JP2005122948A - Sodium-sulfur battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sodium-sulfur battery, capable of high output operation and stably operating over a long period. <P>SOLUTION: The sodium-sulfur battery is formed, by arranging a high-resistance layer having preferential permeability to sodium polysulfide higher than that to sulfur, between a solid electrolyte and a current-collecting electrode, and arranging a cylinder-shaped auxiliary conductor, having preferential permeability to sulfur higher than that to sodium polysulfide on its outer periphery. An appropriate flow path of sodium polysulfide is formed, by making the high-resistance layer penetrate in the radial direction of the auxiliary conductor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a sodium sulfur battery, and more particularly to a sodium sulfur battery suitable for power storage and the like.

  The sodium-sulfur battery is a high-temperature secondary battery in which sodium is used for the negative electrode active material, sulfur and sodium polysulfide are used for the positive electrode active material, and a solid electrolyte tube having conductivity for sodium ions is used for the partition walls of the positive electrode and the negative electrode. is there. Beta alumina is used as a solid electrolyte tube having conductivity for sodium ions, and a bag tube is often used. In general, one battery is composed of a solid electrolyte tube having conductivity with sodium ions and one container containing sodium, sulfur and sodium polysulfide. This is called a single cell. In order to store a large amount of power, a large number of single cells are usually connected in series and parallel.

  Since the normal operating temperature of a sodium sulfur battery is as high as 280 ° C. to 370 ° C., a plurality of single cells are packed in a heat insulating container to form a module. In order to increase the battery output per unit cell, it is necessary to reduce the Joule loss of the battery and perform a discharge operation with a large current. In order to reduce battery Joule loss, it is necessary to reduce the internal resistance of the battery as much as possible.

The discharge reaction of the sodium sulfur battery can be expressed by the following equation.
Positive electrode side: xS + 2Na ⁺ + 2e ⁻ → Na ₂ S _x (x = 3 to 5)
Negative electrode side: 2Na → 2Na ⁺ + 2e ⁻
Total reaction: 2Na + xS → Na ₂ S _x
The charging reaction is the reverse reaction of the above equation.

In the battery reaction described above, Na ₂ Sx is generated and dissociated at the sulfur electrode as the positive electrode. Therefore, most of the internal resistance of the battery is the resistance of the sulfur electrode, and in order to reduce the internal resistance as much as possible, it is most effective to reduce the resistance of the sulfur electrode.

  An example of a conventional sodium-sulfur battery is shown in FIG. The solid electrolyte tube 1 is made of a material such as beta-alumina, and is made into a bag tube with one end closed, and a bag tube made of a metal material such as stainless steel having an opening in the lower portion mounted inside the solid electrolyte tube 1. Sodium is stored in the safety container 2. The outer surface of the safety container 2 and the inner surface of the solid electrolyte tube 1 are arranged at a constant interval so that a minimum amount of sodium necessary for charging and discharging is supplied to the inner surface of the solid electrolyte tube 1. The outer surface side of the solid electrolyte tube 1 is filled with sulfur, which is a positive electrode active material, and sodium polysulfide to form a positive electrode (sulfur electrode). Since sulfur is an insulator and sodium polysulfide is poor in electron conductivity, an auxiliary conductive material having electron conductivity is required for the entire region of the positive electrode (sulfur electrode) 3 in order to establish a battery reaction at the positive electrode. . For this reason, the fluidity of the battery active material in the sulfur electrode is extremely small.

  Further, as a method for reducing the internal resistance of the battery, there is a method using a collector electrode 10 as shown in FIG. FIG. 3 is a cross-sectional view of the solid electrolyte tube 1 in which the shaft is installed horizontally and perpendicular to the axial direction. The solid electrolyte tube 1 is made into a cylindrical tube shape using a material such as beta alumina, and a cylindrical tube-shaped safety container made of a metal material such as stainless steel is mounted inside and filled with sodium 7. A sodium supply body is mounted between the outer surface of the safety container and the inner surface of the solid electrolyte tube 1, and the minimum sodium necessary for charging and discharging the inner surface of the solid electrolyte tube 1 through the opening of the safety container. 7 is supplied. In addition, a cylindrical auxiliary conductor 9 having a higher preferential permeability to sulfur than sodium polysulfide and a high resistance layer 8 having a preferential permeability to sodium polysulfide compared to sulfur are attached, and sulfur 11 and Sodium polysulfide 12 is supplied.

