JP3322797B2 - Sodium-sulfur battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sodium-sulfur battery used as a secondary battery for adjusting a power load, for powering an electric vehicle, and the like.

[0002]

2. Description of the Related Art A sodium-sulfur battery of this type includes a bottomed cylindrical anode container made of a metal material as disclosed in Japanese Patent Application Laid-Open Nos. 5-275109 and 5-275110. A bottomed cylindrical solid electrolyte permeable to sodium ions disposed inside the anode container, a cathode active material composed of metallic sodium contained in the solid electrolyte, the solid electrolyte and the anode container And a positive electrode active material made of sulfur stored between them.

The sodium-sulfur battery has a temperature of 300.degree.
The charge / discharge operation is performed in a state heated to 350 ° C. At the time of discharge, sodium on the cathode chamber side and sulfur on the anode chamber side are ionized, and the ionized sodium permeates the solid electrolyte and reacts with sulfur. Thus, sodium polysulfide is generated and discharged, and at the time of charging, the opposite reaction occurs to be charged.

[0004] However, in the sodium-sulfur battery, sodium polysulfide generated by a reaction at the time of discharge has a high corrosiveness to metals, and when this sodium polysulfide directly contacts the anode container, the inner peripheral surface of the anode container is formed. Corrosion causes damage, lowers durability, and if the corrosion is localized and severe, cracks and through holes may occur in the anode container, and sodium polysulfide, sulfur and the like may leak to the outside.

[0005] Further, as the corrosion of the anode container progresses, sulfur as the anode active material is consumed for sulfuration of the metal constituting the container, and the amount of sulfur that functions as the anode active material decreases,
Accordingly, the battery capacity is reduced, and the life of the battery is shortened. Particularly, when the anode container is made of aluminum or an aluminum alloy in order to make the anode container lightweight and inexpensive, the corrosion caused by sodium polysulfide is more severe than that made of a special steel such as stainless steel.

[0006] Therefore, in the sodium-sulfur battery disclosed in each of the above publications, the anode container is provided on the inner peripheral surface of a bottomed cylindrical base made of aluminum or an aluminum alloy with a higher corrosion resistance than the base. An anode container having a configuration provided with a high coating layer is employed. Further, the coating layer is formed by a sprayed layer of a metal having high corrosion resistance, and the metal employed for forming the sprayed layer includes a cobalt-chromium-tungsten alloy (a stellite alloy), a chromium-iron alloy, and a nickel alloy. -Chrome alloys and the like are known. Further, a coating layer formed of a plurality of sprayed layers is also known.

[0007]

By the way, in a sodium-sulfur battery of the type using an anode container having a corrosion-resistant coating layer on the inner peripheral surface of a substrate as the anode container,
The surface of the sprayed layer is formed of an oxide film and undissolved metal powder remains on the surface, which reacts with the anode active material to form sulfides, which consume the anode active material, and increase the battery capacity. Will be reduced.

[0008] Further, since a defect site such as a pore is locally present on the surface of the sprayed layer, sodium polysulfide generated by the reaction between the two active materials penetrates into the defect site, and from the permeation site. May promote gradual corrosion. Furthermore, the surface of the sprayed layer has many irregularities due to the undissolved metal powder and defect sites described above, and the contact between the surface and graphite felt, which is a conductive material for the anode, is not dense, and the internal resistance of the battery is low. There is a problem that it is large and is not preferable in terms of electric energy efficiency.

Accordingly, it is an object of the present invention to address these problems in sodium-sulfur batteries.

[0010]

The present invention relates to a sodium-sulfur battery. The present invention relates to a sodium-sulfur battery, in which a coating layer made of a metal material having higher corrosion resistance than the base material is provided on the inner peripheral surface of a bottomed cylindrical body made of a metal material. An anode container provided with the same, a bottomed tubular solid electrolyte permeable to sodium ions disposed inside the anode container, a cathode active material comprising metallic sodium contained in the solid electrolyte, and the solid In a sodium-sulfur battery including an electrolyte and an anode active material made of sulfur housed between the anode containers and performing a charge / discharge operation in a heated state, the coating layer of the anode container is made of a metal powder having high corrosion resistance. And a chromium plating layer covering the surface of the thermal spray layer.

In the sodium-sulfur battery, the sprayed layer is a high chromium-iron alloy sprayed layer, the chromium content of the sprayed layer is 60% by weight to 95% by weight, Is 10 μm to 50 μm,
And the thickness of the chrome plating layer is 5 μm to 20 μm, and the surface roughness (Ra) of the surface of the chrome plating layer
Is preferably 3.0 μm or less.

