JPH07138065A - Fiber reinforced β-Al2O3 solid electrolyte - Google Patents

Abstract

(57) [Summary] [Structure] ZrO ₂ fibers and MgO fibers (diameter 0.5 to 10 μm, aspect ratio 5 to 10, addition amount 5 to 20% by weight) were added to β-Al ₂ O ₃ based ceramics. A β-Al ₂ O ₃ based solid electrolyte having an improved fracture toughness value K ₁ c. [Effect] Since the toughness of the β-Al ₂ O ₃ system ceramics is improved, the life of the battery, which is a major drawback of the prior art, can be significantly extended.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte used in batteries, alkaline sensors, thermoelectric converters and the like.

[0002]

2. Description of the Related Art There is a strong demand for the development of electric power storage equipment for storing surplus power during off-peak hours and discharging it during peak times.

The β-alumina type solid electrolyte has an ionic conductive surface in its crystal and has good ionic conductivity. β-
Alumina-based solid electrolytes include β-alumina, β ″ -alumina, etc., and the ions migrating therein are monovalent or divalent metal ions, hydronium ions, ammonium ions, etc. These compounds are recently sodium ions. -It has been tried and applied as a member of an energy conversion device such as a sulfur battery, and has been attracting attention.

However, the β-alumina-based solid electrolyte deteriorates during use as a member of the above-mentioned application example, and is damaged due to internal factors such as current concentration and external factors such as external stress, resulting in β-alumina. The "fragility" of alumina-based solid electrolytes is the cause of the short life of electrochemical devices. Due to this short life, an electrochemical device cannot be put to practical use, and development of a β-alumina solid electrolyte that is electrochemically stable, has a long life, and has high strength is strongly desired.

As a method of extending the life and strength of such a β-alumina solid electrolyte, there is a method of improving the manufacturing process such as a sintering method of the β-alumina solid electrolyte.
The essential improvement of the characteristics of the β-alumina solid electrolyte has not been achieved. On the other hand, there is a method of strengthening by adding an additive to the β-alumina solid electrolyte. Among them, zirconia is considered promising. The technique of adding zirconia to a β-alumina-based solid electrolyte to improve the mechanical strength of the solid electrolyte is to contain a yttria stabilizer in β-alumina and β ″ -alumina as described in “USP 4,358,516”. There is an example in which zirconia is added to improve the strength by stress-induced transformation of tetragonal zirconia, but, for example, a β-alumina-based solid electrolyte to which zirconia partially stabilized by yttria is added has a slight increase in strength, It has been revealed that the strength of the material is greatly reduced during its use as an electrochemical device member, and that the life as a solid electrolyte is not sufficient, and it does not contain yttria as a stabilizer (JP-A-63-60152). (Gazette) Although there is an example in which zirconia is added, the strength is slightly improved as in the above case, but it cannot be said to be sufficient.

[0006]

As described above, the β-alumina used for the solid electrolyte must have increased strength while maintaining its ionic conductivity. For this reason, conventional studies have focused only on improving strength. Therefore, the fracture toughness value K ₁ c, which is an index of the reliability of ceramics, was not so important. The present inventors have noticed that in order to have reliability, it is necessary to improve the strength as well as the fracture toughness value K ₁ c.

[0007]

In order to achieve the above-mentioned object, the present inventors have investigated a method of improving the toughness of the β-alumina-based ceramics, that is, the toughness without impairing the ionic conductivity. As a result, they have found that it is effective to combine specific ceramic fibers in β-alumina ceramics. It was also found that when the added substance reacts with β-alumina-based ceramics, the ionic conductivity is significantly reduced. In this,
The inventors have found that the fibers of zirconia and magnesia have a remarkable effect of lowering the intended ionic conductivity and improving the toughness, and have reached the present invention.

[0008]

The β-alumina ceramics according to the present invention is
The fracture toughness value is improved and the ionic conductivity is not lowered, and excellent performance as a solid electrolyte is exhibited.

[0009]

EXAMPLES Next, the present invention will be specifically described with reference to examples.

(Example 1) In α-alumina powder (average particle size: 0.5 μm), sodium nitrate was calculated to be sodium oxide so that the content was 9.0% by weight, and lithium nitrate was calculated to be lithium oxide. Were weighed so as to be 0.8% by weight and mixed in a ball mill for 24 hours. This powder was put in a platinum crucible and baked at 1250 ° C. for 2 hours to prepare a sodium β ″ -alumina powder. This powder was granulated by a spray dryer and then cold isostatically pressed at a molding pressure of 300 MPa and then 1560. Sintered at 1.0 ° C. for 1.0 hour to obtain a comparative sintered body.

In the composite of the present invention, 2 to 5 zirconia fibers (the diameter and aspect ratio of the fibers are appropriately changed) are added to the sodium β ″ -alumina powder produced by the above method.
0% was added, and an organic binder was further added, and the mixture was mixed for 10 hours with acetone as a solvent in a fryer. Then, after granulating with a spray dryer as in the comparative example, 300MP
a 1560 ° C × 1 after cold isostatic pressing with molding pressure.
Sintered for 0 hours.

