JPH07161380A - Solid electrolyte for sodium-sulfur battery and manufacture of sodium-sulfur battery using the solid electrolyte - Google Patents

Abstract

PURPOSE:To suppress the deterioration of beta-alumina-based ceramics due to humidity absorption by coating the beta-alumina-based ceramics with a water repelling material, granulating the ceramics to have prescribed particle size, and then firing the resulting ceramics. CONSTITUTION:A synthetic powder of beta''-alumina, a beta-alumina-based ceramic consisting of beta-alumina, or a ceramic containing both ceramics is coated with a water repelling material. The resulting powder is granulated into 30-100mum particle size and the granulated powder is molded and then sintered. As a result, at the time of production of solid electrolytes, deterioration and size alteration due to humidity absorption before sintering and damage and crack formation attributed to them at the time of sintering are suppressed and formability is improved. a sodium-sulfur battery having the solid electrolyte prepared in that way surely has high reliability. Furthermore, since coating with the water repelling material is done, materials containing water as a main component may be selected as a binder and a solvent at the time of granulation and thus there is a wide option to select binders and solvents.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a solid electrolyte for sodium-sulfur batteries using β ″ -alumina, β-alumina ceramics composed of β-alumina, or a granulated powder of ceramics containing both, and sodium using the same. Regarding sulfur batteries.

[0002]

2. Description of the Related Art Beta-alumina is a compound of aluminum oxide and sodium oxide. Depending on the composition ratio and the presence or absence of a small amount of additives such as lithia, there are several kinds of compounds such as β-alumina and β ″ -alumina having different crystal forms. The beta-alumina referred to in the present invention is a general term for these compounds and their mixtures, and the beta-alumina-based solid electrolyte is a sintered body containing beta-alumina as a main phase, or It means a sintered body in which one or more compounds that secure the stability of the crystal layer are dispersed.Beta-alumina solid electrolyte has good ionic conductivity, and sodium is the most common conductive ionic species. However, other monovalent or divalent cations can also be conducted. It has been applied to a solid electrolyte of a high energy density secondary battery such as a sodium-sulfur battery, which is expected to be applied to a moving battery.

However, beta-alumina-based ceramic powder composed of β ″ -alumina and / or β-alumina used for a solid electrolyte of a sodium-sulfur battery has a strong hygroscopic property and adsorbs water during the manufacturing process to form a molded product thereof. In some cases, the dimensional change causes cracks or breakage in some cases, and in particular, deterioration of granulated powder or compact before sintering due to moisture absorption is remarkable, which is a serious problem.

Although cracks can be visually confirmed when deterioration is remarkable, some cracks are detected after sintering, which is a serious problem not only in the manufacturing cost of the solid electrolyte but also in its reliability. Was there.

Deterioration of beta-alumina ceramics due to moisture absorption is incomparably larger than that of ceramics such as alumina and silicon nitride due to moisture absorption.

In order to avoid this problem, Japanese Patent Publication No. 57-15
In the 063 publication, in order to reduce the effect of moisture absorption, calcination,
Techniques for sintering and annealing are disclosed. In addition,
Japanese Unexamined Patent Publication No. 2-14872 discloses a technique in which a raw material of beta-alumina ceramics and an intermediate product are filled with an inert gas and stored. In addition, in general ceramic industry,
In Japanese Patent No. 03374, there is disclosed a technique of coating a moisture absorption preventing material on coarse granulated powder of 0.6-4 mm.

[0007]

According to Japanese Patent Publication No. 57-15063 or Japanese Patent Laid-Open No. 2-14872, even if a beta-alumina-based ceramic which is filled with an inert gas and preserved is used, the structure before sintering is particularly required. Since the deterioration of the granular powder or the molded product due to moisture absorption is remarkable, water may be adsorbed during the manufacturing process to cause dimensional changes or cracks. This is a serious problem especially in hot and humid seasons.

The method described in Japanese Patent Laid-Open No. 3-103374 works effectively for a coarse granulated powder of 0.6-4 mm, but it is useful for producing a solid electrolyte tube for sodium-sulfur batteries. For the production of applicable fine granulated powder, the granulated powder may be damaged or agglomerated during coating,
It is technically impossible to use.

