JP2000012077A - Sodium / sulfur secondary battery - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide a sodium-sulfur secondary battery having a long life and excellent charge / discharge characteristics. A negative electrode and a positive electrode are separated by a solid electrolyte having sodium ion conductivity, the negative electrode having sodium as a negative electrode active material, and the positive electrode is provided in a room surrounded by an outer container and the solid electrolyte. A sodium-sulfur secondary battery having a structure containing a positive electrode current collector impregnated with sulfur or sodium polysulfide as a substance, wherein the outer container of the positive electrode has an outermost surface layer and a layer in contact with the positive electrode current collector. Become
A sodium-sulfur secondary battery, wherein a layer in contact with the current collector has excellent corrosion resistance to a positive electrode active material and is not bonded to the outermost surface layer. A sodium-sulfur secondary battery, wherein a layer in contact with the positive electrode current collector is deformed to the outside of the positive electrode container and is in electrical contact with the outermost surface layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a sodium cathode having a structure of a positive electrode container having excellent corrosion resistance to a positive electrode active material.
Sulfur secondary battery

[0002]

2. Description of the Related Art As shown in FIG. 4, a sodium-sulfur secondary battery uses a solid electrolyte having sodium ion conductivity to form a negative electrode chamber containing sodium as a negative electrode active material and a sulfur as a positive electrode active material. It is constituted by a positive electrode chamber for accommodating a substance such as impregnated carbon fiber (hereinafter referred to as a positive electrode current collector).

[0003] The positive electrode container of the sodium-sulfur secondary battery is always exposed to molten sulfur having a strong corrosive action and molten sodium polysulfide at a battery operating temperature of 300 to 350 ° C or lower.

Heretofore, a positive electrode container of the sodium-sulfur secondary battery has been used in which a corrosion-resistant film is formed on the inner peripheral surface of a cylindrical metal material by a method such as chromizing treatment, plating treatment, or plasma spraying. Was.

[0005] JP-A-2-42066 discloses a method of providing a chromium plating layer on a positive electrode container, JP-A-4-349343,
JP-A-6-231802 and JP-A-2,520,986 disclose a powder material made of a corrosion-resistant alloy under an inert gas atmosphere.
Alternatively, a method of forming a corrosion resistant film by plasma spraying under atmospheric pressure is disclosed. Also, JP-A-8-78049
Japanese Patent Application Laid-Open Publication No. H11-157, discloses a method for forming a corrosion-resistant film on a positive electrode container without defects by gradually reducing the Cr content of a corrosion-resistant coating layer composed of a plurality of Cr-Fe alloys from the surface.

However, in order to apply the sodium-sulfur secondary battery to power load leveling and the like, it is essential to achieve a higher current, a higher output, and a higher density. In such an application, the amount of heat generated during operation of the battery increases, and the temperature of the battery body increases and the amplitude of the temperature change increases. For this reason, corrosion-resistant coatings produced by conventional methods such as chromizing, plating, and plasma spraying cause peeling or cracking due to the difference in the coefficient of thermal expansion from the material of the positive electrode container, which increases the resistance inside the battery and causes corrosion of the container. There has been a problem that it becomes a trigger to shorten the battery life and the battery performance.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a sodium-sulfur secondary battery having a long service life and a high safety, which has excellent battery performance and can obtain stable charge / discharge characteristics over a long period of time. provide.

[0008]

The gist of the present invention is as follows.

(1) A negative electrode and a positive electrode are separated by a solid electrolyte having sodium ion conductivity, and the negative electrode has sodium as a negative electrode active material, and the positive electrode is provided in a room surrounded by an outer container and the solid electrolyte. A sodium-sulfur secondary battery having a structure containing a positive electrode current collector impregnated with sulfur or sodium polysulfide as a positive electrode active material, wherein the positive electrode outer container is formed of an outermost surface layer and a layer in contact with the positive electrode current collector. And a layer in contact with the positive electrode current collector has excellent corrosion resistance to the positive electrode active material, and is not bonded to the outermost surface layer.

