producing a cloth-like porous metal body by coating the surface of a carbon fiber or a woven or non-woven fabric of carbon fiber with a metal, and then thermally decomposing and removing the carbon (Japanese Patent Laid-Open No. 58-164705). Gazette).

As an example of application of the metal porous body to various electrodes, a three-dimensional reticulated metal porous body is used as a substrate of an electrode for an alkaline secondary battery (JP-A-49-127145, etc.).
A cloth-like metal porous body (Japanese Patent Laid-Open No. 61-208756, etc.) is used. Further, it has been proposed to apply a three-dimensional mesh-like porous metal body to a lead storage battery electrode (JP-A-49-112130, etc.). Further, an electrode for bioelectricity measurement (JP-A-55-96142, etc.) and an electrode for electrochemical reaction (JP-A-54-62180,
JP-A-54-118387) has also been proposed to apply a porous metal body.

[0004]

However, in these various electrodes, the porosity is further increased, the weight is reduced,
It is desired to increase the specific surface area. For example, in the case of an alkaline secondary battery electrode, its application to mobile devices is expanding, and there is a strong demand for downsizing and weight saving of batteries. Therefore, it is required that the metal porous body used as the electrode substrate also has a reduced porosity to reduce the weight and increase the amount of the active material filled. However, in this case, the size of the pores of the skeleton of the porous structure is limited. Therefore, if the size of the gap is constant, the conventional microstructure of the metal porous body has high porosity and light weight. Therefore, there is a problem that the thickness of the metal layer must be reduced, which causes a decrease in strength and cannot endure the intended use.

Further, for example, in a zinc electrode for a battery, it is preferable to increase the contact area between the electrolytic solution and the zinc surface by increasing the surface area of the electrode to increase the oxidation reaction area due to discharge. With the fine structure of the porous body, there is a limit to the increase in specific surface area, and there is no solution at present. Similarly, in the case of a cadmium electrode, it is desired to improve the charge / discharge utilization rate, it is important to increase the contact area with the active material, and it is desired to increase the specific surface area. Further, in the case of the electrode for electrochemical reaction, it is desired to increase the reaction area, and the increase in specific surface area is a problem.

Also in terms of manufacturing the porous metal body, in the conventional porous metal body in which a metal film is formed on the entire surface of the skeleton, the decomposition gas of the resin generated when the base resin inside the skeleton is removed from the inside of the skeleton. There is a drawback that it is difficult to remove efficiently, and there is a problem that productivity is low. The present invention has found that these problems can be solved by providing fine pores in the skeleton.

[0007]

That is, the present invention is an electrode characterized by being constituted by using a porous structure having a skeleton having fine pores. Further, the electrode is characterized by being configured by using a porous structure having a three-dimensional network structure or a cloth structure having a skeleton having fine pores. Further, the method for producing an electrode is characterized in that a portion of the skeleton surface of the base porous structure which forms fine pores is made non-conductive and then electroplated.

The electrode of the present invention will be described below. FIG. 1 is a diagram schematically showing a skeleton constituting the electrode of the present invention, and a portion where the skeletons intersect with each other when the base porous structure inside the skeleton is removed. The skeleton 1 has micropores 2 and there is a continuous hollow part 3 obtained by removing the substrate porous structure inside the skeleton.
It communicates with the outside through.

FIG. 2 is a sectional view of a portion where the skeletons in FIG. 1 intersect, and it can be seen that the intersecting portion 4 has an integrated hollow portion 3. The electrode of the present invention is not limited to the one in which the base porous structure is removed as described above, but includes one in which the base porous structure remains.

FIG. 3 shows the appearance of the electrode porous structure of the present invention in the case of a three-dimensional network structure having continuous ventilation holes. There is a gap portion 5 surrounded by a skeleton 1 having micropores 2.

FIG. 4 shows the porous structure of the electrode of the present invention.
It is an enlarged view in the case of a cloth-like structure of a three-dimensional woven fabric.

