JPH09110421A - Lithium aluminate and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To industrially produce lithium aluminate based on γ-aluminate, suitable for use as stock especially for the electrolyte holding plate of a molten carbonate cell (MCFC) and having superior thermal and chemical stabilities in the molten carbonate. SOLUTION: This lithium aluminate has 1-15m<2> /g BET specific surface area and >=80% degree (P) of synthesis calculated by the equation P=I2 /I1 ×100 (where I1 and I2 are diffraction intensities in the X-ray diffraction spectrum analysis of lithium aluminate, I1 is the height of the highest peak and I2 is the height of the 2nd peak) as principal properties. It is produced by dry-mixing clustery particles of α-alumina obtd. by firing a fine aluminum compd. with a lithium compd. in a weight ratio close to the stoichiometric ratio and firing the resultant mixture.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lithium aluminate particularly useful as an electrolyte holding plate for a molten carbonate type battery (MCFC) and an industrial production method thereof.

[0002]

2. Description of the Related Art An MCFC electrolyte holding plate is used for the purpose of holding a mixed molten carbonate such as Li ₂ CO ₃ and K ₃ CO ₃ in a high temperature region near 650 ° C. Properties, such as alkali resistance and heat resistance are required. As a material satisfying such required characteristics, lithium aluminate is currently favored as a constituent material of the electrolyte holding plate, and in particular, fine γ-type lithium aluminate having a relatively large specific surface area and excellent electrolyte holding power is used. It is preferably used.

A technique for producing lithium aluminate having such a high specific surface area is described in, for example, JP-A-60-6.
5719, JP-A-60-151975, JP-A-61-295227, and JP-A-61-2952.
No. 28, JP-A-63-270311, JP-A-1-252522, and JP-A-2-80319 have been proposed. These known methods are
A mixture of alumina and lithium hydroxide or lithium carbonate is fired in the temperature range of 600 to 1000 ° C. to suppress the densification of the structure, or secondary porosification or hydration treatment is performed to increase the specific surface area. The point is the manufacturing point.

[0004]

However, when the γ-type lithium aluminate produced by the above-mentioned prior art is exposed to high temperature in the molten electrolyte for a long time, the γ-type structure becomes There are phenomena such as partial α-type transformation and particles growing to reduce the specific surface area. Therefore,
When it is formed as an electrolyte holding plate for MCFC, there is a drawback that the electrolyte holding capacity is drastically lowered during use and the battery life is deteriorated.

From the above, in the conventional production technology of γ-type porous lithium aluminate, there is a high demand for molten carbonate, which is increasingly demanded for the purpose of improving the longevity of MCFC, alkali resistance, It is not possible to sufficiently deal with imparting heat resistance, and there remains a problem to be improved as an industrial production means.

The present inventors have conducted extensive studies to solve the above problems, and as a result, when producing lithium aluminate, α-obtained by firing a fine aluminum compound as an alumina source. When alumina cluster particles are used, the resulting lithium aluminate does not change its particle structure even when exposed to high temperatures in molten carbonate for a long time, and exhibits excellent alkali resistance, heat resistance and high level retention capacity. I confirmed the facts. And, especially when it has a specific BET specific surface area and the diffraction intensity ratio in the X-ray diffraction (X-RD) spectrum analysis of lithium aluminate is in a specific range, it has excellent performance as a material for the electrolyte holding plate of MCFC. It has been found to exert.

The present invention has been completed on the basis of the above findings, and its object to be solved is to obtain excellent thermal stability and chemical stability in molten carbonate by applying it to an electrolyte holding plate of MCFC. The object is to provide lithium aluminate whose properties are guaranteed and an industrial production method thereof.

[0008]

The lithium aluminate according to the present invention for solving the above-mentioned problems is a lithium aluminate particle having a BET specific surface area (N ₂ SA) in the range of 1 to 15 m ² / g. The compositional feature is that the degree of synthesis (P) calculated by the following equation (1) is 80% or more. However, in the formula (1), I ₁ and I ₂ are diffraction intensities in the X-ray diffraction (X-RD) spectrum analysis of lithium aluminate, I ₁ is the height of the strongest intensity peak, and I ₂ is the second It represents the intensity peak height.

