JPS6247974A - Sodium-sulfur battery - Google Patents

Abstract

PURPOSE:To prevent breakage of solid electrolyte caused by solid expansion of sodium in the initial temperature rise by installing a reservoir between solid electrolyte and sodium, and making flow out molten sodium from a part of the bottom the reservoir. CONSTITUTION:Sulfur 10 serving as cathode active material is filled between a cylindrical tube 4, which is a cathode container made of metal, and a cylindrical solid electrolyte 5. A solid electrolyte 5 is beta-alumina or beta''-alumina. A cylindrical reservoir 6 made of stainless steel having a small opening 6A in the center of the bottom is arranged, and metallic sodium 9 serving as anode active material is filled in the reservoir 6. The expansion of sodium in the start of battery operation is performed only in the reservoir 6, and any force is not applied to the solid electrolyte 5. Sodium 9 melted the reservoir 6 flows out to a porous metal fiber layer 11 through the opening 6A, and penetrates into the electrolyte 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a sodium-sulfur battery that is designed to prevent initial damage at elevated temperatures.

[Background of the invention]

In conventional sodium-sulfur batteries, approximately 7% of the total cells were damaged during the first temperature rise in a single cell test, as described in the Institute of Electrical Engineers of Japan study group material ESC-84-54. The reason for this is considered to be thermal distortion of the solid electrolyte tube during battery manufacture. Solid electrolyte with residual thermal distortion during battery manufacturing
W (using β-alumina or β“-alumina, thickness l~
35II+) has sodium placed inside,
It is believed that the solid expansion of the subsulfur, which is placed on the outside, causes external force to be applied as the temperature rises, leading to damage.

In addition, ceramics generally have initial defects such as notches, cracks, and voids on the surface and inside of the base material during the manufacturing process. It is well known as concentration, and it is also known that the degree of concentration is much greater than that of metal materials.

Furthermore, cylindrical and tubular ceramic products have the property of being weaker against internal pressure than external pressure. 5U
The stress concentration described above is more pronounced in the type of sodium-sulfur battery that stores sodium in 9 J of the solid core solute tube than in the type that stores sulfur therein. This is because sodium has a higher coefficient of thermal expansion than sulfur. That is, as described in Japanese Patent Application Laid-Open No. 56-63780, IJ cum is placed inside the solid electrolyte tube. ! According to the fusion-filling method, sodium comes into direct contact with the solid electrolyte tube wall, so it infiltrates into the defects in the solid electrolyte tube, and the sodium that has penetrated into the defects will be absorbed when the temperature rises. Due to solid expansion, external pressure acts on the solid electrolyte tube, and due to stress concentration, the stress becomes particularly noticeable at defective parts, increasing the size of the defect in the solid electrolyte tube. 1! This will damage the decomposition chamber itself, and the sodium and sulfur will react directly, which is unfavorable from a safety standpoint.

In other words, in conventional sodium-sulfur batteries, the solid electrolyte IR due to the solid expansion of sodium when heated
No consideration was given to preventing damage to the pipe (I!).

[Purpose of the invention]

An object of the present invention is to provide a sodium-sulfur battery in which damage to the solid electrolyte due to solid expansion of sodium during initial temperature rise is prevented.

[Summary of the invention]

In the present invention, a reservoir is provided between a fixed electrolyte and sodium, and molten sodium is caused to flow out from a part of the bottom surface of the reservoir.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the sodium-sulfur battery of the present invention. The outermost periphery t constitutes a cylindrical tube 4i-1, which is a metal anode container. Between this cylindrical tube 4 and the cylindrical solid electrolyte 5, a sulfur layer 10-10- is filled as a positive electrode active material. The solid electrolyte 5 has a property of being selectively ion conductive only to sodium ions, and is made of β-alumina or β” alumina. Its electrical conductivity works well in the molten sulfur state.

A reservoir 6 is provided at the innermost circumference of the circular WJ tube 4. This reservoir 6 is required to be corrosion resistant to sodium. For example, use stainless steel. The reservoir 6 has a cylindrical shape, and its circular portion is filled with sodium 9, which serves as a blowing abrasive active material. The solid sodium 9 is metallic sodium. The reservoir 6 has a small opening 6A in the center of its bottom surface.

These six opening members play an extremely important role in this embodiment.

A porous metal fiber 11 is housed between the reservoir 6 and the solid electrolyte 5. The gold IA fiber 11 is compressed and stored.

The outer periphery of the sulfur layer 10 is in contact with the anode container 4 . A metal anode cap 7 was removed from the bottom of the anode container 4 by welding. A rare gas injection pipe 8 was provided in the center of the anode camp 7.

Nawate It has the function of shielding the blown fibers and consists of a dish-shaped structure. ≠ Pole container 20
The peripheral portion contacts the insulating material 3 and is electrically insulated. The insulating material 3 consists of an alumina ring i). Insulation material 3
is in contact with the local electrode container 4 and also with the upper part of the electrolyte #5, thereby providing electrical insulation from each other.

The upper part of the reservoir 6 has an opening 6B. This opening 6
B plays the role of releasing pressure when sodium is melted, compressed and stored in the gap between the reservoir 6 and the solid electrolyte layer 5, flows out into the porous metal chamber, and is sucked up by capillary action.

