JP2001040402A - Porous metallic thin sheet body and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous metallic thin sheet body useful as a current collector plate for battery, and its manufacturing method. SOLUTION: The porous metallic thin sheet body is 10-40 μm in total thickness (t) and has a porous structure consisting of skeletal parts A where metal powder particles of 0.1-20 μm particle size are bonded together and intercommunicating pores B of 1-10 μm pore size and also has 40-70% porosity. In manufacture of this body, a mixture consisting of metal powders, binder components and a disperse medium is prepared, and a thin layer of this mixture is formed on the surface of a sheet body composed of thermally decomposable material. Subsequently, the first heating treatment is performed to remove at least the disperse medium, and then sintering is carried out at a temperature higher than respective thermal decomposition temperatures of the binder components and the sheet body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous metal thin body and a method for producing the same, and more particularly, to a porous metal thin body suitable as a current collector used for supporting an active material in the field of batteries. It relates to a method of manufacturing it.

[0002]

2. Description of the Related Art For example, a nickel electrode, which is a positive electrode of a nickel-hydrogen secondary battery, is usually manufactured as follows. That is, first, a powder of nickel hydroxide that functions as a positive electrode active material and a binder such as carboxymethyl cellulose are kneaded with water to prepare a viscous positive electrode mixture paste. Next, this paste is applied to the surface of a band-shaped current collector plate to be described later, and then dried and press-molded to a predetermined thickness, and then cut into predetermined dimensions.

[0003] In addition, a hydrogen storage alloy electrode as a negative electrode is prepared by kneading the hydrogen storage alloy powder and the above-described binder with water to prepare a viscous negative electrode mixture paste, and collecting the paste into a current collector. After being applied to a plate, drying and forming are sequentially performed, and the plate is cut into a predetermined shape and manufactured. Then, a separator having electrical insulation and liquid retention properties is arranged between the positive electrode and the negative electrode, and then the whole is wound, for example, in a spiral to produce a power generating element. After being housed in a battery can having the dimensions and shapes described above, the entire battery is sealed and a battery is assembled.

[0004] The above-mentioned current collector plate supports an active material component necessary for a battery reaction and simultaneously collects current generated by the battery reaction, and is usually made of a conductive material. A porous sheet is used. Specifically, as the current collector plate for the positive electrode, for example, a punched nickel sheet in which an opening having a predetermined hole diameter is formed in a staggered lattice pattern on a Ni-plated stainless steel plate, Stainless steel sheets and felt-like nickel foam sheets are used.

By the way, in the case of the above-mentioned current collector plate, it can be said that a thinner one is preferable in relation to the capacity of the battery to be assembled. The reason is that, in a power generating element housed in a battery can of a fixed volume, the number of wound layers of the current collector plate forming the same increases and the total area increases, and accordingly, the current collector plate concerned This is because the amount of the active material component supported on the battery also increases, so that the battery capacity increases.

[0006] Further, since it is necessary that the active material component is supported on the current collecting plate without peeling, it is preferable that the current collecting plate has an appropriate porous structure. This is because, in the case of such a porous structure, the above-mentioned positive electrode mixture and negative electrode mixture are also filled in the voids of the porous structure, and it becomes difficult to peel off due to the anchor effect. Each of the above-mentioned conventional current collector plates has a porous structure and has little problem in carrying a mixture or the like, but the thickness is generally 0.05 to 0.1.
Since it is as thick as about mm, it cannot be said that it is always satisfactory as a current collector plate for producing a large capacity battery.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a novel porous metal thin body which has a simple manufacturing process and can manufacture a porous structure, and a method for manufacturing the same.

[0008]

In order to achieve the above object, according to the present invention, the total thickness is 10 to 40 μm.
m, preferably 10 to 25 μm, and the particle size is 0.1 to 0.1 μm.
A porous metal thin body having a porous structure consisting of a skeleton portion formed by bonding 20 μm metal powders to each other and communicating holes having a pore size of 1 to 10 μm, and having a porosity of 40 to 70%. Is provided.