An object of the present invention is to provide a granulated powder before sintering, which is significantly deteriorated by moisture absorption, or a beta-alumina-based ceramic granulated powder which can solve the above-mentioned problems of a molded body and suppress deterioration by moisture absorption. It is intended to provide a solid electrolyte for a sodium-sulfur battery used and a sodium-sulfur battery.

[0010]

In order to solve the above-mentioned problems, the present invention coats a synthetic powder of β ″ -alumina, β-alumina-based ceramics composed of β-alumina or ceramics containing both with a water-repellent substance, Next, it is characterized in that the granulated powder is granulated to a size of 30-100 μm, the granulated powder is molded, and then fired.

Further, the beta-alumina-based ceramic granulated powder has an average particle size of 30 to 100 μm and is synthesized with β ″ -alumina coated with a water-repellent substance, β-alumina-based ceramics composed of β-alumina, or a ceramic containing both. It is composed of an aggregate of powder, and molded and fired using the granulated powder to produce a solid electrolyte for sodium-sulfur battery, and also to produce a sodium-sulfur battery using the solid electrolyte. Characterize.

As the water-repellent substance, it is desirable to use a material having a contact angle with water of 80 degrees or more. For example, paraffinic compounds having a C number of 5 or more, and fats and oils. Oils and fats include palmitic acid, stearic acid, oleic acid, linoleic acid,
It is preferable to be composed of at least one of linoleic acid and sardine acid. Further, the water-repellent substance can be mechanically mixed (using a ball mill or the like) and coated on the synthetic powder. At this time, mixing / coating can be performed without using together with a solvent that dissolves the water-repellent substance.

When a solvent and a binder are added to and mixed with the synthetic powder coated with a water-repellent substance to prepare a slurry to produce granulated powder, the solvent is, for example, water or an organic solvent or water and an organic solvent. The mixed solvent of can be applied. As the organic solvent, it is preferable to use one that is difficult to dissolve the coated water-repellent substance, and preferably one that does not dissolve it. The same applies to the binder. As the binder, for example, a binder made of one or more of polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, carboxymethyl cellulose, polyethylene oxide, hydroxymethyl cellulose, polyethylene oxide and the like can be applied. Also, if necessary, glycerin,
It is also possible to add a plasticizer composed of one or more of ethylene glycol, phthalic acid ester and the like.

For example, the granulated powder has a maximum particle size of 200.
Those having an average particle size of about 30 to 100 μm can be used.

The sodium-sulfur battery referred to in the present invention means, in addition to the sodium-sulfur battery, so-called Na / X which uses a transition metal salt or an aluminum salt as an anode active material.
Batteries, which include aluminum salt, selenium salt, and tellurium salt added to sulfur, and those which use other alkali metal or alkaline earth metal instead of sodium. In the case of a sodium-sulfur battery, both the anode and cathode active materials are liquid at the battery operating temperature, and charge / discharge is performed by the following reversible reaction.

[0016]

[Chemical 1]

[0017]

[Chemical 2]

Here, the value is in the range of 3 ≦ x ≦ 5.

An example of the structure of a sodium-sulfur battery is shown in FIG.
Shown in.

This sodium-sulfur battery has sulfur as an anode active material, an anode 3 as a current collector, an anode container 6 for containing the anode, a cathode 2 made of metallic sodium, and a cathode container 5 for containing the cathode. An insulating material 4 that insulates the anode container 6 and the cathode container 5 from each other, and a solid electrolyte tube 1 that separates the anode 3 and the cathode 2 inside the battery.

The synthetic powder can be obtained by firing a raw material such as α-alumina powder, sodium carbonate powder and lithium carbonate powder to prepare a fired body, and pulverizing the fired body.

[0022]

According to the present invention, β ″ -alumina, β-alumina-based ceramics composed of β-alumina, or synthetic powder of ceramics containing both, or granulated powder composed of the synthetic powder is molded and sintered to produce a solid electrolyte. In this case, deterioration due to moisture absorption before sintering, dimensional change and damage caused by sintering,
It is possible to effectively suppress the occurrence of cracks and improve the formability. Further, it is possible to suppress the occurrence of damage in the firing step, and it is possible to manufacture a good solid electrolyte for sodium-sulfur batteries.