The kind of metal forming the skeleton of the porous structure of the present invention, the size of the gap between the skeletons, the thickness of the skeleton and the thickness of the metal layer, the thickness of the hollow portion, the shape and size of the micropores, The abundance of micropores on the skeleton surface, etc.
It can be adjusted according to the purpose of use such as specific surface area, mechanical durability, elongation and strength, and electrical characteristics. The size of the micropores is selected in consideration of the thickness of the skeleton and the application.
When the size of the fine pores is close to the thickness of the skeleton, the strength may decrease, which is not preferable. The shape of the micropores can be various shapes, but from the viewpoint of strength, a round shape such as a circle or an ellipse is preferable.

The size of the gap between the skeletons depends on the use of the electrode, and is determined in consideration of the usage condition of the electrode such as the flow of the electrolyte solution, the filling property of the active material powder and the distance between the active material and the electrode. For example, in the case of a nickel positive electrode substrate of an alkaline secondary battery, considering the distance between the nickel hydroxide active material and the substrate skeleton, the size of the gap between the skeletons is preferably several mm or less, more preferably 1 mm or less. . in this case,
If the size of the gap between the skeletons is too small, the filling property of the active material becomes low, which is not preferable.

The method for producing the electrode of the present invention is as follows. After making fine pores on the skeleton surface of the porous structure of the substrate having a three-dimensional network structure or a cloth-like structure non-conductive,
The method of electroplating is applied. The electrode of the present invention can be used only as a metal skeleton while leaving the porous structure of the substrate or removing the substrate. The manufacturing method described below is an example of manufacturing the electrode of the present invention and is not limited thereto.

A synthetic resin foam is preferably used as the three-dimensional network structure of the base porous structure used in the present invention. Specific examples thereof include synthetic resin foams having three-dimensional continuous ventilation holes such as polyurethane foam, polystyrene foam, epoxy foam, polyvinyl chloride foam, phenol resin foam, silicone foam, and polyacrylic foam. Of these, urethane foam is preferable, and particularly flexible polyurethane foam having no cell membrane is preferable. As a method for producing a flexible polyurethane foam having no cell membrane, there is a method of eliminating the cell membrane by controlling foaming, or a method of removing the cell membrane by alkali treatment, heat treatment, hydraulic treatment, etc. The method is preferable in terms of completeness of cell film removal. The size of the bubbles of the flexible urethane foam varies depending on the purpose of use of the electrode and is not particularly limited.

The substrate porous structure having a cloth-like structure of the present invention is roughly classified into a cloth, that is, a non-woven fabric, a woven fabric or a knitted fabric. Nonwoven fabrics are fiber aggregates, felts, mats, papers, etc., and woven fabrics use substrates in the form of two-dimensional and three-dimensional woven fabrics, knits, sheets and the like. Examples of the fiber that constitutes the substrate porous structure having the cloth-like structure include conductive or non-conductive fiber.

In addition to conductive carbon fibers and graphite fibers and various metal fibers as the conductive fibers, as inorganic fibers, conductive oxide fibers, conductive nitride fibers such as metal nitrides, and conductive fibers are used. Carbide fibers, conductive boride fibers, etc. may be mentioned. Carbon fibers having a low conductivity to a high conductivity having a high graphitization rate can be used, but a carbon fiber having a high conductivity is preferable because plating can be uniformly performed in the electroplating process. Also,
When the substrate is removed and used, conductive carbon fiber and graphite fiber are preferably used.

The fibers constituting the non-conductive fiber substrate are, for example, polyethylene, polyethylene terephthalate, polypropylene, polyester, polyamide, polystyrene, polyacrylonitrile, polyvinyl alcohol, cellulose, lignin, polyvinylidene chloride, polybutadiene, polyacetylene, nylon. , Various synthetic fibers such as acrylic, polyurethane, epoxy, phenolic resin, polyvinyl chloride, etc., organic fibers such as various natural fibers, or various inorganic fibers such as various glasses such as alumina, zirconia, mullite, silica-based glass, etc. Can be mentioned.

