JP3113799B2 - Sodium-sulfur battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention
The present invention relates to a sodium-sulfur battery used as a secondary battery for a power source of an electric vehicle.

[0002]

2. Description of the Related Art This type of sodium-sulfur battery is disclosed in Japanese Patent Application Laid-Open Nos. 5-109433 and 6-16307.
As shown in Japanese Patent Publication No. 7 (1995) -76, a bottomed cylindrical anode container, a bottomed cylindrical solid electrolyte permeable to sodium ions disposed inside the anode container, and It is configured to include a cathode active material made of metal sodium contained therein, and an anode active material made of sulfur contained between the solid electrolyte and the anode container.

A sodium-sulfur battery of this type has a 300
The charge / discharge operation is performed in a state heated to about 350 ° C. During discharge, sodium in the cathode chamber and sulfur in the anode chamber are ionized, and the ionized sodium permeates the solid electrolyte and reacts with sulfur. Then, sodium polysulfide is generated and discharged, and at the time of charging, the opposite reaction occurs to be charged.

Incidentally, as one type of the sodium-sulfur battery, there is a type in which the anode container is formed of metal and the solid electrolyte is formed of ceramic. 300
When the heating and cooling in which the heating state is maintained at a temperature of from 0 ° C. to 350 ° C. and the operation is stopped to cool to the outside air temperature are repeatedly performed, the difference between the thermal expansion and the thermal contraction between the anode container and the solid electrolyte and the difference between the thermal expansion and the thermal contraction during the discharge are generated. The anode container gradually elongates in the longitudinal direction due to the change between the solid phase and the liquid phase of sodium polysulfide, and a large stress may act on the solid electrolyte to damage the solid electrolyte.

In another form of the sodium-sulfur battery, the anode container has a bottomed cylindrical base made of aluminum or an aluminum alloy and a corrosion-resistant coating layer formed on the inner peripheral surface of the base. And the solid electrolyte is formed of ceramic. In the sodium-sulfur battery of this type, the base is formed of aluminum or an aluminum alloy in order to make the anode container lightweight and inexpensive. Thus, a coating layer is formed on the inner peripheral surface of the base made of aluminum or an aluminum alloy.

That is, in a sodium-sulfur battery, sodium polysulfide is generated by the reaction between sodium and sulfur at the time of discharge. However, sodium polysulfide is highly corrosive to metals, particularly to aluminum and aluminum alloys. When this sodium polysulfide comes in direct contact with aluminum and aluminum alloy, the inner peripheral surface of the anode vessel is corroded and damaged, reducing the durability and
If the corrosion is localized and intense, cracks and through holes may occur in the anode container and sodium polysulfide, sulfur, etc. may leak to the outside. This is because the amount of sulfur that is consumed for sulfuration of the metal constituting the anode container and functions as an anode active material is reduced, and the electric capacity is accordingly reduced to shorten the life of the battery.

In this type of sodium-sulfur battery as well, the anode container is gradually elongated in the longitudinal direction due to heating and cooling during operation and shutdown, and large stress acts on the solid electrolyte to damage the solid electrolyte. May be caused. In addition, in the sodium-sulfur battery of this type, there is a large difference in thermal expansion and thermal contraction between the base and the coating layer constituting the anode container, and this difference causes delamination between the two. In addition, cracks may occur in the coating layer.

[0008]

In order to cope with such a problem, in the sodium-sulfur batteries disclosed in the above publications, the former sodium-sulfur battery has the following problems.
Along the upper side of the cylindrical portion of the anode container is provided a constricted portion that is bent in the radial direction to easily expand and contract in the longitudinal direction of the cylindrical portion,
A rigid container is fitted around the outer periphery of the anode container, the rigid container regulates the amount of longitudinal expansion due to the thermal expansion of the anode container to a predetermined amount, and absorbs and reduces the thermal expansion and thermal contraction of the anode container by deformation of the constricted portion. What you want to do. Further, in the latter sodium-sulfur battery, a constricted portion is formed at the upper part of the cylindrical portion of the anode container to absorb and mitigate the thermal expansion and thermal contraction of the anode container by deformation of the constricted portion, and to reduce the absorption of the anode container. The inner peripheral surface is to be protected by a coating layer.

