KR100294469B1 - Turned-over type sodium/sulfur battery or sodium/nickel chloride battery - Google Patents

Abstract

PURPOSE: Provided is a turned-over type sodium/sulfur battery or sodium/nickel chloride battery, which has a structure performing the function of a current conductor perfectly until complete discharge by molten sodium performing the function of the current conductor in itself. CONSTITUTION: The turned-over type sodium/sulfur battery or sodium/nickel chloride battery comprises: a solid electrolyte(3) transferring sodium ions selectively; a wicking tube(4) located in the solid electrolyte(3) and containing sodium therein, wherein the sodium operates as a cathode; an anode covering the solid electrolyte(3) and containing molten sulfur in a current conductor with pores, wherein the anode is put in a metal container or a metal-coated container(1); an insulating material(6) for insulating the outer terminals of the anode and the cathode; an open hole formed on the lower part of the wicking tube(4), wherein the sodium flows out through the open hole; a stopper(9) of a protection tube, which has 3-8 of projections and supports the lower part of the wicking tube(4) and is made of metal, alloy, polymer, ceramic, or synthetic material molten at 400-450deg.C.

Description

Inverted sodium / sulphur cells or sodium / nickel chloride cells

1 is a cross-sectional view of the sodium / sulfur battery or sodium / nickel chloride battery according to the present invention,

2 is a cross-sectional view schematically showing a protective tube stopper metal used in the sodium / sulfur battery or sodium / nickel chloride battery of the present invention;

3 is a graph showing the charging characteristics of the sodium / sulfur battery according to the present invention,

Figure 4 is a graph showing the discharge characteristics according to the discharge rate of 5 hours of the sodium / sulfur battery according to the present invention.

<Description of the symbols for the main parts of the drawings>

1: Sulfur container or outer case 2: Sulfur or nickel chloride electrode

3: solid electrolyte 4: sodium electrode reservoir and core

5 sodium electrode 6 insulator

7, 8: joining metal for the cathode 9: protective tube stopper metal

10 metal gasket 11 bolt

12: nitrogen gas

The present invention relates to a high-performance secondary battery sodium / sulfur battery or sodium / nickel chloride battery, and more particularly to a sodium / sulfur battery or sodium / nickel chloride battery in an inverted form.

In general, a sodium / sulfur battery is composed of a sodium ion conductive solid electrolyte which simultaneously functions as a sodium cathode, a sulfur anode, and a separator. Meanwhile, the sodium / nickel chloride battery has almost the same structure as the sodium / sulfur battery except for using nickel chloride instead of sulfur in the sodium / sulfur battery. Therefore, the present invention is applicable to both sodium / sulfur battery as well as sodium / nickel battery, but for the sake of technical convenience, the applicable battery of the present invention is limited to the sodium / sulfur battery.

The beta-alumina tube, the most widely used solid electrolyte for sodium / sulphur cells, maintains its ion conductivity at least above 280 ° C, so the normal operating temperature of sodium / sulfur cells is 350 ° C. The general structure of a sodium / sulfur battery is a molten sodium inside the beta "-alumina tube, a metal current conductor inside the molten sodium, and a porous current conductor, for example, carbon anodes with molten sulfur impregnated outside. It is a structure contained in a metal container that also serves as an external terminal.

The operating principle of the sodium / sulfur cell is that sodium, which is molten at 350 ° C., provides electrons to the external circuit through the current conductor and is ionized, and the sodium cation is transferred to the sulfur electrode through the electrolyte. The electron provided to the sulfur electrode through an external circuit reacts with sulfur to form polysulfur anion (Sx ^2- ), and reacts with sodium ions that have moved through the electrolyte to form sodium polysulfur compound (Na ₂ Sx: x = 2.7 5) is produced. The product depends on the depth of discharge and the initial discharge product is Na ₂ S ₅ , which remains in the form of a two-phase mixture because it does not mix well with molten sulfur. As the discharge proceeds further, the electromotive force decreases rapidly to reach 1.78V and Na ₂ Sx (x = 2.7 to 3.0) is generated. At this point, the discharge must be stopped. When the abnormal discharge proceeds, the electromotive force hardly decreases, but since Na ₂ S ₂ is formed in a solid form, the charge performance is deteriorated since it is separated from other liquid components, thereby adversely affecting the performance and life of the battery. Sodium / sulphur cells have a general structure in which molten sodium is contained in a beta "-alumina tube and a molten sulfur electrode is placed in a porous current conductor material outside. In the early stage of development, a separate current conductor is not required on the sodium cathode side. As a result, the structure in which the sulfur electrode is located inside the electrolyte has been developed, but since the efficiency of converting sulfur to sodium polysulfur compound during discharge is about 70%, additional sulfur must be added and the volume increase when generating sodium polysulfur compound (30 This structure leads to a decrease of the battery capacity, since the extra space according to ˜40%) is required, and sodium polysulfur compound due to discharge if there is not enough space on the sulfur electrode side for the battery capacity. As the volume increases due to the formation of, As a result, the current structure of sodium / sulfur cells is generally that the sodium cathode is located inside the electrolyte. Sodium cathode was solved by dipping metal rods (Fe, sus) with excellent sodium wettability into the sodium electrode because the sodium itself has excellent current conductivity. As the height is lowered, the metal rods must be designed to descend sufficiently to the floor.