[0012]

The anode container in the sodium-sulfur battery according to the present invention comprises a sprayed layer made of a highly corrosion-resistant metal powder on the inner peripheral surface of a base made of a metal material, and a chromium formed on the surface. A multi-layer coating layer with a plating layer is provided. For this reason, the coating layer has unique irregularities on the surface of the thermal spray layer,
Pores such as pores near the surface are filled with a chromium plating layer, and the invasion of the active material, sodium polysulfide, etc. to these defect sites is prevented, so that corrosion is promoted due to these invasions. In addition to suppressing the decrease in the battery capacity due to the consumption of the anode active material, the battery can sufficiently withstand long-term use.

In the anode container, the surface of the coating layer is smoothed by a chrome plating layer.
The contact between the surface of the coating layer and the conductive material for the anode is improved, the internal resistance of the battery is significantly reduced, and the efficiency of electric energy can be improved.

In this case, it is preferable that the thermal spray layer is formed of a high chromium-iron alloy having a chromium content of 60% by weight to 95% by weight, and the thermal spray layer has a thickness of 10 μm to 50 μm. Thereby, the corrosion resistance of the anode container can be further improved. Further, it is preferable that the thickness of the chromium plating layer be in the range of 5 μm to 20 μm.

If the thickness of the chromium plating layer is less than 5 μm, undissolved metal powder on the surface of the sprayed layer may not be completely buried in the plating layer, and the surface of the sprayed layer may not be completely covered with the plating layer. May not be coated uniformly. When the thickness of the chromium plating layer exceeds 20 μm, the residual stress after plating remaining between the substrate, the sprayed layer and the chromium plating layer, and the difference in thermal expansion between these three members during repeated heating and cooling of the battery. As a result, cracks or the like are generated in the sprayed layer at an early stage, thereby deteriorating the corrosion resistance of the anode container and shortening the life of the battery.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Sodium-sulfur battery) Hereinafter, the sodium-sulfur battery according to the present invention will be described with reference to the drawings. FIG. 1 shows a longitudinal section of an example of the sodium-sulfur battery according to the present invention, and FIG. 2 shows a partial longitudinal section in which an arrow 2 portion of an anode container constituting the battery is enlarged. . The sodium-sulfur battery includes an anode container 10a and a solid electrolyte 1
0b is a main component, and the cathode active material 10c and the anode active material 10d are main components.

The anode container 10a is formed of a bottomed cylindrical substrate 11
, A sprayed layer 12 forming a coating layer, and a plating layer 13. The base 11 is formed of aluminum or an aluminum alloy, and the sprayed layer 12 is formed of a chromium-iron based alloy sprayed layer. The plating layer 13 is formed of a chrome plating film.

The solid electrolyte 10b is a bottomed cylindrical body having sodium ion permeability, and is formed of beta alumina. The solid electrolyte 10b is disposed concentrically within the anode container 10a in a state of being fitted to an insulating ring 14 formed of alpha alumina,
It is covered with a lid 15b having a cathode terminal 15a.

Thus, the insulating ring 14 and the lid 1
5b seals the anode container 10a and the solid electrolyte 10b, configures the inside of the solid electrolyte 10b as a cathode chamber, and configures the space between the anode container 10a and the solid electrolyte 10b as an anode chamber. The base 11 constituting the anode container 10a has an anode terminal 11a on its outer periphery.

In the sodium-sulfur battery, the cathode compartment contains a cathode active material 10c, and the anode compartment contains an anode active material 10d. The cathode active material 10c is made of metallic sodium, and is housed in the cathode chamber with metal fibers interposed. The anode active material 10d is made of sulfur, and is accommodated in the anode chamber with graphite felt interposed.

In the sodium-sulfur battery, when the battery is heated to 300 ° C. to 350 ° C., an open circuit voltage of about 2.08 V is exhibited. When an external load is connected to the battery, sodium as a cathode active material is ionized in the battery. The sodium ions permeate through the solid electrolyte 10b and pass through the anode active material 1
0d, and reacts with sulfur, which is the same active material 10d, to generate sodium polysulfide and discharge. In addition, in the sodium-sulfur battery, a reaction opposite to the above occurs at the time of charging, and the battery is charged.

Thus, in the sodium-sulfur battery, the thermal spray layer 12 is formed of a high chromium-iron alloy having a chromium content of 60 to 95% by weight, and has a thickness in the range of 10 to 50 μm. Is formed.
The plating layer 13 is formed by applying chromium plating to the surface of the sprayed layer 12 and has a thickness of 5 μm.
The surface roughness (Ra) of the surface is 3.0 μm or less.

