JPH0770325B2 - Sodium-sulfur battery - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sodium-sulfur battery, and in particular, an alumina-based ceramic solid electrolyte disposed between a cathode active material and an anode active material to separate the two materials. Reinforcement of.

[Prior Art] The development of secondary batteries for electric power storage has been attracting attention in recent years, and among them, sodium-sulfur batteries are regarded as important because of their excellent performance and economical efficiency. An example of a specific structure of the sodium-sulfur battery is shown in FIG. In FIG. 6, molten sodium is used as the cathode active material 1, molten sulfur and sodium polysulfide are used as the anode active material 2, and a solid electrolyte 3 having sodium ion (Na ⁺ ion) conductivity is used as the electrolyte. Is. Since the electrolyte 3 has high conductivity of sodium ions, β-type alumina (β-alumina: Na ₂ O · 11Al ₂ O ₃ , β ″ -alumina: Na ₂ O · 6Al ₂ O ₃ )
Is used. Since β-alumina does not have electronic conductivity, it also serves as a partition wall that separates the cathode and the anode.
In FIG. 6, 4 is a cathode chamber container, 5 is an anode chamber container, and an insulating material 6 made of α-alumina or the like is provided around the peripheral portion.
It is assembled by crimping a tightening band 7 made of stainless steel through. Considering the melting point of the anode active material 2, the operating temperature of this battery is considered to be 300 ° C. or higher. The charge / discharge reaction is Therefore, the battery as a whole is as follows.

However, X is usually in the range of 3 to 5.

The solid electrolyte β-based alumina used in the sodium-sulfur battery has a smaller thermal expansion coefficient and thermal conductivity than a metal material, and generally has a small mechanical strength. Therefore, the solid electrolyte is damaged by the temperature difference at the time of starting and stopping the battery, the volume expansion difference between the cathode and the anode active material, and the pressure difference between the cathode chamber and the anode chamber caused by the progress of the battery reaction. there's a possibility that. When the solid electrolyte is damaged, sodium and sulfur of both active materials react with each other.For example, the temperature reached from the reaction heat of both active materials is estimated to be about 850 for a single cell of about 10 Ah.
The boiling point temperature of sodium may reach 883 ℃.

The solid electrolyte is preferably as thin as possible in order to improve the ionic conductivity, but as it becomes thinner, the mechanical strength becomes smaller. Therefore, a stainless steel metal strip having a width substantially equal to the thickness of the cathode chamber is provided as a reinforcing member in the cathode chamber so as to be perpendicular to the surface of the solid electrolyte, thereby giving bending or crossing as a reinforcing member to provide self-supporting property and to prevent sodium migration. There is a conventional example in which the solid electrolyte surface is partially contacted so as not to become an obstacle.

[Problems to be solved by the invention]

However, once the damage of the solid electrolyte occurs, the damage may propagate and spread around the site. With the reinforcement as in the above-mentioned conventional example, the effect of preventing the propagation of such damage is small. Therefore, there is a demand for the development of a reinforcing method that does not lead to large damage even if the solid electrolyte is cracked. As one method, it is possible to attach a metal material having high mechanical strength to the surface of the solid electrolyte. As a metal material, stainless steel is generally required to be used from the viewpoint of corrosion resistance against an active material, but there has been no technique for easily joining stainless steel and a solid electrolyte.

The object of the present invention is to solve the above problems, in a sodium-sulfur battery having a solid electrolyte of alumina ceramics, it is possible to join the solid electrolyte and a reinforcing material to reinforce the solid electrolyte, by this joining It is an object of the present invention to provide a sodium-sulfur battery capable of preventing the damage of the battery and the spread of its propagation.

[Means for solving problems]

As a result of intensive studies conducted by the present inventors in order to achieve the above object, the inventors have obtained a new finding that alumina-based ceramics are bonded to various reinforcing members through a layer made of a titanium-based compound.

The present invention has been made based on such findings,
The structure is such that a cathode active material using molten sodium, an anode active material using molten sulfur, and a solid electrolyte of an alumina-based ceramic disposed between the cathode active material and the anode active material to separate the two materials. In the sodium-sulfur battery having the solid electrolyte, the solid electrolyte is reinforced by a reinforcing material joined through a layer made of a titanium compound.

