JPH1197058A - Sodium-sulfur cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a NAS cell in which a pressure releasing part is ruptured only by the rise of internal pressure due to the temperature rise in the case of abnormality, and in which the rupture of the pressure releasing part by the rise of the internal pressure in the normal operation is prevented. SOLUTION: This cell comprises: a cylindrical positive electrode mold 6 impregnated with sulfur 12 as a positive electrode active material; a positive electrode container 3 for accomodating the positive electrode mold 6; an insulator ring 2 for connecting the positive electrode container 3 to a negative electrode hardware 4; and a bottomed cylindrical soild electrolyte tube 5 connected to an inner peripheral part of the insulator ring 2; and sodium 7 as the negative electrode active material is accomodated in an internal space formed by the soild electrolyte tube 5 and the negative electrode hardware 4. A pressure releasing part 14 to be ruptured by the rise of the internal temperature and the internal pressure of the positive electrode container 3, is formed on a part of the positive electrode container 3, and the pressure relative part 14 is formed in such manner that it is ruptured when the internal temperature of the positive electrode container 3 is within the range of 444 to 660 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a pressure-reducing portion that cleaves by utilizing a decrease in strength of a material constituting an anode container due to a rise in temperature and a rise in the internal pressure of the anode container. The present invention relates to a sodium-sulfur cell in which an active material is discharged outside an anode container to prevent a direct reaction between sodium and sulfur and an explosion of the cell accompanying the reaction.

[0002]

2. Description of the Related Art A sodium-sulfur battery (hereinafter, referred to as a NAS battery) is a high-temperature secondary battery operated at 300 to 350 ° C. Usually, a battery module in which a plurality of unit cells are erected and assembled is insulated. It is used in the form of a collective battery housed in a container. The unit cell, while storing the anode active material sulfur and the cathode active material sodium in the anode metal container inside and outside the solid electrolyte tube made of β-alumina, the active material is in contact with the outside air. A structure is adopted in which the inside of the anode container is hermetically sealed so as to be maintained in a state.

[0003] Therefore, when abnormal heating of the heater, overdischarge, or the like occurs, first, the temperature of the unit cell rises, and accordingly, the vapor pressure of the molten sulfur contained in the anode container increases, and the cell is placed in the anode container. The installed solid electrolyte tube is destroyed,
Eventually, the molten metal sodium and the molten sulfur, which are separated and housed inside and outside by the solid electrolyte tube, come into direct contact with each other to cause a chemical reaction.

[0004] When sulfur and sodium react directly, a large amount of high-temperature flame due to the heat of the reaction also damages the heat insulating container housing the battery module, and there is a risk that the flame spreads outside the heat insulating container. Is done. Therefore, there has been proposed a NAS cell in which a sealed part of the anode container is opened by providing a pressure-releasing portion in a part of the anode container so as to be broken by an increase in the internal pressure, thereby preventing a problem due to the increase in the internal pressure. JP-A-50-143031, JP-A-56-78063, and JP-A-56-84274.

[0005]

Problems to be Solved by the Invention
All NAS cells release internal pressure generated in the anode container,
Although effective in preventing volume expansion and explosion of the anode container due to an increase in internal pressure, there is a possibility that the decompression portion may be broken even during normal battery operation.

[0006] That is, as described above, the NAS cell is 300 to 350
Since the battery is operated at a high temperature of ° C., some internal pressure is generated in the hermetically sealed anode container even during normal operation. Therefore, depending on the design of the decompression unit, there is a possibility that the decompression unit is also split by the internal pressure generated during the normal operation, and sulfur or the like of the active material stored in the anode container is released outside the anode container. is there.

[0007] Once the anode container has been broken,
Such a situation needs to be prevented because the NAS battery becomes unusable. The present invention has been made in view of such problems of the related art, and the object thereof is to:
An object of the present invention is to provide a NAS unit cell in which a pressure-reducing portion is broken only by an increase in internal pressure due to a temperature rise at the time of occurrence of an abnormality, and the cracking portion is prevented from being broken by a rise in internal pressure during normal operation.

