JP2000302582A - beta-ALUMINA CERAMICS, ITS PRODUCTION AND PRODUCTION OF SOLID ELECTROLYTE-TYPE BATTERY USING THE beta-ALUMINA CERAMICS - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance and highly reliable β-alumina ceramics free from the occurrence of surface deterioration or surface defects which are caused by moisture adsorption occurred while a battery assembly is completed after firing, especially rapid desorption of excess moisture from the surface of the β-alumina ceramics by heat treating and rapid re-adsorption of moisture after heat treatment, a method for producing the same and a solid electrolyte- type battery using the ceramics. SOLUTION: The β-alumina ceramics is formed into a prescribed shape by grinding using an aqueous grinding liquid and the shaped β-alumina ceramics is heat-treated at <=200 deg.C so that the amount of the moisture adsorbed is controlled to <=0.7 mg/cm2. Then, the β-alumina ceramics wherein the moisture content is controlled in a prescribed range is stored in an atmosphere having a relative humidity of <=40%. It is preferable that the change rate of the amount of adsorbed moisture is <=50% after the β-alumina ceramics wherein the moisture content is controlled to <=0.7 mg/cm2 is stored in an atmosphere having the relative humidity of <=40% for ten days.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beta-alumina ceramic, a method for producing the same, and a method for producing a solid electrolyte battery using the same. More specifically, by contacting with moisture, hydrophilic ions present in the sintered body move to the surface, causing non-uniform composition distribution and collapse of the crystal structure due to ion migration, or water on the surface. Beta-alumina ceramics having hygroscopicity that causes a reduction in surface activity and a collapse of the surface structure due to the generation of a reactant with, for a long time,
TECHNICAL FIELD The present invention relates to a method for inexpensively and effectively manufacturing without deteriorating its characteristics, and a method for manufacturing a solid electrolyte battery using the same. For example, the present invention is applicable to a solid electrolyte type battery such as a sodium-sulfur battery and a sodium-metal chloride battery.

[0002]

2. Description of the Related Art Beta-alumina ceramics have alkali ion conductivity and are therefore used as solid electrolytes in solid electrolyte batteries such as sodium-sulfur batteries for power storage. Here, the general structure of a sodium-sulfur battery is shown in FIG. The operating temperature of the sodium-sulfur battery is 30
At about 0 ° C., the sulfur (sodium polysulfide) 1 of the positive electrode and the metallic sodium 4 of the cathode are liquefied, and the metallic sodium is partially present as a vapor inside the battery. For this reason, the atmosphere inside the battery needs to be kept at an inert gas or vacuum, and a high airtightness is required at the joint of each battery member. Therefore, the solid electrolyte tube 2 and the α-alumina ring 3 are glass-joined at the glass joint 7. Further, the lid on the cathode side and the mouth of the anode container are joined to an α-alumina ring 3 (not shown) using an active metal brazing material or the like.

In order to obtain a solid electrolyte made of beta-alumina ceramics, it is generally necessary to form a bottomed tubular beta-alumina ceramic sintered body and then process it into a predetermined shape by grinding. However, sodium ions contained in beta-alumina ceramics have high reactivity with moisture, so when processed using an aqueous grinding fluid, alkali ions move from the inside of the beta-alumina ceramics to the surface of the ionic conductor and near the surface. The phenomenon that reacts with water easily occurs.

[0004] As a result, the internal composition of the sintered body becomes non-uniform, the crystal structure is collapsed, and the surface activity is reduced due to the formation of a reaction product of water and alkali ions on and near the surface of the ionic conductor. And problems such as collapse of the surface structure. For example, beta-alumina ceramics are known to deteriorate due to moisture absorption, causing a decrease in mechanical strength and a decrease in sodium ion conductivity.

[0005] Several methods for solving such a problem have been studied. For example, in order to suppress the deterioration of electrical characteristics due to moisture absorption, beta-alumina ceramic
A method of performing heat treatment under the condition of 00 to 1500 ° C. × 1 to 40 hours is disclosed. Also, Japanese Patent Publication No. 57-15063
A similar heat treatment method is disclosed in Japanese Patent Application Laid-Open Publication No. H11-163,873.

