CA2143784C - Beta-alumina solid electrolyte and process for production thereof - Google Patents
Beta-alumina solid electrolyte and process for production thereofInfo
- Publication number
- CA2143784C CA2143784C CA002143784A CA2143784A CA2143784C CA 2143784 C CA2143784 C CA 2143784C CA 002143784 A CA002143784 A CA 002143784A CA 2143784 A CA2143784 A CA 2143784A CA 2143784 C CA2143784 C CA 2143784C
- Authority
- CA
- Canada
- Prior art keywords
- beta
- alumina
- solid electrolyte
- less
- sodium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
- H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
- H01M10/3909—Sodium-sulfur cells
- H01M10/3918—Sodium-sulfur cells characterised by the electrolyte
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/01—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics
- C04B35/10—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on oxide ceramics based on aluminium oxide
- C04B35/111—Fine ceramics
- C04B35/113—Fine ceramics based on beta-aluminium oxide
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
A beta-alumina solid electrolyte for use in sodium-sulfur battery is composed of the beta-alumina crystals having a degree of orientation toward C axis, of 0.2-0.4 and an aspect ratio of 4.0 or less. The beta-alumina solid electrolyte is composed of the beta-alumina crystals having a degree of orientation toward C axis, of 0.2-0.4 and has such a particle diameter distribution that the average particle diameter is 3 µm or less, the proportion of the particles having a particle diameter of 5 µm or less is 90% or more, and the maximum particle diameter is 300 µm or less. A
process for producing a beta-alumina solid electrolyte using an alumina source material, a magnesium source material and a sodium source material has using a magnesium-aluminum spinel as the magnesium source material and subjecting all materials to mixing, granulation, molding and firing to obtain a beta-alumina solid electrolyte without subjecting the materials to calcination. The beta-alumina solid electrolyte has a low electrical resistance and a large strength to internal water pressure and exhibits excellent properties when used as a diaphragm for sodium-sulfur battery.
process for producing a beta-alumina solid electrolyte using an alumina source material, a magnesium source material and a sodium source material has using a magnesium-aluminum spinel as the magnesium source material and subjecting all materials to mixing, granulation, molding and firing to obtain a beta-alumina solid electrolyte without subjecting the materials to calcination. The beta-alumina solid electrolyte has a low electrical resistance and a large strength to internal water pressure and exhibits excellent properties when used as a diaphragm for sodium-sulfur battery.
Description
~ 21~3784 BETA-ALUMINA SOLID ELECTROLYTE
AND PROCESS FOR PRODUCTION THEREOF
BACKGROUND OF THE INVENTION
(1) Field of the Invention The present invention relates to a beta-alumina solid electrolyte having excellent properties such as low electrical resistance, large strength and the like, as well as to a process for production thereof. More particularly, the present invention relates to a process for production of beta-alumina solid electrolyte, which can produce-a beta-alumina solid electrolyte of excellent properties without subjecting the materials to calcination (calcination is conducted in conventional processes).
AND PROCESS FOR PRODUCTION THEREOF
BACKGROUND OF THE INVENTION
(1) Field of the Invention The present invention relates to a beta-alumina solid electrolyte having excellent properties such as low electrical resistance, large strength and the like, as well as to a process for production thereof. More particularly, the present invention relates to a process for production of beta-alumina solid electrolyte, which can produce-a beta-alumina solid electrolyte of excellent properties without subjecting the materials to calcination (calcination is conducted in conventional processes).
(2) Prior Art Beta-Alumina solid electrolytes have a very high sodium ion conductivity, i.e. a low electrical resistance.
Hence, attention is being paid to their use as a diaphragm for sodium-sulfur battery, etc.
Of the beta-alumina solid electrolytes, a MgO-stabilized beta-alumina solid electrolyte has conventionally been produced as follows. That is, the materials, i.e. MgO, a sodium compound and ~-Al203 are mixed at an appropriate ratio; the mixture is calcinated to obtain beta-alumina;
21~3784 then, grinding is conducted; the ground material is then granulated, molded into a desired shape and fired to obtain a beta-alumina solid electrolyte.
The reason why in the above conventional process, the materials are calcinated beforehand to obtain beta-alumi-na, is that when it is tried to produce beta-alumina by direct firing without conducting calcination, there occurs severe volume expansion in the phase transition from a-Al203 to beta-alumina, making it difficult to obtain a beta-alumina solid electrolyte of uniform quality and high strength.
In the conventional process, however, since the materials are calcinated beforehand to obtain beta-alumina, the steps become complex and invite a high cost. Hence, it is strongly desired in production of sodium-sulfur battery, etc. to shorten the total production steps and produce a beta-alumina solid electrolyte more efficiently.
Further, since in the above-mentioned conventional process there are conducted prel; m; n~ry calcination (to obtain beta-alumina), gr;n~; ng, granulation, molding and firing, the crystals constituting the resulting beta-alumina solid electrolyte have high orientation and, moreover, con-tain large crystals because the crystal growth takes place while the beta-alumina formed by calcination is acting as a 21~784 nucleus for crystal growth. In addition, many of the large crystals have a shape of large aspect ratio, i.e. a thin and long shape.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to produce a beta-alumina solid electrolyte efficiently without the calci-nation of the materials. Another object of the present invention is to provide a beta-alumina solid electrolyte has a low electrical resistance and a large strength to internal water pressure.
According to the present invention, there is pro-vided a beta-alumina solid electrolyte for use in sodium-sulfur battery, wherein the beta-alumina crystals consti-tuting said electrolyte has a degree of orientation toward C
axis, of 0.2-0.4 and an aspect ratio of 4.0 or less.
According to the present invention, there is also provided a beta-alumina solid electrolyte for use in sodium-sulfur battery, wherein the beta-alumina crystals consti-tuting said electrolyte has a degree of orientation toward C
axis, of 0.2-0.4 and has such a particle diameter distribu-tion that the average particle diameter is 3 lum or less, the proportion of the particles having a particle diameter of 5 ,um or less is 90% or more, and the maximum diameter is 300 ~m ' ~ 214378~
or less.
The beta-alumina solid electrolyte of the present invention preferably has an electrical resistance of 4.0 n . cm or less, a burst strength to internal pressure, of 150 MPa or more and a density of 3.20 g/cm3 or more.
According to the present invention there is further provided a process for producing a beta-alumina solid elec-trolyte using an alumina source material, a magnesium source material and a sodium source material, which comprises using a magnesium-aluminium spinel as the magnesium source material and subjecting all materials to m;x;ng, granulation, molding and firing to obtain a beta-alumina solid electrolyte without sub;ecting the materials to calcination.
In the process of the present invention, it is preferable that the molar ratio of magnesia and alumina in the magnesium-aluminum spinel is 1 or more and further that the sodium source material is sodium compound(s) cont~;n;ng at least either of NaHC03 and sodium oxalate.
In the process of the present invention, it is also preferable for property improvement in electrical resistance, strength, etc. that the firing is conducted according to a heat curve comprising:
(1) a step of keeping the system temperature at a con-214378~
stant temperature in the range of 1,400-1,550~C for 1-5 hours, or a step of increasing the system temperature at a rate of 50~C/hr or less in said temperature range, (2) a step of keeping the system temperature at the m~X;mum temperature of 1,580-1,650~C for 0.1-3.0 hours, and (3) a step of keeping the system temperature at a con-stant temperature in the range of 1,400-1,550~C for 1-5 hours, or a step of decreasing the system temperature at a rate of 50~C/hr or less in said temperature range.
