JP2000133303A - Sodium sulfur battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve junction strength without requiring excess radial deformation of a brazing by providing a ring-shaped projection on a junction surface side an either of the brazing and flange portions at the bottom of a negative electrode lid and the top of a positive electrode container pipe which are connected through the brazing to an annular insulating ring and its upper and lower surfaces, and pressurizing the upper and lower surfaces of both flanges at high temperature for diffused junction. SOLUTION: Sulfur 11 is impregnated into carbon fibers between a negative electrode containing sodium 1 and jointed inside an insulating ring 3 made of α-alumina or the like at its upper portion and a positive electrode pipe 10 containing β-alumina-made bag-pipe-shaped solid electrolyte pipe 2. Annular aluminum brazings 9, 24 are installed between a negative electrode lower flange 6 of a negative electrode lid 4 and the upper surface of the insulating ring 3 and between a positive electrode flange 15 of a bellows 12 of the positive electrode pipe 10 and the lower surface of the insulating ring 3, and are subjected to the diffused junction by vacuum heating and pressurizing by a jig. They are jointed at high surface pressure at positions of inner and outer peripheral sides ring-shaped projections 7, 8 and 18, 19 projecting to joint surface side of the negative electrode and positive electrode flanges 6, 15, and durability of this battery during temperature increasing/decreasing is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a sodium-sulfur battery.

[0002]

2. Description of the Related Art In general, a sodium-sulfur battery has a bag-shaped beta-alumina solid electrolyte tube having sodium as a negative electrode active material and sulfur outside as a positive electrode active material held by a metal cathode tube. The upper part of the electrolyte tube is fixed inside an annular ceramic insulating ring, and the negative electrode lid that seals the upper part of the negative electrode is diffusion bonded to the upper surface of the insulating ring through brazing at the lower annular plate-shaped flange, and the upper end of the positive electrode tube Is flanged to the lower surface of the insulating ring via a brazing material.

Generally, alpha-alumina is used for the insulating ring material, aluminum alloy is used for the brazing material, and steel material is used for the flange material. When the temperature of the battery changes due to temperature rise or fall, thermal stress is repeatedly applied to the joint. The inner peripheral edge of the joint of the negative electrode lid flange is exposed to sodium vapor,
As described in Japanese Patent Application Laid-Open No. 9-55222, the repetition of this thermal stress may cause the peeling of the joint to gradually progress.

On the other hand, in addition to thermal stress, about 250% of sodium polysulfide existing under the positive electrode is added to the positive electrode container flange.
By solidifying the solid electrolyte tube and the positive electrode tube at a temperature of not more than ° C., an axial force acts at a low temperature as described in Japanese Patent No. 2769284. Therefore, it is necessary that the axial force bearing side of the flange joint portion of the positive electrode container endure these loads caused by the repetition of temperature rise and fall.

[0005] These thermal stresses and axial forces become more remarkable as the capacity of the sodium battery increases and, therefore, the diameter of the joint and the length of the cathode tube increase. In order to improve the strength of the diffusion joint, it is effective to increase the surface pressure at the time of joining.However, when an excessive pressing force is applied, the brazing is greatly crushed and extruded in the inner diameter direction and the outer diameter direction. There is a possibility that a short circuit or other trouble may occur.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sodium-sulfur battery in which the strength of the diffusion joint is improved without excessive radial deformation of the brazing.

[0007]

In order to achieve this object, a sodium-sulfur battery according to the present invention is characterized in that, in the first aspect, the upper portion of the bag-shaped solid electrolyte tube which holds sodium therein and forms a negative electrode has an annular shape. A positive electrode container fixed to the inside of the insulating ring, and a negative electrode lid for sealing the upper part of the negative electrode, a flange portion at a lower end thereof is diffusion-bonded to the upper surface of the insulating ring via brazing, and the positive electrode container wraps the solid electrolyte tube and holds sulfur therebetween. In a sodium-sulfur battery in which the upper flange portion of the tube is diffusion-bonded to the lower surface of the insulating ring via brazing, the flange of the negative electrode lid and / or the flange diffusion bonding portion of the positive electrode container have a ring shape protruding toward the bonding surface. Protrusions are provided on the flange, brazing or insulating ring, and the upper surface of the negative electrode lid flange and the lower surface of the positive electrode container flange are pressurized at high temperature and diffused. Combined, characterized by comprising.

