JPS6251149A - Sodium-sulfur battery and its manufacture - Google Patents

Abstract

PURPOSE:To prevent any reduction in the capacity of a sodium-sulfur battery which might result from corrosion and simplify the step of assembly and sealing by using a case made of a ceramic material which is highly resistant to corrosion and has shape memory. CONSTITUTION:A sodium-sulfur battery is produced by installing sodium 1 used as the anode active material, sulfur or sodium sulfide 2 used as the cathode active material and a solid electrolyte membrane 3 used as the diaphragm located between the active materials in a cathode case 4. The case 4 is made of a ceramic material which is highly resistant to electric discharge reaction products and has shape memory. After the case 4 and the sealing plate 5 are subjected to plastic deformation by heating them to high temperature in order to increase the internal volume and then the battery elements are placed in the case 4, the case 4 and the plate 5 are heated again to make them recover their original shape, thereby sealing and assembling a sodium-sulfur battery. By the means mentioned above, assembly of the battery is facilitated and its life can be increased by preventing any corrosion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a secondary battery for power storage, particularly a sodium-
Sodium with a suitable structure for extending the life of sulfur batteries
Concerning sulfur batteries and their manufacturing method.

[Background of the invention]

Sodium-sulfur batteries use metallic sodium as the cathode active material.
A high-temperature secondary battery consisting of sulfur and/or high-flow sodium as the positive electrode active material and a solid electrolyte made of ceramics that allows only sodium ions to pass through the electrolyte, and operates at around 300°C when both active materials are in a molten state. It is. The structure of a typical conventional battery is shown in FIG. β'-alumina (Nazo ・6AQz○
+1) 8 membrane is used in the form of a bag tube, and the auxiliary conductive material 8 is impregnated with sodium 1 on the inside and sulfur 2 on the outer periphery.

Since sulfur is an insulator, the auxiliary conductive material is inserted to help transfer electrons during charging and discharging. In the case of Fig. 2, the anode container 4 (FJ1 temperature container) is an anode active material such as sulfur, high-flow thorium, and thorium, which are very active and highly corrosive to metal battery container materials. ,
Materials with excellent corrosion resistance are used.

So far, molybdenum, chromium, titanium, etc. have been cited as materials with excellent corrosion resistance, and in the example shown in FIG. 2, a molybdenum lining 11 is provided. Since these corrosion-resistant materials are rare resources and expensive, methods of coating the surface of these metals using cheap metals such as iron are disclosed in JP-A-48-27531 and JP-A-48-27.
No. 533, JP-A-54-293, JP-A-54-152
No. 125 and Japanese Unexamined Patent Publication No. 57-65676.

However, even if the battery is constructed using the above-mentioned corrosion-resistant material, the third
As shown in the figure, when charge and discharge cycles are repeated, a significant decrease in capacity is observed. This decrease in capacity is clearly due to corrosion of the anode container.

On the other hand, the sodium and sulfur used in sodium-sulfur batteries react violently with oxygen in the air at the battery operating temperature of 300 to 350°C, so the battery container must be airtight, as shown in Figure 2. In the battery, the anode 4 is kept airtight by an anode cover 12, and the cathode 6 is kept airtight by a cathode M13. Note that 14 is α- for electrically insulating the anode part and the cathode part.
This is an insulating ring made of alumina (AQ5on). Therefore, when manufacturing a battery, it is necessary to bond β'-alumina and α-alumina, which are solid electrolytes, and to bond α-alumina and metal. Currently, β'-alumina and α-alumina are joined by heat treatment using glass solder. Further, α-alumina and metal are bonded by glass bonding or thermo-pressure welding. In both methods, a temperature of around 800° C. is applied to the joint.

This bonding method leaves thermal strain on the battery components, and due to differences in the coefficient of thermal expansion between the bonding material and the material, battery damage often occurs due to heat cycles such as rising and falling temperatures of the battery. Furthermore, joining these materials requires advanced technology and time.

Furthermore, sulfur, which is an anode active material, must be impregnated into an auxiliary conductive material within the battery. Since the auxiliary conductive material exchanges electrons with the anode container, sufficient electrical contact with the anode container is desired. Therefore, before battery assembly, graphite felt, which is generally used as an auxiliary conductive material, is compressed in the thickness direction, impregnated with sulfur, and cooled and solidified to form a molded body. Use of such a molded body not only provides good electrical contact between the anode container and the graphite felt, but also facilitates battery assembly. However, the molding process required raising the temperature in an inert gas atmosphere, which took a considerable amount of time and labor, and caused problems in workability.

Due to the above circumstances, we will solve these problems and
It is desired to develop a long-life sodium-sulfur battery that exhibits less capacity loss due to charging and discharging cycles and that does not cause battery damage.

