JPH07105971A - Positive electrode vessel for sodium-sulfur battery and manufacture of vessel - Google Patents

Abstract

PURPOSE:To provide a positive electrode vessel for sodium-sulfur battery whose inner wall surface is lined with an anti-corrosive film by means of plasma spraying in an atmospheric condition with the fusion spray efficiency enhanced greatly, wherein the tight attaching of the film is enhanced through making the film with an extra-dense structure and accomplishment of an ultraminute content of oxides, and to produce film which excels in the anti- corrosiveness against attack of sodium polysulfide, presents less deterioration in the battery capacity, has resistance, small internal and is less likely to exfoliate from the anode vessel. CONSTITUTION:Using a thermal spraying gun 1, a fusion spray powder 3 is in the atmospheric condition put in plasma fusion spray to the inner wall surface of a cylindrical positive electrode vessel 2 of metallic make, and thereby an anti-corrosive film 4 is produced. If the power has a mean particle size between 10-20mum while the spraying distance ranges from 10 to 25mm, the resulant film will have a porosity under 0.1% to present an extra-dense structure, an ultraminute content of oxides, and a surface roughness of no more than 4.2mum. Because of reduction of pores due to extra-dense structure of the film, the internal resistance of the battery is reduced to a great extent. Also because of tight attachment of the film in good workmanship, drop of the battery capacity is reduced in heat cycles when the battery is in service, and increment of the internal resistance is inhibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anode container for sodium-sulfur batteries and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in an anode container of a sodium-sulfur battery, a corrosion-resistant film is formed on the inner wall surface of the anode container by plating such as chromizing treatment in order to enhance the corrosion resistance to sodium polysulfide. In addition, JP-A-61
JP-A-264659 discloses a method of forming a corrosion resistant coating by plasma spraying in a low pressure atmosphere.

[0003]

DISCLOSURE OF THE INVENTION The present inventor has conducted an experimental study using a method of forming a film of such an anode container for a sodium-sulfur battery by plasma spraying.
I found the following. The film formation by thermal spraying is
It is composed of a stack of melted particles, and the shape, size, distribution, etc. of the powder for thermal spraying are greatly affected by the quality (denseness) of the coating. Generally, the porosity in the thermal spray coating of a metal material is 3% or more, and that of a ceramic material is 8% or more. The particle size range of the thermal spraying powder used for these is 5 to
It is 125 μm. With respect to the thermal spray coating formed of the above-mentioned laminated layers, many pores, which are defects unique to the thermal spray coating, remain between the laminated layers. Furthermore, due to changes in plasma conditions, the temperature becomes higher and the particle surface is significantly oxidized, and a large amount of oxide film remains. The presence of pores, oxide film, and undissolved particles in the film largely contributes to rapid capacity deterioration and increase in internal resistance due to infiltration of sodium polysulfide during long-term operation of the sodium-sulfur battery. Furthermore, it may reach the metallic material that is the base material, corrode the metallic material, and render it inoperable.

On the other hand, in the long-term operation of the sodium-sulfur battery, defects such as cracks and peeling of the coating film due to temperature rising / falling (thermal cycle) pose the same great problems. This also applies to chromizing steel, that is, defects such as cracks caused by the processing of the chromium carbide layer on the outermost surface of the chromizing steel are largely opened by the thermal cycle, which makes long-term operation impossible. .

Regarding spraying, there are various parameters due to whether the coating quality is good or bad (densification), but it is generally reported that the plasma conditions, the amount of primary gas, and the spraying distance are largely responsible. On the other hand, regarding the adhesion of the thermal spray coating, it is reported that the surface roughness due to blast is mainly, but it is not clear. Also, there are two methods, one is the cooling method of the work and the other is the preheating method, but it is not clear which is more effective in use and spraying. In particular, at present, the correlation between these conditions and the particle size of powder is not known.

However, an anode container having a corrosion-resistant coating formed by chromizing treatment plating or the like has hair cracks on the coating surface due to the processing of the chromium carbide layer on the outermost surface of the coating, resulting in a sodium-sulfur battery. Hair cracks in the outermost layer of the corrosion-resistant coating grow due to thermal stress due to repeated heating / cooling during operation and shutdown, and sodium polysulfide penetrates into the coating through the grown hair cracks, sulfides the coating, or anodic container Various problems such as deterioration of battery capacity due to corrosion of itself, decrease of battery energy efficiency due to increase of internal resistance, etc.,
Stable operation was impossible for a long time. On the other hand, plasma spraying in a low-pressure atmosphere has extremely low productivity and high cost, and is not suitable for industrial mass production.

An object of the present invention is to solve the above-mentioned various problems and to provide a method for forming a film which is excellent in industrial productivity and economy by plasma spraying in an air atmosphere, and the formed film is Excellent corrosion resistance to sodium polysulfide, less deterioration of battery capacity even during long-term operation,
It is to provide a film having a low internal resistance and not peeling from the anode container.

