JP4361330B2 - Anode container for sodium-sulfur battery and manufacturing method thereof - Google Patents

Description

The present invention relates to an anode container constituting a sodium-sulfur battery used as a secondary battery for power load adjustment and the like, and a method for manufacturing the same.

A sodium-sulfur battery is used in a power storage system for realizing functions such as power leveling and peak cut. The structure of the sodium-sulfur battery is schematically shown in FIG. It is as shown in.

The battery structure at the time of manufacture is such that a bottomed cylindrical beta-alumina solid electrolyte tube 12 is glass-bonded to the inner peripheral surface of the α-alumina insulating ring 13 at its upper end outer peripheral surface and further bonded to the upper surface of the insulating ring 13. The cathode chamber 14 partitioned by the cathode fitting 14 and the cathode lid 15, the insulating ring 13 and the beta alumina solid electrolyte tube 12 welded to the cathode fitting 14 is a bottomed cylindrical metallic safety tube 16 and its safety. A sodium storage container 17 containing sodium and a small amount of sodium azide is disposed inside the tube 16, while the anode chamber is connected to an anode fitting 18 joined to the lower surface of the insulating ring 13 and the anode fitting 18. A welded anode container 19, and further a bottom lid 20 welded to the anode container 19, an insulating ring 13, and a beta alumina solid electrolyte tube 12, are impregnated with sulfur. Carbon mat is arranged, at its upper portion a structure that inert gas is filled, such as nitrogen.

After assembling the unit cell, the sodium in the sodium container 17 is melted in the process of raising the temperature to the battery operating temperature, and nitrogen generated by decomposition of sodium azide contained in the upper part of the sodium container 17 Due to the pressure of the gas, molten sodium flows into the cathode chamber from a small hole provided in the bottom of the sodium container 17 and fills the cathode chamber.

The battery operates at a temperature of 290 ° C. to 385 ° C., and sodium conducts ion conduction in the beta alumina solid electrolyte tube 12 as sodium ions, reacts with molten sulfur in the anode chamber, generates sodium polysulfide, and the discharge reaction proceeds. To do. The reverse reaction proceeds during charging, and the molten sodium is returned to the cathode chamber.

In the sodium-sulfur battery having the above-described configuration, an anode container made of an aluminum alloy has a corrosion sprayed coating on its inner peripheral surface because of the problem of corrosion resistance against sodium polysulfide as an anode active material.

When the battery is operated for charging / discharging after assembling the sodium-sulfur battery, there is a problem that the internal resistance of the battery is high at the initial stage of the charging / discharging cycle, a predetermined current cannot flow, and the efficiency of electric energy is low.

If the charging / discharging cycle is repeated about 10 cycles, the internal resistance gradually decreases. However, repeating charging / discharging in the cell inspection before shipment causes a serious problem that productivity is very poor and cost is high.

In order to solve this problem, as described in Patent Document 1, the present inventors focused on the relationship between the electrical resistance in the anode container and the oxygen content of the surface in the coating layer, and the initial stage of the sodium-sulfur battery. The characteristics have been improved. Specifically, a coating layer made of a high chromium-iron alloy formed by plasma spraying is polished on the inner peripheral surface of a cylindrical anode container, and the formed coating layer has a depth of at least 5 μm from the surface. This is a method for producing an anode container having an oxygen content of 2.0% by weight or less.
JP-A-8-180899

However, in this method, the measurement of the oxygen content of the surface layer portion in the coating layer is based on the EPMA analysis method, and only the film is collected and analyzed, which requires a lot of labor and time, and the productivity is high. Low and costly.

Therefore, the present invention has been made in view of the above-described conventional problems, and the object of the present invention is to provide an initial charge / discharge cycle when the battery is charged and discharged after the sodium-sulfur battery is assembled. It is an object of the present invention to provide an anode container for a sodium-sulfur battery in which the internal resistance of the battery is small and the electric energy efficiency is increased. It is another object of the present invention to provide a method for manufacturing an anode container that can be manufactured simply, with high productivity, at low cost and with high quality.