[Purpose of the invention]

The purpose of the present invention is to improve the charge/discharge cycle life of a battery by providing a material with excellent corrosion resistance against sodium, sulfur, and sodium polysulfide produced by a discharge reaction, and to improve the charge/discharge cycle life of a battery by providing a material that has excellent corrosion resistance against sodium, sulfur, and sodium polysulfide produced by a discharge reaction, and to provide a material that can easily process and assemble sodium Our goal is to provide sulfur batteries.

[Summary of the invention] Ceramics are materials that have good coexistence with sodium, sulfur, and multi-flow sodium, and some of these ceramics are easy to process and have shape memory properties if temperature and plastic deformation conditions are adjusted. There is something. Therefore, the present invention is a sodium-sulfur battery in which the battery container has been changed from a metal container to a ceramic container. This is a method of manufacturing a sodium-sulfur battery that eliminates the steps of sealing by pressure welding or glass soldering, and impregnating the auxiliary conductive material with sulfur, making processing and assembly easier.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in more detail based on Examples.

FIG. 1 is a diagram showing the structure of a sodium-sulfur battery according to the present invention. The battery contains sodium 1, which is a cathode active material, inside an anode container 4. It consists of sulfur and sodium polysulfide 2 which are anode active materials, a solid electrolyte membrane 3 which serves as a partition between both active materials, and a sealing plate 5 which isolates these internal structures from the outside air. The anode container 4 is provided with an injection port/anode 7 for injecting the anode active material 2, and the sealing plate 5 is provided with an injection tube/cathode 6 for injecting the cathode active material 1. There is. Furthermore, a cap 9 is provided at the top of the sodium injection tube/cathode 6 for sealing off after injection. Incidentally, an auxiliary conductive material 8 made of graphite felt and a current collector 10 are also incorporated in the anode part.

The assembly process of this battery will be explained using FIGS. 4 and 5. The sealing plate 5 and anode container 4 shown in FIG. 4 are made of ceramics. This ceramic is cut into the shape shown by the solid line at room temperature, then raised to a high temperature and plastically deformed as shown by the dashed line, and then cooled to room temperature while the deformation force is applied.

This deformed state maintains the shape shown by the dashed-dotted line even after unloading. When the ceramic is plastically deformed as shown by the dashed-dotted line and is annealed at a high temperature, it is restored to the shape shown by the solid line. Ceramics that exhibit such morphological changes are called shape memory ceramics. A typical example of shape memory ceramics is glass ceramics containing mica.

Ceramics containing mica are easier to cut because the mica crystals prevent crack propagation. There is a hole 20 in the center of the sealing plate 5, and a circumferential groove 21 in the bottom surface. Hole 2 in the bottom plate of anode container 4
2 is cut (shape memory) at room temperature as shown by the solid line. Heat it to a high temperature (approximately 500°C) at room temperature, expand the holes 20 and 22 as shown by point 1RIIA, expand the groove 21, and seal it. The disc diameter of the stop plate 5 is compressed. On the other hand, the inner diameter of the anode container 4 is expanded using means such as applying internal pressure. The stress required for deformation is approximately 15 MPa, and by cooling to room temperature while applying this deformation force and removing the load, the sealing plate 5 and the anode container 4 take the shape shown by the dashed line (plastic deformation). Next, as shown in FIG.
Insert the sodium injection tube/cathode 6 into the groove 21 provided in the hole 2o.
On the other hand, inside the anode container 4 there is a graphite current collector material 10 divided into circumferential shapes, and on the inside thereof there is an auxiliary conductive material 8.
, and attach the sulfur inlet/anode 7 to the hole 22 provided in the bottom plate of the anode container. Next, the sealing plate 5 was inserted into the anode container 4 from above, reheated (approximately 400 to 500°C), and annealed (shape recovery), resulting in almost 100% shape recovery, as shown in Figure 1. A battery structure is formed. The shape recovery force at this time is 7 MPa, which is sufficient pressure as an airtight sealing pressure.

As shown in FIG. 1, sodium and sulfur, which are battery active materials, are injected in specified amounts in liquid form through the sodium injection port/cathode 6 and the sulfur injection port/anode 7, respectively, and are sealed with caps 9, 7. A load and a charging device (not shown) are connected to the cathode and anode to form a sodium-sulfur secondary battery.

