JP2000208165A - Sodium-sulfur secondary battery - Google Patents

Abstract

(57) [Problem] To provide a sodium-sulfur secondary battery excellent in charge / discharge resistance stability and charge / discharge efficiency. A sodium-sulfur in which an electron conductive material impregnated with sulfur and / or sodium polysulfide is disposed in a positive electrode chamber between a positive electrode container also serving as a positive electrode current collector and a solid electrolyte tube. In the secondary battery, a material layer 7 using a ceramic precursor as a bonding material is interposed and bonded between the solid electrolyte tube 1 and the electron conductive material 3.
Is a sodium-sulfur secondary battery composed of a mixture of an electron conductive fiber and an insulating material having an aspect ratio in the range of 5-290 in terms of fiber length / fiber diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sodium-sulfur secondary battery.

[0002]

2. Description of the Related Art In a sodium-sulfur secondary battery, sodium as a negative electrode active material and sulfur and sodium polysulfide as positive electrode active materials are converted into sodium ion conductive materials such as β-alumina and β ″ -alumina in a battery case. Is a sealed secondary battery that is separated by a solid electrolyte having the following characteristics and operated at 300 to 350 ° C.

[0003] The sodium-sulfur secondary battery having the above structure is
In order to improve the charge depth of the battery, a technique of interposing a ceramic web or woven cloth with excellent sulfur resistance and sodium polysulfide resistance between the solid electrolyte tube and the electron conductive material impregnated with the positive electrode active material is a special feature. This is known from Japanese Unexamined Patent Publication No. Hei 6-283203 and Japanese Unexamined Patent Publication No. Hei 6-80593.

However, these conventionally used webs and sheets are electrically insulative and have a structure in which the electron conductive material is slightly in contact with the solid electrolyte tube for performing the initial discharge of the battery. It was difficult to make the electrolyte surface equipotential. Further, there is a problem that sulfur accumulates in gaps existing between the web or the fabric and the solid electrolyte tube or the electron conductive material, and the charge / discharge resistance is increased by repeating the charge / discharge cycle.

Japanese Patent Application Laid-Open No. 4-71171 discloses a technique in which carbon powder and alumina powder are mixed with sulfur instead of a ceramic web or woven cloth, and the mixture is applied to a solid electrolyte tube or an electron conductive material to form a film. Have been. However, the membrane prepared by this method has a problem that since the operating temperature of the battery is equal to or higher than the melting point of sulfur, it is difficult to maintain the membrane shape by repeating charge and discharge.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and to provide a sodium-sulfur secondary battery excellent in charge / discharge resistance stability and charge / discharge efficiency. Is to do.

[0007]

The gist of the present invention to achieve the above object is as follows.

[1] A sodium-sulfur secondary in which an electron conductive material impregnated with sulfur and / or sodium polysulfide is disposed in a positive electrode chamber between a positive electrode container also serving as a positive electrode current collector and a solid electrolyte tube. In the battery, a material layer using a ceramic precursor as a bonding material is interposed and bonded between the solid electrolyte tube and the electron conductive material, and the material layer has an aspect ratio determined by fiber length / fiber diameter of 5%. A sodium-sulfur secondary battery comprising a mixture of an electron conductive fiber and an insulating material having a range of from 290 to 290.

[2] A sodium-sulfur secondary in which an electron conductive material impregnated with sulfur and / or sodium polysulfide is disposed in a positive electrode chamber between a positive electrode container also serving as a positive electrode current collector and a solid electrolyte tube. In the battery, a material layer made of a mixture of an insulating material and an electron conductive fiber using a ceramic precursor as a bonding material is interposed and adhered between the solid electrolyte tube and the electron conductive material. A slurry or paste comprising a mixture of an insulating material having excellent sulfur resistance and sodium polysulfide resistance and an electron conductive fiber applied to the ceramic precursor is applied to a solid electrolyte tube, and is formed by firing treatment. Sodium-sulfur secondary battery.