In the present invention, the beta-alumina is a generic name for ~-Al203 (Na20.11Al203), ~"-Al203 (Na20.5Al203), ~'"-Al203, etc. and refers particularly to a beta-alumina con-taining ~"-Al203 in an amount of 95% or more.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view of a single crystal of the beta-alumina solid electrolyte of the present invention.
Fig. 2 is a perspective view showing a test piece obtained by cutting the beta-alumina sintered material of the present invèntion in the lengthwise direction.
Fig. 3 is a view showing an example of the consti-tution of the Na/Na conductivity tester for measurement of electrical resistance, used in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
~ 21~3784 The present invention is hereinafter described in detail.
The present invention has a big feature in that in the production of a beta-alumina solid electrolyte, magnesi-um-aluminum spinel is used as a magnesium source material which is a stabilizer for beta-alumina, in place of MgO, etc.
used in the conventional process. All materials including magnesium-aluminum spinel are mixed; the mixture is granulat-ed without being calcinated, followed by molding and firing;
thereby, a beta-alumina having excellent properties when used as a solid electrolyte can be obtained.
The present inventor made a study from various angles in order to shorten the conventional steps for beta-alumina production. As a result, the present inventor found out that when magnesium-aluminum spinel is used in place of conventional MgO, as a magnesium source material, the spinel is presumed to act as a seed crystal for beta-alumina crystal formation in the firing step of beta-alumina production and the calcination of materials for beta-alumina formation becomes unnecessary.
The magnesium-aluminum spinel used as a magnesium source material has a magnesia (MgO)/alumina (Al203) molar ratio of preferably 1 or more (MgO-rich), more preferably ~ 2143784 1.0-1.5. The reason is not clear but, when the molar ratio is outside the above range, the resulting beta-alumina has slightly inferior properties in electrical resistance, strength, etc.
Further, the magnesium-aluminum spinel is preferab-ly fine and specifically has an average particle diameter of preferably 1 ,um or less, more preferably 0.5 ,um or less.
Furthermore, the magnesium-aluminum spinel preferably has a 90% particle diameter of 10 ,um or less, preferably 5 ~um or less. Moreover, the magnesium-aluminum spinel preferably has a specific surface area of 5 m2/g or more. When the magnesi-um-aluminum spinel has the particle diameter and specific surface area in the above ranges, the resulting beta-alumina sintered material has small crystal orientation and a small crystal aspect ratio and thus has good properties.
As the sodium compound as sodium source material, there can be used conventionally known compounds such as Na2CO3 and the like. However, use of sodium hydrogencarbonate (NaHCO3) or sodium oxalate is preferable because there occurs no segregation of sodium compound in granulation product and there can be achieved uniform dispersion. That is, NaHCO3or sodium oxalate, having lower solubility in the solvent used (e.g. water) than Na2CO3, precipitates rapidly during drying 214378~
for granulation and can be dispersed uniformly in the granu-lation production. Use of NaHCO3 or sodium oxalate is also preferable because, when materials including NaHCO3 or sodium oxalate are mixed in a slurry state, the slurry can be con-trolled at a pH of about 10, making easy the selection of organic binder.
NaHCO3 or sodium oxalate may be used singly, or may be used as a mixture with Na2CO3.
The NaHCO3 or sodium oxalate used has an average particle diameter of preferably 5 ~m or less.
The alumina source material is preferably a-Al203.
It is preferably fine and has an average particle diameter of 1 ~m or less, particularly preferably 0.5 ~um or less. The a-Al203 also has a specific surface area of preferably 5 m2/g or more, more preferably 10 m2/g or more. When the a-Al203 has a particle diameter in the above range, the resulting beta-alumina sintered material scarcely contains large crystals and tends to be dense and have a low resistance.
The alumina source material, the magnesium source material and the sodium source material all having desired properties in particle diameter, etc. as mentioned above, are mixed in given proportions allowing for beta-alumina forma-tion. The mixing is conducted by grinding the materials in ~ 214~784 water, whereby a slurry is prepared. Mixing as uniform as possible is preferable because it can improve sinterability in the firing step.
The slurry is granulated using a spray dryer or the like. This granulation step is conducted to make the mixing of materials uniform and improve moldability in the subse-quent molding step. In the granulation step, a granulation product is produced so as to generally have an average parti-cle diameter of 50-100 ,um.
The granulation product is then molded into a de-sired shape.
The molding is made into a tubular shape in many cases because the beta-alumina solid electrolyte of the present invention is suitably used mainly as a diaphragm for sodium-sulfur battery.
The molding is conducted at a pressure of 1.5 ton/cm2 or more, preferably 2.0 ton/cm2 or more, whereby a molded material having a density of 1.9 g/cm3 or more is produced.
Then, the molded material is fired under given conditions, whereby growth of uniform crystals is accelerated and beta-alumina crystals are formed. In this case, it is preferable to set the firing conditions and firing heat curve 214378~
as described below. In the present invention, since magne-sium-aluminum spinel is used as a seed crystal for beta-alumina formation, the volume expansion associated with the phase transition form a-Al203 to beta-alumina poses no big problem. However, it is preferable to appropriately control the heat curve for firing in order to obtain a beta-alumina solid electrolyte of uniform quality, large strength and low electrical resistance.
Hence, it is important to set the maximum firing temperature at 1,580-1,650~C in order to obtain a beta-alumina cont~n;ng a high proportion of ~"-Al203 having good proper-ties. Specifically, the heat curve preferably comprises at least three steps, i.e.
(1) a step of keeping the system temperature at a con-stant temperature in the range of l,400-1,550~C (in this temperature range, ~-Al203 changes to ~"-Al203) for 1-5 hours, or a step of increasing the system temperature at a rate of 50~C/hr or less in said temperature range, (2) a step of keeping the system temperature at the m~X;mum temperature of 1,580-1,650~C for 0.1-3.0 hours, and (3) a step of keeping the system temperature at a con-stant temperature in the range of 1,400-1,550~C for 1-5 hours, or a step of decreasing the system temperature at a rate of 214378~
50~C/hr or less in said temperature range.
The above heat curve is effective because it can increase the ~"-Al203 content in beta-alumina to 95% or more.
The beta-alumina solid electrolyte obtained by the process of the present invention has unique inherent char-acteristics in that the beta-alumina crystals constituting said solid electrolyte have small orientation and a small aspect ratio.
Specifically, the beta-alumina crystals constitut-ing said solid electrolyte have a degree of crystal orient-ation toward C axis, of 0.2-0.4, preferably 0.25-0.35 and an aspect ratio of 4.0 or less, preferably 3.0 or less.
Beta-Alumina crystals have a crystal form of hexa-gonal system and, in each single crystal as seen in Fig. 1 showing a schematic view of beta-alumina solid electrolyte single crystal, have a Na-ion-conductive plane in the plane formed by the A axis and the B axis, i.e. the A-B plane and shows no conductivity toward a direction perpendicular to the A-B plane, i.e. the C axis direction. Further, the crystals, having a cleaving property along the A-B plane, have low mechanical strengths against pulling in the C axis direction.
Hence, the beta-alumina crystals preferably have low orienta-tion. In the conventional process for production of beta-12alumina crystals (said process includes a step of calcination of materials), however, it has been difficult to produce beta-alumina crystals of low orientation.
Incidentally, the degree of crystal orientation toward C axis, of beta-alumina solid electrolyte which is a poly~Lys~al, was measured as follows.