Further, the sodium-sulfur battery incorporating the solid electrolyte can secure high reliability. Further, in the present invention, since the granulated powder is produced using the synthetic powder coated with the water-repellent substance, it is possible to select a binder or solvent containing water as the main component at the time of granulation. The width of the

[0024]

【Example】

(Example 1) α-alumina powder, sodium carbonate powder,
Lithium carbonate powder was added in an oxide conversion weight ratio of 9 each.
Weigh a predetermined amount so that it becomes 0.6%, 8.7%, 0.7%,
The mixture was mixed and calcined at 1200 ° C. for 3 hours to obtain a β ″ -alumina calcined body. The calcined body was crushed for 1 hour by a vibrating ball mill to obtain a β ″ -alumina synthetic powder. At this time, the calcined body 100
3 parts by weight of stearic acid was added to parts by weight. The added stearic acid was uniformly coated on the synthetic powder when the calcined body was pulverized by a vibrating ball mill. The average particle size of the synthetic powder was about 0.7 μm. Next, a 1-butanol solution of PVB (polyvinyl butyral) was mixed as a binder with this synthetic powder, and a granulated powder was obtained using a spray dryer. The average particle size of the granulated powder is 53 μm
was.

For comparison, a synthetic powder without addition of stearic acid at the time of crushing was also produced and granulated in the same manner.

Both of the granulated powders were heated to a temperature of 25 ° C. and a relative humidity of 65.
%, And the change in weight due to moisture absorption was compared. Figure 1
As shown in FIG. 5, the moisture absorption amount of the granulated powder of the present invention is about ⅕ of that of the comparative example when left in the above environment for 2 hours, and it has a remarkable effect of suppressing the moisture absorption deterioration of the beta-alumina solid electrolyte. It was confirmed that there was.

(Example 2) When the same β "-alumina calcined body as in Example 1 was pulverized, palmitic acid, oleic acid, linoleic acid, linoleic acid and sardine acid were added instead of stearic acid. The granulated powder was produced in the same manner as in No. 1, and the amount of moisture absorption was compared, and as a result, the amount of moisture absorption was 1/4 to 1/5 as compared with that without addition of the water-repellent substance. Was recognized.

(Example 3) At the time of pulverizing the same β "-alumina calcined body as in Example 1, the specific gravity was changed to about 0.1 instead of stearic acid.
9. Paraffin having a melting point of 65 degrees was added, and a granulated powder having an average particle size of 76 μm was produced in the same manner as in the example, and the moisture absorption amounts were compared. As a result, it was confirmed that the moisture absorption amount was ⅙ of that of the case without the above water-repellent substance.

Example 4 The synthetic powder produced by pulverization in Example 2 was mixed with an aqueous solution of PVA (polyvinyl alcohol) as a binder and a spray dryer was used to obtain granulated powder having an average particle size of 35 μm.

For comparison, a synthetic powder having no water-repellent substance added at the time of pulverization was also produced and granulated in the same manner.

Both of the granulated powders were heated at a temperature of 25 ° C. and a relative humidity of 65.
%, And the change in weight due to moisture absorption was compared. The moisture absorption amount of the granulated powder of the present invention is about 1/5 to 1/6 of that of the comparative example when left for 2 hours in the same environment as set in Example 1, and the moisture absorption deterioration of the beta-alumina solid electrolyte is remarkable. It was confirmed that there is an effect of suppressing. Also at this time,
In the case of using the powder without addition of the water-repellent substance, when the slurry was prepared by mixing the aqueous solution of PVA (polyvinyl alcohol) before granulation, the viscosity of the slurry was remarkably increased, and the stability was lowered. . However, with the synthetic powder of the present invention to which the water repellent substance was added, the viscosity of the slurry did not change with time, and a stable and consistent granulated powder was obtained.

(Example 5) Using the granulated powders produced in Examples 1 and 4, cold isostatic pressing (CIP) was carried out at a pressure of 200 MPa to obtain an outer diameter of 18.5 mm,
A tubular tubular β ″ -alumina molded product having a thickness of 2 mm and a length of 270 mm was obtained. The molded product was placed in an environment of a temperature of 25 ° C. and a relative humidity of 65% to compare the dimensional change in the radial direction of the molded product due to moisture absorption. As shown in Fig. 2, the molded product using the granulated powder of the present invention has an expansion amount due to moisture absorption of about 1/5 to 1/6 that of the comparative example.
Therefore, it was confirmed that the effect of significantly suppressing the moisture absorption deterioration of the beta-alumina-based solid electrolyte is suppressed.