[0009] However, in the latter sodium-sulfur battery, the constricted portion is covered with the covering layer and is not deformed as intended because the deformation during thermal expansion and contraction is regulated. For this reason, in the sodium-sulfur battery, cracks are remarkably generated in the coating layer of the anode container. Therefore, an object of the present invention is to reduce the occurrence of cracks in the coating layer and improve the life of the anode container in a sodium-sulfur battery of this type.

[0010]

SUMMARY OF THE INVENTION The present invention provides an anode container having a metal bottomed cylindrical base having a coating layer made of a metal having higher corrosion resistance than the base, and an anode container having the same structure. A bottomed cylindrical ceramic solid electrolyte permeable to sodium ions disposed therein, a cathode active material made of metallic sodium housed in the solid electrolyte, and between the solid electrolyte and the anode container A sodium-sulfur battery comprising a contained anode active material made of sulfur and having a constricted portion bent in a radial direction at an upper portion of the cylindrical portion of the anode container, and performing a charge / discharge operation in a heated state. The constricted portion is located at a position above the upper end surface of the anode active material , and the coating layer is located on the lower end of the base.
The upper end extends to the site of the upper end face of al before Symbol anode active material
It is located between the lower base end of the constriction and the top of the constriction .

[0011] Sodium according to the present invention - in the sulfur batteries, forming the upper portion of the front Symbol coating layer gradually thinner towards the top of the constricted portion, the content of the covering layer a stellite alloy or chromium, Is formed of a chromium-iron alloy having 60% by weight or more, the thickness of the coating layer excluding the upper end portion is set to 30 μm or more, and the coating layer is formed of a thermal sprayed layer by plasma spraying. It is preferable to employ

[0012]

Action and effect of the present invention
In a sulfur battery, since the coating layer of the substrate constituting the anode container is located at the upper end surface of the anode active material accommodated in the anode container or at a position higher than this, the substrate constituting the anode container is polysulfided. It can be prevented from corrosion by sodium. Also, in the sodium-sulfur battery, when the coating layer reaches only the top of the constricted portion of the substrate at the maximum and reaches upward from the lower base end of the constricted portion, the base end From the top to the top, the thermal deformation of the constricted part is not subject to any regulation by the coating layer, or the regulation is greatly suppressed, so that the occurrence of cracks in the coating layer is remarkable. Can be reduced.

Further, in the sodium-sulfur battery, the inner peripheral surface of the straight pipe portion below the top of the constricted portion of the substrate is covered with a coating layer, and the entire inner peripheral surface of the conventional substrate is covered. Is not coated with a coating layer, so that the amount of material used for forming the coating layer can be reduced, and the time for forming the coating layer can be shortened, and the cost of the anode container can be reduced. it can.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

(Sodium-sulfur battery) Hereinafter, the sodium-sulfur battery according to the present invention will be described with reference to the drawings. FIG. 1 shows a longitudinal section of a sodium-sulfur battery according to one embodiment of the present invention. The sodium-sulfur battery has an anode container 10a and a solid electrolyte 10b as main components, and a cathode active material 10c and an anode active material 10d as main components. Further, the anode container 10 a is composed of a bottomed cylindrical base 11 and a coating layer 12.

The base 11 is a bottomed cylinder made of aluminum or an aluminum alloy, and the coating layer 12 is made of a sprayed layer of a chromium-iron alloy or a stellite alloy. It is formed on the inner peripheral surface of the base 11. Thus, in the sodium-sulfur battery, a constricted portion having a corrugated cross section is formed at a position above the base 11 constituting the anode container 10a.
1 is formed on both the lower straight pipe portion 11a and the constricted portion 11b.

The solid electrolyte 10b is a cylindrical body having a bottom and has sodium ion permeability, and is made of beta alumina. The solid electrolyte 10b is fitted on an insulating ring 13 made of alpha alumina, and is disposed concentrically in the anode container 10a with the insulating ring 13 fixed to the upper end opening of the anode container 10a. Have been. The lid 14a has a cathode terminal 14b and is fixed to the upper surface of the insulating ring 13 to cover the insulating ring 13. Thereby, the insulating ring 13 and the lid 14a seal the anode container 10a and the solid electrolyte 10b,
The inside of the solid electrolyte 10b is configured as a cathode chamber, and the anode container 1
The space between Oa and the solid electrolyte 10b is an anode chamber. The base 11 forming the anode container 10a has an anode terminal (not shown).