The beta~alumina sintered material obtained by the given production process was cut to obtain a test piece of 1 mm in width and 40 mm in length, shown in Fig. 2. The test piece was polished at the outer surface to remove the uneven-nesses of said surface. The outer surface of the polished test piece was subjected to analysis by X-ray analyzer to obtain the diffraction pattern of said surface, and there were calculated the relative amounts of various crystal faces each directing toward the diameter direction of beta-alumina tube.
In the specific measurement, an X-ray analyzer of goniometer type was used. Using characteristic X-rays, a tube voltage of 35 KV and a tube current of 20 mA, a diffrac-tion pattern was recorded on a chart. For various crystal faces each having a given angle (0~, 33.3~, 60~ or 90~) to the C axis of beta-alumina crystals, there were measured respec-tive peak heights, and the proportion of each crystal face 214378~
was expressed as a relative value. The relative values of beta-alumina crystal faces are shown in Table 1.
214378~
T ~L 1=~ 1 e Peak Orientation degree of crystal face Angle between C axis and Crystal Diffraction angle height (relative value) crystal face~ ~ ) face 2 ~ ( ~ ) measured (mm) 0. 0 006 15. 0~16. 0 Hl Hl / (Hl +H2 +H3 +H4) 33. 3 101 32. 0~32. 5 H2 H2 / (Hl +H2 +H3 +H4) 60. 0 104 20. 0~21. 0 H3 H3 / (Hl +Hz +H3 +H4) 90. 0 110 31. 5~3Z. 0 H4 H4 / (Hl +H2 +H3 +H4) 214378~
In the present invention, "degree of crystal orien-tation toward C axis" refers to the relative value of the peak height (H1 of Table 1) (when the angle between C axis and crystal face is 0~, that is, the crystal face agrees with the C axis, to total peak height (H1+H2+H3+H4), i.e.
Hl/(H1+H2+H3+H4). When the degree of crystal orientation toward C axis is high, the non-conductive face of beta-alumina crystals is directed to the Na-ion-conductive direc-tion of beta-alumina tube and, as a result, the beta-alumina tube has a high resistance.
In the present invention, the aspect ratio of beta-alumina crystals is measured as follows.
The beta-alumina sintered material is cut to obtain a small test piece. The test piece is polished and etched at the section. The resulting section is observed using a sc~nn; n~ type electron microscope and photographed at a magnification allowing for the observation of individual particles. Using the photograph, the major axis and minor axis of each individual partisle were measured and the aver-age of their ratios was taken as the aspect ratio of the sintered material.
When the degree of crystal orientation toward C
axis, of beta-alumina crystals is smaller than 0.2, the crystals have a small electrical resistance but small mechan-ical strengths (e.g. small burst strength to internal pres-sure) and is unsuitable for use as a diaphragm for sodium-sulfur battery. When said degree of crystal orientation is larger than 0.4, the crystals have large mechanical strengths but too large an electrical resistance.
When the aspect ratio of beta-alumina crystals deviates from the above range, the beta-alumina crystals are too thin and long, making it impossible to obtain a beta-alumina solid electrolyte having excellent properties (e.g.
low electrical resistance, high strength, etc.) in good balance.
Further in the present invention, the beta-alumina crystals constituting the beta-alumina solid electrolyte have such a particle diameter distribution that the average parti-cle diameter is 3 ~m or less, the proportion of the parti-cles having a particle diameter of 5 ~m or less is 90% or more, and the maximum particle diameter is 300 ~m or less, preferably 200 um or less. In the beta-alumina crystals, the size of large crystals present therein is small and their amount is also small.
As described above, the beta-alumina solid elect-rolyte of the present invention has a particular crystal 21~3784 structure and shows excellent properties when used as a diaphragm for sodium-sulfur battery.
Specifically, the present beta-alumina solid elec-trolyte has an electrical resistance of 4.0 n . cm or less, preferably 3.5 n . cm or less, a burst strength to internal pressure, of 150 MPa or more, preferably 180 MPa or more, and a density of 3.20 g/cm3 or more, preferably 3.22 g/cm3 or more.
The present invention is hereinafter described in more detail by way of Examples. However, the present inven-tion is not restricted to these Examples.
Example 1 and Comparative Example 1 There were weighed three raw materials, i.e. an a-Al203 powder having an average particle diameter of 1.5 ,um and a specific surface area of 3.5 m2/g as measured by BET
adsorption method, Na2C03 having an average particle diameter of 1 ,um and a magnesium-aluminum spinel having an average particle diameter, a 90% particle diameter and a MgO/Al203 molar ratio all shown in Table 2, in proportions allowing for beta-alumina formation, i.e. proportions of 71% (Al203), 14%
(spinel) and 15% (Na2C03). The raw materials were uniformly mixed in water using a ball mill to prepare a slurry.
The slurry was granulated into grains having an 214378~
average particle diameter of 60 ,um, using a spray dryer. The grains were molded into a tubular molded material having a 25 mm in diameter, 230 mm in length and 1.3 mm in thickness, at a pressure of 2 ton/cmZ using an isostatic press.
The molded material was placed in a MgO-made sagger and fired at the maximum temperature of 1,600~C for 30 minutes to obtain a beta-alumina sintered material. The crystal structure and properties of the beta-alumina sintered materi-al are shown in Table 2.
For comparison, beta-alumina sintered materials (sample Nos. 1-3 of Comparative Example 1) were obtained under the same conditions as in Example 1 except that there were added a step of calcinating the mixture of raw materials at 1,250~C for 120 minutes and a step of grinding the calcin-ation product. Further, beta-alumina sintered materials (sample Nos. 4-6 of Comparative Example 1) were obtained under the same conditions as in Example 1 except that no magnesium-aluminum spinel was used. The crystal structures and properties of these beta-alumina sintered materials (sample Nos. 1-6 of Comparative Example 1) are shown in Table 2.
In Table 2, electrical resistance and strength to internal water pressure were measured as follows.
21~3784 Test method for electrical resistance Electrical resistance was obtained as a value at 350~C using a Na/Na conductivity tester shown in Fig. 3. In Fig. 3, the Na/Na conductivity tester was constituted by a tubular beta-alumina sintered material (a beta-alumina tube) 1, insulating supports 2 and 3, a stainless steel electrode 4 and electrode terminals 5 and 6. By feeding a molten sodium 8 of 350~C into a container 7 and the beta-alumina tube 1 and passing a given electricity between the terminals 5 and 6, the electrical resistance of the beta-alumina tube to be mea-sured was determined as a specific resistance.
Test method for burst strength to internal pressure A water pressure was applied to the inner wall of a tubular beta-alumina sintered material (a beta-alumina tube) via rubber tube. From the water pressure when the beta-alumina tube broke and the ~;m~n~ion of said tube, the burst pressure to internal pressure, of said tube was determined.
21~378~
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Example 2 In order to confirm the effect of addition of sodium compound, beta-alumina sintered materials were ob-tained under the same steps and conditions as in Example 1 except that there were used various sodium compounds as shown in Table 3. The crystal structures and properties of the beta-alumina sintered materials obtained are shown in Table 3.
21~378~
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~r, o o o o 0 CD ~r N
\\ \ ~ o O O O O ,C~ ~ CD ~ 10 N C') N N
O O O O
.,, .,~,,, ,,, ~
_~ 4 4 4 4 ,"
h h h h 'a w ~ el a) N ~ ~() ~ o ,_, h h h h ' ~ t ~I N N N N N N
O O O O
o ~ ~ ~ O O N ~( ~) ~' o c c~ 4 ~q ~ N N N N N N N
~1\ 0 0 0 0 ~ C' C ~?~ O N
Z ~ Z O bO O ~
\ \ \ \ ~ .~ O O O O O O O
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v ~ ~ c) v ~-L N X X ~ X ~
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o _ .~ _d' ~( ~ O ~1 N ~( ~ ~ a .......
