CA2254504A1

CA2254504A1 - Method of manufacturing a porous metallic sheet for use as an electrode substrate of a battery

Info

Publication number: CA2254504A1
Application number: CA002254504A
Authority: CA
Inventors: Hirofumi Sugikawa
Original assignee: Individual
Current assignee: Katayama Special Industries Ltd
Priority date: 1994-11-28
Filing date: 1995-11-27
Publication date: 1996-05-29
Also published as: CA2254551C; CA2254551A1; CA2254640A1

Abstract

The present invention relates to a method of manufacturing a porous metallic sheet for use as an electrode substrate of a battery. The method comprises the steps of forming a mixture by kneading metallic powders and resin binder;
spinning metallic fibers by extruding the mixture from a spinning nozzle; and forming the spun metallic fibers into a porous fibrous structure or a three-dimensional net-shaped structure.

Description

CA 022~4~04 1998-11-23 METHOD OF MANUFACTURING A POROUS METALLIC SHEET FOR USE AS AN
ELECTRODE SUBSTRATE OF A BATTERY

This is a divisional application of co-pending Canadian Patent Application Serial No. 2,163,819 that was filed on November 27, 1995.
The present invention relates to a method of manufacturing a porous metallic sheet to be used as a substrate of a battery electrode. More particularly, the present invention relates to a method of manufacturing a porous metallic sheet to be used as the substrate of positive and negative plates of a nickel hydrogen battery, a nickel cadmium battery, a primary lithium battery, a secondary lithium battery, and the like.
Heretofore, as the substrate of positive and negative electrode plates of a nickel hydrogen battery and a nickel cadmium battery, a nickel-plated punched iron metal on which pores have been formed by a press is principally used. The electrode plate is formed by applying an active substance to the punched metal. A cylindrical battery accommodates belt-shaped positive and negative electrode plates coiled with a separator, while a rectangular solid battery accommodates the positive and negative electrode plates laminated one on the other with a separator.
As the substrate of the positive and negative electrode plates of a primary lithium battery, a metallic plate (SUS, Ti) formed into a lath net is mainly used. An active substance is applied to the lath net to form the electrode plate. In the case of a secondary lithium _. .. .

CA 022~4~04 1998-11-23 battery, the positive plate is formed by applying the active substance in a required thickness to both surfaces of a metallic core made of aluminum foil, whereas the negative plate is formed by applying the active substance in a required thickness to both surfaces of a metallic core made of copper foil.
In recent years, a foamed sheet made of resin, a nonwoven cloth made of resin, and a mesh sheet made of resin have been chemically plated to allow them to be conductive and then, electrically plated. Then, resin removal and sintering operations are performed to form a porous metallic sheet to use it as the substrate of the electrode plate of a nickel hydrogen battery, a nickel cadmium battery, and a primary lithium battery.
The punched metal used as the substrate of the electrode plate for a nickel hydrogen battery and the like has the following disadvantages:
(1) The portions to be formed into pores are cut off when the punched metal is punched by a press. For example, when the percentage of pores is 50~, half of the material is lost. As such, the production cost is high.

(2) It is expensive to operate a press to be used to form the pores.

(3) Because the pores are two-dimensional, the percentage of pores is 50% at most. Thus, there is a limitation in the amount of an active substance to be applied to the pores.

CA 022~4~04 1998-11-23 (4) In order to increase the capacity of a bat-tery, it is preferable to use a thin substrate having a high percentage of pores, so as to enable a large amount of active substance to be applied to the pores. But there is a limitation in the percentage of pores for the reason described above. Further, in order to reduce the thickness of the substrate from 60-80~m to less than 60~m, the material cost is high and the punched metal is plated at low efficiency. That is, the processing cost is high. In addition, if the substrate is thin, it is easily deformed or a burr is easily formed thereon when forming the pores by the press.
In the case of a metallic plate processed into a lath net used as the substrate of the electrode of a primary lithium battery, the metallic plate is deformed and warped due to stress locally concentrated in processing the metallic plate. That is, the metallic plate becomes unflattened. A lath net deformed and warped is corrected by a leveller without changing the original size in order to produce the substrate at a low cost. The active sub-stance is then applied to the lath net. The lath net is then cut into a plurality of pieces having a size that meets the battery standards. At this time, the deformation generated when the metallic plate has been processed into the lath net is regenerated and burrs are likely to occur.
As a result, when the lath net is coiled with a separator, there is a possibility that the burr and the deformation cause leakage. It is preferable for the electrode of a CA 022~4~04 1998-11-23 primary lithium battery to have a high percentage of pores, so long as the lath net has an adequate strength. But structurally, the lath net should not have the percentage of pores more than 63~. There is another problem that, the higher the percentage of pores, the higher the material cost is.
A porous metallic sheet formed by plating a base porous sheet made of resin, successively burning out and sintering the plated material sheet used as the substrate of the electrode plate developed to replace the punched metal and the lath net, has a high percentage of pores and allows a large amount of active substance to be applied to the pores thereof. But it is necessary to chemically and electrically plate a porous sheet of resin, which is a complicated process. Hence, the plated porous metallic sheet is produced with an unfavourable productivity.
Further, chemicals such as a plating liquid are used and much power is consumed. Therefore, the production cost is high. In addition, the management of the treatment liquid and countermeasure against pollution are required.
Furthermore, after the surfaces of organic fibers are chemically plated with a conductive substance, the conductive substance is electrically plated to a thickness of 25~m - 50~m. As a result, the outer diameter of each fiber (mixture fiber) consisting of an organic fiber and plated metal becomes large. When the organic fiber is burnt out continuously the plated metal is sintered, the portion of the fiber occupied by the organic fiber becomes CA 022~4~04 1998-11-23 hollow. As a result, the resultant metallic fiber is annular and has a large diameter. That is, the resultant porous metallic sheet has a structure in which the pores are surrounded by a framework made of metallic sleeves having cavities.
In order to use the porous metallic sheet as an electrode plate, the active substance is applied to pores of the plated sheet. But it cannot be applied to the cavities of the sleeves. Thus, the cavities are reactive portions in the electrode plate. Further, because the outer diameter of each of the sleeves is large, the plated sheet has a small volume of pores surrounded by metallic cylinders. Therefore, a large amount of the active sub-stance cannot be applied to such a plated porous metallic sheet.
When a sheet structure composed of organic fibers, for example, a nonwoven sheet composed of organic fibers, is electrically plated after it is allowed to become conductive, metal is deposited thickly on the surface of the nonwoven sheet, while it is not deposited much in the interior (center portion in the thickness direction of the sheet), i.e., the deposition amount of metal in the interior is about half as much as that on the surface.
That is, it is difficult to make the amount of a metallic framework on the surface equal to that on the entire sheet.
In order to use the porous metallic sheet as the substrate of the electrode of a battery, as described above, the active substance is applied to the pores, and CA 022~4~04 1998-11-23 thereafter it is pressurized to adjust the thickness thereof to the standard one. It is easy to apply the active substance to a porous metallic sheet having a large thickness and a high percentage of pores.
According to the conventional art, it is not easy to produce a thick porous metallic sheet formed by coating the surface of the nonwoven sheet made of organic fibers with a conductive substance and electrical plating.
That is, supposing that in the conventional nonwo-ven sheet comprising organic fibers, the quantity of fiber is 40 - 50 g/m2; the quantity of resin binder is 20 g/m2;
the total weight is 60 - 70 g/m2; and the percentage of pores is 95~, the maximum thickness thereof is 2.5mm -3.5mm. After a nonwoven sheet having the above thickness is subjected to an electric conduction treatment, electric plating, resin burning out, and sintering, it is difficult to produce a porous metallic sheet having a thickness of 1.6mm.
Further, the conventional nonwoven sheet is pro-duced by using short organic fibers. The short organicfibers are knitted into the nonwoven sheet by a spinning carding machine and a resin binder is used to connect the fibers to each other. In a nonwoven sheet composed of organic fibers thus produced, resin binder (R) is collected at the intersections of the organic fibers (f), thus forming lumps at the intersections, as shown in Fig. 28.
When the nonwoven sheet is subjected to an electric conduction treatment and electrical plating, the diameters CA 022~4~04 1998-11-23 of the fibers are large at the intersections. Thus, when the organic fibers are subjected to resin burning out and sintering operations, the resin lumps become hollow at the intersections. Thus, as described above, the active substance cannot be applied to the hollow portions, and thus the hollow portions are unconductive, and further, the diameters of the fibers are great at the intersections.
Accordingly, the nonwoven sheet has a small volume of pores. Thus, a large amount of active substance cannot be applied to the porous metallic sheet.
The higher the percentage of pores, the greater the amount of active substance that can be applied to the porous metallic sheet to be used as the electrode plate, so that the electrode plate has a long life. The smaller the area of each pore, the greater the area of contact between the metal and the active substance. That is, the higher the percentage of pores and the smaller the area of each pore, the more favourable is the performance of the elec-trode plate.
According to the conventional art, in order to reduce the areas of the pores in producing the conventional porous metallic sheet by plating the surface of the organic fibers, it is necessary to make the dense meshes of the sheet comprising the organic fibers small. But the surface of each organic fiber is plated and the organic fibers are burnt out. As a result, the resultant porous metallic sheet has a small percentage of pores and many cavities formed as a result of the removal of the organic fibers.

