JPH01253172A - Sodium-sulfur battery - Google Patents

Abstract

PURPOSE:To improve the energy efficiency of battery by setting higher the fiber filling ratio to the outer layer of a cathode conductive layer, while by setting lower those of the inner and outer layers. CONSTITUTION:A cathode conductive material M formed with carbon filter of mat and cylinder shape is formed of three layers, i.e. an outer cathode conductive layer Ma abutting against the inner face of a cathode vessel 2, an inner cathode conductive layer Mb abutting against the outer peripheral face of a solid electrolytic tube 5, and an intermediate cathode conductive layer Mc positioned between both layers. The carbon fiber filling ratio to the layer Ma is sufficiently set higher, for example 80% or more, while the ratios to the layers Mb, Mc lower, for example 30%. Since the filling ratio to the layer Ma is set high, even if the liquid surface S of a cathode active material (sulfur) is lowered downward in the layers Mb and Mc at the time of changing of battery, the whole inner peripheral face of the vessel 2 is immersed with sulfur as shown by dotted lines by the soaking up retaining action due to the capillary phenomenon, the lowering of electric resistance is restrained while the passing area of the vessel 2 is sufficiently ensured, and the flow of current is smoothened, thereby the energy efficiency of battery can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a sodium-sulfur battery, and more specifically, the electrical resistance of the anode container and/or solid electrolyte tube decreases from the middle to the final stage of charging, thereby improving battery energy efficiency. The present invention relates to a sodium-sulfur battery that can prevent a decrease in energy.

(Prior art) Recently, as a secondary battery for electric vehicles and nighttime power storage, it has been developed to be excellent in both performance and economical aspects.
Research and development is progressing on high-temperature sodium-sulfur batteries that operate at ℃.

In other words, in terms of performance, sodium-sulfur batteries have a higher theoretical energy density than lead-acid batteries, there are no side reactions such as the generation of hydrogen or oxygen during charging and discharging, and the utilization rate of the positive electrode active material is high. It also has the advantage that sulfur is cheap.

A conventional sodium-sulfur battery will be explained based on FIG. 7. In the figure, 2 is an anode container equipped with an anode terminal 1, and 4 is connected to the anode container 2 via an insulating ring 3, and is connected to the anode container 2 through an insulating ring 3. This is a cathode container for storage. Further, 5 is a bottomed cylindrical solid electrolyte tube fixed to the insulating ring 3;
is a cathode tube that has penetrated the cathode container 4 and entered the solid electrolyte tube 5. The anode conductive material M, which is housed between the anode container 2 and the solid electrolyte tube 5 and is made of conductive carbon fibers formed into a cloak-like and cylindrical shape, has a filling rate of the carbon fibers. All parts were uniform.

When charging the battery, sodium in the solid electrolyte tube 5 separates into sodium ions and electrons and enters the conductive material M for the anode, and reacts with molten sulfur as the anode active material impregnated into the conductive material M for the anode. Produces sodium polysulfide.

(Problem to be Solved by the Invention) However, in the conventional sodium-sulfur battery, since the conventional rate of the conductive material M for the anode was uniform as described above, as the charging time elapses, the rate as shown in FIG. As such, the liquid level S of the anode active material (sulfur) gradually decreases at the same level, and as a result, the anode active material becomes insufficient at the upper portions of the inner circumferential surface of the anode container 2 and the outer circumferential surface of the solid electrolyte tube 5, respectively. As a result, the electrical resistance increases due to a decrease in the current-carrying area of the anode container 2 and the solid electrolyte tube 5, resulting in a problem that the battery energy efficiency decreases.

A first object of the present invention is to solve the above-mentioned problems and provide a sodium-sulfur battery that can suppress a large decrease in the electrical resistance of the anode container during charging and improve battery energy efficiency. It's about doing.

A second object of the present invention is to provide a sodium-sulfur battery that can increase the electrical resistance of the solid electrolyte tube during charging and suppress the decrease in battery energy efficiency. be.

Furthermore, a third object of the present invention is to provide a sodium-sulfur battery that can further improve battery energy efficiency by suppressing a decrease in electrical resistance of an anode container and a solid electrolyte tube.

(Means for Solving the Five Problems) In order to achieve the first object, the sodium-sulfur battery according to claim 1 is made up of a collection of conductive fibers such as carbon fibers or ceramic fibers, and has an anode active material. A cathode container that stores molten metal sodium is bonded and fixed to a cylindrical anode container that stores a cylindrical anode conductive material impregnated with sulfur through an insulating ring, and inside the anode container, A bottomed cylindrical solid electrolyte tube whose base end fits into the inner circumference of the insulating ring to communicate with the inside of the cathode container and has a function of selectively transmitting sodium ions is attached to the conductive material for the anode. In the sodium-sulfur battery inserted into the hollow part of the anode container, the fiber charging rate of the outer anode conductive layer that contacts the inner peripheral surface of the anode container is increased, and the inner anode conductive layer that contacts the outer peripheral surface of the solid electrolyte tube. Also, a method is taken in which the fiber filling rate of the intermediate anode conductive layer located between the outer and inner anode conductive layers is set low.