U~ _ ~
N N N N N N N
~, b4 ......
c, 0~ ~ ~ cr c. o c~ o r- CO a ~
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x Example 3 In order to confirm the effect of alumina material, beta-alumina sintered materials were obtained under the same steps and conditions as in Example 1 except that the average particle diameter and BET specific surface area of a-Al203 material were varied as shown in Table 4. The crystal struc-tures and properties of the beta-alumina sintered materials obtained are shown in Table 4.
~ 214378~
o o o o o o o .' ~ ~ a) c- o o ~~
q~ _ o _3 ~D
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~ * ~~ OOOO O . ~
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~ O') ~ ~ â a~ N ~ ~ ~ 8 ~_ ~ N N N N N C~
t3 '*' 10 15~ 15') 00 CO O O ~ C~) 10 d' 1~- a) o CD ' U~
C 10 ~ ~ O O O ~ C~ ~ N ~ ~ ~ ~ N N bO
~ C N
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a) _ , .
.t3 ~ N N C~l N ~ E~
V~ ~ ~ _ ~ ~ ~ ~ ~ ~ O
J ~ N C~l N C~ C~ N N :' a~ (13 S_.
~ 2: ~ ~ O ~ C~ ~~ ~ ~ ~ ~ ~ ~
c~ ~ C~ N C~ cQ ~ C~ N ~0 . .
X G
Table 4 In order to confirm the effect of firing condi-tions, beta-alumina sintered materials were obtained under the same steps and conditions as in Example 1 except that the heat curve for firing was varied as shown in Table 5. The crystal structures and properties of the beta-alumina sint-ered materials obtained are shown in Table 5.
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r ~
214378~
As is clear from the above, the beta-alumina sint-ered materials produced in the scope of the present invention have good properties in electrical resistance, strength to internal water pressure, etc., and the beta-alumina sintered materials produced under more preferable conditions have better properties in electrical resistance, strength to internal water pressure, etc.
As described above, in the present invention, since the magnesium source material is fed in the form of magnesi-um-aluminum spinel, a beta-alumina solid electrolyte can efficiently be produced without subjecting raw materials to calcination.
Further, the beta-alumina solid electrolyte ob-tained by the present process, having a uni~ue crystal struc-ture in that the beta-alumina crystals constituting said solid electrolyte have small orientation and a small aspect ratio, has a low electrical resistance and a large strength to internal water pressure and is excellent as a diaphragm for sodium-sulfur battery.
Hence, attention is being paid to their use as a diaphragm for sodium-sulfur battery, etc.
Of the beta-alumina solid electrolytes, a MgO-stabilized beta-alumina solid electrolyte has conventionally been produced as follows. That is, the materials, i.e. MgO, a sodium compound and ~-Al203 are mixed at an appropriate ratio; the mixture is calcinated to obtain beta-alumina;
21~3784 then, grinding is conducted; the ground material is then granulated, molded into a desired shape and fired to obtain a beta-alumina solid electrolyte.
The reason why in the above conventional process, the materials are calcinated beforehand to obtain beta-alumi-na, is that when it is tried to produce beta-alumina by direct firing without conducting calcination, there occurs severe volume expansion in the phase transition from a-Al203 to beta-alumina, making it difficult to obtain a beta-alumina solid electrolyte of uniform quality and high strength.
In the conventional process, however, since the materials are calcinated beforehand to obtain beta-alumina, the steps become complex and invite a high cost. Hence, it is strongly desired in production of sodium-sulfur battery, etc. to shorten the total production steps and produce a beta-alumina solid electrolyte more efficiently.
Further, since in the above-mentioned conventional process there are conducted prel; m; n~ry calcination (to obtain beta-alumina), gr;n~; ng, granulation, molding and firing, the crystals constituting the resulting beta-alumina solid electrolyte have high orientation and, moreover, con-tain large crystals because the crystal growth takes place while the beta-alumina formed by calcination is acting as a 21~784 nucleus for crystal growth. In addition, many of the large crystals have a shape of large aspect ratio, i.e. a thin and long shape.
OBJECT AND SUMMARY OF THE INVENTION
An object of the present invention is to produce a beta-alumina solid electrolyte efficiently without the calci-nation of the materials. Another object of the present invention is to provide a beta-alumina solid electrolyte has a low electrical resistance and a large strength to internal water pressure.
According to the present invention, there is pro-vided a beta-alumina solid electrolyte for use in sodium-sulfur battery, wherein the beta-alumina crystals consti-tuting said electrolyte has a degree of orientation toward C
axis, of 0.2-0.4 and an aspect ratio of 4.0 or less.
According to the present invention, there is also provided a beta-alumina solid electrolyte for use in sodium-sulfur battery, wherein the beta-alumina crystals consti-tuting said electrolyte has a degree of orientation toward C
axis, of 0.2-0.4 and has such a particle diameter distribu-tion that the average particle diameter is 3 lum or less, the proportion of the particles having a particle diameter of 5 ,um or less is 90% or more, and the maximum diameter is 300 ~m ' ~ 214378~
or less.
The beta-alumina solid electrolyte of the present invention preferably has an electrical resistance of 4.0 n . cm or less, a burst strength to internal pressure, of 150 MPa or more and a density of 3.20 g/cm3 or more.
According to the present invention there is further provided a process for producing a beta-alumina solid elec-trolyte using an alumina source material, a magnesium source material and a sodium source material, which comprises using a magnesium-aluminium spinel as the magnesium source material and subjecting all materials to m;x;ng, granulation, molding and firing to obtain a beta-alumina solid electrolyte without sub;ecting the materials to calcination.
In the process of the present invention, it is preferable that the molar ratio of magnesia and alumina in the magnesium-aluminum spinel is 1 or more and further that the sodium source material is sodium compound(s) cont~;n;ng at least either of NaHC03 and sodium oxalate.
In the process of the present invention, it is also preferable for property improvement in electrical resistance, strength, etc. that the firing is conducted according to a heat curve comprising:
(1) a step of keeping the system temperature at a con-214378~
stant temperature in the range of 1,400-1,550~C for 1-5 hours, or a step of increasing the system temperature at a rate of 50~C/hr or less in said temperature range, (2) a step of keeping the system temperature at the m~X;mum temperature of 1,580-1,650~C for 0.1-3.0 hours, and (3) a step of keeping the system temperature at a con-stant temperature in the range of 1,400-1,550~C for 1-5 hours, or a step of decreasing the system temperature at a rate of 50~C/hr or less in said temperature range.
In the present invention, the beta-alumina is a generic name for ~-Al203 (Na20.11Al203), ~"-Al203 (Na20.5Al203), ~'"-Al203, etc. and refers particularly to a beta-alumina con-taining ~"-Al203 in an amount of 95% or more.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view of a single crystal of the beta-alumina solid electrolyte of the present invention.
Fig. 2 is a perspective view showing a test piece obtained by cutting the beta-alumina sintered material of the present invèntion in the lengthwise direction.
Fig. 3 is a view showing an example of the consti-tution of the Na/Na conductivity tester for measurement of electrical resistance, used in the present invention.
DETAILED DESCRIPTION OF THE INVENTION
~ 21~3784 The present invention is hereinafter described in detail.