CA 022~4~04 1998-11-23 Aluminum foils and copper foils have hitherto been used as the substrate of the electrode plate of a secondary lithium battery. The active substance is applied to both surfaces of each solid metallic foil in the same thickness while the metal foil is being drawn. But, because the metallic foil has a small strength, the production line cannot be operated at high speed. Further, it is not easy to apply the active substance to the upper and lower surfaces of the metallic foil with the same thickness.
Actually, the thickness of the active substance applied to the upper surface of the foil is often different from that applied to its lower surface. As a result, the active substance is not consistent in charge and discharge times, and hence the active substance cannot be utilized effi-ciently in a battery case.
A substrate for an electrode plate that satisfiesall the following requirements has not yet been provided.
(a) The substrate has a high conductivity: The internal resistance of a battery is set to a small value so as to perform the electricity-collection action smoothly.
(b) The substrate has a high percentage of pores:
A large amount of an active substance can be applied to the substrate to increase the capacity of the battery.
Even though a large amount of active substance can be applied to the substrate, electricity-collection action cannot be performed smoothly when the area of contact between the metal and the active substance is small. Thus, it is necessary for the substrate to have a high percentage CA 022~4~04 1998-11-23 of pores and a large area of contact between the metal and the active substance.
(c) The thickness of the substrate is small and the substrate has a large tensile strength. If the substrate is thin, the battery can achieve a high performance by accommodating a large amount of substrate in the battery case.
(d) The substrate is provided with an electricity-collection lead and is produced in a required configuration at low cost.
The present invention has been made in view of the above-described conventional problems, and it is an object of the present invention to provide a porous metallic sheet to be used as an electrode substrate of a battery having the above-described requirements; an electrode plate formed by applying an active substance to the porous metallic sheet; and a method for manufacturing the porous metallic sheet and the electrode plate.
It is another object of the present invention to reduce the manufacturing cost by eliminating a conduction treatment, such as chemical plating, and the management of a treating solution, and by saving the rate of electric power consumption.
In order to achieve the above-described objects, according to the first aspect of the invention, there is provided a porous metallic sheet for use as an electrode substrate of a battery, having a porous fibrous structure or a three-dimensional net-shaped structure in which a CA 022~4~04 1998-11-23 framework surrounding pores of the porous fibrous structure or those of the three-dimensional net-shaped structure is formed of metallic fibers made of metallic powders.
The porous fibrous structure can consist of a nonwoven sheet, a woven sheet, a knitted sheet, a felt sheet, a screen-shaped sheet, an expanded sheet, or a net-shaped sheet. The three-dimensional net-shaped structure can consist of a foamed sheet, a spongelike sheet, or a honey-comb-shaped sheet.
As described above, metallic fibers made of metal-lic powders are formed into a sheet having the porous fibrous structure consisting of a nonwoven sheet, a woven sheet, a knitted sheet, and the like or into the three-dimensional net-shaped structure. The method of forming the metallic fibers into these structures eliminates the plating process.
Heretofore, the porous metallic sheet has been formed by plating organic fibers and then burning out the organic fibers. Thus, cavities to which the active sub-stance cannot be applied are generated in a resultingsheet. According to the present invention, because the framework surrounding the pores consists of solid metallic fibers, cavities to which the active substance cannot be applied are not generated in the porous metallic sheet.
That is, a large amount of an active substance can be applied to the porous metallic sheet.
Further, the conventional metallic fibers are hollow, whereas the metallic fibers according to the CA 022~4~04 1998-11-23 present invention are solid. Thus, the metallic fibers according to the present invention can be allowed to have small diameters, thus increasing the percentage of pores.
Accordingly, a large amount of active substance can be applied to the porous metallic sheet.
That is, supposing that the same spinning nozzle is used, according to the conventional method the surfaces of the organic fibers extruded from the spinning nozzle are plated. Thus, the outer diameters of the organic fibers become large. On the contrary, according to the present invention, fibers extruded from the spinning nozzle are metallic fibers. Therefore, it is unnecessary to plate the surface of the metallic fibers. When the porous sheet made of the metallic fibers is subjected to burning out and sintering operations, the diameters of the metallic fibers become small.
With a high percentage of pores, a large amount of active substance can be applied to the porous metallic sheet per unit area.
The performance of the battery cannot be improved when large area pores are formed to apply a large amount of active substance thereto. However, the performance of the battery can be improved when the gap between the metallic fibers (framework) which flows the electricity to the active substance is small and the area of contact between the metallic fibers and the active substance is large.
Because the percentage of pores in a porous metal-lic sheet of the present invention is the same as that of CA 022~4~04 1998-11-23 a conventional sheet, the porous metallic sheet of the present invention can be composed of a larger number of metallic fibers than the conventional sheet. Therefore, in a metallic sheet of the present invention, the gap between the metallic fibers is allowed to be small, and, in addi-tion, the area of contact between the metallic fibers and the active substance is large. This structure increases the electrical conduction performance of the active sub-stance, thus improving the performance of the electrode plate.
Further, because metallic fibers are woven or knitted and intertwined with each other to form the sheet having the porous fibrous structure, metallic frameworks are present uniformly on the surface and the interior of the sheet. On the other hand, according to the conven-tional art, when a porous metallic sheet is formed by electrically plating the organic fibers, the amount of metal that deposits on the organic fibers located in the interior of the sheet is about half as small as that of the metal that deposits on those located on the surface of the sheet. A porous metallic sheet of the present invention does not have this disadvantage.
The diameters of the metallic powders can be in the range from 0.1~m to 5~m. As a metallic fiber made of metallic powders, continuous or long metallic fibers having diameter 1.0~m - 100~m are preferable. The smaller the diameter of the fiber, the higher percentage of pores, and, CA 022~4~04 1998-11-23 further, the area of one pore can be reduced without decreasing the percentage of pores in the sheet.
A porous metallic sheet made of long or continuous metallic fibers has a tensile strength 1.5 - 3 times as great as that of a porous metallic sheet produced by the conventional method, namely, made by electrically plating the organic fibers and then burning out and sintering them.
Accordingly, because the porous metallic sheet has a high tensile strength, it can be drawn at high speed while it is being fed for the application of the active substance.
As necessary, the surface of the metallic fibers may be electrically plated in the present invention. The plating increases the strength of the porous metallic sheet and its tensile strength, thus allowing the active sub-stance to be applied to the metallic fibers at a higherspeed.
The metallic powders can consist of metals, alloys, oxides of metals, or oxides of alloys. The metallic powders can also consist of one kind of the above metallic powders or a mixture of the above metals, alloys, oxides of metals, and oxides of alloys.
As the metallic powders, Ni, Cu, Al, Ag, Fe, Zn, Sn, In, Ti, Pb, V, Cr, Co, oxides of these metals, alloys of these metals, and mixtures of these metals are prefer-ably used. In this manner, metallic fibers consisting ofa mixture of the metallic powders can be formed.
Preferably, the porous metallic sheet for use as the electrode substrate of a battery, formed of the metal-CA 022~4~04 1998-11-23 lic fibers made of metallic powders has a percentage of pores at more than 90~, and its thickness is set to 5~m -5000~m. In particular, the thickness of the porous metal-lic sheet in the present invention can be made thicker than a conventional one. That is, the maximum thickness of a conventional nonwoven sheet comprising plating organic fibers is 2.5mm - 3.5mm, as described previously, when the quantity of fiber is 40 - 50 g/m2; the quantity of resin binder is 20 g/m2; the total weight is 60 - 70 g/m2; and the percentage of pores is 95~. After an organic sheet having the above thickness is subjected to an electric conduction treatment, electric plating, resin removal, and sintering, the thickness of the resulting porous metallic sheet reduces to 1.6mm. It is difficult to apply the active substance to a porous metallic sheet when it has such a small thickness.
On the other hand, because a porous metallic sheet made of metallic fibers according to the present invention has a high rigidity and elasticity, it can be allowed to have a thickness as great as 3.3mm - 5.Omm. After the porous metallic sheet is burnt to remove the resin binder and sintered the metal, the weight thereof is decreased to a small extent. After the porous metallic sheet has been passed through a pair of skin pass rolls to make the thickness thereof uniform, the sheet has a thickness of more than 1.6mm. Accordingly, the active substance can be applied to a sheet of the present invention more easily than to a conventional one. After the application of the CA 022~4~04 1998-11-23 active substance to the porous metallic sheet, it is pressurized to obtain the predetermined thickness, namely 1/2 to 1/3 of the thickness of an original one.
Preferably, a plurality of porous metallic sheets are laminated one on the other.
Further, a porous metallic sheet in the present invention may be laminated on a porous metallic sheet formed by plating a porous sheet made of an organic or inorganic substance and/or a conductive metallic foil having holes formed thereon, to form a porous metallic sheet for use as an electrode substrate of a battery. The organic substance can consist of porous sheet, such as a foamed sheet, a mesh sheet or a nonwoven sheet made of resin. The porous sheet is plated and then burnt to remove resin and then sintered.
According to a second aspect of the invention, a porous metallic sheet for use as an electrode substrate of a battery has a porous fibrous structure or a three-dimen-sional net-shaped structure in which a framework surround-ing pores of the porous fibrous structure or those of the three-dimensional net-shaped structure is formed of metal-lic fibers that are intertwined with each other and the surface of which are fused to connect the metallic fibers with each other.
In a porous metallic sheet according to this second aspect, the surfaces of the metallic fibers at the points of intersection are fused with each other under pressure at a temperature lower than the melting point. According to CA 022~4~04 l998-ll-23 the conventional method, an organic binder is used to connect the metallic fibers with each other to form them into a sheet. When the organic binder is burnt out and the sintering is processed, the portion of the mixture fiber occupied with the organic binder becomes hollow. As a result, the resultant metallic fiber becomes annular and has a large diameter. According to the present invention, the metallic fibers are connected with each other without using an organic binder. Thus, no hollow portions are generated in the metallic fibers.
As the metallic fibers, Ni, Cu, Al, Ag, Fe, Zn, Sn, In, Ti, Pb, V, Cr, Co, oxides of these metals, alloys of these metals, and mixtures of these metals are favourably used to form the metallic fibers. Stainless steel and titanium are more favourably used, because these substances are corrosion-resistant. As the stainless steel, SUS 304, SUS 316 containing molybdenum, and SUS 444 containing niobium and molybdenum are preferably used. As metals to compose metallic fibers of the electrode substrate for use as the positive electrode plate of a secondary lithium battery, aluminum, titanium, stainless steel, and carbon can be used. As metals to compose metallic fibers of the electrode substrate for use as the negative electrode plate thereof, copper, nickel, stainless steel, and carbon can be used.
The metallic fibers may consist of continuous metallic fibers made of the metallic powders; fine metallic fibers formed by a convergent-drawing method, a metallic CA 022~4~04 l998-ll-23 fiber-spinning method or a metallic foil-cutting method; or metallic fibers formed by a chattering-vibration method for cutting a metallic bar or a coiled metallic foil.
Because the metallic fibers can be intertwined with each other three-dimensionally, short metallic fibers are preferably used to form the porous metallic sheet. In addition, continuous or long metallic fibers may be used to form the porous metallic sheet.
In the porous metallic sheet, because the metallic fibers are intertwined with each other three-dimensionally and both ends thereof are also connected with each other, the ends do not appear on the surface of the porous metal-lic sheet. Thus, when the porous metallic sheet is coiled via a separator after the active substance is applied thereto, a leak rarely occurs.
Preferably, the percentage of pores of the porous metallic sheet is 70~ - 99~ in the case of the substrates of batteries other than a secondary lithium battery, while the percentage of pores of the porous metallic sheet is 30~
- 60~ in the case of a substrate for a secondary lithium battery.
Preferably, the diameters of the metallic fibers are l~m - lOO~m, whereas those of short metallic fibers are l~m - 60~m. It is also preferable to mix metallic fibers of different lengths to form the porous metallic sheet.
Preferably, the thickness of the porous metallic sheet is 5~m - 5000~m.

CA 022~4~04 l998-ll-23 The porous fibrous structure or the three-dimen-sional net-shaped structure composed of the metallic fibers has fine pores. Further, it is preferable to form a great number of through-holes therein in addition to the fine pores. The through-holes are formed to be circular, rectangular or rhombic, thus allowing the porous fibrous structure or the three-dimensional net-shaped structure to be a porous metallic punched sheet, net-shaped sheet or lath-shaped sheet.
Belt-shaped portions to be used as a lead of an electrode plate are formed at regular intervals except in the regions where the through-holes are formed.
In a porous metallic sheet for use as the electrode substrate of a battery in the second aspect, intersections of the metallic fibers intertwined with each other are fused to connect them with each other firmly at many points. Thus, the tensile strength and conductivity of the porous metallic sheet are as high as those of a solid metallic foil. Thus, as the porous metallic sheet has a high tensile strength, the active substance can be applied thereto while being fed at high speed. Hence, the porous metallic sheet can be manufactured with high productivity.
Further, the pores and the through-holes are not clogged, and the active substance can be prevented from dropping from the pores and the through-holes, because the porous metallic sheet has a three-dimensional structure.
Further, the percentage of pores of the metallic sheet in accordance with the second aspect and the thick-. .