Further, in the method for producing lithium aluminate according to the present invention, α-alumina cluster particles obtained by firing a fine aluminum compound and a lithium compound are dry-mixed in a stoichiometric ratio close to the stoichiometric ratio. The structural feature is that the mixture is baked.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium aluminate according to the present invention basically has a BET specific surface area of 1 to 15 m ² / g. When the BET specific surface area is less than 1 m ² / g, which intended function can not be exerted retention capacity of molten carbonate becomes insufficient when the material for the electrolyte retaining plate, the other, 15 m ² / If it exceeds g, the deterioration in the electrolyte becomes large and the durability (stability) tends to be impaired. A particularly preferred range of BET specific surface area is 3 to 12 m ² / g.

In addition to the above basic characteristics, the diffraction of the strongest intensity peak (I ₁ ) and the second intensity peak (I ₂ ) that appears when X-ray diffraction (X-RD) spectrum analysis of lithium aluminate is performed. It is an important requirement of the present invention that the degree of synthesis (P) in the above formula (1) represented by the intensity ratio (I ₂ / I ₁ × 100) is 80% or more. If the degree of synthesis (P) is less than 80%, the particle growth of lithium aluminate proceeds in the molten carbonate, so that when it is used as an electrolyte holding plate, it changes over time and the electrolytic solution is washed away from between the particles. This causes a phenomenon, resulting in a significant deterioration in battery performance.

Further, after satisfying the above property characteristics,
The composition ratio of the components is Li ₂ CO ₃ : K ₂ CO ₃ = 62: 38 m
After mixing ol% electrolyte in a weight ratio of 1: 3, air /
CO ₂ in an electric furnace maintained at 70/30
When the lithium aluminate was treated under the condition of heating at a temperature of 00 ° C. for 200 hours, the BET specific surface area (S ₁ ) before heating
When the BET non-surface area change rate (R), which is the difference in BET specific surface area before and after heating (S ₂ −S ₁ ), is 25% or less, lithium aluminate is more excellent in thermal and chemical stability. . The BET specific surface area change rate (R) is 25%
If it exceeds, the particle growth of lithium aluminate in the molten carbonate will proceed in the same manner as in the case where the degree of synthesis (P) exceeds 80%, and the deterioration of the battery performance due to the aging of the material tends to be promoted. Become.

The lithium aluminate according to the present invention has a particle property in which primary particles are appropriately aggregated,
It has extremely excellent physical and thermal stability. The crystal structure of the lithium aluminate is mainly γ-type, but even if some α-type crystals are mixed, the stability performance in the electrolyte is not particularly affected. A crystal system mainly containing a γ type is also acceptable. These physical properties can be easily confirmed by a BET specific surface area (N ₂ SA) measurement method and an X-ray diffraction analysis method.

In order to industrially produce such lithium aluminate, α-alumina cluster particles obtained by firing a fine aluminum compound and a lithium compound are dry-mixed in a stoichiometric ratio close to each other, The method of the invention is applied which comprises a process of calcining the mixture.

Examples of the fine aluminum compound as the alumina source include γ-alumina, alumina hydroxide, ammonium dosanite, alum and the like, but γ-alumina is preferable. The α-alumina cluster particles are obtained by firing the fine aluminum compound particles having an average particle size of 0.1 to 3 μm in a high temperature range of 1200 ° C. or higher, and X-ray diffraction Are particles confirmed to have a cluster property containing α-alumina as a main component. Alumina has a different crystal structure depending on the firing temperature, but in the temperature range around 1200 ° C., the γ-type crystallinity is low and it is converted into a strong cluster-shaped α-alumina in which primary particles are aggregated. The α-alumina is mainly composed of α-alumina as a crystal type, but may be a crystalline alumina that slightly contains a crystal structure such as θ, δ, or φ. Also, α-
Alumina is preferably a cluster of fine particles.

