JPH0797490B2 - High temperature battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a Fe-Cr alloy excellent in corrosion resistance and toughness for anode active material containers, anode current collectors, etc. in contact with the anode active material of high temperature batteries.
-It relates to a high temperature battery using a Ni alloy.

[Prior Art] The principle of a high-temperature battery was announced by Ford Motor Company of the United States in 1966, and is also called a sodium-sulfur battery because sodium and sulfur are used as active materials.

As shown in FIG. 1, the structure is as follows: 1 cathode terminal, 2 cathode active material (sodium), 3 solid electrolyte tube having sodium ion conductivity (eg beta-alumina), 4
Of the anode active material (for example, sulfur or sodium polysulfide) impregnated with carbon or graphite felt of 5), the anode active material container also serving as the anode terminal current collecting material of 5, and the cathode chamber at the upper open end of the solid electrolyte tube. An insulator 8 (for example, alpha alumina) for electrically insulating the lid that hermetically seals the anode chamber is joined with glass 9.

The operating temperature is usually 300 to 350 ° C in consideration of the melting points of the bipolar active materials and the electric conductivity of the solid electrolyte.

The battery reaction is as shown in the following equation.

High-temperature batteries are being developed in various countries as high-performance secondary batteries for power supply of electric vehicles for power load adjustment. One of the bottleneck of development is the anode active material container with excellent sodium polysulfide resistance and There is a point that an anode current collecting material is necessary.

Sodium polysulfide has a very strong corrosive action, and sulfides are generated when the anode active material container, the anode current collecting material and the like are corroded. As the corrosion progresses, the sulfur in the anode active material is consumed for sulfurization, the amount of sulfur acting as the active material is reduced, and the battery capacity is reduced to reach the end of life.

Further, if corrosion progresses locally, the anode active material container or the like may be punctured, and the active material may flow out to the end of its life.

Regarding the performance required for the anode active material container and the anode current collecting material, etc., a material that has corrosion resistance to the anode active material having a severe corrosive action and mechanical strength and is excellent in workability is required. desirable. Furthermore, good electrical conductivity is also required when conducting anode current collection.

Generally, SUS 304, molybdenum, chromium, etc. are considered as the anode active material container, anode current collector material, etc.
In 304, the corrosion progresses rapidly, and as shown in FIG. 2, the battery capacity is rapidly reduced with a small number of charge / discharge cycles.

Also, in the case of ribden, the total amount of corrosion is small during the charge-discharge cycle in which the discharge is stopped in the partial discharge state where the anode active material composition is near Na ₂ S ₅ , and the battery capacity decreases as shown in Fig. 3. Local corrosion, so-called pitting corrosion,
After all, the life is short.

In addition, during the charge / discharge cycle in which the anode active material composition is discharged to a complete discharge state near Na ₂ S ₃ , the progress of corrosion is accelerated, and as shown in FIG. 4, compared to the partial discharge shown in FIG. Then, the battery capacity decreases sharply.

Chromium is less corrosion of the total amount in the whole of _{Na 2 S 5 ~Na 2 S 3} , that results in pitting, also it is extremely brittle, nearly impossible at present technology be processed into a container or the like, the request Is not satisfied.

The present inventors have proposed a high-purity, high-Cr-Fe alloy as a metal material that has corrosion resistance to an anode active material and is excellent in workability (Japanese Patent Laid-Open No. 58-152379).

Similar to chromium, this alloy has little corrosion in the entire region and is also excellent in pitting corrosion resistance, effective in prolonging the service life of a high temperature battery, and can be processed into an anode active material container.

[Problems to be Solved by the Invention] The high-purity high-Cr-Fe alloy has excellent corrosion resistance for high-temperature batteries as described above, but since it has poor toughness at room temperature, it cannot be molded into a battery container. Is difficult to process, and there is a problem in manufacturing a material for batteries.