According to the present invention, plasma spraying is performed on the inner peripheral surface of a cylindrical anode container base made of a metal material to form a plasma sprayed film made of a Cr—Fe alloy, and then the obtained plasma sprayed film is polished. In the manufacturing method of an anode container for a sodium-sulfur battery in which a sprayed coating having a polished surface is formed on an inner peripheral surface, the method of polishing the plasma sprayed film is performed by fixing the anode container base having the plasma sprayed film and polishing. A method for polishing by rotating up and down while rotating a brush for polishing, wherein the brush material is a metal twisted wire brush, and the wire brush diameter is 1.05-1 of the inner diameter of the anode container base. 15 times, the cross-sectional hardness (Hv) of the wire brush is 430 or more, and the wire diameter of one wire constituting the wire brush is 0.2 to 0.8 mm, 900~1400rpm the rotational speed of the wire brush, that said wire brush traverse speed is polished in the range of 60 to 80 mm / sec, to polish the plasma spray film to the polishing area ratio solution morphism film is 10% or more A manufacturing method (first manufacturing method) of a characteristic anode container for a sodium-sulfur battery is provided.

According to the present invention, in the method for manufacturing a sodium-sulfur battery anode container having an anti-corrosion spray coating on the inner peripheral surface, a plasma comprising a Cr-Fe alloy is formed on the inner peripheral surface of the anode container base by plasma spraying in the air. After forming the sprayed film, the plasma sprayed film surface is polished and polished until the chromium oxide content on the polished surface is 10% or more lower than the chromium oxide content on the surface of the plasma sprayed film , A method for polishing a plasma sprayed film is a method in which an anode container base having the plasma sprayed film is fixed, and the polishing brush is moved up and down while rotating, and the brush material of the polishing brush is made of A twisted wire brush made of metal, the wire brush diameter is 1.05-1.15 times the inner diameter of the anode container base, and the cross-sectional hardness (Hv) of the wire brush 430 or more, the wire diameter of one wire constituting the wire brush is 0.2 to 0.8 mm, the rotation speed of the wire brush is 900 to 1400 rpm, and the wire brush traverse speed is 60 to 80 mm / sec. A method for manufacturing an anode container for a sodium-sulfur battery (second manufacturing method) is provided.

In the first and second manufacturing methods according to the present invention, the method for forming the plasma sprayed film is to perform plasma spraying in the atmosphere by moving the spray gun up and down while rotating the cylindrical anode container base. At this time, the flow rate of the primary gas using the argon gas of the spray gun is 30 to 40 L / min, the flow rate of the secondary gas using hydrogen is 4.0 to 5.5 L / min, the plasma output is 12 to 15 kW, the metal A method in which a plasma sprayed film is formed by plasma spraying in a range where the powder particle size is 5 to 60 μm and the spraying distance is 45 to 55 mm is preferable.

Furthermore, in the 1st and 2nd manufacturing method of this invention, it is still more preferable that the wire diameter of one wire which comprises the said wire brush is 0.3 mm-0.4 mm.

If a battery is assembled using the anode container for sodium-sulfur batteries of the present invention, a sodium-sulfur battery with low internal resistance and high electric energy efficiency can be obtained at the beginning of the charge / discharge cycle. In addition, according to the first and second method for manufacturing an anode container for a sodium-sulfur battery according to the present invention, the labor is low, the productivity is high, the cost can be reduced, and the plasma sprayed film is excessively polished. This is not necessary, and it is possible to obtain a special effect of eliminating waste of polishing and greatly reducing polishing time and polishing cost.

Hereinafter, one example of the embodiment of the anode container for a sodium-sulfur battery according to the present invention will be described. However, the present invention is not limited to these examples and is not deviated from the scope of the present invention. However, various changes can be made based on the knowledge of those skilled in the art, and various modifications and improvements can be added.

The anode container for a sodium-sulfur battery according to the present invention is an anode container for a sodium-sulfur battery in which an anti-corrosion spray coating made of a Cr-Fe alloy is formed on the inner peripheral surface, and the spray coating is plasma sprayed in the atmosphere. A thermal spray coating having a polished surface formed by polishing after being formed by the method, wherein the polishing area ratio with respect to the thermal spray coating area is 10% or more.

