JP2000331708A - Sodium-sulfur secondary battery, positive electrode molding used therefor, manufacture of the battery and molding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a positive electrode molding with high resistant layer, with a simple process, by arranging a circumferentially divided sheet-like product consisting of a powder or fiber having low electron conductivity between a sodium ion conductive solid electrolyte and a positive electrode molding consisting of a positive electrode current collector, impregnated with sulfur and contained in a positive electrode chamber partitioned from a negative electrode chamber containing sodium by the solid electrode. SOLUTION: A positive electrode current collector of corrosion-resistance and electron conductive to sulfur or sodium polysulfide of a positive electrode active material and preferably filled by compression is adhered to a sheet-like product, consisting of a powder or fiber of ceramics or glass through sulfur to form a positive electrode molding. This is molded with a prescribed curvature between a lower protruding fixed die preferably, consisting of aluminum hardly wettable to sulfur and an upper recessed compression movable die to provide a high resistant layer having a uniform prescribed thickness, so that the deviation of current distribution within the positive electrode is minimized. Accordingly, a complicated process as penetration of the positive electrode active material within the high resistant layer to expensive felt is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to a secondary battery, a molded positive electrode used therefor, a method for producing the same, and a molding apparatus.

[0002]

2. Description of the Related Art A sodium-sulfur secondary battery has a solid electrolyte having sodium ion conductivity, a negative electrode chamber containing sodium, which is a negative electrode active material, separated by the solid electrolyte, and sulfur which is a positive electrode active material. The operating temperature of the positive electrode chamber containing a substance such as carbon fiber having corrosion resistance and electron conductivity (hereinafter referred to as a positive electrode current collector) is 3
It is a sealed secondary battery of 00 to 350 ° C.

[0003] A positive electrode molded body of a sodium-sulfur secondary battery is composed of a positive electrode current collector (hereinafter referred to as "felt") formed by applying a needle punch to carbon fiber to form a flat plate, and sulfur. Then, the felt is impregnated with the molten sulfur and molded. Since carbon fibers have excellent wettability to sulfur, only sulfur in a molten state is brought into contact with the felt, and the sulfur naturally enters the felt. If necessary, pressurizing the molten sulfur can more quickly impregnate the felt with sulfur.

Further, it is necessary to attach a high resistance layer made of powder and fibers having poor electron conductivity to the surface of the positive electrode molded body of the sodium-sulfur secondary battery in contact with the solid electrolyte. In the absence of this layer, insulating sulfur precipitates on the surface of the solid electrolyte tube during charging, which lowers charge acceptability and significantly lowers battery capacity. For this reason, in Japanese Patent Application Laid-Open No. 4-71171, as a method of forming a positive electrode molded body provided with this layer, a high resistance layer in which a powder or short fibrous high resistance material and a positive electrode active material are mixed is formed on felt, Further, a method for injecting a positive electrode active material into a felt is disclosed.

Japanese Patent Application Laid-Open No. Hei 6-231800 discloses a method and apparatus for manufacturing a positive electrode molded body. In order to prevent the felt from falling in a jig, the felt is pressed in the width direction of the felt and compressed in the vertical direction. A method and an apparatus for manufacturing a positive electrode molded body to be manufactured are disclosed.

Japanese Patent Application Laid-Open No. 10-302831 discloses a method and apparatus for continuously producing a positive electrode molded body using a continuous press machine equipped with an endless belt capable of heating and cooling.

[0007]

In the above-described method of forming a high-resistance layer in which a positive electrode active material and a high-resistance material are mixed on the upper surface or the concave surface of the felt, the thickness of the high-resistance layer is reduced to the order of tens of μm. Since it is difficult to make the battery uniform, the resistance of each battery component becomes non-uniform, the current distribution in the positive electrode is biased, and the battery efficiency and battery capacity (active material utilization rate) decrease. Further, there is a problem that the number of working steps and the number of devices are increased in order for the positive electrode active material in the high resistance layer to enter the felt.

Further, since an aggregate of carbon fibers such as felt processed into a plate shape by needle punching is expensive, an inexpensive positive electrode current collector such as an aggregate in which carbon powder, carbon fibers, and carbon fibers are entangled is used. A jig structure applicable to the body is required.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and the gist thereof is as follows.

(1) A solid electrolyte having sodium ion conductivity is separated into a positive electrode chamber and a negative electrode chamber, and the negative electrode chamber contains sodium as a negative electrode active material, and the positive electrode chamber contains sulfur as a positive electrode active material. Or in a sodium-sulfur secondary battery containing a positive electrode molded body impregnated with sulfur in a positive electrode current collector having corrosion resistance to sodium polysulfide and electron conductivity, a circumferential direction is formed between the positive electrode molded body and the solid electrolyte. A sodium-sulfur secondary battery comprising a sheet-like processed product made of divided powders or fibers having poor electron conductivity.

