WO2025005195A1 - Method for producing lithium-lanthanum-zirconium composite oxide powder and lithium-lanthanum-zirconium composite oxide powder - Google Patents

Abstract

The method for producing a lithium-lanthanum-zirconium composite oxide powder comprises: a first step for preparing a lanthanum zirconate powder having an average particle size of 20 nm to 200 nm, a lanthanum compound, and a lithium compound, respectively; a second step for depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder to generate a precursor powder; a third step for obtaining a lithium-lanthanum-zirconium composite oxide powder by heating the precursor powder for from one second to 30 seconds at from 900°C to 1200°C with the precursor powder dispersed in a carrier gas, using a gas having an oxygen partial pressure of from more than 1.0×10^-30 atm to 1.0 atm as the carrier gas; and a fourth step for recovering the lithium-lanthanum-zirconium composite oxide powder obtained in the third step. According to the present invention, it is possible to suppress the scattering of Li and obtain a small-particle-size LLZ powder having excellent storage stability.

Description

Method for producing lithium-lanthanum-zirconium composite oxide powder and lithium-lanthanum-zirconium composite oxide powder

The present invention relates to a method for producing lithium-lanthanum-zirconium composite oxide powder and to lithium-lanthanum-zirconium composite oxide powder.

Lithium-lanthanum-zirconium composite oxide powder (hereinafter referred to as "LLZ powder") having a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ is known to be used as a solid electrolyte material for all-solid-state batteries. In recent years, it has also been known to be used as a material for the solid electrolyte layer of capacitors and as a ceramic (so-called co-material) material added to a conductive paste used to form internal electrodes that constitute the capacitors (see, for example, Patent Documents 1 to 3).

The conventional manufacturing method involves mixing a zirconium compound, a lanthanum compound, and a lithium compound, then firing them for a long period of time.

For example, Patent Document 1 discloses a method in which lithium carbonate, lanthanum hydroxide, and zirconium oxide are prepared as raw materials for a solid electrolyte, and these raw materials are weighed in predetermined amounts so that the composition of a Li ion conductive compound is Li ₇ La ₃ Zr ₂ O ₁₂ , to obtain a mixture, which is then heated to 900° C. in an air atmosphere, held for 5 hours, and then naturally cooled to obtain a Li ion conductive compound.

Also, for example, Patent Documents 2 and 3 disclose the following method. First, lithium carbonate, lanthanum hydroxide, and zirconium oxide are weighed out in predetermined amounts to obtain the stoichiometric composition of LLZ, and mixed to prepare a mixed material. This mixed material is mixed with a predetermined amount of ethyl alcohol using a nylon pot and zirconia balls to prepare a mixture. After drying this mixture, it is calcined in an alumina crucible at a maximum temperature of 1000°C in an air atmosphere for 10 hours to prepare LLZ calcined powder. Next, this LLZ calcined powder is mixed with a methyl ethyl ketone/toluene mixed solvent using a nylon pot and zirconia balls, pulverized, and dried to prepare LLZ powder.

Also, for example, Patent Document 4 discloses a method for producing a lithium-lanthanum-zirconium composite oxide powder as follows. First, lithium carbonate, lanthanum hydroxide, and zirconium oxide are mixed and placed in an alumina crucible, heated at 600° C./hour, and held at 900° C. for 6 hours. After that, about half of the weight of the part of the obtained powder that had been in contact with the alumina crucible is removed, and the powder that had not been in contact with the crucible is collected, and then crushed for 30 minutes with a grinding machine, placed again in the alumina crucible, heated at 600° C./hour, and held at 1125° C. for 6 hours to obtain a powder. After that, about half of the weight of the part of this powder that had been in contact with the alumina crucible is removed, and the powder that had not been in contact with the crucible is collected. After the powder is sieved, Al ₂ O ₃ is added to the powder and mixed thoroughly. The resulting mixed powder is press-molded using a die to form pellets. The pellets are embedded in the mixed powder, heated at a rate of 60° C./hour, and held at 1,180° C. for 36 hours to obtain a lithium-lanthanum-zirconium composite oxide.

Patent Document 5 also discloses a method in which lanthanum zirconate, lithium carbonate, and lanthanum hydroxide are mixed in a wet ball mill for 24 hours, then dried at 100°C for 5 hours to prepare a raw material mixture powder, which is then placed in a crucible and heated in an electric furnace at 750°C for 12 hours, and then naturally cooled.

Furthermore, Patent Document 6 discloses a method in which lanthanum-containing zirconia powder with an average particle size of 100 nm is produced by coprecipitation, mixed with alumina powder and lithium carbonate powder, and fired at 700°C for 12 hours.

Patent Document 5 and Patent Document 6 state that long-term firing at high temperatures exceeding 1000°C causes lithium components to scatter, making it difficult to obtain the desired LLZ. Therefore, the invention described in Patent Document 5 uses lanthanum zirconate as one of the raw materials for LLZ, and the invention described in Patent Document 6 uses a coprecipitate of a zirconium compound and a lanthanum compound as one of the raw materials, thereby successfully obtaining a garnet-type LLZ fired body while suppressing the scattering of lithium components at firing temperatures below 1000°C.

JP 2015-130481 A JP 2017-147398 A JP 2018-041902 A JP 2011-051800 A JP 2014-172812 A JP 2018-065704 A

Recently, there has been a demand for the development of small-particle LLZ powder with an average particle size of about 30 nm to 1.0 μm, especially 30 nm to 300 nm, for various applications. However, in the manufacturing methods disclosed in Patent Documents 1 to 6, the mixture of LLZ raw materials is left stationary and heated at high temperatures for a long period of time, so the LLZ inevitably becomes large lumps after heating.

