JPH0782877B2 - Sodium-sulfur battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sodium-sulfur battery capable of improving safety when a solid electrolyte tube is broken.

[Prior Art] As a conventional sodium-sulfur battery, as shown in FIG. 6, a cylindrical anode container 1 for accommodating a conductive material M for an anode such as carbon mat impregnated with molten sulfur S as an anode active material. A cathode metal fitting 3 connected to an upper end portion of the anode container 1 via an insulating ring 2 made of α-alumina, and a molten metal which is fixed to an inner peripheral portion of the insulating ring 2 and which is a cathode active material. Stores metallic sodium Na, sodium ion Na
A cylindrical solid electrolyte tube 4 having a bottom and made of polycrystalline β ″ -alumina extending downward and having a function of selectively transmitting ⁺
Some have and. Further, the solid electrolyte tube 4 divides the inside of the battery into an anode chamber R1 and a cathode chamber R2, and a sodium container 5 for storing sodium is housed inside the cathode chamber R2, and a small hole 5b provided in a bottom portion 5a thereof Sodium comes in and goes out.

Then, at the time of discharge, sodium that has come out of the small holes 5b of the sodium container 5 is once impregnated into the sodium holder 11,
Sodium ions Na ⁺ from the cathode chamber R2 pass through the solid electrolyte tube 4 and react with the sulfur S in the anode chamber R1 as follows to produce sodium polysulfide.

2Na + XS → Na ₂ SX When charging, the reaction opposite to that during discharging occurs, and sodium Na and sulfur S are produced.

When the solid electrolyte tube 4 is damaged due to deterioration or thermal stress, for example, cracks are generated, metallic sodium in the cathode chamber R2 reacts with sulfur in the anode chamber R1 in a large amount and rapidly to generate abnormally high heat. The battery container is destroyed, and as a result, sodium and sulfur flow out to the outside, which is dangerous. In order to solve this, in the above conventional example, the sodium container 5 is provided in the cathode chamber R2, and a small gap is provided between the solid electrolyte tube 4 and the container 5 to reduce the reaction amount of sodium.

[Problems to be Solved by the Invention] However, the safety measure of the conventional battery is that the small hole 5b of the sodium container 5 and the solid electrolyte tube 4 are close to each other and the solid electrolyte tube 4 is damaged near the small hole 5b. At that time, the sodium outflow pressure from the sodium container 5 was high, so that the reaction amount of the active material was large and the safety was insufficient. Further, it is impossible to prevent the movement of sodium from the small gap between the solid electrolyte tube 4 and the container 5 to the side of the anode conductive material M,
There is a possibility that the reaction between sulfur and sodium occurs continuously in the anode container 1 to raise the temperature in the anode chamber and damage the anode container 1.

An object of the present invention is to provide a sodium-sulfur battery that can ensure the safety by preventing the inflow of sodium from the cathode chamber side into the anode chamber when the solid electrolyte tube is damaged.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention provides, inside the cathode chamber side of a bottomed bag-shaped solid electrolyte tube for partitioning the anode chamber and the cathode chamber,
A sodium container containing metal sodium is housed, a small hole is formed through the bottom of the sodium container, and an upper pressure chamber inside the sodium container is filled with an inert gas for pressurizing the metal sodium. A bottomed tubular partition wall is housed between the solid electrolyte tube and the sodium container, and between the inner peripheral surface of the bottomed tubular partition wall and the outer peripheral surface of the sodium container and between the outer peripheral surface of the bottomed tubular partition wall and the solid electrolyte tube. An inner gap and an outer gap are provided between the outer surface and the peripheral surface for vertically guiding the metallic sodium flowing in and out of the small holes during charging / discharging of the battery, and the pressure in the anode chamber during charging and discharging is controlled within the outer gap. The pressure is always higher than the pressure of.

The inner gap may be set to 0.1 to 1 mm and the outer gap may be set to 0.1 to 0.5 mm. A flow rate limiting plate may be accommodated at the bottom of the inner gap corresponding to the small hole, and a biasing member for pushing the sodium container toward the bottom of the bottomed tubular partition may be arranged in the cathode chamber.

[Operation] In this invention, sodium flowing out from the small holes of the sodium container at the time of discharge moves upward in the inner gap, then passes over the upper edge of the bottomed tubular partition wall, and moves downward in the outer gap to move the solid electrolyte tube. Sodium ions permeate and move to the anode chamber. Further, during charging, sodium moves in the opposite direction to the above and flows into the sodium container.