(2) A positive electrode molded body of a sodium-sulfur secondary battery in which sulfur is impregnated in a positive electrode current collector having corrosion resistance and electron conductivity against sulfur or sodium polysulfide as a positive electrode active material, A sodium-sulfur secondary, comprising a compression-filled positive electrode current collector and a sheet-like processed product made of powder or fiber having poor electron conductivity, which are bonded to each other via sulfur as a positive electrode active material. A positive electrode molded body of a battery.

(3) Forming a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. In the method, a sheet-like processed product of powder or fiber having poor electron conductivity and a positive electrode current collector are arranged on the upper part of the fixed mold, and the sheet-shaped processed product is pressed into a lower convex shape by pressing with a movable mold for compression. A method for forming a positive electrode molded body for a sodium-sulfur secondary battery, characterized by being curved into a shape.

(4) Molding of a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. In the method, a sheet-like processed product of powder or fiber with poor electron conductivity and a positive electrode current collector are arranged on the upper part of the fixed mold, and the compressed movable mold is pressurized to pour molten sulfur into the sheet. Sodium / sulfur 2 characterized in that the shaped article and the positive electrode current collector are attached via sulfur.
Method for forming positive electrode molded body for secondary battery.

(5) Molding of a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable compression mold having an upper concave shape. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, wherein the fixed type and the movable movable type are made of a material which is hardly wetted by sulfur.

(6) Molding of a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable compression mold having an upper concave shape. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, wherein the fixed mold and the movable movable mold are made of aluminum.

(7) Molding of a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, wherein the convex surface of the fixed type and the concave surface of the movable type for compression are covered with a substance which is hardly wetted by sulfur.

(8) The positive electrode for a sodium-sulfur secondary battery according to (7), wherein the convex surface of the fixed type and the concave surface of the movable type for compression are covered with a fluorine resin. Body molding equipment.

(9) Molding of a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. An apparatus for forming a positive electrode molded product for a sodium-sulfur secondary battery, wherein the convex surface of the fixed type and the concave surface of the movable type for compression are covered with aluminum. I will provide a.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention uses, for example, a positive electrode molded product in which a positive electrode current collector shown in FIG. 1 and a sheet-like processed product of powder or fiber having poor electron conductivity are adhered via sulfur. Achieved. The sheet-like processed product which plays such a role is formed by molding powder or short fiber made of ceramics such as alumina or glass, or an organic material typified by cellulose as a binder. As this sheet, a sheet having an electronic resistivity of 1 kΩ · cm or more, preferably 50% or more is preferable.

Such a positive electrode molded body is formed by using a jig composed of a fixed mold having a lower convex shape and a movable movable mold for compression having an upper concave shape as shown in FIG. It can be produced by a method of impregnating sulfur with the filled positive electrode current collector being compressed at the same time.

According to this method, a sheet-like processed product can be formed in which the thickness of the high-resistance layer is uniform on the order of several tens of μm. The bias of the current distribution can be kept small.

Further, the molding of the positive electrode molded body and the attachment of the high-resistance layer can be simultaneously performed by a single impregnation with sulfur, so that the number of working steps and the number of devices can be reduced. Also, the jig shown in FIG. 2 does not assume a flat-shaped felt as the positive electrode current collector,
It is not necessary to change it even when using an aggregate in which powder, fibers and fibers are entangled as the positive electrode current collector.

Further, a method of using a material having poor wettability, such as a fluorine-based resin represented by polytetrafluoroethylene, having a wetting angle of 60 ° or more, such as a fluorine-based resin, as a constituent material of the jig or a coating material for the surface thereof, When the method of covering the inner surface of the jig with a film such as an aluminum foil is used, the releasability of the formed positive electrode molded body is improved, and the number of continuous use of the jig can be increased.

Hereinafter, the present invention will be described in detail with reference to examples, but the examples show one embodiment of the present invention and do not limit the present invention.

(Example 1) A positive electrode molded body of the present invention was prepared using a mold jig having a structure shown in FIG. The mold jig is composed of a lower convex fixed mold and an upper concave movable mold.

The mold jig has the following structure: 1) The lower convex fixed mold has a structure in which the side surfaces can be separated in order to facilitate removal of the positive electrode molded body when molding is completed. 2) The surface of the mold jig was coated with a fluororesin containing polytetrafluoroethylene as a main component in order to improve the releasability of the solidified positive electrode molded body. 3) A groove for storing sulfur in the upper concave movable mold and a sulfur introduction hole with a radius of 2 mm connecting this groove and the inside of the mold jig are provided so that sulfur can be impregnated with the positive electrode current collector compressed and filled. Was. 4) An exhaust hole for gas existing in the mold jig was provided so that molten sulfur could be introduced quickly.