Therefore, in order to obtain the small particle size LLZ powder that is now in demand, it is necessary to further pulverize the LLZ obtained by the manufacturing methods described in Patent Documents 1 to 6. For example, Patent Document 3 describes that LLZ calcined powder is pulverized by the above-mentioned method to produce LLZ powder with a D50 of 0.2 μm to 12.1 μm, which is used for the solid electrolyte layer and internal electrode of a solid ion capacitor. In this specification, "pulverization" refers to the operation of applying an external force to a substance to crush it into smaller particles than their original size. In addition, "disintegration" refers to the operation of applying an external force to a material that has aggregated with a relatively weak force, such as a particle aggregate or granulated material, to disperse or loosen it.

In general, when grinding ceramic powder to obtain ceramic powder with a small particle size of 1.0 μm or less, it is necessary to mix the ceramic powder with a solvent to prepare a ceramic slurry, and grind it for a long time with a very strong force using a media mill or the like, which causes a large number of microcracks and highly active surfaces on the surface of the obtained ceramic powder, and the problem of lithium components eluting into the solvent is widely known. In general, the smaller the particle size of the ceramic powder, the higher the surface activity, but in particular in the case of LLZ powder, the lithium components on the surface of the powder react with CO ₂ or H ₂ O, which causes the ceramic to deteriorate, and lithium may escape and cause defects in the crystal structure, which in any case has a negative effect on storage stability.

As a result, for example, when used as a co-material in a conductive paste for the internal electrodes of a capacitor, the lithium components eluted from the surface of the LLZ powder react with the organic vehicle in the conductive paste, causing serious problems such as the conductive paste gelling.

Furthermore, in industrial production of small particle size LLZ powder, for which demand has recently been increasing, it is preferable for the manufacturing time to be as short as possible.

In view of these problems, the present invention aims to provide a method for efficiently producing small-particle size lithium-lanthanum-zirconium composite oxide powder that suppresses lithium scattering and has excellent storage stability. Another aim of the present invention is to provide a lithium-lanthanum-zirconium composite oxide powder that, despite its small particle size, minimizes the activity of the powder surface and has excellent storage stability.

As a result of intensive research to solve the above problems, the present inventors have discovered a method for producing a precursor powder comprising the steps of: a first step of preparing lanthanum zirconate powder having an average particle size of 20 nm or more and 200 nm or less, a lanthanum compound, and a lithium compound; a second step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder to produce a precursor powder; and a second step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder to produce a precursor powder ^. The inventors have found that by using a method for producing a lithium-lanthanum-zirconium composite oxide powder, which comprises: a third step of using a gas having a pressure of more than 1.0 atm and not more than 1.0 atm as a carrier gas, heating the precursor powder at a temperature of 900° C. or more and 1200° C. or less for a time of 1 second to 30 seconds in a state in which the precursor powder is dispersed in the carrier gas to obtain a lithium-lanthanum-zirconium composite oxide powder, and a fourth step of recovering the lithium-lanthanum-zirconium composite oxide powder obtained in the third step, it is possible to efficiently obtain a lithium-lanthanum-zirconium composite oxide powder having a small particle size and excellent storage stability while suppressing lithium scattering, which has led to the completion of the present invention.

That is, the present invention (1) includes a first step of preparing a lanthanum zirconate powder having an average particle size of 20 nm or more and 200 nm or less, a lanthanum compound, and a lithium compound;
a second step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder to produce a precursor powder;
a third step of obtaining a lithium-lanthanum-zirconium composite oxide powder by using a gas having an oxygen partial pressure of more than 1.0×10 ⁻³⁰ atm and not more than 1.0 atm as a carrier gas and heating the precursor powder at a temperature of 900° C. or more and 1200° C. or less for a time of 1 second or more and 30 seconds or less in a state in which the precursor powder is dispersed in the carrier gas;
A fourth step of recovering the lithium-lanthanum-zirconium composite oxide powder obtained in the third step;
The present invention provides a method for producing a lithium-lanthanum-zirconium composite oxide powder having the above formula:

The present invention (2) also provides a method for producing the lithium-lanthanum-zirconium composite oxide powder of the present invention (1), in which the lithium-lanthanum-zirconium composite oxide powder obtained in the third step has an average particle size of 30 nm or more and 1.0 μm or less.

The present invention (3) also provides a method for producing the lithium-lanthanum-zirconium composite oxide powder of the present invention (1), in which the lithium-lanthanum-zirconium composite oxide powder obtained in the third step has an average particle size of 30 nm or more and 300 nm or less.

The present invention (4) also provides a method for producing a lithium-lanthanum-zirconium composite oxide powder according to any one of the present inventions (1) to (3), in which the second step is a step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder, and then calcining the lanthanum zirconate powder to which the lanthanum compound and the lithium compound are deposited to produce a precursor powder.

The present invention (5) also provides a method for producing a lithium-lanthanum-zirconium composite oxide powder according to any one of the present inventions (1) to (3), in which the second step is a step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder, calcining the lanthanum zirconate powder to which the lanthanum compound and the lithium compound are deposited to form a calcined product, and further pulverizing and/or crushing the calcined product to produce a precursor powder having an average particle size of 30 nm to 300 nm.

The present invention (6) also provides a method for producing a lithium-lanthanum-zirconium composite oxide powder according to any one of the present inventions (1) to (5), in which the lanthanum zirconate powder is obtained by heating a coprecipitate of a lanthanum compound and a zirconium compound.

