JPH10302830A - Sodium/molten salt secondary battery and its assembly method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sodium/molten salt secondary battery with sufficient corrosion resistance, heat resistance, and airtightness, structure resistant to repeated temperature rising and falling during battery assembly and operation, and easy to assembly, capable of reducing production cost, and provide its assembly method. SOLUTION: A sodium/molten salt secondary battery has a positive electrode chamber 14 within an inner cylindrical container 4 made of a sodium ion conductive solid electrolyte fit to the inside of an outer cylindrical container 8 and a negative electrode chamber 15 formed between the outer cylindrical container 8 and the inner cylindrical container 4, and the tops of the containers are airtightly sealed by using carbon sealing rings 7a, 7b and a spring washer 11, and fastening by screwing a metal ring with screw 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chargeable / dischargeable sodium / molten salt secondary battery applied to a power storage battery and an electric vehicle drive power supply, and a method of assembling the same.

[0002]

2. Description of the Related Art A sodium / molten salt secondary battery generally has a structure in which positive and negative electrode chambers are provided inside and outside a ceramic tube made of sodium ion-conductive β or β'-alumina. Further, as a similar battery, there is a sodium / sulfur battery using sodium polysulfide (Na ₂ S _X ) as a positive electrode active material. In this type of battery, both the positive and negative electrode active materials are liquid at the operating temperature, so that the positive and negative electrode chambers must have a structure that does not leak liquid. Since it reacts explosively with oxygen and oxygen, it is necessary to have a highly airtight closed structure completely shut off from the atmosphere. Therefore, in order to enhance the airtightness of each joint, the joining of the outer cylindrical container and the internal structural member is a brazing method using an active metal or a glass brazing material,
A thermal diffusion bonding method is used.

FIG. 2 shows NaCl-AlC as a positive electrode active material.
l_Three-SC1_X(X = 0 to 4) using a mixed molten salt
In addition, conventional sodium using liquid sodium as the negative electrode active material
1 shows a structural example of a thorium / molten salt secondary battery. This battery is
Sodium ion conduction in stainless steel outer container 28
Inside of β ″ -alumina tube which is a conductive solid electrolyte
With the cylindrical container 24 attached, the inside of the outer cylindrical container 28 is
Between the positive electrode chamber 27 and the outer cylindrical container 28 and the inner cylindrical container 24.
The anode chamber 26 is divided into two chambers.
NaCl-AlCl as active material_Three-SC1_X(X = 0
To 4) and charged into the negative electrode chamber 26
Liquid sodium as active material is charged and tang at center
The upper cover 1 made of α-alumina with the stainless steel current collecting rod 22 inserted
It is configured to be mounted and hermetically sealed. Natori
Na / Molten salt secondary battery, Na as a positive electrode active material
Cl-AlCl _Three-SC1_X(X = 0 to 4)
The battery using the combined molten salt is 700 to 800 W · h / kg.
With a high theoretical energy density
It is one of the next batteries. However, this mixed molten salt
Materials that are extremely corrosive and can withstand at present
Only tungsten has been identified among metal materials.
Also, use alumina ceramic or carbon materials.
It has been confirmed that it can be used.

Accordingly, in such a battery, as shown in FIG. 2, the structure on the positive electrode side on which the mixed molten salt is provided has an inner cylindrical container 24 made of β ″ -alumina tube capable of withstanding the mixed molten salt, and a carbon electrode. 25 (carbon current collecting rod 22 'and tungsten current collecting rod 22)
The upper lid 21 made of alumina pellets is joined with a glass brazing material at a joining portion 23, and the molten salt entering the cathode chamber 27 is powdered from the portion of the tungsten current collector rod 22 (tungsten pipe) after the battery is assembled. Injecting in the form. In addition, from the viewpoint of corrosion resistance and airtightness, the joint sealing structure between the outer cylindrical container 28 in which the sodium 29 of the negative electrode active material enters and the positive electrode side structural member is entirely embedded and sealed with a glass brazing material (the outer cylindrical container 28 and the upper lid). 2
The sodium 29 is injected in a liquid form from the sodium injection port 30 after the battery is assembled.

[0005]

As described above, among the sodium / molten salt secondary batteries, the cathode active material is NaCl-
A battery using a mixed molten salt of AlCl ₃ -SCl _X (x = 0 to 4) has a very strong corrosiveness of the mixed molten salt, and at present, the material that can be tolerated is tungsten, alumina ceramic, carbon material or carbon material. Only some glass materials have been confirmed. NaCl-AlCl ₃ -S to the positive electrode active material
The battery reaction in the case of using a mixed molten salt of Cl _x (x = 0 to 4) is generally as follows. The discharge reaction is from the left side to the right side, and the charge reaction is the opposite.