In the sodium-sulfur battery, the cathode compartment contains the cathode active material 10c, and the anode compartment contains the anode active material 10d. The cathode active material 10c is made of metallic sodium and is housed in the cathode compartment. Also,
The anode active material 10d is made of sulfur, and is housed in the anode chamber with graphite felt interposed.

In the sodium-sulfur battery, when the battery is heated to 300 to 350 ° C., an open circuit voltage of about 2.08 V is exhibited. When an external load is connected to the battery, sodium as a cathode active material is ionized in the battery. , Sodium ions permeate the solid electrolyte 10b and pass through the anode active material 10b.
d, and reacts with sulfur, which is the same active material 10d, to generate sodium polysulfide and discharge. In addition, in the sodium-sulfur battery, a reaction opposite to the above occurs at the time of charging, and the battery is charged.

In the sodium-sulfur battery, the anode container 10a is composed of the base 11 and the coating layer 12, and the coating layer 12 extends from the lower end of the base 11 to the upper end of the anode active material 10d. positioned. Therefore,
The coating layer 12 covers almost the entire inner peripheral surface of the straight pipe portion 11a of the base 11, and does not cover the inner peripheral surface of the constricted portion 11b at all.

In the sodium-sulfur battery constructed as described above, the coating layer 12 of the base 11 constituting the anode container 10a covers substantially the entire inner peripheral surface of the straight pipe portion 11a of the base 11 and is attached to the anode container 10a. The contained anode active material 10d
The base 11 can be prevented from being corroded by sodium polysulfide. Further, since the coating layer 12 does not reach the lower base end of the constricted portion 11b of the base 11, there is no regulation of the coating layer 12 on the thermal deformation of the constricted portion 11b. The generation of cracks in the coating layer 12 can be significantly reduced.

The anode container 10a constituting the sodium-sulfur battery can be formed by plasma spraying in the atmosphere as shown in FIG. In this case, a cylindrical masking jig 15 is inserted from one end opening of the base 11 and is hooked to the opening end at the outward flange portion, so that a portion corresponding to the upper end surface of the anode active material of the base 11 is Mask the upper end portion and place the spraying gun 16 in the masking jig 15.
Insert and spray. Thereby, the straight pipe portion 1 of the base 11
A thermal spray layer is formed on almost the entire inner peripheral surface of 1a, and a coating layer 12 of the thermal spray layer is formed.

As a material for thermal spraying, a powder of a stellite alloy and a powder of a chromium-iron alloy having a chromium content of 60% by weight or more are used. As a plasma condition, argon (30 to 60 l / min) is used as a primary gas. ) Is replaced with hydrogen gas (0.8-3.
0 l / min) is sprayed under the conditions of a current of 230 to 300 A and a plasma output of 8.5 to 12.5 kW, employing argon as a carrier gas for transferring the raw material powder. The thermal spraying is performed by moving the thermal spray gun 16 in the vertical direction while rotating the base 11 at 300 to 500 rpm.

Therefore, in the sodium-sulfur battery, the straight pipe portion 11 below the narrow portion 11b of the base 11 is provided.
Since only the inner peripheral surface of a is coated with the coating layer 12 and the entire inner peripheral surface of the substrate as in the conventional case is not coated with the coating layer, the amount of the spray material used as the material for forming the coating layer 12 is reduced. Can be reduced, and the time for forming the coating layer 12 can be shortened, so that the cost of the anode container 10a can be reduced.

(Experiment) In this experiment, the sodium-sulfur battery shown in FIG. 1 was constructed using the anode container 10a shown in FIGS. A heat cycle test was conducted to measure the state of occurrence of cracks. In the heat cycle test, the process of raising the temperature of the sodium-sulfur battery from room temperature to 420 ° C. in 4 hours, maintaining the temperature for 5 hours, and then lowering the temperature to room temperature in 4 hours is defined as one cycle (heat cycle), and this cycle is repeated 60 times. The battery is disassembled and the anode container 1
Oa was taken out, and the state of occurrence of cracks in the coating layer 12 was measured by an X-ray transmission method. The results obtained are shown in the graph of FIG.