The present invention (7) also provides a lithium-lanthanum-zirconium composite oxide powder having an average particle size of 30 nm or more and 1.0 μm or less and a viscosity change rate of 1, as measured by the following method:
<Method for measuring viscosity change rate>
100 parts by mass of nickel powder having an average particle size of 0.3 μm, 5 parts by mass of acrylic resin (methacrylic resin having a weight average molecular weight in the range of 40,000 to 50,000 and an acid value of 0 mgKOH/g), 20 parts by mass of the lithium-lanthanum-zirconium composite oxide powder, and 20 parts by mass of terpineol are mixed and kneaded using a three-roll mill to prepare a paste-like composition. The viscosity immediately after preparation and the viscosity after storage at 25° C. for one week after preparation are measured using a rotational viscometer at 25° C. and a shear rate of 100/s, and the ratio of the viscosity one week after preparation to the viscosity immediately after preparation is calculated as the viscosity change ratio.

The manufacturing method of the present invention makes it possible to efficiently obtain a small-particle size lithium-lanthanum-zirconium composite oxide powder that has excellent storage stability while suppressing lithium scattering. Furthermore, despite its small particle size, the lithium-lanthanum-zirconium composite oxide powder of the present invention has minimized powder surface activity and has excellent storage stability.

The present invention is described in detail below, but is not limited to this.

The LLZ powder according to the present invention has a basic composition of Li ₇ La ₃ Zr ₂ O ₁₂ , and has an average particle size of 30 nm to 1.0 μm, particularly 30 nm to 300 nm, and is characterized by excellent storage stability. In this specification (the present invention), the powder is observed using a scanning electron microscope (e.g., SU-1510, manufactured by Hitachi High-Tech Corporation), 100 particles constituting the powder are randomly selected from the observation, their particle sizes are measured, and the cumulative 50% particle size based on the number is calculated based on the particle sizes, and this value is defined as the average particle size. The particle size is defined as the diameter of a perfect circle having the same area as the projected area of the particle. The value calculated by the above method is used not only for the LLZ powder but also for the average particle size of the nickel powder described later.

In the above-mentioned LLZ powder, the ratio of lithium, lanthanum, and zirconium does not necessarily have to be precisely [7:3:2] (molar ratio). That is, as is widely known in the industry, it may be a ratio that is close to that ratio. Furthermore, a part of each element in the above basic composition may be replaced with another element. An example of the other element is aluminum. Furthermore, when the LLZ powder of the present invention is used as a solid electrolyte, it is preferable that it is a cubic crystal, but this is not necessarily limited to this, and when a tetragonal LLZ powder is desired, the heat treatment conditions, etc. may be appropriately adjusted to make it a tetragonal crystal.

<Production Method of the Present Invention>
The production method of the present invention is a method for producing a lithium-lanthanum-zirconium composite oxide powder, comprising: a first step of preparing lanthanum zirconate powder having an average particle size of 20 nm or more and 200 nm or less, a lanthanum compound, and a lithium compound; a second step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder to produce a precursor powder; a third step of using a gas having an oxygen partial pressure of more than 1.0 x 10 ^-30 atm and not more than 1.0 atm under atmospheric pressure as a carrier gas, heating the precursor powder at a temperature of 900°C or more and 1200°C or less for a time of 1 second or more and 30 seconds or less while the precursor powder is dispersed in the carrier gas; and a fourth step of recovering the lithium-lanthanum-zirconium composite oxide powder obtained in the third step.

As described above, the manufacturing method of the present invention is characterized by using a small particle size lanthanum zirconate powder, coating the surface with a lanthanum compound and a lithium compound in advance, and then heating in a gas phase with a controlled atmosphere. Therefore, since the surface activity of the lanthanum zirconate powder is high, the lanthanum compound and lithium compound are easily diffused inside the lanthanum zirconate powder, and since the distance from the surface to the center (deepest part) of each particle constituting the powder is short, the lanthanum compound and lithium compound are easily able to reach the center (deepest part) of each particle constituting the lanthanum zirconate powder. Therefore, even if the precursor powder is heated at a temperature of 900°C to 1200°C for a short period of time of 1 second to 30 seconds, the lanthanum compound and lithium compound are easily diffused throughout the entire interior of each particle constituting the lanthanum zirconate powder, the amount of lithium compound scattered is also suppressed, and the desired LLZ powder can be efficiently manufactured.

The steps that make up the manufacturing method of the present invention are explained below.

The manufacturing method of the present invention may include the first, second, third, and fourth steps described below, but may also include a further step before the first step, a further step between the above steps, or a further step after the fourth step.

[First step]
The first step according to the present invention is a step of preparing a lanthanum zirconate powder having an average particle size of 20 nm or more and 200 nm or less, a lanthanum compound, and a lithium compound.

(Lanthanum zirconate powder)
The average particle size of the lanthanum zirconate powder prepared in the first step may be 20 nm or more and 200 nm or less, but is preferably 30 nm or more and 180 nm or less, more preferably 40 nm or more and 160 nm or less, and particularly preferably 50 nm or more and 140 nm or less. This is preferable in that the lanthanum zirconate powder is more likely to react with other components in the third step described below, making it easier to obtain LLZ even with a short heating time.

Lanthanum zirconate powder may be manufactured, but commercially available powder can also be used. If the average particle size of commercially available lanthanum zirconate powder is greater than 200 nm, it can be used after being pulverized and/or crushed by a suitable known method such as a ball mill or bead mill so that the average particle size falls within the above-mentioned range.

In the present invention, the average particle size refers to the cumulative 50% particle size calculated based on the particle sizes of 100 or more particles randomly selected by observation with a scanning electron microscope.

