JPH09283175A - Sodium/fused salt secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize high performance, a long lifetime and low cost by using the glass brazing material for a battery seal part. SOLUTION: In this battery, a lower part of an α alumina pellet is formed into a recessed shape, and connected for sealing to an upper end of an alumina pipe 5 by a first bonding material 8 made of the glass brazing material. A positive electrode chamber 3 is sealed by the alumina pipe 5 and the (α alumina pellet. Furthermore, a second bonding material made of the glass brazing material 12 and for sealing a negative electrode chamber 4 is bonded between the top surface and a side surface of the alumina pellet and an outer cylindrical container 1. The glass brazing material has the excellent corrosion resistance in relation to the fused salt of the positive electrode. Bonding structure of each part is simple and the material at a low cost can be used so as to reduce the cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sodium / molten salt secondary battery, and more particularly to a charge / dischargeable sodium / molten salt secondary battery applied to a power storage battery for load leveling and a driving power source for an electric vehicle.

[0002]

2. Description of the Related Art Conventionally, as a structure of a sodium / molten salt secondary battery, generally, a positive and negative electrode chamber is provided inside and outside of a ceramic tube called conductive β or β ″ alumina of sodium ions. In addition, as a battery similar to this, sodium polysulfide (Na
There is a sodium / sulfur battery using ₂ Sx).

[0003] 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 need to have a structure free from liquid leakage. Since it reacts explosively, it is necessary to have a highly airtight closed structure completely shut off from the atmosphere. Therefore, in order to improve the sealing property of each joint, a brazing method using an active metal or a thermal diffusion joining method is used for joining the outer cylindrical container and the α-alumina. Further, as a seal for the active material injection port, a mechanical seal method in which metal surfaces are crushed or an electron beam sealing method is known.

[0004]

Among the sodium / molten salt secondary batteries, the inventors of the present invention have proposed 700-800 Wh / K.
Focusing as a positive electrode active material having a high theoretical energy density g in a mixed molten salt of _{NaCl-AlCl 3 -SClx (x =} 0~4), was confirmed assembling performance battery by employing the conventional joining techniques Although the sodium negative electrode chamber side has no problem in the conventional joining method, it has been found that the seal portion of the positive electrode chamber in which the molten salt is disposed is easily corroded and the positive electrode active material leaks. Corrosion of the metal container in contact with the positive electrode molten salt is also significant, and as a result, the capacity of the positive electrode active material is reduced due to consumption of the positive electrode active material.

As a measure against the latter container corrosion, the formation of a corrosion-resistant layer on the inner surface of the container of the positive electrode chamber and the alternative of the container material "Japanese Patent Application No. 5-202302", or the positive electrode active material and the outer cylinder container have not been in direct contact with each other. Although it has been subjected to treatment such as the structure in which the positive electrode chamber is placed inside the β or β "alumina tube, it is not sufficient for practical durability. That is, molten salt corrosion of the positive electrode seal part It was also found that the progress of corrosion of the metal container on the gas phase side even without direct contact with the molten salt is the main cause of hindering the performance and life of the battery.

The present invention has been made in view of these circumstances, and is capable of realizing higher performance, longer life and lower cost than conventional ones, and is suitable for power storage and electric vehicle power sources. The purpose is to provide a secondary battery.

[0007]

Therefore, in the present invention, attention has been paid to a glass-based material having excellent corrosion resistance against the positive electrode molten salt, and a glass brazing material is used for all the battery seal portions. That is, in a battery structure in which a positive electrode chamber is provided inside a β or β ″ alumina tube that does not directly contact the molten salt and the outer cylindrical container, an insulating property obtained by penetrating and joining a positive electrode terminal tube to the upper end opening of the tube and the central part The lower surface of the α-alumina pellets is joined with a high melting point glass brazing material, and the upper surface and side surfaces of the α-alumina pellets are joined with a low melting point glass brazing material, and the sealing of the molten salt injection port is also low. Partial thermal spray sealing is performed using a glass brazing material having a melting point, so that in the positive electrode chamber, the molten salt vapor phase portion does not come into contact with the metal outer container, and the molten salt vapor phase portion and the metal member are unique. As a material of the positive electrode terminal tube which is in contact with the molten salt, tungsten having excellent corrosion resistance against the molten salt is used.

Regarding the positive electrode, Japanese Patent Application Nos. 5-222326 and 6-276407, which the present inventors have already optimized in the same sodium-based secondary battery,
Porosity of at least 8
It has been clarified that a structure in which a carbon electrode having a pore structure having an open pore form of 5% or more and an amorphous dense carbon current collector are bonded with a carbon adhesive is preferable for the battery performance.