Generally, the porosity of the metal coating formed by plasma spraying is 3% or more, and the pores remain in a laminated form between the molten metal liquid particles during the spraying. Furthermore, when spraying in an air atmosphere, the surface of the sprayed high temperature metal liquid particles is oxidized and an oxide film remains. Furthermore, at the time of thermal spraying, a part of the thermal sprayed metal powder remains in the coating film and the coating surface as undissolved particles. Such a coating is not suitable as an anticorrosion coating for an anode container of a sodium-sulfur battery, even if the coating material itself is a material having corrosion resistance to sodium polysulfide.

The object of the present invention is to form a corrosion-resistant film on the inner wall surface of an anode container for sodium-sulfur batteries, and to improve the adhesion of the film by making the film ultra-densified and containing a very small amount of oxide. An object is to provide an anode container for a sulfur battery and a method for manufacturing the same. Another object of the present invention is to provide a method for producing an anode container for sodium-sulfur batteries, which has a significantly improved plasma spraying efficiency when forming a corrosion resistant coating on the inner wall of the anode container.

[0010]

In order to achieve the above object, the sodium-sulfur battery anode container according to the present invention comprises:
In a sodium-sulfur battery anode container in which a sprayed coating made of a stellite alloy is formed on the inner wall of a cylindrical metal anode container of a sodium-sulfur battery, the porosity of the coating is 1.0% or less, and the oxide content is Is extremely small, and the average surface roughness of the coating is 4.2 μm or less.

In the method for producing the anode container for sodium-sulfur battery, the particle size range of the sprayed powder for film formation is 5 to 25 μm.
m, an average particle diameter of 10 to 20 μm is used, and a film is formed on the inner wall of the anode container by plasma spraying.

[0012]

In the battery using the anode container for a sodium-sulfur battery of the present invention, it is possible to suppress the invasion of sodium polysulfide into the film and suppress the decrease in battery capacity. Further, in the coating of the sodium-sulfur battery electrode anode container of the present invention, the internal resistance of the battery is significantly reduced due to the decrease in the porosity due to the superdensification, and the energy efficiency is improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. An example of a method for manufacturing an anode container for sodium-sulfur batteries according to the present invention is shown in FIG. In the production method of this example, as the raw material for the corrosion-resistant film formed on the inner wall of the anode container, Stellite 6 having an average particle diameter of 15 μm was used as the film-forming powder. Then, as shown in FIG. 1, by using the thermal spray gun 1, the powder material 3 is formed on the inner wall surface of the cylindrical container body 2 made of a non-ferrous metal material such as aluminum or aluminum alloy.
Is plasma sprayed in the atmosphere to form the corrosion resistant film 4.

For plasma spraying, argon gas is used as the primary gas and hydrogen gas is added as the secondary gas.
The gas supply rate is argon gas: 40 liters / mi
n, hydrogen gas: set in the range of 0.2 to 3.0 liters / min, current is 250 A, voltage V is 28 to 32 V
And The surface temperature of the container body 2 (surface temperature of the pipe) before thermal spraying is set to 210 ° C. or higher, and the rotation speed is 400 rpm.
And The blast surface roughness of the inner wall surface of the container substrate is 2 to 10μ
It was m. The film thickness was 85 μm.

(Experiment 1) The relationship between the spraying distance and the surface roughness and porosity of the coating was tested. The thermal spraying powder used in the experiment was a cobalt-based alloy, and the powder particle size: 14.5 μm, coating thickness: 65 μm, surface roughness: 1-5 μm, base material of the anode container body: aluminum alloy, plasma conditions were: Ar gas: 42 l / min, H ₂ gas: 0.4 l / min
The current A was 255 A and the voltage V was 29.3 V.
The result is shown in FIG.

As shown in the experimental results of FIG. 2, the porosity of the coating is lowered and the surface roughness of the coating is also lowered in the range of the spray distance of 10 to 25 mm. Therefore, it was proved that the content of the oxide which was densified in this range was extremely small. (Experiment 2) In Experiment 2, the adhesion between the surface temperature of the anode container before the start of thermal spraying (the surface temperature before the start of thermal spraying of the pipe) and the formed film was tested.

Experimental conditions are as follows: coating material: cobalt-based alloy,
Film thickness: 78 μm, base material of anode container body: blast,
An aluminum alloy having a surface roughness of 6 to 10 μm was used. The results are shown in Table 1.

[0018]

[Table 1]

In Table 1, in the evaluation of adhesion, it was judged that the symbol ◯: no peeling portion, Δ: small amount peeling, ×: large amount peeling. As shown in Table 1, the surface temperature of the anode container before the start of thermal spraying was found to be effective when the temperature was 150 ° C. or higher as shown in Examples 1, 2, and 3. On the other hand, in Comparative Examples 1 to 5, it was found that the lower the temperature, the poorer the adhesiveness was, and the adhesiveness was not sufficient even at 80 to 150 ° C.