According to an embodiment of the present invention, the conventional problem of reduction in battery capacity due to corrosion of the anode structural material is solved by using ceramics that have good coexistence with the active materials sulfur and sodium polysulfide. The use of glass solder and thermopressure welding, which were used to bond the solid electrolyte β''-alumina and α-alumina or α-alumina and metal, was reduced by using shape memory ceramics and sealing with shape recovery. Furthermore, in the process of impregnating the auxiliary conductive material with sulfur, which was performed to improve electrical contact between the battery container and β'-alumina, the auxiliary conductive material is compressed by the shape recovery force of the anode container, similar to sealing. In FIG. 1, which is an embodiment of the present invention, the current collecting material 10 is inserted and bonded to the anode 7, but the auxiliary conductive material 8 may be used, although the battery performance will be slightly reduced. If the anode 7 is joined to the current collector material 10
It is also possible to remove.

do. A button type battery also basically has the same structural requirements as the sodium-sulfur battery shown in FIG. A disk-shaped solid electrolyte membrane 20 that allows only sodium ions to pass through is used as a partition, and sodium 21 as a cathode active material is placed on one side, and sulfur and sodium polysulfide 22 as anode active materials are placed on the other side to hold these constituent materials. A cathode container 26 and an anode container 25 are provided for the purpose, and a sodium injection port and cathode 23 are provided in the cathode container 26, and a sulfur injection port and anode 23 are provided in the anode container 25.
This is a sodium-sulfur battery with a structure provided with 4. In addition,
The anode portion is filled with an auxiliary conductive material 27. The cathode container 26 and the anode container 25 may be made of shape memory ceramics, or one of them may be made of a metal material that is compatible with the active material and has approximately the same coefficient of linear expansion as the shape memory ceramics. For the container side using shape memory ceramics, the molding means shown in FIGS. 4 and 5 can be applied as is. In the example shown in FIG. 6, the cathode container 26 is made of a metal material, and the anode container 25 is made of a shape memory seed container 2.
A solid electrolyte 20 is provided inside the convex portion 6, and an anode container 25 made of shape memory ceramic is provided outside.

A diameter slightly smaller than the outer diameter of the convex portion of the anode container 25 is stored in the anode container 25, and the diameter is made larger by a deformation process. After incorporating the internal structural materials, the shape memory ceramics are subjected to recovery treatment. Conversely, the cathode container may be made of a metal material and the anode container may be made of shape memory ceramics. Next, prescribed amounts of each active material are filled from the sodium injection port/cathode 23 and the sulfur injection port/anode 24 to form a button-type sodium-sulfur battery.

The present invention is applicable not only to batteries in which sodium and sulfur are sealed in a battery container, but also to fluidized sodium-sulfur batteries equipped with a sodium and sulfur supply/discharge mechanism.

〔Effect of the invention〕

According to the present invention, by using shape memory ceramics having excellent corrosion resistance against sulfur and sodium polysulfide as a battery container, a decrease in battery capacity due to corrosion can be prevented. In addition, since the coefficient of linear expansion is almost the same as that of a solid electrolyte membrane, distortion caused by differences in thermal expansion can be prevented, and since glass soldering and heat pressure welding processes can be eliminated, there will be no residual thermal distortion, so battery performance can be maintained for a long time. The lifespan is greatly improved. Furthermore, since the step of impregnating the auxiliary conductive material with sulfur can be omitted, there are advantages such as the ability to easily manufacture sodium-sulfur batteries without using specialized technology.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of a sodium-sulfur battery according to the present invention. FIG. 2 is a cross-sectional view of a conventional sodium-sulfur battery. Figure 3 shows its life characteristics. FIG. 4 is a diagram showing the shape memory property of the battery container of the present invention. Fifth
The figure shows an assembly pattern of the battery of the present invention. 6 and 7 are cross-sectional views of other embodiments of the invention. 1.21... Cathode active material (sodium), 2.22.
・・Anode active material (sulfur, sodium polysulfide), 3°20
...Solid electrolyte (β'-alumina), 4.25...
Anode container, 5... Sealing plate, 6, 23... Sodium injection tube and cathode, 7, 24... Sulfur injection port and anode, 8, 27... Auxiliary conductive material (graphite felt)
, 9... Gap, 10... Current collector material (graphite), 11... Molybdenum inner lining, 12... Anode lid. 13... Cathode lid, 14... Insulating ring (α-alumina), 26... Cathode container.

Claims (1)

[Claims] 1. A membrane made of a solid electrolyte through which sodium ions can pass, a cathode active material made of sodium provided on one side of the solid electrolyte membrane, and sulfur or sulfur provided on the other side. In a sodium-sulfur battery comprising an anode active material made of sodium polysulfide or both, and a container containing the solid electrolyte membrane, cathode active material, and anode active material, the container is made of ceramics. A sodium-sulfur battery characterized by: 2. The sodium-sulfur battery according to claim 1, wherein the ceramic is a shape memory ceramic. 3. The container made of ceramics is composed of a cathode container part containing a cathode active material and an anode container part containing an anode active material, at least one of which is made of ceramics. A sodium-sulfur battery according to claim 1 or 2. 4. After cutting the ceramic into the desired battery container shape,
After being deformed at a high temperature, the container is rapidly cooled to maintain the deformed state, and then a cathode active material made of sodium, a solid electrolyte membrane, and an anode active material made of sulfur or multi-flow sodium or both are added to the container. A method for manufacturing a sodium-sulfur battery, comprising inserting the container into a predetermined position and heating the container to a predetermined temperature to restore the deformed state to the original processed shape.