In the sodium-sulfur battery having the above-described structure, the anode container 10a is formed on the inner peripheral surface of the base material 11 made of a metallic material by spraying a chromium-iron alloy powder having high corrosion resistance on the inner peripheral surface thereof. And a chrome-plated layer 13. For this reason, in the coating layer, specific irregularities on the surface of the thermal sprayed layer 12 and pores such as pores near the surface are filled with the chromium plating layer 13, and sodium polysulfide penetrates into these defective portions to cause corrosion. Without accelerating, the reduction of the battery capacity due to the consumption of the anode active material 10d is suppressed, and it is possible to sufficiently endure long-term use without being corroded.

In the anode container 10a, since the surface of the coating layer is smoothed by the chromium plating layer 13, the contact between the surface of the coating layer and graphite felt, which is a conductive material for the anode, is improved, and Can be significantly reduced, and the energy efficiency of the battery can be improved.

In this case, the sprayed layer 12 has a chromium content of 6
Since it is formed of a high chromium-iron alloy of 0 to 95% by weight and the thickness of the sprayed layer is in the range of 10 to 50 μm, the corrosion resistance of the anode container 10a is further improved. be able to. Moreover, since the thickness of the chromium plating layer 13 is formed in the range of 5 μm to 20 μm, the chromium plating layer 13 can completely bury the undissolved metal powder on the surface of the sprayed layer 12 inside. At the same time, the surface of the thermal spray layer 12 can be completely and uniformly coated, and furthermore, the residual stress after plating existing between the substrate 11, the thermal spray layer 12, and the plating layer 13, and the repeated heating of the battery, Cracks and the like do not occur in the sprayed layer 12 at an early stage due to the difference in thermal expansion between these three members during cooling, the corrosion resistance of the anode container 10a is not reduced, and the life of the battery is further increased. Can be improved.

(Experiment 1) In this experiment, a heating / cooling test (heat cycle test) was performed in order to know the relationship between the thickness of the plating layer constituting the coating layer of the anode container and the state of occurrence of cracks in the sprayed layer. Was. In this experiment, the length was 300 m
m, on the inner peripheral surface of a substrate having an outer diameter of 50 mm and a thickness of 1.4 mm,
Cr (78 wt.%)-Fe (21 wt.%)-Si
(1.0 wt.%) After forming a sprayed layer of an alloy and polishing the surface of the sprayed layer to remove oxides and the like on the surface layer to make the surface roughness Ra 4 μm to 15 μm, the results are shown in Table 1. Various anode containers were produced by forming Cr plating layers of various thicknesses, and the sodium-sulfur batteries shown in FIG. 1 were constructed using these anode containers.

For each of the sodium-sulfur batteries thus constructed, the state of occurrence of cracks in the sprayed layer when heating and cooling were repeatedly performed was measured. The results obtained are shown in the graph of FIG.

However, in the heat cycle test, the sodium-sulfur battery was heated from room temperature to 395 ° C. in 5 hours, held at this temperature for 10 hours, and then cooled to room temperature in 5 hours. This was repeated, and the number of cracks in the sprayed layer was measured by the X-ray transmission method at regular heat cycle intervals.

As a comparative test, an anode container having a coating layer alone and no thermal spray layer was prepared, and a sodium-sulfur battery constructed using this anode container was also subjected to the same heat cycle test as described above. Was performed to measure the number of cracks in the coating layer, and the results are shown in the graph of FIG.

[0030]

[Table 1]

Referring to the graph of FIG. 3, the relationship between the thickness of the plating layer and the number of cracks generated in the sprayed layer is within a predetermined thickness range (NO. 1 to NO. 4) where the thickness of the plating layer is small. As the thickness increases, the number of cracks increases gradually, and the subsequent increase in thickness (NO. 5) dramatically increases the number of cracks generated. 0.5 to 8), it is recognized that the number of cracks increases as the thickness increases.

The criticality of the thickness of the plating layer at which the number of cracks increases dramatically is between 18 μm and 26 μm.
0 μm. Further, in the predetermined range where the thickness is small (NO. 1 to NO. 4), the crack generation time is late, whereas the predetermined range where the thickness is large (N.
O. 5 to NO. In 8), cracks occurred early.

