JPH084014B2 - Sodium-sulfur battery - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sodium-sulfur battery, and more particularly to a safety improvement and a joint corrosion prevention structure.

2. Description of the Related Art Sodium-sulfur batteries have a completely sealed structure in which sodium as a cathode active material and sulfur as an anode active material are separated by a sodium ion conductive solid electrolyte tube such as β ″ -alumina. Is a high temperature type secondary battery.

The conventional structure of such a sodium-sulfur battery is
It will be described with reference to the drawings. The α-alumina ring 2 is glass-soldered to the upper end of the solid electrolyte tube 1, the cathode lid 3 is thermocompression-bonded to the upper surface of the α-alumina ring 2, and the anode lid 4 is thermocompression-bonded to the lower surface thereof. A cathode terminal 5 is welded to the cathode lid 3, a cathode pipe 6 as a cathode current collector is welded through the central portion thereof, and the lower portion thereof is inserted into the solid electrolyte tube 1. Metal fibers 7 are arranged in the solid electrolyte tube 1, and the inside of the solid electrolyte tube 1 is evacuated from the cathode pipe 6 while keeping a temperature of about 150 ° C., and then sodium 8 melted at the same temperature is vacuum filled. After filling, the upper end of the cathode terminal 5 is sealed. Such a cathodic structure is inserted into a battery case 9 which also serves as an anode current collector in which a cylindrical sulfur molded body 10 is inserted, and the upper end thereof is vacuum-welded to the anode lid 4 to complete the structure. It is sealed.

In the sodium-sulfur battery having the above structure, the sulfur molded body 10 thermally expands in the process of raising the operating temperature to 350 ° C., and the solid electrolyte tube 1 receives bending stress. However, since the solid electrolyte tube 1 is firmly bonded to the α-alumina ring 2 by the glass solder, there is a drawback that the solid electrolyte tube 1 is damaged at the glass solder bonding portion due to the bending stress. When the battery is damaged, there is a problem in that an internal short circuit causes non-uniform current flow in the other batteries connected in parallel, which damages the normal battery and causes a large-scale accident.

The object of the present invention is to eliminate the above-mentioned drawbacks, and by disposing a metal tube in the gap between the solid electrolyte tube and the metal fibers in the tube, bending stress causes glass solder between the solid electrolyte tube and the α-alumina ring. The purpose is to prevent an internal short circuit when the solid electrolyte tube is damaged at the joint.

The sodium-sulfur battery of the present invention is a sodium-sulfur battery, the lower portion of the metal cylinder is inserted into the gap between the solid electrolyte tube filled with sodium-retaining metal fibers and the metal fibers, and the upper hole is the sodium injection hole of the cathode terminal. Attached to the cathode terminal so as to communicate with, after vacuum filling sodium from the sodium injection hole, the upper end of the cathode terminal is sealed, the cathode and the metal fiber in the metal cylinder during battery operation. Is electrically connected, and when the battery is broken, the metal tube is melted by the reaction heat to interrupt the electrical connection between the cathode terminal and the metal fiber.

Examples Hereinafter, examples will be described. FIG. 2 is a cross-sectional view of the essential parts of the sodium-sulfur battery of the present invention, and the same parts as those in FIG. 1 are designated by the same reference numerals.

The lower surface of the cathode terminal 5 has an outer diameter of about 38.2 mm, a thickness of about 0.2 mm, a height of about 60 mm, and a metal lid 12 made of copper with an upper hole 11 of about 8 mm on the upper lid, with a screw 13 having a hole in the center. Fixed Further, a metal fiber 7 made of iron is provided inside a solid electrolyte tube 1 made of β ″ -alumina having an upper outer diameter of 46 mm, an inner diameter of 39 mm and a length of 400 mm.
(Fiber diameter of about 10 to 20 μm) was filled up to a height of about 50 mm from the upper end of the tube so that the porosity was about 95%, and then the metal tube 12 made of copper was inserted into the solid electrolyte tube 1, The metal tube 12 was inserted into the gap between the metal fiber 7 and the solid electrolyte tube 1 by about 10 mm so that the cathode terminal 5 and the metal fiber 7 were electrically connected in the cathode chamber. The cathode terminal 5 and the cathode lid 3 were welded. This structure was heated to about 150 ° C., the inside was evacuated, and then sodium 8 was vacuum-injected from the tip of the cathode terminal 5. At the time of injection, sodium 8 filled the inner space of copper metal tube 12 (the upper space of metal fiber 7), but since the inert gas was sent from the tip of cathode terminal 5 after injection,
The liquid surface of sodium 8 was pressurized and impregnated into the metal fibers 7. The component filled with this sodium 8 was placed in a battery case together with the sulfur molding, the anode lid was welded to the battery cell, and the anode chamber was vacuum-sealed to manufacture a sodium-sulfur battery.