However, each anode container has a base 11 made of an aluminum alloy having a length of 300 mm, an outer diameter of 50 mm and a thickness of 1.4 mm, and a chromium-iron alloy (chromium content of 75% by weight) on the inner peripheral surface thereof. This is to be formed by the coating layer 12 having a thickness of 80 μm formed by thermal spraying. FIG. 3A shows an anode container (N) in which the upper end of the coating layer 12 reaches the top of the constricted portion 11b.
O. 1), FIG. 1B shows an anode container (NO. 2) in which the upper end of the coating layer 12 reaches an intermediate portion between the lower base end and the top of the constricted portion 11b, and FIG. The anode container (N) whose upper end reaches the lower base end of the constricted part 11b
O. 3), FIG. 4 shows that the upper end of the coating layer 12 has a constricted portion 11b.
Anode container (NO. 4) reaching the upper end of the substrate 11 over the top of the anode container.

Referring to the graph of FIG. 5, the anode container (N) in which the coating layer 12 covers the entire inner peripheral surface of the base 11 is shown.
O. 4) are the other anode containers (NO. 1 to NO. N) in which the upper end of the coating layer 12 is not more than the top of the constricted portion 11b of the base 11.
O. The number of cracks in the coating layer 12 is remarkably large as compared with 3). In addition, each anode container 10a (NO.
O. There is also a slight difference in the number of cracks generated between 3),
The closer the upper end of the coating layer 12 is to the top of the constricted portion 11b of the substrate 11, the more cracks are generated.

Therefore, considering the occurrence of cracks in the coating layer 12, the anode container 10a of the sodium-sulfur battery has an upper end portion similar to that of the anode container 10a shown in FIGS. Anode active material 1 in 11
The anode container 10a located between the upper end surface of Od and the top of the constricted portion 11b is suitable. Particularly, in consideration of both the corrosion prevention function of the coating layer 12 and the generation of cracks, The anode container 10a whose upper end is located at the lower base end of the constricted portion 11b of the base 11 as shown in FIG. 3C is most suitable.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a sodium-sulfur battery according to one embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a production example of an anode container constituting the anode container of the sodium-sulfur battery.

FIG. 3 is a partial longitudinal sectional view showing various examples of an anode container.

FIG. 4 is a partial longitudinal sectional view showing a conventional anode container.

FIG. 5 is a graph showing the state of occurrence of cracks in a coating layer with respect to the number of heat cycles of each anode container.

[Explanation of symbols]

10a: Anode container, 10b: Solid electrolyte, 10c: Cathode active material, 10d: Anode active material, 11: Base, 11a: Straight tube portion, 11b: Constricted portion, 12: Coating layer, 14: Masking jig, 16 ... Thermal spray gun.

Claims (4)

(57) [Claims] An anode container having a coating layer made of a metal having higher corrosion resistance than a metal substrate and a sodium ion disposed inside the anode container. A bottomed cylindrical ceramic solid electrolyte that can transmit
A cathode active material comprising metallic sodium contained in the solid electrolyte; and an anode active material comprising sulfur contained between the solid electrolyte and the anode container. In a sodium-sulfur battery that includes a constricted portion bent in the radial direction and performs a charge / discharge operation in a heated state, the constricted portion is located at a position above an upper end surface of the anode active material , and the coating layer is same from the lower proximal end of the upper end is the constriction extends to the site of the upper end surface of the lower portion or found before Symbol cathode active material of the base body
A sodium-sulfur battery located between the tops of the constrictions . 2. The sodium-sulfur battery according to claim 1, wherein an upper end of the coating layer faces a top of the constriction.
A sodium-sulfur battery characterized in that it is formed gradually thinner . 3. The sodium-sulfur battery according to claim 1 , wherein the coating layer is made of a stellite alloy.
Is a chromium-iron alloy containing 60% by weight or more of chromium
And the thickness excluding the upper end of the coating layer is 3
A sodium-sulfur battery having a thickness of 0 μm or more . 4. The sodium-sulfur battery according to claim 1, wherein said coating layer is formed by plasma spraying.
A sodium-sulfur battery formed by a thermal spray layer .