JP 2002-75438 A JP 2002-367671 A

  In the above background art, when a battery is charged / discharged at a high output, the internal resistance increases and the operating range of the battery is narrowed. As a result, the battery may not have sufficient battery capacity. This is because the battery active material is not sufficiently supplied to the battery reaction region at high output. For example, in order to sufficiently supply sodium polysulfide to the battery reaction region using the high resistance layer, it is necessary to increase the cross-sectional area of the channel composed of the high resistance layer. However, if the cross-sectional area of the flow path is increased, the thickness of the substantial high resistance layer is increased, and the internal resistance of the battery is increased to reduce the energy efficiency of the battery.

  An object of the present invention is to provide a sodium-sulfur battery that can be operated at a high output and can be stably operated for a long time.

  In the sodium-sulfur battery of the present invention, a high-resistance layer having higher preferential permeability for sodium polysulfide than sulfur is disposed between the solid electrolyte tube and the collector electrode, and the preferential permeability for sulfur is higher on the outer periphery than sodium polysulfide. Cylindrical auxiliary conductor is arranged, high resistance layer penetrates in the radial direction of auxiliary conductor, sodium polysulfide necessary for battery reaction is supplied to battery reaction area, and reaction product is discharged In order to facilitate this, a suitable flow path for sodium polysulfide is provided.

  According to the present invention, by improving the high resistance layer of the conventional sodium-sulfur battery, sufficient supply of sodium polysulfide to the battery reaction region and discharge of the reaction product are facilitated, and high output is stable for a long time. Driving.

  The purpose of increasing the channel cross-sectional area of sodium polysulfide and enabling high output operation was achieved without increasing the internal resistance of the battery.

  FIG. 1 shows a first embodiment of a sodium-sulfur battery according to the present invention, which is a cross section cut at right angles to the longitudinal direction (axial direction) of a bag-shaped solid electrolyte tube 1.

  As shown in FIG. 1, the sodium-sulfur battery has a solid electrolyte tube 1 mounted in a positive electrode container 4, and the solid electrolyte tube 1 is filled with sodium to form a sodium electrode 6 that is a negative electrode.

A high resistance layer 13 having a higher resistivity than sodium polysulfide is provided on the outer periphery of the solid electrolyte tube 1. As an example of the high resistance layer 13, an insulating material such as alumina or glass is processed into a porous body or mesh and formed into a sheet shape, or a particulate or powdered material is used. An auxiliary conductor 9 having electron conductivity is provided on the outer periphery of the high resistance layer 13. As an example of the auxiliary conductor 9, graphite, carbon, or other metal is processed into a porous body, mesh, or felt and formed into a sheet, or a particle or powder. Further, a collector electrode 10 is provided on the outer periphery of the auxiliary conductor 9 to flow a charge / discharge reaction current. The collector electrode 10 is electrically connected to the positive electrode container 4.

  In addition, the active material liquid level height 17 of the bulk 15 is arrange | positioned so that the collector electrode 10 whole may become below a liquid level.

  Here, the high resistance layer 13 is made of a material that preferentially gets wet with sodium polysulfide as compared with sulfur, that is, a material having preferential permeability, and is not only attached to the outer periphery of the solid electrolyte tube 1 but also the solid electrolyte tube 1. The auxiliary conductor 9 is attached so as to form a sodium polysulfide flow path in the radial direction of 1. The high-resistance layer 13 penetrating the auxiliary conductor 9 passes through the opening 14 of the collector electrode attached to the outer periphery of the auxiliary conductor 9, and is a bulk composed of a battery active material made of sulfur 11 and sodium polysulfide 12. The structure was in direct contact with 15 active materials. If the high resistance layer is not in direct contact with the bulk, it will not be able to fulfill its role as a through-flow channel due to the influence of the surrounding auxiliary conductors and the members of the collector electrode and the attached active material.

  In this embodiment, the through-flow channel cross-sectional area formed by the high resistance layer 13 in direct contact with the bulk 15 is configured so that the lower half of the solid electrolyte tube 1 is larger than the upper half. In FIG. 1, an example in which the cross-sectional area of the through-flow passage of the high resistance layer 13 in the lower half is twice or more that in the upper half is shown as a conceptual diagram. Of course, it is necessary to select the cross-sectional area of the through-flow passage formed by the high-resistance layer 13 according to usage conditions such as the current density of the battery. The area does not need to be more than twice the upper half. In the embodiment, since sodium polysulfide has a higher density than the sulfur and settles downward, the sodium polysulfide 12 is sucked up from below during charging and is easily supplied to the auxiliary conductor 9.