Further, in order to suppress the deterioration of the sodium-sulfur battery with the lapse of time, a temperature of 300 to 600.degree.
0.3mg / c per unit surface area
A method for adjusting the pressure to m ² or less is disclosed in Japanese Patent No. 27496648.

All of these methods are 300 to 1000
Since the heat treatment is performed at a considerably high temperature such as ℃, rapid extraction of moisture from the surface of the beta alumina ceramics and rapid re-adsorption of moisture after the completion of the heat treatment are likely to occur. The inventors have found that when the amount of rapid re-adsorption of water exceeds a predetermined limit, a surface-deteriorated layer is likely to be generated due to the same effect as in the case of performing an accelerated test. Such a surface-deteriorated layer may become a surface defect due to deterioration over time, from which the solid electrolyte tube may be damaged, or may be damaged during the battery assembly process.

Further, since a large amount of energy is required for the heat treatment, the production cost increases. Unless any measures are taken to adjust the amount of water adsorbed on the beta-alumina ceramics after the heat treatment and before assembling the battery, the reliability of the battery will be significantly affected depending on the amount of water re-adsorbed after the heat treatment. May appear.

[0009]

SUMMARY OF THE INVENTION The present invention relates to the adsorption of water generated after firing to the assembly of a battery, in particular, the rapid and excessive removal of water from the surface of beta-alumina ceramic by heat treatment and heat treatment. High-performance and high-reliability beta-alumina ceramic which prevents surface deterioration and surface defects of beta-alumina ceramic caused by rapid re-adsorption of water after completion, method for producing the same, and solid electrolyte such as sodium-sulfur battery It is an object of the present invention to provide a method for manufacturing a rechargeable battery.

[0010]

According to the first aspect of the present invention, a beta alumina ceramic ground to a predetermined shape using an aqueous grinding fluid is heated at a temperature of 200 ° C. or less,
The gist of the present invention is a method for producing beta alumina ceramics in which the amount of adsorbed water is adjusted to 0.7 mg / cm ² or less. Beta-alumina ceramics ground using an aqueous grinding fluid have adsorbed moisture as a natural result. Heat treatment or the like is required to remove the adsorbed moisture. By setting this heat treatment temperature to a low temperature range of 200 ° C. or less,
By suppressing the sudden and excessive removal of water and adjusting the amount of adsorbed water to 0.7 mg / cm ² or less, which is higher than before, the rapid re-adsorption of water can be suppressed and the generation of a surface deterioration layer can be suppressed. Can be prevented.

The method for producing beta-alumina ceramics of the present invention does not require special equipment, and can reduce the energy consumption of the heat treatment.
It is possible to reduce the manufacturing cost.

According to a second aspect of the present invention, the amount of adsorbed water is set at 0.1.
The gist of the present invention is a method for producing beta-alumina ceramics in which beta-alumina ceramics adjusted to 7 mg / cm ² or less is stored in an atmosphere having a relative humidity of 40% or less. The reason for limiting the amount of adsorbed water to 0.7 mg / cm ² or less is as follows.
If the content is 7 mg / cm ² or more, not only the performance of the beta-alumina ceramic itself, the reliability, and the production yield are reduced, but also the sodium-sulfur battery using it, the performance, the reliability, and the production yield are reduced. It is. A more preferable range of the amount of adsorbed water of the beta alumina ceramic is 0.4 mg / cm ² or less. This is because the performance, reliability, and production yield of beta-alumina ceramics and a sodium-sulfur battery using the same become extremely good.

[0013] The beta-alumina ceramics having the amount of adsorbed water adjusted to a predetermined range is then stored in an atmosphere having a relative humidity of 40% or less. By storing in an atmosphere having a relative humidity of 40% or less, the re-adsorption amount of water can be effectively suppressed. If the relative humidity of the storage atmosphere exceeds 40%,
It is not preferable because control of the amount of water adsorbed on the surface of the beta alumina ceramics becomes ineffective. in this way,
By suppressing rapid and excessive withdrawal of water and rapid re-adsorption, generation of a surface-deteriorated layer can be effectively prevented. Of course, after adjusting the amount of adsorbed water, the process may be continuously performed in the next step. However, it is preferable that the working environment in the next step is also performed in an atmosphere having a relative humidity of 40% or less. This is because the waiting time in the next process is also included in the storage in a broad sense.

