JP2002329525A - Positive electrode container for sodium-sulfur battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode container for a sodium-sulfur battery having a constriction part capable of sufficiently absorbing and moderating the expansion and contraction of the positive electrode container due to thermal variation, preventing the corrosion of the constriction part from easily progressing, and having an improved service life. SOLUTION: This positive electrode container for a sodium-sulfur battery is provided with the constriction part 13 radially bent at a position in the vicinity of the upper end of a bottomed cylindrical container formed of a metal material and having an anticorrosive film 14 formed of a metal having high corrosion resistance formed on the inside surface of the container. The upper end of the anticorrosive film 14 is positioned above the upper end face of a conductive material 12 for the positive electrode impregnated with a positive electrode active material housed in the positive electrode container 1, and below the lowest constriction end part 13a where the lower bend of the constriction part 13 starts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anode container used for accommodating an anode conductive material impregnated with an anode active material in a sodium-sulfur battery.

[0002]

2. Description of the Related Art A sodium-sulfur battery has molten metal sodium as a cathode active material on one side and molten sulfur as an anode active material on the other side, and both have selective permeability to sodium ions. This is a high-temperature secondary battery that operates at a temperature of about 300 to 360 ° C., isolated by a β-alumina solid electrolyte.

As shown in FIG. 8, for example, a structure of such a sodium-sulfur battery has a cylindrical shape with a bottom that accommodates an anode conductive material 12 such as a graphite mat impregnated with molten sulfur S as an anode active material. And a cartridge (sodium protective tube) 6 containing molten sodium metal Na as a cathode active material, and a cartridge 6 containing the cartridge 6 therein and having a function of selectively transmitting sodium ions Na ^+. A bottomed cylindrical solid electrolyte tube 5, and a bottomed cylindrical partition wall disposed at a predetermined distance from the cartridge 6 and the solid electrolyte tube 5 in a gap between the cartridge 6 and the solid electrolyte tube 5. It consists of a tube 11.

The solid electrolyte tube 5 is connected to the anode container 1 via an α-alumina insulating ring 4 and an anode cylindrical metal fitting 3 which are glass-joined to the open end thereof. A cathode fitting 8 is joined to the upper end surface of the insulating ring 4 by heat and pressure, and a cathode lid 9 is fixed to the cathode fitting 8 by welding. An anode terminal 2 and a cathode terminal 10 are provided on the outer peripheral upper portion of the anode container 1 and the upper surface of the cathode lid 9, respectively. An inert gas G such as nitrogen gas or argon gas is sealed at a predetermined pressure in the upper space of the cartridge 6, and sodium Na in the cartridge 6 is removed by the inert gas G.
It is pressurized in the direction of flowing out of the small holes 7 provided at the bottom.

In the sodium-sulfur battery having such a structure, the sodium Na supplied from the small hole 7 of the cartridge 6 at the time of discharging moves upward in the gap between the partition tube 11 and the cartridge 6, 11, moves downward in the gap between the partition tube 11 and the solid electrolyte tube 5, and further passes through the solid electrolyte tube 5 as sodium ions Na ^+, and the sulfur S in the anode container 1 is removed.
And reacts with electrons that have passed through the external circuit to produce sodium polysulfide. During charging, contrary to discharging, sodium Na
And the reaction of producing sulfur S occurs.

Anode container 1 for sodium-sulfur battery
Is formed of a metal material such as aluminum or aluminum alloy into a cylindrical shape, and fits the bottom lid to the lower end opening,
In the vicinity of the upper end, a constricted portion 13 that is bent in the radial direction for absorbing and relaxing expansion and contraction due to thermal change of the container is formed. Further, in the anode container 1, a corrosion-resistant film made of a metal having high corrosion resistance is formed on the inner peripheral surface of the container body by plasma spraying a chromium-iron alloy powder or the like in order to increase the corrosion resistance to a corrosive active material. You.

FIGS. 6 and 7 are partial cross-sectional views of a conventional anode container. The corrosion-resistant coating 14 covers the entire inner peripheral surface of the anode container 1 including the constricted portion 13 as shown in FIG. It is formed or as shown in FIG.
The lowermost lower end portion 1 at which the lower side of the constricted portion 13 starts bending.
In general, it was formed so as to be located above 3a.