When producing lanthanum zirconate powder, the production method is not particularly limited, and it can be obtained by mixing and heating a zirconium compound and a lanthanum compound, but it is preferable to use a coprecipitation method, which is widely known as a powder production method as described in Patent Document 6, and heat a coprecipitate of a lanthanum compound and a zirconium compound to obtain it. When preparing lanthanum zirconate powder by this method, it is preferable to adjust the average particle size so that a coprecipitate having an average particle size of 20 nm to 200 nm is produced, but if the average particle size of the coprecipitate is larger than 200 nm, it is adjusted to 20 nm to 200 nm by crushing and/or disintegration. By setting the average particle size of the coprecipitate in the above range, lanthanum zirconate powder having an average particle size of 20 nm to 200 nm can be easily obtained by heating, and even if the average particle size of the obtained lanthanum zirconate powder is larger than 200 nm, the average particle size can be easily adjusted to 20 nm to 200 nm by crushing and/or disintegration.

The zirconium compound used in the production of lanthanum zirconate is not particularly limited, and for example, zirconium oxide, zirconium hydroxide, zirconium sulfate, zirconium carbonate, zirconium chloride, and zirconium nitrate can be used. The zirconium compound may be in a powder form, and the average particle size of the powder is preferably 10 nm or more and 100 nm or less. When using a zirconium compound powder with an average particle size of more than 100 nm, it can be used after being adjusted to within the above range by a pulverization process and/or crushing process. Furthermore, when using a zirconium compound in a coprecipitation method, it is preferable that the zirconium compound has high dispersibility in the liquid, and is preferably in a sol state.

The lanthanum compound used in the production of lanthanum zirconate is not particularly limited, and for example, lanthanum oxide, lanthanum hydroxide, lanthanum sulfate, lanthanum carbonate, lanthanum chloride, and lanthanum nitrate can be used. The lanthanum compound may be in a powder form, and the average particle size of the powder is preferably 10 nm or more and 100 nm or less. In addition, when the lanthanum compound is used in the coprecipitation method, it is preferable that the lanthanum compound has high dispersibility in the liquid, and is preferably in a sol state.

(Lanthanum compounds)
The lanthanum compound prepared in the first step is not particularly limited, and for example, the above-mentioned lanthanum compounds can be used.

(Lithium compounds)
The lithium compound prepared in the first step is not particularly limited, and for example, lithium carbonate, lithium hydroxide, lithium nitrate, lithium sulfate, and lithium chloride can be used. The lithium compound may be in a powder form, and the average particle size of the powder is preferably 10 nm or more and 100 nm or less. When using a lithium compound powder with an average particle size larger than 100 nm, it can be used after being adjusted to within the above range by pulverization and/or crushing.

[Second step]
The second step according to the present invention is a step of producing a precursor powder by depositing a lanthanum compound and a lithium compound on the surface of lanthanum zirconate powder.

The above-mentioned deposition method is not particularly limited, but for example, when the lanthanum compound and/or lithium compound prepared in the first step is in the form of a powder, the powder can be mixed with lanthanum zirconate powder using a ball mill, bead mill, or the like, to mechanochemically deposit the lanthanum compound powder and/or lithium compound powder onto the surface of the lanthanum zirconate powder, thereby producing a precursor powder.

Alternatively, a solvent that dissolves lanthanum compounds and/or lithium compounds but does not dissolve lanthanum zirconate powder may be prepared, and lanthanum zirconate powder may be introduced into the solution in which the lanthanum compounds and/or lithium compounds are dissolved, and then the lanthanum compounds and/or lithium compounds may be precipitated on the surface of the lanthanum zirconate powder by a method such as reduction or drying the aforementioned solution (solvent), thereby producing a precursor powder.

In addition, an organic binder that is thermally decomposed in a carrier gas by heating in the third step described below may be prepared, and a lanthanum compound and/or lithium compound may be kneaded into the organic binder and then coated onto lanthanum zirconate powder, thereby generating a precursor powder in which the lanthanum compound and/or lithium compound is attached to the surface of the lanthanum zirconate powder via the organic binder.

The above methods can also be used in combination. That is, for example, a lanthanum compound can be deposited on the surface of lanthanum zirconate powder by the above-mentioned liquid precipitation method, and then a lithium compound can be deposited by the above-mentioned mechanochemical method.

The second step described above is preferably a step of depositing a lanthanum compound and a lithium compound on the surface of the lanthanum zirconate powder, and then calcining the lanthanum zirconate powder to which the lanthanum compound and the lithium compound are deposited to produce a precursor powder. The calcination temperature is not particularly limited, but is preferably 100°C to 700°C, more preferably 200°C to 650°C, and particularly preferably 300°C to 600°C. The calcination time is not particularly limited, but is preferably 1 hour to 10 hours, more preferably 2 hours to 9 hours, and particularly preferably 3 hours to 8 hours. The calcination atmosphere is not particularly limited, and calcination can be performed in an appropriate atmosphere such as air or nitrogen.

By carrying out the above-mentioned calcination, the lithium compounds and lanthanum compounds can be more firmly attached to the surface of the lanthanum zirconate powder, so that when the precursor powder is dispersed in a carrier gas in the third step described below, the lithium compounds and lanthanum compounds are less likely to dissociate from the surface of the lanthanum zirconate powder, making it easier to obtain LLZ powder. In addition, because the lithium compounds and lanthanum compounds are less likely to dissociate from the surface of the lanthanum zirconate powder, the precursor powder can be dispersed with stronger force when dispersed in the carrier gas, making it easier to improve the dispersibility of the precursor powder in the carrier gas, and the particles that make up the obtained LLZ powder are less likely to bond or aggregate with each other.