However, in the case of the sulfur electrode, the container itself becomes a current conductor by using a sulfur container as a metal. Since sulfur has no current conductivity, an electron conductive material must be filled to allow electrons to move from the solid electrolyte to the sulfur container. In general, the sulfur electrode is manufactured in the form of a felt containing 90% or more of carbon fibers, which is an electron conductive material, impregnated with molten sulfur, and then manufactured by forming in a desired form. Sulfur electrode must be in close contact with the outer container to decrease the resistance to increase the battery efficiency during charging and discharging. For this purpose, the volume design of the sulfur electrode mold should be made so that the conduction can be reduced by about 40%. In the case of unit cell design, the gap between the outer container and the electrolyte should be kept smaller than that of the fully expanded carbon felt. When the carbon felt impregnated with molten sulfur in the mold is put into a container and heated up to the operating temperature of the battery, the elastic expansion force inherent in the carbon felt causes the volume expansion to occur in the original state, thereby causing the adhesion between the external container and the electrolyte. In the case of the sodium / sulfur battery in which the sodium cathode is placed in the electrolyte tube, the amount of molten sodium decreases as the discharge proceeds, thereby reducing the contact area of sodium in contact with the electrolyte. This not only reduces the power density (W / kg) of the battery but also affects the battery life since sodium ions move intensively to the lower side of the electrolyte.

In U.S. Patent No. 4,407,912, a sodium electrode container was installed on the upper side, and the electrolyte tube was extended to the sulfur electrode on the lower side, and the electrode reaction occurred in the same area even when discharge proceeded. However, this structure, which is mainly manufactured in the early stage of the development of sodium / sulfur battery, is difficult to maintain a constant contact area when discharge is progressed and all sodium in the sodium container flows down to the electrolyte and the amount of sodium in the electrolyte tube is reduced. Therefore, the depth of discharge is not deep, and the structure has the disadvantage of using extra sodium as much as electrolyte and internal capacity rather than design capacity. In British Patent No. 8314331, a wicking tube of metal is installed inside the electrolyte to solve the above problem. Capillary action between the electrolyte base wall and the wick causes the molten sodium to be sucked upwards to form a wick. Even if the discharge proceeds deeply, the capillary force does not change between the electrolyte base wall and the wick, so that the contact area where the battery reaction occurs can be kept constant. Another advantage of this structure is that the core tube close to the electrolyte blocks the broken electrolyte tube when it is broken by the external impact or self-cracking of the electrolyte, thereby preventing the exothermic reaction caused by the sudden reaction of sodium and sulfur. It can also serve as a protection tube. However, this structure may fail to act as a protective tube depending on the form of electrolyte breakdown, and since the wick is floating in molten sodium, a separate current conductor must be used on the sodium electrode side.

British Patent No. 2080607 proposes a structure in which a sulfur electrode is placed inside an electrolyte tube and a separate sodium electrode container is placed below the electrolyte. This structure is designed in such a way that the upper part of the sodium electrode container is sealed and the lower part is open and the inert gas N ₂ is compressed in the container. The molten sodium pushed out through the lower part of the vessel by the pressure of the nitrogen rises up the base wall between the electrolyte base wall and the external vessel to form a wick to maintain a constant contact area with the electrolyte. At this time, aluminum flakes were added to the surface of the electrolyte so that molten sodium could be well wetted. This structure not only requires a separate current conductor on the side of the sulfur electrode, but also has problems such as a decrease in battery capacity and a decrease in electrolyte life due to expansion stress as described above.

Japanese Patent Laid-Open No. 3-194864 describes a wick tube having a structure in which nitrogen compressed in a metal container having a hole formed at the bottom thereof is located at the top of the container, and molten sodium is present at the bottom thereof. It is a structure in which the sodium escapes through the hole formed in the lower part by the pressure of nitrogen and climbs up the open wall between the electrolyte and the metal container to form a wick. The force that forms the wick is the joint contribution of the compressive and capillary forces of nitrogen. At this time, the formed wick is raised above the electrolyte base wall and reaches a height capable of contacting the junction metal for the negative electrode terminal on the upper side, thus eliminating the need for a separate current conductor on the sodium negative electrode side. However, this structure has a disadvantage in that it is weak in its role as a protective tube when the electrolyte is broken.