The present invention has a big feature in that in the production of a beta-alumina solid electrolyte, magnesi-um-aluminum spinel is used as a magnesium source material which is a stabilizer for beta-alumina, in place of MgO, etc.
used in the conventional process. All materials including magnesium-aluminum spinel are mixed; the mixture is granulat-ed without being calcinated, followed by molding and firing;
thereby, a beta-alumina having excellent properties when used as a solid electrolyte can be obtained.
The present inventor made a study from various angles in order to shorten the conventional steps for beta-alumina production. As a result, the present inventor found out that when magnesium-aluminum spinel is used in place of conventional MgO, as a magnesium source material, the spinel is presumed to act as a seed crystal for beta-alumina crystal formation in the firing step of beta-alumina production and the calcination of materials for beta-alumina formation becomes unnecessary.
The magnesium-aluminum spinel used as a magnesium source material has a magnesia (MgO)/alumina (Al203) molar ratio of preferably 1 or more (MgO-rich), more preferably ~ 2143784 1.0-1.5. The reason is not clear but, when the molar ratio is outside the above range, the resulting beta-alumina has slightly inferior properties in electrical resistance, strength, etc.
Further, the magnesium-aluminum spinel is preferab-ly fine and specifically has an average particle diameter of preferably 1 ,um or less, more preferably 0.5 ,um or less.
Furthermore, the magnesium-aluminum spinel preferably has a 90% particle diameter of 10 ,um or less, preferably 5 ~um or less. Moreover, the magnesium-aluminum spinel preferably has a specific surface area of 5 m2/g or more. When the magnesi-um-aluminum spinel has the particle diameter and specific surface area in the above ranges, the resulting beta-alumina sintered material has small crystal orientation and a small crystal aspect ratio and thus has good properties.
As the sodium compound as sodium source material, there can be used conventionally known compounds such as Na2CO3 and the like. However, use of sodium hydrogencarbonate (NaHCO3) or sodium oxalate is preferable because there occurs no segregation of sodium compound in granulation product and there can be achieved uniform dispersion. That is, NaHCO3or sodium oxalate, having lower solubility in the solvent used (e.g. water) than Na2CO3, precipitates rapidly during drying 214378~
for granulation and can be dispersed uniformly in the granu-lation production. Use of NaHCO3 or sodium oxalate is also preferable because, when materials including NaHCO3 or sodium oxalate are mixed in a slurry state, the slurry can be con-trolled at a pH of about 10, making easy the selection of organic binder.
NaHCO3 or sodium oxalate may be used singly, or may be used as a mixture with Na2CO3.
The NaHCO3 or sodium oxalate used has an average particle diameter of preferably 5 ~m or less.
The alumina source material is preferably a-Al203.
It is preferably fine and has an average particle diameter of 1 ~m or less, particularly preferably 0.5 ~um or less. The a-Al203 also has a specific surface area of preferably 5 m2/g or more, more preferably 10 m2/g or more. When the a-Al203 has a particle diameter in the above range, the resulting beta-alumina sintered material scarcely contains large crystals and tends to be dense and have a low resistance.
The alumina source material, the magnesium source material and the sodium source material all having desired properties in particle diameter, etc. as mentioned above, are mixed in given proportions allowing for beta-alumina forma-tion. The mixing is conducted by grinding the materials in ~ 214~784 water, whereby a slurry is prepared. Mixing as uniform as possible is preferable because it can improve sinterability in the firing step.
The slurry is granulated using a spray dryer or the like. This granulation step is conducted to make the mixing of materials uniform and improve moldability in the subse-quent molding step. In the granulation step, a granulation product is produced so as to generally have an average parti-cle diameter of 50-100 ,um.
The granulation product is then molded into a de-sired shape.
The molding is made into a tubular shape in many cases because the beta-alumina solid electrolyte of the present invention is suitably used mainly as a diaphragm for sodium-sulfur battery.
The molding is conducted at a pressure of 1.5 ton/cm2 or more, preferably 2.0 ton/cm2 or more, whereby a molded material having a density of 1.9 g/cm3 or more is produced.
Then, the molded material is fired under given conditions, whereby growth of uniform crystals is accelerated and beta-alumina crystals are formed. In this case, it is preferable to set the firing conditions and firing heat curve 214378~
as described below. In the present invention, since magne-sium-aluminum spinel is used as a seed crystal for beta-alumina formation, the volume expansion associated with the phase transition form a-Al203 to beta-alumina poses no big problem. However, it is preferable to appropriately control the heat curve for firing in order to obtain a beta-alumina solid electrolyte of uniform quality, large strength and low electrical resistance.
Hence, it is important to set the maximum firing temperature at 1,580-1,650~C in order to obtain a beta-alumina cont~n;ng a high proportion of ~"-Al203 having good proper-ties. Specifically, the heat curve preferably comprises at least three steps, i.e.
(1) a step of keeping the system temperature at a con-stant temperature in the range of l,400-1,550~C (in this temperature range, ~-Al203 changes to ~"-Al203) for 1-5 hours, or a step of increasing the system temperature at a rate of 50~C/hr or less in said temperature range, (2) a step of keeping the system temperature at the m~X;mum temperature of 1,580-1,650~C for 0.1-3.0 hours, and (3) a step of keeping the system temperature at a con-stant temperature in the range of 1,400-1,550~C for 1-5 hours, or a step of decreasing the system temperature at a rate of 214378~
50~C/hr or less in said temperature range.
The above heat curve is effective because it can increase the ~"-Al203 content in beta-alumina to 95% or more.
The beta-alumina solid electrolyte obtained by the process of the present invention has unique inherent char-acteristics in that the beta-alumina crystals constituting said solid electrolyte have small orientation and a small aspect ratio.
Specifically, the beta-alumina crystals constitut-ing said solid electrolyte have a degree of crystal orient-ation toward C axis, of 0.2-0.4, preferably 0.25-0.35 and an aspect ratio of 4.0 or less, preferably 3.0 or less.
Beta-Alumina crystals have a crystal form of hexa-gonal system and, in each single crystal as seen in Fig. 1 showing a schematic view of beta-alumina solid electrolyte single crystal, have a Na-ion-conductive plane in the plane formed by the A axis and the B axis, i.e. the A-B plane and shows no conductivity toward a direction perpendicular to the A-B plane, i.e. the C axis direction. Further, the crystals, having a cleaving property along the A-B plane, have low mechanical strengths against pulling in the C axis direction.
Hence, the beta-alumina crystals preferably have low orienta-tion. In the conventional process for production of beta-12alumina crystals (said process includes a step of calcination of materials), however, it has been difficult to produce beta-alumina crystals of low orientation.
Incidentally, the degree of crystal orientation toward C axis, of beta-alumina solid electrolyte which is a poly~Lys~al, was measured as follows.
The beta~alumina sintered material obtained by the given production process was cut to obtain a test piece of 1 mm in width and 40 mm in length, shown in Fig. 2. The test piece was polished at the outer surface to remove the uneven-nesses of said surface. The outer surface of the polished test piece was subjected to analysis by X-ray analyzer to obtain the diffraction pattern of said surface, and there were calculated the relative amounts of various crystal faces each directing toward the diameter direction of beta-alumina tube.
In the specific measurement, an X-ray analyzer of goniometer type was used. Using characteristic X-rays, a tube voltage of 35 KV and a tube current of 20 mA, a diffrac-tion pattern was recorded on a chart. For various crystal faces each having a given angle (0~, 33.3~, 60~ or 90~) to the C axis of beta-alumina crystals, there were measured respec-tive peak heights, and the proportion of each crystal face 214378~
was expressed as a relative value. The relative values of beta-alumina crystal faces are shown in Table 1.