  Hereinafter, the behavior of the active material in the battery accompanying charge / discharge will be described. The battery was operated by heating to 280 ° C. or higher at which the battery active material such as sodium or sulfur was in a liquid state.

  In the discharge operation, sulfur impregnated in the auxiliary conductor 9 reacts with sodium ions that have passed through the solid electrolyte tube 1 from the sodium electrode (negative electrode) 6 to generate sodium polysulfide 12. The generated sodium polysulfide 12 flows down to the bulk 15 using the high resistance layer 13 as a flow path. Insufficient sulfur is supplied from the sulfur 11 in the bulk 15 to the auxiliary conductor 9 via the opening 14 of the collector electrode.

  On the other hand, in charging, the sodium polysulfide 12 in the auxiliary conductor 9 is dissociated into sodium 7 and sulfur 11, and the sodium 7 passes through the high-resistance layer 13 and passes through the solid electrolyte tube 1 and returns to the sodium electrode (negative electrode) 6. Sulfur 11 flows out into the sulfur 15 in the bulk 15 due to a density difference from the sodium polysulfide 12. Of course, in the bulk 15, the sulfur 11 and the sodium polysulfide 12 are separated into two layers. The sodium polysulfide 12 that is insufficient in the charging reaction is supplied through the high resistance layer 13 that penetrates the bulk 15. Even when charging further proceeds, the sodium polysulfide 12 present at the bottom of the battery container is sucked up by the high resistance layer 18 present immediately below the solid electrolyte tube 1 and is supplied to the upper part of the auxiliary conductor 9. Most sodium polysulfide 12 present in the battery can be charged.

  FIG. 4 is a diagram showing a second embodiment of the present invention. A part of the high resistance layer 13 of FIG. 1 is improved. The cross-sectional area of the through-flow passage formed by the high-resistance layer 13 is increased from the solid electrolyte tube 1 to the bulk 15, and the cross-sectional area of the through-flow passage in the portion in contact with the bulk 15 is maximized. Thereby, the flow rate of sodium polysulfide can be increased toward the outer periphery.

  As the high resistance layer material of the example, silica glass with reduced potassium and calcium contents was used so as not to adversely affect the solid electrolyte tube 1. The binder was also examined and binderless silica glass was used. The high resistance layer 13 in contact with the solid electrolyte tube 1 and the high resistance layer 13 passing through the auxiliary conductor 9 and in contact with the bulk 15 do not need to be the same in material and do not have to be an integral structure. .

  In the manufacturing method of the high resistance layer 13 of the example, the high resistance layer material was driven by needle punching from both sides of the auxiliary conductor 9, that is, the side in contact with the solid electrolyte tube 1 and the side in contact with the collector electrode 10 or the bulk 15. . The position where the high resistance layer material is driven by the needle punch is preferably matched with the opening 14 of the collector electrode. Of course, as long as the high resistance layer 13 and the auxiliary conductor 9 can be brought into contact with each other without being driven by a needle punch, the function is not impaired.

  The above description of materials and manufacturing methods can also be applied to Example 1.

  FIG. 5 is a diagram showing a third embodiment of the present invention. A part of the high resistance layer 13 of FIG. 1 is improved. The high resistance layer 13 from the solid electrolyte tube 1 toward the bulk 15 is formed in a ring shape to form a through channel to the bulk 15 in the entire region in the circumferential direction to increase the through channel cross-sectional area.

  In the above Examples 1, 2, and 3, the active material liquid level height 17 of the bulk 15 is arranged so that the entire collector electrode 10 is below the liquid level, but the active material liquid level height 17 is low, and Even if the electrode 10 is exposed, the above function is not impaired. In this case, it is preferable that the space of the cover gas 16 is in a reduced pressure state. The positive electrode active material is easily supplied to the auxiliary conductor 9 in the form of sulfur vapor.

  Further, although the positive electrode container is rectangular in FIG. 14, it does not impair any function even if it has an arbitrary shape such as a circle or an ellipse. Furthermore, in this embodiment, the axis of the solid electrolyte tube is horizontally installed, but the present invention can also be applied to a vertically installed type or an obliquely installed type sodium sulfur battery.