Embedded image 4Na + SCl ₃ AlCl ₄ + 1.5Al ₂ Cl ₆ = S + 4NaAlCl ₄ (4.35V, at180-250 ° C.) (1) 2Na + S + NaAlCl ₄ = NaAlSCl ₂ + 2NaCl (2.75V, at180- 250 ° C) (2)

[0006] In the discharge, first, a reaction occurs without the precipitation of NaCl from tetravalent to zero-valent sulfur represented by the formula (1). Subsequently, NaCl from zero valence to -2 valence of sulfur represented by the formula (2)
Shifts to a reaction involving precipitation of. The corrosion factors due to the molten salt include Al ₂ Cl ₃ and SC contained in the positive electrode active material.
I ₄ , S ₂ Cl ₂ and SCl ₂ are expected to be dominant. These liquids and gases are highly corrosive and most metal materials are rapidly eroded, and only glass-based materials have been confirmed as adhesive materials that can withstand this molten salt corrosion. Therefore, conventionally, both the positive electrode structure portion and the negative electrode structure portion are hermetically bonded with the glass brazing material at the portions requiring hermetic bonding. However, in this case,
Since the glass bonding itself is performed at a high temperature close to 1000 ° C., the temperature is repeatedly raised and lowered each time the bonding is performed, so that the influence of thermal stress becomes a problem, the structure becomes complicated, and sufficient reliable hermetic bonding may not be performed. . In addition, since the joining with the glass brazing material is performed at a high temperature close to 1000 ° C., the molten salt is inevitably injected in small quantities in powder form from above through a thin injection pipe (tungsten pipe) at room temperature after the joining with the glass brazing material. As a result, the work efficiency was extremely poor, and the adjustment of the injection amount of the molten salt was difficult and non-uniform, so that the battery performance could be deteriorated.

On the other hand, the joint sealing structure between the outer cylindrical container in which sodium as the negative electrode active material enters and the structural member on the positive electrode side is also glass brazing from the viewpoints of corrosion resistance, heat resistance (battery operating temperature: 200 to 300 ° C. or higher) and airtightness. The entire surface is sealed with a material, and sodium is injected in liquid form from the sodium injection port after the battery is assembled. In the case of this structure, the outer container (metal)
And the thermal stress generated from the difference in thermal expansion between α-alumina pellets is calculated so that cracks do not occur in the brazing filler metal, but cracks occur due to repeated temperature rise and fall during battery operation. In some cases, airtightness is impaired, battery performance is reduced, and the life is shortened. In view of the situation of the prior art, the present invention has a structure that has sufficient corrosion resistance, heat resistance, and airtightness, and has a structure that can withstand repeated temperature rise and fall during battery assembly and battery operation. It is an object of the present invention to provide a sodium / molten salt secondary battery which leads to improved operability and a longer life, is easy to assemble and can reduce the manufacturing cost, and a method for assembling the same.

[0008]

According to the present invention, in order to solve the above-mentioned problems, a joining method in a hermetically sealed portion of a sodium / molten salt secondary battery is, except for a part, joined by a conventional glass brazing material. In place of the legal method, a carbon-based seal ring and a spring washer were used, and a means for obtaining a holding force for airtightness by tightening with a threaded metal ring was adopted.

That is, the present invention adopts the following constitutions (1) to (3). (1) An inner cylinder made of a sodium ion conductive solid electrolyte is mounted in the outer cylinder, and the outer cylinder is formed between the positive electrode chamber in the inner cylinder, the outer cylinder, and the inner cylinder. The cathode compartment was divided into two compartments, a cathode compartment and NaCl-
A mixed molten salt composed of AlCl ₃ -SCl _X (x = 0 to 4) is charged, liquid sodium as a negative electrode active material is charged into a negative electrode chamber, and an upper lid in which a current collector is inserted in the center is attached. A hermetically sealed sodium / molten salt secondary battery, wherein a sealing portion having an edge for fitting an upper lid and a screw portion for screwing a threaded metal ring is provided at an upper end portion of the outer cylindrical container. An α-alumina ring that seals the opening of the negative electrode chamber and an α-alumina disk in which a current collecting rod around which a carbon electrode is circumferentially inserted is inserted into the center part that seals the opening of the positive electrode chamber. The joint between the inner cylindrical container and the joint between the α-alumina disk and the current collecting rod are joined by a glass brazing material, and the α-alumina joined to the inner cylindrical container at the edge of the outer cylindrical container via a carbon seal ring. Place a ring on top of the α-alumina ring An α-alumina disk to which a current collecting rod is joined via a metal ring is placed, and a metal ring with a screw is screwed from above through a spring washer and tightened with a screw to hermetically seal. Sodium / molten salt secondary battery.

