JPH0613084A - Electrode and its manufacture - Google Patents

Abstract

PURPOSE:To facilitate the measurement of dimension, and manufacture an electrode having a high dimensional precision by forming the electrode from a core part consisting of a porous metal and a metal mesh closely adhered to the outside to cover it. CONSTITUTION:At least one kind selected from the group consisting of metal staples, metal sponge pieces and metal mesh pieces is kneaded with an organic material, for example, a resin solution, and the resulting kneaded material is formed into a sheet to form a metal base 1. A metal mesh 2 is arranged on its outside, and the base 1 is closely adhered to the mesh 2 and laid into a continuable composite sheet state. This is pressurized and integrated by use of a roll, and heat-treated to provide a porous electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode and a method for producing the same, more specifically, a porous electrode which can be used as a positive electrode for a secondary battery by filling the inside thereof with an active material, and the method for producing the same. Regarding the method.

[0002]

2. Description of the Related Art For example, a material obtained by filling a porous Ni substrate with nickel hydroxide (NiOOH) as an active material is used as a positive electrode of a secondary battery having a negative electrode of a Zr-Ni-based hydrogen storage alloy. There is. As the above-mentioned porous Ni substrate, in order to increase the reaction surface area as an electrode and improve the battery efficiency, a porous structure having a porosity (porosity) of about 80% is usually used.

Conventionally, this porous Ni substrate is manufactured as follows. That is, first, the viscosity is 1000 to
A small amount of a polyfunctional polyol of about 2000 cps, a small amount of a polyfunctional polyol, a foaming agent such as Freon 22 or water, and a conductive agent such as carbon or palladium are mixed in a predetermined amount to prepare a main agent. After stirring and mixing a curing agent such as toluene diisocyanate with stirring means such as an impeller attached to the head of a low pressure foaming machine,
The obtained mixed liquid is continuously dropped on, for example, a conveyor belt.

Then, the mixed liquid dropped and conveyed by the conveyor belt causes a self-exothermic reaction in the course of a time of several tens of seconds, foams, and hardens to several tens to several times.
It becomes a polyurethane foam of 100 times and moves continuously on the conveyor belt. The obtained polyurethane foam is cut into a length of a predetermined size with, for example, a cutter, and then the cut piece is further cut with a cutting means such as a slicer to have a thickness of, for example, about 1.4 to 1.7 mm. It is processed into a thin piece with a porous communication structure.

Then, the obtained porous flakes are immersed in a known electroless nickel bath to form a Ni plating film having a thickness of about 0.2 to 2 μm on the surface of the skeleton made of polyurethane. Finally, the electroless nickel-plated foam is left in a circulating hot air oven whose temperature is controlled at 400 to 500 ° C. for about 1 to 2 hours to thermally decompose and remove the polyurethane, which is the skeleton of the foam. . As a result, the Ni plating film covering the surface of the skeleton of polyurethane remains as it is, and a porous body having a communication structure having Ni as a skeleton is obtained there.

[0006]

By the way, the polyurethane foam is an elastic body and its rigidity is low. Therefore, in the case of the conventional method described above, when the cut piece of the polyurethane foam is further sliced and processed into a thin piece, the cut piece sliced by the movement of the slicing blade causes elastic deformation, and the obtained thin piece is The dimensional accuracy drops. Although it is required to keep the dimensional accuracy in the thickness direction within the tolerance range of 0.01 to 0.2 mm due to the relationship with the battery efficiency, it is extremely difficult to put the thickness of the flakes within this tolerance range in the above method. Have difficulty.

When measuring the dimensions of the thin piece, when a measuring tool such as a caliper or a micrometer is used in contact with the thin piece, since the thin piece is an elastic body, the contact point is elastically deformed. Then, the measurement error of the obtained measurement value becomes very large. Such a problem is a thin section -2
This can be solved by taking measures to prevent elastic deformation by freezing to a low temperature of 0 ° C. or less, but such measures are not practical such as requiring a refrigerating device.

Further, regarding the dimension measurement, for example, CCD
It is possible to apply the non-contact type method using a camera, but it is difficult to accurately measure the outer contour of the thin piece to be applied because it is a foam with a communication structure, and the obtained measured value Inevitably, an error of 0.01 to 0.5 mm is unavoidable. Further, the following problems may occur during the thermal decomposition and removal of the polyurethane skeleton by the above method.

That is, when the skeleton of polyurethane is thermally decomposed, decomposed gas is generated. When the Ni plating film covering the skeleton has fine cracks, the decomposed gas evaporates from these cracks, but when the skeleton is completely covered with the Ni plating film, The decomposed gas is sealed in the plating film, and this causes bumping from the weak film portion to partially rupture the Ni plating film, and the surface of the obtained porous Ni skeleton becomes uneven.
As a result, when the porous body is incorporated as an electrode to form a secondary battery, the current efficiency is lowered.

