JP3209066B2 - Battery case for sodium-sulfur battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery case for a sodium-sulfur battery, and more particularly, to an .alpha.-alumina ring joined to an opening of a sodium ion conductive solid electrolyte tube. A cathode chamber was formed inside the solid electrolyte tube by a cathode lid that was hot-pressed to one surface of the ring, and the anode lid was hot-pressure bonded to the other face of the α-alumina ring and was welded to this anode lid. The present invention relates to an improvement in the corrosion resistance of a battery case of a sodium-sulfur battery, in which an anode chamber is formed outside the solid electrolyte tube by the battery case, against an anode active material.

[0002]

2. Description of the Related Art A battery case of a sodium-sulfur battery has a corrosion resistance to these materials because sulfur as an anode active material and sodium polysulfide generated by electric discharge are stored in an anode chamber thereof. In addition, a material having conductivity that can also function as an anode current collector is used.

As a material satisfying the above conditions, a material in which carbon steel or stainless steel is used as a base material and chromium-iron alloy layer is formed by thermally diffusing chromium on the surface, that is, the carbon steel or stainless steel is used. A chromized surface is known.

[0004]

The above-mentioned chromized surface of carbon steel or stainless steel has a chromium carbide layer formed outside the surface, a chromium-iron alloy layer formed inside, and a chromium carbide layer formed outside. Is mainly composed of porous Cr ₂₃ C ₆ and has a thickness of several microns, so that it is easy to peel off, and it is difficult to maintain corrosion resistance to sulfur and sodium polysulfide for a long period of time. Was.

[0005]

In order to solve the above-mentioned problems, the present invention provides an α-alumina ring joined to an opening of a sodium ion conductive solid electrolyte tube, and one surface of the α-alumina ring. A sodium chamber having a cathode chamber in which a cathode lid is hot-pressed and sealed by the cathode lid, and an anode chamber in which an anode lid is hot-pressure bonded to the other surface of the α-alumina ring and sealed by the anode lid. -In a battery case of a sulfur battery, said battery case is 0.2-0.6% by weight;
And a chromium-iron alloy layer formed by chromizing the surface of the ferritic stainless steel containing carbon as a base material.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on its embodiments.

A feature of the present invention is that a battery case also serving as an anode current collector is made of ferritic stainless steel containing 0.2 to 0.6% by weight of carbon as a base material, and chromized on the surface of the ferritic stainless steel. The chromium-iron alloy layer is formed by processing, and the chromium carbide layer formed on the outer surface of the chromium-iron alloy layer is denser than Cr ₂₃ C _6.
The ₇ C ₃ mainly formed, yet is that was made to be even up to about ten microns and its thickness.

[0008]

Embodiment 1 As a ferritic stainless steel base material used for the battery case of the sodium-sulfur battery of the present invention, the content of carbon is 0.24%, the content of chromium is 18.1%, and the content of silicon is A base material A having a content of 0.17% and manganese of 0.32%, a content of carbon of 0.42%, a content of chromium of 17.5%, and a content of silicon of 0.22%; Base material B having a manganese content of 0.29%, a carbon content of 0.54%, a chromium content of 17.9%, a silicon content of 0.26%, and a manganese content of A base material C having a content of 0.38% was prepared. For comparison, a carbon material having a carbon content of 0.02%, a silicon content of 0.22%, and a manganese content of 0.38% was prepared. Steel base material D, carbon content 0.02%, chromium content 17.8%, silicon content 0.24%, A low-carbon ferritic stainless steel base material E having a gangue content of 0.28% was prepared, and each of the base materials was 30 to 80% chromium powder as a chromizing mixture, and 0.5 to 2.0%. Ammonium chloride powder, enclosed in an iron box together with 20-50% alumina powder, heated in a hydrogen stream at about 1170 ° C. for several hours, heated at a temperature of about 1200 ° C. for several minutes, and then rapidly cooled It was chromized.

The thickness of the chromium carbide layer formed on the outer surface of each base material obtained by an optical microscope and an electron beam microanalyzer and the Cr ₇
We investigated the thickness of the C _3, and the results are shown in Table 1.

[0010]

[Table 1]

From Table 1, it can be seen that the greater the content of carbon in the base material, the greater the thickness of the formed chromium carbide layer.

[0012]

Embodiment 2 Next, each of the chromized base materials was vacuum-sealed in Pyrex glass together with the most corrosive Na ₂ S ₃ among the sodium polysulfides produced at the anode of a sodium-sulfur battery. Then, the sample was stored at a temperature of 350 ° C. for 1,000 hours to investigate corrosion resistance. The results are shown in Table 2.

[0013]

[Table 2]

From Table 2, it can be seen that all of the ferritic stainless steel base materials used in the battery case of the sodium-sulfur battery of the present invention have excellent corrosion resistance. The corrosion resistance was investigated by making the corrosion amount of the carbon steel base material D as 100 and comparing the corrosion amounts of the other base materials with each other.

In each of the above-described embodiments, if the carbon content exceeds 0.6% by weight, cracks may occur during processing into a battery case. Therefore, the content is preferably 0.6% by weight or less. .

Further, it goes without saying that the ferritic stainless steel used in each of the above embodiments may contain, as impurities, other components which do not hinder the achievement of the object of the present invention.

[0017]

As described above, according to the present invention, a ferritic stainless steel having a carbon content of 0.2 to 0.6% by weight is used as a base material, and the surface of the ferritic stainless steel is chromized. Can maintain the corrosion resistance to sulfur and sodium polysulfide for a long period of time, so that the corrosion resistance of the battery case also serving as the anode current collector can be improved, and the life of the sodium-sulfur battery can be extended. be able to.

Claims (1)

(57) [Claims] 1. An α-alumina ring is joined to an opening of a sodium ion conductive solid electrolyte tube, and a cathode lid is heat-pressure joined to one surface of the α-alumina ring, and sealed by the cathode lid. In a battery case of a sodium-sulfur battery having a cathode compartment and an anode cover which is hot-press bonded to the other surface of the α-alumina ring and sealed by the anode cover, the battery case has a capacity of 0.2. ~ 0.6% by weight
A ferrite stainless steel containing carbon as a base material, and a chromium-iron alloy layer formed by chromizing the surface of the ferrite stainless steel. Tank