[Action]

According to the configuration of the present invention, a reinforcing material coated with a titanium compound such as titanium nitride or titanium carbide on the surface or a reinforcing material containing a titanium compound is heated in vacuum by contacting with a solid electrolyte of an alumina ceramic. Then, the titanium-based compound coated on the surface of the reinforcing material or the titanium-based compound in the reinforcing material diffuses, precipitates, and grows from the solid electrolyte surface of the alumina ceramic to the inside, and acts as a kind of nailing effect, Adhesion between the solid electrolyte of the alumina-based ceramic and the reinforcing material is improved. As a result, the solid electrolyte of the alumina-based ceramic is reinforced by being joined to the reinforcing material through the layer made of the titanium-based compound and the mechanical strength is increased, so that damage due to various external forces generated during the operation of the sodium-sulfur battery is caused. And it is possible to prevent the damage from expanding. In addition, Na ₂ Sx, which is a reaction product of a sodium-sulfur battery, is highly corrosive,
The titanium-based compound, which is a joining medium, has excellent corrosion resistance and is optimal as a joining medium between the solid electrolyte of the sodium-sulfur battery and the reinforcing material.

〔Example〕

Next, examples of the sodium-sulfur battery according to the present invention will be described. The solid electrolyte constituting the sodium-sulfur battery of the present invention is a solid electrolyte of an alumina-based ceramic that is disposed between a cathode active material and an anode active material and separates both materials, and is a Na ⁺ permeable solid electrolyte. is there.

FIG. 1 is a sectional view showing the structure of the embodiment.

The joining state of the solid electrolyte and the metal as the reinforcing material is as shown in FIG. As the reinforcing material 8 of the solid electrolyte 3 containing β-based alumina as a main component, a metal such as stainless steel having high temperature resistance and excellent corrosion resistance is used, and the solid electrolyte 3 is bonded to titanium carbide or titanium nitride. Is performed through a bonding medium 9 which is a layer made of a titanium compound such as. Further, the reinforcing material 8 and the joining medium 9 are provided with sodium ion conducting holes 10 at the same position as shown in FIG.
It does not interfere with the movement of sodium ions between the solid electrolyte 3 and the cathode chamber.

The method for providing the bonding medium 9 between the solid electrolyte 3 and the reinforcing material 8 is to coat a titanium compound on the bonding surface side of the reinforcing material 8 with the solid electrolyte 3 by a method such as an ion plating method or a sputtering method. A thin film of titanium compound is provided. This coating surface is bonded to the solid electrolyte 3. That is, it is a method of previously providing the joining medium on the reinforcing material 8. Another method is to use a metal containing titanium as the material of the reinforcing material 8, such as stainless steel SUS321,
This is a method in which a titanium-based compound such as titanium carbide is deposited and grown in the alloy from the surface to the inside of the solid electrolyte 3 when the solid electrolyte 3 is joined to the joining surface.

In any of the above methods, heat treatment is performed in a vacuum at about 700 to 1000 ° C. under pressure to bond them. The bonding mechanism is a kind of nailing effect in which the titanium-based compound that becomes the bonding medium 9 by heating treatment precipitates and grows on the contact interface with β-alumina, which is the main component of the solid electrolyte 3, and inside the structure. To work.

When a metal containing titanium is used as the material of the reinforcing material 8, titanium is chemically bonded to carbon contained in the material to form titanium carbide and precipitates and grows in the alumina ceramic.

As a result, the solid electrolyte 3 is reinforced by the reinforcing material 8 via the bonding medium 9.
Will be joined and integrated. As a result, the mechanical strength at the interface is improved.

In the above-described embodiment, a pressure rise during battery operation occurs in the anode chamber, and a force directed to the cathode chamber side acts on the solid electrolyte 3, so that the reinforcing member 8 is joined to the cathode chamber side. Although shown, the reinforcing material 8 can also be joined to both sides of the solid electrolyte 3, that is, the anode chamber side. The joining can be performed by the same method as in the above embodiment, and the joining mechanism is also the same. The advantage of providing the reinforcing materials 8 on both sides of the solid electrolyte is that not only the mechanical strength of the solid electrolyte 3 is further improved, but also in the unlikely event that the solid electrolyte 3 is damaged, the broken pieces are retained in both the reinforcing materials. That is, it is possible to prevent mixing and dispersion in the active material.