Since the pressure in the anode chamber is always higher than the pressure in the outer gap between the solid electrolyte tube and the bottomed tubular partition wall during charging or discharging, the anode chamber is broken when the solid electrolyte tube is ruptured. The molten sulfur flows into the outer gap from the breakage portion of the solid electrolyte tube due to the pressure difference. This sulfur reacts with sodium in the outer gap to generate high-melting-point sodium polysulfide, and the sodium polysulfide solidifies in the outer gap to block the breakage portion of the solid electrolyte tube, so that sodium and sulfur are separated. It is divided, and further inflow of molten sulfur into the outer gap is stopped, so that the reaction between molten sulfur and sodium is prevented and safety is improved.

Particularly, in the present invention, a small hole is provided at the bottom of the sodium container, and the sodium discharged from the small hole is raised in the inner gap so as to get over the upper edge of the bottomed tubular partition wall and be guided to the outer gap. To the inner side surface of the solid electrolyte tube, the reaction site of sodium and sulfur described above can be kept away from the small holes, and safety can be improved. That is, regardless of where the solid electrolyte tube is damaged, for example, even if the bottom of the solid electrolyte tube, which has a very short linear distance from the small hole provided in the bottom of the sodium container, is damaged, the integrity is maintained because the bottomed tubular partition wall is used. Retained. For this reason,
It is effective that the bottomed tubular partition of the present invention is used to provide an inner and outer gap, and the upper edge of the partition communicates the two gaps.

Further, when the outer gap is set to 0.1 to 0.5 mm, the reaction product immediately solidifies and closes the rupture portion, so that the inflow of molten sulfur is stopped early and the reaction between molten sulfur and sodium is prevented. , Further improve safety.

Further, when a flow rate control plate is accommodated at the bottom of the inner gap corresponding to the small hole and a biasing member for pressing the sodium container to the bottom side of the bottomed tubular partition is arranged in the cathode chamber, The flow rate of sodium from the holes to the inner gap and vice versa is stabilized, and the battery is stably discharged and charged.

Embodiment An embodiment embodying the present invention will be described below with reference to FIGS. 1 and 2.
It will be described with reference to the drawings.

In the sodium-sulfur battery of this example, the lower surface of an insulating ring 2 made of α-alumina is thermocompressively bonded to the upper end surface of an anode container 1 having a bottomed cylindrical shape, and the upper surface of the insulating ring 2 has a cathode. The metal fitting 3 is thermocompression bonded. Further, the upper end outer peripheral surface of the solid electrolyte tube 4 made of β ″ -alumina is joined and fixed to the inner peripheral surface of the insulating ring 2.

An anode conductive material M such as carbon mat impregnated with molten sulfur S as an anode active material is housed in an anode chamber R1 formed between the anode container 1 and the solid electrolyte tube 4. Further, in the cathode chamber R2 formed inside the solid electrolyte tube 4, a sodium container 5 having a cylindrical shape with a lid and a bottom for storing metallic sodium Na as a cathode active material is housed. The bottom surface 5a of the sodium container 5 is provided with a small hole 5b through which sodium flows in and out.

Further, in the pressurizing chamber R3 in the upper closed space of the sodium container 5, a gas inert to sodium, such as nitrogen gas or argon gas, is sealed at a predetermined pressure, and sodium is constantly discharged from the small hole 5b to the outside. It is pressurized in the direction of the outflow.

Further, between the inner peripheral surface of the solid electrolyte tube 4 and the outer peripheral surface of the sodium container 5, a bottomed tubular aluminum alloy or a bottomed tubular stainless steel (SUS304) having a melting temperature of 1400 ° C. or higher is used. After the partition wall 6 is arranged, and the sodium flowing out from the small hole 5b of the sodium container 5 at the time of discharge moves upward in the inner gap G1 between the outer peripheral surface of the container 5 and the inner peripheral surface of the tubular partition wall 6. , Overcoming the upper edge of the tubular partition wall 6, and further moving downward in the outer gap G2 between the outer peripheral surface of the tubular partition wall 6 and the inner peripheral surface of the solid electrolyte tube 4, and permeating the solid electrolyte tube 4 as sodium ions. Anode chamber R1
I am trying to move to.