(2) A negative electrode and a positive electrode are separated by a solid electrolyte having sodium ion conductivity, and the negative electrode has sodium as a negative electrode active material. The positive electrode is placed in a room surrounded by an outer container and the solid electrolyte. A sodium-sulfur secondary battery having a structure containing a positive electrode current collector impregnated with sulfur or sodium polysulfide as a positive electrode active material, wherein the outer container of the positive electrode has an outermost surface layer and a layer in contact with the positive electrode current collector. Wherein the layer in contact with the positive electrode current collector is deformed outward toward the outermost surface layer, so that the layer is in electrical contact with the outermost surface layer. battery.

(3) The sodium-sulfur secondary battery according to items 1 and 2, wherein the layer in contact with the positive electrode current collector contains a carbon material.

(4) The sodium-sulfur secondary battery according to (1) or (2), wherein the layer in contact with the positive electrode current collector is an alloy containing at least Cr or Co.

[0013] The present invention relates to a sodium-containing material having the structure shown in FIG.
It is a sulfur secondary battery. The positive electrode container 14 has a positive electrode container inner side 8 having corrosion resistance to a positive electrode active material (sulfur) and a positive electrode container outer side 3 made of a metal or an alloy having mechanical strength.
It is characterized by having a double structure consisting of

[0014] The sodium-sulfur secondary battery of the present invention is a battery having stable and good characteristics by causing charge / discharge reactions to occur evenly in a direction parallel to the cylindrical axis in the positive electrode chamber. Therefore, it is necessary that the positive electrode container 14 uses an electron conductive material that is negligible compared to the electron conductive resistance in the positive electrode chamber, and that the current flowing through the positive electrode current collector 10 has only a radial component. . Therefore, as shown in the drawing, the positive electrode container 14 is provided with an outermost surface layer (hereinafter, referred to as the outside of the positive electrode container) and a layer in contact with the positive electrode current collector (hereinafter, referred to as a positive electrode current collector).
In the case of a double structure of the inside of the positive electrode container), both the inside of the positive electrode container and the outside of the positive electrode container use a good electron conductive material,
In addition, they are installed so as to have electrical connections with each other in more areas and to keep the electronic resistance low.

However, when a structure in which the layer in contact with the positive electrode current collector inside the positive electrode container and the outermost surface layer outside the positive electrode container are joined to make an electrical connection, the temperature from room temperature to the operating temperature of the battery can be reduced. At the time of temperature rise or heat generation from the battery, cracks occur inside the positive electrode container due to the difference in the coefficient of thermal expansion between the inside of the positive electrode container and the outside of the positive electrode container. Therefore, in the present invention, it is preferable to adopt a structure in which the inside of the positive electrode container and the outside of the positive electrode container are not joined.

However, in order to exhibit the performance of the sodium-sulfur secondary battery, it is necessary to electrically connect the inside of the positive electrode container and the outside of the positive electrode container. As this method, the positive electrode current collector 10 is formed in the positive electrode chamber in a compressed form between the inside of the positive electrode container and the outside of the positive electrode container, and the inside of the positive electrode container is deformed outward by the pressure from the positive electrode current collector 10, Contact with the outside of the positive electrode container is effective in obtaining the effects of the present invention.

As the material inside the positive electrode container, any material having excellent corrosion resistance and good electron conductivity may be used. In particular, a carbon material such as graphite or an alloy containing Cr and Co may be used. preferable. Further, in order to prevent a rise in resistance, the inside of the positive electrode container is made as thin as possible as long as it meets the condition that the positive electrode active material does not pass through and does not break, and has an elasticity or a single or plural outside as shown in FIG. It is desirable to have a mechanism for deforming and contacting the container.

In a sodium-sulfur secondary battery, FIG.
As shown in the figure, the inside of the positive electrode container has excellent corrosion resistance by having a structure separated into the inside of the positive electrode container, which has excellent corrosion resistance to the positive electrode active material, and the outside of the positive electrode container, which has mechanical strength. Since it can be used, there is no fear of corrosion due to the positive electrode active material.

Further, since the outside of the positive electrode container only needs to have enough mechanical strength to protect the inside of the battery, an inexpensive material can be used. Further, the roles required for the positive electrode container are separated, so that the degree of freedom in material selection is greatly increased.