Further, in the present invention, a mixture comprising a metal powder, a binder component, and a dispersion medium is prepared, and a thin layer of the mixture is formed on the surface of a sheet made of a thermally decomposable material. A heat treatment for removing at least the dispersion medium, followed by sintering at a temperature higher than a thermal decomposition temperature of the binder component and the sheet body. You.

More specifically, the metal powder has a particle size of 0.1.
The mixture is prepared so that the volume occupied by the metal powder is 25 to 55% by volume, and the volume ratio between the binder component and the dispersion medium is 75 to 35% by volume in the former case. A method for producing a porous metal sheet prepared as described above is provided.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a thin leaf of the present invention is shown in FIG. 1 as a schematic sectional view. This thin leaf has a particle size of 0.1 to 10
a skeleton portion A formed by three-dimensionally bonding metal powders having a diameter of 1 μm, and a communication hole B having a hole diameter of 1 to 10 μm formed as a three-dimensional gap between the skeleton portions A. Has a porous structure consisting of The total thickness t is 10 to 40 μm, and the porosity represented by the volume ratio of the communication hole B in the entire volume is 40 to 70%.

Therefore, when a paste of, for example, a positive electrode mixture is applied to the surface of the thin leaf body, a part of the paste is filled in the communication hole B to exhibit an anchor effect. Is prevented. Further, the current generated by the battery reaction is effectively collected by using the skeleton portion A of the three-dimensional structure formed by bonding the metal powders as a conduction path. And the total thickness t is very thin, 10 to 40 μm, so that the total area of the current collector plate in the manufactured power generation element also becomes large,
Since the amount of the active material component contained in the battery can of a fixed volume also increases, the assembled battery has a high capacity.

This thin leaf can be manufactured as follows. It is described in detail below. First, a viscous mixture is prepared using metal powder, a binder component, and a dispersion medium as essential components. The metal powder having a particle size of 0.1 to 20 μm is used, and these finally constitute the skeleton A described above. As the metal powder, those having conductivity and corrosion resistance to an alkaline electrolyte, for example, are selected, and specific examples thereof include stainless steel powder, Fe-Ni alloy, and Fe-Ni-Co alloy. it can.

The binder component binds the metal powder to each other when forming a thin layer of the mixture to be described later to prevent the thin layer from deforming, and thermally decomposes during sintering to be described later, and most of the gas is a gas. The communication hole B is formed by being formed and dissipating from the thin layer. In addition, the dispersion medium is a component for uniformly mixing the metal powder and the binder component, and it is easy to form the mixture thin layer on the sheet by adjusting the viscosity of the prepared mixture. It is a component for performing. Further, the gasification and gasification during the drying and sintering of a thin layer described later contribute to the formation of the communication hole B.

As described above, the binder component and the dispersion medium in the mixture determine the pore diameter and porosity of the communication hole B of the finally obtained thin leaf. Therefore, in the present invention, the total amount of the binder component and the dispersion medium is 4 in the total volume of the mixture.
The metal powder occupies a ratio of 5 to 75% by volume. Conversely, the occupied volume of the metal powder is set to 25 to 55% by volume.

When the combined amount of the binder component and the dispersion medium is less than 45% by volume, the porosity of the finally obtained thin body is 40%.
On the contrary, if it is more than 75% by volume, the porosity of the obtained thin body exceeds 70% and the pore diameter of the communication hole also becomes larger than 10 μm, and as a result, the strength characteristics of the thin body are greatly reduced. It is because it falls. When the ratio of the binder component and the dispersion medium is too small (the latter is too large), the pore size of the communication hole B is too large and the strength of the skeleton A is reduced, and conversely, the former is too large. In addition, the viscosity of the mixture decreases, and it becomes difficult to form a thin layer of the mixture described below. For this reason, it is preferable to adjust the total amount of the former and the latter so that the former is 5 to 50% by volume (therefore, the latter is 50 to 95% by volume).

The binder component that functions as described above may be any as long as it binds the metal powder to each other and is finally thermally decomposed and removed in the sintering process described later.
For example, synthetic resins such as vinyl acetate, polyvinyl alcohol, and polyvinyl butyral, and natural resins such as rice paste, pine tar, and cellulose can be used.

