JPS61256574A - Sodium-sulfur cell - Google Patents

Abstract

PURPOSE:To achieve good discharge performance by arranging insulation areas and conductive areas alternately over the entire circumference on the surface of solid electrolyte thereby facilitating dispersion of sodium polysulfide to the portion other than the conductive section of solid electrolytic tube. CONSTITUTION:A solid electrolytic tube 5 made of selective ion conductivity having closed lower end and open upper end is provided on the outercircumference of cell in storing area of negative electrode active material or sodium. An area 12 where insulation area and conductive area will exist alternately is provided on the outercircumference at the outside of the electrolytic tube 5. A porous conductive material 10 such as a carbon mat impregnated with sulfur is provided on the outercircumference of said area 12 while metallic positive electrode container 4 is provided at the outside of the conductive member 10. Consequently, dispersion of sodium polysulfide is facilitated resulting in considerable improvement of initial discharge performance.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to sodium-sulfur batteries (hereinafter referred to as Na/S batteries), and particularly relates to sodium-sulfur batteries (hereinafter referred to as Na/S batteries). Regarding Na/8 batteries.

[Background of the invention]

Conventional Na/S batteries pass sodium, the cathode active material, on one side and sulfur, the anode active material, on the other through a solid electrolyte (β or β''-alumina) that selectively allows only sodium ions to pass through. Arrangement, 300-35
It is known as a high-temperature secondary battery that charges and discharges at a temperature of 0C (for example, M. Baralc [Elec
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) It is expressed by the equation of the battery reaction accompanying the charging and discharging of the above Na/8 battery.

That is, during discharge, sodium, which is a cathode active material, liberates electrons and becomes sodium ions.The sodium ions pass through the solid electrolyte partition wall and react with sulfur, which is an anode active material, to produce sodium polysulfide. On the other hand, during charging, by applying a reverse voltage higher than the open circuit voltage of the battery, the reaction is opposite to that during discharging.

However, in the actual battery reaction, as shown in equation (1), N
Instead of a and S reacting directly to Nag's,
This is a so-called two-component region reaction in which Nag 86 and 8 coexist.

It is said to be a reaction in the component range. The above Na and S change to Na, S, and so on.

Carbon, which is a porous electronic conductor, as an anode.

Alternatively, by molding sulfur into graphite felt and making the porous electron conductor function as an electron collector, the above battery reaction during discharge will proceed without problems. However, during charging, although the reaction shown by equation (3) proceeds without any problem, the reaction shown by equation (2) does not proceed. It is known that the reason for this is that sulfur generated during charging is concentrated on the surface of the solid electrolyte, and the sulfur impairs ionic conductivity.

In particular, the reaction represented by formula (2) accounts for approximately 60% of the total battery reaction.
Therefore, unless the reaction of equation (2) is effectively carried out, only about 40% of the theoretical depth of charge shown by equation (1) can be used as an actual capacity.

Therefore, as a conventional example to solve such problems, in Japanese Patent Publication No. 59-10539, the anode surface in contact with the solid electrolyte tube is covered with an insulator made of glass fiber ceramic felt, alumina felt, or zircon felt. Prevents sulfur precipitation on the electrolyte tube surface.

In addition, in the above conventional example, if the entire surface of the solid electrolyte tube was covered with an insulator, the anode/cathode would be completely insulated and the discharge reaction would not proceed. It has been shown to provide a graphite felt that is electronically conductive without an insulator.

In the battery disclosed in Japanese Patent Publication No. 59-10539, the initial discharge reaction proceeds only at the bottom of the solid electrolyte tube, and the ionically conductive sodium polysulfide produced at the bottom is placed in the upper middle of the solid electrolyte tube. It is diffused and absorbed into the provided insulating region and a subsequent discharge reaction takes place.

However, in the above-mentioned conventional Na/S battery, as the battery becomes larger, especially its axis becomes longer, the insulation region becomes longer.
Since the sodium polysulfide generated at the bottom of the battery does not easily diffuse into the entire insulating region, the insulating region remains unchanged into a conductive region, resulting in a problem in that good discharge performance cannot be obtained.

[Purpose of the invention]

An object of the present invention is to provide an Na/S battery which has good discharge performance by easily diffusing sodium polysulfide generated in the conductive region provided on the surface of the solid electrolyte tube to other than the conductive portion of the solid electrolyte tube, that is, to the insulating region. Our goal is to provide the following.

