JPH02142066A - Sodium-sulphur cell - Google Patents

Abstract

PURPOSE:To improve the anticorrosive property of a cathode container by forming the cathode container to form a cathode chamber with an aluminum alloy such as an aluminum-manganese-chromium alloy or an aluminum- manganese alloy, and providing an anticorrosive membrane of a chromium plating layer at the inner surface of the container. CONSTITUTION:A cathode container 1 to form a cathode chamber R2 is formed of an aluminum alloy such as an aluminum-manganese-chromium alloy or an aluminum-manganese alloy, and an anticorrosive membrane of a chromium plating layer is provided at the inner surface of the container 1. That is, while the cathode container 1 is formed of an aluminum alloy, an anticorrosive membrane of a chromium plating layer whose cracking density is less increased even though the temperature is raised near the operational temperature of the cell is provided. As a result, the cathode container 1 is made lightweight, the anticorrosive property is improved, and the cell can bear the service for a long period.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a sodium-sulfur battery that can improve the durability of the anode container.

[Prior Art] As shown in FIG. 2, a conventional sodium-VR precious battery includes a cylindrical anode container 1 that houses a conductive material M for the anode, such as a carbon mat impregnated with molten sulfur S, which is an anode active material. A cathode container 3 is connected to the upper end of the anode container 1 via an insulating ring 2 made of α-alumina, and a cathode container 3 is fixed to the inner circumference of the insulating ring 2 and is an electrode active material. There is one constructed of a solid electrolyte tube 4 having a bottomed cylindrical shape made of polycrystalline β''-alumina and extending downward and having the function of storing molten metal sodium Na and selectively transmitting sodium ions Na+.

During discharge, sodium ions N from the cathode chamber R1
a+ passes through the solid electrolyte tube 4 and becomes sulfur S in the anode chamber R2.
The following reaction occurs with sodium polysulfide.

2Na+X5-Na1 Sx Furthermore, during charging, a reaction opposite to that during discharging occurs, and sodium polysulfide decomposes into sodium Na and sulfur S.

Since highly corrosive molten sodium polysulfide is formed in the anode container 1, the material of the anode container 1 is made of highly corrosion-resistant stainless steel.

As shown in Japanese Patent Publication No. 54-293 as a first conventional example for improving the corrosion resistance of the anode container, the inner peripheral surface of the anode container 1 is electrolytically plated with molybdenum or tungsten to a thickness of 7 μm or more. There were some that formed a corrosion-resistant coating.

Further, as a second conventional example, as shown in Japanese Patent Publication No. 56-46233, an anode container is proposed in which a chromium plating layer is formed on a base material made of stainless steel.

Furthermore, as a third conventional example, Japanese Patent Application Laid-Open No. 62-276767
As shown in the publication, an anti-corrosion coating made of an alloy containing iron, nickel, cobalt, and chromium as main components is disclosed on the inner circumferential surface of an anode container 1.

[Problems to be Solved by the Invention] However, the first conventional example described above has not been put to practical use because the molybdenum or tungsten electrolytic plating film lacks stability, and there is a problem that it lacks reliability. was there.

In addition, the second conventional example has a large number of InA layers in the chromium plating layer.
[II] Since there is a rack and the coefficient of thermal expansion is different between chromium and stainless steel as the base material, there was a problem that the width of the crack increases with temperature rise and the flit nU property deteriorates.

Furthermore, since the third conventional example uses an iron-based alloy that easily forms sulfides, it has poor corrosion resistance and cannot withstand long-term use. Since it becomes a sulfide, the positive electrode active material cannot be used effectively, and there is also the problem that battery efficiency decreases.

The purpose of this invention is to improve the corrosion resistance of the anode container, to prevent accidents in which the anode container breaks due to corrosion and the anode active material leaks out, and to make effective use of the anode active material. An object of the present invention is to provide a sodium-sulfur battery that can improve battery efficiency.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the invention as claimed in claim 1 divides an anode chamber and a cathode chamber by solid electrolyte tubes having alkali ion conductivity, and contains molten sulfur in the anode chamber. accommodates,
In a sodium-sulfur battery containing sodium in the cathode chamber, the anode container forming the anode chamber is formed of an aluminum alloy such as an aluminum-manganese-chromium alloy or an aluminum-manganese alloy, and the inner surface of the anode container is A corrosion-resistant coating consisting of a chrome plating layer is provided.