As the dispersion medium, various ones can be used according to the kind of the binder component.
For example, when the binder component is a water-soluble resin such as vinyl acetate or polyvinyl alcohol, water can be mentioned as a preferred example, and when the binder component is a water-insoluble resin such as chloroprene or polyvinyl butyral. As a preferred example, organic solvents such as hexane and alcohol can be mentioned.

Further, as the dispersion medium, a medium which is solid at room temperature but melts by a slight heat treatment, such as paraffin wax or carnauba wax, can also be used. In that case, a mixture is prepared by mixing the metal powder and the binder component at a temperature at which the dispersion medium is melted and liquefied.
Next, a thin layer of the mixture prepared with the above components is formed on the surface of the sheet body.

For example, as shown in FIG.
The mixture 3 is supplied onto the sheet 2 which is pulled out from the roll 1b and travels to the roll 1b side, and is shaped into a predetermined thickness by, for example, a doctor blade 4 arranged downstream to form a thin layer 3a. At this time, the thickness of the thin layer 3a is adjusted such that the thickness of the thin leaf member finally becomes 10 to 40 μm in view of the contraction of the mixture during drying and sintering described later.

The thin layer 3a thus formed is in a wet state when it passes the doctor blade 4 in FIG. Then, the sheet body 2 is sent to, for example, a drying furnace 5 and heat treatment is performed at a predetermined temperature. During this process, at least the dispersion medium constituting the thin layer 3a is dried and removed. Then, in the thin layer 3a, voids that communicate with each other three-dimensionally are generated with the removal of the dispersion medium, and at the same time, the metal powders are mutually bound by the binder component.

The temperature at this time may be at least a temperature at which the dispersion medium evaporates, but may be set to a temperature higher than the thermal decomposition temperature of the binder component by further increasing the temperature. In that case,
The binder component binding the metal powders to each other is also thermally decomposed, and most of the binder volatilizes from the thin layer 3a, and the residue keeps the binding state of the metal powder and the three-dimensionally formed thin layer 3a. Is formed. Conversely,
At this point, a precursor of the skeleton formed by combining the metal powders is formed.

At this time, the sheet 2 is also subjected to a heat treatment. Then, depending on the type of the sheet body 2, in this process, part or all may be thermally decomposed, or may not be thermally decomposed. In the former case, the support sheet for the thin layer 3a after the heat treatment will disappear,
The strength of the thin layer 3a is appropriately maintained by the shrinkage phenomenon accompanying the volatilization of the dispersion medium and the binder component, and the shape is maintained by the residue of the binder component. Will not wake up.

When, for example, paraffin wax is used as the dispersion medium, the mixture is heated to be in a fluidized state at the time of forming a thin layer and is applied to a sheet, and after the coating is cooled and solidified, The paraffin wax may be dissolved and removed, for example, by immersing the thin layer 3a in methylene chloride without performing the above-described drying treatment. In addition, the thin layer 3a
The formation of is not limited to the application by the doctor blade shown in FIG. 2, but, for example, as shown in FIG. 3, the sheet members 2 and 2 are arranged to face the pair of rolls 6a and 6b, respectively. The thin layer 3a having a desired thickness may be roll-formed between the sheet bodies 2 and 2 by disposing the mixture 3 on the sheet bodies 2 and 2 and rotating the rolls 6a and 6b. At this time, the thickness of the thin layer 3a can be adjusted to a desired thickness by adjusting the interval between the rolls 6a and 6b.

Then, the thin layer 3 thus manufactured
a, or a united sheet of the sheet body 2 and the thin layer 3a is wound by a roll 1b, and then subjected to a sintering process described later. That is, as shown in FIG. 4, the thin layer 3a (or the united sheet) drawn from the roll 1b is sent to the sintering furnace 6, where it is sintered at a predetermined temperature and then wound up on the roll 1c. .

As the sintering furnace 6, a non-oxidizing atmosphere furnace is used in order to prevent oxidation of the metal powder, and specifically, a hydrogen furnace is preferable. In this sintering process, the binder component and the sheet body are completely thermally decomposed and removed, and the metal powder of the skeleton precursor formed during the heat treatment is interconnected by the carbonized binder component, In addition, a part of the metal powder is converted into a skeleton A which is bonded to each other, for example, in a sintered state. That is, after this sintering, as shown in FIG. 1, a thin leaf body composed of only a sheet having a porous structure including a skeleton A and a communication hole B three-dimensionally communicating therewith is manufactured. .