1 is a cross-sectional view showing a first embodiment of a sodium-sulfur battery of the present invention. The longitudinal section which shows the structure of the sodium sulfur battery of a prior art example. The cross-sectional view which shows the structure of the conventional sodium sulfur battery using a collector electrode. The cross-sectional view which shows the 2nd Example of the sodium sulfur battery of this invention. The longitudinal cross-sectional view which shows the 3rd Example of the sodium sulfur battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solid electrolyte tube, 2 ... Safety container, 3 ... Sulfur electrode, 4 ... Positive electrode container, 5 ... Negative electrode container, 6 ... Sodium electrode, 7 ... Sodium, 8, 13, 18 ... High resistance layer, 9 ... Auxiliary conductor DESCRIPTION OF SYMBOLS 10 ... Collector electrode, 11 ... Sulfur, 12 ... Sodium polysulfide, 14 ... Opening part of collector electrode, 15 ... Bulk, 16 ... Cover gas and sulfur vapor | steam, 17 ... Active material liquid level height.

Claims (13)

  A negative electrode active material containing sodium as an essential component, a bulk composed of a positive electrode active material containing sulfur and sodium polysulfide as main components, and a sodium ion that passes between the negative electrode active material and the positive electrode active material. In a sodium-sulfur battery mainly composed of a solid electrolyte tube and a collector electrode that conducts a positive current, a high resistance layer having higher resistivity than sodium polysulfide and the electron conductivity are supplemented between the solid electrolyte tube and the collector electrode. The high-resistance layer has higher preferential permeability to sodium polysulfide than sulfur, and has superior electrical conductivity due to sodium ions, and the sodium polysulfide is removed from the bulk during charging. It can be supplied to the entire area in the radial, circumferential and axial directions of the auxiliary conductor that is charged, and sodium polysulfide is discharged during the discharge reaction. Sodium sulfur battery, characterized in that that the auxiliary conductor of the entire region can be discharged to the bulk.   The sodium-sulfur battery according to claim 1, wherein a high-resistance layer material penetrates all regions in the circumferential direction and the axial direction of the auxiliary conductor in the radial direction.   The sodium-sulfur battery according to claim 1, wherein a through-flow passage cross-sectional area made of a high-resistance layer material penetrating through the auxiliary conductor increases toward the lower side in the gravity direction.   2. The sodium-sulfur battery according to claim 1, wherein the high-resistance layer material penetrating through the auxiliary conductor is in direct contact with the bulk battery active material.   2. The sodium-sulfur battery according to claim 1, wherein the high-resistance layer material penetrating the auxiliary conductor is in direct contact with the bulk battery active material, and is in contact with the bulk as compared with the contact surface with the solid electrolyte tube. A sodium-sulfur battery characterized in that the cross-sectional area of a through-flow passage made of a high-resistance layer material on the surface is increased.   6. The sodium-sulfur battery according to claim 5, wherein a position where a cross-sectional area of a through-flow passage made of a high-resistance layer material on a contact surface with the bulk increases coincides with an opening of the collector electrode. .   2. The sodium-sulfur battery according to claim 1, wherein the high resistance layer material penetrating through the auxiliary conductor is in direct contact with the bulk battery active material, and the high resistance of the contact surface between the bulk and the solid electrolyte tube is high. A sodium-sulfur battery characterized in that a high resistance layer material is driven with a needle punch from both sides of an auxiliary conductor as a method for increasing the cross-sectional area of the through-flow passage made of a layer material.   2. The sodium sulfur battery according to claim 1, wherein a member having a resistivity higher than that of sodium polysulfide is used as the high resistance layer material.   2. The sodium-sulfur battery according to claim 1, wherein the high-resistance layer material is made of silica glass with reduced potassium or calcium.   The sodium-sulfur battery according to claim 1, wherein the high-resistance layer material is made of glass, alumina, or the like that does not contain a binder.   2. The sodium-sulfur battery according to claim 1, wherein the auxiliary conductor and the high resistance layer are immersed in the battery active material from the liquid surface of the battery active material and supplied in liquid form.   2. The sodium-sulfur battery according to claim 1, wherein the collector electrode space exposed from the liquid surface of the battery active material is decompressed so that the vapor pressure of the battery active material is a main component. 2. The sodium-sulfur battery according to claim 1, wherein the axis of the solid electrolyte tube is installed horizontally.

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