JPH11329484A - Sodium-sulfur secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sodium-sulfur secondary battery, equipped with excellent charge/discharge characteristics and easy in manufacture. SOLUTION: This sodium-sulfur secondary battery is equipped with a positive- electrode current collector together with a positive-electrode active material 7 packed in a positive-electrode chamber 6. A mixed material C made by mixing particulate conductors B into lump-shaped fiber conductors A with a void ratio of 80% or more is used for the positive-electrode current collector. By using the mixed material C for the positive-electrode current collector, the distribution of electronic conduction materials in the positive-electrode chamber 6 is made uniform, a risk is eliminated that the diffusion of the active material is deterred in the positive-electrode chamber 6 during charge/discharge reaction, charge- discharge resistance is reduced, and highly efficient charge/discharge is enabled. Because the tensile stress produced in a surface of a solid electrolyte tube 1 is decreased, the breakage of the solid electrolyte tube 1 is suppressed to cause reliability to be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sodium-sulfur secondary battery, and more particularly to a sodium-sulfur secondary battery characterized by the structure of a positive electrode chamber and having excellent charge / discharge cycle characteristics.

[0002]

BACKGROUND OF THE INVENTION As is well known, sodium-
A sulfur secondary battery uses β-alumina or β ″ as an electrolyte.
Using a solid electrolyte having sodium ion conductivity consisting of at least one of alumina and the like, using sodium as the negative electrode active material, and using at least one of sulfur and sodium polysulfide as the positive electrode active material;
It is a sealed secondary battery that operates at a temperature of about 350 ° C. to about 350 ° C., and has excellent charge / discharge cycle characteristics, high energy density, and excellent watt-hour efficiency.
It is the one that is attracting attention.

Accordingly, an example of this sodium-sulfur secondary battery is shown in FIG. 4, for example. FIG. 4 shows an example of a general sodium-sulfur secondary battery, in which 1 is a solid electrolyte tube,
A material such as β-alumina or β ″ -alumina is used to form a bag with one end closed, thereby forming a negative electrode chamber 2 therein. The active material 3 is enclosed.

[0004] The outer peripheral surface of the solid electrolyte tube 1 is made of a material having a relatively low conductivity while exhibiting excellent corrosion resistance to sulfur and / or sodium polysulfide made of a material such as alumina and carbon. High resistance layer 4
Is provided.

[0005] Reference numeral 5 denotes a positive electrode container, which is made of a metal material such as stainless steel and has a bottomed cylindrical shape, constitutes a positive electrode (anode) terminal of the battery, holds the solid electrolyte tube 1 in the center of the inside, and surrounds the solid electrolyte tube 1. To form a positive electrode chamber 6. A positive electrode active material 7 mainly containing at least one of sulfur and sodium polysulfide is sealed in the positive electrode chamber 6.

Reference numeral 8 denotes a negative electrode container, which is also made of a metal material such as stainless steel, seals the negative electrode chamber 2, and inserts a metal electrode inserted into the negative electrode active material 3 in the solid electrolyte tube 1. It holds the rod 9 and serves to configure the negative (cathode) terminal of the battery. Reference numeral 10 denotes an insulator ring, which is made of ceramics such as alumina and serves to heat and pressure join the positive electrode container 5 and the negative electrode container 8 to seal the positive electrode chamber 6 and to separate the positive electrode from the negative electrode.

Incidentally, such sodium-sulfur 2
In the secondary battery, the conductivity of the sulfur and / or sodium polysulfide constituting the positive electrode active material 7 is increased, and the state where the positive electrode active material 7 is properly held in the positive electrode chamber 6 is obtained. For this reason, a current collector made of a porous conductive material is provided in the positive electrode chamber 6, and the current collector is sealed in a state where sulfur and / or sodium polysulfide is impregnated therein.