Also, since the moisture content and hygroscopicity of the precursor powder can be reduced by calcination, dispersibility is improved when the precursor powder is dispersed in a carrier gas in the third step described below. Therefore, it becomes easier to eliminate the need for pulverization and/or crushing processes after the third step described below, and the activity of the powder surface of the LLZ powder can be suppressed, making it easier to achieve excellent storage stability.

In addition, by carrying out the above-mentioned calcination, the lithium compound and lanthanum compound attached to the surface of the lanthanum zirconate powder can be reacted with oxygen to form lithium oxide and lanthanum oxide, respectively, before the third step described below. Therefore, in the third step described below, the reactivity between the lanthanum zirconate powder and the lithium compound and lanthanum compound attached to the powder surface is increased, making it easier to obtain the desired LLZ powder even if the heating time is short.

Furthermore, it is particularly preferable that the second step described above is a step of depositing a lanthanum compound and a lithium compound on the surface of lanthanum zirconate powder, then calcining the lanthanum zirconate powder with the lanthanum compound and lithium compound deposited thereon to form a calcined product, and further pulverizing and/or crushing the calcined product to produce a precursor powder having an average particle size of 30 nm to 300 nm.

Even if calcination is not performed, secondary particles may be generated by the above-mentioned deposition process, etc., so the average particle size of the precursor powder can be adjusted to a specific range by a pulverization process and/or crushing process, if necessary. That is, the above-mentioned second step can be a step in which a lanthanum compound and a lithium compound are deposited on the surface of lanthanum zirconate powder, and then a pulverization process and/or crushing process are performed to generate a precursor powder with an average particle size of 30 nm to 300 nm.

The average particle size of the precursor powder produced in the second step described above is preferably 30 nm or more and 300 nm or less, more preferably 40 nm or more and 250 nm or less, even more preferably 50 nm or more and 200 nm or less, and particularly preferably 60 nm or more and 150 nm or less.

[Third step]
The third step in the present invention is a step of obtaining a lithium-lanthanum-zirconium composite oxide powder by using a gas having an oxygen partial pressure of more than 1.0× ^10-30 atm and not more than 1.0 atm as a carrier gas, dispersing a precursor powder in the carrier gas, and heating the precursor powder at a temperature of 900° C. or more and 1200° C. or less for a time of 1 second or more and 30 seconds or less.

The oxygen partial pressure of the gas constituting the carrier gas under atmospheric pressure may be more than 1.0×10 ⁻³⁰ atm and 1.0 atm or less, but is preferably 1.0×10 ⁻²⁵ atm or more and 9.0×10 ⁻¹ atm or less, more preferably 1.0×10 ⁻²⁰ atm or more and 8.0×10 ⁻¹ atm or less, even more preferably 1.0×10 ⁻¹⁵ atm or more and 7.0×10 ⁻¹ atm or less, and particularly preferably 1.0×10 ⁻¹⁰ atm or more and 6.0×10 ⁻¹ atm or less. By having the oxygen partial pressure in this range, the generation of oxygen vacancies can be suppressed while the scattering of Li can also be suppressed, making it easier to produce LLZ powder. In addition, by setting the upper limit of the oxygen partial pressure as described above, it becomes easier to produce LLZ powder more safely. As the carrier gas, air, oxygen, nitrogen, argon, etc., and mixed gases thereof, etc. can be used. Depending on the necessity for controlling the atmosphere, reducing gases such as hydrogen, carbon monoxide, methane, ammonia gas, etc. It is not essential that the present invention be carried out under "atmospheric pressure," but the present invention can be carried out under any suitable pressure.

The carrier gas may further contain water vapor. When the carrier gas contains water vapor, the partial pressure of the water vapor under atmospheric pressure is preferably 2.3×10 ⁻² atm or more and less than 1.0 atm, more preferably 1.0×10 ⁻¹ atm or more and less than 1.0 atm, more preferably 2.0×10 ⁻¹ atm or more and less than 1.0 atm, more preferably 3.0×10 ⁻¹ atm or more and less than 1.0 atm, more preferably 3.0×10 ⁻¹ atm or more and 9.0×10 ⁻¹ atm or less, even more preferably 3.0×10 ⁻¹ atm or more and 8.0×10 ⁻¹ atm or less, and particularly preferably 3.0×10 ⁻¹ atm or more and 7.0×10 ⁻¹ atm or less. This allows each component in the precursor powder to react more easily, so that the reaction can proceed easily even in a short period of time, promoting the reaction for producing LLZ and making it easier to obtain the desired LLZ powder.

The precursor powder is supplied into the reaction vessel through a nozzle together with the above-mentioned carrier gas, and heated while dispersed in the carrier gas (i.e., in the gas phase). There are no particular limitations on the nozzle, and any shape may be used, including those with a circular, polygonal, or slit-shaped cross section, those with a narrowed tip, and those that are narrowed halfway and widen at the opening.

The precursor powder is preferably dispersed in the reaction vessel so that the concentration of the precursor powder in the gas phase is 10 g/L or less. If the concentration in the gas phase is higher than 10 g/L, the precursor powder particles may come into contact with each other in the gas phase, causing aggregation or coalescence, which may require a crushing process and/or disintegration process in the third step or later. The concentration of the precursor powder in the gas phase may be appropriately determined based on the specifications of the manufacturing device used, but is more preferably 1 g/L or less, more preferably 0.5 g/L or less, even more preferably 0.1 g/L or less, and particularly preferably 0.05 g/L or less. The lower limit of the precursor powder concentration in the gas phase is not particularly limited, but from the viewpoint of manufacturing efficiency, it is preferably 0.001 g/L or more.

The heating temperature of the precursor powder in the third step may be from 900°C to 1200°C, but is preferably from 950°C to 1150°C, and more preferably from 1000°C to 1100°C. Having the heating temperature in this range makes it easier to efficiently produce the LLZ powder.