[3] The method according to [1] or [2], wherein the electron conductive fiber is at least one material selected from a carbon-based material, W, Mo, a Co—Cr alloy, and an Al—Si alloy. The sodium-sulfur secondary battery according to the above.

[4] The ceramic precursor is M
The sodium-sulfur secondary battery according to the above [1] or [2], containing at least one selected from g, Ti, Si, Al, and Zr.

[5] The sodium-sulfur secondary battery according to [1] or [2], wherein the electron conductive fiber is a material having a smaller specific surface area than the insulating material.

[6] The temperature in the firing treatment is 25
The sodium-sulfur secondary battery according to [2], wherein the temperature is 0 to 680 ° C.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sodium-sulfur secondary battery of the present invention has a structure as shown in the schematic sectional view of FIG. 1, in which an insulating ring 4 is joined to the upper end of a solid electrolyte tube 1 and a metal A negative electrode chamber 2 mainly composed of sodium is formed.

Further, a positive electrode chamber 9 in which an electron conductive material 3 impregnated with sulfur and / or sodium polysulfide and a material layer 7 excellent in sulfur resistance and sodium polysulfide resistance are formed. The negative electrode container 5 and the positive electrode container 6 are heat-pressure bonded to the insulating ring 4 and are sealed. A ceramic precursor was used as the material layer 7 having excellent resistance to sulfur and sodium polysulfide and low electron conductivity.

The material layer 7 having excellent sulfur resistance and sodium polysulfide resistance and low electron conductivity is made of an insulating material such as an electron conductive material having an aspect ratio calculated as fiber length / fiber diameter in the range of 5-290. Since it is composed of a mixture with a substance and is chemically bonded to the solid electrolyte tube 1 by firing the substance layer, the properties of the film are excellent even after repeated charge and discharge, and the charge and discharge resistance characteristics of the battery are stable. It is.

Further, since the properties of the film are maintained even when the number of charge / discharge cycles is increased, direct contact between the solid electrolyte and the electron conductive material does not occur, and the equipotential of the electrolyte surface is maintained. The discharge resistance stabilizes.

If the aspect ratio calculated by the fiber length / diameter of the material layer 7 is less than 5, the electron conduction path of the material layer 7 becomes discontinuous, so that the charge / discharge resistance increases and the aspect ratio becomes 290. If it exceeds, the mixing with the insulating material becomes uneven, it becomes difficult to keep the surface of the solid electrolyte at the same potential, and the charge / discharge resistance increases.

The same effect can be obtained by heating the ceramic precursor even when the precursor is partially amorphous without being transformed into oxide crystalline material. However, if the heat treatment temperature is lower than 250 ° C., the micropore structure of the material layer 7 may change during the operation of the battery, and the charge / discharge resistance may increase. If the heat treatment temperature is higher than 680 ° C., the electron conductive fibers may be oxidized or disappear, and the charge / discharge resistance may increase.

It is desirable to use a material having a specific surface area larger than that of the insulating material as the electron conductive fiber.
Thereby, the sulfur generated at the interface between the material layer 7 and the electron conductive material 3 when the battery is charged rapidly diffuses toward the electron conductive material 3, so that the charge resistance is reduced and the charge / discharge efficiency of the battery is improved.

The electron conductive fibers constituting the material layer 7 include carbon-based materials, W, Mo, Co-Cr alloys,
By selecting from the Al-Si alloy, it does not react with the positive electrode active material, and the capacity of the battery does not decrease and the resistance does not increase.

The compounding ratio of the electron conductive fibers and the insulating material constituting the material layer 7 is determined by the ratio of the material layer 7 after the firing treatment having a resistivity 10 times or more the resistivity of the electron conductive fibers. It is desirable to do.

Similarly, when the component constituting the ceramic precursor is at least one selected from the group consisting of Mg, Ti, Si, Al, and Zr, it does not react with the positive electrode active material, so that the capacity of the battery decreases. And stable charge / discharge characteristics can be obtained. Incidentally, the mixing ratio of the ceramic precursor is based on the material layer 7 after the firing treatment.
2-15% by weight is preferred.