According to a third aspect of the present invention, the amount of adsorbed water is set at 0.1.
The gist is that the rate of change in the amount of adsorbed water after storing the beta alumina ceramics adjusted to 7 mg / cm ² or less in an atmosphere having a relative humidity of 40% or less for 10 days is 50% or less. The rate of change of the amount of adsorbed water during the storage period is 50
The reason why the percentage is specified to be not more than 50% is that if the rate of change exceeds 50%, the performance, reliability and production yield of beta-alumina itself and the solid electrolyte type battery using the same will decrease.

The more preferable range of the change rate of the amount of adsorbed water during the storage period is 25% or less. The rate of change is 25%
In the following cases, the performance and reliability of beta alumina itself become extremely good, and the performance, reliability, and production yield of a solid electrolyte battery using the same can be made extremely good.

According to a fourth aspect of the present invention, there is provided a beta-alumina ceramic having a change rate of an adsorbed water amount of 50% or less after being stored in a predetermined atmosphere for a predetermined period of time. ^The gist should be ^-4 cc / cm ² or less. When the heat treatment is performed at a temperature of 200 ° C. or more, the volume of defects existing per unit surface area of the beta-alumina ceramic becomes 7 × 10 ⁻⁴ cc / cm ² or more. Affect. In view of the above results, while adjusting the amount of adsorbed water of the beta alumina ceramics and the like, and also adjusting the volume of defects existing per unit surface area to a predetermined range, a beta alumina ceramic having excellent properties can be obtained. .

According to a fifth aspect of the present invention, there is provided a method of manufacturing a solid electrolyte type battery in which the amount of adsorbed water of beta-alumina ceramics and the relative humidity of the storage atmosphere are defined within predetermined ranges, and the bonding to the insulating member is performed by glass bonding. Is the gist. The configuration of each of the included steps will be described below.

Beta-alumina ceramics ground to a predetermined shape using an aqueous grinding fluid is heated at a temperature of 200 ° C. or less to reduce the amount of adsorbed water to 0.7 mg / cm ^2.
Have the following adjustment process. As described above, by setting the heat treatment temperature to a low temperature range of 200 ° C. or less, it is possible to suppress the sudden and excessive extraction of moisture and to reduce the amount of adsorbed moisture to 0.7 mg / cm ² or less as compared with the conventional method. By adjusting to a higher level, it is possible to suppress rapid re-adsorption of moisture and prevent the occurrence of a surface deterioration layer.

[0019] The method further comprises a step of storing the beta-alumina ceramic having the adjusted amount of adsorbed water in a humidity atmosphere having a relative humidity of 40% or less. As already described above, the beta-alumina ceramic whose amount of adsorbed water has been adjusted to a predetermined range is then stored in an atmosphere having a relative humidity of 40% or less. By storing in an atmosphere with a relative humidity of 40% or less,
The amount of re-adsorption of water can be effectively suppressed. If the relative humidity of the storage atmosphere exceeds 40%, the control of the amount of water adsorbed on the surface of the beta-alumina ceramics is not effective, which is not preferable. As described above, the occurrence of a surface-deteriorated layer can be effectively prevented by suppressing rapid and excessive extraction of water and rapid re-adsorption.

The rate of change in the amount of adsorbed water after the beta alumina ceramic is stored for 10 days in an atmosphere having a relative humidity of 40% or less is preferably 50% or less. The reason why the rate of change of the amount of adsorbed water during the storage period is specified to be 50% or less is that if the rate of change exceeds 50%, the performance and reliability of beta alumina itself and the solid electrolyte type battery using the same decrease. This is because the production yield is reduced.

The more preferable range of the change rate of the amount of adsorbed water during the storage period is 25% or less. The rate of change is 25%
In the following cases, the performance and reliability of beta alumina itself become extremely good, and the performance, reliability, and production yield of a solid electrolyte battery using the same can be made extremely good.