An object of the present invention is to provide an alloy having excellent corrosion resistance and toughness for a material in contact with an anode active material of a sodium-sulfur high temperature battery.

[Means and Actions for Solving Problems] The present invention is a high-temperature battery using a high-purity Fe—Cr—Ni alloy, in which Ti, Nb, Zr, and V are added as necessary. .

The reasons for limiting the components will be described below.

If the Cr content exceeds 60%, the material is significantly deteriorated, such as cracking during forging to cooling and poor ductility during cold working. If it is less than 40%, the corrosion resistance for high temperature batteries is poor. Therefore 40-60
%.

Ni is added for the purpose of improving toughness. If it exceeds 6%, the stable heat treatment condition range is narrow, an austenite phase appears, hot workability deteriorates, and cracks occur during processing. 4% again
Below, the effect of improving toughness is not observed. Addition of more than 4% to 6% makes vTr below 0 ° C.

The amount of Ni added will be described in more detail.

When making a tank-shaped container for high temperature batteries, toughness is an important factor as a material property. Further, an Fe alloy having a high Cr content, such as the alloy of the present invention, may crack and fracture due to lack of toughness during coiling of a hot rolled material and during cold rolling.

Therefore, the present inventor conducted a study on improvement of toughness and found that
It has been found that the toughness near room temperature is significantly improved by adding an appropriate amount of.

Fig. 5 shows the results regarding the toughness obtained by the Charpy impact test by adding Ni to Fe-50Cr steel.

Figure 5 shows the transition temperature (vTrs) at which the Charpy impact value exceeds 2 kgf · m / cm ² .

From this result, vTrs becomes 0 when Ni is added more than 4% to 6%.
It will be below ℃. Also, the amount of Ni added when vTrs is 50 ° C or less is 3
~ 8%.

The condition that the Charpy impact value is 2 kgf ・ m / cm ² or more is
It is an index of the toughness necessary in the manufacturing process of the raw material, and if the toughness satisfying this condition can be empirically secured, it is possible to industrially manufacture the alloy thin plate and pipe-making.

If C exceeds 0.02% or N exceeds 0.02%, carbides or nitrides are generated at the grain boundaries, which causes local corrosion such as grain boundary corrosion and pitting corrosion. In addition, the workability also deteriorates, making it difficult to form the battery container. Therefore, both C and N
It was set to 0.02% or less.

Furthermore, among Ti, Nb, Zr, and V, any one kind or two or more kinds added in a total amount of 0.05 to 0.5% further improves the corrosion resistance, ductility, and toughness.

Addition of Ti, Nb, Zr, and V suppresses grain boundary precipitation of chromium carbonitrides, and thus prevents deterioration of corrosion resistance due to formation of Cr-deficient layer and improves ductility and toughness.

However, if added in excess of the upper limit, an intermetallic compound containing Ti, Nb, Zr, and V will be formed, which will deteriorate ductility and toughness and cause local corrosion.

The environment to which this material is exposed in a high temperature battery is high temperature sodium polysulfide as described above. The anode active material is from where large ratio of Na S, such as S (sulfur) or Na ₂ S ₅ by the discharge, varies almost to the composition of Na ₂ S _3, and most severely corroded by Na ₂ S _3, Sufficient corrosion resistance to Na ₂ S ₃ is required for the anode active material container material, the anode current collecting material, and the like.

The alloy of the present invention sufficiently withstands such a corrosive environment.

[Examples] The results of the corrosion resistance comparison test between the alloy of the present invention and the conventional metal material are shown below.

A 1 × 8 × 30 (mm) test piece of the alloy of the present invention shown in Table 1 was vacuum sealed in a Pyrex glass tube together with 15 g of Na ₂ S ₃ and subjected to a corrosion test at 350 ° C. for 384 hours. It was

The corrosion thickness was determined from the weight loss, surface area and specific gravity of the test piece.
Moreover, the presence or absence of pitting corrosion was examined by a microscope.