As a method for producing a nonwoven fabric, a general production method is applied and is not particularly limited, but for example, 2 to 10 cm.
A method for producing a dry non-woven fabric, in which the fiber length of the fiber is opened with a textile card or the fibers are randomly collected by an air flow, or 1
Any method such as a method of manufacturing a wet non-woven fabric by meshing after dispersing fibers having a size of not more than cm and a spun bond manufacturing method of spinning a melted resin and directly spraying it directly onto a support may be used. . A method for producing a two-dimensional or three-dimensional fabric is generally applicable to the method for producing a fiber woven fabric used in the present invention and is not particularly limited.

The portions of the surface of the skeleton of the base porous structure which form the fine pores are made non-conductive and then electroplated. At this time, when the substrate is non-conductive, an operation is performed to make the portion of the skeleton surface where the fine pores are formed non-conductive during the conductive treatment. Furthermore, removing the substrate after electroplating is also applied depending on the application. The case of using a conductive substrate porous structure made of conductive carbon fiber or the like will be described below. In this case, it is possible to apply a method in which the portions where the fine pores are formed as they are without conducting treatment on the skeleton surface are made non-conductive. Of course, even if it has conductivity, it may be subjected to a conductive treatment.

The method of forming the non-conductive portion in the portion of the skeleton surface where the fine pores are formed is not particularly limited, but a method of applying the non-conductive substance in spots to the portion where the fine pores are formed is preferably applied. it can. As the non-conductive substance to be adhered, a substance that is easily decomposed and removed after the electroplating treatment when it is necessary to decompose and remove is preferable, and an organic substance such as a synthetic resin is preferable. In addition, it may be preferable that it does not contain metal impurities, etc., although it depends on the application. The form of the non-conductive portion is also related to the shape of the fine pores to be formed, but non-conductive particles are preferable in consideration of the strength of the obtained electrode.

Examples of the non-conductive substance in the form of particles include various synthetic resin beads, various latex particles and various emulsion particles. In practice, emulsion particles may aggregate from the particle form into a film of various shapes and attach to the skeleton surface in spots. In addition to the case of attachment, it attaches to the skeleton surface in various shapes such as a film and hemisphere.
In any case, it is desirable that the non-conductive portion is formed without forming the spotted portion, that is, the connection portion where the non-conductive portion extends over a wide area. Further, the shape and size of the non-conductive particles are appropriately selected according to the shape and size of the micropores determined by the application.

As a specific method of forming the non-conductive portion, there is a method of immersing the base porous structure in a liquid containing the above-mentioned various non-conductive substances and adhering it to the skeleton surface. For example, it is a method in which the base porous structure is dipped in a dispersion liquid of synthetic resin beads. At this time, it is preferable to appropriately add additives such as a pressure-sensitive adhesive component and a dispersant, which aid adhesion of the synthetic resin beads to the skeleton surface. Properties of non-conductive materials,
In particular, the state of adhesion to the skeleton surface differs depending on the mutual relationship between the surface property and the skeleton surface property, so it may be necessary to adjust the surface property of the non-conductive substance or skeleton by methods such as surface modification. .

By adjusting the kind and amount of the non-conductive substance in the dispersion and the kind and amount of the additive, the spot-like non-conductive portion formed on the skeleton surface occupies the shape, size and skeleton surface. The ratio can be adjusted appropriately. Further, when the shape of the base porous structure is simple, a method of spraying a liquid containing a non-conductive substance to attach the liquid droplets to the surface of the skeleton is also applicable.