Further, the invention according to claims 2 to 3 is such that the corrosion-resistant coating is an amorphous chromium plating layer or a chromium plating layer consisting of amorphous chromium and carbon.

Furthermore, the invention as set forth in claim 4 is such that the crack density of the corrosion-resistant coating is approximately 2 g/cm to 10 g/cm.

Furthermore, in a fifth aspect of the invention, the corrosion-resistant coating has a thickness of 5 to 50 μm.

[Function] In this invention, the anode container is formed of an aluminum alloy, and the inner peripheral surface of the anode container has a thickness of 5 to 50 μm.
and the crack density is 2ge/cm to 10ge/cm
In addition, we have provided a corrosion-resistant coating consisting of a chrome plating layer that exhibits a small increase in crack density even when the temperature rises to around 350°C, which is the operating temperature of the battery. Improved corrosion resistance and can withstand long-term use.

The crack density may be reduced by adjusting the plating conditions such as the temperature, pH, or current density of the plating bath, or by adjusting the thickness of the plating layer or the surface roughness of the aluminum container. This may be achieved by dispersing a material, such as carbon, in the chromium plating layer, which is also capable of relieving the stress of electrodeposition of chromium.

In a chromium plating layer with a crack density of 2/cm to 10/cm by the above method, the stress caused by the difference in thermal expansion between the aluminum container and chromium is effectively absorbed when the temperature is raised to the battery operating temperature. This suppresses the occurrence of cracks in the plating layer, thereby preventing the chrome plating layer from peeling off and improving the corrosion resistance of the anode container.

Further, since the carbon dispersed in the chrome metal layer has excellent corrosion resistance against sodium polysulfide, the plating layer made of chromium and carbon also has excellent corrosion resistance against sodium polysulfide.

Furthermore, carbon in the plating layer not only reduces cracks in the metal, but also promotes amorphization of the chromium plating layer, further improving the corrosion resistance of the plating layer.

Furthermore, by setting the thickness of the corrosion-resistant coating to 5 to 50 μm, the crack density in the chrome plating layer is reduced, and the increase in crack density due to temperature rise to the battery operating temperature is also reduced, thereby improving the corrosion resistance of the anode container. improved and can withstand long-term use.

[Example] Hereinafter, embodiments embodying this invention will be described.

The basic structure of the sodium-sulfur battery of this embodiment is the same as that of the battery shown in FIG. The composition, formation method, and characteristics of the corrosion-resistant coating will be described in detail below.

The anode container 1 has a low density, and the operating temperature of the battery (
Al-Mn- with sufficient mechanical strength at about 350℃)
It is made of an aluminum alloy such as a Cr alloy or an Al-Mn alloy, and is intended to be lightweight. Furthermore, a corrosion-resistant coating consisting of a chrome plating layer was provided on the inner surface of the anode container 1.

Table 1 The reason for selecting chromium as the main component of the corrosion-resistant coating will be described.

First, rod-shaped specimens with a diameter of 5 curves and a length of 30 mm were prepared from tantalum, niobium, iron, aluminum, macnesium, and chromium, and were placed in molten sodium polysulfide having a composition of Naz S4. After each test piece was immersed and subjected to a current test, the amount of weight loss of each test piece was measured. After that, the amount of reduction in diameter (referred to as the amount of thickness reduction) was calculated using the specific gravity of each test piece, and the obtained results are shown in Figure 1. The zero current test was performed by heating to 350°C in a nitrogen atmosphere. After each test piece was immersed in sodium polysulfide, a current with a current density of 100 mA/cjl was passed through each test piece for 500 hours.

As is clear from Figure 1, among the metal materials tested this time, chromium showed the least amount of decrease after the corrosion test.
It can be seen that it has excellent corrosion resistance.

For this reason, chromium was selected as a corrosion-resistant coating for sodium polysulfide. However, since metallic chromium is brittle, it is difficult to form an anode container with metallic chromium. Since the surface of the anode container that comes into contact with sodium polysulfide only needs to have corrosion resistance against sodium polysulfide, a corrosion-resistant coating consisting of a thin chromium plating layer is provided on the inner surface of the anode container made of an aluminum alloy as in the present invention. It was constructed as follows.