The reason why such a critical thickness is recognized in the thickness of the plating layer is not clear, but the thickness of the plating layer is not more than 20.
When the thickness exceeds μm, cracks are generated in the sprayed layer early due to residual stress after plating existing between the three members of the base, the sprayed layer and the plated layer, and a difference in thermal expansion between these three members during a heat cycle. It is understood that the number of occurrences of cracks increases, and the upper limit of the thickness of the plating layer is 20 μm.

Regarding the lower limit of the thickness of the plating layer, the undissolved metal powder remaining on the surface of the sprayed layer can be completely buried in the plated layer, and the surface of the sprayed layer can be completely uniform. And the surface roughness (R
a) The thickness must be about 3.0 μm or less, and this thickness is 5 μm.

In the case where the coating layer is a plating layer alone and does not have a sprayed layer (NO. 9 and NO. 10), cracks occur in the coating layer at an early stage of the heat cycle experiment, and the cracks rapidly increase thereafter. To increase.

(Experiment 2) In this experiment, a charge / discharge test (charge / discharge) in which charging / discharging is repeatedly performed to find out the relationship between the presence or absence of a plating layer in the coating layer constituting the anode container, the internal resistance of the battery, and the battery capacity (charge / discharge) Cycle test). In this experiment, the length was 300 mm, the outer diameter was 50 mm, and the thickness was 1.4.
A sodium-sulfur battery shown in FIG. 1 was constructed using an anode container having various coating layers shown in Table 2 formed on the inner peripheral surface of a substrate having a thickness of 1 mm. At each interval, the internal resistance (operating at 385 ° C.) and the battery capacity (operating at 350 ° C.) of the battery were measured. The obtained results are shown in the graphs of FIGS.

[0037]

[Table 2]

Referring to FIGS. 4 and 5, regarding the internal resistance of the battery, when the coating layer does not have a plating layer on its surface (NO. 4, NO. 5), a plating layer is provided. Compared with the case (NO. 1 to NO. 3), the internal resistance is already large at the beginning of charging and discharging, and the internal resistance further increases in accordance with the increase in the number of charging and discharging cycles. However,
When the coating layer includes a plating layer (NO. 1 to NO.
Even in 3), the internal resistance similarly increases in response to the increase in the number of charge / discharge cycles. The battery capacity is the same at the initial stage of charging regardless of whether or not the coating layer has a plating layer, but the battery capacity is not provided (NO. 4).
NO. In 5), it is recognized that the decrease in battery capacity is large in accordance with the increase in the number of charge / discharge cycles.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a sodium-sulfur battery according to an example of the present invention.

FIG. 2 is an enlarged partial longitudinal sectional view of a portion indicated by an arrow 2 in FIG. 1 in an anode container constituting the battery.

FIG. 3 is a graph showing the relationship between the thickness of a plating layer and the occurrence of cracks in a sprayed layer in a heat cycle test.

FIG. 4 is a graph showing the relationship between the presence or absence of a plating layer and the internal resistance of a battery in a charge / discharge cycle test.

FIG. 5 is a graph showing the relationship between the presence or absence of a plating layer and the battery capacity in a charge / discharge cycle test.

[Explanation of symbols]

10a: an anode container, 10b: a solid electrolyte, 10c: a cathode active material, 10d: an anode active material, 11: a bottomed cylindrical substrate,
12: Thermal spray layer, 13: Plating layer.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/39

Claims (5)

(57) [Claims] 1. An anode container provided with a coating layer made of a metal material having higher corrosion resistance than the base material on the inner peripheral surface of a bottomed cylindrical base made of a metal material, and disposed inside the anode container. And a cathode active material made of metallic sodium housed in the solid electrolyte, and an anode active material made of sulfur housed between the solid electrolyte and the anode container. In a sodium-sulfur battery comprising a substance and performing a charging / discharging operation in a heated state, a coating layer of the anode container is made of a highly corrosion-resistant metal powder, and a chromium plating is applied to cover the surface of the sprayed layer. Sodium, characterized in that it is composed of multiple layers
Sulfur battery. 2. The sodium-sulfur battery according to claim 1, wherein the sprayed layer is a high chromium-iron alloy sprayed layer. 3. A sodium-sulfur battery according to claim 2, wherein said sprayed layer has a chromium content of 60% by weight to 95% by weight.
% By weight. 4. The sodium-sulfur battery according to claim 2, wherein said sprayed layer has a thickness of 10 μm to 50 μm.
m, and the thickness of the chrome plating layer is 5 μm to 20 μm.
A sodium-sulfur battery, characterized in that: 5. The sodium-sulfur battery according to claim 1, wherein the chromium plating layer has a surface roughness (Ra) of 3.0 μm or less. Sulfur battery.