(2) A metal seal ring having corrosion resistance to sodium is used instead of the carbon seal ring interposed between the edge of the outer cylindrical container and the α-alumina ring. The sodium / molten salt secondary battery according to claim 1.

(3) An inner cylinder made of a sodium ion conductive solid electrolyte is mounted in the outer cylinder, and the inside of the outer cylinder is moved between the positive electrode chamber in the inner cylinder, the outer cylinder, and the inner cylinder. A mixed molten salt composed of NaCl—AlCl ₃ —SCl _x (x = 0 to 4) as a positive electrode active material was charged into the positive electrode chamber, and the negative electrode active material was charged into the negative electrode chamber. Liquid / sodium salt, a hermetically sealed sodium / molten salt secondary battery equipped with an upper lid in which a current collector is inserted in the center thereof, and an edge in which the upper lid is fitted to the upper end of the outer cylindrical container. A sealing portion having a screw portion for screwing a threaded metal ring is provided, and the upper lid is inserted with an α-alumina ring for sealing the opening of the negative electrode chamber and a current collecting rod in a central portion for sealing the opening of the positive electrode chamber. Α-alumina disk, and the connection between the α-alumina ring and the inner cylindrical container. Part and the joint between the α-alumina disk and the current collecting rod are joined by a glass brazing material, and an α-alumina ring joined to the inner cylinder container via a carbon seal ring is placed on the edge of the outer cylinder container. -Α-current collector rod joined to the alumina ring via a carbon seal ring-
A method for assembling a sodium / molten salt secondary battery in which an alumina disk is placed, a threaded metal ring is screwed from above through a spring washer, and hermetically sealed by tightening with a screw. -The joint between the alumina ring and the inner cylindrical container and the joint between the α-alumina disk and the current collecting rod preliminarily covered with the carbon electrode are joined with a glass brazing material, and solid sodium is placed in the outer cylindrical container. After loading, place the α-alumina ring to which the inner cylinder is joined via a carbon seal ring or a metal seal ring on the edge of the outer cylinder, and then join the current collector rod via the carbon seal ring The α-alumina disk was placed, and at this time, the mixed molten salt was loaded in the inner cylindrical container in such an amount that the carbon electrode was sufficiently immersed when the battery was operated,
Finally, a method for assembling a sodium / molten salt secondary battery, wherein a screwed metal ring is screwed from above through a spring washer and hermetically sealed by tightening with a screw.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION As the material of the outer cylindrical container, the inner cylindrical container and the upper lid, which are the main components of the sodium / molten salt secondary battery of the present invention, those conventionally used can be used. As a specific example, stainless steel or carbon steel having corrosion resistance to sodium as the negative electrode active material is used as the outer cylindrical container, and β ″ -alumina having sodium ion conductivity is used as the inner cylindrical container. The material of the upper lid is required to have a glass bonding property with β ″ -alumina, corrosion resistance to the positive electrode and the negative electrode active material, insulation properties, etc., but from the viewpoint of corrosion resistance mainly to the molten salt as the positive electrode active material,
As a material that can be used, only α-alumina is known.

According to the present invention, an α-alumina ring for joining the upper lid to the inner cylindrical container in glass and an α for joining the current collector to glass are used.
-Separation into an alumina disk to facilitate the glass bonding operation, and final assembly can be performed simply by overlapping and tightening with screws via a seal ring. Thereby, there is an effect that charging and final assembly of the cathode and anode active materials that are difficult to handle can be performed simultaneously and easily.

The current collector rod to be charged into the positive electrode chamber from the center of the α-alumina disk of the upper lid is preferably made of tungsten, and the part immersed in the molten salt as the positive electrode active material is made of carbon foam or the like. And a carbon electrode made of a porous carbon material. Note that the lower portion of the current collecting rod may be made of a carbon material.

It has been confirmed that the carbon material has no problem with respect to the corrosion of the mixed molten salt as the positive electrode active material of the battery of the present invention. In addition, during the operation of the battery, the temperature may change in the range of room temperature to 300 ° C. In this case, since the thermal expansion of each member is different, there is a concern that the airtightness of the seal portion is impaired. The battery of the invention has a structure in which a required force is always obtained in an airtight manner by the pressing force of the spring washer, and a sufficient airtightness is obtained by tightening the metal ring with a predetermined force and pressing the carbon seal ring. Can be. The airtight seal between the α-alumina ring and the α-alumina disk exposed to the atmosphere of the mixed molten salt of the positive electrode active material can be applied only to the carbon seal ring from the viewpoint of corrosion resistance. As the airtight seal between the outer cylindrical container containing sodium and the α-alumina ring, a metal seal ring having corrosion resistance to sodium (eg, pure aluminum material, stainless steel, etc.) can be applied in addition to the carbon seal ring. is there.