[Summary of the invention]

The present invention does not adopt a divided structure in which a conductive region is provided at the bottom of the solid electrolyte tube and an insulating region is provided at the upper middle part of the solid electrolyte tube, as in conventional Na/S batteries, but the entire surface of the solid electrolyte is This is an Na/S battery characterized by having a structure in which insulating regions and conductive regions are alternately arranged around the periphery.

According to the above structure of the present invention, the length of the insulating region is reduced from the conventional length N
Since it can be made shorter than an a/S battery, the sodium polysulfide generated in the conductive region can diffuse smoothly into the insulating region.

The alternating arrangement of insulating regions and conductive regions in the present invention does not make the insulator cylindrical, which is disposed on the surface of the solid electrolyte tube, as in conventional Na/S batteries; This can be achieved by dividing the insulator into predetermined intervals. This can also be achieved by providing felt, which is woven with insulating fibers (for example, glass fibers) and conductive fibers (carbon fibers), on the surface of the solid electrolyte tube.

Furthermore, it is also possible to form voids surrounding a part of the outer peripheral surface of the solid electrolyte as an insulator, and to provide the voids alternately to realize the alternating arrangement of the insulating regions and conductive regions. can.

[Embodiments of the invention]

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the overall structure of a cylindrical Na/8 battery according to the present invention.

In the figure, the outer circumferential surface of the battery in the IJ storage region 9 (which is the cathode active material) is made of a material (β or β//-alumina) that has ion conductivity selectively only for Na+, and the lower end is closed. A solid electrolyte tube 5 with an open upper end is provided. A region 12 (hereinafter referred to as an alternating pressure region) in which insulating regions and conductive regions exist alternately is provided on the outer peripheral surface of the solid electrolyte tube 5. This exchange pressure area 1
The outer peripheral surface of 2 is a garbon cloak impregnated with sulfur,
Alternatively, a porous conductive material 10 of graphite mat is provided, and an anode container 4 of gold RH is provided outside the porous conductive material 10. A metal current collector tube 6 is provided in the sodium storage region 9 to function as a current collector, and the upper part of this current collector tube 6 is connected to a metal cathode cap 2. . An anode camp 8 is provided in the lower part of the anode container 4, and a rare gas injection tube 8 is provided in this anode cap 8. An upper opening of the solid electrolyte 5 is connected to a ring 3 made of α-alumina, which is an insulator, and the cathode cap 2 and anode container 4 are sealed at the upper and lower surfaces of the ring 3. The cathode cap 2 is provided with a sodium injection tube 1 .

The IJ injection tube 1 is used to inject sodium and seal off after injection, and the rare gas injection tube 8 is used to seal the anode after filling it with an inert rare gas. It is something.

An example of the exchange pressure area 12 in this embodiment is shown in FIG. 2. FIG. 2 is a sectional view taken along the line AA in FIG. 1.

In the figure, a porous insulator 22 made of glass fiber ceramic felt, alumina felt, or zircon felt is divided into four parts in the vertical direction. Therefore, the initial discharge reaction is initiated in the region 21 where the porous conductor 11 is in contact with the solid electrolyte tube 5.

The sodium polysulfide generated in this region 21 diffuses into the divided porous insulator 22, and thereafter the insulator 22 becomes entirely conductive, and the subsequent discharge progresses smoothly. On the other hand, during charging, sulfur is precipitated in the area 21 where the porous conductor 11 and the solid electrolyte tube 5 are in contact, partially inhibiting the charging reaction, but the surface area of this area 210 is divided into the area where the insulator 22 is in contact with the solid electrolyte tube 5. By reducing the surface area to 1/10 or less, preferably 1/100, the negative effect on the overall charging reaction can be reduced to a negligible level. In particular, the smaller the above ratio is, the better the current performance becomes.

Therefore, it is desirable that the number of divisions of the porous insulator 220 is such that the surface area ratio of the conductive region to the insulating region is 1/0 to 1/100.

In this embodiment, the porous insulator 22 is divided into four parts,
It can also be divided into two, three, or five or more parts. The greater the number of divisions within the range permitted by the manufacturing technology, the shorter the length of the porous insulator and the faster the diffusion rate of sodium polysulfide. Therefore, good discharge performance can be obtained.