CA 022~4~04 1998-11-23 ~ - 19 -ness thereof can be controlled in a range of 20 - 97~ and 5 - 5000~m, respectively, similarly to the porous metallic sheet in accordance with the first aspect. That is, the thickness and the percentage of pores can be adjusted by controlling the density of the metallic fibers. Further, the percentage of pores including the through-holes can be easily adjusted by controlling the percentage of through-holes. For example, the percentage of pores can be increased up to 99~ to apply a large amount of active substance to the porous metallic sheet. Furthermore, because the porous metallic sheet is allowed to have a smaller thickness compared with a conventional punched metal sheet or lath net sheet, the porous metallic sheet can be coiled around an electrode plate with more turns than the conventional punched metal sheet or lath net sheet, thus increasing the capacity of the battery.
Further, a porous metallic sheet in accordance with the first and second aspects is made of fine metallic fibers and is thus flexible. In particular, unlike the conventional punched metal sheet or lath net sheet, the flexibility prevents an external force from being locally applied to the sheet in the process of cutting it to a predetermined size after the active substance has been applied thereto. Thus, the porous metallic sheet is hardly deformed and further, no burr is generated, which prevents leakage when the sheet serves as an electrode plate in a battery.

CA 022~4~04 1998-11-23 Preferably, and similarly to a porous metallic sheet in accordance with the first aspect, a porous metal-lic sheet in accordance with the second aspect is used by laminating a plurality of porous metallic sheets one on the other as necessary. It is possible to overlay a porous metallic sheet according to the first or second aspect with a porous metallic sheet formed by a punched conductive metallic foil, a plated organic porous sheet or an inor-ganic porous sheet, so as to use the resultant porous metallic sheet as the electrode substrate of the battery.
The present invention provides an electrode plate of a battery formed by applying the active substance to the porous metallic sheet in accordance with the first or second aspects. The electrode plate can be used as the electrode plate of a nickel hydrogen battery, a nickel cadmium battery, a primary lithium battery or a secondary lithium battery.
More specifically, an electrode plate of a nickel hydrogen battery and a nickel cadmium battery is formed by applying the active substance to a porous metallic sheet made of nickel fibers.
Cavities to which the active substance cannot be applied are not present in an electrode plate according to the present invention. Thus, a large amount of active substance can be applied and, further, the area of contact between the applied active substance and the metallic fibers (framework) is large, which improves the performance of the battery.

CA 022~4~04 l998-ll-23 The present invention is intended to provide a method of manufacturing a porous metallic sheet of the first aspect. The manufacturing method comprises the steps of forming a mixture by kneading metallic powders and resin binder; spinning metallic fibers by extruding the mixture from a spinning nozzle; and forming the spun metallic fibers into a porous fibrous structure or a three-dimen-sional net-shaped structure. Preferably, the porous fibrous structure or the three-dimensional net-shaped structure is burnt to remove the resin binder and then sintered.
The resin binder is required to have a required viscosity in the spinning process, and thus the following substances having the required viscosity are preferably used: polypropylene, polyester, polyethylene, polyacrylon-itrile, polyvinyl polymer, polyimide, nylon polymer, polyurethane, cellulase, and polymer formed of organic fiber.
Favourably, the mixing ratio between the metallic 20 powder and the resin binder is 70 - 97~ and 30% - 3%, and more favourably, 85~ - 97~ and 15~ - 3~.
Because the metallic powder is mixed with the resin binder at percentages as high as 70~ - 97~, it is not always necessary to plate the resulting sheet in a later 25 process, but the resulting sheet may be plated as necess-ary.
In order to easily spin and draw the mixture of the resin binder and the metallic powder contained at a high CA 022~4~04 1998-11-23 percentage to form fine fibers, the mixture is preferably extruded from the center of a spinning nozzle to form a core, while the resin is extruded from the periphery of the center of the spinning nozzle to form a sheath. In this manner, the mixture is extruded from the spinning nozzle as a compound metallic fiber consisting of the core and the sheath surrounding the core.
The mixture of the resin binder and the metallic powder is preferably extruded from a plurality of discharge portions to form a plurality of cores, and the resin is extruded to the spaces between the cores. In this manner, the mixture is extruded from the spinning nozzle as a compound metallic fiber consisting of a resin portion and a plurality of scattered cores surrounded with the resin portion.
Further, the mixture of the resin binder and the metallic powder is preferably extruded from the spinning nozzle, with the mixture being in contact with resin having a melting point different from the resin contained in the 20 mixture to form a compound metallic fiber. The resultant fibers are curled when they are cooled. This method allows the spun fibers to be curled and a thick sheet to be composed of the curled metallic fibers.
In the above-described methods, metallic powders and the resin binder are mixed with each other, but fibers may be formed of only metallic powders by extruding them from the spinning nozzle. The resultant metallic fibers are formed into the porous fibrous structure or the three-CA 022~4~04 l998-ll-23 dimensional net-shaped structure so as to use them as the electrode substrate of a battery. In this case, the pressurizing force to be applied to the metallic powder can be set at about 30 - 70 times, preferably about 50 times, as great as that to be applied to the mixture of the metallic powders and the resin binder. Because the resin binder is not used in this method, it is not necessary to burn out for removing the resin binder and hence they are only sintered.
Preferably, the porous fibrous structure or the three-dimensional net-shaped structure is burnt out at 800~C - 1200~C for about two minutes to remove the resin binder and then sintered at 1000~C - 1300~C for about 2 -10 minutes.
Continuous metallic fibers extruded from the spinning nozzle can be curved continuously into a coiled configuration by movement of blowing air.
As described above, air is blown to the continuous metallic fibers extruded from the nozzle or air is sucked 20 in to bend the metallic fibers extruded from the nozzle into a continuously curved coil spring-configuration.
Because the metallic fibers are curved, they are rigid and elastic and thus a sheet having a great thickness can be formed in accordance with the curved amount.
Further, a great number of coiled continuous metallic fibers can be fed to a horizontal conveyor, and the conveyor vibrated widthwise to intertwine the continu-CA 022~4~04 1998-11-23 ous metallic fibers with each other to form a sheet having a porous structure.
The above-described method allows a sheet having a porous structure to be easily formed. Further, the density of fibers can be easily altered by adjusting the degree of the widthwise vibration of the conveyor and the feeding speed of the conveyor so as to form a porous sheet having the required percentage of pores made of metallic fibers.
A method of manufacturing a porous metallic sheet for use as an electrode substrate of a battery according to the second aspect comprises the steps of: placing a web comprising metallic fibers on a supporter; injecting fluid having a high pressure and a high speed into the web to intertwine the metallic fibers with each other to form the metallic fibers into a three-dimensional sheet; and heating the three-dimensional sheet comprising intertwined metallic fibers at a pressure and at a temperature lower than the melting point of the metallic fibers so as to fuse the surfaces of the fibers with each other at the points of intersection.
The three-dimensional sheet comprising the inter-twined metallic fibers can be heated under pressure in a nonoxidizing atmosphere, reduction being performed in an atmosphere in which H2 is present.
As the supporter on which the web is placed, a screen or the like which allows the passage of fluid therethrough at a high pressure and a high speed can be used.

CA 022~4~04 l998-ll-23 Preferably, a high pressure-columnar water current is used as the fluid having the high pressure; the high pressure-columnar water current is injected into the web in a direction perpendicular thereto, placed on the supporter 5 SO as to form a metallic fibers-intertwined sheet; the sheet is dehydrated and dried; and the sheet is heated under pressure.
Projections are formed on the upper surface of the supporter so as to form through-holes on the metallic fibers-intertwined sheet corresponding to the locations of the projections. When fluid is injected into the web on the conic or pyramidal convex portions at a high pressure and a high speed, the metallic fibers of the web placed on the projections flow downward from the upper end of the 15 projection to the flat portion of the upper surface of the supporter along the peripheral surface of the projection.
In this manner, through-holes are formed at the portions corresponding to the projections.
A plurality of projections can be formed at regular 20 intervals to form a large number of circular, rectangular or rhombic through-holes corresponding to the configuration of the projections on the metallic fibers-intertwined sheet. Consequently, the sheet becomes like a punched metallic sheet, net-shaped sheet or lath-shaped sheet.
Belt-shaped portions are formed on the supporter at predetermined intervals in regions in which the projections are not formed, so as to form portions for providing leads CA 022~4~04 1998-11-23 of an electrode plate on the metallic fibers-intertwined sheet corresponding to the belt-shaped portions.
That is, owing to the formation of the projections on the supporter on which the web is placed, the metallic fibers-intertwined sheet can be allowed to have holes of various configurations, and the portions for leads can be formed on the metallic fibers-intertwined sheet simulta-neously with the formation of the holes.
Instead of the method of using fluid having a high speed and a high pressure, the following method may be adopted. That is, the method comprises the steps of intertwining metallic fibers of a web with each other three-dimensionally by means of a needle punch to form a sheet; and heating the metallic fibers-intertwined sheet at a pressure and at a temperature lower than the melting point of the metallic fibers so as to fuse the surfaces of the fibers with each other at the points of intersections.
The metallic fibers according to the second aspect are used as follows: fine continuous metallic fibers are formed by a convergent-drawing method, a metallic fiber-spinning method or a metallic foil-cutting method; short metallic fibers are formed by cutting the fine continuous metallic fibers; or short fibers are formed by a chatter-ing-vibration method for cutting a metallic bar or a coiled metallic foil. These metallic fibers are ravelled by a blender and measured by a quantity-measuring feeder, and are then delivered to a carding machine to form the web.

CA 022~4~04 1998-11-23 In carrying out the above metallic fiber-spinning method, after forming fibers by extruding a mixture of the metallic powders and the resin binder by using the spinning method, the fibers are preferably burnt out and then sintered to remove the resin binder before the resulting continuous fibers are formed into the web. It is possible to use a spinning method of extruding metallic powders (not mixed with resin binder) from the spinning nozzle by applying a great pressure thereto so as to form metallic fibers. Thereafter, the resultant metallic fibers are sintered, namely the burning out process can be omitted.
Preferably, after the porous metallic sheet is heated under pressure, it is passed through a pair of rolls to adjust the thickness thereof.
According to this manufacturing method, a porous metallic sheet having a large number of connection points of the metallic fibers can be easily produced by intertwin-ing them with each other three-dimensionally, and the thickness thereof can be adjusted as desired. For example, the porous metallic sheet can have a thickness less than 10 ~m. Because the resin binder is not mixed with metallic powders in this method and it is unnecessary to perform a resin-removing operation, the porous metallic sheet can be made of a metal such as aluminum that is oxidized at the temperature for performing the resin-removing operation and is weakened.
Further, it is possible to heat surfaces of a plurality of the resulting porous metallic sheets laminated CA 022~4~04 1998-11-23 one on the other at a temperature lower than the melting point thereof so as to join them to each other.
Further, in producing the porous metallic sheet by using a fluid, the fluid is injected into a web placed on the upper surface of the finished porous metallic sheet at high pressure and high speed so as to increase the thick-ness thereof. Further, it is possible to inject fluid at high pressure and high speed into the web placed on the upper surface of the porous metallic sheet produced by other methods so as to increase the thickness thereof. The resulting porous metallic sheet laminated with a plurality of sheets are preferably pressed by punch to form through-holes.
According to a method of the present invention the conduction treatment process and plating process required by the conventional method in forming organic fibers into a porous metallic sheet can be eliminated. Thus, the problem of waste solution that occurs in plating the porous metallic sheet can be solved. Further, a method of the present invention reduces the electric power consumption, thus reducing the cost.
If it is preferable to increase the strength of the porous fibrous structure sheet or the three-dimensional net-shaped structure produced by the above-described methods, it is possible to electrically plate the sheet.
Preferably, after they are electrically plated, sintering operations are carried out.