The conventional battery and the battery of the present invention shown in FIG. 2 were made 10 cells each using a solid electrolyte tube having a crack in the glass joint part, and the battery was damaged while performing a thermal cycle test between 350 ° C. and room temperature. The heat cycle and charging / discharging were repeated until. Table 1 shows the number of charging / discharging cycles until the current stopped flowing to the battery after the damage to the battery was confirmed by the voltage drop. Note that the battery voltage in () is that the battery voltage was not completely cut off and a minute current of about 0.01 mA to about 2.5 mA was flowing.

In the above battery, if the metal cylinder 12 has a wall thickness of 0.7 mm or less, preferably 0.1 to 0.2 mm, the current can be cut off immediately after the battery is damaged. Further, as the metal cylinder 12, even if aluminum is used in addition to copper, it can be melted by the reaction heat, and the same effect can be obtained.

After the test, the battery is disassembled, and the state of the upper space in the solid electrolyte tube 1 (in particular, in the battery of the present invention, the state of the metal tube 12 made of copper, that is, whether the cathode terminal 5 and the metal fiber 7 are electrically disconnected) investigated. All the batteries were damaged at the glass solder joint portion of the solid electrolyte tube 1. In the conventional battery, the current was cut off when the cathode pipe 6 was melted in the upper space, but in the battery in which a minute current was flowing, a lump was formed between the metal fiber and the cathode pipe. Since this substance was sodium polysulfide, it was proved that an electric current was flowing. On the other hand, in the battery of the present invention, the current was interrupted by one charge / discharge after the battery was broken. This is because the disassembly of the battery resulted in a lump of sodium polysulfide on the upper part of the metal fiber 7, but the glass solder joint part. It was revealed that the metal tube 12 made of copper had disappeared in the vicinity.

As described above, in the present invention, the metal cylinder can be easily heated by the heat of direct reaction between sulfur and sodium due to the breakage of the solid electrolyte tube.
12 can be melted or destroyed to break the electrical connection in the cathode chamber. Furthermore, the metal cylinder 12 prevents sodium from adhering to the inner surface of the cathode lid, particularly the joint with the α-alumina ring when sodium is filled, and corrosion of the joint due to sodium can be prevented.

EFFECT OF THE INVENTION As described in detail in Examples, the sodium of the present invention
Since the electrical connection of the sulfur battery is immediately cut off even if it is damaged, it is possible to prevent the damage of many batteries connected in series and many batteries connected in parallel to the damaged battery, thus improving safety. be able to. Further, since corrosion of the joint portion due to sodium can be prevented, the battery life can be extended.

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a sodium-sulfur battery of the present invention,
FIG. 2 is a sectional view of a conventional sodium-sulfur battery. 1 ... Solid electrolyte tube, 2 ... α-alumina ring 3 ... Cathode lid, 4 ... Anode lid 5 ... Cathode terminal, 6 ... Cathode pipe 7 ... Metal fiber, 11 ... Upper hole 12 ... Metal tube, 13 …… Screw

Claims (1)

[Claims] 1. An α-alumina ring bonded to an upper end of a sodium ion conductive solid electrolyte tube by glass soldering, and a cathode lid thermally bonded to an upper surface of the α-alumina ring.
An anode lid thermocompression bonded to the lower surface of the α-alumina ring, a cathode terminal having a sodium injection hole welded to the cathode lid to form a cathode chamber in the solid electrolyte tube, and the solid electrolyte In a sodium-sulfur battery comprising a tube encapsulating the tube from below and welding the upper end to the anode lid, and a battery cell for forming an anode chamber in the gap with the solid electrolyte tube, the cathode chamber is filled with that, The upper surface has a metal fiber located below the glass solder joint between the solid electrolyte tube and the α-alumina ring, and the lower part is inserted into the metal fiber along the inner wall of the solid electrolyte tube, and the upper hole is It has a metal cylinder attached to the cathode terminal so as to communicate with the sodium injection hole of the cathode terminal, and when the battery is operating, electrically connects the cathode terminal and the metal fiber with the metal cylinder,
A sodium-sulfur battery characterized in that, when the battery is damaged, the metal cylinder is melted by the reaction heat to interrupt the electrical connection between the cathode terminal and the metal fiber.