[0008]

However, as shown in FIG. 6, when a hard corrosion-resistant film 14 such as a chromium-iron alloy is formed on the entire inner peripheral surface of the constricted portion 13,
The deformation of the constricted portion 13 is regulated by the corrosion-resistant coating 14, and the expansion and contraction of the anode container 1 cannot be sufficiently absorbed and reduced.
There is a problem that cracks are easily generated in the corrosion resistant film 14.

Further, the inner peripheral surface of the anode container 1 is subjected to a blast treatment (roughening treatment) prior to the thermal spraying of the corrosion-resistant coating 14 for the purpose of improving the adhesion with the corrosion-resistant coating 14. The inner peripheral surface of the anode container 1 thus roughened is activated and has improved wettability with multi-flow sodium. For this reason, the upper end of the corrosion-resistant coating 14 having a very good wettability with multi-flow sodium such as a chromium-iron alloy is formed so as to be located above the constricted lowermost end 13a as shown in FIG. In this case, there is a problem that sodium polysulfide soaks up to the constricted portion 13 in a short period of time and remains in the concave portion on the inner peripheral surface of the constricted portion 13 to promote chemical local corrosion.

The present invention has been made in view of such a conventional situation, and an object of the present invention is to make it possible for a constricted portion to sufficiently absorb and alleviate the expansion and contraction of an anode container due to a heat change, and to constrict the constricted portion. It is an object of the present invention to provide an anode container for a sodium-sulfur battery in which corrosion of a part hardly progresses and life is improved.

[0011]

According to the present invention, a constricted portion bent in the radial direction is provided near the upper end of a cylindrical container having a bottom made of a metal material, and the inner peripheral surface of the container has corrosion resistance. An anode container for a sodium-sulfur battery formed with a corrosion-resistant film made of a metal having a high content, wherein the upper end of the corrosion-resistant film is higher than the upper end surface of the anode conductive material impregnated with the anode active material contained in the anode container. And an anode container for a sodium-sulfur battery, wherein the anode container is located below a lowermost end of the constriction where the lower part of the constriction starts to bend.

[0012]

FIG. 1 is a partial sectional view showing an example of an embodiment of the present invention. The upper end of the corrosion-resistant coating 14 formed on the inner peripheral surface of the anode container 1 is located higher than the upper end surface of the anode conductive material 12 such as graphite mat impregnated with the anode active material accommodated in the anode container 1, This prevents the anode container 1 made of aluminum or aluminum alloy which is easily corroded from directly contacting the anode conductive material 12.

Further, the upper end of the corrosion-resistant coating 14 is located at the lowermost lower end portion 13 at which the lower side of the constricted portion 13 starts to bend.
a, that is, in the straight pipe portion below the constricted portion 13, compared with the case where the upper end of the corrosion-resistant coating 14 reaches the upper portion of the constricted lowermost portion 13 a as in the conventional case, the sodium polysulfide is It is difficult to soak up to the constricted part 13,
Corrosion of the constriction 13 by sodium polysulfide is significantly reduced.

Furthermore, the lowermost lower end 13 of the anode container 1
Since the inner peripheral surface of the portion above "a" does not require thermal spraying for forming a corrosion resistant film, it is possible to shorten the thermal spraying time and reduce the amount of the thermal spray material used.

In the present invention, the anode container 1 is moved from the lowermost lower end 13 a where the lower part of the constriction 13 starts to bend.
The inner peripheral surface up to the upper end of the
The arithmetic average roughness Ra of the surface is preferably 1.0 μm or less, more preferably 0.3 to 0.6 μm. In the present invention, the "arithmetic mean roughness Ra"
It is a value defined in JIS B 0601-1994.

Normally, the anode container is formed in a cylindrical shape by a drawing process.
In many cases, the arithmetic average roughness Ra is a smooth surface state of 1.0 μm or less, so that if the surface is not subjected to a roughening treatment such as blasting after the drawing process, the above surface roughness is satisfied. It is.

FIG. 3 is a schematic diagram showing a corroded state of the constricted portion 13 when the inner peripheral surface from the lowermost portion of the constricted portion to the upper end of the anode container 1 is subjected to a roughening process (blasting process). . The anode container is usually made of aluminum or an aluminum alloy, and when blasting is performed on these materials, the surface is unevenly formed and is significantly activated, and the wettability with sodium polysulfide is improved. . Then, when sodium polysulfide soaks into the inner peripheral surface of the constricted portion in such a state, the sodium polysulfide remains in the concave portion, causing scientific local corrosion, and within a short time Corrosion proceeds to a considerable depth.