CA 022~4~04 1998-11-23 Even though electrical plating'is used to increase the strength of the porous metallic sheet, the amount of metal to be applied to the porous metallic sheet is smaller than that to be applied to a conventional porous metallic sheet. Hence, a method of the present invention reduces the electric power consumption, thus reducing the cost.
The present invention is also intended to provide a method for producing a battery electrode formed by applying the active substance to the finished porous metallic sheet. Because the porous metallic sheet produced by a method of the present invention is formed of metallic fibers, it has a high tensile strength. Therefore, the production line speed can be increased when the active substance is applied thereto while it is being drawn continuously. Hence, the porous metallic sheet can be manufactured with high productivity.
In the Drawings:
The present invention taken in conjunction with the invention described in parent co-pending Canadian Patent Application Serial No. 2,163, 819 that was filed on November 27, 1995, will be described in detail with the aid of the accompanying drawings, in which:
Fig. l is a flowchart showing a manufacturing method in accordance with a first embodiment of the present invention;
Fig. 2 iS a schematic view showing apparatus for carrying 2 5 out the manufacturing method;
Fig. 3 iS a partial plan view showing a net conveyor of the manufacturing apparatus;
Fig. 4 is a schematic view showing a porous metallic sheet manufactured by the method of the first embodiment;

~ .... -- . ...

CA 022~4~04 1998-11-23 Fig. 5A is a sectional view showing a metallic fiber of the present invention;
Fig. 5B is a sectional view showing a conventional metallic fiber;
5Figs. 6A and 6C are plan views showing pores formed by metallic fibers in accordance with the present inven-tion;
Fig. 6B is a plan view showing a pore formed by conventional metallic fibers;
10Fig. 7A (with Fig. 5A) is a plan view showing connection portions of metallic fibers in accordance with the present invention before resin is burnt out;
Fig. 7B (with Fig. 5A) is a plan view showing the connection portions of the metallic fibers in accordance with the present invention after the resin is burnt out;
Figs. 8A through 8D are sectional views showing the body of a spinning nozzle and continuous fibers, in accord-ance with the present invention, formed by the spinning nozzle;
20Fig. 9 is a flowchart showing another manufacturing method in accordance with the first embodiment;
Fig. 10 is a flowchart showing still another manufacturing method in accordance with the first embodi-ment;
25Fig. 11 is a flowchart showing a further manufac-turing method in accordance with the first embodiment;

CA 022~4~04 1998-11-23 Figs. 12A and 12B are flowcharts each showing a manufacturing method in accordance with a second embodiment of the present invention;
Fig. 13 (with Fig. 4) is a schematic view showing another porous metallic sheet in accordance with the present invention;
Figs. 14A, 14B, and 14C are schematic sectional views each showing a porous metallic sheet in accordance with a third embodiment of the present invention;
10Fig. 15 is a flowchart showing a manufacturing method in accordance with a fourth embodiment;
Fig. 16 is a flowchart showing a manufacturing method in accordance with a fifth embodiment;
Fig. 17 is a schematic view showing a step of a manufacturing process in accordance with the fifth embodi-ment;
Fig. 18 is a schematic view showing a step of the manufacturing process in accordance with the fifth embodi-ment;
20Figs. l9A and l9B are schematic views showing supporters to be used in the manufacturing process in accordance with the fifth embodiment;
Fig. 20 is a schematic view showing a step of the manufacturing process in accordance with the fifth embodi-ment;
Fig. 21 is a schematic view showing a step of the manufacturing process in accordance with the fifth embodi-ment;

. . ..

CA 022~4~04 1998-11-23 Fig. 22 is a view showing the action of intertwin-ing metallic fibers of a web with each other and forming a through-hole in the manufacturing process in accordance with the fifth embodiment;
Fig. 23A, 23B, and 23C are views showing the relationship between the configuration of projection of a supporter and a formed through-hole in accordance with the first embodiment;
Fig. 24 is a plan view showing a porous metallic sheet on which a portion serving as a lead is formed in accordance with the fifth embodiment;
Fig. 25 is a flowchart showing a manufacturing method in accordance with a sixth embodiment;
Fig. 26 (with Fig. 24) is a schematic view showing a portion of a manufacturing process in accordance with a sixth embodiment;
Figs. 27A, 27B, and 27C (with Fig. 24) are sche-matic sectional views each showing a substrate in accord-ance with a seventh embodiment; and Fig. 28 (with Fig. 8D) is a plan view showing a conventional problem.
The embodiments of the present invention are described below with reference to the drawings.
Initially, there is a first method for manufactur-ing a porous metallic sheet for use as a substrate of a battery electrode, in accordance with a first aspect of the invention, composed of metal fibers made out of metallic powder.

CA 022~4~04 1998-11-23 In the first embodiment, in accordance with the flowchart of Fig. 1, metal fibers are made out of metallic nickel powder by using the manufacturing apparatus shown in Fig. 2, and the metallic fibers are formed into a nonwoven porous metallic sheet 40 shown in Fig. 4 to be used as a substrate of a battery electrode.
Using fine nickel powder of O.l~m - 5~m in diameter as the fine metallic powder and powder of nylon 6 as resin binder, 85~ of the fine nickel powder and 15~ of the nylon powder are fed to a kneader 4 from storing containers 1 and 2, respectively, after the quantity of the fine nickel powder and that of the nylon powder are measured by quan-tity-measuring feeders 3A and 3B, respectively, so as to knead them at step #1. A mixture M comprising the fine nickel powder and the nylon powder kneaded by the kneader 4 is extruded from a nozzle 4a provided at the output end of the kneader 4 to form the mixture M into fibers about 3mm in diameter. The fiber-shaped mixture M is fed inside a cooler 5 by a conveyor 5a to cool it therein.
A pump 12 of the cooler 5 circulates cold water stored in a water tank 11 so as to cool the fiber-shaped M
with the cold water.
While the fiber-shaped mixture M taken out from the cooler 5 is being fed by a roller 6, it is cut to form pellets P of about 3mm in length by a cutter 7 at step #2.
The pellets P are fed through a drier 8 to dry them and accommodate them in a container 9.

.

CA 022~4~04 l998-ll-23 The pellets P are supplied to a fusion furnace 10.
The pellets P are heated therein at 260~C - 280~C to fuse the resin binder at step #3. At this time, the fine metallic powder does not melt.
Then, the pellets P are fed to an extruder 14 after the quantity thereof has been measured by a feeder 13.
The mixture of melted resin binder and unmelted metallic powder is then fed from the extruder 14 into a spinning nozzle 16 via a filter 15, while a gear pump (not shown) of the extruder 14 iS applying pressure thereto.
Large particles and aggregated masses are removed from the mixture by passing it through the filter 15.
A heater 18 circulating heating medium is provided inside a heat retaining wall 17. The heater 18 surrounds 15 a nozzle body 20. The mixture is supplied to the nozzle body 20 via the filter 15 SO as to extrude it from the nozzle body 20 as fibers. In this manner, the fibers are formed at step #4.
A cooling cylinder 21 iS provided below the spin-20 ning nozzle 16. An air blowout port 22 iS provided at aposition proximate to the nozzle body 20, such that the air blowout port 22 iS positioned at an upper portion of the cooling cylinder 21 SO as to horizontally blow air onto the continuous fibers being extruded from the nozzle body 20.
In this manner, the fibers are drawn and cooled.
Air sucked by a blower 24 through a filter 23 iS
fed to the air blowout port 22 through a cooler 25 in which cooling water circulates, a filter 26, and a heater 27 in CA 022~4~04 l998-ll-23 which vapour circulates so as to adjust the temperature of air to a required value, and then blown to the inside of the cooling cylinder 21.
The air blown to the cooling cylinder 21 is exhausted from an air exhaust port 28 located at the lower end of the cooling cylinder 21.
As shown in Fig. 8A, the nozzle body 20 has a large number of discharge ports 51 through which the fibers (about 40 metallic fibers in the embodiment) are extruded in parallel with each other. It is possible to form hundreds to thousands of discharge ports in the nozzle body 20 to extrude hundreds to thousands of continuous fibers at a time.
The diameter of each discharge port 51 of the nozzle body 20 is set to lOO~m - 50~m. When the diameter of each discharge port 51 is set to lOO~m, the diameter of each fiber extruded from the discharge port 51 is about 60~m and then reduced to 3 O~m owing to the air blowing drawing thereof. When the diameter of each discharge port 51 is set to 50~m, the diameter of each fiber extruded therefrom is about 30~m and then reduced to 7~m owing to the air blowing drawing thereof.
Each of the fibers that have moved downward with air being blown thereto to draw and cool them in the cooling cylinder 21 is continuously bent into a coil spring configuration by a pair of crimpers 3 0 of the suction drum type positioned below the cooling cylinder 21.

CA 022~4~04 1998-11-23 The crimpers 30 suck air and blow it towards the fibers from the left and right sides thereof, thus bending the fibers moving downward. The crimpers 30 do not contact the fibers when it bends them.
The fibers formed in the coil spring configuration by the crimpers 30 are supplied to a net conveyor 33 located horizontally below the crimpers 30 and placed thereon.
As shown in Fig. 3, a large number of continuous lo fibers bent in the coil spring configuration are arranged in parallel with each other on the net conveyor 33.
The net conveyor 33 is vibrated in the widthwise direction W. As a result, the fibers arranged in parallel with each other on the net conveyor 33 are vibrated lS widthwise; intertwined with each other; and bonded to each other at random by means of the resin binder which has mixed to metallic fibers. In this manner, a sheet having a nonwoven porous structure is manufactured at step #5.
As shown in Fig. 3, a mens for vibrating the fibers in the widthwise direction W comprises a net conveyor-feeding apparatus comprising a driving motor, a pair of pulleys to be driven by the motor, and an endless conveyor 33 spanned between the pulleys. Rods 36 of cylinder 35 reciprocate to vibrate the entire net conveyor 33 in the widthwise direction W.
Needless to say, other appropriate means may be adopted instead of the above-described vibration means.

CA 022~4~04 1998-11-23 Because each fiber of the sheet having a nonwoven porous structure has the coil spring configuration, the sheet having a nonwoven porous structure has a comparative-ly large thickness. Further, because the fibers are intertwined with each other widthwise, the thickness of the sheet having a nonwoven porous structure is increased to 3.3mm - 5mm.
The percentage of pores of the sheet having a nonwoven porous structure can be adjusted by controlling the feeding speed of the net conveyor 33. That is, with an increasing in the feeding speed, the density of the fibers becomes coarse and thus the percentage of pores becomes high, whereas, with a decrease in the feeding speed, the density of the fibers becomes small and the percentage of pores becomes low.
The sheet having a nonwoven porous structure composed of the fibers is heated at 800~C - 1200~C for about two minutes to burn out the resin binder from the sheet having a nonwoven porous structure at step #6.
The sheet having a nonwoven porous structure is heated at 1000~C - 1300~C for about 2 - 10 minutes to sinter metallic powder at step #7. In this manner, a porous metallic sheet 40 having the construction shown in Fig. 4 is produced.
The percentage of pores of the porous metallic sheet 40 is set to 94% - 98%. The area of one pore is set to 0.005mm2 - 0.942mm2. The thickness of the porous metallic sheet 40 is set to 0.5mm - 5mm.