FIG. 1 shows a conventional comparative example β ″ -alumina and β ″ -alumina according to the present invention with ZrO ₂ fibers (diameter 5 μm,
The measurement results of the fracture toughness value K ₁ c depending on the addition amount of the composite sintered body to which the aspect ratio 5) is added are shown. The fracture toughness value was measured according to JIS-R-1607 (SEPB method). Addition amount is 2
%, The effect is small because the added amount is small, but the effect is recognized in the range of 5% to 25%. Particularly, the range of 10 to 20% is remarkable, and if it exceeds 25%, uniform mixing becomes difficult and the effect is remarkably reduced.

FIG. 2 is similar to FIG. 1 in that β ″ -alumina has ZrO.
It is the measurement result of the fracture toughness value by the aspect ratio of the composite sintered body to which ₂ fibers (diameter 10 μm, addition amount 10 wt /%) were added. When the aspect ratio is 2.5, the effect is small, and when the aspect ratio is 5 to 10, the effect is exhibited.

FIG. 3 shows ZrO ₂ fibers (aspect ratio 10 and addition amount 10 wt /
%) Is the measurement result of the fracture toughness value by the fiber diameter of the composite sintered body. The effect appears at 0.5 μm,
If it exceeds 15 μm, the effect is lost. From this fact, good results can be obtained in the range of 0.5 to 10 μm for improving the fracture toughness value.

Example 2 Table 1 shows the results of measuring the density, bending strength and specific resistance at 350 ° C. of the samples shown in Example 1 and FIG.

[0016]

[Table 1]

In any case, when the addition amount exceeds 25 wt /%, the density and bending strength are lowered and the specific resistance is increased. Further, when the addition amount is 2 wt /%, the fracture toughness value K ₁ c is not improved as described above, and it is appropriate that the addition amount of the ZrO ₂ fiber is in the range of 5 to 20 wt /%.

(Embodiment 3) β ″ as in Embodiments 1 and 2
-Al ₂ O ₃ part of the MgO fibers and ZrO ₂ fibers Mg
A sample in which O fibers and a part of MgO fibers were replaced with ZrO ₂ fibers was prepared and studied. The results are collectively shown in Table 2.

[0019]

[Table 2]

Similar results were obtained as with the ZrO ₂ fiber. In addition, Table 2 also shows the case of the sample to which Al ₂ O ₃ fiber was added as a comparative material, but β ″ -Al ₂
It is significantly inferior to the composite of the present invention because O ₃ and Al ₂ O ₃ fibers react with each other. This result also shows that ZrO _{2 of the} present invention is used.
It can be seen that the addition of a structure that does not react with β-Al ₂ O ₃ -based ceramics such as fibers and MgO fibers is excellent in improving the reliability of the β-Al ₂ O ₃ -based solid electrolyte.

(Example 4) Powder of β-Al ₂ O ₃ based ion conductive material and ZrO ₂ fiber (addition amount 10%, diameter 5 μm)
m, aspect ratio 5) was slurried by adding a solvent and a binder, and the granulated powder having a diameter of 5 to 200 μm was produced by changing the rotation speed of the spray dryer, the temperature and the like. As a result of molding and sintering the granulated powder and measuring the characteristics, good results were obtained in the range of 20 to 100 μm. From this result, fiber-reinforced β-
The granulated powder for producing an Al ₂ O ₃ based solid electrolyte is 20 to 100.
It is appropriate to set it in the range of μm.

[0022]

According to the present invention, by improving the fracture toughness value of the β-Al ₂ O ₃ system, the reliability and the longevity of the solid electrolyte can be improved.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a change in fracture toughness value depending on the amount of fiber added.

FIG. 2 is a characteristic diagram showing changes in fracture toughness values depending on the aspect ratio of fibers.

FIG. 3 is a characteristic diagram showing changes in fracture toughness values depending on fiber diameters.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuo Nakazawa 7-1 Omika-cho, Hitachi-shi, Ibaraki Hitachi Ltd. Hitachi Research Laboratory

Claims (5)

[Claims] 1. A fiber-reinforced β-Al ₂ O ₃ system characterized in that an ion-conductive substance composed of β-Al ₂ O ₃ system is used as a matrix material, and fibers that do not react with the matrix material are added as a reinforcing material. Solid electrolyte. 2. The fiber according to claim 1, wherein the fibers added to the β-Al ₂ O ₃ based ion conductive material are ZrO ₂ and MgO that do not react with the matrix material.
A fiber-reinforced β-Al ₂ O ₃ -based solid electrolyte capable of replacing part of rO ₂ with MgO and part of MgO with ZrO ₂ . 3. The β-Al ₂ O _{3 according to} claim 1 or 2.
The diameter of the fibers added to the ionic conductive material is 0.5.
A fiber-reinforced β-Al ₂ O ₃ based solid electrolyte having an aspect ratio of 5 to 10 μm and a length of 10 to 10 μm. 4. The β-type according to claim 1, 2, or 3.
The amount of fibers added to the Al ₂ O ₃ based ion conductive material is 5
A fiber-reinforced β-Al ₂ O ₃ -based solid electrolyte of about 20% by weight. 5. The second powder containing β-Al ₂ O ₃ type ion conductive material consisting first powder or β-Al ₂ O ₃ type ion conductive material to be obtained component, does not react with the second powder Starting from fibers, a solvent and, if necessary, a binder are added to the mixture of the second powder and the fibers to form a slurry, which is granulated with a spray dryer to 20 to 100 μm, and the granulated powder is A method for producing a fiber-reinforced β-Al ₂ O ₃ -based solid electrolyte produced by molding and sintering.