That is, according to the present invention, an outer cylindrical container, a sodium ion conductive solid electrolyte tube for dividing the outer cylindrical container into a positive electrode chamber and a negative electrode chamber, and an insulating α-alumina in which a positive electrode terminal tube is penetratingly joined in a central portion thereof. A pellet, the upper end of the solid electrolyte tube and the lower surface of the alumina pellet are joined and sealed to seal the positive electrode chamber with the solid electrolyte tube and the alumina pellet.
2. A sodium / molten salt secondary battery, comprising: the bonding material of 1. and a second bonding material that bonds the upper surface and the side surfaces of the alumina pellets to the outer cylinder container to seal the negative electrode chamber.

The operation of the present invention is as follows. That, NaCl-AlCl ₃ -SClx (x positive electrode active material
The cell reaction when the mixed molten salt of (0 to 4) is approximately represented by the following "Chemical formula 1" (Formula 1) and "Chemical formula 2" (Formula 2). The discharge reaction is from the left side to the right side, and the charge reaction is the opposite.

[0011]

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[0012]

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In the discharge, first, in the formula 1, a reaction from the +4 valence of sulfur to the valence of 0 without precipitation of NaCl occurs. Subsequently, the reaction shifts from the 0 valence of sulfur to the -2 valence of which is accompanied by precipitation of NaCl, which is represented by the formula 2. Corrosion factors caused by the molten salt include AlCl ₃ , SCl ₄ , and S contained in the positive electrode active material.
₂ Cl ₂ and SCl ₂ are expected to dominate. It was confirmed that these corrosive liquids and gases hardly react with glass-based materials and tungsten materials. Therefore, according to the battery structure of the present invention, the performance of the battery can be improved and the cycle life can be improved all at once, and Na / having practical durability can be used.
A molten salt secondary battery can be obtained.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG. Reference numeral 1 in the figure is an outer cylinder container having an opening at the top and a sodium injection port 2 at the bottom.
The material of the outer cylindrical container 1 is preferably stainless steel or carbon steel, and here, SUS304 or SUS405.
Of stainless steel. A β or β ″ alumina tube (hereinafter referred to as an alumina tube) 5 as a sodium ion conductive solid electrolyte tube that divides the inside of the outer cylindrical container 1 into a positive electrode chamber 3 and a negative electrode chamber 4 is provided in the outer cylindrical container 1. At the upper end of the alumina tube 5, an insulating α-alumina pellet 7 having a positive electrode terminal tube 6 made of tungsten penetratingly joined to the center is capped.

The lower part of the α-alumina pellet 7 is formed into a concave shape. The upper end of the alumina tube 5 and the α
The lower surface of the alumina pellet 7 is bonded and sealed by a first bonding material 8 made of a glass brazing material. The first bonding material 8 seals the positive electrode chamber 3 with the alumina tube 5 and the α-alumina pellet 7. A second bonding material 9 made of a glass brazing material for sealing the negative electrode chamber 4 is bonded between the upper surface and the side surface of the α-alumina pellet 7 and the outer cylindrical container 1.

The glass brazing material used for the first bonding material 8 and the second bonding material 9 includes α-alumina, β- or β ″ -alumina and a linear expansion coefficient of tungsten (4 to 8 × 10 ^-6 /
It is necessary to select a material having a melting point close to that of the glass brazing material used for joining the outer cylindrical container 1 and the α-alumina pellets 7 to the melting point. Here, if the same glass brazing material is used for the first joining material 8 and the second joining material 9, both joining steps can be performed at the same time and the battery assembling step can be simplified. For example, the bonding materials 8 and 9 are both made of 65% SiO 2.
With _{2 -20% B 2 O 3 -5} % Al 2 O 3 glass brazing material consisting of -10% Na ₂ O other, in an Ar atmosphere, 980 ° C.,
If the heat treatment is performed for 20 minutes, good joining with high airtightness can be obtained.

At the lower end of the positive electrode terminal tube 6, a carbon current collector 10 whose one end extends close to the bottom of the alumina tube 5 is screwed. Here, as the carbon current collector 10,
In order to avoid intercalation with chloride, dense amorphous carbon, tungsten, nickel coated with these, or steel is preferable. A porous electrode 11 is bonded to the outer periphery of the carbon current collector 10 with a carbon adhesive. Here, the porous electrode 11 has a porosity of 9
5 to 97%, pore size 100 to 500 μm, surface area 500
It is preferable to use carbon-based carbon fiber or amorphous carbon foam having a pore structure of 0 m ² / m ³ or more.