[0008]

According to the present invention, a cylindrical anode mold impregnated with sulfur as an anode active material;
An anode container for accommodating the anode mold, an insulator ring for joining the anode container and the cathode metal fitting, a bottomed cylindrical solid electrolyte tube joined to an inner peripheral portion of the insulator ring, and the solid electrolyte; A cartridge containing sodium, which is a cathode active material, disposed in an internal space formed by a tube and the cathode fitting; and a bottomed cylindrical shape disposed in a gap between the cartridge and the solid electrolyte tube. In a sodium-sulfur cell configured with a partition tube of
In a part of the anode container, a decompressed portion that is cleaved by an increase in the internal temperature and internal pressure of the anode container is formed, and the internal pressure of the anode container is within a range of 444 ° C or more and 660 ° C or less. And a sodium-sulfur unit cell is provided. In addition, in the sodium-sulfur unit cell of the present invention, it is preferable that the pressure-releasing unit is provided at the bottom of the anode container.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a NAS cell, and first, an overall structure of a general NAS cell will be outlined. For example, as shown in FIG. 2, the NAS unit cell includes a cylindrical anode mold 36 impregnated with sulfur 42 as an anode active material, an anode container 33 containing the anode mold 36, an anode container 33 and an insulator ring 32. Metal fitting 34, a bottomed cylindrical solid electrolyte tube 35 bonded to the inner periphery of insulator ring 32, and cathode metal fitting 34
And a solid electrolyte tube 35, and accommodates sodium 37, which is a cathode active material, provided in an internal space formed by the solid electrolyte tube 35.

In the NAS unit cell, metallic sodium as a cathode active material and sulfur as an anode active material are separated and stored by a solid electrolyte tube, and an inner bottom portion of an insulated container for housing a whole battery module in which a plurality of unit cells are assembled. Heat the inside of the insulated container to 300-350 ° C by the electric heater
An electrochemical reaction is performed by melting the both active materials and moving the ions to obtain a predetermined energy.

Next, the configuration of the NAS cell of the present invention will be described in detail with reference to the drawings. The NAS cell of the present invention is, for example, as shown in FIG.
A pressure release portion 14 is provided in a part of the anode container 3 of the cell 1 so as to be cleaved by an increase in the internal pressure of the anode container 3. By doing so, when the internal pressure of the anode container 3 rises, first before the solid electrolyte tube 5 is broken,
Since the anode 4 is opened and the sealed state of the anode container 3 is opened, the situation in which the solid electrolyte tube 5 is broken by the internal pressure can be avoided.

As a structure of the pressure release unit 14, for example, a method that is fragile compared to other parts of the anode container 3 can be considered. More specifically, as shown in FIG. It is conceivable to form the thin portion 16 at a part of the three bottoms. In this case, it is theoretically possible to adjust the thickness of the thin portion 16 to release the pressure at a desired internal pressure.

[0013] However, as described above, the NAS cell increases the internal pressure of the anode container even during normal operation.
In practice, it is not easy to control so as to cleave the decompression section only when an abnormality occurs. That is, it is necessary to differentiate and recognize the rise in internal pressure during normal battery operation and the rise in internal pressure when an abnormality occurs.

Here, since the boiling point of sulfur used as the anode active material of the NAS unit cell is 444 ° C./1 atm,
At a normal battery operating temperature of 300 to 350 ° C., the vapor pressure of sulfur is relatively low. Therefore, during normal operation, the fluctuation range of the internal pressure of the anode container due to the vapor pressure of sulfur can be suppressed to a certain low level.

[0015] Further, the sulfur is at 300 to 350 ° C. as described above.
In a low temperature range such as this, the S ₈ molecule has a basic structure, but in a temperature range above the boiling point, S ₈ molecules increase with increasing temperature.
Molecules having a small number of atoms, such as S ₆ , S ₄ , and S ₂ , which are generated by the decomposition of _eight molecules, are dominant. That is, the number of molecules of gaseous sulfur doubles with an increase in temperature.