Further, the above-mentioned manufacturing method has a problem that the whole process is complicated and the manufacturing cost of the obtained electrode is increased. An object of the present invention is to provide an electrode which solves the above-mentioned problems of the conventional porous electrode, enables easy measurement of dimensions, and has high dimensional accuracy, and a method for producing the same. .

[0011]

In order to achieve the above-mentioned object, the present invention comprises a core made of a porous metal substrate and a metal mesh for tightly enclosing the outside of the core. An electrode characterized by the above is provided, and at least one selected from the group of short metal fibers, metal sponge pieces, or metal mesh pieces is kneaded with an organic substance, and the obtained kneaded product is a cylinder made of a metal mesh. A method for manufacturing an electrode, which comprises filling a shaped body, pressurizing and molding, and then heating the obtained shaped body to thermally decompose and remove the organic substance, and metal short fibers, metal sponge pieces, or At least one selected from the group of metal mesh pieces is kneaded with an organic substance, the obtained kneaded product is formed into a sheet, and then the metal mesh is superposed on both sides of the formed sheet, followed by pressure forming to obtain a composite sheet. When , Method of manufacturing an electrode, characterized in that the resulting removal pyrolysis the organic material by heating the composite sheet is provided.

In the electrode of the present invention, as shown in FIG. 1, the core portion is made of a porous metal substrate 1 having a predetermined thickness, and a metal mesh 2 is arranged outside the porous metal substrate 1, and the porous metal substrate 1 and the metal mesh are provided. 2 are in close contact with each other and are in a conductive state. Considering that the electrolyte of the secondary battery is a strong alkali, these porous metal substrates and metal meshes are made of, for example, a strong alkaline resistant material such as Ni, mild steel or stainless steel whose surface is coated with Ni. Is preferably provided.

The porous metal substrate 1 is composed of short fibers or mesh pieces of a predetermined metal intertwined with each other or sponge pieces assembled together, and has a communication structure as a whole. When the substrate 1 is composed of metal short fibers, if the length of the short fibers is longer than the thickness of the substrate 1, the short fibers are entangled with the metal meshes located on the upper and lower surfaces, and electrical continuity is achieved. It is preferable because the condition becomes good.

The electrode having the structure shown in FIG. 1 can be manufactured as follows. First, a short fiber having a predetermined length, a metal sponge piece crushed to a predetermined particle size, or a metal mesh cut into a predetermined size is used as a filler, and an organic substance is mixed with the filler to knead both. As the organic substance, for example, a thermoplastic resin such as acrylic resin, polyvinyl alcohol, or a polyvinyl acetate / polyvinyl alcohol copolymer is dissolved in an organic solvent such as ethyl acetate, isopropyl alcohol, or a methanol / isopropyl alcohol mixed solution. The resin solution is used. At this time, the ratio of the thermoplastic resin to the organic solvent is determined so that the viscosity of the obtained resin liquid allows the kneading of the filler to be sufficiently performed.

The mixing ratio of the filler and the organic substance is determined in consideration of the relationship with the target porosity of the electrode and the difficulty of kneading. For example, if the amount of the filler is too large, the uniform kneading operation becomes difficult, and if the amount of the filler is too small, the kneading property of the obtained kneaded product becomes poor and, at the same time, the resulting electrode becomes excessively porous and its mechanical strength is deteriorated. Therefore, the organic substance is usually added in an amount of 20 to 20 parts by volume with respect to 5 to 20 parts by volume of the filler.
It is preferably 60 parts by volume.

The kneading is preferably carried out at a constant temperature using a kneader equipped with a pressurizing means such as a press kneader. This is because if the filler and the organic substance are kneaded while applying pressure, the both can be uniformly kneaded, and a porous metal substrate having a uniform communication structure can be easily obtained. At the time of kneading, an appropriate amount of a volatile solvent such as polyvinyl alcohol may be added to adjust the viscosity of the kneaded product.

Then, the obtained kneaded product is filled in a mold having a predetermined shape such as a bottomed cylindrical body and dried at a constant temperature to form the kneaded product into the shape of the above-mentioned mold. To do. The molded body of the kneaded material thus obtained is inserted into the tubular body of the metal mesh. The tubular body used is Ni
A braided metal fiber made of Ni alloy or Ni alloy is preferable. This is because the braid is highly stretchable and the pressure molding described later becomes easy.

It should be noted that, without using a tubular body of metal mesh, for example, a known braiding machine is used to continuously knit a predetermined metal fiber as a braid on the outer periphery of the molded body of the kneaded product to form a molded product. You may arrange | position a metal mesh on the outer periphery of. Then, as shown in FIG. 2, the composite A inserted into the tubular body 2 of the metal mesh braided with the molded body 1'of the kneaded material was laid down on the base 3 and the whole was used. The molded body 1 ′ is softened by heating it at a temperature lower than the thermal decomposition temperature of the organic substance, and is pressed from the side surface of the composite A by a plurality (two in the figure) of rollers 4a and 4b to have a predetermined thickness and width. To form a plate-shaped body B having

At this time, by appropriately selecting the distance between the roller 4b and the base 3, it is possible to obtain a plate state having an arbitrary thickness. The plate-shaped body B thus obtained is an electrode precursor in which the molded body 1 ′ is the core portion and the four circumferences are surrounded and bent by the metal mesh 2. In this precursor, the surface of the core portion and the metal mesh are pressure-bonded to each other, so that the soft core portion is press-fitted into the eyes of the metal mesh to realize a good bonding state with each other.

