JP3262740B2 - Anode container for sodium-sulfur battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an anode container used for storing sulfur and sodium polysulfide 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 operated at 300 to 350 ° C. isolated by a β-alumina solid electrolyte.

The configuration of such a sodium-sulfur battery is, for example, as shown in FIG. 1, a cylindrical anode container 3 containing an anode conductive material 6 such as carbon felt impregnated with sulfur as an anode active material. , A bottomed cylindrical solid electrolyte tube (β-alumina tube) 5 having a function of selectively allowing sodium ions to pass therethrough, and a sodium 7 tube disposed inside the solid electrolyte tube 5. And a sodium storage container 10 for storing nitrogen 8.

The solid electrolyte tube 5 is joined to the upper end of the anode container 3 via an insulator ring 1 made of, for example, α-alumina. On the upper surface of the insulator ring 1, a cathode fitting 1 is provided.
1 is thermocompression bonded. The partition tube 9 may be interposed between the sodium storage container 10 and the solid electrolyte tube 5.

[0005] In the sodium-sulfur battery having the above configuration, at the time of discharge, molten sodium emits electrons to become sodium ions, which pass through the solid electrolyte tube 5 to move to the anode side, and Reacts with the sulfur and the electrons that have passed through the external circuit to generate sodium polysulfide and generate a voltage of about 2V. On the other hand, at the time of charging, a reaction of producing sodium and sulfur occurs in reverse to the discharging. In addition, in such a sodium-sulfur battery, the material of the anode container 3 is lightweight and inexpensive because
Al-Mn alloys are used among them because aluminum alloys have high strength and good workability and corrosion resistance. In general, it is manufactured by drawing a raw tube extruded in a hot state, drawing it in a cold state to a diameter of a predetermined accuracy, and adjusting the strength by work hardening. Further, annealing for strength adjustment and strain removal may be performed.

[0006]

However, in general, the cold working lowers the recrystallization temperature, and the sodium-sulfur battery operates at a high temperature of 300 to 350 ° C. In addition, there is a problem that the strength is reduced. Therefore, conventionally, it has been necessary to secure the net strength by increasing the wall thickness. For this reason, there has been a problem that the weight and cost of the sodium-sulfur battery cannot be reduced.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to improve sodium-sulfur which can contribute to weight reduction and cost reduction by improving high-temperature strength. An object of the present invention is to provide an anode container for a battery.

[0008]

Means for Solving the Problems According to the present invention, aluminum manufactured by performing cold drawing after hot extrusion.
An anode container for a sodium-sulfur battery comprising a
Thus, in the alloy composition of the aluminum tube, Mn:
0.5 to 1.5 wt%, the balance being Al and impurities
And Fe as an impurity is 0.4 wt% or less,
i is 0.4 wt% or less, Mg is 0.5 wt% or less, Cu
Is 0.5 wt% or less, and other elements are each 0.2 wt% or less.
Mn solid solution in the alloy structure
Intermetallic compound with an amount of 0.3 wt% or more and a major axis of 1 μm or more
The product is less than 1 × 10 ⁴ pieces / mm ² , before the cold drawing.
The grain structure is a recrystallized alloy structure.
Sodium characterized in that the content is 5-30%
An anode container for a sulfur battery is provided.

[0009]

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The anode container for a sodium-sulfur battery of the present invention has a granular structure in which an aluminum alloy is recrystallized, and is further subjected to in-situ recrystallization at a high temperature during use of the sodium-sulfur battery. It is something that goes.

Here, in-situ recrystallization refers to a method in which a previous crystal grain is not replaced by a newly generated crystal grain or a grain boundary is largely moved by nucleation and crystal growth as in normal recrystallization. This is a phenomenon in which the dislocation density gradually decreases and the strength decreases. For this reason, the softening rate by high temperature can be suppressed.

Hereinafter, the anode container for a sodium-sulfur battery of the present invention will be described in detail.

[0013] The present invention is an anode container for a sodium-sulfur battery comprising an aluminum tube manufactured by performing cold drawing after hot extrusion, wherein Mn: 0.5 to 1. 5 wt%, with the balance being Al and impurities, Fe as impurities being 0.4 wt% or less, Si being 0.4 wt% or less, Mg being 0.5 wt% or less, Cu being 0.5 wt% or less, and others. The elements are each suppressed to 0.2 wt% or less, and in the alloy structure, the Mn solid solution amount is 0.3 wt% or more;
The number of intermetallic compounds having a major axis of 1 μm or more is less than 1 × 10 ⁴ / mm ² , the alloy structure before cold drawing is a recrystallized granular structure, and the drawing reduction is 5 to 30%.

The significance of addition of each element in the alloy composition of the aluminum tube constituting the anode container for a sodium-sulfur battery of the present invention and the reasons for limiting the contents are as follows.

Mn is an element that contributes to improvement in strength by suppressing the growth of recrystallized grains, miniaturizing the recrystallized grains, and suppressing grain boundary movement.