The results are shown in Table 2.

From these results, it can be seen that the alloy of the present invention is extremely excellent in corrosion resistance in Na ₂ S ₃ in view of corrosion thickness and local corrosion as compared with the comparative alloy steel.

Next, using the alloy of the present invention, an anode active material container also serving as an anode terminal electric body shown in FIG. 1 was prepared, a sodium-sulfur battery was assembled, and a charge / discharge cycle test was carried out.

The test temperature was 350 ° C., discharge was performed for 3 hours at a rate current (55 mA / cm ² as the surface current density of the anode active material container) for 3 hours, and after a 10-minute rest, 5 hours were charged with 100% of the discharge amount of electricity. The charging / discharging conditions are such that a pause of 10 minutes is one cycle.

The change of the battery capacity with respect to the cycle of the battery using each anode active material container up to 450 cycles and the investigation of the anode active material container after the test were conducted.

FIG. 7 (a to d) shows the battery capacity change with respect to the charge / discharge cycle of the battery using the anode active material container prepared from the alloy sample of the present invention.

Even when compared with the results (FIGS. 3 and 6) of the battery using molybdenum and Cr as the positive electrode active material under the same test conditions, the battery capacity change is good.

In addition, the surface of the container 5 that was in contact with the anode active material after the test was
All of the alloy samples of the present invention had no abnormality and had excellent corrosion resistance to the anode active material.

EFFECTS OF THE INVENTION As described above, the present invention suppresses corrosion of the anode active material container, the anode current collecting material and the like due to the anode active material, prolongs the service life of the high temperature battery, and has excellent toughness. And its industrial value is enormous.

The present invention relates to a metal material used in a portion in contact with the anode active material, and the structure, usage method and coating method are not limited.

[Brief description of drawings]

Fig. 1 is a vertical cross-sectional view of a high temperature battery, Fig. 2 is a graph of capacity characteristics of a battery using SUS304 as an anode active material container, and Fig. 3 is a partial discharge cycle capacity of a battery using molybdenum as an anode active material container. A graph of characteristics, FIG. 4 is a graph of complete discharge cycle capacity characteristics of a battery using molybdenum as an anode active material container, FIG. 5 is a graph of addition effect of Ni on toughness of the present invention, and FIG. Graph of partial discharge cycle capacity characteristics of battery using chromium-silicon alloy for anode active material container, No. 7
FIGS. 3A to 3D are graphs of partial discharge cycle capacity characteristics of a battery using the alloy sample according to the present invention as the anode active material container. 1 ... Cathode terminal, 2 ... Cathode active material 3 ... Solid electrolyte tube, 4 ... Anode active material 5 ... Anode terminal Anode active material container that also serves as current collector 6 ... Anode lid, 7 ... Cathode Lid 8 ... Insulating ring, 9 ... Glass

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location H01M 10/39 Z (72) Inventor Koichi Watanabe 3434 Shimada, Hikari City, Yamaguchi Prefecture Nippon Steel Co., Ltd. Hikari Steel Works (72) Inventor Tomomi Murata 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Inside Nippon Steel Co., Ltd. Technical Research Institute (56) Reference JP-A-59-177319 (JP, A)

Claims (2)

[Claims] 1. A material in contact with the positive electrode active material, in% by weight, C
r: 40-60%, Ni: over 4% -6%, C: 0.02% or less, N: 0.02%
Hereinafter, a high-temperature battery characterized by using an Fe-Cr-Ni alloy with the balance being Fe and impurities. 2. A material in contact with the positive electrode active material, in% by weight, contains C
r: 40-60%, Ni: over 4% -6%, C: 0.02% or less, N: 0.02%
Below, one or more of Ti, Nb, Zr, and V
A high temperature battery characterized by using an Fe-Cr-Ni alloy containing 0.05 to 0.5% in total of at least one species and the balance being Fe and impurities.