A step of glass-joining the beta alumina ceramic stored in the humidity atmosphere to an insulating member. Beta-alumina ceramics in which the amount of adsorbed water and the like are adjusted have an extremely good surface state, and thus stable glass bonding can be performed. Since the glass bonding state between the beta-alumina ceramic and the insulating member is good, the reliability and the production yield of the solid electrolyte type battery can be remarkably improved. As the insulating member, for example, α-alumina, zirconia, or the like can be used. As the bonding glass, a borosilicate glass-based glass or the like can be used.

As described above, according to the production method of the present invention, it is possible to suppress a decrease in the performance, reliability, and production yield of the solid electrolyte battery due to moisture absorption of the beta alumina ceramic.

[0024]

EXAMPLES (Example 1) (1) Production of beta-alumina tube α-alumina, sodium carbonate, lithium carbonate, and zirconium oxide are used as starting materials. α-alumina and zirconium oxide having a purity of 99.9% are used. For sodium carbonate and lithium carbonate, first-class reagents are used.
α-Alumina, sodium carbonate, and lithium carbonate were weighed and mixed in predetermined amounts so as to be 90.4%, 8.85%, and 0.75% in terms of alumina, sodium oxide, and lithium oxide, respectively. Calcinate for 10 hours. The calcined powder is pulverized with a vibration mill to obtain pulverized alumina powder.

A slurry is prepared by mixing 100 parts by weight of the above-mentioned beta-alumina pulverized raw material powder and 5 parts by weight of zirconium oxide in an aqueous solvent. A granulated powder is obtained by spray-drying the slurry. The granulated powder is formed into a predetermined tube shape, and is held at a predetermined temperature for one hour and fired. The tube-shaped sintered body is ground with a diamond grindstone while pouring water into a processing surface using water as a grinding liquid to obtain a beta alumina tube.
The dimensions of the beta-alumina tube after the grinding are 45 mm in outer diameter × 400 mm in length × 2.5 mm in wall thickness.

(2) Preparation of Evaluation Sample A ring-shaped sample having a length of 5 mm from the opening of the beta-alumina tube is cut out and used as an evaluation sample for the amount of surface defects, the amount of adsorbed moisture, and the relative density.

(3) Drying Conditions The beta-alumina tube and the evaluation sample are brought into contact with water for 30 minutes after grinding and cutting, and then placed in a dryer set at a predetermined temperature and dried for a predetermined time. Table 1 shows combinations of the drying temperature and the drying time.

(4) Defect amount measurement Defect amount per unit area of the evaluation sample surface (unit: c)
c / cm ² ) is a mercury porosimeter (manufactured by Shimadzu Corporation, product name:
(PoreSizer 9320). After measuring the initial weight and surface area, mercury is injected under pressure with a mercury porosimeter. 0.05μ from the amount of mercury injected
The total volume of the surface defects of m or more is calculated and divided by the surface area to obtain data on the amount of defects. Table 1 shows the results.

(5) Measurement of Initial Adsorbed Water Content (dA) After measuring the surface area (S ₁ ) of the evaluation sample, the initial weight (A ₁ ) after drying under the drying conditions shown in Table 1 was used as the evaluation sample. The weight (A ₂ ) after the heat treatment at 1000 ° C. is measured, and the initial amount of adsorbed water (dA) is calculated using the following equation (1). Table 1 shows the results.

[0030]

## EQU1 ## dA = (A ₁ -A ₂ ) / S ₁

(6) SEM Observation of Degraded Layer The degree of deterioration of the beta alumina ceramic surface under each drying condition shown in Table 1 is observed by SEM photograph. The cross section of the evaluation sample was observed at a magnification of 1000 times, and those in which clear deterioration was visually confirmed were judged as rejected, and those with slight deterioration were recognized, but those in the allowable range were evaluated as “Δ”, and deterioration was recognized. Those which cannot be obtained are shown in Table 1 as “○”. 2 and 3 show SEM photographs of Sample No. 4 as an example and Sample No. 11 as a comparative example, respectively.