On the other hand, examples of the lithium compound serving as a lithium source include lithium carbonate, lithium hydroxide and lithium nitrate, and the use of lithium carbonate is most effective for the purpose of the present invention. The lithium compound is used as a powder, and the particle size of the lithium compound is preferably 10 μm or less, preferably 5 μm or less.

The α-alumina cluster particles and the lithium compound powder are blended in an equivalence ratio close to the stoichiometry for obtaining lithium aluminate and mixed under dry conditions. In this mixing step, if the mutual dispersion between the powders is insufficient, the lithium aluminate particles produced by the reaction partially aggregate and become coarse. Therefore, in order to obtain a uniform mixed and dispersed state of the raw materials, one or two selected from a high speed dispersion mixer such as a Hensyl mixer or an impact type crusher such as a jet mill, an atomizer or a bandam mill. It is preferable to process using a mixing device of one or more kinds. However, attrition type milling mixers, such as ball mills used in the prior art, are not suitable for the purposes of the present invention because they tend to destroy the grain structure of the alumina.

The raw material mixture is then calcined. The firing treatment is performed in a temperature range of 800 ° C. or higher for 0.5 to 16 hours,
Preferably, it is carried out at a high temperature of 900 ° C. or higher for 1 to 5 hours to react the α-alumina cluster particles with a lithium compound to generate lithium aluminate.
It can be confirmed by X-ray diffraction that the obtained product is lithium aluminate mainly composed of γ-type crystals.

The lithium aluminate particles produced in this manner have a BET specific surface area in the range of 1 to 15 m ² / g, and the particle properties are fine particles in the form of agglomerated clusters. Has a very high BET specific surface area change rate (R) and has extremely stable physical properties.

Lithium aluminate having such particle characteristics exhibits excellent thermal stability and chemical stability in a molten carbonate under high temperature, and is therefore a suitable material as an electrolyte holding plate for MCFC.

[0021]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. However, the scope of the present invention is not limited to these examples.

Examples 1 to 3 and Comparative Examples 1 to 2 (1) Production of lithium aluminate; average particle diameter 0.05 μm
, Γ-alumina particles having a BET specific surface area of 60 m ² / g
BET specific surface area 12.7m ² / g after firing at 00 ℃ for 4 hours
An alumina source composed of the α-alumina powder of was prepared. This α-alumina powder and lithium carbonate having an average particle diameter of 3.2 μm were mixed so that the atomic ratio of Al and Li would be stoichiometrically equivalent, and the mixture was uniformly mixed with a dry Hensyl mixer and then mixed. The powder was calcined at a temperature stage of 900-1100 ° C. for 2 hours. The crystal form, BET specific surface area (N ₂ SA) and degree of synthesis (P) of the produced lithium aluminate were measured, and the results are shown in Table 1 in comparison with the raw material composition and the firing temperature. Further, for comparison, the physical properties of lithium aluminate produced in the same manner as the alumina source without firing the γ-alumina particles are also shown in Table 1.

FIGS. 1 to 4 show S showing the grain structure at the production stage.
In the EM photograph, FIG. 1 is a particle structure of γ-alumina which is a raw material before firing, FIG. 2 is a particle structure of α-alumina which is an alumina source after firing, and FIG. 3 is a lithium aluminate produced in Example 2. 4 and the particle structure of lithium aluminate produced in Comparative Example 1. By comparing FIG. 1 and FIG. 2, it is recognized that the alumina source of the present invention has a cluster particle structure in which primary particles of γ-alumina are aggregated.