In the case of the conventional structure, the glass bonding is 1000
Since it is performed at a high temperature close to ℃, the injection of molten salt is inevitably performed in small quantities in powder form through a thin injection pipe (tungsten pipe) at room temperature after glass joining, resulting in extremely poor work efficiency. Adjustment of the amount of salt injected was difficult and non-uniform, and there was a possibility that battery performance would be degraded. On the other hand, in the case of the present invention, since the glass-bonded members are assembled together at room temperature by screwing, the carbon electrode is preliminarily formed after glass-bonding the tungsten current collector rod and the α-alumina pellet (α-alumina disk). Can be impregnated with a molten salt to perform the entire assembly. Furthermore, since the shortage of the molten salt can be previously filled in the β ″ -alumina tube which is the inner cylinder,
The molten salt can be easily and reliably filled.

In addition, the injection of sodium has conventionally been a two-step process in which, after assembling the battery, the interior is evacuated through a sodium injection port, and then the sodium is heated to 150 ° C. or more and injected in a liquid state. In the case of the present invention, it is possible to dispose sodium in the form of a solid plate inside the outer cylindrical container before the entire assembly, so that the process can be greatly simplified.

[0018]

The present invention will be described more specifically with reference to the following examples. Note that the present invention is not limited to this embodiment. FIG. 1 shows a battery structure according to one embodiment of the present invention, and its manufacturing process and performance test results are shown below. First, the tungsten current collecting rod 2 in which the α-alumina disk 1 and the carbon electrode 5 are bonded in advance is glass-bonded at the bonding portion 3a. The α-alumina ring 6 and β ″-
The inner cylindrical container 4 made of an alumina tube is glass-joined at the joint 3b. The glass brazing material used for joining the joining portions 3a and 3b is α-alumina, tungsten and β ″
-It is necessary to select a material having a coefficient of linear expansion close to that of alumina (4 to 8 × 10 ⁻⁶ / ° C.) and capable of withstanding corrosion of molten salt.

In this embodiment, 65% SiO_Two-20% B_Two
O_Three-5% Al_TwoO_Three-10% Na _TwoO-based glass brazing
Using a material, in an argon gas atmosphere, at 980 ° C for 20 minutes
Glass bonding was performed under the conditions. Next, the liquid molten salt
A carbon electrode 5 made of a porous carbon material is immersed in a container.
And fully impregnate the molten salt into the carbon foam
Raise and dry. In addition, carbon
Insufficient molten salt component is insufficient only by impregnating the electrode 5.
Add it.

Next, the sealing portion 1 prepared in advance
A sodium plate 9 in a stainless steel outer container 8 having
Is inserted, the carbon seal ring 7b is placed on the edge 12 of the sealing portion 16, and the α-alumina ring 6 joined to the inner cylinder 4 inserted in the outer cylinder 8 is placed thereon. Further, the α-alumina disk 1 on which the tungsten current collector rod 2 is joined is placed on the α-alumina ring 6, and finally, the metal ring 10 with a screw is screwed from above the spring washer 11 to complete the final assembly. The sealing by the carbon seal rings 7a and 7b requires a surface pressure of 200 kg / cm ² or more. Therefore, it is necessary to select the spring washer 11 having a size sufficient to obtain the necessary pressing force. is there.

The battery manufactured in the above process was operated at an operating temperature of 2.
As a result of conducting a charge / discharge cycle test at 30 ° C., the energy density per active material was as high as 300 to 330 W · h / kg, the internal resistance was a stable value of about 9 Ωcm ^2, and at least 300 charge / discharge cycles were obtained. There was no significant performance degradation and good results were obtained.

The structure of the hermetic sealing portion which uses a sealing material such as carbon and a spring washer according to the present invention and is screwed from above and a method of assembling a sodium / molten salt secondary battery are only applicable to cylindrical batteries. Of course, it is needless to say that the present invention can be applied to batteries of various shapes such as a rectangular cross section.