[0032]

[Table 1]

From the results shown in Table 1, it can be seen that the amount of surface defects increases as the drying temperature increases. As can be seen from the results of Sample Nos. 10 and 11, which are comparative examples, under the drying conditions exceeding 200 ° C. which is the range of the present invention, a deteriorated layer is formed on the surface of the beta alumina ceramic, and the drying conditions It is understood that it is not preferable.

(7) Storage Test Next, the beta alumina tube adjusted to a predetermined initial adsorbed water content is stored for 10 days in a desiccator controlled to a predetermined relative humidity. Water content of adsorbed beta alumina tube after storage (d
In the measurement of F), one of the ring-shaped evaluation samples cut out from the same beta alumina tube was used to measure the surface area (S ₂ ) of the evaluation sample, the weight after storage (F ₁ ), and the evaluation sample at 1000 ° C. The weight (F ₂ ) after the heat treatment is measured, and the absorbed water content (dF) after storage is calculated using the following equation ( ₂ ). Table 2 shows the results.

[0035]

## EQU2 ## dF = (F ₁ −F ₂ ) / S ₂

The rate of change of the amount of adsorbed water during storage (d
C) is calculated from the initial amount of adsorbed water (dA) and the amount of adsorbed water after storage (dF) by using the following Expression 3. Table 2 shows the results.

[0037]

## EQU3 ## dC = 100 × (dF−dA) / dA

(8) Evaluation of Characteristics of Beta Alumina after Storage Test Next, characteristics of the beta alumina tube after storage are evaluated.
Evaluation items are relative density, specific resistance value, and internal pressure breaking strength.

The relative density is obtained by measuring a bulk density by a buoyancy method in ethanol using an evaluation sample cut out, and calculating a relative density as a ratio to a theoretical density. Table 3 shows the results.

The specific resistance value was determined by connecting a beta alumina tube to Na-
The sodium ion conductivity (specific resistance) at 350 ° C. is measured by a four-terminal method using a Na cell. Table 3 shows the results.

The internal pressure breaking strength is obtained by applying a pressure substantially uniformly to the entire inner surface of the beta-alumina tube and calculating the strength at the time when the beta-alumina tube breaks from the shape of the beta-alumina tube. For each condition, the internal pressure breaking strength is measured using eight beta alumina tubes, and the average value is determined. Table 3 shows the results.

(9) Evaluation test of sodium-sulfur battery using beta-alumina tube after storage test A reliability test of a sodium-sulfur battery using the beta-alumina tube after the storage test is performed. An α-alumina ring is glass-bonded to the beta alumina tube as an insulating member. Using this, 10 battery cells are produced for each condition. The evaluation items are a production yield rate of the glass joint and a heat cycle test.

The production yield rate of the glass joint is obtained by calculating the ratio of the glass joint which is damaged during the assembly of the battery. Table 3 shows the results.

In the heat cycle test, after assembling the battery, a thermal stress accompanying the temperature rise and fall from room temperature to 350 ° C. (battery operating temperature) is repeatedly applied to check whether there is any defect in the battery characteristics (charge / discharge characteristics) every cycle. To evaluate. The "fault" here was not a problem when assembling the battery,
It means that normal charging / discharging becomes impossible due to breakage or the like occurring at the glass joint between the beta alumina tube and the insulating member during the thermal cycle test. Table 3 shows the results. Note that the numbers in Table 3 indicate the number of thermal cycles at the time when the failure occurred first among the 10 cells.

[0045]

[Table 2]

[0046]

[Table 3]

As is clear from the results in Tables 2 and 3,
Sample Nos. 13 to 15, which are examples of the present invention,
In Sample No. 17, Sample No. 18, Sample No. 20, and Sample No. 21, the specific resistance at 350 ° C. was 3.5 Ω-cm.
It can be seen that good electrical characteristics are shown below. Further, it can be seen that the internal pressure breaking strength also shows good mechanical properties of 160 MPa or more.