Japanese Patent Laid-Open No. 3-208266 somewhat improves the structure of Japanese Patent Laid-Open No. 3-194864. By inserting a metal tube similar to an electrolyte to the outside of the metal container with a hole formed at the bottom, sodium from the bottom hole of the metal container is pushed up between the metal container and the metal tube adjacent to the outside so that the upper part contacts the junction metal for the negative electrode terminal. At the same time, it is a structure that forms a wick as it rides down between the metal tube and the electrolyte base wall. Since this structure has no current conductor, the battery reaction is stopped when the sodium wick is slightly lowered.

As such, in the structure of the conventional patents, a major disadvantage is that the protective tube is incomplete and prevents the reaction of sodium and sulfur at once when the electrolyte is broken, thereby preventing sudden rise in battery temperature, but essentially melted sodium leaks. The temperature rise due to the continuous reaction between molten sulfur and molten sodium cannot be prevented because it cannot be prevented.

Accordingly, an object of the present invention is to solve the above-described problems, the complete discharge (DOD 100%) so that the sodium electrode material is completely out because the molten sodium itself performs the function of a current conductor by manufacturing the battery in an inverted form (DOD 100%) The present invention provides a sodium / sulfur battery having a structure in which a function of a current conductor can be completely performed.

Another object of the present invention is to provide a sodium / nickel chloride battery having the inverted structure.

In the sodium / sulfur battery of the present invention for achieving the above object, in the sodium / sulfur battery, a solid electrolyte that selectively transfers only sodium ions, located in the solid electrolyte and the core tube and the inside of the solid electrolyte in which sodium is injected It consists of an anode containing molten sulfur in a current conductor having pores surrounding the pores, wherein the anode is contained in a metal container or a metal-coated container, and the sodium is operated as a cathode, the outer terminal of the cathode and the anode The outer terminal of is insulated by an insulating material, the wick tube is formed with an opening in the lower portion, the lower portion is supported by a protective tube stopper formed with a protrusion is composed of the sodium flows out through the opening.

In the sodium / nickel chloride battery of the present invention for achieving the above another object, in the sodium / nickel chloride battery, a solid electrolyte that selectively transfers only sodium ions, a wick placed in the solid electrolyte and injecting sodium therein; It consists of a positive electrode containing molten nickel chloride in a current conductor having pores surrounding the solid electrolyte, wherein the positive electrode is contained in a metal container or a container coated with metal, the sodium is operated as a negative electrode, The outer terminal and the outer terminal of the anode are insulated by an insulating material, the wick tube is formed with an opening in the lower portion, the lower portion is supported by a protective tube stopper formed with a protrusion is composed of the sodium flowing out through the opening do.

Hereinafter, the sodium / sulfur battery or sodium / nickel chloride battery of the present invention will be described in more detail with reference to the accompanying drawings.

1 is a cross-sectional view of the sodium / sulfur battery according to the present invention, the reference numeral 1 is a sulfur container or an outer case material is aluminum, it is preferable to use the inner surface coated with Cr to prevent corrosion due to sulfur. Reference numeral 2 is a sulfur electrode, which is manufactured in a semicircular shape. The sulfur electrode 2 is dissolved in a sulfur electrode manufacturing mold by heating sulfur at 150 ° C., and having a carbon felt having a porosity of 95% and a thickness of 8 mm, width of 61 mm, and length. Cut into 135mm (the groove is formed in the width of the inner diameter considering the difference between the inner diameter and the outer diameter) and insert into the mold, and cooled in the state of pressurizing the thickness up to 4.5mm 4.5mm thick, inner diameter 26Φ, outer diameter 35Φ It is manufactured in the form. After the sulfur electrode 2 is inserted into the outer container 1, when the electrode reaches the reaction temperature, sulfur is dissolved and the carbon felt expands to its original shape by the restoring force. On the other hand, the thickness of the sulfur electrode is preferably adjusted to about 6.5 mm in order to keep the contact resistance of the outer container 1, the carbon felt and the electrolyte 3 and the carbon felt to a minimum. Reference numeral 3 is a solid electrolyte of sodium / sulfur battery, which is composed of beta "-alumina. Reference numeral 4 serves as a reservoir and core tube of sodium electrode. Material 5 is aluminum. Is injected in the form of NaN ₃ and decomposes into Na and N ₂ at the cell reaction temperature so that Na is located in the lower part of the wick 4. The symbol 6 is alpha-alumina as an insulator for bonding the cathode and the anode. Alpha-alumina 6 and beta "-alumina 3 are sealed with glass.