As the current collector, for example, JP-A-6-283201 and JP-A-7-122294 disclose a technique in which a conductive felt-like carbon mat (rug) material is provided. doing. Here, the carbon mat material used in these conventional techniques is obtained by subjecting a web (woven fabric) of oxidized carbon fiber obtained as a precursor in a carbon fiber manufacturing process to needle punching and firing.

[0009] For example, see Japanese Patent Application Laid-Open No. 54-109134.
Japanese Patent Application Laid-Open No. 57-27572 discloses a technique of depositing short carbon fibers and providing a positive electrode current collector bonded with carbide. Japanese Patent Application Laid-Open No. 57-27572 discloses a technique of using 2 to 50% by weight of expanded graphite. A technique used as a positive electrode current collector is disclosed. Here, the expanded graphite is graphite obtained by expanding in the C-axis direction in the crystal axis of graphite.

[0010]

The above prior art has the following problems. First, JP-A-6-28320
According to the technology described in Japanese Patent Application Laid-Open No. 7-122294 and Japanese Patent Application Laid-Open No. 7-122294, when the carbon mat material is installed in the positive electrode chamber, it is necessary to store a plurality of arc-shaped ones, which requires a large number of manufacturing steps. However, there is a problem that the mat itself becomes expensive.

The carbon mat material is used for current collection between the solid electrolyte tube and the positive electrode container. Therefore, by installing the carbon mat material in a compressed state in the positive electrode chamber, it is possible to reduce the contact resistance to the solid electrolyte tube. However, as a result, if the compressive force applied to the mat is not kept uniform, a tensile stress is locally applied to the surface of the solid electrolyte tube, and when the battery is operated for a long time, There is a problem that the solid electrolyte tube may be damaged, and when the mat is compressed, the fiber density tends to be uneven, and as a result,
There is a problem that the internal resistance of the battery varies.

Next, in the prior art disclosed in Japanese Patent Application Laid-Open No. 54-109134, a step of accumulating short fibers and a step of carbonizing the binder are required, so that the number of manufacturing steps cannot be simplified. In addition, there is a problem that the electronic conductivity of the binder varies depending on the carbonization conditions of the binder, and the internal resistance increases.

Further, in the prior art described in Japanese Patent Application Laid-Open No. 57-27572, the current collection resistance is higher than when carbon fibers are used as the current collector, and the charge / discharge efficiency is reduced. There was a problem. SUMMARY OF THE INVENTION An object of the present invention is to provide a sodium-sulfur secondary battery which solves the above-mentioned disadvantages of the prior art, has excellent charge / discharge resistance characteristics, and is easy to manufacture.

[0014]

SUMMARY OF THE INVENTION The object of the present invention is to provide a sodium-sulfur secondary battery having a positive electrode active material and a positive electrode current collector in a positive electrode chamber, wherein the positive electrode current collector has a porosity of 80%.
This is achieved by using a mixture of the above-described massive fiber conductor and particulate conductor.

At this time, the particle diameter of the particulate conductor is 1
0 μm or more and 5000 μm or less,
At least one substance selected from PAN-based carbon, pitch-based carbon, amorphous-based carbon, natural graphite, artificial graphite, acetylene black, Ketjen black, Cr-Co-based alloy, Al-Si alloy, or at least It may be composed of a mixture of two or more types.

[0016] Similarly, the object is to provide a sodium-sulfur secondary battery provided with a positive electrode active material and a positive electrode current collector in a positive electrode chamber, wherein the positive electrode current collector comprises a massive fiber conductor having a porosity of 80% or more; This is achieved by comprising a mixture of short fibrous conductors.

At this time, the short fibrous conductor is made of PAN
It may be constituted by one kind of fiber selected from the group consisting of system-based carbon fibers, pitch-based carbon fibers, and amorphous-based carbon fibers, or a mixture of at least two kinds of fibers.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, sodium-
The sulfur secondary battery will be described in detail with reference to the illustrated embodiment. The embodiment of the present invention described here is an example in which the present invention is applied to the sodium-sulfur secondary battery shown in FIG. At this time, in the embodiment of the present invention, the configuration of the positive electrode current collector used for the positive electrode active material 7 containing sulfur and / or sodium polysulfide as a main component in FIG. This is the same as the prior art described above, and therefore, the following description will focus on differences from the prior art.