The inner gap G1 is set to 0.1 to 1 mm, preferably 0.15 mm, and the outer gap G2 is set to 0.1 to 0.5 mm, preferably 0.3 mm. From the safety point of view, it is better to make both the gaps G1 and G2 as small as possible to reduce the amount of sodium, but it is difficult to be less than 0.1 mm due to technical restrictions, and if it is too narrow, the pressure loss becomes too high. The supply of sodium to the surface of the solid electrolyte tube 4 becomes unstable. The inner gap G1 and the outer gap G2 are
Although it is necessary to consider the shape of the battery or the operating conditions (moving speed of sodium: discharge current), it is desirable to set it within the above range in consideration of safety.

Between the bottom surface 5a of the sodium container 5 and the top surface of the bottom of the tubular partition wall 6, a disc-shaped wire mesh made of, for example, aluminum or stainless steel is used to control the moving flow rate (pressure) of sodium flowing out from the small holes 5b. A flow rate control plate 7 made up of

An urging member 8 such as a spring washer is interposed between the sodium container 5 and the cathode fitting 3, and urges the sodium container 5 toward the flow control plate 7 to keep the gap constant. ing.

Next, the main part of the present invention will be described.

In the present invention, the pressure P1 in the anode chamber R1 is set to be always higher than the pressure P2 in the outer gap G2. The setting and adjustment of the pressures P1 and P2 are performed as follows.

First, the pressure P1 in the anode chamber R1 will be described.
The saturated vapor pressure of molten sulfur at the battery operating temperature is 139 m.
Since it is a bar (see the chain line in Fig. 3), an inert gas such as nitrogen gas such as nitrogen gas is filled in the anode chamber R1 and pressurized to 478 mbar, and 617 mbar (chart line in Fig. 3) when charging is completed. However, when the discharge is completed, the saturated vapor pressure becomes almost zero, but due to the decrease in the anode chamber R1 due to the discharge, the saturation vapor pressure becomes 1075 mbar as a whole.

The pressure P1 in the anode chamber R1 is adjusted by nitrogen into the anode chamber R1,
When filling an inert gas such as argon or helium gas, it may be performed by adjusting the pressure of the inert gas, or decomposes at a high temperature such as sodium azide (NaN ₃ ) to generate an inert gas. A predetermined amount of substance may be added to increase the pressure.

On the other hand, the pressure P2 of the outer gap G2 in the cathode chamber R2 causes the sodium in the sodium container 5 to flow out. Therefore, by appropriately setting the inert gas pressure P3 in the pressurizing chamber R3 of the container 5, It is controllable, and as shown in FIG. 4, the pressure P2 in the outer gap G2 is 617 mbar when fully charged.
Therefore, 93.0 mbar is set in the discharge completed state. However, the full charge here means that the active material of the anode becomes 100% sulfur. Then, as shown in FIG. 5, the pressure P1 in the anode chamber R1 is made higher than the pressure P2 in the outer gap G2 in any case.

Next, the operation of the sodium-sulfur battery configured as described above will be described.

Now, when the sodium-sulfur battery is completely charged, most of the sodium is stored in the sodium container 5 as shown by the solid line H in FIG. 1, and molten sulfur is present in the anode conductive material M. There is.

When discharge is started in this state, sodium in the container moves into the inner gap G1 through the small hole 5b due to the pressure P3 in the pressurizing chamber R3. Then, from the upper edge of the tubular partition 6 to the outer gap G2
Then, sodium is converted into sodium ions and permeates the solid electrolyte tube 4, and reacts with sulfur in the anode conductive material M to generate sodium polysulfide.

In the above embodiment, the pressure P1 in the anode chamber R1 is always higher than the pressure P2 in the gap G2 between the solid electrolyte tube 4 and the sodium container 5 regardless of whether the solid electrolyte tube is charged or discharged. The gap from the anode chamber R1 at the time of rupture
The molten sulfur has a pressure difference Δ from G2 to the broken portion of the solid electrolyte tube 4.
Although it flows in by p, this sulfur reacts with sodium in the gap G2 to generate sodium polysulfide, and this sodium polysulfide is generated in the gap G2 to generate the solid electrolyte tube 4
Since the ruptured portion of is blocked, the further outflow of molten sulfur is stopped, the reaction between molten sulfur and sodium is prevented thereafter, and the safety is improved.