Example 6 A bag-shaped β ″ -alumina molded body formed of two kinds of granulated powder molded in Example 5 was debindered and then sintered at 1600 ° C. for 10 minutes. Annealing was performed for 3 hours to obtain a total of 30 β ″ -alumina bag tube sintered bodies of 15 kinds of each kind. For comparison, fifteen β ″ -alumina bag tube sintered compacts, which were samples to which no water-repellent substance was added at the time of pulverization, were also manufactured. All of the β ″ -alumina bag tube sintered products of No. 1 were acceptable products. On the other hand, in the comparative sample, crack defects were generated in 2 of 15 manufactured samples.

(Embodiment 7) The internal pressure fracture strength was measured for each of the β ″ -alumina bag tube sintered bodies of the present invention and the comparative sample manufactured in Example 6, and the results were evaluated. The average value of the strength of the β ″ -alumina bag tube sintered body manufactured according to Example 1 was 141 MPa, and the average value of the strength of the β ″ -alumina bag tube sintered body manufactured according to Example 4 of the present invention was 139M.
It was Pa. On the other hand, the average strength of the β ″ -alumina bag tube sintered body of the comparative sample was 129 MPa, and the strength of the β ″ -alumina bag tube sintered body of the present invention was superior to the comparative sample.
Also, when the radial resistivity of the β ″ -alumina bag tube sintered body was measured by Na / Na cell for each sample, all samples were 2.8 Ω · cm at 350 ° C. The value was suitable for use as a solid electrolyte.

[0035]

According to the present invention, when a solid electrolyte for a sodium-sulfur battery is manufactured, it is possible to suppress deterioration of powder and a molded body due to moisture absorption, deformation of the molded body, generation of cracks, etc., and damage in the firing step. Occurrence of can be reduced. Also, a highly reliable sodium-sulfur battery can be manufactured.

[Brief description of drawings]

FIG. 1 is a time change diagram of a moisture absorption amount of beta-alumina-based granulated powder.

FIG. 2 is a dimensional change diagram associated with moisture absorption of a molded body.

FIG. 3 is a sectional view showing the overall structure of a sodium-sulfur battery to which the present invention is applied.

[Explanation of symbols]

1 ... Solid electrolyte tube, 2 ... Cathode mainly containing sodium metal, 3 ... Anode composed of sulfur and current collector, 4 ... Insulating material, 5 ...
Cathode container, 6 ... Anode container.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideo Okada Inventor Hideo Okada 7-1-1, Omika-cho, Hitachi City, Ibaraki Hitachi Co., Ltd. Hitachi Research Laboratory (72) Inventor Masaaki Oshima 2-chome, Kandajinbocho, Chiyoda-ku, Tokyo No. 30 TEPCO Ltd. R & D Lab. (72) Inventor Tadashi Maruyama 2-30, Kanda Jinbocho, Chiyoda-ku, Tokyo TEPCO R & D Lab.

Claims (3)

[Claims] 1. A process for producing a solid electrolyte for a sodium-sulfur battery, which comprises firing granulated powder of β ″ -alumina, β-alumina-based ceramics composed of β-alumina, or ceramics containing both of them, followed by firing. Synthetic powder of beta-alumina-based ceramics composed of β-alumina or ceramics containing both is coated with a water-repellent substance, and then granulated to a particle size of 30-100 μm,
A method for producing a solid electrolyte for sodium-sulfur batteries, which comprises firing the granulated powder and then firing the granulated powder. 2. A solid electrolyte for a sodium-sulfur battery, which is obtained by molding granulated powder of β ″ -alumina, β-alumina-based ceramics composed of β-alumina, or ceramics containing both, and firing the granulated powder. Β ″ -alumina coated with a water-repellent substance, β-alumina-based ceramics composed of β-alumina or an aggregate of synthetic powders of ceramics containing both, and after molding the granulated powder,
A solid electrolyte for a sodium-sulfur battery, characterized by being calcined. 3. An anode composed of an anode active material and a current collector which is solid at room temperature and liquid at operating temperature, and an anode container for housing the anode, and a cathode active material which is solid at room temperature and liquid metal at operating temperature. And a cathode container for accommodating the cathode, wherein the anode container and the cathode container are insulated from each other, and the anode and the cathode are separated by a solid electrolyte. Is a solid electrolyte according to claim 2,
Sulfur battery.