The embodiment of the present invention described here is merely an embodiment of the present invention. Therefore, the embodiment of the present invention is not limited to the configuration of the battery shown in FIG. In addition, the form of the battery is not limited to the case where the bottomed cylindrical (bag-shaped) solid electrolyte tube shown in FIG. 4 is used. For example, the form of the battery having a parallel plate type electrode structure can be implemented. Needless to say.

FIG. 1 shows sodium-sulfur 2 according to the invention.
1 shows a secondary battery as a first embodiment, including its manufacturing process. First, in the first embodiment, as shown in FIG. 1 (a), a bulk fiber conductor A and a particulate conductor B prepared in advance are weighed and mixed at a predetermined mixing ratio. A mixed material C to be a positive electrode current collector is prepared. Note that the massive fiber conductor A and the particulate conductor B will be described later in detail.

Next, as shown in FIG. 1 (b), after holding the positive electrode container 5 of the battery in an upright state, a jig 20 made of a cylindrical material prepared in advance is inserted into the container. , As shown in the figure. Then, a space 6 ′ having the same shape as the positive electrode chamber 6 (FIG. 4) is formed between the positive electrode container 5 and the jig 20.

Next, a funnel 21 having a predetermined shape as shown in the drawing is placed on the upper end of the jig 20. In this state, the mixture C is put into the funnel 21 as shown in the drawing, The mixed material C is placed in the space 6 ′ formed between the jigs 20.
To be dropped.

When a predetermined amount of the mixture C is injected,
Next, the mixture C is pressurized from above by means (not shown) so that the space 6 'is filled with the mixture C at a predetermined density.

Next, as shown in FIG. 1C, a predetermined amount of sulfur and / or sodium polysulfide D, which is a main component of the positive electrode active material 7, is put into the funnel 21 in a molten state. The sulfur and / or sodium polysulfide D in the space 6 '
Is poured, and the mixed material C filled therein is sufficiently impregnated.

Next, after the temperature of the positive electrode active material 7 is lowered and solidified, the funnel 21 is removed, the jig 20 is pulled out of the positive electrode container 5, and as shown in FIG. The solid electrolyte tube 1 provided with the high-resistance layer 4 is inserted into the hole remaining after being pulled out, the negative electrode active material 3 mainly composed of metallic sodium is sealed therein, and the insulator ring 10 is joined by hot-press bonding. It is assembled as a battery.

Next, a description will be given of the massive fiber conductor A and the particulate conductor B, which are the raw materials of the mixture C serving as the positive electrode current collector. First, the bulk fiber conductor A has a thickness of 8 μm to 15 μm.
Using a conductive fiber such as a PAN-based carbon fiber of about μm, a pitch-based carbon fiber, a mixed carbon fiber composed of one kind of carbon fiber selected from among amorphous carbon fibers or two or more kinds of carbon fibers, This is made into short fibers having a length of about several tens of millimeters, and then entangled with each other.
It is processed into a pill-shaped lump having a porosity of 80% or more, thereby giving a predetermined elasticity.

Next, the particulate conductor B is made of a particulate conductive material, and as a result, is itself in a state of little elasticity. The conductive material is selected from PAN-based carbon, pitch-based carbon, amorphous-based carbon, natural graphite, artificial graphite, acetylene black, Ketjen black, Cr-Co-based alloy, and Al-Si alloy. One type of substance or a mixture of two or more types is used, and the particle size is 10 μm to 100 μm.

Next, the tensile stress applied to the surface of the solid electrolyte tube 1 of the sodium-sulfur secondary battery according to this embodiment was measured. Here, as a comparative example, a conventional sodium-sulfur secondary battery using a carbon-based mat was used.