The adhesion test was judged by the peeling condition of the film generated in the bending test. The device used for the judgment after the bending test was one as shown in FIGS. 3 and 4. That is, a corrosion resistant coating 32 is formed on the surface of a cylindrical base material 30 made of an aluminum alloy, and this is stretched by applying a load with a jig 36. As a result, a flat base material 30 made of an aluminum alloy is formed. The film 32 is used. Then, the quality of the adhesiveness was judged based on the state of occurrence of cracks 34, peeling portions 35 and the like in the film 32 on the base material 30 after the bending test in FIG.

(Experiment 3) Experiment 3 was conducted to evaluate the porosity of the coating obtained by changing the average particle diameter of the raw material powder, the number of undissolved particles in the coating, the yield of the powder, and the fluidity of the powder. The experimental conditions were: substrate: aluminum alloy, substrate thickness: 2.5 mm, raw material powder: cobalt-based alloy powder, substrate preheating temperature: 200 to 250 ° C., film thickness: 85 μm. The results are shown in Table 2.

[0022]

[Table 2]

As shown in Table 2, Examples 11, 12, 13 and Comparative Examples 11, 12, 13, 14, 15, 16 were carried out in the range of the average particle diameter of the thermal spraying powder of 5 to 70 mm. As shown in Table 2, the porosity was measured for n = 5 pieces in the film, and the average porosity of the five pieces was obtained.

Regarding the number of undissolved particles, the number of undissolved particles visually observed on the surface of the coating was counted. The yield of the powder was calculated from the degree of effective film formation of the powder. Regarding the fluidity evaluation of the powder, ◎: good, ○: normal,
Δ: acceptable, ×: not acceptable

As shown in Table 2, Examples 11 and 1
In Nos. 2 and 13, it was found that when a thermal spraying powder having an average particle size of 10 to 20 μm was used, the porosity was less than 1.0% and the film became an ultra-densified film. The number of undissolved particles was 0. From this, it was found that the condition of the film surface was also good. The yield of the powder was 80% or more, which was quite good. It was found that the flowability of the powder was good.

(Experiment 4) Experiment 4 showed the relationship between the charge and discharge cycle of a sodium-sulfur battery using the above-mentioned anode container and the battery capacity. Results are shown in FIG. It was found that the battery capacity of Example 11 was less decreased than that of Comparative Examples 11, 12, 13, 14, 15, 16 even if the charge / discharge cycle was increased.

(Experiment 5) In Experiment 5, the relationship between the charge / discharge cycle and the internal resistance of the sodium-sulfur battery using the anode container was measured. The operating temperature of the battery was 310 ° C. Results are shown in FIG. As shown in FIG. 6, when the charge / discharge cycle was repeated, Comparative Examples 11, 12, 13, 1
The increase of the internal resistance is low in Example 11 as compared with 4, 15, and 16. The initial internal resistance is also low. As a result, it was found that Example 11 was smaller in internal resistance than Comparative Examples 11, 12, 13, 14, and 15, and the battery efficiency was good.

[0028]

As described above, according to the anode container for sodium-sulfur battery according to the present invention, the porosity of the stellite coating formed on the inner wall of the anode container can be 1.0% or less, and the inclusion of oxides can be suppressed. A film having a very small rate and an average surface roughness of 4.2 μm or less was obtained, and thus the adhesion of the film is good, and the decrease in the battery capacity during the thermal cycle during use of the battery is reduced. Further, since the increase in internal resistance is suppressed, there is an effect that the decrease in battery efficiency during long-term use is significantly suppressed.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a method for forming a film on an anode container for a sodium-sulfur battery according to an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between the plasma spraying distance and the porosity and surface roughness of the coating.

FIG. 3 is a schematic diagram showing an apparatus used for evaluating the adhesion of the film used in the experiment.

FIG. 4 is a schematic perspective view showing a film state on a base material stretched by the apparatus of FIG.

FIG. 5 is a data diagram showing the relationship between the charge / discharge cycle and the battery capacity performed in the experiment.

FIG. 6 is a data diagram showing the relationship between the charge / discharge cycle and the internal resistance conducted in the experiment.

[Explanation of symbols]

 1 Thermal spray gun 2 Container body 3 Thermal spray powder 4 Corrosion resistant coating

Claims (3)

[Claims] 1. A sodium-sulfur battery anode container in which a corrosion-resistant coating made of a stellite alloy is formed on the inner wall of a cylindrical metal anode container of a sodium-sulfur battery by thermal spraying, wherein the corrosion-resistant coating has a porosity of 1.0. %, The content of oxides is extremely small, and the average surface roughness is 4.2 μm or less, the anode container for sodium-sulfur batteries. 2. A method for manufacturing an anode container for a sodium-sulfur battery according to claim 1, wherein a sprayed powder for forming a coating has a particle size range of 5 to 25 μm and an average particle size of 10 to 20 μm. A method for producing an anode container for a sodium-sulfur battery, which comprises forming a film on the inner wall of the anode container by plasma spraying. 3. The sodium-sulfur battery anode container according to claim 1, wherein the temperature of the container before the start of plasma spraying is 150 ° C. or higher.
Anode container for sulfur battery.