CA 022~4~04 1998-11-23 The porous metallic sheet 40 manufactured by the method according to the first embodiment has the advantages described below.
As a result of the removal of the resin binder and the sintering of the metallic powder, the diameter of each metallic fiber becomes smaller by 5 - 40~, because the resin binder and metal oxide are burnt out.
That is, as shown in Fig. 5A, each of metallic fibers F obtained in the first embodiment is solid and the diameter thereof is small. As shown in Fig. 5B, supposing that organic fibers are extruded from the discharge port 51, the diameter of a resulting conventional metallic fiber F' is greater than that of the metallic fiber F.
This is because, according to the conventional art, the organic fibers are metal-plated. Further, because the organic fibers are removed from the conventional metallic fiber F', a cavity C is generated therein. An active substance cannot be applied to the cavity C.
More specifically, in the case of the metallic fibers F of the present invention shown in Fig. 5A, the diameter of each of the metallic fibers F is 20~m on average, whereas in the case of the conventional metallic fiber F' shown in Fig. 5B, the diameter thereof is 30~m on average. Thus, the volume of each of the fibers F is smaller by 55.6~ than that of a conventional fiber F'.
Comparing a porous metallic sheet according to the present invention, formed of the metallic fibers F having a smaller diameter than the conventional porous metallic CA 022~4~04 1998-11-23 sheet formed by electrically plating organic fibers, the pore of the porous metallic sheet shown by the oblique lines of Fig. 6A has a greater area than that of the conventional porous metallic sheet shown by the oblique lines of Fig. 6B.
Let it be supposed that the fiber density of the present invention is equal to that of the conventional one.
When the percentage of pores is 93~ in the conventional porous metallic sheet, the percentage of pores is 96.9~ in the porous metallic sheet of the present invention. When the percentage of pores is 96~ in the conventional porous metallic sheet, it is 98.2~ in the porous metallic sheet of the present invention. That is, the percentage of pores of the porous metallic sheet of the present invention is greater than that of the conventional porous metallic sheet. Thus, if the entire area of pores of the present invention to which an active substance can be applied is equal to that of the conventional porous metallic sheet, the porous metallic sheet has the metallic fibers F 2.25 times as great as the conventional porous metallic sheet per unit area. That is, as shown in Fig. 6C, the metallic fibers F can be arranged at a higher density than the conventional metallic fibers F' per unit area. In this case, the gap between the metallic fibers F which sandwich the active substance is smaller than that between the conventional metallic fibers F', and the area of contact between the active substance and the metal fibers F is greater than that between the conventional metallic CA 022~4~04 1998-11-23 fibers F'. Thus, a porous metallic sheet according to the present invention has a higher conductivity than the conventional one, thus allowing a battery to have a more favourable characteristic than a conventional one.
When the weight of metal to be used per unit area to form the porous metallic sheet of the present invention is equal to that to be used per unit area to form the conventional porous metallic sheet, the former is allowed to have more metallic fibers per unit area than the latter by 1.75 times more than that of the latter, without decrea-sing the percentage of pores. Thus, a porous metallic sheet according to the present invention has a higher conductivity than a conventional one, thus allowing a battery to have a more favourable characteristic than a conventional one. Supposing that the same number of metallic fibers is used per centiare to form the porous metallic sheet of the present invention and the conven-tional one, 420g is required per area in the case of the latter, whereas 240g is required in the case of the former.
In this case, there is no problem in respect to the strength of the porous metallic sheet of the present invention even though the weight of metal is smaller per area than that used in a conventional porous metallic sheet, because the metallic fibers of the present invention are solid and continuous and thus have a higher strength than the conventional ones.
A conventional problem of resin lumps R formed at connection points of the metallic fibers F as shown in CA 022~4~04 l998-ll-23 Fig. 28 is now described. Even though resin is collected at each connection point of the metallic fibers F shown in Fig. 7A, it is burnt out during the resin binder removal process and the sintering process. Consequently, as shown in Fig. 7B, the resin lump disappears from the connection points. Accordingly, the diameter of the metallic fibers F can be prevented from becoming larger and thus the percentage of pores can be prevented from being reduced.
Because the metallic fibers F are solid and con-tinuous, they have a strength 1.5 - 3 times higher than the conventional metallic fibers formed by electrically plating organic fibers. Accordingly, in applying an active sub-stance into the pores, the porous metallic sheet 40 can be drawn with a great force. Thus, the active substance can be applied to the pores at high speed.
Further, because the sheet having a nonwoven porous structure is formed by intertwining the solid metallic fibers with each other, the metallic fibers F are present uniformly on the peripheral surface and the inner periph-eral thereof, whereas in the case of the conventionalmetallic porous sheet formed by electrically plating organic fibers, a large amount of metal is deposited on the peripheral surface of the sheet and a small amount of metal is deposited in the inner part of the sheet. Therefore, a porous metallic sheet of the present invention is capable of improving the performance of a battery.
Further, because the continuous metallic fibers F
are bent in the coil spring configuration and intertwined CA 022~4~04 1998-11-23 with each other, the thickness of the porous metallic sheet can be set to as large as 3.3mm - 5mm. Thus, the active substance can be applied to the porous metallic sheet 40 consisting of the metallic fibers F with high efficiency.
In the first embodiment, the discharge ports 51 for extruding the mixture M comprising the resin binder and metallic powder therefrom are arranged in parallel with each other in the nozzle body 20 of the spinning nozzle 16.
When the mixture M contains a large amount of metallic powder and thus when it is not easy to extrude the mixture M from the discharge ports 51, it is preferable to use the nozzle body 20 shown in Figs. 8B through 8D to form the mixture M into compound metallic fibers.
That is, the nozzle body 20 shown in Fig. 8B has the discharge port 51 for discharging the mixture M at the center thereof and a discharge port 52 for discharging only resin in the periphery of the discharge port 51. Thus, the mixture M extruded from the center of the nozzle body 20 forms a core 60 while the resin R extruded from the periph-ery of the center of the nozzle body 20 forms a sheath 61.That is, the mixture M is extruded from the nozzle body 20 as a compound metallic fiber consisting of the core 60 and the sheath 61 surrounding the core 60.
The sheath 61 of the compound metallic fiber thus formed serves as adhesive agent in forming the mixture M
into the sheet having a nonwoven porous structure by vibrating the net conveyor 33 widthwise.

CA 022~4~04 l998-ll-23 Because the sheath 61 is burnt out during the resin binder removal and the sintering process, the diameter of the metallic fibers can be prevented from becoming large.
The nozzle body 20 shown in Fig. 8C has a large number of discharge ports 51, for discharging the mixture M at predetermined intervals inside the discharge port 52 having a large diameter. The mixture M extruded from the discharge ports 51 forms the cores 60, and the resin R is extruded between the cores 60. In this manner, the mixture M is extruded from the nozzle body 20 as a compound metal-lic fiber consisting of a resin portion 62 and a plurality of scattered cores 60 surrounded with the resin portion 62.
In this multi-core compound metallic fiber, the cores 60 are connected to each other during the resin 15 binder removal and sintering processes. As a result, each metallic fiber has a great surface area. When the resin portion 62 made of polyester is dissolved in an alkaline solution to remove the polyester, the metallic fiber can be composed of small diameter-metallic fibers separated from each other.
The nozzle body 20 shown in Fig. 8D has the dis-charge port 51 for discharging the mixture M at one side thereof and a resin discharge port 53 at the other side thereof. Resin different from the resin binder contained in the mixture M is discharged from the resin discharge port 5 3 .
The mixture M is extruded from the discharge ports 51 and 53, with the mixture M being in contact with the CA 022~4~04 1998-11-23 resin different from the resin binder contained in the mixture M to form a compound metallic fiber consisting of the core 60 of the mixture M connected with a resin portion 64 in a bimetallic state.
The contraction coefficients of the core 60 and the resin portion 64 are different from each other. Therefore, when they are cooled in the cooling cylinder 21, the compound metallic fiber is curled. That is, the compound metallic fiber can be curved without using the crimpers 30 of the suction drum type.
In the first embodiment, metallic powder and powdered resin binder are kneaded into filaments, and then the filaments are cut to pellets. Then the pellets are heated to fuse the powdered resin binder. Instead, it is possible to mix the metallic powder with the fused powdered resin binder, knead the mixture of the metallic powder and the fused resin binder, and extrude the mixture from the spinning nozzle.
In the first embodiment, after a sheet having a nonwoven porous structure is formed, it is burnt out to remove the resin binder, and the metallic powder is sintered. But it is possible to omit the burning out process at step #6 and the sintering process at step #7 as necessary, as shown in Fig. 9. If the metallic powder is mixed at high percentages, for example, 95~ - 97~ with the resin binder, it is unnecessary to burn out the sheet having a nonwoven porous structure to remove the resin binder.

CA 022~4~04 1998-11-23 Further, as shown in Fig. 10, after the sheet having a nonwoven porous structure is formed at step #5 of the first embodiment, the sheet having a nonwoven porous structure may be electrically plated at step #6 and then the resin binder may be burnt out at step #7. Then the metallic powder may be sintered at step #8.
That is, if it is necessary to increase the weight of metal per unit area in forming the porous metallic sheet to allow metallic fibers to have a large strength, the sheet having a nonwoven porous structure may be plated. In this case, because the metallic fibers of the sheet having a nonwoven porous structure are solid, a much smaller amount of metal is used to plate it compared with the conventional electrical plating method. Thus, less elec-tric power is consumed in plating the sheet having anonwoven porous structure.
It is possible to omit the burning out process and the sintering process as necessary, as shown in Fig. 11.
The kind of metallic powder to be mixed with the powdered resin binder is not limited to one, but a plural-ity of kinds of metallic powders may be mixed with the resin binder so as to form compound metallic fibers.
In the first embodiment, fine metallic powder and the powdered resin binder are kneaded, while in the second embodiment, fibers are formed of only metallic powder.
That is, as shown in Fig. 12A, at step #l fine metallic powder is supplied under high pressure to the spinning nozzle 16 shown in Fig. 2. The pressurizing force to be CA 022~4~04 l998-ll-23 applied to the fine metallic powder is set at about 30 - 70 times, preferably about 50 times, as great as that to be applied to the mixture of the fine metallic powder and the resin binder in the first embodiment. By applying such a large pressure to the fine metallic powder in supplying the fine metallic powder to the spinning nozzle 16, the metal-lic fibers F are continuously extruded in a larger number from the nozzle body 20 at step #1.
After the metallic fibers F are formed at step #1, similarly to the first embodiment, the metallic fibers F
are drawn and cooled in the cooling cylinder 21 provided below the spinning nozzle 16; continuously bent into a coil spring configuration by the crimpers 30 positioned below the cooling cylinder 21; and then supplied to the net conveyor 33 to form a metallic sheet having a nonwoven porous structure at step #2.
The metallic sheet having a nonwoven porous struc-ture is sintered at 1,000~C - 1,300~C for about 2 - 10 minutes in an atmosphere of a reducing gas to produce a porous metallic sheet for use as a substrate of a battery electrode. It is possible to omit the sintering process, as necessary.
As shown in Fig. 12B, it is possible to plate the metallic sheet having a nonwoven porous structure electri-cally at step #3 after it is formed at step #2 and thensinter the plated metallic sheet having a nonwoven porous structure at step #4.