As a result, in the battery using the positive electrode current collector made of the mixed material C according to the embodiment of the present invention, the tensile stress of the solid electrolyte tube 1 was not more than about 1 MPa at the maximum. In the prior art using a carbon-based mat, it was confirmed that a tensile stress of up to about 30 MPa was generated.

Therefore, according to the embodiment of the present invention, there is no possibility that the solid electrolyte tube 1 is damaged, and as a result, a sodium-sulfur secondary battery is obtained in which there is no possibility that the internal resistance varies. Turned out to be.

Next, in the sodium-sulfur secondary battery according to this embodiment, the relationship between the particle diameter of the particulate conductor B contained in the mixture C serving as the positive electrode current collector and the relative charging resistance of the battery is as follows: As shown in FIG. The comparative example also shown here is a characteristic of a conventional sodium-sulfur secondary battery using a carbon mat as a positive electrode current collector.

As is apparent from FIG. 2, according to the embodiment of the present invention, the relative charge / discharge resistance can be made smaller than that of the prior art, and the particle diameter of the particulate conductor B at this time is 10 μm.
m to 5000 μm. As a result, in the present invention, as a mixed material C to be a positive electrode current collector,
It can be seen that the process may be performed using the particulate conductor B having a particle size of 10 μm to 5000 μm.

According to this embodiment, since the mixture C composed of the massive fiber conductor A and the particulate conductor B is used as the positive electrode current collector, a uniform distribution is obtained only by pouring the mixture into the positive electrode chamber 6. As a result, at the time of the charge / discharge reaction, there is no fear that the diffusion of the active material in the positive electrode chamber 6 is obstructed, the charge / discharge resistance is suppressed, and efficient charge / discharge characteristics are easily obtained. be able to.

As described above, as a result of using the mixed material C, the positive electrode current collector is formed not as a solid but as a collection of massive fibers, and the composition of the massive fiber conductor A is moderate. In order to stop the operation at the time of maintenance or the like, when the battery temperature is returned to normal temperature, the binding force generated by the solidification of the positive electrode active material due to the temperature decrease is reduced, and the solid electrolyte tube 1 The value of the tensile stress generated on the surface of the substrate also decreases.

Therefore, according to this embodiment, the breakage of the solid electrolyte tube 1 can be easily suppressed, and as a result, the occurrence of a dangerous situation due to the breakage of the battery is reliably prevented, and high reliability is achieved. A sodium-sulfur secondary battery can be easily obtained.

Further, as described above, the stress applied to the solid electrolyte tube 1 is suppressed, so that the thickness of the solid electrolyte tube 1 can be reduced. As a result, according to this embodiment, the internal resistance of the battery is reduced. As a result, the amount of generated heat can be reduced even during high current density operation.

Therefore, according to this embodiment, the efficiency can be further improved, and the calorific value can be reduced. As a result, a plurality of unit batteries can be connected in series and parallel to form a module suitable for use as a module. -It is possible to easily provide a sulfur secondary battery.

Here, the particle size of the particulate conductor B, which is one composition of the mixed material C, is 10 μm
Below this, diffusion of the active material becomes difficult, and the resistance of the battery may increase. On the other hand, it is 5000
If it exceeds μm, uniform mixing and uniform filling become difficult.

This fact is also shown in the characteristic diagram of FIG. 2. Therefore, as described above, the embodiment of the present invention employs the particulate conductor B having a particle diameter of 10 μm to 5000 μm as described above. It is desirable to use it.

Next, a second embodiment of the sodium-sulfur secondary battery according to the present invention will be described. In the second embodiment, a short fibrous conductor E is used in place of the particulate conductor B, which is one composition of the mixture C in the first embodiment described with reference to FIG. The positive electrode current collector filled in 6 is composed of a massive fiber conductor A and a short fiber conductor E.
And the other components are the same as those of the first embodiment.