The porous insulator 22 is used to prevent the porous conductor 11 from coming into direct contact with the solid electrolyte tube 5, and the thinner the porous insulator 22, the more preferable it is because it can lower the internal resistance of the anode. A desirable thickness is 0.1 mm or less.

AC pressure region 12 in which insulating regions and conductive regions exist alternately
Another embodiment is shown in FIG. 3.

FIG. 3 is a longitudinal cross-sectional view of the Na/S battery shown in FIG. 1, taken along the central portion B--B.

In the figure, the porous insulator 22 is laterally divided into ring shapes, and the porous conductor 11 and the solid electrolyte tube 5 are in contact with each other in a partial region 31. The smaller the number of regions 31, the smaller the division width of the porous insulator 220, and the thinner the porous insulator 22, the better, as in the embodiment shown in FIG. 2 above. The same applies to the materials used.

Further, the insulator 12 can be formed into a V-ring shape by combining the vertical division of the insulator 12 shown in FIG. 2 and the horizontal division of the insulator 12 shown in FIG. 3.

In this case, the size of the insulator 12 becomes smaller, so that the diffusion of the sodium polysulfide becomes more efficient.

The above-mentioned divided insulator 22 can be provided on the surface of the solid electrolyte tube 5 by arranging the above-mentioned insulator on the surface of the solid electrolyte tube in accordance with the manufacturing of a normal Na/5 battery.

Instead of the insulator 22, porous insulating fibers mixed with conductive fibers may be attached to the solid electrolyte tube 5.

At this time, the amount of conductive fibers may be small, 1/1 of the total.
0 or less, preferably about 1/100. The conductive fibers may be made of gelafalt, which is the same material as the porous conductor 11, but carbon felt, which has a slightly higher resistivity than graphite, is more suitable.

The conductive fibers can be mixed in by weaving them into insulating fibers, or by mixing the fibers and then forming them into a felt or sheet shape.

FIG. 4 shows another embodiment of the alternating pressure region 12, in which insulating regions and conductive regions are alternately present.

In this embodiment, the insulating region is not constructed using a porous insulator as in the other embodiments described above, but instead is constructed using a cavity 42 (in this embodiment) surrounding a part of the outer peripheral surface of the solid electrolyte tube. It is formed with a sawtooth shape. Note that the conductive region in this embodiment is a region 41 where the surrounding line forming the cavity 6 is in contact with the solid electrolyte tube 5.

Next, the results of a comparison of the discharge performance of the Na/S battery shown in FIG. 2 and having nine alternating pressure regions 12 and the conventional Na/8 battery will be explained.

FIG. 5 is a graph schematically showing the results of the comparison, and shows the change in discharge pressure with time.

According to the figure, the discharge voltage of a conventional Na/8 battery (A in the figure) gradually increases from the initial voltage value (Vzt''=0) to the open circuit voltage value (Vt > , the discharge voltage of the Na/S battery (B in the figure) of the type shown in FIG. 2 increases rapidly from v2 to Vl.

Therefore, it can be seen that the initial discharge performance was significantly improved.

〔Effect of the invention〕

As explained above, according to the present invention, the insulating regions and conductive regions divided into small parts are alternately provided on the surface of the solid electrolyte tube, so that sodium polysulfide can diffuse quickly and smoothly in the insulating regions. It will be held in Therefore, it has the effect of significantly improving initial discharge performance.

[Brief explanation of drawings]

FIG. 1 is an overall sectional view showing an embodiment of the Na/S battery according to the present invention, and FIGS. 2 to 4 show a state in which insulating regions and conductive regions are alternately provided on the surface of a solid electrolyte tube. FIG. 5 is a graph showing a comparison of the discharge performance of a conventional Na/S battery and an Na/8 battery according to the present invention. 4... Anode container, 5... Solid electrolyte tube, 9... IJium storage tank, 10... Porous conductor, 12...
...Insulator, 21.31.41...Conductive region, 42.
...Void area.

Claims (1)

[Claims] 1. A solid electrolyte tube in which a cathode active material is disposed;
In a sodium-sulfur battery comprising the cathode active material and a conductor disposed inside of which an anode active material that causes a charge/discharge reaction, a plurality of insulating regions are provided between the solid electrolyte tube and the conductor. A sodium-sulfur battery characterized in that conductive regions are provided alternately.