Further, by deforming the inside of the positive electrode container toward the outside of the positive electrode container by the pressure generated from the positive electrode current collector, a structure is brought into contact with the outside of the positive electrode container,
When the temperature of the battery rises to the operating temperature or when the battery generates heat, distortion caused by a difference in the thermal expansion coefficient between the inside of the positive electrode container and the outside of the positive electrode container can be reduced, so that the electrical connection is not interrupted. Therefore, it is possible to avoid a cause of deterioration such as peeling or cracking which has been a problem in the conventional method of coating the surface of the positive electrode, and the life is improved.

Further, simultaneously with the melting of the positive electrode active material,
Since the inside of the positive electrode container and the outside of the positive electrode container are in contact, when raising the temperature of a module in which many secondary batteries are arranged in series and parallel,
Although there is a possibility that a current may flow in the module due to the variation in the electromotive force of each battery due to the temperature difference between the individual batteries (this is called a continuation flow), according to the present invention, until the positive electrode active material is melted. It also has the advantage of not flowing.

[0022]

Embodiments of the present invention will be described below. The embodiment shown here is a typical example to which the present invention is applied, and is not limited to the embodiment shown here.

[0023]

Example 1 Ten sodium-sulfur secondary batteries having the structure shown in FIG. 1 were manufactured. As the material of each part, the solid electrolyte 1 was β "-alumina, the negative electrode container 4, the negative electrode cap 7, the positive electrode cap 11 was SUS304, the safety tube 6, the positive electrode terminal 12, and the negative electrode terminal 13 were Al metal.

The layer in contact with the positive electrode current collector of the positive electrode container 14 is a graphite foil having a thickness of about 800 μm. Container outer (outermost surface layer) 3 and negative electrode container 4
The α-alumina ring 2 was used as an insulating material between these two. The solid electrolyte 1 and the α-alumina 2 for insulating the positive and negative electrodes were joined by glass solder, and the α-alumina ring 2 was joined to the outside of the positive electrode container 3 of the positive electrode container 14 and the negative electrode container 4 by hot pressing. A molded product is produced by impregnating and solidifying carbon 9 constituting the positive electrode current collector 10 with sulfur 9 serving as a positive electrode active material in a compressed state so as to have a restoring force. This molded product was put into the inside 8 of the positive electrode container, inserted into the positive electrode chamber sandwiched between the solid electrolyte 1 and the outside 3 of the positive electrode container, and covered with a positive electrode cap to produce a sodium-sulfur secondary battery. . The gap between the outside 3 of the positive electrode container and the inside 8 of the positive electrode container was designed to be 0.5 mm.

FIG. 3 shows that the battery prepared above was heated to 330 ° C. and subjected to a charge / discharge cycle (current density was 6 for both charge and discharge).
0 / mA / cm ² ), 500 cycles, heat cycle (room temperature to 330 ° C. at 30 ° C./1 hour, 330 ° C.)
The graph shows the cycle dependence of the average resistance value of 10 batteries when 10 cycles of holding for 3 hours and cooling at 330 ° C. to room temperature (1 cycle) were repeated for 10 cycles, and then further repeated for 500 cycles. FIG. 3 is a graph in which the average resistance value in the third cycle is set to 1 and the average resistance value in each cycle is plotted as a relative value. As can be seen from this graph, the resistance of the battery of the present invention is not deteriorated significantly after 1000 cycles of operation and during the heat cycle during the operation, compared to the initial stage.

Thus, the battery operating temperature of 330
When the sulfur is melted by raising the temperature to ° C., the restoring force of the carbon felt is released, and by this restoration, the inside of the positive electrode container is deformed toward the outside of the positive electrode container, so that a sufficient electrical connection can be obtained.

[0027]

[Comparative Example 1] The inside of the positive electrode container (the layer in contact with the positive electrode current collector) 8 of the positive electrode container was not used, and SUS304 was used as the outside of the positive electrode container (outermost surface layer). The same sodium-sulfur secondary battery as in Example 1 was used except that a corrosion-resistant layer subjected to Ising treatment was used.
This was produced. This battery has the structure shown in FIG. 4, which is a conventional battery structure. In this case, a molded product impregnated with sulfur is inserted into the positive electrode chamber in a state where the carbon felt constituting the positive electrode current collector 10 is compressed, and the outer periphery of the molded product and the outside 3 of the positive electrode container (in this case, simply the positive electrode container 14) are removed. The design was such that the gap with the inner circumference was 0.5 mm.