When the battery is assembled by using the sodium-sulfur battery anode container of the present invention, a special effect is obtained that a battery having an extremely low initial internal resistance can be obtained.

The specific method for measuring the polishing area ratio with respect to the sprayed coating area is to use a scanning electron microscope, take a secondary electron image of the measurement area on the sprayed coating surface, trace the coating polishing area, analyze the image, and measure the area of the measurement area. It is obtained as a percentage of the sum total of each polished area.

FIG. 1 shows an anode container 1 for a sodium-sulfur battery according to the present invention using an aluminum cylinder as the anode container substrate 5. The thermal spray coating surface 2 was divided into five in the height direction, the polishing area ratio in each region (P1 to P5) was determined, and the results are shown in Table 1. FIG. 2 shows, as an example, a photograph of a secondary electron image of a thermal spray coating 2 having a polished surface by a scanning electron microscope. FIG. 3 is a trace diagram (image analysis result) of the thermal spray coating polishing region corresponding to FIG. FIG. 3 shows a thermal spray coating polishing region in the region P5 in FIG. 1. The number of polishing surfaces 3 is 36, the total area of the polishing surfaces is 67027 μm ² , the measurement region area is 214076 μm ² , and the polishing area ratio is Calculated at 31.31%.

In the example of the anode container 1 for a sodium-sulfur battery of the present invention, as shown in Table 1, the polishing area ratio is in the range of 30 to 37%, and the entire area of the sprayed coating 2 is polished almost uniformly. The average polished area ratio with respect to the film area is about 33%.

Various sodium-sulfur battery anode containers having different polishing area ratios were prepared, batteries were assembled, and the initial internal resistance of each battery during battery operation was measured. The results are shown in FIG. As shown in FIG. 4, in the case of a battery using an anode container with a polished area ratio of 0, ie, an unpolished anode container, the initial internal resistance is 7 mΩ, but as the polished area ratio increases, the initial internal resistance of the battery is Decrease.

When an anode container having a polished area ratio of 10% or more is used, the initial internal resistance is remarkably reduced, and a battery having a low initial internal resistance of about 3 mΩ or less can be obtained. When an anode container having a polished area ratio of 20% or more is used, a battery having a low initial internal resistance of about 2.5 mΩ or less can be obtained. From the viewpoint of corrosion resistance, the chromium content of the sprayed coating is preferably 60% by weight or more. Further, the thickness of the thermal spray coating is preferably 40 μm or more from the viewpoint of the service life of the battery.

As the plasma sprayed film is polished to increase the polishing area ratio, the surface roughness (Ra) of the sprayed coating having a polished surface decreases. The relationship between the polishing area ratio and the surface roughness (Ra) is shown in FIG. As shown in FIG. 5, a polishing area ratio of 10% corresponds to a surface roughness (Ra) of 6 μm. Therefore, it is preferable to polish until the surface roughness (Ra) of the thermal spray coating is 6 μm or less.

Not only the polishing area ratio, but also various anode containers with different spray coating thickness and spray coating surface roughness (Ra) were prepared, batteries were assembled, and the initial internal resistance of each battery during operation was measured. . The results are shown in Table 2. Each of the anode containers shown in Table 2 uses an aluminum cylindrical body as an anode container base, and a sprayed coating of 73% Cr—Fe alloy is formed on the inner peripheral surface thereof. The surface roughness (Ra) of the thermal spray coating indicates the surface roughness based on JIS B0601. The polished area ratio is obtained by dividing the sprayed coating surface into five parts in the height direction, obtaining the polished area ratio in each region, and indicating the average polished area ratio of the entire five divided regions. The observation magnification was 200 times.

As shown in Table 2, Examples 1 to 6 which are anode containers of the present invention have a polished area ratio of 10% or more, and the surface roughness (Ra) of the sprayed coating is 6 μm or less, The example whose film thickness is 49 micrometers or more is shown. In any case, the battery assembled using each anode container has an initial internal resistance of 3.1 mΩ or less during charging and discharging. On the other hand, in Comparative Examples 1 to 4 where the polishing area ratios are all lower than 10%, the batteries assembled using each anode container had a high initial internal resistance of the battery at the time of charge / discharge of 5.3 mΩ or higher. showed that.