The heating time of the precursor powder in the third step varies depending on the heating temperature and the average particle size of the precursor powder, but may be from 1 to 30 seconds, preferably from 1 to 20 seconds, more preferably from 1 to 15 seconds, and particularly preferably from 2 to 10 seconds. Having the heating time within this range makes it easier to efficiently produce the LLZ powder.

The heating method is preferably radiant heat, but the precursor powder can also be heated by directly contacting it with a heat source. An electric furnace (electric heater) can be used for radiant heat heating, and radiant heat generated by a flame can also be used. From the viewpoint of uniform heating, heating by radiant heat is preferred. As a method for heating the precursor powder by directly contacting it with a heat source, for example, the precursor powder can be heated by directly contacting it with a flame. From the viewpoint of energy efficiency, it is preferable to heat the precursor powder by directly contacting it with a heat source. The precursor powder can also be heated by contacting it with a heated high-temperature gas. The above heating methods can also be combined appropriately, for example, the precursor powder can be heated directly by a flame and then heated by radiant heat from an electric furnace.

The average particle size of the lithium-lanthanum-zirconium composite oxide powder obtained in the third step is not particularly limited, but is preferably 30 nm or more and 1.0 μm or less, more preferably 30 nm or more and 900 nm or less, more preferably 30 nm or more and 800 nm or less, more preferably 30 nm or more and 700 nm or less, more preferably 30 nm or more and 600 nm or less, more preferably 30 nm or more and 500 nm or less, more preferably 30 nm or more and 400 nm or less, more preferably 30 nm or more and 300 nm or less, more preferably 40 nm or more and 250 nm or less, even more preferably 50 nm or more and 200 nm or less, and particularly preferably 60 nm or more and 150 nm or less. This makes it easier to produce a small particle size LLZ powder. That is, the LLZ powder obtained in the third step can be used as it is after recovery in the fourth step described below, but since it can be easily reduced in particle size by a crushing process, it can also be used after being appropriately further reduced in particle size by a crushing process. However, from the viewpoint of suppressing the activity of the powder surface and improving storage stability, it is preferable not to carry out the crushing process.

[Step 4]
The fourth step according to the present invention is a step of recovering the lithium-lanthanum-zirconium composite oxide powder obtained in the third step. The recovery method is not particularly limited, and for example, the LLZ powder transferred from the reaction vessel together with the carrier gas can be collected by a known means such as a bag filter.

The manufacturing method of the present invention may include a cooling step after the third step and before the fourth step. For example, the LLZ powder in a high temperature state immediately after heating can be cooled and then recovered using a known cooling means such as a cooling tube.

<LLZ powder of the present invention>
In the manufacturing method of the present invention, even if microcracks are generated on the surface of the precursor powder, no microcracks remain on the surface of the LLZ powder after the heat treatment, and neither pulverization nor crushing is required for the obtained LLZ powder, so that the activity of the powder surface is minimized and an LLZ powder with excellent storage stability can be obtained, even though the particle size is small. Note that, depending on the manufacturing conditions, the particles may sinter together, but even in that case, the particles can be crushed with an extremely weak force, so that microcracks and the like are unlikely to occur on the LLZ powder surface after crushing, the activity of the powder surface can be minimized, and the storage stability can be excellent.

The average particle size of the LLZ powder of the present invention may be 30 nm or more and 1.0 μm or less, but is preferably 30 nm or more and 900 nm or less, more preferably 30 nm or more and 800 nm or less, more preferably 30 nm or more and 700 nm or less, more preferably 30 nm or more and 600 nm or less, more preferably 30 nm or more and 500 nm or less, more preferably 30 nm or more and 400 nm or less, preferably 30 nm or more and 300 nm or less, more preferably 40 nm or more and 250 nm or less, more preferably 50 nm or more and 200 nm or less, and particularly preferably 60 nm or more and 150 nm or less.

The LLZ powder of the present invention is subjected to XRD measurement using an XRD measuring device (Rigaku Corporation, SmartLab) with CuKα radiation (wavelength λ: 1.5418 Å) at a diffraction angle 2θ of 10 to 90° under conditions of a tube voltage of 40 kV, a tube current of 30 mA, a step angle of 0.01°, and a scanning speed of 10°/min. The main peaks with the maximum peak intensity are detected for lithium-lanthanum-zirconium composite oxide and lanthanum zirconate, and the peak areas of each peak are measured. The ratio of the peak area of lithium-lanthanum-zirconium composite oxide to the total peak area is calculated. It is sufficient that the ratio is more than 50%, but it is preferably 60% or more, more preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more. For example, the main peak can be around 31° for lithium-lanthanum-zirconium composite oxide, and around 29° for lanthanum zirconate.

The lithium-lanthanum-zirconium composite oxide powder of the present invention can be specified by a viscosity change ratio of 1 obtained by the following "Method for Measuring Viscosity Change Ratio". As the acrylic resin used in the method for measuring viscosity change ratio below, for example, BR-105 (a methacrylic resin with a weight average molecular weight of 45,000, an acid value of 0 mgKOH/g, and a glass transition point of 48°C) manufactured by Mitsubishi Chemical Corporation can be used, but the viscosity change ratio may also be measured using other acrylic resins with similar physical properties. That is, for example, the viscosity change ratio can be measured using a methacrylic resin with a weight average molecular weight of 40,000 to 50,000 or 43,000 to 47,000, an acid value of 0 mgKOH/g, and a glass transition point of 40°C to 60°C or 45°C to 55°C.