The upper opening of the outer cylindrical container 1 and a part of the α-alumina pellet 7 are joined by a glass solder 12 so as to fill a part of the positive electrode terminal tube 6.
Here, the glass solder 12 is preferably close to the linear expansion coefficient of tungsten, which is the material of the positive electrode terminal tube 6, so that residual tensile stress does not occur in the glass solder 12, and the first and second It is necessary to have a melting point lower than that of the glass brazing material used for the joining material. For example, as a material which can satisfy such conditions, 10% SiO ₂ -45% B ₂ O
There are _{3 -35% ZnO-10% Na} 2 O glass brazing material consisting of another, in which the Ar atmosphere, if 20 minutes heat treatment at 650 ° C., a high favorable bond airtight is obtained. The tip of the positive electrode terminal tube 6 is threaded into a taper shape, and a male thread 13 made of tungsten is screwed to this threaded portion. Reference numeral 14 in the drawing is a through hole provided below the positive electrode terminal tube 6.

Next, a method of manufacturing the sodium / molten salt secondary battery having the above structure will be described. First, the α-alumina pellet 7 and the positive electrode terminal tube 6 are glass-bonded by the second bonding material 9. Next, the α-alumina pellets 7 and the upper ends of the alumina tubes 5 are glass-bonded by using the first bonding material 8. The carbon current collector 10 is the α-alumina pellet 7
Before the alumina tube 5 and the alumina tube 5 are joined together, they are screwed into the positive electrode terminal tube 6 so as to maintain electrical contact. Next, the one obtained in the above series of steps is inserted into the outer cylinder container 1. Next, the battery container assembled in the above manufacturing process is
Vacuum dry at ˜400 ° C. to remove water sufficiently. Especially,
In order to remove the water impregnated / adsorbed in the alumina tube 5 which affects the battery performance, vacuum drying at 350 to 400 ° C. for about 1 week is preferable.

High-purity sodium, from which dissolved oxygen has been sufficiently removed in advance, is injected into the negative electrode chamber 4 in a liquid form from the sodium injection port 2 into the vacuum-dried outer cylinder container 1. After injection, the tip of the sodium injection port 2 is vacuum-sealed with an electron beam or mechanically sealed to prevent sodium from leaking. In addition, in order to sufficiently adjust the interface between sodium and β-alumina with sodium and reduce the interfacial resistance at that portion, after injecting sodium, the outer cylindrical container 1 is charged with 200-
It is preferable to heat-treat at 400 ° C. for several hours.

Next, a predetermined amount of dry sulfur powder and sodium chloride powder is put into the positive electrode chamber 3 through the inlet of the positive electrode terminal pipe 6, and the positive electrode chamber 3 is introduced into the positive electrode chamber 3 through the through hole 14 provided in the lower portion thereof. Put in. Then, similarly, 50 already prepared and purified.
mol% NaCl-50 mol% AlCl ₃ (NaAlCl
Inject a prescribed amount of ₄ ) in powder or liquid form. After all the positive electrode active material has been injected, the tip of the positive electrode terminal tube 6 which is threaded into a taper shape is screwed with a male screw 13, and the upper portion is glass sprayed and sealed. Here, as the glass brazing filler material for thermal spraying and sealing, a material having a thermal expansion coefficient close to that of tungsten is preferable, and for example, a low melting point glass brazing filler material containing B ₂ O ₃ used for the glass brazing filler 12 as a main component is suitable.

According to the sodium / molten salt secondary battery according to the above-described embodiment, the upper end opening of the alumina tube 5 and the lower surface of the α-alumina pellet 7 are bonded and sealed with the first bonding material 8 so that the positive electrode chamber 3 is made of alumina. Tube 5 and α-alumina pellet 7
Completely seal, and the upper surface and side surfaces of the α-alumina pellets 7 and the outer cylindrical container 1 are joined with a second joining material 9 to form a negative electrode material 4.
Is a hermetically sealed structure. Therefore, a low-cost battery can be obtained because a simple and inexpensive material can be used for the bonding structure of each part.