Next, the relationship between the oxygen content on the surface of the sprayed coating and the polishing area ratio is shown in FIG. As shown in FIG. 6, the oxygen content of the sprayed coating surface portion at a polishing area ratio of 10% is 4.0% by weight. That is, if a battery is assembled using an anode container that has been polished until the oxygen content on the surface of the thermal spray coating is 4.0% by weight or less, a battery having a low initial internal resistance can be obtained. The oxygen content on the surface of the thermal spray coating is a value obtained by analyzing a surface depth of 5 μm.

Next, the manufacturing method of the anode container for sodium-sulfur batteries of this invention is demonstrated. In the first method for producing an anode container for a sodium-sulfur battery of the present invention, plasma spraying is performed on the inner peripheral surface of a cylindrical anode container base made of a metal material to form a plasma sprayed film made of a Cr-Fe alloy, Next, in the method for manufacturing an anode container for a sodium-sulfur battery, in which the obtained plasma sprayed film is polished to form a sprayed film having a polished surface on the inner peripheral surface, the polishing area ratio with respect to the sprayed film becomes 10% or more. The plasma sprayed film is polished to a maximum.

Specifically, as shown in FIG. 7, a cylindrical body made of an aluminum alloy is used as the base 5 of the anode container, and this anode container base 5 is rotated at a predetermined rotational speed by a rotating jig 6, Plasma spraying is performed in the air on the inner peripheral surface of the anode container base 5 while lowering the spray gun 7 at a predetermined traverse speed. In accordance with the thickness of the plasma sprayed film 4, the spray gun 7 is reciprocated up and down in the anode container base 5 for spraying.

The metal powder for thermal spraying used is Cr—Fe alloy powder, and the powder particle size is in the range of 5 to 60 μm. The thermal spray gun 7 uses argon gas as the primary gas, hydrogen as the secondary gas, sets the primary gas flow rate to 30 to 40 L / min, sets the secondary gas flow rate to 4.0 to 5.5 L / min, and performs hydrogen combustion. The plasma region 8 is formed by the above, and metal powder is blown into the plasma region 8 from the supply pipe 9. Further, the spray gun output is set to 12 to 15 KW, and the distance between the spray gun 7 and the anode container base 5, that is, the spray distance (d) is set to 45 to 55 mm.

The surface of the plasma sprayed film 4 formed on the inner peripheral surface of the anode container base 5 is in a state in which chromium oxide and fume are attached to the surface as shown in the enlarged schematic diagram of FIG. After the plasma sprayed film 4 is formed on the inner peripheral surface of the anode container base 5 in this way, the plasma sprayed film 4 is polished until the polishing area ratio with respect to the sprayed coating becomes 10% or more.

Specifically, as shown in FIG. 9, the anode container base 5 having the plasma sprayed film 4 on the inner peripheral surface is fixed by a fixing jig 11, and the polishing brush 10 is moved up and down while rotating to polish. The brush material of the polishing brush 10 is a metal twisted wire brush, the wire brush has a cross-sectional hardness (Hv) of 430 or more, and the wire diameter of one wire constituting the wire brush Is 0.2 to 0.8 mm, the number of revolutions of the wire brush is set to 900 to 1400 rpm, and the wire brush traverse speed is set to 60 to 80 mm / sec.

Here, the diameter (D1) of the wire brush shown in FIG. 10 is set corresponding to the inner diameter (D2) of the anode container base 5. It is preferable to use a wire brush having a diameter (D1) of 1.05 to 1.15 times the inner diameter (D2) of the anode container base 5. When the anode container base 5 having an inner diameter of 85.6 mm is used, it is preferable to use a wire brush having a diameter of 90 to 95 mm. In addition, it is more preferable to use a wire brush having a wire diameter of 0.3 to 0.4 mm. The wire brush made from a piano wire whose cross-sectional hardness (Hv) of a wire brush is 460 is preferable. FIG. 11 shows a schematic diagram of a locally enlarged polishing surface.

According to the first method for producing an anode container for a sodium-sulfur battery of the present invention, the measurement of the polishing area ratio is easier than the method of collecting and analyzing only the sprayed coating, and it requires less labor and is relatively short in time. It is possible to measure with a high productivity, and there is a remarkable effect that the cost can be reduced.