Reference numerals 7 and 8 denote aluminum bonding metals for the anode, and the bonding metals 7 used in the present invention are manufactured in a bent form to absorb stresses due to the difference in coefficient of thermal expansion with the alpha-alumina 6. The joining metals 7, 8 are fitted with soft metal gaskets 10 and bonded to the alpha-alumina 6 with bolts 11. Reference numeral 9 serves to seal the inlet of the wick tube 4 when the electrolyte is destroyed by the protective tube cap metal and the temperature of the battery rises (about 420 ° C. or more). The material may be a metal, an alloy, a polymer, a ceramic, a composite, or the like, having a melting point of 400 to 600 ° C., preferably a metal or an alloy. Specific examples of the metal are zinc, aluminum or lead, preferably zinc. Specific examples of the alloy include zinc-based, lead-based or aluminum-based alloys, preferably zinc-based alloys. The protective tube stopper metal 9 is provided with a plurality of protrusions having a height of about 3 mm and preferably 3 to 8 in order to maintain a moving path of molten sodium during normal operation of the battery. Numeral 12 denotes a nitrogen gas produced by decomposition of sodium azide at 350 ° C., which is the battery operating temperature.

FIG. 2 is a view schematically showing a protective tube stopper metal 9 used in the sodium / sulfur battery of the present invention, in which four protrusions having a height of 3 mm are formed on a 0.3 t zinc plate having a melting point of 420 ° C. When the battery temperature rises due to this destruction, the protruding portion is dissolved and the wick tube sits down, so that the inlet of the wick tube is sealed.

According to a preferred embodiment of the present invention, by placing a metal disc formed with four protrusions with a metal that is melted at 400 ~ 450 ℃ in the lower part of the wick (4) when the temperature of the battery is raised when the electrolyte is destroyed As the protrusions dissolve and the wicks fall down, the entrance of the wicks is blocked, so that sodium is trapped in the wicks so that the protective tube can be completely fulfilled.

The sodium / sulfur battery of the present invention was measured in the battery voltage while maintaining a constant temperature at 350 ℃ and 400 ℃, 430 ℃ and 450 ℃ is shown in Table 1 below. At the temperature of 350 ° C. and 400 ° C., a constant battery voltage was maintained even after 60 minutes, whereas the battery voltage became zero after 10 minutes at 430 ° C. and 5 minutes at 450 ° C. As the ambient temperature rises, the four protrusions located at the bottom of the battery are melted, and the wick can be lowered, thereby confirming that the inlet of the wick is blocked.

According to a preferred manufacturing example of the sodium-sulfur battery of the present invention having such a structure, sodium azide (NaN ₃ ) is contained in a wick tube container 4 having a hole of 4Φ at the bottom, and a beta "-alumina solid electrolyte After positioning in (3), the 0.3 mm thick metal (Zn) plate (9) was cut into a circular shape having a diameter of 1.5 mm, and punched in four places with a height of about 3 mm, and placed in the lower part of the wick (4). A soft metal gasket 10 is inserted between the joining metal 7 and the alpha-alumina insulator 6 and bonded by bolts 11. Charging the sulfur electrode 2 produces the least precipitation of sodium polysulfur compounds. After manufacturing a mold by designing in a semi-circular shape, the carbon felt is cut to size and put into a mold, impregnated with molten sulfur at 150 ° C., and then cooled under pressure to prepare it. ) Into the aluminum outer container (1) The bonded metal 8 bonded to the alumina 6 and the outer container 1 are combined with the metal gasket 10 and the bolt 11 to manufacture the battery of the present invention.

When the sodium / sulfur battery thus prepared is heated up to 350 ° C., which is the battery operating temperature, sodium azide is decomposed to produce sodium and nitrogen. The produced nitrogen gas is located in the upper part of the wick (4), the molten sodium is pushed out through the lower hole of the wick by the pressure of the nitrogen gas to rise through the base wall of the electrolyte and the wick tube, the electrode reaction throughout the electrolyte surface This will occur. As a result of the charge / discharge test of the fabricated 100Wh sodium / sulfur battery, high energy density was obtained. Especially, the electrode reaction was terminated when the external temperature was maintained at about 430 ~ 450 ℃. Therefore, the sodium / sulfur battery according to the present invention is a battery having a high energy density and a perfect protection device.