[0024]

The present invention will be specifically described below with reference to examples. In the following examples, the structure of the battery was a cylindrical solid electrolyte with a bottom as shown in FIG. 1, but the present invention is not limited to this.

Example 1 An insulating material (alumina) and an electron conductive fiber (polyacrylonitrile (PAN) -based carbon fiber) were added to a predetermined amount of a ceramic precursor (silica sol) and mixed until uniform with a ball mill. I do.
The compounding ratio at this time is: ceramic precursor / (insulating substance +
(Electron conductive fiber) was blended so as to be 1/3 by weight. The compounding ratio of the insulating material to the electron conductive fiber was set to be 10 ⁴ times the resistivity of the electron conductive fiber.

The solid electrolyte tube 1 is immersed in the mixture,
The mixture is applied to its outer surface. Next, after preliminary drying at room temperature, heat treatment was performed at 500 ° C. to form a material layer 7 having excellent sulfur resistance and sodium polysulfide resistance and low electron conductivity.

The solid electrolyte tube 1 on which the material layer 7 is formed
Was used to produce a sodium-sulfur secondary battery as shown in FIG.

In the present embodiment, the means for forming the material layer 7 on the solid electrolyte tube 1 is performed by the dip coating method. However, the present invention is not limited to this. For example, spray coating, brush coating, or the like may be used. Can be.

FIG. 2 shows that the material layer 7 has an aspect ratio of electron conductive fibers of 1, 5, 10, 100, 200, 2
Using a solid electrolyte tube 1 of 90, 300
The measurement result of the cycle characteristic of the relative charge / discharge resistance of the produced sodium-sulfur secondary battery is shown. Here, the thickness of the material layer 7 was 100 microns.

The battery shown as Comparative Example 1 is a battery using a fabric made of alumina as the material layer 7.

From FIG. 2, it was confirmed that the relative charge / discharge resistance of the battery was stable when the aspect ratio of the electron conductive fibers of the material layer 7 was 5 to 290.

[Embodiment 2] FIG. 3 shows that the heat treatment temperature of the material layer 7 is 100, 250, 300, 500, 600,
The measurement result of the cycle characteristic of the relative charge / discharge resistance of the sodium-sulfur secondary battery when it changes to 680 and 700 degreeC, respectively is shown.

The battery shown as Comparative Example 1 is a battery in which the material layer 7 is made of a fabric made of alumina.

FIG. 3 shows that the heat treatment temperature of the material
At 680 ° C., it was confirmed that the relative charge / discharge resistance of the battery was stable.

[Embodiment 3] FIG. 4 shows the relative charge / discharge efficiency of a sodium-sulfur secondary battery when the specific surface area of the insulating material / electron conductive fiber constituting the material layer 7 was changed. The measurement results are shown.

The battery shown as Comparative Example 1 is a battery in which the material layer 7 is made of alumina fabric.

FIG. 4 confirms that the relative charge / discharge efficiency of the battery is improved when the insulating material constituting the material layer 7 has a larger specific surface area than the electron conductive fiber. .

[0038]

In the present invention, a solid electrolyte tube 1 having a material layer 7 which is excellent in sulfur resistance and sodium polysulfide resistance and has low electron conductivity is formed on the outer surface. However, the material layer 7 is composed of a mixture of an electron conductive material having an aspect ratio of 5 to 290 determined by fiber length / fiber diameter and an insulating material, and is chemically bonded to the solid electrolyte tube 1 to be filled. Since the film properties are stable even after repeated discharge, a sodium-sulfur secondary battery having stable charge / discharge resistance characteristics can be provided.

In addition, since the film properties are maintained even when the number of charge / discharge cycles is increased, direct contact between the solid electrolyte and the electron conductive material does not occur, and the equipotential of the electrolyte surface is maintained. The resistance stabilizes.