This short fibrous conductor E has a thickness of 8 μm.
From about 15μm PAN-based carbon fiber, pitch-based carbon fiber, one type of carbon fiber selected from amorphous carbon fiber or a mixed carbon fiber composed of two or more types of carbon fibers, Preferably the fiber length is 0.01 mm
It is desirably in the range of 40 mm.

The short fibrous conductor E is mixed with the massive fibrous conductor A at a predetermined ratio to form a mixed material C ', which is used as a positive electrode current collector. The short fibrous conductor E is not particularly shown.

FIG. 3 shows the relative charge / discharge resistance characteristics of the sodium-sulfur secondary battery according to the second embodiment. The comparative example shown here also shows the comparative example of FIG. 7 shows characteristics of a conventional sodium-sulfur secondary battery using a carbon mat as a positive electrode current collector, as in the case of FIG.

As is apparent from FIG. 3, the second embodiment can also make the relative charge / discharge resistance smaller than that of the prior art, and the length of the short fibrous conductor E at this time is as follows.
It can be seen that the range is from 0.01 mm to 40 mm.

In the case of the second embodiment, the fiber length of the short fibrous conductor E mixed with the massive fibrous conductor A is 0.01.
If it is less than mm, diffusion of the positive electrode active material 7 is hindered, and the charge / discharge resistance of the battery increases. Therefore, as shown in FIG. 3, when the fiber length of the short fibrous conductor E is 0.01 mm or less, the characteristics deteriorate.

Next, in the second embodiment, the fiber length of the short fibrous conductor E mixed with the massive fibrous conductor A is 40 m.
If it exceeds m, it is difficult to mix uniformly with the bulk fiber conductor A, and an uneven current distribution appears in the positive electrode chamber 6, and the internal resistance of the battery increases. Therefore, as shown in FIG. 3, when the fiber length of the short fibrous conductor E is 40 mm or more, the characteristics are deteriorated.

As a result, in the case of the second embodiment of the present invention, as described above, it is desirable that the fiber length of the short fibrous conductor E be in the range of 0.01 mm to 40 mm. is there.

According to the second embodiment, as the positive electrode current collector, the mixed material C ′ of the massive fiber conductor A and the short fiber conductor E is used. Positive electrode chamber 6
A uniform distribution can be obtained only by pouring into the inside, and as a result, at the time of the charge / discharge reaction, there is no possibility that the diffusion of the active material in the positive electrode chamber 6 is obstructed, and the charge / discharge resistance is suppressed low. Efficient charge / discharge characteristics can be easily obtained.

As described above, as a result of using the mixed material C ′, the positive electrode current collector is formed not as a solid but as a group of cluster fibers, and the cluster fiber conductor A having the composition is formed. Since it has appropriate elasticity, when the temperature of the battery is lowered during operation stop or the like, the binding force generated by solidification of the positive electrode active material is reduced, and the value of the tensile stress generated on the surface of the solid electrolyte tube 1 is also reduced. Become smaller.

Therefore, according to the second embodiment,
The breakage of the solid electrolyte tube 1 can be easily suppressed, and as a result, the occurrence of a dangerous situation due to the destruction of the battery can be reliably prevented, and a highly reliable sodium-sulfur secondary battery can be easily obtained. I can do it.

Further, as described above, the stress applied to the solid electrolyte tube 1 is suppressed, so that the thickness of the solid electrolyte tube 1 can be reduced. As a result, the internal resistance of the battery can be reduced according to the second embodiment. Is reduced, so that the amount of generated heat can be reduced even during high current density operation.

Therefore, according to the second embodiment,
As a result of further improving the efficiency and suppressing the amount of heat generated, it is possible to easily provide a sodium-sulfur secondary battery suitable for use by modularly connecting a plurality of unit batteries in series and parallel. it can.