The composition of the anti-corrosion coating is one consisting only of a chrome plating layer, one with a 1ffr layer made of a metal having a coefficient of thermal expansion between the two, or 1 to 5% by weight between the chrome plating layer and the aluminum container surface. A plating layer consisting of carbon and the remainder chromium is preferable, and a layer having an amorphous structure is more preferable.

Next, regarding the test pieces plated using the three types of chromium plating baths listed in Table 1 above, we examined the effects of the number of cracks in the cross section of the plated layer and the thickness on the corrosion resistance against sodium polysulfide. The results of the test are shown in Table 2.

In this test, first, the surface of an aluminum alloy round bar with a diameter of 5 cm and a length of 3011s+ was plated with chrome in the metal coating bath listed in Table 1, and the test pieces listed in Table 2 were prepared. Plating bath No. 1.2 described in No. 1 is a known plating bath described on page 216 of "Plating Technology Handbook" published by Nikkan Kogyo Shimbun. In addition, plating bath No. 3 was released on August 12, 1986.
This is a known plating bath described in Japanese Patent Application Laid-open No. 179890/1989 published on 1986. Regarding these test pieces, the number of cracks in the cross section of the plated layer was determined between the as-plated state and 3.
Measurements were made after heating to 50°C and cooling, and the results are shown in Table 2. Further, each test piece in the as-plated state was immersed in molten sodium polysulfide having a composition of Naz S4 and subjected to an electrical current test, and then the amount of weight loss of each test piece was measured. After that, the specific gravity of each specimen is used to calculate the decrease in diameter J! (Thickness reduction i) was calculated and the obtained results are shown in Table 2.

The current test was performed by immersing each test piece in sodium polysulfide heated to 350° C. in a nitrogen atmosphere, and then passing a current at a current density of 100 mA/− through each test piece for 500 hours.

Table 2 Crack unit 2/■ As is clear from the results listed in Table 2, the test! 'IN0゜1
-3 test specimens are 1 z or more large with sodium polysulfide. This is the chrome metal of test @ No. 1 to 3 test pieces]
? This is because a large number of cracks already exist in the plated layer in the plated state, and the crack density further increases due to heating to 350°C. Note that the crack density referred to here is the number of racks penetrated per unit length (1 cll) of the cross section of the chrome plating layer. Also, test N.

In test specimens 4 to 6, as the plating thickness increases, the number of cracks decreases and corrosion due to sodium polysulfide decreases. This tendency is particularly remarkable in the test piece (No. 6) with a plating thickness of 10 μm. Furthermore, among the test pieces of Tests N017 to 12, Test No.
Sodium polysulfide corrosion was significantly reduced in ~11 specimens. This is because the chromium plating layer of test pieces No. 8 to 11 has a small crack density in the as-plated state, and the crack density does not increase significantly even when heated to 350°C, which is the corrosion test temperature. However, if the thickness of this plating layer is less than 5 μm, even if the crack density is small (Test fi No. 7) - the amount of corrosion due to sodium polysulfide is large, and the plating thickness becomes too large, If the thickness exceeds 5 μm, the crack density will increase (Test No. 12>, corrosion resistance will decrease.)
When the plating thickness is less than 50 μm or more than 50 μm, the corrosion resistance against sodium polysulfide is clearly inferior to that when the plating thickness is 5 μm to 50 μm.

Based on the results in Table 2, when considering the corrosion resistance of each test piece against sodium polysulfide in terms of the relationship between the crack density in the chrome plating layer and the plating thickness, it is found that the crack density in the cross section of the plating layer is 1 ke/am or less ( For No. 7) and 25 pieces/cs or more (No. 12), the amount of thickness reduction after the corrosion test in sodium polysulfide increases, so the corrosion resistance of the chrome plating layer decreases in these test pieces. I know what you're doing.

As mentioned above, the crack density is neither too high nor too low.If the crack density is too low,
The relaxation of the adhesion stress remaining in the plating layer is often insufficient.In this case, the thermal stress generated due to the difference in the thermal expansion coefficients of aluminum and chromium when the temperature is raised to the battery operating temperature and the above-mentioned Due to residual electrodeposition stress, many cracks occur in the plating layer, reducing corrosion resistance. On the other hand, if the crack density is too high, the action of the plating layer as a corrosion-preventing film will be reduced, and the corrosion resistance will be reduced.