The same effect can be obtained by heating the ceramic precursor of the constituent material of the material layer 7 even if all of the precursor does not transform into oxide crystalline and is partially amorphous. Can be

By using a fiber having a specific surface area larger than that of the insulating material mixed with the ceramic precursor, the interface between the material layer 7 and the electron conductive material 3 at the time of charging the battery is used. Is quickly diffused to the electron conductive material 3 side, so that the charge resistance is reduced and the charge / discharge efficiency of the battery is improved.

According to the present invention, it is possible to obtain an excellent sodium-sulfur secondary battery as a secondary battery for storing electric power.

[Brief description of the drawings]

FIG. 1 is a schematic vertical sectional view showing an example of a sodium-sulfur secondary battery.

FIG. 2 is a graph showing the relationship between the charge / discharge cycle and the relative charge / discharge resistance of the sodium-sulfur secondary batteries of the present example and the comparative example.

FIG. 3 is a graph showing the relationship between the charge / discharge cycle and the relative charge / discharge resistance of the sodium-sulfur secondary batteries of the present example and the comparative example.

FIG. 4 is a graph showing the relationship between the specific surface area of the insulating material / electron conductive fibers and the relative charge / discharge efficiency of the sodium-sulfur secondary batteries of the present example and the comparative example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte tube, 2 ... Negative electrode chamber, 3 ... Electronic conductive material, 4 ...
Insulating ring, 5: negative electrode container, 6: positive electrode container, 7: material layer, 9: positive electrode chamber.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Toshiya Doi 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Masaru Kadoshima 7, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1-1 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 Tomokazu Kamo Hitachi, Ibaraki Prefecture 7-1-1, Omika-cho, Hitachi City F-term in Hitachi Research Laboratory, Hitachi, Ltd. 5H029 AJ02 AJ03 AK05 AL13 AM11 CJ02 CJ08 CJ22 DJ05 DJ15 EJ01 EJ04 EJ08 HJ07 HJ14

Claims (6)

[Claims] 1. A sodium-sulfur secondary battery in which an electron conductive material impregnated with sulfur and / or sodium polysulfide is disposed in a positive electrode chamber between a positive electrode container also serving as a positive electrode current collector and a solid electrolyte tube. In the above, a material layer using a ceramic precursor as a bonding material is interposed and bonded between the solid electrolyte tube and the electron conductive material,
The material layer has an aspect ratio of 5 to 5 in terms of fiber length / fiber diameter.
290. A sodium-sulfur secondary battery comprising a mixture of an electron conductive fiber and an insulating material in the range of 290. 2. A sodium-sulfur secondary battery in which an electron conductive material impregnated with sulfur and / or sodium polysulfide is disposed in a positive electrode chamber between a positive electrode container also serving as a positive electrode current collector and a solid electrolyte tube. In the above, a material layer made of a mixture of an insulating material and an electron conductive fiber using a ceramic precursor as a bonding material is interposed and adhered between the solid electrolyte tube and the electron conductive material. It is formed by applying a slurry or paste consisting of a mixture of an insulating material with excellent resistance to sulfur and sodium polysulfide and an electron conductive fiber to a solid electrolyte tube on a ceramic precursor and firing it. Sodium-sulfur secondary battery. 3. The method according to claim 2, wherein the electron conductive fiber is a carbon-based material,
The sodium-sulfur secondary battery according to claim 1, which is at least one material selected from the group consisting of W, Mo, a Co—Cr alloy, and an Al—Si alloy. 4. The ceramic precursor is made of Mg, T
3. The sodium-sulfur secondary battery according to claim 1, comprising at least one selected from i, Si, Al, and Zr. 4. 5. The sodium-sulfur secondary battery according to claim 1, wherein the electron conductive fiber is a material having a specific surface area smaller than that of the insulating material. 6. The temperature in the baking treatment is 250-6.
The sodium-sulfur secondary battery according to claim 2, which is at 80C.