The battery thus manufactured was heated to 330 ° C., and the charge / discharge cycle was changed to 5 under the same conditions as in Example 1.
The charge and discharge of 00 cycles, 10 heat cycles, and then 500 cycles were repeated. FIG. 3 shows the battery 1
The cycle dependence of zero average resistance is shown. As a result of charge / discharge of 1000 cycles, an increase in battery resistance, which is considered to be caused by corrosion, is observed.

From Example 1 and Comparative Example 1, the positive electrode container was made to have a double structure of the positive electrode container outer part 3 and the positive electrode container inner part (the layer in contact with the positive electrode current collector) 8 without joining the two layers.
The battery of the present invention using a carbon material having corrosion resistance for the inside 8 of the positive electrode container can achieve a longer life than a conventional battery.

[0030]

Example 2 The layer (the inside 8 of the positive electrode container) in contact with the positive electrode current collector of the positive electrode container was about 300 μm thick, and the material of the layer was 64% Co, 29% Cr, and 6% Al in composition ratio. , Y: 1%, and five sodium-sulfur secondary batteries were manufactured under the same conditions as in Example 1. In this case, the battery was assembled in such a manner that no gap was formed when the molded product impregnated with sulfur as the positive electrode active material was placed in the positive electrode chamber inside the layer in contact with the positive electrode current collector of the positive electrode container.

FIG. 3 shows the amount of sodium obtained above.
The temperature of the sulfur secondary battery was raised to 330 ° C., and under the same conditions as in Example 1, 500 charge / discharge cycles, 10 heat cycles, and 500 charge / discharge cycles were repeated. This shows the cycle dependence of the resistance value. Similar to Example 1, the average resistance value in the third cycle was set to 1, and the resistance value in each cycle was plotted as a relative value. The 1000 cycles of the sodium-sulfur secondary battery of the present invention and the heat cycle therebetween can suppress an increase in battery resistance as compared with the conventional method.

By comparing Example 2 with Comparative Example 1, even when an alloy containing Cr and Co having excellent corrosion resistance was selected for the inner positive electrode container material, a sodium-sulfur secondary battery having a longer life than the conventional one was obtained. Can be realized.

[0033]

Example 3 The thickness of the inside of the positive electrode container was about 300 μm, and the composition ratio was C
o An alloy composed of 64%, Cr 29%, Al 6% and Y 1%.
Using a battery having a mechanism for outward deformation as described above, ten sodium-sulfur secondary batteries similar to those in Example 1 were produced. The gap between the outside of the positive electrode container and the inside of the positive electrode container was designed to be 0.5 mm.

The sodium-sulfur secondary battery thus produced was heated to 330 ° C.
Cycle, 10 cycles of heat cycle, and then repeat 500 cycles of charge and discharge,
FIG. 3 shows the cycle dependence of the average resistance value of 10 batteries. Also in this case, as in Example 1, the average resistance value in the third cycle was set to 1, and the resistance value in each cycle was plotted as a relative value. As can be seen from this graph, the battery resistance of the present invention slightly increased compared to the initial stage for 1000 cycles of operation and a heat cycle during the operation, but the increase in battery resistance was suppressed as compared with the conventional method. Is made. In addition, with the mechanism in which the inside of the positive electrode container is deformed toward the outside of the positive electrode container, the inside of the positive electrode container can be deformed toward the outside of the positive electrode container by the restoring force of the mold when the temperature of the battery rises. The gap between the inside of the provided positive electrode container and the outside of the provided positive electrode container can be filled.

By comparing Example 3 with Comparative Example 1, it was found that Cr and Cr, which have excellent corrosion resistance but little
If an alloy containing Co is selected as the inner cathode vessel,
By providing a mechanism for deforming the inside of the positive electrode container toward the outside of the positive electrode container, the gap between the inside of the positive electrode container and the outside of the positive electrode container provided at the time of battery assembly can be filled by restoring the molded product, and sufficient electricity Connection can be secured.