[0024]

[Table 1]

(2) Stabilization test under molten carbonate; Example 1
To 3 and lithium aluminate particles obtained in Comparative Examples 1-2 and the solid non-electrolyte (component composition _{Li 2 CO 3: K 2 CO} 3 = 62: 38m
ol%) in a weight ratio of 1: 3 and then air / CO
₂ = 70/30 put in an electric furnace maintained in the atmosphere,
A stability test was performed by heating at a temperature of 00 ° C. for 200 hours. BE before and after heating of heat-treated lithium aluminate
The T specific surface area was measured, and the BET specific surface area change rate (R) was calculated and shown in Table 2. Further, an SEM photograph of the lithium aluminate particles after the stabilization test of Example 2 is shown in FIG.
SEM photographs of the lithium aluminate particles after the stabilization test of Comparative Example 1 are shown in FIG. 6, respectively.

[0026]

[Table 2]

From the results in Table 2, it is recognized that the lithium aluminate according to the present invention, which is mainly composed of γ-type, has remarkably excellent stability under molten carbonate as compared with the comparative example. This state can also be observed from SEM photographs of lithium aluminate mainly consisting of γ type before and after the stabilization test.
On the other hand, it is understood that the conventional lithium aluminate (Comparative Example 1) has a remarkably large particle size after the stabilization test.

[0028]

Industrial Applicability As described above, according to the present invention, the BET specific surface area is in the range of 1 to 15 m ² / g, the crystal structure mainly composed of γ type having a cluster shape in which primary particles are aggregated, and melting It is possible to provide lithium aluminate that exhibits excellent thermal stability and chemical stability in carbonate. Further, according to the production method of the present invention, high-quality lithium aluminate can be industrially advantageously obtained by a simple process. Therefore, it is extremely useful as a lithium aluminate suitable for an electrolyte holding plate of MCFC and a manufacturing technique thereof.

[Brief description of the drawings]

FIG. 1 SE showing the grain structure of γ-alumina before firing.
It is an M photograph (magnification: 30,000 times).

FIG. 2 is an SEM photograph (magnification: 30,000 times) showing a particle structure of α-alumina as an alumina source.

FIG. 3 is an SEM photograph (magnification: 30,000 times) showing the particle structure of lithium aluminate produced in Example 2.

FIG. 4 is an SEM photograph (magnification: 30,000 times) showing the particle structure of lithium aluminate produced in Comparative Example 1.

5 is a SEM photograph showing the particle structure of lithium aluminate after the stabilization test of Example 2 (magnification: 3
0,000 times).

6 is an SEM photograph showing the particle structure of lithium aluminate after the stabilization test of Comparative Example 1 (magnification: 3
0,000 times).

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takenori Watanabe 3-15-1, Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries Co., Ltd. Toni Technical Center (72) Inventor Katsumi Suzuki Mizo Toyosu, Koto-ku, Tokyo No. 1-15 Ishikawajima Harima Heavy Industries Ltd. Technical Research Institute

Claims (3)

[Claims] 1. Lithium aluminate particles having a BET specific surface area (N ₂ SA) in the range of 1 to 15 m ² / g, comprising the following (1)
Lithium aluminate having a degree of synthesis (P) calculated by a formula of 80% or more. However, in the formula (1), I ₁ and I ₂ are diffraction intensities in the X-ray diffraction (X-RD) spectrum analysis of lithium aluminate, I ₁ is the height of the strongest intensity peak, and I ₂ is the second It represents the intensity peak height. 2. The lithium aluminate according to claim 1, wherein the BET specific surface area change rate (R) determined by the following formula (2) is in the range of 25% or less. However, in the equation (2), S ₁ is the BET specific surface area before heating.
(m ² / g), S ₂ represents the BET specific surface area (m ² / g) after heating,
The heating conditions for the porous lithium aluminate were as follows: the sample and the electrolyte (component composition Li ₂ CO ₃ : K ₂ CO ₃ = 62: 38 mol%) were mixed at a weight ratio of 1: 3, and air / CO ₂ = 70/30. It shall be treated at a temperature of 700 ° C. for 200 hours in an electric furnace maintained in the atmosphere. 3. An α-alumina cluster particle obtained by calcining a fine aluminum compound and a lithium compound are dry-mixed in a stoichiometric ratio close to the stoichiometric ratio, and the mixture is calcined. Method for producing lithium aluminate.