When the Mn content is less than 0.5 wt%, the above effect is poor. On the other hand, when the Mn content exceeds 1.5 wt%, the amount of undissolved Mn increases and the coarse intermetallic compound (Al ₆ M
n), growing recrystallized grains and possibly reducing strength at high temperatures. Therefore, the Mn content is 0.5
To 1.5 wt%, preferably 0.8 to 1.3 wt%.
More preferably, it is wt%.

The balance of the elements is Al and impurities, and when Fe and Si are present as impurities in the alloy, intermetallic compounds such as Fe—Si and Fe—Mn are crystallized and easily recrystallized. , Causing a decrease in high-temperature strength. Therefore, each of Fe and Si contains 0.4 wt.
% Or less, and the Fe content is
It is more preferable that the Si content be 0.3 wt% or less and the Si content be 0.2 wt% or less.

Further, when the content of Mg as an impurity is large, deformation resistance at the time of cold working increases, and productivity decreases, so that the content is preferably 0.5 wt% or less.
More preferably, the content is 0.1 wt% or less.

[0019] Cu is an element that contributes to the improvement of strength. However, an increase in the content leads to an increase in extrusion deformation resistance and a deterioration in corrosion resistance.
% Or less, more preferably 0.3% by weight or less.

The other impurity elements are each preferably set to 0.2 wt% or less, and more preferably set to 0.1 wt% or less, in order to suppress crystallization of coarse particles.

In the alloy structure of the aluminum tube having the composition described above, Mn which is not solid-solved forms an intermetallic compound (Al ₆ Mn) and causes a reduction in strength. While limiting to the above range,
By making the amount of Mn solid solution 0.3% by weight or more, more preferably 0.5% by weight or more of the entire alloy, generation of a coarse intermetallic compound (Al ₆ Mn) is suppressed. Furthermore, in order to suppress the coarsening of the recrystallized grains, the intermetallic compound is
It is preferable that the coarse particles having a major axis of 1 μm or more be less than 1 × 10 ⁴ / mm ² , more preferably less than 0.8 × 10 ⁴ / mm ² .

Then, the aluminum tube is formed into a tube having a required diameter by being cold drawn after hot extrusion.
In the present invention, in order to obtain high strength, the alloy structure after hot extrusion, the alloy structure before cold drawing, and the reduction of drawing are further limited. This is because the alloy structure after hot extrusion or the alloy structure before cold drawing suppresses coarsening of crystal grains during subsequent cold drawing and product use in a high-temperature region, and to maintain strength. This is because a recrystallized granular structure is indispensable. In order to maintain strength, the recrystallization is preferably fine grains, and specifically, the crystal grain size is preferably 10 mm or less, more preferably 7 mm or less, and further preferably 1 mm or less. Particularly preferred.

As the extrusion conditions for obtaining such a recrystallized structure, it is preferable that the extrusion temperature is 350 to 550 ° C. and the extrusion speed is 20 m / min or more as the product speed. This is because in low-temperature low-speed extrusion, the crystal structure becomes fibrous, and the strength is significantly reduced by annealing. In high-temperature extrusion, precipitation of Mn and coarsening of crystal grains progress, and the strength particularly at high temperatures tends to decrease. That's why. still,
In order to obtain high strength, the extrusion method may be either the porthole method or the mandrel method, but the mandrel method is more preferable.

Next, in drawing, the reduction represented by the following formula is preferably set to 5 to 30%, and
It is particularly preferred that the content be 5 to 25%. Reduction (%) = (1−A ₁ / A ₀ ) × 100 where A ₀ : cross-sectional area before drawing A ₁ : cross-sectional area after drawing On the other hand, if the reduction is less than 5%, work hardening is insufficient. Therefore, the strength after drawing is low. On the other hand, if the reduction exceeds 30%, the strength is improved by work hardening, but the rate of decrease in strength due to holding at a high temperature increases, and the strength during long-time use at a high temperature is insufficient.

Further, even when the reduction is the same, as the outer diameter reduction amount is larger, the strength after drawing is improved, but the strength after holding at a high temperature is increased at a higher rate. The strength after holding at high temperature may be reversed. For this reason, in order to obtain high strength at the time of high temperature use, it is preferable to adjust the reduction amount of the outer diameter together with the reduction.

[0026] By pulling out the base tube obtained by hot-extruding the aluminum alloy having the above-mentioned alloy composition and structure at a reduction of 5 to 30%, the tube can have a diameter of 50 to 170 N / mm.
^2. 0.2% proof stress can be exhibited. With such a proof strength, it is possible to sufficiently maintain practically sufficient strength even if the strength is slightly reduced due to prolonged exposure to high temperature during use.