On the other hand, the inner peripheral surface from the lowermost part of the constriction to the upper end of the anode container 1 is not subjected to a roughening treatment, and the arithmetic average roughness Ra of the surface is 1.0 μm or less. In this case, as shown in FIG. 2, since the entire inner peripheral surface of the constricted portion 13 is a uniform smooth surface, the soaked sodium polysulfide hardly remains on the inner peripheral surface. Local corrosion is unlikely to occur only to the extent that very shallow corrosion occurs at the position shown. Further, when the surface is not subjected to the surface roughening treatment, the processing time is shortened as compared with the case where the entire inner peripheral surface of the anode container is subjected to the surface roughening treatment, so that the battery manufacturing cost is reduced.

In the present invention, the corrosion-resistant coating 14
Is preferably formed so that an upper end portion thereof gradually becomes thinner upward. As shown in FIG. 5, when the thickness of the corrosion resistant film 14 is substantially constant up to its upper end,
Residual stress at the time of thermal spraying acts on the contact portion between the upper end of the corrosion-resistant coating 14 and the anode container 1, so that the corrosion-resistant coating 14 is likely to be peeled off or deep corrosion is likely to occur at the contact portion due to contact of dissimilar metals.

On the other hand, as shown in FIG.
When the upper end portion is gradually thinned, the residual stress at the time of thermal spraying is reduced, the peeling of the corrosion-resistant coating 14 is less likely to occur, and the corrosion due to the contact of dissimilar metals is also extremely shallow. Can be suppressed.

[0021]

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

(Test No. 1) Length 490 mm, outer diameter 8
A container made of an aluminum alloy having a thickness of 0 mm and a thickness of 2.3 mm was formed by drawing, and a constricted portion bent in the radial direction was provided near the upper end thereof. Next, the inner peripheral surface of the container excluding the range from the lowermost end of the constriction where the lower bend starts to the upper end of the anode container is subjected to blasting to roughen the surface. As shown in FIG. 1, an iron alloy (chromium content: 72% by mass) is thermally sprayed, and the upper end thereof is located above the upper end surface of the anode conductive material 12 accommodated in the anode container 1 and has a narrowed lowermost end portion 13a. A corrosion-resistant film 14 having a thickness of 60 μm was formed so as to be located below. The upper end portion of the corrosion-resistant coating 14 was provided with a gradient in the thickness of the coating so as to gradually become thinner upward.

Using the anode container thus obtained, five sodium-sulfur batteries having a structure as shown in FIG. 8 were manufactured, and a maximum operation temperature of 360 ° C. was performed for 5 years, and a test operation was performed for 2 years The corrosion state (the number of occurrences of corrosion, the maximum corrosion depth) of the constricted part of the anode vessel after the operation and after the operation for 5 years was observed with an optical microscope. Table 1 shows the results.

(Test No. 2) Length 490 mm, outer diameter 8
A container made of an aluminum alloy having a thickness of 0 mm and a thickness of 2.3 mm was formed by drawing, and a constricted portion bent in the radial direction was provided near the upper end thereof. Next, after blasting the entire inner peripheral surface of the container to roughen the surface,
An iron alloy (chromium content: 72% by mass) was thermally sprayed to form a corrosion-resistant coating 14 having a thickness of 60 μm such that the upper end thereof was located above the lowermost lower end portion 13a, as shown in FIG. Using the anode container thus obtained, five sodium-sulfur batteries having a structure as shown in FIG. Test operation and observation were performed in the same manner as in Example 1. Table 1 shows the results.

[0025]

[Table 1]

From the observation results after the test operation shown in Table 1,
In the test No. in which the inner peripheral surface was not subjected to surface roughening treatment in the range from the lowermost part of the neck to the upper end of the anode container, the upper end of the corrosion-resistant film was positioned below the lowermost part of the neck. 1
The anode container of Test No. 1 was subjected to a surface roughening treatment on the entire inner periphery of the container so that the upper end of the corrosion-resistant coating was located above the constricted lowermost end. It was confirmed that the constricted portion was less likely to corrode than the anode container of No. 2.