Further, the following means can be used. 5) When the side surface of the lower fixed die is not separated, it is preferable to provide several pins for extruding the molded body at the lower part of the fixed die. 6) The coating material on the surface of the mold jig is preferably not coated with a fluorine resin, but is coated with a material having poor wettability to sulfur. Further, a method of using aluminum as a constituent material of the mold jig, a method of coating aluminum, and a method of coating the inside of the mold jig with aluminum foil are also effective in improving the releasability of the positive electrode molded body. .

Next, a method for manufacturing a molded positive electrode of the present invention using the above-described mold jig will be described with reference to FIG.

First, a sheet-like processed product made of alumina fibers and having a thickness of about 200 μm is laid inside the lower convex fixed mold. Hereinafter, this is referred to as alumina paper. A felt made by processing carbon fibers into a flat plate is inserted from above the alumina paper. This state is shown in FIG. Then, FIG.
As shown in (b), the felt is compressed by the upper concave movable mold until the felt has a predetermined thickness. At this time, the felt is curved so as to have a predetermined radius of curvature, and the alumina paper is bent into a fixed convex shape by the pressure transmitted through the felt. Then, as shown in FIG. 3 (c), the upper concave movable mold is fixed while the felt and the alumina paper are compressed, a predetermined amount of sulfur is introduced into the groove, and the entire mold jig is heated to 110 ° C. to 160 ° C. Heat to ° C. The molten sulfur passes through the sulfur introduction hole by its own weight and impregnates felt and alumina paper. Alumina paper does not have as good wettability to sulfur as carbon fiber, but if the temperature of the entire jig is kept at 110 ° C. to 160 ° C. and held for about several hours, the felt and the alumina paper adhere via sulfur.

When the positive electrode molded body produced in this manner is produced so as to have a shape obtained by equally dividing a cylindrical shape into n (n = 2, 3, 4) equally on a plane parallel to the axial direction, the shape of the jig is obtained. Needs only one kind.

As shown in FIG. 4, by inserting n pieces of this positive electrode molded article into the positive electrode tube, a sodium-sulfur secondary battery as shown in FIG. 5 can be provided.

Comparative Example 1 As a conventional method, Example 1 was used.
Only the felt was filled in the mold jig used in the above, and a positive electrode molded body impregnated with sulfur was prepared in that state. This positive electrode molded body is inserted into a positive electrode container, and a solid electrolyte tube around which alumina paper as a high resistance layer is wound is further inserted by a method.
A sodium-sulfur secondary battery shown in FIG.

As compared with the production process of the first embodiment, the process of winding alumina paper around the solid electrolyte tube can be reduced. In addition, the actual battery of Comparative Example 1 has a high resistance at the time of initial discharge, so that it takes 9 hours to flow a discharge current of 10 A. However, the sodium-sulfur secondary battery prepared in Example 1 has an initial discharge current of 10 A. It took only 30 minutes to flush. Further, in Example 1, since the adhesiveness between the alumina paper and the felt was good, the charging and discharging efficiency could be improved by about 2% and the battery capacity could be improved by about 3%.

(Example 2) The mold jig used in Example 1 was used, and an aggregate in which carbon fibers were entangled instead of felt as the positive electrode current collector was filled, and the same as in Example 1 shown in FIG. A positive electrode molded body was prepared by the method described above.

Further, a sodium-sulfur secondary battery was prepared using the positive electrode molded body. In terms of initial discharge, charge / discharge resistance and battery capacity, performance equivalent to that of Example 1 could be obtained.

As described above, sufficient performance could be obtained even when expensive felt was not used for the positive electrode molded body.

[0037]

The present invention is a simple process in which a sheet-like processed product of powder and fiber having poor electron conductivity and a positive electrode current collector are loaded in a mold jig, compressed and impregnated with sulfur. And a positive electrode molded body with a high resistance layer. According to the present invention, a conventionally complicated process of forming a high-resistance layer can be eliminated, and a great effect can be obtained in reducing the price of a sodium-sulfur secondary battery used for power storage and the like.

[Brief description of the drawings]

FIG. 1 is a schematic view of a molded positive electrode for a sodium-sulfur secondary battery of the present invention.

FIG. 2 is a partial cross-sectional view of an apparatus for manufacturing a positive electrode molded body for a sodium-sulfur secondary battery of the present invention.

FIG. 3 is a process chart of a method for producing a molded positive electrode for a sodium-sulfur secondary battery according to the present invention.