Next, the case of using a non-conductive substrate porous structure such as an organic substance will be described below. In this case, it is necessary to make the portion of the skeleton surface where the fine pores are formed in the conductive treatment non-conductive. Specific examples of the method of conductive treatment include a method of forming a film with a conductive paste prepared by dispersing powder of a conductive material such as metal or carbon or graphite, or a method of forming a metal salt solution such as electroless plating or silver mirror reaction. A chemical method utilizing a reduction reaction can be mentioned.
In the present invention, the non-conductive portion is formed in spots in the portion where the fine pores are formed during the conductive treatment. The procedure is to perform a conductive treatment on the surface of the non-conductive skeleton, and then form a non-conductive portion by depositing a non-conductive substance in spots and a method of introducing the non-conductive portion at the same time as the conductive treatment. There is.

Specifically, a conductive treatment film is formed by using particles of a non-conductive substance dispersed in a conductive paste, and at the same time, the non-conductive substance is attached to the skeleton surface to remove the non-conductive portion. The forming method may be used. At this time, the shape, size, and amount of the non-conductive substance in the paste are appropriately adjusted according to the application. In addition, it is necessary to pay attention to the points such as surface modification so that the surface of the non-conductive substance is not covered with the conductive substance or a non-conductive substance having a thickness larger than the thickness of the conductive film is used.

The kind, composition and purity of the metal used for electrolytic plating can be variously selected according to the intended use of the electrode. A usual method is applied to the electrolytic plating. The thickness of the metal layer formed by electrolytic plating is several μm to several hundred μm, although it depends on the application. It is also possible to form a multi-layered structure composed of various kinds of metals by sequentially changing the plating composition during electroplating depending on the application.

Further, depending on the application, when an electrode made of only metal is produced, it is preferable to select a porous substrate structure made of carbon fiber or an organic substance which can be easily removed by a method such as thermal decomposition, dissolution with a solvent or melting. desirable. In this case, after the metal plating, the base porous structure is removed. When a porous substrate structure that requires an oxidizing atmosphere when being removed by thermal decomposition is used, oxidation of the metal plating film occurs, so it is preferable to perform a reduction treatment depending on the application. For example, the temperature of the thermal decomposition of the substrate porous structure using an organic substance is 300-
It is about 1300 ° C. The temperature of heat treatment in a reducing atmosphere varies depending on the type of metal, but in the case of nickel it is 90
It is about 0 ° C.

As described above, the present invention may be used as one constituent material for forming an electrode such as an electrode substrate, in addition to the case where the porous structure having a fine pore skeleton is used as it is. In this case, the porous structure is used by forming an electrode in combination with another material such as an active material that constitutes the electrode.

[0030]

EXAMPLES Examples of the present invention will be specifically described below. [Example 1] As a substrate porous structure having a three-dimensional network structure, a flexible polyurethane foam without a cell membrane having a skeleton thickness of about 100 µm and a gap size between skeletons of about 0.5 mm [manufactured by Bridgestone Corporation] Everlight SF: Model HR
-50] having a thickness of 2 mm was used. The skeleton surface was subjected to a conductive treatment by electroless nickel plating. This was immersed in a dispersion liquid containing polystyrene resin particles (particle diameter of about 7 μm) and an organic additive and then dried. This was electroplated with nickel metal to obtain a porous structure having a three-dimensional network structure having continuous ventilation holes. At this time, the plating time was adjusted so that the thickness of the metal plating layer was about 10 μm. The nickel plating bath used consisted of nickel sulfate and boric acid.

When the obtained porous structure was observed with an electron microscope, it was found that the skeleton had fine pores of about 5 to 8 μm in each case. The abundance of the fine pores was 15% of the entire surface of the skeleton. Further, this porous structure is heat-treated in air at a temperature of about 600 ° C. to thermally decompose and remove the synthetic resin portion, and then heated to about 900 ° C. in a reducing atmosphere for reduction treatment, thereby forming only a metal. A porous structure was obtained. Micropores before heat treatment are retained in the skeleton of this porous structure, the polyurethane resin in the skeleton is decomposed and removed, and the internal space of the skeleton is hollow, and through the micropores in the skeleton the outer surface of the skeleton and internal It was confirmed that the surface was in communication. Also,
The thickness of the metal plating layer was the same as before the heat treatment.