According to a second aspect of the present invention, in the first aspect, the ring-shaped projection is provided on the inner peripheral side of the negative electrode lid flange and / or on the axial force bearing side of the positive electrode container flange.

[0009] Further, a third aspect of the present invention is characterized in that, in the second aspect, a ring-shaped projection is provided on each of the inner and outer peripheral sides of the joining surface.

[0010] With this configuration, the pressing force at the time of diffusion bonding is concentrated on the ring-shaped projection, so that the bonding surface pressure at that portion is increased to perform high-strength good bonding, and the brazing radius is increased. Excessive deformation in the direction is also prevented.

Further, by setting the position of the ring-shaped projection on the inner peripheral side of the negative electrode lid flange or / and on the axial force bearing side of the positive electrode container flange, a portion important in strength is effectively strengthened. Further, by providing the ring-shaped protrusions on the inner and outer peripheral sides of the joint surface, it is possible to effectively bear a bending moment and a thermal stress due to an axial force.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will now be described with reference to FIG.
2 will be described with reference to FIG. 2, a cross-sectional view at the time of bellows molding, and FIG. 3 is a cross-sectional view of parts arrangement before diffusion bonding.

A bag-shaped beta-alumina solid electrolyte tube 2 holding a sodium 1 therein to form a negative electrode has an upper outer surface formed on the inside of a ring-shaped alpha alumina insulating ring 3 by using glass solder. Joined at 1050 ° C.
The anode cover 4 for sealing the upper part of the anode is made of JIS S 1.0 mm thick.
A US329J high-strength stainless steel sheet is formed by cold working, and has a communication hole at the lower end in the center of the inside, and a safety pipe 5 inserted into the electrolyte pipe 2 is fixed by welding. The ring-shaped flange 6 is formed at the lower end thereof.

In the same manner as a positive electrode flange described later, ring-shaped projections 7 and 8 are formed on the inner peripheral side and the outer peripheral side of the flange 6 so as to protrude toward the lower joint surface. The brazing 9 has a flat upper surface of the insulating ring 3 and the negative flange 6.
It is arranged between the lower surfaces and has a 0.7 mm-thick annular plate shape in which BA4004 is clad on both sides of JISA3003.

The cathode tube 10 is made of JIS SUS310 steel having corrosion resistance and a small coefficient of linear expansion. The cathode tube 10 has a cylindrical shape with a bottom and encloses the solid electrolyte tube 2 and has a sulfur impregnated with carbon fiber therebetween. Hold 11 This battery has a capacity of 10
The capacity is as large as 00 Ah, so that the positive electrode container 10 has an outer diameter of 100 mm, a wall thickness of 1.5 mm, and a length of 700 mm. Since the linear expansion coefficients of the beta alumina solid electrolyte tube 2 and the cathode tube 10 are 6 × 10 ⁻⁶ / ° C. and 16 × 10 ⁻⁶ / ° C., respectively, the heat between them during the cooling process from 250 ° C. to 20 ° C. The difference in shrinkage amounts to 1.6 mm.

The bellows 12 elastically absorbs this thermal displacement, and is formed by cold working a thin JISSUS329J high strength stainless steel sheet having a thickness of 0.6 mm to raise the yield stress to 1050 MPa. The final molding method of the bellows 12 is shown in FIG. The lower half of the bellows 12 is press-molded and then inserted into the lower mold 13. After the upper half is enlarged with a conical upper mold (not shown), the lower mold 13 is pressed by an upper mold 14 shown in the drawing.
Between them, a high surface pressure of 1000 MPa is applied to the flange portion 15 of the bellows 12.

At a position where flat portions 16 and 17 having a length of 0.9 mm and a length of 1.5 mm on the inner and outer circumferences of the flange portion 15 are left, a portion having a height of 0.1 mm and a radius of curvature of 1.0 mm is provided. Lower mold 13 is formed so as to form ring-shaped projections 18 and 19 protruding toward the joint surface.
Ring-shaped projections 20 and 21 are formed on the upper surface, and ring-shaped recesses 22 and 23 are formed on the lower surface of the upper mold 14.

When the center of the flange portion 15 is bent outward in advance with a conical upper die, the flange portion 15 can be wavy in the radial direction even if the upper die is not provided with the recesses 22 and 23. A ring-shaped projection 18 on the portion 15;
19 can be formed. The brazing 24 has a flat lower surface of the insulating ring 3 and a positive flange 15 parallel thereto.
It is arranged between the upper surfaces and is the same as the brazing 9.