[0036]

According to the present invention, the positive electrode container has a double structure consisting of the inside of the positive electrode container and the outside of the positive electrode container, which are not joined to each other, and are electrically connected to each other by the pressure from the positive electrode current collector. It is in. As a result, it is possible to avoid the causes of deterioration of the positive electrode, such as peeling and cracking of the positive electrode, which are problems of the conventional sodium-sulfur secondary battery, and to improve the life of the battery. Furthermore, since the inside of the positive electrode container and the outside of the positive electrode container come into electrical contact at the same time as the positive electrode active material is melted, when heating a module in which many secondary batteries are arranged in series and parallel,
Subsequent flow that occurs due to variations in the electromotive force of each secondary battery due to the temperature difference between the individual secondary batteries also has the advantage that it does not flow until the positive electrode active material is melted.

Further, the positive electrode container according to the present invention can omit the bonding step and can be manufactured more easily than the conventional method for manufacturing a sodium-sulfur secondary battery.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram of the inner positive electrode container at the time of battery assembly and at the time of operation of the battery when two mechanisms for deforming the inner positive electrode container to the outside are provided.

FIG. 3 is a graph showing the charge / discharge cycle dependency of battery resistance.

FIG. 4 is a longitudinal sectional view of a conventional sodium-sulfur battery.

[Explanation of symbols]

1 ... Solid electrolyte tube, 2 ... α-alumina ring for positive and negative electrode insulation, 3 ... Outside the positive electrode container, 4 ... Negative electrode container, 5 ... Negative electrode active material (sodium), 6 ... Safety tube, 7 ... Negative electrode cap, 8 ... Positive electrode Inside of container, 9 ... Positive electrode active material (sulfur),
10 ... Positive current collector, 11 ... Positive cap, 12 ... Positive terminal, 13 ... Negative terminal, 14 ... Positive container

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuichi Kamo 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Nariko Nishimura Omikamachi, Hitachi City, Ibaraki Prefecture Hitachi 1-1, Hitachi, Ltd. (72) Inventor Seiji Koike 7-1-1, Omika-cho, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (72) Kozo Sakamoto Hitachi, Ibaraki, Japan 7-1-1, Omikamachi, Hitachi City Hitachi, Ltd. Hitachi Research Laboratory, Ltd. (72) Inventor Kazue Kawano 7-1-1, Omikamachi, Hitachi City, Ibaraki Prefecture F-term, Hitachi Research Laboratory, Hitachi Ltd. 5H011 AA02 AA03 AA13 CC06 5H029 AJ02 AJ05 AJ12 AJ13 AK05 AL13 AM15 BJ02 DJ02 DJ07 EJ01 EJ04

Claims (4)

[Claims] A negative electrode and a positive electrode are separated from each other by a solid electrolyte having sodium ion conductivity. The negative electrode has sodium as a negative electrode active material, and the positive electrode is contained in a room surrounded by an outer container and the solid electrolyte. A sodium-sulfur secondary battery having a structure containing a positive electrode current collector impregnated with sulfur or sodium polysulfide as an active material, wherein the outer container of the positive electrode includes an outermost surface layer and a layer in contact with the positive electrode current collector. And a layer in contact with the positive electrode current collector has excellent corrosion resistance to the positive electrode active material, and is not bonded to the outermost surface layer. 2. A negative electrode and a positive electrode are separated by a solid electrolyte having sodium ion conductivity. The negative electrode has sodium as a negative electrode active material, and the positive electrode is contained in a room surrounded by an outer container and the solid electrolyte. A sodium-sulfur secondary battery having a structure containing a positive electrode current collector impregnated with sulfur or sodium polysulfide as an active material, wherein the outer container of the positive electrode includes an outermost surface layer and a layer in contact with the positive electrode current collector. A sodium-sulfur secondary battery, wherein a layer in contact with the positive electrode current collector is deformed toward the outermost surface layer to make electrical contact with the outermost surface layer. 3. The layer according to claim 1, wherein the layer in contact with the positive electrode current collector contains a carbon material.
Sulfur secondary battery. 4. A layer in contact with the positive electrode current collector is an alloy containing at least Cr or Co.
2. A sodium-sulfur secondary battery according to item 1.