214378~
T ~L 1=~ 1 e Peak Orientation degree of crystal face Angle between C axis and Crystal Diffraction angle height (relative value) crystal face~ ~ ) face 2 ~ ( ~ ) measured (mm) 0. 0 006 15. 0~16. 0 Hl Hl / (Hl +H2 +H3 +H4) 33. 3 101 32. 0~32. 5 H2 H2 / (Hl +H2 +H3 +H4) 60. 0 104 20. 0~21. 0 H3 H3 / (Hl +Hz +H3 +H4) 90. 0 110 31. 5~3Z. 0 H4 H4 / (Hl +H2 +H3 +H4) 214378~
In the present invention, "degree of crystal orien-tation toward C axis" refers to the relative value of the peak height (H1 of Table 1) (when the angle between C axis and crystal face is 0~, that is, the crystal face agrees with the C axis, to total peak height (H1+H2+H3+H4), i.e.
Hl/(H1+H2+H3+H4). When the degree of crystal orientation toward C axis is high, the non-conductive face of beta-alumina crystals is directed to the Na-ion-conductive direc-tion of beta-alumina tube and, as a result, the beta-alumina tube has a high resistance.
In the present invention, the aspect ratio of beta-alumina crystals is measured as follows.
The beta-alumina sintered material is cut to obtain a small test piece. The test piece is polished and etched at the section. The resulting section is observed using a sc~nn; n~ type electron microscope and photographed at a magnification allowing for the observation of individual particles. Using the photograph, the major axis and minor axis of each individual partisle were measured and the aver-age of their ratios was taken as the aspect ratio of the sintered material.
When the degree of crystal orientation toward C
axis, of beta-alumina crystals is smaller than 0.2, the crystals have a small electrical resistance but small mechan-ical strengths (e.g. small burst strength to internal pres-sure) and is unsuitable for use as a diaphragm for sodium-sulfur battery. When said degree of crystal orientation is larger than 0.4, the crystals have large mechanical strengths but too large an electrical resistance.
When the aspect ratio of beta-alumina crystals deviates from the above range, the beta-alumina crystals are too thin and long, making it impossible to obtain a beta-alumina solid electrolyte having excellent properties (e.g.
low electrical resistance, high strength, etc.) in good balance.
Further in the present invention, the beta-alumina crystals constituting the beta-alumina solid electrolyte have such a particle diameter distribution that the average parti-cle diameter is 3 ~m or less, the proportion of the parti-cles having a particle diameter of 5 ~m or less is 90% or more, and the maximum particle diameter is 300 ~m or less, preferably 200 um or less. In the beta-alumina crystals, the size of large crystals present therein is small and their amount is also small.
As described above, the beta-alumina solid elect-rolyte of the present invention has a particular crystal 21~3784 structure and shows excellent properties when used as a diaphragm for sodium-sulfur battery.
Specifically, the present beta-alumina solid elec-trolyte has an electrical resistance of 4.0 n . cm or less, preferably 3.5 n . cm or less, a burst strength to internal pressure, of 150 MPa or more, preferably 180 MPa or more, and a density of 3.20 g/cm3 or more, preferably 3.22 g/cm3 or more.
The present invention is hereinafter described in more detail by way of Examples. However, the present inven-tion is not restricted to these Examples.
Example 1 and Comparative Example 1 There were weighed three raw materials, i.e. an a-Al203 powder having an average particle diameter of 1.5 ,um and a specific surface area of 3.5 m2/g as measured by BET
adsorption method, Na2C03 having an average particle diameter of 1 ,um and a magnesium-aluminum spinel having an average particle diameter, a 90% particle diameter and a MgO/Al203 molar ratio all shown in Table 2, in proportions allowing for beta-alumina formation, i.e. proportions of 71% (Al203), 14%
(spinel) and 15% (Na2C03). The raw materials were uniformly mixed in water using a ball mill to prepare a slurry.
The slurry was granulated into grains having an 214378~
average particle diameter of 60 ,um, using a spray dryer. The grains were molded into a tubular molded material having a 25 mm in diameter, 230 mm in length and 1.3 mm in thickness, at a pressure of 2 ton/cmZ using an isostatic press.
The molded material was placed in a MgO-made sagger and fired at the maximum temperature of 1,600~C for 30 minutes to obtain a beta-alumina sintered material. The crystal structure and properties of the beta-alumina sintered materi-al are shown in Table 2.
For comparison, beta-alumina sintered materials (sample Nos. 1-3 of Comparative Example 1) were obtained under the same conditions as in Example 1 except that there were added a step of calcinating the mixture of raw materials at 1,250~C for 120 minutes and a step of grinding the calcin-ation product. Further, beta-alumina sintered materials (sample Nos. 4-6 of Comparative Example 1) were obtained under the same conditions as in Example 1 except that no magnesium-aluminum spinel was used. The crystal structures and properties of these beta-alumina sintered materials (sample Nos. 1-6 of Comparative Example 1) are shown in Table 2.
In Table 2, electrical resistance and strength to internal water pressure were measured as follows.
21~3784 Test method for electrical resistance Electrical resistance was obtained as a value at 350~C using a Na/Na conductivity tester shown in Fig. 3. In Fig. 3, the Na/Na conductivity tester was constituted by a tubular beta-alumina sintered material (a beta-alumina tube) 1, insulating supports 2 and 3, a stainless steel electrode 4 and electrode terminals 5 and 6. By feeding a molten sodium 8 of 350~C into a container 7 and the beta-alumina tube 1 and passing a given electricity between the terminals 5 and 6, the electrical resistance of the beta-alumina tube to be mea-sured was determined as a specific resistance.
Test method for burst strength to internal pressure A water pressure was applied to the inner wall of a tubular beta-alumina sintered material (a beta-alumina tube) via rubber tube. From the water pressure when the beta-alumina tube broke and the ~;m~n~ion of said tube, the burst pressure to internal pressure, of said tube was determined.
21~378~
,*, ,~ ~. X
. . ~, , , , C~ N )~ O C~ CO Cl~ n J~ ~ ~ ~ o 3~
O ~~ ~ ~ 7 s ~
~ al ~ ; L-- X c~ 0~ D
o O Cll . ~~ ~ ~ ~ Y ~ O ~
U ~ ....... ...... _, ~ ~ ~ o o o .~ ~ ~ ~ ~ O 00 ~, ~D U ~ r ~ ~ ~ *
~ 2. ' ~~n cn 1--1-- o o o ~ ~~
o ~ ~ ~ :~
o o o o Co ~ U~ ~ ~ ~ ~ ~ O
* oooooo D ~ ~ ~
O O O O O O O o o o o o ol u ...... ....... ...... ~g <1 0 1-- 0 ~-- N t~ N N N N N N N N N N N N N ~U
~) O Cll tSI ~ C~ O O N ~ ~ 01 Ul O ~ C~ ) N O --...... ....... .,.,..... ~ .
N ~ ,, ,_, ,., ,~ ~ ~ w O ~ CO O ~ c ,~ ~ N
oooooo ooooooo oooooo ~
_.
CD O O O O O O O O O O O O O O O O
0~ ~ ~ Cl~ W C~ W W ~) ~) N C~
c~ .