[0023]

According to the sodium / molten salt secondary battery of the present invention, the hermetically sealed portion has sufficient corrosion resistance, heat resistance and airtightness, and the temperature is repeatedly raised and lowered during battery assembly and battery operation. It has a structure that can withstand NaC as a positive electrode active material.
_{l-AlCl 3 -SCl X (x} = 0~4) based mixed reliability and long life of the sodium / molten salt secondary battery using the molten salt can be achieved. Further, simplification of the manufacturing process makes it possible to reduce the manufacturing cost, and it is possible to provide an inexpensive secondary battery for power storage or applicable to an electric vehicle power supply.

[Brief description of the drawings]

FIG. 1 is a structural explanatory view of a sodium / molten salt secondary battery according to the present invention.

FIG. 2 is a structural explanatory view of a conventional sodium / molten salt secondary battery.

Claims (3)

[Claims] 1. An inner cylindrical container made of a sodium ion conductive solid electrolyte is mounted in an outer cylindrical container, and the outer cylindrical container is formed between a positive electrode chamber in the inner cylindrical container, the outer cylindrical container, and the inner cylindrical container. And a negative electrode chamber, and the positive electrode chamber contains N as a positive electrode active material.
A mixed molten salt composed of aCl-AlCl ₃ -SCl _x (x = 0 to 4) is charged, liquid sodium as a negative electrode active material is charged into a negative electrode chamber, and an upper lid in which a current collector is inserted in the center is mounted. And a hermetically sealed sodium / molten salt secondary battery, wherein a sealing portion having an edge portion for fitting the top lid and a screw portion for screwing a threaded metal ring is provided at an upper end portion of the outer cylindrical container,
The upper lid is composed of an α-alumina ring that seals the opening of the negative electrode chamber, and an α-alumina disk in which a current collecting rod around which a carbon electrode is inserted is inserted at the center of the opening that seals the opening of the positive electrode chamber. Joint between alumina ring and inner cylinder and α-
The joining portion between the alumina disk and the current collecting rod is joined by a glass brazing material, and an α-alumina ring joined to the inner cylinder container via a carbon seal ring is placed on the edge of the outer cylinder container.
-An α-alumina disk with a current collecting rod bonded to it via a carbon seal ring is placed on the alumina ring, and a metal ring with a screw is screwed from above through a spring washer and tightened with a screw to hermetically seal. A sodium / molten salt secondary battery, comprising: 2. A metal seal ring having corrosion resistance to sodium is used instead of a carbon seal ring interposed between an edge of the outer cylindrical container and an α-alumina ring. The sodium / molten salt secondary battery according to claim 1. 3. An inner cylinder made of a sodium ion conductive solid electrolyte is mounted in an outer cylinder, and the inside of the outer cylinder is formed between the positive electrode chamber in the inner cylinder, the outer cylinder, and the inner cylinder. And a negative electrode chamber, and the positive electrode chamber contains N as a positive electrode active material.
A mixed molten salt composed of aCl-AlCl ₃ -SCl _x (x = 0 to 4) is charged, liquid sodium as a negative electrode active material is charged into a negative electrode chamber, and an upper lid in which a current collector is inserted in the center is mounted. And a hermetically sealed sodium / molten salt secondary battery, wherein a sealing portion having an edge portion for fitting the top lid and a screw portion for screwing a threaded metal ring is provided at an upper end portion of the outer cylindrical container,
The upper lid is composed of an α-alumina ring for sealing the opening of the negative electrode chamber and an α-alumina disk having a current collecting rod inserted in the center for sealing the opening of the positive electrode chamber. And the joint between the α-alumina disk and the current collecting rod were joined by a glass brazing material, and the α-alumina disc was joined to the inner cylindrical container via a carbon seal ring at the edge of the outer cylindrical container.
An alumina ring is placed, an α-alumina disk having a current collecting rod joined thereto via a carbon seal ring is placed on the α-alumina ring, and a screwed metal ring is further screwed from above through a spring washer. A method for assembling a sodium / molten salt secondary battery, which is hermetically sealed by tightening, comprises firstly bonding a carbon electrode to a joint between an α-alumina ring and an inner cylindrical container and an α-alumina disk. After joining the joint with the current collector rod with a glass brazing material and charging solid sodium into the outer cylinder container, the inner portion of the outer cylinder container is internally sealed via a carbon seal ring or a metal seal ring. The α-alumina ring to which the cylindrical container is joined is placed, and further the α-alumina disk to which the current collecting rod is joined via the carbon seal ring is placed. At this time, the battery is placed in the inner cylindrical container. An amount of the mixed molten salt sufficient to immerse the carbon electrode during operation is charged, and finally a screwed metal ring is screwed from above through a spring washer, and hermetically sealed by tightening with a screw. A method for assembling a sodium / molten salt secondary battery.