[0027]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Examples 1 to 6 and Comparative Examples 1 to 4) First, billets having the respective alloy compositions and Mn solid solution amounts shown in Table 1 below were cast, and the burets were heated to 450 ° C. and the extrusion speed was increased. Under constant conditions of 60 m / min, outer diameter 72 mm x wall thickness 2.0 m
m tubes were extruded. Further, these extruded raw tubes were drawn under a constant condition of a reduction of 20% and an outer diameter reduction of 3 mm. For each of the obtained drawn tubes, immediately after drawing and 50
After holding at 0 ° C. for 3 hours, 0.2% proof stress was measured by a conventional method. Table 1 shows the results.

[0029]

[Table 1]

From the results in Table 1, it was confirmed that by setting the alloy composition, the amount of Mn solid solution, and the amount of intermetallic compound of 1 μm or more within the range of the present invention, high proof stress was maintained even after holding at a high temperature. In addition, the alloy structure of these extruded raw tubes was examined for the amount of intermetallic compound having a major axis of 1 μm or more, the alloy structure, and the crystal grain size. All the alloy structures were recrystallized granular structures, and the crystal grain size was All were fine crystals of 10 mm or less.

(Examples 7 to 11, Comparative Examples 5 and 6)
An extruded tube made of an alloy having the same composition as that of the above-mentioned Example 3 while changing the extrusion temperature and the extrusion speed was used for reduction 2
It was pulled out under a constant condition of 0% and the outer diameter drop amount was 3 mm. With respect to the obtained drawn tube, the proof stress immediately after drawing and after holding at 500 ° C. for 3 hours was measured by an ordinary method. Table 2 shows the extrusion conditions and the proof stress of the drawn tube.

[0032]

[Table 2]

(Examples 12 to 19, Comparative Examples 7 and 8) Further, a plurality of identical extrusions were extruded using an alloy having the same composition as that of the above-mentioned Example 3 at a billet temperature of 450 ° C. and an extrusion speed of 60 m / min. The base tube was extracted under the conditions shown in Table 3 below. Immediately after drawing and after holding at 500 ° C. for 3 hours, the yield strength of the obtained drawn tube was measured by a conventional method.
Table 3 shows the drawing conditions and the strength of the drawn tube.

[0034]

[Table 3]

From the results shown in Tables 2 and 3, a grain structure obtained by recrystallizing the alloy structure after hot extrusion for an alloy having the alloy composition and the Mn solid solution amount of the present invention and having a suppressed coarse intermetallic compound is obtained. It was confirmed that by setting the reduction in drawing to a predetermined range and maintaining the high strength even after holding at a high temperature.

[0036]

As described above, the anode container for a sodium-sulfur battery of the present invention has a granular structure in which an aluminum alloy is recrystallized, and further maintains the high temperature when the sodium-sulfur battery is used. Field recrystallization Al
-By using the Mn alloy, the softening rate due to annealing at the operating temperature of the sodium-sulfur battery (300 to 350 ° C.) is suppressed, and the durability is improved, and the weight and cost of the anode container for the sodium-sulfur battery are reduced. Can contribute.

Further, the aluminum tube constituting the anode container for a sodium-sulfur battery has an alloy structure
As the crystal grains are refined, the alloy structure after hot extrusion is a recrystallized granular structure, and the growth suppressing effect of the recrystallized grains after cold drawing, without impairing the workability,
Excellent high-temperature strength can be maintained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a structure of a sodium-sulfur battery.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Insulator ring, 3 ... Anode container, 4 ... Sodium-sulfur battery, 5 ... Solid electrolyte tube, 6 ... Conductive material for anode, 7 ... Sodium, 8 ... Nitrogen gas, 9 ... Partition tube, 10 ... Sodium storage container , 11 ... cathode metal fittings.

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Kenji Tomita 6,224, Kaiyamacho, Sakai City, Osaka Prefecture Inside Showa Aluminum Co., Ltd. (72) Inventor Masaji Sakaguchi 6,224 Kaiyamacho, Sakai-shi, Osaka, Japan Showa Aluminum Co., Ltd. (72) Inventor Yuichi Takami 6,224 Kaiyamacho, Sakai-shi, Osaka, Showa Aluminum Co., Ltd. 56) References JP-A-2-142066 (JP, A) "JIS Handbook Non-Ferrous 1987", (Showa 62-4-12), Japan Standards Association, page 356 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/39

Claims (1)

(57) [Claims] 1. An anode container for a sodium-sulfur battery comprising an aluminum tube manufactured by performing cold drawing after hot extrusion, wherein Mn: 0.5 in an alloy composition of the aluminum tube.
~ 1.5 wt%, the balance being Al and impurities, Fe as impurities 0.4 wt% or less, Si 0.4 wt% or less, Mg 0.5 wt% or less, Cu 0.5 wt% Hereinafter, each of the other elements is suppressed to 0.2 wt% or less, and in the alloy structure, 1 × 10 ⁴ intermetallic compounds having a Mn solid solution amount of 0.3 wt% or more and a major axis of 1 μm or more are contained in 1 × 10 ⁴ / mm ^2. An anode container for a sodium-sulfur battery, wherein the alloy structure before cold drawing is a recrystallized granular structure, and the drawing reduction is 5 to 30%.