In diffusion bonding the negative electrode flange 6 and the positive electrode flange 12 to the upper and lower surfaces of the insulating ring 3, as shown in FIG. And the whole is heated in vacuum to 530 ° C., which is slightly lower than the solidus 545 ° C. of A4004. The upper and lower pressing jigs 25 and 26 are made of heat-resistant steel, and the surfaces to be pressed against the flanges 6 and 15 are finished flat. The upper pressing jig 25 has a cylindrical shape, and the lower pressing jig 26 can be inserted into the bellows 12 by dividing an annular one into two parts by diameter.

The pressurizing surface pressure per area of the brazings 9 and 24 is 100 MPa and the pressurizing time is also limited to 10 min. The brazings 9 and 24 are excessively crushed by this pressurization, and the brazings 9 and 24 become large in the inner and outer diameter directions. I try not to be pushed out. During this pressurization, the ring-shaped protrusions 7 and 8 of the negative electrode flange 6 and the ring-shaped protrusions 17 and 18 of the positive electrode flange 15 locally press the brazing 9 and 24.

In order to ensure this local pressurization, the flanges 6 and 15 are made of high-strength steel to prevent bending plastic deformation in the vicinity of the projections. The flat portions 16 and 17 are provided, and the projection 1 is formed.
8 and 19 are prevented from spreading in the radial direction and flattening.

Further, the joining temperature is set to the brazing material A400.
By limiting the pressurized surface pressure and pressurization time below the solidus line of 4, the plastic flow of the brazing 9, 24 is suppressed, so that the local pressurized surface pressure is maintained high and other flat parts are also joined. Is possible. By this pressure, the brazing 9, 24 has an initial thickness of 0.7 mm to 0.5 mm.
And the ring-shaped projections 7, 8,
18 and 19 maintained the initial shape.

The joints thus joined are subjected to high surface pressure joining at the positions where the ring-shaped projections 7, 8 and 18, 19 are present, so that the insulating ring 3 and the brazing 9, 24 and the brazing 9 are joined. , 24 and the flanges 6, 15 are solid because the aluminum oxide is satisfactorily destroyed and the atoms to be joined are close to each other.

With the above structure, the durability of the battery against temperature rise and fall is improved. That is, the joining surface between the brazing 9 of the negative electrode flange joining portion and the alpha-alumina insulating ring 3 is repeatedly subjected to thermal stress in a sodium 1 steam atmosphere, but the solid surface formed at the lower portion of the inner peripheral side ring-shaped projection 7 is formed. The bonding surface shows high resistance to peeling in this state. In addition, the strong joint surface below the ring-shaped protrusion 8 on the outer peripheral side well bears the radial shear force generated based on the difference in linear expansion coefficient between the insulating ring 3 and the brazing 9 and the flange 6, and the ring The thermal stress generated on the lower joint surface of the projection 7 is reduced.

The heat stress resistance at the joint of the positive electrode flange 15 is the same as described above, but when the temperature is lowered, about 25% of the sodium polysulfide 27 existing at the bottom of the positive electrode is removed as described above.
By solidifying at 0 ° C. or lower and fixing the solid electrolyte tube 2 and the cathode tube 10, an axial force acts on the cathode tube 10 at a low temperature.

Therefore, the inner peripheral side, which bears the axial force at the joint of the positive electrode container flange 15, receives these loads due to the repetition of temperature rise and fall. Since the bonding between the flange 24 and the brazing 24 and the flange 15 is strong, the brazing 24 can sufficiently withstand these loads.

The strong joints formed by the ring-shaped projections 19 on the outer peripheral side not only reduce the thermal stress in the radial direction but also effectively support the bending moment to the flange 15 caused by the axial force. The bending peel stress on the inner ring-shaped projection 18 is reduced.

FIG. 4 shows another embodiment of the present invention. The positive electrode bellows 12 and the flange 15 are separately manufactured, and their outer peripheral ends are bent upward. Insulation ring 3 for flange 15
Then, after diffusion bonding in the same manner as in FIG. 3, these ends are welded 28. In this case, the positive electrode flange 15
It is the outer peripheral portion that receives the peeling force due to the axial force at the joint.
The strength on the axial load bearing side is ensured by the high joining force due to the high surface pressure action of the outer ring-shaped projection 19, and the bending moment is obtained by the high joining strength part obtained by the action of the inner ring-shaped projection 18. bear.