On the other hand, another advantage of the sodium / sulfur battery produced by the present invention is that since the cell is located in an inverted form is advantageous in bonding because there is no risk of sodium and sulfur vapor spilled because the molten sodium and sulfur is filled in the lower portion to be. In other words, the junction between the junction electrode of the sodium electrode and the alpha-alumina insulator does not need to be completely sealed to the gas and only enough molten sodium (or sulfur) does not leak out. bonding) may be replaced by a bolt 11 tightening process using a gasket 10.

Figure 3 is a graph showing the charging characteristics of the sodium / sulfur battery according to the present invention, reached a full charge voltage in 3 hours at a charge rate of 20A recorded a charging efficiency of 83%. This is a good result compared to the charging efficiency of 70 to 80% of the general sodium sulfur battery.

4 is a graph showing the discharge characteristics according to the five-hour discharge rate (C5) of the sodium / sulfur battery according to the present invention, there was no difficulty to discharge to about 90% of the discharge depth and discharge efficiency is also about 93% general discharge The efficiency was better than about 90%. In terms of energy conversion efficiency, the output charge / discharge efficiency (Output Wh / Input Wh) of the battery is about 77% (based on C5), which is about 10% higher than the general charge / discharge efficiency of the known sodium / sulfur battery. Therefore, inverted sodium / sulphur cells of the inverted form using a protective tube (9) as a material that melts around 420 ° C, while omitting the current conductor, provide excellent performance as well as a sodium / sulfur cell that functions as a protective tube. Could be manufactured.

Claims (14)

In a sodium / sulfur cell, a solid electrolyte (3) for selectively transporting only sodium ions, positioned in the solid electrolyte (3), surrounding the wick (4) and the outer surface of the solid electrolyte (3) into which sodium is injected It consists of an anode in which molten sulfur is contained in a current conductor having pores, wherein the anode is contained in a metal container or a metal-coated container (1), and the sodium is operated as a cathode, and the external terminal of the cathode The outer terminal of the anode is insulated by an insulating material (6), the wick (4) has an opening in the lower portion, the lower portion is supported by a protective tube stopper (9) formed with a protrusion so that the sodium is the opening An inverted form of sodium / sulfur cell, characterized in that it flows through. The inverted sodium / sulfur battery according to claim 1, wherein the protective tube cap (9) is a metal, an alloy, a polymer, a ceramic, or a composite that is melted at a temperature in the range of 400 to 450 ° C. 3. The inverted sodium / sulfur battery of claim 2 wherein said metal is zinc, aluminum or lead. The inverted sodium / sulphur battery of claim 2, wherein the alloy is a zinc-based, aluminum-based or lead-based alloy. The inverted sodium / sulfur battery according to claim 1, wherein the external terminal of the negative electrode and the external terminal of the positive electrode are combined with an insulating material by a bolt (11) using a gasket (10). The inverted sodium / sulphur battery of claim 1, wherein the number of protrusions is 3 to 8. The inverted sodium / sulfur battery according to claim 1 or 6, wherein the protrusion is formed by punching or welding. In a sodium / nickel chloride battery, a solid electrolyte (3) for selectively transporting only sodium ions, a wick (4) located in the solid electrolyte (3), and the inside of which the sodium is injected, and the outside of the solid electrolyte (3) It consists of an anode in which molten nickel chloride is contained in an encapsulated current conductor having pores, wherein the anode is contained in a metal container or a container coated with metal (1), and the sodium is operated as a cathode, the outside of the cathode The outer terminal of the terminal and the positive electrode is insulated by an insulating material (6), the wick tube (4) has an opening formed in the lower part, the lower part is supported by a protective tube cap (9) formed with a protrusion so that the sodium An inverted sodium / nickel chloride battery, characterized in that flows through the opening. The inverted sodium / nickel chloride battery according to claim 8, wherein the protective tube cap (9) is a metal, an alloy, a polymer, a ceramic or a compound which is melted at a temperature in the range of 400 to 450 ° C. 10. The inverted sodium / nickel chloride battery of claim 9, wherein the metal is zinc, aluminum or lead. The inverted sodium / nickel chloride battery of claim 9, wherein the alloy is a zinc-based, aluminum-based or lead-based alloy. The inverted sodium / nickel chloride battery according to claim 8, wherein the external terminal of the negative electrode and the external terminal of the positive electrode are combined with an insulating material by a bolt (11) using a gasket (10). The inverted sodium / nickel chloride battery of claim 8, wherein the number of protrusions is 3 to 8. The inverted sodium / nickel chloride battery according to claim 8 or 12, wherein the protrusion is formed by punching or welding.