In the sodium-sulfur battery according to claim 2, in order to achieve the second object, in the sodium-sulfur battery according to claim 1, the fiber filling rate of the outer anode conductive layer and the intermediate anode conductive layer is lowered, The method is to set the fiber filling rate of the conductive layer for the inner anode to be high.

In order to achieve the third object, the sodium-sulfur battery according to the third aspect of the present invention takes a step in which the fiber filling rate of the inner anode conductive layer is set high in the sodium-sulfur battery according to the first aspect.

(Function) In the sodium-sulfur battery according to claim 1, even if the sulfur liquid level of the anode active material decreases in the inner anode conductive layer and the intermediate anode conductive layer during charging, the fiber filling of the outer anode conductive layer Due to the high rate, the anode active material is retained within the conductive layer by capillary action, and even after the charging time has elapsed, the entire inner peripheral surface of the anode container is immersed in the anode active material. Electrical resistance does not increase, and battery energy efficiency improves.

In the sodium-sulfur battery according to claim 2, like the sodium-sulfur battery according to claim 1, the outer peripheral surface of the solid electrolyte tube is immersed in the positive electrode active material during charging, so that an increase in electrical resistance is suppressed, and the battery Improves energy efficiency.

Furthermore, since the sodium-sulfur battery according to claim 3 exhibits the combined effects of the sodium-sulfur batteries according to claims 1 and 2, the battery energy efficiency is further improved.

(Example) Next, an example embodying the sodium-sulfur battery according to claim 1 will be described with reference to FIGS. 1 to 3.

As shown in FIG. 2, the sodium-sulfur battery of this embodiment includes an anode container 2 equipped with an anode terminal 1 at the bottom thereof, and a mat-shaped carbon fiber or ceramic fiber housed inside the anode container 2. A conductive material M for an anode, which is formed into a cylindrical shape and impregnated with an anode active material (sulfur), will be described in detail later.
and a cathode container 4 that is connected to the upper end of the anode container 2 via an insulating ring 3 made of α-alumina and stores molten metal sodium Na, and is fixed to the inner circumference of the insulating ring 3, The solid electrolyte tube 5 is made of β-alumina and forms a cylindrical bag tube extending downward and has a function of selectively transmitting a certain sodium ion as a cathode active material. Further, an elongated cathode tube 6 extending through the cathode container 4 to the bottom of the solid electrolyte tube 5 is supported through the center of the upper lid of the cathode container 4, and at the upper end of the cathode tube 6,
A cathode terminal 7 is fixed.

During discharge, sodium ions pass through the solid electrolyte tube 5 through the following reaction and enter the housing space of the anode conductive material M defined by the anode container 2 and the solid electrolyte tube 5, and the inside of the conductive material M. reacts with molten sulfur to form sodium polysulfides, especially finally sodium trisulfide.

2N, a +X5-Na2 S x Also, during charging, a reaction opposite to that during discharging occurs, and sodium and sulfur are generated.

The cathode container 4 and the solid electrolyte tube 5 are filled with a stainless steel wick 8 as a safety measure in case the solid electrolyte tube 5 is damaged.

Next, the characteristic structure of the sodium-sulfur battery of the present invention will be explained.

As described above, the anode conductive material M made of carbon fiber formed into a cloak-like and cylindrical shape includes an outer anode conductive layer Ma that contacts the inner circumferential surface of the anode container 2 and an outer circumferential surface of the solid electrolyte tube 5. an inner anode conductive layer Mb in contact with the inner anode conductive layer Mb; and an intermediate anode conductive layer Ji located between the outer and inner anode conductive materials.
It is formed in three layers with Mc. In this example, the filling rate of the carbon fibers constituting the outer anode conductive layer Ma is set to 80% or more, so that the anode active material f (sulfur) is impregnated and retained in the anode conductive layer Ma by capillary action. I have to.

On the other hand, the conductive layer Mb for the inner anode and the conductive layer J for the intermediate anode
The fiber filling rate of iiMc was set to 30%, respectively, so that the liquid level S of the anode active material could decrease with the passage of charging time.
It is said that

It is sufficient to set the thickness of the conductive NMa for the outer anode to, for example, 10 m, but making it too thick is not desirable because it will affect the utilization rate of the anode active material.

In this example, since the fiber filling rate of the outer anode conductive layer Ma is as high as 80%, when the battery is charged, the inner anode conductive layer Mb and the intermediate anode conductive MMC are Even if the liquid level S of the anode active material decreases downward, the inner periphery of the anode container 2 will ooze out due to capillary action in the outer anode conductive layer Ma, as shown by the chain line in FIG. The entire surface is immersed in the anode active material, thus ensuring a sufficient current-carrying area of the anode container 2, suppressing a decrease in electrical resistance, smoothing the flow of current, and improving battery energy efficiency.

Next, an embodiment of the sodium-sulfur battery according to claim 2 will be described based on FIG. 4.