There are two openings in the center of the sowing container 2, and metal sodium 9 is introduced through these two openings. (metal) After filling the IJum reserve 6, open the inlet 2.
People are shielded with the lid 2B. This shielding is done by welding. A series of sodium filling and welding is carried out using an inert gas (e.g. Ar, N, etc.) to prevent contamination of impurities.
It is preferable to do it inside.

The reservoir 6 has two roles: to reduce the chance of direct contact and reaction between the molten sodium 9 and molten sulfur 10 when the solid electrolyte layer (tube) 5 is damaged, and a role as a cathode current collector tube. have

The metal fiber 11 has a function as a molten metal retaining material to prevent a rapid exothermic reaction between molten sodium and molten sulfur in the event that the solid electrolyte layer 5 is damaged.

After filling the inside of the anode with inert gas, the rare gas injection tube 8
sealed.

Explain the operation.

Sodium-sulfur battery is 2N a + X S d Nag Sx
-” (1) is carried out. → direction indicates discharge, ← indicates charging. The solid 'rt' material layer 5 allows only sodium ions to pass through. The temperature during the reaction is 300C to 350C. Both sodium 9 and sulfur No are in the f6 molten state.

Free M! At L, the sodium in the cathode active material liberates electrons and becomes sodium ions, and the solid passes through the partition wall of the solute 5 and reacts with the sulfur in the anode active material, forming sodium polysulfide (N
azSx).

During charging, sodium polysulfide is separated into sodium and sulfur by applying a negative voltage greater than the open circuit voltage of the battery.

The above operation is a general operation of a sodium-sulfur battery. The operation peculiar to this embodiment will be explained below.

To start the sodium-sulfur klL pond, 300C
It is necessary to heat the metal to ~350C and cause the metallic sodium 9 to become molten sodium and the sulfur 10 to become molten sulfur. Assuming that reservoir 6 does not exist at this stage of heating, the solid electrolyte # has a force (
The so-called β" force) and the thermal stress on β" alumina caused by the volumetric expansion of molten sodium near the melting point where solid and molten sodium coexist act. This beginning,
This has the drawback of accelerating the deterioration of the solid electrolyte 5 and leading to damage.

On the other hand, in this embodiment, the IJum 9 is the reservoir 6
Store it inside. Therefore, when the temperature is increased, the expansion of sodium takes place only within the lisano (6), and no external force is applied to the solid [495.
The same applies to the volumetric expansion of molten sodium at its melting point.

The molten sodium 9 in the reservoir 6 has a small opening 6
It flows out into the porous metal fiber 11 through the person, and further penetrates into the solid material 5.

'feI molten sodium 9ij: The molten sodium 9ij is compressed and stored, and then sucked up in the groove direction and upward by the hexagonal tension of the metal fibers 11, that is, capillary action, and transferred to the solid electrolyte 5.

In order to give the metal fiber 11 the power to absorb sodium, for example, a metal fiber with a wire diameter of 4 to 8 μm and a porosity of g g
In addition, for the reservoir 6, we use a metal with less variation in strength compared to the ceramic material in @solution'i;its, so it is easy to decide on a shape that can overcome the stress exerted by the sodium. It is. In this way, according to this example, the rise is in time) IJ
The negative influence on l"-alumina caused by the expansion of alumina can be completely eliminated.

In addition, when using the battery as a stand-alone battery, install terminals on the anode and cathode, connect the power source for charging and the load for discharging, and use the selector switch to switch between discharging and charging. Make it.

According to this embodiment, during initial high-temperature work such as when operating a 'α battery,
α) When joining the α-alumina ring and solid electrolyte tube for anode and cathode insulation, (2) When joining the anode-cathode container and the α-alumina ring attached to the solid electrolyte tube. The solid electrolyte tube, which has become brittle due to thermal strain that sometimes occurs, is no longer subjected to external force due to the solid expansion of sodium when the temperature rises, and damage during the temperature rise can be prevented.

Also, when looking at solid electrolyte tubes, damage can be prevented because sodium does not exist in a solid state in the initial defective part of the solid electrolyte tube.

That is, this embodiment is intended to eliminate the adverse effect on the solid solute tube due to solid expansion when sodium is heated.

Note that sulfur, which serves as a positive electrode active material, is generally impregnated into a porous metal conductive material to form a positive electrode active material layer, and is dissolved during use. Also, sodium polysulfide may be used instead of sulfur.

〔Effect of the invention〕

According to the present invention, stress on the solid 1 Jt solute can be prevented, and deterioration of the solid electrolyte can be reduced, contributing to longer battery life and improved battery performance.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the present invention. 2... Pole valley device, 3... Insulator, 4... Anode container, 5... Solid electrolyte, 6... Reservoir, 9... Metal) IJum.

Claims (1)

[Claims] 1. A sodium metal layer that is a cathode active material, a sulfur layer that is an anode active material, a solid electrolyte layer provided between the two layers, and the solid electrolyte layer and the metal sodium layer. A sodium-sulfur battery comprising a sodium corrosion-resistant reservoir provided between the reservoir and a molten sodium outflow opening provided in a portion of the reservoir. 2. A metal sodium layer which is a cathode active material, a bag tube-shaped reservoir having sodium corrosion resistance filled with the sodium inside, a porous metal fiber compressed and stored on the outside of the reservoir, and the metal fiber. A solid electrolyte layer is provided on the outside of the reservoir, and an anode active material layer is provided on the outside of the solid electrolyte layer and has sulfur impregnated into a porous electrically conductive material. A sodium-sulfur battery with an opening.