[0053]

According to the present invention, as the positive electrode current collector impregnated with the positive electrode active material, a mixed material of a massive fiber conductor and a particulate conductor, or a mixture of a massive fiber conductor and a short fibrous conductor is used. Since the material is used, the distribution of the positive electrode current collector in the positive electrode chamber is uniform, and there is no possibility that the diffusion of the active material in the positive electrode chamber due to the charge / discharge reaction is obstructed. As a result, the charge / discharge resistance is reduced. Thus, a sodium-sulfur secondary battery having high charge / discharge efficiency can be easily provided.

As a result, according to the present invention, when the temperature of the battery is returned to normal temperature, the binding force generated by the solidification of the positive electrode active material is reduced, and the tensile stress generated on the surface of the solid electrolyte tube is also reduced. There is no possibility that the solid electrolyte tube will be damaged, and it is possible to reliably prevent the occurrence of a dangerous situation due to the destruction of the battery.
A secondary battery can be easily provided.

Further, as a result of suppressing the stress applied to the solid electrolyte tube as described above, according to the present invention, the thickness of the solid electrolyte tube can be reduced and the internal resistance is reduced, so that the efficiency is further improved. In addition, it is possible to easily provide a sodium-sulfur secondary battery suitable for use by modularly connecting a plurality of unit batteries by serially / parallel connection because the amount of heat generated during high current density operation is suppressed. Can be.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a sodium-sulfur secondary battery according to the present invention including a manufacturing process.

FIG. 2 shows a first embodiment of a sodium-sulfur secondary battery according to the present invention.
FIG. 9 is a characteristic diagram showing relative charge / discharge resistance characteristics according to the embodiment.

FIG. 3 shows a second example of the sodium-sulfur secondary battery according to the present invention.
FIG. 9 is a characteristic diagram showing relative charge / discharge resistance characteristics according to the embodiment.

FIG. 4 is a sectional view showing an example of a sodium-sulfur secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte 2 Negative electrode chamber 3 Negative electrode active material 4 High resistance layer 5 Positive electrode container 6 Positive electrode chamber 7 Positive electrode active material 8 Negative electrode container 9 Electrode rod 10 Insulator ring A Bulk fiber conductor B Particulate conductor C Mixed material D Melted state Sulfur and / or sodium polysulfide

Continued on the front page (72) Inventor Yuichi Kamo 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Masaru Kadoshima 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture 1 Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Kozo Sakamoto 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Nariko Nishimura Hitachi, Oita City, Ibaraki Prefecture 7-1-1, Machi-cho, Hitachi Research Laboratory, Ltd.

Claims (5)

[Claims] 1. A sodium-sulfur secondary battery including a positive electrode active material and a positive electrode current collector in a positive electrode chamber, wherein the positive electrode current collector comprises a bulk fiber conductor having a porosity of 80% or more, and a particulate conductor. A secondary battery of sodium-sulfur, characterized by comprising a mixture of the following. 2. The invention according to claim 1, wherein the particle size of the particulate conductor is 10 μm or more and 5000 μm or more.
A sodium-sulfur secondary battery characterized by the following. 3. The method according to claim 1, wherein the material of the particulate conductor is PAN-based carbon, pitch-based carbon, amorphous-based carbon, natural graphite, artificial graphite, acetylene black, Ketjen black, or Cr—. Co-based alloy, Al-
A sodium-sulfur secondary battery comprising one kind of substance selected from Si alloys or a mixture of at least two kinds. 4. A sodium-sulfur secondary battery comprising a positive electrode active material and a positive electrode current collector in a positive electrode chamber, wherein the positive electrode current collector comprises a bulk fiber conductor having a porosity of 80% or more, and a short fiber conductor. A sodium-sulfur secondary battery comprising a body mixture. 5. The fiber according to claim 4, wherein the short fibrous conductor is at least one fiber selected from PAN-based carbon fibers, pitch-based carbon fibers, and amorphous-based carbon fibers. A sodium-sulfur secondary battery comprising a mixture of different kinds of fibers.