In addition, we analyzed the composition and crystal structure of the chromium plating layer of test @ No. 9.10, and these results
was confirmed to be amorphous and composed of chromium and carbon. This shows that it is preferable to form an amorphous chromium plating layer made of chromium and carbon on the inner surface of the anode container housing the anode active material of the sodium-sulfur battery. Next, we conducted an experiment to determine the relationship between the thickness of the corrosion-resistant coating and its battery capacity.

The inner surface of an aluminum alloy (J I 5-A5003) pipe with an outer diameter of 38 mm and an inner diameter of 36 pores and a bottom was plated with chrome to produce a pipe having the plating thickness and crack density shown in Table 3. Also.

For comparison, a pipe was produced whose plating thickness and crack density were outside the range of the present invention. Using this pipe, a sodium-sulfur battery was fabricated in which the solid electrolyte tube is sodium ions, the anode active material is sulfur impregnated with graphite, and the cathode active material is molten sodium. Using this battery, a charge/discharge test was repeated for 1000 cycles at an operating temperature of 350° C., and changes in battery capacity were measured. Table 3 shows the results.

As is clear from Table 3, the thickness is 5 μm to 50 μm.
, for a battery assembled in a container with a plating layer with a crack density of 2 ge/cm to 10 ge/cm, 1000
The battery has a high battery capacity of more than 80% even after a cycle charge-discharge test, and the anode active material is effectively utilized for battery reactions.

On the other hand, in a comparative example battery assembled with a container having a plating layer whose thickness and crack density are outside the range of the present invention, the battery capacity decreased significantly after 1000 cycles of charge/discharge test. This is because the container of the battery corrodes, and the anode active material is consumed by the corrosion reaction of the container, resulting in a decrease in the anode active material.

Table 3 (blank space below) [Effects of the invention] As detailed above, this invention improves the corrosion resistance of the anode container and prevents accidents in which the anode container ruptures due to corrosion and the anode active material leaks. Can be prevented along with the anode active material! This has the effect that battery efficiency can be improved by using it effectively.

In addition, the chrome plating layer, which is composed of chromium and carbon, has excellent corrosion resistance against sodium polysulfide, and the carbon in the composition promotes the reduction of cracks in the chrome plating layer and the amorphization of the chrome plating layer, making it durable. It has the effect of improving sex.

In addition, the crack density of the corrosion-resistant coating is 2ge/cm to 1
When it is 0 pieces/cm, the stress caused by expansion and contraction during battery heating can be properly absorbed, and the peeling and corrosion resistance of the chromium plating layer can be improved.

Furthermore, when the thickness of the corrosion-resistant coating is set to 5 to 50 μm, corrosion resistance is improved and the product can withstand long-term use.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between various metal materials and the average amount of corrosion and friction reduction, and FIG. 2 is a longitudinal sectional view of the central part of an example of a conventional sodium-sulfur battery. DESCRIPTION OF SYMBOLS 1... Anode container, 2... Insulating ring, 3... Cathode container, 4... Solid electrolyte tube, M... Conductive material for anode,
R1...n storage room, R2...anode room. Patent applicant Nippon Glass Co., Ltd. Agent Patent attorney On 1) Hironobu

Claims (1)

[Claims] 1. A sodium-sulfur battery in which an anode chamber and a cathode chamber are partitioned by solid electrolyte tubes having alkali ion conductivity, the anode chamber contains molten sulfur, and the cathode chamber contains sodium. wherein the anode container forming the anode chamber is formed of an aluminum alloy such as an aluminum-manganese-chromium alloy or an aluminum-manganese alloy;
A sodium-sulfur battery characterized in that an anti-corrosion coating consisting of a chrome plating layer is provided on the inner surface of the anode container. 2. The sodium-sulfur battery according to claim 1, wherein the anti-corrosion coating is an amorphous chromium plating layer. 3. The sodium-sulfur battery according to claim 1 or 2, wherein the anti-corrosion coating is a plating layer made of amorphous chromium and carbon. 4. The sodium-sulfur battery according to any one of claims 1 to 3, wherein the corrosion-resistant coating has a crack density of 2 cracks/cm to 10 cracks/cm. 5. The sodium-sulfur battery according to any one of claims 1 to 4, wherein the corrosion-resistant coating has a thickness of 5 to 50 μm.