<Method for measuring viscosity change rate>
100 parts by mass of nickel powder having an average particle size of 0.3 μm, 5 parts by mass of acrylic resin (methacrylic resin having a weight average molecular weight in the range of 40,000 to 50,000 and an acid value of 0 mgKOH/g), 20 parts by mass of the lithium-lanthanum-zirconium composite oxide powder, and 20 parts by mass of terpineol are mixed and kneaded using a three-roll mill to prepare a paste-like composition. The viscosity immediately after preparation and the viscosity after storage at 25° C. for one week after preparation are measured using a rotational viscometer at 25° C. and a shear rate of 100/s, and the ratio of the viscosity one week after preparation to the viscosity immediately after preparation is calculated as the viscosity change ratio.

As mentioned above, when ceramic powder is mixed with a solvent to prepare a ceramic slurry, and then pulverized for a long period of time using a media mill or the like with extremely strong force to reduce the size of the slurry, numerous microcracks and highly active surfaces are generated on the surface of the resulting ceramic powder, and lithium components are dissolved into the solvent. Therefore, when the LLZ powder obtained by this process is mixed and kneaded with the above-mentioned materials to obtain a paste-like composition, the lithium components dissolved from the LLZ powder react with other materials, particularly resins, thereby increasing the viscosity of the paste-like composition. In other words, measuring the viscosity ratio using the above-mentioned method can be used as an index of the amount of defects present in the crystal structure of the LLZ powder.

The lithium-lanthanum-zirconium composite oxide powder of the present invention preferably has a weight loss rate at 100°C as determined by thermogravimetric analysis (air atmosphere, heating at 10°C/min) of 5.0% by mass or less, more preferably 4.0% by mass or less, more preferably 3.0% by mass or less, more preferably 2.0% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.0% by mass. This inhibits the generation of impurities over time in the LLZ powder, and tends to improve storage stability.

Furthermore, the lithium-lanthanum-zirconium composite oxide powder of the present invention preferably has a weight loss rate at 300°C as determined by thermogravimetric analysis (air atmosphere, heating at 10°C/min) of 5.0% by mass or less, more preferably 4.0% by mass or less, more preferably 3.0% by mass or less, more preferably 2.0% by mass or less, more preferably 1.0% by mass or less, even more preferably 0.5% by mass or less, and particularly preferably 0.0% by mass. This inhibits the generation of impurities over time in the LLZ powder, and tends to improve storage stability.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

(Examples 1 to 6, Comparative Examples 1 to 5)
First, lanthanum zirconate powders shown in Table 1 were prepared. Then, lithium carbonate and lanthanum hydroxide were dissolved in a liquid in which the lanthanum zirconate powder was suspended, and lithium hydroxide and lanthanum hydroxide were deposited on the surface of the lanthanum zirconate powder. Next, the lanthanum zirconate powder to which these compounds were attached was calcined at 700° C., and then crushed and/or pulverized to adjust the average particle size to a range of 80 nm to 150 nm (Examples 1 to 6 and Comparative Examples 2 to 5) or 800 nm to 1200 nm (Comparative Example 1), thereby obtaining a precursor powder. Next, a vertical tubular container having a nozzle for spraying the powder at the top was used, and the precursor powder was dispersed in the gas phase from a nozzle with a cross-sectional area of 2 cm ² at the opening by a carrier gas (air was used in Examples 1 to 5 and Comparative Examples 1 to 4, a mixed gas of nitrogen and oxygen was used in Comparative Example 5, and pure oxygen was used in Example 6. The partial oxygen pressure in the gas under atmospheric pressure was as shown in Table 1.). The precursor powder dispersed in the gas phase was then passed through the vertical tubular container described above and heated at the temperature and for the time described in Table 1. An electric furnace was installed outside the vertical tubular container used for heating, and the temperature inside the tubular container was set to the above-mentioned temperature. The powder obtained by heating was then cooled to 180°C while dispersed in the gas phase, and the cooled powder was collected. No pulverization or crushing was performed after heating. The obtained powder was evaluated by the method described below. The results are shown in Table 1.

(Example 7)
A powder was produced in the same manner as in Example 1, except that the precursor powder was dispersed in the gas phase at a concentration (g/L) ten times that of Example 1, and evaluation was carried out in the manner described below. The results are shown in Table 1.

(Example 8)
A powder was produced in the same manner as in Example 7, except that a crushing treatment was carried out after recovery, and evaluation was carried out in the manner described below. The results are shown in Table 1.

(Comparative Example 6)
First, 78 nm lanthanum zirconate powder, lithium carbonate, and lanthanum oxide were mixed for 20 hours using a wet mill, and dried at 100°C for 6 hours to obtain a raw material powder mixture. The obtained raw material powder mixture was then placed in a crucible, heated at 750°C for 10 hours using a batch-type electric furnace, and then cooled to obtain a product. Furthermore, the obtained product was mixed with terpineol to prepare a slurry, and the slurry was used to pulverize the mixture using a bead mill to obtain a powder. The obtained powder was evaluated by the method described below. The results are shown in Table 1.

(Example 9)
A powder was produced in the same manner as in Example 1, except that a coprecipitate obtained by coprecipitating a zirconium compound and a lanthanum compound was fired, and the resulting sintered lanthanum zirconate was pulverized to prepare a lanthanum zirconate powder having an average particle size of 82 nm. The powder was evaluated in the manner described below. The results are shown in Table 1.

(Example 10)
A precursor powder was produced in the same manner as in Example 1, except that a lanthanum zirconate powder having an average particle size of 80 nm, a lithium carbonate powder, and a lanthanum hydroxide powder were mixed in a bead mill to cause the lithium carbonate powder and the lanthanum hydroxide powder to adhere to the surface of the lanthanum zirconate powder, and the powder was evaluated in the manner described below. The results are shown in Table 1.