In addition, it is not necessary to polish the plasma sprayed film excessively, it is sufficient to polish it to an extent that the polishing area ratio is 10% or more, and it is possible to eliminate the waste of polishing, and to significantly reduce the polishing time and polishing cost. Is obtained.

The present inventors paid attention to the correlation between the polishing area ratio and the initial internal resistance of the battery, and completed the first method for producing an anode container for a sodium-sulfur battery of the present invention. When measuring, the chromium oxide content on the plasma sprayed film surface before polishing and the chromium oxide content on the polished surface after polishing are also measured, and the chromium oxide content on the coating surface before and after polishing is measured. Paying attention to the correlation between the reduction rate and the polishing area rate, the second method for producing an anode container for a sodium-sulfur battery of the present invention was completed.

The second method for producing an anode container for a sodium-sulfur battery according to the present invention is a method for producing an anode container for a sodium-sulfur battery having an anti-corrosion spray coating on the inner peripheral surface thereof. After forming a plasma sprayed film made of a Cr—Fe alloy on the peripheral surface, the surface of the plasma sprayed film is polished, and the chromium oxide content on the polished surface is 10% of the chromium oxide content on the surface of the plasma sprayed film. It is characterized by polishing until it becomes smaller.

The chromium oxide content on the film surface was measured by X-ray diffraction, and the reduction rate of the chromium oxide content on the film surface before and after polishing was determined from the peak intensity ratio by X-ray diffraction. There are three types of chromium oxides: Cr ₂ O ₃ , Cr ₃ O ₄ , and FeCr ₂ O ₄ .

FIG. 12 shows the relationship between the polishing area ratio (%) and the chromium oxide content reduction rate (%) on the film surface before and after polishing. As shown in FIG. 12, polishing until the chromium oxide content on the polished surface is 10% or more lower than the chromium oxide content on the surface of the plasma sprayed film is for the first sodium-sulfur battery of the present invention. This corresponds to polishing until the polishing area ratio in the method for manufacturing the anode container reaches 10% or more.

FIG. 13 shows the results of assembling a battery using anode containers manufactured at various reduction rates of chromium oxide content and measuring the initial internal resistance of the battery. As shown in FIG. 12, when the decreasing rate of the chromium oxide content is 10% or more, the initial internal resistance of the battery is remarkably lowered. In all of Examples 1 to 6 shown in Table 2, the reduction rate of the chromium oxide content is 10% or more, and the initial internal resistance of the battery assembled using them is 3.1 mΩ or less.

As described above, according to the second method for producing an anode container for a sodium-sulfur battery of the present invention, the chromium oxide content on the surfaces of the plasma sprayed film and the polished sprayed film is determined by X-ray diffraction. The chromium oxide content reduction rate (%) can be obtained from the peak intensity ratio, which is easier than the method of collecting and analyzing only the sprayed coating, requires less labor, and can be measured in a relatively short time. The effect is high that the cost is reduced.

Further, it is not necessary to polish the plasma sprayed film excessively, and it is possible to obtain an extraordinary effect of eliminating the waste of polishing and greatly reducing the polishing time and the polishing cost.

The anode container of the present invention can be suitably used for a sodium-sulfur battery. In that case, a sodium-sulfur battery with low internal resistance and high electric energy efficiency can be obtained at the initial stage of the charge / discharge cycle.