Although the titanium compound is coated on the reinforcing material 8 in the present embodiment, it is also possible to form the bonding medium 9 by coating the titanium compound on the solid electrolyte side which is an alumina ceramic material.

Further, in the above-described embodiment, the reinforcing material 8 and the joining medium 9 are mechanically processed with the through holes 10 for allowing sodium ions to pass through. However, the reinforcing material 8 has a porous property, for example, a fine mesh or fibrous stainless steel. You may use metals, such as. In this case, sodium ion conduction is performed without mechanical processing, and the function as a battery is ensured.

The thickness of the joining medium 9 increases according to the amount of titanium contained in the coating layer or the reinforcing material. In addition, the longer the heating time, the larger the heating time.

As another embodiment, as shown in FIG.
Then, the reinforcing material 8 is sandwiched in the shape of a Saint-Gerache. The joining method at that time is as follows.
Is provided by a method similar to that described above.

According to the present embodiment, since the reinforcing material 8 is provided in the central portion, when pressure is applied to the solid electrolyte 3, the solid electrolyte 3 can be reinforced while the pressure is evenly distributed. .

In each of the above-described examples, the reinforcing material 8 is bonded to the completed solid electrolyte 3 having the function for a battery, but it is bonded to the reinforcing material in the manufacturing process of the solid electrolyte 3. You can also That is, as shown in FIG. 3, the reinforcing material 8 formed in accordance with the size of the solid electrolyte 3
After applying and molding β-alumina that has been crushed and granulated on both sides of
By sintering at about 1500 ° C., the solid electrolyte 3 having the reinforcing material 8 therein can be manufactured. FIG. 3 is a partial cross-sectional view of the solid electrolyte 3 obtained by this manufacturing method. In this case, about 1500
It is not possible to use the metals mentioned above, such as stainless steel, for sintering at ° C. Therefore, titanium-based ceramics such as titanium carbide or titanium nitride itself is used, and the titanium-based ceramics itself is joined to β-based alumina by the same mechanism as described in FIG. Further, in the present embodiment, as shown in FIG. 2, the structure of the solid electrolyte 3 is similar, but the β-type alumina is also filled in the ion conducting hole 10. Therefore, when the solid electrolyte 3 is reinforced by the method shown in FIG. 2, the presence of gaseous impurities, which may be mixed in the ion conduction hole 10, even though it is a little, is eliminated, and the influence on the ion migration speed is affected. Can be completely ignored.

4 and 5 show two embodiments of the sodium-sulfur battery according to the present invention. FIG. 4 uses a plate-shaped solid electrolyte 3 shown in the conventional example of FIG. 6 to which a reinforcing material 8 according to the present invention is joined, and FIG. 5 shows another solid electrolyte having a cylindrical shape. 2 shows an example in which the present invention is applied to a solid electrolyte 3 having a shape of a circle.

In FIG. 5, the cathode active material 1 is filled inside the cylindrical solid electrolyte 3. Further, the outside is filled with an anode active material 2, which is held by an anode chamber container 5 reinforced by a corrosion-resistant metal plate 11. Electricity is taken out from the cathode rod 12 inserted in the cathode active material 1 and the anode chamber container. The principle as a battery is the same as that shown in the conventional example of FIG.

Generally, the damage of the solid electrolyte 3 is considered to occur initially due to local pinholes or cracks. However, the joint portion of the solid electrolyte 3 and the reinforcing material 8 according to the present invention is not a full joint but a fine non-joint surface ( Ion conduction hole as shown in Fig. 1
10 is present), and the periphery of the non-bonding surface is surrounded by a strong bonding surface (bonding medium 9 in FIG. 1). Therefore, in the event of damage, the negative and positive active materials that participate in the reaction pass only through this fine non-bonding surface, the reaction amount is suppressed, and the instantaneous reaction between sodium and sulfur is suppressed. It can be suppressed. Further, the expansion of the breakage is suppressed and prevented by the strong joint surface surrounding the non-joint surface.