In particular, in the above embodiment, the bottomed tubular partition wall 6 is housed between the solid electrolyte tube 4 and the sodium container 5, and the outer gap G2 is set to 0.1.
Since it is set to ˜0.5 mm, the amount of sodium polysulfide produced when the solid electrolyte tube 4 is ruptured is small, the reaction heat is low, and the safety is improved.

The setting value of each pressure is not limited to the pressure in the above example as long as P1 is always higher than P2, but in order to stably supply sodium to the outer gap G2, the pressure P2 should be 50 mbar or more. Is preferred.

[Effects of the Invention] As described in detail above, in the present invention, a small hole is formed in the bottom of a sodium container, an inner gap and an outer gap are provided inside and outside a bottomed tubular partition, and both gaps are provided at the upper edge of the bottomed tubular partition. And the pressure in the anode chamber was always higher than the pressure in the cathode chamber. Therefore, sodium polysulfide produced by the reaction between sodium and sulfur in the outer gap solidifies and blocks the rupture portion, so that further inflow of molten sulfur can be blocked and safety can be ensured. . Further, regardless of the location of breakage of the solid electrolyte tube, even if the bottom of the solid electrolyte tube, which is very short in linear distance from the small hole provided in the bottom of the sodium container, is broken, safety can be maintained.

Further, when the outer gap is set to 0.1 to 0.5 mm, the amount of sodium polysulfide produced is reduced, and the reaction product solidifies immediately to block the rupture portion, so that the inflow of molten sulfur occurs early. Stops, the reaction between molten sulfur and sodium is prevented, and safety is further improved.

Further, in the invention in which the flow control plate is accommodated at the bottom of the inner gap corresponding to the small hole, and the biasing member for pressing the sodium container to the bottom side of the bottomed tubular partition is arranged in the cathode chamber, the small hole is provided. The flow rate of sodium from the inside to the inside gap and vice versa is stabilized, and the battery can be stably discharged and charged.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a central portion showing an embodiment of a sodium-sulfur battery embodying the present invention, and FIG. 2 is A- of FIG.
Sectional views taken along line A, 3, 4, and 5 show the anode chamber pressure, the gap G2 internal pressure, and the anode chamber pressure and gap during battery operation.
FIG. 6 is a graph showing the pressure difference of the G2 internal pressure, and FIG. 1 ... Anode container, 2 ... Insulation ring, 3 ... Cathode metal fittings,
4 ... Solid electrolyte tube, 5 ... Sodium container, 6 ... Tubular partition with bottom, M ... Anode conductive material, R1 ... Anode chamber, R2 ...
… Cathode chamber, R3 …… Pressurization chamber, P1 …… Anode pressure, P2 …… Pressure in the gap between solid electrolyte tube and sodium container, G1 …… Inner gap, G2 …… Outer gap.

Claims (3)

[Claims] 1. A sodium container (5) containing metallic sodium inside a cathode chamber (R2) side of a bottomed bag-shaped solid electrolyte tube (4) for partitioning an anode chamber (R1) and a cathode chamber (R2). A small hole (5b) through the bottom (5a) of the sodium container (5), and the upper pressure chamber (R3) inside the sodium container is filled with an inert gas for pressurizing the metallic sodium. Further, a bottomed tubular partition wall (6) is housed between the solid electrolyte tube (4) and the sodium container (5), and the inner peripheral surface of the bottomed tubular partition wall (6) and the sodium container (5). Between the outer peripheral surface of the battery and the outer peripheral surface of the bottomed tubular partition wall (6) and the inner peripheral surface of the solid electrolyte tube (4) through the small holes (5b) during charging and discharging of the battery. There is an inner gap (G1) and an outer gap (G2) that guides the The pressure in the chamber (R1) (P1)
Is always higher than the pressure (P2) in the outer gap (G2). 2. The sodium-sulfur battery according to claim 1, wherein the inner gap (G1) is set to 0.1 to 1 mm and the outer gap (G2) is set to 0.1 to 0.5 mm. 3. A flow control plate (7) is accommodated in the bottom of the inner gap (G1) corresponding to the small hole (5b), and the sodium container (5) is closed-ended tubular in the cathode chamber (R2). The sodium-sulfur battery according to claim 1, further comprising a biasing member (8) arranged to press the partition wall (6) toward the bottom thereof.