FIG. 4 shows a positive electrode molded product of the present invention,
(A) Conceptual diagram of insertion process and (b) in positive electrode container of sulfur secondary battery
FIG. 7 is a cross-sectional view after insertion (when n = 4).

FIG. 5 is a longitudinal sectional view of a sodium-sulfur secondary battery prepared using the positive electrode molded body of the present invention.

FIG. 6 is a process diagram of a method for producing a positive electrode molded body of the present invention when the positive electrode current collector is a powder, a fiber, or an aggregate in which fibers are entangled.

[Explanation of symbols]

1 ... flat felt, 2 ... sheet and processed product of powder and fiber with poor electronic conductivity (alumina paper), 3 ... sulfur, 4 ... lower convex fixed type, 5 ... upper concave movable type for compression, 6 ... Sulfur insertion hole, 7: groove for storing sulfur, 8: gas vent hole, 9: aggregate entangled with carbon fiber, 10: positive electrode molded body, 11: positive electrode container, 12: solid electrolyte, 13 ...
Α-alumina ring for positive and negative electrode insulation, 14 ... negative electrode container, 1
5 ... Negative electrode active material sodium, 16 ... Safety tube, 17 ... Negative electrode cap, 18 ... Positive electrode terminal, 19 ... Negative electrode terminal.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazue Kono 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Seiji Koike 7-1 Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Inside Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Kozo Sakamoto 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Yuichi Kamo Hitachi, Ibaraki Prefecture 7-1-1, Omikacho F-term in Hitachi Research Laboratory, Hitachi Ltd. (Reference) 5H029 AJ03 AK01 AL13 AM11 BJ02 CJ03 CJ05 CJ06 CJ22 CJ23 CJ30 DJ04 DJ07 DJ09 DJ15 DJ16 EJ01 EJ12 HJ05 HJ20

Claims (9)

[Claims] A positive electrode compartment and a negative compartment are separated by a solid electrolyte having sodium ion conductivity, the negative compartment contains sodium as a negative active material, and the positive compartment has sulfur or positive active material therein. In a sodium-sulfur secondary battery in which a positive electrode current collector having corrosion resistance and electron conductivity against sodium polysulfide and containing a positive electrode molded product impregnated with sulfur is circumferentially divided between the positive electrode molded product and the solid electrolyte. A sodium-sulfur secondary battery, wherein a sheet-like processed product made of a powder or a fiber having poor electron conductivity is disposed. 2. A positive electrode molded article of a sodium-sulfur secondary battery in which sulfur is impregnated in a positive electrode current collector having corrosion resistance and electron conductivity against sulfur or sodium polysulfide as a positive electrode active material, wherein the positive electrode molded article is compressed. It is composed of a filled positive electrode current collector and a sheet-like processed product made of powder or fiber having poor electron conductivity, and the positive electrode current collector and the positive electrode molded body are bonded to each other via sulfur as a positive electrode active material. A molded positive electrode of a sodium-sulfur secondary battery, characterized in that: 3. A method for forming a positive electrode molded body for a sodium-sulfur secondary battery, which is formed to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. In the above, a sheet-like processed product of powder or fiber having poor electron conductivity and a positive electrode current collector are arranged on the upper part of the fixed mold, and the sheet-like processed product is pressed into a lower convex shape by the compression movable die. Sodium characterized by being curved to
A method for forming a positive electrode formed body for a sulfur secondary battery. 4. A method for molding a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. In the fixed mold, a sheet-like processed product of powder or fiber with poor electron conductivity and a positive electrode current collector are arranged on the upper part of the fixed mold, and pressurized by the movable mold for compression, and sulfur in a molten state is poured into the sheet to form a sheet. A method for forming a positive electrode molded body for a sodium-sulfur secondary battery, comprising attaching a processed product and a positive electrode current collector via sulfur. 5. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, which is molded to a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. , Wherein the fixed die and the movable movable die are made of a material that is hardly wetted by sulfur. 6. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, which is formed into a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. , Wherein the fixed die and the movable movable die are made of aluminum. 7. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, which is formed into a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. 3. The molding apparatus of claim 2, wherein the convex surface of the fixed type and the concave surface of the movable movable type are coated with a substance which is hardly wetted by sulfur. 8. The molded positive electrode for a sodium-sulfur secondary battery according to claim 7, wherein the fixed convex surface and the compression movable concave surface are coated with a fluorine resin. Molding equipment. 9. An apparatus for forming a positive electrode molded body for a sodium-sulfur secondary battery, which is formed into a predetermined radius of curvature in a space formed by a fixed mold having a lower convex shape and a movable movable mold having an upper concave shape. 3. The molding apparatus for a positive electrode molded product for a sodium-sulfur secondary battery according to claim 1, wherein the convex surface of the fixed die and the concave surface of the movable compression die are coated with aluminum.