The case where the present invention is applied to the sealed solid electrolyte of a sodium-sulfur battery has been described above.
It is needless to say that it can be applied not only as a fluid-type solid electrolyte disclosed in Japanese Patent No. 869, but also as a bonding material between alumina and a stainless steel which is a reinforcing material in the fields of nuclear power, thermal power, automobiles, aircraft, electronics, and the like. It can also be used as a Na ⁺ permeable solid electrolyte for sodium thermoelectric generators and as a cation permeable solid electrolyte for Na ⁺ , K ⁺ , Ca ⁺ sensors.

〔The invention's effect〕

As described above, the solid electrolyte of the sodium-sulfur battery of the present invention is reinforced by the reinforcing material joined through the layer made of the titanium-based compound, and thus the contact interface between the solid electrolyte and the reinforcing material and Due to the nailing effect of the layer composed of the titanium-based compound diffused, precipitated, and grown from the surface to the inside of the solid electrolyte of the alumina-based ceramic,
As the strength of the solid electrolyte reinforcement material increases,
Prevents damage to the solid electrolyte and propagation of the damage due to temperature difference when starting and stopping the battery, difference in volume expansion between the cathode and anode active materials, and pressure difference between the cathode chamber and anode chamber caused by the progress of the battery reaction. can do. In addition, Na ₂ Sx, which is a reaction product of sodium-sulfur battery, is highly corrosive, but the titanium-based compound that is the bonding medium is excellent in corrosion resistance, and the bonding medium between the solid electrolyte and the reinforcing material of the sodium-sulfur battery is As is the best.

[Brief description of drawings]

FIG. 1 shows an embodiment of a sodium-sulfur battery according to the present invention, a cross-sectional view of a state in which a reinforcing material is joined to one side of a solid electrolyte, and FIG. 2 shows a sodium-sulfur battery according to the present invention.
FIG. 3 is a cross-sectional view showing another embodiment of a sulfur battery in which a reinforcing material is sandwiched between solid electrolytes, and FIG. 3 shows still another embodiment, in which the reinforcing material is provided inside the solid electrolyte. FIG. 4 is a sectional view of the sodium-sulfur battery according to the present invention, and FIG. 6 is a sectional view of the sodium-sulfur battery according to the related art. 1 ... Cathode active material, 2 ... Anode active material, 3 ... Solid electrolyte, 8 ... Reinforcing material, 9 ... Bonding medium, 10 ... Ion conducting hole.

Front page continuation (72) Inventor Naoshi Soma 1168 Moriyama-cho, Hitachi, Hitachi, Ibaraki Energy Research Institute, Hitachi Ltd. (72) Shigehiro Shimoyashiki, Inventor 1168, Moriyama-cho, Hitachi, Hitachi Energy Research In-house (56) Reference JP-A-58-41774 (JP, A) JP-A-60-180658 (JP, A) Practical application Sho-53-8539 (JP, U)

Claims (5)

[Claims] 1. A cathode active material using molten sodium, an anode active material using molten sulfur, and a solid electrolyte of an alumina-based ceramic which is disposed between the cathode active material and the anode active material to separate the two materials. In the sodium-sulfur battery, the solid electrolyte is reinforced by a reinforcing material joined via a layer made of a titanium-based compound. 2. The titanium compound according to claim 1, wherein the titanium compound is titanium nitride (TiN) or titanium carbide (TiC).
And a sodium-sulfur battery. 3. The sodium-sulfur battery according to claim 1 or 2, wherein the reinforcing material is a metal containing titanium and carbon or nitrogen. 4. The reinforcing material according to claim 1 or 2, wherein the reinforcing material is a titanium-carbon based ceramic, and the reinforcing material is joined through a diffusion layer of titanium carbide diffused from the surface to the inside of the solid electrolyte. A sodium-sulfur battery comprising the reinforcing material. 5. A sodium-sulfur battery according to any one of claims 1 to 4, wherein the solid electrolyte is provided with the reinforcing material bonded to both surfaces of the solid electrolyte.