The temperature at this time is set to a temperature at which the binder component and the sheet are reliably thermally decomposed, and further set to a temperature at which sintering of the metal powder is possible. For example,
When the metal powder is SUS316 equivalent stainless steel powder, the temperature may be set to about 900 to 1350 ° C.
In the above description, the first heat treatment and the next sintering are performed in separate steps. In the present invention, these two steps may be assembled as a continuous step.

[0028]

EXAMPLE 1 15% by volume of vinyl acetate (binder component) was added to water (dispersion medium) 8
53% by volume of a solution dissolved in 0% by volume and a maximum particle size of 15μ
stainless steel powder having a mean particle size of 6 μm (SUS31
And 6% by volume) to prepare a slurry-like mixture.

A cellulose sheet (pyrolysis temperature: 500 ° C.) having a thickness of 100 μm was prepared, and the mixture was applied to one surface thereof, and then a mixture thin layer having a thickness of about 25 μm was formed with a doctor blade. Then, after the sheet is naturally dried, it is sent to a drying oven at a temperature of 150 ° C. and subjected to a heat treatment for 5 minutes.
Minutes of sintering.

A thin metal leaf having a thickness of 22 μm was obtained. When the thin leaf was observed under a microscope, the skeletal portion in a state where the stainless steel powders were bonded to each other, and a pore diameter of 1 to 10 μm
And a porosity of 5%.
It was 0%. Example 2 A slurry was prepared by dissolving 10% by volume of chloroprene in 80% by volume of hexane and mixing 53% by volume of the obtained solution with 47% by volume of SUS434L powder having a maximum particle size of 15 μm and an average particle size of 6 μm. .

This was applied to one surface of a cellulose sheet in the same manner as in Example 1 to form a thin layer having a thickness of about 25 μm. Next, after the sheet was air-dried, it was sent to a drying furnace at a temperature of 150 ° C. and subjected to a heat treatment for 5 minutes. Then, the sheet was introduced into a hydrogen furnace and sintered at a temperature of 1150 ° C. for 15 minutes.

A thin metal body having a thickness of 23 μm and a porosity of 47% was obtained.

[0033]

As is apparent from the above description, according to the present invention, a metal leaf having a porous structure having an extremely thin overall thickness of 10 to 40 μm and a porosity of 40 to 70% is produced. be able to. When the thin metal sheet is used as a current collector plate of a battery, it is possible to prevent the active material carried on the surface from being peeled off due to the porous structure, and to increase the amount of the contained active material, thereby increasing the capacity. Battery can be assembled.

The thin metal leaf can be used in the field of a filter for separating fine particle components since the diameter of the communicating hole formed therein is 1 to 10 μm.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a porous thin metal sheet of the present invention.

FIG. 2 is a schematic diagram showing a state where a mixture is applied to a sheet body.

FIG. 3 is a schematic diagram illustrating another example of forming a thin layer of a mixture.

FIG. 4 is a schematic view showing a state in which a thin layer is sintered.

[Explanation of symbols]

 Reference Signs List A Frame part B Communication hole 1a, 1b, 1c, 6a, 6b Roll 2 Sheet 3 Mixture 3a Thin layer of mixture 3 4 Doctor blade 5 Drying furnace 7 Sintering furnace

Claims (2)

[Claims] 1. The overall thickness is 10 to 40 μm,
It has a porous structure consisting of a skeleton part formed by bonding metal powders having a particle size of 0.1 to 20 μm with each other and a communication hole having a pore diameter of 1 to 10 μm, and has a porosity of 40 to 70%. Porous metal leaf. 2. A mixture comprising a metal powder, a binder component and a dispersion medium is prepared, and a thin layer of the mixture is formed on the surface of a sheet made of a thermally decomposable material. Removing at least the dispersion medium and sintering the binder component and the sheet at a temperature higher than the thermal decomposition temperature of the sheet.