In addition, sample No. 13 which is an embodiment of the present invention
In addition, the production yield rate of the glass bonded portion of the cells using the beta alumina tubes of Sample No. 15, Sample No. 17, Sample No. 18, Sample No. 20, and Sample No. 21 is as good as 100%. Further, even in the heat cycle test, no breakage was observed in the sample of the above example even after 50 cycles. still,
Normally, the heat cycle of a sodium-sulfur battery is performed twice a year, and its reliability is guaranteed for 15 years. Therefore, sufficient reliability can be ensured by 50 heat cycle tests.

In particular, the amount of adsorbed water after storage is 0.4 mg
/ Cm ² or less, and the change rate of the amount of adsorbed water is within 25%, Sample No. 17, Sample No. 18, Sample No. 20,
In sample number 21, the internal pressure breaking strength is 170 MPa or more,
It can be seen that the specific resistance value is 3.0Ω-cm or less, which is extremely excellent.

From these results, even if the initial amount of adsorbed water is small, if the amount of adsorbed water during storage is large, beta alumina ceramics are corroded by water from the surface layer to increase surface defects, resulting in deterioration of strength, Manufacturing yield decline,
This leads to a decrease in battery reliability. Further, even if the initial adsorbed water amount is as small as 0.7 mg / cm ² or less, if the rate of change of the adsorbed water amount after storage is large, defects on the surface of the beta-alumina ceramic due to the sudden adhering of adsorbed water are reduced. It increases at an accelerated rate, resulting in deterioration in strength, reduction in manufacturing yield, and reduction in battery reliability.

[0051]

According to the present invention, the adsorption of water generated during the period from firing to the assembly of the battery, particularly, the sudden and excessive extraction of water from the surface of the beta alumina ceramic by the heat treatment and the completion of the heat treatment -Alumina Ceramics with High Performance and High Reliability Preventing Surface Deterioration and Surface Defects of Beta-Alumina Ceramics Due to Rapid Re-Adsorption of Moisture on Water, Method for Producing the Same, and Production of Solid Electrolyte Battery Using the Same We can provide a method.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a general structure of a sodium-sulfur battery.

FIG. 2 is a SEM image of a cross section of an example having no deterioration layer on the surface of a beta alumina tube.

FIG. 3 is an SEM image of a cross section of a comparative example having a deteriorated layer on the surface of a beta alumina tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sulfur or sodium polysulfide 2 Beta-alumina solid electrolyte tube 3 Alpha-alumina insulating ring 4 Metal sodium 5 Cathode current collector 6 Anode container 7 Glass joint

Continued on front page F-term (reference) 5H029 AJ11 AJ14 AK05 AL13 AM15 BJ02 CJ01 CJ02 CJ05 CJ28 DJ03 EJ06 HJ00 HJ01 HJ07 HJ14

Claims (5)

[Claims] 1. A beta-alumina ceramic, which has been ground into a predetermined shape using an aqueous grinding fluid, is heat-treated at a temperature of 200 ° C. or less to reduce the amount of adsorbed water to 0.7 mg / cm.
^{2. A} method for producing beta-alumina ceramics, which is adjusted to ² or less. 2. A method for producing beta-alumina ceramics according to claim 1, wherein said beta-alumina ceramics is stored in an atmosphere having a relative humidity of 40% or less.
suppress 3. A beta-alumina ceramic obtained by the method for producing beta-alumina ceramic according to claim 1 or 2, wherein the amount of adsorbed water after storage for 10 days in an atmosphere having a relative humidity of 40% or less is measured. A beta-alumina ceramic having a rate of change of 50% or less. 4. The volume of defects existing per unit surface area of the beta alumina ceramic is 7 × 10 ⁻⁴ cc.
/ Cm ² or less, beta alumina ceramics according to claim 3, characterized in that: 5. A beta-alumina ceramic, which has been ground into a predetermined shape using an aqueous grinding fluid, is subjected to a heat treatment at a temperature of 200 ° C. or less to reduce the amount of adsorbed water to 0.7 mg / cm.
Adjusting the water content to ² or less, storing the beta-alumina ceramic with the adjusted amount of adsorbed water in a humidity atmosphere having a relative humidity of 40% or less, and bonding the beta-alumina ceramic stored in the humidity atmosphere to an insulating member by glass bonding And a method for producing a solid electrolyte type battery.