(Test No. 3) Using the anode container manufactured in the same manner as in Example 1, five sodium-sulfur batteries having the structure shown in FIG. 8 were manufactured, and the maximum temperature during operation was set to 340 ° C., and a test operation was performed for 5 years. The corrosion state (corrosion occurrence number, maximum corrosion depth) of the constricted part of the anode vessel after the operation and after the operation for 5 years was observed with an optical microscope. Table 2 shows the results.

(Test No. 4) The test No. 4 was conducted except that the entire inner peripheral surface of the container was subjected to blasting to roughen the surface. 1
Five sodium-sulfur batteries having a structure as shown in FIG. Test operation and observation were performed in the same manner as in Example 3. Table 2 shows the results.

[0029]

[Table 2]

From the observation results after the test operation shown in Table 2,
Test No. in which the inner peripheral surface was not subjected to surface roughening treatment in the range from the lowermost part of the neck to the upper end of the anode container. The anode container No. 3 was a test N in which the inner peripheral surface of the container was roughened.
o. It was confirmed that the constricted portion was less likely to corrode than the anode container of No. 4.

[0031]

As described above, the anode container for a sodium-sulfur battery of the present invention has a degree of freedom of deformation such that the constricted portion can sufficiently absorb and mitigate expansion and contraction due to heat change of the anode container. Corrosion of the constricted portion due to infiltration of sodium polysulfide is significantly reduced as compared with the conventional anode container, so that the durability and reliability of the battery are improved, and the battery can be used stably for a long period of time. In addition, it is possible to reduce the time required for the thermal spraying and the surface roughening treatment, and to reduce the amount of the thermal spraying material used, thereby reducing the battery manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of an embodiment of the present invention.

FIG. 2 is a constricted portion in a case where the inner peripheral surface from the constricted lowermost portion to the upper end of the anode container is not subjected to a surface roughening treatment and the arithmetic average roughness Ra of the surface is 1.0 μm or less. It is a schematic diagram showing the corrosion state of a.

FIG. 3 is a schematic diagram showing a corroded state of a constricted portion when a roughening process is performed on an inner peripheral surface from a lowermost portion of the constricted portion to an upper end of the anode container.

FIG. 4 is a schematic diagram showing a corrosion state of an anode container when a thickness is given a gradient so that an upper end portion of the corrosion resistant film becomes gradually thinner.

FIG. 5 is a schematic diagram showing a state of corrosion of the anode container when the thickness of the corrosion-resistant film is substantially constant up to its upper end.

FIG. 6 is a partial sectional view showing a conventional anode container for a sodium-sulfur battery.

FIG. 7 is a partial sectional view showing a conventional anode container for a sodium-sulfur battery.

FIG. 8 is a sectional view showing an example of the structure of a sodium-sulfur battery.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Anode container, 2 ... Anode side terminal, 3 ... Anode cylindrical fitting, 4
... insulating ring, 5 ... solid electrolyte tube, 6 ... cartridge,
7 ... Small hole, 8 ... Cathode fitting, 9 ... Cathode cover, 10 ... Cathode side terminal, 11 ... Partition tube, 12 ... Anode conductive material, 13 ... Constriction part, 13a ... Constriction lowermost end part, 14 ... Corrosion-resistant coating.

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Claims (3)

[Claims] 1. A cylindrical container having a bottom and made of a metal material, having a constricted portion bent in a radial direction near an upper end thereof, and a corrosion-resistant film made of a metal having high corrosion resistance formed on an inner peripheral surface of the container. An anode container for a sodium-sulfur battery, wherein the upper end of the corrosion-resistant coating is above the upper end surface of the anode conductive material impregnated with the anode active material contained in the anode container, and the lower part of the constriction is bent. The anode container for a sodium-sulfur battery, wherein the anode container is located below the lowermost end of the constriction at which the opening of the container starts. 2. The inner peripheral surface from the lowermost end of the constriction where the lower side of the constricted portion starts to bend to the upper end of the anode container is not subjected to a surface roughening treatment, and the arithmetic average roughness Ra of the surface is not provided. The anode container for a sodium-sulfur battery according to claim 1, wherein a is 1.0 μm or less. 3. The anode container for a sodium-sulfur battery according to claim 1, wherein an upper end portion of the corrosion-resistant film is formed so as to become gradually thinner upward.