C~ N ~ ~ I-- ~ N ~ N t~ N
N ~ ~ N N t~ ~ ~ ~ . a W N t~ OD Ul N ~ I~ CD ~ tn 0 ~ ~
tn N ~ N ~ ~ 0 ~ ~ CO ~ 0 cn ~ a) Ul o tn 00 (~ 0~ N cn o Cl) tO O W ~ Ul ~ N ~ ~ ~. ,,' OOO OC~OoooO OOOOOo ~
21~78~
Example 2 In order to confirm the effect of addition of sodium compound, beta-alumina sintered materials were ob-tained under the same steps and conditions as in Example 1 except that there were used various sodium compounds as shown in Table 3. The crystal structures and properties of the beta-alumina sintered materials obtained are shown in Table 3.
21~378~
C~ , ~ o o o o o o o ~ a) oo o o~
~r, o o o o 0 CD ~r N
\\ \ ~ o O O O O ,C~ ~ CD ~ 10 N C') N N
O O O O
.,, .,~,,, ,,, ~
_~ 4 4 4 4 ,"
h h h h 'a w ~ el a) N ~ ~() ~ o ,_, h h h h ' ~ t ~I N N N N N N
O O O O
o ~ ~ ~ O O N ~( ~) ~' o c c~ 4 ~q ~ N N N N N N N
~1\ 0 0 0 0 ~ C' C ~?~ O N
Z ~ Z O bO O ~
\ \ \ \ ~ .~ O O O O O O O
<
~
v ~ ~ c) v ~-L N X X ~ X ~
o hO _ 2 Z Z Z ~ ~ Z U~ _, ~7 -~ ~OOOOOO
~ -- 00 N c~ N ~1 0 ~1 C_) V~ 1 N N N N N N
o _ .~ _d' ~( ~ O ~1 N ~( ~ ~ a .......
U~ _ ~
N N N N N N N
~, b4 ......
c, 0~ ~ ~ cr c. o c~ o r- CO a ~
C~ ~
x Example 3 In order to confirm the effect of alumina material, beta-alumina sintered materials were obtained under the same steps and conditions as in Example 1 except that the average particle diameter and BET specific surface area of a-Al203 material were varied as shown in Table 4. The crystal struc-tures and properties of the beta-alumina sintered materials obtained are shown in Table 4.
~ 214378~
o o o o o o o .' ~ ~ a) c- o o ~~
q~ _ o _3 ~D
~ '~
C~ 0.
~ * ~~ OOOO O . ~
.' E~. .... . . ~ , ~
~ O') ~ ~ â a~ N ~ ~ ~ 8 ~_ ~ N N N N N C~
t3 '*' 10 15~ 15') 00 CO O O ~ C~) 10 d' 1~- a) o CD ' U~
C 10 ~ ~ O O O ~ C~ ~ N ~ ~ ~ ~ N N bO
~ C N
C ~
n ~ 11 bo O c .......
~ .~ o o o o o o o ~
O
E _ ~ v Q .~ _ O O O O O O O c -I ~ 3 0 _ *
a) _ , .
.t3 ~ N N C~l N ~ E~
V~ ~ ~ _ ~ ~ ~ ~ ~ ~ O
J ~ N C~l N C~ C~ N N :' a~ (13 S_.
~ 2: ~ ~ O ~ C~ ~~ ~ ~ ~ ~ ~ ~
c~ ~ C~ N C~ cQ ~ C~ N ~0 . .
X G
Table 4 In order to confirm the effect of firing condi-tions, beta-alumina sintered materials were obtained under the same steps and conditions as in Example 1 except that the heat curve for firing was varied as shown in Table 5. The crystal structures and properties of the beta-alumina sint-ered materials obtained are shown in Table 5.
h h ~~
, ~ O O O
X X . _ ~
. _ 4 oV V : ~=
~7 0 0 O
~o V~
~) ~ ~ o ~, _ o . Y~, ~ ~ ~
~ ~ Lr~
bO a~
,~
.,l . s_ h p, ~
~ ~C~ ~ N
9~ 0 h h O X
9~ ~ o O O .,~ O
~ ._ . .
a) '~ X X X V~ ~C~ N N
~> ~ C ~
$~ a)oV oV oV C
O O o o O ~ ~ o~
~OCDCD ~o o c 4 ~~ _ ~ ~ .~ O O O
~. ~~ ~ ~ o X - _ Ir S~ h ~ - v o o o u~ ~- ~ N C~
~2~ o a) x x 4 _ ~.
~ OV OV . ~ _~r o ~
O O .~
~ j ~a N N N
~ ~ c~ o ~~
c~ N N ~" N N
~ ~ I!a X
r ~
214378~
As is clear from the above, the beta-alumina sint-ered materials produced in the scope of the present invention have good properties in electrical resistance, strength to internal water pressure, etc., and the beta-alumina sintered materials produced under more preferable conditions have better properties in electrical resistance, strength to internal water pressure, etc.
As described above, in the present invention, since the magnesium source material is fed in the form of magnesi-um-aluminum spinel, a beta-alumina solid electrolyte can efficiently be produced without subjecting raw materials to calcination.
Further, the beta-alumina solid electrolyte ob-tained by the present process, having a uni~ue crystal struc-ture in that the beta-alumina crystals constituting said solid electrolyte have small orientation and a small aspect ratio, has a low electrical resistance and a large strength to internal water pressure and is excellent as a diaphragm for sodium-sulfur battery.
Claims (7)
1. A beta-alumina solid electrolyte for use in a sodium-sulfur battery, wherein the beta-alumina crystals constituting said electrolyte have a degree of orientation toward the C axis thereof of 0.2-0.4 and an aspect ratio of 4.0 or less.
2. A beta-alumina solid electrolyte for use in a sodium-sulfur battery, wherein the beta-alumina crystals constituting said electrolyte have a degree of orientation toward the C axis thereof of 0.2-0.4 and such a particle diameter distribution that the average particle diameter is
3 µm or less, the proportion of the particles having a particle diameter of 5 µm or less is 90% or more, and the maximum particle diameter is 300 µm or less.
3. A beta-alumina solid electrolyte according to claim 1 or 2, wherein said solid electrolyte has an electrical resistance of 4.0 .OMEGA..cm or less, a burst strength to internal pressure of 150 MPa or more, and a density of 3.20 g/cm2 or more.
3. A beta-alumina solid electrolyte according to claim 1 or 2, wherein said solid electrolyte has an electrical resistance of 4.0 .OMEGA..cm or less, a burst strength to internal pressure of 150 MPa or more, and a density of 3.20 g/cm2 or more.
4. A process for producing a beta-alumina solid electrolyte using an alumina source material, a magnesium source material and a sodium source material, which process comprises using a magnesium-aluminum spinel as the magnesium source material, and subjecting all materials to mixing, granulation, molding and firing to obtain a beta-alumina solid electrolyte without subjecting the materials to calcination.
5. A process according to claim 4, wherein the molar ratio of magnesia (MgO) and alumina (Al2O3) in the magnesium-aluminum spinel is 1 or more.
6. A process according to claim 4 or 5, wherein the sodium source material is sodium compound(s) containing at least either of NaHCO3 and sodium oxalate.
7. A process according to claim 4, 5 or 6, wherein the firing is conducted according to a heat curve comprising:
(1) a step of keeping the system temperature at a constant temperature in the range of 1,400° - l,550°C for 1-5 hours, or a step of increasing the system temperature at a rate of 50°C/hr. or less in said temperature range, (2) a step of keeping the system temperature at the maximum temperature of 1,580° - 1,650°C for 0.1-3.0 hours, and (3) a step of keeping the system temperature at a constant temperature in the range of 1,400° - 1,550°C for 1-5 hours, or a step of decreasing the system temperature at a rate of 50°C/hr. or less in said temperature range.