In this example, the fiber filling rate of the conductive iMb for the inner anode was 8.
0% or more, and the fiber filling rate of the conductive layer 1iMa for the outer anode and the conductive layer Mc for the intermediate anode is 30%, but the other configurations are the same as in the previous example. Therefore, since the entire outer peripheral surface of the solid electrolyte tube 5 is filled with the anode active material during charging of the battery, it is possible to suppress the electrical resistance of the solid electrolyte tube 5 from increasing, and as a result, the battery energy efficiency is reduced. will improve.

Next, an embodiment of the sodium-sulfur battery according to claim 3 will be described based on FIG.

In this example, the fiber filling rate of the conductive layer Ma for the outer anode and the conductive layer Mb for the inner anode is 80%, and the conductive layer Ma for the intermediate anode is
The fiber filling rate of MC is 30%. Further, the direction of the fibers of the intermediate anode conductive layer Mc is oriented in the radial direction so that electrons can easily migrate along the fibers to the inner peripheral surface side of the anode container 2.
Although the current flow is made smooth, the other configurations are the same as those of the previous embodiment.

Therefore, in this embodiment, during charging, the electric resistance of both the anode container 2 and the solid electrolyte tube 5 can be suppressed from decreasing, and the battery energy efficiency can be further improved.

Note that the present invention can also be embodied as follows.

As shown in FIG. 6, in the embodiment of claim 1, the fibers of the inner anode conductive layer Mb and the middle anode conductive layer Mc are oriented in the lateral direction. Further, although not shown in the drawings, a similar configuration can be adopted in the embodiment described in claim 2.

(Effects of the Invention) As detailed above, the sodium-sulfur battery according to claim 1 suppresses a decrease in electrical resistance by bringing the anode active material into contact with the inner peripheral surface of the anode container during discharge. , which has the effect of improving battery energy efficiency.

Further, in the sodium-sulfur battery according to claim 2, the anode active material is brought into contact with the inner circumferential surface of the anode container during charging, suppressing a decrease in electrical resistance thereof, and improving battery energy efficiency. effective.

Moreover, the sodium-sulfur battery according to claim 3 is the sodium-sulfur battery according to claim 1.
Moreover, there is an effect that the battery energy efficiency can be further improved than the sodium-sulfur battery according to claim 2. .

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged cross-sectional view showing the operating state of the main parts of the sodium-sulfur battery of the present invention, FIG. 2 is a vertical cross-sectional view of the central part of the sodium-sulfur battery, and FIG. 3 is A-A in FIG. 2. A line sectional view, FIG. 4 is a central longitudinal sectional view showing an embodiment of the sodium-sulfur battery according to claim 2, and FIG. 5 is a central longitudinal sectional view showing an embodiment of the sodium-sulfur battery according to claim 3. Figure, 6th
The figures are a vertical cross-sectional view of the central part showing another embodiment of the present invention, FIG. 7 is a vertical cross-sectional view of the central part of a conventional sodium-sulfur battery, and FIG.
The figure is also a partially enlarged sectional view of the conductive material for an anode shown in FIG. 7. 2... Anode container, 3... Insulating ring, 4... Cathode container 5... Solid electrolyte tube, 6... Cathode tube, M...
Conductive material for anode, Ma... Conductive layer for outer anode, Mb...
・Conductive layer for inner anode, Mc...conductive layer for intermediate anode, S
...Sulfur, Na...Sodium.

Claims (1)

[Claims] 1. A cylindrical anode containing a cylindrical anode conductive material (M) made of a collection of conductive fibers such as carbon fibers or ceramic fibers and impregnated with sulfur as an anode active material. Container (2
) is provided with a cathode container (4) for storing molten metal sodium (Na) via an insulating ring (3), and inside the anode container (2), the proximal end is connected to the insulating ring (3).
fits into the inner circumference of the cathode container (4) and communicates with the inside of the cathode container (4);
A bottomed cylindrical solid electrolyte tube (5) having a function of selectively permeating sodium ions is connected to the anode conductive material (
In the sodium-sulfur battery inserted into the hollow part of M), the fiber filling rate of the outer anode conductive layer (Ma) in contact with the inner peripheral surface of the anode container (2) is increased, and the solid electrolyte tube (M) is
5) The fiber filling rate of the inner anode conductive layer (Mb) in contact with the outer circumferential surface of the inner anode conductive layer (Mb) and the intermediate anode conductive layer (Mc) located between the outer and inner anode conductive layers (Ma, Mb) is lowered. A sodium-sulfur battery characterized by the following: 2. In the sodium-sulfur battery according to claim 1, the fiber filling rate of the outer anode conductive layer (Ma) and the intermediate anode conductive layer (Mb) is lowered, and the fiber filling rate of the inner anode conductive layer (Mc) is lowered. A sodium-sulfur battery characterized by having a high value. 3. The sodium-sulfur battery according to claim 1, wherein the inner anode conductive layer (Mb) has a high fiber filling rate.