Therefore, as shown in the graph of FIG. 3, the vapor pressure of the sulfur gas does not gradually increase with the temperature rise as in the case of ordinary gas molecules.
It will increase at an accelerated rate due to the doubling effect of the number of molecules accompanying the decomposition of the molecules. The pressure-releasing portion, which is a part of the anode container, is usually made of an aluminum alloy of the same material as the anode container. The tensile strength of this aluminum alloy also has a correlation with temperature, and is shown in the graph of FIG. As the temperature rises.

The present inventors have paid attention to such properties of the sulfur and aluminum alloy and have conceived of controlling the cleavage of the decompression section. That is, in the NAS cell of the present invention, the boiling point of sulfur at 1 atm where the vapor pressure of sulfur rapidly rises
It is configured so that the decompression part is cleaved at 444 ° C or more. Four
At a temperature of 44 ° C, in addition to the rapid increase in sulfur vapor pressure, the tensile strength of the aluminum alloy that constitutes the decompression unit also decreases to about 1/2 to 1/3 of that during normal operation. It is relatively easy to design such that the decompression part is cleaved only under such conditions. Therefore, it is possible to differentiate the pressure relief part so that the pressure release part is not broken by the increase in the internal pressure during the normal operation at 300 to 350 ° C.

In the NAS cell of the present invention,
It is necessary to configure the decompression part to be split at 660 ° C or lower, which is the melting point of aluminum. This is because the anode container is mainly made of aluminum and is melted and broken at 660 ° C. or higher.

In order to decompress the anode container made of an aluminum alloy bottomed cylindrical tube in a temperature range of 444 ° C. to 660 ° C., the bottom thin portion is formed by the internal pressure of the anode container in a temperature range of 444 ° C. to 660 ° C. May be designed so that the stress value generated at the same time balances the tensile strength of the aluminum alloy in that temperature range. The thin portion can be provided by machining, etching, or another method.

The decompression unit may be disposed at any part of the anode container. However, by providing the decompression unit on the side surface or the bottom surface of the anode container, the vapor pressure of sulfur itself and the decompression unit are configured. This is preferable in that sulfur can be discharged to the outside of the anode container by utilizing the reduction in the material strength of the aluminum alloy itself, and the possibility of contact between sulfur and sodium can be reduced in combination with the arrangement of the external container described later.

In consideration of more complete discharge of sulfur from the anode container, it is more preferable to provide a decompression section at the bottom of the anode container. Since the bottom surface of the solid electrolyte tube is usually formed thicker than the side surface, the bottom surface of the anode container hardly contributes to the battery reaction and is hardly affected by corrosion. It is also preferable from the aspect that the thickness becomes thin and a situation in which the internal pressure is released at a lower internal pressure than designed can be avoided.

In the present invention, the anode container is provided with the above-described pressure relief section, and the anode container is accommodated therein.
In addition, it is preferable to dispose a bottomed cylindrical outer container for discharging sulfur released from the cracked decompression unit to above the anode container. By doing so, even if the pressure release part is broken by the internal pressure rise of the anode container and sulfur is released,
Due to its vapor pressure, sulfur having a relatively low boiling point (bp .: 444 ° C., 1 atm) is discharged to the outside of the outer container along the side wall of the outer container.

Therefore, after the sulfur is released out of the anode container, if a safety tube or a cartridge disposed in the cathode chamber as described in, for example, JP-A-5-283101 is used, Even if the solid electrolyte tube is damaged due to thermal stress on the solid electrolyte tube due to thermal expansion of the sodium electrolyte and sodium flows out of the anode container through the same path as sulfur, the sulfur has already been released outside the external container. Since sodium having a relatively high boiling point (bp .: 897 ° C., 1 atm) stays in the outer container unless the temperature becomes considerably high, the direct reaction between sulfur and sodium can be avoided.

In the present invention, the term “outer container” refers to a bottomed cylindrical container having an inner diameter capable of loosely inserting the anode container and having an open top. As in the present invention, as a NAS unit cell in which the anode container is housed in an external container, as shown in JP-A-5-109433, the anode container is housed in a rigid container having an annular projection, NA that prevents axial elongation
S cells have been proposed.