CA 022~4~04 1998-11-23 In the first and second embodiments, in order to form a sheet having a nonwoven porous structure, the method involves bending the continuous metallic fibers formed by using the spinning nozzle and then transporting them to the net conveyor. But other methods can be adopted when a porous fiber sheet or a three-dimensional net-shaped sheet having a porous structure is formed of metallic fibers.
For example, the continuous metallic fibers F may be woven in a mesh configuration to form a mesh sheet as shown in Fig. 13.
It is also possible to cut continuous metallic fibers extruded from the spinning nozzle and put them into water so as to form short metallic fibers of 2mm - 60mm and then use a dry nonwoven sheet-producing method to form the sheet having a nonwoven porous structure. That is, after drying the short metallic fibers, they are ravelled or accumulated at random by applying air thereto to form a sheet having a nonwoven porous structure.
It is also possible to use a wet nonwoven sheet-producing method of dispersing the short metallic fibers inwater or water containing an adhesive agent and collecting them with a net to form a sheet having a nonwoven porous structure.
It is also possible to use a melt-blow nonwoven sheet-producing method of applying heated gas to the metallic fibers to draw and cut then to short fibers and then directly accumulating the short fibers on the conveyor to form a sheet having a nonwoven porous structure.

.

CA 022~4~04 1998-11-23 It is also possible to use a span bonding method of applying air to the metallic fibers to draw them, accumu-lating them on the conveyor directly to form a web consist-ing of continuous metallic fibers, and bonding fibers of the web to each other with an adhesive agent.
In the third embodiment, a plurality of porous metallic sheet 40 made of metallic powder is laminated one on the other to form a porous metallic sheet 100 to be used as a substrate of a battery electrode as shown in Fig. 14A.
The porous metallic sheet 40 has a porous fibrous structure having a nonwoven sheet, a woven sheet, knitted sheet, a felt sheet, a screen-shaped sheet, an expanded sheet, a net-shaped sheet; and a three dimensional net-shaped structure having a foamed sheet, a spongelike sheet, a honeycomb-shaped sheet. In addition, as shown in Fig. 14B, it is possible to overlay a conductive metallic foil 101 having a plurality of pores lOla formed thereon on the porous metallic sheet 40 to form a porous metallic sheet 100'. Further, as shown in Fig. 14C, it is possible to form a porous metallic sheet 100" by laminating the porous metallic sheet 40 and a porous metallic sheet 102 formed by plating foamed, mesh or nonwoven sheets made of resin, and then burning out the resin binder and sintering the metal-lic powder.
In a fourth embodiment, as shown in Fig. 15, an active substance is applied to the porous metallic sheets 40 of the first and second embodiment, 100, 100' or 100" of the third embodiment to form an electrode plate for a CA 022~4~04 1998-11-23 battery. As shown in Fig. 15, at step #8, the active substance is applied to the porous metallic sheet formed in the process of steps #1 through #7 of Fig. 1. Needless to say, the active substance may be applied to the porous metallic sheet after performing the operation of the final process shown in Figs. 9, 10 and 11 showing modifications of the first embodiment, after performing the operation of the final process shown in Figs. 12A and 12B showing the second embodiment, or after forming the porous metallic sheet by overlaying the porous metallic sheets 100, 100' or 100" on the porous metallic sheet 40.
The active substance is applied to a nonwoven porous metallic sheet consisting of nickel fibers composed of nickel powder while the porous metallic sheet is being continuously drawn, so that an electrode of a nickel hydrogen battery is formed. Three experiments of the fourth embodiment are described below.
In the first experiment, paste of an active sub-stance was applied to a nonwoven porous metallic sheet made of nickel. The paste was obtained by kneading a mixture of 100 parts by weight of nickel hydroxide powder, 10 parts by weight of cobalt powder, 0.2 parts by weight of methyl cellulose used as an adhesive agent, and 20 parts by weight of water. After the paste is dried, it is molded under pressure to form a positive electrode plate of a nickel hydrogen battery, having a thickness of 0.5mm.
In a second experiment, paste of an active sub-stance was applied to a sheet having a three-dimensional CA 022~4~04 l998-ll-23 net-shaped structure made of nickel. The paste was obtained by kneading a mixture of 90 parts by weight of nickel hydroxide, 10 parts by weight of cobalt oxide, 0.4 parts by weight of carboxyl methyl cellulose, and 43 parts by weight of water. After the paste is dried, it is rolled by a roller press to form a positive electrode plate of a nickel cadmium battery, having a thickness of 0.6mm.
In a third experiment, paste of an active substance was applied to the three dimensional net-shaped sheet made of nickel. The paste was obtained by kneading a mixture of 90 parts by weight of cadmium oxide, 10 parts by weight of nickel powder, 2.8 parts by weight of polyethylene powder, and 2. 5 parts by weight of polytetrafluoroethylene, and organic solvent. After the paste is dried, it is molded 15 under pressure to form a negative electrode plate of a nickel cadmium battery, having a thickness of 0.45mm.
In a porous metallic sheet for use as a substrate of a battery electrode according to the first invention, the diameter of metallic powder is as small as O.l~m-5~m.
Thus, the metallic powder mixed with fused resin binder can be extruded from the spinning nozzle to form the mixture into fibers. Further, because the diameters of the fibers thus formed are as small as l.O~m to lOO~m, the porous metallic sheet formed on the fibers has an improved percen-25 tage of pores, and, further, the area of one pore of theporous metallic sheet of the present invention is smaller area than that of one pore of the conventional porous metallic sheet, supposing that the percentage of pores of CA 022~4~04 1998-11-23 the former is the same as that of the latter. Thus, the former has a higher conductivity than the latter.
Further, because the metallic fibers are continuous or long, a porous metallic sheet made of the fibers has a high strength and thus the active substance can be applied to the porous metallic sheet at high speed.
It is possible to use various kinds of metals to form the porous metallic sheet in order to cause it to have a feature of each of the metals used. Further, a mixture of various kinds of metallic powders may be used to form fibers to cause the porous metallic sheet to have various characteristics that cannot be provided by a porous metal-lic sheet consisting of fibers made of only one kind of metal.
A method for manufacturing a porous metallic sheet to be used as a substrate of a battery electrode in accord-ance with the second aspect of the invention is described below. The porous metallic sheet is characterized in that metallic fibers are intertwined with each other to form a sheet; the sheet is heated under pressure; and the inter-sections of the metallic fibers are connected directly with each other by fusing the surfaces of the intersections.
A porous metallic sheet of the second aspect is produced by the fifth embodiment shown in Fig. 16 showing the process of producing a porous metallic sheet from four kinds of short metallic fibers.

CA 022~4~04 1998-11-23 As shown in Fig. 16, in a first process, short metallic fibers are formed by any one of the following four kinds of methods:
(1) Short metallic fibers are formed by cutting fine metallic fibers formed by a convergent drawing method.
(2) Short metallic fibers are formed by cutting fine metallic fibers formed by a metallic foil cutting method.
(3) Short metallic fibers are formed by cutting metallic bars or metallic foil coils by a chattering-vibration method.
(4) Short metallic fibers are formed by cutting metallic fibers obtained by the metallic fiber-spinning method of the fist aspect of the invention.
The diameter of the metallic fibers formed by 15 method (4) can be set arbitrarily in the range of l~m -lOO~m. It is unnecessary in the case of the metallic fibers formed by extruding only metallic powder from the spinning nozzle, whereas in the case of the metallic fibers formed by spinning a mixture of the metallic powder and the 20 resin binder, the mixture is extruded from the spinning nozzle to obtain continuous fibers. Thus, in the latter case, it is necessary to burn out the resin binder. To this end, as shown in Fig. 17, continuous fibers are cut to a required length of lmm - 60mm by a cutter 201, and then the cut fibers are supplied to a conveyor 202 and then fed to a burning out oven 203 in which the fibers are heated in a nonoxidizing atmosphere at a binder-decomposing tempera-ture lower than the melting point of the metal (850~C -CA 022~4~04 1998-11-23 900~C) to burn out the resin binder, then heated at 1200~C
in a sintering oven 204 having a reducing atmosphere of hydrogen to sinter the metallic powder. In this manner, short metallic fibers F to which the resin binder has not been mixed are formed.
As the fine metallic fibers formed by the conver-gent drawing method (1), a bundle of a plurality of stain-less steel filaments is cold-drawn to reduce the diameter of each filament to less than 20~m. The resulting fila-ments are cut similarly to the metallic fibers formed ofthe metallic powder.
As the fine metallic fibers formed by the metallic foil cutting method (2), 10 aluminum foils of lO~m in thickness are laminated on each other and cut at an inter-val of lO~m, and the resultant fine metallic fibers arecut, similarly to the metallic fibers formed of the metal-lic powder.
In the chattering-vibration method (3), a metallic bar or a metallic foil coil is cut to a plurality of fibers by the self-excited vibration of an elastic cutting tool, while the metallic bar or the metallic foil is rotating.
This method allows the diameter of each fiber to be adjusted to 4~m - lOO~m and the length thereof to lmm -5mm.
25Substances Ni, Cu, Al, Ag, Fe, Zn, Sn, In, Ti, Pb, V, Cr, Co, oxides of these metals, alloys of these metals, and mixtures of these metals are favourably used to form the metallic fibers by using the methods (1) through (4).

CA 022~4~04 l998-ll-23 Stainless steel and titanium are more favourably used because these substances are corrosion-resistant. As the stainless steel, SUS 304, SUS 316 containing molybdenum, and SUS 444 containing niobium and molybdenum are preferab-5 ly used.
The short metallic fibers formed in any one of the four methods are ravelled by a blender in the second process and then measured by a quantity-measuring feeder, and then supplied to a carding machine to form a web B.
The web B consists of fibers that are ravelled and accumu-lated at random like cotton wool.
In the third process, as shown in Fig. 18, the web B consisting of metallic fibers is transferred from the carding machine 205 to a supporter 207 positioned on the conveyor 206 on which a fluid, for example, a columnar water current W is injected under a high pressure into the web B in a direction perpendicular thereto, so as to three-dimensionally intertwine the metallic fibers of the web B
with each other to form a sheet S.
The upper surface of the supporter 207 comprising a screen or a fine mesh sheet is flat and passes the water current. As shown in Figs. l9A and l9B, there are two types of supporter 207. The supporter 207 shown in Fig. l9B has conic or pyramidal convex portion 208 formed 25 on the upper surface thereof at regular intervals length-wise and widthwise. As will be described later, the convex portions 208 serve to form through-pores in a sheet of metallic fibers intertwined with each other. When it is .. ~ . .. _ _ CA 022~4~04 1998-11-23 unnecessary to form the through-pores in the sheet, the supporter 207 having no projections shown in Fig. l9A is used.
Because the sheet S is formed by using the highly pressurized columnar water current W in the third process, the sheet S is dehydrated and dried in the fourth process.
That is, as shown in Fig. 20, the sheet S taken out from the supporter 207 is supplied to a conveyor 209, and then pressed between a pair of dehydration presses 210. It is then passed through a drying oven 211 to heat it at a predetermined temperature to dry it.
In the fifth process, as shown in Fig. 21, the dried sheet S is supplied to a conveyor 212, and then passed through a pressurizing/heating oven 213 to heat it in a nonoxidizing atmosphere at a pressure less than 1 -30kgf/mm, and at a temperature lower than the melting point of the metal used, so as to directly connect the surfaces of intersections of the intertwined short metallic fibers.
Then, the sheet S is supplied to a reducing oven 214 where reduction is performed in a reducing atmosphere at a temperature lower than the melting point of the metal used.
In the sixth process, the resultant porous metallic sheet is passed between a pair of calendar rolls 215 to adjust the thickness thereof to a predetermined value. In the seventh process, a resultant porous metallic sheet 220 having the predetermined thickness is coiled around a roll 216.