After the plate-like body B is cut into an appropriate length,
It is introduced into the furnace at a temperature higher than the thermal decomposition temperature of the organic substance used. The organic substance in the core is thermally decomposed, the generated decomposition gas is volatilized, and only the short metal fibers or metal mesh pieces intertwined with each other or the metal sponge pieces gathered in the state of being pressed against each other remain in the core portion. To do. As a result, a porous electrode having a communication structure as shown in FIG. 1 is obtained.

According to the method of the present invention, the kneaded material is formed into a sheet having a predetermined thickness, and the kneaded material sheet is sandwiched on both sides with a metal mesh to form a composite sheet. By pressurizing and integrating, and finally heat-treating the integrated sheet, as shown in FIG. 3, a porous electrode having a structure in which the metal mesh 2 is integrated on both surfaces of the porous core part 1 is obtained. It can be manufactured.

In the electrode manufactured in this manner, the outer metal mesh and the porous metal substrate of the core are mechanically entangled with each other and bonded together. Is preferable because the binding force of the entangled portions increases.

[0023]

Examples of the invention

Example 1 Ni short fibers having an average diameter of 15 μm and an average length of 0.3 mm, a resin solution prepared by dissolving 40% by volume of an acrylic resin in 60% by volume of ethyl acetate, and polyvinyl alcohol were placed in a pressure kneader. The mixture was added at a volume ratio of 5: 40: 12.5 and kneaded at room temperature for 1 to 2 hours while applying a pressure of 30 to 50 kg / cm ² .

The kneaded product thus obtained was filled in a mold and left to stand at a constant temperature for about 1 hour to be dried to obtain a cylindrical molded product having a diameter of 22.5 mm. A cylinder having a diameter of 30 mm prepared by braiding Ni fibers having a wire diameter of 7.5 μm was prepared, and the above-mentioned cylindrical molded body was inserted into this cylinder to obtain a composite body. Then, the obtained composite was laid on a base, and the whole was heated to 85 ° C. to soften the molded product and pressure-molded using a multistage roller to give a thickness of 40.
The plate was made to have a thickness of 0 μm.

The obtained plate-like body was left in a hot air oven whose temperature was controlled at 400 ± 10 ° C. for 1 hour to remove the acrylic resin and the solvent to obtain a porous electrode of the present invention. The thickness of the obtained electrode was 395 to 397 μm, and the variation was within 2 μm. Example 2 The kneaded material prepared in Example 1 was roll-formed to have a thickness of
I made a 1.4mm sheet.

The fiber diameter is 15 on both sides of the sheet of this kneaded product.
It is sandwiched between meshes of Ni fiber of μm, and the whole temperature is 8
Roll molding was performed at 5 ° C to a thickness of 1.1 mm. The obtained composite sheet was heat-treated under the same conditions as in Example 1. The overall thickness
A porous electrode having a thickness of 1.05 to 1.07 mm and a variation of 20 μm or less was obtained.

[0027]

As is apparent from the above description, according to the method of the present invention, the thickness of the electrode can be strictly controlled by the distance between the base and the roller at the time of pressure molding. The dimensional accuracy of is very high. In addition, since the materials used are not elastic bodies such as polyurethane foam, the dimensions can be easily measured. The electrode manufactured by the method of the present invention has high dimensional accuracy, and thus is very useful as a positive electrode of a secondary battery having a core filled with an active material.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of an electrode of the present invention.

FIG. 2 is a perspective view showing a state in which the precursor of the electrode of FIG. 1 is pressure-molded.

FIG. 3 is a cross-sectional view showing another example of the electrode of the present invention.

[Explanation of symbols]

 1 Porous Metal Substrate 1'Molded Material Formed Body 2 Metal Mesh 3 Base 4a, 4b Roll

Claims (3)

[Claims] 1. An electrode comprising: a core portion made of a porous metal substrate; and a metal mesh that tightly covers and encloses the outside of the core portion. 2. At least one selected from the group of metal short fibers, metal sponge pieces, or metal mesh pieces is kneaded with an organic substance, and the obtained kneaded product is filled in a tubular body made of a metal mesh and then added. A method for producing an electrode, comprising performing pressure molding, and then heating the obtained molded body to thermally decompose and remove the organic substance. 3. At least one selected from the group consisting of short metal fibers, metal sponge pieces, or metal mesh pieces is kneaded with an organic substance, the obtained kneaded product is molded into a sheet, and then the molded sheet A method for producing an electrode, comprising laminating metal meshes on both sides and press-molding to form a composite sheet, and heating the obtained composite sheet to thermally decompose and remove the organic substance.