This unit cell is similar to the present invention in that the anode container is housed in an external container, but is different from the present invention, and aims at preventing the anode container from extending in the axial direction. Therefore, it is sufficient to provide annular projections on the upper and lower surfaces of the rigid container, and the bottom of the rigid container is in an open state.

On the other hand, in the present invention, since it is necessary to release the sulfur flowing out of the anode container to the upper part of the anode container and to capture the sodium flowing out of the anode container, it is necessary to use a bottomed container. It is clearly different in that it is essential. However, also in the present invention, it is preferable to provide an annular projection on the upper end surface of the outer container in order to hold the anode container in the outer container or to obtain the same effect as the NAS unit cell.

The outer diameter of the outer container is formed to be larger than the anode container so that the anode container can be loosely inserted. If the outer surface of the anode container and the inner surface of the outer container are not in close contact with the anode container loaded, Good. By doing so, the sulfur flowing out of the anode container decompression section is discharged to the outside of the external container through the gap between the anode container and the side surface of the external container. The material of the outer container is not particularly limited as long as it has corrosion resistance to sulfur and sodium. For example, stainless steel, ceramics, or the like can be used.

[0028]

Hereinafter, embodiments of the NAS unit cell of the present invention will be described, but the present invention is not limited to the illustrated embodiment.

The structure of the pressure-releasing unit 14 is designed so that the internal temperature of the anode container is released at 500 to 540 ° C.
A 1 mm thick cross cut groove was formed in the 30 mm range to form a thin portion 16. Using the above-mentioned anode container, a normal NAS cell was constituted by the anode container 3, the insulator ring 2, the cathode metal fitting 4, the solid electrolyte tube 5, and the like as shown in FIG.

Although not shown, after a plurality of the NAS cells having the above configuration are erected in a box-shaped heat insulating container, the gap between the heat insulating container and the cells is filled with sand for fire prevention and the heat insulating container is sealed. Stopped. In the NAS assembled battery configured as described above, the decompression section is opened only by an increase in internal pressure when an abnormality occurs, and the decompression section is not opened by an increase in internal pressure during normal operation.

[0031]

As described above, according to the present invention, there is provided a NAS unit cell in which the decompressed portion is broken only by an increase in internal pressure at the time of occurrence of an abnormality and the decomposed portion is prevented from being broken during normal operation. You.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a NAS unit cell of the present invention.

FIG. 2 is a cross-sectional view showing one embodiment of a conventional NAS unit cell.

FIG. 3 is a graph showing a relationship between a vapor pressure of sulfur and a temperature.

FIG. 4 is a graph showing the relationship between tensile strength and temperature of an aluminum alloy.

[Explanation of symbols]

1. NAS cell, 2. Insulator ring, 3. Anode container, 4.
... Cathode fitting, 5 ... Solid electrolyte tube, 6 ... Anode mold, 7
... sodium, 12 ... sulfur, 14 ... pressure relief part, 16 ... thin part, 31 ... NAS unit cell, 32 ... insulator ring, 33 ... anode container, 34 ... cathode metal fittings, 35 ... solid electrolyte tube, 36 ...
Anode mold, 37 ... sodium, 42 ... sulfur.

Claims (2)

[Claims] 1. A cylindrical anode mold impregnated with sulfur as an anode active material, an anode container accommodating the anode mold, an insulator ring for joining the anode container and a cathode fitting, and the insulator ring A solid electrolyte tube having a bottom and a cylindrical shape joined to an inner peripheral portion thereof; a sodium-sulfur configured to contain sodium as a cathode active material in an internal space formed by the solid electrolyte tube and the cathode fitting. In the unit cell, a pressure-release portion that is cleaved by an increase in the internal temperature and internal pressure of the anode container is formed in a part of the anode container, and the pressure-release portion is configured such that the internal temperature of the anode container is 444 ° C. or higher and 660 ° C.
A sodium-sulfur unit cell configured to be cleaved within the following range. 2. The sodium-sulfur unit cell according to claim 1, wherein the pressure-reducing portion is provided at the bottom of the anode container.