<Evaluation method>
(Average particle size)
The powder was observed using a scanning electron microscope (SU-1510, manufactured by Hitachi High-Technologies Corporation), and 100 particles constituting the powder were randomly selected from the observation to measure their particle diameters, and the cumulative 50% particle diameter based on the number was calculated based on the particle diameters, which was taken as the average particle diameter. The particle diameter was measured as the diameter of a perfect circle having the same area as the projected area of the particle.

(LLZ Generation)
XRD measurement was performed using an XRD measuring device (Rigaku Corporation, SmartLab) with CuKα radiation (wavelength λ: 1.5418 Å) at a diffraction angle 2θ of 10° to 90° under the conditions of a tube voltage of 40 kV, a tube current of 30 mA, a step angle of 0.01°, and a scanning speed of 10°/min. For the lithium-lanthanum-zirconium composite oxide and lanthanum zirconate, the main peak with the maximum peak intensity was detected, the peak area of each peak was measured, and the ratio of the peak area of the lithium-lanthanum-zirconium composite oxide to the total peak area was calculated. Those with a ratio of more than 50% were designated "A", and those with a ratio of less than 50% were designated "B". In addition, the main peak was selected to be near 31° in the case of the lithium-lanthanum-zirconium composite oxide, and near 29° in the case of lanthanum zirconate.

(Viscosity change ratio)
100 parts by mass of nickel powder having an average particle size of 0.3 μm, 5 parts by mass of BR-105 (a methacrylic resin having a weight average molecular weight of 45,000, an acid value of 0 mgKOH/g, and a glass transition point of 48 ° C.) manufactured by Mitsubishi Chemical Corporation as an acrylic resin, 20 parts by mass of LLZ powder, and 20 parts by mass of terpineol were mixed and kneaded using a three-roll mill (manufactured by Inoue Seisakusho) to obtain a paste-like composition. Next, the viscosity immediately after production and the viscosity one week after production were measured using a rotational viscometer (manufactured by Brookfield, HADV-II + Pro) at 25 ° C. and a shear rate of 100 / s, and the ratio of the viscosity one week after production to the viscosity immediately after production was calculated as the viscosity change rate. The viscosity change rate rounded off to 1 was designated as "A", and the viscosity change rate exceeding 1 was designated as "B". The paste-like composition was stored in a sealed container at 25° C. until the viscosity was measured one week after preparation.

The manufacturing method according to the present invention can be used as a method for industrially manufacturing LLZ. The LLZ according to the present invention can be used for various applications such as materials for electronic components such as capacitors.

Claims (7)

A first step of preparing a lanthanum zirconate powder having an average particle size of 20 nm or more and 200 nm or less, a lanthanum compound, and a lithium compound;
a second step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder to produce a precursor powder;
a third step of obtaining a lithium-lanthanum-zirconium composite oxide powder by using a gas having an oxygen partial pressure of more than 1.0×10 ⁻³⁰ atm and not more than 1.0 atm as a carrier gas and heating the precursor powder at a temperature of 900° C. or more and 1200° C. or less for a time of 1 second or more and 30 seconds or less in a state in which the precursor powder is dispersed in the carrier gas;
A fourth step of recovering the lithium-lanthanum-zirconium composite oxide powder obtained in the third step;
The present invention relates to a method for producing a lithium-lanthanum-zirconium composite oxide powder having the above structure. The method for producing lithium-lanthanum-zirconium composite oxide powder according to claim 1, wherein the average particle size of the lithium-lanthanum-zirconium composite oxide powder obtained in the third step is 30 nm or more and 1.0 μm or less. The method for producing lithium-lanthanum-zirconium composite oxide powder according to claim 1, wherein the average particle size of the lithium-lanthanum-zirconium composite oxide powder obtained in the third step is 30 nm or more and 300 nm or less. The method for producing a lithium-lanthanum-zirconium composite oxide powder according to any one of claims 1 to 3, wherein the second step is a step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder, and then calcining the lanthanum zirconate powder to which the lanthanum compound and the lithium compound are deposited to produce a precursor powder. The method for producing a lithium-lanthanum-zirconium composite oxide powder according to any one of claims 1 to 3, wherein the second step is a step of depositing the lanthanum compound and the lithium compound on the surface of the lanthanum zirconate powder, calcining the lanthanum zirconate powder to which the lanthanum compound and the lithium compound are deposited to form a calcined product, and further pulverizing and/or crushing the calcined product to produce a precursor powder having an average particle size of 30 nm to 300 nm. The method for producing a lithium-lanthanum-zirconium composite oxide powder according to any one of claims 1 to 3, wherein the lanthanum zirconate powder is obtained by heating a coprecipitate of a lanthanum compound and a zirconium compound. A lithium-lanthanum-zirconium composite oxide powder having an average particle size of 30 nm or more and 1.0 μm or less, and a viscosity change rate of 1, as measured by the following method.
<Method for measuring viscosity change rate>
100 parts by mass of nickel powder having an average particle size of 0.3 μm, 5 parts by mass of acrylic resin (methacrylic resin having a weight average molecular weight in the range of 40,000 to 50,000 and an acid value of 0 mgKOH/g), 20 parts by mass of the lithium-lanthanum-zirconium composite oxide powder, and 20 parts by mass of terpineol are mixed and kneaded using a three-roll mill to prepare a paste-like composition. The viscosity immediately after preparation and the viscosity after storage at 25° C. for one week after preparation are measured using a rotational viscometer at 25° C. and a shear rate of 100/s, and the ratio of the viscosity one week after preparation to the viscosity immediately after preparation is calculated as the viscosity change ratio.