FIG. 5 shows still another embodiment of the present invention.
The ring-shaped projections 7 and 8 of the negative electrode junction and the ring-shaped projections 18 and 19 of the positive electrode junction are formed and sintered on the upper and lower surfaces of the insulating ring 3 at the time of high-pressure molding of ceramic powder. In this case, the negative electrode flange 6 and the positive electrode flange 15 are flat, but when they are pressurized at the time of diffusion bonding, the surface pressure is concentrated on the ring-shaped projections 7, 8 and 18, 19, so that in the above case, A high-strength joint can be obtained in the same manner as described above.

FIG. 6 shows another embodiment of the present invention. In this embodiment, the ring-shaped protrusions 7 and 8 of the negative electrode joint and the ring-shaped protrusions 18 and 19 of the positive electrode joint are both formed on both surfaces of the brazings 6 and 24 by press working. Also in this case, similarly to the above, the pressing surface pressure at the time of diffusion bonding is concentrated on the ring-shaped projections 7, 8, 18, and 19, so that a high-strength bonded portion is obtained at those portions.

[0031]

According to the sodium-sulfur battery of the present invention,
Since surface pressure is concentrated on the ring-shaped protrusion during diffusion bonding, a high-strength joint can be obtained without excessive radial deformation of brazing, and the negative electrode has durability against repeated thermal stress in sodium vapor. The durability against repeated axial force is improved on the positive electrode side.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a sodium-sulfur battery according to one embodiment of the present invention.

FIG. 2 is a sectional view at the time of bellows molding of one embodiment of the present invention.

FIG. 3 is a cross-sectional view of a part before diffusion bonding according to an embodiment of the present invention.

FIG. 4 is an enlarged sectional view of a diffusion bonding portion and a bellow according to another embodiment of the present invention.

FIG. 5 is a sectional view showing the arrangement of components before diffusion bonding in still another embodiment of the present invention.

FIG. 6 is a cross-sectional view of a component arrangement before diffusion bonding according to still another embodiment of the present invention.

[Explanation of symbols]

1 ... sodium, 2 ... solid electrolyte tube, 3 ... insulating ring,
DESCRIPTION OF SYMBOLS 4 ... Negative electrode cover, 6 ... Negative electrode flange, 7 ... Inner ring side protrusion, 8 ... Outer ring ring protrusion, 9, 24 ... Brazing, 10 ... Positive electrode tube, 11 ... Sulfur, 15 ... Positive electrode flange, 18 ... inner peripheral side ring-shaped projection, 19 ... outer peripheral side ring-shaped projection, 27 ... sodium polysulfide.

Continued on the front page (72) Inventor Ryujiro Active 502 Kandachi-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. Hitachi, Ltd. Hitachi Plant (72) Inventor Shigeru Sakaguchi 3-1-1, Sachimachi, Hitachi, Ibaraki Prefecture F-term in Hitachi, Ltd. Hitachi Plant 5H029 AJ11 AJ14 AK05 AL13 AM15 BJ02 CJ02 CJ03 CJ05 CJ25 DJ02 DJ14 EJ01 EJ08

Claims (3)

[Claims] 1. An upper portion of a bag-shaped solid electrolyte tube which forms a negative electrode while holding sodium therein is fixed inside an annular insulating ring, and a negative electrode lid for sealing the upper portion of the negative electrode has a flange at the lower end thereof insulated. Sodium sulfur that is diffusion bonded to the upper surface of the ring via brazing, and the upper flange portion of the positive electrode container tube that wraps the solid electrolyte tube and retains sulfur therebetween and is brazed to the lower surface of the insulating ring via brazing In the battery, the flange of the negative electrode lid or the flange diffusion joint of the positive electrode container has ring-shaped projections protruding toward the joint surface on the flange, brazing or insulating ring, and the upper surface of the negative electrode lid flange and the lower surface of the positive electrode container flange. A sodium-sulfur battery characterized by being pressurized at a high temperature and diffusion bonded. 2. The sodium sulfur battery according to claim 1, wherein the ring-shaped projection is provided on an inner peripheral side of the negative electrode lid flange and / or on an axial force bearing side of the positive electrode container flange. 3. The sodium-sulfur battery according to claim 2, wherein ring-shaped projections are provided on the inner and outer peripheral sides of the joining surface.