[Comparative Example 1] Except that the treatment with the dispersion liquid of polyethylene resin particles was not carried out in Example 1,
It carried out like the Example. No fine pores were found in the obtained skeleton. The thickness of the metal layer was about 10 μm, which was similar to that of the example, but the specific gravity of the porous body was about 1.2 times that of the example 1, which revealed that there was a problem in reducing the weight of the battery. Further, since the skeleton does not have fine pores, the surface area communicating with the outside is about one half, the specific surface area is small, and the contact area with the active material or the electrolytic solution is small, which proves that there is a problem in improving the performance of the electrode. did.

[Example 2] As a substrate-like porous structure having a cloth-like structure, fibers mainly composed of polyethylene terephthalate having a fiber diameter of 17 µm were formed into a nonwoven fabric by a wet method, and this was combined with fiber fusion bonding and adhesive resin bonding. The non-woven fabric manufactured by This non-woven fabric was subjected to electroless nickel plating for electrical conductivity, and then polystyrene resin particles (particle size 3
.About.4 μm) and an organic additive were added to the dispersion and dried. This was electroplated with nickel metal to obtain an electrode having a porous structure. At this time, the thickness of the metal plating layer is 4
The plating conditions were adjusted to be about μm. When the obtained electrode was observed with an electron microscope, it was found that the skeleton portion had micropores of about 3 to 4 μm. The amount of the fine pores was about 15% of the entire surface of the skeleton. The porosity of the entire electrode was about 97%.

[Example 3] The electrode obtained in Example 2 was further heat-treated in air at a temperature of about 600 ° C to thermally decompose and remove the organic fiber portion, and then further heated to about 900 ° C in a reducing atmosphere.
An electrode composed of only a metal was obtained by heating and reducing treatment. When the obtained electrode was observed by an electron microscope, the portion where the organic fibers were removed inside the hollow skeleton was seen as a cavity. Further, it was confirmed that the skeleton portion had the same fine pores as before the heat treatment, and the outer surface and the inner surface of the skeleton communicated with each other through the fine pores. Also,
The amount of the fine pores and the thickness of the metal layer were the same as those before the heat treatment in Example 2.

Comparative Example 2 Except that the treatment with the dispersion liquid of polyethylene resin particles was not carried out in Example 2,
Electrodes were manufactured under the same conditions as in Example 2 and Example 3.
No fine pores were found in the skeleton of the obtained electrode. The thickness of the metal layer was about 4 μm, which was similar to that of Example 3, but the specific gravity of the electrode was about 1.2 times that of Example 2, which revealed that there is a problem in reducing the weight of the electrode. Further, since the skeleton has no fine pores, the surface area communicating with the outside is about one half, the specific surface area is small, and the contact area with the active material or the electrolytic solution is small, which proves that there is a difficulty in improving the performance of the electrode. did.

[Example 4] As a porous substrate having a cloth-like structure, felt-like nonwoven fabric (porosity of about 94%) using conductive carbon fibers having a fiber diameter of 13 μm was used as polystyrene resin particles (particle size 2 to 2). (3 μm) and an organic additive were added to the dispersion, and then it was dried. This was electroplated with nickel metal to obtain an electrode. At this time, the plating conditions were adjusted so that the thickness of the metal layer was about 3 μm.
When the obtained electrode was observed by an electron microscope, it was found that the skeleton portion had fine pores of about 2 to 3 μm. The amount of the micropores is 25% of the entire skeleton surface
The area was about the same. The obtained electrode was further heat-treated in an atmosphere furnace at a temperature of 1100 ° C. to remove the carbon fiber portion. When the obtained electrode was observed with an electron microscope, the portion where the carbon fibers were removed inside the hollow skeleton was seen as a cavity. Further, it was confirmed that the skeleton portion had the same fine pores as before the heat treatment, and the outer surface and the inner surface of the skeleton communicated with each other through the fine pores. Also,
The amount of the fine pores and the thickness of the metal layer were the same as those before the heat treatment.