(1) a step of keeping the system temperature at a constant temperature in the range of 1,400° - l,550°C for 1-5 hours, or a step of increasing the system temperature at a rate of 50°C/hr. or less in said temperature range, (2) a step of keeping the system temperature at the maximum temperature of 1,580° - 1,650°C for 0.1-3.0 hours, and (3) a step of keeping the system temperature at a constant temperature in the range of 1,400° - 1,550°C for 1-5 hours, or a step of decreasing the system temperature at a rate of 50°C/hr. or less in said temperature range.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP6058972A JP2856344B2 (en) | 1994-03-29 | 1994-03-29 | Beta alumina solid electrolyte and method for producing the same |
| JP6-58972 | 1994-03-29 |
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| Publication Number | Publication Date |
|---|---|
| CA2143784A1 CA2143784A1 (en) | 1995-09-30 |
| CA2143784C true CA2143784C (en) | 1998-09-29 |
Family
ID=13099770
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002143784A Expired - Fee Related CA2143784C (en) | 1994-03-29 | 1995-03-02 | Beta-alumina solid electrolyte and process for production thereof |
Country Status (5)
| Country | Link |
|---|---|
| US (2) | US5612154A (en) |
| EP (1) | EP0675558B1 (en) |
| JP (1) | JP2856344B2 (en) |
| CA (1) | CA2143784C (en) |
| DE (1) | DE69505870T2 (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19515490A1 (en) * | 1995-04-27 | 1996-10-31 | Abb Patent Gmbh | Ceramic material and process for its manufacture |
| JP3667403B2 (en) * | 1995-10-05 | 2005-07-06 | サンゴバン・ティーエム株式会社 | β-alumina electroformed refractory |
| JP3706054B2 (en) | 2000-12-11 | 2005-10-12 | 日本碍子株式会社 | Method for producing beta alumina solid electrolyte |
| JP4897163B2 (en) * | 2001-09-19 | 2012-03-14 | 太平洋セメント株式会社 | Method for producing alumina sintered body |
| US7255961B2 (en) * | 2004-03-12 | 2007-08-14 | Trans Ionics Corporation | Thin film composite electrolyte |
| KR101404044B1 (en) * | 2011-10-17 | 2014-06-10 | 건국대학교 산학협력단 | Na+-beta-alumina solid electrolyte and fabrication of Na+-beta-alumina solid electrolyte by infiltration of alkali molten salts with the porous α-alumina preform prepared by slip casting process and the secondary battery using it |
| WO2014178453A1 (en) * | 2013-04-30 | 2014-11-06 | (주)화인테크 | Beta-alumina for sodium secondary battery solid electrolyte and manufacturing method therefor |
| CN105517974B (en) * | 2013-09-12 | 2018-06-01 | 巴斯夫欧洲公司 | The beta- aluminium oxide ceramics that can be obtained by squeezing out the mixture for including sodium oxalate |
| KR101578660B1 (en) * | 2014-12-29 | 2015-12-21 | 주식회사 동국알앤에스 | Method of Producing Solid Electrolyte for Sodium Sulfur Secondary Battery |
| DE102016120941B4 (en) | 2016-11-03 | 2022-01-27 | Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. | Sodium ion conducting membrane based on a sodium beta''-aluminate system and method for producing such |
| US11515564B2 (en) * | 2019-09-04 | 2022-11-29 | The Regents Of The University Of Michigan | Surface treatment of a solid electrolyte to lower the interfacial resistance between the solid electrolyte and an electrode |
Family Cites Families (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4083919A (en) * | 1975-05-02 | 1978-04-11 | Eastman Kodak Company | Beta-alumina composites and methods for producing them |
| US4113928A (en) * | 1976-02-17 | 1978-09-12 | University Of Utah | Method of preparing dense, high strength, and electrically conductive ceramics containing β"-alumina |
| US4307138A (en) * | 1979-04-23 | 1981-12-22 | General Electric Company | Sintered ion-conductive composite electrolyte of beta-alumina and beta"-alumina |
| DE2917590A1 (en) * | 1979-04-30 | 1980-11-06 | Kurt Dipl Chem Dr Hartl | Polycrystalline beta-alumina moulding esp. membrane - with parallel lamellar crystallites, useful in electrolytic cells |
| JPS5642909A (en) * | 1979-09-18 | 1981-04-21 | Ngk Insulators Ltd | Solid electrolyte |
| US4339511A (en) * | 1979-11-30 | 1982-07-13 | The United States Of America As Represented By The United States Department Of Energy | Preparation of powders suitable for conversion to useful β-aluminas |
| DE3247967A1 (en) * | 1982-12-24 | 1984-06-28 | Brown, Boveri & Cie Ag, 6800 Mannheim | FIXED ELECTROLYTE |
| AU577761B2 (en) * | 1985-05-24 | 1988-09-29 | Lilliwyte Societe Anonyme | Method of making beta"-alumina" |
| JPH0774093B2 (en) * | 1987-02-19 | 1995-08-09 | 東京電力株式会社 | Beta-alumina solid electrolyte and method for producing the same |
| JPH0696466B2 (en) * | 1989-07-14 | 1994-11-30 | 日本碍子株式会社 | Method for manufacturing β "alumina sintered body |
| JPH0624149B2 (en) * | 1989-11-20 | 1994-03-30 | 日本碍子株式会社 | Beta-alumina solid electrolyte |
| JPH0686324B2 (en) * | 1989-12-01 | 1994-11-02 | 日本碍子株式会社 | Beta-Alumina Porcelain Manufacturing Method |
| DE4041890A1 (en) * | 1990-12-27 | 1992-07-02 | Abb Patent Gmbh | METHOD FOR PRODUCING ION-CONDUCTING CERAMICS |
| JPH0696468B2 (en) * | 1991-01-18 | 1994-11-30 | 日本碍子株式会社 | Beta-alumina sintered body and method for producing the same |
| JPH0547412A (en) * | 1991-08-12 | 1993-02-26 | Ngk Insulators Ltd | Beta-alumina solid electrolyte |
| US5213911A (en) * | 1991-10-17 | 1993-05-25 | The United States Of America As Represented By The United States Department Of Energy | Solid-oxide fuel cell electrolyte |
| KR950015847A (en) * | 1993-11-09 | 1995-06-17 | 김항덕 | Solid electrolyte for sodium-sulfur battery and preparation method thereof |
-
1994
- 1994-03-29 JP JP6058972A patent/JP2856344B2/en not_active Expired - Lifetime
-
1995
- 1995-03-02 CA CA002143784A patent/CA2143784C/en not_active Expired - Fee Related
- 1995-03-02 US US08/397,756 patent/US5612154A/en not_active Expired - Lifetime
- 1995-03-28 EP EP95302058A patent/EP0675558B1/en not_active Expired - Lifetime
- 1995-03-28 DE DE69505870T patent/DE69505870T2/en not_active Expired - Lifetime
-
1996
- 1996-09-03 US US08/707,293 patent/US5691082A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0675558B1 (en) | 1998-11-11 |
| US5691082A (en) | 1997-11-25 |
| EP0675558A1 (en) | 1995-10-04 |
| DE69505870T2 (en) | 1999-05-12 |
| JPH07272749A (en) | 1995-10-20 |
| CA2143784A1 (en) | 1995-09-30 |
| US5612154A (en) | 1997-03-18 |
| DE69505870D1 (en) | 1998-12-17 |
| JP2856344B2 (en) | 1999-02-10 |
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