CA 022~4~04 l998-ll-23 The operations of the first through seventh pro-cesses may be performed by using a feeding apparatus having a construction for performing the operations successively.
In the third process, the metallic fibers of the 5 web B are three-dimensionally intertwined with each other by means of the columnar water current directed thereto at high pressure. In this case, when the supporter 207 iS not provided with the convex portions 208 on the upper surface thereof as shown in Fig. l9A, the water current presses the entire web B against the upper surface of the supporter 207 at the same pressure, thus forming the sheet S on the upper surface of the supporter 207. The sheet S is taken out from the supporter 207 as a three-dimensional nonwoven porous metallic sheet having pores formed therein. In this 15 case, the percentage of pores of the porous metallic sheet can be adjusted to the desired percentage according to the density of the metallic fibers constituting the web B .
That is, if the metallic fibers are arranged at high density, the porous metallic sheet has a low percentage of 20 pores, i.e. is close to a solid metal, whereas, if they are arranged at low density, the porous metallic sheet has a high percentage of pores.
The projection 208 formed on the supporter 207 shown in Fig. l9B iS conic as shown in Fig. 22 or pyramidal 25 as shown in Figs. 23B and 23C.
When the columnar water current 200 iS injected under high pressure to the web B placed on the upper surface of the projection 208 formed on the supporter 207, CA 022~4~04 l998-ll-23 the web B on the projection 208 flows downward from the upper end of the projection 208 and is forced to drop onto the upper surface of the supporter 207 in the periphery of the projection 208 along the peripheral surface of the 5 projection 208, as shown in Fig. 22, thus forming the annular web B in the periphery of the lower end of the projection 208. Thus, through-holes 218 corresponding to the sectional configuration of the lower end of the projec-tion 208 are former on the sheet S.
When the projections 208 are conic and formed at regular intervals, as shown in Fig. 23A, the circular through-holes 218 are formed at regular intervals on the sheet S. When the projections 208 are pyramidal, as shown in Figs. 23B and 23C, the rhombic or square through-hole 218 are formed on the porous metallic sheet 220. Thus, the lath-shaped through-holes 218 or the net-shaped through-holes 218 are formed on the porous metallic sheet 220. The three-dimensional nonwoven porous metallic sheet 220 having the circular through-holes 218, the lath-shaped through-holes 218 or the net-shaped through-holes 218 has not only the through-holes 218 has not only the through-holes 218 formed therein at regular intervals, but also a large number of fine pores at the portion except for the through-holes 218.
AS shown in Fig. 24, when the projections 208 are formed on the porous metallic sheet 200 at regular inter-vals in a belt configuration, blank portions 219 are formed at regular intervals between rows of the through-holes 218.

CA 022~4~04 l998-ll-23 The blank portions 219 are used as a lead of an electrode plate of a battery. That is, in order to allow the blank portions 219 to be used as the lead, only the blank por-tions 219 are pressed by a roller to decrease the pores so 5 as to increase the density of the metallic fibers, namely, to allow the porous metallic sheet 220 to have a condition close to that of solid metal. It is possible to attach a metallic foil to the porous metallic sheet 220. The active substance is applied to the porous metallic sheet 220 made of metallic fibers produced in the above process while it is being successively transported. At this time, the active substance is applied not only to the through-holes 218 of the porous metallic sheet 220 having the circular through-holes 218, the lath-shaped through-holes 218 or the 15 net-shaped through-holes 218, but also to the fine pores thereof. The active substance is also applied to the porous metallic sheet 220 even though the through-holes 218 are not formed therein because it has fine pores at 90~ -99~. The active substance is also applied to both surface 20 of the porous metallic sheet 220 in a required thickness.
The porous metallic sheet 220 having the active substance applied thereto is cut into a plurality of pieces having a required size to use the cut pieces as a positive or negative plate of a battery.
Fig. 25 iS a flowchart showing a manufacturing method according to the sixth embodiment. Except for the third process, the manufacturing method is the same as that of the fifth embodiment. In the third process, the web B

CA 022~4~04 l998-ll-23 is placed on a conveyor 230 as shown in Fig. 26. The conveyor 230 iS provided with a roll 232 from which needles 231 having a small diameter project. The needles 231 penetrate into the web B so as to intertwine the metallic 5 fibers of the web B with each other three-dimensionally.
In this manner, the sheet S, namely, a porous metallic sheet is formed.
Figs. 27A, 27B, and 27C show an electrode substrate of a battery according to the seventh embodiment. Fig. 27A
shows an electrode substrate comprising a plurality of laminated three-dimensional porous metallic sheets 220, having pores, made of the metallic fibers produced by the manufacturing method according to the fifth embodiment.
The surfaces of the porous metallic sheets 220 are fused at 15 a temperature lower than the melting point of the metal used, so as to laminate them one on the other. Fig. 27B
shows an electrode substrate comprising a metallic foil 233 having holes formed thereon overlaid on the porous metallic sheet 220. Fig. 27C shows an electrode substrate compris-20 ing the porous metallic sheet 220 and a porous metallicsheet 234, overlaid on the porous metallic sheet 220, formed by electrically plating a conductive foamed sheet, a mesh sheet or a nonwoven sheet and by performing resin binder-removing and sintering operations. If it is necess-25 ary to form through-holes in the laminated sheets, circular or rhombic holes are formed by a press with the sheets laminated one on the other to form a porous metallic sheet having circular holes or lath-shaped holes.

CA 022~4~04 1998-11-23 In the fifth through seventh embodiments, short metallic fibers are intertwined with each other three-dimensionally. In the eighth embodiment, using long or continuous metallic fibers intertwined with each other three-dimensionally to form a sheet, the sheet is heated under pressure similarly to the fifth embodiment so as to fuse the surfaces of the fibers with each other at the points of intersection.
For example, the coiled continuous metallic fibers F manufactured as shown in Fig. 4 by using the manufactur-ing apparatus shown in Fig. 2 is supplied to a removal and sintering oven, and then, supplied to a supporter. Then, a columnar water current is injected at high speed to the coiled continuous metallic fibers under high pressure similarly to the fifth embodiment so as to intertwine then with each other. Thereafter, they are heated under pres-sure similarly to the fifth embodiment so as to fuse the surfaces of the fibers with each other at the points of intersection.
When the porous metallic sheet is composed of the continuous metallic fibers, the ends of the metallic fibers hardly project from the surface of the porous metallic sheet. Thus, when the porous metallic sheet is used as an electrode plate, no leaks occur at the edge thereof.
Fourth through 11th experiments of the second aspect of the invention are described below. In these experiments, a columnar water current was injected at high CA 022~4~04 1998-11-23 speed to the metallic fibers under high pressure to inter-twine them with each other three-dimensionally.
Porous metallic sheets described in the fourth through seventh experiments are preferably used as an electrode substrate of a lithium secondary battery.
In the fourth experiment, a web was formed from short fibers of copper, 15~m in diameter and 1.5mm in length, manufactured by a chattering-vibration cutting method using 72.4g of copper per centiare. The web was provided with a flat supporter and then a columnar water current was injected into the web at high pressure in a direction perpendicular thereto so as to intertwine the metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. Thereafter, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 700~C, at a pressure of 3kgf/mm. Then, reduction was performed in an atmosphere of H2 at 700~C. Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a porous metallic sheet having 20~m in thickness and 60~ in percentage of pores. The tensile strength of the porous metallic sheet was 11.5kgf/20mm.
In the fifth experiment, a web was formed from short fibers of stainless steel, having lO~m in diameter and 9mm in length, manufactured by a convergent drawing method using 52.4g of stainless steel per centiare. The web was delivered to the flat supporter and then a columnar water current was injected into the web at high pressure in CA 022~4~04 1998-11-23 a direction perpendicular thereto so as to intertwine the metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. Thereafter, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 1000~C, at a pressure of 6kgf/mm. Then, reduction was performed in an atmosphere of H2 at 1000~C. Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a porous metallic sheet having 15~m in thickness and 39% in percentage of pores. The tensile strength of the porous metallic sheet was 10.5kgf/20mm.
In the sixth experiment, a web was formed from short fibers of only copper powder. Each fiber of the web had 20~m in diameter and 4mm in length, manufactured by a metallic fibers-spinning method, using 80.5g of copper per centiare, without mixing resin binder with the copper powder. The web was delivered to a flat supporter and then a columnar water current was injected into the web at high pressure in a direction perpendicular thereto so as to intertwine the metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. There-after, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 700~C, at a pressure of 3kgf/mm. Then, reduction was performed in an atmosphere of Hz at 700~C. Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a porous metallic sheet having 18~m in thickness and 50% in percentage of pores. The CA 022~4~04 1998-11-23 tensile strength of the porous metallic sheet was 12.1kgf/-20mm.
In the seventh experiment, a web was formed from short fibers of aluminum, having 15~m in diameter and 4mm in length, manufactured by a metallic fibers-spinning method using 38.0g of aluminum per centiare. The web was delivered to a flat supporter and then a columnar water current was injected into the web at high pressure in a direction perpendicular thereto so as to intertwine the metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. Thereafter, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 400~C, at a pressure of 3kgf/mm. Then, reduction was performed in an atmosphere of H2 at 400~C. Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a porous metallic sheet having 20~m in thickness and 30~ in percentage of pores. The tensile strength of the porous metallic sheet was 5.2kgf/20mm.
Porous metallic sheets described in the eighth and ninth experiments are preferably used as an electrode substrate of a primary lithium battery.
In the eighth experiment, a web was formed from short fibers of stainless steel (SUS 444) having 15~m in diameter and 3mm in length, manufactured by a chattering-vibration method using 38.0g of stainless steel per centia-re. The web was delivered to a supporter on which pyra-midal projections were formed widthwise at regular inter-CA 022~4~04 1998-11-23 vals. Flat portions having a width of 7mm were also formed widthwise on the supporter at intervals of 20mm. Each bottom of the projection was rhombic. The longer diagonal line of the rhombic bottom of each convex was 2.5mm and the shorter diagonal line thereof was 0.8mm. A columnar water current was injected into the web at high pressure in a direction perpendicular thereto so as to intertwine the metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. Thereafter, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 1000~C, at a pressure of 6kgf/mm. Then, reduction was performed in an atmosphere of H2 at 1000~C. Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a lath-shaped porous metallic sheet having 200~m in thickness, 76~ in percentage of pores, and having a portion, serving as a lead, with-a width of 7mm, located widthwise at intervals of 20mm. The tensile strength of the porous metallic sheet was 15kgf/20mm.
In the ninth experiment, a web was formed from short fibers of stainless steel (SUS 444) having 8~m in diameter and 5mm in length, manufactured by a convergent drawing method using 254.lg of stainless steel per centiare. The web was delivered to a flat supporter on which quadrangular pyramidal projections each having a square (2mm x 2mm) on its bottom. Then, a columnar water current was injected into the web at high pressure in a direction perpendicular thereto so as to intertwine the CA 022~4~04 1998-11-23 metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. Thereafter, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 1000~C, at a pressure of 5.8kgf/mm. Then, reduction was performed in an atmosphere of H2 at 1000~C. Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a porous metallic sheet having 160~m in thickness and 80~ in percentage of pores. The tensile strength of the porous metallic sheet was 15.6kgf/20mm.
Porous metallic sheets described in the 10th and 11th experiments are preferably used as an electrode substrate of a nickel cadmium battery or that of a nickel hydrogen battery.
In the 10th experiment, a web was formed from short fibers of iron, having 8~m in diameter and lOmm in length, manufactured by a chattering-vibration cutting method using 132g of iron per centiare. The web was delivered to the flat supporter and then a columnar water current was injected into the web at high pressure in a direction perpendicular thereto so as to intertwine the metallic fibers with each other to form a sheet. Then, the sheet was dehydrated and dried. Thereafter, the sheet was nickel-plated. Then, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidiz-ing atmosphere, at 1000~C, at a pressure of 6kgf/mm. Then, reduction was performed in an atmosphere of H2 at 1000~C.
Then, the thickness of the sheet was adjusted to a required CA 022~4~04 1998-11-23 one with a calendar roll to obtain a porous metallic sheet having 50~m in thickness and 66 . 4~ in percentage of pores.
The tensile strength of the porous metallic sheet was 7.2 kgf/20mm.
In the 11th experiment, a nickel-containing com-pound fiber, having 15~m in diameter and 20mm in length, was manufactured from a mixture of nickel powder and resin binder by a metallic fibers-spinning method. The resin binder was burnt out in an atmospheric atmosphere at 850~C, and nickel powder was sintered in an atmosphere of H2 at 1000~C to form a web of nickel fibers having 13~m in diameter and 13mm in length using 150g of nickel per centiare. The metallic fibers were intertwined with each other to form a sheet. Then, the sheet was dehydrated and dried. Then, the surfaces of the metallic fibers were connected to each other by fusing them in a nonoxidizing atmosphere, at 1000~C, at a pressure of 6kgf/mm. Then, reduction was performed in an atmosphere of H2 at 1000~C.
Then, the thickness of the sheet was adjusted to a required one with a calendar roll to obtain a porous metallic sheet having 50~m in thickness and 65~ in percentage of pores.
The tensile strength of the porous metallic sheet was 11.8kgf/2Omm.
Similarly to the first through third experiments, an active substance was applied to the porous metallic sheet obtained in the fifth through 11th experiments. In each of the porous metallic sheets, the contact area between the active substance and the metallic fibers was CA 022~4~04 1998-11-23 large and the tensile strength of each porous metallic sheet was so high that each porous metallic sheet was resistant to a drawing force applied thereto in applying the active substance thereto and coiling it via a separ-ator.
In the 12th experiment, paste of a mixture was applied to 100wt% of an alloy powder containing LmNi42Co2Mn0 8Alo 3~ 0 . 5wt% of sodium polyacrylate, 0.13wt% of carboxym-ethyl cellulose, 1.45wt% of polytetrafluoroethylene of the dispersion type, 1.5wt% of carbon black serving as a conduction material, and water. After the paste was dried, a sheet was molded under pressure to form an electrode plate for a nickel hydrogen battery.
As apparent from the foregoing description, the porous metallic sheet to be used as an electrode substrate of a battery in accordance with the embodiments of the present invention has the following effects.
(1) The thickness of the porous metallic sheet and the percentage of pores thereof can be controlled easily. That is, making the thickness of the conventional punched metal small, for example as small as less than 60~m, the material cost such as an iron plate becomes high and workability becomes inferior. On the other hand, a porous metallic sheet in accordance with the present disclosure is formed of fine metallic fibers, having 1 - 100~m~ in diameter, laminated one on the other. Thus, the thickness of the porous metallic sheet and the percentage of pores can be adjusted to 10~m - 500~m and 20 - 90%, respectively, by CA 022~4~04 1998-11-23 changing the amount of metallic fibers and the diameters thereof. In particular, the thickness of the porous metallic sheet can be reduced to less than 60~m, although it is difficult for the conventional method to do so. As such, the weight of metal per area can be reduced, because a thin porous metallic sheet can be formed and the porous metallic sheet can be allowed to have a high percentage of pores. Thus, according to the present invention, the thinner the porous metallic sheet, the less expensive the material cost becomes.
~2) In applying an active substance to through-holes of the conventional punched metal and coating the surface thereof with the active substance, the degree of adherence of the active substance to the surface is not high, because portions are other than flat and smooth. Thus, in subse-quent processes, there is a possibility that the active substance is removed from the surface of the punched metal sheet. On the other hand, because the metallic fibers of the porous metallic sheet in accordance with the embodi-ments of the present invention are three-dimensionally intertwined with each other, the region other than the through-holes are three-dimensional, which allows the active substance to be applied to pores located in the interior of the porous metallic sheet. Therefore, the active substance comes in close contact with the metallic fibers and, hence, is not removed therefrom in subsequent processes.