[Comparative Example 3] Except that the treatment with the dispersion liquid of polyethylene resin particles was not carried out in Example 4,
An electrode was manufactured under the same conditions as in Example 4. No fine pores were found in the skeleton of the obtained electrode. The thickness of the metal layer is 3
Although it was about μm and similar to that of Example 4, the specific gravity of the electrode was about 1.3 times that of Example 4, and it was found that there is a problem in reducing the weight of the electrode. Further, since the skeleton has no fine pores, the surface area communicating with the outside is about one half, the specific surface area is small, and the contact area with the active material or the electrolytic solution is small.
It turned out that there is a problem in improving the performance of the electrode.

Example 5 A three-dimensional woven fabric using an organic fiber having a fiber diameter of 20 μm was used as a substrate porous structure having a cloth-like structure. This woven fabric was subjected to electroless nickel plating for electrical conductivity, and then polystyrene resin particles (particle size 4 to
5 μm) and an organic additive were added to the dispersion and dried. This was electroplated with nickel metal to obtain an electrode. At this time, the plating conditions were adjusted so that the thickness of the metal layer was about 6 μm. Observation with an electron microscope revealed that the skeleton had fine pores of about 4 to 5 μm. The amount of the fine pores was about 20% of the entire surface of the skeleton. The obtained electrode is further heat-treated in air at a temperature of about 600 ° C. to thermally decompose and remove the base fiber portion, and then further heated at about 900 ° C. in a reducing atmosphere to perform a reduction treatment. Got When the obtained electrode was observed by an electron microscope, the portion where the organic fibers were removed inside the hollow skeleton was seen as a cavity. Further, it was confirmed that the skeleton portion had the same fine pores as before the heat treatment, and the outer surface and the inner surface of the skeleton communicated with each other through the fine pores. The amount of the fine pores and the thickness of the metal layer were the same as before the heat treatment. The porosity of the entire electrode was about 90%.

[0039]

The electrode of the present invention has a high porosity because it uses a porous structure having fine pores in the skeleton, and the internal surface of the skeleton communicates with the outside through the fine pores, so that the specific surface area is very high. It is large and lightweight, and the electrode reaction with the electrolytic solution and the active material is efficiently performed, and it is useful as various electrodes.
Further, according to the method of the present invention, the electrode of the present invention can be manufactured with high productivity.

[0040]

[Brief description of drawings]

FIG. 1 is a partially enlarged view of a cross-sectional structure of an electrode skeleton of the present invention and an intersecting portion thereof as viewed obliquely.

FIG. 2 is a cross-sectional view of an intersecting portion of skeletons in FIG.

FIG. 3 is a diagram showing a typical structure in the case where the porous structure of the present invention is a three-dimensional network structure having continuous air holes.

FIG. 4 is a view showing a typical structure in the case where the porous structure of the present invention is a woven fabric structure.

[Explanation of symbols]

 1 Skeleton 2 Micropores 3 Hollow part 4 Intersection part 5 Gap part surrounded by skeleton

Claims (4)

[Claims] 1. An electrode comprising a porous structure composed of a skeleton having fine pores. 2. The electrode according to claim 1, wherein the porous structure has a three-dimensional network structure having continuous ventilation holes. 3. The electrode according to claim 1, wherein the porous structure has a cloth-like structure. 4. The method for producing an electrode according to claim 1, wherein the portion of the surface of the skeleton of the base porous structure that forms fine pores is made non-conductive and then electroplated.