It is sectional drawing of the anode container for sodium-sulfur batteries of this invention. It is a secondary electron image photograph by the scanning electron microscope of the sprayed coating which has a grinding | polishing surface. FIG. 3 is a trace diagram corresponding to FIG. 2. It is a graph which shows the relationship between polishing area ratio (%) and the initial internal resistance of a battery. It is a graph which shows the relationship between polishing area ratio (%) and surface roughness (Ra) of a thermal spray coating. It is a graph which shows the relationship between polishing area rate (%) and oxygen content in the sprayed coating surface. It is explanatory drawing of the method of plasma spraying to the internal peripheral surface of an anode container base | substrate in air | atmosphere. It is a local expansion schematic diagram of a plasma sprayed film. It is explanatory drawing of the method of grind | polishing the inner peripheral surface of an anode container which has a plasma sprayed film. It is a local enlarged view of an abrasive brush. It is a local expansion schematic diagram of a thermal spray coating having a polished surface. It is a graph which shows the relationship between a grinding | polishing area rate and the chromium oxide content decreasing rate before and behind grinding | polishing in the film | membrane surface. It is a graph which shows the relationship between the chromium oxide content decreasing rate before and behind grinding | polishing in the film | membrane surface, and the initial stage internal resistance of a battery. It is sectional drawing of the conventional sodium-sulfur battery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Anode container for sodium-sulfur batteries of this invention, 2 ... Thermal spray coating, 3 ... Polishing surface, 4 ... Plasma spray coating, 5 ... Anode container base | substrate, 6 ... Rotating jig, 7 ... Thermal spray gun, 8 ... Plasma area , 9 ... Supply pipe, 10 ... Polishing brush, 11 ... Fixing jig, 12 ... Beta alumina solid electrolyte, 13 ... α-alumina insulating ring, 14 ... Cathode fitting, 15 ... Cathode lid, 16 ... Safety tube, 17 ... Sodium container, 18 ... anode fitting, 19 ... anode container, 20 ... bottom lid.

Claims (4)

Plasma spraying is performed on the inner peripheral surface of a cylindrical anode container base made of a metal material to form a plasma sprayed film made of a Cr-Fe alloy, and then the resulting plasma sprayed film is polished to have a polished surface. In the manufacturing method of the anode container for sodium-sulfur batteries formed on the inner peripheral surface,
The method of polishing the plasma sprayed film is a method of fixing the anode container substrate having the plasma sprayed film and moving it up and down while rotating the polishing brush, and polishing the brush material of the polishing brush Is a metal twisted wire brush, the wire brush diameter is 1.05 to 1.15 times the inner diameter of the anode container base, and the cross-sectional hardness (Hv) of the wire brush is 430 or more. The wire diameter of one wire constituting the brush is 0.2 to 0.8 mm, the rotation speed of the wire brush is 900 to 1400 rpm, the wire brush traverse speed is polished in the range of 60 to 80 mm / sec,
A method for producing an anode container for a sodium-sulfur battery, characterized in that the plasma sprayed film is polished until the polishing area ratio to the sprayed film becomes 10% or more. In the method for producing an anode container for a sodium-sulfur battery having an anti-corrosion spray coating on the inner peripheral surface,
After forming a plasma sprayed film made of a Cr—Fe alloy on the inner peripheral surface of the anode container base by plasma spraying in the air, the surface of the plasma sprayed film is polished, and the chromium oxide content on the polished surface is the plasma sprayed film. Polish until the chromium oxide content on the surface of the surface becomes 10% or more smaller ,
The method of polishing the plasma sprayed film is a method of fixing the anode container substrate having the plasma sprayed film and moving it up and down while rotating the polishing brush, and polishing the brush material of the polishing brush Is a metal twisted wire brush, the wire brush diameter is 1.05 to 1.15 times the inner diameter of the anode container base, and the cross-sectional hardness (Hv) of the wire brush is 430 or more. The wire diameter of one wire constituting the brush is 0.2 to 0.8 mm, the rotation speed of the wire brush is 900 to 1400 rpm, and the wire brush traverse speed is 60 to 80 mm / sec. A method for manufacturing an anode container for a sodium-sulfur battery. The method for producing an anode container for a sodium-sulfur battery according to claim 1 or 2 , wherein the wire diameter of one wire constituting the wire brush is 0.3 to 0.4 mm. In the method of forming the plasma sprayed film, when the spray gun is moved up and down and plasma spray is performed in the atmosphere while rotating the cylindrical anode container base, the flow rate of the primary gas using the argon gas of the spray gun Is 30 to 40 L / min, the flow rate of secondary gas using hydrogen is 4.0 to 5.5 L / min, the plasma output is 12 to 15 kW, the metal powder particle size is 5 to 60 μm, and the spraying distance is 45 to 55 mm. The method for producing an anode container for a sodium-sulfur battery according to any one of claims 1 to 3, wherein the plasma sprayed film is formed by plasma spraying.