CA 022~4~04 1998-11-23 (3) The porous metallic sheet according to the embodiments of the present invention is made of metallic fibers three-dimensionally intertwined with each other by using a water current having a high speed and a high pressure or a needle punch. Therefore, the metallic fibers intersect with each other at many points. The intersections of the intertwined metallic fibers are pressurized in a nonoxidizing atmos-phere at a high temperature not exceeding the melting point of the metal to fuse the surfaces of the metallic fibers with each other. At this time, because the surfaces of the metallic fibers are connected directly with each other under pressure by fusing, they intersect with each other at many points and the points of intersections are fused together. Thus, a porous metallic sheet having a high tensile force can be obtained. In addition, ends of the surfaces of the metallic fibers are connected with each other by fusion and hence do not project from the surface of the porous metallic sheet. Accordingly, when the porous metallic sheet is coiled with a separator after applying an active substance thereto, leaks can be prevented. Further, because the active substance and the metallic fibers are in contact at many points, the porous metallic sheet allows an electric current to flow reliably, thus serving as a highly conductive substrate. The resistance of a conventional punched metal (iron + plated nickel) is lOmQ/50mm, while that of a porous sheet made of nickel according to the present invention is 8mQ/50mm which is lower than lOmQ/50mm.

CA 022~4~04 1998-11-23 (4) The projections formed on the supporter on which the web is placed causes metallic fibers to make through-holes with accumulation of the web on flat portions of the supporter. When a columnar water current is injected into the web in a direction perpendicular to the web, in order to intertwine the metallic fibers with each other, the through-holes are formed at the same time. As a result, punched-shaped, lath-shaped or net-shaped patterns are formed on the resulting porous metallic sheet depending on the configuration of the projections. In this manner, the required through-holes can be easily formed, and it is not necessary to from the through-holes in a subsequent pro-cess. Thus, the porous metallic sheet can be manufactured at a low cost. Furthermore, belt-shaped flat portions are formed lengthwise in a region in which the through-holes are not formed, so as to form the belt-shaped flat portions for use as leads of an electrode plate on the metallic fibers-intertwined sheet, simultaneously with the formation of the through-holes.
(5) Further, because the diameters of the metallic fibers composing the porous metallic sheet can be allowed to be small, a thin porous metallic sheet can be produced.
Moreover, because the porous metallic sheet is allowed to have a high percentage of pores, a large amount of active substance can be applied thereto. That is, the porous ~etallic sheet can have a high conductivity to increase the capacity of a battery, because a large amount of active substance can be applied thereto. In addition, as the CA 022~4~04 1998-11-23 electrode substrate is thin and flexible, the substrate disperses any external force applied to it when the porous metallic sheet is cut to a plurality of pieces having a predetermined size after the active substance has been applied thereto. Thus, deformation or burr formation hardly occurs in the substrate. When the substrate is coiled to be accommodated in a spiral type battery, it can be coiled without causing a leak or crack.

(6) Because a sheet having a porous structure is made of solid metallic fibers, the metal surrounding the pores is uniformly distributed on the surface thereof and in the interior thereof. According to the conventional method, the surface of organic fibers is plated and then burnt out.
Therefore, cavities to which the active substance cannot be applied are present in the metallic fibers. On the other hand, because cavities are not present in the metallic fibers of the embodiments of the present invention on the porous metallic sheet, there is no portion to which the active substance cannot be applied. Further, because the diameter of the metallic fibers of the embodiments of the present invention is smaller than that of the conventional metallic fiber having a cavity therein, the percentage of pores can be increased and thus the applied amount of the active substance can be increased. In addition, supposing that the same amount of metal is used per (m2) both in the porous metallic sheet of the present invention and the conventional one, and the percentage of pores of the former is equal to that of the latter, the number of metallic CA 022~4~04 1998-11-23 fibers to be used in the former is greater than in the latter, while the area of one pore of the porous metallic sheet of the former is smaller than that of one pore of the porous metallic sheet of the latter. Thus, a porous metallic sheet of the embodiments of the present invention increases the conductivity of the substrate, thus improving the performance of the battery.

(7) The method of manufacturing a porous metallic sheet to be used as an electrode substrate of a battery according to the embodiments of the present invention eliminates a conductivity imparting process and plating process, which are required conventionally. Thus the method eliminates the problem of waste solution which is produced when plating. That is, the manufacturing method is low on pollution. In addition, the manufacturing method saves electric power, thus reducing the manufacturing cost.

(8) Even though electrical plating is used to increase the strength of the porous metallic sheet, the amount of metal to be applied to the porous metallic sheet of the embodi-ments of the present invention is smaller than that appliedto the conventional porous metallic sheet, thus reducing the rate of electric power consumption.

Claims

1. A method of manufacturing a porous metallic sheet for use as an electrode substrate of a battery, comprising the steps of:
forming a mixture by kneading metallic powders and resin binder;
spinning metallic fibers by extruding the mixture from a spinning nozzle; and forming the spun metallic fibers into a porous fibrous structure or a three-dimensional net-shaped structure.

2. The method of manufacturing the porous metallic sheet according to claim 1, wherein the resin binder is burnt out, and the metallic powders are sintered.

3. The method of manufacturing the porous metallic sheet according to claim 1 or 2, wherein the metallic powders are mixed with the resin binder at a percentage of 70 - 97.

4. A method of manufacturing a porous metallic sheet for use as an electrode substrate of a battery, comprising the steps of:
spinning metallic fibers by extruding metallic powders from a spinning nozzle; and forming the spun metallic fibers into a porous fibrous structure or a three-dimensional net-shaped structure.

5. The method of manufacturing the porous metallic sheet according to claim 4, wherein the porous fibrous structure or the three-dimensional net-shaped structure is sintered.

6. The method of manufacturing the porous metallic sheet according to claim 1, 2, 3, 4 or 5, wherein the continuous metallic fibers extruded from the spinning nozzle are curved continuously into a coiled configuration by movement of air.

7. The method of manufacturing the porous metallic sheet according to claim 1, 2, 3, 4, 5 or 6, wherein a great number of spun continuous metallic fibers is coiled; the coiled continuous metallic fibers are fed to a conveyor; and the conveyor is vibrated to intertwine the continuous metallic fibers with each other to form a sheet having a porous structure.