[0023]

EXAMPLES Next, examples of charge / discharge operation of the Na / molten salt secondary battery manufactured as described above will be described. For the solid electrolyte, high sodium ion conductive β ″ alumina tube stabilized with Li ₂ O ₃ (outer diameter 20 mmφ, thickness 1
mmt, total length 142 mmL (effective length 100 mmL))
Was used as each cell. The filling amount of each battery active material was 20 g of sodium, 2.28 g of dry sulfur, 4.21 g of dry sodium chloride, and 40 of NaAlCl _4.
g. The theoretical battery capacity at this time is 7.62 Ah.
It is. The battery operating temperature was 230 ° C., and the charge / discharge cycle test was carried out by the constant current method. The rated current densities per β ″ alumina surface area during charging / discharging were 25 mA / cm ^{2 on} the charging side and 50 mA / cm ² on the discharging side, respectively.

FIG. 2 shows a typical charge / discharge curve at that time. The discharge curve was flat until the utilization rate of sulfur was about 50%, the average discharge voltage was 3.8 V, and the average power density was 0.19 W / cm ² . Further, the energy efficiency was 88%, and good performance was obtained in each case. When the utilization rate becomes 50% or more, the open circuit voltage sharply drops to 2.75 V while shifting to the reaction of the above-mentioned equation 2 as described above. Since such a sudden change in battery output is not practical for an actual load, it was intentionally not used here.

On the other hand, the charge / discharge cycle characteristics were evaluated by the weight energy density per unit cell and the internal resistance, and the results are shown in FIGS. 3 and 4, respectively. The energy density showed a very high value of 150 Wh / Kg from the beginning, and after that, almost no decrease in the energy density was observed and 1000 cy.
c. Even after the above, stable performance could be maintained. Similarly, the internal resistance does not increase from the initial value and is approximately 9Ω.
It remained stable at cm ² . From the above results, according to the present cell structure, Na / NaCl-AlCl ₃ high output with a -SClx molten salts secondary battery, a high energy density can be stably supplied for a long term charge-discharge cycle.

[0026]

As described above in detail, according to the present invention, higher performance, longer life and lower cost can be realized as compared with the conventional one.
Sodium suitable for power storage and power source for electric vehicles /
A molten salt secondary battery can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a sodium / molten salt secondary battery according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a charge / discharge curve of the sodium / molten salt secondary battery of FIG.

FIG. 3 is a cycle characteristic diagram of energy density of the sodium / molten salt secondary battery of FIG.

FIG. 4 is a cycle characteristic diagram of internal resistance of the sodium / molten salt secondary battery of FIG.

[Explanation of Codes] 1 ... Outer cylinder container, 2 ... Sodium injection port, 3 ... Positive electrode chamber, 4 ... Negative electrode chamber, 5 ... Alumina tube, 6 ... Positive electrode terminal tube, 7 ... α-alumina pellet, 8 ... First joining Material, 9 ... Second bonding material, 10 ... Carbon current collector, 11 ... Porous electrode, 12 ... Glass solder, 13 ... Male screw, 14 ... Through hole.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kei Inouto Kei 717-1, Fukahori-cho, Nagasaki-shi, Nagasaki Sanhishi Heavy Industries Ltd. Nagasaki Research Institute (72) Inventor Nozomu Kawabushi 5-chome, Fukahori-cho, Nagasaki-shi, Nagasaki Prefecture No. 717-1 Sanryo Heavy Industries Co., Ltd. Nagasaki Research Center

Claims (3)

[Claims] 1. An outer cylinder container, a sodium ion conductive solid electrolyte tube for dividing the inside of the outer cylinder container into a positive electrode chamber and a negative electrode chamber, and an insulating α-alumina pellet having a positive electrode terminal tube penetratingly bonded to a central portion thereof, A first joining material for joining and sealing the upper end of the solid electrolyte tube and the lower surface of the alumina pellet to seal the positive electrode chamber with the solid electrolyte tube and the alumina pellet;
A sodium / molten salt secondary battery comprising: a second bonding material for bonding the upper and side surfaces of the alumina pellet to an outer cylinder container to seal the negative electrode chamber. Wherein the inside of the solid electrolyte tube, NaCl-AlCl ₃ -SClx as a positive electrode active material (x = 0 to 4)
2. The sodium / molten salt secondary battery according to claim 1, wherein the mixed molten salt composed of the above component is provided outside of which liquid sodium is provided as a negative electrode active material. 3. The positive electrode uses a carbon fiber or carbon foam and a non-conductive amorphous carbon rod or a metal rod coated with amorphous carbon bonded with a carbon adhesive. The sodium / molten salt secondary battery according to claim 1, wherein the sodium / molten salt secondary battery is connected to the positive electrode terminal tube.